1 23

Phytochemistry ReviewsFundamentals and Perspectives ofNatural Products Research ISSN 1568-7767 Phytochem RevDOI 10.1007/s11101-012-9235-7

The chemopreventive role of dietaryphytochemicals through gap junctionalintercellular communication

Antonella Leone, Cristiano Longo &James E. Trosko

1 23

Your article is protected by copyright and

all rights are held exclusively by Springer

Science+Business Media B.V.. This e-offprint

is for personal use only and shall not be self-

archived in electronic repositories. If you

wish to self-archive your work, please use the

accepted author’s version for posting to your

own website or your institution’s repository.

You may further deposit the accepted author’s

version on a funder’s repository at a funder’s

request, provided it is not made publicly

available until 12 months after publication.

The chemopreventive role of dietary phytochemicalsthrough gap junctional intercellular communication

Antonella Leone • Cristiano Longo •

James E. Trosko

Received: 14 December 2011 / Accepted: 8 May 2012

� Springer Science+Business Media B.V. 2012

Abstract Dietary phytochemicals offer protection

from oxidative damages and lower the risks of chronic

diseases, by complementary and overlapping action

mechanisms. These include antioxidant activity, reg-

ulation of gene expression and cell cycle, stimulation

of the immune and hormonal systems and modulation

of cell–cell communication. Gap-junction intercellu-

lar communication (GJIC) plays an important role in

maintaining tissue homeostasis by allowing the inter-

cellular exchange of ions and regulatory molecules

associated with cell proliferation, differentiation and

apoptosis, and by contributing to intracellular signal-

ing. This mechanism is strictly regulated and abnormal

GJIC can result in several pathological conditions.

GJIC is deregulated in cancer cells and reversible

GJIC inhibition is strongly related to the promotion

phase of carcinogenesis, likely mediated by reactive

oxygen species. Whereas, the reversible inhibition of

GJIC is related to the promotion phase of carcinoge-

nicity, enhancers of GJIC are expected to prevent

cancer. Several dietary plant compounds demon-

strated the ability to control GJIC at the epigenetic

levels and to prevent GJIC down-regulation by tumor

promoting compounds, thus preventing cancers. In

this Commentary, a number of reported studies on

several phytochemicals in dietary and medicinal

plants, which were able to affect GJIC and their

structural proteins, i.e., connexins, in different in vivo

and in vitro systems, were examined. The growing

evidence, on the involvement of plant-derived mole-

cules in the modulation of GJIC and in understanding

of the specific action mechanisms, might offer a new

perspective of the protective and/or preventive effects

of dietary phytochemicals, in addition to possible

chemotherapeutic use.

Keywords Dietary phytochemicals � Gap junction

intercellular communication (GJIC) � Cancer �Antioxidants � Epigenetic mechanisms

Abbreviations

ATBC Alpha-tocopherol, beta-carotene cancer

prevention trial

CARET Beta-carotene and retinol efficacy trial

Cx Connexin

GJIC Gap junction intercellular communication

ROS Reactive oxygen species

ROI Reactive oxygen intermediates

A. Leone (&) � C. Longo

Institute of Science of Food Production, Unit of Lecce

(ISPA-Lecce), National Research Council (CNR), Via

Prov.le Lecce-Monteroni, 73100 Lecce, Italy

e-mail: antonella.leone@ispa.cnr.it

J. E. Trosko

Department of Pediatrics and Human Development, Food

Safety and Toxicology Center, Center for Integrative

Toxicology, Michigan State University, East Lansing,

MI, USA

123

Phytochem Rev

DOI 10.1007/s11101-012-9235-7

Author's personal copy

Introduction

Epidemiological studies have indicated an association

between dietary patterns and cancer rates in different

populations around the world. Marked variations in

chronic disease incidence and mortality occur across

different geographic regions, with a different inci-

dence of several cancer types in developed Western

countries and in developing countries. In addition,

cancer rates often change in populations that migrate

from one country to another, and change over time

within countries, such as the case of increase of

colorectal cancer among Japanese people both on

migration to the USA and, more recently, with the

increasing Westernization of the diet in Japan (Ross

2010; Hall and Crowe 2011). These ecological

observations, based on international variations in diet

and cancer rates, confirm that nutrition is an important

risk factor for many common diseases, and therefore

such diseases might be partly preventable by dietary

changes (Key et al. 2004). Moreover, the shift in

nutrition and diets, from prehistoric hunter-gather

diets to modern agra-business—related diets, that have

been associated with increased caloric abundance,

food processing, packaging, and food supplements and

the eating of red meat, have created a collision

between our survival food-driven biological evolution

and the more recent cultural evolution (Cordain et al.

2000; Mariani-Costantini 2000; Milton 2000; Teaford

and Ungar 2000; Paoloni-Giacobino et al. 2003;

Trosko 2007a, 2011; Trosko in press).

Among the dietary constituents, several plant

secondary metabolites play an important role as

nutraceuticals (Kalra 2003). Phytochemicals are the

active substances found in plant-derived foods, as well

as in commonly used medicinal plant extracts. These

compounds exhibit a range of biological activities in

vitro, which support their contributing to the beneficial

effects of food where they are contained. Growing

evidence indicates that long-term intake of such

phytochemicals can have favorable impacts on the

incidence of cancer and many other chronic diseases,

including cardiovascular disease and Type II diabetes.

As a consequence, the scientific interest in plant

secondary metabolites spans from human nutrition

research to food production and processing technol-

ogies (Martin et al. 2011). This has an impact on the

consumers’ interest in dietary components that offer

health benefits, beyond nutrition, by preventing

degenerative diseases and prolonging life, and that

ultimately affect the food, phytotherapic and cosmetic

industry.

Fruits, vegetables, and whole grains contain a wide

variety of phytochemicals, such as phenolics, carote-

noids, and many other chemical species, which might

help protect cellular systems from oxidative damage,

lowering the risk of chronic diseases, such as cancer,

osteoporosis, cardiovascular diseases, cataracts, and

diseases associated with brain and immune dysfunc-

tion (Block et al. 1992; Duthie et al. 2000; Nishino

et al. 2005; Graf et al. 2005; Vainio and Weiderpass

2006; Okarter and Liu 2010). In addition, an inverse

association between consumption of vegetal foods and

the risk for a number of age-related diseases, such as

Alzheimer’s disease, seems to occur (Kim et al. 2010).

One reason for this protection ability is attributable to

the powerful antioxidant and free radical scavenging

properties of various classes of plant compounds.

Although it is worth noting that the physiological

relevance of the direct antioxidant action, as the only

mechanism to explain the impact of such plant

compounds on disease risk, has been questioned

(Heber 2004). As more work has been carried out, a

number of more specific targeted roles, for the

different phytochemicals, have also been identified

beyond the direct antioxidant activity. These include,

for example, gene expression regulation in cell

proliferation, cell differentiation, oncogenes, and

tumor suppressor genes, induction of cell-cycle arrest

and apoptosis, modulation of enzyme activities in

detoxification, oxidation, and reduction, modulation

of cell–cell communication, stimulation of the

immune system, regulation of hormone metabolism,

and antimicrobial effects.

Another concept is that the chemically different

phytochemicals in fruits and vegetables can have

complementary and overlapping mechanisms of

action, including the antioxidant activity and free

radical scavenging (Liu 2004). Plant extracts often

have stronger activities than the single compounds.

Their total antioxidant activity largely derives from

the combination of different phytochemicals, possibly

having different chemical properties, such as cooper-

ative action of lipo-soluble and hydro-soluble mole-

cules in the different cell compartments. The additive

and/or synergistic effects of phytochemicals in fruits

and vegetables are responsible for the more effective

antioxidant and anticancer activity of whole vegetal

Phytochem Rev

123

Author's personal copy

food (or total extracts) compared to isolated phyto-

chemicals. The overlapping of different action

mechanisms of the various phytochemicals should

be considered in establishing the overall effect. In

addition, it has to be pointed out that the same

compound, shown to have both antioxidant and

chemopreventive biological effects, can, under dif-

ferent conditions, have pro-oxidant and disease-

causing activities (Alarcon de la Lastra and Villegas

2007).

Although the direct antioxidant activity is not the

only mechanisms for antioxidant phytochemicals, one

should consider that oxidative stress/damage is clearly

involved in many pathologic conditions and that

oxidative signaling likely plays a greater role in

chronic diseases. Thus, the balance of various oxidants

and antioxidants, affecting the reactive oxygen species

levels, specifically interacts with cell signaling sys-

tems and ultimately determines gene expression

controlling normal/abnormal cellular tissue pheno-

types. Cell signaling mechanisms, affected by redox

chemistries, are not limited to the only intracellular

signal transduction pathways, but also involve inter-

cellular signaling through gap junctions, since gene

expression must be coordinated between cells of a

tissue, in order to maintain tissue homeostasis (Upham

and Trosko 2009).

Among the suggested different mechanisms by

which phytochemicals exert their anticarcinogenic

effects, the up-regulation or the prevention of the

down-regulation of gap-junction intercellular commu-

nication (GJIC) is considered a basic mechanism for

the neoplastic transformation inhibition, since cell-to-

cell communication, mediated via transmembranal

gap junctions, is crucial in regulating normal cellular

homoeostasis, cell proliferation and differentiation

(Trosko and Ruch 1998;Trosko and Chang 2001).

From this perspective, Upham and Trosko (2009)

have proposed the hypothesis that one potential

function of gap junctions is to modulate levels of

second messengers that are either positive or negative

cofactors needed in signal transduction. Several

reactive oxygen species, such as superoxide, hydrogen

peroxide, nitrous oxide, all have very low molecular

weights, thus can be predicted to readily traverse the

gap junction channels, and can, consequently, serve as

ideal second messengers in a network of signaling

pathways that include gap junctions. Therefore, the

involvement of GJIC as mechanism of action of the

phytochemicals, does not exclude the involvement of

redox systems (Fig. 1).

Gap junction intercellular communication

and their structural proteins

In multicellular organisms, GJIC is a key mechanism

to coordinate cellular electrotonic and metabolic

events in tissues and organs and to maintain homeo-

stasis. GJIC facilitates direct exchanges of essential

cell growth-controlling signals and metabolites, less

than 1–2 kDa, including Na, K, Ca, cyclic AMP and

ATP (Unwin and Zampighi 1980; Goodenough and

Paul 2009). Gap junctions are intercellular membrane

channels, composed by head-to-head docking of

hexameric assemblies (connexons) of tetraspan inte-

gral membrane proteins, the connexins (Cx). These

channels gather in groups, containing tens to thou-

sands of closely packed intercellular channels, so-

called plaques, that span the two plasma membranes of

adjacent cells (Goodenough and Paul 2009).

Gap-junction proteins, connexins or their structural

of functional analogues, are present in a wide variety

of organisms (Panchin 2005; Phelan and Starich

2001). Gap junctions in prechordates are composed

of non-homologue proteins, called innexins (Phelan

2005). Innexin-related proteins, called pannexins, bear

significant sequence homology with the invertebrate

gap junction proteins (innexins), but not with the

chordate gap junction proteins, connexins, although

the predicted membrane topology is similar. Pannex-

ins have persisted in vertebrates (Baranova et al.

2004). Although they can form functional channels

(hesamers or hemichannels) embedded in a single

plasma membrane, it is not clear if they form

functional intercellular channels in vivo (Sosinsky

et al. 2011). Recently, pannexins are considered as

important targets for treatment of neurological disor-

ders, such as stroke and epilepsy (Kim and Kang

2011). It is possible that future research might indicate

specific functions of pannexin proteins as interfering

with cell signaling pathways. In chordates, connexins

arose by convergent evolution (Alexopoulos et al.

2004) to expand by gene duplication into a 21-member

gene family, and in humans, more than twenty

connexin species have already been characterized

(Cruciani and Mikalsen 2002; Beyer and Berthoud

2009). They all share a similar tetraspan structure of

Phytochem Rev

123

Author's personal copy

four membrane-spanning domains, two extracellular

loops, one cytoplasmic loop, and cytosolic N-terminal

tail and C-terminal region. The cytosolic regions are

mainly interested to diversity between the connexin

family members (Evans and Martin 2002). Connexins

are commonly named on the bases of their molecular

weight, as predicted by cDNA sequencing, such as

Cx43, the most common connexin, with molecular

mass of 43 kDa.

Connexins keep tissue homeostasis by forming

intercellular channels and by allowing the intercellular

exchange of molecules associated with cell growth

and cell death (Loewenstein 1981; Trosko and Chang

2001; Wei et al. 2004; Vinken et al. 2006), but seem,

also, to contribute to intracellular signaling by gap-

junction and hemichannel-independent actions (Jiang

and Gu 2005; Vinken et al. 2009). Interestingly, the

formation of functional GJIC seems not to be the only

function of connexins, inhibition of growth upon

transfection of tumor cells with connexin genes is not

always associated with enhanced GJIC activity, an

observation that indicate the diverse functions of

connexins in the control of homeostasis (in Vinken

et al. 2006). However, because of the complexity of

Fig. 1 Putative actions of

phytochemicals on gap

junction system. Dietary

phytochemicals might

interfere with GJIC system

at different levels.

Epigenetic events allow the

modulation of the mRNA

expression of the different

connexin genes; alterations

of translational and

posttranslational events

(mainly phosphorylation)

might modify the correct

connexin protein assembly,

targeting to the cell

membrane and degradation;

finally, hemiconnexon

docking and connexon

gating (opening–closing)

might be regulated (see the

literature cited in the text).

N nucleus, RER rough

endoplasmic reticulum, GAGolgi apparatus, TGN trans

Golgi network, PM plasma

membrane

Phytochem Rev

123

Author's personal copy

trying to explain in vitro results to in vivo results, these

few studies, challenging the primary role of gap

junctions in the transfer of ions and small molecules in

growth control, might have another explanation. On

the other hand, the connexin proteins have been shown

to have other non-channel functions (Naus and Laird

2010).

The mechanisms controlling gap junction’s role in

cellular behavior are strictly regulated (Hesketh et al.

2009) at multiple levels, ranging from connexin gene

transcription to gap junction trafficking and degrada-

tion. Two major kinetic trails of GJIC control have

been described, namely, the fast regulation (millisec-

ond range) and the long-term regulation (hour range)

(Goodenough and Paul 2009). The most rapid time-

scales involve changing the unitary conductance of

single channels or altering their probability of opening

and is triggered by a number of factors, including

transmembrane voltage, and H? and Ca2? ions

(chemical gating) (Holder et al. 1993; Richard

2001). Slower regulation is achieved by altering the

number of channels present in the membrane by

changing rates of synthesis and assembly, posttrans-

lational modification and/or protein degradation

(Martin et al. 2001; Simek et al. 2009; Boassa et al.

2010). Among these actions, connexin phosphoryla-

tion, mainly occurring at the C-terminal cytosolic tail,

has been widely studied. Phosphorylation is involved

both in changing single channel conductance and in

protein trafficking to the cell surface and degradation,

rapid and slow regulation mechanisms, respectively.

The regulation of GJIC by connexin phosphorylation

is quite complex, as the outcome of this posttransla-

tional modification is both connexin- and kinase-

specific (Musil and Goodenough 1991; Matesic et al.

1994; Bruzzone et al. 1996; Laird 2005). Several

kinases are known to target connexin proteins,

including MAP kinases, PKC, PKA, and CK1. In

contrast, little is known about the dephosphorylation

of connexins, but it is thought that specific phospha-

tases (e.g., protein phosphates PP2) are involved in

maintaining the connexin phosphorylation/depho-

sphorylation equilibrium (Cruciani and Mikalsen

2002; Herve and Sarrouilhe 2002; Lampe and Lau

2004; Pahujaa et al. 2007).

As the appropriate GJIC regulation is essential for

maintaining the tissue homeostatic balance, abnormal

GJIC can result in several pathologic conditions as

indicated by most normal cells having functional GJIC

and most cancer cells having dysfunctional GJIC

(Trosko and Chang 2000; King and Bertram 2005).

Gap junctions play many roles in vascular biology,

including control of vascular tone, permeability,

angiogenesis, and remodeling. Recent works support

an important role of diverse connexins in vascular

physiology and a largely multifaceted role in the

development of heart and vascular disease. Disruption

or alterations of the intercellular signaling pathway,

mediated by gap junction, have considerable implica-

tions for development of heart and vascular diseases

(Brisset et al. 2009), as well as for the cancer process.

Malignant transformation is routinely demonstrated in

cultured animal cells as an increase in uncontrolled

cell growth resulting in distinct areas of multilayered

foci (Yamasaki and Enomoto 1985; Yamasaki et al.

1987). Dysfunctional GJIC in most cancer cells and

detrimental reversible changes in GJIC are strongly

related to the promotion phase of cancer development

(Trosko and Ruch 1998; Trosko 2007b) and the

irreversible progression or metastatic step of cancer

process (Trosko 2008).

GJIC and cancer

All cancers have been generally viewed as the result of

the homeostatic regulation disorder, which is related to

the GJIC modulation between the cells within a tissue,

that triggers intra-cellular signal transduction mecha-

nisms. Since cancer cells, unlike normal cells, are

characterized by the lack of growth control (loss of

contact-inhibition), inability to terminally differenti-

ate and to apoptose, normally, and they either have no

connexin expression or have expressed connexins but

no functional GJIC, it would seem that GJIC is the

ultimate down-stream cell function that must be

maintained to prevent cancer (Trosko 2007b). As a

consequence, the cells lose the ability to respond

appropriately to extra-cellular stimuli (Trosko et al.

1998). The classical model of carcinogenesis begins

with initiation, during which, exposure to a carcinogen

results in an irreversible genetic change to a single cell

(Fig. 2).

The following promotion phase (a reversible and

long-term process) results in the clonal expansion of

the single initiated cell, due to selective mitogenesis

and the decreased apoptosis of the initiated cell

(Trosko and Tai 2006). Based on the assumption that

Phytochem Rev

123

Author's personal copy

the target cell for the start of the carcinogenic initiation

event is the adult stem cell (Trosko 2009), and if the

DNA damage to the cell is not adequately repaired or

if an error of replication results in a spontaneous

mutation of a critical gene, the cell is prevented from

terminal differentiation and apoptosis.

The reversible down regulation of GJIC plays a role

during the promotion phase of carcinogenesis and the

presence of GJIC is closely linked to the suppression

of tumorigenic phenotype (Trosko and Chang 2001;

Trosko and Ruch 2002). Cancer prevention strategies,

acting at the promotion stage, are more effective than

those intervening at the tumor initiation stage (an

irreversible and short-term process), because initiation

can occur any time a cell divides. One can reduce the

risk to initiation but the risk cannot be reduced to zero,

Fig. 2 Scheme of postulated actions of phytochemicals in

cancer chemoprevention. Transformation of the normal adult

stem cell into an initiated cell starts the carcinogenesis process.

Initiated cells might undergo the tumour promotion into pre-

neoplastic cells by a number of means, such as chronic

inflammation, surgery, cell killing, growth factors and exoge-

nous chemicals that can cause initiated cells to proliferate and to

inhibit apoptosis. During this promotion phase, other changes

that allow a single initiated cell to invade and to metastasize,

constitutes the Progression phase. The malignant tumor consists

of a mixture of ‘‘cancer stem cells’’ and ‘‘cancer non-stem

cells’’. Phytochemicals might interfere with different steps of

this process. Some chemopreventive phytochemicals inhibit

metabolic activation of the pro-carcinogens or stimulate the

detoxification systems, avoiding their subsequent interaction

with DNA or other cellular target and therefore blocking tumor

initiation (blocking agents). Other phytochemicals might act by

suppressing the later steps (mostly promotion) of multistage

carcinogenesis (suppressing agents). Some phytochemicals can

act as both blocking and suppressing agents

Phytochem Rev

123

Author's personal copy

since every time the DNA replicates, there is always a

finite chance of an error of replication leading to

spontaneous mutations. The promotional phase of

carcinogenesis is a consequence of epigenetic events

involving inflammation (Surh 1999) and the inhibition

of GJIC (Huang et al. 2001), which could be also

mediated by ROS or ROI (Reactive Oxygen Species,

Reactive Oxygen Intermediates).

The association between increased cell prolifera-

tion and decreased GJIC is well known (Yotti et al.

1979; Yamasaki et al. 1993; Yamasaki 1995). Despite

some exceptions, indeed, tumor cells generally display

reduced GJIC as first hallmark of cancer (Trosko and

Ruch 1998). Numerous mechanisms underlie the loss

of GJIC in carcinogenesis. Rather than mutations in

connexin genes, that seem a rare event, epigenetic

modifications can trigger silencing of connexin gene

expression. In deed, if the initiation occurred in an

adult stem cell, which does not express its connexins,

one might not expect to see any connexin expression in

the metastatic cancer cell (Trosko 2007b).These

epigenetic mechanisms yield heritable or non-herita-

ble changes to the methylation and acetylation patterns

of DNA and histones (Upham et al. 1998; Moggs et al.

2004; Trosko et al. 1998; Trosko 2007a). Indeed,

impairment of the epigenetic machinery during cancer

could trigger the silencing of tumor suppressor genes,

including connexins (Pointis et al. 2007). However,

more likely, it is the posttranslational modification of

the expressed connexin proteins that is associated with

many, if not most, cancers. The recent demonstration

of ‘‘cancer stem cells’’ in a mixed population of

‘‘cancer non-stem cells’’ might prove to be a clue to

the two types of cancer cells, which do or do not

express their connexin genes (Trosko and Tai 2006).

Upregulation of connexin expression might therefore

represent an attractive anti-cancer therapy (Vinken

et al. 2009, 2011).

The classical epigenetic mechanisms, such as the

methylation of DNA, modification of histones, and

interfering microRNA (miRNA), represent epigenetic

elements dysregulated in cancer. Growing findings

support the concept that nutritional changes are able to

modulate epigenetic variability at specific transcrip-

tion regulation sites. Therefore, dietary components,

which can affect epigenetic mechanism(s), might

influence tumorigenesis by regulation of the expres-

sion of certain key genes. Essential micronutrients,

such as folate, vitamin B-12, selenium, and zinc, as

well as the dietary phytochemicals, sulforaphane, tea

polyphenols, curcumin, genistein and allyl sulfur

compounds, are among a growing list of agents that

affect epigenetic events as novel mechanisms of

chemoprevention. Some bioactive food components

have been shown to have cancer inhibition activities

by reducing DNA hypermethylation of key cancer-

causing genes through their DNA methyltransferase

(DNMT)-inhibition properties. Well-known bioactive

dietary compounds, such as the soybean isoflavone,

genistein, and the green tea polyphenol, (–)-epigallo-

catechin-3-gallate (EGCG), have been found to inhibit

tumorigenesis through epigenetic control, such as

reactivation of various methylation-silenced genes, in

several cancer cell lines (Li and Tollefsbol 2010).

Both genistein and EGCG have been found, also,

modulate GJIC and connexin expression, at physio-

logical, not toxic and non pro-oxidant concentrations

(see below).

Down-regulation of connexin expression, incorrect

phosphorylation and aberrant cytosolic localization of

connexin proteins are also frequently observed in

tumor cells (Yamasaki and Naus 1996; Vine and

Bertram 2002). The closure of gap junctions is mainly

mediated by phosphorylation-modulated conforma-

tional changes of connexins, as thoroughly described

for connexin 43 (Cx43), the most largely diffused

connexin (Ruch et al. 1993; Solan and Lampe 2009;

Hesketh et al. 2009). The consequent dysfunction in

intercellular communication is thought to allow tumor

cells to escape from normal growth regulation by the

surrounding cells (Yotti et al. 1979). In addition,

inappropriate connexin expression can directly trigger

homeostatic imbalance. In fact, connexin deficiency is

known to result in increased susceptibility to sponta-

neous or chemically induced carcinogenesis (Temme

et al. 1997).

A relationship between oncogenes, such as ras and

src, and connexin function was found (Trosko et al.

2000). The connection between Src tyrosine kinase,

which has been implicated in progression of a wide

variety of cancers and Cx43, has been described in

detail. Src can phosphorylate Cx43, and this event was

associated with the suppression of gap junction

communication. In addition, Src activates multiple

signaling pathways that can also affect intercellular

communication. For example, serine kinases, includ-

ing PKC and MAPK, are downstream effectors of Src

that can also phosphorylate Cx43 and disrupt gap

Phytochem Rev

123

Author's personal copy

junctional communication (Bao et al. 2004; Pahujaa

et al. 2007). Connexin genes are, therefore, considered

as tumor suppressor gene (Pointis et al. 2007) or

conditional tumor suppressors, modulating cell pro-

liferation, adhesion and migration (Naus and Laird

2010). Actually, their overexpression in tumor cells,

that naturally express connexins, is known to decrease

cell proliferation and increase cell death. This could be

related to the gap-junction, hemichannel- independent

activity of connexins.

Whereas the inhibition of GJIC is strongly related

to carcinogenicity, enhancers of GJIC are expected to

prevent cancer. Far from oversimplifying complex

issues and knowing that multiple exogenous and

endogenous causes affect carcinogenesis, GJIC regu-

lation can be undoubtedly considered as a key

mechanism. A consistent observation is that most

oncogenes, growth factors and endogenous and exog-

enous tumor promoters, such as cytokines, hormone,

pesticides, peroxisome proliferators and dietary addi-

tives, are reported to inhibit GJIC (Huang et al. 2001;

Sai et al. 2001; Kang et al. 2002; Mally and Chipman

2002; Rivedal and Leithe 2005), while antitumor-

promoting agents and anticancer drugs can reverse the

down-regulation of GJIC (Sai et al. 2000, 2001;

Trosko and Chang 2001; Kang et al. 2002; Trosko and

Ruch 2002; Lee et al. 2010a, b). In addition, transfec-

tion of gap junction (cx32 or cx43) genes into GJIC-

defective and neoplastic cells resulted in the restora-

tion of GJIC and reversion of the transformed

phenotype (Rose et al. 1993; Omori et al. 1996).

If prevention/treatment of cancer has to occur,

prevention of the chronic down regulation of GJIC by

tumor promoters, in non-tumorigenic but initiated

cells, or the up-regulation of GJIC in stably down-

regulated GJIC in tumor cells, must occur to prevent or

to treat cancers (Trosko and Ruch 1998; Trosko and

Chang 2001; Trosko 2003) Consequently, prevention

of down-regulation of GJIC might be crucial in

preventing tumor promotion (Sai et al. 2000; Choung

et al. 2011).

Phytochemicals and GJIC

Several plant-derived compounds demonstrated the

ability to control GJIC at epigenetic levels (Trosko and

Chang 2001; Lee and Lee 2006). A wide array of

phenolic substances and carotenoids, in dietary and

medicinal plants has been reported to possess this

activity (Table 1). The screening for compounds able

to modulate GJIC could be an effective strategy in the

exploration of naturally occurring products able to

inhibit and/or to prevent cancers. Here we try to

examine, in a non-exhaustive manner, some studies on

the effect of single phytochemicals or plant extracts on

GJIC and/or connexin expression, in specific cell or

animal systems.

Simple methods to measure, qualitatively and

quantitatively, the GJIC in cell cultures are the

microninjection of the fluorescent dye Lucifer Yellow,

or the scrape loading/dye transfer assay, also used as

transfer of Lucifer Yellow in isolated tissue slices in

the in vivo experiments.

Carotenoids

Although tomatoes and tomato products contain many

nutrients and phytochemicals that are proposed to

inhibit carcinogenesis, particularly prostate cancer

(Chan et al. 2009), their main carotenoid, lycopene,

has received the most intense focus. Lycopene is the

most potent carotenoid antioxidant and the predomi-

nant carotenoid in human plasma (Al-Delaimy et al.

2004; van der Pols et al. 2009), various tissues (Cowan

et al. 1999), and the prostate gland (Giovannucci

2002). Interest in lycopene was firstly focused on its

antioxidant properties, however their beneficial effects

are related also to other mechanisms, such as hor-

monal and immune system, inflammation response

(Singh and Goyal 2008; Palozza et al. 2010, 2011;

Ried and Fakler 2011) and modulation of intercellular

gap junction communication.

In studies in vivo, alpha- and beta-carotene, as well

as lycopene, the most represented tomato carotenoids,

were able, differentially, to modulate GJIC in dose-

dependent manner in rat liver. Improving of cell

communication was only detected at the one dose,

where several elevated doses were ineffective or

inhibiting (Krutovskikh et al. 1997).

In vitro cell line studies have shown that carote-

noids, such as beta-carotene, canthaxanthin, lutein,

lycopene and alpha-carotene increased GJIC in a dose-

dependent manner at concentrations up to 1 lmol L-1

in C3H/10T1/2 cells (Zhang et al. 1991). Lycopene at

physiological concentrations (0.5–5 lmol L-1)

strongly, and much better than beta-carotene, inhibited

proliferation, dose dependently and was able to

Phytochem Rev

123

Author's personal copy

Ta

ble

1E

xam

ple

so

fp

hy

toch

emic

als

able

tom

od

ula

teG

JIC

Veg

etal

com

po

un

ds

Eff

ect

on

gap

jun

ctio

nsy

stem

Ref

eren

ces

Alp

ha-

caro

ten

e,b

eta-

caro

ten

e,

lyco

pen

e

Inv

ivo

hig

hd

ose

(50

mg

/kg

-bo

dy

wei

gh

t)in

hib

ited

low

do

se(5

mg

/kg

-bo

dy

wei

gh

t)

enh

ance

dG

JIC

inli

ver

of

rat

Kru

tov

skik

het

al.

(19

97)

Bet

a-ca

rote

ne,

can

thax

anth

in,

lute

in,

alp

ha-

caro

ten

e

Incr

ease

dG

JIC

ina

do

se-d

epen

den

tm

ann

erat

con

cen

trat

ion

su

pto

1l

mo

lL

-1

in

C3

H/1

0T

1/2

cell

s

Zh

ang

etal

.(1

99

1)

Ly

cop

ene

met

abo

lite

s,

acy

clo

reti

no

icac

id

Incr

ease

dG

JIC

thro

ug

hst

abil

izat

ion

of

Cx

43

mR

NA

inh

um

anfe

tal

skin

fib

rob

last

san

d

inW

B-F

34

4ra

tli

ver

epit

hel

ial

cell

s

Sta

hl

etal

.(2

00

0)

Au

stet

al.

(20

03

)

Ly

cop

ene

En

han

ced

GJI

C,

Cx

43

mR

NA

and

pro

tein

exp

ress

ion

inK

B-1

hu

man

ora

ltu

mo

rce

lls

and

inM

CF

-7ce

lls

Incr

ease

dR

ARa

and

Cx

43

mR

NA

and

pro

tein

exp

ress

ion

inM

CF

-7an

dM

DA

-MB

-

23

1,

bre

ast

can

cer

cell

lin

esan

din

MC

F-1

0a

fib

rocy

stic

bre

ast

cell

lin

e

No

chan

ge

inth

ep

rote

inle

vel

so

fC

x4

3in

vit

roo

rin

viv

oin

and

rog

enin

dep

end

ent

DU

14

5p

rost

ate

can

cer

cell

s

No

chan

ge

inC

x4

3p

rote

inle

vel

sin

mo

use

emb

ryo

nic

fib

rob

last

sth

atco

nta

ined

(Cx

43

?/?

)o

rla

cked

(Cx

43

-/-

)ex

pre

ssio

no

fC

x4

3;

red

uce

dg

row

tho

fC

x4

3?

/?

ME

Fb

ut

no

effe

cto

np

roli

fera

tio

no

fC

x4

3-

/-M

EF

cell

s

Ind

uce

dre

-lo

cali

zati

on

of

cyto

pla

smic

Cx

43

on

cell

mem

bra

nes

inM

CF

7

Ch

alab

iet

al.

(20

07

)

Sta

hl

etal

.(2

00

0)

Liv

ny

etal

.(2

00

2)

Fo

rnel

liet

al.

(20

07

)

Fo

rdet

al.

(20

11

)

Fo

rnel

liet

al.

(20

07

)

Fu

cox

anth

inIn

crea

sed

of

Cx

43

and

Cx

32

pro

tein

and

mR

NA

lev

els,

enh

ance

dG

JIC

and

incr

ease

d

intr

acel

lula

rca

lciu

mco

nce

ntr

atio

nin

SK

-Hep

-1h

um

anh

epat

om

ace

lls

Liu

etal

.(2

00

9)

(–)-

Ep

igal

loca

tech

in-3

-gal

late

(EG

CG

)

(–)-

Ep

icat

ech

in(E

C)

Pre

ven

td

ow

n-r

egu

lati

on

of

GJI

Cin

PC

B-i

nd

uce

din

hep

ato

carc

ino

ma

cell

s

Pre

ven

td

ow

n-r

egu

lati

on

of

GJI

Cin

PM

A-i

nd

uce

din

ker

atin

ocy

tes

Pre

ven

tth

eG

JIC

-in

hib

ito

ryef

fect

so

fd

imet

hy

lnit

rosa

min

e,in

MD

CK

cell

s

En

han

ced

the

pro

tein

exp

ress

ion

of

Cx

43

and

the

fun

ctio

no

fG

JIC

bu

tn

ot

affe

cted

on

mR

NA

lev

els

of

Cx

43

,C

x4

0an

dC

x4

5in

neo

nat

alra

tca

rdio

my

ocy

tes

Att

enu

ated

the

red

uct

ion

of

Cx

43

pro

tein

and

GJI

Cin

card

iom

yo

cyte

su

nd

erh

igh

glu

cose

Hig

hd

ose

s(2

00

–8

00

lM)

of

EG

CG

,b

ut

no

tE

C,

inh

ibit

GJI

Cin

WB

-F3

44

no

rmal

rat

liv

erep

ith

elia

lce

lls

and

ind

uce

dp

ho

sph

ory

lati

on

of

Cx

43

Ru

chet

al.

(19

89)

Sai

etal

.(2

00

0)

Ch

ou

ng

etal

.(2

01

1)

Tak

ahas

hi

etal

.(2

00

4)

Yu

etal

.(2

01

0)

Kan

get

al.

(20

08

)

Nar

ing

enin

Incr

ease

dG

JIC

inC

6g

lio

ma

cell

sb

ut

no

to

nn

orm

alce

lls

Sab

arin

ath

anan

dV

anis

ree

(20

10

)

Ap

igen

inan

dta

ng

eret

inIn

crea

sed

GJI

Can

du

p-r

egu

late

dC

x4

3,

anta

go

niz

edth

eG

JIC

inh

ibit

ion

TP

A-

and

BH

T-i

nd

uce

din

rat

liv

erep

ith

elia

lce

lls

and

V7

9lu

ng

fib

rob

last

s

Inh

ibit

ion

of

GJI

Cin

viv

oin

rat

fed

wit

hta

ng

erin

e

Ch

aum

on

tet

etal

.(1

99

6)

Ch

aum

on

tet

etal

.(1

99

7)

Gen

iste

inan

dq

uer

ceti

nIn

crea

sed

Cx

43

pro

tein

lev

els

and

sup

pre

ssed

cell

pro

life

rati

on

inM

DA

-MB

-23

1C

on

kli

net

al.

(20

07

)

Qu

erce

tin

Rev

erse

dH

2O

2-m

edia

ted

inh

ibit

ion

of

GJI

Cb

yth

eH

2O

2-m

edia

ted

ER

K1

/2–

Cx

43

sig

nal

ing

pat

hw

ayin

nW

B-F

34

4ra

tli

ver

epit

hel

ial

cell

s

Lee

etal

.(2

01

0a,

20

10

b)

Phytochem Rev

123

Author's personal copy

Ta

ble

1co

nti

nu

ed

Veg

etal

com

po

un

ds

Eff

ect

on

gap

jun

ctio

nsy

stem

Ref

eren

ces

Res

ver

atro

lR

esto

red

the

GJI

C-i

nh

ibit

ion

,T

PA

-an

dD

DT

-in

du

ced

and

red

uce

dC

x4

3

hy

per

ph

osp

ho

ryla

tio

nin

WB

-F3

44

rat

liv

erep

ith

elia

lce

lls

Ind

uce

dsh

arp

incr

ease

of

GJI

C,

cell

cycl

ear

rest

and

apo

pto

sis

inH

epG

2ce

lls

En

han

ceG

JIC

and

del

ayin

cell

cycl

ep

rog

ress

ion

,al

soin

com

bin

atio

nw

ith

con

tro

lled

exp

osu

reto

Xra

ys,

inh

um

ang

lio

bla

sto

ma

cell

s

Up

ham

etal

.(2

00

7)

Nie

lsen

etal

.(2

00

0)

Yan

etal

.(2

00

6)

Leo

ne

etal

.(2

00

8)

Zam

inet

al.

(20

09

)

Jian

get

al.

(20

10)

Pte

rost

ilb

ene

Rec

ov

eran

dp

rev

ent

fro

mH

2O

2-i

nd

uce

dG

JIC

-in

hib

itio

nin

WB

-F3

44

rat

liv

er

epit

hel

ial

cell

s;d

ow

n-r

egu

late

Cx

43

ph

osp

ho

ryla

tio

nb

yth

ein

acti

vat

ion

of

ER

K1

/2

and

p3

8M

AP

kin

ase

Kim

etal

.(2

00

9)

Gal

lic

acid

Ind

uce

sH

2O

2-p

rod

uct

ion

and

inh

ibit

sG

JIC

inra

tep

ith

elia

lce

lls

by

ph

osp

ho

ryla

tio

no

f

con

nex

in4

3an

dac

tiv

atio

no

fE

RK

1/2

(at

hig

hco

nce

ntr

atio

ns)

Kim

etal

.(2

00

9)

Caf

feic

acid

ph

enet

hy

l

este

r(C

AP

E)

Res

tore

dG

JIC

thro

ug

hth

ep

ho

sph

ory

lati

on

of

Cx

43

inth

eG

JIC

-defi

cien

tH

-ras

WB

cell

san

din

hib

ited

the

con

stit

uti

ve

exp

ress

ion

of

CO

X-2

Na

etal

.(2

00

0)

Lee

etal

.(2

00

4)

Ind

ole

-3-c

arb

ino

lP

rev

ent

H2O

2-i

nd

uce

din

hib

itio

no

fG

JIC

inW

B-F

34

4ra

tli

ver

epit

hel

ial

cell

s,b

y

inh

ibit

ion

of

Ak

tp

ho

sph

ory

lati

on

and

,li

kel

y,

by

Cx

43

ph

osp

ho

ryla

tio

np

rev

enti

on

Hw

ang

etal

.(2

00

8)

Lo

vas

tati

nR

esto

red

GJI

Can

din

hib

ited

the

tum

ori

gen

icp

ote

nti

alo

fK

-ra

s-tr

ansf

orm

edm

uri

ne

lun

gca

rcin

om

ace

lls

Inh

ibit

GJI

Can

dth

em

igra

tio

nan

dp

roli

fera

tio

no

fsm

oo

thm

usc

lece

lls

(SM

Cs)

(an

tip

roli

fera

tiv

eef

fect

tro

ug

hG

JIC

inh

ibit

ion

)

Ru

chet

al.

(19

93)

Sh

enet

al.

(20

10

)

Veg

eta

lex

tra

cts

Su

per

crit

ical

-CO

2-e

xtr

acte

d-

ole

ore

sin

sfr

om

tom

ato

and

tom

ato

/gra

pe

seed

mat

rice

s

Incr

ease

dG

JIC

,al

low

edre

cov

erin

go

fH

gC

l 2-i

nh

ibit

edG

JIC

and

ind

uce

dC

x4

3m

RN

A

exp

ress

ion

inh

um

ank

erat

ino

cyte

s

Incr

ease

dG

JIC

,in

du

ced

Cx

43

mR

NA

and

relo

cali

zati

on

of

Cx

43

pro

tein

inM

CF

-7

cell

s

Zef

feri

no

etal

.(2

00

8)

Leo

ne

etal

.(2

01

0)

Leo

ne

etal

.su

bm

itte

d

Co

coa

po

lyp

hen

ol

extr

act

Pro

tect

edag

ain

stH

2O

2-i

nd

uce

din

hib

itio

no

fG

JIC

inra

tli

ver

epit

hel

ial

cell

sb

y

atte

nu

atin

gin

trac

ellu

lar

RO

San

db

lock

ing

the

ER

K/C

x4

3si

gn

alin

gp

ath

way

,b

ut

no

t

the

p3

8M

AP

Ksi

gn

alin

gp

ath

way

Lee

etal

.(2

00

3)

Kiw

ifru

itex

trac

tsR

eco

ver

fro

mth

eH

2O

2-i

nd

uce

din

hib

itio

no

fG

JIC

blo

ckin

gth

eH

2O

2-m

edia

ted

-

ind

uce

dp

ho

sph

ory

lati

on

of

Cx

43

and

ER

K1

/2in

WB

-F3

44

cell

s

Lee

etal

.(2

01

0a,

20

10

b)

Gra

pe

seed

extr

acts

Tra

nsi

entl

yin

crea

sed

of

GJI

C,

ind

uce

din

crea

seo

fC

x4

3m

RN

Aan

dre

-lo

cali

zati

on

of

Cx

43

pro

tein

inM

CF

-7ce

lls

Leo

ne

etal

.su

bm

itte

d

Pet

asit

esja

po

nic

us

extr

acts

Incr

ease

dG

JIC

and

the

lev

elo

fC

x4

3an

dre

du

ced

the

TP

A-i

nd

uce

din

hib

itio

no

fG

JIC

and

Cx

43

lev

els

inra

tli

ver

epit

hel

ial

cell

sW

B-F

34

4

Kan

get

al.

(20

10

)

Phytochem Rev

123

Author's personal copy

enhance GJIC, likely by upregulation of Cx43 gene

and protein expression in KB-1 human oral tumor cells

(Livny et al. 2002) and in MCF-7 cells (Fornelli et al.

2007).

Other than lycopene, also lycopene metabolites, as

well as the cleavage product acycloretinoic acid, which

could result from lycopene oxidation, stimulated GJIC

through stabilization of connexin43 mRNA in human

fetal skin fibroblasts (Stahl et al. 2000) and in rat liver

epithelial WB-F344 cells (Aust et al. 2003). The

interaction among lycopene, retinoic acid receptors

(RARa and RARb), stimulation of GJIC and synthesis

of connexin 43 were also analyzed in two breast cancer

cell lines, MCF-7 and MDA-MB-231, and in a fibrocystic

breast cell line, MCF-10a. Lycopene exposure increased

RARa and Cx43 expression at both mRNA and protein

levels in the two breast cell lines (Chalabi et al. 2007).

Inversely, no change in the protein levels of Cx43 in vitro

or in vivo with lycopene and apo-lycopenal treatment, in

androgen-independent DU145 prostate cancer cells, was

found (Ford et al. 2011). However, lycopene at supra-

physiological concentrations (15–25 lmol L-1) reduced

DU145 cell proliferation. This apparent contradictory

result might be due not only to the malignancy grade of

the cells, as author suggested, but also to the lycopene

concentrations used and to the experiment design. The

modulation of cell–cell communication could also

depend from activation or re-localization of the preexist-

ing connexin pool. Therefore, GJIC response to carote-

noids and connexin cell localization, rather than the total

level of connexin protein, should be evaluated. Lycopene

induced re-localization of cytoplasmic Cx43 on cell

membranes in breast cancer cells, MCF7 (Fornelli et al.

2007). Thus, from our personal observations on MCF7

cells and, as demonstrated in semioma cells (Roger et al.

2004), the mere relocation/delocalization of the resident

pool of Cx43 to the endomembrane systems is also

associated with the modulation of GJIC and decreased

cell growth in vitro. The relationship between the Cx43

localization on the membrane and growth regulation

could be associated with the phosphorylation of Cx43,

which would result in the cytoplasmic location to the

endosomes through the activation of the extracellular

signal-regulated kinase/mitogen-activated protein kinase

pathway (Mograbi et al. 2003; Fornelli et al. 2007).

Supercritical-CO2-extracted tomato oleoresin is a

complex mixture of highly concentrated lycopene,

other carotenoids, lipids and phenols derivatives from

tomato, showed a much higher antioxidant activity

compared to lycopene standard. Our results demon-

strated that lycopene-enriched oleoresin significantly

increased the production of IL1-b and TNF-R pro-

inflammatory cytokines in HgCl2-treated human

keratinocytes. Oleoresins affected GJIC functionality

and recovery in HgCl2 treated keratinocytes (Zefferino

et al. 2008). Supercritical-CO2-extracted-oleoresins

(0.9 lmol L-1 lycopene), obtained from tomato, and

tomato, added with other plant matrix (grape seeds),

showed a higher in vitro antioxidant activity compared

with pure lycopene and b-carotene and a remarkable

ability to enhance the GJIC and to increase cx43 gene

expression in human keratinocytes. The oleoresins

were also able to completely overcome the GJIC

inhibition induced by 10 nmol L-1 HgCl2, mercury

(II) chloride (Leone et al. 2010). A higher effect of

these oleoresins on GJIC is observed in MCF-7 cells

(Leone et al. unpublished), compared with the stan-

dard lycopene (Fornelli et al. 2007).

In addition, experimental studies, both in vitro and

in vivo, have suggested that the colorless carotenoid

precursors, phytoene and phytofluene, also present in

significant quantities in tomato extracts and in tomato

based foods, exhibited bioactivity (Engelmann et al.

2011). Although little is known about their impact in

humans, it would be interesting to test their ability to

modulate GJIC and connexin expression. The coop-

erative behavior of phytochemicals in natural sources

further suggests that other components required eval-

uation for their effect on gap junction modulation.

These studies suggest that a combination of tomato

phytochemicals, a mixture of precursors, metabolites

and/or cleavage products of carotenoids, present in the

tomato extracts, can be more effective than the single

compound, not only for the antioxidant protection but

is also important in anticancer mechanisms.

Other sources of carotenoids from marine organ-

isms are recently considered (Guedes et al. 2011).

Fucoxanthin is one of the most abundant carotenoids

found in the brown seaweed, Undaria pinnatifida, able

to inhibit tumor proliferation in vitro. The mecha-

nisms, underlying the anti-cancer effects of fucoxan-

thin, are still unclear. Liu et al. (2009) showed that

fucoxanthin (1–20 lmol L-1) strongly and concen-

tration-dependently inhibited the proliferation of SK-

Hep-1 human hepatoma cells, by cell cycle arrest at

G0/G1 phase and induced cell apoptosis, whereas it

facilitated the growth of non-cancer (BNL CL.2) cells.

Fucoxanthin was found to enhance, significantly,

Phytochem Rev

123

Author's personal copy

GJIC of SK-Hep-1 cells without affecting that of BNL

CL.2 cells. A significant increase of protein and

mRNA expressions of Cx43 and Cx32 was also

observed in SK-Hep-1 cells. Moreover, fucoxanthin

markedly increased the concentration of intracellular

calcium levels in SK-Hep-1 cells. Thus, fucoxanthin

seems specifically induced an antiproliferative against

SK-Hep-1 cells, and the effect is associated with

upregulation of Cx32 and Cx43, and enhanced GJIC.

The enhanced GJIC might be also responsible for the

increase of the intracellular calcium level, which then

causes cell cycle arrest and apoptosis (Liu et al. 2009).

Polyphenols

Numerous, and still growing literature, data show that

many dietary polyphenols are able to inhibit neoplastic

transformation. The most phenol compounds dis-

played concentration-dependent cytoprotection.

Importantly, levels of polyphenols, which were effec-

tive in decreasing cancerogenesis in vitro, were within

the range of concentrations detected in human bio

fluids (i.e., urine, plasma and breast milk) following

consumption of an polyphenol-rich meal (Linseisen

and Rohrmann 2008; Obrenovich et al. 2011).

Cocoa contains more phenolic phytochemicals and

exhibits a higher antioxidant capacity than teas and red

wine (Dresoti 2000; Jalil and Ismail 2008). Cocoa and

chocolate products have demonstrated potential benefi-

cial health effects against chronic diseases in epidemi-

ological studies (Maskarinec 2009), and cocoa extracts

are able to inhibit chemical-induced tumorigenesis in

experimental animals (Weisburger 2001). However, the

underlying molecular mechanisms and molecular tar-

get(s) for the potential chemopreventive effects of cocoa

remain unclear. The extracellular signal-regulated pro-

tein kinase 1/2 (ERK1/2)–connexin 43 signaling path-

way is crucial for the regulation of GJIC. Lee et al.

(2003) found that cocoa polyphenol extracts protected

against H2O2-induced inhibition of GJIC in rat liver

epithelial cells by attenuating intracellular ROS and

blocking the ERK/Cx43 signaling pathway, but not the

p38 MAPK signaling pathway. It seems clear that the

chemopreventive action of cocoa phytochemicals is due

not only to their antioxidant potential but also to the

potent ability as a direct inhibitor of MEK, which might

contribute to its chemopreventive effects.

Polyphenolic compounds found in green tea, such

as (–)-epigallocatechin-3-gallate (EGCG) and (–)-

epicatechin (EC), have received much attention

because of their possible beneficial effects on human

health. Green tea polyphenols, including EGCG and

EC, act as anti-tumor-promoting agents against PCP-

induced mouse hepatocarcinogenesis (Ruch et al.

1989; Sai et al. 2000), and have a preventive effect on

PMA-induced down-regulation of GJIC in keratino-

cytes via their ability to prevent downregulation of

GJIC (Choung et al. 2011). Pretreatment with EGCG

at non-cytotoxic concentration (10 microg/mL or

21.8 lmol L-1) greatly ameliorated the GJIC-inhibi-

tory effects of dimethylnitrosamine, a tumor promoter

in Mardin-Darby canine kidney (MDCK) cells

(Takahashi et al. 2004).

Yu et al. (2010) examined the effect of EGCG on

cardiac gap junction inhibited by high glucose. Although

mRNA levels of Cx43, Cx40 and Cx45 in cardiomyo-

cytes, was not altered by EGCG (40 lmol L-1), the

protein expression of Cx43 and the function of GJIC

were significantly recovered by EGCG co-treatment.

EGCG attenuated the reduction of Cx43 protein and

GJIC in cardiomyocytes under high glucose, partly

through p38 MAPK signal transduction pathway.

High doses (200–800 lM) of EGCG, but not (–)-

epicatechin (EC), were found to inhibit GJIC in a

dose-dependent and reversible manner in WB-F344

normal rat liver epithelial cells and induced phosphor-

ylation of Cx43 and of the extracellular signal-

regulated protein kinase 1/2 (ERK1/2) (Kang et al.

2008). The inhibition of GJIC and phosphorylation of

Cx43 and ERK1/2 by EGCG were completely blocked

by U0126, a pharmacological inhibitor of mitogen-

activated protein kinase/ERK kinase. EGCG, but not

EC, actually generated significant amounts of H2O2 in

a dose- dependent manner, and the EGCG-induced

inhibition of GJIC was partly related to the production

of H2O2 in medium (Huang et al. 1999). Furthermore,

catalase partially inhibited the EGCG-induced inhibi-

tion of GJIC and the phosphorylation of Cx43 and

ERK1/2. These results indicated that EGCG inhibited

GJIC mainly due to its prooxidant activity, although

other factors might be linked to the EGCG-induced

inhibition of GJIC.

Among the various types of flavonoids in fruits and

vegetables associated with cancer prevention, the

flavanone, naringenin, is found in grapefruit and citrus

fruits. Naringenin has been reported to induce cyto-

toxicity and apoptosis in various cancer cell line but no

toxic effect after treatment at a similar dose on normal

Phytochem Rev

123

Author's personal copy

cells. In C6 glioma cells, naringenin inhibited the

cancer growth in a dose dependent manner by

increasing gap junction intracellular communication,

inducing cell cycle arrest, DNA damage, reducing

activity of COX-2 (Sabarinathan and Vanisree 2010).

Apigenin and tangeretin, bioflavonoids present in

many plant foods, such as parsley, celery and skin of

citrus fruits, increased GJIC between rat liver epithe-

lial cells in a time- and concentration-dependent

manner and inhibited the transformation of V79 lung

fibroblasts (Chaumontet et al. 1996). Protection is

likely afforded by upregulation of connexin43. In

addition, the incubation of cells with the two com-

pounds antagonizes the inhibition of GJIC induced by

tumor promoters, such as 12-O-tetradecanoyl-phor-

bol-acetate (TPA) and 3,5,di-tertio-butyl-4-hydroxy-

toluene (BHT) (Chaumontet et al. 1997). However, in

studies in vivo, tangeretin fed to rats for 3 months

actually inhibits gap junctional intracellular commu-

nication. No GJIC-inhibitory effect was observed for

quercetin, flavone, and flavanone (Chaumontet et al.

1996), indicating that the relatively high concentra-

tions of tangeretin might be acting as a tumour-

promoter in vivo.

Kiwifruits are well known for their healthy prop-

erty, due to high level of antioxidant polyphenols, and

they are widely used in the traditional Chinese

medicine. Is has been reported that Kiwifruit provides

protection against oxidative DNA damage and

enhances DNA repair, thereby protecting against

mutagenic changes that can lead to cancerogenesis

(Hunter et al. 2011). Kiwifruit inhibited sarcoma 180

growth in mice by 30–40 % (Motohashi et al. 2002).

However, the enhanced DNA repair and ‘‘anti-muta-

genic’’ explanation could not explain the suppression

of tumor growth, which already had its mutations

induced to make the cell tumorigenic. More likely, the

enhanced DNA repair probably involved mitochon-

drial DNA damage, not genomic DNA damage. In

addition, any interpretation of studies, such as these

should involve studying DNA damage, its repair in the

genomic DNA of stem cells (Kang and Trosko 2011).

Further, kiwifruit juice and kiwifruit extracts, from

different cultivars, inhibited the growth of cancer cells

in vitro. Lee et al. (2010a, b) showed that kiwifruit

extracts allowed WB-F344 rat liver epithelial cells to

recover from the H2O2-induced inhibition of GJIC

more efficiently than from their active phenolic

compound, quercetin. The extracellular signal-

regulated protein kinase 1/2 (ERK1/2)–connexin 43

signaling pathway seems involved in these effects.

Kiwifruit extracts blocked the H2O2-induced phos-

phorylation of Cx43 and ERK1/2 in WB-F344 cells.

Quercetin, alone, attenuated the H2O2-mediated

ERK1/2–Cx43 signaling pathway and consequently

reversed H2O2-mediated inhibition of GJIC. The high

antioxidant activity of kiwifruits and quercetin sug-

gests that the chemopreventive effect of quercetin on

H2O2-mediated inhibition of ERK1/2–Cx43 signaling

and GJIC might be mediated through its free radical-

scavenging activity. The carcinogenicity of the reac-

tive oxygen species, such as H2O2, is related to the

inhibition of GJIC, leading to the view that kiwifruit

extracts and quercetin might have chemopreventive

potential by preventing the inhibition of GJIC (Lee

et al. 2010a, 2010b).

Conklin et al. (2007) showed that genistein and

quercetin increased Cx43 and suppressed cell prolif-

eration in a metastatic human breast tumor cell line

(MDA-MB-231) at physiologically relevant concen-

trations. The same concentrations were not toxic to

non-tumorigenic human breast cells (MSTV1-7). In

the MDA-MB-231 cell culture system, Cx43 protein

levels increased, following genistein and quercetin

treatment in a dose-dependent. Some of the Cx43

appeared to localize as punctuate staining at the

plasma membrane following genistein treatment, but

not after quercetin treatment (0.5, 2.5, 5 mg mL-1).

Instead, cells treated with quercetin appeared to retain

Cx43 in the perinuclear region. Genistein and querce-

tin treatment failed to increase GJIC in MDA-MB-231

cells. The suppressed cell proliferation was consid-

ered, therefore, independent of GJIC functionality

and, based on the changes in Cx43 level and locali-

zation observed in MDA-MB-231 cells following

flavonoid treatment. However, in this work, authors

observed the effects on GJIC after 72 h of treatment

with genistein and quercetin, when it is likely that the

triggering effect had already occurred.

The potential chemopreventive effects of grapes

and red wine seem to be ascribed to the presence of

phytochemicals such as resveratrol, gallic acid, cate-

chin, quercetin, procyanidin and anthocyanidin. Res-

veratrol was associated with the decrease in

inflammation and cardiovascular diseases and a delay

in aging (Shakibaei et al. 2009). The health promoting

effect of resveratrol and its relevant documented

mechanisms of action have been critically reviewed

Phytochem Rev

123

Author's personal copy

(Vang et al. 2011). In WB-F344 rat liver epithelial

cells, resveratrol, at concentrations ranging from 17 to

50 lmol L-1, was able to restore the GJIC-inhibition

induced by tumor promoters, such as TPA (12-O-

tetradecanoylphorbol-13-acetate) and 1,1-bis(p-chlo-

rophenyl)-2,2,2-trichlorethane (DDT). (Upham et al.

2007) This recovery was partly correlated with

hindered hyperphosphorylation of Cx43 (Nielsen

et al. 2000). In cancer cells, such as human liver

hepatocellular carcinoma cell line HepG2, resveratrol

arrests HepG2 cell growth in S phase, inhibits DNA

synthesis, induces cell apoptosis and increased GJIC.

The levels of GJIC increased sharply after resveratrol

treatment (100 lmol L-1), which implied that the

increased GJIC level could play a role on the effect of

resveratrol in the cancer chemopreventive activity

(Yan et al. 2006). In human glioblastoma cells,

resveratrol (20 lmol L-1) induced a delay in cell

cycle progression and was able to enhance GJIC both,

alone and in combination with controlled exposure to

X rays, which is one of the most used treatments in

cancer patients (Leone et al. 2008). Although resve-

ratrol is known for its inhibitory effects on various

cellular events associated with carcinogenesis, when

this is taken from food, the effect of other phenolic

compounds in the same food matrix has to be

considered. In addition, because resveratrol is found

in such small quantities in the diet, any protective

effect of this molecule is unlikely at normal nutritional

intakes (Manach et al. 2004).

Pterostilbene, a naturally occurring analogue of

resveratrol, predominantly found in blueberries, sev-

eral types of grapes, and tree wood, has higher

bioavailability compared to resveratrol’s antioxidant

capability and it exerts similar or better anti-carcino-

genic properties. In vitro and in vivo models, ptero-

stilbene inhibits cancer growth tumorigenesis and

metastasis with negligible toxicity (McCormack and

McFadden 2011).

Pretreatment with pterostilbene exerted a protective

effect in WB-F344 rat liver epithelial cells, allowing

recovery from H2O2-induced GJIC-inhibition and

prevented the inhibition of GJIC. The action mecha-

nism, also in this case, involves the down-regulation of

connexin43 phosphorylation by the inactivation of

ERK1/2 and p38 MAP kinase (Kim et al. 2009).

Several phytonutrients can exert prooxidant activ-

ities at high levels or in the presence of transition metal

ions or alkalis. Several studies have shown that metal-

mediated autooxidation of some phenolic phyto-

chemicals generates semiquinone radicals, resulting

in the enhancement of redox activity to produce ROS

including H2O2 (Kobayashi et al. 2004). Gallic acid,

one of the widely distributed phytochemicals and also

one of the major antioxidants in red wine, at high

concentrations, induces H2O2-production and inhibits

GJIC in rat epithelial cells. In addition, gallic acid

induces phosphorylation of connexin 43 by activation

of ERK 1/2. Resveratrol and catalase were able to

reverse this inhibition likely by a different mechanism

of protection. Catalase could attenuate the gallic acid

induced H2O2-production. Resveratrol could protect

cells by inhibition of phosphorylation of connexin 43

(Kim et al. 2009). This further confirms that phos-

phorylation of connexin 43 is a mechanism involved in

the antitumor action of many phytochemicals.

Therefore, the interactions among different phyto-

chemicals are crucial for their ultimate effect. Grape

extracts, containing mixture of polyphenols, are

demonstrated to be able to provide more considerable

health effects (Kaur et al. 2009). Most of the studies

are focused on a single phenolic compound, although

this provides essential information about the active

chemical structure, effective dose and molecular

targets, it is important to associate studies on whole

plant extracts containing the various phytochemicals.

In our lab, grape seed extracts, containing different

polyphenols with a significant amount of proanthocy-

anidins, have been investigated for their ability to

modulate GJIC in breast cancer cells, and we found

interesting changes in GJIC functionality and conn-

exin expression and localization in response to grape

seed extracts (Leone et al. unpublished).

Caffeic acid phenethyl ester

A frequent defect in human cancers is the uncontrolled

activation of the Ras signaling pathways. Increased

expression of cyclooxygenase-2 (COX-2) and inhibi-

tion of GJIC have been frequently observed in several

forms of human malignancies. H-ras-transformed rat

liver epithelial WB-F344 cell line (H-ras WB cells)

exhibits enhanced COX-2 expression, the complete

inhibition of GJIC and predominant unphosphoryla-

tion of connexin 43. Caffeic acid phenethyl ester

(CAPE), a chemopreventive phytochemical derived

from honey propolis, was reported to have anticancer

properties both in vitro and in vivo. CAPE

Phytochem Rev

123

Author's personal copy

significantly inhibited the constitutive expression of

COX-2 and restored the disrupted GJIC through the

phosphorylation of Cx43 in the GJIC-deficient H-ras

WB cells (Na et al. 2000; Lee et al. 2004).

Indole-3-carbinol

Indole-3-carbinol, an indole glucosinolate derived

found in cruciferous vegetables such as cabbage,

broccoli, cauliflower and Brussels sprouts, have

recognized chemopreventive properties attributable

to its ability to interfere with multiple oncogenic

signaling pathways governing cell cycle progression,

survival, invasion, and other aggressive phenotypes of

cancer cells, especially those mediated by EGFR/Src,

Akt, NF-kB, endoplasmic reticulum stress, and

nuclear receptors (Weng et al. 2008). Indole-3-carbi-

nol was demonstrated able to prevent H2O2-induced

inhibition of GJIC in WB-F344 rat liver epithelial cells

(Hwang et al. 2008) and thus prevent the oxidative

stress-related mechanisms during the tumor promotion

phase of carcinogenesis. Although inhibition of GJIC

by H2O2 was shown to implicate activation of both Akt

and MAPK signaling pathways, prevention of GJIC by

indole-3-carbinole was dependent upon inactivation of

the Akt, but not MAPK kinase. Indole-3-carbinole

could prevent H2O2-induced inhibition of GJIC in

WB-F344 cells by inhibition of Akt phosphorylation

that could also prevent phosphorylation of Cx43. Most

significantly, several chemopreventive agents, includ-

ing indole-3-carbinol, were shown to attenuating

environmental cigarette smoke- induced lesions in

rat lungs (Izzotti et al. 2010).

Statins

Recent studies have shown that statins, powerful

HMG-CoA reductase inhibitors, can modulate gap

junction protein expression both in vivo and in vitro.

Statins show very different behavior in the different

cell and animal systems, up-regulating or down-

regulating the different connexin proteins. However,

little work has been done on the effects of statins on

GJIC. Lovastatin, given to ras transformed cells

lacking functional GJIC, restored GJIC and inhibited

the tumorigenic potential of these transformed cells in

vivo without affecting the expression of the Ras

protein (Ruch et al. 1993). Lovastatin, a naturally

occurring drug found in food, such as oyster

mushrooms and red yeast rice, is able to increase the

GJIC in K-ras-transformed murine lung carcinoma

cells. However the mechanism would be different,

since the deficiency of GJIC was increased also by the

K-ras antisense oligonucleotide and PKC inhibition/

downregulation, but was independent from both Cx43

content and phosphorylation (Cesen-Cummings et al.

1998). Instead, lovastatin has been shown to inhibit, in

a dose-dependent manner, the migration and prolifer-

ation of smooth muscle cells (SMCs) through the

inhibition of the GJIC, leading to an antiproliferative

effect (Shen et al. 2010). In fact, during invasion,

connexins and GJIC have been demonstrated to

enhance cancer cells migration, and probably their

dissemination, by establishing communication with

the endothelial barrier. Thus, suppression of gap

junction function could be another explanation of

statin-induced antiproliferative effect, although the

statin-connexin-GJIC relationships need further

elucidation.

Actually, this seems to contradict the concept that

the enhancement of GJIC leads to anti-proliferative

effect. An explanation might come from the complex-

ity of the disease, evolving through various stages

during tumor progression, with cancer cells exhibiting

different activated oncogenes,-induced- phenotypes,

different connexins being expressed, and depending

on the stage of the cancer progression being consid-

ered (Cronier et al. 2009).

Medicinal plants

Because it was previously stated that GJIC has been

shown to be involved in the pathogenesis of many

inherited and acquired human diseases, the effect of

bioactive compounds from medicinal plants on GJIC

and/or connexin expression should be evaluated. One

example is that of the role of fibers from fruits and

vegetables. The long association between diets of high

fiber and low chronic diseases has still not been

adequately explained. Could the chemopreventive

effects of high fiber diets be due to (a) some mechan-

ical action attributed to the fibers during its passage

through the GI tract; (b) some physical–chemical

proteins of fiber size or adherent chemicals; or (c) the

chemical components of the digested fibers? In testing

these possibilities, Nakamura et al. (2005) demon-

strated that a component of the psyllium fiber, beta-

sitosterol, dramatically restored GJIC in Ha-ras

Phytochem Rev

123

Author's personal copy

transformed rat liver epithelial cells, but did not

restored GJIC in src-, neu-, or ras-myc- transformed

cells. This suggests that the beta-sitosterol, by inte-

grating into the mammalian membrane, releases

cholesterol from the membrane and alters the mem-

brane in allowing the Ha-ras protein from being

activated.

In another study, twenty-seven ginsenosides, iso-

lated from Panax ginseng, were examined for their

effect on GJIC (Zhang et al. 2001).

Extracts of Petasites japonicus Maxim, a perennial

grass, used as food and medicinal plant in some Asian

countries, increased the level of Cx43 and GJIC, in rat

liver epithelial cells WB-F344, and it also blocked the

TPA-induced inhibition of gap junction protein

expression (Kang et al. 2010). These results show

that P. jacponicus extract might have some active

components, which stimulate GJIC between cells in

normal cells. Extracts of P. japonicus are rich of

petasin and isopetasin, and petasiphenol, reported as

inhibitors of the biosynthesis of the vasoconstrictive

peptide leukotriene, and as bio-antimutagen and anti-

cancer, respectively. Nevertheless P. japonicus also

contain petasitenine in young flower stalks that can

induce neoplasia in the rat liver. Thus, the tumorigenic

or antitumorigenic effect of P. jacponicus extract

would depend on whether the major component is

petasiphenol or petasitenine. The significance of

enhancement of GJIC has to be further investigated.

The analysis above has included an overall view of

the effect of several phytochemicals on GJIC or

connexins in specific cell systems. From this over-

view, it can be inferred that all these natural chemo-

preventive agents, with different chemical structures,

having different biochemical mechanisms of action,

all share one common cellular endpoint, namely they

either prevent the down regulation of GJIC, post-

translationally, by different classes of tumor promot-

ers (phorbol esters work as a tumour promoter

differently than does DDT as a tumor promoter) or

they up-regulate GJIC at the transcriptional level.

This brief overview does not exclude, however, the

awareness that the situation is far more complex.

Foods consist of complicated mixtures of proteins,

carbohydrates, fats, and both micro- and macronutri-

ents, making it extremely difficult to identify the

contributions of any single component to nutrition and

health. In addition, all nutrients are subject to metab-

olism by the enzymes of the GI tract and by the

microbial flora, and, in turn, phytonutrients might

impact the composition of the gut microflora (Gill

et al. 2006; Turnbaugh, et al. 2009; Hehemann et al.

2010.Wu et al. 2011; Shulzhenko et al. 2011; Muegge

et al. 2011; Kau et al. 2011). The bioavailability might

vary significantly for slightly different chemical

species, and phytonutrients are usually further metab-

olized once absorbed. Finally, the efficacy of different

phytonutrients in promoting health likely varies sig-

nificantly as a result of the specificity with which such

compounds and/or their metabolites impact different

microbiota and their released toxins, which, then, act

on the epithelium of the GI tract of different stages of

development, different genetic backgrounds and dif-

ferent genders (Kang and Trosko 2011).

As an example, resveratrol concentrations effective

on GJIC in vitro are higher than the human plasmatic

concentration found after oral administration of res-

veratrol. Resveratrol is rapidly absorbed after oral

intake, reaches low levels in the plasma, and is likely

altered by rapid metabolism to glucuronide and

sulphate conjugates. In human, after ingestion of

25 mg of trans-resveratrol per 70 kg of body weight, is

detected a peak plasma concentration of approxi-

mately 2 lmol L-1 of resveratrol (Goldberg et al.

2003). High doses as 5 g of trans-resveratrol (in

caplets) (equivalent to the amount contained in several

hundred bottles of red wine) produces concentrations

of 2.4–14 lmol L-1 of trans-resveratrol and derivate

metabolites (Boocock et al. 2007). After a dietary

administration of 85.5 mg of piceid (trans-resveratrol-

3-O-b-D-glycoside, ingested with plant-derived foods

such as red grapes, red wine, or peanuts), correspond-

ing to the content of approximately two bottles of red

wine, the trans-resveratrol metabolites quantified

peaked in the range from 0.1 to 1.0 lmol L-1 (Burkon

and Somoza 2008). However, is difficult to estimate

the specific effect of resveratrol when given as part of

food matrices.

On the other hand, recent studies suggest that the

use of resveratrol at non active low doses, in combi-

nation with other bioactive food components, such as

quercetin (Zamin et al. 2009) and sulforaphane (Jiang

et al. 2010), presented a strong synergism in inducing

apoptosis and senescence-like growth arrest in glioma

cells.

Thus, some phytochemicals might exhibit antimu-

tagenic and antitumor-promoting activities at rela-

tively low doses, whereas excess antioxidant

Phytochem Rev

123

Author's personal copy

remaining in a free form might instead produce acute

toxicity or carcinogenicity. Epidemiological and

human studies support that a low risk of cancer is

more strongly related to a diet rich in multiple

antioxidants than to dietary supplementation with an

individual antioxidant. The CARET and ATBC trials

could be excellent examples of the problems of

intervention with natural compounds without under-

standing the mechanisms of action in human situations

(Duffield-Lillico and Begg 2004; Goodman et al.

2004). The recent demonstration of the induction of

gut hyperplasia and risk to colon cancer, due to

3-omega fatty acids, when empirical studies in animal

or abnormal human in vitro studies show positive

effects could do the opposite in the human in vivo

situation. (Woodworth et al. 2010).

Thus, although it has been generally believed that

antioxidants are beneficial to health, individual anti-

oxidants might exert either good or bad effects

depending on their structures and doses (Nakamura

et al. 2005; Upham and Trosko 2009). Since the

original demonstration of the action of retinoids on

cell growth inhibition of transformed cells (Mehta

et al. 1986) and the correlation of cell growth with

their actions on gap junctional intercellular commu-

nication (Mehta et al. 1989)Similarly the lack of GJIC

induced by several phytochemicals or the inhibition of

GJIC and promotion of skin tumors by retinoids

(Forbes et al. 1979; Welsch et al. 1981; Shuin et al.

1983) can have several roles in the epigenetic

induction of carcinogenesis at both the promotion

and progression stages, suggesting the necessity for

safety standards for dietary supplements made from

isolated compounds.

Another open field is represented from the newly

discovered channel proteins, pannexins, and the roles

ascribed to connexin hemichannels. It is legitimate to

think that most of the functions that have been

attributed to connexin hemichannels, can actually be

ascribed to pannexins (Vinken et al. 2010). In addition,

it seems challenging to discriminate between the

functionality of connexin hemichannels and that of

gap junctions, especially in an in vivo environment.

Anyway, thorough knowledge of the phytochemi-

cal-GJIC response system is certainly a successful

approach to phytotherapy. Although a distinguished

panel, convened to assess future research on the

chronic disease chemoprevention, never considered

the fundamental biological roles of gap junctional

intercellular communication in the regulation of

homeostatic control of basic cell functions of cell

proliferation, differentiation and apoptosis during

human development, it seems from these studies,

one cannot ignore the role of natural cancer chemo-

preventive compounds on GJIC (Kelloff et al. 2006).

In addition, once the causal relationship between GJIC

system and cancer processes has been clearly estab-

lished, the modulation of GJIC and/or connexin

proteins/gene expression could be used as a valid

screening tool for known or new found natural

compounds.

Conclusions

Evidence is increasing that the consumption of

bioactive compounds in vegetables reduces the risk

of chronic diseases, such as cancer. The possibilities of

using foods that will help to reduce the risks of specific

cancers have been a great impetus to the ‘functional

food’ industry.

The growing evidence on the involvement of plant-

derived molecules in the GJIC modulation might offer

a new perspective of the protective and/or preventive

effects of dietary phytochemicals, also in view of a

possible therapeutic use.

Although further research is required to establish

the exact mechanisms of action involving GJIC, the

GJIC- responding system could be considered as a

screening tool for the first evaluation of bioactive

natural compounds or extracts. Also, to determine

range of doses and to establish whether supplementa-

tion beyond normal dietary intake levels is beneficial,

ineffective or toxic. An assessment as to whether the

individual is deficient, normal or super proficient in

any antioxidant system might be reasonable, for to

supplement a normal individual might be a waste of

effect and if the individual was super proficient,

supplementation might even be harmful.

Understanding the specific roles of antioxidants in

cell signaling will better enable us to develop more

effective and safer intervention strategies. Exposure to

high levels of a single antioxidant could easily

overwhelm a specific effect of a precise signaling

protein or small group of signaling proteins, thus

resulting in a toxic rather than beneficial effect.

Timing, internal distribution and concentrations of

the bioactive compound in any organ or in the pre-

Phytochem Rev

123

Author's personal copy

malignant or malignant cell will determine the effec-

tiveness as a chemopreventive agent. In addition, since

the promotion phase of human carcinogenesis can take

decades to occur and since nutrition and diets can

contribute to both the production and prevention of

cancer, it is important to realize that there are multiple

mechanisms of tumor promotion and the progression

(invasive and metastatic) phases of carcinogenesis,

such as activation of Protein Kinase C via exposure to

phorbol ester, inhibition of Ca?? efflux by pesticides,

or activation of MAP kinases by growth factors or

cytokines from causes of chronic inflammatory events.

All of these different intra-cellular mechanisms lead to

the down-regulation of GJIC. Each of the potential

natural bioactive components of foods can trigger or

interfere with SPECIFIC intracellular signaling mech-

anisms. Thus, the major take home lesson is that there

will never be a universal chemopreventive bioactive

compound to protect against cancers derived from all

the different organs of the body.

References

Alarcon de la Lastra C, Villegas I (2007) Resveratrol as an

antioxidant and pro-oxidant agent: mechanisms and clini-

cal implications. Biochem Soc T 35(5):1156–1160

Al-Delaimy WK, van Kappel AL, Ferrari P, Slimani N, Steg-

hens JP, Bingham S, Johansson I, Wallstrom P, Overvad K,

Tjønneland A, Key TJ, Welch AA, Bueno-de-Mesquita

HB, Peeters PH, Boeing H, Linseisen J, Clavel-Chapelon

F, Guibout C, Navarro C, Quiros JR, Palli D, Celentano E,

Trichopoulou A, Benetou V, Kaaks R, Riboli E (2004)

Plasma levels of six carotenoids in nine European coun-

tries: report from the European prospective investigation

into cancer and nutrition (EPIC). Public Health Nutr

7(6):713–722

Alexopoulos H, Bottger A, Fischer S, Levin A, Wolf A, Fujis-

awa T, Hayakawa S, Gojobori T, Davies JA, David CN,

Bacon JP (2004) Evolution of gap junctions: the missing

link? Curr Biol 14:R879–R880

Aust O, Ale-Agha N, Zhang L, Wollersen H, Sies H, Stahl W

(2003) Lycopene oxidation product enhances gap junc-

tional communication. Food Chem Toxicol 41:1399–1407

Bao X, Altenberg GA, Reuss L (2004) Mechanism of regulation

of the gap junction protein connexin 43 by protein kinase

C-mediated phosphorylation. Am J Physiol Cell Physiol

286:C647–C654

Baranova A, Ivanov D, Petrash N, Pestova A, Skoblov M,

Kelmanson I, Shagin D, Nazarenko S, Geraymovych E,

Litvin O, Tiunova A, Born TL, Usman N, Staroverov D,

Lukyanov S, Panchin Y (2004) The mammalian pannexin

family is homologous to the invertebrate innexin gap

junction proteins. Genomics 83(4):706–716

Beyer EC, Berthoud VM (2009) The family of connexin genes:

In: Harris A, Locke D (eds) Connexins: a guide. Springer,

New York, pp 3–26

Block G, Patterson B, Subar A (1992) Fruit, vegetables, and

cancer prevention. A review of the epidemiological evi-

dence. Nutr Cancer 18:1–29

Boassa D, Solan JL, Papas A, Thornton P, Lampe PD, Sosinsky

GE (2010) Trafficking and recycling of the Connexin43

gap junction protein during mitosis. Traffic 11:1471–1486

Boocock DJ, Faust GE, Patel KR, Schinas AM, Brown VA,

Ducharme MP, Booth TD, Crowell JA, Perloff M, Gescher

AJ, Steward WP, Brenner DE (2007) Phase I dose escala-

tion pharmacokinetic study in healthy volunteers of res-

veratrol, a potential cancer chemopreventive agent. Cancer

Epidem Biomar 16:1246–1252

Brisset AC, Isakson BE, Kwak BR (2009) Connexins in vascular

physiology and pathology. Antioxid Redox Sign

11(2):267–282

Bruzzone R, White TW, Paul DL (1996) Connections with

connexins: the molecular basis of direct intercellular sig-

naling. Eur J Biochem 238:1–27

Burkon A, Somoza V (2008) Quantification of free and protein-

bound trans-resveratrol metabolites and identification of

trans-resveratrol-C/O-conjugated diglucuronides—Two

novel resveratrol metabolites in human plasma. Mol Nutr

Food Res 52:549–557

Cesen-Cummings K, Warner KA, Ruch RJ (1998) Role of

protein kinase C in the deficient gap junctional intercellular

communication of K-ras-transformed murine lung epithe-

lial cells. Anticancer Res 18(6A):4343–4346

Chalabi N, Delort L, Satih S, Dechelotte P, Bignon Y-J, Ber-

nard-Gallon DJ (2007) Immunohistochemical expression

of RARa, RARb, and Cx43 in breast tumor cell lines after

treatment with lycopene and correlation with RT-QPCR.

J Histochem Cytochem 55(9):877–883

Chan R, Lok K, Woo J (2009) Prostate cancer and vegetable

consumption. Mol Nutr Food Res 53:201–216

Chaumontet C, Suschetet M, Honikman-Leban E, Krutovskikh

VA, Berges R, Le Bon AM, Heberden C, Shahin MM,

Yamasaki H, Martel P (1996) Lack of tumor-promoting

effects of flavonoids: studies on rat liver preneoplastic foci

and on in vivo and in vitro gap junctional intercellular

communication. Nutr Cancer 26(3):251–263

Chaumontet C, Droumaguet C, Bex V, Heberden C, Gaillard-

Sanchez I, Martel P (1997) Flavonoids (apigenin, tan-

geretin) counteract tumor promoter-induced inhibition of

intercellular communication of rat liver epithelial cells.

Cancer Lett 114(1–2):207–210

Choung Y-H, Choi SJ, Joo JS, Lee JB, Lee HK, Lee SJ (2011)

Green tea prevents down-regulation of gap junction inter-

cellular communication in human keratinocytes treated

with PMA. Eur Arch Otorhinolaryngol 268:885–892

Conklin CMJ, Bechberger JF, MacFabe D, Guthrie N, Ku-

rowska EM, Naus CC (2007) Genistein and quercetin

increase connexin43 and suppress growth of breast cancer

cells. Carcinogenesis 28:93–100

Cordain L, Miller JB, Eaton SB, Mann N, Holt SHA, Speth JD

(2000) Plant-animal subsistence ratios and micronutrient

energy estimates in worldwide huntergather diets and

micronutrient energy estimates in worldwide huntergather

diets. Am J Clin Nutr 71:682–692

Phytochem Rev

123

Author's personal copy

Cowan CG, Calwell EI, Young IS, McKillop DJ, Lamey PJ

(1999) Antioxidant status of oral mucosal tissue and

plasma levels in smokers and nonsmokers. J Oral Pathol

Med 28:360–363

Cronier L, Crespin S, Strale PO, Defamie N, Mesnil M (2009)

Gap junctions and cancer: new functions for an old story.

Antioxid Redox Signal 11(2):323–338

Cruciani V, Mikalsen SO (2002) Connexins, gap junctional

intercellular communication and kinases. Biol Cell

94(7–8):433–443

Dresoti IE (2000) Antioxidant polyphenols in tea, cocoa, and

wine. Nutrition 16:692–694

Duffield-Lillico AJ, Begg CB (2004) Reflections on the land-

mark studies of b-carotene supplementation. J Natl Cancer

Inst 96:1729–1731

Duthie GG, Duthie SJ, Kyle JAM (2000) Plant polyphenols in

cancer and heart disease: implications as nutritional anti-

oxidants. Nutr Res Rev 13:79–106

Engelmann NJ, Clinton SK, Erdman JE Jr (2011) Nutritional

aspects of phytoene and phytofluene, carotenoid precursors

to lycopene. Adv Nutr 2:51–61

Evans WH, Martin PEM (2002) Gap junction structure and

function. Mol Membr Biol 19:121–136

Forbes PD, Urbach F, Davies RE (1979) Enhancement of

experimental photocarcinogenesis by topical retinoic acid.

Cancer Lett 7:85–90

Ford NA, Elsen AC, Zuniga K, Lindshield BL, Erdman JW Jr

(2011) Lycopene and apo-120-lycopenal reduce cell pro-

liferation and alter cell cycle progression in human prostate

cancer cells. Nutr Cancer 63(2):256–263

Fornelli F, Leone A, Verdesca I, Minervini F, Zacheo G (2007)

The influence of lycopene on the proliferation of human

breast cell line (MCF-7). Toxicol In Vitro 21(2):217–223

Gill SR, Pop M, Deboy RT, Eckburg PB, Turnbaugh PJ, Samuel

BS, Gordon JI, Relman DA, Fraser-Liggett CM, Nelson

KE (2006) Metagenomic analysis of the human distal gut

microbiome. Science 312:1355–1359

Giovannucci E (2002) A review of epidemiologic studies of

tomatoes, lycopene, and prostate. Cancer Exp Biol Med

(Maywood) 227(10):852–859

Goldberg DM, Yan J, Soleas GJ (2003) Absorption of three

wine-related polyphenols in three different matrices by

healthy subjects. Clin Biochem 36:79–87

Goodenough DA, Paul DL (2009) Gap junctions. Cold Spring

Harb Perspect Biol 1:a002576

Goodman GE, Thornquist MD, Balmes J et al (2004) The beta-

carotene and retinol efficacy trial: incidence of lung cancer

and cardiovascular disease mortality during 6-year follow-

up after stopping beta-carotene and retinol supplements.

J Natl Cancer Inst 96:1743–1750

Graf BA, Milbury PE, Blumberg JB (2005) Flavonols, flavones,

flavanones, and human health: epidemiological evidence.

J Med Food 8(3):281–290

Guedes AC, Amaro HM, Malcata FX (2011) Microalgae as

sources of carotenoids. Mar Drugs 9(4):625–644

Hall EH, Crowe SE (2011) Environmental and lifestyle influ-

ences on disorders of the large and small intestine: impli-

cations for treatment. Dig Dis 29:249–254. doi:10.1159/

000323930

Heber D (2004) Phytochemicals beyond antioxidation. J Nutr

134(11):3175S–3176S

Hehemann J-H, Correc G, Barbeyron T, Helbert W, Czjzek M,

Michel G (2010) Transfer of carcohydrate-active enzymes

from marine bacteria to Japanese gut microbiota. Nature

464:908–912

Herve JC, Sarrouilhe D (2002) Modulation of junctional com-

munication by phosphorylation: protein phosphatases, the

missing link in the chain. Biol Cell 94:423–432

Hesketh GG, Van Eyk JE, Tomaselli GF (2009) Mechanisms of

gap junction traffic in health and disease. J Cardiovasc

Pharmacol 54(4):263–272

Holder JW, Elmore E, Barrett JC (1993) Gap junction function

and cancer. Cancer Res 53(15):3475–3485

Huang RP, Peng A, Hossain MZ, Fan Y, Jagdale A, Boynton AL

(1999) Tumor promotion by hydrogen peroxide in rat liver

epithelial cells. Carcinogenesis 20(3):485–492

Huang RP, Peng A, Golard A, Hossain MZ, Huang R, Liu YG,

Boynton AL (2001) Hydrogen peroxide promotes trans-

formation of rat liver non-neoplastic epithelial cells

through activation of epidermal growth factor receptor.

Mol Carcinog 30:209–217

Hunter DC, Greenwood J, Zhang J, Skinner MA (2011) Anti-

oxidant and ‘natural protective’ properties of kiwifruit.

Curr Top Med Chem 11(14):1811–1820

Hwang J-W, Jung J-W, Lee Y-S, Kang K-S (2008) Indole-3-

carbinol prevents H2O2-induced inhibition of gap junc-

tional intercellular communication by inactivation of PKB/

Akt. J Vet Med Sci 70(10):1057–1063

Izzotti A, Calin GA, Steele VE, Cartiglia C, Longobardi M,

Croce CM, De Flora S (2010) Chemoprevention of ciga-

rette smoke-induced alterations of MicroRNA expression

in rat lungs. Cancer Prev Res 3(1):62–72

Jalil AM, Ismail A (2008) Polyphenols in cocoa and cocoa

products: is there a link between antioxidant properties and

health? Molecules 13(9):2190–2219

Jiang JX, Gu S (2005) Gap junction- and hemichannel-inde-

pendent actions of connexins. Biochim Biophys Acta

1711(2):208–214

Jiang H, Shang X, Wu H, Huang G, Wang Y, Al-Holou S,

Gautam SC, Chopp M (2010) Combination treatment with

resveratrol and sulforaphane induces apoptosis in human

U251 glioma cells. Neurochem Res 35(1):152–161

Kalra EK (2003) Nutraceutical—definition and introduction.

AAPS Pharm Sci 5(2):article 25. doi:10.1208/ps0502

25

Kang K-S, Trosko JE (2011) Stem cells in toxicology: Funda-

mental biology and practical considerations. Toxicol Sci

120:269–289

Kang KS, Lee YS, Kim HS et al (2002) DI-(2-ethylhexyl)

phthalate-induced cell proliferation is involved in the

inhibition of gap junctional intercellular communication

and blockage of apoptosis in mouse Sertoli cells. J Toxicol

Environ Health A 65:447–459

Kang NJ, Lee KM, Kim JH, Lee BK, Kwon JY, Lee KW, Lee HJ

(2008) Inhibition of gap junctional intercellular commu-

nication by the green tea polyphenol (–)-epigallocatechin

gallate in normal rat liver epithelial cells. J Agric Food

Chem 56:10422–10427

Kang H-G, Sang-Hee Jeong S-H, Cho J-H (2010) Antimuta-

genic and anticarcinogenic effect of methanol extracts of

Petasites japonicus Maxim leaves. J Vet Sci 11(1):

51–58

Phytochem Rev

123

Author's personal copy

Kau AL, Ahern PP, Griffin NW, Goodman AL, Gordon JI

(2011) Human nutrition, the gut microbiome and the

immune system. Nature 474:327–331

Kaur M, Agarwal C, Agarwal R (2009) Anticancer and cancer

chemopreventive potential of grape seed extract and other

grape-based products. J Nutr 139(9):1806S–1812S

Kelloff GJ, Lippman SM, Dannenberg AJ, Sigman CCHL, Reid

BJ, Szabo E, Jordan VC, Spitz MR, Mills GB, Papadi-

mitrakopoulou VA, Lotan R, Aggarwal BB, Bresalier RS,

Banu Arun JK, Lu KH, Thomas ME, Rhodes HE, Brewer

MA, Follen M, Shin DM, Parnes HL, Siegfried JM, Evans

AA, Blot WJ, Chow W-H, Blount PL, Maley CC, Wang

KK, Lam S, Lee JJ, Dubinett SM, Engstrom PF, Meyskens

FL Jr, O’Shaughnessy J, Hawk ET, Levin B, Nelson WG,

Hong WK (2006) Progress in chemoprevention drug

development: the Promise of molecular biomarkers for

prevention of intraepithelial neoplasia and cancer—A plan

to move forward. Clin Cancer Res 12:3661–3697

Key TJ, Schatzkin A, Willett WC, Allen NE, Spencer EA,

Travis RC (2004) Diet, nutrition and the prevention of

cancer. Public Health Nutr 7(1A):187–200

Kim J-E, Kang T-C (2011) The P2X7 receptor–pannexin-1

complex decreases muscarinic acetylcholine receptor—

mediated seizure susceptibility in mice. J Clin Invest

121(5):2037–2047. doi:10.1172/JCI44818

Kim J-S, Ha T-Y, Ahn J, Kim H-K, Kim S (2009) Pterostilbene

from Vitis coignetiae protect H2O2-induced inhibition of

gap junctional intercellular communication in rat liver cell

line. Food Chem Toxicol 47:404–409

Kim J, Lee HJ, Lee KW (2010) Naturally occurring phyto-

chemicals for the prevention of Alzheimer’s disease.

J Neurochem 112(6):1415–1430

King TJ, Bertram JS (2005) Connexins as targets for cancer

chemoprevention and chemotherapy. Biochim Biophys

Acta 1719(1–2):146–160

Kobayashi H, Oikawa S, Hirakawa K, Kawanishi S (2004)

Metal-mediated oxidative damage to cellular and isolated

DNA by gallic acid, a metabolite of antioxidant propyl

gallate. Mutat Res 558:111–120

Krutovskikh V, Asamoto M, Takasuka N, Murakoshi M,

Nishino H, Tsuda H (1997) Differential dose-dependent

effects of alpha-, beta-carotenes and lycopene on gap-

junctional intercellular communication in rat liver in vivo.

Jpn J Cancer Res 88(12):1121–1124

Laird DW (2005) Connexin phosphorylation as a regulatory

event linked to gap junction internalization and degrada-

tion. Biochim Biophys Acta 1711:172–182

Lampe PD, Lau AF (2004) The effects of connexin phosphor-

ylation on gap junctional communication. Int J Biochem

Cell Biol 36(7):1171–1186

Lee KW, Lee HJ (2006) Biphasic effects of dietary antioxidants

on oxidative stress-mediated carcinogenesis. Mech Ageing

Dev 127:424–431

Lee KW, Kim YJ, Lee HJ, Lee CY (2003) Cocoa has more

phenolic phytochemicals and a higher antioxidant capacity

than teas and red wine. J Agric Food Chem 51:7292–7295

Lee KW, Chun KS, Lee JS, Kang KS, Surh YJ, Lee HJ (2004)

Inhibition of cyclooxygenase-2 expression and restoration

of gap junction intercellular communication in H-ras-

transformed rat liver epithelial cells by caffeic acid phen-

ethyl ester. Ann N Y Acad Sci 1030:501–507

Lee DE, Kang NJ, Lee KM, Lee BK, Kim JH, Lee KW, Lee HJ

(2010a) Cocoa polyphenols attenuate hydrogen peroxide-

induced inhibition of gap-junction intercellular communi-

cation by blocking phosphorylation of connexin 43 via the

MEK/ERK signaling pathway. J Nutr Biochem 21(8):

680–686

Lee DE, Shin BJ, Hur HJ, Kim JH, Kim J, Kang NJ, Kim DO,

Lee CY, Lee KW, Lee HJ (2010b) Quercetin, the active

phenolic component in kiwifruit, prevents hydrogen per-

oxide-induced inhibition of gap-junction intercellular

communication Brit. J Nutr 104:164–170

Leone S, Fiore M, Lauro MG, Pino S, Cornetta T, Cozzi R

(2008) Resveratrol and X rays affect gap junction inter-

cellular communications in human glioblastoma cells. Mol

Carcinog 47:587–598

Leone A, Zefferino R, Longo C, Leo L, Zacheo G (2010)

Supercritical CO2-extracted tomato oleoresins enhance gap

junction intercellular communications and recover from

mercury chloride inhibition in keratinocytes. J Agric Food

Chem 58:4769–4778

Li Y, Tollefsbol TO (2010) Impact on DNA methylation in

cancer prevention and therapy by bioactive dietary com-

ponents. Curr Med Chem 17(20):2141–2151

Linseisen J, Rohrmann S (2008) Biomarkers of dietary intake of

flavonoids and phenolic acids for studying diet-cancer

relationship in humans. Eur J Nutr 47(Suppl 2):60–68

Liu RH (2004) Potential synergy of phytochemicals in cancer

prevention: mechanism of action. J Nutr 134(12 Sup-

pl):3479S–3485S

Liu CL, Huang YS, Hosokawa M, Miyashita K, Hu ML (2009)

Inhibition of proliferation of a hepatoma cell line by

fucoxanthin in relation to cell cycle arrest and enhanced

gap junctional intercellular communication. Chem Biol

Interact 182(2–3):165–172

Livny O, Kaplan I, Reifen R, Polak-Charcon S, Madar Z, Sch-

wartz B (2002) Lycopene inhibits proliferation and

enhances gap-junctional communication of KB-1 human

oral tumor cells. J Nutr 132(12):3754–3759

Loewenstein WR (1981) Junctional intercellular communica-

tion: the cell-to-cell membrane channel. Physiol Rev

61:829–913

Mally A, Chipman JK (2002) Non-genotoxic carcinogens: early

effects on gap junctions, cell proliferation and apoptosis in

the rat. Toxicology 180:233–248

Manach C, Scalbert A, Morand C, Remesy C, Liliana Jimenez L

(2004) Polyphenols: food sources and bioavailability. Am J

Clin Nutr 79:727–747

Mariani-Costantini A (2000) Natural and cultural influences on

processes that shaped the eating habits of Western socie-

ties. Nutrition 16:483–486

Martin PE, Blundell G, Ahmad S, Errington RJ, Evans WH

(2001) Multiple pathways in the trafficking and assembly

of connexin 26, 32 and 43 into gap junction intercellular

communication channels. J Cell Sci 114(21):3845–

3855

Martin C, Butelli E, Petroni K, Tonelli C (2011) How can

research on plants contribute to promoting human health?

Plant Cell 23:1685–1699

Maskarinec G (2009) Cancer protective properties of cocoa: a

review of the epidemiologic evidence. Nutr Cancer

61(5):573–579

Phytochem Rev

123

Author's personal copy

Matesic DF, Rupp HL, Bonney WJ, Ruch RJ, Trosko JE (1994)

Changes in gap junction permeability phosphorylation, and

number mediated by phorbol ester and non-phorbol ester

tumor promoters in rat liver epithelial cells’’. Mol Car-

cinogen 10:226–236

McCormack D, McFadden D (2011) Pterostilbene and cancer:

current review. J Surg Res. doi:10.1016/j.jss.2011.09.054

Mehta P, Bertram J, Loewenstein WR (1986) Growth inhibition

of transformed cells correlates with their junctional com-

munication with normal cells. Cell 44:187–196

Mehta P, Bertram J, Loewenstein WR (1989) The actions of

retinoids on cellular growth correlates with their actions on

gap junctional communication. J Cell Biol 108:1053–1065

Milton K (2000) Back to basics: why foods of wild primates

have relevance for modern human health. Nutrition 16:

480–483

Moggs JG, Goodman JI, Trosko JE, Roberts RA (2004) Epi-

genetics and cancer: implications for drug discovery and

safety assessment. Toxicol Appl Pharmacol 196:422–430

Mograbi B, Corcelle E, Defamie N, Samson M, Nebout M,

Segretain D, Fenichel P, Pointis G (2003) Aberrant conn-

exin 43 endocytosis by the carcinogen lindane involves

activation of the ERK/mitogen- activated protein kinase

pathway. Carcinogenesis 24:1415–1423

Motohashi N, Shirataki Y, Kawase M, Tani S, Sakagami H,

Satoh K, Kurihara T, Nakashima H, Mucsi I, Varga A,

Molnar J (2002) Cancer prevention and therapy with ki-

wifruit in Chinese folklore medicine: a study of kiwifruit

extracts. J Ethnopharmacol 81(3):357–364

Muegge BD, Kuczynski J, Knights D, Clemente JC, Gonzalez

A, Fontana L, Henrissat B, Knight R, Gordon JI (2011) Diet

drives convergence in gut microbiome functions across

mammalian phylogeny and within humans. Science 332:

970–974

Musil LS, Goodenough DA (1991) Biochemical analysis of

connexin43 intracellular transport, phosphorylation, and

assembly into gap junctional plaques. J Cell Biol 115:

1357–1374

Na HK, Wilson MR, Kang KS, Chang CC, Grunberger D,

Trosko JE (2000) Restoration of gap junctional intercel-

lular communication by caffeic acid phenethyl ester

(CAPE) in a ras-transformed rat liver epithelial cell line.

Cancer Lett 157(1):31–38

Nakamura Y, Yoshikawa N, Hiroki I, Sato K, Ohtsuki K, Chang

C-C, Upham BL, Trosko JE (2005) Beta-sitosterol from

psyllium seed husk (Plantago ovata Forsk) restores gap

junctional intercellular communication in Ha-ras trans-

fected rat liver cells. Nutr Cancer 51:218–225

Naus CC, Laird DW (2010) Implications and challenges of

connexin connections to cancer. Nat Rev Cancer 10:

435–441

Nielsen M, Ruch RJ, Vang O (2000) Resveratrol reverses tumor-

promoter-induced inhibition of gap-junctional inter- cel-

lular communication. Biochem Biophys Res Commun

275:804–809

Nishino H, Murakoshi M, Mou XY, Wada S, Masuda M, Ohsaka

Y, Satomi Y, Jinno K (2005) Cancer prevention by phy-

tochemicals. Oncology 69(Suppl 1):38–40

Obrenovich ME, Li Y, Parvathaneni K, Yendluri BB, Palacios

HH, Leszek J, Aliev G (2011) Antioxidants in health,

disease and aging. CNS Neurol Disord-Dr 10(2):192–207

Okarter N, Liu RH (2010) Health benefits of whole grain phy-

tochemicals. Crit Rev Food Sci Nutr 50(3):193–208

Omori Y, Krutovskikh V, Mironov N, Tsuda H, Yamasaki H

(1996) Cx32 gene mutation in a chemically induced rat

liver tumour. Carcinogenesis 17:2077–2080

Pahujaa M, Anikin M, Goldberg GS (2007) Phosphorylation of

connexin43 induced by Src: regulation of gap junctional

communication between transformed cells. Exp Cell Res

313(20):4083–4090

Palozza P, Parrone N, Catalano A, Simone R (2010) Tomato

lycopene and inflammatory cascade: basic interactions and

clinical implications. Curr Med Chem 17:2547–2563

Palozza P, Simone RE, Catalano A, Mele MC (2011) Tomato

lycopene and lung cancer prevention: from experimental to

human studies. Cancers 3:2333–2357. doi:10.3390/cancers

3022333

Panchin YV (2005) Evolution of gap junction proteins-the

pannexin alternative. J Exp Biol 208:1415–1419

Paoloni-Giacobino A, Grimble R, Pichard C (2003) Genetics

and nutrition. Clin Nutr 22:429–435

Phelan P (2005) Innexins: members of an evolutionarily con-

served family of gap-junction proteins. Biochim Biophys

Acta 1711(2):225–245

Phelan P, Starich TA (2001) Innexins get into the gap. BioEs-

says 23(5):388–396

Pointis G, Fiorini C, Gilleron J, Carette D, Segretain D (2007)

Connexins as precocious markers and molecular targets for

chemical and pharmacological agents in carcinogenesis.

Curr Med Chem 14:2288–2303

Richard G (2001) Connexin disorders of the skin. Adv Dermatol

17:243–277

Ried K, Fakler P (2011) Protective effect of lycopene on serum

cholesterol and blood pressure: meta-analyses of inter-

vention trials. Maturitas 68:299–310

Rivedal E, Leithe E (2005) Connexin43 synthesis, phosphory-

lation, and degradation in regulation of transient inhibition

of gap junction intercellular communication by the phorbol

ester TPA in rat liver epithelial cells. Exp Cell Res

302:143–152

Roger C, Mograbi B, Chevallier D, Michiels JF, Tanaka H,

Segretain D, Pointis G, Fenichel P (2004) Disrupted traffic

of connexin 43 in human testicular seminoma cells: over-

expression of Cx43 induces membrane location and cell

proliferation decrease. J Pathol 202:241–246

Rose B, Mehta PP, Loewenstein WR (1993) Gap-junction

protein gene suppresses tumorigenicity. Carcinogenesis

14:1073–1075

Ross SA (2010) Evidence for the relationship between diet and

cancer. Exp Oncol 32(3):137–142

Ruch RJ, Cheng SJ, Klaunig JE (1989) Prevention of cytotox-

icity and inhibition of intercellular communication by

antioxidant catechins isolated from Chinese green tea.

Carcinogenesis 10:1003–1008

Ruch RJ, Madhukar BV, Trosko JE, Klaunig JE (1993) Reversal

of ras-induced inhibition of gap-junctional intercellular

communication, transformation, and tumorigenesis by

lovastatin. Mol Carcinog 7(1):50–59

Sabarinathan D, Vanisree AJ (2010) Naringenin, a flavanone

alters the tumorigenic features of C6 glioma cells.

Biomed Pharmacother. doi:10.1016/j.biopha.2010.

06.010

Phytochem Rev

123

Author's personal copy

Sai K, Kanno J, Hasegawa R, Trosko JE, Inoue T (2000) Pre-

vention of the down-regulation of gap junctional intercel-

lular communication by green tea in the liver of mice fed

pentachlorophenol. Carcinogenesis 21(9):1671–1676

Sai K, Kang KS, Hirose A, Hasegawa R, Trosko JE, Inoue T

(2001) Inhibition of apoptosis by pentachlorophenol in

v-myc-transfected rat liver epithelial cells: relation to

down-regulation of gap junctional intercellular communi-

cation. Cancer Lett 173(2):163–174

Shakibaei M, Harikumar KB, Aggarwal BB (2009) Resveratrol

addiction: to die or not to die. Mol Nutr Food Res

53:115–128

Shen J, Wang LH, Zheng LR, Zhu JH, Hu SJ (2010) Lovastatin

inhibits gap junctional communication in cultured aortic

smooth muscle cells. J Cardiovasc Pharm T 15(3):296–302

Shuin T, Nishimura R, Noda K, Umeda M, Ono T (1983)

Concentration-dependent differential effect of retinoic acid

on intercellular metabolic cooperation. Gann 74:100–105

Shulzhenko N, Morgun A, Hsiao W, Battle M, Yao M, Gav-

rilova O, Orandle M, Mayer L, Macpherson AJ, McCoy

KD, Fraser-Liggett C, Matzinger P (2011) Crosstalk

between B lymphocytes, microbiota and the intestinal

epithelium governs immunity versus metabolism in the gut.

Nat Med 17:1585–1590

Simek J, Churko J, Shao Q, Laird DW (2009) Cx43 has distinct

mobility within plasma-membrane domains, indicative of

progressive formation of gap-junction plaques. J Cell Sci

122:554–562

Singh P, Goyal GK (2008) Dietary lycopene: its properties and

anticarcinogenic effects. Compr Rev Food Sci F

7(3):255–270

Solan JL, Lampe PD (2009) Connexin43 phosphorylation:

structural changes and biological effects. Biochem J

419(2):261–272

Sosinsky GE, Boassa D, Dermietzel R, Duffy HS, Laird DW,

MacVicar B, Naus CC, Penuela S, Scemes E, Spray DC,

Thompson RJ, Zhao HB, Dahl G (2011) Pannexin channels

are not gap junction hemichannels. Channels 5(3):193–197

Stahl W, von Laar J, Martin HD, Emmerich T, Sies H (2000)

Stimulation of gap junctional communication: comparison

of acyclo- retinoic acid and lycopene. Arch Biochem

Biophys 373(1):271–274

Surh YJ (1999) Molecular mechanisms of chemopreventive

effects of selected dietary and medicinal phenolic sub-

stances. Mutat Res 428:305–327

Takahashi H, Nomata K, Mori K, Matsuo M, Miyaguchi T,

Noguchi M, Kanetake H (2004) The preventive effect of

green tea on the gap junction intercellular communication

in renal epithelial cells treated with a renal carcinogen.

Anticancer Res 24(6):3757–3762

Teaford MF, Ungar PS (2000) Diet and the evolution of the

earliest human ancestors. Proc Natl Acad Sci USA

97:13506–13511

Temme A, Buchmann A, Gabriel HD, Nelles E, Schwarz M,

Willecke K (1997) High incidence of spontaneous and

chemically-induced liver tumors in mice deficient for

connexin32. Curr Biol 7:713–716

Trosko JE (2003) The role of stem cells and gap junctional

intercellular communication in carcinogenesis. J Biochem

Mol Biol 36:43–48

Trosko JE (2007a) Stem cells and cell–cell communication in

the understanding of the role of diet and nutrients in human

diseases. J Food Hygiene Safety 22(1):1–14

Trosko JE (2007b) Gap junctional intercellular communication

as a biological ‘‘Rosetta stone’’ in understanding, in a

systems biological manner, stem cell behavior, mecha-

nisms of epigenetic toxicology, chemoprevention and

chemotherapy. J Membr Biol 218(1–3):93–100

Trosko JE (2008) Human adult stem cells as targets for cancer

stem cells: evolution: Oct- 4 gene and cell–cell commu-

nication. In: Dittmar T, Zaenkar K (eds) Stem cells and

cancer. Nova Science Publishers, New York, pp 147–187

Trosko JE (2009) Cancer stem cells and cancer non-stem cells:

from adult stem cells or from re-programming of differ-

entiated somatic cells. Vet Pathol 46(2):176–193

Trosko JE (2011) The gap junction as a ‘‘Biological Rosetta

Stone’’: implications of evolution, stem cells to homeo-

static regulation of health and disease in the Barker

hypothesis. J Cell Commun Signal 5(1):53–66

Trosko JE (in press) Prenatal Epigenetic influences on acute and

chronic diseases later in life, such as cancer: global health

crises resulting from a collision of biological and cultural

evolution. J Food Sci Nutrit

Trosko JE, Chang CC (2000) Modulation of cell–cell commu-

nication in the cause and chemoprevention/chemotherapy

of cancer. BioFactors 12(1–4):259–263

Trosko JE, Chang CC (2001) Mechanism of up-regulated gap

junctional intercellular communication during chemopre-

vention and chemotherapy of cancer. Mutat Res 480–481:

219–229

Trosko JE, Ruch RJ (1998) Cell-cell communication in carci-

nogenesis. Front Biosci 3:208–236

Trosko JE, Ruch RJ (2002) Gap junctions as therapeutic targets.

Curr Drug Targets 3(6):465–482

Trosko JE, Tai MH (2006) Adult stem cell theory of the mul-

tistage, multi- mechanism theory of carcinogenesis: role of

inflammation on the promotion of initiated stem cells. In:

Dittmar T, Zaenker KS, Schmidt A (eds) Infection and

inflammation: impacts on oncogenesis. Contrib Microbiol.

Basel, Karger, vol 13, pp 45–65. doi:10.1159/000092965

Trosko JE, Chang CC, Upham B, Wilson M (1998) Epigenetic

toxicology as toxicant-induced changes in intracellular

signalling leading to altered gap junctional intercellular

communication. Toxicol Lett 102–103:71–78

Trosko JE, Chang CC, Wilson MR, Upham B, Hayashi T, Wade

M (2000) Gap junctions and the regulation of cellular

functions of stem cells during development and differen-

tiation. Methods 20(2):245–264

Turnbaugh PJ, Ridaura VK, Faith JJ, Rey FE, Knight R, Gordon

JI (2009) The effect of diet on the human gut microbiome: a

metagenomic analysis in humanized gnotobiotic mice. Sci

Transl Med 1(6): 70–79

Unwin PN, Zampighi G (1980) Structure of the junction

between communicating cells. Nature 283(5747):545–549

Upham BL, Trosko JE (2009) Carcinogenic tumor promotion,

induced oxidative stress signaling, modulated gap junction

function and altered gene expression. Antioxid Redox

Signal 11:297–308

Upham BL, Weis LM, Trosko JE (1998) Modulated gap junc-

tional intercellular communication as a biomarker of PAH

Phytochem Rev

123

Author's personal copy

epigenetic toxicity: structure-function relationship. Envi-

ron Health Perspect 106(Suppl. 4):975–981

Upham BL, Guzvic M, Scott J, Carbone JM, Blaha L, Coe C, Li

LL, Rummel AL, Trosko JE (2007) Inhibition of gap

junctional intercellular communication and activation of

mitogen-activation protein kinase by tumor-promoting

organic peroxides and protection by resveratrol. Nutr

Cancer 57(1):38–47

Vainio H, Weiderpass E (2006) Fruit and vegetables in cancer

prevention. Nutr Cancer 54(1):111–142

van der Pols JC, Heinen MM, Hughes MC, Ibiebele TI, Marks

GC, Green AC (2009) Serum antioxidants and skin cancer

risk: an 8-year community-based follow-up study. Cancer

Epidemiol Biomarkers Prev 18(4):1167–1173

Vang O, Ahmad N, Baile CA, Baur JA, Brown K, Csiszar A, Das

DK, Delmas D, Gottfried C, Lin HY, Ma QY, Mukho-

padhyay P, Nalini N, Pezzuto JM, Richard T, Shukla Y,

Surh YJ, Szekeres T, Szkudelski T, Walle T, Wu JM (2011)

What is new for an old molecule? Systematic review and

recommendations on the use of resveratrol. PLoS ONE

6(6):e19881

Vine AL, Bertram JS (2002) Cancer chemoprevention by con-

nexins. Cancer Metastasis Rev 21(3–4):199–216

Vinken M, Vanhaecke T, Papeleu P, Snykers S, Henkens T,

Rogiers V (2006) Connexins and their channels in cell

growth and cell death. Cell Signal 18(5):592–600

Vinken M, De Rop E, Decrock E, De Vuyst E, Leybaert L,

Vanhaecke T, Rogiers V (2009) Epigenetic regulation of

gap junctional intercellular communication: more than a

way to keep cells quiet? Biochim Biophys Acta 1795(1):

53–61

Vinken M, Vanhaecke T, Rogiers V (2010) Emerging roles of

connexin hemichannels in gastrointestinal and liver path-

ophysiology. World J Gastrointest Pathophysiol 1(4):

115–117

Vinken M, Decrock E, De Vuyst E, Ponsaerts R, D’hondt C,

Bultynck G, Ceelen L, Vanhaecke T, Leybaert L, Rogiers

V (2011) Connexins: sensors and regulators of cell cycling.

Biochim Biophys Acta 1815(1):13–25

Wei CJ, Xu X, Lo CW (2004) Connexins and cell signaling in

development and disease. Ann Rev Cell Dev Biol

20:811–836

Weisburger JH (2001) Chemopreventive effects of cocoa

polyphenols on chronic diseases. Exp Biol Med (May-

wood) 226(10):891–897

Welsch CW, Goodrich-Smith M, Brown CK, Crowe N (1981)

Enhance by retinyl Acetate of hormone induced mammary

tumorigenesis in female GR/A mice. J Natl Cancer Inst

67(4):935–938

Weng JR, Tsai CH, Kulp SK, Chen CS (2008) Indole-3-carbinol

as a chemopreventive and anti-cancer agent. Cancer Lett

262(2):153–163

Woodworth HL, McCaskey SJ, Duriancik DM, Clinthorne JF,

Langohr IM, Gardner EM, Fenton JI (2010) Dietary fish oil

alters T lymphocyte cell populations and exacerbates

disease in a mouse model of inflammatory colitis. Cancer

Res 70(20):7960–7969

Wu GD, Chen J, Hoffmann C, Bittinger K, Chen Y-Y, Keilb-

augh SA, Bewtra M, Knights D, Walters WA, Knight R,

Sinha R, Gilroy E, Gupta K, Baldassano R, Nessel L,

Li H, Bushman FD, Lewis JD (2011) Linking long-term

dietary patterns with gut microbial enterotypes. Science

334(6052):105–108

Yamasaki H (1995) Non-genotoxic mechanisms of carcino-

genesis: studies of cell transformation and gap junctional

intercellular communication. Toxicol Lett 77(1–3):55–61

Yamasaki H, Enomoto T (1985) Role of intercellular commu-

nication in BALB/c 3T3 cell transformation. Carcinog

Compr Surv 9:179–194

Yamasaki H, Naus CC (1996) Role of connexin genes in growth

control. Carcinogenesis 17(6):1199–1213

Yamasaki H, Hollstein M, Mesnil M, Martel N, Aguelon AM

(1987) Selective lack of intercellular communication

between transformed and nontransformed cells as a com-

mon property of chemical and oncogene transformation of

BALB/c 3T3 cells. Cancer Res 47:5658–5664

Yamasaki H, Krutovskikh V, Mesnil M, Columbano A, Tsuda

H, Ito N (1993) Gap junctional intercellular communica-

tion and cell proliferation during rat liver carcinogenesis.

Environ Health Perspect 101(Suppl 5):191–197

Yan F, Tian XM, Ma XD (2006) Effects of resveratrol on growth

inhibition and gap-junctional intercellular communication

of HepG2 cells. Nan Fang Yi Ke Da Xue Xue Bao

26(7):963–966

Yotti LP, Chang CC, Trosko JE (1979) Elimination of metabolic

cooperation in Chinese hamster cells by a tumor promoter.

Science 206(4422):1089–1091

Yu L, Zhao Y, Fan Y, Wang M, Xu S, Fu G (2010) Epigallo-

catechin-3 gallate, a green tea catechin, attenuated the

downregulation of the cardiac gap junction induced by high

glucose in neonatal rat cardiomyocytes. Cell Physiol Bio-

chem 26(3):403–412

Zamin LL, Filippi-Chiela EC, Dillenburg-Pilla P, Horn F, Sal-

bego C, Lenz G (2009) Resveratrol and quercetin cooperate

to induce senescence-like growth arrest in C6 rat glioma

cells. Cancer Sci 100(9):1655–1662

Zefferino R, Leone A, Piccaluga S, Cincione R, Ambrosi L

(2008) Mercury modulates interplay between IL-1b, TNF-

a, and gap junctional intercellular communication in

keratinocytes: mitigation by lycopene. J Immunotoxicol

5(4):353–360

Zhang LX, Cooney RV, Bertram JS (1991) Carotenoids enhance

gap junctional communication and inhibit lipid peroxida-

tion in C3H/10T1/2 cells: relationship to their cancer

chemopreventive action. Carcinogenesis 12(11):2109–

2114

Zhang Y-W, Dou D-Q, Zhang L, Chen Y-J, Yao X-S (2001)

Effects of ginsenosides from Panax ginseng on cell-to-cell

communication function mediated by gap junctions. Planta

Med 67(5):417–422. doi:10.1055/s-2001-15816

Phytochem Rev

123

Author's personal copy