Food and Chemical Toxicology 55 (2013) 304–312

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Food and Chemical Toxicology

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Antioxidant, antimicrobial and anti-proliferative activities of Solanum tuberosum L.var. Vitelotte

Paola Bontempo a,⇑, Vincenzo Carafa a, Roberto Grassi b, Adriana Basile c, Gian Carlo Tenore d,Carmen Formisano e, Daniela Rigano e,⇑, Lucia Altucci a,f,⇑a Department of General Pathology, Second University of Naples, Vico L. de Crecchio 7, 80138 Napoli, Italyb Medical-Surgical Department of Internal and Experimental Clinic ‘Magrassi-Lanzara’, Second University of Naples, Via Pansini 5, 80100 Naples, Italyc Department of Plant Biology, University of Naples ‘‘Federico II’’, Via Foria 223, 80139 Naples, Italyd Department of Pharmaceutical Chemistry, University of Naples ‘‘Federico II’’, Via D. Montesano, 49, 80131 Naples, Italye Department of Chemistry of Natural Compounds, University of Naples ‘‘Federico II’’, Via D. Montesano, 49, 80131 Naples, Italyf Institute of Genetics and Biophysics ‘Adriano Buzzati Traverso’, IGB, Via P. Castellino 111, 80131 Naples, Italy

a r t i c l e i n f o a b s t r a c t

Article history:Received 29 October 2012Accepted 26 December 2012Available online 11 January 2013

Keywords:Solanum tuberosum L. var. VitelotteAnthocyaninAntibacterialAntifungalAnticancer action

0278-6915/$ - see front matter � 2013 Elsevier Ltd. Ahttp://dx.doi.org/10.1016/j.fct.2012.12.048

Abbreviations: AML, Acute Myeloid Leukemia; APLmia; COX-2, cyclooxygenase-2; DPPH, Free Radical ScaAmerican-British; FAS, TNF receptor superfamily, mFRAP, Ferric Reducing/Antioxidant Power; HPLC-DAchromatography-diode array detector; HPLC–ESI–Mchromatography- electrospray ionization mass speBactericidal Concentration; MIC, Minimal inhibitory cFactor-kappa B; PML-RAR, Promyelocytic Leukemia-Reactive Oxygen Species; TE, Trolox Equivalent; TNalpha; VEGF, Vascular Endothelial growth factor.⇑ Corresponding authors. Address: Department o

University of Naples, Vico L. de Crecchio 7, 8010815667569; fax: +39 081450169 (L. Altucci). Tel.:081450169 (P. Bontempo). Tel.: +39 081678546; fax:

E-mail addresses: paola.bontempo@unina2.it (P.(D. Rigano), lucia.altucci@unina2.it (L. Altucci).

Solanum tuberosum L. var. Vitelotte is a potato variety widely used for human consumption. The pigmentsresponsible for its attractive color belong to the class of anthocyanins. The objectives of this study were tocharacterize and measure the concentration of anthocyanins in pigmented potatoes and to evaluate theirantioxidant and antimicrobial activities and their anti-proliferative effects in solid and hematologicalcancer cell lines. Anthocyanins exert anti-bacterial activity against different bacterial strains and a slightactivity against three fungal strains. The Gram-positive bacterium Staphylococcus aureus and the fungusRhyzoctonia solani were the most affected microorganisms. Antioxidant activities were evaluated byDPPH and FRAP methods; the extract showed a higher reducing capability than anti-radical activity.Moreover, we found that in different cancer cell models the anthocyanins cause inhibition of proliferationand apoptosis in a dose dependent manner. These biological activities are likely due to the high content ofmalvidin 3-O-p-coumaroyl-rutinoside-5-O-glucoside and petunidin 3-O-p-coumaroyl-rutinoside-5-O-glucoside.

� 2013 Elsevier Ltd. All rights reserved.

1. Introduction

Solanum tuberosum L. var. Vitelotte is a potato variety with deepblue skin and violet flesh widely used for human consumption andwell appreciated for its good nutritional characteristics. In recentyears there has been an increasing interest in red- and purple-

ll rights reserved.

, Acute Promyelocytic Leuke-venging Ability; FAB, French-ember 6; FASL, FAS ligand;D, high performance liquidS, high performance liquidctrometry; MBC, Minimumoncentration; NF-jb, NuclearRetinoic Acid Receptor; ROS,F-a, Tumor Necrosis Factor

f general Pathology, Second38 Napoli, Italy. Tel.: +39+39 0815665702; fax: +39

+39 081678552 (D. Rigano).Bontempo), drigano@unina.it

fleshed potato varieties because of their color appeal, outstandingtaste and ‘‘mashability’’. There has been consumer interest inpotatoes with colored flesh for use in salads and novelty crisps,especially since color is retained after cooking or frying (Lewiset al., 1999). The pigments responsible for the attractive color ofthese potatoes varieties are anthocyanins, whose concentrationvary in large ranges and correlates with the degree of pigmentationin potato flesh. The pigments in colored potatoes have been iden-tified as the 5-glucoside-3-rhamnosylglucoside derivatives of allthe common anthocyanidins, monoacylated with p-coumaric orferulic acids (Andersen et al., 2002; Harborne, 1960; Lewis et al.,1999). A good correlation between the total anthocyanins andthe biological activities of the tubers was found. It is known thatthese pigments are rapidly adsorbed at the stomach level (Passa-monti et al., 2003). Recently, in vivo absorption of anthocyaninsfrom an extract of Ipomea batatas L. was also demonstrated in ratsand humans after their addition to the diet. Acylated anthocyanins,the main constituents of potato, were detected in plasma and urineafter ingestion (Harada et al., 2004). Anthocyanins are known topossess different pharmacological properties and are used byhumans for therapeutic purpose (Kong et al., 2003). More and more

P. Bontempo et al. / Food and Chemical Toxicology 55 (2013) 304–312 305

studies show that anthocyanins have demonstrated ability to pro-tect against a myriad of human diseases such as liver dysfunction,hypertension, vision disorders, microbial infections, and diarrhea(Rice-Evans and Packer, 1998; Smith et al., 2000; Wang et al.,2000). Due to this fact, a high intake of anthocyanin-rich foodhas been linked to health preventive effects and reduced risk ofpathologies such as aged-related macular degeneration, cancer orcardiovascular disorders. Indeed, the consumption of anthocyaninslowers the risk of cardiovascular disease, diabetes, arthritis andcancer due, at least in part, to their anti-oxidant and anti-inflam-matory activities (Afaq et al., 2005; Huang et al., 2002; Prior andWu, 2006; Reddy et al., 2005; Rodrigo et al., 2006). The anticanceraction of anthocyanins has also been reported. Pure anthocyaninsand anthocyanin-rich extracts from fruits and vegetables haveexhibited anti-proliferative activity towards multiple cancer celltypes in vitro (Rodrigo et al., 2006; Zhang et al., 2005). Cell prolif-eration was inhibited by the ability of anthocyanins to blockvarious stages of the cell cycle by acting on regulatory proteins(e.g., p53, p21, p27, cyclin D1, cyclin A, etc.). Interestingly, severalinvestigations have compared the antiproliferative effects ofanthocyanins on normal vs. cancer cells and found that they selec-tively inhibit the growth of cancer cells with relatively little or noeffect on the growth of normal cells (Galvano et al., 2004;Hakimuddin et al., 2004). Furthermore, anthocyanin-rich extractsfrom berries and grapes, and several pure anthocyanins and anth-ocyanidins, have exhibited pro-apoptotic effects in multiple celltypes in vitro (Afaq et al., 2007; Chen et al., 2005; Martin et al.,2003; Olsson et al., 2004; Reddivari et al., 2007; Seeram et al.,2006), acting via both the mitochondrial and the extrinsic deathpathways (Chang et al., 2005; Reddivari et al., 2007). In the intrin-sic pathway, anthocyanin treatment alters mitochondrial mem-brane potential, leading to cytochrome c release and modulationof caspase-dependent apoptosis. In the extrinsic pathway, antho-cyanins modulate the expression of FAS and FASL (FAS ligand) incancer cells. In addition, treatment of cancer cells, but not normalcells, with anthocyanins leads to an accumulation of ROS (reactiveoxygen species) and subsequent apoptosis, suggesting that theROS-mediated mitochondrial caspase-independent pathway isimportant for anthocyanin-induced apoptosis (Feng et al., 2007).Not surprisingly, anthocyanins also exhibit antioxidant and anti-inflammatory effects. Inflammation has been shown to play a rolein the promotion of some types of cancer in animals, and probablyin humans (Kwon et al., 2007). Abnormal up-regulation of twoinflammatory proteins, nuclear factor-kappa B (NF-jB) and cyclo-oxygenase-2 (COX-2), is a common occurrence in many cancers,and inhibitors of these proteins usually exhibit significant che-mo-preventive potential (Chang et al., 2005;Martin et al., 2003).Interestingly, through their ability to inhibit the mRNA and/or pro-tein expression levels of COX-2, NF-jB and various interleukins,the anthocyanins have exhibited anti-inflammatory effects inmultiple cell types in vitro (Afaq et al., 2005; Huang et al., 2002;Reddy et al., 2005;Rodrigo et al., 2006). In addition, the anticancerpotential can also be correlated to the anthocyanins anti-angio-genic effects that have been investigated in endothelial (Bagchiet al., 2004), oral cancer (Rodrigo et al., 2006) and mouse epidermalJB6 cells (Huang et al., 2006). Anthocyanins have been shown tosuppress angiogenesis through several mechanisms such as: inhi-bition of H2O2-and tumor necrosis factor alpha (TNF-a)-inducedVEGF expression in epidermal keratinocytes (Bagchi et al., 2004),and by reducing VEGF and VEGF receptor expression in endothelialcells. Anthocyanin extracts (2.5–100 lM) from different berrytypes, black rice and eggplant have been evaluated for their abilityto inhibit the invasion of multiple cancer cell types in Matrigel(Coates et al., 2007; Nagase et al., 1998). Prevention and treatmentof cancer through the induction of cellular differentiation offers acell-specific approach to cancer prevention and treatment that is

likely to be less toxic than standard radio/chemotherapy (Fimog-nari et al., 2004).

The objectives of this study were to characterize and measurethe concentration of anthocyanins in pigmented potatoes and toevaluate their antioxidant, antibacterial and antifungal activitiesand their anti-proliferative effects in solid and hematologicalcancer cell lines. Our results indicate the therapeutic value ofS. tuberosum extracts and its contained anthocyanins as potentialantimicrobial, antioxidant and anticancer agents.

2. Materials and methods

2.1. Chemicals

DPPH (1,1-diphenyl-2-picrilhydrazyl), 2,4,6-tris-2,4,6-tripiridyl-2-triazine(TPTZ), ferric chloride dry, 6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylicacid (Trolox), L-ascorbic acid, tert-butyl-4-hydroxy toluene (BHT), gallic acid, werepurchased from Sigma Chemical Co. (St. Louis, MO). Methanol (RPE) was purchasedfrom Carlo Erba (Milano, Italy).

2.2. Plant material

S. tuberosum L. var. Vitelotte (718 g) was collected at Nusco (Avellino) in South-ern Italy, on June 2010. All the tubers had pigmented peel and pigmented flesh.They were washed in running tap water, cut into pieces of approximately 0.5 cm,dried in a heated air drier, and then pulverized by the disintegrator. After dryingthe weight of potatoes was 157 g. Samples were kept at 4 �C.

2.3. Preparation of anthocyanins extract

Several extraction methods have been proposed to obtain extracts rich inanthocyanin, usually based on solvents as methanol, ethanol, acetone, water ormixtures. The addition of a small amount of hydrochloric acid or formic acid is rec-ommended to prevent the degradation of the non-acylated compounds (Kjell andØyvind, 2005). The optimum condition for anthocyanin extraction of potatoeswas determined according to a previous paper (Fan et al., 2008).

Pigmented potato powder was put into a 50 ml conical flask, then added inacid–ethanol (HCl, 1.5 mol/l) with a solid–liquid ratio 1:32 and put in thermostaticwater bath at a selected temperature (80 �C) for 60 min, then, centrifuged at4000 rpm for 15 min. The supernatant was collected and transferred into a 50 mlvolumetric flask for the determination of anthocyanins yield. About 1 g of the sam-ples was used for each treatment.

2.4. Antimicrobial activity assays Microorganisms

Nine bacterial strains from the American Type Culture Collection (ATCC;Rockville, MD, USA) were employed. They included Gram-positive (G+) bacteria:Staphylococcus aureus (ATCC 13709) and Enterococcus faecalis (ATCC 14428), andthe following Gram-negative (G�) bacteria: Proteus mirabilis (ATCC 7002), Proteusvulgaris (ATCC 12454), Pseudomonas aeruginosa (ATCC 27853), Salmonella typhi(ATCC 19430), Enterobacter aerogenes (ATCC 13048), Enterobacter cloacae (ATCC10699), and Klebsiella pneumoniae (ATCC 27736). The same bacterial strains, clini-cally isolated, were used to compare the sensitivity to the extract.

The extract was added with 5 � 10�2 M stock solution in DMSO, and dilutedfrom 0.01 to 1000 lg/ml concentrations in sterile physiological Tris buffer (pH7.4, 0.05 M) (Ieven et al., 1979) immediately before being used.

2.5. MIC and MBC determination

Bacterial strains were grown on MH agar plates (DIFCO, Detroit, MI) andsuspended in MH (Mueller Hinton) broth (DIFCO). The MIC values against bacterialstrains were performed using the Ericcson and Sherris (1971) broth-dilution meth-od (MH broth). The inoculum suspensions were prepared from 6 h broth culturesand adjusted to obtain a 0.5 McFarland standard turbidity. The extract wassterilized by filtration through Millipore filters (0.45 lm) and added to MH brothmedium. Serial 10-fold dilutions were made for a concentration range between0.01 and 1000 lg/ml. In the range between the minimum active and the maximuminactive concentrations were tested 2-fold dilutions to obtain a more precise mea-sure of the MIC. The bacterial suspensions were aerobically incubated for 24 h at37 �C. The MIC was defined as the lowest concentration able to inhibit any visiblebacterial growth. Cultures containing only sterile physiological TRIS buffer (pH7.4, 0.05 M), which did not influence bacterial growth, were used as controls. TheMIC values were also determined for tetracycline hydrochloride (Pharmacia,Milano), benzyl penicillin sodium (Cynamid, Catania) and cefotaxime sodium(Roussel Pharma, Milano) in MH broth using standard method.

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The MBC determination was carried out transferring to the fresh MH broth ali-quots of bacterial suspensions from the test tubes containing extract concentrationsequal or higher (up to 1000 lg/ml) than the MIC. The extract was tested in tripli-cate; the experiment was performed four times.

2.6. Antifungal activity assays

Antifungal tests were done against three fungal strains: the clinically isolated(CI) yeast Candida albicans, potentially pathogenic for humans, and the two filamen-tous phytopathogenic fungi Botrytis cinerea and Rhyzoctonia solani, kindly providedby the Plant Pathology Department of the University Federico II of Naples (Italy).

The fungi were maintained on Sabouraud glucose agar (SGA) medium (Diagnos-tic Pasteur).

Two methods were used for the in vitro assays: (1) method of agar incorporation(dilution on a solid medium) and (2) the minimal inhibitory concentration (MIC)which inhibits the visible growth of fungi was determined by the standardizedbroth micro-dilution method. Both the methods are fully described in a previouspaper (Basile et al., 2010). Positive control cultures were made culturing the fungiwithout and with ketoconazole (Sigma Aldrich, Milan).

2.7. Cell lines and materials

NB4 cells were provided by M. Lanotte (INSERM U-496, Centre G. Hayem Hos-pital Saint-Louis Paris, France). MCF-7, HeLa, MDA-MB231, LNCaP and U937 celllines have been obtained from ATCC and routinely cultured. MCF-7 and HeLa cellswere grown at 37 �C in 5% CO2 atmosphere in Dulbecco’s Modified Eagle Medium(DMEM, Gibco, NY, USA), supplemented with 5% fetal bovine serum (FBS, Gibco),1% L-glutamine, 1% ampicillin/streptomycin and 0.1% gentamicin. U937, MDA-MB231, LNCaP and NB4 cells, were grown at 37 �C in 5% CO2 atmosphere inRPMI-1640 medium (Gibco, NY, USA), supplemented with 10% heat-inactivated fe-tal bovine serum (FBS), 1% L-glutamine, 1% ampicillin/streptomycin and 0.1% genta-micin. 3T3L1 (ATCC) fibroblasts were grown – formulated Dulbecco’s ModifiedEagle Medium (DMEM, Gibco, NY, USA), completed with bovine calf serum to a finalconcentration of 10%.

2.8. Crystal violet and Trypan blu assays

In a 96 multiwell plate (BD), about 1200 cells/well were suspended in 200 ll ofcell cultures medium. After treatment with extract, cells were fixed in 25 ll of 11%gluteraldehyde in PBS (SIGMA) for 15 min, washed in deionized water and dried.Wells were incubated for 20 min in 100 ll of Crystal violet (CV; Sigma), 1 mg/mlin 20% methanol, and then washed again. Wells were incubated immediately for20 min in 100 l of acetic acid (10%). Colorimetric assay carried out in triplicatewas quantified by measuring OD595. As alternative viability assay, we have per-formed a dye exclusion stain, where cells with an intact membrane are able to ex-clude the dye while cells without an intact membrane take up the coloring agent.The dye used for exclusion stain is the Trypan blue (SIGMA). Briefly cells have beenmixed 1:1 with a 0.4% Trypan blu solution and counted in triplicate.

2.9. Cell cycle analysis

2.5 � 105 cells were collected and suspended in 500 ll of a hypotonic buffer(0.1% Triton X-100, 0.1% sodium citrate, 50 lg/ml propidium iodide (PI), RNAseA). Cells were incubated in the dark for 30 min. Samples were acquired on aFACS-Calibur flow cytometer using Cell Quest software (Becton Dickinson) and ana-lyzed with standard procedures using Cell Quest software (Becton Dickinson) andthe ModFit LT version 3 Software (Verity) as previously reported (Nebbioso et al.2011). All the experiments were performed in triplicate.

2.10. Analysis of apoptosis

Apoptosis was measured as pre-G1 analyzed by FACS with Cell Quest software(Becton Dickinson) as previously reported (Altucci et al., 2001; Nebbioso et al.,2005). Moreover, analysis of apoptosis was measured as activation of caspases 8and 3–7 (B-Bridge) or DAPI staining following the manufacturer’s instructions.

2.11. Total monomeric anthocyanin content

The total monomeric anthocyanin content of the potatoes extract was evaluatedby applying a pH-differential method. An aliquot of 1 ml of the sample was added totwo vials containing 10 ml of acetate buffer (pH 3.6) and HCl 1 N, respectively. Thedifference between the absorbance read at 530 nm was calculated. Total anthocya-nin content was expressed as mg malvin equivalents (ME)/100 ml of potato extract.

2.12. Determination of antioxidant capacity

Both sample and analytical standards were dissolved in methanol in order toobtain 1 mg/100 ml solutions, which was chosen as appropriate concentration forassessing antioxidant activity after preliminary studies of the different concentra-

tions. For each antioxidant assay, a Trolox aliquot was used to develop a 0.5–10 mmol/l standard curve. All data were then expressed as Trolox Equivalents(mmol/l) and antioxidant activity referred to as Trolox Equivalents AntioxidantCapacity (TEAC).

2.12.1. Ferric reducing/antioxidant power (FRAP method)The total antioxidant potential of the extract was determined by using the ferric

reducing antioxidant power (FRAP) assay of Benzie and Strain (1996). A solution of10 mmol/l TPTZ in 40 mmol/l HCl and 12 mmol/l ferric chloride was diluted in300 mmol/l sodium acetate buffer (pH 3.6) at a ratio of 1:1:10. Aliquots (40 ll) ofextract solutions were added to 3 ml of the FRAP solution, and allowed to reactfor 90 min. at 37 �C, before reading the absorbance at 593.

2.12.2. Free radical scavenging ability (DPPH method)The ability of the extract to scavenge the DPPH radical was measured using the

method of Brand-Williams et al. (1995). Aliquots (40 ll) of extract solutions wereadded to 3 ml of DPPH solution (6 � 10�5 mol/l) and the absorbance was deter-mined at 515 nm after 90 min.

2.13. Anthocyanin separation, identification and quantification

HPLC separation of anthocyanin extract was performed according to earlierstudies (Downey and Rochfort, 2008). Identification was possible by monitoringanthocyanins at 520 nm and by comparing their spectra and retention times withthose of commercial standards and with those reported in previous works (Downeyand Rochfort, 2008). The sample (20 ll) was directly injected after filtrationthrough a 0.45 lm membrane filter. Elution conditions consisted of 10% formic acidin water (solvent A) and 10% formic acid in a methanol (solvent B) gradient at a flowrate of 1.0 ml/min. The column selected was a C-18 Zorbax (150 mm � 4.6 mm,5 lm packing; Agilent, USA) protected by an Agilent C-18 guard column. Analyseswere run on a Finnigan HPLC system (Thermo Electron Corporation, San Jose, CA)provided with photodiode array detector (DAD). The gradient conditions were:0 min, 18% B; 14 min, 29% B; 16 min, 32% B; 18 min, 41% B; 18.1 min, 30% B;29 min, 41% B; 32 min, 50% B; 34.5 min, 100% B; 35–38 min, 18% B. Calibrationcurves consisted in 0.001–1 mg/ml quercetin- 3-O-glucoside and 0.05–1 mg/mlmalvidin-3-O-glucoside standard solutions. The identity of anthocyanins was con-firmed with LC–ESI/MS/MS experiments and the data were compared with previousworks (Downey and Rochfort, 2008). The same chromatographic conditions wereapplied to a HP1100 HPLC system (Agilent, USA) coupled to a PE-Sciex API-2000 tri-ple-quadruple mass spectrometer (MS) (Warrington, Cheshire, UK) equipped with aturbo-spray (TSI) source. MS detection was carried out in positive ion mode at unitresolution using a mass range of 150–1500 m/z and a mass peak width of 0.7 ± 0.1.Selected ion monitoring (SIM) experiments were carried out using the followingoperational parameters: vaporizer, 350 �C; heated capillary, 150–200 �C; carriergas, nitrogen, at a sheath pressure of 70 psi; auxiliary gas, nitrogen, to assist innebulization, at a pressure of 30 psi; de-clustering potential, 44.0 eV; focusingpotential, 340.0 eV; entrance potential, 10.0 eV; collision energy, 33.0 eV for iondecomposition in the collision cell at 0.8 mTorr. (Tenore et al., 2011).

2.14. Statistical analysis

Triplicate analyses for each measurement were conducted for each sample. Dif-ferences between the means were evaluated with ANOVA, using the Graf Pad Instat3 (Microsoft Software) statistic program. The significance of the model was evalu-ated by ANOVA. The significance of the regression cients was evaluated by Student’st test. The significance level was fixed at 0.05 for all the statistical analysis. Corre-lation coefficients (R), to determine the relationship between antioxidant activityand phenol content, were calculated by using Microsoft Office Excel application.

3. Results

3.1. Antibacterial and antifungal effects of Anthocyanins extract fromS. tuberosum

Anthocyanins showed a high antibacterial activity against allthe nine standard bacterial strains tested. Both Gram-positiveand Gram-negative bacteria were inhibited, but the Gram-positivebacteria were the most sensible to the action of the extract.Minimal inhibitory concentrations (MICs) were in the range of16–250 lg/ml, and ATCC strains were generally more inhibitedon respect to CI (Table 1). Staphylococcus aureus from both standardand clinical sources showed a very high sensitivity to the extract(MIC = 15.6 lg/mL for standard strains and 31.3 lg/mL for clinicalisolates), displaying also good minimum bactericidal concentration(MBC) values.

Table 1MIC and MBC values (lg/ml) of anthocyanins extract from Solanum tuberosum L. var Vitelotte and MICs of reference antibiotics.

MIC(lg/mL) MBC

Anthocyanins CTAX PENG TET Anthocyanins

S. aureus ATCC 13709 15.6 2 0.03 2 62.5S. aureus CI 31.3 R R R 125E. faecalis ATCC 14428 15.6 R 8 2 RE. faecalis CI 31.3 R R R RP. vulgaris ATCC 12454 31.3 2 4 R RP. vulgaris CI 62.5 32 R R RP. mirabilis ATCC 7002 31.3 0.03 4 32 RP. mirabilis CI 62.5 32 R R RS. typhi ATCC 19430 31.3 0.5 4 1 RS. typhi CI 62.5 1 2 1 RE. cloacae ATCC 10699 31.3 R 4 R RE. cloacae CI 62.5 R R R RE. aerogenes ATCC 13048 31.3 R 4 R RE. aerogenes CI 62.5 R R R RP. aeruginosa ATCC 27853 62.5 16 R 32 RP. aeruginosa CI 62.5 32 R R RK. pneumoniae ATCC 27736 125 0.1 R 16 RK. pneumoniae CI 250 32 R R R

CTAX = cefotaxime; PENG = Benzyl Penicillin Sodium; TET = Tetracycline; CI = Clinical Isolated.

Table 2Antifungal activity of anthocyanins from S. tuberosum L. var. Vitelotte.

MIC (lg/mL) MFC

Anthocyanins KCON Anthocyanins

R. solani 250 0.2 –B. cinerea 500 0.2 –C. albicans CI 500 0.4 –

KCON, ketoconazole. A dash indicates not active.

Fig. 1. Antioxidant capability of anthocyanins extract vs. three antioxidant stan-dards measured by using the DPPH method.

Fig. 2. Antioxidant capability of anthocyanins extract vs. three antioxidant stan-dards measured by using the FRAP method.

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The antifungal activity of the anthocyanins extract ofS. tuberosum var. Vitelotte was studied against three strains offungi, including one potentially pathogenic yeast (C. albicans CI)and two filamentous phyto-pathogenic fungi (B. cinerea and R.solani). Anthocyanins inhibited the three fungi: in particular, R.solani from 0% to 50% and C. albicans and B. cinerea from 0% and25%. Because only the samples with a fungal growth inhibitionsuperior or equal to 50% (high) were the object of MIC determina-tion, anthocyanins were successively tested. Results indicate thatthe samples had a fungi-static effect on all the fungi tested, R. solanibeing the most sensitive strain (MIC = 250 lg/mL) (Table 2).

3.2. Anthocyanins extract from S. tuberosum exerts antioxidant action

Antioxidant activities were evaluated using 2,2-diphenyl-1-pic-rylhydrazyl (DPPH) radical scavenging potential and FRAP assays.DPPH and FRAP tests are expressed as trolox equivalents (TEs). Inboth assays the extract antioxidant activity was compared withthat of three standard solutions: the extract showed a higherreducing capacity than anti-radical activity (1.42 ± 0.2 and4.25 ± 0.4 mmol Trolox/L for DPPH and FRAP, respectively). Thesteady state was reached after 110 min in both assays and resultsare shown in Figs. 1 and 2.

3.3. Anthocyanins extract from S. tuberosum exerts anticancer actionin solid and hematological cancer cell lines by inducing anti-proliferative and apoptotic effects

The efficacy of different doses of the anthocyanins extract wasassessed in solid and hematological cancer cell lines (Fig. 3). Testedin proliferation curve with a Crystal violet assay, the crudeanthocyanins extract displayed anti proliferative activity in somesolid cancer cell lines such as HeLa (cervical cancer), MCF-7,MDA-MB231 (breast cancer) and LnCaP (prostate cancer) cells(Fig. 3A). Moreover, this anti-growth action, measured by Trypanblu viability assay, could also be shown in myeloid leukemia cellssuch as U937 and NB4 (the prototype of acute promyelocytic leu-kemia, APL) (Fig. 3B). As shown in Fig. 3A and B, the anti-prolifer-ative effect is dose dependent. In all the described cell lines, themajor effect has been obtained using 5 mg/ml of the crude extract.Investigating for the anti-cancer potential of the anthocyanins ex-tract, we tested its biological effects on cell cycle in solid cancer(HeLa, MDA-MB231, MCF7, LnCap) and in myeloid leukemia cell

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Fig. 3. Anti-proliferative potential of Anthocyanins extract. (A) Proliferation curves by Crystal violet assay and cell cycle analysis in the indicated cell lines at day 3 oftreatment. (B) Proliferation curve by Trypan blu assay and cell cycle analysis in NB4 and U937 cells at day 3 after treatment with the indicated compound (Ac2 and Ac5correspond to the 2 and 5 mg/mL concentrations). Results represent the media of triplicates. (C) Caspase 8 and 3–7 activation in NB4 cells upon 48 h treatment as indicated;apoptosis measured as pre-G1 pick in NB4 and 3T3L1 cells after 72 and 48 h of treatment respectively as indicated; nuclear morphology by DAPI staining after vehicle or 48 htreatment in NB4 cells as indicated.

308 P. Bontempo et al. / Food and Chemical Toxicology 55 (2013) 304–312

lines (U937, NB4). As shown in Fig. 3A and B, the majority of thecell lines responded with a dose dependent block in G1 phase ofcell cycle; only U937 cells showed a dual effect with a S phaseblock for the higher dose and a G1 block for the lower dose. Inagreement, while normal 3T3L1 fibroblasts did not show inductionof apoptosis (Fig. 3C), NB4 leukemia cells displayed nearly 100% ofcells in pre-G1 pick at 72 h and a high induction of caspases 8 and3–7 activation after 48 h of treatment (Fig. 3C). In these settingsalso nuclear morphology stained with DAPI showed a high rateof fragmentation, supporting the induction of a time dependentapoptosis (Fig. 3C). Indeed, all cancer cell lines (but not normalcells) responded with apoptosis to the treatment with anthocyaninextract (Fig. 4), although displaying different sensitivities that

might be related to the intrinsic cell line context. These data werefully supported by the morphological analyses showing the anti-proliferative effect accompanying the apoptotic events.

3.4. Identification and quantification of the active Anthocyanins

Although more than six distinct chromatographic peaks weredetected for the sample, some were present only in trace amounts,thus making their identification and quantification difficult. Theiridentification was based on MS experiments, UV–VIS absorptionspectra, and chromatographic retention times, which were com-pared with both reference compounds and data from other studies(Downey and Rochfort, 2008). Single anthocyanin contents (Table 3)

Ctrl Ac 5 mg/ml

U937

NB4

MDA.MB231

MCF7

LnCap

Hela

0

2

4

6

8

10

12pre-G1

Ac5Ctr

% o

f pr

e-G

1 pi

ck

0

5

10

15

20

25

30pre-G1

Ac5Ctr

% o

f pr

e-G

1 pi

ck

0

3

6

9

12

15pre-G1

Ac5Ctr

% o

f pr

e-G

1 pi

ck

05

10152025303540

pre-G1

Ac5Ctr

% o

f pr

e-G

1 pi

ck

0

5

10

15

20

25

30

35pre-G1

Ac5Ctr

% o

f pr

e-G

1 pi

ck

0

3

6

9

12

15pre-G1

Ac5Ctr

% o

f pr

e-G

1 pi

ck

Fig. 4. Anthocyanins extract induce proliferative block and apoptosis in cancer cells. Apoptosis in the indicated cell lines at day 2 of treatment with 5 mg/ml together with themorphological analyses of the corresponding points.

P. Bontempo et al. / Food and Chemical Toxicology 55 (2013) 304–312 309

results were generally higher than those reported previously (Ieriet al., 2011). As reported by Ieri et al. (2011), the compound malvi-din 3-O-p-coumaroyl-rutinoside-5-O-glucoside was found as the

main monomeric anthocyanin (Table 3). This anthocyanin was fol-lowed by petunidin 3-O-p-coumaroyl-rutinoside-5-O-glucoside,while the remaining ranged from 20.2 ± 1.2 to 27.2 ± 1.3 mg ME/L.

Table 3LC/MS data of tentatively identified anthocyanins in pigmented potatoes extract and their quantitative analysis using DAD at 520 nm.

Peak Compound mg ME/La Retention timeb (min) m/z [M + H]+ Fragment ion (m/z)c

1 Mal-3-O-rut-5-O-glu 20.21 ± 1.1 5.14 ± 0.2 801 331, 493, 6392 Delp-3-O-p-coum-rut-5-O-glu 23.75 ± 1.2 6.62 ± 0.3 919 303, 465, 757, 7733 Mal-3-O-caf-rut-5-O-glu 27.22 ± 1.4 8.12 ± 0.4 963 331, 493, 8014 Pet-3-O-p-coum-rut-5-O-glu 147.83 ± 1.0 10.07 ± 0.5 933 317, 479, 771, 7875 Mal-3-O-p-coum-rut-5-O-glu 360.70 ± 1.9 11.50 ± 0.6 947 331, 493, 785, 8016 Mal-3-O-ferul-rut-5-O-glu 23.22 ± 1.5 15.44 ± 0.7 977 331, 493, 801, 815

Abbreviations used: Pet, Petunidin; Mal, Malvidin; Delp, Delphinidin; Rut, Rutinoside; Glu, Glucoside; Ferul, Feruloyl; p-Coum, para-Coumaroyl; Caf, Caffeoyl.Standards of cyanidin, delphinidin, malvidin, peonidin, pelargonidin and petunidin were purchased from Fluka (Buchs, Switzerland). Caffeic acid (P98% HPLC), ferulic acid(P99% HPLC), para-coumaric acid (P98% HPLC), chlorogenic acid (P99% HPLC) were obtained from Sigma–Aldrich Co. (St. Louis, USA).

a ME: Malvidin-3-O-glucoside Equivalents, expressed as value ± SD.b Expressed as mean value ± SD.c Base peak (100%) is underlined.

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4. Discussion

Anthocyanins both in fruit and vegetables serve two functions –they improve the overall appearance, but also contribute toconsumers’ health and well-being. They are widely ingested byhumans and their daily intake has been estimated at around180 mg (Passamonti et al., 2003). An important attribute of thesepigments is that they are potent antioxidants in the diet and areknown to possess different pharmacological properties and areused by humans for therapeutic purpose (Rice-Evans and Packer,1998; Smith et al., 2000; Wang et al., 2000). They are mainlycontained in red and purple colored potato cultivars in the skinsand flesh of tubers; previous reports on anthocyanins from variouspotatoes reveal a dominance of one or more of the p-coumaroyl-5-glucoside-3-rhamnoglucosides of pelargonidin, cyanidin, peonidin,delphinidin, petunidin and malvidin. So, colored potatoes mayserve as a potential source for natural anthocyanin pigments, sincethey are a low cost crop.

Anthocyanin extract from S. tuberosum var. Vitelotte showed ahigh antibacterial activity against nine standard bacterial strainsand the same bacterial strains clinically isolated. The Gram-posi-tive bacteria were the most sensible to the action of the extract,and Staphylococcus aureus from both standard and clinical sourcesshowed a very high sensitivity (MIC = 15.6 lg/mL for standardstrains and 31.3 lg/mL for clinical isolates), showing also goodMinimum bactericidal concentration (MBC) values. This is a signif-icant datum considering that, so far, Staphylococcus aureus infec-tions are particularly tricky given its intrinsic resistance tomultiple classes of antibiotics and its ability to acquire adaptiveresistance during a therapeutic course (Cowan, 1999). The antho-cyanin extract of S. tuberosum var. Vitelotte had also a fungi-staticeffect against three strains of fungi, including one potentially path-ogenic yeast (C. albicans CI) and two filamentous phytopathogenicfungi (B. cinerea and R. solani), and was particularly active againstR. solani (MIC = 250 lg/mL). Moreover, antioxidant activities ofanthocyanins were evaluated using two complementary assays

methods, namely 2,2-diphenyl-1-picrylhydrazyl (DPPH) radicalscavenging potential and FRAP assays. The reduction of DPPHabsorption is indicative of the capacity of the extract to scavengefree radicals, independently of any enzymatic activity, while theFRAP method is used to determine the capacity of reductants in asample. FRAP test showed a higher reducing activity of anthocya-nin extract from S. tuberosum than antiradical activity evaluatedby DPPH test. This result is of great interest since generally antho-cyanins are well known for their hydrogen donating ability bywhich they are considered potent free radical scavengers. In bothassays the extract antioxidant activity was compared with that ofthree standard solutions showing an appreciable activity, keepinginto consideration that the comparison was made between an ex-tract (a complex mixture of compounds characterized by very dif-ferent levels of biological properties) and standard solutionscomposed by pure substances.

Also the anticancer activity of anthocyanin extract from S.tuberosum var. Vitelotte has been thoroughly investigated in ourstudy. The efficacy of different doses of the anthocyanin extractwas assessed in solid and hematological cancer cell lines (Fig. 3).The crude anthocyanin extract displayed anti proliferative activityin some solid cancer cell lines such as HeLa (cervical cancer), MCF-7, 3, MDA-MB231 (breast cancer) cells and LnCaP (prostate cancer).Moreover, this anti-growth action, could also be shown in myeloidleukemia cells such as U937 and NB4 the prototype of acute pro-myelocytic leukemia (APL), an acute myeloid leukemia (AML) clas-sified as M3 according to the French-American-British (FAB)classification, which carries the chromosomal translocationt(15;17) leading to the expression of the fusion protein PML-RAR-alpha. As shown in Fig. 1a and b the anti-proliferative effect is dosedependent. In all the described cell lines, the major effect has beenobtained using 5 mg/ml of the crude extract. Investigating for theanti-cancer potential of the anthocyanins extract, we tested itsbiological effects on cell cycle and apoptosis. As shown in Fig. 4,four cell lines (HeLa, MCF7, U937, NB4) responded with apoptosisin a dose dependent manner, although displaying different

P. Bontempo et al. / Food and Chemical Toxicology 55 (2013) 304–312 311

sensitivities. These differences in the cell cycle block might be dueto cellular context specific events. In all the described cell lines, themajor effect has been obtained using 5 mg/ml of the crude extract.

Because biological activity of potato anthocyanins results fromthe synergistic effect of each anthocyanin pigment, it is importantto assess the pigmented potato cultivar for individual anthocyanincontent. For this reason, we have characterized and measured theconcentration of anthocyanins in pigmented potatoes, with the re-sults shown in Table 3. Our findings are consistent with results ofIeri et al. (2011) who by means of rapid HPLC/DAD/MS found forthe Vitelotte Noire variety dominant malvidin and petunidin. Inour research, the identity of the major pigments was confirmedby HPLC-DAD and HPLC–ESI–MS analyses as malvidin 3-O-p-cou-maroyl-rutinoside-5-O-glucoside and petunidin 3-O-p-couma-royl-rutinoside-5-O-glucoside (Table 3). Regarding the structureof these anthocyanidins, a high degree of hydroxylation and meth-oxylation of their aromatic rings suggests their higher contributionto antioxidant activity of this potato cultivar (Prior and Wu, 2006).

5. Conclusions

On the whole, our results show that anthocyanins extract of S.tuberosa Vitelotte is able to exert different biological activities. Itis characterized by a worthy radical scavenging and reducingcapacity and causes inhibition of proliferation and apoptosis in adose dependent manner in different solid and hematological can-cer cell lines. We have also demonstrated for the first time the effi-cacy of colored potatoes extract against a particularly resistantbacterium such as Staphylococcus aureus and its antifungal activity.The identification of components that account for the biologicalpotential of pigmented potatoes corroborates the knowledge ofanthocyanins action against cancer and as antimicrobial and anti-oxidant agents. The different biological properties of pigmentedpotatoes and the increased concern regarding their toxicologicalsafety indicate that they have a potential use for the nutraceuticalindustry and might represent promising sources of natural colo-rants with added value for the food industry and human health.

Conflict of Interest

The authors declare that there are no conflicts of interest.

Acknowledgements

This study was supported by: EU (‘Blueprint Contract No.282510), AIRC (Associazione Italiana per la Ricerca sul Cancro,Project No. 4625), by MIUR (PRIN_2009PX2T2E_004;PRIN_2007RZWFBZ_004; PON002782; PON0101227). Weacknowledge Dr. C. Fisher for kindly revising the manuscript.

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