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published online 24 June 2013Toxicol Ind HealthTarek Mostafa Mohammed, Afrah F. Salama, Tarek M. El Nimr and Doaa M. El Gamal

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Article

Effects of phytate on thyroid gland ofrats intoxicated with cadmium

Tarek Mostafa Mohamed1, Afrah F Salama1,Tarek M El Nimr2 and Doaa M El Gamal1

AbstractCadmium (Cd) is one of the most dangerous occupational and environmental toxins. The objective of the presentstudy is to examine the potential prophylactic effects of phytic acid (PA) on thyroid hormones of male ratsintoxicated with Cd. The male albino rats were divided into five groups: group I (control) was fed with the basaldiet, group II was intoxicated with Cd in drinking water, groups III, IV, and V were intoxicated with Cd in drinkingwater and fed with the diet containing 3.5, 7, and 10 g of PA/kg, respectively. The results indicated that the serumcalcium, iron (Fe), and total Fe binding capacity levels and serum T3 and T4 in Cd-treated rats of group II weredecreased when compared with the control group, while PA-administered groups with Cd showed a significantimprovement when compared with the Cd-treated rats only. Serum thyroid stimulating hormone (TSH) level wassignificantly increased in Cd-treated rats compared with the control group, while the addition of PA in dietdecreased the high levels of TSH. These results indicated a prophylactic effect of PA against Cd-induced toxicityin rats.

KeywordsCadmium, phytic acid, thyroid, T3, T4, TSH, toxicity

Introduction

Cadmium (Cd) is a well-known environmental pollu-

tant. Cd usage has increased dramatically during the

last 40–50 years because of the metal’s high resistance

to corrosion and valuable electrochemical properties.

Humans are exposed to Cd through tobacco smoke,

food, industrial, occupational, and environmental pol-

lution (Mitra et al., 2012). Since biological half life

of Cd in humans is found to be more than 20 years and

Cd has the ability to induce severe alterations in vari-

ous organs and tissues following either acute or chronic

exposure, it has been recognized as one of the most

toxic environmental heavy metal pollutants (Mitra

et al., 2012 and Urani et al., 2007).

Cd toxicity causes renal damage, coronary artery dis-

ease, hypertension, emphysema, and other chronic pul-

monary diseases (Ahn et al., 1999; Hu, 2000 and

Shagirtha and Pari, 2011). Cd interacts with the metabo-

lism of four metals: zinc (Zn), iron (Fe), calcium (Ca),

and copper (Bremner and Campbell, 1978; Hayter,

1980 and Petering, 1978). Also, Cd toxicity leads to an

increase in brain deiodinase activity, and decrease in

serum T4 levels, and it also leads to impaired brain

development (Bianco et al., 2002).

The function of the thyroid hormones is stimulation

of heart contractions, maintenance of body weight,

stimulation of protein synthesis and carbohydrate

metabolism, and increase the synthesis and degrada-

tion of cholesterol and triglycerides, that is, regulation

of basal metabolic rate (Czajk-Narins, 1986).

Phytic acid (inositol hexaphosphate; IP6) or phytate

(PA; when its salt is formed) is the principal storage

form of phosphorus in many plant tissues, especially

bran and seeds (Minihan and Rimbach, 2002). It is found

1 Biochemistry Division, Chemistry Department, Faculty ofScience, Tanta University, Tanta, Egypt2 Biophysics Division, Physics Department, Faculty of Science,Tanta University, Tanta, Egypt

Corresponding author:Tarek Mostafa Mohamed, Biochemistry Division, ChemistryDepartment, Faculty of Science, Tanta University, El-Bahr Street,Tanta, El-Gharbia Governorate 31527, Egypt.Email: tarek967@hotmail.com

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in large amounts in unrefined cereals and legumes that

are consumed as staple foods in many countries (Gibson

et al., 2010). IP6 is regarded as an antinutritive factor.

The antinutritional effect of IP6 is primarily related to

the strong chelation associated with its six reactive phos-

phate groups (Urbano et al., 2000).

Potential beneficial effects of IP6 are to prevent over

mineralization of joints, blood vessels, and other parts

of the body. It prevents colon cancer by reducing oxi-

dative stress in the lumen of the intestinal tract, while

its negative effect contributes to mineral deficiencies,

especially in people with low intake of essential miner-

als. IP6 and Fe form insoluble complexes, which are

not available for absorption under the pH conditions

of the small intestine. In vitro studies indicated that

IP6 acts as an antioxidant through its Fe-chelating prop-

erties (Gibson et al., 2010; Minihan and Rimbach,

2002).

High IP6 diets cause Zn deficiency (i.e. the PA con-

tent is negatively correlated to Zn absorption), while

IP6 does not inhibit copper absorption. It has a modest

inhibitory effect on manganese absorption (Brown

et al., 2009; Lonnerdal, 2002). IP6 decreases magnesium

absorption and Ca absorption (Rimbach and Pallauf,

1997). Cd accumulation was estimated in liver and kid-

ney and was increased by the addition of Ca. PA inhib-

ited the increase in tissue Cd promoted by supplements

but did not influence tissue Cd values (Rose and Quar-

terman, 1984). In case of high dietary Zn, IP6 has few

effects on tissue concentration of Cd (Brown et al.,

2010; Rimbach and Pallauf, 1997).

The aim of the present study was to investigate the

hazardous effects of Cd as a heavy metal and the pro-

phylactic effect of IP6 on the structure and function of

male rats’ thyroid gland intoxicated with Cd.

Materials and methods

Experimental animals

A total of 50 adult male Sprague Dawley rats, aged

about 3 months and weighing (180–220 g), purchased

from the breeding unit of Egyptian Organization for

Biological Products and Vaccines (Abbassia, Cairo,

Egypt) were used throughout the present work. The

animals were housed in steel mesh cages and main-

tained for 1 week acclimatization period on commercial

standard diet and drinking water ad libitum as shown in

Table 1 (NRC, 1995). The housing cycle was 12 h

light and 12 hdark cycle under controlled temperature

(20–22�C). The animals’ body weight was noted every

week throughout the entire period of experiment (Briet

et al., 2003; Madapallimattam et al., 2002).All the rats

were randomly divided into five groups with 10 rats in

each group. The groups were group I (control group),

animals were fed with normal diet free of sodium PA

and were allowed to Cd-free drinking water for 4 weeks;

group II, animals were intoxicated with 50 mg Cd/L as

cadmium chloride (81.69 mg) added to the drinking

water daily for 4 weeks; groups III, IV, and V, animals

were intoxicated with Cd as in group II and fed with the

diet containing 3.5, 7, and 10 g sodium PA/kg for 4

weeks, respectively.

Methods

At the end of the experiment (4 weeks), the rats were

killed under anesthesia with diethyl ether as approved

by the Ethical Committee of Tanta University. Blood

samples were collected from orbital venous plexus

and divided into two parts. The first part was collected

into a heparinized tube and mixed well to prevent any

clot formation, and the blood specimens were refri-

gerated (at 4�C) until assayed for blood Cd levels.

The second part was centrifuged at 3000 r/min for

10 min at room temperature; serum was separated and

kept at �20�C until assay. Serum was used for the

determination of biochemical parameters.

Determination of Cd concentration

Whole blood and liver and kidney tissues were

assayed according to the method of Razniewska and

Trzcinka-Ochocka (1995).

Determination of serum Ca, Fe, and Fe bindingcapacity concentrations

Serum Ca and Fe concentrations were assayed using

the commercial kits supplied by Human Co. (Wiesbaden,

Germany) (Callahan and Cook, 1982; Pollard and Marun,

1956). Total Fe binding capacity in serum was assayed

using the commercial kit supplied by ELI Tech Co. (ELI

Tech. Co., France) (Anderson and Cockayne, 1993).

Determination of serum T3, T4, and TSHhormone concentration

Serum triiodothyronine (T3) hormone concentration

and thyroxine (T4) hormone level in serum were assayed

using the commercial kit supplied by Coat-A-Count

(Los Angeles, California, USA) (Hollander et al.,

1972; Prince and Ramsden, 1977). Thyroid stimulating

hormone (TSH) concentration in serum was assayed

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using the commercial kit supplied by Coat-A-Count

TSH IRMA from the Institute of Isotopes Ltd, Budapest

(Beijing Atom High-Tech Co. Ltd, China).

Histopathological investigation

The thyroid gland from the rats was taken and fixed in

10% buffered formalin, embedded in pure paraffin

wax (melting point of 58�C), and then mounted into

blocks and left at 4�C until the time of use. The par-

affin blocks were sectioned using the microtome at

a thickness of 5 mm and mounted on clean glass slides

and then left in the oven at 40�C for drying. The slides

were deparaffinized in xylol and then immersed in the

descending series of alcohol (90%–50%). The ordi-

nary hematoxylin and eosin stain were used for stain-

ing (Drury and Wallington, 1980).

Statistical analysis

Data are presented as mean + SD. One-way analysis

of variance followed by Tukey’s multiple comparison

method was carried out to compare the mean value of

different groups using SPSS 7.5 student version 3.

Comparisons were made between groups I and II–V

and between groups II and III–V. A p < 0.05 was con-

sidered statistically significant.

Table 1. The body weight of male rats in different groups at the start and at the end of work and the percentage of bodyweight changes.

Parametersgroups

Body weight (g)Percentage of body

weight changesaAt start At the end

Group In 10 10 15.15% "Range 180–220 200–260Mean + SD 198 + 14.30 228 + 21.19

Group IICd intoxicated

n 10 10 �17.8% #Range 170–230 150–200Mean + SD 196 + 19.55 161 + 17.29p Value 0.0001

Group IIICd intoxicated þ 3.5 g sodium PA

n 10 10 4.5% "Range 190–247 200–260Mean + SD 214.70 + 23.78 230 + 19.44p Value NSp* Value <0.0001

Group IVCd intoxicated þ 7 g sodium PA

n 10 10 15.9% "Range 180–220 200–250Mean + SD 194 + 12.65 225 + 15.09p Value NSp* Value <0.0001

Group VCd intoxicated þ 10 g sodium PA

n 10 10 5.9% "Range 180–230 220–250Mean + SD 201 + 15.95 235 + 10p Value NSp* Value <0.0001

Cd: cadmium; PA: phytate; NS: not significant.aChange in weight between the start and end of experiment. The significance of difference was analyzed using one-way analysis of var-iance. p value: value versus control (Group I). p* value: value versus Cd group (II).

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Results

The body weight of rats intoxicated with Cd only

(group II) showed a significant decrease as compared

to the normal rats (group I). On the other hand, there

were insignificant changes in the body weights of rats

in groups III, IV, and V as compared to the control

group; however, the body weight in rats intoxicated

with Cd and fed with different concentrations of

sodium PA was significantly elevated as compared

to Cd-intoxicated rats (group II; Table 1).

The blood Cd level of control male rats fed with

basal diet free of sodium PA (group I) was lower than

the detected limit, while the blood Cd level in rats

administrated with only Cd was 8.8 mg/L. The blood

Cd level in rats administrated with Cd and fed with the

diet containing 3.5, 7, and 10 g sodium PA/kg was sig-

nificantly decreased when compared with the Cd-

intoxicated rats. The Cd concentration in kidney was

higher than that in liver in all the five groups. There

were insignificant changes in the concentration of Cd

in the liver of rats administrated with Cd and fed with

the diet containing 3.5, 7, and 10 g sodium PA/kg com-

pared with the rats administrated with only Cd. How-

ever, the Cd concentration in kidney was not changed

from that of the rats administrated with Cd and fed with

the different concentrations of PA (Table 2).

Serum Ca levels in Cd-intoxicated rats were signif-

icantly decreased when compared with the control

rats, while serum Ca levels in rats administrated with

Cd and fed with the diet containing 3.5, 7, and 10 g

sodium PA/kg showed a significant increase when

compared with the Cd group (Table 2).

There was a significant decrease in serum Fe and total

Fe binding capacity levels in rats intoxicated with Cd

compared with the control group. In rats administrated

with Cd and fed with different concentrations of PA, the

serum Fe and total Fe binding capacity levels were

slightly increased but still insignificantly decreased

when compared with the control group (Table 3).

Serum T3 and T4 levels were reduced significantly

in male rats intoxicated with Cd compared with the

Table 2. Blood Cd concentration (in microgram per liter), Cd distribution in liver and kidney tissues (in microgramper gram) and serum Ca concentration (in milligram per deciliter) in the different groups.a

Parameters Groups Serum Cd (mg/L)

Cd Tissues

Serum Ca(mg/dL)Liver (mg/g)

Kidney(mg/g)

Group I (Control)Range – 0.09–0.2 0.2–0.3 10.48 – 12.27Means + SD 0.15 + 0.06 0.29 + 0.08 11.5 + 0.53

Group II (Cd intoxicated)Range 5-12 0.2-0.35 0.35-0.45 8.9–10.6Mean + SD 8.8 + 2 0.25 + 0.07 0.39 + 0.05 9.6 + 0.59p value – <0.01 <0.01 <0.001

Group III (Cd intoxicated þ 3.5 g sodium PA)Range 4.9–6.6 0.08–0.3 0.28–0.46 8.84–11.1Mean + SD 5.6 + 0.6 0.29 + 0.15 0.42 + 0.09 10.15 + 0.6p value – <0.05 <0.01 <0. 001p* value <0.05 NS NS <0.05

Group IV (Cd intoxicated þ 7 g sodium PA)Range 2.5–5.2 0.06–0.26 0.22–0.46 9.2–11.8Mean + SD 3.9 + 1 0.22 + 0.1 0.41 + 0.12 10.34 + 0.7p value – N.S. < 0.05 < 0. 001p* value <0.001 NS NS <0.02

Group V (Cd intoxicated þ 10 g sodium PA)Range 3.7–6 0.03–0.3 0.21–0.5 8.8–10.8Mean + SD 5.1 + 0. 7 0.24 + 0.16 0.39 + 0.15 9.5 + 7p value – NS <0.01 <0. 001p* value <0.001 NS NS NS

Cd: cadmium; PA: phytate; NS: not significant.aThe significance of difference was analyzed using one-way analysis of variance. p value: value versus control (group I). p*value: valueversus Cd group (II).

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control group, whereas the serum TSH level showed a

significant increase compared with the control rats. In

rats administrated with Cd and fed with the diet con-

taining 3.5, 7, and 10 g sodium PA/kg, the serum T3

and T4 levels were elevated nearer to the levels in the

control group and serum TSH level was reduced com-

pared to rats administrated with only Cd (Table 4).

In Cd-intoxicated rats and rats intoxicated with Cd

and fed with the diet containing 3.5, 7, and 10 g sodium

PA/kg, a significant negative correlation was detected

between serum T3 and blood Cd level. Also, serum

T4 had a significant negative correlation with blood

Cd level. In rats administrated with Cd and rats intoxi-

cated with Cd and fed with the diet containing 3.5, 7,

and 10 g sodium PA/kg, a significant positive correla-

tion was observed between serum TSH and blood Cd

level; also, the ratio of T3 and T4 had a significant pos-

itive correlation with blood Cd level (Table 5). In rats

intoxicated with Cd and rats intoxicated with Cd and

fed with the diet containing 3.5, 7, and 10 g sodium

PA/kg, insignificant correlation was observed between

T3/T4 ratio and serum T3 level. On the other hand, there

was a significant negative correlation between T3/T4

ratio and serum T4 level. However, there was an insig-

nificant correlation between T3/T4 ratio and TSH level

(Table 5).

Histological results in rats administrated with Cd

showed damage in the structure of the follicular cells

of thyroid gland and sheets of mature lymphocytes

with acute inflammatory cellular infiltration in the

form of neutrophils (Figure 1(b)). Thyroid gland of

rats intoxicated with Cd and fed with the diet contain-

ing 3.5, 7, and 10 g sodium PA/kg (Figure 2(a) to (c),

respectively) showed dilated oval thyroid follicles

filled with colloid and lined by a single layer of flat

to cuboidal cells having bland small nuclei as an indi-

cation of the prophylactic effect of IP6 on the thyroid

gland of rats intoxicated with Cd.

Discussion

The accumulation and toxicity of Cd in human and

animals depend on various factors such as the daily

intake, the form of Cd in food and food stuffs, and its

multiple interactions with the dietary components

(Mitra et al., 2012 and Rambeck, 1994).

Table 3. Serum Fe concentration (in microgram per deciliter), total Fe-binding capacity (in microgram per deciliter) andblood hemoglobin concentration (in gram per deciliter) in different groups.a

Parameters Groups Fe (mg/dL)Total Fe-bindingcapacity (mg/dL) Hemoglobin (g/dL)

Group I (Control)Range 135.3–183.9 311–613 12.9–16.8Means + SD 152.7 + 16.6 487.3 + 90 14.7 + 1.1

Group II (Cd intoxicated)Range 97–140 264–474 7.5–9.9Mean + SD 114.3 + 14. 404.9 + 76.5 8.06 + 0.6p Value <0.001 <0.05 <0.001

Group III (Cd in toxicated þ 3.5 g sodium PA)Range 102–183 235.8–613.2 7.9–12.3Mean + SD 122.2 + 24.4 413.4 + 117 10.08 + 1.3p Value <0.01 NS <0.001p* Value NS NS <0.001

Group IV (Cd intoxicated þ 7 g sodium PA)Range 120–183 349–577.3 9.7–14.8Mean + SD 130 + 24.4 443.1 + 80 12.1 + 1.6p Value 0.004 NS <0.001p* Value NS NS < 0.001

Group V (Cd intoxicated þ 10 g sodium PA)Range 83–135 301.9–560.4 9–14.4Mean + SD 106.1 + 17.4 439.7 + 98 11.69 + 1.7p Value <0.001 NS <0.001p* Value NS NS <0.001

Cd: cadmium; PA: phytate; NS: not significant; Fe: iron.aThe significance of difference was analyzed using one-way analysis of variance. p: value versus control rats (group I). p*: value versus ratsfed with Cd (group II).

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IP6 is a natural plant compound with a unique struc-

ture that is responsible for its characteristic properties

(Gibson et al., 2010 and Tsao et al., 1997). In the pres-

ent study, it was shown that the body weight of male

rats fed with normal diet free of sodium PA increased

by 15.15% at the end of the experiment. Chronic

administration of Cd led to marked decrease in the

body weight of rats fed with diet free of sodium PA.

The decrease in body weight gain of rats exposed

to Cd could be the result of lowered food and water

intakes, since addition of Cd into drinking water

resulted in a significant decrease in its consumption

especially Cd has a bad taste (Brus et al., 1999; Gupta

and Gill, 2000 and Strbak et al., 1998). The lowered

body weight in the Cd-treated rats may indicate malnu-

trition due to Cd toxicity (Katsumi et al., 1984). On the

other hand, this study showed that the body weight of

rats administrated with Cd and fed with the diet con-

taining 3.5, 7, and 10 g sodium PA/kg was increased

The sodium PA may decrease the Cd absorption in rats

hence decreases the Cd effect on the body weight.

The different concentrations of sodium PA in Cd-

intoxicated groups reflected by the concentration of

Cd in the blood, liver, and kidney. The concentration

Table 4. Serum T3; (in nanogram per deciliter), T4(in microgram per deciliter), and TSH (in micro international units permilliliter) in different male rat groups.a

Parameters Groups T3 (ng/ dL) T4 (mg/ dL) T3/T4 ratio X 10�3 TSH (mIU/mL)

Group I (Control)Range 112–128 5.5–8.6 1.3620.36 0.06–0.11Means + SD 120.1 + 5.4 7.08 + 1.03 17.146 + 2.40 0.08 + 0.01

Group II (Cd intoxicated)Range 67.2–108 2.6–5.2 17.73–37.4 0.11–0.29Mean + SD 88.6 + 11.9 3.8 + 0.9 23.862 + 6.12 0.17 + 0.06p Value <0.001 <0. 001 <0.01 <0.001

Group III (Cd intoxicated þ 3.5 g sodium PA)Range 83–120 3.9–5.7 17.11–26.66 0.07–0.32Mean + SD 97.5 + 11.9 4.56 + 0.6 21.621 + 2.99 0.16 + 0.08p Value <0.001 <0.001 <0.01 <0.01p* Value NS NS NS NS

Group IV (Cd intoxicated þ 7 g sodium PA)Range 99–127 5–8 13.12–21.89 0.07–0.15Mean + SD 111.5 + 11.4 6.51 + 0.8 17.35 + 2.501 0.089 + 0.02p Value <0.05 NS NS NSp* Value <0.001 <0.001 <0.01 <0.001

Group V (Cd intoxicated þ 10 g sodium PA)Range 96–125 5–7.2 13.75–24.4 0.09–0.12Mean + SD 110.5 + 10.6 6.14 + 0.6 18.241 + 3.138 0.097 + 0.009p Value <0.05 NS NS <0.02p* Value <0.001 <0.001 <0.02 <0.01

Cd: cadmium; PA: phytate; NS: not significant; T3: triiodothyronin; T4: thyroxine; TSH: thyroid stimulating hormone.aThe significance of difference was analyzed by one-way analysis of variance. p: value versus control rats (group I). p*: value versus ratsfed with Cd (group II).

Table 5. Correlation between of thyroid hormones (T3 and T4) and TSH with Cd in Cd-intoxicated rats with and withoutsodium PA.a

Parameter

T3 T4 TSH T3/T4 ratio

r p r p r p r p

Cd �0.342 <0.05 0.537 <0.001 0.508 <0.01 0.522 <0.01T3/T4 ratio �0.131 NS �0.810 <0.001 0.208 NS – –

Cd: cadmium; PA: phytate; NS: not significant; T3: triiodothyronin; T4: thyroxine; TSH: thyroid stimulating hormone.ap Value less than <0.05 is significant.

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of blood Cd in rats administrated with only Cd (group

II) was elevated as compared with the rats admini-

strated with Cd and fed with different concentrations

of sodium PA. Insignificant decrease was observed in

liver and kidney Cd concentration of rats admini-

strated with Cd and fed with different concentrations

of PA. In agreement with our result, Rimbach et al.

(1996) showed that kidney Cd concentration was

moderately increased in the PA groups. Cd represents

a dangerous environmental and industrial pollutant. It

is generally known that Cd is mainly accumulated in

the kidneys and liver of animals and humans (Toman

et al., 2005). Also, the present study showed higher

concentrations of Cd in the kidneys than in the liver.

The difference in the concentrations of Cd in these tis-

sues is explained according to the fact that Cd mostly

makes complexes with metallothionein, a protein that

binds to heavy metals for reducing their toxicity,

which separates in kidneys and accumulates in kidney

cortex. Therefore, renal damage is believed to be the

result of free Cd, which does not bind to metallothio-

nein due to localization or an excessive concentration

of Cd. The binding capacity of kidney metallothionein

is lower than that of liver metallothionein (Goyer, 1989

and Klassen, 1978). According to the results of these

authors, this tissue specific difference in binding capac-

ity may account for the sensitivity of the kidney to Cd,

and this is in agreement with the present study that

showed elevation in both liver and kidney and

increased in the kidney tissues, which in turn showed

that PA cannot chelate Cd from the liver and kidney tis-

sues. This is in agreement with the previous results of

Jarup et al. (1998) who reported that the elimination

half life of Cd is 10–30 years in the kidney and approx-

imately 5–10 years in the liver. This may be the reason

that PA ameliorates the toxic effects of Cd by a

mechanism other than metal chelation. Also, the pres-

ent results are in agreement with our previous work,

which showed that curcumin attenuated hepatorenal

toxicity induced by Cd in male rats (Afrah, 2010).

Cd-exposed rats fed with a low Ca diet exhibited a

higher liver and kidney Cd retention than Cd-exposed

rats fed with an adequate amount of Ca (Washko and

Cousins, 1977). It has been shown that the binding affi-

nity of the Ca-binding protein (CaBP) for Cd is almost

as strong as that for Ca (Bredderman and Wasser-

mann, 1974). Thus, a possible explanation could be

expected for the moderately enhanced kidney Cd reten-

tion when PA-containing diets were fed with the

slightly reduced Ca bioavailability owing to PA might

be an increase in the CaBP activity. This could be

accompanied by an increase in the mucosal Cd uptake

(Rimbach, et al., 1996).

In the previous experiment with rats (Rimbach et al.,

1995, 1996), little has been reported concerning the

influence of IP6 on Cd retention. In another study on

Japanese quails and chickens (Guillot et al., 1994,

Rambeck, 1994 and Rambeck and Walther, 1993), it

was demonstrated that IP6 enhanced Cd concentration

in the liver and kidneys. In the present study, serum Ca

concentration in rats administrated with Cd and rats

administrated with Cd and fed with different concen-

tration of sodium PA were decreased as compared to

the control rats.

Serum Fe concentration and total Fe binding capac-

ity level in rats intoxicated with Cd or rats admini-

strated with Cd and different concentrations of

sodium PA showed a significant decrease as compared

to the control rats. Small intestinal mucosal cells are

Figure 1. Control of thyroid gland in rats fed with basaldiet free of (a) sodium PA and (b) Cd-intoxicated rats(H&E, 100�). Cd: cadmium; PA: phytate; H&E: hematoxylinand eosin.

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the major sites of Fe absorption, and serum transferrin

is the major Fe carrier protein (Gibson et al., 2010;

Macgillivray et al., 1983). Fe-transferring complex

binds to the transferrin receptor at the plasma mem-

brane and gets internalized to the cells, where it is used

for heme synthesis. Cd may compete with Fe for the

same binding sites on the transferrin molecules. Ceru-

loplasmin, a copper-containing protein, plays an

important role in oxidation of Fe (II) to Fe (III) in the

cells. Cd may interfere with one of the steps of Fe

metabolism and cause anemia (Wada et al., 1979).

Exposure to Cd caused disorder in Fe metabolism

reflected changes in its bioavalability and concentra-

tion in serum and tissues as well as in its urinary excre-

tion. These observations suggest an antinutritive effect

of Cd on this bioelement (Brown et al., 2009; Moshta-

ghie et al., 1994). On the other hand, renal failure that

develops under the influence of Cd results in

erythropoietin deficiency, which may cause normo-

chromic and normocytic anemia without a proportional

increase in the reticulocytes (Hiratsuka et al., 1996;

Mackova et al., 1996 and Shagirtha and Pari, 2011).

Serum levels of T3 and T4 showed a significant

decrease and serum level of TSH and T3/T4 ratio

showed a significant increase in rats administrated with

Cd compared with the control rats. In rats admini-

strated with Cd and fed with the diet containing 3.5 g

sodium PA/kg, the serum levels of T3, T4, TSH, and

T3/T4 ratio showed significant changes compared with

the Cd group (group II), while in rats administrated

with Cd and fed with the diet containing 7 and 10 g

sodium PA/kg, serum T3 level is increased compared

with the control rats. Similarly, serum T4 and TSH lev-

els and T3/T4 ratio showed insignificant changes com-

pared with the control rats. In agreement with our

results, it was reported that serum T3 and T4 levels

Figure 2. The thyroid gland of rats intoxicated with Cd and fed with the diet containing (a) 3.5 g, (b) 7 g, and (c) 10 gsodium PA/kg(H&E, 100�). Cd: cadmium; PA: phytate; H&E: hematoxylin and eosin.

8 Toxicology and Industrial Health

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were lowered in rats administrated with Cd (Gupta and

Kar, 1999; Nishijo et al., 1994, Pavia et al., 1997), and

the study by Curcic et al. (2011) showed lower dose of

Cd affects thyroid toxicity.

In rats administrated with Cd and rats intoxicated

with Cd and fed with the different concentrations of

PA in diet, a significant negative correlation was

detected between serum T3, serum T4, and blood Cd

concentration. A significant positive correlation was

observed between serum TSH level, T3/T4 ratio, and

blood Cd level. Increasing serum TSH level that is

observed when exposed to Cd is a response to

decreased serum T4 and T3 levels. The lack of signifi-

cant response of TSH to decreased serum T4 and T3

levels may suggest Cd interference with pituitary reg-

ulation of thyroid hormones production and secretion

(Pavia et al., 1997). Yoshizuka et al. (1991) have

speculated that the metal accumulated in the mitochon-

dria of thyroid follicular epithelial cells can inhibit the

synthesis and release of thyroid hormones influencing

the oxidative phosphorylation of these organelles.

Cd causes both structural and functional damage of

the thyroid follicular cells. Declined concentration of

serum T3 in Cd-administrated rats might be due to the

decrease in transformation rate from T4 to T3 according

to inhibition of type 1 iodothyronine 50-monodeiodi-

nase (50-D) activity, being a selenoenzyme containing

a selenocysteine residue as its active site (Chaurasia

et al., 1996; Shyam et al., 1997). Also, the probability

of Cd interference in the synthesis and/or secretion of

T4 by the thyroid follicular cells are supported by the

results of histpathological examinations. These

revealed a damaging effect of Cd on the structure of

follicular cells of the thyroid gland (Yousif and Ahmed,

2009).

In conclusion, sodium PA could reduce the hazar-

dous effects of Cd on thyroid gland. The best concen-

tration of sodium PA is 7 g/kg diet that can allow the

absorption of important inorganic metal and

decreased the hazardous effects of Cd.

Acknowledgment

Authors show their profound gratitude to Prof. Ehab M

Toson, Department of Zoology, Faculty of Science, Tanta

University, Egypt, for his assessment in the histopathologi-

cal studies of thyroid gland.

Funding

This research received no specific grant from any funding

agency in the public, commercial, or not-for-profit sectors.

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