Keywords: polychlorinated biphenyls; Aroclor 1254; ventral prostate; antioxidants; lipid peroxidation; thyroid hormone; vitamin C

Abstract

Aim: To evaluate the effect of polychlorinated biphenyls (PCB) and vitamin C on ventral prostatic antioxidant system in adult male rats. Methods: A group of 20 adult male rats were administered ip Aroclor 1254 in corn oil at a dose of 2 mg·kg^-1·day^-1 for 30 days. Ten control rats were administered only the vehicle. After 30 days the treated rats were divided at random into 2 sub-groups of 10 animals each. One sub-group received vitamin C at a dose of 500 mg·kg^-1·day^-1 for 10 days. The other group was maintained as Aroclor 1254 control. Twenty-four hours after the last treatment the rats were killed by decapitation. Ventral prostatic homogenate was prepared and used for the estimation of enzymatic antioxidants, including superoxide dismutase (SOD), catalase (CAT) and glutathione-S-transferase (GST) and hydrogen peroxide (H₂O₂), lipid peroxidation (LPO) and prostatic acid phosphatase. The serum levels of total T3, total T4, TSH, testosterone and estradiol were also assayed. Results: The body weight and ventral prostatic weight were reduced in PCB treated rats. The activities of SOD, CAT, GST and acid phosphatase were decreased while the levels of H₂O₂ and lipid peroxidation were increased in the ventral prostate of PCB treated rats. Administration of vitamin C restored these parameters. Serum levels of thyroid hormones, estradiol and testosterone were decreased in PCB treated animals. Administration of vitamin C restored the thyroid hormone levels. Conclusion: PCB induces oxidative stress and decreases the antioxidant enzymes in the ventral prostate of adult male rats; the effects could be reversed by the administration of vitamin C

1 Introduction

These properties of PCB may bring about environmental and human health problems. PCBs are distributed throughout the ecosystem, including soil, air and water[3]. PCBs pose health hazard as they get accumulated in food chain due to their lipophilic nature and, therefore, become persistent bio-accumulative toxicants [4].

Developmental exposure to PCB have been reported to cause reduced levels of thyroid hormones [5]. We have observed that administration of PCB causes thinning of the epithelial membrane of ventral prostate and decreased activity of prostate specific acid phosphatase (unpublished data). PCBs have been shown to impair male fertility [6]. Many environmental contaminants increase the levels of reactive oxygen species (ROS); they include superoxide anion, hydroxy radical, hydrogen peroxide, hypochlorite, etc. ROS affects the acrosome activity of human spermatozoa [7] and the testicular degeneration associated with infertility [8]. Antioxidants such as vitamin E [9] and vitamin C [10] have been shown to protect various tissues against the damage caused by ROS [11]. However, the effect of PCB on ventral prostate remains unclear and the production of free radicals and the function of antioxidant defense system require further studies. The present study was designed to clarify the adverse effects of PCB on the ventral prostate, whether the effects are caused by oxidative stress and whether vitamin C could reverse the effects.

2 Materials and methods

Aroclor1254 and chloramine T were purchased from the Sigma Chemical Co., St. Louis, USA and all other reagents from the Sisco Research Laboratories, Mumbai, India. All reagents were of the analytical grade. The total T3 and T4 kits were obtained from DiaSorin, Italy, the testosterone and estradiol kits from the Diagnostics Products Corporation, USA, radioactive iodine (¹²⁵I) from the Board of Radiation and Isotope Technology (BRIT), Mumbai, India, and antigen, antibodies and references for rat TSH from the NIDDK, Pituitary Distribution Program, Baltimore, USA.

Group 2 (Treated, n=20): Rats received intraperitoneal injection of Aroclor 1254 dissolved in corn oil at a dose of 2 mg/kg body weight for 30 days. The rats were then further divided into 2 subgroups of 10 animals each. Animals of Sub-group 1 were administered vitamin C at 500 mg·kg^-1·day^-1 for 10 days. The other were given the vehicle and maintained as Aroclor 1254 treated control.

Protein was estimated by the method of Lowry et al [12]. Estimation of superoxide dismutase (SOD) [13], catalase (CAT) [14], glutathione-S-transferase (GST) [15], acid phosphatase (ACP) [16], lipid peroxidation (LPO) [17] and hydrogen peroxide (H2O2) generation assay [18] were done. Serum total T3, T4, TSH, testosterone and estradiol were assayed by radioimmunoassay (RIA) [19].

2.5.1 Serum total tri-iodothyronine and thyroxine (T3 and T4)

Serum Total T3 and T4 were assayed by solid phase technology by making use of a commercial kit obtained from DiaSorin, Italy. The levels of T3 and T4 were expressed as ng/mL and g/dL, respectively. Sensitivity of the assays was 30 pg/mL for total T4 and 700 pg/mL for total T3. Inter-assay coefficients of variation were as follows: Total T4: 4.5 %-14.5 %; Total T3: 5.7 %-10 %; Intra-assay coefficients of variation were as follows: Total T4: 2.7 %-3.8 %; Total T3: 3.1 %-8.9 %.

TSH, NIDDK-rTSH was iodinated with carrier free 125I using chloramine-T [20] and used for RIA of serum TSH with specific rat antibody (NIDDK-anti rTSH-s-s) and reference preparation (NIDDK-rTSH RP2). Anti rabbit gamma globulin (ARGG) was used as the second antibody to precipitate the antibody bound TSH. Radioactivity was counted in the Pharmacia liquid scintillation system. The sensitivity of the TSH assay was 0.01ng/mL. The intra- and inter- assay coefficients of variation were 5 %-8.2 % and 4 %-6 %, respectively.

Serum estradiol and testosterone were assayed by solid phase radioimmunoassay, coat-A-count procedure, by using a commercial kit obtained from Diagnostic Products Corporation (DPC), USA. The amounts of estradiol and testosterone were expressed as pg/dL and ng/mL, respectively. The sensitivity of the estradiol assay was 0.08 pg/dL and the cross reactivity of the antiserum was 0.1 % with estrone, 0.32 % with estriol, 0.017 % with 17b-estradiol, 0.004 % with DHT and 0.001 % with testosterone. The coefficients of inter- and intra- assay variation were 6 %-8 % and 4 %-6 %, respectively. Sensitivity of the testosterone assay was 0.3 pg/mL and the cross reactivity of the antiserum was 14 % with 5a androstenediol, and 0.001 % with cortisol.

3 Results

PCBs are environmental contaminants classified by the World Health Organization as moderately hazardous[21]. There is much concern that exposure to PCB causes reproductive toxicity in man and wild life [6]. The dose selected in the present study (2 mg.kg-1.day-1) has been shown to cause dysfunction in rat reproductive system [22]. In the present study, the ventral prostate weight decreased significantly which might be due to decreased bioavailability and production of androgens; vitamin C restored the prostatic weight to the control level.

In the present study, PCB-treatment in rats induced a decrease in the specific activities of catalase, SOD and GST and an increase in H₂O₂ generation and lipid peroxidation in the ventral prostate, indicating an increase in oxidative stress, which was effectively reversed by the administration of vitamin C. A similar protective effect of vitamin C on the oxidative damage of goat sperm induced by the environmental contaminant, methoxychlor, has already been reported [23]. The PCB-induced decrease in thyroid hormones may be due to multiple mechanisms, such as induction of uridine diphosphate glucuronyl transferases (UDPGTs) and binding to thyroid transport protein transthyretin (TTR) [24]. Vitamin C also restored the PCB-induced decrease in thyroid hormones. Administration of vitamin C to methimazole-induced hypothyroid rats has been shown to increase serum levels of T3 and T4 by scavenging H₂O₂ in the thyroid gland [25]. PCB was shown to significantly reduce the concentration of 5-hydroxy tryptophan by inhibiting hypothalamic tryptophan hydroxylase (TPH) and GnRH content in pre-optic anterior hypothalamic area of rats [26]. This could be the reason for the decreased testosterone and estradiol levels in the PCB-treated rats. Administration of vitamin C does not restore the testosterone and estradiol levels. Acid phosphatase is an excellent marker for androgen-dependent function of prostate [16]. Thus its decrease in the PCB-treated rats may suggest androgen deprivation in the ventral prostate. In conclusion, PCB alters the ventral prostatic function by inducing oxidative stress, which could be reversed by vitamin C.

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Correspondence to: Dr J Arunakaran, Department of Endocrinology, Dr.ALM Post Graduate Institute of Basic Medical Sciences, University of Madras, Taramani, Chennai 600 113, India.
Email: j_arunakaran@hotmail.com
Received 2003-03-31 Accepted 2004-02-16