PROTECTIVE EFFECTS OF MELATONIN ON BISPHENOL A-INDUCED REPRODUCTIVE TOXICITY IN MALE WISTAR RATS

Abstract

Bisphenol A (BPA), a known Endocrine Disrupting Chemical (EDC) used in the production of plastics has been demonstrated to induce marked reproductive toxicities in animals, while melatonin is a known antioxidant capable of ameliorating EDC-induced toxicity. Studies have demonstrated the protective effect of MLT on male reproductive functions following subacute exposure to BPA. However, little is known about the protective mechanisms. This study was designed to evaluate the mechanisms of MLT protection against reproductive toxicity in adult male Wistar rats exposed to BPA.

Forty adult male Wistar rats (180 ± 10 g) randomly assigned into 4 groups (n=10) were used for the study. Group I (control) received 0.2 ml olive oil orally, group II received MLT (10 mg/kg) intra-peritoneally, group III received BPA (10 mg/kg) orally, while group IV was co-treated with BPA (10 mg/kg) and MLT (10 mg/kg). All rats were treated daily for 45 days. On day 46, blood samples were collected for serum hormone assay [testosterone (T), dehydroepiandrosterone (DHEA), Follicle Stimulating Hormone (FSH), estradiol (E2)]. Testes and epididymides were thereafter harvested. Biochemical markers of oxidative stress (MDA, H2O2, Catalase, SOD, GSH, GPx) and semen characteristics (sperm motility, liveability sperm count) were studied from epididymal tissue. Light Microscopy (LM) and Transmission Electron Microscopy (TEM) were used to study morphological changes in testes and epididymides. Testicular and epididymal immunoreactivities to alpha smooth muscle actin (αSMA), vimentin (Vm) and S-100 proteins were also estimated using standard methods. Data were analyzed using descriptive statistics and ANOVA at α0.05.

Melatonin co-administered with BPA significantly increased the serum levels of T (13.84±1.59 nmol/L), DHEA (0.002±0.0002 µmol/L) compared to BPA-treated rats (6.59±1.23 nmol/L, 0.001±0.00 µmol/L, respectively), but significantly decreased FSH (0.11±0.02 µmol/L) and E2 (13.22±0.59 pmol/L) compared to BPA alone (0.15±0.02 µmol/L, 18.23±0.03 pmol/L, respectively). Similarly, BPA+MLT significantly increased the activities of catalase (6.51±1.07 µmol of H2O2 consumed/min/mg), SOD (5.25±0.09 Units/mg protein), GSH (41.49±9.73 µg/mg protein) and GPx (5.35±0.56 nmol of GSH residual/mg protein) compared to BPA alone (5.87±1.53 µmol of H2O2 consumed/min/mg, 4.76±0.31 Units/mg protein, 24.63±4.92 µg/mg protein, 5.19±0.21 nmol of GSH residual/mg protein, respectively). Melatonin co-administered with BPA significantly decreased the levels of H2O2 (163.58±24.71 to 110.43±7.74 nmole/mg protein) and MDA (23.97±0.62 to10.06±3.04 µmole MDA formed/mg protein) compared to BPA-treated rats. Also, Melatonin co-administered with BPA significant increased sperm motility (71.67±3.07%), livability (88.83±2.77 %) and sperm count (144.00±2.90 x 106 sperm/ml) compared to BPA alone (49.17±2.71 %, 48.33±3.07 %, 137.17±2.57 x 106 sperm/ml, respectively). Melatonin co-administered with BPA prevented necrosis and epithelial sloughing in the testes and epididymides and distortion in the 9+2 axoneme arrangement of the flagellar apparatus of spermatozoa observed in BPA-treated rats. BPA+MLT caused increased expression of αSMA, Vm and S-100 proteins in the testes and epididymides which were significantly reduced in the BPA-treated rats.

Melatonin protected against Bisphenol A-induced male reproductive toxicity. The probable mechanisms were prevention of oxidative stress and upregulation of alpha smooth muscle actin, vimentin and S-100 protein expressions in the testes and epididymides.