Effects of Chromium (Cr) VI on Follicular Atresia Mediated Through Oxidative Stress and Molecular Intervention of Vitamin C Against CrVI Toxicity.

Abstract

Hexavalent chromium (Cr) VI is a carcinogen, teratogen and mutagen. CrVI is used in more than 50 industries, and is a major threat to human health both in the developing and developed countries. Environmental and occupational exposure to CrVI causes various health hazards including infertility, still birth and developmental problems in children (The Blacksmith Institutes Reports, 2010). According to a recent report from the Environmental Working Group (2010), more than 74 million people from 70 communities in the US drink water contaminated with a significant amount of CrVI. Our previous studies have shown that lactational exposure to CrVI delayed follicle development and maturation and decreased steroidogenesis in F1 offspring. Our current studies focus on the molecular mechanisms underlying CrVI-induced ovotoxicity. In vivo studies: Lactating mother rats were ingested with varying doses of CrVI (50 ppm, 100 ppm, and 200 ppm potassium dichromate) in the drinking water with or without supplemented with vitamin C (500 mg/L water) from postpartum day 1-21. During this period (postnatal day 1-21) the F1 pups received CrVI through the mother's milk. From PND 22 onwards the pups were given regular water and diet and were sacrificed on PND 25, 45 and 65. CrVI increased follicular atresia in a dose-dependent manner, and vitamin C mitigated the toxic effects of CrVI. Oxidative stress markers such as lipid peroxide (LPO), hydrogen peroxide (H2O2), and antioxidant enzymes GPx, SOD and catalases were estimated in the plasma and whole ovarian extracts. Serum levels of hormones were measured. CrVI increased LPO, H2O2; decreased GPx, SOD and catalase, and decreased E2, P4 and T with an increase in FSH. In vitro studies: Granulosa and theca cells were isolated from normal PND 23-25 rats and treated with CrVI with or without pretreatment with vitamin C. Quantitative real-time RT-PCR was used to measure mRNA levels of the antioxidant genes SOD1, SOD2, Catalase, GPx1, GLRX1, GSTM1, GSTM2, GSTM4, GSHR, TXN1, TXN2, TXNRD2 and PRDX3. CrVI decreased all the above enzymes which was mitigated or inhibited by vitamin C. CrVI also increased LPO and H2O2 in GC and TC. Taken together, CrVI-induced oxidative stress was mitigated by vitamin C in theca cells while it was inhibited in granulosa cells.