Oxidative stress, steroid hormone concentrations and acetylcholinesterase activity in Oreochromis niloticus exposed to chlorpyrifos

We investigated the endocrine disrupting effects of chlorpyrifos-ethyl which is suspected to be originated from oxidative stress Initially, the 96 h LC50 Values of chlorpyrifos in juvenile and adult of Oreochromis niloticus were determined to be 98.67 mu g/L and 154.01 mu g/L, respectively sub-lethal concentrations of chlorpyrifos-ethyl (5 ppb, 10 ppb, 15 ppb) were administrated to adult fish for 15 and 30 days Fish were then left to depurate for 15 days in pesticide-free water Gonadal somatic indices, serum sex steroids as indicators of reproductive function and cortisol level as indicator of stress condition were measured to observe the endocrine disruption effects of chlorpyrifos-ethyl Gonadal glutathione S-transferase and antioxidant enzyme activities and lipid peroxidation as indicators of oxidative stress were also measured Acetylcholinesterase activity was measured as a marker of chlorpyrifos toxicity Results showed that serum estradiol, testosteron and cortisol levels in fish exposed to chlorpyrifos were lower than those of the control fish while gonad somatic indices did not change during the experiments. After 30 clays, chlorpyrifos exposure decreased GST activity, and increased SOD enzyme activity by up to 215-446% compared with the control, suggesting there was a oxidative stress No statistically significant differences between GPx and CAT specific activities, protein contents and lipid peroxidation were determined between control and treatment groups in all exposure concentrations and periods Acetylcholinesterase activity decreased (45.83-77.28%) in gonad tissues After recovery serum estradiol and testosteron levels were similar to those of the control levels An increase in the GST and SOD enzyme activities were determined Cortisol level and AChE activity in all exposure groups decreased after the depuration period, and fish were unable to overcome the stress of chlorpyrifos. Thus, this study revealed that after chlorpyrifos treatments there exists a protective function of antioxidant enzymes against lipid peroxidation in gonad tissue of O niloticus There also exist lower testosteron and estradiol levels in exposed fish than those of the control fish without any alterations in oxidative stress, which is attributed to the capability of chlorpyrifos to impair steroid hormone levels (C) 2009 Elsevier Inc All rights reserved.