Dawa Bhutia and Joydeb Pal
Abstract
Ethion, an organophosphate pesticide, is highly lipophilic and very toxic to aquatic organisms. Biotransformation, primarily catalyzed by cytochrome P450 (CYP 450), radically alters the chemistry of nonpolar, lipophilic chemicals, converting them into polar, water-soluble metabolites that predominantly facilitate the detoxification and elimination of the parent compounds. The present study investigated the impact of ethion exposure on liver CYP 450 in the fish Channa punctatus and Heteropneustes fossilis. C. punctatus and H. fossilis were treated with sub-lethal concentrations of ethion (14.5 and 18.1 ?g/l) for 5, 10 and 15 days, and their effect on total CYP 450 and the activity of hepatic CYP 450 isoforms was measured. Activities of the enzymes ethoxyresorufin-O-deethylase, N,N-dimethylaniline demethylase, aniline hydroxylase, and erythromycin demethylase, mediated, respectively, by the isoforms CYP1A, CYP2B, CYP2E1, and CYP3A4, were studied. Total CYP 450 content and the liver somatic index were also calculated to assess the physiological status of the fish. Activities of CYP1A and CYP3A4 enzymes increased significantly in both fish species in all experimental groups. CYP2B and CYP2E1 activity were significantly increased in H. fossilis. In contrast, CYP2B activity in C. punctatus was comparable to that of the control, and CYP2E1 activity was significantly elevated only in the 10-day treatment group. There was an increasing trend in activities over the pesticide exposure period. The study indicated that elevated activity of CYP 450 isoforms could serve as a biomarker of pesticide pollution in aquatic environments.