Effects of gamma-hexachlorocyclohexane and L-3,3 ',5-triiodothyronine on rat liver cytochrome P4502E1-dependent activity and content in relation to microsomal superoxide radical generation

Liver microsomal cytochrome P4502E1-dependent p-nitrophenol (PNP) hydroxylation and expression of cytochrome P4502E1 were studied in rats subjected to gamma-hexachlorocyclohexane (HCCH) or L-3,3,5-triiodothyronine (T-3) administration as a possible mechanism contributing to superoxide radical (O-2(.-)) generation. HCCH treatment (a single dose of 40 mg/kg body wt) produced a 43% increase in the content of total cytochrome P450, whereas T-3 (daily doses of 0.1 mg/kg body wt for two consecutive days) led to a 37% decrease. NADPH-dependent O-2(.-) generation was elevated by HCCH and T-3, expressed as either per mg of protein or per nmol of cytochrome P450, with a 135% enhancement in the O-2(.-) production/superoxide dismutase (SOD) activity ratios being observed in both conditions. This was partly due to depression of SOD activity. Concomitantly, the molecular activity of NADPH-cytochrome p450 reductase was enhanced by 90 and 69% by HCCH and T-3, respectively. In these conditions, microsomal PNP hydroxylation showed increases of 58 and 45% in HCCH- and T-3-treated rats over control values, respectively, with a parallel 31% (HCCH) and 41% (T-3) enhancement in the content of cytochrome P4502E1 assessed by western immunoblotting. We conclude that HCCH and T-3 enhance the expression and activity of cytochrome P4502E1 and that of NADPH-cytochrome P450 reductase in rat liver, regardless of the changes in total cytochrome P450 content, representing major contributory mechanisms to microsomal NADPH-dependent O-2(.-) generation.Univ Chile, Fac Med, Inst Ciencias Biomed, Programa Farmacol Mol & Clin, Santiago 70000 7, ChileUniv Sao Paulo, Inst Quim, Dept Bioquim, BR-01498 Sao Paulo, BrazilUNIFESP, Ctr Genet Med, Sao Paulo, BrazilUNIFESP, Dept Med, Disciplina Geriatria, Sao Paulo, BrazilUNIFESP, Ctr Genet Med, Sao Paulo, BrazilUNIFESP, Dept Med, Disciplina Geriatria, Sao Paulo, BrazilWeb of Scienc