Effects of tributyltin in vivo on hepatic cytochrome P450 forms in marine fish

Abstract

The interaction of tributyltin chloride (TBT) in vivo with different forms of hepatic microsomal cytochrome P450 and ethoxyresorfin O-deethylase (EROD) activity was studied in scup ( Stenotomus chrysops). Fish were injected with single doses of 3.3, 8.1 and 16.3 mg/kg TBT. Hepatic microsomes were analyzed 24 h later for total cytochrome P450 content, and three P450 forms by immunoblotting: scup P450E, the major polyaromatic hydrocarbon-inducible form (CYPlAl), scup P450A, the major contributor to microsomal testosterone 6β-hydroxylase activity, and scup P450B, which oxidizes testosterone at several different sites including the 15α position. Spectrally determined conversion of P450 to its degraded form cytochrome P420 occurred at all TBT doses, the conversion being considerable only at the highest dose with more P420 (65%) than P450 (35%). EROD activity tended to be decreased by TBT in all doses. with a significant reduction at 16.3 mg/kg. Microsomal protein degradation as revealed by SDS-polyacrylamide gel electrophoresis occurred at the highest dose. Immunoblot analysis with a monoclonal antibody to P450E (CYPlAl) showed a decrease of CYPlA protein content at all TBT doses, with a significant loss at 16.3 mg/kg, similar to the EROD activity pattern. Immunoblot analysis with polyclonal antibodies to P450A and P450B showed decreases in P450A and P450B protein content only at the highest dose, the decrease being significant for P450A only. Cytochrome b 5 content was unaffected. In the liver, metabolites of TBT, dibutyltin and monobutyltin, were identified at all doses, with a decreased content, however, in fish given the highest dose. This study indicates important biochemical effects of TBT in fish liver, and suggests that exposure to TBT may alter both cytochrome P450 dependent metabolism, and induction response to other environmental pollutants.