Investigation of hepatic cytochrome P‐450 enzyme induction and DNA adduct formation in male CD/1 mice following oral administration of toxaphene

Exposure of experimental animals to toxaphene induces hepatic cytochrome P‐450 (CYP). Although chronic administration of toxaphene to mice was found to cause an increased incidence of liver tumors, a mechanism for its carcinogenicity has yet to be elucidated. We investigated two potential mechanisms of toxaphene‐induced carcinogenicity: peroxisomal proliferation and DNA binding. Peroxisomal proliferation was evaluated by measuring the level of immunodetectable CYP 4A1, an isozyme of CYP that is specifically induced by peroxisomal proliferators, in hepatic microsomes from CD1 mice that were treated by oral gavage for seven consecutive days with corn oil vehicle or 10, 25, 50 or 100 mg kg −1 toxaphene. In comparison to control mice, toxaphene‐treated mice had increased liver weight, increased liver/body weight ratios and increased levels of total hepatic CYP and cytochrome b 5 . No increase in the level of immunodetectable levels of CYP 4A1 was found in hepatic microsomes from toxaphene‐treated mice when compared to controls. In contrast, increases in immunodetectable CYP 4A1 were detected in hepatic microsomes from mice treated with the peroxisomal proliferator clofibrate. These findings suggest that toxaphene‐induced induction of CYP may not involve CYP 4A1 and that peroxisomal proliferation may not be involved in toxicity. Significant increases in immunodetectable levels of CYP 2B were, however, detected in toxaphene‐treated mice, and are consistent with earlier reports demonstrating that toxaphene, like many other pesticides, induces the phenobarbital‐inducible subfamily of CYP. Analysis of DNA adduct levels in the livers of toxaphene‐treated mice by DNA 32 P‐post‐labeling showed no evidence of DNA adduct formation. © 1998 John Wiley & Sons, Ltd.