The effect of tridiphane (2-(3,5-dichlorophenyl)-2-(2,2,2-trichloroethyl)oxirane) on hepatic epoxide-metabolizing enzymes: indications of peroxisome proliferation.

Administration of tridiphane (Tandem, DOWCO 356, 2-(3,5-dichlorophenyl)-2-(2,2,2-trichloroethyl)oxirane) to male Swiss-Webster mice for 3 days at 100, 250, and 500 mg/kg (ip) resulted in increases in liver weight accompanied by an increase in mitotic index and increases in large particle and microsomal protein. Epoxide hydrolase (EH) activity towards cis-stilbene oxide (CSO, microsomal EH) was elevated in microsomes and cytosol, a decrease in microsomal cholesterol EH was found, and hydrolysis of trans-stilbene oxide (TSO, cytosolic EH) was elevated in the cytosol but not in the microsomes. Glutathione S-transferase (GST) activity was elevated in cytosol for CSO, TSO, and 1,2-dichloro-4-nitrobenzene (DCNB), with inconsistent responses found with 1-chloro-2,4-dinitrobenzene (CDNB) and 1,2-epoxy-3-(p-nitrophenoxy)propane (ENPP). Microsomal GST was not consistently effected by tridiphane. Clofibrate (500 mg/kg, 3 daily ip injections) treatment resulted in similar responses in liver size, microsomal protein, and the EHs. The increase in cytosolic EH activity previously has been noted only in animals treated with peroxisome proliferators. Examination of livers from mice treated with 250 mg/kg tridiphane revealed that an increase in hepatic peroxisomes was apparent after 3 days of treatment. This was accompanied by decreases in serum cholesterol and triglyceride levels and increases in liver carnitine acetyl transferase and cyanide-insensitive oxidation of palmitoyl-CoA. This study demonstrates that tridiphane does have in vivo effects on mammalian epoxide-metabolizing enzymes and extends the association of increased cytosolic epoxide hydrolase activity with peroxisome proliferation.