Initial metabolism of gamma-hexachlorocyclohexane (gamma-HCH) by rat liver microsomes

gamma-Hexachlorocyclohexane (gamma-HCH) was metabolized by dehydrochlorination, dehydrogenation and dechlorination in rat liver microsomes and these initial metabolites of gamma-HCH were identified as gamma-pentachlorocyclohexene (gamma-PCCH), gamma-hexachlorocyclohexene (gamma-HCCH) and gamma-tetrachlorocyclohexene (gamma-TCCH) by gas chromatography-mass spectrometry (GC/MS). The dehydrochlorination and dehydrogenation were performed in incubation media containing NADPH and p,p'-tetramethyldiaminodiphenyl methane (TPD, 30 nmol) which is known to inhibit the degradation of initial metabolites formed during an aerobic incubation of gamma-HCH with microsomes at 25 degrees C. The dechlorination was found to proceed well under anaerobic conditions. The dehydrogenation was inhibited by SKF 525-A, CO, piperonyl butoxide, N2 and the absence of NADPH, but not by cyanide. Additionally, pretreatment of rats with phenobarbital (PB), but not with 3-methylcholanthrene (3-MC), induced the dehydrogenation of gamma-HCH. These results suggest that cytochrome P-450 is involved in this reaction. The cytochrome b5 system may not be involved. The dehydrochlorination was inhibited by N2, CO, piperonyl butoxide, KCN and the absence of NADPH, but not by SKF 525-A. This reaction was enhanced by pretreatment of rats with SKF 525-A, CoCl2 and piperonyl butoxide. Pretreatment with PB and 3-MC did not show a significant effect on the dehydrochlorination activity. Thus, the results suggest that the dehydrochlorination could be catalyzed by a specific species of cytochrome P-450 and cytochrome b5 system and/or other microsomal enzyme systems.