Inactivation of hepatic CYP2E1 by an epoxide of diallyl sulfone

Diallyl sulfone (DASO(2)) inhibits hepatic CYP2E1. In this investigation, w e have tested the hypothesis that an epoxide formed from DASO(2) is respons ible for inactivation of hepatic CYP2E1 in mice. An epoxide of DASO(2) (1,2 -epoxypropyl-3,3'-sulfonyl-1'-propene; DASO(3)) was synthesized and conjuga ted to glutathione (GSH) to produce the conjugates S-(1R,S-[[1-hydroxymethy l-2,3'-sulfonyl]-1'- propenyl]ethyl)glutathione (diastereomers) and S-(1-[[ 2R,S-hydroxypropyl]-3,3'-sulfonyl]-1'-propenyl)glutathione (diastereomers). Their identities were confirmed by H-1 NMR analysis, and these were used a s analytical standards. HPLC analysis revealed a major peak for the GSH con jugates that eluted at 20.5 min. This peak was detected in liver microsomal incubations performed with DASO(2) in the presence of NADPH. A similar pea k also was detected in incubations of CYP2E1-expressed lymphoblastoid micro somes, NADPH and DASO(2). The generation of the epoxide-derived GSH conjuga tes in the microsomal incubations was concentration-dependent, and reached saturation at 0.75 to 1.0 mM DASO(2). Formation of the conjugates was also time-dependent and peaked at 2.0 h after DASO(2). Levels of DASO(3) formed from DASO(2), as estimated by production of a 4-(p-nitrobenzyl)pyridine der ivative, were maximal at 1 mM DASO(2) at 30 min. CYP2E1-dependent p-nitroph enol hydroxylase activity was decreased in microsomes incubated with DASO(2 ), with alterations that were proportional to the concentration of DASO(2) (0.25-1.0 mM) used. Dose-dependent decreases in hydroxylase activity also w ere found in microsomes from mice treated in vivo with DASO(2) (25-200 mg/k g). These DASO(2)-induced decreases corresponded with reduced amounts of im munodetectable CYP2E1. Levels of spectrally detectable P450 and heme were b oth diminished by DASO(2). These results supported the contention that an e poxide formed from DASO(2) mediates the inactivation of hepatic CYP2E1.