Inactivation of hepatic CYP2E1 by an epoxide of diallyl sulfone.

Diallyl sulfone (DASO(2)) inhibits hepatic CYP2E1. In this investigation, we have tested the hypothesis that an epoxide formed from DASO(2) is responsible 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 conjugated to glutathione (GSH) to produce the conjugates S-(1R,S-[[ 1-hydroxymethyl-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 (1)H NMR analysis, and these were used as analytical standards. HPLC analysis revealed a major peak for the GSH conjugates 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 peak also was detected in incubations of CYP2E1-expressed lymphoblastoid microsomes, NADPH and DASO(2). The generation of the epoxide-derived GSH conjugates 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 derivative, were maximal at 1 mM DASO(2) at 30 min. CYP2E1-dependent p-nitrophenol 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 were found in microsomes from mice treated in vivo with DASO(2) (25-200 mg/kg). These DASO(2)-induced decreases corresponded with reduced amounts of immunodetectable CYP2E1. Levels of spectrally detectable P450 and heme were both diminished by DASO(2). These results supported the contention that an epoxide formed from DASO(2) mediates the inactivation of hepatic CYP2E1.