BIOACTIVATION OF [C-13]DICHLOROMETHANE IN MOUSE, RAT, AND HUMAN LIVERCYTOSOL - C-13 NUCLEAR-MAGNETIC-RESONANCE SPECTROSCOPIC STUDIES

Dichloromethane is tumorigenic in lungs and liver of B6C3F(1) mice, bu t is not tumorigenic in rats or hamsters, and its toxicity is associat ed with glutathione-dependent bioactivation. The objective of the pres ent studies was to investigate the glutathione-dependent bioactivation of [C-13] dichloromethane in mouse, rat, and human liver cytosol and the fate of dichloromethane-derived reactive intermediates with C-13 N MR. [C-13]Formaldehyde hydrate, [C-13]S-(hydroxy-methyl) glutathione, and [C-13]methanol were identified as metabolites of [C-13] dichlorome thane. [C-13]S-(Chloromethyl) glutathione, a putative intermediate in the glutathione-dependent bioactivation of dichloromethane, or derived adducts were not observed. Moreover, no evidence for the formation of S,S'-methylenebis[glutathione] by reaction of glutathione and formald ehyde under physiological conditions was obtained, although methanol w as observed as a product. S,S'-Methylenebis[glutathione] was, however, formed by reaction of glutathione and formaldehyde at pH 1. S-(Chloro methyl)-N-acetyl-L-cysteine methyl ester, a surrogate for S-(chloromet hyl)glutathione, was prone to hydrolysis. These results corroborate th e finding that formaldehyde is a reactive intermediate formed during t he glutathione-dependent bioactivation of dichloromethane that may be involved in the observed tumorigenicity of dichloromethane in suscepti ble species. The results also indicate that S-(chloromethyl)glutathion e is an intermediate in the glutathione-dependent bioactivation of dic hloromethane and may also play a role in its mutagenicity and carcinog enicity.