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

Dichloromethane is tumorigenic in lungs and liver of B6C3F(1) mice, but is not tumorigenic in rats or hamsters, and its toxicity is associated with glutathione-dependent bioactivation. The objective of the present 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 NMR. [C-13]Formaldehyde hydrate, [C-13]S-(hydroxy-methyl) glutathione, and [C-13]methanol were identified as metabolites of [C-13] dichloromethane. [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 formaldehyde under physiological conditions was obtained, although methanol was observed as a product. S,S'-Methylenebis[glutathione] was, however, formed by reaction of glutathione and formaldehyde at pH 1. S-(Chloromethyl)-N-acetyl-L-cysteine methyl ester, a surrogate for S-(chloromethyl)glutathione, was prone to hydrolysis. These results corroborate the finding that formaldehyde is a reactive intermediate formed during the glutathione-dependent bioactivation of dichloromethane that may be involved in the observed tumorigenicity of dichloromethane in susceptible species. The results also indicate that S-(chloromethyl)glutathione is an intermediate in the glutathione-dependent bioactivation of dichloromethane and may also play a role in its mutagenicity and carcinogenicity.