Hepatotoxicity of N-methylformamide in mice--II. Covalent binding of metabolites of [14C]-labelled N-methylformamide to hepatic proteins.
Incubation of the hepatotoxin N-methylformamide (NMF) labelled either in the methyl group (OHCNH14CH3) or the formyl group (OH14CNHCH3) with mouse hepatic microsomes in the presence of NADPH, but not in its absence, led to covalent binding of metabolites to microsomal proteins. When [14C]NMF was injected into BALB/c mice radioactivity was found to be associated with liver and, to a much lesser extent, with kidney proteins. Association of radioactivity derived from OHCNH14CH3 with hepatic proteins was higher in BALB/c mice than in CBA/CA mice and in these it was higher than in BDF1 mice. Association of label derived from either isotopomer was significantly reduced but not abolished by pretreatment of mice with cycloheximide suggesting both covalent binding and metabolic incorporation of NMF metabolites. Depletion of hepatic glutathione by pretreatment of mice with buthionine sulfoximine or diethyl maleate prior to administration of OH14CNHCH3 enhanced the association of label with hepatic proteins measured 1 hr after drug injection. Covalent binding of [14C]NMF to hepatic microsomes in vitro was abolished in the presence of glutathione. It is argued that the generation of the toxic lesion and the association of NMF metabolites with hepatic proteins may be causally related even though certain mechanistic and enzymatic details of this link remain obscure.
D000818:Animals; D003513:Cycloheximide / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D005559:Formamides / Q000378:metabolism / Q000633:toxicity*; D006358:Hot Temperature; D007668:Kidney / Q000378:metabolism; D008099:Liver / Q000187:drug effects* / Q000378:metabolism; D051379:Mice; D008807:Mice, Inbred BALB C; D008808:Mice, Inbred CBA; D008862:Microsomes, Liver / Q000378:metabolism; D009249:NADP / Q000378:metabolism; D011506:Proteins / Q000378:metabolism*; D013045:Species Specificity
D005559:Formamides; D011506:Proteins; D009249:NADP; D003513:Cycloheximide; C002950:methylformamide