A monoclonal antibody against cytochrome P-450 enhances mutagen activation of N-nitrosodimethylamine by mouse liver S9: studies on the mode of action

The effect of the monoclonal antibody MAb 2-66-3, directed againstthe major rat liver phenobarbital (PB)-induced cytochrome P-450(P-450), on the S9-mediated mutagenicity of N-nitrosodimethylamine(DMN) in Salmonella typhimurium strain TA1530 was studied usingliver S9 from PB-treated mice. This MAb enhanced {small tilde}2-fold S9-mediated mutagenicity of DMN but inhibited both itsN-demethylation and N-denitrosation by 50%. Thus MAb-mediatedenhancement of DMN mutagenesis does not result from alteredactivationl inactivation pathways, both known to involve P-450isozymes. DMSO, a hydroxyl radical (HO⁺) scavenger and desferrioxamine,an inhibitor of HO⁺-dependent reactions, quenched the MAb-mediatedenhancement of DMN mutagenesis, implicating the HO⁺-dependentactivation of DMN to mutagenic species. As a mechanism, we proposethat the binding of this MAb to P-450 isozyme implicated inDMN metabolism decreases the functional coupling between thereductase and the P-450 complex, leading to an increased electronflow from the reductase towards molecular oxygen to form reducedoxygen species (HO⁺) at the expense of the monooxygenase functions.