Mechanism of Dimethylnitrosamine Metabolism and Activation in Rats2

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Abstract
Dimethylnitrosamine (DMN) was metabolized by liver tissue slices to CO2, and reactive metabolites were formed that bound to nucleic acids. SKF 525-A [2-(diethylamlno)ethyl- 2,2-diphenylvalerate hydrochloride], 1 mm or 0.5 mm In the incubation mixture, strongly inhibited both CO2 production and binding. Liver slices derived from Sprague-Dawley rats pretreated with phenobarbital sodium (PB) metabolized less DMN to CO2 but, like the control liver slices, did bind to nucleic acids. Liver slices from rats treated with CoCl2 metabolized less DMN to CO2 and bound less 14C from DMN to nucleic acids than did the control silces. We also observed an NADPH-dependent, heatsensitive DMN activation process leading to reactive metabolites that bound covalently to proteins in both microsomes and 9,000×g supernatants but not In 100,000×g supernatants. Treatment with 1 mM SKF 525-A markedly Inhibited the activation process in microsomes and only slightly inhibited it in 9,000×g supernatants. Microsomes or 9,000×g supernatants from PB-pretreated animals were less able to activate DMN than those from controls. The 9,000×g supernatant preparations from CoCl2- pretreated animals had a markedly decreased capacity for DM~ activation, but the mlcrosomes from these animals had only a moderately decreased capacity. When activation of DMN was studied in an 80% CO atmosphere, the ability for DMN activation was decreased to about 35.6% In microsomes and was completely abolished in 9,000×g supernatants. When an N2 atmosphere was employed during incubation, the ability for DMN activation in microsomes remained unchanged and that in 9,000×g supernatants only partially decreased. The results suggested the presence of multiple pathways for DMN metabolism and activation, only some of them being dependent on cytochrome P450.