Enzymatic mechanisms in the metabolic activation of N-nitrosodialkylamines.
The metabolism of several N-nitrosodialkylamines was studied using rat liver microsomes and purified cytochrome P450 isozymes in a reconstituted monooxygenase system. With purified acetone/ethanol-inducible cytochrome P450 (P450ac), high N-nitrosodimethylamine (NDMA) demethylase activity was observed. Cytochrome b5 was also involved in NDMA metabolism by decreasing the Km of NDMA demethylase. A close relationship between the demethylation and denitrosation of this substrate was observed. P450ac was also active in the metabolism of N-nitrosoethylmethylamine (NEMA), but was less active than phenobarbital-inducible cytochrome P450 (P450b) in the metabolism of N-nitrosobutylmethylamine (NBMA), especially in catalysing the debutylation reaction. Similar substrate specificity was demonstrated with liver microsomes from rats treated with other inducers. With different P450 isozymes and microsomes, a close relationship between metabolism and activation of nitrosamines to mutagens to V79 cells was demonstrated. DNA alkylation by NDMA in vitro was correlated with the rate of metabolism of these compounds, whereas DNA alkylation in vivo was more complex and was dose-dependent. The work demonstrates the importance of knowledge of the substrate specificity of cytochrome P450 isozymes in understanding the mechanisms of the metabolic activation of nitrosamines.
Yang
C S
CS
Department of Biochemistry, University of Medicine and Dentistry of New Jersey, New Jersey Medical School, Newark.
Patten
C
C
Lee
M J
MJ
Li
M
M
Yoo
J S
JS
Pan
J
J
Hong
J
J
D000818:Animals; D001711:Biotransformation; D019392:Cytochrome P-450 CYP2E1; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism*; D003573:Cytochrome b Group / Q000378:metabolism; D015786:Cytochromes b5; D004128:Dimethylnitrosamine / Q000031:analogs & derivatives* / Q000493:pharmacokinetics*; D007527:Isoenzymes / Q000378:metabolism*; D007700:Kinetics; D008862:Microsomes, Liver / Q000201:enzymology; D010089:Oxidoreductases, N-Demethylating / Q000378:metabolism; D051381:Rats; D013379:Substrate Specificity
D003573:Cytochrome b Group; D007527:Isoenzymes; C017510:methylethylnitrosamine; D015786:Cytochromes b5; D003577:Cytochrome P-450 Enzyme System; D019392:Cytochrome P-450 CYP2E1; D010089:Oxidoreductases, N-Demethylating; D004128:Dimethylnitrosamine