Metabolism of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone in human lung and liver microsomes and cytochromes P-450 expressed in hepatoma cells.
4-(Methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), a potent tobacco-specific carcinogen in animals, has been linked to tobacco-related cancers in humans. The cytochrome(s) P-450 (P-450) responsible for the metabolic activation of NNK in humans has not been identified. The present work investigated the ability of human lung and liver microsomes and 12 forms of human P-450, expressed in Hep G2 (hepatoma) cells, to metabolize NNK. Of the 12 P-450 forms, P-450 1A2 had the highest activity in catalyzing the conversion of NNK to the keto alcohol, 4-hydroxy-1-(3-pyridyl)-1-butanone. P-450s 2A6, 2B7, 2E1, 2F1, and 3A5 also had measurable activities in the formation of keto alcohol. The apparent Km and Vmax for the formation of keto alcohol in the P-450 1A2-expressed Hep G2 cell lysate were 309 microM and 55 pmol/min/mg protein, respectively. 4-(Methylnitrosamino)-1-(3-pyridyl)-1-butanol, a reductive product, was the major metabolite formed, whereas the formation of keto alcohol and its aldehyde and acid derivatives (all alpha-hydroxylation products) constituted approximately 1% of the initial amount of NNK in P450-expressed Hep G2 cell lysate. A similar metabolite pattern was observed with human lung or liver microsomes. In human lung microsomes, the apparent Kms for the formation of 4-hydroxy-4-(3-pyridyl)butyric acid, 4-oxo-1-(3-pyridyl)-1-butanone, NNK-N-oxide, and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol were 526, 653, 531, and 573 microM, respectively; the formation of keto alcohol was not observed. For human lung microsomes, there was no sex-related difference in NNK metabolism. Carbon monoxide (90% atmosphere) significantly inhibited the metabolism of NNK in human lung and liver microsomes. 7,8-Benzoflavone, an inhibitor of P-450s 1A1 and 1A2, had no effect on NNK metabolism in human lung microsomes but decreased the formation of keto alcohol by 47% in human liver microsomes. Similarly, antibodies against human P-450s 1A2 and 2E1 decreased keto alcohol formation by 42% and 53%, respectively, in human liver microsomes but did not affect NNK metabolism in lung microsomes. Inhibitory antibodies against P-450s 2A1, 2C8, 2D1, or 3A4 had little or no effect on the metabolism of NNK in human liver or lung microsomes.(ABSTRACT TRUNCATED AT 400 WORDS)
Smith
T J
TJ
Laboratory for Cancer Research, College of Pharmacy, Rutgers University, Piscataway, New Jersey 08855-0789.
Guo
Z
Z
Gonzalez
F J
FJ
Guengerich
F P
FP
Stoner
G D
GD
Yang
C S
CS
D000906:Antibodies; D001711:Biotransformation; D002273:Carcinogens / Q000378:metabolism*; D006528:Carcinoma, Hepatocellular / Q000201:enzymology*; D002460:Cell Line; D065607:Cytochrome P-450 Enzyme Inhibitors; D003577:Cytochrome P-450 Enzyme System / Q000276:immunology / Q000378:metabolism*; D006801:Humans; D007700:Kinetics; D008113:Liver Neoplasms / Q000201:enzymology*; D008168:Lung / Q000378:metabolism*; D008861:Microsomes / Q000378:metabolism*; D008862:Microsomes, Liver / Q000378:metabolism*; D008962:Models, Theoretical; D009602:Nitrosamines / Q000378:metabolism*; D011994:Recombinant Proteins / Q000378:metabolism; D014316:Tritium
D000906:Antibodies; D002273:Carcinogens; D065607:Cytochrome P-450 Enzyme Inhibitors; D009602:Nitrosamines; D011994:Recombinant Proteins; D014316:Tritium; C016583:4-(N-methyl-N-nitrosamino)-1-(3-pyridyl)-1-butanone; D003577:Cytochrome P-450 Enzyme System