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Comparative metabolism of the tobacco-related carcinogens benzo[a]pyrene, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol, and N'- nitrosonornicotine in human hepatic microsomes. 1997

M E Staretz, and S E Murphy, and C J Patten, and M G Nunes, and W Koehl, and S Amin, and L A Koenig, and F P Guengerich, and S S Hecht
American Health Foundation.

We compared the metabolism in human hepatic microsomes of three tobacco smoke carcinogens believed to be involved in the induction of cancer in humans: benzo[a]pyrene (BaP),4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), and N'-nitrosonomicotine (NNN). The metabolism of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL), a major metabolite of NNK, was also investigated. Although the metabolism of some of these compounds by human enzymes or tissue preparations has been previously examined in some studies, they have never been compared in the same human hepatic samples. Moreover, there have been no previous reports of NNAL metabolism by human tissues or enzymes. The tritium-labeled carcinogens (3 microM) were incubated with 10 different human hepatic microsomal preparations and cofactors for 10-20 min, and the products were analyzed by radioflow HPLC. NNN was the best substrate for oxidative metabolism, with the 5'-hydroxylation pathway being the predominant one observed (mean +/- SD = 31 +/- 17 pmol/min/mg protein). alpha-Hydroxylation of NNK by the methylene and methyl hydroxylation metabolic activation pathways was the next fastest reaction, with rates of 3.1 +/- 1.9 and 3.3 +/- 1.1 pmol/min/mg protein, respectively. Metabolism of BaP resulted in the formation of dihydrodiols and phenols; trans-7,8-dihydro-7,8-dihydroxy-BaP, its major proximate carcinogen, was formed at a rate of 1.1 +/- 0.61 pmol/min/mg protein. alpha-Hydroxylation of NNAL proceeded at a rate of 0.53 +/- 0.26 pmol/min/mg protein. The results of this study demonstrate that human hepatic microsomes metabolize all of these tobacco carcinogens resulting in a substantial stream of electrophilic intermediates capable of binding to DNA. The relative rates of oxidative metabolism to electrophiles or their precursors were NNN > NNK > BaP > NNAL. Correlation studies indicated involvement of cytochrome P4502A6 in the 5'-hydroxylation of NNN and cytochrome P4503A4 in the alpha-methylene hydroxylation and pyridine-N-oxidation of NNK and NNAL. The results of this study provide the first data on the comparative metabolism of these important carcinogens in human hepatic microsomes.

UI MeSH Term Description Entries
D008862 Microsomes, Liver Closed vesicles of fragmented endoplasmic reticulum created when liver cells or tissue are disrupted by homogenization. They may be smooth or rough. Liver Microsomes,Liver Microsome,Microsome, Liver
D009602 Nitrosamines A class of compounds that contain a -NH2 and a -NO radical. Many members of this group have carcinogenic and mutagenic properties. Nitrosamine
D010947 Plants, Toxic Plants or plant parts which are harmful to man or other animals. Plants, Poisonous,Plant, Poisonous,Plant, Toxic,Poisonous Plant,Poisonous Plants,Toxic Plant,Toxic Plants
D002273 Carcinogens Substances that increase the risk of NEOPLASMS in humans or animals. Both genotoxic chemicals, which affect DNA directly, and nongenotoxic chemicals, which induce neoplasms by other mechanism, are included. Carcinogen,Oncogen,Oncogens,Tumor Initiator,Tumor Initiators,Tumor Promoter,Tumor Promoters,Initiator, Tumor,Initiators, Tumor,Promoter, Tumor,Promoters, Tumor
D003577 Cytochrome P-450 Enzyme System A superfamily of hundreds of closely related HEMEPROTEINS found throughout the phylogenetic spectrum, from animals, plants, fungi, to bacteria. They include numerous complex monooxygenases (MIXED FUNCTION OXYGENASES). In animals, these P-450 enzymes serve two major functions: (1) biosynthesis of steroids, fatty acids, and bile acids; (2) metabolism of endogenous and a wide variety of exogenous substrates, such as toxins and drugs (BIOTRANSFORMATION). They are classified, according to their sequence similarities rather than functions, into CYP gene families (>40% homology) and subfamilies (>59% homology). For example, enzymes from the CYP1, CYP2, and CYP3 gene families are responsible for most drug metabolism. Cytochrome P-450,Cytochrome P-450 Enzyme,Cytochrome P-450-Dependent Monooxygenase,P-450 Enzyme,P450 Enzyme,CYP450 Family,CYP450 Superfamily,Cytochrome P-450 Enzymes,Cytochrome P-450 Families,Cytochrome P-450 Monooxygenase,Cytochrome P-450 Oxygenase,Cytochrome P-450 Superfamily,Cytochrome P450,Cytochrome P450 Superfamily,Cytochrome p450 Families,P-450 Enzymes,P450 Enzymes,Cytochrome P 450,Cytochrome P 450 Dependent Monooxygenase,Cytochrome P 450 Enzyme,Cytochrome P 450 Enzyme System,Cytochrome P 450 Enzymes,Cytochrome P 450 Families,Cytochrome P 450 Monooxygenase,Cytochrome P 450 Oxygenase,Cytochrome P 450 Superfamily,Enzyme, Cytochrome P-450,Enzyme, P-450,Enzyme, P450,Enzymes, Cytochrome P-450,Enzymes, P-450,Enzymes, P450,Monooxygenase, Cytochrome P-450,Monooxygenase, Cytochrome P-450-Dependent,P 450 Enzyme,P 450 Enzymes,P-450 Enzyme, Cytochrome,P-450 Enzymes, Cytochrome,Superfamily, CYP450,Superfamily, Cytochrome P-450,Superfamily, Cytochrome P450
D006801 Humans Members of the species Homo sapiens. Homo sapiens,Man (Taxonomy),Human,Man, Modern,Modern Man
D001564 Benzo(a)pyrene A potent mutagen and carcinogen. It is a public health concern because of its possible effects on industrial workers, as an environmental pollutant, an as a component of tobacco smoke. 3,4-Benzopyrene,3,4-Benzpyrene,3,4 Benzopyrene,3,4 Benzpyrene
D001711 Biotransformation The chemical alteration of an exogenous substance by or in a biological system. The alteration may inactivate the compound or it may result in the production of an active metabolite of an inactive parent compound. The alterations may be divided into METABOLIC DETOXICATION, PHASE I and METABOLIC DETOXICATION, PHASE II.
D014026 Nicotiana A plant genus of the family SOLANACEAE. Members contain NICOTINE and other biologically active chemicals; the dried leaves of Nicotiana tabacum are used for SMOKING. Tobacco Plant,Nicotiana tabacum,Plant, Tobacco,Plants, Tobacco,Tobacco Plants

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