Activation of amino-alpha-carboline, 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine and a copper phthalocyanine cellulose extract of cigarette smoke condensate by cytochrome P-450 enzymes in rat and human liver microsomes.
The ability of cigarette smoke condensate to induce a genotoxic response has been measured in liver microsomal and reconstituted monooxygenase systems containing rat and human cytochrome P-450 (P-450) enzymes, as determined by umu gene expression in Salmonella typhimurium TA1535/pSK1002. The reactivities of amino-alpha-carboline and 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP), two compounds known to be present at considerable levels in cigarette smoke condensate, were also determined and compared with regard to genotoxicity. Amino-alpha-carboline and PhIP are activated principally by P-450 1A2 enzymes in human and rat liver microsomes: (a) activation of both compounds was catalyzed efficiently by liver microsomes prepared from rats treated with 5,6-benzoflavone, isosafrole, or the commercial polychlorinated biphenyl mixture Aroclor 1254, and the activities could be considerably inhibited by antibodies raised against P-450 1A1 or 1A2; (b) the rates of activation of these compounds were correlated with the amount of human P-450 1A2 and of phenacetin O-deethylation activity in different human liver microsomal preparations, and these activities were inhibited by anti-P-450 1A2; (c) reconstituted enzyme systems containing P-450 1A enzymes isolated from rats and humans showed the highest rates of activation of amino-alpha-carboline and PhIP. In rat liver microsomes PhIP may also be activated by P-450 3A enzymes; activity was induced in rats treated with pregnenolone 16 alpha-carbonitrile and was inhibited by anti-human P-450 3A4. However, in humans the contribution of P-450 3A enzymes could be excluded as judged by the very low effects of anti-P-450 3A4 on the microsomal activities and poor correlation with P-450 3A4-catalyzed activities in various liver samples. Cigarette smoke condensate strongly inhibited the activation of several potent procarcinogens by human liver microsomes, particularly the reactions catalyzed by P-450 1A2, but was not so inhibitory of the activation reactions catalyzed by P-450 3A4 and of P-450 2D6-catalyzed bufuralol 1'-hydroxylation. Genotoxic components of the cigarette smoke condensate were extracted by using copper phthalocyanine cellulose (blue cotton). Genotoxicity of this extract was observed only after activation by P-450, and the inhibition of P-450 1A2 activities by these extracts was slight.(ABSTRACT TRUNCATED AT 400 WORDS)
Shimada
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Department of Biochemistry, Vanderbilt University School of Medicine, Nashville, Tennessee 37232-0146.
Guengerich
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FP
D016604:Aflatoxin B1 / Q000494:pharmacology; D000818:Animals; D001140:Aroclors / Q000494:pharmacology; D001571:Benzoflavones / Q000494:pharmacology; D002243:Carbolines / Q000378:metabolism*; D020111:Chlorodiphenyl (54% Chlorine); D003577:Cytochrome P-450 Enzyme System / Q000502:physiology*; D004247:DNA / Q000187:drug effects*; D004305:Dose-Response Relationship, Drug; D006801:Humans; D007093:Imidazoles / Q000633:toxicity*; D066298:In Vitro Techniques; D008297:Male; D008862:Microsomes, Liver / Q000201:enzymology*; D009153:Mutagens / Q000633:toxicity*; D010947:Plants, Toxic; D011802:Quinidine / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D013014:SOS Response, Genetics; D012451:Safrole / Q000494:pharmacology; D012906:Smoke / Q000009:adverse effects*; D014026:Nicotiana; D001616:beta-Galactosidase / Q000096:biosynthesis
D001140:Aroclors; D001571:Benzoflavones; D002243:Carbolines; D007093:Imidazoles; D009153:Mutagens; D012906:Smoke; D020111:Chlorodiphenyl (54% Chlorine); C011512:alpha-naphthoflavone; D004247:DNA; D003577:Cytochrome P-450 Enzyme System; C049584:2-amino-1-methyl-6-phenylimidazo(4,5-b)pyridine; D016604:Aflatoxin B1; D001616:beta-Galactosidase; D011802:Quinidine; C017822:2-amino-9H-pyrido(2,3-b)indole; D012451:Safrole; C015959:isosafrole