Aflatoxin B1 metabolism by 3-methylcholanthrene-induced hamster hepatic cytochrome P-450s.
We have studied the activation of aflatoxin B1 by hamster liver microsomes and purified hamster cytochrome P-450 isozymes using a umu mutagen test. The hamster liver microsomes or S-9 fractions were much more active than rat liver microsomes or S-9 fractions in the activation of umu gene expression by aflatoxin B1 metabolites. 3-Methyl-cholanthrene treatment increased aflatoxin B1 activation by hamster liver microsomes. Two major 3-methylcholanthrene-inducible cytochrome P-450 isozymes, P-450 MC1 (IIA) and P-450 MC4 (IA2), were purified from 3-methylcholanthrene-treated hamster liver microsomes, and the metabolism of aflatoxin B1 by these two cytochromes was studied. In the reconstituted enzyme system, both P-450 MC1 and P-450 MC4 were highly active in the activation of aflatoxin B1, and antibodies against these P-450s specifically inhibited these activities. Antibody against P-450 MC1 inhibited the activation of aflatoxin B1 by 20% in the presence of 3-methyl-cholanthrene-treated hamster liver microsomes. In contrast, antibody against P-450 MC4 stimulated the activity by 175%. These results indicated that hamster P-450 MC1 might convert aflatoxin B1 to more toxic metabolite(s), whereas P-450 MC4 might convert aflatoxin B1 to less toxic metabolite(s), than aflatoxin B1 in liver microsomes. The metabolite(s) produced by both hamster cytochrome P-450 MC1 and MC4 were genotoxic in the umu mutagen test.
Lai
T S
TS
Department of Biochemistry and Molecular Pathology, Northeastern Ohio Universities College of Medicine, Rootstown 44272.
Chiang
J Y
JY
D016604:Aflatoxin B1; D000348:Aflatoxins / Q000276:immunology / Q000378:metabolism*; D000818:Animals; D000906:Antibodies / Q000276:immunology; D006224:Cricetinae; D003577:Cytochrome P-450 Enzyme System / Q000096:biosynthesis / Q000302:isolation & purification / Q000378:metabolism*; D004790:Enzyme Induction / Q000187:drug effects; D015971:Gene Expression Regulation, Enzymologic; D008099:Liver / Q000187:drug effects / Q000201:enzymology*; D008647:Mesocricetus; D008748:Methylcholanthrene / Q000494:pharmacology*; D008862:Microsomes, Liver / Q000201:enzymology; D009152:Mutagenicity Tests; D051381:Rats; D011919:Rats, Inbred Strains; D012486:Salmonella typhimurium / Q000201:enzymology / Q000235:genetics; D013347:Subcellular Fractions / Q000187:drug effects / Q000201:enzymology
D000348:Aflatoxins; D000906:Antibodies; D008748:Methylcholanthrene; D003577:Cytochrome P-450 Enzyme System; D016604:Aflatoxin B1