Oxidation of 3-aminobenzanthrone, a human metabolite of carcinogenic environmental pollutant 3-nitrobenzanthrone, by cytochromes P450 - similarity between human and rat enzymes.
OBJECTIVE
3-Aminobenzanthrone (3-ABA) is the main human metabolite of carcinogenic environmental pollutant 3-nitrobenzanthrone (3-NBA). Understanding which cytochrome P450 (CYP) enzymes are involved in metabolism of this toxicant is important in the assessment of individual susceptibility. Characterization of 3-ABA metabolites formed by rat hepatic microsomes containing cytochromes P450 (CYPs) and identification of the major rat and human CYPs participating in this process are aims of this study.


METHODS
HPLC with UV detection was employed for the separation and characterization of 3-ABA metabolites. Inducers and inhibitors of CYPs and rat and human recombinant CYPs were used to characterize the enzymes participating in 3-ABA oxidation.


RESULTS
Selective CYP inhibitors and hepatic microsomes of rats pre-treated with specific CYP inducers were used to characterize rat liver CYPs metabolizing 3-ABA (measured as consumption of 3-ABA). Kinetics of these reactions catalyzed by rat hepatic microsomes was also evaluated. Based on these studies, we attribute most of 3-ABA metabolism in rat liver to CYP1A and 3A. Among recombinant rat and human CYP enzymes tested in this study, rat CYP3A2 and human CYP3A4/5, followed by CYP1A1 of both organisms were the most effective enzymes converting 3-ABA. Rat hepatic CYP enzymes oxidize 3-ABA up to three metabolites. Two of them were identified to be the products formed by oxidation of 3-ABA on its amino group back to the parent compound from which 3-ABA is generated in organisms, 3-NBA. Namely, N-hydroxylation metabolite, N-hydroxy-3-ABA and 3-NBA were identified to be these 3-ABA oxidation products. These metabolites are formed by CYPs of a 1A subfamily. Another 3-ABA metabolite, whose structure remains to be characterized, is generated not only by CYP1A but also by other CYP enzymes, predominantly by CYPs of a 3A subfamily.


CONCLUSIONS
The results found in this study, the first report on the metabolism of 3-ABA by human and rat CYPs, clearly demonstrate that CYPs of 3A and 1A subfamilies are the major enzymes metabolizing 3-ABA.
Mizerovska
Jana
J
Department of Biochemistry, Charles University, Prague, Czech Republic.
Dracinska
Helena
H
Arlt
Volker M
VM
Schmeiser
Heinz H
HH
Frei
Eva
E
Stiborova
Marie
M
D000818:Animals; D001551:Benz(a)Anthracenes / Q000378:metabolism*; D002851:Chromatography, High Pressure Liquid / Q000379:methods; D065607:Cytochrome P-450 Enzyme Inhibitors; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism*; D006801:Humans; D020128:Inhibitory Concentration 50; D007700:Kinetics; D008297:Male; D008862:Microsomes, Liver / Q000201:enzymology / Q000378:metabolism*; D010084:Oxidation-Reduction; D051381:Rats; D017208:Rats, Wistar; D011994:Recombinant Proteins / Q000378:metabolism; D013045:Species Specificity; D014466:Ultraviolet Rays
C475568:3-aminobenzanthrone; D001551:Benz(a)Anthracenes; D065607:Cytochrome P-450 Enzyme Inhibitors; D011994:Recombinant Proteins; D003577:Cytochrome P-450 Enzyme System; C117220:3-nitrobenzanthrone