Discovery - University of Dundee - Online Publications

Library & Learning Centre

Effect of hepatic cytochrome P450 (P450) oxidoreductase deficiency on 2-Amino-1-methyl-6-phenylimidazo[4,5-b]pyridine-DNA Adduct Formation in P450 reductase conditional null mice

Effect of hepatic cytochrome P450 (P450) oxidoreductase deficiency on 2-Amino-1-methyl-6-phenylimidazo[4,5-b]pyridine-DNA Adduct Formation in P450 reductase conditional null mice

Research output: Contribution to journalArticle

View graph of relations

Authors

Research units

    Info

    Original languageEnglish
    Pages2169-2173
    Number of pages5
    JournalDrug Metabolism and Disposition
    Journal publication dateDec 2011
    Journal number12
    Volume39
    DOIs
    StatePublished

    Abstract

    2-Amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP), formed during the cooking of foods, induces colon cancer in rodents. PhIP is metabolically activated by cytochromes P450 (P450s). To evaluate the role of hepatic P450s in the bioactivation of PhIP, we used Reductase Conditional Null (RCN) mice, in which cytochrome P450 oxidoreductase (POR), the unique electron donor to P450s, can be specifically deleted in hepatocytes by pretreatment with 3-methylcholanthrene (3-MC), resulting in the loss of essentially all hepatic P450 function. RCN mice were treated orally with 50 mg/kg b.wt. PhIP daily for 5 days, with and without 3-MC pretreatment. PhIP-DNA adducts (i.e., N-(deoxyguanosin-8-yl)-2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine [dG-C8-PhIP]), measured by liquid chromatography-tandem mass spectrometry, were highest in colon (1362 adducts/10(8) deoxynucleosides), whereas adduct levels in liver were similar to 3.5-fold lower. Whereas no differences in PhIP-DNA adduct levels were found in livers with active POR versus inactivated POR, adduct levels were on average similar to 2-fold lower in extrahepatic tissues of mice lacking hepatic POR. Hepatic microsomes from RCN mice with or without 3-MC pretreatment were also incubated with PhIP and DNA in vitro. PhIP-DNA adduct formation was similar to 8-fold lower with hepatic microsomes from POR-inactivated mice than with those with active POR. Most of the hepatic microsomal activation of PhIP in vitro was attributable to CYP1A. Our results show that PhIP-DNA adduct formation in colon involves hepatic N-oxidation, circulation of activated metabolites via the bloodstream to extrahepatic tissues, and further activation, resulting in the formation of dG-C8-PhIP. Besides hepatic P450s, PhIP may be metabolically activated mainly by a non-P450 pathway in liver.

    Documents

    Library & Learning Centre

    Contact | Accessibility | Policy