title: Exposure to benzo[a]pyrene of Hepatic Cytochrome P450 Reductase Null (HRN) and P450 Reductase Conditional Null (RCN) mice: Detection of benzo[a]pyrene diol epoxide-DNA adducts by immunohistochemistry and 32P-postlabelling.
abstract: Benzo[a]pyrene (BaP) is a widespread environmental carcinogen activated by cytochrome P450 (P450) enzymes. In Hepatic P450 Reductase Null (HRN) and Reductase Conditional Null (RCN) mice, P450 oxidoreductase (Por) is deleted specifically in hepatocytes, resulting in the loss of essentially all hepatic P450 function. Treatment of HRN mice with a single i.p. or oral dose of BaP (12.5 or 125mg/kg body weight) resulted in higher DNA adduct levels in liver (up to 10-fold) than in wild-type (WT) mice, indicating that hepatic P450s appear to be more important for BaP detoxification in vivo. Similar results were obtained in RCN mice. We tested whether differences between hepatocytes and non-hepatocytes in P450 activity may underlie the increased liver BaP-DNA binding in HRN mice. Cellular localisation by immunohistochemistry of BaP-DNA adducts showed that HRN mice have ample capacity for formation of BaP-DNA adducts in liver, indicating that the metabolic process does not result in the generation of a reactive species different from that formed in WT mice. However, increased protein expression of cytochrome b(5) in hepatic microsomes of HRN relative to WT mice suggests that cytochrome b(5) may modulate the P450-mediated bioactivation of BaP in HRN mice, partially substituting the function of Por.
authors: Analytical and Environmental Sciences Division, MRC-HPA Centre for Environment and Health, King's College London, London, United Kingdom. volker.arlt@kcl.ac.uk
authors: Volker M
authors: VM
authors: Arlt
authors: Miriam C
authors: MC
authors: Poirier
authors: Sarah E
authors: SE
authors: Sykes
authors: Kaarthik
authors: K
authors: John
authors: Michaela
authors: M
authors: Moserova
authors: Marie
authors: M
authors: Stiborova
authors: C Roland
authors: CR
authors: Wolf
authors: Colin J
authors: CJ
authors: Henderson
authors: David H
authors: DH
authors: Phillips
mesh_terms: D000818:Animals; D001564:Benzo(a)pyrene / Q000378:metabolism / Q000493:pharmacokinetics / Q000633:toxicity*; D019363:Cytochrome P-450 CYP1A1 / Q000378:metabolism; D015786:Cytochromes b5 / Q000378:metabolism; D018736:DNA Adducts / Q000378:metabolism*; D004249:DNA Damage; D005260:Female; D022781:Hepatocytes / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism; D007150:Immunohistochemistry; D008099:Liver / Q000187:drug effects* / Q000201:enzymology / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D008862:Microsomes, Liver / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism; D009251:NADPH-Ferrihemoprotein Reductase / Q000172:deficiency* / Q000235:genetics / Q000378:metabolism*
chemical_list: D018736:DNA Adducts; C056612:benzo(a)pyrene-DNA adduct; D001564:Benzo(a)pyrene; D015786:Cytochromes b5; D019363:Cytochrome P-450 CYP1A1; D009251:NADPH-Ferrihemoprotein Reductase