Qualitative and quantitative differences in the induction and inhibition of hepatic benzo[a]pyrene metabolism in the rat and hamster.
The present study compared the induction and inhibition of the metabolism of the prototype polycyclic aromatic hydrocarbon, benzo[a]pyrene (BaP), in rat and hamster liver microsomes. The production of total polar metabolites was quantitated by separating 3H-metabolites from [3H]-BaP using reverse-phase thin-layer chromatography. The rate of hepatic microsomal BaP metabolism was similar in the rat and hamster (0.81 vs 0.72 nmol/min/nmol cytochrome P-450 respectively). In the rat, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD; 5 micrograms/kg, i.p.) and 3-methylcholanthrene (3-MC; 50 mg/kg, i.p., X 3 days) pretreatments doubled the rate of BaP metabolism, whereas phenobarbital pretreatment (PB; 80 mg/kg, i.p., X 3 days) had no effect. In contrast, hamster hepatic microsomal BaP metabolism was elevated 2.3-fold by PB pretreatment, whereas TCDD and 3-MC pretreatments had no effect. Isosafrole pretreatment (ISO; 150 mg/kg, i.p., X 3 days) elevated the rate by almost 2-fold in each species. Another cytochrome P-448-mediated activity, 7-ethoxyresorufin O-deethylase (EROD), was induced by the same compounds that induced BaP metabolism in the rat. In hamster liver microsomes, in contrast to BaP metabolism, EROD was induced by TCDD and 3-MC but not PB or ISO pretreatments. The results suggest differences in the substrate specificity of the cytochromes P-448-450 induced by TCDD, 3-MC and PB in these species. This was supported by the different selectivity of the in vitro inhibitors, metyrapone and 7,8-benzoflavone, towards BaP metabolism and EROD in hepatic microsomes from TCDD- or PB-pretreated rats and hamsters. Reverse-phase HPLC analysis indicated that, while 3-hydroxy-BaP was the major metabolite formed by the untreated rat, untreated hamster liver microsomes formed predominantly BaP-4,5-diol. Microsomes from TCDD-treated rats generated elevated levels of all BaP-diols, diones and 3-hydroxy-BaP, with the major metabolites being BaP-9,10- and BaP-7,8-diols. In contrast, the metabolite profile from TCDD-pretreated hamsters was unchanged from the control. PB-treated hamster microsomes produced elevated levels of BaP-diones and 3-hydroxy-BaP. However, the major hepatic metabolite formed by PB-pretreated hamsters was BaP-4,5-diol, while BaP-9,10- and BaP-7,8-diols were not detected. The results of the study indicate differences in the induced cytochrome P-450s and the generation of toxic BaP metabolites in the liver of the rat and hamster.
Wroblewski
V J
VJ
Department of Pharmacology and Therapeutics, State University of New York, Buffalo 14214.
Gessner
T
T
Olson
J R
JR
D000818:Animals; D001564:Benzo(a)pyrene / Q000378:metabolism*; D001571:Benzoflavones / Q000494:pharmacology; D006224:Cricetinae; D019363:Cytochrome P-450 CYP1A1; D065607:Cytochrome P-450 Enzyme Inhibitors; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism; D004790:Enzyme Induction / Q000187:drug effects; D008297:Male; D008647:Mesocricetus; D008748:Methylcholanthrene / Q000494:pharmacology; D008797:Metyrapone / Q000494:pharmacology; D008862:Microsomes, Liver / Q000187:drug effects / Q000201:enzymology*; D010088:Oxidoreductases / Q000037:antagonists & inhibitors; D010089:Oxidoreductases, N-Demethylating / Q000378:metabolism; D010634:Phenobarbital / Q000494:pharmacology; D000072317:Polychlorinated Dibenzodioxins / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D012451:Safrole / Q000494:pharmacology; D013045:Species Specificity
D001571:Benzoflavones; D065607:Cytochrome P-450 Enzyme Inhibitors; D000072317:Polychlorinated Dibenzodioxins; D001564:Benzo(a)pyrene; D008748:Methylcholanthrene; C011512:alpha-naphthoflavone; D003577:Cytochrome P-450 Enzyme System; D010088:Oxidoreductases; D019363:Cytochrome P-450 CYP1A1; C019781:benzphetamine N-demethylase; D010089:Oxidoreductases, N-Demethylating; D012451:Safrole; C015959:isosafrole; D010634:Phenobarbital; D008797:Metyrapone