title: Inhibition of trans-dihydrodiol oxidation by the non-steroidal anti-inflammatory drugs.
abstract: The homogeneous dihydrodiol dehydrogenase of rat liver cytosol (EC 1.3.1.20) reduces the mutagenicity of benzo[a]pyrene in the Ames test, suggesting that the enzyme may detoxify the trans-dihydrodiol proximate carcinogens formed from this compound. This report directly demonstrates for the first time that the purified dehydrogenase catalyzes the NADP-dependent oxidation of the potent proximate carcinogen [1,3-3H](+/-)-trans-7,8-dihydroxy-7,8-dihydrobenzo[a]pyrene at physiological pH. An initial velocity of 1.8 nmol [3H]trans-dihydrodiol oxidized/min/mg protein was observed at a substrate concentration of 20 microM. This potential detoxification reaction was potently inhibited by the nonsteroidal anti-inflammatory drug indomethacin, yielding an IC50 value of 10 microM. At higher drug concentrations (30 microM), the inhibition persisted for many hours. In an extension of this work, benzenedihydrodiol (trans-1,2-dihydroxy-3,5-cyclohexadiene) and naphthalenedihydrodiol (trans-1,2-dihydroxy-1,2-dihydronaphthalene) were synthesized as models of the scarce proximate carcinogen trans-7,8-dihydroxy-7,8-dihydrobenzo[a]pyrene and examined as substrates. The Km for benzenedihydrodiol was 1.74 mM and the Vmax was 530 nmol substrate oxidized/min/mg protein, while the Km for naphthalenedihydrodiol was 10.71 mM and the Vmax was 268 nmol oxidized/min/mg protein; the former compound was oxidized to catechol. Eight different non-steroidal anti-inflammatory drugs were found to inhibit the oxidation of these model trans-dihydrodiols, yielding IC50 values comparable to or lower than peak plasma concentrations observed in man. These results suggest that therapeutically relevant concentrations of the non-steroidal anti-inflammatory drugs may inhibit the oxidation of trans-dihydrodiol proximate carcinogens by this route.
authors.forename: T E
authors.initials: TE
authors.lastname: Smithgall
authors.forename: T M
authors.initials: TM
authors.lastname: Penning
mesh_terms: D015096:3-Hydroxysteroid Dehydrogenases / Q000378:metabolism; D000818:Animals; D000893:Anti-Inflammatory Agents / Q000494:pharmacology*; D001241:Aspirin / Q000494:pharmacology; D001580:Benzopyrenes / Q000378:metabolism; D004101:Dihydroxydihydrobenzopyrenes; D005439:Flufenamic Acid / Q000494:pharmacology; D007052:Ibuprofen / Q000494:pharmacology; D007213:Indomethacin / Q000494:pharmacology; D008099:Liver / Q000201:enzymology; D008297:Male; D008469:Meclofenamic Acid / Q000494:pharmacology; D008528:Mefenamic Acid / Q000494:pharmacology; D010088:Oxidoreductases / Q000037:antagonists & inhibitors*; D051381:Rats; D013467:Sulindac / Q000494:pharmacology; D014046:Tolmetin / Q000494:pharmacology
chemical_list: D000893:Anti-Inflammatory Agents; D001580:Benzopyrenes; D004101:Dihydroxydihydrobenzopyrenes; C017228:benzo(a)pyrene 7,8-dihydrodiol; D013467:Sulindac; D008528:Mefenamic Acid; D008469:Meclofenamic Acid; D005439:Flufenamic Acid; D014046:Tolmetin; D010088:Oxidoreductases; D015096:3-Hydroxysteroid Dehydrogenases; C048338:trans-1,2-dihydrobenzene-1,2-diol dehydrogenase; D001241:Aspirin; D007052:Ibuprofen; D007213:Indomethacin