Metabolic activation of polycyclic aromatic hydrocarbon trans-dihydrodiolsby ubiquitously expressed aldehyde reductase (AKR1A1)

Polycyclic aromatic hydrocarbons (PAHs) are metabolized to trans-dihydrodio l proximate carcinogens by CYP1A1 and epoxide hydrolase (EH). CYP1A1 or ald o-keto reductases (AKRs) from the 1C subfamily can further activate the tim zs-dihydrodiols by forming either anti-diol-epoxides or reactive and redox active o-quinones, respectively. To determine whether other AKR superfamily members can divert trans-dihydrodiols to o-quinones, the cDNA encoding hum an aldehyde reductase (AKR1A1) was isolated from hepatoma HepG2 cells using RT-PCR, subcloned into a prokaryotic expression vector, overexpressed in E . coli and purified to homogeneity in milligram amounts. Studies revealed t hat AKR1A1 preferentially oxidized the metabolically relevant(-)-[3R,4R]-di hydroxy-3,4-dihydrobenz[a]anthracene. AKR1A1 also displayed high utilizatio n ratios (V-max/K-m) for the following PAH trans-dihydrodiols: (+/- )trans- 3,3-dihydroxy-3,4-dihydro-7-methylbenz[a]anthracene, (+/- )trans-3,4-dihydr oxy-3,4-dihydro-7, 12-dimethylbenz[fl]anthracene and (+/- )trans-7,8-dihydr oxy-7,8-dihydro-5-methylchrysene. Multiple tissue expression (MTE) arrays w ere used to measure the co-expressed of CYP1A1, EH and AKR1A1. All the thre e enzymes co-expressed to sites of PAH activation. The high catalytic effic iency of AKR1A1 for potent proximate carcinogen trans-dihydrodiols and its presence in tissues that contain CYP1A1 and EH suggests that it plays an im portant role in this alternative pathway of PAH activation (supported by CA 39504). (C) 2001 Elsevier Science Ireland Ltd. All rights reserved.