MUTAGENIC ACTIVATION OF URINARY-BLADDER CARCINOGENS BY CYP4B1 AND THEPRESENCE OF CYP4BI IN BLADDER MUCOSA

We investigated the mutagenic activation of 2-naphthylamine (2-NA), 3, 2'-dimethyl-4-aminobiphenyl (DMAB), and 3,3'-dichlorobenzidine (DCB), bladder carcinogens, by renal and bladder microsomes and by purified P 450s using the umu gene expression system, which detects DNA damage. M ouse renal microsomes had high mutagenic activation toward DCB and low activity toward 2-NA. Purified mouse Cyp4b1 also had high mutagenic a ctivity coward DCB. Anti-Cyp4b1 antibody efficiently inhibited DCB bio activation by mouse renal microsomes with a high Cyp4b1 content. Lauri c acid, a substrate of Cyp4b1, efficiently inhibited DCB bioactivation by renal and bladder microsomes of the mouse and by purified Cyp4b1. To assess the contribution of CYP4B1 to bladder carcinoma, further inv estigation was done with the umu test and an immunochemical study. Ten forms of purified rat P450s including rat CYP4B1 were used in the umu test for 2-NA, DMAB, and DCB. CYP4B1 had the highest activity toward DMAB and DCB. Other P450s had activities of less than 20% that of CYP4 B1. CYP4B1 also activated 2-NA, but its activity was about 10% of that toward DMAB or DCB. Rat bladder epithelium was stained specifically w ith anti-Cyp4b1 antibody, indicating the presence of CYP4B1 in the rat bladder mucosa. Also, CYP4B1 mRNA was detected by northern blotting a nd reverse transcription-polymerase chain reaction (RT-PCR). These fin dings suggested that CYP4B1 could contribute to the initiation of carc inogenesis in rat and mouse bladder by activation of aromatic amines. (C) 1997 Elsevier Science Inc.