Biotransformation of trans-4,5-dihydroxy-4,5-dihydrobenzo[a]pyrene to benzo[a]pyrene bis-diols and DNA adducts by induced rat liver microsomes

The biotransformation of (+/-)-trans-4,5 -dihydroxy-4,5 -dihydrobenzo[a]pyr ene (trans-B[alpha ]P-4,5-diol), the K-region dihydrodiol of B[alpha ]P, by beta -naphthoflavone (BNF)-induced rat liver microsomes was studied, trans -B[alpha ]P-4,5-diol was metabolized to six major products as characterized by NMR, MS, and UV spectroscopy, and all were identified as bis-diols: two diastereomers of trans,trans-4,5 :7,8-tetrahydroxy-4,5:7,8-tetrahydrobenzo [alpha ]pyrene (trans,trans-B[alpha ]P-4,5:7,8-bis-diol), two diastereomers of trans,trans-4,5:9, 10-tetrahydroxy-4,5:9, 10-tetrahydrobenzo[alpha ]pyr ene (trans,trans-B[alpha ]P-4,5:9, 10-bis-diol), and two diastereomers of t he somewhat unusual trans,trans-1,2:4, 5 -tetrahydroxy-1,2: 4, 5-tetrahydro benzo[alpha ]pyrene (trans,trans-B[alpha ]P-1,2 ,4,5-bis-diol). BNF-induced rat liver microsomes also metabolized B [alpha ]P to the same trans-B[alph a ]P-4,5-diol-derived bis-diols. The ability of trans-B[alpha ]P-4,5-diol t o form DNA adducts was investigated using P-32-postlabeling techniques spec ifically designed to detect stable polar DNA adducts. Four DNA adducts were detected after microsomal activation of trans-B[alpha ]P-4,5-diol with cal f thymus DNA. Further analyses indicated that each of these stable polar DN A adducts was derived from the further metabolic activation of the trans,tr ans-B[alpha ]P-4,5: 7,8-bis-diols. We conclude that trans-B[alpha ]P-4,5-di ol can be metabolized to a series of B[alpha ]P-bis-diols, and can also be metabolically activated to form stable polar DNA adducts. The trans,trans-B [alpha ]P-4,5:7,8-bis-diols were shown to be metabolic intermediates in the formation of these DNA adducts.