Nitrite-stimulated DNA-binding of carcinogenic diol epoxides from benzo[a]pyrene-7,8-dihydrodiol in human...

Human polymorphonuclear leukocytes (PMNs) previously treated with 12-O-tetradecanoyl phorbolmyristate-13-acetate (PMA) to initiate the oxidative burst activate (-)-trans-7,8-dihydroxy-7,8- dihydrobenzo[a]pyrene [(-)-BP-7,8-diol)] to DNA-binding intermediates. The 32P-postlabelling technique and HPLC-analysis of enzyme-digested DNA were employed for identification of DNA-adducts following incubation of (-)-BP-7,8-diol in PMNs. The results are consistent with the formation of (+)-anti-BPDE, the ultimate carcinogen of BP, bound via trans-addition of the C-10 position in the diol epoxide molecule to the exocyclic nitrogen of deoxyguanosine (BPDE-N2-dG adduct). Addition of nitrite, the major aqueous dissolution product of NO2, stimulated the formation of (+)-anti-BPDE and subsequent binding to both nuclear DNA in PMNs (about twofold) and to DNA present outside the cells (two- to fourfold). Preliminary experiments suggest that nitrite stimulates the metabolism of (-)-BP-7,8-diol by direct interaction with myeloperoxidase and hydrogen peroxide. Consistent with previous work by us and others, the covalent binding of (+)-anti-BDPE to extracellular targets demonstrate that these reactive products, expected to be formed intracellularly, can be released from the leukocytes. Measurement of hydroxyl radical-induced DNA damage by estimating the formation of 8-hydroxydeoxyguanosine (8-OH-dG) in resting PMNs revealed low amounts of adducts (1 adduct/10(6) dG-1 adduct/10(5) dG). Pretreating the cells with PMA or PMA in conjunction with nitrite had no significant effect on 8-OH-dG adduct formation.