Effect of phytochemical intervention on dibenzo[a,l]pyrene-induced DNA adduct formation.

Dibenzo[a,l]pyrene (DBP) has been found to be the most potent carcinogen of the polycyclic aromatic hydrocarbons (PAHs). Primary sources for DBP in the environment are combustion of wood and coal burning, gasoline and diesel exhaust, and tires. Given the likelihood of environmental exposure to DBP and strong experimental evidence of its potency, it is likely to contribute to lung cancer development. Intervention with compounds of natural origin ("phytochemicals") is considered an effective means to prevent cancer development and favorably modulate the underlying mechanisms, including DNA adduct formation. In this study, several agents have been identified that inhibit environmental carcinogen-induced DNA adduct formation using a cell-free microsomal system. Of the ten agents tested, resveratrol (648 ± 26 adducts/10(9) nucleotides), oltipraz (1007 ± 348 adducts/10(9) nucleotides), delphinidin (1252 ± 142 adducts/10(9) nucleotides), tanshinone I (1981 ± 213 adducts/10(9) nucleotides), tanshinone IIA (2606 ± 478 adducts/10(9) nucleotides) and diindoylmethane (3643 ± 469 adducts/10(9) nucleotides) were the most effective compared to vehicle treatment (14,062 ± 1097 adducts/10(9) nucleotides). DBP is metabolized by phase I metabolizing enzymes CYP1A1, CYP1A2, and CYP1B1. DBP-induced DNA adducts can be inhibited by several mechanisms. We found that all the test agents inhibited DNA adducts by inhibiting one or more of these enzymes. Oltipraz inhibited DNA adducts entirely by inhibiting the CYP450s, while resveratrol and delphinidin inhibited DNA adducts by also interacting directly with the carcinogenic metabolite, anti-dibenzo(a,l)pyrene-11,12-dihydrodiol-13,14-epoxide.