文摘
Tobacco smoking is one of the leading causes for oral cancer. Dibenzo[a,l]pyrene (DB[a,l]P), an environmental pollutant and a tobacco smoke constituent, is the most carcinogenic polycyclic aromatic hydrocarbon (PAH) tested to date in several animal models (target organs: skin, lung, ovary, and mammary tissues). We have recently demonstrated that DB[a,l]P is also capable of inducing oral cancer in mice; however, its metabolic activation to the ultimate genotoxic metabolite dibenzo[a,l]pyrene-11,12-dihydrodiol-13,14-epoxide (DB[a,l]PDE) in mouse oral cavity has not been examined. Here we developed a liquid chromatography鈥搕andem mass spectrometry (LC-MS/MS) method to detect and quantify (卤)-anti-DB[a,l]PDE-dA adducts in oral tissues of mice treated with DB[a,l]P. [15N5]-(卤)-anti-DB[a,l]PDE-N6-dA adducts were synthesized as internal standards. The stereoisomeric adducts were characterized by MS, NMR, and CD analysis. The detection limit of the method is 8 fmol with 100 渭g of digested DNA as the matrix. Two adducts were detected and identified as (鈭?-anti-cis and (鈭?-anti-trans-DB[a,l]PDE-dA in the oral tissues of mice following the direct application of DB[a,l]P (240 nmol per day, for 2 days) into the oral cavity, indicating that DB[a,l]P is predominantly metabolized into (鈭?-anti-DB[a,l]PDE in this target organ. We also compared the formation and removal of adducts as a function of time, following the direct application of DB[a,l]P (24 nmol, 3 times per week for 5 weeks) into the oral cavity of mice. Adducts were quantified at 48 h, 1, 2, and 4 weeks after the last dose. Maximal levels of adducts occurred at 48 h, followed by a gradual decrease. The levels (fmol/渭g DNA) of (鈭?-anti-trans adducts (4.03 卤 0.27 to 1.77 卤 0.25) are significantly higher than (鈭?-anti-cis-DB[a,l]PDE-dA adduct (1.63 卤 0.42 to 0.72 卤 0.04) at each time point (p < 0.005). The results presented here indicate that the formation and persistence of (鈭?-anti-DB[a,l]PDE-dA adducts may, in part, contribute to the initiation of DB[a,l]P-induced oral carcinogenesis.
