Effects of Black Raspberry on Dibenzo[a,l]Pyrene Diol Epoxide Induced DNA Adducts, Mutagenesis and Tumorigenesis in the Mouse Oral Cavity

We previously showed that metabolic activation of the environmental and tobacco smoke constituent dibenzo[a,l]pyrene (DB[a,l]P) to its active fjord region diol epoxide (DB[a,l]PDE) is required to induce DNA damage, mutagenesis and squamous cell carcinoma (SCC) in the mouse oral cavity. In contrast to procarcinogens which were employed previously to induce SCC, DB[a,l]PDE does not require metabolic activation to exert its biological effects and thus, this study was initiated to examine, for the first time, whether black raspberry powder (BRB) inhibits post-metabolic processes such as DNA damage, mutagenesis and tumorigenesis. Prior to long-term chemoprevention studies we initially examined the effect of BRB (5% added to AIN-93M diet) on DNA damage in B6C3F1 mice using LC-MS/MS and on mutagenesis in the lacI gene in the mouse oral cavity. We showed that BRB inhibited DB[a,l]PDE-induced DNA damage (p<0.05) and mutagenesis (p=0.053) in the oral cavity. Tumor incidence in the oral cavity (oral mucosa and tongue) of mice fed diet containing 5% BRB was significantly (p<0.05) reduced from 93% to 66%. Specifically the incidence of benign tumor was significantly (p<0.001) reduced from 90% to 31% (62% to 28% in the oral cavity and 28% to 2% in the tongue); a non-significant reduction of malignant tumors from 52% to 45%. Our preclinical findings demonstrate for the first time that the chemopreventive efficacy of BRB can be extended to direct-acting carcinogens that do not require phase I enzymes and is not just limited to procarcinogens.

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