Influences of chronic alcohol consumption and critical enzyme regulation on the in vivo metabolism of NNK in mice
The progressive clarification of influential factors on the in vivo metabolism of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), one of the potent carcinogens in tobacco, could provide valuable information for precisely evaluating the health risk of tobacco products. The present study was designed to explore the influences of chronic alcohol consumption and critical enzyme regulation on NNK bioactivation in diverse animal models. The sensitive and rapid detection of NNK and its seven metabolites in mouse blood and tissues was achieved by UHPLC-HRMS method. Mouse models with alcohol-induced liver injury were then established and used to determine the variations of NNK metabolism due to organ damage caused by alcohol abuse. To study the role of mouse CYP2A5 in NNK metabolism, specific enzyme regulators (pyrazole and 5-methoxypsoralan) and Cyp2a5-null mouse were applied and compared. Furthermore, the effects of mouse DNA methyltransferase (DNMT) on the generation of DNA adduct (O6-mG) were investigated by using decitabine as a specific inhibitor. The results indicated that α-methylene hydroxylation was the major pathway of NNK metabolism in mice, and alcohol-induced liver injury significantly promoted the α-hydroxylation of NNK and the formation of O6-mG, which suggested that chronic alcohol consumption might increase the risk of carcinogenicity associated with NNK. Significant roles of CYP2A5 in NNK α-hydroxylation (especially α-methylene hydroxylation) was demonstrated through CYP2A5-regulated and Cyp2a5-null mouse models. It was also observed that DNMT activity was highly correlated to the generation of O6-mG through α-methylene hydroxylation. These finds revealed the critical factors influencing the in vivo bioactivation of NNK and rendered important references for the precise evaluation of NNK exposure risk via individual lifestyle and genetic profile.