Brain distribution and metabolic profiling of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone in rats investigated by UHPLC-HRMS/MS following peripheral administration.

4-(Methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) is known to be a tobacco-specific N-nitrosamine and has peripheral carcinogenic properties. It can also induce oxidative stress, glial cell activation, and neuronal damage in the brain. However, the distribution and metabolic characteristics of NNK in the central nervous system are still unclear. Here, a sensitive and effective UHPLC-HRMS/MS method was established to identify and investigate the metabolites of NNK and their distribution in the rat brain. In addition, the pharmacokinetic profiles were simultaneously investigated via blood-brain synchronous microdialysis. NNK and its seven metabolites were well quantified in the hippocampus, cortex, striatum, olfactory bulb, brain stem, cerebellum, and other regions of rat brain after peripheral exposure (5 mg/kg, i.p.). The average content of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL) in all brain regions was at least threefold higher than that of NNK, indicating a rapid carbonyl reduction of NNK in the brain. Lower concentrations of pyridine N-oxidation products in the cortex, olfactory bulb, hippocampus, and striatum might be related to the poor detoxification ability in these regions. Compared to α-methyl hydroxylation, NNK and NNAL were more inclined to the α-methylene hydroxylation pathway. Synchronous pharmacokinetic results indicated that the metabolic activity of NNK in the brain was different from that in the blood. The mean α-hydroxylation ratio in the brain and blood was 0.037 and 0.161, respectively, which indicated poor metabolic activity of NNK in the central nervous system.