The occurrence of tobacco-specific nitrosamines in oral tobacco products and their potential formation under simulated gastric conditions.

The levels of the tobacco-specific nitrosamines: N-nitrosoanabasine, N-nitrosoanatabine, N-nitrosonornicotine and 4-(N-nitrosomethylamino)-1-(3-pyridyl)-1-butanone in a variety of chewing tobaccos, oral snuffs, masheri and zarda samples were determined. The potential endogenous formation of tobacco-specific nitrosamines was estimated by incubation of tobacco samples at pH 2.0 for 1 hr at 37 degrees C and over the pH range 1.0 to 5.5 under conditions simulating the normal fasting stomach, with a constant nitrite concentration of 25 microM. Under the simulated gastric conditions, N-nitrosoanabasine, N-nitrosoanatabine and N-nitrosonornicotine were formed, and maximum formation of these tobacco-specific nitrosamines occurred at pH 2.5. Nicotine, the major alkaloid present in tobacco and precursor to N-nitrosonornicotine and 4-(N-nitrosomethylamino)-1-(3-pyridyl)-1-butanone, was not nitrosated. The formation of N-nitrosonornicotine resulted from nitrosation of nornicotine, another alkaloid also present in tobacco. Under the acidic simulated gastric conditions, slight decomposition of 4-(N-nitrosomethyl-amino)-1-(3-pyridyl)-1-butanone via transnitrosation was observed.