EVIDENCE FOR ENDOGENOUS FORMATION OF TOBACCO-SPECIFIC NITROSAMINES INRATS TREATED WITH TOBACCO ALKALOIDS AND SODIUM-NITRITE

Carcinogenic tobacco-specific nitrosamines are present in tobacco prod ucts and are believed to play a significant role in human cancers asso ciated with tobacco use. Additional amounts of tobacco-specific nitros amines could be formed endogenously, We tested this hypothesis by trea ting rats with nicotine and sodium nitrite and analyzing their urine, Initially, we treated groups of rats with (S)-nicotine (60 mu mol/kg) and NaNO2 (180 mu mol/kg), (S)-nicotine alone, NaNO2 alone or 4-(methy lnitrosamino)-1-(3-pyridyl)-1-butanol (NNK, 12 nmol/kg) by gavage twic e daily for 4 days, We collected urine and analyzed for two metabolite s of NNK; 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol and its glucur onide. We did not detect these metabolites in the urine of rats treate d with nicotine alone or nicotine plus NaNO2, indicating that endogeno us conversion of nicotine to NNK did not occur, However, the urine did contain N'-nitrosonornicotine (NNN), N'-nitrosoanabasine (NAB) and N' -nitrosoanatabine (NAT), Analysis of the (S)-nicotine used in this exp eriment demonstrated that it contained trace amounts of nornicotine, a nabasine and anatabine, In a second experiment, we used an identical p rotocol to compare the endogenous nitrosation of this (S)-nicotine wit h that of synthetic (R,S)-nicotine, which did not contain detectable a mounts of nornicotine, anabasine or anatabine, NNN (0.53x10(-3)% of ni cotine dose), NAB (0.68%) and NAT (2.1%) were detected in the urine of the rats treated with the (S)-nicotine and NaNO2. NNN (0.47x10(-3)% o f dose), but not NAB or NAT, was present in the urine of the rats trea ted with synthetic (RS)-nicotine and NaNO2, NNN probably formed via ni trosation of metabolically formed nornicotine. These results demonstra te for the first time that endogenous formation of tobacco-specific ni trosamines occurs in rats treated with tobacco alkaloids and NaNO2, Th e potential significance of the results with respect to nitrosamine fo rmation in people who use tobacco products or nicotine replacement the rapy is discussed.