Activation of N'-nitrosonornicotine by hydrogen peroxide in vitro

Betel-quid ingredients were found to produce reactive oxygen species, such as superoxide anion and hydrogen peroxide, in vitro. We demonstrated that N'-nitrosonornicotine (NNN) can be converted to its active metabolite, hydrogen peroxide, nonenzymatically in the presence of ferrous ions and ethylenediaminetetracetic acid (EDTA) at pH 7.2. Three ultimate metabolites of NNN--NNN-1-N-oxide, 4-hydroxy-4-(3- pyridyl)butyric acid and 4-oxo-4-(3-pyridyl)butyric acid--and nornicotine were detected by high-performance liquid chromatography. 3H-NNN and 14C-NNN interact with calf thymus DNA in the presence of hydrogen peroxide, ferrous ion and EDTA. The results suggest that formation of reactive oxygen species in the presence of NNN may be a key factor in the initiation of oral tumours in tobacco and betel-quid chewers.