Endogenous formation of N-nitrosoproline and other N-nitrosamino acids in tobacco users

Abstract The endogenous formation of N -nitroso compounds in tobacco users, namely chewers of tobacco + lime, betel quid with tobacco, and without tobacco, was determined by N -nitrosoproline test. Twenty-four- or six-hour urine samples were collected from volunteers for 3 days: day 1 without proline, day 2 after ingesting 100 mg proline three times a day and day 3 after ingesting 100 mg proline together with 100 mg ascorbic acid three times a day. The urine samples were analysed for the following N -nitrosamino acids: N -nitrosoproline, N -nitrososarcosine, N -nitrosopropionic acid, N -nitrosobutyric acid, N -nitrosothiozolidine-4-carboxylic acid, and N -methyl nitrosothiozolidine-4-carboxylic acid using gas chromatography-thermal energy analyser. It was observed that chewers of tobacco + lime excreted high basal levels of N -nitrosoproline on day 1 as compared with betel quid chewers with tobacco and without tobacco and those in the ‘no habit’ group. Levels of N -nitrosoproline on day 2 were 15.14 ± 4.51 μm/mole creatinine in the tobacco + lime group, 3.55 ± 1.22 μm/mole creatinine in the betel quid tobacco group, 4.72 ± 1.35 μm/mole creatinine in the betel quid group while levels were 3.34 ± 0.83 μm/mole creatinine in the ‘no habit’ group. A decrease in the N -nitrosoproline levels was observed in all the four groups on ingestion of ascorbic acid. This preliminary study suggests that there is a statistically significant increase in endogenous nitrosation in tobacco + lime chewers as compared with those with no habit, and ascorbic acid has an anti-nitrosating action in vivo.