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

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 microns/mole creatinine in the tobacco + lime group, 3.55 +/- 1.22 microns/mole creatinine in the betel quid tobacco group, 4.72 +/- 1.35 microns/mole creatinine in the betel quid group while levels were 3.34 +/- 0.83 microns/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.