Increase in the levels of N-nitrosoproline, N-nitrosothioproline and N-nitroso-2-methylthioproline in human urine by cigarette smoking

The effects of cigarette smoking on the urinary excretions of N-nitrosoproline (NPRO) and the sulfur-containing N-nitrosamino acids, N-nitrosothioproline (NTPRO) and N-nitroso-2-methylthioproline (NMTPRO), in a male volunteer were examined. This subject smoked for 20 non-consecutive days and did not smoke for another 20 non-consecutive days during a 4-month-period, and 24-h urine samples were collected. On the days of urine collection, he was given a fixed diet. On the smoking days, the urinary levels of NPRO, NTPRO and NMTPRO increased significantly from 1.1 +/- 0.5 (mean +/- S.D.) micrograms/day to 1.8 +/- 0.9 (P less than 0.01), from 3.9 +/- 1.1 to 8.7 +/- 4.6 micrograms/day (P less than 0.001), and from 5.6 +/- 1.9 to 8.5 +/- 4.1 micrograms/day (P less than 0.01), respectively. Thus, the total amount of these 3 N-nitrosamino acids in the urine also increased significantly by smoking from 10.6 +/- 2.8 to 19.0 +/- 6.5 micrograms/day (P less than 0.001). These results indicated that NOx in cigarette smoke can contribute to in vivo formation of N-nitroso compounds.