Effect of cigarette smoking and dietary factors on the amount of N-nitrosothiazolidine 4-carboxylic acid and N-nitroso-2-methyl-thiazolidine 4-carboxylic acid in human urine

The effects of cigarette smoking and dietary factors on urinary excretion of N-nitrosothiazolidine 4-carboxylic acid (NTCA; N-nitrosothioproline) and N-nitroso-2-methylthiazolidine 4-carboxylic acid (NMTCA; N-nitroso-2-methylthioproline) were studied in a male volunteer and in healthy Japanese subjects from the general population and Seventh-Day Adventists (SDA). Twenty-four-hour urine samples from the male volunteer were collected on 20 smoking days and 20 nonsmoking days during ingestion of a fixed diet, and the amounts of urinary N-nitrosamino acids were analysed by gas chromatography-thermal energy analysis. Cigarette smoking caused about two-fold (significant) increases in the amounts of NTCA and NMTCA in the volunteer. In the male subjects from the general population, not controlled for diet, the amounts of NTCA and NMTCA in 24-h urines of smokers were also significantly higher than those of the nonsmokers. The urinary excretions of NTCA and NMTCA in SDA were lower than those of nonsmokers in the general population. It was concluded that cigarette smoking is one of the important factors in determining the amounts of NTCA and NMTCA in human urine. Dietary factors also apparently influence the urinary levels of these N-nitrosamino acids. In addition, an apparent sex difference in the urinary excretion of NTCA and NMTCA (about two-fold higher in females) was observed in the general population but not in SDA. The N-nitrosoproline (NPRO) level was significantly higher in SDA than in nonsmokers in the general population.