QUANTITATIVE ESTIMATION OF ENDOGENOUS NITROSATION IN HUMANS BY MONITORING N-NITROSOPROLINE EXCRETED IN THE URINE

Abstract

Endogenous formation of N-nitrosoproline (NPRO) was demonstrated by monitoring its excretion in the urine of a male volunteer who had ingested vegetable juice as a source of nitrate and proline. The resulting NPRO was analyzed after derivatization by combined GLC thermal energy analysis. The amount of total NPRO excreted in the urine was proportional to the proline dose and increased exponentially with the nitrate dose ingested. Neither nitrate nor proline, when taken alone, led to a detectable increase in NPRO in urine. The amounts of NPRO formed (as estimated from the amounts excreted within 24 h) after dosing 325 mg nitrate (NO3-) followed by 500 mg proline, ranged from 16.6-30.0 (mean, 23.3) .mu.g per person. The simultaneous intake of ascorbic acid or .alpha.-tocopherol inhibited nitrosation of proline in vivo. Monitoring of NPRO or other N-nitroso compounds excreted in the urine thus appears to be a suitable procedure for estimating daily human exposure to endogenously formed N-nitroso compounds. [Monitoring of urinary levels of NPRO may be helpful for the quantitative estimation of nitrosation of carcinogens.].