High urinary excretion of nitrate and N-nitrosoproline in opisthorchiasis subjects

About 50% of the population in some provinces of north-east Thailand are infested with liver fluke (Opisthorchis viverrini), and many develop cholangiocarcinoma subsequently. This study was designed to demonstrate possible endogenous formation of N-nitrosoproline (NPRO) in this population. Diet samples, saliva and urine were taken from subjects with and without liver fluke and analysed for nitrate and nitrite; urine was also analysed for NPRO. Nitrate and nitrite levels in saliva were higher in subjects with liver fluke than in those without; total nitrate and NPRO excretion was also higher in this group. Subjects with liver fluke may therefore be more heavily exposed to N-nitroso compounds than others, and may be at higher risk for cholangiocarcinoma.