Analysis of the urinary glucose-[15N, 15N]-ureide content in the study of the lactose-[15N, 15N]-ureide metabolism in healthy humans

Background/Objectives: Lactose-[N-15, N-15]-ureide is used to study the fate of the colonic urea-nitrogen metabolism. During the passage through the gastrointestinal tract, lactose ureide is hydrolysed to glucose ureide, which is absorbed to a limited extent from the small intestine and is excreted urinarily. In the present study, a procedure has been developed to quantify the urinary excretion of glucose-[N-15, N-15]-ureide. In addition, urine and faecal samples obtained during a dietary intervention study with the prebiotic lactulose were retrospectively analysed. Subjects/Methods: The glucose ureide and lactose ureide content was measured by GC-MS in 19 healthy volunteers. After consumption of a standard test meal containing 75mg lactose-[N-15, N-15]-ureide, six healthy volunteers performed a fractionated 24 h urine collection to investigate the urinary excretion of glucose-[N-15, N-15]-ureide. In 13 volunteers, the effect of lactulose administration on the urinary excretion of glucose-[N-15, N-15]-ureide was analysed. Results: The urinary excretion of glucose-[N-15, N-15]-ureide reached its maximum level in the 3-6 h urine collection and decreased in the 6-9 h urine. The label was still detectable in the 9-24 h urine collection. The cumulative excretion of N-15-labelled glucose ureide after 24 h amounted 12.91%. No significant differences in glucose-[N-15, N-15]-ureide excretion were found in either of the urine fractions after administration of lactulose, compared with baseline. In none of the urine samples lactose-[N-15, N-15]-ureide was detected. Conclusions: In conclusion, the results obtained in the present study indicated that the percentage dose glucose-[N-15, N-15]-ureide recovered in urine is rather constant and not influenced by the presence of lactulose. European Journal of Clinical Nutrition (2011) 65, 959-964; doi:10.1038/ejcn.2011.63; published online 11 May 2011