Metabolism of glycosyl ureides by human intestinal brush border enzymes

13C-labeled glycosyl ureides were recently proposed as a new marker of the orocecal transit time: after passing the small bowel the sugar-urea bond is split by bacterial allantoicase. Further degradation results in 13CO2 which can be measured in the exhaled breath. The aim of this study was to detect an eventual allantoicase-like activity in the human gut and to elucidate the metabolism of glycosyl ureides by human intestinal brush border enzymes. Biopsies of 15 duodenal specimen and 6 colon specimen were homogenised and incubated with several disaccharides and their corresponding disaccharide ureides under various experimental conditions. Hydrolysis of the sugar-urea bond could not be observed neither in the small bowel nor in the colon. However, the conjugation between the two sugars was split. In a modified Dahlqvist assay lactase showed the same kinetics with lactose and lactose ureide as substrates whereas maltose showed a significantly 2.6-fold higher affinity to maltase than maltose ureide (P < 0.001). No major difference between these two substrates could be detected when total maltase activity was inhibited by acarbose. In summary, the human gut tissue possesses no allantoicase-like activity. Therefore, glycosyl ureides seem to be appropriate substances to test the orocecal transit time.