Decreased incorporation of 14C-glucosamine relative to 3H-N-acetyl glucosamine in the intestinal mucosa of patients with inflammatory bowel disease.

The synthesis of glycoproteins was investigated in intestinal mucosa from patients with inflammatory bowel disease (IBD) and from those with various other conditions. The incorporation into acid-insoluble macromolecules of the amino sugar glucosamine, the first and committed metabolite in the biosynthetic sequence, and its immediate derivative, N-acetyl glucosamine was determined. Tissue was incubated with 1-2 nmol 14C-glucosamine and 3H-N-acetyl glucosamine and the simultaneous incorporation of both isotopes was measured. Bowel tissue from areas microscopically uninvolved in active disease process was examined. Values for the incorporation of both substrates into acid-soluble constituents were similar for both IBD and non-IBD groups, as was also the incorporation of 3H into acid-insoluble constituents. The incorporation of 14C, however, when expressed relative to that of 3H in each individual patient, i.e., 14C/3H, was distinctly different in IBD cases. In 26 non-IBD samples this ratio ranged from 0.04-0.26 with a mean of 0.097 +/- 0.009. In nine cases of Crohn's disease values ranged from 0.013-0.06 with a mean of 0.039 +/- 0.011 (p less than 0.01); in nine cases of ulcerative colitis values were 0.007-0.06 with a mean of 0.031 +/- 0.006 (p less than 0.01). It is concluded that the step involving the N-acetylation of the amino sugar is relatively deficient in patients with IBD and this could reduce the synthesis of the glycoprotein cover which protects the mucosa from damage by bowel contents.