INCREASED RATE OF SIALYLATION OF COLONIC MUCIN BY CULTURED ULCERATIVE-COLITIS MUCOSAL EXPLANTS

Sialylation of mucus glycoproteins confers charge and increased resist ance to enzymatic degradation. The hypothesis that mucus sialylation m ight be altered in ulcerative colitis has been studied using in vitro culture of mucosal biopsies for 24 h with H-3 N-acetyl mannosamine as a specific sialic acid precursor. Rectal biopsies were obtained at col onoscopy from patients with clinically inactive ulcerative colitis (n = 9) and controls (n = 12) who were patients found to have a normal co lonoscopy performed for iron deficiency anaemia or altered bowel habit . The incorporation of H-3 N-acetyl mannosamine into mucin was increas ed in ulcerative colitis (n = 9; 150; 113.3-393.2 dpm/mu g mucin, medi an and interquartile ranges), compared with controls (n = 12; 33.6; 19 .7-68.4 dpm/mu g; p < 0.01). The ratio of incorporation into mucin of H-3 N-acetyl mannosamine/C-14 N-acetyl galactosamine was also increase d in ulcerative colitis (3.27; 1.93-4.98 dpm/dpm), compared with contr ols (1.35; 1.24-1.7 dpm/dpm; p < 0.001) suggesting that the increased incorporation of N-acetyl mannosamine probably reflects an increase in the average extent of sialylation per mucin oligosaccharide chain rat her than an increase in the number of oligosaccharide chains. This inc rease in mucin sialylation seems unlikely to have a pathogenic role in the development of colitis but provides further evidence for the simi larity between the alterations that occur in ulcerative colitis, colon ic polyposis and malignancy.