Glycoprotein composition of colonic mucosa. Specific alterations in ulcerative colitis

Abstract

A micromethod has been developed to permit determination of human colonic mucin glycoprotein heterogeneity in biopsy specimens of colonic mucosa. Sialic acid, galactose, and galactosamine residues of oligosaccharide side chains from colonic glycoproteins were radiolabeled by combined metaperiodate and galactose oxidase treatment followed by sodium borotritide reduction. Mucin glycoproteins were separated from nonmucin components by mini-Sepharose 4B column chromatography. Subsequent chromatography of labeled mucin of normal controls (n = 15) on diethylaminoethyl-cellulose demonstrated at least six labeled mucin species. Labeled mucin species I-VI were found to cochromatograph with corresponding unlabeled mucin species prepared from large surgical specimens. An identical mucin profile was observed in normal biopsy specimens from rectum (n = 5), sigmoid (n = 10), transverse (n = 5), and ascending colon (n = 4). However, mucin profiles from sigmoid mucosa of patients with ulcerative colitis (n = 14) demonstrated a selective decrease in mucin species IV, which was also present in specimens from uninvolved proximal colon (n = 7). This finding persisted in patients who had a subsequent biopsy at times of clinical and histologic remission (n = 8). In addition, colonic mucin from samples of ulcerative colitis patients in remission had a relative decrease in mucin fraction III and an increase in fraction V when compared to patients with active disease. Normal mucin profiles were found in a variety of colonic disease controls including Crohn's (n = 9), ischemic (n = 4), infectious (n = 8), and radiation (n = 3) colitis. These observations indicate the presence of a relatively uniform mucin profile throughout the normal colon and substantiate the association of specific alterations in colonic mucin with ulcerative colitis.