Qualitative and quantitative changes in sialomucins during 1,2-dimethylhydrazine-induced colon carcinogenesis in the rat.

Regional differences in goblet cell glycoproteins have been demonstrated qualitatively and, to a limited extent, quantitatively in the normal adult colon. In disease states, alterations in these glycoproteins, particularly the sialoglycoproteins (SGs), have been reported. The present study defined parallel qualitative and quantitative changes in SGs in three colon regions during 1,2-dimethylhydrazine [(DMH) CAS: 540-73-8]-induced carcinogenesis. SGs were assessed histochemically by use of high iron diamine-Alcian blue (pH 2.5) staining, and tissue sialic acid levels were measured by a modified Warren assay. Two groups of inbred SD rats (n = 28) were pair-fed nutritionally complete liquid diets with 36% of calories supplied as ethanol or isocaloric carbohydrates. The dietary alcohol was added to selectively enhance rectal tumors, a region of prevalent tumors in humans. Both groups received 4 weeks of liquid diet followed by 4 weeks of standard laboratory chow with weekly sc injections of DMH. This 8-week cycle was repeated four times (32 wk). Animals from each group were sacrificed at 8, 16, 24, and 32 weeks, and adjacent tissues from proximal and distal colon and rectum were prepared for histology and biochemical assay. The results showed a progressive increase in sialomucin staining in normal-appearing mucosa in distal colon and rectum in both groups but not in the proximal colon. In contrast, tissue sialic acid increased in all three regions as early as 8 weeks, and significant increases were consistently present by 32 weeks. A different pattern was observed in tissue from frank tumors. Compared with normal-appearing mucosa, both sialomucin staining and tissue sialic acid levels were reduced in tumor tissue by 32 weeks. These studies indicated that tissue sialic acid levels may provide a simple and reliable screening technique in the early diagnosis of premalignant change in all regions of the colon.