Sucrase-isomaltase and other brush border glycosidases in colorectal tumors.

Sucrase-isomaltase (SI), trehalase (T) and lactase-beta-glucosidase (LG) activities were assessed histochemically in samples of colorectal adenomas (11 tubular, 12 tubulovillous, 10 villous) and 30 adenocarcinomas obtained by biopsy during colonoscopy or from specimens removed by surgical intervention. Small samples of tumor tissue, tissue of the transitional zone and of macroscopically normal mucosa were quenched in heptan cooled in an acetone-dry ice mixture. Cryostat sections, transferred to non-precooled slides and in some cases to semipermeable membranes, were dried and subjected to the histochemical reactions for SI, T and LG. Sucrose, 2-naphthyl, 6-Br-2-naphthyl, and 5-Br-4-Cl-3-indoxyl alpha-D-glucosides, trehalose, and 5-Br-4-Cl-3-indoxyl-beta-D-fucoside were used as substrates. Sections of jejunal biopsies with normal activities of brush border glycosidases were used as controls. From samples of 5 adenomas, 5 adenocarcinomas and collected rests of jejunal biopsies with a normal finding 10% (w/vol) homogenates in 2% Triton X-100 were prepared. Homogenates were frozen and thawed 3 times and their supernatants subjected to isoelectric focusing on polyacrylamide gel plates. Zymograms were developed with the same methods as for the detection of alpha-glucosidases in sections. In no colorectal tumor LG was present. SI was found in 70% adenocarcinomas, 50% villous, 25% tubulovillous and 19% tubular adenomas when the method with sucrose, glucose oxidase-peroxidase and 3,3'-diaminobenzidine was used. Hardly discernible traces of activity were found in tumors with azo-coupling reactions applied at pH 5, 6 and 6.5. No reaction was detected with the indigogenic method applied at pH above 6.0. However, jejunal biopsies displayed very strong reactions confined to the brush border of enterocytes under the same conditions. A strongly positive reaction was seen in 7 of 12 tumors investigated recently when the indigogenic reaction was applied at pH below 6.0 (particularly at pH 5.0). In this case the deposition of indigo was due to membrane and lysosomal alpha-glucosidases of the tumor cells and lysosomal alpha-glucosidase of macrophages and leukocytes. These findings were corroborated by zymograms. T was detected in the same tumors as SI; its activity was lower, however. SI activity in colorectal tumors is a useful, but not general marker of these tumors.