SUCRASE-ISOMALTASE AND OTHER BRUSH-BORDER GLYCOSIDASES IN COLORECTAL TUMORS

Sucrase-isomaltase (SI), trehalase (T) and lactase-beta-glucosidase (L G) activities were assessed histochemically in samples of colorectal a denomas (11 tubular, 12 tubulovillous, 10 villous) and 30 adenocarcino mas obtained by biopsy during colonoscopy or from specimens removed by surgical intervention. Small samples of tumor tissue, tissue of the t ransitional zone and of macroscopically normal mucosa were quenched in heptan cooled in an acetone-dry ice mixture. Cryostat sections, trans ferred to non-precooled slides and in some cases to semipermeable memb ranes, 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-indox yl alpha-D-glucosides, trehalose, and 5-Br-4-Cl-3-indoxyl-beta-D-fucos ide were used as substrates. Sections of jejunal biopsies with normal activities of brush border glycosidases were used as controls. From sa mples 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 thei r supernatants subjected to isoelectric focusing on polyacrylamide gel plates. Zymograms were developed with the same methods as for the det ection of alpha-glucosidases in sections. In no colorectal tumor LG wa s present. SI was found in 70% adenocarcinomas, 50% villous, 25% tubul ovillous and 19% tubular adenomas when the method with sucrose, glucos e oxidase-peroxidase and 3,3'-diaminobenzidine was used. Hardly discer nible traces of activity were found in tumors with ate-coupling reacti ons applied at pH 5, 6 and 6.5. No reaction was detected with the indi gogenic method applied at pH above 6.0. However, jejunal biopsies disp layed very strong reactions confined to the brush border of enterocyte s 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 (particuarly at pH 5.0). In this case the dep osition 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 dete cted in the same tumors as SI; its activity was lower, however. SI act ivity in colorectal tumors is a useful, but not general marker of thes e tumors.