Immunohistochemical localization of glutathione S-transferase-pi in human colorectal polyps

Abstract

Aim: To investigate the distribution of the placental form of glutathione-S-transferase (GST) in colon polyps in order to evaluate the role of GST-pi in these tissues.

Methods: Sixteen polyp tissues removed at colonoscopy were examined. Tissues were investigated histologically and ultrastructurally. GST-pi expression was also analysed immunohistochemically, using peroxidase anti-peroxidase (PAP) method and immunogold labelling method, for light and electron microscope respectively.

Results: All polyp tissues examined were adenoma of low, mild and high- grade dysplasia as shown in the histopathological reports. Nevertheless, the examination of the above specimens with electron microscope revealed that 3 of 9 adenoma of mild dysplasia had ultrastuctural features similar to high-grade dysplasia adenoma. GST-pi was variably expressed in adenoma, with the lowest relative levels occurring in low-grade adenoma and the highest levels found in high-grade adenoma. GST-pi was located mainly in undifferentiated epithelial cells. GST-pi positive particles were found in the cytoplasm and especially in the nucleus adjacent to the nuclear membrane of these cells.

Conclusion: The overexpression of GST-pi in mild-grade adenomas with significant subcellular changes and in the majority of high-grade dysplasia adenoma suggests that this might be related to the carcinogenetic proceeding. Immunohistochemical localization of GST-pi in combination with ultrastructural changes indicate that GST-pi might be a sensitive agent for the detection of preneoplastic transformations in adenoma.

Figure 1

Sections of human colorectal adenoma (HE, × 150). A: Low-grade dysplasia; B: Mild-grade dysplasia; C: High-grade dysplasia.

Figure 2

Transmission electron micrograph, routine double staining with uranyl acetate and lead citrate. Nucleus (N), nucleoli (n), mucus granules (m), microvilli (mv). A: From a low-grade dysplasia adenoma (× 5900), desmosomes (d); B: From a mild-grade dysplasia adenoma, desmosomes (arrows); C: From a mild-grade dysplasia tissue (× 11 700), free polyribosomes (arrows), basal lamina (bl); D: From a high-grade dysplasia adenoma (× 5900), intracellular junctions (arrows).

Figure 3

GST-pi positive cells (HE, × 100). A: In low-grade dysplasia colorectal adenoma; B: In mild-grade dysplasia colorectal adenoma, moderate immunoreactivity (a) and strong immunoreactivity (b); C: In high-grade dysplasia colorectal adenoma.

Figure 4

A: Electron micrograph from a mild-grade dysplasia adenoma showing GST-pi positive particles located in ribosomes and nucleus (arrows, × 42 000); B: Ultrathin section from a high-grade dysplasia adenoma showing GST-pi positive particles located in cytoplasmic membranes and nuclear membrane (with uranylacetate and lead citrate arrows, × 57 000).