CATHEPSIN-B IN ANGIOGENESIS OF HUMAN PROSTATE - AN IMMUNOHISTOCHEMICAL AND IMMUNOELECTRON MICROSCOPIC ANALYSIS

Background: Angiogenesis (or neovascularization) is required for the g rowth of solid organ tumors and precedes invasion of the adjacent stro ma by neoplastic cells. We investigated the relative density and distr ibution of cathepsin B (CB) immunostained microvessels (i.e., small bl ood vessels and capillaries) in benign prostatic hyperplasia (BPH), pr ostatic intraepithelial neoplasia (PIN), and prostatic adenocarcinoma (CAP) by immunocytochemical localization of an antibody directed again st a cathepsin B-derived synthetic peptide (Syn-CB). Methods: We studi ed 16 formalin-fixed, prostatectomy specimens that were embedded in pa raffin/paraplast for histological examination by hematoxylin and eosin anti immune-localization of the Syn-CB antibody. Selected paraformald ehyde-fixed specimens were embedded in K4M Lowicryl or LRWhite resins. We localized the antibody in thin sections using immunoelectron micro scopy techniques. Results: Eight patients had BPH [4 patients with BPH alone, 2 with BPH and PIN, and 2 with BPH and CAP]. Ten cancer cases included one with Gleason histologic score 4, two with score 6, four w ith score 7, and three with score 8. In CAP cases, Gleason score 6 and 7 tumors had more microvessels than the score 4 or 8 tumors. In both BPH and CAP cases, the antibody was localized chiefly in the endotheli al cells of microvessels, but occasionally in ductal and glandular epi thelial cells. Ultrastructurally, CB-immunoreactive gold particles wer e markedly increased at the luminal and basal plasma membrane surfaces and folds of endothelial cells in neoplastic prostate, but not in til e endothelial cells of BPH. Furthermore, the presence of CB localizing gold particles in collagen and smooth muscle fibers near the microves sels indicated leakage of the enzyme in prostatic stroma of neoplastic prostate. Similar leakage was not observed in BPH. Morphometric analy sis showed that the relative density of microvessels increased two to three times in cancer patients when compared to patients with BPH alon e. Our study also indicated that BPH associated with PIN or CAP had an increased density of microvessels when compared to BPH alone. Conclus ions: Our study showed that the relative density and distribution of m icrovessels are the most important features of neovascularization in p rostatic tumors. The relative density of microvessels increased in PIN and CAP when compared to BPH alone. Although the localization of CB i s associated with lysosomes of endothelial cells in both BPH and CAP, there is a greater association of CB with the plasma membranes of endo thelial cells in CAP than BPH. Immunoelectron microscopy provided evid ence that CB might be involved in dissolution of basement membranes in neoplastic tumors during angiogenesis. CB localization has the potent ial of defining a role for this protease in degradation of extracellul ar matrix constituents during early steps of angiogenesis. (C) 1995 Wi ley-Liss, Inc.