Cathepsin B (CB) and leukocyte elastase (LE) are proteolytic enzymes widely distributed among various cells and tissues of the human organism. They are also cointained within the azurophilic granules of polymorphonuclear leukocytes (PMN). These proteases play the essential role both in physiological and pathological processes. First of all CB participates in the turnover of proteins, while LE mainly in the non-specific host defence by degradation of engulfed microorganisms or cell debris. The pathological role of LE is mainly manifested in pathogenesis and development of diseases connected with inflammation, and CB - with the carcinoma progression. However both proteases participate in the diabetes development and formation of vascular late complications. The excessive rise in activity of these enzymes, their massive extracellularly release and translocation into cell surface are mainly observed in pathological states. Specific forms of proteases, which are expressed on the cell surface, show some different proprieties, but the most important is increased resistance to the action of endogenous inhibitors. This situation is characteristic for inflammatory diseases, e.g. diabetes, when PMNs are overactivated by higher level of glycaemia. There are informations about membrane expression on PMN such enzymes as LE, cathepsin G and proteinase 3, however not about cathepsin B. The activity of cell surface-bound CB was mainly studied in homogenates or sections of different tissues, but not in PMN’s fractions. Our previously investigations have shown enlarged activity and concentration, both CB and LE in type 2 diabetic patients, in the comparison with healthy persons, particularly in PMN. Now we estimated expression of membrane-bound cathepsin B (MBC) and leukocyte elastase (MBL) in the PMN’s fraction. We developed a modified method for membrane-bound forms of these proteases on the ground of activity measured by fluorimetric assays. PMNs were isolated from the blood, and then was fixed with the solution of PBS containig 3% paraformaldehyde and 1% glutaraldehyde. We also measured total activity of CB and LE in cellular lisates, obtained by homogenisation, as well as in plasma of the same patients. We compared these results with the control group. We noticed the essential increase, both the activity of cell surface-bound CB and LE, and the total activity of these proteases in cell’s lysates and plasma of diabetic patients compared to the control group. Moreover, the percentage participation of MBC and MBL in the total activity of these enzymes was larger in diabetics in comparison with healthy subjects, what confirmed PMNs stimulation. MBC and MBL showed also various degree of sensitivity to their specific endogenous inhibitors, while “typical” forms of CB and LE were almost completely inhibited.

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