cathepsin-g and Diabetes-Mellitus

Transient alkalization caused by activation of the BK(Ca) channels has been reported to be essential for the activation of proteolytic enzymes and bacterial killing in the leukocytic phagosomes. We investigated the effects of high glucose concentrations on these processes in THP-1 cells. While E. coli transiently raised the pH of the phagosomes in THP-1 monocytes, high glucose concentrations impaired the transient rise of pH in a dose-and time-dependent manner. Electrophysiological studies confirmed that the bacteria elicited a transient K+ current, and that a high glucose concentration diminished the current. High glucose concentrations also inhibited the activation of cathepsin G in the THP-1 cells. NS1619, a BK(Ca) channel opener, accentuated the transient alkalization induced by the bacteria, and reversed the inhibitory effect of high concentrations of glucose. However, electrophysiological study revealed that the membrane current differed from the BK(Ca) current. Our findings indicate that high glucose concentrations impair K+ channel activation and the subsequent activation of proteolytic enzymes in THP-1 monocytes. The precise identity of the K+ channel remains unclear, although it dose not appear to be the BK(Ca). Suppression of the transient alkalization and activation of proteases may be one of the mechanisms for bacterial killing by phagocytes in diabetic patients.

Topics: Cathepsin G; Cathepsins; Cells, Cultured; Diabetes Mellitus; Enzyme Activation; Escherichia coli; Glucose; Humans; Hydrogen-Ion Concentration; Hyperglycemia; Monocytes; Phagosomes; Potassium Channels, Calcium-Activated; Serine Endopeptidases; Th1 Cells

Reduced bacterial killing by polymorphonuclear leucocytes has been reported in patients with diabetes mellitus. Whether this is due to reduced content of bactericidal granular proteins has not been determined. We therefore immunochemically measured the content of myeloperoxidase, lactoferrin, lysozyme, cathepsin G and elastase in polymorphonuclear leucocytes from 50 insulin-treated diabetic patients. The peroxidase activity was also measured. Normal contents of myeloperoxidase and lactoferrin as well as normal peroxidase activity were found. The average contents of cathepsin G, elastase and lysozyme were 2.5, 3.2 and 2.6 micrograms/10(6) polymorphonuclear leucocytes, respectively, and thus 14, 45 and 18% higher than the contents of normal polymorphonuclear leucocytes. The results indicate that reduced intracellular killing of bacteria demonstrated in previous studies in diabetic patients does not appear to be related to a reduction in the content of bactericidal proteins.

Topics: Age Factors; Blood Bactericidal Activity; Cathepsin G; Cathepsins; Diabetes Mellitus; Humans; Lactoferrin; Muramidase; Neutrophils; Pancreatic Elastase; Peroxidase; Serine Endopeptidases; Time Factors