Hyperglycemia-Induced Protein Kinase C Activation Inhibits Phagocytosis of C3b- and Immunoglobulin G–Opsonized Yeast Particles in Normal Human Neutrophils

The aim of this study was to investigate the effects of elevated glucose concentrations on complement receptor- and Fcgamma receptor-mediated phagocytosis in normal human neutrophils. D-Glucose at 15 or 25 mM dose-dependently inhibited both complement receptor- and Fcgamma receptor-mediated phagocytosis, as compared to that at a normal physiological glucose concentration. The protein kinase C (PKC) inhibitors GF109203X and Go6976 both dose-dependently and completely reversed the inhibitory effect of 25 mM D-glucose on phagocytosis. Complement receptor-mediated phagocytosis was dose-dependently inhibited by the cell permeable diacylglycerol analogue 1,2-dioctanoyl-sn-glycerol (DAG), an effect that was abolished by PKC inhibitors. Furthermore, suboptimal inhibitory concentrations of DAG and glucose showed an additive inhibitory effect on complement receptor-mediated phagocytosis. The authors conclude that elevated glucose concentrations can inhibit complement receptor and Fcgamma receptor-mediated phagocytosis in normal human neutrophils by activating PKCalpha and/or PKCbeta, an effect possibly mediated by DAG.