Effects of insulin on N-formyl-methionyl-leucyl-phenylalanine (fMet-Leu-Phe)-stimulated production of reactive oxygen metabolites from normal human neutrophils.

Abstract

To further understand the mechanisms behind defective neutrophil function in diabetes mellitus, the ability of insulin to affect the production and metabolism of reactive oxygen metabolites in normal human neutrophils was studied. Neutrophil granulocytes from healthy adults were studied for their N-formyl-methionyl-leucyl-phenylalanine (fMet-Leu-Phe)-stimulated production of reactive oxygen metabolites and release of myeloperoxidase or elastase following treatment with insulin. Preincubation of the neutrophils for 30 min with insulin (40-320 microU/ml), before activation with 1 microM fMet-Leu-Phe, revealed that the hormone at 80 and 160 microU/ml reduced the luminol-enhanced chemiluminescence without affecting the superoxide secretion. The insulin-induced reduction of the chemiluminescence response was reversed by the addition of exogenous peroxidase and was also paralleled by a reduced myeloperoxidase activity, with no effect on the elastase activity, in cell-free supernatants from fMet-Leu-Phe-stimulated neutrophils. Superoxide dismutase removed the inhibitory effect of insulin on myeloperoxidase activity. These results suggest that elevated levels of insulin do not affect the NADPH-oxidase activity but, together with superoxide anions, interfere with myeloperoxidase availability and a subsequent myeloperoxidase-dependent generation of reactive oxygen metabolites in fMet-Leu-Phe-stimulated normal human neutrophils.