Protective actions of gliclazide on high insulin-enhanced neutrophil-endothelial cell interactions through inhibition of mitogen activated protein kinase and protein kinase C pathways

Background and aim: There are many lines of evidence indicating that hyperinsulinemia but not hyperglycemia is linked to the development of atherosclerotic diseases such as coronary events in diabetic patients. K-ATP channel blockers of the sulphonylurea class are used widely to treat type 2 diabetes mellitus even with hyperinsulinemia. In this study, we determined whether K-ATP channel blockers can protect against atherosclerotic processes enhanced by hyperinsulinemia, namely leukocyte-endothelial cell interactions. In addition, we characterized the intracellular mechanisms involved in protective actions of the K-ATP channel blocker(s). Method: Studies of adhesion between neutrophils and human umbilical vein endothelial cells incubated in insulin-rich medium with or without K-ATP channel blockers were performed. Adhered neutrophils were quantified by measuring their myeloperoxidase activities, and surface expression of endothelial ICAM-I was examined using an enzyme immunoassay. Results: Both neutrophil adhesion and ICAM-1 expression enhanced by high insulin (100 muU/ml, 48 h) were attenuated by gliclazide (20 muM), but not by other K-ATP channel blockers (glibenclamide, nateglinide, and glimepiride). In addition, both neutrophil adhesion and ICAM-1 expression which were increased by a MAP kinase activator, anisomycin (I muM), or a PKC activator, phorbol 12-myristate 13-acetate (10 nM) were also attenuated by gliclazide. Nitric oxide (NO) synthase inhibitors did not affect these effects of gliclazide. Conclusions: These results suggest that among K-ATP channel blockers, only gliclazide can act directly on endothelial cells to inhibit neutrophil-endothelial cell adhesion and ICAM-I expression enhanced by hyperinsulinemia. These effects of gliclazide are mediated through inhibiting activation of MAP kinase and PKC, unrelated to NO production. (C) 2003 Elsevier Inc. All rights reserved.