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


METHODS
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-1 was examined using an enzyme immunoassay.


RESULTS
Both neutrophil adhesion and ICAM-1 expression enhanced by high insulin (100 microU/ml, 48 h) were attenuated by gliclazide (20 microM), 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 (1 microM), 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-1 expression enhanced by hyperinsulinemia. These effects of gliclazide are mediated through inhibiting activation of MAP kinase and PKC, unrelated to NO production.
Okouchi
Masahiro
M
Department of Internal Medicine and Bioregulation, Nagoya City University Graduate School of Medical Sciences, 467-8601, Mizuho, Japan. okochi@pg8.so-net.jp
Okayama
Naotsuka
N
Omi
Hitoshi
H
Imaeda
Kenro
K
Fukutomi
Tatsuya
T
Nakamura
Atsushi
A
Itoh
Makoto
M
D002448:Cell Adhesion; D002478:Cells, Cultured; D003920:Diabetes Mellitus / Q000188:drug therapy; D042783:Endothelial Cells / Q000187:drug effects*; D004730:Endothelium, Vascular / Q000166:cytology; D005907:Gliclazide / Q000494:pharmacology*; D006801:Humans; D007004:Hypoglycemic Agents / Q000494:pharmacology; D007124:Immunoenzyme Techniques; D007328:Insulin / Q000378:metabolism*; D018799:Intercellular Adhesion Molecule-1 / Q000378:metabolism; D020935:MAP Kinase Signaling System; D009504:Neutrophils / Q000187:drug effects* / Q000378:metabolism; D009569:Nitric Oxide / Q000378:metabolism; D015221:Potassium Channels / Q000378:metabolism; D011493:Protein Kinase C / Q000037:antagonists & inhibitors*; D014471:Umbilical Veins / Q000166:cytology
D007004:Hypoglycemic Agents; D007328:Insulin; D015221:Potassium Channels; D018799:Intercellular Adhesion Molecule-1; D009569:Nitric Oxide; D011493:Protein Kinase C; D005907:Gliclazide