Carbon monoxide (from CORM-2) inhibits high glucose-induced ICAM-1 expression via AMP-activated protein kinase and PPAR-γ activations in endothelial cells

IntroductionHyperglycemia is a risk factor for cardiovascular complications in diabetic state. Hyperglycemia-induced oxidative stress up-regulates intracellular adhesion molecule-1 (ICAM-1) which aggravates endothelial dysfunction, although the underlying mechanisms remain unclear. We hypothesized that carbon monoxide (CO) attenuates ICAM-1 expression induced by high glucose in endothelial cells through activation of AMP-activated protein kinase (AMPK)/peroxisome proliferator-activated receptor gamma (PPAR-γ) pathway.MethodsHuman umbilical vein endothelial cells (HUVEC) were pre-treated with CO releasing molecule-2 (CORM-2) alone or in combination with troglitazone or GW1929, PPAR-γ agonists or GW9662, PPAR-γ antagonist and then cells were co-treated with high glucose (25 mM) for 48 h for detection of ICAM-1 expression by Western blot or luciferase assay. The involvement of AMPK on PPAR-γ and ICAM-1 expressions was tested using pharmacological inducer or inhibitor, as well as transient transfection with AMPK-DN vector.ResultsCO derived from CORM-2 down-regulated ICAM-1 expression induced by high glucose. CORM-2 induced the activity of PPAR-γ at 24 h, and AMPK from 5 min to 3 h. PPAR-γ agonists significantly suppressed ICAM-1 expression, whereas in the presence of antagonist (GW9662) CORM-2 failed to inhibit ICAM-1. Thus inhibition of ICAM-1 was dependent on activation of PPAR-γ. Transfection with AMPK-DN or AMPK inhibitor resulted in attenuation of inducible effect of CORM-2 on PPAR-γ and subsequently suppressive effect on ICAM-1 expression.ConclusionOur results indicate that PPAR-γ and AMPK pathways activated by CO are required for attenuation of ICAM-1 expression induced by high glucose. Thus, this study highlights a new property for CO derived from CORM-2 as anti-atherogenic drug for diabetic patients.