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

INTRODUCTION: Hyperglycemia 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-gamma) pathway.
METHODS: Human umbilical vein endothelial cells (HUVEC) were pre-treated with CO releasing molecule-2 (CORM-2) alone or in combination with troglitazone or GW1929, PPAR-gamma agonists or GW9662, PPAR-gamma antagonist and then cells were co-treated with high glucose (25mM) for 48h for detection of ICAM-1 expression by Western blot or luciferase assay. The involvement of AMPK on PPAR-gamma and ICAM-1 expressions was tested using pharmacological inducer or inhibitor, as well as transient transfection with AMPK-DN vector.
RESULTS: CO derived from CORM-2 down-regulated ICAM-1 expression induced by high glucose. CORM-2 induced the activity of PPAR-gamma at 24h, and AMPK from 5min to 3h. PPAR-gamma 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-gamma. Transfection with AMPK-DN or AMPK inhibitor resulted in attenuation of inducible effect of CORM-2 on PPAR-gamma and subsequently suppressive effect on ICAM-1 expression.
CONCLUSION: Our results indicate that PPAR-gamma 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.