Abstract

Background: Ghrelin is the endogenous ligand of the growth hormone secretagogue receptor. It has been reported to have cardiovascular protective activities. Elevated plasma free fatty acids trigger apoptosis in vascular endothelial cells. We investigated the effect of ghrelin on palmitate-induced apoptosis in rat aortic endothelial cells and the involved transduction pathway.
Material/Methods: Rat aortic endothelial cells were treated with palmitate in the presence or absence of ghrelin. Apoptosis was detected using an annexin V-FITC/PI binding assay and a caspase-3 activity assay. The intracellular reactive oxygen species formation in endothelial cells was detected by fluorescence measurement with dichlorofluorescein diacetate (DCFH-DA). Western blot analysis was used to examine the changes in the expression levels of Akt, Bcl-2, and Bax.
Results: Exposure of rat aortic endothelial cells to palmitate (0.3 mM) for 24 hours caused a significant increase in cell apoptosis. Ghrelin attenuated palmitate-induced apoptosis in endothelial cells. Exposure of cells to ghrelin caused a rapid activation of Akt. These effects were abolished by [D-Lys3]-GHRH-6, the special antagonist of growth hormone secretagogue receptor. Phosphatidyl inositol 3-kinase (PI3K) inhibitor, LY294002, extenuated the antiapoptotic effect of ghrelin. Reactive oxygen species levels were increased by palmitate, but this effect was inhibited by ghrelin. In addition, ghrelin increased the expression of Bcl-2 and decreased the expression of Bax; thus, the Bcl-2/Bax ratio was increased.
Conclusions: Ghrelin inhibits palmitate-induced apoptosis involved in activating the PI3K/Akt pathway and suppressing palmitate-induced oxidative stress in endothelial cells. Ghrelin may be protective against palmitate-induced endothelial injury.

Keywords: Oligopeptides, Palmitates - toxicity, Morpholines, Ghrelin - pharmacology, Fluorescence, Endothelial Cells - drug effects, Chromones, Cell Survival - drug effects, Blotting, Western, Aorta - cytology, Analysis of Variance, Reactive Oxygen Species - metabolism, Signal Transduction - drug effects, Tetrazolium Salts, Thiazoles