Hexarelin protects H9c2 cardiomyocytes from doxorubicin-induced cell death

Growth hormone secretagogues (GHSs) are synthetic peptidyl and nonpeptidyl molecules that possess strong growth hormone-releasing activity acting on specific pituitary and hypothalamic receptor subtypes. Differ- ently from nonpeptidyl GHSs, peptidyl molecules such as hexarelin, a hexapeptide, possess specific high-affin- ity binding sites in animal and human heart and, after prolonged treatment, protect rats in vivo from ischemia- induced myocardial damage. To verify the hypothesis that peptidyl GHSs protect heart cells from cell death, we have investigated the cellular effects of hexarelin on H9c2 cardiomyocytes, a fetal cardiomyocyte-derived cell line, and on Hend, an endothelial cell line derived from transformed murine heart endothelium. We show that (i)H9c2 cardiomyocytes show specific binding for 125I-Tyr-Ala-hexarelin, which is inhibited by peptidyl GHSs such as Tyr-Ala-hexarelin and hexarelin but not by the nonpeptidyl GHS MK-0677, (ii) hexarelin pro- motes survival of H9c2 cardiomyocytes induced to die by doxorubicin, and (iii) that hexarelin inhibits apoptosis, as measured by DNA fragmentation, in- duced in both H9c2 myocytes and endothelial cells. In conclusion, our findings show that peptidyl GHSs such as hexarelin act as survival factors for cardiomyocytes and endothelium-derived cells in culture. These find- ings suggest that the inhibitory activity of hexarelin on cardiomyocytes and endothelial cell death could explain, at least partially, its cardioprotective effect against ischemia recorded in rats in vivo.