Lack of effect of the ghrelin gene-derived peptide obestatin on cardiomyocyte viability and metabolism

Obestatin is a recently discovered peptide encoded by the ghrelin gene that opposes ghrelin effects on food intake and gastrointestinal function. The biological activity of obestatin depends on amidation at its carboxyl terminus and on its postulated binding to the orphan G protein-coupled receptor 39 (GPR39). We have previously demonstrated that ghrelin is synthesized by cardiomyocytes and has direct effects on its viability. Our aim was to know if obestatin, derived from the same gene as ghrelin, also affects cardiomyocyte physiology. By RT-PCR and immunocytochemistry we have demonstrated that murine cardiomyocytes cultured in vitro and human atrial tissue express GPR39 receptor. Competitive binding studies with radioiodine 125I-labeled obestatin recognized specific binding sites for this peptide in the murine cardiomyocyte cell line HL-1. However, obestatin did not modify the cell cycle or viability of these cells, and it was not able to prevent the cytosine arabinoside-induced apoptosis of HL-1 cardiomyocytes, as assessed by Hoechst dye vital staining, flow cytometry analysis and determination of lactate dehydrogenase in the culture media. Finally, treatment with obestatin did not affect fatty acid or glucose uptake by HL-1 cardiomyocytes. In conclusion, obestatin is not a relevant metabolic or viability modifier for cardiomyocytes.