THE GROWTH HORMONE SECRETAGOGUE RECEPTOR, GHRELIN AND BIOCHEMICAL SIGNALING MOLECULES IN HUMAN HEART DISEASE

Abstract

Diagnosis of heart disease (HD) is based on clinical features, imaging, and circulating biomarkers, such as B-type natriuretic peptide (BNP), the gold standard heart failure biomarker. However, a cardiac-specific biomarker with potential to detect and might have the potential to predict the development of contractile dysfunction is lacking. The growth hormone secretagogue receptor (GHSR) and its ligand ghrelin may be cardiac-specific biomarkers. We have characterized a fluorescent analog of ghrelin, [Ghrelin(1-19), Lys19(Sulf-cyanine5)] to detect changes in cardiac GHSR in situ in diabetic cardiomyopathy and heart failure. We are now using this tool to map changes in regional and cellular distribution of GHSR in HD. Tissue was obtained from the left ventricle (LV) and right atrium (RA) of 23 patients who had aortic valve reconstruction (AVR). Ten patients also had coronary artery bypass grafting (CABG). GHSR levels were measured by quantitative fluorescence microscopy using Cy5-ghrelin(1-19). Immunofluorescence was used to measure ghrelin, BNP, sarcoplasmic reticulum ATPase pump (SERCA, marker of contractility) and phosphorylated extracellular signal-related kinase (pERK, marker of cell metabolism). Fluorescence intensities from 4 slides per patient were quantified using ImageJ FIJI. Data were analysed by two-tailed t-test, one-way ANOVA and Tukey test, Pearson correlation and linear regression (p<0.05). A strong positive correlation (p<0.001) was noted between ghrelin and GHSR (r=0.857) or BNP (r=0.769). Ghrelin strongly correlated with SERCA2a (r=0.789, p<0.0001) and pERK (r=0.430, p<0.0319) relative to BNP (r=0.619, p=0.001 and r=0.508, p=0.0095 respectively). Regional localization analyses showed marked differences in the RA compared with the LV; there were highly significant correlations (p<0.0001) between ghrelin and BNP (r=0.802) or SERCA2a (r=0.847), and GHSR and SERCA2a (r=0.875), only in the RA. In both males and females, there was strong correlation between GHSR and ghrelin. In females BNP was more strongly correlated with ghrelin (r=0.827, p=0.0032) and GHSR (r=0.860, p=0.0014) while in males, SERCA2A was more strongly correlated with GHSR (r=0.714, p=0.0019) and ghrelin (r=0.8243, p<0.0001). Those who also underwent CABG showed significant correlations with ghrelin and BNP (r=0.792, p=0.0013) or SERCA2a (r=0.772, p=0.0033), and GHSR and SERCA2a (r=0.745, p=0.0054). GHSR expression in HD has shown differences in its sensitivity as a biomarker according to regional tissue distribution, gender and HD etiology. These results highlight the potential use of GHSR/ghrelin as a new cardiac-specific biomarker for HD detection from the RA and coronary artery disease, and also highlights the need for gender-specific biomarkers of HD.