Abstract
Background
Apelin, an adipokine peptide and its receptor has recently emerged as a key signaling pathway in maintaining cardiac performance at chronic pressure loads. Apelin has been linked to ventricular dysfunction and therefore maybe of pathophysiologic relevance as a candidate biomarker in HF patients.
Purpose
This study aims to investigate Apelin-13 gene expression and level, and Apelin receptor (APJ) level in a rat model of heart failure induced by chronic systemic hypoxia and their correlation to BNP-45 gene expression and level, the current gold standard biomarker for heart failure, and to cardiac histopathologic changes. The effect of chronic systemic hypoxia on cardiac hypertrophy, remodeling and heart failure parameters is also of interest.
Methods
Twenty-eight male Sprague-Dawley rats (8–12 weeks of age) were placed in special hypoxic chambers divided into 7 groups – a control group provided with normoxia (atmospheric O2 levels) and 6 exposure groups exposed to hypoxia (8% O2) for 6 hours, 1, 3, 5, 7 and 14 days respectively prior to measurement. Changes in the expression of Apelin and BNP-45 were measured using quantitative real-time PCR, whereas changes in Apelin-13, APJ and BNP-45 levels were measured using ELISA. Histopathology staining using Hematoxylin and Eosin was performed on cardiac tissues post-termination.
Results
Compared to control, BNP-45 mRNA expression in the hypoxic heart was only significantly different in day 14, whereas, Apelin mRNA expression had showed significantly higher values starting from day 7 onward. This is in line with the evidence of cardiac hypertrophy based on histopathologic examination present from day 7 onwards. BNP-45 and Apelin-13 levels were significantly higher compared to control from day 5 onwards with a peak on day 7. Although significantly higher than control, Apelin-13 and BNP-45 level decreases in day 14 as compared to day 7. Mean APJ levels showed a similar profile with Apelin-13 and BNP-45 levels with a peak in day 7 (4.619 ng/mL). The cardiac Apelin-13 level shows strong significant correlation with BNP-45 levels (r 0.823, p-value 0.0001). There was also a strong significant correlation between APJ receptor levels with Apelin-13 (r 0.9029, p-value 0.001) and BNP-45 (r 0.9062, p-value 0.0009) levels. Apelin-13, APJ and BNP-45 levels also showed strong significant positive correlation to the duration of hypoxia exposure.
Conclusion
Chronic (≥5 days) and not acute systemic hypoxia in an experimental rat model leads to increase in Apelin-13, APJ and BNP-45 levels. Apelin-13 and BNP-45 were found to significantly increase from 5 days onwards. Apelin mRNA expression was found to show significant increase earlier compared to BNP-45 mRNA expression. Hence, Apelin may serve as a new candidate biomarker for detection of HF due to oxidative stress compared to BNP-45. Exposure to chronic systemic hypoxia can serve as an easily replicable rat model for heart failure.
Acknowledgement/Funding
Department of Biochemistry and Molecular Biology, Faculty of Medicine, Tarumanagara University, Jakarta, Indonesia
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