High dose norepinephrine-induced apoptosis in cultured rat cardiac fibroblast

Abstract

Background Prolonged sympathetic activation is damaging to the heart. Recent findings suggest that norepinephrine (NE) may contribute to the apoptotic cardiac cell loss. This study investigated high doses NE apoptotic effect on cardiac fibroblasts (CF) culture and compared the anti-apoptotic effect of α and β (selective and non-selective) adrenergic receptor antagonists. Methods and results Rat CF were cultured in the presence of NE (1 to 100 µM) for 48 h. bax and bcl XL genes expression were measured by real-time quantitative PCR method. Cell viability percentage, apoptotic cell percentage and caspase 3 activity was measured by MTT assay, flow cytometric method and caspase 3 flurogenic assay kit respectively. NE (100 µM) increased bax gene expression by 1.96 ± 0.96 fold while bcl XL gene decreased by 0.53 ± 0.15 fold when compared with the control group ( p < 0.01). The apoptotic cell percentage increased significantly from 5.09 ± 2.94% in control group to 31.48 ± 6.35% ( p < 0.01) with NE and the caspase 3 activity increased from 1432.2 ± 658.8 in the control group to 5162 ± 2028.6 (OD/µg protein, p < 0.05). Addition of carvedilol (non-selective β blocker with α-blockade activity), doxazosin (α blocker), metoprolol (β1 selective blocker) and propranolol (non-selective β blocker) were not capable of inhibiting the apoptotic effect of high dose NE on CF. Conclusion High dose NE has cytotoxic and apoptotic effect on CF. The process involved the activation of caspase 3, up-regulation of pro-apoptotic gene bax and down-regulation of anti-apoptotic gene bcl XL. Both non-selective and selective adrenergic receptor antagonists tested were not capable of inhibiting the apoptotic effect of high dose NE on CF.