Abstract 1738: The I(f)-inhibitor Ivabradine Exerts Vascular Anti-oxidative And Anti-inflammatory Effects Selectively Mediated By Reduction Of Heart Rate
Objective: In epidemiological studies, elevated resting heart rate (HR) is associated with increased cardiovascular morbidity. We therefore characterized the effects of selective heart rate reduction by inhibition of the I(f)-current by ivabradine (IVA) in mice.
Methods and Results: Male ApoE−/− mice fed a high-cholesterol diet were treated with IVA (10 mg/kg/d) or vehicle for 6 weeks (n = 10 per group). IVA reduced HR by 13.4% (472 ± 9 vs 545 ± 11 bpm, p < 0.01) but did not alter blood pressure or lipid levels. Endothelium dependent relaxation of aortic rings was significantly improved in IVA fed animals (p < 0.01). IVA decreased atherosclerotic plaque size in the aortic root by > 40% and in the ascending aorta by > 70%, p < 0.05. HR reduction had no effect on the number of endothelial progenitor cells in the blood and the bone marrow and did not alter aortic eNOS, p-Akt, VCAM-1 or ICAM-1 expression, but decreased MCP-1 mRNA to 26 ± 7% (p < 0.05). IVA reduced vascular NADPH oxidase activity to 48 ± 6% and decreased L-012 chemiluminescence to 24 ± 9% (both p < 0.05). Lipidperoxidation was reduced to 65 ± 8% in the vasculature of the IVA group compared to vehicle treatment (p < 0.05). DHE fluorescence microscopy in aortic sections detected reduction of ROS release to 62 ± 4% in IVA treated mice (p < 0.01). The in vivo effects of IVA were absent at a dose that did not lower HR and were absent in aortic rings treated ex vivo. Protein expression of p-Akt, eNOS and p-eNOS was not altered in cultured endothelial cells (EC) by increasing doses of Iva. Similarly, NADPH oxidase activity in EC was not changed as well as the Ang II induced free radical release in vascular smooth muscle cells (DCF-fluorescence).
Conclusions: Selective HR reduction improves endothelial function and reduces atherosclerotic plaque formation in ApoE −/− mice. Those effects are in part mediated by decreased markers of oxidative stress and downregulation of MCP-1. The control experiments show that a direct effect of IVA on vascular cells is unlikely and support the reduction of heart rate as the primary mechanism of action.