Heart Rate Reduction by Ivabradine Reduces Oxidative Stress, Improves Endothelial Function, and Prevents Atherosclerosis in Apolipoprotein E–Deficient Mice

Abstract

Background— Elevated heart rate is associated with increased cardiovascular morbidity. We hypothesized that selective heart rate reduction may influence endothelial function and atherogenesis and tested the effects of the I (f) current inhibitor ivabradine in apolipoprotein E–deficient mice. Methods and Results— Male apolipoprotein E–deficient mice fed a high-cholesterol diet were treated with ivabradine (10 mg · kg −1 · d −1 ) or vehicle for 6 weeks (n=10 per group). Ivabradine reduced heart rate by 13.4% (472±9 versus 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 ivabradine-fed animals ( P <0.01). Ivabradine decreased atherosclerotic plaque size in the aortic root by >40% and in the ascending aorta by >70% ( P <0.05). Heart rate reduction by ivabradine had no effect on the number of endothelial progenitor cells and did not alter aortic endothelial nitric oxide synthase, phosphorylated Akt, vascular cell adhesion molecule-1, or intercellular adhesion molecule-1 expression but decreased monocyte chemotactic protein-1 mRNA and exerted potent antioxidative effects. Ivabradine reduced vascular NADPH oxidase activity to 48±6% and decreased markers of superoxide production and lipid peroxidation in the aortic wall ( P <0.05). The in vivo effects of ivabradine were absent at a dose that did not lower heart rate, in aortic rings treated ex vivo, and in cultured vascular cells. In contrast to ivabradine, treatment with hydralazine (25 mg · kg −1 · d −1 for 6 weeks) reduced blood pressure (−15%) but increased heart rate (37%) and did not improve endothelial function, atherosclerosis, or oxidative stress. Conclusions— Selective heart rate reduction with ivabradine decreases markers of vascular oxidative stress, improves endothelial function, and reduces atherosclerotic plaque formation in apolipoprotein E–deficient mice.