Effects of ezetimibe on atherosclerosis in preclinical models.

Ezetimibe (Zetia(®), Ezetrol(®), Merck, Whitehouse Station, NJ) is a potent inhibitor of sterol absorption, which selectively blocks the uptake of biliary and dietary cholesterol in the small intestine. Clinical trials have demonstrated the beneficial effects of ezetimibe on the reduction of atherogenic lipoproteins and the attainment of guideline-recommended lipid levels. Direct evidence that these improvements translate to a reduction in atherosclerosis or cardiovascular events is limited, although reductions in major atherosclerotic events that are consistent with the LDL-C lowering achieved have recently been presented for patients with chronic kidney disease treated with ezetimibe/simvastatin 10/20mg in the SHARP trial. Animal models of atherosclerosis have played a central role in defining the mechanisms involved in initiation and development of disease and have been used in drug development to evaluate potential therapeutic efficacy. The effect of ezetimibe on atherosclerosis has been examined in several of these animal model systems. ApoE knockout mice develop severe hypercholesterolemia and premature atherosclerosis with features similar to that seen in humans and techniques ranging from gross visualization of plaque to high-resolution MRI have demonstrated the consistent ability of ezetimibe to significantly inhibit atherosclerosis. sr-b1(-/-)/apoE(-/-) double knockout mice exhibit additional characteristics common to human coronary heart disease (CHD), and the one study of ezetimibe in sr-b1(-/-)/apoE(-/-) mice showed a significant reduction in aortic sinus plaque (57%), coronary arterial occlusion (68%), myocardial fibrosis (57%), and cardiomegaly (12%) compared with untreated controls. The effects of ezetimibe have also been evaluated in ldlr(-/-)/apoE(-/-) double knockout mice, demonstrating that functional LDL receptors were not required for ezetimibe-mediated reduction of plasma cholesterol or atherosclerosis. For the few studies that have been conducted in rabbits, ezetimibe has been shown to significantly inhibit diet and vascular-injury-induced atherosclerosis as measured by intima/media thickness, atherosclerotic lesion composition, and thrombosis. The current body of preclinical evidence consistently demonstrates that ezetimibe reduces atherosclerosis in animals, presumably due primarily to the decrease in circulating levels of atherogenic lipoproteins that the drug produces. Demonstration that ezetimibe-mediated lowering of atherogenic lipoproteins in humans has a similar effect on atherosclerosis and cardiovascular risk awaits additional results from recently completed and ongoing outcomes trials.