Objective-High plasma cholesterol or homocysteine is a risk factor for atherosclerosis. Cholesterol and methionine, the precursor of homocysteine, are rarely eaten separately. Thus, the aims of this study were to determine neointima formation, aortic reactivity, and factors involved in endothelial function in rabbits fed high dietary cholesterol, methionine, or a combination of the two for 12 weeks. Methods and Results-Rabbit dietary groups were randomized into the following: control (Con), 0.5% cholesterol (Chol), 1% methionine (Meth), and 1% methionineϩ0.5% cholesterol (MethChol). Aortic reactivity was studied by isometric tension techniques, aortic volumetric analysis was determined by stereological techniques, and immunohistochemistry was used to localize endothelial and inducible NO synthases, superoxide dismutase, macrophages, and nitrotyrosine. Atherosclerosis was present in the Chol and MethChol groups. Endothelium-dependent relaxation was virtually abolished in the MethChol group compared with control. Such decrease in relaxation was not attributable to a vascular smooth muscle cell defect or to a decrease in endothelial NO synthase or superoxide dismutase content. Macrophages and inducible NO synthase immunoreactivity were present in Chol and MetChol groups. Key Words: cholesterol Ⅲ homocysteine Ⅲ endothelial function Ⅲ plaque Ⅲ nitric oxide H igh plasma cholesterol 1 or homocysteine 2 are risk factors for cardiovascular disease. They can be brought about by genetic defects in cholesterol or homocysteine metabolism or through dietary regimens. Cholesterol and methionine, the precursor of homocysteine, are rarely ingested separately, because animal products such as eggs, meat, and milk contain both cholesterol and methionine. In fact, it is estimated that 30% of the population in the United States may have high plasma levels of homocysteine 2 and more than 50% have high plasma levels of cholesterol. 3 Thus, it is likely that there are individuals with high plasma levels of both risk factors.
Conclusions-TheExperimental, 4,5 human, 6 -8 and murine genetic knockout studies (cystathionine -synthase-deficient mice) 9,10 in hypercholesterolemia and hyperhomocystinemia show an impairment in endothelial-dependent relaxation to agonist stimulation in both conduit and resistance arteries, which has been partly linked to a decrease in the bioavailability of a major endothelium-derived relaxing factor, nitric oxide (NO). Because NO can inhibit the early events of atherogenesis, 11 a decrease in the bioavailability of NO is thought to promote atherogenesis. The mechanisms whereby cholesterol and homocysteine decrease NO bioavailability are not well understood; however, it is popular opinion that an excess availability of the oxygen free radical O 2 Ϫ (oxygen stress) can scavenge NO, thus decreasing its bioavailability. 12 Furthermore, the reaction of excess O 2 Ϫ with excess NO, which may arise from the increased expression of inducible NO synthase (iNOS) 13 from macrophages and smooth muscle cells, forms peroxyni...