High Methionine and Cholesterol Diet Abolishes Endothelial Relaxation

Abstract

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...

Methionine Supplementation Did Not Augment Oxidative Stress, Atherosclerotic Changes and Hepatotoxicity Induced by High Cholesterol Diet in C57BL/6J Mice

“…It has been reported that the combination of methionine and cholesterol may have a synergistic effect on the development of atherosclerosis. Zulli et al (11,12) found that plasma cholesterol and triglyceride levels and aortic wall tickness increased in rats fed a diet containing 2% methionine plus 2% cholesterol for 15wk, compared with effects seen by feeding with each agent alone, as reported for rabbits (23,24). However, we recently detected that an HM+HC (2% methionine plus 2% cholesterol for 6 mo) diet in rats did not cause any atherosclerotic changes or oxidative stress in the aorta, although the hepatic prooxidant-antioxidant bal ance was affected by this diet (24).…”

“…E-mail: mujdatuysal@hotmail.com together, the combination of these two factors may affect their relative toxic effects. Therefore, it has been postulated that an HM+HC diet may have a synergistic effect in the production of atherosclerotic lesions in the aorta (12,23,24). Indeed, some investigators have reported an augmented effect of HM plus HC feeding on plasma cholesterol and triglyceride levels (11,24) and atherosclerosis (12,23) in rabbits and rats, compared with effects seen by feeding with each agent alone.…”

“…Therefore, it has been postulated that an HM+HC diet may have a synergistic effect in the production of atherosclerotic lesions in the aorta (12,23,24). Indeed, some investigators have reported an augmented effect of HM plus HC feeding on plasma cholesterol and triglyceride levels (11,24) and atherosclerosis (12,23) in rabbits and rats, compared with effects seen by feeding with each agent alone. However, we recently detected that an HM+HC diet in rats did not cause atherosclerrtic changes and oxidative stress in the aorta, although the hepatic prooxidant antioxidant balance was affected by this diet (25).…”

Ratio of S-adenosylmethionine to S-adenosylhomocysteine as a sensitive indicator of atherosclerosis

“…However, the area of the atherosclerotic lesions was decreased by 39.4% in the Meth-F group, compared with the Meth group, (P<0.05). The atherosclerotic lesions in the Meth group were the most severe and widespread, which suggested HHcy may have had an effect in accelerating the development of AS, whereas folate and vitamin B 12 modulated the effect of HHcy on the formation of atherosclerotic plaques (19,20).…”

“…To quantify plaques by stereological methods, ~10 evenly spaced sections of each aortic segment were sampled. The blocks were exhaustively sectioned at 10 µM and stained with hematoxylin and eosin (H&E; Boster Biological Technology, Ltd., Wuhan, China) (19,20) as follows: The aortas were separated carefully and then put into 4% (w/v) formalin for 24 h. The samples subsequently underwent washing with water, dehydration with a Citadel tissue processor (Thermo Fisher Scientific, Inc.), clearing of surplus liquid from tissues, embedding using a Histostar tissue embed-ding system (Thermo Fisher Scientific, Inc.), coating with paraffin wax, slicing (thickness, 4 µM) on a HM340E microtome (Thermo Fisher Scientific, Inc.) and H&E staining. The sampled sections of the aorta were projected onto a table top at 40x magnification using a BX50F4 microscope (Olympus Corporation, Tokyo, Japan).…”