Oxidized Low-Density Lipoprotein Is Associated With Apoptosis of Vascular Smooth Muscle Cells in Human Atherosclerotic Plaques

Abstract

Background-Cytotoxic oxidized LDL (oxLDL) has been shown to promote apoptosis in cultured vascular smooth muscle cells (VSMCs). We investigated the localization of oxLDL and its association with apoptosis and the expression of apoptosis-related proteins in early and advanced atherosclerotic lesions. Methods and Results-Atherosclerotic plaques (nϭ23) from patients undergoing aortic, carotid, or femoral arterial surgery were studied. In early lesions, oxLDL was located predominantly in the superficial intima and in the media just beneath the internal elastic lamina. Medial VSMCs staining positive for oxLDL showed expression of BAX, a proapoptotic protein of the BCL-2 family. Apoptosis, as detected by DNA in situ terminal deoxynucleotidyl transferase end-labeling (TUNEL), was not present in these early lesions. In advanced plaques, areas of the intima positive for oxLDL showed lower ␣-smooth muscle actin immunoreactivity (PϽ0.01) and higher BAX immunoreactivity (PϽ0.05). Furthermore, these areas showed an increased number of apoptotic VSMCs (PϽ0.01). Western blot analysis revealed that oxLDL increases BAX expression in cultured human coronary VSMCs. Conclusions-We conclude that in early atherosclerotic lesions, oxLDL-positive VSMCs express BAX, which increases the susceptibility of these cells to undergo apoptosis. This could be important in our understanding of the transition of early lesions into advanced atherosclerotic plaques, which are characterized by regions of cell death. In advanced plaques, oxLDL-positive areas of the intima show higher BAX immunoreactivity and TUNEL-positive VSMCs, and this may contribute to plaque instability and rupture.

Role of macrophage and smooth muscle cell apoptosis in association with oxidized low-density lipoprotein in the atherosclerotic development

“…Therefore, we considered that the specificity of the three antibodies was comparable. Apoptosis detection using the TUNEL method has hardly shown in the initial lesions of atherosclerosis by previous studies, [7][8][9] whereas, in this study, single-stranded DNA-positive cells were detected consistently throughout atherosclerotic development. The discrepancy in the rate of detection in initial lesions, especially fatty streak, between the previous and present results may originate from differences in the methods using single-stranded DNA antibody for detecting apoptotic cells.…”

“…Then, apoptotic cells were detected mainly around extracellular lipid deposits in the advanced lesions, which is consistent with the results of previous studies. [7][8][9] Considering the contribution of the death of lipid-laden macrophages to the lipid core formation, 30 by using more sensitive single-stranded DNA antibody to detect the apopotic cells in any atherosclerotic lesion, our results clearly further clarify that extracellular lipid deposits in the atherosclerotic intima result partly from the apoptosis of foamy macrophages.…”

“…3,5 It is recognized that apoptosis takes place in atherosclerotic lesions, and that the rate of apoptosis varies (o2-30%). [6][7][8][9] The pathophysiological roles of apoptosis in atherosclerosis have been discussed in conjunction with cell distribution and type as well as with plaque stabilization, plaque rupture, and regression of thickened arterial walls. 7,[10][11][12][13] Apoptotic cells are usually identified by morphological observation using terminal deoxynucleotidyl transferase (TdT)-mediated dUTP-biotin nick end labeling (TUNEL).…”

“…[20][21][22][23] Despite the close relationship between the level of oxLDL expression and the induction of apoptosis, there have been only a few studies in vivo on the role of oxLDL in the apoptosis of intimal cells. 9,11 Furthermore, the difference in distribution of apoptosis between smooth muscle cells and macrophages has not yet been examined with respect to atherosclerosis.…”

Effects of adding tocotrienol-tocopherol mixed fraction and vitamin C on inflammatory status in hypercholesterolaemic patients in the low coronary risk category

“…One of such implications is atherosclerosis, of which hypercholesterolaemia is a risk factor. Low 558 Tocotrienol-tocopherol and vitamin C in hypercholesterolaemic patients rotic plaque instability (Nishi et al, 2002;Okura et al, 2000), leading to thrombus formation and acute coronary events. Inflammation is considered to be the pathway by which oxLDL exerts its adverse cardiovascular effects (Bieghs et al, 2013;Shen et al, 2013).…”