Endothelial injury by oxidized LDL

Recent progress in the research of oxidized LDL has revealed that this lipoprotein causes not only foam cell transformation of macrophages but also several endothelial dysfunction, and the effects on endothelial cells are also involved with the process of atherogenesis. Receptors for oxidized LDL on endothelial cells, such as LOX-1 and SREC, have been cloned and their characteristics are now under investigation. In addition to lowering plasma cholesterol level, it is expected that new strategies to prevent atherosclerosis is established by focusing on the endothelial injury caused by oxidized LDL.     

Positive correlation between in vivo oxidized LDL and LDL immune complexes

OBJECTIVES: To investigate the possible relationship between oxidized low-density lipoprotein (ox-LDL) and LDL immune complexes (IC). METHODS: Both LDL-IC and ox-LDL were detected by sandwich ELISA. The levels were also studied in 60 patients with coronary heart disease (CHD) and 50 control subjects. RESULTS: Compared to controls, both the plasma ox-LDL concentrations (595.5 +/- 194.8 vs. 440.3 +/- 175.0 microg/l, P < 0.001) and LDL-IC levels (2.74 +/- 0.73 vs. 1.38 +/- 0.78 AU, P < 0.001) in the patients with CHD were significantly increased. The relationships between LDL-IC, ox-LDL levels, and other lipid parameters in all the studied subjects (n = 100) were analyzed. LDL-IC levels were positively correlated with TC, TG, LDL-C, lipoprotein(a) [Lp(a)], and apolipoprotein B (apoB) concentration, while negatively correlated with apoA1 concentration, respectively. Similarly, ox-LDL levels were also found positively correlated with TC, LDL-C, and apoB concentrations, respectively. Furthermore, a significantly positive correlation between ox-LDL and LDL-IC levels was found (r = 0.313, P < 0.005). CONCLUSION: In vivo oxidized LDL positively correlates with circulating levels of LDL immune complexes.     

极低密度脂蛋白受体与脂蛋白代谢

极低密度脂蛋白受体是低密度脂蛋白受体家族的成员 ,其生物学功能尚未完全阐明。关于极低密度脂蛋白受体是否参与脂蛋白代谢的问题 ,一直存在争论。最近 ,这方面的研究取得了一些进展 ,证实极低密度脂蛋白受体参与了脂蛋白代谢的调节     

CETP and oxidized LDL levels increase in dyslipidemic subjects

OBJECTIVES: To explore the possible associations among cholesteryl ester transfer protein (CETP), contents of lipids in low-density lipoprotein (LDL), and in vivo oxidized LDL (Ox-LDL). DESIGN AND METHODS: CETP and Ox-LDL were both detected by ELISA. Their levels and the lipid contents of LDL were investigated in 200 subjects with various dyslipidaemias. RESULTS: Compared to the control, CETP levels were significantly increased in subjects with mixed hyperlipidaemia and hypercholesterolaemic. Ox-LDL levels were only significantly increased in mixed hyperlipidaemia subjects. Triacyglycerols to cholesterol ratio in LDL was significantly increased in various dyslipidaemias subjects, of which, hypertriglyceridaemic subjects exhibited the most significant change, while hypercholesterolaemic subjects the least. Multiple linear regression analysis showed that total cholesterol and triacyglycerols levels in very low-density lipoprotein were significantly related with CETP (R(2)=0.066), and triacyglycerols and total cholesterol levels were significantly related with Ox-LDL (R(2)=0.094), respectively. CONCLUSIONS: High CETP promotes the transport of lipids among lipoproteins, which changed the lipid composition of LDL, resulting in the increase of in vivo Ox-LDL level, and subsequently contributing to the atherogenic process in dyslipidaemias subjects.     

Redistribution of intracellular calcium and its effect on apoptosis in macrophages: Induction by oxidized LDL

Calcium signaling, as a key to early step of the elementary intracellular events, has been implicated in controlling the development of atherosclerosis. We have shown previously that oxidized low density lipoprotein OxLDL-induced spatiotemporal increases of intracellular free calcium ([Ca²⁺]_i) in the early formation of macrophage foam cells. Here, we evaluated how spatiotemporal redistribution of intracellular calcium occurs and would affect OxLDL-induced apoptosis. Confocal laser scanning microscopy and flow cytometry showed the time-dependent increase of mitochondrial Ca²⁺ ([Ca²⁺]_m) in acute and chronic exposure of U937-derived macrophages to OxLDL (100 μg/ml). Independent of the presence or absence of external Ca²⁺, OxLDL-induced a peak of [Ca²⁺]_m in acute exposure, whose amplitude in the absence of extracellular Ca²⁺ was obviously lower than the presence of extracellular Ca²⁺. In addition, the thapsigargin-mediated increase of [Ca²⁺]_i, through endoplasmic reticulum (ER) Ca²⁺ pump depletion, was obviously reduced by 1-h pretreatment of OxLDL. OxLDL also caused a time-dependent opening of mitochondrial permeability transition pores (PTPs). EGTA/AM, an intracellular Ca²⁺ chelator, significantly reduced OxLDL-induced apoptosis and failed to prevent OxLDL-induced necrosis at 6 h. In contrast to control cells, chelation of cytosolic Ca²⁺ by EGTA/AM at 6 h did not completely reverse OxLDL-induced apoptosis. OxLDL stimulated depolarization of mitochondrial membrane potential (Δψ) in time-dependent manner. Our data demonstrated that OxLDL-induced spatiotemporal Ca²⁺ redistribution in appropriate organelles and mediated Ca²⁺-dependent apoptosis in relation to depolarization of Δψ. These findings suggested that manipulation of the intracellular calcium balance may be a useful strategy to limit the loss of macrophages in early atherosclerosis.     

Antibodies to oxidized LDL in atherosclerosis development--clinical and animal studies

Atherosclerotic lesions represent the principal cause of death in western industrialized countries. Immune mechanisms have been suggested to play a key role in the development of atherosclerosis. Several lines of evidence support that oxidized LDL (oxLDL) may be a key antigen in atherosclerosis. Antibodies to oxLDL have been found in human and rabbit plasma and in atherosclerotic lesions. So far, it has not been well established if the immune response is predominantly pro- or antiatherogenic. During the last decade, numerous studies have been performed investigating the relationship between circulating antibodies in plasma in relation to endothelial dysfunction, subclinical atherosclerosis and cardiovascular events in different patient categories. Taken together, these studies have shown diverging results. However, most studies have shown that elevated IgG titers to oxLDL are related to atherosclerotic disease. Even if fewer studies have investigated IgM titers, most studies seem to show an inverse relationship between IgM titers and atherosclerotic disease. In animal studies, it has been shown that immunization with oxLDL induces antibody formation (both IgG and IgM) and protects against atherosclerosis development. Furthermore, it has also been shown that immunization with Streptococcus pneumoniae induce an IgM response, which is associated with decreased atherosclerosis development, and plasma from these mice also has the ability to block uptake of oxLDL to macrophages. To conclude, antibodies to oxLDL in clinical cardiovascular disease show diverging results, while animal studies suggest that immunization may have a beneficial role in atherosclerosis development. Prospective and intervention studies, as well as mechanistic studies are clearly needed to elucidate the possible causal role of antibodies to oxLDL in man.     

氧化、丙二醛修饰低密度脂蛋白的ELISA检测法及临床应用

目的 建立血浆氧化、修饰低密度脂蛋白(LDL)ELISA检测法并进行临床研究.方法 采用自制的多克隆抗体建立ELISA分别测定铜离子氧化型(Ox)和丙二醛(MDA)修饰型LDL,并对方法进行考核;对冠心病(CHD)患者、键康对照人群Ox-LDL、MDA-LDL水平进行分析.结果 抗Ox-LDL与MDA-LDL几乎没有反应性;Ox-LDL和MDA-LDL测定平均批内变异(CV)分别为6.1%和6.8%,平均批间CV分别为9.7%和10.1%;Ox-LDL和MDA-LDL测定平均回收率分别为95.1%和93.7%;两法检测限均为0.05～1.5 mg/L.CHD患者较正常人血浆Ox-LDL[(178.1±73.8)mg/L vs.(82.7±29.1)mg/L,P＜0.01]、MDA-LDL[(48.7±25.6)mg/L vs.(39.2±32.9)mg/L,P＜0.05]水平均升高;Ox-LDL作为预测动脉粥样硬化发生指标的价值优于MDA-LDL.Ox-LDL、MDA-LDL分别同TC、TG、LDL-C呈正相关,而与HDL-C呈负相关.结论 建立的方法特异、灵敏、准确,适于临床检测.高Ox-LDL、MDA-LDL与CHD密切相关.     

Association among retinol-binding protein 4, small dense LDL cholesterol and oxidized LDL levels in dyslipidemia subjects

ObjectivesTo investigate retinol-binding protein 4 (RBP4), small dense low-density lipoprotein cholesterol (sdLDL-C) and oxidized low-density lipoprotein (ox-LDL) levels and their associations in dyslipidemia subjects.Design and methodsWe determined RBP4, sdLDL-C, ox-LDL levels in 150 various dyslipidemia subjects and 50 controls. The correlation analysis and multiple linear regression analysis were performed.ResultsThe RBP4, sdLDL-C and ox-LDL levels were found increased in various dyslipidemia subjects. The sdLDL-C levels were positively correlated with RBP4 (r = 0.273, P = 0.001) and ox-LDL (r = 0.273, P = 0.001). RBP4 levels were also correlated with ox-LDL (r = 0.167, P = 0.043). The multiple regression analysis showed that only sdLDL-C was a significant independent predictor for RBP4 (β coefficient = 0.219, P = 0.009; adjusted R² = 0.041) and ox-LDL (β coefficient = 0.253, P = 0.003; adjusted R² = 0.057) levels, respectively.ConclusionsThe independent associations of sdLDL-C with RBP4 and ox-LDL were observed in dyslipidemia subjects. RBP4 may play an important role in lipid metabolism of atherosclerosis, particularly in formation of sdLDL.     

PPARgamma regulates adipocyte cholesterol metabolism via oxidized LDL receptor 1

In addition to its role in energy storage, adipose tissue also accumulates cholesterol. Concentrations of cholesterol and triglycerides are strongly correlated in the adipocyte, but little is known about mechanisms regulating cholesterol metabolism in fat cells. Here we report that antidiabetic thiazolidinediones (TZDs) and other ligands for the nuclear receptor PPARgamma dramatically upregulate oxidized LDL receptor 1 (OLR1) in adipocytes by facilitating the exchange of coactivators for corepressors on the OLR1 gene in cultured mouse adipocytes. TZDs markedly stimulate the uptake of oxidized LDL (oxLDL) into adipocytes, and this requires OLR1. Increased OLR1 expression, resulting either from TZD treatment or adenoviral gene delivery, significantly augments adipocyte cholesterol content and enhances fatty acid uptake. OLR1 expression in white adipose tissue is increased in obesity and is further induced by PPARgamma ligand treatment in vivo. Serum oxLDL levels are decreased in both lean and obese diabetic animals treated with TZDs. These data identify OLR1 as a novel PPARgamma target gene in adipocytes. While the physiological role of adipose tissue in cholesterol and oxLDL metabolism remains to be established, the induction of OLR1 is a potential means by which PPARgamma ligands regulate lipid metabolism and insulin sensitivity in adipocytes.     

Measurement of oxidized lipoprotein (a) in patients with acute coronary syndromes and stable coronary artery disease by 2 ELISAs: Using different capture antibody against oxidized lipoprotein (a) or oxidized LDL

ObjectiveTo evaluate clinical value of oxidized lipoprotein(a) [ox-Lp(a)] levels.Design and methodsOx-Lp(a) were measured by 2 ELISAs using antibodies against ox-Lp(a) [ox-Lp(a)1] or oxidized low-density lipoprotein [ox-Lp(a)2], and studied in 161 acute coronary syndromes (ACS) patients, 114 stable coronary artery disease (CAD) and 100 control subjects.ResultsOx-Lp(a)1 was found related with ox-Lp(a)2 (r = 0.864, P = 0.000). Controlling for plasma lipids, Lp(a) and clinical characteristics, odds ratios of ox-Lp(a)1 on ACS and stable CAD were 5.06 (95% confidence interval 1.82–14.04) and 2.20 (0.78–6.22); those of ox-Lp(a)2 were 3.37 (1.07–10.63) and 1.35 (0.41–4.48), respectively. Receiver-operating characteristic curve analysis confirmed that performances of ox-Lp(a)1 were significantly superior to those for ox-Lp(a)2 in ACS (area: 0.803 vs. 0.723, P < 0.001) and stable CAD (area: 0.670 vs. 0.607, P < 0.01).ConclusionOx-Lp(a) levels using antibodies against ox-Lp(a) may represent a better risk marker than those using antibodies against oxidized low-density lipoprotein for ACS and stable CAD.     

Impaired endothelium-dependent vasodilation in type 2 diabetes. Relation to LDL size, oxidized LDL, and antioxidants.

OBJECTIVE: To search for determinants of endothelial dysfunction in type 2 diabetes. RESEARCH DESIGN AND METHODS: We performed a comprehensive analysis of cardiovascular risk markers and measured blood flow responses to endothelium-dependent (acetylcholine [ACh] and NG-monomethyl-L-arginine) and -independent (sodium nitroprusside [SNP]) vasoactive agents in 30 nonsmoking men with type 2 diabetes (age 51 +/- 1 years, BMI 27.8 +/- 0.4 kg/m2, HbA1c 7.4 +/- 0.3%) and 12 matched normal control men. RESULTS: ACh-induced vasodilation was 37% lower in type 2 diabetic (6.1 +/- 0.5) than in normal subjects (9.7 +/- 1.5 ml.dl-1.min-1, P < 0.01), while flows during SNP were similar (9.1 +/- 0.6 vs. 9.9 +/- 1.3 ml.dl-1.min-1, NS). The ratio of endothelium-dependent vs. -independent flow (ACh:SNP ratio) was 31% lower in type 2 diabetic (0.70 +/- 0.05) than in normal subjects (1.10 +/- 0.18, P < 0.01). Total (2.2 +/- 0.4 vs. 1.3 +/- 0.2 mmol/l, P < 0.05), VLDL, and intermediate-density lipoprotein triglycerides were significantly higher, and the mean LDL particle diameter was significantly smaller in type 2 diabetic than in normal subjects. The lag times for LDL oxidation by Cu2+ in vitro were similar in patients with type 2 diabetes (183 +/- 7) and in normal subjects (183 +/- 9 min, NS). Measured and calculated (sum of concentration of individual antioxidants in serum) total peroxyl radical-trapping capacities (TRAPs) were comparable between the groups. In the patients with type 2 diabetes, LDL size was significantly correlated with endothelium-dependent vasodilation (r = 0.43, P < 0.05), serum triglycerides (r = -0.75, P < 0.001), and the lag time for LDL oxidation in vitro (r = 0.38, P < 0.05). HbA1c was inversely correlated with the lag time for LDL oxidation in vitro (r = -0.41, P < 0.05) and TRAP. CONCLUSIONS: In summary, patients with type 2 diabetes exhibited impaired endothelium-dependent vasodilation in vivo, elevated serum triglycerides, decreased LDL size, and normal antioxidant capacity. Of these parameters, LDL size was significantly correlated with endothelial function.     

Impact of postprandial lipaemia on low-density lipoprotein (LDL) size and oxidized LDL in patients with coronary artery disease

BACKGROUND: Remnant lipoprotein particles (RLPs) and oxidative stress are components of postprandial state. We investigated the concentrations of triglyceride-rich lipoproteins (TRLs), RLPs, low-density lipoprotein (LDL) size, and oxidized LDL (oxLDL) during alimentary lipaemia, and evaluated whether changes among these variables could be associated with the severity and extent of coronary artery disease (CAD). MATERIALS AND METHODS: Eighty men and 27 women with clinically suspected CAD underwent quantitative coronary angiography (QCA). TRLs were isolated by density gradient ultracentrifugation before and 6 h after an oral fat load. RLPs were measured by an immunoseparation method, oxLDL by ELISA, and LDL size by gradient gel electrophoresis. RESULTS: Triglycerides, apolipoprotein (apo) B-48, and apoB-100 concentration in Swedberg flotation units (Sf) > 400 and in Sf 12-400 fractions were markedly increased at 6 h. Postprandial cholesterol content of RLPs (RLP-C) correlated with respective triglycerides in Sf > 400 (r = 0.737) and Sf 12-400 (r = 0.857), apoB-48 in Sf > 400 (r = 0.710) and Sf 12-400 (r = 0.664), apoB-100 in Sf > 400 (r = 0.812) and Sf 12-400 (r = 0.533). RLP-C correlated with oxLDL both in fasting and in fed state (r = 0.482 and r = 0.543, respectively) and inversely with LDL size (r = -0.459 and r = -0.442, respectively). (P < 0.001 for all). OxLDL was elevated postprandially (P < 0.001). In multivariate analysis, oxLDL was a determinant of severity and extent of CAD. CONCLUSION: Postprandial state is associated with oxidative stress. The magnitude of oxLDL increases during alimentary lipaemia and is associated with coronary atherosclerosis.     

Scavenger receptors and oxidized low density lipoproteins.

Oxidized LDL has been shown to exhibit a number of potentially proatherogenic actions and properties, including receptor-mediated uptake and lipid accumulation within macrophages. It has been postulated that rapid, unregulated uptake of oxidatively modified LDL could account for the transformation of monocyte-derived macrophages to foam cells in atherosclerotic lesions. In support of this hypothesis, oxidized LDL and lipid peroxidation products have been shown to exist in atheromas in vivo. Furthermore, a number of cell membrane proteins that can bind oxidized LDL with high affinity have been identified on the surface of macrophages, endothelial cells and smooth muscle cells. One characteristic that almost all of these 'scavenger receptors' share is the ability to bind with high affinity to a broad spectrum of structurally unrelated ligands. Of all of the different classes of scavenger receptors that have been identified, the scavenger receptor class A type I/II (SR-AI/II) has received the most attention. Studies with macrophages from mice deficient in the gene for SR-AI/II provide direct evidence that a receptor other than the SR-AI/II is responsible for most of the uptake of oxidized LDL in murine macrophages. This article provides an overview of the characterization and functions of the scavenger receptors that have been shown to interact with oxidized LDL, including SR-AI/II, CD36, SR-BI, macrosialin/CD68, LOX-1, and SREC. Isolation and characterization of these and other scavenger receptors has increased our understanding of their role in the uptake of oxidized LDL and the pathogenesis of atherosclerosis.     

Stabilization of the bioactivity of tumor necrosis factor by its soluble receptors

The receptors for tumor necrosis factor (TNF) exist in cell-associated as well as soluble forms, both binding specifically to TNF. Since the soluble forms of TNF receptors (sTNF-Rs) can compete with the cell-associated TNF receptors for TNF, it was suggested that they function as inhibitors of TNF activity; at high concentrations, the sTNF-Rs indeed inhibit TNF effects. However, we report here that in the presence of low concentrations of the sTNF-Rs, effects of TNF whose induction depend on prolonged treatment with this cytokine are augmented, reflecting an attenuation by the sTNF-Rs of spontaneous TNF activity decay. Evidence that this stabilization of TNF activity by the sTNF-Rs follows from stabilization of TNF structure within the complexes that TNF forms with the sTNF-Rs is presented here, suggesting that the sTNF-Rs can affect TNF activity not only by interfering with its binding to cells but also by stabilizing its structure and preserving its activity, thus augmenting some of its effects.