Atherogenicity Of LDL Research Articles

Effect of age on atherogenicity of LDL and inflammatory markers in healthy women

Background and aimSince using LDL level alone is insufficient as a method to identify individuals with incident coronary artery disease (CAD), other factors may be implicated in the pathogenesis of CAD. Additionally, controversy still remains regarding whether there is an age-related increase in circulating cytokines in healthy individuals. We investigated the influence of age on atherogenicity of LDL and inflammatory markers in healthy women. Methods and resultsTwo thousand nine hundred forty four healthy women form 30–79 years old (23.3 ± 0.05 kg/m2) were categorized into 5 age groups: 30–39, 40–49, 50–59, 60–69 and 70–79 years. BMI, smoking, drinking, and metabolic syndrome prevalence adjusted mean values of total-cholesterol progressively increased from the group age 30–39 years to the group age 40–49 and 50–59 years and thereafter decreased in the group age 60–69 and 70–79 years. Serum concentrations of C-reactive protein (CRP), tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6) were higher in women aged 60–79 years than women aged 30–59 years. Plasma ox-LDL levels increased in the group age 50–59 years compared with the group age 30–39 and 40–49 years and further increased in the group age 60–69 and 70–79 years. Mean values of LDL particle size were smaller in women aged 60–79 years than those in women aged 30–59 years. After adjustment for BMI, smoking, drinking, and metabolic syndrome status, age was positively correlated with LDL-cholesterol (r = 0.095, P < 0.001), oxidized LDL (r = 0.305, P < 0.001), hs-CRP (r = 0.150, P < 0.001), TNF-α (r = 0.171, P < 0.001) and IL-6 (r = 0.294, P < 0.001) and negatively with LDL particle size (r = −0.239, P < 0.001). ConclusionOur results indicate that LDL atherogenicity and inflammatory mediators can be better markers of CAD risk than known risk factors such as elevated concentrations of total- and LDL-cholesterol, decreased HDL-cholesterol levels and smoking in old healthy women.

The relative atherogenicity of VLDL and LDL is dependent on the topographic site

To evaluate whether the relative atherogenicity of VLDL and LDL is dependent on the topographic site, atherosclerosis was compared at four topographic sites in homozygous LDL receptor (LDLr)-deficient rabbits fed normal chow and in heterozygous LDLr-deficient rabbits with the same genetic background fed a 0.15% cholesterol diet to match cholesterol levels. VLDL cholesterol was significantly higher and LDL cholesterol significantly lower in LDLr(+/-) diet rabbits compared with LDLr(-/-) rabbits. Intimal area in the ascending thoracic aorta and in the abdominal aorta at the level of the renal arteries was 1.4-fold (P < 0.05) and 1.5-fold (P < 0.05) higher, respectively, in LDLr(-/-) rabbits than in LDLr(+/-) diet rabbits, whereas no significant difference occurred in the descending thoracic aorta and in the abdominal aorta just above the bifurcation. Differences remained statistically significant after adjustment for plasma cholesterol, triglycerides, and sex. Compared with LDLr(+/-) diet rabbits, higher intimal lipoprotein lipase (LPL) and apolipoprotein (apo) B levels were observed in LDLr(-/-) rabbits only at the level of the descending thoracic aorta. Intimal apo E levels in LDLr(-/-) rabbits were significantly lower in sites with a larger intima than in LDLr(+/-) diet rabbits. In conclusion, the relative atherogenicity of VLDL and LDL is dependent on the topographic site.

Oxidation-induced aggregation of LDL increases their uptake by smooth muscle cells from human aorta

Oxidative modification of human blood LDL induced by Cu2+, NaOCl, or 2,2-azobis-(2-aminopropane hydrochloride) was followed by their partial aggregation. Separation of oxidized LDL into aggregates and nonaggregated particles showed that they are characterized by a similar degree of oxidative modification. In contrast to nonaggregated particles, LDL aggregates in the same concentration significantly increased cholesterol content in smooth muscle cells from the intact (no involoved in atherosclerosis) human aortic intima. Our results indicate that atherogenicity of LDL oxidized by various factors is mainly associated with the formation of aggregates, but does not depend on the degree of oxidative modification.

Factors Affecting S-Homocysteinylation of LDL Apoprotein B

Hyperhomocysteinemia is an important risk factor for vascular disease and atherosclerosis, but the mechanisms by which homocysteine exerts its deleterious effects are not known. Because oxidation and/or homocysteinylation may increase atherogenicity of LDL, we investigated S-homocysteinylation of LDL as a possible contributor to atherosclerosis pathogenesis. We used capillary electrophoresis to measure LDL-bound thiols [homocysteine, cysteine (Cys), cysteinylglycine, glutathione, and glutamylcysteine] in 104 healthy study participants We also assessed total plasma thiol concentrations and lipid profiles. Our data suggest that apoprotein B (apoB)-cysteinylglycine (CysGly), apoB-Hcy, and apoB-Cys concentrations are markedly higher in men than in women. The percentage of CysGly and glutathione on apoB was higher than that of the same thiols in plasma, whereas the other thiols were markedly less prevalent in lipoprotein than in plasma. Pearson correlation showed that among all thiols, only total plasma Hcy is related to apoB-Hcy concentrations. Multiple correlation analysis confirmed that total Hcy was the most important determinant of apoB-Hcy. Age and LDL cholesterol also showed positive associations, but Cys and, mainly, CysGly were negatively associated with apoB-Hcy concentrations. apoB-Hcy derivative formation is mainly dependent on total homocysteine concentration. Increased cholesterol concentrations are related to increased apoB-Hcy. CysGly seems to compete with Hcy for binding to LDL apoprotein, suggesting that CysGly may protect against atherosclerosis by decreasing the concentrations of Hcy transferred by LDL from plasma to endothelial and subendothelial spaces.

Effects of dairy products naturally enriched with cis-9,trans-11 conjugated linoleic acid on the blood lipid profile in healthy middle-aged men

Interest in the development of dairy products naturally enriched in conjugated linoleic acid (CLA) exists. However, feeding regimens that enhance the CLA content of milk also increase concentrations of trans-18:1 fatty acids. The implications for human health are not yet known. This study investigated the effects of consuming dairy products naturally enriched in cis-9,trans-11 CLA (and trans-11 18:1) on the blood lipid profile, the atherogenicity of LDL, and markers of inflammation and insulin resistance in healthy middle-aged men. Healthy middle-aged men (n = 32) consumed ultra-heat-treated milk, butter, and cheese that provided 0.151 g/d (control) or 1.421 g/d (modified) cis-9,trans-11 CLA for 6 wk. This was followed by a 7-wk washout and a crossover to the other treatment. Consumption of dairy products enriched with cis-9,trans-11 CLA and trans-11 18:1 did not significantly affect body weight, inflammatory markers, insulin, glucose, triacylglycerols, or total, LDL, and HDL cholesterol but resulted in a small increase in the ratio of LDL to HDL cholesterol. The modified dairy products changed LDL fatty acid composition but had no significant effect on LDL particle size or the susceptibility of LDL to oxidation. Overall, increased consumption of full-fat dairy products and naturally derived trans fatty acids did not cause significant changes in cardiovascular disease risk variables, as may be expected on the basis of current health recommendations. Dairy products naturally enriched with cis-9,trans-11 CLA and trans-11 18:1 do not appear to have a significant effect on the blood lipid profile.

Postprandial hypertriglyceridaemia in type 2 diabetic subjects

Postprandial hyperlipidemia is a major risk factor for cardiovascular diseases in type 2 diabetes. The dyslipidemia of diabetes in the postprandial phase is a major determinant of the atherogenicity of LDL. This study was done to study the postprandial triglyceride levels in patients with type 2 diabetes mellitus; to assess the relationship between fasting and postprandial triglyceride levels and postprandial triglyceride levels and fasting blood sugar values in type 2 diabetes; and to analyze the relationship between postprandial hypertriglyceridaemia and conventional coronary risk factors. One hundred type 2 diabetic subjects (M:F - 67:33, mean age 56.6 ± 11.9 years, mean body mass index 24.83 kg/m 2 ) were studied and compared with controls. Fasting and 2-hour postprandial responses with respect to plasma glucose and triglycerides (TG) were measured after a breakfast meal, usually consumed by the patient with usual dose of insulin or oral hypoglycemic drugs. Postprandial hypertriglyceridaemia was taken as a postprandial TG value greater than 15% of the corresponding fasting TG value. There was signi› cant postprandial hypertriglyceridaemia in diabetics in comparison to controls. FBG was signi›cantly related to fasting and postprandial triglycerides. As FBG increased, both fasting and postprandial TG increased. Fasting TG was signi›cantly related to postprandial TG. As fasting TG increased, postprandial TG increased. There was no correlation between postprandial TG and age, sex, smoking, hypertension, total and LDL cholesterol*. is attributable in part to specific disorders of lipoprotein metabolism. These include disordered metabolism of VLDL and chylomicrons that may be atherogenic. The dyslipidemia of diabetes in the postprandial phase is a major determinant of the atherogenicity of LDL, which may account for the up to fivefold increase in atherosclerosis in the diabetic patient. Elevated postprandial triglycerides, peak postprandial triglyceridaemia have been associated in clinical trials with both early coronary artery and carotid artery atherosclerosis for persons with hyperlipidemia, independent of established risk factors. [4,5] Various clinical trials both in India (Chennai) and the West (Spain, USA, Sweden) have shown that postprandial hypertriglyceridaemia is common in type 2 DM. Normalization of the postprandial phase in diabetes will yield important cardiovascular benefits.

Quantification of Thiol-Containing Amino Acids Linked by Disulfides to LDL

Several studies have indicated that plasma proteins interact with homocysteine (Hcy) to form stable disulfide-linked products. Hcy in plasma is mainly bound to albumin, but interactions with ceruloplasmin, fibrin, annexin II, and transthyretin have been also reported (1)(2)(3)(4). In 1991, Olszewski and McCully (5) described the presence of Hcy in lipoproteins in patients with hypercholesterolemia. Because the analysis was performed after acidic hydrolysis of apoprotein, the Hcy measured by these authors was the sum of (a) Hcy incorporated in the primary structure of apolipoprotein B-100 (5), (b) Hcy thiolactone bound to lysine residues of protein by amide or peptide linkages and converted to Hcy by acidic conditions after release (6), and (c) Hcy linked to apolipoprotein B-100 (apoB-100) by a disulfide bond. Recent studies have demonstrated that there are at least nine free sulfhydryl groups (−SH) in the apoB-100 primary structure that could potentially bind plasma free aminothiols by disulfide linkage (7). Because lysyl residues of apoB-100 could react in vivo with plasma Hcy thiolactone by an amide bond, the number of free apoprotein sulfhydryl groups could increase considerably, thus increasing the number of sites that may be bound with plasma aminothiols (6). These LDL modifications are accompanied by an increase in density and in electrophoretic mobility of lipoprotein and are associated with functional alterations that make Hcy-LDL more susceptible to aggregation and to spontaneous precipitation. Moreover, higher uptake of Hcy-LDL by membrane receptor and by phagocytosis and a higher accumulation of intracellular cholesterol have been observed in cultured macrophages, suggesting that homocysteinylation could increase the atherogenicity of LDL (8)(9). Thus, to study the association between Hcy and lipid metabolism, a highly sensitive method to measure Hcy and other thiols bound to apoB-100 is required. Here we describe a simple capillary electrophoresis …

Thermally Oxidized Dietary Fats Increase the Susceptibility of Rat LDL to Lipid Peroxidation but Not Their Uptake by Macrophages

The aim of this study was to investigate the effect of dietary oxidized fats on the lipoprotein profile and the atherogenicity of LDL. Two experiments with male Sprague-Dawley rats were conducted. In Experiment 1, diets with either fresh fat or oxidized fat, prepared by heating at temperatures of 50, 105 or 190 degrees C, containing either 25 or 250 mg alpha-tocopherol equivalents/kg were used. In Experiment 2, diets with fresh or oxidized fat, heated at a temperature of 55 degrees C, containing 25 mg alpha-tocopherol equivalents/kg, were used. In Experiment 1, rats fed all types of oxidized fats had higher concentrations of HDL cholesterol and lower ratios between plasma and HDL cholesterol than rats fed the diet containing the fresh fat. As determined from the lag time, the susceptibility of LDL to copper-induced lipid peroxidation was higher in rats fed oxidized fats heated at 105 or 190 degrees C than in rats fed the diets containing the fresh fat or the oxidized fat treated at 50 degrees C, irrespective of the dietary vitamin E concentration. However, in Experiment 2, the composition of LDL apolipoproteins and uptake of LDL by macrophages were not different between rats fed the fresh fat diet and those fed the oxidized fat diet. We conclude that ingestion of oxidized fats does not adversely affect the lipoprotein profile in the rat model used, and does not cause modifications of apolipoproteins that would lead to enhanced uptake of LDL via macrophage scavenger receptors.

Immunological Quantitation and Localization of ACAT-1 and ACAT-2 in Human Liver and Small Intestine

By using specific anti-ACAT-1 antibodies in immunodepletion studies, we previously found that ACAT-1, a 50-kDa protein, plays a major catalytic role in the adult human liver, adrenal glands, macrophages, and kidneys but not in the intestine. Acyl-coenzyme A:cholesterol acyltransferase (ACAT) activity in the intestine may be largely derived from a different ACAT protein. To test this hypothesis, we produced specific polyclonal anti-ACAT-2 antibodies that quantitatively immunodepleted human ACAT-2, a 46-kDa protein expressed in Chinese hamster ovary cells. In hepatocyte-like HepG2 cells, ACAT-1 comprises 85-90% of the total ACAT activity, with the remainder attributed to ACAT-2. In adult intestines, most of the ACAT activity can be immunodepleted by anti-ACAT-2. ACAT-1 and ACAT-2 do not form hetero-oligomeric complexes. In differentiating intestinal enterocyte-like Caco-2 cells, ACAT-2 protein content increases by 5-10-fold in 6 days, whereas ACAT-1 protein content remains relatively constant. In the small intestine, ACAT-2 is concentrated at the apices of the villi, whereas ACAT-1 is uniformly distributed along the villus-crypt axis. In the human liver, ACAT-1 is present in both fetal and adult hepatocytes. In contrast, ACAT-2 is evident in fetal but not adult hepatocytes. Our results collectively suggest that in humans, ACAT-2 performs significant catalytic roles in the fetal liver and in intestinal enterocytes.

Increased atherogenicity of low-density lipoprotein in heavy proteinuria.

Heavy proteinuria is associated with marked abnormalities of lipoprotein metabolism and increased risk of atherogenesis. It is possible that qualitative as well as quantitative changes occur in lipoproteins to contribute to increased cardiovascular risk; for example, it is known that LDL exhibits heterogeneity, with small, dense LDL III particles being more atherogenic. We investigated LDL subfractions (measured by density gradient ultracentrifugation), VLDL subfractions, and post-heparin lipases in 12 patients with primary glomerular disease and 24-h albuminuria >2.5 g. These were compared to 23 age- and sex-matched controls. Total LDL concentrations were similar in proteinuric patients and controls; however, there was a shift in subfraction distribution. The larger LDL I and LDL II particles were lower in the proteinuric group (29 +/- 24 vs 62 +/- 26 mg/dl P=0.011 and 121 +/- 80 vs 197 +/- 74 mg/dl P=0.028), whereas the concentration of atherogenic LDL III (small dense) was higher (135 +/- 64 vs 75 +/- 71 mg/dl P=0.0016). The concentration of total VLDL and both its subfractions were increased in the patients with proteinuria. Post-heparin hepatic and lipoprotein lipase levels were similar to normal. These findings suggest that the atherogenicity of LDL is increased in patients with heavy proteinuria because of the redistribution towards smaller denser particles. Since small, dense LDL has a lower affinity for the LDL receptor, the altered nature of the lipoprotein in proteinuria may decrease its clearance by the receptor-mediated pathway and contribute to the reduced clearance of LDL observed in this population. This may contribute to progression of renal failure or the accelerated vascular disease found in patients with heavy proteinuria.

冠動脈疾患におけるLDLの被酸化性とその粒子径の関連およびLDL分画中構成脂質成分についての検討

Oxidative modification of LDL is considered to play an important role in the pathogenesis of coronary atherosclerosis. However, LDL is heterogeneous in size, density, and chemical composition and these differences may be responsible for some of the variability in the atherogenicity of LDL in different subjects.We evaluated the association between oxidative susceptibility and particle size or lipid composition of LDL obtained from patients with or without CAD.The subjects were 102 patients who underwent coronary angiography:62 patients with significant coronary artery stenosis ≥50% defined as CAD and 40 patients without CAD. Susceptibility to oxidative modification was assessed by TBARS in plasma and LDL and the monitoring curve of copper-induced oxidation of LDL was separated by an ultracentrifugal method. Peak particle diameter (PPD) was measured by 2.5-16% nondenaturing polyacrylamide gradient-gel and lipid compositions were investigated by the enzymatic method.Patients with CAD had a higher prevalence of hypertension, diabetes mellitus and body mass index (BMI) than patients without CAD. When comparing plasma lipid levels, total cholesterol and apo B were higher, and HDL-C and apo A-I were lower in patients with CAD. LDL in patients with CAD showed significantly higher levels of TBARS(1.37±0.75 vs. 1.10±0.35nmol MDA/mg, p<0.05) and reduced lag time (43.3±6 vs. 48.5±9分, p<0.005) compared to those without CAD. Moreover, their LDL was significantly smaller (25.59±0.51 vs. 26.02±0.71nm, p<0.005) and diminished in lipid contents such as free cholesterol (FC), cholesterol ester (CE), and phospholipid (PL) except for triglycerides. In all patients, we found that LDL-PPD showed a significantly positive correlation with lag time and lipid contents including FC, CE, and PL. In particular, the content of FC per particle had a significantly positive correlation with LDL-PPD and lag time even after adjusting for age, BMI, and plasma lipids.We conclude that increased susceptibility to oxidative modification of small LDL may contribute to the development of coronary atherosclerosis. The lipid composition of LDL per particle associated with size, especially FC, may be responsible for increased susceptibility to oxidative modification and the atherogenicity.

Oxidation of low-density lipoproteins by rat mesangial cells and the interaction of oxidized low-density lipoproteins with rat mesangial cells in vitro

Glomerulosclerosis and atherosclerosis share common pathobiological mechanisms. Experiments carried out in vitro over the past decade using cells thought to be involved in the atherosclerotic process such as endothelial cells, smooth muscle cells, and monocyte/macrophages have shown that postsecretory modifications such as oxidation increase the atherogenicity of LDL. Animal experiments employing antioxidant therapy have also been shown to slow the progression of atherosclerotic lesions. We set out to investigate the interactions between oxidized LDL (oxLDL) and rat mesangial cells (RMC) that might be of importance in the glomerulosclerotic process. Our results show that RMC have the ability to oxidize LDL, that oxLDL binding was 2-3-fold greater than native LDL (nLDL), and that oxLDL was more cytotoxic to these cells than nLDL. We speculate that cell-mediated oxidation of LDL in vivo may play a role in the progression of the glomerulosclerotic process.

Role of oxidized low density lipoprotein in atherogenesis.

Evidence to support an important role of oxidative modification in mediating the atherogenicity of LDL continues to grow. New hypotheses suggest mechanisms by which Ox-LDL or products of Ox-LDL can affect many components of the atherogenic process, including vasomotor properties and thrombosis, as well as lesion initiation and progression itself. These ideas suggest new approaches, that in combination with lowering of plasma cholesterol, could lead to the prevention of atherosclerosis and its complications.

Restriction fragment length polymorphisms in the apo B gene in relation to coronary artery disease

We have determined the frequencies of the alleles at the EcoRI (E), Xbal (X) and PvuII (P) polymorphic restriction sites in the apo B gene in 124 white men with coronary artery disease (CAD) and in 146 white men free from CAD. The frequencies of the E − (restriction site absent) and X − alleles were both significantly higher in normocholesterolaemic men with CAD than in those without CAD, but the frequency of the P + allele (restriction site present) was similar in the 2 groups. The frequency of the E − allele was significantly higher in CAD men with hypertriglyceridaemia than in normal men without hypertriglyceridaemia. In the normocholesterolaemic men without CAD, the mean serum cholesterol concentration was higher in those with genotype X ++ than in those with genotype X −− Mean serum LDL-apo B and LDL-cholesterol concentrations did not differ significantly between men with different XbaI or EcoRI genotypes. Serum apo A-I levels differed significantly between normal men with different XbaI genotypes. Serum HDL-cholesterol levels differed significantly between CAD men with different XbaI genotypes. These results suggest that in white men the E − and X − alleles are in linkage disequilibrium with a nearby allele that is causally related to CAD. It is also possible that the amino acid substitution at position 4154 in apo B, brought about by the nucleotide change responsible for the EcoRI polymorphism, has a direct effect on the atherogenicity of LDL.

培養ヒト臍帯静脈内皮細胞のplatelet-activating factor(PAF)産生に対するリポ蛋白の影響

Human umbilical vein endothelial cells in culture synthesize platelet-activating factor (PAF) in response to the stimulation with thrombin. The most part of newly-synthesized PAF remains cell-associated even in the presence of physiological concentration of extracellular albumin which strongly binds PAF. Therefore, PAF may be incorporated into the surface membrane of endothelial cells as a part of the compositional phospholipids and thereby may lower the antithrombogenic property of these cells; and endothelial PAF generation may result in the activation of effector cells such as leukocytes and thrombocytes contacting with the surface. PAF is known to be inactivated by a specific enzyme called PAF acetylhydrolase, and previous studies have revealed the existence of this enzyme in HDL and LDL. This study was intended to clarify the effects of plasma lipoproteins on thrombin-induced production and extracellular release of PAF by endothelial cells.Confluent monolayers of endothelial cells were incubated with [3H]acetate and thrombin in the presence or absence of either LDL or HDL (500μg protein/ml) of which PAF acetylhydrolase had been inactivated completely by the pretreatment with diisopropylfluorophosphate. [3H]PAF was separated by thin-layer chromatography and quantified by scintillation spectrometry.Thrombin stimulated endothelial cells to produce 1, 200±616.4 dpm/106 cells PAF (n=3). Approximately 2-fold enhancement of PAF production was observed in the presence of LDL (2, 507±125.9 dpm/106 cells, n=3). About 7% of the total [3H]PAF was detected in extracellular medium in the presence of LDL, whereas the release in its absence was estimated to be 3%. HDL displayed no effect on endothelial PAF production and the extracellular release.In conclusion, the atherogenicity of LDL may be mediated, in part, by its enhancing effect on endothelial PAF production. PAF may exert its biological activities being retained by the cells.