Localization of oxidized HDL in atheromatous plaques and oxidized HDL binding sites on human aortic endothelial cells

Lutein and Zeaxanthin Enhance, Whereas Oxidation, Fructosylation, and Low pH Damage High-Density Lipoprotein Biological Functionality

High-density lipoproteins (HDLs) are key regulators of cellular cholesterol homeostasis but are functionally altered in many chronic diseases. The factors that cause HDL functional loss in chronic disease are not fully understood. It is also unknown what roles antioxidant carotenoids play in protecting HDL against functional loss. The aim of this study was to measure how various disease-associated chemical factors including exposure to (1) Cu2+ ions, (2) hypochlorous acid (HOCL), (3) hydrogen peroxide (H2O2), (4) sialidase, (5) glycosidase, (6) high glucose, (7) high fructose, and (8) acidic pH, and the carotenoid antioxidants (9) lutein and (10) zeaxanthin affect HDL functionality. We hypothesized that some of the modifications would have stronger impacts on HDL particle structure and function than others and that lutein and zeaxanthin would improve HDL function. HDL samples were isolated from generally healthy human plasma and incubated with the corresponding treatments listed above. Cholesterol efflux capacity (CEC), lecithin-cholesterol acyl transferase (LCAT) activity, and paraoxonase-1 (PON1) activity were measured in order to determine changes in HDL functionality. Median HDL particle diameter was increased by acidic pH treatment and reduced by HOCl, high glucose, high fructose, N-glycosidase, and lutein treatments. Acidic pH, oxidation, and fructosylation all reduced HDL CEC, whereas lutein, zeaxanthin, and sialidase treatment improved HDL CEC. LCAT activity was reduced by acidic pH, oxidation, high fructose treatments, and lutein. PON1 activity was reduced by sialidase, glycosidase, H2O2, and fructose and improved by zeaxanthin and lutein treatment. These results show that exposure to oxidizing agents, high fructose, and low pH directly impairs HDL functionality related to cholesterol efflux and particle maturation, whereas deglycosylation impairs HDL antioxidant capacity. On the other hand, the antioxidants lutein and zeaxanthin improve or preserve both HDL cholesterol efflux and antioxidant activity but have no effect on particle maturation.

The Association between High-density Lipoproteins and Periodontitis

Periodontitis is one of the most typical chronic dental diseases. This inflammatory disease can change various functions of immune cells and impair lipid metabolism through proinflammatory cytokines. High-Density Lipoprotein (HDL) is considered protective of the cardiovascular system. It has anti-thrombotic and anti-inflammatory effects. In this article, we have reviewed the association between periodontitis and HDL. Various studies have demonstrated a reverse relationship between inflammatory cytokines and HDL. HDL contains antioxidative enzymes and proteins, whereas periopathogens impair HDL's antioxidant function. The presence of periodontal bacteria is associated with a low HDL level in patients with periodontitis. Genetic variants in the interleukin- 6 (IL)-6 gene and cytochrome (CYP)1A1 rs1048943 gene polymorphism are associated with HDL levels and periodontal status. Studies showed that HDL levels improve after treatment for periodontitis. On the one hand, periodontal pathogenic bacteria and their metabolites and pro-inflammatory cytokines from periodontal infection can result in various disorders of lipid metabolism and lipid peroxidation. On the other hand, hyperlipidemia and lipid peroxidation stimulate proinflammatory cytokines, resulting in oxidative stress and delayed wound healing, making individuals susceptible to periodontitis.

A green-inspired method to prepare non-split high-density lipoprotein (HDL) carrier with anti-dysfunctional activities superior to reconstituted HDL

Numerous studies have demonstrated that dysfunctional high-density lipoprotein (HDL), especially oxidized HDL (OxHDL), could generate multifaceted in vivo proatherogenic effects that run counter to the antiatherogenic activities of HDL. It thereby reminded us that the in vitro reconstituted HDL (rHDL) might encountered with oxidation-induced dysfunction. Accordingly, a green-inspired method was employed to recycle non-split HDL from human plasma fraction IV. Then it was compared with rHDL formulated by an ethanol-injection method in terms of physicochemical properties and anti-dysfunctional activities. Results exhibited that rHDL oxidation extent exceeded that of non-split HDL evidenced by higher malondialdehy content, weaker inhibition on low-density lipoprotein (LDL) oxidation and more superoxide anion. The reserved paraoxonase-1 activity on non-split HDL could partially explain for above experimental results. In the targeted transport mechanism experiment, upon SR-BI receptor inhibition and/or CD36 receptor blockage, the almost unchanged non-split HDL uptake in lipid-laden macrophage indicated its negligible oxidation modification profile with regard to rHDL again. Furthermore, compared to rHDL, better macrophage biofunctions were observed for non-split HDL as illustrated by accelerated cholesterol efflux, inhibited oxidized LDL uptake and lessened cellular lipid accumulation. Along with decreased ROS secretion, obviously weakened oxidative stress damage was also detected under treatment with non-split HDL. More importantly, foam cells with non-split HDL-intervention inspired an enhanced inflammation repression and apoptosis inhibition effect. Collectively, the anti-dysfunctional activities of non-split HDL make it suitable as a potential nanocarrier platform for cardiovascular drug payload and delivery.

Oxidized high-density lipoprotein promotes CD36 palmitoylation and increases lipid uptake in macrophages

Oxidized high-density lipoprotein (oxHDL) reduces the ability of cells to mediate reverse cholesterol transport and also shows atherogenic properties. Palmitoylation of cluster of differentiation 36 (CD36), an important receptor mediating lipoprotein uptake, is required for fatty acid endocytosis. However, the relationship between oxHDL and CD36 has not been described in mechanistic detail. Here, we demonstrate using acyl-biotin exchange analysis that oxHDL activates CD36 by increasing CD36 palmitoylation, which promotes efficient uptake in macrophages. This modification increased CD36 incorporation into plasma lipid rafts and activated downstream signaling mediators, such as Lyn, Fyn, and c-Jun N-terminal kinase, which elicited enhanced oxHDL uptake and foam cell formation. Furthermore, blocking CD36 palmitoylation with the pharmacological inhibitor 2-bromopalmitate decreased cell surface translocation and lowered oxHDL uptake in oxHDL-treated macrophages. We verified these results by transfecting oxHDL-induced macrophages with vectors expressing wildtype or mutant CD36 (mCD36) in which the cytoplasmic palmitoylated cysteine residues were replaced. We show that cells containing mCD36 exhibited less palmitoylated CD36, disrupted plasma membrane trafficking, and reduced protein stability. Moreover, in ApoE^−/−CD36^−/− mice, lipid accumulation at the aortic root in mice receiving the mCD36 vector was decreased, suggesting that CD36 palmitoylation is responsible for lipid uptake in vivo. Finally, our data indicated that palmitoylation of CD36 was dependent on DHHC6 (Asp-His-His-Cys) acyltransferase and its cofactor selenoprotein K, which increased the CD36/caveolin-1 interaction and membrane targeting in cells exposed to oxHDL. Altogether, our study uncovers a causal link between oxHDL and CD36 palmitoylation and provides insight into foam cell formation and atherogenesis.

Higher oxidized high-density lipoprotein to apolipoprotein A-I ratio is associated with high-risk coronary plaque characteristics determined by CT angiography

BACKGROUND

Oxidized high-density lipoprotein (oxHDL), unlike native HDL, is characterized by reduced cholesterol efflux capability and anti-inflammatory properties. The ratio of oxHDL to apolipoprotein A-I (oxHDL/apoAI) is a possible marker of dysfunctional HDL. The aim of this study was to evaluate the association between oxHDL/apoAI and coronary plaque characteristics that increase the likelihood of cardiovascular events as determined by coronary computed tomography (CT) angiography.

METHODS

A total of 297 patients (mean age; 67 years, men; 63%) who underwent coronary CT angiography for suspected stable coronary artery disease (CAD) were included. High-risk plaques (HRP) were defined by three characteristics: positive remodeling; low-density plaques; and spotty calcification. Significant stenosis was defined as a luminal narrowing of >70%. Serum concentrations of oxHDL were measured using an enzyme-linked immunosorbent assay.

RESULTS

Patients with higher oxHDL/ApoAI showed significantly greater prevalence of HRP (p = 0.03) and significant stenosis (p < 0.01) compared with patients with low oxHDL/ ApoAI. The multivariate logistic analysis demonstrated that oxHDL/ApoAI significantly associated with the presence of HRP and significant coronary stenosis (p = 0.01 and < 0.01). In the follow-up study including 243 patients for a median period of 1.8 years, univariate cox regression analysis showed that oxHDL/ApoAI, HRP and significant stenosis were significant predictors of cardiovascular events.

CONCLUSIONS

A high oxHDL/apoAI was associated with the presence of HRP and significant stenosis determined by coronary CT angiography, which can lead to cardiovascular events in patients with suspected stable CAD.

LDL and HDL Oxidative Modification and Atherosclerosis

Low-density lipoprotein (LDL) and high-density lipoprotein (HDL) are two kinds of common lipoproteins in plasma. The level of LDL cholesterol in plasma is positively correlated with atherosclerosis (AS), which is related to the complex macromolecular components, especially the easy oxygenation of protein and lipid components. However, the plasma HDL cholesterol level is negatively correlated with AS, but the results of recent studies show that the oxidative modified HDL in pathological state will not reduce and may aggravate the occurrence and development of AS. Therefore, the oxidative modification of lipoproteins is closely related to vascular homeostasis, which has become a hot research area for a long time.

Cardiovascular Disease in Gout and the Protective Effect of Treatments Including Urate-Lowering Therapy

Cardiovascular disease affects more than 90 million Americans. Recent studies support an increased cardiovascular disease risk in inflammatory conditions, such as gout. Increased serum urate levels, or hyperuricemia, are a precursor to gout. Data from meta-analyses have shown hyperuricemia to be linked to hypertension and coronary heart disease. Similarly, gout has been associated with an increased risk of myocardial infarction, cerebrovascular accidents, and death from cardiovascular disease in randomized clinical trials. Urate-lowering therapy reduces serum urate and may decrease systemic inflammation, generation of oxidative species, and reverses endothelial dysfunction through hyperuricemia-dependent or hyperuricemia-independent pathways. Cardioprotective benefits of allopurinol, a first-line agent for the treatment of gout, have been demonstrated to potentially prevent myocardial infarction, stroke, atrial fibrillation, and other cardiovascular diseases in observational studies in select populations. Randomized controlled trials (RCTs) have also examined the role of newer urate-lowering therapies, such as febuxostat and lesinurad, and their risk of cardiovascular-specific mortality in comparison to allopurinol. A large post-marketing study of febuxostat vs. allopurinol showed higher all-cause and cardiovascular-specific mortality in the febuxostat group than in the allopurinol group; a major study limitation was that large numbers of patients were lost to follow-up or discontinued treatment. RCTs are required to assess the comparative effectiveness of urate-lowering therapies, validate findings of observational studies, and to determine which subgroup populations of gout are most likely to benefit from appropriate long-term urate-lowering therapy. This review examines the data for increased cardiovascular disease in gout and potential underlying mechanisms (including hyperuricemia, inflammation, endothelial dysfunction, oxidative stress) and the effect of urate-lowering therapy on cardiovascular disease.

Lipoproteins in Atherosclerosis Process

BACKGROUND

Dyslipidaemias is a recognized risk factor for atherosclerosis, however, new evidence brought to light by trials investigating therapies to enhance HDLcholesterol have suggested an increased atherosclerotic risk when HDL-C is high.

RESULTS

Several studies highlight the central role in atherosclerotic disease of dysfunctional lipoproteins; oxidised LDL-cholesterol is an important feature, according to "oxidation hypothesis", of atherosclerotic lesion, however, there is today a growing interest for dysfunctional HDL-cholesterol. The target of our paper is to review the functions of modified and dysfunctional lipoproteins in atherogenesis.

CONCLUSION

Taking into account the central role recognized to dysfunctional lipoproteins, measurements of functional features of lipoproteins, instead of conventional routine serum evaluation of lipoproteins, could offer a valid contribution in experimental studies as in clinical practice to stratify atherosclerotic risk.

Associations of High-Density Lipoprotein Particle and High-Density Lipoprotein Cholesterol With Alcohol Intake, Smoking, and Body Mass Index - The INTERLIPID Study

BACKGROUND

Recently, high-density lipoprotein particles (HDL-P) have been found to be more strongly inversely associated with coronary artery disease (CAD) risk than their counterpart, HDL cholesterol (HDL-C). Given that lifestyle is among the first targets in CAD prevention, we compared the associations of HDL-P and HDL-C with selected lifestyle factors. Methods and Results: We examined 789 Japanese participants of the INTERLIPID Study: men (n=386) and women (n=403) aged 40-59 years in 1996-1998. Participants treated for dyslipidemias were excluded. Lifestyle factors included alcohol intake, smoking amount, and body mass index (BMI). Multivariable linear regression was used for cross-sectional analyses of these factors with HDL-P, HDL-C, HDL-P size subclasses (small, medium and large) and mean HDL-P size. In men, higher alcohol intake was associated with higher HDL-P and higher HDL-C. The associations of alcohol, however, were strongest with HDL-P. A higher smoking amount tended to be associated with lower HDL-P and HDL-C. In contrast, BMI was not associated with HDL-P, but was strongly inversely associated with HDL-C. While alcohol intake favored larger mean HDL-P size, smoking and BMI favored a lipid profile with smaller HDL-P subclasses and overall smaller mean HDL-P size. Similar, but generally weaker results were observed in women.

CONCLUSIONS

Although both HDL-P and HDL-C are parameters of HDL, they have different associations with alcohol, smoking and BMI.

Porphyromonas gingivalis accelerates atherosclerosis through oxidation of high-density lipoprotein

Purpose

The aim of this study was to evaluate the ability of Porphyromonas gingivalis (P. gingivalis) to induce oxidation of high-density lipoprotein (HDL) and to determine whether the oxidized HDL induced by P. gingivalis exhibited altered antiatherogenic function or became proatherogenic.

Methods

P. gingivalis and THP-1 monocytes were cultured, and the extent of HDL oxidation induced by P. gingivalis was evaluated by a thiobarbituric acid-reactive substances (TBARS) assay. To evaluate the altered antiatherogenic and proatherogenic properties of P. gingivalis-treated HDL, lipid oxidation was quantified by the TBARS assay, and tumor necrosis factor alpha (TNF-α) levels and the gelatinolytic activity of matrix metalloproteinase (MMP)-9 were also measured. After incubating macrophages with HDL and P. gingivalis, Oil Red O staining was performed to examine foam cells.

Results

P. gingivalis induced HDL oxidation. The HDL treated by P. gingivalis did not reduce lipid oxidation and may have enhanced the formation of MMP-9 and TNF-α. P. gingivalis-treated macrophages exhibited more lipid aggregates than untreated macrophages.

Conclusions

P. gingivalis induced HDL oxidation, impairing the atheroprotective function of HDL and making it proatherogenic by eliciting a proinflammatory response through its interaction with monocytes/macrophages.

Current and future therapies for addressing the effects of inflammation on HDL cholesterol metabolism

Cardiovascular disease (CVD) is a major cause of morbidity and mortality worldwide. Inflammatory processes arising from metabolic abnormalities are known to precipitate the development of CVD. Several metabolic and inflammatory markers have been proposed for predicting the progression of CVD, including high density lipoprotein cholesterol (HDL-C). For ~50 years, HDL-C has been considered as the atheroprotective 'good' cholesterol because of its strong inverse association with the progression of CVD. Thus, interventions to increase the concentration of HDL-C have been successfully tested in animals; however, clinical trials were unable to confirm the cardiovascular benefits of pharmaceutical interventions aimed at increasing HDL-C levels. Based on these data, the significance of HDL-C in the prevention of CVD has been called into question. Fundamental in vitro and animal studies suggest that HDL-C functionality, rather than HDL-C concentration, is important for the CVD-preventive qualities of HDL-C. Our current review of the literature positively demonstrates the negative impact of systemic and tissue (i.e. adipose tissue) inflammation in the healthy metabolism and function of HDL-C. Our survey indicates that HDL-C may be a good marker of adipose tissue health, independently of its atheroprotective associations. We summarize the current findings on the use of anti-inflammatory drugs to either prevent HDL-C clearance or improve the function and production of HDL-C particles. It is evident that the therapeutic agents currently available may not provide the optimal strategy for altering HDL-C metabolism and function, and thus, further research is required to supplement this mechanistic approach for preventing the progression of CVD.

LINKED ARTICLES

This article is part of a themed section on Targeting Inflammation to Reduce Cardiovascular Disease Risk. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v174.22/issuetoc and http://onlinelibrary.wiley.com/doi/10.1111/bcp.v82.4/issuetoc.

Associations among apolipoproteins, oxidized high-density lipoprotein and cardiovascular events in patients on hemodialysis

Apolipoproteins are associated with survival among patients on hemodialysis (HD), but these associations might be influenced by dysfunctional (oxidized) high-density lipoprotein (HDL). We assessed associations among apolipoproteins and oxidized HDL, mortality and cardiovascular disease (CVD) events in patients on HD. This prospective observational study examined 412 patients on prevalent HD. Blood samples were obtained before dialysis at baseline to measure lipids, apolipoproteins, oxidized LDL, oxidized HDL, high-sensitivity C-reactive protein (hs-CRP) and interleukin (IL)-6 at baseline, and HDL-C and hs-CRP were measured 12 months later. Patients were then prospectively followed-up (mean, 40 months) and all-cause mortality and composite CVD events were analyzed. Associations between variables at baseline and clinical outcome were assessed by Cox proportional hazards modeling (n = 412) and Cox hazards modeling with a time-varying covariate with HDL-C and hs-CRP (n = 369). Quartiles of apolipoproteins and oxidized HDL were not associated with all-cause mortality. However, Cox proportional hazards models with quartiles of each variable adjusted for confounders and hs-CRP or IL-6 identified apolipoprotein (apo)B-to-apoA-I ratio (apoB/apoA-I) and oxidized HDL, but not apoA-I or apoA-II, as independent risk factors for composite CVD events. These associations were confirmed by Cox proportional hazards modeling with time-varying covariates for hs-CRP. ApoB/apoA-I was independently associated with composite CVD events in 1-standard deviation (SD) increase-of-variables models adjusted for the confounders, oxidized HDL and hs-CRP. However, these associations disappeared from the model adjusted with IL-6 instead of hs-CRP, and oxidized HDL and IL-6 were independently associated with composite CVD events. Findings resembled those from Cox proportional hazards modeling using time-varying covariates with HDL-C adjusted with IL-6. In conclusion, both oxidized HDL and apoB/apoA-I might be associated with CVD events in patients on prevalent HD, while associations of apoB/apoA-I with CVD events differed between models of apoB/apoA-I quartiles and 1-SD increases, and were influenced by IL-6.

Oxidized high density lipoprotein induces macrophage apoptosis via toll-like receptor 4-dependent CHOP pathway

Oxidized HDL (ox-HDL), unlike native HDL that exerts antiatherogenic effects, plays a proatherogenic role. However, the underlying mechanisms are not completely understood. This study was designed to explore the inductive effect of ox-HDL on endoplasmic reticulum (ER) stress-CCAAT-enhancer-binding protein homologous protein (CHOP)-mediated macrophage apoptosis and its upstream mechanisms. Our results showed that ox-HDL could be ingested by macrophages, causing intracellular lipid accumulation. As with tunicamycin (an ER stress inducer), ox-HDL induced macrophage apoptosis with concomitant activation of ER stress pathway, including nuclear translocation of activating transcription factor 6, phosphorylation of protein kinase-like ER kinase and eukaryotic translation initiation factor 2α, and upregulation of glucose-regulated protein 78 and CHOP, which were inhibited by 4-phenylbutyric acid (PBA, an ER stress inhibitor) and CHOP gene silencing. Additionally, diphenyleneiodonium (DPI, an oxidative stress inhibitor), probucol (a reactive oxygen species scavenger), and toll-like receptor 4 (TLR4) silencing reduced ox-HDL-induced macrophage apoptosis, oxidative stress, and CHOP upregulation. Moreover, HDL isolated from patients with metabolic syndrome induced macrophage apoptosis, oxidative stress, and CHOP upregulation, which were blocked by PBA and DPI. These data indicate that ox-HDL may activate ER stress-CHOP-induced apoptotic pathway in macrophages via enhanced oxidative stress and that this pathway may be mediated by TLR4.

Glycoxidized HDL, HDL enriched with oxidized phospholipids and HDL from diabetic patients inhibit platelet function

CONTEXT

High-density lipoproteins (HDL) possess atheroprotective properties including anti-thrombotic and antioxidant effects. Very few studies relate to the functional effects of oxidized HDL on platelets in type 2 diabetes (T2D).

OBJECTIVE

The objective of our study was to investigate the effects of in vitro glycoxidized HDL and HDL from patients with T2D on platelet aggregation and arachidonic acid signaling cascade. At the same time, the contents of hydroxylated fatty acids were assessed in HDL.

RESULTS

Compared with control HDL, in vitro glycoxidized HDL had decreased proportions of linoleic (LA) and arachidonic (AA) acids in phospholipids and cholesteryl esters, and increased concentrations of hydroxy-octadecadienoic acids (9-HODE and 13-HODE) and 15-hydroxy-eicosatetraenoic acid (15-HETE), derived from LA and AA respectively, especially hydroxy derivatives esterified in phospholipids. Glycoxidized HDL dose-dependently decreased collagen-induced platelet aggregation by binding to scavenger receptor BI (SR-BI). Glycoxidized HDL prevented collagen-induced increased phosphorylation of platelet p38 MAPK and cytosolic phospholipase A2, as well as intracellular calcium mobilization. HDL enriched with oxidized phosphatidylcholine (PC), namely PC(16:0/13-HODE) dose-dependently inhibited platelet aggregation. Increased concentrations of 9-HODE, 13-HODE, and 15-HETE in phospholipids (2.1-, 2.1-, and 2.4-fold increase, respectively) were found in HDL from patients with T2D, and these HDL also inhibited platelet aggregation via SR-BI.

CONCLUSIONS

Our results suggest that in vitro glycoxidized HDL as well as HDL from patients with T2D inhibit platelet aggregation, and suggest that oxidized LA-containing phospholipids may contribute to the anti-aggregatory effects of glycoxidized HDL and HDL from patients with T2D.

Oxidized HDL induces cytotoxic effects: implications for atherogenic mechanism

Atherosclerosis can be considered as an inflammatory disease and oxidized low-density lipoprotein (oxLDL) is a critical factor in atherogenesis. Although high-density lipoprotein (HDL) is generally an antiatherogenic lipoprotein, this property can be compromised by functional impairment mainly due to oxidative modification. As such, understanding the proatherogenic properties exerted by oxidized-HDL (oxHDL) becomes more important. This study was focused on examining the role of oxHDL as a proatherogenic agent, using oxLDL as a positive control. The comparative toxicity of oxHDL and oxLDL having same range of malondialdehyde, to monocytes was evaluated. After treatment, markers for oxidative stress, inflammation, and cytotoxicity were quantitated. The results showed that like oxLDL, oxHDL induced significant oxidative stress, cytotoxicity, and release of TNF -alpha and MMP-9 in monocytes/macrophages, but was less potent than oxLDL in promoting these proatherogenic effects. Further, the effects of oxHDL for the enhanced formation of MMP-9 were found to be mediated by NADPH oxidase/ROS-JNK/ERK pathway, as one mechanism.

Effects of cigarette smoking on HDL quantity and function: implications for atherosclerosis

Cigarette smoking has been identified as an independent and preventable risk factor for atherosclerosis and cardiovascular disease. Population studies have shown that plasma high density lipoprotein (HDL) cholesterol levels are inversely related to the risk of developing cardiovascular disease. Cigarette smoking is associated with reduced HDL cholesterol levels. Cigarette smoking can alter the critical enzymes of lipid transport, lowering lecithin: cholesterol acyltransferase (LCAT) activity and altering cholesterol ester transfer protein (CETP) and hepatic lipase activity, which attributes to its impact on HDL metabolism and HDL subfractions distribution. In addition, HDL is susceptible to oxidative modifications by cigarette smoking, which makes HDL become dysfunctional and lose its atheroprotective properties in smokers. Therefore, cigarette smoking has a negative impact on both HDL quantity and function, which can explain, in part, the increased risk of cardiovascular disease in smokers.

Oxidized high-density lipoprotein induces the proliferation and migration of vascular smooth muscle cells by promoting the production of ROS

AIM

As the major atheroprotective particle in plasma, high-density lipoprotein(HDL) is oxidized during atherosclerotic processes. Oxidized HDL(ox-HDL) may lose its cardioprotective properties and develop a proinflammatory and proatherogenic phenotype. The proliferation and migration of vascular smooth muscle cells(VSMCs) play a crucial role in atherogenesis. However, the influence of ox-HDL on VSMC proliferation and migration remains poorly understood.

METHODS

VSMCs were treated with native HDL(N-HDL) or ox-HDL at varying concentrations for different time intervals and used in several analyses. The degree of cell proliferation was assayed using CCK-8 kits. The level of cell migration was determined using a Transwell chamber and scratch-wound assay. The presence of intracellular reactive oxygen species(ROS) was detected based on ROS-mediated 2',7'-dichlorofluorescein fluorescence. The activation of NADPH oxidase was measured in terms of the Rac1 activity and NADP(＋)/NADPH ratio.

RESULTS

Compared to N-HDL, ox-HDL significantly promoted VSMC proliferation and migration in a dose-dependent manner. In addition, ox-HDL remarkably activated NADPH oxidase and enhanced ROS generation in the VSMCs. Diphenyleneiodonium chloride, an inhibitor of NADPH oxidase, and N-acetylcysteine, a ROS scavenger, efficiently inhibited the ROS production triggered by ox-HDL and subsequently blocked the proliferating and migrating effects of ox-HDL in the VSMCs.

CONCLUSIONS

Ox-HDL significantly induces VSMC proliferation and migration by promoting NADPH oxidase activation and ROS production. Furthermore, the inhibition of NADPH oxidase and ROS generation blocks the proliferation and migration of VSMCs induced by ox-HDL. These proliferating and migrating effects of ox-HDL are closely related to its proinflammatory and proatherogenic roles.

Oxidized high-density lipoprotein is associated with increased plasma glucose in non-diabetic dyslipidemic subjects

BACKGROUND

Oxidized high-density lipoprotein (oxHDL) has reduced capacity for cholesterol efflux and some of other anti-atherogenic properties of HDL, but the role of oxHDL in the pathogenesis of cardiometabolic disease has not been fully demonstrated. This study investigated the association of oxHDL with plasma glucose (PG) and the other atherosclerotic risk variables in non-diabetic dyslipidemic subjects.

METHODS

Conventional atherosclerotic markers and LDL particle size (LDL-PS), as determined by gel electrophoresis, were measured in 155 non-diabetic subjects (mean age of 57 years) with dyslipidemia. Serum oxHDL levels were quantified using an antibody against oxidized human apoA-I in a sandwich ELISA format.

RESULTS

Multiple regression analysis adjusted for possible confounders revealed that HDL-cholesterol was independently, significantly and positively correlated with LDL-PS and oxHDL. By multiple regression analysis, oxHDL was independently, significantly and positively correlated with fasting PG (β=0.19, P=0.01). Subjects in the highest PG tertile group had approximately 30% higher oxHDL levels than the lowest PG tertile group.

CONCLUSIONS

These results suggest that high PG levels may contribute to the HDL oxidation, irrespective of HDL-cholesterol levels, even in non-diabetic subjects with dyslipidemia, and that the measurement of oxHDL may be a useful marker of dysfunctional HDL.

Oxidatively modified high density lipoprotein promotes inflammatory response in human monocytes-macrophages by enhanced production of ROS, TNF-α, MMP-9, and MMP-2

It has been proposed that high-density lipoprotein (HDL) loses its cardioprotective ability through oxidative modifications by reactive oxygen species (ROS) and promote atherogenesis. However, the pro-atherogenic pathways undergone by oxidized HDL remain poorly understood. Since monocytes play a crucial role in atherogenesis, this study was aimed to investigate the influence of both native and oxidized HDL (oxHDL) on monocytes-macrophages functions relevant to atherogenesis. HDL particles were isolated from human blood samples by ultracentrifugation and subjected to in vitro oxidation with CuSO(4). The extent of oxidation was quantitated by measurement of lipid peroxides. Human peripheral blood mononuclear cells were isolated and cultured under standard conditions. Cells were treated with native and oxHDL at varying concentrations for different time intervals and used for several analyses. Intracellular ROS production was assessed based on ROS-mediated DCFH fluorescence of the cells. The release of TNF-α and matrix metalloproteinases (MMPs) was quantitated using ELISA kit and gelatine zymography, respectively. Treatment of cells with oxidized HDL enhanced the production of ROS in a concentration-dependent way, while native HDL had no such effect. Further, the release of TNF-α, MMP-9, and MMP-2 was found to be remarkably higher in cells incubated with oxHDL than that of native HDL. Results demonstrate that oxidative modification of HDL induces pro-inflammatory response and oxidative stress in human monocytes-macrophages.

Retention of atherogenic lipoproteins in the artery wall and its role in atherogenesis

AIMS

In this review, we discuss the mechanisms behind the binding of low-density lipoproteins (LDL) to the arterial wall and how this interaction might be targeted to prevent atherosclerosis.

DATA SYNTHESIS

An increasing body of evidence shows that accumulation of LDL in the vessel wall is a critical step in the development of atherosclerosis. The retained lipoproteins subsequently provoke an inflammatory response that ultimately leads to atherosclerosis. In the arterial wall, LDL binds ionically to proteoglycans in the extracellular matrix. In particular, proteoglycans with elongated glycosaminoglycan (GAG) chains seem to play a crucial role in this process.

CONCLUSIONS

The LDL-proteoglycan interaction is a highly regulated process that might provide new therapeutic targets against cardiovascular disease.

Specific binding of hypochlorite-oxidized HDL to platelet CD36 triggers proinflammatory and procoagulant effects

OBJECTIVE

Oxidative stress and systemic inflammation negatively affect several protective functions of high density lipoproteins (HDL) and oxidative modification of HDL by the inflammation-derived oxidant hypochlorite converts HDL into a potent platelet agonist. Therefore it was the aim of this work to clarify if these platelet-activating effects result from specific binding of hypochlorite-oxidized HDL (hyp-OxHDL) to the platelet surface and to identify responsible receptors.

METHODS

Binding and functional studies were performed with hyp-OxHDL in absence and presence of (potential) competitors in normal and CD36-deficient human platelets. Platelet aggregation was quantified by light transmission aggregometry. Surface expression of CD62P, phosphatidylserine and CD40L was quantified by flow cytometry.

RESULTS

Binding studies reveal that hyp-OxHDL show specific and saturable high-affinity binding to the platelet surface. Hyp-OxHDL trigger platelet aggregation and in a dose dependent way provoke the release of significant amounts of CD40L as well as phosphatidylserine on the platelet surface. Blocking specific binding of hyp-OxHDL to the platelet surface interferes with the ability of hyp-OxHDL to stimulate human platelets. CD36-deficient human platelets show markedly reduced binding of hyp-OxHDL. Upon addition of hypochlorite-oxidized HDL, CD36-deficient platelets do not aggregate and completely fail to release CD40L or phosphatidylserine.

CONCLUSIONS

From these results we conclude that specific binding of hyp-OxHDL to platelet CD36 is essential for the proinflammatory and procoagulant effects of hyp-OxHDL shown within this work. The contribution of other receptors besides CD36 to specific binding of hyp-OxHDL to the platelet membrane appears to be minimal, at best.

oxHDL decreases the expression of CD36 on human macrophages through PPARgamma and p38 MAP kinase dependent mechanisms

CD36, belongs to class B scavenger receptor family, is a macrophage receptor for oxidized low-density lipoprotein (oxLDL) and has been proven to play a critical role in atherosclerotic foam cell formation. In addition, CD36 expression is regulated by many factors including oxLDL and HDL. A recent study suggests that CD36 can also bind with oxidized high-density lipoprotein (oxHDL). However, the direct role of oxHDL in atherosclerosis is still not clear and it is not known whether oxHDL has any influence on the expression of CD36 in macrophages. Here, we performed experiments to investigate the effect of oxHDL on the expression of CD36 on human peripheral blood monocytes-macrophages and the possible mechanisms. Our results suggest that the uptake of oxHDL by CD36 on macrophages accelerates foam cell formation. In addition, oxHDL can down-regulate both the mRNA and surface protein expression of CD36 on human peripheral macrophages in vitro. oxHDL increased the mRNA expression and protein phosphorylation of peroxisome proliferators-activated receptor-gamma (PPARgamma). Using different mitogen-activated protein kinase (MAPK) inhibitors, we demonstrated that oxHDL regulated CD36 and PPARgamma expression in a p38-MAP kinase dependent mechanism.

Dysfunctional high-density lipoprotein

PURPOSE OF REVIEW

To address the progress of the investigation on dysfunctional high-density lipoprotein (HDL).

RECENT FINDINGS

HDL is generally considered to be an independent protective factor against cardiovascular disease. However, emerging evidence indicates that HDL can be modified under certain circumstances and lose its protective effect or even become atherogenic. The underlying mechanisms responsible for generating the dysfunctional HDL and the chemical and structural changes of HDL remain largely unknown. Recent studies focus on the role of myeloperoxidase in generating oxidants as participants in rendering HDL dysfunctional in vivo. Myeloperoxidase modifies HDL in humans by oxidation of specific amino acid residues in apolipoprotein A-I, which impairs cholesterol efflux through ATP-binding cassette transporter A1 and contributes to atherogenesis.

SUMMARY

HDL may not always be atheroprotective and can be atherogenic paradoxically under certain conditions. The mechanisms responsible for generating the dysfunctional HDL remain largely unknown. Recent data suggest that myeloperoxidase-associated modification of HDL may be one of the mechanisms. Further studies are needed to investigate the in-vivo mechanisms of HDL modification and identify therapeutic approaches aiming at controlling HDL modification.

Oxidation by hypochlorite converts protective HDL into a potent platelet agonist

High density lipoproteins (HDL) represent a protective factor of central importance that counteracts the development of cardiovascular disease, in part by normalizing platelet (hyper)reactivity. As HDL represent an efficient scavenger of the naturally occurring oxidant hypochlorite, this work was intended to investigate the influence of hypochlorite-oxidized HDL on platelet function. Addition of hypochlorite-oxidized HDL to human platelets results in an immediate and transient raise in intracellular calcium, surface expression of P-selectin and platelet aggregation. The observed effects are dose dependent and can be blocked by an antibody directed against the lipoprotein-binding domain of platelet thrombospondin- and scavenger receptor CD36.

Establishment and evaluation of 2 monoclonal antibodies against oxidized apolipoprotein A-I (apoA-I) and its application to determine blood oxidized apoA-I levels

BACKGROUND

Apolipoprotein A-I (apoA-I) is the major lipoprotein component of high-density lipoprotein(HDL), and plays an important role in reverse cholesterol transport. Its function is known to be influenced by oxidation.

METHODS

Using H2O2-or chloramine T-oxidized apoA-I as antigen, we prepared 2 kinds of monoclonal antibodies, and established an ELISA system for the measurement of oxidized apoA-I.

RESULTS

The 2 monoclonal antibodies obtained, 7D3 and 98A7, exhibited different reactivity characteristics. The serum level of oxidized apoA-I was higher in patients with either inflammatory disease or diabetes than in healthy individuals, and suggested a diversity of oxidized apoA-I.

CONCLUSION

The 2 monoclonal antibodies are useful for the determination of oxidized apoA-I and study of diverse oxidized HDLs.

CD36 is a receptor for oxidized high density lipoprotein: Implications for the development of atherosclerosis

Atherosclerotic plaques result from the excessive deposition of cholesterol esters derived from lipoproteins and lipoprotein fragments. Tissue macrophage within the intimal space of major arterial vessels have been shown to play an important role in this process. We demonstrate in a transfection system using two human cell lines that the macrophage scavenger receptor CD36 selectively elicited lipid uptake from Cu(2+)-oxidized high density lipoprotein (HDL) but not from native HDL or low density lipoprotein (LDL). The uptake of oxHDL displayed morphological and biochemical similarities with the CD36-dependent uptake of oxidized LDL. CD36-mediated uptake of oxidized HDL by macrophage may therefore contribute to atheroma formation.

Effects of oxidized low- and high-density lipoproteins on gene expression of human macrophages

OBJECTIVE

Oxidized low-density lipoprotein (ox-LDL) is a major factor in foam cell formation, whereas the role of oxidized high-density lipoprotein (ox-HDL) in this process is not known. The objective of the present study was to examine the effects of ox-LDL and ox-HDL on the gene expression of cultured human macrophages.

MATERIAL AND METHODS

Gene expression of human macrophages was studied after incubation for 1 day and 3 days with native and oxidized LDL and HDL using cDNA expression array. Expression of granulocyte-macrophage colony-stimulating factor 1, which was constantly up-regulated by ox-LDL and down-regulated by ox-HDL after 1- and 3 days of incubation in cDNA microarray experiments, was verified by quantitative reverse transcriptase-polymerase chain reaction (RT-PCR).

RESULTS

Genes that showed altered expression were divided into six groups; 1) lipid metabolism, 2) inflammation, growth and hemostasis, 3) matrix metalloproteinases and tissue inhibitors of matrix metalloproteinases, 4) enzymes, 5) structural and binding proteins and 6) annexins.

CONCLUSIONS

The microarray method was found to be applicable in analyzing changes in gene expression induced by oxidized lipoproteins in cultured human macrophages. Our results reflect different functional roles of ox-LDL and ox-HDL in foam cell formation.

Modified HDL: biological and physiopathological consequences

Epidemiological and clinical studies have demonstrated the inverse association between HDL cholesterol levels (HDL-C) and the risk of coronary heart disease (CHD). This correlation is believed to relate to the ability of HDL to promote reverse cholesterol transport. Remodeling of HDL due to chemical/physical modifications can dramatically affect its functions, leading to dysfunctional HDL that could promote atherogenesis. HDL modification can be achieved by different means: (i) non-enzymatic modifications, owing to the presence of free metal ions in the atherosclerotic plaques; (ii) cell-associated enzymes, which can degrade the apoproteins without significant changes in the lipid moiety, or can alternatively induce apoprotein cross-linking and lipid oxidation; (iii) association with acute phase proteins, whose circulating levels are significantly increased during inflammation which may modify HDL structure and functions; and (iv) metabolic modifications, such as glycation that occurs under hyperglycaemic conditions. Available data suggest that HDL can easily be modified losing their anti-atherogenic activities. These observation results mainly from in vitro studies, while few in vivo data, are available. Furthermore the in vivo mechanisms involved in HDL modification are ill understood. A better knowledge of these pathways may provide possible therapeutic target aimed at reducing HDL modification.

Psoriasis is associated with lipid abnormalities at the onset of skin disease

BACKGROUND

Psoriasis appears to have increased cardiovascular morbidity. The underlying pathogenetic mechanisms remain unclear. Multiple factors, including systemic inflammation, oxidative stress, aberrant lipid profile, and concomitant established risk factors, have been discussed. However, previous studies consist of heterogeneous patient materials, including persons with highly varying disease duration and treatment.

METHODS

Two-hundred patients were investigated at the onset of psoriasis, comparing plasma concentrations of lipids, lipoproteins, and apolipoproteins with those of matched controls (N = 285).

RESULTS

Psoriasis patients manifest significant lipid abnormalities. Specifically, patients had significantly higher cholesterol concentrations in the very-low-density lipoprotein and high-density-lipoprotein fractions. Adjustment for established environmental risk factors did not affect the results.

LIMITATION

The response rate among control subjects was low. However, an additional analysis of a random subset of nonresponders demonstrated no substantial differences in the main results.

CONCLUSION

The study supports the notion that lipid abnormalities in psoriasis may be genetically determined rather than acquired.

Myeloperoxidase-mediated oxidation of high-density lipoproteins: Fingerprints of newly recognized potential proatherogenic lipoproteins

Substantial evidence supports the notion that oxidative processes participate in the pathogenesis of atherosclerotic heart disease. Major evidence for myeloperoxidase (MPO) as enzymatic catalyst for oxidative modification of lipoproteins in the artery wall has been suggested in numerous studies performed with low-density lipoprotein. In contrast to low-density lipoprotein, plasma levels of high-density lipoprotein (HDL)-cholesterol and apoAI, the major apolipoprotein of HDL, inversely correlate with the risk of developing coronary artery disease. These antiatherosclerotic effects are attributed mainly to HDL's capacity to transport excess cholesterol from arterial wall cells to the liver during 'reverse cholesterol transport'. There is now strong evidence that HDL is a selective in vivo target for MPO-catalyzed oxidation impairing the cardioprotective and antiinflammatory capacity of this antiatherogenic lipoprotein. MPO is enzymatically active in human lesion material and was found to be associated with HDL extracted from human atheroma. MPO-catalyzed oxidation products are highly enriched in circulating HDL from individuals with cardiovascular disease where MPO concentrations are also increased. The oxidative potential of MPO involves an array of intermediate-generated reactive oxygen and reactive nitrogen species and the ability of MPO to generate chlorinating oxidants-in particular hypochlorous acid/hypochlorite-under physiological conditions is a unique and defining activity for this enzyme. All these MPO-generated reactive products may affect structure and function of HDL as well as the activity of HDL-associated enzymes involved in conversion and remodeling of the lipoprotein particle, and represent clinically useful markers for atherosclerosis.

HDL enhances oxidation of LDL in vitro in both men and women

Background

Oxidative modification of low-density lipoprotein (LDL) is a key event in the oxidation hypothesis of atherogenesis. Some in vitro experiments have previously suggested that high-density lipoprotein (HDL) co-incubated with LDL prevents Cu²⁺-induced oxidation of LDL, while some other studies have observed an opposite effect. To comprehensively clarify the role of HDL in this context, we isolated LDL, HDL₂ and HDL₃ from sera of 61 free-living individuals (33 women and 28 men).

Results

When the isolated LDL was subjected to Cu²⁺-induced oxidation, both HDL₂ and HDL₃ particles increased the rate of appearance and the final concentration of conjugated dienes similarly in both genders. Oxidation rate was positively associated with polyunsaturated fatty acid content of the lipoproteins in that it was positively related to the content of linoleate and negatively related to oleate. More saturated fats thus protected the lipoproteins from damage.

Conclusion

We conclude that in vitro HDL does not protect LDL from oxidation, but is in fact oxidized fastest of all lipoproteins due to its fatty acid composition, which is oxidation promoting.

Oxidised-HDL3 induces the expression of PAI-1 in human endothelial cells. Role of p38MAPK activation and mRNA stabilization

Modified lipoproteins have been suggested to modulate endothelial expression of plasminogen activator inhibitor-1 (PAI-1). As oxidized high-density lipoprotein (Ox-HDL) has been found in atheromatous plaques and receptors for modified HDL are present on endothelial cells, we investigated the role of Ox-HDL3 on the expression of PAI-1. Ox-HDL3 but not native HDL3, increased PAI-1 mRNA expression in endothelial cells. Furthermore, PAI-1 antigen expression and activity increased in the supernatant of cells incubated with Ox-HDL3. The intracellular pathways involved in this effect were investigated. Ox-HDL3 activated both extracellular signal-regulated kinases (ERK) 1/2 and p38 mitogen-activated protein kinase (MAPK). Moreover, incubation with specific inhibitors of these kinases showed that p38MAPK was mainly involved in the Ox-HDL3-dependent PAI-1 induction. Transient transfection experiments suggested that none of the response elements in the proximal promoter (-804 to 17) were involved in Ox-HDL3-mediated PAI-1 expression. mRNA stability experiments showed that Ox-HDL3 increased the PAI-1 mRNA half-life. In summary, Ox-HDL3 induced PAI-1 mRNA expression and antigen release through a molecular mechanism involving MAPK activation and mRNA stabilization. Thus, oxidative modification converts HDL to a prothrombotic lipoprotein species.

NF-kappa B activation in endothelial cells treated with oxidized high-density lipoprotein

We first determined whether oxidized high-density lipoprotein (ox-HDL) activates transcription factor nuclear factor-kappa B (NF-kappa B) in cultured human umbilical vein endothelial cells (HUVECs). Treatment for 7h with 100 microg/ml ox-HDL elicited a marked downregulation of I kappa B alpha and upregulation of the phosphorylated form of I kappa B alpha in HUVECs in a manner dependent on the dose of ox-HDL. Electrophoretic mobility shift assay in nuclear fraction from HUVECs showed translocation of NF-kappa B to the nucleus and binding of NF-kappa B to NF-kappa B consensus oligonucleotides during ox-HDL exposure for 7h, suggesting that ox-HDL brings about NF-kappa B activation in endothelial cells. To clarify the mechanism of NF-kappa B activation in HUVECs treated with ox-HDL, we investigated the effect of ox-HDL treatment on intracellular production of reactive oxygen species (ROS) in HUVECs. Ox-HDL induced a significant dose-dependent increase in ROS production during 4h incubation and this enhanced production of ROS was inhibited in the presence of probucol or diphenylene iodonium (DPI), an inhibitor of NADPH oxidase. In addition, pretreatment with probucol or DPI suppressed the phosphorylation and degradation of I kappa B alpha protein induced by ox-HDL, demonstrating that increased generation of ROS by ox-HDL may be associated with NF-kappa B activation. Pretreatment with antibody against oxidized low-density lipoprotein receptor-1 (LOX-1) significantly suppressed the ox-HDL-induced downregulation of I kappa B alpha, suggesting that LOX-1 mediates NF-kappa B activation in endothelial cells stimulated with ox-HDL. Taking all of the above findings together, ox-HDL activates NF-kappa B via binding to LOX-1 on the cell surface, followed by enhancement of intracellular ROS production in endothelial cells.

Detection of oxidized high-density lipoprotein

This paper reviews working procedures for the separation and detection of oxidized high-density lipoproteins (ox-HDL) and their constituents. It begins with an introductory overview of structural alterations of the HDL particle and its constituents generated during oxidation. The main body of the review delineates various procedures for the isolation and detection of ox-HDL as well as the purification and separation of phosphatidylcholine metabolites and denatured apolipoproteins in the particle. The useful methods published more recently are picked up and the utility of the separation techniques is described. The last section covers a clinical evaluation of changes in these factors in ox-HDL as well as future directions of ox-HDL research.

High-density lipoprotein regulates calcification of vascular cells

Accumulating evidence has suggested the protective role of HDL in cardiovascular disease processes. Calcification is a common feature of atherosclerotic lesions and contributes to cardiovascular complications due to the loss of aortic resilience and function. Recent studies have suggested that vascular calcification shares several features with skeletal bone formation at the cellular and molecular levels. These include the presence of osteoblast-like calcifying vascular cells in the artery wall that undergo osteoblastic differentiation and calcification in vitro. We hypothesized that HDL may also protect against vascular calcification by regulating the osteogenic activity of these calcifying vascular cells. When treated with HDL, alkaline phosphatase activity, a marker of osteogenic differentiation of osteoblastic cells, was significantly reduced in those cells. Prolonged treatment with HDL also inhibited calcification of these cells, further supporting the antiosteogenic differentiation property of HDL when applied to vascular cells. Furthermore, HDL inhibited the osteogenic activity that was induced by inflammatory cytokines interleukin (IL)-1beta and IL-6 as well as by minimally oxidized LDL. HDL also partially inhibited the IL-6-induced activation of signal transducer and activator of transcription 3 in calcifying vascular cells, suggesting that HDL may inhibit cytokine-induced signal transduction pathways. The inhibitory effects of HDL were mimicked by lipids extracted from HDL but not by HDL-associated apolipoproteins or reconstituted HDL. Furthermore, oxidation of HDL rendered it pro-osteogenic. Taken together, these results suggest that HDL regulates the osteoblastic differentiation and calcification of vascular cells and that vascular calcification may be another target of HDL action in the artery wall.

Apolipoprotein E mediates the retention of high-density lipoproteins by mouse carotid arteries and cultured arterial smooth muscle cell extracellular matrices

Lipoprotein retention in the vascular extracellular matrix (ECM) plays a critical role in atherogenesis. Previous studies demonstrated the presence of apo A-I and E in atherosclerotic lesions, suggesting that HDL may be trapped by the artery wall. We sought to determine mechanisms by which HDL could be bound and retained by the arterial wall, and whether apo E was a principal determinant of this binding. We evaluated in situ accumulation of fluorescently labeled DiI-human HDL+/-apo E in perfused carotid arteries from apo E-null mice. Apo E was important in mediating HDL binding to the vascular wall, with a 48+/-16% increase in accumulation of DiI-labeled apo E-containing HDL (HDL3+E) compared with DiI-apo E-free HDL (HDL3-E) (P=0.003). To investigate possible mechanisms responsible for retention, we assessed binding of unlabeled HDL3-E and HDL3+E to ECM generated by cultured arterial smooth muscle cells. Similar to the in situ carotid artery data, HDL3+E bound better to the ECM than did HDL3-E (3-fold lower K(a) and 3.5-fold higher B(max) for HDL3+E versus HDL3-E). These differences were eliminated after either neutralization of arginine residues on apo E or digestion of matrix with chondroitin ABC lyase, suggesting that chondroitin and/or dermatan sulfate proteoglycans were responsible for apo E-mediated increased binding. These findings demonstrate that HDL can bind to both intact murine carotid arteries and smooth muscle cell-derived ECM, and that apo E is a principal determinant in mediating the ability of HDL to be trapped and retained via its interaction with ECM proteoglycans.

Serum lipid metabolism abnormalities and change in lipoprotein contents in patients with advanced-stage renal disease

BACKGROUND

Arteriosclerosis is the major cause of death in patients with chronic renal failure. There is much interest in the lipid metabolism of patients treated with hemodialysis.

METHODS

We analyzed low-density lipoproteins (LDL) and high-density lipoproteins (HDL) in chronic renal failure (CRF) patients according to patients on hemodialysis (HD), patients with diabetic nephropathy before initiation of dialysis (DN), and patients with chronic glomerulonephritis in the conservative stage (CGN); and compared the lipid metabolic abnormalities in patients on hemodialysis and those not yet on hemodialysis. We also analyzed the qualitative abnormalities of LDL and HDL and their relationship with the pathological stages.

RESULTS

Electrophoretic patterns identified small LDL particles and small HDL particles in the three groups, and the degree of denaturation was more enhanced in CRF patients in the conservative stage than in HD patients. For LDL susceptibility to oxidation LDL (oxLDL) by addition of Cu(2+), the lag time was approximately 57 min in healthy controls and CGN patients, but was prolonged to approximately 75 min in HD and DN patients. For HDL susceptibility to oxidation HDL (oxHDL), HD, DN and CGN patients showed lag times shorter than those found in healthy control subjects. These results showed that LDL and HDL in the serum of CRF patients were in a state of enhanced susceptibility to oxidative modification. In Western blot analysis using anti-human-denatured LDL and anti-human-oxidized HDL monoclonal antibodies, bands of low molecular oxLDL at 150-197 kDa were detected in all CRF patients, with marked tailing in CGN patients. Similarly, bands of small oxHDL particles at 110 and 120 kDa were found in HD, DN and CGN patients.

CONCLUSIONS

Oxidative modification of both LDL and HDL occurs in patients with advanced CRF resulting in small lipoproteins. Increased production of oxLDL and oxHDL is the main cause of lipid metabolic abnormality in CRF patients.

Effects of a high polyunsaturated fat diet and vitamin E supplementation on high-density lipoprotein oxidation in humans

Oxidative modification of high-density lipoproteins (HDL) impairs several biologic functions critical to its role in reverse cholesterol transport. We therefore investigated the effect of dietary polyunsaturated fat and vitamin E on the kinetics of HDL oxidation. Ten subjects were fed sequentially: a baseline diet in which the major fat source was olive oil; a high polyunsaturated fat diet in which the major fat source was safflower oil; and the safflower oil diet plus 800 I.U. vitamin E per day. Plasma lipoprotein levels, vitamin E content, fatty acid composition, and oxidation lag time and rate were determined after 3 weeks on each diet. The polyunsaturated fat diet increased the mean HDL(2) lag time from 45.8+/-12.5 to 83.3+/-11.6 min with no change in oxidation rate. Addition of vitamin E further increased the HDL(2) lag time to 115.6+/-4.4 min and decreased the HDL(2) oxidation rate 10-fold. Neither the polyunsaturated diet alone nor the diet with vitamin E supplementation had any effect on HDL(3) oxidation. We conclude that under conditions of controlled dietary fat intake, a high polyunsaturated fat intake does not increase the oxidation susceptibility of HDL subfractions, and that in this setting, vitamin E supplementation reduces the oxidation susceptibility of HDL(2). These data suggest that antioxidants could influence HDL function in vivo.

Glycated high-density lipoprotein induces apoptosis of endothelial cells via a mitochondrial dysfunction

Glycation of plasma proteins may contribute to an excess risk of developing atherosclerosis in patients with diabetes mellitus. Although it is believed that high-density lipoprotein (HDL) is nonenzymatically glycosylated at an increased level in diabetic individuals, little is known about a possible linkage between glycated HDL and endothelium dysfunction in diabetes. This study set out to clarify whether glucose-modified HDL affects the function of endothelial cells by examining the apoptosis of cultured human aortic endothelial cells (HAECs) exposed to a glycated-oxidized HDL (gly-ox-HDL) prepared in vitro. Incubation of HAECs with 100 microg/ml of gly-ox-HDL for 48 h showed apoptotic features, such as cell shrinkage, membrane blebbing, and concentration and fragmentation of the nucleus, and the degree of apoptosis was dose-dependent on the glucose used in the preparation of gly-ox-HDL. Stimulation of HAECs with gly-ox-HDL elicited a marked increase in caspase 3 activity and the expressions of active caspase 3 and caspase 9, whereas concomitant treatment with a caspase 3 inhibitor significantly blocked gly-ox-HDL-induced apoptosis of HAECs. The release of cytochrome c into cytosols markedly increased in HAECs during the treatment with gly-ox-HDL. The increased expressions of Bax and Bad were detected in HAECs incubated for 24 h with gly-ox-HDL, but gly-ox-HDL failed to interfere with the expression of Bcl-2 and Bcl-x. Moreover, in vitro experiments with HDL (gly-HDL) glycated in the presence of 2 mM EDTA and Cu(2+)-oxidized HDL suggested that the apoptotic effect of gly-ox-HDL on endothelial cells might be due to an additional oxidative modification of gly-HDL. Taken altogether, additional oxidation of HDL under hyperglycemic conditions may induce endothelial apoptosis through a mitochondrial dysfunction, following the deterioration of vascular function.

Human neutrophils employ the myeloperoxidase/hydrogen peroxide/chloride system to oxidatively damage apolipoprotein A-I

The structural integrity of apolipoprotein A-I (apo A-I) is critical to the physiological function of high-density lipoprotein (HDL). Oxidized lipoproteins are thought to be of central importance in atherogenesis, and oxidation products characteristic of myeloperoxidase, a heme protein secreted by activated phagocytes, have been detected in human atherosclerotic tissue. At plasma concentrations of halide ion, hypochlorous acid is a major product of the myeloperoxidase-hydrogen peroxide-chloride system. We therefore investigated the effects of activated human neutrophils, a potent source of myeloperoxidase and hydrogen peroxide, on the protein and lipid components of HDL. Both free and HDL-associated apo A-I exposed to activated human neutrophils underwent extensive degradation as monitored by RP-HPLC and Western blotting with a polyclonal antibody to apo A-I. Replacement of the neutrophils with reagent HOCl resulted in comparable damage (at molar oxidant : HDL subclass 3 ratio = 100) as observed in the presence of activated phagocytes. Apo A-I degradation by activated neutrophils was partially inhibited by the HOCl scavenger methionine, by the heme inhibitor azide, by chloride-free conditions, by the peroxide scavenger catalase, and by a combination of superoxide dismutase (SOD)/catalase, implicating HOCl in the cell-mediated reaction. The addition of a protease inhibitor (3,4-dichloroisocoumarin) further reduced the extent of apo A-I damage. In contrast to the protein moiety, there was little evidence for oxidation of unsaturated fatty acids or cholesterol in HDL3 exposed to activated neutrophils, suggesting that HOCl was selectively damaging apo A-I. Our observations indicate that HOCl generated by myeloperoxidase represents one pathway for protein degradation in HDL3 exposed to activated phagocytes.