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

Sepsis-Induced Coagulopathy Phenotype Induced by Oxidized High-Density Lipoprotein Associated with Increased Mortality in Septic-Shock Patients

Sepsis syndrome is a highly lethal uncontrolled response to an infection, which is characterized by sepsis-induced coagulopathy (SIC). High-density lipoprotein (HDL) exhibits antithrombotic activity, regulating coagulation in vascular endothelial cells. Sepsis induces the release of several proinflammatory molecules, including reactive oxygen species, which lead to an increase in oxidative stress in blood vessels. Thus, circulating lipoproteins, such as HDL, are oxidized to oxHDL, which promotes hemostatic dysfunction, acquiring prothrombotic properties linked to the severity of organ failure in septic-shock patients (SSP). However, a rigorous and comprehensive investigation demonstrating that oxHDL is associated with a coagulopathy-associated deleterious outcome of SSP, has not been reported. Thus, we investigated the participation of plasma oxHDL in coagulopathy-associated sepsis pathogenesis and elucidated the underlying molecular mechanism. A prospective study was conducted on 42 patients admitted to intensive care units, (26 SSP and 16 non-SSP) and 39 healthy volunteers. We found that an increased plasma oxHDL level in SSP was associated with a prothrombotic phenotype, increased mortality and elevated risk of death, which predicts mortality in SSP. The underlying mechanism indicates that oxHDL triggers an endothelial protein expression reprogramming of coagulation factors and procoagulant adhesion proteins, to produce a prothrombotic environment, mainly mediated by the endothelial LOX-1 receptor. Our study demonstrates that an increased plasma oxHDL level is associated with coagulopathy in SSP through a mechanism involving the endothelial LOX-1 receptor and endothelial protein expression regulation. Therefore, the plasma oxHDL level plays a role in the molecular mechanism associated with increased mortality in SSP.

Serum LDL Levels are a Major Prognostic Factor for Arteriovenous Fistula Thrombosis (AVFT) in Hemodialysis Patients

Introduction

Arteriovenous fistula thrombosis (AVFT) is still a common cause of morbidity in patients undergoing regular hemodialysis (HD). Many factors have been found to induce AVFT. Some of those factors are local and others are systemic ones. In this study, we evaluated some local and systemic factors simultaneously, to predict the most potent risk factor for AVFT in HD patients.

Patients and methods

One hundred and eighteen patients aged 20–80 yrs with end-stage renal disease (ESRD) were evaluated prospectively for a period of 14 months. First, anticardiolipin antibodies (ACLA), TG, cholesterol, low density lipoprotein (LDL) and high density lipoprotein (HDL) were analyzed by conventional methods. Other basic data were accessed from patients' medical records. All fistulas were evaluated clinically as patent at the start of this study. Patients were followed-up for any evidence of AVFT within 14 months. Finally, all factors (diabetes, hypertension, presence of ACLA, ultrafiltration ≥3 L, age, gender, weight, hypotension during dialysis, fistula site, epoetin alpha usage, TG, HDL, LDL and total cholesterol) were analyzed in a stepwise regression analysis.

Results

Eighteen episodes of AVFT documented with Doppler sonography occurred in 17 patients (15.3%). Regression analysis showed only LDL values were the AVFT predictor in our patients (p=0.002, β-coefficient=0.3). Kaplan-Meier analysis showed a significantly lower AVF patency time in patients with LDL >130 mg/dl than those with LDL <130 mg/dl (log rank=0.0014).

Discussion

LDL value is a major prognostic factor for AVFT in HD patients and lowering it to <130 mg/dl could improve fistula patency.

Treatment of Dyslipidemia in Chronic Kidney Disease

Dyslipidemia is a common feature of various renal diseases. This perturbed lipid metabolism results in accelerated atherosclerosis and increased cardiovascular morbidity and mortality. Treatment of dyslipidemia, in addition to normalization of blood pressure and reduction of proteinuria, could provide additional means to retard the progression of chronic renal insufficiency. Possible therapeutic approaches include mainly dietary and life-style modifications, selective use of some technical components of dialysis systems, and the judicious prescriptions of lipid-lowering drugs. Even with relatively normal lipid and lipoprotein profiles statin therapy seems to prevent atherogenesis acceleration. A wide range of therapeutic interventions, targeting the lipid abnormalities that may develop in chronic renal patients and end-stage renal disease (ESRD) are currently available, though still without convincing evidence based on long-term prospective studies which clearly demonstrate a significant reduction in cardiovascular morbidity and mortality of ESRD patients. However, extensive investigations, concerning the best long-term therapeutic strategy for this high-risk population of patients, are still missing.

Oxidized high-density lipoprotein impairs the function of human renal proximal tubule epithelial cells through CD36

Unlike native high-density lipoprotein (HDL), oxidized HDL exerts adverse effects in a number of diseases, including chronic kidney disease (CKD); however, the mechanisms involved in this process remain unclear. In the present study, we investigated the effects of oxidized HDL on renal tubular cells, which play an important role in the progression of CKD. Human renal proximal tubule epithelial cells (HK-2) were cultured and stimulated with various concentrations of oxidized HDL in the absence or presence of CD36 siRNA. The results revealed that oxidized HDL enhanced the production of reactive oxygen species (ROS) and upregulated the expression of pro-inflammatory factors in the HK-2 cells in a dose-dependent manner. Incubation with oxidized HDL also increased the apoptosis of the HK-2 cells and reduced their migration ability in a dose‑dependent manner. Src family kinase, mitogen-activated protein kinase (MAPK) and nuclear factor-κB (NF-κB) were activated following stimulation with oxidized HDL. All these effects mediated by oxidized HDL on HK-2 cells were markedly attenuated by transfection with with CD36 siRNA pior to stimulation with oxidized HDL. These findings suggest that oxidized HDL enhances the pro-inflammatory properties and impairs the function of HK-2 cells, mainly through the scavenger receptor, CD36, as well as through the Src, MAPK and NF-κB pathways.

Pathophysiological and clinical aspects of malnutrition in chronic renal failure

Kidney diseases are the ninth leading cause of death in the USA. In these patients cardiovascular mortality is greater than in the general population. This observation, not completely explained by the so-called 'traditional' cardiovascular risk factors, lead the authors to postulate other 'emerging' ones found in chronic renal failure patients. Among these new findings, nutritional status, considered as the balance existing between nutrient requirements and intakes, plays an important role for the development of cardiovascular diseases. In fact several nutritional parameters are widely known as pathophysiological determinants of cardiovascular disturbances, which are based on accelerated atherosclerosis, due especially to enhanced oxidative stress and endothelial dysfunction. Chronic renal failure is a clinical condition that from many points of view seems to be a chronic inflammatory state, and many studies confirm this observation. This influences nutritional status especially in dialysis patients. Malnutrition is related in turn to accelerated atherosclerosis thus leading to a postulated 'malnutrition, inflammation, atherosclerosis' (MIA) syndrome in which malnutrition, inflammation and atherosclerosis contribute to an elevated cardiovascular mortality rate. The present review explores this issue, first by describing epidemiological aspects of malnutrition in chronic renal failure patients and then by analysing the specific biochemical and metabolic features of these patients.

Increase of electronegative-LDL-fraction ratio and IDL-cholesterol in chronic kidney disease patients with hemodialysis treatment

Background

It is known that the increased level of IDL and oxidized LDL are associated with risk of cardiovascular disease, and the lipoprotein abnormalities accelerate atherosclerosis. Cardiovascular disease is a major cause of mortality in chronic kidney disease patients with hemodialysis treatment (HD-Ps). Therefore, the estimation of lipoprotein profiles is important for prevention of cardiovascular disease in HD-Ps. We previously established an anion-exchange chromatographic method for measurement of cholesterol level in subclasses of HDL and LDL, IDL, VLDL, and chylomicron. An electronegative-LDL-fraction contained minimally oxidized-LDL. Lipoprotein profile can be accurately and conveniently determined by the new method.

Finding

In this study, lipoprotein profiles in HD-Ps and age-matched healthy subjects were estimated by using our established anion-exchange chromatographic method. The ratio of electronegative-LDL-cholesterol to total LDL-cholesterol and IDL-cholesterol in HD-Ps were significant higher than those in healthy subjects.

Conclusions

The results suggest that the ratio of electronegative-LDL-cholesterol to total LDL-cholesterol and IDL-cholesterol obtained by the new method may serve as useful markers for risk of cardiovascular disease in HD-Ps.

Oxidized high-density lipoprotein enhances inflammatory activity in rat mesangial cells

AIMS

Inflammation is a mechanism of glomerular damage in chronic glomerulopathies, in which dyslipidaemia plays an important role. Unlike native high-density lipoprotein (HDL), oxidized HDL is thought to be an adverse factor in chronic ischaemic disease and may increase the production of inflammatory cytokines in atheromatous plaques and plasma, but the effect of oxidized HDL on mesangial cells remains unclear.

METHODS

Intracellular reactive oxygen species level was measured. The inflammatory and proapoptotic effects of oxidized HDL were detected in rat mesangial cells by measuring levels of tumour necrosis factor-alpha, regulated upon activation, normal T-cell expressed and secreted, monocyte chemoattractant protein-1, CXC chemokine ligand-1 and early apoptosis. The expression of mitogen-activated protein kinase (MAPK) (p38/MAPK, extracellular-regulated kinase/MAPK and c-Jun N-terminal kinase/MAPK), nuclear factor-kappaB activity and lipoprotein scavenger receptors (CD36, low-density lipoprotein receptor-1 and scavenger receptor BI) were also detected.

RESULTS

Oxidized HDL enhanced reactive oxygen species production and upregulated expression of proinflammatory factors, including tumour necrosis factor-alpha, regulated upon activation, normal T-cell expressed and secreted (RANTES), monocyte chemoattractant protein-1 and CXC chemokine ligand-1 by rat mesangial cells dose in a dependent fashion. Incubation with oxidized HDL also increased rat mesangial cells apoptosis in a dose-dependent manner. These effects partly depended on scavenger receptors CD36 and low-density lipoprotein receptor-1, but not scavenger receptor BI. In addition, co-culture with oxidized HDL activated P38/MAPK, extracellular-regulated kinase (ERK)/MAPK and nuclear factor-kappaB (NF-kappaB).

CONCLUSIONS

The results of the present study suggest that oxidized HDL enhanced proinflammatory properties in mesangial cells partly via CD36 and low-density lipoprotein receptor-1. MAPK and nuclear factor-kappaB pathways were involved in the process. The ability of oxidized HDL to negatively influence mesangial cell biology may represent an important mechanism of chronic kidney disease.

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.

Low-density lipoprotein oxidizability in children with chronic renal failure

BACKGROUND

In childhood, dyslipidemia and low-density lipoprotein (LDL) oxidation play an important role in the development of atherosclerosis. Alterations of these factors have been shown in adult uremic patients.

METHODS

Nine children affected by chronic renal failure (CRF; urinary tract malformation, n = 8; polycystic kidney disease, n = 1) were studied to investigate the abnormalities of plasma lipoprotein concentration and composition and to assess the susceptibility of LDL to oxidation. All patients with CRF were on conservative treatment and, after informed consent, underwent the evaluation of (i) quantitative and qualitative plasma lipid profile; (ii) lipoprotein oxidation in vitro; and (iii) lipoprotein anti-oxidant content. These results were compared to those of an age-matched control group of eight healthy children.

RESULTS

Total cholesterol, LDL and triglycerides were significantly higher in CRF than in the control group. The composition of lipoproteins was different in the two groups: the amount of anti-oxidant factors (alpha-, gamma-tocopherol and carotenoids) was different in CRF and normal controls children, while LDL susceptibility to oxidation was significantly higher in uremic children than in controls.

CONCLUSIONS

CRF patients, already before dialysis, have a higher LDL oxidizability due to an altered lipoprotein composition and a low anti-oxidant content; therefore they have higher risk factors for atherosclerosis. On the basis of these data, supplementation with anti-oxidants might be useful in CRF children, but further studies are needed to evaluate the efficacy and safety of this therapeutic intervention.

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.

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.

Post-dialysis retention of blood lipoproteins and apolipoproteins in patients with end-stage renal disease on maintenance haemodialysis in Kuwait

BACKGROUND

The commonest cause of death in patients with end-stage renal disease (ESRD) on maintenance haemodialysis (MHD) is coronary heart disease (CHD). It has been suggested that dyslipidaemia, an important CHD risk factor, may be worsened by dialysis. This study evaluated changes in blood lipoproteins and apolipoproteins after dialysis in ESRD patients on MHD.

METHODS

The subjects were 57 (20 M, 37 F; 24 diabetic, 33 nondiabetic) patients with ESRD, aged 21-73 years, undergoing MHD at a major Dialysis Unit in Kuwait. Pre- and post-dialysis non-fasting blood samples were collected from each subject on the same day, and analyzed for plasma glucose, urate, triglycerides (TG), total cholesterol (TC), HDL, LDL and apolipoprotein (apo) A1 and B. Pre- and post-dialysis levels for each of the analytes were compared for the diabetic and non-diabetic subgroups of patients and linear correlations sought between Delta values (corresponding to differences between pre- and post-dialysis levels) of the lipoproteins and apolipoproteins.

RESULTS

There was a general trend towards significant increases in post-dialysis TC, HDL, LDL, and non-HDL levels in both sub-groups, and additionally for the non-diabetic, TG, apo A1 and apo B. The pre- to post-dialysis increases were essentially similar for the diabetic and non-diabetic groups-Diabetic: TC 14%, HDL 25%, LDL 19%, non-HDL 16%, apo A1 14%, apo B 10%; Non-diabetic: TC 20%, TG 29%, HDL 25%, LDL 26%, non-HDL 21%, apo A1 14%, apo B 14%. Generally, there were significant correlations between Delta values for the lipoproteins and apolipoproteins (r, 0.50-0.92) in both groups.

CONCLUSION

Levels of atherogenic lipoproteins increase post-dialysis in diabetic and non-diabetic patients with ESRD and the changing levels of these lipoproteins correlate significantly with corresponding changes in levels of apolipoproteins. The increase in lipid levels is therefore related to retention of apo A1 and B with each dialysis. We speculate that, with repeated dialysis, dyslipidaemia may get progressively worse and further accentuate CHD risk.

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.