The association of antibodies against oxidized low-density lipoprotein with atherosclerosis in hemodialysis patients

Methods on LDL particle isolation, characterization, and component fractionation for the development of novel specific oxidized LDL status markers for atherosclerotic disease risk assessment

The present study uses simple, innovative methods to isolate, characterize and fractionate LDL in its main components for the study of specific oxidations on them that characterize oxidized low-density lipoprotein (oxLDL) status, as it causatively relates to atherosclerosis-associated cardiovascular disease (CVD) risk assessment. These methods are: (a) A simple, relatively time-short, low cost protocol for LDL isolation, to avoid shortcomings of the currently employed ultracentrifugation and affinity chromatography methodologies. (b) LDL purity verification by apoB100 SDS-PAGE analysis and by LDL particle size determination; the latter and its serum concentration are determined in the present study by a simple method more clinically feasible as marker of CVD risk assessment than nuclear magnetic resonance. (c) A protocol for LDL fractionation, for the first time, into its main protein/lipid components (apoB100, phospholipids, triglycerides, free cholesterol, and cholesteryl esters), as well as into LDL carotenoid/tocopherol content. (d) Protocols for the measurement, for the first time, of indicative specific LDL component oxidative modifications (cholesteryl ester-OOH, triglyceride-OOH, free cholesterol-OOH, phospholipid-OOH, apoB100-MDA, and apoB100-DiTyr) out of the many (known/unknown/under development) that collectively define oxLDL status, which contrasts with the current non-specific oxLDL status evaluation methods. The indicative oxLDL status markers, selected in the present study on the basis of expressing early oxidative stress-induced oxidative effects on LDL, are studied for the first time on patients with end stage kidney disease on maintenance hemodialysis, selected as an indicative model for atherosclerosis associated diseases. Isolating LDL and fractionating its protein and main lipid components, as well as its antioxidant arsenal comprised of carotenoids and tocopherols, paves the way for future studies to investigate all possible oxidative modifications responsible for turning LDL to oxLDL in association to their possible escaping from LDL's internal antioxidant defense. This can lead to studies to identify those oxidative modifications of oxLDL (after their artificial generation on LDL), which are recognized by macrophages and convert them to foam cells, known to be responsible for the formation of atherosclerotic plaques that lead to the various CVDs.

Positive Association between Autoantibodies Against Oxidized LDL and HDL-C: A Novel Mechanism for HDL Cardioprotection?

BACKGROUND

In the atherosclerotic plaque microenvironment, oxidized phospholipids expressed in the oxidized low-density lipoprotein (oxLDL) surface bind to scavenger receptors of macrophages eliciting foam cell formation and plaque progression. Auto-antibodies against oxLDL (oxLDL-Ab) interact with oxidative epitopes leading to the formation of immune complexes that are unable to interact with macrophage receptors, thus abrogating atherogenesis. Release of oxLDL-Ab by B cells involves interleukin 5 and Th2 response, which in turn are potentiated by HDL. Thereby, we hypothesized that individuals with higher levels of HDL-C may plausibly display elevated titers of oxLDL-Ab.

OBJECTIVE

To evaluate the relationship between HDL-C and oxLDL-Ab levels.

METHODS

Asymptomatic individuals (n = 193) were grouped according to their HDL-C concentration to one of three categories: low (< 68 mg/dL), intermediate (68 to 80 mg/dL) or high (> 80 mg/dL). P values < 0.05 were considered statistically significant.

RESULTS

Our analysis included 193 individuals (mean age: 47 years; male: 26.3%). Compared to individuals in the lowest HDL-C tertile, those in the highest tertile were older (36 versus 53 years; p = 0.001) and less frequently male (42.6% versus 20.9%; p = 0.001). Mean values of oxLDL-Ab increased as the HDL-C group escalated (0.31, 0.33 and 0.43 units, respectively; p = 0.001 for trend). Simple linear regression found a significant, positive relationship between the independent variable, HDL-C, and the dependent variable, oxLDL-Ab (R = 0.293; p = 0.009). This relation remained significant (R = 0.30; p = 0.044), after adjustment by covariates. Apolipoprotein AI levels were also related to oxLDL-Ab in both simple and adjusted linear regression models.

CONCLUSION

HDL-C and oxLDL-Ab are independently related.

Low-density lipoprotein oxidation biomarkers in human health and disease and effects of bioactive compounds

Based on the significance of oxidized low-density lipoprotein (LDL) in health and disease, this review focuses on human studies addressing oxidation of LDL, including three lines of biomarkers, (i) ex vivo LDL resistance to oxidation, a "challenge test" model, (ii) circulating oxidized LDL, indicating the "current in vivo status", and (iii) autoantibodies against oxidized LDL as fingerprints of an immune response to oxidized LDL, along with circulating oxysterols and 4-hydroxynonenal as biomarkers of lipid peroxidation. Lipid peroxidation and oxidized LDL are hallmarks in the development of various metabolic, cardiovascular and other diseases. Changes further occur across life stages from infancy to older age as well as in athletes and smokers. Given their responsiveness to targeted nutritional interventions, markers of LDL oxidation have been employed in a rapidly growing number of human studies for more than 2 decades. There is growing interest in foods, which, besides providing energy and nutrients, exert beneficial effects on human health, such as protection of DNA, proteins and lipids from oxidative damage. Any health claim, however, needs to be substantiated by supportive evidence derived from human studies, using reliable biomarkers to demonstrate such beneficial effects. A large body of evidence has accumulated, demonstrating protection of LDL from oxidation by bioactive food compounds, including vitamins, other micronutrients and secondary plant ingredients, which will facilitate the selection of oxidation biomarkers for future human intervention studies and health claim support.

Systemic Redox Imbalance in Chronic Kidney Disease: A Systematic Review

Patients with chronic kidney disease (CKD) experience imbalance between oxygen reactive species (ROS) production and antioxidant defenses leading to cell and tissue damage. However, it remains unclear at which stage of renal insufficiency the redox imbalance becomes more profound. The aim of this systematic review was to provide an update on recent advances in our understanding of how the redox status changes in the progression of renal disease from predialysis stages 1 to 4 to end stage 5 and whether the various treatments and dialysis modalities influence the redox balance. A systematic review was conducted searching PubMed and Scopus by using the Cochrane and PRISMA guidelines. In total, thirty-nine studies met the inclusion criteria and were reviewed. Even from an early stage, imbalance in redox status is evident and as the kidney function worsens it becomes more profound. Hemodialysis therapy per se seems to negatively influence the redox status by the elevation of lipid peroxidation markers, protein carbonylation, and impairing erythrocyte antioxidant defense. However, other dialysis modalities do not so far appear to confer advantages. Supplementation with antioxidants might assist and should be considered as an early intervention to halt premature atherogenesis development at an early stage of CKD.

Novel immune assay for quantification of plasma protective capacity against oxidized phospholipids

Aim: Oxidized phospholipids (OxPL) are the major pathogenic component of oxidized low-density lipoproteins (OxLDL). Endogenous anti-OxPL activity, defined as the ability to neutralize adverse effects of oxidized lipids, may have biomarker potential. Methods & results: Using two anti-OxPL monoclonal antibodies (commercial mAB-E06 and custom mAB-509) we developed a novel ELISA that measures the global capacity of plasma to inactivate OxPL. Preincubation of OxLDL with plasma inhibits its binding of anti-OxPL mABs. This phenomenon (‘masking’) reflects anti-OxPL plasma activity. A pilot clinical application of the assay revealed reduced anti-OxPL activity in hypertension, coronary artery disease, acute coronary syndrome and diabetes. Conclusion: Inadequate anti-OxPL protection may contribute to cardiovascular disease and have biomarker potential in conditions associated with abnormal lipid peroxidation.

Oxidized low-density lipoprotein antibodies in myocardial infarction patients without classical risk factors

AIM

To determine whether circulating antibodies against oxidized low-density lipoprotein (LDL; OLAB) levels are associated with acute myocardial infarction (AMI) in individuals without classical cardiovascular risk factors.

METHODS

A case-control study including 34 first AMI patients without classical risk factors (smoking, dyslipidemia, hypertension or diabetes) and 45 population-based healthy controls.

RESULTS

There were no differences in anthropometric variables between cases and controls. Oxidized LDL levels were similar in both groups. Total cholesterol, LDL cholesterol, apolipoprotein B and physical activity were lower in cases than in controls. OLAB levels were also lower in cases than controls (128 versus 447 U/l, P < 0.001). After adjusting for age, oxidized LDL and physical activity, participants with OLAB levels of 165 U/l or less had a higher risk of AMI (odds ratio, OR = 7.48, 95% confidence interval: 1.57-35.66). When the model was fitted with OLAB as a continuous variable, the natural logarithm (LnOLAB) levels were independently associated with AMI with an OR of 0.40 (95% confidence interval: 0.19-0.86). After adjusting the model by Framingham-risk-adapted score and oxidized LDL, the LnOLAB levels maintained their independent association (OR of 0.43, 95% confidence interval: 0.23-0.79).

CONCLUSION

First AMI patients without classical risk factors had lower levels of OLAB compared with healthy controls. It is likely that the immunological reaction due to oxidized LDL participates as a preventive factor in the physiopathology of atherosclerosis.

Dyslipidemia in patients with chronic and end-stage kidney disease

In this review, we discuss the physiology, diagnosis and treatment of dyslipidemia in patients with chronic and end-stage renal disease. The recent important clinical trials in patients with chronic kidney disease and dyslipidemia are reviewed. Because of the lack of evidence in treating lipid abnormalities in this specific patient population, we propose that future studies should focus on the pathophysiological mechanisms and treatment of dyslipidemia in this special patient population.

Adaptive immunity is related to coronary artery disease severity after acute coronary syndrome in subjects with metabolic syndrome

Metabolic syndrome (MetS) is an inflammatory state associated with high coronary disease risk. Inflammation and adaptive immunity modulate atherosclerosis and plaque instability. We examined early changes in anti-oxidized low-density lipoprotein (LDL) (anti-oxLDL) autoantibodies (Abs) in patients with MetS after an acute coronary syndrome (ACS). Patients of both genders (n=116) with MetS were prospectively included after an acute myocardial infarction (MI) or hospitalization due to unstable angina. Anti-oxLDL Abs (IgG class) were assayed at baseline, three and six weeks after ACS. The severity of coronary disease was evaluated by the Gensini score. We observed a decrease in anti-oxLDL Abs titers (p<0.002 vs. baseline), mainly in males (p=0.01), in those under 65 y (p=0.03), and in subjects with Gensini score above median (p=0.04). In conclusion, early decrease in circulating anti-oxLDL Abs is associated with coronary disease severity among subjects with MetS.

Oxidized LDL to autoantibodies against oxLDL ratio - the new biomarker associated with carotid atherosclerosis and cardiovascular complications in dialyzed patients

OBJECTIVE

To investigate the role of autoantibodies against oxidized LDL (oxLDL-Ab) in clearing of oxLDL from circulation in dialyzed uremic patients, as well as the significance of this process in the carotid atherosclerosis and cardiovascular complications.

METHODS

oxLDL, oxLDL-Ab and intima-media thickness (IMT) were measured in 132 uremic patients on hemodialysis (HD), peritoneal dialysis (PD) or conservative treatment both with and without cardiovascular disease (CVD) and in 29 healthy controls. The ratio of oxLDL to oxLDL-Ab (oxLDL/oxLDL-Ab), reflecting the balance between in vivo oxidative LDL modification and the clearance of oxLDL from circulation was also calculated.

RESULTS

oxLDL were lower, whereas oxLDL-Ab were higher in patients without CVD compared to those with CVD. oxLDL/oxLDL-Ab ratio was also significantly lower in dialyzed subjects without CVD compared to their counterparts with CVD and healthy controls. IMT values were significantly higher in uremic patients compared with controls, and patients with CVD had particularly elevated IMT compared with those without CVD. The inverse correlation was between IMT and oxLDL-Ab, whereas the IMT was strongly and positively associated with oxLDL/oxLDL-Ab ratio. There was the weak inverse relationship between oxLDL and oxLDL-Ab levels in dialyzed patients. Multiple stepwise regression analysis identified oxLDL/oxLDL-Ab ratio as one of the predictors of IMT in the whole dialyzed group.

CONCLUSIONS

oxLDL/oxLDL-Ab ratio could be a new biomarker significantly and independently associated with carotid atherosclerosis in dialyzed patients. A titer of oxLDL-Ab and oxLDL/oxLDL-Ab ratio seem to play an important role for distinguishing patients with and without cardiovascular complications.

Neither oxidized nor anti-oxidized low-density lipoprotein level is associated with atherosclerosis or mortality in hemodialysis patients

It is anticipated that oxidized low-density lipoprotein (oxLDL) and anti-oxLDL are associated with atherosclerosis and mortality. However, data on this issue are controversial and limited. We aimed to investigate the effect of these two markers on the extent and progression of atherosclerosis and mortality in a group of hemodialysis patients. In this prospective observational study with a follow-up of 36 months, 124 hemodialysis patients were studied. Ninety-five patients underwent carotid intima media thickness (CA-IMT) measurement by B-Mode ultrasonography both at baseline and at the end of the study. oxLDL and anti-oxLDL were measured by enzyme-linked immunosorbent assay. The extent and progression of CA-IMT, along with overall and cardiovascular mortality, were assessed. The mean age at baseline was 54.0 ± 14.8 years, 57.3% male and 20% diabetic. The mean oxLDL and anti-oxLDL levels were 8.11 ± 3.16 mU/L and 1.30 ± 0.31, respectively. Baseline mean CA-IMT was 0.82 ± 0.20 mm. Fifteen patients died during a follow-up period of 28.5 ± 6.6 months, 11 from cardiovascular causes. Only oxLDL, not anti-oxLDL, was correlated with the extent of atherosclerosis at baseline. However, both had no role in the progression of atherosclerosis. Also, in unadjusted and adjusted models, both parameters were not associated with overall or cardiovascular mortality. Neither oxLDL nor anti-oxLDL level is associated with the progression of atherosclerosis or mortality in hemodialysis patients.

Is zinc-α2-glycoprotein a cardiovascular protective factor for patients undergoing hemodialysis?

BACKGROUND

Zinc-α2-glycoprotein (ZAG) is a lipid mobilizing factor. Its anti-inflammatory action and expression pattern suggest that ZAG could act by protecting against the obesity-associated disorders. In hemodialysis (HD) patients, ZAG levels were described to be elevated but its effects on markers of inflammation and LDL oxidation are still unclear. We investigated the relationship between ZAG and markers of systemic inflammation and LDL atherogenic modification profile in HD patients.

METHODS

Forty-three patients regularly on HD were studied and compared to 20 healthy subjects. Plasma ZAG, adiponectin, electronegative LDL [LDL(-)], an atherosclerotic negatively charged LDL subfraction, and anti-LDL(-) autoantibodies levels were measured by ELISA. Markers of inflammation and atherogenic cell recruitment (TNF-α, interleukin-6, VCAM-1, ICAM-1, MCP-1 and PAI-1) were also determined.

RESULTS

Inflammatory markers and atherogenic cell recruitment were higher in HD patients when compared to healthy subjects. ZAG levels were also higher in HD patients (151.5 ± 50.1 mg/l vs 54.6 ± 23.0 mg/l; p<0.0001) and its levels were negatively correlated with TNF-α (r=-0.39; p=0.001) and VCAM-1 (r=-0.52; p<0.0001) and, positively correlated with anti-LDL(-) autoantibodies (r=0.38; p=0.016). On multivariate analyses, plasma ZAG levels were independently associated with VCAM-1 (p=0.01).

CONCLUSION

ZAG is inversely associated with markers of pro-atherogenic factors linked to systemic inflammation and oxidative stress. Thus, this adipokine may constitute a novel marker of a favorable metabolic profile regarding cardiovascular risk factors in HD population.

Cardiovascular Complications in CKD Patients: Role of Oxidative Stress

Starting with the early stages, patients with chronic kidney disease (CKD) experience higher burden of cardiovascular disease (CVD). Moreover, CVD complications are the major cause of mortality in CKD patients as compared with complications from chronic kidney failure. While traditional CVD risk factors, including diabetes, hypertension, hyperlipidemia, obesity, physical inactivity, may be more prevalent among CKD patients, these factors seem to underestimate the accelerated cardiovascular disease in the CKD population. Search for additional biomarkers that could explain the enhanced CVD risk in CKD patients has gained increasing importance. Although it is unlikely that any single nontraditional risk factor would fully account for the increased CVD risk in individuals with CKD, oxidative stress appears to play a central role in the development and progression of CVD and its complications. We will review the data that support the contribution of oxidative stress in the pathogenesis of CVD in patients with chronic kidney failure.

Oxidative stress in children on hemodialysis: value of autoantibodies against oxidized low-density lipoprotein

The principal causes of morbidity and mortality in children with chronic renal failure on maintenance hemodialysis are cardiovascular complications. Recently, it has been suggested that oxidative stress, chronic inflammation and malnutrition are risk factors for cardiovascular disease. However, to date, biomarkers of oxidative stress have not been well studied in children. The aim of this study was to investigate the relationship between oxidative stress and cardiovascular risk factors in children on hemodialysis therapy. Twenty-eight hemodialysis patients (13 females, 15 males; mean age 15.1 +/- 2.5 years) and 20 healthy children (13 females, seven males; mean age 14.3 +/- 2.7 years) were included in the study. Levels of antibodies to oxidized low-density lipoprotein (oLABs), high sensitivity C-reactive protein (hs-CRP), albumin, prealbumin, transferrin, and ferritin were measured. Antibodies to oxidized low-density lipoprotein (LDL) in hemodialysis patients were lower than those in the controls (P < 0.05). The patients with lower oLAB titers had higher levels of hs-CRP and ratio of erythropoietin to hematocrit (EPO/Htc), and lower levels of albumin, prealbumin, apolipoprotein A-1 (ApoA(1)), and high-density lipoprotein (P < 0.05). Antibodies to oxidized LDL in hemodialysis patients with dyslipidemia were lower than those of patients with normal lipid profile (P < 0,05). This study showed that children treated by hemodialysis are exposed to oxidative stress and chronic inflammation. We suggest that oLAB levels are decreased in children on hemodialysis as a result of severe oxidative stress and that these antibodies are related to inflammation, anemia, malnutrition and dyslipidemia.

Associations between oxidized LDL to LDL ratio, HDL and vascular calcification in the feet of hemodialysis patients

Cardiovascular mortality is associated with vascular calcification (VC) in hemodialysis (HD) patients. The present study was designed to find factors related with medial artery calcification on the plain radiography of feet by comparing C-reactive protein (CRP), plasminogen activator inhibitor type 1 (PAI-1) and lipid profile including oxidized low density lipoprotein (ox-LDL) and to elucidate associations among these factors in HD patients. Forty-eight HD patients were recruited for this study. VC in the feet was detected in 18 patients (37.5%) among total patients and 12 patients (85.7%) among diabetic patients. Diabetes, cardiovascular disease (CVD), pulse pressure, ox-LDL/LDL were higher and high density lipoprotein (HDL) was lower in patients with VC than in patients without VC. Negative associations were found between HDL and CRP, PAI-1. PAI-1 had positive association with ox-LDL/LDL. History of CVD was the only determinant of vascular calcification on the plain radiography of feet. Ox-LDL/LDL, HDL, CRP, and PAI-1 were closely related with one another in HD patients. History of CVD is the most important factor associated with the presence of VC and low HDL and relatively high oxidized LDL/LDL ratio may affect VC formation on the plain radiography in the feet of HD patients.

Endocrinology and Dialysis Jean L. HolleySeries Editor: Lipid Abnormalities Associated with End-Stage Renal Disease

Patients undergoing chronic renal replacement therapy have a high incidence of dyslipidemia. In general, there are increased concentrations of triglyceride-rich apolipoprotein B-containing particles. These elevations lead to increased levels of non-high-density lipoprotein (HDL) levels. This pattern is further modified by the method of dialysis (peritoneal versus hemodialysis) and comorbidities such as diabetes. End-stage renal disease patients also demonstrate increased levels of lipoprotein(a) (Lp(a)) and oxidized low-density lipoprotein (LDL)both of which are highly atherogenic. This review focuses on the pathogenesis of these lipid abnormalities and their role in the atherosclerotic process.

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

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

Chronic kidney disease as a metabolic syndrome with malnutrition--need for strict control of risk factors

Patients with chronic kidney disease (CKD) have an increased risk for death from cardiovascular disease (CVD). They have multiple metabolic abnormalities that may accelerate atherosclerosis, such as hypertension, insulin resistance, and dyslipidemia, along with other CKD-related risk factors. In addition, a considerable proportion of patients with advanced stages of CKD are malnourished, presenting "metabolic syndrome with malnutrition". The presence of malnutrition/inflammation dramatically changes the apparent relationship between CVD death risk and some risk factors. For example, in stage 5 CKD patients on hemodialysis, a higher body mass index and a higher plasma cholesterol are predictors of better survival. To understand the paradoxic epidemiology, we should recognize risk factors for occurrence of CVD events and risk factors of fatality after an event. In this article, we review the unique situation of CKD, emphasizing the need of more strict control of both types of risk factors to improve survival of CKD patients.

[Atherosclerosis and uremia: signifance of non-traditional risk factors]

Arteriosclerosis, atherosclerosis and vascular calcification are causally related to the high morbidity and mortality of patients with chronic renal failure. Oxidative stress and carbonyl stress of uremia, dialysis procedure and/or intravenous iron therapy result in AGE (advanced glycation end-product), ALE (advanced lipoxidation end-product) and AOPP (advanced oxidation protein product) formation, favouring together with elevated CRP (C-reactive protein) levels the development of cardiovascular and cerebrovascular complications. Enhanced plasma levels of homocysteine and ADMA (asymmetric dimethylarginine) contribute to this process. In addition, in chronic renal insufficiency hyperphosphatemia and an enhanced calcium x phosphorus ion product are associated with the morbidity and mortality of the patients, particularly in the presence of fetuin deficiency. Phosphorus, AGEs and AOPPs, beside other factors, catalyze the conversion of vascular smooth muscle cells to osteoblast--like cells (particularly in the presence of monocytes/macrophages), resulting in bone matrix protein formation. Other risk factors, such as age, male sex, smoking, hypertension, diabetes, chronic inflammation, insulin resistance or dyslipidemia (enhanced non-HDL-cholesterol) also contribute to the atherosclerotic risk profile of the patient with chronic renal insufficiency. While there is growing understanding of the mechanisms involved in arteriosclerosis, atherosclerosis and vascular calcification in uremia, we are still missing effective therapeutic maneuvers for reduction of excess mortality in uremic patients.