Antibody titers against oxidized LDL are not elevated in patients with familial hypercholesterolemia

Influence of hypercholesterolemia on serum antibodies against oxidized LDL in children and adolescents

BACKGROUND

The oxidation of low-density lipoprotein (LDL; oxLDL) appears to play a key role in the early development of atherosclerosis. Increased serum antibodies against the oxLDL (anti-oxLDL antibodies) have been found in adults with atherosclerotic disease, as well as in healthy adults. The clinical significance and its precise role (atherogenic or atheroprotective), however, have not yet been clarified. This aim of this study was therefore to evaluate anti-oxLDL antibodies in healthy children and adolescents with and without hypercholesterolemia.

METHODS

The study involved 312 subjects, aged 4-18 years, 141 with LDL cholesterol (LDL-C) ≥130 mg/dL and 171 with acceptable LDL-C (<110 mg/dL). Total anti-oxLDL antibodies, total cholesterol, LDL-C and high-density lipoprotein cholesterol, triglycerides, apolipoproteins A1 and B, lipoprotein (a) and high-sensitivity C-reactive protein were measured in fasting serum. The anti-oxLDL antibodies were measured on enzyme-linked immunosorbent assay.

RESULTS

Anti-oxLDL antibodies were similar in the hypercholesterolemia and non-hypercholesterolemia groups. Girls had significantly higher anti-oxLDL antibodies compared with boys. There was no significant correlation of antibodies with age or body mass index. Increased apolipoprotein B was an important factor for lower anti-oxLDL antibodies, while all other parameters had no significant association with anti-oxLDL antibodies.

CONCLUSION

In children and adolescents with hypercholesterolemia, total anti-oxLDL antibodies cannot serve as a marker for risk for atherosclerosis or for future cardiovascular disease.

Sex differences in the early life correlates of natural antibody concentrations

Innate-like B1a lymphocytes arise from long-lived progenitors produced exclusively by fetal stem cells. Any insults coinciding with this early lymphopoietic wave could have a permanent impact on the B1a population and its unique protein products, the natural antibodies (NAb). We investigated early life nutritional influences on NAb concentrations of pre-adolescent children (n=290) in rural Nepal for whom we had extensive information on exposures from pregnancy and early infancy. Infant size and growth were strongly associated with NAb concentrations at 9-13 years of age among males (e.g., for neonatal weight: βBOYS=0.43; P<0.001), but not females (e.g., for neonatal weight: βGIRLS=-0.16; P=0.26). In females, season of birth was associated with NAb concentrations, with marked reductions among girls born during the pre-monsoon (March-May; βGIRLS=-0.39; P=0.01) and pre-harvest (September-November; βGIRLS=-0.35; P=0.03) seasons. Our findings suggest that nutritional or other environmental influences on immune development may vary by sex, with potential consequences for immune function during infancy and long-term risk of immune-mediated disease.

Pathogenic role of modified LDL antibodies and immune complexes in atherosclerosis

There is strong evidence supporting a key role of the adaptive immune response in atherosclerosis, given that both activated Th cells producing predominantly interferon-γ and oxidized LDL (oxLDL) and the corresponding antibodies have been isolated from atheromatous plaques. Studies carried out using immune complexes (IC) prepared with human LDL and rabbit antibodies have demonstrated proatherogenic and pro-inflammatory properties, mostly dependent on the engagement of Fcγ receptors Ⅰ and Ⅱ in macrophages and macrophage-like cell lines. Following the development of a methodology for isolating modified LDL (mLDL) antibodies from serum and isolated IC, it was confirmed that antibodies reacting with oxLDL and advanced glycation end product-modified LDL are predominantly IgG of subtypes 1 and 3 and that mLDL IC prepared with human reagents possesses pro-inflammatory and proatherogenic properties. In previous studies, LDL separated from isolated IC has been analyzed for its modifications, and the reactivity of antibodies isolated from the same IC with different LDL modifications has been tested. Recently, we obtained strong evidence suggesting that the effects of mLDL IC on phagocytic cells are modulated by the composition of the mLDL. Clinical studies have shown that the level of mLDL in circulating IC is a strong predictor of cardiovascular disease (CVD) and, in diabetic patients, other significant complications, such as nephropathy and retinopathy. In conclusion, there is convincing ex vivo and clinical data supporting the hypothesis that, in humans, the humoral immune response to mLDL is pathogenic rather than protective.

Immunological aspects of atherosclerosis

Cardiovascular disease is the leading cause of death in several countries. The underlying process is atherosclerosis, a slowly progressing chronic disorder that can lead to intravascular thrombosis. There is overwhelming evidence for the underlying importance of our immune system in atherosclerosis. Monocytes, which comprise part of the innate immune system, can be recruited to inflamed endothelium and this recruitment has been shown to be proportional to the extent of atherosclerotic disease. Monocytes undergo migration into the vasculature, they differentiate into macrophage phenotypes, which are highly phagocytic and can scavenge modified lipids, leading to foam cell formation and development of the lipid-rich atheroma core. This increased influx leads to a highly inflammatory environment and along with other immune cells can increase the risk in the development of the unstable atherosclerotic plaque phenotype. The present review provides an overview and description of the immunological aspect of innate and adaptive immune cell subsets in atherosclerosis, by defining their interaction with the vascular environment, modified lipids and other cellular exchanges. There is a particular focus on monocytes and macrophages, but shorter descriptions of dendritic cells, lymphocyte populations, neutrophils, mast cells and platelets are also included.

Antioxidized LDL antibodies are associated with different metabolic pathways in patients with atherosclerotic plaque and type 2 diabetes

OBJECTIVE

Oxidized lipoproteins and antioxidized LDL antibodies (antioxLDL abs) have been detected in human plasma and atherosclerotic lesions. The principle aim of this study was to analyze the possible relationship between IgG and IgM antioxLDL abs and factors involved in different metabolic pathways (inflammation, lipid metabolism, apoptosis, and cell cycle arrest profile) in the occluded popliteal artery (OPA) compared with the femoral vein (FV).

RESEARCH DESIGN AND METHODS

Fifteen patients with advanced atherosclerosis and type 2 diabetes undergoing lower limb amputation participated in this study. Each patient had OPA and FV biopsy specimens and peripheral arterial occlusive disease. By real-time PCR, gene expression was analyzed from the OPA and FV specimens, and antioxLDL ab levels were measured by specific enzyme-linked immunosorbent assay.

RESULTS

The OPA and FV showed a positive correlation between only IgM antioxLDL ab levels and the expression of genes involved in different metabolic pathways, including inflammation (TFPI), apoptosis (BAX, caspase 3, AKT1), plaque disruption (MMP2 and MMP10), lipid metabolism (SCARB1, PPARg), and cell turnover (CDKN1A), and genes for transcription and growth factors (NFkB and VEGFA, respectively).

CONCLUSIONS

The results show that gene expression in the metabolic pathways (apoptosis, lipid metabolism, and inflammation) in the OPA and FV are directly related to the levels of IgM antioxLDL abs.

Immune response to lipoproteins in atherosclerosis

Atherosclerosis, the underlying cause of cardiovascular disease, is characterized by chronic inflammation and altered immune response. Cholesterol is a well-known risk factor associated with the development of cardiovascular diseases. Elevated serum cholesterol is unique because it can lead to development of atherosclerosis in animals and humans even in the absence of other risk factors. Modifications of low-density lipoproteins mediated by oxidation, enzymatic degradation, and aggregation result in changes in their function and activate both innate and adaptive immune system. Oxidized low-density lipoprotein (LDL) has been identified as one of the most important autoantigens in atherosclerosis. This escape from self-tolerance is dependent on the formation of oxidized phospholipids. The emerging understanding of the importance of immune responses against oxidized LDL in atherosclerosis has focused attention on the possibility of development of novel therapy for atherosclerosis. This review provides an overview of immune response to lipoproteins and the fascinating possibility of developing an immunomodulatory therapy for atherosclerosis.

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.

Anti-oxidized low-density lipoprotein (oxLDL) antibody levels are not related to increasing circulating oxLDL concentrations during the course of pregnancy

PROBLEM

To address the question of whether the high levels of oxidative modified low-density lipoproteins (oxLDL) in pregnancy are opposed by an appropriate humoral autoimmune response providing anti-oxLDL autoantibodies in maternal serum of healthy women throughout gestation.

METHOD OF STUDY

Blood was taken from 33 patients at four different time points from early to late gestation and post-partum. OxLDL and anti-oxLDL concentrations were measured by enzyme-linked immunosorbent assays. ANOVA was used for statistical evaluations followed by post hoc test with Bonferoni adjustment.

RESULTS

Oxidized Low Density Lipoprotein concentrations increased while anti-oxLDL levels decreased significantly from early to late gestation. OxLDL was strongly positively correlated with LDL concentration and mildly negatively associated with anti-oxLDL levels. Estimating the status of oxidation by calculating oxLDL/LDL ratio revealed decreasing values with ongoing pregnancy. Multivariate analysis showed that anti-oxLDL levels were dependent on gestational age but neither on oxLDL levels nor on the oxLDL/LDL ratio.

CONCLUSIONS

The results indicate that normal pregnancy is a well-balanced state of oxidative and anti-oxidative processes. However, we could not confirm a dependence of anti-oxLDL autoantibodies on oxLDL concentration. Whether or not the humoral immune system is involved in oxidative defence remains to be elucidated.

IgM-phosphorylcholine autoantibodies and outcome in acute coronary syndromes

BACKGROUND

Antibodies against proinflammatory phosphorylcholine (anti-PC) seem to be protective and reduce morbidity. We sought to determine whether low levels of immunoglobulin-M (IgM) autoantibodies against PC add prognostic information in acute coronary syndromes (ACS).

METHODS

IgM anti-PC titers were measured in serum obtained within 24h of admission from 1185 ACS patients (median age 66 years, 30% women). We evaluated major acute cardiovascular events (MACE) and all-cause mortality short--(6 months), intermediate--(18 months) and long--(72 months) terms.

RESULTS

Low anti-PC titers were associated with MACE and all-cause mortality at all follow-up times. After adjusting for clinical variables, plasma troponin-I, proBNP and CRP levels, associations remained at all times with MACE, short and intermediate terms also with all-cause mortality. With anti-PC titers below median, adjusted hazard ratios at 18months were for MACE 1.79 (95% confidence interval [CI]: 1.31 to 2.44; p=0.0002) and for all-cause mortality 2.28 (95% CI: 1.32 to 3.92; p=0.003). Anti-PC and plasma CRP were unrelated and added to risk prediction.

CONCLUSIONS

Serum IgM anti-PC titers provide prognostic information above traditional risk factors in ACS. The ease of measurement and potential therapeutic perspective indicate that it may be a valuable novel biomarker in ACS.

The immune system in atherosclerosis

Cardiovascular disease, a leading cause of mortality worldwide, is caused mainly by atherosclerosis, a chronic inflammatory disease of blood vessels. Lesions of atherosclerosis contain macrophages, T cells and other cells of the immune response, together with cholesterol that infiltrates from the blood. Targeted deletion of genes encoding costimulatory factors and proinflammatory cytokines results in less disease in mouse models, whereas interference with regulatory immunity accelerates it. Innate as well as adaptive immune responses have been identified in atherosclerosis, with components of cholesterol-carrying low-density lipoprotein triggering inflammation, T cell activation and antibody production during the course of disease. Studies are now under way to develop new therapies based on these concepts of the involvement of the immune system in atherosclerosis.

Circulating oxidized LDL: a biomarker and a pathogenic factor

PURPOSE OF REVIEW

Oxidized LDL (oxLDL) contributes to many atherogenic steps in the vascular wall, but the significance of oxLDL in circulating blood remains unclear. Recent progress in procedures for measuring both human and murine oxLDL has provided growing evidence of the importance of circulating oxLDL.

RECENT FINDINGS

Circulating oxLDL is elevated in patients with advanced atherosclerosis, such as coronary heart disease and ischemic stroke, and also reflects early atherosclerotic changes and metabolic disorders including diabetes and obesity. In-vitro exposure to oxLDL increased mononuclear cell nuclear factor-kappaB activity, suggesting a pathogenic role of circulating oxLDL in exacerbation of oxidative stress. In addition, adenoviral administration of secreted scavenger receptor-A1, which functions as a decoy, suppresses foam cell formation in LDL receptor-deficient mice via a blockade of modified LDL incorporation into macrophages. Furthermore, when lectin-like oxLDL receptor-1 was ectopically expressed in the liver, circulating oxLDL was reduced, resulting in complete prevention of atherosclerotic progression in apolipoprotein E-deficient mice. Thus, circulating oxLDL impacts atherogenic formation.

SUMMARY

The roles of circulating oxLDL in atherosclerotic pathogenesis are now attracting considerable attention. OxLDL removal from circulating blood is a promising therapeutic strategy against atherosclerosis.

Clinical significance of the humoral immune response to modified LDL

Human low density lipoprotein (LDL) undergoes oxidation and glycation in vivo. By themselves, oxidized LDL (oxLDL) and AGE-LDL have proinflammatory properties and are considered atherogenic. But the atherogenicity of these lipoproteins are significantly increased as a consequence of the formation of immune complexes (IC) involving specific autoantibodies. OxLDL and AGE antibodies have been shown to be predominantly of the IgG1 and IgG3 isotypes. OxLDL antibodies are able to activate the complement system by the classical pathway and to induce FcR-mediated phagocytosis. In vitro and ex vivo studies performed with modified LDL-IC have proven their pro-inflammatory and atherogenic properties. Clinical studies have demonstrated that the levels of circulating modified LDL-IC correlate with parameters indicative of cardiovascular and renal disease in diabetic patients and other patient populations. The possibility that spontaneously formed or induced modified LDL antibodies (particularly IgM oxLDL antibodies) may have a protective effect has been suggested, but the data is unclear and needs to be further investigated.

Ethnic variation in levels of circulating IgG autoantibodies to oxidised low-density lipoprotein

BACKGROUND

Oxidised low-density lipoprotein (Ox-LDL) plays a key role in atherosclerosis. Our aim was to determine whether serum autoantibodies against Ox-LDL (Ab Ox-LDL) differ by ethnic group.

DESIGN AND METHODS

Soluble serum Ab Ox-LDL levels were measured in 250 white (113 females), 169 African origin (91 females) and 196 South Asian (92 females) individuals from the Wandsworth Heart and Stroke Study (WHSS) population. All were free from coronary heart disease (CHD), stroke, other cardiovascular disease, diabetes, drug therapy for hypertension or high lipids, hormone replacement therapy or oral contraceptive pill.

RESULTS

There were no sex differences in levels of Ab Ox-LDL, but levels were higher in non-smokers (430U/L [95% CI 471-596]) than in smokers (384U/L [316-468]) (p<0.009). Age- and sex-adjusted levels of Ab Ox-LDL were higher in people of African origin and South Asians compared to whites. This difference was maintained in South Asian women following adjustment for multiple risk factors (82% [21-175]; p=0.004). Ab Ox-LDL levels were negatively associated with serum triglycerides and positively associated with sVCAM-1.

CONCLUSIONS

Higher IgG Ab to Ox-LDL are associated with higher levels of sVCAM-1 and, are elevated in female South Asian individuals who have an increased risk of atherosclerosis compared to whites.

Immune complexes containing modified lipoproteins are related to the progression of internal carotid intima-media thickness in patients with type 1 diabetes

Modified lipoproteins induce autoimmune responses including the synthesis of autoantibodies with pro-inflammatory characteristics. Circulating modified lipoprotein autoantibodies combine with circulating antigens and form immune complexes (IC). We now report the results of a study investigating the role of circulating IC containing modified lipoproteins in the progression of carotid intima-media thickness (IMT) in patients enrolled in the Epidemiology of Diabetes Interventions and Complications (EDIC) Trial, a follow-up study of the Diabetes Control and Complications Trial (DCCT). This cohort includes 1229 patients with type 1 diabetes in whom B-mode ultrasonography of internal and common carotid arteries was performed in 1994-1996 and in 1998-2000. Conventional CHD risk factors, antibodies against modified forms of LDL and modified lipoprotein IC were determined in 1050 of these patients from blood collected in 1996-1998. Cholesterol and apolipoprotein B content of IC (surrogate markers of modified ApoB-rich lipoproteins) were significantly higher in patients who showed progression of the internal carotid IMT than in those showing no progression, regression or mild progression. Multivariate linear and logistic regression modeling using conventional and non-conventional risk factors showed that the cholesterol content of IC was a significant positive predictor of internal carotid IMT progression. In conclusion these data demonstrate that increased levels of modified ApoB-rich IC are associated with increased progression of internal carotid IMT in the DCCT/EDIC cohort of type 1 diabetes.

Autoantibody titers against OxLDL are correlated with Achilles tendon thickness in patients with familial hypercholesterolemia

Achilles tendon xanthomas are associated with increased cardiovascular risk in patients with familial hypercholesterolemia (FH). Oxidized low density lipoprotein (OxLDL), the antibodies against OxLDL, and the LDL-associated phospholipase A(2) (Lp-PLA(2)) may play important roles in atherogenesis. We investigated the possible association between plasma levels of OxLDL, Lp-PLA(2) activity, and autoantibody titers against various types of mildly OxLDL with Achilles tendon thickness (ATT). ATT was determined by sonography in 80 unrelated heterozygous FH patients. Three different types of mildly OxLDL were prepared: OxLDL(L), OxLDL(P), and OxLDL(D), at the end of the lag, propagation, and decomposition phases of oxidation, respectively. Similar types of OxLDL were also prepared after inactivation of the LDL-associated Lp-PLA(2). These types were denoted OxLDL(-)(L), OxLDL(-)(P), and OxLDL(-)(D). FH patients exhibited significantly higher plasma OxLDL levels and serum IgG titers against OxLDL(P) and OxLDL(D) compared with 40 normolipidemic apparently healthy controls. ATT values were positively correlated with autoantibody titers against OxLDL(P) and OxLDL(D); however, in multiple regression analysis, ATT was independently associated only with the autoantibody titers against OxLDL(D). We conclude that the IgG autoantibody titers against OxLDL(D) but not OxLDL or Lp-PLA(2) may play an important role in the pathogenesis of Achilles tendon xanthomas in FH patients.

Oxidized Low-Density Lipoprotein Autoantibodies, Chronic Infections, and Carotid Atherosclerosis in a Population-Based Study

OBJECTIVES

We investigated whether associations exist between immune reactions to oxidized low-density lipoproteins (OxLDLs), chronic infections, and carotid atherosclerosis as quantified by ultrasound.

BACKGROUND

Atherosclerosis is a chronic immuno-inflammatory disease wherein both oxidized lipids and infectious agents are incriminated as possible contributors.

METHODS

We measured immunoglobulin (Ig)G and IgM autoantibody titers to copper-oxidized-LDL and malondialdehyde-LDL (OxLDL-AB), IgG and IgM apolipoprotein B-100-immune complexes (ApoB-IC), and titers of antibodies to Escherichia coli and chlamydial lipopolysaccharide (LPS), mycobacterial heat shock protein 65 (mHSP65), Chlamydia pneumoniae, Helicobacter pylori, and cytomegalovirus and evaluated their relationship to cardiovascular risk factors, chronic infections, and incident/progressive carotid atherosclerosis in the Bruneck study.

RESULTS

The OxLDL-AB and ApoB-IC levels remained stable over time as indicated by strong correlations between 1995 and 2000 measurements (p < 0.001 each). Significant associations existed between all OxLDL markers and antibody titers to pathogens, especially to E. coli-LPS and mHSP65. Both OxLDL-AB and ApoB-IC levels showed a rise with increasing pathogen burden. Notably, OxLDL-ABs were also elevated in subjects with chronic infection as defined by clinical criteria. Titers of IgG, but not IgM, OxLDL-AB, or ApoB-IC inversely correlated with total cholesterol, LDL cholesterol, and apoB concentrations. The IgG OxLDL markers were positively and IgM markers were inversely associated with incident and progressive carotid atherosclerosis in univariate analyses but were not independent predictors in multivariate analyses.

CONCLUSIONS

Our study provides evidence for an association between human oxLDL markers and chronic infections. Moreover, in this population-based study, neither IgG nor IgM OxLDL autoantibodies were independently predictive of atherosclerosis progression in the carotid arteries.

Autoantibodies to oxidized LDL and cardiovascular risk: the Framingham Offspring Study

BACKGROUND

The relation between measures of oxidation of lipid particles and cardiovascular disease has not been extensively investigated prospectively on a population basis.

METHODS

A community cohort of 1192 men and 1427 women with measures of IgG antibodies to oxidized LDL were followed 8 years for the development of initial coronary heart disease (CHD) and cardiovascular disease (CVD) events.

RESULTS

Levels of IgG autoantibodies to a form of oxidized LDL were significantly associated with age in both sexes, positively with fibrinogen in men and negatively with HDL cholesterol in women. In sex-specific models that adjusted for age alone or those that adjusted for age, cholesterol, HDL cholesterol, smoking, and diabetes mellitus, there was no relation between level of antibodies to oxidized LDL and the development of CHD or CVD.

CONCLUSION

Autoantibodies to oxidized LDL were strongly related to age and were not related to incident CHD or CVD over 8 years of follow up.

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.

The autoantibody repertoire against copper- or macrophage-modified LDL differs in normolipidemics and hypercholesterolemic patients

We have analyzed the antibody repertoire from normo- and hypercholesterolemic subjects to investigate how it can be related to macrophage-dependent modification of low-density lipoproteins, in comparison to the commonly used copper-oxidized LDL. Preexisting natural antibodies in plasma from normo- and hypercholesterolemic individuals were tested for their reactivity against copper ion oxidized LDL and LDL modified by macrophages. A crosswise comparison between these two antigen preparations demonstrated a different antibody repertoire in normo- and hypercholesterolemic patients. This study suggest that the search for antibodies that can influence the progression or regression of an atherosclerotic process has to take into account the process by which LDL is modified, and the repertoire of antibodies that is generated in the normal population, in comparison to that with, or at risk for, coronary artery diseases.

Autoimmune mechanisms of atherosclerosis

Accumulating evidence supports an autoimmune mechanism as one of the prime pathogenic processes involved in the development of atherosclerosis. So far, three proteins, including heat shock proteins (HSPs), oxidized low-density lipoprotein (oxLDL), and beta2 glycoprotein1 (beta2GP1) have been recognized as autoantigens. It has been demonstrated that risk factors for atherosclerosis, such as hypercholesterolemia, hypertension, infections, and oxidative stress, evoke increased expression of HSPs in cells of atherosclerotic lesions. Autoantibody levels against HSPs are significantly increased in patients with atherosclerosis and T lymphocytes specifically responding to these autoantigens have been demonstrated within atherosclerotic plaques. Subcutaneous immunization of animals with HSP65 induced atheroma formation in the arterial wall. Furthermore, circulating immunoglobulin (Ig) G and IgM oxidized low-density lipoprotein (oxLDL) antibodies are present in the plasma of animals and humans and form immune complexes with oxLDL in atherosclerotic lesions. These antibodies closely correlate with the progression and regression of atherosclerosis in murine models. Interestingly, recent reports demonstrated that pneumococcal vaccination to LDL receptor-deficient mice results in elevation of anti-oxLDL IgM Ab EO6, which is inversely correlated with the development of atherosclerosis. Finally, it has been observed that autoantigen beta2GP1 localizes in the atheroma and that autoantibodies to beta2GP1 are correlated with the incidence of atherosclerosis in patients. Hence, these autoimmune reactions to HSPs, oxLDL and beta2GP1 can contribute to the initiation and progression of atherosclerosis.

Influence of age and sex on levels of anti-oxidized LDL antibodies and anti-LDL immune complexes in the general population

Most studies of antibodies to oxidized LDL have been undertaken in patients with different diseases and cardiovascular risk factors. However, very few studies have researched the distribution and determining factors of antibodies to oxidized LDL in the general population. A total of 1,354 persons (817 females and 537 males) aged 5-65 years were included in this study. They were selected randomly from the population census of Málaga, in southern Spain. The females had lower levels of total cholesterol and triglycerides and higher levels of HDL-cholesterol and a very significant increase (P < 0.0001) in levels of anti-oxidized LDL [low density lipoprotein modified by malondialdehyde (MDA-LDL)] antibodies but no difference in levels of immune complexes consisting of LDL and IgG antibodies (anti-LDL immune complex). Younger persons (16-35 years) had higher levels of anti-oxidized LDL (MDA-LDL) antibodies than persons older than 35 years (P = 0.05). Levels of immune complexes were significantly higher (P = 0.05) in persons aged 5-15 years than in persons older than 40 years. A very weak association was found between levels of anti-oxidized LDL (MDA-LDL) antibodies and anti-LDL immune complexes. The higher prevalence of anti-oxidized LDL (MDA-LDL) antibodies in females and young persons is in agreement with studies that found an inverse association between atherosclerosis and the level of these antibodies.

Effect of Lipoprotein Apheresis on Oxidative Stress and Antioxidant Status in Familial Hypercholesterolemic Patients

Extracorporeal low-density lipoprotein (LDL) apheresis is an established and highly effective therapy for the patients with familial hypercholesterolemia (FH) not adequately responding to diet and drug therapy alone. This study was designed to measure the effect of lipid apheresis on oxidant and antioxidant status in a patient with FH. The levels of plasma lipid peroxidation were determined as thiobarbituric acid-reactive substances. The activities of the antioxidant enzymes superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GPx) were established in one subject with FH before and after lipid apheresis.

The pre- and post lipid apheresis procedures witness a significant decrease in oxidative stress (p<0.05) but the erythrocyte levels of CAT, SOD and GPx were unchanged.

IgM antibody level against proinflammatory bacterial peptidoglycan is inversely correlated with extent of atherosclerotic disease

OBJECTIVE

Atherosclerosis may lead to acute clinical events by rupture of a vulnerable atherosclerotic plaque. Previously, we demonstrated that peptidoglycan (PGN), a major cell wall component of gram-positive bacteria that induces production of proinflammatory cytokines through TLR2 and CD14, is prevalent in atherosclerotic lesions with histological features associated with plaque vulnerability. We hypothesized that in atherosclerotic patients antibody levels against PGN may differ compared with matched controls.

METHODS AND RESULTS

ELISA was performed to measure immunoglobulin levels against PGN in sera of 80 atherosclerotic patients versus 77 control patients with an increased cardiovascular risk, frequency-matched for age, sex and risk factors for atherosclerotic disease. In all patients and controls, intima-media (IMT) thickness was assessed using an array transducer. Significantly lower levels of IgM directed against PGN were found in atherosclerotic patients compared with the control patients without clinically manifested disease (P = 0.02). The IgM levels against PGN decreased with increasing mean common carotid IMT thickness (P = 0.006).

CONCLUSIONS

These results show that patients suffering from atherosclerotic disease have decreased IgM levels against PGN. The data suggest that an antibody response against PGN could have a protective effect against the development or activity of atherosclerotic disease.

Autoantibodies against oxidized low-density lipoprotein (ox-LDL) and LDL oxidation status

Oxidized low-density lipoproteins (ox-LDLs) and their autoantibodies (OLAB) are involved in the development of atherosclerosis in animal models, but their role in humans is still not clear. For this reason we studied 54 patients with β-thalassemia major (TM), as a model of chronically low circulating LDLs with a high level of oxidation; 44 patients with primary hypercholesterolemia, as model of chronically high circulating LDLs; 24 type 2 diabetic mellitus patients (T2DM) before and after 3 months of atorvastatin treatment (20 mg/day), as a model of acute changes in circulating LDLs; and 41 normolipidemic subjects as a control group. ox-LDLs were measured by the determination of baseline diene concentration in the plasma LDL lipidic fraction after 12 hours fasting and were expressed as the amount of conjugated dienes/liter (BDC/l) or BDC/LDL-cholesterol (LDL-C), which indicate respectively LDL oxidation degree and status. OLABwere determined using an enzyme immunoassay and related to LDL oxidation degree (BDC/l). In TM, BDC/l was lower, while BDC/LDL-C was significantly higher, compared to both hypercholesterolemia and normolipidemic subjects. Patients with hypercholesterolemia had higher BDC/l, but lower BDC/LDL-C and OLAB/BDC-l, than normolipidemic subjects. In T2DM patients at diet, BDC/LDL-C and OLAB/BDC-l were lower than in normolipidemic subjects. After 3 months of atorvastatin treatment, BDC/LDL-C and OLAB/BDC-l ratios increased. When all patients were evaluated together, a significant inverse correlation was evident between OLABand either LDL or BDC/l. Our findings suggest that a relationship between OLABtiter and oxidation indices (BDC/l and BDC/LDL-C) does exist and we may speculate that an increase in OLAB/BDC-l ratio might be protective against the risk of atherosclerosis.

Generation and Characterization of IgG Monoclonal Antibodies Specific for Malondialdehyde

Numerous studies have indicated that the oxidative modification of low-density lipoprotein (LDL) plays a critical role in the pathogenesis of atherosclerosis. Malondialdehyde-modified LDL (MDA-LDL) is one of the candidate oxidative products. Therefore, to allow the assessment of oxidized LDL in human serum, we developed monoclonal antibodies for MDA-LDL. Two of these-MDA1 and MDA2-bound to oxidized LDL but not to native LDL by Western blot analysis. The murine monoclonal antibodies to oxidized LDL have potential clinical implications, as imaging agents, for defining the compositions of atherosclerotic vessels in vivo.

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

BACKGROUND

Immune response to oxidized low-density lipoprotein (oxLDL) may modulate atherogenesis. We recently reported that a high titer of serum anti-oxLDL antibody was an independent predictor of a low risk for cardiovascular death in patients with end-stage renal disease (ESRD). In the present study, we examined a possible association between anti-oxLDL antibody titer and arterial wall thickness in ESRD patients.

METHODS

The subjects were 103 ESRD patients treated with hemodialysis. A high resolution B-mode ultrasound method was used to measure intima-media thickness of carotid (CA-IMT) and femoral arteries (FA-IMT).

RESULTS

In univariate analysis, anti-oxLDL antibody showed a significant negative correlation with FA-IMT. The inverse association between anti-oxLDL antibody and FA-IMT remained significant in multiple regression analysis, including age, gender, blood pressure, plasma lipids, smoking, C-reactive protein, calcium-phosphate product, serum albumin, body mass index, and duration of dialysis as covariates. The antibody titer showed an inverse trend with CA-IMT without statistical significance.

CONCLUSION

These results show for the first time that titer of anti-oxLDL antibody is an independent factor inversely associated with arterial thickness in ESRD, supporting the concept that immunity against oxLDL plays an anti-atherogenic role.

High oxidative stress in patients with stable coronary heart disease

Oxidized low density lipoprotein (oxLDL) plays a pivotal role in the development of atherosclerosis. The aim of the study was to investigate the relationship between oxLDL and other oxidative stress biomarkers with stable coronary heart disease (CHD). We compared the degree of oxidative stress in patients with CHD and sex-matched healthy control subjects in a case-control study. The study included 64 male subjects: 32 patients with stable CHD and 32 normal control subjects. Levels of circulating oxLDL were measured by a monoclonal antibody 4E6-based competition ELISA. Comparison of oxidative stress marker levels between cases and controls, adjusted for age, revealed significantly higher plasma oxLDL levels (63.32+/-25.49 vs. 37.73+/-20.58 U/l, P=0.001), lower serum levels of autoantibodies against oxLDL (341.53+/-350.46 vs. 796.45+/-1034.2 mU/ml, P=0.021), higher activities of the antioxidant enzymes superoxide dismutase in erythrocytes (951+/-70.2 vs. 771.6+/-191.2 U/g, P=0.032) and glutathione peroxidase in whole blood (GSH-Px: 10714.4+/-3705.4 vs. 5512.2+/-1498.1 U/l, P<0.001). The risk of having CHD was 20.6-fold greater (95% CI, 1.86-228.44, P=0.014) in the highest tertile of the oxLDL distribution than in the lowest, determined by logistic regression analysis on the combined study population after adjustment for age and other potential confounding factors. When the risk associated with GSH-Px levels was calculated, the odds ratio was 305.3 (95% CI, 5.07-18369.95, P=0.006) in the highest tertile compared with the lowest. Our results showed that an oxidative stress occurs in patients with CHD despite being clinically stable and under medical treatment. The combination of oxLDL levels and GSH-Px activity may be useful for the identification of patients with stable CHD.

Anti-oxidized LDL antibodies and wine consumption: a population-based epidemiological study in Dicomano, Italy

PURPOSE

In previous studies, higher levels of oxidized low-density lipoprotein (ox-LDL) have been reported to increase the risk of cardiovascular disease. Furthermore, the anti-oxidative properties of red wine have been invoked to explain the paradox of low cardiovascular mortality, in spite of high-fat intake, in the French population. However, the distribution of ox-LDL-antibodies (ox-LDL-Ab) in the unselected population and its relationship with red wine consumption are unknown. This study was carried out to identify factors associated with ox-LDL-Ab, with particular emphasis on the association with wine consumption.

METHODS

We performed a cross-sectional study of 551 unselected, community-dwelling older adults (aged 65 to 94 years) living in Dicomano (Italy). Ox-LDL-Ab titre was measured with an ELISA method.

RESULTS

In the whole study sample, ox-LDL-Ab increased with age and was unrelated to blood lipids, HbA(1c), and smoking habit. A significant inverse relationship was found between ox-LDL-Ab titre and daily wine intake, which persisted after adjusting for possible confounders or in subgroup analyses of participants who reported to drink wine or were free from significant morbidity.

CONCLUSIONS

These results suggest that wine affects ox-LDL-Ab titre in older populations, possibly because of its antioxidant properties.

Increased levels of low-density lipoprotein oxidation in patients with familial hypercholesterolemia and in end-stage renal disease patients on hemodialysis

Patients with familial hypercholesterolemia (FH) and patients with end-stage renal disease (ESRD) undergoing dialysis suffer from accelerated atherosclerosis. Oxidation of low-density lipoprotein (LDL) cholesterol is crucial in atherogenesis. In the present study, we determined the LDL oxidation level and oxidizability of isolated LDL of 11 male patients with FH, 15 male ESRD patients on hemodialysis, and 15 age-matched male normolipidemic healthy controls. FH patients were without lipid-lowering medication for at least 4 weeks and were reassessed after 2 years of cholesterol-lowering therapy (statins). LDL oxidation level was measured by ELISA using monoclonal antibody 4E6 to oxidized LDL (oxLDL) as the capture antibody and anti-human apoB antibody for detection; results were expressed as percentage oxLDL. In FH patients and in ESRD patients on hemodialysis, both groups having a higher percentage of cardiovascular disease, mean plasma LDL oxidation levels were significantly elevated compared with controls (4.9 +/- 1.3; 3.7 +/- 2.0; 1.7 +/- 0.6%, respectively). Within each group of subjects, LDL oxidation level was not associated with history of cardiovascular disease. Furthermore, in neither group was a significant correlation found between plasma concentration of LDL cholesterol and LDL oxidation level. After cholesterol-lowering therapy, LDL oxidation level in FH patients had not changed significantly and remained elevated compared with controls, despite a reduction of LDL cholesterol by 55% on average. Also, absolute plasma oxLDL concentrations, obtained by multiplying LDL oxidation level with plasma LDL cholesterol concentration, were significantly higher in FH patients before and after cholesterol-lowering therapy and in ESRD patients on hemodialysis than in controls (489 +/- 145; 189 +/- 122; 100 +/- 65; and 59 +/- 27 micro moles/L, respectively). No correlation was found between plasma oxLDL concentration and parameters of LDL oxidizability, LDL fatty acids, and LDL alpha-tocopherol content. We conclude that cholesterol-lowering therapy does not normalize elevated LDL oxidation levels in FH patients and elevated LDL oxidation level in FH and in ESRD might mirror atherosclerosis.

Endothelial vasodilatory function is predicted by circulating apolipoprotein B and HDL in healthy humans

Endothelium-dependent vasodilation (EDV), LDL particle size, and antibodies against oxidized LDL (oxLDLab) have been shown to be related to the development of atherosclerosis and cardiovascular disease. In this study, we investigated whether LDL particle size, oxLDLab, apolipoproteins, and lipoproteins are related to endothelial vasodilatory function in a population sample of 58 apparently healthy subjects aged 20 to 69 yr. EDV and endothelium-independent vasodilation (EIDV) were studied in the forearm during local administration of methacholine chloride (2 and 4 microg/min) or sodium nitroprusside (5 and 10 microg/min). Forearm blood flow was determined with venous occlusion plethysmography. In multiple stepwise regression analyses, neither oxLDLab nor small LDL particles were significantly predictive of endothelial vasodilatory function. Instead, a high level of apolipoprotein B (apoB) was an independent predictor of both attenuated EDV and EIDV (r = -0.43, P < 0.01, and r = -0.34, P < 0.05, respectively). HDL cholesterol, on the other hand, was the only lipid variable that was significantly related to the EDV to EIDV ratio, an index of endothelial vasodilatory function (r = 0.35, P < 0.01). The inverse associations between apoB and both EDV and EIDV indicate that apoB might be an early marker of structural vascular changes in healthy subjects, whereas HDL seems to be more specifically related to endothelial vasodilatory function.

Autoantibodies to malondialdehyde-modified low-density lipoprotein in patients with angiographically confirmed coronary artery disease

Oxidised low-density lipoprotein (LDL) has physicochemical properties that are pivotal in atherosclerotic plaque formation. As a consequence, antioxidant regimens may prove an important therapy in the prevention and treatment of cardiovascular disease. Since oxidised LDL is immunogenic, the aims of our study were to measure serum IgG titres to malondialdehyde-modified LDL (MDA-LDL) in patients with coronary artery disease (CAD) and control subjects and assess their potential as a clinical marker for coronary atherosclerosis and, consequently, antioxidant intervention. Serum IgG titres to MDA-LDL were measured in patients with angiographically confirmed CAD (n = 40) and aged-matched controls (n = 40) by enzyme-linked immunosorbant assay (ELISA). Titres were calculated and expressed as both the difference and the ratio of blanked absorbance units (AU) for IgG binding to MDA-LDL and native LDL. For the control population, median IgG titres were 0.26 AU (interquartile range (IQR) 0.20-0.46 AU) and 5.34 (IQR 3.40-8.58), respectively, while the patient population had median IgG titres of 0.30 AU (IQR 0.20-0.47 AU) and 5.08 (IQR 3.30-9.66), respectively. Both sets of calculated titre values were not significantly different between the two groups (P = 0.60 and 0.82, respectively). In conclusion, this study could not establish any significant association between circulating autoantibody titres to MDA-LDL and coronary atherosclerosis. Therefore, the diagnostic value of autoantibodies to oxidised LDL remains unclear.

Antibody to oxidized low-density lipoprotein and cardiovascular mortality in end-stage renal disease

BACKGROUND

Immune response to oxidized low-density lipoprotein (oxLDL) may modulate the process of atherogenesis and cardiovascular disease.

METHODS

We performed a prospective, observational cohort study in 249 patients with end-stage renal disease (ESRD) to examine whether the serum titer of anti-oxLDL antibody can predict cardiovascular mortality.

RESULTS

The median anti-oxLDL antibody titer was 320 mU/mL at baseline. During the follow-up (63 +/- 23 months), 72 deaths including 34 cardiovascular deaths occurred. When the subjects were divided into two groups by the median titer, the high titer group showed a lower risk for cardiovascular mortality (P = 0.040 by Kaplan-Meier analysis and log-rank test). Multivariate Cox proportional hazards model indicated that the lower risk of cardiovascular death in the high titer group remained significant (hazard ratio of 0.46, 95%CI 0.23-0.95, P = 0.037) and independent of age, presence of vascular complications, presence of diabetes mellitus, and elevated C-reactive protein. In contrast, anti-oxLDL antibody titer was not associated with non-cardiovascular mortality.

CONCLUSIONS

These results demonstrate, to our knowledge for the first time, that serum anti-oxLDL antibody titer is an independent predictor of cardiovascular mortality in a cohort of patients with ESRD.

[Atherosclerosis and anti-oxidized low density lipoprotein antibodies in an elderly population]

BACKGROUND

Antibodies to oxidized LDL (anti-OxLDL) have been found to be associated with atherosclerosis. The aim of the study was to evaluate the relationship between anti-OxLDL antibodies and atherosclerosis in the elderly.

PATIENTS AND METHOD

We studied several risk factors and different clinical manifestations of atherosclerosis in 100 people older than 65 years and in 48 healthy blood donor controls (age range: 20 to 55 years). Anti-OxLDL antibodies were measured by ELISA.

RESULTS

Thirty-one percent of the patients tested positive for anti-OxLDL. This percentage increased in the group of subjects without any risk factor or clinical manifestation (66.6%) as it was the case of the mean optical density (O.D.) value (O.D. = 0.671 vs. 0.357 in our general geriatric population). Most of those with a proven atherosclerotic event tested negative for anti-OxLDL antibodies and a statistically significant difference was shown for those with a calcified aortic arch (P = 0.041, 95% CI 0.15-0.97). Mean value of risk factors and clinical manifestations was 3.50 among anti-OxLDL-negative patients, whereas it was 2.51 in the anti-OxLDL-positive group (P = 0.035, 95% CI 0.07-1.91). Actually, when more adverse effects were present, patients' trend to test negative for anti-OxLDL antibodies was higher. An inverse correlation was observed between anti-OxLDL titers and the relative risk of coronary heart disease (P = 0.020).

CONCLUSIONS

The cause of the decrease of free anti-OxLDL antibodies in situations that lead to an oxidative stress is unknown but it may be explained by the formation of immunocomplexes in an effort to ease the clearance of oxidized substrates.

Association of serum MMP-9 with autoantibodies against oxidized LDL

Monocyte-derived macrophages in atherosclerotic plaques secrete matrix metalloproteinases (MMPs), which may contribute to plaque rupture. There has been much speculation as to which factors precipitate in the arterial inflammation. Oxidized low density lipoprotein (oxLDL) has been suggested to have proinflammatory properties, and it has been shown to increase matrix metalloproteinase-9 (MMP-9) secretion by macrophages in vitro. We determined serum MMP-9 concentration and autoantibodies against oxLDL by ELISA in men with angina pectoris (n=243) and age-matched controls (n=238). The association between serum MMP-9 concentration and autoantibodies against oxLDL was evaluated. Autoantibody level against oxLDL, expressed in optical density units, was significantly higher in subjects with angina pectoris compared to controls (0.100+/-0.064 versus 0.088+/-0.051, respectively, P=0.030), but serum levels of MMP-9 did not differ significantly between these groups (54.2+/-29.9 versus 50.6+/-23.1 microg/l). However, autoantibodies against oxLDL correlated positively with serum MMP-9 (r=0.21, P<0.001). In a multiple regression model (including age, diastolic blood pressure, cholesterol, HDL cholesterol, triglycerides, BMI, smoking and MMP-9) serum MMP-9 (beta=0.200, P<0.001) and smoking (beta=0.179, P<0.001) were significantly associated with autoantibodies against oxLDL. In conclusion, autoantibodies against oxLDL were positively associated with angina pectoris and serum MMP-9. Since autoantibody level against oxLDL could be expected to reflect the degree of oxLDL in the vessel wall, our results suggest that oxLDL is associated with MMP-9 in vivo.

Evaluation and characterization of EIA measuring autoantibodies against oxidized LDL

Autoantibodies against oxidized LDL (oxLDL) have been measured in many laboratories. Comparison of data between laboratories is difficult because of methodological variations and differences in the expression of results. We have optimized an enzyme immunoassay (EIA), which measures autoantibodies against oxLDL and evaluated the effect on results of different ways of expressing the data. Optimized conditions were as follows: coating concentration 2 microg/ml of LDL on polysorp plates, 1% human serum albumin (HSA) as a blocking agent, sample dilution 1:50, conjugate dilution 1:8000, and 0.2% HSA in sample and conjugate diluents. The amount of autoantibodies expressed as ratios between oxLDL and native LDL (natLDL), as titers against oxLDL or as differences between binding to oxLDL and natLDL showed significant differences among groups of coronary heart disease (CHD) patients with different diagnosis or treatment procedures. However, there were no differences among the groups when the results were expressed as the ratio between antibody titer against oxLDL and a standard serum (oxLDL/stand). After standardization oxLDL autoantibody test may become a useful tool for analysis of the risk for CHD.

Lipids, cardiovascular disease and atherosclerosis in systemic lupus erythematosus

Systemic lupus erythematosus is commonly associated with early onset cardiovascular disease and is often associated with hyperlipidaemia. This review examines the evidence for an increased prevalence of both CHD and hyperlipidaemia in SLE and mechanisms by which autoimmunity in SLE could accelerate the progression of atheroma. It postulates how lipid lowering therapies used in cardiological disease might help reduce the incidence of CHD in SLE.

Inverse relationship between circulating oxidized low density lipoprotein (oxLDL) and anti-oxLDL antibody levels in healthy subjects

Oxidized low density lipoprotein (oxLDL) has been implicated in the pathogenesis of atherosclerosis. Recent studies have shown that immunization of animals with oxLDL results in suppression of atherogenesis. Antibody against oxLDL (oxLDL Ab) is detectable in human sera, although its biological significance is not well established. We examined the relationship between oxLDL Ab titer and circulating oxLDL level in 130 healthy Japanese subjects. OxLDL was measured as apolipoprotein (apo) B-containing lipoproteins carrying oxidized phosphatidylcholines by a sensitive ELISA. IgG class oxLDL Ab titer was measured by ELISA. Plasma oxLDL concentration was very low and it corresponded on average to one to two out of 1000 apoB-containing lipoproteins in plasma. Plasma oxLDL correlated positively with LDL cholesterol and inversely with oxLDL Ab titer. These associations remained significant and independent in multiple regression analysis including age, gender, smoking, and high-density lipoprotein cholesterol. These data indicate that healthy subjects have a very low concentration of oxLDL in the circulation, and that oxLDL Ab titer is in an inverse relationship with plasma oxLDL concentration in this population. Although these results suggest that oxLDL Ab may play a role in maintaining the low level of plasma oxLDL, its role in atherogenesis awaits further studies.