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

Circulating Oxidized Low-Density Lipoprotein and Its Association With Carotid Intima-Media Thickness in Asymptomatic Members of Familial Combined Hyperlipidemia Families

OBJECTIVE

Oxidized low-density lipoprotein (Ox-LDL)is implicated in the pathogenesis of atherosclerosis. Circulating oxidation-specific epitopes on plasma Ox-LDL has been linked with coronary artery disease, but its determinants and its association with early development of atherosclerosis in familial combined hyperlipidemia (FCHL) has not been very well studied. This study aimed to investigate the determinants of the circulating Ox-LDL and the association between Ox-LDL and carotid intima-media thickness (IMT) in asymptomatic members of FCHL families.

METHODS AND RESULTS

Ox-LDL, susceptibility of LDL to oxidation in vitro, plasma 8-isoprostane and antioxidants, lipids and lipoproteins, LDL particle size, and carotid IMT were measured in 150 asymptomatic FCHL family members. Affected FCHL family members had reduced LDL particle size and lag time for LDL oxidation, increased plasma levels of Ox-LDL, increased plasma urate and alpha-tocopherol, and a trend for the increase of 8-isoprostane as compared with nonaffected FCHL. Ox-LDL was independently associated with serum LDL cholesterol, apoB, and 8-isoprostane in multivariate analysis but only univariately correlated with LDL particle size and lag time for LDL oxidation. In addition, Ox-LDL was significantly associated with carotid mean IMT independently of other clinical and biochemical variables in a multivariate model.

CONCLUSIONS

Serum LDL cholesterol, apoB levels, and 8-isoprostane were the most important determinants of Ox-LDL. Ox-LDL is independently associated with carotid IMT in asymptomatic FCHL family members and can be used as a marker of early atherosclerosis in FCHL.

Associations among oxidized low-density lipoprotein antibody, C-reactive protein, interleukin-6, and circulating cell adhesion molecules in patients with unstable angina pectoris

Oxidized low-density lipoprotein (LDL) is believed to play a key role in the development of atherosclerosis. However, the significance of anti-oxidized LDL antibody in atherogenesis is unclear. The purposes of this study were to assess whether anti-oxidized LDL antibody titers are related to other inflammatory markers of possible interest in atherosclerotic development, such as soluble cell adhesion molecules, interleukin-6, and C-reactive protein (CRP), and to determine the prognostic value of anti-oxidized LDL antibody as a predictor of cardiac events in patients with unstable angina pectoris. Sixty patients (35 men and 25 women; mean age 60 years) with unstable angina were included in this study. The levels of CRP and of intercellular adhesion molecule-1 (ICAM-1) at 24 and 72 hours after admission were significantly higher than their baseline levels (p <0.05, respectively). After adjusting for age, gender, body mass index, and statin use, anti-oxidized LDL antibodies were positively correlated with CRP (r = 0.72, p <0.001) and ICAM-1 (r = 0.68, p <0.001). Elevated anti-oxidized LDL antibodies (mean >11.37 U/ml) and CRP levels (median >2.4 mg/L) on admission were correlated with a significantly lower 16-month, event-free survival rate (Kaplan-Meier event-free survival analysis, log-rank p <0.01 and p <0.05, respectively). Multivariate analysis by logistic regression revealed that elevated levels of anti-oxidized LDL antibody (mean >11.3 U/ml) on admission were an independent risk factor for an adverse cardiac event (odds ratio 2.2, 95% confidence interval 1.5 to 10.7, p = 0.001). This study demonstrates that anti-oxidized LDL antibody expression is associated with the expression of CRP and adhesion molecules, especially ICAM-1, and is a predictor of cardiac events in patients with unstable angina pectoris. The observed elevated levels of anti-oxidized LDL antibody suggest plaque instability and may be useful for identifying patients at higher risk of a cardiac event.

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.

Positive correlation between in vivo oxidized LDL and LDL immune complexes

OBJECTIVES

To investigate the possible relationship between oxidized low-density lipoprotein (ox-LDL) and LDL immune complexes (IC).

METHODS

Both LDL-IC and ox-LDL were detected by sandwich ELISA. The levels were also studied in 60 patients with coronary heart disease (CHD) and 50 control subjects.

RESULTS

Compared to controls, both the plasma ox-LDL concentrations (595.5 +/- 194.8 vs. 440.3 +/- 175.0 microg/l, P < 0.001) and LDL-IC levels (2.74 +/- 0.73 vs. 1.38 +/- 0.78 AU, P < 0.001) in the patients with CHD were significantly increased. The relationships between LDL-IC, ox-LDL levels, and other lipid parameters in all the studied subjects (n = 100) were analyzed. LDL-IC levels were positively correlated with TC, TG, LDL-C, lipoprotein(a) [Lp(a)], and apolipoprotein B (apoB) concentration, while negatively correlated with apoA1 concentration, respectively. Similarly, ox-LDL levels were also found positively correlated with TC, LDL-C, and apoB concentrations, respectively. Furthermore, a significantly positive correlation between ox-LDL and LDL-IC levels was found (r = 0.313, P < 0.005).

CONCLUSION

In vivo oxidized LDL positively correlates with circulating levels of LDL immune complexes.

Oxidative stress: potential of distinct peroxide determination systems

When reactive oxygen species attack biological structures, peroxides, which are short-lived oxidative intermediates, are generated. We evaluated the potential of two different, commercially available peroxide activity assays (Pox-Act and d-ROMS) to see whether the results were associated with the clinical condition of subjects who were participating in a routine health care program. Furthermore, we determined the total antioxidant status (TAS) and the titer of autoantibodies against oxidized low-density lipoprotein (oLAb) to verify the hydroperoxide measurements.

Subjects with medical conditions (hereafter referred to as patients) had significantly increased serum peroxide levels compared to healthy subjects. The d-ROMS kit indicated that 86% of subjects had an increased level of total peroxides. Although the assays had a significant correlation (p < 0.001), 34% of the subjects had an increased total peroxide concentration in the Pox-Act assay that was clearly associated with clinical symptoms. Furthermore, the sensitivity of the Pox-Act assay was 35 times higher than that of the d-ROMS kit. In subjects with medical conditions, there was a trend toward a decreased TAS and a slightly increased oLAb titer in comparison to healthy subjects, but this was not statistically significant. The Pox-Act assay seems to be a valuable tool for the determination of total peroxides, while the results from the d-ROMS kit should be considered with caution.

Oxidative Stress Influences CC-Chemokine Levels in Hemodialyzed Patients

BACKGROUND

Increased oxidative stress (SOX) has been reported in hemodialyzed (HD) patients, but its influence on CC-chemokine levels remains unknown.

METHODS

The levels of 3 distinct SOX markers (Cu/Zn superoxide dismutase (Cu/Zn SOD), total lipid peroxide, and autoantibodies against oxidized LDL (OxLDL-Ab)), as well as those of 4 CC-chemokines (monocyte chemoattractant protein-1 (MCP-1), macrophage inflammatory proteins (MIP-1alpha, MIP-1beta), regulated upon activation, normal T cell expressed and secreted (RANTES), and tumor necrosis factor-alpha (TNF-alpha)) were measured pre- and post-HD session in 15 HD patients with cardiovascular disease (CVD) and 12 HD patients without CVD (pre- and post-HD session) and 17 controls.

RESULTS

Cu/Zn SOD levels were elevated in HD patients (both before and after HD) compared to controls (p < 0.001). Total lipid peroxide levels were similar in the controls in pre-dialysis samples, but were increased after a HD session (p < 0.001). Pre-dialysis OxLDL-Ab levels were increased only in the HD group with CVD compared to controls (p < 0.05). The pre-dialysis plasma levels of TNF-alpha (p < 0.001), MCP-1 (p < 0.001) and MIP-1beta (p < 0.01) were increased both in all HD patients and subgroups with CVD when compared to the controls, and remained significantly elevated when measured after HD. Dialysis increased MCP-1 (p < 0.05) and MIP-1beta (p < 0.001) levels as compared to the controls as well as in patients without CVD. Plasma RANTES was significantly lower before HD (p < 0.05) and after HD (p < 0.001) in patients with CVD. Patients without CVD and all HD patients also had lower RANTES before and after HD when compared to controls (all p < 0.001). A positive correlation was observed between plasma pre-dialysis Cu/Zn SOD levels and the other SOX markers (all p < 0.05), age (p < 0.05) and duration of hemodialysis (p < 0.001). A positive relationship existed between plasma Cu/Zn SOD levels and those of MCP-1, MIP-1beta and TNF-alpha (all p < 0.001). RANTES levels negatively correlated with Cu/Zn SOD (p < 0.0001).TNF-alpha positively correlated with age (p < 0.05), total lipid peroxide (p = 0.010), MCP-1 (p < 0.01) and MIP-1beta levels (p < 0.01). An identifiable association exists between MCP-1 and MIP-1beta levels (p < 0.01), whereas both MCP-1 and MIP-1beta were inversely correlated with RANTES (both p < 0.05).

CONCLUSION

Our data indicate for the first time a probable functional relationship between oxidative stress and CC-chemokine levels in hemodialyzed patients, particularly in those with cardiovascular disease. This relationship may represent one of the mechanisms involved in the progression of atherosclerosis in these patients.

Cardiovascular complications and increased levels of circulating modified low density lipoprotein in HIV patients and patients with lipodystrophy

The introduction of highly active antiretroviral therapy (HAART) for patients infected with HIV has significantly prolonged the life expectancy and to some extent has restored a functional immune response. However, the premature introduction of HAART has led to a significant and alarming increase in cardiovascular complications, including myocardial infarction and the appearance of abnormal distribution of body fat seen as lipodystrophy. One key element in the development of ischemic coronary artery disease is the presence of circulating and tissue-fixed modified low density lipoprotein (mLDL) that contributes to the initiation and progression of arterial lesions and to the formation of foam cells. Even though not completely elucidated, the most likely mechanism involves mLDL in the inflammatory response and the induction of a specific immune response against mLDL. Circulating antibodies against mLDL can serve as an indirect marker of the presence of circulating and vessel-fixed mLDL. In the present study, we measured antibodies to mLDL and correlated them with immune status (i.e., number of CD4+ T cells) in 59 HIV patients and with the clinical manifestation of lipodystrophy in 10 patients. We observed a significant reduction in anti-mLDL antibody levels related both to lipodystrophy and to an immunocompromised state in HIV patients. We speculate that these antibodies may explain in part the rapid development of ischemic coronary artery disease in some patients.

Immunoglobulin M type of autoantibodies to oxidized low-density lipoprotein has an inverse relation to carotid artery atherosclerosis

BACKGROUND

Lipoprotein oxidation plays an important part in atherogenesis. Autoantibodies to oxidation-specific epitopes of LDL occur in plasma and atherosclerotic lesions of humans and animals. The potential role of these autoantibodies in atherogenesis still remains unsolved. We studied the relationship between different isotypes of autoantibodies to copper-oxidized LDL and malondialdehyde-modified LDL (MDA-LDL) and carotid artery intima-media thickness (IMT) in a population-based cohort of 1022 middle-aged men and women. In addition, we studied the relation of C-reactive protein (CRP) to IMT.

METHODS AND RESULTS

The levels of IgM, IgG, and IgG2 autoantibodies binding to MDA-LDL and copper-oxidized LDL were determined in plasma samples by chemiluminescence-based ELISA. IMT and the number of plaques were measured ultrasonographically. The subjects were divided into tertiles for antibody titers. We found an inverse association between IMT and IgM autoantibody titers to MDA-LDL that remained statistically significant after adjusting for age, gender, LDL cholesterol, systolic blood pressure, CRP, and smoking. CRP was not independently associated with IMT.

CONCLUSIONS

These results show that IgM autoantibodies to MDA-LDL have an inverse association with carotid atherosclerosis. The possible implications of this finding are discussed.

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.

Oxidized LDL autoantibodies are related to apolipoprotein E phenotype, independently of postprandial change in plasma triglycerides and LDL size, among patients with angiographically verified coronary artery disease and healthy controls

OBJECTIVE

Oxidized low-density lipoprotein (LDL) autoantibodies (oxLDLab), apolipoprotein E (apoE) phenotype, postprandial triglyceride changes and LDL size are suggested to be risk factors for coronary artery disease (CAD). Our aim was to study the interaction between these new risk factors among patients with CAD and healthy controls.

METHODS

oxLDLab from 31 men with angiographically verified CAD and 31 healthy men were analyzed by enzyme-linked immunosorbent assay. Isoelectric focusing and immunoblotting were used for apoE phenotyping. Triglyceride level was measured after 12 h of fasting and 3, 5 and 7 h after a high-fat meal. Nondenaturing gradient gel electrophoresis was used to separate LDL particles according to size.

RESULTS

oxLD- Lab levels increased according to apoE phenotype in the following order: E2 < E3 < E4 (p = 0.004, ANOVA). The postprandial response of triglycerides, the size of LDL particles and the concentration of LDL and high-density lipoprotein (HDL) cholesterol did not differ between apoE phenotypes, and the use of these variables as covariates did not change the statistically significant difference in oxLDLab levels between apoE phenotypes (p = 0.01, ANCOVA). oxLDLab levels did not differ between the patient and control groups.

CONCLUSION

We found an association between apoE allele epsilon2 and decreased levels of oxLDLab, which was independent of the postprandial response of triglycerides, the size of LDL particles and plasma LDL and HDL cholesterol levels. The mechanism by which apoE affects oxidation of LDL remains unknown.

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.

Antibodies to oxidized low-density lipoprotein in patients following coronary artery revascularization

BACKGROUND

Measurement of antibodies to oxidized low-density lipoprotein (AB-oxLDL) has been proposed as a way of identifying individuals at risk for cardiovascular disease beyond the determination of LDL cholesterol (LDL-c) alone. While this hypothesis is appealing, evidence that AB-oxLDL is a risk factor independent of LDL-c levels remains to be established.

METHODS AND RESULTS

We conducted a cross-sectional study of 158 hypercholesterolemic adults who underwent coronary revascularization. Patients were randomized in a clinical trial to a nurse case management (NURS) or an enhanced usual care (EUC) group. The goal in the NURS group was to achieve an LDL-c <85 mg/dl with pharmacotherapy and lifestyle advice. Six months after revascularization, serum and urine were collected to determine lipids, AB-oxLDL, urinary isoprostanes (an in-vivo marker of oxidative damage), oxygen-radical-absorbing capacity (ORAC) of serum, serum carotenoids, alpha-tocopherol and C-reactive protein (CRP). After 6 months of intervention, the NURS group had a mean (+/-SD) LDL-c of 84 (18) mg/dl compared with 105 (25) mg/dl in the EUC group (P < 0.001). In addition, AB-oxLDL was lower (median +/- 95% confidence interval, -202 milliunits (mU)/ml, -372 to -32, P = 0.02) in the NURS group (488 mU/ml, 399, 588) than in the EUC group (690 mU/ml, 544, 847). The difference in AB-oxLDL between groups persisted after adjustment for LDL-c (-316 mU/ml, -519 to -112, P = 0.005). Further adjustment for ORAC and alpha-tocopherol did not diminish the group effect. The groups did not differ significantly in serum antioxidants, urinary isoprostane excretion or CRP. In additional analyses, change in LDL-c from baseline was not associated with AB-oxLDL at 6 months.

CONCLUSIONS

Our results demonstrate lower AB-oxLDL in patients who achieve greater lipid reduction. However, AB-oxLDL appears to be independent of achieved LDL-c, ORAC levels or serum antioxidant levels. These results support the hypothesis that AB-oxLDL is independent of LDL-c level. Further prospective studies are needed to determine the prognostic value of AB-oxLDL.

Oxidized low-density lipoproteins: what is understood and what remains to be clarified

Oxidized low-density lipoprotein (OxLDL) has previously been thought to promote atherogenesis through foam cell formation. However, the actual nature of OxLDL present in vivo remained obscure until recently. We have produced a monoclonal antibody, DLH3, which specifically binds to OxLDL but not to native LDL. The presence of OxLDL in the LDL fraction of human plasma was demonstrated by introducing a sandwich ELISA procedure using DLH3 together with an anti-apoB antibody. Furthermore, OxLDL levels appeared to increase in certain pathological conditions including acute myocardial infarction and carotid artery atherosclerosis. Accumulation of OxLDL in atherosclerotic lesions has also been demonstrated by immunohistochemical and biochemical studies using the DLH3 antibody. This antibody recognizes oxidized phosphatidylcholines (OxPC) generated during oxidative modification of LDL, and OxPC-apoB adducts formed in OxLDL are the presumed antigens. Measuring OxLDL in plasma would be a useful diagnostic tool for cardiovascular diseases. However, there still remain some major questions related to OxLDL, the answers to which are crucial for understanding the mechanisms of atherogenesis.

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.

Association between plasma oxidized low-density lipoprotein and diabetic nephropathy

To investigate the association of oxidized low-density lipoprotein (ox-LDL) with the development of diabetic nephropathy, plasma levels of ox-LDL were measured in 70 patients with type 2 diabetes mellitus. A sandwich enzyme-linked immunoadsorbent assay (ELISA) using the mouse monoclonal antibody FOH1a/DLH3, which specifically recognizes oxidized phosphatidylcholine, and a horseradish peroxidase (HRP)-labeled goat anti-human apolipoprotein B IgG was used to measure ox-LDL levels. The mean age of the patients was 57.0+/-1 3.4 years, and the mean duration of diabetes was 13.4+/-8.5 years. Plasma ox-LDL levels were similar in patients with normoalbuminuria (13.7+/-3.9 U/ml), patients with microalbuminuria (12.8+/-3.9 U/ml), and normal controls (12.5+/-4.2 U/ml). However, the plasma ox-LDL level in patients with macroalbuminuria (16.8+/-7.5 U/ml) was significantly higher than those in the other groups (P<0.05). Hemoglobin A1c (HbA1c) levels were similar in diabetic patients with normoalbuminuria (8.2+/-2.2%), microalbuminuria (7.8+/-1.3%), or macroalbuminuria (7.2+/-1.4%). There was no significant correlation between the ox-LDL level and the HbA1c level. The significantly elevated plasma ox-LDL levels in patients with macroalbuminuria suggest that ox-LDL may play an important role in the progression of diabetic nephropathy.

Inverse relationship between total testosterone and anti-oxidized low density lipoprotein antibody levels in ageing males

Accumulating evidence indicates the involvement of sex hormones in atherogenesis. Endogenous testosterone is inversely related to the majority of risk factors for atherosclerosis and is known to be a potent immunomodulator. Recently, autoantibodies to oxidized LDL (anti-oxLDL Ab) were shown to predict carotid and coronary atherosclerosis. The aim of this study was to investigate the relationship between these antibodies and testosterone level in ageing males. The study group comprised 65 males over 50 years old (42 with coronary artery disease). Serum anti-oxLDL Ab titer was measured by enzyme-linked immunoassay and total serum testosterone by radioimmunoassay. A significant inverse correlation was found between serum anti-oxLDL Ab titer and testosterone concentration (r=-0.346, P=0.0047). Alteration in serum anti-oxLDL Ab titres showed no correlation to classical cardiovascular risk factors, e.g. body mass index, waist/hip ratio, smoking, total cholesterol, triglycerides, HDL-cholesterol, LDL-cholesterol. In multiple regression analysis only testosterone level was independently associated with anti-oxLDL Ab. These data suggest a that fall of testosterone concentration in ageing men can influence either oxidative modification of LDL or the immune response to these lipoproteins which may be important in the pathogenesis of atherosclerosis.

[Atherosclerosis and sensitive determination of oxidized LDL using monoclonal antibody]

Oxidized low-density lipoprotein (OxLDL) is thought to be involved in atherosclerotic lesion formation. We established a monoclonal antibody, DLH3, that recognizes oxidized phosphatidylcholine (OxPC) formed in OxLDL. A sensitive method for detecting OxLDL was enabled by a sandwich ELISA procedure utilizing DLH3 together with an anti-apoB antibody. Using the method, we demonstrated the presence of OxLDL in human circulating plasma for the first time, and the plasma OxLDL level in healthy subjects was estimated to be about 0.1 ng/microgram LDL protein. OxLDL levels in patients with acute myocardial infarction are more than 3 times higher than in controls. Thus the plasma OxLDL level could be a good marker for cardiovascular disease. There are multiple metabolic enzymes for OxPC in plasma. We demonstrated that lecithin: cholesterol acyltransferase (LCAT) is capable of metabolizing OxPC molecules in OxLDL, and that the plasma OxLDL level in patients with familial LCAT deficiency was about 3.5 times higher than in controls. OxLDL in vivo is likely to be metabolized by enzymatic activities in plasma, the reticuloendothelial system including Kupffer cells, and immunological responses. The OxLDL levels determined by this analytical procedure would reflect the physiologic balance between oxidative modification of LDL and metabolic clearance of OxLDL.

Serum levels of antibodies against oxidised LDL in kidney graft recipients

BACKGROUND/AIMS

Lipid abnormalities present in the post-transplant period may contribute to the development and progression of complications leading to graft and patient loss. In the present study serum levels of antibodies against oxidised LDL (Ab-oxLDL) in kidney graft recipients were investigated along with their possible relation to the development of complications in the post-transplant period, and to the outcome of kidney transplantation.

METHODS

Serum levels of Ab-oxLDL and lipid pattern were evaluated in 92 kidney graft recipients before and at 3, 6, 12, and 24 months after kidney transplantation, as well as in 90 healthy blood donors (control group).

RESULTS

Kidney graft recipients had higher frequency of low levels of Ab-oxLDL as compared with the control group. A decrease in Ab-oxLDL levels was observed at 6 months post-transplant. Patients with early graft loss due to acute rejection had lower pre-transplant Ab-oxLDL levels (p < 0.05) as compared to patients with graft survival >3 months.

CONCLUSIONS

It is suggested that decreased Ab-oxLDL levels found in kidney graft recipients may reflect impaired response to the products of lipid oxidation or increased consumption of Ab-oxLDL, and are associated with graft loss due to acute rejection.

Plasma antioxidants in pediatric patients with glycogen storage disease, diabetes mellitus, and hypercholesterolemia

Oxidative modification of lipoproteins in vessel walls plays a key role in atherogenesis. Patients with glycogen storage disease type Ia (GSD Ia) do not develop premature atherosclerosis despite severe hyperlipidemia. We analyzed antioxidative defense and oxidative stress in plasma and serum of patients with GSD Ia (n = 17) compared to patients with type I diabetes mellitus (DMI, n = 17), familial hypercholesterolemia (FH, n = 18), and healthy controls (n = 20). We measured the total radical-trapping antioxidant parameter (TRAP), single antioxidants (sulfhydryl groups, uric acid, vitamin C, alpha-tocopherol, coenzyme Q10), malondialdehyde, oxidized low density lipoprotein (LDL) antibodies, lipid profile [cholesterol, triglyceride, lipoprotein (a)], homocysteine, and hemoglobin (Hb)A(1C). TRAP levels were elevated in the GSD Ia group (p <.01) and correlated with elevated uric acid levels (r = 0.72, p =.001). None of the other plasma antioxidants correlated with TRAP levels. DMI patients showed decreased sulfhydryl groups (p <.01) and a reduced ubiquinol-10 fraction (p <.01). Malondialdehyde (p <.001) and oxidized LDL autoantibodies (p <.05) were increased in the diabetic group. In FH patients, parameters of oxidative stress and TRAP did not differ from controls. We conclude that in GSD Ia an increased antioxidative defense in plasma may protect against lipid peroxidation and thus against premature atherosclerosis. Furthermore, we demonstrated that in DMI increased oxidative mechanisms are already present in childhood.

Relationship between the sialic acid content of low-density lipoprotein (LDL) and autoantibodies to oxidized LDL in the plasma of healthy subjects and patients with atherosclerosis

To determine whether the sialic acid (SA) content of the low-density lipoprotein (LDL) is related to the plasma concentration of autoantibodies to oxidized LDL (oxLDL), we measured the SA content of LDL and the concentrations of oxLDL and autoantibodies to oxLDL in plasma of 20 apparently healthy subjects and 20 patients with advanced coronary atherosclerosis. In the healthy subjects the SA content of LDL correlated positively with plasma concentration of autoantibodies to oxLDL. In agreement with the literature the decreased SA content of LDL was associated with an increased fraction of oxLDL; a decreased fraction of oxLDL was associated with an increased plasma concentration of autoantibodies to oxLDL. In the patients the SA content of LDL and plasma concentrations of oxLDL and autoantibodies to oxLDL were not related. We conclude that the SA content of LDL correlates positively with plasma concentration of autoantibodies to oxLDL in healthy subjects. However, this association may vary depending on the stage of atherogenesis. Although our results suggest dependence of LDL SA content on the clearance of oxidatively modified (desialylated and oxidized) LDL from blood by autoantibodies to oxLDL, the mechanisms regulating the SA content of LDL await further studies.

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.

Oxidized low density lipoprotein: the occurrence and metabolism in circulation and in foam cells

Oxidatively modified low density lipoprotein (OxLDL) is thought to be involved in the early development of atherosclerotic lesions. The appearance of lipid-laden foam cells is known to be one of the typical features of atherosclerotic lesions, and accumulating evidence has demonstrated that foam cells are formed after taking up OxLDL by macrophages in vitro. However, the modified structures, distribution, and metabolism of OxLDL present in vivo are poorly understood. Recently, our studies, together with others, have demonstrated that OxLDL is actually present in circulating human plasma. Furthermore, we have provided evidence that foam cells accumulate modified apoB fragments derived from OxLDL in the cells. This article reviews recent progress in this field, including the intracellular metabolism of OxLDL in foam cells and the relevance of OxLDL as an in vivo ligand for macrophages.

Effects of alpha-tocopherol on superoxide production and plasma intercellular adhesion molecule-1 and antibodies to oxidized LDL in chronic smokers

Antioxidants have been postulated to exert beneficial effects in atherosclerosis. Atherosclerosis is associated with raised plasma levels of soluble intercellular adhesion molecule-1 (sICAM-1) and autoantibodies against oxidized low-density lipoprotein (oxLDL). It is not known whether antioxidants affect these plasma factors in chronic smokers. In a randomized double-blind placebo-controlled study involving 128 male normolipidemic chronic smokers the effect of a 2-year alpha-tocopherol treatment (400 IU dL-alpha-tocopherol daily) on plasma levels of sICAM-1 and autoantibodies against oxLDL was evaluated. In addition, we monitored production of superoxide by leukocytes ex vivo. It was found that compared to nonsmokers (n = 33) plasma levels of IgG but not IgM autoantibodies against oxLDL and concentrations of sICAM-1 in smokers were significantly elevated (30 and 42%, respectively). After supplementation with alpha-tocopherol concentration of TBARS in plasma and in vitro oxidizability of LDL had decreased, but autoantibodies and sICAM-1 had not changed. Production of superoxide was not different between alpha-tocopherol- and placebo-treated smokers. It is concluded that in chronic smokers, long-term treatment with alpha-tocopherol does not normalize the raised levels of sICAM-1 and autoantibodies against oxLDL, both risk factors for initiation or progression of cardiovascular disease, despite a decrease in in vitro oxidizability of LDL.

Antibodies to oxidized LDL in relation to carotid atherosclerosis, cell adhesion molecules, and phospholipase A(2)

-The role of the humoral immune response to oxidized low density lipoprotein (Ox-LDL) in atherogenesis is unclear and available studies are contradictory. The aims of the present study were (1) to compare antibody titers to modified LDL in a group of patients with hypercholesterolemia (n=102) with those in matched controls (n=102), (2) to analyze whether these titers were related to atherosclerosis development as measured by ultrasound, and (3) to analyze whether these titers were related to soluble cell adhesion molecules and secretory type II phospholipase A(2) in plasma. The results showed that male patients with hypercholesterolemia had lower immunoglobulin G (IgG) titers compared with those in healthy controls. In the control group, there was an inverse correlation between intima-media thickness of the carotid artery bulb and IgM titers against Ox-LDL and malondialdehyde-LDL (r=-0.35, P:=0.001; and r=-0.31, P:=0.003, respectively). In the patient group, however, only weak associations were seen. IgG titers were positively associated with soluble intercellular adhesion molecule-1, soluble E-selectin, and secretory type II phospholipase A(2). Taken together, the results of this study support the concept that the humoral immune response against Ox-LDL may be protective in early atherosclerosis. The pattern, however, is complex, and the role of the immune response may differ in different patient groups as well as at different stages of the disease.

Circulating antibodies recognizing malondialdehyde-modified proteins in healthy subjects

Antibodies against malondialdehyde (MDA)-modified proteins are often increased in patients with diseases related to oxidative stress. However, the clinical significance of these antibodies is hampered by their frequent presence also in healthy controls. Aim of this work has been to characterize the immune reactivity against MDA-derived antigens in healthy subjects. The sera of 120 healthy subjects contained IgG and IgM targeting MDA-modified human albumin (HSA), fibrinogen, and LDL. These sera also displayed weak reactivity with oxidized LDL and HSA complexed with oxidized arachidonic acid. Conversely, oxidized HSA or HSA complexed with other aldehydic lipid peroxidation products was not recognized. Control sera also did not recognize cyclic dihydropyridine-MDA products, while HSA-MDA reactivity was associated (r > 0.9; p <.0005) with the presence of fluorescent lysine-conjugated-imine cross-links. In Western blots both IgG and IgM recognized high molecular weight HSA-MDA aggregates, but not monomeric HSA-MDA adducts. The addition of sodium cyanoborohydride, that prevented conjugated-imine fluorescence and protein aggregation during HSA-MDA preparation, abolished the antibody binding. This suggested that the plasma of healthy subjects contained IgG and IgM recognizing protein aggregates linked through 1-amino-3-imino-propene bridges. The function of these antibodies is at the moment unknown, but they might contribute to scavenging MDA cross-linked proteins.

Acute increases in plasma oxidized low-density lipoprotein immediately after percutaneous transluminal coronary angioplasty

To investigate the acute changes in plasma oxidized low-density lipoprotein before and immediately after coronary angioplasty, we studied 132 consecutive patients who successfully underwent this procedure. Plasma oxidized low-density lipoprotein levels were significantly increased immediately after coronary angioplasty in patients with stable angina pectoris as well as in those with acute coronary syndromes.

Circulating oxidized low density lipoprotein levels. A biochemical risk marker for coronary heart disease

Recent studies have established oxidative modification of low density lipoprotein (LDL) as an important atherogenic factor. We examined the clinical relevance of circulating oxidized LDL (OxLDL) levels in atherosclerotic disease by an enzyme immunoassay with use of specific antibodies against OxLDL (FOH1a/DLH3) and apolipoprotein B. Plasma OxLDL levels were significantly higher in patients with coronary heart disease (n=65) than in control subjects (n=181; 201. 3+/-11.2 versus 112.4+/-3.3 U/dL, respectively; P<0.01). OxLDL levels were not associated with age, sex, total cholesterol, or apolipoprotein B levels in normal control subjects. Our results suggest that circulating OxLDL may be a possible biochemical risk marker for coronary heart disease.

Antibodies against oxidized LDL and carotid artery intima-media thickness in a healthy population

Oxidation of LDLs plays an important role in atherosclerosis, and immune response to oxidized LDL (oxLDL) may modulate atherogenesis. Although immunization with oxLDL is shown to suppress atherogenesis in animal models, the role of the immune response to oxLDL is not well established in humans. We investigated the relationship between the titer of anti-oxLDL antibody (oxLDL Ab) and arterial wall thickness in a healthy population with no clinical signs of atherosclerosis. Intima-media thickness of the carotid arteries (CA-IMT) was measured by high-resolution B-mode ultrasonography in 446 healthy subjects. The titer of IgG-class oxLDL Ab was measured by a solid-phase ELISA. In univariate analysis, CA-IMT correlated positively with age, systolic blood pressure, total cholesterol, triglyceride, LDL cholesterol, body mass index, and waist-to-hip ratio, whereas it correlated negatively with HDL cholesterol and oxLDL Ab titer. The inverse association between oxLDL Ab titer and CA-IMT remained significant in multiple regression analysis, which took other confounding variables into account. These results indicate an independent inverse relationship between oxLDL Ab titer and CA-IMT in healthy subjects, supporting the hypothesis that immune response to oxLDL may have a protective role at an early stage of human atherosclerosis.