Detection of electronegative low density lipoprotein (LDL-) in plasma and atherosclerotic lesions by monoclonal antibody-based immunoassays

Changes in lipoproteins associated with lipid-lowering and antiplatelet strategies in patients with acute myocardial infarction

Background

Despite lipid-lowering and antiplatelet therapy, the pattern of residual lipoproteins seems relevant to long-term cardiovascular outcomes. This study aims to evaluate the effects of combined therapies, commonly used in subjects with acute myocardial infarction, in the quality of low-density lipoprotein (LDL) particles.

Methods

Prospective, open-label trial, included patients with acute myocardial infarction. Patients were randomized to antiplatelet treatment (ticagrelor or clopidogrel) and subsequently to lipid-lowering therapy (rosuvastatin or simvastatin/ezetimibe) and were followed up for six months. Nonlinear optical properties of LDL samples were examined by Gaussian laser beam (Z-scan) to verify the oxidative state of these lipoproteins, small angle X-ray scattering (SAXS) to analyze structural changes on these particles, dynamic light scattering (DLS) to estimate the particle size distribution, ultra violet (UV)-visible spectroscopy to evaluate the absorbance at wavelength 484 nm (typical from carotenoids), and polyacrylamide gel electrophoresis (Lipoprint) to analyze the LDL subfractions.

Results

Simvastatin/ezetimibe with either clopidogrel or ticagrelor was associated with less oxidized LDL, and simvastatin/ezetimibe with ticagrelor to lower cholesterol content in the atherogenic subfractions of LDL, while rosuvastatin with ticagrelor was the only combination associated with increase in LDL size.

Conclusions

The quality of LDL particles was influenced by the antiplatelet/lipid-lowering strategy, with ticagrelor being associated with the best performance with both lipid-lowering therapies. Trial registration: NCT02428374.

Apolipoprotein and LRP1-Based Peptides as New Therapeutic Tools in Atherosclerosis

Apolipoprotein (Apo)-based mimetic peptides have been shown to reduce atherosclerosis. Most of the ApoC-II and ApoE mimetics exert anti-atherosclerotic effects by improving lipid profile. ApoC-II mimetics reverse hypertriglyceridemia and ApoE-based peptides such as Ac-hE18A-NH2 reduce cholesterol and triglyceride (TG) levels in humans. Conversely, other classes of ApoE and ApoA-I mimetic peptides and, more recently, ApoJ and LRP1-based peptides, exhibit several anti-atherosclerotic actions in experimental models without influencing lipoprotein profile. These other mimetic peptides display at least one atheroprotective mechanism such as providing LDL stability against mechanical modification or conferring protection against the action of lipolytic enzymes inducing LDL aggregation in the arterial intima. Other anti-atherosclerotic effects exerted by these peptides also include protection against foam cell formation and inflammation, and induction of reverse cholesterol transport. Although the underlying mechanisms of action are still poorly described, the recent findings suggest that these mimetics could confer atheroprotection by favorably influencing lipoprotein function rather than lipoprotein levels. Despite the promising results obtained with peptide mimetics, the assessment of their stability, atheroprotective efficacy and tissue targeted delivery are issues currently under progress.

Proinflammatory Action of a New Electronegative Low-Density Lipoprotein Epitope

The electronegative low-density lipoprotein, LDL (-), is an endogenously modified LDL subfraction with cytotoxic and proinflammatory actions on endothelial cells, monocytes, and macrophages contributing to the progression of atherosclerosis. In this study, epitopes of LDL (-) were mapped using a phage display library of peptides and monoclonal antibodies reactive to this modified lipoprotein. Two different peptide libraries (X6 and CX8C for 6- and 8-amino acid-long peptides, respectively) were used in the mapping. Among all tested peptides, two circular peptides, P1A3 and P2C7, were selected based on their high affinities for the monoclonal antibodies. Small-angle X-ray scattering analysis confirmed their structures as circular rings. P1A3 or P2C7 were quickly internalized by bone marrow-derived murine macrophages as shown by confocal microscopy. P2C7 increased the expression of TNFα, IL-1 β and iNOS as well as the secretion of TNFα, CCL2, and nitric oxide by murine macrophages, similar to the responses induced by LDL (-), although less intense. In contrast, P1A3 did not show pro-inflammatory effects. We identified a mimetic epitope associated with LDL (-), the P2C7 circular peptide, that activates macrophages. Our data suggest that this conformational epitope represents an important danger-associated molecular pattern of LDL (-) that triggers proinflammatory responses.

Combined LDL and VLDL Electronegativity Correlates with Coronary Heart Disease Risk in Asymptomatic Individuals

The most electronegative constituents of human plasma LDL (i.e., L5) and VLDL (i.e., V5) are highly atherogenic. We determined whether the combined electronegativity of L5 and V5 (i.e., L5 + V5) plays a role in coronary heart disease (CHD). In 33 asymptomatic individuals (ages 32–64), 10-year hard CHD risk correlated with age (r = 0.42, p = 0.01). However, in age-adjusted analyses, 10-year hard CHD risk correlated with L5 + V5 plasma concentration (r = 0.43, p = 0.01) but not age (p = 0.74). L5 + V5 plasma concentration was significantly greater in the group with high CHD risk (39.4 ± 22.0 mg/dL; n = 17) than in the group with low CHD risk (16.9 ± 14.8 mg/dL; n = 16; p = 0.01). In cultured human aortic endothelial cells, L5 + V5 treatment induced significantly more senescence-associated–β-Gal activity than did equal concentrations of L1 + V1 (n = 4, p < 0.001). To evaluate the in vivo relevance of these findings, we fed ApoE^−/− and wild-type mice with a high-fat diet and found that plasma LDL, VLDL, and LDL + VLDL from ApoE^−/− mice exhibited significantly greater electrophoretic mobility than did wild-type counterparts (n = 6, p < 0.01). The increased electronegativity of LDL and VLDL in ApoE^−/− mice was accompanied by increased aortic lipid accumulation and cellular senescence (n = 6, p < 0.05). Clinical trials are warranted to test the predictive value of L5 + V5 concentration in patients with CHD.

LDL electronegativity index: a potential novel index for predicting cardiovascular disease

High cardiovascular risk conditions are frequently associated with altered plasma lipoprotein profile, such as elevated low-density lipoprotein (LDL) and LDL cholesterol and decreased high-density lipoprotein. There is, however, accumulating evidence that specific subclasses of LDL may play an important role in cardiovascular disease development, and their relative concentration can be regarded as a more relevant risk factor. LDL particles undergo multiple modifications in plasma that can lead to the increase of their negative charge. The resulting electronegative LDL [LDL(–)] subfraction has been demonstrated to be especially atherogenic, and became a subject of numerous recent studies. In this review, we discuss the physicochemical properties of LDL(–), methods of its detection, atherogenic activity, and relevance of the LDL electronegativity index as a potential independent predictor of cardiovascular risk.

GFP-SCFV: expression and possible applications as a tool for experimental investigations of atherosclerosis

Experimental studies on atherosclerosis are crucial for investigating its pathophysiology, defining new therapeutic targets, and developing new drugs and diagnostic tools. Thus, many imaging markers have been developed and introduced in experimental studies. The main advantage of these new tools is that they allow the noninvasive diagnosis of atherosclerotic vascular disease. Here, we describe the cloning, expression, purification, and stabilization of a chimeric protein specifically designed to probe cells and tissues for the presence of LDL(-), a relevant marker of atherosclerosis. The DNA sequence that encodes the anti-LDL(-) scFv, previously obtained from a hybridoma secreting an anti-LDL(-) monoclonal antibody, was inserted into the bacterial vector pET-28a(+) in tandem with a DNA sequence encoding GFP. The recombinant protein was expressed in high yields in E. coli as inclusion bodies. The applicability of GFP-scFv was assessed by ELISA, which determined its affinity for LDL(-) and confocal microscopy, that showed macrophage uptake of the protein along with LDL(-). In conclusion, our data suggest that the anti-LDL(-) GFP-scFv chimeric protein could be useful in studies on atherogenesis as well as for developing diagnostic tools for atherosclerosis.

Gender disparity in LDL-induced cardiovascular damage and the protective role of estrogens against electronegative LDL

Background

Increased levels of the most electronegative type of LDL, L5, have been observed in the plasma of patients with metabolic syndrome (MetS) and ST-segment elevation myocardial infarction and can induce endothelial dysfunction. Because men have a higher predisposition to developing coronary artery disease than do premenopausal women, we hypothesized that LDL electronegativity is increased in men and promotes endothelial damage.

Methods

L5 levels were compared between middle-aged men and age-matched, premenopausal women with or without MetS. We further studied the effects of gender-influenced LDL electronegativity on aortic cellular senescence and DNA damage in leptin receptor–deficient (db/db) mice by using senescence-associated–β-galactosidase and γH2AX staining, respectively. We also studied the protective effects of 17β-estradiol and genistein against electronegative LDL–induced senescence in cultured bovine aortic endothelial cells (BAECs).

Results

L5 levels were higher in MetS patients than in healthy subjects (P < 0.001), particularly in men (P = 0.001). LDL isolated from male db/db mice was more electronegative than that from male or female wild-type mice. In addition, LDL from male db/db mice contained abundantly more apolipoprotein CIII and induced more BAEC senescence than did female db/db or wild-type LDL. In the aortas of db/db mice but not wild-type mice, we observed cellular senescence and DNA damage, and the effect was more significant in male than in female db/db mice. Pretreatment with 17β-estradiol or genistein inhibited BAEC senescence induced by male or female db/db LDL and downregulated the expression of lectin-like oxidized LDL receptor-1 and tumor necrosis factor-alpha protein.

Conclusion

The gender dichotomy of LDL-induced cardiovascular damage may underlie the increased propensity to coronary artery disease in men.

Is plasma alpha-tocopherol associated with electronegative LDL in obese adolescents?

Obesity has increased in children and adolescents. What is reflected in the early occurrence of cardiometabolic alterations, like hypertension and type 2 diabetes, where the oxLDL formation is stimulated. Various studies have shown that plasma α-tocopherol (α-TP) can protect LDL against oxidation. Nevertheless, the action of plasma α-TP in cardiovascular diseases remains controversial. We conducted a cross-sectional study to evaluate plasma α-TP and its impact on the concentration of LDL(-). Adolescents (n=150) of both sexes were classified into three groups: healthy weight (HW; 50%), overweight (OV; 22%), and obese (OB; 28%). Lipid profile, LDL(-), anti-oxLDL and anti-LDL(-) antibodies, CRP (ELISA) and plasma α-TP (HPLC) were analyzed. Demographic, anthropometric, and food intake data were evaluated. Crude and energy-adjusted intake of vitamin E in the OB group were higher than in the HW group (p<0.001). Crude and energy-adjusted vitamin E intakes were not correlated with plasma α-TP (r=-0.07; p=0.412 and r=-0.064; p=0.467, respectively). Subjects in the OB group had higher TC and LDL-C and lower HDL-C than in the HW and OV groups. C-reactive protein and anti-oxLDL antibodies changed as a function of BMI. The impact of obesity was reinforced by high values for LDL(-) and low content of plasma α-TP in comparison with the HW (p<0.001) and OV groups (p=0.03). This negative profile was maintained for the ratio between α-TP and TC or LDL-C. Plasma α-TP, α-TP/TC and α-TP/LDL-C were negatively associated with LDL(-) and other cardiometabolic risk factors (BMI, WC, AC and anti-oxLDL). Our results demonstrate that obesity in adolescents is associated with high levels of LDL(-) and low plasma α-TP content.

Effects of two lipid lowering therapies on immune responses in hyperlipidemic subjects

AIMS

To compare the effects of two of the most effective lipid-lowering therapies with similar LDL-cholesterol reduction capacity on the innate and adaptive immune responses through the evaluation of autoantibodies anti-oxidized LDL (anti-oxLDL Abs) and electronegative LDL [LDL(-)] levels.

MAIN METHODS

We performed a prospective, randomized, open label study, with parallel arms and blinded endpoints. One hundred and twelve subjects completed the study protocol and received rosuvastatin 40 mg or ezetimibe/simvastatin 10/40 mg for 12 weeks. Lipids, apolipoproteins, LDL(-), and anti-oxLDL Abs (IgG) were assayed at baseline and end of study.

KEY FINDINGS

Main clinical and laboratory characteristics were comparable at baseline. Lipid modifications were similar in both treatment arms, however, a significant raise in anti-oxLDL Abs levels was observed in subjects treated with rosuvastatin (p=0.026 vs. baseline), but not in those receiving simvastatin/ezetimibe. (p=0.233 vs. baseline), thus suggesting modulation of adaptive immunity by a potent statin. Titers of LDL(-) were not modified by the treatments.

SIGNIFICANCE

Considering atherosclerosis as an immune disease, this study adds new information, showing that under similar LDL-cholesterol reduction, the choice of lipid-lowering therapy can differently modulate adaptive immune responses.

Association between markers of cardiovascular risk and clinical parameters of periodontitis

INTRODUCTION: Periodontal disease is an inflammatory response to bacteria that reside in the gum tissue and can have systemic repercussion. OBJECTIVE: The aim of this study was to assess the relationship between periodontitis and markers of cardiovascular risk. MATERIAL AND METHOD: Ninety selected patients were assigned into two groups in accordance with their levels of probing pocket depth (PPD) and Clinical Attachment Level (CAL): control group, n= 45 (< 4 sites with PPD ≥ 4.0 mm and CAL ≥ 3.0 mm) and case group, n= 45 (≥ 30% of sites with PPD ≥ 4.0 mm and CAL ≥3.0 mm). Plasma concentrations of C-reactive protein, high sensitive CRP, high-density lipoproteins (HDL-c) and electronegative low density lipoproteins (LDL) were assessed in all participants. Data from medical history and socioeconomic level were also collected from patients. RESULT: Plasma levels of HDL-c were lower in subjects with periodontal disease (p = 0.016) and were inversely associated with the number of sites with PPD ≥ 3 mm (rho= -0.325) and number of sites with PPD ≥ 3 mm and CAL ≥ 3 mm (rho= -0.216). These associations remained significant after adjustments for dental plaque and smoking using Univariate Analysis of Covariance (p < 0.05). Adjusted odds ratio between periodontal disease and levels of HDL-c was 0.94 (CI95% 0.88-0.99) after adjusting for age, smoking and dental plaque. Other investigated markers of cardiovascular risk were not related to periodontal disease. CONCLUSION: Clinical parameters of periodontitis were inversely associated with plasma concentrations of HDL-c.

Influence of obesity and cardiometabolic makers on lipoprotein-associated phospholipase A2 (Lp-PLA2) activity in adolescents: the healthy young cross-sectional study

BACKGROUND

Lipoprotein-associated phospholipase A2 activity (Lp-PLA2) is a good marker of cardiovascular risk in adults. It is strongly associated with stroke and many others cardiovascular events. Despite this, the impact of obesity on this enzyme activity and its relation to biomarkers of cardiovascular disease in adolescents is not very well investigated. The purpose of this article is to evaluate the influence of obesity and cardiometabolic markers on Lp-PLA2 activity in adolescents.

RESULTS

This cross-sectional study included 242 adolescents (10-19 years) of both gender. These subjects were classified in Healthy Weight (n = 77), Overweight (n = 82) and Obese (n = 83) groups. Lipid profile, glucose, insulin, HDL size, LDL(-) and anti-LDL(-) antibodies were analyzed. The Lp-PLA2 activity was determined by a colorimetric commercial kit. Body mass index (BMI), waist circumference and body composition were monitored. Food intake was evaluated using three 24-hour diet recalls. The Lp-PLA2 activity changed in function to high BMI, waist circumference and fat mass percentage. It was also positively associated with HOMA-IR, glucose, insulin and almost all variables of lipid profile. Furthermore, it was negatively related to Apo AI (β = -0.137; P = 0.038) and strongly positively associated with Apo B (β = 0.293; P < 0.001) and with Apo B/Apo AI ratio (β = 0.343; P < 0.001). The better predictor model for enzyme activity, on multivariate analysis, included Apo B/Apo AI (β = 0.327; P < 0.001), HDL size (β = -0.326; P < 0.001), WC (β = 0.171; P = 0.006) and glucose (β = 0.119; P = 0.038). Logistic regression analysis demonstrated that changes in Apo B/Apo AI ratio were associated with a 73.5 times higher risk to elevated Lp-PLA2 activity.

CONCLUSIONS

Lp-PLA2 changes in function of obesity, and that it shows important associations with markers of cardiovascular risk, in particular with waist circumference, glucose, HDL size and Apo B/Apo AI ratio. These results suggest that Lp-PLA2 activity can be a cardiovascular biomarker in adolescence.

Model IgG monoclonal autoantibody-anti-idiotype pair for dissecting the humoral immune response to oxidized low density lipoprotein

Increasing evidence implicates IgG autoantibodies against oxidized forms of low density lipoprotein (oxLDL) in the pathophysiology of atherosclerotic arterial disease. However, insufficient knowledge of their structure and function is a key gap. Using an elderly LDL receptor-deficient atherosclerotic mouse, we isolated a novel IgG3k against oxLDL (designated MAb LO1). LO1 reacts with copper-oxidized LDL, but minimally with native LDL. Further analysis showed that MAb LO1 also reacts in vitro with malondialdehyde-conjugated LDL (MDA-LDL), a known key epitope in copper-oxidized LDL preparations. By screening a phage library expressing single chain variable region antibodies (scFv), we selected an anti-idiotype scFv (designated H3) that neutralizes MAb LO1 binding to MDA-LDL. Amino acid substitutions between H3 and an irrelevant control scFv C12 showed that residues in the H3 CDRH2, CDRH3, and CDRL2 are all critical for MAb LO1 binding, consistent with a conformational epitope on H3 involving both heavy and light chains. Comparison of amino acids in H3 CDRH2 and CDRL2 with apoB, the major LDL protein, showed homologous sequences, suggesting H3 has structural similarities to the MAb LO1 binding site on MDA-LDL. Immunocytochemical staining showed that MAb LO1 binds epitopes in mouse and human atherosclerotic lesions. The MAb LO1-H3 combination therefore provides a very promising model for analyzing the structure and function of an individual IgG autoantibody in relation to atherosclerosis.

Association between circulating electronegative low-density lipoproteins and serum ferritin in hemodialysis patients: a pilot study

BACKGROUND

Iron supplementation is a common recommendation to chronic kidney disease patients undergoing hemodialysis (HD). However, iron excess is closely associated with lipid peroxidation and, it is well known that electronegative low-density lipoproteins (LDL[-]) are present at higher plasma concentrations in diseases with high cardiovascular risk such as chronic kidney disease. Thus, the aim of this study was to investigate whether ferritin levels are associated with LDL(-) levels in HD patients.

DESIGN

This was a cross-sectional study.

SETTING

This study was conducted from a private clinic in Rio de Janeiro, Brazil.

PATIENTS

The study included 27 HD patients and 15 healthy subjects.

METHODS AND PROCEDURES

Twenty-seven HD patients (14 men, 58.6 ± 10 years, 62.2 ± 51.4 months on dialysis, and body mass index: 24.4 ± 4.2 kg/m(2)) were studied and compared with 15 healthy individuals (6 men, 53.8 ± 15.4 years, body mass index: 24.5 ± 4.3 kg/m(2)). Serum LDL(-) levels were measured using the enzyme-linked immunosorbent assay method; ferritin levels by commercially available kits, and tumor necrosis factor-α, interleukin-6, monocyte chemoattractant protein-1, and plasminogen activator inhibitor-1 were determined with a multiplex assay kit manufactured by R&D Systems.

RESULTS

The HD patients presented higher LDL(-) and tumor necrosis factor-α levels (0.15 ± 0.13 U/L and 5.9 ± 2.3 pg/mL, respectively) than healthy subjects (0.07 ± 0.05 U/L and 2.3 ± 1.3 pg/mL, respectively) (P = .0001). The mean ferritin level in HD patients was 1,117.5 ± 610.4 ng/mL, and 90% of patients showed ferritin levels exceeding 500 ng/mL. We found a positive correlation between LDL(-) and ferritin in the patients (r = 0.48; P = .01), and ferritin was a significant contributor to LDL(-) concentrations independent of inflammation.

CONCLUSIONS

Excess body iron stores for HD patients was associated with signs of increased oxidative stress, as reflected by increased LDL(-) levels in HD patients.

Timing and Dose of Statin Therapy Define Its Impact on Inflammatory and Endothelial Responses During Myocardial Infarction

Objective—

Clinical trials of statins during myocardial infarction (MI) have differed in their therapeutic regimes and generated conflicting results. This study evaluated the role of the timing and potency of statin therapy on its potential mechanisms of benefit during MI.

Methods and Results—

ST-elevation MI patients (n=125) were allocated into 5 groups: no statin; 20, 40, or 80 mg/day simvastatin starting at admission; or 80 mg/day simvastatin 48 hours after admission. After 7 days, all patients switched their treatment to 20 mg/day simvastatin for an additional 3 weeks and then underwent flow-mediated dilation in the brachial artery. As of the second day, C-reactive protein (CRP) differed between non–statin users (12.0±4.1 mg/L) and patients treated with 20 (8.5±4.0 mg/L), 40 (3.8±2.5 mg/L), and 80 mg/day (1.4±1.5 mg/L), and the daily differences remained significant until the seventh day ( P <0.0001). The higher the statin dose, the lower the elevation of interleukin-2 and tumor necrosis factor-α, the greater the reduction of 8-isoprostane and low-density lipoprotein(−), and the greater the increase in nitrate/nitrite levels during the first 5 days ( P <0.001). Later initiation of statin was less effective than its early introduction in relation to attenuation of CRP, interleukin-2, tumor necrosis factor-α, 8-isoprostane, and low-density lipoprotein(−), as well as in increase in nitrate/nitrite levels ( P <0.0001). At the 30th day, there was no longer a difference in lipid profile or CRP between groups; the flow-mediated dilation, however, was proportional to the initial statin dose and was higher for those who started the treatment early ( P =0.001).

Conclusion—

This study demonstrates that the timing and potency of statin treatment during MI are key elements for their main mechanisms of benefit.

Clinical Trial Registration—

URL: http://www.clinicaltrials.gov . Unique identifier: NCT00906451.

Electronegative low-density lipoprotein is associated with dense low-density lipoprotein in subjects with different levels of cardiovascular risk

Dyslipidemias and physicochemical changes in low-density lipoprotein (LDL) are very important factors for the development of coronary artery disease (CAD). However, pathophysiological properties of electronegative low-density lipoprotein [LDL(-)] remain a controversial issue. Our objective was to investigate LDL(-) content in LDL and its subfractions (phenotypes A and B) of subjects with different cardiovascular risk. Seventy-three subjects were randomized into three groups: normolipidemic (N; n = 30) and hypercholesterolemic (HC; n = 33) subjects and patients with CAD (n = 10). After fasting, blood samples were collected and total, dense and light LDL were isolated. LDL(-) content in total LDL and its subfractions was determined by ELISA. LDL(-) content in total LDL was lower in the N group as compared to the HC (P < 0.001) and CAD (P = 0.006) groups. In the total sample and in those of the N, HC, and CAD groups, LDL(-) content in dense LDL was higher than in light LDL (P = 0.001, 0.001, 0.001, and 0.033, respectively) The impact of LDL(-) on cardiovascular risk was reinforced when LDL(-) content in LDL showed itself to have a positive association with total cholesterol (beta = 0.003; P < 0.001), LDL-C (beta = 0.003; p < 0.001), and non-HDL-C (beta = 0.003; P < 0.001) and a negative association with HDL-C (beta = -0.32; P = 0.04). Therefore, LDL(-) is an important biomarker that showed association with the lipid profile and the level of cardiovascular risk.

Electronegative LDL induction of apoptosis in macrophages: involvement of Nrf2

The aim of this study was to determine the apoptotic pathways and mechanisms involved in electronegative LDL [LDL(-)]-induced apoptosis in RAW 264.7 macrophages and the role of Nrf2 in this process. Incubation of RAW 264.7 macrophages with LDL(-) for 24 h resulted in dose-dependent cell death. Activated caspases were shown to be involved in the apoptosis induced by LDL(-); incubation with the broad caspase inhibitor z-VAD prevented apoptosis in LDL(-)-treated cells. CD95 (Fas), CD95 ligand (FasL), CD36 and the tumor necrosis factor (TNF) ligand Tnfsf10 were overexpressed in LDL(-)-treated cells. However, Bax, Bcl-2 and Mcl-1 protein levels remained unchanged after LDL(-) treatment. LDL(-) promoted hyperpolarization of the mitochondrial membrane, elevated reactive oxygen species (ROS) production and translocation of Nrf2 to the nucleus, a process absent in cells treated with native LDL. Elicited peritoneal macrophages from Nrf2-deficient mice exhibited an elevated apoptotic response after challenge with LDL(-), together with an increase in the production of ROS in the absence of alterations in CD36 expression. These results provide evidence that CD36 expression induced by LDL(-) is Nrf2-dependent. Also, it was demonstrated that Nrf2 acts as a compensatory mechanism of LDL(-)-induced apoptosis in macrophages.

2D-NMR reveals different populations of exposed lysine residues in the apoB-100 protein of electronegative and electropositive fractions of LDL particles

Several potentially atherogenic LDL subfractions present low affinity for the LDL receptor, which result in impaired plasma clearance. Electronegative LDL [LDL(-)] is one of these minor subfractions and the molecular basis for its reduced receptor affinity is not well understood. In the present study, high-resolution 2D-NMR spectroscopy has been employed to characterize the surface-exposed lysine residues of the apolipoprotein (apo)B-100 protein in both LDL(-) and LDL(+) subfractions. LDL(+) showed two populations of lysine residues, similar to those previously described in total LDL. "Normal" Lys have a pk(a) of 10.4 whereas "active" Lys have a pk(a) of 8.8 and have been suggested to be involved in receptor binding. In contrast to LDL(+), the LDL(-) subfraction presented a third type of Lys, named as "intermediate" Lys, with a different microenvironment and higher basicity (pk(a) 10.7). These intermediate Lys cannot be reliably identified by 1D-NMR. Because the abundance of normal Lys is similar in LDL(+) and LDL(-), the intermediate Lys in the apoB-100 molecule of LDL(-) should come from a group of active Lys in LDL(+) particles that have a less basic microenvironment in the LDL(-) particle. These differences between LDL(+) and LDL(-) are indicative of a distinct conformation of apoB-100 that could be related to loss of affinity of LDL(-) for the LDL receptor.

Validation of a novel ELISA for measurement of electronegative low-density lipoprotein

BACKGROUND

Oxidative modification of low-density lipoprotein (LDL) plays a key role in the pathogenesis of atherosclerosis. LDL(-) is present in blood plasma of healthy subjects and at higher concentrations in diseases with high cardiovascular risk, such as familial hypercholesterolemia or diabetes.

METHODS

We developed and validated a sandwich ELISA for LDL(-) in human plasma using two monoclonal antibodies against LDL(-) that do not bind to native LDL, extensively copper-oxidized LDL or malondialdehyde-modified LDL. The characteristics of assay performance, such as limits of detection and quantification, accuracy, inter- and intra-assay precision were evaluated. The linearity, interferences and stability tests were also performed.

RESULTS

The calibration range of the assay is 0.625-20.0 mU/L at 1:2000 sample dilution. ELISA validation showed intra- and inter-assay precision and recovery within the required limits for immunoassays. The limits of detection and quantification were 0.423 mU/L and 0.517 mU/L LDL(-), respectively. The intra- and inter-assay coefficient of variation ranged from 9.5% to 11.5% and from 11.3% to 18.9%, respectively. Recovery of LDL(-) ranged from 92.8% to 105.1%.

CONCLUSIONS

This ELISA represents a very practical tool for measuring LDL(-) in human blood for widespread research and clinical sample use.

Alpha-tocopherol supplementation decreases electronegative low-density lipoprotein concentration [LDL(-)] in haemodialysis patients

BACKGROUND

Oxidative stress is a significant contributor to cardiovascular diseases (CVD) in haemodialysis (HD) patients, predisposing to the generation of oxidized low-density lipoprotein (oxLDL) or electronegatively charged LDL subfraction. Antioxidant therapy such as alpha-tocopherol acts as a scavenger of lipid peroxyl radicals attenuating the oxidative stress, which decreases the formation of oxLDL. The present study was designed to investigate the influence of the alpha-tocopherol supplementation on the concentration of electronegative low-density lipoprotein [LDL(-)], a minimally oxidized LDL, which we have previously described to be high in HD patients.

METHODS

Blood samples were collected before and after 120 days of supplementation by alpha-tocopherol (400 UI/day) in 19 stable HD patients (50 +/- 7.8 years; 9 males). The concentrations of LDL(-) in blood plasma [using an anti-LDL- human monoclonal antibody (mAb)] and the anti-LDL(-) IgG auto-antibodies were determined by ELISA. Calculation of body mass index (BMI) and measurements of waist circumference (WC), triceps skin folds (TSF) and arm muscle area (AMA) were performed.

RESULTS

The plasma alpha-tocopherol levels increased from 7.9 microM (0.32-18.4) to 14.2 microM (1.22-23.8) after the supplementation (P = 0.02). The mean concentration of LDL(-) was reduced from 570.9 microg/mL (225.6-1241.0) to 169.1 microg/mL (63.6-621.1) (P < 0.001). The anti-LDL(-) IgG auto-antibodies did not change significantly after the supplementation. The alpha-tocopherol supplementation also reduced the total cholesterol and LDL-C levels in these patients, from 176 +/- 42.3 mg/dL to 120 +/- 35.7 mg/dL (P < 0.05) and 115.5 +/- 21.4 mg/dL to 98.5 +/- 23.01 mg/dL (P < 0.001), respectively.

CONCLUSION

The oral administration of alpha-tocopherol in HD patients resulted in a significant decrease in the LDL(-), total cholesterol and LDL-C levels. This effect may favour a reduction in cardiovascular risk in these patients, but a larger study is required to confirm an effect in this clinical setting.

Biomarcadores de peroxidação lipídica na aterosclerose

A aterosclerose é caracterizada por uma resposta inflamatória crônica da parede arterial, iniciada por uma lesão do endotélio, cuja etiologia está relacionada à modificação oxidativa da lipoproteína de baixa densidade. O objetivo deste trabalho é apresentar os principais metabólitos envolvidos nos processos bioquímicos de peroxidação lipídica, discutindo as vantagens e desvantagens dos métodos empregados para a mensuração dos biomarcadores de peroxidação lipídica relacionados com a aterosclerose. A avaliação da oxidação das lipoproteínas pode ser realizada pela determinação dos produtos gerados durante a peroxidação lipídica, como os isoprostanos, hidroperóxidos lipídicos, aldeídos, fosfolípides oxidados e os produtos da oxidação do colesterol. A suscetibilidade das partículas de lipoproteína de baixa densidade à oxidação pode ser avaliada in vitro, após a indução da peroxidação lipídica por azoiniciadores radicalares lipossolúveis, hidrossolúveis, ou mais comumente, pelos íons cobre. Por outro lado, as modificações da lipoproteína de baixa densidade, pela ação das lipoxigenases e peroxidases, ou oxidação não-enzimática, resultam no aumento da carga negativa destas partículas e podem contribuir para a geração in vivo de uma subfração de lipoproteína de baixa densidade minimamente oxidada, denominada lipoproteína de baixa densidade eletronegativa (lipoproteína de baixa densidade). A determinação das concentrações desta partícula pode ser realizada em plasma por cromatografia líquida ou por imunoensaios..Diversos métodos podem ser utilizados para a avaliação dos biomarcadores de peroxidação lipídica in vivo e in vitro, porém, a definição do marcador mais adequado, depende de uma avaliação criteriosa das vantagens, desvantagens e particularidades de cada análise, levando-se em consideração os objetivos do estudo que será conduzido.

Lipid peroxidation and decomposition--conflicting roles in plaque vulnerability and stability

The low density lipoprotein (LDL) oxidation hypothesis has generated considerable interest in oxidative stress and how it might affect atherosclerosis. However, the failure of antioxidants, particularly vitamin E, to affect the progression of the disease in humans has convinced even staunch supporters of the hypothesis to take a step backwards and reconsider alternatives. Preponderant evidence for the hypothesis came from animal antioxidant intervention studies. In this review we point out basic differences between animal and human atherosclerosis development and suggest that human disease starts where animal studies end. While initial oxidative steps in the generation of early fatty streak lesions might be common, the differences might be in the steps involved in the decomposition of peroxidized lipids into aldehydes and their further oxidation into carboxylic acids. We suggest that these steps may not be amenable to attenuation by antioxidants and antioxidants might actually counter the stabilization of plaque by preventing the formation of carboxylic acids which are anti-inflammatory in nature. The formation of such dicarboxylic acids may also be conducive to plaque stabilization by trapping calcium. We suggest that agents that would prevent the decomposition of lipid peroxides and promote the formation and removal of lipid hydroxides, such as paraoxonase (PON 1) or apo A1/high density lipoprotein (HDL) might be more conducive to plaque regression.

Electronegative LDL impairs vascular endothelial cell integrity in diabetes by disrupting fibroblast growth factor 2 (FGF2) autoregulation

OBJECTIVE

L5, a circulating electronegative LDL identified in patients with hypercholesterolemia or type 2 diabetes, induces endothelial cell (EC) apoptosis by suppressing fibroblast growth factor (FGF)2 expression. FGF2 plays a pivotal role in endothelial regeneration and compensatory arteriogenesis. It is likely that vasculopathy and poor collateralization in diabetes is a result of FGF2 dysregulation.

RESEARCH DESIGN AND METHODS

To investigate this mechanism, we isolated L5 from type 2 diabetic patients. In cultured bovine aortic ECs (BAECs), L5 inhibited FGF2 transcription and induced apoptosis. Because FGF2 stimulates the phosphatidylinositol 3-kinase (PI3K)-Akt pathway, we examined whether FGF2 transcription is regulated by Akt through a feedback mechanism.

RESULTS

Diabetic L5 reduced FGF2 release to the medium but enhanced caspase-3 activity, with resultant apoptosis. Inhibition of PI3K with wortmannin or suppression of Akt activation with dominant-negative Akt inhibited FGF2 expression. Transfection of BAECs with FGF2 antisense cDNA depleted endogenous FGF2 protein. In these cells, not only was Akt phosphorylation inhibited, but FGF2 transcription was also critically impaired. In contrast, transfecting BAECs with FGF2 sense cDNA augmented Akt phosphorylation. Treatment with constitutively active Akt enhanced FGF2 expression. Augmentation of either FGF2 transcription or Akt phosphorylation rendered BAECs resistant to L5.

CONCLUSIONS

These findings suggest that FGF2 is the primary initiator of its own expression, which is autoregulated through a novel FGF2-PI3K-Akt loop. Thus, by disrupting FGF2 autoregulation in vascular ECs, L5 may impair reendothelialization and collateralization in diabetes.

Soy isoflavones reduce electronegative low-density lipoprotein (LDL(-)) and anti-LDL (-) autoantibodies in experimental atherosclerosis

BACKGROUND

Isoflavones present in soybean may contribute to soy atheroprotective effects.

AIM OF THE STUDY

To investigate the effect of soy isoflavones supplementation on the formation of electronegative LDL (LDL(-)) and its autoantibodies in blood plasma and aortic atheromas of rabbits fed an atherogenic casein-based diet enriched with isoflavones.

METHODS

New Zealand male rabbits (n = 15) were fed an atherogenic diet (27% casein) supplemented with isoflavones (0.73 or 7.3 mg of isoflavones/kg/day, Low and High Iso groups, respectively) for 180 days. Monthly, blood samples were collected after 12-15 h fasting and at 180 days of treatment all animals were sacrificed. Isoflavones were analyzed in plasma and urine samples by HPLC. LDL(-) in plasma and atheromas was detected by ELISA and immunohistochemistry, respectively, with a monoclonal antibody reactive to LDL(-). Autoantibodies reactive to LDL(-) were analyzed in plasma and aorta by ELISA.

RESULTS

Low and High Iso groups had decreased LDL-cholesterol, increased HDL-cholesterol and lower levels of LDL(-) in blood plasma and aortic atherosclerotic lesions than the non-supplemented Control group. IgG autoantibodies reactive to LDL(- )were higher in plasma of the Control group in comparison with the High and Low Iso groups. In contrast, the aortas from animals that consumed isoflavones showed higher levels of IgG reactive to LDL(- )than the Control group.

CONCLUSION

Soy isoflavones showed hypolipidemic effects and decreased the pro-inflammatory LDL(-) subfraction in blood plasma and aorta of hypercholesterolemic rabbits.