Weight loss benefits on HDL cholesterol persist even after weight regaining

BACKGROUND

Obesity-related comorbidities may relapse in patients with weight regain after bariatric surgery. However, HDL cholesterol (HDLc) levels increase after surgery and seem to remain stable despite a gradual increase in BMI. The aim of this study is to analyze the effects of weight regain after bariatric surgery on HDL cholesterol.

MATERIALS AND METHODS

This is a retrospective, observational, cohort study in patients who underwent bariatric surgery in the Hospital de la Santa Creu i Sant Pau (Barcelona) between 2007 and 2015. Patients without at least 5 years of follow-up after surgery, under fibrate treatment, and those who required revisional surgery were excluded from the analysis. Data were collected at baseline, 3 and 6 months after surgery, and then annually until 5 years post-surgery.

RESULTS

One hundred fifty patients were analyzed. 93.3% of patients reached > 20% of total weight loss after surgery. At 5th year, 37% of patients had regained > 15% of nadir weight, 60% had regained > 10%, and 22% had regained < 5% of nadir weight. No differences were found in HDLc levels between the different groups of weight regain, nor in the % of change in HDLc levels between nadir weight and 5 years, or in the proportion of patients with normal HDLc concentrations either.

CONCLUSION

HDLc remains stable regardless of weight regain after bariatric surgery.

Special Issue: New Insight into the Molecular Role of Lipids and Lipoproteins in Vascular Diseases

Lipids and lipoproteins play a key role in cardiovascular diseases (CVD), mainly in the development of atherosclerosis [...].

Circulating lipoprotein-carried miRNome analysis reveals novel VLDL-enriched microRNAs that strongly correlate with the HDL-microRNA profile

Lipoproteins have been described as microRNAs (miRNAs) carriers. Unfortunately, the bibliography on this topic is scarce and shows a high variability between independent investigations. In addition, the miRNA profiles of the LDL and VLDL fractions have not been completely elucidated. Here, we profiled the human circulating lipoprotein-carried miRNome. Lipoprotein fractions (VLDL, LDL and HDL) were isolated from the serum of healthy subjects by ultracentrifugation and purified by size-exclusion chromatography. A panel of 179 miRNAs commonly expressed in circulation was evaluated in the lipoprotein fractions using quantitative real-time PCR (qPCR) assays. A total of 14, 4 and 24 miRNAs were stably detected in the VLDL, LDL and HDL fractions, respectively. VLDL- and HDL-miRNA signatures were highly correlated (rho 0.814), and miR-16-5p, miR-142-3p, miR-223-3p and miR-451a were among the top 5 expressed miRNAs in both fractions. miR-125a-5p, miR-335-3p and miR-1260a, were detected in all lipoprotein fractions. miR-107 and miR-221-3p were uniquely detected in the VLDL fraction. HDL showed the larger number of specifically detected miRNAs (n = 13). Enrichment in specific miRNA families and genomic clusters was observed for HDL-miRNAs. Two sequence motifs were also detected for this group of miRNAs. Functional enrichment analysis including the miRNA signatures from each lipoprotein fraction suggested a potential role in mechanistic pathways previously associated with cardiovascular disease: fibrosis, senescence, inflammation, immune response, angiogenesis, and cardiomyopathy. Collectively, our results not only support the role of lipoproteins as circulating miRNA carriers but also describe for the first time the role of VLDL as a miRNA transporter.

Can Electronegative LDL Act as a Multienzymatic Complex?

Electronegative LDL (LDL(-)) is a minor form of LDL present in blood for which proportions are increased in pathologies with increased cardiovascular risk. In vitro studies have shown that LDL(-) presents pro-atherogenic properties, including a high susceptibility to aggregation, the ability to induce inflammation and apoptosis, and increased binding to arterial proteoglycans; however, it also shows some anti-atherogenic properties, which suggest a role in controlling the atherosclerotic process. One of the distinctive features of LDL(-) is that it has enzymatic activities with the ability to degrade different lipids. For example, LDL(-) transports platelet-activating factor acetylhydrolase (PAF-AH), which degrades oxidized phospholipids. In addition, two other enzymatic activities are exhibited by LDL(-). The first is type C phospholipase activity, which degrades both lysophosphatidylcholine (LysoPLC-like activity) and sphingomyelin (SMase-like activity). The second is ceramidase activity (CDase-like). Based on the complementarity of the products and substrates of these different activities, this review speculates on the possibility that LDL(-) may act as a sort of multienzymatic complex in which these enzymatic activities exert a concerted action. We hypothesize that LysoPLC/SMase and CDase activities could be generated by conformational changes in apoB-100 and that both activities occur in proximity to PAF-AH, making it feasible to discern a coordinated action among them.

Divergent Effects of Glycemic Control and Bariatric Surgery on Circulating Concentrations of TMAO in Newly Diagnosed T2D Patients and Morbidly Obese

High circulating concentrations of the gut microbiota-derived metabolite trimethylamine N-oxide (TMAO) are significantly associated with the risk of obesity and type 2 diabetes (T2D). We aimed at evaluating the impact of glycemic control and bariatric surgery on circulating concentrations of TMAO and its microbiota-dependent intermediate, γ-butyrobetaine (γBB), in newly diagnosed T2D patients and morbidly obese subjects following a within-subject design. Based on HbA1c concentrations, T2D patients achieved glycemic control. However, the plasma TMAO and γBB concentrations were significantly increased, without changes in estimated glomerular filtration rate. Bariatric surgery was very effective in reducing weight in obese subjects. Nevertheless, the surgery reduced plasma γBB concentrations without affecting TMAO concentrations and the estimated glomerular filtration rate. Considering these results, an additional experiment was carried out in male C57BL/6J mice fed a Western-type diet for twelve weeks. Neither diet-induced obesity nor insulin resistance were associated with circulating TMAO and γBB concentrations in these genetically defined mice strains. Our findings do not support that glycemic control or bariatric surgery improve the circulating concentrations of TMAO in newly diagnosed T2D and morbidly obese patients.

Mini-extracorporeal circulation surgery produces less inflammation than off-pump coronary surgery

OBJECTIVES

Both off-pump coronary artery bypass grafting surgery (OPCABG) and mini-extracorporeal circulation (MECC) have been associated with lower morbidity and mortality and less inflammation than conventional cardiopulmonary bypass. However, studies comparing the 2 techniques are scarce and the results are controversial. We compared the clinical outcomes and inflammatory response of low-risk patients undergoing coronary bypass grafting with MECC versus OPCABG.

METHODS

We conducted a prospective, randomized study in patients undergoing coronary heart surgery. Two hundred and thirty consecutive low-risk patients were randomly assigned to either receive OPCABG (n = 117) or MECC (n = 113). Clinical outcomes and postoperative biochemical results were analysed in both groups. We also analysed 19 circulating inflammatory markers in a subgroup of 40 patients at 4 perioperative time points. The area under the curve for each marker was calculated to monitor differences in the inflammatory response.

RESULTS

No significant differences were found between groups regarding perioperative clinical complications and no deaths occurred during the trial. Plasma levels in 9 of the 19 inflammatory markers were undetectable or showed no temporal variation, 3 were higher in the MECC group [interleukin (IL)-10, macrophage inflammatory protein-1β and epidermal growth factor] and 7 were higher in the OPCABG group (growth regulator oncogene, IL-6, IL-8, soluble CD40 ligand, monocyte chemoattractant protein-1, monocyte chemoattractant protein-3 and tumour necrosis factor-α). Differences in 2 proinflammatory cytokines, IL-6 and monocyte chemoattractant protein 1, between the 2 surgical procedures were statistically significant.

CONCLUSIONS

No clinical differences were observed between in low-risk patients undergoing MECC or OPCABG surgery, but OPCABG was associated with an increased release of proinflammatory cytokines compared with MECC. Studies in larger cohorts and in patients at higher risk are needed to confirm these findings.

CLINICAL TRIAL REGISTRATION NUMBER

NCT02118025.

Autoimmune Rheumatic Diseases: An Update on the Role of Atherogenic Electronegative LDL and Potential Therapeutic Strategies

Atherosclerosis has been linked with an increased risk of atherosclerotic cardiovascular disease (ASCVD). Autoimmune rheumatic diseases (AIRDs) are associated with accelerated atherosclerosis and ASCVD. However, the mechanisms underlying the high ASCVD burden in patients with AIRDs cannot be explained only by conventional risk factors despite disease-specific factors and chronic inflammation. Nevertheless, the normal levels of plasma low-density lipoprotein (LDL) cholesterol observed in most patients with AIRDs do not exclude the possibility of increased LDL atherogenicity. By using anion-exchange chromatography, human LDL can be divided into five increasingly electronegative subfractions, L1 to L5, or into electropositive and electronegative counterparts, LDL (+) and LDL (-). Electronegative L5 and LDL (-) have similar chemical compositions and can induce adverse inflammatory reactions in vascular cells. Notably, the percentage of L5 or LDL (-) in total LDL is increased in normolipidemic patients with AIRDs. Electronegative L5 and LDL (-) are not recognized by the normal LDL receptor but instead signal through the lectin-like oxidized LDL receptor 1 (LOX-1) to activate inflammasomes involving interleukin 1β (IL-1β). Here, we describe the detailed mechanisms of AIRD-related ASCVD mediated by L5 or LDL (-) and discuss the potential targeting of LOX-1 or IL-1β signaling as new therapeutic modalities for these diseases.

Carotid atherosclerosis in virologically suppressed HIV patients: comparison with a healthy sample and prediction by cardiovascular risk equations

OBJECTIVES

To compare the prevalence of carotid atherosclerosis in virologically suppressed HIV patients with that of a community sample, and to evaluate the capacity of various cardiovascular risk (CVR) equations for predicting carotid atherosclerosis.

METHODS

This was a cross-sectional study with two randomly selected groups: HIV patients from an HIV unit and a control group drawn from the community. Participants were matched by age (30-80 years) and sex without history of cardiovascular disease. Carotid plaque, common carotid intima-media thickness (cc-IMT) and subclinical atherosclerosis (carotid plaque and/or cc-IMT > 75^th percentile) were assessed by carotid ultrasound. The Systematic Coronary Risk Evaluation (SCORE), Framingham, REGICOR, reduced Data Collection on Adverse Effects of Anti-HIV Drugs (D:A:D), and COMVIH equations were applied, and their abilities to predict carotid plaque were compared using the area under the curve (AUC).

RESULTS

Each group included 379 subjects (77.8% men, age 49.7 years). Duration of antiretroviral therapy was 15.5 years. There were no differences between the groups for carotid plaque (HIV, 33.2%; control, 31.3%), mean cc-IMT (HIV, 0.63 mm; control, 0.61 mm) or subclinical atherosclerosis (HIV, 42.9%; control, 47.9%). Thymidine analogues were independently associated with subclinical atherosclerosis in HIV-infected patients. CVR equations revealed AUCs between 0.715 and 0.807 for prediction of carotid plaque; prediction was better in the control group and did not improve when HIV-adapted scales were used.

CONCLUSIONS

The features of carotid atherosclerosis did not differ between the HIV-infected and the control group, although CVR equations were more predictive for carotid plaque in controls than in HIV-infected patients. HIV-specific equations did not improve prediction.

Electronegative LDL: An Active Player in Atherogenesis or a By- Product of Atherosclerosis?

Low-density lipoproteins (LDLs) are the major plasma carriers of cholesterol. However, LDL particles must undergo various molecular modifications to promote the development of atherosclerotic lesions. Modified LDL can be generated by different mechanisms, but as a common trait, show an increased electronegative charge of the LDL particle. A subfraction of LDL with increased electronegative charge (LDL(-)), which can be isolated from blood, exhibits several pro-atherogenic characteristics. LDL(-) is heterogeneous, due to its multiple origins but is strongly related to the development of atherosclerosis. Nevertheless, the implication of LDL(-) in a broad array of pathologic conditions is complex and in some cases anti-atherogenic LDL(-) properties have been reported. In fact, several molecular modifications generating LDL(-) have been widely studied, but it remains unknown as to whether these different mechanisms are specific or common to different pathological disorders. In this review, we attempt to address these issues examining the most recent findings on the biology of LDL(-) and discussing the relationship between this LDL subfraction and the development of different diseases with increased cardiovascular risk. Finally, the review highlights the importance of minor apolipoproteins associated with LDL(-) which would play a crucial role in the different properties displayed by these modified LDL particles.

Administration of CORM-2 inhibits diabetic neuropathy but does not reduce dyslipidemia in diabetic mice

The antinociceptive effects of the carbon monoxide-releasing molecule tricarbonyldichlororuthenium (II) dimer (CORM-2) during chronic pain are well documented, but most of its possible side-effects remain poorly understood. In this work, we examine the impact of CORM-2 treatment on the lipoprotein profile and two main atheroprotective functions attributed to high-density lipoprotein (HDL) in a mouse model of type 1 diabetes while analyzing the effect of this drug on diabetic neuropathy. Streptozotocin (Stz)-induced diabetic mice treated with CORM-2 (Stz-CORM-2) or vehicle (Stz-vehicle) were used to evaluate the effect of this drug on the modulation of painful diabetic neuropathy using nociceptive behavioral tests. Plasma and tissue samples were used for chemical and functional analyses, as appropriate. Two main antiatherogenic properties of HDL, i.e., the ability of HDL to protect low-density lipoprotein (LDL) from oxidation and to promote reverse cholesterol transport from macrophages to the liver and feces in vivo (m-RCT), were also assessed. Stz-induced diabetic mice displayed hyperglycemia, dyslipidemia and pain hypersensitivity. The administration of 10 mg/kg CORM-2 during five consecutive days inhibited allodynia and hyperalgesia and significantly ameliorated spinal cord markers (Cybb and Bdkrb1expression) of neuropathic pain in Stz mice, but it did not reduce the combined dyslipidemia shown in Stz-treated mice. Its administration to Stz-treated mice led to a significant increase in the plasma levels of cholesterol (∼ 1.4-fold vs. Ctrl, ∼ 1.3- fold vs. Stz-vehicle; p < 0.05) and was attributed to significant elevations in both non-HDL (∼ 1.8-fold vs. Ctrl; ∼ 1.6-fold vs. Stz-vehicle; p < 0.05) and HDL cholesterol (∼ 1.3-fold vs. Ctrl, ∼ 1.2-fold vs. Stz-vehicle; p < 0.05). The increased HDL in plasma was not accompanied by a commensurate elevation in m-RCT in Stz-CORM-2 compared to Stz-vehicle mice; instead, it was worsened as revealed by decreased [³H]-tracer trafficking into the feces in vivo. Furthermore, the HDL-mediated protection against LDL oxidation ex vivo shown by the HDL isolated from Stz-CORM-2 mice did not differ from that obtained in Stz-vehicle mice. In conclusion, the antinociceptive effects produced by a high dose of CORM-2 were accompanied by antioxidative effects but were without favorable effects on the dyslipidemia manifested in diabetic mice.

Increased concentration of clusterin/apolipoprotein J (apoJ) in hyperlipemic serum is paradoxically associated with decreased apoJ content in lipoproteins

OBJECTIVE

Clusterin/apolipoprotein J (apoJ) circulates in blood in part associated to lipoproteins or in unbound form. When bound to HDL, apoJ is antiatherogenic by inhibiting endothelial cell apoptosis; thus, any factor modifying apoJ association to HDL would decrease its antiatherogenic function. However, the exact distribution of apoJ in each lipoprotein fraction, or in lipoprotein-non bound form has not been specifically investigated either in normolipemia or in dyslipemia.

METHODS

Basic lipid profile and apoJ concentration were determined in sera from 70 subjects, including a wide range of cholesterol and triglyceride concentrations. Lipoproteins were isolated by ultracentrifugation and their lipid and apolipoprotein composition was assessed.

RESULTS

In the overall population, serum apoJ positively associated with cholesterol, triglyceride and VLDL-C concentrations, and HDL-C and triglyceride were independent predictors of increased apoJ concentration. Approximately, 20.5% of circulating apoJ was associated with lipoproteins (18.5% HDL, 0.9% LDL and 1.1% VLDL) and 79.5% was not bound to lipoproteins. Serum apoJ concentration was higher in hypercholesterolemic (HC), hypertriglyceridemic (HTG) and combined hyperlipidemic (CHL) sera compared to normolipemic (NL) sera (HC, 98.15 ± 33.6 mg/L; HTG, 103.3 ± 36.8 mg/L; CHL, 131.7 ± 26.8 mg/L; NL, 66.7 ± 33.8 mg/L; P < 0.001). ApoJ distribution was also altered in hyperlipidemia; approximately 30% of circulating apoJ was associated to lipoproteins in the NL group whereas this proportion rounded 15% in hyperlipidemic subjects.

CONCLUSIONS

Our findings indicate that hyperlipidemia increases the concentration of apoJ in serum but, in turn, the content of lipoprotein-associated apoJ decreases. The redistribution of apoJ in hyperlipidemia could compromise the antiatherogenic properties of HDL.

Atherogenic properties of lipoproteins in HIV patients starting atazanavir/ritonavir or darunavir/ritonavir: a substudy of the ATADAR randomized study

OBJECTIVES

To assess LDL subfraction phenotype and lipoprotein-associated phospholipase A2 (Lp-PLA2) in naive HIV-infected patients starting atazanavir/ritonavir or darunavir/ritonavir plus tenofovir/emtricitabine.

METHODS

This was a substudy of a multicentre randomized study. Standard lipid parameters, LDL subfraction phenotype (by gradient gel electrophoresis) and Lp-PLA2 activity (by 2-thio-PAF) were measured at baseline and weeks 24 and 48. Multivariate regression analysis was performed. Results are expressed as the median (IQR).

RESULTS

Eighty-six (atazanavir/ritonavir, n=45; darunavir/ritonavir, n=41) patients were included: age 36 (31-41) years; 89% men; CD4 319 (183-425) cells/mm(3); and Framingham score 1% (0%-2%). No differences in demographics or lipid measurements were found at baseline. At week 48, a mild but significant increase in total cholesterol and HDL-cholesterol was observed in both arms, whereas LDL cholesterol increased only in the darunavir/ritonavir arm and triglycerides only in the atazanavir/ritonavir arm. The apolipoprotein A-I/apolipoprotein B ratio increased only in the atazanavir/ritonavir arm. At week 48, the LDL subfraction phenotype improved in the darunavir/ritonavir arm (increase in LDL particle size and in large LDL particles), whereas it worsened in the atazanavir/ritonavir arm (increase in small and dense LDL particles, shift to a greater prevalence of phenotype B); the worsening was related to the greater increase in triglycerides in the atazanavir/ritonavir arm. No changes in total Lp-PLA2 activity or relative distribution in LDL or HDL particles were found at week 48 in either arm.

CONCLUSIONS

In contrast with what occurred in the atazanavir/ritonavir arm, the LDL subfraction phenotype improved with darunavir/ritonavir at week 48. This difference was associated with a lower impact on plasma triglycerides with darunavir/ritonavir.

Bariatric surgery in morbidly obese patients improves the atherogenic qualitative properties of the plasma lipoproteins

OBJECTIVE

The purpose of this study was to evaluate the effect of weight loss induced in morbidly obese subjects by Roux-en-Y gastric bypass bariatric surgery on the atherogenic features of their plasma lipoproteins.

METHODS

Twenty-one morbidly obese subjects undergoing bariatric surgery were followed up for up to 1 year after surgery. Plasma and lipoproteins were assayed for chemical composition and lipoprotein-associated phospholipase A2 (Lp-PLA2) activity. Lipoprotein size was assessed by non-denaturing polyacrylamide gradient gel electrophoresis, and oxidised LDL by ELISA. Liver samples were assayed for mRNA abundance of oxidative markers.

RESULTS

Lipid profile analysis revealed a reduction in the plasma concentrations of cholesterol and triglycerides, which were mainly associated with a significant reduction in the plasma concentration of circulating apoB-containing lipoproteins rather than with changes in their relative chemical composition. All patients displayed a pattern A phenotype of LDL subfractions and a relative increase in the antiatherogenic plasma HDL-2 subfraction (>2-fold; P < 0.001). The switch towards predominantly larger HDL particles was due to an increase in their relative cholesteryl ester content. Excess weight loss also led to a significant decrease in the plasma concentration of oxidised LDL (∼-25%; P < 0.01) and in the total Lp-PLA2 activity. Interestingly, the decrease in plasma Lp-PLA2 was mainly attributed to a decrease in the apoB-containing lipoprotein-bound Lp-PLA2.

CONCLUSION

Our data indicate that the weight loss induced by bariatric surgery ameliorates the atherogenicity of plasma lipoproteins by reducing the apoB-containing Lp-PLA2 activity and oxidised LDL, as well as increasing the HDL-2 subfraction.

Inflammatory biomarkers in type 2 diabetic patients: effect of glycemic control and impact of LDL subfraction phenotype

Background

Type 2 diabetes mellitus (T2D) is associated with higher cardiovascular risk partly related to an increase in inflammatory parameters. The aim of this study was to determine the association of inflammatory biomarkers with low-density lipoprotein (LDL) subfraction phenotype and glycemic control in subjects with T2D and poor glycemic control.

Methods

A cross-sectional study was performed comparing 122 subjects with T2D (59 ± 11 years old, body mass index 30.2 ± 5.6 kg/m2) with 54 control subjects. Patients with T2D were classified according to their LDL subfraction phenotype and inflammatory biomarkers (C-reactive protein, Interleukin-6, Interleukin-8, Transforming growth factor β₁, Monocyte chemotactic protein 1, Leptin, Adiponectin) were evaluated according to the degree of glycemic control, LDL phenotype and other clinical characteristics. Forty-two subjects with T2D were studied before and after 3 months of improving glycemic control by different strategies.

Results

Patients with T2D had higher C-reactive protein (CRP) and monocyte chemotactic protein-1 (MCP1) levels and lower adiponectin concentration, compared to controls. T2D subjects with body mass index ≥ 30 kg/m2 had higher CRP levels (5.2 ± 4.8 mg/l vs 3.7 ± 4.3 mg/l; p < 0.05). The presence of LDL phenotype B was related to higher levels of transforming growth factor-β₁ (TGF-β₁) (53.92 ± 52.82 ng/l vs 31.35 ± 33.74 ng/l; p < 0.05) and lower levels of adiponectin (3663 ± 3044 ng/l vs 2723 ± 1776 ng/l; p < 0.05). The reduction of HbA1c from 9.5 ± 1.8% at baseline to 7.4 ± 0.8% was associated with a significant reduction of TGF-β₁ (41.86 ± 32.84 ng/l vs 26.64 ± 26.91 ng/l; p = 0.02).

Conclusions

Subjects with T2D, especially those with LDL phenotype B and obesity, have higher levels of inflammatory biomarkers. Improvement of glycemic control reduces TGF-β₁ levels, which may contribute partly to its renoprotective role.

LDL subclasses and lipoprotein-phospholipase A2 activity in suppressed HIV-infected patients switching to raltegravir: Spiral substudy

OBJECTIVE

To analyze the effect of switching the ritonavir-boosted protease inhibitor (PI/r) in a stable combined antiretroviral therapy (cART) regimen to raltegravir on low-density lipoprotein (LDL) particles, and lipoprotein-associated phospholipase A2 (Lp-PLA2).

DESIGN

Substudy of a multicenter randomized trial that compared the efficacy of switching a PI/r to raltegravir-based cART in stable HIV-infected patients.

METHODS

LDL size and phenotype (by gel-gradient electrophoresis), Lp-PLA2 (by 2-thio-PAF [Cayman]), proprotein convertase subtilisin/kexin type 9 (PCSK9) (by ELISA), and standard lipid parameters were measured at baseline and week 48.

RESULTS

Eighty-one (PI/r n = 41 and raltegravir n = 40) patients were evaluated. No differences in baseline demographic and metabolic variables between arms were found except in apolipoprotein (Apo) B (p = 0.042). At week 48, total cholesterol (TC) (p < 0.001), LDL-c (p = 0.023), non-high density lipoprotein cholesterol non-high-density lipoprotein cholesterol (non-HDL-c) (p < 0.001), TC/HDL (p = 0.026), triglyceride (p < 0.001), Apo B (p < 0.001), Apo A-I (p = 0.004) and Lp (a) (p = 0.005) decreased in raltegravir arm compared to PI/r arm. At week 48, a shift from LDL phenotype B to the less atherogenic phenotype A was observed only in raltegravir arm (p < 0.001). LDL size increased (PI/r 2.1 nm, p = 0.019; raltegravir 3.8 nm, p = 0.001) and cholesterol content in small and dense LDL subfractions (LDL 4,5,6) decreased (PI/r p = 0.007, raltegravir p = 0.006) at week 48 in both arms. Total Lp-PLA2 activity (PI/r p = 0.037 and raltegravir p = 0.051) and PCSK9 plasma concentration decreased in both arms (PI/r p = 0.034 and raltegravir p < 0.001).

CONCLUSIONS

Switching a PI/r to a raltegravir-based cART in virologically suppressed HIV-infected patients was associated with an overall improvement in lipid profile, including a shift to a less atherogenic LDL phenotype.

Prevalence of metabolic syndrome among human immunodeficiency virus-infected subjects is widely influenced by the diagnostic criteria

BACKGROUND

The aim of this study was to compare the prevalence of metabolic syndrome in human immunodeficiency virus (HIV)-infected patients treated with highly active antiretroviral therapy (HAART), using the National Cholesterol Education Program Adult Treatment Panel III (NCEP ATP III), European Group for the Study of Insulin Resistance (EGIR), and International Diabetes Federation (IDF) definitions.

METHODS

A cross-sectional study was carried out with 159 consecutive adult HIV-infected subjects (120 males and 39 females) under HAART. Anthropometric and laboratory parameters were measured by standard methods. Hyperinsulinemia was defined by a fasting concentration >75th percentile of values obtained in healthy individuals (107.5 pmol/L).

RESULTS

The prevalence of ATP III-defined metabolic syndrome was 10.1%; it was 28.3% according to EGIR criteria and 15.1% using the IDF definition. The concordance between the definitions was low (kappa coefficient ranging between 0.134 and 0.296). All subjects with EGIR-defined metabolic syndrome had hyperinsulinemia, but only 50% of those with ATP III-defined metabolic syndrome and 62.5% in the IDF metabolic syndrome population had hyperinsulinemia.

CONCLUSIONS

The inclusion of hyperinsulinemia as a criterion in the EGIR metabolic syndrome definition made it more discriminative than the ATP III definition, both in men and women, and than the IDF definition in men to identify metabolic syndrome in HIV-infected subjects under HAART.

Proteomic analysis of electronegative low-density lipoprotein

Low density lipoprotein is a heterogeneous group of lipoproteins that differs in lipid and protein composition. One copy of apolipoprotein (apo)B accounts for over 95% of the LDL protein, but the presence of minor proteins could disturb its biological behavior. Our aim was to study the content of minor proteins in LDL subfractions separated by anion exchange chromatography. Electropositive LDL [LDL(+)] is the native form, whereas electronegative LDL [LDL⁻] is a minor atherogenic fraction present in blood. LC-ESI MS/MS analysis of both LDL fractions identified up to 28 different proteins. Of these, 13 proteins, including apoB, were detected in all the analyzed samples. LDL⁻ showed a higher content of most minor proteins. Statistical analysis of proteomic data indicated that the content of apoE, apoA-I, apoC-III, apoA-II, apoD, apoF, and apoJ was higher in LDL⁻ than in LDL(+). Immunoturbidimetry, ELISA, or Western blot analysis confirmed these differences. ApoJ and apoF presented the highest difference between LDL(+) and LDL⁻ (>15-fold). In summary, the increased content of several apolipoproteins, and specifically of apoF and apoJ, could be related to the physicochemical characteristics of LDL⁻, such as apoB misfolding, aggregation, and abnormal lipid composition.

Aggregated electronegative low density lipoprotein in human plasma shows a high tendency toward phospholipolysis and particle fusion

Aggregation and fusion of lipoproteins trigger subendothelial retention of cholesterol, promoting atherosclerosis. The tendency of a lipoprotein to form fused particles is considered to be related to its atherogenic potential. We aimed to isolate and characterize aggregated and nonaggregated subfractions of LDL from human plasma, paying special attention to particle fusion mechanisms. Aggregated LDL was almost exclusively found in electronegative LDL (LDL(-)), a minor modified LDL subfraction, but not in native LDL (LDL(+)). The main difference between aggregated (agLDL(-)) and nonaggregated LDL(-) (nagLDL(-)) was a 6-fold increased phospholipase C-like activity in agLDL(-). agLDL(-) promoted the aggregation of LDL(+) and nagLDL(-). Lipoprotein fusion induced by α-chymotrypsin proteolysis was monitored by NMR and visualized by transmission electron microscopy. Particle fusion kinetics was much faster in agLDL(-) than in nagLDL(-) or LDL(+). NMR and chromatographic analysis revealed a rapid and massive phospholipid degradation in agLDL(-) but not in nagLDL(-) or LDL(+). Choline-containing phospholipids were extensively degraded, and ceramide, diacylglycerol, monoacylglycerol, and phosphorylcholine were the main products generated, suggesting the involvement of phospholipase C-like activity. The properties of agLDL(-) suggest that this subfraction plays a major role in atherogenesis by triggering lipoprotein fusion and cholesterol accumulation in the arterial wall.

HDL and electronegative LDL exchange anti- and pro-inflammatory properties

Electronegative LDL [LDL(-)] is a minor modified LDL subfraction present in blood with inflammatory effects. One of the antiatherogenic properties of HDL is the inhibition of the deleterious effects of in vitro modified LDL. However, the effect of HDL on the inflammatory activity of LDL(-) isolated from plasma is unknown. We aimed to assess the putative protective role of HDL against the cytokine released induced in monocytes by LDL(-). Our results showed that LDL(-) cytokine release was inhibited when LDL(-) was coincubated with HDL and human monocytes and also when LDL(-) was preincubated with HDL and reisolated prior to cell incubation. The addition of apoliprotein (apo)AI instead of HDL reproduced the protective behavior of HDL. HDL preincubated with LDL(-) promoted greater cytokine release than native HDL. Incubation of LDL(-) with HDL decreased the electronegative charge, phospholipase C-like activity, susceptibility to aggregation and nonesterified fatty acid (NEFA) content of LDL(-), whereas these properties increased in HDL. NEFA content in LDL appeared to be related to cytokine production because NEFA-enriched LDL induced cytokine release. HDL, at least in part through apoAI, inhibits phospholipase-C activity and cytokine release in monocytes, thereby counteracting the inflammatory effect of LDL(-). In turn, HDL acquires these properties and becomes inflammatory.

Standardization of a method to evaluate the antioxidant capacity of high-density lipoproteins

BACKGROUND

A method to evaluate the antioxidant capacity of high-density lipoprotein (HDL) was developed and standardized.

METHODS

This method measure conjugated diene (CD) formation and electrophoretic mobility of low-density lipoprotein (LDL) in agarose gels in the presence and absence of HDL. HDL was isolated from 1 mL of plasma within 24 hours and oxidation assays were performed within 6 hours. Oxidation was induced by adding CuSO4. The lag phase increase in CD kinetics and the inhibition of electrophoretic mobility were defined as the HDL antioxidant capacity.

RESULTS

The optimal conditions for the CD assay were 2.5 μM CuSO4, LDL at 0.1 g apoB/L, HDL at 0.1 g apoA-I/L, at 37°C and for 3h 50 min. Agarose electrophoresis at 100 V, at 4°C for 50 min was then performed immediately. CD formation variability was 21.1% for inter-assay CV and 12.7% for intra-assay CV. Electrophoretic mobility was 26.5% for inter-assay CV and 2.4% for intra-assay CV. Correlation analysis showed a significant association between the antioxidant capacity of HDL and its neutral/polar lipid ratio.

CONCLUSIONS

The method herein described measures of the HDL antioxidant capacity in a reproducible and rapid manner that can be applied to a relatively high number of samples.

Novel phospholipolytic activities associated with electronegative low-density lipoprotein are involved in increased self-aggregation

Electronegative low-density lipoprotein (LDL(-)) is a minor LDL subfraction present in plasma with increased platelet-activating factor acetylhydrolase (PAF-AH) activity. This activity could be involved in the proinflammatory effects of LDL(-). Our aim was to study the presence of additional phospholipolytic activities in LDL(-). Total LDL was fractionated into electropositive (LDL(+)) and LDL(-) by anion-exchange chromatography, and phospholipolytic activities were measured by fluorometric methods. Phospholipolytic activity was absent in LDL(+) whereas LDL(-) presented activity against lysophosphatidylcholine (LPC, 82.4 +/- 34.9 milliunits/mg of apoB), sphingomyelin (SM, 53.3 +/- 22.5 milliunits/mg of apoB), and phosphatidylcholine (PC, 25.7 +/- 4.3 milliunits/mg of apoB). LDL(-), but not LDL(+), presented spontaneous self-aggregation at 37 degrees C in parallel to phospholipid degradation. This was observed in the absence of lipid peroxidation and suggests the involvement of phospholipolytic activity in self-aggregation of LDL(-). Phospholipolytic activity was not due to PAF-AH, apoE, or apoC-III and was not increased in LDL(+) modified by Cu (2+) oxidation, acetylation, or secretory phospholipase A 2 (PLA 2). However, LDL(-) efficiently degraded phospholipids of lipoproteins enriched in LPC, such as oxidized LDL or PLA 2-LDL, but not native or acetylated LDL. This finding supports that LPC is the best substrate for LDL(-)-associated phospholipolytic activity. These results reveal novel properties of LDL(-) that could play a significant role in its atherogenic properties.

Atherogenic and inflammatory profile of human arterial endothelial cells (HUAEC) in response to LDL subfractions

BACKGROUND

Electronegative LDL (LDL(-)) is a minor modified LDL fraction present in plasma that has been demonstrated to be inflammatory in endothelial cells isolated from human umbilical vein (HUVEC).

METHODS

A protein array able to measure 42 cytokines, chemokines and related compounds involved in atherogenesis was used to determine their release into the culture medium of human arterial endothelial cells (HUAEC) activated or not by two low-density lipoprotein (LDL) fractions isolated from human plasma by anion-exchange chromatography.

RESULTS

The results of the protein array (confirmed using specific ELISAs for each induced factor) revealed that HUAEC in the absence of stimuli released small amounts of interleukin 8 (IL-8), monocyte chemotactic protein 1 (MCP-1) and growth-related oncogene (GRO). The major native LDL fraction (named LDL(+)) increased the release of these molecules and also those of interleukin 6 (IL-6) and GROalpha. Compared to LDL(+), the minor modified fraction, named electronegative LDL (LDL(-)), increased all these factors to a greater degree and also induced the release of granulocyte-monocyte colony-stimulating factor (GM-CSF) and platelet-derived growth factor B (PDGF-B). These results were confirmed by ELISA.

CONCLUSIONS

All these results indicate that, compared to LDL(+), LDL(-) fraction promotes not only the release of proinflammatory factors but also those of atherogenic factors in endothelial cells of arterial origin, thereby suggesting a new role for LDL(-) in atherogenesis.

Electronegative low-density lipoprotein subfraction from type 2 diabetic subjects is proatherogenic and unrelated to glycemic control

BACKGROUND

The physicochemical and biological characteristics of electronegative low-density lipoprotein (LDL) (LDL(-)) from type 2 diabetic patients (DM2), before and after insulin therapy, were studied.

METHODS

Total LDL was subfractionated in LDL(+) (native LDL) and LDL(-) by anion-exchange chromatography.

RESULTS

The proportion of LDL(-) was increased in plasma from DM2 patients compared to control subjects (13.8 +/- 4.6% versus 6.1 +/- 2.5, P < 0.05) and was not modified after glycemic optimization (14.0 +/- 5.9%). LDL(-) from DM2 patients presented similar differential characteristics versus LDL(+) than LDL(-) from controls; that is, decreased apoB and oxidizability, and increased triglyceride, nonesterified fatty acids (NEFA), apoE, apoC-III, platelet-activating factor (PAF) acetylhydrolase activity and aggregability. No difference in particle size, antioxidants, malondialdehyde (MDA), fructosamine or glycated low-density lipoprotein (gLDL) was observed between LDL subfractions. Concerning differences between LDL subfractions isolated from DM2 and from control subjects, the former showed increased MDA, fructosamine and gLDL proportion and decreased LDL size and antioxidant content. The only effect of glycemic optimization was a decrease in fructosamine and gLDL in LDL(+) from DM2 subjects. LDL(-) from DM2 patients presented low binding affinity to the low-density lipoprotein receptor (LDLr) in cultured fibroblasts compared to LDL(+) and two- to threefold increased ability to release interleukin-8 (IL-8) and monocyte chemotactic protein 1 (MCP-1) in endothelial cells.

CONCLUSION

These results suggest that, although nonenzymatic glycosylation and oxidation are increased in type 2 diabetes, these features would not be directly involved in the generation of LDL(-). Moreover, LDL(-) properties suggest that the high proportion observed in plasma could promote accelerated atherosclerosis in DM2 patients through increased residence time in plasma and induction of inflammatory responses in artery wall cells.

Wide proinflammatory effect of electronegative low-density lipoprotein on human endothelial cells assayed by a protein array

Electronegative low-density lipoprotein (LDL(-)) is a modified subfraction of LDL present in plasma able to induce the release of interleukin 8 (IL-8) and monocyte chemotactic protein 1 (MCP-1) by human umbilical vein endothelial cells (HUVEC). To ascertain whether further inflammation mediator release could be induced by LDL(-), a protein array system was used to measure 42 cytokines and related compounds. Native LDL and LDL(-) isolated from normolipemic subjects were incubated for 24 h with HUVEC and culture supernatants were used to measure inflammation mediator release. The protein array revealed that IL-6, granulocyte/monocyte colony-stimulating factor (GM-CSF) and growth-related oncogene (GRO) release were increased by cultured HUVEC in response to LDL(-). LDL(-) enhanced production of IL-6 (4-fold vs. LDL(+)), GM-CSF (4-fold), GRObeta (2-fold) and GROgamma (7-fold) was confirmed by ELISA. Time-course experiments revealed that IL-6 was released earlier than the other inflammation mediators, suggesting a first-wave cytokine action. However, the addition of IL-6 alone did not stimulate the production of IL-8, MCP-1 or GM-CSF. Moreover, IL-8, MCP-1 or GM-CSF alone did not promote the release of the other inflammatory molecules. Modification of LDL(+) by phospholipase A(2)-mediated lipolysis or by loading with non-esterified fatty acids (NEFA) reproduced the action of LDL(-), thereby suggesting the involvement of NEFA and/or lysophosphatidylcholine in the release of these molecules. Our results indicate that LDL(-) promotes a proinflammatory phenotype in endothelial cells through the production of cytokines, chemokines and growth factors.

The inflammatory properties of electronegative low-density lipoprotein from type 1 diabetic patients are related to increased platelet-activating factor acetylhydrolase activity

AIMS/HYPOTHESIS

Chemical and biological characteristics of LDL(-) from type 1 diabetic subjects were analysed. The diabetic patients were studied during poor and optimised glycaemic control.

MATERIALS AND METHODS

Total LDL was subfractionated into electropositive LDL(+) and electronegative LDL(-) by anion exchange chromatography and the lipid and protein composition of the two determined.

RESULTS

LDL(-) differed from LDL(+) in that it had higher triglyceride, non-esterified fatty acids, apoE, apoC-III and platelet-activating factor acetylhydrolase (PAF-AH), as well as lower apoB relative content. No evidence of increased oxidation was observed in LDL(-). LDL(-) increased two-fold the release of interleukin 8 (IL-8) and monocyte chemotactic protein 1 (MCP-1) in endothelial cells, suggesting an inflammatory role. Optimisation of glycaemic control after insulin therapy decreased the proportion of LDL(-), but did not modify the composition of LDL subfractions, except for a decrease in PAF-AH activity in LDL(-). The possibility that LDL(-) could be generated by non-enzymatic glycosylation was studied. Fructosamine and glycated LDL content in LDL subfractions from type 1 diabetic patients was greater than in LDL subfractions isolated from normoglycaemic subjects, and decreased after glycaemic optimisation in both subfractions. However, no difference was observed between LDL(+) and LDL(-) before and after insulin therapy.

CONCLUSIONS/INTERPRETATION

These results provide evidence that LDL(-) is not produced by glycosylation. Nevertheless, LDL(-) from diabetic patients displays inflammatory potential reflected by the induction of chemokine release in endothelial cells. This proatherogenic effect could be related to the high PAF-AH activity in LDL(-).

Increased lysophosphatidylcholine and non-esterified fatty acid content in LDL induces chemokine release in endothelial cells. Relationship with electronegative LDL

Electronegative low-density lipoprotein (LDL(-)) is a plasma-circulating LDL subfraction with proinflammatory properties that induces the production of chemokines in cultured endothelial cells. However, the specific mechanism of LDL(-)-mediated chemokine release is presently unknown. A characteristic feature of LDL(-) is an increased content of lysophosphatidylcholine (LPC) and non-esterified fatty acids (NEFA). The effect of increasing amounts of LPC and NEFA associated with LDL on the release of chemokines by endothelial cells was studied. Total LDL was subfractionated by anion-exchange chromatography in electropositive (LDL(+)) and LDL(-). LDL(-) contained two-fold more LPC and NEFA than LDL(+) and induced two- to four-fold more (p < 0.05) interleukin-8 (IL-8, 11.5 +/- 8.2 ng/10(5) cells) and monocyte chemotactic protein-1 (MCP-1, 10.8 +/- 3.8 ng/10(5) cells) release by human umbilical vein endothelial cells (HUVEC) than LDL(+) (IL-8: 3.4 +/- 1.5 ng/10(5) cells, MCP-1: 5.8 +/- 2.9 ng/10(5) cells). The content of LPC and NEFA in LDL(+) was increased by enzymatic treatment with secretory phospholipase A(2) (sPLA(2)) at 5 ng/mL or 20 ng/mL or by incubation with NEFA at 2 mmol/L. Modification of LDL(+) by both methods did not result in oxidative modification as demonstrated by the lack of change in antioxidants, conjugated dienes and malondialdehyde content. sPLA(2) treatment resulted in an increase in LPC and NEFA in LDL(+) which enhanced its ability to release IL-8 and MCP-1 by HUVEC in a concentration-dependent manner (sPLA(2)(5)-LDL; IL-8: 7.1 +/- 3.8ng/10(5) cells, MCP-1: 8.0 +/- 5.1 ng/10(5) cells; sPLA(2)(20)-LDL; IL-8: 20.8 +/- 11.2 ng/10(5) cells, MCP-1: 15.0 +/- 7.5 ng/10(5) cells). NEFA loading of LDL(+) also favored the release of IL-8 and MCP-1 (IL-8: 7.8 +/- 6.1 ng/10(5) cells, MCP-1: 8.4 +/- 2.7 ng/10(5) cells, p < 0.05 versus LDL(+)). These effects were observed when modified LDL(+) reached a content of LPC and/or NEFA similar that of LDL(-). These data indicate that non-oxidized polar lipids associated with LDL promote an inflammatory response in endothelial cells and suggest that increased NEFA and LPC could be involved in the inflammatory activity of LDL(-).

Impaired Binding Affinity of Electronegative Low-Density Lipoprotein (LDL) to the LDL Receptor Is Related to Nonesterified Fatty Acids and Lysophosphatidylcholine Content†

The binding characteristics of electropositive [LDL(+)] and electronegative LDL [LDL(-)] subfractions to the LDL receptor (LDLr) were studied. Saturation kinetic studies in cultured human fibroblasts demonstrated that LDL(-) from normolipemic (NL) and familial hypercholesterolemic (FH) subjects had lower binding affinity than their respective LDL(+) fractions (P < 0.05), as indicated by higher dissociation constant (K(D)) values. FH-LDL(+) also showed lower binding affinity (P < 0.05) than NL-LDL(+) (K(D), sorted from lower to higher affinity: NL-LDL(-), 33.0 +/- 24.4 nM; FH-LDL(-), 24.4 +/- 7.1 nM; FH-LDL(+), 16.6 +/- 7.0 nM; NL-LDL(+), 10.9 +/- 5.7 nM). These results were confirmed by binding displacement studies. The impaired affinity binding of LDL(-) could be attributed to altered secondary and tertiary structure of apolipoprotein B, but circular dichroism (CD) and tryptophan fluorescence (TrpF) studies revealed no structural differences between LDL(+) and LDL(-). To ascertain the role of increased nonesterified fatty acids (NEFA) and lysophosphatidylcholine (LPC) content in LDL(-), LDL(+) was enriched in NEFA or hydrolyzed with secretory phospholipase A(2). Modification of LDL gradually decreased the affinity to LDLr in parallel to the increasing content of NEFA and/or LPC. Modified LDLs with a NEFA content similar to that of LDL(-) displayed similar affinity. ApoB structure studies of modified LDLs by CD and TrpF showed no difference compared to LDL(+) or LDL(-). Our results indicate that NEFA loading or phospholipase A(2) lipolysis of LDL leads to changes that affect the affinity of LDL to LDLr with no major effect on apoB structure. Impaired affinity to the LDLr shown by LDL(-) is related to NEFA and/or LPC content rather than to structural differences in apolipoprotein B.

Human Apolipoprotein A-II Enrichment Displaces Paraoxonase From HDL and Impairs Its Antioxidant Properties

Apolipoprotein A-II (apoA-II), the second major high-density lipoprotein (HDL) apolipoprotein, has been linked to familial combined hyperlipidemia. Human apoA-II transgenic mice constitute an animal model for this proatherogenic disease. We studied the ability of human apoA-II transgenic mice HDL to protect against oxidative modification of apoB-containing lipoproteins. When challenged with an atherogenic diet, antigens related to low-density lipoprotein (LDL) oxidation were markedly increased in the aorta of 11.1 transgenic mice (high human apoA-II expressor). HDL from control mice and 11.1 transgenic mice were coincubated with autologous very LDL (VLDL) or LDL, or with human LDL under oxidative conditions. The degree of oxidative modification of apoB lipoproteins was then evaluated by measuring relative electrophoretic mobility, dichlorofluorescein fluorescence, 9- and 13-hydroxyoctadecadienoic acid content, and conjugated diene kinetics. In all these different approaches, and in contrast to control mice, HDL from 11.1 transgenic mice failed to protect LDL from oxidative modification. A decreased content of apoA-I, paraoxonase (PON1), and platelet-activated factor acetyl-hydrolase activities was found in HDL of 11.1 transgenic mice. Liver gene expression of these HDL-associated proteins did not differ from that of control mice. In contrast, incubation of isolated human apoA-II with control mouse plasma at 37°C decreased PON1 activity and displaced the enzyme from HDL. Thus, overexpression of human apoA-II in mice impairs the ability of HDL to protect apoB-containing lipoproteins from oxidation. Further, the displacement of PON1 by apoA-II could explain in part why PON1 is mostly found in HDL particles with apoA-I and without apoA-II, as well as the poor antiatherogenic properties of apoA-II–rich HDL.

Electronegative low-density lipoprotein

PURPOSE OF REVIEW

The occurrence in blood of an electronegatively charged LDL was described in 1988. During the 1990s reports studying electronegative LDL (LDL(-)) were scant and its atherogenic role controversial. Nevertheless, recent reports have provided new evidence on a putative atherogenic role of LDL(-). This review focuses on and discusses these new findings.

RECENT FINDINGS

In recent years, LDL(-) has been found to be involved in several atherogenic features through its action on cultured endothelial cells. LDL(-) induces the production of chemokines, such as IL-8 and monocyte chemotactic protein 1, and increases tumor necrosis factor-alpha-induced production of vascular cell adhesion molecule 1, with these molecules being involved in early phases of leukocyte recruitment. LDL(-) from familial hypercholesterolemic patients also decreases DNA synthesis and intracellular fibroblast growth factor 2 production, which may contribute to impaired angiogenesis and increased apoptosis. In addition, the preferential association of platelet-activating factor acetylhydrolase with LDL(-) has been reported, suggesting a proinflammatory role of this enzyme in LDL(-).

SUMMARY

Recent findings suggest that LDL(-) could contribute to atherogenesis via several mechanisms, including proinflammatory, proapoptotic and anti-angiogenesis properties. Further studies are required to define the role of LDL(-) in atherogenesis more precisely and to clarify mechanisms involved in endothelial cell activation.

Effect of simvastatin in familial hypercholesterolemia on the affinity of electronegative low-density lipoprotein subfractions to the low-density lipoprotein receptor

The effect of simvastatin therapy on the biologic characteristics of the electronegative low-density lipoprotein (LDL) subfraction of patients with familial hypercholesterolemia (FH) was studied. Total LDL, isolated from FH plasma at 0, 3 and 6 months of simvastatin treatment, was subfractionated into electropositive LDL (LDL[+]) and electronegative LDL (LDL[-]) by anion exchange chromatography. LDL isolated from healthy normolipemic (NL) subjects was used as a control. The LDL(-) proportion was twofold higher in patients with FH than in NL subjects (17.6 +/- 1.6% vs 7.8 +/- 1.5%, respectively; p <0.05) and was progressively reduced by simvastatin therapy (15.7 +/- 1.6% at 3 months; 13.8 +/- 2.5% at 6 months; p <0.05). Both LDL subfractions from patients with FH had a higher relative cholesterol content and decreased apolipoprotein B and triglycerides than NL subfractions. Simvastatin progressively induced changes in lipid content of both LDL subfractions in patients with FH, and lipid composition was closer to these subfractions in NL subjects after 6 months of therapy. Binding displacement experiments in human fibroblasts demonstrated that LDL(-) from both groups of subjects had a lower affinity of binding to the LDL receptor that LDL(+). In addition, LDL(+) in patients with FH presented an intermediate binding affinity between LDL(-) and LDL(+) in NL subjects. Simvastatin-induced changes in LDL composition were accompanied by a progressive increase in affinity of LDL(+) and LDL(-) in patients with FH. After 6 months of therapy, LDL(+) in FH had an affinity similar to that of LDL(+) in NL subjects. The LDL(-)-induced release of chemokines interleukin-8 and monocyte chemotactic protein-1 from cultured endothelial cells was twofold higher compared with that of LDL(+). No difference in chemokine release between patients with FH and NL subjects or the effect of simvastatin were observed. We conclude that simvastatin therapy was able to modify LDL subfraction composition in subjects with FH and increase their affinity to the LDL receptor. This improvement could contribute to the observed reduction in LDL(-) proportion induced by simvastatin.

Platelet-activating factor acetylhydrolase is mainly associated with electronegative low-density lipoprotein subfraction

BACKGROUND

Electronegative LDL [LDL(-)], a modified subfraction of LDL present in plasma, induces the release of interleukin-8 and monocyte chemotactic protein-1 from cultured endothelial cells.

METHODS AND RESULTS

We demonstrate that platelet-activating factor acetylhydrolase (PAF-AH) is mainly associated with LDL(-). LDL(-) had 5-fold higher PAF-AH activity than the nonelectronegative LDL subfraction [LDL(+)] in both normolipemic and familial hypercholesterolemic subjects. Western blot analysis after SDS-PAGE confirmed these results, because a single band of 44 kDa corresponding to PAF-AH appeared in LDL(-) but not in LDL(+). Nondenaturing polyacrylamide gradient gel electrophoresis demonstrated that PAF-AH was bound to LDL(-) regardless of LDL size. In accordance with the above findings, nonesterified fatty acids, a cleavage product of PAF-AH, were increased in LDL(-) compared with LDL(+).

CONCLUSIONS

The high PAF-AH activity observed in LDL(-) could be related to the proinflammatory activity of these lipoproteins toward cultured endothelial cells.

Electronegative LDL of FH subjects: chemical characterization and induction of chemokine release from human endothelial cells

Electronegative LDL (LDL(-)) constitutes a plasma subfraction of LDL with proinflammatory properties. Its proportion is increased in familial hypercholesterolemia (FH); however, the characteristics of LDL(-) isolated from FH subjects have not been previously studied. In this work, the composition, oxidative status, and inflammatory capacity on endothelial cells of LDL(-) from FH and normolipemic (NL) subjects were evaluated. LDL(-) from FH was relatively enriched in esterified and free cholesterol and triglyceride, and had lower apoB and phospholipid content compared with the non-electronegative fraction (LDL(+)). LDL(-) also contained increased amounts of apoE, apoC-III, sialic acid, and non-esterified fatty acids (NEFAs). The same was observed in NL subjects, except that esterified cholesterol and phospholipid were similar in LDL(-) and LDL(+). No difference was observed between the two fractions concerning malondialdehyde, fatty acid hydroxides, and antioxidants, thereby indicating the absence of increased oxidation of LDL(-) compared with LDL(+). When LDL(-) (100 mg/l) from NL and FH subjects was incubated for 24 h with human umbilical vein endothelial cells (HUVECs), interleukin 8 (IL-8) and monocyte chemotactic protein 1 (MCP-1) increased twofold in the culture medium compared with LDL(+). Vascular cell adhesion molecule 1 (VCAM-1) expression was not increased by LDL(-). Our data indicate that LDL(-) from FH or NL subjects shows no evidence of increased oxidative modification compared to LDL(+); however, LDL(-) induces twofold the release of chemokines by endothelial cells. This effect, which may contribute to leukocyte recruitment and promote atherogenesis, may be greater in FH subjects in which LDL(-) can be up to eightfold higher than in NL subjects.

Mechanisms of HDL deficiency in mice overexpressing human apoA-II

To ascertain the mechanisms underlying the hypoalphalipoproteinemia present in mice overexpressing human apolipoprotein A-II (apoA-II) (line 11.1), radiolabeled HDL or apoA-I were injected into mice. Fractional catabolic rate of [(3)H]cholesteryl oleoyl ether HDL ([(3)H]HDL) was 2-fold increased in 11.1 transgenic mice compared with control mice and this was concomitant with increased radioactivity in liver, gonads, and adrenals. However, scavenger receptor class B, type I (SR-BI) was increased only in adrenals. [(3)H]HDL of 11.1 transgenic mice presented greater binding but decreased uptake compared with control mice when Chinese hamster ovary cells transfected with SR-BI were used, thereby pointing to unknown but SR-BI-independent mechanisms as being responsible for the increased (3)H-radioactivity seen in liver and gonads. Synthesis rate (SR) of plasma [(3)H]HDL was 2-fold decreased in 11.1 transgenic mice. Mouse (125)I-apoA-I was 2-fold more rapidly catabolized (mainly by the kidney) in transgenic mice. Mouse apoA-I displacement from HDL by the addition of isolated human apoA-II was reproduced ex vivo; thus, this mechanism may be involved in the increased renal catabolism of apoA-I. ApoA-I SR was 2-fold decreased in 11.1 transgenic mice and this was concomitant with a 2.3-fold decrease in hepatic apoA-I mRNA abundance. Our findings show that multiple mechanisms are involved in the HDL deficiency presented by mice overexpressing human apoA-II.

Density distribution of electronegative LDL in normolipemic and hyperlipemic subjects

The density distribution of electronegative LDL [LDL(-)], a cytotoxic and inflammatory fraction of LDL present in plasma, was studied in 10 normolipemic (NL), 6 FH, and 11 hypertriglyceridemic (HTG) subjects. Six LDL subclasses of increased density (LDL1 to LDL6) were isolated by density-gradient ultracentrifugation (DGU). NL and FH subjects showed prevalence of light LDL, whereas HTG subjects showed prevalence of dense LDL. LDL(-) proportion was determined from total LDL or LDL-density subclasses by anion-exchange chromatography. LDL from FH patients had increased LDL(-) (35.1 +/- 9.9%) compared with LDL from NL and HTG subjects (9.4 +/- 2.3% and 12.3 +/- 4.3%, respectively). Most LDL(-) was contained in dense subclasses in NL (LDL4-6, 67.7 +/- 3.1%) whereas most of LDL(-) from FH patients were contained in light LDL subclasses (LDL1-3) (86.2 +/- 1.6%). In these subjects, simvastatin therapy decreased LDL(-) to 28.2 +/- 6.7% and 21.2 +/- 5.6% at 3 and 6 months of treatment, respectively, due mainly to decreases in light LDL subclasses. In HTG subjects, half LDL(-) was contained in dense LDL subclasses (LDL4-6, 46.1 +/- 2.0%). Non-denaturing acrylamide gradient gel electrophoresis concurred with DGU data, as LDL(-) from NL showed a single band of lower size than non-electronegative LDL [LDL(+)], whereas LDL(-) from FH and HTG presented bands of greater size than its respective LDL(+). These results reveal the existence of light and dense LDL(-), indicate that hyperlipemia could promote the formation of light LDL(-) and suggest that LDL(-) could have different origins.

Changes in low-density lipoprotein electronegativity and oxidizability after aerobic exercise are related to the increase in associated non-esterified fatty acids

The immediate effects of intense aerobic exercise on the composition and oxidizability of low- (LDL) and high-density lipoproteins (HDL) were studied in 11 male athletes. Plasma parameters known to affect lipoprotein oxidizability were also evaluated. Lipophilic antioxidants, including alpha-tocopherol and carotenoids, paraoxonase and malondialdehyde (MDA) in plasma remained unchanged after exercise. Increases in the concentration of uric acid, bilirubin and ascorbic acid after the race resulted in a significant increase in total antioxidant serum capacity. LDL, but not HDL, increased its "in vitro"-induced susceptibility to oxidation and the proportion of electronegative LDL (LDL-). The ability of HDL to inhibit the oxidation of LDL remained unchanged after exercise. The enhanced oxidizability of LDL was not explained by increments in its aldehyde content or by decrements in antioxidants. The major compositional change in LDL was an increase in non-esterified fatty acid (NEFA) content (from 4.00+/-1.24 to 19.00+/-14.18 mol NEFA/mol apoB). NEFA also increased in plasma and HDL. "In vitro" experiments showed that incubation of LDL with increasing amounts of NEFA induced a concentration-dependent increase in the proportion of LDL-. Moreover, a slightly increased NEFA content in LDL (15-50 mol NEFA/mol apoB) induced higher susceptibility to oxidation. These "in vitro" results concur with those observed in LDL obtained from athletes after exercise, i.e. a concentration of approximately 20 mol NEFA/mol apoB increased LDL oxidizability and LDL- proportion. We conclude that changes in the qualitative characteristics of LDL after exercise were unrelated to oxidative stress, but were related to the increase in LDL-associated NEFA content.

Apo(B)-dependent dyslipidemic phenotypes in type 1 diabetic patients

BACKGROUND

The prevalence of apo(B)-dependent dyslipidemic phenotypes, which are associated with cardiovascular disease, is increased in normocholesterolemic type 2 diabetic patients. Our aim was to determine the impact of including apo(B) in the evaluation of normocholesterolemic type 1 diabetic patients.

METHODS

A total of 123 type 1 diabetic patients (47% male, age 36.6+/-12.5 years) were included. The apo(B) cut-off point (1.14 g/l) was obtained from a group of 53 normolipidemic control subjects of similar age and gender distribution; for low density lipoprotein cholesterol (LDLc), triglycerides, and high density lipoprotein cholesterol (HDLc), we used the cut-off points recommended by the National Cholesterol Education Program. LDLc was determined by ultracentrifugation or Friedewald's equation, depending on triglyceride concentrations, and apo(B) by immunoturbidimetry.

RESULTS

A total of 113 (92%) type 1 diabetic patients were normocholesterolemic, and 13% of these were dyslipidemic. The frequency of hyperapo(B) was similar in normocholesterolemic patients and controls (6.2 vs. 9.4%, respectively). Diabetic patients with hyperapo(B) had poorer glycemic control, higher total cholesterol, triglycerides, and LDLc, and a lower HDLc and LDLc/apo(B) ratio.

CONCLUSIONS

Unlike type 2 diabetes, type 1 diabetes is not associated with an increased prevalence of hyperapo(B)-dependent dyslipidemic phenotypes. Thus, only in patients with poor glycemic control who display other components of diabetic dyslipidemia, typical for type 2 diabetes, does determining apo(B) concentrations provide additional information in type 1 diabetes.

Effect of glycemic optimization on electronegative low-density lipoprotein in diabetes: relation to nonenzymatic glycosylation and oxidative modification

The effect of insulin therapy on low-density lipoprotein (LDL) oxidizability, proportion of electronegative LDL [LDL(-)] and LDL composition was studied in 33 type 2 diabetic patients. Before glycemic control improvement, type 2 diabetic subjects presented higher triglyceride and very low-density lipoprotein cholesterol and lower high-density lipoprotein cholesterol than 25 healthy matched subjects. Furthermore, their LDL was more susceptible to oxidation (lag phase 45.9 +/- 5.4 min vs. 49.7 +/- 7.6 min, P < 0.05), contained a higher proportion of LDL(-) (19.0 +/- 8.7% vs. 14.3 +/- 5.5%, P < 0.05), and was enriched in triglyceride and depleted in cholesterol and phopholipids. Lipoprotein profile improved after glycemic optimization but failed to change either LDL oxidizability (45.3 +/- 6.2 min) or LDL(-) (17.9 +/- 8.2%). These data suggest that oxidation rather than nonenzymatic glycosylation could be related to the high LDL(-) found in these patients and disagree with results obtained in a previous study of type 1 diabetic patients. A second study was conducted in 10 type 1 and 10 type 2 diabetic subjects under insulin therapy, and the proportions of glycated LDL (gLDL) and LDL(-) were determined. Basal gLDL (2.8 +/- 0.6%) and LDL(-) (20.7 +/- 6.1%) decreased in type 1 diabetics after glycemic optimization (1.9 +/- 0.6% and 15.4 +/- 3.4%, respectively; P < 0.05). In type 2 patients, even though gLDL decreased (from 2.2 +/- 0.6% to 1.6 +/- 0.6%, P < 0.05) no effect was observed on LDL(-) (from 17.3 +/- 2.9% to 16.0 +/- 4.3%). We conclude that nonenzymatic glycosylation, which appears as a determinant of the high proportion of LDL(-) in type 1 diabetes, does not play a major role in LDL(-) generation in type 2 diabetes.

Prevalence and phenotypic distribution of dyslipidemia in type 1 diabetes mellitus: effect of glycemic control

BACKGROUND

Data on the prevalence of dyslipidemia in type 1 diabetes mellitus are scarce and are based on total triglyceride and total cholesterol concentrations alone.

OBJECTIVE

To assess the effect of glycemic optimization on the prevalence of dyslipidemia and low-density lipoprotein cholesterol (LDL-C) concentrations requiring intervention in patients with type 1 diabetes.

PATIENTS

A total of 334 adults with type 1 diabetes and 803 nondiabetic control subjects.

METHODS

Levels of glycosylated hemoglobin, total cholesterol, total triglyceride, high-density lipoprotein cholesterol (HDL-C), and LDL-C were assessed at baseline and after 3 to 6 months of intensive therapy with multiple insulin doses.

RESULTS

Levels of LDL-C greater than 4.13 mmol/L (>160 mg/dL) and total triglyceride greater than 2.25 mmol/L (>200 mg/dL) and low HDL-C levels (<0.9 mmol/L [<35 mg/dL] in men or <1.1 mmol/L [<45 mg/dL] in women) were found in 16%, 5%, and 20% of patients and 13%, 6%, and 9% of controls, respectively (P<.001 for HDL-C). Diabetic women showed more hypercholesterolemia than nondiabetic women (15.6% vs 8.5%; P =.04). After glycemic optimization (mean +/- SD glycosylated hemoglobin decrease, 2.2 +/- 1.96 percentage points), the prevalence of LDL-C levels greater than 4.13 mmol/L (>160 mg/dL) became lower in diabetic men than in nondiabetic men (9.7% vs 17.5%; P =.04), but women showed frequencies of dyslipidemia similar to their nondiabetic counterparts. The proportion of patients with LDL-C concentrations requiring lifestyle (>2.6 mmol/L [>100 mg/dL]) or drug (>3.4 mmol/L [>130 mg/dL]) intervention decreased from 78% and 42% to 66% and 26%, respectively.

CONCLUSIONS

Low HDL-C is the most frequent dyslipidemic disorder in patients with poorly controlled insulin-treated type 1 diabetes, and a high proportion show LDL-C levels requiring intervention. Less favorable lipid profiles could explain the absence of sex protection in diabetic women. The improvement caused by glycemic optimization puts forward intensive therapy as the initial treatment of choice for dyslipidemia in poorly controlled type 1 diabetes.

Electronegative LDL from normolipemic subjects induces IL-8 and monocyte chemotactic protein secretion by human endothelial cells

The presence in plasma of an electronegative LDL subfraction [LDL(-)] cytotoxic for endothelial cells (ECs) has been reported. We studied the effect of LDL(-) on the release by ECs of molecules implicated in leukocyte recruitment [interleukin-8 (IL-8) and monocyte chemotactic protein-1 (MCP-1)] and in the plasminogen activator inhibitor-1 (PAI-1). LDL(-), isolated by anion-exchange chromatography, differed from nonelectronegative LDL [LDL(+)] in its higher triglyceride, nonesterified fatty acid, apoprotein E and apoprotein C-III, and sialic acid contents. No evidence of extensive oxidation was found in LDL(-); its antioxidant and thiobarbituric acid-reactive substances contents were similar to those of LDL(+). However, conjugated dienes were increased in LDL(-), which suggests that mild oxidation might affect these particles. LDL(-) increased, in a concentration-dependent manner, the release of IL-8 and MCP-1 by ECs and was a stronger inductor of both chemokines than oxidized LDL (oxLDL) or LDL(+). PAI-1 release increased slightly in ECs incubated with both LDL(-) and oxLDL but not with LDL(+). However, no cytotoxic effects of LDL(-) were observed on ECs. Actinomycin D inhibited the release of IL-8 and MCP-1 induced by LDL(-) and oxLDL by up to 80%, indicating that their production is mediated by protein synthesis. Incubation of ECs with N:-acetyl cysteine inhibited production of IL-8 and MCP-1 induced by LDL(-) and oxLDL by >50%. The free radical scavenger butylated hydroxytoluene slightly inhibited the effect of oxLDL but did not modify the effect of LDL(-). An antagonist (BN-50730) of the platelet-activating factor receptor inhibited production of both chemokines by LDL(-) and oxLDL in a concentration-dependent manner. Our results indicate that LDL(-) shows proinflammatory activity on ECs and may contribute to early atherosclerotic events.

Molecular requirements in the recognition of low-density lipoproteins (LDL) by specific platelet membrane receptors

We have demonstrated that platelet low-density lipoprotein (LDL) receptors differ from classic LDL receptors of nucleated cells. Although positively charged Arg and Lys residues of apoprotein B-100 are known to play a key role in LDL recognition by classic LDL receptors, there are no conclusive data on platelet LDL receptors. This study investigated the molecular requirements of LDL particle recognition by platelet LDL receptors. The involvement of lipid and protein fractions was determined by displacement studies of the binding of 125I-LDL to platelets and fibroblasts (used as a classical LDL receptor model). The role of the protein moiety was evaluated by chemically modifying positively charged apoB residues (Lys, Arg, and Tyr) via copper-induced oxidation, cyclohexanedione, and tetranitromethane, respectively. The involvement of the lipid fraction was determined by ligand binding assays using 125I-LDL particles that had previously been delipidated and subjected to apoB solubilization. The degree of particle modification was analyzed by agarose/acrylamide gel electrophoresis and anion exchange chromatography. Modifying the amino acid residues increased particle electronegativity in the following order of potency: CHD-LDL>TNM-LDL>ox-LDL>native LDL. The results obtained by displacement studies in fibroblasts suggested that the gain in the LDL negative charge was the most important factor in the loss of receptor affinity. The chemical models of protein modification used in our study greatly affected LDL binding to the classical fibroblast receptor. In contrast, there was very slight difference in the displacement capacity on platelet 125I-LDL binding, which suggests that the protein fraction does not play a major role in the interaction of LDL with its platelet receptor. On the other hand, whereas modifying the lipid moiety did not alter the ability of solubilized 125I-apoB to interact with the classical fibroblast LDL receptor, platelet LDL receptors were unable to recognize these particles. In conclusion, our results confirm that the protein fraction plays a key role in the fibroblast LDL-receptor recognition process, whereas the lipid fraction appears to have a more relevant role in platelet LDL-receptor recognition.

Effect of physical exercise on lipoprotein(a) and low-density lipoprotein modifications in type 1 and type 2 diabetic patients

To evaluate the effect of physical exercise on blood pressure, the lipid profile, lipoprotein(a) (Lp(a)), and low-density lipoprotein (LDL) modifications in untrained diabetics, 27 diabetic patients (14 type 1 and 13 type 2) under acceptable and stable glycemic control were studied before and after a supervised 3-month physical exercise program. Anthropometric parameters, insulin requirements, blood pressure, the lipid profile, Lp(a), LDL composition, size, and susceptibility to oxidation, and the proportion of electronegative LDL (LDL(-)) were measured. After 3 months of physical exercise, physical fitness improved (maximal O2 consumption [VO2max], 29.6 +/- 6.8 v 33.0 +/- 8.4 mL/kg/min, P < .01). The body mass index (BMI) did not change, but the waist circumference (83.2 +/- 11.8 to 81.4 +/- 11.2 cm, P < .05) decreased significantly. An increase in the subscapular to triceps skinfold ratio (0.91 +/- 0.37 v 1.12 +/- 0.47 cm, P < .01) and midarm muscle circumference ([MMC], 23.1 +/- 3.4 v 24.4 +/- 3.7 cm, P < .001) were observed after exercise. Insulin requirements (0.40 +/- 0.18 v 0.31 +/- 0.19 U/kg/d, P < .05) and diastolic blood pressure (80.2 +/- 10 v 73.8 +/- 5 mm Hg, P < .01) decreased in type 2 diabetic patients. High-density lipoprotein cholesterol (HDL-C) increased in type 1 patients (1.48 +/- 0.45 v1.66 +/- 0.6 mmol/L, P < .05), while LDL cholesterol (LDL-C) decreased in type 2 patients (3.6 +/- 1.0 v3.4 +/- 0.9 mmol/L, P < .01). Although Lp(a) levels did not vary in the whole group, a significant decrease was noted in patients with baseline Lp(a) above 300 mg/L (mean decrease, -13%). A relationship between baseline Lp(a) and the change in Lp(a) (r = -.718, P < .0001) was also observed. After the exercise program, 3 of 4 patients with LDL phenotype B changed to LDL phenotype A, and the proportion of LDL(-) tended to decrease (16.5% +/- 7.4% v 14.0% +/- 5.1%, P = .06). No changes were observed for LDL composition or susceptibility to oxidation. In addition to its known beneficial effects on the classic cardiovascular risk factors, regular physical exercise may reduce the risk of cardiovascular disease in diabetic patients by reducing Lp(a) levels in those with elevated Lp(a) and producing favorable qualitative LDL modifications.

Effect of simvastatin treatment on the electronegative low-density lipoprotein present in patients with heterozygous familial hypercholesterolemia

Most described modifications of low-density lipoprotein (LDL) cholesterol share an increase in its negative electric charge; in fact, an electronegative form of LDL can be identified and isolated from plasma. Although the exact nature of the chemical modification of electronegative LDL is still controversial, its toxicity on endothelial cells has been demonstrated. Statins have protective effects against cardiovascular disease that are independent of their lipid-lowering action and which could be due, at least in part, to the prevention of LDL modification. We evaluated the effect of 6 months of simvastatin therapy (40 mg/day) on electronegative LDL proportion and LDL susceptibility to in vitro induced oxidation in 21 patients with heterozygous familial hypercholesterolemia (FH). Eleven normolipemic subjects were analyzed as a control group. Total cholesterol as well as LDL and very low density lipoprotein cholesterol, triglycerides, and apoprotein B decreased 30% after the first month of therapy, with no further decreases thereafter. LDL susceptibility to oxidation was similar in FH patients and controls and did not change throughout the treatment. Electronegative LDL proportion was 35.1 +/- 9.9% in FH patients and 9.1 +/- 2.4% in control subjects (p <0.0001) but, in contrast to total LDL cholesterol and the rest of lipid parameters, it decreased to 28.6 +/- 9.1% in the third month and to 21.2 +/- 7.7% in the sixth month of therapy. The decrease in these cytotoxic particles may be a relevant mechanism by which simvastatin protects against cardiovascular disease.

Ascorbic acid inhibits the increase in low-density lipoprotein (LDL) susceptibility to oxidation and the proportion of electronegative LDL induced by intense aerobic exercise

BACKGROUND

We have previously reported the finding of an acute increment in the susceptibility of low-density lipoprotein (LDL) to oxidation and in the proportion of electronegative LDL [LDL(-)] after intense exercise. We have now studied the effect of oral supplementation with 1 g ascorbic acid, immediately before a 4-h athletic race, on the susceptibility of LDL to oxidation, the proportion of LDL(-), and the alpha-tocopherol and lipid peroxides content in LDL, in order to inhibit such deleterious changes, and to confirm the oxidative nature of modifications of LDL induced by exercise.

METHODS

We studied seven highly trained runners who received a supplement of 1 g ascorbic acid and a control group of seven who did not receive the supplement. The susceptibility of LDL to oxidation was assessed by measurement of conjugated dienes after CuSO4-induced oxidation, the proportion of LDL(-) was determined by anion exchange chromatography, alpha-tocopherol was quantified by reverse-phase high performance liquid chromatography, and lipid peroxides were measured by the thiobarbituric acid-reactive substances (TBARS) method.

RESULTS

After exercise, in the control group there was an increase in both the susceptibility of LDL to oxidation (change in lag phase from 51.4 +/- 4.7 min to 47.0 +/- 4.6 min, P < 0.05) and the proportion of LDL(-) (from 11.1 +/- 1.4% to 13.0 +/- 2.2%, P < 0.05), but these did not occur in the ascorbic acid group (change in lag phase from 49.7 +/- 2.3 min to 50.4 +/- 4.2 min, and in LDL(-) from 9.7 +/- 1.7% to 10.1 +/- 1.7%). No significant changes in the absolute amount of LDL alpha-tocopherol were observed after exercise (ascorbic acid group: 6.65 +/- 0.94 mol/mol apoB before the race, 7.13 +/- 0.88 mol/mol apoB after the race; control group: 7.34 +/-0.69 mol/mol apoB before the race, 7.06 +/- 0.69 mol/mol apoB after the race), but significant differences were found when increments or decrements of alpha-tocopherol were tested (alpha-tocopherol increased 9.9 +/- 11.5% in the ascorbic acid group, and decreased 0.6 +/- 7.3% in the control group; P < 0.018). TBARS did not change after exercise.

CONCLUSIONS

We conclude that 1 g ascorbic acid inhibits the increase in LDL susceptibility to oxidation after exercise, preventing this acute pro-atherogenic effect. In addition, the observation that LDL(-) enhancement is prevented by ascorbic acid supports the hypothesis that at least some of the circulating LDL(-) originates from oxidative processes.

LDL from aerobically-trained subjects shows higher resistance to oxidative modification than LDL from sedentary subjects

We studied the effect of regular intense aerobic exercise on the LDL susceptibility to oxidation and the electronegative LDL-proportion (LDL(-)). A group of 38 well-trained athletes was compared to a group of 38 age-BMI-matched sedentary individuals. Athletes showed higher concentration of total cholesterol (athletes 5.08 +/- 0.70 versus controls 4.65 +/- 0.75 mmol/l, P = 0.0229) and HDL cholesterol (athletes 1.72 +/- 0.47 versus controls 1.46 +/- 0.39 mmol/l, P = 0.0068); total plasma triglyceride, LDL cholesterol and VLDL cholesterol did not differ between trained and untrained subjects. The susceptibility of LDL to oxidation, determined by conjugated dienes formation and expressed as lag phase, was lower in athletes than in sedentaries (trained subjects 47.0 +/- 5.6 versus sedentary subjects 41.9 +/- 5.0 min, P = 0.0002). LDL(-) was similar in both groups (athletes 10.32 +/- 4.70 versus controls 10.26 +/- 3.71%). The antioxidant content in total plasma and isolated LDL (alpha-tocopherol, retinol, lycopene, alpha-carotene and beta-carotene) was quantitated by HPLC in a subgroup of 32 athletes and 32 control subjects. Athletes showed higher amounts of alpha-tocopherol and retinol in plasma, but not in LDL. However, none of these antioxidants correlated with the lag phase time. Trained subjects showed lower prevalence of smoking. However, no differences were observed between smokers and non-smokers concerning lag phase. No significant difference between athletes and sedentaries concerning LDL density, or composition was observed. We conclude that LDL from trained subjects is more resistant to oxidative modification than LDL from sedentary subjects. This observation could not be attributed to conventional antioxidants as alpha-tocopherol and carotene content of LDL was unchanged in trained subjects. Thus, although none of the variables studied appear as a single predictor of the LDL susceptibility to oxidation, an additive effect of the antioxidant content, the presence of some undetermined co-antioxidant, HDL and/or smoking habits cannot be discarded as responsible for the increased resistance to oxidation of LDL in trained subjects.