Electronegative low-density lipoprotein

Chemical composition-oriented receptor selectivity of L5, a naturally occurring atherogenic low-density lipoprotein

Anion-exchange chromatography resolves human plasma low-density lipoprotein (LDL) into 5 subfractions, with increasing negative surface charge in the direction of L1 to L5. Unlike the harmless L1 to L4, the exclusively atherogenic L5 is rejected by the normal LDL receptor (LDLR) but endocytosed into vascular endothelial cells through the lectin-like oxidized LDL receptor-1 (LOX-1). Analysis with SDS-PAGE and 2-dimensional electrophoresis showed that the protein framework of L1 was composed mainly of apolipoprotein (apo) B100, with an isoelectric point (pI) of 6.620. There was a progressively increased association of additional proteins, including apoE (pI 5.5), apoAI (pI 5.4), apoCIII (pI 5.1), and apo(a) (pI 5.5), from L1 to L5. LC/MSE was used to quantify protein distribution in all subfractions. On the basis of weight percentages, L1 contained 99% apoB-100 and trace amounts of other proteins. In contrast, L5 contained 60% apoB100 and substantially increased amounts of apo(a), apoE, apoAI, and apoCIII. The compositional characteristics contribute to L5's electronegativity, rendering it unrecognizable by LDLR. LOX-1, which has a high affinity for negatively charged ligands, is known to mediate the signaling of proinflammatory cytokines. Thus, the chemical composition-oriented receptor selectivity hinders normal metabolism of L5, enhancing its atherogenicity through abnormal receptors, such as LOX-1.

Immunochemical analysis of the electronegative LDL subfraction shows that abnormal N-terminal apolipoprotein B conformation is involved in increased binding to proteoglycans

Electronegative LDL (LDL(-)) is a minor subfraction of modified LDL present in plasma. Among its atherogenic characteristics, low affinity to the LDL receptor and high binding to arterial proteoglycans (PGs) could be related to abnormalities in the conformation of its main protein, apolipoprotein B-100 (apoB-100). In the current study, we have performed an immunochemical analysis using monoclonal antibody (mAb) probes to analyze the conformation of apoB-100 in LDL(-). The study, performed with 28 anti-apoB-100 mAbs, showed that major differences of apoB-100 immunoreactivity between native LDL and LDL(-) concentrate in both terminal extremes. The mAbs Bsol 10, Bsol 14 (which recognize the amino-terminal region), Bsol 2, and Bsol 7 (carboxyl-terminal region) showed increased immunoreactivity in LDL(-), suggesting that both terminal extremes are more accessible in LDL(-) than in native LDL. The analysis of in vitro-modified LDLs, including LDL lipolyzed with sphingomyelinase (SMase-LDL) or phospholipase A(2) (PLA(2)-LDL) and oxidized LDL (oxLDL), suggested that increased amino-terminal immunoreactivity was related to altered conformation due to aggregation. This was confirmed when the aggregated subfractions of LDL(-) (agLDL(-)) and oxLDL (ag-oxLDL) were isolated and analyzed. Thus, Bsol 10 and Bsol 14 immunoreactivity was high in SMase-LDL, ag-oxLDL, and agLDL(-). The altered amino-terminal apoB-100 conformation was involved in the increased PG binding affinity of agLDL(-) because Bsol 10 and Bsol 14 blocked its high PG-binding. These observations suggest that an abnormal conformation of the amino-terminal region of apoB-100 is responsible for the increased PG binding affinity of agLDL(-).

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.

Oxidized LDL: diversity, patterns of recognition, and pathophysiology

Oxidative modification of LDL is known to elicit an array of pro-atherogenic responses, but it is generally underappreciated that oxidized LDL (OxLDL) exists in multiple forms, characterized by different degrees of oxidation and different mixtures of bioactive components. The variable effects of OxLDL reported in the literature can be attributed in large part to the heterogeneous nature of the preparations employed. In this review, we first describe the various subclasses and molecular composition of OxLDL, including the variety of minimally modified LDL preparations. We then describe multiple receptors that recognize various species of OxLDL and discuss the mechanisms responsible for the recognition by specific receptors. Furthermore, we discuss the contentious issues such as the nature of OxLDL in vivo and the physiological oxidizing agents, whether oxidation of LDL is a prerequisite for atherogenesis, whether OxLDL is the major source of lipids in foam cells, whether in some cases it actually induces cholesterol depletion, and finally the Janus-like nature of OxLDL in having both pro- and anti-inflammatory effects. Lastly, we extend our review to discuss the role of LDL oxidation in diseases other than atherosclerosis, including diabetes mellitus, and several autoimmune diseases, such as lupus erythematosus, anti-phospholipid syndrome, and rheumatoid arthritis.

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.

Molecular Model of Plasma PAF Acetylhydrolase-Lipoprotein Association: Insights from the Structure

Plasma platelet-activating factor acetylhydrolase (PAF-AH), also called lipoprotein-associated phospholipase A₂ (Lp-PLA₂), is a group VIIA PLA₂ enzyme that catalyzes the hydrolysis of PAF and certain oxidized phospholipids. Although the role of PAF-AH as a pro- or anti-atherosclerotic enzyme is highly debated, several studies have shown it to be an independent marker of cardiovascular diseases. In humans the majority of plasma PAF-AH is bound to LDL and a smaller portion to HDL; the majority of the enzyme being associated with small dense LDL and VHDL-1 subclasses. Several studies suggest that the anti- or pro-atherosclerotic tendency of PAF-AH might be dependent on the type of lipoprotein it is associated with. Amino acid residues in PAF-AH necessary for binding to LDL and HDL have been identified. However our understanding of the interaction of PAF-AH with LDL and HDL is still incomplete. In this review we present an overview of what is already known about the interaction of PAF-AH with lipoprotein particles, and we pose questions that are yet to be answered. The recently solved crystal structure of PAF-AH, along with functional work done by others is used as a guide to develop a model of interaction of PAF-AH with lipoprotein particles.

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.

Mediation of electronegative low-density lipoprotein signaling by LOX-1: a possible mechanism of endothelial apoptosis

The lectin-like oxidized LDL receptor LOX-1 mediates endothelial cell (EC) uptake of experimentally prepared copper-oxidized LDL (oxLDL). To confirm the atherogenic role of this receptor cloned against copper-oxLDL, we examined whether it mediates EC uptake of L5, an electronegative LDL abundant in dyslipidemic but not normolipidemic human plasma. Hypercholesterolemic (LDL-cholesterol, >160 mg/dL) human LDL was fractionated into L1-L5, increasingly electronegative, by ion-exchange chromatography. In cultured bovine aortic ECs (BAECs), L5 upregulated LOX-1 and induced apoptosis. Transfection of BAECs with LOX-1-specific small interfering RNAs (siLOX-1) minimized baseline LOX-1 production and restrained L5-induced LOX-1 upregulation. Internalization of labeled L1-L5 was monitored in BAECs and human umbilical venous ECs by fluorescence microscopy. LOX-1 knockdown with siLOX-1 impeded the endocytosis of L5 but not L1-L4. In contrast, blocking LDL receptor with RAP (LDL receptor-associated protein) stopped the internalization of L1-L4 but not L5. Although chemically different, L5 and oxLDL competed for EC entry through LOX-1. Via LOX-1, L5 signaling hampered Akt phosphorylation and suppressed EC expression of fibroblast growth factor-2 and Bcl-2. L5 also selectively inhibited Bcl-xL expression and endothelial nitric oxide synthase phosphorylation but increased synthesis of Bax, Bad, and tumor necrosis factor-alpha. Blocking Akt phosphorylation with wortmannin increased LOX-1 expression, suggesting a modulatory role of Akt in LOX-1 synthesis; L5 upregulated LOX-1 by dephosphorylating Akt. Because endothelial nitric oxide synthase and Bcl-2 activities are Akt-dependent, L5 impairs Akt-mediated growth and survival signals in vascular ECs by way of LOX-1. Thus, the L5/LOX-1 complex may play a critical role in atherogenesis and illuminate important targets for disease intervention.

Effects of rosuvastatin on electronegative LDL as characterized by capillary isotachophoresis: the ROSARY Study

Electronegative LDL, a charge-modified LDL (cm-LDL) subfraction that is more negatively charged than normal LDL, has been shown to be inflammatory. We previously showed that pravastatin and simvastatin reduced the electronegative LDL subfraction, fast-migrating LDL (fLDL), as analyzed by capillary isotachophoresis (cITP). The present study examined the effects of rosuvastatin on the more electronegative LDL subfraction, very-fast-migrating LDL (vfLDL), and small, dense charge-modified LDL (sd-cm-LDL) subfractions. Patients with hypercholesterolemia or those who were being treated with statins (n = 81) were treated with or switched to 2.5 mg/d rosuvastatin for 3 months. Rosuvastatin treatment effectively reduced cITP cm-LDL subfractions of LDL (vfLDL and fLDL) or sdLDL (sd-vfLDL and sd-fLDL), which were closely related to each other but were different from the normal subfraction of LDL [slow-migrating LDL (sLDL)] or sdLDL (sd-sLDL) in their relation to the levels of remnant-like particle cholesterol (RLP-C), apolipoprotein (apo) C-II, and apoE. The percent changes in cm-LDL or sd-cm-LDL caused by rosuvastatin were correlated with those in the particle concentrations of LDL or sdLDL measured as LDL-apoB or sdLDL-apoB and the levels of HDL-C, RLP-C, apoC-II, and apoE. In conclusion, rosuvastatin effectively reduced both the vfLDL subfraction and sd-cm-LDL subfractions as analyzed by cITP.

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.

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.

Reduction of charge-modified LDL by statin therapy in patients with CHD or CHD risk factors and elevated LDL-C levels: the SPECIAL Study

Various forms of atherogenic modified low-density lipoprotein (LDL) including oxidized LDL and small, dense LDL have increased negative charge as compared to normal LDL. Charge-modified LDL (electronegative LDL) and normal LDL subfractions in plasma are analyzed by capillary isotachophoresis (cITP) as fast-migrating LDL (fLDL) and slow-migrating LDL (sLDL). We examined the effects of pravastatin and simvastatin on charge-based LDL subfractions as determined by cITP in patients with hypercholesterolemia. Patients (n=72) with CHD or CHD risk factors and elevated LDL cholesterol (LDL-C) levels were randomly assigned to receive pravastatin or simvastatin. After treatment with statins for 3 and 6 months, both cITP fLDL and sLDL were reduced (p<0.05) from the baseline, but the effects did not differ between treatment with pravastatin and simvastatin. At baseline and after treatment for 3 months, cITP sLDL was correlated with LDL-C, but fLDL was correlated with inflammatory markers, high-sensitive C-reactive protein and LDL-associated platelet-activating factor acetylhydrolase, and atherogenic lipoproteins, remnant-like particle cholesterol and small, dense LDL cholesterol. In conclusion, cITP fLDL was related to inflammatory markers and atherogenic lipoproteins and was reduced by treatment with statins. Charge-modified LDL subfraction could be a potential marker for atherosclerosis and a target for therapy.

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.

Proteomic approach to study the effects of various oxidatively modified low-density lipoprotein on regulation of protein expression in human umbilical vein endothelial cell

Circulating low-density lipoprotein (LDL) isolated by our laboratory, a new form of modified LDL and designated as L5, has been reported to be cytotoxic by inducing apoptosis of vascular endothelial cells in vitro. The objective of this study was to compare the biological functions of three different forms of oxidatively modified LDL on human umbilical vein endothelial cells (HUVEC) by proteomic approaches. HUVEC were incubated with serum-free medium, native LDL (N-LDL), L5 isolated from familial hypercholesterolemic subjects (FH-L5), copper-oxidized LDL (Cu-ox-LDL), and atheroma-derived LDL (a-LDL) at 37 degrees C for 24 h. We found that HUVEC incubated with FH-L5 expressed approximately 3 fold higher concentration of MCP-1 than did cells subject to other treatments. All modified LDL significantly suppressed ATP synthase, Grp58, Grp78, and Prdx3. However, the expression of hnRNP C1/C2 was significantly enhanced by FH-L5 and a-LDL; glutathione transferase was significantly enhanced only by FH-L5. A concordant pattern of protein expression was observed between immunoblotting and 2D electrophoresis. Different forms of oxidatively modified LDL regulated HUVEC protein expression in different patterns, suggesting different roles for different oxLDL forms in inducing atherogenesis.

Effects of reconstituted HDL on charge-based LDL subfractions as characterized by capillary isotachophoresis

Modified LDL in human plasma including small, dense LDL (sdLDL) and oxidized LDL carries a more negative charge than unmodified LDL and is atherogenic. We examined the effects of apolipoprotein A-I (apoA-I)/POPC discs on charge-based LDL subfractions as determined by capillary isotachophoresis (cITP). Three normal healthy subjects and seven patients with metabolic disorders were included in the study. LDL in human plasma was separated into two major subfractions, fast- and slow-migrating LDL (fLDL and sLDL), by cITP. Normal LDL was characterized by low fLDL, and mildly oxidized LDL in vitro and mildly modified LDL in human plasma were characterized by increased fLDL. Moderately oxidized LDL in vitro and moderately modified LDL in a patient with hypertriglyceridemia and HDL deficiency were characterized by both increased fLDL and a new LDL subfraction with a faster mobility than fLDL [very-fast-migrating LDL as determined by cITP (vfLDL)]. cITP LDL subfractions with faster electrophoretic mobility (fLDL vs. sLDL, vfLDL vs. fLDL) were associated with an increased content of sdLDL. Incubation of a plasma fraction with d>1.019 g/ml (depleted of triglyceride-rich lipoproteins) in the presence of apoA-I/POPC discs at 37 degrees C greatly decreased vfLDL and fLDL but increased sLDL. Incubation of whole plasma from patients with an altered distribution of cITP LDL subfractions in the presence of apoA-I/POPC discs also greatly decreased fLDL but increased sLDL. ApoA-I/POPC discs decreased the cITP fLDL level, the free cholesterol concentration, and platelet-activating factor acetylhydrolase activity in the sdLDL subclasses (d=1.040-1.063 g/ml) and increased the size of LDL. ApoA-I/POPC discs reduced charge-modified LDL in human plasma by remodeling cITP fLDL into sLDL subfractions.

Pro-inflammatory action of LDL(−) on mononuclear cells is counteracted by increased IL10 production

OBJECTIVE

LDL(-) is a minor LDL subfraction that induces inflammatory factor release by endothelial cells. Since LDL(-) is present in plasma, its interaction with leucocytes, a cell type involved in atherosclerosis phenomena, is feasible; therefore, the aim of the current study was to evaluate LDL(-) effect on lymphocytes and monocytes isolated from human plasma.

METHODS AND RESULTS

Mononuclear cells were incubated with LDL(+) and LDL(-) and expression and release of several inflammatory mediators were analyzed by protein membrane assay, ELISA and real-time RT-PCR. LDL(-) induced a significantly increased production versus LDL(+) in MCP1, GRObeta, GROgamma, IL6, IL8 and IL10 in monocytes as well as in lymphocytes. These induced molecules are inflammatory, except for IL10 which is considered an anti-inflammatory cytokine. Therefore, the role of IL10 was evaluated in experiments where exogenous IL10 or antibodies anti-IL10 or anti-IL10 receptor were added. IL10 addition diminished the release of the other factors induced by LDL(-) near to basal production both at protein and RNA level. In contrast, the antibody anti-IL10 increased inflammatory cytokine release around two-fold, whereas the antibody anti-IL10 receptor produced a lower effect.

CONCLUSIONS

LDL(-) promoted inflammatory cytokine production in leucocytes; however, it also induced IL10 that minimized this effect. Therefore, IL10 developed a significant role in counteracting the LDL(-) inflammatory action.

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.

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.

Effect of levothyroxine on total lipid profiles as assessed by analytical capillary isotachophoresis in a patient with hypothyroidism

The patient was a 51-year-old Japanese female who had been diagnosed with hyperlipidemia. At the first medical examination, her serum levels of total cholesterol (TC) and triglyceride (TG) were 482 and 205 mg/dl, respectively. Since hyperlipidemia was not improved by pravastatin, atorvastatin or niceritrol, and since the levels of thyroid-stimulating hormone (TSH) and free T4 were 730 IU/ml and 0.3 ng/dl, respectively, the patient was diagnosed as secondary hyperlipidemia with hypothyroidism. A method for the charge isolation of lipoproteins using capillary isotachophoresis (cITP) is proposed as a clinical application because it allows us to quantitatively measure electronegative low-density lipoprotein cholesterol (LDL-C), a potent marker of coronary heart disease. After 5 months of treatment with levothyroxine, Serum TC and LDL-C levels drastically decreased without statin treatment and high-density lipoprotein cholesterol (HDL-C) increased. In the lipoprotein profiles as assessed by cITP after treatment with levothyroxin, all HDL-C subfractions were increased and fast-migrating LDL/electronegative LDL appeared to be greatly reduced after treatment, while the area under the non-modified LDL peak was increased. The cITP analysis was able to obtain more information about coronary risk factors and may be clinically useful for evaluating the effect of treatment with levothyroxine in patients with hypothyroidism and secondary hyperlipidemia.

Dynamics of dense electronegative low density lipoproteins and their preferential association with lipoprotein phospholipase A(2)

Small, dense, electronegative low density lipoprotein [LDL(-)] is increased in patients with familial hypercholesterolemia and diabetes, populations at increased risk for coronary artery disease. It is present to a lesser extent in normolipidemic subjects. The mechanistic link between small, dense LDL(-) and atherogenesis is not known. To begin to address this, we studied the composition and dynamics of small, dense LDL(-) from normolipidemic subjects. NEFA levels, which correlate with triglyceride content, are quantitatively linked to LDL electronegativity. Oxidized LDL is not specific to small, dense LDL(-) or lipoprotein [a] (i.e., abnormal lipoprotein). Apolipoprotein C-III is excluded from the most abundant LDL (i.e., that of intermediate density: 1.034 < d < 1.050 g/ml) but associated with both small and large LDL(-). In contrast, lipoprotein-associated phospholipase A(2) (LpPLA(2)) is highly enriched only in small, dense LDL(-). The association of LpPLA(2) with LDL may occur through amphipathic helical domains that are displaced from the LDL surface by contraction of the neutral lipid core.

Effects of soy germ isoflavones and hormone therapy on nitric oxide derivatives, low-density lipoprotein oxidation, and vascular reactivity in hypercholesterolemic postmenopausal women

OBJECTIVE

To evaluate the effects of soy germ isoflavones and hormone therapy on vascular reactivity, the formation of nitric oxide derivatives, and lipid peroxidation in hypercholesterolemic postmenopausal women.

DESIGN

Women were treated with soy germ, 17beta-estradiol or 17beta-estradiol + noretisterone acetate for 3 months after taking placebo for 1 month. The plasma concentrations of nitrite + nitrate and S-nitrosothiols were evaluated by gaseous phase chemiluminescence; nitrotyrosine, electronegative low-density lipoprotein, and estradiol levels were determined by enzyme-linked immunosorbent assay; cholesterol oxides and isoflavones were determined by gas chromatography and high-performance liquid chromatography, respectively. Vascular reactivity was analyzed by high-resolution ultrasonography.

RESULTS

Soy germ isoflavones and hormone therapy induced a decrease in nitrite + nitrate, electronegative low-density lipoprotein, and cholesterol oxides, as well as an increase in S-nitrosothiols. Soy germ isoflavones lowered electronegative low-density lipoprotein, and cholesterol oxides more efficiently than did hormone therapy. Only soy isoflavones inhibited nitrotyrosine formation. A significant improvement of vascular reactivity was only seen in women treated with 17beta-estradiol.

CONCLUSIONS

The soy germ isoflavones and 17beta-estradiol, alone or associated with noretisterone acetate, in the doses and forms used here, have similar effects on the bioavailability of nitric oxide. Soy germ treatment inhibited lipid peroxidation more effectively than hormone therapy.

Platelet Interaction with Bioactive Lipids Formed by Mild Oxidation of Low-Density Lipoprotein

Oxidation of low-density lipoprotein (LDL) generates pro-inflammatory and pro-thrombotic mediators that play a crucial role in cardiovascular and inflammatory diseases. Mildly oxidized LDL (mox-LDL) and minimally modified LDL (mm-LDL) which escape the uptake of macrophage scavenger receptors accumulate in the atherosclerotic intima. Oxidatively modified LDL is also present within the electronegative LDL fraction in blood, which is elevated in patients at high risk for cardiovascular diseases. Mox-LDL and mm-LDL, but not native LDL are able to induce platelet shape change and aggregation. LDL oxidation generates lipids with platelet stimulatory properties such as lysophosphatidylcholine, certain oxidized phosphatidylcholine molecules, F(2)-isoprostanes and lysophosphatidic acid (LPA). Mox-LDL and mm-LDL are like a Trojan horse carrying these biologically active lipids and attacking cells through activation of physiological receptors and signaling mechanisms. LPA has been identified as the lipid responsible for platelet stimulation by mox-LDL, mm-LDL and also mox-HDL. These lipoproteins activate platelets by stimulating G-protein coupled LPA receptors and a Rho/Rho kinase signaling pathway leading to platelet shape change and subsequent aggregation. LPA-mediated platelet activation might contribute to arterial thrombus formation after rupture of atherosclerotic plaques and to the increased blood thrombogenicity of patients with cardiovascular diseases.

Minimally modified electronegative LDL and its autoantibodies in acute and chronic coronary syndromes

OBJECTIVES

To determine the minimally modified electronegative LDL (LDL-) and its autoantibodies in coronary syndromes.

DESIGN AND METHODS

LDL(-) and its autoantibodies were determined by ELISA in patients with acute (ACS, unstable angina; AMI, acute myocardial infarction) and chronic coronary syndromes (stable angina, SA) and compared to subjects without coronary disease (controls). Results are expressed as median of LDL- (microg/mL) and anti-LDL(-) IgG (OD405 nm).

RESULTS

The concentrations of LDL(-) were higher in patients with coronary disease (ACS: 40.7 microg/mL; SA: 35.0 microg/mL) as compared to controls (21.6 microg/mL). The highest LDL- concentrations were found in patients with AMI (41.8 microg/mL). Anti-LDL(-) IgG was elevated in ACS (1.143) in relation to CCS (0.527) and controls (0.467). A positive correlation was observed between anti-LDL- IgG and CRP levels (r = 0.34, p <0.01) in the studied groups.

CONCLUSIONS

LDL(-) and anti-LDL(-) autoantibodies may be useful markers to follow patients with high risk for coronary events.

Content of redox-active compounds (ie, antioxidants) in foods consumed in the United States

BACKGROUND

Supplements containing ascorbic acid, alpha-tocopherol, or beta-carotene do not protect against oxidative stress-related diseases in most randomized intervention trials. We suggest that other redox-active phytochemicals may be more effective and that a combination of different redox-active compounds (ie, antioxidants or reductants) may be needed for proper protection against oxidative damage.

OBJECTIVE

We aimed to generate a ranked food table with values for total content of redox-active compounds to test this alternative antioxidant hypothesis.

DESIGN

An assay that measures the total concentration of redox-active compounds above a certain cutoff reduction potential was used to analyze 1113 food samples obtained from the US Department of Agriculture National Food and Nutrient Analysis Program.

RESULTS

Large variations in the content of antioxidants were observed in different foods and food categories. The food groups spices and herbs, nuts and seeds, berries, and fruit and vegetables all contained foods with very high antioxidant contents. Most food categories also contained products almost devoid of antioxidants. Of the 50 food products highest in antioxidant concentrations, 13 were spices, 8 were in the fruit and vegetables category, 5 were berries, 5 were chocolate-based, 5 were breakfast cereals, and 4 were nuts or seeds. On the basis of typical serving sizes, blackberries, walnuts, strawberries, artichokes, cranberries, brewed coffee, raspberries, pecans, blueberries, ground cloves, grape juice, and unsweetened baking chocolate were at the top of the ranked list.

CONCLUSION

This ranked antioxidant food table provides a useful tool for investigations into the possible health benefit of dietary antioxidants.

Association between fast-migrating low-density lipoprotein subfraction as characterized by capillary isotachophoresis and intima-media thickness of carotid artery

BACKGROUND

A mildly modified LDL subfraction that is characterized by an increased negative charge exists in plasma. This electronegative LDL separated by ion-exchange chromatography has been shown to be inflammatory and its proportion is increased in patients with hyperlipidemia and diabetes mellitus. The present study examined the association between the level of fast (f)-migrating LDL subfraction characterized by capillary isotachophoresis (cITP) and carotid-artery intima-media thickness (CA-IMT).

METHODS AND RESULTS

This study included 469 subjects who underwent a physical examination. CA-IMT was determined by high-resolution B-model ultrasonoraphy. Levels of charge-based LDL subfractions were measured by cITP on a Beckman P/ACE MDQ system. An increased serum LDL-C level and cITP fLDL level were associated with increased CA-IMT after adjusting for age. The extent of the associations between cITP fLDL and CA-IMT and between LDL-C and CA-IMT were similar as assessed by a receiver-operating characteristic curve analysis. LDL-C, triglyceride, and remnant-like particle cholesterol levels were independently correlated with cITP fLDL, and the LDL-C level had the strongest correlation with cITP fLDL. The association between the cITP fLDL level and CA-IMT was significant in the high LDL-C stratum but not in the low stratum, indicating that it is modified by the LDL-C level. The high-LDL-C-high-fLDL group had the highest relative risk for a high CA-IMT among the groups with each combination of LDL-C and cITP fLDL level.

CONCLUSION

The cITP fLDL level was associated with CA-IMT and its combination with the LDL-C level is a stronger indicator for a high CA-IMT.

[LDL: from metabolic syndrome to instability of the atherosclerotic plaque]

The dyslipidemia of the metabolic syndrome (MS) confers an elevated cardiovascular risk and is characterized by increased concentrations of triglycerides, decreased HDL-cholesterol and qualitative alterations in LDL which renders it more atherogenic, like the small dense LDL. Modified forms of LDL (mLDL) have been detected in vivo in the plasma and atherosclerotic plaques. A minor fraction of the total LDL has an electronegative charge and is represented by a heterogenic subpopulation of particles [LDL(-)], with higher potential to induce endothelial injury. It could be derived from oxidation, glication or other processes that alter its chemical composition and is increased in diabetic, hypercholesterolemic subjects, and in those with established coronary artery disease. mLDL are internalized by macrophages through scavenger receptors, originating foam cells and inducing an immune-inflammatory reaction. In the atherosclerotic process, the action of mLDL continues until plaque rupture and thrombogenesis, when it promotes apoptosis in endothelial and smooth muscle cells, and activates matrix metalloproteinases, weaken the fibrous cap, and further enhance the inflammatory process that ends in the thrombus formation. Development of new laboratory methods is necessary to enhance the clinical applicability of mLDL and the predictive power of the conventional lipid profile and other cardiovascular risk factors of the MS.

Relation between charge-based apolipoprotein B-containing lipoprotein subfractions and remnant-like particle cholesterol levels

OBJECTIVE

Both mildly modified LDL subfraction that carries a more-negative electric charge and remnant-like particles (RLP) are closely related to triglyceride (TG) levels. We examined the relation between the RLP-cholesterol (C) level and charge-based apolipoprotein (apo) B-containing lipoprotein subfractions as determined by capillary isotachophoresis (cITP) in patients with hypercholesterolemia.

METHODS AND RESULTS

cITP apo B lipoprotein subfractions were identified by analyzing plasma depleted of the related lipoproteins. While fast-migrating triglyceride-rich lipoprotein (fTRL) subfraction contained both chylomicrons and VLDL fraction, slow TRL (sTRL) only contained VLDL. cITP fLDL also contained VLDL fraction, i.e., beta-VLDL. Levels of cITP fTRL and sTRL were significantly correlated with serum levels of TG, RLP-C, apo C-II, and C-III. Levels of cITP sTRL were also correlated with apo E. Levels of cITP fLDL were positively correlated with not only LDL-C levels but also levels of TG, RLP-C, apo C-II, C-III, and E.

CONCLUSION

cITP fast LDL correlated with RLP-C levels and modified the relation between RLP-C and TG levels.

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.

Impact of Lipoprotein Glomerulopathy on the Relationship Between Lipids and Renal Diseases

Lipoprotein glomerulopathy (LPG) is a unique entity of renal lipidosis characterized by peculiar histopathologic characteristics of lipoprotein thrombi and an abnormal plasma lipoprotein profile resembling type III hyperlipoproteinemia, with a marked increase in serum apolipoprotein E (apoE) concentrations. At present, 65 cases have been reported worldwide, although most patients are found in Japan and east Asian countries. Recently, we identified 4 types of novel apoE mutations associated with LPG. In particular, a mutation designated apoE Sendai, in which arginine 145 is substituted with proline, occurs in the majority of Japanese patients. The virus-mediated transduction of apoE Sendai resulting in the development of LPG in apoE-deficient mice confirms the etiologic role of apoE mutation in LPG. Conversely, experimental graft-versus-host disease induced in Fc receptor gamma-chain-deficient mice showed LPG-like lesions in glomeruli without apoE mutations. Considered together, we believe that intrinsic factors in the kidney also contribute to the induction of LPG. Today, apoE and related lipid abnormalities are reported to have an important role in the development of various renal diseases, eg, diabetic nephropathy and immunoglobulin A nephropathy. In this article, we review clinical and histopathologic features of LPG, describe the etiologic role of apoE variants and intrinsic renal factors, and discuss the impact of LPG on mechanisms of other renal diseases.

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

OBJECTIVES

To produce a monoclonal antibody (MAb) against electronegative LDL (LDL-) for detecting this modified lipoprotein in blood plasma and tissues.

DESIGN AND METHODS

LDL- was isolated from human blood plasma and used as an antigen for immunization of Balb/c mice. Lymphocytes of immunized mice were fused with myeloma cells (SP2/0) to obtain the hybridomas. LDL- was detected in blood plasma and atherosclerotic lesions of humans and rabbits by MAb-based ELISA and immunohistochemistry, respectively.

RESULTS

LDL- concentrations were higher (P < 0.05) in the blood plasma of hypercholesterolemic subjects (HC, 248 +/- 77 mg/dL of total cholesterol) than in normolipidemic subjects (NL, 173 +/- 82 mg/dL of total cholesterol) and rabbits (HC, 250 +/- 15 mg/dL of cholesterol versus NL, 81 +/- 12 mg/dL of cholesterol). Moreover, LDL- was detected in the atherosclerotic lesions of humans and rabbits.

CONCLUSION

These MAb-based immunoassays are adequate to detect LDL- in biological samples and represent an important tool for investigating the role of LDL- in atherosclerosis.

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(-).

Relation between insulin resistance and fast-migrating LDL subfraction as characterized by capillary isotachophoresis

The proportion of the electronegative low density lipoprotein [LDL(-)] subfraction, which is atherogenic, is increased in type 2 diabetes but is not reduced by glycemic control. Therefore, we evaluated the ability of a new technique, capillary isotachophoresis (cITP), to quantify charge-based LDL subfractions and examined the relation between insulin resistance and the cITP fast-migrating (f) LDL levels. Seventy-five 10-year-old boys were included. The two cITP LDL subfractions, fLDL and major LDL subfractions, were proportional to the LDL protein content within the range of 0.1-0.8 mg/ml LDL protein. Levels of cITP fLDL were positively correlated with triglyceride (TG) levels and negatively correlated with LDL size. Insulin resistance as assessed by the homeostasis model assessment (HOMA-IR) was positively correlated (P < 0.01) with cITP fLDL levels (r = 0.41). The relation between HOMA-IR and cITP fLDL levels depended on TG levels but was independent of body mass index and LDL size. cITP lipoprotein analysis is an accurate and sensitive method for quantifying charge-based LDL subfractions in human plasma, and insulin resistance is related to cITP fLDL independent of LDL size.

Lipoprotein-associated phospholipase A2 as a target of therapy

PURPOSE OF REVIEW

Considerable discussion continues regarding the precise role that secreted lipoprotein-associated phospholipase A2 (Lp-PLA2), also called platelet-activating factor acetylhydrolase, plays in atherosclerosis. Since interest in this enzyme as a putative drug target has been based primarily upon its association with low-density lipoprotein (LDL) in human plasma, this review will focus on Lp-PLA2 and human coronary heart disease.

RECENT FINDINGS

Recent reports have linked Lp-PLA2 enrichment not only to the most atherogenic of LDL particles but also to the most advanced, rupture-prone, plaques. Electronegative LDL has been shown to be highly enriched in Lp-PLA2; and in advanced atheroma, Lp-PLA2 levels are highly upregulated, colocalizing with macrophages in both the necrotic core and fibrous cap. Lp-PLA2 is well placed, whether on an oxidation susceptible LDL particle or in the highly oxidative environment of an advanced rupture-prone plaque, to hydrolyse oxidized phospholipid and generate significant quantities of the two pro-inflammatory mediators, lysophosphatidylcholine and oxidized nonesterified fatty acid. Several studies have confirmed that Lp-PLA2 is an independent risk factor for cardiovascular events (i.e. myocardial infarction and stroke). Although epidemiology studies consistently support a relationship between plasma Lp-PLA2 levels and susceptibility to coronary heart disease this is not the case for Lp-PLA2 polymorphisms. Two clinical studies have linked the Ala-379-->Val polymorphism with a reduced risk of myocardial infarction, but functional differences between the AA and VV polymorphs have yet to be demonstrated.

SUMMARY

Lp-PLA2 is intimately associated with several aspects of human atherogenesis. Although various lipid-lowering therapies, such as statins, have been shown to reduce plasma levels of Lp-PLA2, none has been studied in terms of its ability to lower the large macrophage-mediated upregulation of Lp-PLA2 within advanced plaques.

Dietary antioxidants and cardiovascular disease

PURPOSE OF REVIEW

Oxidative damage is involved in cardiovascular diseases. Intervention with alpha-tocopherol, ascorbic acid and beta-carotene does not appear to reduce pathogenesis. The purpose of this review is to describe alternative antioxidant mechanisms that may be involved.

RECENT FINDINGS

Antioxidants with different chemical properties may recharge each other in an antioxidant network. The total antioxidant content of dietary plants may therefore be a useful tool for testing the "antioxidant network" hypothesis. Several berries, fruits, nuts, seeds, vegetables, drinks and spices have been found to be high in total antioxidants. Initial studies in animals and humans are supportive as to the beneficial effects of dietary plants rich in total antioxidants. Additionally, antioxidants and other plant compounds may also improve the endogenous antioxidant defence through induction of antioxidant and phase 2 enzymes. Dietary plants rich in such compounds include broccoli, Brussels sprouts, cabbage, kale, cauliflower, carrots, onions, tomatoes, spinach and garlic.

SUMMARY

Although initial studies have indicated that antioxidants may reduce oxidative stress, human intervention studies do not support a beneficial effect of antioxidant supplements. Further research is needed to clarify whether other plant antioxidants, plants rich in a combination of antioxidants, or plant compounds that induce the endogenous antioxidant defence can reduce pathogenesis of cardiovascular disease and other oxidative stress-related diseases.

Potent Capillary Isotachophoresis (cITP) for Analyzing a Marker of Coronary Heart Disease Risk and Electronegative Low-Density Lipoprotein (LDL) in Small Dense LDL Fraction

BACKGROUND

The potency and usefulness of capillary isotachophoresis (cITP) for assessing whole-serum lipoprotein profiles and quantifying electronegative low-density lipoprotein (LDL) has been previously reported.

METHODS AND RESULTS

A new cITP method to measure electronegative LDL in the small dense LDL fraction has been established. Both electronegative LDL and electronegative LDL in the small dense LDL fraction decreased after treatment with fenofibrate.

CONCLUSIONS

This method appears to be useful for analyzing a marker of coronary heart disease risk and may be suitable for evaluating the effects of hypolipidemic agents.