HDL Apo Research Articles

Nascent HDL formation in hepatocytes and role of ABCA1, ABCG1, and SR-BI

To study the mechanisms of hepatic HDL formation, we investigated the roles of ABCA1, ABCG1, and SR-BI in nascent HDL formation in primary hepatocytes isolated from mice deficient in ABCA1, ABCG1, or SR-BI and from wild-type (WT) mice. Under basal conditions, in WT hepatocytes, cholesterol efflux to exogenous apoA-I was accompanied by conversion of apoA-I to HDL-sized particles. LXR activation by T0901317 markedly enhanced the formation of larger HDL-sized particles as well as cellular cholesterol efflux to apoA-I. Glyburide treatment completely abolished the formation of 7.4 nm diameter and greater particles but led to the formation of novel 7.2 nm-sized particles. However, cells lacking ABCA1 failed to form such particles. ABCG1-deficient cells showed similar capacity to efflux cholesterol to apoA-I and to form nascent HDL particles compared with WT cells. Cholesterol efflux to apoA-I and nascent HDL formation were slightly but significantly enhanced in SR-BI-deficient cells compared with WT cells under basal but not LXR activated conditions. As in WT but not in ABCA1-deficient hepatocytes, 7.2 nm-sized particles generated by glyburide treatment were also detected in ABCG1-deficient and SR-BI-deficient hepatocytes. Our data indicate that hepatic nascent HDL formation is highly dependent on ABCA1 but not on ABCG1 or SR-BI.

Myeloperoxidase Targets Apolipoprotein A-I, the Major High Density Lipoprotein Protein, for Site-Specific Oxidation in Human Atherosclerotic Lesions

Oxidative damage by myeloperoxidase (MPO) has been proposed to deprive HDL of its cardioprotective effects. In vitro studies reveal that MPO chlorinates and nitrates specific tyrosine residues of apoA-I, the major HDL protein. After Tyr-192 is chlorinated, apoA-I is less able to promote cholesterol efflux by the ABCA1 pathway. To investigate the potential role of this pathway in vivo, we used tandem mass spectrometry with selected reaction monitoring to quantify the regiospecific oxidation of apoA-I. This approach demonstrated that Tyr-192 is the major chlorination site in apoA-I in both plasma and lesion HDL of humans. We also found that Tyr-192 is the major nitration site in apoA-I of circulating HDL but that Tyr-18 is the major site in lesion HDL. Levels of 3-nitrotyrosine strongly correlated with levels of 3-chlorotyrosine in lesion HDL, and Tyr-18 of apoA-I was the major nitration site in HDL exposed to MPO in vitro, suggesting that MPO is the major pathway for chlorination and nitration of HDL in human atherosclerotic tissue. These observations may have implications for treating cardiovascular disease, because recombinant apoA-I is under investigation as a therapeutic agent and mutant forms of apoA-I that resist oxidation might be more cardioprotective than the native form.

High-Resolution Single-Molecule Structure Revealed by Electron Microscopy and Individual Particle Electron Tomography.

The protein is naturally dynamic and heterogeneous in solution. Protein dynamics involves both equilibrium fluctuations that regulate biological function and other non-equilibrium effects of biological motors, which convert chemical energy to mechanical energy. However, a single, unique structure of protein determined from X-ray crystal and conventional single-particle electron microscopy is insufficient to encompass the dynamic nature of proteins in solution. Structure determination of dynamic and heterogeneous protein is essentially required the determination of each individual particle of protein. Recently, Drs. Gang Ren and Lei Zhan published the first single molecule three-dimensional (3D) EM images of individual proteins ever obtained with enough clarity to determine their structure, an IgG antibody (14 Å resolution) and a 17nm HDL (36 Å resolution). These results depended upon four innovations: i) improved cryo-electron microscopy (cryoEM) sample preparation and Electron microscopy (EM) operation conditions resulted in the successful imaging of a 17 nm HDL particle (120-200kDa) by cryo-electron tomography (cryoET); ii) developed an optimized NS (OpNS) protocol that eliminates the rouleau artifact that has plagued EM research for three decades. This OpNS protocol provides high-contrast single lipoprotein images with similar size (<5%) and shape (<5%) to that seen by cryoEM; iii) developed a high-resolution and high contrast sample preparation protocol, cryo-positive-staining (cryoPS) that allows direct visualization of the secondary structure of a small protein, such as the β-strands in CETP and the helical double belt of apoA-I in spherical HDL; iv) developed a robust tomography reconstruction method, Individual Particle Electron Tomography (IPET) that is a high-resolution, high throughput reconstruction method that, to the best of our knowledge, is the only method for determining an individual protein structure. Remarkably, IPET went against the conventional wisdom that a single protein can NOT be reconstructed by EM and this opens a door for the study of protein dynamics via a particle-by-particle structural comparison.

Apolipoprotein E Promotes β-Amyloid Trafficking and Degradation by Modulating Microglial Cholesterol Levels

Allelic variation in the apolipoprotein E (APOE) gene is the major risk factor of sporadic Alzheimer disease. ApoE is the primary cholesterol carrier in the brain. Previously, we demonstrated that intracellular degradation of β-amyloid (Aβ) peptides by microglia is dramatically enhanced in the presence of apoE. However, the molecular mechanisms subserving this effect remain unknown. This study reports a mechanistic link between apoE-regulated cholesterol homeostasis and Aβ degradation. We demonstrate that promoting intracellular Aβ degradation by microglia is a common feature of HDL apolipoproteins, including apoE and apoA-I. This effect was not dependent on the direct interaction of apoE and Aβ. Regulation of Aβ degradation was achieved by solely manipulating cellular cholesterol levels. The expression and the activity of Aβ degrading enzymes, however, were not regulated by cholesterol. We observed that reducing cellular cholesterol levels by apoE resulted in faster delivery of Aβ to lysosomes and enhanced degradation. Moreover, apoE facilitated the recycling of Rab7, a small GTPase responsible for recruiting the motor complex to late endosomes/lysosomes. These data indicate that faster endocytic trafficking of Aβ-containing vesicles in the presence of apoE resulted from efficient recycling of Rab7 from lysosomes to early endosomes. Thus, apoE-induced intracellular Aβ degradation is mediated by the cholesterol efflux function of apoE, which lowers cellular cholesterol levels and subsequently facilitates the intracellular trafficking of Aβ to lysosomes for degradation. These findings demonstrate a direct role of cholesterol in the intracellular Aβ degradation.

Abstract 16815: Cholesterol Efflux Capcity in Genetic Forms of HDL Deficiency

Objective: High-density lipoprotein cholesterol (HDL-C) deficiency is the most frequent lipoprotein abnormality in patients with premature coronary artery disease. In order to determine the functionality of HDL particles in genetically defined HDL deficiency (&lt;5th percentile), we employed a cell-based assay to examine ABCA1-dependent cholesterol efflux capacity in apoB-depleted plasma isolated from 19 probands of French Canadian descent. First degree relatives with normal HDL levels served as controls. Methods and Results: We determined the ability of apoB-depleted plasma to promote cholesterol efflux from [ 3 H] cholesterol-labeled, cAMP-stimulated J774 macrophages. Cases consisted of 16 ABCA1 heterozygotes, and three APOA1 E136X heterozygotes. We obtained evidence that ApoB-depleted plasma isolated from subjects with genetic forms of HDL deficiency had significantly reduced levels of ABCA1-mediated cholesterol efflux as compared to sibling controls (72.33 %). Conversely, when normalized to apoA-I levels, the efflux capacity of apoB-depleted plasma from subjects was attenuated as compared to sibling controls. Linear regression was used to determine which biochemical measurement (apoA-I concentration, HDL-C level and HDL subfractions quantified by 2DPAGGE) best explained the cholesterol efflux results. A strong, positive correlation was found between cholesterol efflux measurements and apoA-I levels, HDL-C levels, alpha-2 HDL levels, and alpha-3 HDL levels (all p&lt; 0.05). However, HDL-C levels only explained approximately 27% of the variability in cellular cholesterol efflux, suggesting that efflux capacity may help better understand HDL functionality. Conclusion: While HDL obtained from subjects with ABCA1 or APOA1 gene defects had decreased cellular cholesterol efflux compared with sibling controls, this difference was markedly attenuated when corrected for apoA-I mass, suggesting that such particles remain functional in cholesterol efflux through ABCA1.

Levels of apoA-I, apoA-IV and SAA both in plasma and high-density lipoprotein in coronary heart disease patients

BackgroundIn recent years, studies have shown that elevated level of HDL may not have a cardiovascular protective effect. Our study is to focus on the protein components in HDL with...

ApoA-I deficiency in mice is associated with redistribution of apoA-II and aggravated AApoAII amyloidosis

Apolipoprotein A-II (apoA-II) is the second major apolipoprotein following apolipoprotein A-I (apoA-I) in HDL. ApoA-II has multiple physiological functions and can form senile amyloid fibrils (AApoAII) in mice. Most circulating apoA-II is present in lipoprotein A-I/A-II. To study the influence of apoA-I on apoA-II and AApoAII amyloidosis, apoA-I-deficient (C57BL/6J.Apoa1⁻/⁻) mice were used. Apoa1⁻/⁻ mice showed the expected significant reduction in total cholesterol (TC), HDL cholesterol (HDL-C), and triglyceride (TG) plasma levels. Unexpectedly, we found that apoA-I deficiency led to redistribution of apoA-II in HDL and an age-related increase in apoA-II levels, accompanied by larger HDL particle size and an age-related increase in TC, HDL-C, and TG. Aggravated AApoAII amyloidosis was induced in Apoa1⁻/⁻ mice systemically, especially in the heart. These results indicate that apoA-I plays key roles in maintaining apoA-II distribution and HDL particle size. Furthermore, apoA-II redistribution may be the main reason for aggravated AApoAII amyloidosis in Apoa1⁻/⁻ mice. These results may shed new light on the relationship between apoA-I and apoA-II as well as provide new information concerning amyloidosis mechanism and therapy.

Novel aspects of HDL level and function in a clinical setting

HDL is composed of heterogeneous particles ranging between 7 and 14 nm. ApoA1, the main HDL apolipoprotein, is synthesized in hepatic and intestinal cells and is a determinant of the formation and stability of HDL and the two main HDL functions: cholesterol esterification and reverse cholesterol transportation [1]. HDL is secreted by the liver as disk-shaped particles constituted by ApoA1, phospholipids and unesterified cholesterol. Nascent HDL becomes progressively spherical by cholesterol esterification. HDL also originates in the plasma compartment, by accretion of ApoA1 to phospholipids and unesterified cholesterol derived from lipolysis of triglyceride-rich lipoproteins [1]. Continuous exchange of lipids and proteins between HDL and the other lipoproteins and cholesterol esterification keeps HDL particles in constant remodeling. Lipid exchange is mediated by cholesteryl ester transfer protein (CETP), mainly for cholesteryl esters and triglycerides and phospholipid transfer protein mainly for phospholipids [2]. Reverse cholesterol transportation begins with the binding of HDL ApoA1 to the ABCA1 protein complex and the transfer of unesterified cholesterol from the cells to HDL. The transfer of cholesterol to nascent HDL is facilitated by ABCA1, whereas ABCAG1 shuttles cholesterol to mature HDL particles. Subsequently, reverse cholesterol transportation is driven by the cholesterol esterification process in HDL particles that are taken up by the liver by SR-BI receptors or transferred to other lipoproteins that are also taken up by the liver for excretion in bile [2].

A reduction of CETP activity, not an increase, is associated with modestly impaired postprandial lipemia and increased HDL-Cholesterol in adult asymptomatic women

BackgroundThe relationship between CETP and postprandial hyperlipemia is still unclear. We verified the effects of varying activities of plasma CETP on postprandial lipemia and precocious atherosclerosis in asymptomatic adult women.MethodsTwenty-eight women, selected from a healthy population sample (n = 148) were classified according to three CETP levels, all statistically different: CETP deficiency (CETPd ≤ 4.5%, n = 8), high activity (CETPi ≥ 23.8, n = 6) and controls (CTL, CETP ≥ 4.6% and ≤ 23.7%, n = 14). After a 12 h fast they underwent an oral fat tolerance test (40 g of fat/m2 of body surface area) for 8 hours. TG, TG-rich-lipoproteins (TRL), cholesterol and TRL-TG measurements (AUC, AUIC, AR, RR and late peaks) and comparisons were performed on all time points. Lipases and phospholipids transfer protein (PLTP) were determined. Correlation between carotid atherosclerosis (c-IMT) and postprandial parameters was determined. CETP TaqIB and I405V and ApoE-ε3/ε2/ε4 polymorphisms were examined. To elucidate the regulation of increased lipemia in CETPd a multiple linear regression analysis was performed.ResultsIn the CETPi and CTL groups, CETP activity was respectively 9 and 5.3 higher compared to the CETPd group. Concentrations of all HDL fractions and ApoA-I were higher in the CETPd group and clearance was delayed, as demonstrated by modified lipemia parameters (AUC, AUIC, RR, AR and late peaks and meal response patterns). LPL or HL deficiencies were not observed. No genetic determinants of CETP deficiency or of postprandial lipemia were found. Correlations with c-IMT in the CETPd group indicated postprandial pro-atherogenic associations. In CETPd the regression multivariate analysis (model A) showed that CETP was largely and negatively predicted by VLDL-C lipemia (R2 = 92%) and much less by TG, LDL-C, ApoAI, phospholipids and non-HDL-C. CETP (model B) influenced mainly the increment in ApoB-100 containing lipoproteins (R2 = 85% negatively) and phospholipids (R2 = 13%), at the 6thh point.ConclusionThe moderate CETP deficiency phenotype included a paradoxically high HDL-C and its sub fractions (as earlier described), positive associations with c-IMT, a postprandial VLDL-C increment predicting negatively CETP activity and CETP activity regulating inversely the increment in ApoB100-containing lipoproteins. We hypothesize that the enrichment of TG content in triglyceride-rich ApoB-containing lipoproteins and in TG rich remnants increases lipoproteins' competition to active lipolysis sites,reducing their catabolism and resulting on postprandial lipemia with atherogenic consequences.

Thyroid hormone enhances the ability of serum to accept cellular cholesterol via the ABCA1 transporter

ObjectiveThe goal of this study was to examine the effects of thyroid hormone status on the ability of serum to accept cellular cholesterol. Methods and resultsSera from hypophysectomized rats treated ±T3 was used to evaluate the role of thyroid hormone on serum efflux capacity. 2D-DIGE analysis of serum proteins showed that T3 treated rats had increased ApoA-I, ApoA-IV and fetuin A levels with decreased Apo E levels. Microarray and real-time RT-PCR analysis of rat liver revealed large increases in ApoA-I, ApoA-IV, ABCG5, and ABCG8 in response to T3. J774 macrophages, BHK cells, and Fu5AH rat hepatoma cells were used to measure cholesterol efflux mediated by ABCA1, ABCG1 transporters or SR-BI. Sera from T3-treated rats stimulated efflux via ABCA1 but not by ABCG1 or SR-BI. Gel filtration chromatography revealed that T3 treatment caused a decrease in HDL particle size accompanied by higher levels of lipid-poor ApoA-I. ConclusionsThyroid hormone enhances the ability of serum to accept cellular cholesterol via the ABCA1 transporter. This effect is most likely attributable to increases in small HDL and lipid poor ApoA-I in response to T3.

Lipid parameters for measuring risk of cardiovascular disease

Besides measuring blood pressure and glucose levels, assessing the lipid spectrum is the method most commonly used to identify individuals at high risk of cardiovascular disease (CVD), as well as those who are likely to benefit most from lipid-lowering therapy. Although lowering LDL-cholesterol levels is the primary target of therapy in most clinical guidelines, accumulating evidence indicates that other lipoprotein-lipid measurements could provide a predictive value over and above that of LDL-cholesterol levels. For example, individuals treated with statins who achieve low LDL-cholesterol levels, but have high concentrations of either non-HDL cholesterol or apolipoprotein (apo) B, remain at increased cardiovascular risk. Similarly, individuals with low levels of either HDL cholesterol or apo A-I are also likely to experience cardiovascular events, despite having normal LDL-cholesterol levels. The residual cardiovascular risk, beyond that characterized by LDL-cholesterol levels alone, is exacerbated by physical inactivity and abdominal obesity, which are both increasingly prevalent risk factors for CVD. In this Review, we discuss the measurement of various lipoprotein-lipid parameters for the prediction of CVD risk, and their importance in identifying those patients who are likely to benefit from lipid-lowering therapy. The impact of recent studies on clinical guidelines is also considered.

Impact of serum amyloid A on high density lipoprotein composition and levels

Serum amyloid A (SAA) is an acute-phase protein mainly associated with HDL. To study the role of SAA in mediating changes in HDL composition and metabolism during inflammation, we generated mice in which the two major acute-phase SAA isoforms, SAA1.1 and SAA2.1, were deleted [SAA knockout (SAAKO) mice], and induced an acute phase to compare lipid and apolipoprotein parameters between wild-type (WT) and SAAKO mice. Our data indicate that SAA does not affect apolipoprotein A-I (apoA-I) levels or clearance under steady-state conditions. HDL and plasma triglyceride levels following lipopolysaccharide administration, as well as the decline in liver expression of apoA-I and apoA-II, did not differ between both groups of mice. The expected size increase of WT acute-phase HDL was surprisingly also seen in SAAKO acute-phase HDL despite the absence of SAA. HDLs from both mice showed increased phospholipid and unesterified cholesterol content during the acute phase. We therefore conclude that in the mouse, SAA does not impact HDL levels, apoA-I clearance, or HDL size during the acute phase and that the increased size of acute-phase HDL in mice is associated with an increased content of surface lipids, particularly phospholipids, and not surface proteins. These data need to be transferred to humans with caution due to differences in apoA-I structure and remodeling functions.

Apolipoprotein A-I Modulates Regulatory T Cells in Autoimmune LDLr−/−, ApoA-I−/− Mice

The immune system is complex, with multiple layers of regulation that serve to prevent the production of self-antigens. One layer of regulation involves regulatory T cells (Tregs) that play an essential role in maintaining peripheral self-tolerance. Patients with autoimmune diseases such as systemic lupus erythematosus and rheumatoid arthritis have decreased levels of HDL, suggesting that apoA-I concentrations may be important in preventing autoimmunity and the loss of self-tolerance. In published studies, hypercholesterolemic mice lacking HDL apoA-I or LDLr(-/-), apoA-I(-/-) (DKO), exhibit characteristics of autoimmunity in response to an atherogenic diet. This phenotype is characterized by enlarged cholesterol-enriched lymph nodes (LNs), as well as increased T cell activation, proliferation, and the production of autoantibodies in plasma. In this study, we investigated whether treatment of mice with lipid-free apoA-I could attenuate the autoimmune phenotype. To do this, DKO mice were first fed an atherogenic diet containing 0.1% cholesterol, 10% fat for 6 weeks, after which treatment with apoA-I was begun. Subcutaneous injections of 500 μg of lipid-free apoA-I was administered every 48 h during the treatment phase. These and control mice were maintained for an additional 6 weeks on the diet. At the end of the 12-week study, DKO mice showed decreased numbers of LN immune cells, whereas Tregs were proportionately increased. Accompanying this increase in Tregs was a decrease in the percentage of effector/effector memory T cells. Furthermore, lipid accumulation in LN and skin was reduced. These results suggest that treatment with apoA-I reduces inflammation in DKO mice by augmenting the effectiveness of the LN Treg response.

Increased leukocyte ABCA1 gene expression in post-menopausal women on hormone replacement therapy

Objective. The ATP binding cassette A1 (ABCA1) is a key participant in the reverse cholesterol process whereby mediates cholesterol efflux directly to HDL particles. The aim of this study was to investigate whether long-term treatment with conventional hormone replacement therapy (HRT) in post-menopausal women could affect their leukocytes ABCA1 expression. Changes in various serum lipids and lipoprotein fractions were also investigated.Material and Methods. A total of 60 non-obese normolipidaemic post-menopausal women treated with oral oestrogen together with progestin therapy for 3 months were selected. Leukocytes ABCA1 gene expression and serum lipid and lipoprotein concentrations were measured at the start and end of the HRT.Results. HRT led to significant increases in HDL cholesterol (P = 0.001) and apoA-I (P = 0.046) and significant decrease in apoB (P = 0.049) and LDL cholesterol (P = 0.022) when compared with the baseline levels. Analysis of leukocytes ABCA1 mRNA showed a significant increase in ABCA1 gene expression after HRT (P = 0.001). There was also a significant inverse association (r = −0.28, P = 0.03) between ABCA1 gene expression and log TG/HDL cholesterol changes related to HRT.Conclusion. The beneficial cardiovascular effects of HRT could be explained, at least in part, by increasing the ABCA1 gene expression.

Effects of weight loss, induced by gastric bypass surgery, on HDL remodeling in obese women

Plasma lipoproteins and glucose homeostasis were evaluated after marked weight loss before and over 12 months following Roux-en-Y gastric-bypass (RYGBP) surgery in 19 morbidly obese women. Standard lipids, remnant-lipoprotein cholesterol (RLP-C); HDL-triglyceride (TG); apolipoproteins (apo) A-I, A-II, E, and A-I-containing HDL subpopulations; lecithin-cholesterol acyltransferase (LCAT) and cholesteryl ester transfer protein (CETP) mass and activity; plasma glucose and insulin levels were measured before and at 1, 3, 6, and 12 months after GBP surgery. Baseline concentrations of TG, RLP-C, glucose, and insulin were significantly higher in obese than in normal-weight, age-matched women, whereas HDL cholesterol (HDL-C), apoA-I, apoA-II, alpha-1 and alpha-2 levels were significantly lower. Over 1 year, significant decreases of body mass index, glucose, insulin, TG, RLP-C, HDL-TG, and prebeta-1 levels were observed with significant increases of HDL-C and alpha-1 levels (all P < 0.05). Changes of fat mass were correlated with those of LDL cholesterol (P = 0.018) and LCAT mass (P = 0.011), but not with CETP mass (P = 0.265). Changes of fasting plasma glucose concentrations were inversely correlated with those of CETP mass (P = 0.005) and alpha-1 level (P = 0.004). Changes of fasting plasma insulin concentrations were positively correlated with those of LCAT mass (P = 0.043) and inversely with changes of alpha-1 (P = 0.03) and alpha-2 (P = 0.05) concentrations. These results demonstrate beneficial changes in HDL remodeling following substantial weight loss induced by RYGBP surgery and that these changes are associated with improvement of glucose homeostasis in these patients.

Antioxidant and anti‐inflammatory properties of apo A‐I milano

The apolipoprotein A‐I Milano (ApoA‐I Milano), the mutant form of ApoA‐I was found to reduce plaque size and composition in an experimental model and enhanced reverse cholesterol transport evident primarily in HDL. We hypothesize that ApoA1 Milano may also possess antioxidant and anti‐inflammatory properties and prevent atherosclerotic disease process. The mouse macrophage cell line J774A‐1 was incubated with apoA‐I Milano or HDL and exposed to oxLDL or TNF‐alpha. The oxidative stress was quantified by the dichlorodihydrofluorescein method, the DNA binding activity of NF‐kB was measured by ELISA and the interleukin‐6 gene expression by PCR. The oxidative stress induced by oxLDL was markedly reduced by apoA‐I Milano or HDL incubation. Similarly the increase in NF‐kB activity induced by oxLDL or TNF‐alpha was reduced by apoA‐I Milano and HDL. However, the induction of inflammatory cytokine IL‐6 gene by TNF‐alpha was markedly downregulated by apoA‐I Milano (P&lt;0.0001) than by HDL (P&lt;0.003). These results indicate apoA1 Milano may possess antioxidant and anti‐inflammatory properties. Our data suggest that apoA‐I Milano downregulates the oxidative and inflammatory response associated with atherosclerotic disease process. Furthermore this study indicates that apoA‐I Milano exhibited enhanced anti‐inflammatory mechanism compared to ApoA1/HDL.

Functional Assessment of HDL: Moving Beyond Static Measures for Risk Assessment

of cardiovascular disease events in 27,748 apparently healthy women [1]. After 11-years, fully-adjusted hazard ratios associated with lower levels of HDL cholesterol were 1.00, 1.18 (0.90–1.53), 1.32 (1.01–1.72), 1.50 (1.15–1.96), and 1.66 (1.26–2.19), Ptrend<0.001. Similar adjusted hazard ratios were observed for apo A-I quintiles: 1.00, 1.11 (0.88–1.41), 1.08 (0.83–1.39), 1.51 (1.18–1.92), and 1.42 (1.10–1.83), Ptrend=0.001. This study of apparently healthy women provides information concerning the additive risk associated with low levels of HDL cholesterol and apo A-I in multivariate models. Despite other studies that showed stronger associations between apo A-I levels and cardiovascular events, the hazard ratios for apo A-I and HDL cholesterol were not different.

Association of apolipoprotein M with high-density lipoprotein kinetics in overweight-obese men

ObjectiveThe aim of this study was to investigate associations between plasma apoM concentration and HDL apoA-I and apoA-II kinetics in 60 overweight-obese, insulin resistant men. MethodsPlasma apoM concentration was determined using a sandwich ELISA with two monoclonal antibodies (CV<5%). The kinetics of HDL apoA-I and apoA-II were measured using intravenous administration of D3-leucine, gas chromatography–mass spectrometry and multi-compartmental modeling. ResultsPlasma apoM was inversely associated with body mass index and positively associated with plasma total cholesterol, LDL cholesterol and HDL cholesterol (p<0.05). There were no associations between plasma apoM and plasma triglyceride, NEFA, insulin, glucose, HOMA score or adiponectin concentrations. Plasma apoM was positively associated with both apoA-I and apoA-II concentrations (r=0.406, p<0.01 and r=0.510, p<0.01, respectively) and negatively associated with HDL apoA-I and apoA-II fractional catabolic rate (FCR) (r=−0.291, p=0.03 and r=−0.291, p=0.026, respectively). No significant associations were observed between plasma apoM and HDL apoA-I and apoA-II production rate. In multivariate regression models, both plasma apoM and triglycerides were significant, independent predictors of HDL apoA-I FCR (adjusted R2=16%, p<0.01) and HDL apoA-II FCR (adjusted R2=14%, p<0.01). ConclusionApoM may be a significant, independent predictor of HDL apoA-I and apoA-II catabolism in overweight-obese, insulin resistant men.

Increased HDL Cholesterol and ApoA-I in Humans and Mice Treated With a Novel SR-BI Inhibitor

Increasing HDL levels is a potential strategy for the treatment of atherosclerosis. ITX5061, a molecule initially characterized as a p38 MAPK inhibitor, increased HDL-C levels by 20% in a human population of hypertriglyceridemic subjects with low HDL levels. ITX5061 also moderately increased apoA-I but did not affect VLDL/LDL cholesterol or plasma triglyceride concentrations. ITX5061 increased HDL-C in WT and human apoA-I transgenic mice, and kinetic experiments showed that ITX5061 decreased the fractional catabolic rate of HDL-CE and reduced its hepatic uptake. In transfected cells, ITX5061 inhibited SR-BI-dependent uptake of HDL-CE. Moreover, ITX5061 failed to increase HDL-C levels in SR-BI(-/-) mice. To assess effects on atherosclerosis, ITX5061 was given to atherogenic diet-fed Ldlr(+/-) mice with or without CETP expression for 18 weeks. In both the control and CETP-expressing groups, ITX5061-treated mice displayed reductions of early atherosclerotic lesions in the aortic arch -40%, P<0.05), and a nonsignificant trend to reduced lesion area in the proximal aorta. Our data indicate that ITX5061 increases HDL-C levels by inhibition of SR-BI activity. This suggests that pharmacological inhibition of SR-BI has the potential to raise HDL-C and apoA-I levels without adverse effects on VLDL/LDL cholesterol levels in humans.

Carbohydrate restriction favorably alters lipoprotein metabolism in Emirati subjects classified with the metabolic syndrome

Background and aims Carbohydrate restriction (CR) has been shown to improve dyslipidemias associated with metabolic syndrome (MetS). We evaluated the effects of CR on lipoprotein subfractions and apolipoproteins in Emirati adults classified with the MetS. Methods and results 39 subjects (15 men/24 women) were randomly allocated to a CR diet [20–25% energy from carbohydrate (CHO)] for 12 wk (CRD group) or a combination treatment consisting of CRD for 6 wk followed by the American Heart Association diet (50–55% CHO, AHA group) for an additional 6 wk. All subjects reduced body weight, LDL cholesterol and triglycerides ( P < 0.01). At baseline all subjects had low concentrations of medium VLDL and total HDL particles associated with the very low plasma triglycerides and HDL cholesterol in this population. After 12 wk, the large VLDL subfraction was decreased over time for subjects in the CRD group ( P < 0.01) while these changes were not observed in those subjects who changed to the AHA diet. The number of medium and small LDL particles decreased for all subjects rendering a less atherogenic lipoprotein profile. In agreement with these results, a significant decrease in apolipoprotein (apo) B was observed ( P < 0.01). The medium HDL subfraction and apo A-II, which can be considered pro-atherogenic, were also decreased over time in the CRD group only. Conclusions These results suggest that weight loss favorably affects lipoprotein metabolism and that the CRD had a better effect on atherogenic VLDL and HDL than the low fat diet recommended by AHA.