High-density Lipoprotein-mediated Cholesterol Efflux Research Articles

ABCG1 is Expressed in an LXR-Independent Manner in Patients with Type 2 Diabetes Mellitus.

Patients with type 2 diabetes mellitus have a high cardiovascular risk due, in part, to abnormalities of high-density lipoprotein mediated cholesterol efflux. The ATP-binding cassette A1 and G1 play a pivotal role in the regulation of cholesterol efflux. However, the regulation of these transporters in type 2 diabetes mellitus remains obscure. This study aimed to investigate the expression of ATP-binding cassette A1 and G1 and their regulation by Liver X receptors in monocyte-derived macrophages in type 2 diabetes mellitus, and to determine whether the alteration of these transporters might affect cholesterol efflux from macrophages. Blood was collected from type 2 diabetic patients and healthy controls. Peripheral monocytes were differentiated into macrophages. Quantitative real-time PCR, western blots, and cholesterol efflux assays were performed. The Liver X receptor and Liver X receptor element complex in the ATP-binding cassette G1 gene promoter were detected by electrophoretic mobility supershift assay. Macrophage ATP-binding cassette G1 expression and high density lipoproteininduced cholesterol efflux were significantly reduced in type 2 diabetic patients. However, the mRNA expression of ATP-binding cassette G1 in type 2 diabetic patients was not inhibited by Liver X receptor siRNA and the Liver X receptor- Liver X receptor element complexes remain unchanged similarly. The study suggested that the expression of ATP-binding cassette G1 and high density lipoprotein-induced cholesterol efflux in macrophages were reduced in type 2 diabetes mellitus. Impairment of cholesterol efflux and ATP-binding cassette G1 gene expression in type 2 diabetes mellitus might be regulated by a Liver X receptorindependent pathway.

Impact of Coffee Consumption on Cardiovascular Health.

Background: Coffee is a widely available beverage that is enjoyed by individuals of many cultures. The publication of new studies prompts a review of the clinical updates regarding the association between coffee consumption and cardiovascular disease. Methods: We present a narrative review of the literature related to coffee consumption and cardiovascular disease. Results: Recent (2000-2021) studies have shown that regular coffee consumption is associated with a decreased risk of developing hypertension, heart failure, and atrial fibrillation. However, results are inconsistent with regard to coffee consumption and risk of developing coronary heart disease. Most studies show a J-shaped association, wherein moderate coffee consumption resulted in decreased risk of coronary heart disease and heavy coffee consumption resulted in increased risk. In addition, boiled or unfiltered coffee is more atherogenic than filtered coffee because of its rich diterpene content that inhibits bile acid synthesis and ultimately affects lipid metabolism. On the other hand, filtered coffee, which is essentially devoid of the aforementioned compounds, exerts antiatherogenic properties by increasing high-density lipoprotein-mediated cholesterol efflux from macrophages through the influence of plasma phenolic acid. As such, cholesterol levels are principally influenced by the manner of coffee preparation (boiled vs filtered). Conclusion: Our findings suggest that moderate coffee consumption leads to a decrease in all-cause and cardiovascular-related mortality, hypertension, cholesterol, heart failure, and atrial fibrillation. However, no conclusive relationship between coffee and coronary heart disease risk has been consistently identified.

Coenzyme Q10 supplementation improves cholesterol efflux capacity and antiinflammatory properties of high-density lipoprotein in Chinese adults with dyslipidemia

ObjectivesCoenzyme Q10 (CoQ10) had shown promising effects in improving the lipid and glycemic profile in dyslipidemic individuals in our previous work, but little is known about how it affects high-density lipoprotein (HDL) function in patients with dyslipidemia. The aim of this study was to explore the effects of CoQ10 supplementation on HDL function in people with dyslipidemia. MethodsA 24-wk, randomized, double-blind, placebo-controlled trial was conducted in 101 people with dyslipidemia. All patients were randomized into the CoQ10 group (120 mg/d, n = 51) or the placebo group (n = 50). High-density lipoprotein–mediated cholesterol efflux capacity (CEC), HDL inflammatory index (HII), and HDL intrinsic oxidation were measured at baseline, 12 wk, and 24 wk. ResultsCoQ10 supplementation for 24 wk significantly improved HDL-mediated CEC (mean change, 1.21±2.44 versus –0.12±2.94; P = 0.014) and reduced HII (mean change, –0.32±0.58 versus –0.05±0.49, P = 0.014) compared with placebo. However, there was no significant difference in the effect of CoQ10 on HDL intrinsic oxidation between the two groups after 24 wk (P = 0.290). A positive correlation was found between the changes in CEC and HDL cholesterol in the CoQ10 group (r, 0.30; P = 0.032). Furthermore, we also found that the improved HDL functions were more obvious in elderly, female, or non-obese individuals, which indicated a specific population that benefits most from CoQ10 intervention. ConclusionsThis study suggested that supplementation of CoQ10 for 24 wk can significantly improve HDL-mediated CEC and antiinflammatory function of HDL in patients with dyslipidemia.

Effects of Cardiac Rehabilitation on High-Density Lipoprotein-mediated Cholesterol Efflux Capacity and Paraoxonase-1 Activity in Patients with Acute Coronary Syndrome.

Aims: We evaluated whether exercised-based cardiac rehabilitation (CR) can ameliorate the HDL function, i.e., cholesterol efflux capacity (CEC) and paraoxonase-1 activity in patients with acute coronary syndrome (ACS).Methods: This study is a retrospective analysis of stored serum from patients with ACS following successful percutaneous coronary intervention. The CEC, measured by a cell-based ex vivo assay using apolipoprotein B-depleted serum and 3H-cholesterol labeled macrophages and arylesterase activity (AREA) at the onset or early phase of ACS, and the follow-up periods were compared between 69 patients who completed the five-month outpatient CR program (CR group) and 15 patients who did not participate and/or dropped out from CR program (non-CR group).Results: Apolipoprotein A-I (apoA-I) and CEC significantly increased by 4.0% and 9.4%, respectively, in the CR group, whereas HDL-cholesterol and AREA were not changed during the follow-up periods in both groups. Among CR patients, the CEC significantly increased, irrespective of the different statin treatment, while HDL-cholesterol and apoA-I significantly increased in patients treated with rosuvastatin or pitavastatin. Although CEC and AREA were significantly correlated each other, there is a discordance between CEC and AREA for their correlations with other biomarkers. Both CEC and AREA were significantly correlated with apoA-I rather than HDL-cholesterol. Changes in CEC and those in AREA were significantly correlated with those in apoA-I (rho = 0.328, p = 0.002, and rho = 0.428, p < 0.0001, respectively) greater than those in HDL-cholesterol (rho = 0.312, p = 0.0042, and rho = 0.343, p = 0.003, respectively).Conclusions: CR can improve HDL function, and it is beneficial for secondary prevention.

Beneficial Effects of Exercise-Based Cardiac Rehabilitation on High-Density Lipoprotein-Mediated Cholesterol Efflux Capacity in Patients with Acute Coronary Syndrome

Recent studies reported that low high-density lipoprotein (HDL)-mediated cholesterol efflux capacity rather than low HDL cholesterol (HDL-C) is strongly associated with the increased risk for coronary artery disease. It remains unclear whether exercised-based cardiac rehabilitation (CR) can increase HDL cholesterol efflux capacity. This study is a retrospective analysis of stored serum from patients with acute coronary syndrome (ACS) who participated in outpatient CR program following successful percutaneous coronary intervention. We employed a cell-based cholesterol efflux system including the incubation of (3)H-cholesterol labeled macrophages with apolipoprotein B-depleted serum at the onset or early phase of ACS and at 6-month follow-up periods in 57 male and 11 female patients with ACS. Cardiopulmonary exercise tests were performed at the beginning and end of CR program. Fifty-seven patients completed the CR program. Compared with patients who dropped out from CR program (non-CR group), CR participants showed marked amelioration in serum lipid levels, increased efflux capacity, and improved exercise capacity. Spearman's rank correlation coefficient analysis revealed that the percent increases of efflux capacity were significantly associated with the percent increases in HDL-C (ρ=0.598, p＜0.0001) and apolipoprotein A1 (ρ=0.508, p＜0.0001), whereas no association between increases in efflux capacity and increases in cardiopulmonary fitness was observed. Increases in cholesterol efflux capacity were not seen in patients who continued smoking and those who did not achieve all risk factor targets and higher exercise tolerance. CR can markedly increase both HDL-C and HDL cholesterol efflux capacity. These results suggest that CR is a very useful therapy for reverse cholesterol transport and secondary prevention.

HIV inhibits endothelial reverse cholesterol transport through impacting subcellular Caveolin-1 trafficking.

BackgroundHuman immunodeficiency virus (HIV) infection leads to decreased reverse cholesterol transport (RCT) in macrophages, and Nef mediated down-regulation and redistribution of ATP-binding cassette transporter A1 (ABCA1) are identified as key factors for this effect. This may partially explain the increased risk of atherosclerosis in HIV infected individuals. Since endothelial dysfunction is key in the initial stages of atherosclerosis, we sought to determine whether RCT was affected in human aortic endothelial cells (HAECs).ResultsWe found that apoA-I does not significantly stimulate cholesterol efflux in HAECs while cholesterol efflux to high-density lipoprotein (HDL) was dramatically reduced in HAECs co-cultured with HIV infected cells. Studies with wild type and Nef defective HIV revealed no significant differences suggesting that multiple factors are working perhaps in concert with Nef to affect cholesterol efflux to HDL from HAECs. Interestingly, treating HAECs with recombinant Nef showed similar effect in HDL mediated cholesterol efflux as observed in HAECs co-cultured with HIV infected cells. Using a detergent-free based subcellular fractionation approach, we demonstrated that exposure of HAECs to HIV infected cells or Nef alone disrupts caveolin 1 (Cav-1) subcellular trafficking upon HDL stimulation. Moreover, Nef significantly enhanced tyrosine 14 phosphorylation of Cav-1 which may have an impact on recycling of Cav-1 and caveolae.ConclusionThese results suggest that HIV interferes with cholesterol efflux by HDL in HAECs through the disruption of Cav-1s’ cellular distribution and that multiple factors are involved, possibly including Nef, for the inhibition of HDL mediated cholesterol efflux and alteration of cellular distribution of Cav-1.Electronic supplementary materialThe online version of this article (doi:10.1186/s12977-015-0188-y) contains supplementary material, which is available to authorized users.

Not All “BAD” Cholesterol Carriers Are Necessarily Bad and Not All “GOOD” Cholesterol Carriers Are as Good as Can Be: Plasma Delipidation, a Non-Pharmacological Treatment for Atherosclerosis

More than four decades ago it was established that an elevated low-density lipoprotein-cholesterol level was a risk for developing coronary artery disease. For the last two decades, statins have been the cornerstone of reducing low-density lipoprotein-cholesterol, but despite significant clinical efficacy in the majority of patients, a large number of patients suffer from side effects and cannot tolerate the required statin dose to reach their recommended low-density lipoprotein-cholesterol goals. Preliminary clinical studies indicate that monoclonal antibodies to PCSK9 appear to be highly efficacious in lowering low-density lipoprotein-cholesterol with a favourable adverse event profile. However, further longer-term clinical studies are required to determine their safety. From the early-proposed concept for high-density lipoprotein-mediated cholesterol efflux for the treatment of coronary artery disease, the concentration of the cholesterol content in high-density lipoprotein particles has been considered a surrogate measurement for the efficacy of the reverse cholesterol transport process. However, unlike the beneficial effects of the statins and monoclonal antibodies to PCSK9 in reducing low-density lipoprotein-cholesterol, no significant advances have been made to increase the levels of high-density lipoprotein-cholesterol. Here it is shown that by a non-pharmacological plasma delipidation means, the atherogenic low-density lipoproteins can be converted to anti-atherogenic particles and that the high-density lipoproteins are converted to particles with extreme high affinity to cause rapid regression of atherosclerosis.

In vitro effects of exogenous carbon monoxide on oxidative stress and lipid metabolism in macrophages.

Carbon monoxide (CO) is a major constituent of traffic-related air pollution and is also produced endogenously under conditions of oxygen-mediated stress. It has been shown to affect both oxidative stress and inflammation. However, its role in lipid metabolism has been neglected. Using short exposure times, the effect of CO on J774A.1 macrophage atherogenic functions was investigated up to 16 h after exposure. Exposure of macrophages was found to be pro-atherogenic as it significantly increased triglyceride mass, up to 60%, and decreased high-density lipoprotein-mediated cholesterol efflux, up to 27%. In contrast, paraoxonase 2 lactonase activity was increased, up to 65%, and cellular oxidative stress was attenuated by 29%, compared with the control cells. The above results on lipid metabolism may lead to arterial macrophage foam cell formation, the hallmark of early atherogenesis.

High-density lipoprotein-mediated cholesterol efflux capacity is improved by treatment with antiretroviral therapy in acute human immunodeficiency virus infection.

Background Individuals infected with human immunodeficiency virus (HIV) have decreased high-density lipoprotein (HDL)-cholesterol and increased cardiovascular disease (CVD). Reverse cholesterol transport from macrophages may be inhibited by HIV and contribute to increased CVD. Human studies have not investigated longitudinal effects of HIV and antiretroviral therapy (ART) on cholesterol efflux.Methods Subjects with acute HIV infection were randomized to ART or not. Cholesterol efflux capacity was determined ex vivo after exposure of murine macrophages to apolipoprotein B-depleted patient sera obtained at baseline and after 12 weeks.Results After 12 weeks, HIV RNA decreased most in subjects randomized to ART. Available data on cholesterol demonstrated that efflux capacity from Abca1+/+ macrophages was increased most by sera obtained from ART-treated subjects (20.5% ± 5.0% to 24.3 % ± 6.9%, baseline to 12 weeks, P = .007; ART group [n = 6] vs 18.0 % ± 3.9% to 19.1 % ± 2.9%, baseline to 12 weeks, P = .30; untreated group [n = 6] [P = .04 ART vs untreated group]). Change in HIV RNA was negatively associated with change in Abca1+/+ macrophage cholesterol efflux (r = − 0.62, P = .03), and this finding remained significant (P = .03) after controlling for changes in HDL-cholesterol, CD4+ cells, and markers of monocyte or macrophage activation.Conclusions In subjects acutely infected with HIV, ATP-binding cassette transporter A1-mediated cholesterol efflux was stimulated to a greater degree over time by apolipoprotein B-depleted serum from subjects randomized to ART. The improvement in cholesterol efflux capacity is independently related to reduction in viral load.

Fibroblast growth factor 21 enhances cholesterol efflux in THP-1 macrophage-derived foam cells.

Fibroblast growth factor 21 (FGF21) is a novel metabolic regulator. The present study aimed to investigate the effect of FGF21 on cholesterol efflux and the expression of ATP binding cassette (ABC) A1 and G1 in human THP-1 macrophage-derived foam cells. Furthermore, the present study aimed to investigate the role of the liver X receptor (LXR) α in this process. A model of oxidized low-density lipoprotein-induced foam cells from human THP-1 cells was established. The effect of FGF21 on cholesterol efflux was analyzed using a liquid scintillation counter. The expression of ABCA1 and ABCG1 was determined using quantitative polymerase chain reaction and western blot analyses. FGF21 was found to enhance apolipoprotein A1- and high-density lipoprotein-mediated cholesterol efflux. FGF21 was also observed to increase the mRNA and protein expression of ABCA1 and ABCG1. Furthermore, LXRα-short interfering RNA attenuated the stimulatory effects induced by FGF21. These findings suggest that FGF21 may have a protective effect against atherosclerosis by enhancing cholesterol efflux through the induction of LXRα-dependent ABCA1 and ABCG1 expression.

The Measurement of High-Density Lipoprotein Mediated Cholesterol Efflux from Macrophage Cells by Liquid Chromatography Tandem Mass Spectrometry

Background: Studies have shown a negative association between macrophage cholesterol efflux and atherosclerotic cardiovascular diseases (CVD). However, the current methods for measuring cholesterol efflux require a radioactive tracer and involve a variety of cell treatments, making the measurement of macrophage cholesterol efflux impractical for use in clinical laboratories. In this study, we developed a non-radioactive and precise LC/MS/MS method for the measurement of high-density lipoprotein (HDL) mediated cholesterol efflux from J774 macrophages. Methods: J774 cells were seeded on 12-well plates at a density of 1.5×10⁵ cells/ml in H-DMEM medium, and when the cells were approximately 80% confluent, they were incubated with H-DMEM medium containing 2% FBS, 0.5 μg/ml ACAT inhibitor Sandoz 58-035, and 20 μg/ml [3,4-¹³C]cholesterol for 6 h. After washing and equilibrating the cells, HDL samples were added at a final concentration of 7% and incubated for 8 h. The cells were lysed, and [3,4-¹³C]cholesterol and cholesterol were measured by LC/MS/MS. Cholesterol efflux was expressed as the percent decrease of cell [3,4-¹³C]cholesterol mass during the incubation. Results: When incubated with [3,4-¹³C]cholesterol enriched J774 cells, HDL mediated higher cell cholesterol efflux than influx compared to serum and isolated LDL; therefore, HDL was used as the extracellular acceptor. The results from healthy volunteers showed that the rate of cholesterol efflux was negatively correlated with weight, BMI, blood pressure, and FER_HDL and positively correlated with HDL-C, HDL2-C, and apoAI levels. Conclusions: A LC/MS/MS method for the measurement of HDL mediated cholesterol efflux from macrophage cells has been established. This method is non-radioactive, precise and reliable and is potentially useful for the assessment of HDL function and cardiovascular disease risks.

Experimental Models for the Investigation of High-Density Lipoprotein–Mediated Cholesterol Efflux

Reduction of low-density lipoprotein cholesterol by statin therapy has only modestly decreased coronary heart disease (CHD)-associated mortality in developed countries, which has prompted the search for alternative therapeutic strategies for CHD. Epidemiologic and interventional studies have clearly established an inverse association between plasma levels of high-density lipoprotein (HDL) cholesterol and incidence of atherosclerosis. The atheroprotective benefits of HDL are not only dependent on HDL concentrations (quantity), but also on HDL function (quality). Therefore, several techniques have been recently developed to assess the different properties of HDL. Because reverse cholesterol transport (RCT) is considered a key player in the beneficial action of HDL, this review focuses on the different methods used to evaluate cholesterol efflux. Measuring the in vivo function of HDL could be of significant importance for both the clinical evaluation of an individual patient and to evaluate the effectiveness of different RCT-enhancing therapeutic approaches.

Polyphenols and Cholesterol Efflux

Despite strong evidence for an inverse association between high-density lipoprotein cholesterol (HDL-C) levels and cardiovascular risk,1 successful therapeutic strategies to target HDL have remained elusive. A recent Phase III clinical trial failed to show clinical benefit with the cholesteryl ester transfer protein inhibitor torcetrapib despite markedly increased HDL-C levels.2,3 This outcome reinforced a growing consensus that measurement of HDL-C alone may be an incomplete surrogate for the in vivo functionality of HDL and the clinical efficacy of targeting HDL. The careful mechanistic assessment of HDL function has thus emerged as a potential way forward.4 Macrophage reverse cholesterol transport (RCT), the process by which cholesterol is transported from macrophage “foam” cells to the liver for ultimate fecal excretion, has been postulated to play a major role in HDL-mediated atheroprotection.5 Indeed, quantitative measures of macrophage RCT are more strongly associated with atherosclerosis than plasma HDL-C concentrations in mice.6 The first critical step of macrophage RCT involves efflux of cellular cholesterol to circulating HDL particles. Research in recent years has documented a specific role for the macrophage transporters ATP-binding cassette subfamilies A1 and G1 (ABCA1 and ABCG1) in cholesterol efflux (see the Figure). These findings have stimulated efforts to target the macrophage at the cellular level as a means of enhancing overall RCT. For example, pharmacological agonism of the liver X receptor (LXR) upregulates both ABCA1 and ABCG1 expression,7,8 promotes macrophage cholesterol efflux ex vivo and RCT in vivo, …

Coffee Consumption Enhances High-Density Lipoprotein-Mediated Cholesterol Efflux in Macrophages

Association of habitual coffee consumption with coronary heart disease morbidity and mortality has not been established. We hypothesized that coffee may enhance reverse cholesterol transport (RCT) as the antiatherogenic properties of high-density lipoprotein (HDL). This study was to investigate whether the phenolic acids of coffee and coffee regulates RCT from macrophages in vitro, ex vivo and in vivo. Caffeic acid and ferulic acid, the major phenolic acids of coffee, enhanced cholesterol efflux from THP-1 macrophages mediated by HDL, but not apoA-I. Furthermore, these phenolic acids increased both the mRNA and protein levels of ATP-binding cassette transporter (ABC)G1 and scavenger receptor class B type I (SR-BI), but not ABCA1. Eight healthy volunteers were recruited for the ex vivo study, and blood samples were taken before and 30 minutes after consumption of coffee or water in a crossover study. The mRNA as well as protein levels of ABCG1, SR-BI, and cholesterol efflux by HDL were increased in the macrophages differentiated under autologous sera obtained after coffee consumption compared to baseline sera. Finally, effects of coffee and phenolic acid on in vivo RCT were assessed by intraperitoneally injecting [(3)H]cholesterol-labeled acetyl low-density lipoprotein-loaded RAW264.7 cells into mice, then monitoring appearance of (3)H tracer in plasma, liver, and feces. Supporting in vitro and ex vivo data, ferulic acid was found to significantly increase the levels of (3)H tracer in feces. Coffee intake might have an antiatherogenic property by increasing ABCG1 and SR-BI expression and enhancing HDL-mediated cholesterol efflux from the macrophages via its plasma phenolic acids.

The role of dysfunctional HDL in atherosclerosis

This review focuses on HDL function in modulating LDL oxidation and LDL-induced inflammation. Dysfunctional HDL has been identified in animal models and humans with chronic inflammatory diseases including atherosclerosis. The loss of antiinflammatory function correlated with a loss of function in reverse cholesterol transport. In animal models and perhaps in humans, dysfunctional HDL can be improved by apoA-I mimetic peptides that bind oxidized lipids with high affinity.

An apolipoprotein A-I mimetic dose-dependently increases the formation of preβ1 HDL in human plasma

Prebeta1 HDL is the initial plasma acceptor of cell-derived cholesterol in reverse cholesterol transport. Recently, small amphipathic peptides composed of D-amino acids have been shown to mimic apolipoprotein A-I (apoA-I) as a precursor for HDL formation. ApoA-I mimetic peptides have been proposed to stimulate the formation of prebeta1 HDL and increase reverse cholesterol transport in apoE-null mice. The existence of a monoclonal antibody (MAb 55201) and a corresponding ELISA method that is selective for the detection of the prebeta(1) subclass of HDL provides a means of establishing a correlation between apoA-I mimetic dose and prebeta1 HDL formation in human plasma. Using this prebeta1 HDL ELISA, we demonstrate marked apoA-I mimetic dose-dependent prebeta1 HDL formation in human plasma. These results correlated with increases in band density of the plasma prebeta1 HDL, when observed by Western blotting, as a function of increased apoA-I mimetic concentration. Increased prebeta1 HDL formation was observed after as little as 1 min and was maximal within 1 h. Together, these data suggest that a high-throughput prebeta1 HDL ELISA provides a way to quantitatively measure a key component of the reverse cholesterol transport pathway in human plasma, thus providing a possible method for the identification of apoA-I mimetic molecules.

Lipoprotein inflammatory properties and serum amyloid A levels but not cholesterol levels predict lesion area in cholesterol-fed rabbits

Rabbits on a 1% cholesterol diet received injections of vehicle with or without D-4F or L-4F. After 1 month, the percent of aorta with atherosclerotic lesions was 24 +/- 15% (vehicle), 10 +/- 6% (D-4F) (P < 0.01 vs. vehicle), and 13 +/- 9% (L-4F) (P < 0.05 vs. vehicle). Inflammatory indexes for HDL and LDL were determined by measuring monocyte chemotactic activity after adding rabbit lipoproteins to human endothelial cells. HDL-inflammatory index (HII) and LDL-inflammatory index (LII), respectively, were 1.39 +/- 0.24; 1.35 +/- 0.29 (vehicle), 0.67 +/- 0.26; 0.63 +/- 0.38 (D-4F) (P < 0.001 vs. vehicle), and 0.67 +/- 0.2; 0.68 +/- 0.32 (L-4F) (P < 0.01 vs. vehicle). Serum amyloid A (SAA) levels were 95 +/- 39, 8 +/- 22, and 7 +/- 19 mug/ml, respectively, for vehicle, D-4F, and L-4F (P < 0.001 vs. vehicle). There was no correlation between lesion area and total plasma or HDL-cholesterol levels. In contrast, there was a positive correlation with HII, LII, and SAA (P = 0.002, P = 0.0026, P = 0.0079, respectively). HII correlated closely with SAA levels (r = 0.6616; r(2) = 0.4377, P < 0.0001). Thus, HII, LII, and SAA are better predictors of lesion area than are total plasma or HDL-cholesterol levels in cholesterol-fed rabbits.

Molecular interaction between caveolin-1 and ABCA1 on high-density lipoprotein-mediated cholesterol efflux in aortic endothelial cells

Caveolin-1 and ATP-binding cassette transporter A1 (ABCA1) are proteins that are involved in cellular cholesterol efflux. In this study, we analyzed the relationships between caveolin-1 and ABCA1 on high-density lipoprotein (HDL)-mediated cholesterol efflux in rat aortic endothelial cells. Overexpression of caveolin-1 by transfection with caveolin-1 cDNA in aortic endothelial cells up-regulated ABCA1 expression and enhanced cholesterol efflux. Suppression of caveolin-1 by siRNA decreased ABCA1 expression and reduced cholesterol efflux. The number of caveolae increased after transfection with caveolin-1 into cells. Immunoprecipitation assays revealed a molecular interaction between caveolin-1 and ABCA1 in the plasma membrane and in the cytoplasm after HDL incubation. Immunoelectron microscopy demonstrated that caveolin-1 colocalized with ABCA1 in the caveolae and in the cytoplasmic vesicles; it was also found that caveolin-1 and ABCA1 colocalized with cellular cholesterol by immunofluorescence microscopy. Blocking of intracellular lipid transport by inhibitors disrupted the interaction between caveolin-1 and ABCA1 and reduced cholesterol to methyl-beta-cyclodextrin and HDL. The molecular interaction between caveolin-1 and ABCA1 is associated with the HDL-mediated cholesterol efflux pathway in aortic endothelial cells.

Familial massive tendon xanthomatosis with decreased high-density lipoprotein–mediated cholesterol efflux

We experienced a family with novel massive tendon xanthomatosis which can be excluded from known disease causing xanthomatosis. The proband was a 58-year-old man who had necrosis in his massive Achilles tendon xanthoma. Three of 5 brothers including him and his nephew had the same clinical phenotype. The systemic tendon xanthomatosis became apparent around 30 years of their age. The proband and his elder brother had mild elevations of serum total cholesterol level (251 and 228 mg/dL, respectively). The low-density lipoprotein receptor activity of the proband's lymphocytes was normal. Neither plant sterol nor cholestanol level was increased in the proband's plasma. Magnetic resonance image of the proband's Achilles tendon demonstrated a massive expansion of the soft tissue with salami sausage–like appearance in his heels (50 mm in thickness). The physiological function of macrophages (M Φ) from the patients was investigated to clarify the mechanism for the formation of xanthomatosis. There was no significant difference in the uptake of oxidized low-density lipoprotein between the proband's M Φ and the control. High-density lipoprotein 3–mediated cholesterol efflux from the patients' M Φ (n = 2) was significantly reduced compared with the controls (n = 3), whereas there was no difference in apolipoprotein (apo) A-I–mediated cholesterol efflux between the patients' M Φ and the controls. Furthermore, there was no reduction of the messenger RNA levels of ATP-binding cassette transporter 1 (ABCA1), which is involved in apo A-I–mediated cholesterol efflux, in the proband's M Φ compared with the control. The present study demonstrates that the mechanism for the formation of novel familial massive tendon xanthomatosis may be, at least in part, associated with decreased high-density lipoprotein 3, but not free apo A-I–mediated cholesterol efflux from M Φ in vivo.

1047-181 High-density lipoprotein-mediated cholesterol efflux from cells is a strong independent predictor of cardiovascular risk

1047-181 High-density lipoprotein-mediated cholesterol efflux from cells is a strong independent predictor of cardiovascular risk