Cholesterol efflux from Fu5AH hepatoma cells induced by plasma of subjects with or without coronary artery disease and non-insulin-dependent diabetes: importance of LpA-I:A-II particles and phospholipid transfer protein

High-Density Lipoprotein Alterations in Type 2 Diabetes and Obesity

Alterations affecting high-density lipoproteins (HDLs) are one of the various abnormalities observed in dyslipidemia in type 2 diabetes mellitus (T2DM) and obesity. Kinetic studies have demonstrated that the catabolism of HDL particles is accelerated. Both the size and the lipidome and proteome of HDL particles are significantly modified, which likely contributes to some of the functional defects of HDLs. Studies on cholesterol efflux capacity have yielded heterogeneous results, ranging from a defect to an improvement. Several studies indicate that HDLs are less able to inhibit the nuclear factor kappa-B (NF-κB) proinflammatory pathway, and subsequently, the adhesion of monocytes on endothelium and their recruitment into the subendothelial space. In addition, the antioxidative function of HDL particles is diminished, thus facilitating the deleterious effects of oxidized low-density lipoproteins on vasculature. Lastly, the HDL-induced activation of endothelial nitric oxide synthase is less effective in T2DM and metabolic syndrome, contributing to several HDL functional defects, such as an impaired capacity to promote vasodilatation and endothelium repair, and difficulty counteracting the production of reactive oxygen species and inflammation.

High levels of oxidized fatty acids in HDL impair the antioxidant function of HDL in patients with diabetes

AIMS

Previous studies demonstrate that the antioxidant functions of high-density lipoprotein (HDL) are impaired in diabetic patients. The composition of HDL plays an important role in maintaining the normal functionality of HDL. In this study, we compared the levels of oxidized fatty acids in HDL from diabetic subjects and non-diabetic healthy controls, aiming to investigate the role of oxidized fatty acids in the antioxidant property of HDL.

METHODS

HDL was isolated from healthy subjects (n=6) and patients with diabetes (n=6, hemoglobin A1c ≥ 9%, fasting glucose ≥ 7 mmol/L) using a dextran sulfate precipitation method. Cholesterol efflux capacity mediated by HDL was measured on THP-1 derived macrophages. The antioxidant capacity of HDL was evaluated with dichlorofluorescein-based cellular assay in human aortic endothelial cells. Oxidized fatty acids in HDL were determined by liquid chromatography-tandem mass spectrometry. The correlations between the levels of oxidized fatty acids in HDL and the endothelial oxidant index in cells treated with HDLs were analyzed through Pearson's correlation analyses, and the effects of oxidized fatty acids on the antioxidant function of HDL were verified in vitro.

RESULTS

The cholesterol efflux capacity of HDL and the circulating HDL-cholesterol were similar in diabetic patients and healthy controls, whereas the antioxidant capacity of HDL was significantly decreased in diabetic patients. There were higher levels of oxidized fatty acids in HDL isolated from diabetic patients, which were strongly positively correlated with the oxidant index of cells treated with HDLs. The addition of a mixture of oxidized fatty acids significantly disturbed the antioxidant activity of HDL from healthy controls, while the apolipoprotein A-I mimetic peptide D-4F could restore the antioxidant function of HDL from diabetic patients.

CONCLUSION

HDL from diabetic patients displayed substantially impaired antioxidant activity compared to HDL from healthy subjects, which is highly correlated with the increased oxidized fatty acids levels in HDL.

Association between cholesterol efflux capacity and peripheral artery disease in coronary heart disease patients with and without type 2 diabetes: from the CORDIOPREV study

Background

Peripheral artery disease (PAD) is recognized as a significant predictor of mortality and adverse cardiovascular outcomes in patients with coronary heart disease (CHD). In fact, coexisting PAD and CHD is strongly associated with a greater coronary event recurrence compared with either one of them alone. High-density lipoprotein (HDL)-mediated cholesterol efflux capacity (CEC) is found to be inversely associated with an increased risk of incident CHD. However, this association is not established in patients with PAD in the context of secondary prevention. In this sense, our main aim was to evaluate the association between CEC and PAD in patients with CHD and whether the concurrent presence of PAD and T2DM influences this association.

Methods

CHD patients (n = 1002) from the CORDIOPREV study were classified according to the presence or absence of PAD (ankle-brachial index, ABI ≤ 0.9 and ABI > 0.9 and < 1.4, respectively) and T2DM status. CEC was quantified by incubation of cholesterol-loaded THP-1 cells with the participants' apoB-depleted plasma was performed.

Results

The presence of PAD determined low CEC in non-T2DM and newly-diagnosed T2DM patients. Coexisting PAD and newly-diagnosed T2DM provided and additive effect providing an impaired CEC compared to non-T2DM patients with PAD. In established T2DM patients, the presence of PAD did not determine differences in CEC, compared to those without PAD, which may be restored by glucose-lowering treatment.

Conclusions

Our findings suggest an inverse relationship between CEC and PAD in CHD patients. These results support the importance of identifying underlying mechanisms of PAD, in the context of secondary prevention, that provide potential therapeutic targets, that is the case of CEC, and establishing strategies to prevent or reduce the high risk of cardiovascular events of these patients.

Trial registrationhttps://clinicaltrials.gov/ct2/show/NCT00924937. Unique Identifier: NCT00924937

HDL and Reverse Cholesterol Transport

Cardiovascular disease, with atherosclerosis as the major underlying factor, remains the leading cause of death worldwide. It is well established that cholesterol ester-enriched foam cells are the hallmark of atherosclerotic plaques. Multiple lines of evidence support that enhancing foam cell cholesterol efflux by HDL (high-density lipoprotein) particles, the first step of reverse cholesterol transport (RCT), is a promising antiatherogenic strategy. Yet, excitement towards the therapeutic potential of manipulating RCT for the treatment of cardiovascular disease has faded because of the lack of the association between cardiovascular disease risk and what was typically measured in intervention trials, namely HDL cholesterol, which has an inconsistent relationship to HDL function and RCT. In this review, we will summarize some of the potential reasons for this inconsistency, update the mechanisms of RCT, and highlight conditions in which impaired HDL function or RCT contributes to vascular disease. On balance, the evidence still argues for further research to better understand how HDL functionality contributes to RCT to develop prevention and treatment strategies to reduce the risk of cardiovascular disease.

Impaired Delivery of Cholesterol Effluxed From Macrophages to Hepatocytes by Serum From CKD Patients May Underlie Increased Cardiovascular Disease Risk

Introduction

Although chronic kidney disease (CKD) is associated with increased risk for coronary artery disease (CAD), the underlying mechanisms are not completely defined. In the present study, we tested the hypothesis that flux of cholesterol from macrophage foam cells to liver is impaired in subjects with CKD.

Methods

Consecutive healthy patients, patients with at least 1 CAD risk factor, patients with established CAD, and patients with CKD stages G3 to G5 (n ≥ 15/group) were recruited prospectively. The ability of total patient serum without any modifications to (i) facilitate efflux of cholesterol from human THP1-macrophage foam cells under physiological conditions (cholesterol efflux capacity [CEC]) and (ii) to deliver this effluxed cholesterol to primary hepatocytes with physiological expression of high-density lipoprotein (HDL) receptor SR-BI (capacity to deliver cholesterol to hepatocytes [CDCH]) was evaluated.

Results

Although healthy patients, patients with at least 1 CAD risk factor, and patients with established CAD all showed similar CEC, patients with CKD showed significantly higher CEC. CDCH was significantly lower in all groups compared with the healthy patients; however, when corrected for higher CEC, CDCH in patients with CKD was significantly lower than in patients with CAD. CDCH correlated with age, body mass index, metabolic parameters, inflammatory markers, and kidney function markers (estimated glomerular filtration rate [eGFR], serum creatinine, and serum cystatin C).

Conclusions

These results suggest that aberrations in delivery of cholesterol effluxed from macrophage foam cells to liver for final elimination or the last step of reverse cholesterol transport, may underlie the increased risk of CAD in patients with CKD.

A critical appraisal of the measurement of serum 'cholesterol efflux capacity' and its use as surrogate marker of risk of cardiovascular disease

The 'cholesterol efflux capacity (CEC)' assay is a simple in vitro measure of the capacities of individual sera to promote the first step of the reverse cholesterol transport pathway, the delivery of cellular cholesterol to plasma HDL. This review describes the cell biology of this model and critically assesses its application as a marker of cardiovascular risk. We describe the pathways for cell cholesterol export, current cell models used in the CEC assay with their limitations and consider the contribution that measurement of serum CEC provides to our understanding of HDL function in vivo.

Impaired HDL cholesterol efflux capacity in patients with non-alcoholic fatty liver disease is associated with subclinical atherosclerosis

Non-alcoholic fatty liver disease (NAFLD) is associated with a substantial increased risk of atherosclerotic cardiovascular disease (ASCVD), which is partly related to dyslipidemia and low HDL-C level. The cardioprotective activity of HDL in the body is closely connected to its role in promoting cholesterol efflux, which is determined by cholesterol efflux capacity (CEC). Hitherto, the role of HDL, as defined by CEC has not been assessed in NAFLD patients. In this research study, we present the results of a study of cAMP-treated J774 CEC and THP-1 macrophage CEC in ApoB-depleted plasma of 55 newly diagnosed NAFLD patients and 30 controls. Circulating levels of ApoA-I, ApoB, preβ-HDL, plasma activity of CETP, PLTP, LCAT and carotid intima-media thickness (cIMT) were estimated. cAMP-treated J774 and THP-1 macrophage CEC were found to be significantly lower in NAFLD patients compared to controls (P < 0.001 and P = 0.003, respectively). In addition, it was discovered that both ApoA-I and preβ1-HDL were significantly lower in NAFLD patients (P < 0.001). Furthermore, cAMP-treated J774 CEC showed independent negative correlation with cIMT, as well as the presence of atherosclerotic plaque in NAFLD patients. In conclusion, our findings showed that HDL CEC was suppressed in NAFLD patients, and impaired cAMP-treated J774 CEC was an independent risk factor for subclinical atherosclerosis in NAFLD patients, suggesting that impaired HDL functions as an independent risk factor for atherosclerosis in NAFLD.

Association of Cholesterol Efflux Capacity With Clinical Features of Metabolic Syndrome: Relevance to Atherosclerosis

BACKGROUND

The contribution of high-density lipoprotein to cardiovascular benefit is closely linked to its role in the cellular cholesterol efflux process; however, various clinical and biochemical variables are known to modulate the overall cholesterol efflux process. The aim of this study was to evaluate the extent to which clinical and biological anomalies associated with the establishment of the metabolic syndrome modulate cholesterol efflux capacity and contribute to development of atherosclerosis.

METHODS AND RESULTS

This study involved patients (n=1202) displaying atherogenic dyslipidemia in primary prevention who were referred to our prevention center. Among these patients, 25% presented at least 3 criteria of the metabolic syndrome, as defined by the National Cholesterol Education Program Adult Treatment Panel III. We measured the capacity of 40-fold diluted serum to mediate cholesterol efflux from cholesterol-loaded human THP-1 macrophages. Cholesterol efflux capacity was reduced progressively by 4% to 11% (P<0.0001) as a function of the increasing number of coexisting criteria for the metabolic syndrome from 1 to 5. This observation was primarily related to reductions in scavenger receptor class B member 1 and ATP binding cassette subfamily G member 1-dependent efflux. Multivariate analyses indicate that serum efflux capacity was significantly associated with established metabolic syndrome (odds ratio 0.45; 95% CI 0.28-0.72; P=0.009) independent of age, low-density lipoprotein cholesterol, status with regard to lipid-lowering therapy, smoking status, and alcohol consumption.

CONCLUSIONS

Our study revealed that individual criteria of metabolic syndrome are closely related synergistically to cholesterol efflux capacity. In addition, established metabolic syndrome and cholesterol efflux capacity were independently associated with clinical features of atherosclerosis.

Cholesterol efflux capacity: An introduction for clinicians

Epidemiologic studies have shown an inverse correlation between high-density lipoprotein (HDL) cholesterol (HDL-C) levels and cardiovascular disease outcomes. However, the hypothesis of a causal relationship between HDL-C and cardiovascular disease has been challenged by genetic and clinical studies. Serum cholesterol efflux capacity (CEC) is an important measure of HDL function in humans. Recent large clinical studies have shown a correlation between in vitro CEC and cardiovascular disease prevalence and incidence, which appears to be independent of HDL-C concentration. The present review summarizes recent large clinical studies and introduces important methodological considerations. Further studies are required to standardize and establish the reproducibility of this measure of HDL function and clarify whether modulating CEC will emerge as a useful therapeutic target.

Modulating cholesterol efflux capacity to improve cardiovascular disease

PURPOSE OF REVIEW

Low HDL-cholesterol (HDL-C) levels are predictive of incident atherosclerotic cardiovascular disease events. However, the use of medication to raise HDL-C levels has not consistently shown clinical benefit. As a result, studies have shifted toward HDL function, specifically cholesterol efflux, which has been inversely associated with prevalent subclinical atherosclerosis as well as subsequent atherosclerotic cardiovascular disease events. The purpose of this review is to summarize the effects of current medications and interventions on cholesterol efflux capacity.

RECENT FINDINGS

Medications for cardiovascular health, including statins, fibrates, niacin, and novel therapeutics, are reviewed for their effect on cholesterol efflux. Differences in population studied and assay used are addressed appropriately. Lifestyle interventions, including diet and exercise, are also included in the review.

SUMMARY

The modification of cholesterol efflux capacity (CEC) by current medications and interventions has been investigated in both large randomized control trials and smaller observational cohorts. This review serves to compile the results of these studies and evaluate CEC modulation by commonly used medications. Altering CEC could be a novel therapeutic approach to improving cardiovascular risk profiles.

Impaired HDL cholesterol efflux in metabolic syndrome is unrelated to glucose tolerance status: the CODAM study

Type 2 diabetes mellitus (T2DM) and metabolic syndrome (MetS) increase atherosclerotic cardiovascular disease risk. Cholesterol efflux capacity (CEC) is a key metric of the anti-atherosclerotic functionality of high-density lipoproteins (HDL). The present study aimed to delineate if T2DM and MetS cross-sectionally associate with altered CEC in a large high cardiometabolic risk population. CEC was determined from THP-1 macrophage foam cells towards apolipoprotein B-depleted plasma from 552 subjects of the CODAM cohort (288 controls, 126 impaired glucose metabolism [IGM], 138 T2DM). MetS was present in 297 participants. CEC was not different between different glucose tolerance categories but was lower in MetS (P < 0.001), at least partly attributable to lower HDL cholesterol (HDL-C) and apoA-I levels (P < 0.001 for each). Low grade inflammation was increased in IGM, T2DM and MetS as determined by a score comprising 8 different biomarkers (P < 0.05-< 0.001; n = 547). CEC inversely associated with low-grade inflammation taking account of HDL-C or apoA-I in MetS (P < 0.02), but not in subjects without MetS (interaction: P = 0.015). This study demonstrates that IGM and T2DM do not impact the HDL CEC function, while efflux is lower in MetS, partly dependent on plasma HDL-C levels. Enhanced low-grade inflammation in MetS may conceivably impair CEC even independent of HDL-C and apoA-I.

Impaired Cholesterol Efflux Capacity of High-Density Lipoprotein Isolated From Interstitial Fluid in Type 2 Diabetes Mellitus-Brief Report

Supplemental Digital Content is available in the text.

Objective—

Patients with type 2 diabetes mellitus (T2D) have an increased risk of cardiovascular disease, the mechanism of which is incompletely understood. Their high-density lipoprotein (HDL) particles in plasma have been reported to have impaired cholesterol efflux capacity. However, the efflux capacity of HDL from interstitial fluid (IF), the starting point for reverse cholesterol transport, has not been studied. We here investigated the cholesterol efflux capacity of HDL from IF and plasma from T2D patients and healthy controls.

Approach and Results—

HDL was isolated from IF and peripheral plasma from 35 T2D patients and 35 age- and sex-matched healthy controls. Cholesterol efflux to HDL was determined in vitro, normalized for HDL cholesterol, using cholesterol-loaded macrophages. Efflux capacity of plasma HDL was 10% lower in T2D patients than in healthy controls, in line with previous observations. This difference was much more pronounced for HDL from IF, where efflux capacity was reduced by 28% in T2D. Somewhat surprisingly, the efflux capacity of HDL from IF was lower than that of plasma HDL, by 15% and 32% in controls and T2D patients, respectively.

Conclusion—

These data demonstrate that (1) HDL from IF has a lower cholesterol efflux capacity than plasma HDL and (2) the efflux capacity of HDL from IF is severely impaired in T2D when compared with controls. Because IF comprises the compartment where reverse cholesterol transport is initiated, the marked reduction in cholesterol efflux capacity of IF-HDL from T2D patients may play an important role for their increased risk to develop atherosclerosis.

High-Density Lipoprotein Function Measurement in Human Studies: Focus on Cholesterol Efflux Capacity

A low plasma level of high-density lipoprotein (HDL) cholesterol (HDL-C) is a major risk factor for the development of atherosclerotic cardiovascular disease (ASCVD). However, several observations have highlighted the shortcomings of using cholesterol content as the sole reflection of HDL metabolism. In particular, several large randomized controlled trials of extended release niacin and cholesteryl-ester transfer protein (CETP) inhibitors on background statin therapy have failed to show improvement in ASCVD outcomes despite significant increases in HDL-C. Reverse cholesterol transport (RCT) is the principal HDL function that impacts macrophage foam cell formation and other functions such as endothelial activation of endothelial nitric oxide synthase, monocyte adhesion, and platelet aggregation. Cholesterol efflux from macrophages to plasma/serum reflects the first critical step of RCT and is considered a key anti-atherosclerotic function of HDL. Whether this function is operative in humans remains to be seen, but recent studies assessing cholesterol efflux in humans suggest that the cholesterol efflux capacity (CEC) of human plasma or serum is a potent marker of ASCVD risk. This review describes the methodology of measuring CEC ex vivo from human samples and the findings to date linking CEC to human disease. Studies to date confirm that CEC can be reliably measured using stored human blood samples as cholesterol acceptors and suggest that CEC may be a promising new biomarker for atherosclerotic and metabolic diseases. Further studies are needed to standardize measurements and clarify the role CEC may play in predicting risk of developing disease and response to therapies.

Relationship between serum cholesterol efflux capacity and glucose intolerance in Japanese-Americans

AIM

Serum cholesterol efflux has been suggested to be a key anti-atherogenic function of reverse cholesterol transport. Meanwhile, the quantitative and qualitative alteration of the levels of lipoproteins in the serum has been reported in patients with diabetes, although it remains unclear whether the serum cholesterol efflux capacity is impaired in cases of newly diagnosed glucose intolerance. We thus assessed the relationship between the serum cholesterol efflux capacity and glucose intolerance as detected using oral glucose tolerance tests (OGTTs).

METHODS

We measured the capacity of whole serum to mediate cholesterol efflux from human THP-1 macrophages in a cohort of 439 Japanese-Americans who underwent 75-g OGTTs. A multiple regression analysis was performed to examine the relationship between the serum cholesterol efflux capacity and glucose intolerance.

RESULTS

The serum cholesterol efflux capacity was found to be negatively correlated with the area under the curve for the serum glucose concentration during the 75-g OGTTs in all subjects. In addition, the serum cholesterol efflux capacity was found to be modestly but significantly lower in the glucose intolerance group (31.4 ± 6.2%) than in the normal glucose tolerance group (33.2 ± 6.1%). There was also a negative association between the serum cholesterol efflux capacity and glucose intolerance after adjusting for age and sex. Moreover, this association remained significant even after further adjustments for serum total cholesterol, high-density lipoprotein cholesterol, apolipoprotein AI and C-reactive protein.

CONCLUSIONS

The serum cholesterol efflux capacity is impaired in Japanese-Americans newly diagnosed with glucose intolerance. This impairment may contribute in some manner to increasing the risk of atherosclerotic disease in subjects with glucose intolerance.

Endothelial lipase and reverse cholesterol transport in type 2 diabetes mellitus

Aims/Introduction:  Endothelial lipase (EL) plays an important role in high‐density lipoprotein (HDL) metabolism and experimental data suggest that EL might be proatherogenic. We have investigated whether serum EL concentration is associated with changes in serum capacity to induce cholesterol efflux and arterial stiffness in type 2 diabetes.

Materials and Methods:  Serum EL was assayed by ELISA in 172 diabetic patients and 175 controls. The ability of serum to induce cholesterol efflux was measured using a cell culture system and arterial stiffness was determined by measuring pulse wave velocity (PWV) between carotid and femoral arteries.

Results:  Diabetic patients had significantly higher C‐reactive protein (CRP) and EL (27.7 ± 16.6 ng/mL vs 24.0 ± 11.3, P < 0.05). Cholesterol efflux to serum mediated through scavenger receptor class B type I was impaired (15.1 ± 2.5%vs 16.7 ± 3.1, respectively, P < 0.01). In controls, serum EL correlated with cholesterol efflux to serum (r = −0.16, P = 0.025), but only a trend was seen in the diabetic patients. Linear regression showed that in controls, HDL, serum EL and waist circumference were major independent determinants of cholesterol efflux; whereas in the diabetic cohort, the major independent determinants of cholesterol efflux were HDL, CRP and age. PWV was increased in the diabetic patients (P < 0.01), but no association between serum EL and PWV was seen in either groups.

Conclusions:  Serum EL was increased in diabetic patients, but impaired serum capacity to induce cholesterol efflux in these patients was mainly related to low HDL and subclinical inflammation. (J Diabetes Invest, doi: 10.1111/j.2040‐1124.2010.00016.x, 2010)

Dietary approaches to improving atheroprotective HDL functions

High-density lipoproteins (HDL) are known to protect against cardiovascular disease (CVD). In addition to facilitating reverse cholesterol transport to remove excess lipids from the body - including atherosclerotic plaques - HDL exhibits antioxidant, anti-inflammatory, vasodilatory, and antithrombotic activities. Together, these properties contribute to the overall atheroprotective nature of HDL. However, similar to many other physiological pathways, these HDL parameters are known to become dysregulated in conditions of metabolic disease. Further, research suggests these alternative HDL properties may be regulated independently of blood HDL-cholesterol (HDL-C) levels, and must therefore be considered when designing HDL-targeted therapies. To date, a number of dietary strategies have been investigated to assess the effect of dietary components on functional properties of HDL beyond HDL-C. This review will highlight the bioactive nutrients, functional foods, and dietary programs known to modulate HDL function as a means of reducing CVD.

Premature and severe cardiovascular disease in a Mexican male with markedly low high-density-lipoprotein-cholesterol levels and a mutation in the lecithin:cholesterol acyltransferase gene: a family study

Epidemiological and clinical studies have shown that a low plasma high‑density lipoprotein cholesterol (HDL-C) level is a strong predictor of cardiovascular disease (CVD). Lecithin:cholesterol acyltransferase (LCAT) is a key enzyme in the formation, maturation and function of HDL. Therefore impaired LCAT function may enhance atherosclerosis because of defective cholesterol transport. In this study, we examined a 34-year old LCAT‑deficient patient and eight first-degree family members. There was a strong family history for CVD and type 2 diabetes mellitus (DM2). The proband was found homozygous for a previously reported LCAT gene mutation (Thr37Met). A sister and two sons of the proband were heterozygous for the same mutation. The proband had DM2 and showed severe multivessel coronary artery disease, corneal opacification and extremely low HDL-C levels. Large HDL particles were absent while small HDL particles were increased. The HDL of the patient had a reduced ability to promote cell cholesterol efflux, and the low‑density lipoproteins (LDL) were more susceptible to oxidation. Among his family members, two heterozygotes and one non-carrier had early carotid or coronary atherosclerosis. In conclusion, as the increased LDL oxidability and structural and functional abnormalities of HDL particles have been reported in patients with obesity and diabetes, the results suggested that the adverse coronary risk profile, and not being LCAT deficient, may be responsible for the CVD found in our proband, and for the early atherosclerosis observed in the two heterozygotes and in the wild‑type family members.

Simvastatin and bezafibrate increase cholesterol efflux in men with type 2 diabetes

BACKGROUND

The importance of functional properties of high-density lipoproteins (HDL) for atheroprotection is increasingly recognized. We determined the impact of lipid-lowering therapy on 3 key HDL functionalities in Type 2 diabetes mellitus (T2DM).

MATERIALS AND METHODS

A placebo-controlled, randomized cross-over study (three 8-week treatment periods with simvastatin (40 mg daily), bezafibrate (400 mg daily), alone and in combination) was carried out in 14 men with T2DM. Cholesterol efflux was determined using human THP-1 monocyte-derived macrophages, HDL antioxidative capacity was measured as inhibition of low-density lipoprotein oxidation in vitro, and HDL anti-inflammatory capacity was assessed as suppression of thrombin-induced monocyte chemotactic protein 1 expression in human umbilical vein endothelial cells. Pre-β-HDL was assayed using crossed immunoelectrophoresis.

RESULTS

While cholesterol efflux increased in response to simvastatin, bezafibrate and combination treatment (+12 to +23%; anova, P = 0.001), HDL antioxidative capacity (P = 0.23) and HDL anti-inflammatory capacity (P = 0.15) did not change significantly. Averaged changes in cellular cholesterol efflux during active treatment were correlated positively with changes in HDL cholesterol, apoA-I and pre-β-HDL (P < 0.05 to P < 0.001). There were no inter-relationships between changes in the three HDL functionalities during treatment (P > 0.10). Changes in HDL antioxidative capacity and anti-inflammatory capacity were also unrelated to changes in HDL cholesterol and apoA-I, while changes in HDL antioxidative capacity were related inversely to pre-β-HDL (P < 0.05).

CONCLUSION

Simvastatin and bezafibrate increase cholesterol efflux, parallel to HDL cholesterol and apoA-I responses. The antioxidative and anti-inflammatory properties of HDL are not to an important extent affected by these therapeutic interventions.

Impact of serum amyloid A on cellular cholesterol efflux to serum in type 2 diabetes mellitus

OBJECTIVE

Serum amyloid A (SAA) is an acute phase response protein and has apolipoprotein properties. Since type 2 diabetes is associated with chronic subclinical inflammation, the objective of this study is to investigate the changes in SAA level in type 2 diabetic patients and to evaluate the relationship between SAA and the capacity of serum to induce cellular cholesterol efflux via the two known cholesterol transporters, scavenger receptor class B type I (SR-BI) and ATP-binding cassette transporter G1 (ABCG1).

METHODS

264 patients with type 2 diabetes mellitus (42% with normoalbuminuria, 30% microalbuminuria, and 28% proteinuria) and 275 non-diabetic controls were recruited. SAA was measured by ELISA. SR-BI and ABCG1-mediated cholesterol efflux to serum were determined by measuring the transfer of [(3)H]cholesterol from Fu5AH rat hepatoma cells expressing SR-BI and from human ABCG1-transfected CHO-K1 cells to the medium containing the tested serum respectively.

RESULTS

SAA was significantly increased in diabetic patients with incipient or overt nephropathy. Both SR-BI and ABCG1-mediated cholesterol efflux to serum were significantly impaired in all three groups of diabetic patients (p < 0.01). SAA inversely correlated with SR-BI-mediated cholesterol efflux (r = -0.36, p < 0.01) but did not correlate with ABCG1-mediated cholesterol efflux. Stepwise linear regression analysis showed that HDL, the presence or absence of diabetes, and log(SAA) were significant independent determinants of SR-BI-mediated cholesterol efflux to serum.

CONCLUSION

SAA was increased in type 2 diabetic patients with incipient or overt nephropathy, and SAA was associated with impairment of SR-BI-mediated cholesterol efflux to serum.

Atherogenic dyslipidemia and combination pharmacotherapy in diabetes: recent clinical trials

Patients with type 2 diabetes (T2D) are at a markedly increased risk of cardiovascular disease (CVD). Dyslipidemia is a common risk factor and a strong predictor of CVD in T2D patients. Although statins decrease the incidence of CVD in T2D, residual cardiovascular risk remains high despite the achievement of optimal or near-optimal plasma low-density lipoprotein (LDL) cholesterol concentrations. This may, in part, be due to uncorrected atherogenic dyslipidemia. Hypertriglyceridemia, the driving force behind diabetic dyslipidemia, results from hepatic overproduction and/or delayed clearance of triglyceride-rich lipoproteins. In patients treated with a statin to LDL-cholesterol goals, the addition of ezetimibe, fenofibrate, niacin, or n-3 fatty acid ethyl esters may be required to correct the persistent atherogenic dyslipidemia. Clinical trial evidence describing best practice is limited, but recent data supports the strategy of adding fenofibrate to a statin, and suggests specific benefits in dyslipidemic patients and in the improvement of diabetic retinopathy. However, based on results from a recent clinical trial, niacin should not be added to a statin in individuals with low high-density lipoprotein cholesterol and very well controlled LDL-cholesterol. Further evidence is required to support the role of ezetimibe and n-3 fatty acids in treating residual CVD risk in statin-treated T2D patients.

Atherogenic dyslipidemia and combination pharmacotherapy in diabetes: recent clinical trials

Patients with type 2 diabetes (T2D) are at a markedly increased risk of cardiovascular disease (CVD). Dyslipidemia is a common risk factor and a strong predictor of CVD in T2D patients. Although statins decrease the incidence of CVD in T2D, residual cardiovascular risk remains high despite the achievement of optimal or near-optimal plasma low-density lipoprotein (LDL) cholesterol concentrations. This may, in part, be due to uncorrected atherogenic dyslipidemia. Hypertriglyceridemia, the driving force behind diabetic dyslipidemia, results from hepatic overproduction and/or delayed clearance of triglyceride-rich lipoproteins. In patients treated with a statin to LDL-cholesterol goals, the addition of ezetimibe, fenofibrate, niacin, or n-3 fatty acid ethyl esters may be required to correct the persistent atherogenic dyslipidemia. Clinical trial evidence describing best practice is limited, but recent data supports the strategy of adding fenofibrate to a statin, and suggests specific benefits in dyslipidemic patients and in the improvement of diabetic retinopathy. However, based on results from a recent clinical trial, niacin should not be added to a statin in individuals with low high-density lipoprotein cholesterol and very well controlled LDL-cholesterol. Further evidence is required to support the role of ezetimibe and n-3 fatty acids in treating residual CVD risk in statin-treated T2D patients.

Advanced glycation end-products (AGEs) and functionality of reverse cholesterol transport in patients with type 2 diabetes and in mouse models

AIMS/HYPOTHESIS

We investigated the contribution of AGEs to the impairment of reverse cholesterol transport (RCT) variables in diabetic individuals and in two animal models of diabetic obesity and of renal impairment.

METHODS

The capacity of plasma and HDL from 26 individuals with moderately controlled type 2 diabetes to support cholesterol efflux was compared with 26 age- and sex-matched individuals without diabetes. We also compared the rates of RCT in vivo in two animal models: db/db mice and mice with chronic renal failure.

RESULTS

Diabetic individuals had characteristic dyslipidaemia and higher levels of plasma AGEs. The capacity of whole plasma, ApoB-depleted plasma and isolated HDL to support cholesterol efflux was greater for diabetic patients compared with controls despite their lower HDL-cholesterol levels. The capacity of plasma to support cholesterol efflux correlated with plasma levels of cholesteryl ester transfer protein and levels of ApoB, but not with levels of AGE. RCT was severely impaired in db/db mice despite elevated HDL-cholesterol levels and no change in AGE concentration, whereas RCT in uraemic mice was unaffected despite elevated AGE levels.

CONCLUSIONS/INTERPRETATION

AGEs are unlikely to contribute significantly to the impairment of RCT in type 2 diabetes.

Cholesterol efflux and metabolic abnormalities associated with low high-density-lipoprotein-cholesterol and high triglycerides in statin-treated coronary men with low-density lipoprotein-cholesterol <70 mg/dl

In 69 statin-treated male coronary patients with low-density lipoprotein cholesterol at goal levels (<70 mg/dl), the investigators tested whether low high-density lipoprotein (HDL) cholesterol (<40 mg/dl) and high triglyceride (>150 mg/dl) are associated with dysfunctional HDL particles and abnormal insulin, adiponectin, C-reactive protein serum levels. Thirty-four patients with low HDL cholesterol and high triglyceride (dyslipidemia) and 35 patients with low-density lipoprotein cholesterol, HDL cholesterol, and triglyceride at target levels (normolipidemia) were studied. Twenty healthy men were also studied. High-sensitivity C-reactive protein was measured using immunonephelometry, insulin using a radioimmunometric assay, and total adiponectin by enzyme-linked immunosorbent assay. Cell cholesterol efflux to serum and total isolated HDL was assayed using rat hepatoma Fu5AH cells for scavenger receptor class B type 1-mediated efflux. Compared to the normolipidemia and healthy groups, and after adjustment for age and waist circumference, patients with dyslipidemia showed higher fasting insulin (14, 9.9, and 8.5 μU/ml, respectively), homeostasis model assessment of insulin resistance values (3.4, 2.3, and 1.8, respectively), lower adiponectin concentrations (5.1, 8.1, and 11 μg/ml, respectively), and reduced cholesterol efflux to serum (14%, 15%, and 19%, respectively) and to HDL fractions (4.4%, 4.6%, and 5.6%, respectively) (p <0.05 for all variables). Multivariate analysis showed that adiponectin and apolipoprotein A1 accounted for 10.7% and 3.9%, respectively, of the variance in cholesterol efflux. In conclusion, the decreased cholesterol efflux and metabolic abnormalities found in the dyslipidemia group may contribute to the residual risk observed in the large statin trials and the higher morbidity and mortality in statin-treated coronary patients with low HDL cholesterol even when attaining low-density lipoprotein cholesterol <70 mg/dl.

High-density lipoprotein cholesterol efflux, nitration of apolipoprotein A-I, and endothelial function in obese women

Subjects at risk of atherosclerosis might have dysfunctional high-density lipoprotein (HDL) despite normal cholesterol content in the plasma. We considered whether the efflux of excess cellular cholesterol to HDL from obese subjects is associated with impaired arterial endothelial function, a biomarker of cardiovascular risk. A total of 54 overweight (body mass index [BMI] 25 to 29.9 kg/m(2)) or obese (BMI ≥30 kg/m(2)) women, aged 46 ± 11 years, were enrolled in a worksite wellness program. The HDL cholesterol averaged 57 ± 17 mg/dl and was inversely associated with the BMI (r = -0.419, p = 0.002). Endothelial function was assessed using brachial artery flow-mediated dilation. Cholesterol efflux from (3)H-cholesterol-labeled baby hamster kidney cells transfected with the adenosine triphosphate-binding cassette transporter 1 showed 8.2% to 22.5% cholesterol efflux within 18 hours when incubated with 1% serum and was positively correlated with brachial artery flow-mediated dilation (p <0.05), especially in the 34 subjects with BMI ≥30 kg/m(2) (r = 0.482, p = 0.004). This relation was independent of age, HDL or low-density lipoprotein cholesterol concentrations in plasma, blood pressure, or insulin resistance on stepwise multiple regression analysis (β = 0.31, R(2) = 0.21, p = 0.007). Nitration of apolipoprotein A-I tyrosine residues (using sandwich enzyme-linked immunosorbent assay) was significantly greater in women with a BMI ≥30 kg/m(2) and the lowest cholesterol efflux than in women with a BMI of 25 to 29.9 kg/m(2) and the greatest cholesterol efflux (p = 0.01). In conclusion, we have shown that decreased cholesterol efflux by way of the adenosine triphosphate-binding cassette transporter 1 is associated with increased nitration of apolipoprotein A-I in HDL and is an independent predictor of impaired endothelial function in women with a BMI of ≥30 kg/m(2). This finding suggests that the functional measures of HDL might be better markers for cardiovascular risk than the HDL cholesterol levels in this population.

Cholesterol efflux from macrophages is influenced differentially by plasmas from overweight insulin-sensitive and -resistant subjects

OBJECTIVE

In vitro measurements of cholesterol efflux from macrophages have recently been shown to associate with cardiovascular risk. We investigated whether cholesterol efflux from macrophages incubated with plasmas from overweight/obese subjects with metabolic syndrome was influenced by the presence of insulin resistance.

METHODS

Plasmas were obtained from 47 men and women with metabolic syndrome, of whom 25 were found to be insulin resistant (IR) and 22 insulin sensitive (IS) (Matsuda, De Fronzo equation based on oral glucose tolerance test). Activated human macrophage THP-1 cells in which cholesterol had been radiolabelled were incubated with the subjects' plasmas to allow calculation of % cholesterol efflux.

RESULTS

Body mass index and waist measurements, as well as plasma lipid levels, did not differ between the two groups. Homeostatic model assessment-insulin resistance value as well as plasma insulin and leptin concentrations were higher in IR subjects. Cholesterol efflux was found to be significantly greater with plasmas from IR subjects (9.1%) than from IS subjects (6.7%) (P=0.005). Further, cholesterol efflux was significantly inversely associated with insulin sensitivity index (P<0.001), directly with arterial insulin concentration (P<0.001) and directly with cholesteryl ester transfer protein (CETP) mass (P=0.044).

CONCLUSION

Plasmas from overweight subjects with insulin resistance induced greater in vitro cholesterol efflux compared with IS subjects. Efflux inversely correlated with insulin sensitivity suggesting an increase in reverse cholesterol transport in the IR state that may lead to greater transfer of cholesterol to apoB lipoproteins from high-density lipoproteins via CETP as a factor in the association between IR and atherosclerosis.

Relationships between cholesterol efflux and high-density lipoprotein particles in patients with type 2 diabetes mellitus

BACKGROUND

High-density lipoprotein (HDL) encompasses a heterogeneous population of lipoproteins with differences in functionality. The impact of HDL heterogeneity on its ability to support HDL-mediated cholesterol efflux has not been previously studied in patients with type 2 diabetes mellitus (T2DM).

OBJECTIVES

To examine the relationships between various HDL subtypes and cholesterol efflux from macrophages in patients with T2DM.

METHODS

Lipoprotein molecular profiles of 44 patients were studied by NMR spectroscopy. Cholesterol efflux was expressed as percentage efflux of radioactivity from lipid-laden THP-1 macrophages preincubated with (3)H-cholesterol and then incubated with serum depleted of apolipoprotein B to provide an HDL-enriched acceptor medium.

RESULTS

There was a predominance of small HDL particles (59%) and small putatively atherogenic low-density lipoprotein particles (56%). Neither HDL-C nor ApoA-I concentrations showed statistically significant correlations with percentage cholesterol efflux, but a significant positive relationship was found with the total HDL particle concentration (r = 0.41, P = .005) contributed to largely by medium HDL particles (r = 0.41, P = .006). The correlation between medium-sized HDL particle concentration remained significantly associated with cholesterol efflux when assessed with the use of a linear regression model that included all the HDL lipoprotein subclass concentrations as well as apolipoprotein A-I. Importantly, no statistically significant association was observed between the number of small HDL particles and cholesterol efflux. Hemoglobin A1c showed a significant inverse correlation with cholesterol efflux (r = -0.31, P = .04).

CONCLUSION

In patients with moderately controlled type 2 diabetes mellitus, cholesterol efflux from macrophages incubated with apolipoprotein B-depleted plasmas correlated significantly and positively with the concentration of total and medium-sized HDL and not with that of the smallest particles.

Macrophage cholesterol efflux to plasma and HDL in subjects with low and high homocysteine levels: a FIELD substudy

OBJECTIVES

Increases of homocysteine (Hcy) by fenofibrate correlated inversely to changes in HDL-C and apoA-I in the FIELD study. This finding raised the question whether high Hcy may influence HDL function and counteract benefits of fenofibrate on cardiovascular outcomes. In a subset of the FIELD study we investigated whether fenofibrate therapy or high Hcy, separately or in concert, modulate: (1) ability of plasma or HDL to facilitate cholesterol efflux from THP-1 foam cells; (2) plasma potential to generate preβ-HDL; (3) plasma phospholipid transfer protein (PLTP) activity, serum PON-1 mass and activity, HDL particle size and distribution.

METHODS

We selected 33 subjects in the FIELD fenofibrate arm according to quartiles of Hcy at 5th year: 17 subjects were in the lowest (Low Hcy group) and 16 subjects were in the highest quartile (High Hcy group). In addition, 14 subjects allocated to placebo were matched by close-out Hcy levels to Low Hcy group. This design allowed us to examine the effects of both fenofibrate (comparison between placebo vs Low Hcy groups) and Hcy (comparison between close-out Low and High Hcy groups) on plasma and HDL ability to facilitate cellular cholesterol removal in the efflux assay in vitro using THP-1 foam cells.

RESULTS

Hcy levels were 13.3±0.7 μmol/L (placebo), 13.2±2 μmol/L (Low Hcy) and 27.4±6.5 μmol/L (High Hcy). Cholesterol efflux values to HDL and plasma, percentage of plasma preβ-HDL, PLTP activity, serum PON-1 mass and HDL particle size and distribution were similar in both fenofibrate groups and comparable to those of the placebo group.

CONCLUSIONS

In the present study cohort fenofibrate and high Hcy levels did not modulate HDL and plasma functions in the first step of reverse cholesterol transport, cholesterol efflux from foam cells.

Cholesterol efflux capacity, high-density lipoprotein function, and atherosclerosis

BACKGROUND

High-density lipoprotein (HDL) may provide cardiovascular protection by promoting reverse cholesterol transport from macrophages. We hypothesized that the capacity of HDL to accept cholesterol from macrophages would serve as a predictor of atherosclerotic burden.

METHODS

We measured cholesterol efflux capacity in 203 healthy volunteers who underwent assessment of carotid artery intima-media thickness, 442 patients with angiographically confirmed coronary artery disease, and 351 patients without such angiographically confirmed disease. We quantified efflux capacity by using a validated ex vivo system that involved incubation of macrophages with apolipoprotein B-depleted serum from the study participants.

RESULTS

The levels of HDL cholesterol and apolipoprotein A-I were significant determinants of cholesterol efflux capacity but accounted for less than 40% of the observed variation. An inverse relationship was noted between efflux capacity and carotid intima-media thickness both before and after adjustment for the HDL cholesterol level. Furthermore, efflux capacity was a strong inverse predictor of coronary disease status (adjusted odds ratio for coronary disease per 1-SD increase in efflux capacity, 0.70; 95% confidence interval [CI], 0.59 to 0.83; P<0.001). This relationship was attenuated, but remained significant, after additional adjustment for the HDL cholesterol level (odds ratio per 1-SD increase, 0.75; 95% CI, 0.63 to 0.90; P=0.002) or apolipoprotein A-I level (odds ratio per 1-SD increase, 0.74; 95% CI, 0.61 to 0.89; P=0.002). Additional studies showed enhanced efflux capacity in patients with the metabolic syndrome and low HDL cholesterol levels who were treated with pioglitazone, but not in patients with hypercholesterolemia who were treated with statins.

CONCLUSIONS

Cholesterol efflux capacity from macrophages, a metric of HDL function, has a strong inverse association with both carotid intima-media thickness and the likelihood of angiographic coronary artery disease, independently of the HDL cholesterol level. (Funded by the National Heart, Lung, and Blood Institute and others.).

High density lipoprotein-anionic peptide factor effect on reverse cholesterol transport in type 2 diabetic patients with and without coronary artery disease

OBJECTIVES

To verify if HDL3 Anionic Peptide Factor (HDL3-APF) is as an apolipoprotein that promotes the reverse cholesterol transport.

DESIGN AND METHODS

We investigated a possible association between plasma HDL3-APF concentration, cholesterol efflux from Fu5AH cells and cholesteryl ester transfer protein (CETP) activity in type 2 diabetic patients with coronary artery disease (CAD) (n=36), those without CAD (n=20), and 37 healthy subjects.

RESULTS

Plasma APF concentrations were decreased in diabetics with CAD compared to controls (p<0.01). Cellular cholesterol efflux was decreased in diabetics without and with CAD, (p<0.01 and p<0.001 respectively). CETP activity was significantly elevated in all patient groups. Multiple linear regression analysis shows that cholesterol efflux was independently and positively related only to APF concentrations in controls.

CONCLUSIONS

APF is likely to be a key independent factor for promoting cellular cholesterol efflux in healthy subjects. However this association is altered in type 2 diabetes.

HDL and LDL cholesterol significantly influence beta-cell function in type 2 diabetes mellitus

PURPOSE OF REVIEW

Patients with type 2 diabetes mellitus (T2DM) display significant abnormalities in both LDL and HDL particles. Recent data suggest that these changes in lipoprotein particles could contribute to the pathogenesis of T2DM. In this review, we focus on these abnormalities and discuss their possible impact on beta-cell function and beta-cell mass.

RECENT FINDINGS

Infusion of reconstituted HDL in T2DM patients improves beta-cell function, whereas carriers of loss-of-function mutations in the cholesterol transporter ABCA1, who have decreased HDL levels, have impaired beta-cell function. In addition, recent studies show that HDL protects against stress-induced beta-cell apoptosis in vitro. Finally, increasing evidence points to a role for islet inflammation in the pathogenesis of T2DM. ABCA1 and ABCG1 may also modulate these inflammatory responses, suggesting an additional pathway by which HDL may impact T2DM.

SUMMARY

Recent findings indicate that HDL protects beta-cells from cholesterol-induced beta-cell dysfunction, stress-induced apoptosis and islet inflammation. As the protective properties of HDL are compromised in patients with metabolic syndrome and T2DM, dysfunctional HDL metabolism could contribute to the pathogenesis of T2DM. Therapeutic normalization of both the quantity and quality of HDL particles may be a novel approach to prevent or treat T2DM.

Impaired serum capacity to induce cholesterol efflux is associated with endothelial dysfunction in type 2 diabetes mellitus

OBJECTIVE

Reverse cholesterol transport (RCT) plays a protective role against atherosclerosis and cholesterol efflux from cells is an early step in the RCT pathway. We investigated whether the capacity of serum to induce cholesterol efflux was associated with endothelial dysfunction in type 2 diabetes.

METHODS

Endothelium-dependent and -independent vasodilation of the brachial artery was measured by high-resolution vascular ultrasound and serum cholesterol efflux capacity was determined by measuring the transfer of [3H]cholesterol from Fu5AH cells to serum in 137 patients with type 2 diabetes and 75 controls.

RESULTS

Serum cholesterol efflux capacity was lower in diabetic patients than in the controls (13.6+/-2.5% vs. 14.6+/-3.4%, respectively, p=0.02), and both endothelium-dependent vasodilation (4.9+/-2.2% vs. 8.8+/-4.1%, respectively, p<0.01) and endothelium-independent vasodilation were impaired (13.4+/-4.3% vs. 16.3+/-5.5%. respectively, p<0.01). Endothelium-dependent vasodilation correlated with serum cholesterol efflux capacity (r=0.26, p=0.003) in diabetic patients and controls (r=0.24, p=0.037). On general linear model analysis, the presence of diabetes, brachial artery diameter and serum cholesterol efflux capacity were significant independent determinants of endothelium-dependent vasodilation.

CONCLUSION

Impaired serum cholesterol efflux capacity was associated with endothelial dysfunction independent of other cardiovascular risk factors.

Effect of lipid-modifying therapies on the functional quality of high-density lipoproteins: implications for drug development

BACKGROUND

Increasing interest has focused on the development of therapeutic strategies to promote the biological activity of high-density lipoproteins (HDL) to achieve more effective prevention of cardiovascular disease. The highly publicized failure of raising HDL cholesterol with the cholesteryl ester transfer protein inhibitor, torcetrapib, has fueled immense discussion with regard to the potential impact of lipid modifying therapies on the functional quality of HDL particles.

OBJECTIVE/METHOD

To review the literature that has investigated the role of HDL functionality in protection against cardiovascular disease.

CONCLUSION

It remains to be unequivocally demonstrated that therapies that directly target HDL are cardioprotective in humans. Increasing attention on the functional quality of HDL will be essentinal for developing new biomarkers and medical therapies.

Reverse cholesterol transport in type 2 diabetes mellitus

High-density lipoprotein (HDL) plays an important protective role against atherosclerosis, and the anti-atherogenic properties of HDL include the promotion of cellular cholesterol efflux and reverse cholesterol transport (RCT), as well as antioxidant, anti-inflammatory and anticoagulant effects. RCT is a complex pathway, which transports cholesterol from peripheral cells and tissues to the liver for its metabolism and biliary excretion. The major steps in the RCT pathway include the efflux of free cholesterol mediated by cholesterol transporters from cells to the main extracellular acceptor HDL, the conversion of free cholesterol to cholesteryl esters and the subsequent removal of cholesteryl ester in HDL by the liver. The efficiency of RCT is influenced by the mobilization of cellular lipids for efflux and the intravascular remodelling and kinetics of HDL metabolism. Despite the increased cardiovascular risk in people with type 2 diabetes, current knowledge on RCT in diabetes is limited. In this article, abnormalities in RCT in type 2 diabetes mellitus and therapeutic strategies targeting HDL and RCT will be reviewed.

Cellular cholesterol efflux to serum is impaired in diabetic nephropathy

BACKGROUND

Cholesterol efflux from cells is an early step of reverse cholesterol transport (RCT) and the capacity of serum to induce cellular cholesterol efflux has recently been shown to be an independent predictor of coronary artery atherosclerosis. Our aim is to evaluate the capacity of serum to induce ATP-binding cassette transporter A1 (ABCA1) and scavenger receptor class B type I (SR-BI) mediated cholesterol efflux in type 2 diabetic patients with nephropathy.

METHODS

Diabetic patients were recruited according to their urinary albumin excretion rate (normoalbuminuria, microalbuminuria and proteinuria) with 20 subjects in each group and compared with 20 age-matched controls. The ability of the serum to induce cholesterol efflux was measured using a cell culture system.

RESULTS

Serum capacity to induce ABCA1-mediated cholesterol efflux was decreased in patients with microalbuminuria or proteinuria (p < 0.05) whereas SR-BI-mediated cholesterol efflux was impaired in all three groups of diabetic patients (p < 0.05). Plasma high-density lipoprotein (HDL) cholesterol and apoAI were reduced in all groups of diabetic patients, but pre-beta-HDL was only significantly decreased in those with microalbuminuria or proteinuria. Serum advanced glycation end products (AGEs) were significantly increased in diabetic patients with microalbuminuria or proteinuria. Serum AGEs and pre-beta-HDL were the significant independent determinants of ABCA1-mediated cholesterol efflux, whereas plasma HDL and log (creatinine) were the significant determinants of SR-BI-mediated cholesterol efflux.

CONCLUSION

The capacity of serum to induce ABCA1- and SR-BI-mediated cholesterol efflux was impaired in diabetic patients with incipient or overt nephropathy. These abnormalities may contribute to the accelerated development of atherosclerotic vascular disease in these patients.

Why is HDL functionally deficient in type 2 diabetes?

High-density lipoprotein (HDL) particles exert a spectrum of atheroprotective activities that can be deficient in type 2 diabetes. Key mechanisms leading to the formation of functionally deficient HDL involve 1) HDL enrichment in triglycerides and depletion in cholesteryl esters with conformational alterations of apolipoprotein A-I; 2) glycation of apolipoproteins and/or HDL-associated enzymes; and 3) oxidative modification of HDL lipids, apolipoproteins, and/or enzymes. Available data identify hypertriglyceridemia, with concomitant compositional modification of the HDL lipid core and conformational change of apolipoprotein A-I, as a driving force in functional alteration of HDL particles in type 2 diabetes. Therapeutic options for correcting HDL functional deficiency should target hypertriglyceridemia by normalizing circulating levels of triglyceride-rich lipoproteins.

Increased phospholipid transfer protein activity associated with the impaired cellular cholesterol efflux in type 2 diabetic subjects with coronary artery disease

Reverse cholesterol transport (RCT) is the pathway, by which the excess of cholesterol is removed from peripheral cells to the liver. An early step of RCT is the efflux of free cholesterol from cell membranes that is mediated by high-density lipoproteins (HDL). Phospholipid transfer protein (PLTP) transfers phospholipids between apolipoprotein-B-containing lipoproteins (i.e., chylomicrons and very low-density lipoproteins) and HDL. PLTP contributes to the HDL maturation and increases the ability of HDL to extract the cellular cholesterol. It is known that RCT is impaired in type 2 diabetic patients, especially when cardiovascular complication is associated with. In this study, we measured the serum capacity that promotes cellular cholesterol efflux and the plasma PLTP activity in type 2 diabetic patients with coronary artery disease (CAD) (n = 35), those without CAD (n = 24), and 35 healthy subjects as a sex- and age-matched control. In patients with CAD, plasma triglyceride level was higher compared to controls (p < 0.01) and HDL-cholesterol was lower (p < 0.01 vs control and the patients without CAD). In diabetic patients with or without CAD, PLTP activity was consistently increased, compared to controls, while cellular cholesterol efflux activity was decreased by 20% (p < 0.001) or 13.5% (p < 0.01), respectively. In conclusion, plasma PLTP activity was increased in type 2 diabetic patients with or without CAD, which could impair cellular cholesterol removal and might accelerate atherosclerosis in diabetic patients.

Indices of reverse cholesterol transport in subjects with metabolic syndrome after treatment with rosuvastatin

OBJECTIVE

The effects of the statin, rosuvastatin on indices of reverse cholesterol transport were studied in a randomized, placebo-controlled, cross-over trial in 25 overweight subjects with defined metabolic syndrome.

RESULT

Four weeks' treatment with 40 mg/day rosuvastatin significantly reduced levels of plasma cholesterol (44%), LDL cholesterol (60%) and triglyceride (38%). HDL cholesterol (mean [S.D.]) rose (0.97[0.17] to 1.05[0.17]mmol/L; P<0.05) and the LpA-I component of HDL from 39[7] to 45[9]mg/dL (P<0.05). LCAT activity fell (0.55[0.13] to 0.35[0.07]nmol/mL/h; P<0.05); CETP activity and mass fell from 89[13] to 80[11]nmol//L/h and from 1.66[0.57] to 1.28[0.41]mug/mL respectively, (P<0.05). Cholesterol efflux in vitro (to plasmas from THP-1 activated cells) fell from 7.1[1.8]% (placebo) to 6.2[1.7]% (rosuvastatin); P<0.05, but when plasmas depleted of apoB lipoproteins were studied, the difference in efflux was no longer statistically significant. During placebo efflux was paradoxically inversely correlated with HDL-C (P=0.016) and LpA-I (P=0.035) concentrations but these correlations were absent after rosuvastatin.

CONCLUSIONS

The data suggest possible HDL dysfunctionality in subjects with metabolic syndrome. The reduced capacity of plasmas following statin treatment to stimulate cholesterol efflux in vitro occurred in association with reduction in apoB lipoproteins and reduced activities of CETP and LCAT, and despite increased levels of HDL cholesterol.

Increased cholesterol efflux from cultured fibroblasts to plasma from hypertriglyceridemic type 2 diabetic patients: roles of pre beta-HDL, phospholipid transfer protein and cholesterol esterification

We tested whether hypertriglyceridemia associated with type 2 diabetes mellitus is accompanied by alterations in pre beta-HDL, which are considered to be initial acceptors of cell-derived cholesterol, and by changes in the ability of plasma to promote cellular cholesterol efflux. In 28 hypertriglyceridemic and 56 normotriglyceridemic type 2 diabetic patients, and in 56 control subjects, we determined plasma lipids, HDL cholesterol and phospholipids, plasma pre beta-HDL and pre beta-HDL formation, phospholipid transfer protein (PLTP) activity, plasma cholesterol esterification (EST) and cholesteryl ester transfer (CET) and the ability of plasma to stimulate cholesterol efflux out of cultured human fibroblasts. HDL cholesterol and HDL phospholipids were lower, whereas plasma PLTP activity, EST and CET were higher in hypertriglyceridemic diabetic patients than in the other groups. Pre beta-HDL levels and pre beta-HDL formation were unaltered, although the relative amount of pre beta-HDL (expressed as % of total plasma apo A-I) was increased in hypertriglyeridemic diabetic patients. Cellular cholesterol efflux to plasma from hypertriglyceridemic diabetic patients was increased compared to efflux to normotriglyceridemic diabetic and control plasma, but efflux to normotriglyceridemic diabetic and control plasma did not differ. Multiple linear regression analysis demonstrated that cellular cholesterol efflux to plasma was positively and independently related to pre beta-HDL formation, PLTP activity and EST (multiple r=0.48), but not to the diabetic state. In conclusion, cholesterol efflux from fibroblasts to normotriglyceridemic diabetic plasma is unchanged. Efflux to hypertriglyceridemic diabetic plasma is enhanced, in association with increased plasma PLTP activity and cholesterol esterification. Unaltered pre beta-HDL formation in diabetic hypertriglyceridemia, despite low apo A-I, could contribute to maintenance of cholesterol efflux.

Plasma phospholipid transfer protein activity, a determinant of HDL kinetics in vivo

OBJECTIVE

Phospholipid transfer protein (PLTP) is an important regulator in the transport of surface components of triglyceride-rich lipoprotein (TRL) to high density lipoprotein (HDL) during lipolysis and may therefore play an important role in regulating HDL transport. In this study we investigated the relationship of plasma PLTP activity with HDL metabolism in men.

DESIGN AND METHODS

The kinetics of HDL LpA-I and LpA-I:A-II were measured using intravenous administration of [D3]-leucine, gas chromatography-mass spectrometry (GCMS) and a new multicompartmental model for HDL subpopulation kinetics (SAAM II) in 31 men with wide-ranging body mass index (BMI 18-46 kg/m2). Plasma PLTP activity was determined as the transfer of radiolabelled phosphatidylcholine from small unilamellar phosphatidylcholine vesicles to ultracentrifugally isolated HDL.

RESULTS

PLTP activity was inversely associated with LpA-I concentration and production rate (PR) after adjusting for insulin resistance (P < 0.05). No significant associations were observed between plasma PLTP activity and LpA-I fractional catabolic rate (FCR). In multivariate analysis, including homeostasis model assessment score (HOMA), triglyceride, cholesteryl ester transfer protein (CETP) activity and PLTP activity, PLTP activity was the only significant determinant of LpA-I concentration and PR (P = 0.020 and P = 0.016, respectively).

CONCLUSIONS

Plasma PLTP activity may be a significant, independent determinant of LpA-I kinetics in men, and may contribute to the maintenance of the plasma concentration of these lipoprotein particles in setting of hypercatabolism of HDL.

High-density lipoproteins: an emerging target in the prevention of cardiovascular disease

High-density lipoproteins (HDLs) have been well established to protect against the development of atherosclerotic cardiovascular disease. It has become apparent that in addition to the promotion of reverse cholesterol transport, HDLs possess a number of additional functional properties that may contribute to their beneficial influence on the arterial wall. A number of exciting therapeutic strategies have been developed that target HDL and its ability to protect against the development of atherosclerotic plaque. This paper will review how the promotion of the functional properties of HDL inhibits the formation of atherosclerotic plaque and stabilises lesions in patients with established disease.

New insight into the pathophysiology of lipid abnormalities in type 2 diabetes

Lipid abnormalities in patients with type 2 diabetes are likely to play an important role in the development of atherogenesis. These lipid disorders include not only quantitative but also qualitative abnormalities of lipoproteins which are potentially atherogenic. The main quantitative abnormalities are increased triglyceride levels, related to an augmented hepatic production of VLDL and a reduction of both VLDL and IDL catabolism, and decreased HDL-Cholesterol levels due to an accelerated HDL catabolism. The main qualitative abnormalities include large VLDL particles (VLDL1), relatively rich in triglycerides, small dense LDL particles, increase in triglyceride content of LDL and HDL, glycation of apolipoproteins and increased susceptibility of LDL to oxidation. Moreover, although plasma LDL-cholesterol level is usually normal in type 2 diabetic patients, LDL particles show significant kinetic abnormalities, such as reduced turn-over, which is potentially harmful. The pathophysiology of lipid abnormalities in type 2 diabetes is not yet totally explained. However, insulin resistance and the "relative" insulin deficiency, observed in patients with type 2 diabetes, are likely to play a crucial role since insulin has an important function in the regulation of lipid metabolism. In addition, it is not excluded that adipocytokines, such as adiponectin, could play a role in the pathophysiology of lipid abnormalities in type 2 diabetes.

Formation of Dysfunctional High-Density Lipoprotein by Myeloperoxidase

Recent studies identify the presence of high-density lipoprotein (HDL) particles in patients with cardiovascular disease, which are "dysfunctional," lacking in typical atheroprotective properties, and promoting proinflammatory effects. The mechanisms for generating dysfunctional HDL have been unclear. New evidence points to a role for myeloperoxidase (MPO)-generated oxidants as participants in rendering HDL dysfunctional within human atherosclerotic plaque. Myeloperoxidase was recently shown to bind to HDL within human atherosclerotic lesions, and biophysical studies reveal MPO binding occurs via specific interactions with apolipoprotein (apo) A-I, the predominant protein of HDL. This likely facilitates the observed selective targeting of apoA-I for site-specific chlorination and nitration by MPO-generated reactive oxidants in vivo. One apparent consequence of MPO-catalyzed apoA-I oxidation includes the functional impairment of the ability of HDL to promote cellular cholesterol efflux via the adenosine triphosphate binding cassette-1 transport system. Myeloperoxidase-mediated loss of the atheroprotective functional properties of HDL may thus provide a novel mechanism linking inflammation and oxidative stress to the pathogenesis of atherosclerosis.

Mechanisms, Significance and Treatment of Vascular Dysfunction in Type 2 Diabetes Mellitus

Endothelial dysfunction and increased arterial stiffness occur early in the pathogenesis of diabetic vasculopathy. They are both powerful independent predictors of cardiovascular risk. Advances in non-invasive methodologies have led to widespread clinical investigation of these abnormalities in diabetes mellitus, generating a wealth of new knowledge concerning the mechanisms of vascular dysfunction, risk factor associations and potential treatment targets. Endothelial dysfunction primarily reflects decreased availability of nitric oxide (NO), a critical endothelium-derived vasoactive factor with vasodilatory and anti-atherosclerotic properties. Techniques for assessing endothelial dysfunction include ultrasonographic measurement of flow-mediated vasodilatation of the brachial artery and plethysmography measurement of forearm blood flow responses to vasoactive agents. Arterial stiffness may be assessed using pulse wave analysis to generate measures of pulse wave velocity, arterial compliance and wave reflection. The pathogenesis of endothelial dysfunction in type 2 diabetes is multifactorial, with principal contributors being oxidative stress, dyslipidaemia and hyperglycaemia. Elevated blood glucose levels drive production of reactive oxidant species (ROS) via multiple pathways, resulting in uncoupling of mitochondrial oxidative phosphorylation and endothelial NO synthase (eNOS) activity, reducing NO availability and generating further ROS. Hyperglycaemia also contributes to accelerated arterial stiffening by increasing formation of advanced glycation end-products (AGEs), which alter vessel wall structure and function. Diabetic dyslipidaemia is characterised by accumulation of triglyceride-rich lipoproteins, small dense low-density lipoprotein (LDL) particles, reduced high-density lipoprotein (HDL)-cholesterol and increased postprandial free fatty acid flux. These lipid abnormalities contribute to increasing oxidative stress and may directly inhibit eNOS activity. Although lipid-regulating agents such as HMG-CoA reductase inhibitors (statins), fibric acid derivatives (fibrates) and fish oils are used to treat diabetic dyslipidaemia, their impact on vascular function is less clear. Studies in type 2 diabetes have yielded inconsistent results, but this may reflect sampling variation and the potential over-riding influence of oxidative stress, dysglycaemia and insulin resistance on endothelial dysfunction. Results of positive intervention trials suggest that improvement in vascular function is mediated by both lipid and non-lipid mechanisms, including anti-inflammatory, anti-oxidative and direct effects on the arterial wall. Other treatments, such as renin-angiotensin-aldosterone system antagonists, insulin sensitisers and lifestyle-based interventions, have shown beneficial effects on vascular function in type 2 diabetes. Novel approaches, targeting eNOS and AGEs, are under development, as are new lipid-regulating therapies that more effectively lower LDL-cholesterol and raise HDL-cholesterol. Combination therapy may potentially increase therapeutic efficacy and permit use of lower doses, thereby reducing the risk of adverse drug effects and interactions. Concomitant treatments that specifically target oxidative stress may also improve endothelial dysfunction in diabetes. Vascular function studies can be used to explore the therapeutic potential and mechanisms of action of new and established interventions, and provide useful surrogate measures for cardiovascular endpoints in clinical trials.

Moderate alcohol consumption increases cholesterol efflux mediated by ABCA1

Moderate alcohol consumption increases HDL cholesterol, which is involved in reverse cholesterol transport (RCT). The aim of this study was to investigate the effect of moderate alcohol consumption on cholesterol efflux, using J774 mouse macrophages and Fu5AH cells, and on other parameters in the RCT pathway. Twenty-three healthy men (45-65 years) participated in a randomized, partially diet-controlled, crossover trial. They consumed four glasses of whisky (40 g of alcohol) or water daily for 17 days. After 17 days of whisky consumption, serum capacity to induce ABCA1-dependent cholesterol efflux from J774 mouse macrophages was increased by 17.5% (P = 0.027) compared with water consumption. Plasma capacity to induce cholesterol efflux from Fu5AH cells increased by 4.6% (P = 0.002). Prebeta-HDL, apolipoprotein A-I (apoA-I), and lipoprotein A-I:A-II also increased by 31.6, 6.2, and 5.7% (P < 0.05), respectively, after whisky consumption compared with water consumption. Changes of cAMP-stimulated cholesterol efflux correlated (r = 0.65, P < 0.05) with changes of apoA-I but not with changes of prebeta-HDL (r = 0.30, P = 0.18). Cholesterol efflux capacities from serum of lean men were higher than those from overweight men. In conclusion, this study shows that moderate alcohol consumption increases the capacity of serum to induce cholesterol efflux from J774 mouse macrophages, which may be mediated by ABCA1.

Effects of medium-chain fatty acids and oleic acid on blood lipids, lipoproteins, glucose, insulin, and lipid transfer protein activities

BACKGROUND

Dietary medium-chain fatty acids (MCFAs) are of nutritional interest because they are more easily absorbed from dietary medium-chain triacylglycerols (MCTs) than are long-chain fatty acids from, for example, vegetable oils. It has generally been claimed that MCFAs do not increase plasma cholesterol, although this claim is poorly documented.

OBJECTIVE

We compared the effects of a diet rich in either MCFAs or oleic acid on fasting blood lipids, lipoproteins, glucose, insulin, and lipid transfer protein activities in healthy men.

DESIGN

In a study with a double-blind, randomized, crossover design, 17 healthy young men replaced part of their habitual dietary fat intake with 70 g MCTs (66% 8:0 and 34% 10:0) or high-oleic sunflower oil (89.4% 18:1). Each intervention period lasted 21 d, and the 2 periods were separated by a washout period of 2 wk. Blood samples were taken before and after the intervention periods.

RESULTS

Compared with the intake of high-oleic sunflower oil, MCT intake resulted in 11% higher plasma total cholesterol (P = 0.0005), 12% higher LDL cholesterol (P = 0.0001), 32% higher VLDL cholesterol (P = 0.080), a 12% higher ratio of LDL to HDL cholesterol (P = 0.002), 22% higher plasma total triacylglycerol (P = 0.0361), and higher plasma glucose (P = 0.033). Plasma HDL-cholesterol and insulin concentrations and activities of cholesterol ester transfer protein and phospholipid transfer protein did not differ significantly between the diets.

CONCLUSIONS

Compared with fat high in oleic acid, MCT fat unfavorably affected lipid profiles in healthy young men by increasing plasma LDL cholesterol and triacylglycerol. No changes in the activities of phospholipid transfer protein and cholesterol ester transfer protein were evident.

Triglyceride-rich lipoproteins inhibit cholesterol efflux to apolipoprotein (apo) A1 from human macrophage foam cells

High circulating levels of triglyceride-rich lipoproteins (TGRL) represent an independent risk factor for coronary artery disease. Here, we show that TGRL inhibit the efflux of cholesterol from 'foam cell' macrophages to lipid-poor apolipoprotein (apo) A1, and may thereby inhibit arterial reverse cholesterol transport and promote the formation of atherosclerotic lesions. Human (THP-1) monocyte-derived macrophages were pre-incubated (48 h) with acetylated low-density lipoprotein (AcLDL) to provide a foam cell model of cholesterol efflux to apoA1. Pre-incubation of macrophage 'foam cells' with TGRL (0-200 microg/ml, 0-24 h) inhibited the efflux of exogenously radiolabelled ([3H]), endogenously synthesised ([14C]) and cellular cholesterol mass to lipid-poor apoA1, but not control medium, during a (subsequent) efflux period. This inhibition is dependent upon the length of prior exposure to, and concentration of, TGRL employed, but is independent of changes in intracellular triglyceride accumulation or turnover of the cholesteryl ester pool. Despite the negative impact of TGRL on cholesterol efflux, major proteins involved in this process--namely apoE, ABCA1, SR-B1 and caveolin-1--were unaffected by TGRL pre-incubation, suggesting that exposure to these lipoproteins inhibits an alternate, and possibly novel, anti-atherogenic pathway.