ABCA1-specific Cholesterol Efflux Capacity Research Articles

Sex differences in the associations of HDL particle concentration and cholesterol efflux capacity with incident coronary artery disease in type 1 diabetes: The RETRO HDLc cohort study

In type 1 diabetes, women lose their relative protection (compared to men) against coronary artery disease (CAD), while high-density lipoprotein cholesterol (HDL-C) is less strongly associated with lower CAD risk in women. We aimed to assess whether sex differences in the HDL particle concentration (HDL-P) and cholesterol efflux capacity (CEC) association with CAD may explain these findings. HDL-P (calibrated differential ion mobility analysis) and total and ATP binding cassette transporter A1 (ABCA1)-specific CEC were quantified among 279 men and 271 women with type 1 diabetes (baseline mean age 27·8 years; diabetes duration, 19·6 years). Clinical CAD was defined as CAD death, myocardial infarction and/or coronary revascularization. Women had higher large HDL-P levels and marginally lower concentrations of small HDL-P and ABCA1-specific CEC than men. No sex differences were observed in extra-small HDL-P, medium HDL-P and total CEC. During a median follow-up of 26 years, 37·6 % of men and 35·8 % of women developed CAD (p = 0·72). In multivariable Cox models stratified by sex (pTotal HDL-P x sex interaction=0·01), HDL-P was negatively associated with CAD incidence in both sexes. However, associations were stronger in men, particularly for extra-small HDL-P (hazard ratio (HR)men=0·11, 95 % confidence interval (CI): 0·04-0·30; HRwomen=0·68, 95 % CI: 0·28-1·66; pinteraction=0·001). CEC did not independently predict CAD in either sex. Despite few absolute differences in HDL-P concentrations by sex, the HDL-P - CAD association was weaker in women, particularly for extra-small HDL-P, suggesting that HDL-P may be less efficient in providing atheroprotection in women and perhaps explaining the lack of a sex difference in CAD in type 1 diabetes.

327-OR: Smaller HDL Particles and ABCA1 Cholesterol Efflux Capacity Predict Incident Proliferative Retinopathy Only among Men with Type 1 Diabetes

Clinical studies have provided evidence for a potential role of dyslipidemia in the development of retinopathy in type 1 diabetes. Existing evidence, however, is generally based on conventional lipid analysis and/or cross-sectional study designs. We therefore assessed the prospective association of HDL particle concentration (HDL-P) and cholesterol efflux capacity (CEC) with incident proliferative diabetic retinopathy (PDR) in a cohort of childhood-onset type 1 diabetes. HDL-P (calibrated differential ion mobility analysis) and total and ABCA1-specific CEC (validated cell-based assays) were quantified in 186 men and 185 women with type 1 diabetes free of PDR (stereo fundus photography) at baseline (mean age 25.6 years; diabetes duration, 17.1 years). Women had higher large HDL-P than men; the concentrations of extra-small, small and medium HDL-P as well as both total and ABCA1 CEC were similar by sex. During a median follow-up of 28 years, 108 men and 100 women developed PDR. In multivariable Cox models stratified by sex, HDL-C did not predict PDR incidence in either sex. However, in addition to increased HbA1c, non-HDL-C, white blood cell count and albumin excretion rate, increased extra-small (HR=0.25, 95% CI=0.09-0.67) and small (HR=0.72, 95% CI=0.55-0.94) HDL-P concentrations and ABCA1 CEC (HR=0.80, 95% CI=0.64-0.998) negatively predicted PDR in men but not women, among whom HbA1c, hypertension and white blood cell count were the only consistent significant predictors of PDR. In conclusion, while extra-small and small HDL-P concentrations and ABCA1 CEC did not differ by sex in type 1 diabetes, they only predicted incident PDR in men, a finding similar to our previously reported results for coronary artery disease. Further research is warranted to better understand the role of HDL in the pathophysiology of PDR and why this appears to differ by sex in type 1 diabetes. Disclosure T.Costacou: None. R.G.Miller: None. T.J.Orchard: None. Funding National Institutes of Health (R01HL130153, R01DK034818)

1141-P: HDL Particle Concentration, Cholesterol Efflux Capacity, and All-Cause Mortality in Type 1 Diabetes

Recent evidence suggests that HDL particle concentration (HDL-P) and cholesterol efflux capacity (CEC) are better predictors of coronary artery disease than HDL-C in type 1 diabetes (T1D) . We hypothesized that these novel HDL markers also predict all-cause mortality better than HDL-C in T1D. HDL-P (calibrated ion mobility analysis) and CEC (validated cell-based assay) were quantified in the first available stored sample from 550 Epidemiology of Diabetes Complications study participants with childhood onset (<17 years) T1D (baseline mean age 27.8 years and T1D duration, 19.6 years) . Vital status was assessed as of September 30, 2019. During a median follow-up of 26 years, there were 167 deaths. At analytic baseline, deceased were older, with longer T1D duration and a worse cardiovascular risk factor profile compared with survivors. In Cox proportional hazards models, after multivariable adjustments including for HDL-C, the concentration of total HDL-P (T-HDL-P, HR=0.90, 95% CI: 0.84-0.96) and that of three of the four major HDL subpopulations - extra small (XS-HDL-P, HR=0.44, 0.21-0.90) , small (S-HDL-P, HR=0.74, 0.60-0.93) and medium (M-HDL-P, HR=0.80, 0.70-0.91) particles - were associated with a lower mortality risk. Marginal protective associations were also observed for the concentration of large-sized particles (L-HDL-P, HR=0.84, 0.68-1.06) , as well as for CEC (HRs per SD was 0.86 (0.74-1.00) and 0.86 (0.73-1.01) for overall J774 and ABCA1-specific CEC, respectively) . These results remained largely unchanged by further adjustment for HDL-P (in the case of HDL-C and CEC) or APOA1 and triglyceride concentrations (for HDL-P) and were similar by sex. HDL-C was not a significant predictor of mortality in either univariate or multivariable analyses. Our findings show that higher HDL-P concentrations are negatively associated with mortality in T1D independent of other risk factors. Disclosure T.Costacou: None. R.G.Miller: Stock/Shareholder; Becton, Dickinson and Company. T.J.Orchard: None. T.Vaisar: Consultant; AstraZeneca. Funding National Institutes of Health (R01HL130153 and R01DK034818) and the Rossi Memorial Fund.

72-OR: HDL Particle Concentration Predicts Incident Coronary Artery Disease (CAD) in Type 1 Diabetes (T1D)

We have shown that elevated HDL cholesterol (HDL-C) levels (≥80 mg/dL) associate with increased CAD risk in women with T1D. Furthermore, HDL-C levels are not necessarily cardioprotective in nondiabetic individuals, suggesting that the cholesterol content of HDL does not accurately assess CAD risk. We thus determined whether two other HDL metrics, HDL particle concentration (HDL-P) and cholesterol efflux capacity (CEC), predicted incident CAD in a large cohort of childhood onset T1D (n=550). At baseline, mean age was 27.8 yrs, T1D duration was 19.6 yrs and 49% were women. HDL-P was assessed by calibrated ion mobility analysis and CEC was quantified with validated assays in cAMP stimulated J774 cells and in ABCA1-expressing BHK cells. CAD was defined as CAD death, myocardial infarction and/or revascularization. During a median follow-up of 26 yrs, we observed 203 incident CAD cases (36.9%). At baseline, incident cases were older, more likely to have smoked, have hypertension, longer duration of T1D, higher non-HDL-C and markers of kidney disease and inflammation. Cases were also more likely to have lower HDL-P concentrations but similar CEC to non-cases. Cox models with backward elimination were constructed for each HDL metric, allowing for potential confounding variables, including HDL-C. In separate multivariable models, higher concentrations of total HDL-P (T-HDL-P, HR=0.88, 95% CI: 0.83-0.92) and 3 major HDL subpopulations - small (S-HDL-P, HR=0.78, 0.67-0.92), medium (M-HDL-P, HR=0.79, 0.71-0.88) and large-sized (L-HDL-P, HR=0.74, 0.61-0.89) particles - associated with a lower CAD incidence whereas HDL-C did not. Higher total CEC in J774 cells also predicted lower CAD risk (HR=0.74, 0.55-0.996) after similar adjustments, but became non-significant after further adjusting for HDL-P. ABCA1-specific CEC did not predict CAD. Our results suggest that increased HDL-P levels are cardioprotective in T1D, in contrast to HDL-C and CEC which did not independently predict CAD. Disclosure T. Costacou: None. T. Vaisar: Consultant; Self; AstraZeneca. K. Bornfeldt: None. T. J. Orchard: None. J. Heinecke: None. Funding National Institutes of Health (HL130153, DK34818)

Perimenopausal transdermal estradiol replacement reduces serum HDL cholesterol efflux capacity but improves cardiovascular risk factors

The cardiovascular (CV) safety of estrogen replacement therapy (ERT) in perimenopausal women remains uncertain. Although exogenous estrogens increase HDL cholesterol (HDL-C), estrogen-mediated effects on alternative metrics of HDL that may better predict CV risk are unknown. To determine the effects of transdermal ERT on HDL composition and cholesterol efflux capacity (CEC), as well as the relationships between these metrics and CV risk factors. Fasting plasma samples were analyzed from 101 healthy, perimenopausal women randomized to receive either transdermal placebo or transdermal estradiol (100 μg/24h) with intermittent micronized progesterone. At baseline and after 6 months of treatment, serum HDL CEC, HDL particle concentration, HDL protein composition, insulin resistance and brachial artery flow-mediated dilatation (FMD) were measured. No difference between groups was found for change in plasma HDL-C (p=0.69). Between-group differences were found for changes in serum HDL total CEC [median change from baseline -5.4 (-17.3,+8.4)% ERT group versus+5.8 (-6.3,+16.9)% placebo group, p=0.01] and ABCA1-specific CEC [median change from baseline -5.3 (-10.7,+6.7)% ERT group versus+7.4 (-1.5,+18.1)% placebo group, p=0.0002]. Relative to placebo, transdermal ERT led to reductions in LDL-C (p<0.0001) and insulin resistance (p=0.0002). An inverse correlation was found between changes in serum HDL total CEC and FMD (β=-0.26, p=0.004). Natural menopause leads to an increase in serum HDL CEC, an effect that is abrogated by transdermal ERT. However, transdermal ERT leads to favorable changes in major CV risk factors.

Genetic control of the mouse HDL proteome defines HDL traits, function, and heterogeneity

HDLs are nanoparticles with more than 80 associated proteins, phospholipids, cholesterol, and cholesteryl esters. The potential inverse relation of HDL to coronary artery disease (CAD) and the effects of HDL on myriad other inflammatory conditions warrant a better understanding of the genetic basis of the HDL proteome. We conducted a comprehensive genetic analysis of the regulation of the proteome of HDL isolated from a panel of 100 diverse inbred strains of mice (the hybrid mouse diversity panel) and examined protein composition and efflux capacity to identify novel factors that affect the HDL proteome. Genetic analysis revealed widely varied HDL protein levels across the strains. Some of this variation was explained by local cis-acting regulation, termed cis-protein quantitative trait loci (QTLs). Variations in apoA-II and apoC-3 affected the abundance of multiple HDL proteins, indicating a coordinated regulation. We identified modules of covarying proteins and defined a protein-protein interaction network that describes the protein composition of the naturally occurring subspecies of HDL in mice. Sterol efflux capacity varied up to 3-fold across the strains, and HDL proteins displayed distinct correlation patterns with macrophage and ABCA1-specific cholesterol efflux capacity and cholesterol exchange, suggesting that subspecies of HDL participate in discrete functions. The baseline and stimulated sterol efflux capacity phenotypes were associated with distinct QTLs with smaller effect size, suggesting a multigenetic regulation. Our results highlight the complexity of HDL particles by revealing the high degree of heterogeneity and intercorrelation, some of which is associated with functional variation, and support the concept that HDL-cholesterol alone is not an accurate measure of HDL’s properties, such as protection against CAD.

Abstract 384: Differential Effects of Niacin and Omega-3 Fatty Acids on HDL-apolipoprotein A-I Exhange and Cholesterol Efflux Capacity in Subjects with Metabolic Syndrome

Objective: Niacin and omega-3 fatty acids are two therapeutic agents that have been extensively studied for their ability to reduce cardiovascular disease risk, but their effectiveness has more recently been called into question. In this study, we investigate whether these agents alone and in combination alter HDL function, in particular, HDL-apolipoprotein A-I exchange (HAE), a measure of HDL dynamics, and serum cholesterol efflux capacity (CEC). Approach: Fifty-six subjects with metabolic syndrome (MetSyn) were recruited to a double-blind trial and randomized to 16 weeks of treatment with dual placebo, extended release niacin (ERN, 2g/day), prescription omega-3 ethyl esters (P-OM3, 4g/day), or combination. HDL function was assessed at baseline and following 16 weeks of treatment by measuring HAE, macrophage CEC, and ABCA1-specific CEC. Results: Compared to placebo, ERN and P-OM3 alone significantly increased HAE by 15.1 [8.2, 22.0] (p&lt;0.0001) and 12.4% [5.9, 18.9] ( P &lt;0.0001) respectively while the combination therapy increased HAE by 10.0% [3.2, 16.8] ( P =0.002). When evaluated by HAE:apoA-I ratio (a measure of apoA-I specific activity), ERN increased apoA-I specific activity by 20.1% [4.8, 36.9] ( P =0.008), P-OM3 by 30.1% [14.4, 45.9] ( P&lt; 0.0001), however with combination there was no increase, 9% [-6.6, 26.6] ( P =0.34). Triglyceride-adjusted macrophage CEC showed marginally significant increases with P-OM3 therapy ( P =0.05). No therapy significantly improved ABCA1-specific CEC. Conclusions: Much of the effect of ERN on HDL function can be attributed to this therapy raising apoA-I levels, but P-OM3 raises HDL function by independent means, increasing apoA-I specific activity. Future investigation is needed to determine whether interaction between ERN and P-OM3 therapies in combination reduces their overall effectiveness.

Sex steroids mediate discrete effects on HDL cholesterol efflux capacity and particle concentration in healthy men

Exogenous testosterone decreases serum concentrations of high-density lipoprotein cholesterol (HDL-C) in men, but whether this alters cardiovascular risk is uncertain. To investigate the effects of testosterone and estradiol on HDL particle concentration (HDL-Pima) and metrics of HDL function. We enrolled 53 healthy men, 19 to 55years of age, in a double-blinded, placebo-controlled, randomized trial. Subjects were rendered medically castrate using the GnRH receptor antagonist acyline and administered either (1) placebo gel, (2) low-dose transdermal testosterone gel (1.62%, 1.25g), (3) full replacement dose testosterone gel (1.62%, 5g) or (4) full replacement dose testosterone gel together with an aromatase inhibitor for 4weeks. At baseline and end of treatment, serum HDL total macrophage and ABCA1-specific cholesterol efflux capacity (CEC), HDL-Pima and size, and HDL protein composition were determined. Significant differences in serum HDL-C were observed with treatment across groups (P=.01 in overall repeated measures ANOVA), with increases in HDL-C seen after both complete and partial testosterone deprivation. Medical castration increased total HDL-Pima (median [interquartile range] 19.1 [1.8] nmol/L at baseline vs 21.3 [3.1] nmol/L at week 4, P=.006). However, corresponding changes in total macrophage CEC and ABCA1-specific CEC were not observed. Change in serum 17β-estradiol concentration correlated with change in total macrophage CEC (β=0.33 per 10 pg/mL change in serum 17β-estradiol, P=.03). Testosterone deprivation in healthy men leads to a dissociation between changes in serum HDL-C and HDL CEC. Changes in serum HDL-C specifically due to testosterone exposure may not reflect changes in HDL function.

Plasminogen promotes cholesterol efflux by the ABCA1 pathway.

Using genetic and biochemical approaches, we investigated proteins that regulate macrophage cholesterol efflux capacity (CEC) and ABCA1-specific CEC (ABCA1 CEC), 2 functional assays that predict cardiovascular disease (CVD). Macrophage CEC and the concentration of HDL particles were markedly reduced in mice deficient in apolipoprotein A-I (APOA1) or apolipoprotein E (APOE) but not apolipoprotein A-IV (APOA4). ABCA1 CEC was markedly reduced in APOA1-deficient mice but was barely affected in mice deficient in APOE or APOA4. High-resolution size-exclusion chromatography of plasma produced 2 major peaks of ABCA1 CEC activity. The early-eluting peak, which coeluted with HDL, was markedly reduced in APOA1- or APOE-deficient mice. The late-eluting peak was modestly reduced in APOA1-deficient mice but little affected in APOE- or APOA4-deficient mice. Ion-exchange chromatography and shotgun proteomics suggested that plasminogen (PLG) accounted for a substantial fraction of the ABCA1 CEC activity in the peak not associated with HDL. Human PLG promoted cholesterol efflux by the ABCA1 pathway, and PLG-dependent efflux was inhibited by lipoprotein(a) [Lp(a)]. Our observations identify APOA1, APOE, and PLG as key determinants of CEC. Because PLG and Lp(a) associate with human CVD risk, interplay among the proteins might affect atherosclerosis by regulating cholesterol efflux from macrophages.

Cholesterol Efflux Capacity and Subclasses of HDL Particles in Healthy Women Transitioning Through Menopause.

Growing evidence challenges the concept that high-density lipoprotein-cholesterol (HDL-C) is cardioprotective after menopause. HDL particle concentration (HDL-P) and cholesterol efflux capacity (CEC) might be better predictors of cardiovascular risk. Quantify alterations in HDL-P and CEC during menopause, correlating those changes with alterations in estradiol (E2) and FSH. Longitudinal study of HDL metrics before and after menopause as indexed by the final menstrual period (FMP). Forty-six women, mean baseline age 47.1 years, 33% black, 67% white. HDL-P concentration (HDL-PIMA) by calibrated ion mobility analysis (IMA); macrophage CEC with cAMP-stimulated macrophages; ATP-binding cassette transporter A1 (ABCA1)-specific CEC with BHK cells expressing human ABCA1. After a median of 2.1 years since FMP, both HDL-C (P = .03) and HDL-PIMA (P = .01) increased, with a selective increase in large HDL-PIMA (P = .01), whereas sizes of medium and small HDL-PIMA were decreased (P < .05). These changes were independent of race, body mass index, and time difference. Macrophage CEC and ABCA1-specific CEC increased after FMP (both P < .001). Greater declines in E2 correlated with larger increases in small HDL-PIMA (P = .01), whereas greater increases in FSH associated with greater reductions in the size of medium HDL-PIMA (P = .04). Macrophage CEC and ABCA1-specific CEC correlated positively with E2 levels only before menopause (P = .04 and .009, respectively). Large HDL-PIMA and CEC increased significantly in the early phase of the menopausal transition. Whether patterns of these alterations differ in late postmenopause is unknown. Further exploration is needed to assess that and to determine whether the reported changes in HDL metrics associate with increased cardiovascular risk after menopause.

Effects of the cholesteryl ester transfer protein inhibitor, TA-8995, on cholesterol efflux capacity and high-density lipoprotein particle subclasses

TA-8995 is a potent inhibitor of cholesteryl ester transfer protein (CETP) with beneficial effects on lipids and lipoproteins. The effect of TA-8995 on cholesterol efflux capacity (CEC), a measure of high-density lipoprotein (HDL) function, and HDL subparticle distribution is largely unknown. To assess the effect of the CETP inhibitor TA-8995 on ABCA1- and non-ABCA1-driven CEC and on HDL particle distribution. Total, non-ABCA1-, and ABCA1-specific CEC from J774cells and HDL subclass distribution assessed by two-dimensional gel electrophoresis were measured at baseline and after 12-week treatment in 187 mild-dyslipidemic patients randomized to placebo, 1mg, 5mg, 10mg TA-8995, or 10mg TA-8995 combined with 10mg rosuvastatin (NCT01970215). Compared with placebo, total, non-ABCA1-, and ABCA1-specific CEC were increased dose dependently by up to 38%, 72%, and 28%, respectively, in patients randomized to 10mg of TA-8995. PreBeta-1 HDL, the primary acceptor for ABCA1-driven cholesterol efflux, was increased by 36%. This increase in preBeta-1 HDL correlated significantly with the total and the ABCA1-driven CEC increase, whereas the high-density lipoprotein cholesterol (HDL-C) increase did not. TA-8995 dose dependently increased not only total and non-ABCA1-specific CEC but also ABCA1-specific CEC and preBeta-1 HDL particle levels. These findings suggest that TA-8995 not only increases HDL-C levels but also promotes functional properties of HDL particles. This CETP inhibitor-driven preBeta-1 HDL increase is an important predictor of both ABCA1 and total CEC increase, independent of HDL-C increase. Whether these changes in HDL particle composition and functionality have a beneficial effect on cardiovascular outcome requires formal testing in a cardiovascular outcome trial.

Abstract 255: Plasminogen Promotes Cholesterol Efflux by the ABCA1

Background: The cholesterol efflux capacity (CEC) of serum HDL, measured using cultured macrophages predicts incident and prevalent CVD risk in humans. The ABCA1 pathway is a key regulator of macrophage cholesterol homeostasis in vivo. Methods: We used genetic and biochemical approaches in mice to identify important mediators of CEC. Results: On high-resolution size-exclusion chromatography of mouse plasma, macrophage CEC and HDL co-eluted as a single major peak, suggesting that HDL mediates cholesterol efflux. In contrast, size-exclusion chromatography revealed two major peaks of material that promoted ABCA1-specific CEC, one of which was distinct from HDL. HDL particle concentration was reduced by 75% in Apoa1 -/- mice; this resulted in a 50% decrease in macrophage CEC but, surprisingly, had no impact on ABCA1-specific CEC. Orthogonal chromatography-mass spectrometric analysis of the non-HDL-associated efflux inducing material isolated from wild-type and APOA1 deficient plasma showed that plasminogen strongly correlated with ABCA1-specific CEC. Moreover, isolated plasminogen promoted cholesterol efflux by the ABCA1 pathway, and the specific activity of ABCA1-specific CEC of non-HDL-associated material was reduced by 50% in plasminogen deficient plasma. Imaging of cells treated with fluorescently-labeled antibodies demonstrated that ABCA1 and plasminogen co-localized on the plasma membrane. Conclusions: HDL particle concentration is an important contributor to macrophage CEC. However, other pathways contribute to ABCA1-specific CEC; our studies identify plasminogen as one potential mediator. Plasminogen associates with CVD risk in human genetic studies, raising the possibility that it plays a role in atherosclerosis by modulating ABCA1-mediated sterol efflux from macrophages.

Proteomic analysis of HDL from inbred mouse strains implicates APOE associated with HDL in reduced cholesterol efflux capacity via the ABCA1 pathway

Cholesterol efflux capacity associates strongly and negatively with the incidence and prevalence of human CVD. We investigated the relationships of HDL’s size and protein cargo with its cholesterol efflux capacity using APOB-depleted serum and HDLs isolated from five inbred mouse strains with different susceptibilities to atherosclerosis. Like humans, mouse HDL carried >70 proteins linked to lipid metabolism, the acute-phase response, proteinase inhibition, and the immune system. HDL’s content of specific proteins strongly correlated with its size and cholesterol efflux capacity, suggesting that its protein cargo regulates its function. Cholesterol efflux capacity with macrophages strongly and positively correlated with retinol binding protein 4 (RBP4) and PLTP, but not APOA1. In contrast, ABCA1-specific cholesterol efflux correlated strongly with HDL’s content of APOA1, APOC3, and APOD, but not RBP4 and PLTP. Unexpectedly, APOE had a strong negative correlation with ABCA1-specific cholesterol efflux capacity. Moreover, the ABCA1-specific cholesterol efflux capacity of HDL isolated from APOE-deficient mice was significantly greater than that of HDL from wild-type mice. Our observations demonstrate that the HDL-associated APOE regulates HDL’s ABCA1-specific cholesterol efflux capacity. These findings may be clinically relevant because HDL’s APOE content associates with CVD risk and ABCA1 deficiency promotes unregulated cholesterol accumulation in human macrophages.

Cholesterol Efflux Capacity and Pre-Beta-1 HDL Concentrations Are Increased in Dyslipidemic Patients Treated With Evacetrapib

BackgroundPotent cholesteryl ester transfer protein (CETP) inhibitors have been shown to substantially increase high-density lipoprotein cholesterol (HDL-C) and apolipoprotein A-I levels as monotherapy and combined with statins. However, data on the effects of this class of drugs on macrophage cholesterol efflux capacity (CEC), a functional assay that characterizes a key step in the process of reverse cholesterol transport, are limited. ObjectivesThis study assessed the impact of evacetrapib, statins, or combination therapy on CEC. MethodsWe analyzed samples from 377 subjects with elevated low-density lipoprotein cholesterol (LDL-C) or low HDL-C levels who were enrolled in a phase 2 trial of evacetrapib. Percent changes from baseline in CEC (total, non–ABCA1-, and ABCA1-specific) and HDL subpopulations were evaluated after 12 weeks of treatment with placebo, statin monotherapy, evacetrapib monotherapy, or evacetrapib combined with statins. Pre–beta-1 HDL levels were quantified by immunofixation and nondenaturing 2-dimensional gel electrophoresis (2DGE). ResultsRelative to placebo, evacetrapib monotherapy increased dose-dependent total and non–ABCA1-specific CEC up to 34% and 47%, respectively. Evacetrapib monotherapy also increased ABCA1-specific CEC up to 26%. Relative to statin monotherapy, evacetrapib with statins also increased total, non–ABCA1-, and ABCA1-specific CEC by 21%, 27%, and 15%, respectively. In contrast, rosuvastatin and simvastatin significantly reduced total and ABCA1-specific CEC, whereas atorvastatin had no significant effect. Consistent with ABCA1-specific CEC, evacetrapib monotherapy and evacetrapib combined with statins significantly increased pre–beta-1 HDL levels as measured by either method. ConclusionsEvacetrapib, as monotherapy and combined with statins, not only increased total CEC, but also increased ABCA1-specific CEC and pre–beta-1 HDL. The mechanisms by which potent CETP inhibition increases ABCA1-specific CEC and pre–beta-1 HDL require further study. (A Study of LY2484595 in Patients With High LDL-C or Low HDL-C; NCT01105975)

HDL-apolipoprotein A-I exchange is independently associated with cholesterol efflux capacity

HDL is the primary mediator of cholesterol mobilization from the periphery to the liver via reverse cholesterol transport (RCT). A critical first step in this process is the uptake of cholesterol from lipid-loaded macrophages by HDL, a function of HDL inversely associated with prevalent and incident cardiovascular disease. We hypothesized that the dynamic ability of HDL to undergo remodeling and exchange of apoA-I is an important and potentially rate-limiting aspect of RCT. In this study, we investigated the relationship between HDL-apoA-I exchange (HAE) and serum HDL cholesterol (HDL-C) efflux capacity. We compared HAE to the total and ABCA1-specific cholesterol efflux capacity of 77 subjects. We found that HAE was highly correlated with both total (r = 0.69, P < 0.0001) and ABCA1-specific (r = 0.47, P < 0.0001) efflux, and this relationship remained significant after adjustment for HDL-C or apoA-I. Multivariate models of sterol efflux capacity indicated that HAE accounted for approximately 25% of the model variance for both total and ABCA1-specific efflux. We conclude that the ability of HDL to exchange apoA-I and remodel, as measured by HAE, is a significant contributor to serum HDL efflux capacity, independent of HDL-C and apoA-I, indicating that HDL dynamics are an important factor in cholesterol efflux capacity and likely RCT.

Abstract 387: HDL Structure and Function in Individuals with Extreme High HDL-C Who Have Coronary Artery Disease Compared with Those Without CAD

Plasma levels of high-density lipoprotein cholesterol (HDL-C) are strongly inversely associated with coronary artery disease (CAD) in epidemiologic studies, and high HDL-C is generally associated with apparent ‘protection’ from CAD. We have been recruiting individuals with high HDL-C for about 15 years, and while most have no CAD, a minority has premature CAD, a paradoxical phenotype. We hypothesize that such individuals may have HDL with altered structure and/ or function, and are systematically comparing these individuals (cases) to older individuals with extreme high HDL-C without CAD (controls) and a healthy control group with normal HDL-C levels. We identified 60 subjects with HDL-C above the 90th percentile, premature CAD, and no other major risk factors for coronary disease. We selected 2 controls per case, each matched for age, race, gender, and HDL level. Demographic information and lipid profile (mean ± SD) of the study groups are shown below. Controls are well matched to the cases. Studies are well underway to assess HDL size distribution by NMR, HDL composition, total and ABCA1-specific cholesterol efflux capacity, lecithin-cholesterol acyltransferase (LCAT) activity, and cholesteryl ester transfer protein (CETP) activity in cases and controls. We will also compare to a group of healthy controls with normal HDL-C levels. We expect that the findings from this study will provide insight into the etiology of CAD in this paradoxical phenotype.