Plasma monomeric ApoA1 and high-density lipoprotein bound ApoA1 are markedly decreased and associated with low levels of lipophilic antioxidants in sickle cell disease: A potential new pathway for therapy.

Patients with sickle cell disease (SCD) exhibit high levels of reactive oxygen species and low plasma levels of lipophilic antioxidants, which may contribute to end-organ damage and disease sequelae. Apolipoprotein A1, the major apolipoprotein of high-density lipoprotein (HDL), is mainly secreted by the intestine and liver in the form of monomeric ApoA1 (mApoA1) present in plasma. Cholesterol and α-tocopherol are delivered to ApoA1 via the ATP-binding cassette transporter, subfamily A, member 1 (ABCA1). We measured cholesterol, mApoA1, ApoA1, and lipophilic antioxidants in the plasma of 17 patients with SCD and 40 healthy volunteers. Mean HDL cholesterol (-C) levels in SCD patients and healthy subjects were 59.3 and 48.1 mg/dL, respectively, and plasma lutein, zeaxanthin, and α-tocopherol were 64.0%, 68.7%, and 9.1% lower, respectively. To compare SCD to healthy subjects with similar HDL-C, we also performed subgroup analyses of healthy subjects with HDL-C above or below the mean. In SCD, the mApoA1 level was 30.4 µg/mL; 80% lower than 141 µg/mL measured in healthy volunteers with similar HDL-C (56.7 mg/dL). The mApoA1 level was also 38.4% greater in the higher versus lower HDL-C subgroups (p = .002). In the higher HDL-C subgroup, lutein and zeaxanthin transported by HDL were 48.9% (p = .01) and 41.9% (p = .02) higher, respectively, whereas α-tocopherol was 31.7% higher (p = .003), compared to the lower HDL-C subgroup. Plasma mApoA1 may be a marker of the capacity of HDL to capture and deliver liposoluble antioxidants, and treatments which raise HDL may benefit patients with high oxidative stress as exemplified by SCD.

Dalcetrapib and anacetrapib increase apolipoprotein E-containing HDL in rabbits and humans.

The large HDL particles generated by administration of cholesteryl ester transfer protein inhibitors (CETPi) remain poorly characterized, despite their potential importance in the routing of cholesterol to the liver for excretion, which is the last step of the reverse cholesterol transport. Thus, the effects of the CETPi dalcetrapib and anacetrapib on HDL particle composition were studied in rabbits and humans. The association of rabbit HDL to the LDL receptor (LDLr) in vitro was also evaluated. New Zealand White rabbits receiving atorvastatin were treated with dalcetrapib or anacetrapib. A subset of patients from the dal-PLAQUE-2 study treated with dalcetrapib or placebo were also studied. In rabbits, dalcetrapib and anacetrapib increased HDL-C by more than 58% (P < 0.01) and in turn raised large apo E-containing HDL by 66% (P < 0.001) and 59% (P < 0.01), respectively. Additionally, HDL from CETPi-treated rabbits competed with human LDL for binding to the LDLr on HepG2 cells more than control HDL (P < 0.01). In humans, dalcetrapib increased concentrations of large HDL particles (+69%, P < 0.001) and apo B-depleted plasma apo E (+24%, P < 0.001), leading to the formation of apo E-containing HDL (+47%, P < 0.001) devoid of apo A-I. Overall, in rabbits and humans, CETPi increased large apo E-containing HDL particle concentration, which can interact with hepatic LDLr. The catabolism of these particles may depend on an adequate level of LDLr to contribute to reverse cholesterol transport.

Red Blood Cell Membrane Cholesterol May Be a Key Regulator of Sickle Cell Disease Microvascular Complications.

Cell membrane lipid composition, especially cholesterol, affects many functions of embedded enzymes, transporters and receptors in red blood cells (RBC). High membrane cholesterol content affects the RBCs' main vital function, O2 and CO2 transport and delivery, with consequences on peripheral tissue physiology and pathology. A high degree of deformability of RBCs is required to accommodate the size of micro-vessels with diameters significantly lower than RBCs. The potential therapeutic role of high-density lipoproteins (HDL) in the removal of cholesterol and its activity regarding maintenance of an optimal concentration of RBC membrane cholesterol have not been well investigated. On the contrary, the focus for HDL research has mainly been on the clearance of cholesterol accumulated in atherosclerotic macrophages and plaques. Since all interventions aiming at decreasing cardiovascular diseases by increasing the plasma level of HDL cholesterol have failed so far in large outcome studies, we reviewed the potential role of HDL to remove excess membrane cholesterol from RBC, especially in sickle cell disease (SCD). Indeed, abundant literature supports a consistent decrease in cholesterol transported by all plasma lipoproteins in SCD, in addition to HDL, low- (LDL) and very low-density lipoproteins (VLDL). Unexpectedly, these decreases in plasma were associated with an increase in RBC membrane cholesterol. The concentration and activity of the main enzyme involved in the removal of cholesterol and generation of large HDL particles-lecithin cholesterol ester transferase (LCAT)-are also significantly decreased in SCD. These observations might partially explain the decrease in RBC deformability, diminished gas exchange and tendency of RBCs to aggregate in SCD. We showed that incubation of RBC from SCD patients with human HDL or the HDL-mimetic peptide Fx5A improves the impaired RBC deformability and decreases intracellular reactive oxygen species levels. We propose that the main physiological role of HDL is to regulate the cholesterol/phospholipid ratio (C/PL), which is fundamental to the transport of oxygen and its delivery to peripheral tissues.

HDL as Bidirectional Lipid Vectors: Time for New Paradigms.

The anti-atherogenic properties of high-density lipoproteins (HDL) have been explained mainly by reverse cholesterol transport (RCT) from peripheral tissues to the liver. The RCT seems to agree with most of the negative epidemiological correlations between HDL cholesterol levels and coronary artery disease. However, therapies designed to increase HDL cholesterol failed to reduce cardiovascular risk, despite their capacity to improve cholesterol efflux, the first stage of RCT. Therefore, the cardioprotective role of HDL may not be explained by RCT, and it is time for new paradigms about the physiological function of these lipoproteins. It should be considered that the main HDL apolipoprotein, apo AI, has been highly conserved throughout evolution. Consequently, these lipoproteins play an essential physiological role beyond their capacity to protect against atherosclerosis. We propose HDL as bidirectional lipid vectors carrying lipids from and to tissues according to their local context. Lipid influx mediated by HDL appears to be particularly important for tissue repair right on site where the damage occurs, including arteries during the first stages of atherosclerosis. In contrast, the HDL-lipid efflux is relevant for secretory cells where the fusion of intracellular vesicles drastically enlarges the cytoplasmic membrane with the potential consequence of impairment of cell function. In such circumstances, HDL could deliver some functional lipids and pick up not only cholesterol but an integral part of the membrane in excess, restoring the viability of the secretory cells. This hypothesis is congruent with the beneficial effects of HDL against atherosclerosis as well as with their capacity to induce insulin secretion and merits experimental exploration.

Inhibition of the 3CL Protease and SARS-CoV-2 Replication by Dalcetrapib.

The severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) 3CL protease is a promising target for inhibition of viral replication by interaction with a cysteine residue (Cys145) at its catalytic site. Dalcetrapib exerts its lipid-modulating effect by binding covalently to cysteine 13 of a cholesteryl ester transfer protein. Because 12 free cysteine residues are present in the 3CL protease, we investigated the potential of dalcetrapib to inhibit 3CL protease activity and SARS-CoV-2 replication. Molecular docking investigations suggested that dalcetrapib-thiol binds to the catalytic site of the 3CL protease with a delta G value of -8.5 kcal/mol. Dalcetrapib inhibited both 3CL protease activity in vitro and viral replication in Vero E6 cells with IC50 values of 14.4 ± 3.3 µM and an EC50 of 17.5 ± 3.5 µM (mean ± SD). Near-complete inhibition of protease activity persisted despite 1000-fold dilution after ultrafiltration with a nominal dalcetrapib-thiol concentration of approximately 100 times below the IC50 of 14.4 µM, suggesting stable protease-drug interaction. The inhibitory effect of dalcetrapib on the SARS-CoV-2 3CL protease and viral replication warrants its clinical evaluation for the treatment of COVID-19.

Role of Adenylate Cyclase 9 in the Pharmacogenomic Response to Dalcetrapib: Clinical Paradigm and Molecular Mechanisms in Precision Cardiovascular Medicine.

Following the neutral results of the dal-OUTCOMES trial, a genome-wide study identified the rs1967309 variant in the adenylate cyclase type 9 (ADCY9) gene on chromosome 16 as being associated with the risk of future cardiovascular events only in subjects taking dalcetrapib, a CETP (cholesterol ester transfer protein) modulator. Homozygotes for the minor A allele (AA) were protected from recurrent cardiovascular events when treated with dalcetrapib, while homozygotes for the major G allele (GG) had increased risk. Here, we present the current state of knowledge regarding the impact of rs1967309 in ADCY9 on clinical observations and biomarkers in dalcetrapib trials and the effects of mouse ADCY9 gene inactivation on cardiovascular physiology. Finally, we present our current model of the interaction between dalcetrapib and ADCY9 gene variants in the arterial wall macrophage, based on the intracellular role of CETP in the transfer of complex lipids from endoplasmic reticulum membranes to lipid droplets. Briefly, the concept is that dalcetrapib would inhibit CETP-mediated transfer of cholesteryl esters, resulting in a progressive inhibition of cholesteryl ester synthesis and free cholesterol accumulation in the endoplasmic reticulum. Reduced ADCY9 activity, by paradoxically leading to higher cyclic AMP levels and in turn increased cellular cholesterol efflux, could impart cardiovascular protection in rs1967309 AA patients. The ongoing dal-GenE trial recruited 6145 patients with the protective AA genotype and will provide a definitive answer to whether dalcetrapib will be protective in this population.

HDL and atherosclerotic cardiovascular disease: genetic insights into complex biology.

Plasma levels of HDL cholesterol (HDL-C) predict the risk of cardiovascular disease at the epidemiological level, but a direct causal role for HDL in cardiovascular disease remains controversial. Studies in animal models and humans with rare monogenic disorders link only particular HDL-associated mechanisms with causality, including those mechanisms related to particle functionality rather than cholesterol content. Mendelian randomization studies indicate that most genetic variants that affect a range of pathways that increase plasma HDL-C levels are not usually associated with reduced risk of cardiovascular disease, with some exceptions, such as cholesteryl ester transfer protein variants. Furthermore, only a fraction of HDL-C variation has been explained by known loci from genome-wide association studies (GWAS), suggesting the existence of additional pathways and targets. Systems genetics can enhance our understanding of the spectrum of HDL pathways, particularly those pathways that involve new and non-obvious GWAS loci. Bioinformatic approaches can also define new molecular interactions inferred from both large-scale genotypic data and RNA sequencing data to reveal biologically meaningful gene modules and networks governing HDL metabolism with direct relevance to disease end points. Targeting these newly recognized causal networks might inform the development of novel therapeutic strategies to reduce the risk of cardiovascular disease.

Dalcetrapib and anacetrapib differently impact HDL structure and function in rabbits and monkeys.

Inhibition of cholesteryl ester transfer protein (CETP) increases HDL cholesterol (HDL-C) levels. However, the circulating CETP level varies and the impact of its inhibition in species with high CETP levels on HDL structure and function remains poorly characterized. This study investigated the effects of dalcetrapib and anacetrapib, the two CETP inhibitors (CETPis) currently being tested in large clinical outcome trials, on HDL particle subclass distribution and cholesterol efflux capacity of serum in rabbits and monkeys. New Zealand White rabbits and vervet monkeys received dalcetrapib and anacetrapib. In rabbits, CETPis increased HDL-C, raised small and large α-migrating HDL, and increased ABCA1-induced cholesterol efflux. In vervet monkeys, although anacetrapib produced similar results, dalcetrapib caused opposite effects because the LDL-C level was increased by 42% and HDL-C decreased by 48% (P < 0.01). The levels of α- and preß-HDL were reduced by 16% (P < 0.001) and 69% (P < 0.01), resulting in a decrease of the serum cholesterol efflux capacity. CETPis modulate the plasma levels of mature and small HDL in vivo and consequently the cholesterol efflux capacity. The opposite effects of dalcetrapib in different species indicate that its impact on HDL metabolism could vary greatly according to the metabolic environment.

Cholesteryl ester transfer between lipoproteins does not require a ternary tunnel complex with CETP.

The cholesteryl ester transfer protein (CETP) enables the transfer of cholesteryl ester (CE) from high-density lipoproteins (HDL) to low-density lipoproteins (LDL) in the plasma compartment. CETP inhibition raises plasma levels of HDL cholesterol; a ternary tunnel complex with CETP bridging HDL and LDL was suggested as a mechanism. Here, we test whether the inhibition of CETP tunnel complex formation is a promising approach to suppress CE transfer from HDL to LDL, for potential treatment of cardio-vascular disease (CVD). Three monoclonal antibodies against different epitopes of CETP are assayed for their potential to interfere with CE transfer between HDL and/or LDL. Surprisingly, antibodies that target the tips of the elongated CETP molecule, interaction sites sterically required to form the suggested transfer complexes, do not interfere with CETP activity, but an antibody binding to the central region does. We show that CETP interacts with HDL, but not with LDL. Our findings demonstrate that a ternary tunnel complex is not the mechanistic prerequisite to transfer CE among lipoproteins.

Adenylyl Cyclase 9 Polymorphisms Reveal Potential Link to HDL Function and Cardiovascular Events in Multiple Pathologies: Potential Implications in Sickle Cell Disease.

Adenylyl cyclase 9 (ADCY9) mediates ß2-adrenoceptor (ß2-AR) signalling. Both proteins are associated with caveolae, specialized cholesterol-rich membrane substructures. Apolipoprotein A1 (ApoA1), the major protein component of high-density lipoprotein (HDL), removes cholesterol from cell membrane and caveolae and may thereby influence ß2-AR signalling, shown in vitro to be modulated by cholesterol. Patients with Sickle Cell Disease (SCD) typically have low HDL and ApoA1 levels. In patients, mainly of African origin, with SCD, ß2-AR activation may trigger adhesion of red blood cells to endothelial cells, leading to vascular occlusive events. Moreover, ADCY9 polymorphism is associated with risk of stroke in SCD. In recent clinical trials, ADCY9 polymorphism was found to be a discriminant factor associated with the risk of cardiovascular (CV) events in Caucasian patients treated with the HDL-raising compound dalcetrapib. We hypothesize that these seemingly disparate observations share a common mechanism related to interaction of HDL/ApoA1 and ADCY9 on ß2-AR signalling. This review also raises the importance of characterizing polymorphisms that determine the response to HDL-raising and -mimicking agents in the non-Caucasian population at high risk of CV diseases and suffering from SCD. This may facilitate personalized CV treatments.

Fenofibrate lowers atypical sphingolipids in plasma of dyslipidemic patients: A novel approach for treating diabetic neuropathy?

BACKGROUND: The condensation of palmitoyl-CoA and L-Serine is the first step in the de novo formation of sphingolipids and catalyzed by the serine-palmitoyltransferase (SPT). Besides other acyl-CoAs the SPT can also metabolize L-alanine and glycine, which forms an atypical category of neurotoxic 1-deoxy-sphingolipids (1-deoxySL). Several mutations in SPT are associated with pathologically increased 1-deoxySL levels, which cause the inherited sensory neuropathy HSAN1. 1-DeoxySL levels are also elevated in individuals with the metabolic syndrome and diabetes mellitus type II and seem to be involved in the pathology of the diabetic neuropathy. OBJECTIVE: In previous studies, we observed a strong correlation between plasma 1-deoxySLs and triglycerides (TGs). We were therefore interested whether lowering plasma TG levels also affects plasma sphingolipid and in particular, 1-deoxySL levels. METHODS: Sixty-six patients with dyslipidemia were treated for 6 wk with the TG-lowering drug fenofibrate (160 mg/d) or extended-release niacin (0.5 g/d for 3 wk, then 1 g/d) with 4 wk of washout between treatments. The sphingoid base profile was analyzed by liquid chromatography-mass spectrometry (LC-MS) before and after each treatment block. RESULTS: Fenofibrate significantly lowered 1-deoxySLs and other atypical sphingoid bases (P < .001) but had no effect on the typical sphingolipids. In contrast, extended-release niacin had no effect on 1-deoxySL levels although both treatments lowered plasma TG levels. CONCLUSIONS: The lowering of plasma 1-deoxySL levels by fenofibrate in dyslipidemic patients might be a novel therapeutic approach in the prevention and treatment of diabetic neuropathy.

Fenofibrate and extended-release niacin improve the endothelial protective effects of HDL in patients with metabolic syndrome.

BACKGROUND: Fibrates and niacin are at present the most effective therapies to increase plasma levels of high density lipoprotein-cholesterol (HDL-C); to date, limited data are available on their effects on HDL protective functions. METHODS AND RESULTS: Within a multicenter, randomized, open-label, cross-over study, 37 patients with metabolic syndrome received 6weeks' treatment with fenofibrate or extended-release niacin (ER niacin), with a 4weeks' wash-out period. HDL ability to preserve endothelial cell homeostasis was assessed by incubating cultured endothelial cells with HDL isolated from patients at baseline and after each treatment. HDL isolated from patients at baseline were as effective as control HDL in inhibiting vascular cell adhesion molecule-1 (VCAM-1) expression, but less efficient in promoting endothelial cell nitric oxide (NO) release. Both fenofibrate and ER niacin increased HDL ability to inhibit TNFα-induced VCAM-1 expression (+7% and +11%, respectively). Fenofibrate and ER niacin also improved the impaired HDL ability to induce the expression of endothelial nitric oxide synthase and NO production (+10% and +8%, respectively). Interestingly, HDL isolated after treatment showed an ability to promote endothelial NO release similar to HDL isolated from controls. No differences were observed between the two drugs. With both drugs, HDL function was improved irrespective of baseline HDL-C levels. CONCLUSION: Treatment with fenofibrate or ER niacin in patients with metabolic syndrome not only increased HDL-C levels but also improved the endothelial protective effects of HDL.

Potential Signal Transduction Regulation by HDL of the ß2-Adrenergic Receptor Pathway. Implications in Selected Pathological Situations.

The main atheroprotective mechanism of high-density lipoprotein (HDL) has been regarded as reverse cholesterol transport, whereby cholesterol from peripheral tissues is removed and transported to the liver for elimination. Although numerous additional atheroprotective mechanisms have been suggested, the role of HDL in modulating signal transduction of cell membrane-bound receptors has received little attention to date. This potential was recently highlighted following the identification of a polymorphism in the adenylyl cyclase 9 gene (ADCY9) that was shown to be a determining factor in the risk of cardiovascular (CV) events in patients treated with the HDL-raising compound dalcetrapib. Indeed, ADCY9 is part of the signaling pathway of the ß2-adrenergic receptor (ß2-AR) and both are membrane-bound proteins affected by changes in membrane-rich cholesterol plasma membrane domains (caveolae). Numerous G-protein-coupled receptors (GPCRs) and ion channels are affected by caveolae, with caveolae composition acting as a 'signalosome'. Polymorphisms in the genes encoding ADCY9 and ß2-AR are associated with response to ß2-agonist drugs in patients with asthma, malaria and with sickle cell disease. Crystallization of the ß2-AR has found cholesterol tightly bound to transmembrane structures of the receptor. Cholesterol has also been shown to modulate the activity of this receptor. Apolipoprotein A1 (ApoA1), the major protein component of HDL, destabilizes and removes cholesterol from caveolae with high affinity through interaction with ATP-binding cassette transporter. Furthermore, ß2-AR activity may be affected by ApoA1/HDL-targeted therapies. Taken together, these observations suggest a common pathway that potentially links a primary HDL function to the regulation of signal transduction.

Statin-induced decrease in ATP-binding cassette transporter A1 expression via microRNA33 induction may counteract cholesterol efflux to high-density lipoprotein.

PURPOSE: Cholesterol efflux from macrophages to HDL, measured in vitro, is augmented by treatment with agents which raise HDL cholesterol. In vitro, cholesterol depletion by statins is known to trigger a positive feedback on the cholesterol synthetic pathway via sterol regulatory element-binding protein (SREBP) transcription and changes in expression of SREBP regulated genes including microRNA33 (miR33) which is co-transcribed with SREBP and down-regulates ABCA1 and ABCG1 expression. METHODS: We investigated whether miR33 up-regulation, associated with SREBP increased transcription by statins, reduces macrophage ATP-binding cassette (ABC) transporter expression, thereby decreasing HDL-mediated cholesterol efflux at the tissue level. RESULTS: In human macrophage THP-1 cells cholesterol-loaded with acetylated LDL, incubation with 1 µM atorvastatin increased miR33 by 33 % (P < 0.05), and decreased ABCA1 messenger RNA (mRNA) and ABCG1 mRNA by 47 % (P < 0.05) and 27 % (NS), respectively. In J774A.1 mouse macrophage, labelled with 3H-cholesterol, ABCA1 mRNA and ABCA1-mediated cholesterol efflux were decreased by 1 µM statin: simvastatin > pitavastatin > atorvastatin > rosuvastatin > pravastatin. HDL incubated with rhCETP and dalcetrapib increased ABCA1-mediated cholesterol efflux. However, incremental simvastatin concentrations decreased cholesterol efflux to HDL treated with rhCETP and dalcetrapib. When HDL was incubated with rhCETP, addition of dalcetrapib augmented ABCA1-mediated cholesterol efflux from J774A.1 macrophages. However, simvastatin ≥1 µM virtually eliminated any HDL-ABCA1-mediated cholesterol efflux and any augmentation of that process by dalcetrapib. CONCLUSIONS: In vitro, statins increase miR33 expression, and decrease ABCA1 expression and cholesterol efflux from peripheral tissues; this may counteract the potential benefit of agents that raise HDL and apolipoprotein A-I in statin-treated patients.

Will Lipidation of ApoA1 through Interaction with ABCA1 at the Intestinal Level Affect the Protective Functions of HDL?

The relationship between levels of high-density lipoprotein cholesterol (HDL-C) and cardiovascular (CV) risk is well recognized; however, in recent years, large-scale phase III studies with HDL-C-raising or -mimicking agents have failed to demonstrate a clinical benefit on CV outcomes associated with raising HDL-C, casting doubt on the "HDL hypothesis." This article reviews potential reasons for the observed negative findings with these pharmaceutical compounds, focusing on the paucity of translational models and relevant biomarkers related to HDL metabolism that may have confounded understanding of in vivo mechanisms. A unique function of HDL is its ability to interact with the ATP-binding cassette transporter (ABC) A1 via apolipoprotein (Apo) A1. Only recently, studies have shown that this process may be involved in the intestinal uptake of dietary sterols and antioxidants (vitamin E, lutein and zeaxanthin) at the basolateral surface of enterocytes. This parameter should be assessed for HDL-raising drugs in addition to the more documented reverse cholesterol transport (RCT) from peripheral tissues to the liver. Indeed, a single mechanism involving the same interaction between ApoA1 and ABCA1 may encompass two HDL functions previously considered as separate: antioxidant through the intestinal uptake of antioxidants and RCT through cholesterol efflux from loaded cells such as macrophages.

Pharmacogenomic determinants of the cardiovascular effects of dalcetrapib.

BACKGROUND: Dalcetrapib did not improve clinical outcomes, despite increasing high-density lipoprotein cholesterol by 30%. These results differ from other evidence supporting high-density lipoprotein as a therapeutic target. Responses to dalcetrapib may vary according to patients' genetic profile. METHODS AND RESULTS: We conducted a pharmacogenomic evaluation using a genome-wide approach in the dal-OUTCOMES study (discovery cohort, n=5749) and a targeted genotyping panel in the dal-PLAQUE-2 imaging trial (support cohort, n=386). The primary endpoint for the discovery cohort was a composite of cardiovascular events. The change from baseline in carotid intima-media thickness on ultrasonography at 6 and 12 months was evaluated as supporting evidence. A single-nucleotide polymorphism was found to be associated with cardiovascular events in the dalcetrapib arm, identifying the ADCY9 gene on chromosome 16 (rs1967309; P=2.41×10(-8)), with 8 polymorphisms providing P<10(-6) in this gene. Considering patients with genotype AA at rs1967309, there was a 39% reduction in the composite cardiovascular endpoint with dalcetrapib compared with placebo (hazard ratio, 0.61; 95% confidence interval, 0.41-0.92). In patients with genotype GG, there was a 27% increase in events with dalcetrapib versus placebo. Ten single-nucleotide polymorphism in the ADCY9 gene, the majority in linkage disequilibrium with rs1967309, were associated with the effect of dalcetrapib on intima-media thickness (P<0.05). Marker rs2238448 in ADCY9, in linkage disequilibrium with rs1967309 (r(2)=0.8), was associated with both the effects of dalcetrapib on intima-media thickness in dal-PLAQUE-2 (P=0.009) and events in dal-OUTCOMES (P=8.88×10(-8); hazard ratio, 0.67; 95% confidence interval, 0.58-0.78). CONCLUSIONS: The effects of dalcetrapib on atherosclerotic outcomes are determined by correlated polymorphisms in the ADCY9 gene. CLINICAL TRIAL INFORMATION: URL: http://www.clinicaltrials.gov. Unique identifiers: NCT00658515 and NCT01059682.

Effect of compounds affecting ABCA1 expression and CETP activity on the HDL pathway involved in intestinal absorption of lutein and zeaxanthin.

The antioxidant xanthophylls lutein and zeaxanthin are absorbed from the diet in a process involving lipoprotein formation. Selective mechanisms exist for their intestinal uptake and tissue-selective distribution, but these are poorly understood. We investigated the role of high-density lipoprotein (HDL), apolipoprotein (apo) A1 and ATP-binding cassette transporter (ABC) A1 in intestinal uptake of lutein in a human polarized intestinal cell culture and a hamster model. Animals received dietary lutein and zeaxanthin and either a liver X receptor (LXR) agonist or statin, which up- or down-regulate intestinal ABCA1 expression, respectively. The role of HDL was studied following treatment with the cholesteryl ester transfer protein (CETP) modulator dalcetrapib or the CETP inhibitor anacetrapib. In vitro, intestinal ABCA1 at the basolateral surface of enterocytes transferred lutein and zeaxanthin to apoA1, not to mature HDL. In hamsters, plasma lutein and zeaxanthin levels were markedly increased with the LXR agonist and decreased with simvastatin. Dalcetrapib, but not anacetrapib, increased plasma and liver lutein and zeaxanthin levels. ABCA1 expression and apoA1 acceptor activity are important initial steps in intestinal uptake and maintenance of lutein and zeaxanthin levels by an HDL-dependent pathway. Their absorption may be improved by physiological and pharmacological interventions affecting HDL metabolism.

Treatment of low HDL-C subjects with the CETP modulator dalcetrapib increases plasma campesterol only in those without ABCA1 and/or ApoA1 mutations.

We investigated the effect of dalcetrapib treatment on phytosterol levels in patients with familial combined hyperlipidemia (FCH) or familial hypoalphalipoproteinemia (FHA) due to mutations in apolipoprotein A1 (ApoA1) or ATP-binding cassette transporter A1 (ABCA1). Patients (n = 40) with FCH or FHA received dalcetrapib 600 mg or placebo in this 4-week, double-blind, crossover study. Lipids, apolipoproteins, cholesteryl ester transfer protein (CETP) activity and mass, and phytosterols were assessed. Dalcetrapib increased high-density lipoprotein cholesterol (HDL-C) and ApoA1 levels to a similar extent in FHA (+22.8, +13.9%) and FCH (+18.4, +12.1%), both p < 0.001 vs. placebo. Changes in CETP activity and mass were comparable for FHA (-31.5, +120.9%) and FCH (-26.6, +111.9%), both p < 0.0001 vs. placebo. Campesterol and lathosterol were unchanged in FHA (+3.8, +3.0%), but only campesterol was markedly increased in FCH (+25.0%, p < 0.0001 vs. placebo). Campesterol increased with dalcetrapib treatment in FCH but not in FHA, despite comparable HDL-C and ApoA1 increases, suggesting that ApoA1 and/or ABCA1 is essential for HDL lipidation by enterocytes in humans.

The effect of cholesteryl ester transfer protein inhibition on lipids, lipoproteins, and markers of HDL function after an acute coronary syndrome: the dal-ACUTE randomized trial.

AIMS: The effects of cholesteryl ester transfer protein (CETP) inhibition on lipids, inflammation, and markers of high-density lipoprotein (HDL) function, following an acute coronary syndrome (ACS), are unknown. METHODS AND RESULTS: The dal-ACUTE study randomized 300 patients (1 : 1) to dalcetrapib 600 mg/day or placebo within 1 week of an ACS. The primary endpoint was per cent change in HDL-cholesterol (HDL-C) after 4 weeks. Secondary endpoints included apolipoprotein levels, markers of HDL function, and inflammation. Dalcetrapib treatment increased HDL-C and apolipoprotein A1 by 33.7 and 11.8%, respectively (both P < 0.001) and total cholesterol efflux by 9.5% (P = 0.003) after 4 weeks, principally via an increase in non-ATP-binding cassette transporter (ABC) A1-mediated efflux, without statistically significant changes in pre-ß1-HDL levels. The increase in total efflux with dalcetrapib correlated most strongly with increases in apolipoprotein A1 and HDL-C (r = 0.46 and 0.43, respectively) rather than the increase in pre-ß1-HDL (r = 0.32). Baseline and on-treatment ABCA1-mediated efflux correlated most strongly with pre-ß1-HDL levels; in contrast, non-ABCA1-mediated efflux correlated better with apolipoprotein A1 and HDL-C levels. CONCLUSIONS: High-density lipoprotein raised through CETP inhibition with dalcetrapib improves cholesterol efflux, principally via a non-ABCA1-mediated pathway. While HDL-C was increased by one-third, apolipoprotein A1 and total efflux were increased only by one-tenth, supporting the concept of dissociation between improvements in HDL function and HDL-C levels, which may be of relevance to ongoing trials and the development of therapeutic interventions targeting HDL.