Combination of mangiferin and T0901317 targeting autophagy promotes cholesterol efflux from macrophage foam cell in atherosclerosis

BACKGROUND

The synthetic liver X receptor ligand (LXR) T0901317 (T0) has been reported to attenuate atherosclerosis (AS) without hyperglyceridemia due to innovative drug combination or nano-sized drug delivery. Given the key roles of mangiferin (MGF) in lipid metabolism and atherogenesis, it is critical to investigate progression of atherosclerotic lesion after combined treatment of MGF and T0.

METHODS

Atherosclerotic plaque formation and hepatic lipid accumulation were compared in Apoe-/- mice among T0 and/or MGF treatment. The in vitro functions of MGF and T0 were analyzed by Oil-red O staining, cholesterol efflux assay, transmission electron microscopy and western blot analyses with or without acetylated low density lipoprotein.

RESULTS

The combination therapy are effective regulators for atherosclerotic plaque formation in Apoe-/- mice, due to upregulation of ABCA1 and ABCG1 induced by LXR activation. Subsequently, we identified autophagy promoted by MGF and T0 treatment establishes a positive feedback loop that increases cholesterol efflux, resulted from LXRα activation. Under atherogenic conditions, the autophagy inhibitor CQ abolished the enhancement effect on cholesterol outflow of MGF and T0. Mechanically, MGF and T0 promotes LXRα and mTOR/AMPK signaling cascade in macrophage, and promotes AMPK signaling cascade in hepatocyte, leading to lipid metabolic homeostasis.

CONCLUSIONS

Altogether, our findings reveal that MGF and T0 engages in AS therapy without side effects by activating AMPK-dependent autophagy to promote macrophage cholesterol efflux, and MGF might serve as a natural compound to assist T0 in AS via targeting autophagy.

Systems immunology-based drug repurposing framework to target inflammation in atherosclerosis

The development of new immunotherapies to treat the inflammatory mechanisms that sustain atherosclerotic cardiovascular disease (ASCVD) is urgently needed. Herein, we present a path to drug repurposing to identify immunotherapies for ASCVD. The integration of time-of-flight mass cytometry and RNA sequencing identified unique inflammatory signatures in peripheral blood mononuclear cells stimulated with ASCVD plasma. By comparing these inflammatory signatures to large-scale gene expression data from the LINCS L1000 dataset, we identified drugs that could reverse this inflammatory response. Ex vivo screens, using human samples, showed that saracatinib-a phase 2a-ready SRC and ABL inhibitor-reversed the inflammatory responses induced by ASCVD plasma. In Apoe-/- mice, saracatinib reduced atherosclerosis progression by reprogramming reparative macrophages. In a rabbit model of advanced atherosclerosis, saracatinib reduced plaque inflammation measured by [18F] fluorodeoxyglucose positron emission tomography-magnetic resonance imaging. Here we show a systems immunology-driven drug repurposing with a preclinical validation strategy to aid the development of cardiovascular immunotherapies.

Targeting macrophages in atherosclerosis using nanocarriers loaded with liver X receptor agonists: A narrow review

Macrophages are involved in the whole process of atherosclerosis, which is characterized by accumulation of lipid and inflammation. Presently, clinically used lipid-lowering drugs cannot completely retard the progress of atherosclerosis. Liver X receptor (LXR) plays a key role in regulation of lipid metabolism and inflammation. Accumulating evidence have demonstrated that synthetic LXR agonists can significantly retard the development of atherosclerosis. However, these agonists induce sever hypertriglyceridemia and liver steatosis. These side effects have greatly limited their potential application for therapy of atherosclerosis. The rapid development of drug delivery system makes it possible to delivery interested drugs to special organs or cells using nanocarriers. Macrophages express various receptors which can recognize and ingest specially modified nanocarriers loaded with LXR agonists. In the past decades, a great progress has been made in this field. These macrophage-targeted nanocarriers loaded with LXR agonists are found to decrease atherosclerosis by reducing cholesterol accumulation and inflammatory reactions. Of important, these nanocarriers can alleviate side effects of LXR agonists. In this article, we briefly review the roles of macrophages in atherosclerosis, mechanisms of action of LXR agonists, and focus on the advances of macrophage-targeted nanocarriers loaded with LXR agonists. This work may promote the potential clinical application of these nanocarriers.

The liver X receptor agonist LXR 623 restricts flavivirus replication

The vector-borne flaviviruses (VBFVs) are well known for causing great misery and death in humans worldwide. The VBFVs include those transmitted by mosquitos, such as Zika virus (ZIKV), dengue virus; and those transmitted by ticks including the tick-borne flavivirus serocomplex and Powassan virus (POWV). Two of our recent reports showed that intracranial POWV infection in the reservoir host, Peromyscus leucopus, was restricted and caused no overt clinical disease. Several modes of analyses suggested activation of the LXR pathway. Activation of the LXR pathway leads to increased efflux of cholesterol from cells and consequent disturbances in membrane biogenesis. Because VBFV replication is dependent on membrane biogenesis, we evaluated the effect of an LXR agonist (LXR623) on POWV and ZIKV infection and observed that the compound impaired permissive replication of both viruses in a human neuroblastoma SK-N-SH cell line. The LXR agonist resulted in failure of the viruses to induce ER expansion and elaborate vesicle formation, suggesting that the efflux of cholesterol was part of the antiviral mechanism. We also observed that the LXR agonist contributed to the mechanism of virus suppression by increased expression of mRNAs encoding for the antiviral cytokines CXCL10, RANTES and IFN1β. In sharp contrast, a LXR antagonist (GSK2033) had no significant effect on VBFV replication. We conclude that LXR623 impairs flavivirus replication by stimulating cellular antiviral factors.

Protective Functions of Liver X Receptor α in Established Vulnerable Plaques: Involvement of Regulating Endoplasmic Reticulum-Mediated Macrophage Apoptosis and Efferocytosis

Background

Liver X receptor (LXR) belongs to the metabolic nuclear receptor superfamily, which plays a critical regulatory role in vascular physiology/pathology. However, effects of systemic LXR activation on established vulnerable plaques and the potential isotype‐specific role involved remain unclear.

Methods and Results

The 8‐week‐old male apolipoprotein E^−/− mice went through carotid branch ligation and renal artery constriction, combined with a high‐fat diet. Plaques in the left carotid artery acquired vulnerable features 4 weeks later, confirmed by magnetic resonance imaging scans and histological analysis. From that time on, mice were injected intraperitoneally daily with PBS or GW3965 (10 mg/kg per day) for an additional 4 weeks. Treatment with LXR agonists reduced the lesion volume by 52.61%, compared with the vehicle group. More important, a profile of less intraplaque hemorrhage detection and necrotic core formation was found. These actions collectively attenuated the incidence of plaque rupture. Mechanistically, reduced lesional apoptosis, enhanced efferocytosis, and alleviated endoplasmic reticulum stress are involved in the process. Furthermore, genetic ablation of LXRα, but not LXRβ, blunted the protective effects of LXR on the endoplasmic reticulum stress–elicited C/EBP‐homologous protein pathway in peritoneal macrophages. In concert with the LXRα‐predominant role in vitro, activated LXR failed to stabilize vulnerable plaques and correct the acquired cellular anomalies in LXRα^−/− apolipoprotein E^−/− mice.

Conclusions

Our results revealed that LXRα mediates the capacity of LXR activation to stabilize vulnerable plaques and prevent plaque rupture via amelioration of macrophage endoplasmic reticulum stress, lesional apoptosis, and defective efferocytosis. These findings might expand the application scenarios of LXR therapeutics for atherosclerosis.

Targeting macrophage liver X receptors by hydrogel-encapsulated T0901317 reduces atherosclerosis without effect on hepatic lipogenesis

BACKGROUND AND PURPOSE

Targeting macrophage but not hepatocyte liver X receptors (LXRs) can reduce atherosclerosis without effect on hepatic lipogenesis. In this study, we encapsulated LXR ligands with D-Nap-GFFY to form a nanofibre hydrogel (D-Nap-GFFY-T0901317 or GFFY-T0901317) and determined its effect on atherosclerosis, hepatic lipogenesis and the underlying mechanisms involved.

EXPERIMENTAL APPROACH

D-Nap-GFFY-T0901317 was subcutaneously injected to proatherogenic diet-fed apoE-deficient (Apoe^-/- ) mice, followed by determination of the development of atherosclerosis, liver steatosis and the involved mechanisms, with comparison of T0901317 oral administration.

KEY RESULTS

Subcutaneous injection of D-Nap-GFFY-T0901317 to Apoe^-/- mice inhibited atherosclerosis at a comparable level as T0901317 oral administration without effect on hepatic lipogenesis. More importantly, D-Nap-GFFY-T0901317 regressed the advanced lesions. In arterial wall, D-Nap-GFFY-T0901317 reduced macrophage/foam cells, necrotic cores and calcification and increased collagen content. It activated expression of ABCA1/G1 and smooth muscle α-actin, while inhibiting expression of intracellular adhesion molecule 1 (ICAM-1) and vascular cell adhesion molecule 1 (VCAM-1). D-Nap-GFFY-T0901317 also reduced serum pro-inflammatory cytokines and facilitated Kupffer cell M2 polarization. Mechanistically, D-Nap-GFFY-T0901317 was selectively taken up by macrophages but not hepatocytes, resulting in activation of macrophage ABCA1/G1 expression, while having no effect on lipogenic genes in hepatocytes. Moreover, the selective uptake of D-Nap-GFFY-T0901317 by macrophages was mainly completed in a scavenger receptor class A-dependent manner.

CONCLUSION AND IMPLICATIONS

Our study demonstrates that D-Nap-GFFY-T0901317 reduces atherosclerosis without effect on hepatic lipogenesis by targeting macrophage LXRs selectively, indicating its potential application for atherosclerosis treatment.

Testosterone stimulates cholesterol clearance from human macrophages by activating LXRα

AIMS

Low testosterone in men is associated with increased cardiovascular events and mortality. Testosterone has beneficial effects on several cardiovascular risk factors including cholesterol, endothelial dysfunction and inflammation as key mediators of atherosclerosis. Although evidence suggests testosterone is anti-atherogenic, its mechanism of action is unknown. The present study investigates whether testosterone exerts anti-atherogenic effects by stimulating cholesterol clearance from macrophages via activation of liver X receptor (LXRα), a nuclear master regulator of cellular cholesterol homeostasis, lipid regulation, and inflammation.

MAIN METHODS

Using human monocyte THP-1 cells differentiated into macrophages, the effect of testosterone (1-10 nM) treatment (24-72 h) on the expression of LXRα and LXR- targets apolipoprotein E (APOE), ATP-binding cassette transporter A1 (ABCA1), sterol regulatory element-binding transcription factor 1 (SREBF1) and fatty acid synthase (FAS), was investigated via qPCR and western blotting, with or without androgen receptor blockade with flutamide or LXR antagonism with CPPSS-50. Cholesterol clearance was measured by monitoring fluorescent dehydroergosterol (DHE) cellular clearance and ABCA1 cellular translocation was observed via immunocytochemistry in testosterone treated macrophages.

KEY FINDINGS

Testosterone increased mRNA and protein expression of LXRα, APOE, ABCA1, SREBF1 and FAS. These effects were blocked by flutamide and independently by LXR antagonism with CPPSS-50. Furthermore testosterone stimulated cholesterol clearance from the macrophages and promoted the translocation of ABCA1 toward the cell membrane.

SIGNIFICANCE

Testosterone acts via androgen receptor-dependent pathways to stimulate LXRα and downstream targets to induce cholesterol clearance in human macrophages. This may, in part, explain the anti-atherogenic effects of testosterone frequently seen clinically.

Combined PET/DCE-MRI in a Rabbit Model of Atherosclerosis: Integrated Quantification of Plaque Inflammation, Permeability, and Burden During Treatment With a Leukotriene A4 Hydrolase Inhibitor

OBJECTIVES

The authors sought to develop combined positron emission tomography (PET) dynamic contrast-enhanced (DCE) magnetic resonance imaging (MRI) to quantify plaque inflammation, permeability, and burden to evaluate the efficacy of a leukotriene A4 hydrolase (LTA4H) inhibitor in a rabbit model of atherosclerosis.

BACKGROUND

Multimodality PET/MRI allows combining the quantification of atherosclerotic plaque inflammation, neovascularization, permeability, and burden by combined ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG) PET, DCE-MRI, and morphological MRI. The authors describe a novel, integrated PET-DCE/MRI protocol to noninvasively quantify these parameters in aortic plaques of a rabbit model of atherosclerosis. As proof-of-concept, the authors apply this protocol to assess the efficacy of the novel LTA4H inhibitor BI691751.

METHODS

New Zealand White male rabbits (N = 49) were imaged with integrated PET-DCE/MRI after atherosclerosis induction and 1 and 3 months after randomization into 3 groups: 1) placebo; 2) high-dose BI691751; and 3) low-dose BI691751. All animals were euthanized at the end of the study.

RESULTS

Among the several metrics that were quantified, only maximum standardized uptake value and target-to-background ratio by ¹⁸F-FDG PET showed a modest, but significant, reduction in plaque inflammation in rabbits treated with low-dose BI691751 (p = 0.03), whereas no difference was detected in the high-fat diet and in the high-dose BI691751 groups. No differences in vessel wall area by MRI and area under the curve by DCE-MRI were detected in any of the groups. No differences in neovessel and macrophage density were found at the end of study among groups.

CONCLUSIONS

The authors present a comprehensive, integrated ¹⁸F-FDG PET and DCE-MRI imaging protocol to noninvasively quantify plaque inflammation, neovasculature, permeability, and burden in a rabbit model of atherosclerosis on a simultaneous PET/MRI scanner. A modest reduction was found in plaque inflammation by ¹⁸F-FDG PET in the group treated with a low dose of the LTA4H inhibitor BI691751.

Discovery of Highly Potent Liver X Receptor β Agonists

Introducing a uniquely substituted phenyl sulfone into a series of biphenyl imidazole liver X receptor (LXR) agonists afforded a dramatic potency improvement for induction of ATP binding cassette transporters, ABCA1 and ABCG1, in human whole blood. The agonist series demonstrated robust LXRβ activity (>70%) with low partial LXRα agonist activity (<25%) in cell assays, providing a window between desired blood cell ABCG1 gene induction in cynomolgus monkeys and modest elevation of plasma triglycerides for agonist 15. The addition of polarity to the phenyl sulfone also reduced binding to the plasma protein, human α-1-acid glycoprotein. Agonist 15 was selected for clinical development based on the favorable combination of in vitro properties, excellent pharmacokinetic parameters, and a favorable lipid profile.

Beneficial and Adverse Effects of an LXR Agonist on Human Lipid and Lipoprotein Metabolism and Circulating Neutrophils

The development of LXR agonists for the treatment of coronary artery disease has been challenged by undesirable properties in animal models. Here we show the effects of an LXR agonist on lipid and lipoprotein metabolism and neutrophils in human subjects. BMS-852927, a novel LXRβ-selective compound, had favorable profiles in animal models with a wide therapeutic index in cynomolgus monkeys and mice. In healthy subjects and hypercholesterolemic patients, reverse cholesterol transport pathways were induced similarly to that in animal models. However, increased plasma and hepatic TG, plasma LDL-C, apoB, apoE, and CETP and decreased circulating neutrophils were also evident. Furthermore, similar increases in LDL-C were observed in normocholesterolemic subjects and statin-treated patients. The primate model markedly underestimated human lipogenic responses and did not predict human neutrophil effects. These studies demonstrate both beneficial and adverse LXR agonist clinical responses and emphasize the importance of further translational research in this area.

Cardiac LXRα protects against pathological cardiac hypertrophy and dysfunction by enhancing glucose uptake and utilization

Pathological cardiac hypertrophy is characterized by a shift in metabolic substrate utilization from fatty acids to glucose, but the molecular events underlying the metabolic remodeling remain poorly understood. Here, we investigated the role of liver X receptors (LXRs), which are key regulators of glucose and lipid metabolism, in cardiac hypertrophic pathogenesis. Using a transgenic approach in mice, we show that overexpression of LXRα acts to protect the heart against hypertrophy, fibrosis, and dysfunction. Gene expression profiling studies revealed that genes regulating metabolic pathways were differentially expressed in hearts with elevated LXRα. Functionally, LXRα overexpression in isolated cardiomyocytes and murine hearts markedly enhanced the capacity for myocardial glucose uptake following hypertrophic stress. Conversely, this adaptive response was diminished in LXRα-deficient mice. Transcriptional changes induced by LXRα overexpression promoted energy-independent utilization of glucose via the hexosamine biosynthesis pathway, resulting in O-GlcNAc modification of GATA4 and Mef2c and the induction of cytoprotective natriuretic peptide expression. Our results identify LXRα as a key cardiac transcriptional regulator that helps orchestrate an adaptive metabolic response to chronic cardiac stress, and suggest that modulating LXRα may provide a unique opportunity for intervening in myocyte metabolism.

ApoA-I-Directed Therapies for the Management of Atherosclerosis

Several recent reports have raised doubts about the atheroprotective role of high-density lipoprotein cholesterol (HDL-C). Nevertheless, a substantial body of work supports the validity of pharmacological interventions able to enhance HDL function, as opposed to raising HDL-C levels per se. In this article, we briefly review the development of pharmacological interventions that target apoA-I and HDL function as a means of reducing atherosclerotic risk: small molecule pharmaceuticals, small HDL mimetic peptides, and infusion of apoA-I-containing particles.

Atorvastatin promotes human monocyte differentiation toward alternative M2 macrophages through p38 mitogen-activated protein kinase-dependent peroxisome proliferator-activated receptor γ activation

M1 and M2 macrophages are detectable in human atherosclerotic lesions, and M2 macrophages are present at locations distant from the lipid core in more stable zones of the plaque and appear to exert anti-inflammatory properties on M1 macrophages. Peroxisome proliferator-activated receptor (PPAR) γ promotes the differentiation of monocytes into anti-inflammatory M2 macrophages. Although both statins and PPARγ ligands have been reported to protect against the progression of atherosclerosis, no data are currently available regarding the implication of statins in the alternative differentiation of human monocytes. In the present study, we hypothesized that atorvastatin may exert novel effects to prime human monocytes toward an anti-inflammatory alternative M2 phenotype. To this aim, we first found that abundant M2 markers were expressed in human circulating monocytes after atorvastatin treatment. Moreover, atorvastatin was able to induce PPARγ expression and activation in human monocytes in vivo and in vitro, resulting in priming primary human monocytes differentiation into M2 macrophages with a more pronounced paracrine anti-inflammatory activity in M1 macrophages. Additional data with molecular approaches revealed that p38 mitogen-activated protein kinase (MAPK) but not extracellular signal-regulated kinase (ERK) 1/2 activation was involved in atorvastatin-mediated PPARγ activation and enhanced alternative M2 macrophage phenotype. Collectively, our data demonstrated that atorvastatin promotes human monocyte differentiation toward alternative M2 macrophages via p38 MAPK-dependent PPARγ activation.

Inhibition of ERK1/2 and activation of LXR synergistically reduce atherosclerotic lesions in ApoE-deficient mice

OBJECTIVE

Activation of liver X receptor (LXR) inhibits atherosclerosis but induces hypertriglyceridemia. In vitro, it has been shown that mitogen-activated protein kinase kinase 1/2 (MEK1/2) inhibitor synergizes LXR ligand-induced macrophage ABCA1 expression and cholesterol efflux. In this study, we determined whether MEK1/2 (U0126) and LXR ligand (T0901317) can have a synergistic effect on the reduction of atherosclerosis while eliminating LXR ligand-induced fatty livers and hypertriglyceridemia. We also set out to identify the cellular mechanisms of the actions.

APPROACH AND RESULTS

Wild-type mice were used to determine the effect of U0126 on a high-fat diet or high-fat diet plus T0901317-induced transient dyslipidemia and liver injury. ApoE deficient (apoE(-/-)) mice or mice with advanced lesions were used to determine the effect of the combination of T0901317 and U0126 on atherosclerosis and hypertriglyceridemia. We found that U0126 protected animals against T0901317-induced transient or long-term hepatic lipid accumulation, liver injury, and hypertriglyceridemia. Meanwhile, the combination of T0901317 and U0126 inhibited the development of atherosclerosis in a synergistic manner and reduced advanced lesions. Mechanistically, in addition to synergistic induction of macrophage ABCA1 expression, the combination of U0126 and T0901317 maintained arterial wall integrity, inhibited macrophage accumulation in aortas and formation of macrophages/foam cells, and activated reverse cholesterol transport. The inhibition of T0901317-induced lipid accumulation by the combined U0126 might be attributed to inactivation of lipogenesis and activation of lipolysis/fatty acid oxidation pathways.

CONCLUSIONS

Our study suggests that the combination of mitogen-activated protein kinase kinase 1/2 inhibitor and LXR ligand can function as a novel therapy to synergistically reduce atherosclerosis while eliminating LXR-induced deleterious effects.

Emerging small molecule drugs

Dyslipidaemia is a major risk factor for cardiovascular diseases. Pharmacological lowering of LDL-C levels using statins reduces cardiovascular risk. However, a substantial residual risk persists especially in patients with type 2 diabetes mellitus. Because of the inverse association observed in epidemiological studies of HDL-C with the risk for cardiovascular diseases, novel therapeutic strategies to raise HDL-C levels or improve HDL functionality are developed as complementary therapy for cardiovascular diseases. However, until now most therapies targeting HDL-C levels failed in clinical trials because of side effects or absence of clinical benefits. This chapter will highlight the emerging small molecules currently developed and tested in clinical trials to pharmacologically modulate HDL-C and functionality including new CETP inhibitors (anacetrapib, evacetrapib), novel PPAR agonists (K-877, CER-002, DSP-8658, INT131 and GFT505), LXR agonists (ATI-111, LXR-623, XL-652) and RVX-208.

Pharmacological characterization of a novel liver X receptor agonist with partial LXRα activity and a favorable window in nonhuman primates

Liver X Receptors (LXRs) α and β are nuclear hormone receptors that regulate multiple genes involved in reverse cholesterol transport (RCT) and are potential drug targets for atherosclerosis. However, full pan agonists also activate lipogenic genes, resulting in elevated plasma and hepatic lipids. We report the pharmacology of BMS-779788 [2-(2-(1-(2-chlorophenyl)-1-methylethyl)-1-(3'-(methylsulfonyl)-4-biphenylyl)-1H-imidazol-4-yl)-2-propanol], a potent partial LXR agonist with LXRβ selectivity, which has an improved therapeutic window in the cynomolgus monkey compared with a full pan agonist. BMS-779788 induced LXR target genes in blood in vivo with an EC50 = 610 nM, a value similar to its in vitro blood gene induction potency. BMS-779788 was 29- and 12-fold less potent than the full agonist T0901317 in elevating plasma triglyceride and LDL cholesterol, respectively, with similar results for plasma cholesteryl ester transfer protein and apolipoprotein B. However, ABCA1 and ABCG1 mRNA inductions in blood, which are critical for RCT, were comparable. Increased liver triglyceride was observed after 7-day treatment with BMS-779788 at the highest dose tested and was nearly identical to the dose response for plasma triglyceride, consistent with the central role of liver LXR in these lipogenic effects. Dose-dependent increases in biliary cholesterol and decreases in phospholipid and bile acid occurred in BMS-779788-treated animals, similar to LXR agonist effects reported in mouse. In summary, BMS-779788, a partial LXRβ selective agonist, has decreased lipogenic potential compared with a full pan agonist in cynomolgus monkeys, with similar potency in the induction of genes known to stimulate RCT. This provides support in nonhuman primates for improving LXR agonist therapeutic windows by limiting LXRα activity.

Liver X receptor agonist treatment attenuates cardiac dysfunction in type 2 diabetic db/db mice

BACKGROUND

Liver X receptor (LXR) plays a critical regulatory role in metabolism and inflammation, and has been demonstrated to be involved in cardiovascular physiology/pathology. In the present study, we investigated the effect of GW3965, a potent LXR agonist, on diabetic cardiomyopathy (DCM) in type 2 diabetic db/db mice.

METHODS AND RESULTS

Non-diabetic db/+ mice and diabetic db/db mice received either vehicle or LXR agonist GW3965 for 12 weeks. Systemic insulin resistance was evaluated by glucose tolerance test and homeostasis model assessment for insulin resistance. Endpoint cardiac function was assessed by echocardiography and catheterization. Ventricular tissue was collected for histology and gene/protein expression analysis. Untreated db/db diabetic mice exhibited diastolic dysfunction with adverse structural remodeling (including myocardial fibrosis and increased apoptosis). Treatment with GW3965 remarkably attenuated myocardial dysfunction and structural remodeling in diabetic db/db mice. Mechanistically, GW3965 restored Akt phosphorylation and inhibited MAP kinases phosphorylation, and reduced oxidative/nitrative stress and inflammation response in the diabetic myocardium.

CONCLUSIONS

Our data demonstrate that GW3965 exerts a cardioprotective effect against DCM by (at least in part) attenuating insulin resistance, modulating Akt and MAP kinases pathways, and reducing oxidative/nitrative stress and inflammatory response. These findings strongly suggest that LXR agonist may have therapeutic potential in treating DCM.

The macrophage LBP gene is an LXR target that promotes macrophage survival and atherosclerosis

The liver X receptors (LXRs) are members of the nuclear receptor superfamily that regulate sterol metabolism and inflammation. We sought to identify previously unknown genes regulated by LXRs in macrophages and to determine their contribution to atherogenesis. Here we characterize a novel LXR target gene, the lipopolysaccharide binding protein (LBP) gene. Surprisingly, the ability of LXRs to control LBP expression is cell-type specific, occurring in macrophages but not liver. Treatment of macrophages with oxysterols or loading with modified LDL induces LBP in an LXR-dependent manner, suggesting a potential role for LBP in the cellular response to cholesterol overload. To investigate this further, we performed bone marrow transplant studies. After 18 weeks of Western diet feeding, atherosclerotic lesion burden was assessed revealing markedly smaller lesions in the LBP(-/-) recipients. Furthermore, loss of bone marrow LBP expression increased apoptosis in atherosclerotic lesions as determined by terminal deoxynucleotidyl transferase dUTP nick end labeling staining. Supporting in vitro studies with isolated macrophages showed that LBP expression does not affect cholesterol efflux but promotes the survival of macrophages in the setting of cholesterol loading. The LBP gene is a macrophage-specific LXR target that promotes foam cell survival and atherogenesis.

Pharmacological interventions in human HDL metabolism

PURPOSE OF REVIEW

This review focuses on the recent developments in the field of drugs that affect HDL metabolism. Additionally, some general (retrospective) thoughts on fighting cardiovascular disease through modulating circulating lipids are discussed.

RECENT FINDINGS

Recently, the large 'Atherothrombosis Intervention in Metabolic Syndrome with Low HDL/High Triglycerides: Impact on Global Health Outcomes', 'Treatment of HDL to Reduce the Incidence of Vascular Events' and dal-OUTCOMES studies have challenged the idea that raising HDL cholesterol (HDL-c) decreases cardiovascular disease risk. Concerning the failure of these trials, it may, however, be noted that patients with close to normal HDL-c levels were included. It is shown that anacetrapib and evacetrapib massively increase HDL-c, and both compounds are currently tested in phase-III clinical trials. More specific and stronger activators of liver X receptor and peroxisome proliferator-activated receptor (PPAR) are being developed and tested in a preclinical setting. RVX-208 treatment failed to decrease atheroma volume in coronary artery disease patients. Lecithin:cholesterol acyltransferase replacement therapy showed positive results in a patient with lecithin:cholesterol acyltransferase deficiency.

SUMMARY

Inhibition of cholesteryl ester transfer protein, antagomirs against microRNA-33, ApoA-I mimetics and PPARα or PPARα/δ agonists hold on the basis of the current data most promise. However, it will in our opinion be the key that patients with low HDL-c and increased triglyceride should be treated and not those at generally increased risk only. In the poststatin era, personalized medicine, which is inevitably on the horizon, is likely to be helpful for patients who do not reach the goals for LDL cholesterol and HDL-c according to the guidelines. Furthermore, functions of HDL will hopefully be identified as future pharmacological targets.

Update on selective treatments targeting neutrophilic inflammation in atherogenesis and atherothrombosis

Atherosclerosis is the most common pathological process underlying cardiovascular diseases. Current therapies are largely focused on alleviating hyperlipidaemia and preventing thrombotic complications, but do not completely eliminate risk of suffering recurrent acute ischaemic events. Specifically targeting the inflammatory processes may help to reduce this residual risk of major adverse cardiovascular events in atherosclerotic patients. The involvement of neutrophils in the pathophysiology of atherosclerosis is an emerging field, where evidence for their causal contribution during various stages of atherosclerosis is accumulating. Therefore, the identification of neutrophils as a potential therapeutic target may offer new therapeutic perspective to reduce the current atherosclerotic burden. This narrative review highlights the expanding role of neutrophils in atherogenesis and discusses on the potential treatment targeting neutrophil-related inflammation and associated atherosclerotic plaque vulnerability.

HDL, Atherosclerosis, and Emerging Therapies

This review aims to provide an overview on the properties of high-density lipoproteins (HDLs) and their cardioprotective effects. Emergent HDL therapies will be presented in the context of the current understanding of HDL function, metabolism, and protective antiatherosclerotic properties. The epidemiological association between levels of HDL-C or its major apolipoprotein (apoA-I) is strong, graded, and coherent across populations. HDL particles mediate cellular cholesterol efflux, have antioxidant properties, and modulate vascular inflammation and vasomotor function and thrombosis. A link of causality has been cast into doubt with Mendelian randomization data suggesting that genes causing HDL-C deficiency are not associated with increased cardiovascular risk, nor are genes associated with increased HDL-C, with a protective effect. Despite encouraging data from small studies, drugs that increase HDL-C levels have not shown an effect on major cardiovascular end-points in large-scale clinical trials. It is likely that the cholesterol mass within HDL particles is a poor biomarker of therapeutic efficacy. In the present review, we will focus on novel therapeutic avenues and potential biomarkers of HDL function. A better understanding of HDL antiatherogenic functions including reverse cholesterol transport, vascular protective and antioxidation effects will allow novel insight on novel, emergent therapies for cardiovascular prevention.

Macrophages transmit potent proangiogenic effects of oxLDL in vitro and in vivo involving HIF-1α activation: a novel aspect of angiogenesis in atherosclerosis

Neovascularization has been linked to the progression and vulnerability of atherosclerotic lesions. Angiogenesis is increased in lipid-rich plaque. Hypoxia-inducible factor alpha (HIF-1α) is a key transcriptional regulator responding to hypoxia and activating genes, which promote angiogenesis, among them vascular endothelial growth factor (VEGF). Oxidized low-density lipoprotein (oxLDL) is generated in lipid-rich plaque by oxidative stress. It triggers an inflammatory response and was traditionally thought to inhibit endothelial cells. New data, however, suggest that oxLDL can activate HIF-1α in monocytes in a hypoxia-independent fashion. We hypothesized that HIF-1α activation in monocyte-macrophages could transmit proangiogenic effects of oxLDL linking hyperlipidemia, inflammation, and angiogenesis in atherosclerosis. First, we examined the effect of oxLDL on HIF-1α and VEGF expression in monocyte-macrophages and on their proangiogenic effect on endothelial cells in vitro in a monocyte-macrophage/endothelial co-culture model. OxLDL strongly induced HIF-1α and VEGF in monocyte-macrophages and significantly increased tube formation in co-cultured endothelial cells. HIF-1α inhibition reversed this effect. Second, we demonstrated a direct proangiogenic effect of oxLDL in an in vivo angiogenesis assay. Again, HIF-1α inhibition abrogated the proangiogenic effect of oxLDL. Third, in a rabbit atherosclerosis model, we studied the effect of dietary lipid lowering on arterial HIF-1α and VEGF expression. The administration of low-lipid diet significantly reduced the expression of both HIF-1α and VEGF, resulting in decreased plaque neovascularization. Our data point to oxLDL as a proangiogenic agent linking hyperlipidemia, inflammation, and angiogenesis in atherosclerosis. This effect is dependent on macrophages and, at least in part, on the induction of the HIF-1α pathway.

Targeting high density lipoproteins in the prevention of cardiovascular disease?

Recent studies involving HDL-raising therapeutics have greatly changed our understanding of this field. Despite effectively raising HDL-C levels, niacin remains of uncertain clinical benefit. Synthetic niacin receptor agonists are unlikely to raise HDL-C or have other beneficial effects on plasma lipids. Despite the failure in phase 3 of 2 CETP inhibitors, 2 potent CETP inhibitors that raise HDL-C levels by >100 % (and reduce LDL-C substantially) are in late stage clinical development. Infusions of recombinant HDL containing 'wild-type' apoA-I or apoA-I Milano, as well as autologous delipidated HDL, all demonstrated promising early results, and remain in clinical development. A small molecule that causes upregulation of endogenous apoA-I production is also in clinical development. Finally, upregulation of macrophage cholesterol efflux pathways through agonism of liver X receptors or antagonism of miR-33 remains of substantial interest. The field of HDL therapeutics is poised to transition from the 'HDL-cholesterol hypothesis' to the 'HDL flux hypothesis' in which the impact on flux from macrophage to feces is deemed to be of greater therapeutic benefit than the increase in steady-state concentrations of HDL cholesterol.

Liver X receptors, atherosclerosis and inflammation

Liver X receptors (LXRs) belong to the nuclear receptor superfamily of ligand-dependent transcription factors. LXRs are activated by oxysterols, metabolites of cholesterol, and therefore act as intracellular sensors of this lipid. There are two LXR genes (α and β) that display distinct tissue/cell expression profiles. LXRs interact with regulatory sequences in target genes as heterodimers with retinoid X receptor. Such direct targets of LXR actions include important genes implicated in the control of lipid homeostasis, particularly reverse cholesterol transport. In addition, LXRs attenuate the transcription of genes associated with the inflammatory response indirectly by transrepression. In this review, we describe recent evidence that both highlights the key roles of LXRs in atherosclerosis and inflammation and provides novel insights into the mechanisms underlying their actions. In addition, we discuss the major limitations of LXRs as therapeutic targets for the treatment of atherosclerosis and how these are being addressed.

Selective liver X receptor modulators (SLiMs): what use in human health?

Liver X receptors (LXR) are members of the nuclear receptor family. As activated transcription factors, their putative association with human diseases makes them promising pharmacological targets because of the large potential to develop ligands. LXR are mainly considered as intracellular cholesterol "sensors" whose activation leads to decreased plasma cholesterol. They also modulate numerous physiological functions: fatty acid synthesis and metabolism, glucose homeostasis, steroidogenesis, immunity, and neurological homeostasis. LXR-deficiency in mouse results in several phenotypes mimicking pathological conditions in humans. This review will be focused on the various natural and synthetic LXR agonists and antagonists. Putative clinical targets including atherosclerosis, diabetes, Alzheimer's disease, skin disorders, and cancer will be covered.