Acute ApoA-I Milano administration induces plaque regression and stabilisation in the long term

Microarray analysis identifies human apoA-IMilano and apoA-II as determinants of the liver gene expression related to lipid and energy metabolism

The phenotype of individuals carrying the apolipoprotein A-IMilano (apoA-IM), the mutant form of human apoA-I (apoA-I), is characterized by very low concentrations of HDL and apoA-I, and hypertriglyceridemia. Paradoxically, these subjects are not found to be at increased risk of premature cardiovascular disease compared to controls. Besides, various in vitro and in vivo studies have demonstrated that apoA-IM possesses greater anti-atherosclerotic activity compared to apoA-I. The molecular mechanisms explaining the apoA-IM carrier's phenotype and the apoA-IM higher efficacy are still not fully elucidated. To investigate such mechanisms, we crossed previously generated apoA-I (A-I k-in) or apoA-IM knock-in mice (A-IM k-in) with transgenic mice expressing human apoA-II but lacking murine apoA-I (hA-II) to generate hA-II/A-I k-in, and hA-II/A-IM k-in, respectively. These genetically modified mice completely reproduced the apoA-IM carrier's phenotype, including hypoalphalipoproteinemia and hypertriglyceridemia. Furthermore, by using the microarray methodology, we investigated the intrinsic differences in hepatic gene expression among these k-in mouse lines. The expression of 871, 1,018, 1129 and 764 genes was significantly altered between 1) hA-II/A-I and hA-II/A-IM k-in; 2) A-IM and hA-II/A-IM k-in; 3) A-I and A-IM; 4) A-I and hA-II/A-I k-in liver samples, respectively. Bioinformatics analysis highlighted that the hepatic expression of two genes, Elovl6 and Gatm, related to fatty acid/lipid and energy metabolism, respectively, is influenced by the presence of the apoA-IM natural variant and/or apoA-II.

Nanoparticle-based "Two-pronged" approach to regress atherosclerosis by simultaneous modulation of cholesterol influx and efflux

Reduction of lipoprotein uptake by macrophages and stimulation of cholesterol efflux are two essential steps required for atherosclerotic plaque regression. We used the optimized mannose-functionalized dendrimeric nanoparticle (mDNP)-based platform for macrophage-specific delivery of therapeutics to simultaneously deliver SR-A siRNA (to reduce LDL uptake) and LXR ligand (LXR-L, to stimulate cholesterol efflux) - a novel "Two-pronged" approach to facilitate plaque regression. mDNP-mediated delivery of SR-A siRNA led to a significant reduction in SR-A expression with a corresponding decrease in uptake of oxLDL. Delivery of LXR-L increased expression of ABCA1/G1 and cholesterol efflux. Combined delivery of siRNA and LXR-L led to a significantly greater decrease in macrophage cholesterol content compared to either treatment alone. Administration of this in vitro optimized formulation of mDNP complexed with SR-A-siRNA and LXR-L (Two-pronged complex) to atherosclerotic LDLR-/- mice fed western diet (TD88137) led to significant regression of atherosclerotic plaques with a corresponding decrease in aortic cholesterol content.

Cardioprotective Properties of HDL: Structural and Functional Considerations

BACKGROUND

As Mendelian Randomization (MR) studies showed no effect of variants altering HDL-cholesterol (HDL-C) levels concerning Cardiovascular Disease (CVD) and novel therapeutic interventions aiming to raise HDL-C resulted to futility, the usefulness of HDL-C is unclear.

OBJECTIVE

As the role of HDL-C is currently doubtful, it is suggested that the atheroprotective functions of HDLs can be attributed to the number of HDL particles, and their characteristics including their lipid and protein components. Scientific interest has focused on HDL function and on the causes of rendering HDL particles dysfunctional, whereas the relevance of HDL subclasses with CVD remains controversial.

METHODS

The present review discusses changes in quality as much as in quantity of HDL in pathological conditions and the connection between HDL particle concentration and cardiovascular disease and mortality. Emphasis is given to the recently available data concerning the cholesterol efflux capacity and the parameters that determine HDL functionality, as well as to recent investigations concerning the associations of HDL subclasses with cardiovascular mortality.

RESULTS

MR studies or pharmacological interventions targeting HDL-C are not in favor of the hypothesis of HDL-C levels and the relationship with CVD. The search of biomarkers that relate with HDL functionality is needed. Similarly, HDL particle size and number exhibit controversial data in the context of CVD and further studies are needed.

CONCLUSION

There is no room for the old concept of HDL as a silver bullet,as HDL-C cannot be considered a robust marker and does not reflect the importance of HDL particle size and number. Elucidation of the complex HDL system, as well as the finding of biomarkers, will allow the development of any HDL-targeted therapy.

HDL therapy today: from atherosclerosis, to stent compatibility to heart failure

Epidemiologically, high-density lipoprotein (HDL) cholesterol levels have been inversely associated to cardiovascular (CV) events, although a Mendelian Randomisation Study had failed to establish a clear causal role. Numerous atheroprotective mechanisms have been attributed to HDL, the main being the ability to promote cholesterol efflux from arterial walls; anti-inflammatory effects related to HDL ligands such as S1P (sphingosine-1-phosphate), resolvins and others have been recently identified. Experimental studies and early clinical investigations have indicated the potential of HDL to slow progression or induce regression of atherosclerosis. More recently, the availability of different HDL formulations, with different phospholipid moieties, has allowed to test other indications for HDL therapy. Positive reports have come from studies on coronary stent biocompatibility, where the use of HDL from different sources reduced arterial cell proliferation and thrombogenicity. The observation that low HDL-C levels may be associated with an enhanced risk of heart failure (HF) has also suggested that HDL therapy may be applied to this condition. HDL infusions or apoA-I gene transfer were able to reverse heart abnormalities, reduce diastolic resistance and improve cardiac metabolism. HDL therapy may be effective not only in atherosclerosis, but also in other conditions, of relevant impact on human health.Key messagesHigh-density lipoproteins have as a major activity that of removing excess cholesterol from tissues (particularly arteries).Knowledge on the activity of high-density lipoproteins on health have however significantly widened.HDL-therapy may help to improve stent biocompatibility and to reduce peripheral arterial resistance in heart failure.

Biological Consequences of Dysfunctional HDL

Epidemiological studies have suggested an inverse correlation between high-density lipoprotein (HDL) cholesterol levels and the risk of cardiovascular disease. HDLs promote reverse cholesterol transport (RCT) and possess several putative atheroprotective functions, associated to the anti-inflammatory, anti-thrombotic and anti-oxidant properties as well as to the ability to support endothelial physiology. The assumption that increasing HDL-C levels would be beneficial on cardiovascular disease (CVD), however, has been questioned as, in most clinical trials, HDL-C-raising therapies did not result in improved cardiovascular outcomes. These findings, together with the observations from Mendelian randomization studies showing that polymorphisms mainly or solely associated with increased HDL-C levels did not decrease the risk of myocardial infarction, shift the focus from HDL-C levels toward HDL functional properties. Indeed, HDL from atherosclerotic patients not only exhibit impaired atheroprotective functions but also acquire pro-atherogenic properties and are referred to as "dysfunctional" HDL; this occurs even in the presence of normal or elevated HDL-C levels. Pharmacological approaches aimed at restoring HDL functions may therefore impact more significantly on CVD outcome than drugs used so far to increase HDL-C levels. The aim of this review is to discuss the pathological conditions leading to the formation of dysfunctional HDL and their role in atherosclerosis and beyond.

Infusions of Large Synthetic HDL Containing Trimeric apoA-I Stabilize Atherosclerotic Plaques in Hypercholesterolemic Rabbits

BACKGROUND

Among strategies to reduce the remaining risk of cardiovascular disease, interest has focused on using infusions of synthetic high-density lipoprotein (sHDL).

METHODS

New Zealand rabbits underwent a perivascular injury at both carotids and were randomly allocated into 2 protocols: (1) a single-dose study, where rabbits were treated with a single infusion of sHDL containing a trimeric form of human apoA-I (TN-sHDL, 200 mg/kg) or with Placebo; (2) a multiple-dose study, where 4 groups of rabbits were treated 5 times with Placebo or TN-sHDL at different doses (8, 40, 100 mg/kg). Plaque changes were analysed in vivo by intravascular ultrasound. Blood was drawn from rabbits for biochemical analyses and cholesterol efflux capacity evaluation.

RESULTS

In both protocols, atheroma volume in the Placebo groups increased between the first and the second intravascular ultrasound evaluation. A stabilization or a slight regression was instead observed vs baseline in the TN-sHDL-treated groups (P < 0.005 vs Placebo after infusion). TN-sHDL treatment caused a sharp rise of plasma-free cholesterol levels and a significant increase of total cholesterol efflux capacity. Histologic analysis of carotid plaques showed a reduced macrophage accumulation in TN-sHDL-treated rabbits compared with Placebo (P < 0.05).

CONCLUSIONS

Our results demonstrate that acute and subacute treatments with TN-sHDL are effective in stabilizing atherosclerotic plaques in a rabbit model. This effect appears to be related to a reduced intraplaque accumulation of inflammatory cells. Besides recent failures in proving its efficacy, sHDL treatment remains a fascinating therapeutic option for the reduction of cardiovascular risk.

Unravelling HDL-Looking beyond the Cholesterol Surface to the Quality Within

High-density lipoprotein (HDL) particles have experienced a turbulent decade of falling from grace with widespread demotion from the most-sought-after therapeutic target to reverse cardiovascular disease (CVD), to mere biomarker status. HDL is slowly emerging from these dark times due to the HDL flux hypothesis wherein measures of HDL cholesterol efflux capacity (CEC) are better predictors of reduced CVD risk than static HDL-cholesterol (HDL-C) levels. HDL particles are emulsions of metabolites, lipids, protein, and microRNA (miR) built on the backbone of Apolipoprotein A1 (ApoA1) that are growing in their complexity due to the higher sensitivity of the respective “omic” technologies. Our understanding of particle composition has increased dramatically within this era and has exposed how our understanding of these particles to date has been oversimplified. Elucidation of the HDL proteome coupled with the identification of specific miRs on HDL have highlighted the “hormonal” characteristics of HDL in that it carries and delivers messages systemically. HDL can dock to most peripheral cells via its receptors, including SR-B1, ABCA1, and ABCG1, which may be a critical step for facilitating HDL-to-cell communication. The composition of HDL particles is, in turn, altered in numerous disease states including diabetes, auto-immune disease, and CVD. The consequence of changes in composition, however, on subsequent biological activities of HDL is currently poorly understood and this is an important avenue for the field to explore in the future. Improving HDL particle quality as opposed to HDL quantity may, in turn, prove a more beneficial investment to reduce CVD risk.

RVX 208: A novel BET protein inhibitor, role as an inducer of apo A-I/HDL and beyond

Low-density cholesterol (LDL) has been the prime target of currently available lipid-lowering therapies although current research is expanding the focus beyond LDL lowering and has included high-density cholesterol (HDL) also as the target. Bromo and extra-terminal (BET) proteins are implicated in the regulation of transcription of several regulatory genes and regulation of proinflammatory pathways. As atherosclerosis is an inflammatory pathway and studies showed that BET inhibition has a role in inhibiting inflammation, the concept of BET inhibition came in the field of atherosclerosis. RVX 208 is a novel, orally active, BET protein inhibitor and the only BET inhibitor currently available in the field of atherosclerosis. RVX 208 acts primarily by increasing apo A-I (apolipoprotein A-I) and HDL levels. RVX 208 has a novel action of increasing larger, more cardio-protective HDL particles. Post hoc analysis of Phase II trials also showed that RVX 208 reduced major adverse cardiovascular events (MACE) in treated patients, over and above that of apo A-I/HDL increasing action. This MACE reducing actions of RVX 208 were largely due to its novel anti-inflammatory actions. Currently, a phase III trial, BETonMACE, is recruiting patients to look for the effects of RVX 208 in patients with increased risk of atherosclerotic cardiovascular disease. So BET inhibitors act in multiple ways to inhibit and modulate atherosclerosis and would be an emerging and potential option in the management of multifactorial disease like coronary artery disease by inhibiting a single substrate. But we need long-term phase III trial data's to look for effects on real-world patients.

Intravenous treatment with human recombinant ApoA-I Milano reduces beta amyloid cerebral deposition in the APP23-transgenic mouse model of Alzheimer's disease

Beyond the crucial role of apolipoprotein A-I (ApoA-I) on peripheral cholesterol metabolism, this apolipoprotein has also been implicated in beta amyloid (Aβ)-related neuropathologies. ApoA-I-Milano (M) is a mutated variant, which showed increased vasoprotective properties compared to ApoA-I-wild type in models of atherosclerosis and cardiovascular damage. We speculated that ApoA-I-M may also protect Aβ-affected vasculature and reverse some of the pathological features associated with Alzheimer's disease (AD). For this purpose, we produced and characterized human recombinant ApoA-I-wild type and ApoA-I-M proteins. Both of them were able to avoid the aggregation of Aβ in vitro, even though recombinant ApoA-I-M was significantly more effective in protecting endothelial cells from Aβ(1-42)-toxicity. Next, we determined the effect of chronic intravenous administration of rApoA-I-M in the APP23-transgenic mouse model of AD. We found reduced cerebral Aβ levels in mice that received rApoA-I-M, which were accompanied by a lower expression of astrocyte and microglia neuroinflammatory markers. Our results suggest an applicability of this molecule as a therapeutic candidate for protecting the brain in AD.

Human apolipoprotein A-I exerts a prophylactic effect on high-fat diet-induced atherosclerosis via inflammation inhibition in a rabbit model

Apolipoprotein A-I (apoA-I) is the major functional protein fraction of high-density lipoprotein. The prophylactic effect and mechanism of human apoA-I on atherosclerosis (AS) were investigated in a high-fat diet-induced AS rabbit model. The rabbits were injected with apoA-I once a week while fed high-fat diet for 20 weeks. Our results showed that apoA-I could raise the serum level of high-density lipoprotein-cholesterol and reduce those of lipid total cholesterol, triglyceride, and low-density lipoprotein-cholesterol in AS rabbits. Decreased aortic plaque area and aortic injury degree were also observed by Oil Red O staining and HE staining in apoA-I-treated high-fat diet-induced AS rabbits. Further study elucidated that apoA-I could down-regulate the expression of some inflammatory mediators including intercellular adhesion molecule type 1, vascular adhesion molecule-1 (VCAM-1), monocyte chemoattractant protein-1, tumor necrosis factor-α, interleukin-6 (IL-6), and C-reactive protein in serum and aorta of AS rabbits. In addition, real-time quantitative RT-PCR analyses showed that the apoA-I infusions decreased the mRNA levels of two pro-inflammatory molecules, i.e. nuclear factor kappa B (NF-κB) and cyclooxygenase-2 (COX-2), in aorta of AS rabbits, which was associated with a concomitant reduction in endothelial VCAM-1 and IL-6 mRNA transcription. Together, our results support the atheroprotective and prophylactic role of apoA-I in vivo, and this activity may be correlated with its anti-inflammatory effect.

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.

Plasma-derived and synthetic high-density lipoprotein inhibit tissue factor in endothelial cells and monocytes

Atheroprotection mediated by high-density lipoproteins could also be related to their ability to inhibit the expression of tissue factor, the main activator of the coagulation cascade, in endothelial cells and in monocytes.

How do we prevent the vulnerable atherosclerotic plaque from rupturing? Insights from in vivo assessments of plaque, vascular remodeling, and local endothelial shear stress

Coronary atherosclerosis progresses both as slow, gradual enlargement of focal plaque and also as a more dynamic process with periodic abrupt changes in plaque geometry, size, and morphology. Systemic vasculoprotective therapies such as statins, angiotensin-converting enzyme inhibitors, and antiplatelet agents are the cornerstone of prevention of plaque rupture and new adverse clinical outcomes, but such systemic therapies are insufficient to prevent the majority of new cardiac events. Invasive imaging methods have been able to identify both the anatomic features of high-risk plaque and the ongoing pathobiological stimuli responsible for progressive plaque inflammation and instability and may provide sufficient information to formulate preventive local mechanical strategies (eg, preemptive percutaneous coronary interventions) to avert cardiac events. Local endothelial shear stress (ESS) triggers vascular phenomena that synergistically exacerbate atherosclerosis toward an unstable phenotype. Specifically, low ESS augments lipid uptake and catabolism, induces plaque inflammation and oxidation, downregulates the production, upregulates the degradation of extracellular matrix, and increases cellular apoptosis ultimately leading to thin-cap fibroatheromas and/or endothelial erosions. Increases in blood thrombogenicity that result from either high or low ESS also contribute to plaque destabilization. An understanding of the actively evolving vascular phenomena, as well as the development of in vivo imaging methodologies to identify the presence and severity of the different processes, may enable early identification of a coronary plaque destined to acquire a high-risk state and allow for highly selective, focal preventive interventions to avert the adverse natural history of that particular plaque. In this review, we focus on the role of ESS in the pathobiologic processes responsible for plaque destabilization, leading either to accelerated plaque growth or to acute coronary events, and emphasize the potential to utilize in vivo risk stratification of individual coronary plaques to optimize prevention strategies to preclude new cardiac events.

Effects of native and myeloperoxidase-modified apolipoprotein a-I on reverse cholesterol transport and atherosclerosis in mice

OBJECTIVE

Preclinical and clinical studies have shown beneficial effects of infusions of apolipoprotein A-I (ApoA-I) on atherosclerosis. ApoA-I is also a target for myeloperoxidase-mediated oxidation, leading in vitro to a loss of its ability to promote ATP-binding cassette transporter A1-dependent macrophage cholesterol efflux. Therefore, we hypothesized that myeloperoxidase-mediated ApoA-I oxidation would impair its promotion of reverse cholesterol transport in vivo and the beneficial effects on atherosclerotic plaques.

APPROACH AND RESULTS

ApoA-I(-/-) or apolipoprotein E-deficient mice were subcutaneously injected with native human ApoA-I, oxidized human ApoA-I (myeloperoxidase/hydrogen peroxide/chloride treated), or carrier. Although early postinjection (8 hours) levels of total ApoA-I in plasma were similar for native versus oxidized human ApoA-I, native ApoA-I primarily resided within the high-density lipoprotein fraction, whereas the majority of oxidized human ApoA-I was highly cross-linked and not high-density lipoprotein particle associated, consistent with impaired ATP-binding cassette transporter A1 interaction. In ApoA-I(-/-) mice, ApoA-I oxidation significantly impaired reverse cholesterol transport in vivo. In advanced aortic root atherosclerotic plaques of apolipoprotein E-deficient mice, native ApoA-I injections led to significant decreases in lipid content, macrophage number, and an increase in collagen content; in contrast, oxidized human ApoA-I failed to mediate these changes. The decrease in plaque macrophages with native ApoA-I was accompanied by significant induction of their chemokine receptor CCR7. Furthermore, only native ApoA-I injections led to a significant reduction of inflammatory M1 and increase in anti-inflammatory M2 macrophage markers in the plaques.

CONCLUSIONS

Myeloperoxidase-mediated oxidation renders ApoA-I dysfunctional and unable to (1) promote reverse cholesterol transport, (2) mediate beneficial changes in the composition of atherosclerotic plaques, and (3) pacify the inflammatory status of plaque macrophages.