A new HDL mimetic peptide that stimulates cellular cholesterol efflux with high efficiency greatly reduces atherosclerosis in mice

Targeting the vivid facets of apolipoproteins as a cardiovascular risk factor in rheumatoid arthritis

Mostly, cardiovascular diseases are blamed for casualties in rheumatoid arthritis (RA) patients. Customarily, dyslipidemia is probably the most prevalent underlying cause of untimely demise in people suffering from RA as it hastens the expansion of atherosclerosis. The engagement of inflammatory cytokines like tumor necrosis factor-α (TNF-α), interleukin-1 (IL-1), interleukin-6 (IL-6), etc., is crucial in the progression and proliferation of both RA and abnormal lipid parameters. Thus, lipid abnormalities should be monitored frequently in patients with both primary and advanced RA stages. An advanced lipid profile examination, i.e., direct role of apolipoproteins associated with various lipid molecules is a more dependable approach for better understanding of the disease and selecting suitable therapeutic targets. Therefore, studying their apolipoproteins is more relevant than assessing RA patients' altered lipid profile levels. Among the various apolipoprotein classes, Apo A1 and Apo B are primarily being focused. In addition, it also addresses how calculating Apo B:Apo A1 ratio can aid in analyzing the disease's risk. The marketed therapies available to control lipid abnormalities are associated with many other risk factors. Hence, directly targeting Apo A1 and Apo B would provide a better and safer option.

A novel apoE-mimetic increases brain apoE levels, reduces Aβ pathology and improves memory when treated before onset of pathology in male mice that express APOE3

BACKGROUND

Alzheimer's disease (AD) is characterized by cognitive dysfunction and amyloid plaques composed of the amyloid-beta peptide (Aβ). APOE is the greatest genetic risk for AD with APOE4 increasing risk up to ~ 15-fold compared to APOE3. Evidence suggests that levels and lipidation of the apoE protein could regulate AD progression. In glia, apoE is lipidated via cholesterol efflux from intracellular pools, primarily by the ATP-binding cassette transporter A1 (ABCA1). Therefore, increasing ABCA1 activity is suggested to be a therapeutic approach for AD. CS-6253 (CS) is a novel apoE mimetic peptide that was developed to bind and stabilize ABCA1 and maintain its localization into the plasma membrane therefore promoting cholesterol efflux. The goal of this study was to determine whether CS could modulate apoE levels and lipidation, Aβ pathology, and behavior in a model that expresses human APOE and overproduce Aβ.

METHODS

In vitro, APOE3-glia or APOE4-glia were treated with CS. In vivo, male and female, E3FAD (5xFAD+/-/APOE3+/+) and E4FAD (5xFAD+/-/APOE4+/+) mice were treated with CS via intraperitoneal injection at early (from 4 to 8 months of age) and late ages (from 8 to 10 months of age). ApoE levels, ABCA1 levels and, apoE lipidation were measured by western blot and ELISA. Aβ and amyloid levels were assessed by histochemistry and ELISA. Learning and memory were tested by Morris Water Maze and synaptic proteins were measured by Western blot.

RESULTS

CS treatment increased apoE levels and cholesterol efflux in primary glial cultures. In young male E3FAD mice, CS treatment increased soluble apoE and lipid-associated apoE, reduced soluble oAβ and insoluble Aβ levels as well as Aβ and amyloid deposition, and improved memory and synaptic protein levels. CS treatment did not induce any therapeutic benefits in young female E3FAD and E4FAD mice or in any groups when treatment was started at later ages.

CONCLUSIONS

CS treatment reduced Aβ pathology and improved memory only in young male E3FAD, the cohort with the least AD pathology. Therefore, the degree of Aβ pathology or Aβ overproduction may impact the ability of targeting ABCA1 to be an effective AD therapeutic. This suggests that ABCA1-stabilizing treatment by CS-6253 works best in conditions of modest Aβ levels.

Isoform-specific modification of apolipoprotein E by 4-hydroxynonenal: protective role of apolipoprotein E3 against oxidative species

High levels of 4-hydroxynonenal (HNE), arising from lipid peroxidation, and HNE-modified proteins have been identified in postmortem brains of ageing and Alzheimer's disease (AD) patients. The goal of this study is to understand the effect of HNE modification on the structure and function of recombinant apolipoprotein E3 (apoE3) and apolipoprotein E4 (apoE4), which play a critical role in brain cholesterol homeostasis. The two isoforms differ in a single amino acid at position 112: Cys in apoE3 and Arg in apoE4. Immunoblot with HNE-specific antibody indicates HNE modification of apoE3 and apoE4 with a major band at ~ 36 kDa, while LC-MS/MS revealed Michael addition at His140 (60-70% abundance) and His299 (3-5% abundance) in apoE3 and apoE4, and Cys112 adduct in apoE3 (75% abundance). Circular dichroism spectroscopy revealed no major differences in the overall secondary structure or helical content between unmodified and HNE-modified apoE. HNE modification did not affect their ability to promote cholesterol efflux from J774.1 macrophages. However, it led to a 3-fold decrease in their ability to bind lipids and 25-50% decrease in the ability of cerebral cortex endothelial cells to uptake lipoproteins bearing HNE-modified HNE-apoE3 or HNE-apoE4 as noted by fluorescence microscopy and flow cytometry. Taken together, the data indicate that HNE modification impairs lipid binding and cellular uptake of both isoforms, and that apoE3, bearing a Cys, offers a protective role by sequestering lipid peroxidation products that would otherwise cause indiscriminate damage to biomolecules. ApoE4, lacking Cys, is unable to protect against oxidative damage that is commensurate with ageing.

Current models of apolipoprotein A-I lipidation by adenosine triphosphate binding cassette transporter A1

PURPOSE OF REVIEW

The primary cardioprotective function of high-density lipoprotein (HDL) is to remove excess cellular free cholesterol (FC) from peripheral tissues and deliver it to the liver. Here, we summarize recent research that examines apolipoprotein A-I (apoA-I) lipidation models by adenosine triphosphate binding cassette transporter A1 (ABCA1) and discuss its relevance in atherosclerotic cardiovascular disease (ASCVD).

RECENT FINDINGS

The first step in HDL formation involves the interaction between apoA-I and ABCA1, where ABCA1 mediates the removal of FC and phospholipids from lipid-laden macrophages to form discoidal nascent HDL (nHDL). However, there are currently no clear-cut systematic models that characterize HDL formation. A number of recent studies have investigated the importance of apoA-I C- and N-terminal domains required for optimal cholesterol efflux and nHDL production. Furthermore, functional ABCA1 is required for direct or indirect binding to apoA-I where ABCA1 dimer-monomer interconversion facilitates apoA-I lipidation from plasma membrane microdomains. Microparticles are also another lipid source for apoA-I solubilization into nHDL.

SUMMARY

ApoA-I and ABCA1 are key factors in macrophage-mediated cholesterol efflux and nHDL production. Understanding of the key steps in HDL formation may unlock the therapeutic potential of HDL and improve clinical management of ASCVD.

Are apolipoprotein E fragments a promising new therapeutic target for Alzheimer’s disease?

Human apolipoprotein E (ApoE) is a 299-amino acid secreted glycoprotein that binds cholesterol and phospholipids. ApoE exists as three common isoforms (ApoE2, ApoE3, and ApoE4) and heterozygous carriers of the ε4 allele of the gene encoding ApoE (APOE) have a fourfold greater risk of developing Alzheimer’s disease (AD). The enzymes thrombin, cathepsin D, α-chymotrypsin-like serine protease, and high-temperature requirement serine protease A1 are responsible for ApoE proteolytic processing resulting in bioactive C-terminal-truncated fragments that vary depending on ApoE isoforms, brain region, aging, and neural injury. The objectives of the present narrative review were to describe ApoE processing, discussing current hypotheses about the potential role of various ApoE fragments in AD pathophysiology, and reviewing the current development status of different anti-ApoE drugs. The exact mechanism by which APOE gene variants increase/decrease AD risk and the role of ApoE fragments in the deposition are not fully understood, but APOE is known to directly affect tau-mediated neurodegeneration. ApoE fragments co-localize with neurofibrillary tangles and amyloid β (Aβ) plaques, and may cause neurodegeneration. Among anti-ApoE approaches, a fascinating strategy may be to therapeutically overexpress ApoE2 in APOE ε4/ε4 carriers through vector administration or liposomal delivery systems. Another approach involves reducing ApoE4 expression by intracerebroventricular antisense oligonucleotides that significantly decreased Aβ pathology in transgenic mice. Differences in the proteolytic processing of distinct ApoE isoforms and the use of ApoE fragments as mimetic peptides in AD treatment are also under investigation. Treatment with peptides that mimic the structural and biological properties of native ApoE may reduce Aβ deposition, tau hyperphosphorylation, and glial activation in mouse models of Aβ pathology. Alternative strategies involve the use of ApoE4 structure correctors, passive immunization to target a certain form of ApoE, conversion of the ApoE4 aminoacid sequence into that of ApoE3 or ApoE2, and inhibition of the ApoE-Aβ interaction.

Remembering your A, B, C's: Alzheimer's disease and ABCA1

The function of ATP binding cassette protein A1 (ABCA1) is central to cholesterol mobilization. Reduced ABCA1 expression or activity is implicated in Alzheimer's disease (AD) and other disorders. Therapeutic approaches to boost ABCA1 activity have yet to be translated successfully to the clinic. The risk factors for AD development and progression, including comorbid disorders such as type 2 diabetes and cardiovascular disease, highlight the intersection of cholesterol transport and inflammation. Upregulation of ABCA1 can positively impact APOE lipidation, insulin sensitivity, peripheral vascular and blood–brain barrier integrity, and anti-inflammatory signaling. Various strategies towards ABCA1-boosting compounds have been described, with a bias toward nuclear hormone receptor (NHR) agonists. These agonists display beneficial preclinical effects; however, important side effects have limited development. In particular, ligands that bind liver X receptor (LXR), the primary NHR that controls ABCA1 expression, have shown positive effects in AD mouse models; however, lipogenesis and unwanted increases in triglyceride production are often observed. The longstanding approach, focusing on LXRβ vs. LXRα selectivity, is over-simplistic and has failed. Novel approaches such as phenotypic screening may lead to small molecule NHR modulators that elevate ABCA1 function without inducing lipogenesis and are clinically translatable.

Peptides as Therapeutic Agents for Atherosclerosis

More than three decades ago, as a test for the amphipathic helix theory, an 18 amino acid residue peptide and its analogs were designed with no sequence homology to any of the exchangeable apolipoproteins. Based on the apolipoprotein A-I (the major protein component of high density lipoproteins, HDL) mimicking properties, they were termed as ApoA-I mimicking peptides. Several laboratories around the world started studying such de novo-designed peptides for their antiatherogenic properties. The present chapter describes the efforts in bringing these peptides as therapeutic agents for atherosclerosis and several lipid-mediated disorders.

Efficacy and Safety of High-Density Lipoprotein/Apolipoprotein A1 Replacement Therapy in Humans and Mice With Atherosclerosis: A Systematic Review and Meta-Analysis

Background: Although elevation of HDL-C levels by pharmaceutical drugs have no benefit of cardiovascular endpoint, the effect of high-density lipoprotein/apolipoprotein A1 (HDL/apoA-1) replacement therapy on atherosclerosis is controversial. The current meta-analysis analyzed the effects of HDL/apoA-1 replacement therapies on atherosclerotic lesions both in humans and mice.

Methods: The PubMed, Cochrane Library, Web of Science, and EMBASE databases were searched through June 6, 2020. The methodological quality of the human studies was assessed using Review Manager (RevMan, version 5.3.). The methodological quality of the mouse studies was assessed using a stair list. STATA (version 14.0) was used to perform all statistical analyses.

Results: Fifteen randomized controlled human trials and 17 animal studies were included. The pooled results showed that HDL/apoA-1 replacement therapy use did not significantly decrease the percent atheroma volume (p = 0.766) or total atheroma volume (p = 0.510) in acute coronary syndrome (ACS) patients (N = 754). However, HDL/apoA-1 replacement therapies were significantly associated with the final percent lesion area, final lesion area, and changes in lesion area (SMD, −1.75; 95% CI: −2.21~-1.29, p = 0.000; SMD, −0.78; 95% CI: −1.18~-0.38, p = 0.000; SMD: −2.06; 95% CI, −3.92~-0.2, p = 0.03, respectively) in mice.

Conclusions: HDL/apoA-1 replacement therapies are safe but do not significantly improve arterial atheroma volume in humans. The results in animals suggest that HDL/apoA-1 replacement therapies decrease the lesion area. Additional studies are needed to investigate and explain the differences in HDL/apoA-1 replacement therapy efficacies between humans and animals.

Trial registration number: Human pooled analysis: PROSPERO, CRD42020210772. prospectively registered.

Apolipoprotein and LRP1-Based Peptides as New Therapeutic Tools in Atherosclerosis

Apolipoprotein (Apo)-based mimetic peptides have been shown to reduce atherosclerosis. Most of the ApoC-II and ApoE mimetics exert anti-atherosclerotic effects by improving lipid profile. ApoC-II mimetics reverse hypertriglyceridemia and ApoE-based peptides such as Ac-hE18A-NH2 reduce cholesterol and triglyceride (TG) levels in humans. Conversely, other classes of ApoE and ApoA-I mimetic peptides and, more recently, ApoJ and LRP1-based peptides, exhibit several anti-atherosclerotic actions in experimental models without influencing lipoprotein profile. These other mimetic peptides display at least one atheroprotective mechanism such as providing LDL stability against mechanical modification or conferring protection against the action of lipolytic enzymes inducing LDL aggregation in the arterial intima. Other anti-atherosclerotic effects exerted by these peptides also include protection against foam cell formation and inflammation, and induction of reverse cholesterol transport. Although the underlying mechanisms of action are still poorly described, the recent findings suggest that these mimetics could confer atheroprotection by favorably influencing lipoprotein function rather than lipoprotein levels. Despite the promising results obtained with peptide mimetics, the assessment of their stability, atheroprotective efficacy and tissue targeted delivery are issues currently under progress.

The benzoate plant metabolite ethyl gallate prevents cellular- and vascular-lipid accumulation in experimental models of atherosclerosis

Ethyl gallate (EG) is a well-known constituent of medicinal plants, but its effects on atherosclerosis development are not clear. In the present study, the anti-atherosclerosis effects of EG and the underlying mechanisms were explored using macrophage cultures, zebrafish and apolipoprotein (apo) E deficient mice. Treatment of macrophages with EG (20 μM) enhanced cellular cholesterol efflux to HDL, and reduced net lipid accumulation in response to oxidized LDL. Secretion of monocyte chemotactic protein-1 (MCP-1) and interleukin-6 (IL-6) from activated macrophages was also blunted by EG. Fluorescence imaging techniques revealed EG feeding of zebrafish reduced vascular lipid accumulation and inflammatory responses in vivo. Similar results were obtained in apoE^-/- mice 6.5 months of age, where plaque lesions and monocyte infiltration into the artery wall were reduced by 70% and 42%, respectively, after just 6 weeks of injections with EG (20 mg/kg). HDL-cholesterol increased 2-fold, serum cholesterol efflux capacity increased by ∼30%, and the levels of MCP-1 and IL-6 were reduced with EG treatment of mice. These results suggest EG impedes early atherosclerosis development by reducing the lipid and macrophage-content of plaque. Underlying mechanisms appeared to involve HDL cholesterol efflux mechanisms and suppression of pro-inflammatory cytokine secretion.

Apolipoprotein Mimetic Peptides: Potential New Therapies for Cardiovascular Diseases

Since the seminal breakthrough of treating diabetic patients with insulin in the 1920s, there has been great interest in developing other proteins and their peptide mimetics as therapies for a wide variety of other medical disorders. Currently, there are at least 60 different peptides that have been approved for human use and over 150 peptides that are in various stages of clinical development. Peptides mimetic of the major proteins on lipoproteins, namely apolipoproteins, have also been developed first as tools for understanding apolipoprotein structure and more recently as potential therapeutics. In this review, we discuss the biochemistry, peptide mimetics design and clinical trials for peptides based on apoA-I, apoE and apoC-II. We primarily focus on applications of peptide mimetics related to cardiovascular diseases. We conclude with a discussion on the limitations of peptides as therapeutic agents and the challenges that need to be overcome before apolipoprotein mimetic peptides can be developed into new drugs.

Synergetic Effect of rHDL and LXR Agonist on Reduction of Atherosclerosis in Mice

High-density lipoproteins (HDLs) are unique in that they play an important role in the reverse cholesterol transport process. However, reconstituted HDL (rHDL) infusions have demonstrated limited beneficial effect in clinical practice. This is perhaps a consequence of the limited cholesterol efflux abilities of atheroma macrophages due to decreased expression of cholesterol transporters in advanced atheromas and following rHDL infusion treatment. Thus, we propose that a combination therapy of rHDL and a liver X receptor (LXR) agonist could maximize the therapeutic benefit of rHDL by upregulating ATP-binding cassette transporters A-1 (ABCA1) and ATP-binding cassette transporter G-1 (ABCG1), and enhancing cholesterol efflux to rHDL. In macrophages, rHDL downregulated the expression of ABCA1/G1 in a dose- and rHDL composition-dependent manner. Although LXR agonist, T0901317 (T1317), upregulated the expression of ABCA1 and ABCG1, the drug itself did not have any effect on cholesterol efflux (6.6 ± 0.5%) while the combination of rHDL and T1317 exhibited enhanced cholesterol efflux from [³H]-cholesterol loaded J774A.1 macrophages (23.3 ± 1.3%). Treatment with rHDL + T1317 significantly reduced the area of aortic plaque in ApoE^-/- mice compared to PBS treated control animals (24.16 ± 1.42% vs. 31.59 ± 1.93%, p < 0.001), while neither rHDL nor T1317 treatment alone had a significant effect. Together, we show that rHDL paired with an LXR agonist can induce a synergetic effect in reducing atheroma burden. This synergy could lead to lower overall effective dose for both drugs, potentially overcoming the existing barriers in clinical development and renewing pharmaceutical interest in these two drug classes.

Cholesterol Efflux Efficiency of Reconstituted HDL Is Affected by Nanoparticle Lipid Composition

Cardiovascular disease (CVD), the leading cause of mortality worldwide is primarily caused by atherosclerosis, which is promoted by the accumulation of low-density lipoproteins into the intima of large arteries. Multiple nanoparticles mimicking natural HDL (rHDL) have been designed to remove cholesterol excess in CVD therapy. The goal of this investigation was to assess the cholesterol efflux efficiency of rHDLs with different lipid compositions, mimicking different maturation stages of high-density lipoproteins (HDLs) occurring in vivo. Methods: the cholesterol efflux activity of soybean PC (Soy-PC), 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), DPPC:Chol:1-palmitoyl-2-hydroxy-sn-glycero-3-phosphocholine (LysoPC) and DPPC:18:2 cholesteryl ester (CE):LysoPC rHDLs was determined in several cell models to investigate the contribution of lipid composition to the effectiveness of cholesterol removal. Results: DPPC rHDLs are the most efficient particles, inducing cholesterol efflux in all cellular models and in all conditions the effect was potentiated when the ABCA1 transporter was upregulated. Conclusions: DPPC rHDLs, which resemble nascent HDL, are the most effective particles in inducing cholesterol efflux due to the higher physical binding affinity of cholesterol to the saturated long-chain-length phospholipids and the favored cholesterol transfer from a highly positively curved bilayer, to an accepting planar bilayer such as DPPC rHDLs. The physicochemical characteristics of rHDLs should be taken into consideration to design more efficient nanoparticles to promote cholesterol efflux.

Brothers in Arms: ABCA1- and ABCG1-Mediated Cholesterol Efflux as Promising Targets in Cardiovascular Disease Treatment

Atherosclerosis is a leading cause of cardiovascular disease worldwide, and hypercholesterolemia is a major risk factor. Preventive treatments mainly focus on the effective reduction of low-density lipoprotein cholesterol, but their therapeutic value is limited by the inability to completely normalize atherosclerotic risk, probably due to the disease complexity and multifactorial pathogenesis. Consequently, high-density lipoprotein cholesterol gained much interest, as it appeared to be cardioprotective due to its major role in reverse cholesterol transport (RCT). RCT facilitates removal of cholesterol from peripheral tissues, including atherosclerotic plaques, and its subsequent hepatic clearance into bile. Therefore, RCT is expected to limit plaque formation and progression. Cellular cholesterol efflux is initiated and propagated by the ATP-binding cassette (ABC) transporters ABCA1 and ABCG1. Their expression and function are expected to be rate-limiting for cholesterol efflux, which makes them interesting targets to stimulate RCT and lower atherosclerotic risk. This systematic review discusses the molecular mechanisms relevant for RCT and ABCA1 and ABCG1 function, followed by a critical overview of potential pharmacological strategies with small molecules to enhance cellular cholesterol efflux and RCT. These strategies include regulation of ABCA1 and ABCG1 expression, degradation, and mRNA stability. Various small molecules have been demonstrated to increase RCT, but the underlying mechanisms are often not completely understood and are rather unspecific, potentially causing adverse effects. Better understanding of these mechanisms could enable the development of safer drugs to increase RCT and provide more insight into its relation with atherosclerotic risk. SIGNIFICANCE STATEMENT: Hypercholesterolemia is an important risk factor of atherosclerosis, which is a leading pathological mechanism underlying cardiovascular disease. Cholesterol is removed from atherosclerotic plaques and subsequently cleared by the liver into bile. This transport is mediated by high-density lipoprotein particles, to which cholesterol is transferred via ATP-binding cassette transporters ABCA1 and ABCG1. Small-molecule pharmacological strategies stimulating these transporters may provide promising options for cardiovascular disease treatment.

The Role of HDL and HDL Mimetic Peptides as Potential Therapeutics for Alzheimer's Disease

The role of high-density lipoproteins (HDL) in the cardiovascular system has been extensively studied and the cardioprotective effects of HDL are well established. As HDL particles are formed both in the systemic circulation and in the central nervous system, the role of HDL and its associated apolipoproteins in the brain has attracted much research interest in recent years. Alzheimer’s disease (AD) is the most prevalent neurodegenerative disorder and the leading cause of dementia worldwide, for which there currently exists no approved disease modifying treatment. Multiple lines of evidence, including a number of large-scale human clinical studies, have shown a robust connection between HDL levels and AD. Low levels of HDL are associated with increased risk and severity of AD, whereas high levels of HDL are correlated with superior cognitive function. Although the mechanisms underlying the protective effects of HDL in the brain are not fully understood, many of the functions of HDL, including reverse lipid/cholesterol transport, anti-inflammation/immune modulation, anti-oxidation, microvessel endothelial protection, and proteopathy modification, are thought to be critical for its beneficial effects. This review describes the current evidence for the role of HDL in AD and the potential of using small peptides mimicking HDL or its associated apolipoproteins (HDL-mimetic peptides) as therapeutics to treat AD.

ApoE-Derived Peptides Attenuated Diabetes-Induced Oxidative Stress and Inflammation

BACKGROUND

Peptides derived from the apolipoproteins (apo-mimetic peptides) have emerged as a potential candidate for the treatment of various inflammatory conditions. Our previous results have shown that peptides derived from human apolipoprotein-E interact with various pro-inflammatory lipids and inhibit their inflammatory functions in cellular assays.

OBJECTIVE

In this study, two apoE-derived peptides were selected to investigate their antiinflammatory and anti-oxidative effects in streptozotocin-induced diabetic model of inflammation and oxidative stress.

METHODS

The peptides were injected intraperitoneally into the streptozotocin-induced diabetic rats and their anti-inflammatory and anti-oxidative effects were evaluated by monitoring various oxidative and inflammatory markers.

RESULTS

Administration of 4F, E5 and E8 peptides decreased the oxidative and inflammatory markers in STZ-induced diabetic rats to different extent, while had no significant effect on the other diabetic parameters (viz. total body weight of animals and increased blood glucose level). E5 peptide was found to be relatively more effective than 4F and E8 peptides in decreasing inflammation and oxidative stress.

CONCLUSION

E5 peptide can be developed as a potential candidate for inflammatory conditions.

Subcutaneous Administration of Apolipoprotein J-Derived Mimetic Peptide d-[113-122]apoJ Improves LDL and HDL Function and Prevents Atherosclerosis in LDLR-KO Mice

Mimetic peptides are potential therapeutic agents for atherosclerosis. d-[113–122]apolipoprotein (apo) J (d-[113–122]apoJ) is a 10-residue peptide that is predicted to form a class G* amphipathic helix 6 from apoJ; it shows anti-inflammatory and anti-atherogenic properties. In the present study, we analyzed the effect of d-[113–122]apoJ in low-density lipoprotein receptor knockout mice(LDLR-KO) on the development of atherosclerosis and lipoprotein function. Fifteen-week-old female LDLR-KO mice fed an atherogenic Western-type diet were treated for eight weeks with d-[113–122]apoJ peptide, a scrambled peptide, or vehicle. Peptides were administered subcutaneously three days per week (200 µg in 100 µL of saline). After euthanasia, blood and hearts were collected and the aortic arch was analyzed for the presence of atherosclerotic lesions. Lipoproteins were isolated and their composition and functionality were studied. The extent of atherosclerotic lesions was 43% lower with d-[113–122]apoJ treatment than with the vehicle or scramble. The lipid profile was similar between groups, but the high-density lipoprotein (HDL) of d-[113–122]apoJ-treated mice had a higher antioxidant capacity and increased ability to promote cholesterol efflux than the control group. In addition, low-density lipoprotein (LDL) from d-[113–122]apoJ-treated mice was more resistant to induced aggregation and presented lower electronegativity than in mice treated with d-[113–122]apoJ. Our results demonstrate that the d-[113–122]apoJ peptide prevents the extent of atherosclerotic lesions, which could be partially explained by the improvement of lipoprotein functionality.

Reconfiguring Nature's Cholesterol Accepting Lipoproteins as Nanoparticle Platforms for Transport and Delivery of Therapeutic and Imaging Agents

Apolipoproteins are critical structural and functional components of lipoproteins, which are large supramolecular assemblies composed predominantly of lipids and proteins, and other biomolecules such as nucleic acids. A signature feature of apolipoproteins is the preponderance of amphipathic α-helical motifs that dictate their ability to make extensive non-covalent inter- or intra-molecular helix-helix interactions in lipid-free states or helix-lipid interactions with hydrophobic biomolecules in lipid-associated states. This review focuses on the latter ability of apolipoproteins, which has been capitalized on to reconstitute synthetic nanoscale binary/ternary lipoprotein complexes composed of apolipoproteins/peptides and lipids that mimic native high-density lipoproteins (HDLs) with the goal to transport drugs. It traces the historical development of our understanding of these nanostructures and how the cholesterol accepting property of HDL has been reconfigured to develop them as drug-loading platforms. The review provides the structural perspective of these platforms with different types of apolipoproteins and an overview of their synthesis. It also examines the cargo that have been loaded into the core for therapeutic and imaging purposes. Finally, it lays out the merits and challenges associated with apolipoprotein-based nanostructures with a future perspective calling for a need to develop "zip-code"-based delivery for therapeutic and diagnostic applications.

Incorporation of α-methylated amino acids into Apolipoprotein A-I mimetic peptides improves their helicity and cholesterol efflux potential

Apolipoprotein A-I (ApoA-I) mimetic peptides are potential therapeutic agents for promoting the efflux of excess cellular cholesterol, which is dependent upon the presence of an amphipathic helix. Since α-methylated Ala enhances peptide helicity, we hypothesized that incorporating other types of α-methylated amino acids into ApoA-I mimetic peptides may also increase their helicity and cholesterol efflux potential. The last helix of apoA-I, peptide 'A' (VLESFKVSFLSALEEYTKKLNT), was used to design peptides containing a single type of α-methylated amino acid substitution (Ala/A_α, Glu/D_α, Lys/K_α, Leu/L_α), as well as a peptide containing both α-methylated Lys and Leu (6_α). Depending on the specific residue, the α-helical content as measured by CD-spectroscopy and calculated hydrophobic moments were sometimes higher for peptides containing other types of α-methylated amino acids than those with α-methylated Ala. In ABCA1-transfected cells, cholesterol efflux to the peptides showed the following order of potency: 6_α>K_α≈L_α≈A_α≫D_α≈A. In general, α-methylated peptides were resistant to proteolysis, but this varied depending on the type of protease and specific amino acid substitution. In summary, increased helicity and amphilicity due to α-methylated amino acid substitutions in ApoA-I mimetic peptides resulted in improved cholesterol efflux capacity and resistance to proteolysis, indicating that this modification may be useful in the future design of therapeutic ApoA-I mimetic peptides.

Synthetic apolipoprotein A-I mimetic peptide 4F protects hearts and kidneys after myocardial infarction

Patients undergoing coronary angiography after myocardial infarction (MI) often develop cardiac and renal dysfunction. We hypothesized that the apolipoprotein A-I mimetic peptide 4F (4F) would prevent those complications. Male Wistar rats were fed a high-cholesterol diet for 8 days. The rats were then anesthetized with isoflurane and randomly divided into five groups: a control group (sham-operated rats), and four groups of rats induced to MI by left coronary artery ligation, the rats in three of those groups being injected 6 h later, with the nonionic contrast agent iopamidol, 4F, and iopamidol plus 4F, respectively. At postprocedure hour 24, we performed the following experiments/tests (n = 8 rats/group): metabolic cage studies; creatinine clearance studies; analysis of creatinine, urea, sodium, potassium, triglycerides, total cholesterol, very low-, low- and high-density lipoproteins (VLDL, LDL, and HDL); immunohistochemistry; histomorphometry; Western blot analysis; and transmission electron microscopy. In another set of experiments (n = 8 rats/group), also performed at postprocedure hour 24, we measured mean arterial pressure, heart rate, heart rate variability, echocardiographic parameters, left ventricular systolic pressure, and left ventricular end-diastolic pressure. 4F protected against MI-induced increases in total cholesterol, triglycerides, and LDL; increased HDL levels; reversed autonomic and cardiac dysfunction; decreased the myocardial ischemic area; minimized renal and cardiac apoptosis; protected mitochondria; and strengthened endothelia possibly by minimizing Toll-like receptor 4 upregulation (thus restoring endothelial nitric oxide synthase protein expression) and by upregulating vascular endothelial growth factor protein expression. 4F-treated animals showed signs of cardiac neovascularization. The nitric oxide-dependent cardioprotection and renoprotection provided by 4F could have implications for post-MI treatment.

Phospholipid Component Defines Pharmacokinetic and Pharmacodynamic Properties of Synthetic High-Density Lipoproteins

Synthetic high-density lipoprotein (sHDL) nanoparticles composed of apolipoprotein A-I mimetic peptide and phospholipids have been shown to reduce atherosclerosis in animal models. Cholesterol is mobilized from atheroma macrophages by sHDL into the blood compartment and delivered to the liver for elimination. Historically, sHDL drug discovery efforts were focused on optimizing peptide sequences for interaction with cholesterol cellular transporters rather than understanding how both sHDL components, peptide and lipid, influence its pharmacokinetic and pharmacodynamic profiles. We designed two sets of sHDL having either identical phospholipid but variable peptide sequences with different plasma stability or identical peptide and phospholipids with variable fatty acid chain length and saturation. We found that sHDL prepared with proteolytically stable 22A-P peptide had 2-fold longer circulation half-time relative to the less stable 22A peptide. Yet, longer half-life did not translate into any improvement in cholesterol mobilization. In contrast, sHDL with variable phospholipid compositions showed significant differences in phospholipid PK, with distearoyl phosphatidylcholine-based sHDL demonstrating the longest half-life of 6.0 hours relative to 1.0 hour for palmitoyl-oleoyl phosphatidylcholine-based sHDL. This increase in half-life corresponded to an approx. 6.5-fold increase in the area under the curve for the mobilized cholesterol. Therefore, the phospholipid component in sHDL plays a major role in cholesterol mobilization in vivo and should not be overlooked in the design of future sHDL. SIGNIFICANCE STATEMENT: The phospholipid composition in sHDL plays a critical role in determining half-life and cholesterol mobilization in vivo.

Low-density lipoprotein aggregation is inhibited by apolipoprotein J-derived mimetic peptide D-[113-122]apoJ

Mimetic peptides are promising therapeutic agents for atherosclerosis prevention. A 10-residue class G* peptide from apolipoprotein J (apoJ), namely, D-[113-122]apoJ, possesses anti-inflammatory and anti-atherogenic properties. This prompted us to determine its effect on the aggregation process of low-density lipoprotein (LDL) particles, an early event in the development of atherosclerosis. LDL particles with and without [113-122]apoJ peptide were incubated at 37 °C with sphingomyelinase (SMase) or were left to aggregate spontaneously at room temperature. The aggregation process was analyzed by size-exclusion chromatography (SEC), native gradient gel electrophoresis (GGE), absorbance at 405 nm, dynamic light scattering (DLS), and transmission electronic microscopy (TEM). In addition, circular dichroism was used to determine changes in the secondary structure of apoB, and SDS-PAGE was performed to assess apoB degradation. At an equimolar ratio of [113-122]apoJ peptide to apoB-100, [113-122]apoJ inhibited both SMase-induced or spontaneous LDL aggregation. All methods showed that [113-122]apoJ retarded the progression of SMase-induced LDL aggregation at long incubation times. No effect of [113-122]apoJ on apoB secondary structure was observed. Binding experiments showed that [113-122]apoJ presents low affinity for native LDL but binds readily to LDL during the first stages of aggregation. Laurdan fluorescence experiments showed that mild aggregation of LDL resulted in looser lipid packaging, which was partially prevented by D-[113-122]apoJ. These results demonstrate that [113-122]apoJ peptide prevents SMase-induced LDL aggregation at an equimolar ratio and opens the possibility for the use of this peptide as a therapeutic tool.

The future of apolipoprotein E mimetic peptides in the prevention of cardiovascular disease

PURPOSE OF REVIEW

This review aims to discuss the recent developments in the area of apolipoprotein E (apoE) mimetics and their therapeutic potential for treating cardiovascular disease, the leading cause of mortality worldwide.

RECENT FINDINGS

Ongoing research efforts target the development of novel therapies that would not only reduce circulating levels of atherogenic lipoproteins, but could also increase high density lipoprotein cholesterol (HDL-C) levels and/or improve HDL function. Among them, synthetic peptides that mimic the structure of natural human apoE, a component of triglyceride-rich lipoproteins and HDL, have been designed and proven to be functionally similar to apoE. In specific, apoE mimetic peptides mediate hepatic clearance of circulating atherogenic lipoproteins, dramatically reduce plasma cholesterol, and lead to attenuation of atherosclerosis development in vivo. These peptides also exhibit pleiotropic antiatherogenic properties, such as macrophage cholesterol efflux capacity, as well as anti-inflammatory and antioxidative functions.

SUMMARY

ApoE mimetics are undergoing preclinical and clinical evaluation with promising results to date that render them attractive candidates in cardiovascular disease prevention and treatment.

Vulnerable Plaque, Characteristics, Detection, and Potential Therapies

Plaque development and rupture are hallmarks of atherosclerotic vascular disease. Despite current therapeutic developments, there is an unmet necessity in the prevention of atherosclerotic vascular disease. It remains a challenge to determine at an early stage if atherosclerotic plaque will become unstable and vulnerable. The arrival of molecular imaging is receiving more attention, considering it allows for a better understanding of the biology of human plaque and vulnerabilities. Various plaque therapies with common goals have been tested in high-risk patients with cardiovascular disease. In this work, the process of plaque instability, along with current technologies for sensing and predicting high-risk plaques, is debated. Updates on potential novel therapeutic approaches are also summarized.

Apoproteins E, A-I, and SAA in Macrophage Pathobiology Related to Atherogenesis

Macrophages are core cellular elements of both early and advanced atherosclerosis. They take up modified lipoproteins and become lipid-loaded foam cells and secrete factors that influence other cell types in the artery wall involved in atherogenesis. Apoproteins E, AI, and SAA are all found on HDL which can enter the artery wall. In addition, apoE is synthesized by macrophages. These three apoproteins can promote cholesterol efflux from lipid-loaded macrophages and have other functions that modulate macrophage biology. Mimetic peptides based on the sequence or structure of these apoproteins replicate some of these properties and are potential therapeutic agents for the treatment of atherosclerosis to reduce cardiovascular diseases.

ABCA1 and metabolic syndrome; a review of the ABCA1 role in HDL-VLDL production, insulin-glucose homeostasis, inflammation and obesity

ATP-binding cassette transporter A1 (ABCA1) is an integral cell-membrane protein that mediates the rate-limiting step of high density lipoprotein (HDL) biogenesis and suppression of inflammation by triggering a number of signaling pathways via interacting with an apolipoprotein acceptor. The hepatic ABCA1 is involved in regulation of very low density lipoprotein (VLDL) production by affecting the apolipoprotein B trafficking and lipidation of VLDL particles. This protein is involved in protecting the function of pancreatic β-cells and insulin secretion by cholesterol homeostasis. Adipose tissue lipolysis is associated with ABCA1 activity. This transporter is involved in controlling obesity and insulin sensitivity by regulating triglyceride (TG) lipolysis and influencing on adiponectin, visfatin, leptin, and GLUT4 genes expression. The ABCA1 of skeletal muscle cells play a role in increasing the glucose uptake by enhancing the Akt phosphorylation and transferring GLUT4 to the plasma membrane. Abnormal status of ABCA1-regulated phenotypes is observed in metabolic syndrome. This syndrome is associated with the occurrence of many diseases. This review is a summary of the role of ABCA1 in HDL and VLDL production, homeostasis of insulin and glucose, suppression of inflammation and obesity controlling to provide a better insight into the association of this protein with metabolic syndrome.

Novel ABCA1 peptide agonists with antidiabetic action

Previously, apoE-derived ABCA1 agonist peptides have been shown to possess anti-atherosclerotic and possibly antidiabetic properties. Here we assessed the in vitro and in vivo actions of a second generation of ABCA1 peptide agonists, CS6253 and T6991-2, on glucose homeostasis. The results show that these two peptides improve glucose tolerance in a prediabetic diet-induced obesity mouse model by enhancing insulin secretion. It was further demonstrated that T6991-2 also improved glucose tolerance in leptin-deficient (ob/ob) mice. CS6253 increased insulin secretion both under basal conditions and in response to high glucose stimulation in pancreatic INS-1 β-cells rendered leptin receptor deficient with specific siRNA. Additional in vitro cell studies suggest that the CS6253 agonist attenuates hepatic gluconeogenesis and glucose transport. It also potentiates insulin-stimulated glucose uptake and utilization. These observed anti-diabetic actions suggest additional benefits of the CS6253 and T6991-2 ABCA1 peptide agonists for cardiovascular disease beyond their direct anti-atherosclerosis properties previously described.

Apoprotein E and Reverse Cholesterol Transport

Apoprotein E (apoE) is a multifunctional protein. Its best-characterized function is as a ligand for low-density lipoprotein (LDL) receptor family members to mediate the clearance of apoB-containing atherogenic lipoproteins. Among its other functions, apoE is involved in cholesterol efflux, especially from cholesterol-loaded macrophage foam cells and other atherosclerosis-relevant cells, and in reverse cholesterol transport. Reverse cholesterol transport is a mechanism by which excess cellular cholesterol is transported via lipoproteins in the plasma to the liver where it can be excreted from the body in the feces. This process is thought to have a role in the attenuation of atherosclerosis. This review summarizes studies on the role of apoE in cellular cholesterol efflux and reverse cholesterol transport and discusses the identification of apoE mimetic peptides that may promote these pathways.

Reconstituted Discoidal High-Density Lipoproteins: Bioinspired Nanodiscs with Many Unexpected Applications

PURPOSE OF REVIEW

Summarize the initial discovery of discoidal high-density lipoprotein (HDL) in human plasma and review more recent innovations that span the use of reconstituted nanodisc HDL for membrane protein characterization to its use as a drug carrier and a novel therapeutic agent for cardiovascular disease.

RECENT FINDINGS

Using a wide variety of biophysical techniques, the structure and composition of endogenous discoidal HDL have now largely been solved. This has led to the development of new methods for the in vitro reconstitution of nanodisc HDL, which have proven to have a wide variety of biomedical applications. Nanodisc HDL has been used as a platform for mimicking the plasma membrane for the reconstitution and investigation of the structures of several plasma membrane proteins, such as cytochrome P450s and ABC transporters. Nanodisc HDL has also been designed as drug carriers to transport amphipathic, as well as hydrophobic small molecules, and has potential therapeutic applications for several diseases. Finally, nanodisc HDL itself like native discoidal HDL can mediate cholesterol efflux from cells and are currently being tested in late-stage clinical trials for cardiovascular disease. The discovery of the characterization of native discoidal HDL has inspired a new field of synthetic nanodisc HDL, which has offered a growing number of unanticipated biomedical applications.

Apolipoprotein A1 mimetic peptide ATI-5261 reverses arterial stiffness at late pregnancy and early postpartum in a COMT-/- mouse model of preeclampsia

Background

Preeclampsia (PE) is a serious maternal complication during pregnancy. Associated arterial stiffness in PE patients leads to increased risks of cardiovascular diseases later in life. Cholesterol efflux capacity, especially ATP binding cassette transporter A1 (ABCA1) dependent capacity, has been proposed to be a likely mediator of arterial stiffness. In the present study, we aimed to evaluate the effect of an apolipoprotein A1 mimetic peptide ATI-5261 on arterial stiffness in a mouse model of PE.

Methods

Pregnant COMT^-/- mice were randomized to receive vehicle or ATI-5261 (30 mg/kg per day) via subcutaneous injection from gestational days (GD) 10.5 to GD 18.5 or to 10 days postpartum. Pregnant C57BL/6 J mice received vehicle during paralleled periods were served as normal controls.

Results

COMT^-/- mice displayed maternal hypertension and proteinuria during pregnancy. Carotid-femoral pulse wave velocity (PWV) was increased at GD 18.5 and 10 days postpartum. ATI-5261 treatment in COMT^-/- mice significantly reduced PWV and partially normalized impaired ex vivo vascular function at late pregnancy and early postpartum. ATI-5261 treatment also increased serum ABCA1 concentrations and cholesterol efflux capacity, as well as ABCA1 expressions in the placenta. Pup weights, crown to rump lengths and abdominal circumferences were reduced in COMT^-/- mice. Treatment with ATI-5261 did not alter these fetal measurements but significantly reduced placental weights and increased fetal to placental ratios in COMT^-/- mice.

Conclusion

ATI-5261 reversed arterial stiffness at late pregnancy and early postpartum in a COMT^-/- mouse model of PE and may be a potential therapy for arterial stiffness associated with PE.

HDL Mimetics Infusion and Regression of Atherosclerosis: Is It Still Considered a Valid Therapeutic Option?

Purpose of Review

This review aims to summarize and discuss the recent findings in the field of using HDL mimetics for the treatment of patients with coronary artery disease.

Recent Findings

Following the largely disappointing results with the cholesteryl ester transfer protein inhibitors, focus moved to HDL functionality rather than absolute HDL cholesterol values. A number of HDL/apoA-I mimicking molecules were developed, aiming to enhance reverse cholesterol transport that has been associated with an atheroprotective effect. Three HDL mimetics have made the step from bench-testing to clinical trials in humans and are discussed here: apoA-I Milano, CSL-112, and CER-001. Unfortunately, with the exception of CSL-112 where the results of the clinical trial are not yet known, none of the agents was able to demonstrate a clinical benefit.

Summary

HDL mimetics have failed to date to prove a beneficial effect in clinical practice. Reverse cholesterol transport remains a challenging therapeutic pathway to be explored.

Pharmacological Management of Dyslipidemia in Atherosclerosis: Limitations, Challenges, and New Therapeutic Opportunities

Clinical and epidemiological studies during the last 7 decades indicated that elevated low-density lipoprotein cholesterol (LDL-C) levels and reduced high-density lipoprotein cholesterol (HDL-C) levels correlate with the pathogenesis and progression of atherosclerotic lesions in the arterial wall. This observation led to the development of LDL-C-lowering drugs for the prevention and treatment of atherosclerosis, some with greater success than others. However, a body of recent clinical evidence shows that a substantial residual cardiovascular risk exists even at very low levels of LDL-C, suggesting that new therapeutic modalities are still needed for reduction of atherosclerosis morbidity and mortality. Unfortunately, HDL-C-raising drugs developed toward this goal had disappointing results thus far. Here, we critically review the literature presenting available evidence and challenges that need to be met and discuss possible new avenues for the development of novel lipid pharmacotherapeutics to reduce the burden of atherosclerosis.

Structural properties of apolipoprotein A-I mimetic peptides that promote ABCA1-dependent cholesterol efflux

Peptides mimicking the major protein of highdensity lipoprotein (HDL), apolipoprotein A-I (apoA-I), are promising therapeutics for cardiovascular diseases. Similar to apoA-I, their atheroprotective property is attributed to their ability to form discoidal HDL-like particles by extracting cellular cholesterol and phospholipids from lipid microdomains created by the ABCA1 transporter in a process called cholesterol efflux. The structural features of peptides that enable cholesterol efflux are not well understood. Herein, four synthetic amphipathic peptides denoted ELK, which only contain Glu, Leu, Lys, and sometimes Ala, and which have a wide range of net charges and hydrophobicities, were examined for cholesterol efflux. Experiments show that ELKs with a net neutral charge and a hydrophobic face that subtends an angle of at least 140° are optimal for cholesterol efflux. All-atom molecular dynamics simulations show that peptides that are effective in promoting cholesterol efflux stabilize HDL nanodiscs formed by these peptides by the orderly covering of the hydrophobic acyl chains on the edge of the disc. In contrast to apoA-I, which forms an anti-parallel double belt around the HDL, active peptides assemble in a mostly anti-parallel “picket fence” arrangement. These results shed light on the efflux ability of apoA-I mimetics and inform the future design of such therapeutics.

ABCA1 Agonist Reverses the ApoE4-Driven Cognitive and Brain Pathologies

The allele ɛ4 of apolipoprotein E (apoE4) is the most prevalent genetic risk factor for Alzheimer's disease (AD) and is therefore a promising therapeutic target. Human and animal model studies suggest that apoE4 is hypolipidated; accordingly, we have previously shown that the retinoid X receptor (RXR) agonist bexarotene upregulates ABCA1, the main apoE-lipidating protein, resulting in increased lipidation of apoE4, and the subsequent reversal of the pathological effects of apoE4, namely: accumulation of Aβ42 and hyperphosphorylated tau, as well as reduction in the levels of synaptic markers and cognitive deficits. Since the RXR system has numerous other targets, it is important to devise the means of activating ABCA1 selectively. We presently utilized CS-6253, a peptide shown to directly activate ABCA1 in vitro, and examined the extent to which it can affect the degree of lipidation of apoE4 in vivo and counteract the associated brain and behavioral pathologies. This revealed that treatment of young apoE4-targeted replacement mice with CS-6253 increases the lipidation of apoE4. This was associated with a reversal of the apoE4-driven Aβ42 accumulation and tau hyperphosphorylation in hippocampal neurons, as well as of the synaptic impairments and cognitive deficits. These findings suggest that the pathological effects of apoE4 in vivo are associated with decreased activation of ABCA1 and impaired lipidation of apoE4 and that the downstream brain-related pathology and cognitive deficits can be counteracted by treatment with the ABCA1 agonist CS-6253. These findings have important clinical ramifications and put forward ABCA1 as a promising target for apoE4-related treatment of AD.

Cell-specific and region-specific transcriptomics in the multiple sclerosis model: Focus on astrocytes

Changes in gene expression that occur across the central nervous system (CNS) during neurological diseases do not address the heterogeneity of cell types from one CNS region to another and are complicated by alterations in cellular composition during disease. Multiple sclerosis (MS) is multifocal by definition. Here, a cell-specific and region-specific transcriptomics approach was used to determine gene expression changes in astrocytes in the most widely used MS model, experimental autoimmune encephalomyelitis (EAE). Astrocyte-specific RNAs from various neuroanatomic regions were attained using RiboTag technology. Sequencing and bioinformatics analyses showed that EAE-induced gene expression changes differed between neuroanatomic regions when comparing astrocytes from spinal cord, cerebellum, cerebral cortex, and hippocampus. The top gene pathways that were changed in astrocytes from spinal cord during chronic EAE involved decreases in expression of cholesterol synthesis genes while immune pathway gene expression in astrocytes was increased. Optic nerve from EAE and optic chiasm from MS also showed decreased cholesterol synthesis gene expression. The potential role of cholesterol synthesized by astrocytes during EAE and MS is discussed. Together, this provides proof-of-concept that a cell-specific and region-specific gene expression approach can provide potential treatment targets in distinct neuroanatomic regions during multifocal neurological diseases.

Swapping the N- and C-terminal domains of human apolipoprotein E3 and AI reveals insights into their structure/activity relationship

Apolipoprotein (apo) E3 and apoAI are exchangeable apolipoproteins that play a dominant role in regulating plasma lipoprotein metabolism. ApoE3 (299 residues) is composed of an N-terminal (NT) domain bearing a 4-helix bundle and a C-terminal (CT) domain bearing a series of amphipathic α-helices. ApoAI (243 residues) also comprises a highly helical NT domain and a less structured CT tail. The objective of this study was to understand their structural and functional role by generating domain swapped chimeras: apoE3-NT/apoAI-CT and apoAI-NT/apoE-CT. The bacterially overexpressed chimeras were purified by affinity chromatography and their identity confirmed by immunoblotting and mass spectrometry. Their α-helical content was comparable to that of the parent proteins. ApoE3-NT/apoAI-CT retained the denaturation profile of apoE3 NT domain, with apoAI CT tail eliciting a relatively unstructured state; its lipid binding ability improved dramatically compared to apoE3 indicative of a significant role of apoAI CT tail in lipid binding interaction. The LDL receptor interaction and ability to promote ABCA1-mediated cholesterol efflux of apoE3-NT/apoAI-CT was comparable to that of apoE3. In contrast, apoAI-NT/apoE-CT elicited an unfolding pattern and lipid binding ability that were similar to that of apoAI. As expected, DMPC/apoAI-NT/apoE-CT discoidal particles did not elicit LDLr binding ability, and promoted SR-B1 mediated cellular uptake of lipids to a limited extent. However, apoAI-NT/apoE-CT displayed an enhanced ability to promote cholesterol efflux compared to apoAI, indicative of a significant role for apoE CT domain in mediating this function. Together, these results indicate that the functional attributes of apoAI and apoE3 can be conferred on each other and that NT-CT domain interactions significantly modulate their structure and function.

The Potential Therapeutic Application of Peptides and Peptidomimetics in Cardiovascular Disease

Cardiovascular disease (CVD) remains a leading cause of mortality and morbidity worldwide. Numerous therapies are currently under investigation to improve pathological cardiovascular complications, but yet, there have been very few new medications approved for intervention/treatment. Therefore, new approaches to treat CVD are urgently required. Attempts to prevent vascular complications usually involve amelioration of contributing risk factors and underlying processes such as inflammation, obesity, hyperglycaemia, or hypercholesterolemia. Historically, the development of peptides as therapeutic agents has been avoided by the Pharmaceutical industry due to their low stability, size, rate of degradation, and poor delivery. However, more recently, resurgence has taken place in developing peptides and their mimetics for therapeutic intervention. As a result, increased attention has been placed upon using peptides that mimic the function of mediators involved in pathologic processes during vascular damage. This review will provide an overview on novel targets and experimental therapeutic approaches based on peptidomimetics for modulation in CVD. We aim to specifically examine apolipoprotein A-I (apoA-I) and apoE mimetic peptides and their role in cholesterol transport during atherosclerosis, suppressors of cytokine signaling (SOCS)1-derived peptides and annexin-A1 as potent inhibitors of inflammation, incretin mimetics and their function in glucose-insulin tolerance, among others. With improvements in technology and synthesis platforms the future looks promising for the development of novel peptides and mimetics for therapeutic use. However, within the area of CVD much more work is required to identify and improve our understanding of peptide structure, interaction, and function in order to select the best targets to take forward for treatment.

Influence of route of administration and lipidation of apolipoprotein A-I peptide on pharmacokinetics and cholesterol mobilization

apoA-I, apoA-I mimetic peptides, and their lipid complexes or reconstituted high-density lipoprotein (HDL) have been studied as treatments for various pathologies. However, consensus is lacking about the best method for administration, by intravenous (IV) or intraperitoneal (IP) routes, and formulation, as an HDL particle or in a lipid-free form. The objective of this study was to systematically examine peptide plasma levels, cholesterol mobilization, and lipoprotein remodeling in vivo following administration of lipid-free apoA-I peptide (22A) or phospholipid reconstituted 22A-sHDL by IV and IP routes. The mean circulation half-life was longer for 22A-sHDL (T1/2 = 6.27 h) than for free 22A (T1/2 = 3.81 h). The percentage of 22A absorbed by the vascular compartment after the IP dosing was ∼50% for both 22A and 22A-sHDL. The strongest pharmacologic response came from IV injection of 22A-sHDL, specifically a 5.3-fold transient increase in plasma-free cholesterol (FC) level compared with 1.3- and 1.8-fold FC increases for 22A-IV and 22A-sHDL-IP groups. Addition of either 22A or 22A-sHDL to rat plasma caused lipoprotein remodeling and appearance of a lipid-poor apoA-I. Hence, both the route of administration and the formulation of apoA-I peptide significantly affect its pharmacokinetics and pharmacodynamics.

Inducing apolipoprotein A-I synthesis to reduce cardiovascular risk: from ASSERT to SUSTAIN and beyond

Increasing attention has focused on efforts to promote the biological activities of high-density lipoproteins (HDL) in order to reduce cardiovascular risk. Targeting apolipoprotein A-I (apoA-I), the major protein carried on HDL particles, represents an attractive approach to promoting HDL by virtue of its ability to increase endogenous synthesis of functional HDL particles. A number of pharmacological strategies that target apoA-I, including upregulation of its production with the bromodomain and extraterminal (BET) protein inhibitor RVX-208, development of short peptide sequences that mimic its action, and administration as a component of reconstituted HDL particles, have undergone clinical development. The impact of these approaches on cardiovascular biomarkers will be reviewed.

Differential Effects of apoE4 and Activation of ABCA1 on Brain and Plasma Lipoproteins

Apolipoprotein E4 (apoE4), the leading genetic risk factor for Alzheimer's disease (AD), is less lipidated compared to the most common and AD-benign allele, apoE3. We have recently shown that i.p. injections of the ATP-binding cassette A1 (ABCA1) agonist peptide CS-6253 to apoE mice reverse the hypolipidation of apoE4 and the associated brain pathology and behavioral deficits. While in the brain apoE is the main cholesterol transporter, in the periphery apoE and apoA-I both serve as the major cholesterol transporters. We presently investigated the extent to which apoE genotype and CS-6253 treatment to apoE3 and apoE4-targeted replacement mice affects the plasma levels and lipid particle distribution of apoE, and those of plasma and brain apoA-I and apoJ. This revealed that plasma levels of apoE4 were lower and eluted faster following FPLC than plasma apoE3. Treatment with CS-6253 increased the levels of plasma apoE4 and rendered the elution profile of apoE4 similar to that of apoE3. Similarly, the levels of plasma apoA-I were lower in the apoE4 mice compared to apoE3 mice, and this effect was partially reversed by CS-6253. Conversely, the levels of apoA-I in the brain which were higher in the apoE4 mice, were unaffected by CS-6253. The plasma levels of apoJ were higher in apoE4 mice than apoE3 mice and this effect was abolished by CS-6253. Similar but less pronounced effects were obtained in the brain. In conclusion, these results suggest that apoE4 affects the levels of apoA-I and apoJ and that the anti-apoE4 beneficial effects of CS-6253 may be related to both central and peripheral mechanisms.

Recombinant high-density lipoproteins and their use in cardiovascular diseases

The unique anti-atherosclerosis abilities and other cardioprotective properties make high-density lipoprotein (HDL) a promising solution in treating cardiovascular diseases. A number of studies showed that HDL-based therapy was well tolerated and has great potential in the future. Among all these new agents, the most studied ones including recombinant HDL, recombinant human apolipoproteins, apolipoprotein mimetic peptides and recombinant HDL used as contrast agents in cardiovascular imaging are discussed here. Recombinant HDL and apolipoproteins are promising in diagnosing and treating cardiovascular diseases.

Transintestinal transport of the anti-inflammatory drug 4F and the modulation of transintestinal cholesterol efflux

The site and mechanism of action of the apoA-I mimetic peptide 4F are incompletely understood. Transintestinal cholesterol efflux (TICE) is a process involved in the clearance of excess cholesterol from the body. While TICE is responsible for at least 30% of the clearance of neutral sterols from the circulation into the intestinal lumen, few pharmacological agents have been identified that modulate this pathway. We show first that circulating 4F selectively targets the small intestine (SI) and that it is predominantly transported into the intestinal lumen. This transport of 4F into the SI lumen is transintestinal in nature, and it is modulated by TICE. We also show that circulating 4F increases reverse cholesterol transport from macrophages and cholesterol efflux from lipoproteins via the TICE pathway. We identify the cause of this modulation of TICE either as 4F being a cholesterol acceptor with respect to enterocytes, from which 4F enhances cholesterol efflux, or as 4F being an intestinal chaperone with respect to TICE. Our results assign a novel role for 4F as a modulator of the TICE pathway and suggest that the anti-inflammatory functions of 4F may be a partial consequence of the codependent intestinal transport of both 4F and cholesterol.

Common links between metabolic syndrome and inflammatory bowel disease: Current overview and future perspectives

Metabolic syndrome (MS) features a constellation of central obesity, dyslipidemia, impaired glucose metabolism and often hypertension joined by insulin resistance and chronic inflammation. All these elements greatly raise patient's risk of cardiovascular disease and type 2 diabetes, resulting in an increased mortality. Metabolic syndrome affects approximately 20-25% of the world's adult population and thus it is essential to study its pathophysiology and seek new pharmacological targets. There is a thoroughly studied link between MS and inflammatory diseases of the gastrointestinal (GI) system, i.e. steatohepatitis. However, recent findings also indicate similarities in pathophysiological features between MS and inflammatory bowel disease (IBD), including adipose tissue dysregulation, inadequate immune response, and inflammation. In this review we aim to outline the pathophysiology of MS and emphasize the aspects revealed recently, such as mineralocorticoid activity, involvement of sex hormones and an accompanying increase in prolactin secretion. More importantly, we focus on the common links between MS and IBD. Finally, we describe new strategies and drug targets that may be utilized in MS therapy, namely adiponectin mimetics, GLP-1-based multi agonists, ABCA1 agonists and possible role of miRNA. We also discuss the possible utility of selected agents as adjuvants in IBD therapy.

Amphipathic polyproline peptides stimulate cholesterol efflux by the ABCA1 transporter

ApoA-I mimetics are short synthetic peptides that contain an amphipathic α-helix and stimulate cholesterol efflux by the ABCA1 transporter in a detergent-like extraction mechanism. We investigated the use of amphipathic peptides with a polypro helix for stimulating cholesterol efflux by ABCA1. Polypro peptides were synthesized with modified prolines, containing either a hydrophobic phenyl group (Prop) or a polar N-acetylgalactosamine (Prog) attached to the pyrrolidine ring and were designated as either PP-2, 3, 4, or 5, depending on the number of 3 amino acid repeat units (Prop-Prog-Prop). Based on molecular modeling, these peptides were predicted to be relatively rigid and to bind to a phospholipid bilayer. By CD spectroscopy, PP peptides formed a Type-II polypro helix in an aqueous solution. PP-2 was inactive in promoting cholesterol efflux, but peptides with more than 2 repeat units were active. PP-4 showed a similar Vmax as a much longer amphipathic α-helical peptide, containing 37 amino acids, but had a Km that was approximately 20-fold lower. PP peptides were specific in that they did not stimulate cholesterol efflux from cells not expressing ABCA1 and were also non-cytotoxic. Addition of PP-3, 4 and 5 to serum promoted the formation of smaller size HDL species (7 nM) and increased its capacity for ABCA1-dependent cholesterol efflux by approximately 20-35% (p < 0.05). Because of their relatively small size and increased potency, amphipathic peptides with a polypro helix may represent an alternative structural motif for the development of apoA-I mimetic peptides.

High-density lipoprotein mimetics: promises and challenges

The concept of lipoprotein mimetics was developed and extensively tested in the last three decades. Most lipoprotein mimetics were designed to recreate one or several functions of high-density lipoprotein (HDL) in the context of cardiovascular disease; however, the application of this approach is much broader. Lipoprotein mimetics should not just be seen as a set of compounds aimed at replenishing a deficiency or dysfunctionality of individual elements of lipoprotein metabolism but rather as a designer concept with remarkable flexibility and numerous applications in medicine and biology. In the present review, we discuss the fundamental design principles used to create lipoprotein mimetics, mechanisms of their action, medical indications and efficacy in animal models and human studies.

ABCA1 agonist peptides for the treatment of disease

PURPOSE OF REVIEW

The review summarizes information pertaining to the preclinical development of new apolipoprotein (apo) E mimetic peptides that stimulate cellular cholesterol efflux.

RECENT FINDINGS

Small α-helical peptides based on the C-terminal domain of apoE have been developed for therapeutic applications. These peptides stimulate cellular cholesterol efflux via the ATP-binding cassette transporter A1 (ABCA1) with high potency, like native apolipoproteins on a molar basis. This potent activity has been related to the unique ability of these peptides to maintain α-helix structure upon dilution. Recent structure-activity studies improving the safety features of these mimetic peptides have greatly improved their potential for clinical use. These studies have identified structural features of the class A α-helix motif that induce muscle toxicity and hypertriglyceridemia, which may have implications for the design of other HDL mimetic peptides.

SUMMARY

ABCA1 is an integral membrane protein that plays a central role in biology. Its principal function is to mediate the efflux of cholesterol and phospholipid from cells to extracellular apo, preventing a build-up of excess cholesterol in membranes. This process generates HDL particles that perform a variety of functions to protect against disease. A number of these functions can be viewed as directly or indirectly supporting ABCA1 activity, thus constituting a positive feedback system to optimize cellular lipid efflux responses and disease prevention. Consequently, therapeutic approaches that mimic the activities of apos may prove highly effective to combat disease. One such approach involves the use of peptides. The broad biological relevance of ABCA1 suggests these apo mimetic peptides may be useful for the treatment of a number of diseases, such as atherosclerosis, diabetes, and Alzheimer's disease.