Aromatic residue position on the nonpolar face of class a amphipathic helical peptides determines biological activity

The scientific adventures of Richard Epand

This essay summarizes the many areas of science that my career has contributed to. It attempts to highlight some of the innovative concepts that developed from this work. The discussion encompasses studies I undertook from graduate school to the present but it will not attempt to be comprehensive. I apologize to individuals whose work I omitted. Because of space I cannot acknowledge all the contributions from other individuals that made these achievements possible.

Systematic Design and Validation of Ion Channel Stabilization of Amphipathic α-Helical Peptides Incorporating Tryptophan Residues

Aromatic interactions such as π-π interaction and cation-π interaction are present in membrane proteins and play important roles in both structure and function. To systematically investigate the effect of aromatic residues on the structural stability and ion permeability of peptide-formed ion channels, we designed several peptides with one or two tryptophan (Trp) residues incorporated at different positions in amphipathic α-helical peptides. Circular dichroism (CD) studies revealed the preferable position of Trp residues for self-association in these designed peptides. Systematically designed di-substituted peptides with two Trps at each helix termini demonstrated intermolecular Trp-Trp interactions caused by aggregation. In the presence of liposomes, Trp on the hydrophilic face of the peptide enhanced interaction with the lipid membrane to increase the amphipathic α-helical contents. Appropriate incorporation and positioning of Trp enabled peptides to form more stable channels and had notable effects with Trp di-substituted peptides. The ion channel forming capability of a series of these peptides showed that the cation-π interactions between Trp and Lys residues in adjacent transmembrane helices contribute to remarkable stabilization of the channel structure.

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.

Artificial High Density Lipoprotein Nanoparticles in Cardiovascular Research

Lipoproteins are endogenous nanoparticles which are the major transporter of fats and cholesterol in the human body. They play a key role in the regulatory mechanisms of cardiovascular events. Lipoproteins can be modified and manipulated to act as drug delivery systems or nanocarriers for contrast agents. In particular, high density lipoproteins (HDL), which are the smallest class of lipoproteins, can be synthetically engineered either as nascent HDL nanodiscs or spherical HDL nanoparticles. Reconstituted HDL (rHDL) particles are formed by self-assembly of various lipids and apolipoprotein AI (apo-AI). A variety of substances including drugs, nucleic acids, signal emitting molecules, or dyes can be loaded, making them efficient nanocarriers for therapeutic applications or medical diagnostics. This review provides an overview about synthesis techniques, physicochemical properties of rHDL nanoparticles, and structural determinants for rHDL function. We discuss recent developments utilizing either apo-AI or apo-AI mimetic peptides for the design of pharmaceutical rHDL formulations. Advantages, limitations, challenges, and prospects for clinical translation are evaluated with a special focus on promising strategies for the treatment and diagnosis of atherosclerosis and cardiovascular diseases.

The apoA-I mimetic peptide 4F protects apolipoprotein A-I from oxidative damage

High density lipoprotein (HDL) is prone to modification by the oxidizing and chlorinating agent hypochlorite anion (OCl^-). Oxidation of apolipoprotein (apo) A-I, the major protein in HDL, reduces ABCA-1 mediated cholesterol efflux and other protective responses to HDL. The apoA-I mimetic peptide 4F has been shown to undergo oxidation; however, the ability of the peptide to mediate cholesterol efflux remains intact. Here, we show that 4F protects apoA-I from hypochlorite-mediated oxidation. Mass spectral analysis of apoA-I shows that tyrosine residues that are prone to hypochlorite-mediated chlorination are protected in the presence of 4F. Furthermore, 4F enhances the cholesterol efflux ability of apoA-I to a greater extent than either 4F or apoA-I alone, even after hypochlorite oxidation. These observations suggest that apoA-I in lipid complexes may be protected by the presence of 4F, resulting in the preservation of its anti-inflammatory and anti-atherogenic properties. These studies also form the basis for the future studies of nanoparticles possessing both apoA-I and 4F.

Peptide Amphiphile Nanostructures for Targeting of Atherosclerotic Plaque and Drug Delivery

Co-assembled peptide amphiphile nanofibers designed to target atherosclerotic plaque and enhance cholesterol efflux are shown to encapsulate and deliver a liver X receptor agonist to increase efflux from murine macrophages in vitro. Fluorescence microscopy reveals that the nanofibers, which display an apolipoprotein-mimetic peptide, localize at plaque sites in LDL receptor knockout mice with or without the encapsulated molecule, while nanofibers displaying a scrambled, non-targeting peptide sequence do not demonstrate comparable binding. These results show that nanofibers functionalized with apolipoprotein-mimetic peptides may be effective vehicles for intravascular targeted drug delivery to treat atherosclerosis.

Apolipoprotein A-I mimetic peptide reverses impaired arterial healing after injury by reducing oxidative stress

OBJECTIVE

Endothelial cell (EC) migration is essential for healing of arterial injuries caused by angioplasty, but a high cholesterol diet inhibits endothelial repair. In vivo studies suggest that apolipoprotein A-I (apoA-I), the major protein constituent of HDL, is essential for normal healing of arterial injuries. ApoA-I mimetics, including 4F, have been designed to mimic the amphipathic portion of the apoA-I molecule. This study was undertaken to determine if 4F improves endothelial migration and healing.

METHODS

A razor scrape assay was used to analyze the effect of 4F on EC migration in vitro. Endothelial healing in vivo was assessed following electrical injury of carotid arteries in mice. Markers of oxidative stress were also examined.

RESULTS

Lipid oxidation products inhibited EC migration in vitro, but preincubation with L-4F preserved EC migration. Endothelial healing of carotid arterial injuries in mice on a high cholesterol diet was delayed compared with mice on a chow diet with 27.8% vs. 48.2% healing, respectively, at 5 days. Administration of D-4F improved endothelial healing in mice on a high cholesterol diet to 43.4%. D-4F administration had no effect on lipid levels but decreased markers of oxidation. In vivo, there was a significant inverse correlation between endothelial healing and plasma markers of oxidative stress.

CONCLUSION

These studies suggested that an apoA-I mimetic can improve endothelial healing of arterial injuries by decreasing oxidative stress.

Apolipoprotein A-I mimetic peptide 4F blocks sphingomyelinase-induced LDL aggregation

Lipolytic modification of LDL particles by SMase generates LDL aggregates with a strong affinity for human arterial proteoglycans and may so enhance LDL retention in the arterial wall. Here, we evaluated the effects of apoA-I mimetic peptide 4F on structural and functional properties of the SMase-modified LDL particles. LDL particles with and without 4F were incubated with SMase, after which their aggregation, structure, and proteoglycan binding were analyzed. At a molar ratio of L-4F to apoB-100 of 2.5 to 20:1, 4F dose-dependently inhibited SMase-induced LDL aggregation. At a molar ratio of 20:1, SMase-induced aggregation was fully blocked. Binding of 4F to LDL particles inhibited SMase-induced hydrolysis of LDL by 10% and prevented SMase-induced LDL aggregation. In addition, the binding of the SMase-modified LDL particles to human aortic proteoglycans was dose-dependently inhibited by pretreating LDL with 4F. The 4F stabilized apoB-100 conformation and inhibited SMase-induced conformational changes of apoB-100. Molecular dynamic simulations showed that upon binding to protein-free LDL surface, 4F locally alters membrane order and fluidity and induces structural changes to the lipid layer. Collectively, 4F stabilizes LDL particles by preventing the SMase-induced conformational changes in apoB-100 and so blocks SMase-induced LDL aggregation and the resulting increase in LDL retention.

Comparison between the behavior of different hydrophobic peptides allowing membrane anchoring of proteins

Membrane binding of proteins such as short chain dehydrogenase reductases or tail-anchored proteins relies on their N- and/or C-terminal hydrophobic transmembrane segment. In this review, we propose guidelines to characterize such hydrophobic peptide segments using spectroscopic and biophysical measurements. The secondary structure content of the C-terminal peptides of retinol dehydrogenase 8, RGS9-1 anchor protein, lecithin retinol acyl transferase, and of the N-terminal peptide of retinol dehydrogenase 11 has been deduced by prediction tools from their primary sequence as well as by using infrared or circular dichroism analyses. Depending on the solvent and the solubilization method, significant structural differences were observed, often involving α-helices. The helical structure of these peptides was found to be consistent with their presumed membrane binding. Langmuir monolayers have been used as membrane models to study lipid-peptide interactions. The values of maximum insertion pressure obtained for all peptides using a monolayer of 1,2-dioleoyl-sn-glycero-3-phospho-ethanolamine (DOPE) are larger than the estimated lateral pressure of membranes, thus suggesting that they bind membranes. Polarization modulation infrared reflection absorption spectroscopy has been used to determine the structure and orientation of these peptides in the absence and in the presence of a DOPE monolayer. This lipid induced an increase or a decrease in the organization of the peptide secondary structure. Further measurements are necessary using other lipids to better understand the membrane interactions of these peptides.

Ac‑hE‑18A‑NH2, a novel dual‑domain apolipoprotein mimetic peptide, inhibits apoptosis in macrophages by promoting cholesterol efflux

A novel synthetic dual-domain apolipoprotein (apo)-mimetic peptide, Ac-hE-18A-NH2, has been proposed to possess several apo A-I- and apo E-mimetic properties. This study investigated the protective effect of this peptide on oxidized low-density lipoprotein (ox-LDL)-induced apoptosis in RAW264.7 cells. For this purpose, RAW264.7 cells were exposed to 50 µg/ml ox-LDL for 48 h, and then incubated with the peptide Ac-hE-18A-NH2 at various concentrations. Apoptosis was detected using annexin V-fluorescein isothiocyanate staining and flow cytometric analysis. The study revealed that the peptide Ac-hE-18A-NH2 (1, 10 and 50 µg/ml) inhibited ox-LDL-mediated apoptosis, and this was accompanied by an increased rate of intracellular cholesterol efflux, and decreased total cholesterol levels in the cells in a concentration-dependent manner. The peptide also decreased caspase-3 activity and increased B-cell lymphoma 2 protein (Bcl-2) expression in macrophages in a dose-dependent manner. Moreover, blockage of cholesterol efflux by brefeldin A decreased the protective effect of Ac-hE-18A-NH2 against ox-LDL induced apoptosis, while increasing the cholesterol efflux by β-cyclodextrin administration led to a marked decrease in the rate of apoptosis of the cells. These findings demonstrate that the apo-mimetic peptide Ac-hE-18A-NH2 exerts a protective effect against apoptosis by reducing the accumulation of cholesterol.

Properties of apolipoprotein E derived peptide modulate their lipid-binding capacity and influence their anti-inflammatory function

Apolipoprotein-derived peptides are promising candidates for the treatment of various inflammatory conditions. The beneficial effects of these peptides are based on multiple mechanisms; prominent among them being high-affinity binding to pro-inflammatory oxidized phospholipids (Ox-PLs) and facilitating their sequestration/metabolism/clearance in the body. This indicates that peptides which can bind exclusively to Ox-PLs without recognizing normal, non-oxidized phospholipids (non-Ox-PLs) will be more potent anti-inflammatory agent than that of the peptides that bind to both Ox-PLs and non-Ox-PLs. In order to develop such Ox-PL-specific peptides, the knowledge about the properties (molecular determinants) of peptides that govern their Ox-PL preference is a must. In this study we have synthesized eleven peptides corresponding to the conserved regions of human apolipoprotein E and compared their biochemical properties, lipid-binding specificities, and anti-inflammatory properties. Our results show that these peptides exhibit considerably different specificities towards non-Ox-PL and different species of Ox-PLs. Some of these peptides bind exclusively to the Ox-PLs and inhibit the pro-inflammatory function of Ox-PLs in human blood. Biochemical characterization revealed that the peptides possess substantially different properties. Our results suggest that physicochemical properties of peptides play an important role in their lipid-binding specificity.

Systemic inflammation, intestine, and paraoxonase-1

Serum paraoxonase 1 (PON1) has been shown to act as an important guardian against cellular damage from oxidized lipids in low-density lipoprotein (LDL), plasma membrane, against toxic agents such as pesticide residues including organophosphates and against bacterial endotoxin. PON1 associated with circulating high-density lipoprotein (HDL) has the ability to prevent the generation of pro inflammatory oxidized phospholipids by reactive oxygen species. The activities of the HDL-associated PON1 and several other anti-inflammatory factors in HDL are in turn negatively regulated by these oxidized lipids. In rabbits, mice, and humans there appears to be an increase in the formation of these oxidized lipids during the acute phase response. This results in the association of acute phase proteins with HDL and inhibition of the HDL-associated PON1 that renders HDL pro inflammatory.In populations, low serum HDL-cholesterol is a risk factor for atherosclerosis and efforts are directed toward therapies to improve the quality and the relative concentrations of LDL and HDL. Apolipoprotein A-I (apoA-I) has been shown to reduce atherosclerotic lesions in laboratory animals. ApoA-I, however, is a large protein that is costly and needs to be administered parenterally. Our group has developed apoA-I mimetic peptides that are much smaller than apoA-I (18 amino acids long vs 243 in ApoA-I itself). These HDL mimetic peptides are much more effective in removing the oxidized phospholipids and other oxidized lipids. They improve LDL and HDL composition and function and reduce lesion formation in animal models of atherogenesis. Following is a brief description of some of the HDL mimetic peptides that can improve HDL and the effect of the peptide on PON1 activity.

Molecules that mimic apolipoprotein A-I: potential agents for treating atherosclerosis

Certain amphipathic α-helical peptides can functionally mimic many of the properties of full-length apolipoproteins, thereby offering an approach to modulate high-density lipoprotein (HDL) for combating atherosclerosis. In this Perspective, we summarize the key findings and advances over the past 25 years in the development of peptides that mimic apolipoproteins, especially apolipoprotein A-I (apoA-I). This assemblage of information provides a reasonably clear picture of the state of the art in the apolipoprotein mimetic field, an appreciation of the potential for such agents in pharmacotherapy, and a sense of the opportunities for optimizing the functional properties of HDL.

FAMP, a novel apoA-I mimetic peptide, suppresses aortic plaque formation through promotion of biological HDL function in ApoE-deficient mice

Background

Apolipoprotein (apo) A‐I is a major high‐density lipoprotein (HDL) protein that causes cholesterol efflux from peripheral cells through the ATP‐binding cassette transporter A1 (ABCA1), thus generating HDL and reversing the macrophage foam cell phenotype. Pre‐β₁ HDL is the smallest subfraction of HDL, which is believed to represent newly formed HDL, and it is the most active acceptor of free cholesterol. Furthermore it has a possible protective function against cardiovascular disease (CVD). We developed a novel apoA‐I mimetic peptide without phospholipids (Fukuoka University ApoA‐I Mimetic Peptide, FAMP).

Methods and Results

FAMP type 5 (FAMP5) had a high capacity for cholesterol efflux from A172 cells and mouse and human macrophages in vitro, and the efflux was mainly dependent on ABCA1 transporter. Incubation of FAMP5 with human HDL or whole plasma generated small HDL particles, and charged apoA‐I‐rich particles migrated as pre‐β HDL on agarose gel electrophoresis. Sixteen weeks of treatment with FAMP5 significantly suppressed aortic plaque formation (scrambled FAMP, 31.3±8.9% versus high‐dose FAMP5, 16.2±5.0%; P<0.01) and plasma C‐reactive protein and monocyte chemoattractant protein‐1 in apoE‐deficient mice fed a high‐fat diet. In addition, it significantly enhanced HDL‐mediated cholesterol efflux capacity from the mice.

Conclusions

A newly developed apoA‐I mimetic peptide, FAMP, has an antiatherosclerotic effect through the enhancement of the biological function of HDL. FAMP may have significant atheroprotective potential and prove to be a new therapeutic tool for CVD.

Peptide Mimetics of Apolipoproteins Improve HDL Function

Over the past decade evidence has accumulated that suggests that the anti-inflammatory properties of HDL may be at least as important as the levels of HDL-cholesterol. The recent failure of the torcetrapib clinical trails has highlighted the potential differences between HDL-cholesterol levels and HDL function. Agents to improve HDL function including HDL anti-inflammatory properties provide a new therapeutic strategy for ameliorating atherosclerosis and other chronic inflammatory conditions related to dyslipidemia. Seeking guidance from the structure of the apolipoproteins of the plasma lipoproteins has allowed the creation of a series of polypeptides that have interesting functionality with therapeutic implications. In animal models of atherosclerosis, peptide mimetics of apolipoproteins have been shown to improve the anti-inflammatory properties of HDL, significantly reduce lesions and improve vascular inflammation and function without necessarily altering HDL-cholesterol levels. Some of these are now entering the clinical arena as interventions in pharmacologic and pharmacodynamic studies.

The effect of HDL mimetic peptide 4F on PON1

Several lines of evidence indicate that serum paraoxonase 1 (PON1) acts as an important guardian against cellular damage from oxidized lipids in plasma membrane, in low-density lipoprotein (LDL), against bacterial endotoxin and against toxic agents such as pesticide residues including organophosphates. In circulation, the high-density lipoprotein (HDL)-associated PON1 has the ability to prevent the formation of proinflammatory oxidized phospholipids. These oxidized phospholipids negatively regulate the activities of the HDL-associated PON1 and several other anti-inflammatory factors in HDL. During the acute phase response in rabbits, mice, and humans, there appears to be an increase in the formation of these oxidized lipids that results in the inhibition of the HDL-associated PON1 and an association of acute phase proteins with HDL that renders HDL proinflammatory. Low serum HDL is a risk factor for atherosclerosis and attempts are directed toward therapies to improve the quality and the relative concentrations of LDL and HDL. Apolipoprotein A-I (apoA-I) has been shown to reduce atherosclerotic lesions in laboratory animals. ApoA-I, however, is a large protein and needs to be administered parenterally, and it is costly. We have developed apoA-I mimetic peptides that are much smaller than apoA-I, and much more effective in removing the oxidized phospholipids and other oxidized lipids. These mimetic peptides improve LDL and HDL composition and function and reduce lesion formation in animal models of atherogenesis. Following is a brief description of some of the HDL mimetic peptides that can improve HDL and the effect of the peptide on PON1 activity.

Influence of C-terminal α-helix hydrophobicity and aromatic amino acid content on apolipoprotein A-I functionality

The apoA-I molecule adopts a two-domain tertiary structure and the properties of these domains modulate the ability to form HDL particles. Thus, human apoA-I differs from mouse apoA-I in that it can form smaller HDL particles; the C-terminal α-helix is important in this process and human apoA-I is unusual in containing aromatic amino acids in the non-polar face of this amphipathic α-helix. To understand the influence of these aromatic amino acids and the associated high hydrophobicity, apoA-I variants were engineered in which aliphatic amino acids were substituted with or without causing a decrease in overall hydrophobicity. The variants human apoA-I (F225L/F229A/Y236A) and apoA-I (F225L/F229L/A232L/Y236L) were compared to wild-type (WT) apoA-I for their abilities to (1) solubilize phospholipid vesicles and form HDL particles of different sizes, and (2) mediate cellular cholesterol efflux and create nascent HDL particles via ABCA1. The loss of aromatic residues and concomitant decrease in hydrophobicity in apoA-I (F225L/F229A/Y236A) has no effect on protein stability, but reduces by a factor of about three the catalytic efficiencies (V(max)/K(m)) of vesicle solubilization and cholesterol efflux; also, relatively large HDL particles are formed. With apoA-I (F225L/F229L/A232L/Y236L) where the hydrophobicity is restored by the presence of only leucine residues in the helix non-polar face, the catalytic efficiencies of vesicle solubilization and cholesterol efflux are similar to those of WT apoA-I; this variant forms smaller HDL particles. Overall, the results show that the hydrophobicity of the non-polar face of the C-terminal amphipathic α-helix plays a critical role in determining apoA-I functionality but aromatic amino acids are not required. This article is part of a Special Issue entitled Advances in High Density Lipoprotein Formation and Metabolism: A Tribute to John F. Oram (1945-2010).

Apolipoprotein A-I and A-I mimetic peptides: a role in atherosclerosis

Cardiovascular disease remains a major cause of morbidity and mortality in the westernized world. Atherosclerosis is the underlying cause of most cardiovascular diseases. Atherosclerosis is a slowly evolving chronic inflammatory disorder involving the intima of large and medium sized arteries that is initiated in response to high plasma lipid levels, especially LDL. Cells of both the innate and adaptive immunity are involved in this chronic inflammation. Although high plasma LDL levels are a major contributor to most stages of the evolution of atherosclerosis, HDL and its major protein apoA-I possess properties that attenuate and may even reverse atherosclerosis. Two major functions are the ability to induce the efflux of cholesterol from cells, particularly lipid-loaded macrophages, in the artery wall for transfer to the liver, a process referred to as reverse cholesterol transport, and the ability to attenuate the pro-inflammatory properties of LDL. The removal of cellular cholesterol from lipid-loaded macrophages may also be anti-inflammatory. One of the most promising therapies to enhance the anti-atherogenic, anti-inflammatory properties of HDL is apoA-I mimetic peptides. Several of these peptides have been shown to promote cellular cholesterol efflux, attenuate the production of pro-inflammatory cytokines by macrophages, and to attenuate the pro-inflammatory properties of LDL. This latter effect may be related to their high affinity for oxidized lipids present in LDL. This review discusses the functional properties of the peptides and their effect on experimental atherosclerosis and the results of initial clinical studies in humans.

HDL mimetic peptide ATI-5261 forms an oligomeric assembly in solution that dissociates to monomers upon dilution

ATI-5261 is a 26-mer peptide that stimulates cellular cholesterol efflux with high potency. This peptide displays high aqueous solubility, despite having amphipathic α-helix structure and a broad nonpolar surface. These features suggested to us that ATI-5261 may adopt a specific form in solution, having favorable structural characteristics and dynamics. To test this, we subjected ATI-5261 to a series of biophysical studies and correlated self-association with secondary structure and activity. Gel-filtration chromatography and native gel electrophoresis indicated ATI-5261 adopted a discrete self-associated form of low molecular weight at concentrations >1 mg/mL. Formation of a discrete molecular species was verified by small-angle X-ray scattering (SAXS), which further revealed the peptide formed a tetrameric assembly having an elongated shape and hollow central core. This assembly dissociated to individual peptide strands upon dilution to concentrations required for promoting high-affinity cholesterol efflux from cells. Moreover, the α-helical content of ATI-5261 was exceptionally high (74.1 ± 6.8%) regardless of physical form and concentration. Collectively, these results indicate ATI-5261 displays oligomeric behavior generally similar to native apolipoproteins and dissociates to monomers of high α-helical content upon dilution. Optimizing self-association behavior and secondary structure may prove useful for improving the translatability and efficacy of apolipoprotein mimetic peptides.

Synthesis and evaluation of a tri-tyrosine decorated dextran MR contrast agent for vulnerable plaque detection

This communication reports the synthesis, characterization and in vivo evaluation in mice of a new tri-tyrosine conjugated MR contrast agent, which may help to identify vulnerable plaques in atherosclerosis by targeting the lipid core.

HDL apolipoprotein-related peptides in the treatment of atherosclerosis and other inflammatory disorders

Elevations of HDL levels or modifying the inflammatory properties of HDL are being evaluated as possible treatment of atherosclerosis, the underlying mechanism responsible for most cardiovascular diseases. A promising approach is the use of small HDL apoprotein-related mimetic peptides. A number of peptides mimicking the repeating amphipathic α-helical structure in apoA-I, the major apoprotein in HDL, have been examined in vitro and in animal models. Several peptides have been shown to reduce early atherosclerotic lesions, but not more mature lesions unless coadministered with statins. These peptides also influence the vascular biology of the vessel wall and protect against other acute and chronic inflammatory diseases. The biologically active peptides are capable of reducing the pro-inflammatory properties of LDL and HDL, likely due to their high affinity for oxidized lipids. They are also capable of influencing other processes, including ABCA1 mediated activation of JAK-2 in macrophages, which may contribute to their anti-atherogenic function. The initial studies involved monomeric 18 amino acid peptides, but tandem peptides are being investigated for their anti-atherogenic and anti-inflammatory properties as they more closely resemble the repeating structure of apoA-I. Peptides based on other HDL associated proteins such as apoE, apoJ and SAA have also been studied. Their mechanism of action appears to be distinct from the apoA-I based mimetics.

D-4F, an apoA-1 mimetic, decreases airway hyperresponsiveness, inflammation, and oxidative stress in a murine model of asthma

Asthma is characterized by oxidative stress and inflammation of the airways. Although proinflammatory lipids are involved in asthma, therapies targeting them remain lacking. Ac-DWFKAFYDKVAEKFKEAFNH(2) (4F) is an apolipoprotein (apo)A-I mimetic that has been shown to preferentially bind oxidized lipids and improve HDL function. The objective of the present study was to determine the effects of 4F on oxidative stress, inflammation, and airway resistance in an established murine model of asthma. We show here that ovalbumin (OVA)-sensitization increased airway hyperresponsiveness, eosinophil recruitment, and collagen deposition in lungs of C57BL/6J mice by a mechanism that could be reduced by 4F. OVA sensitization induced marked increases in transforming growth factor (TGF)β-1, fibroblast specific protein (FSP)-1, anti-T15 autoantibody staining, and modest increases in 4-hydroxynonenal (4-HNE) Michael's adducts in lungs of OVA-sensitized mice. 4F decreased TGFβ-1, FSP-1, anti-T15 autoantibody, and 4-HNE adducts in the lungs of the OVA-sensitized mice. Eosinophil peroxidase (EPO) activity in bronchial alveolar lavage fluid (BALF), peripheral eosinophil counts, total IgE, and proinflammatory HDL (p-HDL) were all increased in OVA-sensitized mice. 4F decreased BALF EPO activity, eosinophil counts, total IgE, and p-HDL in these mice. These data indicate that 4F reduces pulmonary inflammation and airway resistance in an experimental murine model of asthma by decreasing oxidative stress.

Two adjacent domains (141-150 and 151-160) of apoE covalently linked to a class A amphipathic helical peptide exhibit opposite atherogenic effects

OBJECTIVE

We recently described anti-atherogenic properties of the dual domain peptide Ac-hE18A-NH(2) derived by covalently linking the heparin binding domain 141-150 of apoE to 18A, a class A amphipathic helical peptide. In this paper we have compared the properties of Ac-hE18A-NH(2) with the non-heparin binding 151-160 region of apoE linked to 18A (Ac-nhE18A-NH(2)).

METHODS AND RESULTS

Both peptides were highly helical in solution and in association with lipids. Ac-hE18A-NH(2) and not Ac-nhE18A-NH(2) enhanced uptake of low density lipoprotein (LDL) in HepG2 cells. While Ac-hE18A-NH(2) retarded the electrophoretic mobility of LDL, Ac-nhE18A-NH(2) slightly enhanced mobility. Ac-hE18A-NH(2) reduced monocyte association with endothelial cells, while Ac-nhE18A-NH(2) increased it. Ac-hE18A-NH(2) also reduced lipid hydroperoxide content of LDL while Ac-nhE18A-NH(2) increased it. A single administration of Ac-hE18A-NH(2) (100 μg/mouse) into apoE null mice dramatically reduced cholesterol (from 600 mg/dL to 180 mg/dL at 5 min and to 60 mg/dL at 5h) while Ac-nhE18A-NH(2) had no effect. Administration (100 μg/mouse/day, three days a week) into apoE null mice for six weeks showed Ac-hE18A-NH(2) group having a moderate aortic sinus lesion reduction compared with the control group (-15.1%), while the Ac-nhE18A-NH(2) administered group had increased lesion area (+33.0% vs controls and 36.1% vs Ac-hE18A-NH(2)). Plasma from mice administered Ac-hE18A-NH(2) for six weeks showed a significant reduction in plasma cholesterol and triglyceride levels and increase in paraoxonase-1 (PON-1) activity compared to controls, while Ac-nhE18A-NH(2) caused no change in plasma cholesterol and decreased PON-1 activity.

CONCLUSION

It is proposed that Ac-hE18A-NH(2) reduced lesion progression in apoE null mice due to its anti-inflammatory and lipoprotein clearing properties, while Ac-nhE18A-NH(2) exhibited pro-atherogenic effects.

Oral administration of L-mR18L, a single domain cationic amphipathic helical peptide, inhibits lesion formation in ApoE null mice

We have shown that Ac-hE18A-NH₂, a dual-domain cationic apolipoprotein-mimetic peptide, reduces plasma cholesterol levels in dyslipidemic mice. Two single-domain cationic peptides based on the lytic class L peptide 18L were developed to test the hypothesis that a single-domain cationic amphipathic peptide can reduce atherosclerosis in apolipoprotein (apo)E null mice when orally administered. To incorporate anti-inflammatory properties, aromatic residues were clustered in the nonpolar face similar to peptide 4F, resulting in modified 18L (m18L). To reduce lytic properties, the Lys residues of 18L were replaced with Arg with the resulting peptide called modified R18L (mR18L). Biophysical studies showed that mR18L had stronger interactions with lipids than did m18L. Peptide mR18L was also more effective than m18L in promoting LDL uptake by HepG2 cells. ApoE null mice received normal chow or chow containing m18L or mR18L for six weeks. A significant reduction in plasma cholesterol and aortic sinus lesion area was seen only in the mR18L group. Plasma from mice administered mR18L, unlike those from the control and m18L groups, did not enhance monocyte adhesion to endothelial cells. Thus oral administration of mR18L reduces plasma cholesterol and lesion formation and inhibits monocyte adhesion.

High density lipoprotein-anionic peptide factor effect on reverse cholesterol transport in type 2 diabetic patients with and without coronary artery disease

OBJECTIVES

To verify if HDL3 Anionic Peptide Factor (HDL3-APF) is as an apolipoprotein that promotes the reverse cholesterol transport.

DESIGN AND METHODS

We investigated a possible association between plasma HDL3-APF concentration, cholesterol efflux from Fu5AH cells and cholesteryl ester transfer protein (CETP) activity in type 2 diabetic patients with coronary artery disease (CAD) (n=36), those without CAD (n=20), and 37 healthy subjects.

RESULTS

Plasma APF concentrations were decreased in diabetics with CAD compared to controls (p<0.01). Cellular cholesterol efflux was decreased in diabetics without and with CAD, (p<0.01 and p<0.001 respectively). CETP activity was significantly elevated in all patient groups. Multiple linear regression analysis shows that cholesterol efflux was independently and positively related only to APF concentrations in controls.

CONCLUSIONS

APF is likely to be a key independent factor for promoting cellular cholesterol efflux in healthy subjects. However this association is altered in type 2 diabetes.

Oxpholipin 11D: an anti-inflammatory peptide that binds cholesterol and oxidized phospholipids

Background

Many Gram-positive bacteria produce pore-forming exotoxins that contain a highly conserved, 12-residue domain (ECTGLAWEWWRT) that binds cholesterol. This domain is usually flanked N-terminally by arginine and C-terminally by valine. We used this 14-residue sequence as a template to create a small library of peptides that bind cholesterol and other lipids.

Methodology/Results

Several of these peptides manifested anti-inflammatory properties in a predictive in vitro monocyte chemotactic assay, and some also diminished the pro-inflammatory effects of low-density lipoprotein in apoE-deficient mice. The most potent analog, Oxpholipin-11D (OxP-11D), contained D-amino acids exclusively and was identical to the 14-residue design template except that diphenylalanine replaced cysteine-3. In surface plasmon resonance binding studies, OxP-11D bound oxidized (phospho)lipids and sterols in much the same manner as D-4F, a widely studied cardioprotective apoA-I-mimetic peptide with anti-inflammatory properties. In contrast to D-4F, which adopts a stable α-helical structure in solution, the OxP-11D structure was flexible and contained multiple turn-like features.

Conclusion

Given the substantial evidence that oxidized phospholipids are pro-inflammatory in vivo, OxP-11D and other Oxpholipins may have therapeutic potential.

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

Here, we report the creation of a single-helix peptide (ATI-5261) that stimulates cellular cholesterol efflux with K(m) molar efficiency approximating native apolipoproteins. Anti-atherosclerosis activity of ATI-5261 was evaluated in LDLR(-/-) and apolipoprotein (apo)E(-/-) mice approximately 5-7 months of age, following 13-18 weeks on a high-fat Western diet (HFWD). Treatment of fat-fed LDLR(-/-) mice with daily intraperitoneal injections of ATI-5261 (30 mg/kg) for 6 weeks reduced atherosclerosis by 30%, as judged by lesion area covering the aorta (7.9 +/- 2 vs.11.3 +/- 2.5% control, P = 0.011) and lipid-content of aortic sinus plaque (25 +/- 5.8 vs. 33 +/- 4.9% control, P = 0.014). In apoE(-/-) mice, the peptide administered 30 mg/kg ip on alternate days for 6 weeks reduced atherosclerosis by approximately 45% (lesion area = 15 +/- 7 vs. 25 +/- 8% control, P = 0.00016; plaque lipid-content = 20 +/- 6 vs. 32 +/- 8% control, P < 0.0001). Similar reductions in atherosclerosis were achieved using ATI-5261:POPC complexes. Single intraperitoneal injection of ATI-5261 increased reverse cholesterol transport from macrophage foam-cells to feces over 24-48 h. In summary, relatively short-term treatment of mice with the potent cholesterol efflux peptide ATI-5261 reduced substantial atherosclerosis. This was achieved using an L-amino acid peptide, in the presence of severe hypercholesterolemia/HFWD, and did not require daily injections or formulation with phospholipids when administered via intraperitoneal injection.

Tyrosine polyethylene glycol (PEG)-micelle magnetic resonance contrast agent for the detection of lipid rich areas in atherosclerotic plaque

Vulnerable or high-risk atherosclerotic plaques often exhibit large lipid cores and thin fibrous caps that can lead to deadly vascular events when they rupture. In this study, polyethylene glycol (PEG)-micelles that incorporate a gadolinium diethylenetriamine pentaacetic acid (Gd-DTPA) amphiphile were used as an MR contrast agent. In an approach inspired by lipoproteins, the micelles were functionalized with tyrosine residues, an aromatic, lipophilic amino acid, to reach the lipid-rich areas of atherosclerotic plaque in a highly efficient manner. These micelles were applied to apolipoprotein E(-/-) (ApoE(-/-)) mice as a model of atherosclerosis. The abdominal aortas of the animals were imaged using T(1)-weighted (T(1)W) high-resolution MRI at 9.4T before and up to 48 h after the administration of the micelles. PEG-micelles modified with 15% tyrosine residues yielded a significant enhancement of the abdominal aortic wall at 6 and 24 h postinjection (pi) as compared to unmodified micelles. Fluorescence microscopy on histological sections of the abdominal aorta showed a correlation between lipid-rich areas and the distribution of the functionalized contrast agent in plaque. Using a simple approach, we demonstrated that lipid-rich areas in atherosclerotic plaque of ApoE(-/-) mice can be detected by MRI using Gd-DTPA micelles.

Apolipoproteins A-I, A-II and E are independently distributed among intracellular and newly secreted HDL of human hepatoma cells

Whereas hepatocytes secrete the major human plasma high density lipoproteins (HDL)-protein, apo A-I, as lipid-free and lipidated species, the biogenic itineraries of apo A-II and apo E are unknown. Human plasma and HepG2 cell-derived apo A-II and apo E occur as monomers, homodimers and heterodimers. Dimerization of apo A-II, which is more lipophilic than apo A-I, is catalyzed by lipid surfaces. Thus, we hypothesized that lipidation of intracellular and secreted apo A-II exceeds that of apo A-I, and once lipidated, apo A-II dimerizes. Fractionation of HepG2 cell lysate and media by size exclusion chromatography showed that intracellular apo A-II and apo E are fully lipidated and occur on nascent HDL and VLDL respectively, while only 45% of intracellular apo A-I is lipidated. Secreted apo A-II and apo E occur on small HDL and on LDL and large HDL respectively. HDL particles containing both apo A-II and apo A-I form only after secretion from both HepG2 and Huh7 hepatoma cells. Apo A-II dimerizes intracellularly while intracellular apo E is monomeric but after secretion associates with HDL and subsequently dimerizes. Thus, HDL apolipoproteins A-I, A-II and E have distinct intracellular and post-secretory pathways of hepatic lipidation and dimerization in the process of HDL formation. These early forms of HDL are expected to follow different apolipoprotein-specific pathways through plasma remodeling and reverse cholesterol transport.

Structure and function of HDL mimetics

HDL mimetics have been constructed from a number of peptides and proteins with varying structures, all of which bind lipids found in HDL. HDL mimetics containing a peptide or protein have been constructed with as few as 4 and as many as 243 amino acid residues. Some HDL mimetics have been constructed with lipid but without a peptide or protein component. Some HDL mimetics promote cholesterol efflux, some have been shown to have a remarkable ability to bind oxidized lipids compared to human apolipoprotein A-I (apoA-I). Many of these peptides have been shown to have antiinflammatory properties. Based on studies in a number of animal models and in early human clinical trials, HDL mimetics appear to have promise as diagnostic and therapeutic agents.

Anti-inflammatory peptides grab on to the whiskers of atherogenic oxidized lipids

The peptide 4F is known to have potent anti-atherogenic activity. 4F is an 18 residue peptide that has a sequence capable of forming a class A amphipathic helix. Several other class A amphipathic helical, 18 residue peptides with the same polar face but with increasing Phe residues on the nonpolar face have been synthesized with varying degrees of biological activity. In this work we compared the properties of the original 2F peptide, modeled on the consensus sequence of the amphipathic helical segments of the apolipoprotein A-I with the peptide 4F that has two Leu residues replaced with Phe. We demonstrate that the more biologically active 4F peptide has the greatest affinity for binding to several molecular species of oxidized lipids. Lipoprotein particles can be formed by solubilizing 1-palmitoyl-2-oleoyl phosphatidylcholine (POPC) with peptides. These solubilized lipoprotein particles extract oxidized lipid from liposomes of POPC containing 5 mol% of oxidized lipid. The peptides with the strongest anti-atherogenic activity interact most strongly with the oxidized lipid. The results show that there is a correlation between the biological potency of these peptides and their ability to interact with certain specific cytotoxic lipids, suggesting that this interaction may contribute favourably to their biological properties.

Apoprotein A-I mimetic peptides and their potential anti-atherogenic mechanisms of action

PURPOSE OF REVIEW

Peptides that resemble in physicochemical properties the helices of apoprotein A-I, the major protein of atheroprotective HDL, show promise for the treatment of atherosclerosis-related vascular disease. The properties and promise of these so-called mimetic peptides will be explored in this review.

RECENT FINDINGS

Both HDL and mimetic peptides are able to scavenge and sequester oxidized lipids and hence protect endothelial cells and arteries from the pro-inflammatory action of oxidized LDL. Active mimetic peptides have an amphipathic alpha-helical secondary structure, whose hydrophobic face is particularly important for its bioactivity. The most frequently employed peptide is 4F. The comparative bioactivity of variants of 4F, particularly tandem helical peptides, has been explored. The recent observation of the very high affinity of bioactive peptides for oxidized fatty acids and phospholipids provides a likely mechanism for the action of these peptides in inhibiting early atherosclerosis formation. It is not clear that these peptides alone are effective in reversing established atherosclerosis, although they may achieve this outcome in synergy with statin therapy.

SUMMARY

Recent observations of mimetic peptides have pointed to promising therapies for patients with cardiovascular disease. The peptides appear to be well tolerated and effective in promoting the anti-inflammatory properties of HDL.

Oral apolipoprotein A-I mimetic peptide improves cognitive function and reduces amyloid burden in a mouse model of Alzheimer's disease

Recent evidence indicates that inflammation may significantly contribute to the pathogenesis of Alzheimer's disease (AD). Since the apo A-I mimetic peptide D-4F has been shown to inhibit atherosclerotic lesion formation and regress already existing lesions (in the presence of pravastatin) and the peptide also decreases brain arteriole inflammation, we undertook a study to evaluate the efficacy of oral D-4F co-administered with pravastatin on cognitive function and amyloid beta (A beta) burden in the hippocampus of APPSwe-PS1 Delta E9 mice. Three groups of male mice were administered D-4F and pravastatin, Scrambled D-4F (ScD-4F, a control peptide) and pravastatin in drinking water, while drinking water alone served as control. The escape latency in the Morris Water Maze test was significantly shorter for the D-4F+statin administered animals compared to the other two groups. While the hippocampal region of the brain was covered with 4.2+/-0.5 and 3.8+/-0.6% of A beta load in the control and ScD-4F+statin administered groups, in the D-4F+statin administered group A beta load was only 1.6+/-0.1%. Furthermore, there was a significant decrease in the number of activated microglia (p<0.05 vs the other two groups) and activated astrocytes (p<0.05 vs control) upon oral D-4F+statin treatment. Inflammatory markers TNFalpha and IL-1 beta levels were decreased significantly in the D-4F+statin group compared to the other two groups (for IL-1 beta p<0.01 vs the other two groups and for TNF-alpha p<0.001 vs control) and the expression of MCP-1 were also less in D-4F+statin administered group compared to the other two groups. These results suggest that the apo A-I mimetic peptide inhibits amyloid beta deposition and improves cognitive function via exerting anti-inflammatory properties in the brain.

The role of dysfunctional HDL in atherosclerosis

This review focuses on HDL function in modulating LDL oxidation and LDL-induced inflammation. Dysfunctional HDL has been identified in animal models and humans with chronic inflammatory diseases including atherosclerosis. The loss of antiinflammatory function correlated with a loss of function in reverse cholesterol transport. In animal models and perhaps in humans, dysfunctional HDL can be improved by apoA-I mimetic peptides that bind oxidized lipids with high affinity.

Effect of leucine to phenylalanine substitution on the nonpolar face of a class A amphipathic helical peptide on its interaction with lipid: high resolution solution NMR studies of 4F-dimyristoylphosphatidylcholine discoidal complex

Model class A amphipathic helical peptides mimic several properties of apolipoprotein A-I (apoA-I), the major protein component of high density lipoproteins. Previously, we reported the NMR structures of Ac-18A-NH(2) (renamed as 2F because of two phenylalanines), the base-line model class A amphipathic helical peptide in the presence of lipid ( Mishra, V. K., Anantharamaiah, G. M., Segrest, J. P., Palgunachari, M. N., Chaddha, M., Simon Sham, S. W., and Krishna, N. R. (2006) J Biol. Chem. 281, 6511-6519 ). Substitution of two Leu residues on the nonpolar face (Leu(3) and Leu(14)) with Phe residues produced the peptide 4F (so named because of four phenylalanines), which has been extensively studied for its anti-inflammatory and antiatherogenic properties. Like 2F, 4F also forms discoidal nascent high density lipoprotein-like particles with 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC). Since subtle structural changes in the peptide-lipid complexes have been shown to be responsible for their antiatherogenic properties, we undertook high resolution NMR studies to deduce detailed structure of 4F in 4F.DMPC discs. Like 2F, 4F adopts a well defined amphipathic alpha-helical structure in association with the lipid at a 1:1 peptide/lipid weight ratio. Nuclear Overhauser effect (NOE) spectroscopy revealed a number of intermolecular close contacts between the aromatic residues in the hydrophobic face of the helix and the lipid acyl chain protons. Similar to 2F, the pattern of observed peptide-lipid NOEs is consistent with a parallel orientation of the amphipathic alpha helix, with respect to the plane of the lipid bilayer, on the edge of the disc (the belt model). However, in contrast to 2F in 2F.DMPC, 4F in the 4F.DMPC complex is located closer to the lipid headgroup as evidenced by a number of NOEs between 4F and DMPC headgroup protons. These NOEs are absent in the 2F.DMPC complex. In addition, the conformation of the DMPC sn-3 chain in 4F.DMPC complex is different than in the 2F.DMPC complex as evidenced by the NOE between lipid 2.CH and betaCH(2) protons in 4F.DMPC, but not in 2F.DMPC, complex. Based on the results of this study, we infer that the antiatherogenic properties of 4F may result from its preferential interaction with lipid headgroups.

Asymmetry in the lipid affinity of bihelical amphipathic peptides. A structural determinant for the specificity of ABCA1-dependent cholesterol efflux by peptides

ApoA-I contains a tandem array of amphipathic helices with varying lipid affinity, which are critical in its ability to bind and remove lipids from cells by the ABCA1 transporter. In this study, the effect of asymmetry in the lipid affinity of amphipathic helices in a bihelical apoA-I mimetic peptide, 37pA, on lipid efflux by the ABCA1 transporter was examined. Seven peptide variants of 37pA were produced by substituting a varying number of hydrophobic amino acids for alanine on either one or both helices. The 5A peptide with five alanine substitutions in the second helix had decreased helical content compared with 37pA (5A, 12+/-1% helicity; 37pA, 28+/-2% helicity) and showed less self-association but, similar to the parent peptide, was able to readily solubilize phospholipid vesicles. Furthermore, 5A, unlike the parent peptide 37pA, was not hemolytic (37pA, 27+/-2% RBC lysis, 2 h, 18 microm). Finally, the 5A peptide stimulated cholesterol and phospholipid efflux by the ABCA1 transporter with higher specificity (ABCA1-transfected versus untransfected cells) than 37pA (5A, 9.7+/-0.77%, 18 h, 18 microm versus 1.5+/-0.27%, 18 h, 18 microm (p<0.0001); 37pA, 7.4+/-0.85%, 18 h, 18 microm versus 5.8+/-0.20%, 18 h, 18 microm (p=0.03)). In summary, we describe a novel bihelical peptide with asymmetry in the lipid affinity of its helices and properties similar to apoA-I in terms of specificity for cholesterol efflux by the ABCA1 transporter and low cytotoxicity.

Inflammatory lipids as a target for therapy in the rheumatic diseases

As patients with autoimmune rheumatic diseases live longer due to improved therapies and preventive measures, death and disability from cardiovascular events are increasing. Patients with rheumatoid arthritis and systemic lupus erythematosus have an increased risk of atherosclerosis that persists even after accounting for traditional cardiac risk factors. Recent studies strongly suggest that the mechanism is due in part to increased levels of oxidized lipids (such as oxidized low density lipoprotein and pro-inflammatory high density lipoproteins) which cause the inflammatory cascade that ultimately leads to plaque formation. The objective of this review is to discuss how inflammatory lipids contribute to the increased risk of atherosclerosis in rheumatoid arthritis and systemic lupus erythematosus, as well as to propose that these oxidized lipids are a rational target for therapeutic intervention in autoimmune diseases. Published literature was examined to review treatments for pro-inflammatory lipids in autoimmune diseases such as rheumatoid arthritis and systemic lupus erythematosus. In conclusion, it is possible that these oxidized lipids may also contribute to increased disease manifestations in rheumatic conditions. Several new and existing therapies, including statins and high density lipoprotein-associated protein peptide mimetics such as D-4F (apoA-1) target these oxidized lipids and may be useful in both preventing atherosclerosis and treating inflammation in patients with rheumatic diseases.

Anti-inflammatory apoA-I-mimetic peptides bind oxidized lipids with much higher affinity than human apoA-I

4F is an anti-inflammatory, apolipoprotein A-I (apoA-I)-mimetic peptide that is active in vivo at nanomolar concentrations in the presence of a large molar excess of apoA-I. Physiologic concentrations ( approximately 35 microM) of human apoA-I did not inhibit the production of LDL-induced monocyte chemotactic activity by human aortic endothelial cell cultures, but adding nanomolar concentrations of 4F in the presence of approximately 35 microM apoA-I significantly reduced this inflammatory response. We analyzed lipid binding by surface plasmon resonance. The anti-inflammatory 4F peptide bound oxidized lipids with much higher affinity than did apoA-I. Initially, we examined the binding of PAPC (1-palmitoyl-2-arachidonoyl-sn-glycero-3-phosphatidylcholine) and observed that its oxidized products bound 4F with an affinity that was approximately 4-6 orders of magnitude higher than that of apoA-I. This high binding affinity was confirmed in studies with defined lipids and phospholipids. 3F-2 and 3F(14) are also amphipathic alpha-helical octadecapeptides, but 3F-2 inhibits atherosclerosis in mice and 3F(14) does not. Like 4F, 3F-2 also bound oxidized phospholipids with very high affinity, whereas 3F(14) resembled apoA-I. The extraordinary ability of 4F to bind pro-inflammatory oxidized lipids probably accounts for its remarkable anti-inflammatory properties.

Lipoprotein inflammatory properties and serum amyloid A levels but not cholesterol levels predict lesion area in cholesterol-fed rabbits

Rabbits on a 1% cholesterol diet received injections of vehicle with or without D-4F or L-4F. After 1 month, the percent of aorta with atherosclerotic lesions was 24 +/- 15% (vehicle), 10 +/- 6% (D-4F) (P < 0.01 vs. vehicle), and 13 +/- 9% (L-4F) (P < 0.05 vs. vehicle). Inflammatory indexes for HDL and LDL were determined by measuring monocyte chemotactic activity after adding rabbit lipoproteins to human endothelial cells. HDL-inflammatory index (HII) and LDL-inflammatory index (LII), respectively, were 1.39 +/- 0.24; 1.35 +/- 0.29 (vehicle), 0.67 +/- 0.26; 0.63 +/- 0.38 (D-4F) (P < 0.001 vs. vehicle), and 0.67 +/- 0.2; 0.68 +/- 0.32 (L-4F) (P < 0.01 vs. vehicle). Serum amyloid A (SAA) levels were 95 +/- 39, 8 +/- 22, and 7 +/- 19 mug/ml, respectively, for vehicle, D-4F, and L-4F (P < 0.001 vs. vehicle). There was no correlation between lesion area and total plasma or HDL-cholesterol levels. In contrast, there was a positive correlation with HII, LII, and SAA (P = 0.002, P = 0.0026, P = 0.0079, respectively). HII correlated closely with SAA levels (r = 0.6616; r(2) = 0.4377, P < 0.0001). Thus, HII, LII, and SAA are better predictors of lesion area than are total plasma or HDL-cholesterol levels in cholesterol-fed rabbits.

Effects of D-4F on vasodilation, oxidative stress, angiostatin, myocardial inflammation, and angiogenic potential in tight-skin mice

Systemic sclerosis (scleroderma, SSc) is an autoimmune, connective tissue disorder that is characterized by impaired vascular function, increased oxidative stress, inflammation of internal organs, and impaired angiogenesis. Tight skin mice (Tsk−/+) have a defect in fibrillin-1, resulting in replication of many of the myocardial and vascular features seen in humans with SSc. D-4F is an apolipoprotein A-I (apoA-I) mimetic that improves vascular function in diverse diseases such as hypercholesterolemia, influenza, and sickle cell disease. Tsk−/+ mice were treated with either phosphate-buffered saline (PBS) or D-4F (1 mg·kg−1·day−1 for 6–8 wk). Acetylcholine and flow-induced vasodilation were examined in facialis arteries. Proinflammatory HDL (p-HDL) in murine and human plasma samples was determined by the cell-free assay. Angiostatin levels in murine and human plasma samples were determined by Western blot analysis. Hearts were examined for changes in angiostatin and autoantibodies against oxidized phosphotidylcholine (ox-PC). Angiogenic potential in thin sections of murine hearts was assessed by an in vitro vascular endothelial growth factor (VEGF)-induced endothelial cell (EC) tube formation assay. D-4F improved endothelium-, endothelial nitric oxide synthase-dependent, and flow-mediated vasodilation in Tsk−/+ mice. Tsk−/+ mice had higher plasma p-HDL and angiostatin levels than C57BL/6 mice, as did SSc patients compared with healthy control subjects. Tsk−/+ mice also had higher triglycerides than C57BL/6 mice. D-4F reduced p-HDL, angiostatin, and triglycerides in the plasma of Tsk−/+ mice. Tsk−/+ hearts contained notably higher levels of angiostatin and autoantibodies against ox-PC than those of control hearts. D-4F ablated angiostatin in Tsk−/+ hearts and reduced autoantibodies against ox-PC by >50% when compared with hearts from untreated Tsk−/+ mice. Angiogenic potential in Tsk−/+ hearts was increased only when the Tsk−/+ mice were treated with D-4F (1 mg·kg−1·day−1, 6–8 wk), and cultured sections of hearts from the D-4F-treated Tsk−/+ micewere incubated with D-4F (10 μg/ml, 5–7 days). Failure to treat the thin sections of hearts and Tsk−/+ mice with D-4F resulted in loss of VEGF-induced EC tube formation. D-4F improves vascular function, decreases myocardial inflammation, and restores angiogenic potential in the hearts of Tsk−/+ mice. As SSc patients have increased plasma p-HDL and angiostatin levels similar to the Tsk−/+ mice, D-4F may be effective at treating vascular complications in patients with SSc.

Structural requirements for antioxidative and anti-inflammatory properties of apolipoprotein A-I mimetic peptides

Recently, attention has been focused on pharmacological treatments that increase HDL cholesterol to prevent coronary artery disease. Despite three decades of extensive research of human apolipoprotein A-I (apoA-I), the major protein component of HDL, the molecular basis for its antiatherogenic and anti-inflammatory functions remain elusive. Another protein component of HDL, apoA-II, has structural features similar to those of apoA-I but does not possess atheroprotective properties. To understand the molecular basis for the effectiveness of apoA-I, we used model synthetic peptides. We designed analogs of the class A amphipathic helical motif in apoA-I that is responsible for solubilizing phospholipids. None of these analogs has sequence homology to apoA-I, but all are similar in their lipid-associating structural motifs. Although all of these peptide analogs interact with phospholipids to form peptide:lipid complexes, the biological properties of these analogs are different. Physical-chemical and NMR studies of these peptides have enabled the delineation of structural requirements for atheroprotective and anti-inflammatory properties in these peptides. It has been shown that peptides that interact strongly with lipid acyl chains do not have antiatherogenic and anti-inflammatory properties. In contrast, peptides that associate close to the lipid head group (and hence do not interact strongly with the lipid acyl chain) are antiatherogenic and anti-inflammatory. Understanding the structure and function of apoA-I and HDL through studies of the amphipathic helix motif may lead to peptide-based therapies for inhibiting atherosclerosis and other related inflammatory lipid disorders.

ApoA-I mimetic peptides with differing ability to inhibit atherosclerosis also exhibit differences in their interactions with membrane bilayers

Two homologous apoA-I mimetic peptides, 3F-2 and 3F(14), differ in their in vitro antiatherogenic properties (Epand, R. M., Epand, R. F., Sayer, B. G., Datta, G., Chaddha, M., and Anantharamaiah, G. M. (2004) J. Biol. Chem. 279, 51404-51414). In the present work, we demonstrate that the peptide 3F-2, which has more potent anti-inflammatory activity in vitro when administered intraperitoneally to female apoE null mice (20 microg/mouse/day) for 6 weeks, inhibits atherosclerosis (lesion area 15,800 +/- 1000 microm(2), n = 29), whereas 3F(14) does not (lesion area 20,400 +/- 1000 microm(2), n = 26) compared with control saline administered (19,900 +/- 1400 microm(2), n = 22). Plasma distribution of the peptides differs in that 3F-2 preferentially associates with high density lipoprotein, whereas 3F(14) preferentially associates with apoB-containing particles. After intraperitoneal injection of (14)C-labeled peptides, 3F(14) reaches a higher maximal concentration and has a longer half-time of elimination than 3F-2. A study of the effect of these peptides on the motional and organizational properties of phospholipid bilayers, using several NMR methods, demonstrates that the two peptides insert to different extents into membranes. 3F-2 with aromatic residues at the center of the nonpolar face partitions closer to the phospholipid head group compared with 3F(14). In contrast, only 3F(14) affects the terminal methyl group of the acyl chain, decreasing the (2)H order parameter and at the same time also decreasing the molecular motion of this methyl group. This dual effect of 3F(14) can be explained in terms of the cross-sectional shape of the amphipathic helix. These results support the proposal that the molecular basis for the difference in the biological activities of the two peptides lies with their different interactions with membranes.

Functionally defective high-density lipoprotein: a new therapeutic target at the crossroads of dyslipidemia, inflammation, and atherosclerosis

High-density lipoproteins (HDL) possess key atheroprotective biological properties, including cellular cholesterol efflux capacity, and anti-oxidative and anti-inflammatory activities. Plasma HDL particles are highly heterogeneous in physicochemical properties, metabolism, and biological activity. Within the circulating HDL particle population, small, dense HDL particles display elevated cellular cholesterol efflux capacity, afford potent protection of atherogenic low-density lipoprotein against oxidative stress and attenuate inflammation. The antiatherogenic properties of HDL can, however be compromised in metabolic diseases associated with accelerated atherosclerosis. Indeed, metabolic syndrome and type 2 diabetes are characterized not only by elevated cardiovascular risk and by low HDL-cholesterol (HDL-C) levels but also by defective HDL function. Functional HDL deficiency is intimately associated with alterations in intravascular HDL metabolism and structure. Indeed, formation of HDL particles with attenuated antiatherogenic activity is mechanistically related to core lipid enrichment in triglycerides and cholesteryl ester depletion, altered apolipoprotein A-I (apoA-I) conformation, replacement of apoA-I by serum amyloid A, and covalent modification of HDL protein components by oxidation and glycation. Deficient HDL function and subnormal HDL-C levels may act synergistically to accelerate atherosclerosis in metabolic disease. Therapeutic normalization of attenuated antiatherogenic HDL function in terms of both particle number and quality of HDL particles is the target of innovative pharmacological approaches to HDL raising, including inhibition of cholesteryl ester transfer protein, enhanced lipidation of apoA-I with nicotinic acid and infusion of reconstituted HDL or apoA-I mimetics. A preferential increase in circulating concentrations of HDL particles possessing normalized antiatherogenic activity is therefore a promising therapeutic strategy for the treatment of common metabolic diseases featuring dyslipidemia, inflammation, and premature atherosclerosis.

Potential clinical utility of high-density lipoprotein-mimetic peptides

PURPOSE OF REVIEW

To determine the potential clinical utility of high-density lipoprotein-mimetic peptides.

RECENT FINDINGS

Oral administration of D-4F together with pravastatin caused lesion regression in old apoE null mice. Administration of D-4F to low-density lipoprotein receptor null mice fed a Western diet reduced the association of myeloperoxidase with apoA-I and reduced the 3-nitrotyrosine content of apoA-I. Oral D-4F improved arterial vasoreactivity independent of apoA-I. Mice genetically lacking apoA-I showed significant improvement in vasoreactivity but, in contrast to mice with apoA-I, did not demonstrate reduced arterial wall thickness after D-4F treatment. In a rat model of diabetes, D-4F administration induced heme oxygenase-1 and extracellular superoxide dismutase, prevented endothelial sloughing, and dramatically improved arterial vasoreactivity. A peptide with 10 D-amino acid residues taken from the sequence of apoJ rendered high-density lipoprotein anti-inflammatory in mice and monkeys, and dramatically reduced atherosclerosis in apoE null mice. Oral administration of tetrapeptides synthesized from either L-amino acids or D-amino acids rendered high-density lipoprotein anti-inflammatory in mice and monkeys, and reduced atherosclerosis in apoE null mice.

SUMMARY

Peptides that sequester lipoprotein lipid hydroperoxides release a series of high-density lipoprotein-associated antioxidant enzymes such as paraoxonase from inhibition and protect apoA-I from oxidative damage that would impair cholesterol efflux.

Synthetic peptides: managing lipid disorders

PURPOSE OF REVIEW

Recent publications related to the potential use of synthetic peptides for the management of lipid disorders and their vascular complications are reviewed.

RECENT FINDINGS

The potential use of synthetic peptides for the management of lipid disorders and their vascular complications has emerged in recent years. These peptides are models of apolipoproteins, but are much smaller in size than the apolipoproteins. Oral peptides that improve the antiinflammatory properties of HDLs have been shown to potently inhibit atherosclerosis in mouse models. Injection of a peptide with a class A amphipathic helix in a rat model of diabetes dramatically reduced endothelial sloughing and improved vasoreactivity. Injected synthetic peptides have also been described that dramatically lower plasma cholesterol and restore endothelial function in a rabbit model of familial hypercholesterolemia. These studies suggest the therapeutic potential for synthetic peptides in the management of lipid disorders and their vascular complications.

SUMMARY

Synthetic peptides much smaller than exchangeable human plasma apolipoproteins but with physical and chemical characteristics similar to the plasma apolipoproteins have shown promise in the management of lipid disorders and their vascular complications in animal models. The initial success of these animal studies suggests that synthetic peptides have the potential to emerge as a new therapeutic class of agents in the management of patients with lipid disorders.

Apolipoprotein A-I-mimetic peptides with antioxidant actions

To augment antioxidant action of apolipoprotein A-I (Apo A-I)-mimetic peptide, the peptide F3,6,14,18 18A (DWFKAFYDKVAEKFKEAF) was modified by incorporating antioxidant amino acid residues. Introduction of His residue at position 2 or 3 at N-terminal of the peptide remarkably enhanced antioxidant action against Cu2+ oxidation of LDL and the capability of sequestering Cu2+. Likewise, the substitution of Ala for Cys residue at position 12 increased antioxidant action against Cu2+ oxidation of LDL. Additionally, the Cys substitution contributed to enhanced capabilities in the removal of hypochlorous acid (HOCl) and 13-hydroperoxyoctadecadienoic acid. Furthermore, the combined incorporation of His and Cys residues enhanced antioxidant actions in preventing Cu2+ oxidation and reducing HOCl and hydroperoxide levels. Separately, in solubilizing phosphatidylcholine, either peptides with His residue at N-terminal position 2 or 3, or those containing Cys residue at position 11 or 12 were equipotent to peptide F3,6,14,18 18A. Further, the lipid-solubilizing ability of those containing both His and Cys residues was comparable to that of peptide F3,6,14,18 18A. In support of this, a similar structural importance was observed with Trp fluorescence study illustrating the penetration of peptides in phosphatidylcholine liposome. Besides, the modified peptides were also comparable to peptide F3,6,14,18 18A in restoring phosphatidylserine-induced loss of PON1 activity. These results indicate that the insertion of His or Cys residue into peptide F3,6,14,18 18A at appropriate positions could lead to enhanced antioxidant action with no significant change of lipid-solubilizing action.

Association of a Model Class A (Apolipoprotein) Amphipathic α Helical Peptide with Lipid

Class A amphipathic helical peptides have been shown to mimic apolipoprotein A-I, the major protein component of high density lipoproteins and have been shown to inhibit atherosclerosis in several dyslipidemic mouse models. Previously we reported the NMR structure of Ac-18A-NH2, the base-line model class A amphipathic helical peptide in a 50% (v/v) trifluoroethanol-d3/water mixture, a membrane-mimic environment (Mishra, V. K., Palgunachari, M. N., Anantharamaiah, G. M., Jones, M. K., Segrest, J. P., and Krishna, N. R. (2001) Peptides 22, 567-573). The peptide Ac-18A-NH2 forms discoidal nascent high density lipoprotein-like particles with 1,2-dimyristoyl-sn-glycero-3-phosphocholine. Because subtle structural changes in the peptide.lipid complexes have been shown to be responsible for their antiatherogenic properties, we undertook high resolution NMR studies to deduce detailed structure of recombinant peptide.1,2-dimyristoyl-sn-glycero-3-phosphocholine complexes. The peptide adopts a well defined amphipathic alpha helical structure in association with the lipid at a 1:1 peptide:lipid weight ratio. Nuclear Overhauser effect spectroscopy revealed a number of intermolecular close contacts between the aromatic residues in the hydrophobic face of the helix and the lipid acyl chain protons. The pattern of observed peptide-lipid nuclear Overhauser effects is consistent with a parallel orientation of the amphipathic alpha helix, with respect to the plane of the lipid bilayer, on the edge of the disc (the belt model). Based on the results of chemical cross-linking and molecular modeling, we propose that peptide helices are arranged in a head to tail fashion to cover the edge of the disc. This arrangement of peptides is also consistent with the pKa values of the Lys residues determined previously. Taken together, these results provide for the first time a high resolution structural view of the peptide.lipid discoidal complexes formed by a class A amphipathic alpha helical peptide.

Apolipoprotein A-I Mimetic Peptides: Potential Role in Atherosclerosis Management

Atherothrombotic vascular disease continues to be a leading cause of morbidity and mortality in much of the world. Although a healthy lifestyle and low-density lipoprotein cholesterol lowering significantly reduce cardiovascular morbidity and mortality, substantial number of adverse vasoocclusive events continue to occur. These realities have brought attention to additional therapies that could further reduce cardiovascular events. High-density lipoprotein (HDL)/apolipoprotein A-I (apo A-I)-based therapies are a potential therapeutic strategy against atherothrombotic vascular disease because of the known inverse relationship between HDL cholesterol and coronary heart disease, favorable and pleotrophic biologic effects of HDL/apo A-I, results of preclinical experimental studies, and emerging proof of concept in clinical studies. A variety of HDL/apo A-I-based therapies are currently under investigation, including synthetic peptides that mimic the function of HDL. Such apo A-I mimetic peptides are the focus of this review.