D-4F, an apolipoprotein A-I mimetic peptide, inhibits the inflammatory response induced by influenza A infection of human type II pneumocytes

Apolipoprotein A-I attenuates ovalbumin-induced neutrophilic airway inflammation via a granulocyte colony-stimulating factor-dependent mechanism

Apolipoprotein A-I (apoA-I) is a key component of high-density lipoproteins that mediates reverse cholesterol transport from cells and reduces vascular inflammation. We investigated whether endogenous apoA-I modulates ovalbumin (OVA)-induced airway inflammation in mice. We found that apoA-I expression was significantly reduced in the lungs of OVA-challenged, compared with saline-challenged, wild-type (WT) mice. Next, to investigate the role of endogenous apoA-I in the pathogenesis of OVA-induced airway inflammation, WT and apoA-I(-/-) mice were sensitized by intraperitoneal injections of OVA and aluminum hydroxide, followed by multiple nasal OVA challenges for 4 weeks. OVA-challenged apoA-I(-/-) mice exhibited a phenotype of increased airway neutrophils compared with WT mice, which could be rescued by an administration of a 5A apoA-I mimetic peptide. Multiple pathways promoted neutrophilic inflammation in OVA-challenged apoA-I(-/-) mice, including the up-regulated expression of (1) proinflammatory cytokines (IL-17A and TNF-α), (2) CXC chemokines (CXCL5), (3) vascular adhesion molecules (i.e., vascular cell adhesion molecule-1), and (4) granulocyte colony-stimulating factors (G-CSF). Because concentrations of G-CSF in bronchoalveolar lavage fluid (BALF) were markedly increased in OVA-challenged apoA-I(-/-) mice, we hypothesized that enhanced G-CSF expression may represent the predominant pathway mediating increased neutrophilic inflammation. This was confirmed by the intranasal administration of a neutralizing anti-G-CSF antibody, which significantly reduced BALF neutrophilia by 72% in OVA-challenged apoA-I(-/-) mice, compared with mice that received a control antibody. We conclude that endogenous apoA-I negatively regulates OVA-induced neutrophilic airway inflammation, primarily via a G-CSF-dependent mechanism. Furthermore, these findings suggest that apoA-I may play an important role in modulating the severity of neutrophilic airway inflammation in asthma.

Physiological effects of oxidized phospholipids and their cellular signaling mechanisms in inflammation

Oxidized phospholipids, such as the products of the oxidation of 1-palmitoyl-2-arachidonoyl-sn-glycero-3-phosphocholine by nonenzymatic radical attack, are known to be formed in a number of inflammatory diseases. Interest in the bioactivity and signaling functions of these compounds has increased enormously, with many studies using cultured immortalized and primary cells, tissues, and animals to understand their roles in disease pathology. Initially, oxidized phospholipids were viewed largely as culprits, in line with observations that they have proinflammatory effects, enhancing inflammatory cytokine production, cell adhesion and migration, proliferation, apoptosis, and necrosis, especially in vascular endothelial cells, macrophages, and smooth muscle cells. However, evidence has emerged that these compounds also have protective effects in some situations and cell types; a notable example is their ability to interfere with signaling by certain Toll-like receptors (TLRs) induced by microbial products that normally leads to inflammation. They also have protective effects via the stimulation of small GTPases and induce up-regulation of antioxidant enzymes and cytoskeletal rearrangements that improve endothelial barrier function. Oxidized phospholipids interact with several cellular receptors, including scavenger receptors, platelet-activating factor receptors, peroxisome proliferator-activated receptors, and TLRs. The various and sometimes contradictory effects that have been observed for oxidized phospholipids depend on their concentration, their specific structure, and the cell type investigated. Nevertheless, the underlying molecular mechanisms by which oxidized phospholipids exert their effects in various pathologies are similar. Although our understanding of the actions and mechanisms of these mediators has advanced substantially, many questions do remain about their precise interactions with components of cell signaling pathways.

HDLs, immunity, and atherosclerosis

PURPOSE OF REVIEW

HDLs possess several physiological activities that may explain their antiatherosclerotic properties. Among them, the most relevant is the ability of HDL to promote the efflux of excess cholesterol from peripheral tissues to the liver for excretion.

RECENT FINDINGS

The ability of HDL to promote cholesterol efflux results also in the modulation of a series of responses in the immune cells involved in atherosclerosis, including monocyte-macrophages, B and T lymphocytes. HDL also acts as a reservoir for a number of biologically active substances that may impact the immune system, and as the HDL composition varies to a large extent during inflammation.

SUMMARY

The understanding of how these interactions take place and how biologically active substances can be delivered to relevant targets during atherogenesis is of great interest and may provide a better understanding for the role of HDL in atherogenesis.

Apolipoprotein A-I, A-II, and H mRNA and protein accumulation sites in the developing lung in late gestation

BACKGROUND

Expression of apolipoprotein A-I (apoA-I), A-II, and H was previously observed at 16 to 50-fold higher levels in the fetal than the adult mouse lung. Here, sites of apoA-I, A-II, and H mRNA and protein accumulation were determined in mouse fetal lungs by in situ hybridization and immunohistochemistry in late gestation.

RESULTS

Expression sites vary for the three genes and change for the distal epithelium before the end of the canalicular stage, thus where and when the surge of surfactant synthesis occurs. Messenger of apoH, but not those of apoA-I and A-II, was also observed in the proximal epithelium and smooth muscles surrounding arteries. In contrast to apoC-II protein, none of the three studied apolipoproteins accumulated within secretory granule-like structures. Immunohistochemistry revealed that apoA-I and apoH accumulated mainly in capillaries. Three different positive signals with the anti-apoA-II antibody were found: one transient signal in the nucleus of a portion of mesenchymal cells, a second at lower levels throughout the mesenchyme, and another in capillaries with a specific increase from gestation day 17.5/18.5.

CONCLUSION

Temporal and geographic co-expression of apoAI, AII, and H genes with surfactant production site suggests that the three apolipoproteins are secreted to play roles supporting the lung-specific surfactant lipid-related metabolism.

Emerging role of high density lipoproteins as a player in the immune system

High density lipoproteins (HDL) possess a number of physiological activities. The most studied and, perhaps, better understood is the ability of HDL to promote excess cholesterol efflux from peripheral tissues and transport to the liver for excretion, a mechanism believed to confer protection against atherosclerotic cardiovascular disease. The ability of HDL to modulate cholesterol bioavailability in the lipid rafts, membrane microdomains enriched in glycosphingolipids and cholesterol, is evolutionary conserved and affects the properties of cells involved in the innate and adaptive immune response, tuning inflammatory response and antigen presentation functions in macrophages as well as B and T cell activation. Also sphingosine-1 phosphate (S1P), a major active sphingolipid carried by HDL, is of relevance in the pathogenesis of several immuno-inflammatory disorders through the modulation of macrophage and lymphocyte functions. Furthermore, HDL influence the humoral innate immunity by modulating the activation of the complement system and the expression of pentraxin 3 (PTX3). Finally, in humans, HDL levels and functions are altered in several immune-mediated disorders, such as rheumatoid arthritis, systemic lupus eritematosus, Crohn's disease and multiple sclerosis as well as during inflammatory responses. Altogether these observations suggest that the effects of HDL in immunity could be related, to either the ability of HDL to modulate cholesterol content in immune cell lipid rafts and to their role as reservoir for several biologically active substances that may impact the immune system.

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.

Apolipoprotein mimetic peptides: Mechanisms of action as anti-atherogenic agents

Apolipoprotein mimetic peptides are short synthetic peptides that share structural, as well as biological features of native apolipoproteins. The early positive clinical trials of intravenous preparations of apoA-I, the main protein component of high density lipoproteins (HDL), have stimulated great interest in the use of apolipoprotein mimetic peptides as possible therapeutic agents. Currently, there are a wide variety of apolipoprotein mimetic peptides at various stages of drug development. These peptides typically have been designed to either promote cholesterol efflux or act as anti-oxidants, but they usually exert other biological effects, such as anti-inflammatory and anti-thrombotic effects. Uncertainty about which of these biological properties is the most important for explaining their anti-atherogenic effect is a major unresolved question in the field. Structure-function studies relating the in vitro properties of these peptides to their ability to reduce atherosclerosis in animal models may uncover the best rationale for the design of these peptides and may lead to a better understanding of the mechanisms behind the atheroprotective effect of HDL.

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.

5A, an apolipoprotein A-I mimetic peptide, attenuates the induction of house dust mite-induced asthma

New treatment approaches are needed for patients with asthma. Apolipoprotein A-I (apoA-I), the major structural protein of high-density lipoproteins, mediates reverse cholesterol transport and has atheroprotective and anti-inflammatory effects. In this study, we hypothesized that an apoA-I mimetic peptide might be effective at inhibiting asthmatic airway inflammation. A 5A peptide, which is a synthetic, bihelical apoA-I mimetic, was administered to wild-type A/J mice via osmotic mini-pump prior to the induction of house dust mite (HDM)-induced asthma. HDM-challenged mice that received the 5A apoA-I mimetic peptide had significant reductions in the number of bronchoalveolar lavage fluid eosinophils, lymphocytes, and neutrophils, as well as in histopathological evidence of airway inflammation. The reduction in airway inflammation was mediated by a reduction in the expression of Th2- and Th17-type cytokines, as well as in chemokines that promote T cell and eosinophil chemotaxis, including CCL7, CCL17, CCL11, and CCL24. Furthermore, the 5A apoA-I mimetic peptide inhibited the alternative activation of pulmonary macrophages in the lungs of HDM-challenged mice. It also abrogated the development of airway hyperresponsiveness and reduced several key features of airway remodeling, including goblet cell hyperplasia and the expression of collagen genes (Col1a1 and Col3a1). Our results demonstrate that the 5A apoA-I mimetic peptide attenuates the development of airway inflammation and airway hyperresponsiveness in an experimental murine model of HDM-induced asthma. These data support the conclusion that strategies using apoA-I mimetic peptides, such as 5A, might be developed further as a possible new treatment approach for asthma.

High-density lipoprotein suppresses the type I interferon response, a family of potent antiviral immunoregulators, in macrophages challenged with lipopolysaccharide

BACKGROUND

High-density lipoprotein (HDL) protects the artery wall by removing cholesterol from lipid-laden macrophages. However, recent evidence suggests that HDL might also inhibit atherogenesis by combating inflammation.

METHODS AND RESULTS

To identify potential antiinflammatory mechanisms, we challenged macrophages with lipopolysaccharide, an inflammatory microbial ligand for Toll-like receptor 4. HDL inhibited the expression of 30 (277 of 911) of the genes normally induced by lipopolysaccharide, microarray analysis revealed. One of its major targets was the type I interferon response pathway, a family of potent viral immunoregulators controlled by Toll-like receptor 4 and the TRAM/TRIF signaling pathway. Unexpectedly, the ability of HDL to inhibit gene expression was independent of macrophage cholesterol stores. Immunofluorescent studies suggested that HDL promoted TRAM translocation to intracellular compartments, which impaired subsequent signaling by Toll-like receptor 4 and TRIF. To examine the potential in vivo relevance of the pathway, we used mice deficient in apolipoprotein A-I, the major protein of HDL. After infection with Salmonella typhimurium, a Gram-negative bacterium that expresses lipopolysaccharide, apolipoprotein A-I-deficient mice had 6-fold higher plasma levels of interferon-β, a key regulator of the type I interferon response, than did wild-type mice.

CONCLUSIONS

HDL inhibits a subset of lipopolysaccharide-stimulated macrophage genes that regulate the type I interferon response, and its action is independent of sterol metabolism. These findings raise the possibility that regulation of macrophage genes by HDL might link innate immunity and cardioprotection.

Apolipoprotein A-I mimetic peptides: a potential new therapy for the prevention of atherosclerosis

The beneficial effects of high-density lipoprotein (HDL) on atherosclerosis have largely been attributed to its major protein, apolipoprotein A-I (apoA-I). Used as a therapeutic intervention, apoA-I is a large protein that requires venous administration, and is both difficult and expensive to manufacture. Because of these problems with apoA-I, the generation of smaller, easier to manufacture apoA-I mimetic peptides has become a target for pharmacologic development in the therapeutic management of human atherosclerosis. A potent apoA-I mimetic peptide, 4F, was found to have significant activity in various inflammatory states in both mice and monkeys. The anti-inflammatory and antiatherogenic effects of 4F include increased pre-beta HDL formation, increased cholesterol efflux, the conversion of pro-inflammatory HDL to anti-inflammatory HDL, and reduced lipoprotein oxidation. In addition, improved arterial vasoreactivity is another important function of 4F. In a rat model of diabetes, D-4F increased arterial concentrations of heme oxygenase-1 (HO-1) and superoxide dismutase, decreased superoxide levels, reduced levels of circulating endothelial cells, decreased endothelial cell fragmentation, and restored arterial vasoreactivity to normal. In a mouse model of systemic sclerosis, D-4F functioned to improve vasodilation and angiogenic potential, while reducing myocardial inflammation and oxidative stress. With respect to mouse models of heart transplant-associated atherosclerosis, D-4F induced HO-1. In addition, D-4F was shown to improve cognitive performance in low-density lipoprotein-receptor null mice with Western diet-induced cognitive decline. D-4F also reduced the kidney content of oxidized phospholipids in a mouse model of hyperlipidemia-induced renal inflammation. In early human studies in patients with significant cardiovascular risk, a single dose of oral D-4F was found to safely improve the anti-inflammatory index of HDL. L-4F is also being studied in clinical trials as a potential treatment modality for obesity and the metabolic syndrome.

Inhibitory effects of carbocisteine on type A seasonal influenza virus infection in human airway epithelial cells

Type A human seasonal influenza (FluA) virus infection causes exacerbations of bronchial asthma and chronic obstructive pulmonary disease (COPD). l-carbocisteine, a mucolytic agent, reduces the frequency of common colds and exacerbations in COPD. However, the inhibitory effects of l-carbocisteine on FluA virus infection are uncertain. We studied the effects of l-carbocisteine on FluA virus infection in airway epithelial cells. Human tracheal epithelial cells were pretreated with l-carbocisteine and infected with FluA virus (H(3)N(2)). Viral titers in supernatant fluids, RNA of FluA virus in the cells, and concentrations of proinflammatory cytokines in supernatant fluids, including IL-6, increased with time after infection. l-carbocisteine reduced viral titers in supernatant fluids, RNA of FluA virus in the cells, the susceptibility to FluA virus infection, and concentrations of cytokines induced by virus infection. The epithelial cells expressed sialic acid with an alpha2,6-linkage (SAalpha2,6Gal), a receptor for human influenza virus on the cells, and l-carbocisteine reduced the expression of SAalpha2,6Gal. l-carbocisteine reduced the number of acidic endosomes from which FluA viral RNA enters into the cytoplasm and reduced the fluorescence intensity from acidic endosomes. Furthermore, l-carbocisteine reduced NF-kappaB proteins including p50 and p65 in the nuclear extracts of the cells. These findings suggest that l-carbocisteine may inhibit FluA virus infection, partly through the reduced expression of the receptor for human influenza virus in the human airway epithelial cells via the inhibition of NF-kappaB and through increasing pH in endosomes. l-carbocisteine may reduce airway inflammation in influenza virus infection.

Structure/function relationships of apolipoprotein a-I mimetic peptides: implications for antiatherogenic activities of high-density lipoprotein

RATIONALE

Apolipoprotein (apoA)-I mimetic peptides are a promising type of anti-atherosclerosis therapy, but how the structural features of these peptides relate to the multiple antiatherogenic functions of HDL is poorly understood.

OBJECTIVE

To establish structure/function relationships of apoA-I mimetic peptides with their antiatherogenic functions.

METHODS AND RESULTS

Twenty-two bihelical apoA-I mimetic peptides were investigated in vitro for the capacity and specificity of cholesterol efflux, inhibition of inflammatory response of monocytes and endothelial cells, and inhibition of low-density lipoprotein (LDL) oxidation. It was found that mean hydrophobicity, charge, size of hydrophobic face, and angle of the link between the helices are the major factors determining the efficiency and specificity of cholesterol efflux. The peptide with optimal parameters was more effective and specific toward cholesterol efflux than human apoA-I. Charge and size of hydrophobic face were also the major factors affecting antiinflammatory properties, and the presence of cysteine and histidine residues was the main factor determining antioxidant properties. There was no significant correlation between capacities of the peptides to support individual functions; each function had its own optimal set of features.

CONCLUSIONS

None of the peptides was equally effective in all the antiatherogenic functions tested, suggesting that different functions of HDL may have different mechanisms and different structural requirements. The results do suggest, however, that rationalizing the design of apoA-I mimetic peptides may improve their therapeutic value and may lead to a better understanding of mechanisms of various antiatherogenic functions of HDL.

Generation and biological activities of oxidized phospholipids

Glycerophospholipids represent a common class of lipids critically important for integrity of cellular membranes. Oxidation of esterified unsaturated fatty acids dramatically changes biological activities of phospholipids. Apart from impairment of their structural function, oxidation makes oxidized phospholipids (OxPLs) markers of "modified-self" type that are recognized by soluble and cell-associated receptors of innate immunity, including scavenger receptors, natural (germ line-encoded) antibodies, and C-reactive protein, thus directing removal of senescent and apoptotic cells or oxidized lipoproteins. In addition, OxPLs acquire novel biological activities not characteristic of their unoxidized precursors, including the ability to regulate innate and adaptive immune responses. Effects of OxPLs described in vitro and in vivo suggest their potential relevance in different pathologies, including atherosclerosis, acute inflammation, lung injury, and many other conditions. This review summarizes current knowledge on the mechanisms of formation, structures, and biological activities of OxPLs. Furthermore, potential applications of OxPLs as disease biomarkers, as well as experimental therapies targeting OxPLs, are described, providing a broad overview of an emerging class of lipid mediators.

Apolipoprotein A-I mimetic 4F alters the function of human monocyte-derived macrophages

HDL and its major protein component apolipoprotein A-I (apoA-I) exert anti-inflammatory effects, inhibit monocyte chemotaxis/adhesion, and reduce vascular macrophage content in inflammatory conditions. In this study, we tested the hypothesis that the apoA-I mimetic 4F modulates the function of monocyte-derived macrophages (MDMs) by regulating the expression of key cell surface receptors on MDMs. Primary human monocytes and THP-1 cells were treated with 4F, apoA-I, or vehicle for 7 days and analyzed for expression of cell surface markers, adhesion to human endothelial cells, phagocytic function, cholesterol efflux capacity, and lipid raft organization. 4F and apoA-I treatment decreased the expression of HLA-DR, CD86, CD11b, CD11c, CD14, and Toll-like receptor-4 (TLR-4) compared with control cells, suggesting the induction of monocyte differentiation. Both treatments abolished LPS-induced mRNA for monocyte chemotactic protein-1 (MCP-1), macrophage inflammatory protein-1 (MIP-1), regulated on activation, normal T-expressed and presumably secreted (RANTES), IL-6, and TNF-alpha but significantly upregulated LPS-induced IL-10 expression. Moreover, 4F and apoA-I induced a 90% reduction in the expression of CD49d, a ligand for the VCAM-1 receptor, with a concurrent decrease in monocyte adhesion (55% reduction) to human endothelial cells and transendothelial migration (34 and 27% for 4F and apoA-I treatments) compared with vehicle treatment. In addition, phagocytosis of dextran-FITC beads was inhibited by 4F and apoA-I, a response associated with reduced expression of CD32. Finally, 4F and apoA-I stimulated cholesterol efflux from MDMs, leading to cholesterol depletion and disruption of lipid rafts. These data provide evidence that 4F, similar to apoA-I, induces profound functional changes in MDMs, possibly due to differentiation to an anti-inflammatory phenotype.

Macrophage scavenger receptor A mediates adhesion to apolipoproteins A-I and E

Macrophage scavenger receptor A (SR-A) is a multifunctional, multiligand pattern recognition receptor with roles in innate immunity, apoptotic cell clearance, and age-related degenerative pathologies, such as atherosclerosis and Alzheimer's disease. Known endogenous SR-A ligands are polyanionic and include modified lipoproteins, advanced glycation end products, and extracellular matrix proteins. No native plasma ligands have been identified, but it is known that SR-A recognition of unidentified serum components mediates integrin-independent macrophage adhesion, which may drive chronic local inflammation. In this study, we used a high-throughput fractionation and screening method to identify novel endogenous SR-A ligands that may mediate macrophage adhesion. SR-A was found to recognize the exchangeable apolipoproteins A-I and E (apo A-I and apo E, respectively) in both lipid-free and lipid-associated form, suggesting the shared amphipathic alpha-helix as a potential recognition motif. Adhesion of RAW 264.7 macrophages to surfaces coated with apo A-I and apo E4 proved to be integrin-independent and could be blocked by anti-SR-A antibodies. The presence of apo A-I and apo E in pathological deposits, such as atherosclerotic lesions and neurotoxic Alzheimer's plaques, suggests a possible contribution of SR-A-dependent adhesion of macrophages to an inflammatory microenvironment.

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.

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.

Host-derived oxidized phospholipids and HDL regulate innate immunity in human leprosy

Intracellular pathogens survive by evading the host immune system and accessing host metabolic pathways to obtain nutrients for their growth. Mycobacterium leprae, the causative agent of leprosy, is thought to be the mycobacterium most dependent on host metabolic pathways, including host-derived lipids. Although fatty acids and phospholipids accumulate in the lesions of individuals with the lepromatous (also known as disseminated) form of human leprosy (L-lep), the origin and significance of these lipids remains unclear. Here we show that in human L-lep lesions, there was preferential expression of host lipid metabolism genes, including a group of phospholipases, and that these genes were virtually absent from the mycobacterial genome. Host-derived oxidized phospholipids were detected in macrophages within L-lep lesions, and 1 specific oxidized phospholipid, 1-palmitoyl-2-(5,6-epoxyisoprostane E2)-sn-glycero-3-phosphorylcholine (PEIPC), accumulated in macrophages infected with live mycobacteria. Mycobacterial infection and host-derived oxidized phospholipids both inhibited innate immune responses, and this inhibition was reversed by the addition of normal HDL, a scavenger of oxidized phospholipids, but not by HDL from patients with L-lep. The accumulation of host-derived oxidized phospholipids in L-lep lesions is strikingly similar to observations in atherosclerosis, which suggests that the link between host lipid metabolism and innate immunity contributes to the pathogenesis of both microbial infection and metabolic disease.

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.

The effect of apolipoprotein mimetic peptides in inflammatory disorders other than atherosclerosis

Apolipoprotein mimetic peptides have been shown to dramatically reduce atherosclerosis in animal models. Atherosclerosis is an example of an inflammatory disorder. Published studies of apolipoprotein mimetic peptides in models of inflammatory disorders other than atherosclerosis suggest that they may have efficacy in a wide range of inflammatory conditions.

Acute respiratory tract infections: a potential trigger for the acute coronary syndrome

Clinical studies suggest that acute respiratory tract infection (ARTI) may be a risk factor for the acute coronary syndrome (ACS). ARTI is associated with an increased risk for ACS up to 2 weeks prior to a cardiac event. The mechanism that may underlie this association is unclear. Infections are thought to play a role in the progression and instability of atherosclerotic plaques, resulting in plaque rupture, sudden constriction, and/or blockage of coronary arteries. Inflammation, endothelial dysfunction and thrombotic activation seem to play an important role in this. Influenza vaccination may reduce the risk of ACS in patients with coronary artery disease. Future studies will provide more information about the underlying mechanisms of infection-related ACS.

D-4F reduces EO6 immunoreactivity, SREBP-1c mRNA levels, and renal inflammation in LDL receptor-null mice fed a Western diet

LDL receptor-null (LDLR(-/-)) mice on a Western diet (WD) develop endothelial dysfunction and atherosclerosis, which are improved by the apolipoprotein A-I (apoA-I) mimetic peptide D-4F. Focusing on the kidney, LDLR(-/-)mice were fed a WD with D-4F or the inactive control peptide scrambled D-4F (ScD-4F) added to their drinking water. The control mice (ScD-4F) developed glomerular changes, increased immunostaining for MCP-1/CCL2 chemokine, increased macrophage CD68 and F4/80 antigens, and increased oxidized phospholipids recognized by the EO6 monoclonal antibody in both glomerular and tublo-interstitial areas. All of these parameters were significantly reduced by D-4F treatment, approaching levels found in wild-type C57BL/6J or LDLR(-/-) mice fed a chow diet. Sterol-regulatory element binding protein-1c (SREBP-1c) mRNA levels and triglyceride levels were elevated in the kidneys of the control mice (ScD-4F) fed the WD compared with C57BL/6J and LDLR(-/-) mice on chow (P < 0.001 and P < 0.001, respectively) and compared with D-4F-treated mice on the WD (P < 0.01). There was no significant difference in plasma lipids, lipoproteins, glucose, blood pressure, or renal apoB levels between D-4F- and ScD-4F-treated mice. We conclude that D-4F reduced renal oxidized phospholipids, resulting in lower expression of SREBP-1c, which, in turn, resulted in lower triglyceride content and reduced renal inflammation.

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.

Oral amphipathic peptides as therapeutic agents

Cholesterol can promote inflammation by its ability to stimulate the production of reactive oxygen species that result in the formation of pro-inflammatory oxidised phospholipids. High-density lipoproteins (HDLs) are part of the innate immune response and can be either pro- or anti-inflammatory independently of plasma HDL-cholesterol levels. During systemic inflammation as occurs with atherosclerosis, Apolipoprotein A-I can be altered, reducing its ability to promote reverse cholesterol transport and HDL can become pro-inflammatory. Amphipathic peptides with either a class A amphipathic helix (D-4F) or a class G* amphipathic helix (D-[113-122]apoJ), or even those that are too small to form a helix (KRES and FREL) have some similar characteristics. Their interaction with lipids leads to a reduction in lipoprotein-lipid hydroperoxides that releases HDL-associated antioxidant enzymes, such as paraoxonase, therefore providing antiatherosclerosis and anti-inflammatory activity. In addition, the peptide D-4F stimulates the formation and cycling of pre-beta HDL. These amphipathic peptides appear to have therapeutic potential as oral agents.

Apolipoprotein A-I mimetic peptides and their role in atherosclerosis prevention

The importance of apolipoprotein A-I (apoA-I) in atherosclerosis was established by testing in animal models, and its potential usefulness in humans has been confirmed in preliminary studies. ApoA-I is a large protein comprising 243 amino acids, which means that venous administration is necessary. In addition, manufacture of apoA-I is difficult and expensive. Research has, therefore, been directed towards finding smaller peptide mimetics that produce similar results to apoA-I, but that are easier to manufacture and administer. The earliest peptides mimicked some of the lipid-binding properties of apoA-I but did not prevent atherosclerosis in mice. A detailed study of the physical-chemical characteristics of these peptides led to the realization that the hydrophobic region of the peptide was critical in determining bioactivity. A potent peptide, 4F, which was synthesized wholly from D-amino acids, could be given orally. Use of 4F significantly improved the function of HDL in mice and monkeys. When 4F was administered in combination with a statin, lesion size and macrophage content were reduced in mice with atherosclerosis, and lesions regressed in older mice. Vasoreactivity and endothelial sloughing were also improved in other rodent studies. Early human clinical trials are now being carried out on 4F. Here, we review the studies on apoA-I mimetic peptides that have been carried out so far.

D-4F decreases brain arteriole inflammation and improves cognitive performance in LDL receptor-null mice on a Western diet

LDL receptor-null mice on a Western diet (WD) have inflammation in large arteries and endothelial dysfunction in small arteries, which are improved with the apolipoprotein A-I mimetic D-4F. The role of hyperlipidemia in causing inflammation of very small vessels such as brain arterioles has not previously been studied. A WD caused a marked increase in the percent of brain arterioles with associated macrophages (microglia) (P < 0.01), which was reduced by oral D-4F but not by scrambled D-4F (ScD-4F; P < 0.01). D-4F (but not ScD-4F) reduced the percent of brain arterioles associated with CCL3/macrophage inflammatory protein-1alpha (P < 0.01) and CCL2/monocyte chemoattractant protein-1 (P < 0.001). A WD increased (P < 0.001) brain arteriole wall thickness and smooth muscle alpha-actin, which was reduced by D-4F but not by ScD-4F (P < 0.0001). There was no difference in plasma lipid levels, blood pressure, or arteriole lumen diameter with D-4F treatment. Cognitive performance in the T-maze continuous alternation task and in the Morris Water Maze was impaired by a WD and was significantly improved with D-4F but not ScD-4F (P < 0.05). We conclude that a WD induces brain arteriole inflammation and cognitive impairment that is ameliorated by oral D-4F without altering plasma lipids, blood pressure, or arteriole lumen size.

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.

Current understanding of the role of high-density lipoproteins in atherosclerosis and senescence

Numerous epidemiologic and interventional studies revealed that high-density lipoprotein (HDL) is an important risk factor for coronary heart disease. There are several well documented HDL functions that may account for the antiatherogenic effects of this lipoprotein. The best recognized of these is the capacity of HDL to transport cholesterol from the periphery to the liver, and thereby prevent cholesterol deposition in the arterial wall. Further properties of HDL that may also be antiatherogenic include its potent anti oxidative and anti-inflammatory action. In addition, HDL seems to be involved in processes related to senescence at both the cellular and whole-organism level. Both protein components of HDL (such as apolipoprotein A-I) and its lipid components (such as, lysosphingolipids) appear to mediate the antiatherogenic and anti-aging effects of HDL. The purpose of this review is to summarize the novel functions of HDL that may protect from atherosclerosis and senescence.

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.

LDL-cholesterol lowering or HDL-cholesterol raising for cardiovascular prevention

A number of reports have indicated that both lowering low density lipoprotein (LDL)-cholesterol and raising high density lipoprotein (HDL)-cholesterol can result in significant cardiovascular benefit, both in terms of reduction of events and also, to a variable extent, of atheromatous lesions. LDL and HDL have opposite roles in body cholesterol regulation and, in theory, both reduced deposition (LDL reduction) and increased removal (raised HDL) can improve vascular disease. A number of reports over the last 30 years have attempted to quantitate with cholesterol balance/turnover studies, the correlations between LDL and HDL levels and body cholesterol pool sizes. More recently, these studies have evaluated the effects of LDL or HDL changes on cholesterol elimination. Data have, at times, been fully consistent with theoretical expectations, whereas at others they have not. Evaluation of these, at times, historical data provides, however, an important clue to the understanding of current results with different medications for the management of lipoprotein disorders.

Therapeutic use of the high-density lipoprotein protein and peptides

High-density lipoprotein (HDL) therapy is a novel and emerging area of therapeutic development in the cardiovascular field. It attempts to supplement and improve the vascular benefit exerted by other agents that are active on lipid metabolism, for example, hypolipidaemic drugs. Furthermore, it takes advantage of the novel techniques of coronary evaluation. A number of reports have examined the potential therapeutic properties of the synthetic HDLs prepared by complexing recombinant apolipoprotein (apo) A-I(Milano), a variant form of native apoA-I, with phospholipids. The availability of synthetic HDL complexes containing recombinant apoA-I(Milano) has opened up a new era of therapeutic management for coronary disease. HDL formulations of recombinant apoA-I(Milano)-phospholipid complexes have clearly shown rapid regression of a focal carotid atheroma as well as powerful protection from myocardial infarction in a rabbit model. In a pilot study, ETC-216 showed a significant reduction in coronary plaque burden after five weekly treatments, assessed by intravascular ultrasound in patients with acute coronary syndrome. Other therapeutic options of HDL therapy have recently became available.

Pharmacologic augmentation of high-density lipoproteins: mechanisms of currently available and emerging therapies

PURPOSE OF REVIEW

With the limited effects of low-density lipoprotein-based lipid intervention, more attention is being paid to drugs that augment or mimic high-density lipoprotein's beneficial effects. A thorough understanding of the anti-atherogenic effects of high-density lipoprotein, and the mechanisms of existing or emerging high-density lipoprotein-based therapies, is essential for rational strategy for the prevention of cardiovascular disease.

RECENT FINDINGS

High-density lipoprotein mediates its beneficial effects through reverse cholesterol transport and direct anti-inflammatory effects of apolipoprotein AI and other component parts. Currently available drugs increase high-density lipoprotein-C through increasing apoAI synthesis (statins, fibrates) and decreasing apolipoprotein AI catabolism (niacin). Cholesteryl ester transfer protein inhibitors dramatically raise high-density lipoprotein-C, but clinical data are still required to verify their cardioprotective effects. Novel therapies such as apolipoprotein AImilano, apolipoprotein AI mimetic peptide, and exogenous phospholipids show tremendous promise as treatments for atherosclerosis.

SUMMARY

High-density lipoprotein and its defining functional protein apoAI prevent atherosclerosis through reverse cholesterol transport and other direct effects. Research has led to the development of novel therapies that increase high-density lipoprotein-C or that mimic direct anti-atherogenic effects of apolipoprotein AI. As these emerging therapies find a place in clinical medicine, we can anticipate preventing a much higher degree of cardiovascular events.

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.

High-Density Lipoprotein Function

Although high-density lipoproteins (HDL) possess many features that contribute to the association between elevated HDL cholesterol and protection from atherosclerosis, these lipoproteins may be modified in certain individuals and/or circumstances to become proinflammatory. The ability of HDL to inhibit or paradoxically to enhance vascular inflammation, lipid oxidation, plaque growth, and thrombosis reflects changes in specific enzyme and protein components. The anti-inflammatory and proinflammatory functional properties of HDL can now be assessed using cell-based and cell-free assays. Acute or chronic systemic inflammation and the metabolic syndrome appear to render HDL proinflammatory. In contrast, statins and experimental agents such as apolipoprotein A-1 mimetics render HDL more anti-inflammatory. Functional characterization of HDL is a promising method for enhanced assessment of cardiovascular risk and effectiveness of risk reduction.

An oral apoJ peptide renders HDL antiinflammatory in mice and monkeys and dramatically reduces atherosclerosis in apolipoprotein E-null mice

OBJECTIVE

To determine the properties of a peptide synthesized from D-amino acids corresponding to residues 113 to 122 in apolipoprotein (apo) J.

METHODS AND RESULTS

In contrast to D-4F, D- [113-122]apoJ showed minimal self-association and helicity in the absence of lipids. D-4F increased the concentration of apoA-I with pre-beta mobility in apoE-null mice whereas D- [113-122]apoJ did not. After an oral dose D- [113-122]apoJ more slowly associated with lipoproteins and was cleared from plasma much more slowly than D-4F. D- [113-122]apoJ significantly improved the ability of plasma to promote cholesterol efflux and improved high-density lipoprotein (HDL) inflammatory properties for up to 48 hours after a single oral dose in apoE-null mice, whereas scrambled D- [113-122]apoJ did not. Oral administration of 125 microg/mouse/d of D- [113-122]apoJ reduced atherosclerosis in apoE-null mice (70.2% reduction in aortic root sinus lesion area, P=4.3 x 10(-13); 70.5% reduction by en face analysis, P=1.5 x 10(-6)). In monkeys, oral D- [113-122]apoJ rapidly reduced lipoprotein lipid hydroperoxides (LOOH) and improved HDL inflammatory properties. Adding 250 ng/mL of D-[113-122]apoJ (but not scrambled D- [113-122]apoJ) to plasma in vitro reduced LOOH and increased paraoxonase activity.

CONCLUSIONS

Oral D- [113-122]apoJ significantly improves HDL inflammatory properties in mice and monkeys and inhibits lesion formation in apoE-null mice.

Antiinflammatory properties of HDL

There are several well-documented functions of high-density lipoprotein (HDL) that may explain the ability of these lipoproteins to protect against atherosclerosis. The best recognized of these is the ability of HDL to promote the efflux of cholesterol from cells. This process may minimize the accumulation of foam cells in the artery wall. However, HDL has additional properties that may also be antiatherogenic. For example, HDL is an effective antioxidant. The major proteins of HDL, apoA-I and apoA-II, as well as other proteins such as paraoxonase that cotransport with HDL in plasma, are well-known to have antioxidant properties. As a consequence, HDL has the capacity to inhibit the oxidative modification of low-density lipoprotein (LDL) in a process that reduces the atherogenicity of these lipoproteins. HDL also possesses other antiinflammatory properties. By virtue of their ability to inhibit the expression of adhesion molecules in endothelial cells, they reduce the recruitment of blood monocytes into the artery wall. These antioxidant and antiinflammatory properties of HDL may be as important as its cholesterol efflux function in terms of protecting against the development of atherosclerosis.

HDL as a target in the treatment of atherosclerotic cardiovascular disease

Lipid abnormalities are among the key risk factors for cardiovascular disease. Indeed, lipid-modifying drugs - in particular, the statins, which primarily lower plasma levels of low-density lipoprotein (LDL) cholesterol - considerably reduce the risk of cardiovascular events, leading to their widespread use. Nevertheless, it seems that there might be limits to the degree of benefit that can be achieved by lowering LDL-cholesterol levels alone, which has led to increased interest in targeting other lipid-related risk factors for cardiovascular disease, such as low levels of high-density lipoprotein (HDL) cholesterol. In this article, we first consider the mechanisms that underlie the protective effect of HDL cholesterol, and then discuss several strategies that have recently emerged to increase levels of HDL cholesterol to treat cardiovascular disease, including nuclear receptor modulation, inhibition of cholesteryl ester transfer protein and infusion of apolipoprotein/phospholipid complexes.