Preservation of biological function despite oxidative modification of the apolipoprotein A-I mimetic peptide 4F.

Myeloperoxidase (MPO)-derived hypochlorous acid induces changes in HDL function via redox modifications at the level of apolipoprotein A-I (apoA-I). As 4F and apoA-I share structural and functional properties, we tested the hypothesis that 4F acts as a reactive substrate for hypochlorous acid (HOCl). 4F reduced the HOCl-mediated oxidation of the fluorescent substrate APF in a concentration-dependent manner (ED(50) ∼ 56 ± 3 µM). This reaction induced changes in the physical properties of 4F. Addition of HOCl to 4F at molar ratios ranging from 1:1 to 3:1 reduced 4F band intensity on SDS-PAGE gels and was accompanied by the formation of a higher molecular weight species. Chromatographic studies showed a reduction in 4F peak area with increasing HOCl and the formation of new products. Mass spectral analyses of collected fractions revealed oxidation of the sole tryptophan (Trp) residue in 4F. 4F was equally susceptible to oxidation in the lipid-free and lipid-bound states. To determine whether Trp oxidation influenced its apoA-I mimetic properties, we monitored effects of HOCl on 4F-mediated lipid binding and ABCA1-dependent cholesterol efflux. Neither property was altered by HOCl. These results suggest that 4F serves as a reactive substrate for HOCl, an antioxidant response that does not influence the lipid binding and cholesterol effluxing capacities of the peptide.

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.

ApoE mimetic peptide reduces plasma lipid hydroperoxide content with a concomitant increase in HDL paraoxonase activity.

ApoE mimetic peptide possesses the putative receptor binding domain 141-150 (LRKLRKRLLR) of apoE covalently linked to the class A amphipathic helical peptide 18A. It dramatically reduces plasma cholesterol in dyslipidemic mouse and rabbit models. Recycling of apoE mimetic peptide increases the duration of preß-HDL formation leading to extended anti-inflammatory and atheroprotective properties.

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.

Anti-inflammatory and recycling properties of an apolipoprotein mimetic peptide, Ac-hE18A-NH(2).

Apolipoprotein E (apoE) exerts prominent anti-inflammatory effects and undergoes recycling by target cells. We previously reported that the peptide Ac-hE18A-NH(2), composed of the receptor binding domain (LRKLRKRLLR) of apoE covalently linked to the Class A amphipathic peptide 18A, dramatically lowers plasma cholesterol and lipid hydroperoxides and enhances paraoxonase activity in dyslipidemic animal models. The objective of this study was to determine whether this peptide, analogous to apoE, exerts anti-inflammatory effects and undergoes recycling under in vitro conditions. Pulse chase studies using [(125)I]-Ac-hE18A-NH(2) in THP-1 derived macrophages and HepG2 cells showed greater amounts of intact peptide in the cells at later time points indicating recycling of the peptide. Ac-hE18A-NH(2) induced a 2.5-fold increase in prebeta-HDL in the conditioned media of HepG2 cells. This effect persisted for 3 days after removal of the peptide from culture medium. Ac-hE18A-NH(2) also induced the secretion of cell surface apoE from THP-1 macrophages. In addition, the peptide increased cholesterol efflux from THP-1 cells by an ABCA1 independent mechanism. Moreover, Ac-hE18A-NH(2) inhibited LPS-induced vascular cell adhesion molecule-1 (VCAM-1) expression, and reduced monocyte adhesion in human umbilical vein endothelial cells (HUVECs). It also reduced the secretion of interleukin-6 (IL-6) and monocyte chemoattractant protein-1 (MCP-1) from THP-1 macrophages even when administered post-LPS and abolished the 18-fold increase in LPS-induced mRNA levels for MCP-1 in THP-1 cells. Taken together, these results suggest that addition of the putative apoE receptor-domain to the Class A amphipathic peptide 18A results in a peptide that, similar to apoE, recycles, thus enabling the potentiation and prolongation of its anti-atherogenic and anti-inflammatory effects. Such a peptide has great potential as a therapeutic agent in the management of atherosclerosis and other inflammatory diseases.

HDL therapy for cardiovascular diseases: the road to HDL mimetics.

3-Hydroxy-3-methylglutaryl coenzyme A reductase inhibitors (statins) are currently the drug of choice for the clinical management of elevated low-density lipoprotein (LDL) cholesterol. Although statin treatment provides an overall improvement in outcomes, clinical trial data reveal a significant number of cardiac events despite reaching targeted LDL levels. A low serum high-density lipoprotein (HDL) cholesterol level is an independent predictor of cardiovascular risk. Accordingly, there has been interest in determining whether HDL elevation, in addition to LDL lowering, further reduces risk in patients with coronary artery disease. Several commonly prescribed lipid-lowering therapies modestly raise HDL, but their use may be limited by the development of adverse reactions. Emerging data suggest that HDL quality and function may also be significantly reduced by atherosclerosis and other inflammatory diseases. The goal of this review is to discuss the current status of HDL therapeutics, with emphasis on a novel class of agent, the apolipoprotein A-I mimetic peptides, which improve the functional properties of HDL cholesterol.

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.

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.

Association of a model class A (apolipoprotein) amphipathic alpha helical peptide with lipid: high resolution NMR studies of peptide.lipid discoidal complexes.

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 E mimetic Peptide dramatically lowers plasma cholesterol and restores endothelial function in watanabe heritable hyperlipidemic rabbits.

BACKGROUND: These studies were designed to determine whether the dual-domain peptide with a class A amphipathic helix linked to the receptor-binding domain of apolipoprotein (apo) E (Ac-hE-18A-NH2) possesses both antidyslipidemic and antiinflammatory properties. METHODS AND RESULTS: A single bolus (15 mg/kg IV) of Ac-hE-18A-NH2 that contains LRKLRKRLLR (141- to 150-residue region of apo E) covalently linked to apo A-I mimetic peptide 18A not only reduced plasma cholesterol levels (baseline, 562+/-29.0 mg/dL versus 287.7+/-22.0 mg/dL at 18 hours, P<0.001) in the Watanabe heritable hyperlipidemic rabbit model but also significantly improved arterial endothelial function. This improvement was associated with a reduction in 2 markers of oxidative stress. First, the plasma lipid hydroperoxide content was reduced significantly, an effect associated with a 5-fold increase in HDL paraoxonase activity. Second, the formation of superoxide anion, a scavenger of nitric oxide, was also significantly reduced in arteries of these animals. CONCLUSIONS: Because dyslipidemia and endothelial dysfunction are common features of the atherosclerotic disease process, this unique dual-domain peptide has ideal composite properties that ameliorate key contributory factors to atherosclerosis.

Two homologous apolipoprotein AI mimetic peptides. Relationship between membrane interactions and biological activity.

Two related 18-amino acid, class A, amphipathic helical peptides termed 3F-2 and 3F14 were chosen for this study. Although they have identical amino acid compositions and many similar biophysical properties, 3F-2 is more potent than 3F14 as an apolipoprotein AI mimetic peptide. The two peptides exhibit similar gross conformational properties, forming structures of high helical content on a membrane surface. However, the thermal denaturation transition of 3F-2 is more cooperative, suggesting a higher degree of oligomerization on the membrane. Both 3F-2 and 3F14 promote the segregation of cholesterol in membranes containing phosphatidylcholine and cholesterol, but 3F-2 exhibits a greater selectivity for partitioning into cholesterol-depleted regions of the membrane. Magic angle spinning/NMR studies indicate that the aromatic residues of 3F-2 are stacked in the presence of lipid. The aromatic side chains of this peptide also penetrate more deeply into membranes of phosphatidylcholine with cholesterol compared with 3F14. Using the fluorescent probe, 1,3-dipyrenylpropane, we monitored the properties of the lipid hydrocarbon environment. 3F-2 had a greater effect in altering the properties of the hydrocarbon region of the membrane. The results are consistent with our proposed model of the effect of peptide shape on the nature of the difference in peptide insertion into the bilayer.

Model class A and class L peptides increase the production of apoA-I-containing lipoproteins in HepG2 cells.

Class A peptides inhibit atherosclerosis and protect cells from class L peptide-mediated lysis. Because the cytolytic process is concentration dependent, we hypothesized that at certain concentrations both classes of peptides exert similar effect(s) on cells. To test this hypothesis, we studied the effects of a class L peptide (18L = GIKKFLGSIWKFIKAFVG) and a class A peptide, 18A-Pro-18A (18A = DWLKAFYDKVAEKLKEAF) (37pA), on apolipoprotein and lipoprotein production in HepG2 cells. Secretion of (35)S-labeled apolipoprotein A-I (apoA-I) was stimulated by both 18L (110%) and 37pA (135%) at 10 and 20 nM of peptides, respectively. Both peptides enhanced the secretion of (3)H-labeled phospholipids by 140% and (14)C-labeled HDL-cholesterol (HDL-C) by 35% but had no significant effect on the total cholesterol mass or secretion. These results indicate that class L and class A peptides cause redistribution of cholesterol among lipoproteins in favor of HDL-C. Both peptides remodeled apoA-I-containing particles forming prebeta- as well as alpha-HDL. This study suggests that increased secretion of phospholipids and apoA-I and the formation of prebeta-HDL particles might contribute to the antiatherogenic properties of these peptides.

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

The apolipoprotein A-I mimetic peptide 4F (Ac-DWFKAFYDKVAEKFKEAF-NH(2)), with four Phe residues on the nonpolar face of the amphipathic alpha-helix, is strongly anti-inflammatory, whereas two 3F analogs (3F(3) and 3F(14)) are not. To understand how changes in helix nonpolar face structure affect function, two additional 3F analogs, Ac-DKLKAFYDKVFEWAKEAF-NH(2) (3F-1) and Ac-DKWKAVYDKFAEAFKEFL-NH(2) (3F-2), were designed using the same amino acid composition as 3F(3) and 3F(14). The aromatic residues in 3F-1 and 3F-2 are near the polar-nonpolar interface and at the center of the nonpolar face of the helix, respectively. Like 4F, but in contrast to 3F(3) and 3F(14), these peptides effectively inhibited lytic peptide-induced hemolysis, oxidized phospholipid-induced monocyte chemotaxis, and scavenged lipid hydroperoxides from low density lipoprotein. High pressure liquid chromatography retention times and monolayer exclusion pressures indicated that there is no direct correlation of peptide function with lipid affinity. Fluorescence studies suggested that, although the peptides bind phospholipids similarly, the Trp residue in 4F, 3F-1, and 3F-2 is less motionally restricted than in 3F(3) and 3F(14). Based on these results and molecular modeling studies, we propose that the arrangement of aromatic residues in class A amphipathic helical molecules regulates entry of reactive oxygen species into peptide-phospholipid complexes, thereby reducing the extent of monocyte chemotaxis, an important step in atherosclerosis.

Effect of an arginine-rich amphipathic helical peptide on plasma cholesterol in dyslipidemic mice.

We have shown that the dual domain peptide Ac-hE18A-NH(2), in which LRKLRKRLLR, (141-150 region of human apo E) covalently linked to a class A lipid-associating domain, is able to associate with apo B-containing lipoproteins and enhance their clearance both in vitro and in vivo. We present here the differential effects of this peptide on the plasma cholesterol levels in different mouse models. The peptide intravenously administered (100 microg) into C57BL/6J mice on atherogenic diet, apo E null, and apo E null/LDL-receptor (LDL-R) null double knock out mouse models, was able to rapidly reduce plasma cholesterol levels within 2 min, and the effect persisted for more than 6 h. The reduction was limited to the VLDL and IDL/LDL fractions; HDL was not reduced in any mouse model studied. However, the peptide had no effect on the plasma cholesterol levels in C57BL/6J mice on normal diet, LDL-R null mice on normal chow, and LDL-R null mice on Western diet. Administration to LDL-R null mice of 125I-labelled human lipoproteins incubated with peptide resulted in accelerated human VLDL and LDL clearance with associated increase of radioactivity in the liver. These results, coupled with our earlier in vitro observations, indicate that the Arg-rich peptide-assisted rapid clearance of plasma cholesterol in dyslipidemic mice is due to the peptide targeting apo B-48-containing atherogenic lipoproteins to the liver for increased uptake and degradation.

Oral administration of an Apo A-I mimetic Peptide synthesized from D-amino acids dramatically reduces atherosclerosis in mice independent of plasma cholesterol.

When apolipoprotein A-I mimetic peptides synthesized from either D- or L-amino acids were given orally to LDL receptor-null mice, only the peptide synthesized from D-amino acids was stable in the circulation and enhanced the ability of HDL to protect LDL against oxidation. The peptide synthesized from L-amino acids was rapidly degraded and excreted in the urine. When a peptide synthesized from D-amino acids (D-4F) was administered orally to LDL receptor-null mice on a Western diet, lesions decreased by 79%. When added to the drinking water of apoE-null mice, D-4F decreased lesions by approximately 75% at the lowest dose tested (0.05 mg/mL). The marked reduction in lesions occurred independent of changes in total plasma or HDL-cholesterol.