L-4F, an apolipoprotein A-1 mimetic, dramatically improves vasodilation in hypercholesterolemia and sickle cell disease

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.

Genetic deletion of apolipoprotein A-I increases airway hyperresponsiveness, inflammation, and collagen deposition in the lung

The relationship between high-density lipoprotein and pulmonary function is unclear. To determine mechanistic relationships we investigated the effects of genetic deletion of apolipoprotein A-I (apoA-I) on plasma lipids, paraoxonase (PON1), pro-inflammatory HDL (p-HDL), vasodilatation, airway hyperresponsiveness and pulmonary oxidative stress, and inflammation. ApoA-I null (apoA-I(-/-)) mice had reduced total and HDL cholesterol but increased pro-inflammatory HDL compared with C57BL/6J mice. Although PON1 protein was increased in apoA-I(-/-) mice, PON1 activity was decreased. ApoA-I deficiency did not alter vasodilatation of facialis arteries, but it did alter relaxation responses of pulmonary arteries. Central airway resistance was unaltered. However, airway resistance mediated by tissue dampening and elastance were increased in apoA-I(-/-) mice, a finding also confirmed by positive end-expiratory pressure (PEEP) studies. Inflammatory cells, collagen deposition, 3-nitrotyrosine, and 4-hydroxy-2-nonenal were increased in apoA-I(-/-) lungs but not oxidized phospholipids. Colocalization of 4-hydroxy-2-nonenal with transforming growth factor beta-1 (TGFbeta-1 was increased in apoA-I(-/-) lungs. Xanthine oxidase, myeloperoxidase and endothelial nitric oxide synthase were increased in apoA-I(-/-) lungs. Dichlorodihydrofluorescein-detectable oxidants were increased in bronchoalveolar lavage fluid (BALF) in apoA-I(-/-) mice. In contrast, BALF nitrite+nitrate levels were decreased in apoA-I(-/-) mice. These data demonstrate that apoA-I plays important roles in limiting pulmonary inflammation and oxidative stress, which if not prevented, will decrease pulmonary artery vasodilatation and increase airway hyperresponsiveness.

Amelioration of nephropathy with apoA-1 mimetic peptide in apoE-deficient mice

BACKGROUND

There is mounting evidence that dyslipidaemia may contribute to development and progression of renal disease. For instance, hyperlipidaemia in apolipoprotein E-deficient (apoE(-/-)) mice is associated with glomerular inflammation, mesangial expansion and foam cell formation. ApoA-1 mimetic peptides are potent antioxidant and anti-inflammatory compounds which are highly effective in ameliorating atherosclerosis and inflammation in experimental animals. Given the central role of oxidative stress and inflammation in progression of renal disease, we hypothesized that apoA-1 mimetic peptide, D-4F, may attenuate renal lesions in apoE(-/-) mice.

METHODS

Twenty-five-month-old female apoE(-/-) mice were treated with D-4F (300 µg/mL in drinking water) or placebo for 6 weeks. Kidneys were harvested and examined for histological and biochemical characteristics.

RESULTS

Compared with the control mice, apoE(-/-) mice showed significant proteinuria, tubulo-interstitial inflammation, mesangial expansion, foam cell formation and up-regulation of oxidative [NAD(P)H oxidase subunits] and inflammatory [NF-κB, MCP-1, PAI-1 and COX-2] pathways. D-4F administration lowered proteinuria, improved renal histology and reversed up-regulation of inflammatory and oxidative pathways with only minimal changes in plasma lipid levels.

CONCLUSIONS

The apoE(-/-) mice develop proteinuria and glomerular and tubulo-interstitial injury which are associated with up-regulation of oxidative and inflammatory mediators in the kidney and are ameliorated by the administration of apoA-1 mimetic peptide. These observations point to the role of oxidative stress and inflammation in the pathogenesis of renal disease in hyperlipidaemic animals and perhaps humans.

Hydroethidine- and MitoSOX-derived red fluorescence is not a reliable indicator of intracellular superoxide formation: another inconvenient truth

Hydroethidine (HE; or dihydroethidium) is the most popular fluorogenic probe used for detecting intracellular superoxide radical anion. The reaction between superoxide and HE generates a highly specific red fluorescent product, 2-hydroxyethidium (2-OH-E(+)). In biological systems, another red fluorescent product, ethidium, is also formed, usually at a much higher concentration than 2-OH-E(+). In this article, we review the methods to selectively detect the superoxide-specific product (2-OH-E(+)) and the factors affecting its levels in cellular and biological systems. The most important conclusion of this review is that it is nearly impossible to assess the intracellular levels of the superoxide-specific product, 2-OH-E(+), using confocal microscopy or other fluorescence-based microscopic assays and that it is essential to measure by HPLC the intracellular HE and other oxidation products of HE, in addition to 2-OH-E(+), to fully understand the origin of red fluorescence. The chemical reactivity of mitochondria-targeted hydroethidine (Mito-HE, MitoSOX red) with superoxide is similar to the reactivity of HE with superoxide, and therefore, all of the limitations attributed to the HE assay are applicable to Mito-HE (or MitoSOX) as well.

Apolipoprotein A-I and serum amyloid A plasma levels are biomarkers of acute painful episodes in patients with sickle cell disease

BACKGROUND

Acute painful episodes are the clinical hallmark of sickle cell disease and have been linked to morbidity and mortality in the sickle cell population.

DESIGN AND METHODS

We undertook exploratory proteomic studies on paired plasma samples collected from a cohort of 26 adult sickle cell patients during steady state and on the first day of an acute painful episode. We screened for changes in abundance of specific protein peaks via surface-enhanced laser desorption/ionization time of flight mass spectrometry (SELDI-TOF MS), and confirmed the identify of candidate protein peaks by specific immunoassays.

RESULTS

The levels of hemoglobin, hematocrit, total protein, and albumin were lower and the levels of lactate dehydrogenase and absolute reticulocytes higher during acute painful episodes than during the steady state. Surface-enhanced laser desorption/ionization time of flight mass spectrometry spectral analysis consistently showed a mass-to-charge peak at 11.7 kDa with elevated intensities during acute painful episodes, which correlated significantly with the serum amyloid A immunoassay. Serum amyloid A levels were significantly elevated during acute painful episodes, especially in four patients with marked end-organ complications of such episodes. A second, recurring peak, less abundant during acute painful episodes, was present at 28.1 kDa; this peak was correlated significantly with immunoassay measurements of apolipoprotein A1.

CONCLUSIONS

On the average, plasma serum amyloid A rises and apolipoprotein AI falls during acute painful episodes. The serum amyloid A/apolipoprotein AI ratio increased in 81% of the patients during acute painful episodes, potentially making it a useful objective marker of such episodes. We propose that these protein alterations, known to contribute to endothelial dysfunction in other settings, might do likewise acutely in acute painful episodes and present a new target for therapeutic intervention in sickle cell disease. (ClincalTrials.gov Identifier: NCT00081523).

HDL metabolism and activity in chronic kidney disease

Chronic kidney disease (CKD) is associated with development of atherosclerosis and premature death from cardiovascular disease. The predisposition of patients with CKD to atherosclerosis is driven by inflammation, oxidative stress and dyslipidemia, all of which are common features of this condition. Markers of dyslipidemia in patients with advanced CKD are impaired clearance and heightened oxidation of apolipoprotein-B-containing lipoproteins and their atherogenic remnants, and a reduction of the plasma concentration, antioxidant, and anti-inflammatory properties of high-density lipoprotein (HDL). Studies in animal models of CKD indicate that the disease promotes lipid accumulation in the artery wall and kidney, leading to atherosclerosis, glomerulosclerosis and tubulointerstitial injury. These effects seem to be mediated by an increased cellular influx of lipids, elevated cellular production and reduced cellular catabolism of fatty acids, and impaired antioxidant, anti-inflammatory and reverse lipid transport properties of HDL. Available pharmacological therapies have been largely ineffective in ameliorating oxidative stress, inflammation, HDL deficiency and/or dysfunction, and the associated atherosclerosis and cardiovascular disease in patients with end-stage renal disease. This Review aims to provide an overview of the mechanisms and consequences of CKD-induced HDL deficiency and dysfunction.

The 5A apolipoprotein A-I mimetic peptide displays antiinflammatory and antioxidant properties in vivo and in vitro

OBJECTIVE

The apolipoprotein (apo)A-I mimetic peptide 5A is highly specific for ATP-binding cassette transporter (ABC)A1-mediated cholesterol efflux. We investigated whether the 5A peptide shares other beneficial features of apoA-I, such as protection against inflammation and oxidation. Methods- New Zealand white rabbits received an infusion of apoA-I, reconstituted high-density lipoprotein (HDL) containing apoA-I ([A-I]rHDL), or the 5A peptide complexed with phospholipids (1-palmitoyl-2-linoleoyl phosphatidylcholine [PLPC]), before inserting a collar around the carotid artery. Human coronary artery endothelial cells (HCAECs) were incubated with (A-I)rHDL or 5A/PLPC before stimulation with tumor necrosis factor alpha. Results- ApoA-I, (A-I)rHDL, and 5A/PLPC reduced the collar-mediated increase in (1) endothelial expression of cell adhesion molecules vascular cell adhesion molecule-1 and intercellular adhesion molecule-1; (2) production, as well as the expression of the Nox4 catalytic subunits of the NADPH oxidase; and (3) infiltration of circulating neutrophils into the carotid intima-media. In HCAECs, both 5A/PLPC and (A-I)rHDL inhibited tumor necrosis factor-alpha-induced intercellular adhesion molecule-1 and vascular cell adhesion molecule-1 expression, as well as the nuclear factor kappaB signaling cascade and production. The effects of the 5A/PLPC complex were no longer apparent in HCAECs knocked down for ABCA1.

CONCLUSIONS

Like apoA-I, the 5A peptide inhibits acute inflammation and oxidative stress in rabbit carotids and HCAECs. In vitro, the 5A peptide exerts these beneficial effects through interaction with ABCA1.

Pathophisiology of sickle cell disease and new drugs for the treatment

A homozygous mutation in the gene for β globin, a subunit of adult hemoglobin A (HbA), is the proximate cause of sickle cell disease (SCD). Sickle hemoglobin (HbS) shows peculiar biochemical properties, which lead to polymerizing when deoxygenated. HbS polymerization is associated with a reduction in cell ion and water content (cell dehydration), increased red cell density which further accelerate HbS polymerization. Dense, dehydrated erythrocytes are likely to undergo instant polymerization in conditions of mild hypoxia due to their high HbS concentration, and HbS polymers may be formed under normal oxygen pressure. Pathophysiological studies have shown that the dense, dehydrated red cells may play a central role in acute and chronic clinical manifestations of sickle cell disease, in which intravascular sickling in capillaries and small vessels leads to vaso-occlusion and impaired blood flow in a variety of organs and tissue. The persistent membrane damage associated with HbS polymerization also favors the generation of distorted rigid cells and further contributes to vaso-occlusive crisis (VOCs) and cell destruction in the peripheral circulation. These damaged, dense sickle red cells also show a loss of phospholipid asymmetry with externalization of phosphatidylserine (PS), which is believed to play a significant role in promoting macrophage recognition with removal of erythrocytes (erythrophagocytosis). Vaso-occlusive events in the microcirculation result from a complex scenario involving the interactions between different cell types, including dense, dehydrated sickle cells, reticulocytes, abnormally activated endothelial cells, leukocytes, platelets and plasma factors such as cytokine and oxidized pro-inflammatory lipids. Hydroxycarbamide (hydroxyurea) is currently the only drug approved for chronic administration in adult patients with sickle cell disease to prevent acute painful crises and reduce the incidence of transfusion and acute chest crises. Here, we will focus on consolidated and experimental therapeutic strategies for the treatment of sickle cell disease, including:

agents which reduce or prevent sickle cell dehydration

agents which reduce sickle cell-endothelial adhesive events

nitric oxide (NO) or NO-related compounds

anti-oxidant agents

Correction of the abnormalities ranging from membrane cation transport pathways to red cell-endothelial adhesive events, might constitute new pharmacological targets for treating sickle cell disease.

In vitro stimulation of HDL anti-inflammatory activity and inhibition of LDL pro-inflammatory activity in the plasma of patients with end-stage renal disease by an apoA-1 mimetic peptide

Features of end-stage renal disease such as oxidative stress, inflammation, hypertension, and dyslipidemia are associated with accelerated atherosclerosis and increased risk of death from cardiovascular disease. By inhibiting the formation and increasing the disposal of oxidized lipids, HDL exerts potent antioxidant and anti-inflammatory actions. Given that apolipoproteinA-1 can limit atherosclerosis, we hypothesized that an apolipoproteinA-1 mimetic peptide, 4F, may reduce the proinflammatory properties of LDL and enhance the anti-inflammatory properties of HDL in uremic plasma. To test this, plasma from each of 12 stable hemodialysis patients and age-matched control subjects was incubated with 4F or vehicle. The isolated HDL and LDL fractions were added to cultured human aortic endothelial cells to quantify monocyte chemotactic activity, thus measuring their pro- or anti-inflammatory index. The LDL from the hemodialysis patients was more pro-inflammatory and their HDL was less anti-inflammatory than those of the control subjects. Pre-incubation of the plasma from the hemodialysis patients with 4F decreased LDL pro-inflammatory activity and enhanced HDL anti-inflammatory activity. Whether 4F or other apolipoproteinA-1 mimetic peptides will have any therapeutic benefit in end-stage renal disease will have to be examined directly in clinical studies.

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.

Vasculoprotective Effects of Apolipoprotein Mimetic Peptides: An Evolving Paradigm In Hdl Therapy (Vascular Disease Prevention, In Press.)

Anti-atherogenic effects of high density lipoprotein (HDL) and its major protein component apolipoprotein A-I (apoA-I) are principally thought to be due to their ability to mediate reverse cholesterol transport. These agents also possess anti-oxidant properties that prevent the oxidative modification of low density lipoprotein (LDL) and anti-inflammatory properties that include inhibition of endothelial cell adhesion molecule expression. Results of the Framingham study revealed that a reduction in HDL levels is an independent risk factor for coronary artery disease (CAD). Accordingly, there has been considerable interest in developing new therapies that specifically elevate HDL cholesterol. However, recent evidence suggests that increasing circulating HDL cholesterol levels alone is not sufficient as a mode of HDL therapy. Rather, therapeutic approaches that increase the functional properties of HDL may be superior to simply raising the levels of HDL per se. Our laboratory has pioneered the development of synthetic, apolipoprotein mimetic peptides which are structurally and functionally similar to apoA-I but possess unique structural homology to the lipid-associating domains of apoA-I. The apoA-I mimetic peptide 4F inhibits atherogenic lesion formation in murine models of atherosclerosis. This effect is related to the ability of 4F to induce the formation of pre-β HDL particles that are enriched in apoA-I and paraoxonase. 4F also possesses anti-inflammatory and anti-oxidant properties that are independent of its effect on HDL quality per se. Recent studies suggest that 4F stimulates the expression of the antioxidant enzymes heme oxygenase and superoxide dismutase and inhibits superoxide anion formation in blood vessels of diabetic, hypercholesterolemic and sickle cell disease mice. The goal of this review is to discuss HDL-dependent and -independent mechanisms by which apoA-I mimetic peptides reduce vascular injury in experimental animal models.

The L-4F mimetic peptide prevents insulin resistance through increased levels of HO-1, pAMPK, and pAKT in obese mice

We examined mechanisms by which L-4F reduces obesity and diabetes in obese (ob) diabetic mice. We hypothesized that L-4F reduces adiposity via increased pAMPK, pAKT, HO-1, and increased insulin receptor phosphorylation in ob mice. Obese and lean mice were divided into five groups: lean, lean-L-4F-treated, ob, ob-L-4F-treated, and ob-L-4F-LY294002. Food intake, insulin, glucose adipocyte stem cells, pAMPK, pAKT, CB1, and insulin receptor phosphorylation were determined. Subcutaneous (SAT) and visceral adipose tissue (VAT) were determined by MRI and hepatic lipid content by magnetic resonance spectroscopy. SAT and VAT volumes decreased in ob-L-4F-treated animals compared with control. L-4F treatment decreased hepatic lipid content and increased the numbers of small adipocytes (P < 0.05) and phosphorylation of insulin receptors. L-4F decreased CB1 in SAT and VAT and increased pAKT and pAMPK in endothelium. L-4F-mediated improvement in endothelium was prevented by LY294002. Inhibition of pAKT and pAMPK by LY294002 was associated with an increase in glucose levels. Upregulation of HO-1 by L-4F produced adipose remodeling and increased the number of small differentiated adipocytes. The anti-obesity effects of L-4F are manifested by a decrease in visceral fat content with reciprocal increases in adiponectin, pAMPK, pAKT, and phosphorylation of insulin receptors with improved insulin sensitivity.

Proteomic identification of altered apolipoprotein patterns in pulmonary hypertension and vasculopathy of sickle cell disease

Pulmonary arterial hypertension (PAH) is emerging as a major complication and independent risk factor for death among adults with sickle cell disease (SCD). Using surface-enhanced laser desorption/ionization time of flight mass spectrometry (SELDI-TOF MS), we searched for biomarkers of PAH in plasma specimens from 27 homozygous sickle cell anemia (HbSS) patients with PAH and 28 without PAH. In PAH patients, analysis consistently showed lower abundance of a 28.1-kDa peak (P < .001), identified by high-resolution mass spectrometry as the oxidant-scavenging protein apolipoprotein A-I (apoA-I), which correlated with clinical assays of apoA-I (r = .58, P < .001) and high-density lipoprotein (HDL) levels (r = .50, P = .001). Consistent with endothelial dysfunction that may mediate this effect in PAH, HbSS patients with lower apoA-I levels also displayed impaired vasodilatory responses to acetylcholine (mean +/- SEM, 189% +/- 34% [n = 13] vs 339% +/- 51% [n = 13], P < .001). As a group, patients with SCD demonstrated significantly lower apoA-I levels than African-American control subjects. The PAH cohort was further characterized by high levels of apolipoproteins A-II and B and serum amyloid A, and low levels of haptoglobin dimers and plasminogen. These results imply a relationship of apolipoproteins to the development of PAH vasculopathy in SCD, potentially involving an unexpected mechanistic parallel to atherosclerosis, another proliferative vasculopathy.

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.

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.

Emerging antidyslipidemic drugs

BACKGROUND

Many patients at high risk for coronary heart disease (CHD) fail to reach target lipid levels with currently available medications, and a small but clinically relevant proportion of patients experience adverse effects. Thus, additional pharmaceutical strategies are required to fill these gaps in efficacy and tolerability.

OBJECTIVE

To provide an overview of both current and emerging antidyslipidemic drugs.

METHODS

For the current antidyslipidemic drugs, we focus primarily on statins, bile acid sequestrants, fibrates, ezetimibe, and niacin. Emerging antidyslipidemic drugs herein discussed were identified by searching the Pharmaprojects database for 'hypercholesterolemia drugs' (Phase II or Phase III), 'HDL-based therapies', and 'PCSK9 inhibition'.

RESULTS/CONCLUSIONS

Combinations of currently existing medications are most easily applicable. Meanwhile, strategies to raise HDL-C rely on a deep understanding of the complexity of HDL metabolism. Furthermore, novel approaches to further reduce LDL-C warrant careful evaluation of benefit-risk ratio. Finally, the medical community will have to rely on late-phase CHD outcome studies as the final arbiter of clinical application for any new antidyslipidemia treatment.

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.

Vascular dysfunction in a murine model of severe hemolysis

Spectrin is the backbone of the erythroid cytoskeleton; sph/sph mice have severe hereditary spherocytosis (HS) because of a mutation in the murine erythroid alpha-spectrin gene. sph/sph mice have a high incidence of thrombosis and infarction in multiple tissues, suggesting significant vascular dysfunction. In the current study, we provide evidence for both pulmonary and systemic vascular dysfunction in sph/sph mice. We found increased levels of soluble cell adhesion molecules in sph/sph mice, suggesting activation of the vascular endothelium. We hypothesized that plasma hemoglobin released by intravascular hemolysis initiates endothelial injury through nitric oxide (NO) scavenging and oxidative damage. Likewise, electron paramagnetic resonance spectroscopy showed that plasma hemoglobin is much greater in sph/sph mice. Moreover, plasma from sph/sph mice had significantly higher oxidative potential. Finally, xanthine oxidase, a potent superoxide generator, is decreased in subpopulations of liver hepatocytes and increased on liver endothelium in sph/sph mice. These results indicate that vasoregulation is abnormal, and NO-based vasoregulatory mechanisms particularly impaired, in sph/sph mice. Together, these data indicate that sph/sph mice with severe HS have increased plasma hemoglobin and NO scavenging capacity, likely contributing to aberrant vasoregulation and initiating oxidative damage.

Sickle cell disease vasculopathy: a state of nitric oxide resistance

Sickle cell disease (SCD) is a hereditary hemoglobinopathy characterized by microvascular vaso-occlusion with erythrocytes containing polymerized sickle (S) hemoglobin, erythrocyte hemolysis, vasculopathy, and both acute and chronic multiorgan injury. It is associated with steady state increases in plasma cell-free hemoglobin and overproduction of reactive oxygen species (ROS). Hereditary and acquired hemolytic conditions release into plasma hemoglobin and other erythrocyte components that scavenge endothelium-derived NO and metabolize its precursor arginine, impairing NO homeostasis. Overproduction of ROS, such as superoxide, by enzymatic (xanthine oxidase, NADPH oxidase, uncoupled eNOS) and nonenzymatic pathways (Fenton chemistry), promotes intravascular oxidant stress that can likewise disrupt NO homeostasis. The synergistic bioinactivation of NO by dioxygenation and oxidation reactions with cell-free plasma hemoglobin and ROS, respectively, is discussed as a mechanism for NO resistance in SCD vasculopathy. Human physiological and transgenic animal studies provide experimental evidence of cardiovascular and pulmonary resistance to NO donors and reduced NO bioavailability that is associated with vasoconstriction, decreased blood flow, platelet activation, increased endothelin-1 expression, and end-organ injury. Emerging epidemiological data now suggest that chronic intravascular hemolysis is associated with certain clinical complications: pulmonary hypertension, cutaneous leg ulcerations, priapism, and possibly stroke. New therapeutic strategies to limit intravascular hemolysis and ROS generation and increase NO bioavailability are discussed.

Apolipoprotein A-I mimetic peptide helix number and helix linker influence potentially anti-atherogenic properties

We hypothesize that apolipoprotein A-I (apoA-I) mimetic peptides better mimicking the punctuated alpha-helical repeats of full-length apoA-I are more anti-inflammatory and anti-atherogenic. This study compares a monomeric apoA-I mimetic helix to three different tandem helix peptides in vitro: 4F (18 mer), 4F-proline-4F (37 mer, Pro), 4F-alanine-4F (37 mer, Ala), and 4F-KVEPLRA-4F [the human apoA-I 4/5 interhelical sequence (IHS), 43 mer]. All peptides cleared turbid lipid suspensions, with 4F being most effective. In contrast to lipid clearance, tandem peptides were more effective at remodeling mouse HDL. All four peptides displaced apoA-I and apoE from the HDL, leaving a larger particle containing apoA-II and peptide. Peptide-remodeled HDL particles show no deficit in ABCG1 cholesterol efflux despite the loss of the majority of apoA-I. Tandem peptides show greater ability to efflux cholesterol from lipid-loaded murine macrophages, compared with 4F. Although 4F inhibited oxidation of purified mouse LDL, the Ala tandem peptide increased oxidation. We compared several tandem 4F-based peptides with monomeric 4F in assays that correlated with suggested anti-inflammatory/anti-atherogenic pathways. Tandem 4F-based peptides, which better mimic full-length apoA-I, exceed monomeric 4F in HDL remodeling and cholesterol efflux but not LDL oxidation protection. In addition, apoA-I mimetic peptides may increase reverse cholesterol transport through both ABCA1 as well as ABCG1 pathways.

Is raising HDL a futile strategy for atheroprotection?

The dramatic failure of clinical trials evaluating the cholesterol ester transfer protein inhibitor torcetrapib has led to considerable doubt about the value of raising high-density lipoprotein cholesterol (HDL-C) as a treatment for cardiovascular disease. These results have underscored the intricacy of HDL metabolism, with functional quality perhaps being a more important consideration than the circulating quantity of HDL. As a result, HDL-based therapeutics that maintain or enhance HDL functionality warrant closer investigation. In this article, we review the complexity of HDL metabolism, discuss clinical-trial data for HDL-raising agents, including possible reasons for the failure of torcetrapib, and consider the potential for future HDL-based therapies.

Mechanisms of vasculopathy in sickle cell disease and thalassemia

Many mechanisms contribute to the complex pathophysiology of sickle cell disease (SCD), with dysfunction of the vascular endothelium as a unifying theme. Specifically, hemolysis-associated low arginine and nitric oxide (NO) bioavailability, amplified by NO synthase uncoupling, elevated arginase activity, superoxide production, oxidative stress, accumulation of arginine analogs such as asymmetric dimethylarginine, ischemia-reperfusion injury, inflammation, apolipoprotein A-1 depletion, and a hypercoagulable state are significant mechanisms contributing to endothelial dysfunction. Genetic polymorphisms also influence disease severity. Clearly the variable spectrum of disease is the consequence of multiple events and genetic susceptibility that go beyond the occurrence of a single amino acid substitution in the beta globin chain of hemoglobin. Recent studies begin to demonstrate overlap among these seemingly unrelated processes. Impaired NO bioavailability represents the central feature of endothelial dysfunction, and is a common denominator in the pathogenesis of vasculopathy in SCD. The consequences of decreased NO bioavailability include endothelial cell activation, upregulation of the potent vasoconstrictor endothelin-1, vasoconstriction, platelet activation, increased tissue factor, and activation of coagulation, all of which ultimately translate into the clinical manifestations of SCD. Evidence supporting vasculopathy subphenotypes in SCD, including pulmonary hypertension, priapism, cutaneous leg ulceration, and stroke, will be reviewed and relevance to other hemolytic disorders including the thalassemia syndromes will be considered.

Novel small molecule therapeutics for sickle cell disease: nitric oxide, carbon monoxide, nitrite, and apolipoprotein A-I

A hemolysis-linked subphenotype of sickle cell disease (SCD), characterized by pulmonary hypertension, stroke, priapism and leg ulcers, is associated with decreased nitric oxide bioavailability and vasculopathy. Vasculopathy appears to have a multifactorial etiology, including mechanisms primarily that involve deficient nitric oxide (NO) signaling, but also involving altered function of NO synthase related to substrate availability and cooperating factors such as apolipoproteins. Improved understanding of the vascular pathophysiology of SCD has led to new vascular targets for translational research in SCD. This growing vascular therapeutics field in SCD is complementary to the ongoing efforts to reduce the morbidity of vaso-occlusive pain crisis. This presentation will review the current biology and translational clinical development of novel small molecules targeting sickle cell vasculopathy. Strategies targeting the hemeoxygenase-carbon monoxide pathway, the arginine-NO synthase-cGMP-phosphodiesterase 5 pathway, the nitrate-nitrite-NO pathway, and the apolipoprotein A-I pathways will be reviewed. In this context, current clinical trials of inhaled NO, CO, nitrite, sildenafil and apoA-I mimetics will be discussed.

Redox-dependent impairment of vascular function in sickle cell disease

The vascular pathophysiology of sickle cell disease (SCD) is influenced by many factors, including adhesiveness of red and white blood cells to endothelium, increased coagulation, and homeostatic perturbation. The vascular endothelium is central to disease pathogenesis because it displays adhesion molecules for blood cells, balances procoagulant and anticoagulant properties of the vessel wall, and regulates vascular homeostasis by synthesizing vasoconstricting and vasodilating substances. The occurrence of intermittent vascular occlusion in SCD leads to reperfusion injury associated with granulocyte accumulation and enhanced production of reactive oxygen species. The participation of nitric oxide (NO) in oxidative reactions causes a reduction in NO bioavailability and contributes to vascular dysfunction in SCD. Therapeutic strategies designed to counteract endothelial, inflammatory, and oxidative abnormalities may reduce the frequency of hospitalization and blood transfusion, the incidence of pain, and the occurrence of acute chest syndrome and pulmonary hypertension in patients with SCD.

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.

A heat shock protein 90 binding domain in endothelial nitric-oxide synthase influences enzyme function

Previous reports suggest heat shock protein 90 (hsp90) associates with endothelial nitric-oxide synthase (eNOS) to increase nitric oxide (*NO) generation. Ansamycin inhibition of chaperone-dependent activity increases eNOS generation of superoxide anion (O(2)(*)) upon enzyme activation. In the present study we identify where hsp90 binds to eNOS using overlapping decoy peptides based on the amino acid (aa) sequence of eNOS (291-420). B1, B2, and B3 peptides inhibited hsp90 association with eNOS in cell lysates from proliferating bovine aortic endothelial cells. B2 (aa 301-320), common to both B1 and B3, decreased stimulated *NO production and hsp90 association in bovine aortic endothelial cells. The B2/B3 peptide was redesigned to TSB2 that includes a TAT protein transduction domain and shortened to 14 aa. TSB2 impaired vasodilation of isolated facialis arteries in vitro and in vivo and increased eNOS-dependent O(2)(*) generation in native endothelial cells on mouse aortas, whereas a control peptide, TSB(Ctr), which has the four glutamic acids in TSB2 substituted with alanine, showed no such effects. Site-directed mutagenesis of eNOS at 310, 314, 318, and 323 Glu to Ala yields an eNOS mutant that exhibited reduced hsp90 association and generated O(2)(*) rather than *NO upon activation. Together, these data demonstrate that hsp90 associates with eNOS at aa 310-323. Moreover, a decoy peptide based on this sequence is sufficient to displace hsp90 from eNOS and uncouple eNOS activity from *NO generation. Thus, Glu-310, Glu-314, Glu-318, and Glu-323 in eNOS, although each does not do much by itself, synergistically they increase "cooperativity" in the association step that is critical for maintaining hsp90-eNOS interactions and promoting coupled eNOS activity. Such chaperone-dependent signaling may play an important role in modulating the balance of *NO and O(2)(*) generation from eNOS and, therefore, vascular function.

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.

Increasing apoA-I production as a target for CHD risk reduction

Dyslipidemia leading to coronary heart diseases (CHD) enables venues to prevent or treat CHD by other strategies than only lowering serum LDL cholesterol (LDL-C) concentrations, which is currently the most frequently targeted change. Unlike LDL-C, elevated high-density lipoprotein cholesterol (HDL-C) concentrations may protect against the development of CHD as demonstrated in numerous large-scale epidemiological studies. In this review we describe that besides elevating serum HDL-C concentrations by increasing alpha-HDL particles, approaches to elevate HDL-C concentrations by increasing pre-beta HDL particle concentrations seems more attractive. Besides infusion of apoA-I(Milano), using apoA-I mimetics, or delipidation of alpha-HDL particles, elevating de novo apoA-I production may be a suitable target to functionally increase pre-beta HDL particle concentrations. Therefore, a detailed description of the molecular pathways underlying apoA-I synthesis and secretion, completed with an overview of known effects of pharmacological and nutritional compounds on apoA-I synthesis will be presented. This knowledge may ultimately be applied in developing dietary intervention strategies to elevate apoA-I production and serum HDL-C concentrations and consequently lower CHD risk.

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.

The strange case of Dr HDL and Mr HDL: Does a NO’s story illuminate the mystery of HDL’s dark side uncovered by Dr HDL’s drug targeting CETP?

Recently, the first large-scale morbidity and mortality trial (ILLUMINATE) to evaluate the cardiovascular end points of a CETP inhibitor (torcetrapib) has been prematurely stopped because the mortality was significantly increased in the treated group. Why torcetrapib caused excess death is not known. Based on the fact that HDL interacts with endothelial nitric oxyde synthase (eNOS) and nitric oxide (NO) secretion, which partly controlled blood pressure and than torcetrapib could increase blood pressure among some patients, we hypothesize that CETP inhibition could have significantly inhibit eNOS. CETP inhibition would have enlarged HDL size resulting in a deficit in the interaction between HDL and the Scavenger Receptor class B type I (SR-BI), which is an important link between HDL and eNOS activation. We suggest than the deficit in NO secretion would have been sufficient among all patients to induce a destabilization of the plaques of atheroma, but could have induced a pathogenic increase in blood pressure only in patients whose eNOS activity was naturally weak due to genetic polymorphisms of this enzyme. We also hypothesize that the increase in HDL levels, induced by CETP inhibition, coupled with the capacity of HDL to induce endothelin-1 secretion would have aggravated the cardiovascular risks under this CETP inhibitor treatment.

Endothelium-derived microparticles induce endothelial dysfunction and acute lung injury

Acute lung injury (ALI) carries a high mortality in critically ill patients. Recent reports correlate elevated concentrations of endothelium-derived microparticles (EMPs) with diseases of endothelial dysfunction. Many of these diseases have ALI sequelae. We hypothesize that EMPs contribute to endothelial cell (EC) dysfunction and development of ALI. To test this hypothesis, we treated isolated vessels with EMPs and examined changes in vasodilation. Endothelial cell cultures were incubated with EMPs and examined for changes in stimulated nitric oxide (*NO) production and nitric oxide synthase (eNOS) activation. Finally, EMPs were injected into rats and mice and lungs examined for ALI. In both mouse and human ex vivo vessel preparations, we found a marked attenuation of endothelium-mediated vasodilation after EMP treatment (4 x 10(6)/mL). This dysfunction was not corrected by pretreatment of EMPs with free radical scavengers. Coincubation of EMPs with EC cultures yielded a three-fold reduction in A23187-stimulated *NO release. Western analysis of these cells showed a corresponding decrease in eNOS phosphorylation at Ser1179 and a decrease in hsp90 association. Measurements of lung permeability, myeloperoxidase activity, and histology of EMPs-treated Brown Norway rats demonstrated pulmonary edema, neutrophil recruitment, and compromise of the endothelial-alveolar barrier as a second hit phenomenon. In C57BL/6 mice, exogenous EMPs caused a significant rise in pulmonary capillary permeability both as a primary and secondary injury. These findings demonstrate EMPs are capable of inducing significant lung injury at pathophysiologically relevant concentrations. Endothelium-derived microparticles inhibit endothelium-mediated vasodilation and *NO generation from eNOS. Once elucidated, EMP mechanisms of inducing ALI and endothelial dysfunction may present new therapeutic targets.

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.

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.

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.

Endothelial and antithrombotic actions of HDL

It is well recognized that high-density lipoprotein (HDL)-cholesterol is antiatherogenic and serves a role in mediating cholesterol efflux from cells. However, HDL has multiple additional endothelial and antithrombotic actions that may also afford cardiovascular protection. HDL promotes the production of the atheroprotective signaling molecule nitric oxide (NO) by upregulating endothelial NO synthase (eNOS) expression, by maintaining the lipid environment in caveolae where eNOS is colocalized with partner signaling molecules, and by stimulating eNOS as a result of kinase cascade activation by the high-affinity HDL receptor scavenger receptor class B type I (SR-BI). HDL also protects endothelial cells from apoptosis and promotes their growth and their migration via SR-BI-initiated signaling. As importantly, there is evidence of a variety of mechanisms by which HDL is antithrombotic and thereby protective against arterial and venous thrombosis, including through the activation of prostacyclin synthesis. The antithrombotic properties may also be related to the abilities of HDL to attenuate the expression of tissue factor and selectins, to downregulate thrombin generation via the protein C pathway, and to directly and indirectly blunt platelet activation. Thus, in addition to its cholesterol-transporting properties, HDL favorably regulates endothelial cell phenotype and reduces the risk of thrombosis. With further investigation and resulting greater depth of understanding, these mechanisms may be harnessed to provide new prophylactic and therapeutic strategies to combat atherosclerosis and thrombotic 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.

Advances in the management of sickle cell disease

This article summarizes my presentation at the Pediatric Hematology-Oncology Symposium in honor of Dr. Stephen A. Feig in April 2005. Areas highlighted reflect key topics whose evolution parallel and were impacted by Steve's exceptional academic career. It is by no means an exhaustive summation of all advances in the biology and treatment of sickle cell disease. The interested reader is encouraged to consider a number of well written recently published reviews that cover additional areas of scientific and medical advancement in the pathophysiology and care of sickle cell disease 1-5.

Inflammatory markers and serum lipids in idiopathic dilated cardiomyopathy

Coronary microcirculation is impaired in idiopathic dilated cardiomyopathy (IDC), possibly because of endothelial dysfunction. High-density lipoproteins (HDLs) have the potential to regulate endothelial function and modulate inflammation and the innate immune response. This study investigated whether reduced HDLs, concomitantly with the activation of inflammation, are associated with IDC. Fifty-five patients with IDC, without evidence of other organ or systemic, chronic, or recurrent diseases, were compared with 55 healthy controls for HDLs and complete lipid profiles, C-reactive protein, C3 and C4 complement fractions, soluble intercellular adhesion molecule-1 and soluble endothelial leukocyte adhesion molecule-1, haptoglobin, and ceruloplasmin. Patients with IDC differed from controls, with lower HDL levels, lower apolipoprotein A-I and A-II levels, and higher triglyceride levels, but not on total and low-density lipoprotein cholesterol, apolipoprotein B, or lipoprotein(a). In addition, all measured inflammation markers were significantly greater in patients with IDC than in controls and were negatively correlated with HDLs. A strong and independent association with IDC was found for age, soluble intercellular adhesion molecule-1, and HDLs that, when categorized as <40 or >40 mg/dl, showed the strongest association (prevalence odds ratio 0.10, p <0.0005) with the disease. In conclusion, the data here reported on reduced HDLs and increased endothelial inflammatory activation and the linear negative correlation between HDLs and inflammation markers, particularly soluble intercellular adhesion molecule-1, could suggest a role for HDLs in the endothelial-microvascular dysfunction seen in IDC.

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.

Effects of D-4F on vasodilation and vessel wall thickness in hypercholesterolemic LDL receptor-null and LDL receptor/apolipoprotein A-I double-knockout mice on Western diet

Previously we showed L-4F, a novel apolipoprotein A-I (apoA-I) mimetic, improved vasodilation in 2 dissimilar models of vascular disease: hypercholesterolemic LDL receptor-null (Ldlr(-/-)) mice and transgenic sickle cell disease mice. Here we determine the mechanisms by which D-4F improves vasodilation and arterial wall thickness in hypercholesterolemic Ldlr(-/-) mice and Ldlr(-/-)/apoA-I null (apoA-I(-/-)), double-knockout mice. Ldlr(-/-) and Ldlr(-/-)/apoA-I(-/-) mice were fed Western diet (WD) with and without D-4F. Oral D-4F restored endothelium- and endothelial NO synthase (eNOS)-dependent vasodilation in direct relationship to duration of treatments and reduced wall thickness in as little as 2 weeks in vessels with preexisting disease in Ldlr(-/-) mice. D-4F had no effect on total or HDL cholesterol concentrations but reduced proinflammatory HDL levels. D-4F had no effect on plasma myeloperoxidase concentrations but reduced myeloperoxidase association with apoA-I as well as 3-nitrotyrosine in apoA-I. D-4F increased endothelium- and eNOS-dependent vasodilation in Ldlr(-/-)/apoA-I(-/-) mice but did not reduce wall thickness as it had in Ldlr(-/-) mice. Vascular endothelial cells were treated with 22(R)-hydroxycholesterol with and without L-4F. 22(R)-Hydroxycholesterol decreased NO (*NO) and increased superoxide anion (O2*-) production and increased ATP-binding cassette transporter-1 and collagen expression. L-4F restored *NO and O2*- balance, had little effect on ATP-binding cassette transporter-1 expression, but reduced collagen expression. These data demonstrate that although D-4F restores vascular endothelial cell and eNOS function to increase vasodilation, HDL containing apoA-I, or at least some critical concentration of the antiatherogenic lipoprotein, is required for D-4F to decrease vessel wall thickness.

High-density lipoprotein cholesterol in the cardiovascular equation: does the "good" still count?

This article will discuss our current understanding of the role of HDL-C in the statin era, focusing on the question as to whether HDL-C still "counts" when determining cardiovascular risk. Epidemiologic evidence consistently demonstrates that low HDL-C is a strong and independent risk factor for CHD. The epidemiologic evidence is complimented by clinical data showing that interventions that raise HDL-C are associated with reductions in CHD risk, as well as by a growing body of experimental data demonstrating biologically plausible mechanisms that may underlie the observed clinical findings. Analyses of large statin trials also indicate that the significant and independent relationship between HDL-C and CHD risk persists despite the therapeutic effects of statins, and that HDL-C levels in statin-treated patients, both at baseline and in response to statin therapy, are relevant. Early studies on novel HDL targeting therapies are promising, but their long term safety profile and impact on clinical outcomes is yet to be determined in larger studies. Recent guidelines emphasize low HDL-C as an independent risk factor for cardiovascular disease, specifically identify HDL-C as a target for intervention, and encourage the use of HDL-C raising interventions in high-risk patients with low HDL-C levels.