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.

Reduced levels of HDL cholesterol (HDL-C) are a strong independent predictor of coronary artery disease (CAD) risk. The major anti-atherogenic function of HDL is to mediate reverse cholesterol transport. This response is highly dependent on apoA-I and apoE, protein components of HDL. Randomized clinical trials have assessed effects of several classes of drugs on plasma cholesterol levels in CAD patients. Agents including cholestyramine, fibrates, niacin, and statins significantly lower LDL cholesterol (LDL-C) and induce modest increases in HDL-C, but tolerance issues and undesirable side effects are common. Additionally, residual risk may be present in patients with persistently low HDL-C and other complications despite a reduction in LDL-C. These observations have fueled interest in the development of new pharmacotherapies that positively impact circulating lipoproteins. The goal of this review is to discuss the therapeutic potential of synthetic apolipoprotein mimetic peptides. These include apoA-I mimetic peptides that have undergone initial clinical assessment. We also discuss newer apoE mimetics that mediate the clearance of atherogenic lipids from the circulation and possess anti-inflammatory properties. One of these (AEM-28) has recently been given orphan drug status and is undergoing clinical trials.

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-NH ₂ ) possesses both antidyslipidemic and antiinflammatory properties. Methods and Results— A single bolus (15 mg/kg IV) of Ac-hE-18A-NH ₂ 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.

We previously showed ( 1 Datta G. Chaddha M. Garber D.W. Chung B-H. Tytler E.M. Dashti N. Bradley W.A. Gianturco S.H. Anantharamaiah G.M. The receptor binding domain of apolipoprotein E, linked to a model class A amphipathic helix, enhances internalization and degradation of LDL by fibroblasts. Biochemistry. 2000; 39 : 213-220 Crossref PubMed Scopus (55) Google Scholar ) that a peptide, Ac-hE18A-NH₂, in which the arginine-rich heparin-binding domain of apolipoprotein E (apoE) [residues 141–150] (LRKLRKRLLR), covalently linked to 18A (DWLKAFYDKVAEKLKEAF; a class A amphipathic helix with high lipid affinity), enhanced LDL uptake and clearance. Because VLDL and remnants contain more cholesterol per particle than LDL, enhanced hepatic clearance of VLDL could lead to an effective lowering of plasma cholesterol. Therefore, in the present article we compared the ability of this peptide to mediate/facilitate the uptake and degradation of LDL and VLDL in HepG2 cells. The peptide Ac-hE18A-NH₂, but not Ac-18A-NH₂, enhanced the uptake of LDL by HepG2 cells 5-fold and its degradation 2-fold. The association of the peptides with VLDL resulted in the displacement of native apoE; however, only Ac-hE18A-NH₂ but not Ac-18A-NH₂ caused markedly enhanced uptake (6-fold) and degradation (3-fold) of VLDL. Ac-hE18A-NH₂ also enhanced the uptake (15-fold) and degradation (2-fold) of trypsinized VLDL Sf 100–400 (containing no immunodetectable apoE), indicating that the peptide restored the cellular interaction of VLDL in the absence of its essential native ligand (apoE). Pretreatment of HepG2s with heparinase and heparitinase abrogated all peptide-mediated enhanced cellular activity, implicating a role for cell-surface heparan sulfate proteoglycans (HSPG). Intravenous administration of Ac-hE18A-NH₂ into apoE gene knockout mice reduced plasma cholesterol by 88% at 6 h and 30% at 24 h after injection. We conclude that this dual-domain peptide associates with LDL and VLDL and results in rapid hepatic uptake via a HSPG-facilitated pathway. —Datta, G., D. W. Garber, B. H. Chung, M. Chaddha, N. Dashti, W. A. Bradley, S. H. Gianturco, and G. M. Anantharamaiah. Cationic domain 141-150 of apoE covalently linked to a class A amphipathic helix enhances atherogenic lipoprotein metabolism in vitro and in vivo.