Synthesis and Application of Novel Apolipoprotein Mimetics

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DESCRIPTION (provided by applicant): Apolipoprotein A-I (apoA-I), the major protein component of high-density lipoprotein (HDL), regresses atherosclerosis in animals by several biological mechanisms. Elevated plasma levels of discoidal (pre-?) HDL particles, which are rich in apoA-I, protect against atherosclerosis and coronary heart disease in humans. Human apoA-I is comprised of 10 amphiphilic (or amphipathic) ?-helices (eight 22-mers and two 11-mers) that act together to bind lipids and engender a range of HDL particles. Interestingly, the 18-mer amphiphilic, class A, ?-helical peptide Ac-DWFKAFYDKVAEKFKEAF-NH2 (4F) can mimic many of apoA-I's functional properties. The dramatic difference between the apoA-I and 4F molecules raises important questions about structure vs. function in that we may wonder: (1) how a simple, isolated helix can function so well and (2) what would be the effect of incorporating multiple helices of this type into a single molecular entity. A principal aim of this proposal is to devise molecules with a multiplicity of amphiphilic ?-helices that are attached to a molecular scaffold, covering a range of 2-8 helical subunits systematically. We propose to design, synthesize, characterize, and explore novel chemical species that can mimic apoA-I. These nanomaterials, composed of a distinct scaffold bearing multiple, amphiphilic, class A ?-helical peptides, of appropriate dimensions in the size domain of native HDL (6-12 nm), will be physically characterized and biologically evaluated in vitro, alone and lipidated in the form of HDL-like nanoparticles (i.e. nanolipids). The structures of interest will constitute dimers, trimers, tetramers, hexamers, and octamers with linear and branched chain topologies. We plan to investigate these designer materials packaged with phospholipid, such as (R)-(+)-1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) or soy lecithin, in the form of recombinant HDL (rHDL) particles. Studies will be conducted on the self-assembled nanolipids in lipid-poor (discoidal) and lipid-rich (spherical) states, with and without cholesterol present, to gain insight into structure and function, in comparison with 4F and native apoA-I. We plan to assess the potential antiatherogenic properties of derived HDL-like nanodiscs via in vitro bioassays, such as HDL particle remodeling and cholesterol efflux from cells in culture. We plan to analyze our designer nanolipids for acquired protein components after their exposure to plasma by using proteomics techniques (e.g. MALDI-TOF MS). This lipidology research should provide valuable information on: (1) factors involved in nanolipid particle stabilization and morphology, (2) structure-function properties of nanolipid particles, and (3) protein-lipid association that is relevant to HDL. Our results may establish a platform for potential therapeutic agents to treat atherosclerosis by the regression of atherosclerotic plaque in vivo. PUBLIC HEALTH RELEVANCE: In human studies, elevated plasma levels of apoA-I, the major protein in HDL, correlated inversely with the development of coronary heart disease. We propose to design, synthesize, and explore specific molecular entities that can mimic apoA-I. This project could provide a blueprint for new drugs to combat heart disease.