Templated Spherical High Density Lipoprotein Nanoparticles

Abstract

We report the synthesis of high density lipoprotein (HDL) bio-mimetic nanoparticles capable of binding cholesterol. These structures use a gold nanoparticle core to template the assembly of a mixed phospholipid layer and the adsorption of apolipoprotein A-I. These synthesized structures have the general size and surface composition of natural HDL, and importantly, bind free cholesterol (K d = 4 nM). The determination of the K d for these particles, with respect to cholesterol complexation, provides a key starting and comparison point for measuring and evaluating the properties of subsequently developed synthetic versions of HDL.High density lipoprotein (HDL) is a dynamic serum nanostructure protective against the development of atherosclerosis and resultant illnesses such as heart disease and stroke.1 Increasing circulating serum HDL levels provides a promising therapeutic approach to preventing and, potentially, reversing atherosclerosis by augmenting reverse cholesterol transport.2 -4 However, a facile route to synthetic HDL remains a challenge, as methods to control and mimic the size, surface chemistry, and activity of HDL in vitro diagnostic probes.9 -11 Herein, we report a new Au NP core-shell structure, where the Au NP core serves as a size-and shape-controllable scaffold 12 for constructing an HDL-like particle from phospholipids and apolipoprotein A-I (APOA1). Importantly, the proof-ofconcept HDL-Au NP structure we report is designed to be within the size range of HDL and to mimic the general surface composition of HDL. Furthermore, we demonstrate that, like HDL, HDL-Au NPs are capable of binding cholesterol.In a typical synthesis, an aqueous suspension of citrate-stabilized gold nanoparticles (5 ± 0.75 nm) is mixed with an aqueous solution of purified APOA1 and stirred overnight (Scheme 1).APOA1, comprised of 10 amphipathic alpha helices each with a hydrophobic domain and a negatively charged hydrophilic domain, is the main protein component of HDL and defines the structure and physiology of HDL in vivo. [13][14][15][16] Next, a 1:1 solution of disulfidefunctionalized lipid, 1,2-dipalmitoyl-sn-glycero-3-phosphoethanolamine-N-[3-(2-pyridyldithio)propionate], and amine functionalized lipid, 1-2-dipalmitoyl-sn-glycero-3-phosphocholine, was mixed in CHCl 3 and added to the aqueous suspension of particles in 100-fold excess with respect to the Au NPs. While several ratios were tried, these ratios were found to give loadings of lipid and protein similar to that of natural HDL (vide infra). The disulfide lipid was selected since the disulfide functionality allows for chemisorption to the surface of the Au NP. The amine-modified lipid is a naturally occurring phospholipid known to electrostatically and hydrophobically associate with APOA1. [13][14][15][16] This addition results in a two-phase mixture. Upon gradual heating, CHCl 3 is evaporated and the lipids are transferred to the aqueous phase containing the dispersed Au NPs with APOA1. Note that if the disulfide lipid is added alone and without pri...

Biomimetic, synthetic HDL nanostructures for lymphoma

“…Recently, we developed a biomimetic spherical nanoparticle (HDL-NP) with surface chemical properties similar to natural HDL, including the ability to sequester cholesterol (11)(12)(13). Biomimetic HDL-NPs are synthesized using a 5-nm-diameter gold (Au) nanoparticle (NP) as a size-and shape-restrictive template on which to assemble the surface chemical components of natural HDLs, including phospholipids and the HDL-defining apolipoprotein A1 (Apo A1) (Scheme S1) (11).…”

“…Biomimetic HDL-NPs are synthesized using a 5-nm-diameter gold (Au) nanoparticle (NP) as a size-and shape-restrictive template on which to assemble the surface chemical components of natural HDLs, including phospholipids and the HDL-defining apolipoprotein A1 (Apo A1) (Scheme S1) (11). Importantly, the core AuNP template occupies the real estate in natural cholesterol-rich HDLs reserved for esterified cholesterol, which inherently limits the ability of HDL-NPs to deliver cholesterol.…”

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“…Thaxton et al (22) developed a biomimetic spherical nanoparticle, termed HDL-NP (high density lipoprotein nanoparticle), which has the ability to sequester cholesterol, a feature that is similar to natural HDL. The HDL-NPs were synthesized on a gold nanoparticle (AuNP) on which phospholipids and apolipoprotein A1 were assembled.…”

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“…[1][2][3][4][5] In particular, the conjugation of biomolecules (proteins, enzymes, deoxyribonucleic acid (DNA), and lipids) as well as living cells to both flat and structured gold has been extensively documented. [6][7][8][9][10][11][12][13][14][15][16] Traditionally, biomolecule coupling to gold (or other substrates) is often facilitated by a cross-linking agent and rarely directly to the gold surface itself. Integration of a gold-binding peptide into a biomolecule of interest allows utilization of more complex chemistry and offers the advantage of direct integration with the surface.…”