Evaluation of Lipid-Based Nanoparticles for the Treatment of Cardiovascular Diseases

Abstract

Nearly 17.9 million people die every year from cardiovascular-related diseases, which accounts for 31% of all deaths worldwide. Endogenous high-density lipoproteins (HDL) are natural cardioprotective particles that have been shown to reduce cardiovascular related risks, such as progression of atherosclerosis, inflammation, and endothelial dysfunction. Therefore, synthetic high-density lipoproteins (sHDL) have been synthesized to mimic the natural cardioprotective behaviors of endogenous HDL. In this work, we investigated the therapeutic potential of both sHDL and HDL-mimetic micelles for improving endothelial function and treating atherosclerosis, respectively, and understand how the lipid composition affects the activity of particles in vitro and in vivo, and the remodeling of the particle in the presence of other endogenous lipoproteins contained in human serum.

In chapter 2, we synthesized a library of micelles composed of different phosphatidylcholine (PC) lipids and ratios of PC to PEGylated lipids and tested these micelles in vitro and in vivo to better understand how lipid properties influence the physiochemical activity and therapeutic potential of our micelles for the treatment of atherosclerosis. Overall, micelle composition did not affect the cholesterol efflux capabilities of the particles in vitro. Micelles composed of more fluid lipids and micelles containing less PEG lipid had a more potent effects on cytokine levels in vitro, while more PEGylated micelles had a longer circulation half-life and mobilized more cholesterol in vivo. Therefore, a fine balance must be achieved to determine the composition of micelles with optimal therapeutic benefit and favorable pharmacokinetics.

In Chapter 3, we investigated the potential therapeutic benefit of sHDLs on endothelial function. sHDLs were prepared using 22A, an ApoA-1 mimetic peptide, and different PC lipids. In lipopolysaccharide (LPS) activated human umbilical vein endothelial cells (HUVECs), sHDL decreased the expression of adhesion molecules, including VCAM-1, ICAM-1, and E-selectin. DMPC-sHDLs showed the ability to increase nitric oxide release from HUVECs. Furthermore, DMPC-sHDL treatment slightly reduced Evans blue dye leakage through the blood brain barrier on the injured hemisphere in a traumatic brain injury murine model, suggesting positive effects of sHDLs on endothelial integrity. Further studies will need to be completed to determine the optimal composition of sHDL and to explore its potential in improving endothelial function.

In Chapter 4, we evaluated the effect of lipid composition on the stability and remodeling of sHDL in human serum containing other endogenous lipoprotein populations. Blank sHDLs, as well as sHDLs encapsulating DiD or GW3965, were prepared with different PC lipids (POPC, DMPC, DPPC and DSPC) and 22A. Lipoprotein populations were separated out by size exclusion chromatography (SEC) after incubation of sHDL with human serum and concentration of sHDL components within each fraction was measured by liquid chromatography-mass spectrometry (LCMS). Overall, DSPC-sHDLs remained the most intact with sHDL components and cargo staying within HDL elution times to the largest extent after incubation with human serum. POPC-sHDLs showing the most remodeling and movement of components to larger lipoprotein populations over time. Together, our findings show that the lipid composition of sHDLs affects the remodeling in human serum, suggesting that lipid composition must be considered when designing sHDLs as therapeutics and drug delivery systems.

In summary, we found that the lipid composition of HDL-mimicking micelles and sHDL affects the particle’s overall activity, pharmacokinetics, stability and remodeling, making composition a crucial factor to consider when optimizing lipid-based nanoparticles as therapeutics.