The pharmacological manipulation of Liver X Receptors (LXRs) has been an attractive therapeutic strategy for atherosclerosis treatment as they control reverse cholesterol transport and inflammatory response. In this study, we present the development and efficacy of nanoparticles (NPs) incorporating the synthetic LXR agonist GW3965 (GW) in targeting atherosclerotic lesions. Collagen IV (Col IV) targeting ligands were employed to functionalize the NPs to improve targeting to the atherosclerotic plaque, and formulation parameters such as the length of the polyethylene glycol (PEG) coating molecules were systematically optimized. In vitro studies indicated that the GW-encapsulated NPs upregulated the LXR target genes and downregulated pro-inflammatory mediator in macrophages. The Col IV-targeted NPs encapsulating GW (Col IV-GW-NPs) successfully reached atherosclerotic lesions when administered for 5 weeks to mice with preexisting lesions, substantially reducing macrophage content (~30%) compared to the PBS group, which was with greater efficacy vs. non-targeting NPs encapsulating GW (GW-NPs) (~18%). In addition, mice administered the Col IV-GW-NPs did not demonstrate increased hepatic lipid biosynthesis or hyperlipidemia during the treatment period, unlike mice injected with the free GW. These findings suggest a new form of LXR-based therapeutics capable of enhanced delivery of the LXR agonist to atherosclerotic lesions without altering hepatic lipid metabolism.

Objective: We previously reported smooth muscle cells (SMCs) represent ≥50% of foam cells in human coronary and ≈70% in apoE (apolipoprotein E)-deficient mouse aortic atheromas and exhibit reduced expression of the cholesterol exporter ABCA1 (ATP-binding cassette transporter A1). A major stimulus for ABCA1 expression is flux of cholesterol out of lysosomes, generated by hydrolysis of lipoprotein cholesteryl esters by LAL (lysosomal acid lipase). In this study, we investigated the potential role lysosomal dysfunction might play in foam cell formation by arterial SMCs. Approach and Results: Human monocyte-derived macrophages (macrophages) and arterial SMCs were treated with aggregated LDL (low-density lipoprotein) to increase intracellular cholesterol and investigated for lysosomal and postlysosomal cholesterol metabolism defects. Human and mouse atheromas were analyzed for LAL expression. Unlike macrophages, aggregated LDL uptake failed to upregulate ABCA1 expression, downregulate new cholesterol synthesis, or to significantly increase 27-hydroxycholesterol levels in SMCs. Confocal microscopy revealed retention of neutral lipids within lysosomal compartments in SMCs, while macrophages showed most lipids as cytosolic droplets. LIPA mRNA levels and LAL protein were markedly reduced in SMCs. Treatment of SMCs with medium containing LAL resulted in significantly reduced lysosomal lipid accumulation and increased cholesterol efflux to apoA-I (apolipoprotein AI). Human and mouse atheromas exhibited low LAL/ Lipa expression in intimal SMCs when compared with intimal macrophages. Conclusions: These findings indicate the inherently low level of LAL in SMCs compared with macrophages is associated with reduced capacity to catabolize atherogenic lipoproteins and is a mechanism for SMC foam cell formation in atherosclerosis.

Purpose of review Smooth muscle cells (SMCs) are the major cell type in human atherosclerosis-prone arteries and take up excess lipids, thereby contributing to luminal occlusion. Here we provide a focused review on pathways by which smooth muscle cells (SMCs) can become foam cells in atherosclerosis. Recent findings A synthesis of recent and older investigations provides key mechanistic insights into SMC foam cell formation. LDL and other apoB-containing lipoproteins are modified by a diverse array of oxidative, enzymatic, and nonenzymatic processes present in the arterial intima. These modifications of LDL all promote the aggregation of LDL (agLDL), a key finding from analysis of arterial lesion particles. Scavenger receptor and phagocytic capacity of SMCs can vary greatly, perhaps related to differences in SMC phenotype or in-vitro cell culture environments, and can be increased with exposure to cytokines, growth factors, and cholesterol. Macrophages promote the formation of SMC foam cells in direct or indirect co-culture models. Summary SMCs contribute significantly to the foam cell population in atherosclerosis. Further investigation and identification of key mechanisms of SMC foam cell formation will help drive new therapeutics to reduce cardiovascular disease.