Cholesterol Within Phosphatidylcholine Liposomes Attenuates the Expression of Cytokines

Lipid nanoparticles (LNPs) have gained increased interest for their use as carriers of therapeutic drugs and vaccines. These particles can encapsulate high concentrations of chemical drugs and nucleic acids within their lumen, providing protection from the activity of lytic agents. The central components of LNPs are phospholipids that, due to their amphiphilic nature, spontaneously assemble into vesicular structures. The major phospholipid used for LNPs is phosphatidylcholine (PC), which is often supplemented with cholesterol and polyethylene glycol. Phospholipids within LNPs have been considered inert components. However, we have shown that liposomes made of palmitoyl oleoyl phosphatidylcholine (POPC) or palmitoyl oleoyl phosphatidylserine (POPS) induce a massive alteration of gene expression within macrophages (Mϕ), particularly genes involved in the inflammatory response. These observations suggest that phospholipids could play an independent biological role in modulating cellular responses. Since cholesterol plays a crucial role in cellular functions and is a regular component of LNPs, we investigated the effect of the sterol on the inflammatory response induced by POPC liposomes. We reported herewith that the presence of free cholesterol within liposomes reduces the inflammatory response induced by phospholipids. This effect was not recapitulated by esterified or water-soluble cholesterol and was not dependent on the acidification of late endosomes/lysosomes. Finally, the reduction in cytokine expression by the sterol was due to a decrease in the activation of NF-kB. Thus, the incorporation of cholesterol into LNPs suppresses the inflammatory response induced by the particles.