Modulation of the anti-inflammatory effects of phosphatidylserine-containing liposomes by PEGylation.

Inhibiting liposome uptake by macrophages using polyethylene glycol (PEG) surface modifications is a widely used approach for extending the half-life of liposomes circulating in the blood. However, the biological effects of PEGylated liposomes on macrophages have not yet been thoroughly investigated. The purpose of this study was to examine the effects of PEGylated phosphatidylserine-containing liposomes (PEG-PSLs) on the expression of two inflammation-associated cytokines, tumor necrosis factor-α (TNF-α) and transforming growth factor-β (TGF-β), in the murine macrophage-like cell line RAW 264.7. Previous studies have demonstrated that PSLs inhibit TNF-α secretion and enhance TGF-β synthesis in macrophages by mimicking apoptotic cells. We found that PEGylation differentially affected the TNF-α and TGF-β levels. The PSL-mediated inhibitory effect on TNF-α secretion was enhanced by PEGylation, and PEG-PSLs decreased TGF-β levels compared with non-PEGylated PSLs. Fluorescence-activated cell sorting analysis demonstrated that 1% PEGylation disturbed the incorporation of PSLs into macrophages. The interference of uptake is thought to extend the binding interaction between PS to PS receptors for PSL-mediated inhibition of TNF-α expression. Together, these findings indicate that PEG-PSLs can prevent TNF-α secretion without increasing TGF-β levels in macrophages, and they support the potential clinical use of PEG-PSLs as anti-inflammatory agents with a relatively low potential to induce tissue fibrosis. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 1479-1486, 2017.