Phosphatidylserine-containing liposomes: Potential pharmacological interventions against inflammatory and immune diseases through the production of prostaglandin E₂ after uptake by myeloid derived phagocytes

Phosphatidylserine (PS), which is normally located on the inner leaflet of the plasma membrane, translocates to the outer leaflet at the early stage of apoptosis. The PS externalization provides a signal for phagocytes to initiate uptake of apoptotic cells. After phagocytosis of apoptotic cells, phagocytes induce the secretion of anti-inflammatory mediators including prostaglandin E₂ (PGE₂). PS-containing liposomes (PSLs) can mimic the effects of apoptotic cells on phagocytes to induce the secretion of PGE ₂. PSLs induce the PGE₂ secretion from microglia without induction of either cyclooxygenase (COX)-2 or microsomal prostaglandin E synthase (mPGES)-1. PSLs are found to rather utilize COX-1/mPGES-2 system to produce PGE₂ secretion and then shift microglia and macrophages from pro- to anti-inflammatory phenotype by an autocrine action of PGE₂. Moreover, PSLs inhibit the maturation of dendritic cells and osteoclast precursors. Therefore, PSLs will be potential pharmacological interventions for inflammatory and immune diseases through feedback mechanism utilizing PGE ₂.