PEGylated phospholipid-coated polylactic acid-glycolic acid microspheres to escape the phagocytosis of alveolar macrophages

Microspheres based on polylactic acid-glycolic acid (PLGA) copolymer have unique advantages in pulmonary controlled drug delivery. However, the clearance mechanism dominated by lung macrophage phagocytosis greatly limits the long-term retention of drugs in the deep lung. In order to avoid the scavenging effect of lung macrophages, the PLGA microspheres coated by polyethylene glycol-distearoyl-glycero-phosphoethanolamine (PEG-DSPE) was designed in this study, and the effect of chain length of PEG-DSPE and its ratio on the macrophage uptake was investigated. With coumarin 6 as a fluorescent probe, the coumarin 6-loaded PLGA microspheres was prepared by premix membrane emulsification/solvent evaporation. The particle size was controlled to 3-5 μm and the encapsulation efficiency was over 90%. After incubation in the cell culture fluid for 48 h, the in vitro leakage of fluorescein from the microspheres was less than 1.5%, eliminating the interference of free fluorescein on the cellular uptake. Murine macrophages RAW264.7 cell line was selected for the in vitro cell study. The preparations showed little toxicity to cells in the cytotoxicity study. Results of the macrophage uptake study showed that PEG₅₀₀₀-DSPE and PEG₁₀₀₀₀-DSPE coated groups with both high and low proportions (PEG-DSPE/PLGA 1:1, 0.25:1) could significantly reduce the phagocytosis of macrophages to microspheres compared with the uncoated PLGA group. For PEG₂₀₀₀-DSPE coated microspheres, the effect of escaping macrophage phagocytosis could be achieved by increasing the ratio of polyethylene glycol (PEG) on the surface of particles. Overall, the chain length of PEG-DSPE and its ratio are the key factors affecting the macrophage uptake. In pulmonary controlled drug delivery, high molecular weight of PEG-DSPE (PEG₅₀₀₀-DSPE and PEG₁₀₀₀₀-DSPE) and the high ratio (PEG-DSPE/PLGA 1:1) of PEG₂₀₀₀-DSPE can be selected to escape the phagocytosis of alveolar macrophages and prolong the drug retention in the lungs.