Phagostimulatory effect of uptake of PLGA microspheres loaded with rifampicin on alveolar macrophages

Our previous results on the phagocytic activity of alveolar macrophages (Mϕs) toward poly(lactic-co-glycolic) acid microspheres (PLGA MS) loaded with the anti-tuberculosis agent rifampicin (R-PLGA MS) suggest that the phagocytosis of R-PLGA MS enhances the phagocytic activity of Mϕ cells [17]. To confirm this possibility, we examined the effect of phagocytosis of R-PLGA MS and polystyrene latex (PSL) MS on the phagocytic uptake of fluorescent PSL (F-PSL) MS by cells of the rat alveolar macrophage cell line NR8383 at 37 °C. Phagocytic activity was examined in terms of the population of Mϕ cells that had phagocytosed MS (Ntotal) and the total number of MS phagocytosed (ntotal) by counting the phagocytic Mϕ cells and the MS ingested in optical microscopic fields. Phagocytosis of R-PLGA MS enhanced about 1.5 times the values of Ntotal and ntotal of the phagocytosis of F-PSL MS under the conditions where the phagocytosis of F-PSL MS did not attain the saturated level. In contrast, the phagocytosis of PSL MS did not enhance the phagocytic activity of Mϕ cells toward F-PSL MS. In conclusion, R-PLGA MS are favorable for drug delivery of anti-tuberculosis agents into alveolar Mϕs due to their ability to up-regulate the phagocytosis of MS.