Amphiphilic galactomannan nanoparticles trigger the alternative activation of murine macrophages

Macrophages are highly plastic phagocyte cells that can exist in distinct phenotypes and play a key role in physiological and pathological pathways and they can be classically activated macrophages to the pro-inflammatory M1 phenotype or alternatively activated to an M2 anti-inflammatory one by various stimuli in the biological milieu. Different biomaterials have been shown to trigger macrophage polarization to M1 or M2 phenotypes and emerged as a very promising strategy to modulate macrophage activation. In this work, we investigated the ability of amphiphilic nanoparticles made of hydrolyzed galactomannan, a natural polysaccharide of galactose and mannose, and poly(methyl methacrylate) with a hydrodynamic diameter of approximately 130 nm, which can encapsulate drug, to trigger macrophage polarization. The macrophage compatibility and uptake are shown in RAW264.7 murine macrophages by a metabolic assay, confocal laser scanning fluorescence microscopy (CLSFM) and imaging flow cytometry in the absence and the presence of endocytosis inhibitors. Results indicated that the nanoparticles internalized by both clathrin- and caveolin- mediated endocytosis. The ability of these drug-free nanoparticles to change macrophages phenotype towards the M2- like phenotype is confirmed by the downregulation of the M1 marker cluster of differentiation 80 (CD80), and upregulation of M2 markers CD163 and CD206, as measured by flow cytometry and CLSFM, and switch an M1 to an M2 phenotype. In addition, we preliminarily assess the effect of the nanoparticles on wound healing by tracking the healing of an artificial wound of RAW264.7 macrophages in a scratch assay. Findings indicate a faster closure of the wound in the presence of the nanoparticles with respect to untreated cells. Finally, a migration assay utilizing a macrophage/fibroblast co-culture model in vitro demonstrates that M2 polarization increases fibroblast migration by 24-fold. These findings demonstrate the ability of this nanotechnology platform to interfere and change the macrophages phenotype in vitro and represent solid evidence for the investigation of their therapeutic performance in vivo.