Secretion of growth factors from macrophages when cultured with microparticles.

The aim of this study is to investigate the influence of macrophages on osteoblast (OB) performance and differentiation. In this regard, we studied the secretion of growth factors including bone morphogenetic proteins (BMPs) from before and after activation of macrophages. We also evaluated osteogenic markers in the co-culture of macrophages and OBs. The macrophages were seeded on microparticles (MPs) based on chitosan (CS). Two types of MPs were fabricated including CS MPs and 10% calcium phosphate (CaHPO4 )-incorporated CS MPs. Macrophage seeded on MPs was activated using lipopolysaccharide (LPS). The expression of BMP-2, BMP-6, BMP-7, and transforming growth factor beta (TGF-β) from macrophages seeded and cultured on hybrid MPs before and after activation of LPS at predetermined times was quantified using a quantitative reverse transcription-polymerase chain reaction (RT-PCR). All of the above growth factors were expressed from MP-macrophage cultures before LPS activation. Osteogenic markers such as alkaline phosphatase (ALP), osteocalcin (OCN), and collagen I (COL-I) in the cultures of MP-OB-macrophage were quantified using a quantitative RT-PCR at days 2, 4, and 7. We found an elevation of gene expression of ALP and COL-1 in the co-cultures of OB-macrophage on MPs compared to OB on MP cultures. These data suggest that macrophages enhance expression of osteogenic markers in OBs, and demonstrate the importance of the role of macrophages in bone regeneration.