Hydroxyapatite Coatings Did not Increase TGF-β and BMP-2 Secretion in Murine J774A.1 Macrophages, but Induced a Pro-inflammatory Cytokine Response

Hydroxyapatite (Ca-10(PO2)(6)(OH)(2), HA) coatings are widely used in un-cemented total hip arthroplasties because it increases implant fixation and bone in-growth. HA adsorbs high levels of proteins (e. g., fibronectin) and adhering macrophages release higher levels of BMP-2 compared to non-coated surfaces. Inflammation, however, can block the BMP-2 production from macrophages and it has been suggested that roughened surfaces activate macrophages. Therefore, the aim of the present study was to investigate whether commercially available 3D surfaces would generate increased BMP-2 and TGF-beta production and establish how this production is affected by macrophage activation. A mouse macrophage cell line (J774A.1) was incubated with 3D coatings resembling clinically used protestic surfaces, i.e., plasmaspray TiAlV coating with or without HA and porous TiAlV coating with or without HA. BMP-2 and TGF-beta production was determined after 24 h with ELISA and real time-reverse transcriptase-PCR (real time RT-PCR). Changes in pro-inflammatory response were established with ELISA after 6 and 24 h. The increased surface roughness of HA-coated surfaces was characterized with confocal microscopy. HA coating on plasmasprayed TiAlV coating was not found to induce BMP-2 and TGF-beta secretion in the J774A.1 macrophage cell line. In contrast, LPS-activated macrophages increased their TGF-beta, but not BMP-2, secretion when exposed to the prosthetic surfaces. These results imply that the well-known bone-inductive effects of HA may not be dependent on macrophage BMP-2 and TGF-beta secretion. Surface topography and protein adhesion may play a more pivotal role. (C) Koninklijke Brill NV, Leiden, 2009