Abstract
Titanium and titanium-based alloys are widely used in orthopaedic implants. Total joint replacement is very successful; however, the foreign body response and chronic inflammation caused by implant-derived biomaterial debris still remain as unsolved issues. Aseptic loosening accompanied by wear debris-induced osteolysis (bone loss) is one of the most frequent causes for late failure and revision surgery. Mesenchymal stem cells (MSCs) and IL-4 may be possible treatment strategies because of their immunomodulatory properties. We investigated the efficacy of novel MSC-based treatments on immunomodulation and osteogenic differentiation in an innovative cell coculture model of titanium particle-induced inflammation in the periprosthetic tissues. MSCs and macrophages were collected from the bone marrow of Balb/c mice. Both MSCs and macrophages (representing endogenous cells at the periprosthetic tissue) were seeded on the bottom wells of the 24-well transwell plates. We generated genetically modified NF-κB sensing IL-4 secreting MSCs (inflammatory responsive MSCs) and MSCs preconditioned by lipopolysaccharide and TNF-α to further enhance their immunomodulatory function. These modified MSCs (representing exogenous therapeutic cells implanted to the periprosthetic tissue) were seeded on the upper chambers of the transwell plates. These cocultures were then exposed to titanium particles for 7 days. NF-κB sensing IL-4 secreting MSCs showed strong immunomodulation (significantly reduced TNF-α and induced Arg1 expression) and promoted early osteogenesis (significantly induced Runx2, ALP, and β-catenin as well as reduced Smurf2 expression) at day 7. IL-4 secreting MSCs also decreased TNF-α protein secretion as early as day 3 and increased IL-1ra protein secretion at day 7, suggesting efficacious immunomodulation of particle-induced inflammation. Preconditioned MSCs did not show significant immunomodulation in this short-term experiment, but ALP and β-catenin expression were significantly induced at day 7. Our results suggest that genetically modified IL-4 secreting MSCs and preconditioned MSCs have the potential to optimize bone regeneration in inflammatory conditions including periprosthetic osteolysis.