Viability, Proliferation, and Chondrogenesis of Equine Bone Marrow-Derived Mesenchymal Stromal Cells After Exposure to Varying Concentrations of Allogeneic Synovial Fluid In Vitro

Intraarticular administration of bone marrow-derived mesenchymal stromal cells (BMSCs) for treatment of acute or chronic joint pathology of the equine athlete has gained clinical interest. The objective of this study was to evaluate the effects of equine allogeneic synovial fluid on viability, proliferation, and chondrogenesis of BMSCs. Bone marrow was collected from eight horses aged 8-14 years old. Synovial fluid was collected from 25 horses aged 4-20 years old. Bone marrow-derived mesenchymal stem cells were cultured in medium supplemented with 25, 50, or 100% (vol/vol) synovial fluid for 72 hours. Viability and proliferation were measured after 24 and 72 hours. Bone marrow-derived mesenchymal stem cells were cultured in micromass for 28 days after which cell viability and glycosaminoglycan (GAG) content was quantified to assess chondrogenesis. A significant increase in viability was observed after 24 hours in culture with greater than 25% synovial fluid supplementation, but no difference in viability was observed after 72 hours of culture. A significant increase in cell number was observed in BMSCs exposed to 100% synovial fluid after 24 and 72 hours. However, no significant difference in cellular proliferation was detected between BMSCs cultured in 100% synovial fluid and control medium after 24 and 72 hours. Bone marrow-derived mesenchymal stem cells became elongated and aggregated into three-dimensional colonies during culture. Additionally, GAG production per viable BMSC in 100% synovial fluid was significantly increased compared to control medium. Supplementation or substitution of culture medium with synovial fluid was able to support BMSC viability, proliferation, and chondrogenesis in vitro.