Background: Osteoarthritis (OA) in the horse is an economic and welfare issue and there are no current disease modifying drugs available. Stem cells have been suggested as a therapeutic intervention for OA, originally on the basis of their regenerative capacity. However, it is hypothesised that mesenchymal stem cells (MSC) exert their effects via paracrine factors including the production of extracellular vesicles that can themselves recapitulate the MSC effects in the joint. Objectives: To isolate extracellular vesicles from bone marrow MSC and investigate their anti-inflammatory effects on chondrocytes. Study design: An in vitro assessment of the effect of direct culturing extracellular vesicles on artificially inflamed chondrocytes. Methods: Extracellular vesicles were isolated from bone marrow MSC using differential sequential ultracentrifugation. Vesicles were characterised using electron microscopy, nanoparticle tracing analysis and protein analysis. Vesicle internalisation was carried out via vesicles being pre-stained and co-cultured with equine chondrocytes before analysis using confocal microscopy. The effects of vesicles on artificially inflamed chondrocytes was examined using quantitative PCR. Results: To the best of the authors' knowledge, this is the first study to isolate and characterise extracellular vesicles from equine bone MSC. Vesicles were taken up by autologous chondrocytes and had anti-inflammatory effects on gene expression following chondrocyte exposure to tumour necrosis factor α and Interleukin 1β. Main limitations: Only three independent biological repeats were performed and the work was done in vitro. Conclusion: Extracellular vesicles can be isolated from equine bone marrow MSC; they may be taken up by chondrocytes and have an anti-inflammatory action.

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Background Osteoarthritis (OA) in the horse is an economic and welfare issue and there are no current disease modifying drugs available. Stem cells have been suggested as potential therapeutics for OA, originally on the basis of their regenerative capacity. However, it is now hypothesised that MSCs exert their effects via paracrine factors including the production of extracellular vesicles, that can themselves recapitulate the MSC effects in the joint. Results In this study we have, for the first time, isolated and characterised extracellular vesicles from equine bone marrow stem cells. We have shown these vesicles can be taken up by autologous chondrocytes and have anti-inflammatory effects on gene expression following chondrocyte exposure to tissue necrosis factor α and Interleukin 1β. No effects on chonodrocyte proliferation or migration was observed. Conclusion Extracellular vesicles can be isolated from equine bone marrow mesenchymal stem cells, they are taken up by chondrocytes and have an anti-inflammatory action.