Abstract
BACKGROUND: Safe, efficacious therapy for treating degenerate deep digital flexor tendon (DDFT) and navicular bone fibrocartilage (NBF) in navicular horses is critically necessary. While archetypal orthobiologic therapies for navicular disease are used empirically, their safety and efficacy are unknown. Mesenchymal stem cell-derived extracellular vesicles (EV) may overcome several limitations of current orthobiologic therapies. OBJECTIVES: To (1) characterise cytokine and growth factor profiles of equine bone marrow mesenchymal stem cell (BM-MSC)-derived extracellular vesicles (BM-EV) and (2) evaluate the in vitro anti-inflammatory and extracellular matrix (ECM) protective potentials of BM-EV on DDFT and NBF explant co-cultures in an IL-1β inflammatory environment. STUDY DESIGN: In vitro experimental study. METHODS: Cytokines (IL-1β, IL-6, IL-10, IL-1ra and TNF-α) and growth factors (TGFβ1, VEGF, IGF1 and PDGF) in equine BM-EV isolated via ultracentrifugation and precipitation methods were profiled. Forelimb DDFT and NBF explant co-cultures from seven horses were exposed to media alone, or media containing 2 × 10(9) ± 0.1 × 10(9) particles/mL or 10 μg/mL BM-EV (BM-EV), 10 ng/mL interleukin-1β (IL-1β), or IL-1β + BM-EV for 48 h. Co-culture media IL-6, TNF-α, MMP-3, MMP-13 concentrations and explant sulphated glycosaminoglycan (sGAG) content were quantified. RESULTS: IL-6, IGF1 and VEGF concentrations were 102.1 (37.61-256.2) and 182.3 (163.1-226.3), 72.3 (8-175.6) and 2.4 (0.1-2.6), 108.3 (38.3-709.1) and 211.4 (189.1-318.2) pg/mL per 2 × 10(9) ± 0.1 × 10(9) particles/mL or 10 μg/mL 10 μg of BM-EV isolated via ultracentrifugation and precipitation methods, respectively. Co-culture media MMP-3 in BM-EV- (p = 0.03) and BM-EV + IL-1β-treated (p = 0.01) groups were significantly lower than the respective media and IL-1β groups. DDFT explant sGAG content of BM-EV (p = 0.003) and BM-EV + IL-1β groups were significantly higher compared with IL-1β group. MAIN LIMITATIONS: Specimen numbers are limited, in vitro model may not replicate clinical case conditions, lack of non-MSC-derived EV control group. CONCLUSIONS: Equine BM-EV contains IL-6 and growth factors, IGF1 and VEGF. The anti-inflammatory and ECM protective potentials of BM-EV were evident as increased IL-6 and decreased MMP-3 concentrations in the DDFT-NBF explant co-culture media. These results support further evaluation of BM-EV as an acellular and 'off-the-shelf' intra-bursal/intrasynovial therapy for navicular pathologies.