Effect of adipose-derived nucleated cell fractions on tendon repair in horses with collagenase-induced tendinitis

Objective - To assess the potential of adipose-derived nucleated cell (ADNC) fractions to improve tendon repair in horses with collagenase-induced tendinitis. Animals - 8 horses. Procedures - Collagenase was used to induce tendinitis in the superficial digital flexor tendon of 1 forelimb in each horse. Four horses were treated by injection of autogenous ADNC fractions, and 4 control horses were injected with PBS solution. Healing was compared by weekly ultrasonographic evaluation. Horses were euthanatized at 6 weeks. Gross and histologic evaluation of tendon structure, fiber alignment, and collagen typing were used to define tendon architecture. Biochemical and molecular analyses of collagen, DNA, and proteoglycan and gene expression of collagen type I and type III, decorin, cartilage oligomeric matrix protein (COMP), and insulin-like growth factor-I were performed. Results - Ultrasonography revealed no difference in rate or quality of repair between groups. Histologic evaluation revealed a significant improvement in tendon fiber architecture; reductions in vascularity, inflammatory cell infiltrate, and collagen type III formation; and improvements in tendon fiber density and alignment in ADNC-treated tendons. Repair sites did not differ in DNA, proteoglycan, or total collagen content. Gene expression of collagen type I and type III in treated and control tendons were similar. Gene expression of COMP was significantly increased in ADNC-injected tendons. Conclusions and Clinical Relevance - ADNC injection improved tendon organization in treated tendons. Although biochemical and molecular differences were less profound, tendons appeared architecturally improved after ADNC injection, which was corroborated by improved tendon COMP expression. Use of ADNC in horses with tendinitis appears warranted.