The effect of intralesional injection of bone marrow derived mesenchymal stem cells and bone marrow supernatant on collagen fibril size in a surgical model of equine superficial digital flexor tendonitis

Reasons for performing study: Collagen fibril size is decreased in repair tissue following tendon injury compared to normal tendon matrix in horses. Mesenchymal stem cells have been suggested to promote regeneration of tendon matrix rather than fibrotic repair following injury, although this concept remains unproven. Objectives: To explore the hypothesis that implantation of autologous mesenchymal stem cells derived from bone marrow into a surgically created central core defect in the superficial digital flexor tendon (SDFT) of horses would induce the formation of a matrix with greater ultrastructural similarities to tendon matrix than the fibrotic scar tissue formed in control defects. Methods: Tissue was collected 16 weeks after induction of injury and 12 weeks after treatment from normal and injured regions of control and treated limbs of 6 horses and examined using transmission electron microscopy. Collagen fibril diameters were measured manually with image analysis software and surface areas calculated. Three parameters assessed for normal and injured tissue were mass average diameter (MAD), collagen fibril index (CFI) and the area dependent diameter (ADD). Results: Normal regions from both treated and control limbs displayed higher MAD and CFI values, as well as a characteristic bimodal distribution in fibril size. Injured regions from both treated and control limbs displayed significantly lower MAD and CFI values, as well as a unimodal distribution in fibril size. There were no significant differences between treated and control limbs for any of the parameters assessed. Conclusions: Intralesional injection of autologous bone marrow derived mesenchymal stem cells had no measurable effect on the fibril diameter of collagen in healing tissue in the SDFT of this experimental model 16 weeks after injury. Potential relevance: Favouring matrix regeneration over fibrotic repair may not be the mechanism by which autologous mesenchymal stem cells assist healing of tendon injury.     

A new insight into cystatin C contained in milk basic protein to bone metabolism: Effects on osteoclasts and osteoblastic MC3T3‐E1 cells in vitro

A milk protein fraction possessing alkaline isoelectric points (milk basic protein [MBP]) improves bone metabolism in vivo, and it inhibits bone resorption by osteoclasts and promotes mouse osteoblastic MC3T3‐E1 cells proliferation in vitro. Cystatin C (CysC) is a component of MBP and shows bone resorption inhibitory activity. Therefore, it is likely that MBP with higher CysC content improves bone metabolism more effectively. In this study, we prepared MBP with low and high contents of CysC and compared its effects on bone metabolism with standard MBP in vitro. Our results showed that the CysC content in MBP was positively related to not only bone resorption inhibitory activity but also MC3T3‐E1 cells proliferative activity. Furthermore, purified CysC stimulated MC3T3‐E1 cells proliferation. These results indicate that CysC contributes to promotion of MC3T3‐E1 cells proliferation, and MBP with higher CysC content shows enhanced bone resorption inhibitory activity and MC3T3‐E1 cells proliferative activity. CysC is considered an important factor in the effect on bone metabolism of MBP.