Assessment of healing in tendons treated with mannose-6-phosphate versus platelet-rich plasma

Tendon healing is plagued by the complications of rupture and adhesion formation. Both of these tend to occur early in healing and are due to improper regulation of collagen formation. Two potential adjunct treatments were vetted for being able to improve the regulation of collagen formation during the early phases of healing. Mannose-6-phosphate (M6P) is a natural sugar that acts at the same receptor as TGF-beta on fibroblasts. Research on M6P has been scarce and centered on its anti-fibrotic effects in multiple body tissues. Platelet-rich plasma (PRP) is a concentrated source of physiologic growth factors. PRP has been widely studied for the treatment of chronic tendinopathy, but available evidence for treatment of acute ruptures is controversial and insufficient. Both treatments were analyzed in a series of in vitro experiments with McCoy fibroblasts to determine safe and effective doses for use in animals.;The rat Achilles tendon is a standard model for use in studies of tendon healing. In this dissertation, rat Achilles tendons were transected and repaired using a double-loop locking suture technique. The tendons were then treated with nothing, directly applied M6P, directly applied PRP, sustained delivery (SD) of M6P, or SD of PRP. Animals were sacrificed after two or four weeks of healing. Tendons from the operative leg and vital organs were harvested upon sacrifice. Organs were processed and prepared for histopathologic examination for evidence of systemic damage. One tendon from each group of eight was processed and sections were stained with H&E, elastin, and trichrome. Additional sections underwent immunostaining for Type I and Type III collagen. The remainder of the tendons in each group were set aside for tensile testing. The choice of seven tendons per group for biomechanical testing was based on a pre hoc calculation of the number of samples required to decipher a significant difference in elastic modulus. All tendons were scanned in a micro-CT scanner prior to tensile testing in order to obtain accurate measurements for cross-sectional area.;Tendons given no adjunct treatment were slow to close the wound gap. Tendon callus contained immature collagen at the periphery, and these tendons had poor biomechanical parameters initially. Direct application of M6P resulted in faster wound closure with more highly organized collagen and higher elastin content. These tendons showed the greatest benefit of all treatment groups over repair alone. Direct application of PRP caused increased production of immature collagen and neovascularization. SD groups showed quicker wound closure than repair alone, but with disorganized collagen and many adipocytes in the PRP SD group. These groups had inferior biomechanical parameters to those seen in tendons that received no adjunct treatment. Immunohistochemistry revealed that all the treatment groups showed more intense staining for Type I collagen, and Type III collagen staining was most prevalent in the PRP groups.;Conclusions drawn from this series of experiments were: 1) conventional application of M6P represents a viable adjunct therapy for the promotion of improved healing through faster, better organized Type I collagen production; 2) PRP does not appear to improve healing in tendons which have undergone acute rupture and repair. Further studies designed to clarify the mechanism of action of M6P on collagen production in fibroblasts and tenocytes are recommended.