The effect of chondroitinase on nerve regeneration following composite tissue allotransplantation

Purpose: To improve the degree of functional return and sensibility provided by composite tissue allotransplantation, enhanced nerve regeneration is essential. Chondroitin sulfate proteoglycans are found in the extracellular matrix of nerves and inhibit regenerating axons after injury. Treatment with chondroitinase to remove chondroitin sulfate proteoglycans has been shown to improve nerve regeneration in isolated nerve graft and transection-and-repair models. This study assesses the efficacy of chondroitinase as a neurotherapeutic agent in the setting of composite tissue allotransplantation. Methods: Adult Lewis rats received either orthotopic hind limb transplants from Brown Norway rat donors (n = 12) or sciatic nerve transection and repair (n = 6). Following approximation of the sciatic nerve, half the animals received intraneural injections of chondroitinase in saline and the other half received intraneural injections of saline alone. Five weeks after transplantation, we killed the animals and analyzed nerves with nonbiased quantitative nerve histomorphometry. One day after transection and repair, we killed animals and harvested sciatic nerves for immunohistochemical staining of cleaved chondroitin sulfate proteoglycans epitope and laminin. We used unpaired t-tests for statistical analysis. Results: Distal to the suture line, chondroitinase-treated animals demonstrated statistically greater total number of fibers and nerve density compared with controls. There were no statistically significant differences in fiber number or nerve density proximal to the suture line or in fiber widths. We observed staining of cleaved chondroitin sulfate proteoglycan epitopes only in treated animals, with no differences observed in the degree of laminin staining. Conclusions: Intraneural injection of chondroitinase cleaved inhibitory chondroitin sulfate proteoglycans without disrupting proregenerative laminin and resulted in enhanced nerve regeneration after composite tissue allotransplantation. Studies at later time points are needed to assess whether this enhanced nerve regeneration will produce improved functional return. Clinical relevance: This study identifies a promising therapeutic agent that has the potential to enhance nerve regeneration and functional outcomes for patients undergoing composite tissue allotransplantation.