Pharmacological immunomodulation enhances peripheral nerve regeneration

Enhanced femoral nerve regeneration after tubulization with a tyrosine-derived polycarbonate terpolymer: effects of protein adsorption and independence of conduit porosity

Following complete nerve transection, entubulation of the nerve stumps helps guide axons to reconnect distally. In this study, a biodegradable and noncytotoxic tyrosine-derived polycarbonate terpolymer composed of 89.5 mol% desaminotyrosyl tyrosine ethyl ester (DTE), 10 mol% desaminotyrosyl tyrosine (DT), and 0.5 mol% poly(ethylene glycol) (PEG, molecular weight [Mw]=1 kDa) [designated as E10-0.5(1K)] was used to fabricate conduits for peripheral nerve regeneration. These conduits were evaluated against commercially available nonporous polyethylene (PE) tubes. The two materials are characterized in vitro for differences in surface properties, and the conduits are then evaluated in vivo in a critical-sized nerve defect in the mouse femoral nerve model. Conduits were fabricated from E10-0.5(1K) in both porous [P-E10-0.5(1K)] and nonporous [NP-E10-0.5(1K)] configurations. The results illustrate that adsorption of laminin, fibronectin, and collagen type I was enhanced on E10-0.5(1K) compared to PE. In addition, in vivo the E10-0.5(1K) conduits improved functional recovery over PE conduits, producing regenerated nerves with a fivefold increase in the number of axons, and an eightfold increase in the percentage of myelinated axons. These increases were observed for both P-E10-0.5(1K) and NP-E10-0.5(1K) after 15 weeks. When conduits were removed at 7 or 14 days following implantation, an increase in Schwann cell proteins and fibrin matrix formation was observed in E10-0.5(1K) conduits over PE conduits. These results indicate that E10-0.5(1K) is a pro-regenerative material for peripheral nerves and that the porosity of P-E10-0.5(1K) conduits was inconsequential in this model of nerve injury.

Effect of neurotrophic factor, MDP, on rats' nerve regeneration

Our objective was to determine the immune-modulating effects of the neurotrophic factor N-acetylmuramyl-L-alanyl-D-isoglutamine (MDP) on median nerve regeneration in rats. We used male Wistar rats (120-140 days of age, weighing 250-332 g) and compared the results of three different techniques of nerve repair: 1) epineural neurorrhaphy using sutures alone (group S - 10 rats), 2) epineural neurorrhaphy using sutures plus fibrin tissue adhesive (FTA; group SF - 20 rats), and 3) sutures plus FTA, with MDP added to the FTA (group SFM - 20 rats). Functional assessments using the grasp test were performed weekly for 12 weeks to identify recovery of flexor muscle function in the fingers secondary to median nerve regeneration. Histological analysis was also utilized. The total number and diameter of myelinated fibers were determined in each proximal and distal nerve segment. Two indices, reported as percentage, were calculated from these parameters, namely, the regeneration index and the diameter change index. By the 8th week, superiority of group SFM over group S became apparent in the grasping test (P = 0.005). By the 12th week, rats that had received MDP were superior in the grasping test compared to both group S (P < 0.001) and group SF (P = 0.001). Moreover, group SF was better in the grasping test than group S (P = 0.014). However, no significant differences between groups were identified by histological analysis. In the present study, rats that had received MDP obtained better function, in the absence of any significant histological differences.