Delayed repair of singly transected and segmental-loss peripheral nerve injuries in rat sciatic nerves using optimized PEG-fusion protocols and stored viable peripheral nerve allografts.

Abstract

Singly transected and segmental-loss peripheral nerve injuries (ST- and SL-PNIs) produce immediate loss of sensorimotor functions. Polyethylene glycol (PEG)-fusion repairs performed immediately following ST- and SL-PNIs improve long-term outcomes in animal models, with SL-PNIs repaired using fresh or 1-to-3 day stored viable peripheral nerve allografts (VPNAs). Here, we propose several optimizations for the existing PEG-fusion protocols to repair ST- and SL-PNIs with a delay of 24-48 h post-injury, using longer stored VPNAs for SL-PNIs, both conditions critical for translating PEG-fusion to the clinic. Optimized PEG-fusion protocols to repair ST- and SL-PNIs of the rat sciatic nerve include the additional steps of topical application of low-dose epinephrine and/or local administration of methylprednisolone. Electrophysiological recordings were used to assess the success of surgeries, and Sciatic Functional Index and end-point nerve morphology were performed to assess long-term recovery. For longer VPNA storage, a static storage protocol was established, and the viability of VPNAs was assessed electrophysiologically prior to transplantation and morphologically. Together, our optimized PEG-fusion and static storage protocols successfully repair ST- and SL-PNIs with a delay of at least 24 h, with SL-PNIs repaired using VPNAs stored for at least 3 weeks. Topical application of low-dose epinephrine stops intraoperative bleeding and improves behavioral recovery. Local administration of methylprednisolone following PEG-fusion eliminates microvasculitis and further improves behavioral recovery. The findings in this study using rats, along with the ongoing PEG-fusion clinical trials, suggest the feasibility of clinically translating delayed PEG-fusion repair for ST- or SL-PNIs in humans, and support further investigation into the storage of VPNAs at tissue banks.