TEMPOL Enhances Polyethylene Glycol Axon Fusion Following Sciatic Nerve Transection in Adult Rats

Neurotmesis, the most severe form of peripheral nerve injury, involves complete transection and loss of motor and sensory function. Surgical repair, typically via end-to-end neurorrhaphy (NRR), is often required. A key pathological feature is Wallerian degeneration (WD) in the distal stump, which, along with slow axonal regeneration, leads to muscle atrophy and poor functional recovery. Polyethylene glycol (PEG)-mediated axonal fusion has emerged as a promising strategy to bypass WD by rapidly reconnecting severed axons and restoring conduction. Methylene blue (MB) has previously enhanced PEG-fusion outcomes. This study investigated whether TEMPOL (TMP), a potent antioxidant, could further improve PEG-fusion-mediated repair following sciatic nerve transection in rats. Adult female Lewis rats underwent unilateral sciatic nerve transection and were randomly assigned to one of three groups: end-to-end neurorrhaphy (NRR), MB-PEG-fusion (MB-fusion), or TEMPOL-PEG-fusion (TMP-fusion). Functional recovery was assessed for 8 weeks using CatWalk gait analysis (Peroneal Functional Index, PFI). Electrophysiological recordings (CMAPs) were obtained at baseline, immediately post-repair, and at 8 weeks. Histological and immunofluorescence analyses (neurofilament, S100, synaptophysin, GFAP, Iba-1) were performed to evaluate axonal integrity, Schwann cell activity, synaptic coverage, and glial response. TMP-fusion significantly improved motor recovery compared to MB-fusion and NRR. Animals treated with TMP-fusion demonstrated superior sensorimotor function by week 8 (PFI; p = 0.0232, step sequence; p < 0.05), enhanced nerve conduction (CMAPs amplitude, p < 0.05), preserved axonal morphology (NF; p < 0.0001, S100, p = 0.0004), and reduced glial activation (Iba-1, p = 0.0035; GFAP, p = 0.001) compared to NRR. Synaptic integrity in the spinal cord was better maintained in the TMP-fusion group, indicating a more complete restoration of neuromuscular connectivity (p < 0.0001; p = 0.0003). TEMPOL-PEG-fusion significantly enhances structural and functional recovery after neurotmesis, outperforming current gold-standard techniques. These results support TMP-fusion as a promising strategy for peripheral nerve repair.