Neurorrhaphy in Presence of Polyethylene Glycol Enables Immediate Electrophysiological Conduction in Porcine Model of Facial Nerve Injury

Abstract

Facial nerve trauma often leads to disfiguring facial muscle paralysis. Despite several promising advancements, facial nerve repair procedures often do not lead to complete functional recovery. Development of novel repair strategies requires testing in relevant preclinical models that replicate key clinical features. Several studies have reported that fusogens, such as polyethylene glycol (PEG), can improve functional recovery by enabling immediate reconnection of injured axons; however, these findings have yet to be demonstrated in a large animal model. We first describe a porcine model of facial nerve injury and repair, including the relevant anatomy, surgical approach, and naive nerve morphometry. Next, we report positive findings from a proof-of-concept experiment testing whether a neurorrhaphy performed in conjunction with a PEG solution maintained electrophysiological nerve conduction at an acute time point in a large animal model. The buccal branch of the facial nerve was transected and then immediately repaired by direct anastomosis and PEG application. Immediate electrical conduction was recorded in the PEG-fused nerves (n = 9/9), whereas no signal was obtained in a control cohort lacking calcium chelating agent in one step (n = 0/3) and in the no PEG control group (n = 0/5). Nerve histology revealed putative-fused axons across the repair site, whereas no positive signal was observed in the controls. Rapid electrophysiological recovery following nerve fusion in a highly translatable porcine model of nerve injury supports previous studies suggesting neurorrhaphy supplemented with PEG may be a promising strategy for severe nerve injury. While acute PEG-mediated axon conduction is promising, additional work is necessary to determine if physical axon fusion occurs and the longer-term fate of distal axon segments as related to functional recovery.

Engineered neuronal microtissue provides exogenous axons for delayed nerve fusion and rapid neuromuscular recovery in rats

“…Notably, no electrophysiological response was obtained after a delayed nerve repair was completed following TE-NMI transplantation without PEG application ( Fig. S2 , bottom), corroborating our previous findings demonstrating PEG is necessary for electrical conduction [ 34 ]. These electrophysiological findings suggest immediately after nerve repair, exogenous TE-NMI axons were suitable for the PEG nerve fusion protocol at a delayed time point.…”

“…Therefore, additional testing using a human-compatible starting cell source, such as human iPSC-derived neurons, is necessary in immunocompetent and immunocompromised preclinical models. For example, human iPSC-derived TE-NMIs may be tested in a clinically-relevant rodent or porcine models of nerve injury to determine the effects of immunosuppression on babysitting and axon fusion phenomenon [ 34 , 50 ].…”

Orally administered boldine reduces muscle atrophy and promotes neuromuscular recovery in a rodent model of delayed nerve repair

“…For example, a scaled safe and effective dose range can be calculated based on the species body weight and body surface area ( Nair and Jacob, 2016 ). While boldine may be a promising intervention, additional preclinical testing in large animal models is necessary to determine the mechanism(s)-of-action and evaluate functional recovery ( Burrell et al, 2020 , 2021 ; Petrov et al, 2022 ). Additionally, pharmacological treatment of muscle denervation may be a useful adjunct for advanced tissue engineering strategies that replace damaged nervous structures ( Zhang et al, 2018a , b , 2021 , 2022 ; Katiyar et al, 2020 , 2021 ; Shultz et al, 2021 ; Burrell et al, 2022 ; Smith et al, 2022 ).…”