Local (4‐Aminopyridine)‐PLGA‐PEG Treatment Improves Functional Recovery and Muscle Morphology after Traumatic Peripheral Nerve Injury in Mice

Abstract

Traumatic peripheral nerve injury (TPNI) represents a major medical problem resulting in loss of both motor and sensory function, and in severe cases, permanent disability. Inadequate axonal regeneration and delayed muscle reinnervation contribute to muscle atrophy and poor functional recovery. To date, there is no effective pharmacologic treatment which can promote neuromuscular outcomes after TPNI. In repurposing studies, we have shown that daily systemic 4-aminopyridine (4-AP), an FDA-approved potassium channel blocker for multiple sclerosis, enhances functional recovery, improves myelination, and attenuates muscle atrophy after TPNI. However, 4-AP at higher doses cause adverse effects such as seizures. Thus, we sought to develop a novel locally injectable formulation of 4-AP which could be administered to a nerve injury site and deliver 4-AP at a sustained rate for several weeks. We developed (4-AP)-Poly(lactide-co-glycolide)-b-Poly(ethylene glycol)-b-Poly(lactide-co-glycolide) (PLGA-PEG-PLGA), consisting of two FDA-approved, biodegradable, and biocompatible hydrogels. It is unknown whether this locally injectable formulation of 4-AP would have an impact on TPNI-induced functional recovery, as well as on muscle atrophy. In this study, an established mouse model of right sciatic nerve crush injury was used and mice received one of 4 treatments: (4-AP)-PLGA-PEG, PLGA-PEG vehicle, systemic 4-AP, or saline control (n = 5/group). Functional recovery was assessed using sciatic function index, grip strength, and von Frey filament testing. At post-injury day 28, gastrocnemius (GN) and tibialis anterior (TA) muscles were harvested from both injured (innervated by crushed nerve) and uninjured (contralateral healthy) hind limbs for histomorphological analysis. Our results show that a single local administration of (4-AP)-PLGA-PEG remarkably enhanced motor and sensory functional recovery on post-sciatic nerve crush injury days 1, 3, 7, 14, and 21. Histomorphometric analysis of the muscles revealed that (4-AP)-PLGA-PEG treatment significantly increased right TA cross-sectional area (CSA) (1488.2 µm2 vs. 438.4 µm2, p<0.01) and minimum Feret's diameter (MFD) (53.9 µm vs. 30.3 µm, p<0.01) compared with the other groups. Similarly, (4-AP)-PLGA-PEG treatment significantly increased right GN CSA (1213.8 µm2 vs. 471.9 µm2, p<0.001) and MFD (48.5 µm vs. 32.6 µm, p<0.01) compared with the other groups. These preliminary findings on global functional and muscle fiber morphological parameters demonstrate that (4-AP)-PLGA-PEG can be used locally for neuromuscular outcomes after TPNI. Further cellular, molecular, and biochemical studies will define the mechanistic insights for this promising long-acting local therapeutic agent in TPNI.