(4-Aminopyridine)–PLGA–PEG as a Novel Thermosensitive and Locally Injectable Treatment for Acute Peripheral Nerve Injury

Abstract

Traumatic peripheral nerve injury (TPNI) represents a major medical problem that results in loss of motor and sensory function, and in severe cases, limb paralysis and amputation. To date, there are no effective treatments beyond surgery in selective cases. In repurposing studies, we found that daily systemic administration of the FDA-approved drug 4aminopyridine (4-AP) enhanced functional recovery after acute peripheral nerve injury. This study was aimed at constructing a novel local delivery system of 4-AP using thermogelling polymers. We optimized a thermosensitive (4-AP)−poly(lactide-co-glycolide)−b-poly(ethylene glycol)−b-poly(lactide-co-glycolide) (PLGA−PEG−PLGA) block copolymer formulation. (4-AP)− PLGA−PEG exhibited controlled release of 4-AP both in vitro and in vivo for approximately 3 weeks, with clinically relevant safe serum levels in animals. Rheological investigation showed that (4-AP)−PLGA−PEG underwent a solution to gel transition at 32 °C, a physiologically relevant temperature, allowing us to administer it to an injured limb while subsequently forming an in situ gel. 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. Moreover, immunohistochemical studies of injured nerves treated with (4-AP)-PLGA-PEG demonstrated an increased expression of neurofilament heavy chain (NF-H) and myelin protein zero (MPZ) proteins, two major markers of nerve regeneration. These findings demonstrate that (4-AP)−PLGA−PEG may be a promising long-acting local therapeutic agent in TPNI, for which no pharmacologic treatment exists.

Erythropoietin-PLGA-PEG as a local treatment to promote functional recovery and neurovascular regeneration after peripheral nerve injury

“…This study used PLGA-PEG-PLGA block copolymers to encapsulate the pro-angiogenic protein EPO in FDA-approved, biodegradable, and biocompatible hydrogels. We anticipated that a block copolymer formulation could be used as a versatile vector for the delivery of protein to a localized nerve injury [ 20 ]. We engineered a novel thermoresponsive formulation of EPO which undergoes a liquid-to-solid phase transition at physiologically relevant temperatures, making it an ideal candidate for in situ controlled-release drug delivery.…”

“…However, conduits must be surgically placed and have time and cost limitations [ 41 ]. Unlike nerve conduits, EPO-PLGA-PEG can be locally injected into an injured limb, reducing the need for surgical exposure of the nerve [ 20 ]. In addition to nerve conduits, natural hydrogel systems such as hyaluronic acid, chitosan, and collagen have been published for peripheral nerve regeneration [ 41 – 43 ].…”

“…Next, 1 mL of PBS (1X, pH 7.4) was added to each test tube as release media and the samples were left in the water bath at 37 °C for 21 days. At designated timepoints, 10 µL of release media was extracted from the tubes and replaced with the same amount of fresh PBS to maintain the sink condition [ 20 ]. The samples were stored at -20 °C until analyzed.…”

“…Block copolymers are biodegradable, thermosensitive drug delivery systems that allow for sustained drug release [ 20 , 21 ]. We developed an EPO block copolymer consisting of amphiphilic polyethylene glycol/poly lactic acid-co-glycolic acid (PEG/PLGA) polymers.…”

Construction of tissue-customized hydrogels from cross-linkable materials for effective tissue regeneration

“…[216][217][218][219] For instance, Manto incorporated 4-aminopyridine (4-AP) into PLGA-PEG-PLGA thermally cross-linked injectable hydrogels for traumatic peripheral nerve injury. 220 PHBV solutions cross-linked using chloroform and trifluoroethanol have presented tensile strengths of AE12 MPa good for peripheral-nerve repair and enhanced neurolike proliferation of PC12 cells if magnesium-oleate (MgOl) is added. 221 In addition, hybrid materials with thermosensitive and magnetically stimulated properties are suggested to support the drug-delivery function.…”