A sustained-release gel alleviates neuropathic pain in SNI mice by reversing Glu/GABA imbalance and chloride efflux disorders.

Impaired spinal GABAergic inhibitory neuronal system is one popular target for developing new drugs or procedures for treatment of neuropathic pain, but effective and transferable methods are still lacking. We designed an assembled, temperature sensitive and sustained releasing hydrogel to repair the impaired GABAergic neural system by reversing imbalance of glutamic acid (Glu) and γ-aminobutyric acid (GABA) and healing impaired Cl extrusion capacity of neurons. Hydrogel solution is a mixture of pluronic F-127, recombinant glutamate decarboxylase 67 (rGAD67) protein and CLP257, a K-Cl cotransporter isoform 2 (KCC2) enhancer. The temperature sensitive properties, gel properties and slow-releasing properties of the drug system were determined in vitro. After intrathecal injected in sural spared nerve injury mice model, the hydrogel solution turned into gel, capturing Glu and transforming it into GABA. CLP257 released from gel reversed the suppressed expression of KCC2 in spinal cord, maintaining a low intracellular Cl concentration in neurons and allowing the normal work of GABA receptors. Combination of rGAD67 and CLP257 showed synergistic effects in alleviating hyperalgesia, altering glia activation, and inhibiting cell apoptosis and inflammatory response. In conclusion, the in situ assembled gel is a long-term effective tool for repairing damaged GABAergic inhibitory system and alleviating neuropathic pain.