Neuroprotective effect of liquiritin against neuropathic pain induced by chronic constriction injury of the sciatic nerve in mice.

Managing of neuropathic pain remains clinically challenging because the existing pharmacotherapies are either ineffective or non-specific. Therefore, developing novel alternatives is essential for better treatment. Liquiritin is an active component extracted from Glycyrrhizae radix and has potential neuroprotective action. This study aimed to investigate the protective efficacy of liquiritin on chronic constriction injury (CCI)-induced neuropathic pain in mice. Liquiritin (30, 60, and 120mg/kg) and pregabalin (40mg/kg) were administered intragastrically for 7 consecutive days starting on the 8th day post-surgery. Behavioral parameters and sciatic functional index were assessed on days 0, 7, 8, 10, 12, and 14. Electrophysiological and histopathological changes were analyzed on the 14th day. Immunofluorescence and Western blot were used to evaluate the expression of glial cells and the protein levels of inflammatory cytokines in the spinal cord, respectively. Results showed that liquiritin dose-dependently reduced hyperalgesia and allodynia and increased the sciatic functional index and motor nerve conduction velocities. Moreover, liquiritin restored the injured axon and myelin sheath, inhibited the activation of astrocyte and microglia, down-regulated the pro-inflammatory cytokines including tumor necrosis factor alpha (TNF-α), interleukin (IL-6, and IL-1β), and simultaneously up-regulated the anti-inflammatory cytokine IL-10. Our study revealed that liquiritin exerted a neuroprotective effect on CCI-induced neuropathic pain, which might be attributed to its direct protective effect on damaged nerves and its anti-inflammatory activity at the level of the spinal cord. Therefore, liquiritin shows promise as a compound for the development of novel analgesic agents that can be used to effectively treat intractable neuropathic pain.