Gallic acid exerts protective effects in spinal cord injured rats through modulating microglial polarization

Spinal cord injury (SCI) is a highly traumatic injury that causes mechanical damage to the spinal cord. Our study aimed to investigate whether gallic acid has protective effects against SCI injury. Adult male rats were subjected to contusive spinal cord injuries. For behavioural evaluation, the rats were given gallic acid by i.p. injection at the doses of 10, 50 or 100 mg/kg immediately after SCI once daily for consecutive 28 days. Behavioral tests were used to evaluate locomotor functions, mechanical sensitivity and nerve conduction functions. For biochemical experiments, the rats were randomly divided into three groups: sham group, SCI group and SCI+gallic acid group. The rats in the SCI+gallic acid group were given gallic acid at the dose of 100 mg/kg immediately after SCI once daily for consecutive 14 days. The levels of inflammatory factors were evaluated. Gallic acid treatment could improve locomotive and sensory function and reduce the functional impairments in SCI rats. The effects were more effective with increasing gallic acid dose. The levels of M1 markers (inducible nitric oxide synthase and cyclooxygenase-2) were decreased in gallic acid-treated SCI rats, whereas the levels of M2 markers (arginase 1 and cluster of differentiation 206) were increased in response to gallic acid administration. Gallic acid treatment resulted in a significant reduction in pro-inflammatory cytokines and an increase in anti-inflammatory cytokine levels. Gallic acid enhances the recovery in SCI rats by regulating microglial polarization. The underlying mechanism may involve the promotion of M2 polarization and the suppression of M1 polarization in microglia.