Analgesic effects and pharmacologic mechanisms of the Gelsemium alkaloid koumine on a rat model of postoperative pain

Postoperative pain (POP) of various durations is a common complication of surgical procedures. POP is caused by nerve damage and inflammatory responses that are difficult to treat. The neuroinflammation-glia-steroid network is known to be important in POP. It has been reported that the Gelsemium alkaloid koumine possesses analgesic, anti-inflammatory and neurosteroid modulating activities. This study was undertaken to test the analgesic effects of koumine against POP and explore the underlying pharmacologic mechanisms. Our results showed that microglia and astroglia were activated in the spinal dorsal horn post-incision, along with an increase of proinflammatory cytokines (interleukin 1β, interleukin 6, and tumor necrosis factor α). Both subcutaneous and intrathecal (i.t.) koumine treatment after incision significantly prevented mechanical allodynia and thermal hyperalgesia, inhibited microglial and astroglial activation, and suppressed expression of proinflammatory cytokines. Moreover, the analgesic effects of koumine were antagonized by i.t. administration of translocator protein (18 kDa) (TSPO) antagonist PK11195 and GABAA receptor antagonist bicuculline. Together, koumine prevented mechanical allodynia and thermal hyperalgesia caused by POP. The pharmacologic mechanism of koumine-mediated analgesia might involve inhibition of spinal neuroinflammation and activation of TSPO. These data suggested that koumine might be a potential pharmacotherapy for the management of POP.