Koumine, an
indole alkaloid, is a major bioactive component of Gelsemium elegans. Previous studies have demonstrated that
koumine has noticeable anti-inflammatory and
analgesic effects in inflammatory and
neuropathic pain (NP) models, but the mechanisms involved are not well understood. This study was designed to explore the
analgesic effect of
koumine on chronic constriction injury (CCI)-induced NP in rats and the underlying mechanisms, including astrocyte autophagy and apoptosis in the spinal cord. Rats with CCI-induced NP were used to evaluate the
analgesic and anti-inflammatory effects of
koumine.
Lipopolysaccharide (LPS)-induced
inflammation in rat primary astrocytes was also used to evaluate the anti-inflammatory effect of
koumine. We found that repeated treatment with
koumine significantly reduced and inhibited CCI-evoked astrocyte activation as well as the levels of pro-inflammatory
cytokines. Meanwhile, we found that
koumine promoted autophagy in the spinal cord of CCI rats, as reflected by decreases in the LC3-II/I ratio and P62 expression. Double immunofluorescence staining showed a high level of colocalization between LC3 and GFAP-positive glia cells, which could be decreased by
koumine.
Intrathecal injection of an autophagy inhibitor (
chloroquine) reversed the
analgesic effect of
koumine, as well as the inhibitory effect of
koumine on astrocyte activation in the spinal cord. In addition, TUNEL staining suggested that CCI-induced apoptosis was inhibited by
koumine, and this inhibition could be abolished by
chloroquine. Western blot analysis revealed that
koumine significantly increased the level of Bcl-xl while inhibiting Bax expression and decreasing cleaved
caspase-3. In addition, we found that
koumine could decrease astrocyte-mediated
neuroinflammation and enhance autophagy in primary cultured astrocytes. These results suggest that the
analgesic effects of
koumine on CCI-induced NP may involve inhibition of astrocyte activation and pro-inflammatory
cytokine release, which may relate to the promotion of astrocyte autophagy and the inhibition for apoptosis in the spinal cord.