Palmatine mitigates ischemic brain injury by regulating microglial polarization and sphingolipid metabolism.

Background: To elucidate the therapeutic effects and underlying mechanisms of palmatine, a principal alkaloid derived from Coptis chinensis, on neuroinflammation in ischemic stroke rat models induced by middle cerebral artery occlusion (MCAO).

Methods: Initially, qPCR was employed to assess the impact of neurotrophic factors secreted by SH-SY5Y neuroblastoma cells on the phenotypes of BV2 cells. Alterations in sphingolipid profiles within neuronal supernatants were characterized using liquid chromatography-tandem mass spectrometry, and molecular docking studies were conducted to investigate the interaction of palmatine with key enzymes involved in sphingolipid metabolism. Subsequently, Rats were subjected to MCAO to mimic cerebral ischemia in vivo. Neurological function was evaluated using standardized tests, and brain pathology was assessed. LC-MS/MS was also utilized to quantify sphingolipid levels within the brain. BV2 cells and rats were subjected to TREM2 knockdown using lentiviral transfection and adeno-associated virus (AAV)-mediated delivery, respectively. The neuroprotective effects of palmatine were further delineated.

Results: In vitro, palmatine counteracted ischemia-induced microglial M1 polarization, promoting a neuroprotective M2 phenotype in BV2 cells. It modulated sphingolipid metabolism, normalizing ceramide and ceramide-1-phosphate levels in neuronal supernatants. In vivo, palmatine significantly ameliorated neurological deficits and restored sphingolipid homeostasis in MCAO-induced rats. TREM2 downregulation exacerbated ischemic injury, whereas SH-SY5Y-derived neurotrophic factors suppressed BV2 activation. Inhibition of the PI3K/AKT/mTOR/HIF-1α signaling cascade significantly attenuated palmatine's microglia-mediated neuroprotection.

Conclusion: Palmatine exerts neuroprotection by reducing levels of ceramide through its conversion to ceramide-1-phosphate, a process that is mediated by TREM2 on microglia and the PI3K/AKT/mTOR/HIF-1α signaling pathway.