Impact of NBP on acute ischemic stroke: Tracking therapy effect on neuroinflammation

Background: Ischemic stroke is the leading cause of death and long-term disability worldwide. After stroke, microglia exhibit not only pro-inflammatory phenotype to aggravate the neuroinflammation, but also antiinflammatory phenotype to play a neuroprotective role. Studies on the spatial and temporal changes in microglia and the underlying mechanisms help to elucidate the inflammatory cascade after stroke. The regulation of microglia polarization provides new insights for the intervention of post-stroke inflammation. Objective: We aimed to investigate the phenotypic change of microglia in the acute phase of ischemic stroke and the effects of Dl-3-n-butylphthalide (NBP) on microglia. TSPO-PET was used to image microglia and evaluate the efficacy of NBP. Methods: We constructed an MCAO model in rats and administered NBP daily. The infarct volumes in the NBPtreated and control groups were measured. TSPO-PET/CT was used to demonstrate the activation of microglia and the effects of NBP. Additionally, we investigated the effects of NBP on TSPO expression. In vitro, microglia were exposed to glucose oxygen deprivation, and the effects of NBP on microglia and TSPO expression were verified. Results: NBP improved neurological severity scores and reduced infarct volume in the acute phase of ischemic stroke. NBP facilitated microglia to adopt the anti-inflammatory phenotype and reduce the pro-inflammatory phenotype. NBP decreased the expressions of inflammatory cytokines. TSPO-PET/CT observed increase in uptake in the infarct lesion, and this uptake was reduced in response to NBP. NBP reduced TSPO expression in microglia after stroke. In vitro experiments further verified that NBP facilitated the transition of microglia towards the anti-inflammatory phenotype, and inhibited inflammatory cytokine secretion and TSPO expression. Conclusion: We illustrated that NBP fosters the shift of microglia towards the anti-inflammatory phenotype while diminishing their inclination towards the pro-inflammatory phenotype, thereby exerting neuroprotective effects. NBP reduces TSPO expression in microglia, which can be observed by TSPO-PET/CT imaging.