Saikosaponin D mitigate pilocarpine‐induced astrocyte injury by regulating the NLRP3/caspase‐1 signaling pathway

Abstract Studies have shown that saikosaponin D (SSD) has favorable neurotherapeutic effects. Therefore, the objective of this study was to explore the efficacy and possible molecular mechanisms of SSD on pilocarpine (PP)‐induced astrocyte injury. Primary astrocytes were isolated from juvenile rats and identified using immunofluorescence. The cells were treated with PP and/or SSD for 6 h and 12 h, respectively, followed by measurement of their viability through 3‐(4,5‐dimethylthiazol)‐2,5‐diphenyl‐tetrazolium bromide (MTT) assay. Next, quantitative real‐time polymerase chain reaction (qRT‐PCR) was used to measure the expression levels of Glial fibrillary acidic protein (GFAP), C3, S100 calcium binding protein A10 (S100a10), pentraxin 3 (Ptx3), toll‐like receptor 4 (TLR4), and RAG in astrocytes after different treatments. Enzyme‐linked immunosorbent assay and biochemical tests were utilized to evaluate the level of inflammatory factors [interleukin (IL)‐1β, IL‐6, and tumor necrosis factor alpha (TNF‐α)] secreted by cells and the content of oxidative stress‐related factors (malondialdehyde [MDA] and glutathione [GSH]) or enzyme activity (catalase [CAT] and glutathione peroxidase [GPX]) in cells. The JC‐1 mitochondrial membrane potential (MMP) fluorescence probe was used to measure the MMP in astrocytes. Additionally, western blot was applied to test the expression of proteins related to the nod‐like receptor protein 3 (NLRP3)/caspase‐1 signaling pathway. PP treatment (1 mM) induced cell injury by significantly reducing the viability of astrocytes and expression of cellular markers. SSD treatment (4 μM) had no toxicity to astrocytes. Besides, SSD (4 μM) treatment could significantly up‐regulate the cell viability and marker expression of PP‐induced astrocytes. Furthermore, SSD could be employed to inhibit inflammation (reduce IL‐1β, IL‐6, and TNF‐α levels) and oxidative stress (decrease MDA level, elevate GSH level, the activity of CAT and GPX), and ameliorate mitochondrial dysfunction (upregulate JC‐1 ratio) in PP‐induced astrocytes. Moreover, further mechanism exploration revealed that SSD treatment significantly reduced the activity of the NLRP3/caspase‐1 signaling pathway activated by PP induction. SSD increased cell viability, inhibited inflammation and oxidative stress response, and ameliorated mitochondrial dysfunction in PP‐induced astrocyte injury model, thus playing a neuroprotective role. The mechanism of SSD may be related to the inhibition of the NLRP3/caspase‐1 inflammasome.