Increasing evidence has underscored the significance of post-stroke alterations along gut-brain axis, while its role in pathogenesis and treatment of ischemic stroke (IS) remains largely unexplored. This study aimed to elucidate the therapeutic effects and action targets of Panax notoginseng saponins (PNS) on IS and explore a novel pathogenesis and treatment strategy of IS via profiling the microbial community and metabolic characteristics along gut-brain axis. Our findings revealed for the first time that the therapeutic effect of PNS on IS was microbiota-dependent. Ischemia/reperfusion (I/R) modeling significantly down-regulated Lactobacilli in rats, and PNS markedly recovered Lactobacilli, particularly Lactobacillus reuteri (L.Reu). Metabolomics showed a significant reduction in serum histidine (HIS) in clinical obsolete IS patients and rehabilitation period I/R rats. Meanwhile, the L.Reu colonization in I/R rats exhibited significant neuroprotective activity and greatly increased HIS in serum, gut microbiota, and brain. Moreover, exogenous HIS demonstrated indirect neuroprotective effects through metabolizing to histamine. Notably, vagus nerve severance in I/R rats was performed to investigate HIS's neuroprotective mechanism. The results innovatively revealed that PNS could promote HIS synthesis in gut by enhancing L.Reu proportion, thereby increasing intracerebral HIS through peripheral pathway. Consequently, our data provided novel insights into HIS metabolism mediated by L.Reu in the pathogenesis and treatment of IS.

An innovative approach to quantitatively analyze the histamine and its precursor histidine simultaneously in biological matrices was established for the first time based on double adsorption combined with high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS).The internal standard was 2-dihydroxybenzoic acid (DHB).The plasma and brain tissue homogenate was protein precipitated with 3-fold acetonitrile, and the supernatant was then sampled for injection analysis.The chromatographic separation of the target components was achieved on an amino chromatography column (ODS-SPXBridge? Amide).Gradient elution was carried out with the mobile phase consisting of solvent A (0.1% formic acid and 1mmol/L ammonium formate in water) and solvent B (acetonitrile).Mass spectrometry was employed for quantitative analysis with ESI ion source in multiple reaction monitoring (MRM) mode.In order to improve the specificity and accuracy, activated carbon and calcite were used for the double adsorption of biological matrices for the first time.The adsorbed matrix was then used for methodology validation.The results showed that histamine and histidine were linear in the quantitative range (correlation coefficient r ≥ 0.999).Accuracy, precision, extraction recovery, matrix effect and stability all met the requirements of biological sample analysis.All results suggested that the present method could not only be efficiently and reliably used for simultaneous quantitative analysis of histamine and histidine in biological samples, but also provide reference for the detection of other endogenous substances.