Plant Compound Icariside II Fights Post-Stroke Depression via Gut-Brain Axis

Post-stroke depression (PSD) affects nearly one-third of stroke survivors and significantly worsens recovery outcomes. Current antidepressants face limitations including delayed onset, side effects, and drug resistance, creating an urgent need for novel mechanistic approaches. This study investigated whether Icariside II (ICS II), a bioactive flavonoid metabolite derived from the traditional Chinese herb Epimedium, could address PSD by targeting the Sirt6/NF-κB pathway and reshaping the gut-brain axis.

Researchers established a PSD mouse model by combining middle cerebral artery occlusion (MCAO)—which induces ischemic stroke—with 21 days of chronic unpredictable mild stress (CUMS). Mice were pretreated with ICS II at doses of 2.5–20 mg/kg or fluoxetine (positive control) for seven days prior to PSD induction. Behavioral tests (sucrose preference, forced swim, tail suspension) confirmed depressive phenotypes and treatment responses. RNA sequencing of medial prefrontal cortex tissue, molecular docking, surface plasmon resonance (SPR), and microscale thermophoresis (MST) were used to identify and validate Sirt6 as the direct molecular target. Gut microbiota was profiled via 16S rDNA sequencing, and short-chain fatty acids (SCFAs) were quantified by UPLC-Q/Orbitrap/MS.

ICS II dose-dependently reversed depressive-like behaviors, with 20 mg/kg achieving optimal efficacy comparable to fluoxetine. Transcriptomic analysis of mPFC tissue revealed 2,128 differentially expressed genes between PSD and PSD+ICS II groups, with Sirt6 emerging as the central regulatory hub connected to NF-κB signaling, oxidative phosphorylation, and cellular senescence pathways. Western blot confirmed that ICS II upregulated Sirt6 and IκB while reducing H3K9 acetylation and NF-κBp65 phosphorylation. Molecular docking showed ICS II binds Sirt6 at a binding energy of −9.008 kcal/mol via three hydrogen bonds, and molecular dynamics simulations confirmed complex stability. Critically, antidepressant effects were abolished in Sirt6 knockout mice, confirming Sirt6 dependency.

On the gut microbiota front, ICS II significantly increased the relative abundance of beneficial bacteria including Akkermansia and Ligilactobacillus, elevated concentrations of SCFAs (acetate, propionate, butyrate), repaired intestinal barrier integrity, and upregulated tight junction protein expression. Fecal microbiota transplantation (FMT) from ICS II-treated PSD mice into antibiotic-depleted PSD recipients recapitulated the antidepressant benefits, causally linking the remodeled microbiome to behavioral improvement. ICS II also reduced lipopolysaccharide levels in blood, mitochondrial dysfunction markers, and pro-inflammatory cytokines in both brain and intestinal tissue.

These findings position ICS II as a novel Sirt6 activator that simultaneously targets neuroinflammation, oxidative stress, and gut dysbiosis in PSD—three interconnected pathological axes that existing antidepressants fail to address comprehensively. The microbiota-targeted mechanism opens a potentially translatable therapeutic avenue for PSD.