Lachnospira eligens attenuates epileptogenesis via gut-brain axis regulation of blood-brain barrier integrity and neuroinflammation.

Rationale: Emerging evidence implicates the gut microbiota in epilepsy pathogenesis through the microbiota-gut-brain axis, yet the functional contribution of specific microbial taxa to epileptogenesis remains unclear. This study aimed to investigate whether Lachnospira eligens (L. eligens) can alleviate epileptic activity by modulating the gut-brain axis, with a focus on intestinal barrier integrity, blood-brain barrier (BBB) integrity, and neuroimmune responses. Methods: Using a cobalt wire-induced rat epilepsy model, we performed fecal 16S rDNA sequencing to assess gut microbiota alterations. Rats received daily oral gavage of L. eligens or PBS for 15 days, with colonization confirmed by qPCR. Seizure activity was monitored using long-term video electroencephalogram (EEG) and Racine scores. Barrier function, systemic inflammation, and microglial activation were assessed using FITC-dextran (FD-4, 4 kDa) assay, Western blotting (WB), immunohistochemistry (IHC), immunofluorescence (IF), ELISA, and qPCR. Serum short-chain fatty acids (SCFAs) were measured by liquid chromatography-tandem mass spectrometry (LC-MS/MS). Results: Epileptic rats exhibited early gut microbiota dysbiosis, with a significant decline in Lachnospira abundance both preceding and succeeding seizure onset (P = 0.041, P = 0.026). L. eligens stably colonized the gut (Day 6 and Day 15, both P < 0.001). Supplementation significantly reduced grade 4-5 seizure frequency (P = 0.002) and prolonged seizure latency (P = 0.005). Barrier integrity improved, as indicated by lower plasma FD-4 (P < 0.001), increased colonic (WB: P = 0.013; IHC: P = 0.003) and cortical occludin expression (WB: P = 0.002; IHC: P = 0.01), and decreased serum lipopolysaccharide-binding protein (LBP) (P = 0.011). Neuroinflammation was attenuated, including reduced microglial activation (P = 0.048), lower pro-inflammatory cytokines (IL-1β, P = 0.047; IL-6, P = 0.001; TNF-α, P = 0.002), and decreased M1 polarization (P = 0.004). Serum butyrate increased (P = 0.014), and SCFAs, especially butyrate, suppressed lipopolysaccharide (LPS)-induced iNOS (P = 0.031) in BV2 cells. Conclusions: These findings demonstrate that L. eligens mitigates epileptic activity by restoring intestinal barrier and BBB integrity and suppressing neuroinflammation. Our study highlights L. eligens as a promising microbiota-based intervention for epilepsy through modulation of the gut-brain axis.