Microbiota and Guillain-Barré syndrome: role of microbial metabolites, biomarkers, and emerging therapeutic strategies.

Guillain-Barré syndrome (GBS) is an acute autoimmune polyradiculoneuropathy that follows infection and is characterized by immune-mediated demyelination or axonal injury of the peripheral nervous system. While established triggers such as Campylobacter jejuni are well recognized, increasing evidence implicates the gut microbiota as a key modulator of immune responses relevant to GBS pathogenesis. The intestinal microbiota produces a diverse array of bioactive metabolites, including short-chain fatty acids (SCFAs), tryptophan-derived indoles, and neurotransmitter-like molecules, which influence immune tolerance, gut barrier integrity, and neuroinflammatory signaling. SCFAs, particularly butyrate, exert anti-inflammatory effects and support epithelial and blood-nerve barrier function. Microbial tryptophan metabolites regulate astrocyte and microglial activity via aryl hydrocarbon receptor (AHR) signaling, thereby restraining central and peripheral neuroinflammation. In contrast, dysbiosis-associated metabolites such as lipopolysaccharide (LPS) may enhance systemic inflammation, disrupt immune tolerance, and promote autoantibody production through mechanisms including molecular mimicry. Studies suggest that specific microbial taxa and metabolite signatures may serve as diagnostic or prognostic biomarkers in GBS, offering insights into disease susceptibility and progression. Microbiota-targeted therapeutic strategies are emerging as promising adjuncts to immunotherapy. Probiotics and prebiotics may restore beneficial microbial communities and rebalance immunoregulatory metabolite production, while host-directed metabolic interventions such as creatine supplementation may further support mitochondrial function, immunometabolic homeostasis, and neuroprotection. Fecal microbiota transplantation (FMT), though still experimental in GBS, has shown benefit in related neuroinflammatory disorders by reestablishing eubiosis and dampening immune activation. Future studies integrating metagenomic, metabolomic, and immunologic profiling in well-characterized GBS cohorts are essential to validate these findings and advance personalized microbiota-based interventions.