Microbiome-Derived Tryptophan Metabolite Neuroprotection

**Molecular Mechanism and Rationale** The gut-brain axis represents a critical bidirectional communication pathway that fundamentally influences neuroinflammation and neurodegeneration through microbial metabolite signaling. Central to this mechanism is the tryptophan-aryl hydrocarbon receptor (AHR) axis, where beneficial commensal bacteria, particularly *Clostridium sporogenes*, *Peptostreptococcus russellii*, and certain *Lactobacillus* species, metabolize dietary tryptophan through the indol...