ABSTRACT: Purpose: To determine whether capsaicin (CAP) exacerbates experimental autoimmune uveitis (EAU) and whether this effect is associated with impaired intestinal homeostasis, gut microbiota re-modeling, and altered metabolic profiles. Methods: An EAU mouse model was used to evaluate the dose-dependent effects of CAP on ocular inflammation and intestinal homeostasis. EAU severity was assessed by fundus examination, clinical scoring, and retinal histopathology. Ileal and colonic morphology, colonic ZO-1 and MUC2 expression, and IL-17A levels in the colon and spleen were evaluated using hematox-ylin and eosin staining, immunofluorescence, and enzyme-linked immunosorbent assays. 16S rRNA gene sequencing, untargeted fecal metabolomics, and colonic RNA sequencing were performed to characterize CAP-associated changes in the gut microbiota, metabolome, and transcriptome. Kynurenic acid (KYNA) was subsequently administered to determine whether supplementation attenuated CAP-induced exacerbation of EAU and intestinal barrier injury. Results: CAP exacerbated EAU in a dose-dependent manner. At 80 mg/kg, CAP aggravated retinal inflammation and tissue injury, increased clinical and histopathologic scores, and elevated IL-17A levels in the colon and spleen. High-dose CAP was also associated with ileal archi-tectural abnormalities, reduced colonic mucosal thickness, and decreased colonic ZO-1 and MUC2 expression. 16S rRNA gene sequencing revealed alterations in gut microbial diversity and community structure. CAP-associated differential metabolites were enriched in the tryp-tophan metabolism pathway, and fecal KYNA levels were significantly reduced. Colonic RNA sequencing showed enrichment of the IL-17 signaling pathway, upregulation of Il17a, Il17f, and Rorc, and altered expression of genes involved in tryptophan metabolism. KYNA supplementation reduced clinical and histopathologic scores, decreased IL-17A levels in the colon and spleen, and partially restored colonic ZO-1 and MUC2 expression. Conclusion: Under these experimental conditions, high-dose CAP exacerbated EAU and was associat-ed with intestinal barrier disruption, gut microbiota remodeling, altered tryptophan metabo-lism, and enhanced IL-17-related inflammation. The partial attenuation observed after KYNA supplementation supports further investigation of KYNA as a candidate metabolic factor in high-dose CAP-treated EAU mice.
