Background and Objectives: Acute ulcerative colitis is characterized by excessive mucosal inflammation and epithelial disruption, often driven by dysregulated cytokine and immune signaling. Indoximod (1-methyl-DL-tryptophan), although not a direct enzymatic inhibitor, modulates the indoleamine 2,3-dioxygenase (IDO) pathway and has been reported to exert immunoregulatory effects in various models of inflammation. This study aimed to evaluate the protective effects of Indoximod in an acetic acid-induced colitis model in rats, focusing on histopathological changes and inflammatory mediators. Materials and Methods: Thirty male Wistar albino rats were randomly assigned to three groups (n = 10 per group): Group 1 (Control) received 0.9% saline oral gavage; Group 2(Colitis) received intrarectal 4% acetic acid to induce colitis and were then treated with saline; Group 3 (Colitis + Indoximod) received 4% acetic acid followed by oral gavage administration of Indoximod (30 mg/kg) for 15 consecutive days. Histopathological evaluation of colonic tissues was performed using hematoxylin and eosin (H&E) staining. Colonic expression of Toll-like receptor 4 (TLR4) and plasma levels of tumor necrosis factor-alpha (TNF-α), pentraxin-3 (PTX-3), and platelet-activating factor (PAF) were quantified using enzyme-linked immunosorbent assay (ELISA). Results: Acetic acid-induced colitis significantly increased mucosal damage, TLR4 expression, and circulating levels of TNF-α, PTX-3, and PAF compared with controls (p < 0.001). Indoximod treatment markedly reduced histological injury and significantly suppressed TLR4 and TNF-α levels (p < 0.01), along with partial reductions in PTX-3 (p < 0.05). However, PAF levels remained elevated despite treatment, indicating limited efficacy in PAF-associated pathways. Conclusions: Indoximod exhibited anti-inflammatory effects in this acute colitis model, likely by downregulating key proinflammatory mediators.
Keywords: IDO inhibitor; Indoximod; PAF; TLR4; TNF-α; acetic acid-induced colitis; pentraxin-3.