Preventive effect of indoleamine 2,3-dioxygenase 1 inhibition on lipopolysaccharide-induced prostatitis
Introduction and Objectives: Bacterial infections are the main cause of acute prostatitis and are treated with appropriate antimicrobial therapy. However, approximately 5% of patients continue to have inflammatory symptoms even after receiving antibacterial therapy, leading to refractory conditions. Bacterial prostatitis requires additional therapy, focusing on inflammatory changes. Indoleamine 2,3-dioxygenase 1 (IDO1) catalysis is the first rate-limiting step of tryptophan metabolism. IDO1 is expressed in the prostate and plays a key role in the immune response. As the first step in investigating the relationship between acute prostatitis and IDO1, we investigated the preventive effect of IDO1 inhibition on lipopolysaccharide (LPS)-induced prostatitis using IDO knockout (Ido1 −/−) mice in this study. Materials and Methods: The study used Ido1 −/− and wild-type (Ido1 +/+) C57BL/6J male mice aged 10–15 weeks. LPS Escherichia coli O26 (100μg/PBS, 100μL) was administered transurethrally into the lower urinary tract to create a mouse model of LPS-induced prostatitis. The prostates were removed 1, 3, 5, and 7 days after creating the model mice. Histological, immunohistochemical, and biochemical analyses were used to compare the preventive effect in Ido1 −/− mice compared with that in Ido1+/+ mice. Results: HE staining showed suppression of ductal destruction following infiltration of inflammatory cells in Ido1 −/− mice compared with Ido1 +/+ mice. The enzyme-linked immunosorbent assay (ELISA) method was used for kynurenine pathway analysis, which showed significantly maintained tryptophan levels and decreased L-kynurenine levels in Ido1 −/− mice compared to Ido1 +/+ mice. The IDO1 assay in Ido1 +/+ mice showed significantly increased levels during all observation periods after creating the model compared with that under normal conditions. Immunofluorescent staining using five types of cytokines and chemokines (IL-2, IL-4, IL-17, CCL2, and CCL3) related to the pathophysiology of acute prostatitis showed decreased expression of these cytokines and chemokines in Ido1 -/- mice compared with Ido1 +/+ mice. Inflammation-related proteome assays showed decreased levels of IL-1β, IL-4, IL-5, IL-6, IL-17, CCL2, CCL3, CXCL1, CXCL11, and tissue inhibitor of matrix metalloproteinases (TIMP)-1 in Ido1 −/− mice compared with Ido1 −/− mice during all observation periods after model creation. Conclusions: IDO1 is involved in LPS-induced prostatitis through cytokines and chemokines. IDO1 inhibition contributes to the prevention of LPS-induced prostatitis. IDO1 inhibition has the potential to serve as an additional therapy for acute prostatitis.