The Potential Role of Indoleamine 2,3 Dioxygenase in the Pathogenesis of Type 2 Diabetes and Periodontitis

Introduction Periodontal medicine is a subdiscipline of periodontology, where the relationship between periodontal diseases and overall health is examined. Inflammation serves as a pivotal mechanism linking diabetes and periodontal disease. Indoleamine 2,3-dioxygenase (IDO) is the rate-limiting enzyme in the catabolic pathway of tryptophan, resulting in the generation of kynurenines, which regulate immune functions. Recently, IDO as a potential biomarker has been investigated in many systemic conditions with underlying inflammatory pathology. This review aimed to formulate a potential hypothesis suggesting the role of IDO as one of the common links for the bidirectional relationship between type 2 diabetes and periodontitis. Methods Electronic databases, including PubMed, Scopus, ProQuest, and Google Scholar, were searched using keywords, such as “indoleamine 2,3 dioxygenase,” “tryptophan-kynurenine pathway,” “diabetes,” and “periodontitis.” All study types performed in humans and animal models were included. Results A summary of the available literature is provided to illustrate the topics related to the potential mechanism linking the inflammatory basis of diabetes and periodontitis. The studies exploring the mechanistic pathways related to IDO in diabetes and periodontitis are also described. Discussion The pathways through which IDO may potentiate the link between diabetes and periodontitis are discussed based on available literature evidence. The need for maintenance of immune homeostasis through regulatory T cells and inflammatory cytokines is emphasized. Conclusion This literature review summarizes the mechanisms through which IDO enzyme exerts complex and multifaceted roles in immune regulation, inflammation, and tryptophan metabolism, thereby influencing the pathogenesis of periodontitis and type 2 diabetes.