Effect of Probiotic Administration on Serum Tryptophan Metabolites in Pediatric Type 1 Diabetes Patients

Type 1 diabetes (T1D) is characterized by anomalous functioning of the immuno regulatory, tryptophan-catabolic enzyme indoleamine 2,3 dioxygenase 1 (IDO1). In T1D, the levels of kynurenine—the first byproduct of tryptophan degradation via IDO1—are significantly lower than in nondiabetic controls, such that defective immune regulation by IDO1 has been recognized as potentially contributing to autoimmunity in T1D. Because tryptophan catabolism—and the production of immune regulatory catabolites—also occurs via the gut microbiota, we measured serum levels of tryptophan, and metabolites thereof, in pediatric, diabetic patients after a 3-month oral course of Lactobacillus rhamnosus GG. Daily administration of the probiotic significantly affected circulating levels of tryptophan as well as the qualitative pattern of metabolite formation in the diabetic patients, while it decreased inflammatory cytokine production by the patients. This study suggests for the first time that a probiotic treatment may affect systemic tryptophan metabolism and restrain proinflammatory profile in pediatric T1D.