Indoxyl sulphate, a tryptophan metabolite, affects astrocyte response during neuroinflammation

Indoxyl sulfate (IS) is a protein-bound uremic toxin derived from dietary tryptophan metabolism. Tryptophan is metabolized into indole by intestinal bacteria, after intestinal absorption is further converted to IS in the liver and then excreted by kidneys. In patients with impaired kidney function, such as chronic kidney disease (CKD), IS is recognized as a uremic toxin that accumulates in the blood inducing nephrotoxicity and impairing immune response. CKD is characterized by various complications such as neurological dysfunction. Since neuroinflammation has also been recognized to contribute to cognitive complications, and because CKD patients are also affected by immune dysfunction, we evaluated the effect of IS on C6 rat astroglial cell line in inflammatory conditions. IS, at uremic concentrations (60-15 pM), added for I h and then simultaneously with lipopolysaccharide from E coli (LPS; I ltgl ml) + Interferon y (IFN; 100u/ml) for 24h, significantly increased nitric oxide release in C6 cells at all tested concentrations. In the same experimental conditions, IS induced also a significant increase in inducible nitric oxide synthase and cyclooxygenase-2 expression, in tumor necrosis factor-d levels and in nitrotyrosine formation in astrocytes. Moreover, IS induced also nuclear factor-kB activation and aryl hydrocarbons receptor nuclear translocation in C6 cells in presence of LPS + IFN, thus contributing to inflammatory response modulation. In addition, wound healing assay indicated that IS caused also a reduction in astrocytes migration during inflammation. These results indicate that IS significantly affects astrocyte function increasing inflammatory response during neuroinflammation, thus potentially contributing to neurological complications observed in CKD.