TDO2 and chronic kidney disease: For example, Lobel et al. demonstrated that an increase in the consumption of sulfur-containing AAs induces post-translational modifications of bacterial tryptophanase leading to a decrease in the capacity for indole generation.35 Fecal transplantation experiments further support the toxic role of uremic microbiota,17,36 with transplanted CKD mice showing higher UT levels and reduced kidney function,17 while feces from sham mice lowered plasma UTs.37 Deciphering UT production by the microbiota is complex due to the interaction between kidney function and intestinal barrier leakage.