Uremic toxin indoxyl sulfate and its possible influence by diet

Overview

Indoxyl sulfate (IS) is produced in the body by degradation from the amino acid tryptophan contained in the diet. It reaches the large intestine as part of the residual protein, where it is converted into indole by the action of gastrointestinal bacteria and subsequently absorbed into the bloodstream. Enzymatic hydroxylation and conversion of indole to IS then occurs in the liver. Physiologically, IS is excreted in the urine -⁠ tubular secretion, and its serum concentration is <5.4 µmol/L. As a uremic toxin that is 90% protein bound, it is very difficult to remove by dialysis techniques. IS accumulates in patients with impaired kidney function, which negatively affects the entire organism, e.g. causes progression of cardiovascular diseases and stimulates oxidative stress. The aim of the study was to confirm the connection between the concentration of IS and the speed of protein catabolism using the predialysis and postdialysis concentration of urea and, therefore, the possibility of influencing the concentration of IS with a suitable diet.
Type of study: A monocentric prospective open cohort study was conducted on 108 patients undergoing dialysis treatment at the Nephrology Clinic of the Hradec Králové University Hospital.

Results: A positive effect of residual diuresis on the reduction of IS levels was confirmed (p=0.005), in anuric patients the concentration of IS is 160.4 µmol/L (122.6; 200.5), while in oligouric patients it is 124.6 µmol/L (98.7; 168.1). Furthermore, a correlation was found between increasing protein intake in the diet and increasing IS rate (p=0.040).

Conclusion: An appropriate personalized adjustment of the diet composition while maintaining the necessary protein intake would lead to a decrease in the serum concentration of IS in these patients.

Keywords:

dialysis – kidney failure – uremic toxins – indoxyl sulfate