Indoxyl Sulfate Impairs Endothelial Progenitor Cells and Might Contribute to Vascular Dysfunction in Patients with Chronic Kidney Disease

Background/Aims: Indoxyl sulfate (IS) is a protein-bound uremic toxin that accumulates in patients with chronic kidney disease (CKD). We explored the effect of IS on human early endothelial progenitor cells (EPCs) and analyzed the correlation between serum IS levels and parameters of vascular function, including endothelial function in a CKD-based cohort. Methods: A cross-sectional study with 128 stable CKD patients was conducted. Flow-mediated dilation (FMD), pulse wave velocity (PWV), ankle brachial index, serum IS and other biochemical parameters were measured and analyzed. In parallel, the activity of early EPCs was also evaluated after exposure to IS. Results: In human EPCs, a concentration-dependent inhibitory effect of IS on chemotactic motility and colony formation was observed. Additionally, serum IS levels were significantly correlated with CKD stages. The total IS (T-IS) and free IS (F-IS) were strongly associated with age, hypertension, cardiovascular disease, blood pressure, PWV, blood urea nitrogen, creatine and phosphate but negatively correlated with FMD, the estimated glomerular filtration rate (eGFR), hemoglobin, hematocrit, and calcium. A multivariate linear regression analysis also showed that FMD was significantly associated with IS after adjusting for other confounding factors. Conclusions: In humans, IS impairs early EPCs and was strongly correlated with vascular dysfunction. Thus, we speculate that this adverse effect of IS may partly result from the inhibition of early EPCs.