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Patients with chronic kidney disease (CKD) have a much higher risk of cardiovascular diseases than the general population. Endothelial dysfunction, which participates in accelerated atherosclerosis, is a hallmark of CKD. Patients with CKD display impaired endothelium-dependent vasodilatation, elevated soluble biomarkers of endothelial dysfunction, and increased oxidative stress. They also present an imbalance between circulating endothelial populations reflecting endothelial injury (endothelial microparticles and circulating endothelial cells) and repair (endothelial progenitor cells). Endothelial damage induced by a uremic environment suggests an involvement of uremia-specific factors. Several uremic toxins, mostly protein-bound, have been shown to have specific endothelial toxicity: ADMA, homocysteine, AGEs, and more recently, p-cresyl sulfate and indoxyl sulfate. These toxins, all poorly removed by hemodialysis therapies, share mechanisms of endothelial toxicity: they promote pro-oxidant and pro-inflammatory response and inhibit endothelial repair. This article (i) reviews the evidence for endothelial dysfunction in CKD, (ii) specifies the involvement of protein-bound uremic toxins in this dysfunction, and (iii) discusses therapeutic strategies for lowering uremic toxin concentrations or for countering the effects of uremic toxins on the endothelium. [ABSTRACT FROM AUTHOR]

Protein-bound uremic retention solutes constitute a group whose common characteristic is their difficult removal by dialysis. In 2003, the EUTox group described 25 protein-bound solutes. They comprised six advanced glycation end products (AGE), four phenols (including p-cresol), six indoles (including indoxylsulfate), two hippurates, three polyamines, and two peptides, homocysteine and 3-carboxy-4-methyl-5-propyl-2-furanpropionic acid (CMPF). As then, three new compounds have been added to the list: phenylacetic acid, dinucleoside polyphosphates, and IL-18. During the last years, protein-bound compounds have been identified as some of the main toxins involved in vascular lesions of chronic kidney disease. The removal of these solutes by conventional hemodialysis (HD) is low because only the free fraction of the solute is available for diffusion. The increase in the convective part with hemodiafiltration improves the performance of depuration but convection only applies to the free fraction and its benefit is limited. One possibility to improve the removal of a protein-bound solute would be to stimulate its dissociation from the binding protein. This could be obtained in experiments by setting the dialysate flow rate and the dialyzer mass transfer area coefficient (KoA) at much higher levels than the plasma flow rate, or by adding to the dialysate a sorbent such as activated charcoal or albumin. In the future, specific adsorbents may be developed. Today, the only possibility is to use approaches such as daily HD and long HD which could allow better equilibration between extravascular and vascular compartments and consequently result in greater removal of protein-bound compounds.