Removal of protein-bound uraemic toxins by haemodialysis

Accumulating evidence suggests that protein-bound uraemic toxins play an important role in uraemic complications, especially in cardiovascular disease. Notably, protein-bound uraemic toxins such as indoxyl sulphate, p-cresyl sulphate, and 3-carboxy-4-methyl-5-propyl-2-furanpropionic acid (CMPF) have emerged as important targets of therapeutic removal. Indoxyl sulphate stimulates reactive oxygen species production in human umbilical vein endothelial cells (HUVEC) most intensely, followed by CMPF. Indoxyl sulphate and CMPF inhibit cell growth of HUVEC. Haemodialysis (HD) even with a high-flux membrane cannot efficiently remove the protein-bound uraemic toxins because of their high albumin-binding property. Especially, indoxyl sulphate, p-cresyl sulphate, and CMPF showed high protein-binding ratios (more than 95%) and low reduction rates by HD (less than 35%). Removal of indoxyl sulphate and p-cresyl sulphate can be improved to some extent by increasing the diffusion of the free forms with super-flux membrane HD, increasing the dialyzer mass transfer area coefficient and dialysate flow, haemodiafiltration, daily HD, and addition of a sorbent to dialysate. However, CMPF is more strongly bound to albumin (with a binding ratio of 99-100%) than indoxyl sulphate and p-cresyl sulphate, and cannot be removed at all by conventional HD. Uraemic toxins strongly or covalently bound to albumin such that CMPF can be removed by protein-leaking HD. Protein-leaking HD with a polymethylmethacrylate membrane BK-F dialyzer can reduce serum levels of CMPF with improvement of anaemia as well as reduce plasma levels of homocysteine, pentosidine, and inflammatory cytokines.