Effects of uremic solutes on reactive oxygen species in vitro model systems as a possibility of support the renal function management

BACKGROUND: In view of the prevalence of oxidative stress in chronic kidney disease (CKD) patients, the loss of low-molecular-weight biomolecules by hemodialysis and the antioxidant potential of some uremic solutes that accumulate in CKD, we used in vitro model systems to test the antioxidant potential of the following uremic solutes: uric acid, hippuric acid, p-cresol, phenol, methylguanidine, L-arginine, L-tyrosine, creatinine and urea. METHODS: The in vitro antioxidant efficiencies of the uremic solutes, isolated or in mixtures, were tested with the following assays: i) ABTS radical cation decolorization assay; ii) hypochlorous acid (HOCl/OCl(−)) scavenging activity; iii) superoxide anion radical (O(2)(•-)) scavenging activity; iv) crocin bleaching assay (capture of peroxyl radical, ROO(•)); v) hydrogen peroxide (H(2)O(2)) scavenging activity. RESULTS: Four of the tested uremic solutes (p-cresol, phenol, L-tyrosine, uric acid) were effective antioxidants and their IC(50) were found in three model systems: ABTS(•+), HOCl/OCl(−) and crocin bleaching assay. In the 4-solutes mixtures, each one of the solute captured 12.5% for the IC(50) of the mixture to ABTS(•+) or HOCl/OCl(−), exhibiting a virtually exact additive effect. In the 2-solutes mixtures, for ROO(•) capture, it was observed the need of more mass of uremic solutes to reach an IC(50) value that was higher than the projected IC(50), obtained from the IC(50) of single solutes (25% of each, in the binary mixtures) in the same assay. In model systems for O(2)(•-) and H(2)O(2), none of the uremic solutes showed scavenging activity. CONCLUSIONS: The use of the IC(50) as an analytical tool to prepare and analyze mixtures allows the determination of their scavenging capacities and may be useful for the assessment of the antioxidant status of biological samples under conditions of altered levels of the endogenous antioxidant network and/or in the employment and monitoring of exogenous antioxidant therapy.