Background/Aims: Red blood cell (RBC) death could contribute to anemia in chronic kidney disease (CKD) patients. Recent observational research has suggested a relationship between RBC death (eryptosis) and hypoxemia in hemodialysis patients. Thus, we studied the isolated and joint effects of a uremic toxin (indoxyl sulfate; IS) and hypoxia on RBC biology. Methods: We incubated RBC from healthy donors with IS at concentrations of 0.01mM, 0.09mM and 0.17mM under both normoxic (21% O 2 ) and

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... c (5% O 2 ) conditions for 24 hours. Eryptosis was evaluated by RBC phosphatidylserine (PS) exposure, cell volume, and cytosolic calcium which were quantified by Annexin-V+, forward scatter, and Fluo-3AM+ binding, respectively. RBC redox balance was reported by reactive oxygen species (ROS) production and intracellular reduced glutathione (GSH). Analyses were performed by flow cytometry. Results: Hypoxia induced a 2-fold ROS production compared to normoxia. PS exposure and cytosolic calcium increased, while cell volume decreased by hypoxia and likewise by IS. IS increased ROS production in a dose-dependent manner under conditions of both normoxia and hypoxia. The same conditions promoted a GSH decrease with IS intensifying the hypoxia-induced effects. Conclusion: In summary, our results indicate that the concurrent presence of hypoxia and uremia augments RBC death and may therefore, contribute to the genesis of anemia in CKD. redox imbalance and reduction of RBCLS, predominantly in patients that suffer from chronic hypoxemia during dialysis.