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RESULTSIncubation of RBC with CMPF and Jedi1 significantly increased RBC osmotic fragility, an effect prevented by GsMTx-4. At 6.0 g/L NaCl, incubation with CMPF and Jedi1 increased exposure of phosphatidylserine and elevated icCa2+ levels of RBC, indicating increased eryptosis. Notably, at an isotonic NaCl concentration of 9.0 g/L, CMPF - but not Jedi1 - significantly increased RBC phosphatidylserine exposure and icCa2+ levels; both effects were diminished by GsMTx-4.BACKGROUND AND HYPOTHESISIn patients with advanced chronic kidney disease (CKD), the lifespan of red blood cells (RBC) is often shortened, a condition attributed to the "uremic milieu." We reported recently that the uremic solute 3-carboxy-4-methyl-5-propyl-2-furanpropionate (CMPF) shares structural similarities with Jedi1, a chemical activator of the mechanosensitive cation channel Piezo1, whose activation increases calcium influx into cells. Against this backdrop, we hypothesized that CMPF may induce premature RBC death (eryptosis) through prolonged CMPF-induced activation of Piezo1 located on RBC. To test this hypothesis, we explored if CMPF, at concentrations found in uremia, interacts with Piezo1 located on RBC, increases intracellular calcium (icCa2+), and induces eryptosis.CONCLUSIONOur findings support the hypothesis that CMPF may function as an endogenous activator of Piezo1, increase icCa2+ levels, trigger eryptosis, and, through this pathway, possibly shorten the RBC life span. To what extent these in vitro findings are operative in advanced CKD warrants clinical studies.METHODSRBC from healthy individuals were incubated with CMPF or Jedi1 (both at a concentration of 87 µM), in the presence or absence of the Piezo1 inhibitor GsMTx-4 (2 µM). We challenged RBC osmotically through incubation in solutions of NaCl at concentrations between 3.0 and 9.0 g/L and determined their osmotic fragility. Using flow cytometry, we quantified in incubated RBC icCa2+ levels and phosphatidylserine exposure, a cellular marker of eryptosis.

RESULTSTwelve anuric patients were studied (six female patients; 44±19 years; dialysis vintage 35.2±28 months). The blood flow was 369±23 ml/min, dialysate flow was 495±61 ml/min, and ultrafiltration volume was 2.8±0.74 L. No significant differences were found regarding the removal of B2M, vitamin B12, and water-soluble solutes between dialytic modalities and dialyzers. Albumin and total protein loss were significantly higher in MCO groups than HFX groups when compared with the same modality. HDF groups had significantly higher albumin and total protein loss than HD groups when compared with the same dialyzer. MCO-HDF showed the highest protein loss among all groups.KEY POINTSHDF and MCO have shown greater clearance of middle-size uremic solutes in comparison with HF dialyzers; MCO has never been studied in HDF. MCO in HDF does not increase the clearance of B2M and results in a higher loss of albumin.CONCLUSIONSMCO-HD is not superior to HFX-HD and HFX-HDF for both middle molecule and water-soluble solute removal. Protein loss was more pronounced with MCO when compared with HFX on both HD and HDF modalities. MCO-HDF has no additional benefits regarding better removal of B2M but resulted in greater protein loss than MCO-HD.BACKGROUNDMiddle molecule removal and albumin loss have been studied in medium cutoff (MCO) membranes on hemodialysis (HD). It is unknown whether hemodiafiltration (HDF) with MCO membranes provides additional benefit. We aimed to compare the removal of small solutes and β2-microglobulin (B2M), albumin, and total proteins between MCO and high-flux (HFX) membranes with both HD and HDF, respectively.METHODSThe cross-over study comprised 4 weeks, one each with postdilutional HDF using HFX (HFX-HDF), MCO (MCO-HDF), HD with HFX (HFX-HD), and MCO (MCO-HD). MCO and HFX differ with respect to several characteristics, including membrane composition, pore size distribution, and surface area (HFX, 2.5 m2; MCO, 1.7 m2). There were two study treatments per week, one after the long interdialytic interval and another midweek. Reduction ratios of vitamin B12, B2M, phosphate, uric acid, and urea corrected for hemoconcentration were computed. Dialysis albumin and total protein loss during the treatment were quantified from dialysate samples.

RESULTSHere, we show that HD-RBC have less intracellular oxygen and that it is further decreased post-HD. Also, incubation in 5% O2 and uremia triggered eryptosis in vitro by exposing PS. Hypoxia itself increased the PS exposure in HD-RBC and CON-RBC, and the addition of uremic serum aggravated it. Furthermore, inhibition of the organic anion transporter 2 with ketoprofen reverted eryptosis and restored the levels of intracellular oxygen. Cytosolic levels of the uremic toxins pCS and IAA were decreased after dialysis.CONCLUSIONThese findings suggest the participation of uremic toxins and hypoxia in the process of eryptosis and intracellular oxygenation.BACKGROUND/AIMSChronic kidney disease is frequently accompanied by anemia, hypoxemia, and hypoxia. It has become clear that the impaired erythropoietin production and altered iron homeostasis are not the sole causes of renal anemia. Eryptosis is a process of red blood cells (RBC) death, like apoptosis of nucleated cells, characterized by Ca2+ influx and phosphatidylserine (PS) exposure to the outer RBC membrane leaflet. Eryptosis can be induced by uremic toxins and occurs before senescence, thus shortening RBC lifespan and aggravating renal anemia. We aimed to assess eryptosis and intracellular oxygen levels of RBC from hemodialysis patients (HD-RBC) and their response to hypoxia, uremia, and uremic toxins uptake inhibition.METHODSUsing flow cytometry, RBC from healthy individuals (CON-RBC) and HD-RBC were subjected to PS (Annexin-V), intracellular Ca2+ (Fluo-3/AM) and intracellular oxygen (Hypoxia Green) measurements, at baseline and after incubation with uremic serum and/or hypoxia (5% O2), with or without ketoprofen. Baseline levels of uremic toxins were quantified in serum and cytosol by high performance liquid chromatography.

Red blood cells (RBC) are the most abundant cells in the blood. Despite powerful defense systems against chemical and mechanical stressors, their life span is limited to about 120 days in healthy humans and further shortened in patients with kidney failure. Changes in the cell membrane potential and cation permeability trigger a cascade of events that lead to exposure of phosphatidylserine on the outer leaflet of the RBC membrane. The translocation of phosphatidylserine is an important step in a process that eventually results in eryptosis, the programmed death of an RBC. The regulation of eryptosis is complex and involves several cellular pathways, such as the regulation of non-selective cation channels. Increased cytosolic calcium concentration results in scramblase and floppase activation, exposing phosphatidylserine on the cell surface, leading to early clearance of RBCs from the circulation by phagocytic cells. While eryptosis is physiologically meaningful to recycle iron and other RBC constituents in healthy subjects, it is augmented under pathological conditions, such as kidney failure. In chronic kidney disease (CKD) patients, the number of eryptotic RBC is significantly increased, resulting in a shortened RBC life span that further compounds renal anemia. In CKD patients, uremic toxins, oxidative stress, hypoxemia, and inflammation contribute to the increased eryptosis rate. Eryptosis may have an impact on renal anemia, and depending on the degree of shortened RBC life span, the administration of erythropoiesis-stimulating agents is often insufficient to attain desired hemoglobin target levels. The goal of this review is to indicate the importance of eryptosis as a process closely related to life span reduction, aggravating renal anemia.

RESULTSA total of 26 spent PD dialysate samples were collected from 11 patients from ten dialysis centers. Spent PD dialysate samples were collected, on average, 25±13 days (median, 20; range, 10-45) after the onset of symptoms. The temporal distance of PD effluent collection relative to the closest positive nasal-swab RT-PCR result was 15±11 days (median, 14; range, 1-41). All 26 PD effluent samples tested negative at three SARS-CoV-2 genomic regions.CONCLUSIONSOur findings indicate the absence of SARS-CoV-2 in spent PD dialysate collected at ≥10 days after the onset of COVID-19 symptoms. We cannot rule out the presence of SARS-CoV-2 in spent PD dialysate in the early stage of COVID-19.BACKGROUNDTo date, it is unclear whether SARS-CoV-2 is present in spent dialysate from patients with COVID-19 on peritoneal dialysis (PD). Our aim was to assess the presence or absence of SARS-CoV-2 in spent dialysate from patients on chronic PD who had a confirmed diagnosis of COVID-19.METHODSSpent PD dialysate samples from patients on PD who were positive for COVID-19 were collected between March and August 2020. The multiplexed, real-time RT-PCR assay contained primer/probe sets specific to different SARS-CoV-2 genomic regions and to bacteriophage MS2 as an internal process control for nucleic acid extraction. Demographic and clinical data were obtained from patients' electronic health records.