Uremic serum damages endothelium by provoking excessive neutrophil extracellular trap formation.

Cardiovascular disease (CVD) is the leading cause of death in patients with chronic kidney disease (CKD). Endothelial cell (EC) dysfunction is a key CKD-specific risk factor; however, the mechanisms by which uremia harms the endothelium are still unclear. We report a role for excessive neutrophil extracellular trap (NET) formation induced by uremic serum on EC injury. Level of plasma nucleosome and myeloperoxidase-DNA, established in vivo markers of NETs, as well as intracellular adhesion molecule (ICAM)-1 were measured in hemodialysis (HD) patients and healthy volunteers (HV) and their prognostic role evaluated. For in vitro studies, HV-derived neutrophils and differentiated HL-60 cells by retinoic acid were used to determine the effect of uremic serum-induced NETs on human umbilical vein EC (HUVEC). The level of in vivo NETs was significantly higher in incident HD patients compared to HV, and these markers were strongly associated with ICAM-1. Specifically, nucleosome and ICAM-1 levels were independent predictors of a composite endpoint, all-cause mortality, or vascular access failure. In vitro, HD-derived uremic serum significantly increased NET formation both in dHL-60 and isolated neutrophils compared to control serum, and these NETs decreased EC viability and induced their apoptosis. In addition, the level of ICAM-1, E-selectin and von Willebrand factor in HUVEC supernatant was significantly increased by uremic serum-induced NETs compared to control serum-induced NETs. Dysregulated neutrophil activities in the uremic milieu may play a key role in vascular inflammatory responses. The high mortality and CVD rates in ESRD may be explained in part by excessive NET formation leading to EC damage and dysfunction.

Hepatic and Vascular Vitamin K Status in Patients with High Cardiovascular Risk.

Vitamin K dependent proteins (VKDP), such as hepatic coagulation factors and vascular matrix Gla protein (MGP), play key roles in maintaining physiological functions. Vitamin K deficiency results in inactive VKDP and is strongly linked to vascular calcification (VC), one of the major risk factors for cardiovascular morbidity and mortality. In this study we investigated how two vitamin K surrogate markers, dephosphorylated-undercarboxylated MGP (dp-ucMGP) and protein induced by vitamin K absence II (PIVKA-II), reflect vitamin K status in patients on hemodialysis or with calcific uremic arteriolopathy (CUA) and patients with atrial fibrillation or aortic valve stenosis. Through inter- and intra-cohort comparisons, we assessed the influence of vitamin K antagonist (VKA) use, vitamin K supplementation and disease etiology on vitamin K status, as well as the correlation between both markers. Overall, VKA therapy was associated with 8.5-fold higher PIVKA-II (0.25 to 2.03 AU/mL) and 3-fold higher dp-ucMGP (843 to 2642 pM) levels. In the absence of VKA use, non-renal patients with established VC have dp-ucMGP levels similar to controls (460 vs. 380 pM), while in HD and CUA patients, levels were strongly elevated (977 pM). Vitamin K supplementation significantly reduced dp-ucMGP levels within 12 months (440 to 221 pM). Overall, PIVKA-II and dp-ucMGP showed only weak correlation (r2 ≤ 0.26) and distinct distribution pattern in renal and non-renal patients. In conclusion, VKA use exacerbated vitamin K deficiency across all etiologies, while vitamin K supplementation resulted in a vascular VKDP status better than that of the general population. Weak correlation of vitamin K biomarkers calls for thoughtful selection lead by the research question. Vitamin K status in non-renal deficient patients was not anomalous and may question the role of vitamin K deficiency in the pathogenesis of VC in these patients.

Inferior survival outcomes of pancreas transplant alone in uremic patients.

Theoretically, pancreas transplant alone in uremic (PTAU) patients could also be one of the options for those waiting for both pancreas and kidney grafts, but it has never been reported. There were 160 cases of pancreas transplant in this study, including 16% PTAU. The 5-year patient survival was 66.2% after PTAU, 94.5% after SPK, 95.8% after PAK, and 95.4% after PTA. Rejection of pancreas graft was significantly lower in PTAU group (3.8%), followed by 16.7% in pancreas after kidney transplant (PAK), 29.8% in simultaneous pancreas and kidney transplant (SPK) and 37.0% in pancreas transplant alone (PTA). Fasting blood sugar and serum HbA1c levels after PTAU were not significantly different from those by other subgroups. The 5-year death-censored pancreas graft survival was 100% after PTAU and PAK, and 97.0% after SPK and 77.9% after PTA. However, the 5-year death-uncensored pancreas graft survival was 67.0% after PTAU, 100% after PAK, 91.3% after SPK, and 74.0% after PTA. The superior graft survival in the PTAU group was achieved only if deaths with a functioning graft were censored. In conclusion, given the inferior patient survival outcome, PTAU is still not recommended unless SPK and PAK is not available. Although PTAU could be a treatment option for patients with diabetes complicated by end-stage renal disease (ESRD) in terms of surgical risks, endocrine function, and immunological and graft survival outcomes, modification of the organ allocation policies to prioritize SPK transplant in eligible patients should be the prime goal.

Indoleamine 2,3-dioxygenase-1, a Novel Therapeutic Target for Post-Vascular Injury Thrombosis in CKD.

BACKGROUND: CKD, characterized by retained uremic solutes, is a strong and independent risk factor for thrombosis after vascular procedures . Urem ic solutes such as indoxyl sulfate (IS) and kynurenine (Kyn) mediate prothrombotic effect through tissue factor (TF). IS and Kyn biogenesis depends on multiple enzymes, with therapeutic implications unexplored. We examined the role of indoleamine 2,3-dioxygenase-1 (IDO-1), a rate-limiting enzyme of kynurenine biogenesis, in CKD-associated thrombosis after vascular injury. METHODS: IDO-1 expression in mice and human vessels was examined. IDO-1-/- mice, IDO-1 inhibitors, an adenine-induced CKD, and carotid artery injury models were used. RESULTS: Both global IDO-1-/- CKD mice and IDO-1 inhibitor in wild-type CKD mice showed reduced blood Kyn levels, TF expression in their arteries, and thrombogenicity compared with respective controls. Several advanced IDO-1 inhibitors downregulated TF expression in primary human aortic vascular smooth muscle cells specifically in response to uremic serum. Further mechanistic probing of arteries from an IS-specific mouse model, and CKD mice, showed upregulation of IDO-1 protein, which was due to inhibition of its polyubiquitination and degradation by IS in vascular smooth muscle cells. In two cohorts of patients with advanced CKD, blood IDO-1 activity was significantly higher in sera of study participants who subsequently developed thrombosis after endovascular interventions or vascular surgery. CONCLUSION: Leveraging genetic and pharmacologic manipulation in experimental models and data from human studies implicate IS as an inducer of IDO-1 and a perpetuator of the thrombotic milieu and supports IDO-1 as an antithrombotic target in CKD.

Cytokines and chemokines systemic levels are related to dialysis adequacy and creatinine clearance in patients with end-stage renal disease undergoing hemodialysis.

Although the clearance of low-molecular weight toxins is modulated by dialysis dose, the relationship between dialysis adequacy and middle systemic inflammatory mediators is often overlooked. Thus, the relationship between dialysis adequacy, pro- and anti-inflammatory cytokines and chemokines in hemodialysis (HD) patients was investigated. Forty-eight HD patients (19 women and 25 men) were investigated. Age, body mass index, time in HD, nutritional status, Kt/V and blood biochemical parameters was similar in patients of both sexes (P > 0.05). Thus, patients were stratified by dialysis adequacy measured by Kt/V method (adequate Kt/V ≥ 1.2). Post-HD urea, creatinine, cytokines (IFN-γ, IL-4 and IL-10) and chemokines (CCL-2, CCL-5, CXCL-8 and CXCL-10) were higher in patients with Kt/V < 1.2 (P < 0.05). Kt/V exhibited significant correlation with CXCL-10/IP-10 serum levels. Positive correlation between creatinine with IFN-γ, CCL-2/MCP-1, and CXCL-10/IP-10, and negative correlation with IL-10 was identified in patients with Kt/V < 1.2 (P < 0.05). In patients with Kt/V ≥ 1.2, only IL-10 was positively and CXCL-10/IP-10 negatively correlated with creatinine levels (P < 0.05). Kt/V and creatinine levels exhibited variable predictive value (Kt/V = 27% to 37%, creatinine = 29% to 47%) to explain cytokines and chemokines circulating levels in patients with adequate and inadequate dialysis dose. Taken together, our findings provide evidence that in addition to modulating uremic toxins levels, such as urea and creatinine, dialysis dose is associated with circulating levels of inflammatory mediators. Thus, low Kt/V results and creatinine accumulation are potential indicators of the systemic inflammatory stress determined by up-regulation of proinflammatory cytokines and chemokines, and downregulation of anti-inflammatory cytokines.

Uremia and Inadequate Oxygen Supply Induce Eryptosis and Intracellular Hypoxia in Red Blood Cells.

BACKGROUND/AIMS: Chronic 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. METHODS: Using 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. RESULTS: Here, 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. CONCLUSION: These findings suggest the participation of uremic toxins and hypoxia in the process of eryptosis and intracellular oxygenation.

Sphingolipid imbalance and inflammatory effects induced by uremic toxins in heart and kidney cells are reversed by dihydroceramide desaturase 1 inhibition.

Non-dialysable protein-bound uremic toxins (PBUTs) contribute to the development of cardiovascular disease (CVD) in chronic kidney disease (CKD) and vice versa. PBUTs have been shown to alter sphingolipid imbalance. Dihydroceramide desaturase 1 (Des1) is an important gatekeeper enzyme which controls the non-reversible conversion of sphingolipids, dihydroceramide, into ceramide. The present study assessed the effect of Des1 inhibition on PBUT-induced cardiac and renal effects in vitro, using a selective Des1 inhibitor (CIN038). Des1 inhibition attenuated hypertrophy in neonatal rat cardiac myocytes and collagen synthesis in neonatal rat cardiac fibroblasts and renal mesangial cells induced by the PBUTs, indoxyl sulfate and p-cresol sulfate. This is at least attributable to modulation of NF-κB signalling and reductions in ß-MHC, Collagen I and TNF-α gene expression. Lipidomic analyses revealed Des1 inhibition restored C16-dihydroceramide levels reduced by indoxyl sulfate. In conclusion, PBUTs play a critical role in mediating sphingolipid imbalance and inflammatory responses in heart and kidney cells, and these effects were attenuated by Des1 inhibition. Therefore, sphingolipid modifying agents may have therapeutic potential for the treatment of CVD and CKD and warrant further investigation.

Association of Plasma Uremic Solute Levels with Residual Kidney Function in Children on Peritoneal Dialysis.

BACKGROUND AND OBJECTIVES: Residual native kidney function confers health benefits in patients on dialysis. It can facilitate control of extracellular volume and inorganic ion concentrations. Residual kidney function can also limit the accumulation of uremic solutes. This study assessed whether lower plasma concentrations of uremic solutes were associated with residual kidney function in pediatric patients on peritoneal dialysis. DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS: Samples were analyzed from 29 pediatric patients on peritoneal dialysis, including 13 without residual kidney function and ten with residual kidney function. Metabolomic analysis by untargeted mass spectrometry compared plasma solute levels in patients with and without residual kidney function. Dialytic and residual clearances of selected solutes were also measured by assays using chemical standards. RESULTS: Metabolomic analysis showed that plasma levels of 256 uremic solutes in patients with residual kidney function averaged 64% (interquartile range, 51%-81%) of the values in patients without residual kidney function who had similar total Kt/Vurea. The plasma levels were significantly lower for 59 of the 256 solutes in the patients with residual kidney function and significantly higher for none. Assays using chemical standards showed that residual kidney function provides a higher portion of the total clearance for nonurea solutes than it does for urea. CONCLUSIONS: Concentrations of many uremic solutes are lower in patients on peritoneal dialysis with residual kidney function than in those without residual kidney function receiving similar treatment as assessed by Kt/Vurea.

Wharton's Jelly Mesenchymal Stem Cell-Derived Extracellular Vesicles Reduce SARS-CoV2-Induced Inflammatory Cytokines Under High Glucose and Uremic Toxin Conditions.

Cytokine storm is recognized as one of the factors contributing to organ failures and mortality in patients with COVID-19. Due to chronic inflammation, COVID-19 patients with diabetes mellitus (DM) or renal disease (RD) have more severe symptoms and higher mortality. However, the factors that contribute to severe outcomes of COVID-19 patients with DM and RD have received little attention. In an effort to investigate potential treatments for COVID-19, recent research has focused on the immunomodulation functions of mesenchymal stem cells (MSCs). In this study, the correlation between DM and RD and the severity of COVID-19 was examined by a combined approach with a meta-analysis and experimental research. The results of a systematic review and meta-analysis suggested that the odd of mortality in patients with both DM and RD was increased in comparison to those with a single comorbidity. In addition, in the experimental research, the data showed that high glucose and uremic toxins contributed to the induction of cytokine storm in human lung adenocarcinoma epithelial cells (Calu-3 cells) in response to SARS-CoV Peptide Pools. Of note, the incorporation of Wharton's jelly MSC-derived extracellular vesicles (WJ-EVs) into SARS-CoV peptide-induced Calu-3 resulted in a significant decrease in nuclear NF-κB p65 and the downregulation of the cytokine storm under high concentrations of glucose and uremic toxins. This clearly suggests the potential for WJ-EVs to reduce cytokine storm reactions in patients with both chronic inflammation diseases and viral infection.

CE-MS-Based Identification of Uremic Solutes Specific to Hemodialysis Patients.

Uremic toxins are suggested to be involved in the pathophysiology of hemodialysis (HD) patients. However, the profile of uremic solutes in HD patients has not been fully elucidated. In this study using capillary electrophoresis mass spectrometry (CE-MS), we comprehensively quantified the serum concentrations of 122 ionic solutes before and after HD in 11 patients. In addition, we compared the results with those in non-HD patients with chronic kidney disease (CKD) to identify HD patient-specific solutes. We identified 38 solutes whose concentrations were higher in pre-HD than in CKD stage G5. Ten solutes among them did not significantly accumulate in non-HD CKD patients, suggesting that these solutes accumulate specifically in HD patients. We also identified 23 solutes whose concentrations were lower in both pre- and post-HD than in CKD stage G5. The serum levels of 14 solutes among them were not affected by renal function in non-HD patients, suggesting that these solutes tend to be lost specifically in HD patients. Our data demonstrate that HD patients have a markedly different profile of serum uremic solute levels compared to that in non-HD CKD patients. The solutes identified in our study may contribute to the pathophysiology of HD patients.

Predialysis and Dialysis Therapies Differently Affect Nitric Oxide Synthetic Pathway in Red Blood Cells from Uremic Patients: Focus on Peritoneal Dialysis.

Red blood cells (RBCs) have been found to synthesize and release both nitric oxide (NO) and cyclic guanosine monophosphate (cGMP), contributing to systemic NO bioavailability. These RBC functions resulted impaired in chronic kidney disease (CKD). This study aimed to evaluate whether predialysis (conservative therapy, CT) and dialysis (peritoneal dialysis, PD; hemodialysis, HD) therapies used during CKD progression may differently affect NO-synthetic pathway in RBCs. Our data demonstrated that compared to PD, although endothelial-NO-synthase activation was similarly increased, HD and CT were associated to cGMP RBCs accumulation, caused by reduced activity of cGMP membrane transporter (MRP4). In parallel, plasma cGMP levels were increased by both CT and HD and they significantly decreased after hemodialysis, suggesting that this might be caused by reduced cGMP renal clearance. As conceivable, compared to healthy subjects, plasma nitrite levels were significantly reduced by HD and CT but not in patients on PD. Additionally, the increased carotid intima-media thickness (IMT) values did not reach the significance exclusively in patients on PD. Therefore, our results show that PD might better preserve the synthetic NO-pathway in CKD-erythrocytes. Whether this translates into a reduced development of uremic vascular complications requires further investigation.

Thrombolome and Its Emerging Role in Chronic Kidney Diseases.

Patients with chronic kidney disease (CKD) are at an increased risk of thromboembolic complications, including myocardial infarction, stroke, deep vein thrombosis, and pulmonary embolism. These complications lead to increased mortality. Evidence points to the key role of CKD-associated dysbiosis and its effect via the generation of gut microbial metabolites in inducing the prothrombotic phenotype. This phenomenon is known as thrombolome, a panel of intestinal bacteria-derived uremic toxins that enhance thrombosis via increased tissue factor expression, platelet hyperactivity, microparticles release, and endothelial dysfunction. This review discusses the role of uremic toxins derived from gut-microbiota metabolism of dietary tryptophan (indoxyl sulfate (IS), indole-3-acetic acid (IAA), kynurenine (KYN)), phenylalanine/tyrosine (p-cresol sulfate (PCS), p-cresol glucuronide (PCG), phenylacetylglutamine (PAGln)) and choline/phosphatidylcholine (trimethylamine N-oxide (TMAO)) in spontaneously induced thrombosis. The increase in the generation of gut microbial uremic toxins, the activation of aryl hydrocarbon (AhRs) and platelet adrenergic (ARs) receptors, and the nuclear factor kappa B (NF-κB) signaling pathway can serve as potential targets during the prevention of thromboembolic events. They can also help create a new therapeutic approach in the CKD population.

Medium Cut-Off Dialysis Membrane and Dietary Fiber Effects on Inflammation and Protein-Bound Uremic Toxins: A Systematic Review and Protocol for an Interventional Study.

The aim of this systematic review is to investigate the effects of the use of a medium cut-off membrane (MCO) and dietary fiber on the concentration of protein-bound uremic toxins (PBUTs) and inflammatory markers in hemodialysis (HD) patients. Of 11,397 papers originally found, eight met the criteria of randomized controlled trial design. No study examined the effects of MCO membranes on PBUTs. Three studies examined the reduction in inflammatory markers with MCO membranes compared to high-flux HD membranes and showed no significant differences. Five studies of dietary fiber supplementation showed an inconclusive positive effect on PBUT levels and a significant positive effect on the reduction in inflammatory markers (interleukin-6 reduction: standardized difference in means -1.18; 95% confidence interval -1.45 to -0.9 for dietary fiber supplementation vs. control; p < 0.001). To date, no study has combined the use of an MCO membrane and fiber supplementation to reduce PBUT levels and inflammation with online hemodiafiltration as a comparator. A rationale and protocol for an interventional trial using a combination of MCO membrane dialysis and fiber supplementation to lower inflammatory markers and PBUT concentrations are presented.

Dietary Fibre Intake Is Associated with Serum Levels of Uraemic Toxins in Children with Chronic Kidney Disease.

Imbalanced colonic microbial metabolism plays a pivotal role in generating protein-bound uraemic toxins (PBUTs), which accumulate with deteriorating kidney function and contribute to the uraemic burden of children with chronic kidney disease (CKD). Dietary choices impact the gut microbiome and metabolism. The aim of this study was to investigate the relation between dietary fibre and gut-derived PBUTs in paediatric CKD. Sixty-one (44 male) CKD children (9 ± 5 years) were prospectively followed for two years. Dietary fibre intake was evaluated by either 24-h recalls (73%) or 3-day food records (27%) at the same time of blood sampling for assessment of total and free serum levels of different PBUTs using liquid chromatography. We used linear mixed models to assess associations between fibre intake and PBUT levels. We found an inverse association between increase in fibre consumption (g/day) and serum concentrations of free indoxyl sulfate (-3.1% (-5.9%; -0.3%) (p = 0.035)), free p-cresyl sulfate (-2.5% (-4.7%; -0.3%) (p = 0.034)), total indole acetic acid (IAA) (-1.6% (-3.0%; -0.3%) (p = 0.020)), free IAA (-6.6% (-9.3%; -3.7%) (p < 0.001)), total serum p-cresyl glucuronide (pCG) (-3.0% (-5.6%; -0.5%) (p = 0.021)) and free pCG levels (-3.3% (-5.8%; -0.8%) (p = 0.010)). The observed associations between dietary fibre intake and the investigated PBUTs highlight potential benefits of fibre intake for the paediatric CKD population. The present observational findings should inform and guide adaptations of dietary prescriptions in children with CKD.

Protection of Residual Renal Function and Nutritional Treatment: First Step Strategy for Reduction of Uremic Toxins in End-Stage Kidney Disease Patients.

The retention of uremic toxins and their pathological effects occurs in the advanced phases of chronic kidney disease (CKD), mainly in stage 5, when the implementation of conventional thrice-weekly hemodialysis is the prevalent and life-saving treatment. However, the start of hemodialysis is associated with both an acceleration of the loss of residual kidney function (RKF) and the shift to an increased intake of proteins, which are precursors of uremic toxins. In this phase, hemodialysis treatment is the only way to remove toxins from the body, but it can be largely inefficient in the case of high molecular weight and/or protein-bound molecules. Instead, even very low levels of RKF are crucial for uremic toxins excretion, which in most cases are protein-derived waste products generated by the intestinal microbiota. Protection of RKF can be obtained even in patients with end-stage kidney disease (ESKD) by a gradual and soft shift to kidney replacement therapy (KRT), for example by combining a once-a-week hemodialysis program with a low or very low-protein diet on the extra-dialysis days. This approach could represent a tailored strategy aimed at limiting the retention of both inorganic and organic toxins. In this paper, we discuss the combination of upstream (i.e., reduced production) and downstream (i.e., increased removal) strategies to reduce the concentration of uremic toxins in patients with ESKD during the transition phase from pure conservative management to full hemodialysis treatment.

The Impact of CKD on Uremic Toxins and Gut Microbiota.

Numerous studies have indicated that the progression of chronic kidney disease (CKD) to end-stage renal disease (ESRD) is strictly associated with the accumulation of toxic metabolites in blood and other metabolic compartments. This accumulation was suggested to be related to enhanced generation of toxins from the dysbiotic microbiome accompanied by their reduced elimination by impaired kidneys. Intestinal microbiota play a key role in the accumulation of uremic toxins due to the fact that numerous uremic solutes are generated in the process of protein fermentation by colonic microbiota. Some disease states, including CKD, are associated with the presence of dysbiosis, which can be defined as an "imbalanced intestinal microbial community with quantitative and qualitative changes in the composition and metabolic activities of the gut microbiota". The results of studies have confirmed the altered composition and functions of gut microbial community in chronic kidney disease. In the course of CKD protein-bound uremic toxins, including indoxyl sulfate, p-cresyl glucuronide, p-cresyl sulfate and indole-3-acetic acid are progressively accumulated. The presence of chronic kidney disease may be accompanied by the development of intestinal inflammation and epithelial barrier impairment leading to hastened systemic translocation of bacterial-derived uremic toxins and consequent oxidative stress injury to the kidney, cardiovascular and endocrine systems. These findings offer new therapeutic possibilities for the management of uremia, inflammation and kidney disease progression and the prevention of adverse outcomes in CKD patients. It seems that dietary interventions comprising prebiotics, probiotics, and synbiotics could pose a promising strategy in the management of uremic toxins in CKD.

Optical Method and Biochemical Source for the Assessment of the Middle-Molecule Uremic Toxin ß2-Microglobulin in Spent Dialysate.

Optical monitoring of spent dialysate has been used to estimate the removal of water-soluble low molecular weight as well as protein-bound uremic toxins from the blood of end stage kidney disease (ESKD) patients. The aim of this work was to develop an optical method to estimate the removal of ß2-microglobulin (ß2M), a marker of middle molecule (MM) uremic toxins, during hemodialysis (HD) treatment. Ultraviolet (UV) and fluorescence spectra of dialysate samples were recorded from 88 dialysis sessions of 22 ESKD patients, receiving four different settings of dialysis treatments. Stepwise regression was used to obtain the best model for the assessment of ß2M concentration in the spent dialysate. The correlation coefficient 0.958 and an accuracy of 0.000 ± 0.304 mg/L was achieved between laboratory and optically estimated ß2M concentrations in spent dialysate for the entire cohort. Optically and laboratory estimated reduction ratio (RR) and total removed solute (TRS) of ß2M were not statistically different (p > 0.35). Dialytic elimination of MM uremic toxin ß2M can be followed optically during dialysis treatment of ESKD patients. The main contributors to the optical signal of the MM fraction in the spent dialysate were provisionally identified as tryptophan (Trp) in small peptides and proteins, and advanced glycation end-products.

Uremic Toxins and Blood Purification: A Review of Current Evidence and Future Perspectives.

Accumulation of uremic toxins represents one of the major contributors to the rapid progression of chronic kidney disease (CKD), especially in patients with end-stage renal disease that are undergoing dialysis treatment. In particular, protein-bound uremic toxins (PBUTs) seem to have an important key pathophysiologic role in CKD, inducing various cardiovascular complications. The removal of uremic toxins from the blood with dialytic techniques represents a proved approach to limit the CKD-related complications. However, conventional dialysis mainly focuses on the removal of water-soluble compounds of low and middle molecular weight, whereas PBTUs are strongly protein-bound, thus not efficiently eliminated. Therefore, over the years, dialysis techniques have been adapted by improving membranes structures or using combined strategies to maximize PBTUs removal and eventually prevent CKD-related complications. Recent findings showed that adsorption-based extracorporeal techniques, in addition to conventional dialysis treatment, may effectively adsorb a significant amount of PBTUs during the course of the sessions. This review is focused on the analysis of the current state of the art for blood purification strategies in order to highlight their potentialities and limits and identify the most feasible solution to improve toxins removal effectiveness, exploring possible future strategies and applications, such as the study of a synergic approach by reducing PBTUs production and increasing their blood clearance.

Uremic serum induces prothrombotic changes in venous endothelial cells and inflammatory changes in aortic endothelial cells.

BACKGROUND: Uremia induces various pathologic changes in the endothelium. However, there is limited information about the differences of these effects in endothelial cells originating from different parts of the vascular tree. METHODS: The effect of uremic serum obtained from patients with end stage renal failure on the gene expression and secretory activity of venous endothelial cells (VEC) and aortic endothelial cells (AEC) was studied in in vitro culture. RESULTS: In VEC, the expression of genes regulating the synthesis of von Willebrand factor (vWF) was increased by 254% (p<.005), vascular endothelial growth factor (VEGF) synthesis by 150% (p<.001), tissue plasminogen activator (t-PA) synthesis by 62% (p<.005), platelet endothelial cell adhesion molecule by 89% (p<.005), and the expression of gene regulating interleukin-6 (IL-6) synthesis was reduced. In AEC, the expression of the gene regulating synthesis of IL-6 was increased by 174% (p<.001), and the expression of the other genes was reduced. The secretion of IL-6 was reduced in VEC by 38% (p<.01) and increased in AEC by 55% (p<.005). In VEC, increased synthesis of VEGF 64% (p<.001) vWF (+34%, p<.01), and t-PA (+53%, p<.002) was observed, and in AEC it was reduced. CONCLUSIONS: VEC and AEC respond in different ways after exposure to uremic serum. VEC acquires the prothrombotic phenotype, whereas in AEC the inflammatory phenotype appears.

GSTM1 Modulates Expression of Endothelial Adhesion Molecules in Uremic Milieu.

Deletion polymorphism of glutathione S-transferase M1 (GSTM1), a phase II detoxification and antioxidant enzyme, increases susceptibility to end-stage renal disease (ESRD) as well as the development of cardiovascular diseases (CVD) among ESRD patients and leads to their shorter cardiovascular survival. The mechanisms by which GSTM1 downregulation contributes to oxidative stress and inflammation in endothelial cells in uremic conditions have not been investigated so far. Therefore, the aim of the present study was to elucidate the effects of GSTM1 knockdown on oxidative stress and expression of a panel of inflammatory markers in human umbilical vein endothelial cells (HUVECs) exposed to uremic serum. Additionally, we aimed to discern whether GSTM1-null genotype is associated with serum levels of adhesion molecules in ESRD patients. HUVECs treated with uremic serum exhibited impaired redox balance characterized by enhanced lipid peroxidation and decreased antioxidant enzyme activities, independently of the GSTM1 knockdown. In response to uremic injury, HUVECs exhibited alteration in the expression of a series of inflammatory cytokines including retinol-binding protein 4 (RBP4), regulated on activation, normal T cell expressed and secreted (RANTES), C-reactive protein (CRP), angiogenin, dickkopf-1 (Dkk-1), and platelet factor 4 (PF4). GSTM1 knockdown in HUVECs showed upregulation of monocyte chemoattractant protein-1 (MCP-1), a cytokine involved in the regulation of monocyte migration and adhesion. These cells also have shown upregulated intracellular and vascular cell adhesion molecules (ICAM-1 and VCAM-1). In accordance with these findings, the levels of serum ICAM-1 and VCAM-1 (sICAM-1 and sVCAM-1) were increased in ESRD patients lacking GSTM1, in comparison with patients with the GSTM1-active genotype. Based on these results, it may be concluded that incubation of endothelial cells in uremic serum induces redox imbalance accompanied with altered expression of a series of cytokines involved in arteriosclerosis and atherosclerosis. The association of GSTM1 downregulation with the altered expression of adhesion molecules might be at least partly responsible for the increased susceptibility of ESRD patients to CVD.