2-Deoxy-glucose ameliorates the peritoneal mesothelial and endothelial barrier function perturbation occurring due to Peritoneal Dialysis fluids exposure.

Peritoneal dialysis (PD) and prolonged exposure to PD fluids (PDF) induce peritoneal membrane (PM) fibrosis and hypervascularity, leading to functional PM degeneration. 2-deoxy-glucose (2-DG) has shown potential as PM antifibrotic by inhibiting hyper-glycolysis induced mesothelial-to-mesenchymal transition (MMT). We investigated whether administration of 2-DG with several PDF affects the permeability of mesothelial and endothelial barrier of the PM. The antifibrotic effect of 2-DG was confirmed by the gel contraction assay with embedded mesothelial (MeT-5A) or endothelial (EA.hy926) cells cultured in Dianeal® 2.5 % (CPDF), BicaVera® 2.3 % (BPDF), Balance® 2.3 % (LPDF) with/without 2-DG addition (0.2 mM), and qPCR for αSMA, CDH2 genes. Moreover, 2-DG effect was tested on the permeability of monolayers of mesothelial and endothelial cells by monitoring the transmembrane resistance (RTM), FITC-dextran (10, 70 kDa) diffusion and mRNA expression levels of CLDN-1 to -5, ZO1, SGLT1, and SGLT2 genes. Contractility of MeT-5A cells in CPDF/2-DG was decreased, accompanied by αSMA (0.17 ± 0.03) and CDH2 (2.92 ± 0.29) gene expression fold changes. Changes in αSMA, CDH2 were found in EA.hy926 cells, though αSMA also decreased under LPDF/2-DG incubation (0.42 ± 0.02). Overall, 2-DG mitigated the PDF-induced alterations in mesothelial and endothelial barrier function as shown by RTM, dextran transport and expression levels of the CLDN-1 to -5, ZO1, and SGLT2. Thus, supplementation of PDF with 2-DG not only reduces MMT but also improves functional permeability characteristics of the PM mesothelial and endothelial barrier.

Differential effects of biocompatible peritoneal dialysis fluids on human mesothelial and endothelial cells in 2D and 3D phenotypes.

INTRODUCTION: Peritoneal dialysis (PD) is a life maintaining treatment in patients with end-stage renal disease. Its chronic application leads to peritoneal mesothelial layer denudation and fibrotic transformation along with vascular activation of inflammatory pathways. The impact of different PD fluids (PDF) on mesothelial and endothelial cell function and repair mechanisms are not comprehensively described. MATERIALS AND METHODS: Mesothelial (MeT-5A) and endothelial cells (EA.hy926) were cultured in 1:1 ratio with cell medium and different PDF (icodextrin-based, amino acid-based, and glucose-based). Cell adhesion, cell migration, and cell proliferation in 2D and spheroid formation and collagen gel contraction assays in 3D cell cultures were performed. RESULTS: Cell proliferation and cell-mediated gel contraction were both significantly decreased in all conditions. 3D spheroid formation was significantly reduced with icodextrin and amino acid PDF, but unchanged with glucose PDF. Adhesion was significantly increased by amino acid PDF in mesothelial cells and decreased by icodextrin and amino acid PDF in endothelial cells. Migration capacity was significantly decreased in mesothelial cells by all three PDF, while endothelial cells remained unaffected. CONCLUSIONS: In 3D phenotypes the effects of PDF are more uniform in both mesothelial and endothelial cells, mitigating spheroid formation and gel contraction. On the contrary, effects on 2D phenotypes are more uniform in the icodextrin and amino acid PDF as opposed to glucose ones and affect mesothelial cells more variably. 2D and 3D comparative assessments of PDF effects on the main peritoneal membrane cell barriers, the mesothelial and endothelial, could provide useful translational information for PD studies.

Knockdown of AK142426 suppresses M2 macrophage polarization and inflammation in peritoneal fibrosis via binding to c-Jun.

BACKGROUND: Peritoneal fibrosis is a common complication of peritoneal dialysis, which may lead to ultrafiltration failure and ultimately treatment discontinuation. LncRNAs participate in many biological processes during tumorigenesis. We investigated the role of AK142426 in peritoneal fibrosis. METHODS: The AK142426 level in peritoneal dialysis (PD) fluid was detected by quantitative real-time-PCR assay. The M2 macrophage distribution was determined by flow cytometry. The inflammatory cytokines of TNF-α and TGF-ß1 were measured by ELISA assay. The direct interaction between AK142426 and c-Jun was evaluated by RNA pull-down assay. In addition, the c-Jun and fibrosis related proteins were assessed by western blot analysis. RESULTS: The PD-induced peritoneal fibrosis mouse model was successfully established. More importantly, PD treatment induced M2 macrophage polarization and the inflammation in PD fluid, which might be associated with exosome transmission. Fortunately, AK142426 was observed to be upregulated in PD fluid. Mechanically, knockdown of AK142426 suppressed M2 macrophage polarization and inflammation. Furthermore, AK142426 could upregulate c-Jun through binding c-Jun protein. In rescue experiments, overexpression of c-Jun could partially abolish the inhibitory effect of sh-AK142426 on the activation of M2 macrophages and inflammation. Consistently, knockdown of AK142426 alleviated peritoneal fibrosis in vivo. CONCLUSIONS: This study demonstrated that knockdown of AK142426 suppressed M2 macrophage polarization and inflammation in peritoneal fibrosis via binding to c-Jun, suggesting that AK142426 might be a promising therapeutic target for patients of peritoneal fibrosis.

Peritoneal transformation shortly after kidney transplantation in pediatric patients with preceding chronic peritoneal dialysis.

BACKGROUND: The unphysiological composition of peritoneal dialysis (PD) fluids induces progressive peritoneal fibrosis, hypervascularization and vasculopathy. Information on these alterations after kidney transplantation (KTx) is scant. METHODS: Parietal peritoneal tissues were obtained from 81 pediatric patients with chronic kidney disease stage 5 (CKD5), 72 children on PD with low glucose degradation product (GDP) PD fluids, and from 20 children 4-8 weeks after KTx and preceding low-GDP PD. Tissues were analyzed by digital histomorphometry and quantitative immunohistochemistry. RESULTS: While chronic PD was associated with peritoneal hypervascularization, after KTx vascularization was comparable to CKD5 level. Submesothelial CD45 counts were 40% lower compared with PD, and in multivariable analyses independently associated with microvessel density. In contrast, peritoneal mesothelial denudation, submesothelial thickness and fibrin abundance, number of activated, submesothelial fibroblasts and of mesothelial-mesenchymal transitioned cells were similar after KTx. Diffuse peritoneal podoplanin positivity was present in 40% of the transplanted patients. In subgroups matched for age, PD vintage, dialytic glucose exposure and peritonitis incidence, submesothelial hypoxia-inducible factor 1-alpha abundance and angiopoietin 1/2 ratio were lower after KTx, reflecting vessel maturation, while arteriolar and microvessel p16 and cleaved Casp3 were higher. Submesothelial mast cell count and interleukin-6 were lower, whereas transforming growth factor-beta induced pSMAD2/3 was similar as compared with children on PD. CONCLUSIONS: Peritoneal membrane damage induced with chronic administration of low-GDP PD fluids was less severe after KTx. While peritoneal microvessel density, primarily defining PD transport and ultrafiltration capacity, was normal after KTx and peritoneal inflammation less pronounced, diffuse podoplanin positivity and profibrotic activity were prevalent.

Association of longitudinal high-sensitive C-reactive protein levels with changing membrane characteristics in peritoneal dialysis.

BACKGROUND: Increasing peritoneal permeability with ultrafiltration and solute removal inadequacy is a challenging issue in peritoneal dialysis (PD). Decreasing permeability is less frequent but also results in diminished solute clearance. We evaluated the association between longitudinal high-sensitive C-reactive protein (hs-CRP) values and the change in transport characteristics of the peritoneal membrane in PD patients. METHODS: This is a retrospective, single-center study of incident PD patients. An increase or decrease in peritoneal transport status is defined as two or more categories of a rise or decline in the peritoneal equilibration test (PET) from their baseline during follow-up. The 4-h dialysate/plasma creatinine ratio was used to classify transport characteristics. Hs-CRP values were obtained from the routine annual examinations of the patients. RESULTS: Baseline demographics, residual kidney function, frequency of high glucose-containing dialysate, and icodextrin use were similar between the groups. Total episodes of peritonitis within the first 5 years of follow-up were higher in stable transporters than in increased and decreased transporters (p = 0.009). Stable transporters' mean hs-CRP values did not change within 5 years (Wilks' λ = 0.873, F (2.317, 180.740) = 2.210, p = 0.10). Increased and decreased transporters' hs-CRP values significantly raised over the years (Wilks' λ = 0.422, F (1.979, 77.163) = 3.405, p = 0.04 and Wilks' λ = 0.558, F (3.673, 66.107) = 4.396, p = 0.001, respectively). CONCLUSIONS: Our study shows that the peritoneal membrane may change into different characteristics in many patients over time, despite very low peritonitis frequencies and similar baseline characteristics that may be significantly affected by systemic inflammation.

Phloretin Improves Ultrafiltration and Reduces Glucose Absorption during Peritoneal Dialysis in Rats.

BACKGROUND: Harmful glucose exposure and absorption remain major limitations of peritoneal dialysis (PD). We previously showed that inhibition of sodium glucose cotransporter 2 did not affect glucose transport during PD in rats. However, more recently, we found that phlorizin, a dual blocker of sodium glucose cotransporters 1 and 2, reduces glucose diffusion in PD. Therefore, either inhibiting sodium glucose cotransporter 1 or blocking facilitative glucose channels by phlorizin metabolite phloretin would reduce glucose transport in PD. METHODS: We tested a selective blocker of sodium glucose cotransporter 1, mizagliflozin, as well as phloretin, a nonselective blocker of facilitative glucose channels, in an anesthetized Sprague-Dawley rat model of PD. RESULTS: Intraperitoneal phloretin treatment reduced glucose absorption by >30% and resulted in a >50% higher ultrafiltration rate compared with control animals. Sodium removal and sodium clearances were similarly improved, whereas the amount of ultrafiltration per millimole of sodium removed did not differ. Mizagliflozin did not influence glucose transport or osmotic water transport. CONCLUSIONS: Taken together, our results and previous results indicate that blockers of facilitative glucose channels may be a promising target for reducing glucose absorption and improving ultrafiltration efficiency in PD.

Bioengineered Kidney Tubules Efficiently Clear Uremic Toxins in Experimental Dialysis Conditions.

Patients with end-stage kidney disease (ESKD) suffer from high levels of protein-bound uremic toxins (PBUTs) that contribute to various comorbidities. Conventional dialysis methods are ineffective in removing these PBUTs. A potential solution could be offered by a bioartificial kidney (BAK) composed of porous membranes covered by proximal tubule epithelial cells (PTECs) that actively secrete PBUTs. However, BAK development is currently being hampered by a lack of knowledge regarding the cytocompatibility of the dialysis fluid (DF) that comes in contact with the PTECs. Here, we conducted a comprehensive functional assessment of the DF on human conditionally immortalized PTECs (ciPTECs) cultured as monolayers in well plates, on Transwell® inserts, or on hollow fiber membranes (HFMs) that form functional units of a BAK. We evaluated cell viability markers, monolayer integrity, and PBUT clearance. Our results show that exposure to DF did not affect ciPTECs' viability, membrane integrity, or function. Seven anionic PBUTs were efficiently cleared from the perfusion fluid containing a PBUTs cocktail or uremic plasma, an effect which was enhanced in the presence of albumin. Overall, our findings support that the DF is cytocompatible and does not compromise ciPTECs function, paving the way for further advancements in BAK development and its potential clinical application.

Presence of galectin-3 in peritoneal dialysate. Does it have a role in the peritoneal membrane inflammatory process?

Peritoneal dialysis (PD) causes structural and functional changes in the peritoneal membrane, which are attributed to local inflammatory process. This study assessed the presence of galectin-3 (Gal-3), a known inflammatory modulator, in dialysate effluent and correlated its levels with markers of inflammatory process. Gal-3 levels in serum and dialysate effluent were measured in prevalent PD patients on morning visits (n = 27) or during peritoneal equilibration tests (PET, n = 16), it association with clinical and laboratory parameters, including dialysate/plasma creatinine (D/P creatinine) and interleukin-6 (IL-6) levels was analysed. Gal-3 levels in dialysate effluent correlated with D/P creatinine (0.663, p = 0.005) and dialysate effluent IL-6 levels (0.674, p = 0.002), but not with serum Gal-3 levels or dialysis vintage. Patients who were high transporters had higher Gal-3 levels in dialysate effluent, as compared to lower transporters. In multivariate regression analysis, dialysate IL-6 level was the strongest predictor of dialysate Gal-3 levels. This study found Gal-3 in dialysate effluent correlated with D/P creatinine and dialysate IL-6 levels. These findings may imply that Gal-3 has a role in the intraperitoneal inflammatory process. However, this needs to be investigated further.

Fibrosis of Peritoneal Membrane as Target of New Therapies in Peritoneal Dialysis.

Peritoneal dialysis (PD) is an efficient renal replacement therapy for patients with end-stage renal disease. Even if it ensures an outcome equivalent to hemodialysis and a better quality of life, in the long-term, PD is associated with the development of peritoneal fibrosis and the consequents patient morbidity and PD technique failure. This unfavorable effect is mostly due to the bio-incompatibility of PD solution (mainly based on high glucose concentration). In the present review, we described the mechanisms and the signaling pathway that governs peritoneal fibrosis, epithelial to mesenchymal transition of mesothelial cells, and angiogenesis. Lastly, we summarize the present and future strategies for developing more biocompatible PD solutions.

Relationship between measured and prescribed dialysate sodium in haemodialysis: a systematic review and meta-analysis.

BACKGROUND: Dialysate sodium (DNa) prescription policy differs between haemodialysis (HD) units, and the optimal DNa remains uncertain. We sought to summarize the evidence on the agreement between prescribed and delivered DNa, and whether the relationship varied according to prescribed DNa. METHODS: We searched MEDLINE and PubMed from inception to 26 February 2020 for studies reporting measured and prescribed DNa. We analysed results reported in aggregate with random-effects meta-analysis. We analysed results reported by individual sample, using mixed-effects Bland-Altman analysis and linear regression. Pre-specified subgroup analyses included method of sodium measurement, dialysis machine manufacturer and proportioning method. RESULTS: Seven studies, representing 908 dialysate samples from 10 HD facilities (range 16-133 samples), were identified. All but one were single-centre studies. Studies were of low to moderate quality. Overall, there was no statistically significant difference between measured and prescribed DNa {mean difference = 0.73 mmol/L [95% confidence interval (CI) -1.12 to 2.58; P = 0.44]} but variability across studies was substantial (I2 = 99.3%). Among individually reported samples (n = 295), measured DNa was higher than prescribed DNa by 1.96 mmol/L (95% CI 0.23-3.69) and the 95% limits of agreement ranged from -3.97 to 7.88 mmol/L. Regression analysis confirmed a strong relationship between prescribed and measured DNa, with a slope close to 1:1 (ß = 1.16, 95% CI 1.06-1.27; P < 0.0001). CONCLUSIONS: A limited number of studies suggest that, on average, prescribed and measured DNa are similar. However, between- and within-study differences were large. Further consideration of the precision of delivered DNa is required to inform rational prescribing.

Comparison between standard single chamber versus dual chamber low glucose degradation product peritoneal dialysis fluids.

Dual chamber (DC) peritoneal dialysis (PD) dialysates contain fewer glucose degradation products (GDPs), so potentially reducing advanced glycosylation end products (AGEs), which have been reported to increase inflammation and cardiovascular risk. We wished to determine whether use of DC dialysates resulted in demonstrable patient benefits. Biochemical profiles, body composition, muscle strength, and skin autofluorescence measurements of tissue AGEs (SAF) were compared in patients using DC and standard single chamber dialysates. We studied 263 prevalent PD patients from 2 units, 62.4% male, mean age 61.8 ± 16.1 years, 78 (29.7%) used DC dialysates. DC patients were younger (55.9 ± 16.4 vs. 64.2 ± 15.4 years), and more had lower Davies comorbidity score (median 1 (0-1) vs. 1 (0, 2)), slower peritoneal transport (D/P creatinine 0.67 ± 0.12 vs. 0.73 ± 0.13), greater extracellular water-to-total body water (ECW/TBW) ratio (0.46 ± 0.05 vs. 0.42 ± 0.06), all P < .001, whereas there were no differences in the duration of PD (median (IQR) 19 (8-32) vs. 14 (8-23) months), residual renal function (Kt/Vurea 0.71 ± 0.71 vs. 0.87 ± 0.82), urine volume (642 (175-1200) vs. 648 (300-1200) mL/day), hand grip strength (26.9 ± 10.5 vs. 24.9 ± 10.7 kg), C-reactive protein (4(1-10) vs. 4(2-12) mg/L), and SAF (median 3.60 (3.02, 4.40) vs. 3.50 (3.00, 4.23)) AU. In our cross-sectional observational study, we were not able to show a demonstrable advantage for using low GDP dialysates over conventional glucose dialysates, in terms of biochemical profiles, residual renal function, muscle strength, or tissue AGE deposition. More patients using low GDP dialysates were slower peritoneal transporters with higher ECW/TBW ratios.

Short-Term Effects of Branched-Chain Amino Acids-Enriched Dialysis Fluid on Branched-Chain Amino Acids Plasma Level and Mass Balance: A Randomized Cross-Over Study.

OBJECTIVE(S): The hemodialysis (HD) session per se is a catabolic event contributing to protein-energy wasting via several mechanisms including nutrient losses. Amino acids (AAs) losses in the dialysate are estimated from 6 to 10 g per treatment. The HD patient plasma AA concentration is usually lower than in normal subjects. This is even more marked in patients with long dialysis vintage or malnutrition. METHODS: The aim of the study was to evaluate the effect on mass balance of a branched-chain AA (BCAA)-enriched (valine, isoleucine, leucine) dialysis fluid in a group of 6 stable HD anuric patients, fasting since 12 hours. The specific choice of BCAA relied on their key role on protein and muscle anabolism and their usual decreased plasma concentration in HD patients. Each patient was prescribed in a cross-over design and random order, either receiving a standard high-flux HD or an HD treatment using a BCAA-enriched acid concentrate designed to achieve a physiological plasma concentration of BCAAs. HD prescription remained unchanged during the 2 phases of study. Dialysate electrolytes prescription was kept constant for each individual patient, as well as dialysate glucose concentration (5.5 mmol/L). Pre- and post-dialysis BCAAs concentrations were measured by Ion-Exchange Liquid Chromatography. Postdialysis concentrations were corrected for hemoconcentration, and net mass transfer was calculated. RESULTS: Six stable prevalent end-stage kidney disease patients were studied. They consisted of 5 men and 1 woman, aged 69.9 years, with body mass index of 25.2 kg/m2. Treatment schedule consisted of treatment time 4 hours, high-flux polysulfone membrane (1.8 m2), blood flow 350 mL/minute, and dialysate/blood flow ratio at 1.5. The average BCAAs concentration in dialysate was targeted to physiological levels and assessed in 6 different samples, respectively for plasma valine, isoleucine, and leucine at 271, 78, and 145 µmol/L. With standard dialysate, plasma valine decreased from 204.5 to 130.8 (P = .0014). Plasma isoleucine and leucine changes were not significant, respectively from 65.7 to 59.3 µmol/L and 110.3 to 113.4 µmol/L. When using the BCAA-enriched dialysis fluid, plasma valine increased from 197.2 to 269.2 µmol/L (P = .0001), plasma isoleucine and leucine respectively from 63.2 to 84.7 (P = .0022) and from 107.2 to 161.6 µmoles/L (P = .0002). Dialysis dose estimated from KT/V did not differ between the sessions. The mass transfer with BCAA-enriched dialysate was +115, +16, and + 83 µmol per session for leucine, isoleucine, and valine, respectively. CONCLUSION(S): In conclusion, the addition of BCAAs at physiological concentration in the dialysis fluid contributes to restore physiological plasma concentrations for valine, isoleucine, and leucine at the end of a dialysis session. As BCAAs are essential to muscle balance, this could help to limit losses of BCAAs, restore physiological BCAAs concentrations, and decrease muscle catabolism observed during the HD treatment. Further outcome-based studies are needed to confirm this hypothesis on a larger scale and longer treatment time.

Proteomics of Muscle Microdialysates Identifies Potential Circulating Biomarkers in Facioscapulohumeral Muscular Dystrophy.

Facioscapulohumeral muscular dystrophy (FSHD) is caused by a complex epigenetic mechanism finally leading to the misexpression of DUX4 in skeletal muscle. Detecting DUX4 and quantifying disease progression in FSHD is extremely challenging, thus increasing the need for surrogate biomarkers. We applied a shotgun proteomic approach with two different setups to analyze the protein repertoire of interstitial fluids obtained from 20 muscles in different disease stages classified by magnetic resonance imaging (MRI) and serum samples from 10 FSHD patients. A total of 1156 proteins were identified in the microdialysates by data independent acquisition, 130 of which only found in muscles in active disease stage. Proteomic profiles were able to distinguish FSHD patients from controls. Two innate immunity mediators (S100-A8 and A9) and Dermcidin were upregulated in muscles with active disease and selectively present in the sera of FSHD patients. Structural muscle and plasminogen pathway proteins were downregulated. Together with the upstream inhibition of myogenic factors, this suggests defective muscle regeneration and increased fibrosis in early/active FSHD. Our MRI targeted exploratory approach confirmed that inflammatory response has a prominent role, together with impaired muscle regeneration, before clear muscle wasting occurs. We also identified three proteins as tissue and possibly circulating biomarkers in FSHD.

Protein kinase C beta deficiency increases glucose-mediated peritoneal damage via M1 macrophage polarization and up-regulation of mesothelial protein kinase C alpha.

BACKGROUND: Peritoneal membrane (PM) damage during peritoneal dialysis (PD) is mediated largely by high glucose (HG)-induced pro-inflammatory and neo-angiogenic processes, resulting in PM fibrosis and ultrafiltration failure. We recently demonstrated a crucial role for protein kinase C (PKC) isoform α in mesothelial cells. METHODS: In this study we investigate the role of PKCß in PM damage in vitro using primary mouse peritoneal macrophages (MPMΦ), human macrophages (HMΦ) and immortalized mouse peritoneal mesothelial cells (MPMCs), as well as in vivo using a chronic PD mouse model. RESULTS: We demonstrate that PKCß is the predominant classical PKC isoform expressed in primary MPMΦ and its expression is up-regulated in vitro under HG conditions. After in vitro lipopolysaccharides stimulation PKCß-/- MPMΦ demonstrates increased levels of interleukin 6 (IL-6), tumour necrosis factor α, and monocyte chemoattractant protein-1 and drastically decrease IL-10 release compared with wild-type (WT) cells. In vivo, catheter-delivered treatment with HG PD fluid for 5 weeks induces PKCß up-regulation in omentum of WT mice and results in inflammatory response and PM damage characterized by fibrosis and neo-angiogenesis. In comparison to WT mice, all pathological changes are strongly aggravated in PKCß-/- animals. Underlying molecular mechanisms involve a pro-inflammatory M1 polarization shift of MPMΦ and up-regulation of PKCα in MPMCs of PKCß-/- mice. Finally, we demonstrate PKCß involvement in HG-induced polarization processes in HMΦ. CONCLUSIONS: PKCß as the dominant PKC isoform in MPMΦ is up-regulated by HG PD fluid and exerts anti-inflammatory effects during PD through regulation of MPMΦ M1/M2 polarization and control of the dominant mesothelial PKC isoform α.

Peritoneal vasculopathy in the pathophysiology of long-term ultrafiltration failure: A hypothesis based on clinical observations
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Ultrafiltration failure in long-term peritoneal dialysis patients is a well-known and important, but poorly-explained complication of the treatment. Transcapillary ultrafiltration consists mainly of small-pore fluid transport and partly of free-water transport. The former is to a large extent dependent on the hydrostatic pressure gradient and on the number of perfused peritoneal microvessels. Free-water transport depends mainly on the crystalloid osmotic gradient. A longitudinal analysis of peritoneal transport has shown a dramatic decrease of net ultrafiltration and small-pore fluid transport after 4 years of peritoneal dialysis. It will be argued that in contrast to common belief, a decrease of osmotically induced water transport cannot be the major contributor to long-term ultrafiltration failure. By exclusion of potential alternatives, the presence of vasculopathy in the peritoneal microcirculation is the most likely explanation. The resulting narrowing of vascular lumina will decrease the hydrostatic pressure gradient and thereby small-pore fluid transport and net ultrafiltration. Deposition of advanced glycosylation end products in peritoneal vessels may be important in the development of vasculopathy. This hypothesis is supported by morphological and functional results of dialysis with "biocompatible" solutions.
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Mechanisms of Crystalloid versus Colloid Osmosis across the Peritoneal Membrane.

Background Osmosis drives transcapillary ultrafiltration and water removal in patients treated with peritoneal dialysis. Crystalloid osmosis, typically induced by glucose, relies on dialysate tonicity and occurs through endothelial aquaporin-1 water channels and interendothelial clefts. In contrast, the mechanisms mediating water flow driven by colloidal agents, such as icodextrin, and combinations of osmotic agents have not been evaluated.Methods We used experimental models of peritoneal dialysis in mouse and biophysical studies combined with mathematical modeling to evaluate the mechanisms of colloid versus crystalloid osmosis across the peritoneal membrane and to investigate the pathways mediating water flow generated by the glucose polymer icodextrin.ResultsIn silico modeling and in vivo studies showed that deletion of aquaporin-1 did not influence osmotic water transport induced by icodextrin but did affect that induced by crystalloid agents. Water flow induced by icodextrin was dependent upon the presence of large, colloidal fractions, with a reflection coefficient close to unity, a low diffusion capacity, and a minimal effect on dialysate osmolality. Combining crystalloid and colloid osmotic agents in the same dialysis solution strikingly enhanced water and sodium transport across the peritoneal membrane, improving ultrafiltration efficiency over that obtained with either type of agent alone.Conclusions These data cast light on the molecular mechanisms involved in colloid versus crystalloid osmosis and characterize novel osmotic agents. Dialysis solutions combining crystalloid and colloid particles may help restore fluid balance in patients treated with peritoneal dialysis.

Removal of urea by electro-oxidation in a miniature dialysis device: a study in awake goats.

The key to success in developing a wearable dialysis device is a technique to safely and efficiently regenerate and reuse a small volume of dialysate in a closed-loop system. In a hemodialysis model in goats, we explored whether urea removal by electro-oxidation (EO) could be effectively and safely applied in vivo. A miniature dialysis device was built, containing 1 or 2 "EO units," each with 10 graphite electrodes, with a cumulative electrode surface of 585 cm2 per unit. The units also contained poly(styrene-divinylbenzene) sulfonate beads, FeOOH beads, and activated carbon for respective potassium, phosphate, and chlorine removal. Urea, potassium, and phosphate were infused to create "uremic" conditions. Urea removal was dependent on total electrode surface area [removal of 8 mmol/h (SD 1) and 16 mmol/h (SD 2) and clearance of 12 ml/min (SD 1) and 20 ml/min (SD 3) with 1 and 2 EO units, respectively] and plasma urea concentration but not on flow rate. Extrapolating urea removal with 2 EO units to 24 h would suffice to remove daily urea production, but for intermittent dialysis, additional units would be required. EO had practically no effects on potassium and phosphate removal or electrolyte balance. However, slight ammonium releasewas observed, and some chlorine release at higher dialysate flow rates. Minor effects on acid-base balance were observed, possibly partly due to infusion of chloride. Mild hemolysis occurred, which seemed related to urea infusion. In conclusion, clinically relevant urea removal was achieved in vivo by electro-oxidation. Efficacy and safety testing in a large-animal model with uremia is now indicated.

Primary outcomes of the Monitoring in Dialysis Study indicate that clinically significant arrhythmias are common in hemodialysis patients and related to dialytic cycle.

Sudden death is one of the more frequent causes of death for hemodialysis patients, but the underlying mechanisms, contribution of arrhythmia, and associations with serum chemistries or the dialysis procedure are incompletely understood. To study this, implantable loop recorders were utilized for continuous cardiac rhythm monitoring to detect clinically significant arrhythmias including sustained ventricular tachycardia, bradycardia, asystole, or symptomatic arrhythmias in hemodialysis patients over six months. Serum chemistries were tested pre- and post-dialysis at least weekly. Dialysis procedure data were collected at every session. Associations with clinically significant arrhythmias were assessed using negative binomial regression modeling. Sixty-six patients were implanted and 1678 events were recorded in 44 patients. The majority were bradycardias (1461), with 14 episodes of asystole and only one of sustained ventricular tachycardia. Atrial fibrillation, although not defined as clinically significant arrhythmias, was detected in 41% of patients. With thrice-weekly dialysis, the rate was highest during the first dialysis session of the week and was increased during the last 12 hours of each inter-dialytic interval, particularly the long interval. Among serum and dialytic parameters, only higher pre-dialysis serum sodium and dialysate calcium over 2.5 mEq/L were independently associated with clinically significant arrhythmias. Thus, clinically significant arrhythmias are common in hemodialysis patients, and bradycardia and asystole rather than ventricular tachycardia may be key causes of sudden death in hemodialysis patients. Associations with the temporal pattern of dialysis suggest that modification of current dialysis practices could reduce the incidence of sudden death.

Modulation of leucocytic angiotensin-converting enzymes expression in patients maintained on high-permeable haemodialysis.

BACKGROUND: High mortality of haemodialysis patients is associated with systemic chronic inflammation and overactivation of the renin-angiotensin system (RAS). Insufficient elimination of pro-inflammatory immune mediators, especially in the molecular weight range of 15-45 kDa, may be one of the reasons for this. Employment of haemodialysis membranes with increased permeability was shown to ameliorate the inflammatory response and might modulate the effects of local RAS. In this study, we tested the impact of high cut-off (HCO), medium cut-off (MCO) and high-flux (HF) dialysis on leucocytic transcripts of angiotensin-converting enzymes (ACE and ACE2). Additionally, the impact of HCO, MCO and HF sera and dialysates on local ACEs and inflammation markers was tested in THP-1 monocytes. METHODS: Patients' leucocytes were obtained from our recent clinical studies comparing HCO and MCO dialysers with HF. The cells were subjected to quantitaive polymerase chain reaction (qPCR) analyses with TaqMan probes specific for ACE, ACE2 and angiotensin II (AngII) and Ang1-7 receptors. Sera and dialysates from the clinical trials as well as samples from in vitro dialysis were tested on THP-1 monocytic cells. The cells were subjected to qPCR analyses with TaqMan probes specific for ACE, ACE2, interleukin-6 and tumour necrosis factor α and immunocytochemistry with ACE and ACE2 antibodies. RESULTS: Leucocytes obtained from patients treated with HCO or MCO demonstrated decreased transcript expression of ACE, while ACE2 was significantly upregulated as compared with HF. Receptors for AngII and Ang1-7 remained unchanged. THP-1 monocytes preconditioned with HCO and MCO patients' or in vitro dialysis sera reflected the same expressional regulation of ACE and ACE2 as those observed in HCO and MCO leucocytes. As a complementary finding, treatment with HCO and MCO in vitro dialysates induced a pro-inflammatory response of the cells as demonstrated by elevated messenger RNA expression of tumour necrosis factor α and interleukin-6, as well as upregulation of ACE and decreased levels of ACE2. CONCLUSIONS: Taken together, these data demonstrate that employment of membranes with high permeability eliminates a spectrum of mediators from circulation that affect the RAS components in leucocytes, especially ACE/ACE2.

Should we look beyond Kt/V urea in assessing dialysis adequacy?

Since the advent of maintenance dialysis therapy, our interpretation of what adequate dialysis really is has broadened and become more controversial. This is not only due to our changing and aging dialysis population but also to our evolving knowledge base. As nephrologists, we strive to achieve both quality and (often) quantity of life for our patients and we feel reassured when we have a quantifiable marker to show for our efforts. However, we suggest that adequate dialysis reaches far beyond the realms of attaining a particular biochemical result. Dialysis adequacy should encompass a more comprehensive assessment of patient well-being. This metric could comprise quality of life and patient-specified goals, sufficient small solute and middle molecule clearance, optimal blood pressure control, and effective bone-mineral balance, all in the context of minimizing mortality and morbidity, and a livable dialysis regimen for the patient.