Hemodynamic effects of peritoneal dialysis solutions on the rat peritoneal membrane: role of acidity, buffer choice, glucose concentration, and glucose degradation products

Adequacy of Peritoneal Dialysis in Children: Consider the Membrane for Optimal Prescription

The peritoneal dialysis (PD) prescription should be adequate before being optimal. The peritoneal membrane is a dynamic dialyzer: the surface area and the vascular area both have recruitment capacity.

At bedside, prescription is based mainly on tolerance of the prescribed fill volume, and therefore a too-small fill volume is often prescribed. A too-small fill volume may lead to a hyperpermeable exchange, with potentially enhanced morbidity—or even mortality—risks. Better understanding of the peritoneal membrane as a dynamic dialysis surface area allows for an individually adapted prescription, which is especially suitable for children on automated PD.

Fill volume should be scaled for body surface area (mL/m2) and, to avoid a hyperpermeable exchange, for a not-too-small amount. Fill volume enhancement should be conducted under clinical control and is best determined by intraperitoneal pressure measurement in centimeters of H2O. In children 2 years of age and older, a peak fill volume of 1400 – 1500 mL/m2 can be prescribed in terms of tolerance, efficiency, and peritoneal membrane recruitment.

Dwell times should be determined individually with respect to two opposing parameters:

• Short dwell times provide adequate small-solute clearance and maintain the crystalloid osmotic gradient (and, thereby, the ultrafiltration capacity).

• Long dwell times enhance phosphate clearance, but can lead to dialysate reabsorption.

The new PD fluids (that is, those free of glucose degradation products, with a neutral pH, and not exclusively lactate-buffered) appear to be the best choice both in terms of membrane recruitment and of preservation of peritoneal vascular hyperperfusion.

IL-17A as a Potential Therapeutic Target for Patients on Peritoneal Dialysis

Chronic kidney disease (CKD) is a health problem reaching epidemic proportions. There is no cure for CKD, and patients may progress to end-stage renal disease (ESRD). Peritoneal dialysis (PD) is a current replacement therapy option for ESRD patients until renal transplantation can be achieved. One important problem in long-term PD patients is peritoneal membrane failure. The mechanisms involved in peritoneal damage include activation of the inflammatory and immune responses, associated with submesothelial immune infiltrates, angiogenesis, loss of the mesothelial layer due to cell death and mesothelial to mesenchymal transition, and collagen accumulation in the submesothelial compact zone. These processes lead to fibrosis and loss of peritoneal membrane function. Peritoneal inflammation and membrane failure are strongly associated with additional problems in PD patients, mainly with a very high risk of cardiovascular disease. Among the inflammatory mediators involved in peritoneal damage, cytokine IL-17A has recently been proposed as a potential therapeutic target for chronic inflammatory diseases, including CKD. Although IL-17A is the hallmark cytokine of Th17 immune cells, many other cells can also produce or secrete IL-17A. In the peritoneum of PD patients, IL-17A-secreting cells comprise Th17 cells, γδ T cells, mast cells, and neutrophils. Experimental studies demonstrated that IL-17A blockade ameliorated peritoneal damage caused by exposure to PD fluids. This article provides a comprehensive review of recent advances on the role of IL-17A in peritoneal membrane injury during PD and other PD-associated complications.

Blood pressure and volume management in dialysis: conclusions from a Kidney Disease: Improving Global Outcomes (KDIGO) Controversies Conference

Blood pressure (BP) and volume control are critical components of dialysis care and have substantial impacts on patient symptoms, quality of life, and cardiovascular complications. Yet, developing consensus best practices for BP and volume control have been challenging, given the absence of objective measures of extracellular volume status and the lack of high-quality evidence for many therapeutic interventions. In February of 2019, Kidney Disease: Improving Global Outcomes (KDIGO) held a Controversies Conference titled Blood Pressure and Volume Management in Dialysis to assess the current state of knowledge related to BP and volume management and identify opportunities to improve clinical and patient-reported outcomes among individuals receiving maintenance dialysis. Four major topics were addressed: BP measurement, BP targets, and pharmacologic management of suboptimal BP; dialysis prescriptions as they relate to BP and volume; extracellular volume assessment and management with a focus on technology-based solutions; and volume-related patient symptoms and experiences. The overarching theme resulting from presentations and discussions was that managing BP and volume in dialysis involves weighing multiple clinical factors and risk considerations as well as patient lifestyle and preferences, all within a narrow therapeutic window for avoiding acute or chronic volume-related complications. Striking this challenging balance requires individualizing the dialysis prescription by incorporating comorbid health conditions, treatment hemodynamic patterns, clinical judgment, and patient preferences into decision-making, all within local resource constraints.

PD Fluids Contain High Concentrations of Cytotoxic GDPs Directly after Sterilization

Objective

Glucose degradation products (GDPs) in peritoneal dialysis (PD) fluids are cytotoxic and affect the survival of the peritoneal membrane. One of the most reactive GDPs in PD fluids is 3,4-dideoxyglucosone-3-ene (3,4-DGE). 3,4-DGE has been reported as an intermediate between 3-deoxyglucosone (3-DG) and 5-hydroxymethyl furaldehyde (5-HMF) during degradation of glucose. In PD fluids, 3,4-DGE exists in a temperature-dependent equilibrium with a pool of unidentified substances. The aim of this study was to explore this equilibrium and its temperature dependence during the first months of storage after the sterilization procedure.

Methods

GDPs and inhibition of cell growth (ICG) were measured directly after sterilization of the PD fluid and during storage at different temperatures for 60 days. The following GDPs were analyzed: 3-DG, 3,4-DGE, 5-HMF, formaldehyde, acetaldehyde, glyoxal, and methylglyoxal.

Results

Immediately after sterilization, the concentration of 3,4-DGE was 125 μmol/L. During the first weeks of storage, it decreased by about 80%. At the same time, the 3-DG concentration increased. None of the other GDPs were significantly affected. Cytotoxicity correlated well with the concentration of 3,4-DGE. When pure 3,4-DGE was substituted for the lost amount of 3,4-DGE after 30 days of storage, the initial ICG was almost completely regained.

Conclusions

Heat sterilization of PD fluids promotes the formation of large quantities of 3,4-DGE, rendering the fluid highly cytotoxic. During storage, the main part of 3,4-DGE is reversibly converted in a temperature-dependent manner to a less cytotoxic pool, consisting mainly of 3-DG. Cytotoxicity seems to be dependent exclusively on 3,4-DGE. In order to avoid higher levels of 3,4-DGE concentrations, PD fluids should not be used too soon after sterilization and should not be stored at temperatures above room temperature.

Improvement of Peritoneal Ultrafiltration with Peritoneal Dialysis Solution Buffered with Bicarbonate/Lactate Mixture

Background

In computer simulations, according to the three-pore model of peritoneal transport, neutralization of conventional acidic peritoneal dialysis fluids is predicted to produce an improved ultrafiltration (UF). However, in a previous study, a two-compartment peritoneal dialysis system with a minimum of glucose degradation products (GDP), PD-Bio, having a pH of 6.3 and being conventionally lactate buffered, did not produce an increased UF.

Setting

We tested a newly formulated, glucose-based, GDP-reduced solution, denoted “N” for “neutral,” containing a mixture of lactate (30 mmol/L) and bicarbonate (10 mmol/L) as buffer system, and having a pH of 7.2. This new formulation was compared with Gambrosol trio (GT) (identical in composition to PD-Bio, but delivered in a three-compartment system; both by Gambro Lundia AB, Lund, Sweden) in an open, prospective controlled study of 13 patients.

Material and Methods

Each of the 13 patients used GT for 14 days, followed by 14 days of N. All bags were weighed on a digital scale before instillation and after drainage to assess the UF in each dwell (and during 24 hours). Glucose concentration in each bag was noted. In the morning and night dwells, dialysis fluid glucose concentration was standardized to 2.5%. Body weight was measured every morning (empty abdomen). In the middle of each 14-day period, a 4-hour standardized (“study day”) dwell was performed, using 125I-albumin (RISA) as volume marker, during which blood and dialysate samples were taken repeatedly and analyzed for RISA, creatinine, urea, phosphate, glucose, standard bicarbonate, lactate, and pH. The permeability surface area product (PS) for small solutes (and A0/ΔX; “area parameter”) was calculated. Clearance (Cl) of RISA to plasma (P) (Cl→P), “direct lymphatic absorption,” and total Cl of RISA out of the peritoneal cavity (Clout) were also determined.

Results

The 13 patients using N, compared to GT, displayed an increased daily UF, the difference being 233 mL ( p < 0.05). The pH values of N were higher during the first 90 minutes of the 4-hour dwell compared to the pH values of GT. Neither the small solute PS values nor RISA determined UF, nor did body weight differ significantly between the GT and the N periods.

Conclusions

A new bicarbonate/lactate-buffered solution, N, with neutral pH (of 7.2) and low in GDP seems to produce an improved UF compared to a lactate-buffered solution with a pH of 6.3, equally low in GDP, partly in agreement with our earlier predictions. A dialysis solution with a neutral pH combined with a reduced lactate concentration, partially replaced by bicarbonate, evidently increases UF, conceivably by causing less peritoneal vasodilatation than solutions buffered by lactate or high concentrations of bicarbonate alone.

Does the Biocompatibility of the Peritoneal Dialysis Solution Matter in Assessment of Peritoneal Function?

Background

Peritoneal function tests are performed in peritoneal dialysis (PD) patients to characterize peritoneal membrane status. A low pH/high glucose degradation product (GDP) dialysis solution is used as the test solution. The objective of the present study was to compare a 3.86% glucose, low pH/high GDP dialysis solution (pH 5.5) with a 3.86% glucose, normal pH/low GDP dialysis solution (pH 7.4) in assessments of peritoneal membrane function.

Methods

Two standard peritoneal permeability analyses (SPA) were performed in 10 stable PD patients within 2 weeks. One SPA was done with the 3.86% low pH/high GDP solution, and the other with the 3.86% normal pH/low GDP solution. The sequence of the two tests was randomized.

Results

Fluid transport parameters and glucose absorption were not different between the two groups. No differences were found for the mass transfer area coefficients (MTACs) of low molecular weight solutes calculated over the whole dwell. However, MTAC urea in the first hour of the dwell was higher in the test done with low pH/high GDP dialysate, suggesting more peritoneal vasodilation. No difference was found in protein clearances. Sodium sieving at multiple time points during the dwell was similar with the two solutions.

Conclusion

The results obtained with the glucose-containing normal pH/low GDP dialysis solution were similar to those obtained with the glucose-containing low pH/high GDP dialysate in assessments of peritoneal membrane function.

Comparison between Bicarbonate/Lactate and Standard Lactate Dialysis Solution in Peritoneal Transport and Ultrafiltration: A Prospective, Crossover Single-Dwell Study

Objective

It has been proposed that biocompatible bicarbonate/lactate based (Bic/Lac), physiologic-pH peritoneal dialysis (PD) solutions will be beneficial in long-term PD. However, we do not yet have detailed knowledge concerning the comparative physiology of buffer transport for these new solutions and their impact on underlying peritoneal transport of solutes and ultrafiltration (UF). The purpose of this study was to investigate the profile of buffer handling and peritoneal membrane transport characteristics during a single dwell of the new Bic/Lac-based versus standard lactate-based (Lac) PD solution.

Methods

In this prospective crossover study, we compared a 25 mmol/L bicarbonate/15 mmol/L lactate buffered, physiologic pH, low glucose degradation product (GDP) solution (Physioneal; Baxter Healthcare, McGaw Park, Illinois, USA) with a standard lactate buffered, acidic pH, conventional solution (Dianeal; Baxter). 18 patients underwent two peritoneal equilibration tests (PETs) with 2.5% Dianeal and 2.5% Physioneal separated by 1 week. Buffer transport, mass transfer area coefficients (MTACs), solute transport, and UF were determined for the two PETs. All bags were weighed by a nurse before instillation and after drainage to assess the net UF in each dwell.

Results

18 patients that met the inclusion criteria were enrolled in this study. Whereas intraperitoneal pH remained constant at 7.52 ± 0.11 throughout the dwell with the Bic/Lac solution, pH was still in the acidic range with the Lac solution after 1 hour (7.29 ± 0.13, p < 0.001); this difference disappeared after the second hour of dwell. The MTACs for creatinine (10.68 ± 3.66 vs 10.73 ± 2.96 mL/minute/ 1.73 m2, p > 0.05) and urea (27.94 ± 10.50 vs 27.62 ± 6.95 mL/min/1.73 m2, p > 0.05), for Bic/Lac versus Lac respectively, did not differ between these two solutions; transport of glucose and other solutes was also similar. However, after a 4-hour dwell with Bic/Lac solution, net UF was significantly lower than that observed with Lac solution (274.2 ± 223.3 mL vs 366.1 ± 217.3 mL, p = 0.026).

Conclusions

Compared to standard Lac-based solution, Bic/Lac based, pH neutral, low-GDP solution avoids intra-peritoneal acidity. Peritoneal mass transport kinetics are similar for small solutes. Net UF is significantly lower with Bic/Lac solution; the mechanism for this is unclear.

How to Avoid Glucose Degradation Products in Peritoneal Dialysis Fluids

Objective

The formation of glucose degradation products (GDPs) during sterilization of peritoneal dialysis fluids (PDFs) is one of the most important aspects of biocompatibility of glucose-containing PDFs. Producers of PDFs are thus trying to minimize the level of GDPs in their products. 3,4-Dideoxyglucosone-3-ene (3,4-DGE) has been identified as the most bioreactive GDP in PDFs. It exists in a temperature-dependent equilibrium with a pool of 3-deoxyglucosone (3-DG) and is a precursor in the irreversible formation of 5-hydroxymethyl furaldehyde (5-HMF). The aim of the present study was to investigate how to minimize GDPs in PDFs and how different manufacturers have succeeded in doing so.

Design

Glucose solutions at different pHs and concentrations were heat sterilized and 3-DG, 3,4-DGE, 5-HMF, formaldehyde, and acetaldehyde were analyzed. Conventional as well as biocompatible fluids from different manufacturers were analyzed in parallel for GDP concentrations.

Results

The concentrations of 3-DG and 3,4-DGE produced during heat sterilization decreased when pH was reduced to about 2. Concentration of 5-HMF decreased when pH was reduced to 2.6. After further decrease to a pH of 2.0, concentration of 5-HMF increased slightly, and below a pH of 2.0 it increased considerably, together with formaldehyde; 3-DG continued to drop and 3,4-DGE remained constant. Inhibition of cell growth was paralleled by 3,4-DGE concentration at pH 2.0 – 6.0. A high glucose concentration lowered concentrations of 3,4-DGE and 3-DG at pH 5.5 and of 5-HMF at pH 1. At pH 2.2 and 3.2, glucose concentration had a minor effect on the formation of GDPs. All conventional PDFs contained high levels of 3,4-DGE and 3-DG. Concentrations were considerably lower in the biocompatible fluids. However, the concentration of 5-HMF was slightly higher in all the biocompatible fluids.

Conclusion

The best way to avoid reactive GDPs is to have a pH between 2.0 and 2.6 during sterilization. If pHs outside this range are used, it becomes more important to have high glucose concentration during the sterilization process. There are large variations in GDPs, both within and between biocompatible and conventionally manufactured PDFs.

No Significant Differences in Peritoneal Fluid Handling in Children Using pH-Neutral or Acidic Solutions

Objectives

Differences in peritoneal fluid handling in the acute setting can be expected if children are converted to pH-neutral dialysis solutions because conventional acidic solutions exert toxic effects on peritoneal mesothelial cells and microcirculation. Peritoneal fluid kinetics was therefore investigated with both types of solutions in a group of children.

Design

Peritoneal equilibration tests (PETs) were performed in 12 patients [mean age 70 months, mean time on peritoneal dialysis (PD) 18 months] using a pH-neutral PD fluid (Physioneal 3.86%; Baxter Ltd, Castlebar, Ireland) and dextran 70 as a volume marker. The results of these PETs were compared to those of a historic group of 12 children (mean age 75 months, mean time on PD 17 months).

Setting

Pediatric dialysis unit in a tertiary institute.

Patients

Stable pediatric PD patients.

Main Outcome Measures

Transcapillary ultrafiltration (TCUF) and marker clearance, dialysate-to-plasma (D/P) ratios for urea and creatinine, and Dt/D0ratio for glucose.

Results

TCUF and lymphatic absorption were not different between the two groups. There was also no significant difference in small solute clearance measured by D/P ratio for urea and creatinine and Dt/D0ratio for glucose.

Conclusion

Peritoneal fluid kinetics is not significantly altered if pH-neutral dialysis solutions are applied compared to acidic solutions. An altered TCUF, as is hypothetically possible using an acidic solution, was not established.

A Comparison of Peritoneal Equilibration Tests Performed 1 and 4 Weeks after PD Commencement

Objective

The aim of this study was to prospectively evaluate the ability of a peritoneal equilibration test (PET) performed in the first week of peritoneal dialysis (PD) to predict subsequent transport status, as determined by a PET at 4 weeks and >1 year after PD commencement.

Design

Prospective observational study of an incident PD cohort at a single center.

Setting

Tertiary-care institutional dialysis center.

Participants

The study included 50 consecutive patients commencing PD at the Princess Alexandra Hospital between 25/2/2001 and 14/5/2003 (mean age 60.9 ± 12.2 years, 54% male, 92% Caucasian, 38% diabetic). All patients were initially prescribed continuous ambulatory PD.

Main Measurements

Measurements performed during paired PETs included dialysate-to-plasma ratios of urea (D/P urea) and creatinine (D/P creatinine) at 4 hours, the ratio of dialysate glucose concentrations at 0 and 4 hours (D/D0glucose), and drain volumes at 4 hours.

Results

When paired 1-week and 1-month PET data were analyzed, significant changes were observed in measured D/P urea (0.91 ± 0.07 vs 0.94 ± 0.07 respectively; p < 0.05), D/P creatinine (0.55 ± 0.12 vs 0.66 ± 0.11, p < 0.001), and D/D0glucose (0.38 ± 0.08 vs 0.36 ± 0.10, p < 0.05). Using Bland–Altman analysis, the repeatability coefficients were 0.17, 0.20, and 0.13, respectively. Agreement between 1-week and 1-month PET measurements with respect to peritoneal transport category was moderate for D/D0glucose (weighted κ 0.52), but poor for D/P urea (0.30), D/P creatinine (0.35), and drain volumes (0.20). The PET measurements performed more than 1 year following PD commencement ( n = 28) generally agreed closely with 1-month measurements, and poorly with 1-week measurements.

Conclusions

Peritoneal transport characteristics change significantly within the first month of PD. PETs carried out during this time should be considered preliminary and should be confirmed by a PET 4 weeks later. Nevertheless, performing an early D/D0glucose measurement at 1 week predicted ultimate transport status sufficiently well to facilitate early clinical decision-making about optimal PD modality while patients were still receiving PD training. On the other hand, the widespread practice of using measured drain volumes in the first week to predict ultimate transport category is highly inaccurate and not recommended.

Vasoactive Components of Dialysis Solution

Background

Conventional peritoneal dialysis (PD) solutions elicit vasodilation, which is implicated in the variable rate of solute transport during the dwell. The components causing such vasoactivity are still controversial. This study was conducted to define the vasoactive components of conventional and new PD solutions.

Methods

Three visceral peritoneal microvascular levels were visualized by intravital video microscopy of the terminal ileum of anesthetized rats. Anesthesia-free decerebrate conscious rats served as control. Microvascular diameter and blood flow by Doppler measurements were conducted after topical peritoneal exposure to 4 clinical PD solutions and 6 prepared solutions designed to isolate potential vasoactive components of the PD solution.

Results

All clinically available PD solutions produced a rapid and generalized vasodilation at all intestinal microvascular levels, regardless of the osmotic solute. The pattern and magnitude of this dilation was not affected by anesthesia but was determined by arteriolar size, the osmotic solute, and the solution's buffer anion system. The greatest dilation occurred in the small precapillary arterioles and was elicited by conventional PD solution and heat re-sterilized solution containing low glucose degradation products (GDPs). Hypertonic mannitol solutions produced a dilation that was approximately 50% less than the dilation obtained with glucose solutions with identical osmolarity and buffer. Increasing a solution's osmolarity did not produce a parallel increase in the magnitude of dilation, suggesting a nonlinear relationship between the two variables. Lactate dissolved in an isotonic solution was completely non-vasoactive unless the solution's H+concentration was increased. At low pH, isotonic lactate produced a rapid but transient vasodilation. This vascular reactivity was similar in magnitude and pattern to that obtained with the isotonic 7.5% icodextrin solution (Extraneal; Baxter Healthcare, Deerfield, Illinois, USA).

Conclusions

( 1 ) Hyperosmolarity is the major vasoactive component of PD solution. ( 2 ) Hyperosmolarity and active intracellular glucose uptake account together for approximately 75% of PD solution-induced dilation, whereas GDPs contribute to approximately 25%. ( 3 ) Lactate is vasoactive only at low pH (high [H+]). ( 4 ) The magnitude of PD solution-mediated vasodilation is partially dependent on the nature of the osmotic solute, the GDP contents, and the [H+], which determine the vasoactivity of the lactate-buffer anion system. Studies are required to define the molecular mechanisms of PD-induced vasodilation and to determine the vasoactive properties of these solutions after chronic infusion.

The Potential Cardiovascular Benefits of Low-Glucose Degradation Product, Biocompatible Peritoneal Dialysis Fluids: A Review of the Literature

Cardiovascular mortality in the end-stage renal disease (ESRD) population remains the leading cause of death. Targeting traditional cardiovascular risk factors has proven unsuccessful in this patient population, and therefore attention has turned to risk factors related to chronic kidney disease (CKD). The toxicity of high-glucose peritoneal dialysis (PD) solutions has been well documented. The breakdown of glucose into glucose degradation products (GDP) and advanced glycation end-products (AGE) has the ability to alter cell viability and cause premature apoptosis and is strongly correlated with interstitial fibrosis and microvascular sclerosis. Biocompatible solutions have been introduced to combat the hostile milieu to which PD patients are exposed.

Given the considerable cardiovascular burden for PD patients, little is known about the cardiovascular impact the new biocompatible solutions may have. This review analyzes the existing literature regarding the mechanisms through which low-GDP solutions may modulate cardiovascular risk. Interventions using low-GDP solutions have provided encouraging changes in structural cardiovascular measures such as left ventricular mass (LVM), although metabolic changes from reduced GDP and AGE exposure yield inconclusive results on vascular remodelling. It is thought that the local effects of reduced glucose exposure may improve membrane integrity and therefore fluid status. Further research in the form of a robust randomized controlled trial should be carried out to assess the true extent of the cardiovascular benefits these biocompatible solutions may hold.

IL-17 in Peritoneal Dialysis-Associated Inflammation and Angiogenesis: Conclusions and Perspectives

Long-term peritoneal dialysis (PD) is associated with peritoneal membrane remodeling. This includes changes in peritoneal vasculature, which may ultimately lead to inadequate solute and water removal and treatment failure. The potential cause of such alterations is chronic inflammation induced by repeated episodes of infectious peritonitis and/or exposure to bioincompatible PD fluids. While these factors may jeopardize the peritoneal membrane integrity, it is not clear why adverse peritoneal remodeling develops only in some PD patients. Increasing evidence points to the differences that occur between patients in response to the same invading microorganism and/or the differences in the course of inflammatory reaction triggered by different species. Such differences may be related to the involvement of different inflammatory mediators. Here, we discuss the potential role of IL-17 in these processes with emphasis on its impact on peritoneal mesothelial cells and peritoneal vascularity.

Hypoxia, cytokines and stromal recruitment: parallels between pathophysiology of encapsulating peritoneal sclerosis, endometriosis and peritoneal metastasis

Peritoneal response to various kinds of injury involves loss of peritoneal mesothelial cells (PMC), danger signalling, epithelial-mesenchymal transition and mesothelial-mesenchymal transition (MMT). Encapsulating peritoneal sclerosis (EPS), endometriosis (EM) and peritoneal metastasis (PM) are all characterized by hypoxia and formation of a vascularized connective tissue stroma mediated by vascular endothelial growth factor (VEGF). Transforming growth factor-β1 (TGF-β1) is constitutively expressed by the PMC and plays a major role in the maintenance of a transformed, inflammatory micro-environment in PM, but also in EPS and EM. Persistently high levels of TGF-β1 or stimulation by inflammatory cytokines (interleukin-6 (IL-6)) induce peritoneal MMT, adhesion formation and fibrosis. TGF-β1 enhances hypoxia inducible factor-1α expression, which drives cell growth, extracellular matrix production and cell migration. Disruption of the peritoneal glycocalyx and exposure of the basement membrane release low molecular weight hyaluronan, which initiates a cascade of pro-inflammatory mediators, including peritoneal cytokines (TNF-α, IL-1, IL-6, prostaglandins), growth factors (TGF-α, TGF-β, platelet-derived growth factor, VEGF, epidermal growth factor) and the fibrin/coagulation cascade (thrombin, Tissue factor, plasminogen activator inhibitor [PAI]-1/2). Chronic inflammation and cellular transformation are mediated by damage-associated molecular patterns, pattern recognition receptors, AGE-RAGE, extracellular lactate, pro-inflammatory cytokines, reactive oxygen species, increased glycolysis, metabolomic reprogramming and cancer-associated fibroblasts. The pathogenesis of EPS, EM and PM shows similarities to the cellular transformation and stromal recruitment of wound healing.

Functional vascular anatomy of the peritoneum in health and disease

The peritoneum consists of a layer of mesothelial cells on a connective tissue base which is perfused with circulatory and lymphatic vessels. Total effective blood flow to the human peritoneum is estimated between 60 and 100 mL/min, representing 1-2 % of the cardiac outflow. The parietal peritoneum accounts for about 30 % of the peritoneal surface (anterior abdominal wall 4 %) and is vascularized from the circumflex, iliac, lumbar, intercostal, and epigastric arteries, giving rise to a quadrangular network of large, parallel blood vessels and their perpendicular offshoots. Parietal vessels drain into the inferior vena cava. The visceral peritoneum accounts for 70 % of the peritoneal surface and derives its blood supply from the three major arteries that supply the splanchnic organs, celiac and superior and inferior mesenteric. These vessels give rise to smaller arteries that anastomose extensively. The visceral peritoneum drains into the portal vein. Drugs absorbed are subject to first-pass hepatic metabolism. Peritoneal inflammation and cancer invasion induce neoangiogenesis, leading to the development of an important microvascular network. Anatomy of neovessels is abnormal and characterized by large size, varying diameter, convolution and blood extravasation. Neovessels have a defective ultrastructure: formation of large "mother vessels" requires degradation of venular and capillary basement membranes. Mother vessels give birth to numerous "daughter vessels". Diffuse neoangiogenesis can be observed before appearance of macroscopic peritoneal metastasis. Multiplication of the peritoneal capillary surface by neoangiogenesis surface increases the part of cardiac outflow directed to the peritoneum.

Hydration Status of Patients Dialyzed with Biocompatible Peritoneal Dialysis Fluids

♦

BACKGROUND

Biocompatible fluids for peritoneal dialysis (PD) have been introduced to improve dialysis and patient outcome in end-stage renal disease. However, their impact on hydration status (HS), residual renal function (RRF), and dialysis adequacy has been a matter of debate. The aim of the study was to evaluate the influence of a biocompatible dialysis fluid on the HS of prevalent PD patients. ♦

METHODS

The study population consisted of 18 prevalent PD subjects, treated with standard dialysis fluids. At baseline, 9 patients were switched to a biocompatible solution, low in glucose degradation products (GDPs) (Balance; Fresenius Medical Care, Bad Homburg, Germany). Hydration status was assessed through clinical evaluation, laboratory parameters, echocardiography, and bioimpedance spectroscopy over a 24-month observation period. ♦

RESULTS

During the study period, urine volume decreased similarly in both groups. At the end of the evaluation, there were also no differences in clinical (body weight, edema, blood pressure), laboratory (N-terminal pro-brain natriuretic peptide, NTproBNP), or echocardiography determinants of HS. However, dialysis ultrafiltration decreased in the low-GDP group and, at the end of the study, equaled 929 ± 404 mL, compared with 1,317 ± 363 mL in the standard-fluid subjects (p = 0.06). Hydration status assessed by bioimpedance spectroscopy was +3.64 ± 2.08 L in the low-GDP patients and +1.47 ± 1.61 L in the controls (p = 0.03). ♦

CONCLUSIONS

The use of a low-GDP biocompatible dialysis fluid was associated with a tendency to overhydration, probably due to diminished ultrafiltration in prevalent PD patients.

Encapsulating peritoneal sclerosis-a rare but devastating peritoneal disease

Encapsulating peritoneal sclerosis (EPS) is a devastating but, fortunately, rare complication of long-term peritoneal dialysis. The disease is associated with extensive thickening and fibrosis of the peritoneum resulting in the formation of a fibrous cocoon encapsulating the bowel leading to intestinal obstruction. The incidence of EPS ranges between 0.7 and 3.3% and increases with duration of peritoneal dialysis therapy. Dialysis fluid is hyperosmotic, hyperglycemic, and acidic causing chronic injury and inflammation in the peritoneum with loss of mesothelium and extensive tissue fibrosis. The pathogenesis of EPS, however, still remains uncertain, although a widely accepted hypothesis is the "two-hit theory," where, the first hit is chronic peritoneal membrane injury from long standing peritoneal dialysis followed by a second hit such as an episode of peritonitis, genetic predisposition and/or acute cessation of peritoneal dialysis, leading to EPS. Recently, EPS has been reported in patients shortly after transplantation suggesting that this procedure may also act as a possible second insult. The process of epithelial-mesenchymal transition of mesothelial cells is proposed to play a central role in the development of peritoneal sclerosis, a common characteristic of patients on dialysis, however, its importance in EPS is less clear. There is no established treatment for EPS although evidence from small case studies suggests that corticosteroids and tamoxifen may be beneficial. Nutritional support is essential and surgical intervention (peritonectomy and enterolysis) is recommended in later stages to relieve bowel obstruction.

Compare the effects of intravenous and intraperitoneal mesenchymal stem cell transplantation on ultrafiltration failure in a rat model of chronic peritoneal dialysis

AIM

The purpose of this study was to compare the possible healing effects of intraperitoneal (IP) and intravenous (IV) mesenchymal stem cell (MSC) transplantation on ultrafiltration failure (UFF) in a chronic rat model of peritoneal dialysis (PD).

METHODS

Rats were initially divided into two groups. The UFF-group received once-daily IP injections of 20 mL of 3.86% glucose PD solution for six weeks to stimulate the development of UFF, and a control group received no injections. The UFF group was sub-divided into four groups: an UFF-C group, a MSC-IP group, a MSC-IV group and a placebo (P) group. Peritoneal equilibration tests (PETs) and peritoneal biopsies were performed in the control and UFF-C groups. MSCs were administered by IP injection in the MSC-IP group and by IV injection in the MSC-IV group. The P group received IP injection of placebo. PETs and peritoneal biopsies were performed in the MSC-IP, MSC-IV and P groups at the three weeks after receiving MSCs or placebo.

RESULTS

When compared with the control group, ultrafiltration capacity significantly decreased, and the submesothelial thickness increased in the UFF-C and P group, but there were no differences between the control and MSC-IP and MSC-IV groups. The rate of glucose transport was high in the UFF-C and P group compared with the control group, and D/PCr rates in the UFF-C and P group were lower than in the control group. However, D/D0glucose was higher and D/PCr was lower in the MSC-IP group than in the UFF-C and P groups, but D/D0glucose rate of MSC-IV group similar to UFF-C and P groups and there was no difference between MSC-IV group and the other groups in terms of D/PCr rates. The MSC-IP, MSC-IV and P groups had significantly decreased tumor necrosis factor α concentrations compared with the UFF-C group. MSC-IP group had lower levels of TGF-β1 compared with the P group; MSC-IP group had also lower levels of interleukin-6 compared with UFF-C group.

CONCLUSION

The UFF group had a high permeability UFF. These results showed that IV and IP MSC transplantation exerted positive effects on UFF in a chronic rat model of PD. However, healing effect of small solute transport in MSC-IP group was better than MSC-IV group. IP MSC transplantation may be more effective than IV MSC transplantation for the renewal of the peritoneum in chronic PD patients with UFF.

Stability of the combination of ceftazidime and cephazolin in icodextrin or pH neutral peritoneal dialysis solution

INTRODUCTION

The objective of this study was to investigate the stability of ceftazidime and cephazolin in a 7.5% icodextrin or pH neutral peritoneal dialysis (PD) solution.

METHODS

Ceftazidime and cephazolin were injected into either a 7.5% icodextrin or pH neutral PD bag to obtain the concentration of 125 mg/L of each antibiotic. A total of nine 7.5% icodextrin or pH neutral PD bags containing ceftazidime and cephazolin were prepared and stored at 1 of 3 different temperatures: 4°C in a domestic refrigerator; 25°C at room temperature; or 37°C (body temperature) in an incubator. An aliquot was withdrawn immediately before (0 hour) or after 12, 24, 48, 96, 120, 144, 168 and 336 hours of storage. Each sample was analyzed in duplicate for the concentration of ceftazidime and cephazolin using a stability-indicating high-performance liquid chromatography technique. Ceftazidime and cephazolin were considered stable if they retained more than 90% of their initial concentration. Samples were also assessed for pH, colour changes and evidence of precipitation immediately after preparation and on each day of analysis.

RESULTS

Ceftazidime and cephazolin in both types of PD solution retained more than 90% of their initial concentration for 168 and 336 hours respectively when stored at 4°C. Both of the antibiotics lost more than 10% of the initial concentration after 24 hours of storage at 25 or 37°C. There was no evidence of precipitation at any time under the tested storage conditions. Change in the pH and color was observed at 25 and 37°C, but not at 4°C.

CONCLUSION

Premixed ceftazidime and cephazolin in a 7.5% icodextrin or pH neutral PD solution is stable for at least 168 hours when refrigerated. This allows the preparation of PD bags in advance, avoiding the necessity for daily preparation. Both the antibiotics are stable for at least 24 hours at 25 and 37°C, permitting storage at room temperature and pre-warming of PD bags to body temperature prior to its administration.

Mesenchymal stem cells ameliorate experimental peritoneal fibrosis by suppressing inflammation and inhibiting TGF-β1 signaling

Mesenchymal stem cells (MSCs) are multipotent adult stem cells that have regenerative capability and exert paracrine actions on damaged tissues. Since peritoneal fibrosis is a serious complication of peritoneal dialysis, we tested whether MSCs suppress this using a chlorhexidine gluconate model in rats. Although MSCs isolated from green fluorescent protein–positive rats were detected for only 3 days following their injection, immunohistochemical staining showed that MSCs suppressed the expression of mesenchymal cells, their effects on the deposition of extracellular matrix proteins, and the infiltration of macrophages for 14 days. Moreover, MSCs reduced the functional impairment of the peritoneal membrane. Cocultures of MSCs and human peritoneal mesothelial cells using a Transwell system indicated that the beneficial effects of MSCs on the glucose-induced upregulation of transforming growth factor-β1(TGF-β1) and fibronectin mRNA expression in the human cells were likely due to paracrine actions. Preincubation in MSC-conditioned medium suppressed TGF-β1-induced epithelial-to-mesenchymal transition, α-smooth muscle actin, and the decrease in zonula occludens-1 in cultured human peritoneal mesothelial cells. Although bone morphogenic protein 7 was not detected, MSCs secreted hepatocyte growth factor and a neutralizing antibody to this inhibited TGF-β1 signaling. Thus, our findings imply that MSCs ameliorate experimental peritoneal fibrosis by suppressing inflammation and TGF-β1 signaling in a paracrine manner.

Peritoneal equilibration test with conventional 'low pH/high glucose degradation product' or with biocompatible 'normal pH/low glucose degradation product' dialysates: does it matter?

BACKGROUND

The evaluation of the peritoneal transport characteristics is mandatory in peritoneal dialysis (PD) patients. This is usually performed in routine clinical practice with a peritoneal equilibration test (PET) using conventional dialysates, with low pH and high glucose degradation product (GDP) concentrations. An increasing proportion of patients are now treated with biocompatible dialysates, i.e. with physiological pH and lower GDP concentrations. This questions the appropriateness to perform a PET with conventional solutions in those patients. The aim of our study is to compare the results of the PET using biocompatible and conventional dialysates, respectively.

METHODS

Nineteen stable PD patients (13 males, 6 females; mean age: 67.95±2.36 years, mean body surface area: 1.83±0.04 m2, dialysis vintage: 2.95±0.19 years) were included, among which 10 were usually treated with biocompatible and 9 with conventional solutions. Two PETs were performed, within a 2-week interval, in each patient. PET sequence (conventional solution first or biocompatible solution first) was randomized in order to avoid 'time bias'. Small (urea, creatinine and glucose), middle (beta-2-microglobulin) and large molecules' (albumin and alpha-2-macroglobulin) dialysate/plasma (D/P) concentration ratios and clearances were measured during each PET. Ultrafiltration (UF) and sodium filtration were also recorded. Results of both tests were compared by the Wilcoxon paired test.

RESULTS

No statistical difference was found between both dialysates for small molecule transport rates or for sodium filtration and UF. However, a few patients were not similarly classified for small-solute transport characteristics within the PET categories. Beta-2-microglobulin and albumin D/P ratios at different time points of the PET were significantly higher with the biocompatible, when compared with the conventional, solutions: 0.10±0.03 versus 0.08±0.02 (P<0.01) and 0.008±0.003 versus 0.007±0.003 (P=0.01), respectively. A similar difference was also observed for beta-2-microglobulin that was higher with biocompatible dialysates (1.04±0.32 versus 0.93±0.32 mL/min, respectively).

CONCLUSION

Peritoneal transport of water and small solutes is independent of the type of dialysate which is used. This is not the case for the transport of beta-2-microglobulin and albumin that is higher under biocompatible dialysates. Vascular tonus modification could potentially explain such differences. The PET should therefore always be carried out with the same dialysate to make longitudinal comparisons possible.

Effect of the dialysis fluid buffer on peritoneal membrane function in children

BACKGROUND AND OBJECTIVES

Double-chamber peritoneal dialysis fluids exert less toxicity by their neutral pH and reduced glucose degradation product content. The role of the buffer compound (lactate and bicarbonate) has not been defined in humans.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

A multicenter randomized controlled trial in 37 children on automated peritoneal dialysis was performed. After a 2-month run-in period with conventional peritoneal dialysis fluids, patients were randomized to neutral-pH, low-glucose degradation product peritoneal dialysis fluids with 35 mM lactate or 34 mM bicarbonate content. Clinical and biochemical monitoring was performed monthly, and peritoneal equilibration tests and 24-hour clearance studies were performed at 0, 3, 6, and 10 months.

RESULTS

No statistically significant difference in capillary blood pH, serum bicarbonate, or oral buffer supplementation emerged during the study. At baseline, peritoneal solute equilibration and clearance rates were similar. During the study, 4-hour dialysis to plasma ratio of creatinine tended to increase, and 24-hour dialytic creatinine and phosphate clearance increased with lactate peritoneal dialysis fluid but not with bicarbonate peritoneal dialysis fluid. Daily net ultrafiltration, which was similar at baseline (lactate fluid=5.4±2.6 ml/g glucose exposure, bicarbonate fluid=4.9±1.9 ml/g glucose exposure), decreased to 4.6±1.0 ml/g glucose exposure in the lactate peritoneal dialysis fluid group, whereas it increased to 5.1±1.7 ml/g glucose exposure in the bicarbonate content peritoneal dialysis fluid group (P=0.006 for interaction).

CONCLUSIONS

When using biocompatible peritoneal dialysis fluids, equally good acidosis control is achieved with lactate and bicarbonate buffers. Improved long-term preservation of peritoneal membrane function may, however, be achieved with bicarbonate-based peritoneal dialysis fluids.

The effect of low glucose degradation product, neutral pH versus standard peritoneal dialysis solutions on peritoneal membrane function: the balANZ trial

Background

The balANZ trial recently reported that neutral pH, low glucose degradation product (biocompatible) peritoneal dialysis (PD) solutions significantly delayed anuria and reduced peritonitis rates compared with conventional solutions. This article reports a secondary outcome analysis of the balANZ trial with respect to peritoneal membrane function.

Methods

Adult, incident PD patients with residual renal function were randomized to receive either biocompatible or conventional (control) PD solutions for 2 years. Peritoneal equilibration tests were performed at 1, 6, 12, 18 and 24 months. Peritoneal small solute clearances and ultra-filtration (UF) were measured at 3, 6, 9, 12, 18 and 24 months.

Results

Of the 185 patients recruited into the trial, 85 patients in the Balance group and 82 patients in the control group had peritoneal membrane function evaluated. Mean 4-h dialysate:plasma creatinine ratios (D:P Cr 4h) at 1 month were significantly higher in the Balance group compared with controls (0.67 ± 0.10 versus 0.62 ± 0.10, P = 0.002). Over the 2-year study period, mean D:P Cr 4 h measurements remained stable in the Balance group but increased significantly in controls [difference −0.004 per month, 95% confidence interval (95% CI) −0.005 to −0.002, P < 0.001]. Similar results were obtained for dialysate glucose ratios (D/D0 glucose). Peritoneal UF was significantly lower in the Balance group than in controls at 3 and 6 months. Over the 2-year study period, peritoneal UF increased significantly in the Balance group but remained stable in controls (difference 24 mL/day/month, 95% CI 9–39, P = 0.002). No differences in peritoneal small solute clearances, prescribed dialysate fill volumes or peritoneal glucose exposure were observed between the two groups.

Conclusions

Biocompatible and conventional PD solutions exert differential effects on peritoneal small solute transport rate and UF over time. Adequately powered trials assessing the impact of these differential membrane effects on PD technique and patient survival rates are warranted.

The impact of dialysis solution biocompatibility on ultrafiltration and on free water transport in rats

This study compares different peritoneal dialysis fluids (PDF) in rats over a short contact time. For greater accuracy, net ultrafiltration (UF) and peritoneal transport indices, mass transfer area coefficient (MTAC) were scaled for the in vivo peritoneal surface area recruited (ivPSA) measured by microcomputerized tomography. Wistar rats underwent nephrectomy (5/6ths), were randomized into two groups and given 1.5% glucose PDF, either conventional acidic lactate (n = 14) or pH neutral bicarbonate (BicaVera) (n = 13); MTAC and UF were measured using a 90-min peritoneal equilibrium test (PET), fill volume (IPV) of 10 ml/100 g; small pore fluid transport was determined from sodium balance and used to calculate free water transport (FWT). Each ivPSA value was significantly correlated with the actual IPV, which varied from one rat to another. At 90 min of contact, there was no difference in recruited ivPSA in relation to PDFs. There was a difference (p < 0.01) in net UF/ivPSA 0.45 vs. 1.41 cm(2)/ml for bicarbonate versus lactate, as there was in the proportion of FWT with bicarbonate (42 ± 5% of net UF) compared to lactate (29 ± 4% of net UF). Net UF for individual values of ivPSA differs between conventional PDF and more biocompatible solutions, such as bicarbonate PDF. This observed change in UF cannot be fully explained by differences in glucose transport. The changes in FWT may be explained by the impact of the PDF biocompatibility on aquaporin function.

Solutions for peritoneal dialysis in children: recommendations by the European Pediatric Dialysis Working Group

The purpose of this article is to provide recommendations on the choice of peritoneal dialysis (PD) fluids in children by the European Pediatric Dialysis Working Group. The literature on experimental and clinical studies with PD solutions in children and adults was analyzed together with consensus discussions within the group. A grading was performed based on the international KDIGO nomenclature and methods. The lowest glucose concentration possible should be used. Icodextrin may be applied once daily during the long dwell, in particular in children with insufficient ultrafiltration. Infants on PD are at risk of ultrafiltration-associated sodium depletion, while anuric adolescents may have water and salt overload. Hence, the sodium chloride balance needs to be closely monitored. In growing children, the calcium balance should be positive and dialysate calcium adapted according to individual needs. Limited clinical experience with amino acid-based PD fluids in children suggests good tolerability. The anabolic effect, however, is small; adequate enteral nutrition is preferred. CPD fluids with reduced glucose degradation products (GDP) content reduce local and systemic toxicity and should be preferred whenever possible. Correction of metabolic acidosis is superior with pH neutral bicarbonate-based fluids compared with single-chamber, acidic, lactate-based solutions. Prospective comparisons of low GDP solutions with different buffer compositions are still few, and firm recommendations cannot yet be given, except when hepatic lactate metabolism is severely compromised.

Salt intake induces epithelial-to-mesenchymal transition of the peritoneal membrane in rats

BACKGROUND

Dietary salt intake has been linked to hypertension and cardiovascular disease through volume-mediated effects. Accumulating evidence points to direct negative influence of salt intake independent of volume overload, such as cardiac and renal fibrosis, mediated through transforming growth factor beta (TGF-beta). Epithelial-to-mesenchymal transition (EMT) has been implicated as a key process in chronic fibrotic diseases, such as chronic kidney disease or heart failure. The potential role of dietary salt intake on cell transdifferentiation has never been investigated. This study analysed the effect of dietary salt intake on EMT and fibrosis in the peritoneal membrane (PM) in a rat model.

METHODS

Twenty-eight Wistar rats were randomized to a normal salt (NS) or a high salt (HS) intake. NS and HS rats had free access to tap water or NaCl 2% as drinking water, respectively. After 2 weeks, samples of peritoneum were taken, and TGF-beta(1), Interleukin 6 (IL-6) and vascular endothelial growth factor (VEGF) mRNA expression were quantified with qRT-PCR. Fibrosis and submesothelial PM thickness were scored. EMT was evaluated using fluorescence staining with cytokeratin and alpha smooth muscle actin (alpha-SMA).

RESULTS

Dietary salt intake caused peritoneal fibrosis and thickening of the submesothelial layer and induced EMT as identified by colocalization of cytokeratin and alpha-SMA in cells present in the submesothelial layer. Peritoneal TGF-beta(1) and IL-6 mRNA expression were upregulated in the HS group.

CONCLUSION

High dietary salt intake induces EMT and peritoneal fibrosis, a process coinciding with upregulation of TGF-beta1.

Peritoneal dialysis prescription in children: bedside principles for optimal practice

There is no unique optimal peritoneal dialysis prescription for all children, although the goals of ultrafiltration and blood purification are universal. In turn, a better understanding of the physiology of the peritoneal membrane, as a dynamic dialysis membrane with an exchange surface area recruitment capacity and unique permeability characteristics, results in the transition from an empirical prescription process based on clinical experience alone to the potential for a personalized prescription with individually adapted fill volumes and dwell times. In all cases, the prescribed exchange fill volume should be scaled for body surface area (ml/m(2)), and volume enhancement should be conducted based on clinical tolerance and intraperitoneal pressure measurements (IPP; cmH(2)O). The exchange dwell times should be determined individually and adapted to the needs of the patient, with particular attention to phosphate clearance and ultrafiltration capacity. The evolution of residual kidney function and the availability of new, more physiologic, peritoneal dialysis fluids (PDFs) also influence the prescription process. An understanding of all of these principles is integral to the provision of clinically optimal PD.

Acute effects of peritoneal dialysis solutions in the mesenteric microcirculation

Long-term peritoneal dialysis induces morphological changes that may lead to gradual functional impairment of the peritoneal membrane. These changes are characterized by progressive reduction in solute transport or ultrafiltration failure. The mechanism of the peritoneal response to dialysis fluids has not yet been fully elucidated. We used video-microscopy for in vivo evaluation of microhemodynamics and peritoneal microvascular inflammatory response, after a single intraperitoneal exposure of rats to commercial PD fluids: (1) glucose 1.5 % PD solution; (2) lactate buffered glucose 4.25% PD solution; (3) Icodextrin 7%; (4) bicarbonate buffered glucose 3.86% PD fluid; and 5) Hanks solution. Sham-control groups were not injected. A 5-h exposure of the peritoneal membrane to glucose 1.5% PD solution or to Hanks solution did not induce a significant change in leukocyte rolling and adhesion. In contrast, PD solutions containing glucose 4.25% or Icodextrin 7.5% caused a significant 2-3-fold increase in leukocyte rolling (P < 0.001) and adhesion (P < 0.001) and a significant increase in venular blood flow velocity (P < 0.01) and shear rates (P < 0.05 for glucose 4.25%, and P < 0.01 for Icodextrin). Exposure to glucose 3.86% bicarbonate buffered (Physioneal) solution was associated with the lowest values of leukocyte rolling and adhesion among the PD solutions and with extremely higher venular flow velocities and shear rates. A single exposure to conventional PD solutions with a high concentration of glucose (4.25%) or polyglucose (Icodextrin 7.5%) induces changes consistent with an early peritoneal inflammatory response that may be attenuated by the use of bicarbonate-based fluids.

Benefits of biocompatible PD fluid for preservation of residual renal function in incident CAPD patients: a 1-year study

BACKGROUND

In vitro studies of peritoneal dialysis (PD) solutions demonstrated that a biocompatible fluid with neutral-pH and low glucose degradation products (LF) has better biocompatibility than a conventional acidic lactate-buffered fluid (CF). However, few clinical trials have investigated the effects of the biocompatible solution on residual renal function (RRF). We performed a prospective, randomized trial with patients starting continuous ambulatory peritoneal dialysis (CAPD).

METHODS

Ninety-one incident patients started CAPD for 12-month treatment with either LF (Balance, Fresenius, n = 48) or CF (CAPD/DPCA, Fresenius, n = 43). RRF, peritoneal solute transport rate and solute clearance were measured every 6 months.

RESULTS

LF had a significant effect on the change of glomerular filtration rate (GFR) (P = 0.048 by the mixed model). In per-protocol analysis, GFR in the LF group did not decrease over a 12-month period, while GFR in the control group significantly decreased (0.13 +/- 33.4 L/ week/1.73 m(2) for LF versus -13.6 +/- 19.4 L/week/1.73 m(2) for CF, P = 0.049). Subgroup analysis for patients with initial GFR of 2 mL/min/1.73 m(2) or above showed a significantly higher GFR for the LF group over the 12-month period. At Month 13, serum total CO(2) levels were higher and serum albumin levels were lower in the LF group. No differences between the two groups were observed for the C-reactive protein. Over the 12-month period, effluent cancer antigen-125 levels significantly increased in the LF group, compared with those of the CF group, while effluent interleukin-6 levels were not different between the two groups.

CONCLUSION

Our study suggests that LF may better preserve RRF over the 12-month treatment period in incident CAPD patients.

Conventional versus biocompatible peritoneal dialysis fluids: more questions than answers?

The most important challenge in peritoneal dialysis (PD) is long-term preservation of peritoneal membrane structure and function. Introduction of dialysis fluids into the peritoneal cavity induces changes. These changes are related to duration of dialysis, occurrence of peritonitis and components of the dialysis solution. Bioincompatibility is considered to be the major cause of the development of morphological changes of the peritoneal membrane. pH neutral PD fluids that are low in glucose degradation products (GDP) seem to better preserve the peritoneal membrane and have less systemic effects than the conventional ones. However, the long-term effects are not clear. An overview of the effects of conventional PD fluids and glucose-based PD fluids with neutral pH in ex vivo and in vivo animal and clinical studies is presented.

Correlation of metabolic syndrome with residual renal function, solute transport rate and peritoneal solute clearance in chronic peritoneal dialysis patients

BACKGROUND

Metabolic syndrome (MetS) and insulin resistance (IR) strongly promote macrovascular complications and endothelial dysfunction. They accelerate the progression of renal dysfunction in chronic kidney disease patients. However, their correlation with residual renal function (RRF) and peritoneal characteristics have never been investigated.

METHODS

The inter-relationships of IR (homeostatic model assessment, HOMA(IR)), serum adiponectin level, body mass index (BMI), highly sensitive C-reactive protein (hs-CRP), RRF, peritoneal solute clearance (Kt/V(urea)) and solute transport rate of 104 chronic peritoneal dialysis (PD) patients were examined.

RESULTS

Patients with (n = 57) and without (n = 47) clinically diagnosed MetS had the same degree of RRF, peritoneal Kt/V(urea), and solute transport rate. Higher HOMA(IR) (p = 0.011), BMI (p = 0.01) and hs-CRP (p = 0.032), as well as lower adiponectin (p = 0.019), were associated with lower peritoneal Kt/V(urea). Serum adiponectin was negatively associated with solute transport rate (p = 0.02). In multiple regression analysis, higher HOMA(IR) (p = 0.005), BMI (p = 0.021) and hs-CRP (p < 0.001) correlated with lower peritoneal Kt/V(urea).

CONCLUSIONS

MetS plays an important role in both macrovascular complications and endothelial dysfunction in chronic PD patients, which correlates with changes in peritoneal solute clearance and solute transport rate but not RRF.

Decreased leukocyte recruitment in the mesenteric microcirculation of rats with cirrhosis is partially restored by treatment with peginterferon: an in vivo study

BACKGROUND/AIMS

Patients with liver cirrhosis are predisposed to develop bacterial infections. An essential process in inflammatory responses is the recruitment of circulating leukocytes through the activation of adhesion molecules. Interferon-alpha2a is a cytokine reported to influence the expression of adhesion molecules. We investigated the effect of peginterferon-alpha2a (PegIFN-alpha(2a)) in vivo on the leukocyte recruitment in the mesenteric microcirculation of cirrhotic rats after lipopolysaccharide exposure.

METHODS

Leukocyte rolling, adhesion and extravasation were visualized by intravital microscopy in sham-operated and common bile duct ligated (CBDL) rats. PegIFN-alpha(2a) was administered to influence leukocyte recruitment. Endothelial P-selectin, E-selectin and ICAM-1 expression were studied by immunohistochemistry.

RESULTS

CBDL placebo rats showed significantly impaired rolling, adhesion and extravasation of leukocytes compared to Sham-operated placebo rats. Endothelial P-selectin, E-selectin and ICAM-1 expressions in CBDL placebo rats were significantly reduced compared to Sham-operated placebo rats. PegIFN-alpha(2a) 18 microg normalized number of rolling leukocytes in CBDL rats, without influencing on adhering and extravasated leukocytes. PegIFN-alpha(2a) upregulates the expression of P-selectin and E-selectin in CBDL rats, but ICAM-1 expression remained significantly lower than in Sham rats.

CONCLUSIONS

Leukocyte recruitment is significantly impaired in the mesenteric microcirculation of cirrhotic rats. This deficiency appears to result from a reduced endothelial P-selectin, E-selectin and ICAM-1 expression. Peginterferon-alpha(2a) treatment normalizes rolling of leukocytes in cirrhotic rats by upregulation of P-selectin and E-selectin expressions, but has no influence on adhesion and extravasation possibly due to the absence of effect on ICAM-1 expression.

Glucose degradation products (GDP's) and peritoneal changes in patients on chronic peritoneal dialysis: will new dialysis solutions prevent these changes?

As peritonitis rates are declining, the rate of technique failure due to ultrafiltration failure and inadequate solute removal is becoming more important. The failure of the peritoneal membrane to provide adequate dialysis increases with longer duration on PD and correlates with the structural changes in the peritoneal membrane. The exact mechanism responsible for these structural changes is unclear. Conventional PD fluids with glucose as the osmotic agent and more importantly the glucose degradation products (GDP) generated during the heat sterilization of these solutions seems to be responsible for inducing many of these changes in the peritoneum. GDP's in addition to causing structural and functional alterations of the peritoneal cells is also a leading cause of advanced glycation end-products (AGE) production. There is evidence to suggest that the GDP's and AGE's are not limited to the peritoneal cavity and the membrane. They have been shown to get deposited in the vascular walls. In addition they also interact with receptors on endothelial cells and smooth muscle. Thus they could contribute to the vascular dysfunction similar to that seen in diabetes. Formation of GDP's can be reduced and even be avoided with the use of newer "biocompatible" solutions by sterilizing the glucose and the buffer in separate chambers. These newer solutions have been shown to have several local and systemic advantages over the conventional PD solutions. It remains to be seen whether their chronic use from the start of peritoneal dialysis will prevent the development of peritoneal damage thus allowing these patients to remain on this modality for longer periods.

Improved biocompatibility of bicarbonate/lactate-buffered PDF is not related to pH

BACKGROUND

Chronic exposure to conventional peritoneal dialysis fluid (PDF) is associated with functional and structural alterations of the peritoneal membrane. The bioincompatibility of conventional PDF can be due to hypertonicity, high glucose concentration, lactate buffering system, presence of glucose degradation products (GDPs) and/or acidic pH. Although various investigators have studied the sole effects of hyperosmolarity, high glucose, GDPs and lactate buffer in experimental PD, less attention has been paid to the chronic impact of low pH in vivo.

METHODS

Rats received daily 10 ml of either conventional lactate-buffered PDF (pH 5.2; n=7), a standard bicarbonate/lactate-buffered PDF with physiological pH (n=8), bicarbonate/lactate-buffered PDF with acidic pH (adjusted to pH 5.2 with 1 N hydrochloride, n=5), or bicarbonate/lactate buffer, without glucose, pH 7.4 (n=7). Fluids were instilled via peritoneal catheters connected to implanted subcutaneous mini vascular access ports for 8 weeks. Control animals with or without peritoneal catheters served as control groups (n=8/group). Various functional (2 h PET) and morphological/cellular parameters were analyzed.

RESULTS

Compared with control groups and the buffer group, conventional lactate-buffered PDF induced a number of morphological/cellular changes, including angiogenesis and fibrosis in various peritoneal tissues (all parameters P<0.05), accompanied by increased glucose absorption and reduced ultrafiltration capacity. Daily exposure to standard or acidified bicarbonate/lactate-buffered PDF improved the performance of the peritoneal membrane, evidenced by reduced new vessel formation in omentum (P<0.02) and parietal peritoneum (P<0.008), reduced fibrosis (P<0.02) and improved ultrafiltration capacity. No significant differences were found between standard and acidified bicarbonate/lactate-buffered PDF. During PET, acidic PDF was neutralized within 15 to 20 min.

CONCLUSION

The bicarbonate/lactate-buffered PDF, acidity per se did not contribute substantially to peritoneal worsening in our in vivo model for PD, which might be explained by the buffering capacity of the peritoneum.

Disparity in osmolarity-induced vascular reactivity

Conventional peritoneal dialysis solutions (PDS) are vasoactive. This study was conducted to identify vasoactive components of PDS and to describe quantitatively such vasoactivity. Anesthetized nonheparinized rats were monitored continuously for hemodynamics while the microvasculature of the jejunum was studied with in vivo intravital microscopy. In separate experiments, vascular reactivity of rat endothelium-intact and -denuded aortic rings (2 mm) was studied ex vivo in a standard tissue bath. In both studies, suffusion of the vessels was performed with filter-sterilized isotonic and hypertonic solutions that contained glucose or mannitol as osmotic agents. PDS served as a control (Delflex 2.25%). Hypertonic glucose and mannitol solutions produced a significant vascular reactivity in aortic rings and instantaneous and sustained vascular relaxation at all levels of the intestinal microvasculature. Similarly, lactate that was dissolved in a low-pH isotonic physiologic salt solution produced significant force generation in aortic rings. Whereas isotonic glucose and mannitol solutions had no vasoactivity in aortic rings, isotonic glucose produced a selective, insidious, and time-dependent vasodilation in the intestinal premucosal arterioles (18 +/- 0.2% of baseline), which was not observed in the larger inflow arterioles (100 mum). This isotonic glucose-mediated vascular relaxation can be attenuated by approximately 50% with combined adenosine A(2a) and A(2b) receptor antagonists and completely abolished by adenosine A(1) receptor inhibition. By using two different experimental techniques, this study demonstrates that hyperosmolality and lactate are the major vasoactive components of clinical peritoneal dialysis solutions. The pattern and the magnitude of such reactivity are dependent on vessel size and on the solutes' metabolic activity. Low pH of conventional PDS is not a vasoactive component by itself but renders lactate vasoactive. Energy-dependent transport of glucose into cells mediates vasodilation of small visceral arterioles by an adenosine receptor-mediated mechanism and constitutes a significant fraction of PDS-mediated vascular reactivity in the visceral microvasculature.

Effects of new peritoneal dialysis solutions on leukocyte recruitment in the rat peritoneal membrane

OBJECTIVES

Peritonitis remains a principal cause of dropout in peritoneal dialysis (PD). The physiological host response to a peritoneal infection involves a rise in numbers of circulating leukocytes to the peritoneal cavity. We evaluated the effects of (1) conventional peritoneal dialysis fluid (PDF), (2) bicarbonate-based PDF, low in glucose degradation products, and (3) non-glucose PDF on peritoneal leukocyte recruitment in response to an inflammatory stimulus using intravital microscopy.

METHODS

The visceral peritoneum was exposed to EBSS, conventional lactate-buffered and bicarbonate/lactate-buffered glucose-based PDF and three lactate-buffered non-glucose PDF-icodextrin, amino acid-based PDF and amino acid/glycerol-based PDF. The number of rolling, adhering and extravasated leukocytes and leukocyte rolling velocity was assessed at different time intervals after stimulation with lipopolysaccharide (LPS).

RESULTS

Exposure to LPS dissolved in EBSS dramatically increased the number of rolling, adhering and extravasated leukocytes and decreased leukocyte rolling velocity. Conventional PDF completely abolished LPS-induced leukocyte recruitment. Bicarbonate/lactate-buffered PDF only minimally affected the process of leukocyte recruitment, whereas icodextrin PDF resulted in partial inhibition of the immune response. The amino acid-based and the amino acid/glycerol-based PDF inhibited leukocyte recruitment to a similar extent as conventional PDF.

CONCLUSIONS

Bicarbonate/lactate-buffered PDF has superior biocompatibility towards peritoneal host defense, in spite of its high glucose concentrations. Lactate-buffered non-glucose containing PDF has substantial inhibitory effects on leukocyte recruitment, indicating that the bioincompatibility of high lactate concentrations and/or low pH may not be underestimated.

Angiotensin II induces fibronectin expression in human peritoneal mesothelial cells via ERK1/2 and p38 MAPK

BACKGROUND

The renin-angiotensin system has been implicated in the pathogenesis of fibrosis in various organs. However, its involvement in peritoneal fibrosis, a crucial complication of peritoneal dialysis, is unclear. Human peritoneal mesothelial cells (HPMC) play a major role in peritoneal fibrosis by producing extracellular matrix (ECM). However, there is scant data regarding the effect of angiotensin II (Ang II) on ECM expression and signal transduction pathways in HPMC.

METHODS

The concentration of Ang II in the peritoneal dialysis effluent was measured by radioimmunoassay. We investigated the expression of Ang II type 1 (AT1) and type 2 (AT2) receptors by HPMC. We also examined the effect of Ang II upon fibronectin production by HPMC, and dissected the receptor and intracellular signaling pathways involved.

RESULTS

Ang II levels in the peritoneal dialysis effluent at the onset of peritonitis were 30 times higher than baseline levels. HPMC expression of AT1 and AT2 receptors was confirmed at the mRNA and protein level by reverse transcriptase-polymerase chain reaction (PCR), Western blotting, and immunocytochemistry. Quantitative reverse transcriptase-PCR and Western blotting showed that 10 nmol/L Ang II increased fibronectin mRNA expression followed by secretion of fibronectin protein. This response was completely inhibited by the AT1 receptor antagonist RNH6270, while the AT2 receptor antagonist PD123319 had no effect. Ang II-induced fibronectin expression was mediated by the activation of extracellular signal-regulated kinase 1/2 (ERK1/2) and p38 mitogen-activated protein kinase (p38 MAPK), but not c-Jun N-terminal kinase.

CONCLUSION

These results indicate the potential importance of ERK1/2 and p38 MAPK signaling pathways in Ang II-induced fibronectin expression in HPMC, and suggest the therapeutic potential of AT1 receptor blockers in the prevention or treatment of peritoneal fibrosis in patients on peritoneal dialysis.

Immunopathological changes in a uraemic rat model for peritoneal dialysis

BACKGROUND

Peritoneal dialysis (PD) is a treatment modality for patients with renal failure. Both the uraemic state of these patients and chronic exposure to PD fluid are associated with the development of functional and structural alterations of the peritoneal membrane. In a well-established chronic PD rat model, we compared rats with normal renal function with subtotal nephrectomized rats that developed uraemia.

METHODS

Uraemic and control rats received daily 10 ml conventional glucose containing PD fluid, via peritoneal catheters during a 6 week period. Uraemic and control rats receiving no PD fluid served as controls. Parameters relevant for peritoneal defence and serosal healing responses were analyzed.

RESULTS

Uraemic animals were characterized by 2-3-fold increased serum urea and creatinine levels, accompanied by a significantly reduced haematocrit. Uraemia (without PD fluid exposure) induced new blood vessels in different peritoneal tissues, accompanied by increased accumulation of advanced glycation end products (AGEs) and elevated levels of angiogenic factors such as vascular endothelial growth factor and monocyte chemoattractant protein-1 (MCP-1) in peritoneal lavage fluid. A much stronger peritoneal response was observed upon PD fluid exposure in non-uraemic rats. This included the induction of angiogenesis and fibrosis in various peritoneal tissues, accumulation of AGEs, immunological activation of the omentum, damage to the mesothelial cell layer, focal formation of granulation tissues and increased MCP-1 and hyaluronan levels in peritoneal lavage fluid. Finally, chronic PD fluid instillation in uraemic rats did not induce an additional peritoneal response compared to PD fluid exposure in non-uraemic rats, except for the degree of AGE accumulation.

CONCLUSIONS

Both uraemia and PD fluid exposure result in pathological alterations of the peritoneum. However, uraemia did not induce major additive effects to PD fluid-induced injury. These results substantially contribute to the understanding of the pathobiology of the peritoneum under PD conditions.

La biocompatibilité des solutions de dialyse péritonéale

Repeated and long-term exposure to conventional glucose-based peritoneal dialysis fluids (PDFs) with poor biocompatibility plays a central role in the pathogenesis of the functional and structural changes of the peritoneal membrane. We have used immortalized human peritoneal mesothelial cells in culture to assess in vitro the biocompatibility of PDFs. Low pH, high glucose concentration and heat sterilization represent major factors of low biocompatibility. Two recent groups of glucose derivatives have been described. Glucose degradation products (GDPs) are formed during heat sterilization (glycoxidation) and storage. GDPs can bind protein and form AGEs (Advanced Glycation End-products), which can also result from the binding of glucose to free NH2 residues of proteins (glycation). The physiological pH, and the separation of glucose during heat sterilization (low GDP content) in the most recent PDFs dramatically increase the biocompatibility. The choice of PD programs with high biocompatibility PDFs allows preserving the function of the peritoneal membrane. Improvement of PDF biocompatibility may limit the occurrence of chronic chemical peritonitis and may allow long-term PD treatment.

Increases in peritoneal small solute transport in the first month of peritoneal dialysis predict technique survival

BACKGROUND

Peritoneal transport of small solutes generally increases during the first month of peritoneal dialysis (PD). The aim of this study was to prospectively evaluate the ability of the peritoneal equilibration test (PET), carried out 1 and 4 weeks after the commencement of PD, to predict subsequent technique survival.

METHODS

Fifty consecutive patients commencing PD at the Princess Alexandra Hospital between 1 February 2001 and 31 May 2003 participated in the study. Paired 1 week and 1 month PET data were collated and correlated with subsequent technique survival.

RESULTS

A significant increase was observed in the dialysate : plasma creatinine ratio at 4 h (D/P Cr) between 1 and 4 weeks after the onset of PD (0.55 +/- 0.12 vs 0.66 +/- 0.11, P <0.001). Mean death-censored technique survival was superior in patients who experienced > or =20% rise in D/P Cr during the first month of PD compared with those who did not (2.3 +/- 0.2 vs 1.6 +/- 0.2 years, P <0.05). Using a multivariate Cox proportional hazards model analysis, the significant independent predictors of death-censored technique survival were an increase in D/P Cr of greater than 20% during the first month (adjusted hazard ratio [HR] 0.20, 95% CI 0.05-0.75), the absence of diabetes mellitus, the absence of ischaemic heart disease, body mass index and baseline peritoneal creatinine clearance.

CONCLUSIONS

A 20% or greater rise in D/P Cr during the first month of commencing PD is independently predictive of PD technique survival. Further investigations of the mechanisms underlying this phenomenon are warranted.

BIOKID: randomized controlled trial comparing bicarbonate and lactate buffer in biocompatible peritoneal dialysis solutions in children [ISRCTN81137991]

BACKGROUND

Peritoneal dialysis (PD) is the preferred dialysis modality in children. Its major drawback is the limited technique survival due to infections and progressive ultrafiltration failure. Conventional PD solutions exert marked acute and chronic toxicity to local tissues. Prolonged exposure is associated with severe histopathological alterations including vasculopathy, neoangiogenesis, submesothelial fibrosis and a gradual loss of the mesothelial cell layer. Recently, more biocompatible PD solutions containing reduced amounts of toxic glucose degradation products (GDPs) and buffered at neutral pH have been introduced into clinical practice. These solutions contain lactate, bicarbonate or a combination of both as buffer substance. Increasing evidence from clinical trials in adults and children suggests that the new PD fluids may allow for better long-term preservation of peritoneal morphology and function. However, the relative importance of the buffer in neutral-pH, low-GDP fluids is still unclear. In vitro, lactate is cytotoxic and vasoactive at the concentrations used in PD fluids. The BIOKID trial is designed to clarify the clinical significance of the buffer choice in biocompatible PD fluids.

METHODS/DESIGN

The objective of the study is to test the hypothesis that bicarbonate based PD solutions may allow for a better preservation of peritoneal transport characteristics in children than solutions containing lactate buffer. Secondary objectives are to assess any impact of the buffer system on acid-base status, peritoneal tissue integrity and the incidence and severity of peritonitis. After a run-in period of 2 months during which a targeted cohort of 60 patients is treated with a conventional, lactate buffered, acidic, GDP containing PD fluid, patients will be stratified according to residual renal function and type of phosphate binding medication and randomized to receive either the lactate-containing Balance solution or the bicarbonate-buffered Bicavera solution for a period of 10 months. Patients will be monitored by monthly physical and laboratory examinations. Peritoneal equilibration tests, 24-h dialysate and urine collections will be performed 4 times. Peritoneal biopsies will be obtained on occasion of intraabdominal surgery. Changes in small solute transport rates, markers of peritoneal tissue turnover in the effluent, acid-base status and peritonitis rates and severity will be analyzed.