Long-term clinical effects of a peritoneal dialysis fluid with less glucose degradation products

Do low GDP neutral pH solutions prevent or retard peritoneal membrane alterations in long-term peritoneal dialysis?

Several studies have been published in the last decade on the effects of low glucose degradation product (GDP) neutral pH (L-GDP/N-pH) dialysis solutions on peritoneal morphology and function during the long-term PD treatment. Compared to conventional solutions, the impact of these solutions on the morphological and functional alterations of the peritoneal membrane is discussed, including those of effluent proteins that reflect the status of peritoneal tissues. Long-term PD with conventional solutions is associated with the loss of mesothelium, submesothelial and interstitial fibrosis, vasculopathy, and deposition of advanced glycosylation end products (AGEs). L-GDP/N-pH solutions mitigate these alterations, although vasculopathy and AGE deposition are still present. Increased vascular density was found in some studies. Small solute transport increases with PD duration on conventional solutions. Initially, higher values are present on L-GDP/N-pH treatment, but these may be reversible and remain stable with PD duration. Consequently, ultrafiltration (UF) is lower initially but remains stable thereafter. At 5 years, UF and small pore fluid transport are higher, while free water transport decreased only slightly during follow-up. Cancer antigen 125 was initially higher on L-GDP/N-pH solutions, suggesting better mesothelial preservation but decreased during follow-up. Therefore, L-GDP/N-pH solutions may not prevent but reduce and retard the peritoneal alterations induced by continuous exposure to glucose-based dialysis fluids.

Oxidative stress, inflammation, and peritoneal dialysis: A molecular biology approach

The key role of oxidative stress (OxSt) and inflammation for the induction of cardiovascular disease, the leading cause of excess morbidity/mortality in chronic kidney disease and dialysis patients, is known and both the activations of NADPH oxidase and RhoA/Rho kinase (ROCK) pathway are pivotal for their effects. While specific hemodialysis procedures, such as hemodiafiltration with on‐line reinfusion of ultrafiltrate and/or the use of vitamin E‐coated dialyzers, are beneficial for OxSt and inflammation, studies in peritoneal dialysis (PD) are instead scarce and results seem not favorable. In nine patients under PD OxSt in terms of mononuclear cell protein level of p22^phox (Western blot), subunit of NADPH oxidase, essential for the generation of OxSt, and MYPT‐1 phosphorylation state (Western blot), a marker of ROCK activity, have been measured at the beginning and after 3 and 6 months of PD. Blood levels of interleukin 6 (IL‐6), ferritin, and albumin have been considered for evaluating the inflammatory state. p22^phox protein expression, MYPT‐1‐phosphorylation, and ferritin level were increased both at baseline vs healthy subjects (P = .02, P < .0001, P = .004, respectively) and vs baseline after 3 and 6 months of peritoneal dialysis (P = .007, P < .001, P = .004, respectively). Albumin was lower after 6 months of PD (P = .0014). IL‐6 was increased at baseline vs reference values and remained unchanged at 3 and 6 months. OxSt and inflammation increase during PD confirming via molecular biology approach a report at biochemical level. To improve OxSt state in PD, a multitarget approach is necessary. It might include the use of more physiologic pH, low glucose degradation products, low lactate and iso‐osmolar PD solutions, patients’ strict glycemic control, optimal volume management, and antioxidant administration, such as N‐acetylcysteine.

Role of the Renin–angiotensin System in the Pathogenesis of Peritoneal Fibrosis

⋄ Background

Although the effects of angiotensin type 1 receptor blocker (ARB) have been studied, little is known about ARBs in hypertensive patients undergoing dialysis. In the present study, we evaluated the effect of an ARB, olmesartan medoxomil (CS866), on the progression of peritoneal fibrosis in peritoneal dialysis by examining its effect in a model of peritoneal fibrosis in hypertensive rats.

⋄ Materials and Methods

W e all ocated 40 male Wistar rats with 2-kidney, 1-clip renovascular hypertension (2K1C-RVH) to 4 groups (each n = 10) that were dialyzed using various solutions for 42 days as follows: • Group I—10 mL pH 3.5 dialysis solution containing 1.35% glucose • Group II—10 mL pH 3.5 dialysis solution, plus oral administration of CS866 5 mg/kg daily • Group III—10 mL pH 3.5 dialysis solution, plus oral administration of the calcium channel blocker (CCB) amlodipine 3 mg/kg daily • Group IV—10 mL pH 7.0 dialysis solution Dialysis solution was injected every day for 42 days.

⋄ Results

Treatment with CS866 and amlodipine induced a significant reduction of blood pressure in 2K1C-RVH rats. In rats treated with pH 3.5 dialysis solution, necropsy findings revealed features identical to those of encapsulating peritoneal sclerosis (EPS). The typical appearance was multiple surfaces covered with granulation tissue or fibrosic tissue or both. Multiple adhesions were present. Microscopic findings revealed that acidic dialysis solution induced peritoneal fibrosis and loss of mesothelium. Treatment with CS866 prevented the progression of peritoneal fibrosis and adhesions. However amlodipine did not improve the progression of peritoneal fibrosis and peritoneal adhesions. In CS866-treated rats, no signs of EPS were present.

⋄ Conclusions

Long-term intraperitoneal exposure to acidic dialysis solution produced features typical of EPS. Acidic dialysis solution induces activation of the peritoneal renin– angiotensin system and progression of peritoneal fibrosis. For the peritoneum undergoing peritoneal dialysis, ARB protects against progression of peritoneal fibrosis and peritoneal adhesions.

30 Years of Peritoneal Dialysis Development: The past and the Future

A review is given of 30 years of development in peritoneal dialysis (PD). After a short description of the first 20 years, the main emphasis is put on the last 10 years. Subjects discussed are the increasing use of PD in high-risk populations, peritonitis and other catheter-related problems, adequacy of dialysis and nutrition, patient outcomes in comparison with hemodialysis, and peritoneal membrane changes with time on PD. Topics that have emerged during the last decade and the challenges for the next decennium are discussed. The great importance of quality assurance in fast-growing PD populations and of prevention of long-term membrane alterations are emphasized.

Could Solutions Low in Glucose Degradation Products Preserve Residual Renal Function in Incident Peritoneal Dialysis Patients? A 1-Year Multicenter Prospective Randomized Controlled Trial (Balnet Study)

⋄ Objectives

In vitro studies of peritoneal dialysis (PD) solutions demonstrated that a lactate-buffered 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 evaluated the long-term benefit of the biocompatible solution on residual renal function (RRF). To compare LF with CF, we performed a prospective, randomized study with patients starting PD.

⋄ Patients and Methods

After 1-month run-in period, 91 new PD patients were randomized for 12 months of treatment with either LF (Balance: Fresenius Medical Care, Bad Homburg, Germany; n = 48) or CF (Stay•Safe: Fresenius; n = 43). We measured RRF, acid–base balance, peritoneal equilibration test, and adequacy of dialysis every 6 months after the run-in period.

⋄ Results

After 12 months of treatment, the residual glomerular filtration rate (GFR) in patients using LF tended to be higher than that of patients on CF ( p = 0.057 by repeated-measures analysis of variance). We observed a significant difference in the changes of residual GFR between the two groups ( p = 0.009), a difference that was especially marked in the subgroup whose baseline residual GFR was more than 2 mL/min/1.73 m2. In addition, serum total CO2 levels were higher ( p = 0.001) and serum anion gap was lower ( p = 0.019) in the LF group. We observed no differences between groups for Kt/V, C-reactive protein, or normalized protein equivalent of nitrogen appearance.

⋄ Conclusions

In incident PD patients with significant residual GFR, LF may better preserve RRF over a 12-month treatment period. Additionally, pH-neutral PD fluid may improve acid–base balance as compared with CF.

Non-invasive assessment of peritoneal membrane alterations

The peritoneal dialysis membrane is subject to remodelling in the course of peritoneal dialysis. In the absence of longitudinal morphological studies, this process is mainly studied indirectly by the investigation of changes in peritoneal transport. Non-invasive assessment of the peritoneum is also possible by assessment of substances that originate from peritoneal tissues and can be determined either as their gene expression in peritoneal effluent cells and/or as proteins in peritoneal effluent. Three of these biomarkers will be discussed, because longitudinal data are available. Cancer antigen 125 (CA 125) is present on the mesothelium,while its gene (MUC 16) is expressed in peritoneal effluent cells and is related to dialysate CA 125 protein. The constitutive production and the small intra-individual variability of 15% indicate its usefulness as a follow-up marker of mesothelial cell mass. Dialysate appearance rate is higher on biocompatible than on conventional solutions, but both decrease during long-term follow-up. Interleukin-6 (Il-6) is present in peritoneal effluent due to both transport from the circulation and local intraperitoneal production. Its appearance rate is unrelated to its gene expression in peritoneal cells. The intra-individual variation of effluent Il-6 averages 28%, hampering the interpretation of cross-sectional values. The relationships between effluent Il-6 and peritoneal transport have been interpreted as microinflammation, but are difficult to interprete due to mathematical coupling. Plasminogen activator inhibitor-1 (PAI-1) is encoded by the SERPINE 1 gene. A relationship is present between effluent concentration and gene expression. PAI-1 production is stimulated by glucose. PAI-1 appearance rate increases with PD duration. The sensitivity of effluent PAI-1 for the diagnosis of encapsulating peritoneal sclerosis was 100% one year prior to the diagnosis and the specificity 56%. It can be concluded that the discussed biomarkers are useful extensions to transport in assessment of the peritoneum during dialysis.  

Generation of TNFα and Interleukin-6 by Peritoneal Macrophages after Overnight Dwells with Bicarbonate- or Lactate-Buffered Dialysis Fluid

Objective

In order to evaluate the biocompatibility profile of a newly designed peritoneal dialysis fluid (PDF), we evaluated peritoneal leukocyte (PMΦ) cytokine release following overnight in vivo dwells using standard, lactate-buffered, single-chamber bag PDF (Lac-PDF) and purely bicarbonate-buffered, double-chamber bag PDF containing 34 (Bic-PDF) or 39 (Bic Hi-PDF) mmol/L bicarbonate.

Design

A randomized, open, crossover clinical trial with single weekly test dwells was performed in stable, long-term continuous ambulatory PD patients ( n = 8). During 8-hour overnight dwells, PMΦ were exposed to different PDF containing 1.5% glucose. After drainage, peritoneal cells were isolated and incubated with RPMI 1640 medium for 2 or 3 hours, with and without stimulation by lipopolysaccharide (LPS). Ex vivo release of tumor necrosis factor (TNF)-α and interleukin (IL)-6 was measured by specific ELISA technique.

Results

After pre-exposure to Lac-PDF, PMΦ generated 242 ± 279 pg TNFα/106 cells and 157 ± 105 pg IL-6/106 cells. When pre-exposed to Bic-PDF and Bic Hi-PDF, TNFα and IL-6 production of PMΦ was not significantly different from Lac-PDF. After LPS stimulation (100 ng/mL), PMΦ secretion of TNFα and IL-6 pre-exposed to three PDF revealed no significant differences between groups: TNFα was 2864 ± 1216, 2910 ± 1202, and 3291 ± 558 pg/106 cells after overnight dwells with Lac-PDF, Bic-PDF, and Bic Hi-PDF, respectively. Comparably, LPS-stimulated (100 pg/mL) PMΦ showed IL-6 secretion of 891 ± 335, 1380 ± 1149, and 1442 ± 966 pg/106 cells for Lac-PDF, Bic-PDF, and Bic Hi-PDF.

Conclusion

After long-term overnight dwells, initial pH, the different buffers, and varying glucose degradation product levels of PDF do not strongly affect PMΦ function with respect to cytokine release. The lack of significant differences between fluids may result from the complete dialysate equilibration achieved during the overnight intraperitoneal dwell.

Superior Patient Survival for Continuous Ambulatory Peritoneal Dialysis Patients Treated with a Peritoneal Dialysis Fluid with Neutral pH and Low Glucose Degradation Product Concentration (Balance)

Background

In recent years, laboratory and clinical research has suggested the need for peritoneal dialysis fluids (PDFs) that are more biocompatible than the conventional PDFs commonly used today. Bioincompatibility of PDF has been attributed to low pH, lactate, glucose, glucose degradation products (GDPs), and osmolality. PDFs with neutral pH and low GDPs are now available commercially. In vitro and early clinical studies suggest that these solutions are indeed more biocompatible but, as of now, there is no evidence that their use improves patient outcome.

Methods

Using a dedicated database of over 2000 patients treated with PD in Korea, we were able to conduct a retrospective observational study comparing outcomes for incident continuous ambulatory PD patients treated with a standard, conventional, heat-sterilized PDF to the outcomes for patients treated with a novel, low GDP, neutral-pH PDF prepared in a dual-compartment, double-bag PD system (Balance; Fresenius Medical Care, St. Wendel, Germany). In an intention-to-treat analysis, patient and technique survival, peritonitis-free survival, and peritonitis rates were compared in 611 patients treated with Balance for up to 30 months and 551 patients with a standard PDF (stay·safe; Fresenius Medical Care) treated in the same era and with equivalent follow-up.

Results

The patients were well matched for most relevant characteristics except older age distribution for the patients treated with the standard PDF. Patients treated with Balance had significantly superior survival compared to those treated with the standard PDF (74% vs 62% at 28 months, p = 0.0032). In a multivariate Cox regression model including age, diabetes, and gender, the survival advantage persisted (relative risk of death for Balance 0.75, 95% confidence interval 0.56 – 0.99, p = 0.0465). Modality technique survival was similar in Kaplan–Meier analysis for both PDFs. No differences were detected in peritonitis-free survival or in peritonitis rates between the two solutions.

Conclusion

This study, for the first time, suggests that treatment with a novel biocompatible PDF with low GDP concentration and neutral pH confers a significant survival advantage. The exact mechanisms for such a survival advantage cannot be determined from this study. The usual criticisms of observational studies apply and the results reported here strongly warrant the undertaking of appropriately designed, randomized, controlled clinical trials.

Lessons from Basic Research for Pd Treatment

Over the past 30 years, the focus of peritoneal dialysis research has changed from the technical issues related to the establishment of clinical peritoneal dialysis to complex problems of peritoneal membrane biology. Here, we present how these research topics developed, discuss their significance for clinical science, and outline future challenges for peritoneal dialysis research.

Temperature: The Single Most Important Factor for Degradation of Glucose Fluids during Storage

Objective

Bioincompatible glucose degradation products (GDPs) develop during heat sterilization of peritoneal dialysis (PD) fluids. However, degradation may also take place during storage. Consequently, storage may add to the bioincompatibility caused by heat sterilization. The aim of the present study was to investigate how different factors such as the sterilization procedure, pH, glucose concentration, and temperature influence GDP production during storage.

Design

Degradation in glucose solutions was followed by pH and UV absorbance at 228 nm and 284 nm over 2 years of storage. Different sterilization times, storage temperatures, pH, and glucose concentrations were included in the study. Peritoneal dialysis fluids were also used in the experiment. Bioincompatibility was estimated through inhibition of cell growth in L-929 fibroblasts, and GDPs through UV absorption and liquid chromatography.

Results

The most important factor determining the rate of GDP production during storage was temperature. The GDPs created by heat sterilization promoted further degradation of glucose during subsequent storage. A pH of around 3.2 protected glucose from degradation during both heat sterilization and storage. At a storage temperature of 20°C and a pH of 3.2, degradation was almost negligible. Heat sterilization produced considerable amounts of GDPs absorbing at 228 nm. During initial storage, these 228 nm-absorbing GDPs almost disappeared. After reaching a nadir, absorbance at 228 nm again started to increase. Contrary to this, absorbance at 284 nm [caused mainly by 5-hydroxymethyl-2-furaldehyde (5-HMF)] increased during the whole storage period. After 2 years at 40°C, the concentrations of GDPs produced during storage were of the same magnitude as those caused by heat sterilization. Inhibition of cell growth of L-929 fibroblasts correlated well with the part of the absorbance at 228 nm not caused by 5-HMF in glucose solutions that were heat sterilized under a wide range of conditions. This part of 228 nm absorbance (denoted 228corr) was caused almost entirely by 3,4-dideoxyglucosone-3-ene (3,4-DGE).

Conclusions

Temperature is the single most important factor for glucose degradation during storage. The concentrations of bioincompatible GDPs produced may, under improper conditions, be as high as those produced during sterilization. High concentrations of glucose and low pH protect glucose from being degraded during both sterilization and storage. A good estimate of 3,4-DGE concentration in the fluids can be obtained correcting the UV absorbance at 228 nm for the influence from 5-HMF (and, when appropriate, for lactate). The 228corrmay thus be used as a simple quality control for the fluids.

Impact of Glucose in Peritoneal Dialysis: Saint or Sinner?

Peritoneal dialysis (PD) solutions using glucose as osmotic agent have been used for more than two decades as effective treatment for patients with end-stage renal disease. Although alternative osmotic agents such as amino acids and macromolecular solutions, including polypeptides and glucose polymers, are now available, glucose is still the most widely used osmotic agent in PD. It has been shown to be safe, effective, readily metabolized, and inexpensive. On the other hand, it is widely assumed that exposure of the peritoneal membrane to high glucose concentrations contributes to both structural and functional changes in the dialyzed peritoneal membrane. As in diabetes, glucose, either directly or indirectly through the generation of glucose degradation products or the formation of advanced glycation end products, may contribute to peritoneal membrane failure. Although efforts to reduce glucose toxicity have been made for years, only a few suggestions, such as dual-bag systems with bicarbonate as buffer system, have found broader acceptance. Recently, some interesting new approaches to the problem of glucose-related toxicity have been made, but further investigations will be necessary before they can be used clinically. This review will focus on adverse effects of glucose in PD solutions and summarize different aspects of glucotoxicity and potential therapeutic interventions.

Effect of Glucose Degradation Products on the Peritoneal Membrane in a Chronic Inflammatory Infusion Model of Peritoneal Dialysis in the Rat

Background

Long-term use of the peritoneal membrane as a dialyzing membrane is hampered by its eventual deterioration. One of the contributing factors is glucose degradation products (GDPs) in the dialysis solution. In this study, we evaluated the effect of a low GDP solution on peritoneal permeability, the structural stability of the peritoneal membrane, and vascular endothelial growth factor (VEGF) production in a chronic inflammatory infusion model of peritoneal dialysis (PD) in the rat.

Methods

Male Sprague–Dawley rats were divided into 3 groups: a conventional solution group (group C, n = 12), a test solution group (group T, n = 12), and a normal control group (group NC, n = 8). Group T rats were infused with low GDP solution (2.3% glucose solution with two compartments), and group C rats with conventional dialysis solution (2.3% glucose solution), adjusted to pH 7.0 before each exchange. Animals were infused through a permanent catheter with 25 mL of dialysis solution. In both groups, peritoneal inflammation was induced by infusing dialysis solution supplemented with lipopolysaccharide on days 8, 9, and 10 after starting dialysate infusion. Peritoneal membrane function was assessed before and 6 weeks after initiating dialysis using the 1-hour peritoneal equilibration test (PET) employing 4.25% glucose solution. Both VEGF and transforming growth factor β1 (TGFβ1) in the dialysate effluent were measured by ELISA. The number of vessels in the omentum was counted after staining with anti-von Willebrand factor, and the thickness of submesothelial matrix of the trichrome-stained parietal peritoneum was measured. Peritoneal tissue was analyzed for VEGF protein using immunohistochemistry.

Results

At the end of 6 weeks, the rate of glucose transport (D/D0, where D is glucose concentration in the dialysate and D0 is glucose concentration in the dialysis solution before it is infused into the peritoneal cavity) was higher in group T ( p < 0.05) than in group C. Dialysate-to-plasma ratio (D/P) of protein was lower in group T ( p < 0.05) than in group C; D/Purea, D/Psodium, and drain volumes did not differ significantly between groups C and T. Dialysate VEGF and TGFβ levels were lower in group T ( p < 0.05) than in group C. Immunohistochemical studies also revealed less VEGF in the peritoneal membranes of group T. There were significantly more peritoneal blood vessels in group C ( p < 0.05) than in group T, but the thickness of submesothelial matrix of the parietal peritoneum was not different between the two groups. The VEGF levels in the dialysate effluent correlated positively with the number of blood vessels per field ( r = 0.622, p < 0.005).

Conclusion

Using a chronic inflammatory infusion model of PD in the rat, we show that dialysis with GDP-containing PD fluid is associated with increased VEGF production and peritoneal vascularization. Use of low GDP solutions may therefore be beneficial in maintaining the function and structure of the peritoneal membrane during long-term PD.

Peritoneal Dialysis in Japan: The Issue of Encapsulating Peritoneal Sclerosis and Future Challenges

Encapsulating peritoneal sclerosis (EPS) is a life-threatening complication of peritoneal dialysis (PD). The overall prevalence of EPS in Japanese PD patients is 2.3%. Among patients on PD for less than 5 years, the rate is 0.9%; among patients on PD for 5 – 10 years, the rate is 3.8%; and among patients on PD for >10 years, it is 11.5%. Thus, the longer the treatment duration, the higher the prevalence of EPS.

Encapsulating peritoneal sclerosis does not result solely from the natural progression of peritoneal sclerosis. A “second hit” event, such as bacterial peritonitis, abdominal bleeding, or abdominal surgery may be needed to trigger the onset of EPS in the face of advanced peritoneal sclerosis.

To prevent development of EPS, PD treatment is replaced by other treatments when patients reached high-transport status. Peritoneal lavage and prednisolone administration have been reported to be effective in preventing or stopping the progress of EPS. When bowel obstruction has occurred, total enterolysis to remove the fibrous capsule from the bowel is indicated.

To maximize overall quality of life, patients with end-stage renal disease (ESRD) should have the choice to make use of all the treatment modalities available: PD, hemodialysis (HD), and transplantation. Furthermore, the development of truly biocompatible PD equipment—including peritoneal catheters, solutions, and systems—are desirable to extend PD treatment for the long term. The cost of individual products could decrease significantly if PD use were to increase to 30% from 10% among ESRD patients worldwide. As practitioners, we have to further improve the technical survival rate and functional duration of PD treatment so that adequate peritoneal function can be maintained for 10 years in at least 40% of PD patients. The goal is to place PD on par with HD using high-flux dialysis membranes and ultrapure dialysis solution.

Glucose Degradation Products in Peritoneal Dialysis Fluids: How they can be Avoided

♦ Objectives

A patient on peritoneal dialysis (PD) uses 3 – 7 tons of PD fluid every year. The result is considerable stress on the peritoneal tissue. Aspects of PD fluids that have been considered responsible for bioincompatibility are low pH, high osmolality, high glucose and lactate concentrations, and the presence of glucose degradation products (GDPs). However, the relative importance of each factor in PD fluid has so far not been investigated. Discovering their relative importance was the aim of the present study.

♦ Methods

Two main methods for investigating biocompatibility were used in this study: cytotoxicity measured as in vitro inhibition of cell growth, and in vitro AGE formation measured as albumin-linked fluorescence.

♦ Results

The two most important factors for determining in vitro bioincompatibility of PD fluids were the presence of GDPs, which caused both severe cytotoxicity and strong AGE promotion, and low pH, which induced severe cytotoxicity.

♦ Conclusions

The biocompatibility of PD fluids can be monitored through fairly simple in vitro methods such as cell proliferation and AGE formation. Bioincompatibility of PD fluids is caused mainly by the presence of GDPs and low pH. These findings correlate well with known clinical bioincompatibility.

Biocompatibility of Peritoneal Dialysis Fluids: Long-term Exposure of Nonuremic Rats

Objectives

Long-term peritoneal dialysis (PD) leads to structural and functional changes in the peritoneum. The aim of the present study was to investigate the long-term effects of PD fluid components, glucose and glucose degradation products (GDP), and lactate-buffered solution on morphology and transport characteristics in a nonuremic rat model.

Methods

Rats were subjected to two daily intraperitoneal injections (20 mL/day) during 12 weeks of one of the following: commercial PD fluid (Gambrosol, 4%; Gambro AB, Lund, Sweden), commercial PD fluid with low GDP levels (Gambrosol trio, 4%; Gambro AB), sterile-filtered PD fluid (4%) without GDP, or a glucose-free lactate-buffered PD fluid. Punctured and untreated controls were used. Following exposure, the rats underwent a single 4-hour PD dwell (30 mL, 4% glucose) to determine peritoneal function. Additionally, submesothelial tissue thickness, percentage of high mesothelial cells (perpendicular diameter > 2 μm), vascular density, vascular endothelial growth factor (VEGF), and transforming growth factor (TGF) β1mRNA expression were determined. Submesothelial collagen concentration was estimated by van Gieson staining.

Results

Submesothelial tissue thickness and vascular density, mediated by VEGF and TGFβ production, in the diaphragmatic peritoneum increased significantly in rats exposed to any PD fluid. Gambrosol induced a marked increased fibrosis of the hepatic peritoneum. A significant increase in high mesothelial cells was observed in the Gambrosol group only. Net ultrafiltration was reduced in the Gambrosol and in the glucose-free groups compared to untreated controls. Small solute transport was unchanged, but all groups exposed to fluids showed significantly increased lymph flow.

Conclusions

Our results show that long-term exposure to different components of PD fluids leads to mesothelial cell damage, submesothelial fibrosis, and neoangiogenesis. Mesothelial cell damage could be connected to the presence of GDP; the other changes were similar for all fluids. Peritoneal transport characteristics did not change in any consistent way and the neoangiogenesis observed was not paralleled by increased solute transport.

What Can We Do to Preserve the Peritoneum?

Background

Long-term peritoneal dialysis may lead to peritoneal membrane failure. Loss of ultrafiltration is the most important clinical abnormality. Loss of ultrafiltration is associated with an increased number of peritoneal blood vessels, with fibrotic alterations, and with loss of mesothelium. Continuous exposure to bioincompatible dialysis solutions is likely to be important in the pathogenesis of these alterations.

Methods

This article reviews the toxicity of various constituents of dialysate, current assessments of interventions, and the results of interventions aimed at preserving the peritoneum.

Results

Glucose, possibly in combination with lactate, and glucose degradation products (GDPs) are likely to be the most toxic constituents of dialysate. Diabetiform peritoneal neoangiogenesis is likely to be mediated by vascular endothelial growth factor (VEGF). Release of VEGF might be influenced by glucose-induced cellular pseudohypoxia, which is likely to be increased by exposure to lactate. Glucose and GDPs are both toxic to peritoneal cells. Glucose degradation products induce the formation of advanced glycosylation end-products at a much faster rate than does glucose itself, but the relative importance of GDPs and glucose in clinical PD has not been clarified. The effects of interventions should first be assessed in long-term animal models, followed by clinical studies on peritoneal transport and on effluent markers that may reflect the status of the peritoneum. Possible interventions aim at reducing peritoneal exposure to glucose, GDPs, and lactate. Techniques include peritoneal resting, replacing some glucose-based exchanges with amino acid–based and icodextrin-based dialysate, using bicarbonate as a buffer, and administering solutions that have a low GDP content. Exposure to various dialysis solutions with a reduced GDP content has resulted in an increase in the effluent concentration of the mesothelial cell marker CA125, irrespective of the buffer used. Experimental studies in a long-term peritoneal exposure model in rats showed that the combination of a reduction in the concentration of lactate and replacement of lactate with pyruvate resulted in a reduction of the number of peritoneal blood vessels. Results of drug therapy have been studied in various animal models. Their use in patients is still experimental.

Conclusions

Strategies to preserve the peritoneum aim at reducing membrane exposure to bioincompatible solutions. Currently available dialysis fluids that are more biocompatible are likely to have some beneficial effects. Further research on the development of dialysis solutions that use combinations of osmotic agents and alternative buffers is necessary.

New Animal Models for Encapsulating Peritoneal Sclerosis—Role of Acidic Solution

Objective

Encapsulating peritoneal sclerosis (EPS), in which all or part of the intestine is enveloped in a fibrous ball resembling a cocoon, is a serious complication of peritoneal dialysis (PD). The aim of the present study was to investigate whether pH-neutral or acidic dialysis solutions induce peritoneal fibrosis.

Design

We divided 18 male Wistar–Kyoto (WKY) rats into three groups and dialyzed them with various solutions as follows: group I, 10 mL acidic dialysis solution (pH 3.8, containing 1.35% glucose), n = 6; group II, 10 mL pH 5.0 dialysis solution, n = 6; and group III, 10 mL neutral dialysis solution (pH 7.0), n = 6. Peritoneal catheters were inserted, and dialysis solution was injected every day for 40 days. At the end of the experiment, a peritoneal equilibration test (PET) was performed. Expression of mRNA of aquaporins 1 and 4 (AQP-1 and AQP-4) in the peritoneum were studied by semiquantitative reverse-transcriptase polymerase chain reaction (RT-PCR).

Results

In rats treated with pH 3.8 dialysis solution, necropsy findings revealed features identical to those of EPS. The typical appearance was of granulation tissue or fibrotic tissue (or both) covering multiple surfaces. Multiple adhesions were present. In microscopic examinations, peritoneal fibrosis and loss of mesothelium were found. In rats treated with pH 7.0 dialysis solution, no signs of EPS were seen. In rats treated with pH 5.0 dialysis solution, milder changes (subserosal thickening and partial adhesion of the peritonea) were observed. The mRNA of AQP-1 and AQP-4 were expressed in the peritonea of the rats. The expression of the AQPs was significantly suppressed in rats treated with pH 3.8 dialysis solution.

Conclusions

In rats, long-term intraperitoneal injection of acidic dialysis solution produced features typical of EPS in humans. Newly developed neutral dialysis solutions protected the against the development of EPS during peritoneal dialysis in rats.

Biocompatibility of a Bicarbonate/Lactate-Buffered PD Fluid Tested with a Double-Chamber Cell Culture System

Objective

In peritoneal dialysis (PD), neutrally buffered PD fluids with lower concentrations of glucose degradation products (GDP) have tested superior to conventional fluids in terms of biocompatibility. However, conventional in vitro studies provoke debate because, due to the lack of subsequent equilibration with the blood, they do not resemble the true intraperitoneal situation of PD.

Methods

We established a double-chamber cell culture system with peritoneal mesothelial cells seeded on top of a permeable membrane, with a physiological buffer below. Thus adequately reflecting the in vivo equilibration pattern, we compared a conventional fluid with a neutral bicarbonate/lactate-buffered PD solution. Using an exchange pattern adapted from an 8-hour continuous ambulatory PD regimen, cell viability was assessed with an MTT assay, and cell function via constitutive and stimulated interleukin (IL)-6 release. As an indicator of potential induction of fibrosis and as a parameter of mesothelial cell integrity, respectively, transforming growth factor-beta 1 (TGF-β1) generation and cancer antigen 125 (CA125) release were measured.

Results

The conventional solution significantly compromised mesothelial cell viability and function in terms of mitochondrial activity ( p < 0.05) and stimulated IL-6 release ( p < 0.05). The bicarbonate/lactate fluid had no effect on cell viability or IL-6 release and turned out to be equivalent to the properties of the growth medium. Whereas lactate-incubated cells did not respond to IL-1β stimulation, bicarbonate/lactate-treated cells adequately increased IL-6 release after stimulation ( p < 0.0005). Release of TGF-β1 and CA125 did not differ between the different fluids and the control.

Conclusions

Due to the sustained equilibration process, the double-chamber cell culture model allows a more realistic insight into mesothelial cell viability and function in terms of PD. As in classic in vitro studies, an adverse effect of conventional PD solutions on mesothelial cells was overt in the present cell culture system. The neutral bicarbonate/lactate-buffered fluid with low GDP content, however, did not interfere with mesothelial cell vitality or function, indicating superior biocompatibility.

Take Care in how you Store Your PD Fluids: Actual Temperature Determines the Balance between Reactive and Non-Reactive GDPs

Objective

During heat sterilization and during prolonged storage, glucose in peritoneal dialysis fluids (PDF) degrades to carbonyl compounds commonly known as glucose degradation products (GDPs). Of these, 3,4-dideoxyglucosone-3-ene (3,4-DGE) is the most cytotoxic. It is an intermediate in degradation between 3-deoxyglucosone (3-DG) and 5-hydroxymethyl-2-furaldehyde (5-HMF). We have earlier reported that there seems to be equilibrium between these GDPs in PDF. The aim of the present study was to investigate details of this equilibrium.

Methods

Aqueous solutions of pure 3-DG, 3,4-DGE, and 5-HMF were incubated at 40°C for 40 days. Conventional and low-GDP fluids were incubated at various temperatures for up to 3 weeks. Formaldehyde, acetaldehyde, glyoxal, methylglyoxal, 3-DG, 3,4-DGE, and 5-HMF were analyzed using high performance liquid chromatography.

Results

Incubation of 100 μmol/L 3,4-DGE resulted in the production of 36 μmol/L 3-DG, 4 μmol/L 5-HMF, and 40 μmol/L unidentified substances. With the same incubation, 200 μmol/L 3-DG was converted to 9 μmol/L 3,4-DGE, 6 μmol/L 5-HMF, and 14 μmol/L unidentified substances. By contrast, 100 μmol/L 5-HMF was uninfluenced by incubation. In a conventional PDF incubated at 60°C for 1 day, the 3,4-DGE concentration increased from 14 to a maximum of 49 μmol/L. When the fluids were returned to room temperature, the concentration decreased but did not reach original values until after 40 days. In a low GDP fluid, 3,4-DGE increased and decreased in the same manner as in the conventional fluid but reached a maximum of only 0.8 μmol/L.

Conclusions

Considerable amounts of 3,4-DGE may be recruited by increases in temperature in conventional PDFs. Lowering the temperature will again reduce the concentration but much more time will be needed. Precursors for 3,4-DGE recruitment are most probably 3-DG and the enol 3-deoxyaldose-2-ene, but not 5-HMF. Considering the ease at which 3,4-DGE is recruited from its pool of precursors and the difficulty of getting rid of it again, one should be extremely careful with the temperatures conventional PDFs are exposed to.

A Randomized Clinical Trial with a 0.6% Amino Acid/1.4% Glycerol Peritoneal Dialysis Solution

Background

Glucose is an accepted osmotic agent for peritoneal dialysis (PD) although it has several drawbacks. Some of these drawbacks have been addressed by the introduction of solutions with low glucose degradation products and physiological pH in dual-chambered bags. Despite this achievement, there is a need for alternative osmotic agents. This randomized clinical trial analyzes 3-month's clinical experience with a mixture of 0.6% amino acids and 1.4% glycerol.

Methods

The study was performed at the renal units of the University Hospitals Ghent, Belgium, and Utrecht, The Netherlands. Stable PD patients were randomized for either protocol A (test solution, n = 5) or protocol B (control regimen, n = 5). In both protocols, there was a run-in phase of 1 month with a dialysis regimen of 2 × 2 L 2.27% glucose solution (Dianeal; Baxter, Nivelles, Belgium), 1 × 2 L Extraneal (Baxter), and 1 × 2 L glucose solution (Dianeal). After this month-long run-in period, patients in group A received during 3 months 2 × 2 L amino acid/glycerol solution, 1 × 2 L Extraneal, and at least 1 × 2 L of a classic glucose solution.

Results

Glucose absorption decreased in the test group during the test phase (from 84.2 ± 8.7 to 11.7 ± 11.6 g/24 hours, p = 0.001). Dialysate levels of cancer antigen 125 (CA125) increased in the test group, from 17.5 ± 11.0 to 32.4 ± 4.6 units/L ( p = 0.04), whereas, in the control group, the levels remained stable (15.5 ± 8.7 and 14.9 ± 9.8 units/L respectively, p = 0.4). There were no differences in serum urea, serum bicarbonate, serum osmolarity, serum albumin, or parameters related to skin-fold thickness or serum glycerol levels between control and test solutions. No differences were observed in obtained ultrafiltration after a 4-hour dwell with 2.27% glucose or the test solution, both measured at week 4 of the run-in period and week 12 of the test period.

Conclusion

This study demonstrated that the use of a new 0.6% amino acid/1.4% glycerol-containing dialysis solution is safe and well tolerated. Glucose load was reduced significantly and dialysate CA125 levels improved significantly. Ultrafiltration was comparable with that of a 2.27% glucose solution. All these factors, in combination with the potential nutritional benefits, can contribute to a beneficial impact on the success of the PD technique. Further long-term studies in larger patient groups are warranted to explore the potential of this promising new solution.

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.

Effects of Peritoneal Dialysis Solutions on the Secretion of Growth Factors and Extracellular Matrix Proteins by Human Peritoneal Mesothelial Cells

♦ Objective

To compare the effects of different peritoneal dialysis solutions (PDS) on secretion of vascular endothelial growth factor (VEGF), transforming growth factor-β1 (TGFβ1), procollagen I C-terminal peptide (PICP), procollagen III N-terminal peptide (PIIINP), and fibronectin by cultured human peritoneal mesothelial cells (HPMC).

♦ Design

Using M199 culture medium as control, commercial PDS containing 1.5% or 4.25% glucose and 40 mmol/L lactate [Dianeal 1.5 (D 1.5) and Dianeal 4.25 (D 4.25), respectively; Baxter Healthcare, Deerfield, Illinois, USA]; PDS containing 1.5% or 4.25% glucose with 25 mmol/L bicarbonate and 15 mmol/L lactate [Physioneal 1.5 (P 1.5) and Physioneal 4.25 (P 4.25), respectively; Baxter]; and PDS containing 7.5% icodextrin [Extraneal (E); Baxter] were tested. Growth-arrested and synchronized HPMC were continuously stimulated for 48 hours by test PDS diluted twofold with M199, TGFβ1 1 ng/mL, or different concentrations of icodextrin. VEGF, TGFβ1, and fibronectin secreted into the media were analyzed by ELISA, and PICP and PIIINP by radioimmunoassay.

♦ Results

Dianeal 1.5, D 4.25, and P 4.25, but not P 1.5 and E, significantly increased VEGF secretion compared with control M199. D 4.25- and P 4.25-induced VEGF secretion was significantly higher than induction by D 1.5 and P 1.5, respectively, suggesting that high glucose may be involved in the induction of VEGF. Physioneal 1.5- and P 4.25-induced VEGF secretion was significantly lower than induction by D 1.5 and D 4.25, respectively, suggesting a role for glucose degradation products (GDP) in VEGF production. TGFβ1 secretion was significantly increased by D 4.25 and E. Icodextrin increased TGFβ1 secretion in a dose-dependent manner. All PDS tested significantly increased secretion of PIIINP compared with control. D 1.5- and D 4.25-induced PIIINP secretion was significantly higher than P 1.5, P 4.25, and E. Physioneal 4.25-induced PIIINP secretion was significantly higher than P 1.5, again implicating high glucose and GDP in PIIINP secretion by HPMC. There was no significant increase in PICP or fibronectin secretion using any of the PDS tested. Addition of TGFβ1 1 ng/mL into M199 control significantly increased VEGF, PICP, PIIINP, and fibronectin secretion by HPMC.

♦ Conclusions

The present study provides direct evidence that HPMC can secrete VEGF, TGFβ1, and PIIINP in response to PDS, and that HPMC may be actively involved in the development and progression of the peritoneal membrane hyperpermeability and fibrosis observed in long-term PD patients. This study also suggests that both high glucose and GDP in PDS may play important roles in inducing VEGF and PIIINP production/secretion by HPMC.

Degradation in Peritoneal Dialysis Fluids May be Avoided by Using Low pH and High Glucose Concentration

Objective

When glucose is present in a medical fluid, the heat applied during sterilization leads to degradation. The glucose degradation products (GDPs) give rise to bioincompatible reactions in peritoneal dialysis patients. The extent of the degradation depends on a number of factors, such as heating time, temperature, pH, glucose concentration, and catalyzing substances. In the present work, we investigated the influence of pH and concentration in order to determine how to decrease the amounts of GDPs produced.

Design

Glucose solutions (1% - 60% glucose; pH 1 - 8) were heat sterilized at 121°C. Ultraviolet (UV) absorption, aldehydes, pH, and inhibition of cell growth (ICG) were used as measures of degradation.

Results

Glucose degradation was minimum at an initial pH (prior to sterilization) of around 3.5 and at a high concentration of glucose. There was considerable development of acid degradation products during the sterilization process when the initial pH was high. Two different patterns of development of UV-absorbing degradation products were seen: one below pH 3.5, dominated by the formation of 5-hydroxy-methyl-2-furaldehyde (5-HMF); and one above, dominated by degradation products absorbing at 228 nm. 3-Deoxyglucosone (3-DG) concentration and the portion of 228 nm UV absorbance not caused by 5-HMF were found to relate to the in vitro bioincompatibility measured as ICG; there was no relation between 5-HMF or absorbance at 284 nm and bioincompatibility.

Conclusion

In order to minimize the development of bioincompatible GDPs in peritoneal dialysis fluids during heat sterilization, pH should be kept around 3.2 and the concentration of glucose should be high. 5-HMF and 284 nm UV absorbance are not reliable as quality measures. 3-DG and the portion of UV absorbance at 228 nm caused by degradation products other than 5-HMF seem to be reliable indicators of bioincompatibility.

Chronic Inflammation in Peritoneal Dialysis: The Search for the Holy Grail?

Mortality and morbidity in chronic kidney disease (CKD) patients are unacceptably high. The annual mortality rate due to cardiovascular disease (CVD) is approximately 9%, which, for the middle-aged person, is at least 10- to 20-fold higher than for the general population. Classic risk factors for CVD are highly prevalent in CKD patients, but they cannot fully account for the excessive rate of CVD in this population. Instead, it has become increasingly clear that nontraditional risk factors, such as systemic inflammation, may play a key role in the development of atherosclerosis. It is well established that inflammatory markers are very powerful predictors of high CVD morbidity and mortality not only in the general population, but particularly in CKD patients. Signs of a sustained low-grade inflammation, such as increased levels of C-reactive protein (CRP), are present in the majority of stage 5 CKD patients, even in patients in clinically stable condition, and they are also commonly observed after the initiation of dialysis therapy. Dialysis therapy — hemodialysis as well as peritoneal dialysis (PD) — may itself contribute to systemic inflammation. Local intraperitoneal inflammation can also occur in patients treated with PD. These local effects may result in a low-grade inflammation, caused by the bioincompatibility of conventional glucose-based dialysis fluids, to intense inflammation associated with peritonitis. Given these circumstances, it is reasonable to hypothesize that strategies aiming to reduce inflammation are potentially important and novel, and could serve to reduce CVD, thereby lowering morbidity and mortality in patients with CKD. In this review we provide information supporting the hypothesis that systemic inflammation is tightly linked to the most common complications of CKD patients, in particular those on PD, and that local inflammation in PD may contribute to various related complications. The aims of this review are to discuss the reasons that make inflammation an attractive target for intervention in CKD, the particular aspects of the inflammation–CVD axis during PD treatment that are likely involved, and possible means for the detection and management of chronic inflammation in PD patients.

Dialysate Cancer Antigen 125 Concentration as Marker of Peritoneal Membrane Status in Patients Treated with Chronic Peritoneal Dialysis

Objective

This study reviews publications on the history of cancer antigen 125 (CA125), the background of its use as a marker of mesothelial cell mass, determination in peritoneal effluent, and its practical use in both the follow-up of peritoneal dialysis (PD) patients and as a marker of in vivo biocompatibility of dialysis solutions.

Design

Review article.

Results

CA125 is a high molecular weight glycoprotein. Previous studies in ascites suggested its release by mesothelial cells. In vitro studies with cultured mesothelial cells showed constitutive production, the majority of which was dependent on mesothelial cell mass. Serum CA125 is normal in PD patients, but its concentration in peritoneal dialysate suggests local release, probably from mesothelial cells. Effluent CA125 can be considered a marker of mesothelial cell mass in stable PD patients, but large amounts are found during peritonitis, due probably to necrosis of mesothelial cells. The majority of studies found no relationship between dialysate CA125 and peritoneal transport parameters. Some cross-sectional studies reported a relationship with duration of PD, but others were unable to confirm this, due probably to the large interindividual variability. Longitudinal follow-up has shown a decrease in dialysate CA125, indicating loss of mesothelial cell mass. Application of theoretically morebiocompatible PD solutions causes an increase in dialysate CA125.

Conclusions

Dialysate CA125 is a mesothelial cell mass marker. The concentration of CA125 should be determined after a standardized dwell. A single low value is not informative. A decrease with time on PD suggests loss of mesothelial cell mass. Dialysate CA125 is a marker of in vivo biocompatibility of (new) dialysis solutions. More research is necessary on the best methodology for measuring low concentrations and establishing normal values and a significant change.

Interleukin-6 Levels Decrease in Effluent from Patients Dialyzed with Bicarbonate/Lactate–Based Peritoneal Dialysis Solutions

♦ Objective

Conventional lactate-buffered peritoneal dialysis (PD) solutions have several bioincompatible characteristics, including acidic pH, lactate buffer, and the presence of glucose degradation products (GDPs). These characteristics, along with inflammation, are believed to contribute to membrane dysfunction in peritoneal dialysis patients. A new PD solution containing a bicarbonate/ lactate buffer system with physiologic pH and low GDPs has shown improved biocompatibility in both in vitro and ex vivo studies. In the present study, the concentrations of cytokines interleukin-6 (IL-6), tumor necrosis factor alpha (TNFα), and vascular endothelial growth factor (VEGF), were measured in timed overnight effluents from PD patients continuously dialyzed with either lactate-based control solution (C) or bicarbonate/lactate–based solution (B/L) for 6 months.

♦ Methods

Effluents from 92 continuous ambulatory peritoneal dialysis (CAPD) patients were collected when the patients were entered into the study (baseline, all patients on C for more than 3 months), and at 3 and 6 months following randomization to C ( n = 31) or to B/L ( n = 61). Effluent samples were filtered, stored frozen, and then assayed for IL-6, TNFα, and VEGF by ELISA.

♦ Results

A significant decrease in effluent IL-6 was seen at 3 months and at 6 months in the B/L-treated patients. Levels of VEGF were significantly reduced at 3 months. No changes in the levels of IL-6 or VEGF were seen in the C-treated patients, and no changes in TNFα were seen in either group over time.

♦ Conclusions

Treatment with B/L is associated with decreased IL-6 synthesis and decreased VEGF secretion. The data suggest that the use of B/L solution is associated with reduced intraperitoneal inflammation and potential for angiogenesis. The use of B/L solution may, over time, help to restore peritoneal homeostasis and therefore preserve the function of the membrane in peritoneal dialysis.

Glucose Degradation Products in Peritoneal Dialysis Fluids May Have Both Local and Systemic Effects: A Study of Residual Fluid and Mesothelial Cells

Objective

When peritoneal dialysis (PD) fluids are heat sterilized, glucose is degraded to carbonyl compounds. These compounds are known to interfere with many cellular functions and to promote the formation of advanced glycation end-products. However, little is known about what actually happens with glucose degradation products (GDPs) after infusion into the peritoneal cavity. The aim of the present study was to investigate possible targets for GDPs in the peritoneal cavity.

Design

In vitro reactions between residual fluid and GDPs were studied by incubating unused PD fluid with overnight dialysate. Confluent monolayer cultures of human mesothelial cells were used as a model to study the reactions of GDPs with the cells lining the peritoneal cavity.

Methods

Samples were analyzed, using high pressure liquid chromatography, for the presence of formaldehyde, acetaldehyde, 5-hydroxymethyl-2-furaldehyde (5-HMF), methylglyoxal, and 3-deoxyglucosone (3-DG). Cytotoxicity was determined as inhibition of proliferation of cultured fibroblasts.

Results

None of the analyzed GDPs reacted with overnight dialysate. Formaldehyde and methylglyoxal, in contrast to 3-DG and 5-HMF, reacted with the cultured mesothelial cells.

Conclusions

Low molecular weight carbonyls such as formaldehyde and methylglyoxal most probably react with the mesothelial cells lining the peritoneal cavity, and could be responsible for the disappearance of these cells during long-term treatment. 3-Deoxyglucosone showed remarkably low reactivity and was most probably transported within the patient.

Evidence for Less Irritation to the Peritoneal Membrane in Rats Dialyzed with Solutions Low in Glucose Degradation Products

Background

Acidic pH and the presence of glucose degradation products (GDP) are believed to compromise the biocompatibility of peritoneal dialysis fluids (PDF). The present study examines the effects of long-term exposure to GDP and low pH by comparing conventional PDF and a new, neutral pH, low GDP solution.

Methods

All experiments were performed using a chronic infusion model of dialysis in nonuremic rats. The animals were treated for 6 weeks with 2 daily injections of 4.25% glucose-containing PDF. The following PDF were tested: CAPD3 (single-chamber bag, low pH, high GDP), CAPD3 pH 7.4 (single-chamber bag, neutral pH, high GDP), CAPD3-Balance (double-chamber bag, neutral pH, low GDP). All test solutions were obtained from Fresenius Medical Care, Bad Homburg, Germany.

Results

After 6 weeks of exposure, peritoneal permeability to water, urea, creatinine, glucose, and sodium, assessed by peritoneal equilibration test, was similar in all groups. However, compared to other PDF, dialysis with CAPD3-Balance was associated with reduced concentrations of protein and hyaluronan in the dialysate, decreased peritoneal eosinophilia, and reduced dialysate levels of chemokines CCL2/MCP-1 and CCL5/RANTES. Morphologic changes in the peritoneal membrane of CAPD3-Balance-treated animals were much less pronounced and included reduced vascular density, preservation of the mesothelial monolayer and intercellular junction, and no reduplication of the submesothelial basement membrane.

Conclusions

A new generation of PDF with physiologic pH and low GDP level produce less irritation to the peritoneal membrane and better preserve its structural integrity. This effect seems to be related predominantly to minimized GDP concentrations.

Effects of Peritoneal Dialysis Solutions on the Peritoneal Membrane: Clinical Consequences

This review provides an overview of recent studies that show the clinical significance of biocompatibility of peritoneal dialysis fluids.

Short-Term Effects of a New Bicarbonate/Lactate-Buffered and Conventional Peritoneal Dialysis Fluid on Peritoneal and Systemic Inflammation in CAPD Patients: A Randomized Controlled Study

Objectives

This study was designed to compare the local peritoneal and systemic inflammatory effects of a conventional lactate-based (Lac) peritoneal dialysis (PD) solution and a new biocompatible bicarbonate/lactate-based (Bic/ Lac) solution having low concentration of glucose degradation products.

Methods

26 stable, prevalent PD patients were enrolled in this prospective study. They sequentially underwent 3 months of therapy with the Lac solution and 3 months with the Bic/Lac solution in a randomized order. Flow cytometry was used to measure the expression of inflammatory molecules on peritoneal cells in overnight effluent collected at the end of each study period.

Results

21 patients successfully completed the study. Mean fluorescence intensity of human leukocyte antigen (HLA)-DR and CD14 expression by macrophages were not different between Lac and Bic/Lac. The peritoneal appearance rate of cancer antigen 125 (kU/minute) was 68 ± 37 with Lac and 133 ± 66 with Bic/Lac ( p < 0.001), and of interleukin (IL)-6 (ng/minute), 0.28 ± 0.2 with Lac and 0.18 ± 0.16 with Bic/Lac ( p = 0.014). HLA-DR macrophage expression and IL-6 peritoneal appearance rates did not correlate. Serum concentrations with Lac and Bic/Lac were, for IL-6, 3.49 ± 2.28 and 3.72 ± 2.46 ng/L ( p = 0.17), and for high-sensitivity C-reactive protein, 2.31 ± 2.98 and 2.71 ± 3.31 mg/L ( p = 0.32) respectively. The concentration of effluent macrophages (x106/L) with Lac was 1.6 ± 1.6 and with Bic/Lac 2.6 ± 3.3 ( p = 0.07).

Conclusions

We conclude that, although there was a significant reduction in peritoneal IL-6 in patients using Bic/ Lac solution, systemic levels of inflammatory markers did not differ between the two solutions and no changes were present in macrophage surface activation markers, suggesting perhaps a less important role of peritoneal macrophages in the intraperitoneal chronic inflammatory process. The number of effluent macrophages tended to be higher in patients using the Bic/Lac solution, possibly contributing to improved intraperitoneal defense.

Carbonyl Stress Reduction in Peritoneal Dialysis Fluid: Development of a Novel High-Affinity Adsorption Bead

Objective

Heat sterilization of glucose peritoneal dialysis (PD) fluid generates reactive carbonyl compounds (RCOs), which have been implicated in the formation of advanced glycation end products (AGEs) on peritoneal proteins, with an attendant deterioration of peritoneal permeability in PD patients. To reduce their levels in PD fluid, we had previously devised beads coupled with RCO-trapping agents. The hazards linked to the diffusion of RCO-trapping compounds in the systemic circulation are avoided. Hydrazine-epoxy beads proved the most effective. Still, the amount needed to trap all RCOs remained relatively large.

Methods

We developed a novel agent linking a powerful RCO-trapping AGE inhibitor, pyrazolinone-polyethyleneimine, with cellulose beads (PPCBs). We tested its effectiveness to lower RCOs and AGE formation.

Results

Mixed with glucose PD fluid, PPCBs markedly lowered RCOs (α–dicarbonyls and aldehydes) and inhibited the generation of pentosidine, an AGE, to levels similar to those of filter-sterilized PD fluid. Their effectiveness is more than one order of magnitude above those of previously developed beads. The PPCBs markedly improved PD fluid biocompatibility. Incubation of 1 L commercial glucose PD fluid at 25°C for 24 hours with 10 or 30 g of wet PPCBs reduced RCO content by 75% – 90% and 100% respectively, without altering the pH or glucose and electrolyte contents of the PD fluid.

Conclusions

We developed a high-affinity adsorption bead to reduce the toxic RCO content and AGE formation potential (carbonyl stress) of PD fluid.

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.

3,4-DGE in Peritoneal Dialysis Fluids Cannot be Found in Plasma after Infusion into the Peritoneal Cavity

Objective

Glucose degradation products (GDPs) are important in the outcome of peritoneal dialysis (PD) treatment. 3,4-dideoxyglucosone-3-ene (3,4-DGE) is the most cytotoxic GDP found in conventionally manufactured fluids and may, in addition, be recruited from 3-deoxyglucosone (3-DG). It is not known what happens with those GDPs in patients during PD. The aim of this study was to investigate if the 3,4-DGE and 3-DG in PD fluids can be found in plasma during treatment.

Design

PD patients were dialyzed with a conventional PD fluid containing 43 μmol/L 3,4-DGE and 281 μmol/L 3-DG. Parallel experiments were performed in rats as well as in vitro with human plasma. The rats were dialyzed with a PD fluid containing 100 μmol/L 3,4-DGE and 200 μmol/L 3-DG.

Results

The concentration of 3,4-DGE in the peritoneum decreased at a much higher rate than 3-DG during the dwell. 3,4-DGE was not, however, detected in the plasma of patients or rats during dialysis. The concentration of 3-DG in plasma peaked shortly after infusion of the fluid to the peritoneal cavity. The concentration of 3,4-DGE during experimental incubation in plasma decreased rapidly, while the concentration of 3-DG decreased only 10% as rapidly or less.

Conclusion

3,4-DGE could not be detected in plasma from either PD patients or rats during dialysis. This is presumably due to its high reactivity. 3-DG may, on the other hand, pass through the membrane and be detected in the blood.

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.

The Clinical Usefulness of Peritoneal Dialysis Fluids with Neutral pH and Low Glucose Degradation Product Concentration: An Open Randomized Prospective Trial

Background

Long-term peritoneal dialysis (PD) is associated with the development of various structural and functional changes to the peritoneal membrane when bioincompatible conventional peritoneal dialysis fluids (PDFs) are used. In this study, we looked at patients that were treated with conventional PDFs and then changed to novel biocompatible PDFs with a neutral pH and a low concentration of glucose degradation products (GDPs) to investigate whether this change could result in the arrest or reversal of peritoneal membrane deterioration.

Methods

In an open label, randomized prospective trial, the clinical effects of conventional PDFs and biocompatible PDFs with neutral pH and very low concentration of GDPs were compared in 104 patients equally divided between both study PDFs. Blood and effluent dialysate samples, peritoneal equilibration tests, and adequacy evaluation were undertaken at baseline, 4, 8, and 12 months. The target variables were the ratio of dialysate-to-plasma (D/P) creatinine, peritoneal ultrafiltration, residual renal function, dialysis adequacy indices, and effluent cancer antigen 125 (CA125).

Results

D/P creatinine values were not different in the two groups. Peritoneal ultrafiltration was significantly higher in the low-GDP PDF group than in the conventional PDF group at all follow-up times (4 months: 9.1 ± 4.3 vs 6.0 ± 3.0; 8 months: 8.3 ± 3.4 vs 6.0 ± 3.0; 12 months: 8.9 ± 3.3 vs 6.1 ± 3.3 mL/g dextrose/day; p < 0.05). Peritoneal Kt/V urea values and total weekly Kt/V urea values at 4 months were significantly higher in the low-GDP PDF group than in the conventional PDF group. Residual renal function was not statistically significant. Effluent CA125 levels were significantly higher in the low-GDP PDF group at all follow-up visits (4 months: 37.8 ± 20.8 vs 22.0 ± 9.5; 8 months: 41.2 ± 20.3 vs 25.9 ± 11.3; 12 months: 40.4 ± 21.4 vs 28.6 ± 13.0 U/mL; p < 0.05). Among anuric patients, peritoneal ultrafiltration at 4, 8, and 12 months, total weekly Kt/V at 4 and 8 months, and CA125 levels at all follow-up visits were significantly higher in patients treated with low-GDP PDF than those treated with conventional PDF. However, among anuric patients, D/P creatinine showed no significant differences between the low-GDP PDF group and the conventional PDF group.

Conclusion

The use of biocompatible PDFs with neutral pH and low GDP concentration can contribute to improvement of peritoneal ultrafiltration and peritoneal effluent CA125 level, an indicator of peritoneal membrane integrity in PD patients.

The Roles of Complement Factor C5a and CINC-1 in Glucose Transport, Ultrafiltration, and Neutrophil Recruitment during Peritoneal Dialysis

Background

In a recent experimental study, we showed that low molecular weight heparin improved ultrafiltration and blocked complement activation and coagulation in a single peritoneal dialysis (PD) dwell.

Objective

The aim of the present study was to evaluate the possible contribution of the complement factor C5a and the potential interactions between C5a, the coagulation system, and cytokines of the interleukin (IL)-8 family (cytokine-induced neutrophil chemoattractant; CINC-1).

Methods

Nonuremic rats were exposed through an indwelling catheter to a single dose of 20 mL glucose- (2.5%) based filter-sterilized PD fluid, with or without the addition of anti-rat C5 antibody. The dwell fluid was analyzed 2 and 4 hours later concerning activation of the coagulation cascades, neutrophil recruitment, ultrafiltration volume; CINC-1, glucose, urea, and histamine concentrations; and ex vivo intraperitoneal chemotactic activity.

Results

The numbers of neutrophils and levels of thrombin–antithrombin complex (TAT) and CINC-1 increased significantly during the PD dwell. C5 blockade significantly reduced the levels of TAT and increased the ultrafiltration volumes at 2 hours. Glucose concentrations were significantly positively correlated to ultrafiltration volumes.

Conclusions

Blockade of C5 leads to an increase in ultra-filtration, probably by a mechanism that involves a reduction in glucose transport. This effect may form a basis for improving PD efficiency in situations where high glucose transport limits ultrafiltration. Mechanisms connected to complement activation during PD may involve coagulation. Further studies of the intraperitoneal cascade systems under conditions of PD are indicated.

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.

Peritoneal Injury by Methylglyoxal in Peritoneal Dialysis

Background

Peritoneal dialysis (PD) is a common treatment for patients with reduced or absent renal function. Long-term PD leads to peritoneal injury with structural changes and functional decline, such as ultrafiltration loss. At worst, peritoneal injury leads to encapsulating peritoneal sclerosis, a serious complication of PD. Glucose degradation products contained in PD fluids contribute to the bioincompatibility of conventional PD fluids. Methylglyoxal (MGO) is an extremely toxic glucose degradation product. The present study examined the injurious effect of MGO on peritoneum in vivo.

Methods

Male Sprague–Dawley rats ( n = 6) were administered PD fluids (pH 5.0) containing 0, 0.66, 2, 6.6, or 20 mmol/L MGO every day for 21 days. On day 22, peritoneal function was estimated by the peritoneal equilibration test. Drained dialysate was analyzed for type IV collagen-7S, matrix metalloproteinase (MMP), and vascular endothelial growth factor (VEGF). Histological analysis was also performed.

Results

In rats receiving PD fluids containing more than 0.66 mmol/L MGO, peritoneal function decreased significantly and levels of type IV collagen-7S and MMP-2 in drained dialysate increased significantly. In the 20-mmol/L MGO-treated rats, loss of body weight, expression of VEGF, thickening of the peritoneum, and formation of abdominal cocoon were induced. MMP-2 and VEGF were produced by infiltrating cells in the peritoneum. Type IV collagen was detected in basement membrane of microvessels.

Conclusion

MGO induced not only peritoneal injury but also abdominal cocoon formation in vivo. The decline of peritoneal function may result from reconstitution of microvessel basement membrane or neovascularization.

Computer simulations of steady concentration peritoneal dialysis

BACKGROUND

Steady concentration peritoneal dialysis (SCPD), which maintains transperitoneal osmotic gradient by infusing 50% glucose solution throughout the dwell time, has been proposed as a potent treatment for peritoneal dialysis (PD) patients with fluid overload. However, SCPD has yet to be explored theoretically. Here, we investigated SCPD via computer simulations.

METHODS

A model was developed by adding the variables for infusing 50% glucose solution to a traditional three-pore model for continuous ambulatory PD. The simulated scenarios involved the instillation of 2-L dialysate, 1.36% or 2.27%, followed by the infusion of 50% glucose solution, varying the rate from 0 mL/h to 90 mL/h. A dwell with 3.86% dialysate was also simulated for the purpose of comparison. Four sets of patient parameters corresponding to peritoneal transport categories were used.

RESULTS

The net ultrafiltration (UF) during SCPD increased with time as well as with glucose infusion rate. The glucose absorption and sodium removal of SCPD were slightly higher than those of the conventional dwell with 3.86% dialysate under the condition of the same net UF and dwell time. SCPD resulted in the larger UF and the lower peak intraperitoneal glucose concentration when it was simulated with the higher transport properties.

CONCLUSIONS

These simulations indicate that SCPD can improve UF beyond those achievable by a conventional 3.86% glucose exchange while also exhibiting a lower peak osmolarity in the dialysate as compared to a conventional 3.86% dwell. However, further studies are needed to confirm these theoretical findings.

Alpha-1 antitrypsin inhibits formaldehyde-induced apoptosis of human peritoneal mesothelial cells

BACKGROUND

The alpha-1 antitrypsin (AAT) protein has an important role in the anti-inflammatory and apoptotic response. AAT inhibits not only serine proteases but also cysteine and aspartic proteases. Apoptosis results from the sequential activation of cysteine proteases of the caspase family. This study aimed to evaluate the effect of AAT on formaldehyde-induced apoptosis of human peritoneal mesothelial cells (HPMCs).

METHODS

HPMCs were cultured and treated with formaldehyde (250 µM) to induce apoptosis. In the AAT group, the cultured HPMCs were pretreated with AAT (2 mg/mL) for 1 h before formaldehyde treatment. We used 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assays to determine cell viability, and flow cytometry and terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL) assays to detect apoptosis. The MTT assays were used to find optimal concentrations of formaldehyde and AAT. We measured caspase-3 activity and used Western blotting to estimate Bcl-2 and Bad expression.

RESULTS

Flow cytometry and TUNEL assays revealed that formaldehyde exposure significantly increased apoptosis compared with the control treatment, but pretreatment with AAT significantly inhibited this effect. Compared with the control, caspase-3 activity was significantly increased and the ratio of Bcl-2 to Bad expression significantly decreased following treatment with formaldehyde. However, caspase-3 activity was significantly lower and the Bcl-2 to Bad expression ratio higher in the AAT group than in the formaldehyde-only group.

CONCLUSION

AAT inhibits formaldehyde-induced apoptosis of HPMCs via a caspase-mediated pathway. These data support a potential use for AAT as a therapeutic agent for the inhibition of peritoneal cell apoptosis during peritoneal dialysis.

Biocompatible dialysis fluids for peritoneal dialysis

BACKGROUND

Biocompatible peritoneal dialysis (PD) solutions, including neutral pH, low glucose degradation product (GDP) solutions and icodextrin, have previously been shown to favourably influence some patient-level outcomes, albeit based on generally sub-optimal quality studies. Several additional randomised controlled trials (RCT) evaluating biocompatible solutions in PD patients have been published recently. This is an update of a review first published in 2014.

OBJECTIVES

This review aimed to look at the benefits and harms of biocompatible PD solutions in comparison to standard PD solutions in patients receiving PD.

SEARCH METHODS

The Cochrane Kidney and Transplant Specialised Register was searched up to 12 February 2018 through contact with the Information Specialist using search terms relevant to this review. Studies in the Specialised Register are identified through searches of CENTRAL, MEDLINE, and EMBASE, conference proceedings, the International Clinical Trials Register Search Portal and ClinicalTrials.gov.

SELECTION CRITERIA

All RCTs and quasi-RCTs in adults and children comparing the effects of biocompatible PD solutions (neutral pH, lactate-buffered, low GDP; neutral pH, bicarbonate(± lactate)-buffered, low GDP; glucose polymer (icodextrin)) in PD were included. Studies of amino acid-based solutions were excluded.

DATA COLLECTION AND ANALYSIS

Two authors extracted data on study quality and outcomes. Summary effect estimates were obtained using a random-effects model, and results were expressed as risk ratios and 95% confidence intervals (CI) for categorical variables, and mean differences (MD) or standardised mean differences (SMD) and 95% CI for continuous variables.

MAIN RESULTS

This review update included 42 eligible studies (3262 participants), including six new studies (543 participants). Overall, 29 studies (1971 participants) compared neutral pH, low GDP PD solution with conventional PD solution, and 13 studies (1291 participants) compared icodextrin with conventional PD solution. Risk of bias was assessed as high for sequence generation in three studies, allocation concealment in three studies, attrition bias in 21 studies, and selective outcome reporting bias in 16 studies.Neutral pH, low GDP versus conventional glucose PD solutionUse of neutral pH, low GDP PD solutions improved residual renal function (RRF) preservation (15 studies, 835 participants: SMD 0.19, 95% CI 0.05 to 0.33; high certainty evidence). This approximated to a mean difference in glomerular filtration rate of 0.54 mL/min/1.73 m2 (95% CI 0.14 to 0.93). Better preservation of RRF was evident at all follow-up durations with progressively greater preservation observed with increasing follow up duration. Neutral pH, low GDP PD solution use also improved residual urine volume preservation (11 studies, 791 participants: MD 114.37 mL/day, 95% CI 47.09 to 181.65; high certainty evidence). In low certainty evidence, neutral pH, low GDP solutions may make little or no difference to 4-hour peritoneal ultrafiltration (9 studies, 414 participants: SMD -0.42, 95% CI -0.74 to -0.10) which approximated to a mean difference in peritoneal ultrafiltration of 69.72 mL (16.60 to 122.00 mL) lower, and may increase dialysate:plasma creatinine ratio (10 studies, 746 participants: MD 0.01, 95% CI 0.00 to 0.03), technique failure or death compared with conventional PD solutions. It is uncertain whether neutral pH, low GDP PD solution use led to any differences in peritonitis occurrence, hospitalisation, adverse events (6 studies, 519 participants) or inflow pain (1 study, 58 participants: RR 0.51, 95% CI 0.24 to 1.08).Glucose polymer (icodextrin) versus conventional glucose PD solutionIn moderate certainty evidence, icodextrin probably reduced episodes of uncontrolled fluid overload (2 studies, 100 participants: RR 0.30, 95% CI 0.15 to 0.59) and augmented peritoneal ultrafiltration (4 studies, 102 participants: MD 448.54 mL/d, 95% CI 289.28 to 607.80) without compromising RRF (4 studies, 114 participants: SMD 0.12, 95% CI -0.26 to 0.49; low certainty evidence) which approximated to a mean creatinine clearance of 0.30 mL/min/1.73m2 higher (0.65 lower to 1.23 higher) or urine output (3 studies, 69 participants: MD -88.88 mL/d, 95% CI -356.88 to 179.12; low certainty evidence). It is uncertain whether icodextrin use led to any differences in adverse events (5 studies, 816 participants) technique failure or death.

AUTHORS' CONCLUSIONS

This updated review strengthens evidence that neutral pH, low GDP PD solution improves RRF and urine volume preservation with high certainty. These effects may be related to increased peritoneal solute transport and reduced peritoneal ultrafiltration, although the evidence for these outcomes is of low certainty due to significant heterogeneity and suboptimal methodological quality. Icodextrin prescription increased peritoneal ultrafiltration and mitigated uncontrolled fluid overload with moderate certainty. The effects of either neutral pH, low GDP solution or icodextrin on peritonitis, technique survival and patient survival remain uncertain and require further high quality, adequately powered RCTs.