Biocompatibility and buffers: effect of bicarbonate-buffered peritoneal dialysis fluids on peritoneal cell function

Current Progress in Peritoneal Dialysis: A Narrative Review of Progress in Peritoneal Dialysis Fluid

Peritoneal dialysis (PD) is a renal replacement therapy that removes solutes, electrolytes, and water via the infusion of dialysis fluid into the peritoneal cavity. However, the non-physiological composition of conventional PD fluids can cause peritoneal injury, leading to complications such as peritoneal fibrosis and encapsulating peritoneal sclerosis. This review highlights recent advancements in PD fluid formulations aimed at improving biocompatibility and reducing peritoneal damage. While glucose-based solutions remain the standard because of their affordability, their glucose degradation products (GDPs) and advanced glycation end-products significantly contribute to peritoneal fibrosis. Innovations, such as neutral pH and low-GDP solutions, have been developed to counter these effects, enhancing peritoneal integrity and preserving residual renal function. Alternative osmotic agents, such as icodextrin, offer superior ultrafiltration. Advancements in buffer formulations, including bicarbonate-based and bicarbonate/lactate combinations, have further enhanced the biocompatibility of PD fluids. Despite these progressions, challenges persist. Therefore, future research should prioritize patient-specific PD solutions to optimize long-term outcomes and minimize adverse effects.

The Choice of Dialysis Solutions in Pediatric Chronic Peritoneal Dialysis: Guidelines by AnAD HOCEuropean Committee

Objective

To provide guidelines on choosing dialysis solutions for children on chronic peritoneal dialysis (PD).

Setting

European Paediatric Peritoneal Dialysis Working Group.

Data Source

Literature on the application of PD solutions in children ( Evidence), and discussions within the group ( Opinion).

Conclusions

Glucose is the standard osmotic agent for PD in children ( Evidence). The lowest glucose concentration needed should be used ( Opinion). Low calcium solution (1.25 mmol/L) should be applied, wherever possible, with careful monitoring of parathyroid hormone levels ( Opinion). The use of amino acid-containing dialysis fluids can be considered in malnourished children, although aggressive enteral nutrition is preferred ( Opinion). There is insufficient evidence documenting the efficacy of intraperitoneally administered amino acids ( Evidence). When ultrafiltration and/or solute removal are insufficient, poly-glucose solutions are a welcome addition to the treatment of children on nocturnal intermittent PD ( Evidence). However, in the absence of any reported long-term experience with children, their use must be closely monitored ( Opinion). Bicarbonate would appear to be the preferred buffer for PD in children, but more in vivo studies are required before it replaces the present lactate-containing solutions ( Evidence/Opinion).

The Effects of Peritoneal Dialysis Solutions on Peritoneal Host Defense

Conventional peritoneal dialysis fluid (PDF) is a bioincompatible solution owing to the acidic pH, the high glucose concentrations and the associated hyperosmolarity, the high lactate concentrations, and the presence of glucose degradation products (GDPs). This unphysiologic composition adversely affects peritoneal host defense and may thus contribute to the development of PD-related peritonitis. The viability of polymorphonuclear leukocytes, monocytes, peritoneal macrophages, and mesothelial cells is severely depressed in the presence of conventional PDF. In addition, the production of inflammatory cytokines and chemoattractants by these cells is markedly affected by conventional PDF. Further, conventional PDF hampers the recruitment of circulating leukocytes in response to an infectious stimulus. Finally, phagocytosis, respiratory burst, and bacterial killing are markedly lower when polymorphonuclear leukocytes, monocytes, and peritoneal macrophages are exposed to conventional PDF. Although there are a few discrepant results, all major PDF components have been implicated as causative factors. Generally, novel PDF with alternative osmotic agents or with alternative buffers, neutral pH, and low GDP content have much milder inhibitory effects on peritoneal host defense. Clinical studies, however, still need to demonstrate their superiority with respect to the incidence of PD-related peritonitis.

Biocompatibility of New Peritoneal Dialysis Solutions: What Can We Hope to Achieve?

Despite the bioincompatibility of the “old”, standard, high glucose, lactate-buffered peritoneal dialysis (PD) solutions, PD is itself a highly successful dialysis modality with patient survival equivalent to that of hemodialysis (HD) during the initial 3 – 5 years of dialysis therapy. Nevertheless, PD technique survival is often limited by infectious complications and alterations in the structure and function of the peritoneal membrane. These local changes also have a negative impact on patient survival owing to systemic effects such as those often seen in patients with high peritoneal transport rate and loss of ultrafiltration (UF) capacity.

Patient mortality remains unacceptably high in both HD and PD patients, with most premature deaths being associated with signs of malnutrition, inflammation, and atherosclerotic cardiovascular disease (MIA syndrome). These systemic signs are likely to be influenced by PD solutions both directly and indirectly (via changes in the peritoneal membrane). New, biocompatible PD solutions may have favorable local effects (viability and function of the peritoneal membrane) and systemic effects (for example, on MIA syndrome). Amino acid–based solution [Nutrineal (N): Baxter Healthcare Corporation, Deerfield, IL, U.S.A.] may improve nutritional status as well as peritoneal membrane viability. Bicarbonate/lactate–buffered solution [Physioneal (P): Baxter Healthcare Corporation] may ameliorate local and systemic effects of low pH, high lactate, and high glucose degradation products. Icodextrin-based solution [Extraneal (E): Baxter Healthcare SA, Castlebar, Ireland] may improve hypertension and cardiovascular problems associated with fluid overload and may extend time on therapy in patients with loss of UF capacity.

The positive effects of each of these new, biocompatible solutions have been demonstrated in several studies. It is likely that the combined use of N, P, and E solutions will produce favorable synergies in regard to both local effects (peritoneal viability) and systemic effects (less malnutrition, inflammation, and fluid overload). Solution combination is an exciting area for clinical study in the coming years. Furthermore, dialysis fluid additives such as hyaluronan, which protects and improves the function of the peritoneal membrane, may further improve PD solutions. The new, biocompatible PD solutions represent an entirely new era in the evolution of the PD therapy; they are likely to have markedly positive effects on both PD technique and PD patient survival in coming years.

Better Preservation of the Peritoneum in Rats Exposed to Amino Acid-Based Peritoneal Dialysis Fluid

Background

Glucose-containing peritoneal dialysis fluids (PDF) show impaired biocompatibility, which is related partly to their high glucose content, presence of glucose degradation products, low pH, and lactate buffer, or a combination of these factors. In a rat chronic peritoneal exposure model, we compared effects of an amino acid-based PDF (AA-PDF) with a glucose-containing PDF on the peritoneal microcirculation and morphology.

Method

Two groups of rats received 10 mL of either fluid daily for 5 weeks via peritoneal catheters connected to implanted subcutaneous mini vascular access ports. Leukocyte–endothelium interactions in the mesenteric venules were investigated by intravital microscopy. Quantification of angiogenesis and fibrosis and inspection of the mesothelial cell layer were performed by light and electron microscopy.

Results

Daily exposure to glucose-containing PDF resulted in a significant increase in the number of rolling leukocytes in mesenteric venules, whereas instillation of AA-PDF did not change the level of leukocyte rolling. Glucose-containing PDF evoked a significantly higher number of milky spots in the omentum, whereas this response was significantly reduced in animals exposed to the AA-PDF ( p < 0.02). Chronic instillation of glucose-containing PDF induced angiogenesis in various peritoneal tissues, accompanied by fibrosis in the mesentery and parietal peritoneum. Quantitative morphometric evaluation of omentum and mesentery showed a clear trend toward less angiogenesis after treatment with the AA-PDF compared to the glucose-containing PDF, which reached statistical significance in the parietal peritoneum ( p < 0.04). Instillation of AA-PDF resulted in approximately 50% reduction of fibrosis in the mesentery ( p < 0.04) and approximately 25% reduction in the parietal peritoneum ( p < 0.009) compared to glucose-containing PDF. Glucose-containing PDF damaged the mesothelial cell layer, whereas the mesothelium was intact after AA-PDF treatment, as evidenced by electron microscopy.

Conclusion

Our data in a rat chronic peritoneal exposure model clearly demonstrate reduced immune activation (evidenced by decreased number of rolling leukocytes and decreased induction of omental milky spots) and reduced neoangiogenesis, fibrosis, and mesothelial damage of the peritoneal membrane after treatment with AA-PDF compared to glucose-containing PDF.

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.

Technological Advances in Peritoneal Dialysis Research Peritoneal Cell Culture: Fibroblasts

Fibroblasts have been traditionally viewed as providing little more than a structural lattice for other cell types. However, recent data indicate that fibroblasts play a key and early role in many pathophysiological processes, including inflammation, fibrosis, and neoplasia. Moreover, depending on the anatomical location, fibroblasts display significant functional heterogeneity. Therefore, it is important to study the subpopulation of fibroblasts derived exactly from the organ of interest rather than to extrapolate the observations made in other fibroblast subsets. Cell culture provides a powerful tool for studying the role of fibroblasts in various contexts. In this review, we describe procedures for establishing and identifying primary cultures of human peritoneal fibroblasts. We also briefly discuss the potential involvement of peritoneal fibroblasts in peritoneal pathology.

The Peritoneal Surface Proteome in a Model of Chronic Peritoneal Dialysis Reveals Mechanisms of Membrane Damage and Preservation

Peritoneal dialysis (PD) fluids are cytotoxic to the peritoneum. Recent studies have shown that alanyl-glutamine (AlaGln) modulates the cellular stress response, improves mesothelial cell survival, reduces submesothelial thickening in experimental models of PD, and in clinical studies improves PD effluent cell stress and immune responses. However, the mechanisms of AlaGln-mediated membrane protection are not yet fully understood. Here, we explore those mechanisms through application of a novel proteomics approach in a clinically relevant in vivo model in rats. Experimental PD was performed for 5 weeks using conventional single-chamber bag (SCB) or neutral dual-chamber bag (DCB), PD fluid (PDF), with or without AlaGln supplementation, via a surgically implanted catheter. Rats subjected to a single dwell without catheter implantation served as controls. The peritoneal surface proteome was directly harvested by detergent extraction and subjected to proteomic analysis by two-dimensional difference gel electrophoresis (2D-DiGE) with protein identification by mass spectrometry. An integrated bioinformatic approach was applied to identify proteins significantly affected by the treatments despite biological variation and interfering high abundance proteins. From 505 of 744 common spots on 59 gels, 222 unique proteins were identified. Using UniProt database information, proteins were assigned either as high abundance plasma proteins, or as cellular proteins. Statistical analysis employed an adapted workflow from RNA-sequencing, the trimmed mean of M-values (TMM) for normalization, and a mixed model for computational identification of significantly differentially abundant proteins. The most prominently enriched pathways after 5 weeks chronic treatment with SCB or DCB, PDFs belonged to clusters reflecting tissue damage and cell differentiation by cytoskeletal reorganization, immune responses, altered metabolism, and oxidative stress and redox homeostasis. Although the AlaGln effect was not as prominent, associated enriched pathways showed mostly regression to control or patterns opposite that of the PDF effect. Our study describes the novel peritoneal surface proteome through combined proteomic and bioinformatic analyses, and assesses changes elicited by chronic experimental PD. The biological processes so identified promise to link molecular mechanisms of membrane damage and protection in the in vivo rat model to pathomechanisms and cytoprotective effects observed in vitro and in clinical PD.

Peritoneal dialysis fluid biocompatibility impact on human peritoneal membrane permeability

Background

We have compared the effects of conventional lactate-based peritoneal dialysis fluid (CPDF) with respect to bicarbonate/lactate-based fluid on peritoneal ultrafiltration (UF) and peritoneal permeability, and on variations on gene expression in cells isolated from effluents of patients' peritoneal bags.

Methods

This was a non-randomized sequential prospective study including all incident peritoneal dialysis (PD) patients (n = 40) recruited in our centre. Peritoneal equilibration tests (PETs) were performed using CPDF or BPDF both containing 2.27% glucose during a 48-h interval in four different sequences. Gene expression variation of selected genes was measured by reverse transcription polymerase chain reaction in mesothelial cells obtained from the total drained fluid during the PET.

Results

In the overall study, the use of BPDF was associated with significantly lower mass transfer area coefficient for urea and creatinine, longer accelerated peritoneal examination test times for urea and creatinine, lower total pore area available for exchange over diffusion distance and lower UF. There were no differences in the gene expression of aquaporins 1-3, endothelial and inducible nitric oxide synthase (NOS3 and NOS2), or interleukin-6. The SNAIL and E-CADHERIN gene expression normalized ratio was evaluated in peritoneal effluents of cells obtained from CPDF and BPDF. We observed that the SNAIL/E-CADHERIN mRNA ratio decreased when the dialysis sequence started with BPDF and went on to CPDF, but not when the sequence was the opposite.

Conclusion

This study shows that those patients who started PD treatment with BPDF were characterized by a better biocompatibility profile. BPDF associates with lower peritoneal permeability to small molecules and lower UF.

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.

pH-mediated upregulation of AQP1 gene expression through the Spi-B transcription factor

Background

Bicarbonate-based peritoneal dialysis (PD) fluids enhance the migratory capacity and damage-repair ability of human peritoneal mesothelial cells by upregulating AQP1. However, little is known about the underlying molecular mechanisms.

Results

Here we used HEK-293T cells to investigate the effect of pH on AQP1 gene transcription levels. We found that AQP1 mRNA levels increases with pH. Transfection of HEK-293T cells with luciferase reporter vectors containing different regions of the AQP1 promoter identified an upstream region in the AQP1 gene between − 2200 and – 2300 bp as an enhancer required for pH-mediated regulation of AQP1 expression. Site-directed mutagenesis of this specific promoter region revealed a critical region between − 2257 and − 2251 bp, and gene knock-down experiments and ChIP assays suggested that the Spi-B transcription factor SPIB is involved in pH-mediated regulation of AQP1 expression.

Conclusions

We identified an upstream region in the AQP1 gene and the transcription factor SPIB that are critically involved in pH-mediated regulation of AQP1 expression. These findings provide the basis for further studies on the pH- and buffer-dependent effects of PD fluids on peritoneal membrane integrity and function.

Electronic supplementary material

The online version of this article (10.1186/s12867-018-0104-9) contains supplementary material, which is available to authorized users.

A Short Review of Experimental Peritoneal Sclerosis: From Mice to Men

Peritoneal sclerosis has been induced in rodents in vivo by exposing the membrane to a variety of experimental interventions: asbestos, 0.1% chlorexidine, iron dextran, glucose degradation products, AGE deposits derived from uremia per se, sodium hypochlorite, lypopolysaccharide, low pH, pure water, silica or zymosan. With a few exceptions (pure water, chlorhexidine and low pH), the other substances mentioned operate setting out different degrees of oxidative stress. This short review describes several experimental interventions in rodents, aimed at acute exfoliation or long-term, sustained injury of the mesothelial monolayer performed by means of intraperitoneal injections of different oxidant agents.

Acute exfoliation induced by deoxycholate resulted in a depopulated monolayer coincident with immediate alteration of the peritoneal permeability, evidenced by increased urea D/P ratio, higher glucose absorption rate, elevated albumin losses in the effluent and significant reduction of the ultrafiltration rate.

In the long term (30 days), these manifestations of membrane failure persisted and coincided with substantial peritoneal sclerosis.

Peritoneal sclerosis was also induced by IP injections of 0.125% trypsin and 6.6 mM/L solution of formaldehyde. Using the doughnut rat model of mesothelial regeneration, exposure to 4.25% glucose or 7.5% icodextrin solutions severely hampered repopulation of the monolayer, which was replaced by a thick sheet of fibrous tissue.

It is concluded that peritoneal sclerosis derives mostly from sustained oxidative injury to the peritoneal membrane. Loss of the mesothelial monolayer is the first step in the chain of events leading to this complication.

Renal Association Clinical Practice Guideline on peritoneal dialysis in adults and children

These guidelines cover all aspects of the care of patients who are treated with peritoneal dialysis. This includes equipment and resources, preparation for peritoneal dialysis, and adequacy of dialysis (both in terms of removing waste products and fluid), preventing and treating infections. There is also a section on diagnosis and treatment of encapsulating peritoneal sclerosis, a rare but serious complication of peritoneal dialysis where fibrotic (scar) tissue forms around the intestine. The guidelines include recommendations for infants and children, for whom peritoneal dialysis is recommended over haemodialysis.Immediately after the introduction there is a statement of all the recommendations. These recommendations are written in a language that we think should be understandable by many patients, relatives, carers and other interested people. Consequently we have not reworded or restated them in this lay summary. They are graded 1 or 2 depending on the strength of the recommendation by the authors, and A-D depending on the quality of the evidence that the recommendation is based on.

Bicarbonate versus lactate solutions for acute peritoneal dialysis

BACKGROUND

The high mortality rate among critically ill patients with acute kidney injury (AKI) remains an unsolved problem in intensive care medicine, despite the use of renal replacement therapy (RRT). Increasing evidence from clinical studies in adults and children suggests that the new peritoneal dialysis (PD) fluids may allow for better long-term preservation of peritoneal morphology and function. Formation of glucose degradation products (GDPs) can be reduced and even avoided with the use of newer "biocompatible" solutions. However, it is still unclear if there are any differences in using conventional (lactate) solutions compared with low GDP (bicarbonate) solutions for acute PD.

OBJECTIVES

To look at the benefits and harms of bicarbonate versus lactate solutions in acute PD.

SEARCH METHODS

We searched the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE (from 1966), EMBASE (from 1980), Latin American and Caribbean Health Sciences Literature Database LILACS (from 1982), and reference lists of articles.Date of last search: 6 May 2014.

SELECTION CRITERIA

Randomised controlled trials (RCTs) comparing bicarbonate to lactate solution for acute PD.

DATA COLLECTION AND ANALYSIS

Two authors independently assess the methodological quality of studies. One author abstracted data onto a standard form, and a second author checked data extraction. We used the random-effects model and expressed the results as relative risk (RR) for dichotomous outcomes and mean difference (MD) for continuous outcomes with 95% confidence intervals (CI).

MAIN RESULTS

We included one study (20 patients) in this review. In shock patients, bicarbonate did not differ from lactate with respect to mortality (RR 0.50, 95% CI 0.06 to 3.91); however there were significant differences in blood lactate (MD -1.60 mmol/L, 95% CI -2.04 to -1.16), serum bicarbonate (MD 5.00 mmol/L, 95% CI 3.26 to 6.74) and blood pH (MD 0.12, 95% CI 0.06 to 0.18). In non-shock patients there was a significance difference in blood lactate (MD -0.60 mmol/L, 95% CI -0.85 to -0.35) but not in serum bicarbonate (MD 1.10 mmol/L, 95% CI -0.27 to 2.47) or blood pH (MD -0.02, 95% CI -0.02 to -0.06). Other outcomes could not be analysed because of the limited data available.

AUTHORS' CONCLUSIONS

There is no strong evidence that any clinical advantage for patients requiring acute PD for AKI when comparing conventional (lactate) with low GDP dialysis solutions (bicarbonate).

Biocompatible dialysis fluids for peritoneal dialysis

BACKGROUND

The longevity of peritoneal dialysis (PD) is limited by high rates of technique failure, some of which stem from peritoneal membrane injury. 'Biocompatible' PD solutions have been developed to reduce damage to the peritoneal membrane.

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

We searched the Cochrane Renal Group's Specialised Register (28 February 2013), through contact with the Trials Search Co-ordinator using search terms relevant to this review. Studies contained in the Specialised Register are identified through search strategies specifically designed for CENTRAL, MEDLINE and EMBASE, and handsearching conference proceedings.

SELECTION CRITERIA

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

DATA COLLECTION AND ANALYSIS

Two authors extracted data on study quality and outcomes (including adverse effects). The authors contacted investigators to obtain missing information. Summary estimates of effect were obtained using a random-effects model, and results were expressed as risk ratios (RR) and their 95% confidence intervals (CI) for categorical variables, and mean difference (MD) or standardised mean difference (SMD) and 95% CI for continuous variables.

MAIN RESULTS

Thirty-six eligible studies (2719 patients) were identified: Neutral pH, lactate-buffered/bicarbonate (± lactate)-buffered, low GDP PD solution (24); icodextrin (12). Allocation methods and concealment were generally incompletely reported, and adequate in only ten studies (27.8%). Patients lost to follow-up ranged from 0% to 83.4%. Neutral pH, low GDP versus conventional glucose PD solutionBased on generally sub-optimal quality evidence, the use of neutral pH, low GDP PD solutions was associated with larger urine volumes at the end of the studies, up to three years of therapy duration (7 studies, 520 patients: MD 126.39 mL/d, 95% CI 26.73 to 226.05). Improved preservation of residual renal function was evident in studies with greater than 12 month follow-up (6 studies, 360 patients: SMD 0.31, 95% CI 0.10 to 0.52). There was no significant effect on peritonitis, technique failure or adverse events with the use of neutral pH, low GDP PD solutions. Glucose polymer (icodextrin) versus conventional glucose PD solutionThere was a significant reduction in episodes of uncontrolled fluid overload (2 studies, 100 patients: RR 0.30, 95% CI 0.15 to 0.59) and improvement in peritoneal ultrafiltration (4 studies, 102 patients, MD 448.54 mL/d, 95% CI 289.28 to 607.80) without compromising residual renal function (4 studies, 114 patients: SMD 0.12, 95% CI -0.26 to 0.49) or urine output (3 studies, 69 patients: MD -88.88 mL/d, 95% CI -356.88 to 179.12) with icodextrin use. A comparable incidence of adverse events with the icodextrin (four studies) was reported.

AUTHORS' CONCLUSIONS

Based on generally sub-optimal quality studies, use of neutral pH, low GDP PD solution led to greater urine output and higher residual renal function after use exceeded 12 months. Icodextrin prescription improved peritoneal ultrafiltration and mitigated uncontrolled fluid overload. There were no significant effects on peritonitis, technique survival, patient survival or harms identified with their use. Based on the best available evidence, the use of these 'biocompatible' PD solutions resulted in clinically relevant benefits without added risks of harm.

The impact of neutral-pH peritoneal dialysates with reduced glucose degradation products on clinical outcomes in peritoneal dialysis patients

Neutral-pH peritoneal dialysates, with reduced glucose degradation products (GDPs), have been developed to reduce peritoneal membrane damage. Here our review evaluated the impact of these solutions on clinical outcomes using data from The Cochrane CENTRAL Registry, MEDLINE, Embase, and reference lists for randomized trials of biocompatible solutions. Summary estimates of effect were obtained using a random-effects model of 20 eligible trials encompassing 1383 patients. The quality of studies was generally poor, such that 13 studies had greater than a 20% loss to follow-up and only 3 trials reported adequate concealment of allocation. Use of neutral-pH dialysates with reduced GDPs resulted in larger urine volumes (7 trials; 520 patients; mean difference 126 ml/day, 95% CI 27-226), improved residual renal function after 12 months (6 trials; 360 patients; standardized mean difference 0.31, 95% confidence interval 0.10-0.52), and a trend to reduced inflow pain (1 trial; 58 patients; relative risk 0.51, 95% CI 0.24-1.08). However, there was no significant effect on body weight, hospitalization, peritoneal solute transport rate, peritoneal small-solute clearance, peritonitis, technique failure, patient survival, or adverse events. No significant harms were identified. Thus, based on generally poor quality trials, the use of neutral-pH peritoneal dialysates with reduced GDPs resulted in greater urine volumes and residual renal function after 12 months, but without other clinical benefits. Larger, better-quality studies are needed for accurate evaluation of the impact of these newer dialysates on patient-level hard outcomes.

The effects of biocompatible compared with standard peritoneal dialysis solutions on peritonitis microbiology, treatment, and outcomes: the balANZ trial

BACKGROUND

A multicenter, multi-country randomized controlled trial (the balANZ study) recently reported that peritonitis rates significantly improved with the use of neutral-pH peritoneal dialysis (PD) solutions low in glucose degradation products ("biocompatible") compared with standard solutions. The present paper reports a secondary outcome analysis of the balANZ trial with respect to peritonitis microbiology, treatment, and outcomes.

METHODS

Adult incident PD patients with residual renal function were randomized to receive either biocompatible or conventional (control) PD solutions for 2 years.

RESULTS

The safety population analysis for peritonitis included 91 patients in each group. The unadjusted geometric mean peritonitis rates in those groups were 0.30 [95% confidence interval (CI): 0.22 to 0.41] episodes per patient-year for the biocompatible group and 0.49 (95% CI: 0.39 to 0.62) episodes per patient-year for the control group [incidence rate ratio (IRR): 0.61; 95% CI: 0.41 to 0.90; p = 0.01]. When specific causative organisms were examined, the rates of culture-negative, gram-positive, gram-negative, and polymicrobial peritonitis episodes were not significantly different between the biocompatible and control groups, although the biocompatible group did experience a significantly lower rate of non-pseudomonal gram-negative peritonitis (IRR: 0.41; 95% CI: 0.18 to 0.92; p = 0.03). Initial empiric antibiotic regimens were comparable between the groups. Biocompatible fluid use did not significantly reduce the risk of peritonitis-associated hospitalization (adjusted odds ratio: 0.80; 95% CI: 0.48 to 1.34), but did result in a shorter median duration of peritonitis-associated hospitalization (6 days vs 11 days, p = 0.05). Peritonitis severity was more likely to be rated as mild in the biocompatible group (37% vs 10%, p = 0.001). Overall peritonitis-associated technique failures and peritonitis-related deaths were comparable in the two groups.

CONCLUSIONS

Biocompatible PD fluid use was associated with a broad reduction in gram-positive, gram-negative, and culture-negative peritonitis that reached statistical significance for non-pseudomonal gram-negative organisms. Peritonitis hospitalization duration was shorter, and peritonitis severity was more commonly rated as mild in patients receiving biocompatible PD fluids, although other peritonitis outcomes were comparable between the groups.

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.

Neutral solution low in glucose degradation products is associated with less peritoneal fibrosis and vascular sclerosis in patients receiving peritoneal dialysis

BACKGROUND

The effects of novel biocompatible peritoneal dialysis (PD) solutions on human peritoneal membrane pathology have yet to be determined. Quantitative evaluation of human peritoneal biopsy specimens may reveal the effects of the new solutions on peritoneal membrane pathology. ♢

METHODS

Peritoneal specimens from 24 PD patients being treated with either acidic solution containing high-glucose degradation products [GDPs (n = 12)] or neutral solution with low GDPs (n = 12) were investigated at the end of PD. As controls, pre-PD peritoneal specimens, obtained from 13 patients at PD catheter insertion, were also investigated. The extent of peritoneal fibrosis, vascular sclerosis, and advanced glycation end-product (AGE) accumulation were evaluated by quantitative or semi-quantitative methods. The average densities of CD31-positive vessels and podoplanin-positive lymphatic vessels were also determined. ♢

RESULTS

Peritoneal membrane fibrosis, vascular sclerosis, and AGE accumulation were significantly suppressed in the neutral group compared with the acidic group. The neutral group also showed lower peritoneal equilibration test scores and preserved ultrafiltration volume. The density of blood capillaries, but not of lymphatic capillaries, was significantly increased in the neutral group compared with the acidic and pre-PD groups. ♢

CONCLUSIONS

Neutral solutions with low GDPs are associated with less peritoneal membrane fibrosis and vascular sclerosis through suppression of AGE accumulation. However, contrary to expectation, blood capillary density was increased in the neutral group. The altered contents of the new PD solutions modified peritoneal membrane morphology and function in patients undergoing PD.

Buffer-dependent regulation of aquaporin-1 expression and function in human peritoneal mesothelial cells

BACKGROUND

Biocompatible peritoneal dialysis fluids (PDF) are buffered with lactate and/or bicarbonate. We hypothesized that the reduced toxicity of the biocompatible solutions might unmask specific effects of the buffer type on mesothelial cell functions.

METHODS

Human peritoneal mesothelial cells (HPMC) were incubated with bicarbonate (B-)PDF or lactate-buffered (L-)PDF followed by messenger RNA (mRNA) and protein analysis. Gene silencing was achieved using small interfering RNA (siRNA), functional studies using Transwell culture systems, and monolayer wound-healing assays.

RESULTS

Incubation with B-PDF increased HPMC migration in the Transwell and monolayer wound-healing assay to 245 ± 99 and 137 ± 11% compared with L-PDF. Gene silencing showed this effect to be entirely dependent on the expression of aquaporin-1 (AQP-1) and independent of AQP-3. Exposure of HPMC to B-PDF increased AQP-1 mRNA and protein abundance to 209  ± 80 and 197  ±  60% of medium control; the effect was pH dependent. L-PDF reduced AQP-1 mRNA. Addition of bicarbonate to L-PDF increased AQP-1 abundance by threefold; mRNA half-life remained unchanged. Immunocytochemistry confirmed opposite changes of AQP-1 cell-membrane abundance with B-PDF and L-PDF.

CONCLUSIONS

Peritoneal mesothelial AQP-1 abundance and migration capacity is regulated by pH and buffer agents used in PD solutions. In vivo studies are required to delineate the impact with respect to long-term peritoneal membrane integrity and function.

Differentiation of bone marrow-derived cells into regenerated mesothelial cells in peritoneal remodeling using a peritoneal fibrosis mouse model

Marked thickening of the peritoneum and vasculopathy in the submesothelial compact zone have been reported in long-term peritoneal dialysis patients. Bone marrow (BM)-derived cell lines are considered to be useful tools for therapy of various diseases. To clarify the role of BM-derived cells in the peritoneal fibrosis (PF) model, we analyzed several lineages of cells in the peritoneum. BM cells from green fluorescent protein (GFP) transgenic mice were transplanted into naïve C57Bl/6 mice. Chlorhexidine gluconate (CG) was injected intraperitoneally to induce PF. Immunohistochemical analysis was performed with parietal peritoneum using anti-Sca-1 or -c-Kit and -GFP antibodies. Isolated BM cells were also transplanted into the CG-stimulated peritoneum. BM-derived cells from GFP transgenic mice appeared in the submesothelium from days 14 to 42. Both GFP- and stem cell marker-positive cells were observed in the submesothelium and on the surface. Isolated c-Kit-positive cells, transplanted into the peritoneal cavity, differentiated into mesothelial cells. In this study, we investigated whether or not BM-derived cells play a role in the repair of PF and immature cells have the potential of inducing repair of the peritoneum. The findings of this study suggest a new concept for therapy of PF.

Peritoneal morphology after long-term peritoneal dialysis with biocompatible fluid: recent clinical practice in Japan

BACKGROUND

Morphology changes of the peritoneal membrane after long-term peritoneal dialysis (PD) consist of denudation of peritoneal mesothelial cells, interstitial sclerosis, and hyalinizing vasculopathy. Those changes are considered to be the result of uremia and bioincompatible effects of conventional acidic lactate-buffered dialysate with glucose degradation products (GDPs). In the last decade, biocompatible dialysate with neutral pH and low GDPs has become widely used. Clinical practice has been modified in Japan, especially for anuric patients, and now includes the use of hybrid therapy. The impact on peritoneal morphology has not been well reported.

OBJECTIVE

The aim of the present study was to investigate the long-term effect on peritoneal morphology and function of biocompatible fluid use and current clinical practice in Japan, including hybrid dialysis therapy.

METHODS

We evaluated peritoneal biopsy specimens from patients who had undergone PD for more than 3 years. We used the average peritoneal thickness (APT) of the submesothelial compact zone as a marker of interstitial sclerosis and the lumen/vessel diameter ratio (L/V ratio) at postcapillary venules as a marker of hyalinizing vasculopathy. Demography and other data for the patients, including dialysate-to-plasma (D/P) ratio of creatinine, were obtained at baseline and every 6 months by peritoneal equilibration test.

RESULTS

Between 2002 and 2009, 110 patients started PD therapy with biocompatible dialysate at Tokyo University Hospital. Among them, 11 patients (8 men, 3 women; age: 54.2 ± 11.8 years; 1 with diabetes mellitus) were enrolled into this morphology study. The mean duration of PD in this group was 61 ± 11.3 months, and the mean time to peritoneal biopsy was 58 ± 15.1 months. The median APT was 180 μm (96 - 1424 μm), and the median L/V ratio was 0.66 (0.46 - 0.74). No obvious correlations between APT, L/V ratio, and PD duration were detected. The D/P creatinine of the 11 patients was maintained at a favorably low value, comparable with that of the other 99 patients.

CONCLUSIONS

Peritoneal dialysis therapy using biocompatible dialysate in conjunction with modification of clinical practice may minimize the progression of peritoneal interstitial sclerosis and hyalinizing vasculopathy, preserving favorable peritoneal function for more than 3 years.

Interleukin-1 receptor-mediated inflammation impairs the heat shock response of human mesothelial cells

Bioincompatibility of peritoneal dialysis fluids (PDF) limits their use in renal replacement therapy. PDF exposure harms mesothelial cells but induces heat shock proteins (HSP), which are essential for repair and cytoprotection. We searched for cellular pathways that impair the heat shock response in mesothelial cells after PDF-exposure. In a dose-response experiment, increasing PDF-exposure times resulted in rapidly increasing mesothelial cell damage but decreasing HSP expression, confirming impaired heat shock response. Using proteomics and bioinformatics, simultaneously activated apoptosis-related and inflammation-related pathways were identified as candidate mechanisms. Testing the role of sterile inflammation, addition of necrotic cell material to mesothelial cells increased, whereas addition of the interleukin-1 receptor (IL-1R) antagonist anakinra to PDF decreased release of inflammatory cytokines. Addition of anakinra during PDF exposure resulted in cytoprotection and increased chaperone expression. Thus, activation of the IL-1R plays a pivotal role in impairment of the heat shock response of mesothelial cells to PDF. Danger signals from injured cells lead to an elevated level of cytokine release associated with sterile inflammation, which reduces expression of HSP and other cytoprotective chaperones and exacerbates PDF damage. Blocking the IL-1R pathway might be useful in limiting damage during peritoneal dialysis.

Bicarbonate versus lactate solutions for acute peritoneal dialysis

BACKGROUND

The high mortality rate among critically ill patients with acute kidney injury (AKI) remains an unsolved problem in intensive care medicine, despite the use of renal replacement therapy (RRT). Increasing evidence from clinical studies in adults and children suggests that the new peritoneal dialysis (PD) fluids may allow for better long-term preservation of peritoneal morphology and function. Formation of glucose degradation products (GDPs) can be reduced and even avoided with the use of newer "biocompatible" solutions. However, it is still unclear if there are any differences in using conventional (lactate) solutions compared with low GDP (bicarbonate) solutions for acute PD.

OBJECTIVES

To look at the benefits and harms of bicarbonate versus lactate solutions in acute PD.

SEARCH STRATEGY

We searched the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE (from 1966), EMBASE (from 1980), Latin American and Caribbean Health Sciences Literature Database LILACS (from 1982), and reference lists of articles.

SELECTION CRITERIA

Randomised controlled trials (RCTs) comparing bicarbonate to lactate solution for acute PD.

DATA COLLECTION AND ANALYSIS

Two authors independently assess the methodological quality of studies. One author abstracted data onto a standard form, and a second author checked data extraction. We used the random-effects model and expressed the results as relative risk (RR) for dichotomous outcomes and mean difference (MD) for continuous outcomes with 95% confidence intervals (CI).

MAIN RESULTS

We included one study (20 patients) in this review. In shock patients, bicarbonate did not differ from lactate with respect to mortality (RR 0.50, 95% CI 0.06 to 3.91); however there were significant differences in blood lactate (MD -1.60 mmol/L, 95% CI -2.04 to -1.16), serum bicarbonate (MD 5.00 mmol/L, 95% CI 3.26 to 6.74) and blood pH (MD 0.12, 95% CI 0.06 to 0.18). In non-shock patients there was a significance difference in blood lactate (MD -0.60 mmol/L, 95% CI -0.85 to -0.35) but not in serum bicarbonate (MD 1.10 mmol/L, 95% CI -0.27 to 2.47) or blood pH (MD -0.02, 95% CI -0.02 to -0.06). Other outcomes could not be analysed because of the limited data available.

AUTHORS' CONCLUSIONS

There is no strong evidence that any clinical advantage for patients requiring acute PD for AKI when comparing conventional (lactate) with low GDP dialysis solutions (bicarbonate).

Peritoneal dialysis fluids can alter HSP expression in human peritoneal mesothelial cells

BACKGROUND

Acute exposure of mesothelial cells to peritoneal dialysis fluid (PDF) has been shown not only to result in injury but also to induce cytoprotective heat shock proteins (HSP). The aim of the present study was to evaluate the expression of HSP in a more chronic in vitro PDF exposure system, searching for a role of glucose degradation products (GDP).

METHODS

Human peritoneal mesothelial cells (HPMC) were chronically incubated in filter- or heat-sterilized PDF (mixed 1:1 with cell culture medium), or in control cell culture medium. After incubation periods of 1, 3 and 10 days, cell extract was assessed for Ezrin, Hsp27 and Hsp72, and supernatant for IL-6 and IL-8. After 24-h exposure to the GDP 3.4-di-deoxyglucosone-3-ene (3.4-DGE), HPMC were assessed for expression of Hsp27 and Hsp72, and for release of LDH, IL-6 and IL-8.

RESULTS

In vitro PDF exposure for more than 1 day resulted in reduced cell mass, lower expression of the epithelial marker Ezrin and depressed cellular levels of both HSP, associated with increased IL-6 and IL-8 release. These effects occurred earlier and stronger with heat-sterilized than with filter-sterilized PDF. Exposure of HPMC to 3.4-DGE resulted in suppression of HSP, and increased release of LDH, IL-6 and IL-8.

CONCLUSION

Our data show that GDP (dys)regulate the mesothelial cell stress response. This was associated with reduced cell mass, loss of the epithelial phenotype and sterile cellular inflammation following extended exposure to heat-sterilized PDF. Toxic effects of PDF might thus be extended to reduced mesothelial cell stress responses.

Peritoneal inflammation after twenty-week exposure to dialysis solution: effect of solution versus catheter-foreign body reaction

BACKGROUND

We hypothesized that both sterile solutions and foreign body reaction to the peritoneal dialysis catheter are associated with inflammatory changes in rats exposed to hypertonic solution.

METHODS

Four hypertonic solutions (30 - 40 mL) were injected daily via needle and syringe over 20 weeks in 4 groups of rats: 4.25% standard clinical solution (LAC), LAC plus pyridoxamine (PYR), LAC plus ethyl pyruvate (EP), and a biocompatible 4% dextrose solution (BIC). Two groups received catheters: a non-injected 4-week catheter group (C4) and a group injected for 20 weeks with the BIC solution (CI). Control animals (CON) were not injected. In the C4 group, adherent cells were separated from the catheter and examined by culture and electron microscopy to ensure that animals were bacteria free prior to exposure to solution. Animals underwent transport experiments to determine mass transfer coefficients of mannitol (MTC(M)) and albumin (MTC(A)), osmotic filtration flux (J(osm)), and hydrostatic pressure-driven flux (J(p)). After euthanasia, tissues were examined for submesothelial thickness, vascular density, and immunohistochemistry for various cytokines.

RESULTS

The catheter cell layer was free of bacteria and consisted of macrophages, lymphocytes, mesothelial cells, and fibroblastic cells. Marked differences in angiogenesis and submesothelial thickening were noted for the catheter groups. Transport differences were mixed: MTC(M) was significantly less for the CI group and MTC(A) was variable among the groups. There were no differences among groups for J(osm) or J(p). Inflammatory markers in the catheter-adherent cells correlated with inflammatory changes in the tissue. These data demonstrate significant changes in submesothelial thickness, angiogenesis, transport function, and inflammatory markers between animals injected with sterile solutions over 20 weeks with and without catheters.

CONCLUSION

An indwelling catheter amplifies peritoneal inflammation from dialysis solutions through a foreign body reaction. Our data also suggest that additives to existing solutions may have limited the effect on inflammatory response to non-biocompatible solutions.

Biocompatibility and Tolerability of a Purely Bicarbonate-Buffered Peritoneal Dialysis Solution

Background

Novel peritoneal dialysis solutions are characterized by a minimal content of glucose degradation products and a neutral pH. Many studies have shown the biocompatibility of neutral lactate-buffered solutions; however, until now, the effect of purely bicarbonate-buffered solutions has not been intensively studied in vivo.

Methods

This study was an open label, prospective, crossover multicenter trial to investigate the biocompatibility of a purely bicarbonate-buffered solution (bicPDF) by measuring biocompatibility parameters such as cancer antigen 125 (CA125) in peritoneal effluent. 55 patients were enrolled in the study. After a 2-week run-in phase, 53 patients could be randomized into 2 groups, starting with either standard lactate-buffered peritoneal dialysis fluid (SPDF) for 12 weeks (phase 1) and then switching to bicPDF for 12 weeks (phase 2), or vice versa. Overnight peritoneal effluents were collected at baseline and at the end of phases 1 and 2 and were tested for CA125, hyaluronic acid, vascular endothelial growth factor (VEGF), tumor necrosis factor-alpha (TNF-α), interleukin 6 (IL-6), interferon gamma (IFNγ), and transforming growth factor-beta1 (TGF-β1). Total ultrafiltration and residual renal function were also assessed. At the end of the study, pain during fluid exchange and dwell was evaluated using special questionnaires.

Results

34 patients completed the study; 27 of them provided data for analysis of the biocompatibility parameters. CA125 levels in overnight effluent were significantly higher with bicPDF (61.9 ± 33.2 U/L) than with SPDF (18.6 ± 18.2 U/L, p < 0.001). Hyaluronic acid levels were significantly lower after the use of bicPDF (185.0 ± 119.6 ng/mL) than after SPDF (257.4 ± 174.0 ng/mL, p = 0.013). Both TNF-α and TGF-β1 showed higher levels with the use of bicPDF than with SPDF. No differences were observed for IL-6, VEGF, or IFNγ levels. We observed an improvement in the glomerular filtration rate with the use of bicPDF but no differences were observed for total fluid loss. Pain scores could be analyzed in 23 patients: there was no difference between the solutions.

Conclusions

The use of a purely bicarbonate-buffered low-glucose degradation product solution significantly changes most of the peritoneal effluent markers measured, suggesting an improvement in peritoneal membrane integrity. Additionally, it seems to have a positive effect on residual renal function.

Factors Contributing to Peritoneal Tissue Remodeling in Peritoneal Dialysis

Peritoneal dialysis (PD) is associated with functional and structural changes of the peritoneal membrane. In this review we describe factors contributing to peritoneal tissue remodeling, including uremia, peritonitis, volume loading, the presence of a catheter, and the PD fluid itself. These factors initiate recruitment and activation of peritoneal cells such as macrophages and mast cells, as well as activation of peritoneal cells, including mesothelial cells, fibroblasts, and endothelial cells. We provide an overview of cytokines, growth factors, and other mediators involved in PD-associated changes. Activation of downstream pathways of cellular modulators can induce peritoneal tissue remodeling, leading to ultrafiltration loss. Identification of molecular pathways, cells, and cytokines involved in the development of angiogenesis, fibrosis, and membrane failure may lead to innovative therapeutic strategies that can protect the peritoneal membrane from the consequences of long-term PD.

Acid-base balance in peritoneal dialysis patients: a Stewart-Fencl analysis

BACKGROUND

Evaluation of acid-base disorders using the Stewart-Fencl principle is based on assessment of independent factors: strong ion difference (SID) and the total concentration of non-volatile weak acids (Atot). This approach allows for a more detailed evaluation of the cause of acid-base imbalance than the conventional bicarbonate-centered approach based on the Henderson-Hasselbalch principle, which is a necessary yet insufficient condition to describe the state of the system. The aim of our study was to assess acid-base disorders in peritoneal dialysis (PD) patients using both of these principles.

METHODS

A total of 17 patients with chronic renal failure (10 men), aged 60.7 (22-84) years, treated by PD for 25.7 (1-147) months were examined. A control group included 17 healthy volunteers (HV) (8 males), with a mean age of 42.7 (22-77) years and normal renal function. Patients were treated with a solution containing bicarbonate (25 mmol/L) and lactate (15 mmol/L) as buffers; eleven of them used, during the nighttime dwell, a solution with icodextrin buffered by lactate at a concentration of 40 mmol/L. The following equations were employed for calculations of acid-base parameters according to the Stewart-Fencl principle. The first is SID = [Na+] + [K+] + 2[Ca(2+)] + 2[Mg(2+)] - [Cl-] - [UA-], where SID is the strong ion difference and [UA-] is the concentration of undetermined anions. For practical calculation of SID, the second equation, SID = [HCO3-] + [Alb-] + [Pi-], was used, where [Alb-] and [Pi-] are the charges carried by albumin and phosphates. The third is Atot, the total concentration of weak non-volatile acids, albumin [Alb] and phosphates [Pi].

RESULTS

The capillary blood pH in PD group was 7.41 (7.27-7.48), [HCO3-] levels 23.7 (17.6-29.5) mmol/L, SID 36.3 (29.5-41.3) mmol/L, sodium-chloride difference 39.0 (31.0-44.0) mmol/L, [Pi] 1.60 (0.83-2.54) mmol/L, and [Alb] 39.7 (28.8-43.4) g/L (median, min-max). Bicarbonate in blood correlated positively with SID (Rho = 0.823; p < 0.001), with the sodium-chloride difference (Rho = 0.649; p < 0.01) and pH (Rho = 0.754; p < 0.001), and negatively with residual renal function (Rho = -0.517; p < 0.05). Moreover, the sodium-chloride difference was also found to correlate with SID (Rho = 0.653; p < 0.01). While the groups of PD and HV patients did not differ in median bicarbonate levels, significantly lower median value of SID were observed in PD patients, 36.3 vs. 39.3 mmol/L (p < 0.01); additionally, PD patients were shown to have significantly lower mean value of serum sodium levels, 138 vs. 141 mmol/L (p < 0.01), and serum chlorides levels, 100 vs. 104 mmol/L (p < 0.001). Despite the higher [UA-] levels in PD patients, 9.1 vs. 5.4 mmol/L (p < 0.001), this parameter was not found to correlate with bicarbonate levels.

CONCLUSIONS

The results suggest that the decreased bicarbonate in PD patients results from a combination of decreased sodium-chloride difference and mildly increased unmeasured anions.

Randomized controlled study of biocompatible peritoneal dialysis solutions: effect on residual renal function

Residual kidney function is important for patient and technique survival in peritoneal dialysis (PD). Biocompatible dialysis solutions are thought to improve function and viability of peritoneal mesothelial cells and to preserve residual renal function (RRF). We conducted a randomized controlled study comparing use of biocompatible (B) with standard (S) solutions in 93 incident PD patients during a 1-year period. The demographics, comorbidities, and RRF of both groups were similar. At 3 and 12 months, 24-h urine samples were collected to measure volume and the mean of urea and creatinine clearance normalized to body surface area. Surrogate markers of fluid status, diuretic usage, C-reactive protein concentration, peritonitis episodes, survival data, and peritoneal equilibrium tests were also collected. Changes in the normalized mean urea and creatinine clearance were the same for both groups, with no significant differences in secondary end points. Despite non-randomized studies suggesting benefits of these newer biocompatible solutions, we could not detect any clinically significant advantages. Additional studies are needed to determine if advantages are seen with longer term use.

Impact of new dialysis solutions on peritonitis rates

Peritonitis remains a major cause of morbidity among patients on peritoneal dialysis (PD), yet there is little information about the effect of new biocompatible dialysis solutions on peritonitis rates and treatment. In our unit, information on each peritonitis episode is prospectively collected. Since 2003, bicarbonate/lactate dialysate has been gradually introduced for new patients and for patients experiencing abdominal pain with conventional lactate solutions. From 2002 to 2005, data from 121 episodes of peritonitis (71 automated PD and 50 continuous ambulatory PD) were analyzed; 107 episodes occurred in patients using standard lactate dialysate and 14 episodes in patients using bicarbonate/lactate solution. Patients using bicarbonate/lactate had a significantly lower peritonitis rate of 1 per 52.5 patient-months compared to those using standard lactate dialysate (1 per 26.9 patient-months) (P=0.0179). Response to treatment, however, was not affected by the type of dialysate; cure rates (71.4 and 69.1%, respectively) and recurrence rates (21.4 and 15.8%, respectively) were not significantly different. Catheter removal was required in three (21.4%) patients using bicarbonate/lactate and 23 (22.4%) patients using lactate solution. Use of biocompatible dialysate appears to reduce the peritonitis rate by 50%, although this has to be confirmed in a randomized study. The type of dialysate, on the other hand, does not affect response to treatment.

Effect of hyperosmolality on beta-defensin gene expression by human corneal epithelial cells

PURPOSE

As human beta-defensins (hBD) are important antimicrobial peptides at epithelial surfaces, including the ocular surface, we tested the effect of hyperosmolar conditions on the expression of these peptides by human corneal epithelial cells (HCECs).

METHODS

Simian virus 40-transformed HCECs (n = 5) or primary cultured HCECs (n = 5) were treated with serum-free media or serum-free hyperosmolar (400-500 mOsm/kg) media for 24 hours or serum-free 500 mOsm/kg media for 12 to 48 hours. The effect of hyperosmolality on interleukin-1beta (IL-1beta)-induced hBD-2 expression was also tested. IL-6 expression was studied as a marker of IL-1beta function. Expression of hBD-1, -2, and -3 and IL-6 mRNA was detected by reverse transcription-polymerase chain reaction (RT-PCR). The levels of active IL-1beta (culture supernatants and cell lysates) and pro-IL-1beta (cell lysates) were detected by enzyme-linked immunosorbent assay.

RESULTS

HCECs constitutively expressed hBD-1 and -3 but not hBD-2. Hyperosmolar media had no effect on the basal expression of hBD-1 or -3 and did not induce the expression of hBD-2. Treatment with 500 mOsm/kg media for 24 hours decreased the ability of IL-1beta to upregulate hBD-2 and IL-6 expression. Active or pro-IL-1beta was not detected in any cell culture sample.

CONCLUSION

Our results suggest that the hyperosmolar environment observed in diseases such as dry eye does not alter defensin expression. However, a hyperosmolar environment may influence cytokine function in ocular surface cells and thus affect their response to injury and inflammation.

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.

Peritoneal dialysis fluid-induced changes of the peritoneal membrane are reversible after peritoneal rest in rats

BACKGROUND

Peritoneal dialysis (PD) is associated with functional and structural alterations of the peritoneal membrane. However, the (ir)reversibility of these pathological changes of the peritoneum is not understood fully.

METHODS

In an experimental PD model, rats (n = 15) received daily 10 ml conventional glucose containing PD fluid, via peritoneal catheters connected to implanted subcutaneous mini vascular access ports. After 5 weeks of treatment, the first group of animals (PDF; n = 10) was sacrificed, while peritoneal catheters of the remaining group of rats (PD-rest; n = 5) were removed 1 week later. The latter group (PD-rest) was sacrificed 12 weeks after removing catheters. At both time points, untreated rats were included as controls. Cellular and morphological parameters were analysed by light and electron microscopy.

RESULTS

Rats exposed to PD fluid for 5 weeks showed a severe angiogenesis in various peritoneal tissues. Peritoneal rest resulted in a significant reduction in blood vessel density in visceral (mesentery, P<0.05), but not in parietal peritoneum. Five weeks' exposure to PD fluid resulted in a profound fibrosis in the parietal peritoneum, whereas the degree of fibrosis was significantly reduced in the PD-rest group (P<0.02). Daily exposure to PD fluid induced a higher number of mast cells in the omentum compared with untreated rats, whereas peritoneal rest normalized the increased mast cell density completely (P<0.03). Likewise, continued PD fluid instillation evoked a strong omental milky spot response, which was returned to the control level after peritoneal rest (P<0.009). Furthermore, the number of mesothelial cells on the liver was significantly increased in rats treated with PD fluid, whereas animals from the PD-rest group had a lower number of mesothelial cells, although this was not statistically significant (P = 0.08). Finally, as evidenced by electron microscopy, daily exposure to PD fluid resulted in severe damage to the mesothelial cell layer covering the peritoneum, whereas this cell layer was completely recovered after peritoneal rest.

CONCLUSIONS

We show that PD fluid-induced cellular and morphological alterations of the peritoneal membrane are generally reversible.

In vitro biocompatibility performance of Physioneal

In vitro biocompatibility performance of Physioneal. toneal dialysis (PD) has been a successful and effective form of chronic renal replacement therapy since its introduction over 20 years ago. Despite its overall success, there is a growing body of evidence that suggests shortcomings in the preservation of membrane integrity. This has led to the development of several second-generation PD solutions that demonstrate improved biocompatibility. Physioneal, a neutral pH, bicarbonate/lactate-buffered solution, was one of the first of these new PD solutions to become commercially available. This review will focus on one of the first preclinical stages in the development of Physioneal: studies on in vitro biocompatibility testing. Studies in leukocyte, mesothelial cell, and fibroblast populations demonstrated significantly improved biocompatibility of neutral pH, bicarbonate/lactate-based solutions compared to conventional solutions. The solutions contributed to improved leukocyte viability and response to bacterial infection (e.g., phagocytosis, superoxide radical generation, and endotoxin-stimulated cytokine release). Studies on peritoneal mesothelial cells demonstrate improved cell viability, proliferation, and response to proinflammatory stimuli, and a reduced potential for angiogenesis and peritoneal fibrosis, all suggesting a better preservation of membrane structure and function. The bicarbonate/lactate-based solutions demonstrated decreased cytotoxicity and preserved cell growth in fibroblast cultures as well. In vitro biocompatibility testing has clearly demonstrated that neutral pH, bicarbonate/lactate-buffered Physioneal solutions are superior to conventional solutions in preserving cell viability and function in cell populations that contribute to peritoneal homeostasis. This positive assessment now provides a foundation and rationale for moving forward with the next stages in preclinical testing: in vivo animal models and human ex vivo studies.

In vitro and in vivo models for peritonitis demonstrate unchanged neutrophil migration after exposure to dialysis fluids

BACKGROUND

Recurrent infections in peritoneal dialysis (PD) patients may alter the abdominal wall resulting in an impairment of its dialysis capacity. In this study we investigated both in vitro and in vivo the effects of mesothelial exposure to dialysis fluids on the migration of neutrophils and their capacity to clear a bacterial infection.

METHODS

First, we evaluated neutrophil migration in an in vitro transwell model for the peritoneal membrane with monolayers of primary human mesothelial cells (MC) on the lower side and primary human endothelial cells (EC) on top of the same transwell membrane, upon exposure of MC to PD fluid (PDF)-derived components. In addition to this in vitro model, we combined chronic peritoneal exposure to PDF with a peritoneal infection model in the rat. We investigated the kinetics of the chemokine response, neutrophil recruitment and bacterial clearance.

RESULTS

Known chemoattractants, such as fMLP and IL-8, strongly increased neutrophil migration across both cell layers in the in vitro model of the peritoneal membrane. Pre-incubation of the MC layer for 48 h with 55 mM glucose, a combination of two glucose degradation products, methylglyoxal and 3-deoxyglucosone, or conventional dialysis fluid (1:4 dilution), however, did not change the IL-8-induced migration of neutrophils. In concert with this finding we demonstrated an unchanged MC expression of ICAM-1 and VCAM-1 after these pre-treatments. Unexpectedly, chronic i.p. exposure to conventional PDF or a recently developed lactate/bicarbonate-buffered PDF in a rat peritoneal exposure model strongly hampered the chemokine response upon bacterial challenge. Nevertheless, neutrophil recruitment and bacterial clearance were effective and did not differ from rats not pre-exposed to PDF.

CONCLUSIONS

We conclude that exposure of MC to PDF does not hamper the recruitment of functional neutrophils upon challenge.

Effluent CA 125 concentration in chronic peritoneal dialysis patients: influence of PD duration, peritoneal transport and PD regimen

In terms of the integrity of the peritoneal membrane in peritoneal dialysis (PD), the peritoneal mesothelial cells play a pivotal role since its monolayer constitutes the first line of the peritoneal membrane. Cancer antigen 125 (CA 125) is released by peritoneal mesothelial cells and correlates with the mesothelial cell mass in PD. Since its effluent concentration is easy to determine in chronic PD patients, CA 125 serves as an in vivo marker of biocompatibility. We performed a cross-sectional study to investigate the relation between PD duration, peritoneal transport and the PD regimen (CAPD/CCPD) on effluent CA 125 concentration in 22 chronic PD patients. We compared long-term (>6 months) with short-term PD treatment, patients with high small solute transport properties (MTAC >11 ml/min, d/p ratio of creatinine >0.72) to patients with low small solute transport and CAPD with APD patients. A peritoneal equilibration test was performed with 1.36% glucose. Dialysate/plasma (D/P) ratio and mass transfer area coefficient (MTAC) of creatinine were calculated and the 4-hour effluent concentration of CA 125 was determined. CA 125 tended to be lower in the long-term PD patients and also in APD patients, but statistical significance was missing. Effluent CA 125 was significantly increased in patients with an MTAC of creatinine >11 ml/min (40.2 +/- 11.2 vs. 20.7 +/- 1.2 U/ml) and in patients with a d/p ratio of creatinine >0.72 (48.2 +/- 11.0 vs. 21.6 +/- 1.6 U/ml). CA 125 and the d/p ratio of creatinine were positively correlated (r = 0.68). The positive correlation of CA 125 with peritoneal small solute transport especially in the early phase of PD treatment indicates an initial correlation of the mesothelial cell mass with the peritoneal surface area. A direct relation between the CA 125 concentration and peritoneal transport is unlikely. In our study the CA 125 effluent concentration tended to be lower in long-term PD patients and also in APD patients, possibly indicating a cell depletory influence of the conventional PD fluid.

Glucose degradation products in peritoneal dialysis: from bench to bedside

In continuous ambulatory peritoneal dialysis patients, treatment success is inextricably linked to the functional and morphological integrity of the peritoneal membrane. This membrane, however, is repeatedly exposed to peritoneal dialysis fluids (PDFs) with unphysiological composition (e.g., acidic pH, high glucose content, hyperosmolarity). More recently, attention of researchers and clinicians has been focused on the presence of glucose degradation products (GDPs) that are generated during heat sterilization of PDF. These GDPs were found to adversely affect peritoneal cell function both acutely and chronically. Recently, a new family of multi-chambered PDFs has been introduced into clinical practice. By keeping the glucose in a separate compartment at very low pH, the generation of GDPs during heat sterilization is markedly reduced. Initial clinical studies indicate that treatment with these novel PDFs may lead to improved clinical outcomes. The current article reviews recent experimental and clinical experience with both conventional and multi-chambered PDFs.

Contribution of lactate buffer, glucose and glucose degradation products to peritoneal injury in vivo

BACKGROUND

Long-term peritoneal dialysis (PD) is associated with the development of functional and structural alterations of the peritoneal membrane. In this study, we investigated the contribution of low pH lactate buffer, high glucose concentration and glucose degradation products to peritoneal injury in a rat peritoneal exposure model.

METHODS

Rats received daily 10 ml of either heat-sterilized (3.86% glucose, pH 5.2, n = 8) or filter-sterilized PD fluid (3.86% glucose, pH 5.2, n = 8), or lactate buffer (pH 5.2, n = 8) via a mini vascular access port during a 10 week period. Untreated rats served as controls.

RESULTS

The low pH lactate buffer instillation induced pronounced morphological changes including the induction of angiogenesis in various peritoneal tissues and mild damage to the mesothelial cell layer covering the peritoneum. It also evoked a cellular response characterized by an increased mesothelial cell density on the liver, the induction of milky spots and accumulation of omental mast cells in the omentum, and significant changes in the composition of peritoneal leukocytes. The addition of glucose to low pH lactate buffer (filter-sterilized PD fluid) strengthened most, but not all of the responses described above and induced a fibrogenic response. In addition to glucose and low pH lactate buffer, the presence of glucose degradation products (heat-sterilized PD fluid) significantly induced an additional omental milky spot response (P < 0.03) and caused profound mesothelial damage. The vessel density in the omentum and the mesentery was significantly correlated to both the number of tissue mast cells and the hyaluronan content in the peritoneal lavage, which might suggest a role for mast cells and hyaluronan in the induction of angiogenesis.

CONCLUSIONS

Instillations of low pH lactate buffer, a high glucose concentration and glucose degradation products contribute differently and often cumulatively to peritoneal injury in vivo.

Effects of bicarbonate buffered dialysate on human peritoneal mesothelial cell intracellular calcium homeostasis

This study compares the biocompatibility of two bicarbonate-based peritoneal dialysis (PD) solutions using the measurement of intracellular free calcium (Ca(i)2+)) as a sensitive parameter of cell function in human peritoneal mesothelial cells (hPMC). Fura-2-loaded hPMC suspensions were exposed to bicarbonate (38 mmol/L) and bicarbonate (25 mmol/L), lactate-buffered PD (15 mmol/L) solutions at pH 7.4 and compared with Krebs-Ringer physiological saline (KRS; pH = 7.4). Resting Ca(i)2+ values and 4br-A23187 (1.0 micro mol/L) induced transients were compared in treatment and control groups. In separate studies, the effect that low saline pH had on Ca(i)(2+) homeostasis was examined. Suspended cells or cells attached to coverslips were bathed in citric acid-phosphate (McIllvaine's) buffered saline (MBS, pH = 7.4). Cells were acidified (pH = 5.3) with citric acid and then challenged with ionophore. Ionophore challenge produced a significantly reduced Ca(i)2+ transient response in cells exposed to the bicarbonate/lactate fluid compared with bicarbonate or KRS. Acidified cell suspensions produced a small monophasic Ca(i)2+ transient rise that was short lived. Gradual recovery of MBS to pH 7.4 produced no changes to Ca(i)2+ homeostasis of cell monolayers. Ionophore treatment produced a biphasic response identical to cells bathed in KRS. This study has demonstrated that short-term exposure to bicarbonate did not alter Ca(i)2+ homeostasis directly, or subsequent modulation of intracellular pH. The MBS system provided a reliable method of modifying the external pH during continuous Ca(i)2+ measurement.