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

Impact of systemic and local peritoneal inflammation on peritoneal solute transport rate in new peritoneal dialysis patients: a 1-year prospective study

BACKGROUND

The association between peritoneal solute transport rates (PSTRs) and inflammatory markers in patients on peritoneal dialysis (PD) is still under investigation. We aimed to elucidate their relationship during the first year on PD.

METHODS

We performed a prospective observational study with 187 incident PD patients who were treated with either biocompatible solution (BCS) or conventional solution (CS). Peritoneal dialysate effluent (PDE) and blood samples for the markers and the calculation of mass transfer area coefficient of creatinine (MTAC) were performed at 1, 6 and 12 months after commencing PD.

RESULTS

Of the 187 enrolled patients, 110 completed a 1-year study protocol. All PDE markers [interleukin-6 (IL-6), transforming growth factor-beta (TGF-beta), TGF-beta-induced gene-h3 (beta ig-h3), vascular endothelial growth factor (VEGF)] except CA125 increased over time, whereas PSTRs, high-sensitivity C-reactive protein (hs-CRP) and serum IL-6 levels did not change. Serum albumin and log PDE appearance rates (ARs) of IL-6, TGF-beta and CA125 predicted MTAC. The Delta value (12-month minus 1-month) of PDE AR of IL-6 was correlated with those of all other PDE markers. Both 12-month IL-6 and Delta IL-6 ARs in PDE were highest in the upper Delta MTAC tertile. PSTRs in the CS group, unlike BCS, had a tendency to increase over time, demonstrating a time-by-group interaction. Solution type and MTAC were not associated with patient and technique survival.

CONCLUSIONS

The change in PSTR during the first year of PD is related to PDE IL-6 AR, which may represent intraperitoneal inflammation; however, there does not seem to be a close association between PSTR and the degree of systemic inflammation.

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.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSION

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

Effects of Peritoneal Dialysis Solutions Low in GDPs on Peritonitis and Exit-Site Infection Rates

Background

Peritoneal dialysis (PD) solutions sterilized at a low pH level contain only minimal amounts of glucose degradation products (GDPs). The latter are known to have an adverse effect on the peritoneal membrane. The present study retrospectively analyzes the effects on the incidences of peritonitis and exit-site infections.

Materials and Methods

Data concerning the frequency of peritonitis and exit-site infections for 120 patients treated with PD were collected. Before 2000, 67 of these patients received conventional dialysates and from 2000 on, 53 patients were treated with the new dialysis fluids. Furthermore, a correlation between the incidence of infections and the duration of treatment with dialysis was established.

Results

It was observed that the use of dialysis solutions low in GDPs resulted in significantly lower rates of peritonitis ( p = 0.002) and exit-site infections ( p = 0.02). When using the new treatment, peritonitis occurred, on average, after 48 months of treatment and exit-site infections after 34 months of treatment.

Discussion

The result supports the hypothesis that the use of the new, biocompatible, PD solutions contributes to considerable reduction in the rates of peritonitis and exit-site infections. As it is not expected that randomized prospective studies will be conducted in the future, further observational studies should be carried out in order to affirm the observed tendencies.

Monitoring of the peritoneal membrane

Background. Indirect methods can be used to provide valuable information about peritoneal structure and function for the indirect analysis of peritoneal membrane. Methods. The focus of this paper will be on the commonly available tools for this purpose. First, the value and clinical relevance of CA125 as a marker of mesothelial cell mass in peritoneal effluent will be evaluated. Thereafter, monitoring the peritoneal membrane by using its properties to transport solutes and water will be discussed. Results. The data obtained can be useful for tailoring dialysis adequacy, analysis of clinical problems such as ultrafiltration failure or to predict the development of peritoneal sclerosis.

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

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

The alteration of dialysate cancer antigen 125 concentration under a biocompatible bicarbonate peritoneal dialysis solution and the preservation of the mesothelial cell viability

BACKGROUND

The importance to maintain the peritoneal membrane integrity for peritoneal dialysis (PD) patients by using biocompatible solutions (with low or no glucose as osmotic factor and low in glucose degradation products-GDPs, without lactate as a buffer and with normal pH) becomes progressively more evident. The aim of the present study was to investigate the clinical effects of a novel bicarbonate-based biocompatible PD fluid, evaluating the alteration in the concentrations of dialysate marker CA125, a glucoprotein indicator of mesothelial cell mass. PATIENTS AND METHODS; This is a single-center, prospective cohort study of 12 stable CAPD patients (4 women, 8 men), mean age 71.3 +/- of 6.01 years, mean PD duration 31.9 +/- 21.33 months, treated with the usual conventional PD solutions (with increased GDPs, low pH, and lactate as a buffer system). After a six-month period, the patients changed for the next six-month period into bicarbonate PD solutions (BicaVera, Fresenius), after which they returned into their previous schema of conventional solutions for another six months. The dialysate marker of CA125 was repeatedly estimated at the beginning of the study (T0), after six months phase with the bicarbonate solutions (T6), and at the end of study (T12), after the second six-month use of the conventional PD solutions. All the samples were taken at the end of a four-hour dwell of an exchange with PD solution 2.5% glucose.

RESULTS

The dialysate mean value of CA125 at the beginning of the study (Td0-with conventional PD solutions) was 15.07 +/- 5.72U/mL. After six months with bicarbonate PD solutions, the mean CA125 value increased to 111.97 +/- 66.21U/mL, while the mean values dropped again to 22.72 +/- 16.06 U/mL at the end of the study, after the patients' return for another six months to the conventional solutions use. There was a statistically significant difference between the mean CA125 levels at the beginning (Td0) and the middle of the study (Td6; p = 0.00079) as well as between the mean levels of CA125 in the middle (Td6) and at the end of the study (Td12; p = 0.0014). In contrast, comparing the mean dialysate values of CA125 at the beginning (Td0) and at the end of the study (Td12), no statistically significant difference was revealed (p = 0.13).

CONCLUSIONS

For the use of the bicarbonate-based PD, more biocompatible solutions for six months produced a statistically significant increase in the dialysate concentration of the mesothelial cell mass indicator CA125. The decrease at the end of the study of CA125 mean value at a level similar with that observed at the beginning, after the six-month period of the conventional PD solutions, indicates that the clinical use of the new bicarbonate-based PD solutions may have an advantageous role in the preservation of peritoneal cell mass, maintaining also the integrity and longevity of the peritoneal membrane.

Peritoneal membrane structural and functional changes during peritoneal dialysis

Peritoneal dialysis is now utilized as a renal replacement therapy modality in a substantial percentage of patients with end-stage renal disease, with excellent short-term patient and technique survival rates. However, the potential complications associated with longer-term therapy, such as ultrafiltration failure or encapsulating peritoneal sclerosis, have led to raise some concern about peritoneal dialysis as an adequate mode of treatment of end-stage renal disease in the long term. In the last decade, a substantial amount of information has been gathered on the characteristics of the peritoneal membrane at the onset of peritoneal dialysis, and on the anatomical and pathophysiologic changes that occur with long-term peritoneal dialysis. I will review this subject with a special focus on the various strategies that can help protect the peritoneal membrane during peritoneal dialysis so as to allow peritoneal dialysis to succeed as a long-term dialysis modality.

Effects of Ionized Sodium Concentrations on Ultrafiltration Rate in Peritoneal Dialysis Using Lactate and Lactate/Bicarbonate Solutions

Objective

To investigate the possible effects of different concentrations of ionized sodium (NaI) on peritoneal ultrafiltration (UF) rate using lactate (Lac) and lactate/bicarbonate (Lac/Bic) dialysis solutions.

Design

Two random consecutive (after an interval of 48 hours) peritoneal equilibration tests (PETs) were performed in 13 patients (4 males and 9 females) on regular continuous ambulatory peritoneal dialysis (PD) treatment for at least 3 months. Two different PD solutions containing anhydrous glucose 3.86% were used: a 40 mmol/L Lac solution and a 15/25 mmol/L mixed Lac/Bic solution. Concentrations of total sodium (NaT) and NaI were measured by flame photometer and direct ion-selective electrode respectively.

Results

Dialysate concentrations of NaT were not different during PETs using Lac and Lac/Bic. Dialysate concentrations of NaI in fresh PD solutions were different (133.3 ± 1.7 vs 128.2 ± 3.9 mmol, p < 0.0001); however, these differences disappeared just after the end of the infusion of the fresh solutions. Peritoneal UF rate was not significantly different during PETs using Lac versus Lac/Bic (609 ± 301 mL vs 542 ± 362 mL). The dialysate-to-plasma ratios of sodium concentrations at 60 minutes of the PETs (which are expressions of free water transport) were not different using Lac versus Lac/Bic (0.89 ± 0.04 vs 0.89 ± 0.04 respectively, p = 0.96). All the other classical parameters of the PET were not different between Lac and Lac/Bic.

Conclusions

The higher dialysate concentrations of NaI due to lower dialysate pH and consequently the higher effective osmolality of the fresh Lac PD solutions did not influence peritoneal UF rate, probably because of the fast reduction of NaI concentrations due to rapid correction of dialysate pH at the end of the infusion of Lac solutions into the peritoneal cavity.

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.

Effects of low glucose degradation products peritoneal dialysis fluid on the peritoneal fibrosis and vascularization in a chronic rat model

In the present study, we examined the effects of a new peritoneal dialysis fluid (PDF) with a low level of low glucose degradation products (GDP) on the functional and structural stability of the peritoneal membrane (PM). Male Sprague-Dawley rats were divided into three groups: group C (n = 8), without dialysate infusion; group P (n = 12), infused with low-level GDP solution (4.25% Physioneal, pH 7.0-7.4); and group D (n = 12), infused with conventional solution (4.25% Dianeal, pH 5.2, adjusted to pH 7.0). In groups D and P, animals were infused through a permanent catheter with 25 mL of PDF, twice daily for 8 weeks. Lipopolysaccharide was added into the PDF immediately before infusion on days 8, 9 and 10 in the two dialysis groups. When compared with group P, group D showed a higher glucose mass transfer at weeks 6 and 8, D/P urea at week 8, TGF-beta1 at weeks 4 and 8, and VEGF level at week 8. The submesothelial matrix layer of the parietal peritoneum was significantly thickened in group D and the lectin-stained blood vessels in this layer were well-visualized in group D compared with group P. There were significantly more peritoneal blood vessels in group D than group P. The transforming growth factor-beta induced gene-h3 (betaig-h3) and TGF-beta1 levels in the peritoneal effluent correlated with the submesothelial thickness, which correlated with the dialysate-to-plasma ratio (D/P) of protein and, inversely, with the rate of glucose transport (D/D(0) glucose, where D is glucose concentration in the dialysate and D(0) is glucose concentration in the dialysis solution before it is infused into the peritoneal cavity). The present study showed that low-GDP PDF effectively attenuated the peritoneal vascularization and fibrosis related to conventional solution.

Changing prescribing practice in CAPD patients in Korea: increased utilization of low GDP solutions improves patient outcome

BACKGROUND

Novel, biocompatible peritoneal dialysis (PD) solutions have become available in recent years. In 2001, low glucose degradation products (GDP), neutral pH solutions became commercially available in Korea. To date, there are no reports regarding the large scale adoption of these solutions in clinical practice and regarding what, if any, impact these solutions have on patient outcomes.

METHODS

Using a database of almost 4000 patients treated by PD in Korea, we conducted a prospective, longitudinal observational study documenting the patterns of use of one novel low GDP solution (balance, Fresenius Medical Care, St Wendel, Germany) in 1909 PD incident patients between 1 January 2002 and midyear 2005. Outcomes including patient and technique survival and peritonitis rates were analysed using univariate and multivariate analysis.

RESULTS

Prescription of low GDP solutions reached between 70 and 80% by the year 2003 and persisted at this level. Patients prescribed low GDP PD solution tended to be younger and were more likely to be treated in centres with larger enrollment in the database. Survival of diabetic patients treated with the new PD solution was identical to that of the non-diabetic patients treated with standard PD fluids (PDF) and treatment with low GDP PDF independently reduced the relative risk (RR) of death (RR = 0.613; CI 0.50-0.74; P < 0.00001) in a proportional hazards model which included age, diabetes and centre experience. In a univariate analysis, low GDP PD solution was associated with a longer technique survival (P = 0.049) but this effect was not significant in multivariate analysis. No significant differences in peritonitis-free interval or peritonitis rate could be attributed to the prescribed PDF.

CONCLUSION

Prescription of low GDP, pH-neutral PD solutions has rapidly increased in Korea. This change has resulted in a significant improvement in patient and technique survival without any measurable change in peritonitis incidence or rate. Reasons for the improved patient survival cannot be determined from this analysis and require further study.

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

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

Pyridoxamine improves functional, structural, and biochemical alterations of peritoneal membranes in uremic peritoneal dialysis rats

BACKGROUND

We previously suggested that biochemical alterations of peritoneal membrane associated with long-term peritoneal dialysis might be, at least in part, accounted for by reactive carbonyl compounds overload originating both from uremic circulation and heat sterilization of glucose peritoneal dialysis fluid. In the present study, we utilized a uremic rat model on peritoneal dialysis and evaluated the protective effects of pyridoxamine, a recently developed inhibitor of advanced glycation end product (AGE), on structural, functional, and biochemical alterations of peritoneal membrane.

METHODS

Uremic rats were generated by subtotal nephrectomy, some of which were undergone peritoneal dialysis with dialysate and/or given intraperitoneal pyridoxamine. Functional [dialysate/plasma ratio (D/P)(urea, creatinine), D/D(0 glucose)], structural (density of blood vessels in peritoneal membrane tissues), and molecular biochemical [formation of pentosidine, an AGE, by high-performance liquid chromatography (HPLC) assay and expressions of vascular endothelial growth factor (VEGF), and fibroblast growth factor 2 (FGF-2), by semiquantitative polymerase chain reaction (PCR) and/or immunohistochemistry] alterations of peritoneal membrane were assessed.

RESULTS

Uremic peritoneal membrane was characterized by an increased functional area of exchange for small solutes between blood and dialysate, vascular proliferation, increased AGE genesis, and up-regulated expressions of angiogenic cytokines. The peritoneal membrane alterations associated with peritoneal dialysis are similar but more severe than those in uremia without peritoneal dialysis. Pyridoxamine given in uremic rats with peritoneal dialysis significantly improved functional and structural alterations. This improvement was accompanied by reduction of AGE accumulation and of angiogenic cytokines expressions.

CONCLUSION

Peritoneal carbonyl stress derived from uremia as well as peritoneal dialysis procedure might contribute to the vascular proliferation through induction of bioactive molecules and to an increased functional area, eventually leading to ultrafiltration failure. Pyridoxamine may be beneficial in protection of uremic peritoneal membrane on peritoneal dialysis.

Peritoneal Dialysis: A Viable Renal Replacement Therapy Option

The number of patients with end-stage renal disease requiring dialysis has increased markedly over the last decade and continues to grow at an alarming rate in the United States. Of the currently available dialysis options for end-stage renal disease (hemodialysis and peritoneal dialysis), peritoneal dialysis (PD) is underutilized in the United States for nonmedical reasons. In fact, PD is the less expensive dialysis modality and may provide a survival advantage over hemodialysis in first 2 to 4 years of treatment, but that advantage is not as robust with increasing age and with the presence of diabetes. Moreover, the initial survival advantage is lost in long-term PD, mainly owing to changes in the peritoneal membrane from the use of conventional bio-incompatible PD solutions. Current data suggest that not many patients continue on PD beyond 10 years. The recent development of a more biocompatible PD solution should help to preserve membrane function, promote ultrafiltration, improve nutritional status, and, it is hoped, prolong the survival advantage of PD. Identification of molecular mechanisms involved in cellular responses leading to peritoneal fibrosis and angiogenesis evokes new therapeutic strategies that might protect the peritoneal membrane against the consequences of long-term PD.

Limitations of CA125 as an index of peritoneal mesothelial cell mass

BACKGROUND

CA125 is commonly used as an index of the mesothelial cell mass in patients treated with peritoneal dialysis. However, we have no data that show a direct relationship between the number of mesothelial cells, their functional properties, and the amount of CA125 produced in these cells.

METHODS

Experiments were performed on primary in vitro cultures of human peritoneal mesothelial cells obtained from 32 donors of various ages and of both sexes. Spontaneous release of CA125 from the confluent mesothelial cells was measured and correlated with the number of cells in monolayers and with their functional properties. We also studied acute effects of cytokines (IL-1beta, TNF-alpha, and INF-gamma) and the chronic effects of glucose (45 mM) on the CA125 content in mesothelial cells and the release of this antigen from their cytosol.

RESULTS

Cells from older donors released more CA125, but we found no correlation between the number of cells and the amount of CA125 released from their cytosol. The synthesis of CA125 in mesothelial cells does not correlate with the amount of monocyte chemoattractant protein 1 or interleukin-6 produced in these cells. Acute exposure to cytokines did not modify CA125 content or its release from mesothelial cells. Chronic exposure of mesothelial cells for 4 weeks to glucose (45 mM) decreased the CA125 content of their cytosol and the release of this antigen into the culture medium. Mannitol, at the same concentration and under the same conditions, did not produce these effects, namely a decrease in the CA125 content in the cytosol or its release into the cultural medium.

CONCLUSIONS

The amount of CA125 released from mesothelial cells is not a good index of their number or their functional properties, because the CA125 release depends not only on the number of cells, but also on their properties. Furthermore, the process is affected by the age of the cell donor and environmental factors such as a high glucose content. The results of this study show the limitations of CA125 as an index of the mesothelial cell mass and viability.

La biocompatibilité des solutions de dialyse péritonéale

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

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

BACKGROUND

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

METHODS/DESIGN

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

Oxidative stress induced by iron released from transferrin in low pH peritoneal dialysis solution

BACKGROUND

Transferrin binds extracellular iron and protects tissues from iron-induced oxidative stress. The binding of iron and transferrin is pH dependent and conventional peritoneal dialysis (PD) solutions have unphysiologically low pH values. Herein, we investigated whether conventional PD solution releases iron from transferrin and if the released iron causes oxidative stress.

METHODS

Effects of PD solutions on iron binding to transferrin were examined with purified human transferrin and transferrin in dialysates drained from PD patients. Oxidative stress induced by iron released from transferrin was evaluated in terms of the formation of thiobarbituric acid reactive substance (TBARS) and protein carbonylation in the human red blood cell (RBC) membrane. The iron deposition in peritoneal tissue from PD patients was evaluated by Perls' staining with diaminobenzidine intensification.

RESULTS

Low pH PD solution released iron from transferrin. This iron release occurred within 1 min. Iron release was not observed in neutralized PD solution. Iron released from transferrin in low pH PD solution increased TBARS formation and protein carbonylation in the human RBC membrane. Iron deposition, which is prominent in the fibrotic area facing the peritoneal cavity, was observed in the peritoneum of PD patients.

CONCLUSIONS

Iron released from transferrin in low pH PD solution can produce oxidative stress in the peritoneum of a PD patient. Neutralizing PD solution can avoid this problem. Iron deposition in the peritoneum may participate in the pathogenesis of peritoneal fibrosis in PD patients.

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.

The Euro-Balance Trial: The effect of a new biocompatible peritoneal dialysis fluid (balance) on the peritoneal membrane

BACKGROUND

Although peritoneal dialysis (PD) is a widely accepted form of renal replacement therapy (RRT), concerns remain regarding the bioincompatible nature of standard PD fluid. In order to evaluate whether a newly formulated fluid of neutral pH, and containing low levels of glucose degradation products (GDP), resulted in improved in vivo biocompatibility, it was compared in a clinical study to a standard PD fluid.

METHODS

In a multicenter, open, randomized, prospective study with a crossover design and parallel arms, a conventional, acidic, lactate-buffered fluid (SPDF) was compared with a pH neutral, lactate-buffered, low GDP fluid (balance). Overnight effluent was collected and assayed for cancer antigen 125 (CA125), hyaluronic acid (HA), procollagen peptide (PICP), vascular endothelial growth factor (VEGF), and tumor necrosis factor alpha (TNFalpha). Serum samples were assayed for circulating advanced glycosylation end products (AGE), N(epsilon)-(carboxymethyl)lysine (CML), and imidazolone. Clinical end points were residual renal function (RRF), adequacy of dialysis, ultrafiltration, and peritoneal membrane function. Eighty-six patients were randomized to either group I starting with SPDF for 12 weeks (Phase I), then switching to "balance" for 12 weeks (Phase II), or group II, which was treated vice versa. Seventy-one patients completed the study with data suitable for entry into the per protocol analysis. Effluent and serum samples, together with peritoneal function tests and adequacy measurements, were undertaken at study centers on three occasions during the study: after the four-week run-in period, after Phase I, and again after Phase II.

RESULTS

In patients treated with balance there were significantly higher effluent levels of CA125 and PICP in both arms of the study. Conversely, levels of HA were lower in patients exposed to balance, while there was no change in the levels of either VEGF or TNFalpha. Serum CML and imidazolone levels fell significantly in balance-treated patients. Renal urea and creatinine clearances were higher in both treatment arms after patients were exposed to balance. Urine volume was higher in patients exposed to balance. In contrast, peritoneal ultrafiltration was higher in patients on SPDF. When anuric patients were analyzed as a subgroup, there was no significant difference in peritoneal transport characteristics or in ultrafiltration on either fluid. There were no changes in peritonitis incidence on either solution.

CONCLUSION

This study indicates that the use of balance, a neutral pH, low GDP fluid, is accompanied by a significant improvement in effluent markers of peritoneal membrane integrity and significantly decreased circulating AGE levels. Clinical parameters suggest an improvement in residual renal function on balance, with an accompanying decrease in peritoneal ultrafiltration. It would appear that balance solution results in an improvement in local peritoneal homeostasis, as well as having a positive impact on systemic parameters, including circulating AGE and residual renal function.

Biocompatibility pattern of a bicarbonate/lactate-buffered peritoneal dialysis fluid in APD: a prospective, randomized study

BACKGROUND

In chronic ambulatory peritoneal dialysis, bicarbonate-buffered fluids, with their neutral pH and less advanced glycosylation end-products (AGE) and glucose degradation products (GDP), have better biocompatibility than conventional peritoneal dialysis (PD) solutions. That difference may be more beneficial in automated peritoneal dialysis (APD), due to its more frequent exchanges and longer contact times with fresh dialysate. We performed a prospective, randomized study in APD patients to compare the biocompatibility of conventional and bicarbonate/lactate-buffered PD fluids.

METHODS

We randomized 14 APD patients to have APD with either conventional or bicarbonate/lactate-based fluids. After 6 months, both groups changed to the other solution. The overall observation period was 12 months. After 1 and 5 months and again after 7 and 11 months, phagocytotic and respiratory burst capacities of effluent peritoneal macrophages were determined. Plasma interleukin (IL)-6 and C-reactive protein (CRP) as well as effluent IL-6, CRP, transforming growth factor (TGF)-beta 1, AGE and CA125 concentrations were measured. Inflow pain was quantified using a patient questionnaire.

RESULTS

Respiratory burst capacity remained unchanged and phagocytotic activity increased significantly during APD (P<0.001) with the bicarbonate/lactate fluid. Effluent IL-6 release was significantly lower than with the lactate fluid (P<0.05). While in the effluent TGF-beta 1 was unaffected, AGE concentration was lower after bicarbonate/lactate treatment (P<0.05). Effluent CA125 concentration, an indicator of mesothelial cell integrity, was higher (P<0.05) in neutral effluents. Finally, patients' inflow pain diminished (P = 0.05) when using the neutral fluid.

CONCLUSIONS

The use of a neutral PD fluid in APD improved patients' inflow pain as well as biocompatibility parameters reflecting enhanced phagocytotic activity of peritoneal macrophages, reduced constitutive inflammatory stimulation (IL-6), reduced AGE accumulation in the peritoneal cavity and better preservation of the mesothelial cell integrity. From the biocompatibility point of view, a neutral fluid with low GDP content can be recommended as the primary choice for APD.

Short-term biological effects of a new and less acidic fluid for peritoneal dialysis

BACKGROUND

Conventional peritoneal dialysates are potentially bioincompatible and seem to be a causative factor for peritoneal sclerosis. Recent studies demonstrated that a new type of dialysate has a positive long-term clinical effect on dialysis patients.

METHODS

In this study, to elucidate the short-term biological effects of a newly developed dialysate of higher pH on the peritoneal membrane, we assessed macrophage proportions and several markers (inflammatory cytokines, cancer antigen 125 (CA125) and albumin) in spent dialysates before and 2 weeks after the change to the new fluid from a conventional fluid.

RESULTS

We found that the use of the new dialysate decreased intraperitoneal levels of inflammatory cytokines, CA125 and albumin associated with the decrease of macrophage populations in dialysis effluents.

CONCLUSION

These observations suggest that a new and less acidic fluid reduces pro-inflammatory potential in the peritoneum, and thus affords better preservation of peritoneal membrane integrity in uremic patients on peritoneal dialysis.

Peritoneal dialysis with solutions low in glucose degradation products is associated with improved biocompatibility profile towards peritoneal mesothelial cells

BACKGROUND

In vitro experiments point to a better biocompatibility profile of new pH-neutral peritoneal dialysis fluids (PDFs) containing low levels of glucose degradation products (GDPs). The present study examines the impact on human peritoneal mesothelial cells (HPMCs) of equilibrated dialysates obtained during dialysis with either conventional or new PDFs.

METHODS

Peritoneal dialysate was collected from 17 patients participating in a randomized, controlled, cross-over trial comparing a pH-neutral low-GDP solution (Balance) to a conventional solution (S-PDF). All patients were treated sequentially for 3 months with both PDFs. At the end of each treatment phase, peritoneal effluent was drained after a timed 10 h dwell. Samples of dialysate were then mixed with standard culture medium and added to in vitro cultures of HPMCs from healthy donors. Cells were assessed for proliferation, viability and cytokine release.

RESULTS

Proliferation and viability of HPMCs were better preserved in the presence of effluent obtained during dialysis with Balance (P<0.046 and P<0.035, respectively). The proliferative response of HPMCs correlated with the concentration of fibronectin in dialysates (P = 0.0024). Effluent drained following a 3 month dialysis with Balance contained significantly increased levels of fibronectin (P = 0.004) and CA125 antigen (P = 0.0004) compared with S-PDF. There was no significant difference in constitutive and stimulated cytokine (IL-6, MCP-1, VEGF) synthesis by HPMCs treated with either Balance- or S-PDF-derived effluents.

CONCLUSIONS

These results suggest that therapy with new pH-neutral low-GDP solutions contribute to an intraperitoneal milieu that improves mesothelial cell proliferation and viability. It may positively impact on the preservation of the peritoneal membrane integrity during long-term dialysis.

Effect of peritoneal dialysis fluid composition on peritoneal area available for exchange in children

BACKGROUND

Although conventional peritoneal dialysis fluids (PDFs), such as Dianeal, are non-physiological in composition, new PDFs including Physioneal have a more neutral pH, are at least partially buffered with bicarbonate and, most importantly, contain low concentrations of glucose degradation products (GDPs).

METHODS

To evaluate the impact of new PDFs in childcare, we performed a comparative crossover study with Dianeal and Physioneal. We examined both intraperitoneal pressure (IPP), which partly reflects pain induction, and the total pore area available for exchange, which indicates the number of capillaries perfused in the peritoneal membrane at any given moment and therefore partly reflects peritoneal dialysis capacity. The IPP was determined after inflow of 1000 ml/m(2) body surface area (BSA) of dialysate (intraperitoneal volume; IPV). The steady-state unrestricted area over diffusion distance (A(0)/ triangle up x, in cm(2)/cm per 1.73 m(2) BSA) was calculated from the three-pore theory. Six children were enrolled in the study. On the first day, two consecutive peritoneal equilibration tests of 90 min each were performed using first Dianeal and then Physioneal. On the second study day, the procedure was repeated with the fluids given in the opposite order.

RESULTS

The mean IPP normalized to IPV (ml/m(2)) was significantly higher for Dianeal (9.5 +/- 0.9 cm/1000 ml/m(2)) than for Physioneal (7.9 +/- 1.2 cm/1000 ml/m(2), P < 0.01). The mean A(0)/ triangle up x was 17 +/- 4% larger with Dianeal (36 095 +/- 2009 cm(2)/cm per 1.73 m(2)) than with Physioneal (31 780 +/- 2185 cm(2)/cm per 1.73 m(2), P < 0.001; based on 24 data pairs).

CONCLUSIONS

These pilot study results suggest a higher biocompatibility for Physioneal than for Dianeal. Less inflow pain associated with Physioneal induced a lower IPP reflecting enhanced fill volume tolerance, and the lower A(0)/ triangle up x reflected less capillary recruitment. Taken together, these results suggest that the new more biocompatible PDFs will improve peritoneal dialysis therapy, although this conclusion will require verification in extended clinical trials.

Volume Control in Peritoneal Dialysis Patients: Role of New Dialysis Solutions

This paper reviews the most recent clinical data on the volume status of long-term peritoneal dialysis (PD) patients. It appears that many PD patients are volume overloaded, associated with a high prevalence of hypertension and left ventricular hypertrophy. In the presence of the poor results in patients with peritoneal ultrafiltration, the introduction of the polyglucose solution, icodextrin, has ameliorated volume control in some of these patients. In a second part of the review, some of the structural and functional alterations in the peritoneal membrane and the role of glucose degradation products (GDP) in the commonly used dialysates as well as the resulting formation of advanced glycation end products are described. The introduction of low GDP-containing solutions at normal pH has at least in experimental models of PD attenuated the hemodynamic changes observed with the classical solutions. The solutions at normal pH containing either bicarbonate or a mixture of bicarbonate/lactate were clinically associated with less inflow pain.

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.

The application of animal models to study the biocompatibility of bicarbonate-buffered peritoneal dialysis solutions

The application of animal models to study the biocompatibility of bicarbonate-buffered peritoneal dialysis solutions. Patients treated with peritoneal dialysis (PD) are at risk for development of ultrafiltration failure and peritonitis. These two significant complications can result in the termination of PD treatment. The relative unphysiologic composition of the currently used standard peritoneal dialysis fluids (PDF) is considered to be a major cause for the development of morphologic changes of the peritoneal membrane, ultimately resulting in ultrafiltration failure and probably contributing to changes in local defense mechanisms with the associated increased risk of peritonitis. In recent years, a major research focus has become the development of new and improved PD solutions. This has resulted in the development of an amino-acid-based PDF, a glucose polymer-based PDF, and several bicarbonate-buffered PDF. Typically, the first phase of biocompatibility testing of new PD solutions involves in vitro testing, employing isolated cells such as peritoneal macrophages or cell culture systems using human peritoneal mesothelial cells. The results of such evaluations are useful in providing insights into the biocompatibility performance of any given formulation, but suffer from several disadvantages, which can be better addressed using animal models. In vivo studies using animals permit the analysis of biocompatibility under conditions that allow for cell-to-cell interactions and dynamic changes in solution composition that more closely mimic the clinical situation. In this paper, we will review the use of animal models for the study of PDF biocompatibility and their application to the assessment of bicarbonate-buffered PDF.

Clinical indices of in vivo biocompatibility: The role of ex vivo cell function studies and effluent markers in peritoneal dialysis patients

Clinical indices of in vivo biocompatibility: The role of ex vivo cell function studies and effluent markers in peritoneal dialysis patients. Over the past 20 years, studies of the biocompatibility profile of peritoneal dialysis solutions (PDF) have evolved from initial in vitro studies assessing the impact of solutions on leukocyte function to evaluations of mesothelial cell behavior. More recent biocompatibility evaluations have involved assessments of the impact of PDF on membrane integrity and cell function in peritoneal dialysis (PD) patients. The development of ex vivo systems for the evaluation of in vivo cell function, and effluent markers of membrane integrity and inflammation in patients exposed both acutely and chronically to conventional and new PDF will be interpreted in the context of our current understanding of the biology of the dialyzed peritoneum. The available data indicate that exposure of the peritoneal environment to more biocompatible PDF is associated with improvements in peritoneal cell function, alterations in markers of membrane integrity, and reduced local inflammation. These data suggest that more biocompatible PDF will have a positive impact on host defense, peritoneal homeostasis, and the long-term preservation of peritoneal membrane function in PD patients.

Recent concepts in the molecular biology of the peritoneal membrane - implications for more biocompatible dialysis solutions

This paper reviews some important recent findings on the molecular biology of the peritoneal membrane. It attempts to correlate in vitro and in vivo experimental results with the possible clinical consequences. The most common functional alteration during long-term CAPD is increased peritoneal small-solute transport rate, resulting in impaired ultrafiltration and decreased dialysis efficiency. This contribution first discusses the most relevant advances in the biochemistry and molecular biology of the peritoneal membrane following peritonitis and as consequence of the continuous exposure to unphysiological dialysis fluids. In a second part the preliminary experimental and clinical experience with more biocompatible fluids is summarized. The most relevant structural and functional alterations of the membrane following repeated peritonitis is the consequence of the response of the peritoneum to infective organisms involving the inflammatory cytokines and the interaction between membrane resident cell populations: macrophages, mesothelial cells and fibroblasts. In this setting, human biopsy studies and animal experiments have identified an increase in the peritoneal-associated vasculature, which seems to be the primary cause of increased solute transport. The structural and functional alterations in the membrane in long-term peritoneal dialysis are thought to be the consequence of the toxicity of glucose, either directly or indirectly through the generation of glucose degradation products or the formation of advanced glycation end-products. In particular, an important role for vascular endothelial growth factor and nitric oxide as downstream mediators of the alterations has been suggested. Finally, the last part of this paper reviews the actual and future research aimed at an amelioration of the biocompatibility of the dialysis fluids. Replacing glucose by other osmotic agents, changing the sterilization process, replacing the lactate buffer by bicarbonate, blocking the formation of reactive carbonyl products and of the neoangiogenesis are the most promising changes to enhance the biocompatibility. Finally, gene therapy may in the future have an important contribution. Ex vivo gene therapy involves harvesting peritoneum samples to isolate mesothelial cells that will be genetically modified before re-implantation into the peritoneal cavity.

Glucose degradation products (GDP) retard remesothelialization independently of d-glucose concentration

BACKGROUND

Glucose degradation products (GDP) present in heat-sterilized dialysis fluids are thought to contribute to cellular dysfunction and membrane damage during peritoneal dialysis. To examine the effects of specific GDP on the remesothelialization process, the impact of conventional and low GDP peritoneal dialysis solutions, D-glucose, and individual GDP in a scratch-wounding model was assessed.

METHODS

Scratch (0.5 to 0.6 mm)-wounded human peritoneal mesothelial cells (HPMC) were treated, at pH 7.4, with either (1) control medium (M199), (2) laboratory-prepared heat or filter-sterilized solutions, (3) 10% to 80% vol/vol solution of Gambrosol or Gambrosol-trio (1.5% and 4.0% glucose), (4) D-glucose (5 to 80 mmol/L), or (5) individual or combined GDP [acetaldehyde, formaldehyde, glyoxal, methylglyoxal, 3-deoxyglucosone (3-DG), 5-hydroxy methylfufural (5-HMF), or 3,4-di-deoxyglucosone-3-ene (3,4-DGE)]. Wound closure was recorded by time-lapse photomicroscopy.

RESULTS

In untreated HPMC, the rate of wound closure was linear and the process was complete by 18.4 +/- 3.6 hours (N = 16). In wounded HPMC exposed to dilutions of heat-sterilized but not filtered laboratory solutions (1.5% or 4.0% glucose, pH 7.4), remesothelialization was significantly retarded (P = 0.04 and P = 0.009 vs. M199, respectively). In Gambrosol, remesothelialization was significantly retarded in both 1.5% and 4.0% solutions. In contrast in Gambrosol-trio-treated HPMC, this rate was not significantly reduced in either 1.5% or 4.0% glucose peritoneal dialysis fluids. Remesothelialization was dose-dependently retarded in HPMC exposed to 3,4-DGE (>10 microl/L), formaldehyde (>5 micromol/L) but not by exposure to the other GDP tested even at 5 times the concentration present in low glucose solutions. The rate of remesothelialization was not significantly altered by exposure to D-glucose concentrations up to 80 mmol/L.

CONCLUSION

These data identify that the formaldehyde and 3,4-DGE present in heat-sterilized peritoneal dialysis solutions are important in reducing mesothelial cell regeneration. Specifically targeting their removal may have major benefits in preserving the mesothelium during long-term peritoneal dialysis.

Low glucose degradation products dialysis solution modulates the levels of surrogate markers of peritoneal inflammation, integrity, and angiogenesis: preliminary report

The presence of glucose degradation products (GDPs) in peritoneal dialysis (PD) fluids has many adverse effects, namely clinically significant abdominal pain or discomfort during infusion, inhibition of cell proliferation, impairment of inflammatory cell function, cytotoxicity, and the induction of vascular endothelial growth factor (VEGF). In a prospective, randomized, controlled trial comparing a low GDP PD solution (pH 7.0, two compartment bag: low GDP) to conventional PD solution (pH 5.5: high GDP), the overnight dialysate levels of the markers of inflammation/wound healing (hyaluronic acid (HA)), mesothelial cell mass/membrane integrity (cancer antigen 125 (CA125)), and angiogenesis (VEGF) were assessed over a 12-month period. Twenty-six newly commencing continuous ambulatory peritoneal dialysis (CAPD) patients were randomly assigned to either the Low GDP group (n = 16) or the High GDP group (n = 10). Standard peritoneal permeability analysis for membrane transport characteristics and dialysis adequacy with nutritional status (serum albumin, nPCR) were evaluated at 1, 6, and 12 months. In patients treated with high GDP solution, there was significant increase in VEGF with time (time = 1 month, 67.2 +/- 10.8; time = 6 months, 189.8 +/- 90.2; and time = 12 months, 169.3 +/- 83.1 pg/mg of protein; P < 0.05). There was no significant change of VEGF with time in the low GDP group. Significantly higher concentrations of CA125 (65.5 +/- 10.4 vs. 19.7 +/- 2.6 at 1 month, P < 0.0001; 66.6 +/- 9.8 vs. 29.7 +/- 5.0 at 6 months, P < 0.01; 68.7 +/- 10.5 vs. 30.7 +/- 10.0 U/mL at 12 months, P < 0.01) and lower concentrations of HA (114.6 +/- 18.8 vs. 254.3 +/- 69.2 at 1 month, P < 0.05; 417.5 +/- 57.2 vs. 1277.5 +/- 367.9 ng/mg of protein at 12 month, P < 0.05) were observed in the low GDP group compared with the high GDP group. In conclusion, continuous therapy with the low GDP solution modulates the levels of surrogate markers of peritoneal inflammation, integrity and angiogenesis. The results strongly suggest that the use of a low GDP solution would be beneficial to maintain the function and structural integrity of the peritoneal membrane.

Improved Acidosis Correction and Recovery of Mesothelial Cell Mass with Neutral-pH Bicarbonate Dialysis Solution among Children Undergoing Automated Peritoneal Dialysis

ABSTRACT. Acid-base balance and peritoneal membrane longevity are of utmost relevance for pediatric patients undergoing peritoneal dialysis (PD). PD fluids with neutral pH and reduced glucose degradation product contents are considered more biocompatible, because they preserve peritoneal cell functionsin vitro. To investigate the clinical effects of a novel PD fluid buffered with 34 mM pure bicarbonate at neutral pH, a randomized, prospective, crossover comparison with conventional, acidic, 35 mM lactate PD fluid was performed for two consecutive 12-wk periods with 28 children (age, 6 mo to 15 yr) undergoing automated PD (APD). Blood bicarbonate levels and arterial pH were significantly higher after 3 mo of bicarbonate PD (24.6 ± 2.3 mM and 7.43 ± 0.06, respectively), compared with lactate PD (22.8 ± 3.9 mM and 7.38 ± 0.05, respectively;P< 0.05). This effect was reversible among patients who returned from bicarbonate to lactate fluid. Low initial pH and young patient age independently predicted increased blood pH during bicarbonate APD. Peritoneal equilibration tests revealed subtle changes in solute transport, with a less steep creatinine equilibration curve during bicarbonate dialysis, suggesting reduced peritoneal vasodilation. The peritoneal release of carcinogen antigen-125 increased twofold during bicarbonate APD (29 ± 15versus15 ± 8 U/ml per 4 h,P< 0.01), which is consistent with recovery of the mesothelial cell layer. This effect was fully reversed when the patients returned to lactate fluid. Effluent carcinogen antigen-125 levels were inversely correlated with peritoneal glucose exposure during lactate but not bicarbonate APD, indicating improvedin vivomesothelial cell tolerance of high-dose glucose with the neutral-pH PD fluid with reduced glucose degradation product content. Among children undergoing APD, neutral-pH, bicarbonate-buffered PD fluid provides more effective correction of metabolic acidosis and better preservation of peritoneal cell mass than do conventional, acidic, lactate-based fluids. E-mail: franz_schaefer@med.uni-heidelberg.de

Short- and Medium-Term Increase of CA125 in Peritoneal Effluent using a Neutral-pH Solution

♦ Objective

To investigate the effects of an alternative peritoneal dialysis (PD) solution composed of a lactate/bicarbonate (Lac/Bic) mixture (35/2 mmol/L), pH 7.0, on the appearance of cancer antigen 125 (CA125) in the peritoneal effluent.

♦ Methods

Eight stable PD patients received a conventional solution containing 35 mmol/L lactate (Lac) for 11.9 ± 9.2 months, and then changed to Lac/Bic for 3.1 ± 0.7 months. Each patient acted as his/her own control.

♦ Results

We studied 4 males and 4 females with a mean age of 57.4 ± 16.8 years. Higher concentrations (U/mL) ( p < 0.005) and appearance rates (AR) (U/min) ( p < 0.05) of CA125 in the dialysate were observed with Lac/Bic than with Lac, during the sampling times of the peritoneal equilibration test (10, 120, and 240 minutes) and in the overnight effluent: CA125 5.7 versus 0.6, 18.9 versus 1.9, 29.7 versus 3.7, and 43.2 versus 5.5 U/mL; and AR 1177 versus 125, 354 versus 36,297 versus 37, and 194 versus 26 U/min, respectively. Mean CA125 content in the 24-hour dialysate was 34.2 U/min (baseline) and 30.9 U/min (11.9 months) with Lac, and 207.9 U/min and 185 U/min after 1.6 and 3.1 months with Lac/Bic ( p = 0.009). The intraperitoneal pH was more physiological during the dwell with the Lac/Bic solution.

♦ Conclusions

The CA125 levels in the peritoneal effluent with Lac/Bic are an effect of the solution's neutral pH, as other factors of the prescription were constant. The Lac/Bic solution is more biocompatible than Lac, reflecting short- and medium-term changes in the mesothelial cells, whose clinical significance has not yet been determined.

Mesothelial Toxicity of Peritoneal Dialysis Fluids is Related Primarily to Glucose Degradation Products, Not to Glucose Per Se

♦ Objectives

High concentrations of glucose and/or formation of glucose degradation products (GDPs) during heat sterilization of peritoneal dialysis fluids (PDFs) are believed to be key factors in the limited biocompatibility of PDFs. We have previously shown that several identified GDPs can specifically impair human peritoneal mesothelial cell (HPMC) function. In the present study we aimed at differentiating the respective roles of glucose and GDPs in the toxicity of PDF to mesothelial cells.

♦ Methods

HPMCs were acutely pre-exposed to or incubated chronically in the presence of pH-neutral PDF sterilized by either heat (H-PDF) or filtration (F-PDF). In addition, HPMCs were treated with commercially available H-PDF manufactured either conventionally, that is, in single-chamber containers, or using novel dual-chamber bags that help to substantially decrease GDP formation. Functional assessment of HPMCs included viability, release of interleukin (IL)-6, and proliferation.

♦ Results

Viability and release of IL-6 from HPMCs pretreated with H-PDF (pH 7.3) for 1 to 4 hours were significantly reduced compared to cells exposed to corresponding F-PDF. Incubation in medium mixed (1:1) with H-PDF considerably impaired growth of HPMCs, and over a period of 10 days gradually decreased both the viability of HPMCs and their ability to generate IL-6. These effects were either absent from or significantly less in HPMCs exposed to F-PDF. Similar differences were observed when commercial GDP-containing H-PDFs were compared with newly designed H-PDFs free of GDPs.

♦ Conclusions

Impaired viability and function of HPMCs exposed to glucose-containing pH-neutral PDF is related predominantly to the presence of GDP and, to a significantly lesser extent, to the presence of glucose per se. Prevention of GDP formation during auto-claving markedly improves the biocompatibility of H-PDF with HPMCs.