Effect of two-chambered bicarbonate lactate-buffered peritoneal dialysis fluids on peripheral blood mononuclear cell and polymorphonuclear cell function in vitro

Studying the Effects of New Peritoneal Dialysis Solutions on the Peritoneum

♦ Background

Compelling data underscore the bioincompatible nature of glucose-based peritoneal dialysis (PD) solutions and their detrimental effects on peritoneal physiology and morphology. New PD solutions have been formulated to tackle common clinical problems such as inadequate ultrafiltration or malnutrition, and to improve biocompatibility—the latter aimed at preserving the structural and functional integrity of the peritoneum and reducing adverse systemic effects on the patient.

♦ Methods

This article reviews the factors in PD fluids that alter normal peritoneal anatomy and physiology, and the data that illustrate approaches to investigating the local and systemic biocompatibility of new PD solutions.

♦ Results

Chronic exposure of the peritoneal membrane to glucose-based PD solutions results in denudation of the mesothelium, thickened submesothelium, and hyalinization of the vasculature, often resulting in reduced or lost solute and water clearance. Data from in vitro or animal experiments and clinical studies have shown improved bio-compatibility profiles with new PD solutions that are glucose-free (that is, dialysates with amino acids or icodextrin), bicarbonate-buffered, or compartmentalized during heat sterilization to reduce levels of glucose degradation products. Improved biocompatibility is denoted by reduced induction of proinflammatory, profibrotic, or angiogenic growth factors in mesothelial cells and macrophages, or by less perturbation of leukocyte phagocytic function.

♦ Conclusions

Data from in vitro and animal experiments show more favorable biocompatibility profiles with new PD fluids than with glucose-based dialysates. Clinical studies are ongoing to assess the impact of the new PD fluids on peritoneal function, morbidity, and mortality.

Glucose Degradation Products and Peritoneal Membrane Function

Background

The bioincompatibility of peritoneal dialysis fluids (PDF) in current use has been partially attributed to the presence of glucose degradation products (GDPs), which are generated during heat sterilization of PDF. Several of the GDPs have been identified and we have recently demonstrated that these GDPs per se may impair the viability and function of human peritoneal mesothelial cells (HPMC) in vitro. It is also possible that GDP-related toxicity is further exacerbated by the milieu of PDF. We review the current literature on GDP and present the results of experiments comparing the impact of heat- and filter-sterilized PDF on the viability and function of HPMC.

Methods

Peritoneal dialysis fluids with low (1.5%) and high (4.25%) glucose concentrations were laboratory prepared according to the standard formula and sterilized either by heat (H-PDF; 121°C, 0.2 MPa, 20 minutes) or filtration (F-PDF; 0.2 μ). The buildup of GDP was confirmed by UV absorbance at 284 nm. Confluent HPMC monolayers were exposed to these solutions mixed 1:1 with standard M199 culture medium. After 24 hours, cell viability was assessed with the MTT assay, and interleukin-1β–stimulated monocyte chemotactic protein-1 (MCP-1) release with specific immunoassay.

Results

Exposure of HPMC to H-PDF resulted in a significant decrease in cell viability, with solutions containing 4.25% glucose being more toxic than 1.5% glucose-based PDF (27.4% ± 3.4% and 53.4% ± 11.0% of control values, respectively). In contrast, viability of HPMC exposed to F-PDF was not different from that of control cells. Moreover, treatment with H-PDF impaired the release of MCP-1 from HPMC to a significantly greater degree compared to F-PDF (17.4% and 24.9% difference for low and high glucose PDF, respectively).

Conclusions

Exposure of HPMC to H-PDF significantly impairs cell viability and the capacity for generating MCP-1 compared to F-PDF. This effect is likely to be mediated by GDPs present in H-PDF but not in F-PDF.

Bicarbonate/Lactate Dialysis Solution ImprovesIn VivoFunction of Peritoneal Host Defense in Rats

Objective

To assess the in vivo peritoneal inflammatory reaction in rats dialyzed with neutral, bicarbonatelactate-buffered dialysis fluid.

Methods

Chronic peritoneal dialysis was performed for 4 weeks in Wistar rats with two solutions: (1) 40 mmol/l lactate-buffered fluid, pH 5.2, with a glucose concentration of 2.27 gldl (lac); and, (2) 15 mmolll lactate and 25 mmolll bicarbonate-buffered fluid, pH 7.0 -7.5, with a glucose concentration of 2.27gldl (Bic-lac). After 4 weeks, two peritoneal equilibration tests (PET 1 and PET 2) were performed in all animals with each respective solution. PET 1 was done with test solutions alone, whereas, on a subsequent day, PET 2 was performed with test solutions supplemented with endotoxin [lipopolysaccharide (IPS)] to induce peritonitis.

Results

During PET 1 no consistent differences were detected in peritoneal permeability between the lac and Bic-lac groups. Total dialysate cell count in the Bic-lac animals was lower than in rats treated with lac fluid: that is, at 8 hours, the respective counts were 1858 ± 524 cellslμl versus 2785 ± 1162 cellslμl (p < 0.01). Dialysate from animals dialyzed with Bic-lac contained more macrophages (at 4 hours: 53.6% ± 35.8% versus 35.8% ± 8.8%, p < 0.001) and fewer neutrophils (at 4 hours: 3.6% ± 1.8% versus 15.4%± 6.1%, p < 0.001) as compared to those dialyzed with the lac solution. Concentration of nitrites in 8-hour dwell dialysate samples from Bic-lac rats was lower than that in the lac group (0.98 ± 0.28 μmollml versus 2.32 ± 0.87 μmollml, p < 0.002), but cytokine levels in the dialysates were comparable. During PET 2, the in -crease in peritoneal permeability resulting from the lPS induced inflammatory response was similar for both test solutions. Dialysate cell count was higher in the lac group versus the Bic-lac group (at 8 hours: 8789 ± 4862 cellslμl versus 3961 ± 581 cellslμl, p < 0.001), contained more neutrophils (at 8 hours: 80.0% ± 11.3% versus 54.8% ± 4.4%, p < 0.001) and fewer macrophages (at 8 hours: 6.8% ± 5.6% versus 21.2% ± 3.3%, p < 0.05). During peritonitis, we found a higher overall dialysate concentration of both tumor necrosis factor (TNFα: +53%, p < 0.05) and of interferon gamma (lFN-y: +303%, p < 0.02), in the Bic-lac group than in the lac group.

Conclusions

A lower dialysate cell count, higher percentage of macrophages, and lower percentage of neutrophils in dialysate suggest that Bic-lac fluid induces a diminished nonspecific inflammatory response of the peritoneal cavity during dialysis. However, after in vivo stimulation, peritoneal cells from animals dialyzed with Bic-lac solution possess an augmented ability to produce inflammatory cytokines.

Single Exposure of Mesothelial Cells to Glucose Degradation Products (GDPs) Yields Early Advanced Glycation End-Products (AGEs) and a Proinflammatory Response

← Background

Fluids commonly used for peritoneal dialysis (PD) have a low pH and a high glucose content. Furthermore, heat sterilization of dialysis fluids degrades some of the glucose into glucose degradation products (GDPs), such as methylglyoxal (MGO) and 3-deoxyglucosone (3-DG). Mesothelial cells (MCs) form the first line in the peritoneal cavity and are constantly exposed to these nonphysiological conditions. Since MCs play an important role in the regulation of inflammatory responses in the peritoneal cavity, we studied the kinetics of MC uptake of highly purified GDP species, along with their effect on various cellular biological and immunological parameters.

← Methods

Methylglyoxal and 3-DG were purified and added to MC cultures. Complexing to medium components or uptake by MCs was analyzed over time by HPLC of the culture supernatant and by immunocytochemistry of MCs for MGO-modified proteins. Furthermore, MCs were exposed to a single dose of MGO or 3-DG and analyzed for apoptosis, proliferation by MTT assay, and [3H]-thymidine incorporation. Incorporation of [35S]-methionine was determined in order to analyze de novo protein synthesis. Expression of the adhesion molecules intercellular adhesion molecule-1 (ICAM-1), CD44, and vascular cell adhesion molecule-1 (VCAM-1) was analyzed by cell-bound ELISA. Effects of MGO and 3-DG on cytokine production were also analyzed.

← Results

Substitution of MGO and 3-DG in culture medium resulted in a spontaneous decrease in MGO over time, whereas 3-DG levels decreased minimally. The concentration of these GDPs was more reduced in the presence of MCs, indicating binding to and/or uptake by MCs of these GDPs. Mesothelial cells that had been cultured in the presence of MGO showed positive staining with a monoclonal that specifically recognizes MGO-modified proteins, demonstrating complexing to mesothelial cellular proteins. Cell-bound ELISA showed a two- to threefold induction of expression of VCAM-1 by MGO and 3-DG; the expression of ICAM-1 and CD44 was not changed. Mesothelial cells showed a twofold increase in interleukin (IL)-6 and IL-8 production after exposure to 3-DG. Furthermore, incubation with MGO and 3-DG induced apoptosis and reduced the proliferation of cells, but did not influence protein synthesis.

← Conclusions

In the current report we demonstrate that MCs take up MGO and 3-DG and form early advanced glycation end-products. Upon short exposure to a single GDP, MCs react with enhanced cytotoxic damage and a proinflammatory response, evidenced by increased VCAM-1 expression and elevated production of IL-6 and IL-8.

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.

Glucose Degradation Products and the Peritoneal Mesothelium

Conventional heat-sterilized, glucose-based peritoneal dialysis (PD) fluids contain significant amounts of glucose degradation products (GDPs) such as aldehydes and dicarbonyl compounds (glyoxal, methylglyoxal). These GDPs have been shown to impair cell functions in various in vitro experimental models. In peritoneal mesothelial cells, GDPs dose-dependently inhibit cell proliferation and mediator synthesis. In addition, some GDPs potently promote generation of advanced glycation end-products (AGEs). Immunohistochemistry finds AGEs in the peritoneal membrane of chronic continuous ambulatory peritoneal dialysis (CAPD) patients, suggesting that peritoneal AGE accumulation may be involved in chronic peritoneal fibrosis.

The formation of GDPs might be prevented by filter-sterilization of PD fluids. Another option is to separate the glucose and the buffer system in dual-chambered or multi-chambered containers. In these systems, the glucose is kept in a separate compartment at high concentration and very low pH—both conditions being known to minimize the degree of glucose decomposition during autoclaving. Initial experimental evidence suggests that these novel, multi-chambered fluids significantly improve in vitro biocompatibility; however, the clinical relevance of these results remains to be established in clinical trials.

Biocompatibility of New Peritoneal Dialysis Solutions: Clinical Experience

The successful development of peritoneal dialysis (PD) during the last two decades has been made possible by using well-established glucose-based solutions with lactate as buffer. On the other hand, awareness has been increasing about the potentially negative effects of the high concentrations of glucose and lactate, and the low pH of conventional PD solutions. This awareness has prompted an intensive effort to search for and test alternative solutions.

As a result, three new, more biocompatible solutions— containing either less glucose or less lactate—are available. Amino acid–based solution uses amino acids instead of glucose as the osmotic agent; it is indicated for treatment of malnutrition. The higher pH and absence of glucose in this solution may prevent alterations of the peritoneal membrane caused by acidity and high glucose concentrations. Bicarbonate/lactate–buffered solution contains a physiologic concentration of bicarbonate and a reduced concentration of lactate; it also has a physiologic pH and markedly reduced levels of glucose degradation products (GDPs). Icodextrin-based solution contains icodextrin as the osmotic agent; it is indicated for long dwells, delivering sustained ultrafiltration for more than 16 hours. This iso-osmolar glucose-free solution may reduce peritoneal membrane alterations caused by glucose or the hyperosmolality (or both) of conventional solutions.

Clinical experience of the new solutions is now extensive, and their efficacy and safety are well documented. It therefore seems appropriate to state that we have entered a new era of PD therapy. Each of the new solutions may be less damaging to the peritoneal membrane than conventional solution. In addition, they permit better management of malnutrition and fluid status, and may thus help to improve PD patient survival.

Although the effects of each of these new solutions have been well described, clinical documentation of the combined use of these new biocompatible PD solutions is still insufficient. However, the results of studies are expected, during the coming years, to support the combined use of the new solutions as the preferred standard practice for PD.

FirstIn VitroandIn VivoExperiences with Stay·Safe Balance, A pH-Neutral Solution in a Dual-Chambered Bag

In addition to low pH and high osmolarity, glucose degradation products (GDPs) are considered to play a major role in the bioincompatibility of peritoneal dialysis fluids (PDFs). The formation of GDPs can be reduced by separating the glucose component of the solution (kept at very low pH) from the lactate component of the solution (kept at alkaline pH) during sterilization and storage. This development has been achieved by the use of a dual-chambered bag. Immediately before infusion, the seam between the two chambers is opened, and the contents are mixed. The result is a fluid with a more physiologic pH in the range 6.8 – 7.4.

Concentrations of 3-deoxyglucosone (3-DG), methyl-glyoxal (MG), acetaldehyde (AA), and formaldehyde (FA) in Stay·Safe Balance (Fresenius Medical Care, Bad Homburg, Germany) were remarkably reduced when compared to conventional PD solution [conventional PDF (1.5% glucose): 172 μmol/L, 6 μmol/L, 152 μmol/L, and 7 μmol/L respectively; Stay·Safe Balance (1.5% glucose): 42 μmolL, < 1 μmol/L, < 2 μmol/L, and < 3 μmol/L respectively; conventional PDF (4.25% glucose): 324 μmol/L, 10 μmol/L, 182 μmol/L, and 13 μmol/L respectively; Stay·Safe Balance (4.25% glucose): 60 μmol/L, < 1 μmol/L, < 2 μmol/L, and < 3 μmol/L respectively).

Human peritoneal mesothelial cells (HPMCs) were exposed to a control solution, a conventional PDF [CAPD 2, 1.5% glucose (Fresenius Medical Care, Bad Homburg, Germany)], and Stay·Safe Balance, either in a co-incubation model (24-hour PDF exposure) or in a pre-incubation model (30-min PDF exposure), followed by 24-hour recovery in culture medium. Interleukin-1β (IL-1β)–stimulated (1 ng/mL) IL-6 secretion from HPMCs was assessed by ELISA. Exposure of HPMCs to conventional PDF resulted in a significant reduction in IL-6 release, which was fully restored following exposure to Stay·Safe Balance. In addition to the short-term investigations, long-term in vitro studies were also carried out. All fluids had near-neutral pH and were changed every second day. After 1, 3, 5, 7, 10, and 13 days of exposure, cell viability was assessed. Whereas exposure to conventional PDF resulted in a significant reduction in HPMC viability after just 3 – 5 days, no significant toxicity of filter-sterilized or dual-chambered fluid was observed for up to 13 days.

An observational study with 9 patients suggested that the efficacy of Stay·Safe Balance is equivalent to that of conventional solution. However, even short-term treatment (8 ± 1 weeks) with this more biocompatible solution seems to improve mesothelial cell mass as indicated by a rise in cancer antigen 125 (CA125) from a baseline of 47 ± 37 U/ min to 172 ± 90 U/min.

Our data indicate that Stay·Safe Balance may help to better preserve peritoneal membrane cell function. An ongoing European multicenter study is expected to confirm these results.

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

Objectives

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

Methods

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

Results

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

Conclusions

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

Peritoneal Infections in Children Undergoing Acute Peritoneal Dialysis at a Tertiary/Quaternary Central Hospital in Kwazulu-Natal, South Africa

Background

In a resource-limited setting, acute peritoneal dialysis (APD) is the modality of choice as a form of renal replacement therapy in children with acute kidney injury (AKI). However, there is a high risk of peritonitis that causes significant morbidity and mortality. Data on PD and peritonitis in developing countries are scarce. The purpose of this retrospective study was to determine the prevalence of APD-related peritonitis at a central referral hospital in KwaZulu-Natal, South Africa.

Methods

A retrospective study from January 2010 until December 2014 was done at Inkosi Albert Luthuli Central Hospital (IALCH). All children under the age of 13 years with AKI requiring APD were included in the study.

Results

Forty children were included in the study. Age ranged from 0.2 years to 12.25 years; 25 (62.5%) were male and 15 (37.5%) female. Twenty-seven (67.5%) were admitted to the intensive care unit (ICU) and 13 (32.5%) to the pediatric high care ward. Septicemia with multi-organ dysfunction was the was the main cause of AKI requiring APD in 18 (45%) children followed by poststreptococcal glomerulonephritis in 8 (20%). Acute PD was complicated by culture-proven peritonitis in 19 (47.5%) children of whom 16 (84.2%) had a single organism cultured while in 3, (15.7%) there was a mixed culture. The total number of organisms cultured was 24: 8 (33.3%) were gram-positive organisms, 12 (50%) gram-negative organisms, and 4 (16.67%) fungal. The Paediatric Index of Mortality (PIM) 2 Score risk of mortality was 99.4% for patients admitted to ICU. Mortality rate was 65%, and 14 (53%) of the children who demised had peritonitis.

Conclusion

This study showed an inordinately high complication rate of peritonitis, mostly secondary to gram-negative organisms, of children undergoing APD in a central referral hospital. The use of surgically placed, tunneled catheters, meticulous attention to aseptic techniques and judicious use of antimicrobials is highly recommended in reducing the incidence of peritonitis in children undergoing APD.

Hydration Status of Patients Dialyzed with Biocompatible Peritoneal Dialysis Fluids

♦

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Peritoneal dialysis associated infections: An update on diagnosis and management

Peritoneal dialysis (PD) is associated with a high risk of infection of the peritoneum, subcutaneous tunnel and catheter exit site. Although quality standards demand an infection rate < 0.67 episodes/patient/year on dialysis, the reported overall rate of PD associated infection is 0.24-1.66 episodes/patient/year. It is estimated that for every 0.5-per-year increase in peritonitis rate, the risk of death increases by 4% and 18% of the episodes resulted in removal of the PD catheter and 3.5% resulted in death. Improved diagnosis, increased awareness of causative agents in addition to other measures will facilitate prompt management of PD associated infection and salvage of PD modality. The aims of this review are to determine the magnitude of the infection problem, identify possible risk factors and provide an update on the diagnosis and management of PD associated infection. Gram-positive cocci such as Staphylococcus epidermidis, other coagulase negative staphylococcoci, and Staphylococcus aureus (S. aureus) are the most frequent aetiological agents of PD-associated peritonitis worldwide. Empiric antibiotic therapy must cover both gram-positive and gram-negative organisms. However, use of systemic vancomycin and ciprofloxacin administration for example, is a simple and efficient first-line protocol antibiotic therapy for PD peritonitis - success rate of 77%. However, for fungal PD peritonitis, it is now standard practice to remove PD catheters in addition to antifungal treatment for a minimum of 3 wk and subsequent transfer to hemodialysis. To prevent PD associated infections, prophylactic antibiotic administration before catheter placement, adequate patient training, exit-site care, and treatment for S. aureus nasal carriage should be employed. Mupirocin treatment can reduce the risk of exit site infection by 46% but it cannot decrease the risk of peritonitis due to all organisms.

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.

Prevention of membrane damage in patient on peritoneal dialysis with new peritoneal dialysis solutions

Peritoneal dialysis (PD) is now an established and successful alternative to hemodialysis. Multiple studies have confirmed its equivalent dialysis adequacy, mortality and fluid balance status, at least for the first 4-5 years. Peritoneal membrane failure is now one of the leading cause of technique failure. This review describes the role of glucose, glucose degradation product, pH, lactate, advanced glycosylation end product (AGE) in causing this membrane damage, and gives insight how the use of newer peritoneal dialysis fluids (PDFs) containing icodextrin, amino acids and bicarbonate buffer can prevent peritoneal membrane damage.

Kinin-dependent hypersensitivity reactions in hemodialysis: metabolic and genetic factors

Although the association of angiotensin I-converting enzyme inhibitors (ACEis) with a negatively charged membrane is thought to be responsible for hypersensitivity reactions (HSRs) during hemodialysis, we hypothesize that these complications are due to changes in plasma aminopeptidase P (APP) activity and genotype. To test this hypothesis, we measured plasma APP activity in 14 patients who suffered HSR (HSR+) while dialyzed with an AN69 membrane and simultaneously treated with an ACEi. APP activity was also studied in a control group (n=39) dialyzed under the same conditions, but who did not suffer any side effect (HSR-). We found significantly decreased plasma APP activity (P=0.013) in HSR+ subjects as well as altered degradation of endogenous des-Arginine(9)-bradykinin, with a significantly lower beta value (P<0.001). The same analytical approach was taken in 171 relatives of HSR+ patients. Variance component analysis suggested that genetic differences may explain 61% of the phenotypic variability of plasma APP activity (P<0.001) and the kinetic parameters that characterized kinin degradation. We also showed that the C-2399A single-nucleotide polymorphism at the XPNPEP2 locus was a significant predictor of APP activity in the 39 HSR- controls (P=0.029). Furthermore, a recessive genetic model for the A allele disclosed a significant difference in mean APP activity by genotype (P<0.001). Finally, our study defined the nonspecific inhibition of recombinant APP by some ACEis. In conclusion, this paper highlights the complexity of HSR in hemodialysis, suggesting, as with angioedema, that these rare, but life-threatening adverse events are governed by several metabolic and genetic factors.

Benefits of switching from a conventional to a low-GDP bicarbonate/lactate-buffered dialysis solution in a rat model

BACKGROUND

Long-term exposure to standard peritoneal dialysis fluid (PDF) results in alterations in peritoneal morphology and function. Studies investigating the long-term effects on the peritoneum of a low-glucose degradation product (GDP) bicarbonate/lactate-buffered PDF demonstrated its superior biocompatibility. We examined the potential of the low-GDP bicarbonate/lactate-buffered solution to reverse or reduce standard PDF-induced peritoneal alterations.

METHODS

Female Wistar rats received twice daily intraperitoneal infusions with either a lactate-buffered solution with 3.86% glucose at pH 5.5 (Dianeal, referred to as standard PDF), or a low-GDP bicarbonate/lactate-buffered solution with 3.86% glucose at physiologic pH (Physioneal, referred to as bicarbonate/lactate PDF) for different periods of time: (1) 12 weeks Dianeal (N= 9); (2) 12 weeks Physioneal (N= 9); (3) 20 weeks Dianeal (N= 11); (4) 20 weeks Physioneal (N= 10); (5) 12 weeks Dianeal followed by 8 weeks Physioneal (N= 10).

RESULTS

Chronic standard PDF exposure resulted in loss of ultrafiltration capacity, increased VEGF expression and vascular density, higher advanced glycation end product (AGE) accumulation, up-regulation of TGF-beta expression, and development of fibrosis compared to low-GDP bicarbonate/lactate-buffered PDF. The PDF-induced alterations were time-dependent. Crossover from standard PDF to low-GDP bicarbonate/lactate PDF resulted in a less impaired ultrafiltration (UF), less pronounced VEGF expression and neoangiogenesis, and less severe AGE accumulation, TGF-beta expression, and fibrosis compared to continuous standard PDF exposure for 20 weeks.

CONCLUSION

Low-GDP bicarbonate/lactate-buffered PDF has the potential to slow down standard PDF-induced peritoneal membrane damage.

Pyridoxal Phosphate and Hepatocyte Growth Factor Prevent Dialysate-Induced Peritoneal Damage

Glucose-based peritoneal dialysate (PD) is responsible for increased accumulation of advanced glycation end products (AGE) in the peritoneum of continuous ambulatory peritoneal dialysis patients. Pyridoxal 5'-phosphate (PLP), a derivative of vitamin B(6), protects proteins from glycation. Hepatocyte growth factor (HGF) heals damaged tissues in a reciprocal manner against TGF-beta1. First, with the use of gas chromatography-mass spectrometry, whether PLP traps 3-deoxyglucosone (3DG), a major glucose degradation product in PD, was determined. Then, whether rat peritoneal tissue damages induced by intraperitoneal administration of glucose-based PD is ameliorated by PLP or HGF was examined. In vitro incubation with PLP markedly decreased concentration of 3DG in a dose-dependent manner, demonstrating the 3DG-trapping effect of PLP. The peritoneum of PD-treated rats was significantly thickened compared with that of physiologic saline-treated rats. Both PLP and HGF prevented the thickening of rat peritoneum induced by PD and ameliorated accumulation of AGE and expression of TGF-beta1, vascular endothelial growth factor, and type 1 collagen and a number of blood vessels. Furthermore, expression of HGF was significantly increased in the peritoneum of PLP-treated rats compared with that of PD-treated rats. In conclusion, PLP shows 3DG-trapping effect. PLP and HGF prevented peritoneal thickening; accumulation of AGE; expression of TGF-beta1, vascular endothelial growth factor, and type 1 collagen; and neoangiogenesis in rat peritoneum induced by PD.

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.

Effects of customized bicarbonate buffered solutions for continuous renal replacement therapies on polymorphonuclear leukocytes function and viability

It has previously been shown that the mixture of bicarbonate and calcium in the solutions used for continuous renal replacement therapy led to crystallization and significant changes in calcium concentration and pH. The aim of this study was to investigate the impact of bicarbonate/calcium and lactate/calcium solutions for Continuous Renal Replacement Therapies (CRRT) on the viability and function of polymorphonuclear cells (PMN). We tested four customized bicarbonate buffered solutions: single bag (bicarbonate and calcium mixed 24 h before testing), double bag (mixed immediately before testing), filtered single bag and double bag solutions, and a commercial lactate buffered solution. Blood from 6 volunteers was incubated with the solutions for 30 min followed by PMN isolation. After overnight incubation, viability, phagocytosis, and peroxide production by PMN were determined by flow cytometry. There was no difference between the test solutions with respect to PMN viability and function. Therefore, the presence of microcrystals and the consequent changes in electrolyte concentrations do not seem to impair PMN function.

Buffer transport in peritoneal dialysis

Buffer transport in peritoneal dialysis. The success of peritoneal dialysis as a robust modality of renal replacement therapy has invited a quest for ameliorations in its underlying technology aimed at enhancing patient satisfaction and preserving the central instrument of the therapy, namely the peritoneal membrane. The health and longevity of the membrane have motivated and continue to drive a series of iterative innovations in the composition, methods of production, and delivery of dialysis solutions. It is the purpose of this article to review aspects of these innovations pertaining to buffer composition in dialysis solutions and the peritoneal mechanisms of buffer transport.

Apoptosis of Mesothelial Cells Caused by Unphysiological Characteristics of Peritoneal Dialysis Fluids

There is an ongoing debate as to which peritoneal dialysis fluids (PDFs) provide the best preservation of peritoneal cells. To investigate this topic further, we measured apoptosis and necrosis of cultured mesothelial cells (MCs) after exposure to different single unphysiological features of PDFs and PDFs for whole. MCs were incubated in buffers containing plasticizers, high osmolarity by sodium chloride, low pH, and high glucose for 0.5, 4, and 24 h. The same procedure was repeated with different PDFs. Apoptosis and necrosis were measured by FACS-analysis (annexin-FITC and propidium iodide). We found that plasticizers were clearly able to induce apoptosis after 24 h (18 +/- 4%). The same result was observed with high osmolarity by sodium chloride (17 +/- 5%), but not for high glucose (9 +/- 8%). All fluids with low pH (5.2) caused severe and almost complete necrosis (after 4 and 24 h). Incubation in neutral, two-compartment PDFs (glucose 4.25%) without plasticizers for 4 h showed no significant necrosis (3%), but after 24 h apoptosis was detectable in 10 +/- 9% and necrosis in 29 +/- 8% of MCs. In conclusion, after improving PDFs and introducing neutral fluids, further attention should be drawn to inducers of apoptosis. Apoptosis can be detected quite early (24 h) and is caused by plasticizers and high osmolarity.

Peritoneal dialysate fluid composition determines heat shock protein expression patterns in human mesothelial cells

BACKGROUND

Low biocompatibility of peritoneal dialysis fluids (PDF) contributes to mesothelial injury. We investigated whether the heat shock proteins (HSP)-27, HSP-72, and HSP-90 are differentially induced upon exposure of mesothelial cells to PDF and whether this was affected by selective modulation of the physicochemical properties of PDF.

METHODS

Human mesothelial cells (Met5A and primary human mesothelial cells) were exposed to acidic lactate and glucose-monomer based PDF (CAPD2 and CAPD3), to control culture media, or to a neutral lactate and glucose-monomer-based PDF with reduced levels of glucose degradation products (BALANCE). Expression of HSP-27, HSP-72, and HSP-90 and cellular distribution of HSP-72 were assessed by Western blotting and immunocytochemistry.

RESULTS

Mesothelial cells exhibited strong constitutive expression of HSP-27 and to a lesser extent HSP-72 and HSP-90. Exposure of the cells to CAPD2 and CAPD3 resulted in strong up-regulation of HSP-72. HSP-27 levels were slightly increased, but HSP-90 levels were unchanged upon exposure to CAPD2 or CAPD3. In contrast, exposure of the cells to BALANCE did not affect HSP-27 or HSP-72 expression. The acidic pH and glucose degradation products were found to be principal in mediating increased HSP-72 expression upon exposure to PDF.

CONCLUSIONS

Analysis of HSP expression represents a novel tool to assess biocompatibility of PDF. Among the HSP investigated, HSP-72 is the most predictive and accurate parameter to assess mesothelial cell injury in the early phase of exposure to PDF.

Prolonged exposure to glucose degradation products impairs viability and function of human peritoneal mesothelial cells

Bioincompatibility of peritoneal dialysis fluids (PDF) has been linked to the presence of glucose degradation products (GDP). Previous experiments have shown that short-term exposure to several GDP at concentrations found in commercially available PDF had no significant effect on human peritoneal mesothelial cells (HPMC). During continuous ambulatory peritoneal dialysis, however, cells are continually exposed to GDP for extended periods of time. Thus, the impact of GDP on HPMC during long-term exposure was assessed. HPMC were cultured for up to 36 d in the presence of 6 identified GDP (acetaldehyde, formaldehyde, furaldehyde, glyoxal, methylglyoxal, and 5-HMF) at doses that reflect their concentrations in conventional PDF. At regular time intervals, the ability of HPMC to secrete cytokines (interleukin-6 [IL-6]) and extracellular matrix molecules (fibronectin) was evaluated. In addition, cell viability, morphology, and proliferative potential were assessed. Exposure to GDP resulted in a significant reduction in mesothelial IL-6 and fibronectin release. Approximately 80% of this decrease occurred during the first 12 d of the exposure and was paralleled by a gradual loss of cell viability and development of morphologic alterations. After 36 d of exposure, the number of cells in GDP-treated cultures was reduced by nearly 60%. However, GDP-treated cells were able to resume normal proliferation when transferred to a normal GDP-free medium. HPMC viability and function may be impaired during long-term exposure to clinically relevant concentrations of GDP, which suggests a potential role of GDP in the pathogenesis of peritoneal membrane dysfunction during chronic peritoneal dialysis.

Localization of imidazolone in the peritoneum of capd patients: a factor for a loss of ultrafiltration

The presence of dicarbonyl compounds, potent precursors of advanced glycation end products (AGEs), has been recognized in unused peritoneal dialysis (PD) fluids. Accumulation of AGEs has been implicated in the alteration of peritoneal membrane properties during continuous ambulatory peritoneal dialysis (CAPD) therapy. To determine whether imidazolone, an AGE specifically derived from 3-deoxyglucosone (3-DG), contributes to a decrease in ultrafiltration (UF) capacity of the peritoneal membrane in CAPD patients, we immunohistochemically evaluated the localization of imidazolone in peritoneal tissues from CAPD patients. Mesothelial thickening in the peritoneum was found in six of seven CAPD patients. Imidazolone distinctly accumulated in peritoneal tissues of CAPD patients, whereas it was hardly detected in those of patients with nonrenal disease. CAPD patients with a low UF capacity showed more extensive peritoneal deposition of imidazolone and more pronounced mesothelial thickening than those with a normal UF capacity. A CAPD patient with sclerosing peritonitis showed the most abundant localization of imidazolone among all CAPD patients. Gas chromatography/mass spectrometry showed that unused PD fluids contained high 3-DG concentrations (mean, 34.6 +/- 14.1 [SD] microgram/mL). In conclusion, the accumulation of imidazolone was noted in peritoneal tissues of CAPD patients, which preceded a decrease in UF capacity. Imidazolone modification may alter the quality of peritoneal membranes, presumably leading to a loss of UF and finally the development of sclerosing peritonitis.

Continuous flow peritoneal dialysis: solution formulation and biocompatibility

When peritoneal dialysis was introduced several years ago an important alternative dialysis therapy to hemodialysis was made available for the treatment of end-stage chronic disease. However, a continuous search for new developments and technologies is necessary to find the optimal peritoneal dialysis fluid (PDF) to preserve peritoneal membrane function as long as possible. Conventional PDFs are known to compromise the functional integrity of the peritoneal membrane as a consequence of their acidic pH in combination with their high lactate content, as well as the high concentrations of glucose and glucose degradation products (GDPs) present in currently used conventional solutions. Novel solutions such as bicarbonate-buffered PDF (at neutral pH) display improved in vitro biocompatibility as compared to conventional, acidic lactate-buffered PDF. Since these novel solutions are manufactured in dual-chambered bags they also contain fewer GDPs, thus further reducing their potential toxicity and protein glycation. Clinically the novel solutions reduce inflow pain and improve peritoneal membrane transport characteristics, ultrafiltration capacity, and effluent markers of peritoneal membrane integrity. The concept of continuous flow peritoneal dialysis (CFPD) is another approach to optimize PDF. The technique of CFPD not only enables the individualization of acid-base correction by variable concentrations of HCO3- but may also help to restore peritoneal cell functions by neutral pH, reduced glucose load, diminished GDP content, and reduced advanced glycation end product (AGE) formation, thereby potentially contributing to the improved preservation of peritoneal membrane function.

Innovative approaches to the preservation of the peritoneal membrane: from bench to bedside

The functional integrity of the peritoneal membrane is of critical importance for the long-term success of peritoneal dialysis therapy. In addition to water and solute transport properties, the function of the membrane encompasses complex interactions with immune cells, invading microorganisms, and dialysis fluid components. During chronic peritoneal dialysis, intraperitoneal homeostasis is threatened by the repeated exposure to an unphysiologic environment that is created by the instilled solutions. Whereas their acidic pH and hyperosmolality were shown to primarily induce alterations of acute cell function, long-term peritoneal function might be affected by the repeated exposure to high concentrations of glucose and glucose degradation products. In addition to their intrinsic toxicity, these might induce or accelerate glycation processes, such as formation and deposition of advanced glycation end products in the peritoneal membrane. Presently, a new generation of dual-chambered peritoneal dialysis solutions combining the advantages of neutral pH and reduced glucose degradation products content is being introduced into clinical practice. In addition to an improved in vitro biocompatibility profile, emerging clinical trials of these novel solutions indicate that they might also improve the host defense status, membrane transport characteristics, ultrafiltration capacity, and effluent markers of peritoneal membrane integrity, while being safe and effective in correcting uremic acidosis and providing relief of inflow pain. Overall, these findings suggest that these new dialysis solutions might constitute an important step toward better preservation of long-term peritoneal membrane function during peritoneal dialysis.

Better correction of metabolic acidosis, blood pressure control, and phagocytosis with bicarbonate compared to lactate solution in acute peritoneal dialysis

Lactate solution has been the standard dialysate fluid for a long time. However, it tends to convert back into lactic acid in poor tissue-perfusion states. The aim of this study was to evaluate the efficacy of magnesium (Mg)- and calcium (Ca)-free bicarbonate solution compared with lactate solution in acute peritoneal dialysis (PD). Renal failure patients who were indicated for dialysis and needed acute PD were classified as shock and nonshock groups, and then were randomized to receive either bicarbonate or lactate solution. Twenty patients were enrolled in this study (5 in each subgroup). In the shock group, there were more rapid improvements and significantly higher levels of blood pH (7.40 +/- 0.04 versus 7.28 +/- 0.05, p < 0.05), serum bicarbonate (23.30 +/- 1.46 versus 18.37 +/- 1.25 mmol/L, p < 0.05), systolic pressure (106.80 +/- 3.68 versus 97.44 +/- 3.94 mm Hg, p < 0.05), mean arterial pressure (80.72 +/- 2.01 versus 73.28 +/- 2.41 mm Hg, p < 0.05), percentages of phagocytosis of circulating leukocytes (65.85% +/- 2.22 versus 52.12% +/- 2.71, p < 0.05), and percentages of positive nitroblue tetrazolium (NBT) reduction test without and with stimulation (14.43 +/- 1.93 versus 9.43 +/- 2.12, p < 0.05 and 65.08 +/- 6.80 versus 50.23 +/- 4.21, p < 0.05, respectively) in the bicarbonate subgroup compared with the lactate subgroup. In the nonshock group, blood pH, serum bicarbonate, and phagocytosis assays in both subgroups were comparable. Lactic acidosis was more rapidly recovered and was significantly lower with bicarbonate solution for both shock and nonshock groups (3.63 +/- 0.37 versus 5.21 +/- 0.30 mmol/L, p < 0.05 and 2.92 +/- 0.40 versus 3.44 +/- 0.34 mmol/L, p < 0.05, respectively). Peritoneal urea and creatinine clearances in both subgroups were comparable for both shock and nonshock groups. There was no peritonitis observed during the study. Serum Mg and Ca levels in the bicarbonate subgroup were significantly lower, but no clinical and electrocardiographic abnormality were observed. We concluded that Mg- and Ca-free bicarbonate solution could be safely used and had better outcomes in correction of metabolic acidosis, blood pressure control, and nonspecific systemic host defense with comparable efficacy when compared to lactate solution. It should be the dialysate of choice for acute PD especially in the poor tissue-perfusion states such as shock, lactic acidosis, and multiple organ failure.

Kinetics and dose response of the effects of heated glucose peritoneal dialysis fluids on the respiratory burst of rat peritoneal leukocytes

Heat sterilization of glucose containing peritoneal dialysis (PD) fluids induces the production of cytotoxic glucose degradation products (GDPs), some of which are still unidentified. The present study was performed to characterize the kinetics and the dose-response of the respiratory burst inhibition of GDPs and to compare different fluids in this respect. The zymosan-induced respiratory burst of rat peritoneal neutrophils and macrophages was measured by chemiluminescence (CL) after incubation in vitro for 1, 2, and 4 hours in different homemade and commercially available PD fluids, followed by one hour of recovery in Hanks' buffer. Heat sterilized fluids were compared with their filter sterilized equivalents at two different pH levels. The results revealed that the inhibitory effect of heat sterilized fluids on the respiratory burst of peritoneal neutrophils is additive to that of low pH, but more fast-acting and, in contrast to the pH effect, similar in magnitude to its in vivo equivalent. The effect developed within 1 hour and had a linear dose response. The low GDP fluid Gambrosol-Bio was less toxic than the conventional fluid Gambrosol, but the difference was smaller than expected in relation to measured concentrations of known GDPs. Macrophages were less sensitive than neutrophils to the GDP effect.

Effect of glucose degradation products on human peritoneal mesothelial cell function

Bioincompatibility of conventional glucose-based peritoneal dialysis fluids (PDF) has been partially attributed to the presence of glucose degradation products (GDP) generated during heat sterilization of PDF. Most previous studies on GDP toxicity were performed on animal and/or transformed cell lines, and the impact of GDP on peritoneal cells remains obscure. The short-term effects of six identified GDP on human peritoneal mesothelial cell (HPMC) functions were examined in comparison to murine L929 fibroblasts. Exposure of HPMC to acetaldehyde, formaldehyde, glyoxal, methylglyoxal, furaldehyde, but not to 5-hydroxymethyl-furfural, resulted in dose-dependent inhibition of cell growth, viability, and interleukin-1beta (IL-1beta)-stimulated IL-6 release; for several GDP, this suppression was significantly greater compared with L929 cells. Although the addition of GDP to culture medium at concentrations found in PDF had no major impact on HPMC function, the exposure of HPMC to filter-sterilized PDF led to a significantly smaller suppression of HPMC proliferation compared to that induced by heat-sterilized PDF. The growth inhibition mediated by filter-sterilized PDF could be increased after the addition of clinically relevant doses of GDP. These effects were equally evident in L929 cells. In conclusion, GDP reveal a significant cytotoxic potential toward HPMC that may be underestimated in test systems using L929 cells. GDP-related toxicity appears to be particularly evident in experimental systems using proliferating cells and the milieu of dialysis fluids. Thus, these observations may bear biologic relevance in vivo where HPMC are repeatedly exposed to GDP-containing PDF for extended periods of time.

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

BACKGROUND

Conventional peritoneal dialysis fluids (PDF) have been shown to compromise the function of both leukocytes and human peritoneal mesothelial cells (HPMC). Various in vitro studies have identified the low initial pH in combination with high lactate content, as well as the hyperosmolality and high glucose concentration present in currently used solutions as the primary determinants of their bioincompatibility. Bicarbonate buffered PDF (at neutral pH) display improved in vitro biocompatibility as compared to conventional, lactate buffered PDF. However, little information is currently available regarding the potential impact of PDF on the function of human peritoneal fibroblasts (HPFB), the major cell population present in peritoneal interstitium.

METHODS

The current study compares the effect of bicarbonate and lactate buffered PDF in a model system of resting peritoneal mesothelial cells and fibroblasts cultured from human omentum. Interleukin-1 beta-stimulated IL-6 release from HPMC and HPFB was used as the cell functional parameter.

RESULTS

While short (30 min) pre-exposure to lactate buffered PDF significantly reduced the IL-1 beta-stimulated IL-6 release from HPMC during a subsequent recovery period (24 hr), a significant decrease in HPMC IL-6 secretion with bicarbonate buffered PDF was only observed after prolonged (> or = 60 min) exposure. In contrast, no significant IL-6 inhibition was detected with HPFB pre-exposed to PDF for up to 90 minutes. A significant suppression of HPFB IL-6 secretion was only observed in coincubation experiments (24 hr) with dilutions of both types of PDF.

CONCLUSIONS

These results indicate that (i) bicarbonate buffered PDF are less inhibitory to peritoneal cell function as compared to conventional, lactate buffered PDF; and (ii) HPFB may be more resistant than HPMC to bioincompatible PDF.

Effect of two-chambered bicarbonate lactate-buffered peritoneal dialysis fluids on peripheral blood mononuclear cell and polymorphonuclear cell function in vitro

Low pH, high osmolality, increasing glucose concentration, and glucose degradation products (GDP) formed during heat sterilization of conventional peritoneal dialysis (PD) fluids have been shown to have a detrimental effect on cells involved in peritoneal host defense. The two-chambered PD fluid bag in which glucose at pH approximately 3 is separated from a bicarbonate (25 mmol/L)-lactate (15 mmol/L) buffer during heat sterilization permits PD fluids with lower GDP to be delivered to the patient at neutral pH. To establish the possible benefit of two-chambered bag PD fluids on peripheral blood mononuclear cell (PBMC) and polymorphonuclear (PMN) cell function, we compared conventional 1.5% Dianeal (1.5%D) with 1.5% two-chambered bag bicarbonate-lactate (1.5%D-B), and conventional 4.25% Dianeal (4.25%D) with 4.25% two-chambered bag bicarbonate-lactate (4.25%D-B). Furthermore, to study the effect of the sterilization process on PBMC and PMN function, we compared filter-sterilized 4.25%D (4.25%D-F) with 4.25%D and 4.25%D-B. PBMC were harvested by Ficoll-Hypaque separation, and 2.5 x 10(6) cells in RPMI were incubated with an equal volume of the test fluids for 4 hours, pelleted, and resuspended in RPMI containing 10 ng endotoxin for a further 20 hours. Tumor necrosis factor alpha (TNF-alpha) production by endotoxin-stimulated PBMC was not significantly different (P = 0.10) between 1.5%D-B and 1.5%D, but was significantly higher (P = 0.01) with 4.25%D-B compared with 4.25%D. PBMC exposed to filter-sterilized fluid (4.25%D-F) showed significantly higher endotoxin-stimulated TNF-alpha production compared with 4.25%D (P = 0.02), but was not significantly different from 4.25%D-B (P = 0.40). PMN were harvested by Ficoll-Hypaque separation and 10 x 10(6) cells incubated with test fluids for 30 minutes. After incubation, phagocytosis (phagocytosis index) was determined by the uptake of 14C-labeled Staphylococcus aureus, oxidative burst by reduction of ferricytochrome C to ferrocytochrome C on stimulation with PMA, and enzyme release by measurement of endotoxin-stimulated bactericidal/permeability increasing protein (BPI). Bicarbonate-lactate two-chambered fluids of similar osmolality and glucose concentration conferred a significant improvement in phagocytosis (P = 0.02 for 1.5%D-B and P < 0.001 for 4.25%D-B). Oxidative burst and BPI release were significantly higher in 4.25%D-B compared with 4.25%D (P < 0.001). Filter-sterilized 4.25%D-F conferred a significant improvement in phagocytosis and oxidative burst compared with 4.25%D (P < 0.001) or 4.25%D-B (P < 0.001). Furthermore, conventional 4.25%D was associated with significantly lower BPI release compared with 4.25%D-F (P = 0.01). GDP's acetaldehyde and 5-HMF were analyzed in 4.25%D-B, 4.25%D, and 4.25%D-F. Acetaldehyde was below the lower limit (0.79 ppm) of the standard curve in 4.25%D-B and 4.25%D-F fluids but was detected (3.76 to 5.12 ppm) in all of the 4.25%D fluids. Relative levels of 5-HMF in the 4.25%D-B (0.032 to 0.041 Abs @ 284 nm) and 4.25%D (0.031 to 0.036 Abs @ 284 nm) were similar. The lowest levels (0.001 Abs @ 284 nm) were observed in the filter-sterilized 4.25%D-F. The beneficial effects of two-chambered bicarbonate lactate-buffered PD fluids on PBMC and PMN function are probably related to reduction of GDP from heat sterilization of glucose in a separate chamber at a lower pH. This improvement in biocompatibility could have a beneficial affect on peritoneal defenses.