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

Effects of pH-neutral, bicarbonate-buffered dialysis fluid on peritoneal transport kinetics in children

BACKGROUND

Due to their superior biocompatibility, pH-neutral solutions are beginning to replace acidic lactate-buffered peritoneal dialysis (PD) fluids. We hypothesized that pH-neutral and acidic solutions might differentially affect peritoneal transport in the early dwell phase, due to differences in ionic shifts and initial peritoneal vasodilation. Such differences may become clinically relevant in patients with frequent short cycles on automated PD (APD).

METHODS

Twenty-five children were treated with a lactate-buffered (35 mmol/L, pH 5.5) or a bicarbonate-buffered PD solution (34 mmol/L, pH 7.4) in randomized order on two sequential days. Each day a four-hour Standardized Permeability Analysis (SPA) was performed, followed by overnight APD (7 cycles, fill volume 1000 mL/m2, dwell time 75 min). Functional peritoneal surface area was dynamically assessed using the three-pore model.

RESULTS

While intraperitoneal pH was constant at 7.41 +/- 0.03 throughout the SPA with bicarbonate fluid, the dialysate remained acidic for more than one hour with lactate solution (pH 7.12 +/- 0.08 at 1 h). Total pore area was 60% higher during the first 30 minutes of the dwell than under steady-state conditions, without a difference between acidic and pH-neutral fluid. Net base gain, intraperitoneal volume kinetics, glucose absorption, ultrafiltration rate, effective lymphatic absorption and the transport of urea, potassium, beta2-microglobulin and albumin were similar with both fluids. However, phosphate and creatinine elimination were 10% lower with bicarbonate PD fluid, resulting in corresponding significant decreases in the 24-hour clearances of these solutes.

CONCLUSION

The peritoneal surface area is not measurably influenced by pH-neutral PD fluid. Creatinine and phosphate elimination appears to be slightly reduced with bicarbonate fluid; this observation awaits clarification in extended therapeutical trials.

Better preservation of peritoneal morphologic features and defense in rats after long-term exposure to a bicarbonate/lactate-buffered solution

The long-term effects of a standard lactate-buffered dialysis fluid and a new, two-chamber, bicarbonate/lactate-buffered dialysis fluid (with fewer glucose degradation products and a neutral pH) were compared in an in vivo peritoneal exposure model. Rats were given daily injections, via an access port, of 10 ml of standard solution or bicarbonate/lactate-buffered solution for 9 to 10 wk. The omentum, peritoneum, and mesothelial cell layer were screened for morphologic changes. In addition, the bacterial clearing capacity of the peritoneal cells was studied. Significantly more milky spots and blood vessels were observed in the omenta of animals treated with standard solution (P < 0.03 for both parameters). Electron-microscopic analysis demonstrated dramatic changes in the appearance of the vascular endothelial cells of the milky spots and a severely damaged or even absent mesothelium on the peritoneal membrane of the standard solution-treated animals. In contrast, the mesothelium was still present in the bicarbonate/lactate-buffered solution group, although the cells lost microvilli. Both peritoneal dialysis fluids significantly increased the density of mesothelial cells (per square millimeter) on the surface of the liver and the thickness of the submesothelial extracellular matrix of the peritoneum (both P < 0.04 for both fluids versus control). A significantly better ex vivo bacterial clearing capacity was observed with peritoneal cells from the bicarbonate/lactate-buffered solution group, compared with the standard solution group (P < 0.05 in both experiments). These results demonstrate that instillation of bicarbonate/lactate-buffered solution into rats for 9 to 10 wk preserves both morphologic and immune parameters much more effectively, compared with standard solution. These findings may be of considerable clinical importance.

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.

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.

A new lactate-based, plasticizer-free, neutral peritoneal dialysis fluid provided in a two-compartment system: effect on peripheral leukocyte function

BACKGROUND

A new neutral peritoneal dialysis fluid (PDF; Balance) provided in a two-compartment bag (pH 7.4, no plasticizers, minimal glucose degradation products - GDP) was investigated in comparison with a neutral control (Hanks' balanced salt solution with gelatin 0.1%) and other PDFs with standard properties and plasticizers (Andy plus, pH 5.2, GDP), plasticizer free (stay safe, pH 5.2, GDP), and in addition plasticizer free after sterile filtration instead of heat sterilization (pH 5.2) regarding the function of peripheral blood leukocytes.

METHODS

Blood was drawn from 12 volunteers, and blood monocytes (MN) and polymorphonuclear leukocytes (PMNL) were collected. The cells were incubated for 30 min in control medium and the PDFs: glucose 1.5% (83 mmol/l) and 4.25% (238 mmol/l). Respiratory burst of cells was evaluated by chemiluminescence and superoxide (SO) generation after stimulation with phorbol myristate acetate.

RESULTS

In comparison with the control medium, incubation of MN in the two-compartment PDF showed preservation of respiratory burst. In contrast, the incubation of MN in standard PDF and plasticizer-free PDF showed impaired functions. The same was found for PMNL. SO anion measurement in MN and PMNL after incubation in the new two-compartment PDF also showed preservation of cell function in comparison with the control medium. The incubation of PMNL in standard PDF and plasticizer-free PDF with a high glucose content showed depressed SO anion generation.

CONCLUSIONS

These in vitro data demonstrate a better preservation of in vitro phagocyte function with adaptation of pH and reduction of glucose, GDP, and plasticizers in PDFs. The best results are achieved with the two-compartment, lactate-based neutral PDF.

Changes of cytokine profiles during peritonitis in patients on continuous ambulatory peritoneal dialysis

Continuous ambulatory peritoneal dialysis (CAPD) has emerged as an important dialysis treatment modality worldwide. One of the major complications is bacterial peritonitis, which may result in subsequent technique failure because of loss of peritoneal clearance or peritoneal fibrosis. Bacterial peritonitis leads to the release of proinflammatory cytokines from resident and infiltrating cells in the peritoneal cavity. We studied 35 patients undergoing CAPD with acute bacterial peritonitis. All patients treated with antibiotics for 2 weeks after the clinical diagnosis of peritonitis had a good recovery. Peritoneal dialysate effluent (PDE) was collected on days 1, 3, 5, 10, 21, and 42 after the start of treatment. Cell populations were monitored by flow cytometry. PDE levels of interleukin-1beta (IL-1), IL-6, transforming growth factor-beta (TGF-beta), and basic fibroblast growth factor (FGF) were measured by enzyme-linked immunosorbent assay. Gene transcription of TGF-beta in macrophages from PDE was measured by quantitative polymerase chain reaction. Bacterial peritonitis was associated with a sharp increase in total cell and neutrophil counts (400-fold) in PDE up to 3 weeks after peritonitis despite clinical remission (P < 0.0001). There was an increased absolute number of macrophages during the first 3 weeks despite the reduced percentage of macrophages among total cells in PDE compared with noninfective PDE. There was a progressive increase in the percentage of mesothelial cells or dead cells in the total cell population in PDE over the entire 6-week period. PDE levels of IL-1, IL-6, TGF-beta, and FGF increased markedly on day 1 before their levels decreased gradually. PDE levels of these cytokines or growth factors were significantly greater than those in noninfective PDE (n = 76) throughout the study period (P < 0.01). Similarly, TGF-beta complementary DNA (cDNA) molecules per macrophage were significantly greater than those of macrophages in noninfective PDE throughout this period (P < 0.01). There was no significant correlation between PDE levels of TGF-beta and TGF-beta cDNA molecules per macrophage, suggesting that peritoneal macrophages are not the only source of TGF-beta in PDE. We conclude there is an active release of proinflammatory cytokines and sclerogenic growth factors through at least 6 weeks despite apparent clinical remission of peritonitis. The peritoneal cytokine networks after peritonitis may potentially affect the physiological properties of the peritoneal membrane.

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.

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.