Dialysis fluids and local host resistance in patients on continuous ambulatory peritoneal dialysis

Acute in Vivotoxicity of Heat-Sterilized Glucose Peritoneal Dialysis Fluids to Rat Peritoneal Macrophages

Objective

To evaluate the in vivo effects of heat-sterilized peritoneal dialysis (PD) fluids on the respiratory burst response of rat peritoneal leukocytes.

Design

Rats were exposed to intraperitoneal injections of a laboratory-made PD fluid that was either heat-sterilized (HPD) or filtered (F-PD). Control groups of animals were given Hank's buffer (HBSS) or saline (NaCI). Leukocytes were harvested by intraperitoneal lavage at different times in different animals and analyzed with respect to cell numbers, differential counts, and production of superoxide (chemiluminescence) in response to opsonized zymosan. The chemiluminescence responses of the macrophage and the neutrophil populations, respectively, were obtained by curve-fitting techniques from the responses of the mixed populations.

Results

All fluids induced a recruitment of neutrophils, the PD fluids causing a cell number increase that was more transient than that caused by NaCI and HBSS. Macrophage numbers were only slightly influenced, but were generally higher after NaCI and HBSS injections than after PD fluid injections. The H-PD exposure induced a significant inhibition of the macrophage chemiluminescence response after 2 and 12 hours, compared with the exposure to F-PD. The neutrophil chemiluminescence response was not significantly affected.

Conclusion

The toxins produced by heat-sterilization of glucose-containing PD fluids inhibit in vivo the respiratory burst response of peritoneal macrophages.

Cytotoxic Effects of Commercial Continuous Ambulatory Peritoneal Dialysis (CAPD) Fluids and of Bacterial Exoproducts on Human Mesothelial Cells in Vitro

Cultured human mesothelial cells were exposed to peritoneal dialysis fluids, supernatants from cultures of Staphylococcus aureus and S. epidermidis, and antibiotics. Mesothelial cell monolayer cultures were derived from surgically removed omentum. The cytotoxicity of various agents for the cultured mesothelial cells was measured by a 51 Cr-release assay. All brands of fresh peritoneal dialysis fluids induced a more than 50% 51 Cr-release after 18 h. Morphological changes observed included retraction and shrinking of cells, pyknosis of the nuclei and, finally, detachment of cells over an 18-h period. Neutralization of the acid (pH 5.2–5.5) fluids to pH 7.3 did not abolish the cytotoxicity. In contrast, effluent dialysis fluids were not toxic for mesothelial cells; neither was acid (pH 5.5) culture medium nor culture medium with glucose up to 2%. However, higher glucose concentrations induced increasing 51 Cr-release. Furthermore, filter-sterilized supernatants of S. aureus were cytotoxic for mesothelial cell monolayers in 4/7 (57%) strains of S. aureus tested. In contrast, only 4/29 (14%) strains of S. epidermidis produced cytotoxic exoproducts (p = 0.03). Antibiotics were not found to be cytotoxic, with the possible exception of erythromycin.

We conclude that currently available peritoneal dialysis fluids are cytotoxic for mesothelial cells in vitro and that during episodes of peritonitis exoproducts of some bacterial strains may further reduce mesothelial cell viability.

Peritoneal Defense Using Icodextrin Or Glucose for Daytime Dwell in Ccpd Patients

Objective

To investigate peritoneal defense during icodextrin use in continuous cyclic peritoneal dialysis (CCPD).

Design

In an open, prospective, 2-year follow-up study, CCPD patients were randomized to either glucose (Glu) or icodextrin (Ico) for their long daytime dwell.

Setting

University hospital and teaching hospital.

Patients

Both established and patients new to CCPD were included. A life expectancy of more than 2 years, a stable clinical condition, and written informed consent were necessary before entry. Patients aged under 18 years, those who had peritonitis in the previous month, and women of childbearing potential, unless taking adequate contraceptive precautions, were excluded. Thirty-eight patients (19 Glu, 19 Ico) started the study. The median follow-up was 16 and 17 months for Glu and Ico respectively (range 0.5 – 25 months and 5 – 25 months, respectively).

Outcome Measures

Peritoneal defense characteristics and peritoneal dialysis-related infections were recorded every 3 months.

Results

Total peritoneal white cell count tended to decrease over time in both groups. After 1 year, absolute numbers and percentages of effluent peritoneal macrophages (PMΦs) were significantly higher in Ico than in Glu patients; this difference in the percentage persisted after 2 years. Percentage of mesothelial cells increased over time in Ico patients. The phagocytic capacity of PMΦs decreased over time, resulting in a borderline significant difference for coagulase-negative staphylococci ( p = 0.05) and a significant difference for Escherichia coli ( p < 0.05) phagocytosis in favor of Ico patients. PMΦ oxidative metabolism remained stable over time without a difference between the groups. PMΦ cytokine production and effluent opsonic capacity also remained stable over time. Finally, 16 peritonitis episodes in Glu and 14 in Ico patients occurred. Glucose patients had 37 and Ico patients 32 exit-site infections during the study.

Conclusion

CCPD patients using Ico did equally as well as Glu-treated patients with respect to clinical infections and most peritoneal defense characteristics. However, in a few peritoneal defense tests, Ico-treated patients did better.

Assessment of the Effectiveness, Safety, and Biocompatibility of Icodextrin in Automated Peritoneal Dialysis

Objective

Our study assessed the efficacy, safety, and biocompatibility of icodextrin (I) solution compared to glucose (G) solution as the daytime dwell in continuous cycling peritoneal dialysis (CCPD).

Design

In a randomized, open, prospective, parallel group study of two years’ duration, either I or G was used for the long daytime dwell in CCPD patients.

Method

The study was carried out in a university hospital and teaching hospital. Established CCPD patients and patients new to the modality were both included. Clinic visits were made at three-month intervals. In all patients, clinical data were gathered; ultrafiltration (UF) was recorded; and serum, urine, and dialysate samples and effluents were collected. Peritoneal defense characteristics and mesothelial markers were determined. Every six months, peritoneal kinetics studies were performed, and serum samples for icodextrin metabolites were taken.

Results

Thirty-eight patients (19 G, 19 I) started the study. The median follow-up was 16 months and 17 months respectively (range: 0.5 – 26 months and 3 – 26 months, respectively). Daytime UF volumes increased significantly (p < 0.001), and 24-hour UF tended to increase from baseline in the I group. Dialysate creatinine clearance increased non significantly in both groups over time. In I patients, serum disaccharides (maltose) concentration increased from 0.05 ± 0.01 mg/mL [mean ± standard error of mean (SEM)] at baseline, to an average concentration in the follow-up visits of 1.15 ± 0.04 mg/mL (p < 0.001). At the same time, serum sodium levels decreased from 138.1 ± 0.7 mmol/L to an average concentration in the follow-up visits of 135.9 ± 0.8 mmol/L (p < 0.05). At 12 months, the serum sodium concentration increased to a non significant difference from baseline. Serum osmolality increased, but did not differ significantly from G users at any visit. During peritonitis (P), daytime dwell UF decreased significantly compared to non peritonitis (NP) episodes in G patients (p < 0.001), but remained stable in I patients. Total 24-hour UF also decreased in G patients (p < 0.001), but not in I patients. In these I patients, serum disaccharides increased from 0.05 ± 0.01 mg/mL to 1.26 ± 0.2 mg/mL during follow-up. During peritonitis, serum disaccharides concentration did not increase further (1.47 ± 0.2 mg/mL, p = 0.56). Thirty P episodes occurred during follow-up: 16 in G patients and 14 in I patients (1 per 17.6 months and 1 per 21.9 months, respectively). After one year, absolute number and percentage of effluent peritoneal macrophages (PMΦs) were significantly higher in I patients than in G patients. The difference in percentage persisted after two years. The phagocytic capacity of PMΦs decreased over time, resulting in a borderline significant difference for coagulase-negative staphylococci phagocytosis (p = 0.05) and a significant difference for E. coli phagocytosis (p < 0.05) in favor of I patients. PMΦ oxidative metabolism, PMΦ cytokine production, and effluent opsonic capacity remained stable over time with no difference between the groups. Mass transfer area coefficients (MTACs) and clearances were stable and appeared unaffected by G or I treatment. Effluent cancer antigen 125 (CA125) was stable in G users and tended to decrease in I users. Effluent interleukin-8 (IL-8), carboxy-terminal propeptide of type I procollagen (PICP), and amino-terminal propeptide of type III procollagen (PIIINP) did not change over time and did not differ between the groups.

Conclusions

The use of I for the long daytime dwell in CCPD led to an increase in total UF of at least 261 mL per day, which was maintained over at least 24 months. During I treatment, serum I metabolites increased significantly and serum sodium concentrations decreased initially. As a result, serum osmolality increased slightly. Clinical adverse effects did not accompany these findings. The UF gain in the I patients was even higher during P, without a further increase in serum I metabolites. CCPD patients using I did equally well as G-treated patients with regard to clinical infections and most peritoneal defense characteristics. However, in a few peritoneal defense tests, I-treated patients did better. Peritoneal transport variables did not change over time. Peritoneal membrane markers did not change throughout the study and did not differ between the groups.

Phagocytosis and Killing of Suspended and Adhered Bacteria by Peritoneal Cells after Dialysis

Objective

To determine the effect of dialysis fluid containing various glucose concentrations on the phagocytosis and killing of Staphylococcus aureus by rat peritoneal cells under conditions mimicking the in vivo situation.

Design

Phagocytosis and killing were evaluated by quantitation of the killing capacity of macrophages after in vivo phagocytosis of the bacteria as well as by an in vitro flow cytometric assay of the phagocytosis and killing of adhered bacteria by peritoneal cells.

Animals

Male Wistar rats.

Main Outcome Measure

It was expected that the intraperitoneal administration of dialysis fluid would im pair the capacity of peritoneal cells to eliminate bacteria.

Results

The first test revealed no effects of glucose concentration or dwell time on the killing of phagocytosed bacteria by macrophages, median percentages ranging between 29% and 64%. In the second series of experiments no effect of glucose concentration on the phagocytosis and killing of adhered bacteria was found either; however, longer dwell times significantly enhanced both the phagocytosis (at a dwell time of 1 hour, under 20%; at dwell times of 4 or 18 hours, above 20%, p < 0.02) and the killing (at a dwell time of 1 hour, under 53%; at dwell times of 4 and 18 hours, above 70%, p < 0.01).

Conclusions

Glucose concentration has no effect on the phagocytosis and killing of Staphylococcus aureus, whereas the dwell time significantly enhances both of these functional capacities of peritoneal cells if the bacteria are adhered to surfaces.

Bicarbonate versus Lactate-Based Capd Fluids: A Biocompatibility Study in Rabbits

Previous in vitrobiocompatibility studies have shown bicarbonate-based continuous ambulatory peritoneal dialysis (CAPD) fluids to be superior to those based upon lactate/acetate. To evaluate these findings in vivo, 41 rabbits were subjected to CAPD for four weeks in a randomized prospective study using either Dianeal, a commercially available dialysis fluid containing lactate, or 87b, a bicarbonate-based CAPD fluid. Ten rabbits with CAPD catheters, which were flushed with a heparin solution every 36 hours, served as controls.

None of the control rabbits showed clinical or histopathological signs of peritonitis, while 8 of 20 in the Dianeal group and 6 of 21 in the 87b group contracted peritonitis. Four rabbits in the Dianeal group had to be sacrificed early due to severe peritonitis. Post mortem examinations, including scanning and light microscopy, did not reveal any macroscopic or microscopic differences among the three groups of noninfected animals. No significant distinctions between the groups could be made for body temperature, weight gain, dialysate volume, dialysate differential leukocyte count, dialysate protein content, and food intake during the course of the study.

In conclusion, the present animal model did not reveal any major difference in the biocompatibility between the lactate and the bicarbonate-based CAPD fluids.

The Effect of Dialysate Acidity on Peritoneal Solute Transport in the Rat

Objective

To investigate the possible effect of unphysiologically low pH in dialysis fluid on peritoneal transport.

Design

A 4-hour single-cycle experimental session of peritoneal dialysis was performed in six 5prague-Dawley rats using Dianeal 3.86% solution modified by adding 5 mmol/L of sodium hydroxide, neutral pH solution (NpH5) (pH 7.4). The intraperitoneal volume (V D) and peritoneal bulkfluid reabsorption (aa) were calculated using a marker, 1311–labeled human serum albumin (RI5A). The diffusive mass transport coefficient (KBD) as well as sieving coefficient (5) for glucose, urea, sodium, and potassium were calculated using the Babb-Randerson-Farrell model. The same study was performed in seven rats using Dianeal 3.86% solution, acidic pH solution (ApH5) (pH 5.7) to provide control values.

Results

The dialysate pH was stable with NpH5; 45 min after the infusion of ApH5 it increased rapidly and reached the physiological value 7.4. Dialysate volume and KBD values for sodium and potassium with NpH5 were significantly higher than with ApH5, while the KBD values for glucose and urea did not differ between the two solutions. 5 values for sodium and urea did not differ between the two solutions, while the values for glucose and potassium with NpH5 were significantly higher and lower, respectively, than the values with ApH5 (0.92±1.04 vs 0.04±0.63 and 0.56±060 vs 1.15±0.39, p < 0.05). The absorption of glucose from the dialysis solution expressed as a percentage of the initial amount of dialysate glucose was significantly lower with NpH5 than with ApH5 at 30 min (17.3±1.7% vs 29.7±2.0%, p < 0.05).

Conclusion

We conclude that the peritoneal transport of fluid and small solutes might to some extent be influenced by the acidity of the dialysis solution. The vasodilatory effect of acidic dialysis solution might be the most important mechanism for these differences. However, a larger KBD value and a lower 5 value for potassium and higher 5 values for glucose during dialysis with the neutral dialysis solution may indicate that transport mechanisms other than simple passive transport are involved in peritoneal transport for glucose and electrolytes.

Compatibility of Peritoneal Dialysis Fluids Containing Alternative Osmotic Agents with Cells Present in the Peritoneal Cavity

The success of continuous ambulatory peritoneal dialysis (CAPD) lies in preserving the peritoneum as a dialyzing membrane. Repeated infusions of nonphysiological fluids are potentially detrimental to the peritoneal membrane and its host defense. The disadvantages of the currently used peritoneal dialysis fluids (PDPs) containing glucose as an osmotic agent (short ultrafiltration profile, systemic carbohydrate load, nonphysiological composition) have stimulated the search for alternative, less toxic osmotic agents devoid of metabolic side effects and capable of sustaining ultrafiltration. PDFs containing glycerol, amino acids, or glucose polymers have had clinical usage in CAPD patients and were reviewed with regard to their compatibility with cells present in the peritoneal cavity.

Overall, glycerol appears to have no advantage over glucose-based PDFs, although it is less inhibitory for mesothelial cell proliferationin vitro. The optimum formulation of amino acid-based PDFs has not yet been established; its lactate and specific amino acid content may limit their biocompatibility. The virtually iso-osmolar glucose polymer (icodextrin)-containing PDFs were associated with improved biocompatibility compared to glucose monomer-based solutions.

Modifications of PDFs towards a more balanced salt solution with a neutral pH may further increase their compatibility with peritoneal host defense as well as with the integrity of the mesothelial membrane. Such improvement in PDF biocompatibility may result in clinical benefit, that is, enhanced resistance to infection and preservation of peritoneal ultrafiltration capacity.

Icodextrin Effluent Leads to a Greater Proliferation than Glucose Effluent of Human Mesothelial Cells StudiedEx Vivo

Objective

To compare the effect of glucose (Glu) and icodextrin (Ico) dialysate on in vitro culture of mesothelial cells (MC) from peritoneal dialysis (PD) patients.

Design

Prospective, controlled comparative study on the effects of two PD solutions.

Setting

A tertiary-care public university hospital.

Patients

Sixteen PD patients regularly using Glu dialysate were asked to collect an 8-hour dwell peritoneal effluent on 2 different days, with an interval shorter than 7 days. In the first collection, 2.27% Glu solution and in the last, 7.5% Ico solution was infused. Human MC were isolated from the nocturnal peritoneal effluent bags and grown ex vivo.

Main Outcome Measures

Mesothelial cell proliferative capacity ex vivo.

Results

Mesothelial cells were present in all patient dialysates except that of a single patient's Glu dialysate. The number of MC drained was similar with both solutions. After the initial culture reached confluence, MC were identified in 14 and 12 patients receiving Ico and Glu, respectively. However, in 1 patient using Ico and in 2 using Glu, the MC count at this stage was so low that further subculture could not be performed. Cells from Ico-derived solutions exhibited a higher degree of proliferation than cells from Glu-derived solutions. The morphology of MC was also different. Cells from drained effluent were typical in 11 patients using Glu solution in contrast with 14 patients using Ico. At confluence, the percentages of typical appearance were 50% and 92.9% ( p < 0.05) in Glu and Ico respectively.

Conclusions

Mesothelial cells taken from icodextrin effluent show a greater proliferation ex vivo than those taken from glucose effluent.

The Effect of Peritoneal Dialysis Fluid on the Release of Il-113 and Tnfa by Macrophages/Monocytes

Objective

To study the effect of dialysis fluid on the release of interleukin-1β (IL-1β) and tumor necrosis factor (TNFα) by peritoneal macrophages (PM) and peripheral blood mononuclear cells (MNC), and the time course and factors involved in this effect

Design

PM and MNC were incubated for various periods with Dianeal itself, or Dianeal of varying pH and composition.IL-1 β was measured by radioimmunoassay and TNFα by cytotoxicity assay.

Patients

PM were obtained by centrifugation of dialysis effluent from 3 continuous ambulatory peritoneal dialysis (CAPD) patients. MNC were obtained from healthy volunteers.

Results

Dialysis fluid inhibited the release of both cytokines. Indomethacin had no effect on the inhibition of TNFα release caused by dialysis fluid. Thus prostaglandins are not involved in this inhibition. Solutions of pH 5.2 and high lactate concentration caused an identical inhibition to that caused by dialysate, whereas the presence or absence of glucose had no effect. Thus it seems that pH and lactate are the important inhibitory factors. Time course studies showed that the inhibition of TNFα release was substantial after only 15 minutes of incubation with dialysate, whereas the inhibition of IL-1 β became significant only after 60 minutes of incubation.

Conclusions

Even though dialysate pH rises within 15–30 minutes after instillation into the abdomen, the initial low pH present for only a short time could have a significant effect on TNFα release by peritoneal macrophages, and thus on their ability to mount a normal inflammatory response. Lactate also has a significant inhibitory role. It is suggested that commercial dialysis solutions should have a pH of 7. Oandthata physiological buffer other than lactate be used.

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.

Host Defense Mechanisms in the Peritoneal Cavity of Continuous Ambulatory Peritoneal Dialysis Patients: First of Two Parts

This article provides a review of studies on peritoneal white blood cells (WBC) in CAPD patients. To some extent these studies support the concept that the peritoneal cavity of these patients contains adequate-functioning WBC that can provide effective antimicrobial defenses when they are studied in dialysate-free media. Commercially available dialysis solutions significantly impair WBC function. In some patients with high incidences of peritonitis, there appears to be reduced bactericidal capacity of their peritoneal macrophages. CAPD seems to contribute to a state of both macrophage and lymphocyte activation in the peritoneal cavity. The clinical consequences of this chronic activation are not known.

Biocompatibility Studies on Peritoneal Cells

This review outlines the problems involved in assessing the biocompatibility of PD fluids. It has summarized the data available from conventional in vitro studies and highlights many of the inadequacies of this approach. In viva data are lacking both on host defense and on the clinical effect of changing conven tional PD fluids for a more “ideal” formulation. The best parameters for assessing biocompatibility need to be defined. Alternative formulation of fluids must be aimed towards (1) a system that interferes minimally with host defense, and (2) a system that maintains the integrity of the peritoneal membrane for ultrafiltration and clearance.

Cell culture studies should be designed to model the in viva situation. Ex viva studies (cells exposed within the peritoneal cavity) should be used to support in viva findings. Finally, in vitra results must be related to clinical significance, and changes in fluid composition should be followed by improvements in clinical outcome.

Effect of Different Buffers on the Biocompatibility of Capd Solutions

Commercially available solutions for continuous ambulatory peritoneal dialysis (CAPO) affect the viability and function of the cells in the peritoneal cavity. The low biocompatibility of the solutions may be caused by a low pH, hyperosmolality, high glucose content, and lack of potassium, glutamine, and other components essential for normal cellular functions. The nature of the buffer employed is also important for the cytotoxicity of the solutions. Lactate, the most frequently used buffer, has been shown to inhibit cellular functions important for the peritoneal defense system including phagocytosis, bacterial killing, and secretion of cytokines. It is generally believed that the cytotoxicity of lactate is caused by lowering of intracellular pH and impairment of metabolism due to changed redox potentials. However, the cytotoxicity of lactate is highly dependent upon the pH of the solutions, indicating that passive or active diffusion across the cell membrane is determining the effects of lactate. Bicarbonate has been heavily advocated as an alternative buffer because it is the most important naturally occurring buffer in plasma and it enables a pH of approximately 7.4 in the solutions. However, due to sedimentation of calcium carbonate (CaCO3) and production of toxic glucose metabolites it is difficult to prepare and store bicarbonate-based solutions. Moreover, investigations have revealed that even bicarbonate-based solutions are not optimal regarding biocompatibility, presumably due to a paradoxical intracellular acidification caused by influx of carbon dioxide (CO2). More recently, the effect of other buffers such as pyruvate and histidine have been examined. Especially pyruvate is a promising new buffer candidate.

Conventional CAPD solutions based on lactate have been shown to impair a wide variety of cell functions important for the peritoneal host defense. Apart from the influence of hyperosmolality, high glucose concentration, lack of potassium, glutamine, and other factors, this seems to be due to the combination of low pH and high lactate concentration. Presumably, lactate carries protons across the membrane, which results in intracellular acidification and increased intracellular lactate concentration, both of which may impair cell metabolism and function.

Bicarbonate-based solutions are less toxic than lactate-based solutions -primarily attributable to the higher pH. However, experiments performed by our group have indicated that bicarbonate concentrations that are too high may also affect cell function, and that a solution containing both bicarbonate and lactate may be superior. However, further studies are needed to fully elucidate this problem.

Pyruvate seems to be a promising new buffer candidate with lower toxicity than lactate solutions at identical pH and glucose content. Comparison of pyruvate, lactate, and bicarbonate solutions regarding cytotoxicity and especially intracellular acidification will hopefully shed new light on the toxic properties of these solutions.

Neutrophilic Intracellular Acidosis Induced by Conventional, Lactate-Containing Peritoneal Dialysis Solutions

Exposure of human neutrophils to a conventional, acidic, lactate-containing peritoneal dialysis solution (PDS) resulted in the development of a prompt and substantial intracellular acidosis. It is possible that this intracellular acidosis contributes to cellular dysfunction.

Effects of a pH 7.4, lactate-based and a pH 7.4, bicarbonate-based peritoneal dialysis solutions on neutrophil superoxide generation

Neutrophil superoxide formation was similar when cells were incubated in self-made, non-autoclaved, pH 7.4, lactate-based peritoneal dialysis solutions or in their self-made, non-autoclaved, pH 7.4, bicarbonate-based counterparts. On the other hand, commercially available, autoclaved, pH 7.4, lactate-based peritoneal dialysis solutions resulted in inhibition of superoxide production when compared to their self-made, non-autoclaved, pH 7.4, lactate-based or bicarbonate-based counterparts. The cause for this inhibition of superoxide generation is at present unknown.

Failure of Neutrophils to Recover Their Ability to Produce Superoxide after Stunning by a Conventional, Acidic, Lactate-Based Peritoneal Dialysis Solution

Exposure of human neutrophils to conventional, acidic, lactate-based peritoneal dialysis solutions for 5 minutes results in a depression of superoxide generation. In spite of restoration of extracellular pH to 7.4, these stunned cells failed to recover their ability to generate the anion after a period of an hour.

"Biocompatible" Neutral pH Low-GDP Peritoneal Dialysis Solutions: Much Ado About Nothing?

Adverse outcomes in peritoneal dialysis (PD), including PD related infections, the loss of residual kidney function (RKF), and longitudinal, deleterious changes in peritoneal membrane function continue to limit the long-term success of PD therapy. The observation that these deleterious changes occur upon exposure to conventional glucose-based PD solutions fuels the search for a more biocompatible PD solution. The development of a novel PD solution with a neutral pH, and lower in glucose degradation products (GDPs) compared to its conventional predecessors has been labeled a "biocompatible" solution. While considerable evidence in support of these novel solutions' biocompatibility has emerged from cell culture and animal studies, the clinical benefits as compared to conventional PD solutions are less clear. Neutral pH low GDP (NpHLGDP) PD solutions appear to be effective in reducing infusion pain, but their effects on other clinical endpoints including peritoneal membrane function, preservation of RKF, PD-related infections, and technique and patient survival are less clear. The literature is limited by studies characterized by relatively few patients, short follow-up time, heterogeneity with regards to the novel PD solution type under study, and the different patient populations under study. Nonetheless, the search for a more biocompatible PD solution continues with emerging data on promising non glucose-based solutions.

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.

Mononuclear leucocyte function tests in the assessment of the biocompatibility of peritoneal dialysis fluids

BACKGROUND

Previous studies showed that the currently used dextrose based peritoneal dialysis fluids impair several leucocyte functions.

AIMS

To determine which in vitro mononuclear leucocyte (monocyte) function tests most clearly reflect the biocompatibility of peritoneal dialysis fluid.

METHODS

Monocytes were tested for phagocytic capacity, bactericidal activity, Fc and C3 receptor expression, and chemiluminescence response, and by analysis of the release of interleukin 8 (IL-8) and tumour necrosis factor alpha (TNF alpha) in the presence of test fluids. Cytokine release was studied in an alternative dynamic in vitro peritoneal dialysis model in which monocytes were exposed to test fluid that was continuously equilibrated with an interstitial fluid-like medium through a microporous membrane. The chemiluminescence response by stressed monocytes was also tested after an 18 h recovery period. All tests were performed during or after exposure to different degrees of glycerol induced osmotic stress and after exposure to a 1% milk-whey derived, polypeptide enriched test fluid. Cells incubated in 0.1% gel Hanks buffer (GH) served as control.

RESULTS

Osmotic stress induced impairment of leucocyte function was found by the chemiluminescence assay (mean (SEM): 179 (20)% v 138 (23)% after 30 minutes in 0.5% and 1.5% glycerol, respectively) and by the analysis of IL-8 released by monocytes (44 (9) ng in 0.7% glycerol v 40 (7) ng in 2.0% glycerol). Only the chemiluminescence assay showed a protective effect of polypeptides on leucocyte function (after > or = 60 minutes). If monocytes were allowed to recover in culture medium after exposure to test fluids, the changes in chemiluminescence response appeared to be reversible after a 30 minute exposure, but became more pronounced after 60 and 120 minutes. The phagocytosis and bacterial killing assays were less sensitive. The observations carried out with the phagocytosis assay did not correspond with the Fc or C3 receptor density data.

CONCLUSIONS

The release of IL-8 by peripheral blood monocytes in a two compartment model and their chemiluminescence response are appropriate assays for the assessment of changes in leucocyte function in response to different peritoneal dialysis fluids.

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.

Hydrogen peroxide generation by polymorphonuclear leukocytes exposed to peritoneal dialysis effluent

In the presence of peritoneal dialysis effluent (PDE), human polymorphonuclear leukocytes (PMN) showed reduced production of hydrogen peroxide and hypochlorous acid (H2O2 and HOCl, respectively) when at rest and when stimulated with both soluble (formylmethionyl-leucyl-phenylalanine and phorbol myristate acetate) and particulate (Staphylococcus epidermidis) agonists. This effect occurred in a concentration-dependent manner between 0 and 70%. (vol/vol) dialysis effluent. The inhibition of H2O2 and HOCl observed in resting, formy-methionylleucyphenyalanine-stimulated, and S. epidermidis-stimulated PMN was confined to a low-molecular-mass (< 10,000-Da) fraction of PDE, whereas the inhibition of the PMA response was equally dispersed throughout both low (< 10,000-Da)- and high-molecular-mass (> 10,000-Da) fractions. Human serum albumin, a major component of PDE, also inhibited H2O2 and HOCl production by PMN; however, results from cell-free systems suggested that human serum albumin was not wholly responsible for the inhibition of PMN function seen with PDE. The solute(s) responsible did not affect myloperoxidase but very rapidly scavenged H2O2 and HOCl. These data suggest that the factors capable of affecting H2O2 and HOCl production by PMN accumulate in uremia and are removed from the circulation into dialysis effluent.

In vitro effects of bicarbonate- versus lactate-buffered continuous ambulatory peritoneal dialysis fluids on peritoneal macrophage function

At present, lactate is the most commonly used buffer in peritoneal dialysis fluids (PDFs). The high lactate concentration in combination with low original pH was demonstrated to suppress phagocytic function. We evaluated the in vitro effects of a newly formulated bicarbonate-buffered PDF containing glycylglycine (BiGG15 and BiGG40; Pierre Fabre Medicament, Castres, France) on peritoneal macrophage (PMO) function, and compared them with those of equiosmolar lactate-buffered PDF (1.5% and 4.25% glucose; pH 5.4 and pH 7.4) and control buffer. Peritoneal macrophages were isolated from the effluents of 10 continuous ambulatory peritoneal dialysis patients and tested for luminol- and lucigenin-enhanced chemiluminescence, superoxide (O2-) generation measured by cytochrome c reduction, killing capacity, and phagocytosis after incubation in the PDF used. Exposure of PMO to lactate-buffered PDF with an original pH of 5.4 resulted in a significant suppression of all PMO functions measured, compared with bicarbonate- and lactate-buffered PDFs with a pH of 7.4. At physiological pH (7.4), chemiluminescence generation of PMO exposed to BiGG15/40 was significantly higher compared with the corresponding equiosmolar lactate-buffered PDF (1,992 +/- 858 x 10(3) cpm/10(4) cells v 856 +/- 398 x 10(3) cpm/10(4) cells; P < 0.004). O2- generation, killing capacity, and phagocytosis were not significantly different after PMO exposure to bicarbonate compared with exposure to lactate-buffered PDF with a neutral pH. Irrespective of the buffer used, high-osmolality PDFs suppressed PMO function significantly more than low-osmolar PDFs. In conclusion, bicarbonate-buffered PDFs are less detrimental to PMO function than lactate-containing PDFs; these preliminary in vitro results need to be confirmed in vivo.

In vitro effects of low-calcium peritoneal dialysis solutions on peritoneal macrophage functions

The use of low-calcium peritoneal dialysis solutions (PDS) for continuous ambulatory peritoneal dialysis is becoming widely accepted to reduce the risk of serum hypercalcemia in patients taking calcium salts as phosphate binders. We compared the in vitro effects of low-calcium PDS (1,000 mumol calcium/L), calcium-free buffer, and buffers with increasing calcium concentrations (500 to 5,000 mumol calcium/L) on peritoneal macrophage (PMO) functions. Peritoneal macrophages isolated from 10 continuous ambulatory peritoneal dialysis patients were incubated in the different solutions and tested for phagocytic and killing capacity, superoxide generation (cytochrome-C reduction and lucigenin-enhanced chemiluminescence), and the rate of myeloperoxidase-dependent oxidative metabolism (luminol-enhanced chemiluminescence). All functions of the PMO incubated in calcium-free buffer were significantly suppressed compared with the PMO incubated in calcium buffers. No dose-dependent increase of a single PMO function could be found after incubating the PMO in calcium buffer with increasing concentrations. Incubation of PMO in otherwise identical PDS containing 1,000, 1,450, or 1,750 mumol calcium/L did not result in significantly different PMO functions. Acidic PDS (pH 5.3 to 5.5) suppressed all measured PMO functions as compared with their neutralized counterparts (pH 7.4), irrespective of the calcium concentration. Results of our in vitro study show that low-calcium PDS does not suppress PMO functions any more than standard-calcium PDS (1,750 mumol calcium/L) does.

Effect of lactate-buffered peritoneal dialysis fluids on human peritoneal mesothelial cell interleukin-6 and prostaglandin synthesis

The present study focused on the evaluation of constitutive and cytokine-stimulated human peritoneal mesothelial cell (HPMC) IL-6 and 6-keto-PGF1 alpha release following pre-exposure to peritoneal dialysis fluid (PDF). Exposure of HPMC to PDF pH 5.2 resulted in a time-dependent increase in cell cytotoxicity [as assessed by lactate dehydrogenase (LDH) release] and concomitant inhibition of constitutive and IL-1 beta stimulated IL-6 and 6-keto-PGF1 alpha synthesis. After 15 minutes of exposure to PDF constitutive and IL-1 beta stimulated IL-6 release were reduced by 32.0 +/- 9.7% and 76.0 +/- 7.4% (N = 6, P < 0.046 and P < 0.027, respectively). PCR amplification of reverse transcribed mRNA from HPMC pre-exposed to PDF pH 5.2 demonstrated suppression of IL-1 beta stimulated IL-6 and cyclooxygenase (Cox-1 and Cox-2) transcripts. In order to mimic the dialysis cycle in vivo, an in vitro dialysis system was established. HPMC were exposed first to control medium, PDF pH 5.2 or PDF 7.3 for 15 minutes and then sequentially to pooled spent peritoneal dialysis effluent for up to four hours. The cells were subsequently allowed to recover in control medium for 12 hours in the presence or absence of IL-1 beta or TNF-alpha (both at 1000 pg/ml). There was no evidence of significant cell toxicity as assessed by LDH release during either the 'in vitro dialysis' or 'recovery' phases. Under these conditions short term exposure to PDF pH 5.2 followed by 'in vitro dialysis' resulted in significant inhibition of cytokine stimulated IL-6 (69.6 +/- 18.2 vs. 96.7 +/- 27.9 pg/microgram, N = 13; P < 0.020 for IL-1 beta) and 6-keto-PGF1 alpha (197.5 +/- 89.2 vs. 289.6 +/- 114.5 pg/microgram, N = 13; P < 0.020 for IL-1 beta) and 6-keto-PGF1 alpha (197.5 +/- 89.2 vs. 289.6 +/- 114.5 pg/microgram, N = 13; P < 0.003) release when compared to cells incubated in control medium. Adjustment of the pH of PDF to 7.3 reversed its inhibitory effects. We conclude that short-term exposure to PDF pH 5.2 significantly inhibits HPMC cytokine and prostaglandin release, an effect which appears to be related to its initial pH. Repeated exposure to nonphysiological PDF might impair mesothelial cell function and thus modulate intraperitoneal inflammatory processes.

Immunohistochemical studies of the peritoneal membrane and infiltrating cells in normal subjects and in patients on CAPD

We performed immunohistochemical studies on biopsies of the parietal peritoneal membrane of 33 subjects to investigate whether other cell populations, in addition to mononuclear cells free in the dialysate, might participate in the defense of the peritoneum against microbial invasion during CAPD. Leukocytes were found to concentrate in two areas: a submesothelial layer composed of elongated macrophages displaying activation and maturation markers, and perivascular, less mature macrophages closely associated with T cells and HLA-DR, ICAM-1 and VCAM-1 expressing endothelial cells. Normal mesothelial cells were found to express constitutively the transferrin receptor and the adhesion molecules ICAM-1 and VCAM-1 but not ELAM-1. There were no major differences between normal and uremic subjects, while peritoneal dialysis patients exhibited minor derangements of the submesothelial layer and slight up-regulation of the expression of HLA-DR on endothelial cells. Peritonitis was associated with increased submesothelial cellularity and, particularly, perivascular leukocyte infiltration accompanied by increased expression of HLA-DR and adhesion molecules. Besides mononuclear cells free in the dialysate, this study demonstrates the existence of two additional peritoneal membrane leukocyte populations: submesothelial macrophages, and perivascular macrophages and T cells. It also suggests the existence of a fourth population of intracavitary leukocytes adherent to mesothelial cells. Studies are now necessary to evaluate their exact role in the host defence against peritonitis during CAPD.

Biocompatibility of a glucose-polymer-containing peritoneal dialysis fluid

The currently available glucose-containing peritoneal dialysis fluids (PDF), which are all hyperosmolar, are toxic to the cells present in the peritoneal cavity. However, glucose-polymer solutions, being isosmolar, may have improved biocompatibility in this respect. We therefore compared in vitro the effects of PDF containing glucose-polymers with that of glucose solutions on the function of donor granulocytes and monocytes (MN), and on the viability of mesothelial cells. In addition, the function of peritoneal macrophages (PMO) of eight patients was studied in a randomized cross-over setting following intraperitoneal exposure to glucose-polymer-versus glucose-monomer-containing fluid of comparable ultrafiltration capacity. Donor granulocytes, as well as MN, showed significantly better phagocytosis of both Staphylococcus epidermidis and Escherichia coli after incubation in the glucose-polymer solution as compared with the 3.86% glucose-containing fluid. Their oxidative metabolism, as measured by chemiluminescence, also showed that the glucose-polymer solution was less inhibitory than fluids containing 2.27 or 3.86% glucose. Patient-derived PMO showed a significantly better phagocytic capacity for S epidermidis and E coli, a significantly higher killing of E coli, and a significantly higher chemiluminescence response after intraperitoneal exposure to the glucose-polymer solution as compared with the glucose-monomer-based fluid. Increasing the osmolality of the glucose-polymer solution to that of the respective glucose solutions blunted the favorable effect on phagocyte function, suggesting the beneficial effect to be osmolality-mediated. However, no major difference was observed between the glucose-polymer solution and the glucose-based fluid in their effects on mesothelial viability.(ABSTRACT TRUNCATED AT 250 WORDS)

Specific opsonic activity for staphylococci in peritoneal dialysis effluent during continuous ambulatory peritoneal dialysis

In a prospective study of intraperitoneal opsonins in 30 patients undergoing continuous ambulatory peritoneal dialysis (CAPD), the IgG concentration, the fibronectin concentration, the specific antistaphylococcal antibody level, and the opsonic activity against Staphylococcus epidermidis were measured in peritoneal dialysis effluent from the initiation of CAPD and monthly for 6 months. Significant correlation was found between the four assays, but the interindividual and intraindividual variations were considerable. No statistically significant correlation was observed between susceptibility of the patients to CAPD-related infectious peritonitis and any of the above-mentioned parameters of humoral defense. We conclude that at the present time it is not feasible to use these assays for the establishment of prognosis with regard to peritonitis in CAPD.

Microbiological aspects of peritonitis associated with continuous ambulatory peritoneal dialysis

The process of continuous ambulatory peritoneal dialysis has provided a useful, relatively inexpensive, and safe alternative for patients with end-stage renal disease. Infectious peritonitis, however, has limited a more widespread acceptance of this technique. The definition of peritonitis in this patient population is not universally accepted and does not always include the laboratory support of a positive culture (or Gram stain). In part, the omission of clinical microbiological findings stems from the lack of sensitivity of earlier microbiological efforts. Peritonitis results from decreased host phagocytic efficiency with depressed phagocytosis and bactericidal capacity of peritoneal macrophages. During episodes of peritonitis, fluid movement is reversed, away from the lymphatics and peritoneal membrane and toward the cavity. As a result, bloodstream infections are rare. Most peritonitis episodes are caused by bacteria. Coagulase-negative staphylococci are the most frequently isolated organisms, usually originating from the skin flora, but a wide array of microbial species have been documented as agents of peritonitis. Clinical microbiology laboratories need to be cognizant of the diverse agents so that appropriate primary media can be used. The quantity of dialysate fluid that is prepared for culture is critical and should constitute at least 10 ml. The sensitivity of the cultural approach depends on the volume of dialysate, its pretreatment (lysis or centrifugation), the media used, and the mode of incubation. The low concentration of microorganisms in dialysate fluids accounts for negative Gram stain results. Prevention of infection in continuous ambulatory peritoneal dialysis patients is associated with the socioeconomic status of the patient, advances in equipment (catheter) technology, and, probably least important, the application of prophylactic antimicrobial agents.

Surface phagocytosis and host defence in the peritoneal cavity during continuous ambulatory peritoneal dialysis

Since patients on continuous ambulatory peritoneal dialysis are at high risk for peritonitis, the opsonins in peritoneal dialysis effluent responsible for phagocytosis and a neutrophil chemiluminescence response to surface-adherent Staphylococcus epidermidis were examined. In surface phagocytosis assays uninfected dialysate was as opsonic as 1% serum. The opsonic activity was heat stable and equal to that of purified IgG at the same concentration (0.1 mg/ml). In contrast, optimal chemiluminescence to surface-adherent Staphylococcus epidermidis was dependent on complement. C3 deposition on Staphylococcus epidermidis opsonized in dialysate was quantitated by an enzyme immunoassay (EIA) and represented 13% of control C3 deposited with opsonization in 10% serum. Unused dialysate was found to be inhibitory to neutrophil phagocytosis and complement deposition. A combination of the low pH and high dextrose concentration of dialysate was responsible, but restoration of the pH to 7.4 largely restored both indices. During peritonitis there was a parallel increase in IgG levels and C3 deposition (r = 0.8), and surface phagocytosis was also enhanced. On further analysis, subjects with a single episode of peritonitis had a significantly more opsonic peritoneal effluent than those who had two infections during the study. This latter group had a poor IgG response to infection. This study demonstrates the relative deficiencies of host defence in the peritoneal cavity and indicates that measures to improve opsonin delivery and reduce the inhibitory effects of dialysate would be beneficial.