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.

Are Aldehydes in Heat-Sterllized Peritoneal Dialysis Fluids Toxic in Vitro?

Objective

Chemical analysis of several brands of peritoneal dialysis fluids (PD fluids) has revealed the presence of 2-furaldehyde, 5-HMF (5-hydroxymethylfuraldehyde), acetaldehyde, formaldehyde, glyoxal, and methylglyoxal. The aim of this study was to investigate if the in vitro side effects caused by glucose degradation products, mainly formed during heat sterilization, are due to any of these recently identified aldehydes.

Design

Cell growth media or sterile filtered PD fluids were spiked with different concentrations ofthealdehydes.

Measurements

In vitro side effects were determined as the inhibition of cell growth of cultured mouse fibro blasts or stimulated superoxide radical release from human peritoneal cells.

Results

Our results demonstrate that the occurrences of 2-furaldehyde, 5-HMF, acetaldehyde, formaldehyde, glyoxal, or methylglyoxal in heat-sterilized PD fluids are probably not the direct cause of in vitro side effects. In order to induce the same magnitude of cell growth inhibition as the heat-sterilized PD fluids, the concentrations of 2-furaldehyde, glyoxal, and 5-HMF had to be 50 to 350 times higher than those quantified in the PD fluids. The concentrations of acetaldehyde, formaldehyde, and methylglyoxal observed in the heat-sterilized PD fluids were closer to the cytotoxic concentrations although still 3 to 7 times lower.

Conclusion

Since none of these aldehydes caused in vitro toxicity at the tested concentrations, the toxicity found in PD fluids is likely to be due to another glucose degradation product, not yet identified. However, it is possible that these aldehydes may still have adverse effects for patients on peritoneal dialysis.

Short Term Clinical Study with Bicarbonate-Containing Peritoneal Dialysis Solution

Objective

The evaluation of the efficacy, adequacy, clinical tolerance, and safety of a new bicarbonate continuous ambulatory peritoneal dialysis (CAPD) solution.

Design and Patients

A 6–week cross-over clinical study in 6 stable CAPD patients was performed. After a control period (2 weeks) with a standard CAPD solution (lactate, 35 mmol/L), a two-chamber bag containing 34 mmol/L of bicarbonate was used for 4 weeks. A breakable valve divided the two chambers, one containing bicarbonate and the other calcium. The two solutions were mixed just before use, thus avoiding the calcium and magnesium carbonate precipitation.

Results

No differences between control and study periods were found for blood urea nitrogen, creatinine, total proteins, albumin, total and ionized calcium, phosphate, sodium, potassium, chlorine, and hemoglobin. Blood bicarbonate significantly increased from 21.25±2.02 to 23.36±1.15 (p<0.05) during the study. The peritoneal equilibration tests for urea nitrogen, creatinine, proteins, sodium, potassium, and glucose were slightly reduced during bicarbonate dialysate, but this effect was compensated for by a slight increase of ultrafiltration, thus keeping peritoneal clearances constant. Residual renal function did not change during the study. No side effects occurred during the bicarbonate period.

Conclusion

A CAPD bicarbonate solution is effective in uremic acidosis correction, does not affect dialysis adequacy, is safe, and well tolerated.

Factors Affecting Bicarbonate Transfer with Bicarbonate-Containing CAPD Solution

Objective

To evaluate bicarbonate fluxes across the peritoneal membrane and bicarbonate gain in patients treated with continuous ambulatory peritoneal dialysis (CAPD) using dialysis solutions with different bicarbonate concentrations.

Patients and Design

Ninety-seven exchanges, using different dwell times and glucose and bicarbonate concentrations were performed in 43 stable CAPD patients. Dialysate effluent bicarbonate concentration and volumes were measured at different dwell times. Net dialytic bicarbonate gain was calculated. Patients’ acid-base status was determined at the middle of the dwell.

Results

In prolonged dwells (6 –12 hours)thedialysate effluent bicarbonate concentration correlated with arterial plasma bicarbonate concentration (F = 129, p < 0.0001), but not with ultrafiltration rate or dialysis solution bicarbonate concentration. In 4-hour dwells, effluent bicarbonate concentration correlated with both plasma bicarbonate concentration and ultrafiltration rate (F = 32.52, p < 0.0001 and F = 4.4, p < 0.05, respectively). The effluent bicarbonate concentration may be predicted from the patient's plasma bicarbonate concentration and net ultrafiltration rate for either a 4-hour or prolonged (6 –12 hours) dwell time. Net bicarbonate gain by the patient correlated with ultrafiltration rate, plasma bicarbonate, and dialysis solution bicarbonate concentration (F = 100.56, p < 0.0001 at 4 hours and F = 108.08, p < 0.0001 at 6 12 hours), with the ultrafiltration rate being the predominant parameter.

Conclusions

The effluent bicarbonate concentration is related to plasma bicarbonate concentration, with ultrafiltration playing a marginal role only during short dwells. However, the ultrafiltration rate has a profound effect on net patient bicarbonate gain. Multiple linear regression analysis allows the prediction of the effect of acid-base status, ultrafiltration, dwell time, and dialysis solution bicarbonate content on net patient bicarbonate gain. It seems that bicarbonate content in the CAPD dialysis solution should be progressively increased with increasing solution osmolality.

How to Reduce 3-Deoxyglucosone and Acetaldehyde in Peritoneal Dialysis Fluids

Objective

3-Deoxyglucosone (3-DG) and acetaldehyde were found to be the major reactive carbonyl compounds in conventional heat-sterilized peritoneal dialysis fluids (PDFs). The aim of this study was to identify factors in the production of PDFs promoting or inhibiting the formation of acetaldehyde and 3-DG.

Design

Single-chamber bag PDFs with different buffer systems and pH values were analyzed for acetaldehyde. 3-Deoxyglucosone was determined in double-chamber bag PDFs with different pH values, in commercially available samples, and in double-chamber products stored under defined conditions.

Results

Acetaldehyde was found in the presence of lactate and malate, whereas in 2-hydroxybutanoate-buffered solution propionaldehyde was detected instead. Between pH 5.0 and 6.0 the acetaldehyde content in lactate-buffered solutions increased strongly. The concentration of 3-DG in the chamber containing glucose in double-chamber bags increased between pH 3.0 and 5.0 by a factor of 6. 3-Deoxyglucosone concentrations in commercially available products vary greatly, reflecting the different pH values of these products. A time- and temperature-dependent reaction leads to a reduction in 3-DG and an increase in 5-hydroxymethyl-furan-2-carbaldehyde during storage.

Conclusion

Acetaldehyde is produced by a reaction that requires both lactate and glucose. Thus, its formation can be prevented by a separation of the reaction partners, glucose and lactate, in a double-chamber bag. In double-chamber bags, pH greatly influences the formation of 3-DG. Minimal formation is observed in the region of pH 3.0. This finding should be taken into account for the development of new double-chamber bag PDFs.

Stimulation of Mesothelial Cells Proliferation by Endogenous Growth Factor(s)

We have attempted to determine whether human mesothelial cells (MC) have the power to influence their own proliferation. A serum -free medium was conditioned with the mesothelial monolayer for 24 hours and then applied to proliferating MC. Conditioned medium increased proliferation rate of MC. When the medium was heated at 60°C for 60 minutes, the growth-promoting activity of the conditioned medium decreased by 50%, suggesting that MC produce at least 2 growth factors, 1 heat-Iabile and the other heat-stable. When MC were exposed continuously to a medium containing 90 mM glucose growth factor, production was decreased by 35%. However, when the cells were exposed to glucose only on alternate days, growth-factor production was similar to that in the control medium. On the other hand, MC exposed continuously for 10 days to 90 mM of glucose exhibited a weaker response to endogenous growth factor, even in a normotonic medium with low glucose concentration. Our results suggest that MC syn thesize factor(s), which stimulate their own proliferation, and that high glucose concentrations interfere with this production and the subsequent action of growth factor.

A Randomized Controlled Trial of a Bicarbonate and a Bicarbonate/Lactate-Containing Dialysis Solution in Capd

Objective

To evaluate the safety and efficacy of bicarbonate and bicarbonate/lactate-based PD fluids.

Design

A randomly allocated prospective controlled trial lasting eight weeks.

Setting

Five renal units in Europe.

Patients

Individuals who have been treated by CAPD for at least three months and who have had at least one month's therapy with 40 mmol/L lactate PD fluid. Those with recent infection, diabetes or other serious illness are excluded. Forty-seven individuals have entered the study so far.

Interventions

Patients are randomly allocated to three groups. Group 1 receive 40 mmol/L lactate dialysate, Group 2 are given 38 mmol/L bicarbonate fluid and Group 3 are tested with a 25 mmol/L bicarbonate and 15 mmol/L lactate dialysate.

Outcome measures

The primary outcome measure is the plasma bicarbonate level. Adverse events and ease of use of the two-chambered bags used by Groups 2 and 3 are also being assessed.

Results

To date, plasma bicarbonate levels have been the same in all treatment groups up to the end of the trial period. There are no differences in serum lactate levels. No side effects are attributable to the test fluids. The patients have managed the two-chambered bags successfully.

Conclusion

This trial is still ongoing, but to date, neutral bicarbonate based fluids have been as effective as lactate dialysate in treating uremic acidosis.

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.

Induction of 1,2-Dicarbonyl Compounds, Intermediates in the Formation of Advanced Glycation End-Products, during Heat-Sterilization of Glucose-Based Peritoneal Dialysis Fluids

Objective

To study the presence of 1,2-dicarbonyl compounds in peritoneal dialysis (PD) fluids, their concentration in effluents with increasing dwell time, and their role in the formation of advanced glycation end-products (AGEs).

Measurements

Dicarbonyl compounds in heat- and filter-sterilized PD fluids were quantified by reverse-phase high performance liquid chromatography (HPLC) after derivatization to dimethoxyquinoxaline derivatives. Kinetics of the in vitro formation of AGEs upon incubation of 1,2-dicarbonyl compounds or PD fluids with albumin, with or without aminoguanidine, were measured by AGE fluorescence (excitation/emission wavelengths of 350 nm/430 nm).

Patients

AGEs and dicarbonyl compounds were measured in effluents collected from standardized 4-hour dwells from 8 continuous cycling peritoneal dialysis patients.

Results

In PD fluids, 3-deoxyglucosone (3-DG) has been identified as the major dicarbonyl compound formed during the process of heat sterilization. The process also formed glyoxal (GO) and methylglyoxal (MGO), with the amount of 3-DG being approximately 25 – 60 times higher than GO and MGO. When incubated with albumin, the identified 1,2-dicarbonyl compounds rapidly formed AGEs. The formation of AGEs was more pronounced in conventional heat-sterilized PD fluids compared with filter-sterilized PD fluids, and was completely inhibited by aminoguanidine. In effluents, the concentration of MGO, GO, and 3-DG decreased with increasing dwell time, with a concomitant increase in AGE fluorescence.

Conclusions

The dicarbonyl compounds 3-DG, MGO, and GO are potent promoters of AGE formation. The presence of these and possibly other dicarbonyl compounds formed during heat sterilization of glucose-based PD fluids is, to a large extent, responsible for the in vitro AGE formation by these fluids, as evidenced by the speed of AGE formation in PD fluids and the complete inhibition by aminoguanidine. Because 3-DG, MGO, and GO are rapidly cleared from PD fluids during dialysis, these compounds may contribute to the in vivo AGE formation in PD patients.

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.

The Mesothelial Cells in CAPD Effluent and Their Relation to Peritonitis Incidence

The total cell count and cell differentiation of the overnight peritoneal dialysis effluent (PDE) was analysed in 34 long-term CAPD patients. The mean percentage and yield of mesothelial cells were 3.1% and 0.17 × 106 per PDE. There was a significant lower percentage and yield of mesothelial cells in the PDE of patients with a peritonitis incidence (PI) of more than 2 episodes a year. Independent of dwell time, a positive correlation between the total yield of leucocytes and the yield of mesothelial cells was found. No relation between the amount of phospholipids in the PDE and the yield of mesothelial cells could be shown. Mesothelial cells in the PDE are probably reflecting the turn-over rate of a reactive mesothelium. Whether a low turn-over rate of the mesothelium is causing or is caused by a high PI needs further investigation.

In Vitro Study of the Mechanism of Potassium Transport into Human Mesothelial Cells. I: Effect of Hyperosmolality

Objective

To study the mechanism(s) of potassium transport into human mesothelial cells (HMC) exposed to osmotic solutes.

Design

Using potassium analog 86Rb, we evaluated its intracellular transport through three pathways: 1. blocked by ouabain; 2. blocked by furosemide but not by ouabain; 3. blocked by neither furosemide nor ouabain. Experiments were performed in a normotonic medium (control) or in a medium supplemented with osmotic solutes (glucose, glycerol, mannitol). Both the acute and chronic effects of osmotic solutes on potassium transport were studied.

Results

The acute exposure of mesothelial cells to osmotic solutes modifies the intracellular transport of potassium through all studied channels, and the effect is specific for every solute. In mesothelial cells exposed over 7 days to glucose (90 mM), the intracellular transport via ouabain and furosemide-blocked channels is decreased, whereas it is increased through the third pathway. Total intracellular accumulation of 86Rb (potassium) ions in mesothelial cells cultured in a medium supplemented with various concentrations of glucose is decreased, and this effect is proportional to the concentration of glucose in the medium.

Conclusions

The intracellular transport of potassium in mesothelial cells is regulated through at least three independent mechanisms. Acute or chronic exposure of mesothelial cells to a hypertonic medium affects the intracellular accumulation of potassium, an d this effect is specific for the various osmotic solutes.

Effects of Conventional and New Peritoneal Dialysis Solutions on Human Peritoneal Mesothelial Cell Viability and Proliferation

Objective

To investigate the biocompatibility of “new” peritoneal dialysis (PD) solutions with bicarbonate/lactate buffer, non glucose osmotic agents (icodextrin or amino acids), neutral pH, and low levels of glucose degradation products (GDPs).

Design

Using M199 culture medium as a control, we compared conventional and new PD solutions with respect to their effects on the viability of human peritoneal mesothelial cells (HPMCs) [using lactate dehydrogenase (LDH) release], on DNA damage in HPMCs [using single-cell gel electrophoresis (Comet assay)], and on HPMC proliferation (using [3H]-thymidine incorporation). The experiments were performed after cell growth was synchronized by incubation with serum-free media for 24 hours. The PD solutions tested included commercial 1.5% glucose and 4.25% glucose solutions with 40 mmol/L lactate (D 1.5 and D 4.25, respectively), 7.5% icodextrin (E), 1.1% amino acid (N), 1.5% glucose solution in a triple-chambered bag (Bio 1.5), 1.5% glucose solution in a dual-chambered bag with neutral pH (Bal 1.5), and 1.5% glucose and 4.25% glucose solution containing 25 mmol/L bicarbonate and 15 mmol/L lactate (P 1.5 and P 4.25, respectively).

Results

When HPMCs were continuously exposed to undiluted PD solutions, D 1.5, D 4.25, P 4.25, and E increased LDH release by more than 60% at 24 hours. All PD solutions tested increased LDH release by more than 75% at 96 hours. With 2-fold diluted PD solutions, only D 4.25 significantly increased LDH release at 96 hours, though not at 24 hours. When cells were exposed to undiluted PD solutions for 60 min and allowed to recover in M199 for up to 96 hours, LDH release was significantly higher at 24 – 96 hours in E (55% – 69%) and D 1.5 (48% –72%) as compared with control [M199 (18%)]. Release of LDH was significantly lower with PD solutions containing lower levels of GDPs than those in D 1.5, suggesting that GDPs may have a role in cell viability. The D solutions (D 1.5 and D 4.25) and E solution also induced significant DNA damage. Both LDH release and DNA damage by D and E were significantly attenuated by adjusting the solution pH to 7.4, suggesting that low pH may be implicated in PD solution–induced DNA damage and cell death. When diluted 2-fold, D 1.5, D 4.25, and P 4.25 decreased [3H]-thymidine incorporation to 43%, 34%, and 41% of control, respectively, at 24 hours and to 45%, 26%, and 35% of control, respectively, at 96 hours. When cells were exposed to undiluted PD solutions for 5 minutes and allowed to recover in M199 for up to 96 hours, D 1.5 and P 4.25—but not D 4.25—significantly inhibited cell proliferation at 24 hours. This effect was sustained up to 96 hours.

Conclusions

The present in vitro data demonstrate that PD solutions with low pH, or high levels of GDPs, or both, promote HPMC death and DNA damage, and that PD solutions with high osmolality inhibit cell proliferation. Solutions with neutral pH, amino acids, and “low GDPs” appear to be more biocompatible than conventional PD solutions. These results require confirmation in in vivo animal and clinical studies.

Clinical and Physiological Effects of a New, Less Toxic and Less Acidic Fluid for Peritoneal Dialysis

Objective

To report our first clinical experience with a new continuous ambulatory peritoneal dialysis (CAPD)fiuid (PD-Bio), which is nearly devoid of glucose degradation products and has a higher pH (6.3) than conventional peritoneal dialysis (PD) solutions, and to discuss in general terms some acute and long-term effects of conventional acidic solutions containing glucose degradation products.

Design

1) Pilot study on 4 patients investigated using a modified peritoneal equilibration test (PET) and cytobiology parameters. 2) Computer simulation study, assuming that conventional acidic solutions cause vasodilatation and recruitment of capillary surface area initially (during 0–60 minutes) in a PD dwell.

Patients

Four stable CAPD patients were chosen in an open cross-over study. After a period of three months using conventional PD fluid, the patients were switched to three months on the new PD fluid.

Results

Cancer antigen 125 increased significantly, and patients with discomfort/infusion pain during the control period improved during the period with the new fluid. No significant changes were observed in mass-transfer coefficients or drained volumes with the new solution. PH in the effluent dialysis was, however, higher for PD-Bio at all times during a two-hour dwell. In the computer simulation study, a less acidic solution caused an initially lower rate of glucose dissipation and improved ultrafiltration (UF) after a four -hour dwell, as compared to a conventional PD solution.

Conclusion

A new, differently produced, less toxic and less acidic PD fluid (PD-Bio) seems to be better tolerated than a conventional acidic solution with respect to discomfort/infusion pain. Theoretically, neutralized solutions should show slightly improved UF profiles over conventional acidic solutions, according to the computer simulation analysis. Furthermore, it is speculated that a neutral, less acidic, less toxic fluid would cause less interstitial-mesothelial alterations and less impairment of UF capacity than conventional solutions during longterm CAPD.

Peritoneal Kinetics and Mesothelial Markers in CCPD Using Icodextrin for Daytime Dwell for Two Years

Objective

To evaluate the safety, efficacy, and biocompatibility of icodextrin (Ico), continuous cycling peritoneal dialysis (CCPD) patients were treated for 2 years with either Ico- or glucose (Glu)-containing dialysis fluid for their daytime dwell (14 – 15 hours). Prior to entry into the study, all patients used standard Glu solutions (Dianeal, Baxter BV, Utrecht, The Netherlands).

Design

Open, randomized, prospective two-center study.

Setting

University hospital and teaching hospital.

Patients

Both established patients 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 or with peritonitis in the previous month, and women of childbearing potential unless taking adequate contraceptive precautions, were excluded. Thirty-eight patients entered the study (19 Glu, 19 Ico).

Main Outcome Measures

Daytime dwell peritoneal effluents were collected every 3 months in combination with other study variables (clinical data, laboratory measurements, dialysis-related data, and urine collection). Peritoneal transport studies were carried out every 6 months.

Results

In Glu- and Ico-treated patients, peritoneal transport of low molecular weight solutes and protein clearances neither changed during follow-up nor differed between the two groups. Peritoneal membrane markers (CA125, interleukin-8, carboxyterminal propeptide of type I procollagen, and aminoterminal propeptide of type III procollagen) measured in effluents did not differ between the groups and did not change over time. All these markers showed a dialysate/plasma ratio of more than 1, suggesting local production. Residual renal function remained stable during follow-up and adverse clinical effects were not observed.

Conclusions

Peritoneal membrane transport kinetics and markers remained stable in both groups over a 2-year follow-up period. Membrane markers were higher in effluents than in serum, suggesting local production. No clinical side effects were demonstrated. Icodextrin was a well-tolerated effective treatment.

Heat Sterilization of Fluids for Peritoneal Dialysis Gives Rise to Aldehydes

Objective

To chemically identify and quantify glucose degradation products in heat sterilized fluids for peritoneal dialysis.

Design

Three different brands of commercial PD-fluids and one laboratory made fluid, sterilized either by heat or filtration, were investigated for the presence of aldehydes.

Measurements

Aldehydes were identified and quantified using high performance liquid chromatography and gas chromatography.

Results

The tested brands of heat sterilized PD-fluids were found to contain several different aldehydes while the sterile filtered PD-fluid contained none. The highest concentrations in commercial PD-fluids of these aldehydes were: acetaldehyde (420 μm), glyoxal (14 μm), methylglyoxal (12 μm) and formaldehyde (11 μm). Valeraldehyde was also identified but not quantified. The presence of 5–HMF (15 μm) and 2-furaldehyde (2 μm), which has been identified by others, was confirmed.

Conclusions

The heat sterilization of commercial PD fluids gives rise to several aldehydes which may contribute to adverse effects of PD-fluids on patients.

Changes in Volume of Peritoneal Mesothelial Cells Exposed to Osmotic Stress

Objective

To evaluate changes in volume of mesothelial cells exposed to hypertonic medium and the role of volume regulatory mechanisms in adaptation to hyperosmolality.

Design

Experiments were performed on primary cultures of human peritoneal mesothelial cells. Cell volume was estimated by measuring equilibrated (intracellular/ extracellular space) 14C-urea in cellular water. Cells in monolayers were exposed to hyperosmotic media and changes in cellular water or intracellular uptake of 3H-proline were measured.

Results

Exposure of mesothelial cell monolayers to hyperosmotic media reduced the cell volume; the effect was proportional to the osmolality of the medium. Volume of cells exposed to medium supplemented with glucose (180 mmol/L) decreased by 26%, p < 0.001, after 30 minutes’ incubation. Prolonged exposure of mesothelial cells to hyperosmotic medium resulted in gradual recovery, after initial decline, of their volume. Intracellular uptake of amino acid 3H-proline increased after 240 minutes’ exposure of the mesothelial cells to medium supplemented with glucose (90 mmol/L) (+40%, p < 0.05). When cells cultured for 7 days in medium supplemented with glucose (45 mmol/L) were exposed to medium with low glucose content (5 mmol/L) their volume increased by 17%, p < 0.05.

Conclusion

Mesothelial cells shrink after exposure to hypertonic medium. Increased intracellular uptake of amino acids may be one of the regulatory mechanisms that ensure subsequent volume increase in these cells. Mesothelial cells chronically exposed to hypertonic medium swell after transfer to a medium with physiologic osmolality.

Peritoneal Transport Characteristics with Glycerol-Based Dialysate in Peritoneal Dialysis

Background

Glycerol is a low molecular weight solute (MW 92 D) that can be used as an osmotic agent in continuous ambulatory peritoneal dialysis (CAPD). Due to its low molecular weight, the osmotic gradient disappears rapidly. Despite the higher osmolality at the beginning of a dwell, ultrafiltration has been found to be lower for glycerol compared to glucose (MW 180 D) when equimolar concentrations are used. Previous studies have shown glycerol to be safe for long-term use, but some discrepancies have been reported in small solute transport and protein loss.

Objective

To assess permeability characteristics for a 1.4% glycerol dialysis solution compared to 1.36% glucose.

Design

Two standardized peritoneal permeability analyses (SPA), one using 1.4% glycerol and the other using 1.36% glucose, in random order, were performed within a span of 2 weeks in 10 stable CAPD patients. The length of the study dwell was 4 hours. Fluid kinetics and solute transport were calculated and signs of cell damage were compared for the two solutions.

Setting

Peritoneal dialysis unit in the Academic Medical Center, Amsterdam.

Results

Median values for the 1.4% glycerol SPA were as follows: net ultrafiltration 251 mL, which was higher than that for 1.36% glucose (12 mL, p < 0.01); transcapillary ultrafiltration rate 2.12 mL/min, which was higher than that for glucose (1.52 mL/min, p = 0.01); and effective lymphatic absorption rate 1.01 mL/min, which was not different from the glucose-based solution. Calculation of peritoneal reflection coefficients for glycerol and glucose showed lower values for glycerol compared to glucose (0.03 vs 0.04, calculated with both the convection and the diffusion models). A marked dip in dialysate-to-plasma ratio for sodium was seen in the 1.4% glycerol exchange, suggesting uncoupled water transport through water channels. Mass transfer area coefficients for urea, creatinine, and urate were similar for both solutions. Also, clearances of the macromolecules P2-microglobulin, albumin, IgG, and α2-macroglobulin were not different for the two osmotic agents. The median absorption was higher for glycerol, 71% compared to 49% for glucose ( p < 0.01), as could be expected from the lower molecular weight. The use of a 1.4% glycerol solution during a 4-hour dwell caused a small but significant median rise in plasma glycerol, from 0.22 mmol/L to 0.45 mmol/L ( p = 0.02). Dialysate cancer antigen 125 and lactate dehydrogenase (LDH) concentrations during the dwell were not different for both solutions.

Conclusions

These findings show that glycerol is an effective osmotic agent that can replace glucose in short dwells and show no acute mesothelial damage. The higher net ultrafiltration obtained with 1.4% glycerol can be explained by the higher initial net osmotic pressure gradient. This was seen especially in the first hour of the dwell. Thereafter, the osmotic gradient diminished as a result of absorption. The dip in dialysate-to-plasma ratio for sodium seen in the glycerol dwell can also be explained by this high initial osmotic pressure gradient, implying that the effect of glycerol as an osmotic agent is more dependent on intact water channels than is glucose.

Amino Acid-Based Peritoneal Dialysis Solution Stimulates Mesothelial Nitric Oxide Production

Objective

Ultrafiltration failure is a common problem in continuous ambulatory peritoneal dialysis. Recent work has indicated a role of enhanced expression of nitric oxide synthase (NOS) in ultrafiltration failure. However, the conditions predisposing to increased generation of NO by the peritoneum have not been studied in detail and the cell types potentially involved have not been tested individually.

Design

We performed experiments in human peritoneal mesothelial cells (HPMC) in culture. Amino acid-based dialysis solution (Nutrineal; Baxter Deutschland GmbH, München, Germany), L-arginine, and glucose-containing control solutions were used and we observed the effects on the HPMC. We reasoned that amino acid-based dialysis solutions containing L-arginine, the substrate of NOS, might influence mesothelial NO generation. Nitric oxide production was measured in the supernatant using the Griess reaction. We studied the effect of the combined NOS inhibitor L-NMMA and specified the isoform of NOS involved.

Results

In serum-free control medium, the cells exhibited baseline generation of nitrite at a rate of 5.4 ± 0.5 μmol/g protein. Addition of 6 mmol/L L-arginine to the control medium increased nitrite significantly (11.8 ± 0.66 μmol/g protein, p < 0.002), as did amino acid-based dialysis solution (15.7 ± 1.3 μmol/g protein, p < 0.002); L-NMMA caused a significant reduction of this nitrite. HPMC expressed eNOS (NOSIII) when grown in L-arginine-supplemented medium, shown by immunocytochemistry and by reverse transcriptase-polymer chain reaction. Biochemical exposure to a calcium ionophore in 1 μmol/L concentration approximately doubled the nitrite production by L-arginine-incubated cells.

Conclusion

Peritoneal mesothelial cells generate NO in vitro. Generation of NO increased further in response to L-arginine supplementation of the culture medium and to amino acid-containing dialysis solution. Mesothelial cells express eNOS, which was likely involved in the observed peritoneal NO generation.

A Long-Term Study of a Bicarbonate/Lactate-Based Peritoneal Dialysis Solution — Clinical Benefits

Objective

A bicarbonate/lactate peritoneal dialysis solution (Bic/Lac) has been developed based on in vitro and ex vivo data showing better preservation of cell function and correction of pain on infusion.

Design

This was a randomized, prospective, controlled, open-label study comparing a new 25 mmol/L bicarbonate/15 mmol/L lactate with a standard 40 mmol/L lactate-buffered peritoneal dialysis solution (Lac) over a 12-month treatment period.

Setting

17 European nephrology centers.

Patients

106 (70 Bic/Lac and 36 Lac) well-dialyzed continuous ambulatory peritoneal dialysis (CAPD) patients.

Interventions

Dialysis adequacy and peritoneal equilibration test (PET, week –4, months 3, 6, and 12); 24-hour ultrafiltration (week –4, months 1, 3, and 6); blood biochemistry (week –2, day 0, months 1, 2, 3,6, 9, and 12); and a product acceptability questionnaire (months 1 and 6).

Results

88 patients completed the first 6 months, and 44 the full year. The solutions were shown to be therapeutically equivalent with respect to plasma bicarbonate and peritoneal urea and creatinine clearances. Ultrafiltration in the Bic/Lac group increased significantly from baseline by about 150 mL/day for the whole of the 6-month treatment period ( p < 0.05). The biochemistry profile, adverse events, and physical examination (except body weight where there was a statistically significant increase in the Bic/Lac group) results did not differ significantly between the two groups. Reduced pain/discomfort on infusion or an increased sense of well-being was reported by 41% of patients on the Bic/Lac fluid.

Conclusions

The Bic/Lac solution is safe and effective in correcting uremic acidosis, provides relief of inflow pain/discomfort, and improves ultrafiltration and body weight.

In Vitro Study of the Effect of Osmotic Solutes on the Interactions between Cells from the Peritoneum and Peritoneal Cavity

Objective

To study how the presence of osmotic solutes in medium affects growth of the peritoneal mesothelial cells and fibroblasts and how osmotic solutes influence the production of factors regulating growth of these cells.

Design

The proliferation of mesothelial cells and fibroblasts was evaluated by measuring the incorporation of 3H-thymidine into the cells. Cells were exposed to osmotic solutes; the concentration of the latter in the medium was continuously lowered over the time of the experiment to simulate changes of their concentration in the dialysate. The synthesis of factors influencing the proliferation of the mesothelial cells or fibroblasts, by mesothelial cells or fibroblasts themselves, or by peritoneal leukocytes, was tested by the characteristics of the “conditioned” medium. The conditioned medium was produced by exposing standard medium to mesothelial or fibroblasts monolayer or to peritoneal leukocytes over 24 hours; following filtration it was applied to growing test cells for the study of growth factors.

Results

The effect of osmotic solutes on the growth of mesothelial cells is less inhibitory when their concentration is gradually lowered over the time of the study, compared to previous findings with a constant concentration. Peritoneal leukocytes produce growth factors for mesothelial cells and fibroblasts. Glucose and amino acids inhibit production of peritonealleukocyte-derived growth factors for mesothelial cells, while glycerol increases synthesis of such growth factors for fibroblasts. Mesothelial cells produce factors stimulating the proliferation of mesothelial cells and fibroblasts. In the presence of glycerol or amino acids synthesis of mesothelium derived growth factors for fibroblasts is augmented. Finally, fibroblasts produce factors that inhibit the proliferation of the mesothelial cells, and this effect is potentiated in the presence of amino acids.

Conclusions

Cytotoxicity of the osmotic solutes measured by the inhibition of growth of the mesothelial cells or their increased damage is significantly reduced during in vitro kinetic study when the concentration of these solutes is gradually lowered. Presence of osmotic solutes in the medium affects synthesis of growth factors derived from mesothelium, fibroblasts, or peritoneal leukocytes, which affect the proliferation of mesothelial cells or fibroblasts.

Generalized Dilation of the Visceral Microvasculature by Peritoneal Dialysis Solutions

Objectives

Conventional peritoneal dialysis solutions are vasoactive. This vasoactivity is attributed to hyperosmolality and lactate buffer system. This study was conducted to determine if the vasodilator property of commercial peritoneal dialysis solutions is a global phenomenon across microvascular levels, or if this vasodilation property is localized to certain vessel types in the small intestine.

Design

Experimental study in a standard laboratory facility.

Interventions

Hemodynamics of anesthetized rats were monitored while the terminal ileum was prepared for in vivo intravital microscopy. Vascular reactivity of inflow arterioles (A1), branching (A2), and arcade, as well as pre-mucosal (A3) arterioles was assessed after suffusion of the terminal ileum with a non-vasoactive solution or a commercial 4.25% glucose-based solution (Delflex; Fresenius USA, Ogden, Utah, USA). Vascular reactivity of three different level venules was also assessed. Maximum dilation response was obtained from sequential applications of the endothelial-dependent dilator, acetylcholine (10–5 mol/L), and the endothelial-independent nitric oxide donor, sodium nitroprusside (NTP; 10–4mol/L).

Results

Delflex induced an instant and sustained vasodilation that averaged 28.2% ± 2.4% of baseline diameter in five different-level arterioles, ranging in size between 7 μ and 100 μ. No significant vascular reactivity was observed in three different-level venules. Delflex increased intestinal A1 blood flow from baseline 568 ± 31 nL/second to 1049 ± 46 nL/sec ( F = 24.7, p < 0.001). Similarly, intestinal venous outflow increased to 435 ± 17 nL/sec from a baseline outflow of 253 ± 59 nL/sec ( F = 4.7, p < 0.05). Adjustment of the initial pH of Delflex from 5.5 to 7.4 resulted in similar microvascular responses before pH adjustment.

Conclusions

Ex vivo exposure of intestinal arterioles to conventional peritoneal dialysis solutions produces a sustained and generalized vasodilation. This vasoactivity is independent of arteriolar level and the pH of the solution. Dialysis solution-mediated vasodilation is associated with doubling of A1 intestinal arteriolar blood flow. Addition of NTP at an apparent clinical dose does not appear to produce any further significant arteriolar dilation than that induced by dialysis solution alone. Experimental data that estimate the exchange vessel surface area per unit volume of tissue will be required to make a correlation with permeability in order to extrapolate our findings to clinical in vivo conditions.

Peritonitis Occurrence in a Multicenter Study of Icodextrin and Glucose in CAPD

Objective

To compare peritonitis occurrence and outcome in a large U.K. study Multicentre Investigation of Icodextrin in Ambulatory Dialysis (MIDAS).

Design

Prospective, randomized, controlled 6-month comparison of icodextrin with glucose for the long dwell in continuous ambulatory peritoneal dialysis (CAPD) patients.

Setting

Eleven CAPD units in U.K. teaching hospitals.

Patients

A total of 209 patients established on CAPD for at least 3 months (103 control, 106 icodextrin). Twentythree control (C) and 22 icodextrin (I) patients experienced peritonitis during the study.

Intervention

Patients who had peritonitis remained on treatment (unless CAPD was withdrawn, temporarily or permanently).

Main Outcome Measures

The main outcome measures were the rate of peritonitis and duration of CAPD treatment prestudy; the rate of peritonitis episodes and their outcome during study; the effect of peritonitis on laboratory variables, serum icodextrin metabolites, and ultrafiltration efficacy.

Results

Prestudy: Nine (39%) of C but 14 (64%) of I patients had suffered previous peritonitis episode(s), with overall rates of 0.58 and 0.78 episodes per patient year, respectively.

During study

There were 31 C episodes and 35 I episodes, with overall rates of 0.76 and 0.93 per patient year, respectively. The increase in the C and I groups was 31% and 19%, respectively. Serum osmolality and sodium levels were unaffected by peritonitis, and there was no increase in serum icodextrin metabolites during peritonitis. Overnight ultrafiltration volume during peritonitis (mean±SD) declined slightly from 218±354 mL to 185±299 mL (NS) in the control group, but increased in the icodextrin group from 570±146 mL to 723±218 mL (p < 0.01).

Conclusions

Using icodextrin for the long dwell in CAPD does not increase the rate of peritonitis, nor does it alter the outcome of peritonitis. Peritonitis does not affect uptake of icodextrin from the peritoneum.

Acidosis Correction with a new 25 Mmol/L Bicarbonate/15 Mmol/L Lactate Peritoneal Dialysis Solution

Objective

The aim of this study was to evaluate the effects of a combined 25 mmol/L bicarbonate/15 mmol/L lactate-based solution (Bic/Lac), compared to a 35 mmol/L lactate solution (Lac) — the most commonly used solution for patients in southern Europe — on the venous plasma bicarbonate level in patients treated with continuous ambulatory peritoneal dialysis (CAPD).

Design

This was a randomized, parallel, controlled, open-label study, with patients studied for a period of 3 months preceded by a 1-month baseline and followed by a 1-month follow-up. Patients used the 35 mmol/L lactate solution during baseline and follow-up periods.

Setting

Four Spanish nephrology centers.

Patients

Thirty-one (20 Bic/Lac, 11 Lac) well-dialyzed (creatinine clearance > 55 L/week/1.73 m2body surface area) CAPD patients.

Interventions

Blood samples were taken for biochemistry tests at all visits. A physical examination was completed at baseline and month 3, and a medical update was completed after 1, 2, and 3 months, and at the follow-up visit. Adverse-event monitoring and notation of prescription changes were carried out continuously.

Main Outcome Measure

Effect on venous plasma bicarbonate level.

Results

Venous plasma bicarbonate rose by 3.1 mmol/L (confidence intervals 1.6 – 4.8), from a baseline level of 23.0 mmol/L during the treatment period in those patients treated with Bic/Lac ( p < 0.05 vs Lac). The number of acidotic patients (venous plasma bicarbonate < 24 mmol/L) was statistically significantly reduced at every treatment period visit in the Bic/Lac group ( p < 0.05). There were no adverse findings with respect to vital signs, physical examination, or clinical symptoms, apart from one death in the control group.

Conclusions

The new Bic/Lac solution allowed better correction of acid–base status than the lactate solution.

Changes in Biocompatibility of Dialysis Fluid during Its Dwell in the Peritoneal Cavity

Objective

To evaluate the changes in biocompatibility of peritoneal dialysis solutions during intraperitoneal dwell.

Design

We studied the effect of the drained dialysates at time 0 and after 30, 60, 120, 240, and 360 minutes of intraperitoneal dwell on the growth of peritoneal mesothelial cells and fibroblasts and the synthesis of proteins by these cells. On one day the patients were dialyzed with glucose-based Dianeal and on alternate days with an amino acid-containing solution based on Travasol.

Patients

Dialysates were collected from 4 patients during continuous ambulatory peritoneal dialysis (CAPD) training.

Results

Unused dialysis solutions containing glucose or amino acids inhibit growth of mesothelial cells and fibroblasts. Dialysates obtained after 30 or 60 minutes of intraperitoneal dwell support the growth of these cells in a way similar to 10% fetal calf serum, but dialysates drained after a longer dwell of 120 360 minutes had a stronger effect on growth of these cells than did serum. All glucose-based dialysates stimulate the synthesis of collagen in mesothelial cells, whereas they reduce the synthesis of non-collagen proteins. All glucose-based dialysates reduce the synthesis of collagen and noncollagen proteins in fibroblasts compared with the production of these proteins in the presence of serum.

Conclusion

Changes in the properties of the dialysis solutions during their intraperitoneal dwells do not seem to increase their biocompatibility. Indeed, excessive mitogenic effect and the stimulation of collagen synthesis of the dialysates may induce pathological changes in the peritoneum.

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.

Cell Function and Viability in Glucose Polymer Peritoneal Dialysis Fluids

Objective

To investigate the biocompatibility profile of a new peritoneal dialysis fluid containing glucose polymer (GPF).

Design

Viability and function of peripheral neutrophils (PMN) from healthy donors and cultured human peritoneal mesothelial cells were assessed in vitro after exposure to dialysis fluids. Phagocytosis, leukotriene B4 synthesis, and respiratory burst activation were measured following stimulation with serum-treated zymosan (STZ) or opsonized Staphylococcus epidermidis (S. epidermidis). Bacterial growth in the fluids was also investigated. In vivo pH equilibration of GPF and subsequent respiratory burst activation following incubation in spent dialysate were studied.

Results

For all the host defense parameters measured, commercial dialysis fluids (Dianeal; 1.36% and 3.86% glucose) and GPF (pH 5.2) were significantly more inhibitory than the control buffer (pH 7.3). Mesothelial cell viability was reduced by all the fluids tested irrespective of pH. Glucose polymer fluid was significantly more inhibitory than DianeaI 1.36% for STZ phagocytosis and respiratory burst activation. In contrast, it was less suppressive than DianeaI3.86% for L TB4 synthesis. For all parameters tested, except LTB4 generation, there was a marked effect of pH, with GPF being significantly more inhibitory at pH 5.2 than at pH 7.3. None of the fluids tested supported the growth of S. epidermidis, although the viable counts in GPF were significantly higher than in Dianeal. Fluid inhibition of PMN respiratory burst activation and cytotoxicity were reduced in a time-dependent manner following increasing dwell time in vivo.

Conclusions

GPF does not appear to be significantly different from Dianeal as far as host defense parameters are concerned. However, the cell viability and bacterial survival data suggest some possibly negative aspects of this fluid formation.

In Vitro Biocompatibility of a Heat -Sterilized, Low Toxic, and Less Acidic Fluid for Peritoneal Dialysis

Objective

The aim of this study was to investigate a peritoneal dialysis (PD) fluid (PD-Bio), produced with the intention of reducing the amount of glucose degradation products and to increase the final pH. The heat sterilization of the fluid was performed with the glucose separated from the electrolytes. After sterilization the two solutions were combined.

Methods

The in vitro biocompatibility of PD-Bio was measured as the inhibition of cell growth of a cultured fibroblast cell line and as the stimulated release of interleukin-1β from cultured human mononuclear cells. The glucose degradation products were measured as UV absorbance at 228 nm or 284 nm and the concentration of aldehydes was estimated with high-performance liquid chromatography and gas chromatography.

Results

Our results demonstrate that in comparison to conventional PD fluids the pH of PD-Bio was increased, to about 6.5. Due to less contaminating glucose degradation products in PD-Bio, basal cytotoxicity was significantly decreased for both 1.5% and 4% glucose-containing fluids, and the stimulated release of interleukin-1β was normalized compared to sterile filtered controls with the same pH. UV absorbance measured at 228 nm was decreased, whereas the absorbance at 284 nm was equal to that of a conventional fluid. In PD-Bio the concentrations of formaldehyde, acetaldehyde, methylglyoxal, and 2-furaldehyde were found to be below the detection limit, whereas glyoxal was present in the same and 5hydroxymethylfurfural (5-HMF) in higher concentrations than in conventionally produced PD fluid.

Conclusions

The results demonstrate that it is possible to improve biocompatibility of PD fluids by simply changing the way the fluid is produced.

Development of Toxic Degradation Products during Heat Sterilization of Glucose-Containing Fluids for Peritoneal Dialysis: Influence of Time and Temperature

Objective

Fluids for peritoneal dialysis (PD) cause cytotoxic reactions in many different in vitro systems. The low pH, the high osmolality of the fluids, and the glucose degradation products formed during heat sterilization have been considered responsible. In the present study, we investigate the influence of temperature and time during heat sterilization of PD fluids and glucose solutions on glucose degradation and cytotoxicity of the solutions.

Design

Ampoules containing PD-fluid or glucose solution were heated in an oil bath to predetermined F o values (combinations of time and temperature giving equal energy/bacteriallethality). Cytotoxicity of the solutions was measured as groWth inhibition of cultured L-929 fibroblasts. Glucose degradation was measured as UV absorbance at 228 and 284 nm.

Results

The same general pattern was seen in both PD fluid and glucose solution. Cytotoxicity decreased from 90% to 15% when the sterilization temperature was increased from 115° to 140°C and concomitantly the length of time shortened in order to maintain equal bacteriallethality. Under the same conditions, degradation products, measured as UV absorbance at 284 nm, decreased from 0.2 to 0.02.

Conclusion

To minimizethe development of cytotoxic breakdown products, high temperatures over short periods of time should be used to heat-sterilize PD fluids. Even as small an increase as 5°C at around 120°C will improve the quality of the solutions.

High Glucose Solution and Spent Dialysate Stimulate the Synthesis of Transforming Growth Factor-β1of Human Peritoneal Mesothelial Cells: Effect of Cytokine Costimulation

Objective

To investigate the effect of high glucose and spent peritoneal dialysate on the transforming growth factor-β1(TGFβ1) synthesis of cultured human peritoneal mesothelial cells (HPMCs) and to examine the effect of costimulation with high glucose or spent dialysate, and cytokines, interleukin-1β (IL-1β), and tumor necrosis factor-α (TNFα) on TGFβ1synthesis of HPMCs.

Design

HPMCs were exposed to different concentrations of glucose (30, 60, and 90 mmol/L) or spent peritoneal dialysate for 48 hours in the absence or presence of IL-1β (1 ng/mL) and TNFα (1 ng/mL). TGFβ1mRNA expression was assessed by Northern blot analysis and TGFβ1protein release by Western blot analysis and enzymelinked immunosorbent assay (ELISA).

Results

Exposure of HPMCs to high glucose conditions (30, 60, and 90 mmol/L of D-glucose) induced 2.3-, 3.6-, and 4.0-fold increases in TGFβ1mRNA expression of HPMC with enhanced TGFβ1protein synthesis and secretion into the media, whereas there were no significant changes in TGFβ1synthesis with equimolar concentrations of D-mannitol. Incubation with spent dialysate also significantly increased TGFβ1mRNA expression and protein secretion compared to control media ( p < 0.05). Stimulation with IL-1β (1 ng/mL) or TNFα (1 ng/mL) resulted in a significant increase in TGFβ1mRNA expression after 48 hours: 2.7 and 2.1 times the control level, respectively. However, TNFα-induced increase in TGFβ1mRNA expression was not translated into TGFβ1protein secretion, while IL-1β stimulation induced a significant increase in TGFβ1protein secretion as well as TGFβ1mRNA expression. Combined stimulation by high glucose or spent dialysate, together with IL-1β or TNFα, showed a greater increase in TGFβ1mRNA expression and protein secretion compared to stimulation by high glucose or spent dialysate alone.

Conclusion

Our results clearly show that high glucose solution and spent dialysate themselves might be sufficient to stimulate the production of TGFβ1by peritoneal mesothelial cells. In peritoneal dialysis patients, this state of chronic induction of TGFβ1is further exacerbated in the presence of peritonitis because of the stimulatory effect of proinflammatory cytokines, resulting in augmented TGFβ1synthesis, thus promoting peritoneal fibrosis.

Peritonitis Occurrence in a Multicenter Study of Icodextrin and Glucose in Capd

Objective

To compare peritonitis occurrence and outcome in a large U.K. study Multicentre Investigation of Icodextrin in Ambulatory Dialysis (MIDAS).

Design

Prospective, randomized, controlled 6-month comparison of icodextrin with glucose for the long dwell in continuous ambulatory peritoneal dialysis (CAPD) patients.

Setting

Eleven CAPD units in U.K. teaching hospitals.

Patients

A total of 209 patients established on CAPD for at least 3 months (103 control, 106 icodextrin). Twentythree control (C) and 22 icodextrin (I) patients experienced peritonitis during the study.

Intervention

Patients who had peritonitis remained on treatment (unless CAPD was withdrawn, temporarily or permanently).

Main Outcome Measures

The main outcome measures were the rate of peritonitis and duration of CAPD treatment prestudy; the rate of peritonitis episodes and their outcome during study; the effect of peritonitis on laboratory variables, serum icodextrin metabolites, and ultrafiltration efficacy.

Results

Prestudy: Nine (39%) of C but 14 (64%) of I patients had suffered previous peritonitis episode(s), with overall rates of 0.58 and 0.78 episodes per patientyear, respectively.

During study

There were 31 C episodes and 35 I episodes, with overall rates of 0.76 and 0.93 per patientyear, respectively. The increase in the C and I groups was 31% and 19%, respectively. Serum osmolality and sodium levels were unaffected by peritonitis, and there was no increase in serum icodextrin metabolites during peritonitis. Overnight ultrafiltration volume during peritonitis (mean±SD) declined slightly from 218±354 mL to 185±299 mL (NS) in the control group, but increased in the icodextrin group from 570±146 mL to 723±218 mL (p < 0.01).

Conclusions

Using icodextrin for the long dwell in CAPD does not increase the rate of peritonitis, nor does it alter the outcome of peritonitis. Peritonitis does not affect uptake of icodextrin from the peritoneum.

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.