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.

Risk Factors for Early Mortality in U.S. Peritoneal Dialysis Patients: Impact of Residual Renal Function

Background

Potential risk factors for 1-year mortality, including the peritoneal component of dialysis dose, residual renal function, demographic data, hematocrit, serum albumin, dialysate-to-plasma creatinine ratio, and blood pressure, were examined in a national cohort of peritoneal dialysis patients randomly selected for the Centers for Medicare and Medicaid Services End-Stage Renal Disease (ESRD) Core Indicators Project.

Methods

The study involved retrospective analysis of a cohort of 1219 patients receiving chronic peritoneal dialysis who were alive on December 31, 1996.

Results

During the 1-year follow-up period, 275 patients were censored and 200 non censored patients died. Among the 763 patients who had at least one calculable adequacy measure, the mean [± standard deviation (SD)] weekly Kt/V urea was 2.16 ± 0.61 and the mean weekly creatinine clearance was 66.1 ± 24.4 L/1.73 m2. Excluding the 365 patients who were anuric, the mean (±SD) urinary weekly Kt/V urea was 0.64 ± 0.52 (median: 0.51) and the mean (±SD) urinary weekly creatinine clearance was 31.0 ± 23.3 L/1.73 m2 (median: 26.3 L/1.73 m2). By Cox proportional hazard modeling, lower quartiles of renal Kt/V urea were predictive of 1-year mortality; lower quartiles of renal creatinine clearance were of borderline significance for predicting 1-year mortality. The dialysate component of neither the weekly creatinine clearance nor the weekly Kt/V urea were predictive of 1-year mortality. Other predictors of 1-year mortality ( p < 0.01) included lower serum albumin level, older age, and the presence of diabetes mellitus as the cause of ESRD, and, for the creatinine clearance model only, lower diastolic blood pressure.

Conclusion

Residual renal function is an important predictor of 1-year mortality in chronic peritoneal dialysis patients.

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.

The Biology of the Mesothelium during Peritoneal Dialysis

Substantial derangements of mesothelial biology are observed during experimental simulations of dialysis conditions, inferred from the content of human dialysis effluent and visualized by microscopy of human mesothelial biopsies. Canosmotically active solutions be made biocompatible with the osmoregulatory system of the mesothelium? Can the contributions of the mesothelium to host defenses against inflammation and/or infection be supported during CAPD? Do underlying metabolic derangements present in various kidney diseases and end-stage renal disease, regardless of cause, require customized CAPD protocols and solutions? Use of dialysis solutions less directly toxic to the mesothelium is a necessary step toward some day manipulating peritoneal biology by pharmacological and therapeutic modalities.

The Potential of Gene Therapy in the Peritoneal Cavity

Gene therapy is a promising new treatment modality based on molecular genetic modification to achieve a therapeutic benefit. We believe that gene therapy in the peritoneal cavity holds considerable promise, and we describe strategies by which genetic modification can be used to treat a variety of disease states or conditions. First, we can envision a strategy, based on genetic modification of the peritoneal membrane, to improve the practice of peritoneal dialysis through the production of proteins that would be of therapeutic value in preventing membrane damage and in preserving or enhancing its function as a dialyzing membrane. Second, the membrane could be genetically modified for either local or systemic delivery of therapeutic proteins. This approach could be applied to a variety of pathologies or conditions that require either sustained or transient delivery of therapeutic proteins, such as enzymes or growth factors. Third, gene transfer has already been incorporated into several strategies for the treatment of intra-abdominal carcinomas, and it has been effective in animal models of ovarian and bladder cancer and of peritoneal mesothelioma. Finally, gene transfer can be a valuable tool in increasing our understanding of the biology of the peritoneal membrane. By being able to manipulate the expression of specific genes through gene transfer, their role in various (patho)physiological processes can be identified. In summary, gene therapy in the peritoneal cavity has significant potential to address a variety of diseases or pathophysiological conditions, and to further our knowledge of peritoneal cavity biology.

The Clinical Usefulness of Peritoneal Dialysis Fluids with Neutral pH and Low Glucose Degradation Product Concentration: An Open Randomized Prospective Trial

Background

Long-term peritoneal dialysis (PD) is associated with the development of various structural and functional changes to the peritoneal membrane when bioincompatible conventional peritoneal dialysis fluids (PDFs) are used. In this study, we looked at patients that were treated with conventional PDFs and then changed to novel biocompatible PDFs with a neutral pH and a low concentration of glucose degradation products (GDPs) to investigate whether this change could result in the arrest or reversal of peritoneal membrane deterioration.

Methods

In an open label, randomized prospective trial, the clinical effects of conventional PDFs and biocompatible PDFs with neutral pH and very low concentration of GDPs were compared in 104 patients equally divided between both study PDFs. Blood and effluent dialysate samples, peritoneal equilibration tests, and adequacy evaluation were undertaken at baseline, 4, 8, and 12 months. The target variables were the ratio of dialysate-to-plasma (D/P) creatinine, peritoneal ultrafiltration, residual renal function, dialysis adequacy indices, and effluent cancer antigen 125 (CA125).

Results

D/P creatinine values were not different in the two groups. Peritoneal ultrafiltration was significantly higher in the low-GDP PDF group than in the conventional PDF group at all follow-up times (4 months: 9.1 ± 4.3 vs 6.0 ± 3.0; 8 months: 8.3 ± 3.4 vs 6.0 ± 3.0; 12 months: 8.9 ± 3.3 vs 6.1 ± 3.3 mL/g dextrose/day; p < 0.05). Peritoneal Kt/V urea values and total weekly Kt/V urea values at 4 months were significantly higher in the low-GDP PDF group than in the conventional PDF group. Residual renal function was not statistically significant. Effluent CA125 levels were significantly higher in the low-GDP PDF group at all follow-up visits (4 months: 37.8 ± 20.8 vs 22.0 ± 9.5; 8 months: 41.2 ± 20.3 vs 25.9 ± 11.3; 12 months: 40.4 ± 21.4 vs 28.6 ± 13.0 U/mL; p < 0.05). Among anuric patients, peritoneal ultrafiltration at 4, 8, and 12 months, total weekly Kt/V at 4 and 8 months, and CA125 levels at all follow-up visits were significantly higher in patients treated with low-GDP PDF than those treated with conventional PDF. However, among anuric patients, D/P creatinine showed no significant differences between the low-GDP PDF group and the conventional PDF group.

Conclusion

The use of biocompatible PDFs with neutral pH and low GDP concentration can contribute to improvement of peritoneal ultrafiltration and peritoneal effluent CA125 level, an indicator of peritoneal membrane integrity in PD patients.

Activation of salt-inducible kinase 2 promotes the viability of peritoneal mesothelial cells exposed to stress of peritoneal dialysis

Maintaining mesothelial cell viability is critical to long-term successful peritoneal dialysis (PD) treatment. To clarify the viability mechanism of peritoneal mesothelial cells under PD solutions exposure, we examined the mechanisms of cellular response to this stress conditions. Here we report that the proteasome activity is inhibited when treated with PD solutions. Proteasome inhibition-mediated activation of salt-inducible kinase 2 (SIK2), an endoplasmic reticulum-resident protein, is important for mesothelial cell viability. SIK2 is mobilized to promote autophagy and protect the cells from apoptosis under PD solution or MG132 treatment. Immunofluorescence staining showed that SIK2 is colocalized with LC3B in the autophagosomes of mesothelial cells treated with PD solution or derived from patients undergoing PD treatment. SIK2 activation is likely via a two-step mechanism, upstream kinases relieving the autoinhibitory conformation of SIK2 molecule followed by autophosphorylation of Thr175 and activation of kinase activity. These results suggest that activation of SIK2 is required for the cell viability when proteasome activity is inhibited by PD solutions. Maintaining or boosting the activity of SIK2 may promote peritoneal mesothelial cell viability and evolve as a potential therapeutic target for maintaining or restoring peritoneal membrane integrity in PD therapy.

TGF-β1 promotes transition of mesothelial cells into fibroblast phenotype in response to peritoneal injury in a cell culture model

BACKGROUND

Peritoneal adhesions are a clinical problem. A key to the understanding of peritoneal adhesions is to study the healing of mesothelial cells within the peritoneal cavity following surgery. Transforming growth factor beta (TGF-βs) affects this healing process. The aim of this study was to investigate the effects of different concentrations of TGF-β1 on the healing rate and healing properties of mesothelial cells.

MATERIALS AND METHODS

Human mesothelial cells from peritoneal fluid were collected, cultured and a mechanical wound was created. The restoration of the mesothelial surface with and without increasing concentrations of TGF-β1 was monitored.

RESULTS

The denuded area was restored within 24 h. The healing rate was most extensive between the first and second hour after the damage (61.9 ± 22.8 μm/h). No significant difference in healing rate were observed when increasing levels of TGF-β1 were used. However, higher concentrations of TGF-β1 increased cell size and the cells presented more fibroblast specific properties. Lower TGF-β1 concentrations increased the number of proliferating cells.

CONCLUSIONS

This study indicates the importance of high levels TGF-β1 in mesothelial cell healing, mainly by changing the actual healing properties of the cells. Elevated levels of TGF-β1 might promote mesothelial cell transition towards a more fibroblast-like appearance.

Adenoviral-mediated gene expression of hepatocyte growth factor prevents postoperative peritoneal adhesion in a rat model

BACKGROUND

Mesothelial cell proliferation and migration play important roles in reducing formation of postoperative peritoneal adhesions. Hepatocyte growth factor (HGF) is a multifunctional cytokine that stimulates proliferation and migration of various cell types, including mesothelial cells.

METHODS

We investigated the effect of adenovirus-mediated HGF gene expression on the proliferation and migration of mesothelial cells and evaluated its preventive effects on postoperative formation of peritoneal adhesions. Rat mesothelial cells were isolated and characterized by expression of cytokeratin and vimentin.

RESULTS

Immunohistochemical staining showed that these cells expressed c-Met, the receptor for HGF. Adenoviral-mediated HGF gene transfer into mesothelial cells resulted in high expression of HGF and enhanced migration. To evaluate the preventive effects of adenoviral-mediated HGF gene transfer on the formation of postoperative peritoneal adhesion, we employed a rat model of cecum abrasion-induced adhesion formation in which 80% of the rats developed postoperative peritoneal adhesions. Local application of recombinant adenovirus carrying the HGF gene reduced adhesion formation in 16 of 20 control rats compared with 7 of 20 treated rats in this model.

CONCLUSIONS

These results suggest that adenoviral-mediated HGF gene transfer may be a novel strategy for preventing postoperative peritoneal adhesions.

In vitro biocompatibility performance of Physioneal

In vitro biocompatibility performance of Physioneal. toneal dialysis (PD) has been a successful and effective form of chronic renal replacement therapy since its introduction over 20 years ago. Despite its overall success, there is a growing body of evidence that suggests shortcomings in the preservation of membrane integrity. This has led to the development of several second-generation PD solutions that demonstrate improved biocompatibility. Physioneal, a neutral pH, bicarbonate/lactate-buffered solution, was one of the first of these new PD solutions to become commercially available. This review will focus on one of the first preclinical stages in the development of Physioneal: studies on in vitro biocompatibility testing. Studies in leukocyte, mesothelial cell, and fibroblast populations demonstrated significantly improved biocompatibility of neutral pH, bicarbonate/lactate-based solutions compared to conventional solutions. The solutions contributed to improved leukocyte viability and response to bacterial infection (e.g., phagocytosis, superoxide radical generation, and endotoxin-stimulated cytokine release). Studies on peritoneal mesothelial cells demonstrate improved cell viability, proliferation, and response to proinflammatory stimuli, and a reduced potential for angiogenesis and peritoneal fibrosis, all suggesting a better preservation of membrane structure and function. The bicarbonate/lactate-based solutions demonstrated decreased cytotoxicity and preserved cell growth in fibroblast cultures as well. In vitro biocompatibility testing has clearly demonstrated that neutral pH, bicarbonate/lactate-buffered Physioneal solutions are superior to conventional solutions in preserving cell viability and function in cell populations that contribute to peritoneal homeostasis. This positive assessment now provides a foundation and rationale for moving forward with the next stages in preclinical testing: in vivo animal models and human ex vivo studies.

High glucose activates the p38 MAPK pathway in cultured human peritoneal mesothelial cells

BACKGROUND

Peritoneal fibrosis is a serious complication in long-term continuous ambulatory peritoneal dialysis (CAPD) patients, but the underlying mechanism is not well understood. Since high glucose activates the p38 mitogen-activated protein kinase (MAPK) pathway in various kinds of cells, and because mesothelial cells are always exposed to high glucose dialysate, we examined the activity and expression of p38 MAPK members in cultured human peritoneal mesothelial cells (HPMCs) under high glucose conditions.

METHODS

HPMCs were isolated from omentum and subcultured. After serum restriction, HPMCs were exposed to 5.6 mmol/L glucose (low glucose), 5.6 mmol/L glucose + 34.5 mmol/L mannitol (low glucose + mannitol), or 40 mmol/L glucose (high glucose) for 3 minutes to 48 hours with or without SB203580. Reverse transcription-polymerase chain reaction (RT-PCR) and Western blot were performed to determine mRNA and protein expression, respectively.

RESULTS

p38 MAPK and cyclic adenosine monophosphate (cAMP)-responsive element binding protein (CREB) activities and mRNA expressions were significantly increased in HPMCs exposed to high glucose compared to low glucose or low glucose + mannitol after 10 minutes and remain at higher levels to 48 hours (P < 0.05), but total p38 MAPK and CREB protein expressions did not differ. MAPK kinase 3/6 (MKK3/6) activity and mRNA expression were also higher in high glucose cells after 3 minutes (P < 0.05), and fibronectin mRNA expression was significantly increased in HPMCs exposed to high glucose after 2 hours (P < 0.05). In contrast, high glucose significantly inhibited MAPK phosphatase-1 (MKP-1) protein and mRNA expression after 10 minutes (P < 0.05). SB203580 (1 micromol/L) pretreatment for 1 hour significantly reduced high glucose-induced CREB activity and fibronectin mRNA expression by 89% and 75%, respectively (P < 0.05).

CONCLUSION

p38 MAPK activity was increased in HPMCs exposed to high glucose, in parallel with increased MKK3/6 activity and decreased MKP-1 expression, resulting in CREB activation. This activated p38 MAPK pathway may play a role in the pathogenesis of peritoneal fibrosis.

Peritoneal dialysis fluids with a physiologic pH based on either lactate or bicarbonate buffer-effects on human mesothelial cells

Conventional lactate (Lac)-buffered peritoneal dialysis (PD) solutions have turned out to be detrimental to human peritoneal cells, especially because of a low pH. In the present study, we focus on potential differences between Lac and bicarbonate (Bic) as a buffer when adjusted to a physiological pH. All test fluids were buffered with either 40 mmol/L of Lac or 34 mmol/L of Bic, sterile filtered, and adjusted to a pH of 7.4. Osmotic agents used were 1.36% glucose (Glu), 3.86% Glu, 1% amino acids (AA), and 7.5% Glu polymer (Glupoly). Human peritoneal mesothelial cells (HPMCs) were isolated from the omentum majus, grown to confluence, and incubated after the second passage for 15 minutes (37 degrees C and 5% carbon dioxide) with the test fluids. Cytotoxicity was controlled by measuring apoptotic and necrotic cells with cytofluorometry. Aerobic cell metabolism (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide [MTT] assay) and intracellular adenosine triphosphate (ATP) concentrations were measured to assess cell viability. Release of interleukin-6 (IL-6) from HPMCs was determined as a parameter of cellular host defense. No significant difference in apoptosis or necrosis rates was found between the solutions adjusted to normal pH. However, in the MTT assay, Bic solutions were superior to corresponding Lac pendants at an identical pH of 7.4 (P < 0.01). Intracellular ATP concentrations reflected a very similar pattern (P < 0.05). Glupoly in combination with Lac showed an impaired pattern with both the MTT and ATP assays. Regarding IL-1beta-stimulated IL-6 release, there was a small, but not significantly better, response for Bic. Differences in manifest cell cytotoxicity reflected by apoptosis and necrosis rates could not be detected comparing PD solutions buffered with Lac or Bic at a physiological pH. However, distinct parameters of cell metabolism were superior with Bic compared with Lac. Especially Glupoly was inferior in combination with Lac as a buffer.

High glucose induces MCP-1 expression partly via tyrosine kinase-AP-1 pathway in peritoneal mesothelial cells

BACKGROUND

High glucose in peritoneal dialysis solutions has been implicated in the pathogenesis of peritoneal fibrosis in chronic ambulatory peritoneal dialysis (CAPD) patients. However, the mechanisms are not very clear. Peritoneal macrophages seem to participate in the process of peritoneal fibrosis and monocyte chemoattractant protein-1 (MCP-1) plays a key role in the recruitment of monocytes toward the peritoneal cavity. However, little is known about the effect of high glucose on MCP-1 expression and its signal transduction pathway in human peritoneal mesothelial cells.

METHODS

Mesothelial cells were cultured with glucose (5 to 100 mmol/L) or mannitol chronically for up to seven days. MCP-1 expression of mRNA and protein was measured by Northern blot analysis and enzyme-linked immunosorbent assay (ELISA). Chemotactic activity of high-glucose-conditioned culture supernatant was measured by chemotactic assay. To examine the roles of the transcription factors activator protein-1 (AP-1) and nuclear factor-kappaB (NF-kappaB), electrophoretic mobility shift assay (EMSA) was performed.

RESULTS

Glucose induced MCP-1 mRNA expression in a time- and dose-dependent manner. MCP-1 protein in cell culture supernant was also increased. Equivalent concentrations of mannitol had no significant effect. High-glucose-conditioned supernatant possessed an increased chemotactic activity for monocytes, which was neutralized by anti-MCP-1 antibody. EMSA revealed that glucose increased the AP-1 binding activity in a time- and dose-dependent manner, but not NF-kappaB. Curcumin, an inhibitor of AP-1, dose-dependently suppressed the induction of MCP-1 mRNA by high glucose. Tyrosine kinase inhibitors such as genistein (12.5 to 50 micromol/L) and herbimycin A (0.1 to 1 micromol/L) inhibited the high-glucose-induced MCP-1 mRNA expression in a dose-dependent manner, and also suppressed the high-glucose-induced AP-1 binding activity.

CONCLUSIONS

: High glucose induced mesothelial MCP-1 expression partly via the tyrosine kinase-AP-1 pathway.

High glucose-induced PKC activation mediates TGF-beta 1 and fibronectin synthesis by peritoneal mesothelial cells

BACKGROUND

Progressive peritoneal fibrosis, membrane hyperpermeability, and ultrafiltration failure have been observed in long-term peritoneal dialysis (PD) using glucose as an osmotic agent. High glucose activates protein kinase C (PKC), which is one important signal pathway in the activation of transforming growth factor-beta 1 (TGF-beta 1) and fibronectin (FN). To gain a better understanding of mechanisms involved in peritoneal fibrosis, we examined the effects of high glucose on human peritoneal mesothelial cell (HPMC) TGF-beta 1 and FN mRNA expression and protein synthesis and determined the involvement of PKC in the high glucose-induced HPMC activation.

METHODS

Synchronized confluent HPMC were incubated with different concentrations of glucose with and without inhibition of PKC. PKC activity and diacylglycerol (DAG) levels were measured. The expression of TGF-beta 1 and FN mRNAs by HPMC was measured by Northern blot analysis. TGF-beta 1 protein was measured by enzyme-linked immunosorbent assay (ELISA) and mink lung epithelial cell growth inhibition assay. FN protein was measured by Western blot analysis and ELISA.

RESULTS

PKC activity and DAG levels in HPMC cultured under 50 mmol/L (high) glucose increased 2.3- and 2.0-fold, respectively, that of 5.6 mmol/L (control) glucose at 24 hours and this was sustained up to 72 hours. The expression of TGF-beta 1 and FN mRNA by HPMC cultured under high glucose increased 1.6- and 1.7-fold, respectively, that of control values at 24 hours. TGF-beta bioactivity as well as protein content in heat-activated conditioned media from high glucose was significantly higher than that of control values at 24 and 48 hours. FN protein also increased in response to high glucose, as measured by Western blot analysis and ELISA. PKC activator phorbol 12-myristate 13-acetate (PMA) induced 2.2- and 1.4-fold increase in TGF-beta 1 and FN mRNA expression, respectively. Depletion of PKC and calphostin C, a PKC inhibitor, effectively prevented both PMA and high glucose-induced, but not constitutive, expression of TGF-beta 1 and FN.

CONCLUSION

The present data demonstrate that high glucose up-regulates TGF-beta 1 and FN synthesis by HPMC, and that this high glucose-induced up-regulation is largely mediated by PKC. These results suggest that activation of PKC by high glucose in conventional PD solutions may constitute an important signal for activation of HPMC, leading to progressive accumulation of extracellular matrix and eventual peritoneal fibrosis.

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

BACKGROUND

Glucose degradation products (GDPs) are cytotoxic in vitro and potentially toxic in vivo during peritoneal dialysis (PD). We are presenting the results of a two-year randomized clinical trial of a new PD fluid, produced in a two-compartment bag and designed to minimize heat-induced glucose degradation while producing a near neutral pH. The effects of the new fluid over two years of treatment on membrane transport characteristics, ultrafiltration (UF) capacity, and effluent markers of peritoneal membrane integrity were investigated and compared with those obtained during treatment with a standard solution.

DESIGN

A two-group parallel design with 80 continuous ambulatory peritoneal dialysis patients was used. The patients were randomly assigned to either the new fluid (N = 40) or to a conventional one (N = 40), and were stratified with respect to age, diabetes, and time on PD. Peritoneal transport characteristics were assessed by the Personal Dialysis Capacity (PDCtrade mark) test at 1, 6, 12, 18, and 24 months after inclusion and by weighing the overnight bag daily. Infusion pain and handling were evaluated using a questionnaire. Peritoneal mesothelial and interstitial integrity were evaluated by analyzing overnight effluent dialysate concentrations of CA 125, hyaluronan (HA), procollagen-1-C-terminal peptide (PICP), and procollagen-3-N-terminal peptide (PIIINP) at 1, 6, 12, 18, and 24 months.

RESULTS

The handling of the new two-compartment bag was considered easy, and there were no indications of increased discomfort with the new system. Furthermore, no changes in peritoneal fluid or solute transport characteristics were observed during the study period for either fluid, and neither were there any differences with regard to peritonitis incidence. However, significantly higher dialysate CA 125 (73 +/- 41 vs. 25 +/- 18 U/mL), PICP (387 +/- 163 vs. 244 +/- 81 ng/mL), and PIIINP (50 +/- 24 vs. 29 +/- 13 ng/mL) and significantly lower concentrations of HA (395 +/- 185 vs. 530 +/- 298 ng/mL) were observed in the overnight effluent during treatment with the new fluid.

CONCLUSIONS

We conclude that the new fluid with a higher pH and less GDPs is safe and easy to use and has no negative effects on either the frequency of peritonitis or peritoneal transport characteristics as compared with conventional ones. Our results indicate that the new solution causes less mesothelial and interstitial damage than conventional ones; that is, it may be considered more biocompatible than a number of conventional PD solutions currently in use.

l-2-oxothiazolidine-4-carboxylic acid modulates function of peritoneal mesothelial cells in vitro

The influence of the glutathione precursor, l-2-oxothiazolidine-4-carboxylic acid (OTZ), on the function of human peritoneal mesothelial cells in vitro, in conditions that mimic the in vivo effect of peritoneal dialysis solutions on mesothelium, was studied. Mesothelial monolayers were exposed to dialysis fluids (Dianeal 1.36 or Dianeal 3.86; Baxter Healthcare Corp, Round Lake, IL) that were diluted gradually with pooled-effluent dialysate obtained from patients undergoing continuous ambulatory peritoneal dialysis. In vitro exposure of mesothelium to standard dialysis fluid enhances their susceptibility to injury by hydrogen peroxide. OTZ added to dialysis solution in concentrations of 1 mmol/L prevented the toxic effect of hydrogen peroxide, probably by increasing intracellular glutathione. Mesothelial cells exposed to dialysis fluid become activated, evidenced by increased release of interleukin-6 and hyaluronan. OTZ used in concentrations of 1 mmol/L reduced that effect. Furthermore, the addition of glucose to the culture medium in a concentration of 45 mmol/L inhibits the proliferation of mesothelial cells; the presence of OTZ, 1 mmol/L, partially prevents the inhibitory effect of glucose. The results presented in this report show that by augmenting the intracellular concentration of glutathione in mesothelial cells by the addition of OTZ to the dialysis fluid, we can increase their resistance to the acute toxicity of free radicals and long-term toxicity of glucose. In addition, mesothelial cells with an increased glutathione level are less activated after their exposure to dialysis fluid.

Remodeling of peritoneal-like structures by mesothelial cells: its role in peritoneal healing

BACKGROUND

Intraabdominal adhesions are a common complication following laparotomy. Since the exact mechanisms involved in this processes are unknown we have analyzed in vitro the role of mesothelial cells in peritoneal healing.

MATERIAL AND METHODS

Human mesothelial cells from omental tissue were cultivated for 2 weeks in a three-dimensional culture either on or in a collagen type I matrix. The effects of blood and collagen matrix were analyzed by exposing mesothelial cells to an overlying blood clot, simulating intraperitoneal bleeding, or a second collagen layer. The production of collagen types III and IV, fibronectin, and laminin was analyzed with immunohistochemical methods.

RESULTS

Mesothelial cells grown on a collagen matrix formed a monolayer of flat or cobblestone-like cells whereas those cultivated in a collagen matrix exhibited spindle-like morphology. Mesothelial cells failed to grow into an overlying collagen matrix, but did grow into a blood clot, emphasizing a potential role of blood clots in peritoneal adhesion formation. Independent of the culture systems mesothelial cells produced collagen type III, fibronectin, and laminin but not collagen type IV.

CONCLUSIONS

Our experiments demonstrate remodeling of peritoneal-like structures by mesothelial cells in a three-dimensional culture reflecting their putative role in the reepithelialization after serosal defects, and also in the formation of peritoneal adhesions.