Morphology of the peritoneal membrane during continuous ambulatory peritoneal dialysis

Iron increases the profibrotic properties of the senescent peritoneal mesothelial cells

BACKGROUND

Treatment of anemia in peritoneal dialysis patients often requires intravenous iron supplementation. Iron diffuses into the peritoneal cavity and is injurious to the peritoneum. We studied how intermittent exposure to iron changes the properties of the senescent peritoneal mesothelial cells (MC).

METHODS

Replicative senescence was induced in MC in control medium (Con) or in control medium with intermittent exposure to iron isomaltoside 15 µg/dL (Con-IIS). After 10 passages properties of MC from both groups were compared to MC not exposed to replicative senescence.

RESULTS

In senescent MC population doubling time was elongated, intracellular generation of free radicals and staining for β-galactosidase was stronger than in MC not exposed to replicative senescence. All these effects were stronger in MC intermittently exposed to IIS. In these cells intracellular iron content was also higher. Also expression of genes p21 and p53 was stronger in MC intermittently treated with IIS. In senescent cells higher release and expression of IL6 and TGFβ1 was observed and that effect was stronger in MC treated with iron. Senescent MC had reduced fibrinolytic activity, what may predispose to the peritoneal fibrosis. Synthesis of collagen was higher in senescent cells, more in MC treated with iron.

CONCLUSION

MC aging results in change of their genotype and phenotype which lead to their profibrotic effect. Exposure to iron enhances these changes.

Assessment of peritoneal thickness using CT in relation to dialysis adequacy in peritoneal dialysis patients

Studies assessing peritoneal thickness by CT in peritoneal dialysis (PD) patients are lacking. In this study, we aimed to investigate the association between peritoneal thickness as measured by CT and dialysis adequacy with peritoneal membrane characteristics in PD patients. Ninety-four PD patients were enrolled. Peritoneal thickness was measured by CT. Patients with and without a decrease in Kt/V of at least 0.3 over time were classified as Group 1 and Group 2, respectively. An increase of 0.1 unit of dialysate/plasma (D/P) creatinine over time were considered significant. The relationship between peritoneal membrane thickness, change in Kt/V, and peritoneal membrane characteristics were investigated. There were 31 (33.0%) patients in Group 1. The duration of PD (86.0 ± 64.1 vs. 59.6 ± 45.2 months, p: 0.023), peritoneal thickness (1.02 ± 0.37 vs. 0.87 ± 0.21 mm, p: 0.015), peritoneal calcification (7 [22.6%] vs. 3 [4.8%] patients, p: 0.013], increased D/P creatinine ratio (14 [45.2%] vs. 14 [22.2%] patients, p: 0.031) and CRP (13.9 ± 11.2 vs. 7.1 ± 4.8 mg/L, p: 0.045) were significantly higher in Group 1, whereas albumin (3.6 ± 0.5 vs. 3.8 ± 0.6 g/dL, p: 0.047) and parathyroid hormone (355.2 ± 260.2 vs. 532.1 ± 332.9 ng/L, p: 0.015) levels were significantly lower. Peritoneal thickness was significantly correlated with duration of PD (r: 0.775, p < 0.001) and CRP (r: 0.282, p: 0.006). Regression analysis showed that peritoneal thickness (Exp (B) [95% CI]: 0.029 [0.003-0.253], p: 0.001) was independent predictor of decreased Kt/V in PD patients. In conclusion, prolonged PD duration and increased peritoneal thickness are associated with a decrease in Kt/V over time. CT may be an alternative and noninvasive method instead of peritoneal biopsy for determining the structural changes of the peritoneal membrane .

Mesothelial Cells

♦ Background

The introduction of peritoneal dialysis (PD) as a modality of renal replacement therapy has provoked much interest in the biology of the peritoneal mesothelial cell. Mesothelial cells isolated from omental tissue have immunohistochemical markers that are identical to those of mesothelial stem cells, and omental mesothelial cells can be cultivated in vitro to study changes to their biologic functions in the setting of PD.

♦ Method

The present article describes the structure and function of mesothelial cells in the normal peritoneum and details the morphologic changes that occur after the introduction of PD. Furthermore, this article reviews the literature of mesothelial cell culture and the limitations of in vitro studies.

♦ Results

The mesothelium is now considered to be a dynamic membrane that plays a pivotal role in the homeostasis of the peritoneal cavity, contributing to the control of fluid and solute transport, inflammation, and wound healing. These functional properties of the mesothelium are compromised in the setting of PD. Cultures of peritoneal mesothelial cells from omental tissue provide a relevant in vitro model that allows researchers to assess specific molecular pathways of disease in a distinct population of cells. Structural and functional attributes of mesothelial cells are discussed in relation to long-term culture, proliferation potential, age of tissue donor, use of human or animal in vitro models, and how the foregoing factors may influence in vitro data.

♦ Conclusions

The ability to propagate mesothelial cells in culture has resulted, over the past two decades, in an explosion of mesothelial cell research pertaining to PD and peritoneal disorders. Independent researchers have highlighted the potential use of mesothelial cells as targets for gene therapy or transplantation in the search to provide therapeutic strategies for the preservation of the mesothelium during chemical or bacterial injury.

Dialysate Markers of Peritoneal Tissue during Peritonitis and in Stable Capd

Objective

To investigate whether dialysateconcentrations of substances that are locally produced within the peritoneal cavity can be used to study the effects of inflammation on peritoneal tissue.

Design

We followed the appearance rates (AR) of concentrations of cancer antigen (CA) 125, phospholipids (PHL), hyaluronan (HA), and the procollagen peptides PICP (procollagen 1 C-terminal) and PIIINP (procollagen 3 N-terminal) in dialysate during peritonitis (8 consecutive days) and after recovery. Data were compared with the stable situation.

Setting

CAPD (continuous ambulatory peritoneal dialysis) unit in the Academic Medical Center in Amsterdam.

Patients

Twelve CAPD patients with a total of 16 episodes of peritonitis and 10 clinically stable CAPD patients were studied.

Results

All substances showed temporal increments in dialysate during peritonitis compared to control. No difference was found between the control day of peritonitis and the stable patients. Maximum AR were reached in the acute phase of peritonitis for CA 125, PHL, and HA and on day 4 for both PICP and P111NP. A second increment in CA125 occurred on days 4 to 6. These findings indicate acute damage to the mesothelium (CA 125) and other cells (PHL) by the infection. HA may reflect stromal changes. Subsequently, peritoneal healing (PICP, PIIINP) and remesothelialization (second peak CA125) are likely to occur.

Conclusions

Dialysate concentrations of these substances can be used as markers for the effects of peritonitis on the peritoneum of CAPD patients in vivo. The similarity between the marker concentrations in the effluent after recovery from peritonitis and those in stable CAPD patients implies that complete peritoneal healing is likely to occur after uncomplicated peritonitis.

Osmotic Agents Hamper Mesothelial Repopulation as Seen in the Doughnut In Vivo Model

♦ Background

The problem of mesothelial cell injury derived from the use of peritoneal dialysis solutions has been explored deeply. Conversely, the eventual detrimental effects upon mesothelial cell regeneration have awaked less investigative efforts than those focused on injury.

♦ Objective

To evaluate in the in vivo and in situ rat “doughnut” model of mesothelial repopulation, the eventual effect of peritoneal lavage with Hank's Balanced Salt Solution (HBSS) as well as that of 4.25% glucose and 7.5% icodextrin dialysis solutions.

♦ Experimental Animals

100 Sprague–Dawley albino rats were included in the study. Animals were divided into five groups of 20 rats each: group 1: control at zero time; group 2: sham-injected rats; group 3: rats exposed to HBSS; group 4: rats treated with 4.25% glucose peritoneal dialysis solution; group 5: rats injected with 7.5% icodextrin.

♦ Methods

Selective exfoliation of a ring of mesothelium (width 0.8 mm, diameter 4 mm) covering the anterior surface of the liver was performed in 80 animals. The control zero-time group was used to evaluate the normal density distribution of the mesothelial cells forming the monolayer. The other groups were treated by means of daily sham injections or intraperitoneal infusion of each experimental solution for a period of 30 consecutive days. After a recovery period of 15 days, imprints and biopsies from the monolayer covering the exfoliated area were taken and processed for light microscopy.

♦ Results

Macroscopic observation of the abdominal cavity at the end of the 15-day recovery period showed that the prevalence of fibrotic adhesions between the peritoneal exfoliated area and the neighboring diaphragm was 10% for the sham-injected group, 5% for the HBSS-exposed animals, 85% for the rats injected with 4.25% glucose, and 95% for the icodextrin-treated group. Prevalence of fibrous adhesions in sham-injected animals and rats exposed to HBSS were devoid of statistically significant differences. Conversely, comparison of these groups with results observed in animals treated with the osmotic agents was significant, at the p < 0.0039 level. Regarding density distribution of mesothelial cells observed in imprints, there were no significant differences between the control zero-time and the sham-injected group. This parameter was marginally lower ( p < 0.05) in the HBSS-treated rats. Imprints were not taken from animals exposed to glucose or icodextrin because a dense layer of connective tissue replaced the exfoliated mesothelial area.

♦ Conclusions

Observations made in this study support the contention that both osmotic agents, 4.25% glucose and 7.5% icodextrin, substantially restrain the normal process of mesothelial cell repopulation and induce repair by means of connective tissue. The underlying mechanism is most likely sustained oxidative stress.

Peritoneal Ultrafiltration after Chronic Exposure to Dialysis Fluid

Eleven rats were given twice-daily intraperitoneal injections of 20 mL of dialysis fluid containing 4.5% glucose for 6 weeks. The peritoneal ultrafiltration capacity of this group was compared with that of a control group of 10 rats that had received no injections by measuring the volume and glucose concentration of the dialysate remaining in the peritoneal cavity 2 hours after injection. Animals that had received injections of dialysis fluid showed significant loss of peritoneal ultrafiltration: volume of dialysate remaining in the control group was 31 (13–35) mL, and in the experimental group was 25 (11–45) mL, with p<0.02 (Mann-Whitney). This was associated with enhanced glucose absorption: glucose absorbed by the control group was 382 (312–706) mg, and 595 (435–738) mg in the experimental group (p<0.002, Mann-Whitney).

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

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

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

Vascular and Interstitial Changes in the Peritoneum of Capd Patients with Peritoneal Sclerosis

Objective

To analyze morphological changes in the peritoneum of peritoneal sclerosis (PS) patients. Emphasis was put on vascular abnormalities, because the continuous exposure to glucose-based dialysis solutions could cause diabetiform changes and because longitudinal transport studies suggested the development of a large peritoneal vascular surface area.

Design

Peritoneal biopsies from continuous ambulatory peritoneal dialysis (CAPD) patients were investigated in two studies. Diabetic patients were excluded. In study 1, 11 PS biopsies were compared to three control groups varying in duration of CAPD treatment: 0 months ( n = 15), 2 – 25 months ( n = 7), and > 25 months CAPD ( n = 7). The second study was a case-control study, comparing six biopsies from the long-term control group to six PS biopsies, matched for age and duration of CAPD. All biopsies were scored for presence and type of fibrosis [Picro Sirius red, type IV collagen, α-smooth muscle actin (αSMA)] and for neoangiogenesis (factor VIII). Thickening of vascular walls by type IV collagen and vasodilation of capillaries were measured by computer-aided planimetry.

Results

In study 1 the presence of sclerosing fibrosis, deposition of interstitial type IV collagen, and the number of myofibroblasts (αSMA-positive cells) was greater in the PS biopsies than biopsies from all control groups ( p < 0.002). Moreover, the number of vessels per field was higher in PS biopsies ( p < 0.01). Vascular wall thickening of small arteries ( p < 0.008) and vasodilation of capillaries were found in PS biopsies compared to all control groups ( p < 0.007). The second study revealed differences in the presence of sclerosis but not in the extent of fibrosis between PS biopsies and their controls. The number of vessels per field in PS biopsies was higher compared to controls ( p = 0.04). Also, thickening of the vascular wall was more marked in PS biopsies ( p = 0.03). Vasodilation of capillaries was greater in PS biopsies than in controls ( p = 0.07).

Conclusion

Fibrosis of the peritoneum may precede peritoneal sclerosis. The deposition of type IV collagen and the presence of myofibroblasts in the interstitial layer could be part of a pathologic process similar to the scarring in diabetic nephropathy. Neoangiogenesis and thickening of the vascular wall by type IV collagen are consistent with glucose-induced microangiopathy. These abnormalities and the vasodilation of the capillaries can explain the high dialysate-to-plasma ratios or mass transfer area coefficients of low molecular weight solutes that can be found in long-term CAPD patients.

Variability of Peritoneal Protein Loss in Diabetic and Nondiabetic Patients on Continuous Ambulatory Peritoneal Dialysis

In order to evaluate the Influence of diabetes mellitus on peritoneal membrane permeability, we studied the peritoneal protein loss In two groups of patients. Group A consisted of 16 patients (9 nondlabetics and 7 diabetics) who were In the first month of treatment on continuous ambulatory peritoneal dialysis (CAPO). Group B consisted of 13 patients (7 nondlabetics and 6 diabetics) who had been on CAPO for approximately 15 months.

In both groups we measured the body weight, serum total protein, albumin, and total protein, urea, and glucose In the peritoneal fluid.

We did not find any difference In groups A and B between diabetics and nondlabetics as far as the estimated parameters were concerned. Age, body weight, serum biochemistry, and protein and urea content In peritoneal fluid were similar, when group A was compared to group B. Patients of group B hed on average higher protein losses than those who had been on the method for a short period (mean 7.9 g/dL, vs 6.09 g/dL).

Six patients were followed for over 15 months and were found to have significantly Increased protein losses (p=0.02).

Glucose levels In peritoneal fluid were significantly lower In patients In group B, p<0.05 (mean 51.8 g/dL vs 37.1 g/dL).

Peritoneal protein loss does not seem to differ between diabetic and nondiabetic patients with end-stage renal disease treated with CAPO, at any given time of the treatment.

We observed an Increase In protein loss In some patients and a tendency to Increase the protein loss In others. This, along with the fall In glucose levels, might reflect progressive alterations In structure and permeability of the elements Involved In peritoneal transport, and It should receive further evaluation.

Oral Lecithin Improves Ultrafiltration in Patients on Peritoneal Dialysis

Three patients on peritoneal dialysis (two on continuous ambulatory and one on intermittent) with severe ultrafiltration failure were treated with 2 capsules of Lecithin three times a day (containing of 1.08 g of phosphatidylcholine). Their ultrafiltration improved significantly to the point that their edema improved and were able to continue on peritoneal diaysis with fewer daily hypertonic exchange.

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.

Pathology of Encapsulating Peritoneal Sclerosis

Pathology findings of encapsulating peritoneal sclerosis (EPS) are reviewed to establish histologic criteria for a diagnosis of EPS. The typical macroscopic finding is a cocoon-like encapsulation of the entire intestine. This encapsulation is frequently accompanied by fibrin deposition, focal bleeding on the peritoneum, and various quantities of bloody ascites. A thin membrane on the visceral peritoneum contributes to the formation of the intestinal encapsulation. Histologically, the membrane is composed mainly of organized fibrin, probably derived from plasma exudation from the peritoneal microvasculature. The peritoneal fibroblasts appear swollen and exhibit an increased level of cellularity, accompanied by expression of various activation and proliferation markers. According to the “two-hit” theory of EPS pathogenesis, deterioration of the peritoneum as a result of the peritoneal dialysis (PD) procedure (the first “hit”) and superimposition of inflammatory stimuli such as infectious peritonitis (the second “hit”) are thought to play key roles in the pathogenesis of EPS. Based on histologic examination of peritoneal biopsy specimens, the detection of fibrin deposition and fibroblast phenotypic alteration were proposed as important findings for early diagnosis of EPS. Persistent inflammatory changes are also predictive of the future onset of EPS. Careful histologic evaluation of peritoneal biopsy specimens, combined with laparoscopic observations after withdrawal of PD, is required for the early diagnosis and treatment of EPS.

Peritoneal Vascular Changes in Continuous Ambulatory Peritoneal Dialysis (CAPD): An in Vivo Model for the Study of Diabetic Microangiopathy

Replication of the basement membrane of the peritoneal capillaries and the mesothelium is observed in all uremic patients after a period of continuous ambulatory peritoneal dialysis (CAPD). Biopsy specimens of the parietal peritoneum were taken in diabetic and non-diabetic patients on insertion or repositioning of the CAPD catheter. The basement membrane of the capillaries and mesothelium was normal in non-diabetics on insertion of the catheter, but after 2 to 66 months of CAPD, multiple replication was found. In nearly all the diabetics there was already replication of the basement membrane of the peritoneal capillaries before CAPD was begun but the basement membrane of the mesothelium was intact. After several months of CAPD thickening of the basement membrane of the capillaries was found in 36% of diabetics, sometimes to the point of occlusion. After CAPD, replication of the basement membrane of the mesothelium has been observed in both diabetics and nondiabetics although it is initially perfectly normal in both. CAPD is proposed as an experimental model for diabetic microangiopathy in man.

Cell Function, Viability, and Icodextrin

The bioincompatibility of conventional dialysis fluids is related primarily to the combination of low pH and high lactate concentrations. This results in the reduction of intracellular pH and a consequent inhibition of cell function. The use of high glucose concentrations to increase fluid osmolality adds to the cytotoxicity and has a further inhibitory effect on peritoneal cells.

The clinical need for fluids that provide sustained ultrafiltration has led to a novel approach using a high molecular weight glucose polymer (icodextrin) to generate an ultrafiltration gradient in an iso-osmolar fluid. In the studies presented we have had the opportunity of examining, in the laboratory setting, the biocompatibility of such a fluid.

As in previous studies with conventional fluids, pH per se has a profound effect on most modalities of cell function. In addition, there appearto be a few areas where problems can be ascribed to icodextrin itself. Furthermore, it is possible that Staph. epidermidis survives better in icodextrin than in conventional dialysate. Whether the benefits of sustained ultrafiltration outweigh the possible disadvantages outlined can only be judged when the results from ongoing clinical trials are available.

Preventing Peritoneal Fibrosis—Insights from the Laboratory

Objective

Peritoneal fibrosis is one of the most serious complications of peritoneal dialysis (PD). Peritoneal fibrosis is characterized by activation of the peritoneal resident cells, accumulation and deposition of excess matrix proteins within the interstitium, and neoangiogenesis and vasculopathy of the peritoneal microvasculature. Compelling evidence now exists to show that elevated glucose concentrations present as the osmotic agent in PD solutions are, per se, responsible for those detrimental changes. Until alternative osmotic agents can fully replace glucose in PD solutions, novel therapeutic strategies are essential to preserve the structural and functional properties of the peritoneum. This review highlights recent experimental data that may offer potential strategies for preservation of the peritoneal structure and improvement of clinical outcome.

Method

Literature review.

Results

Compelling evidence now exists to show that the bioincompatible nature of PD solutions—in particular, elevated glucose concentrations and glucose byproducts—play a pivotal role in the initiation of peritoneal fibrosis. Animal and in vitro studies provide some insight into methods that can potentially be employed to alleviate or retard peritoneal fibrosis. Those methods include use of alterative osmotic agents (polyglucose or amino acids), administration of TGFβ1 antagonists, gene therapy, and pharmacologic interventions.

Conclusions

Knowledge of the pathogenesis of peritoneal fibrosis has allowed independent researchers to design therapeutic strategies that abrogate excess matrix synthesis and deposition in cultured peritoneal cells and in animal models of experimental peritoneal fibrosis alike. Encouraging results have been obtained in those studies, but it remains to be determined whether the studied strategies can alleviate clinical disease. Future studies will enable us to establish specific molecules that can be targeted clinically to restrict the progressive deterioration of the peritoneal membrane as a biologic dialyzing organ.

Emodin Ameliorates Glucose-Induced Morphologic Abnormalities and Synthesis of Transforming Growth Factor β1 and Fibronectin by Human Peritoneal Mesothelial Cells

♦ Objective

Excessive synthesis and deposition of matrix proteins by peritoneal mesothelial cells can lead to structural and functional changes in the peritoneal membrane, jeopardizing the long-term efficacy of peritoneal dialysis (PD). Prolonged exposure to high glucose concentrations in PD fluid has been implicated as a major stimulus to matrix accumulation, through the induction of transforming growth factor β1 (TGFβ 1). This study investigated the effect of emodin (3-methyl-1,6,8-trihydroxyanthraquinone) on TGFβ 1 and fibronectin (FN) synthesis in human peritoneal mesothelial cells (HPMCs) under high glucose concentration.

♦ Design

The HPMCs were preconditioned in either 5 mmol/L or 30 mmol/L d-glucose for 2 weeks prior to the addition of emodin. Cell viability was assessed by MTT assay and lactate dehydrogenase (LDH) release. Morphology of HPMCs was studied by phase-contrast microscopy. Modulation of TGFβ 1 and FN synthesis at transcription and translation were investigated by reverse transcriptase polymerase chain reaction (RT-PCR), ELISA, and Western blot analysis.

♦ Results

When cultured under 30 mmol/L d-glucose, HPMCs demonstrated increased cell volume, multi-nucleation, and denudation of the monolayer, as compared with cells cultured under a physiologic (5 mmol/L) glucose concentration. High glucose concentration induced TGFβ 1 synthesis by HPMCs (217.17 ± 14.88 pg/mL at 5 mmol/L d-glucose vs 370.33 ± 20.67 pg/mL at 30 mmol/L d-glucose, p < 0.0001), and FN synthesis was induced at transcription and translation. Mannitol at 30 mmol/L did not affect HPMC morphology; matrix synthesis was also unaltered. Administration of emodin together with 30 mmol/L d-glucose resulted in amelioration of cell enlargement and exfoliation, and abrogation of TGFβ 1 induction (370.33 ± 20.67 pg/mL for 30 mmol/L d-glucose alone vs 260.50 ± 17.89 pg/mL for 30 mmol/L d-glucose + emodin, p < 0.0001). Synthesis of FN induced by high glucose was also reduced by 40% in the presence of emodin.

♦ Conclusions

These findings provide the first evidence that emodin can ameliorate high glucose–induced matrix synthesis in HPMCs by suppression of TGFβ 1. Emodin may thus be useful in preserving peritoneal integrity in PD.

Thrombin Upregulates Production of Plasminogen Activator Inhibitor Type 1 in Human Peritoneal Mesothelial Cells

Objective

To determine the influence of thrombin, which is generated intraperitoneally during peritoneal dialysis, on the synthesis of fibrinolytic system components in human peritoneal mesothelial cells (HMC).

Methods

Confluently grown HMC, isolated from the omental tissue, were used in the experiments. Conditioned media were obtained by incubating cells with serum-free M199 containing the appropriate concentration of the test compound. Tissue type plasminogen activator (tPA) and plasminogen activator inhibitor type 1 (PAI-1) antigen concentrations were measured by ELISA. Northern blot analysis was conducted for mRNA expression experiments. To test thrombin specificity, we used the thrombin inhibitor hirudin. The protein kinase C (PKC) inhibitor Ro 31-8220 was inserted to examine whether the effect of thrombin depends on PKC activity.

Results

Thrombin increased PAI-1 antigen in the conditioned media of HMC in a time- and concentration-dependent manner. After 24 hours incubation, PAI-1 levels increased from 350 ± 30 ng/105cells in control conditions to 620 ± 30 ng/105cells in HMC exposed to 5 U/mL thrombin ( n = 8, p < 0.05). In contrast, there was no effect of thrombin on tPA antigen levels. An increase of PAI-1 mRNA expression was also observed by Northern blot hybridization. Hirudin (10 U/mL) inhibited the thrombin-induced increase in PAI-1 synthesis. In addition, a complete inhibition of the stimulating effect of thrombin on PAI-1 synthesis was obtained by blocking PKC activity with Ro 31-8220 (3 μmol/L).

Conclusions

Thrombin increases PAI-1 synthesis in HMC via a PKC-dependent mechanism. Thereby the synthesis of tPA is not affected. Thus, thrombin may not only promote fibrin formation in the peritoneal cavity, but may also inhibit fibrin degradation by release of free PAI-1 from HMC.

Structural and Functional Alterations of the Peritoneum after Prolonged Exposure to Dialysis Solutions: Role of Aminoguanidine

Objective

The effect of long-term use of high glucose dialysate on peritoneal structure and function, and its relation with accumulation of advanced glycosylation end-product (AGE) in the peritoneum was investigated in this study.

Methods

Dialysates with 4.25% glucose were injected into the peritoneal cavity of normal rats for 12 weeks without (PD, n = 7) and with (1 g/L, PD+AG, n = 7) aminoguanidine in their drinking water. Rats not having intraperitoneal (IP) injection served as control ( n = 9). After 12 weeks of IP injection, a 2-hour peritoneal equilibration test (PET) was performed using 30 mL 4.25% glucose dialysate. Intraperitoneal volume (IPV), dialysate-to-plasma urea ratio at 2 hours (D2/P2), the ratio of dialysate glucose at 2 hours to initial dialysate glucose (D2/D0), and the peritoneal fluid absorption rate (Qa) were evaluated. After the PET, samples of the parietal peritoneum were taken for hematoxylin and eosin (H&E) staining and immunohistochemical staining for AGE.

Results

The IPV and D2/D0glucose were significantly lower and Qaand D2/P2urea significantly higher in the PD group than in the control group. Aminoguanidine reversed in part the changes in IPV and D2/P2urea in the PD group; it had no effect on Qaand D2/D0glucose. The H&E staining showed a linear mesothelial lining with negligible cells and capillaries in the narrow submesothelial space in the control group. Mesothelial denudation and submesothelial infiltration of monocytes and capillary formation were observed in the PD group. Mesothelial denudation was relatively intact in the PD+AG group compared with the PD group. Submesothelial monocyte infiltration and capillary formation in the PD+AG group were not as prominent as in the PD group. Positive AGE staining was found in the submesothelial space, vascular walls, and endomysium in the PD group, while it was markedly attenuated in PD+AG group and negligible in the control group.

Conclusion

Long-term use of high glucose solutions induced peritoneal AGE accumulation and mesothelial denudation, and increased peritoneal permeability and peritoneal fluid absorption rate. Inhibition of peritoneal AGE accumulation prevented those functional and structural damages to the peritoneum.

Biocompatibility of Peritoneal Dialysis Fluids: Long-term Exposure of Nonuremic Rats

Objectives

Long-term peritoneal dialysis (PD) leads to structural and functional changes in the peritoneum. The aim of the present study was to investigate the long-term effects of PD fluid components, glucose and glucose degradation products (GDP), and lactate-buffered solution on morphology and transport characteristics in a nonuremic rat model.

Methods

Rats were subjected to two daily intraperitoneal injections (20 mL/day) during 12 weeks of one of the following: commercial PD fluid (Gambrosol, 4%; Gambro AB, Lund, Sweden), commercial PD fluid with low GDP levels (Gambrosol trio, 4%; Gambro AB), sterile-filtered PD fluid (4%) without GDP, or a glucose-free lactate-buffered PD fluid. Punctured and untreated controls were used. Following exposure, the rats underwent a single 4-hour PD dwell (30 mL, 4% glucose) to determine peritoneal function. Additionally, submesothelial tissue thickness, percentage of high mesothelial cells (perpendicular diameter > 2 μm), vascular density, vascular endothelial growth factor (VEGF), and transforming growth factor (TGF) β1mRNA expression were determined. Submesothelial collagen concentration was estimated by van Gieson staining.

Results

Submesothelial tissue thickness and vascular density, mediated by VEGF and TGFβ production, in the diaphragmatic peritoneum increased significantly in rats exposed to any PD fluid. Gambrosol induced a marked increased fibrosis of the hepatic peritoneum. A significant increase in high mesothelial cells was observed in the Gambrosol group only. Net ultrafiltration was reduced in the Gambrosol and in the glucose-free groups compared to untreated controls. Small solute transport was unchanged, but all groups exposed to fluids showed significantly increased lymph flow.

Conclusions

Our results show that long-term exposure to different components of PD fluids leads to mesothelial cell damage, submesothelial fibrosis, and neoangiogenesis. Mesothelial cell damage could be connected to the presence of GDP; the other changes were similar for all fluids. Peritoneal transport characteristics did not change in any consistent way and the neoangiogenesis observed was not paralleled by increased solute transport.

Influence of Phosphatidylcholine on Lymphatic Absorption during Peritoneal Dialysis in the Rat

The mechanism whereby i.p. administration of phosphatidylcholine increases net ultrafiltration and solute clearances after long-dwell exchanges is not established. We performed 4-h exchanges in rats using 4.25% dextrose dialysis solution with and without the addition of 50 mgl L phosphatidylcholine. Net ultrafiltration was enhanced in the treated rats (p < 0.005) by a reduction in cumulative lymphatic absorption (p < 0.01) and without a concurrent increase in total net transcapillary ultrafiltration during the dwell time. Likewise, urea and phosphate clearances with i.p. phosphatidylcholine were enhanced mainly by the increase in the drain volume since serum to dialysate solute concentration ratios did not differ significantly between the treated and control rats. Thus, phosphatidylcholine increases net ultrafiltration and solute clearances in the rat by decreasing lymphatic absorption and without increasing transperitoneal transport of water and solutes into the peritoneal cavity. The uptake of the india ink by the lymphatics of rats who received dialysis exchanges without phosphatidylcholine and the lack of uptake in rats treated with phosphatidylcholine are supported by this observation. Reduction in lymphatic absorption with the addition of phosphatidylcholine to the infused dialysis solution offers an alternative means of enhancing the efficiency of long-dwell peritoneal dialysis.

Dialysate Markers of Peritoneal Tissue during Peritonitis and in Stable CAPD

Objective

To investigate whether dialysate concentrations of substances that are locally produced within the peritoneal cavity can be used to study the effects of inflammation on peritoneal tissue.

Design

We followed the appearance rates (AR) of concentrations of cancer antigen (CA) 125, phospholipids (PHL), hyaluronan (HA), and the procollagen peptides PICP (procollagen 1 C-terminal) and PIIINP (procollagen 3 N-terminal) in dialysate during peritonitis (8 consecutive days) and after recovery. Data were compared with the stable situation.

Setting

CAPD (continuous ambulatory peritoneal dialysis) unit in the Academic Medical Center in Amsterdam.

Patients

Twelve CAPD patients with a total of 16 episodes of peritonitis and 10 clinically stable CAPD patients were studied.

Results

All substances showed temporal increments in dialysate during peritonitis compared to control. No difference was found between the control day of peritonitis and the stable patients. Maximum AR were reached in the acute phase of peritonitis for CA 125, PHL, and HA and on day 4 for both PICP and P111NP. A second increment in CA125 occurred on days 4 to 6. These findings indicate acute damage to the mesothelium (CA 125) and other cells (PHL) by the infection. HA may reflect stromal changes. Subsequently, peritoneal healing (PICP, PIIINP) and remesothelialization (second peak CA125) are likely to occur.

Conclusions

Dialysate concentrations of these substances can be used as markers for the effects of peritonitis on the peritoneum of CAPD patients in vivo. The similarity between the marker concentrations in the effluent after recovery from peritonitis and those in stable CAPD patients implies that complete peritoneal healing is likely to occur after uncomplicated peritonitis.

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.

N-Acetylglucosamine Changes Permeability of Peritoneum during Chronic Peritoneal Dialysis in Rats

Objective

To evaluate the effect of supplementation of dialysis fluid with N-acetylglucosamine (NAG) on the permeability of peritoneum during chronic peritoneal dialysis in rats.

Design

Experiments were performed on rats with surgically implanted peritoneal catheters. Dialysis solution [DianeaI1.5% (Baxter, Deerfield, IL, U.S.A.) supplemented with either NAG 50 mmol/L or glucose 50 mmol/L (control)] was infused intraperitoneally twice, every day, for 8 weeks. Peritoneal equilibration tests (PET) were performed in all animals at the beginning of the study and after 8 weeks of dialysis. Additionally, at the end of each week, dialysis solution infused in the morning was drained after 4 hours of intraperitoneal dwell. White blood cell count, creatinine, and total protein concentrations were measured in the effluent dialysate. After 8 weeks of dialysis, the morphology of the peritoneum was studied.

Results

In rats exposed to dialysis fluid supplemented with NAG, peritoneal permeability to creatinine and proteins was reduced when compared to animals dialyzed with glucose solution. In NAG treated animals, staining with alcian blue for polyanions in the peritoneal interstitium was significantly stronger than in rats dialyzed with glucose solution.

Conclusions

Chronic peritoneal dialysis with dialysis solution supplemented with N-acetylglucosamine causes accumulation of glycosaminoglycans in the peritoneal interstitium, which results in a change of peritoneal permeability.

Preliminary Evaluation of Incremental Peritoneal Dialysis in 25 Patients

Background

Incremental dialysis has been suggested for patients with some residual renal function. However, very little published clinical data exist on the feasibility of this schedule.

Objectives

To assess feasibility of incremental dialysis, with regard to its effect, complications, and impact on quality of life.

Design

Pilot prospective study, not controlled.

Setting

Nephrology division, public clinical research hospital.

Patients

Twenty-five patients (19 men, mean age 61 ± 13 years, body weight 63 ± 11 kg) began peritoneal dialysis (the first treatment of uremia) with a single nightly exchange lasting 10 hours or 2 daily exchanges over 12 hours according to creatinine clearance and Kt/V. Patients gave informed consent and reported their work activity, degree of rehabilitation, and their quality of life by answering a questionnaire prepared for this purpose.

Outcome Measures

Survival rate, complications related to peritoneal dialysis, and residual renal and peritoneal clearances.

Results

During the study period no patient died. Complications related to dialysis were peritonitis (0.41 episodes/year) and exit-site infection (0.32 episodes/year). All patients continued to work with full rehabilitation and considered 1 or 2 exchanges per day less troublesome than 3 or 4.

Conclusions

Incremental dialysis is well accepted by patients and staff. This technique does not involve a high risk of complications and is economical. Therefore incremental dialysis is feasible.

Can Artifact Mimic the Pathology of the Peritoneal Mesothelium?

Objective

A peritoneal biopsy registry was established to examine morphological and functional changes to the peritoneum during peritoneal dialysis (PD). During the early stages of this study, it became clear that surgical trauma to the peritoneum at the time of biopsy could cause a variety of changes to the surface. We examined the effects of surgical trauma in a rat biopsy model.

Design

Rat peritoneum was subjected to a variety of traumas that might occur at biopsy and compared with peritoneal biopsies that had been collected, using the suture method described here, from PD patients. Changes in the quality of non-PD biopsies taken before and after the development of the suture technique were evaluated.

Results

In the rat model, external massaging of the peritoneum induced moderate loss of microvilli. Brief light touching caused distortion of the mesothelial surface. Pressing resulted in mesothelial denudation and thin strands of presumed cellular remains. Rubbing caused complete loss of mesothelial cells and their basement membrane. Air drying caused progressive loss of microvilli and eventual cellular distortion. Comparison with peritoneal biopsies from PD patients revealed similarities with certain types of trauma, namely, air drying and pressing. Collection of peritoneal biopsies using the suture method significantly improved specimen quality compared with specimens taken before its introduction ( p < 0.025%).

Conclusion

These results illustrate the sensitivity of the mesothelium to mechanical trauma, the possibility of confusing trauma with genuine pathology, and, hence, the necessity of employing a trauma-free method of biopsy collection, such as the technique described here.

The Longitudinal Effect of a Single Peritonitis Episode on Peritoneal Membrane Transport in CAPD Patients

Objective

To evaluate the longitudinal effect of a single peritonitis episode on peritoneal membrane transport.

Design

A prospective longitudinal study.

Setting

Department of nephrology in a university hospital.

Patients

Eighteen continuous ambulatory peritoneal dialysis patients with peritonitis.

Methods

Peritoneal transport for low, middle, and high molecular weight (MW) solutes was evaluated by peritoneal equilibration test (PET). The first PET was performed on the day following the diagnosis of peritonitis. The test was repeated at weeks 1, 2, 4, 12, and 24 and the results were compared to baseline PET data obtained before peritonitis. In addition, dialysate CA125 concentration and leukocyte count were measured.

Results

During peritonitis there were significant increases in dialysate-to-plasma (D/P) ratios for all low, middle, and high MW solutes except potassium, and decreases in D4/D0 glucose ratio and ultrafiltration (UF) volume. Over the subsequent 2 weeks, solute transport gradually decreased to the baseline values then remained unchanged during follow-up. Although net UF volume demonstrated a similar course during the study, it did not completely return to the baseline value. No decrease in D/P sodium ratio was found at 60 minutes during the PET performed 24 weeks after peritonitis. The percent change in solute transport during peritonitis compared to baseline value was significantly correlated with a solute's MW ( r = 0.776, p = 0.014). The slope of the regression line for D/P ratios versus MW, in double logarithmic scale, before peritonitis (-0.73 ± 0.09) was steeper than the slope during peritonitis (-0.59 ± 0.08).

Conclusions

These findings indicate that a single peritonitis episode does not permanently affect peritoneal solute transport. However, the loss of net UF that accompanies peritonitis is not completely recovered, probably due to impairment of transcellular water transport. The transport changes associated with peritonitis may be due to the combined effect of increased effective peritoneal surface area and intrinsic permeability. Our findings suggest that the latter mechanism seems to be more important.

Increased Leukocyte Rolling in Newly Formed Mesenteric Vessels in the Rat during Peritoneal Dialysis

Objective

Long-term peritoneal dialysis (PD) is associated with the development of functional and structural alterations of the peritoneal membrane. The present study reports the effects of chronic exposure to PD fluid on mesenteric leukocyte–endothelium interactions, using intravital video microscopy.

Methods

Rats ( n = 7) received 10 mL lactate-buffered 3.86% glucose-containing PD fluid daily during a 5-week period via a subcutaneously implanted mini access port that was connected via a catheter to the peritoneal cavity. In a first control group ( n = 8), catheters were implanted but no fluid was instilled; a second control group ( n = 8) remained untreated. The number of rolling and adherent leukocytes as well as blood flow and other fluid dynamic variables were analyzed in mesenteric postcapillary (diameter 10 – 25 μ) and collecting (diameter 26 – 40 μ) venules. Neovascularization was semiquantitatively assessed after inspection of video images and by light and electron microscopy. Using FITC-labeled albumin, microvascular leakage was examined.

Results

Rats exposed to PD fluid showed a more than twofold increase in the number of rolling leukocytes ( p < 0.01); the number of adherent leukocytes was not changed. Furthermore, exposure to PD fluid induced severe neovascularization in rat mesentery. No microvascular leakage was observed in the various groups. The observed differences could not be explained by differences in systemic or local hemodynamic parameters or peripheral leukocyte counts, but is most likely associated with new vessel formation.

Conclusions

Exposure of rat peritoneal membrane to conventional PD fluid for 5 weeks affected local leukocyte–endothelium interactions. In addition, severe angiogenesis was induced, whereas microvascular permeability remained unaltered.

Dialysate Cancer Antigen 125 Concentration as Marker of Peritoneal Membrane Status in Patients Treated with Chronic Peritoneal Dialysis

Objective

This study reviews publications on the history of cancer antigen 125 (CA125), the background of its use as a marker of mesothelial cell mass, determination in peritoneal effluent, and its practical use in both the follow-up of peritoneal dialysis (PD) patients and as a marker of in vivo biocompatibility of dialysis solutions.

Design

Review article.

Results

CA125 is a high molecular weight glycoprotein. Previous studies in ascites suggested its release by mesothelial cells. In vitro studies with cultured mesothelial cells showed constitutive production, the majority of which was dependent on mesothelial cell mass. Serum CA125 is normal in PD patients, but its concentration in peritoneal dialysate suggests local release, probably from mesothelial cells. Effluent CA125 can be considered a marker of mesothelial cell mass in stable PD patients, but large amounts are found during peritonitis, due probably to necrosis of mesothelial cells. The majority of studies found no relationship between dialysate CA125 and peritoneal transport parameters. Some cross-sectional studies reported a relationship with duration of PD, but others were unable to confirm this, due probably to the large interindividual variability. Longitudinal follow-up has shown a decrease in dialysate CA125, indicating loss of mesothelial cell mass. Application of theoretically morebiocompatible PD solutions causes an increase in dialysate CA125.

Conclusions

Dialysate CA125 is a mesothelial cell mass marker. The concentration of CA125 should be determined after a standardized dwell. A single low value is not informative. A decrease with time on PD suggests loss of mesothelial cell mass. Dialysate CA125 is a marker of in vivo biocompatibility of (new) dialysis solutions. More research is necessary on the best methodology for measuring low concentrations and establishing normal values and a significant change.

Morphologic Aspects of Chronic Peritoneal Dialysis in a Rat Model

Objective

We previously put forward an experimental model for evaluating peritoneal function in chronically dialyzed rats. In the present paper, we show the morphologic alterations detected by electron microscopy in the peritonea of chronically dialyzed rats.

Materials and Methods

The study was done in male Wistar rats. Animals were divided into two groups: control (non dialyzed) rats and dialyzed rats [intraperitoneally exposed to Dianeal 3.86% (Baxter Healthcare Corporation, Deerfield, IL, U.S.A.) for 1 month]. At the end of the study, the rats were humanely killed by bleeding, and samples of the visceral peritoneum covering the liver were taken from 3 rats in each group. The samples were examined by transmission electron microscopy (TEM).

Results

In control rats, the peritoneum was composed of flattened mesothelial cells covering the thin layer of the submesothelial connective tissue (ST), containing few fibroblasts. In dialyzed animals, a dramatic expansion of the ST was found. We saw compartmentalization of the ST, with changed morphology of the fibroblasts, altered organization of collagen fibers, and changes in the cells infiltrating the ST. Apart from the fibroblasts, mast cells were relatively numerous.

Conclusions

Our work underlines the capabilities of morphology studies in an animal model for assessing peritoneal dialysis fluid biocompatibility.

Detrimental Effects of Peritoneal Dialysis Solutions upon In Vivo and In Situ Exposed Mesothelium

The constancy of the internal environment is in itself evidence that physiological agencies are acting, or ready to act, to maintain this constancy. W.B. Cannon (1)

Production and Regulation of Matrix Metalloproteinases and Their Inhibitors by Human Peritoneal Mesothelial Cells

Objective

Human peritoneal mesothelial cells (HPMC) are likely to be involved in maintenance of the peritoneal membrane. We determined whether these cells were able to synthesize the matrix degrading enzymes, matrix metalloproteinases (MMPs), likely to be responsible for the breakdown of this membrane, and whether this secretion could be modulated by cytokines involved in the inflammatory response.

Design

MMP activity in conditioned medium of growth-arrested HPMC was measured by zymography. Cultures were incubated in the presence and absence of the cytokines transforming growth factor-beta (TGFβ) and interleukin (IL)-1β in order to determine the effects of these cytokines on this process. The mRNA for these MMPs, together with that of their specific inhibitors, tissue inhibitors of metalloproteinases (TIMPs), was also examined by reverse transcriptase polymerase chain reaction (RT-PCR).

Results

HPMC were shown to constitutively secrete the metalloproteinases MMP-2 and MMP-3 in vitro. In response to the proinflammatory cytokine IL-1β, the protein and mRNA for MMP-9 was induced, while secretion of MMP-2 was unaltered. Similarly, the mRNA for MMP-3 was also increased relative to actin following the addition of IL-1β. TGFβ was shown to slightly induce the secretion of MMP-2 together with the mRNA for TIMP I, TIMP II, and, to a greater extent, TIMP III. Used peritoneal dialysate was also shown to induce MMP-9 secretion, and this effect was blocked by the co-incubation of IL-1 receptor antagonist. The secretion of enzyme activity was shown to be from the apical surface of the cells.

Conclusion

HPMC have the ability to control the accumulation of extracellular matrix by secreting the matrix degrading molecules MMP-2, MMP-3, and MMP-9. In addition, the secretion of these enzymes, together with that of their inhibitors (TIMPs) is regulated by the cytokines IL-1β and TGFβ. This process is likely to be important in both the normal maintenance of the integrity of the peritoneal membrane and in the changes that occur following prolonged peritoneal dialysis.

Anti-fibrotic effect of decorin in peritoneal dialysis and PD-associated peritonitis

BACKGROUND

Progressive peritoneal fibrosis is a common complication in patients on long-term peritoneal dialysis (PD). PD-associated peritonitis is a major exacerbating factor. We investigated the anti-fibrotic properties of decorin secreted by peritoneal mesothelial cells.

METHODS

Dialysate decorin level in stable PD patients and those with peritonitis was measured. In vitro experiments were conducted to investigate the effect of decorin in fibrotic response in human peritoneal mesothelial cells (HPMC).

FINDINGS

Increasing PD duration was associated with a progressive decrease of dialysate decorin and CA125 levels. Dialysate decorin level correlated with CA125 level. Peritonitis episodes were associated with a massive drop of dialysate decorin, which persisted for over three months despite clinical recovery. Dialysate decorin level correlated with that of TGF-β1, but was inversely related to IL-1β and IL-8. TGF-β1, IL-1β, IL-6, IL-8, or TNF-α reduced decorin secretion in HPMC, but induced fibronectin expression. The effects were mediated in part through increased p38 MAPK and AKT/PI3K phosphorylation. Decorin abrogated the induction of fibronectin expression in mesothelial cells by PD fluids or pro-fibrotic cytokines, through decreased TGF-βRI, p38 MAPK and AKT/PI3K phosphorylation and increased glycogen synthase kinase-3β phosphorylation. Decorin gene-silencing resulted in increased fibronectin expression under these conditions.

INTERPRETATION

Our data demonstrate anti-fibrotic actions of decorin in HPMC, when these cells are subjected to the pro-fibrotic effect of peritoneal dialysate and pro-fibrotic cytokines in PD, especially during peritonitis.

Peritoneal Dialysis Vintage and Glucose Exposure but Not Peritonitis Episodes Drive Peritoneal Membrane Transformation During the First Years of PD

The impact of peritoneal dialysis (PD) associated peritonitis on peritoneal membrane integrity is incompletely understood. Children are particularly suited to address this question, since they are largely devoid of preexisting tissue damage and life-style related alterations. Within the International Peritoneal Biobank, 85 standardized parietal peritoneal tissue samples were obtained from 82 children on neutral pH PD fluids with low glucose degradation product (GDP) content. 37 patients had a history of peritonitis and 16 of the 37 had two or more episodes. Time interval between tissue sampling and the last peritonitis episode was 9 (4, 36) weeks. Tissue specimen underwent digital imaging and molecular analyses. Patients with and without peritonitis were on PD for 21.0 (12.0, 36.0) and 12.8 (7.3, 27.0) months (p = 0.053), respectively. They did not differ in anthropometric or histomorphometric parameters [mesothelial coverage, submesothelial fibrosis, blood, and lymphatic vascularization, leukocyte, macrophage and activated fibroblast counts, epithelial-mesenchymal transition (EMT), podoplanin positivity and vasculopathy]. VEGF and TGF-ß induced pSMAD abundance were similar. Similar findings were also obtained after matching for age and PD vintage and a subgroup analysis according to time since last peritonitis (<3, <6, >6 months). In patients with more than 24 months of PD vintage, submesothelial thickness, vessel number per mmm section length and ASMA fibroblast positivity were higher in patients with peritonitis history; only the difference in ASMA positivity persisted in multivariable analyses. While PD duration and EMT were independently associated with submesothelial thickness, and glucose exposure and EMT with peritoneal vessel density in the combined groups, submesothelial thickness was independently associated with EMT in the peritonitis free patients, and with duration of PD in patients with previous peritonitis. This detailed analysis of the peritoneal membrane in pediatric patients on PD with neutral pH, low GDP fluids, does not support the notion of a consistent long-term impact of peritonitis episodes on peritoneal membrane ultrastructure, on inflammatory and fibrotic cell activity and EMT. Peritoneal alterations are mainly driven by PD duration, dialytic glucose exposure, and associated EMT.

Mesothelial to mesenchyme transition as a major developmental and pathological player in trunk organs and their cavities

The internal organs embedded in the cavities are lined by an epithelial monolayer termed the mesothelium. The mesothelium is increasingly implicated in driving various internal organ pathologies, as many of the normal embryonic developmental pathways acting in mesothelial cells, such as those regulating epithelial-to-mesenchymal transition, also drive disease progression in adult life. Here, we summarize observations from different animal models and organ systems that collectively point toward a central role of epithelial-to-mesenchymal transition in driving tissue fibrosis, acute scarring, and cancer metastasis. Thus, drugs targeting pathways of mesothelium’s transition may have broad therapeutic benefits in patients suffering from these diseases.

Tim Koopmans and Yuval Rinkevich review recent findings linking the mesothelium’s embryonic programs that drive epithelial-to-mesenchyme transition with adult pathologies, such as fibrosis, acute scarring, and cancer metastasis. They highlight new avenues for drug development that would target pathways of the mesothelium’s mesenchymal transition.

Implant of Autologous Mesothelial Cells in Animals and a Peritoneal Dialysis Patient

Success in culturing human and animal peritoneal mesothelial cells for the purpose of study, led us to determine whether these cells could be autoimplanted in animals and man during peritoneal dialysis in cases of acute and extensive loss of mesothelial surface area. Using an original biopsy technique, we were able to cultivate and characterize from the structural and caryological point of view, human and rabbit peritoneal mesothelial cells. Staphylococcal peritonitis was provoked in 12 rabbits with in-dwelling peritoneal catheters and after 4 days of antibiotic therapy, 6 of them were autoimplanted with cultured mesothelial cells. In the animals sacrificed on the third and sixth days, direct morphological observation and autoradiographic techniques showed that the transplanted cells had taken and revealed a different picture from that in the non-transplanted rabbits.

In a 56 year old female diabetic patient, upon insertion of the first peritoneal catheter, a specimen of mesothelial cells was cultured and then frozen. Seven months later after an episode of peritonitis from Candida which dictated removal of the peritoneal catheter, since there was a sufficient number of cultured mesothelial cells and the patient consented, the implant was performed. Peritoneal biopsy by laparoscopy three and six days later showed that the cells had taken. The purpose of the study was merely to show that autoimplant of mesothelium in man and animals is possible.

Possible Role of Hepatocyte Growth Factor in Regeneration of Human Peritoneal Mesothelial Cells

Human peritoneal mesothelial cells (HPMCs) play an important role in peritoneal functions. During long term peritoneal dialysis, it has been reported that HPMCs are damaged by high glucose solution via the signal of transforming growth factor (TGF)- ß1 produced by HPMCs. In this study, we focused on the effect of hepatocyte growth factor (HGF), known as an anti-fibrotic and anti-TGF-ß1 agent, on HPMCs damaged by high glucose solution. HPMCs were isolated from specimens of the omentum from nonuremic patients after informed consent had been obtained. After confirming adhesion for 6 hours, 100 μL of DMEM with 0.5%FCS were added at different concentrations (D-glucose; 6, 30mM) with or without HGF (10, 30, 100 ng/mL) for 48 hours. We examined the effects of a high concentration of glucose and then focused on following four critical points: 1) the production of HGF from HPMCs exposed to a high concentration of glucose, 2) the expression of c-Met on HPMCs, 3) the viability of those cells, and 4) matrix metalloproteinase-2 (MMP-2) and tissue inhibitors of metalloproteinase-2 (TIMP-2). The following significant changes are described herein: high glucose solution and TGF-ß1 i) decreased HGF production from HPMCs and ii) up-regulated expression of c-Met on HPMCs, and addition of HGF iii) restored viability of HPMCs damaged by glucose, iv) suppressed TGF-ß1 production by HGF, and v) induced up-regulation of MMP-2 and decreased TIMP-2 production by HPMCs. Levels of HGF decreased by high concentrations of glucose in the peritoneal cavity may induce the loss of HPMCs and thereby result in peritoneal fibrosis. These results suggest that HGF is an effective agent in the regeneration of peritoneal membrane damaged by high glucose solution.

A Short Review of Experimental Peritoneal Sclerosis: From Mice to Men

Peritoneal sclerosis has been induced in rodents in vivo by exposing the membrane to a variety of experimental interventions: asbestos, 0.1% chlorexidine, iron dextran, glucose degradation products, AGE deposits derived from uremia per se, sodium hypochlorite, lypopolysaccharide, low pH, pure water, silica or zymosan. With a few exceptions (pure water, chlorhexidine and low pH), the other substances mentioned operate setting out different degrees of oxidative stress. This short review describes several experimental interventions in rodents, aimed at acute exfoliation or long-term, sustained injury of the mesothelial monolayer performed by means of intraperitoneal injections of different oxidant agents.

Acute exfoliation induced by deoxycholate resulted in a depopulated monolayer coincident with immediate alteration of the peritoneal permeability, evidenced by increased urea D/P ratio, higher glucose absorption rate, elevated albumin losses in the effluent and significant reduction of the ultrafiltration rate.

In the long term (30 days), these manifestations of membrane failure persisted and coincided with substantial peritoneal sclerosis.

Peritoneal sclerosis was also induced by IP injections of 0.125% trypsin and 6.6 mM/L solution of formaldehyde. Using the doughnut rat model of mesothelial regeneration, exposure to 4.25% glucose or 7.5% icodextrin solutions severely hampered repopulation of the monolayer, which was replaced by a thick sheet of fibrous tissue.

It is concluded that peritoneal sclerosis derives mostly from sustained oxidative injury to the peritoneal membrane. Loss of the mesothelial monolayer is the first step in the chain of events leading to this complication.