Peritoneal mast cells in peritoneal dialysis patients, particularly in encapsulating peritoneal sclerosis patients

Peritoneal Dialysis-Induced Encapsulating Peritonitis: Diagnostic and Therapeutic Challenges in Women with Benign Gynecological Pathology

Background: Peritoneal sclerosis (PS) and its most severe form, encapsulating PS (EPS), are rare entities that can occur in various procedures (liver transplantation, intraperitoneal chemotherapy) or secondary to medications (beta-blockers); however, PS or EPS typically occur in patients undergoing peritoneal dialysis as a form of renal function substitution. Medical or surgical treatments can be applied, but morbidity and mortality have high rates. This condition typically presents clinically as an intestinal obstruction caused by the inclusion of the intestinal loops in the peritoneal fibrous membrane. Methods: Herein, we present data from a single tertiary surgery center that has dedicated teams for patients receiving dialysis. Over 12 years, we analyzed a group of 63 patients admitted for catheter replacement/removal or for acute surgical pathology. In five cases (7.9%), we diagnosed EPS. Two patients with EPS presented with atypical abdominal pathologies requiring emergency surgery: one case of hemoperitoneum caused by a ruptured ovarian cyst and one case of uterine fibroids and metrorrhagia. Results: The definitive diagnoses were established intraoperatively and by analyzing the morpho-pathological changes in the peritoneum. The possible intraoperative challenges included laborious dissection, difficulties in restoring the correct anatomical landmarks, an increased duration of the surgical intervention and a high rate of incidents and accidents. Conclusions: The aim of the present study was to emphasize the possibility of other surgical pathologies overlapping with EPS, increasing the complexity of the surgical intervention.

Sterile inflammation of peritoneal membrane caused by peritoneal dialysis: focus on the communication between immune cells and peritoneal stroma

Peritoneal dialysis is a widely used method for treating kidney failure. However, over time, the peritoneal structure and function can deteriorate, leading to the failure of this therapy. This deterioration is primarily caused by infectious and sterile inflammation. Sterile inflammation, which is inflammation without infection, is particularly concerning as it can be subtle and often goes unnoticed. The onset of sterile inflammation involves various pathological processes. Peritoneal cells detect signals that promote inflammation and release substances that attract immune cells from the bloodstream. These immune cells contribute to the initiation and escalation of the inflammatory response. The existing literature extensively covers the involvement of different cell types in the sterile inflammation, including mesothelial cells, fibroblasts, endothelial cells, and adipocytes, as well as immune cells such as macrophages, lymphocytes, and mast cells. These cells work together to promote the occurrence and progression of sterile inflammation, although the exact mechanisms are not fully understood. This review aims to provide a comprehensive overview of the signals from both stromal cells and components of immune system, as well as the reciprocal interactions between cellular components, during the initiation of sterile inflammation. By understanding the cellular and molecular mechanisms underlying sterile inflammation, we may potentially develop therapeutic interventions to counteract peritoneal membrane damage and restore normal function.

Intercellular communication in peritoneal dialysis

Long-term peritoneal dialysis (PD) causes structural and functional alterations of the peritoneal membrane. Peritoneal deterioration and fibrosis are multicellular and multimolecular processes. Under stimulation by deleterious factors such as non-biocompatibility of PD solution, various cells in the abdominal cavity show differing characteristics, such as the secretion of different cytokines, varying protein expression levels, and transdifferentiation into other cells. In this review, we discuss the role of various cells in the abdominal cavity and their interactions in the pathogenesis of PD. An in-depth understanding of intercellular communication and inter-organ communication in PD will lead to a better understanding of the pathogenesis of this disease, enabling the development of novel therapeutic targets.

Novel Aspects of the Immune Response Involved in the Peritoneal Damage in Chronic Kidney Disease Patients under Dialysis

Chronic kidney disease (CKD) incidence is growing worldwide, with a significant percentage of CKD patients reaching end-stage renal disease (ESRD) and requiring kidney replacement therapies (KRT). Peritoneal dialysis (PD) is a convenient KRT presenting benefices as home therapy. In PD patients, the peritoneum is chronically exposed to PD fluids containing supraphysiologic concentrations of glucose or other osmotic agents, leading to the activation of cellular and molecular processes of damage, including inflammation and fibrosis. Importantly, peritonitis episodes enhance peritoneum inflammation status and accelerate peritoneal injury. Here, we review the role of immune cells in the damage of the peritoneal membrane (PM) by repeated exposure to PD fluids during KRT as well as by bacterial or viral infections. We also discuss the anti-inflammatory properties of current clinical treatments of CKD patients in KRT and their potential effect on preserving PM integrity. Finally, given the current importance of coronavirus disease 2019 (COVID-19) disease, we also analyze here the implications of this disease in CKD and KRT.

Mechanisms of Peritoneal Fibrosis: Focus on Immune Cells-Peritoneal Stroma Interactions

Peritoneal fibrosis is characterized by abnormal production of extracellular matrix proteins leading to progressive thickening of the submesothelial compact zone of the peritoneal membrane. This process may be caused by a number of insults including pathological conditions linked to clinical practice, such as peritoneal dialysis, abdominal surgery, hemoperitoneum, and infectious peritonitis. All these events may cause acute/chronic inflammation and injury to the peritoneal membrane, which undergoes progressive fibrosis, angiogenesis, and vasculopathy. Among the cellular processes implicated in these peritoneal alterations is the generation of myofibroblasts from mesothelial cells and other cellular sources that are central in the induction of fibrosis and in the subsequent functional deterioration of the peritoneal membrane. Myofibroblast generation and activity is actually integrated in a complex network of extracellular signals generated by the various cellular types, including leukocytes, stably residing or recirculating along the peritoneal membrane. Here, the main extracellular factors and the cellular players are described with emphasis on the cross-talk between immune system and cells of the peritoneal stroma. The understanding of cellular and molecular mechanisms underlying fibrosis of the peritoneal membrane has both a basic and a translational relevance, since it may be useful for setup of therapies aimed at counteracting the deterioration as well as restoring the homeostasis of the peritoneal membrane.

IL-17A as a Potential Therapeutic Target for Patients on Peritoneal Dialysis

Chronic kidney disease (CKD) is a health problem reaching epidemic proportions. There is no cure for CKD, and patients may progress to end-stage renal disease (ESRD). Peritoneal dialysis (PD) is a current replacement therapy option for ESRD patients until renal transplantation can be achieved. One important problem in long-term PD patients is peritoneal membrane failure. The mechanisms involved in peritoneal damage include activation of the inflammatory and immune responses, associated with submesothelial immune infiltrates, angiogenesis, loss of the mesothelial layer due to cell death and mesothelial to mesenchymal transition, and collagen accumulation in the submesothelial compact zone. These processes lead to fibrosis and loss of peritoneal membrane function. Peritoneal inflammation and membrane failure are strongly associated with additional problems in PD patients, mainly with a very high risk of cardiovascular disease. Among the inflammatory mediators involved in peritoneal damage, cytokine IL-17A has recently been proposed as a potential therapeutic target for chronic inflammatory diseases, including CKD. Although IL-17A is the hallmark cytokine of Th17 immune cells, many other cells can also produce or secrete IL-17A. In the peritoneum of PD patients, IL-17A-secreting cells comprise Th17 cells, γδ T cells, mast cells, and neutrophils. Experimental studies demonstrated that IL-17A blockade ameliorated peritoneal damage caused by exposure to PD fluids. This article provides a comprehensive review of recent advances on the role of IL-17A in peritoneal membrane injury during PD and other PD-associated complications.

Encapsulating Peritoneal Sclerosis: Pathophysiology and Current Treatment Options

Encapsulating peritoneal sclerosis (EPS) is a life-threatening complication of long-term peritoneal dialysis (PD), which may even occur after patients have switched to hemodialysis (HD) or undergone kidney transplantation. The incidence of EPS varies across the globe and increases with PD vintage. Causative factors are the chronic exposure to bioincompatible PD solutions, which cause long-term modifications of the peritoneum, a high peritoneal transporter status involving high glucose concentrations, peritonitis episodes, and smoldering peritoneal inflammation. Additional potential causes are predisposing genetic factors and some medications. Clinical symptoms comprise signs of intestinal obstruction and a high peritoneal transporter status with incipient ultrafiltration failure. In radiological, macro-, and microscopic studies, a massively fibrotic and calcified peritoneum enclosed the intestine and parietal wall in such cases. Empirical treatments commonly used are corticosteroids and tamoxifen, which has fibrinolytic properties. Immunosuppressants like azathioprine, mycophenolate mofetil, or mTOR inhibitors may also help with reducing inflammation, fibrin deposition, and collagen synthesis and maturation. In animal studies, N-acetylcysteine, colchicine, rosiglitazone, thalidomide, and renin-angiotensin system (RAS) inhibitors yielded promising results. Surgical treatment has mainly been performed in severe cases of intestinal obstruction, with varying results. Mortality rates are still 25–55% in adults and about 14% in children. To reduce the incidence of EPS and improve the outcome of this devastating complication of chronic PD, vigorous consideration of the risk factors, early diagnosis, and timely discontinuation of PD and therapeutic interventions are mandatory, even though these are merely based on empirical evidence.

1,25-Dihydroxyvitamin D3 Prevents Epithelial-Mesenchymal Transition of HMrSV5 Human Peritoneal Mesothelial Cells by Inhibiting Histone Deacetylase 3 (HDAC3) and Increasing Vitamin D Receptor (VDR) Expression Through the Wnt/β-Catenin Signaling Pathway

Background

Peritoneal dialysis is the most common treatment for end-stage renal disease. However, peritoneal fibrosis resulting from long-term peritoneal dialysis restricts peritoneal ultrafiltration. Previous studies have shown a role for 1,25-dihydroxyvitamin D3 (1,25[OH]₂D3) in preventing fibrosis, but the potential mechanisms remain unknown. This study aimed to investigate the role of 1,25(OH)₂D3 in epithelial-mesenchymal transition (EMT) and the downstream signaling pathway in HMrSV5 human peritoneal mesothelial cells in vitro.

Material/Methods

An in vitro cell model of peritoneal fibrosis was established using the HMrSV5 human peritoneal mesothelial cell line. High glucose and lipopolysaccharide (LPS) culture conditions, with or without 1,25(OH)₂D3, were used. Wnt agonist 1, a Wnt signaling pathway activator, was applied. Quantitative real-time polymerase chain reaction (qRT-PCR) and western blot were used to measure the vitamin D receptor (VDR) and histone deacetylase 3 (HDAC3) gene and protein expression levels, β-catenin, and EMT-associated biomarkers.

Results

High glucose plus LPS culture medium inhibited cell proliferation, induced cell apoptosis and promoted EMT in HMrSV5 cells, which was reversed by 1,25(OH)₂D3 by down-regulation of HDAC3 and upregulation of VDR. HDAC3 inhibited VDR gene expression. The expression of EMT-associated biomarkers was increased by Wnt agonist 1 and inhibited by 1,25(OH)₂D3.

Conclusions

In HMrSV5 human peritoneal mesothelial cells, 1,25(OH)₂D3 reversed EMT by inhibiting the expression of HDAC3 and upregulating VDR gene expression via the Wnt/β-catenin signaling pathway.

Calcium mediates cell shape change in human peritoneal mesothelial cells

Mast cells in the peritoneal membrane (PM) may degranulate to release preformed inflammatory mediators including histamine which is capable of diffusing into the surrounding interstitium, modulating cells in their vicinity including, human peritoneal mesothelial cells (hPMC). The present study aimed to investigate the quorum intracellular calcium ([Ca²⁺_i]) response to histamine compared to the membrane soluble ionophore, A23187, in adherent cultured hPMC. To examine [Ca²⁺_i] handling, Fura - 2 loaded cells were exposed to histamine and A23187. Agonist induced transient [Ca²⁺_i] event(s) (TCE) were defined and compared including, resting calcium, peak height, recovery and transient kinetics. Changes in cell shape were examined with immunocytochemistry of the cortical actin (CA) and microtubule (MT) cytoskeleton. To investigate whether histamine induced changes in cell shape were mediated by [Ca²⁺_i], mobilization of [Ca²⁺_i] was prevented with 20 μmol/l of the calcium chelator 1,2-bis-(2-aminophenoxy) ethane-N,N,N',N'-tetraacetic acid (BAPTA-AM). Histamine produced a dose dependent increase of [Ca²⁺_i], maximal at 1.0 mmol/l which recovered to the pre-challenge resting value. Transient multiplicity with repeated challenge was evident below a histamine threshold of 10^-2 mmol/l. Morphometric analysis of MTs and CA showed significant cell elongation plus histamine and A23187. The histamine induced cell elongation was eliminated with [Ca²⁺_i] clamping. This data indicated that increased [Ca²⁺_i] was essential for cell elongation and the formation of stress fibres and therefore has a pivotal role in the regulation of the PM barrier.

Encapsulating peritoneal sclerosis-a rare but devastating peritoneal disease

Encapsulating peritoneal sclerosis (EPS) is a devastating but, fortunately, rare complication of long-term peritoneal dialysis. The disease is associated with extensive thickening and fibrosis of the peritoneum resulting in the formation of a fibrous cocoon encapsulating the bowel leading to intestinal obstruction. The incidence of EPS ranges between 0.7 and 3.3% and increases with duration of peritoneal dialysis therapy. Dialysis fluid is hyperosmotic, hyperglycemic, and acidic causing chronic injury and inflammation in the peritoneum with loss of mesothelium and extensive tissue fibrosis. The pathogenesis of EPS, however, still remains uncertain, although a widely accepted hypothesis is the "two-hit theory," where, the first hit is chronic peritoneal membrane injury from long standing peritoneal dialysis followed by a second hit such as an episode of peritonitis, genetic predisposition and/or acute cessation of peritoneal dialysis, leading to EPS. Recently, EPS has been reported in patients shortly after transplantation suggesting that this procedure may also act as a possible second insult. The process of epithelial-mesenchymal transition of mesothelial cells is proposed to play a central role in the development of peritoneal sclerosis, a common characteristic of patients on dialysis, however, its importance in EPS is less clear. There is no established treatment for EPS although evidence from small case studies suggests that corticosteroids and tamoxifen may be beneficial. Nutritional support is essential and surgical intervention (peritonectomy and enterolysis) is recommended in later stages to relieve bowel obstruction.

Pharmacologic targets and peritoneal membrane remodeling

Peritoneal dialysis (PD) is associated with functional and structural changes of the peritoneal membrane, also known as peritoneal remodeling. The peritoneal membrane is affected by many endogenous and exogenous factors such as cytokines, PD fluids, and therapeutic interventions. Here, we present an overview of various studies that have investigated pharmacologic interventions aimed at regression of peritoneal damage and prolongation of PD treatment.

Effect of DNA demethylation in experimental encapsulating peritoneal sclerosis

Encapsulating peritoneal sclerosis (EPS) involves excessive peritoneal fibrosis in patients on peritoneal dialysis, eventually leading to visceral constriction and bowel obstruction. Few studies have investigated epigenetic mechanisms relating to EPS. Here we evaluated the therapeutic effects of DNA demethylation in experimental EPS. Experimental EPS was induced by intraperitoneal injection of 0.1% chlorhexidine gluconate (CG) and 15% ethanol in non-uremic male Sprague-Dawley (SD) rats. Rats were divided into three groups: group C (N=5) with saline injection only, group CG (N=7) with EPS induction for 4 weeks, and chlorhexidine gluconate and azacytidine (CGA) treated group (N=7) with EPS induction for 4 weeks and 5'-azacytidine injection for the last 2 weeks. Morphometric analysis of peritoneum and immunohistochemical staining for type 1 collagen and α-smooth muscle actin (α-SMA) were performed. Expressions of transforming growth factor-β (TGF-β), fibroblast-specific protein 1 (FSP1), and DNA methyltransferase 1 (DNMT1) were analyzed by Western blot. Methylation-specific polymerase chain reaction (PCR) for Ras GTPase activating-like protein 1 (RASAL1) was performed with measurement of RASAL1 protein expression. Parietal peritoneal thickness and the number of vessels in omental tissue were significantly decreased in group CGA compared to group CG, as were the expressions of type 1 collagen, α-SMA, TGF-β, and FSP1. DNMT1 was significantly increased in group CG, and reduced in group CGA. RASAL1 hypermethylation was associated with decreased RASAL1 protein expression in group CG, which was reversed in group CGA. DNA demethylation by 5'-azacytidine treatment improved pathologic changes of the peritoneum in experimental EPS, and was associated with reversal of increased DNMT1 expression and RASAL1 hypermethylation.

Histological and clinical findings in patients with post-transplantation and classical encapsulating peritoneal sclerosis: a European multicenter study

BACKGROUND

Encapsulating peritoneal sclerosis (EPS) commonly presents after peritoneal dialysis has been stopped, either post-transplantation (PT-EPS) or after switching to hemodialysis (classical EPS, cEPS). The aim of the present study was to investigate whether PT-EPS and cEPS differ in morphology and clinical course.

METHODS

In this European multicenter study we included fifty-six EPS patients, retrospectively paired-matched for peritoneal dialysis (PD) duration. Twenty-eight patients developed EPS after renal transplantation, whereas the other twenty-eight patients were classical EPS patients. Demographic data, PD details, and course of disease were documented. Peritoneal biopsies of all patients were investigated using histological criteria.

RESULTS

Eighteen patients from the Netherlands and thirty-eight patients from Germany were included. Time on PD was 78(64-95) in the PT-EPS and 72(50-89) months in the cEPS group (p>0.05). There were no significant differences between the morphological findings of cEPS and PT-EPS. Podoplanin positive cells were a prominent feature in both groups, but with a similar distribution of the podoplanin patterns. Time between cessation of PD to the clinical diagnosis of EPS was significantly shorter in the PT-EPS group as compared to cEPS (4(2-9) months versus 23(7-24) months, p<0.001). Peritonitis rate was significantly higher in cEPS.

CONCLUSIONS

In peritoneal biopsies PT-EPS and cEPS are not distinguishable by histomorphology and immunohistochemistry, which argues against different entities. The critical phase for PT-EPS is during the first year after transplantation and therefore earlier after PD cessation then in cEPS.

Transcriptional patterns in peritoneal tissue of encapsulating peritoneal sclerosis, a complication of chronic peritoneal dialysis

Encapsulating peritoneal sclerosis (EPS) is a devastating complication of peritoneal dialysis (PD), characterized by marked inflammation and severe fibrosis of the peritoneum, and associated with high morbidity and mortality. EPS can occur years after termination of PD and, in severe cases, leads to intestinal obstruction and ileus requiring surgical intervention. Despite ongoing research, the pathogenesis of EPS remains unclear. We performed a global transcriptome analysis of peritoneal tissue specimens from EPS patients, PD patients without EPS, and uremic patients without history of PD or EPS (Uremic). Unsupervised and supervised bioinformatics analysis revealed distinct transcriptional patterns that discriminated these three clinical groups. The analysis identified a signature of 219 genes expressed differentially in EPS as compared to PD and Uremic groups. Canonical pathway analysis of differentially expressed genes showed enrichment in several pathways, including antigen presentation, dendritic cell maturation, B cell development, chemokine signaling and humoral and cellular immunity (P value<0.05). Further interactive network analysis depicted effects of EPS-associated genes on networks linked to inflammation, immunological response, and cell proliferation. Gene expression changes were confirmed by qRT-PCR for a subset of the differentially expressed genes. EPS patient tissues exhibited elevated expression of genes encoding sulfatase1, thrombospondin 1, fibronectin 1 and alpha smooth muscle actin, among many others, while in EPS and PD tissues mRNAs encoding leptin and retinol-binding protein 4 were markedly down-regulated, compared to Uremic group patients. Immunolocalization of Collagen 1 alpha 1 revealed that Col1a1 protein was predominantly expressed in the submesothelial compact zone of EPS patient peritoneal samples, whereas PD patient peritoneal samples exhibited homogenous Col1a1 staining throughout the tissue samples. The results are compatible with the hypothesis that encapsulating peritoneal sclerosis is a distinct pathological process from the simple peritoneal fibrosis that accompanies all PD treatment.

Phenotypes of encapsulating peritoneal sclerosis--macroscopic appearance, histologic findings, and outcome

BACKGROUND

Encapsulating peritoneal sclerosis (EPS) is a rare but devastating complication of peritoneal dialysis (PD), with clinical signs of abdominal pain, bowel obstruction, and weight loss in late stages.

METHODS

We retrospectively analyzed all patients who were diagnosed with EPS between March 1998 and October 2011 in our department of nephrology. We focused on the 24 EPS patients who underwent surgery because of symptomatic late-stage EPS. We identified 3 different macroscopic phenotypes of EPS that we categorized as types I - III. We correlated histologic findings with those macroscopic phenotypes of EPS. The postoperative and long-term outcomes were evaluated by macroscopic phenotype.

RESULTS

Duration of PD was longer in type III than in types I and II EPS (p = 0.05). We observed no other statistically significant differences between the groups in baseline characteristics, except for operation time, which was longer in the type I than in the type III group (p = 0.02). Furthermore, we observed no statistically significant difference between the groups with respect to the onset of complaints before surgery (7.8 ± 5.9 months vs 7.0 ± 7.0 months vs 6.5 ± 5.3 months). Concerning patient outcomes, there was no evidence that any of the macroscopic EPS types was associated with more major or minor complications after surgery. For all study patients, follow-up was at least 3 years, with 19 patients still being alive, and 16 having no or very mild complaints. The typical histologic findings of EPS were present in all macroscopic types; only fibrin deposits were more prominent in type II than in type III.

CONCLUSIONS

We describe 3 subtypes of EPS based on macroscopic findings. Postoperative treatment should probably not be influenced by the macroscopic EPS phenotype. Whether the different phenotypes represent different pathophysiologic processes remains unclear and has to be further evaluated.

Periostin: a matricellular protein involved in peritoneal injury during peritoneal dialysis

BACKGROUND

Periostin is a matricellular protein involved in tissue remodeling through the promotion of adhesion, cell survival, cellular dedifferentiation, and fibrogenesis. It can be induced by transforming growth factor beta and high glucose concentrations. We hypothesized that this protein might be expressed in the peritoneal cavity of patients on peritoneal dialysis (PD) and even more in patients with signs of encapsulating peritoneal sclerosis (EPS).

METHOD

In this retrospective study, we included peritoneal biopsies from patients on PD with EPS (n = 7) and without signs of EPS (n = 10), and we compared them with biopsies taken during hernia repair from patients not on PD (n = 11) and during various procedures from uremic patients not on PD (n = 6). Periostin was localized by immunohistochemistry, scored semiquantitatively, and quantified by morphometry. Periostin protein concentrations were measured by ELISA in dialysates from 15 patients. Periostin messenger RNA was quantified in vitro in peritoneal fibroblasts.

RESULTS

In control biopsies, periostin was present in the walls of larger arteries and focally in extracellular matrix in the submesothelial zone. Patients on PD demonstrated interstitial periostin in variable amounts depending on the severity of submesothelial fibrosis. In EPS, periostin expression was very prominent in the sclerosis layer. The area of periostin was significantly larger in EPS biopsies than in control biopsies, and the percentage of periostin-positive area correlated with the thickness of the submesothelial fibrosis zone. Periostin concentrations in dialysate increased significantly with time on PD in patients without signs of EPS; in patients with EPS, periostin concentrations in dialysate were low and demonstrated the smallest increase with time. In vitro, periostin was found to be strongly expressed by peritoneal fibroblasts.

CONCLUSION

Periostin is strongly expressed by fibroblasts and deposited in the peritoneal cavity of patients with EPS and with simple peritoneal fibrosis on PD. This protein might play a role in the progression of peritoneal injury, and low levels of periostin after prolonged time on PD might be a marker of EPS.

The spectrum of podoplanin expression in encapsulating peritoneal sclerosis

Encapsulating peritoneal sclerosis (EPS) is a life threatening complication of peritoneal dialysis (PD). Podoplanin is a glycoprotein expressed by mesothelial cells, lymphatic endothelial cells, and myofibroblasts in peritoneal biopsies from patients with EPS. To evaluate podoplanin as a marker of EPS we measured podoplanin mRNA and described the morphological patterns of podoplanin-positive cells in EPS. Included were 20 peritoneal biopsies from patients with the diagnosis of EPS (n = 5), patients on PD without signs of EPS (n = 5), and control patients (uremic patients not on PD, n = 5, non-uremic patients n = 5). EPS patient biopsies revealed significantly elevated levels of podoplanin mRNA (p<0.05). In 24 peritoneal biopsies from patients with EPS, podoplanin and smooth muscle actin (SMA) were localized by immunohistochemistry. Four patterns of podoplanin distribution were distinguishable. The most common pattern (8 of 24) consisted of organized, longitudinal layers of podoplanin-positive cells and vessels in the fibrotic zone (“organized” pattern). 7 of 24 biopsies demonstrated a diffuse distribution of podoplanin-positive cells, accompanied by occasional, dense clusters of podoplanin-positive cells. Five biopsies exhibited a mixed pattern, with some diffuse areas and some organized areas ("mixed"). These contained cuboidal podoplanin-positive cells within SMA-negative epithelial structures embedded in extracellular matrix. Less frequently observed was the complete absence of, or only focal accumulations of podoplanin-positive fibroblasts outside of lymphatic vessels (podoplanin “low”, 4 of 24 biopsies). Patients in this group exhibited a lower index of systemic inflammation and a longer symptomatic period than in EPS patients with biopsies of the "mixed" type (p<0.05). In summary we confirm the increased expression of podoplanin in EPS, and distinguish EPS biopsies according to different podoplanin expression patterns which are associated with clinical parameters. Podoplanin might serve as a useful adjunct to the morphological workup of peritoneal biopsies.

Histological criteria for encapsulating peritoneal sclerosis - a standardized approach

Background

The two most relevant pathologies of long-term peritoneal dialysis (PD) are simple sclerosis and encapsulating peritoneal sclerosis (EPS). The histological differentiation of those two entities is difficult. The Aim of the study was to establish a method to standardize and facilitate the differentiation between simple sclerosis and EPS

Methods

We investigated 58 peritoneal biopsies - 31 EPS patients and 27 PD patients. Two blinded investigators analyzed 20 histological characteristics in EPS and PD patients.

Results

The following findings were significantly more common in EPS than in patients on PD without EPS: fibroblast like cells (FLC) (p<0.0001), mesothelial denudation (p<0.0001), decreased cellularity (p = 0.008), fibrin deposits (p<0.03), Fe deposits (p = 0.05), podoplanin vascular (p<0.0001), podoplanin avascular (p<0.0001). Using all predictor variables we trained the classification method Random Forest to categorize future cases. Podoplanin vascular and avascular were taken together (p<0.0001), FLC (p<0.0001), mesothelial denudation (p = 0.0005), calcification (p = 0.0026), acellular areas (p = 0.0094), and fibrin deposits (p = 0.0336) showed up as significantly important predictor variables. Estimated misclassification error rate when classifying new cases turned out to be 14%.

Conclusion

The introduced statistical method allows discriminating between simple sclerosis and EPS. The misclassification error will likely improve with every new case added to the database.

Encapsulating peritoneal sclerosis: the state of affairs

Encapsulating peritoneal sclerosis (EPS) is a severe complication of long-term peritoneal dialysis (PD) with a 50% mortality rate. EPS is characterized by progressive and excessive fibrotic thickening of the peritoneum, leading to encapsulation of the bowels and intestinal obstruction. At present, EPS cannot be detected with certainty during its early stages; however, a progressive loss of ultrafiltration capacity often precedes its development. Studies that attempted to elucidate the pathogenesis of EPS have shown that the duration of exposure to PD fluids is the most important risk factor for EPS, and that young age and possibly the effects of peritonitis are additional contributory factors. The pathophysiology of EPS is probably best described as a multiple-hit process with a central role for transforming growth factor β. A form of EPS that develops shortly after kidney transplantation has also been recognized as a distinct clinical entity, and may be a common form of EPS in countries with a high transplantation rate. Criteria have been developed to identify EPS by abdominal CT scan at the symptomatic stage, but further clinical research is needed to identify early EPS in asymptomatic patients, to clarify additional risk factors for EPS and to define optimal treatment strategies.

Angiogenesis in peritoneal dialysis

Long-term exposure to peritoneal dialysis fluid induces morphological alterations, including angiogenesis, leading to a loss of ultrafiltration (UF) capacity. We discuss the effect of different factors in peritoneal dialysis (PD) on angiogenesis. In addition, we describe the process of angiogenesis and the possible role of different cell types in the peritoneum upon PD contributing to new blood vessel formation. Furthermore, we review several interventions used in our rat PD exposure model to decrease angiogenesis in PD. Moreover, we show new data on the use of sunitinib to inhibit angiogenesis in this rat model. Although various interventions seem to be promising, well-randomised clinical trials showing absolute prevention of angiogenesis and UF failure are, yet, still missing. To make real progress in PD treatment, the aim should be to prevent angiogenesis as well as peritoneal fibrosis and PD-induced inflammation.

Difference in the expression of hormone receptors and fibrotic markers in the human peritoneum--implications for therapeutic targets to prevent encapsulating peritoneal sclerosis

OBJECTIVE

Encapsulating peritoneal sclerosis (EPS) is a rare but life-threatening complication of peritoneal dialysis (PD). The optimal management of patients with EPS is uncertain. In the present study, we investigated differences in the expression of nuclear receptors [progesterone (PR), androgen (AR), vitamin D (VDR), and glucocorticoid (GCR)] in the human peritoneum. We also investigated estrogen receptor (ER), matrix metalloproteinase 9 (MMP9), and transforming growth factor β1 (TGFβ1) in the context of their potential role in tamoxifen therapy.

METHODS

We analyzed clinical and histologic characteristics of 72 peritoneal biopsy specimens (22 from EPS patients, 11 from PD patients, 15 from uremic patients, and 24 from control subjects undergoing hernia repair). For immunophenotyping, we used antibodies against VDR, GCR, ER, PR, AR, MMP9, and TGFβ1.

RESULTS

In human peritoneum, VDR and GCR are highly expressed (98.6% and 87.3% respectively). Except in the case of VDR (p = 0.0012), we observed no significant difference in receptor expression between the groups. Expression of ER and PR was sparse (11.4% and 31% respectively), with higher expression in women, and AR was absent. Minimal MMP9 expression and moderate TGFβ1 expression were observed in all groups. The differences between the groups were nonsignificant.

CONCLUSIONS

Nuclear receptors are present in human peritoneum. Except in the case of VDR, the pattern for any one group is nonspecific. Glucocorticoids, vitamin D, and angiotensin converting-enzyme inhibitors or angiotensin II receptor blockers (via the vitamin D/angiotensin II pathway) might be suitable interventions for preservation of the integrity of the peritoneal membrane. The mechanism of action of tamoxifen is still not elucidated, ER expression in the peritoneum is sparse, and data about the studied pathways (MMP9, TGFβ) are inconsistent.

Podoplanin-positive cells are a hallmark of encapsulating peritoneal sclerosis

BACKGROUND

Encapsulating peritoneal sclerosis (EPS) and simple peritoneal sclerosis are important complications of long-term peritoneal dialysis (PD). Podoplanin is expressed by mesothelial cells and lymphatic vessels, which are involved in inflammatory reactions in the peritoneal cavity.

METHODS

We studied 69 peritoneal biopsies from patients on PD (n = 16), patients with EPS (n = 18) and control biopsies taken at the time of hernia repair (n = 15) or appendectomy (n = 20). Immunohistochemistry was performed to localize podoplanin. Additionally, markers of endothelial cells, mesothelial cells, myofibroblasts (smooth muscle actin), proliferating cells, and double labelling for smooth muscle actin/podoplanin were used on selected biopsies.

RESULTS

Podoplanin was present on the endothelium of lymphatic vessels in the submesothelial fibrous tissue and on mesothelial cells. In patients on PD and in biopsies with appendicitis, the mesothelial cells demonstrated a cuboidal appearance and circumferential podoplanin staining, with gaps between the cells. The number of lymphatic vessels was variable, but prominent at sites of fibrosis. In patients with EPS, a diffuse infiltration of podoplanin-positive cells with a fibroblastic appearance was present in 15 out of 18 biopsies. This pattern was focally present in 3 out of 16 on PD and none in the 35 controls. The podoplanin-positive cells did not express the endothelial marker or the mesothelial marker (calretinin).

CONCLUSIONS

EPS is characterized by a population of podoplanin and smooth muscle actin double-positive cells. Podoplanin might be a suitable morphological marker supporting the diagnosis and might be involved in the pathogenesis of EPS.

Factors Contributing to Peritoneal Tissue Remodeling in Peritoneal Dialysis

Peritoneal dialysis (PD) is associated with functional and structural changes of the peritoneal membrane. In this review we describe factors contributing to peritoneal tissue remodeling, including uremia, peritonitis, volume loading, the presence of a catheter, and the PD fluid itself. These factors initiate recruitment and activation of peritoneal cells such as macrophages and mast cells, as well as activation of peritoneal cells, including mesothelial cells, fibroblasts, and endothelial cells. We provide an overview of cytokines, growth factors, and other mediators involved in PD-associated changes. Activation of downstream pathways of cellular modulators can induce peritoneal tissue remodeling, leading to ultrafiltration loss. Identification of molecular pathways, cells, and cytokines involved in the development of angiogenesis, fibrosis, and membrane failure may lead to innovative therapeutic strategies that can protect the peritoneal membrane from the consequences of long-term PD.

Update on Mechanisms of Ultrafiltration Failure

Ultrafiltration failure (UFF) continues to be a major complication of peritoneal dialysis (PD), particularly long-term PD. Continuous exposure to bioincompatible PD solutions causes inflammation of the peritoneal membrane, which progressively undergoes fibrosis and angiogenesis and, ultimately, UFF. There is emerging evidence that epithelial–mesenchymal transition (EMT) of peritoneal mesothelial cells (MCs) may play an important role in the failure of peritoneal membrane function. Submesothelial myofibroblasts originating from MCs through EMT and from activated resident fibroblasts participate in inflammatory responses, extracellular matrix accumulation, and angiogenesis. High glucose and glucose degradation products from PD solutions are responsible for production of transforming growth factor β (TGFβ) and vascular endothelial growth factor (VEGF) by MCs, which induce EMT. Leptin and receptor for advanced glycation end-products (AGEs) augment myofibroblastic conversion through the TGFβ signaling system.

A reduction in osmotic conductance in addition to increased solute transport causes UFF. This situation may be caused by loss of aquaporin (AQP) function and formation of the submesothelial fibrotic layer. During PD, AQP1 plays an essential role in water permeability and ultrafiltration (UF), modulating processes such as endothelial permeability and angiogenesis. During a hypertonic dwell, AQP1 mediates 50% of UF. Insufficient AQP1 function may be causative for inadequate UFF. A significant amount of evidence from animal studies now exists to show that mast cells communicate with fibroblasts and are implicated in fibrogenesis, angiogenesis, and UFF. However, it is not confirmed in human studies that mast cells contribute to the fibrosis seen in the peritoneum of PD patients.

The patterns of UFF in PD patients depend on duration of treatment. Inherently high small-solute transport status is associated with hypoalbuminemia and a greater comorbidity index. However, most of the variability in peritoneal transport remains unexplained, pointing to the potential role of genetic factors. Gene polymorphisms associated with peritoneal membrane transport have been identified. Recent studies have shown that VEGF, interleukin-6, endothelial NO synthase, AGE receptor, and RAS gene polymorphisms are associated with transport properties in PD patients. Current insights into the mechanisms of UFF will provide rationales for new therapeutic strategies.

Pathogenesis and Treatment of Encapsulating Peritoneal Sclerosis: Basic and Translational Research

Encapsulating peritoneal sclerosis is a devastating condition in long-term peritoneal dialysis patients. Animal models have employed chemical insults to simulate its pathology and have provided insights into its pathophysiology, which appears to include inflammation, angiogenesis, and fibrosis. Monitoring of biomarkers and interruption of molecular pathways have provided potential interventions to slow or prevent the disease process. However, there remain many questions concerning the trigger that alters chronic peritoneal inflammation in peritoneal dialysis to severe sclerosis, peritoneal adhesions, and bowel obstruction. Further advances in therapy will likely require an effective means of an early diagnosis through related biomarkers, which in turn will require further advances in the understanding of the pathogenesis of this disease process.

Case report of encapsulating peritoneal sclerosis: the interpretation of functional and structural peritoneal changes

A case report describing the evolution of encapsulating peritoneal sclerosis is presented to illustrate some of the functional and structural peritoneal membrane changes characteristic of this complication of peritoneal dialysis. The appropriate monitoring of peritoneal transport rates and ultrafiltration, together with attention to clinical signs and symptoms, are essential to the early diagnosis of peritoneal membrane deterioration. Recent reports suggest that timely interventions such as a peritoneal membrane rest period may effectively halt the progression of these functional and structural changes. While the optimal surgical and pharmacological treatment of encapsulating peritoneal sclerosis remains uncertain, the latest literature provides a certain degree of optimism.

Mast cell functions in the innate skin immune system

Mast cells are not only potent effector cells in allergy, but are also important players in protective immune responses against pathogens. Most of our knowledge about mast cells in innate immunity is derived from models of sepsis, whereas their role in innate immune responses of the skin has largely been neglected in the past. Their particular pattern of distribution in the skin and their ability to sense and react to pathogens and other danger signals indicate that mast cells can be important sentinels and effector cells in skin immune responses. The recent findings reviewed here have confirmed this hypothesis and have established a prominent role for skin mast cells in innate immunity.