Hypochlorite-induced porcine model of peritoneal fibrosis through the activation of IL1β-CX3CL1-TGFβ1 signal axis

Patients with kidney failure rely on life-saving peritoneal dialysis to facilitate waste exchange and maintain homeostasis of physical conditions. However, peritoneal dialysis often results in peritoneal fibrosis and organ adhesion that subsequently compromise the efficiency of peritoneal dialysis and normal functions of visceral organs. Despite rodent models provide clues on the pathogenesis of peritoneal fibrosis, no current large animal model which shares high degree of physiological and anatomical similarities to human is available, limiting their applications on the evaluation of pre-clinical therapeutic efficacy. Here we established for the first time, hypochlorite-induced porcine model of peritoneal fibrosis in 5-week-old piglets. We showed that administration 15–30 mM hypochlorite, a dose- and time-dependent severity of peritoneal fibrosis characterized by mesothelium fragmentation, αSMA⁺ myofibroblasts accumulation, organ surface thickening and type I collagen deposition were observed. We also demonstrated in vitro using human mesothelial cells that hypochlorite-induced fibrosis was likely due to necrosis, but not programmed apoptosis; besides, overexpression of IL1β, CX3CL1 and TGFβ on the peritoneal mesothelium in current model was detected, similar to observations from peritoneal dialysis-induced peritoneal fibrosis in human patients and earlier reported mouse model. Moreover, our novel antemortem evaluation using laparoscopy provided instant feedback on the progression of organ fibrosis/adhesion which allows immediate adjustments on treatment protocols and strategies in alive individuals that can not and never be performed in other animal models.

Experimental Animal Models of Encapsulating Peritoneal Sclerosis

Encapsulating peritoneal sclerosis (EPS) is an infrequent, but extremely serious complication of long-term peritoneal dialysis. The cause of EPS is unclear, but the low incidence suggests that it is most likely multifactorial. The elucidation of developmental pathways and predictive markers of EPS would facilitate the identification and management of high-risk patients.

Animal models are often used to define pathways of disease progression and to test strategies for treatment and prevention in the patient population. Ideally such models could help to define the cause of EPS and its developmental pathways, to facilitate the identification of contributing factors and predictive markers, and to provide a system to test therapeutic strategies.

Researchers have studied several rodent models of EPS that rely on chronic chemical irritation (for example, bleach, low-pH solution, chlorhexidine gluconate) to induce peritoneal sclerosis and abdominal encapsulation. Development in all models is progressive, with inflammation giving way to peritoneal fibrosis or sclerosis with accumulating membrane damage, culminating in cocoon formation. Microscopic findings are similar to those proposed as diagnostic criteria for clinical EPS: an initial inflammatory infiltrate and submesothelial thickening, collagen deposition, and activation and proliferation of peritoneal fibroblasts. The potential to block progression of peritoneal sclerosis in these models by anti-inflammatory, antifibrotic, and antiangiogenic agents, and by inhibitors of the renin–angiotensin system have been demonstrated.

Animal models based on clinically relevant risk factors (for example, uremia, peritonitis, and long-term exposure to dialysis solutions) now represent the next step in model development.

Anti-C5a complementary peptide mitigates zymosan-induced severe peritonitis with fibrotic encapsulation in rats pretreated with methylglyoxal

In a previous study of fungal peritoneal injury in peritoneal dialysis patients, complement (C)-dependent pathological changes were developed in zymosan (Zy)-induced peritonitis by peritoneal scraping. However, the injuries were limited to the parietal peritoneum and did not show any fibrous encapsulation of the visceral peritoneum, which differs from human encapsular peritoneal sclerosis (EPS). We investigated peritoneal injury in a rat model of Zy-induced peritonitis pretreated with methylglyoxal (MGO) instead of scraping (Zy/MGO peritonitis) to clarify the role of C in the process of fibrous encapsulation of the visceral peritoneum. Therapeutic effects of an anti-C5a complementary peptide, AcPepA, on peritonitis were also studied. In Zy/MGO peritonitis, peritoneal thickness, fibrin exudation, accumulation of inflammatory cells, and deposition of C3b and C5b-9 with loss of membrane C regulators were increased along the peritoneum until day 5. On day 14, fibrous encapsulation of the visceral peritoneum was observed, resembling human EPS. Peritoneal injuries and fibrous changes were significantly improved with AcPepA treatment, even when AcPepA was administered following injection of Zy in Zy/MGO peritonitis. The data show that C5a might play a role in the development of encapsulation-like changes in the visceral peritoneum in Zy/MGO peritonitis. AcPepA might have therapeutic effects in fungal infection-induced peritoneal injury by preventing subsequent development of peritoneal encapsulation.

Animal Models of Peritoneal Dialysis: Thirty Years of Our Own Experience

Experimental animal models improve our understanding of technical problems in peritoneal dialysis PD, and such studies contribute to solving crucial clinical problems. We established an acute and chronic PD model in nonuremic and uremic rats. We observed that kinetics of PD in rats change as the animals are aging, and this effect is due not only to an increasing peritoneal surface area, but also to changes in the permeability of the peritoneum. Changes of the peritoneal permeability seen during chronic PD in rats are comparable to results obtained in humans treated with PD. Effluent dialysate can be drained repeatedly to measure concentration of various bioactive molecules and to correlate the results with the peritoneal permeability. Additionally we can study in in vitro conditions properties of the effluent dialysate on cultured peritoneal mesothelial cells or fibroblasts. We can evaluate acute and chronic effect of various additives to the dialysis fluid on function and permeability of the peritoneum. Results from such study are even more relevant to the clinical scenario when experiments are performed in uremic rats. Our experimental animal PD model not only helps to understand the pathophysiology of PD but also can be used for testing biocompatibility of new PD fluids.

Encapsulating peritoneal sclerosis is associated with T-cell activation

BACKGROUND

Encapsulating peritoneal sclerosis (EPS) is an excessive fibrotic response of the peritoneum that may occur after long-term peritoneal dialysis (PD). The underlying pathophysiology is poorly understood, but involvement of peritoneal inflammatory T helper 1 cells may be pivotal.

METHODS

Soluble interleukin-2 receptor alpha (sCD25) concentration was measured as a marker for T-cell activation in serum and ascites from EPS patients and various control patient groups. Peritoneal biopsies were stained for the presence of T cells, and T cells isolated from ascites of EPS patients were characterized in detail for differentiation status and cytokine expression.

RESULTS

Serum sCD25 concentrations are significantly and specifically increased in EPS patients compared with haemodialysis, PD and predialysis patients. Peritoneal effluent of stable PD patients contains very low levels of sCD25, while sCD25 levels in ascites of EPS patients are high and indicative of local production. In the years preceding the diagnosis of EPS, the serum sCD25 concentrations increased while remaining at stable levels in control PD patients. The peritoneum and ascites of EPS patients showed a significant influx of T cells with relatively increased numbers of CD4(+) T cells. These T cells were fully differentiated and displayed a T helper 1 cell type with a pro-inflammatory cytokine profile.

CONCLUSIONS

Increased serum sCD25 concentrations and peritoneal lymphocytosis in EPS patients indicate the involvement of activated T cells in the pathophysiology of excessive fibrosis.

CD4-Positive T Cells and M2 Macrophages Dominate the Peritoneal Infiltrate of Patients with Encapsulating Peritoneal Sclerosis

Background

Encapsulating peritoneal sclerosis (EPS) is a severe complication of peritoneal dialysis (PD). Previously, it has been shown that infiltrating CD4-positive T cells and M2 macrophages are associated with several fibrotic conditions. Therefore, the characteristics of the peritoneal cell infiltrate in EPS may be of interest to understand EPS pathogenesis. In this study, we aim to elucidate the composition of the peritoneal cell infiltrate in EPS patients and relate the findings to clinical outcome.

Study Design, Setting, and Participants

We studied peritoneal membrane biopsies of 23 EPS patients and compared them to biopsies of 15 PD patients without EPS. The cellular infiltrate was characterized by immunohistochemistry to detect T cells(CD3-positive), CD4-positive (CD4+) and CD8-positive T cell subsets, B cells(CD20-positive), granulocytes(CD15-positive), macrophages(CD68-positive), M1(CD80-positive), and M2(CD163-positive) macrophages. Tissues were analysed using digital image analysis. Kaplan-Meier survival analysis was performed to investigate the survival in the different staining groups.

Results

The cellular infiltrate in EPS biopsies was dominated by mononuclear cells. For both CD3 and CD68, the median percentage of area stained was higher in biopsies of EPS as opposed to non-EPS patients (p<0.001). EPS biopsies showed a higher percentage of area stained for CD4 (1.29%(0.61-3.20)) compared to CD8 (0.71%(0.46-1.01), p = 0.04), while in the non-EPS group these cells were almost equally represented (respectively 0.28%(0.05-0.83) versus 0.22%(0.17-0.43), p = 0.97). The percentage of area stained for both CD80 and CD163 was higher in EPS than in non-EPS biopsies (p<0.001), with CD163+ cells being the most abundant phenotype. Virtually no CD20-positive and CD15-positive cells were present in biopsies of a subgroup of EPS patients. No relation was found between the composition of the mononuclear cell infiltrate and clinical outcome.

Conclusions

A characteristic mononuclear cell infiltrate consisting of CD4+ and CD163+ cells dominates the peritoneum of EPS patients. These findings suggest a role for both CD4+ T cells and M2 macrophages in the pathogenesis of EPS.

Lineage tracing reveals distinctive fates for mesothelial cells and submesothelial fibroblasts during peritoneal injury

Fibrosis of the peritoneal cavity remains a serious, life-threatening problem in the treatment of kidney failure with peritoneal dialysis. The mechanism of fibrosis remains unclear partly because the fibrogenic cells have not been identified with certainty. Recent studies have proposed mesothelial cells to be an important source of myofibroblasts through the epithelial-mesenchymal transition; however, confirmatory studies in vivo are lacking. Here, we show by inducible genetic fate mapping that type I collagen-producing submesothelial fibroblasts are specific progenitors of α-smooth muscle actin-positive myofibroblasts that accumulate progressively in models of peritoneal fibrosis induced by sodium hypochlorite, hyperglycemic dialysis solutions, or TGF-β1. Similar genetic mapping of Wilms' tumor-1-positive mesothelial cells indicated that peritoneal membrane disruption is repaired and replaced by surviving mesothelial cells in peritoneal injury, and not by submesothelial fibroblasts. Although primary cultures of mesothelial cells or submesothelial fibroblasts each expressed α-smooth muscle actin under the influence of TGF-β1, only submesothelial fibroblasts expressed α-smooth muscle actin after induction of peritoneal fibrosis in mice. Furthermore, pharmacologic inhibition of the PDGF receptor, which is expressed by submesothelial fibroblasts but not mesothelial cells, attenuated the peritoneal fibrosis but not the remesothelialization induced by hypochlorite. Thus, our data identify distinctive fates for injured mesothelial cells and submesothelial fibroblasts during peritoneal injury and fibrosis.

Encapsulating peritoneal sclerosis: incidence, predictors, and outcomes

Encapsulating peritoneal sclerosis is a complication of peritoneal dialysis characterized by persistent, intermittent, or recurrent adhesive bowel obstruction. Here we examined the incidence, predictors, and outcomes of encapsulating peritoneal sclerosis (peritoneal fibrosis) by multivariate logistic regression in incident peritoneal dialysis patients in Australia and New Zealand. Matched case-control analysis compared the survival of patients with controls equivalent for age, gender, diabetes, and time on peritoneal dialysis. Of 7618 patients measured over a 13-year period, encapsulating peritoneal sclerosis was diagnosed in 33, giving an incidence rate of 1.8/1000 patient-years. The respective cumulative incidences of peritoneal sclerosis at 3, 5, and 8 years were 0.3, 0.8, and 3.9%. This condition was independently predicted by younger age and the duration of peritoneal dialysis, but not the rate of peritonitis. Twenty-six patients were diagnosed while still on peritoneal dialysis. Median survival following diagnosis was 4 years and not statistically different from that of 132 matched controls. Of the 18 patients who died, only 7 were attributed directly to peritoneal sclerosis. Our study shows that encapsulating peritoneal sclerosis is a rare condition, predicted by younger age and the duration of peritoneal dialysis. The risk of death is relatively low and not appreciably different from that of competing risks for mortality in matched dialysis control patients.

Zymosan, but Not Lipopolysaccharide, Triggers Severe and Progressive Peritoneal Injury Accompanied by Complement Activation in a Rat Peritonitis Model

Fungal peritonitis is an important complication in peritoneal dialysis patients; either continuous or recurrent peritonitis may enhance peritoneal damage. Even when the peritoneal dialysis catheter is removed in patients with fungal peritonitis, peritoneal fibrosis can progress and evolve into encapsular peritoneal sclerosis. It is unclear why fungal infections are worse than bacterial in these respects. Zymosan is a cell wall component of yeast that strongly activates the complement system. In this study, we compared the effects of zymosan and bacterial LPS on peritoneal inflammation in a rat peritoneal injury model induced by mechanical scraping. Intraperitoneal administration of zymosan, but not LPS or vehicle, caused markedly enhanced peritonitis with massive infiltration of cells and deposition of complement activation products C3b and membrane attack complex on day 5. In rats administered zymosan and sacrificed on days 18 or 36, peritoneal inflammation persisted with accumulation of ED-1-positive cells, small deposits of C3b and membrane attack complex, exudation of fibrinogen, and capillary proliferation in subperitoneal tissues. When zymosan was administered daily for 5 days after peritoneal scrape, there was even greater peritoneal inflammation with peritoneal thickening, inflammatory cell accumulation, and complement deposition. Inhibition of systemic complement by pretreatment with cobra venom factor or local inhibition by i.p. administration of the recombinant complement regulator Crry-Ig reduced peritoneal inflammation in zymosan-treated rats. Our results show that yeast components augment inflammation in the injured peritoneum by causing complement activation within the peritoneal cavity. Local anticomplement therapy may therefore protect from peritoneal damage during fungal infection of the peritoneum.

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.

How Can Genetic Advances Impact on Experimental Models of Encapsulating Peritoneal Sclerosis?

In this review we discuss how animal models have contributed to the understanding of pathological pathways that may be involved in the development of encapsulating peritoneal sclerosis. We review the various interventional procedures that, so far, have ameliorated disease progression in animals. Reviewing advancements in molecular biology and genetic technologies, we discuss how future experimental models may impact our understanding of the pathogenesis and treatment of this rare but complex disease.

Experimental Encapsulating Peritoneal Sclerosis Models: Pathogenesis and Treatment

Encapsulating peritoneal sclerosis (EPS) is rare but, with its high morbidity and mortality, it represents one of the most serious complications of long-term peritoneal dialysis. The pathogenesis of EPS has not been elucidated yet; therefore, there has been a growing interest in establishing appropriate animal models for EPS that would explain the pathogenesis of EPS and verify the efficacy of therapeutic agents targeting pathways such as angiogenesis and/ or fibrosis. This brief review provides an update on previously published animal experimental models of EPS. Based on this review, we discuss some aspects of pathogenesis and treatment options in patients with EPS. Experimental models of EPS cannot exactly reproduce human EPS because the latter most likely has a diverse etiology, including the influences of uremia, dialysis, and genetic factors. There is a need for new animal models that would test interventions targeting multiple risk factors while also taking into account putative genetic diversities that most likely are involved in human EPS.

Sclerosing encapsulating peritonitis as a complication of long-term continuous ambulatory peritoneal dialysis in Korea

Sclerosing encapsulating peritonitis (SEP) is a rare yet serious complication in patients with continuous ambulatory peritoneal dialysis (CAPD). Incidence and prevalence of this syndrome have been defined in some large populations and a few single-centre experiences, but there is no satisfactory estimate of the comparative incidence of dialysis related SEP. The pathogenesis of SEP still remains uncertain, but there could be various causative factors. The diagnosis of SEP remains based on clinical suspicion confirmed with radiologic and/or pathologic findings. The possible variable etiologies and probable distinct pathways leading to this syndrome may make a uniform therapeutic approach unlikely. To determine the prevalence, etiologic factors, clinical features, effect of dialysis duration, and outcome of SEP in Korea, patients undergoing CAPD who developed SEP were retrospectively studied in five University Hospital dialysis centres with large numbers of CAPD patients in Korea. Out of a total 3888 CAPD studied patients between January 1981 to December 2002 in those five medical centres, 31 cases developed SEP with the overall prevalence 0.8%. There were 15 men and 16 women. The mean age of these patients was 44.0 +/- 9.8 years old. The mean duration of CAPD before SEP was 70.3 +/- 41.9 months (range 9-144 months) and 67.8% of patients (21/31) had been on CAPD more than 4 years. Peritonitis, including one fungal peritonitis, was the main cause of SEP in 25 cases (80.6%). Seventy percent of these cases used beta-blocker and the mean duration of the usage was 61.7 +/- 47.6 months. Seven cases were surgically treated and others were treated conservatively with intermittent total parenteral nutrition. The mortality rate was 25.8%. In conclusion, SEP is a serious life threatening complication of CAPD, and most cases had long-term peritoneal dialysis (PD) duration more than 4 years. To reduce the incidence of SEP, careful monitoring may be needed especially in patients with long-term CAPD and peritonitis.

Selective depletion of fibroblasts preserves morphology and the functional integrity of peritoneum in transgenic mice with peritoneal fibrosing syndrome

BACKGROUND

A peritoneal fibrosing syndrome (PFS) can progressively reduce peritoneal ultrafiltration during chronic peritoneal dialysis in patients with renal failure. The pathogenesis of PFS is unclear and the role of peritoneal fibroblasts has not been evaluated experimentally.

METHODS

We followed the fate of fibroblasts producing PFS in a mouse model using fibroblast-specific protein 1 (FSP1) as a marker. PFS was induced by daily peritoneal infusions of chlorhexidine gluconate (CHG) saline into transgenic mice expressing the thymidine kinase (Delta tk) gene under the control of the FSP1 promoter (FSP1.Delta tk mice). To demonstrate the role of fibroblasts in PFS, we treated these FSP1.Delta tk mice with a nucleoside analogue to induce DNA chain termination and fibroblast death.

RESULTS

Mice receiving peritoneal infusions of CHG saline every other day for 2 weeks developed increasing numbers of FSP1+ fibroblasts in the subserosal layers of the visceral peritoneum. Mac-3+ monocytes (macrophages) subsequently accumulated over the next 2 weeks in association with increased deposition of type I collagen and increased endothelial vascularity (CD31+) in these subserosal tissues. Since these peritoneal fibroblasts expressed monocyte chemoattractant protein-1 (MCP-1), heat shock protein 47 (HSP47), and vascular endothelial growth factor (VEGF), we suspect they were partially responsible for macrophage recruitment, matrix production, and the neoangiogenesis in the subserosal tissue. Treatment of PFS in FSP1.Delta tk transgenic mice with a nucleoside analogue selectively reduced the numbers of peritoneal fibroblasts and attenuated the attendant changes in peritoneal histology. Rescuing the peritoneal membrane from chronic thickening and neoangiogenesis by reducing the number of fibroblasts also preserved ultrafiltration.

CONCLUSION

Peritoneal fibroblasts play a pivotal role in PFS, and their deletion using a fibroblasts-specific transgene was effective in preventing peritoneal fibrogenesis.

Bloody ascites in a patient after transfer from peritoneal dialysis to hemodialysis

A 65-year-old woman with end-stage renal disease (ESRD) presented with bloody ascites. She had been maintained on peritoneal dialysis (PD) for 7 years and had eight episodes of peritonitis. She was eventually transferred to hemodialysis (HD) because of ultrafiltration failure. This was associated with "high" peritoneal transport by peritoneal equilibration test (PET). A period of "peritoneal rest" did not improve PET results. Within a year of transfer to HD, ascites developed, which was hemorrhagic upon evaluation. A computed tomography (CT) scan suggested encapsulating sclerosing peritonitis, which was confirmed upon peritonoscopy. The patient was treated with prednisone and tamoxifen. Encapsulating peritoneal sclerosis (EPS) is a devastating complication of PD. Although it is rare and its development often unpredictable, this case demonstrates several clinical features commonly observed in the condition. These include more than 6 years on PD, a high transporter status, recurrent peritonitis, and the development of blood-stained dialysis effluent (or ascites if PD has been discontinued, as was the case in this patient). The initial presentation is often incipient with vague abdominal pain. Symptoms are progressive, however, and EPS has a high mortality rate, with most patients dying within 1 year of diagnosis, usually from malnutrition and sepsis. Treatment options include systemic immunosuppression and regular peritoneal irrigation after transfer to HD. Response to treatment is more likely to occur in the early inflammatory stage of EPS, when symptoms are nonspecific and imaging is relatively normal. Hence a high degree of suspicion for the diagnosis should be present in patients "at risk" of this condition, as early diagnosis is essential if progressive encapsulation of the abdominal viscera is to be prevented.

Peritoneal toxicity of water: a model of chronic peritonitis caused by osmotic dysequilibrium in rats

The purpose of this work was to determine whether the osmotic dysequilibrium created by intraperitoneal (i.p.) injection of pure water has any permanent, damaging toxic sequelae. Rats were injected i.p. with pure water on five successive days. Necropsies were performed 1 week after the last injection. Necropsies revealed fibrosis of peritoneal surfaces of liver and spleen, similar to the effects of chemical irritants but milder. The severity of the lesions depended on the dose of water and the number of injections. A few minutes of contact with pure water was sufficient to ensure subsequent development of fibrosis. Soon after the initial injury, the inoculum became less hypotonic and then isotonic. Isotonic or moderately hypotonic electrolyte solutions did not produce peritoneal fibrosis but very hypotonic solutions were toxic. Injection of the synthetic compound 48/80, which is known to cause discharge of mast cell granules, did not produce peritonitis, nor was contamination by endotoxin or by blood responsible for the lesions. Injection of water may be a useful method for investigating the role, if any, of mast cells and/or mesothelial cells in the toxic effects of osmotic dysequilibrium.

Repeated toxic injury of peritoneum: accumulation of toxicity and adaptation to injury

In order to develop new methods for the study of pathogenesis of post-injury fibroplasia, a rat model of chemical peritonitis was explored. Sodium hypochlorite (NaOCl) of various concentrations was injected intraperitoneally one or more times using different intervals between doses. Some time later, the surface fibrosis of liver, spleen, omentum and other abdominal organs was evaluated. A dose-response relation at intermediate concentrations and an apparent threshold at low concentrations were observed. Fibroplasia was increased by repeated doses (accumulation) but it was ameliorated compared to the same total amount of chemical given as a single injection (adaptation during repeated dosing). The rapid disappearance of the chemical irritant and the large size and easy accessibility of the peritoneal cavity suggest that this model may be useful in further study of chemical toxicity and fibroplasia in relation to human fibrosing diseases and injuries (trauma, surgery, peritoneal dialysis). The model has the unique feature of evaluating the morphological effects of the toxic injury and secondary functional effects at the same time.

Peritoneal sclerosis: one or two nosological entities?

The frequency, pathology, animal models, pathogenesis, clinical manifestations, diagnostic criteria, therapy and prevention of peritoneal sclerosis are reviewed. Many of these aspects have a bimodal configuration which suggests that peritoneal sclerosis, usually considered a single pathology in peritoneal dialysis, is actually two distinct nosological entities: simple sclerosis and sclerosing peritonitis. The former is very frequent, with minor anatomical alterations and low clinical impact; it is reproducible in animals by means of peritoneal dialysis, and is clearly due to the poor biocompatibility of peritoneal dialysis solutions. The latter is rare, with radical anatomical alterations and high mortality requiring valid methods of diagnosis, therapy and prevention; it can only be reproduced in animal models by means other than peritoneal dialysis and seems to be due to factors both related and unrelated to peritoneal dialysis.