Changes of cytokine profiles during peritonitis in patients on continuous ambulatory peritoneal dialysis

Autophagy in peritoneal fibrosis

Peritoneal dialysis (PD) is a widely accepted renal replacement therapy for patients with end-stage renal disease (ESRD). Morphological and functional changes occur in the peritoneal membranes (PMs) of patients undergoing long-term PD. Peritoneal fibrosis (PF) is a common PD-related complication that ultimately leads to PM injury and peritoneal ultrafiltration failure. Autophagy is a cellular process of "self-eating" wherein damaged organelles, protein aggregates, and pathogenic microbes are degraded to maintain intracellular environment homeostasis and cell survival. Growing evidence shows that autophagy is involved in fibrosis progression, including renal fibrosis and hepatic fibrosis, in various organs. Multiple risk factors, including high-glucose peritoneal dialysis solution (HGPDS), stimulate the activation of autophagy, which participates in PF progression, in human peritoneal mesothelial cells (HPMCs). Nevertheless, the underlying roles and mechanisms of autophagy in PF progression remain unclear. In this review, we discuss the key roles and potential mechanisms of autophagy in PF to offer novel perspectives on future therapy strategies for PF and their limitations.

From MIA to FIFA: The vicious matrix of frailty, inflammation, fluid overload and atherosclerosis in peritoneal dialysis

Cardiovascular disease (CVD) is a major cause of mortality and morbidity in peritoneal dialysis (PD) patients. Two decades ago, the common co-existence of malnutrition and systemic inflammation PD patients with atherosclerosis and CVD led to the proposed terminology of 'malnutrition-inflammation-atherosclerosis (MIA) syndrome'. Although the importance of malnutrition is well accepted, frailty represents a more comprehensive assessment of the physical and functional capability of the patient and encompasses the contributions of sarcopenia (a key component of malnutrition), obesity, cardiopulmonary as well as neuropsychiatric impairment. In recent years, it is also increasingly recognized that fluid overload is not only the consequence but also play an important role in the pathogenesis of CVD. Moreover, fluid overload is closely linked with the systemic inflammatory status, presumably by gut oedema, gastrointestinal epithelial barrier dysfunction and leakage of bacterial fragments to the systemic circulation. There are now a wealth of published evidence to show intricate relations between frailty, inflammation, fluid overload and atherosclerotic disease in patients with chronic kidney disease (CKD) and those on PD, a phenomenon that we propose the term 'FIFA complex'. In this system, frailty and atherosclerotic disease may be regarded as two patient-oriented outcomes, while inflammation and fluid overload are two inter-connected pathogenic processes. However, there remain limited data on how the treatment of one component affect the others. It is also important to define how treatment of fluid overload affect the systemic inflammatory status and to develop effective anti-inflammatory strategies that could alleviate atherosclerotic disease and frailty.

Eryptosis in Peritoneal Dialysis-Related Peritonitis: The Potential Role of Inflammation in Mediating the Increase in Eryptosis in PD

Background: Peritonitis and exit site infections are the main complications of patients treated with peritoneal dialysis (PD). Erythrocytes (red blood cells—RBCs) are very sensitive cells, and they are characterized by eryptosis (programmed cell death). The purpose of this research was to assess eryptosis in PD patients with PD-related peritonitis and its connection to inflammatory markers in vivo and in vitro. Material and Methods: In this study, we included 65 PD patients: 34 PD patients without systemic inflammation nor PD-related peritonitis in the previous 3 months, and 31 PD patients with an acute episode of PD-related peritonitis. We measured C-reactive protein (CRP) and cytokine (IL-1β, IL-6, and IL-18) levels as systemic inflammatory markers. Eryptosis was evaluated by flow cytometric analyses in freshly isolated RBCs. The induction of eryptosis due to in vitro exposure to IL-1β, IL-6, and IL-18 was verified. Results: Eryptosis was significantly higher in PD patients with peritonitis (9.6%; IQR 4.2−16.7), compared to the those in the other group (2.7%; IQR 1.6−3.9) (p < 0.0001). Significant positive correlations were noticed between eryptosis and CRP, IL-1β, and IL-6. RBCs, incubated with greater concentrations of all cytokines in vitro, resulted in significantly higher occurrences of eryptosis in comparison with those incubated with lower concentration and with untreated cell (p < 0.05), and for those with extensive exposure (p < 0.05). Conclusion: In conclusion, we investigated a potential relationship between systemic eryptosis and the in vivo and in vitro inflammatory damage of the peritoneal membrane during peritonitis. Thus, the presented results revealed that upregulated inflammatory markers and immune system dysregulation could be the cause of high levels of systemic eryptosis during PD-related peritonitis.

Restoration of WT1/miR-769-5p axis by HDAC1 inhibition promotes MMT reversal in mesenchymal-like mesothelial cells

Histone acetylation/deacetylation play an essential role in modifying chromatin structure and in regulating cell plasticity in eukaryotic cells. Therefore, histone deacetylase (HDAC) pharmacological inhibitors are promising tools in the therapy of fibrotic diseases and in cancer. Peritoneal fibrosis is a pathological process characterized by many cellular and molecular alterations, including the acquisition of invasive/pro-fibrotic abilities by mesothelial cells (MCs) through induction of mesothelial to mesenchymal transition (MMT). The aim of this study was to characterize the molecular mechanism of the antifibrotic role of HDAC1 inhibition. Specifically, treatment with MS-275, an HDAC1-3 inhibitor previously known to promote MMT reversal, induced the expression of several TGFBRI mRNA-targeting miRNAs. Among them, miR-769-5p ectopic expression was sufficient to promote MMT reversal and to limit MC migration and invasion, whereas miR-769-5p silencing further enhanced mesenchymal gene expression. These results were confirmed by HDAC1 genetic silencing. Interestingly, miR-769-5p silencing maintained mesenchymal features despite HDAC1 inhibition, thus indicating that it is necessary to drive MMT reversal induced by HDAC1 inhibition. Besides TGFBRI, miR-769-5p was demonstrated to target SMAD2/3 and PAI-1 expression directly. When analyzing molecular mechanisms underlying miR-769-5p expression, we found that the transcription factor Wilms' tumor 1 (WT1), a master gene controlling MC development, binds to the miR-769-5p promoter favoring its expression. Interestingly, both WT1 expression and binding to miR-769-5p promoter were increased by HDAC1 inhibition and attenuated by TGFβ1 treatment. Finally, we explored the significance of these observations in the cell-to-cell communication: we evaluated the ability of miR-769-5p to be loaded into extracellular vesicles (EVs) and to promote MMT reversal in recipient mesenchymal-like MCs. Treatment of fibrotic MCs with EVs isolated from miR-769-5p over-expressing MCs promoted the down-regulation of specific mesenchymal targets and the reacquisition of an epithelial-like morphology. In conclusion, we highlighted an HDAC1-WT1-miR-769-5p axis potentially relevant for therapies aimed at counteracting organ fibrosis.

Involvement of Mitochondrial Dysfunction in the Inflammatory Response in Human Mesothelial Cells from Peritoneal Dialysis Effluent

Recent studies have related mitochondrial impairment with peritoneal membrane damage during peritoneal dialysis (PD) therapy. Here, we assessed the involvement of mitochondrial dysfunction in the inflammatory response in human mesothelial cells, a hallmark in the pathogenesis of PD-related peritoneal membrane damage. Our ex vivo studies showed that IL-1β causes a drop in the mitochondrial membrane potential in cells from peritoneal effluent. Moreover, when mitochondrial damage was induced by inhibitors of mitochondrial function, a low-grade inflammatory response was generated. Interestingly, mitochondrial damage sensitized mesothelial cells, causing a significant increase in the inflammatory response induced by cytokines, in which ROS generation and NF-κB activation appear to be involved, since inflammation was counteracted by both mitoTEMPO (mitochondrial ROS scavenger) and BAY-117085 (NF-κB inhibitor). Furthermore, the natural anti-inflammatory antioxidant resveratrol significantly attenuated the inflammatory response, by reversing the decline in mitochondrial membrane potential and decreasing the expression of IL-8, COX-2 and PGE2 caused by IL-1β. These findings suggest that IL-1β regulates mitochondrial function in mesothelial cells and that mitochondrial dysfunction could induce an inflammatory scenario that sensitizes these cells, causing significant amplification of the inflammatory response induced by cytokines. Resveratrol may represent a promising strategy in controlling the mesothelial inflammatory response to PD.

High intraperitoneal interleukin-6 levels predict ultrafiltration (UF) insufficiency in peritoneal dialysis patients: A prospective cohort study

Introduction

UF insufficiency is a major limitation in PD efficiency and sustainability. Our study object to investigate the efficacy of intraperitoneal inflammation marker, IL-6 level as a predictor of UF insufficiency in continuous ambulatory peritoneal dialysis (CAPD) patients.

Methods

Stable prevalent CAPD patients were enrolled in this prospective study. IL-6 concentration in the overnight effluent was determined and expressed as the IL-6 appearance rate (IL-6 AR). Patients were divided into two groups according to the median of IL-6 AR and prospectively followed up until death, transfer to permanent HD, recovery of renal function, kidney transplantation, transfer to other centers, lost to follow-up or to the end of study (January 31, 2021). Factors associated with UF capacity as well as dialysate IL-6 AR were assessed by multivariable linear regression. Cox proportional hazards model was used to examine the association between dialysate IL-6 AR and UF insufficiency.

Results

A total of 291 PD patients were enrolled, including 148 males (51%) with a mean age of 56.6 ± 14.1 years and a median PD duration of 33.4 (12.7–57.5) months. No correlation was found between dialysate IL-6 AR and UF capacity at baseline. PD duration was found positively correlated with baseline dialysate IL-6 AR, while 24h urine volume was negatively correlated with baseline dialysate IL-6 AR (P < 0.05). By the end of study, UF insufficiency was observed in 56 (19.2%) patients. Patients in the high IL-6 AR group showed a significantly inferior UF insufficiency-free survival when compared with their counterparts in the low IL-6 AR group (P = 0.001). In the multivariate Cox regression analysis, after adjusting for DM, previous peritonitis episode and 24h urine volume, higher baseline dialysate IL-6 AR (HR 3.639, 95% CI 1.776–7.456, P = 0.002) were associated with an increased risk of UF insufficiency. The area under the ROC curve (AUC) for baseline IL-6 AR to predict UF insufficiency was 0.663 (95% CI, 0.580–0.746; P < 0.001).

Conclusion

Our study suggested that the dialysate IL-6 AR could be a potential predictor of UF insufficiency in patients undergoing PD.

Glycoprotein 96 in Peritoneal Dialysis Effluent-Derived Extracellular Vesicles: A Tool for Evaluating Peritoneal Transport Properties and Inflammatory Status

Background

Extracellular vesicles (EVs) from peritoneal dialysis effluent (PDE), containing molecules such as proteins and microRNAs (miRNAs), may be potential biological markers to monitor peritoneal function or injury. Peritoneal inflammation is an important determinant of peritoneal solute transport rate (PSTR). Thus, the aim of this study is to determine whether the specific proteins capable of evaluating the PSTR could be found in PDE-EVs, and explore the underlying mechanism for the association between PSTR and peritoneal inflammation.

Methods

Sixty patients undergoing peritoneal dialysis (PD) were divided into two groups: high/high average transport (H/A) group (PET >0.65) and low/low average transport (L/A) group (PET <0.65). EVs derived from PDE (PDE-EVs) were isolated by ultracentrifugation. Proteomic analysis was performed to explore the differentially expressed proteins and identify the potential biomarkers in PDE-EVs from the two groups, and we focused on glycoprotein 96 (GP96) as it could be involved in the inflammatory process. The expression of GP96 in PDE-EVs and inflammatory cytokines was quantified by real-time PCR and enzyme-linked immunosorbent assay. The infiltration of macrophages and neutrophils into the peritoneum was detected using immunohistochemistry in a PD rat model.

Results

The expression of PDE-EVs-GP96 was significantly higher in the H/A group, and was positively correlated with the PSTR and the level of the inflammatory factor interleukin (IL)-6. GP96-enriched EVs enhanced the secretion of proinflammatory cytokines IL-1β, IL-6, tumor necrosis factor (TNF)-α, and IL-8 in macrophages, which was reversed by a pharmacological GP96-specific inhibitor (PU-WS13). The GP96 inhibitor also reduced local peritoneal inflammation by decreasing the infiltration of inflammatory cells and levels of proinflammatory cytokines (IL-6 and TNF-α) and chemokines (CCL2, CXCL1, and CXCL2) in a PD rat model.

Conclusions

PDE-EVs-GP96 is a new promising tool to evaluate the status of peritoneal inflammation and PSTR, and the mechanism may be related to affecting the inflammatory properties of macrophages.

Negative regulators of TGF-β1 signaling in renal fibrosis; pathological mechanisms and novel therapeutic opportunities

Elevated expression of the multifunctional cytokine transforming growth factor β1 (TGF-β1) is causatively linked to kidney fibrosis progression initiated by diabetic, hypertensive, obstructive, ischemic and toxin-induced injury. Therapeutically relevant approaches to directly target the TGF-β1 pathway (e.g., neutralizing antibodies against TGF-β1), however, remain elusive in humans. TGF-β1 signaling is subjected to extensive negative control at the level of TGF-β1 receptor, SMAD2/3 activation, complex assembly and promoter engagement due to its critical role in tissue homeostasis and numerous pathologies. Progressive kidney injury is accompanied by the deregulation (loss or gain of expression) of several negative regulators of the TGF-β1 signaling cascade by mechanisms involving protein and mRNA stability or epigenetic silencing, further amplifying TGF-β1/SMAD3 signaling and fibrosis. Expression of bone morphogenetic proteins 6 and 7 (BMP6/7), SMAD7, Sloan-Kettering Institute proto-oncogene (Ski) and Ski-related novel gene (SnoN), phosphate tensin homolog on chromosome 10 (PTEN), protein phosphatase magnesium/manganese dependent 1A (PPM1A) and Klotho are dramatically decreased in various nephropathies in animals and humans albeit with different kinetics while the expression of Smurf1/2 E3 ligases are increased. Such deregulations frequently initiate maladaptive renal repair including renal epithelial cell dedifferentiation and growth arrest, fibrotic factor (connective tissue growth factor (CTGF/CCN2), plasminogen activator inhibitor type-1 (PAI-1), TGF-β1) synthesis/secretion, fibroproliferative responses and inflammation. This review addresses how loss of these negative regulators of TGF-β1 pathway exacerbates renal lesion formation and discusses the therapeutic value in restoring the expression of these molecules in ameliorating fibrosis, thus, presenting novel approaches to suppress TGF-β1 hyperactivation during chronic kidney disease (CKD) progression.

Comparison of mesenchymal stromal cells from peritoneal dialysis effluent with those from umbilical cords: characteristics and therapeutic effects on chronic peritoneal dialysis in uremic rats

Background

A long-term of peritoneal dialysis (PD) using a hypertonic PD solution (PDS) leads to patient’s peritoneal membrane (PM) injury, resulting in ultrafiltration failure (UFF) and PD drop-out. Our previous study shows that PD effluent-derived mesenchymal stromal cells (pMSCs) prevent the PM injury in normal rats after repeated exposure of the peritoneal cavity to a PDS. This study was designed to compare the cytoprotection between pMSCs and umbilical cord-derived MSCs (UC-MSCs) in the treatment of both PM and kidney injury in uremic rats with chronic PD.

Methods

5/6 nephrectomized (5/6Nx) Sprague Dawley rats were intraperitoneally (IP) injected Dianeal (4.25% dextrose, 10 mL/rat/day) and were treated with pMSCs or umbilical cord (UC)-MSCs (approximately 2 × 10⁶/rat/week, IP). Ultrafiltration was determined by IP injection of 30 mL of Dianeal (4.25% dextrose) with 1.5-h dewell time, and kidney failure by serum creatinine (SCr) and blood urea nitrogen (BUN). The structure of the PM and kidneys was assessed using histology. Gene expression was examined using quantitative reverse transcription PCR, and protein levels using flow cytometric and Western blot analyses.

Results

We showed a slight difference in the morphology between pMSCs and UC-MSCs in plastic dishes, and significantly higher expression levels of stemness-related genes (NANOG, OCT4, SOX2, CCNA2, RAD21, and EXO1) and MSCs surface markers (CD29, CD44, CD90 and CD105) in UC-MSCs than those in pMSCs, but no difference in the differentiation to chondrocytes, osteocytes or adipocytes. pMSC treatment was more effective than UC-MSCs in the protection of the MP and remnant kidneys in 5/6Nx rats from PDS-induced injury, which was associated with higher resistance of pMSCs than UC-MSCs to uremic toxins in culture, and more reduction of peritoneal mesothelial cell death by the secretome from pMSCs than from UC-MSCs in response to PDS exposure. The secretome from both pMSCs and UC-MSCs similarly inactivated NOS2 in activated THP1 cells.

Conclusions

As compared to UC-MSCs, pMSCs may more potently prevent PDS-induced PM and remnant kidney injury in this uremic rat model of chronic PD, suggesting that autotransplantation of ex vivo-expanded pMSCs may become a promising therapy for UFF and deterioration of remnant kidney function in PD patients.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-021-02473-9.

Impact of peritoneal dialysis-related peritonitis on PD discontinuation and mortality: A population-based national cohort study

BACKGROUND

The impact of peritoneal dialysis-associated peritonitis (PD peritonitis) on long-term outcomes is uncertain. This nationwide retrospective study was conducted in Taiwan to understand the incidence, risk factors and long-term outcomes of PD peritonitis.

METHODS

A total of 11,202 incident adult peritoneal dialysis (PD) patients from 2000 to 2010 were collected from a Longitudinal Health Insurance Database and followed up until the end of 2011. Definition of peritonitis, the primary outcome, simultaneously met the diagnosis of peritonitis (International Classification of Diseases, Ninth Revision, Clinical Modification 567) and antibiotic use. Secondary outcomes included the impact of peritonitis on PD discontinuation and survival. Cox proportional hazards models with and without time-dependent variables were used to calculate hazard ratios (HRs) and 95% confidence intervals (CIs).

RESULTS

There were 7634 peritonitis episodes in 4245 patients during the follow-up period. The overall incidence of peritonitis was 0.18 episodes per patient-year. Peritonitis-associated risk factors included older age, female gender, chronic heart failure, cerebrovascular disease, liver cirrhosis and lower monthly income. In an adjusted Cox hazard proportional regression with the time-dependent model, peritonitis patients had a higher risk of PD discontinuation (HR 2.71, 95% CI 2.52-2.92) and mortality (HR 1.68, 95% CI 1.57-1.81) compared to patients without peritonitis. The adjusted HRs for mortality increased with each prior episode: one episode, two episodes and more than two episodes (all p < 0.05). The adjusted HRs for PD discontinuation also increased with the frequency of peritonitis. These negative effects were greatest during the first year and persisted significantly after 5 years. In a sensitivity analysis in which peritonitis within 30 days of death or PD discontinuation was excluded, peritonitis patients still had significantly increased risk of PD discontinuation and mortality compared to patients without peritonitis.

CONCLUSIONS

Although peritonitis incidence was low, our findings reveal that peritonitis carried acute and long-term sequelae of higher PD discontinuation and lower patient survival.

Associations between dialysate interleukin-6 and Tie-2 and peritoneal solute transport rate and outcomes for patients undergoing peritoneal dialysis: A prospective cohort study

Objectives

We designed this prospective observational study to clarify the associations between dialysate IL-6, a marker of ongoing peritoneal inflammation, Tie2, an important factor in angiogenesis in the peritoneum, and a high peritoneal solute transport rate (PSTR) in patients undergoing peritoneal dialysis (PD) and to investigate their outcome predictive roles.

Methods

A total of 60 stable continuous ambulatory peritoneal dialysis (CAPD) patients from a single center in China were analyzed in this prospective study. We measured dialysate levels of IL-6 and Tie-2 using ELISAs. Our primary study endpoint was all-cause mortality with 10 years' follow-up.

Results

For the evaluation of PSTR, we used the Dialysis/Plasma creatinine (D/Pcr) ratio. We subdivided the patients into two groups for statistical evaluation: low and low average D/Pcr (<0.64; L/A), and high and high average D/Pcr (≥0.65; H/A) transporters. The mean levels of dialysates IL-6 (21.71 ± 8.88 pg/mL) and Tie-2 (1.23 ± 0.43 ng/mL) were significantly higher in the H/A (high and high average, group than those in the L/A group (13.94 ± 5.43 pg/mL, p<0.001 and 0.95 ± 0.43 ng/mL, p=0.019; respectively). Moreover, IL-6 and Tie-2 were positively correlated with D/Pcr (r=0.366, p=0.004 and r=0.402, p=0.001; respectively). Both dialysates IL-6 and Tie-2 were independent determinants of a high peritoneal solute transport rate. After follow-up for 42.65±18.08 months, 30 patients (50.0%) had died. An increased D/Pcr increased the risk of all-cause mortality in patients with CAPD (p=0.018), but the dialysates IL-6 and Tie2 were not independent predictors of all-cause mortality (p>0.05).

Conclusion

Our results suggest that patients undergoing CAPD have a high peritoneal solute transport status with local peritoneal inflammation and angiogenesis. Increased D/Pcr is a relative risk factor for mortality and technique failure in patients undergoing CAPD.

Mediators of Inflammation and Fibrosis

During peritoneal dialysis, peritoneal cells are repeatedly exposed to a non-physiologic hypertonic environment with high glucose content and low pH. Current sterile dialysis solutions cause inflammation in the submesothelial compact zone, leading to fibrosis, angiogenesis, and, eventually, ultrafiltration failure. Although the normal interstitium separates the peritoneal microvasculature from the dialysis fluid and makes transperitoneal transport less efficient, changes in the submesothelial compact zone can result in progressive increases in solute transfer and ultrafiltration diminution. This peritoneal dysfunction will further be amplified with the development of an epithelial-to-mesenchymal transition of mesothelial cells and dissipation of the osmotic driving force through the increased area and solute transport that accompany neoangiogenesis of the submesothelial microvasculature. The alteration of the peritoneal membrane can be further aggravated by peritonitis, advanced glycation end-products, and glucose degradation products. Furthermore, new data are emerging to support a proinflammatory role for peritoneal adipocytes.

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.

Molecular pathways in peritoneal fibrosis

Peritoneal dialysis (PD) is a renal replacement therapy for patients with end-stage renal disease that is equivalent to hemodialysis with respect to adequacy, mortality, and other outcome parameters, yet providing superior quality-of-life measures and cost savings. However, long-term usage of the patient's peritoneal membrane as a dialyzer filter is unphysiological and leads to peritoneal fibrosis, which is a major factor of patient morbidity and PD technique failure, resulting in a transfer to hemodialysis or death. Peritoneal fibrosis pathophysiology involves chronic inflammation and the fibrotic process itself. Frequently, inflammation precedes membrane fibrosis development, although a bidirectional relationship of one inducing the other exists. This review aims at highlighting the histopathological definition of peritoneal fibrosis, outlining the interplay of fibrosis, angiogenesis and epithelial-to-mesenchymal transition (EMT), delineating important fibrogenic pathways involving Smad-dependent and Smad-independent transforming growth factor-β (TGF-β) as well as connective tissue growth factor (CTGF) signaling, and summarizing historic and recent studies of inflammatory pathways involving NOD-like receptor protein 3 (NLRP3)/interleukin (IL)-1β, IL-6, IL-17, and other cytokines.

Measurement of innate immune response biomarkers in peritoneal dialysis effluent using a rapid diagnostic point-of-care device as a diagnostic indicator of peritonitis

Peritonitis is the commonest complication of peritoneal dialysis and a major reason for treatment failure. Current diagnosis is based on clinical symptoms, cloudy effluent and a dialysate white cell count (over 100 cells/μl). A rapid point-of-care diagnostic test would accelerate diagnosis and potentially improve outcomes from infection. Here, in a clinical audit project, we used PERiPLEX®, a point-of-care device which detects when levels of matrix metalloproteinase-8 and interleukin-6 are elevated above a threshold within minutes in dialysis effluent, to assess whether it could confirm or exclude peritonitis in 107 patients undergoing peritoneal dialysis. Mean patient age was 64.6 years with a median duration of peritoneal dialysis of 13.3 months (interquartile range 6.3 - 33.5 months). Presence of peritonitis was confirmed by clinical criteria. There were 49 positive tests of which 41 patients had peritonitis, three had other causes of intra-peritoneal inflammation, three had severe urosepsis and two patients required no treatment. Fifty-eight tests were negative with one patient having a false negative result. The positive predictive value of the test was 83.7% (95% confidence interval 72.8 - 90.8) and the negative predictive value was 98.3% (89.1 - 99.8). Sensitivity and specificity were 97.6% (87.4 - 99.9) and 87.7% (77.2 - 94.5) respectively. Thus, PERiPLEX® could be used as a rapid point-of-care test that can aid the diagnosis or exclusion of peritonitis with a high negative predictive value.

Effects of Peritoneal Dialysis with an Overnight Icodextrin Dwell on Parameters of Glucose and LIPID Metabolism

Objective

To examine whether a reduced daily glucose load by overnight application of the less-absorbed glucose polymer icodextrin would have favorable effects on lipid profiles of continuous ambulatory peritoneal dialysis (CAPD) patients.

Study Design

Randomized crossover study with two subsequent periods of 6 weeks.

Setting

Home PD unit of a secondary-care hospital.

Patients

Twenty-one nondiabetic CAPD patients (15 male, 6 female; mean age 50.3 ± 11.8 years).

Intervention

Participants were randomly assigned to receive an overnight dwell with either standard glucose solution or with a 7.5% icodextrin-containing solution.

Main Outcome Measures

Relation between reduction in the total amount of intraperitoneal infused glucose and parameters of glucose (plasma glucose, insulin, and HbA1C) and lipid metabolism [free fatty acids, plasma lip-ids, lipoproteins, and low density lipoprotein (LDL) sub-fraction profile].

Results

After the icodextrin dwells, a reduction of plasma total cholesterol (from 5.43 ± 0.85 to 4.86 ± 0.70 mmol/L, p < 0.001) and LDL cholesterol (from 3.38 ± 0.87 to 2.93 ± 0.73 mmol/L, p = 0.001) was observed. Also, high density lipoprotein (HDL) cholesterol (from 0.95 ± 0.27 to 0.90 ± 0.24 mmol/L, p = 0.029) was reduced, but the plasma total cholesterol-to-HDL ratio remained similar. Plasma free fatty acids and triglyceride levels tended to decrease (from 0.16 ± 0.10 to 0.13 ± 0.08 mmol/L, p = 0.06, and from 2.14 ± 1.96 to 1.92 ± 1.03 mmol/L, respectively). Evaluation of LDL subfraction profiles after ultra-centrifugation showed a more buoyant LDL subfraction profile with fewer dense LDL particles in 6 patients and no changes in 14 patients after icodextrin. The effects on lipids were not accompanied by a decrease in fasting plasma glucose (from 5.76 ± 1.29 to 5.86 ± 0.80 mmol/L) or insulin levels (from 19.5 ± 14.4 to 20.3 ± 13.0 mU/L).

Conclusion

These results suggest a beneficial effect on lipid profiles of CAPD patients with the use of an overnight dwell with icodextrin.

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.

A Chronic Inflammatory Infusion Model of Peritoneal Dialysis in Rats

Objectives

Peritoneal membrane changes are related to daily exposure to non physiologic dialysate and recurrent acute inflammation. We modified a daily infusion and inflammation model and evaluated it for fibrotic and angiogenic features. The feasibility of adenovirus-mediated gene transfer in the model was also assessed.

Methods

Peritoneal catheters were implanted in rats. Over a period of 4 weeks, the animals received a daily infusion of Dianeal 4.25% (Baxter Healthcare Corporation, Deerfield, IL, U.S.A.) with an initial three doses of lipopolysaccharide (LPS) or physiologic saline. Peritoneal fluid was assayed for transforming growth factor beta (TGFβ) and vascular endothelial growth factor (VEGF). Animals were humanely killed at week 5. Net ultrafiltration was then measured, and tissue samples were immunostained for factor VIII. Mesenteric tissue was assayed for hydroxyproline content. Adenovirus-mediated gene transfer of β-galactosidase was assayed by intraperitoneal administration of the virus, 4 days before the end of the experiment.

Results

Animals treated with either Dianeal or physiologic saline showed peritoneal membrane thickening and increased vascularity. Fibrosis was demonstrated by increased hydroxyproline concentration. Ultrafiltration was impaired. We found increased concentrations of VEGF and TGFβ in the peritoneal fluid of animals treated with LPS and daily infusion. Adenovirus-mediated gene transfer to the peritoneal membrane was demonstrated in the model.

Conclusions

Exposure to LPS and daily Dianeal or physiologic saline leads to peritoneal fibrosis and neoangiogenesis. Vascularization and glucose transport correlate with ultrafiltration failure. The present animal model mimics changes seen in humans on peritoneal dialysis and may be valuable for evaluating short-term interventions to prevent membrane damage.

Transforming Growth Factor-β: Importance in Long-Term Peritoneal Membrane Changes

We have provided evidence from adenovirus-mediated gene transfer to the peritoneum that transforming growth factor-β1 mimics many of the functional and structural changes in the peritoneum in patients on long-term peritoneal dialysis, including fibrosis, increased submesothelial thickness, angiogenesis, increased solute transport, and ultrafiltration dysfunction. We review several key properties of this important fibrogenic molecule.

Interleukin-6 Levels Decrease in Effluent from Patients Dialyzed with Bicarbonate/Lactate–Based Peritoneal Dialysis Solutions

♦ Objective

Conventional lactate-buffered peritoneal dialysis (PD) solutions have several bioincompatible characteristics, including acidic pH, lactate buffer, and the presence of glucose degradation products (GDPs). These characteristics, along with inflammation, are believed to contribute to membrane dysfunction in peritoneal dialysis patients. A new PD solution containing a bicarbonate/ lactate buffer system with physiologic pH and low GDPs has shown improved biocompatibility in both in vitro and ex vivo studies. In the present study, the concentrations of cytokines interleukin-6 (IL-6), tumor necrosis factor alpha (TNFα), and vascular endothelial growth factor (VEGF), were measured in timed overnight effluents from PD patients continuously dialyzed with either lactate-based control solution (C) or bicarbonate/lactate–based solution (B/L) for 6 months.

♦ Methods

Effluents from 92 continuous ambulatory peritoneal dialysis (CAPD) patients were collected when the patients were entered into the study (baseline, all patients on C for more than 3 months), and at 3 and 6 months following randomization to C ( n = 31) or to B/L ( n = 61). Effluent samples were filtered, stored frozen, and then assayed for IL-6, TNFα, and VEGF by ELISA.

♦ Results

A significant decrease in effluent IL-6 was seen at 3 months and at 6 months in the B/L-treated patients. Levels of VEGF were significantly reduced at 3 months. No changes in the levels of IL-6 or VEGF were seen in the C-treated patients, and no changes in TNFα were seen in either group over time.

♦ Conclusions

Treatment with B/L is associated with decreased IL-6 synthesis and decreased VEGF secretion. The data suggest that the use of B/L solution is associated with reduced intraperitoneal inflammation and potential for angiogenesis. The use of B/L solution may, over time, help to restore peritoneal homeostasis and therefore preserve the function of the membrane in peritoneal dialysis.

Alpha-2-Macroglobulin and Albumin are Useful Serum Proteins to Detect Subclinical Peritonitis in the Rat

Background

In experimental peritoneal dialysis (PD) studies, the occurrence of peritonitis is a confounder in the interpretation of effects of chronic peritoneal exposure to dialysis solutions. Since fluid cannot be drained in most experimental PD models in the rat, it is impossible to diagnose peritonitis based on dialysate white blood cell counts. To study the value of serum markers for the presence of peritonitis, alpha-2-macroglobulin (α2M) and albumin were measured in rats with and without peritonitis after chronic exposure to dialysis solutions. To further investigate the time course of these markers in relation to the severity of peritonitis, nondialyzed rats were challenged with increasing numbers of bacteria and followed for 28 days.

Methods

In the first study, α2M and albumin were measured in rats exposed to glucose/lactate-based dialysis fluid before sacrifice. A comparison was made between animals with peritonitis, as judged from the presence of extensive infiltrates after sacrifice (gold standard) and/or clinical signs of peritonitis, or absence of peritonitis and infiltrates. In the second study, rats were intraperitoneally (IP) injected with 3 different concentrations of Staphylococcus aureus, and serum α2M and albumin were measured at various time points.

Results

In the first study, serum α2M was higher and serum albumin was lower in animals with peritonitis compared to animals without peritonitis (both p < 0.05). In the second study, induction of α2M was clearly dependent on the inoculum concentration. Peak values of α2M were found at days 1 and 3. At all time points after inoculation, α2M was higher in all injected groups compared to the control group. Serum albumin values decreased in the highest inoculum group and remained decreased until 28 days after IP injection. Despite a low sensitivity, serum α2M >40 mg/L and albumin <32 g/L had a specificity of 100% for peritonitis.

Conclusions

Measurement of α2M and albumin once per month is an additional tool in the diagnosis of silent peritonitis in the chronic peritoneal exposure model in the rat. Levels of α2M >40 mg/L and albumin <32 g/L are strong indicators for peritonitis. However, normal values do not exclude infectious peritonitis.

Systemic and Intraperitoneal Interleukin-6 System during the First Year of Peritoneal Dialysis

Objective

To investigate if intraperitoneal and systemic interleukin-6 (IL-6) and soluble IL-6 receptor (sIL-6R) are related to each other and to peritoneal solute transport rate (PSTR).

Design

Longitudinal study in retrospectively selected patients.

Setting

Peritoneal dialysis (PD) unit of a university-based hospital.

Patients and Methods

31 PD patients on treatment with conventional glucose-based solutions participated in a longitudinal study. IL-6 and sIL-6R were measured in plasma and overnight effluent, both at baseline and after 12 ± 2 months on PD. C-reactive protein (CRP) and serum albumin were used as surrogate markers of inflammation. PSTR of small solutes was evaluated using the dialysate-to-plasma ratio (D/P) of creatinine after a 4-hour dwell; PSTR of large solutes was evaluated using the 24-hour D/P ratio of albumin.

Results

D/P creat increased over time (0.67 ± 0.15 vs 0.80 ± 0.11, p < 0.0001) and correlated to D/P albumin only at the baseline evaluation. Patients with plasma IL-6 ≥median had higher ( p < 0.005) D/P creat at baseline [0.74 (0.62 – 0.87)] compared to patients with IL-6 < median [0.57 (0.47 – 0.66)]. Dialysate IL-6 at baseline was also higher ( p < 0.05) in patients with plasma IL-6 ≥median [24.7 (16.5 – 38.5) pg/mL] compared to patients with IL-6 < median [14.1 (10 – 25.7) pg/mL]. Neither CRP nor albumin changed over time on PD, although they were closely linked to plasma IL-6 levels. A strong positive correlation was found between D/P creat and dialysate IL-6 (rho = 0.77, p < 0.0001) at baseline, but not at 1 year. In contrast, there was a significant correlation between D/P creat and dialysate sIL-6R (rho = 0.39, p < 0.05) at 1 year, but not at baseline. At 1 year, 17 patients with increasing PSTR had higher increases in dialysate IL-6 (28 ± 26 vs –21 ± 78 pg/mL, p < 0.05) and levels of dialysate sIL-6R (693 ± 392 vs 394 ± 274 pg/mL, p = 0.05) compared to patients with stable PSTR ( n = 11). Patients who had peritonitis presented higher baseline serum IL-6 concentration (6.8 ± 1.0 pg/mL) compared with patients without peritonitis (4.0 ± 0.6 pg/mL, p < 0.05). Finally, both at baseline and after 1 year, there were significant correlations between plasma and dialysate IL-6 (rho = 0.46, p < 0.05, and rho = 0.40, p < 0.05) respectively.

Conclusions

These findings indicate that, ( 1 ) intraperitoneal and systemic inflammation increase in PD patients during the first year of therapy; ( 2 ) intraperitoneal and systemic inflammation may be interrelated and the IL-6 system may be the link; ( 3 ) the IL-6 system (both intraperitoneal and systemic) is associated with PSTR, particularly in the early phase of PD treatment, in which small and large solute transport are linked. Signs of a transition between acute and chronic inflammation were observed in the follow-up evaluation. Inflammation may, at least in part, be responsible for the development of a high PSTR, and this could be one reason for the high mortality in patients with high PSTR.

Ex Vivo Analysis of Dialysis Effluent-Derived Mesothelial Cells as an Approach to Unveiling the Mechanism of Peritoneal Membrane Failure

During peritoneal dialysis (PD), the peritoneum is exposed to bioincompatible dialysis fluids, which causes progressive fibrosis and angiogenesis and, ultimately, ultrafiltration failure. In addition, repeated episodes of peritonitis or hemoperitoneum may accelerate all these processes. Fibrosis has been classically considered the main cause of peritoneal membrane functional decline. However, in parallel with fibrosis, the peritoneum also displays increases in capillary number (angiogenesis) and vasculopathy in response to PD. Nowadays, there is emerging evidence pointing to peritoneal microvasculature as the main factor responsible for increased solute transport and ultrafiltration failure. However, the pathophysiologic mechanism(s) involved in starting and maintaining peritoneal fibrosis and angiogenesis remain(s) elusive. Peritoneal stromal fibroblasts have been considered (for many years) the cell type mainly involved in structural and functional alterations of the peritoneum; whereas mesothelial cells have been considered mere victims of peritoneal injury caused by PD. Recently, ex vivo cultures of effluent-derived mesothelial cells, in conjunction with immunohistochemical analysis of peritoneal biopsies from PD patients, have identified mesothelial cells as culprits, at least in part, in peritoneal membrane deterioration. This review discusses recent findings that suggest new peritoneal myofibroblastic cells may arise from local conversion of mesothelial cells by epithelial-to-mesenchymal transition during the repair responses that take place in PD. The transdifferentiated mesothelial cells may retain a permanent mesenchymal state, as long as initiating stimuli persist, and contribute to PD-induced fibrosis and angiogenesis, and hence to membrane failure. Future therapeutic interventions could be designated in order to prevent or reverse epithelial-to-mesenchymal transition of mesothelial cells, or its pernicious effects.

Effects of SMAD7 Overexpression on Peritoneal Inflammation in a Rat Peritoneal Dialysis Model

Objective

Transforming growth factor-beta (TGF-β) has been shown to play a role in peritoneal complications due to long-term peritoneal dialysis (PD). In this study, we examined the effects of the TGF-β signaling pathway on peritoneal inflammation associated with PD in rats by over-expressing Smad7, an inhibitor of TGF-β/Smad signaling.

Methods

Peritoneal inflammation was induced in male Sprague-Dawley rats by intraperitoneal injections of 4.25% glucose dialysate (100 mg/kg body weight) daily for 4 weeks, with the addition of lipopolysaccharides (0.6 mg/kg body weight) on days 8, 10, 12, 22, 24, and 26. Peritoneal Smad7 gene transfer was achieved using an ultrasound microbubble mediated, doxycycline regulated, Smad7-expressing plasmid on day 0 and day 14 after initiation of PD. An empty vector was used as control. All rats were sacrificed after 4 weeks of PD. Peritoneal inflammatory response, including infiltration of total leukocytes (OX-1 positive) and macrophages (ED-1 positive) and expression of interleukin (IL)-1β) and tumor necrosis factor-alpha (TNF-α), was examined by immunofluorescence and RT-PCR.

Results

After PD, peritoneal inflammation developed in control animals, as demonstrated by an increase in the number of OX-1-positive and ED-1-positive cells and upregulation of IL-1β and TNF-α mRNA and protein expression. In contrast, in animals treated with Smad7 gene transfer, IL-1β and TNF-α expression and OX-1-positive and ED-1-positive cell infiltration were significantly inhibited. Furthermore, prevention of peritoneal inflammation by overexpression of Smad7 was associated with inhibition of phosphorylation of Smad2/3, a downstream of the TGF-β signaling pathway, as well as TGF-β1 expression.

Conclusion

Overexpression of Smad7 suppresses peritoneal inflammation induced by high glucose and lipopolysaccharides. The ability of Smad7 gene transfer to inhibit peritoneal inflammation indicates that targeting TGF-β/Smad signaling may represent a new therapeutic strategy for the treatment of peritoneal complications associated with PD.

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.

IL-6 trans-signaling drives a STAT3-dependent pathway that leads to structural alterations of the peritoneal membrane

IL-6 is a vital inflammatory factor in the peritoneal cavity of patients undergoing peritoneal dialysis (PD). The present study examined the effect of IL-6 trans-signaling on structural alterations of the peritoneal membrane. We investigated whether the epithelial-to-mesenchymal transition (EMT) process of human peritoneal mesothelial cells (HPMCs) and the production of proangiogenic factors were controlled by IL-6 trans-signaling. Its role in the peritoneal alterations was detected in a mouse model. The morphology of HPMCs and levels of cytokines in PD effluent were also explored. Stimulation of HPMCs with the IL-6 and soluble IL-6 receptor complex (IL-6/S) promoted the EMT process of HPMCs depending on the STAT3 pathway. In a coculture system of HPMCs and human umbilical vein endothelial cells, IL-6/S mediated the production of VEGF and angiopoietins so as to downregulate the expression of endothelial junction molecules and finally affect vascular permeability. Daily intraperitoneal injection of high glucose-based dialysis fluid induced peritoneal fibrosis, angiogenesis, and macrophage infiltration in a mouse model, accompanied by phosphorylation of STAT3. Blockade of IL-6 trans-signaling prevented these peritoneum alterations. The fibroblast-like appearance of HPMCs ex vivo was upregulated in patients undergoing prevalent PD accompanied by increasing levels of IL-6, VEGF, and angiopoietin-2 in the PD effluent. Taken together, these findings identified a critical link between IL-6 trans-signaling and structural alterations of the peritoneal membrane, and it might be a potential target for the treatment of patients undergoing PD who have developed peritoneal alterations.

Association Between Peritonitis and Low Muscle Mass in Peritoneal Dialysis Patients

OBJECTIVE

Peritoneal dialysis (PD) peritonitis is a common complication in PD patients. The remission of peritonitis is easily achieved, but its presence is associated with local/systemic inflammation in PD patients, which would lead to decreases in muscle mass. Here, we hypothesized that the history of PD peritonitis is associated with low muscle mass (LMM) in PD patients.

METHODS

We identified incident PD patients for whom body composition measurements at baseline and 1 year after PD initiation were available. Finally, we analyzed 230 incident PD patients. The PDP group was defined as patients with a PD peritonitis event during the period and the Non-PDP group was defined as patients without a PD peritonitis event during the period. Body compositions were calculated using bioimpedance and includes regional lean mass (LM), fat mass (FM), and sarcopenia index.

RESULTS

There were no significant intergroup differences in baseline limb LM, total LM, or total FM. Total FM and body mass index at follow-up (FU) increased in both groups compared to that at baseline. There was no significant difference in total LM between baseline and FU in either group. Limb LM at FU increased in only the Non-PDP group compared to that at baseline. Sarcopenia index at FU decreased in only the PDP group compared to that at baseline. The prevalence of LMM at FU was higher in the PDP group than in the Non-PDP group. Among the participants without LMM at baseline, those in the PDP group had a higher prevalence of LMM at FU. Logistic regression showed that the PDP group was associated with a higher odds ratio for LMM at FU in the multivariate analyses.

CONCLUSION

LMM was found to be associated with the presence of PD peritonitis in incident PD patients.

Connective tissue growth factor is correlated with peritoneal lymphangiogenesis

Lymphatic absorption in the peritoneal cavity may contribute to ultrafiltration failure in peritoneal dialysis (PD). Lymphatic vessels develop during PD-related peritoneal fibrosis. Connective tissue growth factor (CTGF, also called CCN2) is an important determinant of fibrotic tissue remodeling, but little is known about its possible involvement in lymphangiogenesis. In this study, we investigated the relationship between CTGF and peritoneal lymphangiogenesis. A positive correlation was observed between vascular endothelial growth factor-C (VEGF-C), a major lymphangiogenic growth factor, and the CTGF concentration in human PD effluents. CTGF expression was positively correlated with expression of lymphatic markers and VEGF-C in human peritoneal biopsies. We found a positive correlation between the increase in CTGF and the increase in VEGF-C in cultured human peritoneal mesothelial cells (HPMCs) treated with transforming growth factor-β1 (TGF-β1). The diaphragm is a central player in peritoneal lymphatic absorption. CTGF expression was also correlated with expression of VEGF-C and lymphatics in a rat diaphragmatic fibrosis model induced by chlorhexidine gluconate (CG). Furthermore, CTGF gene deletion reduced VEGF-C expression and peritoneal lymphangiogenesis in the mouse CG model. Inhibition of CTGF also reduced VEGF-C upregulation in HPMCs treated with TGF-β1. Our results suggest a close relationship between CTGF and PD-associated lymphangiogenesis.

Network-based integrated analysis of omics data reveal novel players of TGF-β1-induced EMT in human peritoneal mesothelial cells

Long-term peritoneal dialysis is associated with progressive fibrosis of the peritoneum. Epithelial-mesenchymal transition (EMT) of mesothelial cells is an important mechanism involved in peritoneal fibrosis, and TGF-β1 is considered central in this process. However, targeting currently known TGF-β1-associated pathways has not proven effective to date. Therefore, there are still gaps in understanding the mechanisms underlying TGF-β1-associated EMT and peritoneal fibrosis. We conducted network-based integrated analysis of transcriptomic and proteomic data to systemically characterize the molecular signature of TGF-β1-stimulated human peritoneal mesothelial cells (HPMCs). To increase the power of the data, multiple expression datasets of TGF-β1-stimulated human cells were employed, and extended based on a human functional gene network. Dense network sub-modules enriched with differentially expressed genes by TGF-β1 stimulation were prioritized and genes of interest were selected for functional analysis in HPMCs. Through integrated analysis, ECM constituents and oxidative stress-related genes were shown to be the top-ranked genes as expected. Among top-ranked sub-modules, TNFAIP6, ZC3H12A, and NNT were validated in HPMCs to be involved in regulation of E-cadherin, ZO-1, fibronectin, and αSMA expression. The present data shows the validity of network-based integrated analysis in discovery of novel players in TGF-β1-induced EMT in peritoneal mesothelial cells, which may serve as new prognostic markers and therapeutic targets for peritoneal dialysis patients.

Roles of the TGF-β⁻VEGF-C Pathway in Fibrosis-Related Lymphangiogenesis

Lymphatic vessels drain excess tissue fluids to maintain the interstitial environment. Lymphatic capillaries develop during the progression of tissue fibrosis in various clinical and pathological situations, such as chronic kidney disease, peritoneal injury during peritoneal dialysis, tissue inflammation, and tumor progression. The role of fibrosis-related lymphangiogenesis appears to vary based on organ specificity and etiology. Signaling via vascular endothelial growth factor (VEGF)-C, VEGF-D, and VEGF receptor (VEGFR)-3 is a central molecular mechanism for lymphangiogenesis. Transforming growth factor-β (TGF-β) is a key player in tissue fibrosis. TGF-β induces peritoneal fibrosis in association with peritoneal dialysis, and also induces peritoneal neoangiogenesis through interaction with VEGF-A. On the other hand, TGF-β has a direct inhibitory effect on lymphatic endothelial cell growth. We proposed a possible mechanism of the TGF-β–VEGF-C pathway in which TGF-β promotes VEGF-C production in tubular epithelial cells, macrophages, and mesothelial cells, leading to lymphangiogenesis in renal and peritoneal fibrosis. Connective tissue growth factor (CTGF) is also involved in fibrosis-associated renal lymphangiogenesis through interaction with VEGF-C, in part by mediating TGF-β signaling. Further clarification of the mechanism might lead to the development of new therapeutic strategies to treat fibrotic diseases.

HDAC1 inhibition by MS-275 in mesothelial cells limits cellular invasion and promotes MMT reversal

Peritoneal fibrosis is a pathological alteration of the peritoneal membrane occurring in a variety of conditions including peritoneal dialysis (PD), post-surgery adhesions and peritoneal metastases. The acquisition of invasive and pro-fibrotic abilities by mesothelial cells (MCs) through induction of MMT, a cell-specific form of EMT, plays a main role in this process. Aim of this study was to evaluate possible effects of histone deacetylase (HDAC) inhibitors, key components of the epigenetic machinery, in counteracting MMT observed in MCs isolated from effluent of PD patients. HDAC inhibitors with different class/isoform selectivity have been used for pharmacological inhibition. While the effect of other inhibitors was limited to a partial E-cadherin re-expression, MS-275, a HDAC1-3 inhibitor, promoted: (i) downregulation of mesenchymal markers (MMP2, Col1A1, PAI-1, TGFβ1, TGFβRI) (ii) upregulation of epithelial markers (E-cadherin, Occludin), (iii) reacquisition of an epithelial-like morphology and (iv) marked reduction of cellular invasiveness. Results were confirmed by HDAC1 genetic silencing. Mechanistically, MS-275 causes: (i) increase of nuclear histone H3 acetylation (ii) rescue of the acetylation profile on E-cadherin promoter, (iii) Snail functional impairment. Overall, our study, pinpointing a role for HDAC1, revealed a new player in the regulation of peritoneal fibrosis, providing the rationale for future therapeutic opportunities.

High Intraperitoneal Interleukin-6 Levels Predict Peritonitis in Peritoneal Dialysis Patients: A Prospective Cohort Study

BACKGROUND

To evaluate the predictive value of dialysate interleukin-6 (IL-6) representing local subclinical intraperitoneal inflammation for the development of peritonitis in continuous ambulatory peritoneal dialysis (CAPD) patients.

METHODS

Stable prevalent CAPD patients were enrolled in this prospective study. IL-6 concentration in the overnight effluent was determined and expressed as the IL-6 appearance rate (IL-6AR). Patients were divided into 2 groups according to the median of IL-6AR and prospectively followed up until the first episode of peritonitis, cessation of PD, or the end of the study (December 30, 2017). The utility of IL-6AR in predicting peritonitis-free survival was analyzed using the Kaplan-Meier and Cox proportional hazards models.

RESULTS

A total of 149 patients were enrolled, including 72 males (48%) with mean age 52.0 ± 13.6 years and median PD duration 26 (5.9-45.5) months. During follow-up, 7,923 patient months were observed and 154 episodes of peritonitis occurred in 82 patients. Previous peritonitis episodes were significantly associated with log dialysate IL-6AR levels (β = 0.187 [0.022-0.299], p = 0.023). Patients in the high IL-6AR group showed a significantly inferior peritonitis-free survival when compared with their counterparts in the low IL-6AR group (48.8 vs. 67.7 months, p = 0.026), as well as higher treatment failure percentage of peritonitis (20.3 vs. 9.3%, p = 0.049). A multivariate Cox regression showed that high dialysate IL-6AR (hazard ratio [HR] 1.247 [1.052-1.478]; p = 0.011) and high serum C-reactive protein (HR 1.072 [1.005-1.144]; p = 0.036) were independent risk factors for inferior peritonitis-free survival.

CONCLUSION

This prospective study suggested that the intraperitoneal inflammation marker, dialysate IL-6 level, might be a potential predictor of peritonitis development in patients undergoing PD.

TGF-β1-VEGF-A pathway induces neoangiogenesis with peritoneal fibrosis in patients undergoing peritoneal dialysis

The characteristic features of chronic peritoneal injury with peritoneal dialysis (PD) are submesothelial fibrosis and neoangiogenesis. Transforming growth factor (TGF)β and vascular endothelial growth factor (VEGF)-A are the main mediators of fibrosis and neoangiogenesis, respectively; however, the effect of the interaction between them on the peritoneum is not well known. In this study, we investigated the relationship between TGF-β1 and VEGF-A in inducing peritoneal fibrosis by use of human tissues and dialysate, cultured cells, and animal models. The VEGF-A concentration correlated with the dialysate-to-plasma ratio of creatinine (D/P Cr) ( P < 0.001) and TGF-β1 ( P < 0.001) in human PD effluent. VEGF-A mRNA levels increased significantly in the peritoneal tissues of human ultrafiltration failure (UFF) patients and correlated with number of vessels ( P < 0.01) and peritoneal thickness ( P < 0.001). TGF-β1 increased VEGF-A production in human mesothelial cell lines and fibroblast cell lines, and TGF-β1-induced VEGF-A was suppressed by TGF-β receptor I (TGFβR-I) inhibitor. Incremental peak values of VEGF-A mRNA stimulated by TGF-β1 in human cultured mesothelial cells derived from PD patients with a range of peritoneal membrane functions correlated with D/P Cr ( P < 0.05). To evaluate the regulatory mechanisms of VEGF-A and neoangiogenesis in vivo, we administered TGFβR-I inhibitor intraperitoneally in a rat chlorhexidine-induced peritoneal injury (CG) model. TGFβR-I inhibitor administration in the CG model decreased peritoneal thickness ( P < 0.001), the number of vessels ( P < 0.001), and VEGF-A levels ( P < 0.05). These results suggest that neoangiogenesis is associated with fibrosis through the TGF-β1-VEGF-A pathway in mesothelial cells and fibroblasts. These findings are important when considering the strategy for management of UFF in PD patients.

Pathogenesis of Peritoneal Sclerosis

Peritoneal sclerosis is an almost invariable consequence of peritoneal dialysis. In most circumstances it is “simple” sclerosis, manifesting clinically with an increasing peritoneal transport rate and loss of ultrafiltration capacity. In contrast, encapsulating peritoneal sclerosis is a life threatening and usually irreversible condition, associated with bowel obstruction, malnutrition and death. It is unknown whether common etiological factors underlie the development of these 2 clinically and pathologically distinct forms of peritoneal sclerosis. The majority of studies to date have investigated factors that contribute to “simple” sclerosis, although it remains possible that similar mechanisms are amplified in patients who develop encapsulated peritoneal sclerosis. The cellular elements that promote peritoneal sclerosis include the mesothelial cells, peritoneal fibroblasts and inflammatory cells. Factors that stimulate these cells to promote peritoneal fibrosis and neoangiogenesis, both inherent in the development of peritoneal sclerosis, include cytokines that are induced by exposure of the peritoneal membrane to high concentrations of glucose, advanced glycation of the peritoneal membrane and oxidative stress. The cumulative exposure to bioincompatible dialysate is likely to have an etiological role as the duration of dialysis correlates with the likelihood of developing peritoneal sclerosis. Indeed peritoneal dialysis using more biocompatible fluids has been shown to reduce the development of peritoneal sclerosis. The individual contribution of the factors implicated in the development of peritoneal sclerosis will only be determined by large scale peritoneal biopsy registries, which will be able to prospectively incorporate clinical and histological data and support clinical decision making.

Inflammation and Peritoneal Dialysis

Inflammation is one of the well-recognized nontraditional risk factors that contributes to the excessive cardiovascular mortality in peritoneal dialysis (PD) patients. Serum C-reactive protein and interleukin-6 levels are common surrogate markers used to measure inflammatory burden and predict adverse clinical outcomes in PD patients. Causes of inflammation are complex and can be categorized into factors related to a decrease in renal function and factors related to dialysis. They interact with each other and finally result in systemic and intraperitoneal inflammation. This review discusses the various causes and clinical implications of inflammation in PD patients. More importantly, potential therapeutic options that target the underlying pathogenic mechanisms are explored.

Nano-sized carriers in gene therapy for peritoneal fibrosis in vivo

Peritoneal fibrosis is a crucial complication in patients receiving peritoneal dialysis. It is a major pathological feature of peritoneal membrane failure, which leads to withdrawal of peritoneal dialysis. No specific therapy has yet been established for the treatment of peritoneal fibrosis. However, gene therapy may be a viable option, and various nano-sized carriers, including viral and non-viral vectors, have been shown to enhance the delivery and efficacy of gene therapy for peritoneal fibrosis in vivo. This review focuses on the use of nano-sized carriers in gene therapy of peritoneal fibrosis in vivo.

The impact of peritoneal dialysis-related peritonitis on mortality in peritoneal dialysis patients

BACKGROUND

Results concerning the association between peritoneal dialysis-related peritonitis and mortality in peritoneal dialysis patients are inconclusive, with one potential reason being that the time-dependent effect of peritonitis has rarely been considered in previous studies. This study aimed to evaluate whether peritonitis has a negative impact on mortality in a large cohort of peritoneal dialysis patients. We also assessed the changing impact of peritonitis on patient mortality with respect to duration of follow-up.

METHODS

This retrospective cohort study included incident patients who started peritoneal dialysis from 1 January 2006 to 31 December 2011. Episodes of peritonitis were recorded at the time of onset, and peritonitis was parameterized as a time-dependent variable for analysis. We used the Cox regression model to assess whether peritonitis has a negative impact on mortality.

RESULTS

A total of 1321 patients were included. The mean age was 48.1 ± 15.3 years, 41.3% were female, and 23.5% with diabetes mellitus. The median (interquartile) follow-up time was 34 (21-48) months. After adjusting for confounders, peritonitis was independently associated with 95% increased risk of all-cause mortality (hazard ratio, 1.95; 95% confidence interval: 1.46-2.60), 90% increased risk of cardiovascular mortality (hazard ratio, 1.90; 95% confidence interval: 1.28-2.81) and near 4-fold increased risk of infection-related mortality (hazard ratio, 4.94; 95% confidence interval: 2.47-9.86). Further analyses showed that peritonitis was not significantly associated with mortality within 2 years of peritoneal dialysis initiation, but strongly influenced mortality in patients dialysed longer than 2 years.

CONCLUSIONS

Peritonitis was independently associated with higher risk of all-cause, cardiovascular and infection-related mortality in peritoneal dialysis patients, and its impact on mortality was more significant in patients with longer peritoneal dialysis duration.

The Role of Tyrosine Kinase Receptors in Peritoneal Fibrosis

Peritoneal dialysis (PD) is a modality for treatment of patients with end-stage renal disease (ESRD) that depends on the structural and functional integrity of the peritoneal membrane. However, long-term PD can lead to morphological and functional changes in the peritoneum; in particular, peritoneal fibrosis has become one of the most common complications that ultimately results in ultrafiltration failure (UFF) and discontinuation of PD. Several factors and mechanisms such as inflammation and overproduction of transforming growth factor-β1 have been implicated in the development of peritoneal fibrosis, but there is no effective therapy to prevent or delay this process. Recent studies have shown that activation of multiple receptor tyrosine kinases (RTKs) is associated with the development and progression of tissue fibrosis in various organs, and there are also reports indicating the involvement of some RTKs in peritoneal fibrosis. This review will describe the role and mechanisms of RTKs in peritoneal fibrosis and discuss the possibility of using them as therapeutic targets for prevention and treatment of this complication.

Toll-Like Receptors 2 and 4 Are Potential Therapeutic Targets in Peritoneal Dialysis-Associated Fibrosis

Peritoneal dialysis (PD) remains limited by dialysis failure due to peritoneal membrane fibrosis driven by inflammation caused by infections or sterile cellular stress. Given the fundamental role of Toll-like receptors (TLRs) and complement in inflammation, we assessed the potential of peritoneal TLR2, TLR4 and C5a receptors, C5aR and C5L2, as therapeutic targets in PD-associated fibrosis. We detected TLR2-, TLR4-, and C5aR-mediated proinflammatory and fibrotic responses to bacteria that were consistent with the expression of these receptors in peritoneal macrophages (TLR2/4, C5aR) and mesothelial cells (TLR2, C5aR). Experiments in knockout mice revealed a major role for TLR2, a lesser role for TLR4, a supplementary role for C5aR, and no apparent activity of C5L2 in infection-induced peritoneal fibrosis. Similarly, antibody blockade of TLR2, TLR4, or C5aR differentially inhibited bacteria-induced profibrotic and inflammatory mediator production by peritoneal leukocytes isolated from the peritoneal dialysis effluent (PDE) of noninfected uremic patients. Additionally, antibodies against TLR2, TLR4, or the coreceptor CD14 reduced the profibrotic responses of uremic leukocytes to endogenous components present in the PDE of noninfected patients. Enhancing TLR2-mediated inflammation increased fibrosis in vivo Furthermore, soluble TLR2 (sTLR2), a negative modulator of TLRs that we detected in PDE, inhibited PDE-induced, TLR2- or TLR4-mediated profibrotic responses. Notably, sTLR2 treatment markedly reduced Gram-positive and -negative bacteria-induced fibrosis in vivo, inhibiting proinflammatory and fibrotic genes without affecting infection clearance. These findings reveal the influence of peritoneal TLR2 and TLR4 on PD-associated fibrosis and describe a therapeutic strategy against fibrosis.

Diverse properties of the mesothelial cells in health and disease

Mesothelial cells (MCs) form the superficial anatomic layer of serosal membranes, including pleura, pericardium, peritoneum, and the tunica of the reproductive organs. MCs produce a protective, non-adhesive barrier against physical and biochemical damages. MCs express a wide range of phenotypic markers, including vimentin and cytokeratins. MCs play key roles in fluid transport and inflammation, as reflected by the modulation of biochemical markers such as transporters, adhesion molecules, cytokines, growth factors, reactive oxygen species and their scavengers. MCs synthesize extracellular matrix related molecules, and the surface of MC microvilli secretes a highly hydrophilic protective barrier, "glycocalyx", consisting mainly of glycosaminoglycans. MCs maintain a balance between procoagulant and fibrinolytic activation by producing a whole range of regulators, can synthetize fibrin and therefore form adhesions. Synthesis and recognition of hyaluronan and sialic acids might be a new insight to explain immunoactive and immunoregulatory properties of MCs. Epithelial to mesenchymal transition of MCs may involve serosal repair and remodeling. MCs might also play a role in the development and remodeling of visceral adipose tissue. Taken together, MCs play important roles in health and disease in serosal cavities of the body. The mesothelium is not just a membrane and should be considered as an organ.

MicroRNA expression profiling in peritoneal fibrosis

Peritoneal fibrosis (PF) is an intractable complication leading to peritoneal membrane failure in peritoneal dialysis (PD). The aim of this study was to identify microRNAs (miRNAs) involved in PF. Peritoneal tissue from a PF rat model was screened for miRNA expression using microarray analysis. The expression levels of differentially expressed miRNAs were evaluated in serum and drained dialysate and associated with peritoneal membrane functions, as measured by the peritoneal equilibrium test in 33 PD patients. Furthermore, an miRNA inhibitor (anti-miRNA-21-5p locked nucleic acid (LNA): anti-miRNA-21-LNA) was intraperitoneally injected to PF model mice to investigate its effects on PF. The initial profiling study of PF rat peritoneal tissue identified 6 miRNAs (miRNA-142-3p, miRNA-21-5p, miRNA-221-3p, miRNA-223-3p, miRNA-34a-5p, and miRNA-327) whose expression was increased more than 2-fold and no miRNAs whose expression was decreased more than half. Among them, serum levels of miRNA-21-5p, miRNA-221-3p, and miRNA-327 and drained dialysate levels of miRNA-221-3p and miRNA-34a-5p were significantly correlated with peritoneal membrane functions in PD patients. Anti-miRNA-21-LNA significantly inhibited miRNA-21-5p expression in the PF mouse peritoneum, inhibited peritoneal fibrous thickening, and maintained peritoneal membrane functions. These results suggest that several miRNAs are involved in PF and that they may be useful as novel diagnostic biomarkers and therapeutic targets for PF.

The effects of Panax notoginseng saponins on the cytokines and peritoneal function in rats with peritoneal fibrosis

BACKGROUND

Due to the long-term and chronic exposure to the peritoneal dialysis fluid, patients could develop peritoneal fibrosis and ultrafiltration failure which compromises treatment efficacy and outcome, and fibrosis is the major cause of peritoneal dialysis (PD) withdraw among patients.

METHODS

Twenty-one male WISTAR rats were randomly assigned to three groups, namely saline group, standard peritoneal dialysis fluid (PDF) group, and panax notoginseng saponins (PNS) group. Peritoneal fibrosis was induced by daily injection of PDF for 4 weeks. After execution, multiple histological techniques including HE and Masson's trichrome staining and transmission electron microscopy (TEM) were applied to observe the pathological changes and concentrations of multiple cytokines may involve in the process of fibrosis were determined by enzyme-linked immune sorbent assay (ELISA). Biochemistry parameters were determined by automated chemistry analyzer.

RESULTS

PNS can significantly inhibit the expression of transforming growth factor beta (TGF-β1), connective tissue growth factor (CTGF), and monocyte chemoattractant protein (MCP-1) in the peritoneum of rats. Furthermore, pathological damages, including extracellular matrix deposition, vascularization, and fibroblast, were ameliorated in PNS group when being compared with standard PDF group. Peritoneal functions were improved by regular PNS treatment with significantly elevated ultrafiltration.

CONCLUSION

PNS is capable of improving peritoneal function in subjects with PDF exposure and can possibly applied in patients with PD after further verification.

Caveolin-1 deficiency induces a MEK-ERK1/2-Snail-1-dependent epithelial-mesenchymal transition and fibrosis during peritoneal dialysis

Peritoneal dialysis (PD) is a form of renal replacement therapy whose repeated use can alter dialytic function through induction of epithelial–mesenchymal transition (EMT) and fibrosis, eventually leading to PD discontinuation. The peritoneum from Cav1^−/− mice showed increased EMT, thickness, and fibrosis. Exposure of Cav1^−/− mice to PD fluids further increased peritoneal membrane thickness, altered permeability, and increased the number of FSP-1/cytokeratin-positive cells invading the sub-mesothelial stroma. High-throughput quantitative proteomics revealed increased abundance of collagens, FN, and laminin, as well as proteins related to TGF-β activity in matrices derived from Cav1^−/− cells. Lack of Cav1 was associated with hyperactivation of a MEK-ERK1/2-Snail-1 pathway that regulated the Smad2-3/Smad1-5-8 balance. Pharmacological blockade of MEK rescued E-cadherin and ZO-1 inter-cellular junction localization, reduced fibrosis, and restored peritoneal function in Cav1^−/− mice. Moreover, treatment of human PD-patient-derived MCs with drugs increasing Cav1 levels, as well as ectopic Cav1 expression, induced re-acquisition of epithelial features. This study demonstrates a pivotal role of Cav1 in the balance of epithelial versus mesenchymal state and suggests targets for the prevention of fibrosis during PD.

The aldosterone receptor antagonist spironolactone prevents peritoneal inflammation and fibrosis

Peritoneal fibrosis is a complication of patients with long-term continuous ambulatory peritoneal dialysis (CAPD). Reports have indicated that angiotensin (Ang) II may correlate with the development of peritoneal fibrosis. However, it is unknown whether aldosterone also has a role in the development of peritoneal inflammation and fibrosis. The aim of the present study was to clarify the role of aldosterone in peritoneal inflammation and fibrosis. A rat model of peritoneal inflammation and fibrosis was established by daily intraperitoneal injection of dialysates and lipopolysaccharide in a 4-day interval over a period of 7 days. The animals were randomly assigned to five groups as follows: control (C); peritoneal dialysis (PD); peritoneal dialysis-spironolactone (PD-S); peritoneal dialysis-cilazapril (PD-C); and peritoneal dialysis-spironolactone-cilazapril (PD-SC). After 30 days, the TGF-β1 concentration in dialysates from all treatment groups was determined by ELISA. The histopathology of the parietal peritoneum was examined, and the expression of MCP-1, c-Jun, fibronectin (FN) and TGF-β1 in the abdominal membrane was determined by immunohistochemistry. Mineralocorticoid receptor (MR), 11β-hydroxysteroid dehydrogenase type 2 (11β-HSD2) and CYP11B2 (aldosterone synthase) were analyzed by real time-PCR. Collagen deposition was significantly higher in PD compared with the other groups. The expression of MR, 11β-HSD2 and CYP11B2 was significantly higher in PD compared with the other groups. Spironolactone and/or cilazapril treatment partially ablated the increase in monocyte chemoattractant protein (MCP)-1, p-c-Jun, transforming growth factor (TGF)-β1, FN, MR, 11β-HSD2 and CYP11B2. Furthermore, treatment with spironolactone and/or cilazapril also reduced the infiltration of CD-4- and ED-1-positive cells in rat peritoneal tissues after peritoneal fibrosis. Exogenous aldosterone may have a key role in the development of peritoneal inflammation and fibrosis. Spironolactone decreased peritoneal inflammation and fibrosis, which was associated with reduced secretion from peritoneal macrophages, inactivation of the c-Jun N-terminal kinase (JNK) pathway and subsequent downregulation of the expression of TGF-β1.

Fos-icking for control of angiogenesis: increasing the longevity of peritoneal dialysis

Recurring peritonitis reduces the effectiveness of peritoneal dialysis by increasing fibrosis and angiogenesis, ultimately causing ultrafiltration failure (UFF). Identifying the processes underlying UFF will provide new hope for patients with chronic kidney disease. Catar and colleagues demonstrate that transforming growth factor-β, tumor necrosis factor-α, and interleukin-1 synergize to significantly increase the production and release of vascular endothelial growth factor by mesothelial cells, which, if untreated, will promote peritoneal angiogenesis, leading to UFF.

Opposing roles for Smad2 and Smad3 in peritoneal fibrosis in vivo and in vitro

Peritoneal fibrosis is a major cause of ultrafiltration failure in patients receiving continuous ambulatory peritoneal dialysis. Transforming growth factor (TGF)-β1 is an important mediator in this process; however, its signaling mechanisms had not been explored. Thus, we examined TGF-β1/Smad signaling in human peritoneal biopsy specimens associated with continuous ambulatory peritoneal dialysis. We found that TGF-β/Smad2/3 signaling was highly activated in patients with increased collagen deposition and thickening of the peritoneal membrane who were receiving continuous ambulatory peritoneal dialysis. Long-term exposure of wild-type mice to 4.25% peritoneal dialysis solution for 30 days induced significant peritoneal fibrosis with impaired peritoneal equilibrium, which was prevented in Smad3 knockout mice. In contrast, conditional Smad2 gene deletion in the peritoneum exacerbated peritoneal fibrosis and dysfunction. The contrasting roles of Smad2 and Smad3 in peritoneal fibrosis were also examined in vitro. Cultured mesothelial cells from Smad3 knockout mice were resistant to TGF-β1-induced collagen I production and the transition toward a myofibroblast phenotype as seen in wild-type cells, whereas Smad2 deficiency in mesothelial cells failed to modulate the profibrotic response to TGF-β1. In conclusion, this study found activation of TGF-β/Smad signaling in peritoneal fibrosis in patients receiving continuous ambulatory peritoneal dialysis and identifies opposing roles for Smad2 and Smad3 in peritoneal dialysis-associated peritoneal fibrosis. These findings provide a mechanistic basis for future therapies targeting TGF-β/Smad signaling in peritoneal fibrosis.