BRG1 accelerates mesothelial cell senescence and peritoneal fibrosis by inhibiting mitophagy through repression of OXR1

Peritoneal mesothelial cell senescence promotes the development of peritoneal dialysis (PD)-related peritoneal fibrosis. We previously revealed that Brahma-related gene 1 (BRG1) is increased in peritoneal fibrosis yet its role in modulating peritoneal mesothelial cell senescence is still unknown. This study evaluated the mechanism of BRG1 in peritoneal mesothelial cell senescence and peritoneal fibrosis using BRG1 knockdown mice, primary peritoneal mesothelial cells and human peritoneal samples from PD patients. The augmentation of BRG1 expression accelerated peritoneal mesothelial cell senescence, which attributed to mitochondrial dysfunction and mitophagy inhibition. Mitophagy activator salidroside rescued fibrotic responses and cellular senescence induced by BRG1. Mechanistically, BRG1 was recruited to oxidation resistance 1 (OXR1) promoter, where it suppressed transcription of OXR1 through interacting with forkhead box protein p2. Inhibition of OXR1 abrogated the improvement of BRG1 deficiency in mitophagy, fibrotic responses and cellular senescence. In a mouse PD model, BRG1 knockdown restored mitophagy, alleviated senescence and ameliorated peritoneal fibrosis. More importantly, the elevation level of BRG1 in human PD was associated with PD duration and D/P creatinine values. In conclusion, BRG1 accelerates mesothelial cell senescence and peritoneal fibrosis by inhibiting mitophagy through repression of OXR1. This indicates that modulating BRG1-OXR1-mitophagy signaling may represent an effective treatment for PD-related peritoneal fibrosis.

BET Protein Inhibitor JQ1 Ameliorates Experimental Peritoneal Damage by Inhibition of Inflammation and Oxidative Stress

Peritoneal dialysis (PD) is a current replacement therapy for end-stage kidney diseases (ESKDs). However, long-term exposure to PD fluids may lead to damage of the peritoneal membrane (PM) through mechanisms involving the activation of the inflammatory response and mesothelial-to-mesenchymal transition (MMT), leading to filtration failure. Peritoneal damage depends on a complex interaction among external stimuli, intrinsic properties of the PM, and subsequent activities of the local innate-adaptive immune system. Epigenetic drugs targeting bromodomain and extra-terminal domain (BET) proteins have shown beneficial effects on different experimental preclinical diseases, mainly by inhibiting proliferative and inflammatory responses. However the effect of BET inhibition on peritoneal damage has not been studied. To this aim, we have evaluated the effects of treatment with the BET inhibitor JQ1 in a mouse model of peritoneal damage induced by chlorhexidine gluconate (CHX). We found that JQ1 ameliorated the CHX-induced PM thickness and inflammatory cell infiltration. Moreover, JQ1 decreased gene overexpression of proinflammatory and profibrotic markers, together with an inhibition of the nuclear factor-κB (NF-κB) pathway. Additionally, JQ1 blocked the activation of nuclear factor erythroid 2-related factor 2 (NRF2) and restored changes in the mRNA expression levels of NADPH oxidases (NOX1 and NOX4) and NRF2/target antioxidant response genes. To corroborate the in vivo findings, we evaluated the effects of the BET inhibitor JQ1 on PD patients' effluent-derived primary mesothelial cells and on the MeT-5A cell line. JQ1 inhibited tumor necrosis factor-α (TNF-α)-induced proinflammatory gene upregulation and restored MMT phenotype changes, together with the downmodulation of oxidative stress. Taken together, these results suggest that BET inhibitors may be a potential therapeutic option to ameliorate peritoneal damage.

A review of research progress on mechanisms of peritoneal fibrosis related to peritoneal dialysis

Peritoneal dialysis (PD) is an effective alternative treatment for patients with end-stage renal disease (ESRD) and is increasingly being adopted and promoted worldwide. However, as the duration of peritoneal dialysis extends, it can expose problems with dialysis inadequacy and ultrafiltration failure. The exact mechanism and aetiology of ultrafiltration failure have been of great concern, with triggers such as biological incompatibility of peritoneal dialysis solutions, uraemia toxins, and recurrent intraperitoneal inflammation initiating multiple pathways that regulate the release of various cytokines, promote the transcription of fibrosis-related genes, and deposit extracellular matrix. As a result, peritoneal fibrosis occurs. Exploring the pathogenic factors and molecular mechanisms can help us prevent peritoneal fibrosis and prolong the duration of Peritoneal dialysis.

Inflammatory chemokine (C-C motif) ligand 8 inhibition ameliorates peritoneal fibrosis

Peritoneal fibrosis (PF) is an irreversible complication of peritoneal dialysis (PD) that leads to loss of peritoneal membrane function. We investigated PD effluent and serum levels and the tissue expression of chemokine (C-C motif) ligand 8 (CCL8) in patients with PD. Additionally, we investigated their association with PF in a mouse model. Eighty-two end-stage renal disease (ESRD) patients with PD were examined. CCL8 levels were measured via enzyme-linked immunosorbent assays in PD effluents and serum and analyzed with peritoneal transport parameters. Human peritoneal mesothelial cells (hPMCs) were obtained from the PD effluents of 20 patients. Primary cultured hPMCs were treated with recombinant (r) transforming growth factor (TGF)-β, and CCL8 expression was assessed via western blotting. As the duration of PD increased, the concentration of CCL8 in PD effluents significantly increased. Correlations between peritoneal transport parameters and dialysate CCL8 levels were observed. Western blotting analysis showed that CCL8 was upregulated via rTGF-β treatment, accompanied by increases in markers of inflammation, fibrosis, senescence, and apoptosis in hPMCs after induction of fibrosis with rTGF-β. Anti-CCL8 monoclonal antibody (mAb) treatment suppressed the rTGF-β-induced increase in all analyzed markers. Immunohistochemical analysis revealed that CCL8 along with fibrosis- and inflammation-related markers were significantly increased in the PF mouse model. Functional blockade of CCL8 using a CCR8 inhibitor (R243) abrogated peritoneal inflammation and fibrosis in vivo. In conclusion, high CCL8 levels in PD effluents may be associated with an increased risk of PD failure, and the CCL8 pathway is associated with PF. CCL8 blockade can ameliorate peritoneal inflammation and fibrosis.

Fibrosis of Peritoneal Membrane as Target of New Therapies in Peritoneal Dialysis

Peritoneal dialysis (PD) is an efficient renal replacement therapy for patients with end-stage renal disease. Even if it ensures an outcome equivalent to hemodialysis and a better quality of life, in the long-term, PD is associated with the development of peritoneal fibrosis and the consequents patient morbidity and PD technique failure. This unfavorable effect is mostly due to the bio-incompatibility of PD solution (mainly based on high glucose concentration). In the present review, we described the mechanisms and the signaling pathway that governs peritoneal fibrosis, epithelial to mesenchymal transition of mesothelial cells, and angiogenesis. Lastly, we summarize the present and future strategies for developing more biocompatible PD solutions.

How to Improve the Biocompatibility of Peritoneal Dialysis Solutions (without Jeopardizing the Patient's Health)

Peritoneal dialysis (PD) is an important, if underprescribed, modality for the treatment of patients with end-stage kidney disease. Among the barriers to its wider use are the deleterious effects of currently commercially available glucose-based PD solutions on the morphological integrity and function of the peritoneal membrane due to fibrosis. This is primarily driven by hyperglycaemia due to its effects, through multiple cytokine and transcription factor signalling-and their metabolic sequelae-on the synthesis of collagen and other extracellular membrane components. In this review, we outline these interactions and explore how novel PD solution formulations are aimed at utilizing this knowledge to minimise the complications associated with fibrosis, while maintaining adequate rates of ultrafiltration across the peritoneal membrane and preservation of patient urinary volumes. We discuss the development of a new generation of reduced-glucose PD solutions that employ a variety of osmotically active constituents and highlight the biochemical rationale underlying optimization of oxidative metabolism within the peritoneal membrane. They are aimed at achieving optimal clinical outcomes and improving the whole-body metabolic profile of patients, particularly those who are glucose-intolerant, insulin-resistant, or diabetic, and for whom daily exposure to high doses of glucose is contraindicated.

Biological Effects of XyloCore, a Glucose Sparing PD Solution, on Mesothelial Cells: Focus on Mesothelial-Mesenchymal Transition, Inflammation and Angiogenesis

Glucose-based solutions remain the most used osmotic agents in peritoneal dialysis (PD), but unavoidably they contribute to the loss of peritoneal filtration capacity. Here, we evaluated at a molecular level the effects of XyloCore, a new PD solution with a low glucose content, in mesothelial and endothelial cells. Cell viability, integrity of mesothelial and endothelial cell membrane, activation of mesothelial and endothelial to mesenchymal transition programs, inflammation, and angiogenesis were evaluated by several techniques. Results showed that XyloCore preserves mesothelial and endothelial cell viability and membrane integrity. Moreover XyloCore, unlike glucose-based solutions, does not exert pro-fibrotic, -inflammatory, and -angiogenic effects. Overall, the in vitro evidence suggests that XyloCore could represent a potential biocompatible solution promising better outcomes in clinical practice.

In Vitro Study of Peritoneal Fibrosis

Peritoneal fibrosis (PF) is an important issue in peritoneal dialysis (PD) because it remains one of the leading causes of patient drop-out from PD. In this review, we focus on in vitro approaches to the pathogenesis and therapeutic potential of PF and on associated clinical implications. Representative Asian studies, initiated since mid-1990s, that have investigated matrix accumulation in peritoneal tissue possibly leading to PF in the PD population will be highlighted as examples to learn how to apply this research tool. As compared with data from well-designed clinical trials, observations from in vitro models may be far from becoming solid evidence; however, they do cast new light on options for investigations into therapeutic pharmaceuticals.

Peritoneal Fibrosis Intervention

Peritoneal fibrosis (PF) is invariably observed in patients undergoing long-term peritoneal dialysis (PD). The condition is thought to occur in response to a variety of insults, including bioincompatible dialysates (acidic solution, high glucose, glucose degradation products, or a combination), peritonitis, uremia, and chronic inflammation. Recently, the pathophysiologic mechanisms that contribute to the fibrosing process have been intensively studied. Transforming growth factor-β has been shown to be a key mediator of PF. Loss of the mesothelial cell layer has been identified in several studies and shown to correlate with submesothelial thickening and vasculopathy. An association has also been identified between increased submesothelial thickness in the peritoneal membrane and increased solute transport, suggesting a relationship between PF and loss of ultrafiltration capacity. Thus, to maintain long-term PD and improve quality of life for patients, it is important to develop interventions for prevention and treatment of PF.

Several strategies for peritoneal fibrosis intervention have been reported, including developing biocompatible dialysate, targeting mediators responsible for inflammation and fibrosis, and reconstituting the peritoneum using mesothelial or bone marrow–derived cells. Recent experimental trials in animal models and clinical studies are presented in this review.

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.

Unfavorable Effects of Peritoneal Dialysis Solutions on the Peritoneal Membrane: The Role of Oxidative Stress

One of the main limitations to successful long-term use of peritoneal dialysis (PD) as a renal replacement therapy is the harmful effects of PD solutions to the structure and function of the peritoneal membrane (PM). In PD, the PM serves as a semipermeable membrane that, due to exposure to PD solutions, undergoes structural alterations, including peritoneal fibrosis, vasculopathy, and neoangiogenesis. In recent decades, oxidative stress (OS) has emerged as a novel risk factor for mortality and cardiovascular disease in PD patients. Moreover, it has become evident that OS plays a pivotal role in the pathogenesis and development of the chronic, progressive injury of the PM. In this review, we aimed to present several aspects of OS in PD patients, including the pathophysiologic effects on the PM, clinical implications, and possible therapeutic antioxidant strategies that might protect the integrity of PM during PD therapy.

Does Enalapril Prevent Peritoneal Fibrosis Induced by Hypertonic (3.86%) Peritoneal Dialysis Solution?

Objective

Peritoneal fibrosis (PF) is one of the most serious causes of failure in continuous ambulatory peritoneal dialysis (PD). Although the underlying mechanism responsible for the genesis of PF is still unknown, transforming growth factor p (TGFβ1) has been shown to be associated with PF. Angiotensin converting enzyme inhibitors have been shown to prevent the stimulating effect of growth factors. The aim of the present study was to investigate the effect of enalapril on peritoneal function and morphology in a rat model of experimental PF.

Methods

Twenty-one albino Wistar rats were divided into three groups: ( 1 ) the control group (C) received 10 mL isotonic saline intraperitoneally (IP), ( 2 ) the dextrose (Dx) group 10 mL 3.86% dextrose PD solution IP, and ( 3 ) the enalapril-treated group (ENA) 10 cc 3.86% dextrose PD solution IP plus 100 mg/L enalapril in drinking water. After 4 weeks, a 1-hour peritoneal equilibration test was performed with 20 mL 2.27% dextrose PD solution. Dialysate-to-plasma urea ratio (D/P urea), glucose reabsorption (D1/D0 glucose), ultrafiltration (UF) volume, and levels of dialysate protein, TGFβ1, and cancer antigen 125 (CA125) were determined. The parietal peritoneum was evaluated histologically by light microscopy.

Results

Administration of enalapril resulted in preserved UF (-0.2 ± 0.7 mL vs 1.7 ± 0.3 mL, p < 0.05), protein loss (2.3 ± 0.5 g/L vs 1.6 ± 0.2 g/L, p > 0.05), and peritoneal thickness (77 ± 7 μ vs 38 ± 5 μ, p < 0.001). D/P urea increased significantly in the Dx group ( p < 0.05). Both higher levels of TGFβ1 (undetectable vs 298 ± 43 pg/mL, p < 0.001) and lower levels of CA125 in dialysate effluent (0.94 ± 0.5 U/L vs 0.11 ± 0.1 U/L, p > 0.05) were determined in the Dx group.

Conclusion

These findings show that peritoneal morphology and function tests were dramatically deranged in the Dx group. The same properties were partially preserved in the ENA group. The production of TGFβ1 was significantly reduced but peritoneal thickness was not completely inhibited. In conclusion, by inhibiting the production of TGFβ1, enalapril can preserve peritoneal histology, peritoneal function, and remodeling of mesothelial cells.

Influence of Neutral-Ph Dialysis Solutions on the Peritoneal Membrane: A Long-Term Investigation in Rats

♦ Objective

Glucose degradation products (GDPs) and low pH are potential causes of bioincompatibility of peritoneal dialysis fluids (PDFs). The aim of the present study was to compare the effect of 6 weeks’ exposure of the peritoneum in rats to two different PDFs: a standard PDF with a low pH and high level of GDPs (CAPD 3: Fresenius Medical Care, Bad Homburg, Germany), and a modified PDF with a low level of GDPs and a physiologic pH (CAPD 3 Balance: Fresenius Medical Care).

♦ Methods

After catheter implantation, rats were exposed twice daily for 6 weeks to CAPD 3 fluid or to CAPD 3 Balance. At the beginning and at the end of the study, a 4-hour dwell was performed in every rat to evaluate intraperitoneal inflammation and its effect on total collagen synthesis in the in vitro cultured rat mesothelial cells ( ex vivo study). Additionally, after 6 weeks’ exposure, the peritoneal cavity was opened, and macroscopic changes were evaluated according to a semiquantitative scale. Peritoneal samples were also taken for morphology study.

♦ Results

In rats treated with CAPD 3 fluid, intraperitoneal inflammation was comparable at the beginning and at the end of the experiment. In animals exposed to CAPD 3 Balance, the intensity of the intraperitoneal inflammation decreased during the study (cell count, p = 0.0781; neutrophil:macrophage ratio, p < 0.01; nitrite concentration, p < 0.05; hyaluronan level, p < 0.05). The capacity of effluent dialysate from CAPD 3 rats to activate collagen synthesis in in vitro–cultured mesothelial cells was the same at the beginning and at the end of the study. In the CAPD 3 Balance group, this capacity was statistically significantly lower at the end of the study than at the beginning ( p < 0.05). The mean thickness of the visceral peritoneum was comparable in both groups of animals, but, macroscopically, more severe fibrosis was found in the peritoneum of rats exposed to CAPD 3 as compared with animals treated with CAPD 3 Balance ( p < 0.05).

♦ Conclusion

We showed that, in the rat model of peritoneal dialysis, chronic exposure of the peritoneum to PDFs with low GDPs and a physiologic pH diminished the intraperitoneal inflammatory reaction induced by dialysis, and reduced peritoneal fibrosis.

Effect of Glucose Degradation Products on the Peritoneal Membrane in a Chronic Inflammatory Infusion Model of Peritoneal Dialysis in the Rat

Background

Long-term use of the peritoneal membrane as a dialyzing membrane is hampered by its eventual deterioration. One of the contributing factors is glucose degradation products (GDPs) in the dialysis solution. In this study, we evaluated the effect of a low GDP solution on peritoneal permeability, the structural stability of the peritoneal membrane, and vascular endothelial growth factor (VEGF) production in a chronic inflammatory infusion model of peritoneal dialysis (PD) in the rat.

Methods

Male Sprague–Dawley rats were divided into 3 groups: a conventional solution group (group C, n = 12), a test solution group (group T, n = 12), and a normal control group (group NC, n = 8). Group T rats were infused with low GDP solution (2.3% glucose solution with two compartments), and group C rats with conventional dialysis solution (2.3% glucose solution), adjusted to pH 7.0 before each exchange. Animals were infused through a permanent catheter with 25 mL of dialysis solution. In both groups, peritoneal inflammation was induced by infusing dialysis solution supplemented with lipopolysaccharide on days 8, 9, and 10 after starting dialysate infusion. Peritoneal membrane function was assessed before and 6 weeks after initiating dialysis using the 1-hour peritoneal equilibration test (PET) employing 4.25% glucose solution. Both VEGF and transforming growth factor β1 (TGFβ1) in the dialysate effluent were measured by ELISA. The number of vessels in the omentum was counted after staining with anti-von Willebrand factor, and the thickness of submesothelial matrix of the trichrome-stained parietal peritoneum was measured. Peritoneal tissue was analyzed for VEGF protein using immunohistochemistry.

Results

At the end of 6 weeks, the rate of glucose transport (D/D0, where D is glucose concentration in the dialysate and D0 is glucose concentration in the dialysis solution before it is infused into the peritoneal cavity) was higher in group T ( p < 0.05) than in group C. Dialysate-to-plasma ratio (D/P) of protein was lower in group T ( p < 0.05) than in group C; D/Purea, D/Psodium, and drain volumes did not differ significantly between groups C and T. Dialysate VEGF and TGFβ levels were lower in group T ( p < 0.05) than in group C. Immunohistochemical studies also revealed less VEGF in the peritoneal membranes of group T. There were significantly more peritoneal blood vessels in group C ( p < 0.05) than in group T, but the thickness of submesothelial matrix of the parietal peritoneum was not different between the two groups. The VEGF levels in the dialysate effluent correlated positively with the number of blood vessels per field ( r = 0.622, p < 0.005).

Conclusion

Using a chronic inflammatory infusion model of PD in the rat, we show that dialysis with GDP-containing PD fluid is associated with increased VEGF production and peritoneal vascularization. Use of low GDP solutions may therefore be beneficial in maintaining the function and structure of the peritoneal membrane during long-term PD.

Selected Growth Factors in Peritoneal Dialysis: Their Relationship to Markers of Inflammation, Dialysis Adequacy, Residual Renal Function, and Peritoneal Membrane Transport

Objectives

Markers of chronic inflammation, acute-phase reactants, and growth factors may be concomitantly involved in a number of pathologic processes in the general population and uremic patients. In addition, growth factors may influence peritoneal membrane transport characteristics. However, the association between plasma growth factors, markers of chronic inflammation, and peritoneal membrane transport remains largely unknown. The aim of this study was to evaluate the relationship between plasma levels of selected growth factors [basic fibroblast growth factor (bFGF), transforming growth factor β1 (TGFβ1), vascular endothelial growth factor (VEGF)] and markers of chronic inflammation [interleukin (IL)-6, C-reactive protein (CRP), and fibrinogen] in continuous ambulatory peritoneal dialysis (CAPD) patients. The potential link between the above substances and dialysis adequacy was also explored.

Design

Single-center, cross-sectional study.

Setting

Peritoneal Dialysis Unit, Medical Faculty, Jagiellonian University Hospital, Kraków, Poland.

Patients

32 stable end-stage renal disease patients (13 M, 19 F; mean age 53.6 ± 13.7 years) on CAPD for a median period of 19.5 months. Patients free from signs and symptoms of any inflammatory disease (including peritonitis) for at least 3 months were included into the study. All patients underwent measurements of dialysis dose [Kt/V, weekly creatinine clearance (wCCr)] and peritoneal solute transport using a standard peritoneal equilibration test (PET).

Methods

TGFβ1, bFGF, VEGF, and IL-6 were measured with ELISA, CRP was assayed with immunonephelometry, and fibrinogen with Multifibren U reagent (Dade Behring Marburg GmbH, Marburg, Germany). Nephron 97 for Windows software was used to assess dialysis adequacy.

Results

Significant positive correlations between plasma bFGF and IL-6, as well as fibrinogen concentrations ( R = 0.36, p < 0.05 and R = 0.39, p < 0.05, respectively), were found. VEGF correlated significantly with IL-6 and CRP ( R = 0.65, p < 0.0001 and R = 0.51, p < 0.005, respectively). An association between VEGF and bFGF was also found ( R = 0.59, p < 0.0005). Serum level of TGFβ1 revealed no relationship with any marker of acute-phase activation, remaining growth factors, or dialysis adequacy. Positive correlation between TGFβ1 concentration and dialysate-to-plasma ratio for creatinine in PET ( R = 0.35, p < 0.05) was found. In addition, patients with lower solute transport (low/low-average transporters) had lower serum levels of both bFGF and TGFβ1 compared to patients with higher solute transport. Patients with total wCCr > 60 L/week/m2 were characterized by lower levels of bFGF and IL-6. Serum level of IL-6 and plasma levels of bFGF and VEGF were significantly lower among subjects with residual renal function (RRF) > 2.0 mL/minute.

Conclusions

Our results indicate that systemic inflammation in peritoneal dialysis patients is associated with increased plasma VEGF and bFGF but not TGFβ1. The negative correlation with RRF suggests that either the renal clearance of these cytokines and growth factors may contribute to their elimination, or cytokines and growth factors have a negative impact on RRF. We also suggest an association between serum levels of growth factors tested and peritoneal membrane function.

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

Objective

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

Methods

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

Results

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

Conclusion

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

Biocompatibility of New Peritoneal Dialysis Solutions: What Can We Hope to Achieve?

Despite the bioincompatibility of the “old”, standard, high glucose, lactate-buffered peritoneal dialysis (PD) solutions, PD is itself a highly successful dialysis modality with patient survival equivalent to that of hemodialysis (HD) during the initial 3 – 5 years of dialysis therapy. Nevertheless, PD technique survival is often limited by infectious complications and alterations in the structure and function of the peritoneal membrane. These local changes also have a negative impact on patient survival owing to systemic effects such as those often seen in patients with high peritoneal transport rate and loss of ultrafiltration (UF) capacity.

Patient mortality remains unacceptably high in both HD and PD patients, with most premature deaths being associated with signs of malnutrition, inflammation, and atherosclerotic cardiovascular disease (MIA syndrome). These systemic signs are likely to be influenced by PD solutions both directly and indirectly (via changes in the peritoneal membrane). New, biocompatible PD solutions may have favorable local effects (viability and function of the peritoneal membrane) and systemic effects (for example, on MIA syndrome). Amino acid–based solution [Nutrineal (N): Baxter Healthcare Corporation, Deerfield, IL, U.S.A.] may improve nutritional status as well as peritoneal membrane viability. Bicarbonate/lactate–buffered solution [Physioneal (P): Baxter Healthcare Corporation] may ameliorate local and systemic effects of low pH, high lactate, and high glucose degradation products. Icodextrin-based solution [Extraneal (E): Baxter Healthcare SA, Castlebar, Ireland] may improve hypertension and cardiovascular problems associated with fluid overload and may extend time on therapy in patients with loss of UF capacity.

The positive effects of each of these new, biocompatible solutions have been demonstrated in several studies. It is likely that the combined use of N, P, and E solutions will produce favorable synergies in regard to both local effects (peritoneal viability) and systemic effects (less malnutrition, inflammation, and fluid overload). Solution combination is an exciting area for clinical study in the coming years. Furthermore, dialysis fluid additives such as hyaluronan, which protects and improves the function of the peritoneal membrane, may further improve PD solutions. The new, biocompatible PD solutions represent an entirely new era in the evolution of the PD therapy; they are likely to have markedly positive effects on both PD technique and PD patient survival in coming years.

Effects of Peritoneal Dialysis Solutions on the Secretion of Growth Factors and Extracellular Matrix Proteins by Human Peritoneal Mesothelial Cells

♦ Objective

To compare the effects of different peritoneal dialysis solutions (PDS) on secretion of vascular endothelial growth factor (VEGF), transforming growth factor-β1 (TGFβ1), procollagen I C-terminal peptide (PICP), procollagen III N-terminal peptide (PIIINP), and fibronectin by cultured human peritoneal mesothelial cells (HPMC).

♦ Design

Using M199 culture medium as control, commercial PDS containing 1.5% or 4.25% glucose and 40 mmol/L lactate [Dianeal 1.5 (D 1.5) and Dianeal 4.25 (D 4.25), respectively; Baxter Healthcare, Deerfield, Illinois, USA]; PDS containing 1.5% or 4.25% glucose with 25 mmol/L bicarbonate and 15 mmol/L lactate [Physioneal 1.5 (P 1.5) and Physioneal 4.25 (P 4.25), respectively; Baxter]; and PDS containing 7.5% icodextrin [Extraneal (E); Baxter] were tested. Growth-arrested and synchronized HPMC were continuously stimulated for 48 hours by test PDS diluted twofold with M199, TGFβ1 1 ng/mL, or different concentrations of icodextrin. VEGF, TGFβ1, and fibronectin secreted into the media were analyzed by ELISA, and PICP and PIIINP by radioimmunoassay.

♦ Results

Dianeal 1.5, D 4.25, and P 4.25, but not P 1.5 and E, significantly increased VEGF secretion compared with control M199. D 4.25- and P 4.25-induced VEGF secretion was significantly higher than induction by D 1.5 and P 1.5, respectively, suggesting that high glucose may be involved in the induction of VEGF. Physioneal 1.5- and P 4.25-induced VEGF secretion was significantly lower than induction by D 1.5 and D 4.25, respectively, suggesting a role for glucose degradation products (GDP) in VEGF production. TGFβ1 secretion was significantly increased by D 4.25 and E. Icodextrin increased TGFβ1 secretion in a dose-dependent manner. All PDS tested significantly increased secretion of PIIINP compared with control. D 1.5- and D 4.25-induced PIIINP secretion was significantly higher than P 1.5, P 4.25, and E. Physioneal 4.25-induced PIIINP secretion was significantly higher than P 1.5, again implicating high glucose and GDP in PIIINP secretion by HPMC. There was no significant increase in PICP or fibronectin secretion using any of the PDS tested. Addition of TGFβ1 1 ng/mL into M199 control significantly increased VEGF, PICP, PIIINP, and fibronectin secretion by HPMC.

♦ Conclusions

The present study provides direct evidence that HPMC can secrete VEGF, TGFβ1, and PIIINP in response to PDS, and that HPMC may be actively involved in the development and progression of the peritoneal membrane hyperpermeability and fibrosis observed in long-term PD patients. This study also suggests that both high glucose and GDP in PDS may play important roles in inducing VEGF and PIIINP production/secretion by HPMC.

Effect of High Glucose on Peritoneal Mesothelial Cell Biology

Objective

This study reviews evidence that implicates high glucose (HG) in the pathogenesis of peritoneal fibrosis and proposes mechanisms potentially involved in the HG-induced peritoneal fibrosis that is observed in long-term peritoneal dialysis (PD) patients.

Design

Selected Western literature is reviewed, examining the effect of HG on rat or human peritoneal mesothelial cell (HPMC) biology with particular reference to extracellular matrix (ECM) gene expression and protein synthesis.

Results

HG up-regulated the expression of monocyte chemotactic peptide–1 (MCP-1), transforming growth factor beta 1 (TGFβ1), and fibronectin messenger RNAs (mRNAs) and proteins. These HG-induced up-regulations were effectively blocked by the inhibition of protein kinase C (PKC). In addition, cytosolic reactive oxygen species (ROS) rapidly increased in HPMC cultured under HG, and treatment with antioxidant effectively inhibited HG-induced fibronectin protein synthesis by HPMC.

Conclusion

Continuous exposure of the peritoneal membrane to HG may induce changes in HPMC biology, leading to excessive deposition of ECM and peritoneal injury. HG-induced activation of diacylglycerol PKC (DAG–PKC) plays a major role in up-regulation of MCP-1, TGFβ1, and fibronectin synthesis by HPMC cultured under HG. In addition, ROS, recently recognized as signalling molecules, are rapidly generated in HPMC as a result of increased glucose metabolism and may prove to be an important mediator of HG-induced peritoneal injury.

Dendritic Cells as Arbiters of Peritoneal Immune Responses

During the past few years, there has been a substantial increase in the understanding of innate immunity. Dendritic cells are emerging as key players in the orchestration of this early phase of immune responses, with a role that will translate into the subsequent type of adaptive immune response against infection. Here we provide an overview of dendritic cell differentiation and function, with particular emphasis on those features unique to the immune defense of the peritoneal cavity and in the context of peritoneal dialysis-associated immune responses. The reader is referred to the primary references included in the accompanying list for specific details in this fascinating field.

No Significant Differences in Peritoneal Fluid Handling in Children Using pH-Neutral or Acidic Solutions

Objectives

Differences in peritoneal fluid handling in the acute setting can be expected if children are converted to pH-neutral dialysis solutions because conventional acidic solutions exert toxic effects on peritoneal mesothelial cells and microcirculation. Peritoneal fluid kinetics was therefore investigated with both types of solutions in a group of children.

Design

Peritoneal equilibration tests (PETs) were performed in 12 patients [mean age 70 months, mean time on peritoneal dialysis (PD) 18 months] using a pH-neutral PD fluid (Physioneal 3.86%; Baxter Ltd, Castlebar, Ireland) and dextran 70 as a volume marker. The results of these PETs were compared to those of a historic group of 12 children (mean age 75 months, mean time on PD 17 months).

Setting

Pediatric dialysis unit in a tertiary institute.

Patients

Stable pediatric PD patients.

Main Outcome Measures

Transcapillary ultrafiltration (TCUF) and marker clearance, dialysate-to-plasma (D/P) ratios for urea and creatinine, and Dt/D0ratio for glucose.

Results

TCUF and lymphatic absorption were not different between the two groups. There was also no significant difference in small solute clearance measured by D/P ratio for urea and creatinine and Dt/D0ratio for glucose.

Conclusion

Peritoneal fluid kinetics is not significantly altered if pH-neutral dialysis solutions are applied compared to acidic solutions. An altered TCUF, as is hypothetically possible using an acidic solution, was not established.

Impact of ACE Inhibitors and AII Receptor Blockers on Peritoneal Membrane Transport Characteristics in Long-Term Peritoneal Dialysis Patients

Background

Long-term peritoneal dialysis (PD) may lead to peritoneal fibrosis and ultrafiltration failure. The latter occurs due to high solute transport rates and diabetiform peritoneal sclerosis. Angiotensin-II (AII) is known to be a growth factor in the development of fibrosis and a number of animal studies have shown it likely that inhibiting the effects of AII by angiotensin-converting enzyme (ACE) or angiotensin receptor blocker (ARB) will attenuate these complications.

Objective

To investigate the effects of ACE/AII inhibitors in long-term PD patients.

Patients and Setting

We analyzed data from 66 patients treated with PD therapy at our center for at least 2 years, during which time at least 2 standard peritoneal permeability analyses (SPAs) were performed. 36 patients were treated with ACE/AII inhibitors (ACE/ARB group); the other 30 received none of the above drugs during the entire follow-up (control group). The two groups were compared with respect to changes in peritoneal transport over the follow-up time.

Results

A significant difference in time course of peritoneal transport was found between the 2 groups: in the ACE/ARB group, small solute transport had decreased, while it had increased in the control group. This finding was confirmed by analysis using mixed model for repeated measures. The value of mass transfer area coefficient of creatinine was influenced by the duration of PD therapy ( p = 0.017) and this interaction was different with respect to use of ACE/AII inhibitors ( p = 0.037). The trend was not found in protein clearances or fluid kinetics.

Conclusion

Our findings suggest that ACE/AII inhibition is likely to prevent the increase in mass transfer area coefficients that occurs in long-term PD, which is in line with results of experimental animal studies.

The Role of Cathepsin B in Peritoneal Fibrosis due to Peritoneal Dialysis

Glucose-containing peritoneal dialysis (PD) solution causes peritoneal fibrosis (PF) characterized by accumulation of extracellular matrix (ECM) in the submesothelial layer. Cathepsin B is a lysosomal cysteine protease that degrades ECM, but its role in the PF remains unclear. Thus, we investigated the role of cathepsin B in PF. Procathepsin B was measured in the 73 PD effluents of 68 patients. Procathepsin B and cathepsin B after exposure of glucose and the effects of cathepsin B on the expression of matrix metalloproteinases (MMPs), tissue inhibitor of metalloproteinases (TIMPs), and urokinase-type plasminogen activator (uPA) were measured in the supernatant of cultured human peritoneal mesothelial cells (HPMCs). The effect of cathepsin B and its inhibitor, cystatin C, on PF was investigated in the murine model. Procathepsin B was measured at 3.6 μg/L in serum and 5.4 μg/L in PD effluent and positively correlated to the cancer antigen (CA) 125. The treatment with 4.25% glucose increased procathepsin B by 3.1-fold and cathepsin B by 5.9-fold in the HPMCs. Cathepsin B induced the secretion of MMP-1, -2, and -3 and TIMP-1 in the HPMCs, but uPA was not excreted. In the PF murine models, cathepsin B reduced the thickness of the submesothelial layer and cystatin C attenuated the effect of cathepsin B. HPMCs secrete cathepsin B with exposure of PD solution, and cathepsin B might help protect against PF.

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.

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.

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.

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

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

Atorvastatin Improves Peritoneal Sclerosis Induced by Hypertonic PD Solution in Rats

Background

Peritoneal sclerosis is a complication of peritoneal dialysis and results in ultrafiltration failure. It is related to chronic peritoneal injury due to dialysis solution content and recurrent peritonitis. Statins have anti-inflammatory properties which may be of value in modulating responses to injury. We evaluated the capacity of atorvastatin to modify peritoneal alterations secondary to hypertonic glucose.

Methods

Thirty-two non-uremic rats were divided into three groups: group I (Sham) rats received no treatment (n=11), group II received hypertonic (3.86%, 10 ml/day) PD solution (n=10) and group III received hypertonic PD solution (10 ml/day) plus 80 mg/L atorvastatin in drinking water (n=11). After four weeks, a one-hour peritoneal equilibration test (PET) was performed with 3.86% PD solution. Dialysate-to-plasma urea ratio (D/P urea), glucose reabsorption (D1/D0 glucose), ultrafiltration volume (UF), dialysate protein, TGF-ß1 and VEGF levels were determined.

Results

Administration of atorvastatin resulted in preserved UF (4.9±0.8 vs 7.5±0.6 mL, p <0.01), protein loss (2.2±0.2 vs 2.1±0.1 g/L, p >0.05), and peritoneal thickness (53±3 vs 26±4 μm, p <0.01). D1/D0 glucose was significantly reduced in the dextrose group (0.70±0.02 vs 0.56±0.04, p <0.01). Both higher levels of TGF-ß1 (206±40 vs 474±120 pg/mL, p<0.05), and VEGF in dialysate effluent (4±0.4 vs 7.9±3 pg/mL, p>0.05), was determined in the dextrose group.

Conclusion

Exposure to hypertonic glucose solution resulted in alterations in peritoneal transport manifested by a rapid dissipation of the glucose gradient and resultant impaired UF response. Administration of atorvastatin led to prevention of these alterations. We suggest that the anti-inflammatory properties of statins are useful in providing protection of the peritoneal membrane from the effects of hypertonic glucose.

Aberrant Wnt/Beta-Catenin Pathway Activation in Dialysate-Induced Peritoneal Fibrosis

Peritoneal dialysis (PD)-associated peritoneal fibrosis is a chronic progress which induces ultrafiltration failure. It remains a challenge to prevent the progression of PD-associated fibrosis in clinic practice. Wnt/β-catenin pathway plays important role in many severe fibrotic diseases, here we investigated its contribution to the development of peritoneal damage. We isolated mesothelial cells (MC) from the effluent of PD patients and found that the expressions of Wnt1, Wnt5a, β-catenin, and LEF1 were increased in patients with more than 1-year PD compared with patients who just started with PD (<1 month). The elevated expressions of Wnts and β-catenin were accompanied with changes in the expressions of E-cadherin, α-SMA, COL-I, and FN mRNA and proteins, which are known related to mesothelial-mesenchymal transition (MMT). In addition, treatment with high glucose significantly increased the expression of Wnt1, Wnt5a, β-catenin, and LEF1 as well as the expression of α-SMA, COL-I, and FN in human peritoneal mesothelial cells (HPMC), whereas the expression of E-cadherin was reduced. Dickkopf-1 (DKK-1) is an endogenous inhibitor of Wnt/β-catenin signaling. Overexpression of DKK1 transgene significantly decreased the expression of β-catenin and attenuated the process of MMT as indicated by the decreased expression of α-SMA, COL-I, and FN and the increased expression of E-cadherin. Furthermore, TGF-β1 treatment significantly activated the Wnt/β-catenin pathway in HPMCs, while DKK1 blocked the TGF-β1-induced Wnt signaling activation and significantly inhibited the process of MMT. These data suggest that the canonical Wnt/β-catenin pathway plays an important role in the MMT and fibrosis induced by PD.

Interleukin-6 trans-signalling induces vascular endothelial growth factor synthesis partly via Janus kinases-STAT3 pathway in human mesothelial cells

AIMS

Interleukin-6 (IL-6) is a vital inflammatory factor in the peritoneal cavity of peritoneal dialysis (PD) patients. Because intraperitoneal inflammation is closely associated with angiogenesis, we sought to explore the effect of IL-6 on vascular endothelial growth factor (VEGF) synthesis and its transduction pathway in mesothelial cells.

METHODS

Human mesothelial cells (Met-5A) were incubated with different concentrations of glucose and mannitol, and the effect of glucose and mannitol on the expression of IL-6 was determined. Then, the cells were stimulated by IL-6 with or without two soluble receptors of IL-6 (sIL-6R or sgp130), and VEGF synthesis was detected. Finally, the cells were incubated with IL-6/sIL-6R combined with or without the inhibitor of Janus kinases (JAK) AG490. The phosphorylation of the signal transducer and activator of transcription 3 (STAT3) and its intracellular translocation were examined.

RESULTS

1. High glucose and mannitol could upregulate IL-6 mRNA expression and IL-6 secretion in mesothelial cells significantly, and there was no difference of its effect between high glucose and mannitol. 2. Met-5A was a cell line with a single IL-6 receptor. The IL-6/sIL-6R complex induced VEGF synthesis of mesothelial cells, which was alleviated by sgp130 or AG490. IL-6 trans-signalling could induce the phosphorylation of STAT3, which is recruited to the cellular nucleus of Met-5A cells.

CONCLUSION

The present study might provide evidence that high glucose upregulates IL-6 synthesis in Met-5A cells, to some extent, depending on its osmolality and that IL-6 trans-signalling could induce VEGF synthesis partly dependent on the JAK/STAT3 pathway.

Linagliptin Ameliorates Methylglyoxal-Induced Peritoneal Fibrosis in Mice

Recent studies have reported increases of methylglyoxal (MGO) in peritoneal dialysis patients, and that MGO-mediated inflammation plays an important role in the development of peritoneal fibrosis through production of transforming growth factor-β1 (TGF-β1). Linagliptin, a dipeptidyl peptidase-4 inhibitor, exerts anti-inflammatory effects independent of blood glucose levels. In this study, we examined whether linagliptin suppresses MGO-induced peritoneal fibrosis in mice. Male C57/BL6 mice were divided into three groups: control, MGO injection plus saline, and MGO injection plus linagliptin (n = 6 per group). Peritoneal fibrosis was induced by daily intraperitoneal injection of saline containing 40 mmol/L MGO for 21 days. Saline was administered intraperitoneally to the control group. Linagliptin (10 mg/kg) or saline were administrated by once-daily oral gavage from 3 weeks before starting MGO injections. Immunohistochemical staining revealed that linagliptin suppressed expression of α-smooth muscle actin and fibroblast-specific protein-1, deposition of type I and III collagen, and macrophage (F4/80) infiltration. Peritoneal equilibration testing showed improved peritoneal functions in mice treated with linagliptin. Peritoneal injection of MGO increased plasma levels of glucagon-like peptide-1 (GLP-1) in mice, and a further increase was observed in linagliptin-treated mice. Although MGO increased plasma glucose levels, linagliptin did not decrease plasma glucose levels. Moreover, linagliptin reduced the TGF-β1 concentration in the peritoneal fluid of MGO-treated mice. GLP-1 receptor (GLP-1R) was expressed in monocytes/macrophages and linagliptin suppressed GLP-1R expression in MGO-injected mice. These results suggest that oral administration of linagliptin ameliorates MGO-induced peritoneal fibrosis.

Endoplasmic reticulum stress as a novel target to ameliorate epithelial-to-mesenchymal transition and apoptosis of human peritoneal mesothelial cells

Epithelial-to-mesenchymal transition (EMT) and apoptosis of peritoneal mesothelial cells are known to be the earliest mechanisms of peritoneal fibrosis in peritoneal dialysis (PD). Endoplasmic reticulum (ER) stress with an unfolded protein response is regarded to have a role in the development of organ fibrosis. To investigate the potential role of ER stress as a target to prevent and/or delay the development of peritoneal fibrosis, we examined the effect of ER stress on EMT or apoptosis of human peritoneal mesothelial cells (HPMCs) and elucidated the mechanisms underlying the protective effect of ER stress preconditioning on TGF-β1-induced EMT. ER stress inducers, tunicamycin (TM) and thapsigargin (TG), induced EMT with Smad2/3 phosphorylation, an increased nuclear translocation of β-catenin and Snail expression. Low concentrations of TM and TG did not induce apoptosis within 48 h; however, high concentrations of TM- (>1 ng/ml) and TG- (>1 nM) induced apoptosis at 12 h with a persistent increase in C/EBP homologous protein. TGF-β1 induced EMT and apoptosis in HPMCs, which was ameliorated by taurine-conjugated ursodeoxycholic acid, an ER stress blocker. Interestingly, pre-treatment with TM or TG for 4 h also protected the cells from TGF-β1-induced EMT and apoptosis, demonstrating the role of ER stress as an adaptive response to protect HPMCs from EMT and apoptosis. Peritoneal mesothelial cells isolated from PD patients displayed an increase in GRP78/94, which was correlated with the degree of EMT. These findings suggest that the modulation of ER stress in HPMCs could serve as a novel approach to ameliorate peritoneal damage in PD patients.

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.

Effect of aldosterone on epithelial-to-mesenchymal transition of human peritoneal mesothelial cells

BACKGROUND

Peritoneal fibrosis is one of the major causes of technical failure in patients on peritoneal dialysis. Epithelial-to-mesenchymal transition (EMT) of the peritoneum is an early and reversible mechanism of peritoneal fibrosis. Human peritoneal mesothelial cells (HPMCs) have their own renin-angiotensin-aldosterone system (RAAS), however, it has not been investigated whether aldosterone, an end-product of the RAAS, induces EMT in HPMCs, and which mechanisms are responsible for aldosterone-induced EMT.

METHODS

EMT of HPMCs was evaluated by comparing the expression of epithelial cell marker, E-cadherin, and mesenchymal cell marker, α-smooth muscle actin after stimulation with aldosterone (1-100nM) or spironolactone. Activation of extracellular signal-regulated kinase (ERK)1/2 and p38 mitogen-activated protein kinase (MAPK) and generation of reactive oxygen species (ROS) were assessed by western blotting and 2',7'-dichlorofluororescein diacetate staining, respectively. The effects of MAPK inhibitors or antioxidants (N-acetyl cysteine, apocynin, and rotenone) on aldosterone-induced EMT were evaluated.

RESULTS

Aldosterone induced EMT in cultured HPMCs, and spironolactone blocked aldosterone-induced EMT. Aldosterone induced activation of both ERK1/2 and p38 MAPK from 1 hour. Either PD98059, an inhibitor of ERK1/2, or SB20358, an inhibitor of p38 MAPK, attenuated aldosterone-induced EMT. Aldosterone induced ROS in HPMCs from 5 minutes, and antioxidant treatment ameliorated aldosterone-induced EMT. N-acetyl cysteine and apocynin alleviated activation of ERK and p38 MAPK.

CONCLUSION

Aldosterone induced EMT in HPMCs by acting through the mineralocorticoid receptor. Aldosterone-induced generation of ROS followed by activation of ERK, and p38 MAPK served as one of the mechanisms of aldosterone-induced EMT of HPMCs.

EGF-induced adipose tissue mesothelial cells undergo functional vascular smooth muscle differentiation

Recent studies suggested that the post-natal mesothelium retain differentiative potential of the embryonic mesothelium, which generates fibroblasts and vascular smooth muscle cells (VSMCs), in developing coelomic organs via epithelial-to-mesenchymal transition (EMT). Whether adult mesothelial cells (MCs) are able to give rise to functional VSMCs in vitro and which are the factors and mechanisms directing this process remain largely unknown. Here, we isolated adipose tissue MCs (ATMCs) from adult mice, and demonstrated that ATMCs cultured in a serum-containing media supplemented with epidermal growth factor (EGF) efficiently increased both their proliferation and EMT above levels found in only serum-containing media cultures. EGF-induced ATMCs gained phosphorylation of the EGF receptor and activated simultaneously ILK/Erk1/2, PI3K/Akt and Smad2/3-dependent pathways. Sequential subculture onto collagen-I surface efficiently improved their vasculogenic EMT towards cells featuring VSMCs (α-SMA, calponin, caldesmon, SM22α, desmin, SM-MHC, smoothelin-B and PDGFR-β) that could actively contract in response to receptor and non-receptor-mediated vasoactive agonists. Overall, our results indentify EGF signalling as a robust vasculogenic inductive pathway for ATMCs, leading to their transdifferentiation into functional VSMC-like cells.

Alterations of intercellular junctions in peritoneal mesothelial cells from patients undergoing dialysis: effect of retinoic Acid

BACKGROUND

Dialysis patients are classified according to their peritoneal permeability as low transporter (LT, low solute permeability) or high transporter (HT, high solute permeability). Tight junction (TJ) proteins are critical to maintain ions, molecules and water paracellular transport through peritoneum. Exposure to peritoneal dialysis solutions causes damage to TJ in human peritoneal mesothelial cells (HPMCs). We analyzed the quantity, distribution and function of TJ proteins: claudin-1, -2 and -8, ZO-1 and occludin, in HPMC cultures from LT and HT patients. Since all-trans retinoic acid (ATRA) might modify the expression of TJ proteins, we studied its effect on HPMCs.

METHODS

Control HPMCs were isolated from human omentum, while HT or LT cells were obtained from dialysis effluents. Cells were cultured in presence of ATRA 0, 50 or 100 nM. Transepithelial electrical resistance (TER) measurement, immunostaining and Western blot analyses were performed.

RESULTS

HT exhibited lower TER than control and LT monolayers. Immunofluorescence for TJ was weak and discontinuous along the cell contour, in LT and HT. Furthermore, claudin-1, occludin and ZO-1 expressions were decreased. In all groups, claudin-2 was localized at nuclei. We observed that ATRA improved TJ distribution and increased TJ expression in HT. This retinoid did not modify claudin-2 and -8 expressions. All-trans retinoic acid decreased TER in HT, but had no effect in LT.

CONCLUSIONS

Tight junctions were altered in HPMCs from dialyzed patients. The HT monolayer has lower TER than LT, which might be associated with the peritoneal permeability in these patients. ATRA might be a therapeutic alternative to maintain mesothelial integrity, since it improved TJ localization and expression.

Crosstalk between the mesothelium and lymphomatous cells: insight into the mechanisms involved in the progression of body cavity lymphomas

The peculiar localization of body cavity lymphomas implies a specific contribution of the intracavitary microenvironment to the pathogenesis of these tumors. In this study, primary effusion lymphoma (PEL) was used as a model of body cavity lymphoma to investigate the role of mesothelial cells, which line the serous cavities, in lymphoma progression. The crosstalk between mesothelial and lymphomatous cells was studied in cocultures of primary human mesothelial cells (HMC) with PEL cells and a xenograft mouse model of peritoneal PEL. PEL cells were found to induce type 2 epithelial–mesenchymal transition (EMT) in HMC, which converted into a myofibroblastic phenotype characterized by loss of epithelial markers (pan cytokeratin and E-cadherin), expression of EMT-associated transcriptional repressors (Snail1, Slug, Zeb1, Sip1), and acquisition of α-smooth muscle actin (α-SMA), a mesenchymal protein. A progressive thickening of serosal membranes was observed in vivo, accompanied by loss of cytokeratin staining and appearance of α-SMA-expressing cells, confirming that fibrosis occurred during intracavitary PEL development. On the other hand, HMC were found to modulate PEL cell turnover in vitro, increasing their resistance to apoptosis and proliferation. This supportive activity on PEL cells was retained after transdifferentiation, and was impaired by interferon-α₂b treatment. On the whole, our results indicate that PEL cells induce type 2 EMT in HMC, which support PEL cell growth and survival, providing a milieu favorable to lymphoma progression. Our findings provide new clues into the mechanisms involved in lymphoma progression and may indicate new targets for effective treatment of malignant effusions growing in body cavities.

Retinoic acid improves morphology of cultured peritoneal mesothelial cells from patients undergoing dialysis

Patients undergoing continuous ambulatory peritoneal dialysis are classified according to their peritoneal permeability as low transporter (low solute permeability) or High transporter (high solute permeability). Factors that determine the differences in permeability between them have not been fully disclosed. We investigated morphological features of cultured human peritoneal mesothelial cells from low or high transporter patients and its response to All trans retinoic Acid (ATRA, vitamin A active metabolite), as compared to non-uremic human peritoneal mesothelial cells. Control cells were isolated from human omentum. High or low transporter cells were obtained from dialysis effluents. Cells were cultured in media containing ATRA (0, 50, 100 or 200 nM). We studied length and distribution of microvilli and cilia (scanning electron microscopy), epithelial (cytokeratin, claudin-1, ZO-1 and occludin) and mesenchymal (vimentin and α-smooth muscle actin) transition markers by immunofluorescence and Western blot, and transforming growth factor β1 expression by Western blot. Low and high transporter exhibited hypertrophic cells, reduction in claudin-1, occludin and ZO-1 expression, cytokeratin and vimentin disorganization and positive α-smooth muscle actin label. Vimentin, α-smooth muscle actin and transforming growth factor-β1 were overexpressed in low transporter. Ciliated cells were diminished in low and high transporters. Microvilli number and length were severely reduced in high transporter. ATRA reduced hypertrophic cells number in low transporter. It also improved cytokeratin and vimentin organization, decreased vimentin and α-smooth muscle actin expression, and increased claudin 1, occludin and ZO-1 expression, in low and high transporter. In low transporter, ATRA reduced transforming growth factor-β1 expression. ATRA augmented percentage of ciliated cells in low and high transporter. It also augmented cilia length in high transporter. Alterations in structure, epithelial mesenchymal markers and transforming growth factor-β1 expression were differential between low and high transporter. Beneficial effects of ATRA were improved human peritoneal mesothelial cells morphology tending to normalize structures.

TGF-β1 promotes lymphangiogenesis during peritoneal fibrosis

Peritoneal fibrosis (PF) causes ultrafiltration failure (UFF) and is a complicating factor in long-term peritoneal dialysis. Lymphatic reabsorption also may contribute to UFF, but little is known about lymphangiogenesis in patients with UFF and peritonitis. We studied the role of the lymphangiogenesis mediator vascular endothelial growth factor-C (VEGF-C) in human dialysate effluents, peritoneal tissues, and peritoneal mesothelial cells (HPMCs). Dialysate VEGF-C concentration correlated positively with the dialysate-to-plasma ratio of creatinine (D/P Cr) and the dialysate TGF-β1 concentration. Peritoneal tissue from patients with UFF expressed higher levels of VEGF-C, lymphatic endothelial hyaluronan receptor-1 (LYVE-1), and podoplanin mRNA and contained more lymphatic vessels than tissue from patients without UFF. Furthermore, mesothelial cell and macrophage expression of VEGF-C increased in the peritoneal membranes of patients with UFF and peritonitis. In cultured mesothelial cells, TGF-β1 upregulated the expression of VEGF-C mRNA and protein, and this upregulation was suppressed by a TGF-β type I receptor (TGFβR-I) inhibitor. TGF-β1-induced upregulation of VEGF-C mRNA expression in cultured HPMCs correlated with the D/P Cr of the patient from whom the HPMCs were derived (P<0.001). Moreover, treatment with a TGFβR-I inhibitor suppressed the enhanced lymphangiogenesis and VEGF-C expression associated with fibrosis in a rat model of PF. These results suggest that lymphangiogenesis associates with fibrosis through the TGF-β-VEGF-C pathway.

Cannabinoid receptors as therapeutic targets for dialysis-induced peritoneal fibrosis

BACKGROUND

Long-term exposure to bioincompatible peritoneal dialysis solutions is frequently complicated with peritoneal fibrosis and ultrafiltration failure. As cannabinoid receptor (CBR) ligands have been reported to be beneficial to ameliorate the process of liver fibrosis, we strove to investigate their therapeutic potential to prevent peritoneal fibrosis.

METHODS

We used the rat model of peritoneal fibrosis induced by intraperitoneal injection of methylglyoxal and in vitro mesothelial cell culture to test the effects of CBR ligands, including the type 1 CBR (CB(1)R) antagonist and the type 2 CBR (CB(2)R) agonist.

RESULTS

In the methylglyoxal model, both intraperitoneal CB(1)R antagonist (AM281) and CB(2)R agonist (AM1241) treatment significantly ameliorated peritoneal fibrosis. In addition, CB(1)R antagonist was able to alleviate TGF-β(1)-induced dedifferentiation of mesothelial cells and to maintain epithelial integrity in vitro.

CONCLUSIONS

Intraperitoneal administration of CBR ligands (CB(1)R antagonist and CB(2)R agonist) offers a potential therapeutic strategy to reduce dialysis-induced peritoneal fibrosis and to prolong the peritoneal survival in peritoneal dialysis patients.

The effect of low-GDP solution on ultrafiltration and solute transport in continuous ambulatory peritoneal dialysis patients

BACKGROUND

Several studies have reported benefits for human peritoneal mesothelial cell function of a neutral-pH dialysate low in glucose degradation products (GDPs). However, the effects of low-GDP solution on ultrafiltration (UF), transport of solutes, and control of body water remain elusive. We therefore investigated the effect of low-GDP solution on UF, solute transport, and control of body water.

METHODS

Among 79 new continuous ambulatory peritoneal dialysis (CAPD) patients, 60 completed a 12-month protocol (28 in a lactate-based high-GDP solution group, 32 in a lactate-based low-GDP solution group). Clinical indices--including 24-hour UF volume (UFV), 24-hour urine volume (UV), residual renal function, and dialysis adequacy--were measured at months 1, 6, and 12. At months 1, 6, and 12, UFV, glucose absorption, 4-hour dialysate-to-plasma (D/P) creatinine, and 1-hour D/P Na(+) were assessed during a modified 4.25% peritoneal equilibration test (PET). Body composition by bioelectric impedance analysis was measured at months 1 and 12 in 26 CAPD patients.

RESULTS

Daily UFV was lower in the low-GDP group. Despite similar solute transport and aquaporin function, the low-GDP group also showed lower UFV and higher glucose absorption during the PET. Factors associated with UFV during the PET were lactate-based high-GDP solution and 1-hour D/P Na(+). No differences in volume status and obesity at month 12 were observed, and improvements in hypervolemia were equal in both groups.

CONCLUSIONS

Compared with the high-GDP group, the low-GDP group had a lower UFV during a PET and a lower daily UFV during the first year after peritoneal dialysis initiation. Although the low-GDP group had a lower daily UFV, no difficulties in controlling edema were encountered.

Heme oxygenase-1 attenuates epithelial-to-mesenchymal transition of human peritoneal mesothelial cells

BACKGROUND

Epithelial-to-mesenchymal transition (EMT) of peritoneal mesothelial cells has been regarded as an early mechanism of peritoneal fibrosis. A substantial and rapidly growing literature indicates that HO-1 provides the provenance for pathways that can interrupt virtually all major mechanisms of tissue injury. The effects of HO-1 expression on EMT, which plays a critical role in the development of peritoneal membrane (PM) fibrosis, are unknown and its roles in peritoneal fibrosis has not been studied, yet.

METHODS

A piece of human omentum obtained from consenting patients undergoing elective abdominal surgery was used for study. We treated the human peritoneal mesothelial cells (HPMCs) with high glucose solution and HO-1 inducer (hemin, 10 μmol/L). To further investigate the pure effect of HO-1 on EMT of mesothelium, gene transfer of recombinant Adenovirus-harboring human HO-1 (Adv-HO-1 gene) to HPMCs was done.

RESULTS

Exposure of HPMCs to HG solution resulted in an increase of the expression of mesenchymal markers such as α-smooth muscle actin (α-SMA) and was associated with a decrease in the expression of epithelial markers, E-cadherin. HO-1 protein expression was decreased in the same situation. Treatment of HPMCs with HO-1 inducer, hemin showed a dosage-dependent amelioration of HG induced changes in markers of EMT with increase of expression of HO-1. Human HO-1 gene transfection resulted in a significant increase in HO-1 expression and ameliorated HG-induced changes in expression of E-cadherin and α-SMA.

CONCLUSION

Taken together, our results suggest that HO-1 has a critical role in the modulation of peritoneal fibrosis, and, more important, the suppression of EMT. This study is the first to show the beneficial effect of HO-1 on reversing EMT in MC.

Mechanisms and interventions in peritoneal fibrosis

Peritoneal dialysis (PD) is an attractive treatment for patients with end-stage kidney disease (ESKD). However, long-term peritoneal dialysis is associated with development of functional and structural alterations of the peritoneal membrane. Several factors are implicated in the development of peritoneal fibrosis in PD patients. Inflammatory cytokines, which are induced in the peritoneal cavity during peritonitis, may also induce chronic inflammation and fibrosis. Transforming growth factor β1 (TGF-β1) is generally considered to play an important role in peritoneal fibrosis. The objective of this review is to summarize the mechanisms of peritoneal fibrosis using in vitro and in vivo studies, and the current status and future prospects of interventions in the peritoneal fibrosis.