Preserving the peritoneal membrane in long-term peritoneal dialysis patients

Astragaloside IV ameliorates peritoneal fibrosis by promoting PGC-1α to reduce apoptosis in vitro and in vivo

Prolonged exposure of the peritoneum to high glucose dialysate leads to the development of peritoneal fibrosis (PF), and apoptosis of peritoneal mesothelial cells (PMCs) is a major cause of PF. The aim of this study is to investigate whether Astragaloside IV could protect PMCs from apoptosis and alleviate PF. PMCs and rats PF models were induced by high glucose peritoneal fluid. We examined the pathology of rat peritoneal tissue by HE staining, the thickness of rat peritoneal tissue by Masson's staining, the number of mitochondria and oxidative stress levels in peritoneal tissue by JC-1 and DHE fluorescence staining, and mitochondria-related proteins and apoptosis-related proteins such as PGC-1α, NRF1, TFAM, Caspase3, Bcl2 smad2 were measured. We used hoechst staining and flow cytometry to assess the apoptotic rate of PMCs in the PF model, and further validated the observed changes in the expressions of PGC-1α, NRF1, TFAM, Caspase3, Bcl2 smad2 in PMCs. We further incubated PMCs with MG-132 (proteasome inhibitor) and Cyclohexylamine (protein synthesis inhibitor). The results demonstrated that Astragaloside IV increased the expression of PGC-1α by reducing the ubiquitination of PGC-1α. It was further found that the protective effects of Astragaloside IV on PMCs were blocked when PGC-1α was inhibited. In conclusion, Astragaloside IV effectively alleviated PF both in vitro and in vivo, possibly by promoting PGC-1α to enhance mitochondrial synthesis to reduce apoptotic effects.

Inhibition of calpain9 attenuates peritoneal dialysis-related peritoneal fibrosis

Aim: Peritoneal dialysis is a common renal replacement method for end-stage renal disease. Long-term peritoneal dialysis leads to peritoneal dialysis-related peritoneal fibrosis, which leads to a cessation of treatment. Calpain is a protein belonging to calcium-dependent endopeptidase family and plays an important role in extracellular matrix remodeling. Here, we evaluated the effect of calpain in peritoneal dialysis-related peritoneal fibrosis.

Methods: We established two animal models of peritoneal fibrosis and inhibited the activity of Calpain, and then collected peritoneal tissue to evaluate the progress of fibrosis and the changes of Calpain and β-catenin. We obtained Rat peritoneal mesothelial cells and Human peritoneal mesothelial cell line and stimulated with TGF-β to produce extracellular matrix. Next we inhibited Calpain activity or reduced Calpain9 expression, and then assessed changes in extracellular matrix and β-catenin.

Results: Inhibition of calpain activity attenuated chlorhexidine glucose and peritoneal dialysis-induced peritoneal thickening and β-catenin expression in mice. In addition, compared with the control group, when primary rat peritoneal mesothelial cells or human peritoneal mesothelial cells were treated with transforming growth factor beta, down-regulation of calpain activity inhibited the expression of Fibronectin and Collagen I, and increased the expression of E-cadherin. These changes could be adjusted after silencing calpain9. Finally, calpain9 deficiency was associated with down-regulation of Fibronectin and β-catenin in human peritoneal mesothelial cells.

Conclusion: Our results suggest that calpain9 may be a key molecule in mediating peritoneal dialysis-related peritoneal fibrosis.

Peritoneal dialysis and peritoneal fibrosis: molecular mechanisms, risk factors and prospects for prevention

Peritoneal dialysis (PD) leads to structural and functional changes in the peritoneal membrane, the endpoint of which is peritoneal fibrosis. Peritoneal fibrosis is diagnosed in 50% and 80% of PD patients within 1 and 2 years of treatment initiation, respectively. A key role in the development of peritoneal fibrosis is played by mesothelial-mesenchymal transformation, a complex biological process of transition from mesothelium to mesenchyme. This review summarizes the current knowledge on the changes in peritoneal function and morphology, the molecular mechanisms of peritoneal fibrosis development, and its clinical consequences during PD. Special attention is given to established and potential risk factors for peritoneal fibrosis, and existing prevention strategies are considered.

[Calpain activation promotes dialysis-associated peritoneal fibrosis in rats]

OBJECTIVE

To explore the role of calpain activation in the progression of peritoneal fibrosis.

OBJECTIVE

Twenty-four male Sprague-Dawley rats were randomized equally into control group, MDL28170 (a calpain inhibitor)+normal saline group, peritoneal dialysis (PD) model group and PD + MDL28170 group. In the latter two groups, the rats received daily intraperitoneal injections of 100 mL/kg of 4.25% glucose PD solution, and those in PD+MDL28170 group and MDL28170 saline group received daily infusion of 4 mg/kg MDL28170 every other day. Eight weeks later, the rats were euthanized for pathological examination of the parietal peritoneum, and the visceral peritoneum was used for examining the activation status of calpain and the expressions of fibronectin (FN) and collagen I (COL-I). Calpain activation and expressions of FN, COL-I and α-SMA were also examined using Western blotting and immunofluorescence assay in primary cultures of rat peritoneal mesothelial cells treated with MDL28170, transforming growth factor-β (TGF-β), or both.

OBJECTIVE

Compared with the control rats, the rats in PD model group showed significantly increased peritoneal peritoneum thickness, calpain activation in the peritoneal tissue, and expressions of FN and COL-I (P < 0.05). Treatment with MDL28170 significantly alleviated associated peritoneal fibrosis, decreased the thickness of the peritoneum (P < 0.05), and reduced the expressions of FN and COL-I in the rats with daily PD (P < 0.05). In the in vitro experiment, the expressions of FN and COL-I were also significantly lower in rat peritoneal mesothelial cells treated with both MDL28170 and TGF-β than in the cells treated with TGF-β alone (P < 0.05).

OBJECTIVE

Peritoneal calpain activity and expressions FN and COL-I all increase significantly in rat models of PD-associated peritoneal fibrosis. Calpain activation can promote peritoneal fibrosis, and inhibition of calpain can alleviate peritoneal fibrosis.

Evaluation of New Baskent University Preservation Solution for Kidney Graft During Cold Ischemia: Preliminary Experimental Animal Study

OBJECTIVES

Organ damage due to long cold ischemia time remains a hurdle in transplantation. In this preliminary animal study, we compared the new Baskent University Preservation Solution (BUPS) with the University of Wisconsin (UW) and histidine-tryptophan-ketoglutarate (HTK) solutions.

MATERIALS AND METHODS

BUPS composition included electrolytes, raffinose, mannitol, N-acetylcysteine, taurine, adenosine, and ascorbic acid. In experiment 1, kidneys from 50 male Sprague-Dawley rats were placed into BUPS, HTK, or UW solution to assess cold ischemia injury, with biopsies taken at different time points for pathologic evaluation. In experiment 2, to investigate ischemia-reperfusion injury, 5 rats were renal transplant donors to 10 rats and 6 pigs were used as transplant donors-recipients among each other.

RESULTS

In experiment 1, no significant cellular injury was shown at up to 3 hours of perfusion with any solution. At 6- to 48-hour perfusion, tubular injury was shown, with lowest injury in BUPS and HTK versus UW and control groups (P < .01). The BUPS group showed more moderate degree of tubular apoptosis and cytoskeletal rearrangement than the HTK and UW groups at 12-, 24-, and 48-hour perfusion (P < .01). In experiment 2, after ischemia-reperfusion injury, no significant differences were found between HTK and BUPS groups regarding tubular damage. Although no significant differences were shown regarding tubular cytoskeletal rearrangment and apoptosis in pig reperfusion group with BUPS versus HTK, significant differences were shown with these solutions in other groups.

CONCLUSIONS

Tubular damage during ischemia-reperfusion injury (cytoskeletal disruption, increased apoptosis) were lower with BUPS. BUPS can be a cost-effective perfusion solution in transplantation.

Quercetin alleviates lipopolysaccharide-induced inflammatory responses by up-regulation miR-124 in human renal tubular epithelial cell line HK-2

Chronic kidney disease (CKD) is a persistent kidney structural and functional disorder. Quercetin is one of active extracted flavonoids and has protective effects. Therefore, we proposed to survey the effect of Quercetin on CKD. HK-2 cells were preprocessed by Quercetin and then irritated with lipopolysaccharide (LPS). CCK-8 assay and flow cytometry were utilized to test viability and apoptosis. ELISA assay was utilized to estimate the IL-6 and TNF-α secretion. Western blot was performed to examine the expression of apoptosis and inflammation-associated mediators. After that HK-2 cells were transfected by miR-124 inhibitor. And the above-mentioned parameters were reassessed. LPS stimulated apoptosis and declined viability in HK-2 cells. Additionally, LPS stimulated inflammatory responses. Meanwhile, Quercetin attenuated LPS-stimulated apoptosis, production of IL-6, and TNF-α in experimental cells. Subsequently, MyD88 and miR-124 expression was elevated by LPS and alleviated by Quercetin. Finally, Quercetin exerted its protective function through NF-κB pathway via up-regulating miR-124. Our data demonstrated that Quercetin reduced apoptosis and inflammation stimulated by LPS in HK-2 cells. Moreover, Quercetin alleviated LPS-stimulated injury by up-regulating miR-124.

Visceral adipogenesis inhibited by Pref-1 is associated with peritoneal angiogenesis

AIM

Studies showed an increased visceral adipose tissue and peritoneal angiogenesis in peritoneal dialysis (PD) patients. However, the relationship between the visceral adipose expands and peritoneal angiogenesis remains unclear.

METHODS

Pref-1 (preadipocyte factor-1) recombinant adeno-associated virus (AAV) and control AAV were constructed. Mice were divided into four groups, mice in control and PD group were injected intraperitoneally with PBS, mice in control-AAV-PD were injected intraperitoneally with plaque-forming unit (PFU) control AAV and mice in pref-1-AAV-PD group were injected with PFU recombinant AAV. Two weeks later, control group was injected intraperitoneally with normal saline while other groups were injected intraperitoneally with 4.25% peritoneal dialysis fluid (PDF). Thirty days later, viscerall adipose tissue was collected and weighed. Pref-1 protein expression was measured by Western blot, and peritoneal permeability was measured by Evans blue. Cluster of differentiation 31(CD31) immunohistochemical staining was used to detect mesenteric blood vessel number, and vascular endothelial growth factor (VEGF) in serum were measured by enzyme-linked immunosorbent assay.

RESULTS

Pref-1 protein expression increased in pref-1-AAV-PD group. Visceral adipose expanded in PD and control-AAV-PD group while decreased in pref-1-AAV-PD group, which approves PD fluid enhance visceral adipogensis, and the process could be inhibited by Pref-1 recombinant AAV. The reduction of peritoneal vessel number and the decrease of vascular permeability as well as down-regulation of serum vascular endothelial growth factor observed in pref-1-AAV-PD group suggested peritoneal angiogenesis could be inhibited following visceral adipose tissue reduction.

CONCLUSION

Visceral adipose expands is associated with peritoneal angiogenesis in PD treatment, and prevention of visceral adipogenesis may be an alternative way to protect the validity of peritoneum. Copyright © 2019 John Wiley & Sons, Ltd.

PPAR-γ agonist rosiglitazone ameliorates peritoneal deterioration in peritoneal dialysis rats with LPS-induced peritonitis through up-regulation of AQP-1 and ZO-1

Peritonitis is still a major cause of the death in peritoneal dialysis (PD) patients despite the significant decline of the peritonitis rates in recent years. The present study is designed to evaluate the therapeutic potential of peroxisome proliferator-activated receptor-γ agonist, rosiglitazone, on the structure and function of the peritoneum in a PD rat accompanied with peritonitis induced by lipopolysaccharide (LPS). Our data showed that the peritoneal membrane in the LPS-only group showed increased peritoneal thickness, vessel density, and hypercellularity compared with the PD-only group. Rosiglitazone administration significantly inhibited increase of the three indicators in PD rats with LPS treatment. In line with this, rosiglitazone improved function of the peritoneum in LPS-induced PD rats receiving rosiglitazone, which was reflected by decreased D/P urea and D/P albumin. Mechanistically, rosiglitazone-mediated improvements in the damaged structure and function of the peritoneum in PD rats with LPS treatment were associated with reduced inflammation and preserving mesothelial cell monolayer resulted from up-regulation of AQP-1 and ZO-1. Our findings thus suggest that peroxisome proliferator-activated receptor γ (PPAR-γ) activation might be a reasonable strategy to prevent and ameliorate peritoneal deterioration in PD patients, especially with peritonitis.

Peritoneal Dialysis Fluid-Induced Fragmentation of Golgi Apparatus as a Biocompatibility Marker

In vitro biocompatibility assessments that consider physiologically appropriate conditions of cell exposure to peritoneal dialysis fluids (PDFs) are still awaited. In this study, we found that fragmentation of Golgi apparatus occurred in a pH-dependent manner within 30-min exposure to five distinct commercially available PDFs, which showed no marked difference in their effects on cell viability in the conventional MTT assay. Fluorescence microscopy analysis of labeling antibody against cis-Golgi protein GM130 indicated that the stacked cisternal structure was maintained in the perinuclear area of both M199 culture medium and a neutral-pH PDF groups. However, this specific structure became partially disassembled over time even in a neutral-pH PDF, and fragmentation was markedly enhanced in cells exposed to neutralized-pH PDFs in correspondence with their intracellular pH; moreover, in acidic PDFs, Golgi staining was diffuse and scattered in the entire cytoplasm and showed partial aggregation. The Golgi fragmentation markedly observed with the neutralized PDFs could be reversed by replacing either the media with a neutral-pH medium or a mixture of PDF and PD effluent (PDF) in a gradient manner mimicking clinical conditions. Furthermore, although weaker than pH effect, notable effects of other PDF-related factors were also observed after 30-min exposure to pH-adjusted PDFs. Lastly, the results of studies conducted using MAPK/SAPK inhibitors indicated that the mechanism underlying the Golgi fragmentation described here differs from that associated with the fragmentation that occurs at the G2/M checkpoint in the cell cycle. We conclude that Golgi fragmentation is suitable for rapid biocompatibility assessment of PDF not only because of its strong pH dependence but also because the fragmentation is recognizably affected by PDF constituents.

Chronic kidney disease induces inflammation by increasing Toll-like receptor-4, cytokine and cathelicidin expression in neutrophils and monocytes

TLR expression in neutrophils and monocytes is associated with increased cytokine synthesis, resulting in increased inflammation. However, the inflammatory pathway related to TLR and cathelicidin expression in these cells from CKD patients is unclear. To evaluate TLR4, cathelicidin, TNF-α, IL-6, IL-10 and MCP-1 expression in neutrophils and monocytes from HD and CKD patients. Blood samples were drawn from 47 CKD and 43 HD patients and 71 age and gender-matched healthy volunteers (CONT). TLR4 was analyzed using flow cytometry. Cathelicidin, TNF-α, IL-6, IL-10 and MCP-1 were analyzed via ELISA.TLR4 expression in neutrophils was higher in HD patients than in stage 3 and 4 CKD patients. In these cells, we observed a positive correlation between TLR4 and cathelicidin, TNF-α, IL-6, IL-10 and MCP-1 levels. In monocytes, TLR4 expression was significantly higher in CKD 3 and 4 groups than in the control and HD groups and positively and negatively correlated with IL-6 and MCP-1 and cathelicidin, respectively. TNF-α, IL-6 and MCP-1 serum levels were higher in HD and CKD patients than in control. Cathelicidin and IL-10 levels were only higher in HD patients. IL-6 serum levels were positively correlated with all cytokines, and cathelicidin was negatively correlated with MCP-1 (r = - 0.35; p < 0.01) and positively correlated with IL-10 (r = 0.37; p = 0.001). These results suggest that a uremic environment induces high TLR4, cathelicidin and cytokine expression and may increase inflammation. Thus, future studies should be conducted to evaluate whether TLR4 and cathelicidin should be targets for anti-inflammatory therapeutic strategies.

Acidic organelles mediate TGF-β1-induced cellular fibrosis via (pro)renin receptor and vacuolar ATPase trafficking in human peritoneal mesothelial cells

TGF-β1, which can cause renal tubular injury through a vacuolar-type H⁺-ATPase (V-ATPase)-mediated pathway, is induced by the glucose degradation product methylglyoxal to yield peritoneal injury and fibrosis. The present study investigated the roles of V-ATPase and its accessory protein, the (pro)renin receptor, in peritoneal fibrosis during peritoneal dialysis. Rats daily administered 20 mM methylglyoxal intraperitoneally developed significant peritoneal fibrosis after 7 days with increased expression of TGF-β and V-ATPase, which was reduced by the inhibition of V-ATPase with co-administration of 100 mM bafilomycin A1. The (pro)renin receptor and V-ATPase were expressed in acidic organelles and cell membranes of human peritoneal mesothelial cells. TGF-β1 upregulated the expression of collagens, α-SMA, and EDA-fibronectin, together with ERK1/2 phosphorylation, which was reduced by inhibition of V-ATPase, (pro)renin receptor, or the MAPK pathway. Fibronectin and the soluble (pro)renin receptor were excreted from cells by acidic organelle trafficking in response to TGF-β1; this excretion was also suppressed by inhibition of V-ATPase. Soluble (pro)renin receptor concentrations in effluents of patients undergoing peritoneal dialysis were associated with the dialysate-to-plasma ratio of creatinine. Together, these results demonstrate a novel fibrosis mechanism through the (pro)renin receptor and V-ATPase in the acidic organelles of peritoneal mesothelial cells.

Peritoneal Membrane Preservation

Peritoneal dialysis (PD) is a successfully used method for renal replacement therapy. However, long-term PD may be associated with peritoneal fibrosis and ultrafiltration failure. The key factors linked to their appearance are repeated episodes of inflammation associated with peritonitis and long-term exposure to bioincompatible PD fluids. Different strategies have been proposed to preserve the peritoneal membrane. This article reviews the functional and structural alterations related to PD and strategies whereby we may prevent them to preserve the peritoneal membrane. The use of new, more biocompatible, PD solutions is promising, although further morphologic studies in patients using these solutions are needed. Blockade of the renin-angiotensin-aldosterone system appears to be efficacious and strongly should be considered. Other agents have been proven in experimental studies, but most of them have not yet been tested appropriately in human beings.

PPAR‑γ agonist rosiglitazone protects rat peritoneal mesothelial cells against peritoneal dialysis solution‑induced damage

Long-term peritoneal dialysis (PD) leads to ultrafiltration failure (UFF). Peritoneal mesothelial cells, which form the innermost monolayer of the peritoneal cavity, have been shown to regulate various responses, including inflammation, in UFF. The present study was designed to investigate the effect of the peroxisome proliferator‑activated receptor‑γ (PPAR‑γ) agonist, rosiglitazone, on peritoneal dialysis solution (PDS)‑induced injuries in rat peritoneal mesothelial cells (RPMCs). RPMCs were cultured for different durations and with different concentrations of PDS. The gene expression levels of aquaporin‑1 (AQP‑1) and zonula occluden‑1 (ZO‑1) were determined using reverse transcription‑quantitative polymerase chain reaction analysis. The protein levels of AQP‑1, ZO‑1 and PPAR‑γ were measured using western blot analysis. Interleukin (IL)‑6 and IL‑8 were detected using ELISA. The RPMCs were damaged by stimulation with 4.25% PDS for 72 h. The expression levels of AQP‑1 and ZO‑1 were increased, and the secretion of IL‑6 and IL‑8 were decreased by rosiglitazone. The use of the PPAR‑γ inhibitor, GW‑9662, completely prevented the effects of rosiglitazone. These results indicated that PDS exposure stimulated an inflammatory response in the RPMCs. The PPAR‑γ activator, rosiglitazone, appeared to relieve the injury by inhibiting inflammation, and regulating the expression of AQP‑1 and ZO‑1, however further investigations are required to elucidate the potential underlying mechanism.

Newly Developed Neutralized pH Icodextrin Dialysis Fluid: Nonclinical Evaluation

A two-compartment system (NICOPELIQ; NICO, Terumo Co., Tokyo, Japan) has recently been developed to neutralize icodextrin peritoneal dialysis fluid (PDF). In this study, a nonclinical evaluation of NICO was carried out to evaluate biocompatibility as well as water transport ability. Glucose degradation products (GDPs) in the icodextrin PDFs were analyzed via high-performance liquid chromatography (HPLC). The cell viability of human peritoneal mesothelial cells derived from peritoneal dialysis effluent (PDE-HPMCs) was evaluated as well as the amount of lactate dehydrogenase (LDH) released after exposure to different PDFs (NICO and EXTRANEAL [EX, Baxter Healthcare Corp., Chicago, IL, USA]) and neutralized pH glucose PDF MIDPELIQ 250 (M250, Terumo). The water transport ability of NICO, EX, and M250 was tested using dialysis tube membranes with various pore sizes: 1, 2, 6-8, and 12-16 kDa. Although cell viability decreased by 30% after 30 min exposure to NICO, it was maintained for 6 h while a significant decrease was observed after 6 h exposure to EX. However, following adjustment of the pH to the same pre-exposure pH value, there was no significant difference in cell viability within the same pH group despite a doubling of the difference in the total amount of GDPs (44.6 ± 8.6 µM in NICO and 91.9 ± 9.5 µM in EX, respectively). In contrast, a significant decrease in cell viability was observed when the pH decreased to less than pH 6. Levels of released LDH, a cytotoxic marker, were within 5% after a 6-h exposure of NICO to PDE-HPMCs. There was no significant difference in water transport ability represented as overall osmotic gradients between NICO and EX. In conclusion, neutralization of icodextrin PDF is beneficial for maintaining cell viability and minimizing LDH release while water transport ability is comparable to the conventional icodextrin PDF.

Is there such a thing as biocompatible peritoneal dialysis fluid?

Introduction of the so-called biocompatible peritoneal dialysis (PD) fluids was based on a large body of experimental evidence and various clinical trials suggesting important clinical benefits. Of these, until now, only preservation of residual renal function-likely due to lower glucose degradation product load and, in case of icodextrin, improved fluid and blood pressure control-have consistently been proven, whereas the impact on important clinical endpoints such as infectious complications, preservation of PD membrane transport function, and patient outcome, are still debated. In view of the high morbidity and mortality rates of PD patients, novel approaches are warranted and comprise the search for alternative osmotic agents and enrichment of PD fluids with specific pharmacologic agents, such as alanyl-glutamine, potentially counteracting local but also systemic sequelae of uremia and PD.

Active compounds extracted from extra virgin olive oil counteract mesothelial-to-mesenchymal transition of peritoneal mesothelium cells exposed to conventional peritoneal dialysate: in vitro and in vivo evidences

During peritoneal dialysis (PD), peritoneal mesothelial cells undergo a transition from an epithelial phenotype to a mesenchymal phenotype that, together with the inflammatory process, promotes tissue fibrosis and a failure of peritoneal membrane function. To date, there is no definitive treatment for the progressive thickening and angiogenesis of the peritoneal membrane associated with PD. In this study we tested, in vitro and in vivo, the ability of active compounds extracted from extra virgin olive oil (AC-EVOO) to counteract the mesothelial-to-mesenchymal transition process (MMT) observed in mesothelial cells chronically exposed to the conventional peritoneal dialysate (DL). In particular, we used a cultivar from southern Italy known to have a high polyphenol content. Our results showed that, in mesothelial cells exposed to DL, the combined treatment with AC-EVOO prevented the genic and protein upregulation of key mesenchymal and inflammatory markers, as well as the MCs' migratory capacity. Concomitantly, we tested the antifibrotic efficacy of AC-EVOO in mesothelial cells obtained from effluents of patients undergoing PD, whose "fibroblast-like" phenotype was defined by flow-cytometry assay. We observed that in these cells AC-EVOO significantly mitigated, but did not reverse, the MMT process. In conclusion, our preliminary results suggest that AC-EVOO can interfere with critical factors in the process of differentiation, preventing myofibroblast formation, but once fibrosis has already progressed it is unable to promote the redifferentiation to the epithelial phenotype. Further studies are needed to establish whether AC-EVOO could represent a new therapeutic target to prevent peritoneal fibrosis.