Peritoneal changes after exposure to sterile solutions by catheter

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

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

Encapsulating Peritoneal Sclerosis: Pathophysiology and Current Treatment Options

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

Protection of the Peritoneal Membrane by Peritoneal Dialysis Effluent-Derived Mesenchymal Stromal Cells in a Rat Model of Chronic Peritoneal Dialysis

Peritoneal dialysis (PD) is a renal replacement option for patients with end-stage renal disease. However, a long-term exposure to hypertonic PD solutions leads to peritoneal membrane (PM) injury, resulting in ultrafiltration (UF) failure. This study was designed to primarily evaluate efficacy of PD effluent-derived mesenchymal stromal cells (pMSCs) in the prevention of PM injury in rats. The pMSCs were isolated from PD effluent. Male Wistar rats received daily intraperitoneal (IP) injection of 10 mL of Dianeal (4.25% dextrose) and were treated with pMSCs (1.2‐1.5 × 10⁶/rat/wk, IP). UF was determined by IP injection of 30 mL of Dianeal (4.25% dextrose) with dwell time of 1.5 h, and PM injury was examined by histology. Apoptosis was quantitated by using flow cytometric analysis, and gene expression by using the PCR array and Western blot. Here, we showed that as compared to naive control, daily IP injection of the Dianeal PD solution for 6 weeks without pMSC treatment significantly reduced UF, which was associated with an increase in both PM thickness and blood vessel, while pMSC treatment prevented the UF loss and reduced PM injury and blood vessels. In vitro incubation with pMSC-conditioned medium prevented cell death in cultured human peritoneal mesothelial cells (HPMCs) and downregulated proinflammatory (i.e., CXCL6, NOS2, IL1RN, CCL5, and NR3C1) while upregulated anti-inflammatory (i.e., CCR1, CCR4, IL9, and IL-10) gene expression in activated THP1 cells. In conclusion, pMSCs prevent bioincompatible PD solution-induced PM injury and UF decline, suggesting that infusing back ex vivo-expanded pMSCs intraperitoneally may have therapeutic potential for reduction of UF failure in PD patients.

Encapsulating peritoneal sclerosis in a patient after allogeneic hematopoietic stem cell transplantation: a case report

BACKGROUND

Encapsulating peritoneal sclerosis (EPS) is a chronic clinical syndrome of acute or subacute gastrointestinal obstruction seen mainly in patients undergoing peritoneal dialysis. Although there are a few reports on EPS developing in non-peritoneal dialysis patients, it has not been reported in patients undergoing allogeneic haematopoietic stem cell transplantation (HSCT). Here, we report a case of EPS after a second HSCT.

CASE PRESENTATION

A 46-year-old man with myelodysplastic syndrome showed relapse after HSCT and received a second HSCT. The patient was diagnosed with chronic graft-versus-host disease (cGVHD)-associated serositis because of persistent ascites. His ascites improved gradually and disappeared without immunosuppressive therapy. He presented with nausea, weight loss, and constipation 1 year after improvement of ascites. Computed tomography revealed no organic obstruction, but did reveal dilated, thickened, and adhered small bowel loops with a mass-like appearance. He was diagnosed with EPS on the basis of clinical symptoms and image findings. He received corticosteroid therapy (20 mg/body) without any improvement in symptoms. He developed recurrence of myelodysplastic syndrome at 1 month after initiation of corticosteroid therapy. This progressed into acute myeloid leukaemia after 3 months. He died 31 months after the second HSCT. At autopsy, the small and large intestines had formed extensive adhesions and showed signs of progressive fibrosis with peritoneal sclerosis, fibroblast swelling, fibrin deposition, and inflammatory cell infiltration, which confirmed the diagnosis of EPS.

CONCLUSION

This case suggests that EPS may complicate patients with cGVHD-associated serositis. Although the mechanism of EPS development is not clear, clinicians should be aware of this eventuality.

Preventing Peritoneal Dialysis-Associated Fibrosis by Therapeutic Blunting of Peritoneal Toll-Like Receptor Activity

Peritoneal dialysis (PD) is an essential daily life-saving treatment for end-stage renal failure. PD therapy is limited by peritoneal inflammation, which leads to peritoneal membrane failure as a result of progressive fibrosis. Peritoneal infections, with the concomitant acute inflammatory response and membrane fibrosis development, worsen PD patient outcomes. Patients who remain infection-free, however, also show evidence of inflammation-induced membrane damage and fibrosis, leading to PD cessation. In this case, uraemia, prolonged exposure to bio-incompatible PD solutions and surgical catheter insertion have been reported to induce sterile peritoneal inflammation and fibrosis as a result of cellular stress or tissue injury. Attempts to reduce inflammation (either infection-induced or sterile) and, thus, minimize fibrosis development in PD have been hampered because the immunological mechanisms underlying this PD-associated pathology remain to be fully defined. Toll-like receptors (TLRs) are central to mediating inflammatory responses by recognizing a wide variety of microorganisms and endogenous components released following cellular stress or generated as a consequence of extracellular matrix degradation during tissue injury. Given the close link between inflammation and fibrosis, recent investigations have evaluated the role that TLRs play in infection-induced and sterile peritoneal fibrosis development during PD. Here, we review the findings and discuss the potential of reducing peritoneal TLR activity by using a TLR inhibitor, soluble TLR2, as a therapeutic strategy to prevent PD-associated peritoneal fibrosis.

Surgical Techniques for Catheter Placement and 5/6 Nephrectomy in Murine Models of Peritoneal Dialysis

Peritoneal dialysis (PD) is a renal replacement therapy consistent on the administration and posterior recovery of a hyperosmotic fluid in the peritoneal cavity to drain water and toxic metabolites that functionally-insufficient kidneys are not able to eliminate. Unfortunately, this procedure deteriorates the peritoneum. Tissue damage triggers the onset of inflammation to heal the injury. If the injury persists and inflammation becomes chronic, it may lead to fibrosis, which is a common occurrence in many diseases. In PD, chronic inflammation and fibrosis, along with other specific processes related to these ones, lead to ultrafiltration capacity deterioration, which means the failure and subsequent cessation of the technique. Working with human samples provides information about this deterioration but presents technical and ethical limitations to obtain biopsies. Animal models are essential to study this deterioration since they overcome these shortcomings. A chronic mouse infusion model was developed in 2008, which benefits from the wide range of genetically modified mice, opening up the possibility of studying the mechanisms involved. This model employs a customized device designed for mice, consisting of a catheter attached to an access port that is placed subcutaneously at the back of the animal. This procedure avoids continuous puncture of the peritoneum during long-term experiments, reducing infections and inflammation due to injections. Thanks to this model, peritoneal damage induced by chronic PD fluid exposure has been characterized and modulated. This technique allows the infusion of large volumes of fluids and could be used for the study of other diseases in which inoculation of drugs or other substances over extended periods of time is necessary. This article shows the method for the surgical placement of the catheter in mice. Moreover, it explains the procedure for a 5/6 nephrectomy to mimic the state of renal insufficiency present in PD patients.

Targeting Toll-like receptors with soluble Toll-like receptor 2 prevents peritoneal dialysis solution-induced fibrosis

Peritoneal membrane failure due to fibrosis limits the use of peritoneal dialysis (PD). Peritoneal fibrosis may potentially be induced by sterile inflammation caused by ongoing cellular stress due to prolonged exposure to PD solutions (PDS). Effective therapies to prevent this process remain to be developed. Toll-like receptors (TLRs) mediate sterile inflammation by recognizing damage-associated molecular patterns (DAMPs) released by cellular stress. We evaluated the involvement of TLRs and DAMPs in PDS-induced fibrosis models and the therapeutic potential of TLR-DAMP targeting for preventing fibrosis. A range of PDS elicited pro-inflammatory and fibrotic responses from PD patient peritoneal leukocytes, mesothelial cells and mouse peritoneal leukocytes. TLR2/4 blockade of human peritoneal cells or TLR2/4 knockouts inhibited these effects. PDS did not induce rapid ERK phosphorylation or IκB-α degradation, suggesting that they do not contain components capable of direct TLR activation. However, PDS increased the release of Hsp70 and hyaluronan, both TLR2/4 DAMP ligands, by human and mouse peritoneal cells, and their blockade decreased PDS-driven inflammation. Soluble TLR2, a TLR inhibitor, reduced PDS-induced pro-inflammatory and fibrotic cytokine release ex vivo. Daily catheter infusion of PDS in mice caused peritoneal fibrosis, but co-administration of soluble TLR2 prevented fibrosis, suppressed pro-fibrotic gene expression and pro-inflammatory cytokine production, reduced leukocyte/neutrophil recruitment, recovered Treg cell levels and increased the Treg:Th17 ratio. Thus, TLR2/4, Hsp70 and hyaluronan showed major roles in PDS-induced peritoneal inflammation and fibrosis. The study demonstrates the therapeutic potential of a TLR-DAMP targeting strategy to prevent PDS-induced fibrosis.

Use of the embedded peritoneal dialysis catheter

Introduction The use of embedded peritoneal dialysis (PD) catheters is purported to offer numerous benefits over standard placement. However, the optimum period of embedment and the effect of prolonged embedment on subsequent catheter function remain unclear. Methods This retrospective observational study looked at adult patients undergoing embedded PD catheter insertion in a large tertiary referral centre in the UK. Possible predictors for catheter non-function at externalisation were investigated. These included patient factors (age, sex, diabetic status, body mass index, ethnicity, smoking status, previous surgery, estimated glomerular filtration rate), procedural factors (modality of surgery, concurrent surgical procedure), duration of catheter embedment and catheter damage at externalisation. Outcomes examined were proportion of catheters functioning after externalisation, futile placement rate, surgical reintervention rate, infectious complication rate and proportion of externalised catheters lost owing to malfunction. Results Sixty-six catheters were embedded and two-thirds (n=47, 63.6%) were externalised after a median embedment period of 39.4 weeks. Of these, 25 (53.2%) functioned on externalisation. Fourteen (63.6%) of the 22 non-functioning catheters were salvaged. The overall utilisation of PD was 34/47 (72.3%) and the futile placement rate was 12.1%. Over half of the externalised catheters (n=27, 57.4%) were lost directly as a result of catheter related complications, with a median survival time of 39.4 weeks. In adjusted analysis, increasing embedment duration was significantly predictive of catheter non-function at externalisation (adjusted odds ratio: 0.957, 95% confidence interval [CI]: 0.929-0.985, p=0.003) while subsequent catheter loss was highly dependent on catheter function at externalisation (hazard ratio: 0.258, 95% CI: 0.112-0.594, p=0.001). Conclusions Prolonged embedment of PD catheters is associated with a significantly higher likelihood of catheter dysfunction following externalisation, which is in turn associated with subsequent catheter loss. We have discontinued the use of this technique in our unit.

Establishment of colonic dialysis model in uremic rats by right nephrectomy and left partial nephrectomy

BACKGROUND

Conventional treatments for patients suffering with end-stage renal disease (ESRD) has several disadvantages, highlighting the importance of other reproducible modalities such as colonic dialysis (CD).

OBJECTIVES

The aim was to establish a CD model in uremic rats and evaluate the effect of two different peritoneal dialysis (PD) solutions.

METHODS

Thirty-two male Wistar rats were randomly divided into four groups. After right nephrectomy and left partial nephrectomy, a Malone antegrade continence enema (MACE) stoma was created. Seven days after the procedure, blood sampling was performed. In group I (N = 8) no postoperative intervention was performed. In group II (N = 8), CD was started through the MACE stoma by a low osmolar PD solution. Rats of group III (N = 8) underwent the same procedure with a high osmolar PD solution. Rats of group IV (N = 8) underwent CD without nephrectomy in order to evaluate the feasibility of this technique. Mannitol and activated charcoal were also added to both PD solutions. Weekly blood sampling was performed in order to evaluate the plasma creatinine and blood urea nitrogen (BUN) level.

RESULTS

In rats of the control group, the respective mean ± SD creatinine level was 1.5 ± 0.04 mg/dL, 7 days after the surgical procedure, but a lower creatinine level was found in groups II and III (0.8 ± 0.02 and 0.5 ± 0.03, respectively). Despite the fact that the creatinine level was in steady low states after regular CD in group II (1 ± 0.05) and group III (0.6 ± 0.02), it remained at higher levels in the control group (1.7 ± 0.08) 2 weeks postoperatively. Rats of group I did not survive until the third postoperative week, while the creatinine level was still lower in group III than in group II (0.6 ± 0.02 vs. 1.1 ± 0.03). Similar results were obtained for the BUN level at these timepoints. The mean ± SD survival period was 11 ± 2, 20 ± 3, and 33 ± 2 days in the animals of groups I, II, and III, respectively.

DISCUSSION

To the best of our knowledge, this is the first study of CD establishment in a rat model. Unfortunately, the amount of protein loss, elevation of blood glucose levels, and electrolyte disturbance were not evaluated in the current study because of the limited amount of blood samples. Disturbance of these factors might be a cause of mortality in experimental groups undergoing CD while a significant decrease in BUN and creatinine levels was obtained.

CONCLUSION

CD with an efficient PD solution through a MACE stoma may be a valuable option when conventional methods are not available.

Inflammation and Peritoneal Dialysis

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

TRPA1 Mechanoreceptors Mediate the IL-6 Response to a Single PD Dwell in the Rat

BACKGROUND

The development of modern, biocompatible peritoneal dialysis (PD) fluids has not entirely eliminated the local pro-inflammatory effects of PD fluid administration. The present study was performed in order to establish the importance of known signaling pathways connected to mechano-, osmo- and chemo-sensors of the transient receptor potential (TRP) family for the acute inflammatory response to PD.

METHODS

Rats were exposed to a single 4-hour dwell of lactate-buffered, 2.5% glucose, filter-sterilized PD fluid through an implanted PD catheter. In some groups, the PD dwell was preceded by intravenous administration of blockers of TRPV1 (BCTC), TRPA1 (HC030031), or neurokinin 1 (NK1) (Spantide II) receptors. Cytokine messenger ribonucleic acid (mRNA) expressions were quantified in tissue biopsies (real-time polymerase chain reaction [qPCR]), and cytokine concentrations were quantified in dialysate samples by enzyme-linked immunosorbent assay (ELISA). Tissue expressions of TRPV1, TRPA1, and NK1 were evaluated immuno-histochemically.

RESULTS

The PD dwell induced peritoneal synthesis of Il1b, Tnf, and Il6 and a secretion of interleukin-6 (IL-6) into the dialysate. The catheter implantation already induced the transcription of Il1b and Tnf but did not significantly affect Il6 transcription. The Il6 response to the PD dwell could be virtually eliminated by blocking TRPA1 but was not affected by TRPV1 blockade. Blocking the substance P receptor, NK1, produced an insignificant trend towards Il6 inhibition. TRPA1 and NK1 showed a stronger immuno-reactivity than TRPV1 on cells of the peritoneal tissue.

CONCLUSION

The results show that IL-6 synthesis and secretion were connected to acute PD fluid exposure, and this response was triggered by TRPA1 receptors, possibly located to non-neuronal cells.

Alteration of membrane complement regulators is associated with transporter status in patients on peritoneal dialysis

Introduction

A growing body of evidence from animal models and cell culture studies indicate an important role of a local regulatory complement system (CS) in peritoneal injury during peritoneal dialysis (PD). We investigated the expression of the local regulatory CS (reflected by CD46,CD55,CD59) in the peritoneal tissue of patients with different membrane function characteristics.

Patients and methods

Biopsies from the parietal peritoneum were taken from 24 patients on PD, 22 uremic patients prior to PD. PD patients were grouped according to the dialysate-to-plasma ratio of creatinine (D/P Cre) and ratio of dialysate glucose at 4 hours versus dialysate glucose at time zero (D/D0 glucose) into low or low-average peritoneal transport status (L/LA) and high-average or high-transport status (HA/H) groups. CD46, CD55, and CD59 RNA expression were analyzed by real-time polymerase chain reaction (RT-PCR). Further localization of membrane complement regulators (CRegs) and semiquantitatively analysis was done by immunohistochemistry (IHC).

Results

CD46 and CD59 expression were similar in all groups. CD55 expression was significantly decreased in the HA/H group compared to the L/LA group and to uremic controls (p < 0.05 and p = 0.05, respectively). No statistically significant differences in CD46, CD55, and CD55 expression were detected when considering the history of peritonitis. There was no statistically significant correlation between PD duration and the expressions of CD46, CD55, and CD59. IHC revealed strong CD46, CD55, and CD59 expression in mesothelial cells. CD55 and CD59 were additionally detected in the vasculature. Using IHC, CD46 was lower in PD patients compared to uremic controls (p>0.05), but there was no difference between the L/LA compared to the H/HA group. Moreover IHC confirmed decreased expression of CD55 in the HA/H group compared to the L/LA group and uremic controls (p<0.0001 and p = 0.0001, respectively).

Conclusion

CD55 expression is decreased in patients with fast transporter membrane function, whereas peritonitis and PD duration do not appear to alter CReg expression.

TNF Signaling in Peritoneal Mesothelial Cells: Pivotal Role of cFLIPL

♦ BACKGROUND: Peritoneal dialysis (PD) coincides with high concentrations of proinflammatory cytokines, such as tumor necrosis factor (TNF), in the peritoneal cavity. During treatment, chronic inflammatory processes lead to damage of the peritoneal membrane and a subsequent ultrafiltration failure. Human peritoneal mesothelial cells (HPMCs) play a central role as mediators and targets of PD-related inflammatory changes. Although TNF Receptor 1 (TNFR1) is expressed in high numbers on the cells, TNF-induced apoptosis is inhibited. Here, the underlying molecular mechanisms of TNFR1 signaling in HPMCs are investigated. ♦ METHODS: Human peritoneal mesothelial cells were isolated from the omentum of healthy donors and the dialysis solution of PD patients. Flow cytometry was applied to determine cell surface expression of TNFR1 on HPMCS from healthy donors in absence or presence of TNF or PD fluid (PDF) and were compared to TNFR1 expression on cells from PD patients. To investigate TNFR1-mediated signaling, HPMCs were treated with PDF or TNF, and expression patterns of proteins involved in the TNFR1 signaling pathway were assessed by western blot. ♦ RESULTS: Incubation with PDF led to a significant up-regulation of TNFR1 on the cell surface correlating with elevated TNFR1 numbers on HPMCs from PD patients. Investigations of underlying molecular mechanisms of TNFR1 signaling showed that PDF affects TNFR1 signaling at the proapoptotic signaling pathway by upregulation of IκBα and downregulation of cFLIP_L. In contrast, TNF exclusively induces the activation of NFκB by an increase of phosphorylated IκBα. ♦ CONCLUSIONS: Novel and relevant insights into the mechanisms of TNFR1-mediated signaling in HPMCs with an impact on our understanding of PD-associated damage of the peritoneal membrane are shown.

Rapamycin inhibits epithelial-to-mesenchymal transition of peritoneal mesothelium cells through regulation of Rho GTPases

Epithelial-mesenchymal transition (EMT) of peritoneal mesothelial cells (PMCs) is a key process of peritoneal fibrosis. Rapamycin has been previously shown to inhibit EMT of PMCs and prevent peritoneal fibrosis. In this study, we investigated the undefined molecular mechanisms by which rapamycin inhibits EMT of PMCs. To define the protective effect of rapamycin, we initially used a rat PD model which was daily infused with 20 mL of 4.25% high glucose (HG) dialysis solution for 6 weeks to induce fibrosis. The HG rats showed decreased ultrafiltration volume and obvious fibroproliferative response, with markedly increased peritoneal thickness and higher expression of α-smooth muscle actin (α-SMA) and transforming growth factor-β1. Rapamycin significantly ameliorated those pathological changes. Next, we treated rat PMCs with HG to induce EMT and/or rapamycin for indicated time. Rapamycin significantly inhibited HG-induced EMT, which manifests as increased expression of α-SMA, fibronectin, and collagen I, decreased expression of E-cadherin, and increased mobility. HG increased the phosphorylation of PI3K, Akt, and mTOR. Importantly, rapamycin inhibits the RhoA, Rac1, and Cdc42 activated by HG. Moreover, rapamycin repaired the pattern of F-actin distribution induced by HG, reducing the formation of stress fiber, focal adhesion, lamellipodia, and filopodia. Thus, rapamycin shows an obvious protective effect on HG-induced EMT, by inhibiting the activation of Rho GTPases (RhoA, Rac1, and Cdc42).

New Insights into the Effects of Chronic Kidney Failure and Dialysate Exposure on the Peritoneum

♦ INTRODUCTION: Chronic uremia and the exposure to dialysis solutions during peritoneal dialysis (PD) induce peritoneal alterations. Using a long-term peritoneal exposure model, we compared the effects of chronic kidney failure (CKD) itself and exposure to either a 'conventional' or a 'biocompatible' dialysis solution on peritoneal morphology and function. ♦ METHODS: Wistar rats (Harlan, Zeist, the Netherlands) were grouped into: normal kidney function (NKF), CKD induced by 70% nephrectomy, CKD receiving daily peritoneal infusions with 3.86% glucose Dianeal (CKDD), or Physioneal (both solutions from Baxter Healthcare, Castlebar, Ireland) (CKDP). At 16 weeks, a peritoneal function test was performed, and histology, ultrastructure, and hydroxyproline content of peritoneal tissue were assessed. ♦ RESULTS: Comparing CKD with NKF, peritoneal transport rates were higher, mesothelial cells (MC) displayed increased number of microvilli, blood and lymph vasculature expanded, vascular basal lamina appeared thicker, with limited areas of duplication, and fibrosis had developed. All alterations, except lymphangiogenesis, were enhanced by exposure to both dialysis fluids. Distinct MC alterations were observed in CKDD and CKDP, the latter displaying prominent basolateral protrusions. In addition, CKDP was associated with a trend towards less fibrosis compared to CKDD. ♦ CONCLUSIONS: Chronic kidney failure itself induced peritoneal alterations, which were in part augmented by exposure to glucose-based dialysis solutions. Overall, the conventional and biocompatible solutions had similar long-term effects on the peritoneum. Importantly, the latter may attenuate the development of fibrosis.

Peritoneal Dialysis Catheter Increases Leukocyte Recruitment in the Mouse Parietal Peritoneum Microcirculation and Causes Fibrosis

♦

BACKGROUND

The objective of this study was to examine the effects of a conventional dialysis solution and peritoneal catheter on leukocyte-endothelial cell interactions in the microcirculation of the parietal peritoneum in a subacute peritoneal dialysis (PD) mouse model. ♦

METHODS

An intraperitoneal (IP) catheter with a subcutaneous injection port was implanted into mice and, after a 2-week healing period, the animals were injected daily for 6 weeks with a 2.5% dextrose solution. Intravital microscopy (IVM) of the parietal peritoneum microcirculation was performed 4 hours after the last injection of the dialysis solution. Leukocyte-endothelial cell interactions were quantified and compared with catheterized controls without dialysis treatment and naïve mice. ♦

RESULTS

The number of rolling and extravascular leukocytes along with peritoneal fibrosis and neovascularization were significantly increased in the catheterized animals compared with naïve mice but did not significantly differ between the 2 groups of catheterized animals with sham injections or dialysis solution treatment. ♦

CONCLUSION

The peritoneal catheter implant increased leukocyte rolling and extravasation, peritoneal fibrosis and vascularization in the parietal peritoneum independently from the dialysis solution treatment.

Encapsulating peritoneal sclerosis-a rare but devastating peritoneal disease

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

Membrane nanotubes between peritoneal mesothelial cells: functional connectivity and crucial participation during inflammatory reactions

Peritoneal dialysis (PD) has attained increased relevance as continuous renal replacement therapy over the past years. During this treatment, the peritoneum functions as dialysis membrane to eliminate diffusible waste products from the blood-stream. Success and efficacy of this treatment is dependent on the integrity of the peritoneal membrane. Chronic inflammatory conditions within the peritoneal cavity coincide with elevated levels of proinflammatory cytokines leading to the impairment of tissue integrity. High glucose concentrations and glucose metabolites in PD solutions contribute to structural and functional reorganization processes of the peritoneal membrane during long-term PD. The subsequent loss of ultrafiltration is causal for the treatment failure over time. It was shown that peritoneal mesothelial cells are functionally connected via Nanotubes (NTs) and that a correlation of NT-occurrence and defined pathophysiological conditions exists. Additionally, an important participation of NTs during inflammatory reactions was shown. Here, we will summarize recent developments of NT-related research and provide new insights into NT-mediated cellular interactions under physiological as well as pathophysiological conditions.

Syndecan-1 in the mouse parietal peritoneum microcirculation in inflammation

Background

The heparan sulfate proteoglycan syndecan-1 (CD138) was shown to regulate inflammatory responses by binding chemokines and cytokines and interacting with adhesion molecules, thereby modulating leukocyte trafficking to tissues. The objectives of this study were to examine the expression of syndecan-1 and its role in leukocyte recruitment and chemokine presentation in the microcirculation underlying the parietal peritoneum.

Methods

Wild-type BALB/c and syndecan-1 null mice were stimulated with an intraperitoneal injection of Staphylococcus aureus LTA, Escherichia coli LPS or TNFα and the microcirculation of the parietal peritoneum was examined by intravital microscopy after 4 hours. Fluorescence confocal microscopy was used to examine syndecan-1 expression in the peritoneal microcirculation using fluorescent antibodies. Blocking antibodies to adhesion molecules were used to examine the role of these molecules in leukocyte-endothelial cell interactions in response to LTA. To determine whether syndecan-1 co-localizes with chemokines in vivo, fluorescent antibodies to syndecan-1 were co-injected intravenously with anti-MIP-2 (CXCL2), anti-KC (CXCL1) or anti-MCP-1 (CCL2).

Results and Conclusion

Syndecan-1 was localized to the subendothelial region of peritoneal venules and the mesothelial layer. Leukocyte rolling was significantly decreased with LPS treatment while LTA and TNFα significantly increased leukocyte adhesion compared with saline control. Leukocyte-endothelial cell interactions were not different in syndecan-1 null mice. Antibody blockade of β₂ integrin (CD18), ICAM-1 (CD54) and VCAM-1 (CD106) did not decrease leukocyte adhesion in response to LTA challenge while blockade of P-selectin (CD62P) abrogated leukocyte rolling. Lastly, MIP-2 expression in the peritoneal venules was not dependent on syndecan-1 in vivo. Our data suggest that syndecan-1 is expressed in the parietal peritoneum microvasculature but does not regulate leukocyte recruitment and is not necessary for the presentation of the chemokine MIP-2 in this tissue.

Janus kinase signaling activation mediates peritoneal inflammation and injury in vitro and in vivo in response to dialysate

Peritoneal membrane pathology limits long-term peritoneal dialysis (PD). Here, we tested whether JAK/STAT signaling is implicated and if its attenuation might be salutary. In cultured mesothelial cells, PD fluid activated, and the pan-JAK inhibitor P6 reduced, phospho-STAT1 and phospho-STAT3, periostin secretion, and cleaved caspase-3. Ex vivo, JAK was phosphorylated in PD effluent cells from long-term but not new PD patients. MCP-1 and periostin were increased in PD effluent in long term compared with new patients. In rats, twice daily, PD fluid infusion induced phospho-JAK, mesothelial cell hyperplasia, inflammation, fibrosis, and hypervascularity after 10 days of exposure to PD fluid. Concomitant instillation of a JAK1/2 inhibitor virtually completely attenuated these changes. Thus, our studies directly implicate JAK/STAT signaling in the mediation of peritoneal membrane pathology as a consequence of PD.

Clinical causes of inflammation in peritoneal dialysis patients

Inflammation at both systemic and local intraperitoneal levels commonly affects peritoneal dialysis (PD) patients. Interest in inflammatory markers as targets of therapeutic intervention has been considerable as they are recognised as predictors of poor clinical outcomes. However, prior to embarking on strategies to reduce inflammatory burden, it is of paramount importance to define the underlying processes that drive the chronic active inflammatory status. The present review aims to comprehensively describe clinical causes of inflammation in PD patients to which potential future strategies may be targeted.

Isolation of interstitial fluid and demonstration of local proinflammatory cytokine production and increased absorptive gradient in chronic peritoneal dialysis

In peritoneal dialysis (PD) patients, the frequent exposure to "unphysiological" dialysis fluids elicits a chronic state of a low-grade peritoneal inflammation leading to interstitial matrix remodeling and angiogenesis. Proinflammatory cytokines are important regulators involved in this inflammatory process that ultimately leads to dysfunction of the peritoneum as a dialysis membrane. We aimed to measure the local concentrations of proinflammatory cytokines in the peritoneal interstitial fluid (IF). Furthermore, we wanted to assess how the driving forces for fluid and solute exchanges are affected in a remodeled interstitial matrix and thus measured the colloid osmotic pressure (COP) gradient in rats that were exposed to chronic PD. After 8 wk of peritoneal dialysis, IF from peritoneum was isolated using a centrifugation method, and was analyzed for cytokine content and COP along with plasma. For several of the proinflammatory cytokines there were gradients from IF to plasma, showing local production. For some cytokines, the concentration in IF was increased severalfold, whereas IL-18 was increased systemically due to PD. Furthermore, the presence of the catheter per se seemed to increase cytokine levels. COP in IF was significantly decreased in the PD group, while collagen and hyaluronan content was increased. Collectively, our data suggest that the increased levels of proinflammatory cytokines after PD may be an integral component of the development of fibrosis and angiogenesis commonly seen in PD patients, and the decreased COP in IF after chronic PD may shift the Starling equilibrium across peritoneal capillaries to an absorptive state.

Ultrafiltration characteristics of glucose polymers with low polydispersity

BACKGROUND

Icodextrin, a glucose polymer with a polydispersity [ratio of weight-average molecular weight (Mw) to number-average molecular weight] of approximately 2.6, has been shown, compared with glucose, to provide superior ultrafiltration (UF) efficiency [ratio of UF to carbohydrate (CHO) absorbed] when used as an osmotic agent during a long-dwell peritoneal dialysis exchange. In an experimental rabbit model, we evaluated the effect of Mw on the UF and UF efficiency of glucose polymers with low polydispersity.

METHODS

A crossover trial in female New Zealand White rabbits (2.20 - 2.65 kg) with surgically implanted peritoneal catheters evaluated two glucose polymers at nominal concentrations of 7.5 g/dL: a 6K polymer (Mw: 6.4 kDa; polydispersity: 2.3) and a 19K polymer (Mw: 18.8 kDa; polydispersity: 2.0). Rabbits were randomized to receive either the 6K (n = 11) or the 19K (n = 12) solution during the first exchange (40 mL/kg body weight). The alternative solution was evaluated in a second exchange 3 days later. During each 4-hour dwell, the UF and total glucose polymer CHO absorbed were determined.

RESULTS

The UF was higher for the 6K (p < 0.0001) than for the 19K polymer (mean ± standard deviation: 73.6 ± 30.8 mL vs. 43.0 ± 20.2 mL), as was the amount of CHO absorbed (42.5% ± 9.8% vs. 35.7% ± 11.0%, p = 0.021). In spite of higher CHO absorption, an approximately 50% higher (p = 0.029) UF efficiency was achieved with the 6K polymer (28.3 ± 18.8 mL/g) than with the 19K polymer (19.0 ± 11.3 mL/g). The results were independent of the order of the experimental exchanges.

CONCLUSIONS

Glucose polymers with low polydispersity are effective osmotic agents in a rabbit model. The low-Mw polymer was more effective at generating UF and had a higher UF efficiency, but those results came at the expense of the polymer being more readily absorbed from the peritoneal cavity.

Protecting the peritoneal membrane: factors beyond peritoneal dialysis solutions

Functional deterioration of the peritoneal membrane in patients on peritoneal dialysis has been described as being the result of a combination of neoangiogenesis and fibrosis. Glucose, glucose degradation products, and the unphysiological pH of the dialysate solution contribute to these changes. Although newer solutions clearly perform better in terms of their biocompatibility in an in vitro setting and in animal models, the benefit of such solutions over older solutions in the clinical setting is so far unproven. The difficulties in showing a benefit of the newer, more biocompatible solutions in the clinical setting can be explained by the fact that other factors also affect the properties of the peritoneal membrane. These factors are often neglected in clinical studies, which results in unnoticed differences in case-mix and blurs the potential impact of the novel solutions. However, many of these factors are modifiable, and attention should be paid to them in clinical practice to maintain the integrity of the peritoneal membrane. This Review focuses on factors that potentially influence the integrity of the peritoneal membrane, other than those associated with the peritoneal dialysis fluid itself.

Inflammation and the peritoneal membrane: causes and impact on structure and function during peritoneal dialysis

Peritoneal dialysis therapy has increased in popularity since the end of the 1970s. This method provides a patient survival rate equivalent to hemodialysis and better preservation of residual renal function. However, technique failure by peritonitis, and ultrafiltration failure, which is a multifactorial complication that can affect up to 40% of patients after 3 years of therapy. Encapsulant peritoneal sclerosis is an extreme and potentially fatal manifestation. Causes of inflammation in peritoneal dialysis range from traditional factors to those related to chronic kidney disease per se, as well as from the peritoneal dialysis treatment, including the peritoneal dialysis catheter, dialysis solution, and infectious peritonitis. Peritoneal inflammation generated causes significant structural alterations including: thickening and cubic transformation of mesothelial cells, fibrin deposition, fibrous capsule formation, perivascular bleeding, and interstitial fibrosis. Structural alterations of the peritoneal membrane described above result in clinical and functional changes. One of these clinical manifestations is ultrafiltration failure and can occur in up to 30% of patients on PD after five years of treatment. An understanding of the mechanisms involved in peritoneal inflammation is fundamental to improve patient survival and provide a better quality of life.

Nanotube action between human mesothelial cells reveals novel aspects of inflammatory responses

A well-known role of human peritoneal mesothelial cells (HPMCs), the resident cells of the peritoneal cavity, is the generation of an immune response during peritonitis by activation of T-cells via antigen presentation. Recent findings have shown that intercellular nanotubes (NTs) mediate functional connectivity between various cell types including immune cells - such as T-cells, natural killer (NK) cells or macrophages - by facilitating a spectrum of long range cell-cell interactions. Although of medical interest, the relevance of NT-related findings for human medical conditions and treatment, e.g. in relation to inflammatory processes, remains elusive, particularly due to a lack of appropriate in vivo data. Here, we show for the first time that primary cultures of patient derived HPMCs are functionally connected via membranous nanotubes. NT formation appears to be actin cytoskeleton dependent, mediated by the action of filopodia. Importantly, significant variances in NT numbers between different donors as a consequence of pathophysiological alterations were observable. Furthermore, we show that TNF-α induces nanotube formation and demonstrate a strong correlation of NT connectivity in accordance with the cellular cholesterol level and distribution, pointing to a complex involvement of NTs in inflammatory processes with potential impact for clinical treatment.

Are ex vivo mesothelial cells representative of the in vivo transition from epithelial-to-mesenchymal cells in peritoneal membrane?

BACKGROUND

We investigated whether ex vivo mesothelial cells found in peritoneal dialysis (PD) effluents were representative of the in vivo epithelial-to-mesenchymal transition (EMT) in peritoneal membrane.

METHODS

Thirty-six male Sprague-Dawley rats were equally divided into three groups: Group C (control), no PD; Group D, infused with 4.25% Dianeal and Group P, infused with 4.25% Physioneal. PD infusions (25 mL) were given twice daily for 8 weeks. The in vivo study included morphometric analyses performed on the peritoneal membranes of tissue specimens obtained at the end of the study. The ex vivo study included peritoneal mesothelial cells collected from PD effluent and cultured to confluence. Cells were scored with light microscopy.

RESULTS

PD for 8 weeks induced significant EMT. The in vivo expression of EMT markers (α-smooth muscle actin:E-cadherin ratio, matrix metalloproteinase-2 and Snail) was higher in Group D than in Group P. However, ex vivo EMT marker expression was similar in cells derived from Groups D and P. A significant correlation was observed among in vivo EMT markers. Moreover, the ex vivo cell score increased with time on PD. However, changes in the ex vivo cell score did not correlated with changes in the in vivo EMT marker expression. Furthermore, we found no correlation between ex vivo and in vivo cells in the expression of EMT markers.

CONCLUSIONS

In this animal study, ex vivo findings did not reflect the in vivo EMT changes in the peritoneum. It may be necessary to improve the current methodology for ex vivo studies.

Neuropeptide release augments serum albumin loss and reduces ultrafiltration in peritoneal dialysis

BACKGROUND

The triggers of the acute local inflammatory response to peritoneal dialysis (PD) fluid exposure remain unknown. In the present study, we investigated the effects of neurogenic inflammation and mast cell degranulation on water and solute transport in experimental PD.

METHODS

Single 2-hour dwells in rats with PD catheters were studied. Histamine and the neuropeptides substance P and calcitonin gene-related peptide (CGRP) were measured in PD fluid samples by ELISA. Radiolabeled albumin ((125)I and (131)I respectively) was used as an intraperitoneal (IP) and intravascular tracer. Glucose and urea concentrations were measured in plasma and PD fluid. The effects of varying the volume and osmolarity of a lactate-buffered PD fluid were compared and related to the effects of pharmacologic intervention.

RESULTS

Application of 20 mL 3.9% glucose PD fluid induced an IP histamine release during the first 30 minutes, blockable by the mast cell stabilizer doxantrazole and the substance P neurokinin-1 receptor (NK1R)-blocker spantide. Histamine release was also inhibited at a reduced PD volume (14 mL), but was not affected by normalizing the PD fluid osmolarity. Blockade of NK1R also reduced plasma albumin leakage to the peritoneal cavity. Inhibition of CGRP receptors by CGRP8-37 improved osmotic (transcapillary) and net ultrafiltration and reduced the dialysate urea concentration. Neuropeptide release was not clearly related to activation of the TrpV1 receptor, the classic trigger of neurogenic inflammation.

CONCLUSIONS

Neuropeptide release exaggerated albumin loss and reduced ultrafiltration in this rat PD model. Intervention aimed at the neuropeptide action substantially improved PD efficiency.

Prolonged Duration of Peritoneal Dialysis Catheter Embedment Does not Lower the Catheter Success Rate

Objective

Since 2000, we have used the Moncrief–Popovich technique as our standard method for peritoneal dialysis (PD) catheter insertion. The subcutaneous portion of the catheter is externalized immediately before initiation of PD. We undertook the present review to investigate whether duration of catheter embedment affects catheter or patient outcome.

Methods

All catheters inserted beginning 1 January 2000 and externalized by 31 December 2008 were included. The primary outcome was catheter survival. Secondary outcomes were catheter patency (no fibrin plug or omental wrap) and complications within 90 days after externalization. A standard peritoneal equilibration test was used to classify peritoneal membrane transport status. Proportional hazards regression models were used to test whether duration of embedment affected catheter outcomes. The models treated embedment duration as both a continuous predictor and a categorical predictor categorized by tertile.

Results

A total of 134 catheters were implanted and externalized. Twelve patients received 2 catheters each. To ensure statistical independence of the observations, 12 of the latter 24 catheters were excluded (1 chosen randomly from each patient), resulting in a useable sample size of 122 catheters. The total duration of observation was 2359 patient–months. The median duration of catheter embedment was 40.5 days (range: 2 – 788 days). After controlling for sex, race, age, and diabetes status, embedment duration did not have a significant effect on catheter survival as a continuous predictor or as a categorical predictor. Additionally, the 95% confidence interval for the 30-day effect of embedment duration ruled out a change of more than 20.6% in the hazard of catheter malfunction or infection. Of the studied catheters, 89.3% were patent and functioned properly immediately upon externalization. The remaining 13 catheters (10.7%) lacked patency on externalization because of fibrin plug or kinking ( n = 10) or omental wrap ( n = 3); however, 12 of the 13 non-patent catheters were corrected laparoscopically, and the patients resumed PD. Only 1 patient transferred to hemodialysis. Overall, 121 of 122 buried catheters (99.2%) were used for PD. Other complications within 90 days of catheter externalization included incision site and tunnel infection in 2 cases (1.6%), exit-site leak in 2 cases (1.6%), and coagulase-negative staphylococcal peritonitis in 1 case (0.8%).

Conclusions

Duration of catheter embedment before externalization did not affect catheter survival and did not influence subsequent peritoneal membrane transport status. The overall effect of increasing embedment duration by 30 days is, at most, a 20.6% increase or decrease in the hazard of catheter failure, but the actual hazard may be much smaller or nonexistent. Larger studies are needed to further explore the ideal duration of embedment.

Bioincompatible impact of different peritoneal dialysis fluid components and therapeutic interventions as tested in a rat peritoneal dialysis model

Peritoneal dialysis (PD) is associated with functional and structural changes of the peritoneal membrane. In this paper, we describe the impact of different factors contributing to peritoneal incompatibility of PD fluid installation including presence of a catheter, volume loading, and the PD fluid components itself. These factors initiate recruitment and activation of peritoneal immune cells such as macrophages and mast cells, as well as activation of peritoneal cells as mesothelial cells in situ. We provide an overview of PD-associated changes as seen in our rat PD-exposure model. Since these changes are partly reversible, we finally discuss therapeutic strategies in the rat PD model with possible consequences of long-term PD in the relevant human setting.

Peritoneal morphology after long-term peritoneal dialysis with biocompatible fluid: recent clinical practice in Japan

BACKGROUND

Morphology changes of the peritoneal membrane after long-term peritoneal dialysis (PD) consist of denudation of peritoneal mesothelial cells, interstitial sclerosis, and hyalinizing vasculopathy. Those changes are considered to be the result of uremia and bioincompatible effects of conventional acidic lactate-buffered dialysate with glucose degradation products (GDPs). In the last decade, biocompatible dialysate with neutral pH and low GDPs has become widely used. Clinical practice has been modified in Japan, especially for anuric patients, and now includes the use of hybrid therapy. The impact on peritoneal morphology has not been well reported.

OBJECTIVE

The aim of the present study was to investigate the long-term effect on peritoneal morphology and function of biocompatible fluid use and current clinical practice in Japan, including hybrid dialysis therapy.

METHODS

We evaluated peritoneal biopsy specimens from patients who had undergone PD for more than 3 years. We used the average peritoneal thickness (APT) of the submesothelial compact zone as a marker of interstitial sclerosis and the lumen/vessel diameter ratio (L/V ratio) at postcapillary venules as a marker of hyalinizing vasculopathy. Demography and other data for the patients, including dialysate-to-plasma (D/P) ratio of creatinine, were obtained at baseline and every 6 months by peritoneal equilibration test.

RESULTS

Between 2002 and 2009, 110 patients started PD therapy with biocompatible dialysate at Tokyo University Hospital. Among them, 11 patients (8 men, 3 women; age: 54.2 ± 11.8 years; 1 with diabetes mellitus) were enrolled into this morphology study. The mean duration of PD in this group was 61 ± 11.3 months, and the mean time to peritoneal biopsy was 58 ± 15.1 months. The median APT was 180 μm (96 - 1424 μm), and the median L/V ratio was 0.66 (0.46 - 0.74). No obvious correlations between APT, L/V ratio, and PD duration were detected. The D/P creatinine of the 11 patients was maintained at a favorably low value, comparable with that of the other 99 patients.

CONCLUSIONS

Peritoneal dialysis therapy using biocompatible dialysate in conjunction with modification of clinical practice may minimize the progression of peritoneal interstitial sclerosis and hyalinizing vasculopathy, preserving favorable peritoneal function for more than 3 years.

Benfotiamine protects against peritoneal and kidney damage in peritoneal dialysis

Residual renal function and the integrity of the peritoneal membrane contribute to morbidity and mortality among patients treated with peritoneal dialysis. Glucose and its degradation products likely contribute to the deterioration of the remnant kidney and damage to the peritoneum. Benfotiamine decreases glucose-induced tissue damage, suggesting the potential for benefit in peritoneal dialysis. Here, in a model of peritoneal dialysis in uremic rats, treatment with benfotiamine decreased peritoneal fibrosis, markers of inflammation, and neovascularization, resulting in improved characteristics of peritoneal transport. Furthermore, rats treated with benfotiamine exhibited lower expression of advanced glycation endproducts and their receptor in the peritoneum and the kidney, reduced glomerular and tubulointerstitial damage, and less albuminuria. Increased activity of transketolase in tissue and blood contributed to the protective effects of benfotiamine. In primary human peritoneal mesothelial cells, the addition of benfotiamine led to enhanced transketolase activity and decreased expression of advanced glycation endproducts and their receptor. Taken together, these data suggest that benfotiamine protects the peritoneal membrane and remnant kidney in a rat model of peritoneal dialysis and uremia.

Catheter Patency and Peritoneal Morphology and Function in a Rat Model of Citrate-Buffered Peritoneal Dialysis

Background

Single-dwell studies in rats and humans have shown that supplementing citrate for lactate in peritoneal dialysis (PD) fluids improves ultrafiltration (UF).

Methods

The long-term effects of citrate-substituted PD fluids on PD catheter patency, UF, and peritoneal morphology were evaluated in a rat model over 5 weeks of daily PD fluid exposure. A standard 2.5% glucose 40 mmol/L lactate PD fluid and a corresponding 10/30 mmol/L citrate/lactate PD fluid were compared. In a control group, rats with catheters received no PD fluid.

Results

The average patency time (% of 36 days) of silicone rubber PD catheters was significantly longer in the citrate PD group (98.8% ± 1.2%) and the control group (100% ± 0%) compared to the lactate PD group (54.7% ± 9.5%). In a separate experiment, heparin-coated polyurethane catheters were used to study peritoneal morphology and fluid transport. The citrate group had a higher net UF than the lactate group at the beginning and at the end of the 5 weeks. During the experiment, both fluid-treated groups suffered from UF loss; the control group showed the highest net UF at the end of the 5 weeks. Peritoneal vascular density and submesothelial thickness, indicators of angiogenesis and fibrosis, were not significantly different among the groups. Fibrosis was significantly negatively correlated to osmotic UF.

Conclusion

A positive acute effect of citrate on UF was confirmed and conserved over time. Citrate PD strongly improved PD catheter patency time compared with lactate. Both citrate PD and lactate PD induced negative long-term effects on UF compared with control animals.

A new non-uremic rat model of long-term peritoneal dialysis

Together with the development of peritoneal dialysis (PD), appropriate animal models play an important role in the investigation of physiological, pathophysiological and clinical aspects of PD. However, there is still not an ideal experimental PD animal model. In this study, 45 Sprague-Dawley rats were divided into three groups. Group 1 (n=15) was receiving daily peritoneal injection through the catheter connected to the abdominal cavity, using PD solution containing 3.86 % D-glucose. Group 2 (n=15) was receiving daily peritoneal injection of 0.9 % physiological saline through a catheter. Group 3 (n=15), which was subjected to sham operation, served as controls. Our results showed that WBC counts in peritoneal effluent of Group 1 were slightly higher than those of Group 2 and control group, respectively (p<0.05). However, there was no episode of infection in any group. In addition, there was no significant difference in neutrophils fractions among these three groups. Hematoxylin-eosin and Masson's trichrome staining demonstrated a dramatic increase in thickness of the mesothelium-to-muscle layer of peritoneum exposed to high glucose (Group 1) compared to Group 2 and controls (p<0.01). These data indicated that we established a novel rat model of PD with a modified catheter insertion method. This model is more practical, easy to operate, not too expensive and it will facilitate the investigate of long-term effects of PD.

Mouse model of foreign body reaction that alters the submesothelium and transperitoneal transport

To address the hypothesis that sterile intraperitoneal (ip) catheters alone promote a progressive foreign body reaction (FBR), silicone catheters were surgically implanted in C57BL mice. Controls (CON) underwent sham operations. After 1-5 wk (E1-E5 for catheter-bearing mice), catheters were recovered, and the adherent cell layer (ACL) was separated and cultured to demonstrate sterility. Transperitoneal transport experiments were performed to determine the mass transfer coefficients of mannitol (MTCM) and albumin (MTCA) and the osmotic filtration flux (Josm). After euthanasia, tissue samples were analyzed for submesothelial thickness, angiogenesis, and cytokine immunohistochemistry (IHC). Progressive increases with time were observed in submesothelial thickness (μm: CON, 18.8±12.3; E1, 46.1±20.0; E2, 72.0±17.9; E4, 97.3±20.0; E5, 131.7±10.3; P<0.003), angiogenesis (no. of vessels/mm of peritoneum: CON, 10.7±9.4; E1, 15.4±15.6; E2, 27.0±14.0; E4, 39.8±15.7; E5, 90.1±8.1; P<0.0003), MTCA (6.5±1.5×10(-5) cm/min, mean CON; 18.0±1.1×10(-5) cm/min, mean E1-E5, P<0.0001), Josm (0.0013±0.0001 cm/min, mean CON; 0.0017±0.0001 cm/min, mean E1-E5, P<0.01). No significant differences were found for MTCM. IHC demonstrated strong staining for all treated animals and correlated with the ACL. This mouse model demonstrates that ip silicone catheters result in progressive FBR, altering the submesothelial anatomy and transperitoneal transport, and will form the basis for mechanistic studies in genetically-altered animals.

Strategies for improving long-term survival in peritoneal dialysis patients

The incidence and prevalence of ESRD in the United States continues to increase. Currently there are over 26,000 patients maintained on peritoneal dialysis. Mortality rates have fallen over the past several years, but long-term survival remains poor, with only 11% of peritoneal dialysis patients surviving past 10 years. Cardiovascular disease accounts for most deaths, and dialysis patients have many traditional and nontraditional cardiovascular risk factors. Lowering of these risk factors has not resulted in reduced cardiovascular morbidity and mortality in dialysis patients. Maneuvers to improve long-term peritoneal dialysis patient survival must therefore focus on modifiable risk factors including residual renal function, peritoneal membrane integrity, rate of infections, and peritoneal dialysis center size. This article reviews strategies for preserving residual renal function and peritoneal membrane integrity as well as strategies for reducing the rate of infections to enhance long-term survival in peritoneal dialysis patients.

Peritoneal inflammation after twenty-week exposure to dialysis solution: effect of solution versus catheter-foreign body reaction

BACKGROUND

We hypothesized that both sterile solutions and foreign body reaction to the peritoneal dialysis catheter are associated with inflammatory changes in rats exposed to hypertonic solution.

METHODS

Four hypertonic solutions (30 - 40 mL) were injected daily via needle and syringe over 20 weeks in 4 groups of rats: 4.25% standard clinical solution (LAC), LAC plus pyridoxamine (PYR), LAC plus ethyl pyruvate (EP), and a biocompatible 4% dextrose solution (BIC). Two groups received catheters: a non-injected 4-week catheter group (C4) and a group injected for 20 weeks with the BIC solution (CI). Control animals (CON) were not injected. In the C4 group, adherent cells were separated from the catheter and examined by culture and electron microscopy to ensure that animals were bacteria free prior to exposure to solution. Animals underwent transport experiments to determine mass transfer coefficients of mannitol (MTC(M)) and albumin (MTC(A)), osmotic filtration flux (J(osm)), and hydrostatic pressure-driven flux (J(p)). After euthanasia, tissues were examined for submesothelial thickness, vascular density, and immunohistochemistry for various cytokines.

RESULTS

The catheter cell layer was free of bacteria and consisted of macrophages, lymphocytes, mesothelial cells, and fibroblastic cells. Marked differences in angiogenesis and submesothelial thickening were noted for the catheter groups. Transport differences were mixed: MTC(M) was significantly less for the CI group and MTC(A) was variable among the groups. There were no differences among groups for J(osm) or J(p). Inflammatory markers in the catheter-adherent cells correlated with inflammatory changes in the tissue. These data demonstrate significant changes in submesothelial thickness, angiogenesis, transport function, and inflammatory markers between animals injected with sterile solutions over 20 weeks with and without catheters.

CONCLUSION

An indwelling catheter amplifies peritoneal inflammation from dialysis solutions through a foreign body reaction. Our data also suggest that additives to existing solutions may have limited the effect on inflammatory response to non-biocompatible solutions.

Factors Contributing to Peritoneal Tissue Remodeling in Peritoneal Dialysis

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

Update on Mechanisms of Ultrafiltration Failure

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

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

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

How to Assess Transport in Animals?

The general principles for assessing solute and fluid transport across the peritoneum in animal models are not different from those in human studies. Animal models allow for extensive standardization of experimental conditions and also for sampling of peritoneal tissues for analysis. The present review will focus on ( 1 ) the scaling issue between various species, ( 2 ) how to measure intraperitoneal volume in animal models, ( 3 ) the impact of an indwelling catheter, ( 4 ) the difference between acute and chronic experiments, and ( 5 ) the particular problems associated with transport measurements in mice. If done correctly and after proper scaling, mass transfer area coefficients and clearance measurements show marked similarity among different species. Although animal models only partly mimic human peritoneal dialysis, they are valuable tools for understanding the basic physiology and biology of peritoneal dialysis.

Peritoneal membrane structural and functional changes during peritoneal dialysis

Peritoneal dialysis is now utilized as a renal replacement therapy modality in a substantial percentage of patients with end-stage renal disease, with excellent short-term patient and technique survival rates. However, the potential complications associated with longer-term therapy, such as ultrafiltration failure or encapsulating peritoneal sclerosis, have led to raise some concern about peritoneal dialysis as an adequate mode of treatment of end-stage renal disease in the long term. In the last decade, a substantial amount of information has been gathered on the characteristics of the peritoneal membrane at the onset of peritoneal dialysis, and on the anatomical and pathophysiologic changes that occur with long-term peritoneal dialysis. I will review this subject with a special focus on the various strategies that can help protect the peritoneal membrane during peritoneal dialysis so as to allow peritoneal dialysis to succeed as a long-term dialysis modality.

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

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