Contribution of lactate buffer, glucose and glucose degradation products to peritoneal injury in vivo

Glucose Induces ER Stress Response-Mediated Peritoneal Mesothelial Cell Death

Peritoneal dialysis (PD) fluid, which contains a high concentration of glucose, is involved in peritoneal damage after long-term use. The mechanisms through which glucose induces damage to the mesothelium have not been clearly elucidated. Although, endoplasmic reticulum (ER) stress response is associated with several diseases, the involvement of ER stress in peritoneal damage has not yet been demonstrated. Primary-cultured rat peritoneal mesothelial cells (RPMCs) and rat PD model were used to investigate the influence of glucose on the peritoneum. Cells treated with glucose were examined for cytotoxicity, induction of apoptosis, and activation of the ER stress pathway. Glucose treatment of RPMCs induced cell death at concentrations higher than 3%. Annexin V positive, that is a feature of apoptosis, occurred in dead cells. Treatment with glucose led to the activation of protein kinase R-like ER kinase (PERK) and eukaryotic translation initiation factor-2α (eIF-2α). Glucose also induced the expression and nuclear translocation of homologous protein C/EBP. Cell death was rescued by the integrated stress response inhibitor, ISRIB, which suppresses the integrated stress response pathway, including ER stress. Glucose in PD fluid induces PERK/eIF-2α-mediated ER stress in RPMCs, resulting in apoptosis. This cellular stress may cause peritoneal damage in patients receiving PD.

Vascular endothelial growth factor-mediated peritoneal neoangiogenesis in peritoneal dialysis

Peritoneal dialysis (PD) is an important renal replacement therapy for patients with end-stage renal diseases, which is limited by peritoneal neoangiogenesis leading to ultrafiltration failure (UFF). Vascular endothelial growth factor (VEGF) and its receptors are key angiogenic factors involved in almost every step of peritoneal neoangiogenesis. Impaired mesothelial cells are the major sources of VEGF in the peritoneum. The expression of VEGF will be up-regulated in specific pathological conditions in PD patients, such as with non-biocompatible peritoneal dialysate, uremia and inflammation, and so on. Other working cells (i.e. vascular endothelial cells, macrophages and adipocytes) can also stimulate the secretion of VEGF. Meanwhile, hypoxia and activation of complement system further aggravate peritoneal injury and contribute to neoangiogenesis. There are several signalling pathways participating in VEGF-mediated peritoneal neoangiogenesis including tumour growth factor-β, Wnt/β-catenin, Notch and interleukin-6/signal transducer and activator of transcription 3. Moreover, VEGF is highly expressed in dialysate effluent of long-term PD patients and is associated with peritoneal transport function, which supports its role in the alteration of peritoneal structure and function. In this review, we systematically summarize the angiogenic effect of VEGF and evaluate it as a potential target for the prevention of peritoneal neoangiogenesis and UFF. Preservation of the peritoneal membrane using targeted therapy of VEGF-mediated peritoneal neoangiogenesis may increase the longevity of the PD modality for those who require life-long dialysis.

Animal Models in Peritoneal Dialysis Research: A Need for Consensus

The development of an adequate animal model for peritoneal research remains an object of concern. In vivo peritoneal dialysis (PD) research is hampered by the large variety of available models that make interpretation of results and comparison of studies very difficult. Species and strain of experimental animals, method of peritoneal access, study duration, measures of solute transport and ultrafiltration, and sampling for histology differ substantially among the various research groups. A collective effort to discuss the shortcomings and merits of the different experimental models may lead to a consensus on a standardized animal model of PD.

Omental Milky Spots and Peritoneal Dialysis — Review and Personal Experience

Background

Little research has been dedicated to milky spots (MS), except for their role in oncology. In the field of peritoneal dialysis (PD), studying MS could help in understanding peritoneal defenses.

Methods

We reviewed the methods for detecting and counting omental MS and studied modifications induced by chemical and inflammatory stimuli. The reactions of MS to peritoneal catheters, PD solutions, and infection were studied in 32 rabbits. We also evaluated changes in MS in 39 serial omental biopsies from 16 patients with different histories of PD, and examined peritoneal biopsies from 38 patients with sclerosing peritonitis.

Results

The catheter provoked an immediate increase in the number and size of MS in rabbits. Intraperitoneal infusion of commercial PD solution containing 1.38% or 3.86% glucose for 30 days led to a slight but significant increase in the number and size of MS, without differences between the two glucose concentrations. Peritonitis caused a sharp increase in the number of MS in rabbits and humans, and a particular transformation. In patients with simple sclerosis, we observed normal MS having the same number and size as in patients without simple sclerosis. A few MS were found in only 2 patients with sclerosing peritonitis.

Conclusions

Peritoneal dialysis activates omental MS. Peritoneal infection leads to a marked increase in the activity of MS, some of which undergo a singular transformation, casting doubt on previous theories about differentiation of MS from other lymphatic organs. Comparison with oncological studies indicates certain contact points. The presence of MS in PD patients with simple sclerosis is in contradiction to other morphological studies sustaining that MS act only when in contact with a fenestrated mesothelial basement membrane. Finally, the shortage of MS in patients with sclerosing peritonitis raises certain questions about etiopathogenesis.

Better Preservation of the Peritoneum in Rats Exposed to Amino Acid-Based Peritoneal Dialysis Fluid

Background

Glucose-containing peritoneal dialysis fluids (PDF) show impaired biocompatibility, which is related partly to their high glucose content, presence of glucose degradation products, low pH, and lactate buffer, or a combination of these factors. In a rat chronic peritoneal exposure model, we compared effects of an amino acid-based PDF (AA-PDF) with a glucose-containing PDF on the peritoneal microcirculation and morphology.

Method

Two groups of rats received 10 mL of either fluid daily for 5 weeks via peritoneal catheters connected to implanted subcutaneous mini vascular access ports. Leukocyte–endothelium interactions in the mesenteric venules were investigated by intravital microscopy. Quantification of angiogenesis and fibrosis and inspection of the mesothelial cell layer were performed by light and electron microscopy.

Results

Daily exposure to glucose-containing PDF resulted in a significant increase in the number of rolling leukocytes in mesenteric venules, whereas instillation of AA-PDF did not change the level of leukocyte rolling. Glucose-containing PDF evoked a significantly higher number of milky spots in the omentum, whereas this response was significantly reduced in animals exposed to the AA-PDF ( p < 0.02). Chronic instillation of glucose-containing PDF induced angiogenesis in various peritoneal tissues, accompanied by fibrosis in the mesentery and parietal peritoneum. Quantitative morphometric evaluation of omentum and mesentery showed a clear trend toward less angiogenesis after treatment with the AA-PDF compared to the glucose-containing PDF, which reached statistical significance in the parietal peritoneum ( p < 0.04). Instillation of AA-PDF resulted in approximately 50% reduction of fibrosis in the mesentery ( p < 0.04) and approximately 25% reduction in the parietal peritoneum ( p < 0.009) compared to glucose-containing PDF. Glucose-containing PDF damaged the mesothelial cell layer, whereas the mesothelium was intact after AA-PDF treatment, as evidenced by electron microscopy.

Conclusion

Our data in a rat chronic peritoneal exposure model clearly demonstrate reduced immune activation (evidenced by decreased number of rolling leukocytes and decreased induction of omental milky spots) and reduced neoangiogenesis, fibrosis, and mesothelial damage of the peritoneal membrane after treatment with AA-PDF compared to glucose-containing PDF.

Short-Term Effects of a New Bicarbonate/Lactate-Buffered and Conventional Peritoneal Dialysis Fluid on Peritoneal and Systemic Inflammation in CAPD Patients: A Randomized Controlled Study

Objectives

This study was designed to compare the local peritoneal and systemic inflammatory effects of a conventional lactate-based (Lac) peritoneal dialysis (PD) solution and a new biocompatible bicarbonate/lactate-based (Bic/ Lac) solution having low concentration of glucose degradation products.

Methods

26 stable, prevalent PD patients were enrolled in this prospective study. They sequentially underwent 3 months of therapy with the Lac solution and 3 months with the Bic/Lac solution in a randomized order. Flow cytometry was used to measure the expression of inflammatory molecules on peritoneal cells in overnight effluent collected at the end of each study period.

Results

21 patients successfully completed the study. Mean fluorescence intensity of human leukocyte antigen (HLA)-DR and CD14 expression by macrophages were not different between Lac and Bic/Lac. The peritoneal appearance rate of cancer antigen 125 (kU/minute) was 68 ± 37 with Lac and 133 ± 66 with Bic/Lac ( p < 0.001), and of interleukin (IL)-6 (ng/minute), 0.28 ± 0.2 with Lac and 0.18 ± 0.16 with Bic/Lac ( p = 0.014). HLA-DR macrophage expression and IL-6 peritoneal appearance rates did not correlate. Serum concentrations with Lac and Bic/Lac were, for IL-6, 3.49 ± 2.28 and 3.72 ± 2.46 ng/L ( p = 0.17), and for high-sensitivity C-reactive protein, 2.31 ± 2.98 and 2.71 ± 3.31 mg/L ( p = 0.32) respectively. The concentration of effluent macrophages (x106/L) with Lac was 1.6 ± 1.6 and with Bic/Lac 2.6 ± 3.3 ( p = 0.07).

Conclusions

We conclude that, although there was a significant reduction in peritoneal IL-6 in patients using Bic/ Lac solution, systemic levels of inflammatory markers did not differ between the two solutions and no changes were present in macrophage surface activation markers, suggesting perhaps a less important role of peritoneal macrophages in the intraperitoneal chronic inflammatory process. The number of effluent macrophages tended to be higher in patients using the Bic/Lac solution, possibly contributing to improved intraperitoneal defense.

A Pyruvate-Buffered Dialysis Fluid Induces Less Peritoneal Angiogenesis and Fibrosis than a Conventional Solution

Background

Conventional lactate-buffered peritoneal dialysis (PD) fluids containing glucose and glucose degradation products are believed to contribute to the development of fibrosis and angiogenesis in the dialyzed peritoneum. To reduce potential negative effects of lactate, pyruvate was substituted as a buffer and its effects on peritoneal pathological alterations were studied in a chronic peritoneal exposure model in the rat.

Methods

20 Wistar rats were infused intraperitoneally with pyruvate-buffered ( n = 9) or lactate-buffered PD fluid. After 20 weeks of daily infusion, peritoneal function was assessed. In omental peritoneal tissue, the number of blood vessels was analyzed following alpha-smooth muscle actin staining. The degree of fibrosis was quantitated in Picro Sirius Red-stained sections and by assessment of the hydroxyproline content. Plasma lactate/pyruvate and beta-hydroxybutyrate/acetoacetate (BBA/AA) ratios were determined. Plasma and dialysate vascular endothelial growth factor (VEGF) levels were quantitated by ELISA.

Results

The mass transfer area coefficient of creatinine was higher and the dialysate-to-plasma ratio of sodium was lower in pyruvate-treated animals compared to the lactatetreated group (0.11 vs 0.05 mL/min, p < 0.05, and 78% vs 89%, p < 0.05). The BBA/AA ratio tended to be lower in the pyruvate animals ( p = 0.07). The number of blood vessels was lower in pyruvate-treated animals (16 vs 37 per field, p < 0.001). Total surface area, luminal area, and wall/total area of the vessels were larger in the pyruvate group. The degree of fibrosis was lower in intersegmental and perivascular areas of pyruvate-exposed animals. Effluent VEGF was higher in the pyruvate group.

Conclusions

Replacement of lactate by pyruvate resulted in changes in peritoneal solute transport, accompanied by a reduction in both peritoneal membrane angiogenesis and fibrosis, suggesting potentially novel mechanisms to reduce glucose-driven alterations to the peritoneal membrane in PD patients.

A Short Review of Experimental Peritoneal Sclerosis: From Mice to Men

Peritoneal sclerosis has been induced in rodents in vivo by exposing the membrane to a variety of experimental interventions: asbestos, 0.1% chlorexidine, iron dextran, glucose degradation products, AGE deposits derived from uremia per se, sodium hypochlorite, lypopolysaccharide, low pH, pure water, silica or zymosan. With a few exceptions (pure water, chlorhexidine and low pH), the other substances mentioned operate setting out different degrees of oxidative stress. This short review describes several experimental interventions in rodents, aimed at acute exfoliation or long-term, sustained injury of the mesothelial monolayer performed by means of intraperitoneal injections of different oxidant agents.

Acute exfoliation induced by deoxycholate resulted in a depopulated monolayer coincident with immediate alteration of the peritoneal permeability, evidenced by increased urea D/P ratio, higher glucose absorption rate, elevated albumin losses in the effluent and significant reduction of the ultrafiltration rate.

In the long term (30 days), these manifestations of membrane failure persisted and coincided with substantial peritoneal sclerosis.

Peritoneal sclerosis was also induced by IP injections of 0.125% trypsin and 6.6 mM/L solution of formaldehyde. Using the doughnut rat model of mesothelial regeneration, exposure to 4.25% glucose or 7.5% icodextrin solutions severely hampered repopulation of the monolayer, which was replaced by a thick sheet of fibrous tissue.

It is concluded that peritoneal sclerosis derives mostly from sustained oxidative injury to the peritoneal membrane. Loss of the mesothelial monolayer is the first step in the chain of events leading to this complication.

Strategies for preventing peritoneal fibrosis in peritoneal dialysis patients: new insights based on peritoneal inflammation and angiogenesis

Peritoneal dialysis (PD) is an established form of renal replacement therapy. Long-term PD leads to morphologic and functional changes to the peritoneal membrane (PM), which is defined as peritoneal fibrosis, a known cause of loss of peritoneal ultrafiltration capacity. Inflammation and angiogenesis are key events during the pathogenesis of peritoneal fibrosis. This review discusses the pathophysiology of peritoneal fibrosis and recent research progress on key fibrogenic molecular mechanisms in peritoneal inflammation and angiogenesis, including Toll-like receptor ligand-mediated, NOD-like receptor protein 3/interleukin-1β, vascular endothelial growth factor, and angiopoietin-2/Tie2 signaling pathways. Furthermore, novel strategies targeting peritoneal inflammation and angiogenesis to preserve the PM are discussed in depth.

Identification of Gene Transcripts Implicated in Peritoneal Membrane Alterations

♦ BACKGROUND: Permanent stimulation of the peritoneum during peritoneal dialysis (PD) is likely to result in increased expression of genes encoding proteins involved in inflammation and tissue remodeling. Peritoneal fibrosis and neoangiogenesis may develop. ♦ OBJECTIVE: To assess highly expressed genes potentially in volved in peritoneal alterations during PD treatment using an animal model. ♦ METHODS: A PD catheter was implanted in 36 male Wistar rats after 70% nephrectomy. The rats were divided into 3 groups, exposed to dialysis solution for 8 weeks, and sacrificed 2 weeks later. Group B was exposed to a buffer, group D was exposed to a 3.86% glucose-based dialysis solution, and in group D+H, a second hit of intraperitoneal blood on top of the dialysis solution was given to induce the development of peritoneal sclerosis. Before sacrifice, peritoneal function was assessed. Omental tissue was obtained for analysis of gene expression using RT-qPCR. ♦ RESULTS: Fibrosis scores, vessel counts, and peritoneal function parameters were not different between the groups. Genes involved in the transforming growth factor beta signaling pathway, cell proliferation, angiogenesis, and inflammation were more expressed (p < 0.05) in the D+H group. Almost no differences were found between the control groups. We identified 4 genes that were related to peritoneal transport. ♦ CONCLUSION: Already a mid-term peritoneal exposure, when no microscopical and functional alterations are present, provokes activation of gene pathways of cell proliferation, fibrosis, neoangiogenesis, and inflammation.

A Novel Mouse Model of Peritoneal Dialysis: Combination of Uraemia and Long-Term Exposure to PD Fluid

Different animal models for peritoneal dialysis (PD) have been used in the past decades to develop PD fluids compatible with patient life and to identify markers of peritoneal fibrosis and inflammation. Only few of those studies have taken into account the importance of uraemia-induced alterations at both systemic and peritoneal levels. Moreover, some animal studies which have reported about PD in a uremic setting did not always entirely succeed in terms of uraemia establishment and animal survival. In the present study we induced uraemia in the recently established mouse PD exposure model in order to obtain a more clinically relevant mouse model for kidney patients. This new designed model reflected both the slight thickening of peritoneal membrane induced by uraemia and the significant extracellular matrix deposition due to daily PD fluid instillation. In addition the model offers the opportunity to perform long-term exposure to PD fluids, as it is observed in the clinical setting, and gives the advantage to knock out candidate markers for driving peritoneal inflammatory mechanisms.

Effects of reducing the lactate and glucose content of PD solutions on the peritoneum. Is the future GLAD?

Background. Long-term peritoneal dialysis (PD) may lead to functional and morphologic changes in the peritoneal membrane, probably because of the continuous exposure to conventional dialysis solutions.

Methods. The morphologic changes include neoangiogenesis and fibrosis. The authors of this article developed a long-term peritoneal exposure model in rats, in which the morphological alterations could be induced after daily peritoneal infusion of a 3.86% glucose/lactate-buffered conventional PD solution.

Results and Conclusions. In the present article, a review of the model and of the results obtained with various available and experimental solutions is given. It appeared that high lactate concentrations contributed to the glucose-induced neoangiogenesis by pseudohypoxia. Glucose degradation products were probably more important in the induction of peritoneal fibrosis. The promising results of a combination of amino acids, glycerol and glucose, each in a low concentration, buffered with either pyruvate or bicarbonate/lactate, are presented and discussed. The combination of glycerol, amino acids and dextrose, dissolved in a bicarbonate/lactate buffer (GLAD), may be an option for a new generation of dialysis fluids.

Pharmacologic targets and peritoneal membrane remodeling

Peritoneal dialysis (PD) is associated with functional and structural changes of the peritoneal membrane, also known as peritoneal remodeling. The peritoneal membrane is affected by many endogenous and exogenous factors such as cytokines, PD fluids, and therapeutic interventions. Here, we present an overview of various studies that have investigated pharmacologic interventions aimed at regression of peritoneal damage and prolongation of PD treatment.

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.

Inflammatory factors for hypoalbuminemia in Japanese peritoneal dialysis patients

AIM

Hypoalbuminaemia is a common complication of peritoneal dialysis (PD), and the leakage of albumin through peritoneal membrane may be a principal reason for hypoalbuminaemia. However, the relationship between peritoneal inflammation, peritoneal transport properties and hypoalbuminaemia has not been fully elucidated.

METHODS

A cross-sectional study was performed on 76 Japanese PD patients who had been using a low-glucose PD solution and icodextrin. Systemic inflammatory markers of C-reactive protein (CRP) and serum interleukin-6 (IL-6), peritoneal effluent markers of dialysate IL-6 and CA125, the dialysate-to-plasma ratio of creatinine (D/Pcr) and the dialysate protein concentration were measured and examined for their relationship with hypoalbuminaemia.

RESULTS

There was a significant positive correlation between serum IL-6 and dialysate IL-6, mean dialysate IL-6 being significantly higher than mean serum IL-6, suggesting that intraperitoneal inflammation was a principal origin of systemic inflammation. Both serum and dialysate IL-6 were significantly correlated with serum albumin (r= -0.25, P<0.05 and r=-0.32, P<0.01, respectively). Dialysate IL-6 was significantly correlated with D/Pcr and the dialysate protein concentration, and there was a significantly positive association between D/Pcr and the dialysate protein concentration. Dialysate CA125, which is argued to be a marker of mesothelial cell mass in this study, was positively correlated with D/Pcr and the dialysate protein concentration. The dialysate protein, dialysate IL-6 and dialysate CA125 all increased according to the peritoneal transport rate defined by D/Pcr. A multiple-regression analysis showed that serum albumin was independently associated with the age, D/Pcr and serum IL-6.

CONCLUSION

Hypoalbuminaemia was attributable to both the increased peritoneal permeability and systemic inflammation, and intraperitoneal inflammation might contribute to developing these complications.

Peritoneal dialysis fluid activates calcium signaling and apoptosis in mesothelial cells

A larger diffusion of peritoneal dialysis (PD) is limited by the progressive deterioration of the dialysis membrane structure and function, characterized in vitro and in vivo by mesothelial cell loss and closely related to the use of bioincompatible dialysis solutions. The apoptosis rate of rat and human mesothelial cells incubated in commercial PD fluid (PDF, 4.25 g/dL dextrose) became significant as early as 1 h after PDF addition and reached a plateau at 4-5 h. This pattern was unchanged after exposure to 1.5 g/dL dextrose PDF or freshly prepared PDF, indicating that effects were independent on the dextrose strength and manufacturing procedures but strictly dependent on PDF composition. Molecular studies revealed that PDF exposure inactivated the physiological volume recovery from hypertonic shrinkage, accompanied by an abnormal Ca(2+) signaling: a progressive intracellular Ca(2+) ([Ca(2+)](i)) rise resulting from an increased Ca(2+) entry. PDF also affected cytoskeleton integrity: early dissolution of actin filaments occurred well before the appearance of typical apoptosis features. Lastly, the PDF dependent apoptosis was almost completely prevented by the contemporary Ca(2+) concentration decrease and K(+) addition. This study suggests that the PDF dependent apoptosis arises from the extreme volume perturbations in mesothelial cells, turned out unable to regulate their volume back once exposed to a hyperosmolal medium containing high Ca(2+) levels in the absence of K(+), such PDF.

A peritoneal dialysis regimen low in glucose and glucose degradation products results in increased cancer antigen 125 and peritoneal activation

BACKGROUND

Glucose and glucose degradation products (GDPs) in peritoneal dialysis fluids (PDFs) are both thought to mediate progressive peritoneal worsening.

METHODS

In a multicenter, prospective, randomized crossover study, incident continuous ambulatory peritoneal dialysis patients were treated either with conventional lactate-buffered PDF (sPD regimen) or with a regimen low in glucose and GDPs: Nutrineal×1, Extraneal×1, and Physioneal×2 (NEPP regimen; all solutions: Baxter Healthcare, Utrecht, The Netherlands). After 6 months, patients were switched to the alternative regimen for another 6 months. After 6 weeks of run-in, before the switch, and at the end of the study, 4-hour peritoneal equilibration tests were performed, and overnight effluents were analyzed for cells and biomarkers. Differences between the regimens were assessed by multivariate analysis corrected for time and regimen sequence.

RESULTS

The 45 patients who completed the study were equally distributed over both groups. During NEPP treatment, D(4)/D(0) glucose was lower (p < 0.01) and D/P creatinine was higher (p = 0.04). In NEPP overnight effluent, mesothelial cells (p < 0.0001), cancer antigen 125 (p < 0.0001), hyaluronan (p < 0.0001), leukocytes (p < 0.001), interleukins 6 (p = 0.001) and 8 (p = 0.0001), and vascular endothelial growth factor (VEGF, p < 0.0001) were increased by a factor of 2-3 compared with levels in sPD effluent. The NEPP regimen was associated with higher transport parameters, but that association disappeared after the addition of VEGF to the model. The association between NEPP and higher effluent levels of VEGF could not be attributed to glucose and GDP loads.

CONCLUSIONS

Study results indicate preservation of the mesothelium and increased peritoneal activation during NEPP treatment. Whether the increase in VEGF reflects an increase in mesothelial cell mass or whether it points to another, undesirable mechanism cannot be determined from the present study. Longitudinal studies are needed to finally evaluate the usefulness of the NEPP regimen for further clinical use.

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.

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.

Solutions for peritoneal dialysis in children: recommendations by the European Pediatric Dialysis Working Group

The purpose of this article is to provide recommendations on the choice of peritoneal dialysis (PD) fluids in children by the European Pediatric Dialysis Working Group. The literature on experimental and clinical studies with PD solutions in children and adults was analyzed together with consensus discussions within the group. A grading was performed based on the international KDIGO nomenclature and methods. The lowest glucose concentration possible should be used. Icodextrin may be applied once daily during the long dwell, in particular in children with insufficient ultrafiltration. Infants on PD are at risk of ultrafiltration-associated sodium depletion, while anuric adolescents may have water and salt overload. Hence, the sodium chloride balance needs to be closely monitored. In growing children, the calcium balance should be positive and dialysate calcium adapted according to individual needs. Limited clinical experience with amino acid-based PD fluids in children suggests good tolerability. The anabolic effect, however, is small; adequate enteral nutrition is preferred. CPD fluids with reduced glucose degradation products (GDP) content reduce local and systemic toxicity and should be preferred whenever possible. Correction of metabolic acidosis is superior with pH neutral bicarbonate-based fluids compared with single-chamber, acidic, lactate-based solutions. Prospective comparisons of low GDP solutions with different buffer compositions are still few, and firm recommendations cannot yet be given, except when hepatic lactate metabolism is severely compromised.

Angiogenesis in peritoneal dialysis

Long-term exposure to peritoneal dialysis fluid induces morphological alterations, including angiogenesis, leading to a loss of ultrafiltration (UF) capacity. We discuss the effect of different factors in peritoneal dialysis (PD) on angiogenesis. In addition, we describe the process of angiogenesis and the possible role of different cell types in the peritoneum upon PD contributing to new blood vessel formation. Furthermore, we review several interventions used in our rat PD exposure model to decrease angiogenesis in PD. Moreover, we show new data on the use of sunitinib to inhibit angiogenesis in this rat model. Although various interventions seem to be promising, well-randomised clinical trials showing absolute prevention of angiogenesis and UF failure are, yet, still missing. To make real progress in PD treatment, the aim should be to prevent angiogenesis as well as peritoneal fibrosis and PD-induced inflammation.

Peritoneal dialysis fluid bioincompatibility and new vessel formation promote leukocyte-endothelium interactions in a chronic rat model for peritoneal dialysis

Peritoneal dialysis (PD)-induced peritonitis leads to dysfunction of the peritoneal membrane. During peritonitis, neutrophils are recruited to the inflammation site by rolling along the endothelium, adhesion, and transmigration through vessel walls. In a rat PD-model, long-term effects of PD-fluids (PDF) on leukocyte-endothelium interactions and neutrophil migration were studied under baseline and inflammatory conditions. Rats received daily conventional-lactate-buffered PDF (Dianeal), bicarbonate/lactate-buffered PDF (Physioneal) or bicarbonate/lactate buffer (Buffer) during five weeks. Untreated rats served as control. Baseline leukocyte rolling and N-formylmethionyl-leucyl-phenylalanine (fMLP) induced levels of transmigration in the mesentery were evaluated and quantified by intra-vital videomicroscopy and immunohistochemistry. Baseline leukocyte rolling was unaffected by buffer treatment, approximately 2-fold increased after Physioneal and 4-7-fold after Dianeal treatment. After starting fMLP superfusion, transmigrated leukocytes appeared outside the venules firstly after Dianeal treatment (15 minutes), thereafter in Physioneal and Buffer groups (20-22 minutes), and finally in control rats (>25 minutes). Newly formed vessels and total number of transmigrated neutrophils were highest in Dianeal-treated animals, followed by Physioneal and Buffer, and lowest in control rats and correlated for all groups to baseline leukocyte rolling (r = 0.78, P < 0.003). This study indicates that the start of inflammatory neutrophil transmigration is related to PDF bio(in)compatibility, whereas over time neutrophil transmigration is determined by the degree of neo-angiogenesis.

Peritoneal adipocytes and their role in inflammation during peritoneal dialysis

Adipose tissue is a major site of chronic inflammation associated with peritoneal dialysis (PD) frequently complicating peritonitis. Adiposity-associated inflammation plays a significant contributory role in the development of chronic inflammation in patients undergoing maintenance PD. However, the molecular and cellular mechanisms of this link remain uncertain. Adipose tissue synthesizes different adipokines and cytokines that orchestrate and regulate inflammation, insulin action, and glucose metabolism locally and systemically. In return, inflammation retards adipocyte differentiation and further exacerbates adipose dysfunction and inflammation. An understanding of the inflammatory roles played by adipose tissue during PD and the healing mechanism of injured mesothelium will help to devise new therapeutic approach to slow the progression of peritoneal damage during peritoneal dialysis. This article reviews the roles of peritoneal adipose tissue in chronic peritoneal inflammation under PD and in serosal repair during PD.

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.

Celecoxib treatment reduces peritoneal fibrosis and angiogenesis and prevents ultrafiltration failure in experimental peritoneal dialysis

BACKGROUND

Daily peritoneal exposure to peritoneal dialysis fluid (PDF) induces severe morphological alterations including fibrosis and angiogenesis that lead to a loss of peritoneal ultrafiltration (UF) capacity. Since cyclooxygenase (COX)-2 is involved in fibrosis and angiogenesis, we investigated the in vivo effects of a selective COX-2 inhibitor (celecoxib) in a rat-PD model.

METHODS

Sixteen rats daily received 10 ml of conventional PDF for 4-5 weeks intraperitoneally. Half of them (n = 8) daily received celecoxib (20 mg/kg BW) via oral gavage, and the other half (n = 8) received vehicle via oral gavage. The study also included two control groups (no PDF instillations), each consisting of n = 8 animals that daily received celecoxib or vehicle, respectively, via oral gavage. Functional, morphological and cellular parameters were analysed.

RESULTS

PDF exposure induced an inflammatory condition evidenced by the increased leucocyte number and synthesis of MCP-1, VEGF and hyaluronic acid. After PDF exposure, the omentum showed intense angiogenesis and milky spots formation. Parietal peritoneum showed increased angiogenesis, lymphangiogenesis, submesothelial matrix thickness and enhanced expression of mesothelial aquaporin1 (Aqp1). Concomitant PDF and celecoxib exposure drastically reduced PGE2 levels, angiogenesis, lymphangiogenesis, fibrosis and milky spot formation in studied tissues, but did not modify mesothelial Aqp1 expression nor the tissue expression of VEGF and inflammatory markers. PDF exposure induced severe UF failure that celecoxib treatment completely prevented.

CONCLUSIONS

Altogether, celecoxib treatment improves UF capacity and reduces morphological alterations in our rat PD model.

Conventional versus biocompatible peritoneal dialysis fluids: more questions than answers?

The most important challenge in peritoneal dialysis (PD) is long-term preservation of peritoneal membrane structure and function. Introduction of dialysis fluids into the peritoneal cavity induces changes. These changes are related to duration of dialysis, occurrence of peritonitis and components of the dialysis solution. Bioincompatibility is considered to be the major cause of the development of morphological changes of the peritoneal membrane. pH neutral PD fluids that are low in glucose degradation products (GDP) seem to better preserve the peritoneal membrane and have less systemic effects than the conventional ones. However, the long-term effects are not clear. An overview of the effects of conventional PD fluids and glucose-based PD fluids with neutral pH in ex vivo and in vivo animal and clinical studies is presented.

The alteration of dialysate cancer antigen 125 concentration under a biocompatible bicarbonate peritoneal dialysis solution and the preservation of the mesothelial cell viability

BACKGROUND

The importance to maintain the peritoneal membrane integrity for peritoneal dialysis (PD) patients by using biocompatible solutions (with low or no glucose as osmotic factor and low in glucose degradation products-GDPs, without lactate as a buffer and with normal pH) becomes progressively more evident. The aim of the present study was to investigate the clinical effects of a novel bicarbonate-based biocompatible PD fluid, evaluating the alteration in the concentrations of dialysate marker CA125, a glucoprotein indicator of mesothelial cell mass. PATIENTS AND METHODS; This is a single-center, prospective cohort study of 12 stable CAPD patients (4 women, 8 men), mean age 71.3 +/- of 6.01 years, mean PD duration 31.9 +/- 21.33 months, treated with the usual conventional PD solutions (with increased GDPs, low pH, and lactate as a buffer system). After a six-month period, the patients changed for the next six-month period into bicarbonate PD solutions (BicaVera, Fresenius), after which they returned into their previous schema of conventional solutions for another six months. The dialysate marker of CA125 was repeatedly estimated at the beginning of the study (T0), after six months phase with the bicarbonate solutions (T6), and at the end of study (T12), after the second six-month use of the conventional PD solutions. All the samples were taken at the end of a four-hour dwell of an exchange with PD solution 2.5% glucose.

RESULTS

The dialysate mean value of CA125 at the beginning of the study (Td0-with conventional PD solutions) was 15.07 +/- 5.72U/mL. After six months with bicarbonate PD solutions, the mean CA125 value increased to 111.97 +/- 66.21U/mL, while the mean values dropped again to 22.72 +/- 16.06 U/mL at the end of the study, after the patients' return for another six months to the conventional solutions use. There was a statistically significant difference between the mean CA125 levels at the beginning (Td0) and the middle of the study (Td6; p = 0.00079) as well as between the mean levels of CA125 in the middle (Td6) and at the end of the study (Td12; p = 0.0014). In contrast, comparing the mean dialysate values of CA125 at the beginning (Td0) and at the end of the study (Td12), no statistically significant difference was revealed (p = 0.13).

CONCLUSIONS

For the use of the bicarbonate-based PD, more biocompatible solutions for six months produced a statistically significant increase in the dialysate concentration of the mesothelial cell mass indicator CA125. The decrease at the end of the study of CA125 mean value at a level similar with that observed at the beginning, after the six-month period of the conventional PD solutions, indicates that the clinical use of the new bicarbonate-based PD solutions may have an advantageous role in the preservation of peritoneal cell mass, maintaining also the integrity and longevity of the peritoneal membrane.

Peritoneal mast cells in peritoneal dialysis patients, particularly in encapsulating peritoneal sclerosis patients

BACKGROUND

We assumed that increased mast cell numbers contribute substantially to the fibrosis often seen in the peritoneum of peritoneal dialysis (PD) patients, particularly those with encapsulating peritoneal fibrosis (EPS). Therefore, we investigated mast cells in different pathological conditions of the peritoneum.

METHODS

One hundred fifteen tissue probes with different peritoneal pathological states were selected (normal, n = 20; chronic appendicitis, n = 25; herniotomy, n = 24; fibrosis, n = 11; PD, n = 26; and EPS, n = 9). For staining of mast cells, we used alpha-naphtol-AS-d-chloracetate-esterase and mast cell tryptase. Next, we counted numbers of mast cells per square millimeter. Tryptase was measured by using image analysis.

RESULTS

Measurements by means of both methods correlated well (r = 0.812). Numbers of mast cells per square millimeter were as follows: normal, 26 +/- 16; chronic appendicitis, 241 +/- 217; herniotomy, 115 +/- 88; fibrosis, 99 +/- 66; PD, 81 +/- 64, and EPS, 24 +/- 23 (P = 0.00006). Amounts of tryptase present were 2.900 +/- 0.118, 2.871 +/- 0.150, 2.733 +/- 0.183, 3.041 +/- 0.176, 2.780 +/- 0.184, and 2.609 +/- 0.234, respectively (P = 0.00002).

CONCLUSION

We found upregulation of mast cells in specimens of chronic inflammatory diseases of the peritoneum. This also was true for PD patients, with the exclusion of patients with EPS. Therefore, loss-of-control functions of mast cells may contribute to the ill-understood disease entity of EPS.

Impact of 3,4-dideoxyglucosone-3-ene (3,4-DGE) on cytotoxicity of acidic heat-sterilized peritoneal dialysis fluid

Of the glucose degradation products (GDPs) in glucose-rich peritoneal dialysate, we investigated the influence of 3,4-dideoxyglucosone-3-ene (3,4-DGE) on the cytotoxicity of acidic heat-sterilized peritoneal dialysis fluid (L-H PDF) using human peritoneal mesothelial cells (HPMC). We prepared acidified filtration-sterilized PDF (glucose concentration 3.86%) containing eight types of added GDP [3,4-DGE, glyoxal (GO), methylglyoxal (MGO), 3-deoxyglucosone (3-DG), formaldehyde (FA), acetaldehyde (AA), 5-hydroxymethyl-2-furaldehyde (5-HMF), and furfural (FF)] or seven types of GDP (GO, MGO, 3-DG, FA, AA, 5-HMF, and FF). HPMC were exposed to these two types of solution and acidic heat-sterilized PDF (glucose concentration 3.86%, L-H 3.86) for 4 h. Cell viability was determined by 3,(4,5-dimethythiazol-2-yl)2,5-diphenyl-terazolium bromide (MTT) assay. MTT viability was decreased significantly compared with the control when treated with L-H 3.86 or acidified neutral filtration-sterilized PDF (glucose concentration 3.86%) containing eight GDPs. However, no significant decrease in MTT viability was observed when HPMC were treated with acidified neutral filtration-sterilized PDF (glucose concentration 3.86%) containing seven GDPs. Thus, 3,4-DGE strongly affects the cytotoxicity of L-H PDF. It is suggested that the cytotoxicity of L-H PDF is based on the presence of 3,4-DGE.

Novel role for mast cells in omental tissue remodeling and cell recruitment in experimental peritoneal dialysis

Because of its dynamic structure, the omentum plays a key role in the immunity of the peritoneal cavity by orchestrating peritoneal cell recruitment. Because mast cells accumulate in the omentum upon experimental peritoneal dialysis (PD) and may produce angiogenic/profibrotic factors, it was hypothesized that mast cells mediate omental tissue remodeling during PD. Daily treatment with conventional PD fluid (PDF) for 5 wk resulted in a strong omental remodeling response, characterized by an approximately 10-fold increase in mast cell density (P < 0.01), an approximately 20-fold increase in vessel density (P < 0.02), an approximately 20-fold increase in the number of milky spots (P < 0.01), and a four-fold increase in submesothelial matrix thickness (P < 0.0003) in wild-type rats. In contrast, all PDF-induced omental changes were significantly reduced in mast cell-deficient Ws/Ws rats or in wild-type rats that were treated orally with a mast cell stabilizer cromoglycate. A time-course experiment showed mast cell accumulation immediately before the formation of blood vessels and milky spots. Functionally, PDF evoked a peritoneal cell influx, which was significantly reduced in Ws/Ws rats (P < 0.04) and in wild-type rats that were treated with cromoglycate (P < 0.03). Cromoglycate treatment also completely prevented PDF-induced omental adhesions to the catheter tip (P = 0.0002). Mesothelial damage, angiogenesis, and fibrosis of mesentery and parietal peritoneum as well as glucose absorption rate and ultrafiltration capacity proved to be mast cell independent. Data strongly support the hypothesis that mast cells mediate PDF-induced omental tissue remodeling and, subsequently, peritoneal cell influx and adhesion formation, providing therapeutic possibilities of modulating omental function.

Prevention of membrane damage in patient on peritoneal dialysis with new peritoneal dialysis solutions

Peritoneal dialysis (PD) is now an established and successful alternative to hemodialysis. Multiple studies have confirmed its equivalent dialysis adequacy, mortality and fluid balance status, at least for the first 4-5 years. Peritoneal membrane failure is now one of the leading cause of technique failure. This review describes the role of glucose, glucose degradation product, pH, lactate, advanced glycosylation end product (AGE) in causing this membrane damage, and gives insight how the use of newer peritoneal dialysis fluids (PDFs) containing icodextrin, amino acids and bicarbonate buffer can prevent peritoneal membrane damage.

Mast cell quantification in normal peritoneum and during peritoneal dialysis treatment

CONTEXT

Mast cells (MCs) have been implicated in fibrogenesis, angiogenesis, and immunity against bacteria. These 3 mechanisms participate in the peritoneal pathology secondary to peritoneal dialysis (PD) treatment. Despite their potential relevance to PD-related pathology, few studies have focused on MCs.

OBJECTIVE

To evaluate possible variations in the number of MCs during PD treatment.

DESIGN

A quantitative study of tissue MCs in normal and pathologic peritoneum. Parietal peritoneal biopsies were collected from 4 groups: (1) normal controls (n = 9), (2) uremic non-PD patients (n = 16), (3) uremic patients on PD (n = 26), and (4) non-renal patients with inguinal hernia (n = 20). MCs were evaluated using immunohistochemistry for the detection of tryptase. The total number of cross sections of vessels per peritoneal field was examined in 22 of the 26 peritoneal biopsies of PD patients.

RESULTS

PD tissue samples showed fibrosis, mesothelial cell loss, and variable hyalinizing vasculopathy. The number of MCs was similar in normal controls and non-PD uremic patients (mean +/- SE: 7.13 +/- 0.67 and 7.74 +/- 0.74 MCs/mm2, respectively). Peritoneal dialysis patients showed a reduction (4 +/- 0.38 MCs/mm2, P < .001), whereas hernia sac samples showed an increase (10.59 +/- 3.48 MCs/mm2). MC reduction showed no correlation with time on dialysis, fibrosis, number of vessels, or previous episodes of peritonitis.

CONCLUSIONS

The peritoneum of patients receiving PD treatment shows a reduction of MCs. Despite such a reduction, fibrosis takes place, suggesting that MCs do not play a critical role in fibrosis genesis. Mast cell loss may be a contributory factor to peritonitis episodes in PD patients.

Peritoneal Dialysis Fluid–Induced Angiogenesis in Rat Mesentery Is Increased by Lactate in the Presence or Absence of Glucose

Angiogenesis may be an important mechanism behind the functional deterioration of the peritoneum leading to ultrafiltration failure in peritoneal dialysis. The present study was designed to compare the angiogenic properties of lactate-, bicarbonate-, and pyruvate-buffered fluids, evaluated separately with and without glucose. Five different fluids (lactate and bicarbonate with and without 2.5% glucose and pyruvate without glucose) were studied for 5 weeks of twice-daily injections in rats. The respective buffers (40 mmol/l) were adjusted to pH 7.2, and sodium, chloride, calcium, and magnesium were present at standard concentrations. The mesenteric window model, based on observation of the translucent peritoneal sections of the small intestine mesentery, was used for immunohistochemical imaging of microvessels (RECA-1 antigen) and macrophages (ED1 and ED2 antigens). All fluids induced angiogenesis as compared with untreated controls. The lactate-buffered fluids induced larger vascularized zones than did their bicarbonate- and pyruvate-buffered counterparts. Angiogenesis was accompanied by a local recruitment of ED1 macrophages from blood. Addition of glucose to the lactate- and bicarbonate-buffered fluids did not seem to alter their pro-angiogenic properties. In conclusion, intraperitoneal exposure to lactate buffer, compared with bicarbonate, stimulates angiogenesis in the presence or absence of glucose.

Electrophysiological changes in isolated spinal cord white matter in response to oxygen deprivation

STUDY DESIGN

In vitro studies using isolated guinea pig spinal cord white matter.

OBJECTIVES

To determine whether lack of oxygen can cause irreversible impairment of electrical impulse conduction.

SETTING

Department of Basic Medical Sciences, Purdue University, West Lafayette, Indiana, USA.

METHODS

The hypoxic injury was induced by reducing the oxygen tension of the perfused solution by 80%. Compound action potentials (CAPs) were monitored before, during, and after oxygen deprivation.

RESULTS

We have found that 60 min of hypoxia reduced the conduction to 30% of preinjury level and recovered to approximately 60% of the preinjury level upon reoxygenation. Larger axons appeared to be more vulnerable to oxygen deprivation. We noted a significant decrease and recovery of the depolarizing afterpotential (DAP). Likewise, there was a delay and recovery of absolute and relative refractory period. Concomitantly, the ability of axons to follow repetitive stimuli was suppressed following oxygen deprivation but recovered upon reoxygenation.

CONCLUSION

Following 60 min of oxygen deprivation and 30 min of reoxygenation, mammalian spinal cord white matter can partially recover electrical impulse conduction. However, within the same period, cords gained a complete recovery of other electrical properties, such as the depression of DAP, the delaying of refractory period, and the decreased ability to respond to repetitive stimuli. Compared to previous findings when both oxygen and glucose were deprived, we conclude that glucose plays a relatively minor role during the acute stage of oxygen deprivation in mammalian spinal cord white matter.

Improved biocompatibility of bicarbonate/lactate-buffered PDF is not related to pH

BACKGROUND

Chronic exposure to conventional peritoneal dialysis fluid (PDF) is associated with functional and structural alterations of the peritoneal membrane. The bioincompatibility of conventional PDF can be due to hypertonicity, high glucose concentration, lactate buffering system, presence of glucose degradation products (GDPs) and/or acidic pH. Although various investigators have studied the sole effects of hyperosmolarity, high glucose, GDPs and lactate buffer in experimental PD, less attention has been paid to the chronic impact of low pH in vivo.

METHODS

Rats received daily 10 ml of either conventional lactate-buffered PDF (pH 5.2; n=7), a standard bicarbonate/lactate-buffered PDF with physiological pH (n=8), bicarbonate/lactate-buffered PDF with acidic pH (adjusted to pH 5.2 with 1 N hydrochloride, n=5), or bicarbonate/lactate buffer, without glucose, pH 7.4 (n=7). Fluids were instilled via peritoneal catheters connected to implanted subcutaneous mini vascular access ports for 8 weeks. Control animals with or without peritoneal catheters served as control groups (n=8/group). Various functional (2 h PET) and morphological/cellular parameters were analyzed.

RESULTS

Compared with control groups and the buffer group, conventional lactate-buffered PDF induced a number of morphological/cellular changes, including angiogenesis and fibrosis in various peritoneal tissues (all parameters P<0.05), accompanied by increased glucose absorption and reduced ultrafiltration capacity. Daily exposure to standard or acidified bicarbonate/lactate-buffered PDF improved the performance of the peritoneal membrane, evidenced by reduced new vessel formation in omentum (P<0.02) and parietal peritoneum (P<0.008), reduced fibrosis (P<0.02) and improved ultrafiltration capacity. No significant differences were found between standard and acidified bicarbonate/lactate-buffered PDF. During PET, acidic PDF was neutralized within 15 to 20 min.

CONCLUSION

The bicarbonate/lactate-buffered PDF, acidity per se did not contribute substantially to peritoneal worsening in our in vivo model for PD, which might be explained by the buffering capacity of the peritoneum.

Beneficial effects of aminoguanidine on peritoneal microcirculation and tissue remodelling in a rat model of PD

BACKGROUND

The formation of glucose degradation products (GDPs) and accumulation of advanced glycation end products (AGEs) partly contribute to the bioincompatibility of peritoneal dialysis fluids (PDF). Aminoguanidine (AG) scavenges GDPs and prevents the formation of AGEs.

METHODS

In a peritoneal dialysis (PD) rat model, we evaluated the effects of the addition of AG to the PDF on microcirculation and morphology of the peritoneum, by intravital microscopy and quantitative morphometric analysis.

RESULTS

AG-bicarbonate effectively scavenged different GDPs from PDF. Daily exposure to PDF for 5 weeks resulted in a significant increase in leucocyte rolling in mesenteric venules, which could be reduced for approximately 50% by addition of AG-bicarbonate (P<0.02). Vascular leakage was found in rats treated with PDF/AG-bicarbonate, but not with PDF alone. Evaluation of visceral and parietal peritoneum showed the induction of angiogenesis and fibrosis after PDF instillation. PDF/AG-bicarbonate significantly reduced vessel density in omentum and parietal peritoneum (P<0.04), but not in mesentery. PDF-induced fibrosis was significantly reduced by AG (P<0.02). PDF instillation led to AGE accumulation in mesentery, which was inhibited by supplementation of AG. Since addition of AG-bicarbonate to PDF raised pH from 5.2 to 8.5, a similar experiment was performed with AG-hydrochloride that did not change the fluid acidity. We could reproduce most of the results obtained with AG-bicarbonate; however, AG-hydrochloride induced no microvascular leakage and had a minor effect on angiogenesis.

CONCLUSION

The supplementation of either AG reduced a number of PDF-induced alterations in our model, emphasizing the involvement of GDPs and/or AGEs in the PDF-induced peritoneal injury.

Immunopathological changes in a uraemic rat model for peritoneal dialysis

BACKGROUND

Peritoneal dialysis (PD) is a treatment modality for patients with renal failure. Both the uraemic state of these patients and chronic exposure to PD fluid are associated with the development of functional and structural alterations of the peritoneal membrane. In a well-established chronic PD rat model, we compared rats with normal renal function with subtotal nephrectomized rats that developed uraemia.

METHODS

Uraemic and control rats received daily 10 ml conventional glucose containing PD fluid, via peritoneal catheters during a 6 week period. Uraemic and control rats receiving no PD fluid served as controls. Parameters relevant for peritoneal defence and serosal healing responses were analyzed.

RESULTS

Uraemic animals were characterized by 2-3-fold increased serum urea and creatinine levels, accompanied by a significantly reduced haematocrit. Uraemia (without PD fluid exposure) induced new blood vessels in different peritoneal tissues, accompanied by increased accumulation of advanced glycation end products (AGEs) and elevated levels of angiogenic factors such as vascular endothelial growth factor and monocyte chemoattractant protein-1 (MCP-1) in peritoneal lavage fluid. A much stronger peritoneal response was observed upon PD fluid exposure in non-uraemic rats. This included the induction of angiogenesis and fibrosis in various peritoneal tissues, accumulation of AGEs, immunological activation of the omentum, damage to the mesothelial cell layer, focal formation of granulation tissues and increased MCP-1 and hyaluronan levels in peritoneal lavage fluid. Finally, chronic PD fluid instillation in uraemic rats did not induce an additional peritoneal response compared to PD fluid exposure in non-uraemic rats, except for the degree of AGE accumulation.

CONCLUSIONS

Both uraemia and PD fluid exposure result in pathological alterations of the peritoneum. However, uraemia did not induce major additive effects to PD fluid-induced injury. These results substantially contribute to the understanding of the pathobiology of the peritoneum under PD conditions.

Synergistic Cytotoxicity of Acidity and 3,4-Dideoxyglucosone-3-ene Under the Existence of Lactate in Peritoneal Dialysis Fluid

Of the non-physiological compounds in glucose-rich peritoneal dialysis fluid, we investigated the synergistic cytotoxicity of acidity and 3,4-Dideoxyglucosone-3-ene(3,4-DGE) under the existence of lactate using human peritoneal mesothelial cells (HPMC). The effect of pH on cell viability at various levels of pH (5.5, 6.7, 7.15), with or without lactate was examined by adding 1N-HCl to phosphate buffer solution. We also examined the cytotoxic effects of 3,4-DGE and pH (5.5, 6.7 or 7.15). Additionally, we compared the cytotoxic effects of 3,4-DGE and pH (5.5, 6.7 or 7.15) under existence of lactate (40 meq/L) or absence of lactate. The cells were exposed to these solutions for 2 or 4 h. Cell viability was determined by MTT (3-[4, 5-dimethylthiazol-2-yl]-2, 5-diphenylterazolium bromide) assay. 3,4-DGE or acidic solution alone had no significant effects on MTT viability under the absence of lactate. However, acidic solutions containing 3,4-DGE significantly decreased MTT viability under the existence of lactate. The MTT viability of HPMC was not decreased by 3,4-DGE or acidity alone under the absence of lactate. However, the combination of acidity and 3,4-DGE markedly decreased MTT viability under the existence of lactate, strongly suggesting the synergistic cytotoxicity of 3,4-DGE and acidity under the existence of lactate.

A comparative study of the structure of human and murine greater omentum

In humans, the greater omentum is a fatty peritoneal fold that extends from the greater curvature of the stomach to cover most abdominal organs. It performs many functions, which include acting as a reservoir of resident peritoneal inflammatory cells, a storage site for lipid, and a regulator of fluid exchange in and out of the peritoneal cavity. Most importantly, the omentum readily adheres to areas of inflammation and peritoneal damage, often leading to adhesion formation. Despite its clinical importance, the omentum remains an understudied organ, and discrepancies exist as to its exact morphology. This study uses a combination of phase contrast microscopy, scanning electron microscopy (SEM), and transmission electron microscopy (TEM) to elucidate the structure of the greater omentum of both human and mouse and determine whether it possesses a typical surface mesothelial cell lining similar to other serosa. Results indicated that both human and murine omenta were of similar structure and composed of two distinct types of tissue, one adipose-rich and the other translucent and membranous. The adipose-rich regions were well-vascularised and covered by a continuous mesothelial cell layer except at the sites of milky spots. In contrast, translucent areas were poorly vascularised and contained numerous fenestrations of varying size. The possible function and developmental origin of these gaps is unclear; however, their role in promoting omental adhesion formation and in the successful use of omental graft material is discussed.

Peritoneal dialysis fluid-induced changes of the peritoneal membrane are reversible after peritoneal rest in rats

BACKGROUND

Peritoneal dialysis (PD) is associated with functional and structural alterations of the peritoneal membrane. However, the (ir)reversibility of these pathological changes of the peritoneum is not understood fully.

METHODS

In an experimental PD model, rats (n = 15) received daily 10 ml conventional glucose containing PD fluid, via peritoneal catheters connected to implanted subcutaneous mini vascular access ports. After 5 weeks of treatment, the first group of animals (PDF; n = 10) was sacrificed, while peritoneal catheters of the remaining group of rats (PD-rest; n = 5) were removed 1 week later. The latter group (PD-rest) was sacrificed 12 weeks after removing catheters. At both time points, untreated rats were included as controls. Cellular and morphological parameters were analysed by light and electron microscopy.

RESULTS

Rats exposed to PD fluid for 5 weeks showed a severe angiogenesis in various peritoneal tissues. Peritoneal rest resulted in a significant reduction in blood vessel density in visceral (mesentery, P<0.05), but not in parietal peritoneum. Five weeks' exposure to PD fluid resulted in a profound fibrosis in the parietal peritoneum, whereas the degree of fibrosis was significantly reduced in the PD-rest group (P<0.02). Daily exposure to PD fluid induced a higher number of mast cells in the omentum compared with untreated rats, whereas peritoneal rest normalized the increased mast cell density completely (P<0.03). Likewise, continued PD fluid instillation evoked a strong omental milky spot response, which was returned to the control level after peritoneal rest (P<0.009). Furthermore, the number of mesothelial cells on the liver was significantly increased in rats treated with PD fluid, whereas animals from the PD-rest group had a lower number of mesothelial cells, although this was not statistically significant (P = 0.08). Finally, as evidenced by electron microscopy, daily exposure to PD fluid resulted in severe damage to the mesothelial cell layer covering the peritoneum, whereas this cell layer was completely recovered after peritoneal rest.

CONCLUSIONS

We show that PD fluid-induced cellular and morphological alterations of the peritoneal membrane are generally reversible.

Long-term exposure to new peritoneal dialysis solutions: Effects on the peritoneal membrane

BACKGROUND

Chronic exposure to peritoneal dialysis fluid (PDF) affects the peritoneum, but precise causative factors are incompletely understood. We examined the effects of standard and new PDF on peritoneal function and structure.

METHODS

Female Wistar rats received twice daily intraperitoneal infusions of a standard lactate-buffered 3.86% glucose PDF at pH 5.5 (Dianeal) (N= 12), a low glucose degradation product (GDP) containing bicarbonate/lactate-buffered 3.86% glucose PDF at pH 7.4 (Physioneal) (N= 12), a lactate-buffered amino acid-based PDF at pH 6.7 (Nutrineal) (N= 12) or Earle's Balanced Salt Solution at pH 7.4 (EBSS) (N= 12) during 12 weeks.

RESULTS

Net ultrafiltration was lower after treatment with standard PDF, but not with low-GDP bicarbonate/lactate-buffered and amino acid-based PDF, compared to EBSS. Peritonea exposed to standard PDF were characterized by an increased expression of vascular endothelial growth factor (VEGF), microvascular proliferation as well as submesothelial fibrosis, which were not observed in other groups. Staining for methylglyoxal adducts was prominent in the standard PDF-exposed group, mild in the low GDP bicarbonate/lactate-buffered group and absent in the other groups. Standard PDF induced accumulation of advanced glycation end products (AGEs) and up-regulation of the receptor for AGE (RAGE). AGEs accumulation was absent and RAGE expression was only modestly increased in low-GDP bicarbonate/lactate-buffered and amino acid-based PDF.

CONCLUSION

Long-term in vivo exposure to standard PDF adversely affects peritoneal function and structure. A low-GDP bicarbonate/lactate-buffered and amino acid-based PDF better preserved peritoneal integrity and may thus improve the longevity of the peritoneal membrane. GDPs and associated accelerated AGE formation are the main causative factors in PDF-induced peritoneal damage.

Biocompatibility pattern of a bicarbonate/lactate-buffered peritoneal dialysis fluid in APD: a prospective, randomized study

BACKGROUND

In chronic ambulatory peritoneal dialysis, bicarbonate-buffered fluids, with their neutral pH and less advanced glycosylation end-products (AGE) and glucose degradation products (GDP), have better biocompatibility than conventional peritoneal dialysis (PD) solutions. That difference may be more beneficial in automated peritoneal dialysis (APD), due to its more frequent exchanges and longer contact times with fresh dialysate. We performed a prospective, randomized study in APD patients to compare the biocompatibility of conventional and bicarbonate/lactate-buffered PD fluids.

METHODS

We randomized 14 APD patients to have APD with either conventional or bicarbonate/lactate-based fluids. After 6 months, both groups changed to the other solution. The overall observation period was 12 months. After 1 and 5 months and again after 7 and 11 months, phagocytotic and respiratory burst capacities of effluent peritoneal macrophages were determined. Plasma interleukin (IL)-6 and C-reactive protein (CRP) as well as effluent IL-6, CRP, transforming growth factor (TGF)-beta 1, AGE and CA125 concentrations were measured. Inflow pain was quantified using a patient questionnaire.

RESULTS

Respiratory burst capacity remained unchanged and phagocytotic activity increased significantly during APD (P<0.001) with the bicarbonate/lactate fluid. Effluent IL-6 release was significantly lower than with the lactate fluid (P<0.05). While in the effluent TGF-beta 1 was unaffected, AGE concentration was lower after bicarbonate/lactate treatment (P<0.05). Effluent CA125 concentration, an indicator of mesothelial cell integrity, was higher (P<0.05) in neutral effluents. Finally, patients' inflow pain diminished (P = 0.05) when using the neutral fluid.

CONCLUSIONS

The use of a neutral PD fluid in APD improved patients' inflow pain as well as biocompatibility parameters reflecting enhanced phagocytotic activity of peritoneal macrophages, reduced constitutive inflammatory stimulation (IL-6), reduced AGE accumulation in the peritoneal cavity and better preservation of the mesothelial cell integrity. From the biocompatibility point of view, a neutral fluid with low GDP content can be recommended as the primary choice for APD.