Recent concepts in the molecular biology of the peritoneal membrane - implications for more biocompatible dialysis solutions

miR-15a-5p suppresses peritoneal fibrosis induced by peritoneal dialysis via targeting VEGF in rats

Aim

When peritoneal fibrosis (PF) causes ultrafiltration failure in peritoneal dialysis (PD) patients, PD has to be discontinued. Currently, there is no effective way to relieve PF. In this study, we aimed to determine whether miR-15a-5p is involved in PF and to determine the underlying mechanism.

Methods

Six normal rats were used as the control group. A uremic rat model was constructed using 5/6 nephrectomy in a Sprague–Dawley model. The uremic rats were randomly divided into PD, lentivirus-transfected, negative control, VEGFR-inhibited and gavage control groups. Except for the control group, all uremia rats received continuous PD for 28 days. In the lentivirus-transfected group, the miR-15a-5p plasmid was injected into the peritoneal cavity to upregulate miR-15a-5p expression. Axitinib was used to block vascular endothelial growth factor receptor (VEGFR) in the peritoneum. The mRNA levels of miR-15a-5p and VEGF were detected by qRT-PCR and FISH. Protein levels of VEGF, E-cadherin, collagen IV, fibronectin and α-SMA were detected by western blot and immunohistochemistry.

Results

PD leads to peritoneal thickening and fibrosis. The expression level of miR-15a-5p decreased and that of VEGF increased in the PD group than in the controls. Additionally, E-cadherin was significantly reduced while collagen IV, fibronectin and α-SMA were obviously increased in the PD group compared to controls. FISH showed that VEGF might be the target gene of miR-15a-5p. Overexpression of miR-15a-5p or inhibition of VEGFR could reverse PF.

Conclusion

miR-15a-5p may participate in the endothelial to mesenchymal transition of PF caused by PD through VEGF.

Impact of Glucose in Peritoneal Dialysis: Saint or Sinner?

Peritoneal dialysis (PD) solutions using glucose as osmotic agent have been used for more than two decades as effective treatment for patients with end-stage renal disease. Although alternative osmotic agents such as amino acids and macromolecular solutions, including polypeptides and glucose polymers, are now available, glucose is still the most widely used osmotic agent in PD. It has been shown to be safe, effective, readily metabolized, and inexpensive. On the other hand, it is widely assumed that exposure of the peritoneal membrane to high glucose concentrations contributes to both structural and functional changes in the dialyzed peritoneal membrane. As in diabetes, glucose, either directly or indirectly through the generation of glucose degradation products or the formation of advanced glycation end products, may contribute to peritoneal membrane failure. Although efforts to reduce glucose toxicity have been made for years, only a few suggestions, such as dual-bag systems with bicarbonate as buffer system, have found broader acceptance. Recently, some interesting new approaches to the problem of glucose-related toxicity have been made, but further investigations will be necessary before they can be used clinically. This review will focus on adverse effects of glucose in PD solutions and summarize different aspects of glucotoxicity and potential therapeutic interventions.

1,25(OH)2D3 inhibits high glucose-induced apoptosis and ROS production in human peritoneal mesothelial cells via the MAPK/P38 pathway

The regulation of cell proliferation, differentiation and immunomodulation are affected by 1,25(OH)2D3. However, its function during apoptosis and oxidative stress in human peritoneal mesothelial cells (HPMCs) remains unknown. The aim of the present study was to investigate whether the regulation of apoptosis and oxidative stress have therapeutic relevance in peritoneal dialysis (PD) therapy. The present study investigated the effects of 1,25(OH)2D3 on high glucose (HG)-induced apoptosis and reactive oxygen species (ROS) production in HPMCs, and examined the underlying molecular mechanisms. Flow cytometry and western blotting were performed to detect cell apoptosis, 2,7-dichlorofluorescein diacetate was used to measure reactive oxygen species production and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide was used to measure cell viability. The results of the present study demonstrated that exposure to HG increased apoptosis and ROS production in HPMCs, whereas pretreatment with 1,25(OH)2D3 significantly inhibited HG‑induced apoptosis and ROS production. Further analysis revealed that 1,25(OH)2D3 facilitated cell survival via the MAPK/P38 pathway. The results of the present study indicate that 1,25(OH)2D3 inhibits apoptosis and ROS production in HG‑induced HPMCs via inhibition of the MAPK/P38 pathway.

Effect of Ligustrazine on rat peritoneal mesothelial cells treated with lipopolysaccharide

The apoptosis of peritoneal mesothelial cells (PMCs) and peritoneal fibrosis may induce failure of peritoneal membrane function. The study explored the changes of apoptosis and fibrosis in PMCs under lipopolysaccharides (LPS) culture and investigated whether Ligustrazine can affect LPS-induced apoptosis and fibrosis. We found that exposure of rat PMCs to 5 mg·L(-1) LPS for 24 h resulted in a significant induction of apoptosis and increased levels in Reactive oxygen species, and caspase-3 activity. Fibronectin, Collagen I, p-p38, and matrix metalloprotein-9 (MMP-9) levels were also significantly increased by LPS. But superoxide dismutase levels were remarkably decreased. Ligustrazine can restore the changes induced by LPS. The protective effect of Ligustrazine on LPS-induced apoptosis and fibrosis may act through inhibition of oxidative stress and p38/MAPKS, ROS/MMP-9 activation in PMCs.

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.

Role of CIP4 in high glucose induced epithelial--mesenchymal transition of rat peritoneal mesothelial cells

BACKGROUND

Peritoneal mesothelial cell (PMC) plays a key role in the process of peritoneal fibrosis. Epithelial-mesenchymal transition (EMT) of PMCs is an important mechanism of peritoneal fibrosis. Prolonged exposure to peritoneal dialysis fluid containing a high concentration of glucose may lead to EMT of PMCs. Cdc42-interacting protein-4 (CIP4) is a critical regulator of cell skeleton and downstream effector of Cdc42 and participates in EMT of tubular epithelial cells. In the present study, we investigate the possible role of CIP4 in EMT of PMC under high glucose (HG) condition in vitro and further explore the potential therapeutic point for peritoneal fibrosis.

METHODS

Rat peritoneal mesothelial cells (RPMCs) were isolated from the peritonea of rats by enzymatic digestion. Under HG conditions (1.5%, 2.5% and 4.25%), E-cadherin, α-SMA and CIP4 expression were assessed by Western blot. Effect of CIP4-siRNA and pcDNA3.1-CIP4 transfection on E-cadherin, α-SMA and CIP4 expression were also assessed respectively under 2.5% HG concentration. Cells were pretreated for 24 h with PI3K/Akt signaling inhibitor perifosine and effect of perifosine on CIP4 expression were detected by Western blot.

RESULTS

EMT induction by HG was confirmed by the prevalence of morphological changes, loss of E-cadherin, increase in α-SMA expression. CIP4-siRNA transfection can reverse EMT of RPMCs. Over-expression of CIP4 promoted characteristics similar to those commonly observed in EMT. Furthermore, the increased CIP4 in response to HG was efficiently inhibited by perifosine.

CONCLUSION

This study shows that CIP4 promotes high glucose-induced EMT through PI3K-Akt signaling pathway in RPMCs.

The impact of neutral-pH peritoneal dialysates with reduced glucose degradation products on clinical outcomes in peritoneal dialysis patients

Neutral-pH peritoneal dialysates, with reduced glucose degradation products (GDPs), have been developed to reduce peritoneal membrane damage. Here our review evaluated the impact of these solutions on clinical outcomes using data from The Cochrane CENTRAL Registry, MEDLINE, Embase, and reference lists for randomized trials of biocompatible solutions. Summary estimates of effect were obtained using a random-effects model of 20 eligible trials encompassing 1383 patients. The quality of studies was generally poor, such that 13 studies had greater than a 20% loss to follow-up and only 3 trials reported adequate concealment of allocation. Use of neutral-pH dialysates with reduced GDPs resulted in larger urine volumes (7 trials; 520 patients; mean difference 126 ml/day, 95% CI 27-226), improved residual renal function after 12 months (6 trials; 360 patients; standardized mean difference 0.31, 95% confidence interval 0.10-0.52), and a trend to reduced inflow pain (1 trial; 58 patients; relative risk 0.51, 95% CI 0.24-1.08). However, there was no significant effect on body weight, hospitalization, peritoneal solute transport rate, peritoneal small-solute clearance, peritonitis, technique failure, patient survival, or adverse events. No significant harms were identified. Thus, based on generally poor quality trials, the use of neutral-pH peritoneal dialysates with reduced GDPs resulted in greater urine volumes and residual renal function after 12 months, but without other clinical benefits. Larger, better-quality studies are needed for accurate evaluation of the impact of these newer dialysates on patient-level hard outcomes.

Zinc transporter 5 and zinc transporter 7 induced by high glucose protects peritoneal mesothelial cells from undergoing apoptosis

Zinc is an essential micronutrient and cytoprotectant involved in many types of apoptosis. The zinc transporter family SLC30A (ZnTs) is an important factor in the regulation of zinc homeostasis; however, its function in apoptosis in peritoneal mesothelial cells (PMCs) remains unknown. This study explores the regulation of zinc transporters and how they play a role in cell survival, particularly in rat peritoneal mesothelial cells (RPMCs), surrounding glucose concentrations, and the molecular mechanism involved. The messenger RNA (mRNA) transcripts were quantitatively measured by real-time polymerase chain reaction for all known nine zinc transport exporters (SLC30A1-8,10), as well as in primary RPMCs and the cells cultured under nonstimulated and HG-stimulated conditions. While many zinc transporters were constitutively expressed, ZnT5 mRNA and ZnT7 mRNA were strongly induced by HG. Overexpression of ZnT5 and ZnT7 respectively resulted in a decrease in the expression of caspace 3, caspace 8, BAX, and AIF and coincided with cell survival in the presence of HG. Inhibition of ZnT5 and ZnT7 expression using considerable siRNA-mediated knockdown of RPMCs was examined and, afterwards, the impact on cell apoptosis was investigated. Increased levels of apoptosis were observed after knockdown of ZnT5 and ZnT7. Furthermore, overexpression of ZnT5 and ZnT7 is accompanied by activation of PI3K/Akt pathway and inhibiting HG-induced apoptosis. This study suggests that the zinc transporting system in RPMCs is influenced by exposure to HG, particularly ZnT5 and ZnT7. This may account for the inhibition of HG-induced RPMC apoptosis and peritoneum injury, likely through targeting PI3K/Akt pathway-mediated cell survival.

Zinc inhibits high glucose-induced apoptosis in peritoneal mesothelial cells

Zinc (Zn) plays an important role in influencing many types of apoptosis. However, its function in apoptosis in peritoneal mesothelial cells (PMCs) remains unknown. Here, we studied the effects of Zn on high glucose (HG)-induced apoptosis in rat PMCs (RPMCs) and examined the underlying molecular mechanisms. We found that Zn supplementation inhibited HG-induced RPMC apoptosis significantly, by attenuating reactive oxygen species (ROS) production, inhibiting HG-induced sFasR and sFasL over-expression, caspase-8 and caspase-3 activation, and inhibiting release of cytochrome c from mitochondria to the cytosol. Further analysis revealed that Zn supplementation facilitated cell survival through activation of the phosphatidylinositol 3-kinase/Akt signaling pathway and MAPK/ERK pathways. These results indicate that Zn can inhibit apoptosis in HG-induced RPMCs by several independent mechanisms, including an indirect antioxidative effect and probably by inhibition of caspase-8 and caspase-3 activation.

Biocompatible peritoneal dialysis fluids: clinical outcomes

Peritoneal dialysis (PD) is a preferred home dialysis modality and has a number of added advantages including improved initial patient survival and cost effectiveness over haemodialysis. Despite these benefits, uptake of PD remains relatively low, especially in developed countries. Wider implementation of PD is compromised by higher technique failure from infections (e.g., PD peritonitis) and ultrafiltration failure. These are inevitable consequences of peritoneal injury, which is thought to result primarily from continuous exposure to PD fluids that are characterised by their "unphysiologic" composition. In order to overcome these barriers, a number of more biocompatible PD fluids, with neutral pH, low glucose degradation product content, and bicarbonate buffer have been manufactured over the past two decades. Several preclinical studies have demonstrated their benefit in terms of improvement in host cell defence, peritoneal membrane integrity, and cytokine profile. This paper aims to review randomised controlled trials assessing the use of biocompatible PD fluids and their effect on clinical outcomes.

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.

Aliskiren prevents the toxic effects of peritoneal dialysis fluids during chronic dialysis in rats

The benefits of long-term peritoneal dialysis (PD) in patients with end-stage renal failure are short-lived due to structural and functional changes in the peritoneal membrane. In this report, we provide evidence for the in vitro and in vivo participation of the renin-angiotensin-aldosterone system (RAAS) in the signaling pathway leading to peritoneal fibrosis during PD. Exposure to high-glucose PD fluids (PDFs) increases damage and fibrosis markers in both isolated rat peritoneal mesothelial cells and in the peritoneum of rats after chronic dialysis. In both cases, the addition of the RAAS inhibitor aliskiren markedly improved damage and fibrosis markers, and prevented functional modifications in the peritoneal transport, as measured by the peritoneal equilibrium test. These data suggest that inhibition of the RAAS may be a novel way to improve the efficacy of PD by preventing inflammation and fibrosis following peritoneal exposure to high-glucose PDFs.

Atorvastatin Reduces High Glucose Toxicity in Rat Peritoneal Mesothelial Cells

Objective

Continuous exposure of the peritoneal membrane to high glucose dialysis solutions can produce functional alterations in this membrane. We studied the toxic effects of high glucose (50 mmol/L and 83 mmol/L) and its reversal by atorvastatin (0.5 – 5 μmol/L) on cultures of rat peritoneal mesothelial cells (PMCs).

Methods

Rat PMCs were harvested from the peritonea of male Sprague–Dawley rats and grown in M199 medium supplemented with 10% fetal bovine serum. The effects of high glucose (50 mmol/L and 83 mmol/L) on levels of reactive oxygen species (ROS), on caspase 3 activity, and on phospho-p38 mitogen-activated protein kinase (MAPK) in the cultures were evaluated.

Results

Exposure to high glucose (for 4, 8, and 24 hours) increased intracellular levels of ROS and phospho-p38 MAPK (indices of cellular toxicity). Atorvastatin blocked these toxic effects of high glucose, being more effective against 50 mmol/L glucose (protective effects were observed above 0.5 μmol/L) than against 83 mmol/L (protective effects were observed above 2.5 μmol/L). Atorvastatin was also able to prevent glucose-induced increase in caspase 3 activity.

Conclusions

The present study shows that high glucose may promote oxidative stress and may activate apoptotic pathways in rat PMCs. These toxic effects could be reversed by atorvastatin.

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.

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.

Heat shock response protects human peritoneal mesothelial cells from dialysate-induced oxidative stress and mitochondrial injury

BACKGROUND

Chronic peritoneal dialysis (PD) is one of the major therapies for uremic patients. However, the peritoneal mesothelial cells (PMCs) are subject to the injury by bioincompatible dialysates. The aim of this study is to investigate the protective roles and mechanisms of heat shock response in PMCs.

METHODS

Primary cultured human PMCs (HPMCs) were subjected to commercial peritoneal dialysates. The cell viability was assayed by MTT test and Annexin V assay. The expression of HSPs was detected by Western blots analysis. Intracellular hydrogen peroxide and superoxide anion were detected using H(2)DCFDA and dHE probe, respectively, with flow cytometry. The mitochondrial membrane potential (DeltaPsim) of HPMCs was evaluated using JC1 probe with flow-cytometry.

RESULTS

Exposure of HPMCs to 1.5%, 2.5%, and 4.25% dextrose, and 7.5% icodextrin dialysates, respectively, for 60 min resulted in significantly accumulation of intracellular reactive oxygen species (ROS), DeltaPsim loss, and cell death in HPMCs. Amino acid dialysates exhibited no significant cytotoxicity. Adjusting the acidity in 1.5% dextrose and icodextrin dialysate significantly attenuated the dialysate-induced ROS generation and cell death in HPMCs. Heat pretreatment (41 degrees C, 30 minutes), which induced HSP 27 and 72 syntheses, significantly attenuated the dialysate-induced intracellular ROS accumulation, Dym loss, and cell death in HPMCs.

CONCLUSIONS

In conclusion, the acidic bioincompatible dialysates induce oxidative stress, DeltaPsim loss, and subsequent cell death in HPMCs. Amino acid dialysates is more biocompatible than glucose and icodextrin dialysates to HPMCs. Heat shock response protects HPMCs from the bioincompatible dialysates-induced cellular damage.

Erythropoietin Prevents Dialysis Fluid-Induced Apoptosis of Mesothelial Cells

Background

In peritoneal dialysis (PD)-treated patients, denudation of the mesothelium correlates with peritoneal fibrosis and vascular changes. Since recombinant human erythropoietin (rHuEPO) induces a range of cytoprotective cellular responses, rHuEPO treatment may reduce PD fluid (PDF)-induced damage.

Methods

To investigate the antiapoptotic effect and mechanism of rHuEPO in peritoneal mesothelial cells (PMCs), isolated mice PMCs were used for in vitro characterization of rHuEPO effects. To confirm the in vitro effects, active caspase-3 was analyzed in imprints of liver visceral peritoneum of mice pretreated overnight with rHuEPO (5000 U/kg intraperitoneally) and exposed to PDF (Dianeal 4.25%; Baxter Healthcare, Deerfield, Illinois, USA) for 4 hours.

Results

Mouse PMCs expressed EPO-receptor mRNA and protein. Short exposure to rHuEPO (5 U/mL) induced phosphorylation of JAK2, STAT5, and ERK1/2. PMCs pretreated for 1 hour with rHuEPO showed reduced PDF-induced caspase-3 activation (49.6%) and DNA fragmentation (38.4%) in comparison to cells treated by PDF alone ( p < 0.05). rHuEPO treatment induced an increase in ERK1/2 phosphorylation and reduced levels of PDF-induced phospho-P38. PD98059, a specific inhibitor of ERK activation, fully blocked the protective effect of rHuEPO. In mice, rHuEPO reduced the apoptotic effect of PDF, as assessed by the level of active caspase-3.

Conclusions

Our study presents new insights into clinical use of rHuEPO in the setting of PD. We found that rHuEPO provides ERK1/2-dependent protection to PMCs from PDF-induced apoptosis. The use of rHuEPO, or any of its new derivatives that do not stimulate erythropoiesis, should be considered for peritoneal preservation.

Cytotoxicity of Mononuclear Cells as Induced by Peritoneal Dialysis Fluids: Insight into Mechanisms that Regulate Osmotic Stress-Related Apoptosis

Objective

High glucose content of peritoneal dialysis fluids (PDFs) has been shown to contribute to loss of peritoneal function during long-term peritoneal dialysis. However, hyperosmolality and hypertonicity of PDF are usually seen as similar stress events inducing osmotic stress-induced programmed cell death. In this study, we examined the impact of various osmotic agents on apoptosis induced by hyperosmolar PDFs, focusing on the mechanisms underlying the lethal effects of PDFs on peripheral blood mono-nuclear cells (PBMCs).

Methods

We assessed apoptosis and necrosis by annexin V–propidium iodide (PI) labeling, and caspase-3 activity by fluorescence assay. F-actin remodeling was measured using fluorescent phalloidin labeling.

Results

Hyperosmolality does not cause the cytotoxicity observed with PDF, but exposure to agents incapable of permeating cell membranes results in a significant increase in the percentage of apoptotic PBMCs by annexin V–PI labeling, which is confirmed by the increase in caspase-3 activity. Interestingly, inhibition of caspase-3 by Z-VAD-FMK did not suppress apoptosis. Extracellular hypertonicity produced polymerization of filamentous actin and cell shrinkage, which displayed similar time courses. Cell shrinkage was blocked by cytochalasin D, indicating an active role for actin cytoskeleton in hypertonicity-induced cell shrinkage. F-actin polymerization was related to an increase in intra-cellular ionic strength. Finally, we excluded a direct role for actin remodeling in osmotic stress-induced programmed cell death.

Conclusions

Exposure to osmolytes that cannot penetrate cell membranes results in a hypertonicity-induced apoptosis that cannot be blocked by the broad-spectrum caspase inhibitor Z-VAD-FMK. In addition, extracellular hypertonicity induced by impermeant solutes produces F-actin polymerization through an increase in intracellular ionic strength. The remodeling of the cytoskeleton does not modulate apoptosis but participates in cell shrinkage.

Histomorphological and functional changes of the peritoneal membrane during long-term peritoneal dialysis

In long-term peritoneal dialysis (PD) morphological and functional changes of the peritoneal membrane are common. Sub-mesothelial fibrosis, angiogenesis and vasculopathy are typical histomorphological alterations of the peritoneal membrane, which, to a certain degree, are induced by uremia and recurrent peritonitis. The most important causative factor, however, represents the chronic exposure to PD solutions. Glucose, glucose degradation products and advanced glycation end-products (AGEs) via different pathways induce inflammation, fibrosis and angiogenesis. As a functional consequence ultrafiltration failure due to peritoneal hyperpermeability and an increased effective peritoneal surface area represents a major clinical problem. An insufficient function of the water-selective aquaporin 1 (AQP-1) channel may also be causative for inadequate ultrafiltration. A rare but life-threatening complication of long-term PD is encapsulating peritoneal sclerosis (EPS). For both impaired AQP-1 function and EPS, the long-term effects of PD fluids are believed to be responsible, even though the mechanisms are not yet understood. The avoidance of glucose and modern PD fluids with fewer glucose degradation products, as well as first pharmacological attempts may help to preserve the peritoneal membrane in the long term.

Quercetin protects human mesothelial cells against exposure to peritoneal dialysis fluid

During peritoneal dialysis, mesothelial cells have been shown to undergo severe damage due to continuous exposure to peritoneal dialysis fluid (PDF) with cytotoxic physicochemical properties. In this study, we investigated the cytoprotective role of the bioflavonoid Quercetin in the in vitro model of peritoneal dialysis. Immortalized human mesothelial cells (Met5A) were exposed either to regular growth medium or to standard acidic lactate-buffered PDF (Dianeal PD4) or to a more biocompatible lactate-bicarbonate-buffered PDF (Physioneal 40). Parallel cell cultures were supplemented with 200 microM Quercetin. Cytotoxicity was assessed qualitatively by morphologic assessment and quantitatively by the release of cytoplasmic lactate dehydrogenase and fluorescence-activated cell sorting (FACS). PDF exposure with bioincompatible Dianeal PD4 resulted in severe disruption of cell cultures and in significantly increased lactate dehydrogenase (LDH) release (p=0.0007 vs. control). Addition of 200 microM Quercetin significantly decreased the LDH release (p=0.04 vs. "pure" Dianeal PD4 exposure), comparable to control exposure and to more biocompatible Physioneal 40 exposure (p=0.37) and resulted in marked preservation of cell culture monolayers and cellular viability as assessed by FACS. Introduction of cytoprotective agents such as Quercetin may represent an alternate approach to protect mesothelial cells from cytotoxicity of frequently used PDFs, comparably effective to the introduction of novel, more biocompatible, PDFs.

Oxidative stress contributes to accelerated development of the senescent phenotype in human peritoneal mesothelial cells exposed to high glucose

Increasing evidence indicates that cells exposed to high glucose exhibit shortened proliferative lifespan and enter the state of senescence earlier. However, the contribution of hyperglycemia-induced oxidative stress to premature cell senescence is not entirely clear. In the current study we have examined the role of oxidative stress in cellular senescence of human peritoneal mesothelial cells (HPMC) exposed to high glucose. The experiments were performed on primary omental-derived HPMC grown into senescence in the presence of normal (5 mM) and high (30 mM) glucose. Senescence of HPMC was associated with increased generation of reactive oxygen species (ROS) and decreased cellular glutathione (GSH). Exposure to high glucose significantly exacerbated these effects and increased the level of senescence-associated beta-galactosidase (SA-beta-Gal) and 8-hydroxy-2'-deoxyguanosine (8-OH-dG) expression. Furthermore, high glucose markedly increased senescence-related HPMC hypertrophy. The addition of L-2-oxothiazolidine-4-carboxylic acid, a GSH precursor, restored partially GSH levels and decreased ROS release. This effect was associated with reduced levels of SA-beta-Gal and 8-OH-dG, diminished TGF-beta1 and fibronectin release, and less pronounced hypertrophy of aged HPMC. These results indicate that the accelerated senescence response in HPMC exposed to high glucose is strongly related to oxidative stress.

Inhibitory Effects of the Peptide (CKPV)2 on Endotoxin-Induced Host Reactions

BACKGROUND

alpha-Melanocyte stimulating hormone (alpha-MSH) is an endogenous peptide that has remarkable anti-inflammatory and antimicrobial effects. These activities have been traced to the C-terminal tripeptide Lys-Pro-Val (KPV). A dimer composed of two KPV sequences connected with a Cys-Cys linker, (CKPV)2, is currently under clinical investigation for antimicrobial use. The present research was designed to evaluate effects of (CKPV)(2) on endotoxin-induced host reactions in vitro and in vivo.

MATERIALS AND METHODS

Effects of (CKPV)2, KPV, and [Nle4-dPhe7]-alpha-MSH (NDP-alpha-MSH) on tumor necrosis factor alpha (TNF-alpha) production were determined: 1) in human peripheral blood mononuclear cells (PBMC) stimulated with lipopolysaccharide (LPS) in vitro, and 2) in rats injected with LPS i.v. and sacrificed at 1 h. In additional experiments, dialysis peritonitis was induced in rats by adding LPS to dialysis fluid. Net ultrafiltrate was calculated and concentrations of nitrite (NO2-) and TNF-alpha were measured in blood and peritoneal fluid at 7 h.

RESULTS

(CKPV)2 inhibited TNF-alpha production by LPS-stimulated human PBMC. This small peptide was as effective as NDP-alpha-MSH and more potent than KPV. Similar effectiveness was observed in vivo: 1 h after LPS injection, the large increase in circulating TNF-alpha was markedly reduced by (CKPV)2 treatment. In LPS-induced peritonitis, (CKPV)2 restored net ultrafiltrate to control values and significantly inhibited concentrations of TNF-alpha and NO2- both in plasma and in dialysate.

CONCLUSIONS

The remarkable capacity of (CKPV)2 to inhibit endotoxin-induced host reactions suggests that it may be useful in treatment of inflammatory disorders.

Prevention of peritoneal sclerosis: a new proposal to substitute glucose with carnitine dialysis solution (biocompatibility testing in vitro and in rabbits)

AIM

Commercial glucose peritoneal dialysis solutions expose the peritoneum to hyperosmolar glucose containing variable amounts of non-enzymic breakdown products of glucose. These solutions are toxic for the peritoneum. The aim of the present study is to compare in vitro and in vivo characteristics of a new dialysis solution containing carnitine, a naturally occurring compound, as substitute of glucose.

MATERIAL AND METHODS

We compared in vitro and in the rabbit a new peritoneal dialysis solution containing carnitine, with two standard bicarbonate glucose peritoneal dialysis solutions and a solution containing icodextrin.

RESULTS

In vitro and in vivo the solution containing carnitine seems to be more biocompatible than standard glucose solutions and those containing icodextrin.

CONCLUSIONS

In our study the peritoneal dialysis solution containing carnitine seems to prevent the mesothelial changes observed with solutions containing glucose. Since carnitine has been extensively studied and seems to be well tolerated by hemodialysis patients, even at high doses for long periods, clinical trials in humans may be planned in the near future.

Volume Control in Peritoneal Dialysis Patients: Role of New Dialysis Solutions

This paper reviews the most recent clinical data on the volume status of long-term peritoneal dialysis (PD) patients. It appears that many PD patients are volume overloaded, associated with a high prevalence of hypertension and left ventricular hypertrophy. In the presence of the poor results in patients with peritoneal ultrafiltration, the introduction of the polyglucose solution, icodextrin, has ameliorated volume control in some of these patients. In a second part of the review, some of the structural and functional alterations in the peritoneal membrane and the role of glucose degradation products (GDP) in the commonly used dialysates as well as the resulting formation of advanced glycation end products are described. The introduction of low GDP-containing solutions at normal pH has at least in experimental models of PD attenuated the hemodynamic changes observed with the classical solutions. The solutions at normal pH containing either bicarbonate or a mixture of bicarbonate/lactate were clinically associated with less inflow pain.

Advanced glycation end products in uremia

The term "advanced glycation end products" (AGEs) stands for a heterogeneous group of amino acid derivatives that are formed via glycation processes between peptide-bound lysine or arginine derivatives and carbonyl compounds, processes originally known from food systems as "Maillard reactions." AGEs accumulate in plasma and tissues with advancing age, diabetes, and particular renal failure. In vivo and in vitro studies indicate that AGEs represent an important class of uremic toxins. This review focuses on the chemistry behind the formation of AGEs, possible mechanisms underlying the accumulation of AGEs in uremia, clinical and therapeutic implications, and possible nutritional consequences.