Icodextrin-induced lipid peroxidation disrupts the mesothelial cell cycle engine

Novel Aspects of the Immune Response Involved in the Peritoneal Damage in Chronic Kidney Disease Patients under Dialysis

Chronic kidney disease (CKD) incidence is growing worldwide, with a significant percentage of CKD patients reaching end-stage renal disease (ESRD) and requiring kidney replacement therapies (KRT). Peritoneal dialysis (PD) is a convenient KRT presenting benefices as home therapy. In PD patients, the peritoneum is chronically exposed to PD fluids containing supraphysiologic concentrations of glucose or other osmotic agents, leading to the activation of cellular and molecular processes of damage, including inflammation and fibrosis. Importantly, peritonitis episodes enhance peritoneum inflammation status and accelerate peritoneal injury. Here, we review the role of immune cells in the damage of the peritoneal membrane (PM) by repeated exposure to PD fluids during KRT as well as by bacterial or viral infections. We also discuss the anti-inflammatory properties of current clinical treatments of CKD patients in KRT and their potential effect on preserving PM integrity. Finally, given the current importance of coronavirus disease 2019 (COVID-19) disease, we also analyze here the implications of this disease in CKD and KRT.

Lithium preserves peritoneal membrane integrity by suppressing mesothelial cell αB-crystallin

Life-saving renal replacement therapy by peritoneal dialysis (PD) is limited in use and duration by progressive impairment of peritoneal membrane integrity and homeostasis. Preservation of peritoneal membrane integrity during chronic PD remains an urgent but long unmet medical need. PD therapy failure results from peritoneal fibrosis and angiogenesis caused by hypertonic PD fluid (PDF)-induced mesothelial cytotoxicity. However, the pathophysiological mechanisms involved are incompletely understood, limiting identification of therapeutic targets. We report that addition of lithium chloride (LiCl) to PDF is a translatable intervention to counteract PDF-induced mesothelial cell death, peritoneal membrane fibrosis, and angiogenesis. LiCl improved mesothelial cell survival in a dose-dependent manner. Combined transcriptomic and proteomic characterization of icodextrin-based PDF-induced mesothelial cell injury identified αB-crystallin as the mesothelial cell protein most consistently counter-regulated by LiCl. In vitro and in vivo overexpression of αB-crystallin triggered a fibrotic phenotype and PDF-like up-regulation of vascular endothelial growth factor (VEGF), CD31-positive cells, and TGF-β-independent activation of TGF-β-regulated targets. In contrast, αB-crystallin knockdown decreased VEGF expression and early mesothelial-to-mesenchymal transition. LiCl reduced VEGF release and counteracted fibrosis- and angiogenesis-associated processes. αB-crystallin in patient-derived mesothelial cells was specifically up-regulated in response to PDF and increased in peritoneal mesothelial cells from biopsies from pediatric patients undergoing PD, correlating with markers of angiogenesis and fibrosis. LiCl-supplemented PDF promoted morphological preservation of mesothelial cells and the submesothelial zone in a mouse model of chronic PD. Thus, repurposing LiCl as a cytoprotective PDF additive may offer a translatable therapeutic strategy to combat peritoneal membrane deterioration during PD therapy.

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

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

Osmotic Agents Hamper Mesothelial Repopulation as Seen in the Doughnut In Vivo Model

♦ Background

The problem of mesothelial cell injury derived from the use of peritoneal dialysis solutions has been explored deeply. Conversely, the eventual detrimental effects upon mesothelial cell regeneration have awaked less investigative efforts than those focused on injury.

♦ Objective

To evaluate in the in vivo and in situ rat “doughnut” model of mesothelial repopulation, the eventual effect of peritoneal lavage with Hank's Balanced Salt Solution (HBSS) as well as that of 4.25% glucose and 7.5% icodextrin dialysis solutions.

♦ Experimental Animals

100 Sprague–Dawley albino rats were included in the study. Animals were divided into five groups of 20 rats each: group 1: control at zero time; group 2: sham-injected rats; group 3: rats exposed to HBSS; group 4: rats treated with 4.25% glucose peritoneal dialysis solution; group 5: rats injected with 7.5% icodextrin.

♦ Methods

Selective exfoliation of a ring of mesothelium (width 0.8 mm, diameter 4 mm) covering the anterior surface of the liver was performed in 80 animals. The control zero-time group was used to evaluate the normal density distribution of the mesothelial cells forming the monolayer. The other groups were treated by means of daily sham injections or intraperitoneal infusion of each experimental solution for a period of 30 consecutive days. After a recovery period of 15 days, imprints and biopsies from the monolayer covering the exfoliated area were taken and processed for light microscopy.

♦ Results

Macroscopic observation of the abdominal cavity at the end of the 15-day recovery period showed that the prevalence of fibrotic adhesions between the peritoneal exfoliated area and the neighboring diaphragm was 10% for the sham-injected group, 5% for the HBSS-exposed animals, 85% for the rats injected with 4.25% glucose, and 95% for the icodextrin-treated group. Prevalence of fibrous adhesions in sham-injected animals and rats exposed to HBSS were devoid of statistically significant differences. Conversely, comparison of these groups with results observed in animals treated with the osmotic agents was significant, at the p < 0.0039 level. Regarding density distribution of mesothelial cells observed in imprints, there were no significant differences between the control zero-time and the sham-injected group. This parameter was marginally lower ( p < 0.05) in the HBSS-treated rats. Imprints were not taken from animals exposed to glucose or icodextrin because a dense layer of connective tissue replaced the exfoliated mesothelial area.

♦ Conclusions

Observations made in this study support the contention that both osmotic agents, 4.25% glucose and 7.5% icodextrin, substantially restrain the normal process of mesothelial cell repopulation and induce repair by means of connective tissue. The underlying mechanism is most likely sustained oxidative stress.

Influence of Icodextrin on Plasma and Dialysate Levels of N∊-(Carboxymethyl)Lysine and N∊-(Carboxyethyl)Lysine

Rationale

Standard peritoneal glucose solutions may induce the formation of advanced glycation end products (AGEs). Preliminary data suggest that AGE formation may be less with the use of polyglucose solutions (icodextrin). Therefore, we investigated whether the use of icodextrin for the long dwell would result in a reduction in plasma and dialysate levels of the AGE products N∊-(carboxymethyl) lysine (CML) and N∊-(carboxyethyl)lysine (CEL).

Patients and Methods

40 patients were randomized to treatment with standard glucose solutions (1.36%) and icodextrin for the long dwell during a 4-month study period; 32 patients completed the study. CML was assessed by stable isotope dilution/tandem mass spectrometry.

Results

CML levels in plasma increased significantly in patients treated with icodextrin (0.146 ± 0.056 at start vs 0.188 ± 0.069 μmol/mmol Lys at the end of the study, p < 0.0001) but did not change in the control group (0.183 ± 0.090 vs 0.188 ± 0.085 μmol/mmol Lys). The same held true for CML levels in dialysate (0.28 ± 0.09 at start vs 0.33 ± 0.11 μmol/mmol Lys at the end of the study, p < 0.025). No change was observed in patients treated with the control solutions (0.31 ± 0.11 at start vs 0.31 ± 0.07 μmol/mmol Lys).

Conclusion

Contrary to the hypothesis, plasma and dialysate levels of CML increased in patients treated using icodextrin for the long dwell.

Agents that Modulate Peritoneal Membrane Structure and Function

Extensive experience with chronic peritoneal dialysis has identified a series of functional and anatomical pathologic changes in the peritoneal membrane thought to be the result of repeated insults from bioincompatible solutions. Laboratory and clinical findings from recent investigations often conflict and are difficult to interpret due to variations in methodologies, animal models, study designs, and data analyses. The principal pathophysiologic mechanisms identified thus far are oxidative stress, inflammation, and their consequences. Many substances used to neutralize the action of these insults, prevent formation of toxic compounds, or directly alter solute and water transport to improve peritoneal membrane performance have been studied. We herein review the most promising of these substances or those that deserve attention because their use has contributed to better understanding of peritoneal pathophysiology. Most peritoneal solution additives have proved useless due to their toxicity and undesirable effects, ineffectiveness, or manufacturing limitations. A few substances deserve more attention, particularly those capable of restoring negatively charged membrane sites, those that somehow improve permselectivity, scavengers of oxidants, and advanced glycation end-product inhibitors and breakers. Recent publications on clinical experience with neutral pH, low glucose degradation product (GDP) peritoneal solutions, although few and preliminary, are most encouraging. The virtual elimination of GDPs in these novel solutions will probably preclude the need for GDP scavengers and inhibitors. Nonetheless, there is room for further significant improvement in solution biocompatibility and for compounds that may restore peritoneal function.

Epithelial-to-Mesenchymal Transition and Migration of Human Peritoneal Mesothelial Cells Undergoing Senescence

BACKGROUND

Epithelial-to-mesenchymal transition (EMT) of human peritoneal mesothelial cells (HPMCs) contributes to fibrotic thickening of the peritoneum that develops in patients on peritoneal dialysis (PD). The process is thought to be largely mediated by transforming growth factor-beta (TGF-β). As TGF-β has also been implicated in senescence of HPMCs, we have performed an exploratory study to examine if senescent HPMCs can undergo EMT.

METHODS

Omentum-derived HPMCs were rendered senescent by repeated passages in culture. Features of EMT were assessed by immunostaining and quantitative polymerase chain reaction (qPCR) at various stages of the HPMC lifespan and after treatment with or without TGF-β. The motility of HPMCs was assessed in a scratch wound migration assay.

RESULTS

Replicative senescence of HPMCs was associated with a gradual increase in the constitutive expression of EMT markers, including increased production of extracellular matrix proteins. However, senescent HPMCs also retained epithelial cell features such as cytokeratin, calretinin, and E-cadherin and showed decreased, rather than increased, motility. In contrast, exposure to TGF-β resulted in an up-regulation of mesenchymal markers and down-regulation of epithelial markers. Such effects of TGF-β occurred both in young and senescent cells, although they were less pronounced in senescence.

CONCLUSIONS

Senescence of HPMCs is associated with spontaneous development of several EMT features. At the same time, senescent HPMCs preserve epithelial cell-like characteristics and are less prone to develop a full EMT phenotype in response to TGF-β. These observations may support the concept of cellular senescence being antagonistically pleiotropic with regard to EMT.

Effect of Neutral pH Icodextrin Peritoneal Dialysis Fluid on Mesothelial Cells

Conventional acidic icodextrin peritoneal dialysate (CI) has low biocompatibility due to its low pH, and a neutral pH icodextrin dialysate (NI) was developed. The influence of NI on the peritoneum has not been clarified. The effects of the two dialysates on cultured rat mesothelial cells were examined. CI, but not NI, increased α-smooth muscle actin, collagen type 1 and 3, and P21 mRNA expressions. CI with neutralized pH did not improve these harmful effects. With NI+ glucose degradation products (GDPs: same concentration as CI), mRNA expressions were comparable to those with NI alone. However, if NI + GDPs was acidified, mRNA levels matched those with CI. The proportion in the G2/M phase of the cell cycle was lower with CI than with NI stimulation. From these results, CI stimulated epithelial-mesenchymal transition, fibrotic changes, inhibited cell growth, and induced cell senescence. These effects were attributed to the combined low pH and high GDPs.

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.

Targeting cannabinoid signaling for peritoneal dialysis-induced oxidative stress and fibrosis

Long-term exposure to bioincompatible peritoneal dialysis (PD) solutions frequently results in peritoneal fibrosis and ultrafiltration failure, which limits the life-long use of and leads to the cessation of PD therapy. Therefore, it is important to elucidate the pathogenesis of peritoneal fibrosis in order to design therapeutic strategies to prevent its occurrence. Peritoneal fibrosis is associated with a chronic inflammatory status as well as an elevated oxidative stress (OS) status. Beyond uremia per se, OS also results from chronic exposure to high glucose load, glucose degradation products, advanced glycation end products, and hypertonic stress. Therapy targeting the cannabinoid (CB) signaling pathway has been reported in several chronic inflammatory diseases with elevated OS. We recently reported that the intra-peritoneal administration of CB receptor ligands, including CB₁ receptor antagonists and CB₂ receptor agonists, ameliorated dialysis-related peritoneal fibrosis. As targeting the CB signaling pathway has been reported to be beneficial in attenuating the processes of several chronic inflammatory diseases, we reviewed the interaction among the cannabinoid system, inflammation, and OS, through which clinicians ultimately aim to prolong the peritoneal survival of PD patients.

Senescence-Associated Changes in Proteome and O-GlcNAcylation Pattern in Human Peritoneal Mesothelial Cells

INTRODUCTION

Senescence of peritoneal mesothelial cells represents a biological program defined by arrested cell growth and altered cell secretory phenotype with potential impact in peritoneal dialysis. This study aims to characterize cellular senescence at the level of global protein expression profiles and modification of proteins with O-linked N-acetylglucosamine (O-GlcNAcylation).

METHODS

A comparative proteomics analysis between young and senescent human peritoneal mesothelial cells (HPMC) was performed using two-dimensional gel electrophoresis. O-GlcNAc status was assessed by Western blot under normal conditions and after modulation with 6-diazo-5-oxo-L-norleucine (DON) to decrease O-GlcNAcylation or O-(2-acetamido-2-deoxy-D-glucopyranosylidene) amino N-phenyl carbamate (PUGNAc) to increase O-GlcNAcylation.

RESULTS

Comparison of protein pattern of senescent and young HPMC revealed 29 differentially abundant protein spots, 11 of which were identified to be actin (cytoplasmic 1 and 2), cytokeratin-7, cofilin-2, transgelin-2, Hsp60, Hsc70, proteasome β-subunits (type-2 and type-3), nucleoside diphosphate kinase A, and cytosolic 5'(3')-deoxyribonucleotidase. Although the global level of O-GlcNAcylation was comparable, senescent cells were not sensitive to modulation by PUGNAc.

DISCUSSION

This study identified changes of the proteome and altered dynamics of O-GlcNAc regulation in senescent mesothelial cells. Whereas changes in cytoskeleton-associated proteins likely reflect altered cell morphology, changes in chaperoning and housekeeping proteins may have functional impact on cellular stress response in peritoneal dialysis.

Mesothelial morphology and organisation after peritoneal treatment with solid and liquid adhesion barriers--a scanning electron microscopical study

Separation of traumatized tissue represents the only promising strategy in postoperative adhesion prevention, a relevant clinical problem after surgical intervention. In the present study scanning electron microscopy (SEM) and subsequent morphometry were used to analyse the tissue response to five commercial adhesion barriers. Standardised peritoneal lesions in Wistar rats were covered with solid and viscous barrier materials and semiquantitatively analysed 14 days postoperatively. Striking morphological differences in lesion surface organisation between the barrier groups became apparent with colonisation of the barrier by mesothelial cells to different degrees. Furthermore, the mesothelial cells showed either a normal or activated phenotype depending on the underlying biomaterial. These experiments demonstrate that the examination by SEM gives useful insights into the performance of barrier materials and the cellular processes of adhesion prevention, since mesothelial cells play an active role in the pathogenesis of adhesion formation.

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.

Comparison of icodextrin- and glucose-based peritoneal dialysis fluids in their acute and chronic effects on human peritoneal mesothelial cells

BACKGROUND

Icodextrin-based peritoneal dialysis fluids (PDFs) display several features that may potentially improve their biocompatibility compared to conventional glucose-containing solutions. So far, however, the studies assessing the biocompatibility profile of icodextrin toward human peritoneal mesothelial cells (HPMC) has produced mixed results. The present study was performed to examine the acute and chronic impact of icodextrin on HPMC in vitro in comparison with standard glucose-based PDF.

METHODS

Omentum-derived HPMC were either acutely pre-exposed to or incubated chronically (for up to 10 days) in the presence of icodextrin-PDF. Parallel cultures were treated with conventional PDFs containing either 1.5% or 4.25% glucose. All fluids were tested at neutral pH. HPMC were assessed for viability, proliferation, IL-6 secretion and generation of reactive oxygen species (ROS).

RESULTS

Incubation in the presence of icodextrin-PDF significantly reduced HPMC proliferation in a manner similar to that of 1.5% glucose-PDF. In addition, exposure to icodextrin-PDF impaired viability and IL-6 release from HPMC. This effect occurred both after the short pre-treatment with neat icodextrin-PDF for 1-4 hours and after prolonged incubation (up to 10 days) in media supplemented with icodextrin-PDF (1:1). The dysfunction of icodextrin-treated HPMC was of the magnitude that was between the effects exerted by 1.5%- and 4.25%-glucose PDF. Furthermore, exposure of HPMC to icodextrin-PDF induced a dose-dependent increase in ROS generation which was comparable to that produced by 1.5%-glucose PDF.

CONCLUSION

Exposure to icodextrin-PDF may impair viability and function of HPMC. The detrimental effects of icodextrin-PDF are at least as serious as those produced by conventional heat-sterilized low glucose-based PDF.

Accelerated senescence of human peritoneal mesothelial cells exposed to high glucose: the role of TGF-beta1

Cellular senescence can be activated in response to noxious environmental stimuli. A senescent-like phenotype has been detected in the peritoneal mesothelium of mice exposed to high intraperitoneal glucose. We have sought to examine whether high glucose (HG) can induce the senescence program in human peritoneal mesothelial cells (HPMC) in vitro. Senescence of omentum-derived HPMC was induced by serial passages. Cells were cultured in media containing either 5 mM glucose, 30 mM glucose, or 5 mM glucose and 25 mM mannitol (M) for osmotic control. Compared with HPMC cultured in low glucose, the growth rate of cells exposed to HG was significantly decreased so that the cells reached fewer population doublings before entering senescence. Exposure to HG led to increased expression of senescence-associated beta-galactosidase (SA-beta-Gal) and of the cell cycle inhibitors p21(Waf1) and p27(Kip1). Late-passage HPMC exposed to HG displayed marked hypertrophy and released increased amounts of fibronectin and TGF-beta1. These effects were absent from HPMC treated with equimolar M. Exposure of early-passage HPMC to exogenous recombinant TGF-beta1 induced a senescence marker SA-beta-Gal in a dose-dependent manner and mimicked other senescence-associated alterations induced by HG. The addition of anti-TGF-beta1 neutralizing antibody partially reduced the activation of HG-induced SA-beta-Gal. These results indicate that chronic exposure to elevated glucose may result in TGF-beta1-mediated accelerated senescence of HPMC in vitro, which may hypothetically contribute to the peritoneal membrane dysfunction during peritoneal dialysis in vivo.

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.

Mesothelial progenitor cells and their potential in tissue engineering

The mesothelium consists of a single layer of flattened mesothelial cells that lines serosal cavities and the majority of internal organs, playing important roles in maintaining normal serosal integrity and function. A mesothelial 'stem' cell has not been identified, but evidence from numerous studies suggests that a progenitor mesothelial cell exists. Although mesothelial cells are of a mesodermal origin, they express characteristics of both epithelial and mesenchymal phenotypes. In addition, following injury, new mesothelium regenerates via centripetal ingrowth of cells from the wound edge and from a free-floating population of cells present in the serosal fluid, the origin of which is currently unknown. Recent findings have shown that mesothelial cells can undergo an epithelial to mesenchymal transition, and transform into myofibroblasts and possibly smooth muscle cells, suggesting plasticity in nature. Further evidence for a mesothelial progenitor comes from tissue engineering applications where mesothelial cells seeded onto tubular constructs have been used to generate vascular replacements and grafts to bridge transected nerve fibres. These findings suggest that mesothelial cell progenitors are able to switch between different cell phenotypes depending on the local environment. However, only by performing detailed investigations involving selective cell isolation, clonal analysis together with cell labelling and tracking studies, will we begin to determine the true existence of a mesothelial stem cell.

Acute oxidative stress induces peritoneal hyperpermeability, mesothelial loss, and fibrosis

We explored the acute and long-term effects of short-lived, intense oxidative stress on peritoneal permeability and structure, induced with intraperitoneal injection of the oxidant agent deoxycholate, in rats. Ten minutes after the experimental intervention, peritoneal dialysis, performed over an exposure time of 60 minutes, revealed an increased urea dialysate/plasma ratio, greater glucose absorption, increased albumin losses in the effluent dialysate, and a reduced ultrafiltration rate. Mesothelial-cell imprints taken from the anterior liver surface indicated a substantially decreased density in the cell population. After the recovery period of 30 days, all alterations were still evident. Additionally, macroscopic and histologic observations made at this time interval detected peritoneal fibrosis and sclerosis, characterized by peritoneal adhesions, wrapping of intestinal loops, and the presence of a layer of fibrous tissue dressing the cavitary aspect of the liver peritoneal envelope. This report describes a reproducible experimental model of peritoneal fibrosis induced by acute oxidative injury. On the basis of these findings, it may be speculated that functional and structural alterations observed in patients are related to long-term continuous exposure of the monolayer to oxidative injury resulting from the high concentrations of d-glucose present in peritoneal dialysis solutions.