IL-1 beta, a major stimulator of hyaluronan synthesis in vitro of human peritoneal mesothelial cells: relevance to peritonitis in CAPD

Endogenously-Produced Hyaluronan and Its Potential to Regulate the Development of Peritoneal Adhesions

Formation of peritoneal adhesions (PA) is one of the major complications following intra-abdominal surgery. It is primarily caused by activation of the mesothelial layer and underlying tissues in the peritoneal membrane resulting in the transition of mesothelial cells (MCs) and fibroblasts to a pro-fibrotic phenotype. Pro-fibrotic transition of MCs—mesothelial-to-mesenchymal transition (MMT), and fibroblasts activation to myofibroblasts are interconnected to changes in cellular metabolism and culminate in the deposition of extracellular matrix (ECM) in the form of fibrotic tissue between injured sides in the abdominal cavity. However, ECM is not only a mechanical scaffold of the newly synthetized tissue but reciprocally affects fibrosis development. Hyaluronan (HA), an important component of ECM, is a non-sulfated glycosaminoglycan consisting of N-acetyl-D-glucosamine (GlcNAc) and D-glucuronic acid (GlcUA) that can affect the majority of processes involved in PA formation. This review considers the role of endogenously produced HA in the context of different fibrosis-related pathologies and its overlap in the development of PA.

Patient-derived and artificial ascites have minor effects on MeT-5A mesothelial cells and do not facilitate ovarian cancer cell adhesion

The presence of ascites in the peritoneal cavity leads to morphological and functional changes of the peritoneal mesothelial cell layer. Cells loose cell-cell interactions, rearrange their cytoskeleton, activate the production of fibronectin, and change their cell surface morphology in a proinflammatory environment. Moreover, ovarian cancer cell adhesion has been shown to be facilitated by these changes due to increased integrin- and CD44-mediated binding sites. In this study, the biological responsiveness of the human pleural mesothelial cell line MeT-5A to patient-derived and artificial ascites was studied in vitro and adhesion of ovarian cancer cells, i.e. SKOV-3 cells, investigated. Changes were mainly observed in cells exposed to artificial ascites containing higher cytokine concentrations than patient-derived ascites. Interestingly, reduced cell-cell interactions were already observed in untreated MeT-5A cells and effects on tight junction protein expression and permeability upon exposure to ascites were minor. Ascites induced upregulation of CDC42 effector protein 2 expression, which affects stress fiber formation, however significant F-actin reorganization was not observed. Moreover, fibronectin production remained unchanged. Analysis of mesothelial cell surface characteristics showed upregulated expression of intercellular adhesion molecule 1, slightly increased hyaluronic acid secretion and decreased microvillus expression upon exposure to ascites. Nevertheless, the observed changes were not sufficient to facilitate adhesion of SKOV-3 cells on MeT-5A cell layer. This study revealed that MeT-5A cells show a reduced biological responsiveness to the presence of ascites, in contrast to published studies on primary human peritoneal mesothelial cells.

Glycosaminoglycans and Proteoglycans: Overlooked Entities?

♦ Background

By virtue of their high net negative charge, glycosaminoglycans and proteoglycans play pivotal roles in biologic processes such as cell–cell and cell–matrix interactions, sequestration of growth factors, activation of chemokines and cytokines, and permselectivity of basement membranes.

♦ Methods

The present article reviews the putative roles of glycosaminoglycans and proteoglycans in the peritoneal cavity during normal peritoneal homeostasis and chronic inflammation, the latter induced by constant exposure of the peritoneum to non-physiologic peritoneal dialysis (PD) solutions.

♦ Results

Glycosaminoglycans have been identified in the mesothelial glycocalyx, a slippery, non-adhesive layer that protects the peritoneal membrane from abrasion and infection. Dermatan sulfate proteoglycans can neutralize the activity of transforming growth factor β1 and can thus play an essential role in modulating peritoneal fibrosis. Heparan sulfate proteoglycans play a crucial role in the sequestration of growth factors; they also modulate selective permeability of proteins across the peritoneal cavity. Reduced expression of perlecan, a heparan sulfate proteoglycan of the basement membrane, is observed in peritoneal biopsies obtained from established PD patients, consequent to prolonged exposure to the elevated glucose concentrations in conventional PD solutions. Supplementation of PD fluids with glycosaminoglycans has been shown to be beneficial to both the structural and functional integrity of the peritoneum.

♦ Conclusions

Recent advances in the field of glycobiology have revealed a multitude of biologic processes that are controlled or influenced by glycosaminoglycans and proteoglycans. Altered synthesis of these macromolecules during PD has serious implications for the peritoneal transport of proteins, host defense, wound healing, inflammation, and fibrosis.

Intraperitoneal Hyaluronan Administration in Conscious Rats: Absorption, Metabolism, and Effects on Peritoneal Fluid Dynamics

Background

Hyaluronan (HA) is a major component of interstitial tissue that participates in fluid homeostasis, response to inflammation, and wound healing. Previous studies have shown that intraperitoneal administration of HA can affect peritoneal fluid transport during short peritoneal dialysis exchanges in anesthetized rats. We sought to investigate the effect of high molecular weight HA on peritoneal permeability in conscious rats during dialysis exchanges up to 8 hours in duration. In addition, we sought to investigate the absorption of HA from the peritoneal cavity, its accumulation in peritoneal tissues, and its metabolism in normal and uremic rats.

Methods

Experiments were performed on male Wistar rats infused with 30 mL peritoneal dialysis solution (Dianeal, Baxter Healthcare; Castelbar, Ireland) containing 10 mg/dL HA or with Dianeal alone (control). Peritoneal fluid removal (net ultrafiltration), permeability to glucose, creatinine, and total proteins, and tissue and blood levels of HA were determined in separate groups of rats at 1, 2, 4, 6, and 8 hours after intraperitoneal infusion. Hyaluronan appearance and disappearance from plasma were also studied for 24 hours in separate groups of normal and uremic rats.

Results

Net ultrafiltration was significantly greater (27%) in rats infused with HA at 4, 6, and 8 hours ( p < 0.01) compared to controls. Transperitoneal equilibration of protein was reduced by 27% ( p < 0.001) at 4 hours and by 30% ( p < 0.01) at 8 hours. During the 8-hour exchange, peritoneal clearance of creatinine increased by 27% ( p < 0.01), whereas the clearance of total protein decreased by 27% ( p < 0.005). After 8 hours, 25.7% ± 3.1% of the administered HA was absorbed from the peritoneal cavity, peritoneal tissue HA concentration was increased by 117% ( p < 0.001), and plasma HA levels increased by 435% ( p < 0.001). Plasma HA levels returned to normal within 24 hours after intraperitoneal administration in both healthy and uremic rats.

Conclusions

Hyaluronan added to dialysis fluid is absorbed from the peritoneal cavity and accumulates in peritoneal tissues. Hyaluronan supplementation produces changes in peritoneal permeability, leading to higher net ultrafiltration and peritoneal creatinine clearance, whereas total protein clearance decreases. The HA that is absorbed from the peritoneal cavity appears to be rapidly metabolized in both healthy and uremic rats.

Effects of Intraperitoneal Hyaluronan on Peritoneal Fluid and Solute Transport in Peritoneal Dialysis Patients

← Background

Hyaluronan (HA) is a glycosaminoglycan found in connective tissues and tissue spaces, including the peritoneal cavity. In vivo studies in a rat model of peritoneal dialysis (PD) have shown that addition of HA to PD solution during an intraperitoneal dwell can alter peritoneal fluid transport and protect the peritoneal membrane from the effects of inflammation and repeated infusions of dialysis solution. The current study sought to evaluate the safety of intraperitoneal HA and its effect on peritoneal fluid and solute transport when administered during a dialysis dwell in humans.

← Methods

13 PD patients were enrolled in a prospective, randomized crossover study involving three dialysis treatments using the following PD solutions: ( 1 ) a commercially available PD solution (Dianeal PD-4, 1.36% glucose; Baxter Healthcare Corporation, Alliston, Ontario, Canada); ( 2 ) Dianeal PD-4 containing 0.1 g/L HA, and ( 3 ) Dianeal PD-4 containing 0.5 g/LHA. Each 6-hour dialysis exchange was separated from the other exchanges by a 2-week washout period. Radioiodinated human serum albumin (RISA) was administered with the dialysis solution to evaluate intraperitoneal volume, net ultrafiltration (UF), and fluid reabsorption. Peritoneal clearances, dialysate/plasma ratios (D/P), and mass transfer area coefficients (MTACs) were determined for sodium, urea, creatinine, albumin, and glucose. Safety was evaluated by monitoring adverse events and changes in serum chemistries. Ten patients completed all three dialysis exchanges and two additional patients completed at least one treatment exchange.

← Results

There were no reported adverse events related to HA administration and no significant changes in serum chemistries. There were no significant differences in net UF or peritoneal volume profiles among the three treatments. Mean net UF calculated using residual volumes, estimated by RISA dilution, tended to be slightly higher during treatment with solution containing 0.1 g/L HA and 0.5 g/L HA [74 ± 86 (SE) and 41 ± 99 mL, respectively] compared to control treatment (–58 ± 129 mL). Although not statistically significant, there was a trend toward decreased fluid reabsorption during treatment with HA. Solute clearances, D/P ratios, and MTACs were similar for the three treatments. Serum levels of HA were also unaffected by the two treatment solutions.

← Conclusions

These data support the acute safety of HA when administered intraperitoneally with the dialysis solution to PD patients. Due to the small sample size and variability in net UF and fluid reabsorption, statistically significant differences were not demonstrated for these parameters. However, a trend toward decreased fluid reabsorption was observed, suggesting that HA may act by a mechanism similar to that observed in animal studies. Further studies are necessary to evaluate whether the beneficial effects of HA observed in animal studies can be shown in humans.

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.

Role of Peritoneal Mesothelial Cells and Fibroblasts in the Synthesis of Hyaluronan during Peritoneal Dialysis

Objective

To assess the in vitro synthesis rate of hyaluronan (HA) by human peritoneal mesothelial cells and peritoneal fibroblasts in the presence of effluent dialysate from continuous ambulatory peritoneal dialysis (CAPD) patients.

Methods

We used primary cultures of human peritoneal mesothelial cells and peritoneal fibroblasts from nonuremic patients to study the effect of interleukin-1 β (11–1 β) and pooled effluent dialysate, from noninfected and infected CAPD patients, on the synthesis of HA by the studied cells. We also tested the effect of the exogenous HA on the synthesis rate of that glycosaminoglycan. We studied the correlation between HA concentration in effluent dialysate and the stimulatory effect of that solution on in vitro synthesis of HA by mesothelium.

Results

Peritoneal fibroblasts produce more HA than mesothelial cells. Noninfected effluent dialysates or dialysates from CAPD patients with peritonitis stimulate synthesis of HA by mesothelial cells and fibroblasts. Interleukin-1 β has a stimulating effect, which was synergistic with effluent dialysates, on the synthesis of HA by mesothelium and peritoneal fibroblasts. A weak correlation was demonstrated between the level of HA in effluent dialysate and the stimulatory effect of that dialysate on in vitro synthesis of HA by mesothelial cells.

Conclusions

Peritoneal fibroblasts are a more potent source of HA than are mesothelial cells, but probably the latter are the main source of HA in drained dialysate. Although effluent dialysates contain factors that stimulate the production of HA by mesothelium, there is weak correlation between that stimulatory effect and the actual HA concentration in the dialysate, which, in some patients, might suggest low “responsiveness” of the membrane.

High Glucose Solution and Spent Dialysate Stimulate the Synthesis of Transforming Growth Factor-β1of Human Peritoneal Mesothelial Cells: Effect of Cytokine Costimulation

Objective

To investigate the effect of high glucose and spent peritoneal dialysate on the transforming growth factor-β1(TGFβ1) synthesis of cultured human peritoneal mesothelial cells (HPMCs) and to examine the effect of costimulation with high glucose or spent dialysate, and cytokines, interleukin-1β (IL-1β), and tumor necrosis factor-α (TNFα) on TGFβ1synthesis of HPMCs.

Design

HPMCs were exposed to different concentrations of glucose (30, 60, and 90 mmol/L) or spent peritoneal dialysate for 48 hours in the absence or presence of IL-1β (1 ng/mL) and TNFα (1 ng/mL). TGFβ1mRNA expression was assessed by Northern blot analysis and TGFβ1protein release by Western blot analysis and enzymelinked immunosorbent assay (ELISA).

Results

Exposure of HPMCs to high glucose conditions (30, 60, and 90 mmol/L of D-glucose) induced 2.3-, 3.6-, and 4.0-fold increases in TGFβ1mRNA expression of HPMC with enhanced TGFβ1protein synthesis and secretion into the media, whereas there were no significant changes in TGFβ1synthesis with equimolar concentrations of D-mannitol. Incubation with spent dialysate also significantly increased TGFβ1mRNA expression and protein secretion compared to control media ( p < 0.05). Stimulation with IL-1β (1 ng/mL) or TNFα (1 ng/mL) resulted in a significant increase in TGFβ1mRNA expression after 48 hours: 2.7 and 2.1 times the control level, respectively. However, TNFα-induced increase in TGFβ1mRNA expression was not translated into TGFβ1protein secretion, while IL-1β stimulation induced a significant increase in TGFβ1protein secretion as well as TGFβ1mRNA expression. Combined stimulation by high glucose or spent dialysate, together with IL-1β or TNFα, showed a greater increase in TGFβ1mRNA expression and protein secretion compared to stimulation by high glucose or spent dialysate alone.

Conclusion

Our results clearly show that high glucose solution and spent dialysate themselves might be sufficient to stimulate the production of TGFβ1by peritoneal mesothelial cells. In peritoneal dialysis patients, this state of chronic induction of TGFβ1is further exacerbated in the presence of peritonitis because of the stimulatory effect of proinflammatory cytokines, resulting in augmented TGFβ1synthesis, thus promoting peritoneal fibrosis.

Intraperitoneal Hyaluronan Production in Stable Continuous Ambulatory Peritoneal Dialysis Patients

Objective

Several cytokines and proteins are excreted intraperitoneally during the course of peritonitis and stable states in continuous ambulatory peritoneal dialysis (CAPD) patients. Dialysate hyaluronan (HYA) is also regarded as a marker of peritoneal healing during bacterial peritonitis. We examined here, intraperitoneal HYA production in stable CAPD patients and compared the results to those of the peritoneal equilibration test (PET), the length of time on dialysis, and other marker proteins.

Design

We determined the concentration of HYA and other marker proteins in the 4-hour-dwell dialysate at 1-year intervals.

Setting

CAPD unit in Hitachi General Hospital.

Patients

The subjects were 46 stable CAPD patients who underwent 104 PETs.

Results

A correlation was found between the length of time on dialysis and the amount of HYA excretion in the 4-hr-dwell dialysate ( r = 0.403, p < 0.001). A positive but weak correlation was found between the dialysate-to-plasma ratio of the creatinine concentration and dialysate HYA excretion ( r = 0.229, p < 0.05). Seven patients were over the 90th percentile in both the concentration of HYA (>349.2 ng/mL) and the amount of HYA (>743.6 μg/4-hr dwell). Five patients exceeded 1000 μg of HYA excretion in the 4-hr-dwell dialysate, 4 of whom showed an abrupt increase of HYA excretion to more than 1000 μg/4-hr dwell, and discontinued CAPD within 6 months due to ultrafiltration failure. Two of these 4 patients were diagnosed with sclerosing encapsulating peritonitis at autopsy.

Conclusion

Intraperitoneal HYA production increased with both higher permeable membrane and the length of time on CAPD. Monitoring of HYA in the peritoneal dialysate may be useful as a marker to assess functional and morphological changes in the peritoneum in long-term CAPD patients.

Anti-fibrotic effect of decorin in peritoneal dialysis and PD-associated peritonitis

BACKGROUND

Progressive peritoneal fibrosis is a common complication in patients on long-term peritoneal dialysis (PD). PD-associated peritonitis is a major exacerbating factor. We investigated the anti-fibrotic properties of decorin secreted by peritoneal mesothelial cells.

METHODS

Dialysate decorin level in stable PD patients and those with peritonitis was measured. In vitro experiments were conducted to investigate the effect of decorin in fibrotic response in human peritoneal mesothelial cells (HPMC).

FINDINGS

Increasing PD duration was associated with a progressive decrease of dialysate decorin and CA125 levels. Dialysate decorin level correlated with CA125 level. Peritonitis episodes were associated with a massive drop of dialysate decorin, which persisted for over three months despite clinical recovery. Dialysate decorin level correlated with that of TGF-β1, but was inversely related to IL-1β and IL-8. TGF-β1, IL-1β, IL-6, IL-8, or TNF-α reduced decorin secretion in HPMC, but induced fibronectin expression. The effects were mediated in part through increased p38 MAPK and AKT/PI3K phosphorylation. Decorin abrogated the induction of fibronectin expression in mesothelial cells by PD fluids or pro-fibrotic cytokines, through decreased TGF-βRI, p38 MAPK and AKT/PI3K phosphorylation and increased glycogen synthase kinase-3β phosphorylation. Decorin gene-silencing resulted in increased fibronectin expression under these conditions.

INTERPRETATION

Our data demonstrate anti-fibrotic actions of decorin in HPMC, when these cells are subjected to the pro-fibrotic effect of peritoneal dialysate and pro-fibrotic cytokines in PD, especially during peritonitis.

Peritoneal Membrane Preservation

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

Chemistry and clinical relevance of carbohydrate degradation in drugs

Carbohydrate degradation products are formed during heat sterilization in drugs containing (poly-)glucose as osmotic agents. Given this situation, peritoneal dialysis fluids (PDFs) and infusion fluids are of particular clinical relevance, because these drugs deliver process contaminants either over a longer period or directly into the circulation of patients who are critically ill. For the development of suitable mitigation strategies, it is important to understand the reaction mechanisms of carbohydrate degradation during sterilization and how the resulting products interact with physiological targets at the molecular level. Furthermore, reliable, comprehensive, and highly sensitive quantification methods are required for product control and toxicological evaluation.

Impact of a low-glucose peritoneal dialysis regimen on fibrosis and inflammation biomarkers

BACKGROUND

The impact of a low-glucose peritoneal dialysis (PD) regimen on biomarkers of peritoneal inflammation, fibrosis and membrane integrity remains to be investigated.

METHODS

In a randomized, prospective study, 80 incident PD patients received either a low-glucose regimen comprising Physioneal (P), Extraneal (E) and Nutrineal (N) (Baxter Healthcare Corporation, Deerfield, IL, USA) (PEN group), or Dianeal (control group) for 12 months, after which both groups continued with Dianeal dialysis for 6 months. Serum and dialysate levels of vascular endothelial growth factor (VEGF), decorin, hepatocyte growth factor (HGF), interleukin-6 (IL-6), macrophage migration inhibitory factor (MIF), hyaluronan (HA), adiponectin, soluble-intracellular adhesion molecule (s-ICAM), vascular cell adhesion molecule-1 (VCAM-1) and P-selectin, and dialysate cancer antigen 125 (CA125), were measured after 12 and 18 months. This paper focuses on results after 12 months, when patients in the PEN group changed to glucose-based PD fluid (PDF).

RESULTS

At the end of 12 months, effluent dialysate levels of CA125, decorin, HGF, IL-6, adiponectin and adhesion molecules were significantly higher in the PEN group compared to controls, but all decreased after patients switched to glucose-based PDF. Macrophage migration inhibitory factor level was lower in the PEN group but increased after changing to glucose-based PDF and was similar to controls at 18 months. Serum adiponectin level was higher in the PEN group at 12 months, but was similar in the 2 groups at 18 months. Body weight, residual renal function, ultrafiltration volume and total Kt/V did not differ between both groups. Dialysate-to-plasma creatinine ratio at 4 h was higher in the PEN group at 12 months and remained so after switching to glucose-based PDF.

CONCLUSION

Changes in the biomarkers suggest that the PEN PD regimen may be associated with better preservation of peritoneal membrane integrity and reduced systemic vascular endothelial injury.

Regulation of synthesis and roles of hyaluronan in peritoneal dialysis

Hyaluronan (HA) is a ubiquitous extracellular matrix glycosaminoglycan composed of repeated disaccharide units of alternating D-glucuronic acid and D-N-acetylglucosamine residues linked via alternating β-1,4 and β-1,3 glycosidic bonds. HA is synthesized in humans by HA synthase (HAS) enzymes 1, 2, and 3, which are encoded by the corresponding HAS genes. Previous in vitro studies have shown characteristic changes in HAS expression and increased HA synthesis in response to wounding and proinflammatory cytokines in human peritoneal mesothelial cells. In addition, in vivo models and human peritoneal biopsy samples have provided evidence of changes in HA metabolism in the fibrosis that at present accompanies peritoneal dialysis treatment. This review discusses these published observations and how they might contribute to improvement in peritoneal dialysis.

Mesothelial cells in tissue repair and fibrosis

Mesothelial cells are fundamental to the maintenance of serosal integrity and homeostasis and play a critical role in normal serosal repair following injury. However, when normal repair mechanisms breakdown, mesothelial cells take on a profibrotic role, secreting inflammatory, and profibrotic mediators, differentiating and migrating into the injured tissues where they contribute to fibrogenesis. The development of new molecular and cell tracking techniques has made it possible to examine the origin of fibrotic cells within damaged tissues and to elucidate the roles they play in inflammation and fibrosis. In addition to secreting proinflammatory mediators and contributing to both coagulation and fibrinolysis, mesothelial cells undergo mesothelial-to-mesenchymal transition, a process analogous to epithelial-to-mesenchymal transition, and become fibrogenic cells. Fibrogenic mesothelial cells have now been identified in tissues where they have not previously been thought to occur, such as within the parenchyma of the fibrotic lung. These findings show a direct role for mesothelial cells in fibrogenesis and open therapeutic strategies to prevent or reverse the fibrotic process.

Damage of the endothelial glycocalyx in dialysis patients

Damage to the endothelial glycocalyx, which helps maintain vascular homeostasis, heightens the sensitivity of the vasculature to atherogenic stimuli. Patients with renal failure have endothelial dysfunction and increased risk for cardiovascular morbidity and mortality, but the state of the endothelial glycocalyx in these patients is unknown. Here, we used Sidestream Darkfield imaging to detect changes in glycocalyx dimension in dialysis patients and healthy controls from in vivo recordings of the sublingual microcirculation. Dialysis patients had increased perfused boundary region and perfused diameters, consistent with deeper penetration of erythrocytes into glycocalyx, indicating a loss of glycocalyx barrier properties. These patients also had higher serum levels of the glycocalyx constituents hyaluronan and syndecan-1 and increased hyaluronidase activity, suggesting the shedding of these components. Loss of residual renal function had no influence on the imaging parameters but did associate with greater shedding of hyaluronan in blood. Furthermore, patients with higher levels of inflammation had more significant damage to the glycocalyx barrier. In conclusion, these data suggest that dialysis patients have an impaired glycocalyx barrier and shed its constituents into blood, likely contributing to the sustained endothelial cell activation observed in ESRD.

Pathophysiological changes to the peritoneal membrane during PD-related peritonitis: the role of mesothelial cells

The success of peritoneal dialysis (PD) is dependent on the structural and functional integrity of the peritoneal membrane. The mesothelium lines the peritoneal membrane and is the first line of defense against chemical and/or bacterial insult. Peritonitis remains a major complication of PD and is a predominant cause of technique failure, morbidity and mortality amongst PD patients. With appropriate antibiotic treatment, peritonitis resolves without further complications, but in some PD patients excessive peritoneal inflammatory responses lead to mesothelial cell exfoliation and thickening of the submesothelium, resulting in peritoneal fibrosis and sclerosis. The detrimental changes in the peritoneal membrane structure and function correlate with the number and severity of peritonitis episodes and the need for catheter removal. There is evidence that despite clinical resolution of peritonitis, increased levels of inflammatory and fibrotic mediators may persist in the peritoneal cavity, signifying persistent injury to the mesothelial cells. This review will describe the structural and functional changes that occur in the peritoneal membrane during peritonitis and how mesothelial cells contribute to these changes and respond to infection. The latter part of the review discusses the potential of mesothelial cell transplantation and genetic manipulation in the preservation of the peritoneal membrane.

Pathophysiology of the peritoneal membrane during peritoneal dialysis: the role of hyaluronan

During peritoneal dialysis (PD), constant exposure of mesothelial cells to bioincompatible PD solutions results in the denudation of the mesothelial monolayer and impairment of mesothelial cell function. Hyaluronan, a major component of extracellular matrices, is synthesized by mesothelial cells and contributes to remesothelialization, maintenance of cell phenotype, and tissue remodeling and provides structural support to the peritoneal membrane. Chronic peritoneal inflammation is observed in long-term PD patients and is associated with increased hyaluronan synthesis. During inflammation, depolymerization of hyaluronan may occur with the generation of hyaluronan fragments. In contrast to native hyaluronan which offers a protective role to the peritoneum, hyaluronan fragments exacerbate inflammatory and fibrotic processes and therefore assist in the destruction of the tissue. This paper will discuss the contribution of mesothelial cells to peritoneal membrane alterations that are induced by PD and the putative role of hyaluronan in these processes.

Intra-abdominal hyaluronan concentration in peritoneal fluid of horses with sudden signs of severe abdominal pain

OBJECTIVE

To determine hyaluronan concentrations in peritoneal fluid from healthy horses and horses with sudden signs of severe abdominal pain and to identify the cellular sources of hyaluronan within the peritoneal cavity.

ANIMALS

7 client-owned horses that were evaluated for sudden signs of severe abdominal pain, 6 healthy teaching horses, and 13 euthanized horses (11 with no abdominal disease and 2 that had undergone abdominal surgery 2 weeks previously for a different study).

PROCEDURES

Abdominal fluid was collected from the client-owned and teaching horses. Hyaluronan concentrations were determined with an ELISA. Equine mesothelial cells were aseptically harvested from euthanized horses immediately after euthanasia, cultured, and processed for western blot immunoassays to detect expression of the following mesothelial cell markers: cytokeratins 8 and 18, vimentin, calretinin, mesothelin, and CD44. A reverse transcriptase-PCR assay was used to detect genetic expression of hyaluronan synthase-2 (HAS-2) from cultured and native equine tissue.

RESULTS

The mean ± SD abdominal hyaluronan concentration in peritoneal fluid from horses with signs of abdominal pain (1,203.3 ± 46.3 ng/mL) was significantly greater than that in healthy horses (228.4 ± 167.3 ng/mL). Harvested cells were maintained, and immunoblotting analyses confirmed expression of the mesothelial markers. Gene expression of HAS-2 from cultured mesothelial cells and fibroblasts was confirmed.

CONCLUSIONS AND CLINICAL RELEVANCE

Peritoneal hyaluronan concentration was much higher in horses with severe abdominal pain than in healthy horses. Cultured equine mesothelial cells and fibroblasts can produce hyaluronan through HAS-2. Future investigation should focus on establishing the effect of exogenous hyaluronan administration on mesothelial cell function in horses with abdominal disease.

Human peritoneal fibroblasts are a potent source of neutrophil-targeting cytokines: a key role of IL-1beta stimulation

Polymorphonuclear leukocyte (PMN) infiltration is a cardinal feature of peritonitis. CXC chemokine ligands 1 and 8 (CXCL1 and CXCL8), and the cytokine granulocyte colony-stimulating factor (G-CSF) are the key mediators of PMN accumulation. Increasing evidence points to an important role of human peritoneal fibroblasts (HPFB) in the response of the peritoneum to infection. We have examined the synthesis of PMN-targeting cytokines by HPFB exposed to intraperitoneal milieu as represented by peritoneal dialysate effluent (PDE) from patients undergoing peritoneal dialysis. PDE obtained during peritonitis, but not during infection-free periods, significantly increased production of CXCL1, CXCL8, and G-CSF by HPFB. The effect was largely blocked by antibodies to interleukin-1beta (IL-1beta), whereas neutralization of tumor necrosis factor-alpha (TNFalpha) had no major effect. Similar pattern of inhibition was observed when HPFB were exposed to conditioned media from endotoxin-stimulated peritoneal macrophages. Significance of IL-1beta stimulation was further shown in experiments with recombinant cytokines. Compared with TNFalpha, exposure of HPFB to recombinant IL-1beta resulted in a much higher release of PMN-targeting cytokines. The assessment of mRNA degradation revealed that the IL-1beta-induced transcripts of CXCL1, CXCL8, and G-CSF were more stable compared with those induced by TNFalpha. These data indicate that HPFB can be a significant source of PMN-targeting cytokines when stimulated with IL-1beta in the inflamed peritoneum.

Intrinsic Cells: Mesothelial Cells — Central Players in Regulating Inflammation and Resolution

Background

Preservation of the structural and functional integrity of the peritoneum is essential to maintain the dialytic efficacy of the peritoneal membrane. Although much improvement has been made to peritoneal dialysis (PD) fluids, they remain bioincompatible, and together with peritonitis, they continue to induce peritoneal inflammation and fibrosis.

Method

This article reviews the putative factors that mediate mesothelial cell inflammation during PD, and the mechanisms by which mesothelial cells attempt to regulate and resolve peritoneal inflammation.

Results

The mesothelium is the first line of defense to foreign particles and chemicals in the peritoneal cavity. Constant exposure of the mesothelium to the bioincompatible constituents of PD solutions results in denudation of the mesothelium and loss of the peritoneal cavity's protective layer. Detached mesothelial cells in PD solutions have the capacity to replenish the mesothelial layer through their ability to migrate and attach to areas of denudation. Mesothelial cells synthesize a plethora of growth factors, matrix proteins, and proteoglycans that aid in the reparative process and regulate the formation of chemotactic gradients that are essential for infiltration of leukocytes to sites of injury.

Conclusions

Far from being bystanders in peritoneal function, mesothelial cells have been shown to play a dynamic role in peritoneal homeostasis and immunoregulation. Studies have highlighted the potential use of mesothelial cells in gene therapy and cell transplantation, both of which may provide novel therapeutic strategies for the preservation of the peritoneum during PD.

Hyaluronan induces the selective accumulation of matrix- and cell-associated proteoglycans by mesangial cells

Mesangial cells (MCs) are essential for normal renal function through the synthesis of their own extracellular matrix, which forms the structural support of the renal glomerulus. In many renal diseases this matrix is reorganized in response to a variety of cytokines and growth factors. This study examines proteoglycan and hyaluronan (HA) synthesis by MCs triggered by proinflammatory agents and investigates the effect of an exogenous HA matrix on matrix synthesis by MCs. Metabolic labeling, ion exchange and size exclusion chromatography, Western blotting, and immunocytochemistry were used to identify changes in matrix accumulation. When incubated with interleukin-1, platelet-derived growth factor, or fetal calf serum, MCs initiated rapid HA synthesis associated with the up-regulation of HA synthase-2 and increased the synthesis of versican, perlecan, and decorin/biglycan. HA was both released into the medium and incorporated into extensive pericellular coats. Adding exogenous HA to unstimulated cells that had undetectable pericellular coats of HA selectively reduced perlecan and versican turnover, whereas other proteoglycans were unaffected. These results suggest that high levels of HA in the mesangium in disease is a mechanism controlling the accumulation of specific mesangial matrix components. HA may thus be an attractive target for therapeutic intervention.

Hyaluronan--regulator and initiator of peritoneal inflammation and remodeling

Although previously described as an inert space filler, there is now compelling evidence to underscore the importance of hyaluronan in physiologic and pathologic processes. Despite its simple structure, hyaluronan plays essential roles in embryonic development, phenotypic changes, proliferation, wound healing, inflammation and angiogenesis. Hyaluronan is a major component of the glycocalyx that forms a protective barrier around mesothelial cells, and bestows upon the peritoneal membrane a slippery non-adhesive surface preventing abrasion, infection and tumor dissemination. Hyaluronan is associated with mesothelial-to-mesenchymal transdifferentiation, recruitment of leukocytes to sites of inflammation, and mediates the reparative process after tissue injury by initiating increased synthesis of growth factors. Serum and dialysate levels of hyaluronan are increased in patients maintained on peritoneal dialysis (PD), of which the levels are further increased during episodes of peritonitis. The level of hyaluronan in PD effluents is often used as a surrogate marker for peritoneal inflammation and can predict patient survival. This review will describe the multifaceted roles of hyaluronan in the peritoneum and how these roles are modulated during PD.

Increased mesangial cell hyaluronan expression in lupus nephritis is mediated by anti-DNA antibody-induced IL-1beta

The mechanism by which anti-DNA antibodies contribute to the pathogenesis of lupus nephritis (LN) remains to be fully elucidated. Hyaluronan (HA) is an important extracellular matrix constituent that accumulates during tissue injury, and participates in lymphocyte recruitment to sites of inflammation. The role of HA in the pathogenesis of LN has not been defined. We investigated the expression of HA in renal biopsies and circulating HA levels in patients with diffuse proliferative LN, and the effect of human anti-DNA antibodies on HA synthesis in cultured human mesangial cells (HMC). HA expression was increased in the mesangium, and in the periglomerular and tubular distribution in LN kidney biopsies. LN patients showed increased levels of circulating HA, especially during active disease, which correlated with anti-DNA antibody titers (r=0.35, P=0.0234). Anti-DNA antibodies isolated during active LN but not remission increased de novo synthesis of (3)H-labeled HA, which was accompanied by induction of HA synthase (HAS) II transcription, and enhanced IL-1beta, IL-6, and tumor necrosis factor-alpha secretion in HMC (P<0.001 for all). Only anti-DNA antibody induction of IL-1beta enhanced HA synthesis, which was abrogated by inhibitors of de novo mRNA or protein synthesis. Our findings demonstrate that HA expression is significantly increased within the mesangium in diffuse proliferative LN mediated through anti-DNA antibody-induced IL-1beta. Given that HA plays a pivotal role during inflammatory responses, influences cellular behavior and assists in the recruitment of lymphocytes to sites of injury, it is likely that HA contributes to the pathogenesis of LN.

Impact of a genetic polymorphism of the interleukin-1 receptor antagonist on technique survival in peritoneal dialysis patients

BACKGROUND/AIMS

There is a clear association between one allele of the interleukin-1 receptor-antagonist gene (IL-1RN) and inflammatory diseases in which IL-1 is implicated. We evaluated patient survival and technique survival of peritoneal dialysis (PD) patients, while analyzing independent risk factors, in a PD program. We also tested the association between IL-1RN polymorphism, patient survival and technique survival.

METHODS

We retrospectively evaluated 129 Japanese CAPD patients undergoing initial treatment in eight centers in Japan. Using PCR, IL-1RN genotype and allele frequencies were determined, and clinical and biochemical variables were recorded at the start of PD. The relation of patient survival or technique survival with IL-1RN polymorphism and those variables was analyzed with a multivariate Cox's proportional-hazard model.

RESULTS

The frequencies of IL-1RN*1/IL-1RN*1 and IL-1RN*1/IL-1RN*2 genotypes were 84.5 and 15.5%, respectively. Median patient survival was 37.0 months, and overall patient survival was 92.8 and 87.9% at 2 and 5 years, respectively. Age, cardiovascular disease and serum albumin were found to be independent predictors of patient survival. Median technique survival was 32 months. PD failure occurred in 37 patients, with technique survival rates of 92.0 and 72.7% at 2 and 5 years, respectively. Serum albumin, peritonitis and the presence of the IL-1RN*2 genotype were found to be independent predictors of technique survival.

CONCLUSION

Serum albumin was the strongest predictive factor for mortality and technique failure in PD. Technique failure was also affected by IL-1RN polymorphism in this patient population.

In vitro biocompatibility performance of Physioneal

In vitro biocompatibility performance of Physioneal. toneal dialysis (PD) has been a successful and effective form of chronic renal replacement therapy since its introduction over 20 years ago. Despite its overall success, there is a growing body of evidence that suggests shortcomings in the preservation of membrane integrity. This has led to the development of several second-generation PD solutions that demonstrate improved biocompatibility. Physioneal, a neutral pH, bicarbonate/lactate-buffered solution, was one of the first of these new PD solutions to become commercially available. This review will focus on one of the first preclinical stages in the development of Physioneal: studies on in vitro biocompatibility testing. Studies in leukocyte, mesothelial cell, and fibroblast populations demonstrated significantly improved biocompatibility of neutral pH, bicarbonate/lactate-based solutions compared to conventional solutions. The solutions contributed to improved leukocyte viability and response to bacterial infection (e.g., phagocytosis, superoxide radical generation, and endotoxin-stimulated cytokine release). Studies on peritoneal mesothelial cells demonstrate improved cell viability, proliferation, and response to proinflammatory stimuli, and a reduced potential for angiogenesis and peritoneal fibrosis, all suggesting a better preservation of membrane structure and function. The bicarbonate/lactate-based solutions demonstrated decreased cytotoxicity and preserved cell growth in fibroblast cultures as well. In vitro biocompatibility testing has clearly demonstrated that neutral pH, bicarbonate/lactate-buffered Physioneal solutions are superior to conventional solutions in preserving cell viability and function in cell populations that contribute to peritoneal homeostasis. This positive assessment now provides a foundation and rationale for moving forward with the next stages in preclinical testing: in vivo animal models and human ex vivo studies.

Image analysis of remesothelialization following chemical wounding of cultured human peritoneal mesothelial cells: the role of hyaluronan synthesis

BACKGROUND

To understand what happens during the wound healing process of the mesothelium, we have developed an in vitro wounding model of cultured human peritoneal mesothelial cells (HPMCs) utilizing an image acquisition and analysis system. Using this system, cell mobility and hyaluronan synthesis were quantified and their interrelationship discussed.

METHODS

1N NaOH was used to create circular wounds in cultured HPMC monolayers, which were then exposed for 30 minutes to the peritoneal dialysis solutions or fetal calf serum (FCS)-free M199 culture medium, followed by incubation with 0.3% FCS/M199 culture medium for up to 96 hours. Digitalized microscopic date was captured every 30 minutes to quantify the wound healing process. In separate experiments, the HPMC monolayers were stained with biotin-conjugated hyaluronan-binding protein (B-HABP) at a regular time interval.

RESULTS

Centripetal migration of the HPMCs into the wound area was the predominant process involved in wound repair with proliferation playing a secondary role. Two noticeable observations were made from the digital video movies: (1) cell mobility varied and was dependent upon the morphology and location of the cell relative to the wound edge, and (2) cell migration continued even after wound closure. Staining for B-HABP was confined to the remesothelialized area when wound closure was complete at 24 hours. At 48 hours after wound closure, the stained area was even more visible, although somewhat diffuse; thereafter, staining was reduced to almost background levels.

CONCLUSION

The cell culture model of wound healing used in our study has enabled us to demonstrate quantitative image data of the cellular processes that occur during wound healing. We have been able to continuously observe cell migration, proliferation, and transformation. Synthesis and subsequent decomposition of hyaluronan appears to be related to the mobility of the wounded and intact HPMCs in this model system.

The Euro-Balance Trial: The effect of a new biocompatible peritoneal dialysis fluid (balance) on the peritoneal membrane

BACKGROUND

Although peritoneal dialysis (PD) is a widely accepted form of renal replacement therapy (RRT), concerns remain regarding the bioincompatible nature of standard PD fluid. In order to evaluate whether a newly formulated fluid of neutral pH, and containing low levels of glucose degradation products (GDP), resulted in improved in vivo biocompatibility, it was compared in a clinical study to a standard PD fluid.

METHODS

In a multicenter, open, randomized, prospective study with a crossover design and parallel arms, a conventional, acidic, lactate-buffered fluid (SPDF) was compared with a pH neutral, lactate-buffered, low GDP fluid (balance). Overnight effluent was collected and assayed for cancer antigen 125 (CA125), hyaluronic acid (HA), procollagen peptide (PICP), vascular endothelial growth factor (VEGF), and tumor necrosis factor alpha (TNFalpha). Serum samples were assayed for circulating advanced glycosylation end products (AGE), N(epsilon)-(carboxymethyl)lysine (CML), and imidazolone. Clinical end points were residual renal function (RRF), adequacy of dialysis, ultrafiltration, and peritoneal membrane function. Eighty-six patients were randomized to either group I starting with SPDF for 12 weeks (Phase I), then switching to "balance" for 12 weeks (Phase II), or group II, which was treated vice versa. Seventy-one patients completed the study with data suitable for entry into the per protocol analysis. Effluent and serum samples, together with peritoneal function tests and adequacy measurements, were undertaken at study centers on three occasions during the study: after the four-week run-in period, after Phase I, and again after Phase II.

RESULTS

In patients treated with balance there were significantly higher effluent levels of CA125 and PICP in both arms of the study. Conversely, levels of HA were lower in patients exposed to balance, while there was no change in the levels of either VEGF or TNFalpha. Serum CML and imidazolone levels fell significantly in balance-treated patients. Renal urea and creatinine clearances were higher in both treatment arms after patients were exposed to balance. Urine volume was higher in patients exposed to balance. In contrast, peritoneal ultrafiltration was higher in patients on SPDF. When anuric patients were analyzed as a subgroup, there was no significant difference in peritoneal transport characteristics or in ultrafiltration on either fluid. There were no changes in peritonitis incidence on either solution.

CONCLUSION

This study indicates that the use of balance, a neutral pH, low GDP fluid, is accompanied by a significant improvement in effluent markers of peritoneal membrane integrity and significantly decreased circulating AGE levels. Clinical parameters suggest an improvement in residual renal function on balance, with an accompanying decrease in peritoneal ultrafiltration. It would appear that balance solution results in an improvement in local peritoneal homeostasis, as well as having a positive impact on systemic parameters, including circulating AGE and residual renal function.

Differential Regulation by IL-1β and EGF of Expression of Three Different Hyaluronan Synthases in Oral Mucosal Epithelial Cells and Fibroblasts and Dermal Fibroblasts: Quantitative Analysis Using Real-Time RT-PCR

Using "real-time RT-PCR", we assessed the expression of three different hyaluronan synthase genes, HAS1, HAS2, and HAS3, by measuring their mRNA amounts in cultured human oral mucosal epithelial (COME) cells, oral mucosal fibroblasts, and dermal fibroblasts, and investigated the effects of interleukin-1beta (IL-1beta) and epidermal growth factor (EGF). When COME cells were treated with IL-1beta or EGF, early and marked increases and subsequent rapid decreases were observed for all HAS genes and, moreover, actual changes in hyaluronan synthesis subsequently occurred. The effects of IL-1beta stimulation were concentration-dependent and the maximal response to the EGF stimulation was observed at a low concentration (0.1 ng per mL). When two different types of fibroblasts were treated with IL-1beta or EGF, increased expression with different degrees and rates of three different HAS genes and subsequent increased synthesis of hyaluronan were also observed. In addition, HAS1 gene expression was not detectable in the mucosal fibroblasts, while weak HAS3 gene expression was detected in the dermal fibroblasts. Taken together, it is likely that the regulation of the expression of the three different HAS genes is different between oral mucosa and skin, which may be of significance for elucidating some of the differences between these tissues in wound healing.

Identification and analysis of the promoter region of the human hyaluronan synthase 2 gene

Hyaluronan (HA) is a linear glycosaminoglycan of the vertebrate extracellular matrix that is synthesized at the plasma membrane by the HA synthase (HAS) enzymes HAS1, -2 and -3. The regulation of HA synthesis has been implicated in a variety of extracellular matrix-mediated and pathological processes, including renal fibrosis. We have recently described the genomic structures of each of the human HAS genes. In the present study, we analyzed the HAS2 promoter region. In 5'-rapid amplification of cDNA ends analysis of purified mRNA from human renal epithelial proximal tubular cells, we detected an extended sequence for HAS2 exon 1, relocating the transcription initiation site 130 nucleotides upstream of the reference HAS2 mRNA sequence, GenBank accession number NM_005328. A luciferase reporter gene assay of nested fragments spanning the 5' terminus of NM_005328 demonstrated the constitutive promoter activity of sequences directly upstream of the repositioned transcription initiation site but not of the newly designated exonic nucleotides. Using reverse transcription-PCR, expression of this extended HAS2 mRNA was demonstrated in a variety of human cell types, and orthologous sequences were detected in mouse and rat kidney. Alignment of human, murine, and equine genomic DNA sequences upstream of the repositioned HAS2 exon 1 provided evidence for the evolutionary conservation of specific transcription factor binding sites. The location of the HAS2 promoter will facilitate analysis of the transcriptional regulation of this gene in a variety of pathological contexts as well as in developmental models in which HAS2 null animals have an embryonic lethal phenotype.

The human hyaluronan synthase genes: genomic structures, proximal promoters and polymorphic microsatellite markers

The glycosaminoglycan (GAG) hyaluronan (HA) is a key component of the vertebrate extracellular matrix (ECM) and is synthesised by the HA synthase (HAS) enzymes HAS1, HAS2 and HAS3 at the plasma membrane. Accumulating evidence emphasises the relevance of HA metabolism in an increasing number of processes of clinical interest including renal fibrosis and peritoneal mesothelial wound healing. In the present study, the genomic sequences and organisation of the genes encoding the human HAS isoforms were deduced, in silico, from reference cDNA and genomic sequence data. These data were confirmed in vitro by sequencing of PCR-amplified HAS exons and flanking genomic sequences, comparison with sequence data for the corresponding murine Has orthologues, rapid amplification of 5' cDNA ends analysis and luciferase reporter assays on putative proximal promoter sequences. The HAS1 gene comprised five exons, with the translation start site situated 9bp from the 3' end of exon 1. In contrast, the genomic structures for HAS2 and both HAS3 variants spanned four exons, exon 1 forming a discrete 5'-untranslated region (5'-UTR) and the translation start site lying at nucleotide 1 of exon 2. Dinucleotide microsatellite loci were identified in intron 1 of HAS1 and HAS2, and immediately upstream of the HAS3 gene and their utility as linkage markers demonstrated in genomic DNA (gDNA) studies. We thus present a comprehensive resource for mutation detection screening of all HAS exons and/or linkage analysis of each HAS gene in a variety of disorders for which they are attractive candidates.

Early detection of peritonitis in continuous ambulatory peritoneal dialysis patients by cytokine measurements

Continuous ambulatory peritoneal dialysis (CAPD) carries a risk of peritonitis which is accompanied by mild symptomatology. Culture of effluent has yielded organism in 50% of cases. Peritoneal phagocytes produce tumor necrosis factor-alpha and interleukin (IL)-1 in response to contact with bacteria, initiating an inflammatory cascade which leads to IL-6 and IL-8 secretion. Additonally, neutrophils undergo an increase in oxidative metabolism. We have evaluated the diagnostic accuracy of effluent measurements of TNF-alpha, IL-6, IL-8, and oxidative metabolism markers in these patients. Dialysate fluids (n = 65) were collected from non-infected patients and those presenting with acute peritonitis. Positive culture proved the diagnosis. Oxidative markers and nitric oxide were measured by chemiluminescence. Cytokines were measured by solid phase chemiluminescent immunometric assay (Immulite, DPC, USA). Receiver operating characteristic (ROC) curves were used to assess the diagnostic accuracy and the areas under curves were calculated for comparison. All effluent cytokines and oxidative markers were significantly higher in patients with peritonitis when compared to those without (p < 0.05). Significant correlations were evident between IL-6 and IL-8, lucigenin chemiluminescence and luminol chemiluminescence, lucigenin chemiluminescence and IL-6 or IL-8, and luminol chemiluminescence and IL-6 or IL-8. ROC curves showed that the ability of IL-6, IL-8, lucigenin chemiluminescence, and luminol chemiluminescence to differentiate CAPD patients with peritonitis from non-infected cases exceeds that of polymorphonuclear leukocyte count.

Inflammatory cytokines, angiogenesis, and fibrosis in the rat peritoneum

Peritonitis, a common complication of peritoneal dialysis, is followed by acute changes in the function of the peritoneum. The role of inflammatory cytokines in these processes is not clearly identified. We used adenoviral-mediated gene transfer to transiently overexpress interleukin (IL)-1 beta (AdIL-1 beta) or tumor necrosis factor (TNF)-alpha (AdTNF-alpha) in the rat peritoneum then used a modified equilibrium test to study the histological and functional changes. Overexpression of IL-1 beta or TNF-alpha led to an acute inflammatory response. Both inflammatory cytokines induced an early expression of the angiogenic cytokine, vascular endothelial growth factor, along with increased expression of the profibrotic cytokine, transforming growth factor-beta1, along with fibronectin expression and collagen deposition in peritoneal tissues. Both inflammatory cytokines induced angiogenesis, increased solute permeability, and ultrafiltration dysfunction at earlier time points. Changes in structure and function seen in AdTNF-alpha-treated animals returned to normal by 21 days after infection, whereas AdIL-1 beta-treated animals had persistently increased vasculature with submesothelial thickening and fibrosis. This was associated with up-regulation TIMP-1. TNF-alpha or IL-1 beta both induce acute changes in the peritoneum that mimic those seen in peritoneal dialysis patients who experience an episode of peritonitis. These functional changes were associated with early angiogenesis that resolved rapidly after exposure to TNF-alpha. IL-1 beta exposure, however, led to a different response with sustained vascularization and fibrosis. IL-1 beta inhibition may be a therapeutic goal in acute peritonitis to prevent peritoneal damage.

Ratio of serum vascular endothelial growth factor to platelet count correlates with disease activity in a patient with POEMS syndrome

Vascular endothelial growth factor (VEGF) is known to be involved in the pathogenesis of POEMS (polyneuropathy, organomegaly, endocrine disorder, M-protein, and skin lesion) syndrome. Because platelets have recently been recognized as transporters of VEGF, enhanced blood coagulation activity in this syndrome may accelerate vasopermeability by releasing VEGF from platelets in vivo. Here we report a case of POEMS syndrome with anasarca showing a high ratio of serum VEGF to platelet count, indicative of massive VEGF release from aggregated platelets in vivo. Changes in the ratio clearly reflected disease activity. This observation suggests that the ratio of serum VEGF to platelet count is more precise in monitoring disease activity than serum VEGF alone, and that VEGF released in vivo is critically involved in the pathogenesis of POEMS syndrome, causing hypervasopermeability.

Mesothelial cell-associated hyaluronic acid promotes adhesion of endometrial cells to mesothelium

OBJECTIVE

To evaluate the role of hyaluronic acid in the attachment of endometrial cells to mesothelium.

DESIGN

In vitro study of adhesion of endometrial stromal and epithelial cells to mesothelial cells.

SETTING

University medical center.

PATIENT(S)

Reproductive-age women without endometriosis undergoing surgery for benign conditions.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

The effect of hyaluronidase treatment of mesothelial cells or endometrial cells on adhesion of (51)Cr labeled endometrial stromal and epithelial cells to monolayers of mesothelium was evaluated. The expression of CD44, the hyaluronate receptor, was evaluated by western blot.

RESULT(S)

Hyaluronidase pretreatment of mesothelial cells decreased the binding of endometrial stromal and epithelial cells to mesothelium by 39% (P< .02) and 31% (P< .03), respectively. There was no effect on endometrial cell binding to mesothelial cells or to collagen IV when the endometrial cells were pretreated with hyaluronidase. CD44 expression by endometrial stromal and epithelial cells was demonstrated by western blot.

CONCLUSIONS

This study demonstrates that mesothelial cell-associated hyaluronic acid is involved in attachment of endometrial stromal and endometrial epithelial cells to the mesothelium. We hypothesize that binding of hyaluronic acid by endometrial cells is involved in the pathogenesis of the early endometriotic lesion.

Bicarbonate/lactate-based peritoneal dialysis solution increases cancer antigen 125 and decreases hyaluronic acid levels

BACKGROUND

In a randomized, controlled trial comparing a pH neutral, bicarbonate/lactate (B/L)-buffered PD solution to conventional acidic, lactate-buffered solution (C), the overnight dialysate levels of markers of inflammation/wound healing [hyaluronic acid (HA)], mesothelial cell mass/membrane integrity [cancer antigen 125 (CA125)], and fibrosis [transforming growth factor-beta1 (TGF-beta1) and procollagen I peptides (PICP)] were assessed over a six-month treatment period.

METHODS

One hundred six patients were randomized (2:1) to either the B/L group or C group. Overnight effluents were collected at entry into the study (time = 0 all patients on control solution) and then at three and six months after randomization. Aliquots were filtered, stored frozen, and assayed for HA, CA125, TGF-beta1, and PICP. Differences between groups were assessed by repeated-measures analysis of variance for unbalanced data using the SAS procedure MIXED.

RESULTS

In patients treated with B/L, there was a significant (P = 0.03) increase in CA125 after six months compared with time = 0 (19.76 +/- 11.8 vs. 24.4 +/- 13.8 U/mL; mean +/- SD; N = 51). In the same group of patients, HA levels were significantly decreased at both three and six months in the B/L-treated group (time = 0, 336.0 +/- 195.2; time = 3 months, 250.6 +/- 167.6; and time = 6 months, 290.5 +/- 224.6 ng/mL; mean +/- SD; P = 0.006, N = 47 and P = 0.003, N = 48, respectively). No significant changes in CA125 or HA levels were observed in the control group. There were no significant changes observed in the levels of PICP or TGF-beta1 in the B/L or C group over the six-month treatment period.

CONCLUSIONS

These results suggest that continuous therapy with the B/L solutions modulates the levels of putative markers of peritoneal membrane integrity and inflammation. In the long term, this may positively impact the peritoneal membrane, increasing its life as a dialyzing organ.

Hyaluronan modifies inflammatory response and peritoneal permeability during peritonitis in rats

The effect of high-molecular-weight hyaluronan (HA) on peritoneal and systemic inflammation and peritoneal permeability to water and solutes was studied during endotoxin-induced peritonitis in rats. Acute peritonitis was induced by adding lipopolysaccharide (LPS) to the dialysis fluid (Dianeal 3.86; Baxter Healthcare, Ireland, Castlebar). HA was added to the dialysis solution in a concentration of 10 mg/dL. During 4- and 8-hour dwells of the dialysis fluid, we studied the intensity of peritoneal (dialysate) and systemic (blood) inflammation (dialysate cell count and differential, cytokine and HA levels), as well as the transperitoneal transport of solutes and water. In rats, the addition of LPS to the dialysis fluid induced changes in inflammatory reaction and transperitoneal transport similar to those seen in continuous ambulatory peritoneal dialysis patients with peritonitis. During peritonitis, the addition of HA to the dialysis fluid reduced the loss of ultrafiltration, which resulted in a greater peritoneal creatinine clearance during the 8 hours of dwell (29.9 +/- 6.7 mL/8 h in the HA-LPS group versus 19.7 +/- 7.8 mL/8 h in the LPS group; P < 0.05). Dialysate interferon-gamma (INF-gamma) levels during peritonitis were greater in HA-treated animals (536.8 +/- 296.6 pg/mL in the HA-LPS group versus 169.8 +/- 137.8 pg/mL in the LPS group; P < 0.05). Dialysate elastase activity increased during peritonitis (44.4 +/- 9.3 versus 14.2 +/- 4.1 U/mL in peritonitis-free rats); during peritonitis, the increase in dialysate elastase activity was less pronounced in the rats that had HA in the dialysate (27.3 +/- 4.1 U/mL versus the LPS group; P: < 0.01). We conclude that HA added to the dialysis fluid reduces loss of ultrafiltration during peritonitis in rats. In the presence of HA dialysate, INF-gamma levels during peritonitis increased, whereas elastase activity decreased; these changes might improve the peritoneal immune reaction during peritonitis and at the same time prevent peritoneal membrane injury.

Induction of hyaluronan metabolism after mechanical injury of human peritoneal mesothelial cells in vitro

BACKGROUND

Hyaluronan (HA) is an important extracellular matrix component that is involved in cell movement and tissue repair. In vertebrates, HA synthase genes (HAS 1, HAS 2, and HAS 3) that control the synthesis of HA have been identified. In this article, we investigated HA synthesis in the response of human peritoneal mesothelial cells (HPMCs) to injury.

METHODS

The expression of HAS 1, HAS 2, and HAS 3 mRNA and the synthesis of [(3)H]-labeled HA were examined in an in vitro model of peritoneal mesothelial cell damage. The staining for uridine diphosphoglucose dehydrogenase, a key enzyme in the synthesis of HA, and biotinylated HA-binding protein was used to determine the cellular location of HA synthesis and its site of deposition.

RESULTS

Growth-arrested human HPMCs expressed low levels of mRNA for HAS 2 and HAS 3 but not HAS 1. Following injury to the monolayer, HAS 2 was up-regulated by 6 hours, reaching maximal expression between 12 and 24 hours. In contrast, the expression of HAS 3 was down-regulated. During the same time period, synthesis of HA was increased in the injured monolayer. This synthetic activity appeared to be restricted to cells at the edge of the wound and to cells entering the wound. In a separate series of experiments, the addition of HA to the injured monolayer at a concentration range found in peritoneal fluid (50 to 3300 ng/mL) increased the migration of cells into the wound in a dose-dependent manner.

CONCLUSIONS

These studies provide evidence that HA is an important component of peritoneal mesothelial cell migration. The results also suggest that in this process, there is differential regulation of HAS gene expression and that the synthesis of HA is limited to cells located at the leading edge of the wound.

Long-term peritoneal membrane changes

There is increasing evidence that long-term peritoneal dialysis (PD) is associated with structural changes in the peritoneal membrane. These consist of thickening of the sub-mesothelial space owing to collagen deposition and alterations in small blood vessel morphology. These alterations become more pronounced with duration of PD therapy. These changes are associated with a tendency to increasing small solute transport rate with reduced ultrafiltration. The relationship between these structural and functional changes remains unknown, but the evidence suggests that both peritonitis and exposure to dialysate contribute. The most likely components of the fluid responsible for this effect are glucose and/or its degradation products generated during heat sterilisation. Serial monitoring of peritoneal function is well established, but repeat biopsies are not practical. Effluent markers are not yet of proven value but do alter in response to a change in dialysate composition. Hopefully, a combination of reduced inflammation and more biocompatible fluids will reduce long-term changes in peritoneal membrane structure and function with a consequent improvement in patient and technique survival.

Dialysate hyaluronan concentration predicts survival but not peritoneal sclerosis in continuous ambulatory peritoneal dialysis

Hyaluronan is an important component of extracellular matrix and plays a critical role in early phases of wound healing. Peritoneal mesothelium is a major site of hyaluronan production. Serum hyaluronan concentration has been shown to predict survival in maintenance hemodialysis patients. We hypothesize that mesothelial production of hyaluronan during the stable phase of continuous ambulatory peritoneal dialysis (CAPD) predicts the risk of peritoneal adhesion and mortality. We studied peritoneal dialysate effluent (PDE) hyaluronan levels from 116 stable CAPD patients. They were then followed-up for 3 years. During the follow-up period, there were 196 episodes of peritonitis in 78 patients. Tenckhoff catheter was removed in 31 episodes (15.8%). Tenckhoff catheter was reinserted successfully in 12 cases, and CAPD was resumed. Peritoneal adhesion developed in 16 cases. Three patients died before Tenckhoff catheter reinsertion was attempted. There was no difference in stable-phase PDE hyaluronan levels between patients who developed peritoneal adhesion and those who did not (159 +/- 63 versus 227 +/- 194 microgram/L, P = 0.27). Thirty-three patients died during the study period. Patients who died had significantly higher PDE hyaluronan concentration than survivors (272 +/- 194 versus 170 +/- 105 microgram/L, P < 0.01). Univariate analysis showed that increased PDE hyaluronan level was associated with a shorter patient survival (P < 0.001). There was no association between PDE hyaluronan level and serum albumin, protein nitrogen appearance, and percentage of lean body mass. Multivariate analysis confirmed that PDE hyaluronan level, serum albumin, and diabetic state were independent predictors of survival. We conclude that PDE hyaluronan level during stable phase of CAPD does not predict the risk of postperitonitis adhesion. However, it is a strong independent predictor of survival in CAPD patients.

A three-dimensional in-vitro model for the study of peritoneal tumour metastasis

Peritoneal metastasis is a frequent complication of gastrointestinal malignancy. We have developed a three-dimensional model of the human peritoneum that simulates the metastatic process in vitro. Peritoneal fibroblasts were incorporated into collagen lattices, allowed to contract, then overlaid with mesothelial cells. Scanning and transmission electron microscopy showed the model to have similar physical properties to human peritoneum. Mesothelial expression of the beta1 integrin family, the basement membrane proteins fibronectin, laminin, collagen types III and IV, and the cell adhesion molecules ICAM-1, VCAM-1 and PECAM were assessed and showed similar results to in vivo tissue. Gastrointestinal tumour cells seeded onto the model exhibited mesothelial adhesion, cell spreading and vesicle formation, and invasion of the mesothelial monolayer on scanning electron microscopy. Two distinct patterns of tumour cell growth were observed using light microscopy: a superficial spreading layer, and discrete invasive deposits. Invasion was accompanied by disruption of the mesothelial monolayer, degradation and re-orientation of the matrix, and rudimentary tumour cell differentiation. We believe the use of this in vitro peritoneal model will facilitate the study of the molecular mechanisms involved in the metastatic process.

Dialysis solution containing hyaluronan: effect on peritoneal permeability and inflammation in rats

BACKGROUND

Hyaluronan (HA), a high molecular weight mucopolysaccharide found in interstitial tissues and fluid, is lost from the peritoneal cavity during peritoneal dialysis. In order to determine the role of HA in peritoneal function, we investigated the effects of exogenous HA on peritoneal permeability, markers of intraperitoneal inflammation, and peritoneal morphology in rats exposed to peritoneal dialysis solution for four weeks.

METHODS

Wistar rats were infused intraperitoneally, twice daily, with conventional, hypertonic dialysis solution (Dianeal 3.86%; control) or Dianeal solution containing 10 mg/dL of high molecular weight HA. Peritoneal permeabilities and clearances of solutes and protein were determined using a modified peritoneal permeability test (peritoneal equilibration test) at the beginning and the end of the treatment. Peritoneal volume and ultrafiltration were determined using a macromolecular marker and by gravimetric methods. Peritoneal inflammation was determined by cell counts and differential and by the measurement of cytokine concentrations in the dialysate effluent. Peritoneal thickness and HA content were determined in liver and mesentery biopsies taken at the end of the experiment.

RESULTS

After four weeks of exposure to the dialysis solution, transperitoneal protein equilibration was significantly lower in HA-treated rats compared with rats treated with Dianeal alone (46% lower for albumin, P < 0.003; 33% lower for total protein, P < 0.001). The total drained volume after a four hour dwell was 29% higher in the HA group compared with the control (P < 0.001), yielding a positive net ultrafiltration in the HA group versus a negative net ultrafiltration in controls. Peritoneal clearances of urea and creatinine tended to be elevated in HA-treated rats, while clearances of total protein and albumin tended to be lower. Dialysate effluent from rats exposed to HA contained a lower percentage of neutrophils (8.8 +/- 22.8 +/- 9.5%, P < 0.01) and lower levels of the cytokines, tumor necrosis factor-alpha (11.2 +/- 14.7 vs. 42.3 +/- 35.3 pg/mL, P < 0.05) and monocyte chemoattractant protein-1 MCP-1 (72.0 +/- 86.5 vs. 402.4 +/- 258.3 pg/mL, P < 0.02), compared with rats treated with Dianeal alone. The thickness of the peritoneal interstitium showed a similar increase in both groups, but mesenteric tissue from the HA group contained more HA (48%, P < 0.01) than tissue from control animals.

CONCLUSIONS

The addition of HA to peritoneal dialysis solution decreases protein permeability, increases ultrafiltration, and decreases cytokine levels and the proportion of peritoneal neutrophils in dialysate from rats exposed to hypertonic dialysis solution. These results suggest that exogenous HA may help to protect the peritoneal membrane during exposure to dialysis solutions. These benefits, if sustained in the clinical setting, could lead to improvements in the therapy of peritoneal dialysis.

Increased production of hyaluronan by peritoneal cells and its significance in patients on CAPD

Hyaluronan (HA) is a polysaccharide that forms a critical component of extracellular matrices. HA is present in high concentrations in tissues undergoing remodeling and morphogenesis, and it appears to have an important role in the early stages of wound healing. Here, we studied the level of HA in the peritoneal dialysate effluent (PDE) from 116 stable continuous ambulatory peritoneal dialysis (CAPD) patients. Longitudinal studies over a period of 6 weeks were performed in seven of these patients who developed peritonitis. The median HA level in PDE from these patients was 154.6 microg/L (range, 29.7 to 820.2 microg/L). Dialysate level of HA increased with age of the patients, but no such correlation was shown between HA level in PDE and duration of CAPD treatment or previous episodes of peritonitis. Patients with high or average peritoneal membrane transport of small solutes had a higher HA level in the PDE than those with a low peritoneal membrane transport (P = 0.046). A significant correlation was observed between PDE level of HA and interleukin-1beta (IL-1beta) or IL-6. The plasma level of HA in these patients was significantly greater than that of healthy controls (P < 0.0001), yet the plasma concentration of HA was only 85% that of the PDE concentration. In CAPD patients with peritonitis, there was a sharp increase in the PDE levels of HA, IL-1beta, and IL-6. These values decreased progressively with resolution of peritonitis. The changes in the PDE levels of HA closely followed those of IL-1beta or IL-6. In vitro [3H]-glucosamine incorporation studies suggest that the main bulk of HA is derived from synthesis by the peritoneal mesothelial cells, whereas the amount synthesized by macrophages is trivial. We conclude that elevated levels of HA found in the PDE of stable CAPD patients originate from increased synthesis by peritoneal mesothelial cells. This event may serve as a marker of regeneration and remodeling of the peritoneal lining.

Response of the human peritoneal mesothelial cell to injury: an in vitro model of peritoneal wound healing

BACKGROUND

The denudation of the peritoneal mesothelium and damage to the underlying interstitium is a frequent finding in patients receiving continuous ambulatory peritoneal dialysis as a treatment for end-stage renal failure. The response of the mesothelium to injury from repeated episodes of infection or from exposure to dialysis fluids has not been extensively studied. The present study describes a simple and reproducible method with which to investigate the response of human mesothelial cells to injury.

METHODS

The model of peritoneal injury consists of mechanically wounding a monolayer of human peritoneal mesothelial cells with a glass probe and following the repopulation of the denuded area by time-lapse photomicroscopy. In addition immunohistochemistry was used to follow the response of marker proteins for stress fibers and focal adhesions as well as macromolecules associated with the extracellular matrix.

RESULTS

Under serum-free conditions the wound (0.58 +/- 0.094 mm; mean +/- SD; N = 20) closed within 72 +/- 5 hours (N = 8). This rate of healing was enhanced by fetal calf serum, by human serum (10%) and by undiluted spent non-infected dialysate. The repair process over the first 48 hours was the result of cell migration, was independent of cell proliferation and involved the de novo synthesis of several different extracellular matrix components. An early event in the healing process was the rapid reorganization of intracellular stress fibers together with the formation of associated focal adhesions in cells at the wound edge.

CONCLUSION

This in vitro model should prove invaluable in characterizing the process of wound healing within the peritoneal cavity, thus allowing a better understanding of the response to infection as well as any effect of dialysis fluids in this pattern of cell behavior.

Production of prostanoids via increased cyclo-oxygenase-2 expression in human amnion cells in response to low molecular weight hyaluronic acid fragment

Increased concentrations of hyaluronic acid (HA) have been found in serum and at uterine cervix at term. In its native form, HA exists as a high molecular weight (MW) polymer, but during parturition a lower MW HA fragment accumulates. The aim of this study was to investigate the regulatory mechanisms responsible for increased amnion prostanoid production and cyclo-oxygenase (COX) expression in response to HA. Human term amnion cells in culture were exposed to native HA polymer (MW 2.2x106) and its fragment (MW 3.5x104). We have determined levels of prostanoids, prostaglandins E2 and F2alpha, in conditioned media using specific immunoassays. Expression of COX-1 and COX-2 was examined with Western blot. Results were analyzed for statistical significance with Mann-Whitney U-test. Human amnion cells treated with HA fragment (100 nmol/l) produced significantly more PGE2 (2.3+/-0.21 (mean+/-S.D.) pg/106 cells/24 h) than controls (0.34+/-0.03) or high MW HA-treated cells (1.2+/-0.21). Protein levels of COX-2, but not COX-1, were substantially increased in amnion cells treated with HA fragment. HA fragment-mediated prostanoid production is markedly diminished by pretreatment with indomethacin. Our results indicate that HA fragment, rather than physiologic native HA polymer, induces amnion cell-derived prostanoid production via increased COX-2 expression. COX-2-mediated prostanoid production is likely a key physiologic event in HA fragment-mediated cervical ripening and the labor onset.