Mechanisms and interventions in peritoneal fibrosis

Peritoneal dialysis (PD) is an attractive treatment for patients with end-stage kidney disease (ESKD). However, long-term peritoneal dialysis is associated with development of functional and structural alterations of the peritoneal membrane. Several factors are implicated in the development of peritoneal fibrosis in PD patients. Inflammatory cytokines, which are induced in the peritoneal cavity during peritonitis, may also induce chronic inflammation and fibrosis. Transforming growth factor β1 (TGF-β1) is generally considered to play an important role in peritoneal fibrosis. The objective of this review is to summarize the mechanisms of peritoneal fibrosis using in vitro and in vivo studies, and the current status and future prospects of interventions in the peritoneal fibrosis.

Encapsulating peritoneal sclerosis: what have we learned?

Encapsulating peritoneal sclerosis (EPS) is a rare complication of peritoneal dialysis (PD), but carries significant morbidity and mortality. We review the clinical features and radiologic and histologic changes found at diagnosis of EPS. Although EPS is strongly associated with the duration of PD, the pathogenesis remains only partly understood. We discuss the mechanisms thought to underlie the abnormally thickened, sclerotic peritoneal membrane seen in long-term PD patients including epithelial to mesenchymal transition and the molecular mediators of fibrosis and angiogenesis. We review how exposure to high-glucose, nonphysiological dialysis fluids, peritonitis, and uremia may be responsible for these changes. Much remains to be learned about optimal management of EPS, both medical and surgical, because the literature lacks controlled studies. Future research challenges include defining the role of surgery, immunosuppression, and antifibrotic agents in the management of EPS. We also need to understand why some patients progress from asymptomatic peritoneal sclerosis to the extreme levels of fibrin deposition and bowel encapsulation seen in EPS. Screening PD patients for potential future EPS remains difficult, and we need strategies for monitoring patients on longer-term PD that enable us to better quantify the risk of EPS for the individual patient.

Protective measures against ultrafiltration failure in peritoneal dialysis patients

Ultrafiltration failure in patients undergoing peritoneal dialysis is a condition with an incidence that increases over time. It is related to increased cardiovascular morbidity and mortality and is a major cause of the abandonment of the treatment technique. Because the number of patients undergoing renal replacement therapy is increasing with society aging and because approximately 10% of this population is treated with peritoneal dialysis, this matter is becoming more common in everyday practice for clinicians involved in the care of patients with chronic renal failure. In this review, we summarize the available measures used to prevent and treat ultrafiltration failure and the current state of research in the field, both in the experimental and clinical settings, focusing on the possible clinical applications of recent findings.

Maltose, a promising osmotic agent in peritoneal dialysis solution

Peritoneal dialysis has undergone considerable development from a technological point of view, and osmotic agent has played the essential role in peritoneal dialysis fluid. Because the most commonly used osmotic agent is glucose and icodextrin, there are some disadvantages related to the use of glucose-based solutions and icodextrin. So it is urgent to develop a new peritoneal dialysis osmotic agent. According to these characteristics of glucose and icodextrin, it is promising to explore a better osmotic agent of peritoneal dialysis solution which is able to allow maintenance of the maximum ultrafiltration gradient, and prevent toxicity or accumulation of unwanted substances in the blood, being non-toxic or less-toxic, furthermore the metabolite should not cause significant metabolic disturbance. Maltose may be one of promising osmotic agent and may put an important influence on development of peritoneal dialysis.

The Effect of Colchicine on the Peritoneal Membrane

Peritoneal dialysis (PD) is a treatment modality for patients with renal failure. Peritoneal fibrosis is one of the most serious complications after long-term continuous ambulatory peritoneal dialysis (CAPD). Histological studies in both humans and animals show that chronic peritoneal dialysis results in fibrosis of the peritoneal membrane. In our study, we investigated the effect of colchicine on peritoneal alterations induced by hypertonic PD solution in rats. Sprague-Dawley rats intraperitoneally received saline (control group) once daily, for 28 days, or 3.86% glucose (PDF group), or 3.86% glucose plus colchicine (colchicine group). Animals from each group were sacrificed after 28 days with anesthetized ketamine (60 mg/kg BW). For the PD fluid assessment, 1 h before the sacrifice of animals, 10 mL PD fluid of 2.27% glucose was given, and this fluid was obtained after the sacrifice. The levels of transforming endothelial growth factor beta (TGF-beta), tumor necrosis factor alpha (TNF-alpha) and albumin were investigated both in the peritoneal dialysate and blood, and the levels of malondialdehyde (MDA) were investigated only in peritoneal dialysate. The peritoneal membrane was evaluated histologically by light microscopy. When groups were compared in terms of body weight change, the colchicine group significantly lost weight compared to controls and PDF group (-4.7% + 4.5, 3.5% +/- 7.2, 3.0% +/- 1.3, respectively, p = 0.018). Also, the blood albumin level was significantly lower for these in the colchicine group compared to those in the PDF group (2.7 +/- 0.35 versus 3.2 +/- 0.3 g/dL, respectively, p = 0.048). The blood TGF-beta level was significantly lower in the control group, and no difference was observed between the PDF and colchicine groups (294.4 +/- 67.5 versus 787.4 +/- 237.4 versus 615.3 +/- 235.1 pg/mL, respectively, p = 0.004). The mesothelial thickness found in groups was as follows: control group 102 +/- 18.9 microm, PDF group 128.33 +/- 33.1 microm, colchicine group 117 +/- 35.6 microm (p = 0.34). In conclusion, a rat model for peritoneal dialysis associated peritoneal derangement without fibrosis could be induced. Colchicine could not prevent peritoneal derangement in this model.

Evaluation of Taurine as an Osmotic Agent for Peritoneal Dialysis Solution

Objective

The development of a glucose-free peritoneal dialysis (PD) solution is important because glucose has been associated with functional and morphological damage to the peritoneal membrane. The ultrafiltration (UF) and biocompatibility of new PD solutions containing taurine (PD-taurine) instead of glucose as an osmolite were tested in a rat PD model.

Methods

To determine the solution's UF ability, different concentrations of taurine in PD solutions were compared to glucose-based PD solutions (PD-glucose) by giving single intraperitoneal injections for 2, 4, and 6 hours. To examine the biocompatibility of PD-taurine, the rats were divided into 3 groups: a 3.86% PD-glucose group, a 3.5% PD-taurine group and a not dialyzed group. The rats were given 10-mL injections of PD fluids intraperitoneally 3 times daily for 7 days. A peritoneal equilibration test (PET) was performed using a 1.9% xylitol solution at the time the rats were sacrificed. Mesothelial cell monolayers were obtained from the animals and studied based on a population analysis.

Results

The net UF of PD-taurine increased in a dose-dependent manner; the 3.5% PD-taurine solution was equivalent to the 3.86% PD-glucose solution after 4 hours. The PET showed that the drainage volume and the D4/D0 ratio for xylitol after 4 hours with PD-taurine solution were significantly greater than with the PD-glucose solution ( p < 0.001 and p < 0.001 respectively). Mesothelial and fibroblast-like cell proliferation was significantly less with PD-taurine than with PD-glucose ( p < 0.01).

Conclusions

These results indicate that PD-taurine resulted in net UF equivalent to that of PD-glucose and was more biocompatible than PD-glucose with respect to the peritoneal membrane.

HGF and BMP-7 ameliorate high glucose-induced epithelial-to-mesenchymal transition of peritoneal mesothelium

Over time, peritoneal dialysis results in functional and structural alterations of the peritoneal membrane, but the underlying mechanisms and whether these changes are reversible are not completely understood. Here, we studied the effects of high levels of glucose, which are found in the dialysate, on human peritoneal mesothelial cells (HPMCs). We found that high concentrations of glucose induced epithelial-to-mesenchymal transition (EMT) of HPMC, suggested by decreased expression of E-cadherin and increased expression of alpha-smooth muscle actin, fibronectin, and type I collagen and by increased cell migration. Normalization of glucose concentration on day 2 reversed the phenotypic transformation, but the changes were irreversible after 7 d of stimulation with high glucose. In addition, exposure of HPMC to high glucose resulted in a decreased expression of the antifibrotic cytokines, hepatocyte growth factor (HGF) and bone morphogenic protein 7 (BMP-7). Exogenous treatment with HGF resulted in a dosage-dependent prevention of high glucose-induced EMT. Both BMP-7 peptide and gene transfection with an adenoviral vector of BMP-7 also protected HPMCs from EMT. Furthermore, adenoviral BMP-7 transfection decreased peritoneal EMT and ameliorated peritoneal thickening in an animal model of peritoneal dialysis. In summary, high concentrations of glucose induce a reversible EMT of HPMCs, associated with decreased production of HGF and BMP-7. Treatment of HPMCs with HGF or BMP-7 blocks high glucose-induced EMT, and BMP-7 ameliorates peritoneal fibrosis in an animal model of peritoneal dialysis.

Correlation of metabolic syndrome with residual renal function, solute transport rate and peritoneal solute clearance in chronic peritoneal dialysis patients

BACKGROUND

Metabolic syndrome (MetS) and insulin resistance (IR) strongly promote macrovascular complications and endothelial dysfunction. They accelerate the progression of renal dysfunction in chronic kidney disease patients. However, their correlation with residual renal function (RRF) and peritoneal characteristics have never been investigated.

METHODS

The inter-relationships of IR (homeostatic model assessment, HOMA(IR)), serum adiponectin level, body mass index (BMI), highly sensitive C-reactive protein (hs-CRP), RRF, peritoneal solute clearance (Kt/V(urea)) and solute transport rate of 104 chronic peritoneal dialysis (PD) patients were examined.

RESULTS

Patients with (n = 57) and without (n = 47) clinically diagnosed MetS had the same degree of RRF, peritoneal Kt/V(urea), and solute transport rate. Higher HOMA(IR) (p = 0.011), BMI (p = 0.01) and hs-CRP (p = 0.032), as well as lower adiponectin (p = 0.019), were associated with lower peritoneal Kt/V(urea). Serum adiponectin was negatively associated with solute transport rate (p = 0.02). In multiple regression analysis, higher HOMA(IR) (p = 0.005), BMI (p = 0.021) and hs-CRP (p < 0.001) correlated with lower peritoneal Kt/V(urea).

CONCLUSIONS

MetS plays an important role in both macrovascular complications and endothelial dysfunction in chronic PD patients, which correlates with changes in peritoneal solute clearance and solute transport rate but not RRF.

Effects of low glucose degradation products peritoneal dialysis fluid on the peritoneal fibrosis and vascularization in a chronic rat model

In the present study, we examined the effects of a new peritoneal dialysis fluid (PDF) with a low level of low glucose degradation products (GDP) on the functional and structural stability of the peritoneal membrane (PM). Male Sprague-Dawley rats were divided into three groups: group C (n = 8), without dialysate infusion; group P (n = 12), infused with low-level GDP solution (4.25% Physioneal, pH 7.0-7.4); and group D (n = 12), infused with conventional solution (4.25% Dianeal, pH 5.2, adjusted to pH 7.0). In groups D and P, animals were infused through a permanent catheter with 25 mL of PDF, twice daily for 8 weeks. Lipopolysaccharide was added into the PDF immediately before infusion on days 8, 9 and 10 in the two dialysis groups. When compared with group P, group D showed a higher glucose mass transfer at weeks 6 and 8, D/P urea at week 8, TGF-beta1 at weeks 4 and 8, and VEGF level at week 8. The submesothelial matrix layer of the parietal peritoneum was significantly thickened in group D and the lectin-stained blood vessels in this layer were well-visualized in group D compared with group P. There were significantly more peritoneal blood vessels in group D than group P. The transforming growth factor-beta induced gene-h3 (betaig-h3) and TGF-beta1 levels in the peritoneal effluent correlated with the submesothelial thickness, which correlated with the dialysate-to-plasma ratio (D/P) of protein and, inversely, with the rate of glucose transport (D/D(0) glucose, where D is glucose concentration in the dialysate and D(0) is glucose concentration in the dialysis solution before it is infused into the peritoneal cavity). The present study showed that low-GDP PDF effectively attenuated the peritoneal vascularization and fibrosis related to conventional solution.

Biocompatibility of peritoneal dialysis fluid and influence of compositions on peritoneal fibrosis

Conventional peritoneal dialysis fluid (PDF) is a bioincompatible solution because of several components. These unphysiological compositions might contribute to the development of peritoneal fibrosis. In the present overview we summarize the influence of each composition of PDF (acidic pH, high concentration of glucose and glucose degradation products; advanced glycation end-products and lactate) on the peritoneal fibrotic changes in long peritoneal dialysis (PD) patients. We also summarized the report of new approaches to the prevention of peritoneal fibrosis in Japan.

Troglitazone inhibits synthesis of transforming growth factor-?1 and reduces matrix production in human peritoneal mesothelial cells

AIM

Peritoneal matrix accumulation is a characteristic of peritoneal fibrosis (PF). Continuous ambulatory peritoneal dialysis (CAPD) patients with up-regulation of transforming growth factor-beta1 (TGF-beta1) in their drained effluent show an increased risk of PF. Inhibition of TGF-beta1 expression in human peritoneal mesothelial cells (HPMC) may provide a potential treatment for PF. Peroxisome proliferator-activated receptor-gamma (PPAR-gamma) agonists are increasingly used in patients with diabetes, but their effects on extracellular matrix (ECM) turnover are unknown. The aims of this study were to investigate the effects of the PPAR-gamma agonist troglitazone on TGF-beta1 expression and matrix production in HPMC.

METHODS

Human peritoneal mesothelial cells were cultured from human omentum by an enzyme digestion method, grown in a medium containing 30 mmol/L D-glucose. TGF-beta1 expression and matrix production and turnover were measured in HPMC in the presence and absence of 15 micromol/L troglitazone. The mRNA expressions of TGF-beta(1), Collagen I (Col I) and fibronectin (FN) were determined by semiquantification reverse-transcriptive polymerase chain reaction (RT-PCR). The protein of TGF-beta1 was determined by ELISA and proteins of Col I, FN were determined by western blot.

RESULTS

The mRNA expression and protein of TGF-beta(1), Col I, FN were significantly increased in HPMC stimulated with 30 mmol/L D-glucose compared to the control group with F12 media (P < 0.01), which was reversed in the presence of troglitazone (15 micromol/L). Obvious decrease of TGF-beta(1) was found in troglitazone-treated groups as compared to groups stimulated with GS (P < 0.05). Exposure of HPMC to troglitazone reduced collagen I secretion (P < 0.05), and fibronectin secretion (P < 0.05).

CONCLUSION

Troglitazone reduce the expression of TGF-beta(1) in HPMC stimulated by 30 mmol/L D-glucose, and reduces ECM production. These studies suggest that the PPAR-gamma agonists may have a specific role in ameliorating the course of progressive peritoneal fibrosis under long-term peritoneal dialysis states.

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

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

Connective Tissue Growth Factor Is Responsible for Transforming Growth Factor-Beta-Induced Peritoneal Mesothelial Cell Apoptosis

BACKGROUND

Previous studies found that transforming growth factor-beta (TGF-beta) induces mesothelial production of connective tissue growth factor (CTGF), which may be downstream mediators of TGF-beta. Since high dose TGF-beta induces apoptosis of peritoneal mesothelial cells (PMC), we study the effect of CTGF blockade in the system of TGF-beta-induced PMC apoptosis.

METHOD

We examined the effect of TGF-W in primary culture of rat peritoneal mesothelial cells (PMC). PMC apoptosis was studied by flow cytometry. The effect of CTGF was blocked by antibody and short-interfering RNA (siRNA). Expression of apoptotic gene was studied by real-time polymerase chain reaction.

RESULT

In cultured unstimulated rat PMC, there is a low but definite incidence of spontaneous apoptosis. Stimulation with TGF-beta 50 pg/ml induces an upregulation of apoptotic gene BAX expression and a downregulation of anti-apoptotic gene BCL-2L expression, and a 4-fold increase in PMC apoptosis. The effect of TGF-beta-induced PMC apoptosis was partly prevented by antibody against CTGF, and completely abolished by CTGF-specific siRNA, while CTGF-blockade by siRNA had no effect on PMC necrosis. CTGF silencing by siRNA prevented the down-regulation of BCL-2L expression induced by TGF-beta, had no effect on the BAX expression.

CONCLUSION

Our results indicate that CTGF is an important downstream mediator of TGF-beta-induced PMC apoptosis.

Inhibition of TGF-beta1 expression in human peritoneal mesothelial cells by pcDU6 vector-mediated TGF-beta1 shRNA

BACKGROUND AND AIM

Transforming growth factor-beta(1) (TGF-beta(1)) is an important mediator of the fibrosis process. High expression of TGF-beta(1) is closely related to peritoneal fibrosis. RNA interference using short hairpin RNA (shRNA) can mediate sequence-specific inhibition of gene expression in mammalian cells. The aim of this study was to assess the effect of shRNA targeting TGF-beta(1) on the expression of TGF-beta(1) in human peritoneal mesothelial cells (HPMC).

METHODS

TGF-beta(1) specific shRNA expression vectors were constructed and introduced to HPMC stimulated with 4.25% D-glucose (Gs) and 10 microg/mL of lipopolysaccharide (LPS). Expression of TGF-beta(1) mRNA was assessed by semiquantification reverse transcription polymerase chain reaction (RT-PCR). The TGF-beta(1) protein level in the culture supernatant was determined by sandwich enzyme-linked immunosorbent assay.

RESULTS

The expression of TGF-beta(1) was upregulated significantly in HPMC stimulated with 4.25% D-Gs and 10 microg/mL LPS P < 0.01. TGF-beta(1) expression in pcDU6 plasmid vector-mediated TGF-beta(1) shRNA groups were obviously downregulated when compared to the 4.25% D-Gs and 10 microg/mL LPS group (P < 0.01) and the pcDU6 void vector group (P < 0.05), with no significant difference among pcDU6 plasmid vector -mediated TGF-beta(1) shRNA groups (P > 0.05). No significant difference was found between teh pcDNA3.1(-) vector plasmid-mediated TGF-beta(1) antisense RNA group and pcDU6 void vector group (P > 0.05). The expression of TGF-beta(1) in pcDU6 plasmid vector-mediated TGF-beta(1) shRNA groups were obviously downregulated when compared to the pcDNA3.1(-) plasmid vector-mediated TGF-beta(1) antisense RNA group (P < 0.05).

CONCLUSION

TGF-beta(1)-specific shRNA can significantly inhibit the expression of TGF-beta(1) in HPMC stimulated with 4.25% D-Gs and 10 microg/mL LPS in HPMC. These results suggest the possible application of TGF-beta(1)-specific shRNA in preventing peritoneal fibrosis in patients receiving peritoneal dialysis.

Effects of glucose and plasminogen activator inhibitor-1 on collagen metabolism in the peritoneum

Nonphysiological solutions containing high glucose levels have been considered an important factor in the etiology of fibrotic changes in long-term continuous ambulatory peritoneal dialysis (CAPD) patients. At the same time, increased Plasminogen Activator Inhibitor (PAI)-1 secretion has been reported to correlate with fibrotic changes. We suspected that the high glucose content of peritoneal dialysis solution may induce peritoneal sclerosis via up-regulation of PAI-1 gene expression. In this study, we evaluated the effects of glucose on PAI-1 activity in peritoneal fibrosis in a rat model of CAPD. The effects of glucose on the expressions of PAI-1 and several other genes correlated with collagen metabolism were also examined in cultured rat peritoneal mesothelial cells and fibroblasts. Sprague-Dawley rats were intraperitoneally injected twice daily for 28 days with phosphate-buffered saline (PBS) (control group), PBS containing 4% glucose (glucose group), or PBS containing 4% glucose plus a PAI-1 inhibitor (PAI-1 inhibitor group). Thickening of the peritoneum with increase the deposition of collagens type I and III in the submesothelial interstitium were observed in the glucose and the PAI-1 inhibitor group, but these were less severe in the PAI-1 inhibitor group. Glucose stimulated expression of the mRNA of PAI-1, collagen type I and III, and tissue inhibitor of metalloproteinase (TIMP)-1 in fibroblasts but not in mesothelial cells. Glucose stimulated matrix metalloproteinase (MMP)-13 mRNA expression in both cell types. The PAI-1 inhibitor suppressed expression of the mRNAs induced by glucose. In conclusion, glucose induces peritoneal fibrosis, including changes in collagen metabolism, by stimulating PAI-1 expression.

Damage to the peritoneal membrane by glucose degradation products is mediated by the receptor for advanced glycation end-products

Peritoneal dialysis is limited by morphologic changes of the peritoneal membrane. Use of peritoneal dialysis fluids (PDF) that contain glucose degradation products (GDP) generates advanced glycation end-products (AGE) within the peritoneal cavity. It is unknown whether peritoneal damage is causally related to AGE-receptor for AGE (RAGE) interaction. The effects of PDF were compared with different amounts of GDP on morphologic changes of the peritoneal membrane in 48 wild-type (WT) and 48 RAGE-deficient mice. PDF (1 ml) were instilled twice daily over a period of 12 wk. Groups with eight animals each received no manipulation (sham); sham instillation (sham i.p.); or filter-sterilized, glucose-free, conventional low GDP- or high GDP PDF. In vitro (generation of AGE fluorescence in PDF) and in vivo (immunohistochemistry for carboxymethyllysine), a GDP-dependent increase of AGE formation occurred. Inflammation and neoangiogenesis were augmented in WT mice that were treated with high GDP accompanied by upregulation of CD3+ T cells, increased NF-kappaB binding activity, increased lectin, and vascular endothelial growth factor expression. Furthermore, pronounced submesothelial fibrosis was found with increased expression of TGF-beta1. Exposure to low GDP resulted in only mild inflammation and neoangiogenesis (compared with sham i.p.) and no fibrosis in WT mice. The findings in WT contrasted with those in RAGE-deficient mice, which showed no increased inflammation (CD3+ T cells and NF-kappaB binding activity), neoangiogenesis (by lectin and vascular endothelial growth factor expression), or fibrosis (expression of TGF-beta1) after long-term exposure to GDP-containing PDF. Peritoneal damage by GDP in PDF is dependent at least in part on AGE-RAGE interaction.

The relation between serum levels of osteoprotegerin and postoperative epidural fibrosis in patients who underwent surgery for lumbar disc herniation

OBJECTIVES

Epidural fibrosis (EF) is a part of the normal physiological tissue response to laminectomy and it is an important cause of failed back surgery syndrome (FBSS). Osteoprotegerin (OPG) is a soluble member of the tumor necrosis factor receptor family, and is expressed in high concentrations by a variety of tissues and cell types. The objective of this study was to evaluate the relationship between serum OPG levels, and the existence of postoperative EF in patients with lumbar disc herniation. It has been suggested that cytokines and growth factors, which play a role in the wound healing, may enhance the expression of OPG.

METHODS

Forty women who underwent surgery for lumbar disc herniation were included in this study. Postoperative MRI was performed to assess EF in all patients.

RESULTS

The serum OPG levels of subjects with postoperative EF were significantly higher than those of subjects without postoperative EF (4.72 +/- 0.27 versus 3.25 +/-0.41 pmol/l; p=0.005)

DISCUSSION

Although the role of OPG in the development of EF is poorly understood, our results suggest that elevated levels of serum OPG are associated with and may play a role in the pathogenesis of fibrotic process.

Advanced glycation end-products and peritoneal sclerosis

Long-term continuous ambulatory peritoneal dialysis (CAPD) often causes peritoneal fibrosis and sclerosis with a loss of function, and some CAPD patients develop sclerosing encapsulating peritonitis. Glucose-based peritoneal dialysis fluids readily produce glucose degradation products by heat sterilization, and glucose degradation products accelerate the formation of advanced glycation end-products (AGE) in the peritoneal cavity. The accumulation of AGE is observed in peritoneal mesothelial and submesothelial layers in CAPD patients, accompanied by enhanced expression of various growth factors and peritoneal thickening. The expression of transforming growth factor-beta1 (TGF-beta1), macrophage-colony stimulating factor, and vascular endothelial growth factor (VEGF) is distributed in the peritoneum similarly to that of AGE. In CAPD patients with low ultrafiltration (UF) capacity, peritoneal membrane is thickened owing to an increase in the number of cells such as fibroblasts and macrophages and collagen in the submesothelial layer. AGE is detected in the fibroblasts and macrophages as well as degenerated collagen. These cells in the submucosal layer are almost positive for the receptor for AGE (RAGE) and uptake AGE. The intensity of AGE accumulation and the expression of growth factors are associated with the severity of UF impairment. In fact, the accumulation of AGE and the expression of growth factors are recognized most markedly in the peritoneum of CAPD patients with low UF and sclerosing encapsulating peritonitis. In conclusion, long-time CAPD with heat-sterilized peritoneal dialysis fluid promotes AGE accumulation in the peritoneal membrane and alteration in peritoneal cell function and dialysis quality, followed by peritoneal sclerosis, and, finally, sclerosing encapsulating peritonitis.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSION

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

Reactive oxygen species amplify protein kinase C signaling in high glucose-induced fibronectin expression by human peritoneal mesothelial cells

BACKGROUND

We previously demonstrated that high glucose up-regulates fibronectin mRNA and protein expression by human peritoneal mesothelial cells (HPMC) through activation of protein kinase C (PKC). PKC is known to induce cellular reactive oxygen species (ROS) and PKC-dependent activation of the reduced form of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase has recently been shown to be responsible, in part, for increased oxidative stress in diabetes. On the other hand, high glucose-induced mitochondrial overproduction of superoxide anion was found to activate PKC. We, therefore, hypothesized that high glucose-induced activation of PKC in HPMC may increase cellular ROS and ROS, in turn, may activate PKC and thus provide signal amplification in high glucose-induced fibronectin up-regulation in HPMC.

METHODS

The role of ROS in high glucose- and PKC-induced fibronectin expression was examined by quantification of cellular ROS after stimulation with high glucose and phorbol 12-myristate 13-acetate (PMA), by the effect of hydrogen peroxide (H(2)O(2)) and PMA on fibronectin expression, and finally by inhibition of ROS and PKC. The source of cellular ROS was further examined by inhibition of NADPH oxidase and mitochondrial metabolism.

RESULTS

D-glucose increased dichlorofluorescein (DCF)-sensitive cellular ROS in HPMC in a dose-dependent manner. l-glucose did not induce ROS generation and cytochalasin B completely blocked high glucose-induced ROS generation, suggesting that glucose uptake, but not media hyperosmolality, is required in ROS generation in HPMC. PMA increased cellular ROS and fibronectin secretion. A single dose of H(2)O(2) or H(2)O(2) continuously generated by glucose oxidase up-regulated fibronectin expression [corrected]. Antioxidants trolox and catalase inhibited high glucose- and PMA-induced fibronectin mRNA and protein expression. Inhibition of PKC inhibited high glucose-and H(2)O(2)-induced fibronectin secretion. NADPH oxidase inhibitors (diphenyleneiodinium and apocynin) and an inhibitor of mitochondrial electron transport chain subunit I (rotenone) all effectively inhibited high glucose-induced cellular ROS generation and fibronectin secretion.

CONCLUSION

The present data demonstrate that high glucose increases cellular ROS in HPMC through activation of PKC, NADPH oxidase, and mitochondrial metabolism and that ROS, thus generated, up-regulate fibronectin expression by HPMC. ROS are not only downstream but also upstream signaling molecules to PKC and provide signal amplification in high glucose-induced fibronectin expression by HPMC. The present data imply that cellular ROS may be potential therapeutic targets in progressive accumulation of extracellular matrix in the peritoneal tissue of long-term peritoneal dialysis patients using high glucose-containing peritoneal dialysis solutions.

BIOKID: randomized controlled trial comparing bicarbonate and lactate buffer in biocompatible peritoneal dialysis solutions in children [ISRCTN81137991]

BACKGROUND

Peritoneal dialysis (PD) is the preferred dialysis modality in children. Its major drawback is the limited technique survival due to infections and progressive ultrafiltration failure. Conventional PD solutions exert marked acute and chronic toxicity to local tissues. Prolonged exposure is associated with severe histopathological alterations including vasculopathy, neoangiogenesis, submesothelial fibrosis and a gradual loss of the mesothelial cell layer. Recently, more biocompatible PD solutions containing reduced amounts of toxic glucose degradation products (GDPs) and buffered at neutral pH have been introduced into clinical practice. These solutions contain lactate, bicarbonate or a combination of both as buffer substance. Increasing evidence from clinical trials in adults and children suggests that the new PD fluids may allow for better long-term preservation of peritoneal morphology and function. However, the relative importance of the buffer in neutral-pH, low-GDP fluids is still unclear. In vitro, lactate is cytotoxic and vasoactive at the concentrations used in PD fluids. The BIOKID trial is designed to clarify the clinical significance of the buffer choice in biocompatible PD fluids.

METHODS/DESIGN

The objective of the study is to test the hypothesis that bicarbonate based PD solutions may allow for a better preservation of peritoneal transport characteristics in children than solutions containing lactate buffer. Secondary objectives are to assess any impact of the buffer system on acid-base status, peritoneal tissue integrity and the incidence and severity of peritonitis. After a run-in period of 2 months during which a targeted cohort of 60 patients is treated with a conventional, lactate buffered, acidic, GDP containing PD fluid, patients will be stratified according to residual renal function and type of phosphate binding medication and randomized to receive either the lactate-containing Balance solution or the bicarbonate-buffered Bicavera solution for a period of 10 months. Patients will be monitored by monthly physical and laboratory examinations. Peritoneal equilibration tests, 24-h dialysate and urine collections will be performed 4 times. Peritoneal biopsies will be obtained on occasion of intraabdominal surgery. Changes in small solute transport rates, markers of peritoneal tissue turnover in the effluent, acid-base status and peritonitis rates and severity will be analyzed.

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.

CD40 is expressed on rat peritoneal mesothelial cells and upregulates ICAM-1 production

BACKGROUND

CD40 has been identified on a variety of cell types, and it plays an important role in adaptive immunity and inflammation. Peritoneal mesothelial cells (PMCs) are the main cell layer that line the peritoneal membrane. Previously we found that CD40 ligand (CD154) is functionally expressed on peritoneal macrophages during continuous ambulatory peritoneal dialysis peritonitis. However, there are few studies that have examined both CD40 expression on PMCs and the function of CD40 signalling in peritoneal local defence. The purpose of this study was to determine whether PMCs express CD40 and to investigate potential mechanisms of CD40-CD154 interactions that may be involved in the inflammation of the peritoneal membrane.

METHODS

Rat PMCs were harvested from the peritoneal cavity and maintained under defined in vitro conditions. We examined expression of CD40 on PMCs under normal culture or stimulation with interferon-gamma (IFN-gamma), tumour necrosis factor-alpha (TNF-alpha) or interleukin (IL)-1 by reverse transcription-polymerase chain reaction and fluorescence-activated cell sorting (FACS) analysis. After activation with CD40 monoclonal antibody (mAb), the expression of intercellular adhesion molecule-1 (ICAM-1) on PMCs was analysed by FACS.

RESULTS

A portion of rat PMCs cultured in vitro expressed CD40 constitutively. The expression of CD40 mRNA and protein was upregulated markedly following stimulation with IFN-gamma, but not following IL-1 or TNF-alpha. The expression of ICAM-1 on PMCs was significantly increased after activation of CD40 with IFN-gamma and with CD40 mAb.

CONCLUSION

PMCs functionally express CD40. The interaction between CD40 on PMCs and CD154-positive cells in the peritoneal cavity may play an important role in peritoneal local defence and may be involved in the inflammation process of the peritoneum.

Improved Acidosis Correction and Recovery of Mesothelial Cell Mass with Neutral-pH Bicarbonate Dialysis Solution among Children Undergoing Automated Peritoneal Dialysis

ABSTRACT. Acid-base balance and peritoneal membrane longevity are of utmost relevance for pediatric patients undergoing peritoneal dialysis (PD). PD fluids with neutral pH and reduced glucose degradation product contents are considered more biocompatible, because they preserve peritoneal cell functionsin vitro. To investigate the clinical effects of a novel PD fluid buffered with 34 mM pure bicarbonate at neutral pH, a randomized, prospective, crossover comparison with conventional, acidic, 35 mM lactate PD fluid was performed for two consecutive 12-wk periods with 28 children (age, 6 mo to 15 yr) undergoing automated PD (APD). Blood bicarbonate levels and arterial pH were significantly higher after 3 mo of bicarbonate PD (24.6 ± 2.3 mM and 7.43 ± 0.06, respectively), compared with lactate PD (22.8 ± 3.9 mM and 7.38 ± 0.05, respectively;P< 0.05). This effect was reversible among patients who returned from bicarbonate to lactate fluid. Low initial pH and young patient age independently predicted increased blood pH during bicarbonate APD. Peritoneal equilibration tests revealed subtle changes in solute transport, with a less steep creatinine equilibration curve during bicarbonate dialysis, suggesting reduced peritoneal vasodilation. The peritoneal release of carcinogen antigen-125 increased twofold during bicarbonate APD (29 ± 15versus15 ± 8 U/ml per 4 h,P< 0.01), which is consistent with recovery of the mesothelial cell layer. This effect was fully reversed when the patients returned to lactate fluid. Effluent carcinogen antigen-125 levels were inversely correlated with peritoneal glucose exposure during lactate but not bicarbonate APD, indicating improvedin vivomesothelial cell tolerance of high-dose glucose with the neutral-pH PD fluid with reduced glucose degradation product content. Among children undergoing APD, neutral-pH, bicarbonate-buffered PD fluid provides more effective correction of metabolic acidosis and better preservation of peritoneal cell mass than do conventional, acidic, lactate-based fluids. E-mail: franz_schaefer@med.uni-heidelberg.de

Peritoneal dialysis solutions inhibit the differentiation and maturation of human monocyte-derived dendritic cells: effect of lactate and glucose-degradation products

Peritoneal dialysis (PD) is a well-established therapy for end-stage renal failure, but its efficiency is limited by recurrent peritonitis. As PD solutions impair local inflammatory responses within the peritoneal cavity, we have analyzed their influence on the in vitro maturation of human monocyte-derived dendritic cells (MDDC). Evaluation of MDDC maturation parameters [expression of adhesion and costimulatory molecules, receptor-mediated endocytosis, allogeneic T cell activation, production of tumor necrosis factor alpha, interleukin (IL)-6 and IL-12 p70, and nuclear factor (NF)-kappaB activation] revealed that currently used PD solutions differentially inhibit the lipopolysaccharide (LPS)-induced maturation of MDDC, an inhibition that correlated with their ability to impair the LPS-stimulated NF-kappaB activation. Evaluation of PD components revealed that sodium lactate and glucose-degradation products impaired the acquisition of maturation parameters and NF-kappaB activation in a dose-dependent manner. Moreover, PD solutions impaired monocyte-MDDC differentiation, inhibiting the acquisition of DC markers such as CD1a and DC-specific intercellular adhesion molecule-3 grabbing nonintegrin (CD209). These findings have important implications for the initiation of immune responses under high lactate conditions, such as those occurring within tumor tissues or after macrophage activation.

Glucose-mediated induction of TGF-beta 1 and MCP-1 in mesothelial cells in vitro is osmolality and polyol pathway dependent

BACKGROUND

Glucose is converted to sorbitol and then to fructose via the polyol pathway that has been implicated in the pathogenesis of organ damage. The contribution of the polyol pathway to mesothelial cell activation has, however, not been fully determined.

METHODS

The effect of increasing glucose concentrations on transforming growth factor-beta 1 (TGF-beta 1) and monocyte chemoattractant protein-1 (MCP-1) secretion by human peritoneal mesothelial cells (HPMC) was examined. The importance of the polyol pathway was identified by its specific inhibition with an aldose reductase inhibitor.

RESULTS

Incubation of HPMC with 5 to 100 mmol/L glucose resulted in an induction of aldose reductase mRNA and intracellular sorbitol accumulation accompanied by the induction of TGF-beta 1 and MCP-1 mRNA expression and protein secretion. Mannitol at the same concentrations also induced aldose reductase, TGF-beta 1 and MCP-1 mRNA and protein expression but at a lower level than glucose. Sorbinil dose-dependently reduced both intracellular sorbitol levels (79.8% reduction of 60 mmol/L D-glucose induced intracellular sorbitol with 100 micromol/L sorbinil (N = 3, P < 0.01) and glucose-induced TGF-beta 1 and MCP-1 secretion. Mannitol induced TGF-beta 1 and MCP-1 secretion was not reduced by sorbinil. The addition of 15 to 40 mmol/L sodium lactate, either alone or in the presence of D-glucose enhanced TGF-beta 1 and MCP-1 secretion, which was inhibited by sorbinil. In contrast, sodium pyruvate appeared to antagonize D-glucose-induced TGF-beta 1 and MCP-1 secretion.

CONCLUSION

These data suggest that the polyol pathway and osmolality contribute to the regulation of HPMC function by glucose. Control of polyol pathway activation might reduce glucose-mediated damage to the peritoneal membrane and promote its long-term survival.

Role of advanced glycation end products and growth factors in peritoneal dysfunction in CAPD patients

High levels of glucose degradation products in peritoneal dialysis fluids are believed to cause excess accumulation of advanced glycation end products (AGEs) in the peritoneum during continuous ambulatory peritoneal dialysis (CAPD) treatment, resulting in functional and structural changes in the peritoneal membrane of CAPD patients. In this study, we investigated whether AGEs, the receptor for AGE (RAGE), and growth factors are involved in deteriorating ultrafiltration (UF) capacity of the peritoneal membrane in patients on CAPD therapy. Immunohistochemical staining showed that ODI-GLC19, a novel monoclonal anti-AGE antibody, was localized exclusively in peritoneal cells, in contrast to imidazolone, localized mostly in peritoneal degenerative collagen. Numbers of ODI-GLC19- and RAGE-positive cells in the peritoneum were increased significantly in CAPD patients, even before a decrease in UF capacity, compared with patients with nonrenal disease. Cells positive for ODI-GLC19 were identified as myofibroblasts and RAGE-positive cells and partly as CD68-positive macrophages in the peritoneum. The peritoneal membrane was thickened significantly in CAPD patients, especially patients with low UF. The number of blood vessels was increased significantly in CAPD patients with low UF. Transforming growth factor-beta1, macrophage colony-stimulating factor, and vascular endothelial growth factor were recognized in the peritoneum of CAPD patients, especially those with low UF, where imidazolone was deposited. Focal hepatocyte growth factor expression was noted in the peritoneum of patients with low UF in moderate intensity, specifically in the area without severe structural changes. In conclusion, progressive accumulation of AGEs in the peritoneum may promote peritoneal expression of various growth factors and subsequently deteriorate UF capacity in CAPD patients.

Effects of pH-neutral, bicarbonate-buffered dialysis fluid on peritoneal transport kinetics in children

BACKGROUND

Due to their superior biocompatibility, pH-neutral solutions are beginning to replace acidic lactate-buffered peritoneal dialysis (PD) fluids. We hypothesized that pH-neutral and acidic solutions might differentially affect peritoneal transport in the early dwell phase, due to differences in ionic shifts and initial peritoneal vasodilation. Such differences may become clinically relevant in patients with frequent short cycles on automated PD (APD).

METHODS

Twenty-five children were treated with a lactate-buffered (35 mmol/L, pH 5.5) or a bicarbonate-buffered PD solution (34 mmol/L, pH 7.4) in randomized order on two sequential days. Each day a four-hour Standardized Permeability Analysis (SPA) was performed, followed by overnight APD (7 cycles, fill volume 1000 mL/m2, dwell time 75 min). Functional peritoneal surface area was dynamically assessed using the three-pore model.

RESULTS

While intraperitoneal pH was constant at 7.41 +/- 0.03 throughout the SPA with bicarbonate fluid, the dialysate remained acidic for more than one hour with lactate solution (pH 7.12 +/- 0.08 at 1 h). Total pore area was 60% higher during the first 30 minutes of the dwell than under steady-state conditions, without a difference between acidic and pH-neutral fluid. Net base gain, intraperitoneal volume kinetics, glucose absorption, ultrafiltration rate, effective lymphatic absorption and the transport of urea, potassium, beta2-microglobulin and albumin were similar with both fluids. However, phosphate and creatinine elimination were 10% lower with bicarbonate PD fluid, resulting in corresponding significant decreases in the 24-hour clearances of these solutes.

CONCLUSION

The peritoneal surface area is not measurably influenced by pH-neutral PD fluid. Creatinine and phosphate elimination appears to be slightly reduced with bicarbonate fluid; this observation awaits clarification in extended therapeutical trials.

AGEs bind to mesothelial cells via RAGE and stimulate VCAM-1 expression

BACKGROUND

Excess advanced glycation end-products (AGEs) are formed during renal failure, and AGE formation also may be connected with the high glucose concentration of peritoneal dialysis (PD) fluids. To determine the effect of human peritoneal mesothelial cell (HPMC) exposure to glycated proteins, we studied the HPMC receptor of AGE expression (RAGE), and analyzed the results of AGE-RAGE interaction on adhesion molecule expression and leukocyte binding.

METHODS

RAGE was detected by FACS analysis, and RAGE mRNA by reverse transcription-polymerase chain reaction (RT-PCR). Vascular and intercellular cell adhesion molecule (VCAM-1 and ICAM-1) expression was measured by a known radiometric technique under basal conditions, after the addition of an AGE-specific compound, Nepsilon-carboxylmethyllysine (CML-albumin). Leukocyte adhesion on HPMC was analyzed by videomicroscopy after HPMC stimulation.

RESULTS

RAGE protein was detected on HPMC, and RAGE mRNA was evidenced by RT-PCR. VCAM-1 expression was stimulated by CML-albumin (P < 0.01), while ICAM-1 was unchanged. By blocking the AGE-RAGE interaction, anti-RAGE antibodies or recombinant RAGE inhibited the increase in VCAM-1 expression. CML-albumin stimulation potentiated leukocyte adhesion to HPMC (P < 0.001). This effect was prevented by the incubation of leukocytes with recombinant VCAM-1 (P < 0.001).

CONCLUSIONS

AGE binding to RAGE stimulated mesothelial cell activity, and resulted in the overexpression of VCAM-1, a structure for leukocyte adhesion. The AGE-RAGE interaction resulted in HPMC activation, which may promote local inflammation, and thus is implicated in the peritoneal injury found in long-term PD patients.

Gene transfer of transforming growth factor-beta1 to the rat peritoneum: effects on membrane function

Long-term peritoneal dialysis is limited by physiologic changes in the peritoneum that lead to ultrafiltration failure. To determine the role of profibrotic cytokines in the alteration of peritoneal transport, a rodent model of transforming growth factor-beta (TGF-beta)-mediated peritoneal fibrosis was established. An adenoviral vector driving the active form of TGF-beta1 (AdTGFbeta1) was administered intraperitoneally, and peritoneal structure and function were evaluated for 28 d after infection. Seven days after AdTGFbeta1 infection, thickening of the peritoneum, with cellular proliferation and increased vascularization, was noted. By day 28, there was persistent thickening and extensive collagen deposition. The mesenteric collagen content was significantly elevated, compared with control adenovirus-treated animals, 21 d after infection (2.9 versus 1.8 mg hydroxyproline/g tissue, P = 0.006). Blood vessel density, as measured using factor VIII immunohistochemical analyses, was significantly increased from day 4 to day 21 but decreased by day 28. Animals infected with AdTGFbeta1 demonstrated increased transport of solutes and decreased net ultrafiltration, which was maximal on day 7 and returned to baseline levels by day 28. It was demonstrated in vitro and in vivo that TGF-beta1 induced production of vascular endothelial growth factor. Overexpression of TGF-beta1 after adenovirus-mediated gene transfer causes peritoneal fibrosis, neoangiogenesis, and increased peritoneal membrane solute transport. This model should allow further delineation of the relative contributions of profibrotic and angiogenic cytokines to changes in peritoneal function and may lead to potential new interventions for peritoneal membrane failure.

Evolution of continuous flow peritoneal dialysis and the current state of the art

Continuous flow peritoneal dialysis (CFPD) was first conceived more than three decades ago in an attempt to enhance peritoneal clearances using the continuous flow technique. Its progress was halted by technical limitations and by the high cost required to generate large volumes of dialytic solution. The recent demand for higher PD doses and technical innovations have revived the interest in this therapy. This article reviews the basic mechanical principles governing CFPD, its potential advantages and disadvantages, and the various methods to generate dialysate. Recent clinical experiences strongly suggest that CFPD can achieve higher small solute clearances than any modality of conventional PD or three times a week hemodialysis, and perhaps comparable to those obtained with daily hemodialysis. Attention can now be directed at improving peritoneal access and developing systems compatible with current reimbursement.

Overproduction of transforming growth factor-beta1 (TGF-beta1) is associated with adhesion formation and peritoneal fibrinolytic impairment

BACKGROUND

Reduction in peritoneal fibrinolytic capacity and increased transforming growth factor-beta1 (TGF-beta1) production are associated with adhesion development. This study investigated the expression of TGF-beta1 in peritoneal tissue, and possible correlation with components of the fibrinolytic system locally in peritoneal tissue.

MATERIALS AND METHODS

Peritoneal samples were taken from 22 patients at relaparotomy. Samples of adhesions were collected from 10 patients. The patients were categorized into different groups depending on the quantity and the quality of adhesions. TGF-beta1 and components of the fibrinolytic system in tissue extracts were assayed using enzyme-linked immunosorbent assays.

RESULTS

The concentration of active TGF-beta1 in peritoneal samples from patients with extensive adhesions was double (P <.01) that of healthy subjects, but the total levels of TGF-beta1 were similar (P =.63). In adhesion tissue, both active (P <.003) and total (P <.008) TGF-beta1 concentrations were more than twice as high as unaffected peritoneum. There was a significant correlation between the concentration of plasminogen activator inhibitor type 1 in peritoneal samples with active TGF-beta1 (P <.03, r = 0.693) and adhesion tissue with total TGF-beta1 (P =.001, r = 0.872). The other components of the fibrinolytic system did not correlate significantly with TGF-beta1.

CONCLUSIONS

These data indicate that an overexpression of TGF-beta1 is associated with adhesion formation, possibly through a mechanism involving local regulation of plasminogen activator inhibitor type 1.

High glucose-induced PKC activation mediates TGF-beta 1 and fibronectin synthesis by peritoneal mesothelial cells

BACKGROUND

Progressive peritoneal fibrosis, membrane hyperpermeability, and ultrafiltration failure have been observed in long-term peritoneal dialysis (PD) using glucose as an osmotic agent. High glucose activates protein kinase C (PKC), which is one important signal pathway in the activation of transforming growth factor-beta 1 (TGF-beta 1) and fibronectin (FN). To gain a better understanding of mechanisms involved in peritoneal fibrosis, we examined the effects of high glucose on human peritoneal mesothelial cell (HPMC) TGF-beta 1 and FN mRNA expression and protein synthesis and determined the involvement of PKC in the high glucose-induced HPMC activation.

METHODS

Synchronized confluent HPMC were incubated with different concentrations of glucose with and without inhibition of PKC. PKC activity and diacylglycerol (DAG) levels were measured. The expression of TGF-beta 1 and FN mRNAs by HPMC was measured by Northern blot analysis. TGF-beta 1 protein was measured by enzyme-linked immunosorbent assay (ELISA) and mink lung epithelial cell growth inhibition assay. FN protein was measured by Western blot analysis and ELISA.

RESULTS

PKC activity and DAG levels in HPMC cultured under 50 mmol/L (high) glucose increased 2.3- and 2.0-fold, respectively, that of 5.6 mmol/L (control) glucose at 24 hours and this was sustained up to 72 hours. The expression of TGF-beta 1 and FN mRNA by HPMC cultured under high glucose increased 1.6- and 1.7-fold, respectively, that of control values at 24 hours. TGF-beta bioactivity as well as protein content in heat-activated conditioned media from high glucose was significantly higher than that of control values at 24 and 48 hours. FN protein also increased in response to high glucose, as measured by Western blot analysis and ELISA. PKC activator phorbol 12-myristate 13-acetate (PMA) induced 2.2- and 1.4-fold increase in TGF-beta 1 and FN mRNA expression, respectively. Depletion of PKC and calphostin C, a PKC inhibitor, effectively prevented both PMA and high glucose-induced, but not constitutive, expression of TGF-beta 1 and FN.

CONCLUSION

The present data demonstrate that high glucose up-regulates TGF-beta 1 and FN synthesis by HPMC, and that this high glucose-induced up-regulation is largely mediated by PKC. These results suggest that activation of PKC by high glucose in conventional PD solutions may constitute an important signal for activation of HPMC, leading to progressive accumulation of extracellular matrix and eventual peritoneal fibrosis.

HB-EGF is produced in the peritoneal cavity and enhances mesothelial cell adhesion and migration

BACKGROUND

The mesothelial cell monolayer lining the peritoneal membrane needs constant repair in response to peritonitis and to the toxicity of peritoneal dialysate. In many continuous ambulatory peritoneal dialysis (CAPD) patients, the repair process progressively fails, and membrane dysfunction and fibrosis occur. Heparin-binding epidermal growth factor-like growth factor (HB-EGF) has an important role in wound repair and is also fibrogenic, and thus may be involved in these processes in the peritoneal cavity.

METHODS

The presence of HB-EGF, its receptors, and its associated proteins was determined in peritoneal membrane biopsies, cultured human peritoneal mesothelial cells (HPMCs), and peritoneal macrophages from CAPD patients by reverse transcription-polymerase chain reaction, flow cytometry, and immunofluorescence immunocytochemistry with confocal microscopy. HB-EGF effects on HPMC adhesion were measured by a static adhesion assay, on integrin expression by flow cytometry, and on migration by wound healing and chemotaxis assays.

RESULTS

HB-EGF, its receptors HER-1 and HER-4, and the associated proteins CD9, CD44, and integrin alpha(3)beta(1) were expressed by HPMCs and peritoneal macrophages. HB-EGF colocalized with HER-1 and HER-4 in HPMCs and induced their adhesion to collagen type I, expression of beta 1 integrins, and migration.

CONCLUSIONS

HB-EGF is produced by cells in the peritoneal cavity of CAPD patients and has functional effects on HPMCs that would facilitate repair of the mesothelial layer.

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.