Human peritoneal fibroblast proliferation in 3-dimensional culture: modulation by cytokines, growth factors and peritoneal dialysis effluent

Effects of Pentoxifylline on Peritoneal Fibroblasts and Silica-Induced Peritoneal Fibrosis

♦ Background

Peritoneal fibrosis is a long-term complication following continuous ambulatory peritoneal dialysis (CAPD). Peritoneal fibroblasts may play an important role in peritoneal fibrosis. Up to now, the treatment of peritoneal fibrosis in patients with CAPD remains unsatisfactory. Pentoxifylline (PTX) is a xanthine derivative and is used in the treatment of peripheral vascular and cerebrovascular diseases. Several studies have demonstrated that PTX can ameliorate fibrosis of the skin, liver, and kidney.

♦ Objective

To investigate the effect of PTX on in vitro growth and collagen synthesis of human peritoneal fibroblasts (HPFBs), and to evaluate the effects of PTX on silica-induced peritoneal fibrosis in vivo.

♦ Design and Measurements

In the in vitro study, HPFBs were cultured from human omentum. The effect of PTX on the growth of serum-stimulated HPFBs was evaluated by MTT assay. The effect of PTX on the collagen synthesis of HPFB was measured by [3H]-proline incorporation. Expression of type I and type III collagen mRNA was evaluated by Northern blotting. The effects of PTX on matrix metalloproteinase (MMP) activity and cAMP level in HPFBs were measured by immunoassays. In the in vivo study, Wistar rats were randomly divided into five groups. All rats received intraperitoneal (IP) injection of silica suspension (250 mg/100 g body weight) on day 0. The rats of group 1 (control group) were injected with vehicle IP every day for 14 days. The rats of groups 2, 3, and 4 were injected with PTX (4 mg/100 g body weight) IP every day for 3, 7, and 14 days, respectively. The rats in group 5 received an intravenous infusion of PTX (8 mg/100 g body weight) every day for 7 days. On the 15th day after silica injection, all rats were sacrificed. Their parietal and visceral peritoneums were removed and processed for pathology, and the severity of fibrosis was measured and scored. ♦ Results: In vitro, PTX inhibited serum-stimulated HPFB growth (maximum was 93% at 1 mg PTX/mL) in a dose-dependent manner. Collagen synthesis by HPFB was reduced (47% at 1 mg PTX/mL), and collagen I and III mRNA expression in HPFBs was suppressed by PTX. The PTX did not affect the MMP (including MMP-1, MMP-8, and MMP-13) activities of HPFBs. The mechanism of PTX was through increasing cAMP by its phosphodiesterase inhibiting activity. In vivo, the severity of fibrosis was significantly reduced in groups 4 and 5 compared to group 1 ( p < 0.05).

♦ Conclusion

These results suggest that PTX can inhibit growth of and collagen synthesis by HPFBs in vitro. The fibrosis derived from silica-induced peritonitis in vivo was also ameliorated by PTX. Therefore, pentoxifylline may have the potential to be used to treat peritoneal fibrosis in patients on CAPD.

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.

Technological Advances in Peritoneal Dialysis Research Peritoneal Cell Culture: Fibroblasts

Fibroblasts have been traditionally viewed as providing little more than a structural lattice for other cell types. However, recent data indicate that fibroblasts play a key and early role in many pathophysiological processes, including inflammation, fibrosis, and neoplasia. Moreover, depending on the anatomical location, fibroblasts display significant functional heterogeneity. Therefore, it is important to study the subpopulation of fibroblasts derived exactly from the organ of interest rather than to extrapolate the observations made in other fibroblast subsets. Cell culture provides a powerful tool for studying the role of fibroblasts in various contexts. In this review, we describe procedures for establishing and identifying primary cultures of human peritoneal fibroblasts. We also briefly discuss the potential involvement of peritoneal fibroblasts in peritoneal pathology.

The Effects of Irbesartan and Spironolactone in Prevention of Peritoneal Fibrosis in Rats

Background

Bacterial peritonitis episodes may disturb the functional and histological integrity of the peritoneum in peritoneal dialysis patients. The renin–angiotensin–aldosterone system may have fibrotic effects on the peritoneum.

Objective

To study the effects of an angiotensin II receptor antagonist (irbesartan) and an aldosterone antagonist (spironolactone) in the prevention of peritoneal fibrosis in a rat model of bacterial peritonitis.

Methods

40 Wistar rats were randomized into 5 groups: bacteria (B), bacteria–irbesartan (BI), bacteria–spironolactone (BS), bacteria–irbesartan–spironolactone (BIS), and control (C) groups. The C group received only dextran beads (Cytodex; Sigma Chemicals, St Louis, Missouri, USA); the others were given bacteria and dextran beads intraperitoneally. Irbesartan and/or spironolactone were given to 3 groups: BI, BS, and BIS. On the eighth day, the rats were sacrificed, peritoneal adhesion was quantified, and peritoneal tissue sections were evaluated histologically.

Results

The peritoneal total adhesion score was significantly higher in the B group than in the BI, BIS, and C groups ( p < 0.01). Mean peritoneal thickness, mean inflammation score, and mean fibrosis score were significantly higher in the B group in comparison to the C group ( p < 0.05). Mean peritoneal thickness of all treatment groups was significantly lower than the B group ( p < 0.05). Serum transforming growth factor beta-1 level was significantly higher in the B group than in the BI, BS, and C groups ( p < 0.05).

Conclusion

Irbesartan and spironolactone seem to decrease the extent of peritoneal injury caused by bacterial peritonitis.

Intraperitoneal Administration of Telmisartan Prevents Postsurgical Adhesion Band Formation

BACKGROUND

Angiotensin II receptor blockers (ARBs) have a potential role in reducing inflammation and fibrosis. We have integrated systems and molecular biology approaches to investigate the therapeutic potential of ARBs in preventing postsurgical adhesion band formation.

MATERIAL AND METHODS

we have followed the ARRIVE guidelines point by point during experimental studies. Telmisartan (1 and 9 mg/kg), valsartan (1 and 9 mg/kg), and losartan (1 and 10 mg/kg) were administered intraperitoneally in different groups of male albino Wistar rat. After 7 d of treatment, macroscopic evidence and score of fibrotic bands based on scaling methods was performed. Moreover, the anti-inflammatory and antifibrosis effects of telmisartan on reduction of fibrotic bands were investigated by using histopathology, ELISA, and real-time polymerase chain reaction methods.

RESULTS

Telmisartan, but not losartan or valsartan, prevented the frequency as well as the stability of adhesion bands. Telmisartan appears to elicit anti-inflammatory responses by attenuating submucosal edema, suppressing proinflammatory cytokines, decreasing proinflammatory cell infiltration, and inhibiting oxidative stress at the site of peritoneal surgery. We also showed that telmisartan prevents fibrotic adhesion band formation by reducing excessive collagen deposition and suppression of profibrotic genes expression at the peritoneum adhesion tissues.

CONCLUSIONS

These results support the potential application of telmisartan in preventing postsurgical adhesion band formation by inhibiting key pathologic responses of inflammation and fibrosis in postsurgery patients.

Pathogenesis of Peritoneal Sclerosis

Peritoneal sclerosis is an almost invariable consequence of peritoneal dialysis. In most circumstances it is “simple” sclerosis, manifesting clinically with an increasing peritoneal transport rate and loss of ultrafiltration capacity. In contrast, encapsulating peritoneal sclerosis is a life threatening and usually irreversible condition, associated with bowel obstruction, malnutrition and death. It is unknown whether common etiological factors underlie the development of these 2 clinically and pathologically distinct forms of peritoneal sclerosis. The majority of studies to date have investigated factors that contribute to “simple” sclerosis, although it remains possible that similar mechanisms are amplified in patients who develop encapsulated peritoneal sclerosis. The cellular elements that promote peritoneal sclerosis include the mesothelial cells, peritoneal fibroblasts and inflammatory cells. Factors that stimulate these cells to promote peritoneal fibrosis and neoangiogenesis, both inherent in the development of peritoneal sclerosis, include cytokines that are induced by exposure of the peritoneal membrane to high concentrations of glucose, advanced glycation of the peritoneal membrane and oxidative stress. The cumulative exposure to bioincompatible dialysate is likely to have an etiological role as the duration of dialysis correlates with the likelihood of developing peritoneal sclerosis. Indeed peritoneal dialysis using more biocompatible fluids has been shown to reduce the development of peritoneal sclerosis. The individual contribution of the factors implicated in the development of peritoneal sclerosis will only be determined by large scale peritoneal biopsy registries, which will be able to prospectively incorporate clinical and histological data and support clinical decision making.

Feasibility of Mesothelial Transplantation during Experimental Peritoneal Dialysis and Peritonitis

The mesothelial cell layer lining the peritoneum orchestrates peritoneal homeostasis. Continuous exposure to peritoneal dialysis fluids and episodes of peritonitis may damage the monolayer irreversibly, eventually leading to adhesion formation and fibrosis/sclerosis of the peritoneum. Autologous mesothelial cell transplantation is thought to be one of the options to reduce dysfunction of the peritoneal membrane. In this article we will review the mesothelial cell transplantation experiments performed in the field of peritoneal dialysis and peritonitis. In addition we will focus on the trouble shooting using cultured autologous mesothelial cells for transplantation.

Thy-1+/- fibroblast subsets in the human peritoneum

Fibrotic thickening of the peritoneum develops in patients receiving peritoneal dialysis (PD) for renal failure. For unknown reasons, however, in some patients it progresses to extensive fibrosis that compromises dialysis capacity of the peritoneum. It is increasingly clear that fibroblasts display large heterogeneity not only between but also within tissues. Differential surface expression of thymocyte differentiation antigen 1 (Thy-1) has been shown to identify functionally distinct fibroblast subsets in several organs. Here, we isolated Thy-1^+/- subsets of human peritoneal fibroblasts (HPFB) and analyzed them in terms of profibrotic myofibroblast features. In healthy individuals, Thy-1⁺ cells constituted ~45% of the HPFB population found in the greater omentum but were not detected in the parietal peritoneum. When propagated in culture and compared with Thy-1^- cells, omentum-derived Thy-1⁺ HPFB consistently displayed an increased expression of α-smooth muscle actin, collagen I, and transforming growth factor-β1. They also showed greater proliferation capacity and enhanced contractile properties. The number of Thy-1⁺ HPFB increased significantly in PD patients and made up more than 70 and 95% of all HPFB found in the omentum and parietal peritoneum, respectively. These data indicate that the expansion of Thy-1⁺ fibroblasts may contribute to fibrotic thickening of the peritoneal membrane during PD.

Unconventional Human T Cells Accumulate at the Site of Infection in Response to Microbial Ligands and Induce Local Tissue Remodeling

The antimicrobial responsiveness and function of unconventional human T cells are poorly understood, with only limited access to relevant specimens from sites of infection. Peritonitis is a common and serious complication in individuals with end-stage kidney disease receiving peritoneal dialysis. By analyzing local and systemic immune responses in peritoneal dialysis patients presenting with acute bacterial peritonitis and monitoring individuals before and during defined infectious episodes, our data show that Vγ9/Vδ2⁺ γδ T cells and mucosal-associated invariant T cells accumulate at the site of infection with organisms producing (E)-4-hydroxy-3-methyl-but-2-enyl pyrophosphate and vitamin B₂, respectively. Such unconventional human T cells are major producers of IFN-γ and TNF-α in response to these ligands that are shared by many microbial pathogens and affect the cells lining the peritoneal cavity by triggering local inflammation and inducing tissue remodeling with consequences for peritoneal membrane integrity. Our data uncover a crucial role for Vγ9/Vδ2 T cells and mucosal-associated invariant T cells in bacterial infection and suggest that they represent a useful predictive marker for important clinical outcomes, which may inform future stratification and patient management. These findings are likely to be applicable to other acute infections where local activation of unconventional T cells contributes to the antimicrobial inflammatory response.

The Role of Tyrosine Kinase Receptors in Peritoneal Fibrosis

Peritoneal dialysis (PD) is a modality for treatment of patients with end-stage renal disease (ESRD) that depends on the structural and functional integrity of the peritoneal membrane. However, long-term PD can lead to morphological and functional changes in the peritoneum; in particular, peritoneal fibrosis has become one of the most common complications that ultimately results in ultrafiltration failure (UFF) and discontinuation of PD. Several factors and mechanisms such as inflammation and overproduction of transforming growth factor-β1 have been implicated in the development of peritoneal fibrosis, but there is no effective therapy to prevent or delay this process. Recent studies have shown that activation of multiple receptor tyrosine kinases (RTKs) is associated with the development and progression of tissue fibrosis in various organs, and there are also reports indicating the involvement of some RTKs in peritoneal fibrosis. This review will describe the role and mechanisms of RTKs in peritoneal fibrosis and discuss the possibility of using them as therapeutic targets for prevention and treatment of this complication.

Myofibroblastic Conversion and Regeneration of Mesothelial Cells in Peritoneal and Liver Fibrosis

Mesothelial cells (MCs) form a single epithelial layer and line the surface of body cavities and internal organs. Patients who undergo peritoneal dialysis often develop peritoneal fibrosis that is characterized by the accumulation of myofibroblasts in connective tissue. Although MCs are believed to be the source of myofibroblasts, their contribution has remained obscure. We determined the contribution of peritoneal MCs to myofibroblasts in chlorhexidine gluconate (CG)-induced fibrosis compared with that of phenotypic changes of liver MCs. CG injections resulted in disappearance of MCs from the body wall and the accumulation of myofibroblasts in the connective tissue. Conditional linage tracing with Wilms tumor 1 (Wt1)-CreERT2 and Rosa26 reporter mice found that 17% of myofibroblasts were derived from MCs in peritoneal fibrosis. Conditional deletion of transforming growth factor-β type II receptor in Wt1(+) MCs substantially reduced peritoneal fibrosis. The CG treatment also induced myofibroblastic conversion of MCs in the liver. Lineage tracing with Mesp1-Cre mice revealed that Mesp1(+) mesoderm gave rise to liver MCs but not peritoneal MCs. During recovery from peritoneal fibrosis, peritoneal MCs, but not liver MCs, contribute to the regeneration of the peritoneal mesothelium, indicating an inherent difference between parietal and visceral MCs. In conclusion, MCs partially contribute to myofibroblasts in peritoneal and liver fibrosis, and protection of the MC layer leads to reduced development of fibrous tissue.

Platelet-derived growth factor receptor-β expression in human peritoneum

INTRODUCTION

Simple peritoneal fibrosis and encapsulating peritoneal sclerosis (EPS) are important lesions in the peritoneum of patients on peritoneal dialysis (PD). We have previously described a population of podoplanin-positive myofibroblasts in peritoneal biopsies from patients with EPS. Platelet-derived growth factor receptor-β (PDGFRβ) is a marker of pericytes, and PDGFs might be involved in the fibrotic response of the peritoneum. This study aimed to describe PDGFRβ in the human peritoneum.

METHODS

In this retrospective analysis, we localized PDGFRβ in peritoneal biopsies from patients with EPS (n = 6) and patients on PD without signs of EPS (n = 5), and compared them with normal peritoneum (n = 4) and peritoneum from uremic patients (n = 5). Consecutive sections were stained for smooth-muscle actin (SMA) and podoplanin. Slides were scored semiquantitatively by 2 observers blinded to the diagnosis.

RESULTS

PDGFRβ was expressed by cells of arterial walls in all biopsies. A prominent population of PDGFRβ-positive cells was present in the normal peritoneum, which were SMA negative on consecutive sections. In patients on PD, a high number of PDGFRβ were also positive for SMA. In EPS, the majority of podoplanin-positive cells were positive for PDGFRβ. In peritoneal biopsies from normal and uremic patients, the expression of SMA was mainly restricted to cells of arterial walls. Podoplanin expression was restricted to lymphatic vessels in normal peritoneum, in uremic patients, and in patients on PD without EPS.

CONCLUSIONS

As podoplanin-positive myofibroblasts express PDGFRβ, these cells might be related to pericytes (rather than other sources of fibroblasts). PDGFRβ might turn out to be a therapeutic target in EPS.

Lineage tracing reveals distinctive fates for mesothelial cells and submesothelial fibroblasts during peritoneal injury

Fibrosis of the peritoneal cavity remains a serious, life-threatening problem in the treatment of kidney failure with peritoneal dialysis. The mechanism of fibrosis remains unclear partly because the fibrogenic cells have not been identified with certainty. Recent studies have proposed mesothelial cells to be an important source of myofibroblasts through the epithelial-mesenchymal transition; however, confirmatory studies in vivo are lacking. Here, we show by inducible genetic fate mapping that type I collagen-producing submesothelial fibroblasts are specific progenitors of α-smooth muscle actin-positive myofibroblasts that accumulate progressively in models of peritoneal fibrosis induced by sodium hypochlorite, hyperglycemic dialysis solutions, or TGF-β1. Similar genetic mapping of Wilms' tumor-1-positive mesothelial cells indicated that peritoneal membrane disruption is repaired and replaced by surviving mesothelial cells in peritoneal injury, and not by submesothelial fibroblasts. Although primary cultures of mesothelial cells or submesothelial fibroblasts each expressed α-smooth muscle actin under the influence of TGF-β1, only submesothelial fibroblasts expressed α-smooth muscle actin after induction of peritoneal fibrosis in mice. Furthermore, pharmacologic inhibition of the PDGF receptor, which is expressed by submesothelial fibroblasts but not mesothelial cells, attenuated the peritoneal fibrosis but not the remesothelialization induced by hypochlorite. Thus, our data identify distinctive fates for injured mesothelial cells and submesothelial fibroblasts during peritoneal injury and fibrosis.

Functional and structural alterations of peritoneum and secretion of fibrotic cytokines in rats caused by high glucose peritoneal dialysis solutions

OBJECTIVE

To determine functional and structural alterations of peritoneum and fibrotic cytokines expression in peritoneal dialysis (PD) rats.

METHODS

28 Sprague-Dawley (S-D) rats were randomly divided into four groups and dialyzed with various solutions daily for four weeks: (1) no solution (CON group), (2) 0.9% Saline solution (NS group), (3) 1.5% Dianeal (LG group), (4) 4.25% Dianeal (HG group). Peritoneal equilibration tests, ultrafiltration function and effluent protein quantification were measured. Peritoneum morphology was studied and immunohistochemistry were performed for detection of transforming growth factor β1 (TGF-β1), connective tissue growth factor (CTGF), and fibronectin (FN) proteins. Reverse transcriptional-polymerase chain reaction was used to analyze the expression of TGF-β1, CTGF mRNA.

RESULTS

Administration of 4.25% Dianeal caused functional and structural changes of peritoneum, including protein loss through the transport process, decrease of peritoneal solute transport rate and ultrafiltration capacity. The collagen of peritoneum in the HG group was thicker than the other groups. The levels of CTGF, TGF-β1, and FN proteins were significantly the highest in the HG group, followed by the LG group. The liner correlation analysis showed positive correlations between the levels of CTGF, TGF-β1, and FN proteins and the collagen thickness. The expression of TGF-β1 and CTGF mRNA in the HG group were significantly higher than those in the other groups and were indicated positive correlation.

CONCLUSION

Using high glucose peritoneal dialysis solutions in rats may not only lead to processing of peritoneal fibrosis, which is promoted by ectopic expression of TGF-β1, but also increase the expression of CTGF. CTGF is an important fibrotic media of peritoneal fibrosis in PD rats.

Impact of intraperitoneal pressure of a CO2 pneumoperitoneum on the surgical peritoneal environment

BACKGROUND

Animal experiments have suggested that a high intraperitoneal pressure (IPP) might adversely affect the surgical peritoneal environment. The present experimental study investigates the impact of IPP of a CO(2) pneumoperitoneum on human peritoneum.

METHODS

Patients undergoing laparoscopic surgery were subjected to either low (8 mmHg) or standard (12 mmHg) IPP. Normal peritoneum was collected from the parietal wall at the beginning of surgery and every 60 min thereafter. Expression levels of 168 genes that encode extracellular matrix proteins, adhesion molecules or inflammatory cytokine signaling molecules were measured in peritoneal tissues using real-time polymerase chain reaction (PCR)-based assay panels. Human peritoneal mesothelial cells (HPMCs) and human peritoneal fibroblasts (HPFBs) were incubated in a CO(2) insufflation chamber for 1 h at 12 or 8 mmHg. Hyaluronan (HA) synthesis and mRNA expression levels of hyaluronic acid synthases (HAS) and hyaluronidases (Hyal) in HPMCs and HPFBs were measured at 0, 4, 8, 12, 24 and 48 h after CO(2) gas exposure by ELISA and real-time PCR, respectively.

RESULTS

Expression levels of connective tissue growth factor (CTGF), matrix metalloproteinase-9, E-selectin, chemokine (C-X-C motif) ligand 2 (CXCL-2), Hyal-1 and Hyal-2 were significantly higher and those of HAS-1, HAS-3, thrombospondin-2 (TSP-2) and interleukin-10 were significantly lower in the 12 mmHg group compared with the 8 mmHg group. HA synthesis was significantly lower in the 12 mmHg group compared with the 8 mmHg group in HPMCs and HPFBs throughout the time course.

CONCLUSIONS

A low IPP (8 mmHg) may be better than the standard IPP (12 mmHg) to minimize the adverse impact on the surgical peritoneal environment during a CO(2) pneumoperitoneum.

Fibroblasts in omentum activated by tumor cells promote ovarian cancer growth, adhesion and invasiveness

Omentum metastasis is a common occurrence in epithelial ovarian cancer (EOC), which is often accompanied by ascites that facilitates the spread of EOC cells. A subpopulation of fibroblasts-the cancer-associated fibroblasts (CAFs) are important promoters of tumor progression. We have shown previously that CAFs exist not only in omentum with EOC metastasis but also in omentum without metastasis. In the present study, using primary human fibroblasts isolated from normal omentum (NFs) and omentum with ovarian cancer metastasis (CAFs), we established in vitro coculture models and a 3D culture model mimicking human omentum structure for investigation of interactions between fibroblasts and cancer cells. We demonstrate that EOC cells activate NFs and promote their proliferation via transforming growth factor-β1 (TGF-β1) signaling, and the activated fibroblasts contribute to the invasion and adhesion of EOC cells. Moreover, EOC cells and NFs coculture led to overexpression of hepatocyte growth factor (HGF) and matrix metalloproteinase-2 (MMP-2) and adhesion and invasion of EOC cells could be partially suppressed by blocking the function of HGF or MMP-2. Additionally, mouse peritoneal dissemination models of EOC confirmed the activation of fibroblasts by cancer cells and the tumor growth- and metastasis-promoting effects of activated fibroblasts in vivo. Our findings indicate that activated fibroblasts in omentum form a congenial environment to promote EOC cells implantation. It is an intriguing concept that targeting the activation of omentum fibroblast through the inhibition of TGF-β1 signaling can be used as a new therapeutic strategy against ovarian cancer omentum metastases, which needs further study.

Peritoneal dialysis research in the UK: the Cardiff contribution

The hallmark of the Cardiff contribution to our understanding of peritoneal dialysis over the past quarter century has been their translational approach to research, combining strong basic science with intelligent clinical questions. Their themes have included describing the biology of the dialyzed membrane; elucidation of several overlapping mechanisms of bioincompatibility, resulting in the development and testing of more biocompatible solutions; and describing the morphological changes with time on treatment and the membrane's response to infection. This has extended to investigation of the mechanisms controlling initiation and resolution by the innate immune system, relevant to both long-term membrane injury and a wider understanding of immunobiology. More than any other group, they have held the torch for basic science in peritoneal dialysis research.

Platelet derived growth factor B and epithelial mesenchymal transition of peritoneal mesothelial cells

Platelet derived growth factor (PDGF) is involved in wound healing in various organ systems. Its potential role in the context of peritoneal injury following long-term peritoneal dialysis is unclear. We used an adenovirus expressing the B chain of PDGF (AdPDGF-B) to assess its effect on pro-fibrotic pathways in the peritoneal membrane. To assess the transforming growth factor (TGF) beta independent effects of PDGF, we over-expressed PDGF-B in the peritoneum of either wild-type mice (Smad3+/+) or those with a deletion of the TGFbeta signaling protein Smad3 (Smad3(-/-)). PDGF-B induced sustained angiogenesis in both Smad3+/+ and Smad3(-/-) mice. Despite increased collagen gene expression, collagen accumulation was transient and fibrogenesis was associated with induction of collagenase activity. We observed epithelial to mesenchymal transition (EMT) involving the peritoneal mesothelial cells, as shown by increased SNAIL and decreased E-Cadherin expression with evidence of mesothelial cells expressing both epithelial and mesenchymal markers. Unlike TGFbeta-induced EMT, PDGF-B exposure did not lead to mobilization of the mesothelial cells; they remained as a single monolayer throughout the observation period. This "non-invasive" EMT phenomenon is a novel finding and may have implications concerning the role of EMT in peritoneal fibrosis and injury to other organ systems. The observed effects were similar in Smad3(-/-) and Smad3+/+ animals, suggesting that the PDGF-B effects were independent of TGFbeta or Smad signaling.

Factors Contributing to Peritoneal Tissue Remodeling in Peritoneal Dialysis

Peritoneal dialysis (PD) is associated with functional and structural changes of the peritoneal membrane. In this review we describe factors contributing to peritoneal tissue remodeling, including uremia, peritonitis, volume loading, the presence of a catheter, and the PD fluid itself. These factors initiate recruitment and activation of peritoneal cells such as macrophages and mast cells, as well as activation of peritoneal cells, including mesothelial cells, fibroblasts, and endothelial cells. We provide an overview of cytokines, growth factors, and other mediators involved in PD-associated changes. Activation of downstream pathways of cellular modulators can induce peritoneal tissue remodeling, leading to ultrafiltration loss. Identification of molecular pathways, cells, and cytokines involved in the development of angiogenesis, fibrosis, and membrane failure may lead to innovative therapeutic strategies that can protect the peritoneal membrane from the consequences of long-term PD.

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.

IL-1beta differently involved in IL-8 and FGF-2 release in crystalline silica-treated lung cell co-cultures

Background

Inhalation of crystalline silica particles is in humans associated with inflammation and development of fibrosis. The aim of the present study was to investigate the effect of crystalline silica on the release of the fibrosis- and angiogenesis-related mediator FGF-2 and the pro-inflammatory mediator IL-8, and how IL-1β and TNF-α were involved in this release from various mono- and co-cultures of monocytes, pneumocytes and endothelial cells.

Results

Silica exposure induced an increase of IL-8 release from monocytes and from pneumocytes alone, and the FGF-2 level in the medium increased upon silica exposure of pneumocytes. Both the responses were enhanced in non-contact co-cultures with endothelial cells. The FGF-2 release seemed to increase with the silica-induced decrease in the number of pneumocytes. The release of IL-8 and FGF-2 was partially suppressed in cultures with pneumocytes in contact with monocytes compared to non-contact cultures. Treatment with anti-TNF-α and the IL-1 receptor antagonist revealed that release of IL-1β, and not TNF-α, from monocytes dominated the regulation of IL-8 release in co-cultures. For release of FGF-2, IL-1ra was without effect. However, exogenous IL-1β reduced the FGF-2 levels, strongly elevated the FGF-2-binding protein PTX3, and prevented the reduction in the number of pneumocytes induced by silica.

Conclusion

IL-1β seems to be differently involved in the silica-induced release of IL-8 and FGF-2 in different lung cell cultures. Whereas the silica-induced IL-8 release is regulated via an IL-1-receptor-mediated mechanism, IL-1β is suggested only indirectly to affect the silica-induced FGF-2 release by counteracting pneumocyte loss. Furthermore, the enhanced IL-8 and FGF-2 responses in co-cultures involving endothelial cells show the importance of the interaction between different cell types and may suggest that both these mediators are important in angiogenic or fibrogenic processes.

Glucose degradation products (GDP's) and peritoneal changes in patients on chronic peritoneal dialysis: will new dialysis solutions prevent these changes?

As peritonitis rates are declining, the rate of technique failure due to ultrafiltration failure and inadequate solute removal is becoming more important. The failure of the peritoneal membrane to provide adequate dialysis increases with longer duration on PD and correlates with the structural changes in the peritoneal membrane. The exact mechanism responsible for these structural changes is unclear. Conventional PD fluids with glucose as the osmotic agent and more importantly the glucose degradation products (GDP) generated during the heat sterilization of these solutions seems to be responsible for inducing many of these changes in the peritoneum. GDP's in addition to causing structural and functional alterations of the peritoneal cells is also a leading cause of advanced glycation end-products (AGE) production. There is evidence to suggest that the GDP's and AGE's are not limited to the peritoneal cavity and the membrane. They have been shown to get deposited in the vascular walls. In addition they also interact with receptors on endothelial cells and smooth muscle. Thus they could contribute to the vascular dysfunction similar to that seen in diabetes. Formation of GDP's can be reduced and even be avoided with the use of newer "biocompatible" solutions by sterilizing the glucose and the buffer in separate chambers. These newer solutions have been shown to have several local and systemic advantages over the conventional PD solutions. It remains to be seen whether their chronic use from the start of peritoneal dialysis will prevent the development of peritoneal damage thus allowing these patients to remain on this modality for longer periods.

Cytokines and growth factors involved in peritoneal fibrosis of peritoneal dialysis patients

Peritoneal fibrosis is initiated by exposure of peritoneal tissues to numerous harmful agents encountered during peritoneal dialysis. These agents interact with cells within the peritoneum to induce growth factors and cytokines that are important in the initiation, progression and maintenance of fibrosis. Some of the mediators implicated in the pathogenesis of peritoneal fibrosis include transforming growth factor (TGF) beta, connective tissue growth factor (CTGF), fibroblast growth factors (FGF), and platelet derived growth factor (PDGF).

Macrophages in streptozotocin-induced diabetic nephropathy: potential role in renal fibrosis

BACKGROUND

Renal fibrosis is central to the progression of diabetic nephropathy; however, the mechanisms responsible for fibroblast and matrix accumulation in this disease are only partially understood. Macrophages accumulate in diabetic kidneys, but it is unknown whether macrophages contribute to renal fibrosis. Therefore, we examined whether macrophage accumulation is associated with the progression of renal injury and fibrosis in type 1 diabetic nephropathy and whether macrophages exposed to the diabetic milieu could promote fibroblast proliferation.

METHODS

Kidney macrophages, renal injury and fibrosis were analysed in diabetic C57BL/6J mice at 2, 8, 12 and 18 weeks after streptozotocin injection. Isolated rat bone marrow macrophages were stimulated with diabetic rat serum or carboxymethyllysine (CML)-bovine serum albumin (BSA) to determine whether macrophage-conditioned medium could promote the proliferation of rat renal (NRK-49F) fibroblasts.

RESULTS

Progressive injury and fibrosis in diabetic nephropathy was associated with increased numbers of kidney macrophages. Macrophage accumulation in diabetic mice correlated with hyperglycaemia (blood glucose, HbA1c levels), renal injury (albuminuria, plasma creatinine), histological damage and renal fibrosis (myofibroblasts, collagen IV). Culture supernatant derived from bone marrow macrophages incubated with diabetic rat serum or CML-BSA induced proliferation of fibroblasts, which was inhibited by pre-treating fibroblasts with interleukin-1 (IL-1) receptor antagonist or the platelet-derived growth factor (PDGF) receptor kinase inhibitor, STI-571.

CONCLUSION

Kidney macrophage accumulation is associated with the progression of renal injury and fibrosis in streptozotocin-induced mouse diabetic nephropathy. Elements of the diabetic milieu can stimulate macrophages to promote fibroblast proliferation via IL-1- and PDGF-dependent pathways which may enhance renal fibrosis.

Dialysate Leukocytes, sICAM-1, Hyaluronan and IL-6: Predictors of Outcome of Peritonitis?

BACKGROUND/AIMS

Despite effective antibiotic therapy, peritonitis still remains a major problem in peritoneal dialysis (PD). The aim of the present study was to investigate changes of CRP, dialysate leukocytes and IL-6, hyaluronan (HA) and sICAM-1 in dialysate during and after peritonitis and their association to the outcome of peritonitis.

METHODS

Dialysate IL-6, HA and sICAM-1 were measured at the onset and on day 4, at the end of the treatment and 2 months after onset of peritonitis. Furthermore, CRP and dialysate leukocytes were measured on days 1-4.

RESULTS

All measured soluble factors were higher on the first and fourth day than at the end of the treatment. sICAM-1 and HA were lower at the end of the treatment in patients who later had a relapse/re-infection. IL-6 remained higher 2 months after clinically cured peritonitis. CRP and dialysate leukocytes were higher on day 4 in patients with poor outcome.

CONCLUSIONS

Peritonitis causes increased excretion of soluble factors. Low concentrations of sICAM-1 and HA at the end of the treatment were negative prognostic indicators. Higher IL-6 levels after peritonitis could be a sign of ongoing inflammation in the peritoneal membrane. Delayed decrease in CRP and dialysate leukocytes may indicate poor outcome.

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.

Selective depletion of fibroblasts preserves morphology and the functional integrity of peritoneum in transgenic mice with peritoneal fibrosing syndrome

BACKGROUND

A peritoneal fibrosing syndrome (PFS) can progressively reduce peritoneal ultrafiltration during chronic peritoneal dialysis in patients with renal failure. The pathogenesis of PFS is unclear and the role of peritoneal fibroblasts has not been evaluated experimentally.

METHODS

We followed the fate of fibroblasts producing PFS in a mouse model using fibroblast-specific protein 1 (FSP1) as a marker. PFS was induced by daily peritoneal infusions of chlorhexidine gluconate (CHG) saline into transgenic mice expressing the thymidine kinase (Delta tk) gene under the control of the FSP1 promoter (FSP1.Delta tk mice). To demonstrate the role of fibroblasts in PFS, we treated these FSP1.Delta tk mice with a nucleoside analogue to induce DNA chain termination and fibroblast death.

RESULTS

Mice receiving peritoneal infusions of CHG saline every other day for 2 weeks developed increasing numbers of FSP1+ fibroblasts in the subserosal layers of the visceral peritoneum. Mac-3+ monocytes (macrophages) subsequently accumulated over the next 2 weeks in association with increased deposition of type I collagen and increased endothelial vascularity (CD31+) in these subserosal tissues. Since these peritoneal fibroblasts expressed monocyte chemoattractant protein-1 (MCP-1), heat shock protein 47 (HSP47), and vascular endothelial growth factor (VEGF), we suspect they were partially responsible for macrophage recruitment, matrix production, and the neoangiogenesis in the subserosal tissue. Treatment of PFS in FSP1.Delta tk transgenic mice with a nucleoside analogue selectively reduced the numbers of peritoneal fibroblasts and attenuated the attendant changes in peritoneal histology. Rescuing the peritoneal membrane from chronic thickening and neoangiogenesis by reducing the number of fibroblasts also preserved ultrafiltration.

CONCLUSION

Peritoneal fibroblasts play a pivotal role in PFS, and their deletion using a fibroblasts-specific transgene was effective in preventing peritoneal fibrogenesis.

Relaxin down-regulates renal fibroblast function and promotes matrix remodelling in vitro

BACKGROUND

Renal fibroblasts are important effector cells in tubulointerstitial fibrosis, with experimental antifibrotic strategies focusing on the functional down-regulation of these cells. Several experimental models of fibrosis have provided evidence for the effectiveness of the polypeptide hormone relaxin as a potential antifibrotic agent. This study was conducted to further elucidate the antifibrotic mechanisms of relaxin on renal fibroblasts in vitro.

METHODS

Rat cortical fibroblasts were obtained from outgrowth culture of renal tissue isolated from kidneys 3 days post-unilateral ureteric obstruction and constituted 100% of cells studied. A relaxin radio-receptor assay was used to establish binding of relaxin to renal fibroblasts in vitro. Functional studies then examined the effects of H2 relaxin (0, 1, 10 and 100 ng/ml) on fibroblast kinetics, expression of alpha-smooth muscle actin (alpha-SMA), total collagen synthesis, collagenase production and collagen-I lattice contraction. CTGF mRNA expression was also measured by northern analysis.

RESULTS

H2 relaxin bound with high affinity to rat renal fibroblasts, but receptor numbers were low. Consistent with its previously reported bimodal effect, transforming growth factor (TGF-beta 1) reduced fibroblast proliferation, an effect abrogated by H2 relaxin. Fibroblasts exposed to H2 relaxin (100 ng/ml) for 24 h demonstrated decreased immunostaining for alpha-SMA and reduced alpha-SMA protein expression compared with controls. There was a trend for a relaxin-mediated reduction in total collagen synthesis and alpha 1(I) mRNA expression with large dose-related increases in collagenase protein expression being observed. TGF-beta 1-stimulated collagen-I lattice contraction was significantly inhibited following co-incubation with 100 ng/ml relaxin. Incremental doses of H2 relaxin had no significant effect on CTGF mRNA expression.

CONCLUSIONS

The findings of this study suggest that the antifibrotic effects of relaxin involve down-regulation of fibroblast activity, increase in collagenase synthesis and restructuring of collagen-I lattices, which are consistent with its known physiological role of matrix remodelling. Although there appears to be an interaction between TGF-beta 1 and H2 relaxin, this does not appear to involve a reduction in CTGF mRNA expression.

Ascites from patients with encapsulating peritoneal sclerosis augments NIH/3T3 fibroblast proliferation

Encapsulating peritoneal sclerosis (EPS) remains one of the major causes of dropout in continuous ambulatory peritoneal dialysis by reducing ultrafiltration capacity. To demonstrate whether ascites from patients with EPS (EPS ascites) has fibroblast proliferation activity, we used NIH/3T3 fibroblasts to examine the effects of EPS ascites on fibroblast proliferation activity by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. Encapsulating peritoneal sclerosis ascites dose-dependently augmented NIH/3T3 fibroblast proliferation. The protein kinase C inhibitors and the tyrosine kinase inhibitors partially inhibited the stimulatory effects of EPS ascites on fibroblast proliferation activity. In EPS ascites, levels of interleukin (IL)-1beta, IL-6, IL-8, transforming growth factor (TGF)-beta1, hepatocyte growth factor (HGF), and platelet-derived growth factor (PDGF)-AB were elevated. The treatment with IL-1beta, HGF, TGF-beta1, and PDGF-AB alone or in combination at similar concentrations to those in EPS ascites exhibited small but significant fibroblast proliferation activities. We conclude that EPS ascites stimulate NIH/3T3 fibroblast proliferation via protein kinase C and tyrosine kinase. The elevated cytokine and growth factors partly contribute to the EPS ascites-induced fibroblast proliferation.

Glucose degradation products (GDP) retard remesothelialization independently of d-glucose concentration

BACKGROUND

Glucose degradation products (GDP) present in heat-sterilized dialysis fluids are thought to contribute to cellular dysfunction and membrane damage during peritoneal dialysis. To examine the effects of specific GDP on the remesothelialization process, the impact of conventional and low GDP peritoneal dialysis solutions, D-glucose, and individual GDP in a scratch-wounding model was assessed.

METHODS

Scratch (0.5 to 0.6 mm)-wounded human peritoneal mesothelial cells (HPMC) were treated, at pH 7.4, with either (1) control medium (M199), (2) laboratory-prepared heat or filter-sterilized solutions, (3) 10% to 80% vol/vol solution of Gambrosol or Gambrosol-trio (1.5% and 4.0% glucose), (4) D-glucose (5 to 80 mmol/L), or (5) individual or combined GDP [acetaldehyde, formaldehyde, glyoxal, methylglyoxal, 3-deoxyglucosone (3-DG), 5-hydroxy methylfufural (5-HMF), or 3,4-di-deoxyglucosone-3-ene (3,4-DGE)]. Wound closure was recorded by time-lapse photomicroscopy.

RESULTS

In untreated HPMC, the rate of wound closure was linear and the process was complete by 18.4 +/- 3.6 hours (N = 16). In wounded HPMC exposed to dilutions of heat-sterilized but not filtered laboratory solutions (1.5% or 4.0% glucose, pH 7.4), remesothelialization was significantly retarded (P = 0.04 and P = 0.009 vs. M199, respectively). In Gambrosol, remesothelialization was significantly retarded in both 1.5% and 4.0% solutions. In contrast in Gambrosol-trio-treated HPMC, this rate was not significantly reduced in either 1.5% or 4.0% glucose peritoneal dialysis fluids. Remesothelialization was dose-dependently retarded in HPMC exposed to 3,4-DGE (>10 microl/L), formaldehyde (>5 micromol/L) but not by exposure to the other GDP tested even at 5 times the concentration present in low glucose solutions. The rate of remesothelialization was not significantly altered by exposure to D-glucose concentrations up to 80 mmol/L.

CONCLUSION

These data identify that the formaldehyde and 3,4-DGE present in heat-sterilized peritoneal dialysis solutions are important in reducing mesothelial cell regeneration. Specifically targeting their removal may have major benefits in preserving the mesothelium during long-term peritoneal dialysis.

Emodin ameliorates glucose-induced matrix synthesis in human peritoneal mesothelial cells

Emodin ameliorates glucose-induced matrix synthesis in human peritoneal mesothelial cells. Prolonged exposure of human peritoneal mesothelial cells (HPMC) to high glucose concentrations in peritoneal dialysate is the principal factor leading to matrix accumulation and thickening of the peritoneal membrane, accompanied by progressive deterioration of transport functions. These changes are mediated in part through protein kinase C (PKC) activation and the induction of transforming growth factor-beta 1 (TGF-beta 1). Emodin (3-methyl-1,6,8 trihydroxyanthraquinone) has previously been demonstrated to reduce cell proliferation and fibronectin synthesis in cultured mesangial cells. How emodin modulates glucose-induced abnormalities in HPMC has not been elucidated and thus constitutes the theme of this study.

METHODS

We investigated the effects of emodin on the expression of PKC alpha, TGF-beta 1, fibronectin, and collagen type I in HPMC, and its effects on HPMC proliferation under physiologic (5 mmol) or high (30 mmol) glucose concentrations.

RESULTS

Exposure of HPMC cultured with 5 mmol or 30 mmol D-glucose to emodin (20 microg/mL) resulted in an initial lag of proliferation by 2.3 to 2.7 days, but did not affect cell viability or morphology at confluence. D-glucose (30 mmol) induced TGF-beta 1 secretion in a time-dependent manner (3.72 +/- 0.29 and 4.30 +/- 0.50 pg/microg cellular protein at 24 hours and 48 hours respectively, compared to 2.13 +/- 0.23 and 2.65 +/- 0.32 pg/microg cellular protein at 24 hours and 48 hours, respectively for 5 mmol glucose; P < 0.001 at both time points). Such induction was ameliorated by emodin (20 microg/mL) (TGF-beta 1 concentration 2.25 +/- 0.15 and 2.96 +/- 0.33 pg/microg cellular protein at 24 hours and 48 hours, respectively, in the presence of emodin and 30 mmol D-glucose; P < 0.001 compared to 30 mmol D-glucose alone at both time points). Induction of TGF-beta 1 synthesis by 30 mmol D-glucose was associated with induction of PKC alpha, phosphorylation of cAMP-responsive element binding protein (CREB) and activating transcription factor-1 (ATF-1), and increased fibronectin and type I collagen translation. Emodin abrogated all these effects of concentrated glucose. Immunohistochemical staining showed that 30 mmol D-glucose induced cytoplasmic, perinuclear, and extracellular fibronectin and type I collagen expression by HPMC. Emodin reduced 30 mmol D-glucose-induced cytoplasmic and extracellular matrix synthesis to near basal levels.

CONCLUSION

Our findings demonstrate that emodin ameliorates the undesirable effects of concentrated glucose on HPMC via suppression of PKC activation and CREB phosphorylation, and suggest that emodin may have a therapeutic potential in the prevention or treatment of glucose-induced structural and functional abnormalities in the peritoneal membrane.

Connective tissue growth factor and its regulation in the peritoneal cavity of peritoneal dialysis patients

BACKGROUND

Connective tissue growth factor (CTGF) is a fibrogenic cytokine that is highly expressed in wound healing and fibrotic lesions. The role of transforming growth factor-beta (TGF-beta) in fibrosis is well documented, and the emerging understanding that its fibrogenic actions are mediated through CTGF has provided an attractive target molecule for the modulation of matrix overproduction in fibrotic disease. The involvement of CTGF in the pathogenesis of peritoneal membrane fibrosis in peritoneal dialysis (PD) patients has not been investigated, and so the aim of this study was to ascertain whether CTGF is produced in the peritoneal cavity of PD patients and to investigate its regulation by cytokines.

METHODS

Reverse transcription-polymerase chain reaction (RT-PCR), Northern blotting, and Western blotting were used to study CTGF expression by cultured human peritoneal mesothelial cells (HPMC) from peritoneal dialysis patients. Western blotting was used to detect CTGF expression in spent peritoneal dialysate from patients with and without peritonitis.

RESULTS

RT-PCR analysis demonstrated the expression of CTGF mRNA in cultured primay HPMCs isolated from spent peritoneal effluent. The production of the major 36 to 38 kD CTGF protein doublet by HPMC in addition to a 23 to 25 kD proteolytically processed form was confirmed by Western blotting. Several molecular weight forms of CTGF (18 to 38 kD) were also detected by Western blotting in peritoneal dialysate, with levels markedly elevated during episodes of peritonitis. Northern and Western blot analysis revealed that CTGF mRNA and protein production by HPMC was up-regulated by TGF-beta, with mRNA levels significantly increasing above the control (P < 0.01). In contrast, platelet-derived growth factor (PDGF), epidermal growth factor (EGF), and tumor necrosis factor-alpha (TNF-alpha) had no measurable effects on CTGF mRNA expression.

CONCLUSION

These results are the first to demonstrate the production of CTGF by HPMC and its presence in the peritoneal cavity of PD patients. The marked increase in CTGF levels by factors implicated in the development of peritoneal membrane fibrosis suggests its involvement in the underlying pathophysiologic mechanism(s).

Cytokines and other soluble factors in dialysate -- indicators of altered peritoneal function?

OBJECTIVE

The bioincompatibility of dialysis solutions and recurrent episodes of peritonitis may alter peritoneal function. Cytokines and growth factors may play a role in inflammatory and fibrotic processes. We therefore investigated whether there is a correlation between peritoneal function and excretion of cytokines and other soluble factors in dialysate.

MATERIAL AND METHODS

A personal dialysis capacity test was performed in 40 stable peritoneal dialysis patients. Tumour necrosis factor-alpha, interleukin-6 (IL-6), hyaluronan, soluble intercellular cell adhesion molecule-1 and transforming growth factor-beta1 were analysed from overnight and 24-h dialysates during the test.

RESULTS

We found little evidence for a direct correlation between cytokines and other soluble factors in dialysate and dialysis adequacy. There was, however, a strong correlation between the measured soluble factors and characteristics of the peritoneal membrane. Furthermore, IL-6 correlated with the number of previous episodes of peritonitis.

CONCLUSIONS

Soluble factors in dialysate may indicate ongoing inflammatory processes in the peritoneal membrane, which may gradually lead to alterations in peritoneal function.

Inflammatory cytokines mediate C-C (monocyte chemotactic protein 1) and C-X-C (interleukin 8) chemokine expression in human pleural fibroblasts

Current knowledge implicates pleural mesothelial cells as mainly responsible for inflammatory responses in the pleural space. However, a vast body of recent evidence underscores the important role of fibroblasts in the process of inflammation in several types of tissues. We hypothesize that HPFBs (human pleural fibroblasts) play an important role in pleural responses and also when activated by bacterial endotoxin LPS (lipopolysaccharide), IL-1 beta (interleukin-1 beta), or TNF-alpha (tumor necrosis factor-alpha) release of C-C and C-X-C chemokines-specifically, MCP-1 and IL-8. Our results show that pleural fluid-isolated human fibroblasts release IL-8 and MCP-1 upon stimulation with IL-1 beta, TNF-alpha, and LPS in both a concentration- and time-dependent manner. RT-PCR (reverse-transcriptase-polymerase chain reaction) studies have also confirmed IL-8- and MCP-1-specific mRNA expression in activated pleural fibroblasts. On the time-dependent response curve, IL-8 was found in maximum concentrations at 144 hr, whereas MCP-1 continued to increase even after 196 hr following stimulation. IL-1 beta induced the maximum release of IL-8 (800-fold) and MCP-1 (164-fold), as compared to the controls. TNF-alpha induced a 95-fold increase in IL-8 and an 84-fold increase in MCP-1 levels, as compared to the controls. Collectively, our results show that human pleural fibroblasts contribute to the inflammatory cascade in the pleural space.

Critical role of type IV collagens in the growth of bile duct carcinoma. In vivo and in vitro studies

Most extrahepatic bile duct carcinomas (EBDC) are characterized by a striking stromal response (desmoplasia). Our previous studies showed deposition of type IV collagen in the desmoplastic stroma beyond the basement membrane. Although type IV collagen is expressed in EBDC, little is known about the pattern of deposition in tumor stroma and how this matrix component influences the behavior of tumor cells. With the progression of desmoplasia in EBDC, different changes occurred in the quantity and localization of type IV collagen from that of type I collagen. Type I collagen was diffusely distributed in the stroma and appeared to be concentrated in the center of the tumors. In contrast, type IV collagen was deposited in the interstitium alongside carcinoma cells at the tumors' periphery. Weak or no type IV collagen deposition was detected in the more central portion of the tumors containing sclerotic collagens. To investigate the role of stromal type IV collagen in tumor cell proliferation, EBDC cell lines were cultured in a three-dimensional matrix containing varying compositions of type I collagen and type IV collagen. They were also assayed for cell adhesion and migration using in vitro models. Type IV collagen more extensively stimulated tumor cell proliferation, adhesion and migration in a dose-dependent manner than did type I collagen. All of these results suggest that modified tumor stroma with the presence of type IV collagen in EBDC provides a better environment for tumor growth and invasion.

Glucose and prednisolone alter basic fibroblast growth factor expression in peritoneal mesothelial cells and fibroblasts

The mechanism of peritoneal fibrosis in patients on continuous ambulatory peritoneal dialysis is poorly understood. The production of basic fibroblast growth factor (bFGF) by human peritoneal mesothelial cells cultured in high glucose medium was investigated, and the behavior of peritoneal fibroblasts, as well as the inhibitory effect of prednisolone, was assessed. Reverse transcriptase-PCR and immunocytochemistry showed the expression of glucocorticoid receptors in mesothelial cells. The semiquantitative reverse transcriptase-PCR showed that high glucose medium (4.0%) increased bFGF mRNA by 2.5-fold relative to control medium (0.1% glucose), with 83% suppression of the increase by 1 microM prednisolone. The bFGF protein level in culture supernatant was also increased by 1.5-fold in high glucose medium, with this change showing 45% suppression by 1 microM prednisolone. These effects of prednisolone were prevented by a glucocorticoid receptor antagonist (RU486) in a concentration-dependent manner. The proliferation of peritoneal fibroblasts was increased 1.9-fold by the supernatant of mesothelial cells cultured in high glucose medium, with 85% suppression by 1 microM prednisolone and suppression to 16% below basal proliferation by an anti-bFGF neutralizing antibody (10 microg/ml), whereas proliferation showed a concentration-dependent increase on addition of an anti-transforming growth factor beta-neutralizing antibody. Recombinant bFGF (50 to 1000 pg/ml) likewise caused a concentration-dependent increase of peritoneal fibroblast proliferation and fibronectin release by these cells was also increased (at 50 to 5000 pg/ml). These results suggest the potential importance of bFGF for initiation of peritoneal fibrosis and the possible efficacy of glucocorticoids for preventing such fibrosis in patients receiving peritoneal dialysis.

Regulation of renal proximal tubular epithelial cell fibroblast growth factor-2 generation by heparin

Progression of renal disease is closely correlated to the degree of renal interstitial fibrosis, and evidence is increasing that epithelial cells of the renal proximal tubule (PTCs) may contribute to its pathogenesis. Such cytokines as basic fibroblast growth factor (FGF-2) have been implicated in progressive renal injury, and we previously showed that PTCs are a source of this cytokine. FGF-2 is characterized by its high affinity for heparin, and numerous studies have suggested that heparin may modify the progression of renal disease. The current study examined how heparin influenced FGF-2 generation and bioactivity in the human renal epithelial PTC line, HK-2. Incubation of HK-2 cells with heparin led to a dose- and time-dependent increase in FGF-2 concentration in the culture supernatant that was not accompanied by alterations in FGF-2 messenger RNA expression, assessed by reverse-transcriptase polymerase chain reaction and Northern analysis. The heparin-induced increase in FGF-2 concentration was accompanied by a decrease in the amount of FGF-2 bound to the extracellular matrix, although this accounted for only a small proportion of the total FGF-2 generated. Induction of FGF-2 by 2-O-desulfated heparin, together with a reduction in total cell-associated FGF-2 and anti-FGF-2 antibody binding to fixed permeabilized cells after the addition of heparin, suggested that the FGF-2 released was mainly derived from a preformed intracellular source. That FGF-2 was predominantly derived from an intracellular pool was also confirmed by pulse chase experiments. The addition of heparin resulted in the generation of bioinactive FGF-2, judged by in vitro fibroblast proliferation. Conversely, heparitinase treatment of supernatant samples from heparin-treated cells and the addition of 2-O-desulfated heparin resulted in the generation of active FGF-2, suggesting that the generation of bioinactive FGF-2 was related to binding of FGF-2 by extracellular heparin after its release from cells. These data show that heparin depletes both the cell and surrounding matrix of FGF-2 and suggest that FGF-2 released from cells was mainly derived from a preformed intracellular source. Furthermore, FGF-2 released from epithelial PTCs after the application of heparin was bioinactive. This likely resulted from released FGF-2 binding to an excess of extracellular heparin. Results presented here therefore suggest a mechanism by which heparin, through its effect on depletion of matrix and cells of FGF-2 and its generation in an inactive form, may influence progressive renal interstitial fibrosis.

Dipyridamole inhibits PDGF-stimulated human peritoneal mesothelial cell proliferation

BACKGROUND

It has been proposed that proliferation of human peritoneal mesothelial cells (HPMCs) accompanied by collagen synthesis may contribute to the development of peritoneal fibrosis (PF) in patients of long-term continuous ambulatory peritoneal dialysis (CAPD). However, the precise molecular mechanism regulating HPMC proliferation has never been reported. Dipyridamole has been reported to have potential as an antiproliferative and antifibrotic agent. We investigated the mechanism and effect of dipyridamole in regulation of HPMC proliferation.

METHODS

HPMCs were cultured from human omentum by an enzyme digestion

METHOD

Cell proliferation was measured by the methyltetrazolium assay and intracellular cAMP was measured using an enzyme immunoassay kit. Cell-cycle distribution of HPMC was analyzed by flow cytometry. Extracellular signal-regulated protein kinase (p44/p42 ERK) activity and expressions of cell-cycle proteins (cyclin D(1), CDK4, pRB and p27(Kip1)) were determined by Western blotting.

RESULTS

The addition of DP suppressed PDGF-stimulated HPMC proliferation by cell-cycle arrest at the G1 phase. The antimitogenic effect of dipyridamole was mediated through the cAMP pathway. PDGF (25 ng/mL) increased the ERK1/2 activity of HPMC within 15 minutes, which maximized at 30 minutes, and the pretreatment with dipyridamole (17 microg/mL) substantially reduced the ERK response to PDGF by approximately 78.5%. PDGF induced elevated protein levels of cyclin D(1), but the CDK4 protein level did not change. Dipyridamole and DBcAMP had no effect on the levels of cyclin D(1) and CDK4 in PDGF-stimulated HPMC. PDGF decreased p27(Kip1) and induced pRB phosphorylation of HPMC. In contrast, dipyridamole prevented PDGF-induced p27(Kip1) degradation and attenuated PDGF-stimulated pRB phosphorylation.

CONCLUSION

Dipyridamole appears to inhibit PDGF-stimulated HPMC proliferation through attenuated ERK activity, preservation of p27(Kip1), and decreased pRB phosphorylation. Thus, dipyridamole may have therapeutic efficacy to prevent or alleviate PF.

High glucose induces MCP-1 expression partly via tyrosine kinase-AP-1 pathway in peritoneal mesothelial cells

BACKGROUND

High glucose in peritoneal dialysis solutions has been implicated in the pathogenesis of peritoneal fibrosis in chronic ambulatory peritoneal dialysis (CAPD) patients. However, the mechanisms are not very clear. Peritoneal macrophages seem to participate in the process of peritoneal fibrosis and monocyte chemoattractant protein-1 (MCP-1) plays a key role in the recruitment of monocytes toward the peritoneal cavity. However, little is known about the effect of high glucose on MCP-1 expression and its signal transduction pathway in human peritoneal mesothelial cells.

METHODS

Mesothelial cells were cultured with glucose (5 to 100 mmol/L) or mannitol chronically for up to seven days. MCP-1 expression of mRNA and protein was measured by Northern blot analysis and enzyme-linked immunosorbent assay (ELISA). Chemotactic activity of high-glucose-conditioned culture supernatant was measured by chemotactic assay. To examine the roles of the transcription factors activator protein-1 (AP-1) and nuclear factor-kappaB (NF-kappaB), electrophoretic mobility shift assay (EMSA) was performed.

RESULTS

Glucose induced MCP-1 mRNA expression in a time- and dose-dependent manner. MCP-1 protein in cell culture supernant was also increased. Equivalent concentrations of mannitol had no significant effect. High-glucose-conditioned supernatant possessed an increased chemotactic activity for monocytes, which was neutralized by anti-MCP-1 antibody. EMSA revealed that glucose increased the AP-1 binding activity in a time- and dose-dependent manner, but not NF-kappaB. Curcumin, an inhibitor of AP-1, dose-dependently suppressed the induction of MCP-1 mRNA by high glucose. Tyrosine kinase inhibitors such as genistein (12.5 to 50 micromol/L) and herbimycin A (0.1 to 1 micromol/L) inhibited the high-glucose-induced MCP-1 mRNA expression in a dose-dependent manner, and also suppressed the high-glucose-induced AP-1 binding activity.

CONCLUSIONS

: High glucose induced mesothelial MCP-1 expression partly via the tyrosine kinase-AP-1 pathway.

Innovative approaches to the preservation of the peritoneal membrane: from bench to bedside

The functional integrity of the peritoneal membrane is of critical importance for the long-term success of peritoneal dialysis therapy. In addition to water and solute transport properties, the function of the membrane encompasses complex interactions with immune cells, invading microorganisms, and dialysis fluid components. During chronic peritoneal dialysis, intraperitoneal homeostasis is threatened by the repeated exposure to an unphysiologic environment that is created by the instilled solutions. Whereas their acidic pH and hyperosmolality were shown to primarily induce alterations of acute cell function, long-term peritoneal function might be affected by the repeated exposure to high concentrations of glucose and glucose degradation products. In addition to their intrinsic toxicity, these might induce or accelerate glycation processes, such as formation and deposition of advanced glycation end products in the peritoneal membrane. Presently, a new generation of dual-chambered peritoneal dialysis solutions combining the advantages of neutral pH and reduced glucose degradation products content is being introduced into clinical practice. In addition to an improved in vitro biocompatibility profile, emerging clinical trials of these novel solutions indicate that they might also improve the host defense status, membrane transport characteristics, ultrafiltration capacity, and effluent markers of peritoneal membrane integrity, while being safe and effective in correcting uremic acidosis and providing relief of inflow pain. Overall, these findings suggest that these new dialysis solutions might constitute an important step toward better preservation of long-term peritoneal membrane function during peritoneal dialysis.

Synthesis of C-X-C and C-C chemokines by human peritoneal fibroblasts: induction by macrophage-derived cytokines

Leukocyte accumulation during peritonitis is believed to be controlled by chemotactic factors released by resident peritoneal macrophages or mesothelial cells. Recent data indicate, however, that in many tissues fibroblasts play a key role in mediating leukocyte recruitment. We have therefore examined human peritoneal fibroblasts (HPFBs) for the expression and regulation of C-X-C and C-C chemokines. Quiescent HPFBs secreted monocyte chemoattractant protein (MCP)-1 and interleukin (IL)-8 constitutively. This release could be dose-dependently augmented with the pro-inflammatory cytokines IL-1beta and tumor necrosis factor-alpha. Stimulated IL-8 production reached a plateau within 48 hours while MCP-1 continued to accumulate throughout 96 hours. Induction of IL-8 and MCP-1 synthesis by HPFBs was also triggered by peritoneal macrophage-conditioned medium. This effect was partly related to the presence of IL-1beta as demonstrated by IL-1 receptor antagonist inhibition. Pretreatment of HPFBs with actinomycin D or puromycin dose-dependently reduced cytokine-stimulated IL-8 and MCP-1 secretion, which suggested de novo chemokine synthesis. Indeed, exposure of HPFBs to IL-1beta and tumor necrosis factor-alpha produced a significant up-regulation of IL-8 and MCP-1 mRNA. This effect was associated with the rapid induction of nuclear factor-kappaB binding activity mediated through p65 and p50 subunits, and with a transient increase in the mRNA expression for RelB and inhibitory protein kappaB-alpha proteins. These data indicate that peritoneal fibroblasts are capable of generating large quantities of chemokines under a tight control of nuclear factor-kappaB/Rel transcription factors. Thus, peritoneal fibroblast-derived chemokines may contribute to the intraperitoneal recruitment of leukocytes during peritonitis.

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.