Dipyridamole inhibits TGF-beta-induced collagen gene expression in human peritoneal mesothelial cells

Hub genes, diagnostic model, and predicted drugs in systemic sclerosis by integrated bioinformatics analysis

Background: Systemic sclerosis (scleroderma; SSc), a rare and heterogeneous connective tissue disease, remains unclear in terms of its underlying causative genes and effective therapeutic approaches. The purpose of the present study was to identify hub genes, diagnostic markers and explore potential small-molecule drugs of SSc. Methods: The cohorts of data used in this study were downloaded from the Gene Expression Complex (GEO) database. Integrated bioinformatic tools were utilized for exploration, including Weighted Gene Co-Expression Network Analysis (WGCNA), least absolute shrinkage and selection operator (LASSO) regression, gene set enrichment analysis (GSEA), Connectivity Map (CMap) analysis, molecular docking, and pharmacokinetic/toxicity properties exploration. Results: Seven hub genes (THY1, SULF1, PRSS23, COL5A2, NNMT, SLCO2B1, and TIMP1) were obtained in the merged gene expression profiles of GSE45485 and GSE76885. GSEA results have shown that they are associated with autoimmune diseases, microorganism infections, inflammatory related pathways, immune responses, and fibrosis process. Among them, THY1 and SULF1 were identified as diagnostic markers and validated in skin samples from GSE32413, GSE95065, GSE58095 and GSE125362. Finally, ten small-molecule drugs with potential therapeutic effects were identified, mainly including phosphodiesterase (PDE) inhibitors (BRL-50481, dipyridamole), TGF-β receptor inhibitor (SB-525334), and so on. Conclusion: This study provides new sights into a deeper understanding the molecular mechanisms in the pathogenesis of SSc. More importantly, the results may offer promising clues for further experimental studies and novel treatment strategies.

Exosomal HMGB1 Promoted Cancer Malignancy

Simple Summary

In addition to their role in hemostasis and thrombosis, platelets have been implicated in cancer malignancy and thrombocytosis in cancer patients and have been associated with an adverse prognosis. These phenomena indicate that antiplatelet drugs may be useful as an anticancer therapy. Using K562-differentiated megakaryocytes and murine platelets, conditioned medium and exosomes obtained from megakaryocytes and platelets contained high-mobility group box 1 (HMGB1) and promoted cancer cell survival, as well as protected cancer cells from doxorubicin cytotoxicity. Data of tumor-bearing mice established by Lewis lung carcinoma (LLC) cells and C57BL/6 mice revealed that antiplatelet drug dipyridamole and exosome release inhibitor GW4869 mitigated tumor growth and ameliorated concurrent alterations in blood circulation and tumor tissues, as well as platelet infiltration in tumor tissues. Therefore, exosomes and exosomal HMGB1 appear to have roles in platelet-driven cancer malignancy and represent targets of antiplatelet drugs in anticancer treatment.

Abstract

Reciprocal crosstalk between platelets and malignancies underscores the potential of antiplatelet therapy in cancer treatment. In this study, we found that human chronic myeloid leukemia K562 cell-differentiated megakaryocytes and murine platelets produced bioactive substances and these are released into the extracellular space, partly in their exosomal form. High-mobility group box 1 (HMGB1) is a type of exosomal cargo, and the antiplatelet drugs aspirin and dipyridamole interfered with its incorporation into the exosomes. Those released substances and exosomes, along with exogenous HMGB1, promoted cancer cell survival and protected cells from doxorubicin cytotoxicity. In a tumor-bearing model established using murine Lewis lung carcinoma (LLC) cells and C57BL/6 mice, the tumor suppressive effect of dipyridamole correlated well with decreased circulating white blood cells, soluble P-selectin, TGF-β1 (Transforming Growth Factor-β1), exosomes, and exosomal HMGB1, as well as tumor platelet infiltration. Exosome release inhibitor GW4869 exhibited suppressive effects as well. The suppressive effect of dipyridamole on cancer cell survival was paralleled by a reduction of HMGB1/receptor for advanced glycation end-products axis, and proliferation- and migration-related β-catenin, Yes-associated protein 1, Runt-related transcription factor 2, and TGF- β1/Smad signals. Therefore, exosomes and exosomal HMGB1 appear to have roles in platelet-driven cancer malignancy and represent targets of antiplatelet drugs in anticancer treatment.

In Vitro Study of Peritoneal Fibrosis

Peritoneal fibrosis (PF) is an important issue in peritoneal dialysis (PD) because it remains one of the leading causes of patient drop-out from PD. In this review, we focus on in vitro approaches to the pathogenesis and therapeutic potential of PF and on associated clinical implications. Representative Asian studies, initiated since mid-1990s, that have investigated matrix accumulation in peritoneal tissue possibly leading to PF in the PD population will be highlighted as examples to learn how to apply this research tool. As compared with data from well-designed clinical trials, observations from in vitro models may be far from becoming solid evidence; however, they do cast new light on options for investigations into therapeutic pharmaceuticals.

Peritoneal Fibrosis Intervention

Peritoneal fibrosis (PF) is invariably observed in patients undergoing long-term peritoneal dialysis (PD). The condition is thought to occur in response to a variety of insults, including bioincompatible dialysates (acidic solution, high glucose, glucose degradation products, or a combination), peritonitis, uremia, and chronic inflammation. Recently, the pathophysiologic mechanisms that contribute to the fibrosing process have been intensively studied. Transforming growth factor-β has been shown to be a key mediator of PF. Loss of the mesothelial cell layer has been identified in several studies and shown to correlate with submesothelial thickening and vasculopathy. An association has also been identified between increased submesothelial thickness in the peritoneal membrane and increased solute transport, suggesting a relationship between PF and loss of ultrafiltration capacity. Thus, to maintain long-term PD and improve quality of life for patients, it is important to develop interventions for prevention and treatment of PF.

Several strategies for peritoneal fibrosis intervention have been reported, including developing biocompatible dialysate, targeting mediators responsible for inflammation and fibrosis, and reconstituting the peritoneum using mesothelial or bone marrow–derived cells. Recent experimental trials in animal models and clinical studies are presented in this review.

Preventing Peritoneal Fibrosis—Insights from the Laboratory

Objective

Peritoneal fibrosis is one of the most serious complications of peritoneal dialysis (PD). Peritoneal fibrosis is characterized by activation of the peritoneal resident cells, accumulation and deposition of excess matrix proteins within the interstitium, and neoangiogenesis and vasculopathy of the peritoneal microvasculature. Compelling evidence now exists to show that elevated glucose concentrations present as the osmotic agent in PD solutions are, per se, responsible for those detrimental changes. Until alternative osmotic agents can fully replace glucose in PD solutions, novel therapeutic strategies are essential to preserve the structural and functional properties of the peritoneum. This review highlights recent experimental data that may offer potential strategies for preservation of the peritoneal structure and improvement of clinical outcome.

Method

Literature review.

Results

Compelling evidence now exists to show that the bioincompatible nature of PD solutions—in particular, elevated glucose concentrations and glucose byproducts—play a pivotal role in the initiation of peritoneal fibrosis. Animal and in vitro studies provide some insight into methods that can potentially be employed to alleviate or retard peritoneal fibrosis. Those methods include use of alterative osmotic agents (polyglucose or amino acids), administration of TGFβ1 antagonists, gene therapy, and pharmacologic interventions.

Conclusions

Knowledge of the pathogenesis of peritoneal fibrosis has allowed independent researchers to design therapeutic strategies that abrogate excess matrix synthesis and deposition in cultured peritoneal cells and in animal models of experimental peritoneal fibrosis alike. Encouraging results have been obtained in those studies, but it remains to be determined whether the studied strategies can alleviate clinical disease. Future studies will enable us to establish specific molecules that can be targeted clinically to restrict the progressive deterioration of the peritoneal membrane as a biologic dialyzing organ.

Dimethylaminomicheliolide ameliorates peritoneal fibrosis through the activation of autophagy

Peritoneal fibrosis (PF) is a major cause of ultrafiltration failure in patients receiving long-term peritoneal dialysis (PD), and effective prevention and treatment strategies are urgently needed. The dimethylamino Michael adduct of a natural product-derived micheliolide (MCL), dimethylaminomicheliolide (DMAMCL), is a new lead compound with the advantages of high stability, low toxicity, and sustainable release of MCL. This study aimed to investigate the protective effect of DMAMCL against PD-related PF and the mechanisms involved. In this study, we found that DMAMCL significantly decreased PD-induced extracellular matrix (ECM) deposition in a mouse model of PD, and that delayed DMAMCL administration halted the progression of PF in an established PD model. In addition, rapamycin administration induced autophagy and significantly ameliorated PF. The protective effect of DMAMCL against PF was weakened when co-administered with DMAMCL and 3-methyladenine. Inducing autophagy by rapamycin decreased transforming growth factor-β1-induced ECM accumulation in vitro. MCL promoted autophagy and inhibited ECM deposition. The anti-fibrotic effect of MCL was eliminated when knocking down ATG7 by siRNA. Taken together, DMAMCL might prevent against PF through activating autophagy. The anti-fibrotic effect of DMAMCL may be a new candidate for the treatment in patients with PD-related PF. KEY MESSAGES: Dimethylaminomicheliolide, the pro-drug of micheliolide, protects against peritoneal fibrosis in a mouse peritoneal dialysis model. Micheliolide inhibits TGF-β1-induced extracellular matrix accumulation in vitro. Autophagy plays a protective role against peritoneal fibrosis. The antifibrogenic effect of dimethylaminomicheliolide may be due to the activation of autophagy.

Dipyridamole reduces penile apoptosis in a rat model of post-prostatectomy erectile dysfunction

Purpose:

Despite the nerve-sparing technique, many patients suffer from erectile dysfunction after radical prostatectomy (RP) due to cavernous nerve injury. The aim of this study was to evaluate dipyridamole as a potential treatment agent of post-radical prostatectomy erectile dysfunction.

Material and methods:

A total of 18 male Sprague-Dawley rats were randomized into three experimental Groups (SHAM+DMSO, BCNI+DMSO and BCNI+DIP). An animal model of bilateral cavernous nerve crush injury (BCNI) was established to mimic the partial nerve damage during nerve-sparing RP. After creating of BCNI, dimethyl sulphoxide (DMSO) was administered transperitoneally as a vehicle to SHAM+DMSO and BCNI+DMSO Groups. BCNI+DIP Group received dipyiridamole (10mg/kg/day) as a solution in DMSO for 15 days. Afterwards, rats were evaluated for in vivo erectile response to cavernous nerve stimulation. Penile tissues were also analyzed biochemically for transforming growth factor-β1 (TGF-β1) level. Penile corporal apoptosis was determined by TUNEL method.

Results:

Erectile response was decreased in rats with BCNI and there was no significant improvement with dipyridamole treatment. TGF-β1 levels were increased in rats with BCNI and decreased with dipyridamole treatment. Dipyridamole led to reduced penile apoptosis in rats with BCNI and there was no significant difference when compared to sham operated rats.

Conclusions:

Although fifteen-day dipyridamole treatment has failed to improve erectile function in rats with BCNI, the decline in both TGF-β1 levels and apoptotic indices with treatment may be helpful in protecting penile morphology after cavernous nerve injury.

Nonmyocyte ERK1/2 signaling contributes to load-induced cardiomyopathy in Marfan mice

Among children with the most severe presentation of Marfan syndrome (MFS), an inherited disorder of connective tissue caused by a deficiency of extracellular fibrillin-1, heart failure is the leading cause of death. Here, we show that, while MFS mice (Fbn1C1039G/+ mice) typically have normal cardiac function, pressure overload (PO) induces an acute and severe dilated cardiomyopathy in association with fibrosis and myocyte enlargement. Failing MFS hearts show high expression of TGF-β ligands, with increased TGF-β signaling in both nonmyocytes and myocytes; pathologic ERK activation is restricted to the nonmyocyte compartment. Informatively, TGF-β, angiotensin II type 1 receptor (AT1R), or ERK antagonism (with neutralizing antibody, losartan, or MEK inhibitor, respectively) prevents load-induced cardiac decompensation in MFS mice, despite persistent PO. In situ analyses revealed an unanticipated axis of activation in nonmyocytes, with AT1R-dependent ERK activation driving TGF-β ligand expression that culminates in both autocrine and paracrine overdrive of TGF-β signaling. The full compensation seen in wild-type mice exposed to mild PO correlates with enhanced deposition of extracellular fibrillin-1. Taken together, these data suggest that fibrillin-1 contributes to cardiac reserve in the face of hemodynamic stress, critically implicate nonmyocytes in disease pathogenesis, and validate ERK as a therapeutic target in MFS-related cardiac decompensation.

Preventing peritoneal membrane fibrosis in peritoneal dialysis patients

Long-term peritoneal dialysis causes morphologic and functional changes in the peritoneal membrane. Although mesothelial-mesenchymal transition of peritoneal mesothelial cells is a key process leading to peritoneal fibrosis, and bioincompatible peritoneal dialysis solutions (glucose, glucose degradation products, and advanced glycation end products or a combination) are responsible for altering mesothelial cell function and proliferation, mechanisms underlying these processes remain largely unclear. Peritoneal fibrosis has 2 cooperative parts, the fibrosis process itself and the inflammation. The link between these 2 processes is frequently bidirectional, with each one inducing the other. This review outlines our current understanding about the definition and pathophysiology of peritoneal fibrosis, recent studies on key fibrogenic molecular machinery in peritoneal fibrosis, such as the role of transforming growth factor-β/Smads, transforming growth factor-β β/Smad independent pathways, and noncoding RNAs. The diagnosis of peritoneal fibrosis, including effluent biomarkers and the histopathology of a peritoneal biopsy, which is the gold standard for demonstrating peritoneal fibrosis, is introduced in detail. Several interventions for peritoneal fibrosis based on biomarkers, cytology, histology, functional studies, and antagonists are presented in this review. Recent experimental trials in animal models, including pharmacology and gene therapy, which could offer novel insights into the treatment of peritoneal fibrosis in the near future, are also discussed in depth.

Preserving the peritoneal membrane in long-term peritoneal dialysis patients

WHAT IS KNOWN AND OBJECTIVE

Peritoneal dialysis (PD) has been widely used by patients with end-stage renal disease. However, chronic exposure of the peritoneal membrane to bioincompatible PD solutions, and peritonitis and uraemia during long-term dialysis result in peritoneal membrane injury and thereby contribute to membrane changes, ultrafiltration (UF) failure, inadequate dialysis and technical failure. Therefore, preserving the peritoneal membrane is important to maintain the efficacy of PD. This article reviews the current literature on therapeutic agents for preserving the peritoneal membrane.

METHODS

A literature search of PubMed was conducted using the search terms peritoneal fibrosis, peritoneal sclerosis, membrane, integrity, preserve, therapy and peritoneal dialysis, but not including peritonitis. Published clinical trials, in vitro studies, experimental trials in animal models, meta-analyses and review articles were identified and reviewed for relevance.

RESULTS AND DISCUSSION

We focus on understanding how factors cause peritoneal membrane changes, the characteristics and mechanisms of peritoneal membrane changes in patients undergoing PD and the types of therapeutic agents for peritoneal membrane preservation. There have been many investigations into the preservation of the peritoneal membrane, including PD solution improvement, the inhibition of cytokine and growth factor expression using renin-angiotensin-aldosterone system (RAAS) blockade, glycosaminoglycans (GAGs), L-carnitine and taurine additives. In addition, there are potential future therapeutic agents that are still in experimental investigations.

WHAT IS NEW AND CONCLUSION

The efficacy of many of the therapeutic agents is uncertain because there are insufficient good-quality clinical studies. Overall membrane preservation and patient survival remain unproven in using more biocompatible PD solutions. With RAAS blockade, results are still inconclusive, as many of the clinical studies were retrospective. With GAGs, L-carnitine and taurine additives, there is no sufficiently long follow-up clinical study with a large sample size to support its efficacy. Therefore, better quality clinical studies within this area should be performed.

Simvastatin alleviates cardiac fibrosis induced by infarction via up-regulation of TGF-β receptor III expression

BACKGROUND AND PURPOSE

Statins decrease heart disease risk, but their mechanisms are not completely understood. We examined the role of the TGF-β receptor III (TGFBR3) in the inhibition of cardiac fibrosis by simvastatin.

EXPERIMENTAL APPROACH

Myocardial infarction (MI) was induced by ligation of the left anterior descending coronary artery in mice given simvastatin orally for 7 days. Cardiac fibrosis was measured by Masson staining and electron microscopy. Heart function was evaluated by echocardiography. Signalling through TGFBR3, ERK1/2, JNK and p38 pathways was measured using Western blotting. Collagen content and cell viability were measured in cultures of neonatal mouse cardiac fibroblasts (NMCFs). Interactions between TGFBR3 and the scaffolding protein, GAIP-interacting protein C-terminus (GIPC) were detected using co-immunoprecipitation (co-IP). In vivo, hearts were injected with lentivirus carrying shRNA for TGFBR3.

KEY RESULTS

Simvastatin prevented fibrosis following MI, improved heart ultrastructure and function, up-regulated TGFBR3 and decreased ERK1/2 and JNK phosphorylation. Simvastatin up-regulated TGFBR3 in NMCFs, whereas silencing TGFBR3 reversed inhibitory effects of simvastatin on cell proliferation and collagen production. Simvastatin inhibited ERK1/2 and JNK signalling while silencing TGFBR3 opposed this effect. Co-IP demonstrated TGFBR3 binding to GIPC. Overexpressing TGFBR3 inhibited ERK1/2 and JNK signalling which was abolished by knock-down of GIPC. In vivo, suppression of cardiac TGFBR3 abolished anti-fibrotic effects, improvement of cardiac function and changes in related proteins after simvastatin.

CONCLUSIONS AND IMPLICATIONS

TGFBR3 mediated the decreased cardiac fibrosis, collagen deposition and fibroblast activity, induced by simvastatin, following MI. These effects involved GIPC inhibition of the ERK1/2/JNK pathway.

Mesothelial cells in tissue repair and fibrosis

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

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.

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: the state of affairs

Encapsulating peritoneal sclerosis (EPS) is a severe complication of long-term peritoneal dialysis (PD) with a 50% mortality rate. EPS is characterized by progressive and excessive fibrotic thickening of the peritoneum, leading to encapsulation of the bowels and intestinal obstruction. At present, EPS cannot be detected with certainty during its early stages; however, a progressive loss of ultrafiltration capacity often precedes its development. Studies that attempted to elucidate the pathogenesis of EPS have shown that the duration of exposure to PD fluids is the most important risk factor for EPS, and that young age and possibly the effects of peritonitis are additional contributory factors. The pathophysiology of EPS is probably best described as a multiple-hit process with a central role for transforming growth factor β. A form of EPS that develops shortly after kidney transplantation has also been recognized as a distinct clinical entity, and may be a common form of EPS in countries with a high transplantation rate. Criteria have been developed to identify EPS by abdominal CT scan at the symptomatic stage, but further clinical research is needed to identify early EPS in asymptomatic patients, to clarify additional risk factors for EPS and to define optimal treatment strategies.

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.

Connective tissue growth factor knockdown attenuated matrix protein production and vascular endothelial growth factor expression induced by transforming growth factor-beta1 in cultured human peritoneal mesothelial cells

Connective tissue growth factor (CTGF), a downstream mediator of transforming growth factor-beta1 (TGF-beta1) inducing fibrosis, has recently been implicated in peritoneal fibrosis. Extracellular matrix (ECM) accumulation and angiogenesis are characteristic changes in peritoneal fibrosis. In this study we investigated the effect of CTGF knockdown via interference RNA (RNAi) on ECM production and vascular endothelial growth factor (VEGF) expression induced by TGF-beta1 in human peritoneal mesothelial cells (HPMCs). Four CTGF short hairpin RNA (shRNA) expression constructs were generated using the pRetroSuper vector, and infectious retroviral particles were prepared to infect HPMCs. Expression levels of CTGF, fibronectin(FN), collagen 1 (col 1), laminin, and VEGF mRNA and protein were measured by semi-quantitative reverse transcription polymerase chain reaction and western blot assay. CTGF expression was increased after stimulation with TGF-beta1, but inhibited using each of the four independent CTGF shRNA constructs (P < 0.01). Moreover, expression of ECM proteins (FN, col 1, and laminin) and VEGF were upregulated after incubation with TGF-beta1, but elevated levels of ECM and VEGF induced by TGF-beta1 were significantly inhibited by RNAi (P < 0.01), but not by the empty retroviral vector (P > 0.05). From these results, we concluded that retrovirus-mediated CTGF shRNA can effectively inhibit ECM production and VEGF expression induced by TGF-beta1 in HPMCs. This study suggests that downregulation of CTGF may represent a potential therapeutic approach for peritoneal fibrosis through decreasing ECM accumulation and angiogenesis.

Preservation of peritoneal morphology and function by pentoxifylline in a rat model of peritoneal dialysis: molecular studies

BACKGROUND

High-glucose (HG) content of dialysate accelerated peritoneal fibrosis. We investigated in vitro mechanisms and the in vivo potential of pentoxifylline (PTX) to prevent this fibrogenic process.

METHODS

For human peritoneal mesothelial cell (HPMC) culture, a normal-glucose (NG, 5.5 mM) or HG (138 mM) medium was established through pilot experiments. The rat peritoneal dialysis (PD) model consists of four groups (n = 8): group 1, intraperitoneal (IP) HG (4.25%) solution; group 2, as group 1 plus daily IP PTX (4 mg/in 1 h); group 3, IP PTX and group 4 as control.

RESULTS

In HPMC culture, PTX significantly prevented HG-stimulated gene and protein production of collagen and transforming growth factor-beta1 (TGF-ss1) (reduction rate of 72-81%). The p38 mitogen-activated protein kinase (MAPK) pathway was activated significantly in HG-treated HPMCs. Blockade of p38 MAPK by SB203580 (25 microM) or PTX (300 microg/ml) resulted in an effective suppression of collagen and TGF-ss1 gene expression in HG-cultured HPMCs. In PD experimental animals, peritoneal thickness and collagen expression in the peritoneum were significantly increased in HG-treated rats, and was attenuated by PTX (P < 0.01). Impaired peritoneal ultrafiltration (1.9 +/- 0.5 ml versus 2.4 +/- 0.4 ml, P < 0.05) and stimulated proinflammatory IL-6, MCP-1 and TGF-beta1 activation were observed in HG-treated rats. PTX well preserved the functional characteristics of peritoneum and cytokine profiles.

CONCLUSIONS

These in vitro and in vivo data suggest that PTX may have therapeutic benefits for the prevention or retardation of peritoneal fibrosis.

Smad7 transgene attenuates peritoneal fibrosis in uremic rats treated with peritoneal dialysis

Transforming growth factor beta (TGF-beta) plays a critical role in the pathogenesis of the peritoneal fibrosis that complicates long-term peritoneal dialysis (PD). We studied the TGF-beta/Smad signaling pathway in peritoneal fibrosis induced in uremic rats treated with PD and explored the therapeutic potential of Smad7 to prevent fibrogenesis. After subtotal nephrectomy, uremic rats were treated with peritoneal dialysis using 4.25% dextrose-containing fluid. The peritoneum of uremic rats treated with PD demonstrated fibrosis, increased TGF-beta expression, increased Smad2/3 activation, decreased Smad7 expression, and increased expression of fibrogenic and angiogenic factors. In addition, peritoneal function was impaired and its structure was altered, including a thickened submesothelial layer. In rats transfected with a Smad7 transgene using an ultrasound-microbubble-mediated system, peritoneal fibrosis was attenuated, peritoneal function was improved, and Smad2/3 activation was inhibited. We suggest that administration of Smad7 inhibits peritoneal fibrogenesis in uremic rats treated with PD by correcting the imbalance between downregulated Smad7 and activated Smad2/3. Blockade of the TGF-beta/Smad signaling pathway may represent a novel therapeutic approach to prevent peritoneal fibrosis in patients treated with PD.

Epithelial to Mesenchymal Transition and Peritoneal Membrane Failure in Peritoneal Dialysis Patients: Pathologic Significance and Potential Therapeutic Interventions

Peritoneal dialysis (PD) is a form of renal replacement and is based on the use of the peritoneum as a semipermeable membrane across which ultrafiltration and diffusion take place. Nevertheless, continuous exposure to bioincompatible PD solutions and episodes of peritonitis or hemoperitoneum cause acute and chronic inflammation and injury to the peritoneal membrane, which progressively undergoes fibrosis and angiogenesis and, ultimately, ultrafiltration failure. The pathophysiologic mechanisms that are involved in peritoneal functional impairment have remained elusive. Resident fibroblasts and infiltrating inflammatory cells have been considered the main entities that are responsible for structural and functional alterations of the peritoneum. Recent findings, however, demonstrated that new fibroblastic cells may arise from local conversion of mesothelial cells (MC) by epithelial-to-mesenchymal transition (EMT) during the inflammatory and repair responses that are induced by PD and pointed to MC as protagonists of peritoneal membrane deterioration. Submesothelial myofibroblasts, which participate in inflammatory responses, extracellular matrix accumulation, and angiogenesis, can originate from activated resident fibroblasts and from MC through EMT. This heterogeneous origin of myofibroblasts reveals new pathogenic mechanisms and offers novel therapeutic possibilities. This article provides a comprehensive review of recent advances on understanding the mechanisms that are implicated in peritoneal structural alterations, which have allowed the identification of the EMT of MC as a potential therapeutic target of membrane failure.

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.

Connective tissue growth factor induces extracellular matrix in asthmatic airway smooth muscle

Transforming growth factor (TGF)-beta and connective tissue growth factor may be implicated in extracellular matrix protein deposition in asthma. We have recently reported that TGF-beta increased connective tissue growth factor expression in airway smooth muscle cells isolated from patients with asthma. In this study, we examined fibronectin and collagen production and signal transduction pathways after stimulation with TGF-beta and connective tissue growth factor. In both asthmatic and nonasthmatic airway smooth muscle cells, TGF-beta and connective tissue growth factor led to the production of fibronectin and collagen I. Fibronectin and collagen expression was extracellular regulated kinase-dependent in both cell types but phosphoinositide-3 kinase-dependent only in asthmatic airway smooth muscle cells. p38 was implicated in fibronectin but not collagen expression in both cell types. TGF-beta induction of fibronectin and collagen was in part mediated by an autocrine action of connective tissue growth factor. Phosphorylation of SMAD-2 may represent an additional pathway because this was increased in asthmatic cells. Our results suggest that these two cytokines may be important in the deposition of extracellular matrix proteins and that the signal transduction pathways may be different in asthmatic and nonasthmatic cells.

Peritoneal fibrosing syndrome: pathogenetic mechanism and current therapeutic strategies

Peritoneal dialysis (PD) has been established as a main renal replacement therapy for approximately 20 years. However, long-term peritoneal exposure to high glucose and other unphysiologic contents in the PD solution may potentiate the development of peritoneal fibrosing syndrome (PFS) in PD patients. PFS is composed of a wide spectrum of peritoneal alterations, which has been observed in PD patients. Molecular studies have shown that the fibrogenic effect of peritoneal mesothelial cells and the accompanying accumulation of extracellular matrix in the peritoneum are key events leading to PFS. In this review, we highlight the impact of PFS and its pathogenetic factors, including bioincompatible PD solution, multidisciplinary inflammatory mediators, and stimulatory cytokines in the peritoneal cavity. Current therapeutic strategies based on both clinical and basic evidence for the prevention or treatment of PFS are also reviewed.

Pathogenesis of pleural fibrosis

Pleural fibrosis resembles fibrosis in other tissues and can be defined as an excessive deposition of matrix components that results in the destruction of normal pleural tissue architecture and compromised function. Pleural fibrosis may be the consequence of an organised haemorrhagic effusion, tuberculous effusion, empyema or asbestos-related pleurisy and can manifest itself as discrete localised lesions (pleural plaques) or diffuse pleural thickening and fibrosis. Although the pathogenesis is unknown, it is likely that the complex interactions between resident and inflammatory cells, profibrotic mediators and coagulation, and fibrinolytic pathways are integral to pleural remodelling and fibrosis. It is generally considered that the primary target cell for pleural fibrosis is the subpleural fibroblast. However, increasing evidence suggests that mesothelial cells may also play a significant role in the pathogenesis of this condition, both by initiating inflammatory responses and producing matrix components. A greater understanding of the interactions between pleural and inflammatory cells, cytokines and growth factors, and blood derived proteins is required before adequate therapies can be developed to prevent pleural fibrosis from occurring.

Differential effects of transforming growth factor-beta on the synthesis of connective tissue growth factor and vascular endothelial growth factor by peritoneal mesothelial cell

BACKGROUND

Previous studies found that transforming growth factor-beta (TGF-beta) plays a conflicting role in peritoneal fibrosis. We hypothesise that TGF-beta acts on peritoneal mesothelial cells (PMC) via VEGF and CTGF as downstream mediators.

METHODS

The effect of TGF-beta in primary culture of rat PMC was studied. VEGF and CTGF mRNA expression was examined by real time quantitative polymerase chain reaction (RT-QPCR), and VEGF antigen level in cell supernatant by ELISA.

RESULTS

Incubation of rat PMC with TGF-beta resulted in a time- (3-72 h) and concentration- (0-50 pg/ml) dependent increase in VEGF mRNA expression, and VEGF protein level in the cell supernatant. When stimulated with TGF-beta 100 pg/ml, there was a 20-fold up-regulation of VEGF mRNA expression (p < 0.001). The CTGF mRNA expression and protein level of PMC was slightly increased at low concentration of TGF-beta (50 pg/ml) but decreased at a higher concentration (100 pg/ml or above). The effect of TGF-beta on PMC CTGF, but not VEGF, gene expression was inhibited by Smad decoy oligodeoxynucleotide. The effect of TGF-beta on PMC VEGF gene expression and protein synthesis was inhibited by PD98059 (a specific MAP kinase inhibitor) and chelerythrine (a specific protein kinase C inhibitor), but not cholera toxin (activator of cyclic AMP) or herbimycin A (inhibitor of protein tyrosine kinase). The up-regulation of CTGF mRNA expression was inhibited by PD98059, but not chelerythrine, cholera toxin or herbimycin A. Furthermore, CTGF gene expression in TGF-beta-stimulated PMC was inhibited by co-administration of recombinant VEGF.

CONCLUSIONS

Our data demonstrate that TGF-beta induces PMC production of VEGF and CTGF via different signalling pathways. At high concentration of TGF-beta, VEGF production predominates and CTGF production was inhibited. Since CTGF and VEGF have different biologic effects, our results may explain the complex activity of TGF-beta in peritoneal physiology.

Possible effects of hepatocyte growth factor for the prevention of peritoneal fibrosis

OBJECTIVE

Some patients who had carried out long-term continuous ambulatory peritoneal dialysis discontinued the treatment because of progressive peritoneal fibrosis. It has been previously reported that transforming growth factor-beta1 (TGF-beta1) is one of the factors that induces peritoneal fibrosis. Also, hepatocyte growth factor (HGF) plays a role in the prevention of fibrosis and in inhibiting TGF-beta1 production. In this study, we examined the effects of HGF on peritoneal fibrosis by TGF-beta1 induced by high concentrations of D-glucose.

DESIGN

We transfected a full-length human HGF cDNA in an expression vector into human peritoneal mesothelial cells (HPMCs) using the calcium phosphate method. Transfected HPMCs were cultured with high concentrations of D-glucose solution and co-cultured with fibroblasts using a transwell system. Cell proliferation was determined using the Tetra Color One method. TGF-beta1 and HGF protein were measured by enzyme-linked immunosorbent assay.

RESULTS

In addition to recombinant HGF, the growth inhibition of HPMCs by high concentration D-glucose or TGF-beta1 was significant. By transfecting HGF cDNA into HPMCs, growth inhibition by high concentration D-glucose was completely restored. Furthermore, the production of TGF-beta1 was also significantly decreased.

CONCLUSION

These results suggested that exogenous HGF could possibly prevent peritoneal fibrosis.

Proximal Tubular Toxicity of Ochratoxin A Is Amplified by Simultaneous Inhibition of the Extracellular Signal-Regulated Kinases 1/2

Ochratoxin A (OTA) is a mycotoxin involved in the development of chronic nephropathies and a known carcinogen. As we have shown previously, OTA activates mitogen-activated protein kinases [extracellular signal-regulated kinase 1 and 2 (ERK1/2), c-jun amino-terminal kinase (JNK), and extracellular-regulated protein kinase 38 (p38)] in proximal tubular cells (opossum kidney and normal rat kidney epithelial). ERK1/2, JNK, or p38 are thought to mediate opposite action on apoptosis, fibrosis, and inflammation. As we have already shown, OTA activates the latter processes. Here, we investigated the effect of OTA in the absence or presence of the ERK1/2 inhibitor U0126 [1,4-diamino-2,3-dicyano-1,4bis(2-aminophenylthio)-butadiene] to test whether OTA then will exert increased toxicity. In the presence of ERK1/2 inhibition, OTA decreased cell number and protein to a significantly larger extent compared with OTA alone. The same was true for epithelial tightness, apoptosis (caspase-3 activity), and necrosis (lactate dehydrogenase release). Furthermore, simultaneous inhibition of ERK1/2 amplified the effect of OTA on markers of inflammation (nuclear factor of the kappa-enhancer in B cells activity), fibrosis (collagen secretion), and epithelial mesenchymal transition (alpha smooth muscle actin). OTA induces phenomena typical for chronic interstitial nephropathy and activates ERK1/2, JNK, and p38 in proximal tubular cells. Inhibition of ERK1/2 aggravates the effects of OTA or even induces toxicity at normally nontoxic concentrations. This is highly likely due to activation of JNK and p38. Our data indicate a new mechanistic explanation for the toxic actions induced by OTA, and they are notable with respect to a possible coexposition of the kidney to OTA and naturally occurring ERK1/2 inhibitors. Finally, our data give rise to an attractive hypothesis on the coincidence of increased OTA exposition and urinary tract tumors in humans.

Intrapleural Injection of Transforming Growth Factor-β Antibody Inhibits Pleural Fibrosis in Empyema

STUDY OBJECTIVES

Transforming growth factor (TGF)-beta is a cytokine that has been demonstrated to be an important modulator of inflammation and angiogenesis, as well as a potent stimulator of pleural fluid production and fibrosis. We previously demonstrated that rising levels of pleural fluid TGF-beta(1) correlate with pleural fibrosis in experimental empyema in rabbits. In this study, our hypothesis is that neutralization of TGF-beta with an intrapleural injection of a monoclonal antibody to TGF-beta will decrease pleural fibrosis in empyema.

DESIGN

Prospective, randomized, blinded study.

SETTING

Animal research laboratory.

SUBJECTS

Nineteen rabbits.

INTERVENTIONS

An empyema was induced in 19 rabbits by intrapleural injection of Pasteurella multocida. A panspecific monoclonal antibody to TGF-beta was injected into the pleural space on 2 subsequent concurrent days in nine rabbits. Ten rabbits received intrapleural injections of bacteria alone and served as controls. All animals were then killed on day 6. Immunohistochemistry, using the antibody to TGF-beta, was performed on pleural tissue specimens from the control rabbits.

MEASUREMENTS AND RESULTS

Immunohistochemistry revealed localization of TGF-beta to macrophages in the exudative material and the visceral pleura. After injection of the antibody to TGF-beta, the amount of purulent, exudative material in the pleural space of the nine experimental animals was markedly decreased at autopsy on day 6, relative to control animals. All markers of empyema and pleural fibrosis were also significantly decreased in the rabbits receiving intrapleural anti-TGF-beta.

CONCLUSIONS

TGF-beta localizes to macrophages in experimental empyema. Early intrapleural injection of an antibody to TGF-beta inhibits empyema formation and significantly decreases pleural fibrosis in experimental empyema.

Combined ETA/ETB receptor blockade of human peritoneal mesothelial cells inhibits collagen I RNA synthesis

BACKGROUND

Peritoneal fibrosis is a serious complication of peritoneal dialysis; however, the mechanisms are poorly understood. We studied osmolarity and physical stress-induced effects on collagen I RNA synthesis in human peritoneal mesothelial cells (HPMCs) and focused on endothelin as a possible mediator.

METHODS

HPMCs were grown in a medium containing either d-glucose or glycerol to analyze the impact of osmolarity on mesothelial endothelin-1 (ET-1) release and on collagen I RNA synthesis [reverse transcription-polymerase chain reaction (RT-PCR)]. A cellular model of nonlaminar fluid shear stress and cellular stretch was used to analyze the effects of physical forces. To neutralize the endothelin effects, a combined ETA/ETB receptor antagonist (LU 302 872) was chosen.

RESULTS

Glucose, but not glycerol, increased mesothelial ET-1 release in a concentration and time-dependent manner (P < 0.05 vs. controls). Collagen I RNA synthesis was significantly higher in glucose-challenged cell cultures (P < 0.05 vs. controls). The glucose-mediated collagen I RNA synthesis was completely inhibited by adding the combined ETA/ETB receptor antagonist to the medium. Fluid shear stress, but not cellular stretch, led to a significant increase in the mesothelial ET-1 release (P < 0.005 vs. controls) and collagen I RNA synthesis (P < 0.05 vs. controls). LU 302 872 completely inhibited these effects.

CONCLUSION

We found that glucose and fluid shear stress are potent stimuli for ET-1 release and collagen I RNA synthesis in a model cellular system. Although our system is highly artificial, our findings raise the hypothesis that similar effects may occur in the peritoneal membranes of peritoneal dialysis patients and suggest that endothelin might be involved.

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.

Transforming growth factor-beta1 produced by ovarian cancer cell line HRA stimulates attachment and invasion through an up-regulation of plasminogen activator inhibitor type-1 in human peritoneal mesothelial cells

The processes of ovarian cancer dissemination are characterized by altered local proteolysis, cellular proliferation, cell attachment, and invasion, suggesting that the urokinase-type plasminogen activator (uPA) and its specific inhibitor (plasminogen activator inhibitor type-1 (PAI-1)) could be involved in the pathogenesis of peritoneal dissemination. We showed previously that expression of uPA and PAI-1 in the human ovarian cancer cell line HRA can be down-regulated by exogenous bikunin (bik), a Kunitz-type protease inhibitor, via suppression of transforming growth factor-beta1 (TGF-beta1) up-regulation and that overexpression of the bik gene can specifically suppress the in vivo growth and peritoneal dissemination of HRA cells in an animal model. We hypothesize that the plasminogen activator system in mesothelial cells can be modulated by HRA cells. To test this hypothesis, we used complementary techniques in mesothelial cells to determine whether uPA and PAI-1 expression are altered by exposure to culture media conditioned by HRA cells. Here we show the following: 1) that expression of PAI-1, but not uPA, was markedly induced by culture media conditioned by wild-type HRA cells but not by bik transfected clones; 2) that by antibody neutralization the effect appeared to be mediated by HRA cell-derived TGF-beta1; 3) that exogenous TGF-beta1 specifically enhanced PAI-1 up-regulation at the mRNA and protein level in mesothelial cells in a time- and concentration-dependent manner, mainly through MAPK-dependent activation mechanism; and 4) that mesothelial cell-derived PAI-1 may promote tumor invasion possibly by enhancing cell-cell interaction. This represents a novel pathway by which tumor cells can regulate the plasminogen activator system-dependent cellular responses in mesothelial cells that may contribute to formation of peritoneal dissemination of ovarian cancer.

Pentoxifylline modulates intracellular signalling of TGF-beta in cultured human peritoneal mesothelial cells: implications for prevention of encapsulating peritoneal sclerosis

BACKGROUND

Peritoneal matrix accumulation is a major characteristic of encapsulating peritoneal sclerosis (EPS), which is a serious complication in long-term peritoneal dialysis (PD) patients. We reported previously that TGF-beta stimulates collagen gene expression in cultured HPMC, and is attenuated by pentoxifylline (PTX). The SMAD family and the mitogen-activated protein kinase (MAPK) (ERK1/2, JNK and p38(HOG)) pathways have been shown to participate in TGF-beta signalling. However, how PTX modulates the intracellular signalling downstream to TGF-beta remains undetermined in HPMC. In this study, we explored these signalling pathways in HPMC, and investigated the molecular mechanisms involved in the inhibitory effects of PTX on TGF-beta-induced collagen gene expression in HPMC.

METHODS

HPMC was cultured from human omentum by an enzyme digestion method. The expression of collagen alpha1(I) mRNA was determined by northern blotting, while the SMAD proteins and the MAPK kinase activity were determined by western blotting.

RESULTS

TGF-beta-stimulated collagen alpha1(I) mRNA expression of HPMC was inhibited by PTX. The Smad2, ERK1/2 and p38(HOG) pathways were activated in response to TGF-beta. However, TGF-beta displayed no activation of the JNK pathway in HPMC. The addition of PD98059 and SB203580, which blocked the activation of ERK1/2 and p38(HOG), respectively, suppressed the TGF-beta-induced collagen alpha1(I) mRNA expression. At a concentration (300 micro g/ml) that inhibited the collagen gene expression, PTX suppressed the ERK1/2 and p38(HOG) activation by TGF-beta. In contrast, PTX had no effect on the TGF-beta-induced activation of Smad2, under the same concentration.

CONCLUSION

PTX inhibits the TGF-beta-induced collagen gene expression in HPMC through modulating the ERK1/2 and p38(HOG) pathways. Our study of PTX may provide the therapeutic basis for clinical applications in the prevention of EPS.

High glucose activates the p38 MAPK pathway in cultured human peritoneal mesothelial cells

BACKGROUND

Peritoneal fibrosis is a serious complication in long-term continuous ambulatory peritoneal dialysis (CAPD) patients, but the underlying mechanism is not well understood. Since high glucose activates the p38 mitogen-activated protein kinase (MAPK) pathway in various kinds of cells, and because mesothelial cells are always exposed to high glucose dialysate, we examined the activity and expression of p38 MAPK members in cultured human peritoneal mesothelial cells (HPMCs) under high glucose conditions.

METHODS

HPMCs were isolated from omentum and subcultured. After serum restriction, HPMCs were exposed to 5.6 mmol/L glucose (low glucose), 5.6 mmol/L glucose + 34.5 mmol/L mannitol (low glucose + mannitol), or 40 mmol/L glucose (high glucose) for 3 minutes to 48 hours with or without SB203580. Reverse transcription-polymerase chain reaction (RT-PCR) and Western blot were performed to determine mRNA and protein expression, respectively.

RESULTS

p38 MAPK and cyclic adenosine monophosphate (cAMP)-responsive element binding protein (CREB) activities and mRNA expressions were significantly increased in HPMCs exposed to high glucose compared to low glucose or low glucose + mannitol after 10 minutes and remain at higher levels to 48 hours (P < 0.05), but total p38 MAPK and CREB protein expressions did not differ. MAPK kinase 3/6 (MKK3/6) activity and mRNA expression were also higher in high glucose cells after 3 minutes (P < 0.05), and fibronectin mRNA expression was significantly increased in HPMCs exposed to high glucose after 2 hours (P < 0.05). In contrast, high glucose significantly inhibited MAPK phosphatase-1 (MKP-1) protein and mRNA expression after 10 minutes (P < 0.05). SB203580 (1 micromol/L) pretreatment for 1 hour significantly reduced high glucose-induced CREB activity and fibronectin mRNA expression by 89% and 75%, respectively (P < 0.05).

CONCLUSION

p38 MAPK activity was increased in HPMCs exposed to high glucose, in parallel with increased MKK3/6 activity and decreased MKP-1 expression, resulting in CREB activation. This activated p38 MAPK pathway may play a role in the pathogenesis of peritoneal fibrosis.

Affinity adsorption of glucose degradation products improves the biocompatibility of conventional peritoneal dialysis fluid

BACKGROUND

Reactive carbonyl compounds (RCOs) present in peritoneal dialysis (PD) fluid have been incriminated in the progressive deterioration of the peritoneal membrane in long-term PD patients. They are initially present in fresh conventional heat-sterilized glucose PD fluid and are supplemented during dwell time by the diffusion of blood RCOs within the peritoneal cavity. In the present study, RCO entrapping agents were immobilized on affinity beads to adsorb RCOs both in fresh PD fluid and in PD effluent.

METHODS

The RCO trapping potential of various compounds was assessed in vitro first by dissolving them in the tested fluid and subsequently after coupling with either epoxy- or amino-beads. The tested fluids include fresh heat-sterilized glucose and non-glucose PD fluids, and PD effluent. Their RCOs contents, that is, glyoxal (GO), methylglyoxal (MGO), 3-deoxyglucosone (3-DG), formaldehyde, 5-hydroxymethylfuraldehyde, acetaldehyde, and 2-furaldehyde were monitored by reverse-phase high-pressure liquid chromatography. The biocompatibility of PD fluid was assessed by a cytotoxic assay with either human epidermoid cell line A431 cells or with primary cultured human peritoneal mesothelial cells.

RESULTS

Among the tested RCO entrapping agents, hydrazine coupled to epoxy-beads proved the most efficient. It lowered the concentrations of three dicarbonyl compounds (GO, MGO, and 3-DG) and those of aldehydes present in fresh heat-sterilized glucose PD fluid toward the low levels observed in filter-sterilized glucose PD fluid. It did not change the glucose and electrolytes concentration of the PD fluid but raised its pH from 5.2 to 5.9. Hydrazine-coupled epoxy-bead also lowered the PD effluent content of total RCOs, measured by the 2,4-dinitrophenylhydrazone (DNPH) method. The cytotoxicity of heat-sterilized PD fluid incubated with hydrazine-coupled epoxy-beads was decreased to the level observed in filter-sterilized PD fluid as the result of the raised pH and the lowered RCOs levels.

CONCLUSION

Hydrazine-coupled epoxy-beads reduce the levels of a variety of dicarbonyls and aldehydes present in heat-sterilized glucose PD fluid to those in filter-sterilized PD fluid, without altering glucose, lactate, and electrolytes contents but with a rise in pH. Incubated with PD effluents, it is equally effective in reducing the levels of serum-derived RCOs. RCO entrapping agents immobilized on affinity beads improve in vitro the biocompatibility of conventional heat-sterilized glucose PD fluid. Their clinical applicability requires further studies.

Dipyridamole inhibits in vitro renal fibroblast proliferation and collagen synthesis

Fibroblasts are universally recognized in situations of tubulointerstitial injury, where their presence has been shown to be a marker of disease progression. The objective of this study was to determine whether the functions of fibroblasts relevant to fibrogenesis can be modified in vitro with dipyridamole. Cells were obtained from obstructed rat renal tissue and characterized on the basis of immunohistochemical findings. Fibroblasts constituted all of the cells from passage 3. Functional parameters were measured in cells cultured with 1, 5, and 50 micromol/L dipyridamole and compared to basal parameters of cells grown in Dulbecco's modified Eagle's medium plus 10% fetal calf serum (control). Northern-blot analysis indicated that dipyridamole decreased procollagen alpha1(I) messenger ribonucleic acid expression (P <.05, 50 micromol/L vs control), results that were reflected in a reduction in total collagen secretion as measured on the basis of hydroxyproline incorporation (P <.001, 50 micromol/L vs control). Mitogenesis, as measured on the basis of incorporation of tritiated thymidine, was decreased in a dose-dependent fashion by dipyridamole. Likewise, 50 micromol/L dipyridamole reduced cell-population growth to 16.8% +/- 2.1% of basal growth over 3 days (P <.001 vs control). Effects of dipyridamole on population growth were prevented by coincubation with a protein kinase G inhibitor peptide (P <.001 vs 50 micromol/L dipyridamole; P = not significant vs control). No such effect was observed with inhibitors for protein kinase A (H-89) and protein kinase C (bisindolylmaleimide I). Consistent with a protein kinase G-dependent mechanism, immunofluorescence staining indicated that dipyridamole increased basal expression of the inducible form of nitric oxide synthase. In conclusion, the results of this study demonstrate that at clinically relevant concentrations, dipyridamole inhibits profibrotic activities of renal fibroblasts. Effects on mitogenesis are mediated through a cyclic guanosine monophosphate-protein kinase G effector pathway.