Tissue factor expression in mesothelial cells: induction both in vivo and in vitro

Revisiting the Use of Normal Saline for Peritoneal Washing in Ovarian Cancer

The omentum is the predominant site of ovarian cancer metastasis, but it is difficult to remove the omentum in its entirety. There is a critical need for effective approaches that minimize the risk of colonization of preserved omental tissues by occult cancer cells. Normal saline (0.9% sodium chloride) is commonly used to wash the peritoneal cavity during ovarian cancer surgery. The omentum has a prodigious ability to absorb fluid in the peritoneal cavity, but the impact of normal saline on the omentum is poorly understood. In this review article, we discuss why normal saline is not a biocompatible solution, drawing insights from clinical investigations of normal saline in fluid resuscitation and from the cytopathologic evaluation of peritoneal washings. We integrate these insights with the unique biology of the omentum and omental metastasis, highlighting the importance of considering the absorptive ability of the omentum when administering agents into the peritoneal cavity. Furthermore, we describe insights from preclinical studies regarding the mechanisms by which normal saline might render the omentum conducive for colonization by cancer cells. Importantly, we discuss the possibility that the risk of colonization of preserved omental tissues might be minimized by using balanced crystalloid solutions for peritoneal washing.

Proteomic study of mesothelial and endothelial cross-talk: key lessons

INTRODUCTION

The peritoneum, pleura, and pericardium are yet understudied multicellular systems where mesothelial cells (MCs) and endothelial cells (ECs) are in close proximity. Crosstalk between these cell types likely plays role in molecular transport, immunological reactions, and metabolic processes in health, disease, and therapeutic intervention.

AREAS COVERED

In this review, we discuss recent proteomic efforts to characterize the crosstalk between MC and EC. We describe the proteomic methods necessary for investigation of crosstalk between MC and EC, as well as the in-vitro models that can be employed. Potential experimental approaches range from conditioned medium, via co-culture on semi-permeable membranes, to 3D cell culture based organoid models. While the biological and clinical relevance of the models may increase with their ability to mimic close cell communication, the practicality of these complex experiments corresponds vice versa, making standardization more difficult and expensive.

EXPERT OPINION

Currently, data and reports on mesothelial-to-endothelial crosstalk are still very scarce. In our opinion, the in-vitro model using semi-permeable cell culture inserts will allow to establish a basic understanding of cellular crosstalk that may occur between those cell types. Later-on, more sophisticated 3D cell cultures may be better able to simulate the transport dynamics within the peritoneal membrane.

Folliculin haploinsufficiency causes cellular dysfunction of pleural mesothelial cells

Birt–Hogg–Dubé syndrome (BHDS), an autosomal dominant inheritance disease caused by folliculin (FLCN) mutations, is associated with lung cysts and spontaneous pneumothorax. The possibility of FLCN haploinsufficiency in pleural mesothelial cells (PMCs) contributing to development of pneumothorax has not yet been clarified. Electron microscopy revealed exposed intercellular boundaries between PMCs on visceral pleura and decreased electron density around the adherens junctions in BHDS. To characterize cellular function of PMCs in BHDS patients (BHDS-PMCs), during surgery for pneumothorax, we established the flow cytometry-based methods of isolating high-purity PMCs from pleural lavage fluid. BHDS-PMCs showed impaired cell attachment and a significant decrease in proliferation and migration, but a significant increase in apoptosis compared with PMCs from primary spontaneous pneumothorax (PSP) patients (PSP-PMCs). Microarray analysis using isolated PMCs revealed a significant alteration in the expression of genes belonging to Gene Ontology terms “cell–cell adhesion junction” and “cell adhesion molecule binding”. Gene set enrichment analysis demonstrated that CDH1, encoding E-cadherin, was identified in the down-regulated leading edge of a plot in BHDS-PMCs. AMPK and LKB1 activation were significantly impaired in BHDS-PMCs compared with PSP-PMCs. Our findings indicate that FLCN haploinsufficiency may affect the E-cadherin-LKB1-AMPK axis and lead to abnormal cellular function in BHDS-PMCs.

Mesothelial cells and peritoneal homeostasis

The mesothelium was traditionally thought to be a simple tissue with the sole function of providing a slippery, nonadhesive, and protective surface to allow easy movement of organs within their body cavities. However, our knowledge of mesothelial cell physiology is rapidly expanding, and the mesothelium is now recognized as a dynamic cellular membrane with many other important functions. When injured, mesothelial cells initiate a cascade of processes leading either to complete regeneration of the mesothelium or the development of pathologies such as adhesions. Normal mesothelial healing is unique in that, unlike with other epithelial-like surfaces, healing appears diffusely across the denuded surface, whereas for epithelium healing occurs solely at the wound edges. This is because of a free-floating population of mesothelial cells which attach to the injured serosa. Taking advantage of this phenomenon, intraperitoneal injections of mesothelial cells have been assessed for their ability to prevent adhesion formation. This review discusses some of the functions of mesothelial cells regarding maintenance of serosal integrity and outlines the mechanisms involved in mesothelial healing. In addition, the pathogenesis of adhesion formation is discussed with particular attention to the potential role of mesothelial cells in both preventing and inducing their development.

Diverse properties of the mesothelial cells in health and disease

Mesothelial cells (MCs) form the superficial anatomic layer of serosal membranes, including pleura, pericardium, peritoneum, and the tunica of the reproductive organs. MCs produce a protective, non-adhesive barrier against physical and biochemical damages. MCs express a wide range of phenotypic markers, including vimentin and cytokeratins. MCs play key roles in fluid transport and inflammation, as reflected by the modulation of biochemical markers such as transporters, adhesion molecules, cytokines, growth factors, reactive oxygen species and their scavengers. MCs synthesize extracellular matrix related molecules, and the surface of MC microvilli secretes a highly hydrophilic protective barrier, "glycocalyx", consisting mainly of glycosaminoglycans. MCs maintain a balance between procoagulant and fibrinolytic activation by producing a whole range of regulators, can synthetize fibrin and therefore form adhesions. Synthesis and recognition of hyaluronan and sialic acids might be a new insight to explain immunoactive and immunoregulatory properties of MCs. Epithelial to mesenchymal transition of MCs may involve serosal repair and remodeling. MCs might also play a role in the development and remodeling of visceral adipose tissue. Taken together, MCs play important roles in health and disease in serosal cavities of the body. The mesothelium is not just a membrane and should be considered as an organ.

Circulating non-hematological cells during cardiopulmonary bypass: new findings in cardiac surgery procedures

BACKGROUND

Several factors have been historically advocated to explain the coagulative and inflammatory disorders following cardiopulmonary bypass (CPB). In this paper, we describe the presence of circulating non-hematological cells, introduced within the bloodstream during CPB. We defined the origin of the cells and tested their impact on coagulation.

METHODS

We collected peripheral arterial blood samples in twenty consecutive coronary artery bypass graft cases at four different surgical moments and assessed the presence and nature of circulating cells with the use of the CELLSEARCH® Test, immunocytochemistry and immunofluorescence, evaluating the expression of cytokeratin and calretinin. The effect of the circulating non-hematological cells on coagulation was tested in vitro, using the ROTEM assay.

RESULTS

A mean of 263.85 ± 57.5 (median 258.5) cells were present in the samples following the suction of blood from the surgical field while all the other samples were negative (zero cells) (p<0.00001). Immunologic tests confirmed the mesothelial origin of the cells. The ROTEM® assay of the blood samples contaminated by the mesothelial cells presented longer clotting times (53.4 ± 8.2 secs 48.3 ± 8.9 sec, p=0.05), longer clot formation times (137.1 ± 31.5 sec vs 111.9 ± 25.2 sec, p=0.009), smaller alfa angle amplitudes (66.7 ± 9.1° vs 71.1 ± 5.1°, p=0.04) and maximum clot firmness times (59.0 ± 5.4 sec vs 61.9 ±4.6 sec, p=0.004) than the controls.

CONCLUSION

The presence of circulating non-hematological cells during CPB with a mesothelial immunophenotype alters in vitro coagulation assays. This finding can help to further understand the pathophysiology of CPB.

Thrombin down-regulates tissue factor pathway inhibitor expression in a PI3K/nuclear factor-κB-dependent manner in human pleural mesothelial cells

Tissue factor pathway inhibitor (TFPI) is the primary inhibitor of the extrinsic coagulation cascade, and its expression is reported to be relatively stable. Various pathophysiologic agents have been shown to influence TFPI activity by regulating its expression or by modifying the protein. It is not clear how TFPI activity is regulated in normal physiology or in injury. Because thrombin and TFPI are locally elaborated in pleural injury, we sought to determine if thrombin could regulate TFPI in human pleural mesothelial cells (HPMCs). Thrombin significantly decreased TFPI mRNA and protein levels by > 70%. Thrombin-mediated down-regulation of TFPI promoted factor X activation by HPMCs. The ability of thrombin to significantly decrease TFPI mRNA and protein levels was maintained at nanomolar concentrations. Protease-activated receptor (PAR)-1, a mediator of thrombin signaling, is detectable in the mesothelium in human and murine pleural injury. PAR-1 silencing blocked thrombin-mediated decrements of TFPI in HPMCs. Thrombin activates PI3K/Akt and nuclear factor κB (NF-κB) signaling in HPMCs. Inhibition of PI3K (by PX-866) and NF-κB (by SN50) prevented thrombin-mediated TFPI mRNA and protein down-regulation. These are the first studies to demonstrate that thrombin decreases TFPI expression in HPMCs. Our findings demonstrate a novel mechanism by which thrombin regulates TFPI expression in HPMCs and promotes an unrestricted procoagulant response, and suggest that interactions between PI3K and NF-κB signaling pathways are linked in HPMCs and control TFPI expression. These findings raise the possibility that targeting this pathway could limit the ability of the mesothelium to support extravascular fibrin deposition and organization associated with pleural injury.

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.

Intraoperative blood loss is a critical risk factor for peritoneal recurrence after curative resection of advanced gastric cancer

BACKGROUND

Perioperative blood transfusion has been shown to be associated with poor outcome in various types of malignancy. However, the relationship between the amount of blood loss and specific types of cancer recurrence has not been documented.

METHODS

We retrospectively examined the amount of intraoperative blood loss and the recurrence pattern in 146 patients who underwent curative gastrectomy for advanced gastric cancer and assessed the possible correlation between intraoperative blood loss and peritoneal, locoregional, and hematogenous recurrences.

RESULTS

The amount of intraoperative blood loss in patients who developed peritoneal recurrence was significantly greater than that in patients without peritoneal recurrence, irrespective of blood transfusion. In contrast, the blood loss was not associated with nodal or hematogenous recurrence. Multivariate analysis demonstrated that large blood loss as well as operative curability B and adjuvant chemotherapy were independent risk factors for peritoneal recurrence and a worse outcome in advanced gastric cancer.

CONCLUSIONS

Intraoperative blood loss in curative gastrectomy for advanced gastric cancer may have a specific association with the development of peritoneal recurrence. Surgeons must remember that clean and dry surgery may lessen not only 30-day mortality and morbidity but long-term peritoneal recurrence in gastric cancer.

Plasmin enhances cell surface tissue factor activity in mesothelial and endothelial cells

BACKGROUND

Mesothelial cells that line the thoracic cavity play an important role in maintaining the local balance between procoagulant and fibrinolytic activity, a role akin to the endothelial cells in blood vessels. The mechanism(s) responsible for increased tissue factor (TF) expression in mesothelial cells in response to injury are at present unclear.

OBJECTIVE

To investigate whether plasmin or thrombin, two major proteases that may be generated on the pleural surface upon injury, induce TF expression in human pleural mesothelial cells (HMC) and elucidate the underlying mechanism(s).

METHODS

Confluent monolayers of HMC and human umbilical vein endothelial cells (HUVEC) were exposed to plasmin or thrombin for varying time periods and TF expression was analyzed by measuring its activity in a factor Xa generation assay, TF antigen levels by immunoblot analysis and TF mRNA by Northern blot analysis.

RESULTS

Both plasmin and thrombin treatments increased cell surface TF activity in HMC by 3- to 4-fold. In contrast to thrombin, plasmin-induced TF activity is not dependent on the de novo synthesis of TF. In HUVEC, plasmin had a minimal effect on unperturbed HUVEC whereas it markedly increased TF activity of activated HUVEC. Plasmin treatment neither affected anionic phospholipid levels at the cell surface nor released protein disulfide isomerase, an oxidoreductase protein that was newly described to play a role in TF activation. Plasmin cleaved cell-associated TFPI.

CONCLUSION

Thrombin up-regulates TF activity in HMC through the transcriptional activation of TF whereas plasmin increases TF activity by inactivating the cell-associated TFPI by a limited proteolysis.

Simvastatin suppresses tissue factor expression and increases fibrinolytic activity in tumor necrosis factor-alpha-activated human peritoneal mesothelial cells

BACKGROUND

Patients treated with peritoneal dialysis frequently suffer from recurrent peritonitis episodes. During peritonitis, inflammatory mediators are released and a serofibrinous exudate is formed in the peritoneal cavity, which promotes fibrosis and abdominal adhesion development. Human peritoneal mesothelial cells (HMC) play a critical role in maintaining the intraperitoneal balance between fibrinolysis and coagulation by expressing the fibrinolytic enzyme tissue-type plasminogen activator (t-PA) and its specific inhibitor, plasminogen activator inhibitor-1 (PAI-1) as well as the procoagulant protein, tissue factor.

METHODS

Cultured HMC were used to examine the effect of a 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitor, simvastatin, on the expression of t-PA, PAI-1 and tissue factor after activation of the cells with tumor necrosis factor-alpha (TNF-alpha). Antigen concentrations in the cell supernatants were measured by enzyme-linked immunosorbent assay (ELISA). Northern blot analysis was conducted for mRNA expression. Luciferase reporter gene assays and Western blot analysis in human fibrosarcoma HT1080 cells and HMC were performed to analyze the effect of simvastatin on the transcription factors nuclear factor kappa B (NF-kappa B) and activator protein-1 (AP-1), which regulate tissue factor gene expression.

RESULTS

Incubation of HMC with TNF-alpha resulted in significantly decreased t-PA and increased PAI-1 synthesis. In the presence of simvastatin t-PA synthesis in control and TNF-alpha-treated cells dose-dependently increased, reaching 5.8-fold and 7.7-fold higher t-PA levels, respectively, at 5 micromol/L simvastatin after 48 hours. Simvastatin dose-dependently suppressed PAI-1 production in both control and TNF-alpha-treated cells. At 5 micromol/L, simvastatin lowered PAI-1 synthesis 3.4-fold and 4.0-fold, respectively, thereby also completely suppressing the TNF-alpha effect itself. Similarly, simvastatin down-regulated the expression of tissue factor and also completely opposed the TNF-alpha-induced tissue factor expression. The effects of simvastatin on t-PA, PAI-1 and tissue factor expression were prevented by mevalonate and geranylgeraniol (GG), suggesting the involvement of geranylgeranyl-modified intermediates in simvastatin's mode of action. Also, simvastatin reduced NF-kappa B- and AP-1-dependent reporter gene activity in TNF-alpha-treated HT-1080 fibrosarcoma cells and reduced the nuclear levels of p50-NF-kappa B, p65-NF-kappa B, and the AP-1 components c-fos and c-jun in HMC.

CONCLUSION

The HMG-CoA reductase inhibitor simvastatin is an effective stimulator of the mesothelial fibrinolytic capacity and suppresses the procoagulant activity both under normal and inflammatory conditions. Our findings provide a molecular explanation for the anti-inflammatory properties of statins in HMC and a rationale for the use of these drugs to protect peritoneal dialysis patients from peritoneal fibrosis and adhesion development during bacterial peritonitis.

Exudative effusions in congestive heart failure

OBJECTIVES

Pleural effusions due to congestive heart failure (CHF) typically are transudates, but an occasional patient with CHF is found to have an exudate in the absence of an apparent cause other than CHF. We sought to determine the incidence and clinical significance of such exudative effusions.

DESIGN

Patients with CHF and effusions seen during the 7-year period from January 1994 through December 2000 were identified from their hospital discharge diagnoses and radiographs, while those who had undergone thoracentesis were identified from a review of the laboratory logs. The presenting symptoms and clinical course were determined from a review of the medical records. The effect of RBC contamination on pleural fluid lactate dehydrogenase (LDH) levels was determined by measuring the LDH activity of mock pleural fluid containing known amounts of RBC.

RESULTS

Seven hundred seventy patients had CHF with an effusion, but only 175 patients underwent a thoracentesis. In this select group, 86 patients had transudates and 89 had exudates. A noncardiac cause for the exudate was readily identified in 59 patients by hospital discharge, and 7 more patients had an etiology found during follow-up. Eleven of the remaining 23 patients had undergone coronary artery bypass graft (CABG) surgery > or = 1 year prior to presentation, and 50% of the effusions in patients who had undergone CABG surgery were exudates. Thus, CHF-related exudates were identified in only 12 patients, and in 4 of these patients the exudates could be explained by RBC contamination of the pleural fluid. The clinical presentation of patients with CHF-associated exudates was similar to that of CHF patients with transudates.

CONCLUSION

In most patients who have CHF and an exudative effusion, there is a noncardiac cause for the pleural effusion. The high frequency of exudates in patients with a history of CABG indicates a persistent impairment in lymphatic clearance from the pleural cavity. Exudative effusions due solely to CHF are rare.

Mesothelial cells: their structure, function and role in serosal repair

The mesothelium is composed of an extensive monolayer of specialized cells (mesothelial cells) that line the body's serous cavities and internal organs. Traditionally, this layer was thought to be a simple tissue with the sole function of providing a slippery, non-adhesive and protective surface to facilitate intracoelomic movement. However, with the gradual accumulation of information about serosal tissues over the years, the mesothelium is now recognized as a dynamic cellular membrane with many important functions. These include transport and movement of fluid and particulate matter across the serosal cavities, leucocyte migration in response to inflammatory mediators, synthesis of pro-inflammatory cytokines, growth factors and extracellular matrix proteins to aid in serosal repair, release of factors to promote both the deposition and clearance of fibrin, and antigen presentation. Furthermore, the secretion of molecules, such as glycosaminoglycans and lubricants, not only protects tissues from abrasion, but also from infection and possibly tumour dissemination. Mesothelium is also unlike other epithelial-like surfaces because healing appears diffusely across the denuded surface, whereas in true epithelia, healing occurs solely at the wound edges as sheets of cells. Although controversial, recent studies have begun to shed light on the mechanisms involved in mesothelial regeneration. In the present review, the current understanding of the structure and function of the mesothelium and the biology of mesothelial cells is discussed, together with recent insights into the mechanisms regulating its repair.

Human mesothelial cells express tissue factor when switched to proliferating state. Pharmacological modulation in vitro

Covering the inner surface of small-diameter arterial prostheses with endothelial cells (ECs) has been proposed as a means of improving biocompatibility and thrombosis resistance. Because the availability of autologous ECs is limited, autologous human mesothelial cells (HMCs) have been suggested as a substitute for ECs. However, HMCs express tissue factor (TF) in vitro, a deleterious characteristic in vivo. We investigated the distribution of TF antigen and of its inhibitor, tissue factor pathway inhibitor, on HMCs and the effect of pharmacological agents on TF expression. TF antigen was measured by enzyme-linked immunosorbent assay and localized by confocal microscopy. Three distinct pools of TF antigen were demonstrated: within the cells, at the cell surface, and in the extracellular matrix. The effects of ilomedin (10 microg/ml) and heparin (500 U/ml), known to affect procoagulant activity, were evaluated by incubating HMCs for 24 h with or without these agents. Ilomedin, but not heparin, decreased TF antigen expression by 30% (P < 0.05). Despite the theoretical potential of HMCs as a vascular prosthesis lining, TF expression by HMCs remains a major drawback. A technique capable of blocking TF expression until the HMCs return to their resting state is needed. Genetic manipulation of HMCs may hold promise for such a technique.

Characterization and fibrinolytic properties of mesothelial cells isolated from peritoneal lavage

Human peritoneal mesothelial cells were harvested from patients undergoing open or laparoscopic surgery for non-septic conditions using three different approaches: (1) from a peritoneal biopsy, (2) from peritoneal fluid, and (3) from lavage fluid collected from peritoneal cavity. When these different methods were compared, cells derived from peritoneal fluid or lavage were more likely to result in established cultures than those obtained from biopsies. The cells displayed morphological, immunohistochemical and ultrastructural characteristics of mesothelial cells. The cultured mesothelial cells produced tissue type plasminogen activator (t-PA), urokinase plasminogen activator (uPA), and plasminogen activator inhibitor type-1 and type-2 (PAI-1 and PAI-2) during unstimulated conditions. Treatment with the proinflammatory mediators LPS and TNF-alpha resulted in an overall decreased fibrinolytic capacity with a decrease in the release of t-PA and an increase in plasminogen activator inhibitors PAI-1 and PAI-2. TNF-alpha had a more profound effect than LPS, especially on the release of t-PA. This may be an important mechanism by which inflammatory mediators disrupt the fibrin degradation. In conclusion, peritoneal lavage is a convenient and reproducible source of mesothelial cells for culture.