Streptococcus pneumoniae potently induces cell death in mesothelial cells.

Pleural infection/empyema is common and its incidence continues to rise. Streptococcus pneumoniae is the commonest bacterial cause of empyema in children and among the commonest in adults. The mesothelium represents the first line of defense against invading microorganisms, but mesothelial cell responses to common empyema pathogens, including S. pneumoniae, have seldom been studied. We assessed mesothelial cell viability in vitro following exposure to common empyema pathogens. Clinical isolates of S. pneumoniae from 25 patients with invasive pneumococcal disease and three reference strains were tested. All potently induced death of cultured mesothelial cells (MeT-5A) in a dose- and time-dependent manner (>90% at 107 CFU/mL after 24 hours). No significant mesothelial cell killing was observed when cells were co-cultured with Staphylococcus aureus, Streptococcus sanguinis and Streptococcus milleri group bacteria. S. pneumoniae induced mesothelial cell death via secretory product(s) as cytotoxicity could be: i) reproduced using conditioned media derived from S. pneumoniae and ii) in transwell studies when the bacteria and mesothelial cells were separated. No excess cell death was seen when heat-killed S. pneumoniae were used. Pneumolysin, a cytolytic S. pneumoniae toxin, induced cell death in a time- and dose-dependent manner. S. pneumoniae lacking the pneumolysin gene (D39 ΔPLY strain) failed to kill mesothelial cells compared to wild type (D39) controls, confirming the necessity of pneumolysin in D39-induced mesothelial cell death. However, pneumolysin gene mutation in other S. pneumoniae strains (TIGR4, ST3 and ST23F) only partly abolished their cytotoxic effects, suggesting different strains may induce cell death via different mechanisms.

Malignant pleural fluid from mesothelioma has potent biological activities.

BACKGROUND AND OBJECTIVE: Malignant pleural effusion (MPE) affects >90% of mesothelioma patients. Research on MPE has focused on its physical impact on breathlessness; MPE is rich in growth mediators but its contribution to tumour biology has not been investigated. We aimed to examine the potential effects of MPE in promoting growth, migration and chemo-resistance of mesothelioma. METHODS: Pleural fluid samples from 151 patients (56 mesothelioma, 60 metastatic pleural cancer and 35 benign) were used. Seven validated human mesothelioma cell lines and three primary cultured mesothelioma lines were employed. RESULTS: Pleural fluid from mesothelioma patients (diluted to 30%) consistently stimulated cell proliferation (trypan-blue cell viability assay) in five mesothelioma cell lines tested by (median) 2.23-fold over controls (all P < 0.0001). The fluid also induced cell migration by (median) 2.13-fold in six mesothelioma cell lines using scratch-wound assay. In a murine flank model of mesothelioma, tumour infused with daily instillations of pleural fluid grew significantly faster over saline controls (median 52.5 cm2 vs 28.0 cm2 at day 13, P = 0.028). Addition of MPE (diluted to 30%) to culture media significantly protected mesothelioma from cisplatin/pemetrexed-induced cell death in all three cell lines tested (median fold reduction of 1.29, 1.98 and 3.90, all P < 0.001 vs control). The growth effects of matched pleural fluid and cultured mesothelioma cells from the same patients did not differ significantly from unmatched pairs. CONCLUSION: This 'proof-of-concept' study reveals potent biological capabilities of malignant pleural fluid in mesothelioma pathobiology.

Preclinical assessment of adjunctive tPA and DNase for peritoneal dialysis associated peritonitis.

A major complication of peritoneal dialysis is the development of peritonitis, which is associated with reduced technique and patient survival. The inflammatory response elicited by infection results in a fibrin and debris-rich environment within the peritoneal cavity, which may reduce the effectiveness of antimicrobial agents and predispose to recurrence or relapse of infection. Strategies to enhance responses to antimicrobial agents therefore have the potential to improve patient outcomes. This study presents pre-clinical data describing the compatibility of tPA and DNase in combination with antimicrobial agents used for the treatment of PD peritonitis. tPA and DNase were stable in standard dialysate solution and in the presence of antimicrobial agents, and were safe when given intraperitoneally in a mouse model with no evidence of local or systemic toxicity. Adjunctive tPA and DNase may have a role in the management of patients presenting with PD peritonitis.

Tissue plasminogen activator potently stimulates pleural effusion via a monocyte chemotactic protein-1-dependent mechanism.

Pleural infection is common. Evacuation of infected pleural fluid is essential for successful treatment, but it is often difficult because of adhesions/loculations within the effusion and the viscosity of the fluid. Intrapleural delivery of tissue plasminogen activator (tPA) (to break the adhesions) and deoxyribonuclease (DNase) (to reduce fluid viscosity) has recently been shown to improve clinical outcomes in a large randomized study of pleural infection. Clinical studies of intrapleural fibrinolytic therapy have consistently shown subsequent production of large effusions, the mechanism(s) of which are unknown. We aimed to determine the mechanism by which tPA induces exudative fluid formation. Intrapleural tPA, with or without DNase, significantly induced pleural fluid accumulation in CD1 mice (tPA alone: median [interquartile range], 53.5 [30-355] µl) compared with DNase alone or vehicle controls (both, 0.0 [0.0-0.0] µl) after 6 hours. Fluid induction was reproduced after intrapleural delivery of streptokinase and urokinase, indicating a class effect. Pleural fluid monocyte chemotactic protein (MCP)-1 levels strongly correlated with effusion volume (r = 0.7302; P = 0.003), and were significantly higher than MCP-1 levels in corresponding sera. Mice treated with anti-MCP-1 antibody (P < 0.0001) or MCP-1 receptor antagonist (P = 0.0049) demonstrated a significant decrease in tPA-induced pleural fluid formation (by up to 85%). Our data implicate MCP-1 as the key molecule governing tPA-induced fluid accumulation. The role of MCP-1 in the development of other exudative effusions warrants examination.

A commercially available preparation of Staphylococcus aureus bio-products potently inhibits tumour growth in a murine model of mesothelioma.

BACKGROUND AND OBJECTIVE: Mesothelioma is an incurable cancer with a rising global incidence. Intrapleural delivery of a commercially available compound made up of proteins produced by Staphylococcus aureus has been used clinically to induce pleurodesis. We investigate if this bacterial compound has anti-tumoural activities against pleural malignancies, in addition to its pleurodesing effect. METHODS: The effects of the treatment on mesothelioma cells were evaluated in vitro and further tested in two validated murine models. RESULTS: This S. aureus bio-product mixture effectively kills mesothelioma cells and induces the release of interleukin (IL)-8, monocyte chemotactic protein (MCP)-1 and vascular endothelial growth factor from primary human mesothelial cells but not malignant pleural mesothelioma cells in vitro. Intratumoural delivery of the treatment in BALB/c mice induced tumour necrosis and local activation of T cells. Tumour growth was significantly inhibited in the treatment group during and after the treatment period (size of tumour 58.8 ± 10.3 mm(2) vs 118.3 ± 6.7 mm(2) from saline controls at day 23, n = 9-12 per group), P < 0.001. Tumour growth resumed on cessation of treatment, confirming the inhibition was treatment related. Treatment benefits were further validated in an orthotopic peritoneal model of mesothelioma and the compound significantly reduced the mesothelioma load (P < 0.05 vs saline controls). Mice in the treatment group had a significant increase in the percentage of activated CD4(+) and CD8(+) T cells in tumour-draining lymph nodes. No histological side-effects were observed with the treatment. CONCLUSIONS: This proof-of-principle study demonstrates promising antitumoural activity of a commercially available compound of S. aureus bio-products against mesothelioma.

Bacterial infection elicits heat shock protein 72 release from pleural mesothelial cells.

Heat shock protein 70 (HSP70) has been implicated in infection-related processes and has been found in body fluids during infection. This study aimed to determine whether pleural mesothelial cells release HSP70 in response to bacterial infection in vitro and in mouse models of serosal infection. In addition, the in vitro cytokine effects of the HSP70 isoform, Hsp72, on mesothelial cells were examined. Further, Hsp72 was measured in human pleural effusions and levels compared between non-infectious and infectious patients to determine the diagnostic accuracy of pleural fluid Hsp72 compared to traditional pleural fluid parameters. We showed that mesothelial release of Hsp72 was significantly raised when cells were treated with live and heat-killed Streptococcus pneumoniae. In mice, intraperitoneal injection of S. pneumoniae stimulated a 2-fold increase in Hsp72 levels in peritoneal lavage (p<0.01). Extracellular Hsp72 did not induce or inhibit mediator release from cultured mesothelial cells. Hsp72 levels were significantly higher in effusions of infectious origin compared to non-infectious effusions (p<0.05). The data establish that pleural mesothelial cells can release Hsp72 in response to bacterial infection and levels are raised in infectious pleural effusions. The biological role of HSP70 in pleural infection warrants exploration.

Mesothelial cells activate the plasma kallikrein-kinin system during pleural inflammation.

Abstract Pleural inflammation underlies the formation of most exudative pleural effusions and the plasma kallikrein-kinin system (KKS) is known to contribute. Mesothelial cells are the predominant cell type in the pleural cavity, but their potential role in plasma KKS activation and BK production has not been studied. Bradykinin concentrations were higher in pleural fluids than the corresponding serum samples in patients with a variety of diseases. Bradykinin concentrations did not correlate with disease diagnosis, but were elevated in exudative effusions. It was demonstrated, using a range of primary and transformed mesothelial and mesothelioma cell lines, that cells assembled high molecular weight kininogen and plasma prekallikrein to liberate bradykinin, a process inhibited by novobiocin, a heat shock protein 90 (HSP90) inhibitor, cysteine, bradykinin and protamine sulphate. Of the common plasma prekallikrein activators, mesothelial cells expressed HSP90, but not prolylcarboxypeptidase or Factor XII. Calcium mobilisation was induced in some mesothelium-derived cell lines by bradykinin. Des-Arg(9)-bradykinin was inactive, indicating that mesothelial cells are responsive to bradykinin, mediated via the bradykinin receptor subtype 2. In summary, pleural mesothelial cells support the assembly and activation of the plasma KKS by a mechanism dependent on HSP90, and may contribute to KKS-mediated inflammation in pleural disease.