Phagocytosis of chrysotile fibers by pleural mesothelial cells in culture.

Pleural mesothelial cells (PMC) from the parietal pleura of rats were incubated in culture with UICC A chrysotile fibers. The sequence of events in phagocytosis was studied by electron microscopy: phases of attachment sequestration, and degranulation of lysosomal content into the phagocytic vacuole were observed. This demonstrates that PMC can engage in phagocytosis of chrysotile fibers.     

Formation of a clastogenic factor by asbestos-treated rat pleural mesothelial cells

The data of the present study indicate that chrysotile induces the formation of a clastogenic factor (CF) when mesothelial cells are exposed to these fibersin vitro. Ultrafiltrates of culture media induce chromosome damage in human lymphocytes used as a test system for the detection of clastogenic activity in conditioned media. According to the cut off of the filters (10000 dalton), CF is a small molecule. Its exact nature is unknown. The intermediacy of active oxygen species in CF formation is suggested by the anticlastogenic effect of antioxidant enzymes such as superoxide dismutase and catalase. The data are similar to those obtained with other membrane-active agents, in particular the tumor promoter tetra-decanoylphorbol acetate (TPA). The model of membrane-mediated chromosome damage with CF formation is proposed for asbestos-induced cell injury.This work was supported by INSERM, CNRS, and GEFLUC funds.     

DNA breakage in asbestos-treated normal and transformed (TSV40) rat pleural mesothelial cells

Asbestos has been shown to induce cell cycle arrest, DNA repair and some abnormalities consistent with DNA damage but not DNA breakage. The purpose of the study was to investigate DNA breakage in asbestos-exposed rat pleural mesothelial cells (RPMC). RPMC were compared with their transformed counterparts, RPMC-TSV40 (i.e. p53-inactivated by infection with a retroviral recombinant encoding the SV40 large T antigen), as in the latter cells the cell cycle does not arrest and DNA repair is deficient due to ineffective p53-dependent cell cycle control. RPMC and RPMC-TSV40 were exposed to chrysotile and crocidolite asbestos and also to camptothecin for comparison. The presence of DNA breakage was determined using the single cell gel (Comet) assay with alkaline electrophoresis and quantified by measuring comet tail length (TL) and the percentage of total DNA in the tail and calculating tail moment (TM). We found that comets were generated by both types of asbestos in RPMC and in RPMC-TSV40 as well as by camptothecin in RPMC. On a per weight basis, chrysotile induced more abnormalities in comet parameters than did crocidolite. The comet TL and TM increased with fibre concentration, although less so with crocidolite than with chrysotile. When exposed to chrysotile at similar concentrations, RPMC consistently showed more abnormal comet parameters than did RPMC-TSV40. We concluded that asbestos causes DNA breakage and suggest that some of the DNA breakage measured was due to repair mechanisms in the normal RPMC.     

Antioxidant defense mechanisms in cultured pleural mesothelial cells.

The role of different antioxidant pathways in cultured rat pleural mesothelial cells was studied by exposing the cells to various hydrogen peroxide (H2O2) concentrations and by measuring H2O2 cell cytotoxicity and the capacity of the cells to scavenge H2O2. The antioxidant enzymes, glutathione peroxidase, glutathione reductase, glucose-6-phosphate dehydrogenase, and catalase were analyzed biochemically. Catalase and CuZn superoxide dismutase were localized by immunocytochemistry. To enable investigation of the glutathione redox cycle and catalase pathways, glutathione reductase was inactivated with 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) and catalase was inactivated with aminotriazole. When the cells were exposed to a low, sublethal (0.030 mM) H2O2 concentration, glutathione reductase but not catalase inactivation resulted in a decreased capacity to remove H2O2 from the extracellular medium. When the cells were exposed to a high (0.25 mM) H2O2 concentration, H2O2-scavenging capacity decreased remarkably when catalase was inactivated. When the cells were exposed to 0.1 to 0.5 mM H2O2, cell cytotoxicity (lactate dehydrogenase release) increased significantly if glutathione reductase was inactivated; catalase inactivation resulted in a significant cytotoxicity only at high (greater than or equal to 0.25 mM) H2O2 concentrations. Immunocytochemical studies showed that the cells, both in situ and in vitro, contained low amounts of catalase. This suggests that the results of the catalase-inhibition studies are probably not due to a change in the characteristics of the cells in culture. 3-Aminobenzamide is a compound that is known to prevent NAD depletion through inhibition of poly(ADP-ribose) polymerase during oxidant stress. When intact cells were treated with different antioxidants and exposed to 0.5 mM H2O2, both catalase and 3-aminobenzamide protected the cells completely.(ABSTRACT TRUNCATED AT 250 WORDS)     

Expression and regulation of epithelial Na+ channels by nucleotides in pleural mesothelial cells

Pleural effusions are commonly clinical disorders, resulting from the imbalance between pleural fluid turnover and reabsorption. The mechanisms underlying pleural fluid clearance across the mesothelium remain to be elucidated. We hypothesized that epithelial Na(+) channel (ENaC) is expressed and forms the molecular basis of the amiloride-sensitive resistance in human mesothelial cells. Our RT-PCR results showed that three ENaC subunits, namely, alpha, beta, gamma, and two delta ENaC subunits, are expressed in human primary pleural mesothelial cells, a human mesothelioma cell line (M9K), and mouse pleural tissue. In addition, Western blotting and immunofluorescence microscopy studies revealed that alpha, beta, gamma, and delta ENaC subunits are expressed in primary human mesothelial cells and M9K cells at the protein level. An amiloride-inhibitable short-circuit current was detected in M9K monolayers and mouse pleural tissues when mounted in Ussing chambers. Whole-cell patch clamp recordings showed an ENaC-like channel with an amiloride concentration producing 50% inhibition of 12 microM in M9K cells. This cation channel has a high affinity for extracellular Na+ ions (K(m): 53 mM). The ion selectivity of this channel to cations follows the same order as ENaC: Li+ > Na+ > K+. The unitary Li(+) conductance was 15 pS in on-cell patches. Four ENaC subunits form a functional Na+ channel when coinjected into Xenopus oocytes. Furthermore, we found that both forskolin and cGMP increased the short-circuit currents in mouse pleural tissues. Taken together, our data demonstrate that the ENaC channels are biochemically and functionally expressed in human pleural mesothelial cells, and can be up-regulated by cyclic AMP and cyclic GMP.     

Pathways of fibrin turnover of human pleural mesothelial cells in vitro.

The mesothelium contains both procoagulant and fibrinolytic activities. An imbalance between these activities could account for the abnormal fibrin turnover and pleural fibrin deposition that is characteristic of pleural inflammation. Procoagulant activity of human pleural mesothelial cells (HPMC) is in part due to tissue factor, and the prothrombinase complex can also assemble at the HPMC surface. HPMC express tissue plasminogen activator (tPA) but no detectable fibrinolytic activity in a fibrin plate assay. Inhibition of HPMC fibrinolytic activity is due, in part, to elaboration of plasminogen activator inhibitors-1 and -2 (PAI-1 and PAI-2) as well as antiplasmins. Synthesis of PAI-1 and PAI-2 is inhibited by actinomycin D and cyclohexamide. HPMC PAI-1 is increased by transforming growth factor-beta (TGF-beta) and tumor necrosis factor-alpha (TNF-alpha), as is tPA release, while PAI-1 mRNA is unchanged and tPA mRNA is increased. PAI-2 release is induced by TNF-alpha and TGF-beta. Because they are a rich source of PAI-1 and PAI-2, HPMC may contribute to the high levels of these inhibitors in pleural exudates. Stimulation of HPMC by TNF-alpha or TGF-beta in vitro did not alter HPMC procoagulant activity nor the balance of elevated PAI and antiplasmins relative to PA, changes that collectively favor formation and persistence of pericellular fibrin.     

Measurement of telomere length in cells from pleural effusion: Asbestos exposure causes telomere shortening in pleural mesothelial cells

We estimated the telomere lengths of neoplastic and non‐neoplastic mesothelial cells and examined their correlation with asbestos exposure and the expression of markers of mesothelial malignancy. Cell blocks of pleural effusion obtained from 35 cases of non‐neoplastic disease (NN), 12 cases of malignant mesothelioma (MM) and 12 cases of carcinomatous effusion due to lung adenocarcinoma (LA) were examined. Fifteen of the 35 NN cases had pleural plaques (NNpp+) suggestive of asbestos exposure, and the other 20 cases had no pleural plaques (NNpp‐). Telomere length was measured using the tissue quantitative fluorescence in situ hybridization method, and expressed as normalized telomere‐to‐centromere ratio. NN cases had significantly longer telomeres than MM (P < 0.001) and LA (P < 0.001) cases. Telomeres in NNpp+ cases were slightly shorter than those of NNpp‐ cases (P = 0.047). MM and LA showed almost the same telomere length. NN cases with shorter telomeres tended to show aberrant expression of epithelial membrane antigen (EMA), CD146, glucose transporter 1 (GLUT1) and IGF‐II messenger RNA‐binding protein 3 (IMP3). These results suggest that telomere shortening and subsequent genetic instability play an important role in the development of MM. Measurement of telomere length of cells in pleural effusion might be helpful for earlier detection of MM.     

DNA single strand breaks induced by asbestos fibers in human pleural mesothelial cells in vitro

The mechanisms of the cellular effects and DNA damage caused by asbestos fibers in human mesothelial cells are not well understood. We exposed transformed human pleural mesothelial cells to 1-4 microg/cm2 crocidolite and to 10-100 ng/ml tumor necrosis factor alpha for up to 48 hr and studied the induction of DNA damage using the Comet assay. As a positive control, 100 microM H2O2 was used. The DNA single strand breaks were assessed as the mean tail moments and as distributions of the tail DNA in the cell. The Comet assay showed significant but reversible increases in the mean tail moments, but not in the distribution of Comet tails in the histograms in cells exposed to 1 microg/cm2 crocidolite for 6 hr. At higher concentrations of asbestos fibers all the indices in the Comet assay showed significant and irreversible change. All the doses of TNF-alpha caused marginal increase in the mean tail moments. The mean tail moments were highest in the cells with concurrent treatment to TNF-alpha and crocidolite. In the cells pretreated with inhibitors of antioxidant enzymes (aminotriazole for catalase and buthionine sulfoximine for gamma-glutamylcysteine synthetase) asbestos fibers slightly increased oxidant-related fluorescence of dichlorofluorescein (DCFH) but did not cause any further increases in the mean tail moments. This study shows that asbestos fibers cause DNA single strand breaks in human mesothelial cells. Since the inhibition of antioxidant enzymes did not have an effect on the DNA damage caused by the fibers, other mechanisms than free radicals seem to be involved in the induction of DNA damage by mineral fibers.     

Cytological and ultrastructural characteristics of DNA synthesizing mesothelial cells in pleural effusion

Cytologic examination of 3H-thymidine-labeled mesothelial cells in the pleural fluid revealed that single and small-sized cells with slight basophilic cytoplasm scarcely stainable by PAS and colloidal iron are in the DNA-synthetic phase and that these are exfoliating cells from the pleural surface. While abnormal labeling in a few arranged and binuclear cells suggesting accelerated or disturbed mesothelial mobilization was frequently found in congestive cardiac failure, liver cirrhosis, and uremia, it never occurred in single and large-sized activated cells possessing rich PAS-positive granules, cells in large clusters or sheet-like arrangements, or multinuclear giant cells. Transmission electron microscopical observation of these labeled cells proved that a smooth cellular surface and scant intracytoplasmic organelles, by which undifferentiated cells are generally characterized, are essential for DNA-synthesizing mesothelial cells. Probably as a result of some pleural irritation, surface lining cells immediately enter the cell cycle and at once revert to an undifferentiated form capable of DNA synthesis, after which they may be released as a single form, and differentiate and transform into mature, activated cells with a bleb-like surface structure or microvilli, and finally may proliferate in the fluid.     

Mesothelial cell response to pleural injury: thrombin-induced proliferation and chemotaxis of rat pleural mesothelial cells.

Injury to the pleura ultimately results in either repair with fibrosis or repair without fibrosis and a reestablishment of the normal mesothelial monolayer. The role of the mesothelial cell, and of local mediators, in these repair processes remains essentially undefined. In order for repair without fibrosis to occur, mesothelial cells, in response to local mediators, must be capable of migration and/or proliferation to cover the injured and denuded mesothelium. We hypothesized that rat pleural mesothelial cells were capable of both chemotaxis and proliferation in response to thrombin. In an in vitro assay, mesothelial cells demonstrated directed migration in response to a known chemoattractant, formylmethionylleucylphenylalanine. In addition, mesothelial cells demonstrated chemotaxis in a dose-dependent manner in response to thrombin, with a maximal response at a concentration of 10(-8) M. Finally, this chemotaxis was blocked by a specific blocker of thrombin, antithrombin 3. Thrombin also stimulated mesothelial cell proliferation, which was measured both in a [3H]thymidine incorporation assay and by direct cell counts. Again, the response was dose dependent, with the maximal response at 10(-8) M causing the same amount of [3H]thymidine incorporation as 10% fetal bovine serum. As before, this response was completely blocked by antithrombin 3. These results demonstrate that mesothelial cells are capable of both chemotaxis and proliferation in response to thrombin. Thrombin may play an important role in the regulation of pleural repair without fibrosis and the re-establishment of the mesothelial monolayer.     

Pleomorphic lobular carcinoma in pleural fluid: diagnostic pitfall for atypical mesothelial cells

Pleomorphic lobular carcinoma (PLC) is a subtype of infiltrating lobular carcinoma because of its dyscohesiveness, linear infiltration pattern, and lack of membranous E-cadherin staining. However, it differs from classic lobular carcinoma because of its high-grade cytology and more aggressive clinical behavior. In breast fine-needle aspiration biopsies, PLC can be confused with invasive ductal carcinoma, particularly the apocrine variant. In this report, we illustrate how metastatic PLC in body fluid specimens shows many of the same cytomorphologic changes that occur in reactive/atypical mesothelial cells. Fortunately, the immunohistochemical staining pattern of PLC can help to distinguish it from other possible diagnoses in the differential, such as reactive/atypical mesothelial cells and other metastatic neoplasms. However, the frequent apocrine features seen in this variant of breast carcinoma can cause nonspecific immunohistochemical positivity that may make the interpretation difficult. This is the first report illustrating the cytopathology and immunohistochemical findings of pleomorphic lobular carcinoma in body cavity fluid cytology. Our case highlights the important issues and pitfalls to be aware of when making this diagnosis.     

Role of mesothelial and submesothelial stromal cells in matrix remodeling following pleural injury.

The pleural response to injury is a complex and poorly understood multifactorial process that can result in the development of fibrosis or obliteration of the pleural space. Pleural fibroblasts are considered the main source of extracellular matrix but cell culture studies have demonstrated synthesis of matrix components by mesothelial cells. We assessed the mesothelial cell contribution to extracellular matrix during pleural healing using immunohistochemical technique. Paraffin-embedded tissue of 3 normal adult lungs and 7 adults with active pleuritis were studied using monoclonal antibodies to cytokeratin, type IV collagen, vimentin, and type I procollagen (PCI). Normal pleural had a single layer of cytokeratin-positive and PCI-negative mesothelium over a thin, continuous type IV collagen-positive basement membrane and PCI-negative submesothelial stroma. Areas of active pleuritis showed loss of the continuous linear staining with anti-type IV collagen antibody. Coexpression of cytokeratin, vimentin and PCI was identified in spindle and/or cuboidal cells located in the fibrin layer, submesothelial connective tissue layer, or on the pleural surface. These findings suggest that reactive mesothelial cells play an active role in the production of extracellular matrix during pleural injury, and that disruption of the submesothelial basement membrane is a key event in determining subsequent fibrous organization of pleural exudate.     

Proliferation of rat pleural mesothelial cells in response to hepatocyte and keratinocyte growth factors

The proliferative response of cultured pulmonary mesothelial cells (MCs) to epithelial cell mitogens such as keratinocyte growth factor (KGF) and hepatocyte growth factor (HGF) is investigated. A cell line of rat pleural MCs and freshly prepared rat visceral and parietal MCs were studied. Both KGF and HGF stimulated thymidine uptake in the cell line when cultured for 2 d in serum-free conditions; the growth increase was magnified when tumor necrosis factor (TNF)-alpha was also added to the cultures. Adding asbestos fibers alone to MCs in culture did not enhance DNA synthesis by these cells. The MCs were also shown to synthesize significant amounts of HGF but much less KGF when cultured for 2 d. When freshly prepared MCs were examined, normal cell growth was more rapid in the parietal cells, which also had a more epithelial-type morphology. The addition of HGF and KGF resulted in increased DNA synthesis in each cell type, but no effect of added TNF-alpha was found. The results indicate that pulmonary MCs have the potential to proliferate in response to cytokines such as HGF and KGF that are usually associated with epithelial cell regeneration after injury.     

联合抗体在胸水细胞块肺腺癌细胞和增生性间皮细胞中的表达及意义

目的：探讨联合抗体的运用在鉴别胸水肺腺癌细胞和反应性增生间皮细胞中的意义。方法：胸水细胞块切片后行免疫组织化学sP法检N25例胸水转移性肺腺癌细胞和20例反应性增生间皮细胞中甲状腺转录因子．1、细胞角蛋白-7、间皮细胞及钙结合蛋白表达。结果：甲状腺转录因子-1、细胞角蛋白．7、间皮细胞和钙结合蛋白在胸水肺腺癌细胞和反应性增生间皮细胞中的表达比较差异有统计学意义fP〈0．05）。甲状腺转录因子．1和细胞角蛋白-7联合标记胸水肺腺癌细胞的敏感性为88％,特异性为100％;间皮细胞和钙结合蛋白联合标记胸水增生性间皮细胞的敏感性为60％,特异性为95％。结论：联合应用甲状腺转录因子．1、细胞角蛋白-7、间皮细胞和钙结合蛋白抗体检测胸水细胞块对鉴别肺腺癌细胞和反应性增生间皮细胞具有较高的应用价值。     

Inhibition of asbestos-induced transformation of rat pleural mesothelial cells in co-culture with rat macrophages.

The aim of this work was to investigate the influence of macrophages on the process of rat pleural mesothelium cells (RPMC) transformation in vitro. For this purpose prolonged many-passage co-cultivation of rat pleural mesothelial cells and rat peritoneal macrophages was performed both in the presence (to study macrophage influence on asbestos-induced morphologic transformation) and in the absence (to study spontaneous transformation) of asbestos. It was shown that spontaneous transformation of RPMC slightly accelerated in the co-cultures, whereas asbestos-induced transformation was strongly inhibited. For instance, RPMC acquired the ability to form multilayer cell growth foci and colonies in semisolid agar at 22-24 passages in the absence and at 14-16 passages in the presence of asbestos, while in co-culture with macrophages these signs of transformation appeared at 17-19 passages without asbestos treatment and were not observed at the 40th passage under exposure to asbestos. It was shown that the observed inhibition of transformation was caused by preferential depletion of transformed cells in co-cultures of mesothelium and macrophages in the presence of asbestos: when equal concentrations of macrophages and asbestos were taken, the viability of early-passage RPMC was greater as compared with late passages, and the viability of late-passage RPMC was greater than that of mesothelioma cells. The amount of late-passage RPMC and mesothelioma cells able to form colonies in semisolid media was also drastically decreased in these conditions. These findings suggest that though macrophages can influence the process of asbestos-induced mesothelium transformation by different ways, as a whole the inhibitory action appears to be the strongest.     

地塞米松对大鼠胸膜间皮细胞水通道蛋白1表达的调节

 目的：观察胸膜间皮细胞水通道蛋白1（AQP-1）的表达及地塞米松（Dex）对其表达的影响，为进一步研究胸水治疗的机制提供实验依据。方法:体外培养大鼠胸膜间皮细胞，细胞鉴定后，采用免疫细胞化学、RT-PCR方法检测AQP-1表达；应用Western blotting检测以不同浓度Dex（10^-8、10^-7、10^-6、10^-5、10^-4 mmol/L）处理细胞 24 h 及以10^-4 mmol/L Dex处理细胞 6 h、12 h、24 h、36 h、48 h、72 h后AQP-1表达情况。结果:发现胸膜间皮细胞存在AQP-1表达， 10^-8、10^-7、10^-6、10^-5、10^-4 mmol/ L Dex干预胸膜间皮细胞 24 h 后，AQP-1蛋白表达量(积分吸光度)分别为755.04±19.81、843.72±19.41、862.96±26.53、694.80±32.00、938.08±13.32，分别高于正常对照组（372.90±16.46） 2.02、2.26、2.31、1.86、2.52倍 (P<0.01)，AQP-1表达升高与地塞米松浓度无关；以10-4 mmol/L Dex干预细胞 6 h、12 h、24 h、36 h、48 h、72 h 后，AQP-1蛋白表达量分别为：554.14±23.57、917.78±38.62、1 587.20±61.22、1 322.09±28.65、918.40±26.62、1 117.60±51.32，分别高于正常对照组（495.91±23.12）1.12、1.85、3.20、2.67、1.85、2.25倍(P<0.01)，AQP-1表达与地塞米松作用时间有关。结论:胸膜间皮细胞存在AQP-1表达，地塞米松对胸膜间皮细胞AQP-1表达有明显的增强性调节作用，具有时间依赖性。     

Evaluation of AgNOR count in distinguishing benign from malignant mesothelial cells in pleural fluids.

The authors have evaluated in eight reactive and eight malignant pleural effusions the number of intranuclear dots representing the nucleolar associated proteins stained with silver colloid technique (interphase nucleolar organizer regions-AgNORs). The mean number per nucleus in benign reactive effusions was 1.56 (SD 0.77) while in mesotheliomatous effusions it was 2.81 (SD 1.44). The statistical analysis of values, by Mann-Whitney U Wilcoxon Rank Sum W Test, revealed a significant difference of AgNOR counts in the two cytological samples. The variability of AgNOR areas and morphologies in reactive and mesotheliomatous nuclei in pleural fluids is evaluated applying automatic image analysis.