Expression of growth factor and growth factor receptor RNA in rat pleural mesothelial cells in culture

Osteopontin mRNA expression by rat mesothelial cells exposed to multi-walled carbon nanotubes as a potential biomarker of chronic neoplastic transformation in vitro

Mesothelioma is a cancer of the lung pleura primarily associated with inhalation of asbestos fibers. Multi-walled carbon nanotubes (MWCNTs) are engineered nanomaterials that pose a potential risk for mesothelioma due to properties that are similar to asbestos. Inhaled MWCNTs migrate to the pleura in rodents and some types cause mesothelioma. Like asbestos, there is a diversity of MWCNT types. We investigated the neoplastic potential of tangled (tMWCNT) versus rigid (rMWCNT) after chronic exposure using serial passages of rat mesothelial cells in vitro. Normal rat mesothelial (NRM2) cells were exposed to tMWCNTs or rMWCNTs for 45 weeks over 85 passages to determine if exposure resulted in transformation to a neoplastic phenotype. Rat mesothelioma (ME1) cells were used as a positive control. Osteopontin (OPN) mRNA was assayed as a biomarker of transformation by real time quantitative polymerase chain reaction (qPCR) and transformation was determined by a cell invasion assay. Exposure to rMWCNTs, but not tMWCNTs, resulted in transformation of NRM2 cells into an invasive phenotype that was similar to ME1 cells. Moreover, exposure of NRM2 cells to rMWCNTs increased OPN mRNA that correlated with cellular transformation. These data suggest that OPN is a potential biomarker that should be further investigated to screen the carcinogenicity of MWCNTs in vitro.

Erionite and asbestos differently cause transformation of human mesothelial cells

Malignant mesothelioma (MM) is an aggressive tumor associated with environmental or occupational exposure to asbestos fibers. Erionite is a fibrous zeolite, morphologically similar to asbestos and it is assumed to be even more carcinogenic. Onset and progression of MM has been suggested as the result of the cooperation between asbestos and other cofactors, such as SV40 virus infection. Nevertheless, several cases of MM were associated with environmental exposure to erionite in Turkey, where SV40 was never isolated in MM specimens. We show here that erionite is poorly cytotoxic, induces proliferating signals and high growth rate in human mesothelial cells (HMC). Long term exposure to erionite, but not to asbestos fibers, transforms HMC in vitro, regardless of the presence of SV40 sequences, leading to foci formation in cultured monolayers. Cells derived from foci display constitutive activation of Akt, NF-kappaB and Erk1/2, show prolonged survival and a deregulated cell cycle, involving cyclin D1 and E overexpression. Our results reveal that erionite is able per se to turn HMC into transformed highly proliferating cells and disclose the carcinogenic properties of erionite, prompting for a careful evaluation of environmental exposure to these fibers. The genetic predisposition to the effect of erionite is a separate subject for investigation.

Growth factors in pleural fibrosis

PURPOSE OF REVIEW

Pleural fibrosis is a double-edged sword in clinical settings. Successful induction of pleural fibrosis is the basis of therapeutic pleurodesis. On the other hand, pleural septations and fibrosis are undesirable outcomes in pleural infection and fibrothoraces. The significance of growth factors in the pathogenesis of pleural fibrosis has become increasingly apparent.

RECENT FINDINGS

Recent findings have indicated that transforming growth factor beta is a key mediator of pleural fibrosis and demonstrated the therapeutic potential of both transforming growth factor beta itself and transforming growth factor beta inhibitors. Basic fibroblast growth factor has been highlighted as a key factor in successful pleurodesis, and in the formation of pleural effusions. Vascular endothelial growth factor inhibition has been shown to decrease pleural fibrosis in vivo. By contrast, hepatocyte growth factor stimulates non-fibrotic healing, while inhibition increases fibrosis.

SUMMARY

The actions of the growth factors, and their inhibitors, are potentially and/or currently applicable in a clinical setting. Understanding the biology of these growth factors may allow therapeutic manipulation of these cytokines to create pleurodesis or to inhibit pleural (and peritoneal) adhesion/fibrosis.

The extracellular domain of p185(c-neu) induces density-dependent inhibition of cell growth in malignant mesothelioma cells and reduces growth of mesothelioma in vivo

EGFR is involved in the density-dependent inhibition of cell growth, while coexpression of EGFR with erbB2 can render normal cells transformed. In this study, we have examined the effect of a species of p185 that contains the transmembrane domain and the extracellular domain of p185(c-neu), on growth properties of a human malignant mesothelioma cell line that coexpresses EGFR and erbB2. The ectodomain form of p185(c-neu) enhanced density-dependent inhibition of cell growth and we found that p21 induction appeared to be responsible for this inhibitory effect. Previously, the extracellular domain species was shown to suppress the transforming abilities of EGFR and p185(c-neu/erbB2) in a dominant-negative manner. The ability of this subdomain to affect tumor growth is significant, as it reduced in vivo tumor growth. Unexpectedly, we found that the domain did not abrogate all of EGFR functions. We noted that EGFR-induced density-dependent inhibition of cell growth was retained. Tyrosine kinase inhibitors of EGFR did not cause density-dependent inhibition of cell growth of malignant mesothelioma cells. Therefore, simultaneously inhibiting the malignant phenotype and inducing density-dependent inhibition of cell growth in malignant mesothelioma cells by the extracellular domain of p185(c-neu) may represent an important therapeutic advance.

α-Tocopheryl Succinate Inhibits Malignant Mesothelioma byDisrupting the Fibroblast Growth Factor Autocrine Loop

We have studied the potential effect against human malignant mesotheliomas (MM) of alpha-tocopheryl succinate (alpha-TOS), a redox-silent vitamin E analog with strong pro-apoptotic and anti-cancer activity. alpha-TOS at sub-apoptotic levels inhibited proliferation of MM cell lines, while being nontoxic to nonmalignant mesothelial cells. Because MM cells are typified by a highly metastatic phenotype, we investigated the effect of alpha-TOS on genes playing a major role in MM progression. Of these, alpha-TOS down regulated fibroblast growth factor (FGF)-1 and, in particular, FGF-2 on the transcriptional level in MM cells, and this was not observed in their nonmalignant counterparts. FGF-2 short interfering RNA suppressed proliferation of MM cells. Down-regulation of FGF-2 was likely because of inhibition of the egr-1 transcription activity that was decreased in MM cells via oxidative stress induced by alpha-TOS, as evidenced by EPR spectroscopy, whereas nonmalignant cells did not show this response. Treatment of MM cells with egr-1 short interfering RNA suppressed proliferation, which was overridden by exogenously added recombinant FGF-1 and, in particular, FGF-2. An analog of coenzyme Q targeted to mitochondria and superoxide dismutase overrode inhibition of MM cell proliferation by alpha-TOS as well as alpha-TOS-induced inhibition of egr-1-dependent transactivation. Finally, alpha-TOS significantly suppressed experimental MM in immunocompromised mice. Our data suggest that alpha-TOS suppresses MM cell proliferation by disrupting the FGF-FGF receptor autocrine signaling loop by generating oxidative stress and point to the agent as a selective drug against thus far fatal mesotheliomas.

Defective core-apoptosis signalling in diffuse malignant pleural mesothelioma: opportunities for effective drug development

Because of a lack of effective treatments, survival from diffuse pleural mesothelioma remains poor. Many people do not think that treatments for this disease are effective. The understanding of the biology of mesothelioma relevant to the apoptosis-resistant phenotype has been slow to advance. However, this is now changing, and strategies for rational therapeutic drug development are emerging that have the potential to change the natural history and improve survival in the increasing number of patients that will be diagnosed in the next two decades. This review discusses recent developments in apoptosis biology that are specific to mesothelioma and the therapeutic implications for this aggressive cancer.

α-Tocopheryl succinate inhibits proliferation of mesothelioma cells by selective down-regulation of fibroblast growth factor receptors

alpha-Tocopheryl succinate (alpha-TOS), a redox-silent analogue of vitamin E, inhibits malignant mesotheliomas (MM) in a pre-clinical model. Here we investigated the underlying mechanism. Exposure of MM cells to alpha-TOS triggered apoptosis at higher and inhibited proliferation at lower concentrations, while this effect was not observed in non-malignant mesothelial cells. Sub-apoptotic doses of alpha-TOS caused down-regulation of fibroblast growth factor receptor-1 (FGFR1) selectively in MM cells, while the effect on FGFR2 was only marginal. FGF1 and FGF2 enhanced MM cell proliferation that was suppressed by alpha-TOS. Over-expression of E2F1, a transcriptional factor of FGFR1, but not its dominant-negative counterpart, partially blocked the inhibitory activity of alpha-TOS on MM cell proliferation. Our data suggest a novel mechanism by which a clinically intriguing agent selectively suppresses proliferation of cancer cells, as shown here for the untreatable mesotheliomas.

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.

Steady-state pleural fluid flow and pressure and the effects of lung buoyancy

Both theoretical and experimental studies of pleural fluid dynamics and lung buoyancy during steady-state, apneic conditions are presented. The theory shows that steady-state, top-to-bottom pleural-liquid flow creates a pressure distribution that opposes lung buoyancy. These two forces may balance, permitting dynamic lung floating, but when they do not, pleural-pleural contact is required. The animal experiments examine pleural-liquid pressure distributions in response to simulated reduced gravity, achieved by lung inflation with perfluorocarbon liquid as compared to air. The resulting decrease in lung buoyancy modifies the force balance in the pleural fluid, which is reflected in its vertical pressure gradient. The data and model show that the decrease in buoyancy with perfluorocarbon inflation causes the vertical pressure gradient to approach hydrostatic. In the microgravity analogue, the pleural pressures would be toward a more uniform distribution, consistent with ventilation studies during space flight. The pleural liquid turnover predicted by the model is computed and found to be comparable to experimental values from the literature. The model provides the flow field, which can be used to develop a full transport theory for molecular and cellular constituents that are found in pleural fluid.

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.

Expression and function of cyclooxygenase-2 in mesothelial cells during late phase of rat carrageenin-induced pleurisy

We have previously shown that the inducible isoform of the cyclooxygenases, COX-2, is strongly expressed in pleural exudate leukocytes early (between 3 and 7 hr after irritation) during rat carrageenin-induced pleurisy. The present study further examined COX-2 expression and disclosed that mesothelial cells expressed COX-2 later (12 to 24 hr after irritation) in this model. A COX-2 inhibitor, nimesulide, lowered the intrapleural level of 6-keto-PGF1alpha and inhibited hyperplasia of the pleural matrix, suggesting that COX-2 expressed in mesothelial cells may play a role in the synthesis of extracellular matrix through formation of PGI2.

Helper T cell type 1 and 2 cytokines regulate C-C chemokine expression in mouse pleural mesothelial cells

The recruitment of leukocytes to an area of injury or inflammation site is one of the most fundamental host defenses. Pulmonary tuberculosis is characterized by granulomatous inflammation with an extensive infiltration of mononuclear cells. In tuberculous pleurisy pleural mesothelial cells are exposed to mycobacteria in the pleural space. In this study we demonstrate that mouse pleural mesothelial cells (PMCs), when stimulated with BCG or IFN-gamma, produced MIP-1alpha and MCP-1 in vitro. IFN-gamma enhanced the BCG-mediated MIP-1alpha and MCP-1 expression in a concentration-dependent manner. The RT-PCR studies also confirmed that both BCG and IFN-gamma induce chemokine expression. IL-4 inhibited the BCG-mediated MIP-1alpha and MCP-1 expression in a concentration-dependent manner. The lower concentrations of IL-4 were ineffective; however, at higher concentrations, the inhibitory effect of IL-4 persisted for 24 h and decreased thereafter. BCG stimulation resulted in an increase of IFN-gamma and IL-4 receptors on PMCs. Our results demonstrate that Th1 and Th2 cytokines may regulate the C-C chemokine expression in PMCs and thus play a biologically important role in mononuclear cell recruitment to the pleural space.

Impaired healing of extraperitoneal intestinal anastomoses

BACKGROUND

The extra-anatomical position of a cervical oesophagogastrostomy might be a reason for impaired anastomotic healing.

METHODS

This hypothesis was tested in a rat model. Jejunal resection with an end-to-end jejunojejunostomy was placed intra-abdominally in group 1 (n = 24) and subcutaneously in group 2 (n = 30). Jejunum without anastomosis was placed subcutaneously in group 3 (n = 12). After 3, 7 or 14 days the rats were killed; the bursting pressure of the anastomosis or jejunum was measured and the hydroxyproline level was determined.

RESULTS

Two of 24 rats in group 1 and eight of 30 in group 2 died following anastomotic leakage (P not significant) and were excluded from other measurements. Bursting pressure was decreased after 3 days in group 1 (mean(s.e.) 62(10) mmHg) and group 2 (57(10) mmHg) compared with that in group 3 (204(17) mmHg) (P < 0.001). After 7 days, it was in the normal range in group 1 (200(14) mmHg), but lower in group 2 (104(15) mmHg) compared with that in group 3 (230(8) mmHg) (P < 0.001). Differences in hydroxyproline levels were not statistically significant between the groups after 3, 7 and 14 days.

CONCLUSION

Healing of jejunojejunostomies is impaired in an extraperitoneal position compared with an intra-abdominal position.

Cellular sources of transforming growth factor-beta isoforms in early and chronic radiation enteropathy

The three mammalian transforming growth factor (TGF)-beta isoforms (TGF-beta1, TGF-beta2, and TGF-beta3) differ in their putative roles in radiation-induced fibrosis in intestine and other organs. Furthermore, tissue specificity of TGF-beta action may result from temporal or spatial changes in production and/or activation. The present study examined shifts in the cell types expressing TGF-beta mRNA relative to TGF-beta immunoreactivity and histopathological injury during radiation enteropathy development. A 4-cm loop of rat small intestine was locally exposed to O, 12, or 21-Gy single doses of x-irradiation. Sham-irradiated and irradiated intestine were procured 2 and 26 weeks after irradiation. Cells expressing the TGF-beta1, TGF-beta2, or TGF-beta3 transcripts were identified by in situ hybridization with digoxigenin-labeled riboprobes. Intestinal wall TGF-beta immunoreactivity was measured using computerized image analysis, and structural radiation injury was assessed by quantitative histopathology. Normal intestinal epithelium expressed transcripts for all three TGF-beta isoforms. Two weeks after irradiation, regenerating crypts, inflammatory cells, smooth muscle cells, and mesothelium exhibited increased TGF-beta1 expression and, to a lesser degree, TGF-beta2 and TGF-beta3 expression. Twenty-six weeks after irradiation, TGF-beta2 and TGF-beta3 expression had returned to normal. In contrast, TGF-beta1 expression remained elevated in smooth muscle, mesothelium, endothelium, and fibroblasts in regions of chronic fibrosis. Extracellular matrix-associated TGF-beta1 immunoreactivity was significantly increased at both observation times, whereas, TGF-beta2 and TGF-beta3 immunoreactivity exhibited minimal postradiation changes. Intestinal radiation injury is associated with overexpression of all three TGF-beta isoforms in regenerating epithelium. Radiation enteropathy was also associated with sustained shifts in the cellular sources of TGF-beta1 from epithelial cells to cells involved in the pathogenesis of chronic fibrosis. TGF-beta2 and TGF-beta3 did not exhibit consistent long-term changes. TGF-beta1 appears to be the predominant isoform in radiation enteropathy and may be more important in the mechanisms of chronicity than TGF-beta2 and TGF-beta3.

An enhanced and sensitive autocrine stimulation by transforming growth factor-alpha is acquired in the brain metastatic variant of a human non-small-cell lung cancer cell line

Transforming growth factor-alpha (TGF-alpha)-mediated autocrine regulation in human non-small-cell lung cancer (NSCLC) cells NCI-H226 and its brain metastatic variant H226Br were compared. An enhanced TGF-alpha-induced dose-dependent mitogenic responsiveness in H226Br cells was observed. Neutralising antibody that binds TGF-alpha inhibits H226Br cell growth more effectively than NCI-H226 cell growth. Binding assay with 125I-labelled epidermal growth factor (EGF) revealed that H226Br has two types of EGF receptors (EGFRs), whereas the parental cell line, NCI-H226, has only one. H226Br cells contain twice as many EGFRs as H226 cells, as proved by Scatchard analysis and immune kinase assay. Northern analysis indicated that there is more EGFR transcript in H226Br than in NCI-H226, indicating a transcriptional EGFR gene elevation during metastasis progression. The level of accumulated immunoactive TGF-alpha is lower in the conditioned medium of H226Br than in that of NCI-H226. demonstrating down-regulation of TGF-alpha transcript. The accumulated data suggest an elevated and sensitive autocrine modulation by TGF-alpha and EGFR in immortalising the brain metastatic variant cells that were derived from a human NSCLC squamous cell line.

Enhanced paracellular barrier function of rat mesothelial cells partially protects against cancer cell penetration

To study pathophysiological roles of mesothelial barrier functions in protection against cancer cell invasion, we isolated mesothelial cells from the rat abdominal cavity and then cultured them with 10(-6)M all-trans-retinoic acid (RA) for 10 days. Mesothelial barrier function assessed by measuring transcellular electrical resistance (TER) and the expression of 7H6 tight junction-associated antigen at the cell border were induced by the treatment (10.01 +/- 0.8 vs 6.05 +/- 0.7 omega cm2, without RA; mean +/- s.e.m., n = 10). Then we quantified the attachment and penetration of rat mammary cancer cells (SST-2 cells) into the mesothelial cell monolayer by prelabelling of the cancer cells with fluorescent dye and by observing optical sections at different heights using a laser confocal scanning microscope. When SST-2 cells were overlaid onto the mesothelial cell monolayer treated with RA, the number of cancer cells found at the basal level of the monolayer was significantly reduced. These results showed that enhanced mesothelial barrier function at least partially prevents the penetration of cancer cells into mesothelial cells and suggested that 7H6 antigen serves as a reliable immunocytochemical marker for monitoring mesothelial barrier function.

Nitric oxide synthesis by rat pleural mesothelial cells: induction by growth factors and lipopolysaccharide

The purpose of this study was to determine if certain growth factors and bacterial products induce pleural mesothelial cells (PMC) to produce nitric oxide (NO). Confluent monolayers of rat PMC were exposed to epidermal growth factor (EGF), platelet-derived growth factor (PDGF), or lipopolysaccharide (LPS) individually and in various combinations for 24-72 h. Concentrations of nitrite and nitrate were quantified and used as an indirect measure of NO production. LPS stimulation resulted in a significant increase in nitrite/nitrate concentration, but neither EGF nor PDGF alone or combined had any significant effect relative to control. However, LPS combined with either EGF or PDGF caused a significant increase in nitrite/nitrate concentration relative to LPS alone and growth factor alone. The highest level level of nitrite/nitrate concentration was observed with the triple combination of LPS, EGF, and PDGF. Nitrite/nitrate accumulation was significantly increased at 24 h by all combinations, and continued to increase, with the highest concentration observed after 72 h of exposure. Nitrite/nitrate production was significantly inhibited by NG-nitro-L-arginine methyl ester and this inhibition was reversed by the addition of L-arginine, suggesting that nitrite and nitrate were derived from the L-arginine-dependent formation of NO. These data indicate that PMC can be induced to produce relatively large amounts of NO in response to growth factors combined with LPS.

Characterization of proteoglycans produced by rat pleural mesothelial cells in vitro

The mesothelial cell envelopes the surface of the parietal and visceral pleura. These cells are known to synthesize most of the protein constituents of the pleural basement membrane and interstitium. This study examined the ability of a rat pleural mesothelial cell line to synthesize proteoglycans in vitro. Cells were labeled with inorganic 35SO4 to label the glycosaminoglycan moiety of proteoglycans. The medium and combined cell membrane/extracellular matrix fractions contained 73 and 25% of the proteoglycan radioactivity, respectively. The medium contained a single chondroitin/dermatan sulfate proteoglycan of approximately 190 kDa, consistent with biglycan. As determined by Northern analysis of steady-state levels of messenger RNA, the cells contained message for biglycan. Stimulation of the cells with epidermal growth factor resulted in the appearance of a second chondroitin/dermatan sulfate proteoglycan of approximately 97 kDa, characteristic of decorin. The cell membrane/matrix contained a biglycan-like chondroitin/dermatan proteoglycan and several heparan sulfate proteoglycans. Pleural mesothelial cells in vitro are capable of synthesizing a variety of interstitial and basement membrane proteoglycans.

Expression of cytochrome P450 in rat pleural mesothelial cells in secondary cultures

Cultured rat pleural mesothelial cells (RPMC) isolated from male Sprague-Dawley rats have been shown to metabolize polycyclic aromatic hydrocarbons to more oxygenated metabolites. This capacity, which is maintained with passages, suggested the presence of monooxygenase enzymes. In order to clarify the enzymatic pathway, we investigated the expression of cytochromes P450 (CYP) in cultured RPMC by Western and Northern blot analyses. Cells were cultured in Ham's F10 medium supplemented with 10% fetal calf serum. The CYP expression was studied from passage 9 to 16 on different cell strains treated for 48 hours with P450 inducers. CYP1A1 apoprotein expression was very low in untreated cells, but was markedly induced after treatment with 1 microM 3-methylcholanthrene or 22 microM beta-naphthoflavone. CYP1A1 mRNA was not detected in untreated cells and appeared after 3-methylcholanthrene treatment. CYP2E1 apoprotein was constitutively expressed in cultured RPMC, and markedly increased by 170 mM ethanol, and 0.1 microM or 1 microM dexamethasone treatments. Unexpectedly, whereas the amount CYP2E1 mRNA was not modified by ethanol treatment, dexamethasone has a marked inductive effect on CYP2E1 mRNA level. The CYP expression pattern was found similar in RPMC issued from different rats, and not dependent on passage number. The CYP expression and the detection of NADPH-P450 reductase, and of epoxide hydrolase, ascertained that RPMC contain the overall enzymatic pathway required for the biotransformation and activation of procarcinogen compounds, such as polycyclic aromatic hydrocarbons and nitrosamines. Both expression and regulation properties are maintained in long-term cultures of RPMC.

Growth factor modulation of rat pleural mesothelial cell mitogenesis and collagen synthesis. Effects of epidermal growth factor and platelet-derived factor

This study examined the effects of an epithelial and a mesenchymal growth factor on pleural mesothelial cell proliferation and collagen synthesis, functions that may be important in the response of the pleura to injury. Epidermal growth factor (EGF) and platelet-derived growth factor (PDGF) added singly caused significant increases relative to control in both the uptake of [3H]thymidine into the cellular DNA of subconfluent monolayers and of [3H]proline into collagenase-sensitive protein. Combinations of EGF and PDGF resulted in more than additive increases in proliferation and additive increases in collagen production relative to each factor alone. Media from control and growth factor-stimulated PMC demonstrated no gelatinase or collagenase activity, suggesting that the increase in net collagen production was secondary to enhanced synthesis. These data demonstrate that both epithelial and mesenchymal growth factors can stimulate PMC proliferation and collagen synthesis and that these growth factors have even greater effects when combined, particularly in regard to cellular proliferation. Increases in PMC proliferation and collagen synthesis in response to these growth factors may be important in healing the pleura after injury by a variety of disease processes.

Growth stimulation of ovarian and extraovarian mesothelial cells by corpus luteum extract

Ovarian (OM) and extraovarian (EM) mesothelia represent a common source of gynecologic malignancies with yet unclear pathogenesis. Ovulation triggers a finite wave of DNA synthesis and morphogenesis only in native OM cells, probably through the activation of intraovarian growth factors. To evaluate their growth response to such factors, OM and EM cells were obtained from estrous New Zealand white rabbits by enzymatic dispersion and unit gravity sedimentation. Cell cultures were maintained in serumless, fibronectin-rich, HL-1 medium without or with rabbit corpora lutea tissue extracts (CLE). The growth effects of CLE were evaluated by measuring percent changes in cell number relative to controls (CCN), cell population doublings (CPD), cell population doubling time in hours (CPDT). After 7.5 days, CLE enhance (P < 0.001) the growth of both OM and EM cells, which exhibited, respectively, a CCN of 214 and 257%; a CPD of 2.89 and 2.87; and a CPDT of 54.39 and 59.49. CLE-treated OM and EM cells were smaller, formed more cohesive monolayers, and exhibited more frequent and diffuse microvilli than control cells. These data show a similar in vitro response of OM and EM cells to luteal growth factors, suggesting that the lack of postovulatory morphogenesis in native extraovarian mesothelia is due to the spatially restricted activity of intraovarian growth factors.

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)

Possible cellular and molecular mechanisms for asbestos carcinogenicity

Asbestos fibers may exert their carcinogenic effects on mesothelial cells and bronchial epithelial cells by direct and indirect mechanisms. Direct effects can occur following the physical interaction of fibers with target cells or by the generation of free radicals from the fiber surface; indirect effects, following the interaction of fibers with inflammatory cells can result in the production of cellular mediators such as cytokines and various reactive oxygen species. As a result, target cells may be induced to proliferate and/or sustain genetic alterations, which lead to tumor development.

Mesothelial cells produce a chemoattractant for lung fibroblasts: role of fibronectin

Pleural fibrosis may complicate several types of non-exudative pleural injury. Although the pathogenesis of such lesions is poorly understood, it is conceivable that mesothelial cells may recruit fibroblasts to sites of pleural damage. In order to test this possibility, conditioned medium from cultured rat mesothelial cells was tested for chemoattractant activity towards RL-87 rat lung fibroblasts. For this purpose, rat pleural or pericardial mesothelial cells were maintained in vitro for 6 to 96 h. Conditioned medium from each source was obtained at defined culture times and tested for chemotactic activity in a 48-well microchemotaxis assembly. A progressive, time-dependent increase in fibroblast chemoattractant activity was detected in both pleural and pericardial mesothelial cell conditioned medium samples. This effect was maximal in 96-h cultures. Checkerboard analysis revealed that the conditioned medium was truly chemotactic for lung fibroblasts. Characterization of the chemoattractant demonstrated that it was a nondialyzable (greater than 16 kD), thermolabile (100 degrees C for 15 min), acid-stable (pH 2.5), trypsin-sensitive, and pepsin-sensitive protein. The chemotaxin was shown to be fibronectin, since activity was abolished, in a dose-dependent manner, by treatment with anti-rat fibronectin antiserum as well as by passage through a gelatin agarose affinity column. This product consisted of two bands on sodium dodecyl sulfate polyacrylamide gel electrophoresis of apparent molecular masses 250 and 220 kD. The secretion of a mesothelial cell-derived fibroblast chemoattractant may play a role in the response of the pleura to injury and in the pathogenesis of pleural fibrosis.