Toxicity and cytogenetic studies of ultrafine titanium dioxide in cultured rat liver epithelial cells

The in vitro cytotoxicity and the induction of micronuclei of two ultrafine titanium dioxide (TiO(2)) samples was assessed in a rat liver epithelial cell (RLE) assay. Pigmentary TiO(2) was used as a control particle, and mitomycin C, a potent inducer of chromosome damage, was used as a positive control agent in the micronucleus experiments. Since photoexcitation of TiO(2) particles has been reported to increase the cell-killing effect of the dust, a duplicate series of experiments was carried out by irradiating the TiO(2) exposed cells with near-UV light. Neither of the ultrafine TiO(2) samples was toxic to the cells at the concentration range of 5-200 mug/cm(2). The UV treatment had no significant effect on the results. The induction of micronuclei was tested in three concentrations (5, 10 and 20 mug/cm(2)). None of the TiO(2) samples, either ultrafine or pigmentary, increased the numbers of micronuclei in the RLE cells. By contrast, all three samples had a slight decreasing effect on the frequency of micronuclei at the lowest treatment concentration of 5 mug/cm(2), both in the absence and in the presence of UV irradiation. The results suggest that ultrafine particles, similar to pigmentary TiO(2), have no direct clastogenic potential.

Mutagenicity of bitumen and asphalt fumes

The mutagenicity of asphalt fumes was tested with the Salmonella bioassays. The aim was to investigate if recycled additives modify the genotoxicity of emissions. Recycling of old asphalt is increasing, and we studied also the mutagenicity of emissions sampled during the re-use of asphalt. The composition of vapours and fumes were analysed by gas chromatography and by liquid chromatography. Bitumens containing coal fly ash (CFA) or waste plastics were heated to the paving temperatures in the laboratory. In the field, bitumen fumes were collected during paving of stone mastic asphalts (lime or CFA as a filler), remixing of stone mastic asphalt (lime or CFA as a filler), and of asphalt concrete. All the lab-generated vapour fractions were non-mutagenic. The particulate fractions were mutagenic with TA98 in the presence of the S9 activation. In addition, the lab-fumes from bitumen containing waste plastics were positive with both strains without S9. Only particulate fractions sampled in the field were tested. They were mutagenic with and without metabolic activation with both strains. The mutagenic potency of the field samples was higher than that of the lab-generated fumes without S9, and the remixing fumes were more mutagenic than the normal paving and lab-generated fumes with S9. The use of inorganic additive, CFA, did not change the mutagenicity of the fumes, whereas the organic additive, waste plastics, increased the mutagenicity of the laboratory emissions significantly.

Expression and prognostic significance of catalase in malignant mesothelioma

BACKGROUND

Free radicals and antioxidant enzymes (AOEs) may play a critical role in cell proliferation and in the resistance of malignant cells against cytotoxic drugs and radiation. Malignant mesothelioma is a resistant tumor with high levels of manganese superoxide dismutase, a central superoxide scavenging AOE. In the current study, the authors assessed the expression and prognostic role of catalase, an important hydrogen peroxide scavenging AOE, in malignant pleural mesothelioma.

METHODS

Catalase expression was investigated by immunohistochemistry in 5 cases of nonmalignant healthy pleura and in tumor tissue of 32 mesothelioma patients, and by Western blot in 7 continuous human mesothelioma cell lines. The distribution of catalase in mesothelioma cells was assessed by immunoelectron microscopy. Furthermore, to investigate the effect of catalase inhibition in the drug resistance of these cells in vitro, the authors exposed mesothelioma cells with the highest catalase level to epirubicin with and without aminotriazole pretreatment.

RESULTS

Nonmalignant mesothelial cells showed no catalase immunoreactivity whereas most mesothelioma cases (24 of 32, 75%) were catalase positive, 17 cases (53%) showing moderate or high expression. Higher catalase expression in mesothelioma was associated with a better prognosis, mean survival rate from diagnosis being 6 and 24 months for negative/low expression and moderate/high expression, respectively. Furthermore, a coordinately high expression of both manganese-superoxide dismutase (Mn-SOD) and catalase predicted even more favorable outcome of the mesothelioma patients. Catalase also could be detected in all mesothelioma cell lines, the most resistant cell line showing the highest protein expression and compartmentalization of catalase mainly to peroxisomes. Aminotriazole inhibition of catalase had a marginal effect on the toxicity caused by epirubicin.

CONCLUSIONS

Catalase may have multifactorial effects in malignant cells; high catalase and/or coordinated high expression of Mn-SOD and catalase may decrease tumor progression by modulating the cellular redox state, but enhanced antioxidant capacity of mesothelioma cells also may protect tumor cells against exogenous oxidants, at least in vitro.

Gene expression profiling of malignant mesothelioma cell lines: cDNA array study

To reveal genes relevant for malignant mesothelioma (MM), we carried out cDNA array experiments on 4 MM cell lines and 2 primary mesothelial cell cultures established from pleural fluid of non-cancer patients. Human cancer gene filters including 588 genes were used for the cDNA array experiments. Our study revealed 26 over-expressed genes that play a role in the regulation of cell fate, cell cycle, cell growth and DNA damage repair and 13 under-expressed genes encoding growth factors, receptors and proteins involved in cell adhesion, motility and invasion to be common to 3 or 4 MM cell lines. We confirmed the cDNA array results using RT-PCR for 5 of the over-expressed genes and for 3 of the under-expressed genes. Our study presents gene expression profiles in MM cell lines and shows the involvement of several genes, such as those encoding JAGGED1, ser/thr protein kinase NIK, Ku80 and cyclin D2, novel in MM.

Modulation of cell and DNA damage by poly(ADP)ribose polymerase in lung cells exposed to H(2)O(2) or asbestos fibres

Poly(ADP)ribose polymerase (PARP) may participate in cell survival, apoptosis and development of DNA damage. We investigated the role of PARP in transformed human pleural mesothelial (MeT-5A) and alveolar epithelial (A549) cells exposed from 0.05 to 5mM hydrogen peroxide (H(2)O(2)) or crocidolite asbestos fibres (1-10 microg/cm(2)) in the presence and absence of 3-aminobenzamide (ABA), a PARP inhibitor. The cells were investigated for the development of cell injury, DNA single strand breaks and depletion of the cellular high-energy nucleotides. Compared to H(2)O(2), fibres caused a minor decrease in cell viability and effect on the cellular high-energy nucleotide depletion, and a marginal effect on the development of DNA strand breaks when assessed by the single cell gel electrophoresis (the Comet assay). Inhibition of PARP transiently protected the cells against acute H(2)O(2) related irreversible cell injury when assessed by microculture tetrazolium dye (XTT) assay and potentiated oxidant related DNA damage when assessed by the Comet assay. However, PARP inhibition had no significant effect on fibre-induced cell or DNA toxicity with the exception of one fibre concentration (2 microg/cm(2)) in MeT-5A cells. Apoptosis is often associated with PARP cleavage and caspase activation. Fibres did not cause PARP cleavage or activation of caspase 3 further confirming previous results about relatively low apoptotic potential of asbestos fibres. In conclusion, maintenance of cellular high-energy nucleotide pool and high viability of asbestos exposed cells may contribute to the survival and malignant conversion of lung cells exposed to the fibres.

Proliferation, apoptosis, and manganese superoxide dismutase in malignant mesothelioma

Proliferation and apoptotic indices of tumour cells may have important prognostic significance. Manganese superoxide dismutase (MnSOD), an important anti-oxidant enzyme, has been shown to decrease proliferation of malignant cells transfected with the MnSOD gene. The aim of the present study was to investigate the indices of cell proliferation and apoptosis and their prognostic significance in human mesothelioma and to assess the effect of MnSOD on the proliferation and apoptosis of the mesothelioma cells expressing high constitutive MnSOD activity. Tissue sections from 35 subjects with malignant pleural mesothelioma were studied for cell proliferation by Ki-67 immunohistochemistry and for apoptosis by the TUNEL assay. In additional experiments, 2 mesothelioma cell lines expressing either low (M14K) or high (M38K) MnSOD levels were assessed for proliferative and apoptotic responses to epirubicin. The median proliferation and apoptotic indices of the mesothelioma tissue were 8.2% and 0.75%, respectively. Patients with a high proliferation (>8%) or apoptotic index (>0.75%) showed a worse prognosis (p < 0.001). MnSOD expression was inversely correlated with cell proliferation (p = 0.02). Our cell line experiments indicated that cells expressing high MnSOD levels were more resistant to apoptosis and showed lower proliferation when exposed to epirubicin in vitro. These findings show that high proliferation and apoptosis are associated with a poor prognosis of mesothelioma and that a high MnSOD level is associated with low proliferation of tumour cells. Furthermore, experiments with cultured mesothelioma cells suggest the importance of MnSOD in the proliferation and apoptosis caused by drug exposure.

Docetaxel and irinotecan (CPT-11) in the treatment of malignant pleural mesothelioma--a feasibility study

We chose to treat malignant pleural mesothelioma with a combination of docetaxel and irinotecan (CPT-11), because there have been preliminary reports that CPT-11 is active against mesothelioma, and docetaxel and CPT-11 were the most active agents in our in vitro experiments in human mesothelioma cell lines. Fifteen previously untreated patients with pleural mesothelioma (IMIG Stage III-IV) were given docetaxel 60 mg/m2 followed by CPT-11 190 mg/m2 on day 1, repeated every 3 weeks. All the patients were evaluable for toxicity and 13 patients were evaluated for response. No objective responses (complete or partial) were achieved, but there were two minor responses (overall response rate 15%) each of a duration of 4 months. Three patients had stable disease (23%); median time to progression was 7 months. Median survival in all the patients was 8.5 months from the first chemotherapy cycle and 11 months from diagnosis. Toxicity was severe with seven of 15 patients suffering neutropenic fever and six of 15 patients grade 3-4 diarrhea. The trial was discontinued because of toxicity and lack of activity. We do not recommend the combination of docetaxel and CPT-11 using the schedule presented here for further investigation in malignant mesothelioma. However, CPT-11 and docetaxel, individually, still warrant further study in this disease, especially in combination with cisplatin.

Antioxidant defense mechanisms of human mesothelioma and lung adenocarcinoma cells

The development of drug resistance of tumors is multifactorial and still poorly understood. Some cytotoxic drugs generate free radicals, and, therefore, antioxidant enzymes may contribute to drug resistance. We investigated the levels of manganese superoxide dismutase (Mn SOD), its inducibility, and its protective role against tumor necrosis factor-alpha and cytotoxic drugs (cisplatin, epirubicin, methotrexate, and vindesin) in human pleural mesothelioma (M14K) and pulmonary adenocarcinoma (A549) cells. We also studied other major antioxidant mechanisms in relation to oxidant and drug resistance of these cells. A549 cells were more resistant than M14K cells toward both oxidants (hydrogen peroxide and menadione) and all the cytotoxic drugs tested. M14K cells contained higher basal Mn SOD activity than A549 cells (28.3 +/- 3.4 vs. 1.8 +/- 0.3 U/mg protein), and Mn SOD activity was significantly induced by tumor necrosis factor-alpha only in A549 cells (+524%), but the induction did not offer any protection during subsequent oxidant or drug exposure. Mn SOD was not induced significantly in either of these cell lines by any of the cytotoxic drugs (0.007-2 microM, 48 h) tested when assessed by Northern blotting, Western blotting, or specific activity. A549 cells contained higher catalase activity than M14K cells (7.6 +/- 1.3 vs. 3.6 +/- 0.5 nmol O(2). min(-1). mg protein(-1)). They also contained twofold higher levels of glutathione and higher immunoreactivity of the heavy subunit of gamma-glutamylcysteine synthetase than M14K cells. Experiments with inhibitors of gamma-glutamylcysteine synthetase and catalase supported our conclusion that mechanisms associated with glutathione contribute to the drug resistance of these cells.

In vitro sensitivity of normal human mesothelial and malignant mesothelioma cell lines to four new chemotherapeutic agents

In this study, we used four human mesothelioma cell lines (M14K, M24K, M25K and M38K), one transformed human mesothelial cell line (MeT-5A) and one primary mesothelial culture (UPL) to test for in vitro sensitivity to docetaxel, paclitaxel, SN-38 [an active metabolite of irinotecan (CPT-11)] and gemcitabine, as single agents. Subconfluent cell cultures were treated with 2x10(-9), 5x10(-9), 10(-8), 2x10(-8) and 5x10(-8) M concentrations of each drug for 48 h. The sensitivity was measured in terms of cell viability using the Trypan blue exclusion method. All four drugs were potent inhibitors of mesothelioma cell growth, but cell lines from different patients diverged in their sensitivity to the individual agents. In most cases docetaxel, paclitaxel and SN-38 were more potent killers of mesothelioma cells than gemcitabine. The induction of DNA damage was investigated using the Comet assay; cells from two cell lines (M14K and M25K) were treated with subtoxic 10(-8) M concentrations of each drug for 4, 24 and 48 h. Each of the agents caused a slight increase in DNA single-strand breaks at a concentration of 10(-8) M.

Apoptosis and expression of apoptosis regulating proteins bcl-2, mcl-1, bcl-X, and bax in malignant mesothelioma

We investigated apoptosis and the expression of bcl-2, mcl-1, bcl-X, and bax in histological sections from 35 malignant mesotheliomas and 21 metastatic adenocarcinomas. Moreover, the expression of bcl-2, mcl-1, bcl-X, and bax were assessed by Western blotting in nonmalignant human mesothelial cells (Met5A) and seven malignant cell lines. The apoptotic index in mesotheliomas was 1.07+/-1.14%. Patients with mesotheliomas showing a high apoptotic index (> or =0.75%) had a worse prognosis (P = 0.008). bcl-2 positivity was observed in only seven cases, but bcl-X, mcl-1, and bax positivity was seen in all of them. In immunoblotting experiments, all mesothelioma cell lines were negative for bcl-2 but positive for bcl-X, mcl-1, and bax. The apoptotic index in bcl-2-negative mesotheliomas was 1.25+/-1.24% and in bcl-2-positive ones, 0.47+/-0.42% (P = 0.014). The apoptotic index did not significantly associate with bcl-X, mcl-1, or bax expression (P = 0.19, P = 0.25, and P = 0.46, respectively). No significant difference was observed in apoptosis or expression of bcl-2, bcl-X, or bax between malignant mesotheliomas and metastatic adenocarcinomas. The former, however, showed more often weak mcl-1 immunoreactivity (P = 0.01). The results show that the extent of apoptosis may influence patient prognosis. bcl-2 is inversely associated with the apoptotic index but is relatively infrequently expressed in malignant mesotheliomas. Widespread expression of bcl-X, mcl-1, and bax suggests that these proteins may also take part in apoptosis regulation in mesotheliomas.

Simian virus 40 (SV40)-like DNA sequences not detectable in finnish mesothelioma patients not exposed to SV40-contaminated polio vaccines

Occupational asbestos exposure can be demonstrated in 80% of mesothelioma cases. A possible role of simian virus 40 (SV40) in the etiology of mesothelioma was raised because several studies reported the presence and expression of SV40-like DNA sequences in human mesotheliomas. It is also known that expression of SV40 large T antigen inhibits cellular Rb and p53. This suggests that SV40 might render infected cells more susceptible to asbestos carcinogenicity. The SV40-like sequences are suggested to have arisen from contaminated polio vaccines. Millions of people in the United States and most European countries were inoculated with SV40-contaminated polio vaccine in 1955-1963. However, in Finland, where polio vaccination started in 1957, no SV40-contaminated vaccine was used. We used a polymerase chain reaction-based method to test for the presence of SV40-like sequences in DNA extracted from the frozen tumor tissues of 49 Finnish mesothelioma patients, most of whom had been occupationally exposed to asbestos. All of the Finnish tumor tissues tested negative for SV40-like sequences. The results suggest that the SV40-like sequences detected in mesothelioma tissue in some previous studies may indeed originate from SV40-contaminated polio vaccines. It is a matter of speculation whether the absence of SV40 infection has contributed to the relatively low incidence of mesothelioma in Finland (1/10(5) in 1990-1995).

Asbestos induction of extended lifespan in normal human mesothelial cells: interindividual susceptibility and SV40 T antigen

Normal human mesothelial cells from individual donors were studied for susceptibility to asbestos-induction of apoptosis and generation of an extended lifespan population. Such populations were generated after death of the majority of cells and arose from a subset of mesothelial cultures (4/16) whereas fibroblastic cells (5/5) did not develop extended lifespan populations after asbestos exposure. All mesothelial cultures were examined for the presence of SV40 T antigen to obtain information on (i) the presence of SV40 T antigen expression in normal human mesothelial cells and (ii) the relationship between generation of an extended lifespan population and expression of SV40 T antigen. Immunostaining for SV40 T antigen was positive in 2/38 normal human mesothelial cultures. These cultures also had elevated p53 expression. However, the two isolates expressing SV40 T antigen did not exhibit enhanced proliferative potential or develop an extended lifespan population. Asbestos-generated extended lifespan populations were specifically resistant to asbestos-mediated but not to alpha-Fas-induced apoptosis. Deletion of p16Ink4a was shown in 70% of tumor samples. All mesothelioma cell lines examined showed homozygous deletion of this locus which extended to exon 1beta. Extended lifespan cultures were examined for expression of p16Ink4a to establish whether deletion was an early response to asbestos exposure. During their rapid growth phase, extended lifespan cultures showed decreased expression of p16Ink4a relative to untreated cultures, but methylation was not observed, and p16Ink4a expression became elevated when cells entered culture crisis. These data extend the earlier observation that asbestos can generate extended lifespan populations, providing data on frequency and cell type specificity. In addition, this report shows that generation of such populations does not require expression of SV40 T antigen. Extended lifespan cells could represent a population expressing early changes critical for mesothelioma development. Further study of these populations could identify such changes.

Generation of reactive oxygen species by human mesothelioma cells

Malignant mesothelioma cells contain elevated levels of manganese superoxide dismutase (MnSOD) and are highly resistant to oxidants compared to non-malignant mesothelial cells. Since the level of cellular free radicals may be important for cell survival, we hypothesized that the increase of MnSOD in the mitochondria of mesothelioma cells may alter the free radical levels of these organelles. First, MnSOD activity was compared to the activities of two constitutive mitochondrial enzymes; MnSOD activity was 20 times higher in the mesothelioma cells than in the mesothelial cells, whereas the activities of citrate synthase and cytochrome c oxidase did not differ significantly in the two cell lines. This indicates that the activity of MnSOD per mitochondrion was increased in the mesothelioma cells. Superoxide production was assayed in the isolated mitochondria of these cells using lucigenin chemiluminescence. Mitochondrial superoxide levels were significantly lower (72%) in the mesothelioma cells compared to the mesothelial cells. Oxidant production in intact cells, assayed by fluorimetry using 2',7'-dichlorodihydrofluorescein as a fluorescent probe, did not differ significantly between these cells. We conclude that mitochondrial superoxide levels are lower in mesothelioma cells compared to nonmalignant mesothelial cells, and that this difference may be explained by higher MnSOD activity in the mitochondria of these cells. Oxidant production was not different in these cells, which may be due to the previously observed increase in H2O2-scavenging mechanisms of mesothelioma cells.

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.

A multi-institutional study confirms the presence and expression of simian virus 40 in human malignant mesotheliomas

Exposure to the carcinogen asbestos is a major factor in the development of malignant mesothelioma. However, not all mesotheliomas are associated with asbestos exposure, and only a small minority of people exposed to asbestos develop mesothelioma. Therefore, the identification of the cofactors that render certain individuals more susceptible to asbestos or that cause mesothelioma in people not exposed to asbestos has been a major priority of the International Mesothelioma Interest Group. The possible association of SV40 with mesothelioma was recently discussed in a special session at the Fourth International Mesothelioma Interest Group Conference, and it was decided to conduct a multi-institutional study to independently verify the presence of this tumor virus in mesotheliomas. We report the results of this investigation: (a) DNA and protein analyses revealed SV40 sequences and SV40 large T antigen expression in 10 of 12 mesotheliomas tested (83%); and (b) electron microscopy demonstrated variable amounts of asbestos fibers in 5 (71%) of 7 corresponding lung tissues available for analysis. Our results demonstrate that SV40 DNA is frequently present and expressed in mesotheliomas in the United States. Because our data demonstrate that some patients test positive for both SV40 and asbestos, the possibility that these two carcinogens interact should be investigated in future studies.

Tenascin and fibronectin expression in human mesothelial cells and pleural mesothelioma cell-line cells

Fibronectin (Fn) and tenascin (Tn) are two major extracellular matrix (ECM) glycoproteins that may have important roles both in fibrotic lung diseases and in lung tumors. The significance of Fn and Tn in human pleural mesothelial cells and pleural diseases is unclear. Transformed human pleural mesothelial cells (Met5A), primary cultures of mesothelial cells, and cultured mesothelioma cell lines were investigated for Fn and Tn immunoreactivity. Mesothelial cells were exposed for 48 to 96 h to transforming growth factor-beta (TGF-beta), tumor necrosis factor-alpha (TNF-alpha), amosite asbestos fibers, or oxidants (H2O2 and menadione, a compound that auto-oxidizes to produce superoxide). Immunofluorescence and Western blotting with monoclonal anti-Fn and anti-Tn antibodies, and Northern blotting with a complementary DNA (cDNA) probe for Tn showed that mesothelial cells are capable of producing Fn and Tn. The mRNA level and immunoreactivity of Tn was enhanced by TGF-beta and TNF-alpha, whereas Fn was intensified only by TGF-beta. A wide range of amosite, H2O2, or menadione concentrations had no clear effect on Fn or Tn reactivity. Fn and Tn were present at low or undetectable concentrations in five of six mesothelioma cell lines, whereas the organization of Fn immunoreactivity in these cell lines was variable. Furthermore, results obtained with the tumor tissue of these same mesothelioma patients suggested that Fn and Tn expressions do not necessarily parallel either each other or results obtained with the cultured cells.

Endogenous antioxidant enzymes and glutathione S-transferase in protection of mesothelioma cells against hydrogen peroxide and epirubicin toxicity

We have previously shown that cultured malignant mesothelioma cells contain elevated manganese superoxide dismutase (MnSOD) mRNA levels and activities compared with non-malignant mesothelial cells. As many cytotoxic drugs generate both superoxide and hydrogen peroxide, we assessed the relative significance of catalase and the glutathione redox cycle, as well as glutathione S-transferase (GST), in protecting these cells against hydrogen peroxide and epirubicin toxicity. Mesothelioma cell lines containing high (M38K cells) and low (M14K cells) MnSOD, and non-malignant MeT-5A mesothelial cells were selected for the study. M38K cells were the most resistant of these three cell types to hydrogen peroxide (0.1-0.5 mM, 4 h) and epirubicin (0.1-0.5 microg ml(-1), 48 h) as judged by lactate dehydrogenase (LDH) release and by high-energy nucleotide (ATP, ADP, AMP) depletion. Total glutathione was higher in M38K cells (63.8 +/- 20.3 nnmol mg(-1) protein) than in M14K (25.2 +/- 8.2 nmol mg[-1]) or MeT-5A cells (23.5 +/- 4.5 nmol mg[-1]). Furthermore, GST specific activity was higher in M38K cells (111.3 +/- 15.8 U mg[-1]) than in M14K cells (77.4 +/- 6.6 U mg[-1]) or in MeT-5A cells (68.8 +/- 7.6 U mg[-1]). Western blotting indicated the presence of GST-pi in all these cells, the reactivity again being highest in M38K cells. Depletion of glutathione by buthionine sulphoximine and inhibition of catalase by aminotriazole enhanced hydrogen peroxide toxicity in all cell types, while only the depletion of glutathione increased epirubicin toxicity. We conclude that simultaneous induction of multiple antioxidant enzymes can occur in human mesothelioma cells. In addition to the high MnSOD activity, hydrogen peroxide scavenging antioxidant enzymes, glutathione and GST can partly explain the high hydrogen peroxide and epirubicin resistance of these cells in vitro.

Manganese superoxide dismutase in healthy human pleural mesothelium and in malignant pleural mesothelioma

We hypothesized that manganese superoxide dismutase (MnSOD), known to be induced in rat mesothelial cells by asbestos fibers, cytokines, and hyperoxia, may also be induced in asbestos-related pleural diseases such as mesothelioma. MnSOD was assessed in healthy human pleural mesothelium (n = 6), in biopsy samples of human pleural mesothelioma (n = 7), in transformed nonmalignant human mesothelial cells (Met5A), and in two human mesothelioma cell lines (M14K and M38K) established from the tumor tissue of mesothelioma patients. There was no MnSOD immunoreactivity in five of the six samples of healthy pleural mesothelium, whereas MnSOD immunoreactivity was high in the tumor cells in all the mesothelioma samples. Northern blotting, immunohistochemistry, Western blotting, and specific activity measurements showed lower MnSOD in the nonmalignant Met5A mesothelial cells than in the M14K and M38K mesothelioma cells. In additional experiments the mesothelial and mesothelioma cells were exposed to menadione, which generates superoxide intracellularly, and to epirubicin, a cytotoxic drug commonly used to treat mesothelioma. The M38K mesothelioma cells were most resistant to menadione and epirubicin when assessed by LDH release or by adenine nucleotide (ATP, ADP, and AMP) depletion. These same cells showed not only the highest MnSOD levels, but also the highest mRNA levels and activities of catalase, whereas glutathione peroxidase and glutathione reductase levels did not differ significantly. We conclude that MnSOD expression is low in healthy human pleural mesothelium and high in human malignant mesothelioma. The most resistant mesothelioma cells contained coordinated induction of MnSOD and catalase.

Glutathione S-transferase and N-acetyltransferase genotypes and asbestos-associated pulmonary disorders

BACKGROUND

Humans vary in their ability to metabolize endogenous and exogenous compounds. Glutathione S-transferases (GSTs) and N-acetyltransferases (NATs) are enzymes involved in the detoxification of hazardous agents. The GSTM1 and GSTT1 genes exhibit null (i.e., deletion) polymorphisms; in specific individuals, homozygous deletion (i.e., both copies lost) of these genes can be detected. Polymorphism of the NAT2 gene results in slow and fast acetylators of potentially toxic substances. The GSTM1-null and the NAT2 slow-acetylator genotypes have been associated with increased risks for the development of environmentally induced cancers.

PURPOSE

We assessed whether homozygous GSTM1-null or GSTT1-null genotypes or the NAT2 slow-acetylator genotype were associated with increased risks for the development of malignant and nonmalignant asbestos-related pulmonary disorders in a cohort of Finnish construction workers.

METHODS

The study population consisted of 145 asbestos insulators who were classified as having been exposed to high levels of asbestos; 69 of these individuals had no pulmonary disorders (control subjects), and 76 had either malignant mesothelioma (n = 24) or nonmalignant pulmonary disorders, such as asbestosis and/or pleural plaques (n = 52). Lymphocyte DNA and the polymerase chain reaction were used to determine the GSTM1, GSTT1, and NAT2 genotypes of the study subjects. Odds ratios (ORs) and 95% confidence intervals (CIs) estimating the relative risks of disease associated with specific genotypes were calculated from 2 x 2 tables by use of Fisher's exact method.

RESULTS

Risks for the development of asbestos-related pulmonary disorders were not affected significantly by homozygous deletion of the GSTM1 or GSTT1 genes. However, the risk of developing both malignant and nonmalignant pulmonary disorders for individuals with a NAT2 slow-acetylator genotype was more than twice that observed for those with a NAT2 fast-acetylator genotype (OR = 2.3; 95% CI = 1.1-4.7); the risk of developing malignant mesothelioma for NAT2 slow acetylators was increased almost fourfold (OR = 3.8; 95% CI = 1.2-14.3). Individuals who lacked the GSTM1 gene and possessed a NAT2 slow-acetylator genotype had a risk of developing malignant and nonmalignant pulmonary disorders that was approximately fivefold greater than that observed for those who had the GSTM1 gene and a NAT2 fast-acetylator genotype (OR = 5.1; 95% CI = 1.6-17.6); these individuals had a fourfold increased risk of developing nonmalignant pulmonary disorders (OR = 4.1; 95% CI = 1.1-17.2) and an eightfold increased risk of developing malignant mesothelioma (OR = 7.8; 95% CI = 1.4-78.7) when compared with the same reference group.

CONCLUSIONS

Individuals with homozygous deletion of the GSTM1 gene and a NAT2 slow-acetylator genotype who are exposed to high levels of asbestos appear to have enhanced susceptibility to asbestos-related pulmonary disorders.

High levels of MDM2 are not correlated with the presence of wild-type p53 in human malignant mesothelioma cell lines

Prior analysis of 20 human mesothelioma cell lines for p53 status revealed only two mutations and one p53 null cell line, although p53 expression was detected in most cell lines. In addition, mRNA and protein expression of the retinoblastoma gene product in human mesothelioma cell lines is similar to normal controls. We have tested for p53 induction after exposure to ionising radiation and demonstrate this induction and, to a lesser extent, p21(WAF1) induction, in both normal mesothelial cells and p53-positive mesothelioma cell lines. We postulated that high levels of MDM2 might alter p53 and retinoblastoma tumour-suppressor function in mesothelioma. However, Southern blot analysis for mdm2 indicated that no amplification had occurred in 18 mesothelioma cell lines tested. Steady-state mRNA and protein levels also did not indicate overexpression. These results indicate that high levels of MDM2 are not responsible for inactivating the functions of wild-type p53 or the retinoblastoma gene product during the pathogenesis of malignant mesothelioma.

Gains and losses of DNA sequences in malignant mesothelioma by comparative genomic hybridization

The molecular basis of malignant mesothelioma is poorly known. We examined genetic changes in 11 mesothelioma specimens by comparative genomic hybridization (CGH). Five DNA specimens originated from uncultured tumor tissues and six from cell lines established from the same patients. Findings from the classical karyotypic characterization of both primary tumors and cell lines have been reported previously. In the CGH analyses the most common genetic alterations in the 11 mesothelioma specimens were losses of chromosomal regions in 1p, 8p, 14q, and 22q and gains of 5p, 6p, 8q, 15q, 17q, and 20. The cell lines had on average a much higher total number of genetic changes than the uncultured tumor specimens. Clonal relationship between the cell lines and the uncultured tissue specimens could not usually be demonstrated even though they originated from the same patient. The observed differences may partly be due to high frequency of chromosomal rearrangements, which CGH cannot detect, partly due to contamination of tumor specimens with normal tissue, and partly due to genetic evolution in tumor cell lines.

Nongenotoxic carcinogens: development of detection methods based on mechanisms: a European project

While the accumulation of genetic changes in a somatic cell is considered essential for the genesis of a cancer, it has become clear that not all carcinogens are genotoxic, suggesting that some carcinogens indirectly participate in the generation of genetic changes during carcinogenesis. A European project funded by the European Community was thus conceived to study mechanisms of nongenotoxic aspects of carcinogenesis. Two main strategical approaches were adapted: (i) to study whether and how Syrian hamster embryo (SHE), Syrian hamster dermal (SHD) and BALB/c 3T3 cell transformation systems simulate in vivo carcinogenesis, and to examine whether they can detect nongenotoxic carcinogens; (ii) to study, refine and validate mechanisms-based end-points for detection of nongenotoxic carcinogens. For mechanisms-based research, the proposed end-points included gap junctional intercellular communication (GJIC) inhibition, altered expression of critical genes, immortalization and aberrant cell proliferation. We also selected model compounds commonly usable for various endpoints. Our major results can be summarized as follows: (1) SHE and BALB/c 3T3 transformation systems reflect both genotoxic and nongenotoxic carcinogenic events; they detect not only genotoxic but also many although not all, nongenotoxic carcinogens. This is further supported by the fact that both genotoxic and nongenotoxic carcinogens were able to immortalize SHD cells. (2) Many nongenotoxic carcinogens, although not all, inhibit GJIC in vitro as well as in vivo. Mechanistic studies suggest an important role of blocked GJIC in carcinogenesis and that different mechanisms are involved in inhibition of the communication by different agents used. However, inhibition of GJIC is not a prerequisite for the enhancement (or induction) of transformation of SHE or BALB/c 3T3 cells. (3) Among compounds examined, there was a good correlation between induction of micronuclei and cell transformation in SHE cells while no such correlation was found between the induction of cell transformation and ornithine decarboxylase activity. (4) Two transgenic mouse mutation assays (lacI and lacZ) were established and validated. The genotoxin dimethylnitrosamine was shown to be mutagenic to the liver in both assays. Ortho-anisidine, a bladder-specific carcinogen that was inactive in standard rodent genetic toxicity assays was uniquely mutagenic to the bladder of the transgenic mice. The peroxisome proliferator methyl clofenipate was established as nonmutagenic to the liver of both transgenic mice. That eliminated DNA damage as a cause of the liver tumours produced by this chemical and weakened the idea that induced cell division leads to mutation induction. (5) With an in vitro DNA replication model, it was found that DNA damage induced by genotoxic agents can be responsible for inhibition of DNA replication, while certain nongenotoxic agents such as phorbol esters increase DNA replication. (6) An attempt to use structure-activity relationship for subfamilies of nongenotoxic carcinogens, e.g., receptor-mediated carcinogens, has been initiated with some promising results. Our results support the idea that there are multiple nongenotoxic mechanisms in carcinogenesis, and that working hypothesis-oriented approaches are encouraged rather than simple screening of chemicals in developing test systems for the detection of nongenotoxic carcinogens.

Differential effects of tumor necrosis factor and asbestos fibers on manganese superoxide dismutase induction and oxidant-induced cytotoxicity in human mesothelial cells

We compared induction of manganese superoxide dismutase (MnSOD) by asbestos fibers and tumor necrosis factor alpha (TNF) using cultured human mesothelial cells. Transformed pleural mesothelial cells (MET 5A) were exposed for 48 h to amosite asbestos fibers (2 micrograms/cm2), to TNF (10 ng/ml), and to the combination of these two. TNF and amosite+TNF caused significant MnSOD mRNA upregulation. Similarly MnSOD specific activity was increased by TNF (290% increase) and the amosite+TNF combination (313% increase) but not by amosite alone. In cell injury experiments, amosite and amosite+TNF exposures caused significant cell membrane injury when assessed by lactate dehydrogenase release, which was 31% and 57% higher than in the unexposed cells. However, only the amosite+TNF combination caused significant depletion of cellular high-energy nucleotide when expressed as percentage of [14C]adenine labeling in cellular high-energy nucleotides. The nucleotide levels were 91.5 +/- 2.0% in the unexposed cells, 89.9 +/- 3.9% in amosite-exposed cells, 90.1 +/- 2.2% in TNF-exposed cells, and 79.8 +/- 9.4% in amosite+TNF-exposed cells. Amosite+TNF-exposed cells were also most sensitive to menadione (20 mumol/L, 2 h), a compound which generates superoxide radicals intracellularly. In conclusion, our data suggests that in human mesothelial cells inflammatory cytokines but not asbestos fibers alone can cause MnSOD induction. In this study, however amosite asbestos+TNF treatment rendered these cells more vulnerable to oxidant-induced cell damage despite elevated MnSOD activity.

Radiosensitivity of mesothelioma cell lines

The present study was carried out in order to examine the radiosensitivity of malignant pleural mesothelioma cell lines. Cell kinetics, radiation-induced delay of the cell cycle and DNA ploidy of the cell lines were also determined. For comparison an HeLa and a human foetal fibroblast cell line were simultaneously explored. Six previously cytogenetically and histologically characterized mesothelioma tumor cell lines were applied. A rapid tiazolyl blue microtiter (MTT) assay was used to analyze radiosensitivity and cell kinetics and DNA ploidy of the cultured cells were determined by flow cytometry. The survival fraction after a dose of 2 Gy (SF2), parameters alpha and beta of the linear quadratic model (LQ-model) and mean inactivation dose (D(MID)) were also estimated. The DNA index of four cell lines equaled 1.0 and two cell lines equaled 1.5 and 1.6. Different mesothelioma cell lines showed a great variation in radiosensitivity. Mean survival fraction after a radiation dose of 2 Gy (SF2) was 0.60 and ranged from 0.36 to 0.81 and mean alpha value was 0.26 (range 0.48 - 0.083). The SF2 of the most sensitive diploid mesothelioma cell line was 0.36: less than that of the foetal fibroblast cell line (0.49). The survival fractions (0.81 and 0.74) of the two most resistant cell lines, which also were aneuploid, were equal to that of the HeLa cell line (0.78). The alpha/beta ratios of the most sensitive cell lines were almost an order of magnitude greater than those of the two most resistant cell lines. Radiation-induced delay of the most resistant aneuploid cell line was similar to that of HeLa cells but in the most sensitive (diploid cells) there was practically no entry into the G1 phase following the 2 Gy radiation dose during 36 h.

Manganese superoxide dismutase in human pleural mesothelioma cell lines

Mesothelioma is a malignant pleural or intraperitoneal tumor attributable to asbestos exposure in more than 80% of the cases. Manganese superoxide dismutase (MnSOD), a mitochondrial superoxide radical scavenging enzyme, is low in most tumors but is known to be induced by asbestos fibers and certain cytokines. Induction of MnSOD may be associated in asbestos-related pulmonary diseases in vivo. We investigated here MnSOD specific activity and MnSOD mRNA level using healthy human lung tissue, SV40-transformed human pleural mesothelial cells (Met5A), and six human malignant mesothelioma cell line cells. Total SOD (CuZnSOD + MnSOD) and MnSOD activities were 20.0 +/- 4.8 U/mg protein and 3.2 +/- 1.2 U/mg protein in healthy human lung tissue, and 25.6 +/- 10.7 U/mg and 3.8 +/- 1.0 U/mg in Met5A cells, respectively. In four mesothelioma cell lines MnSOD activity was significantly elevated, the highest activity (30.1 +/- 8.2 U/mg) was almost 10-fold compared to the activity in Met5A cells. The steady state mRNA level of MnSOD was low in Met5A cells and markedly higher in all mesothelioma cell lines roughly in proportion with enzyme activities. Cytotoxicity experiments, which were conducted in four cell lines, indicated that cells containing high MnSOD mRNA level and activity were resistant to the mitochondrial superoxide-producing agent menadione. In conclusion, our results suggest that human mesothelioma may express high levels of MnSOD, which is associated with high oxidant resistance of these cells.

Inherited GSTM1 and NAT2 defects as concurrent risk modifiers in asbestos-related human malignant mesothelioma

Besides asbestos exposure, the factors that determine susceptibility to malignant mesothelioma are unknown. We evaluated the risk of GSTM1 null genotype and slow acetylation-associated NAT2 genotype for malignant mesothelioma in relation to asbestos exposure. Both the GSTM1 null genotype and the NAT2 slow acetylator genotype placed individuals at about 2-fold increased risk of developing malignant mesothelioma [odds ratio (OR) = 1.8, 95% confidence interval (CI) = 1.0-3.5 and OR = 2.1, 95% CI = 1.1-4.1, for the GSTM1 and NAT2 genes, respectively]. When the patients were divided into low/moderate and high exposure groups according to their asbestos exposure histories, the effect of the at-risk genotypes was mostly attributable to the high exposure groups (OR = 2.3, 95% CI = 1.0-5.6 and OR = 3.7, 95% CI = 1.3-10.2, for the GSTM1 and NAT2 genes, respectively). The individuals with combined GSTM1 and NAT2 defects had about a 4-fold risk of developing malignant mesothelioma compared to those with the GSTM1 gene and NAT2 fast acetylator genotype (OR = 3.6; 95% CI = 1.3-9.6). Moreover, the risk among subjects highly exposed to asbestos with the double at-risk genotype was more than 7-fold greater compared to those with the more beneficial genotypes of both GSTM1 and NAT2 genes (OR = 7.4; 95% CI = 1.6-34.0).

Cytogenetic response to asbestos fibers in cultured human primary mesothelial cells from 10 different donors

The ability of amosite asbestos fibers to induce chromosomal aberrations in human primary mesothelial cells obtained from pleural effusions of 10 noncancerous patients was investigated. The glutathione S-transferase M1 (GSTM1) genotypes of the patients were determined, since the GSTM1 null genotype has been associated with increased susceptibility to lung cancer and chemically induced cytogenetic damage. Four of the patients represented the GSTM1 null genotype, and six the GSTM1 positive genotype. Successful chromosome aberration analyses were obtained from six cases, three of them with the GSTM1 null genotype. The level of aberrant cells in unexposed cultures ranged from 2.0% to 7.5%. Statistically significant increases (2.3-3.0-fold compared to controls) in the number of aberrant cells were observed in two cases only: in one case treated with 1 microgram/cm2 of amosite, and in another treated with 2 micrograms/cm2 of amosite. Cell cultures from four individuals showed minor or no increases in the numbers of aberrant cells in the doses tested (1 and 2 micrograms/cm2). Chromosome breaks were the major type of aberration. The amosite exposed cells with significantly increased aberrations were from patients with GSTM1 positive genotypes. Two cases that showed no cytogenetic response to asbestos fibers were of the GSTM1 null genotype. Thus, our results suggest that the lack of the GSTM1 gene does not render human mesothelial cells more susceptible to chromosomal damage induced by asbestos. GSTM1 null cells appeared, however, to be more sensitive to the growth inhibitory effects of asbestos than did GSTM1 positive cells. Variation in the cytogenetic response of human primary mesothelial cells to asbestos fibers was observed to exist, but the fibers do not appear to be potent inducers of structural chromosomal aberrations in these cells. It remains to be established whether individual sensitivity to asbestos fibers, due to specific genetic traits, exists.

Neutrophil and asbestos fiber-induced cytotoxicity in cultured human mesothelial and bronchial epithelial cells

This study investigates reactive oxygen species generation and oxidant-related cytotoxicity induced by amosite asbestos fibers and polymorphonuclear leucocytes (PMNs) in human mesothelial cells and human bronchial epithelial cells in vitro. Transformed human pleural mesothelial cells (MET 5A) and bronchial epithelial cells (BEAS 2B) were treated with amosite (2 micrograms/cm2) for 48 h. After 24 h of incubation, the cells were exposed for 1 h to nonactivated or amosite (50 micrograms) activated PMNs, washed, and incubated for another 23 h. Reactive oxygen species generation by the PMNs and the target cells was measured by chemiluminescence. Cell injury was assessed by cellular adenine nucleotide depletion, extracellular release of nucleotides, and lactate dehydrogenase (LDH). Amosite-activated (but also to a lesser degree nonactivated) PMNs released substantial amounts of reactive oxygen metabolites, whereas the chemiluminescence of amosite-exposed mesothelial cells and epithelial cells did not differ from the background. Amosite treatment (48 h) of the target cells did not change intracellular adenine nucleotides (ATP, ADP, AMP) or nucleotide catabolite products (xanthine, hypoxanthine, and uric acid). When the target cells were exposed to nonactivated PMNs, significant adenine nucleotide depletion and nucleotide catabolite accumulation was observed in mesothelial cells only. In separate experiments, when the target cells were exposed to amosite-activated PMNs, the target cell injury was further potentiated compared with the amosite treatment alone or exposure to nonactivated PMNs. In conclusion, this study suggests the importance of inflammatory cell-derived free radicals in the development of amosite-induced mesothelial cell injury.

Interferon (IFN)-alpha and IFN-gamma in combination with methotrexate: in vitro sensitivity studies in four human mesothelioma cell lines

Mesothelioma is a malignant tumor of the serous surfaces in the thorax and abdomen, which has proved exceptionally resistant to treatment. A recent phase II trial of a high-dose methotrexate regime on 63 Norwegian patients has, however, achieved a response rate of 37%. Some responses have also been achieved using interferon (IFN)-gamma administered intrapleurally or recombinant (r) IFN-alpha administered subcutaneously. Our earlier in vitro sensitivity studies of mesothelioma cell lines showed that IFN augments the response to chemotherapeutic agents in mesothelioma. The aim of this study was to assess the response of four mesothelioma cell lines, derived from diffuse asbestos-related pleural malignant mesothelioma, to methotrexate alone and in combination with recombinant IFN-alpha and IFN-gamma. Anti-proliferative effects were assayed by vital dye exclusion. A combination of IFN-alpha and IFN-gamma consistently augmented the response of the cell lines to methotrexate, by as much as 75% for one cell line, although the response to the individual IFNs was variable. We were also able to compare the effects of natural IFN-beta with those of IFN-alpha and IFN-gamma. The IFN-beta sensitivity profile for each of the four cell lines was similar to that of IFN-alpha. In two cell lines, the combination of IFN-beta and IFN-gamma produced a similar effect to the IFN-alpha and IFN-gamma combination.

Effects of asbestos and man-made vitreous fibers on cell division in cultured human mesothelial cells in comparison to rodent cells

We report the effects of chrysotile and crocidolite asbestos, and glass and rock wool fibers (man-made vitreous fibers, MMVF) on the induction of binucleate cells in vitro. The response of human mesothelial cells (target cells in fiber carcinogenesis) and rodent cells was compared. Human primary mesothelial cells, MeT-5A cells (an immortalized human mesothelial cell line), and rat liver epithelial (RLE) cells were exposed to asbestos and MMVF samples of similar size range. Milled glass wool, milled rock wool, and titanium dioxide were used as non-fibrous particle controls. All four fiber types caused statistically significant increases in the amount of binucleate cells in human primary mesothelial cells and MeT-5A cells (in the dose range 0.5-5.0 micrograms/cm2). Chrysotile and crocidolite asbestos were more effective (1.3-3.0-fold increases) than thin glass wool and thin rock wool fibers (1.3-2.2-fold increases). However, when the fiber doses were expressed as the number of fibers per culture area, the asbestos and MMVF appeared equally effective in human mesothelial cells. In RLE cells, chrysotile was the most potent inducer of binucleation (2.9-5.0-fold increases), but the response of the RLE cells to crocidolite, thin glass wool, and thin rock wool fibers was similar to the response of the human mesothelial cells. No statistically significant increases in the number of bi- or multinucleate cells were observed in human primary mesothelial cells or RLE cells exposed to the non-fibrous dusts. In MeT-5A cells exposed to 5 micrograms/cm2 of milled glass wool and milled rock wool, as well as in cultures exposed to 2 and 5 micrograms/cm2 of TiO2, significant increases were, however, observed. Our results show that rodent cells respond differently to mineral fibers than human cells. The results also add evidence to the suggested importance of disturbed cell division in fiber carcinogenesis.

Expression of cell adhesion molecules and connexins in gap junctional intercellular communication deficient human mesothelioma tumour cell lines and communication competent primary mesothelial cells

Gap junctional intercellular communication (GJIC) has been reported to be markedly reduced in human mesothelioma tumour cell lines compared with primary mesothelial cells. Immunofluorescence stainings have shown that the gap junction protein connexin43 (Cx43) is expressed in both malignant and normal mesothelial cells. In this study the mRNA expression of Cx43 and three different connexins--Cx37, Cx40 and Cx45, which are highly expressed in lung tissue--was investigated in eight human mesothelioma cell lines, and in human primary mesothelial cells from several donors. The expression of the intercellular adhesion molecules A-CAM (N-cadherin) and L-CAM (E-cadherin) was studied at the protein level. No mRNA expression of Cx37, Cx40 or Cx45 in either mesothelioma tumour cells or the primary mesothelial cells was detected. Cx43 was expressed at both the mRNA and the protein level, in seven out of eight mesothelioma cell lines, as well as in all the primary mesothelial cell cultures. The well as in all the primary mesothelial cell cultures. The intercellular adhesion molecule A-CAM was expressed at the cell-cell borders in six out of seven mesothelioma cell lines, as well as in normal mesothelial cells. No expression of L-CAM was observed in these cells. The results suggest that Cx43 and A-CAM are the major proteins in gap and adherens junctions respectively in human mesothelial cells. Most mesothelioma tumour cell lines with markedly reduced GJIC still express both Cx43 and A-CAM. Only one of our mesothelioma tumour cell lines severely deficient in GJIC lacks both the gap junction protein Cx43 and the cell adhesion molecule A-CAM.

Cancer risk in humans predicted by increased levels of chromosomal aberrations in lymphocytes: Nordic study group on the health risk of chromosome damage

Cytogenetic assays in peripheral blood lymphocytes (PBL) have been used extensively to survey the exposure of humans to genotoxic agents. The conceptual basis for this has been the hypothesis that the extent of genetic damage in PBL reflects critical events for carcinogenic processes in target tissues. Until now, no follow-up studies have been performed to assess the predictive value of these methods for subsequent cancer risk. In an ongoing Nordic cohort study of cancer incidence, 3182 subjects were examined between 1970 and 1988 for chromosomal aberrations (CA), sister chromatid exchange or micronuclei in PBL. In order to standardize for the interlaboratory variation, the results were trichotomized for each laboratory into three strata: low (1-33 percentile), medium (34-66 percentile), or high (67-100 percentile). In this second follow-up, a total of 85 cancers were diagnosed during the observation period (1970-1991). There was no significant trend in the standardized incidence ratio with the frequencies of sister chromatid exchange or micronuclei, but the data for these parameters are still too limited to allow firm conclusions. There was a statistically significant linear trend (P = 0.0009) in CA strata with regard to subsequent cancer risk. The point estimates of the standardized incidence ratio in the three CA strata were 0.9, 0.7, and 2.1, respectively. Thus, an increased level of chromosome breakage appears to be a relevant biomarker of future cancer risk.

Cytotoxicity of oxidants and asbestos fibers in cultured human mesothelial cells

The authors investigated the mechanisms caused by oxidants (superoxide and hydrogen peroxide) and asbestos (amosite) fibers in human mesothelial cells. Immortalized human pleural mesothelial cells (MET 5A) were exposed in vitro to one of the following: hypoxanthine (100-200 microM) plus xanthine oxidase (10-20 mU/ml) as a superoxide-generating system, H2O2 (50 microM-5 mM); or amosite (1-100 micrograms/cm2). Cellular adenine nucleotide depletion, DNA single strand breaks, extracellular release of nucleotides, and their catabolites and lactate dehydrogenase (LDH) were assessed as markers of cell damage after 4-6 h exposure to the oxidants or fibers. The effect of intracellular antioxidant enzymes and exogenous antioxidants on cell damage were investigated during oxidant and amosite exposure. Superoxide radical and H2O2 exposure resulted in the depletion of adenine nucleotides, accumulation of the products of nucleotide catabolism, induction of DNA single strand breaks, and extracellular LDH release. Amosite exposure did not cause nucleotide depletion or induction of DNA single strand breaks. Inactivation of the intracellular antioxidant enzymes glutathione reductase or catalase augmented cell damage during H2O2 exposure but not during amosite exposure.

Gap junctional intercellular communication of primary and asbestos-associated malignant human mesothelial cells

We examined gap junctional intercellular communication (GJIC) of primary human mesothelial cells and cell lines of asbestos-associated human pleural mesotheliomas, and the effect of asbestos and other mineral fibres on these cells. In homologous cultures, the GJIC capacity of six out of seven tumour cell lines was markedly less than for primary mesothelial cells. This defect in GJIC appeared not to be at the expression level of mRNA and protein of the gene encoding the 43 kDa gap junction protein. In heterologous cocultures of tumour cells and primary mesothelial cells, however, 80-90% of the tumour cell/normal cell contacts were functional. Exposure of primary mesothelial cells to TPA, a phorbol ester tumour promoter, resulted in marked inhibition of GJIC, being an action common to numerous tumour promoters. Such an effect though was not observed with the carcinogenic mesothelioma-inducing mineral fibres chrysotile and amosite, neither with glass wool. These results suggest that a permanent defect in GJIC capacity is a common feature of human mesothelioma cells, but how mineral fibres are involved in the process of mesotheliomagenesis is still unclear.

Interferon-alpha and interferon-gamma combined with chemotherapy: in vitro sensitivity studies in non-small cell lung cancer cell lines

Non-small cell lung cancers (NSCLC) are often resistant to chemotherapy. Cisplatin has shown the most activity against all the histological subtypes and is now used in most combined treatment programmes. Interferon (IFN)-alpha has been shown to potentiate cisplatin and other drugs experimentally and in clinical trials involving NSCLC. We are looking at the responses of different NSCLC cell lines to cisplatin (P), etoposide (VP-16) and IFN [recombinant human IFN-alpha 2c (IFN-alpha) and IFN-gamma 1b (IFN-gamma)], individually and in combination. We then compare the results with those from a clinical trial of etoposide and cisplatin with interferon in advanced NSCLC. We report here the results from the first of our cell lines, established from a large cell anaplastic carcinoma. We have confirmed earlier findings that NSCLC cell lines are not sensitive to either IFN-alpha or IFN-gamma alone. However a combination of IFN-alpha and IFN-gamma does reduce cell proliferation in our cell lines. This IFN combination potentiates the response of the cells to etoposide far more than to cisplatin. There is a trend towards greater activity when a combination of cisplatin and etoposide is used, compared with the activity of either drug alone. This effect is further increased by the interferon combination.

Interferon-alpha and -gamma in combination with chemotherapeutic drugs: in vitro sensitivity studies in four human mesothelioma cell lines

Mesothelioma is a tumor of the serous surfaces in the thorax and abdomen. This tumor has proved to be exceptionally resistant to treatment, although a variety of multi-modality therapies have been tried. We have used four human mesothelioma cell lines, originating from diffuse asbestos-related malignant (pleural) mesothelioma, to assess in vitro sensitivity to five chemotherapeutic drugs, to recombinant human interferon (IFN)-alpha and -gamma and to combined immuno-chemotherapy. The cytotoxic effects were assayed by vital dye exclusion. The drugs tested were etoposide, cisplatin, mitoxantrone, 4-epirubicin and vindesine. The combinations tested were etoposide+cisplatin, and etoposide+cisplatin+mitoxantrone. All the drugs and combinations were also tested with recombinant human (rHu) IFN-alpha 2C (rHuIFN-alpha), rHuIFN-gamma, and rHuIFN-alpha+rHuIFN-gamma. The cell lines were most sensitive to mitoxantrone, 4-epirubicin and vindesine (TC50 < or = 0.001 micrograms/ml), and least sensitive to etoposide and cisplatin (TC50 > or = 0.1 micrograms/ml) used singly. There was no improvement in sensitivity when the drugs were combined. To further investigate the lack of response to cisplatin treatment, we examined the binding of cisplatin to the mesothelioma cell DNA. The tumor cell DNA bound markedly less cisplatin than human fetal fibroblast DNA. Three cell lines were tested with rHuIFN-alpha and rHuIFN-gamma on their own or rHuIFN-alpha+rHuIFN-gamma. They were consistently sensitive to rHuIFN-alpha, but the sensitivity to rHuIFN-gamma varied with the cell lines. Finally, we tested two cell lines with the drugs singly and in combination, together with 0.01 micrograms/ml each of rHuIFN-alpha and rHuIFN-gamma.(ABSTRACT TRUNCATED AT 250 WORDS)

p53 and Kirsten-ras mutations in human mesothelioma cell lines

Twenty cell lines from 17 individuals with malignant mesothelioma have been examined for p53 alterations by direct sequencing of genomic DNA, by evaluation of mRNA expression levels, and by immunocytochemical analysis of p53 protein expression in comparison with normal human pleural mesothelial cells. The results of this study show p53 abnormalities in cell lines from 3 individuals. These include 2 point mutations and one null cell line. Interestingly, while both cell lines with point mutations exhibit high levels of p53 protein, normal mesothelial cells as well as 12 of the mesotheliomas evaluated express low but significant levels. In addition, sequencing of K-ras at codons 12, 13, and 61 reveals wild-type sequence in all 20 mesothelioma cell lines. The capacity to induce tumors in athymic nude mice did not correlate with the presence of a p53 mutation or elevated p53 protein levels. These data suggest that neither p53 alteration nor K-ras activation constitutes a critical step in the development of human mesothelioma.

Genotoxic effects and chemical compositions of four creosotes

Four creosotes used in Finland for impregnating wood were tested in the Ames Salmonella test, the SCE test and the SOS chromotest. Compounds volatile at 37 degrees C were assayed using the taped plate testing protocol. The creosotes were fractionated according to their natural boiling ranges and the fractions were tested in the Ames Salmonella assay. Chemical compositions of creosotes and fractions were determined by high resolution gas chromatography/mass spectrophotometry techniques and by reversed phase high performance liquid chromatography. Mutagenic activities were shown to reside in fractions having the highest boiling point ranges (greater than 290 degrees C). The concentrations of mutagenic polycyclic aromatic hydrocarbons in creosotes and in some of their corresponding distillation fractions, when compared with mutagenic activities, indicated synergistic or antagonistic interactions.

Malignant mesothelioma: the antiproliferative effect of cytokine combinations on three human mesothelioma cell lines

Tumour necrosis factor (TNF) combined with gamma-interferon (IFN gamma) is known to have antiproliferative effects on many tumour cells, both in vitro and in vivo. We investigated whether human mesothelioma cells would respond in a similar way. Mesothelioma cell lines established from primary tumours did not respond significantly in vitro to either TNF or IFN gamma alone but were inhibited by combinations of TNF and IFN gamma at concentrations as low as 5 ng/ml. In contrast, a mesothelioma cell line established from a metastatic tumour was sensitive to IFN gamma both alone and in combination with TNF but not to TNF alone. We also looked at the responses of one primary tumour cell line and the metastatic tumour cell line to alpha-interferon (IFN alpha) both alone and in combination with TNF. Both cell lines were sensitive to IFN alpha but were more sensitive to the THF/IFN alpha combination. We conclude that these low dose combinations of cytokines are worth further investigation in the development of mesothelioma therapy.

An inter-Nordic prospective study on cytogenetic endpoints and cancer risk. Nordic Study Group on the Health Risk of Chromosome Damage

To investigate whether high rates of chromosomal aberrations (CAs), sister chromatid exchange (SCE), or micronuclei(MN) in peripheral lymphocytes indicate an increased risk for subsequent cancer, a prospective cohort study of 2,969 subjects cytogenetically examined between 1970 and 1988 in four Swedish, two Finnish, and two Norwegian laboratories was initiated. To standardize for the interlaboratory variation, the results of the three cytogenetic endpoints were trichotomized for each laboratory into "low" (1st to 33rd percentile), "medium" (34th to 66th percentile), and "high" (67th to 100th percentile]. Thirty-four cancers had been diagnosed in the cohort during the observation period (1970 to 1985). The point-estimates of the standardized morbidity ratio (SMR) in the three CA strata were 90, 92, and 180, respectively. This trend for a positive association was not statistically significant (p = 0.06). There was no significant trend between SMR and the trichotomized rates of SCE. In the subcohort examined for MN only two cases of cancer had been diagnosed until now. If subjects with "high" frequencies of CA or SCE have a two-fold (or greater) risk of developing cancer as compared with individuals who have "medium" or "low" frequencies, we estimate that there is a likelihood of 80% and 70%, respectively, that this will be detectable as significant (p less than or equal to 0.05) differences after a further follow-up period of 5 years. Weaker associations between cancer risk and the cytogenetic endpoints would not be possible to evaluate until even later follow-ups.

Effects of commercial chlorophenolate, 2,3,7,8-TCDD, and pure phenoxyacetic acids on hepatic peroxisome proliferation, xenobiotic metabolism and sister chromatid exchange in the rat

The induction of hepatic peroxisome proliferation and drug metabolizing enzymes and of sister chromatid exchange (SCE) in lymphocytes was studied in male Han/Wistar rats after exposing them for 2 weeks to a commercial chlorophenolate formulation (Ky-5) (100 mg/kg/day), to 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD; 0.05-5 micrograms/kg/wk) and to the pure phenoxyacetic acids, 2,4-dichlorophenoxyacetic acid (2,4-D; 100 mg/kg/day) and 2-chloro-4-methylphenoxyacetic acid (MCPA; 100 mg/kg/day). The chlorophenolate formulation and pure 2,4-D and MCPA caused significant increases in the number of peroxisomes in liver cells, although the average size of peroxisomes was not affected, whereas the effect of even the highest dose of 2,3,7,8-TCDD remained small. This finding indicates that dioxin impurities do not account for the peroxisome proliferation induced by chlorophenolate. The relative weight of the liver increased significantly in rats treated with the chlorophenolate formulation and with 2,3,7,8-TCDD (5.0 and 0.5 micrograms/kg). The pattern of induction of xenobiotic metabolizing enzymes showed some differences between chlorophenolate treatment and 2,3,7,8-TCDD treatment. Furthermore, the effects of pure phenoxyacetic acids were different from that seen with chlorophenolate and 2,3,7,8-TCDD. The highest dose of 2,3,7,8-TCDD increased the frequency of SCE in circulating lymphocytes slightly, but significantly.