A Very Fast and Momentum-conserving Tree Code.

The tree code for the approximate evaluation of gravitational forces is extended and substantially accelerated by including mutual cell-cell interactions. These are computed by a Taylor series in Cartesian coordinates and in a completely symmetric fashion, such that Newton's third law is satisfied by construction and that therefore momentum is exactly conserved. The computational effort is further reduced by exploiting the mutual symmetry of the interactions. For typical astrophysical problems with N=105 and at the same level of accuracy, the new code is about 4 times faster than the tree code. For large N, the computational costs are found to scale almost linearly with N, which can also be supported by a theoretical argument, and the advantage over the tree code increases with ever larger N.

mRNA expression patterns in different stages of asbestos-induced carcinogenesis in rats.

Human malignant mesotheliomas are induced almost exclusively by fibrous dusts. The nature of interactions between fibers and target cells, and the molecular mechanisms leading to tumorigenesis, are not yet understood. Here, the mRNA expression patterns at different stages of asbestos-induced carcinogenesis in rats were monitored by suppression subtractive hybridization (SSH) and array assay. Several genes were upregulated in pretumorous tissues from asbestos-treated rats, in asbestos-induced tumors and in cells treated with asbestos in vitro. The upregulation of the proto-oncogene c-myc, fra-1 and egfr in fiber-induced carcinogenesis was demonstrated at different stages of carcinogenesis. A possible role of Fra-1 as one of the dimeric proteins generating the AP-1 transcription factor was substantiated by its dose-dependent expression in mesothelial cells treated with asbestos in vitro. The upregulation of osteopontin (an extracellular matrix protein) and of zyxin and integrin-linked kinase (intracellular proteins associated with the focal adhesion contact), indicate that fibers may affect integrin-linked signal transduction and extracellular matrix proteins.

DNA fingerprint analysis reveals differences in mutational patterns in experimentally induced rat peritoneal tumors, depending on the type of environmental mutagen.

We performed tumor DNA fingerprint analysis using the synthetic minisatellite probe S3315x2 based on the 33.15-repeat unit. The aim of the study was to investigate fingerprinting patterns of peritoneal tumors induced experimentally in Wistar rats by two carcinogens with unknown mechanism of action (crocidolite asbestos and nickel powder) and, as a positive control, benzo[a]pyrene. The carcinogens were administered intraperitoneally into rats. The banding patterns obtained with DNA from 71 peritoneal tumors were compared to the corresponding normal tissues. DNA derived from peritoneal tumors induced by the three carcinogens differed with respect to mutation frequencies and mutation patterns. The mutation frequencies in these tumors, revealed by DNA fingerprinting, were 18.2% for benzo[a]pyrene, 14.8% for crocidolite asbestos, and 40.9% for nickel powder. The alterations detected in the banding pattern of benzo[a]pyrene-induced peritoneal tumors were exclusively additional bands. On the contrary, in the DNA from asbestos-induced peritoneal tumors, only deletions of bands were observed on the autoradiographs. In the DNA from nickel-induced peritoneal tumors, both types of mutations occurred. The different mutation frequencies and mutation patterns appear to discriminate between benzo[a]pyrene, crocidolite asbestos, and nickel powder, and may be related to the mechanisms of action of these compounds.

Fiber-specific molecular features of tumors induced in rat peritoneum.

Molecular markers such as mutational spectra or mRNA expression patterns may give some indication of the mechanisms of carcinogenesis induced by fibers and other carcinogens. In our study, tumors were induced by application of crocidolite asbestos or benzo[a]pyrene (B[a]P) to rat peritoneum. DNA and RNA of these tumors were subjected to analysis of point mutations and to investigation of mRNA expression patterns. With both assays we found typical features depending on the type of carcinogen applied. The analysis of point mutations in the tumor suppressor gene p53 revealed mutations in the B[a]P-induced tumors. However, in the tumors induced by crocidolite asbestos that were of the same tumor type as those induced by B[a]P, mutations in p53 were not detectable. Every mutation detected on the DNA level causes an amino acid substitution within one of the functional domains of the tumor suppressor protein. Therefore, these mutations seem to be of biological relevance for tumor progression and indicate a difference in the carcinogenesis regarding the type of the carcinogenic substance. An additional specificity of crocidolite-induced tumors was detectable by analyzing the mRNA expression of the tumor suppressor gene WT1, which is known to be expressed in human mesothelial and mesothelioma cells. A relatively high amount of WT1 mRNA was measured by quantitative competitive reverse transcription-polymerase using RNA extracted from crocidolite-induced tumors. However, WT1 seems to be expressed on a rather low level in tumors induced by B[a]P.

P53 mutations in tumours induced by intraperitoneal injection of crocidolite asbestos and benzo[a]pyrene in rats.

Mutation analysis of the tumour suppressor gene p53 in tumours induced in the peritoneal cavity of rats revealed differences in the mutational pattern with regard to the carcinogenic substances applied. In tumours induced by benzo[a]pyrene a considerable amount of p53 mutations resulting in an altered protein structure could be detected. For the development of these tumours an escape from the p53 mediated cell cycle control can be assumed. However, in tumours of the same tumour type induced by crocidolite asbestos no mutations could be observed. Since there were even no spontaneous p53 mutations detectable in this tumour group, it is obvious that in these tumours the escape from cell cycle control does not take place via inactivation of p53. Therefore, it is concluded that the molecular mechanisms of carcinogenesis and tumour development in this tumour type depend on the type of carcinogen applied.

Sensitive gas chromatographic method for determination of mercapturic acids in human urine.

A method was developed for sensitive determination of the specific benzene metabolite S-phenylmercapturic acid and the corresponding toluene metabolite S-benzylmercapturic acid in human urine for non-occupational and occupational exposure. The sample preparation procedure consists of liquid extraction of urine samples followed by precolumn derivatization and a clean-up by normal-phase HPLC. Determination of analytes occurs by gas chromatography with electron-capture detection. With this highly sensitive method (detection limits 60 and 65 ng/l, respectively) urinary S-phenylmercapturic and S-benzylmercapturic acid concentrations for non-occupationally exposed persons (e.g. non-smokers) can be measured precisely in one chromatographic run. Validation of the method occurred by comparison with a HPLC method we have published recently.

Sensitive determination of the benzene metabolite S-phenylmercapturic acid in urine by high-performance liquid chromatography with fluorescence detection.

A method was developed for the determination of the specific benzene metabolite S-phenylmercapturic acid in urine. The analyte is determined by HPLC with fluorescence detection after solid-phase extraction of urine with C18 material and hydrolysis followed by precolumn derivatization. The samples are separate by a column-switching method with a dual column system. As the method is highly sensitive (detection limit ca. 1 microgram/l), urinary S-phenylmercapturic acid concentrations for non-exposed persons (e.g., non-smokers) can also be measured precisely.

A study on urinary thioethers by detecting N-acetylcysteine and thiophenol after alkaline hydrolysis.

A method is described for the selective determination of thiol compounds liberated by alkaline hydrolysis of urine. It is based on the procedure described by Newton et al. Two thiol compounds were detected selectively: N-acetylcysteine and thiophenol. The following results were obtained: 1. On alkaline hydrolysis (at room temperature) among other thiols N-acetylcysteine is released. The amount of NAC increases after administration to rats of compounds, which directly or after metabolisation are bound by glutathione conjugation, such as diethylmaleate. 2. In these cases the amount of total thiols and NAC released by alkaline hydrolysis are closely related to each other. 3. Monitoring urines of smokers and non-smokers revealed a significant difference between non-smokers and smokers of the released NAC. So it may be concluded that exposure to certain electrophilic agents reacting with GSH increases the NAC as well as total thiols detected after alkaline hydrolysis of urine. 2. On alkaline hydrolysis (at 95 degrees C) thiophenol can be detected. Evidence is presented that thiophenol is derived from the benzene metabolite S-phenyl-N-acetyl-cysteine: 1. after treatment with radioactive benzene of rats the peak of the thiophenol-derivative elutes together with a radioactive peak; 2. inhalation of benzene increases the peak of the thiophenol-derivative in the urine of a human volunteer. 3. The amount of thiophenol detected by the described method in the urines of smokers is increased in comparison to non-smokers. This is in accordance with the observation that the benzene concentration is elevated in the blood of smokers.

[The correlation between the excretion of thioethers and their mutagenic activity in urine in workers of different occupational groups]. / Untersuchungen über die Korrelation zwischen Ausscheidung von Thioethern und mutagener Aktivität im Urin bei Arbeitnehmern von verschiedenen Berufsgruppen.

Electrophilic substances can be inactivated by binding to glutathione or other SH-bearing molecules leading to urinary excretion of mercapturic acids or other thioether products. The mutagenic activity in urine as detected by mutagenicity assay (Ames-Test) is caused by genotoxic agents or their electrophilic metabolites. Therefore, it has been suggested that an effective protection by the glutathione system may diminish the urinary excretion of mutagens after exposure to genotoxicants. We determined the thioether concentration and mutagenic activity in urine samples of exposed workers (20 workers of a repair shop exposed to car exhaust, 35 workers of several dry cleaning shops exposed to halogenated hydrocarbons and 26 workers of a metal processing factory exposed to polycyclic aromatic hydrocarbons). We performed microfluctuation assay using Salmonella typhimurium TA98 and applied a method for the determination of urinary thioethers based on liquid chromatographic quantification of N-acetylcysteine. Our results show a linear correlation between the two exposure parameters which is independent on exposure conditions described above.

[Cellular and molecular biological aspects in environmental toxicology]. / Zelluläre und molekularbiologische Aspekte in der Umwelttoxikologie.

Health effects of substances in the environment are considered from the viewpoint of cellular and molecular biology. There are nephrotoxic effects of cadmium to be discussed as well as mechanisms of carcinogenesis and neurotoxicity. Finally, the influences of noxious substances on lung clearance and immune reactions are demonstrated.

Pulmonary changes in the rat following low phosgene exposure.

Minimal inhalation doses (or concentrations) of phosgene necessary for the production of changes within the blood-air barrier were determined in rats. At least 50 ppm.min (5 ppm X 10 min) was necessary for the production of alveolar oedema (the minimal effective phosgene concentration being 5 ppm). While the smallest phosgene dose to produce an increase in pulmonary lavage protein content was also 50 ppm.min and while the smallest phosgene dose to produce widening of pulmonary interstices was 25 ppm.min, there was no phosgene threshold concentration (down to 0.1 ppm) for these two latter parameters, which are assumed to be indicators of physiological compensatory mechanisms within the blood-air barrier. The primary localisation of pulmonary damage seemed to depend on the concentration of phosgene used: at low concentrations (0.1-2.5 ppm) the changes were primarily located at the transition from terminal bronchioles to the alveolar ducts; at higher concentrations (5 ppm) damage to the alveolar pneumocytes (type I) was more conspicuous.

[Comparative study of the behavior of particulate emissions from diesel and gasoline engines in animal lungs: elimination rate and induction of benzo(a)pyrene hydroxylase and ethoxycoumarin de-ethylase]. / Vergleichende Untersuchung zum Verhalten von partikulären Diesel- und Ottomotoremissionen in Tierlungen: Eliminationsrate und Induktion der Benzo(a)pyren Hydroxylase und Ethoxycumarin Deethylase.

The emitted particulates of five diesel-engined and two gasoline-engined passenger cars were investigated for the elimination rate from hamster lungs after intratracheal instillation. In addition extracts of these particulates were studied for their influence on the mixed function oxidase activity (MFO; Benzo(a)pyrene Hydroxylase, Ethoxycoumarine Deethylase). Differences in the elimination rates of diesel soot and particulates from gasoline engines were not found. Compared with the blanc the extracts of diesel soot from two vehicles proved to give a moderate increase of the MFO activity, but a significant difference to the blanc was observed with the extracts of the gasoline engines. It should be mentioned that the effects were studied without taking into account the quantitative relations of the emissions in the ambient air. However, the amounts of particulates were extremely high in relation to the natural conditions. In the limits of our test model there is no indication of a higher toxicity of diesel-emissions.

The influence of various factors on the methylation of DNA by the oesophageal carcinogen N-nitrosomethylbenzylamine. I. The importance of alcohol.

Alcohol appears to be a predisposing factor for the high incidence of oesophageal cancer in Western France. Therefore, we have investigated the influence of ethanol on the alkylation of DNA by a carcinogen which reacts selectively with oesophageal tissue. Female Wistar rats (approximately 80 g) received a single i.v. injection of N-nitroso-[methyl-14C]benzylamine (2.5 mg/kg body weight). Four hours after injection of the carcinogen, methylation of purine bases in the DNA isolated from various organs was measured. We found that pretreating the rats with alcohol (45-69 micrograms/day/kg) for a period of 3-4 weeks leads to an enhancement of DNA methylation in the oesophagus. An increased amount of methylated purine base was also noted in lung DNA. In contrast, a reduction in the methylation rate of liver DNA was observed.

[Studies on the induction by extracts from airborne particulates of benzo(a)pyrene hydroxylase and the binding of benzo(a)pyrene to DNA in the rat lung in vivo after pertracheal administration (author's transl)]. / Untersuchungen über die Induktion der Benzo(a)pyren Hydroxylase und die Binding von Benzo(a)pyren an die DNA der Lunge in vivo unter der Einwirkung von Schwebstoffextrakt nach pertrachealer Applikation.

A method is described for the administration of suspended material into the rat lung. The rat is narcotized by CO2/air, the trachea is punctured and the suspension is sucked into the lung by the inhaled air (pertracheal administration, p. t. a.). BaP administered by this method is eliminated from the lung rapidly, while metabolites persist for a longer period. The radioactivity detected in the blood can be attributed predominantly to metabolites, a small fraction is unmetabolized benzo(a)pyrene. The activity of benzo(a)pyrene hydroxylase is induced in the lung after p. t. a. of extracts from airborne particulate matter. The activity increases depending on the dose until a plateau of activity is reached at high doses. Pertracheally administered BaP is bound to DNA of the lung. Pretreatment with extracts p.t.a. enhances the binding. After enzymatic digestion of DNA BaP-nucleoside adducts are detected by HPLC. According to data published in the literature to adducts are supposed to be derived from BaP-phenols and BaP-diolepoxides. It is concluded tht the components of airborne particulates can modify the activity of metabolizing enzymes and increase the rate of formation of adducts in the lung in vivo.

[Studies on the mutagenic effect of extracts derived from airborne particulates within one year in differently burdened areas using the Ames test (author's transl)]. / Untersuchungen zur mutagenen Wirkung von Schwebstoffextrakten unterschiedlich belasteter Gebiete im Ames-Test während eines Jahres.

Suspended matter was collected at three sampling sites with different air pollution levels (DU = Duisburg, mining, iron and steel industry; D = Düsseldorf, residential city; K = Krahm, rural district) in 1978. The seasonal variations of the mutagenicity of extracts from samples collected monthly were assayed by the Ames-test. Th results are presented as the number of revertants related to air volume, weight of the suspended matter, weight of the dried extract and to the amount of benzo(a)pyrene in the extract. The mutagenicity varies according to the benzo(a)pyrene concentration in the atmosphere: the highest values are found during the winter, the lowest during the summer. When the mutagenicity is based on the benzo(a)pyrene content, it remains nearly constant throughout the year (sampling site DU) or rises in the summer (sampling sites D and K). These results indicate that at least in heavily polluted areas the larger part of the mutagens may originate from the same sources as benzo(a)pyrene (e.g. incomplete combustion). The direct (assayed without activating system) mutagenicity of the extracts is somewhat higher in winter than in summer. However, these differences are low or missing, when the mutagenicity is expressed as number of revertants per weight of suspended matter or dried extract. The mutagenicity reaches a maximum in summer, provided, the number of revertants is related to the benzo(a)pyrene concentration. These results indicate that the direct acting mutagens present in the air originate from other sources than that of benzo(a)pyrene (e.g. automobile exhaust). The mean values of the mutagenicity related to the number of revertants per dry-weight and weight of suspended matter do not differ among the three sampling sites. It can be assumed that the composition of the particulate matter may be similar with respect to mutagens regardless the level of pollution.

[Studies on the activity of the aryl hydrocarbon hydroxylase and metabolism of benzo(a)pyrene in cell strains and cell lines used for testing cytotoxic and transforming ability of foreign compounds (author's transl)]. / Untersuchungen über die Aktivität der Aryl-hydrokarbon-Hydroxylase und den Benzo(a)pyrenabbau in Zellstämmen und Zellinien, die für Zytotoxizitäts- und Transformationstests verwendet werden.

The activity of the AHH and the formation of polar metabolites from BaP was examined in several cell strains and lines, which are used for testing cytotoxic and transforming activity of environmental agents, the highest activity of the AHH and the highest capacity to metabolize BaP was found in hamster kidney cells. Much lower values were measured in kidney cells from Cercopithecus aethiops, BHK21/C13 cells, and SV-40 transformed hamster kidney cells (14-1b). The activity of AHH was inducible by BA in all these cells. However no correlation could be established between the increase in AHH activity and the formation of polar metabolites. In cells derived from a human bronchial carcinoma (E-14), a very low BaP metabolism was detectable which increased 3-fold after exposure (o BA. No BaP metabolism could be detected in HeLa cells.

Effect of NO2 and SO2 inhalation on benzo(a)pyrene metabolism in rat lung.

Male Wistar rats were continuously exposed to NO2 (14.4 ppm), SO2 (46.5 ppm) and to a mixture of both gases and their effect on lung microsomal aryl hydrocarbon (benzo(a)pyrene) hydroxylase (AHH) activity was determined. The pre-exposed animals were administered methylcholanthrene (MC) to investigate the exposure effect on enzyme inducibility and pattern of B(a)P metabolites. NO2 significantly increased AHH activity but no marked change was noted with SO2. Induction of AHH by MC was markedly inhibited by SO2, only slightly by mixture of NO2-SO2 but not with NO2 alone.

The mutagenicity of airborne particulate pollutants.

The mutagenic effect of extracts derived from airborne particulate matter was investigated with the Ames-test. The whole extract proved to be distinctly mutagenic. To find out whether the content of polycyclic aromatic hydrocarbons may be responsible for the mutagenic effect, the extract was split into several fractions. The fraction containing the polycyclic compounds showed the lowest mutagenic rate that was enzymatically mediated. The other fractions required metabolic activation for some of their components, but some components were active without metabolic activation.