DNA-Methylierung von monohalogenierten Methanen in F-344 Ratten

Monohalogenated methanes (methyl chloride, methyl bromide and methyl iodide) are mutagenic and carcinogenic. The possible mechanism of these effects, DNA methylation, was studied. DNA adducts from orgnas of F344 rats exposed to these chemicals were separated and identified with high performance liquid chromatography (HPLC) and gaschro-matography/massspectrometry (GC/ MS). DNA adducts, 7-methylguanine (7-MeG) and O⁶-Methylguanine(0⁸-MeG), incorporation of¹⁴C into de novo synthesis of nucleobases could be observed in enzymatic DNA hydrolysates by HPLC and determination of the radioactivity in the fractions. The formation of DNA add,ue,ts in the studied organs was only quantitatively different. The formation of O⁶-MeG was further pioved by analysing the acidic hydrolysates using HPLC with non-radioactive O⁶MeG as internal standard. 7-MeG and 3-MeA were identified with GC/MS analysis.     

Intervention study on the influence of reduction of occupational exposure to styrene on sister chromatid exchanges in lymphocytes

An intervention study was performed on 28 workers exposed by inhalation to styrene in the reinforced plastics industry and 20 controls not occupationally exposed to the compound. The workers involved were 14 laminators exposed to a time-weighted average of approximately 40 ppm styrene and 14 formers exposed to an average of about 10 ppm styrene. Ambient air monitoring data and the concentration of mandelic acid in the urine were used for the assessment of exposure. From each subject, peripheral blood lymphocytes were analysed for sister chromatid exchanges (SCEs). In the laminators, the mean SCE frequency was significantly higher than in the controls in both the group of smokers (9.59 ± 0.77 SCEs/cell vs 7.23 ± 1.00 SCEs/cell) and the group of non-smokers (10.25 ± 1.08 SCEs/cell vs 5.98 ± 0.60 SCEs/cell). The mean SCE frequency of the formers (7.42 ± 128 SCEs/cell in smokers) did not differ statistically from the controls (7.23 ± 1.00 SCEs/cell in smokers). No evaluation was made for non-smoking formers since all but one worker in this group were smokers. In order to comply with a lowering of the occupational exposure limit (MAK value) for occupational exposure to styrene in the Federal Republic of Germany from 100 ppm to 20 ppm, considerable technical and hygienic improvements were made at the work site of the laminators. This intervention led to a reduction of average exposure of these workers by inhalation from 40 ppm to approximately 20 ppm. One year after these improvements were made, a second investigation was performed. In all but one of the laminators, the concentration of mandelic acid in urine had dropped considerably. The SCE frequency in blood lymphocytes of the laminators had likewise dropped significantly to 7.74 ± 0.59 SCEs/cell in the non-smokers. In the smokers, it was also lower than on the first occasion (9.02 ± 1.19), yet statistical evaluation was not possible due to insufficient numbers. Overall, the results of the intervention study show that the lowering of the occupational exposure limit for styrene to 20 ppm in Germany was justified and that a reduction of occupational exposure to the chemical has led to a prevention of adverse cytogenetic effects.     

Roles of etheno-DNA adducts in tumorigenicity of olefins

Cyclic DNA adducts bearing an "etheno" structure have been described to occur after interaction with metabolites of halogenated olefins. Extensive work has been published on adducts of vinyl chloride, both in vitro and in vivo. The major DNA adduct of vinyl chloride is 7-(2-oxoethyl)guanine, but an important minor adduct appears to be N2,3-ethenoguanine. Other etheno adducts, i.e., 1, N6-ethenoadenine and 3, N4-ethenocytosine, are readily formed with DNA, vinyl chloride, and a metabolizing system in vitro and with RNA in vivo, but usually are not detected as DNA adducts in vivo. Other compounds that have been studied with respect to possible formation of etheno DNA adducts are vinyl bromide (which is more or less completely analogous to vinyl chloride), acrylonitrile, vinyl acetate and vinyl carbamate. Proposals of possible structures of DNA adducts with an etheno structure have been promutagenic potential of these lesions which may lead to misincorporation of wrong DNA bases in newly synthesized DNA.     

Induced luteolysis in the primate: rapid loss of luteinizing hormone receptors

The molecular mechanisms involved in luteolysis are still unclear in the primate. This study aimed to investigate the effect of induced luteolysis on the ovarian luteinizing hormone (LH) receptor and the steroidogenic enzyme, 3beta-hydroxysteroid dehydrogenase (3beta-HSD) in the marmoset monkey. Luteolysis was induced in the mid-luteal phase either directly by systemic prostaglandin F2alpha (PGF2alpha), or indirectly by LH withdrawal using systemic gonadotrophin releasing hormone antagonist (GnRHant) treatment. The LH receptor was studied by isotopic mRNA in-situ hybridization and in-situ ligand binding and 3beta-HSD expression was studied using isotopic mRNA in-situ hybridization and immunohistochemistry. Induced luteolysis was associated with a reduction in the expression of LH receptor (P < 0.0001) and 3beta-HSD mRNA, closely followed by a reduction in the LH receptor (P < 0.05) and 3beta-HSD protein concentrations within 24 h. There were no differences in the findings whether luteolysis was induced with PGF2alpha or GnRHant. This study shows that disparate mechanisms to induce luteolysis in the primate result in an identical rapid loss of the LH receptor and 3beta-HSD. In conclusion, induced luteolysis leads to rapid loss of the steroidogenic pathway in luteal cells.      

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Adaptation of wild-type measles virus to CD46 receptor usage

Summary.  Vaccine strains of measles virus (MV) use CD46 as receptor and downregulate CD46 from the surface of infected cells. MVs isolated and passaged on B-lymphoid cells (wild-type MVs) seem to use another receptor and do not downregulate CD46. In the present study, we found that isolation of MV on human or marmoset B-lymphoid cells did not alter the MV haemagglutinin (H) protein relative to that in the patient. The wild-type isolates were adapted to the human epithelial HEp-2 cell line or the monkey fibroblast Vero cell line. All HEp-2 cell adapted viruses and 1 out of 4 Vero cell adapted viruses acquired the capacity to use CD46 as receptor, as measured by their ability to infect murine cells expressing human CD46. Adaptation to CD46 receptor usage was coupled to substitution of amino acid 481 of the MV H protein from asparagine to tyrosine but not to CD46 downregulation. The present study demonstrates that CD46 receptor usage can be induced by adaptation of wild-type MV to cells that do not express a wild-type receptor and suggests that a similar mechanism acted on the progenitor viruses of the present MV vaccine strains during their isolation and attenuation. Received June 5, 2000 Accepted October 5, 2000