Mutation Research\/environmental Mutagenesis and Related Subjects最新文献

Chromosome analysis of peripheral lymphocytes from two Norwegian populations (44 reindeer herding South samis from Røros and Snåsa, 12 sheep farmers from Valdres) exposed to fallout from the Chernobyl accident were made. The doses from caesium through the years 1987–1991 were calculated based on whole-body measurement of ¹³⁴Cs and ¹³⁷Cs giving a total cumulative mean internal dose of 5.54 mSv for the total group of 56 persons. Chromosome aberrations were within the normal range when compared with historical controls with the exception of dicentrics (0.3% per cell, which is a 10-fold increase) and rings (0.07% per cell). A dose-dependent increase in dicentrics and rings based on caesium exposure was not observed.

Asbestos fibers are widespread environmental carcinogens whose mutagenicity is now established. Nonetheless, the molecular nature of these mutations and the mechanisms by which they accelerate carcinogenesis remain poorly understood. We have assessed the ability of asbestos fibers to promote homologous recombination, a potent mechanism for generating intrachromosomal rearrangements, such as deletions, and mitotic recombination. For this, we have developed a new assay which determines the extent to which a marker gene present in DNA introduced by asbestos can recombine with homologous genes residing in a transfected cell. We have demonstrated that Calidria chrysotile fibers are mutagenic and are able to mediate transfection of molecularly marked mutant lacI genes in a manner that results in their preferential recombination with homologous wild-type genes in the transfected cell. Asbestos induced recombination events may play a significant role in asbestos mutagenesis and carcinogenesis, and promotion of recombination may underlie the well-recognized synergy of asbestos with other carcinogens.

We present a plasmid rescue from transgenic Drosophila to study spontaneous and mutagen-induced mutations in vivo. Transgenic Drosophila lines were established by tranformation with a shuttle vector containing the bacterial lacZ gene as a target for mutagenesis. The target gene cen be recovered into bacteria by restriction endonuclease treatment of total genomic DNA, followed by ligation on the recircularized shuttle vectors. The resulting circular plasmids are then transformed back into E. coli lacZ⁻ mutants, where the activity of the lacZ genes is scored on the induction substrate X-Gal. The number of inactivated versus intact lacZ genes directly indicates the mutation frequency. By the described target gene rescue procedure up to 5000 lacZ gene copies can be rescued from one fly routinely. Spontaneous background mutation rates using this system are 2.6±0.6×10⁻⁴. Treatment of larvae with ethylnitrosourea (ENU) resulted in a dose-dependent increase of the mutation frequency to 4.8±0.6×10⁻⁴ for 0.5 mM and 6.9±1.2×10⁻⁴ for 1 mM ENU, respectively.

Four isolates, A₁, C₁, D₃, and F₂, from the ethanol extract of the green leaves of Plumeria acuminata Ait. showed antimutagenic activity. The antimutagens were isolated from he bioactive hexane and carbon tetrachloride fractions

Four isolates, A₁, C₁, D₃, and F₂, from the ethanol extract of the green leaves of Plumeria acuminata Ait. showed antimutagenic activity. The antimutagens were isolated from the bioactive hexane and carbon tetrachloride fractions following a bioactivity-directed fractionation scheme and using the micronucleus test to monitor the antimutagenic activities. Structure elucidation studies indicated that C₁ is stigmast-7-enol [1], D₃ is lupeol carboxylic acid [2] and F₂ is ursolic acid [3]. The structure of A₁ was not fully elucidated but MS data suggested that it contained a long hydrocarbon chain. At a dosage of 2 mg isolate/25 g mouse, A₁ reduced the number of micronucleated polychromatic erythrocytes (MPCE) induced by the mutagen, mitomycin C, by 75%, C₁ by 80%, D₃ by 57%, and F₂ by 76%. Compound A₂ was also isolated but was found inactive. Its structure was identified to be lupeol acetate [4].

In the present study, compared to other cytogenetic methods, we measured the number of aneuploid cells directly by analyzing anomalies of the mitotic spindle. Qualitative and quantitative abnormalities of the mitotic spindle apparatus in transformed and non-transformed cell lines in vitro were classified. We treated the different cell lines with well known aneugenic agents as Benomyl and Griseofulvin and investigated the mitotic spindle under different experimental conditions. The spindle apparatus was stained by indirect immunofluorescence and the chromatin was counterstained by fluorescent dyes. The mitotic spindle showed a great sensitivity to the aneuploidy-inducing substances used in our experiments. The spindle-disturbing effect of the tested substances was demonstrated to be dose-dependent. The morphological alterations appeared to be independent of the aneuploidy-inducing test substance used, but showed a relation to the dose and length of treatment. Thus, the analysis of the mitotic spindle may be a useful screening parameter for the detection of aneuploidy-inducing substances and further investigations will provide additional results to specific parameters.

The induction of sister chromatid exchanges (SCEs) by a 48-h treatment with 3,4-epoxybutane-1,2-diol (EBD), a metabolite of 1,3-butadiene, was studied in whole-blood lymphocyte cultures of 22 human donors with known genotypes of two polymorphic glutathione S-transferases (GSTs), GSTT1 and GSTM1. For both genes, donors representing a homozygous ‘null’ genotype lacking the respective GST gene and isozyme and a ‘positive’ genotype with at least one intact gene and GST activity were included. The mean frequencies of SCE/cell were similar in all genotype groups: GSTT1 null (n = 10) (mean 22.0 for 250 μM and 32.9 for 250 500 μM of EBD), GSTT1 positive (n = 14) (21.3 and 34.6, respectively), GSTM1 null (n = 10) (20.3 and 33.5) and GSTM1 positive donors (n = 15) (20.6 and 34.8). At 500 μM concentration of EBD, the lymphocyte cultures of all donors showed a significantly decreased replication index. No differences in EDB-induced SCEs or in replication index could be associated with the GSTM1 and GSTT1 genotypes either separately or in combination. When SCEs induction by EBD was compared to that of two other known epoxide metabolites of butadiene, 1,2:3,4-diepoxybutane (DEB) was effective at concentrations over two orders of magnitude lower than EBD or 1,2-epoxy-3-butene (MEB). It is concluded that EBD is an efficient inducer of SCE in cultured human lymphocytes, although not quite as effective as MEB and clearly less effective than DEB. Contrary to previous findings with DEB and MEB, the polymorphic GSTM1 and GSTT1 do not appear to be involved in the detoxification of EBD in human lymphocytes.

Alterations in mitotic index and cell cycle kinetics are reported to be dependent on both the culture conditions and the ability of the lymphocytes of each individual to respond to phytohaemagglutinin stimulus. Thus, the frequency of structural chromosome aberrations (CA) could prove to be affected to some degree by these parameters. CA frequency and cell proliferation index (PI) were assessed in a group of healthy subjects after adding colcemid to cultured lymphocytes 3 h (standard) and 22 h (modified) before cell fixation at 48 h. All control cultures treated with colcemid for 22 h consisted exclusively of first metaphases, whereas the proportion of second-division lymphocytes in standard cultures (3 h colcemid) ranged from 4% to 49%. In addition, CA frequencies with and without gaps were always elevated in modified cultures as compared to the standard ones, and the difference between CA percentages obtained with the two methods was found to be significantly related with increasing PI values.