Mutation Research Letters最新文献

N-Nitrosodialkylamines are promutagens and proclastogens, requiring metabolic activation for their actions. Previously, we showed that direct-acting bacterial mutagens can be formed from N-nitrosodialkylamines on exposure to near-UV. We have now found that N-nitrosodialkylamines with near-UV irradiation are clastogenic to Chinese hamster lung cells. When the cells in culture were irradiated with near-UV for 3 h in the presence of N-nitrosodimethylamine (NDMA), N-nitrosodiethylamine (NDEA), N-nitrosopyrrolidine (NPYR), N-nitrosopiperidine (NPIP) or N-nitrosomorpholine (NMOR), and then further incubated for a total period of 24 h with the N-nitrosodialkylamines, chromosome aberrations were induced. Neither the N-nitrosodialkylamine nor near-UV alone were clastogenic. Severe clastogenicity (> 50% of cells examined showing aberrations) was observed for 0.5 mM NDEA, NPYR and NPIP. The order of the clastogenic activity was NDEA, NPYR > NPIP, NDMA > NMOR. This order differed from that of bacterial mutagenicity previously reported for these N-nitrosodialkylamines plus near-UV, in which NMOR gave the strongest activity. The chromosome aberrations induced by the NPYR and NDEA plus near-UV in CHL-cells were inhibited by superoxide dismutase, glutathione and l-cysteine. Dimethylsulfoxide or d-mannitol, scavengers of hydroxy radical, and l-histidine, a scavenger of singlet oxygen, were ineffective. These results suggest that superoxide formed by a synergistic action of an N-nitrosodialkylamine and near-UV is the cause of the chromosome aberrations observed, an assumption consistent with the known ability of superoxide to cleave DNA.

DNA alterations induced in V79 cells treated with UV light or methyl-nitro-nitrosoguanidine were analyzed by the mutagenicity test at the hprt locus and by DNA fingerprint analysis. Treated and control cells were seeded in the presence or absence of 6-thioguanine to determine mutant frequency and cell survival. From clonal cultures of the same cell populations we isolated a number of clones and grew them up individually to obtain appropriate amounts of DNA. High molecular weight DNA was digested with HinfI or HaeIII and hybridized with ³²P-labelled 33.15 multilocus probe. The induction of 6-thioguanine resistant cells depended on the mutagen does. The highest value of mutant frequency obtained was 7475 × 10⁻⁶ (MNNG, 27μM), corresponding to 0.7 percent of clonable cells. DNA fingerprint analysis carried out on the same treated cells showed that DNA rearrangements occurred at minisatellites much more frequently than in transcribed sequences. UV irradiation produced the highest frequency of variation, modifying minisatellite patterns in about 50 percent of the analyzed clones.

The reversion of frequency of an adenovirus 2 temperature-sensitive growth mutant treated with different doses of nitrous acid was determined after infection of control. UV-irradiated, cadmium chloride and zinc chloride treated HeLa cells. No enhanced mutagenesis was observed.

Styrene is converted into styrene-7,8-oxide in human lymphocyte cultures, in a reaction probably mediated by oxyhemoglobin. As a consequence, styrene induces sister-chromatid exchanges (SCEs) in whole-blood lymphocyte cultures without exogenous metabolic activation systems. Another metabolic pathway that could be involved in the metabolism of styrene is cooxidation by prostaglandin-endoperoxide synthase (PES). To study the role of PES in the metabolism of styrene, human whole-blood lymphocyte cultures were treated for the entire culture time of 72 h with styrene (0.5 and 1 mM) or styrene-7,8-oxide (50 and 100 μM), in the presence and absence of 75 or 150 μM indomethacin (an inhibitor of PES) and arachidonic acid (substrate of PES). Indomethacin potentiated SCE induction by both styrene and styrene-7,8-oxide; a slight but statistically significant enhancement (16–32%; p < 0.05−0p < 0.001) was observed in all treatments with styrene and at 150 μM indomethacin in the case of styrene-7,8-oxide. At 150 μM, arachidonic acid induced a 15–20% suppression (p < 0.01) in SCE induction by both styrene (1 mM only) and styrene-7,8-oxide (100 μM only). Indomethacin or arachidonic acid did not alone influence the frequency of SCEs. The results suggest that PES acts as an inactivation route for styrene and styrene-7,8-oxide in human whole-blood lymphocyte cultures, possibly through PES-mediated binding to glutathione.

The DNA damaging and cell proliferative activity of 1-methyl-1-nitrosourea (MNU), a glandular stomach carcinogen, was studied in the pyloric mucosa of male F344 rats after administration by gastric tube. DNA damage was measured with unscheduled DNA synthesis (UDS) and DNA single strand scission as markers, while cell proliferation was measured with replicative DNA synthesis (RDS) and ornithine decarboxylase (ODC) as markers. MNU at doses of 30 and 60 mg/kg body wt and 80 min after administration dose-dependently induced UDS (49 and 79 (0 dose, 19) dpm/μg DNA) measured by liquid scintillation counting in the presence of hydroxyurea (an inhibitor of RDS). RDS (DNA synthesis in the absence of hydroxyurea; 239 dpm/μg DNA at 0 dose) did not increase at that time. MNU at doses of 10 and 60 mg/kg body wt and 2 h after administration dose-dependently induced DNA single strand scission of 8.2 and 43.5 (0 dose, 1.4) elution rate constant (×10⁻³/ml). MNU at doses of 30 and 60 mg/kg body wt and 24 h after administration dose-dependently induced an increase in RDS (1362 and 2393 (0 dose, 682) dpm/μg DNA). MNU at doses of 60, 90 and 120 mg/kg body wt and 24 h after administration dose-dependently induced an increase in ODC activity (22.0, 29.4 and 38.4 (0 dose, 6.3) p mol CO₂/30 min/mg protein). These results suggest that MNU has possible tumor initiating activity (UDS and DNA single strand scission) and tumor promoting activity (RDS and ODC) in rat stomach mucosa.

3-Chloro-4-(dichloromethyl)-5-hydroxy-2(5H)-furanone (MX is a potent direct-acting mutagen found in chlorinated drinking water. In the present study, the induction of DNA strand breaks and apurinic/apyrimidinic (AP) sites by MX in supercoiled PM2 DNA was examined using exonuclease III, which specifically cleaves the DNA at AP sites. The results showed that MX induced AP sites in great excess of direct strand breaks. In view of the known mutagenicity of AP sites, these results provide insight into the mechanism of MX-induced mutagenesis.

Fluorescence in situ hybridization with chromosome-specific DNA probes is being increasingly utilized for the detection of chromosome aberrations induced in vitro and in vivo by chemical and physical agents. Although potentially a powerful technique, FISH studies for aneupoloidy can be heavily influenced by cellular phenomena and hybridization artifacts which make the performance and interpretation of the results difficult. As a consequence, frequently hyperdiploid frequencies are reported in the literature which are substantially higher than one would expect based upon frequencies seen in conventional metaphase analyses. In this article, a number of the potential pitfalls that we have encountered while performing FISH analyses for aneuploidy are discussed and their potential impact on the observed hybridization frequencies is described. After considering these factors, the frequencies of lymphocyte nuclei containing 3 and 4 chromosome copies are compared between metaphase values obtained from published human population studies and interphase values obtained from similar studies using FISH. It is concluded that by using caution in the evaluation of slides, interphase studies using FISH to detect hyperdiploidy and polyploidy can provide estimates of numerical alterations which closely reflect those seen during metaphase analysis using either FISH or conventional approaches. However, due to the inability of interphase analysis to distinguish hyperdiploidy from polyploidy as well as other potential problems, frequencies of aneuploid nuclei obtained using single label FISH should only be considered approximations of absolute frequencies. For additional accuracy, multi-color FISH with two or more different probes shold be performed.

The chlorination by-products chloral hydrate and chloropierine were assayed for genotoxicity in three short-term tests. Chloropicrine was 100-fold more potent than chloral in inducing mutations in strain TA100 of S. typhimurium (fluctuation test) and, at variance with chloral, was positive in the SOS chromotest using strain PQ37 of E. coli. On the other hand, only chloral caused a significant increase in the frequency of micronucleated erythrocytes following in vivo exposure of the amphibian Pleurodeles waltl newt larvae.

The rate of ribosomal gene activity was evaluated by silver straining of the Nucleolus Organisers (NOs) in cultured CHO-K1 cells after a 12 h pulse with two demethylating agents (L-ethionine and 5-azacytidine). Silver staining of the NOs was measured every 24 h, from 24 up to 110 h after seeding. The purpose was to test the hypothesis that drug-induced demethylation is associated to heritable modifications of rDNA activity. Ribosomal gene activity was shown to be significantly increased by both agents. The increase persisted throughout the experiments, thereby suggesting the heritability of this epigenetic modification. The analysis of heritable DNA damage or modification is an important task in studying the risk of cancer onset and the mechanisms of cancer induction. In these studies two main results were obtained; (i) heritable DNA variations can be induced by both mutational and epigenetic changes; (ii) the modified end-point was not negatively selected.