Mutation Research Letters最新文献

In the small intestine of heterozygous mice (Dlb-1^b/Dlb^a), the Dlb-1 allele results in a stainable epithelium. The mutation or loss of the dominant Dlb-1^b allele in a stem cell results in a non-staining ribbon of cells on a villus of the small intestine. To determine if dominant mutations resulting in the gain of staining — the induction of a Dlb-1^b-like allele — could also be detected, we examined Dlb-1^a homozygous mice (SWR) 2 weeks after a single treatment with 250 mg/kg ethylnitrosourea. Mutations to the dominant allele should appear as brown ribbons on unstained villi. Such ribbons were observed in the treated group but not in controls. The mutant frequency was low compared to the frequency of Dlb-1^a-like mutations reported at the Dlb-1-^b allele in heterozygous mice.

The repair of X-ray-induced DNA damage during G₂ cell-cycle phase has been examined in lines of skin fibroblasts from three patients with trichothiodystrophy (TTD), one with apparently normal and two with defective nucleotide excision repair (NER). These responses are compared with those of five lines from clinically normal controls, lines from xeroderma pigmentosum (XP), Cockayne syndrome (CS), Down syndrome (DS), and ataxia telangiectasia (AT) patients. Chromosomal DNA repair was measured as the chromatid aberration frequency (CAF) or total number of chromatid breaks and long gaps per 100 metaphase cells, determined 0.5–1.5 h after X-irradiation (53 rad). Chromatid breaks and gaps (as defined herein) represent unrepaired DNA strand breaks. Only one of the TTD lines, TTD 1BR, showed an abnormally high CAF. This line was shown subsequently to be of a different complementation group, representing a new nucleotide excision repair gene. An abnormally high CAF was also observed, as reported previously, in XP-C, AT and DS but not in CS skin fibroblasts. In addition, cell lines were examined for DNA incision activity by an indirect method in which chromatid aberrations were enumerated with or without ara-C, an inhibitor of repair synthesis, added after X-irradiation. All TTD lines had abnormally low incision activity.

This paper introduces a new parameter, derivable from dose-response data for induced mutagenesis in bacteria, that can be used to quantify mutational responses in short-term tests. We called this parameter the mutational response of the bipartite experimental system (agent plus cells). We define it as being jointly proportional to the efficiency of the mutagen and the sensitivity of the test. We show how this quantity can be used to rank order chemical carcinogens on the basis of their mutagenicity and to determine the strength of any quantitative correlation that may exist between mutagenicity in bacteria and carcinogenicity in rodents. We find that this particular measure of mutational response for 10 direct-acting monofunctional alkylating agents correlates remarkably well with the rodent carcinogenicity of these chemicals measured in terms of their reciprocal TD₅₀ values.

The lymphoblastoid cell lines WI-L2-NS and TK6 were derived from a non-clonal pool of cells taken from a human spleen. Despite their common background they exhibit marked differences in radiosensitivities; D₀ values of 93 and 67 cGy have been reported for WI-L2-NS and TK6 cells respectively. We show here that this differential radiosensitivity is due to a decreased ability of the WI-L2-NS cell line to undergo radiation-induced apoptosis. Further, the WI-L2-NS cell line overexpresses the p53 gene product as a result of a mutation in codon 237 of the p53 gene. These data indicate that WI-L2-NS cells through disruption of normal p53 function are unable to engage the radiation-induced apoptosis program and so are relatively radioresistant.

Many studies on DNA repair mechanisms in mammalian cells have used liquid holding (LH) recovery to evaluate premutational damage repair. We used human peripheral lymphocytes (HPL) to assess damage reduction during the G0 phase. This technique was matched with the three-way differential (TWD) staining that allows identification of sister-chromatid exchanges (SCE) per cell cycle in third metaphases. By adopting this approach, the persistence of diepoxybutane (DEB)-induced lesions during subsequent cycles and individual repair capacity in LH conditions were measured. Our results show that most DEB-induced damage was repaired during the first cell cycle; a large part of lesions were removed during LH recovery, demonstrating G0 HPL repair capacity.

The effect of high molecular carboxymethyl-chitin-glucan (CMCG), administered either intraperitoneally, intravenously or orally prior to cyclophosphamide injection, on the frequency of micronucleated reticulocytes was evaluated in peripheral blood of female ICR mice. Both intraperitoneal and intravenous administration of CMCG decreased the clastogenic effect of cyclophosphamide. The protective effect of CMCG was concentration dependent, with a higher decrease achieved by 100 mg/kg than by 50 mg/kg body weight. On the other hand, not even five peroral pretreatments with CMCG in the dose of 200 mg/kg body weight during the week prior to simultaneous administration of CMCG and cyclophosphamide induced a decrease of micronucleated reticulocytes in peripheral blood. It is therefore conceivable that CMCG failed to pass through the gastrointestinal tract, probably due to its high molecular weight. The antimutagenic effect of CMCG against cyclophosphamide was manifested by its intraperitoneal and intravenous administration to female ICR mice.

Damage-inducible DNA replication (iSDR) was followed in UV-irradiated E. coli uvr⁺ and uvrB5. Owing to the inhibition of dimer excision in the former (caused by the metabolic treatment), both contained similar amounts of unexcised dimers. Since iSDR took place in uvr⁺ but not in uvrB5 cells, it is concluded that the uvr system can tolerate unexcised dimers through the recombinogenic iSDR.

Male Syrian golden hamsters were exposed for 1 or 2 weeks to smoke produced by commercial non-filter cigarettes for 5 consecutive days in a Hamburg type II smoking machine. Postmitochondrial fractions (S9) prepared from the liver, lungs, and pancreas were used in the Ames liquid incubation assay, in order to assess the effect of cigarette smoke (CS) on the metabolic activation of four groups of procarcinogens. The mutagenic activities of five heterocyclic amines on strain TA98 in the presence of liver S9 mix were induced up to 3.7 times above controls including sham smoke control, while no significant alteration of mutagenicity was observed with 3′-hydroxymethyl-N,N-dimethyl-4-aminoazobenzene and benzo[a]pyrene on TA98 or with N-nirosobis(2-oxopropyl)amine (BOP) on TA100. A similar stimulation of metabolic activation was also observed for 3-amino-1,4-dimethyl-5H-pyridol[4,3,-b]indole (Trp-P-1) with S9 from the lungs but not from the pancreas. The mutagenic potential of 11 carcinogens including aflatoxin B₁ (AFB₁) and two other heterocyclic amines was also examined using liver S9 from male hamsters pretreated with phenobarbital (PB) or 3-methylcholanthrene (MC). The numbers of revertant colonies were much higher (2-20-fold) in the presence of MC-treated liver S9 than in the presence of PB-treated liver S9, except in the case of AFB₁ which showed a higher mutagenicity with PB-induced S9. 7,8-Benzoflavone considerably inhibited the activities of 2-amino-3-3-methylimidazo[4,5-f]quinoline (IQ) and Trp-P-1 in the presence of either untreated, MC- or CS-treated liver S9, whereas metyrapone was totally lacking this effect, indicating that cy

In a comparative study, henzo[a]pyrene (BaP), cyclophosphamide (CP), N-methyl-N′-nitro-N-nitrosoguanidine (MNNG) and tetrachloroethylene (PER) were tested for their ability to induce genotoxic effects in the single cell gel (SCG) test and the sister-chromatid exchange (SCE) test with human blood cells. MNNG as well as S9 mix activated BaP- and CP-induced DNA effects in both tests in a dose-dependent manner. While the range of concentrations which induced DNA migration or SCE was the same for MNNG and for Bap, much higher CP concentrations were necessary for a positive response in the SCG test than in the SCE test. PER was tested in the absence and in the presence of S9 mix and neither induced DNA migration nor increased SCE frequencies. In these experiments, a clear cytotoxic effect of PER was observed. To investigate a possible influence of DNA repair on the effects in the SCG test, cells were treated for 2 h and further incubated for 1 h after removal of the test substance. This procedure caused a clear decrease in induced DNA migration in experiments with Bap and CP, whereas no reduction was found with MNNG. This modified protocol did not lead to the detection of DNA effects after treatment with PER. The results indicate that the SCG test responds to various DNA lesions and does not seem to be sensitive to non-genotoxic cell killing. Its sensitivity obviously depends on the type(s) of induced DNA lesions and the effects can be modified by DNA repair processes in a complex manner. For the detection of genotoxic properties of chemicals with the in vitro SCG test, a single evaluation at the end of the exposure period seems to be sufficient.

Evidence is provided that ascorbic acid (vitamin C), when used as a pretreatment, protects against mutation/recombination induced by γ-rays and chromium (VI) oxide in mwh+/+flr³ larvae in the wing spot test in Drosophila