Effect of novobiocin on the frequencies of chromatid-type aberrations and sister-chromatid exchanges following gamma-irradiation

Influence of novobiocin on <FONT FACE=Symbol>g</font>-irradiation G0-lymphocytes as analyzed by cytogenetic endpoints

Experiments with novobiocin (NB) post-treatment were performed to verify its effect on the frequencies of micronuclei (MN) and chromosomal aberrations (CA) induced by <FONT FACE="Symbol">g</font>-irradiation (0.75, 1.5 and 3.0 Gy) in human lymphocytes at G0-phase. The frequencies of MN significantly decreased by 44 and 50%, for the treatment with NB 50 µg/ml (30-min pulse) after radiation doses of 1.5 and 3.0 Gy, respectively. However, CA frequencies were not significantly affected. No significant effect on CA was observed when lymphocyte cultures were exposed to a single dose of 2.0 Gy at the G0-phase and posttreated with 25 µg/ml NB for three hours either immediately after irradiation (G0-phase) or after 24 h (S-phase). The significant suppressive effect of NB on MN frequencies supports the hypothesis that NB interaction with chromatin increases access to DNA repair enzymes.

Sister-chromatid exchange: second report of the Gene-Tox Program

This paper reviews the ability of a number of chemicals to induce sister-chromatid exchanges (SCEs). The SCE data for animal cells in vivo and in vitro, and human cells in vitro are presented in 6 tables according to their relative effectiveness. A seventh table summarizes what is known about the effects of specific chemicals on SCEs for humans exposed in vivo. The data support the concept that SCEs provide a useful indication of exposure, although the mechanism and biological significance of SCE formation still remain to be elucidated.

o-Vanillin enhances chromosome aberrations induced by alkylating agents in cultured Chinese hamster cells

The enhancing effects of o-vanillin (2-hydroxy-3-methoxybenzaldehyde) on structural chromosome aberrations induced by alkylating agents were studied in cultured Chinese hamster cells. o-Vanillin was not a clastogen by itself. When cells were treated with N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) in the presence of 400 micrograms/ml of o-vanillin for 2 h, the frequency of aberrant cells with chromosome aberrations was increased 2.8-fold compared with cells treated with MNNG alone. The total number of breakage-type and exchange-type aberrations was increased 18.5- and 8.3-fold, respectively. The enhancing effects were also observed for chromosome aberrations induced by N-methyl-N-nitrosourea and N-ethyl-N-nitrosourea. On the other hand, those induced by N-butyl-N-nitrosourea were only slightly enhanced. The frequency of chromosome aberrations induced by mitomycin C or bleomycin was not changed by o-vanillin treatment. It was considered that DNA repair of methylated damage may be inhibited by o-vanillin.

Influence of nalidixic acid on killing and mutation of V79 cells exposed to different damaging agents

The effect of treatment with nalidixic acid, an inhibitor of DNA topoisomerase, after exposure of V79 cells to different DNA-damaging agents on the induction of killing and mutation has been studied. The DNA-damaging agents were ultraviolet light, gamma-rays and N-methyl-N'-nitro-N-nitrosoguanidine (MNNG). It was seen that treatment with nalidixic acid potentiated the killing by MNNG and suppressed the induction of mutation. However, it had no influence upon killing and mutation by UV light and gamma-rays. The difference in the observed results could be due to the nature of the damage induced and its repair in relation to the function of topoisomerases.

Modification of radiation dose-rate sparing effects in a human carcinoma of the cervix cell line by inhibitors of DNA repair

The in vitro cell survival of a human cervix carcinoma cell line (HX156c) has been assessed using 60Co gamma-rays administered at either high (150 cGy/min) or low (3.2 cGy/min) dose rate. Recovery during low dose-rate irradiation was observed; the dose reduction factor at 10(-2) cell kill for 150 versus 3.2 cGy/min was around 1.3. An insight into the possible underlying mechanisms of this recovery process has been investigated by addition of non-toxic concentrations of various agents thought to inhibit eukaryotic DNA repair. Agent were added 2 h prior to irradiation and removed after 24 h exposure. Differential effects among the inhibitors were observed; aphidicolin had no effect on cell survival, novobiocin, hydroxyurea and 3-aminobenzamide reduced survival by a similar extent at both dose rates, beta-ara A and caffeine reduced survival to a greater extent during low dose-rate irradiation. beta-ara A and caffeine seemed to exert their effects mainly by increasing the alpha component of the acute survival curve. Since survival curves obtained at dose rates of around 3 cGy/min help define a dominant component of the initial slope of the acute curve we have demonstrated that beta-ara A and caffeine modify the initial slope, probably by inhibiting DNA repair processes involved in the sparing of tumour cells during protracted irradiation.

Suppressive effect of novobiocin on the frequency of chromosome-type aberrations induced by ara C in the G1 phase of human lymphocytes

1-beta-D-Arabinofuranosylcytosine (ara C) induces chromosome-type aberrations in mammalian cells by inhibiting repair replication in the G1 phase. The effect of novobiocin, an inhibitor of prokaryotic gyrases, on G1 repair in human cells was studied cytogenetically using this characteristic of ara C. The experiment was based on the assumption that if novobiocin inhibits the relaxation of chromatin required prior to repair replication, it would reduce the frequency of chromosome-type aberrations in cells treated with a mutagen followed by posttreatment with ara C. It has also been shown that in lymphocytes ara C induces chromosome-type aberrations which were not caused by any induced DNA lesion, and that the frequency of these aberrations changes with the age of the blood donor. The effect of novobiocin on the frequency of chromosome-type aberrations induced by ara C in lymphocytes without mutagen pretreatment was also investigated for blood samples from donors of different ages. Human peripheral blood lymphocytes, which were either untreated of treated with 4-nitroquinoline-N-oxide (4NQO) or methyl methanesulfonate (MMS), were posttreated in their early G1 phase with ara C only or ara C and novobiocin. The resulting chromosome-type aberrations were observed in cells in their first mitoses, and a comparison was made between the frequency of aberrations occurring in the presence of novobiocin and in its absence. The results showed that novobiocin reduced the frequency of chromosome-type aberrations induced by ara C in both mutagen-pretreated and -non-pretreated cells, and that lymphocytes from younger donors were less sensitive to novobiocin. The present study demonstrated cytogenetically the existence of a novobiocin-sensitive process to induce chromosome recombination in G1 lymphocytes.

Effects of vanillin on sister-chromatid exchanges and chromosome aberrations induced by mitomycin C in cultured Chinese hamster ovary cells

Effects of vanillin on the induction of sister-chromatid exchanges (SCEs) and structural chromosome aberrations by mitomycin C (MMC) were investigated in cultured Chinese hamster ovary cells. Vanillin induced neither SCEs nor chromosome aberrations by itself. However, an obvious increase in the frequency of SCEs was observed when MMC-treated cells were cultured in the presence of vanillin. The effect of vanillin was S-phase-dependent. On the contrary, the frequency of cells with chromosome aberrations was significantly decreased by the post-treatment with vanillin at G2 phase.

Influence of pulsing electromagnetic field on the frequency of sister-chromatid exchanges in cultured mammalian cells

Exposures of Chinese hamster cells to pulsing electromagnetic field (PEMF) with 0.18-2.5 mT did not influence the baseline frequency of sister-chromatid exchanges (SCE). The results suggest that PEMF with the magnetic intensity examined does not interfere with DNA replication nor produce DNA lesions, thereby leading to an increased frequency of SCE.

Chromatid aberrations in a novobiocin-resistant subline of Chinese hamster V79 cells after exposure to novobiocin

We examined effects of novobiocin alone or in combination with gamma-irradiation, on the frequencies of chromatid-type aberrations in a novobiocin-resistant subline of Chinese hamster V79 cells (NOVOr-1). NOVOr-1 cells were significantly resistant to novobiocin, as compared to wild-type V79 (WT) cells, with respect to cell survival and DNA synthesis. Survival responses of WT and NOVOr-1 cells to gamma-rays in the range 2-10 Gy differed only slightly and the number of chromatid aberrations produced by irradiation at 1 Gy was fairly comparable in the two cell types. Post-irradiation treatment of cells with novobiocin at concentrations exceeding 200 micrograms/ml significantly increased the number of chromatid gaps plus breaks in WT cells as compared with NOVOr-1 cells. With 200 micrograms/ml the increase was 1.2-fold (t-test, P less than 0.05) and with 400 micrograms/ml, 2.3-fold (P less than 0.01) the number produced in NOVOr-1 cells.