International journal of radiation biology and related studies in physics, chemistry, and medicine最新文献

Prior UV irradiation strongly increased the sensitivity to H2O2 of wild-type E. coli K-12 cells. This synergistic lethal interaction was also observed to a reduced extent in a polA mutant but was absent in uvrA, uvrArecA and xthA mutants. In a recA mutant an antagonist effect was observed. Prior H2O2 treatment did not sensitize the wild-type cells to UV irradiation. Alkaline and neutral sucrose gradient analysis, as well as DNA degradation studies, demonstrated that the synergism is due to the production of DNA double-strand breaks and a block of their repair. The possible mechanism of induction of such lesions is discussed.

Nuclear matrices of heated and non-heated HeLa S3 cells were isolated and average DNA loop-sizes were compared. Heat treatment (30 min at 45 degrees C) resulted in an ultimate survival level of the cells of about 10 per cent. The loop-size determinations were done on nuclear material isolated from the cells directly after heat treatment. In the nuclear matrices isolated from the heated cells about 1.8 times more protein was bound as compared to the matrices from control cells. Enzymatic analysis using DNase I digestion, followed by centrifugation on neutral sucrose gradients, was performed. Also, halo visualization was combined with autoradiography. Both methods revealed no gross alterations in DNA loop-sizes. The possible function of DNA loop organization in the effect of hyperthermic interference with DNA-related processes is discussed.

A supercoiled plasmid of 7300 base pairs was isolated and exposed in various aqueous environments to 60Co gamma-radiation. Conversion of the supercoiled form to the relaxed circular and linear forms was monitored by agarose gel electrophoresis and quantified by fluorescence scanning of the gel. Acetate, which has been reported to affect the conformation of DNA in solution, decreased the radiosensitivity of the supercoil in a concentration-dependent manner. Acetate, formate, and azide anions, as well as mannitol, all protected the supercoil from relaxation in approximate proportion to the rate at which their solutions quench the hydroxyl radical. At concentrations greater than 300 mmol dm-3, however, the efficiency of acetate radioprotection is reduced. Disodium ethylenediaminetetraacetate protected the supercoil more efficiently than would be expected from the published value of its rate constant for quenching the hydroxyl radical.

The clonogenic potential of the progeny of irradiated cells was tested in vitro by replating irradiated cultures after various times, allowing between five and over 25 subsequent divisions to take place after irradiation. Whereas the plating efficiency of surviving Chinese hamster cells was not decreased, in C3H10T1/2 cells a dose-dependent but slight decrease in plating efficiency was observed even after the longest follow-up period. These data do not contradict the prevalent hypothesis in radiobiology that the proliferation potential of a clonogenic cell surviving after irradiation is not significantly different from that of a non-irradiated cell.

In order to examine enhanced killing that might be induced by Auger cascades in the incorporated atoms in cells, bromouracil(BrU)-labelled E. coli cells were irradiated with monoenergetic X-rays at 13.49 and 12.40keV, just above and below the K-absorption edge of bromine. In both cases BrU-labelled cells were more sensitive for killing than were normal cells. However, when the degree of BrU-sensitization was compared between the two energies of X-rays, the enhanced killing at 13.49 keV was only small, 2 +/- 8 per cent based on the D0 value in saline. By the addition of DMSO, which is believed to suppress radical-mediated effects, killing of BrU-labelled cells was enhanced at 13.49 keV by 8 +/- 4 per cent as compared with 12.40 keV, based on D0. These results have been examined in terms of absorbed energy in BrU-labelled cells and in terms of the number of induced Auger events.

Mouse L cells were synchronized in early S-phase by two 12 h incubations in medium containing aphidicolin (2 micrograms/ml), separated by 8 h in drug-free medium. The relationship between X-ray-induced cell killing and DNA double-strand breakage was then examined for cells that had entered S-phase, G2-phase, mitosis, and G1-phase following release from aphidicolin and was compared to the response of asynchronous cultures. Aphidicolin-synchronized cells showed cycle phase-dependent changes in their dose-responses for both killing and DNA dsb. However, on the basis of the level of DNA dsb per unit length of DNA required to produce a lethal lesion, aphidicolin-synchronized cells were more sensitive to X-rays than were asynchronous cultures. This sensitivity peaked 2 h after release from aphidicolin treatment and then progressively declined towards the asynchronous culture value. It is argued that these results are due to deregulation of the temporal order of DNA replication following aphidicolin treatment, and can be incorporated into the critical DNA target size model (Radford, Hodgson, and Matthews, in preparation) by postulating that the targets for radiation action in mammalian cells are DNA-associated with potentially transcriptionally active proto-oncogenes or constitutive fragile sites.

Transfection of UV-hypersensitive, DNA repair-deficient Chinese hamster ovary (CHO) cell lines and parental, repair-proficient CHO cells with UV-irradiated pHaprt-1 or pSV2gpt plasmids resulted in different responses by recipient cell lines to UV damage in transfected DNA. Unlike results that have been reported for human cells, UV irradiation of transfecting DNA did not stimulate the genetic transformation of CHO recipient cells. In repair-deficient CHO cells, proportionally fewer transformants were produced with increasing UV damage than in repair-proficient cells in transfections with the UV-irradiated hamster adenine phosphoribosyltransferase (APRT) gene contained in plasmid pHaprt-1. However, transfection of CHO cells with UV-irradiated pSV2gpt resulted in neither decline in transformation frequencies in repair-deficient cell lines relative to repair-proficient cells nor stimulation of genetic transformation by UV damage in the plasmid. Blot hybridization analysis of DNA samples isolated from transformed cells showed no dramatic changes in copy number or arrangement of transfected plasmid DNA with increasing UV dose. We conclude that the responses of recipient cells to UV-damaged transfecting plasmids depend both on the type of recipient cell and the characteristics of the genetic sequence used for transfection.

The relationship between the endogenous cytoplasmic levels of the enzymes superoxide dismutase and catalase and the inhibition of cell proliferation by radiation has been studied in 11 mouse cell lines. The resistance of these mouse cell lines to radiation was found to vary by over 25-fold. No correlation was found between the cytoplasmic level of CuZn-superoxide dismutase or catalase and the resistance to radiation as measured by extrapolation number (EN), quasi-threshold dose (Dq), or DO. None of the cell lines had detectable cytoplasmic Mn-superoxide dismutase. The apparent Ki of potassium cyanide for mouse CuZn-superoxide dismutase was determined (Ki = 6.5 mumol dm-3).

Eggs of domestic chickens and black-headed gulls were continuously exposed to gamma-rays during incubation, using dose rates ranging from 0.004 to 0.08 Gy h-1 for 20 days. Acute-dose experiments were also conducted, and eggs were irradiated on day 10 of incubation with doses of between 1.92 and 28.8 Gy. Hatchability and numbers reaching full-term developed were affected only after chronic doses of 9.6 Gy and acute doses of 4.8 Gy or higher. Maximum embryo mortality occurred around days 10-11 of incubation and just before hatching, in all experiments. An increase in foot and limb deformities was observed above acute and chronic doses of 9.6 Gy.