Irradiated Mammalian Cells Research Articles

Fast Kinetics of the Oxygen Effect in Irradiated Mammalian Cells

(1978). Fast Kinetics of the Oxygen Effect in Irradiated Mammalian Cells. International Journal of Radiation Biology and Related Studies in Physics, Chemistry and Medicine: Vol. 33, No. 2, pp. 195-199.

Negative Pion Irradiation of Mammalian Cells

The effect of negative pi-mesons on cell-cycle progression of exponentially-growing V 79 monolayer cultures was examined by flow-microfluorometric analysis. Comparison with proliferative changes of the same cell-line after cobalt gamma-irradiation yielded r.b.e. values (relative biological effectiveness) of 2.2 for both, G2+M accumulation and division delay after irradiation at the pion peak. A dose-dependent prolongation of S-phase was found after Co gamma-irradiation which, however, was not detectable after pi-exposure. This observation is so far the only qualitative difference demonstrated in the effects of the two types of radiation.

Effect of radioprotective aminothiols on the induction and repair of single-strand breaks in the DNA of irradiated mammalian cells.

The effect of cysteamine and 2-mercapto-propionyl-glycine on the induction and repair of single-strand breaks in the DNA of Chinese hamster cells by irradiation in vitro in the presence of oxygen or in anoxia was investigated. The substances protected against the formation of breaks by irradiation both under oxic and anoxic conditions. The substances also exhibited a toxic effect which resulted in degradation of DNA. Cysteamine inhibited the rejoining of breaks after radiation exposure.

Proceedings: Effect of caffeine on DNA repair of irradiated mammalian cells.

Proceedings: Effect of caffeine on DNA repair of irradiated mammalian cells.

The Rate of Strand Separation in Alkali of DNA of Irradiated Mammalian Cells

The Rate of Strand Separation in Alkali of DNA of Irradiated Mammalian Cells

Concerning pyrimidine dimers as "blocks" to DNA replication in bacteria and mammalian cells.

Irradiated UV-sensitive bacteria which are mutant in the uvrA6 locus, and cannot excise pyrimidine dimers, are capable of continued DNA replication with the same orientation as that in unirradiated cells. Replication of dimer-containing DNA is also accomplished by irradiated mammalian cells, suggesting that pyrimidine dimers do not act as absolute blocks to DNA synthesis. Thus, the role that dimers play in reducing the amount and size of DNA synthesized after exposure must be reassessed.

Letter: Effect of oxygen on DNA strand breaks in irradiated thymocytes.

Single and double-strand breaks were determined in DNA of rat thymocytes irradiated with 10-MeV electrons over a range of 0 to 6 Mrads in the presence of O/sub 2/ or N/sub 2/, under rapid conditions where the repair of breaks should have been negligible. The numbers of double and single strand breaks in irradiated cells increased linearly with dose. The ratio between single and double strand breaks was 19.5 plus or minus 1.3 in DNA from cells irradiated under O/sub 2/ and N/sub 2/. DNA from irradiated cells contained fewer singlestrand breaks after heating than after alkaline denaturation. The frequency of single strand breaks in unirradiated DNA was identical after both methods of denaturation. The ratio of the slopes of the dose-effect curves yielded 27.8% plus or minus 3.8% alkali labile breaks under O/sub 2/ and 49.8 plus or minus 4.7% under N/sub 2/. An o.e.r. of ~3.7 was deduced from these results for the initial yield of single- and doublestrand breaks in irradiated mammalian cells. (UK)

The effect of oxygen on DNA single-strand breaks produced by ionizing radiation in mammalian cells.

SummaryMouse L-60 cells were irradiated in O2 or N2 atmospheres, and DNA single-strand breaks were measured using alkaline sucrose gradients. It was found that the presence of oxygen increased the yield of single-strand breaks. The oxygen enhancement ratio (OER) was 2·9, a value comparable to the OER for its colony-forming ability in L-60 cells. This observation was made using two different sedimentation techniques.

Growth fraction and cell cycle time of gamma-rays irradiated mammalian cells.

Population kinetic analysis was made for growth fraction and median cell cycle time over 9 days after irradiation of a mouse mammary tumor cell population (FM3A) treated with 500 and 700 R of 60Co gamma-rays, where the growth fraction was estimated from labeling indices determined by the staggered addition method with 3H-thymidine and colchicine, and the median cell cycle time from the rate of c-mitosis accumulation by colchicine as well as the growth fraction. The analysis revealed a modest proliferation of the median cell cycle time of proliferating cells in the gamma-irradiated population. Irrespective of the doses of irradiation, the most remarkable reduction in the growth fraction was noted to occur on the third day of irradiation. The data obtained indicate that the diminution of the rate of increase in total cell number is derived primarily from decrement of the growth fraction and not largely attributable to prolonged cell cycle time, and the decline in the growth fraction is due to departure from the cell cycle and/or death of the cell.

Biochemical and genetic studies on mammalian cells.

A methodology is developed for the investigation of biochemical and genetic phenomena associated with mammalian cell cultures. During the course of the discussion, the mutagenic effects of EMS, X rays, and ultraviolet radiation are mentioned. The modifying effects of caffeine on the survival curves of x- and ultraviolet irradiated mammalian cells is also discussed.

Daughter cell repair by mammalian cells in culture after potentially lethal radiation damage.

COLONY formation by irradiated surface-attached mammalian cells in culture requires that at least one of the progeny produced at the first post-irradiation division retains the capacity for unlimited division. Abortive colonies result when the irradiated parent cell has experienced sufficient damage to suppress eventual colony formation, but not to prevent the production of a small number of progeny. We now present data which indicate that, if given a suitable environment, progeny from cells “lethally” damaged by X-radiation (not capable of producing a macroscopic colony) can repair damage transferred (sectored) from the parent cell.

Low-dose-rate irradiation of mammalian cells with radium and californium 252. A comparison of effects on an actively proliferating cell population.

Abstract Mammalian cells were exposed to a range of low dose-rates from radium and californium 252. From the results obtained, it was possible to calculate the biological effectiveness of the mixed neutron and gamma-ray emission from 252Cf relative to radium gamma rays. It was found that this RBE increased as the dose-rate was decreased, according to the relationship RBE of 252Cf compared to radium α (californium dose-rate)−0.47. This factor, together with the already high RBE of neutrons, calls for extreme caution in the handling and clinical use of 252Cf.

Comparative studies on rejoining of DNA-strand breaks induced by X-irradiation in mammalian cell lines in vitro

Single strand breaks of the DNA in cultured mouse L cells, porcine kidney stable (PS) cells and Ehrlich ascites tumor cells were induced to almost the same degree in alkaline sucrose gradient, as a linear function of dose. However, it was shown by the alkaline sucrose gradient method and autoradiographic observations of unscheduled DNA synthesis in X-irradiated cells that these three cell lines can repair to almost the same degree the single strand breaks in DNA induced by X-irradiation. These results agree well with the fact that there are no striking differences in sensitivity to X-irradiation among these three cell lines obtained by the colony-forming method. Hamster lung (HL) cells, an X-ray resistent cell line obtained by screening from various mammalian cell lines in vitro, seem to have a higher activity of repair enzyme that joins together most of the single strand breaks of DNA induced by X-irradiation. On the other hand, we were unable to demonstrate any significant rejoining activity of damaged double strand DNA from these cell lines in the neutral sucrose gradient. These findings suggest that double strand breaks of DNA induced by X-irradiation are the lesions principally responsible for the lethal effect of ionizing radiation in mammalian cells in vitro.

DNA repair and radiation sensitivity in human (xeroderma pigmentosum) cells.

SummaryHuman skin fibroblasts from neurological and other forms of the disease xeroderma pigmentosum perform repair replication after ultra-violet irradiation at 0 to 25 per cent of normal levels. The reduced repair is correlated with reduced survival in terms of colony formation; normal and xeroderma pigmentosum fibroblasts have exponential survival curves with a D0 of 29 ergs/mm2 and 9 ergs/mm2 respectively. These results demonstrate the importance of repair replication in the survival of irradiated mammalian cells and in the aetiology of xeroderma pigmentosum. Transformation by SV 40 virus does not appear to alter the level of repair replication in xeroderma pigmentosum.

On the increased precursor incorporation into DNA of irradiated mammalian cells.

On the increased precursor incorporation into DNA of irradiated mammalian cells.

Minimum clone size for estimating normal reproductive capacity of cultured cells.

The end-points used for estimating the survival of irradiated mammalian cells are discussed. The single-cell cloning method as used for monolayer cultures in vitro is a much less demanding criterion of survival than those used for mammalian cells growing in vivo and also for suspension cultures in vitro. Comparisons were made of the survival levels of HeLa cells in monolayer culture and P388F lymphoma cells in suspension culture, using the end-points of clone-forming ability and backward extrapolation from growth curves. With the monolayer cultures the usual minimum clone size is 50 cells and with this criterion much higher levels of survival were found in comparison with those from growth curves. This discrepancy could be removed when a larger minimum clone size was used for the end-point. With the suspension cultures the levels of survival obtained from agar clones were in agreement with those from growth curves. The minimum agar clone size was already larger than 50 cells and survival was assessed earlier, i.e. a more demanding end-point was used. It is proposed that the various end-points can be reconciled if the more demanding criterion is used of survival of normal reproductive capacity.

Repair replication in HeLa cells after large doses of x-irradiation.

WE have observed “unscheduled DNA synthesis” and non-conservative synthesis of DNA after the irradiation of mammalian cells with ultraviolet light1. We have presented autoradiographic evidence that unscheduled DNA synthesis occurred in HeLa cells after X-irradiation with 5,000 r.1. Normal semi-conservative DNA replication is considerable at this dose, so neutral equilibrium density gradient experiments to examine the molecular nature of this synthesis were precluded. In this communication we report that, after very large doses of X-rays to HeLa cells, incorporation of precursors into DNA occurs as a result of a process which has the characteristics of “repair-replication”, a phenomenon which has been correlated with enhanced survival in bacteria2.

"Small clones" in irradiated tumour cells in vivo. Kinetics of re-growth of murine leukaemia cells surviving irradiation with x-rays, fast neutrons and accelerated charged particles.

The growth of the intraperitoneally injected P–388 lymphocytic leukaemia cells until they cause the death of isologous recipient mice has been studied in vivo, with unirradiated cells and with cells surviving after irradiation under anoxic conditions with X rays, fast neutrons and accelerated charged particles. Maximum delay in re-growth of tumour cells after irradiation occurs when re-growth takes place from the smallest possible number of surviving cells. The fact that this delay in re-growth can exceed the mean time from inoculation of one unirradiated tumour cell to death of the recipient animal strongly suggests a reduction in the growth rate of some surviving cells analogous to the formation of “small clones” after irradiation of mammalian cells in vitro. The rate of re-growth of tumour cells surviving fast neutron irradiation of intermediate LET (14 MeV monoenergetic neutrons and 6 MeV cyclotron-produced fast neutrons) is no more rapid than that of tumour cells depopulated to the same degree by irradiation with low-LET X rays and accelerated charged particles; in fact the intermediate- LET fast neutron irradiation appears to produce a slightly higher percentage of slowly growing tumour cells among those which survive. The RBE for tumour re-growth after irradiation with fission-spectrum (high-LET) fast neutrons is only slightly lower than the RBE of the same radiation for producing cell reproductive death.

Influence of Incubation Temperature and of Storage on the Viability of Fungal Spores damaged by Phenol

THE evidence for an improved revival of damaged bacteria on incubation at temperatures below the optimal for the undamaged species applies mainly to irradiated cells (see, for example, refs. 1 and 2), but optimal revival at 27°–29° C of E. coli damaged by phenol has also been reported3,4. The storage of irradiated bacteria and mammalian cells at sub-optimal growth temperature for some hours leads to an increase in the number of survivors5. We find that storage has a beneficial effect, but not a lower optimal incubation temperature with fungal spores damaged by phenol.

The effect of 5-bromodeoxyuridine on the recovery phenomenon in sub-lethally irradiated cells

Recovery phenomena in sub-lethally irradiated mammalian cells in culture were studied after treatment with 5-bromodeoxyuridine to examine whether the general shape of the recovery curve could be altered when DNA thymine was partially replaced by 5-bromouracil. The extent of replacement of thymine in the H.Ep. No. 1 and HeLa S-3 cells by 5-bromouracil was about one and twelve per cent respectively. The recovery was evident even after treatment with 5-bromodeoxyuridine and the pattern of the recovery curve was not appreciably altered in both the H.Ep. No. 1 and HeLa S-3 cells.