Hiromichi Matsudaira

Iodine contrast medium sensitizes cultured mammalian cells to x rays but not to. gamma. rays

The influence of an iodine contrast medium on several responses to radiation was examined in mammalian cells in culture (L5178Y). The presence of the medium at the time of irradiation enhanced cell killing, frequency of micronuclei, and yield of DNA single-strand breaks induced by x rays, depending on the concentration used, whereas no such effect was found with ..gamma.. rays. It was concluded that the contrast medium sensitizes mammalian cells in culture primarily by means of the photoelectric effect, thereby increasing the absorbed dose of x rays in the cells.

Second analysis of mortality of nuclear industry workers in Japan, 1986-1997.

Abstract Iwasaki, T., Murata, M., Ohshima, S., Miyake, T., Kudo, S., Inoue, Y., Narita, M., Yoshimura, T., Akiba, S., Tango, T., Yoshimoto, Y., Shimizu, Y., Sobue, T., Kusumi, S., Yamagishi, C. and Matsudaira, H. Second Analysis of Mortality of Nuclear Industry Workers in Japan, 1986–1997. Radiat. Res. 159, 228–238 (2003). A cohort study of nuclear industry workers was initiated in 1990 to determine the possible health effects of low-level radiation. A total of 5,527 deaths were ascertained among 176,000 male workers who had been retrospectively and/or prospectively followed for an average of 7.9 years during the observation period 1986–1997. Statistical analyses were made mainly on the prospective follow-up outcome of 120,000 workers followed for an average of 4.5 years. The standardized mortality ratio (and its 95% confidence interval) was 0.94 (0.90, 0.97) for 2,934 cases of all causes combined and 0.86 (0.82, 0.91) for 1,305 cases of non-malignant diseases combined, which suggested a healthy worker effect. For 1,191 cases of all cancers combined, it was 0.98 (0.93, 1.04), indicating no difference in mortality from that of the general population. In tests for trend of death rate with increasing radiation dose, no significant correlation was found for all cancers combined. For site-specific cancers, most cancers including leukemia showed no positive correlation with dose, except for cancers of the esophagus, stomach and rectum and multiple myeloma. External causes showed a significant correlation with dose. A separate questionnaire study indicated that these positive findings could be ascribed in part to lifestyle characteristics of the workers. For leukemia only, we attempted to estimate the excess relative risk per unit dose of radiation, which, with reservations because of its wide confidence interval, was within the range of variation of the risks reported in other radiation epidemiological studies. This population must be studied for a longer time and with a consideration of the possible effects of confounding factors.

Possible Requirement of Adenosine Triphosphate for the Rejoining of X-ray-induced Breaks in the DNA of Ehrlich Ascites-tumour Cells

SummaryChanges in the metabolism of Ehrlich ascites-tumour cells were examined after in vitro incubation under nitrogen at 1 atmosphere in phosphate-buffered saline in the absence of glucose, conditions which do not allow the rejoining of x-ray-induced breaks in the DNA.There was a marked reduction in the incorporation of radioactive precursors into DNA, RNA, protein, and TTP under these conditions compared with incubation in air. The reduction was partially or completely abolished by adding glucose to the incubation medium. After incubation under nitrogen without glucose, the intracellular content of ATP was greatly decreased. This decrease was also partially prevented by the addition of glucose. No significant change was observed in the content of NAD in the cells incubated under similar conditions.It was concluded that ATP is probably necessary for the rejoining of x-ray-induced breaks in the DNA of the ascites-tumour cells.

Induction of cell killing, micronuclei, and mutation to 6-thioguanine resistance after exposure to low-dose-rate gamma rays and tritiated water in cultured mammalian cells (L5178Y).

Cell killing and induction of micronuclei and mutation to 6-thioguanine resistance were studied in growing cultured mammalian cells (L5178Y) after exposure for a fixed period to low-dose-rate ..gamma.. rays and tritiated water (HTO) at comparable dose rates, from about 10 to 40 rad/hr. From the analysis of dose-response relationships, RBE values of HTO ..beta.. rays relative to ..gamma.. rays were calculated. These were 1.5 for cell killing, 2.0 for micronuclei, and 1.8 for mutation induction. Reported RBE values for HTO were reviewed.

Inhibition of gamma-ray dose-rate effects by D2O and inhibitors of poly(ADP-ribose) synthetase in cultured mammalian L5178Y cells.

Effects of deuterium oxide (D2O) and 3-aminobenzamide, an inhibitor of poly(ADP-ribose) synthetase, on cell proliferation and survival were studied in cultured mammalian L5178Y cells under growing conditions and after acute and low-dose-rate irradiation at about 0.1 to 0.4 Gy/hr of gamma rays. Growth of irradiated and unirradiated cells was inhibited by 45% D2O but not by 3-aminobenzamide at 10 mM, except for treatments longer than 30 hr. The presence of these agents either alone or in combination during irradiation at low dose rates suppressed almost totally the decrease in cell killing due to the decrease in dose rate. The D2O did not inhibit the radiation-induced increase in poly(ADP-ribose) synthesis as measured by the incorporation of [14C]NAD into the acid insoluble fraction, contrary to 3-aminobenzamide. Among other inhibitors tested, theobromine and theophylline were found to be effective in eliminating the dose-rate effects of gamma rays. Possible mechanisms underlying the inhibition are discussed.

Mutation induction by very low dose rate gamma rays in cultured mouse leukemia cells L5178Y

Induction of cell killing and mutation to 6-thioguanine resistance was studied in growing mouse leukemia cells in culture following gamma rays at dose rates of 30 Gy/h, 20 cGy/h, and 6.3 mGy/h, i.e., acute, low dose rate, and very low dose rate irradiation. A marked increase was observed in the cell survival with decreasing dose rate; no reduction in the surviving fraction was detected after irradiation at 6.3 mGy/h until a total dose of 4 Gy. Similarly, the induced mutation frequency decreased after low dose rate irradiation compared to acute irradiation. However, the frequency after irradiation at 6.3 mGy/h was unexpectedly high and remained at a level which was intermediate between acute and low dose rate irradiation. No appreciable changes were observed in the responses to acute gamma rays (in terms of cell killing and mutation induction) in the cells which had experienced very low dose rate irradiation.

Mutation induction by different dose rates of gamma rays in near-diploid mouse cells in plateau- and log-phase culture

Induction of mutation to 6-thioguanine resistance was studied in cultured near-diploid mouse cells (m5S) in plateau and log phase after exposure to gamma rays at dose rates of 30 Gy/h, 180 mGy/h, or 13 mGy/h. In plateau-phase culture, lowering the dose rate from 30 Gy/h to 13 mGy/h resulted in an increase in cell survival and a marked decrease in induced mutation frequency. On the other hand, in the log-phase culture, the magnitude of the dose-rate effects was not as marked as in the plateau-phase culture, particularly within a dose range below 5 Gy. These results, together with those indicating the inverse dose-rate effects in growing mouse leukemia cells (Radiat Res. 115, 273-280, 1988), demonstrate the significant influence of cell growth that takes place during protracted irradiation, particularly for the induction of mutation.

Cell killing and mutation to 6-thioguanine resistance after exposure to tritiated amino acids and tritiated thymidine in cultured mammalian cells (L5178Y).

Cell killing and mutation to 6-thioguanine resistance were studied in growing mouse leukemia cells in culture after exposure to tritiated amino acids and tritiated thymidine. These effects varied widely among the tritiated compounds tested, being greatest for tritiated thymidine followed by tritiated arginine and tritiated lysine, in that order, for a given concentration of 3H expressed in kBq/ml of 3H in the medium. The differences between each tritiated amino acid disappeared almost totally when the effects were compared on the basis of the absorbed dose to the cells. The effects of tritiated thymidine, however, remained more than twofold greater compared to other tritiated compounds. These results indicate the importance of determining the absorbed dose for assessment of the radiotoxicity of tritiated organic compounds. For an exceptional case (tritiated thymidine), contribution of a mechanism(s) other than beta irradiation should also be taken into account.

Mutation induction by different dose rates of gamma rays in radiation-sensitive mutants of mouse leukemia cells

Induction of cell killing and mutation to 6-thioguanine resistance was examined in a radiation-sensitive mutant strain LX830 of mouse leukemia cells following gamma irradiation at dose rates of 30 Gy/h (acute), 20 cGy/h (low dose rate), and 6.2 mGy/h (very low dose rate). LX830 cells were hypersensitive to killing by acute gamma rays. A slight but significant increase was observed in cell survival with decreasing dose rate down to 6.2 mGy/h, where the survival leveled off above certain total doses. The cells were also hypersensitive to mutation induction compared to the wild type. The mutation frequency increased linearly with increasing dose for all dose rates. No significant difference was observed in the frequency of induced mutations versus total dose at the three different dose rates so that the mutation frequency in LX830 cells at 6.2 mGy/h was not significantly different from that for moderate or acute irradiation.

Effects of X-irradiation on the Synthesis of Rapidly Labelled RNA in an Experimental Tumour of the Rat

SummaryEffects of ionizing radiations on the synthesis of rapidly labelled RNA were studied on the Yoshida ascites hepatoma cells (AH 130) of the rat, at different intervals (0·5, 1·5, 4, 20 hours) after a whole-body x-irradiation of 1000 R.An increase was observed in the incorporation of 3H-5-uridine into rapidly labelled RNA, notably into the RNA of high molecular weight, when the irradiated cells were labelled in vivo.In contrast, when the irradiated cells were labelled in vitro, a slight inhibition or no change was observed in the synthesis of the rapidly labelled RNA.The reason for the difference between the results of in vivo and in vitro experiments was discussed.