Radiation hormesis: Stimulatory effects of low doses ionizing radiation

Low to small doses of ionizing radiation conditionally show stimulatory effects in various cells and organisms, contrasting with detrimental effects induced at high doses. Radiation hormesis is defined as biopositive health effects, such as augmentation of growth and survival, enhancement of immune response, suppression of mutagenesis, and increase in resistance to damages induced by subsequent high dose exposure. Accumulating data on molecular, cellular, and organism levels demonstrate a variety of hormetic phenomena produced by low dose radiation. Living organisms have been exposed to low doses radiation since the early period of evolution, therefore, radiation hormesis may be established at least in part as a defense mechanism, and thus has important implications for health and diseases. In this review, data of radiation hormesis were presented with special emphasis on the responses of organisms. Recent studies also show potential application of low dose radiation for intervention of diseases. Research on radiation hormesis will indisputably contribute to elucidate aging processes

Radiation Hormesis: Stimulatory Effects of Low Doses Ionizing Radiation

High doses of ionizing radiation (HDR) induce a variety of harmfuleffects. However, low-doses radiation (LDR) can conditionally result instimulatory effects in various cells and organisms. Radiation hormesis isdefined as biopositive effects, such as augmentation of growth and survival,enhancement of immune response, suppression of mutagenesis and increase inresistance to the effects of further HDR. Adaptive response refers toLDR-induced resistance to the subsequent HDR. Radioadaptive responsemanifests a wide cross-resistance against oxidative damage from otherstresses. In this presentation, first we would like to introduce briefly thedose effect relationship of ionizing radiation and then review theexperimental, epidemiological and clinical data of radiation hormesis, withspecial emphasis on the studies conducted with whole-body irradiation.Second, we present our data clearly demonstrating radiation hormesis in thewhole body irradiated animals. Living organisms have always lived in thepresence of LDR. Radiation hormesis may be established at least in partevolutionarily as a cellular defense mechanism and thus have importantbiological significance and implications for health and disease. Researchon radiation hormesis will indisputably contribute to elucidate agingprocess.第7回アジア・オセアニア国際老年学会

Protective and Detrimental Bystander Effects Induced by X-Irradiation in the Limb Bud Cell Cultures of Fetal Mice

Radioadaptive response and bystander effect represent important phenomena in radiobiology with an impact on the novel bioresponse mechanisms and risk estimates. The micromass cultures of limb bud cells (LBCs) provide an in vitro cellular maturation system, in which progress of cellular proliferation and differentiation is comparably paralleled to that of in vivo. This paper reports for the first time the evidential correlation and interaction, which simultaneously exist in the micromass culture system, between radioadaptive response and bystander effect. A radioadaptive response was induced in LBCs of embryonic day 11 (E11) ICR mice. Conditioning irradiation of the E11 cells with 30 cGy resulted in a significant protective effect against the occurrence of apoptosis, inhibition of cellular proliferation and differentiation induced by a challenging dose of 5 Gy given next day. Both protective and detrimental bystander effects were observed, namely, irradiating 50% of the E11 cells with 30 cGy led to a successful induction of radioadaptive response, and irradiating 70% of the E12 cells with 5 Gy produced comparably the detrimental effect to that of when all the cells were irradiated. Further, the bystander effects were markedly vanishedby pretreatment of the cells with inhibitors to block the gap junction-mediated intracellular communication. These results indicated that the bystander effect played an important role in both the induction of a protective effect by the conditioning dose and the detrimental effect by the challenging irradiation. Concerning the underlying mechanism, the gap junction-mediated intracellular communication was suggested being involved in the induction of the bystander effects.12th International Congress of Radiation Researc

Effects of Pre-exposure on the Survival and Hematological Changes in the Lethally Irradiated C57BL Mice

Exposing mice to 0.5 Gy 2 weeks before lethal (around LD50/30) whole-body irradiation has been reported to induce marked radio-resistance and to rescue them from "bone marrow death." It is widely accepted that cause of the death after dose around LD50/30 is mainly mediated by hematological failure. In order to elucidate the mechanism underlying the adaptive response, we examined effects of 0.5 Gy pre-exposure on the survival and hematological changes in C57BL mice irradiated with 6.5 Gy X-rays. The pre-exposure 2 weeks before the challenging dose enhanced survival to 77% at day 30, whereas without exposure, the survival decreased to 20 % at day 20 and 0% at day 26 after 6.5 Gy. Hematopoietic progenitor CFU-GM in the pre-irradiated mice began to recover around day 20 and then increased markedly. However, peripheral blood cell counts depleted to reach a nadir at day 20, regardless of the pre-irradiation, in spite of marked difference in the survival between the pre-irradiated and non-pre-irradiated mice. These cell counts in the pre-exposed mice recovered at day 30. We found that OK432, a bio-response modifier, could further enhance the survival of pre-exposed mice to 97%, when administrated 2 days before 0.5 Gy. The OK432 administrated mice also survived without recovery of the peripheral blood cell counts at day 20. These results manifest that the lethally irradiated mice are rescued by pre-exposure without recovery of hematological failure at least by day 20. Furthermore, we have observed long-term effect of pre-exposure for 1 year. More than half of the survivor of the pre-irradiated mice and the OK432 injected mice survived 1 year, even though they showed a variety of abnormalities.低線量放射線の生物影響に関する国際シンポジウ