Radiation cancer risk at different dose rates: new dose-rate effectiveness factors derived from revised A-bomb radiation dosimetry data and non-tumor doses.

The dose rate of atomic bomb (A-bomb) radiation to the survivors has still remained unclear, although the dose-response data of A-bomb cancers has been taken as a standard in estimating the cancer risk of radiation and the dose and dose-rate effectiveness factor (DDREF). Since the applicability of the currently used DDREF of 2 derived from A-bomb data is limited in a narrow dose-rate range, 0.25-75 Gy/min as estimated from analysis of DS86 dosimetry data in the present study, a non-tumor dose (Dnt) was applied in an attempt to gain a more universal dose-rate effectiveness factor (DREF), where Dnt is an empirical parameter defined as the highest dose at which no statistically significant tumor increase is observed above the control level and its magnitude depends on the dose rate. The new DREF values were expressed as a function of the dose rate at four exposure categories, i.e. partial body low LET, whole body low linear energy transfer (LET), partial body high LET and whole body high LET and provided a value of 14 for environmental level radiation at a dose rate of 10-9 Gy/min for whole body low LET.

Bacterial SOS Genes mucAB/umuDC Promote Mouse Tumors by Activating Oncogenes Nedd9/Aurkb via a miR-145 Sponge.

The mechanism of cancer induction involves an aberrant expression of oncogenes whose functions can be controlled by RNAi with miRNA. Even foreign bacterial RNA may interfere with the expression of oncogenes. Here we show that bacterial plasmid mucAB and its Escherichia coli genomic homolog umuDC, carrying homologies that match the mouse anti-miR-145, sequestered the miR-145 function in mouse BALB 3T3 cells in a tetracycline (Tet)-inducible manner, activated oncogene Nedd9 and its downstream Aurkb, and further enhanced microcolony formation and cellular transformation as well as the short fragments of the bacterial gene containing the anti-miR-145 sequence. Furthermore, mucAB transgenic mice showed a 1.7-fold elevated tumor incidence compared with wild-type mice after treatments with 3-methylcolanthrene. However, the mutation frequency in intestinal stem cells of the mucAB transgenic mice was unchanged after treatment with X-rays or ethyl-nitrosourea, indicating that the target of mucAB/umuDC is the promotion stage in carcinogenesis. IMPLICATIONS: Foreign bacterial genes can exert oncogenic activity via RNAi, if endogenously expressed. VISUAL OVERVIEW: http://mcr.aacrjournals.org/content/molcanres/18/9/1271/F1.large.jpg.

Meta-analysis of non-tumour doses for radiation-induced cancer on the basis of dose-rate.

PURPOSE: Quantitative analysis of cancer risk of ionising radiation as a function of dose-rate. MATERIALS AND METHODS: Non-tumour dose, D(nt), defined as the highest dose of radiation at which no statistically significant tumour increase was observed above the control level, was analysed as a function of dose-rate of radiation. RESULTS: An inverse correlation was found between D(nt) and dose-rate of the radiation. D(nt) increased 20-fold with decreasing dose-rate from 1-10(-8) Gy/min for whole body irradiation with low linear energy transfer (LET) radiation. Partial body radiation also showed a dose-rate dependence with a 5- to 10-fold larger D(nt) as dose rate decreased. The dose-rate effect was also found for high LET radiation but at 10-fold lower D(nt) levels. CONCLUSIONS: The cancer risk of ionising radiation varies 1000-fold depending on the dose-rate of radiation and exposure conditions. This analysis explains the discrepancy of cancer risk between A-bomb survivors and radium dial painters.

Suppression of thymic lymphoma induction by life-long low-dose-rate irradiation accompanied by immune activation in C57BL/6 mice.

The induction of thymic lymphomas by whole-body X irradiation with four doses of 1.8 Gy (total dose: 7.2 Gy) in C57BL/6 mice was suppressed from a high frequency (90%) to 63% by preirradiation with 0.075 Gy X rays given 6 h before each 1.8-Gy irradiation. This level was further suppressed to 43% by continuous whole-body irradiation with 137Cs gamma rays at a low dose rate of 1.2 mGy/h for 450 days, starting 35 days before the challenging irradiation. Continuous irradiation at 1.2 mGy/h resulting in a total dose of 7.2 Gy over 258 days yielded no thymic lymphomas, indicating that this low-dose-rate radiation does not induce these tumors. Further continuous irradiation up to 450 days (total dose: 12.6 Gy) produced no tumors. Continuously irradiated mice showed no loss of hair and a greater body weight than unirradiated controls. Immune activities of the mice, as measured by the numbers of CD4+ T cells, CD40+ B cells, and antibody-producing cells in the spleen after immunization with sheep red blood cells, were significantly increased by continuous 1.2-mGy/h irradiation alone. These results indicate the presence of an adaptive response in tumor induction, the involvement of radiation-induced immune activation in tumor suppression, and a large dose and dose-rate effectiveness factor (DDREF) for tumor induction with extremely low-dose-rate radiation.

HST-1/FGF-4 plays a critical role in crypt cell survival and facilitates epithelial cell restitution and proliferation.

The fibroblast growth factor-4 (HST-1/FGF-4) is a heparin-binding growth factor that influences on epithelial and many other cells through interaction with FGF receptors. It has been demonstrated that the HST-1/FGF-4 gene protects mice from lethal irradiation by preventing bone marrow damage and intestinal tract damage. However, the radioprotective mechanism is unknown. In this study, we have investigated the expression of Hst-1/Fgf-4 in mouse small intestine after irradiation, and determined the role of HST-1/FGF-4 in mouse intestinal crypt cell survival and epithelial cell proliferation and restitution. We found the induction of endogenous Hst-1/Fgf-4 expression in intestine when mice are exposed to 9.0 Gy irradiation. Laser-captured microdissection (LCM) coupled with RT-PCR analysis revealed that expression of Hst-1/Fgf-4 was found in epithelial cell of the villi and crypt cells. Pretreatment of HST-1/FGF-4 caused an increase in the number of surviving crypt cells, and clearly suppresses the radiation-induced apoptosis of the crypt cells. Moreover, exogenous HST-1/FGF-4 enhances epithelial cell restitution and proliferation in an in vitro model. These data suggest that HST-1/FGF-4 is induced by irradiation injury, and that HST-1/FGF-4 will find a therapeutic role in the prevention of intestinal cell toxicity following intensive chemotherapy and radiation therapy protocols, and in allogenic cell transplantation.