The Ku protein is a complex of two subunits, Ku70 and Ku80, and was originally identified as an autoantigen recognized by the sera of patients with autoimmune diseases. The Ku protein plays a key role in multiple nuclear processes, e.g., DNA repair, chromosome maintenance, transcription regulation, and V(D)J recombination. The mechanism underlying the regulation of all the diverse functions of Ku is still unclear, although it seems that Ku is a multifunctional protein that works in nuclei. On the other hand, several studies have reported cytoplasmic or cell surface localization of Ku in various cell types. To clarify the fundamental characteristics of Ku, we have examined the expression, heterodimerization, subcellular localization, chromosome location, and molecular mechanisms of the nuclear transport of Ku70 and Ku80. The mechanism that regulates for nuclear localization of Ku70 and Ku80 appears to play, at least in part, a key role in regulating the physiological function of Ku in vivo.

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We here investigated and reported the effects of beer drinking on radiation-induced chromosome aberrations in blood lymphocytes. Human blood that was collected either before or after drinking a 700 ml beer was in vitro irradiated with 200 kVp X rays or 50 keV/μm carbon ions. The relation between the radiation dose and the aberration frequencies (fragments and dicentrics) was significantly (p < 0.05) lower for lymphocytes collected 3 h after beer drinking than those before drinking. Fitting the dose response to a linear quadratic model showed that the alpha term of carbon ions was significantly (p < 0.05) decreased by beer drinking. A decrease of dicentric formation was detected as early as 0.5 h after beer drinking, and lasted not shorter than 4.5 h. The mitotic index of lymphocytes was higher after beer drinking than before, indicating that a division delay would not be responsible for the low aberrations induced by beer drinking. An in vitro treatment of normal lymphocytes with 0.1 M ethanol, which corresponded to a concentration of 6-times higher than the maximum ethanol concentration in the blood after beer drinking, reduced the dicentric formation caused by X-ray irradiation, but not by carbon-ion irradiation. The beer-induced reduction of dicentric formation was not affected by serum. It is concluded that beer could contain non-ethanol elements that reduce the chromosome damage of lymphocytes induced by high-LET radiation.

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The relative biological effectiveness (RBE) for animal tumors treated with fractionated doses of 290 MeV/u carbon ions was studied. The growth delay of NFSa fibrosarcoma in mice was investigated following various daily doses given with carbon ions or those given with cesium γ-rays, and the RBE was determined. Animal tumors were irradiated with carbon ions of various LET (linear energy transfer) in a 6-cm SOBP (spread-out Bragg peak), and the isoeffect doses; i.e. the dose necessary to induce a tumor growth delay of 15 days were studied. The isoeffect dose for carbon ions of 14 and 20 keV/μm increased with an increase in the number of fractions up to 4 fractions. The increase in the isoeffect dose with the fraction number was small for carbon ions of 44 keV/μm, and was not observed for 74 keV/μm. The α and β values of the linear-quadratic model for the radiation dose-cell survival relationship were calculated by the Fe-plot analysis method. The α values increased linearly with an increase in the LET, while the β values were independent of the LET. The α/β ratio was 129 ± 10 Gy for γ-rays, and increased with an increase in the LET, reaching 475 ± 168 Gy for 74 keV/μm carbon ions. The RBE for carbon ions relative to Cs-137 γ-rays increased with the LET. The RBE values for 14 and 20 keV/μm carbon ions were 1.4 and independent of the number of fractions, while those for 44 and 74 keV/μm increased from 1.8 to 2.3 and from 2.4 to 3.0, respectively, when the number of fractions increased from 1 to 4. Increasing the number of fractions further from 4 to 6 was not associated with an increase in the RBE. These results together with our earlier study on the skin reaction support the use of an RBE of 3.0 in clinical trials of 80 keV/μm carbon beams. The RBE values for low doses of carbon beams were also considered.

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Suzuki presented models for mixed irradiation with two and multiple types of radiation by extending the Zaider and Rossi model, which is based on the theory of dual radiation action. In these models, the repair function was simply assumed to be semi-logarithmically linear (i.e., monoexponential), or a first-order process, which has been experimentally contradicted. Fowler, however, suggested that the repair of radiation damage might be largely a second-order process rather than a first-order one, and presented data in support of this hypothesis. In addition, a second-order repair function is preferred to an n-exponential repair function for the reason that only one parameter is used in the former instead of 2n-1 parameters for the latter, although both repair functions show a good fit to the experimental data. However, according to a second-order repair function, the repair rate depends on the dose, which is incompatible with the experimental data. We, therefore, revised the models for mixed irradiation by Zaider and Rossi and by Suzuki, by substituting a `reciprocal-time' pattern of the repair function, which is derived from the assumption that the repair rate is independent of the dose in a second-order repair function, for a first-order one in reduction and interaction factors of the models, although the underlying mechanism for this assumption cannot be well-explained. The reduction factor, which reduces the contribution of the square of a dose to cell killing in the linear-quadratic model and its derivatives, and the interaction factor, which also reduces the contribution of the interaction of two or more doses of different types of radiation, were formulated by using a `reciprocal-time' pattern of the repair function. Cell survivals calculated from the older and the newly modified models were compared in terms of the dose-rate by assuming various types of single and mixed irradiation. The result implies that the newly modified models for mixed irradiation can express or predict cell survival more accurately than the older ones, especially when irradiation is prolonged at low dose rates.

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To study the effects of heavy-ion radiosurgery on the hemopoietic function of a silkworm, hemopoietic organs of larvae were locally irradiated with carbon-ion beams, and the changes in the hemocyte density and in the hemocyte function were investigated. When the larvae were irradiated by 50 Gy to 300 Gy carbon ions on the 3rd day of the 4th instar, the hemocyte densities did not change for a while, though they gradually increased at a later stage, but were finally still significantly lower than those of unirradiated controls. The hemocyte densities of the larvae irradiated at different developmental stages showed suppressed increments, and carbon-ion irradiation given to larvae at early stages compared to the later stages had a significant suppressive effect on the hemocyte densities. On unilateral irradiated larvae a hemocyte intermediate increment between those of bilateral irradiated larvae and unirradiated controls was observed. The percentage of dead hemocytes was obviously higher for irradiated larvae than unirradiated controls during the later 5th instar. Thus, it is evident that carbon-ion radiosurgery on hemopoietic organs of silkworm induced not only a quantitative change, but also a qualitative change in the hemocytes.

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To elucidate the mechanisms involved in deleterious neuronal and behavioral changes after prenatal ionizing irradiation, in vitro muscarinic acetylcholine (mACh) receptor binding and histological construction were investigated in 9-week old rat brains after 1.5 Gy X-ray exposure on embryonic day 15 (E15). A gross anatomical examination with a magnetic-resonance imaging system showed an irregular tissue construction in the hippocampus and cortex of the irradiated rat brain. Histological sections stained with hematoxylin and eosin also indicated that the structures of the hippocampus and cortex were obviously changed. In irradiated rats, the laminar structure of pyramidal cells was selectively deranged in the CA1 region. In vitro ³H-Quinuclidinyl benzilate binding in the hippocampus was significantly decreased (about 10%) in prenatal irradiated rats compared to that in sham-treated rats. On the other hand, no significant change in mACh receptor binding was observed in the cerebral cortex. The present study revealed that prenatal exposure to ionizing radiation may induce dysfunction of the cholinergic neuronal systems, especially in the hippocampus, resulting in deleterious changes in memory and behavior.

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To assess the role of NF-κB in cellular radiosensitivity, we constructed mutated IκB expression plasmids for SY-IκB (with mutations at residues of 32, 36 and 42) expression in human malignant glioma cells (radiosensitive MO54 and radioresistant T98 cells), giving respective cell types referred to as MO54-SY4 and T98-SY14. Both of the clones expressing SY-I κB became radiosensitive, compared with the parental MO54 and T98 cells. A treatment with herbimycin A or genistein did not change the radiosensitivity of cells expressing SY-IκB, but made both the MO54 and T98 parental cells more sensitive to ionizing radiation. A treatment with TNF-α induced DNA fragmentation and apoptosis in cells expressing SY-IκB, but not in MO54 and T98 cells. The survival after X-ray exposure of the parental MO54 cells was slightly increased by a TNF-α treatment, but that of the parental T98 cells did not change. The change in sensitivity to ultra-violet (UV) radiation and adriamycin in MO54-SY4 cells was very similar to that for X-ray sensitivity, but no change was observed in T98-SY14 cells. Significant sublethal damage repair was observed in T98 cells, whereas MO54 cells showed little repair activity. The expression of p53 was enhanced in the parental MO54 cells, while the p53 levels in the MO54-SY4, and in the parent and clonal T98 cells, did not change. Our data suggest that the serine and tyrosine phosphorylation of IκB-α may play a role in determining the radiosensitivity of malignant glioma cells.

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A series of 2-imino-3-[(chromone-2-yl) carbonyl]thiazolidines substituted at the C-5 and / or C-7 positions of a chromone ring were synthesized. The in vivo toxicity and radioprotective efficacy of these agents were evaluated in male NMRI mice against cobalt-60 γ-rays. The LD₅₀ values as determined by a Probit analysis, were 659, 1216 and 790 mg/kg for compounds, 2, 3 and 4, respectively. For studying radioprotective effects, one half of the toxic LD₅₀ values were used, namely 330, 605 and 395 mg/kg for compounds 2, 3 and 4, respectively. The dose reduced factor (DRF) was determined by dividing the LD_50/30 values obtained from the radiation survival curve in the presence of a radioprotective agent by the LD_50/30 value obtained from a control radiation survival curve. A compound with a hydroxyl group substituent at the C-5 position afforded better radioprotective activity than those without this substituent. The radioprotective effect of chromone having a hydroxyl group at only the C-7 position was similar to that of the unsubstituted chromone. The most active compound has hydroxyl groups at the C-5 and C-7 positions of the chromone ring; it had a DRF of 1.48.

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Immunohistochemical examinations were performed on rat pulmonary tumors induced by inhalation exposures to ²³⁹PuO ₂ aerosols, or by X-ray-irradiation to identify and compare cellular origins or, in turn, target cells at risk for radiation carcinogenesis. Both plutonium-induced and X-ray-induced pulmonary tumors appeared to occur from the lower respiratory tract epithelium through bronchioles into alveoli, and were histopathologically diagnosed as adenoma, adenocarcinoma, adenosquamous carcinoma, and squamous cell carcinoma. Immunohistochemical staining of neoplastic lesions using rabbit polyclonal antibodies to rat surfactant apoprotein A specific for alveolar type II pneumocytes, and Clara cell antigen specific for nonciliated bronchiolar Clara cells, showed that most of the adenomatous and adenocarcinomatous lesions from plutonium-exposed or X-irradiated rats were positive for either or both antigens, while, in contrast, adenosquamous and squamous lesions were mostly negative for both antigens. Even though there were some differences in the proportions and distributions of immunoreactive cells between plutonium- and X-ray-induced tumors and among neoplastic lesions, the results indicate that radiation-induced pulmonary adenomas and adenocarcinomas mostly originate from either alveolar type II pneumocytes or bronchiolar Clara cells, while adenosquamous and squamous carcinomas may be derived from the other epithelial cell components, or might have lost specific antigenicity during their transforming differentiation.

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The dose-response relationships for the lifetime excess mortality and temporal distribution of excess mortality were analysed using a data set from an experiment on the long-term effects of gamma irradiation in neonatal mice. The excess mortality was calculated based on an assumption that any increase in the mortality rate was attributable to radiation exposure. The dose-response relationship for the lifetime excess mortality was convex upward, whereas the shortening of the mean life span was proportional to the dose. The excess mortality at 1 Gy was estimated to be 35.6%. The relative risk decreased markedly with increasing age. However, the mortality rate in the irradiated group was persistently higher than the background rate of death, and the absolute risk increased with age. A logistic specification was used to analyze the temporal distribution of the excess mortality. The results of the analysis indicated a dose-dependent shortening of the latent period and a broadening of the distribution.

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The insulin-like growth factor I receptor (IGF-IR) is known to induce clonogenic radioresistance in cells following ionizing irradiation. To explore the downstream signaling pathways, we focused on the phosphatidylinositol-3 kinase (PI3-K) pathway, which is thought to be the primary cell survival signal originating from the receptor. For this purpose, R- cells deficient in the endogenous IGF-IR were used as a recipient of the human IGF-IR with or without mutations at potential PI3-K activation sites: NPXY⁹⁵⁰ and Y¹³¹⁶XXM. Mutants with double mutation at Y950/Y1316 exhibited not abrogated, but reduced activation of IRS-1, PI3-K, and Akt upon IGF-I stimulation. However, the mutants had the same clonogenic radioresistance as cells with wild type (WT) receptors. Neither wortmannin nor LY294002, specific inhibitors of PI3-K, affected the radioresistance of cells with WT receptors at concentrations specific for PI3-K. Collectively, these results indicate that the PI3-K pathway is not essential for IGF-IR-mediated clonogenic radioresistance.

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ESR dosimetry is useful to estimate the external dose for the general population as well as for occupational workers in a nuclear emergency. Three teeth were extracted from two exposed workers (A and B) related to the JCO criticality accident. Tooth enamel was carefully separated from other tooth parts and subjected to ESR dosimetry. Doses equivalent to the γ-ray dose of ⁶⁰Co were estimated as follows: for worker A, the buccal and lingual sides of the eighth tooth in the upper right side, 11.8 ± 3.6 and 12.0 ± 3.6 Gy, respectively; for worker B, the buccal and lingual sides of the fourth tooth in the upper right side and the fifth tooth in the upper left side, 11.3 ± 3.4 and 10.8 ± 3.3 Gy, 11.7 ± 3.5 and 11.4 ± 3.4 Gy, respectively. The estimated doses were found to be similar and not dependent on the tooth positions, whether the buccal or lingual sides in each tooth.

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