Takaharu Nomura

Proton-donative antioxidant activity of fucoxanthin with 1,1-diphenyl-2-picrylhydrazyl (DPPH).

Reactions between a carotenoid, fucoxanthin and 1,1‐diphenyl‐2‐picrylhydrazyl were investigated both under anoxic and aerobic conditions. Fucoxanthin equimolarly reacted with 1,1‐diphenyl‐2‐picrylhydrazyl under anoxic conditions. Under aerobic conditions, only a part of fucoxanthin consumed 1,1‐diphenyl‐2‐picrylhydrazyl and the degree of reaction fluctuated with repeated trials. β‐Carotene or other carotenoids, β‐cryptoxanthin, zeaxanthin, licopen and lutein, were also examined in the reaction with 1,1‐diphenyl‐2‐picrylhydrazyl under anoxic conditions. All these compounds scarcely reacted with 1,1‐diphenyl‐2‐picrylhydrazyl.

Elevation of antioxidant potency in the brain of mice by low-dose γ-ray irradiation and its effect on 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced brain damage

The elevation of endogenous thiol-related antioxidants and free radical scavenging enzymes in the brain of C57BL/6 female mice after low-dose gamma-ray irradiation and its inhibitory effect on 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced brain damage were investigated. The brain level of the reduced form of glutathione (GSH) increased soon after irradiation with 50 cGy of gamma-rays, reached a maximum at 3 h post-treatment, and remained elevated until 12 h. Thioredoxin (TRX) was also transiently increased after irradiation. The activities of free radical scavenging enzymes, including Cu/Zn-superoxide dismutase, catalase and glutathione peroxidase, were significantly induced after irradiation as well. Cerebral malondialdehyde was remarkably elevated by MPTP treatment, and this elevation was suppressed by pre-irradiation (50 cGy). The contents of GSH and TRX were significantly decreased by MPTP treatment in comparison with those of the control group. These reductions both seemed to be attenuated by pre-irradiation with gamma-rays. These results suggest that low-dose gamma-ray irradiation induces endogenous antioxidative potency in the brain of mice and might be effective for the prevention and/or therapy of various reactive oxygen species-related neurodegenerative disorders, such as Parkinsons disease and Alzheimers disease.

Induction of mRNAs for glutathione synthesis-related proteins in mouse liver by low doses of γ-rays

We examined the elevation of the reduced form of glutathione (GSH)level and the induction of MRNAs for proteins involved in the synthesis and regeneration of GSH in the liver of mice after low-dose gamma-ray irradiation. The liver GSH level increased soon after irradiation with 50 cGy of gamma-rays, reached a maximum at around 12 h post-treatment. The mRNA of gamma-glutamylcysteine synthetase (gamma-GCS), the rate-limiting enzyme for de novo synthesis for GSH, showed a small increase that peaked at 6 h after gamma-ray irradiation at a dose of 50 cGy. Only a small increase in gamma-GCS activity was observed throughout the 24-h post-irradiation period. In the case of glutathione reductase (GR), which is involved in the regeneration of GSH from the oxidized form (GSSG), the mRNA level peaked strongly at 1 h, while the activity peaked at twice the control level 12 h after irradiation. The level of mRNA for thioredoxin (TRX), which contributes to GSH biosynthesis by supplying cysteine to the de novo pathway, peaked at 1 h and declined thereafter, while the activity peaked at 3 h and then declined sharply. These results indicate that the increase in endogenous GSH immediately following low-dose gamma-ray irradiation is predominantly due to operation of the regeneration cycle and not de novo synthesis. We also examined the dependence of mRNA induction on the gamma-ray dose.

Suppression of carcinogenic processes in mice by chronic low dose rate gamma-irradiation

Effects of low dose rate radiation on the process of carcinogenesis induced by a chemical carcinogen were examined. ICR female mice, 35 or 36 mice for each group, were kept and exposed to 137 Cs gamma-rays in the long- term low dose rate irradiation facility at the Central Research Institute of Electric Power Industry at a dose rate of 0.3, 0.96, or 2.5 mGy/h. Thirty-five days later, the mice were injected in the groin with 0.5 mg of 20-methylcholanthrene (MC) dissolved in olive oil, and irradiation was continued. Tumours started to appear 2 months after MC injection. Cumulative tumour incidences after 216 days following MC injection were 94% in the mice irradiated at 0.3 mGy/h, 76% at 0.95 mGy/h, 89% at 0.30 mGy/h, and 94% in non-irradiated control mice. The difference between the tumour incidence in the control mice and that in the mice irradiated at 0.95 mGy/h was statistically significant. These results indicate the suppressive effect of low dose rate irradiation on the process of tumour induction initiated by MC with an optimum dose rate of approximately 1 mGy/h.

Change of glutathione peroxidase synthesis along with that of superoxide dismutase synthesis in mice spleens after low-dose X-ray irradiation

We have previously demonstrated that the activity of superoxide dismutase (SOD), an antioxidant, is enhanced by low-dose X-ray irradiation in various organs of animals such as rats. Since SOD is an enzyme that mediates the dismutation of O2- to H2O2, the question as to whether the resultant H2O2 is further detoxicated into H2O and O2 or not must still be evaluated. Hence, we studied the effect of low-dose X-ray irradiation on the synthesis of glutathione peroxidase (GSHPx), which is an antioxidant that catalyzes this reaction. The results suggest that H2O2 produced by increased SOD activity can be detoxicated into H2O and O2 due to simultaneous enhancement of the GSHPx activity by X-ray irradiation at 20 cGy, in contrast to irradiation at 400 cGy. The results also show the enhancement in enzyme activities by induction of their synthesis shortly after irradiation at 20 cGy. Moreover, as this phenomenon was observed in BALB/c mice (which are more radiation-sensitive compared to other mouse strains) and radiation-resistant C57BL/6NJcl mice, it was considered to be a common phenomenon in the rat spleen.

Low-dose γ-ray irradiation reduces oxidative damage induced by CCl4 in mouse liver

Abstract We examined the effects of irradiation (50 cGy of γ-ray) reducing the oxidative damage in carbon tetrachloride (CCl4)-hepatopathy mice. We made pathological examinations and analyzed transaminase activity (glutamic oxaloacetic transaminase and glutamic pyruvic transaminase), lipid peroxide level and the activities of endogenous antioxidants in the mouse. The irradiation was found to accelerate the recovery. Based on pathological examination as well as changes in each transaminase activity and lipid peroxide levels, it was shown that hepatopathy improved 3 d after the irradiation. The activities of glutathione reductase and glutathione peroxidase rapidly elevated after irradiation, and the total glutathione content gradually increased in the irradiation group. Both activities of γ-glutamylcysteine synthetase and catalase were higher than normal at all times after the irradiation and gradually increased. In addition, the γ-glutamylcysteine synthetase activity changed in a similar fashion to the total glutathione content. However, superoxide dismutase activity in both groups decreased and that of the irradiation group was significantly lower than that of the sham-irradiation group. These findings suggest that low-dose radiation relieved functional disorder at least in the liver of mice with active oxygen diseases.

Localization of glutathione and induction of glutathione synthesis- related proteins in mouse brain by low doses of γ-rays

First, we determined the cerebral localization of reduced glutathione (GSH) in normal mice by means of autoradiography using 99mTc-meso-hexamethyl propylene oxime. A highly specific localization of GSH in the cerebellum and hippocampus was observed. Secondly, we measured the elevation of GSH level in the brain after low-dose gamma-irradiation. The cerebral GSH levels increased soon after irradiation with 50 cGy of gamma-rays, reaching a maximum at 3 h post-treatment, then remaining significantly higher than that of the non-irradiated control until 12 h and returning to the control level by 24 h. Thirdly, we examined the induction of the activities and the mRNAs of proteins involved in the synthesis and regeneration of GSH in the brain of mice subjected to low-dose gamma-ray irradiation. The level of mRNA for gamma-glutamylcysteine synthetase was significantly increased at 0.5 h, and remained high until 2 h post-irradiation (50 cGy). The level was transiently lowered to the non-irradiated control level at 3 h and slightly increased again after 6 h post-irradiation. gamma-Glutamylcysteine synthetase activity was significantly increased 3 h after irradiation, and remained high up to 24 h post-irradiation. As for glutathione reductase, the mRNA level was increased at 0.5 h, and peaked strongly at 2 h, while the enzyme activity was significantly increased at 6 h after irradiation, and continued to increase up to 24 h. The level of mRNA for thioredoxin, which contributes to GSH biosynthesis by supplying cysteine to the de novo pathway, peaked between 0.5 h and 2 h post-irradiation, and rapidly declined thereafter. The content of thioredoxin showed a transient decrease immediately after irradiation, but was then remarkably elevated, reaching a maximum at 3 h, and thereafter declining sharply. These results indicate that the increase in endogenous GSH in mouse brain soon after low-dose gamma-ray irradiation is a consequence of the induction of GSH synthesis-related proteins and occurs via both the de novo synthesis and the regeneration pathways.

Genes and genetic networks responsive to mild hyperthermia in human lymphoma U937 cells

In this study, to better understand the molecular mechanism underlying cellular responses to mild hyperthermia, we investigated gene expression patterns and genetic networks in human myelomonocytic lymphoma U937 cells using high-density oligonucleotide microarrays and computational gene expression analysis tools. The cells were incubated at 41°C for 30 min (mild hyperthermia treatment) and then at 37°C for 0–6 h. Although the mild hyperthermia treatment of the cells did not induce apoptosis, significant increases in the protein expression levels of heat shock proteins (HSPs), namely, Hsp27, Hsp40 and Hsp70, were observed following the activation of heat shock factor-1. Of the 22,283 probe sets analyzed, 423 probe sets were up-regulated and 515 probe sets were down-regulated by >1.5-fold in the cells 3 h post-treatment. Computational gene network analysis demonstrated that the significant genetic network A that contained many HSPs such as DNAJB1, HSPA1A, and HSPA1B was associated with cellular function and maintenance, post-transcriptional modification, or protein folding. Moreover, the significant genetic network B whose core contained v-myc myelocytomatosis viral oncogene homolog (MYC) was associated with cell morphology, cell cycle, and cellular development. The expression levels of nine selected genes were comparable to those determined by microarray analysis with real-time quantitative PCR assay. The present results indicate that mild hyperthermia affects the expression of a large number of genes and provides additional novel insights into the molecular basis of mild hyperthermia in cells.

Emerging issues in radiogenic cataracts and cardiovascular disease

In 2011, the International Commission on Radiological Protection issued a statement on tissue reactions (formerly termed non-stochastic or deterministic effects) to recommend lowering the threshold for cataracts and the occupational equivalent dose limit for the crystalline lens of the eye. Furthermore, this statement was the first to list circulatory disease (cardiovascular and cerebrovascular disease) as a health hazard of radiation exposure and to assign its threshold for the heart and brain. These changes have stimulated various discussions and may have impacts on some radiation workers, such as those in the medical sector. This paper considers emerging issues associated with cataracts and cardiovascular disease. For cataracts, topics dealt with herein include (i) the progressive nature, stochastic nature, target cells and trigger events of lens opacification, (ii) roles of lens protein denaturation, oxidative stress, calcium ions, tumor suppressors and DNA repair factors in cataractogenesis, (iii) dose rate effect, radiation weighting factor, and classification systems for cataracts, and (iv) estimation of the lens dose in clinical settings. Topics for cardiovascular disease include experimental animal models, relevant surrogate markers, latency period, target tissues, and roles of inflammation and cellular senescence. Future research needs are also discussed.

Enhancement of Bio-Protective Functions by Low Dose/Dose-Rate Radiation

Effects of low-dose-rate gamma-irradiation on the process of tumorigenesis were investigated in mice treated with a carcinogenic agent or irradiated with high dose X-rays at a high dose rate. A prolonged gamma irradiation at approximately 1 mGy/hr suppressed the appearance of skin tumors induced by methylcholanthrene and delayed the appearance of radiation-induced thymic lymphomas in C57BL/6 mice. We also investigated the effects of low-dose-rate irradiation on disease model mice. In Type II diabetic C57BL/KsJ-db/db (db) mice, the urine glucose level was improved in some of the mice irradiated at 0.70 mGy/hr, but not in non-irradiated control mice. In MRL-lpr/lpr (lpr) mice with severe autoimmune diseases, immunological status was kept better in the mice irradiated at 0.35 or 1.2 mGy/hr. The incidence of a number of symptoms, including lymphadenopathy, splenomegaly and proteinuria, was suppressed by the irradiation. Furthermore, in both of the strains, the low-dose-rate irradiation prolonged the life span of the irradiated mice.