2007 Fiscal Year Final Research Report Summary
Direct ESR measurement of mutagenic slow releasing long-lived radicals inind iated manmalian cells with adequate dose forradiaion biology
| Project/Area Number |
18510044
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Risk sciences of radiation/Chemicals
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| Research Institution | Nagoya University |
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Principal Investigator |
KUMAGAI Jun Nagoya University, Graduate School of Engineering, Associate Professor (20303662)
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| Project Period (FY) |
2006 – 2007
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| Keywords | Slow-Releasing Long-lived Radicals / Delayed Effect on Radiation Biology / Hydrogen Peroxide / Vitamin C / Mitochondria / ESR |
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| Research Abstract |
We newly found novel slow-releasing long-lived radicals (SRLLRs) in 4 Gy y-irradiated Syrian hamster embryo (SHE) cells by ESR spectroscopy without any spin-trapping agent. As far as we know, it might be fast time to report the radicals those were deft directly by ESR from whole mammalian cells without any extraction or concentration. Primary SHE cells at population doublings of 21^st have ca. 1.8 (±0.07) ×10^6 spins/cell. When the cell were y-irradiated in 4 Gy and stored for I, 5, 12, and 20 h, concentrations of radicals increased to 1.9(±0.09)×10^6, 2.2 (±0.15)×10^6, 2.2 (±0.12) ×10^6 and 2.1(±0.05)×10^6 spins/cell, respectively, and the increments were 1.0×10^5(+6 %), 3.8×10^5 (+21%), 3.6×10^5 (+20%), and 3.2×10^5(+17%), spins/cell, respectively. Because ROS or RNS directly induced by ionizing radiation are completely disappeared in the course of time as I to 20 h after irradiation, the increase is not due to direct or indirect radiolysis of cell components but due to some induced
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reactions those may be enhanced by the radiation. Pest-treatment of ascorbate 2 h suppressed the increase in the levels of SRLLRs within 70%. Addition of myxothiazol, as an inhibitor of electron transportation in mitochondria, suppressed the increase in the levels of SRLLRs in irradiated cells. The treatment of myxothiazol in 0.5 μM mainly blocks the electron transportation within the cytochrone b-c1 segment of the respiratory chain in complex III in mitochondria. Abnormal leaks of electron from radiation-modified studious in the irradiated mitochondria produce superoxide with solvated oxygen molecules in irradiated cells, then superoxide dysmutase convert superoxide to hydrogen peroxide. The reaction with the hydrogen peroxide is likely to produce the slow releasing long-lived radicals. Direct addition of hydrogen peroxide to the culture medium increased the levels of them. These results indicate that SRLLRs are likely to be produced by hydrogen peroxide from dysfunctional mitochondria. Because SRLLRs have a long lifetime over 20h and reduced by L-ascorbic acid treatment, they might be responsible of delayed effects of radiation. Less
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