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Volume 22 (2008)
- Issue 4 Pages 141-
- Issue 3 Pages 93-
- Issue 2 Pages 41-
- Issue 1 Pages 3-
Volume 22, Issue 2
Displaying 1-4 of 4 articles from this issue
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Nobuyuki Hamada, Meinan Ni, Tomoo Funayama, Tetsuya Sakashita, Sakura ...2008 Volume 22 Issue 2 Pages 41-45
Published: 2008
Released on J-STAGE: June 30, 2009
JOURNAL FREE ACCESSBiological effectiveness varies with the linear energy transfer (LET) of ionizing radiation. Plentiful evidence has been presented demonstrating that at physically equivalent doses, high-LET energetic heavy ions are more cytotoxic and genotoxic than low-LET photons like X-rays and γ-rays. Notwithstanding, its potential impact at isosurvival doses is yet to be characterized. Here we investigated the cell-killing effectiveness of γ-rays (0.2 keV/μm) and five different beams of heavy ions with LET ranging from 16.2 to 1610 keV/μm in confluent cultures of normal human fibroblasts. The relative biological effectiveness based on the dose giving 10% clonogenic survival peaked at 108 keV/μm. In cultures exposed to the 10% survival doses, the yield of apoptotic cells escalated with time postirradiation but declined with LET. Our results imply that the cell death mode differs with LET at isosurvival levels.View full abstractDownload PDF (512K) -
Nobuyuki Hamada, Takamitsu Hara, Motoko Omura-Minamisawa, Meinan Ni, T ...2008 Volume 22 Issue 2 Pages 46-53
Published: 2008
Released on J-STAGE: June 30, 2009
JOURNAL FREE ACCESSSignificant evidence indicates that ionizing radiation causes biological effects in nonirradiated bystander cells having received signals from directly irradiated cells. There is little information available hitherto as to the bystander effect of energetic heavy ions; however, our previous work has shown that in confluent cultures of normal human fibroblast AG01522 cells, targeted exposure of 0.0003% of cells to microbeams of 18.3 MeV/u 12C (103 keV/μm) and 13.0 MeV/u 20Ne (375 keV/μm) ions can similarly cause almost 10% decreases in the clonogenic survival, and twofold increments in the incidence of apoptosis whose temporal kinetics varies between irradiated and bystander cells. Using this experimental system, here we further report that bystander responses of AG01522 cells to 17.5 MeV/u 20Ne ions (294 keV/μm) are consistent with those to 18.3 MeV/u 12C and 13.0 MeV/u 20Ne ions. We also demonstrate that such bystander-induced reductions in the survival are less pronounced and occur independently of Bcl-2 overexpression in human cervical cancer HeLa cells.View full abstractDownload PDF (636K) -
Sakura Sora, Nobuyuki Hamada, Takamitsu Hara, Tomoo Funayama, Tetsuya ...2008 Volume 22 Issue 2 Pages 54-58
Published: 2008
Released on J-STAGE: June 30, 2009
JOURNAL FREE ACCESSHere we investigated the potential impact of energetic heavy ions on fibroblast differentiation. The differentiation pattern was morphologically determined at days 3 and 5 after exposure to graded dose of γ-rays (0.2 keV/μm) or carbon ions (18.3 MeV/u, 108 keV/μm). The cells irradiated with higher doses progressed toward later differentiation stages as time goes postirradiation, but underwent fewer cell divisions. Thus, radiation exposure accelerated morphological differentiation, for which carbon ions were more effective than γ-rays. The relative biological effectiveness of carbon ions for differentiation was higher than that for the clonogenic survival, and this was the most case for terminally differentiated cells that may not divide any more. The results are suggestive of the distinct mechanism underlying inactivation of clonogenic potential between the radiation quality, such that the contribution of the differentiation to heavy ion-induced reductions in the survival is greater than to those induced by photons. Such accelerated differentiation could be a protective mechanism that minimizes further expansion of aberrant cells.View full abstractDownload PDF (586K) -
Kanako Hayatsu, Makoto Hareyama, Shingo Kobayashi, Naoyuki Yamashita, ...2008 Volume 22 Issue 2 Pages 59-66
Published: 2008
Released on J-STAGE: June 30, 2009
JOURNAL FREE ACCESSOn the lunar surface, every human being would be exposed to galactic cosmic rays (GCRs) and their secondary products such as gamma rays and neutrons. For the human activity on the lunar surface in the future, it is important to estimate the effect of these particles on radiation doses. The annual ambient dose equivalent on the lunar surface was estimated on the basis of the latest observational data of GCRs. It is found that the annual ambient dose equivalent amount to about 570 mSv/yr during the intermediate period between the maximum and the minimum phases of the solar activity. This amount of dose is mainly produced from primary components of GCRs heavier than proton and helium nuclei. The annual ambient dose equivalent due to iron nuclei during this period is about 130 mSv/yr, more than 20% of the total dose on the lunar surface. Moreover, the dose due to these neutrons among the secondary particles reaches 50 mSv/yr, suggesting that the dose due to neutrons must be considered from the viewpoint of the human activity on the lunar surface.View full abstractDownload PDF (1289K)
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