Biomedical subjects

Hisako Nakano

Publications and source records attributed to Hisako Nakano.

5 recordsLinked to original sources

PubMed2006

Contribution of indirect action to radiation-induced mammalian cell inactivation: dependence on photon energy and heavy-ion LET.

The contribution of indirect action mediated by OH radicals to cell inactivation by ionizing radiations was evaluated for photons over the energy range from 12.4 keV to 1.25 MeV and for heavy ions over the linear energy transfer (LET) range from 20 keV/microm to 440 keV/microm by applying competition kinetics analysis using the OH radical scavenger DMSO. The maximum level of protection provided by DMSO (the protectable fraction) decreased with decreasing photon energy down to 63% at 12.4 keV. For heavy ions, a protectable fraction of 65% was found for an LET of around 200 keV/microm; above that LET, the value stayed the same. The reaction rate of OH radicals with intracellular molecules responsible for cell inactivation was nearly constant for photon inactivation, while for the heavy ions, the rate increased with increasing LET, suggesting a reaction with the densely produced OH radicals by high-LET ions. Using the protectable fraction, the cell killing was separated into two components, one due to indirect action and the other due to direct action. The inactivation efficiency for indirect action was greater than that for direct action over the photon energy range and the ion LET range tested. A significant contribution of direct action was also found for the increased RBE in the low photon energy region.

Cell Survival↗

PubMed2004

Effects of single-pulse (< or = 1 ps) X-rays from laser-produced plasmas on mammalian cells.

The effects of low linear energy transfer (LET) radiation on mammalian cells have been studied at dose-rates as high as 10(9) Gy/sec delivered as a single 3-nanosecond pulse, and no increase in cytotoxicity was shown compared with delivery at a conventional dose-rate. There have been no observations on the effects of radiation delivered at even higher dose-rates on the picosecond time-scale. Here we examined, for the first time, the effects on cultured mouse L5178Y cells and its radiosensitive XRCC4-deficient mutant M10 cells of sub-picosecond X-rays emitted from laser-produced plasmas at the ultrahigh dose-rate of 10(12)-10(13) Gy/sec. No increase in the sensitivity to the X-rays was observed compared with gamma-rays at a conventional dose-rate. The increase in the sensitivity of L5178Y cells by labeling with 5-iododeoxyuridine was smaller than those irradiated with gamma-rays at a conventional dose-rate, while the difference was apparently the reverse in M10 cells. The D10 ratio between L5178Y cells and M10 cells produced by the X-rays at temporally dense ionization was the same as that produced by X(gamma)-rays at the conventional dose-rate, while the ratio is greatly reduced in the case of particle radiation. These results suggest that there is no increase in the cytotoxic effects of X-rays at dose-rates as high as 10(13) Gy/sec, and that the increased cytotoxicity of particle radiation is not attributable to temporally dense ionization. It is discussed that the mechanism for the induction of radiation damage responsible for cytotoxicity may be slightly modified at ultrahigh dose-rates.

Animals↗

PubMed2003

Delayed expression of apoptosis in X-irradiated human leukemic MOLT-4 cells transfected with mutant p53.

The effects of X-rays on cell survival, apoptosis, and long-term response in the development of cell death as measured by the dye exclusion test were studied in human leukemic MOLT-4 cells (p53 wild-type) stably transfected with a mutant p53 cDNA expression vector. Cell survival, as determined from colony-forming ability, was increased in an expression level dependent manner, but the increase was partial even with the highest-expressing clone (B3). This contrasts with the prior observation that cell death and apoptosis in B3 are completely inhibited at 24 h after irradiation with 1.8 Gy of X-rays. The examination of B3 cells incubated for longer than 24 h after X-irradiation showed a delay in the induction of cell death and apoptosis. Western blot analysis revealed that the time required to reach the highest level of wild-type p53 protein in B3 was longer than the time in MOLT-4 and that the p53 may be stabilized by the phosphorylation at Ser-15. These results suggest that the introduction of mutant p53 into MOLT-4 merely delays the development of apoptosis, during which the cells could repair the damage induced by X-rays, and results in the partial increase in cell survival.

Apoptosis↗

PubMed2002

Time sequence analysis of caspase-3-independent programmed cell death and apoptosis in X-irradiated human leukemic MOLT-4 cells.

It has been demonstrated that caspase-3 is responsible for determining the mode of cell death, i.e., apoptosis or necrosis. To characterize the mode of cell death induced by the inhibition of caspase-3, we have studied the effects of Ac-DEVD-CHO, Ac-YVAD-CHO, and Ac-IETD-CHO, inhibitors of caspases, on structural changes in X-irradiated human leukemic MOLT-4 cells. When cells were irradiated with X-rays and incubated in the presence of Ac-DEVD-CHO, the expression of cell death, as measured by the dye exclusion test, was inhibited, whereas no such change was observed in colony-forming ability. The hallmarks of apoptosis, i.e., nuclear condensation and DNA ladder formation, were depressed. However, a new type of nuclear morphology appeared. The sum of the frequencies of apoptosis and this new type of nuclear structure corresponded to the frequency of X-ray-induced apoptosis for cells incubated in the absence of Ac-DEVD-CHO. Removal of Ac-DEVD-CHO during the course of post-irradiation incubation increased apoptotic nuclear condensation accompanied by a slight decrease in the frequency of the new type of nuclear structure. When Ac-IETD-CHO was used in place of Ac-DEVD-CHO, inhibition of cell death (apoptosis) was also observed, but not in the case of Ac-YVAD-CHO. These results suggest that the inhibition of caspase-3 diminishes the expression of apoptotic hallmarks with no effect on cell survival, that the morphology observed in the presence of Ac-DEVD-CHO is an apoptosis-related structure, and that the cell death observed is a programmed cell death independent of caspase-3. The development of this mode of cell death was slower than that of apoptosis by 4 h.

Apoptosis↗

PubMed2002

A possible intermediate step during apoptotic execution.

Many proteases are known to be involved in apoptosis. Among them, interleukin-1beta converting enzyme (ICE) and its family proteases, which are called caspases, play critical roles in the execution stage of apoptosis. We previously reported that a proteasome-inhibitor, benzyloxycarbonyl Leu-Leu-leucinal (ZLLLal), induced apoptosis in MOLT-4 cells. In the present study, in order to analyze the detailed mechanism of ZLLLal-induced apoptosis, we examined the effect of a caspase-inhibitor, acetyl(Ac)-Tyr-Val-Ala-Asp-chloromethyl ketone (AcYVADcmk), on ZLLLal-induced apoptosis in the cells. Agarose gel electrophoresis revealed that low concentrations of AcYVADcmk efficiently suppressed apoptotic DNA fragmentation. However, the cells presented morphology different from normal, apoptotic or necrotic cells, although DNA fragmentation was suppressed. The same examination was performed on the cells with anti-Fas antibody-induced apoptosis, and the same results were obtained. Some cells with a similar morphology were found even without the caspase-inhibitor in the early stage of anti-Fas antibody-induced physiological apoptosis. In addition, apoptotic cascade was reactivated by washing out the caspase inhibitor from the DNA degradation-suppressed cells. Therefore, this newly found morphological feature shows the presence of a step prior to caspase activation in the cells, and this is the first report presenting the pre-caspase-activated step in the apoptotic cascade.

Amino Acid Chloromethyl Ketones↗