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PubMed1998

Cell death induced by high-linear-energy transfer carbon beams in human glioblastoma cell lines.

The cytotoxic effect of high-linear-energy transfer (LET) carbon beams on two human glioblastoma cell lines (A172 and TK1) was analyzed, especially concerning cell death, including apoptosis. Gamma-ray radiation was used for comparison. The results of standard colony formation assay showed that the survival fraction of each cell line decreased in an LET-dependent manner. The results of other direct cytotoxic assays, dye exclusion test, and lactate dehydrogenase (LDH) release assay, also displayed a similar relationship between the cytotoxic effect of carbon beams and LET. The maximum values of the cell death index (CDI) were 50.2% in A172 and 37.5% in TK1, both obtained on day 7 after exposure to carbon beams of 80 keV/microm. Apoptosis was observed only on days 4 and 7 after carbon beam irradiation, with maximum values of 7% in A172 and 4.5% in TK1, and the induction of apoptosis after high-LET radiation could be p53-independent. This indicated that a combination of multiple assays to detect cell death was important in evaluating the radiosensitivity of tumor cells, because this approach could more precisely reflect the clinical effectiveness of radiotherapy.

Apoptosis↗
PubMed1975

Survival of synchronized Chinese hamster cells exposed to radiation of different linear-energy transfer.

Chinese hamster V79 cells were exposed to ionizing radiations of a wide range of linear-energy transfer (LET), including 145kV x-rays and six different heavy ions accelerated in the Berkeley heavy-ion linear accelerator. The LET of the ions ranged from 19 keV/um to 2000 keV/um. Survival curves were determined for both synchronized and asynchronous cells, using survival of colony-forming capacity as the end-point. Results with asynchronous cultures were similar to results reported previously for mammalian cells. There was increased effectiveness of killing per dose with increased LET until a change in shape of the single-cell survival curves resulted, from sigmoidal to exponential, with carbon ions (LET of 190 keV/um). With heavier ions, exponential curves were obtained, but with decreased effectiveness per unit dose. Synchronized cultures were obtained by mitotic selection. The expected Chinese hamster cell-cycle survival curve variation was found for X-rays, mainly reflecting the variation in the single-cell extrapolation number, with late S-phase cells the most resistant to radiation. When synchronized cultures were irradiated with the heavy ions that produce exponential survival curves; the survival curves were independent of the cell-cycle time of irradiation. With radiations of LET values between the low and high extremes, a reduced cell-cycle survival curve variation was found, indicating a gradual reduction in the cell-cycle survival curve variation as a function of increased LET.

Animals↗
PubMed1994

A statistical theory of cell killing by radiation of varying linear energy transfer.

A theory is presented that provides an explanation for the observed features of the survival of cultured cells after exposure to densely ionizing high-linear energy transfer (LET) radiation. It starts from a phenomenological postulate based on the linear-quadratic form of cell survival observed for low-LET radiation and uses principles of statistics and fluctuation theory to demonstrate that the effect of varying LET on cell survival can be attributed to random variation of dose to small volumes contained within the nucleus. A simple relation is presented for surviving fraction of cells after exposure to radiation of varying LET that depends on the alpha and beta parameters for the same cells in the limit of low-LET radiation. This relation implies that the value of beta is independent of LET. Agreement of the theory with selected observations of cell survival from the literature is demonstrated. A relation is presented that gives relative biological effectiveness (RBE) as a function of the alpha and beta parameters for low-LET radiation. Measurements from microdosimetry are used to estimate the size of the subnuclear volume to which the fluctuation pertains.

Cell Death↗
PubMed1996

Measurements of the linear energy transfer spectra on the Mir orbital station and comparison with radiation transport models.

A tissue equivalent proportional counter designed to measure the linear energy transfer spectra (LET) in the range 0.2-1250 keV/micrometer was flown in the Kvant module on the Mir orbital station during September 1994. The spacecraft was in a 51.65 degrees inclination, elliptical (390 x 402 km) orbit. This is nearly the lower limit of its flight altitude. The total absorbed dose rate measured was 411.3 +/- 4.41 microGy/day with an average quality factor of 2.44. The galactic cosmic radiation (GCR) dose rate was 133.6 microGy/day with a quality factor of 3.35. The trapped radiation belt dose rate was 277.7 microGy/day with an average quality factor of 1.94. The peak rate through the South Atlantic Anomaly was approximately 12 microGy/min and nearly constant from one pass to another. A detailed comparison of the measured LET spectra has been made with radiation transport models. The GCR results are in good agreement with model calculations; however, this is not the case for radiation belt particles and again points to the need for improving the AP8 omni-directional trapped proton models.

Brazil↗
PubMed2002

Induction of apoptosis by high linear energy transfer radiation: role of p531.

The involvement of the tumor suppressor p53 gene in the sensitivity of many cell types towards low linear energy transfer (LET) radiation is now well established. However, little information is available on the relationship between p53 status of tumor cells and their ability to undergo apoptosis following exposure to high-LET radiation. Here we present the results of experiments carried out with the human lymphoblastoid cell line TK6 and its p53 knock-out counterpart NH32. Cells were irradiated at doses ranging from 0.25 to 8 Gy with fast neutrons (65 MeV), carbon ions (95 MeV/nucleon), and X rays (15 MV). For both cell lines, the occurrence of apoptosis, determined by the quantification of hypodiploid particles as well as the activation of several caspases, was compared with their sensitivity towards high-LET radiation. Results indicate that p53 is involved in the response of TK6 cells to fast neutrons and carbon ions, as measured by cell proliferation and occurrence of apoptosis. However, p53-deficient cells are still able to undergo apoptosis following irradiation. This suggests that heavy ions and fast neutrons induce cellular damage that is not under the control of p53. The involvement of executioner caspases in high-LET radiation induced apoptosis was also evaluated by use of specific inhibitors.

Apoptosis↗
PubMed1997

Dependence of induction of interphase death of Chinese hamster ovary cells exposed to accelerated heavy ions on linear energy transfer.

Induction of interphase death was examined in Chinese hamster ovary cells exposed to accelerated heavy ions (carbon, neon, argon and iron) of various linear energy transfers (LETs) (10-2000 keV/microm). The fraction of cells that underwent interphase death was determined by observing individual cells with time-lapse photography (direct method) as well as by counting cells undergoing interphase death made visible by the addition of caffeine (indirect method). After exposure to X rays, interphase death increased linearly with dose above a threshold of about 10 Gy, whereas it increased at a higher rate without a threshold after exposure to high-LET heavy ions. The relative biological effectiveness (RBE) compared to X rays, as determined at the 50% level of induction, increased with LET, reached a maximum at an LET of approximately 230 keV/microm and then decreased with further increase in LET. The range of LET values corresponding to the maximum RBE appears to be narrower for interphase death than for reproductive death (120-230 keV/microm), as assayed using loss of colony-forming ability as a criterion. The inactivation cross section for interphase cell death reached a plateau of 5-10 microm2. This means that the probability for the induction of interphase death by traversal of a single heavy-ion track through the nucleus (size: about 130 microm2) is about 0.04-0.08.

Animals↗
PubMed1987

Critical values of linear energy transfer, dose rates and doses for radiation hormesis.

Estimates are given of the critical values of linear energy transfer (LET), dose rate and dose, below which radiation hormesis is likely to occur but above which it is unlikely to occur. The critical value of LET is estimated to be 15 congruent to 20 keV/micron, and hence radiation hormesis may occur with beta, gamma or x rays, but is unlikely to occur with alpha radiation. The critical value of dose rate is estimated to be 1 congruent to 10 mGy d-1 for the lifetime exposure, but could be higher than this value for the short period exposure. These estimates are consistent with experimental data. The critical value of dose is also estimated, but cannot be compared with experiment because of lack of data. Brief comparison of plants with animals is made, and it is suggested that the value of the critical dose rate for plants in dry conditions, such as seeds or bulbs, could be higher than the above estimate by about a factor 1000. Some sociological considerations are also given.

Animals↗
PubMedDate not supplied

Effect of exogenous wild-type p53 on melanoma cell death pathways induced by irradiation at different linear energy transfer.

We investigated the effect of exogenous wild-type p53 on the radiation-induced cells apoptosis and necrosis at different levels of linear energy transfer (LET) to evaluate its mechanisms. The human melanoma cell line A375, which bears wild-type p53 gene status, was used, as well as the transfectant A375 cells (A375/p53) with adenoviral vector containing the wild-type p53 gene. We exposed these cells to X-rays and to accelerated carbon-ion (C-) beams. Cellular sensitivities were determined by using clonogenic assay. Apoptotic and necrotic cell deaths were determined morphologically by dual staining (acridine orange and ethidium bromide) using fluorescence microscopy. We discovered that (1) there was no significant difference in survival fraction between A375 cells and A375/p53 cells irradiated by C-beams with greater than 32 KeV/microm LET, (2) although apoptosis in the two kinds of cells increased in an LET-dependent manner, exogenous wild-type P53 induced cell apoptosis efficiently in A375/p53 relative to A375 cells with X-rays or high-LET irradiation, and (3) by high-LET irradiation, the number of necrosis in A375 cells increased significantly (P < 0.05) in comparison with A375/p53 cells. These results indicate that in high-LET irradiation apoptosis induction is p53 dependent partly and exogenous wild-type P53 plays an important role in modulating cell death type, although there was no significant difference in cellular radiosensitivities. Our observation in the study offers the potential application of high-LET radiation combined with p53 in the management of human patients with melanoma.

Apoptosis↗
PubMedDate not supplied

Microbeam developments and applications: a low linear energy transfer perspective.

In the last few years there has been a significant increase in the number of centers having, or developing, both high- and low-linear energy transfer (LET) microbeams for radiobiological investigations. In this review, we will discuss the various approaches for developing low-LET single cell irradiation devices and consider the instrument designs and how the machines capabilities can be exploited to investigate targeted and non-targeted effects of low-LET irradiation.

Electrons↗
PubMed1993

The inverse dose-rate effect for oncogenic transformation by charged particles is dependent on linear energy transfer.

Mouse C3H 10T1/2 cells were exposed to single or fractionated doses of charged particles of defined linear energy transfer (LET) from 25 to 200 keV/microns. Dose fractionation with prolonged time intervals enhanced the yield of transformed foci compared with a single acute dose for a range of LET values between 40 and 120 keV/microns. Radiations of lower or higher LET did not show the enhancement that is commonly referred to as the inverse dose-rate effect. The fractionation scheme that was used consisted of three dose fractions; the maximum enhancement of transformation occurred with an interval of 150 min between dose fractions. This inverse dose-rate effect, demonstrated for cycling cells in log phase, was not seen for cells in plateau phase.

Animals↗
PubMed1994

Evidence against the "oxygen-in-the-track" hypothesis as an explanation for the radiobiological low oxygen enhancement ratio at high linear energy transfer radiation.

Oxygen sensitizes cells toward the effect of ionizing radiation. This sensitization, quantified by the oxygen enhancement ratio (OER), decreases with increasing ionization density or linear energy transfer (LET) of the radiation applied. One explanation for the decreased OER at high LET offers the "oxygen-in-the-track" hypothesis. It claims that oxygen is produced in the track of densely ionizing particles providing an oxic microenvironment around the relevant cellular target molecules, even if cells are exposed under anoxic atmospheric conditions. Experimental evidence is presented against this hypothesis. It is based on the different kinetic pattern of DNA double-strand-break rejoining observed in yeast cells exposed under oxic or anoxic conditions to 3.5 MeV alpha-particles.

DNA↗
PubMed1998

Effect of high linear energy transfer radiation on biological membranes.

Cellular membranes are vital elements, and their integrity is extremely essential for the viability of the cells. We studied the effects of high linear energy transfer (LET) radiation on the membranes. Rabbit erythrocytes (1 x 10(7) cells/ml) and microsomes (0.6 mg protein/ml) prepared from liver of rats were irradiated with 7Li ions of energy 6.42 MeV/u and 16O ions of energy 4.25 MeV/u having maximum LET values of 354 keV/microm and 1130 keV/microm, respectively. 7Li- and 16O-induced microsomal lipid peroxidation was found to increase with fluence. The 16O ions were more effective than 7Li ions, which could be due to the denser energy distribution in the track and the yield of free radicals. These findings suggested that the biological membranes could be peroxidized on exposure to high-LET radiation. Inhibition of the lipid peroxidation was observed in the presence of a membrane-active drug, chlorpromazine (CPZ), which could be due to scavenging of free radicals (mainly HO* and ROO*), electron donation, and hydrogen transfer reactions. The 7Li and 16O ions also induced hemolysis in erythrocytes. The extent of hemolysis was found to be a function of time and fluence, and showed a characteristic sigmoidal pattern. The 16O ions were more effective in the lower fluence range than 7Li ions. These results were compared with lipid peroxidation and hemolysis induced by gamma-radiation.

Animals↗
PubMed1998

Lethality of high linear energy transfer cosmic radiation to Escherichia coli DNA repair-deficient mutants during the 'SL-J/FMPT' space experiment.

We investigated the lethal and mutagenic effects of high linear energy transfer cosmic radiation on 11 strains of Escherichia coli, including DNA repair-deficient mutants, using the Radiation Monitoring Container and Dosimeter in the space shuttle 'Endeavour' as part of the 'SL-J/FMPT' space experiment, the 'Fuwatto '92' project. After the return to earth of the shuttle, we evaluated survival and mutations of samples in space and matched controls. The surviving fractions were determined by means of colony count on broth agar plates, and the mutation frequencies were estimated by appearance of arg' revertants on minimal agar plates. The average of the total equivalent dose rate during this space flight was 0.202 mSv/day as measured by the plastic radiation detectors and the thermoluminescent dosimeters in the Radiation Monitoring Container and Dosimeter. The combined action of DNA polymerase and 3'-->5' exonuclease activities was found to make the greatest contribution to the repair of cosmic radiation-induced DNA damage, 5'-->3' exonuclease and recombination repair enzyme activities made a moderate contribution, whereas UV endonuclease activity was not involved in this DNA repair process.

Colony Count, Microbial↗
PubMed1996

A new silicon detector telescope for measuring the linear energy transfer distribution over the range from 0.2 to 400 keV/micrometer in space.

A new telescope consisting of three two-dimensional position-sensitive silicon detectors which can measure the linear energy transfer (LET) distribution over the range from 0.2 to 400keV/micrometers has been developed as a real-time radiation monitor in manned spacecraft. First, the principle of LET measurement and its design method are described. Second, suitable electronic parameters for the LET measurement are experimentally determined. Finally the telescope performance is investigated by using, relativistic heavy ions. The first in-flight test of this type of telescope on the US Space Shuttle (STS-84) is scheduled for May, 1997.

Astronomy↗
PubMedDate not supplied

Measurement of dose distributions of linear energy transfer in matter irradiated by fast neutrons.

A detector has been developed and used to measure dose distributions versus linear energy transfer to thin gas targets in spherical geometry from fast neutron irradiation of tissue-equivalent plastic and carbon. The detector is a hemispherical proportional counter with a Cs(T1) scintillator at the center of the hemisphere. The coincidence of the proportional counter signals constrain the measurements to charged particles traversing the radius of the hemisphere. The charged particle energy deposition distributions are directly measured for a known pathlength. The A-150 kerma factor was measured at a neutron energy of 14.8 MeV and is in agreement with tabulated values. The carbon kerma factor measurements are less than the tabulated value at 14.8 MeV. The alpha-particle production in carbon was measured for neutron energies from 14.1 to 14.8 MeV and is compared with existing data.

Energy Transfer↗
PubMed2005

Immunochemical analysis of protein expression in breast epithelial cells transformed by estrogens and high linear energy transfer (LET) radiation.

Breast cancer is a complex disease involving numerous genetic aberrations. Immunochemical analysis of protein expression is presented in a human breast epithelial cell line neoplastically transformed by high linear energy transfer (LET) alpha particle radiation in the presence of 17beta estradiol (E) and in the parental human breast epithelial cell line (MCF-10F) which served as a non-tumorigenic control. The aim of this work was to determine the levels of mRNA and protein expression in control and transformed cells at various stages of the neoplastic process. The levels of mRNA and protein expression of PCNA, c-fos, JNK2 and Fra-1 were increased in the transformed cell line compared to the levels in non-tumorigenic control cells. The transforming factor Rho A was significantly increased only in the tumor cell line. Furthermore, the levels of mRNA and protein expression of ErbB2 were significantly increased in the transformed cell line and in tumor cells derived from the transformed cells after injecting them into nude mice. A decrease in RbA/p48 protein expression and mRNA levels was observed in cells treated with double doses of alpha particle radiation in the presence of estrogen, regardless of tumorigenicity. Such expression was lower than that in the control untreated MCF-10F cells. In summary, these studies show that estrogen and high LET-radiation induce changes in oncoprotein expression and mRNA levels of human breast cell lines. These changes are indicative of a cascade of events that characterize the process of cell transformation in breast cancer. These results provide evidence that multiple steps with consecutive changes are involved when normal cells become tumorigenic cells as a result of alpha particle irradiation and estrogen treatments.

Adult↗