Activation of DNA damage response signaling in lung adenocarcinoma A549 cells following oxygen beam irradiation.

Oxygen beams are high linear energy transfer (LET) radiation characterized by higher relative biological effectiveness than low LET radiation. The aim of the current study was to determine the signaling differences between γ- and oxygen ion-irradiation. Activation of various signaling molecules was looked in A549 lung adenocarcinoma cells irradiated with 2Gy oxygen, 2Gy or 6Gy γ-radiation. Oxygen beam was found to be three times more cytotoxic than γ-radiation. By 4h there was efficient repair of DNA in A549 cells exposed to 2Gy or 6Gy gamma radiation but not in cells exposed to 2Gy oxygen beam as determined by γ-H2AX counting. Number of ATM foci was found to be significantly higher in cells exposed to 2Gy oxygen beam. Percentage of cells showing ATR foci were more with gamma however number of foci per cell were more in case of oxygen beam. Oxygen beam irradiated cells showed phosphorylation of Chk1, Chk2 and p53. Many apoptotic nuclei were seen by DAPI staining in cells exposed to oxygen beam. The noteworthy finding of this study is the activation of the sensor proteins, ATM and ATR by oxygen irradiation and the significant activation of Chk1, Chk2 and p53 only in the oxygen beam irradiated cells.

Effect of 7Li radiation on endogenous hormonal level on developing cotton fiber.

Influence of radiation doses (7Li) on cellular metabolism, specially endogenous hormonal level, was studied in monolayer of cotton fibers. Changes in endogenous phytohormone level were determined with two different fluences of 7Li equivalent to radiation doses of 1 Gy and 4 Gy. To estimate the endogenous indole-3-acetic acid (IAA), phenoxy acetic acid (PAA), and abscisic acid (ABA) levels, indirect ELISA was performed with the help of antibodies raised against each hormone. In samples at later stage, dose dependent response was apparent in PAA. Results showed that in vivo content of each hormone increased with radiation treatment except ABA.

Cell killing, nuclear damage and apoptosis in Chinese hamster V79 cells after irradiation with heavy-ion beams of (16)O, (12)C and (7)Li.

Chinese hamster V79 cells were exposed to high LET (linear energy transfer) (16)O-beam (625keV/mum) radiation in the dose range of 0-9.83Gy. Cell survival, micronuclei (MN), chromosomal aberrations (CA) and induction of apoptosis were studied as a follow up of our earlier study on high LET radiations ((7)Li-beam of 60keV/mum and (12)C-beam of 295keV/mum) as well as (60)Co gamma-rays. Dose dependent decline in surviving fraction was noticed along with the increase of MN frequency, CA frequency as well as percentage of apoptosis as detected by nuclear fragmentation assay. The relative intensity of DNA ladder, which is a useful marker for the determination of the extent of apoptosis induction, was also increased in a dose dependent manner. Additionally, expression of tyrosine kinase lck-1 gene, which plays an important role in response to ionizing radiation induced apoptosis, was increased with the increase of radiation doses and also with incubation time. The present study showed that all the high LET radiations were generally more effective in cell killing and inflicting other cytogenetic damages than that of low LET gamma-rays. The dose response curves revealed that (7)Li-beam was most effective in cell killing as well as inducing other nuclear damages followed by (12)C, (16)O and (60)Co gamma-rays, in that order. The result of this study may have some application in biological dosimetry for assessment of genotoxicity in heavy ion exposed subjects and in determining suitable doses for radiotherapy in cancer patients where various species of heavy ions are now being generally used.

Genotoxic effects in M5 cells and Chinese hamster V79 cells after exposure to 7Li-beam (LET=60 keV/microm) and correlation of their survival dynamics to nuclear damages and cell death.

Chinese hamster V79 cell and a cell strain M5, derived from V79 cells and reported to be relatively resistant to gamma-ray, hydrogen peroxide, and N-methyl-N-nitro-N-nitrosoguanidine (MNNG; a potent human carcinogen), were exposed to high LET (7)Li-beam (LET=60 keV/microm) at approximately 90% confluent state in the dose range of 0-1 Gy. Effects of (7)Li-beam exposure on cell survival, micronuclei induction (MN), chromosomal aberrations (CA) and apoptosis were compared in both the cell lines. A dose-dependent decline in survival for both the cell lines was noted, relatively less in M5 cells (mostly p<0.01) indicating greater radio-resistance in this strain. The MN, CA and apoptosis increased in a dose-dependent manner in both V79 and M5 cells. Significant differences in various other parameters between these two cell lines were also noted. The relative intensity of DNA ladder, which is a useful marker for the determination of the extent of apoptosis induction, was much higher in V79 cells. A good correlation between the reduction of the surviving fractions and the increase in frequencies of MN or CA or apoptosis was noted for both the cell lines.

Response of the FBX system to a carbon beam: its potential as a dosimeter in heavy particle radiotherapy.

The FBX aqueous chemical dosimeter contains 0.2 mol m(-3) ferrous ammonium sulphate, 5.0 mol m(-3) benzoic acid and 0.20 mol m(-3) xylenol orange in 40.0 mol m(-3) sulphuric acid. The dosimeter can measure photon and electron doses in the range 0.1 to 3000 cGy in radiotherapy. The response of this dosimeter was measured for a 53.2 MeV carbon beam in the present work. Our initial result indicates that the sensitivity of the FBX system to the carbon beam as compared to cobalt-60 gamma rays is 25.5%, and thus we believe that the FBX system could be a useful dosimeter for carbon beams and similar heavy ions considered useful in radiotherapy.

Expression of NF-kappaB and ERK following heavy ion irradiation.

Heavy ion irradiation of cells is known to increase cytotoxic, mutagenic, and carcinogenic effects. The increased biological effectiveness of these ions is as yet unexplained, except for the fact that, unlike gamma-radiation, they result in clustered damage. It is likely that the increased biological effectiveness is a consequence of altered signaling pattern, which in turn may be due to the difference in the nature of damage produced. Gamma irradiation has been known to activate both pro- and anti-apoptotic signaling pathways. Nuclear factor-kappaB (NF-kappaB) and extracellular signal regulated kinase (ERK) contribute to the survival of the irradiated cell. Moreover, NF-kappaB acts as a redox sensor. In the present study, we examined NF-kappaB and ERK as antiapoptotic factors that could lead to the inhibition of apoptosis and, consequently, to increased mutagenicity. Both these signaling factors show a fluctuation in their levels with time.

Effect of heavy ion irradiation on DNA DSB repair in Methanosarcina barkeri.

Archaea are expected to be highly repair proficient since they survived the vicious onslaught of radiation damage at the time of their early appearance. The DNA double strand break repairing ability of mesophilic archaea Methanosarcina barkeri (DSM 804) was studied using (7)Li, (12)C and (16)O heavy ions and compared with that of (60)Co gamma-rays. They can repair double strand breaks and, as in eukaryotes, the nature as well as extent of induction and its subsequent repair were dependent on the linear energy transfer of the radiation source.