Chromosome structural damages to the myelokaryocytes of rats in late periods after chronic exposure to tritium and external gamma irradiation

A pronounced variation in the total amount and spectrum of chromosome aberrations of rat myelocarycytes was found at later times following long-term exposure to tritium oxide and external gamma-radiation (137Cs). Cells with atypical chromosomes (symmetrical exchanges) were 1.5-2 times more frequent in bone marrow of tritium-treated rats throughout the entire lifetime.     

Gene expression profiles in mouse liver after long-term low-dose-rate irradiation with gamma rays

Changes in gene expression profiles in mouse liver induced by long-term low-dose-rate γ irradiation were examined by microarray analysis. Three groups of male C57BL/6J mice were exposed to whole-body radiation at dose rates of 17-20 mGy/day, 0.86-1.0 mGy/day or 0.042-0.050 mGy/day for 401-485 days with cumulative doses of approximately 8 Gy, 0.4 Gy or 0.02 Gy, respectively. The gene expression levels in the livers of six animals from each exposure group were compared individually with that of pooled sham-irradiated animals. Some genes revealed a large variation in expression levels among individuals within each group, and the number of genes showing common changes in individuals from each group was limited: 20 and 11 genes showed more than 1.5-fold modulation with 17-20 mGy/day and 0.86-1.0 mGy/day, respectively. Three genes showed more than 1.5-fold modulation even at the lowest dose-rate of 0.04-0.05 mGy/day. Most of these genes were down-regulated. RT-PCR analysis confirmed the expression profiles of the majority of these genes. The results indicate that a few genes are modulated in response to very low-dose-rate irradiation. The functional analysis suggests that these genes may influence many processes, including obesity and tumorigenesis.     

Resuscitation of microorganisms after gamma irradiation.

Microbiological analysis of rock exposed to gamma-radiation doses between 0 and 9.34 kGy indicated that some microorganisms became viable but nonculturable (VBNC) and lost metabolic capacity as measured by BIOLOG microtiter plates. To investigate this phenomenon, portions of irradiated rock were placed at 4 degrees C for 2 months in an attempt to resuscitate the microbes to a culturable state. Culturable heterotrophs were enumerated and BIOLOG plates were used to determine the metabolic capability of the microbial community. Culturable bacteria that had previously been nonculturable were found at all doses. The number of colony types decreased from 26 in the nonirradiated control rock to between 9 and 10 in rock irradiated at doses ranging from 2.34 to 9.34 kGy. BIOLOG plates indicated partial recovery of metabolic capacity in all the samples tested. Fatty acid methyl ester analysis of the recovered isolates using the MIDI system (Microbial ID, Inc.) yielded three distinct groups of related bacteria. All resuscitated isolates clustered with the original nonirradiated isolates at the genus level, and 92% of them clustered at the species level. These results indicate that microbes were likely resuscitated from a VBNC state.     

Potential role of the membrane in the development of intestinal cellular damage after whole-body gamma irradiation of the rat

Our study emphasizes the effect of gamma irradiation on intestinal cell membrane fluidity and addresses the potential relationships existing between radiation-induced lipoperoxidation, membrane fluidity, and changes in membrane protein activities. Male Wistar rats were exposed to an 8-Gy total body irradiation (60Co source) and studied 1, 4, and 7 days after irradiation (D1, D4, and D7). Membrane enzyme activities and fluorescence anisotropy were determined on small intestinal crude membrane preparations. The supernatants of membrane preparations as well as plasma were used for malonedialdehyde (MDA) quantification. The effect of carbamylcholine on electrical parameters was estimated on distal ileum placed in Ussing chambers. We observed a decrease in fluorescence anisotropy for at least 7 days, an increase in membrane production of MDA at D4, a decrease in membrane enzyme activities at D4, but an amplification of carbamylcholine-induced increase in short-circuit current at D4 and D7. Furthermore, correlations were observed between the 1,6-diphenyl-1,3,5-hexatriene anisotropy coefficient and sucrase activity and between MDA levels and leucine aminopeptidase activity. Thus, total body irradiation induces changes in intestinal membrane fluidity and an increase in lipoperoxidation. These modifications may have an impact on the activity of membrane proteins involved in intestinal function.     

Cytogenetic studies on the effect of chronic gamma irradiation onVicia faba

Vicia faba seeds (cv. Giza 1) were planted in the Inshas gamma radiation field where they were chronically irradiated during the whole life of the plant. The percentage of the induced abnormal P.M.Cs, as well as the frequency of abnormal P.M.Cs in the different meiotic stages were proportional with the given doses. The main types of chromosome aberrations were anaphase and telophase bridges, fragmentation and lagging chromosomes. The nearest plants to the source showed an inhibition of shoot growth, flower and seed sterility and irregular branching. At the dosage levels used irradiation had no effect on pollen fertility. Seeds of the 1st filial generation were used for both mitotic and meiotic studies. The percentage of the mitotic abnormalities was proportional with the doses. The most dominant type of anomaly was the presence of micronuclei in the different stages of mitosis and in the resting cells. Irradiation affected also other types of anomaliese.g. lagging chromosomes, fragments, bridges...etc. Meiosis, and pollen fertility (2nd generation) were normal.     

Depletion of glutathione after gamma irradiation modifies survival

The relationship between the intracellular glutathione (GSH) concentration and the aerobic radiation response was studied in Chinese hamster ovary cells. Various degrees of GSH depletion were produced by exposure to buthionine sulfoximine (BSO) and/or diethyl maleate (DEM). Diethyl maleate did not act as a classical radiosensitizer under the experimental conditions employed, nor did exposure to DEM/BSO nonspecifically affect protein thiols as measured by thiol blotting. Dose-response curves were obtained using cells irradiated in the absence or presence of DEM/BSO, which decreased GSH levels by 90-95%. Exposure to DEM/BSO did not affect the formation of DNA single-strand breaks or DNA-protein crosslinks measured immediately after irradiation performed at ice temperatures. Analysis of survival curves indicated that the Dq was decreased by 18% when GSH depletion occurred prior to, during, and after irradiation. The DEM/BSO exposure did not affect D0. To study postirradiation conditions, cells were exposed to 10 microM DEM prior to and during irradiation, which was performed at ice temperatures. Levels of GSH were depleted by 75% by this protocol. Immediately after irradiation, the cells were rapidly warmed by the addition of 37 degrees C growth medium containing either 10 or 90 microM DEM. Addition of 10 microM DEM after irradiation did not affect the degree of depletion, which remained constant at 75%. In contrast, GSH depletion was increased to 90% 10 min after addition of the 90 microM DEM. Addition of 90 microM DEM after irradiation produced a statistically significant difference in survival compared to addition of 10 microM DEM. In a second depletion protocol, cells were exposed to 100 microM DEM at room temperature for 5 min, irradiated, incubated at 37 degrees C for 1 h, washed, and then incubated in 50 microM BSO for 24 h. This depletion protocol reduced survival by a factor of 2.6 compared to cells not exposed to the combination of DEM/BSO. Survival was not affected if the cells were exposed to the DEM or BSO alone. This was interpreted to indicate that survival was not affected by GSH depletion occurring after irradiation unless depletion was rapid and sustained. The rate of repair of sublethal and potentially lethal damage was measured and found to be independent of the DEM/BSO exposure. These experimental results in addition to previous ones (Freeman and Meredith, Int. J. Radiat. Oncol. Biol. Phys. 13, 1371-1375, 1987) were interpreted to indicate that under aerobic conditions GSH depletion may alter the expression of radiation damage by affecting metabolic fixation.     

Activation of the DNA repair system in tissues of mice subjected to chronic gamma irradiation

Mice exposed to gamma-quanta during 47 and 82 days at a dose-rate of 1.3 mGy/h and cumulative doses of 1.45 and 2.54 Gy, respectively, were subsequently subjected to a single acute irradiation with a dose of 20 Gy. Repair of DNA damages induced by the acute exposure was shown to proceed in the brain, pulmonary and splenic tissues of chronically exposed mice more readily than in the tissues of mice not subjected to chronic irradiation. The data obtained indicate that the induced adaptive response activates DNA repair in tissues of mice exposed to long-term low-level radiation.     

Increased synthesis of low-molecular-weight nuclear ribonucleic acids of rat liver after gamma irradiation and hepatectomy.

Incorporation of [3H]orotic acid into low-molecular-weight nRNA of rat liver, fractionated on polyacrylamide gels, increased 6-12h after partial hepatectomy and 6h after gamma-irridation at 2000 R. The incorporation of orotic acid was particularly increased into the 4.5S, 5S and approx. 10S nRNA fractions. If the irradiation was given after 6h of regeneration and RNA was isolated from the nucleus 12h after hepatectomy then the incorporation of orotic acid into these low-molecular-weight nRNA components was greater than after hepatectomy or irradiation alone.     

Simulation of DNA damage after proton irradiation

The biophysical radiation track simulation model PARTRAC was improved by implementing new interaction cross sections for protons in water. Computer-simulated tracks of energy deposition events from protons and their secondary electrons were superimposed on a higher-order DNA target model describing the spatial coordinates of the whole genome inside a human cell. Induction of DNA double-strand breaks was simulated for proton irradiation with LET values between 1.6 and 70 keV/microm and various reference radiation qualities. The yield of DSBs after proton irradiation was found to rise continuously with increasing LET up to about 20 DSBs per Gbp and Gy, corresponding to an RBE up to 2.2. About half of this increase resulted from a higher yield of DSB clusters associated with small fragments below 10 kbp. Exclusion of experimentally unresolved multiple DSBs reduced the maximum DSB yield by 30% and shifted it to an LET of about 40 keV/microm. Simulated fragment size distributions deviated significantly from random breakage distributions over the whole size range after irradiation with protons with an LET above 10 keV/microm. Determination of DSB yields using equations derived for random breakage resulted in an underestimation by up to 20%. The inclusion of background fragments had only a minor influence on the distribution of the DNA fragments induced by radiation. Despite limited numerical agreement, the simulations reproduced the trends in proton-induced DNA DSBs and fragment induction found in recent experiments.     

Action of chronic gamma irradiation on chipmunks in a vivarium

The activity, the dynamics of changes in the body mass and the weight of some internal organs of chipmunks at different physiological status were studied in normal conditions (0.86 pA/kg) and during chronic gamma-irradiation at low dose-rates (46.3 pA/kg). The stated higher indications of body mass and the lower activity of the animals from the experimental group during the hibernation period can be regarded as the favourable protective reaction of the organism to the chronic effects of gamma-irradiation with low doses.