Low Doses Of Γ-rays Research Articles

Synthesis, Characterization, and Performance of Pyridomethene-BF2 Fluorescence Dye-Doped PVA Thin Film and PVP Nanofibers as Low γ-ray Dosimeters.

Currently, particular attention is paid to public health related to the field of γ-ray dosimetry, which is becoming increasingly important in medical diagnostic processes. Incorporating sensitive dyes as radiation dose sensors in different material hosts has shown promising radiation dosimetry application routes. In this perspective, the current study proposes a new fluorescent dye based on boron difluoride complex, the pyridomethene–BF2 named 2-(1-(difluoroboraneyl)-1,2-dihydroquinolin-2-yl)-2-(1-methylquinoxalin-2-ylidene) acetonitrile (DBDMA) as an indicator for low γ-ray doses. The different optical and quantum chemical parameters and the spectral behavior of the selected fluorescent dye were first studied. Then, PVP/DBDMA electrospun nanofibers and PVA/DBDMA thin films were prepared. The different UV–vis spectrophotometric and fluorescence studies revealed a clear change after exposure to different γ-ray doses. Thermogravimetric analysis exhibited excellent thermal stability of the prepared nanocomposite films, showing altered thermal behavior after γ-ray treatment. Furthermore, the SEM evaluation displayed a significant modification in the surface morphology of the two designed nanomaterials with increased radiation dose intensity. These novel forms of dosimeter designed in nanoscale composites could therefore constitute a promising and efficient alternative for rapid and accurate detection of low doses of γ-rays in various medical applications.

Imaging flow cytometry and fluorescence microscopy in assessing radiation response in lymphocytes from umbilical cord blood and cancer patients.

DNA double strand breaks (DSB) induced by ionizing radiation (IR) are usually measured using γH2AX/53BP1 DNA repair foci, that is considered to be the most sensitive assay for DSB analysis. While fluorescence microscopy (FM) is the gold standard for this analysis, imaging flow cytometry (IFC) may offer number of advantages such as lack of the fluorescence background, higher number of cells analyzed, and higher sensitivity in detection of DNA damage induced by IR at low doses. Along with appearance of γH2AX foci, the variable fraction of the cells exhibits homogeneously stained γH2AX signal resulting in so-called γH2AX pan-staining, which is believed to appear at early stages of apoptosis. Here, we investigated incidence of γH2AX pan-staining at different time points after irradiation with γ-rays using IFC and compared the obtained data with the data from FM. Appearance of γH2AX pan-staining during the apoptotic process was further analyzed by fluorescence-activated cell sorting (FACS) of cells at different stages of apoptosis and subsequent immunofluorescence analysis. Our results show that IFC was able to reveal dose dependence of pan-staining, while FM failed to detect all pan-staining cells. Moreover, we found that γH2AX pan-staining could be induced by therapeutic, but not low doses of γ-rays and correlate well with percentage of apoptotic cells was analyzed using flow cytometric Annexin-V/7-AAD assay. Further investigations showed that γH2AX pan-staining is formed in the early phases of apoptosis and remains until later stages of apoptotic process. Apoptotic DNA fragmentation as detected with comet assay using FM correlated with the percentage of live and late apoptotic/necrotic cells as analyzed by flow cytometry. Lastly, we successfully tested IFC for detection of γH2AX pan-staining and γH2AX/53BP1 DNA repair foci in lymphocyte of breast cancer patients after radiotherapy, which may be useful for assessing individual radiosensitivity in a clinically relevant cohort of patients.

Detection of XRCC1 Expression and (8-OHdG) Levels as a marker of Oxidative DNA Damage in Individuals Exposed to Low Dose of Gamma Rays

To study ionizing radiation (IR) effects on biological systems there several techniques are used to identify molecular features of IR exposure, urinary detection of 8-ohdG by ELISA as a marker of DNA oxidative stress is one of the techniques was used in this research, when IR absorbs in a cell so that causing DNA damage and releases 8-ohdG through correction damage. The detection of XRCC1 expression by QRT- PCR is else technique in this study. The genotoxic of IR can be observed even at a low doses 5cGy, According to RPC (Radiation Protection Center) limited place in Baghdad as a source of low-dose IR( Europium 152) before it is removed, some of workers and slums are exposed to low dose of γ-rays ( 5cGy to 10 cGy ). The study groups included the (G1)fifty workers in metal melting are working closely with ( IR source), (G2)twenty five individuals from slums near the IR source, and(G3) twenty five volunteers individuals of male in different age, didn’t exposure to diagnostic x-ray examination or other radiotherapy. Peripheral blood are collected and urine from all individuals. The results indicate that the level of 8-OHDG factor in workers higher than slums individuals and negatively related with XRCC1 expression, also the expression of XRCC1 decreased in individuals exposed for more than 5cGy, and increasing in slums exposed to 5cGy. The low dose of γ-rays causing genotoxic effects due to a combination of DNA-damaging effects and reduced capacity of DNA repair.

BIOINFORMATIC ANALYSIS OF DOSE- AND TIME-DEPENDENT miRNome RESPONSES.

The advent of new 'omics' techniques determined a massive boost in the measurement of the whole spectra of molecules within cells, favoring promising new radiobiological studies at low doses. The main aim of this work was to assess the radiation-induced perturbations of miRNA profiles and their temporal dynamics. Human Umbilical Vein Endothelial Cells were irradiated with low doses of γ-rays. At different time points post-irradiation, cells were harvested and miRNAs isolated. A full mapping of the miRNA sequences via Next-Generation-Sequencing analysis was performed followed by bioinformatic analyses. Pathway enrichment analyses on the differentially expressed miRNAs focused both on the averaged effects of different doses over the 24-h experiment and on the altered temporal dynamics of the miRNA profiles. These complementary analyses provided a picture of the dose- and time-dependent miRNAs responses, allowing to better explore the candidate biomarkers linked to radiation exposures and their corresponding pathways and functions.

An innovative in vitro device providing continuous low doses of γ-rays mimicking exposure to the space environment: A dosimetric study

Astronauts are exposed to microgravity and chronic irradiation but experimental conditions combining these two factors are difficult to reproduce on earth. We have created an experimental device able to combine chronic irradiation and altered gravity that may be used for cell cultures or plant models in a ground based facility.Irradiation was provided by thorium nitrate powder, conditioned so as to constitute a sealed source that could be placed in an incubator. Cell plates or plant seedlings could be placed in direct contact with the source or at various distances above it. Moreover, a random positioning machine (RPM) could be positioned on the source to simulate microgravity. The activity of the source was established using the Bateman formula. The spectrum of the source, calculated according to the natural decrease of radioactivity and the gamma spectrometry, showed very good adequacy. The experimental fluence was close to the theoretical fluence evaluation, attesting its uniform distribution. A Monte Carlo model of the irradiation device was processed by GATE code. Dosimetry was performed with radiophotoluminescent dosimeters exposed for one month at different locations (x and y axes) in various cell culture conditions. Using the RPM placed on the source, we reached a mean absorbed dose of gamma rays of (0.33 ± 0.17) mSv per day.In conclusion, we have elaborated an innovative device allowing chronic radiation exposure to be combined with altered gravity. Given the limited access to the International Space Station, this device could be useful to researchers interested in the field of space biology.

A new approach to reduce uncertainties in space radiation cancer risk predictions.

The prediction of space radiation induced cancer risk carries large uncertainties with two of the largest uncertainties being radiation quality and dose-rate effects. In risk models the ratio of the quality factor (QF) to the dose and dose-rate reduction effectiveness factor (DDREF) parameter is used to scale organ doses for cosmic ray proton and high charge and energy (HZE) particles to a hazard rate for γ-rays derived from human epidemiology data. In previous work, particle track structure concepts were used to formulate a space radiation QF function that is dependent on particle charge number Z, and kinetic energy per atomic mass unit, E. QF uncertainties where represented by subjective probability distribution functions (PDF) for the three QF parameters that described its maximum value and shape parameters for Z and E dependences. Here I report on an analysis of a maximum QF parameter and its uncertainty using mouse tumor induction data. Because experimental data for risks at low doses of γ-rays are highly uncertain which impacts estimates of maximum values of relative biological effectiveness (RBEmax), I developed an alternate QF model, denoted QFγAcute where QFs are defined relative to higher acute γ-ray doses (0.5 to 3 Gy). The alternate model reduces the dependence of risk projections on the DDREF, however a DDREF is still needed for risk estimates for high-energy protons and other primary or secondary sparsely ionizing space radiation components. Risk projections (upper confidence levels (CL)) for space missions show a reduction of about 40% (CL∼50%) using the QFγAcute model compared the QFs based on RBEmax and about 25% (CL∼35%) compared to previous estimates. In addition, I discuss how a possible qualitative difference leading to increased tumor lethality for HZE particles compared to low LET radiation and background tumors remains a large uncertainty in risk estimates.

Dose response of micronuclei induced by combination radiation of α-particles and γ-rays in human lymphoblast cells

Combination radiation is a real situation of both nuclear accident exposure and space radiation environment, but its biological dosimetry is still not established. This study investigated the dose–response of micronuclei (MN) induction in lymphocyte by irradiating HMy2.CIR lymphoblast cells with α-particles, γ-rays, and their combinations. Results showed that the dose–response of MN induced by γ-rays was well-fitted with the linear-quadratic model. But for α-particle irradiation, the MN induction had a biphasic phenomenon containing a low dose hypersensitivity characteristic and its dose response could be well-stimulated with a state vector model where radiation-induced bystander effect (RIBE) was involved. For the combination exposure, the dose response of MN was similar to that of α-irradiation. However, the yield of MN was closely related to the sequence of irradiations. When the cells were irradiated with α-particles at first and then γ-rays, a synergistic effect of MN induction was observed. But when the cells were irradiated with γ-rays followed by α-particles, an antagonistic effect of MN was observed in the low dose range although this combination radiation also yielded a synergistic effect at high doses. When the interval between two irradiations was extended to 4h, a cross-adaptive response against the other irradiation was induced by a low dose of γ-rays but not α-particles.

Cellular radiosensitivity and cell-type-specific activation of apoptosis signaling pathways

We have examined the cell-type-dependent sensitivity to UV-induced apoptosis using mouse lymphoma 3SB and human leukemic Jurkat cells and three human carcinoma cell lines (HeLa S3, HeLa SC and MCF-7). Exposure of 3SB and Jurkat cells resulted in large amounts of cytochrome c being released into the cytosol, and a clear laddering pattern of DNA fragments and morphological changes characteristic of apoptosis were detected within 3 h of incubation after irradiation. HeLa S3, HeLa SC and MCF-7 cells also showed extensive release of cytochrome c at 4–6 h after exposure, but apoptotic morphologic changes appeared much later. Similar differences in induction of apoptosis after γ irradiation were observed between two kinds of cells. Interestingly, 3SB cells that express wild-type p53 protein showed a steep increase in number of apoptotic cells when irradiated with low doses of γ-rays, and the dose response of apoptosis induction was not influenced by radiation dose rate. This result suggests that signaling for radiation-induced apoptosis in hematopoietic cells showing rapid apoptosis can be triggered by initial DNA damage, and not determined by DNA repair.

Possible role of elevation of glutathione in acquisition of enhanced immune function of mouse splenocytes exposed to low-dose γ-rays

The relation between induction of an increased glutathione level and the enhanced immune functions, including proliferative response and natural killer (NK) activity, of mouse splenocytes by a low dose of γ-rays was investigated. Glutathione level in mouse splenocytes significantly increased 2 h after whole-body γ-ray irradiation at 0.5 Gy, peaked at 4 h and thereafter, decreased almost to the initial (0 h) level within 12 h after irradiation. A significant enhancement of Con A-induced proliferation was recognized in the splenocytes from the whole-body-irradiated animals obtained at post-irradiation between 2 and 6 h. NK activity was also enhanced at the same time periods after the irradiation. Addition of glutathione to splenocytes obtained from normal mice enhanced both Con A-induced proliferative response and NK activity in a dose-dependent manner. These enhancements were completely blocked by buthionine sulfoximine, a specific inhibitor of the de novo pathway of glutathione synthesis. These results suggest that induction of endogenous glutathione synthesis in splenocytes after low-dose γ-ray irradiation is partially responsible for the appearance of enhanced immune function.

The radioprotective effects of bu-zhong-yi-qi-tang: a prescription of traditional Chinese medicine.

We evaluated the effect of bu-zhong-yi-qi-tang, a prescription of traditional Oriental medicine, and its major ingredients on protection of the intestine and hematopoietic organs against radiation damage in this study. The jejunal crypt survival, endogenous spleen colony formation, and apoptosis in jejunal crypt cells were investigated in mice irradiated with high and low doses of gamma-rays. bu-zhong-yi-qi-tang administration before irradiation protected the jejunal crypts (p < 0.0001), increased the formation of the endogenous spleen colony (p < 0.05) and reduced the frequency of radiation-induced apoptosis (p < 0.05). In experiments on the effects of the individual ingredient of bu-zhong-yi-qi-tang, Rensan (Radix Ginseng), Danggui (Radix Angelicae gigantis), Shengma (Rhizoma Cimicifugae) and Chaihu (Radix Bupleuri) might have major radioprotective effects, and each might have different degrees of effect on these three endpoints. These results indicated that bu-zhong-yi-qi-tang might be a better agent than any one of its ingredients to satisfy all three endpoints. Although the mechanisms of this inhibitory effect remain to be elucidated, these results indicated that bu-zhong-yi-qi-tang might be a useful radioprotector, especially since it is a relatively non-toxic natural product. Further studies are needed to better characterize the protective nature of bu-zhong-yi-qi-tang extract and its ingredients.

Localization of glutathione and induction of glutathione synthesis-related proteins in mouse brain by low doses of γ-rays

First, we determined the cerebral localization of reduced glutathione (GSH) in normal mice by means of autoradiography using 99mTc - meso-hexamethyl propylene oxime. A highly specific localization of GSH in the cerebellum and hippocampus was observed. Secondly, we measured the elevation of GSH level in the brain after low-dose γ-irradiation. The cerebral GSH levels increased soon after irradiation with 50 cGy of γ-rays, reaching a maximum at 3 h post-treatment, then remaining significantly higher than that of the non-irradiated control until 12 h and returning to the control level by 24 h. Thirdly, we examined the induction of the activities and the mRNAs of proteins involved in the synthesis and regeneration of GSH in the brain of mice subjected to low-dose γ-ray irradiation. The level of mRNA for γ-glutamylcysteine synthetase was significantly increased at 0.5 h, and remained high until 2 h post-irradiation (50 cGy). The level was transiently lowered to the non-irradiated control level at 3 h and slightly increased again after 6 h post-irradiation. γ-Glutamylcysteine synthetase activity was significantly increased 3 h after irradiation, and remained high up to 24 h post-irradiation. As for glutathione reductase, the mRNA level was increased at 0.5 h, and peaked strongly at 2 h, while the enzyme activity was significantly increased at 6 h after irradiation, and continued to increase up to 24 h. The level of mRNA for thioredoxin, which contributes to GSH biosynthesis by supplying cysteine to the de novo pathway, peaked between 0.5 h and 2 h post-irradiation, and rapidly declined thereafter. The content of thioredoxin showed a transient decrease immediately after irradiation, but was then remarkably elevated, reaching a maximum at 3 h, and thereafter declining sharply. These results indicate that the increase in endogenous GSH in mouse brain soon after low-dose γ-ray irradiation is a consequence of the induction of GSH synthesis-related proteins and occurs via both the de novo synthesis and the regeneration pathways.

Induction of mRNAs for glutathione synthesis-related proteins in mouse liver by low doses of γ-rays

We examined the elevation of the reduced form of glutathione (GSH) level and the induction of mRNAs for proteins involved in the synthesis and regeneration of GSH in the liver of mice after low-dose γ-ray irradiation. The liver GSH level increased soon after irradiation with 50 cGy of γ-rays, reached a maximum at around 12 h post-treatment. The mRNA of γ-glutamylcysteine synthetase (γ-GCS), the rate-limiting enzyme for de novo synthesis for GSH, showed a small increase that peaked at 6 h after γ-ray irradiation at a dose of 50 cGy. Only a small increase in γ-GCS activity was observed throughout the 24-h post-irradiation period. In the case of glutathione reductase (GR), which is involved in the regeneration of GSH from the oxidized form (GSSG), the mRNA level peaked strongly at 1 h, while the activity peaked at twice the control level 12 h after irradiation. The level of mRNA for thioredoxin (TRX), which contributes to GSH biosynthesis by supplying cysteine to the de novo pathway, peaked at 1 h and declined thereafter, while the activity peaked at 3 h and then declined sharply. These results indicate that the increase in endogenous GSH immediately following low-dose γ-ray irradiation is predominantly due to operation of the regeneration cycle and not de novo synthesis. We also examined the dependence of mRNA induction on the γ-ray dose.

Induction of DNA single-strand breaks in human lymphocytes by low doses of gamma-rays.

We hypothesized that very low doses of gamma-rays have a genotoxic effect as measured by DNA single-strand breaks (ssbs). To test our hypothesis we used a newly developed alkaline microgel electrophoretic technique to quantitate DNA ssbs in freshly isolated human lymphocytes. An enhanced sensitivity to detect low levels of DNA damage was made possible by this method due to an additional step of DNA precipitation by ethanol in agarose microgels. We exposed lymphocytes from three subjects for 1 h at 4 degrees C to 740 MBq of technetium 99-m at a distance of 20 cm (0.25 mGy), 10 cm (1.02 mGy), and 5 cm (4.08 mGy) from the source vial. Doses of 1.02 and 4.08 mGy induced a significant dose-dependent increase in DNA ssbs in human lymphocytes from three subjects, each examined on three different days.

Low doses of γ-rays can induce the expression of mdr gene

We reported earlier that human cervical carcinoma HeLa cells exposed to 30 fractions of 0.5 Gy γ-rays became resistant to cisplatin, methotrexate and vincristine, but retained the same sensitivity to γ-rays and ultraviolet light. The aim of this study was to examine whether a small number of γ-ray fractions, with a lower daily dose, may also change the sensitivity of preirradiated cells to different cytotoxic drugs. Using the modified MTT staining procedure, we found that cells preirradiated with 5 or 10 daily fractions of only 0.17 Gy γ-rays did not alter their sensitivity to mitomycin, cisplatin, methotrexate, 5-fluorouracil, etoposide and doxorubicin. However, 10 fractions of γ-rays induced resistance to vincristine and vinblastine. Our immunocytochemical experiments using monoclonal antibody JSB-1 show that the plasma membrane P-glycoprotein is involved in the induced resistance to Vinca alkaloids.

An analysis of γ-ray-induced DNA damage in human blood leukocytes, lymphocytes and granulocytes

Lymphocytes and granulocytes were separated from human peripheral blood and irradiated with low doses of γ-rays (0.05–0.5 Gy) from a 137Cs source. The magnitude and intercellular distribution of DNA damage, i.e., single-strand breaks and alkali-labile lesions, were compared with those obtained in unfractionated leukocytes irradiated in whole blood, using the alkaline single-cell gel-electrophoresis technique. Based on the extent of DNA migration, irradiation resulted in a linear and dose-dependent increase in DNA damage in all 3 cell populations, with a significant increase being detected at 0.05 Gy. The dose-dependent increase for DNA migration was not significantly different between separated lymphocytes and granulocytes, but their responses were significantly elevated over that obtained for leukocytes irradiated in whole blood. Based on an analysis of the ration of the range to the standard deviation for each cell population at each dose of radiation, the distribution of damage among cells was relatively homogeneous and independent of dose and cell population. These results are consistent with a hypothesis that irradiation of leukocytes in whole blood partially protects against radical-induced DNA damage.

Radio-adaptive response: characterization of a cytogenetic repair induced by low-level ionizing radiation in cultured Chinese hamster cells

Pretreatment with low doses of β-rays from incorporated tritiated thymidine ([ 3H]dThd) or of Co-60 γ-rays (1 or 5 cGy) rendered actively growing Chinese hamster V79 cells more resistant to the induction of micronuclei or sister-chromatid exchanges (SCEs) by a subsequent high dose of γ-rays (1 Gy). This adaptive response to ionizing radiation (radio-adaptive response) can be induced by an optimal range of low doses of 3H β-rays, but not by much lower or higher adapting doses. Full expression of the adaptive response induced by the exposure to low doses of 60Co γ-rays occurred 4 h after the adapting dose. The cells pre-exposed to low doses of γ-rays showed cross-resistance to challenge doses of γ-rays themselves and also of mitomycin C(MMC) and near ultraviolet light (UV-B, 313 nm), but not to those of ethyl methanesulfonate (EMS) or cis-platinum (II) diammine dichloride (cisplatin) for SCE induction. These results suggest that the radio-adaptive response mechanistically couples to the repair network which copes with chromatin lesions induced by MMC and UV-B.

Radiostimulation of barley seeds treated with 2-mercaptoethanol of ascorbate

In model experiments with Bonus barley,where the growth of a fraction of the seedlings is retarded by a raised thiol content, obtained through treatment with 2-mercaptoethanol, stimulation of growth is reproducibly induced by low doses of γ-rays. As illustrated by a probit representation of seedling heights, and by the decrease of coefficients of variation, the radiostimulation is restricted to that fraction of seedlings which exhibits a suppressd growth. The validity of the model to natural situations was sustained in studies of the variety Impala, which was shown by Fendrik and Bors to respond regularly to stimulating doses of X-rays. In this variety the response was shown to be restricted to a sub-population of seedlings with retarded growth, i.e. the same pattern as observed in thiol-treated Bonus barley.

Radiation-induced chromosomal aberrations in human lymphocytes. I. Dependence on the dose of gamma-rays and an anomaly at low doses

Cultures of human lymphocytes obtained from blood of healthy adult donors were irradiated with different doses of 60Co γ-rays and the irradiated cells were analysed in metaphase 50 h after irradiation. The effect (total yield of abberations of chromosome type, or total yield of exchange type abberations) produced by the lowest dose (5 rad) appears to be statistically significant in a sample of 1500 cells. In the usual dose range (25–400 rad), both parabolic and linear-quadratic equations give a satisfactory fit of experimental data (dicentrics, fragments, or all aberrations of chromosome type). Low doses of γ-rays, however, produced more aberrations than expected, if one extrapolates dose-effect curves from higher doses. Both relations should be considered, therefore, merely as empirical equations. Dicentrics show at low doses (10–30 rad) a plateau which appears to be statistically significant. Some indications are obtained that the total number of chromosome-type aberrations is a more reliable criterion of cytogenetic damage than the usually accepted yeild of dicientrics and rings.