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PubMedDate not supplied

Sensitivity of germ cells and embryos to ionizing radiation.

Experiments performed in laboratory animals suggest that ionizing radiation can induce DNA damage in the germ cells of exposed individuals and lead to various deleterious effects in their progeny, including miscarriage, low birth weight, congenital abnormalities and perhaps cancer. However, no clear evidence for such effects has been found in epidemiological studies of people exposed to radiation. The predicted risks of hereditary effects of any kinds resulting from parental exposure to relatively low doses of ionizing radiation remain very low, compared to the spontaneous risks in the absence of irradiation. Irradiation of the mouse embryo can lead to various effects (lethality, growth retardation, congenital abnormalities), depending on the period of gestation at which irradiation occurs. In humans, prenatal irradiation has only been exceptionally associated with congenital abnormalities, but irradiation between weeks 8-25 has been shown to be able to induce severe mental retardation. Although being not proven, the risk of developing a childhood cancer following prenatal irradiation may also not be excluded. Like for genetic effects, the risk of adverse effects following exposure of the embryo to relatively low doses remains quite low compared to the natural risks.

Animals↗
PubMed1986

Reversible alterations in cultured pulmonary artery endothelial cell monolayer morphology and albumin permeability induced by ionizing radiation.

The effects of ionizing irradiation (0, 600, 1,500, or 3,000 rads) on the permeability of pulmonary endothelial monolayers to albumin were studied. Pulmonary endothelial cells were grown to confluence on gelatin-coated polycarbonate filters, placed in serum-free medium, and exposed to a 60Co source. The monolayers were placed in modified flux chambers 24 hours after irradiation; 125I-albumin was added to the upper well, and both the upper and lower wells were serially sampled over 4 hours. The amount of albumin transferred from the upper well/hour over the period of steady-state clearance (90-240 min after addition of 125I-albumin) was 2.8 +/- 0.2% in control monolayers and was increased in monolayers exposed to 1,500 or 3,000 rads (increase of 63 +/- 10% and 61 +/- 10%, respectively, P less than 0.01). No increase was found in monolayers exposed to 600 rads. The increases in endothelial albumin transfer rates were associated with morphologic evidence of monolayer disruption and endothelial injury which paralleled the changes in albumin permeability. Dose-dependent alterations in endothelial actin filament organization were also found. Incubation of the monolayers exposed to 3,000 rads with medium supplemented with 10% fetal calf serum for 24 hours resulted in normalization of albumin permeability, improvement in morphologic appearance of the monolayers, and reorganization of the actin filament structure. These studies demonstrate that ionizing radiation is an active principle in the reversible disorganization of cultured pulmonary endothelial cell monolayers without the need of other cell types or serum components.

Albumins↗
PubMed1984

Inhibition of ribosomal RNA synthesis in yeast by ionizing radiations.

The effects of ionizing radiations on transcriptional activity were studied in the diploid yeast Saccharomyces cerevisiae. As experimental indicator the synthesis of ribosomal RNA (r-RNA) was measured for 1 h after exposure of cells to gamma-rays, X-rays or alpha-particles. gamma- or X-ray induced transcription inhibition was always found to decrease exponentially with dose. D0 values of 2150 or 1950 Gy were determined in wild-type cells, corresponding to a mean energy of about 60 eV per r-RNA gene. The finding of differential sensitivities of the two high molecular-weight r-RNA species which are cotranscribed from r-DNA is compatible with the existence of a transcription terminating mechanism. Cells from a mutant strain (rad-9), radiation sensitive with respect to colony forming ability, show an approximately equal sensitivity for transcription inhibition compared to the wild-type (D0 (2095) = 2400 Gy). Inactivation of r-RNA synthesis in cells exposed to alpha-particles at room-temperature showed a decreased sensitivity with higher particle fluences ('resistant tail'). This phenomenon, however, was drastically reduced if the temperature during irradiation was lowered to 4 degrees C, and was completely abolished when dried cells were used. The results may be explained by the presence of recovery processes in vegetative cells during prolonged exposures to alpha-particles at room temperature. An inactivation cross-section for alpha-particle induced transcription inhibition of about 0.02 micron 2 can be derived from the experimental data. When comparing this value with the estimated target volume, it appears that no single genes but the whole cluster of about 120 r-RNA genes on each of the chromosomes XII in the diploid cell may be inactivated by a single alpha-particle.

Alpha Particles↗
PubMed1990

Effects of prenatal exposure to ionizing radiation.

Prenatal exposure to ionizing radiation induces some effects that are seen at birth and others that cannot be detected until later in life. Data from A-bomb survivors in Hiroshima and Nagasaki show a diminished number of births after exposure under 4 wk of gestational age. Although a wide array of congenital malformations has been found in animal experimentation after such exposure to x rays, in humans only small head size (exposure at 4-17 wk) and mental retardation (exposure primarily at 8-15 wk) have been observed. In Hiroshima, small head size occurred after doses of 0.10-0.19 Gy or more, and an excess of mental retardation at 0.2-0.4 Gy or more. Intelligence test scores were reduced among A-bomb survivors exposed at 8-15 wk of gestational age by 21-29 IQ points per Gy. Other effects of in-utero exposure to atomic radiation include long-lasting complex chromosome abnormalities.

Abnormalities, Radiation-Induced↗
PubMed1967

Detoxification of Salmonella typhimurium lipopolysaccharide by ionizing radiation.

The efficiency of ionizing radiation in detoxifying the lethal determinant(s) of the lipopolysaccharide (LPS) of Salmonella typhimurium, S. enteritidis, and Escherichia coli in aqueous solution and associated with heat-killed S. typhimurium cells in suspension decreased with doses above 1 Mrad. The 50% end point of inactivation was more than 7.0 Mrad for heat-killed salmonellae and 4.8, 4.5, and 1.0 Mrad for the LPS of S. typhimurium, S. enteritidis, and E. coli, respectively. After exposure to 20 Mrad, S. typhimurium LPS retained a small portion of its lethal properties although the ld(50) was much greater than 9.5 mg per 20-g mouse. However, at -184 C, no inactivation of the lethal determinant(s) occurred after exposure to as much as 20 Mrad. This demonstrated the significance of the indirect effect and the mobility and formation of free radicals. At 22 C, the optical density at 400 mmu increased and the pH decreased with increasing radiation dose, but no qualitative changes were observed in the infrared spectrum. No change was observed in the pyrogenicity of S. typhimurium LPS; a slight decrease in antigenicity was revealed when 6 days, but not when 1 day, elapsed between vaccination and challenge in the mouse protection test. The results were interpreted as evidence of the existence of two or more lethal and antigenic determinants. The differential effect of radiation on these properties and on the pyrogenic component(s) probably are indicative of separate functional sites for lethal, antigenic, and pyrogenic activities.

Animals↗
PubMed2005

Long-term follow-up for brain tumor development after childhood exposure to ionizing radiation for tinea capitis.

Ionizing radiation is an established risk factor for brain tumors, yet quantitative information on the long-term risk of different types of brain tumors is sparse. Our aims were to assess the risk of radiation-induced malignant brain tumors and benign meningiomas after childhood exposure and to investigate the role of potential modifiers of that risk. The study population included 10,834 individuals who were treated for tinea capitis with X rays in the 1950s and two matched nonirradiated groups, comprising population and sibling comparison groups. The mean estimated radiation dose to the brain was 1.5 Gy. Survival analysis using Poisson regression was performed to estimate the excess relative and absolute risks (ERR, EAR) for brain tumors. After a median follow-up of 40 years, an ERR/Gy of 4.63 and 1.98 (95% CI = 2.43-9.12 and 0.73-4.69) and an EAR/Gy per 10(4) PY of 0.48 and 0.31 (95% CI = 0.28-0.73 and 0.12-0.53) were observed for benign meningiomas and malignant brain tumors, respectively. The risk of both types of tumors was positively associated with dose. The estimated ERR/Gy for malignant brain tumors decreased with increasing age at irradiation from 3.56 to 0.47 (P = 0.037), while no trend with age was seen for benign meningiomas. The ERR for both types of tumor remains elevated at 30-plus years after exposure.

Adolescent↗
PubMedDate not supplied

[High resistance of some oligotrophic bacteria to ionizing radiation].

The resistance against ionizing radiation of seven cultures of oligotrophic and eutrophic bacteria was investigated in the interval 0-360 Gr/h. It is determine that all of tested bacteria are distributed into three groups according to the lever of their resistance. Most resistant were: Methylobacterium organophilum, Pedodermatophilus halotolerans (LD50 = 270 Cr/h). These organisms are close to Deinococcus radiodurans in the survival. Middle resistance shown water-born ring-forming bacteria Flectobacillus major, Arcocella aquatica (LD50 = 173 and 210 Gr/h respectively). High sensitive were eutrophs: Pseudomonas fluorescens, Escherichia coli (LD50 = 43 and 38 Gr/h respectively). By use of X-ray microanalysis was shown that after the radiation potassium content in cell was increased and calcium content was decreased. The elements content in the cells of eutrophs (Escherichia coli) remains without change. In present paper are also discussed possible mechanisms of the resistance of oligotrophs against gamma-irradiation.

Bacteria↗
PubMed1993

Molecular biology of mutagenesis of mammalian cells by ionizing radiation.

In mammalian cells, ionizing radiation induces comparable numbers of point mutations (principally base changes, frameshifts and small deletions) and of large deletions of more than a hundred base pairs. The latter are formed either by misrepair of an end from one double-strand break with an end from another, or by a second mechanism which, it is suggested, is initiated by slowly repaired single-strand nicks. The ratio of deletions to point mutations is variable from one gene to another, and is greatest for genes in which very large deletions still allow cells to survive.

Animals↗
PubMed2005

NF-kappaB inhibition radiosensitizes Ki-Ras-transformed cells to ionizing radiation.

Most cancer cells show resistance to ionizing radiation (IR)-induced cell death. Recently, Ki-Ras was reported to be responsible for the increased radioresistance. We report here that inhibition of IR-induced activaton of nuclear transcription factor kappa B (NF-kappaB) but not of either Akt or MAPK kinase (MEK), increased the radiosensitization of Ki-Ras transformed human prostate epithelial 267B1/K-ras cells. Proteosome inhibitor-1 (Pro1) reduced NF-kappaB activation, and this inhibition was accompanied by increased levels of cytoplasmic IkappaBalpha and p65/RelA. However, translocation of p50/NF-kappaB1 did not occur on exposure to IR, suggesting the cell-specific involvement of p50 in radiation signaling. Clonogenic cell survival and soft agar assays further confirmed the increased radiosensitivity of 267B1/K-ras cells by proteosome inhibition. In addition, proteosome inhibition enhanced the IR-induced degradation of apoptotic protein caspases 8 and 3, with the level of antiapoptotic protein Bcl-2 being unaffected, suggesting the involvement of an apoptotic process in IR-induced cell death of 267B1/K-ras cells. LY294002 and PD98059, specific inhibitors of phosphatidylinositol-3-kinase (PI3K) and MEK, respectively however, did not affect the radiosensitization. All these results suggest an application of blocking NF-kappaB activation pathway to the development of anticancer therapeutics in IR-induced radiotherapy of Ki-Ras-transformed cancer cells.

Apoptosis↗
PubMed1999

Greater sensitivity to ionizing radiation at older age: follow-up of workers at Oak Ridge National Laboratory through 1990.

BACKGROUND: Workers at Oak Ridge National Laboratory (ORNL) were individually monitored for whole body exposure to ionizing radiation. Studies of these workers may provide valuable information about the long-term effects of occupational exposure to ionizing radiation. Since biological changes occur as adults age, a potentially important question in these investigations is whether sensitivity to the carcinogenic effects of ionizing radiation changes with age at exposure. METHODS: Vital status and cause of death were ascertained through 1990 for 8307 white males hired at ORNL from 1943 through 1972. Associations between whole body ionizing radiation dose and all-cancer mortality were quantified using life table regression methods for time dependent exposures. Analyses focused of differences in radiation-cancer associations with age at exposure. Length of follow-up, period of hire, and age at risk were considered as alternative explanations for effects of age at exposure. RESULTS: Cumulative radiation dose was associated with a 1.8% (SE = 0.9) increase in all-cancer mortality per 10 mSv, assuming a 10-year lag between exposure and mortality. However, radiation doses received at older ages exhibited larger associations with cancer mortality than doses received at younger ages. Doses received after age 45 were associated with a 5.9% (SE = 1.7) increase in cancer mortality per 10 mSv, adjusted for doses received before age 45. Dose-response associations between cancer mortality and doses received after age 45 appeared consistent across periods of follow-up, periods of hire, and ages at risk. CONCLUSIONS: Findings suggest that sensitivity to the carcinogenic effects of ionizing radiation may increase with older ages at exposure. More attention should be given to the role of age at exposure in studies of the health effects of low-level exposure to ionizing radiation, and to efforts to limit exposure to ionizing radiation.

Adult↗
PubMed1992

Mitogenic signal transduction: a common target for oncogenes that induce resistance to ionizing radiations.

We hypothesized that resistance to ionizing radiations accompanying neoplastic transformation caused by some oncogenes was due to common biochemical pathways affecting the mechanism of mitogenic signal transduction. In order to verify this hypothesis, we studied the formation of mitogenic second messengers in cells transformed by oncogenes that induce radioresistance. We observed an increase of diacylglycerol which activates protein kinase C, an increase of phosphatidylcholine metabolism, with a concomitant decrease of inositol lipid metabolism. Our data show that sensitivity to ionizing radiations was inversely related to the intracellular level of diacylglycerol; study of signalling alterations in spontaneous tumors could provide predictive indications about the responsiveness of neoplasia to radiation therapy.

3T3 Cells↗
PubMed1997

[Pulmonary and cardiac late effects of ionizing radiations alone or combined with chemotherapy].

High doses of ionizing radiation (> 40 Gy) cause severe lung fibrosis in approximately 5% of the cases. There is a twofold increase when chemotherapy is added to ionizing radiation. Lung fibrosis is due to the destruction of lung tissue by ionizing radiation but also to various cytokine effects (PDGF-beta, TGF-beta). Only a minority of patients (approximately 10%) with abnormal X-rays will experience clinical symptoms. The most important radiobiological parameters which accounts for pulmonary tolerance is the fraction size. Irradiation of the heart begets multifarious late sequelae which are often left unrecognized. Chronic pericarditis affects approximately 5% of the patients when the irradiation dose exceeds 40 Gy. Coronary artery disease can be diagnosed in 5 to 10% of the patients. This late complication is more likely to occur if the patient was young at the time of the irradiation or if other risk factors are associated. Valvular defects can be found in 15 to 30% of the patients. However, the mortality rate is very low (0.5%). Finally, conduction defects can also be seen in approximately 5% of the patients. It is very likely that the radiation dose given to the heart should not exceed 30 Gy if late sequelae are to be avoided.

Antineoplastic Combined Chemotherapy Protocols↗
PubMed1993

Increased expression of the epidermal growth factor receptor in human epidermal keratinocytes after exposure to ionizing radiation.

The effect of exposure of human epidermal keratinocytes to ionizing radiation, both in vivo and in vitro, on the expression of the epidermal growth factor receptor (EGF-R) was studied on the protein, mRNA, and functional levels. Quantitative fluorometry of short-term organ cultures incubated with a monoclonal antibody against human EGF-R revealed a dose-dependent increase of EGF-R expression 24 h after irradiation with 4 and 6 Gy, with an additional increase after 48 h. In biopsy specimens from patients undergoing radiation therapy a markedly increased expression could be determined by quantitative fluorometry during radiation therapy which wa still considerably above the baseline level 4 weeks after termination of treatment. Radioligand binding assays demonstrated a 50% increase in 125I-EGF binding to primary keratinocytes and A431 cells, at doses of 1 Gy, with a further increase after 72 and 96 h. Northern blots were performed with total RNA from two human epidermal cell lines (SCLII and A431). In A431 cells, increased EGF-R transcript levels could be detected 48 h after irradiation. In cells of the SCLII cell line, EGF-R expression was not affected by irradiation. These results were confirmed by semiquantitative polymerase chain reaction of primary cultured keratinocytes, demonstrating an increase of transcripts of EGF-R 24 h after irradiation with single doses of 6 Gy. Thus exposure to ionizing radiation leads to an increased expression of functionally intact EGF-R in human keratinocytes, at the protein and mRNA levels, both in vitro and in vivo; we hypothesize that this effect is part of a stress program of epidermal cells in response to ionizing radiation, ensuring rapid repopulation of irradiated areas.

Base Sequence↗
PubMed1990

The influence of electromagnetic interference and ionizing radiation on cardiac pacemakers.

Adverse effects of the ionizing and non-ionizing electromagnetic fields on five pacemaker models have been tested. The study consisted of three parts: 1. measurement of magnetic fields in a radiotherapy room (microtron MM14), 2. the application of non-ionizing electromagnetic fields on pacemakers in a test laboratory (1...1000 microT, 10...10000 Hz), and 3. the application of ionizing radiation of different types of radiotherapy devices on the pacemakers. The magnetic field strength in the microtron treatment room was found to be under 7.5 microT, which is one order of magnitude lower than the tolerance level obtained for the pacemakers in the test laboratory. All the tested pacemakers tolerated the ionizing radiation dose levels (less than 60 Gy) which are used in the radiotherapy.

Electromagnetic Fields↗
PubMed2005

Gene expression profiles of normal human fibroblasts after exposure to ionizing radiation: a comparative study of low and high doses.

Several types of cellular responses to ionizing radiation, such as the adaptive response or the bystander effect, suggest that low-dose radiation may possess characteristics that distinguish it from its high-dose counterpart. Accumulated evidence also implies that the biological effects of low-dose and high-dose ionizing radiation are not linearly distributed. We have investigated, for the first time, global gene expression changes induced by ionizing radiation at doses as low as 2 cGy and have compared this to expression changes at 4 Gy. We applied cDNA microarray analyses to G1-arrested normal human skin fibroblasts subjected to X irradiation. Our data suggest that both qualitative and quantitative differences exist between gene expression profiles induced by 2 cGy and 4 Gy. The predominant functional groups responding to low-dose radiation are those involved in cell-cell signaling, signal transduction, development and DNA damage responses. At high dose, the responding genes are involved in apoptosis and cell proliferation. Interestingly, several genes, such as cytoskeleton components ANLN and KRT15 and cell-cell signaling genes GRAP2 and GPR51, were found to respond to low-dose radiation but not to high-dose radiation. Pathways that are specifically activated by low-dose radiation were also evident. These quantitative and qualitative differences in gene expression changes may help explain the non-linear correlation of biological effects of ionizing radiation from low dose to high dose.

Cells, Cultured↗
PubMed1997

Ionizing radiation induces, via generation of reactive oxygen intermediates, intercellular adhesion molecule-1 (ICAM-1) gene transcription and NF kappa B-like binding activity in the ICAM-1 transcriptional regulatory region.

Ionizing radiation produces reactive oxygen intermediates in mammalian tissues and may serve as a model system for the investigation of the biologic effects of free radicals. We have previously shown that the adhesion molecule ICAM-1 is induced by ionizing radiation, and here we have investigated the molecular mechanisms responsible. ICAM-1 mRNA and cell surface expression was induced in HeLa and HaCaT cells after exposure to ionizing radiation. This induction was blocked by preincubation with the antioxidants PDTC and N-acetyl cysteine. ICAM-1 promoter activity was assessed by transiently transfecting HeLa cells with CAT-reporter gene constructs containing sequential ICAM-1 5' deletions. ICAM-1 5' fragments -1162/+1 (relative to the transcription start site) and -277/+1 displayed increased promoter activity when cells were exposed to ionizing radiation, but no induction was seen in a -182/+1 construct associating positions -277 to around -182 with inducibility by ionizing radiation. Nuclear extracts from HaCaT cells were tested in mobility shift assays using an NF kappa B-like binding site of the ICAM-1 5' region (positions -186/-177). There was marked enhancement of DNA-protein complex forming in extracts from irradiated versus untreated cells. Incubation of cells with antioxidants prior to irradiation prevented the radiation-dependent increase in complex formation. We conclude that reactive oxygen intermediates are involved in ICAM-1 induction by ionizing radiation. The ionizing radiation-induced, antioxidant-inhibitable binding at the ICAM-1 NF kappa B-like binding site is consistent with the view that NF kappa B is a pro-oxidant transcription factor.

Binding Sites↗
PubMedDate not supplied

Diminished cellular and humoral immunity in workers occupationally exposed to low levels of ionizing radiation.

BACKGROUND: It has been reported that subgroups of T-lymphocytes are affected at different levels and different cell groups of immune system give different responses in individuals exposed to long-term ionizing radiation. The aim of this study was to investigate the effect of occupational exposure to low levels of ionizing radiation in selected indices of cellular and humoral immunity in radiology workers. METHODS: Level of subgroups of peripheral blood lymphocytes, complements (C(3), C(4)), and total immunoglobulins (IgG, IgA, IgM) were analyzed in 50 radiology workers occupationally exposed to low levels of ionizing radiation and 35 age-matched healthy controls. RESULTS: CD4(+) T lymphocyte (T-helper) levels were determined as significantly low in radiology workers exposed to ionizing radiation compared with controls (p <0.05). There were no statistically significant differences in groups in terms of other subgroups of lymphocytes (p >0.05). In addition, levels of serum total IgG, IgA, IgM, C(3,) and C(4) were determined as significantly lower in workers exposed to ionizing radiation compared with controls (p <0.001). Total IgA and IgM levels in radiology workers who were smokers were determined as significantly lower compared with non-smoking radiology workers (p >0.05). CONCLUSIONS: Levels of CD4(+) T lymphocytes and humoral immune response (total immunoglobulins and complements) were determined as weaker in workers exposed to low levels of ionizing radiation compared with controls, indicating the importance of taking appropriate measures to protect radiology workers from exposure to ionizing radiation and for these workers to avoid smoking. Further studies are needed for determining the appropriateness of periodic check-ups of immune functions and the most efficient and cost-effective ways of monitoring immune functions in radiology workers for detecting early changes in the immune system.

Adult↗