Recent reports on the effect of low doses of ionizing radiation and its dose–effect relationship

Recently, the risk associated with low doses of ionizing radiation has gained new interest. Here, we analyze and discuss the major differences between two reports recently published on this issue; the report of the French Academy of Sciences and of the French Academy of Medicine published in March 2005, and the BEIR VII—Phase 2 Report of the American National Academy of Sciences published as a preliminary version in July 2005. The conclusion of the French Report is that the linear no-threshold relationship (LNT) may greatly overestimate the carcinogenic effect of low doses (<100 mSv) and even more that of very low doses (<10 mSv), such as those delivered during X-ray examinations. Conversely, the conclusion of the BEIR VII report is that LNT should be used for assessing the detrimental effects of these low and very low doses. The causes of these diverging conclusions should be carefully examined. They seem to be mostly associated with the interpretation of recent biological data. The point of view of the French Report is that these recent data are incompatible with the postulate on which LNT is implicitly based, namely the constancy of the carcinogenic effect per unit dose, irrespective of dose and dose rate.     

Alleviation of salt stress by low dose γ-irradiation in rice

The effects of salt stress on the growth, photosynthesis, and antioxidative ability of the rice (Oryza sativa L.) plants raising from -irradiated seeds were investigated using two cultivars, Ilpumbyeo and Sanghaehyanghyella. The 50 and 100 mM NaCl solutions caused a remarkable decrease of the early germination rate and seedling growth. However, the salt stress-induced inhibition of the growth was significantly alleviated in the -irradiated plants. The chlorophyll contents and the effective quantum yield of photosystem 2 ( _{PS 2}) were lower in the NaCl-treated plants than in the control ones, while the non-photochemical quenching was higher in the former ones. Activities of the antioxidant enzymes such as superoxide dismutase (SOD) and ascorbate peroxidase (APX) increased with increasing NaCl concentrations, and the irradiated groups had even higher SOD and APX activities than the non-irradiated ones. These alleviation effects were observed similarly in both the cultivars tested.     

Implementation of a dose–response curve for γ-radiation in the Portuguese population by use of the chromosomal aberration assay

An in vitro dose–response curve following exposure to γ-radiation was determined at the IST/ITN, by use of the chromosomal aberration assay. This is the first study of this kind carried out among the Portuguese population. Un-irradiated and γ-irradiated peripheral blood lymphocytes from 16 healthy donors were cultured. A total of 22,395 metaphases were analyzed for frequency and distribution of dicentrics and centric rings, as a function of the radiation dose. The dose–response data for dicentrics and dicentrics plus centric rings were fitted by use of a linear–quadratic model: Y_dic = (0.0011 ± 0.0006) + (0.0105 ± 0.0035)D + (0.0480 ± 0.0019)D² and Y_{dic + rings} = (0.0011 ± 0.0006) + (0.0095 ± 0.0036)D + (0.0536 ± 0.0020)D². Also, calibration curves related to age and gender were determined, but no significant differences were found. Following the establishment of the dose–response curves, a validation experiment was carried out with three individuals. Real and estimated doses, obtained with the dose–response curves, were in agreement. These results give us confidence to apply both dose–response calibration curves in future biological dosimetry requirements.     

Demonstration of a radiation-induced bystander effect for low dose low LET β-particles

Radiation-induced bystander mutagenesis at a relatively low dose range was investigated using low LET β-particles in a three-dimensional cell culture model. CHO cells were labeled with 0, 0.5, 1.0 or 5.0 μCi tritiated thymidine (³HdTTP) for 12 h and subsequently incubated with A_L cells for 24 h at 11°C. The cell mixture was centrifuged to produce a spheroid of 4 × 10⁶ cells of which there was five times more A_L than CHO cells. The short-range β-particles emitted by ³HdTTP result in self-irradiation of labeled CHO cells, thus biological effects on neighboring A_L cells can be attributed to the bystander response. To evaluate such response, non-labeled bystander A_L cells were isolated from among labeled CHO cells and studied independently for survival and mutagenesis. Treatment of CHO cells with ³HdTTP resulted in a dose-dependent increase in bystander mutation incidence among neighboring A_L cells compared to controls. In addition, multiplex PCR analysis revealed the types of mutants to be significantly different from those of spontaneous origin. These data provide evidence that low dose low LET radiation can induce bystander mutagenesis in a three-dimensional model. The results of this study will address the relevant issues of actual target size and radiation quality, and are likely to have a significant impact on our current understanding of radiation risk assessment.     

Protective effect of an aminothiazole compound against γ-radiation induced oxidative damage

Ionizing radiation causes its biological effects mainly through oxidative damage induced by reactive oxygen species. During radiotherapy of cancer, one of the undesirable side-effects is toxicity to normal cells. Compounds with antioxidant activities are being tried as 'prophylactic radioprotectants' to overcome this problem. We evaluated the protective effect of an aminothiazole compound, in the form of dendrodoine analogue (DA) originally derived from a marine tunicate, against γ-radiation-induced damage to lipid, protein, and DNA besides its cytotoxicity. Oxidative damage was examined by different biochemcial assays. Our studies reveal that DA gave significant protection, in fairly low concentrations, against damage induced by γ-radiation to rat liver mitochondria, plasmid pBR322 DNA, and mouse splenic lymphocytes in vitro. It also protected against oxidative damage in whole-body irradiated mice exposed to therapeutic dose of radiation (2 Gy) in vivo. Spleen, a major target organ for radiation damage, of the irradiated mice showed significant protection when treated with DA, as examined by histopathology. In conclusion, due to the possible protective effects against normal cells/tissues both in vitro and in vivo, DA shows potential to be a radioprotector for possible use during radiotherapy.     

Protective effect of an aminothiazole compound against γ-radiation induced oxidative damage

Abstract

Ionizing radiation causes its biological effects mainly through oxidative damage induced by reactive oxygen species. During radiotherapy of cancer, one of the undesirable side-effects is toxicity to normal cells. Compounds with antioxidant activities are being tried as ‘prophylactic radioprotectants’ to overcome this problem. We evaluated the protective effect of an aminothiazole compound, in the form of dendrodoine analogue (DA) originally derived from a marine tunicate, against γ-radiation-induced damage to lipid, protein, and DNA besides its cytotoxicity. Oxidative damage was examined by different biochemcial assays. Our studies reveal that DA gave significant protection, in fairly low concentrations, against damage induced by γ-radiation to rat liver mitochondria, plasmid pBR322 DNA, and mouse splenic lymphocytes in vitro. It also protected against oxidative damage in whole-body irradiated mice exposed to therapeutic dose of radiation (2 Gy) in vivo. Spleen, a major target organ for radiation damage, of the irradiated mice showed significant protection when treated with DA, as examined by histopathology. In conclusion, due to the possible protective effects against normal cells/tissues both in vitro and in vivo, DA shows potential to be a radioprotector for possible use during radiotherapy.     

Effect of γ-radiation on some elements in certain organs of albino rats

Energy-dispersive X-ray fluorescence (EDXRF) was used to determine the concentrations of Ca, Cl, Fe, Ni, P, K, Se, S, and Zn in heart, lung, liver, spleen, and kidney of adult albino rats 2 mo after they were subject to a single gamma γ-radiation dose from⁶⁰Co at 5 gy. In female rats, K levels were significantly higher and the Ca levels significantly lower for the irradiated animals when compared to age-matched nonirradiated controls. Significant differences between irradiated and nonirradiated tissues were observed for other elements, although no sex-related differences could be found. Tissue damage and disturbances of biological functions were observed as a result of γ-irradiation.     

The effect of high pass filtering and non-linear normalization on the EMG–force relationship during sub-maximal finger exertions

Muscle force estimates are important for full understanding of the musculoskeletal system and EMG is a modeling method used to estimate muscle force. The purpose of this investigation was to examine the effect of high pass filtering and non-linear normalization on the EMG–force relationship of sub-maximal finger exertions. Sub-maximal isometric ramp exertions were performed under three conditions (i) extension with restraint at the mid-proximal phalanx, (ii) flexion at the proximal phalanx and (iii) flexion at the distal phalanx. Thirty high pass filter designs were compared to a standardized processing procedure and an exponential fit equation was used for non-linear normalization. High pass filtering significantly reduced the %RMS error and increased the peak cross correlation between EMG and force in the distal flexion condition and in the other two conditions there was a trend towards improving force predictions with high pass filtering. The degree of linearity differed between the three contraction conditions and high pass filtering improved the linearity in all conditions. Non-linear normalization had greater impact on the EMG–force relationship than high pass filtering. The difference in optimal processing parameters suggests that high pass filtering and linearity are dependent on contraction mode as well as the muscle analyzed.     

Thermoluminescence dose–response of synthesized and doped hydroxyapatite: effect of formed crystal phases

In this research work, pure and doped hydroxyapatite samples were synthesized using hydrolysis and hydrothermal methods to produce powder material. The crystal structure was carried out by producing data using the X-ray diffraction system and the Rietveld method using material analysis using diffraction software. Then the sample was irradiated with different radiation absorbed doses, and their thermoluminescence response was investigated from the dosimetry point of view. The results showed that the synthesis method, doping, and annealing temperature could significantly affect the crystal structure and thermoluminescence dosimetry response of hydroxyapatite samples, consequently. The results showed that the high-temperature annealing process and dopant could lead to the formation of the β-TCP crystal phase during or after the synthesis of hydroxyapatite, and the percentage of this formed phase increased when raising the temperature, and finally led to increase in the thermoluminescence response.     

Chromosome elimination and chromosome pairing in tetraploid hybrids of Hordeum vulgare × H. bulbosum

Summary The C₀ tetraploid counterparts of diploid hybrids of Hordeum vulgare × H. bulbosum were meiotically analysed, and were found to be chromosomally less stable than the same genotypes had been as diploids. The 14 bulbosum chromosomes present in the tetraploid cytotypes were probably eliminated as pairs rather than randomly or one genome at the time. Development of the vulgare and bulbosum genomes was asynchronous in some hybrids, the bulbosum chromosomes appearing less advanced than the vulgare chromosomes in the same cell. This appeared to reduce pairing between bulbosum homologues and also suppressed homoeologous pairing.     

Effect of inhibitors of gibberellin biosynthesis on the induction of α-amylase in embryoless caryopses of Hordeum vulgare cv. Himalaya

The induction of -amylase by exogenously supplied gibberellin A₁ (GA₁) and GA₄ in embryoless caryopses of Hordeum vulgare (cv. Himalaya) was determined indirectly by measuring reducing sugars released from the endosperm. The presence of the inhibitors of GA biosynthesis, 2-isopropyl-4-dimethylamino-5-methylphenyl-1-piperidinecarboxylate methyl chloride (Amo 1618), Ancymidol, 2-chloroethyl trimethyl ammonium chloride (CCC) or (R,S)-1-(4-chlorophenyl)-4,4-dimethyl-2-(1,2,3-triazolyl)pentan-3-ol (PP333) did not inhibit -amylase production by either GA₁ or GA₄.Abbreviations Amo-1618 2-isopropyl-4-dimethylamino-5-methylphenyl-1-piperidinecarboxylate methyl chloride - CCC 2-chloroethyl trimethyl ammonium chloride - cv. cultivar - GA gibberellin - GC gas chromatography - GC-MS combined gas chromatography-mass spectrometry - PP333 (R,S)-1-(4-chlorophenyl)-4,4-dimethyl-2-(1,2,3-triazolyl) pentan-3-01     

Buthionine sulfoximine mediated enhancement of γ-radiation induced mutation frequency in Drosophila melanogaster

Experiments were carried out to investigate whether or not depletion of the glutathione (GSH) level in Drosophila melanogaster larvae with buthionine sulfoximine (BSO) treatment can result in the modulation of the frequency of sex-linked recessive lethal (SLRL) mutations induced by γ-radiation. Third instar larvae were fed on BSO for 24 h before exposure to 10 Gy γ-radiation. Immediately after this the larvae were divided into two batches, which were used to determining the GSH level and the induction of SLRL mutations respectively. The results obtained suggest that the depletion of the GSH level with BSO can lead to an enhancement in the frequency of SLRL mutations (significant at the 5% level). In a subsequent experiment in which adult Drosophila melanogaster male flies were fed on BSO for 72 h before irradiation, a significant increase was observed in the incidence of SLRL mutations.     

Hormonal regulation of gene expression in the “slender” mutant of barley (Hordeum vulgare L.)

The slender mutant of barley resembles a normal barley plant treated with high doses of gibberellic acid (GA₃). Expression of GA₃-regulated and abscisic acid (ABA)-regulated mRNAs was studied in the endosperm and roots of mutant and wild-type (WT) plants.Production of -amylase (EC 3.2.1.1) by WT embryoless half-grains was dependent on the presence of GA₃, and was prevented by ABA. In contrast, -amylase was produced by half-grains of the slender mutant in the absence of added GA₃, although it was still reduced by ABA. The spectrum of -amylase mRNAs in slender embryoless half-grains incubated in the absence of added GA₃ was the same as in WT endosperm half-grains incubated in the presence of GA₃. These results indicate that the endosperm of the slender mutant exhibits similar properties to WT endosperm treated with GA₃.In roots the expression of an ABA-inducible mRNA was similar in slender and WT seedlings either treated with exogenous ABA or exposed to dehydration. This result, and the effect of ABA on -amylase production by the endosperm, indicate that the slender plants retain sensitivity to ABA.Abbreviations ABA abscisic acid - AMV avian myeloblastosis virus - GA gibberellin - GA₁ gibberellin A₁ - GA₃ gibberellic acid - WT wild-type     

Genotypic differences in manganese efficiency: field experiments with␣winter barley (Hordeum vulgare L.)

Eight different winter barley genotypes were grown in a plot experiment in northern Denmark, on soil where Mn deficiency had been previously demonstrated, to assess field performance and grain yield under two treatments: with foliar Mn fertilisation and without foliar Mn fertilisation. A high Mn efficiency was demonstrated for two of the genotypes and a low Mn efficiency was observed for one of the genotypes in three consecutive years; highly variable results were obtained for other genotypes. Mn efficiency based on grain yields could not be related to whole shoot Mn concentration, biomass or Mn uptake at various vegetative growth stages. Chlorophyll a fluorescence analysis was able to differentiate between the two Mn treatments up to 7weeks after the last Mn application, whereas Mn concentrations, shoot biomass and Mn accumulation could not. It was not possible to fully alleviate Mn deficiency by repeated foliar spraying on the control plots. Given the growing conditions at the trial site and the low Mn in plant tissue, it is possible that Mn deficiency was extreme enough that Mn efficiency mechanisms broke down.     

The effect of ”living high–training low” on physical performance in rats

In this research, we hypothesized that, in rats, adaptation to high altitude (2500 m) plus training at low altitude (610 m), ”living high–training low”, improves physical performance at low altitude more than living and training at low altitude (610 m). Rats were divided into four groups: (1) living at low altitude (LL, n=12), (2) living and training at low altitude (LLTL, n=13), (3) living at high altitude (LH, n=12), (4) living at high altitude and training at low altitude (LHTL, n=13). The program for living at high altitude involved raising rats under hypobaric hypoxia (equivalent to 2500 m), and the training program consisted of running on a tread-mill at low altitude. All groups were raised at each altitude and trained to run at 35 m/min for 40 min/day, 6 days/week for 6 weeks. During this program, we measured heart rates both at rest and during exercise, and performed running-time trials. The mean heart rate during exercise was lower in groups with training than in groups without training, and the groups receiving training could run longer than the untrained groups. The LHTL group especially showed the lowest mean heart rate during exercise and the longest running time among all groups. After 6 weeks of the training program, all rats had a catheter implanted into the carotid artery, and the mean systemic arterial pressure was continuously measured during treadmill running. The rate of increase of this pressure as the running intensity increased was lower in groups with training than in groups without training, especially in the LHTL group. Finally, we anesthetized all the rats and extracted both the right and left ventricles, and the triceps surae and liver. Training increased the weight of the left ventricle, triceps surae, and liver. The increase in weight of the left ventricle and triceps surae was higher in the LHTL group than in the LLTL group in particular. It appeared that living high– training low may be an effective strategy to improve performance ability at low altitude. Received: 16 July 1999 / Revised: 24 January 2000 / Accepted: 25 January 2000     

Ionizing radiation stimulates secretion of pro-inflammatory cytokines: dose–response relationship,mechanisms and implications

In previous studies we showed a marked increase in secretion of inflammatory cytokines TNFα and interleukin (IL)-1β by mouse macrophages in response to different doses of ionizing radiation (IR). Here we show the stimulation of IL-12 and IL-18 secretion by mouse peritoneal macrophages after whole-body irradiation with exploration of the possible mechanisms and implications in cancer radiotherapy. Both low (0.075 Gy) and high (2 Gy) doses of IR were found to cause sustained stimulation of IL-12 and IL-18 secretion by mouse macrophages; this paralleled the activation of NF-κB as well as up-regulated expression of CD14 and TLR4–MD2 on the macrophage surface and MyD88 in the cytoplasm. The expression of CD14, TLR4–MD2 and MyD88 increased in a dose-dependent manner from radiation doses between 0.05 and 2 Gy. The secretion of IL-12 and IL-18 showed a dose-dependent increase from doses between 0.05 and 4 Gy. It is concluded that IR can stimulate the secretion of IL-12 and IL-18 presumably via activation of the Toll signaling pathway in macrophages. The potential harmful effect of repeated doses of radiation used in radiotherapy for certain cancers is discussed. Yu-Xing Shan and Shun-Zi Jin contributed equally to the present work.     

Inhibition of Notch signaling pathway using γ-secretase inhibitor delivered by a low dose of Triton-X100 in cultured oral cancer cells

How to effectively delivering therapeutic agents, including γ-secretase inhibitors (GSIs), into live cells, remains a significant challenge. This study assessed the effect of Notch signaling inhibition by examining levels of the Notch1 intracellular domain (N1ICD) in cultured oral cancer cells analyzed with random stitched images (2D) and 3D visualizations using confocal microscopy and quantitative gene analysis. Substantially, we have developed a novel method to assist the delivery of γ-secretase inhibitor, DAPT, into live cells in the presence of an effective minimum concentration of Triton-X100 (0.001%) without damaging cell activity and membrane integrity assessed with cell proliferation assays. The images obtained in this study showed that DAPT alone could not block the γ-secretase inhibitor despite inhibiting cell growth. Further analysis of quantitative gene expressions of Notch signaling canonical pathway to verify the effectiveness of the novel method for delivering inhibitor into live cells, displayed deregulation of Notch1, Delta-like ligand 1 (DLL1) and hairy and enhancer of split 1 (Hes1). Our data suggest that Notch1/Hes1 signaling pathway is deactivated using DAPT with a low dose of Triton-X100 in this cancer cells. And the finding also suggests that Notch1 could be engaged by DLL1 to promote differentiation in oral cancer cells. Using this approach, we demonstrate that Triton-X100 is a promising and effective permeabilization agent to deliver γ-secretase inhibitor DAPT into live oral epithelial cells. This strategy has the potential to implicate in the treatment of cancer diseases.