Adaptive response and split-dose effect of radiation on the survival of mice

Although the importance of radiation-induced adaptive response has been recognized in human health, risk assessment and clinical application, the phenomenon has not been understood well in terms of survival of animals. To examine this aspect Swiss albino mice were irradiated with different doses (2–10 Gy) at 0015 Gy/s dose rate and observed on a regular basis for 30 days. Since almost 50% lethality was seen with 8 Gy, it was selected as the challenging dose for further studies. Irradiation of mice with conditioning doses (0.25 or 0.5 Gy) and subsequent exposure to 8 Gy caused significant increase in the survival of mice compared to irradiated control. The splitting of challenging dose did not influence the efficiency of conditioning doses (0.25 Gy and 0.5 Gy) to induce an adaptive response. However conditioning doses given in fractions (0.25 Gy + 0.25 Gy) or (0.5 Gy + 0.5 Gy) were able to modulate the response of challenging dose of 8 Gy. These results clearly showed the occurrence of adaptive response in terms of survival of animals. The conditioning dose given in small fractions seemed to be more effective. The findings have been discussed from a mechanistic point of view. The possible biological implications, potential medical benefits, uncertainties and controversies related to adaptive response have also been addressed     

The response of primary keratinocytes and fibroblasts from cancer patients to multiple low-dose irradiations

In our previous study, using the micronucleus (MN) assay, a hyper-radiosensitivity (HRS)-like phenomenon was observed after single low doses for fibroblasts from two and keratinocytes from four of the 40 patients studied. In this paper, we report the response of primary keratinocytes from 23 and fibroblasts from 21 of these cancer patients to multiple low-dose irradiations and answer the question regarding whether the patients with an HRS-like response after single low doses also demonstrate chromosomal hypersensitivity after multiple low doses. The cells were irradiated with three doses of 0.25 Gy separated by 4-h intervals, and MN induction was compared with that after the same total dose given as a single fraction of 0.75 Gy. Similarly, the effect of three doses of 0.5 Gy was compared with that of a single dose of 1.5 Gy. For fibroblasts from two and keratinocytes from four patients who demonstrated a single-dose HRS-like response, a significant inverse effect of fractionation (greater MN induction after three doses of 0.25 Gy than after a single dose of 0.75 Gy) was observed, which suggests a repeated hypersensitive response after each dose of 0.25 Gy. Such an effect was not seen for the cells from 19 patients who were single-dose HRS-like negative. In conclusion, an inverse fractionation effect for MN induction that was observed in fibroblasts from two and keratinocytes from four patients after three doses of 0.25 Gy (but not 3 x 0.5 Gy) reflects the chromosomal hyper-radiosensitivity seen in the same patients in response to single low doses.     

Possibilities of using bacterial cultures for the biological indication of relatively small doses of gamma radiation

Some approaches to using bacterial cultures as test objects in biological indication of relatively low gamma-radiation doses have been considered. The survival rate, mutability and induction of prophages in the lysogenic strains have been investigate. A model for the prophage induction in Pseudomonas aeruginosa is proposed to estimate the biological effect of gamma-irradiation with doses of 0.25 to 10 Gy.     

Dose-response relationship of gamma-ray-induced reciprocal translocations at low doses in spermatogonia of the crab-eating monkey (Macaca fascicularis)

The yield of translocations induced by acute gamma-irradiation at low doses (0.25 and 0.50 Gy) in the crab-eating monkey's (Macaca fascicularis) spermatogonia was examined. The frequencies of translocations per cell were 0.53% at 0.25 Gy and 1.07% at 0.50 Gy. Over the low dose range from 0 to 1 Gy, the dose-response relationship for translocation yield was a linear one with a regression coefficient of 1.79 X 10(-2). To estimate the sensitivity to the induction of translocations in the crab-eating monkey's spermatogonia, the slope of the regression line was compared with those in other mammalian species. Consequently, over the low dose range below 1 Gy, the sensitivity of the crab-eating monkey's spermatogonia to translocation induction was similar to several mammalian species, the mouse. Chinese hamster, and the rabbit, but significantly higher than that of the rhesus monkey and lower than that of the marmoset.     

Evaluation of the cataractogenic effect of 9 GeV protons

A study was made of the regularities of formation of lenticular opacity in mice exposed to 9 GeV protons and 60Co-gamma-rays. The RBE coefficients, calculated by the nonparametric method, were found to depend upon dose and time after irradiation. It was shown that after small radiation doses (0.25 to 0.50 Gy) the RBE coefficients increased from 1 to 8 with increasing period of observation. With higher doses (up to 5.0 Gy) the RBE coefficient increase in time was less pronounced.     

Secondary carcinogenesis in patients treated with radiation: a review of data on radiation-induced cancers in human, non-human primate, canine and rodent subjects

Concern for risk of radiation-induced cancer is growing with the increasing number of cancer patients surviving long term. This study examined data on radiation transformation of mammalian cells in vitro and on the risk of an increased cancer incidence after irradiation of mice, dogs, monkeys, atomic bomb survivors, occupationally exposed persons, and patients treated with radiation. Transformation of cells lines in vitro increased linearly with dose from approximately 1 to approximately 4-5 Gy. At <0.1 Gy, transformation was not increased in all studies. Dose-response relationships for cancer incidence varied with mouse strain, gender and tissue/organ. Risk of cancer in Macaca mulatta was not raised at 0.25-2.8 Gy. From the atomic bomb survivor study, risk is accepted as increasing linearly to 2 Sv for establishing exposure standards. In irradiated patients, risk of cancer increased significantly from 1 to 45 Gy (a low to a high dose level) for stomach and pancreas, but not for bladder and rectum (1-60 Gy) or kidney (1-15 Gy). Risk for several organs/tissues increased substantially at doses far above 2 Gy. There is great heterogeneity in risk of radiation-associated cancer between species, strains of a species, and organs within a species. At present, the heterogeneity between and within patient populations of virtually every parameter considered in risk estimation results in substantial uncertainty in quantification of a general risk factor. An implication of this review is that reduced risks of secondary cancer should be achieved by any technique that achieved a dose reduction down to approximately [corrected] 0.1 Gy, i.e. dose to tissues distant from the target. The proportionate gain should be greatest for dose decrement to less than 2 Gy.     

Radiosensitivity of a thymocyte subpopulation capable of stimulating erythropoiesis in locally irradiated animals

It was shown that, in contrast to intact thymocytes and to those irradiated with a dose of 0.25 Gy, thymocytes exposed in vivo to doses from 0.5 to 1.5 Gy and transplanted to locally irradiated (7 Gy) thymectomized BALB/c mice failed to stimulate the recovery of the erythron.     

氧离子辐射对体外人精子自化学发光,运动性,顶体反应和存活率的影响

Effects of 16O+6 ion irradiation with different doses on human sperm spontaneous chemiluminescence (SCL), motility, acrosome reaction (AR) and viability were examined. Spermatozoa were irradiated with 0, 0.25, 0.5, 1, 2, 4, 8, 16, 32, or 64 Gy 16O+6 ion beam at the energy of 3.17 MeV/u. After irradiation, samples were analyzed by SCL measurement at 1, 2 and 3 h of incubation; motility was determined by the transmembrane migration method within 2 h of incubation; the percentage of AR and viability was evaluated by the triple-stain technique at 3.5 h of incubation. The results showed: sperm SCL was significantly increased with irradiation doses and the lowest effective dose was 0.5 Gy; compared with controls, the transmembrane migration ratio of spermatozoa progressively elevated with irradiation doses at 0.5, 1, and 2 Gy; the percentage of sperm AR markedly increased in 0.5-4 Gy irradiation and the optimal dose was 2 Gy, and then significant decreased with further increase of irradiation doses; the viability had no significant change within 0.25-8 Gy, but was progressively decreased at 16, 32 and 64 Gy. These data suggested that heavy ion at low doses increased motility and AR, whereas had deleterious effects at higher doses, which are associated with free radical reactions induced by heavy ion irradiation.     

Isolation of specialized lambda transducing bacteriophages for flagellar genes (fla) of Escherichia coli K-12.

Specialized transducing lambda phages carrying the region III flagellar genes (fla) of Escherichia coli K-12 were isolated by a new method. A strain carrying both a cryptic lambda prophage near the his genes and a deletion of the attlambda gene was used as a starting strain. The lysogen of lambdacI857pga18-bio69 was isolated in which the prophage was integrated within the lambda cryptic genes by means of recombination with the residual lambda DNA. The strains with deletions starting within the prophage and ending in these fla genes were selected from among the heat-resistant survivors of the lysogen. They were then infected with heat-inducible and lysis-defective lambda phages and, thus, specialized transducing phage lines for hag and fla were obtained. High-frequency transfer lines of rare phages carrying the fla genes were isolated by inducing a strain carrying a heat-inducible lambda prophage near the his genes and selecting by transduction of a fla deletion strain. Preliminary characterization of these transducing phages is also reported.     

Differential expression of oxidative stress and extracellular matrix remodeling genes in low- or high-dose-rate photon-irradiated skin

Changes in the expression of genes implicated in oxidative stress and in extracellular matrix (ECM) remodeling and selected protein expression profiles in mouse skin were examined after exposure to low-dose-rate or high-dose-rate photon irradiation. ICR mice received whole-body γ rays to total doses of 0, 0.25, 0.5 and 1 Gy at dose rates of 50 cGy/h or 50 cGy/min. Skin tissues were harvested for characterization at 4 h after irradiation. For oxidative stress after low-dose-rate exposure, 0.25, 0.5 and 1 Gy significantly altered 27, 23 and 25 genes, respectively, among 84 genes assessed (P < 0.05). At doses as low as 0.25 Gy, many genes responsible for regulating the production of reactive oxygen species (ROS) were significantly altered, with changes >2-fold compared to 0 Gy. For an ECM profile, 18-20 out of 84 genes were significantly up- or downregulated after low-dose-rate exposure. After high-dose-rate irradiation, of 84 genes associated with oxidative stress, 16, 22 and 22 genes were significantly affected after 0.25, 0.5 and 1 Gy, respectively. Compared to low-dose-rate radiation, high-dose-rate exposure resulted in different ECM gene expression profiles. The most striking changes after low-dose-rate or high-dose-rate exposure on ECM profiles were on genes encoding matrix metalloproteinases (MMPs), e.g., Mmp2 and Mmp15 for low dose rate and Mmp9 and Mmp11 for high dose rate. Immunostaining for MMP-2 and MMP-9 proteins showed radiation dose rate-dependent differences. These data revealed that exposure to low total doses with low-dose-rate or high-dose-rate photon radiation induced oxidative stress and ECM-associated alterations in gene expression profiles. The expression of many genes was differentially regulated by different total dose and/or dose-rate regimens.     

Comparative evaluation of the in vitro micronucleus test and the comet assay for the detection of genotoxic effects of X-ray radiation

The genotoxic effects of X-ray radiation on human lymphocytes were measured using the single cell gel electrophoresis (SCGE) assay (comet assay) and the cytokinesis-blocked micronucleus (CBMN) test; both were carried out in vitro on isolated human lymphocytes in order to compare the relationship and sensitivity of these two detecting methods. The radiation-doses were 0.00, 0.02, 0.05, 0.10, 0.25, 0.50, 1.00 and 2.00 Gy. In the comet assay, the average comet length (38.6+/-0.8 microm) of 0.05 Gy was significantly longer than that (29.4+/-1.1 microm) of 0 Gy (P<0.01), moreover, the average comet length increased with the dose of X-ray radiation. In the CBMN, both the average micronucleus rate (MN) and micronucleated cell rate (MNC) of 0.05 Gy were 11.5+/-4.5 per thousand, which showed no difference with that (7.5+/-0.5 per thousand) of 0 Gy (P>0.05). The lowest dose, which induced significant increase of average MN and MNC, was 0.25 Gy. The average MN and MNC rates increased with radiation-dose. The results showed that there was correlation between SCGE and CBMN, and the sensitivity of SCGE was significantly higher than that of CBMN.     

Absence of a dose-rate effect in the transformation of C3H 10T1/2 cells by alpha-particles

The findings of Hill et al. (1984) on the greatly enhanced transformation frequencies at very low dose rates of fission neutrons induced us to perform an analogous study with alpha-particles at comparable dose rates. Transformation frequencies were determined with gamma-rays at high dose rate (0.5 Gy/min), and with alpha-particles at high (0.2 Gy/min) and at low dose rates (0.83-2.5 mGy/min) in the C3H 10T1/2 cell system. alpha-particles were substantially more effective than gamma-rays, both for cell inactivation and for neoplastic transformation at high and low dose rates. The relative biological effectiveness (RBE) for cell inactivation and for neoplastic transformation was of similar magnitude, and ranged from about 3 at an alpha-particle dose of 2 Gy to values of the order of 10 at 0.25 Gy. In contrast to the experiments of Hill et al. (1984) with fission neutrons, no increased transformation frequencies were observed when the alpha-particle dose was protracted over several hours.     

Development of long-term radiation effects in rats after whole-body fractionated gamma-irradiation

Albino male rats were divided into four groups and exposed to gamma-radiation (137Cs) for 80, 40, 20 and 10 days at dose rates of 0.25, 0.5, 1.0 and 2.0 Gy/day, respectively. The development of lesions and remote aftereffects was shown to depend upon conditions of formation of the absorbed dose. With fractionated irradiation at dose rates above 1.0 Gy/day the dose-rate played a major role in producing the effect.     

Adjustment function among antioxidant substances in acatalasemic mouse brain and its enhancement by low-dose X-ray irradiation

The catalase activities in blood and organs of the acatalasemic (C3H/AnLCsbCsb) mouse of the C3H strain are lower than those of the normal (C3H/AnLCsaCsa) mouse. We conducted a study to examine changes in the activities of antioxidant enzymes, such as catalase, superoxide dismutase (SOD) and glutathione peroxidase (GPX), the total gluathione content, and the lipid peroxide level in the brain, which is more sensitive to oxidative stress than other organs, at 3, 6, or 24 hr following X-ray irradiation at doses of 0.25, 0.5, or 5.0 Gy to the acatalasemic and the normal mice. No significant change in the lipid peroxide level in the acatalasemic mouse brain was seen under non-irradiation conditions. However, the acatalasemic mouse brain was more damaged than the normal mouse brain by excessive oxygen stress, such as a high-dose (5.0 Gy) X-ray. On the other hand, we found that, unlike 5.0 Gy X-ray, a relatively low-dose (0.5 Gy) irradiation specifically increased the activities of both catalase and GPX in the acatalasemic mouse brain making the activities closer to those in the normal mouse brain. These findings may indicate that the free radical reaction induced by the lack of catalase is more properly neutralized by low dose irradiation.     

The induction of reciprocal translocations in rhesus monkey stem-cell spermatogonia: effects of low doses and low dose rates

The induction of reciprocal translocation in rhesus monkey spermatogonial stem cells was studied following exposure to low doses of acute X rays (0.25 Gy, 300 mGy/min) or to low-dose-rate X rays (1 Gy, 2 mGy/min) and gamma rays (1 Gy, 0.2 mGy/min). The results obtained at 0.25 Gy of X rays fitted exactly the linear extrapolation down from the 0.5 and 1.0 Gy points obtained earlier. Extension of X-ray exposure reduced the yield of translocations similar to that in the mouse by about 50%. The reduction to 40% of translocation rate after chronic gamma exposure was clearly less than the value of about 80% reported for the mouse over the same range of dose rates. Differential cell killing with ensuing differential elimination of aberration-carrying cells is the most likely explanation for the differences between mouse and monkey.     

Small chromosomal integration site of classical CTX prophage in Mozambique <Emphasis Type="Italic">Vibrio cholerae</Emphasis> O1 biotype El Tor strain

An unusual strain of Vibrio cholerae O1 biotype El Tor harbouring multiple tandem copies of classical CTX prophage caused a cholera epidemic in Mozambique in 2004. However, the location of the classical CTX prophage in the genome of the Mozambique strain was unknown. In this study, pulsed field gel electrophoresis (PFGE) of the whole genome along with Southern hybridization experiments indicated that the classical CTX prophage present in the Mozambique strain is located in the small chromosome. To determine the CTX prophage integration site in the small chromosome of Mozambique strain, the 5'and 3' junctions of the prophage and small chromosome were PCR amplified, cloned and sequenced. Sequence analysis indicated that the prophage was integrated in the conserved dif site of the replication terminus region of the Mozambique strain. While using an O1 El Tor isolate VC44 as a control strain, which carries tandem copies of CTX prophage in its small chromosome like the Mozambique strain, it was unexpectedly detected that the strain VC44 also possesses classical cholera toxin B gene allele. Since the strain VC44 was isolated in India in the year 1992, it appears that the Mozambique strain has probably originated from a VC44-like strain.     

Mechanism of Haemophilus influenzae transfection by single and double prophage deoxyribonucleic acid.

Whole phages HP1 and HP3, vegetative-phage deoxyribonucleic acid (DNA), and single and tandem double prophage DNA were exposed to ultraviolet radiation and then assayed on a wild-type (DNA repair-proficient) Haemophilus influenzae Rd strain and on a repair-deficient uvr-1 strain. Host cell reactivation (DNA repair) was observed for whole-phage and vegetative-phage DNA but not for single and double prophage DNA. Competent (phage-resistant) Haemophilus parainfluenzae cells were normally transfected with H. influenzae-grown phage DNA and with tandem double prophage DNA but not at all with single prophage DNA. CaCl2-treated H. influenzae suspensions could be transfected with vegetative phage DNA and with double prophage DNA but not with single prophage DNA. These observations support the hypothesis that transfection with single prophage DNA occurs through prophage DNA single-strand insertion into the recipient chromosome (at the bacterial att site) followed by DNA replication and then prophage induction.     

Gamma ray induced bone marrow micronucleated erythrocytes in seven strains of mouse

We have investigated the effect of gamma-radiation on the frequency of bone marrow micronucleated erythrocytes in seven inbred strains of adult male mice. Twenty animals of each strain viz. Swiss, C57BL/6, C57BR/cd, C3H, CBA, DBA, and AKR were irradiated at 0.0, 0.125, 0.25, 0.50, and 1.00Gy of gamma-rays at a dose rate of 0.46Gy/min using a 60Co-teletharapy machine. Animals were sacrificed 24h post-irradiation, bone marrow smears were made and stained in May-Grunwald Giemsa for evaluating the frequency of micronucleated erythrocytes as indicators of chromosomal damage. About 2000 polychromatic erythrocytes (PCEs) and the corresponding normochromatic erythrocytes (NCEs) were scored for each mouse. Thus, at least 8000 PCEs were scored for each dose point in all the groups. The spontaneous frequency of mn-PCEs per thousand (per thousand ) cells varied considerably among the strains with C57BR/cd (3.47 per thousand ) exhibiting highest as compared to CBA (2.47 per thousand ) and DBA (2.35 per thousand). Radiation exposure, even at lowest dose of 0.125Gy, induced a significant increase in the frequency of mn-PCEs and a dose dependent response was observed among all the strains. However, the animals irradiated at lower doses (0.125-0.50Gy) showed marked differences in the extent of radiation induced chromosomal damage among the various genotypes. At highest dose of radiation (1.00Gy), genotype dependent variability in the frequency of mn-PCEs was not so marked but relatively comparable among the various strains. This study clearly shows that the magnitude of variability of radiation induced chromosomal damage among different strains of mouse can be different at different doses. Therefore, use of single dose point comparisons and/or use of only higher doses of radiation for ascertainment of genotype dependent variability in mouse may lead to erroneous conclusions.     

60Coγ射线对杏鲍菇菌丝的诱变效应

采用^60Coγ射线诱变杏鲍菇菌丝,在辐照剂量为1000Gy,剂量率为67．8Gy／h的条件下,经过拮抗试验和酯酶同功酶电泳验证,选育出一株杏鲍菇新菌株,诱变菌株与供试菌株比较,菌丝积累量差异均达到极显著水平。