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.     

The micronucleus assay as a biological dosimeter in hospital workers exposed to low doses of ionizing radiation

The health risk associated with low levels of ionizing radiation is still a matter of debate. A number of factors, such as non-target effects, adaptive responses and low-dose hypersensitivity, affect the long-term outcome of low-dose exposures. Cytogenetic bio-dosimetry provides a measure of the absorbed dose, taking into account the individual radiation sensitivity. The aim of the present study is to evaluate the value of the micronucleus (MN) test as a bio-dosimeter in hospital workers exposed to low doses of ionizing radiation. Blood samples were obtained from 30 subjects selected among workers exposed to X- and gamma-radiation, and 30 controls matched for sex, age and smoking from the same hospital. Micronucleus frequencies were analyzed by use of the cytokinesis-block method. The MN frequency was compared among the groups considering the confounding factors and the length of employment. No increase in the number of bi-nucleated cells with MN (BNMN), but a significant increase in the number of mono-nucleated cells with micronuclei (MOMN) was observed in exposed subjects compared with the controls. The relationship between MN frequency and accumulated dose (mSv) was evaluated. The length of employment did not affect the extent of MN frequency, but an increase of BNMN and MOMN cells was observed based on the accumulated radiation dose. Our study shows the sensitivity of the MN test in the detection of cytogenetic effects of cumulative exposure levels, suggesting the potential usefulness of this assay in providing a biological index in medical surveillance programs.     

Responses in continuous cultures of lysogenic Escherichia coli following induction

Bacteriophages are widely distributed in nature and may be important factors in regulating populations of their hosts. Model continuous culture systems of a single bacterial species and a temperate parasitic phage have been studied. Steady state cultures of lysogenic Escherichia coli 159T^? (λcts) produced a small quantity of free λ cts phage. Temperature shocking such a culture resulted in a sharp increase in phage concentration with a concomitant fall in cell population. With time the system returned to a steady state condition.     

Vicia faba chromosome damage induced by low doses of gamma radiation

The rate of radiation damage to chromosomes by low doses of gamma rays (0.01-0.30 Gy) was studied in the root tips ofVicia faba. As criteria of the effect of ionizing radiation, the frequency of sister chromatid exchanges (SCEs), incidence of chromosomal aberrations and the number of micronuclei were evaluated and compared in irradiated cells. The results obtained confirmed that the analysis of SCEs did not represent an efficient indicator of radiation damage to chromosomes. On the contrary, the formation of chromosomal aberrations and micronuclei was effectively stimulated by low radiation doses, there being linear dose-effect relationships in the low doses region used.     

The induction of micronuclei in human lymphocytes by low doses of radiation

The appearance of micronuclei (MN) is delayed with respect to cell division in populations of irradiated human lymphocytes, so that the length of time in culture, as well as the number of divisions, is a factor in MN assays. Using two assays that control for cell kinetics, we measured the yield of cells with MN exposed to graded doses of 60Co gamma rays and 90KVP X-rays. The yields showed a non-linear increase with dose. They can be represented by two straight lines: the one in the range below 0.15 Gy has a slight slope, the other in the range above 0.15 Gy has a significantly greater slope. The radical scavengers cysteamine and glycerol, which reduced the MN yields sharply at 3 Gy, were less effective at 0.3 Gy, indicating that terminal deletions arising from the direct ionization of DNA are a major source of the MN induced by low radiation doses. It is likely that the non-linear dose response is due to the saturation of a DNA repair process.     

The action of low doses of gamma radiation on mammalian cells]

Effect of gamma irradiation in low doses (10, 20, 40 and 50 cGy) on HeLa cells was studied. The survival of cells exposed to the irradiation in the dose of 50 cGy was decreased while it remained unchanged in cells irradiated in the dose of 10-40 cGy and their descendants. Nonetheless, their survival following an additional treatment with a mixture of cytosine arabinoside and hydroxyurea was reduced. It was suggested that the genome stability was diminished in irradiated cells and their descendants.     

The Trp53 pathway is induced in vivo by low doses of gamma radiation

The induction of the Trp53 response after very low doses (0.01-1 Gy) of ionizing radiation was studied in the adult mouse using immunochemical and immunohistochemical methods. We found a detectable response at 0.01 Gy and an increased induction of Trp53 with increasing dose in both radiation-resistant and radiation-sensitive tissues. These results suggest that there is no lower threshold for induction. This response was heterogeneous, since cells that received the same dose had different staining intensities, suggesting that the induction of Trp53 is not based simply on dose-dependent responses to DNA damage. These data also demonstrate the exquisite sensitivity of the Trp53 pathway and show that this response is controlled by cell- and tissue-specific factors that have yet to be defined.     

Genotoxicity assessment of low-level doses of gamma radiation with the SOS chromotest and the Ames test

This is the first study to present data on the genotoxicity of low γ-irradiation doses for E. coli and S. typhimurium cells obtained using the SOS chromotest and the Ames test. The most pronounced effect was recorded in the first 24 h of γ-irradiation. After 72 h in the Ames test and after 96 h in the SOS chromotest, a significant effect of γ-irradiation on bacterial cells was detected. The absence of genotoxicity at the later stages can be explained by the adaptation of bacterial cells to the conditions of exposure. The findings allow the bacterial test system to be used for studying the effects of low doses at the early stages of exposure to radiation.     

Winter illness and vitamin C: the effect of relatively low doses.

After their random -llocation to one of three treatment aroups, 622 volunteers received either vitamin C or placebo in a maintenance dose of 500 mg once weekly and a therapeutic dose of 1500 mg daily on the 1st day and 1000 mg on the next 4 days of any illness. Two forms of vitamin C were employed: a sustained-release capsule containing ascorbic acid and a regular tabet containing a mixture of sodium and calcium ascorbate. In the 448 subjects who completed an average of 15 weeks in the study of total of 635 episodes of illness were recroded. Respiratory symptoms were recorded on at least 1 day in 92 per cent of these episodes. There were no consistent or significant differences in the sickness experience of the subjects receiving the sustained-release vitamin capsules compared to those receiving the vitamin tablets, but subjects in both vitamin groups experienced less severe illness than subjects in the placebo group, with approximately 25 per cent fewer days spent indoors because of the illness (P smaller than 0.05). These results are compatible with the belief that supplementary vitamin C can reduce the burden of winter illness, but the intake need not be as high as has sometimes been claimed.     

Drosophila melanogaster larvae detect low doses of UVC radiation as manifested by a writhing response

Exposure of insects and higher orders of animals to UVC radiation has been shown to result in toxicity with a delayed expression. We have observed an immediate writhing response in slowly wandering third instar larvae of Drosophila melanogaster exposed to UVC radiation at doses that were not lethal. UVB and UVA radiation had no effect. Mutants for the visual and sensory systems appeared to respond normally, but CO₂ anesthesia resulted in reversible inhibition, ebony and silver mutants, which affect different pathways in catecholamine metabolism, showed an absent to reduced response. Using UVC lasers, we were able to demonstrate a response in different regions of the larval body. Furthermore, a 193 nm laser that penetrates only 2–5 μm was able to induce a response but unable to kill the larvae. These results suggest a photochemical reaction occurs in the cuticle which produces free radicals that stimulate the nerves and muscle which are present immediately below the epidermis. Possible targets for the UVC radiation are catecholic compounds secreted and processed into the cuticle of third instar larvae just prior to pupariation whose primary function is to crosslink the protein and carbohydrate components. © 1996 Wiley-Liss, Inc.     

The effect of chronic exposure to cadmium and gamma radiation at low doses on the genetic structures in mice

The DNA-protein cross-links (DPC) in mouse thymocytes and spleen lymphocytes, the number of abnormal sperm heads (ASH) and the number of micronuclei (MN) in normochromatic erythrocytes (NCE) of peripheral blood were studied in mice exposed to long-term low-intensity gamma radiation (0.072 cGy/days) and/or cadmium with drinking water (0.01 mg Cd2+/l) for 20, 40 and 80 days. The dependence of DPC level on the total dose (exposure time) of gamma radiation and/or cadmium is nonlinear. The maximal level of DPC in cells of lymphoid organs upon exposure to gamma radiation or cadmium was recorded on the 40-th day, and under combined exposure on the 20-th day of the experiment. The long-term exposure to cadmium or gamma radiation causes an increase in the ASH frequency. The increase in frequencies of MN in NCE and reciprocal translocations in spermatocytes was not found.     

Nutritive value of some agricultural wastes as affected by relatively low gamma irradiation levels and chemical treatments

An experiment was carried out to study the changes in the values of in vitro organic matter digestibility (IVOMD) and metabolizable energy (ME) of wheat straw, sunflower seed shell, olive cake wood, date palm seeds and peanut shell after irradiation with various levels of gamma radiation (0, 20, 40, 60 kGy; kiloGray) or after spraying with different amounts of hydrobromic acid (HBr; 47%) and sodium hydroxide (NaOH): 0, 3, 6 ml HBr and 3, 6 g NaOH in 25 ml water/100 g DM. The results indicated that chemical treatments increased the IVOMD and ME values significantly for all samples treated except the date palm seeds. There was no significant effect of irradiation on IVOMD and ME. Combined treatments of irradiation and HBr or NaOH were also found to be ineffective in increasing the IVOMD and ME values.