Response of Biological Systems to Low Doses of Ionizing Radiation

Study of Lipid Peroxidation-antioxidant Defense Systems in Rats under Radiation Exposure

Abstract BACKGROUND: Experimental data on the effect of a high dose of gamma radiation 6 Gy on the activity of antioxidant defense enzymes and lipid peroxidation products (LPO) are presented immunocompetent organs in the body of animals in the experiment. It was found that the effect of ionizing radiation led to an increase in the level of diene conjugates (DC) and malondialdehyde (MDA), inhibition of the activity of catalase (CАT) and glutathione peroxidase (GlP), glutathione reductase (GlR) enzymes in almost all the studied objects, as a result of which the development of oxidative stress was observed in them. The results of the study indicate serious changes in the lipid peroxidation and antioxidant system (AOS) under radiation stress. An imbalance of POL-AOS creates prerequisites for the occurrence of immunopathological conditions, contributing to the development of radiation-related tumor infection. pathologies. Violations of functional relationships of the catalytic redox system. AIM: The aim of the study was to study the effect of radiation at a dose of 6 Gy on the parameters of lipoperoxidation and the antioxidant system in experimental rats. MATERIAL AND METHODS: The work was carried out on 20 male Wistar rats weighing 240 ± 20 g. Experimental animals are divided into two groups: I - normal group; II - group exposed to γ-rays at a dose of 6 Gy. RESULTS: After radiation exposure, all objects showed a tendency to increase the product of lipid peroxidation. As is known, the activation of lipid peroxidation is based on excessive generation of reactive oxygen species, which exceeds the physiological capabilities of antioxidant systems that occur after the depletion of enzyme systems. CONCLUSION: Based on the results obtained, it was found, that irradiation increases the intensity of the formation of POL products and their accumulation, reduces the activity of enzymes of the antioxidant system in immunocompetent organs in irradiated animals, as a result, the lack of the antioxidant system causes oxidative stress in the body.

Low doses and non-targeted effects in environmental radiation protection; where are we now and where should we go?

The field of low dose radiobiology has advanced considerably in the last 30 years from small indications in the 1980's that all was not simple, to a paradigm shift which occurred during the 1990's, which severely dented the dose-driven models and DNA centric theories which had dominated until then. However while the science has evolved, the application of that science in environmental health protection has not. A reason for this appears to be the uncertainties regarding the shape of the low dose response curve, which lead regulators to adopt a precautionary approach to radiation protection. Radiation protection models assume a linear relationship between dose (i.e. energy deposition) and effect (in this case probability of an adverse DNA interaction leading to a mutation). This model does not consider non-targeted effects (NTE) such as bystander effects or delayed effects, which occur in progeny cells or offspring not directly receiving energy deposition from the dose. There is huge controversy concerning the role of NTE with some saying they reflect "biology" and that repair and homeostatic mechanisms sort out the apparent damage while others consider them to be a class of damage which increases the size of the target. One thing which has recently become apparent is that NTE may be very critical for modelling long-term effects at the level of the population rather than the individual. The issue is that NTE resulting from an acute high dose such as occurred after the A-bomb or Chernobyl occur in parallel with chronic effects induced by the continuing residual effects due to radiation dose decay. This means that if ambient radiation doses are measured for example 25 years after the Chernobyl accident, they only represent a portion of the dose effect because the contribution of NTE is not included.

Carcinogenesis Induced by Low-dose Radiation

Background

Although the effects of high dose radiation on human cells and tissues are relatively well defined, there is no consensus regarding the effects of low and very low radiation doses on the organism. Ionizing radiation has been shown to induce gene mutations and chromosome aberrations which are known to be involved in the process of carcinogenesis. The induction of secondary cancers is a challenging long-term side effect in oncologic patients treated with radiation. Medical sources of radiation like intensity modulated radiotherapy used in cancer treatment and computed tomography used in diagnostics, deliver very low doses of radiation to large volumes of healthy tissue, which might contribute to increased cancer rates in long surviving patients and in the general population. Research shows that because of the phenomena characteristic for low dose radiation the risk of cancer induction from exposure of healthy tissues to low dose radiation can be greater than the risk calculated from linear no-threshold model. Epidemiological data collected from radiation workers and atomic bomb survivors confirms that exposure to low dose radiation can contribute to increased cancer risk and also that the risk might correlate with the age at exposure.

Conclusions

Understanding the molecular mechanisms of response to low dose radiation is crucial for the proper evaluation of risks and benefits that stem from these exposures and should be considered in the radiotherapy treatment planning and in determining the allowed occupational exposures.

Low Doses of Oxygen Ion Irradiation Cause Acute Damage to Hematopoietic Cells in Mice

One of the major health risks to astronauts is radiation on long-duration space missions. Space radiation from sun and galactic cosmic rays consists primarily of 85% protons, 14% helium nuclei and 1% high-energy high-charge (HZE) particles, such as oxygen (16O), carbon, silicon, and iron ions. HZE particles exhibit dense linear tracks of ionization associated with clustered DNA damage and often high relative biological effectiveness (RBE). Therefore, new knowledge of risks from HZE particle exposures must be obtained. In the present study, we investigated the acute effects of low doses of 16O irradiation on the hematopoietic system. Specifically, we exposed C57BL/6J mice to 0.1, 0.25 and 1.0 Gy whole body 16O (600 MeV/n) irradiation and examined the effects on peripheral blood (PB) cells, and bone marrow (BM) hematopoietic stem cells (HSCs) and hematopoietic progenitor cells (HPCs) at two weeks after the exposure. The results showed that the numbers of white blood cells, lymphocytes, monocytes, neutrophils and platelets were significantly decreased in PB after exposure to 1.0 Gy, but not to 0.1 or 0.25 Gy. However, both the frequency and number of HPCs and HSCs were reduced in a radiation dose-dependent manner in comparison to un-irradiated controls. Furthermore, HPCs and HSCs from irradiated mice exhibited a significant reduction in clonogenic function determined by the colony-forming and cobblestone area-forming cell assays. These acute adverse effects of 16O irradiation on HSCs coincided with an increased production of reactive oxygen species (ROS), enhanced cell cycle entry of quiescent HSCs, and increased DNA damage. However, none of the 16O exposures induced apoptosis in HSCs. These data suggest that exposure to low doses of 16O irradiation induces acute BM injury in a dose-dependent manner primarily via increasing ROS production, cell cycling, and DNA damage in HSCs. This finding may aid in developing novel strategies in the protection of the hematopoietic system from space radiation.