Considering Existing Factors That May Cause Radiation Hormesis at <100 mSv and Obey the Linear No-Threshold Theory at ≥100 mSv

The linear no-threshold (LNT) theory describes the linear relationship between a radiation dose and its effects. However, whether the linear relationship is maintained at low radiation doses has yet to be determined. Many previous studies support the radiation hormesis theory, which states that radiation has beneficial effects on health. In this viewpoint, we propose a mathematical function fitted to a model consistent with both the LNT at ≥100 mSv and radiation hormesis theories at <100 mSv, and the model requires a factor whose amount or activity takes a mountain-like shape versus the radiation dose and have one maximum value at 40.9 mSv. We searched a wide range of factors with these features based on searches on PubMed, and then evaluated whether these factors were suitable candidates consistent with both the LNT and radiation hormesis theories. Our consideration indicated that these factors did not completely follow the equation suggested at this time. Of course, other theories do not deny that these factors are involved in hormesis. However, based on our theory, still unknown factors may be involved in radiation hormesis, and then such unknown factors which are activated at <100 mSv should be searched.

Two sides of radon - a radioactive and healing component of water and air

This work presents two sides of radon - a radioactive, toxic element which has healing properties. Authors in this work present selected data about radon measurements in medicinal waters commonly used for radon therapy, to describe a phenomenon of radiation hormesis and healing properties of radon waters. From the other side, authors present the data about radon as a component of the atmosphere: radon-enriched air in health resorts, buildings (indoor radon). Authors present advantages and disadvantages of radon occurrence in human environment.

Radiation Hormesis and Epidemiology of Carcinogenesis: ‘Never the Twain Shall Meet’

The review considers the reasons that do not allow the use of radiation hormesis for public health and for the prevention of diseases in the population. It is noted that evidence of the hormesis effects of low doses radiation with low LET was obtained only in laboratory experiments on cells and animals, using a hypothetical-deductive method and adequate controls. Some confirmation was found in balneology (radon therapy) and in the clinic (immunostimulation in cancer patients). At the same time, in epidemiological, observational studies, which mainly involve the induction method, there are no unambiguous data on hormesis effects on the frequency of carcinogenesis. This is due to the fact that in the region of low doses (up to 0.1 Gy), in addition to linear, any forms of dose dependence are equally probable, and it is impossible to isolate the radiation effect due to the iinfluence of non-radiation factors, as well as confounders and biases. The epidemiological designs used to confirm radiation hormesis in terms of the frequency of malignant neoplasms have such significant drawbacks and limitations for small magnitudes of effects that, according to epidemiology, there is no possibility for conclusions about hormesis. The stated is, among other things, the position of UNSCEAR, ICRP, BEIR and NCRP, which in the relevant documents, however, is presented insufficiently. For many experimental researchers and clinicians (of any rank), who are not familiar with the basics of classical epidemiology and descriptive disciplines, this position remains incomprehensible and incomprehensible. It is concluded that although hormesis may exist at low doses of radiation, it will hardly be possible to prove and, moreover, to use it in epidemiology and medicine for the prevention of a healthy population. At the same time, it is necessary to actively develop the clinical use of radiation in low doses, but only as a therapeutic immunostimulation in severe pathologies.

Modeling of Molecular Mechanisms of Radiation Adaptive Response Formation

The phenomenon of adaptive response is expressed in the increase of resistance of a biological object to high doses of mutagens under the conditions of previous exposure to these (or other) mutagens in low doses. Low doses of mutagen activate a number of protective mechanisms in a living object, which are called hormetic. Thus, the adaptive response and hormesis are links in the same chain. Radiation hormesis refers to the generally positive effect of low doses of low LET radiation on biological objects. The phenomenology of radiation-induced adaptive response and radiation hormesis for biological objects of different levels of organization is considered; the review of existing theories describing the dose-effect relationship has been reviewed. The hypothesis proposing one of the mechanisms of formation of radiation adaptive response of cells taking into account the conformational structure of chromatin has been submitted. The analysis of modern concepts of the phenomenon of hormesis on the basis of modeling of molecular mechanisms of formation of hormetic reactions to low-dose low LET radiation has been carried out. The parameters that can be used for quantitative and graphical evaluation of the phenomenon of hormesis was considered, and a formula for calculating the coefficient of radiation-induced adaptive response has been proposed. A review of mathematical models describing the radiation relative risk of gene mutations and neoplastic transformations at low-dose irradiation of cohorts has been performed. The following conclusions have been made: radiation hormesis and adaptive response are generally recognized as real and reproducible biological phenomena, which should be considered as very important phenomena of evolutionarily formed biological protection of living organisms from ionizing radiation. The hormesis model of dose-response relationship makes much more accurate predictions of a living object's response to radiation (or other stressors) in the low-dose range than the linear threshold (LNT) model does. The LNT model can adequately describe reactions only in the region of high doses of radiation, and, therefore, extrapolation modeling of biological object’s reactions from the zone of high doses to low doses is not correct.

Studying Gene Expression in Irradiated Barley Cultivars: PM19L-like and CML31-like Expression as Possible Determinants of Radiation Hormesis Effect

Gamma (γ)-irradiation of plants at low doses can provoke a broad range of growth-stimulating effects. In order to reveal universal target genes that are involved in molecular pathways of radiation hormesis establishment, we studied nine barley cultivars for their tolerance to γ-irradiation of seeds. Four morphological traits were assessed in barley seedlings after γ-irradiation of seeds at 20 Gy. Nine cultivars were sorted according to the sensitivity to irradiation as γ-stimulated, “no morphological effect”, or γ-inhibited. Gene expression of 17 candidate genes was evaluated for the 7 most contrasting cultivars. Changes in expression of barley homologues of PM19L and CML31 were suggested as possible determinants of radiation hormesis effect. The possible role of jasmonate signaling in roots in radiation growth stimulations was revealed. Morphological analysis and gene expression study showed that the genetic background of a cultivar plays an important role in eustress responses to low-dose γ-irradiation of seeds.