Radiation hormesis: the good, the bad, and the ugly

Physical Methods for Seed Invigoration: Advantages and Challenges in Seed Technology

In the context of seed technology, the use of physical methods for increasing plant production offers advantages over conventional treatments based on chemical substances. The effects of physical invigoration treatments in seeds can be now addressed at multiple levels, ranging from morpho-structural aspects to changes in gene expression and protein or metabolite accumulation. Among the physical methods available, "magneto-priming" and irradiation with microwaves (MWs) or ionizing radiations (IRs) are the most promising pre-sowing seed treatments. "Magneto-priming" is based on the application of magnetic fields and described as an eco-friendly, cheap, non-invasive technique with proved beneficial effects on seed germination, vigor and crop yield. IRs, as γ-rays and X-rays, have been widely regarded as a powerful tool in agricultural sciences and food technology. Gamma-rays delivered at low dose have showed to enhance germination percentage and seedling establishment, acting as an actual 'priming' treatment. Different biological effects have been observed in seeds subjected to MWs and X-rays but knowledge about their impact as seed invigoration agent or stimulatory effects on germination need to be further extended. Ultraviolet (UV) radiations, namely UV-A and UV-C have shown to stimulate positive impacts on seed health, germination, and seedling vigor. For all mentioned physical treatments, extensive fundamental and applied research is still needed to define the optimal dose, exposition time, genotype- and environment-dependent irradiation conditions. Electron paramagnetic resonance has an enormous potential in seed technology not fully explored to monitor seed invigoration treatments and/or identifying the best suitable irradiation dose or time-point to stop the treatment. The present manuscript describes the use of physical methods for seed invigoration, while providing a critical discussion on the constraints and advantages. The future perspectives related to the use of these approaches to address the need of seed technologists, producers and trade markers will be also highlighted.

Heat shock proteins and hormesis in the diagnosis and treatment of neurodegenerative diseases

Modulation of endogenous cellular defense mechanisms via the vitagene system represents an innovative approach to therapeutic intervention in diseases causing chronic tissue damage, such as in neurodegeneration. The possibility of high-throughoutput screening using proteomic techniques, particularly redox proteomics, provide more comprehensive overview of the interaction of proteins, as well as the interplay among processes involved in neuroprotection. Here by introducing the hormetic dose response concept, the mechanistic foundations and applications to the field of neuroprotection, we discuss the emerging role of heat shock protein as prominent member of vitagene network in neuroprotection and redox proteomics as a tool for investigating redox modulation of stress responsive vitagenes. Hormetic mechanisms are reviewed as possibility of targeted therapeutic manipulation in a cell-, tissue- and/or pathway-specific manner at appropriate points in the neurodegenerative disease process.

The Inhibitory Effects of Low-Dose Ionizing Radiation in IgE-Mediated Allergic Responses

Ionizing radiation has different biological effects according to dose and dose rate. In particular, the biological effect of low-dose radiation is unclear. Low-dose whole-body gamma irradiation activates immune responses in several ways. However, the effects and mechanism of low-dose radiation on allergic responses remain poorly understood. Previously, we reported that low-dose ionizing radiation inhibits mediator release in IgE-mediated RBL-2H3 mast cell activation. In this study, to have any physiological relevance, we investigated whether low-dose radiation inhibits allergic responses in activated human mast cells (HMC-1(5C6) and LAD2 cells), mouse models of passive cutaneous anaphylaxis and the late-phase cutaneous response. High-dose radiation induced cell death, but low-dose ionizing radiation of <0.5 Gy did not induce mast cell death. Low-dose ionizing radiation that did not induce cell death significantly suppressed mediator release from human mast cells (HMC-1(5C6) and LAD2 cells) that were activated by antigen-antibody reaction. To determine the inhibitory mechanism of mediator released by low-dose ionizing radiation, we examined the phosphorylation of intracellular signaling molecules such as Lyn, Syk, phospholipase Cγ, and protein kinase C, as well as the intracellular free Ca²⁺ concentration ([Ca²⁺]_i). The phosphorylation of signaling molecules and [Ca²⁺]_i following stimulation of FcεRI receptors was inhibited by low dose ionizing radiation. In agreement with its in vitro effect, ionizing radiation also significantly inhibited inflammatory cells infiltration, cytokine mRNA expression (TNF-α, IL-4, IL-13), and symptoms of passive cutaneous anaphylaxis reaction and the late-phase cutaneous response in anti-dinitrophenyl IgE-sensitized mice. These results indicate that ionizing radiation inhibits both mast cell-mediated immediate- and delayed-type allergic reactions in vivo and in vitro.

Association Between Air Temperature and Cancer Death Rates in Florida: An Ecological Study

Proponents of global warming predict adverse events due to a slight warming of the planet in the last 100 years. This ecological study tests one of the possible arguments that might support the global warming theory - that it may increase cancer death rates. Thus, average daily air temperature is compared to cancer death rates at the county level in a U.S. state, while controlling for variables of smoking, race, and land elevation. The study revealed that lower cancer death rates were associated with warmer temperatures. Further study is indicated to verify these findings.

Heart Disease Death Rates in Low Versus High Land Elevation Counties in the U.S

Previous research on land elevation and cancer death rates in the U.S. revealed lower cancer death rates in higher elevations. The present study further tests the possible effect of land elevation on a diffident health outcome, namely, heart disease death rates. U.S. counties not overlapping in their land elevations according to their lowest and highest elevation points were identified. Using an ecological design, heart disease death rates for two races (black and white) corresponding to lower elevation counties were compared to heart disease death rates in higher land elevation counties using the two-sample t-test and effect size statistics. Death rates in higher land elevation counties for both races were lower compared to the death rates in lower land elevation counties (p < 0.001) with large effect sizes (of > 0.70). Since this is an observational study, no causal inference is claimed, and further research is indicated to verify these findings.

Optimal conditions of LDR to protect the kidney from diabetes: exposure to 12.5 mGy X-rays for 8 weeks efficiently protects the kidney from diabetes

AIMS

We reported the attenuation of diabetes-induced renal dysfunction by exposure to multiple low-dose radiation (LDR) at 25 mGy every other day by suppressing renal oxidative damage. We here explored the optimal conditions of LDR to protect the kidney from diabetes.

MAIN METHODS

Male C57BL/6J mice with type 1 diabetes were induced with multiple injections of low-dose streptozotocin. Diabetic mice received whole body X-irradiation at a dose of 12.5, 25 or 50 mGy every other day for either 4 or 8 weeks. Age-matched normal mice were similarly irradiated at the dose of 25 mGy for 4 or 8 weeks. The renal function and histopathological changes were examined at the 4th and 8th weeks of the study.

KEY FINDINGS

Diabetes induced renal dysfunction is shown by the decreased creatinine and increased microalbumin in the urine. Renal oxidative damage, detected by protein nitration and lipid oxidation, and remodeling, reflected by increased expression of connective tissue growth factor, collagen IV and fibronectin, were significantly increased in diabetic mice. All these renal pathological and function changes in diabetic mice were significantly attenuated by exposure to LDR at all regimens, among which, however, exposure to LDR at 12.5 mGy for 8 weeks provided the best protective effect on the kidney of diabetic mice.

SIGNIFICANCE

Our results suggest that whole-body LDR at 12.5 mGy every other day for 8 weeks is the optimal condition of LDR to protect the kidney from diabetes.

Foxp3(+)-Treg cells enhanced by repeated low-dose gamma-irradiation attenuate ovalbumin-induced allergic asthma in mice

Gamma radiation is used for several therapeutic indications such as cancers and autoimmune diseases. Low-dose whole-body γ irradiation has been shown to activate immune responses in several ways, however, the effect and mechanism of irradiation on allergic asthma remains poorly understood. This study investigated whether or not irradiation exacerbates allergic asthma responses and its potential mechanism. C57BL/6 mice were sensitized and challenged with ovalbumin (OVA) to induce asthma. The mice received whole-body irradiation once daily for 3 consecutive days with a dose of 0.667 Gy using (137)Cs γ rays 24 h before every OVA challenge. Repeated low-dose irradiation reduced OVA-specific IgE levels, the number of inflammatory cells including mast cells, goblet cell hyperplasia, collagen deposition, airway hyperresponsiveness, expression of inflammatory cytokines, CCL2/CCR2, as well as nuclear factor kappa B (NF-κB) and activator protein-1 activities. All of these factors were increased in BAL cells and lung tissue of OVA-challenged mice. Irradiation increased the number of Treg cells, expression of interleukin (IL)-10, IL-2 and IL-35 in BAL cells and lung tissue. Irradiation also increased Treg cell-expressed Foxp3 and IL-10 by NF-κB and RUNX1 in OVA-challenged mice. Furthermore, while Treg cell-expressing OX40 and IL-10 were enhanced in lung tissue or act-bone marrow-derived mast cells (BMMCs) with Treg cells, but BMMCs-expressing OX40L and TGF-β were decreased. The data suggest that irradiation enhances Foxp3(+)- and IL-10-producing Treg cells, which reduce OVA-induced allergic airway inflammation and tissue remodeling through the down-regulation of migration by the CCL2/CCR2 axis and activation of mast cells via OX40/OX40L in lung tissue of OVA-challenged mice.

Modeling non-monotonic dose-response relationships: model evaluation and hormetic quantities exploration

Non-monotonic (biphasic) dose-response relationships, known as hormetic relationships, have been observed across multiple experimental systems. Several models were proposed to describe non-monotonic relationships. However, few studies provided comprehensive description of hermetic quantities and their potential application. In this study, five biphasic models were used to fit five hormetic datasets from three different experimental systems of our lab. The bisection algorithm based on individual monotone functions was proposed to calculate arbitrary hormetic quantities instead of traditional methods (e.g., model reparameterization) which need complex mathematical manipulation. Results showed that all the five biphasic models could describe those datasets fairly well with coefficient of determination ( R(2) adj) greater than 0.95 and root mean square error (RMSE) smaller than 0.10. The best-fit model could be selected based on EC(R10), RMSE, and a supplemental criterion of Akaike information criterion (AIC). Hormetic quantities that trigger 10% stimulation at the left (EC(L10)) and right (EC(R10)) side of stimulatory peak were calculated and emphasized for their implication in hormesis exploration for the first time. Furthermore, the EC(L10), proposed as an alarm threshold for hormesis, was expected to be useful in risk assessment of environmental chemicals. This study lays a foundation in the quantitative description of the low dose hormetic effect and the investigation of hormesis in environmental risk assessment.

Hormesis: its impact on medicine and health

This article offers a broad assessment of the hormetic dose response and its relevance to biomedical researchers, physicians, the pharmaceutical industry, and public health scientists. This article contains a series of 61 questions followed by relatively brief but referenced responses that provides support for the conclusion that hormesis is a reproducible phenomenon, commonly observed, with a frequency far greater than other dose-response models such as the threshold and linear nonthreshold dose-response models. The article provides a detailed background information on the historical foundations of hormesis, its quantitative features, mechanistic foundations, as well as how hormesis is currently being used within medicine and identifying how this concept could be further applied in the development of new therapeutic advances and in improved public health practices.

Whole body imaging in the diagnosis of blunt trauma, ionizing radiation hazards and residual risk

Ever since the introduction of radiographic imaging, its utility in identifying injuries has been well documented and was incorporated in the workup of injured patients during advanced trauma life support algorithms [American College of Surgeons, 8th ed. Chicago, 2008]. More recently, computerized tomography (CT) has been shown to be more sensitive than radiography in the diagnosis of injury. Due to the increased use of CT scanning, concerns were raised regarding the associated exposure to ionizing radiation [N Engl J Med 357:2277-2284, 2007]. During the last several years, a significant amount of research has been published on this topic, most of it being incorporated in the BEIR VII Phase 2 report, published by the National Research Council of the National Academies [National Academy of Sciences, Washington DC, 2006]. The current review will analyze the scientific basis for the concerns over the ionizing radiation associated with the use of CT scanning and will examine the accuracy of the typical advanced trauma life support work-up for diagnosis of injuries.

The cancer mortality in high natural radiation areas in poland

The cancer mortality ratios (CMRs) in Poland in high and low level radiation areas were analyzed based on information from national cancer registry. Presented ecological study concerned six regions, extending from the largest administration areas (a group of voivodeships), to the smallest regions (single counties). The data show that the relative risk of cancer deaths is lower in the higher radiation level areas. The decrease by 1.17%/mSv/year (p = 0.02) of all cancer deaths and by 0.82%/mSv/year (p = 0.2) of lung cancers only are observed.Tribute to Prof. Zbigniew Jaworowski (1927-2011).

Cancer mortality, state mean elevations, and other selected predictors

This ecological inquiry compares cancer mortality rates in the U.S. to the predictor of natural background radiation (via land elevation means) along with eight other predictors thought to be associated with cancer mortality. Age-adjusted cancer mortality in 2006 was compared to the predictors of mean land elevation, percent of smokers, educational attainment, percent of population without health insurance, income, obesity, health perception, physical activity, and diet. Among the six predictors considered appropriate for multiple linear regression, three were found to be statistically significant; from strongest to weakest, these three were: smoking, land elevation, and educational attainment. The predictors of smoking and educational attainment have long been considered associated with cancer mortality. The finding that the predictor of land elevation / natural background radiation is inversely related to cancer mortality is another piece of evidence supporting the theory of radiation hormesis. In this study, land elevation / natural background radiation ranked second in predictive strength regarding cancer mortality, behind smoking and ahead of educational attainment. Since this is an ecological inquiry, no causal inferences can be made.

Cancer mortality in six lowest versus six highest elevation jurisdictions in the u.s

Low levels of background radiation exist around us continuously. These levels increase with increasing land elevation, allowing a comparison of low elevations to high elevations in regard to an outcome such as cancer death rates. The present study compares archived cancer mortality rates in six low versus six high elevation jurisdictions. The study also compares mortality rates for all causes, heart disease, and diabetes in low versus high elevation jurisdictions in an effort to see if other mortality outcomes are different in low versus high elevations. Statistically significant decreases in mortality, with very large effect sizes, were observed in high land elevation for three of the four outcomes, including cancer. One possible explanation for the decreased mortality in high elevation jurisdictions is radiation hormesis. Another possible explanation, at least in the case of heart disease mortality, is the physiologic responses that accompany higher elevations regarding decreased oxygen levels. Since this is an ecological study, no causal inferences can be made, particularly when viewpoints on possible effects of low level radiation are diametrically opposed. Further research is indicated.

A brief review of radiation hormesis

This paper reviews physical, experimental and epidemiological evidence for and against radiation hormesis and discusses implications with regards to radiation protection. The scientific community is still divided on the premise of radiation hormesis, with new literature published on a regular basis. The International Commission on Radiological Protection (ICRP) recommends the use of the Linear No Threshold (LNT) model, for planning radiation protection. This model states that the probability of induced cancer and hereditary effects increases with dose in a linear fashion. As a consequence, all radiation exposures must be justified and have a sufficient protection standard in place so that exposures are kept below certain dose limitations. The LNT model has sufficient evidence at high doses but has been extrapolated in a linear fashion to low dose regions with much less scientific evidence. Much experimentation has suggested discrepancies of this extrapolation at low doses. The hypothesis of radiation hormesis suggests low dose radiation is beneficial to the irradiated cell and organism. There is definite standing ground for the hormesis hypothesis both evolutionarily and biophysically, but experimental evidence is yet to change official policies on this matter. Application of the LNT model has important radiation protection and general human health ramifications, and thus it is important that the matter be resolved.

Mean cancer mortality rates in low versus high elevation counties in Texas

There is controversy as to whether low levels of radiation (i.e., < 5 rem) pose a health risk. This brief inquiry compares archived cancer mortality data in counties having relatively low (0-250 feet above sea level), medium (500-1000 feet above sea level), and high (3000+ feet above sea level) elevations also having corresponding greater natural background levels of radiation respectively. Cancer mortality was found to be lowest in the high elevation counties (mean = 58.2) followed by low elevation counties (67.5) and then medium elevation counties (70.4). Statistically significant differences were found between low -high elevations (p = 0.003), and medium - high elevations (p = 0.010), but not between low and medium elevations (p = 0.5). More rigorous research, with an accounting of confounding variables, is indicated.

DNA and cytogenetic damage in white blood cells of postmenopausal breast cancer patients treated with radiotherapy

The primary and residual genome damage and its elimination rate were evaluated in peripheral blood lymphocytes of breast cancer patients treated with adjuvant radiotherapy after surgical removal of the tumor by mastectomy or quadrantectomy. The levels of DNA/chromosome damage were estimated before, throughout, as well as after six months, respectively one year after the radiotherapy, using the alkaline comet assay, the chromosome aberration analysis and the cytokinesis-block micronucleus assay. The marked individual differences in the baseline genome damage were observed in patients, which additionally increased until the end of the radiotherapy cycle. The levels of DNA/cytogenetic damage slowly declined during post-irradiation period; although in the majority of subjects they did not return to pre-therapy levels. In addition to the well-established comet parameters, the long-tailed nuclei were also proved as a useful indicator of individual DNA damage and response to radiation. One of the most important observation was that older breast cancer patients, irradiated after mastectomy, had higher values of almost all parameters evaluated. We found positive correlations between the comet assay parameters and the cytogenetic biomarkers that confirmed their complementary value in the assessment of the radiation sensitivity/susceptibility in elderly breast cancer patients. The specific patterns of DNA damage observed in the majority of subjects after a prolonged exposure to ionizing radiation indicate the possibility of adaptive response. Such results may also be linked to the hormesis theory and support previous observations, but the underlying mechanisms should be further investigated on a much larger population.

Prospectus. Survival across the fitness-stress continuum under the ecological stress theory of aging: caloric restriction and ionizing radiation

Free living organisms typically occur in harsh environments challenged by abiotic stresses of varying intensities. Taking ionizing radiation and caloric restriction as examples, environmental variation from benign to extreme gives a fitness-stress continuum where energetic efficiency, a measure of fitness, is inversely related to stress level. Hormesis occurs in benign regions for these examples. In contrast aging emphasizes survival towards the limits of survival under accumulating stress from Reactive Oxygen Species, ROS. An energetic evolutionary approach underlies an ecological aging theory based principally upon survival, which incorporates hormesis. Multiple environmental agents contributing to hormesis should be considered by those attempting to improve the quality of life by delaying the onset of senescence, so enhancing survival. Caloric restriction has wider acceptance in this process than ionizing radiation.

Myelodysplasia paranoia: iron as the new radon

Few areas concerning the care of patients with myelodysplastic syndromes (MDS) have prompted as much disagreement among clinicians as the appropriate role of iron chelation therapy. At least eight conflicting guidelines or consensus statements on iron management in MDS have been published by medical organizations during the past 6 years. Uncertainties about the clinical importance of iron overload and the necessity for iron chelation in transfusion-requiring patients with MDS have caused confusion for patients. Here, I summarize what we have learned and what we still do not know about the diagnosis, prognosis, monitoring and treatment of iron overload in patients with MDS, including the merits and drawbacks of the oral iron chelator, deferasirox. I also draw parallels between iron and radon with respect to the possibility of biological harm, lack of definitive study results, existence of groups at special risk, and fear that the ongoing uncertainties about these elements incite in patients.

It's time for a new low-dose-radiation risk assessment paradigm--one that acknowledges hormesis

The current system of radiation protection for humans is based on the linear-no-threshold (LNT) risk-assessment paradigm. Perceived harm to irradiated nuclear workers and the public is mainly reflected through calculated hypothetical increased cancers. The LNT-based system of protection employs easy-to-implement measures of radiation exposure. Such measures include the equivalent dose (a biological-damage-potential-weighted measure) and the effective dose (equivalent dose multiplied by a tissue-specific relative sensitivity factor for stochastic effects). These weighted doses have special units such as the sievert (Sv) and millisievert (mSv, one thousandth of a sievert). Radiation-induced harm is controlled via enforcing exposure limits expressed as effective dose. Expected cancer cases can be easily computed based on the summed effective dose (person-sievert) for an irradiated group or population. Yet the current system of radiation protection needs revision because radiation-induced natural protection (hormesis) has been neglected. A novel, nonlinear, hormetic relative risk model for radiation-induced cancers is discussed in the context of establishing new radiation exposure limits for nuclear workers and the public.