Unraveling the fundamental molecular mechanisms of morphological and cognitive defects in the irradiated brain

Comprehensive brain tissue metabolomics and biological network technology to decipher the mechanism of hydrogen-rich water on Radiation-induced cognitive impairment in rats

BACKGROUND

Hydrogen-rich water (HRW) has been shown to prevent cognitive impairment caused by ionizing radiation. This study aimed to investigate the pharmacological effects and mechanisms of HRW on ionizing radiation by coupling the brain metabolomics and biological target network methods.

METHODS AND RESULTS

HRW significantly improves the cognitive impairment in rats exposed to ionizing radiation. Based on metabolomics and biological network results, we identified 54 differential metabolites and 93 target genes. The KEGG pathway indicates that glutathione metabolism, ascorbic acid and aldehyde acid metabolism, pentose and glucuronic acid interconversion, and glycerophospholipid metabolism play important roles in ionizing radiation therapy.

CONCLUSION

Our study has systematically elucidated the molecular mechanism of HRW against ionizing radiation, which can be mediated by modulating targets, pathways and metabolite levels. This provides a new perspective for identifying the underlying pharmacological mechanism of HRW.

An integrative systems biology strategy to support the development of adverse outcome pathways (AOPs): a case study on radiation-induced microcephaly

Adverse Outcome Pathways (AOPs) are useful tools for assessing the potential risks associated with exposure to various stressors, including chemicals and environmental contaminants. They provide a framework for understanding the causal relationships between different biological events that can lead to adverse outcomes (AO). However, developing an AOP is a challenging task, particularly in identifying the molecular initiating events (MIEs) and key events (KEs) that constitute it. Here, we propose a systems biology strategy that can assist in the development of AOPs by screening publicly available databases, literature with the text mining tool AOP-helpFinder, and pathway/network analyses. This approach is straightforward to use, requiring only the name of the stressor and adverse outcome to be studied. From this, it quickly identifies potential KEs and literature providing mechanistic information on the links between the KEs. The proposed approach was applied to the recently developed AOP 441 on radiation-induced microcephaly, resulting in the confirmation of the KEs that were already present and identification of new relevant KEs, thereby validating the strategy. In conclusion, our systems biology approach represents a valuable tool to simplify the development and enrichment of Adverse Outcome Pathways (AOPs), thus supporting alternative methods in toxicology.

BRIDE v2: A Validated Collection of Genes Involved in the Mammalian Brain Response to Low-Dose Ionizing Radiation

There is significant interest in the response of the mammalian brain to low-dose ionizing radiation (LDIR), mainly examined by gene or protein expression, with applications in radiation safety on Earth, the atmosphere and outer space. Potential associations of molecular-level responses with sensory or cognitive defects and neurodegenerative diseases are currently under investigation. Previously, we have described a light-weight approach for the storage, analysis and distribution of relevant datasets, with the platform BRIDE. We have re-implemented the platform as BRIDE v2 on the cloud, using the bioinformatics infrastructure ELIXIR. We connected the annotated list of 3174 unique gene records with modern omics resources for downstream computational analysis. BRIDE v2 is a cloud-based platform with capabilities that enable researchers to extract, analyze, visualize as well as export the gene collection. The resource is freely available online at <http://bride-db.eu>.

Prenatal Radiation Exposure Leads to Higher-Order Telencephalic Dysfunctions in Adult Mice That Coincide with Reduced Synaptic Plasticity and Cerebral Hypersynchrony

Higher-order telencephalic circuitry has been suggested to be especially vulnerable to irradiation or other developmentally toxic impact. This report details the adult effects of prenatal irradiation at a sensitive time point on clinically relevant brain functions controlled by telencephalic regions, hippocampus (HPC), and prefrontal cortex (PFC). Pregnant C57Bl6/J mice were whole-body irradiated at embryonic day 11 (start of neurogenesis) with X-ray intensities of 0.0, 0.5, or 1.0 Gy. Female offspring completed a broad test battery of HPC-/PFC-controlled tasks that included cognitive performance, fear extinction, exploratory, and depression-like behaviors. We examined neural functions that are mechanistically related to these behavioral and cognitive changes, such as hippocampal field potentials and long-term potentiation, functional brain connectivity (by resting-state functional magnetic resonance imaging), and expression of HPC vesicular neurotransmitter transporters (by immunohistochemical quantification). Prenatally exposed mice displayed several higher-order dysfunctions, such as decreased nychthemeral activity, working memory defects, delayed extinction of threat-evoked response suppression as well as indications of perseverative behavior. Electrophysiological examination indicated impaired hippocampal synaptic plasticity. Prenatal irradiation also induced cerebral hypersynchrony and increased the number of glutamatergic HPC terminals. These changes in brain connectivity and plasticity could mechanistically underlie the irradiation-induced defects in higher telencephalic functions.

BRAIN AND EYE AS POTENTIAL TARGETS FOR IONIZING RADIATION IMPACT: PART II - RADIATION CEREBRO/OPHTALMIC EFFECTS IN CHILDREN, PERSONS EXPOSED IN UTERO, ASTRONAUTS AND INTERVENTIONAL RADIOLOGISTS

BACKGROUND

Ionizing radiation (IR) can affect the brain and the visual organ even at low doses, while provoking cognitive, emotional, behavioral, and visual disorders. We proposed to consider the brain and the visual organ as potential targets for the influence of IR with the definition of cerebro-ophthalmic relationships as the «eye-brain axis».

OBJECTIVE

The present work is a narrative review of current experimental, epidemiological and clinical data on radiation cerebro-ophthalmic effects in children, individuals exposed in utero, astronauts and interventional radiologists.

MATERIALS AND METHODS

The review was performed according to PRISMA guidelines by searching the abstract and scientometric databases PubMed/MEDLINE, Scopus, Web of Science, Embase, PsycINFO, Google Scholar, published from 1998 to 2021, as well as the results of manual search of peer-reviewed publications.

RESULTS

Epidemiological data on the effects of low doses of IR on neurodevelopment are quite contradictory, while data on clinical, neuropsychological and neurophysiological on cognitive and cerebral disorders, especially in the left, dominant hemisphere of the brain, are nore consistent. Cataracts (congenital - after in utero irradiation) and retinal angiopathy are more common in prenatally-exposed people and children. Astronauts, who carry out longterm space missions outside the protection of the Earth's magnetosphere, will be exposed to galactic cosmic radiation (heavy ions, protons), which leads to cerebro-ophthalmic disorders, primarily cognitive and behavioral disorders and cataracts. Interventional radiologists are a special risk group for cerebro-ophthalmic pathology - cognitivedeficits, mainly due to dysfunction of the dominant and more radiosensitive left hemisphere of the brain, andcataracts, as well as early atherosclerosis and accelerated aging.

CONCLUSIONS

Results of current studies indicate the high radiosensitivity of the brain and eye in different contingents of irradiated persons. Further research is needed to clarify the nature of cerebro-ophthalmic disorders in different exposure scenarios, to determine the molecular biological mechanisms of these disorders, reliable dosimetric support and taking into account the influence of non-radiation risk factors.

The role of Atg7-mediated autophagy in ionizing radiation-induced neural stem cell damage

Impairment of neurogenesis is thought to be one of the important mechanisms underlying radiation-induced cognitive decline. Self-renewal and differentiation of neural stem cells (NSCs) are important components of neurogenesis. It has been well established that autophagy plays an important role in neurodegenerative conditions, however, its role in radiation-induced cognitive decline remains unclear. Our previous studies have found that ionizing radiation (IR) induces autophagy in mouse neurons, and minocycline, an antibiotic that can cross the blood-brain barrier, protects neurons from radiation-induced apoptosis through promoting autophagy, thus may contribute to the improvement of mouse cognitive performance after whole-brain irradiation. In the present study, we investigated whether autophagy is involved in radiation-induced damage in self-renewal and differentiation of NSCs. We found that NSCs were extremely sensitive to IR. Irradiation induced autophagy in NSCs in a dose-dependent manner. Atg7 knockdown significantly decreased autophagy, thus increased the apoptosis levels in irradiated NSCs, suggesting that autophagy protected NSCs from radiation-induced apoptosis. Moreover, compared with the negative control NSCs, the neurosphere size was significantly reduced and the neuronal differentiation was notably inhibited in Atg7-deficient NSCs after irradiation, indicating that autophagy defect could exacerbate radiation-induced reduction in NSC self-renewal and differentiation potential. In conclusion, down-regulating autophagy by selective Atg7 knockdown in NSCs enhanced radiation-induced NSC damage, suggesting an important protective role of autophagy in maintaining neurogenesis. Along with the protective effect of autophagy on irradiated neurons, our results on NSCs not only shed the light on the involvement of autophagy in the development of radiation-induced cognitive decline, but also provided a potential target for preventing cognitive impairment after cranial radiation exposure.

Effect of Hydrogen-Rich Water on Radiation-Induced Cognitive Dysfunction in Rats

The goal of this work was to determine whether hydrogen-rich water (HRW) could attenuate radiation-induced cognitive dysfunction in rats and to explore the underlying mechanisms. Rats received 30 Gy whole-brain irradiation using a 6-MeV electron beam. Either purified water or HRW (0.8-0.9 ppm) was administrated at 10 min prior to irradiation, as well as a daily HRW treatment after irradiation for 30 consecutive days. The Morris water maze was used to test spatial memory in the rats. The concentration of glutathione (GSH), malondialdehyde (MDA), 8-hydroxydeoxyguanosine (8-OHdG) and the super-oxidedismutase (SOD) activity in cerebral cortex, as well as brain-derived neurotrophic factor (BDNF) level in serum, were measured. Immunofluorescence staining was adopted to detect proliferating cells. The expression of BDNF-TrkB pathway-related genes and proteins were detected using qRT-PCR and Western blot. Models of cognitive dysfunction were successfully established using a 30 Gy dose of ionizing radiation. Compared to the radiation treated group, the radiation-HRW treated group showed significantly decreased escape latency (P < 0.05), but increased retention time, swimming distance of original platform quadrant (P < 0.05) and number of platform crossings (P < 0.05). Furthermore, the SOD, GSH (P < 0.05) and BDNF (P < 0.05) levels in the radiation-HRW treated group were higher compared to the radiation treated group. The MDA and 8-OHdG levels (P < 0.05) were decreased in the radiation-HRW treated group when compared to the radiation treated group. Additionally, treatment with HRW increased the number of BrdU⁺NeuN⁺ cells in the radiation treated group. The mRNA and protein levels of BDNF and TrkB (P < 0.05) in radiation-HRW treated group was higher than that in the radiation treated group. Collectively, our study indicates that HRW has a protective effect on radiation-induced cognitive dysfunction, and that the possible mechanisms mainly involve anti-oxidative and anti-inflammatory reactions, and its protection of newborn neurons by regulating the BDNF-TrkB signaling pathway.

Age-Dependent Responses of Brain Myelin Integrity and Behavioral Performance to Radiation in Mice

Radiation therapy is widely used to treat primary and metastatic brain tumors, but it may also lead to delayed neurological complications. Oligodendrocytes in the central nervous system produce myelin, and myelin integrity becomes highly vulnerable after brain irradiation. In this study, mice at different developmental stages were used to test the age-dependent sensitivity of myelin formation and maintenance, as well as behavioral performance after whole-brain irradiation (WBI). Mice at postnatal days 21 and 28 and at 2 months received a single dose of 25 Gy WBI. Behavioral tests for general locomotor activity and motor coordination revealed an age-dependent response after WBI. Quantitative observation revealed a sharp decrease in the number of oligodendrocytes beginning at day 1 after WBI, which recovered during different observation intervals in white matter and gray matter in mice of different ages. Myelin basic protein (MBP) staining revealed disparate quantities in an age- and brain-region-dependent pattern between groups after WBI, which was confirmed using Black-Gold staining. In summary, the response to radiation in mice of different ages provided insight into the potential of oligogenesis in microenvironments at respective stages of myelin regeneration, which may reduce central nervous system impairment and optimize the prognosis after radiation treatment.

Exposure to low doses of 137cesium and nicotine during postnatal development modifies anxiety levels, learning, and spatial memory performance in mice

Radiation therapy is a major cause of long-term complications observed in survivors of pediatric brain tumors. However, the effects of low-doses of ionizing radiation (IR) to the brain are less studied. On the other hand, tobacco is one of the most heavily abused drugs in the world. Tobacco is not only a health concern for adults. It has also shown to exert deleterious effects on fetuses, newborns, children and adolescents. Exposure to nicotine (Nic) from smoking may potentiate the toxic effects induced by IR on brain development. In this study, we evaluated in mice the cognitive effects of concomitant exposure to low doses of internal radiation (¹³⁷Cs) and Nic during neonatal brain development. On postnatal day 10 (PND10), two groups of C57BL/6J mice were subcutaneously exposed to 137-Cesium (¹³⁷Cs) (4000 and 8000 Bq/kg) and/or Nic (100 μg/ml). At the age of two months, neurobehavior of mice was assessed. Results showed that exposure to IR-alone or in combination with Nic-increased the anxiety-like of the animals without changing the activity levels. Moreover, exposure to IR impaired learning and spatial memory. However, Nic administration was able to reverse this effect, but only at the low dose of ¹³⁷Cs.

Current Evidence for Developmental, Structural, and Functional Brain Defects following Prenatal Radiation Exposure

Ionizing radiation is omnipresent. We are continuously exposed to natural (e.g., radon and cosmic) and man-made radiation sources, including those from industry but especially from the medical sector. The increasing use of medical radiation modalities, in particular those employing low-dose radiation such as CT scans, raises concerns regarding the effects of cumulative exposure doses and the inappropriate utilization of these imaging techniques. One of the major goals in the radioprotection field is to better understand the potential health risk posed to the unborn child after radiation exposure to the pregnant mother, of which the first convincing evidence came from epidemiological studies on in utero exposed atomic bomb survivors. In the following years, animal models have proven to be an essential tool to further characterize brain developmental defects and consequent functional deficits. However, the identification of a possible dose threshold is far from complete and a sound link between early defects and persistent anomalies has not yet been established. This review provides an overview of the current knowledge on brain developmental and persistent defects resulting from in utero radiation exposure and addresses the many questions that still remain to be answered.

Brain Radiation Information Data Exchange (BRIDE): integration of experimental data from low-dose ionising radiation research for pathway discovery

BACKGROUND

The underlying molecular processes representing stress responses to low-dose ionising radiation (LDIR) in mammals are just beginning to be understood. In particular, LDIR effects on the brain and their possible association with neurodegenerative disease are currently being explored using omics technologies.

RESULTS

We describe a light-weight approach for the storage, analysis and distribution of relevant LDIR omics datasets. The data integration platform, called BRIDE, contains information from the literature as well as experimental information from transcriptomics and proteomics studies. It deploys a hybrid, distributed solution using both local storage and cloud technology.

CONCLUSIONS

BRIDE can act as a knowledge broker for LDIR researchers, to facilitate molecular research on the systems biology of LDIR response in mammals. Its flexible design can capture a range of experimental information for genomics, epigenomics, transcriptomics, and proteomics. The data collection is available at: .

Effects of prenatal exposure to cancer treatment on neurocognitive development, a review

Due to the increasing incidence of cancer during pregnancy, the need to better understand long-term outcome after prenatal exposure to chemo- and/or radiotherapy has become more urgent. This manuscript focuses on the neurocognitive development after prenatal exposure to cancer treatment. We will review possible pathways for brain damage that could explain the subtle changes in neurocognition and behavior found after in utero exposure to cancer treatment. Contrary to radiation, which has a direct effect on the developing nervous system, chemotherapy has to pass the placental and blood brain barrier to reach the fetal brain. However, there are also indirect effects such as inflammation and oxidative stress. Furthermore, the indirect effects of the cancer itself and its treatment, e.g., poor maternal nutrition and high maternal stress, as well as prematurity, can be related to cognitive impairment. Although the available evidence suggests that cancer treatment can be administered during pregnancy without jeopardizing the fetal chances, larger numbers and longer follow up of these children are needed.

Quality of life and symptoms in pediatric brain tumor survivors: a systematic review

Little is known about the quality of life of children and youth under the age of 20 who have completed treatment for a pediatric brain tumor. This systematic review was conducted to (a) describe the health-related quality of life (HRQL) outcomes in pediatric brain tumor survivors, (b) identify instruments used to measure HRQL, and (c) determine the relationship between symptoms and HRQL. Using a systematic search and review methodology, databases searched included CINAHL, Medline, Embase, and PsycInfo. No date restrictions were used. Search results elicited 485 articles, of which16 met the inclusion criteria. Compared with their healthy peers, pediatric brain tumor survivors did worse on most measures of physical, psychosocial, social, and cognitive domains of HRQL. Compared with other cancer patients, survivors scored themselves significantly lower on the Pediatric Quality of Life Inventory (PedsQL) social functioning scale, and parents of brain tumor survivors reported lower PedsQL social and total functioning scores for their children. Other variables that were associated with decreased HRQL were degree of hypothalamic tumor involvement, osteopenia, need for special education, older age at diagnosis, greater than 1 year since treatment, and radiation treatment. In these studies, pediatric brain tumor survivors fared worse compared with other cancer survivors or healthy peers on several HRQL domains. Only 3 studies explored the relationship between symptoms, including pain or fatigue, and HRQL in pediatric brain tumor survivors. The relationship between symptoms and HRQL was not well elucidated. More research is needed to explore the multidimensional symptom experience and HRQL outcomes in pediatric brain tumor survivors.

A multidisciplinary approach unravels early and persistent effects of X-ray exposure at the onset of prenatal neurogenesis

Background

In humans, in utero exposure to ionising radiation results in an increased prevalence of neurological aberrations, such as small head size, mental retardation and decreased IQ levels. Yet, the association between early damaging events and long-term neuronal anomalies remains largely elusive.

Methods

Mice were exposed to different X-ray doses, ranging between 0.0 and 1.0 Gy, at embryonic days (E) 10, 11 or 12 and subjected to behavioural tests at 12 weeks of age. Underlying mechanisms of irradiation at E11 were further unravelled using magnetic resonance imaging (MRI) and spectroscopy, diffusion tensor imaging, gene expression profiling, histology and immunohistochemistry.

Results

Irradiation at the onset of neurogenesis elicited behavioural changes in young adult mice, dependent on the timing of exposure. As locomotor behaviour and hippocampal-dependent spatial learning and memory were most particularly affected after irradiation at E11 with 1.0 Gy, this condition was used for further mechanistic analyses, focusing on the cerebral cortex and hippocampus. A classical p53-mediated apoptotic response was found shortly after exposure. Strikingly, in the neocortex, the majority of apoptotic and microglial cells were residing in the outer layer at 24 h after irradiation, suggesting cell death occurrence in differentiating neurons rather than proliferating cells. Furthermore, total brain volume, cortical thickness and ventricle size were decreased in the irradiated embryos. At 40 weeks of age, MRI showed that the ventricles were enlarged whereas N-acetyl aspartate concentrations and functional anisotropy were reduced in the cortex of the irradiated animals, indicating a decrease in neuronal cell number and persistent neuroinflammation. Finally, in the hippocampus, we revealed a reduction in general neurogenic proliferation and in the amount of Sox2-positive precursors after radiation exposure, although only at a juvenile age.

Conclusions

Our findings provide evidence for a radiation-induced disruption of mouse brain development, resulting in behavioural differences. We propose that alterations in cortical morphology and juvenile hippocampal neurogenesis might both contribute to the observed aberrant behaviour. Furthermore, our results challenge the generally assumed view of a higher radiosensitivity in dividing cells. Overall, this study offers new insights into irradiation-dependent effects in the embryonic brain, of relevance for the neurodevelopmental and radiobiological field.

Electronic supplementary material

The online version of this article (doi:10.1186/1866-1955-7-3) contains supplementary material, which is available to authorized users.

Joint research towards a better radiation protection-highlights of the Fifth MELODI Workshop

MELODI is the European platform dedicated to low-dose radiation risk research. From 7 October through 10 October 2013 the Fifth MELODI Workshop took place in Brussels, Belgium. The workshop offered the opportunity to 221 unique participants originating from 22 countries worldwide to update their knowledge and discuss radiation research issues through 118 oral and 44 poster presentations. In addition, the MELODI 2013 workshop was reaching out to the broader radiation protection community, rather than only the low-dose community, with contributions from the fields of radioecology, emergency and recovery preparedness, and dosimetry. In this review, we summarise the major scientific conclusions of the workshop, which are important to keep the MELODI strategic research agenda up-to-date and which will serve to establish a joint radiation protection research roadmap for the future.

Embryonic ionizing radiation exposure results in expression alterations of genes associated with cardiovascular and neurological development, function, and disease and modified cardiovascular function in zebrafish

The relationship between ionizing radiation (IR) and carcinogenesis is long established, but recently the association between IR and other diseases is starting to be recognized. Currently, there is limited information on the genetic mechanisms governing the role of IR in non-cancer related adverse health effects and in regards to an early developmental exposure. In this study, zebrafish embryos were exposed to a range of IR doses (0, 1, 2, 5, 10 Gy) at 26 h post fertilization (hpf). No significant increase in mortality or hatching rate was observed, but a significant decrease in total larval length, head length, and eye diameter was observed in the 10 Gy dose. Transcriptomic analysis was conducted at 120 hpf to compare gene expression profiles between the control and highest IR dose at which no significant differences were observed in morphological measurements (5 Gy). 253 genes with well-established function or orthology to human genes were significantly altered. Gene ontology and molecular network analysis revealed enrichment of genes associated with cardiovascular and neurological development, function, and disease. Expression of a subset of genetic targets with an emphasis on those associated with the cardiovascular system was assessed using Quantitative PCR (qPCR) to confirm altered expression at 5 Gy and then to investigate alterations at lower doses (1 and 2 Gy). Strong correlation between microarray and qPCR expression values was observed, but zebrafish exposed to 1 or 2 Gy resulted in a significant expression alteration in only one of these genes (LIN7B). Moreover, heart rate was analyzed through 120 hpf following IR dosing at 26 hpf. A significant decrease in heart rate was observed at 10 Gy, while a significant increase in heart rate was observed at 1, 2, and 5 Gy. Overall these findings indicate IR exposure at doses below those that induce gross morphological changes alters heart rate and expression of genes associated with cardiovascular and neurological functions.

Endocrine-disrupting chemicals: associated disorders and mechanisms of action

The incidence and/or prevalence of health problems associated with endocrine-disruption have increased. Many chemicals have endocrine-disrupting properties, including bisphenol A, some organochlorines, polybrominated flame retardants, perfluorinated substances, alkylphenols, phthalates, pesticides, polycyclic aromatic hydrocarbons, alkylphenols, solvents, and some household products including some cleaning products, air fresheners, hair dyes, cosmetics, and sunscreens. Even some metals were shown to have endocrine-disrupting properties. Many observations suggesting that endocrine disruptors do contribute to cancer, diabetes, obesity, the metabolic syndrome, and infertility are listed in this paper. An overview is presented of mechanisms contributing to endocrine disruption. Endocrine disruptors can act through classical nuclear receptors, but also through estrogen-related receptors, membrane-bound estrogen-receptors, and interaction with targets in the cytosol resulting in activation of the Src/Ras/Erk pathway or modulation of nitric oxide. In addition, changes in metabolism of endogenous hormones, cross-talk between genomic and nongenomic pathways, cross talk with estrogen receptors after binding on other receptors, interference with feedback regulation and neuroendocrine cells, changes in DNA methylation or histone modifications, and genomic instability by interference with the spindle figure can play a role. Also it was found that effects of receptor activation can differ in function of the ligand.

Cancer and non-cancer brain and eye effects of chronic low-dose ionizing radiation exposure

BACKGROUND

According to a fundamental law of radiobiology ("Law of Bergonié and Tribondeau", 1906), the brain is a paradigm of a highly differentiated organ with low mitotic activity, and is thus radio-resistant. This assumption has been challenged by recent evidence discussed in the present review.

RESULTS

Ionizing radiation is an established environmental cause of brain cancer. Although direct evidence is lacking in contemporary fluoroscopy due to obvious sample size limitation, limited follow-up time and lack of focused research, anecdotal reports of clusters have appeared in the literature, raising the suspicion that brain cancer may be a professional disease of interventional cardiologists. In addition, although terminally differentiated neurons have reduced or mild proliferative capacity, and are therefore not regarded as critical radiation targets, adult neurogenesis occurs in the dentate gyrus of the hippocampus and the olfactory bulb, and is important for mood, learning/memory and normal olfactory function, whose impairment is a recognized early biomarker of neurodegenerative diseases. The head doses involved in radiotherapy are high, usually above 2 Sv, whereas the low-dose range of professional exposure typically involves lifetime cumulative whole-body exposure in the low-dose range of < 200 mSv, but with head exposure which may (in absence of protection) arrive at a head equivalent dose of 1 to 3 Sv after a professional lifetime (corresponding to a brain equivalent dose around 500 mSv).

CONCLUSIONS

At this point, a systematic assessment of brain (cancer and non-cancer) effects of chronic low-dose radiation exposure in interventional cardiologists and staff is needed.

Early brain response to low-dose radiation exposure involves molecular networks and pathways associated with cognitive functions, advanced aging and Alzheimer's disease

Understanding the cognitive and behavioral consequences of brain exposures to low-dose ionizing radiation has broad relevance for health risks from medical radiation diagnostic procedures, radiotherapy and environmental nuclear contamination as well as for Earth-orbit and space missions. Analyses of transcriptome profiles of mouse brain tissue after whole-body irradiation showed that low-dose exposures (10 cGy) induced genes not affected by high-dose radiation (2 Gy) and that low-dose genes were associated with unique pathways and functions. The low-dose response had two major components: pathways that are consistently seen across tissues and pathways that were specific for brain tissue. Low-dose genes clustered into a saturated network (P < 10(-53)) containing mostly down-regulated genes involving ion channels, long-term potentiation and depression, vascular damage, etc. We identified nine neural signaling pathways that showed a high degree of concordance in their transcriptional response in mouse brain tissue after low-dose irradiation, in the aging human brain (unirradiated), and in brain tissue from patients with Alzheimer's disease. Mice exposed to high-dose radiation did not show these effects and associations. Our findings indicate that the molecular response of the mouse brain within a few hours after low-dose irradiation involves the down-regulation of neural pathways associated with cognitive dysfunctions that are also down-regulated in normal human aging and Alzheimer's disease.

Cranial irradiation alters the behaviorally induced immediate-early gene arc (activity-regulated cytoskeleton-associated protein)

Therapeutic irradiation of the brain is commonly used to treat brain tumors but can induce cognitive impairments that can severely affect quality of life. The underlying mechanisms responsible for radiation-induced cognitive deficits are unknown but likely involve alterations in neuronal activity. To gain some mechanistic insight into how irradiation may affect hippocampal neurons known to be associated with cognitive function, we quantitatively assessed the molecular distribution of the behaviorally induced immediate-early gene Arc (activity-regulated cytoskeleton-associated protein) at the level of mRNA and the protein. Young adult C57BL/6J mice received whole-brain irradiation with 0 or 10 Gy, and 1 week or 2 months later, exploration of a novel environment was used to induce Arc expression. The fractions of neurons expressing Arc mRNA and Arc protein were detected using fluorescence in situ hybridization and immunocytochemistry, respectively. Our results showed that there was a significant reduction in the percentage of neurons expressing Arc protein 1 week after irradiation, whereas 2 months after irradiation, there was a reduction in the percentage of neurons expressing both Arc mRNA and Arc protein. Importantly, radiation-induced changes in Arc expression were not a result of neuronal cell loss. The changes observed at 2 months were associated with a significant increase in the number of activated microglia, supporting the idea that inflammation may contribute to neuronal dysfunction. These findings are the first to show that local brain irradiation initiates changes in hippocampal neurons that disrupt the activity patterns (Arc expression) associated with neuroplasticity and memory.

Embryonic oxidative stress as a mechanism of teratogenesis with special emphasis on diabetic embryopathy

Reactive oxygen species (ROS) are involved in the etiology of numerous diseases including cardio-vascular diseases and diabetes mellitus. There is evidence that several teratogens affect the developing embryo by increasing its oxidative stress and, because of its relatively weak antioxidant defense, especially at the early stages of organogenesis, result in severe embryonic damage. This mechanism seems to operate in diabetes-induced embryonic damage as well as in the mechanism of teratogenicity caused by ionizing radiation, hypoxia, alcohol and cocaine use and cigarette smoking. We studied the role of oxidative stress in diabetic induced embryopathy, both in vivo and in vitro. Under diabetic condition there was a significant decrease in the activity of endogenous antioxidant enzymes and of vitamins C and E in the embryos and their yolk sacs. The lowest activity was observed in the malformed experimental embryos when compared to experimental embryos without anomalies. Similar results were obtained in the Cohen diabetic rats, where the diabetic prone (CDs) rats were unable to increase their antioxidant enzyme activity in spite of the diabetes. Studies performed by other investigators show similar results. Human and animal studies show that the main mechanism of fetal damage induced by high levels of ionizing irradiation, cocaine and alcohol abuse, hypoxia and cigarette smoking is also by increased embryonic oxidative stress. Similarly, several drugs exert their teratogenic activity via embryonic oxidative stress. Abnormal placentation may also cause enhanced placental oxidative stress, resulting in embryonic death, preeclampsia or congenital anomalies. Inability of the developing embryo to cope with that stress may result in embryonic death and/or congenital anomalies. Animal studies also show that a variety of antioxidants are effective in decreasing the damaging effects of heightened oxidative stress induced by teratogens. Effective antioxidants, which might also be of clinical use, include vitamins C and E, carotenoids, folic acid, as well as synthetic products. Appropriate clinical studies with antioxidants in pregnancies of high risk to develop oxidative stress are needed, since non-toxic antioxidants might prove an efficient and inexpensive way to reduce the rate of some serious and sometimes fatal congenital anomalies.