NEUROPSYCHOBIOLOGICAL MECHANISMS OF AFFECTIVE AND COGNITIVE DISORDERS IN THE CHORNOBYL CLEAN-UP WORKERS TAKING INTO ACCOUNT THE SPECIFIC GENE POLYMORPHISMS

AOP report: Development of an adverse outcome pathway for deposition of energy leading to learning and memory impairment

Understanding radiation-induced non-cancer effects on the central nervous system (CNS) is essential for the risk assessment of medical (e.g., radiotherapy) and occupational (e.g., nuclear workers and astronauts) exposures. Herein, the adverse outcome pathway (AOP) approach was used to consolidate relevant studies in the area of cognitive decline for identification of research gaps, countermeasure development, and for eventual use in risk assessments. AOPs are an analytical construct describing critical events to an adverse outcome (AO) in a simplified form beginning with a molecular initiating event (MIE). An AOP was constructed utilizing mechanistic information to build empirical support for the key event relationships (KERs) between the MIE of deposition of energy to the AO of learning and memory impairment through multiple key events (KEs). The evidence for the AOP was acquired through a documented scoping review of the literature. In this AOP, the MIE is connected to the AO via six KEs: increased oxidative stress, increased deoxyribonucleic acid (DNA) strand breaks, altered stress response signaling, tissue resident cell activation, increased pro-inflammatory mediators, and abnormal neural remodeling that encompasses atypical structural and functional alterations of neural cells and surrounding environment. Deposition of energy directly leads to oxidative stress, increased DNA strand breaks, an increase of pro-inflammatory mediators and tissue resident cell activation. These KEs, which are themselves interconnected, can lead to abnormal neural remodeling impacting learning and memory processes. Identified knowledge gaps include improving quantitative understanding of the AOP across several KERs and additional testing of proposed modulating factors through experimental work. Broadly, it is envisioned that the outcome of these efforts could be extended to other cognitive disorders and complement ongoing work by international radiation governing bodies in their review of the system of radiological protection.

Ionizing radiation, cerebrovascular disease, and consequent dementia: A review and proposed framework relevant to space radiation exposure

Space exploration requires the characterization and management or mitigation of a variety of human health risks. Exposure to space radiation is one of the main health concerns because it has the potential to increase the risk of cancer, cardiovascular disease, and both acute and late neurodegeneration. Space radiation-induced decrements to the vascular system may impact the risk for cerebrovascular disease and consequent dementia. These risks may be independent or synergistic with direct damage to central nervous system tissues. The purpose of this work is to review epidemiological and experimental data regarding the impact of low-to-moderate dose ionizing radiation on the central nervous system and the cerebrovascular system. A proposed framework outlines how space radiation-induced effects on the vasculature may increase risk for both cerebrovascular dysfunction and neural and cognitive adverse outcomes. The results of this work suggest that there are multiple processes by which ionizing radiation exposure may impact cerebrovascular function including increases in oxidative stress, neuroinflammation, endothelial cell dysfunction, arterial stiffening, atherosclerosis, and cerebral amyloid angiopathy. Cerebrovascular adverse outcomes may also promote neural and cognitive adverse outcomes. However, there are many gaps in both the human and preclinical evidence base regarding the long-term impact of ionizing radiation exposure on brain health due to heterogeneity in both exposures and outcomes. The unique composition of the space radiation environment makes the translation of the evidence base from terrestrial exposures to space exposures difficult. Additional investigation and understanding of the impact of low-to-moderate doses of ionizing radiation including high (H) atomic number (Z) and energy (E) (HZE) ions on the cerebrovascular system is needed. Furthermore, investigation of how decrements in vascular systems may contribute to development of neurodegenerative diseases in independent or synergistic pathways is important for protecting the long-term health of astronauts.

Cranial irradiation induces cognitive decline associated with altered dendritic spine morphology in the young rat hippocampus

OBJECTIVE

Therapeutic irradiation is commonly used to treat brain cancers but can induce cognitive dysfunction, especially in children. The mechanism is unknown but likely involves alterations in dendritic spine number and structure.

METHODS

To explore the impact of radiation exposure on the alteration of dendritic spine morphology in the hippocampus of young brains, 21-day-old Sprague-Dawley rats received cranial irradiation (10 Gy), and changes in spine density and morphology in dentate gyrus (DG) granules and CA1 pyramidal neurons were detected 1 and 3 months later by using Golgi staining. Moreover, we analyzed synapse-associated proteins within dendritic spines after irradiation.

RESULT

Our data showed that cognitive deficits were detected in young rats at both time points postirradiation, accompanied by morphological changes in dendritic spines. Our results revealed significant reductions in spine density in the DG at both 1 month (40.58%) and 3 months (28.92%) postirradiation. However, there was a decrease in spine density only at 1 month (33.29%) postirradiation in the basal dendrites of CA1 neurons and no significant changes in the apical dendrites of CA1 neurons at either time point. Notably, among our findings were the significant dynamic changes in spine morphology that persisted 3 months following cranial irradiation. Meanwhile, we found that depletion of the synapse-associated proteins PSD95 and Drebrin coincided with alterations in dendritic spines.

CONCLUSION

These data suggest that the decreased levels of PSD95 and Drebrin after ionizing radiation may cause changes in synaptic plasticity by affecting the morphological structure of dendritic spines, blocking the functional connectivity pathways of the brain and leading to cognitive impairment. Although the mechanism involved is unclear, understanding how ionizing radiation affects young brain hippocampal tissue may be useful to gain new mechanistic insights into radiation-induced cognitive dysfunction.

Effects of Chemotherapy on Neuroinflammation, Neuronal Damage, Neurogenesis, and Behavioral Performance in Bone Marrow Transplantation Recipient Mice

As bone marrow transplant (BMT) is gradually applied to the study of central nervous system (CNS) disease, it is needed to investigate the proper dose of chemotherapy to eradicate bone marrow cells while bringing little damage to brain. In the present study, we established a BMT model with varied busulfan and cyclophosphamide (Bu-Cy) dosages. The recipient mice's chimera rate, neuronal death, neuroinflammation, and behavioral functions were all investigated. Chimerism of peripheral blood cells was shown to rise with Bu-Cy treatment doses, with 60.7% in the Bu(20 mg/kg)/Cy(100 mg/kg) group and 93.0% in the Bu(35 mg/kg)/Cy(100 mg/kg) group. Recipients with Bu(35 mg/kg)/Cy(100 mg/kg) therapy had brain injury, increased neuroinflammation, diminished neurogenesis and cognitive abnormalities, whereas animals given a lesser dosage had no such brain damages. Conclusively, considering the chimerism and the possibility to damage brain, we recommend Bu(20 mg/kg)/Cy(100 mg/kg) is the ideal dose in BMT for studying CNS diseases in the C57/BL6 mouse strain.

Early Life Irradiation-Induced Hypoplasia and Impairment of Neurogenesis in the Dentate Gyrus and Adult Depression Are Mediated by MicroRNA- 34a-5p/T-Cell Intracytoplasmic Antigen-1 Pathway

Early life radiation exposure causes abnormal brain development, leading to adult depression. However, few studies have been conducted to explore pre- or post-natal irradiation-induced depression-related neuropathological changes. Relevant molecular mechanisms are also poorly understood. We induced adult depression by irradiation of mice at postnatal day 3 (P3) to reveal hippocampal neuropathological changes and investigate their molecular mechanism, focusing on MicroRNA (miR) and its target mRNA and protein. P3 mice were irradiated by γ-rays with 5Gy, and euthanized at 1, 7 and 120 days after irradiation. A behavioral test was conducted before the animals were euthanized at 120 days after irradiation. The animal brains were used for different studies including immunohistochemistry, CAP-miRSeq, Real-Time Quantitative Reverse Transcription PCR (qRT-PCR) and western blotting. The interaction of miR-34a-5p and its target T-cell intracytoplasmic antigen-1 (Tia1) was confirmed by luciferase reporter assay. Overexpression of Tia1 in a neural stem cell (NSC) model was used to further validate findings from the mouse model. Irradiation with 5 Gy at P3 induced depression in adult mice. Animal hippocampal pathological changes included hypoplasia of the infrapyramidal blade of the stratum granulosum, aberrant and impaired cell division, and neurogenesis in the dentate gyrus. At the molecular level, upregulation of miR-34a-5p and downregulation of Tia1 mRNA were observed in both animal and neural stem cell models. The luciferase reporter assay and gene transfection studies further confirmed a direct interaction between miR-43a-5p and Tia1. Our results indicate that the early life γ-radiation-activated miR-43a-5p/Tia1 pathway is involved in the pathogenesis of adult depression. This novel finding may provide a new therapeutic target by inhibiting the miR-43a-5p/Tia1 pathway to prevent radiation-induced pathogenesis of depression.

Mental Health and Neuropsychiatric Aftermath 35 Years After the Chernobyl Catastrophe: Current State and Future Perspectives

OBJECTIVE

The Chernobyl nuclear power plant (ChNPP) disaster that happened in Ukraine on the 26th of April 1986 still represents the most severe nuclear accident in human history. Its consequences, especially those involving mental health are increasingly emerging as long-term detrimental effects. Therefore, the aim of the present paper was to review the results of some of authors' studies and their personal reflections on this topic.

METHOD

The authors selected and commented on the findings mainly derived from their contributions on the prevalence of long-term psychopathological symptoms and neuropsychiatric disorders in diferent groups of exposed and non exposed individuals, including the workers at the NPP the so-called liquidators (CUWs), the most exposed group, evacuees and people living in more or less contaminated areas.

RESULTS

The main findings derived from a series of studies carried out by the authors throughout the following decades after the disaster indicate the high prevalence of cerebrovascular diseases, organic mental and depressive disorders, cognitive impairment and even dementia that increase with the irradiation dose mainly amongst the liquidators. The organic disorders are probably related to a peculiar effect of radiation on left, dominant brain hemisphere. Interestingly, recent studies revealed abnormalities of the serotonin transporter and other genes disorders possibly at the basis of depression of exposed individuals.

CONCLUSIONS

The high prevalence of neuropsychiatric disorders amongst irradiated subjects following the ChNPP disaster highlights the impact of radiation exposure on the lifelong onset of neuropsychiatric disorders, for too long neglected by international agencies. Such findings require to be deepened in the future possibly within the frame of the so-called "ecological psychiatry".

Cognitive effects of low dose of ionizing radiation - Lessons learned and research gaps from epidemiological and biological studies

The last decades have seen increased concern about the possible effects of low to moderate doses of ionizing radiation (IR) exposure on cognitive function. An interdisciplinary group of experts (biologists, epidemiologists, dosimetrists and clinicians) in this field gathered together in the framework of the European MELODI workshop on non-cancer effects of IR to summarise the state of knowledge on the topic and elaborate research recommendations for future studies in this area. Overall, there is evidence of cognitive effects from low IR doses both from biology and epidemiology, though a better characterization of effects and understanding of mechanisms is needed. There is a need to better describe the specific cognitive function or diseases that may be affected by radiation exposure. Such cognitive deficit characterization should consider the human life span, as effects might differ with age at exposure and at outcome assessment. Measurements of biomarkers, including imaging, will likely help our understanding on the mechanism of cognitive-related radiation induced deficit. The identification of loci of individual genetic susceptibility and the study of gene expression may help identify individuals at higher risk. The mechanisms behind the radiation induced cognitive effects are not clear and are likely to involve several biological pathways and different cell types. Well conducted research in large epidemiological cohorts and experimental studies in appropriate animal models are needed to improve the understanding of radiation-induced cognitive effects. Results may then be translated into recommendations for clinical radiation oncology and imaging decision making processes.

RADIATION DAMAGE OF THE NERVOUS SYSTEM AND ENDOCANABINOIDS

The review analyzes the change of the existing paradigm of high radioresistance of the nervous system according tothe results of the study of neuropsychiatric disorders in in the aftermath of the Chornobyl accident in both earlyand remote post-accident period. The participation of the endocannabinoid system in ensuring homeostasis andpathology formation, potential possibilities of using cannabis drugs, agonists and antagonists of endocannabinoidreceptors for the treatment of early and long-term effects of radiation are considered.

Radiation Risk Analysis of Neuropsychiatric Disorders in Ukrainian Chornobyl Catastrophe Liquidators

Goal: To explore the possible impact of ionizing radiation in the pathophysiology of neuropsychiatric disorders amongst clean-up workers of the Chornobyl catastrophe (liquidators). Design, object, and methods: Retrospective-prospective study (1987-2015) of liquidators from the State Register of Ukraine (SRU) with radiation doses records and Clinical-Epidemiological Register (CER) of the State Institution ≪National Research Center for Radiation Medicine of the National Academy of Medical Sciences of Ukraine≫ (NRCRM). Moreover, cohort and cross-sectional studies of the randomized sample of liquidators from the CER (exposed group, 198 subjects) were examined. Internal control group included the liquidators irradiated in doses <50.0 mSv (42 persons). All subjects were assessed by a detailed clinical examination and a battery of standardized neuropsychiatric scales, psychometric, and neuropsychological tests. Descriptive and variation statistics, non-parametric criteria, regression-correlation analysis, survival analysis by Kaplan & Meier, and risk analysis were used. Results: Exposed group vs. control group showed cognitive disorders in 99 (50.0%) vs. 20 (18.1%), (P = 0.04); affective disorders in 96 (48.3%) vs. 36 (32.7%) (P = 0.007), and stress-related disorders in 115 (58.4%) vs. 8 (7.3%) (P < 0.001). In the main group exposed to ≥50 mSv vs. internal control group (exposed to <50 mSv), affective disorders were present, respectively, in 89 (56.4%) vs. 7 (19.1%) (P < 0.001), and stress-related disorders in 98 (62.8%) vs. 17 (40.4%) (P = 0.009). Relative risks (RR) and 95% confidential intervals (95%CI) of Incidence of some neuropsychiatric disorders in liquidators of 1986-1987 related to internal control (doses <50 mSv) were as follows: organic psychosis (RR = 3.15; 95% CI: 2.6; 3.7); non-psychotic organic brain damage (RR = 1.99; 95% CI: 1.6; 2.5); acute (RR = 1.40, 95% CI: 1.3; 1.5), and chronic cerebrovascular disorders (RR = 1.23; 95% CI 1.0;1.5). Neuropsychiatric diseases show a strong, increasing, and approximately quadratic statistically significant (Pv < 0.001) relationship with individual dose, yielding an estimated excess relative risk ERR = 2.76 Sv-2 (95% CI 1.06-7.15). Conclusions: Liquidators have an excess of cognitive, affective, and stress-related disorders. The risk of diseases rises with radiation dose. Radiation risks are revealed for organic psychoses, non-psychotic organic brain damage, acute and chronic cerebrovascular pathology.

Environmental, Neuro-immune, and Neuro-oxidative Stress Interactions in Chronic Fatigue Syndrome

Chronic fatigue syndrome/myalgic encephalomyelitis (CFS) is a complex, multisystem disease that is characterized by long-term fatigue, exhaustion, disabilities, pain, neurocognitive impairments, gastrointestinal symptoms, and post-exertional malaise, as well as lowered occupational, educational, and social functions. The clinical and biomarker diagnosis of this disorder is hampered by the lack of validated diagnostic criteria and laboratory tests with adequate figures of merit, although there are now many disease biomarkers indicating the pathophysiology of CFS. Here, we review multiple factors, such as immunological and environmental factors, which are associated with CFS and evaluate current concepts on the involvement of immune and environmental factors in the pathophysiology of CFS. The most frequently reported immune dysregulations in CFS are modifications in immunoglobulin contents, changes in B and T cell phenotypes and cytokine profiles, and decreased cytotoxicity of natural killer cells. Some of these immune aberrations display a moderate diagnostic performance to externally validate the clinical diagnosis of CFS, including the expression of activation markers and protein kinase R (PKR) activity. Associated with the immune aberrations are activated nitro-oxidative pathways, which may explain the key symptoms of CFS. This review shows that viral and bacterial infections, as well as nutritional deficiencies, may further aggravate the immune-oxidative pathophysiology of CFS. Targeted treatments with antioxidants and lipid replacement treatments may have some clinical efficacy in CFS. We conclude that complex interactions between immune and nitro-oxidative pathways, infectious agents, environmental factors, and nutritional deficiencies play a role in the pathophysiology of CFS.

STATE OF COGNITIVE FUNCTIONS IN CHILDREN WITH PATHOLOGY OF DIGESTIVE ORGANS, WHO LIVE AT RADIOACTIVE CONTAMINATED TERRITORIES OF UKRAINE

OBJECTIVE

to study the state of cognitive functions in children who were born and permanently live at radioactive contaminated territories (RCT) with pathology of the upper digestive tract, using pathopsychological testing; to increase the effectiveness of treatment and prophylactic measures aimed at preserving and restoring the health of RCT residents.

DESIGN, PATIENTS AND METHODS

A randomized blind controlled clinical trial was conducted. There were examined, a total of 90 persons aged 6 to 17 years (35 boys and 55 girls) who were divided into two groups: the control group (I) included 30 persons of the conventional «clean» territories, and the main group (II) - 60 patients with patho- logy of the digestive organs who were born and live at the RCT. The study program included: the collection of anam- nesis, complaints; clinical and instrumental examinations. The following tests were applied by us: «What things are hidden in the drawings», Toulouse-Pieron, Raven, and Luria testing. For detecting the anxiety level, and the subjec- tive signs of autonomic dysfunctions were used the Spilberg-Hanin self-diagnosis and the Wein questionnaire, respectively.

RESULTS

It was shown that in children aged 6-11 years, according to the results of the Toulouse-Pieron test, speed of cognitive information-processing was significantly decreased by 7.17 conventional units, while on the back- ground of the etiopathogenetic treatment of the digestive tract - by 10.24 conventional units relative to the va- lues of the control group. The long-term memory was statistically significantly decreased in the examined children of senior school age (from 12 to 17 years). A significant increase in reactive anxiety and a reverse correlation between the personal anxiety (PA) and speed of cognitive information-processing (r = -0.331) were recorded in patients aged 6-11 years. In older patients, PA was increased.Сonclusions. The obtained results indicate that the state of cognitive functions was characterized by a decrease in speed of cognitive information-processing, long-term memory and a high level of anxiety in children aged from 6 to 17 years residents of RСT with pathology of digestive organs, according to the used testing.

Radiation-Induced Cerebro-Ophthalmic Effects in Humans

Exposure to ionizing radiation (IR) could affect the human brain and eyes leading to both cognitive and visual impairments. The aim of this paper was to review and analyze the current literature, and to comment on the ensuing findings in the light of our personal contributions in this field. The review was carried out according to the PRISMA guidelines by searching PubMed, Scopus, Embase, PsycINFO and Google Scholar English papers published from January 2000 to January 2020. The results showed that prenatally or childhood-exposed individuals are a particular target group with a higher risk for possible radiation effects and neurodegenerative diseases. In adulthood and medical/interventional radiologists, the most frequent IR-induced ophthalmic effects include cataracts, glaucoma, optic neuropathy, retinopathy and angiopathy, sometimes associated with specific neurocognitive deficits. According to available information that eye alterations may induce or may be associated with brain dysfunctions and vice versa, we propose to label this relationship "eye-brain axis", as well as to deepen the diagnosis of eye pathologies as early and easily obtainable markers of possible low dose IR-induced brain damage.

BRAIN AND EYE AS POTENTIAL TARGETS FOR IONIZING RADIATION IMPACT. Part І. THE CONSEQUENCES OF IRRADIATION OF THE PARTICIPANTS OF THE LIQUIDATION OF THE CHORNOBYL ACCIDENT

BACKGROUND

Exposure to ionizing radiation could affect the brain and eyes leading to cognitive and vision impairment, behavior disorders and performance decrement during professional irradiation at medical radiology, includinginterventional radiological procedures, long-term space flights, and radiation accidents.

OBJECTIVE

The objective was to analyze the current experimental, epidemiological, and clinical data on the radiation cerebro-ophthalmic effects.

MATERIALS AND METHODS

In our analytical review peer-reviewed publications via the bibliographic and scientometric bases PubMed / MEDLINE, Scopus, Web of Science, and selected papers from the library catalog of NRCRM - theleading institution in the field of studying the medical effects of ionizing radiation - were used.

RESULTS

The probable radiation-induced cerebro-ophthalmic effects in human adults comprise radiation cataracts,radiation glaucoma, radiation-induced optic neuropathy, retinopathies, angiopathies as well as specific neurocognitive deficit in the various neuropsychiatric pathology including cerebrovascular pathology and neurodegenerativediseases. Specific attention is paid to the likely stochastic nature of many of those effects. Those prenatally and inchildhood exposed are a particular target group with a higher risk for possible radiation effects and neurodegenerative diseases.

CONCLUSIONS

The experimental, clinical, epidemiological, anatomical and pathophysiological rationale for visualsystem and central nervous system (CNS) radiosensitivity is given. The necessity for further international studieswith adequate dosimetric support and the follow-up medical and biophysical monitoring of high radiation riskcohorts is justified. The first part of the study currently being published presents the results of the study of theeffects of irradiation in the participants of emergency works at the Chornobyl Nuclear Power Plant (ChNPP).