Postnatal irradiation-induced hippocampal neuropathology, cognitive impairment and aging

Radiation-Induced Brain Injury with Special Reference to Astrocytes as a Therapeutic Target

Radiotherapy is one of the primary modalities for oncologic treatment and has been utilized at least once in over half of newly diagnosed cancer patients. Cranial radiotherapy has significantly enhanced the long-term survival rates of patients with brain tumors. However, radiation-induced brain injury, particularly hippocampal neuronal damage along with impairment of neurogenesis, inflammation, and gliosis, adversely affects the quality of life for these patients. Astrocytes, a type of glial cell that are abundant in the brain, play essential roles in maintaining brain homeostasis and function. Despite their importance, the pathophysiological changes in astrocytes induced by radiation have not been thoroughly investigated, and no systematic or comprehensive review addressing the effects of radiation on astrocytes and related diseases has been conducted. In this paper, we review current studies on the neurophysiological roles of astrocytes following radiation exposure. We describe the pathophysiological changes in astrocytes, including astrogliosis, astrosenescence, and the associated cellular and molecular mechanisms. Additionally, we summarize the roles of astrocytes in radiation-induced impairments of neurogenesis and the blood-brain barrier (BBB). Based on current research, we propose that brain astrocytes may serve as potential therapeutic targets for treating radiation-induced brain injury (RIBI) and subsequent neurological and neuropsychiatric disorders.

Pathological Mechanisms of Irradiation-Induced Neurological Deficits in the Developing Brain

Cranial irradiation or radiotherapy (CRT) is one of the essential therapeutic modalities for central nervous system (CNS) tumors, and its efficacy is well known. Nevertheless, CRT is also associated with brain damages such as focal cerebral necrosis, neuroinflammation, cerebral microvascular anomalies, neurocognitive dysfunction, and hormone deficiencies in children. Children's brains are much more sensitive to CRT compared to the adult's brains. Thus, children's brains are also more likely to develop long-term CRT complication, which severely lessens their long-term quality of life after treatment. CRT to the juvenile rat led to a retardation of growth of the cerebellum; both the gray and white matter and neurogenic regions like the subventricular zone and the dentate gyrus in the hippocampus were predominantly vulnerable to CRT. Also, CRT-induced cognitive changes typically manifested as deficits in hippocampal-related functions of learning as well as memory, such as spatial information processing. Fractionated CRT-stimulated cognitive decline and hormone deficiencies were precisely associated with augmented neuronal cell death, blockade of neurogenesis, and stimulation of astrocytes and microglia. Thus, the aim of this review is to highlight the pathological mechanism of CRT-induced neurological deficits in the developing brain.

Radiosensitivity-related Variation in MicroRNA-34a-5p Levels and Subsequent Neuronal Loss in the Hilus of the Dentate Gyrus after Irradiation at Postnatal Days 10 and 21 in Mice

The radiosensitivity of mice differs between postnatal days 10 (P10) and 21(P21); these days mark different stages of brain development. In the present study, Ki67 and doublecotin (DCX) immunostaining and hematoxylin staining was performed, which showed that acute radiation exposure at postnatal day 10 induced higher cell apoptosis and loss in the hilus of the dentate gyrus at day 1 postirradiation than postnatal day 21. MicroRNA (miRNA) sequencing and real-time quantitative reverse transcription PCR (qRT-PCR) analysis indicated the upregulation of miRNA-34a-5p at days 1 and 7 after irradiation at postnatal day 10, but not at postnatal day 21. Down-regulation of T-cell intracytoplasmic antigen-1 pathway (Tia1) was indicated by qRT-PCR at day 1 day but not day 7 after irradiation at postnatal day 10. Neurobehavioral testing in mature mice irradiated at postnatal day 10 demonstrated the impairment of short-term memory in novel object recognition and spatial memory, compared to those irradiated at postnatal day 21. Combined with our previous luciferase assay showing the direct interaction of miRNA34a-5p and Tia1, these findings suggest that radiation-induced abnormal miR-34a-5p/Tial interaction at day 1 after irradiation at postnatal day 10 may be involved in apoptosis of the dentate gyrus hilar, impairment of neurogenesis and subsequent short-term memory loss as observed in the novel object recognition and Barnes maze tests.

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.

Secretome from iPSC-derived MSCs exerts proangiogenic and immunosuppressive effects to alleviate radiation-induced vascular endothelial cell damage

BACKGROUND

Radiation therapy is the standard of care for central nervous system tumours. Despite the success of radiation therapy in reducing tumour mass, irradiation (IR)-induced vasculopathies and neuroinflammation contribute to late-delayed complications, neurodegeneration, and premature ageing in long-term cancer survivors. Mesenchymal stromal cells (MSCs) are adult stem cells that facilitate tissue integrity, homeostasis, and repair. Here, we investigated the potential of the iPSC-derived MSC (iMSC) secretome in immunomodulation and vasculature repair in response to radiation injury utilizing human cell lines.

METHODS

We generated iPSC-derived iMSC lines and evaluated the potential of their conditioned media (iMSC CM) to treat IR-induced injuries in human monocytes (THP1) and brain vascular endothelial cells (hCMEC/D3). We further assessed factors in the iMSC secretome, their modulation, and the molecular pathways they elicit.

RESULTS

Increasing doses of IR disturbed endothelial tube and spheroid formation in hCMEC/D3. When IR-injured hCMEC/D3 (IR ≤ 5 Gy) were treated with iMSC CM, endothelial cell viability, adherence, spheroid compactness, and proangiogenic sprout formation were significantly ameliorated, and IR-induced ROS levels were reduced. iMSC CM augmented tube formation in cocultures of hCMEC/D3 and iMSCs. Consistently, iMSC CM facilitated angiogenesis in a zebrafish model in vivo. Furthermore, iMSC CM suppressed IR-induced NFκB activation, TNF-α release, and ROS production in THP1 cells. Additionally, iMSC CM diminished NF-kB activation in THP1 cells cocultured with irradiated hCMEC/D3, iMSCs, or HMC3 microglial lines. The cytokine array revealed that iMSC CM contains the proangiogenic and immunosuppressive factors MCP1/CCL2, IL6, IL8/CXCL8, ANG (Angiogenin), GROα/CXCL1, and RANTES/CCL5. Common promoter regulatory elements were enriched in TF-binding motifs such as androgen receptor (ANDR) and GATA2. hCMEC/D3 phosphokinome profiling revealed increased expression of pro-survival factors, the PI3K/AKT/mTOR modulator PRAS40 and β-catenin in response to CM. The transcriptome analysis revealed increased expression of GATA2 in iMSCs and the enrichment of pathways involved in RNA metabolism, translation, mitochondrial respiration, DNA damage repair, and neurodevelopment.

CONCLUSIONS

The iMSC secretome is a comodulated composite of proangiogenic and immunosuppressive factors that has the potential to alleviate radiation-induced vascular endothelial cell damage and immune activation.

Effects of radiation exposure on brain health: a state of the art and new challenges

Good brain health refers to a condition in which a person may fully realize their talents and improve their psychological, emotional, cognitive, and behavioral functioning to cope with life's challenges. Various causes of CNS diseases are now being investigated. Radiation is one of the factors that affects the brain and causes a variety of problems. The emission or transmission of energy in the form of waves or particles via space or a material medium is known as radiation. Particle beams and electromagnetic waves are two types of ionizing radiation that have the potential to ionize atoms in a material (separating them into positively charged ions and negatively charged electrons). Radiation to the CNS can induce delayed puberty, which can lead to hyperprolactinemia, and the hypothalamic-pituitary axis can lead to gonadotropin deficit if the hypothalamic-pituitary axis is involved in the radiation field. Ionizing radiation is the most common kind of radiation. Here, we focus on the different effects of radiation on brain health. In this article, we will look at a variety of CNS diseases and how radiation affects each one, as well as how it affects the brain's numerous processes.

Comparison of whole brain radiation therapy for synchronous brain metastases with irradiation protecting the hippocampus versus whole brain radiotherapy for sequential brain metastases to boost irradiation in the treatment of brain metastases from SCLC: study protocol for a randomized controlled trial

Background

This study is in regard to the comparison of whole brain radiation therapy for synchronous brain metastases with irradiation protecting the hippocampus versus whole brain radiotherapy for sequential brain metastases to boost irradiation in the treatment of brain metastases from small cell lung cancer (SCLC). Therapeutically, they have notably varying dose distributions. Based on theoretical and model studies, it has long been speculated that these modes may result in different prognostic outcomes. We aim to assess the efficacy of tomotherapy in the treatment of SCLC brain metastases while protecting the key functional area, the hippocampus, and minimizing any neurocognitive impairments incurred by radiation.

Methods

This is a randomized, controlled, prospective study including 102 SCLC patients with brain metastases randomized (1:1) to the experimental (whole brain radiation therapy for synchronous brain metastases with irradiation to protect the hippocampus) or control (whole brain radiotherapy for sequential brain metastases to boost irradiation) group. The sample size is calculated through a single-sided test; 102 participants will be required for the main results to have statistical and clinical significance. We aim to provide clinical trial data support for better prognostic treatment options in patients with SCLC and brain metastases. The clinical trial data include both the primary and secondary outcomes; the primary outcome is the intracranial progression-free survival time after the new technology application. The secondary study outcomes include the assessment of neurological function, the quality of life, and the overall survival rate. Follow-up consultations will be conducted every 2 months. After the final patient completes follow-up, the Statistical Product and Service Solutions software will be used for scientific and rigorous data analysis. Version 1.0 of the protocol was implemented on January 1, 2021; the recruitment process for this clinical trial commenced on April 1, 2021, and will end on March 31, 2024.

Discussion

The study will provide high-quality clinical evidence to support the efficacy and safety of whole brain radiation therapy for synchronous brain metastases with dose irradiation protecting the hippocampus versus whole brain radiotherapy for sequential brain metastases with push volume irradiation for the treatment of patients who have lung cancer as well as brain metastases. This has not been previously reported.

Trial registration

This trial is registered with the Chinese Clinical Trial Registry (ChiCTR1900027539; November 17, 2019) (URL: https://www.chictr.org.cn/hvshowproject.aspx?id=20515).

Neurocognitive function and survival in children with average-risk medulloblastoma treated with hyperfractionated radiation therapy alone: Long-term mature outcomes of a prospective study

Background

The purpose of this study was to report long-term neurocognitive and clinical outcomes in children treated for average-risk medulloblastoma with hyperfractionated radiation therapy (HFRT) alone.

Methods

Between 2006 and 2010, 20 children with rigorously staged average-risk medulloblastoma were treated on a prospective study with HFRT without upfront adjuvant systemic chemotherapy after written informed consent. HFRT was delivered as twice-daily fractions (1 Gy/fraction, 6-8 hours apart, 5 days/week) to craniospinal axis (36 Gy/36 fractions) plus conformal tumor-bed boost (32 Gy/32 fractions). Neurocognitive function was assessed at baseline and periodically on follow-up using age-appropriate intelligence quotient (IQ) scales.

Results

Median age was 8 years (range 5-14 years) with 70% being males. Mean and standard deviation (SD) scores at baseline were 90.5 (SD = 17.08), 88 (SD = 16.82) and 88 (SD = 17.24) for Verbal Quotient (VQ), Performance Quotient (PQ), and Full-Scale IQ (FSIQ) respectively. Mean scores remained stable in the short-to-medium term but declined gradually beyond 5 years with borderline statistical significance for VQ (P = .042), but nonsignificant decline in PQ (P = .259) and FSIQ (P = .108). Average rate of neurocognitive decline was <1 IQ point per year over a 10-year period. Regression analysis stratified by age, gender, and baseline FSIQ failed to demonstrate any significant impact of the tested covariates on longitudinal neurocognitive function. At a median follow-up of 145 months, 10-year Kaplan-Meier estimates of progression-free survival and overall survival were 63.2% and 74.1% respectively.

Conclusion

HFRT alone without upfront adjuvant chemotherapy in children with average-risk medulloblastoma is associated with modest decline in neurocognitive functioning with acceptable long-term survival outcomes and may be most appropriate for resource-constrained settings.

Porous Se@SiO2 Nanoparticles Attenuate Radiation-Induced Cognitive Dysfunction via Modulating Reactive Oxygen Species

Radiotherapy has been widely used to manage primary and metastatic brain tumors. However, hippocampal damage and subsequent cognitive dysfunction are common complications of whole brain radiation (WBI). In this study, Se@SiO₂ nanoparticles (NPs) with antioxidant properties were synthesized. Se@SiO₂ NPs were characterized using X-ray diffraction (XRD) and transmission electron microscopy (TEM). The reactive oxygen species (ROS) scavenging ability of Se@SiO₂ NPs was assessed using a dichloro-dihydro-fluorescein diacetate (DCFH-DA) probe. Apoptosis of HT-22 cells treated with H₂O₂ and Se@SiO₂ NPs was assessed by annexin V-FITC/PI and JC-1 staining. Western blotting was used to evaluate inflammation-related signaling pathways. In vivo, the distribution and excretion of Se@SiO₂ NPs were assessed using in vivo imaging system (IVIS). The biosafety and antioxidant effects of Se@SiO₂ NPs were assessed. Neurogenesis in the hippocampus of mice was detected through neuron-specific nuclear protein (NeuN) and 5-bromo-2'-deoxyuridine (BrdU) immunofluorescence staining. The cognitive abilities of mice were also assessed using the Morris water maze test. Results showed that porous Se@SiO₂ NPs were successfully synthesized with uniform spherical structures. In vitro, Se@SiO₂ NPs inhibited ROS levels in mouse hippocampal neuronal cell line HT-22 treated with H₂O₂. Furthermore, Se@SiO₂ NPs suppressed the apoptotic rate of HT-22 cells by regulating apoptosis-related proteins. Se@SiO₂ NPs regulated the nuclear factor kappa B (NF-κB) and mitogen-activated protein kinase (MAPK) signaling pathways, thereby reducing the expression of inflammatory factors. In vivo, Se@SiO₂ NPs showed high biocompatibility at a concentration of 1.25 μg/μL. Se@SiO₂ NPs inhibited ROS and promoted neurogenesis in the hippocampus, as well as improved cognitive ability in radiation-induced mice. In conclusion, Se@SiO₂ NPs protected the hippocampus from oxidative stress injury and neuroinflammation. Se@SiO₂ NPs treatment may be a potential therapeutic strategy for radiation-induced cognitive dysfunction.

Neuroprotective Effects of Lycium barbarum Berry on Neurobehavioral Changes and Neuronal Loss in the Hippocampus of Mice Exposed to Acute Ionizing Radiation

Background: Brain exposure to ionizing radiation during the radiotherapy of brain tumor or metastasis of peripheral cancer cells to the brain has resulted in cognitive dysfunction by reducing neurogenesis in hippocampus. The water extract of Lycium barbarum berry (Lyc), containing water-soluble Lycium barbarum polysaccharides and flavonoids, can protect the neuronal injury by reducing oxidative stress and suppressing neuroinflammation. Reseach Design: To demonstrate the long-term radioprotective effect of Lyc, we evaluated the neurobehavioral alterations and the numbers of NeuN, calbindin (CB), and parvalbumin (PV) immunopositive hippocampal neurons in BALB/c mice after acute 5.5 Gy radiation with/without oral administration of Lyc at the dosage of 10 g/kg daily for 4 weeks. Results: The results showed that Lyc could improve irradiation-induced animal weight loss, depressive behaviors, spatial memory impairment, and hippocampal neuron loss. Immunohistochemistry study demonstrated that the loss of NeuN-immunopositive neuron in the hilus of the dentate gyrus, CB-immunopositive neuron in CA1 strata radiatum, lacunosum moleculare and oriens, and PV-positive neuron in CA1 stratum pyramidum and stratum granulosum of the dentate gyrus after irradiation were significantly improved by Lyc treatment. Conclusion: The neuroprotective effect of Lyc on those hippocampal neurons may benefit the configuration of learning related neuronal networks and then improve radiation induced neurobehavioral changes such as cognitive impairment and depression. It suggests that Lycium barbarum berry may be an alternative food supplement to prevent radiation-induced neuron loss and neuropsychological disorders.

Exosomes Derived From Adipose-Derived Mesenchymal Stem Cells Ameliorate Radiation-Induced Brain Injury by Activating the SIRT1 Pathway

Objective

Studies have shown that the therapeutic effects of mesenchymal stem cells (MSCs) are mediated in a paracrine manner, mainly through extracellular vesicles such as exosomes. Here, we designed a study to investigate whether exosomes derived from adipose-derived mesenchymal stem cells (ADMSC-Exos) had protective effects in a rat model of radiation-induced brain injury and in microglia.

Methods

Male adult Sprague-Dawley (SD) rats were randomly divided into three groups: the control group, the radiation group (30 Gy), and the radiation + exosomes group (30 Gy + 100 ug exosomes). Meanwhile, microglia were divided into four groups: the control group, the radiation group (10 Gy), the radiation + exosomes group (10 Gy + 4 ug exosomes), and radiation + exosomes + EX527 group (10 Gy + 4 ug exosomes + 100 nM EX527). Tissue samples and the levels of oxidative stress and inflammatory factors in each group were compared.

Results

Statistical analysis showed that after irradiation, ADMSC-Exos intervention in vivo significantly reduced the levels of caspase-3, malondialdehyde (MDA), 8-hydroxydeoxyguanosine (8-OHdG), tumor necrosis factor-α (TNF-α), interleukin-4 (IL-4), and promoted the recovery of superoxide dismutase (SOD), catalase (CAT), IL-4, and IL-10. Moreover, ADMSC-Exos intervention inhibited microglial infiltration and promoted the expression of SIRT1. Furthermore, the results in vitro showed that the above effects of ADMSC-Exos could be reversed by SIRT-1 inhibitor EX527.

Conclusion

This study demonstrated that ADMSC-Exos exerted protective effects against radiation-induced brain injury by reducing oxidative stress, inflammation and microglial infiltration via activating the SIRT1 pathway. ADMSC-Exos may serve as a promising therapeutic tool for radiation-induced brain injury.

Astroglial Connexins in Neurological and Neuropsychological Disorders and Radiation Exposure

Radiotherapy is a common treatment for brain and spinal cord tumors and also a risk factor for neuropathological changes in the brain leading to different neurological and neuropsychological disorders. Astroglial connexins are involved in brain inflammation, development of Alzheimer's Disease (AD), depressive, epilepsy, and amyotrophic lateral sclerosis, and are affected by radiation exposure. Therefore, it is speculated that radiation-induced changes of astroglial connexins may be related to the brain neuropathology and development of neurological and neuropsychological disorders. In this paper, we review the functional expression and regulation of astroglial connexins expressed between astrocytes and different types of brain cells (including oligodendrocytes, microglia, neurons and endothelial cells). The roles of these connexins in the development of AD, depressive, epilepsy, amyotrophic lateral sclerosis and brain inflammation have also been summarized. The radiation-induced astroglial connexins changes and development of different neurological and neuropsychological disorders are then discussed. Based on currently available data, we propose that radiation-induced astroglial connexins changes may be involved in the genesis of different neurological and neuropsychological disorders which depends on the age, brain regions, and radiation doses/dose rates. The abnormal astroglial connexins may be novel therapeutic targets for the prevention of radiation-induced cognitive impairment, neurological and neuropsychological disorders.

Early postnatal irradiation-induced age-dependent changes in adult mouse brain: MRI based characterization

BACKGROUND

Brain radiation exposure, in particular, radiotherapy, can induce cognitive impairment in patients, with significant effects persisting for the rest of their life. However, the main mechanisms leading to this adverse event remain largely unknown. A study of radiation-induced injury to multiple brain regions, focused on the hippocampus, may shed light on neuroanatomic bases of neurocognitive impairments in patients. Hence, we irradiated BALB/c mice (male and female) at postnatal day 3 (P3), day 10 (P10), and day 21 (P21) and investigated the long-term radiation effect on brain MRI changes and hippocampal neurogenesis.

RESULTS

We found characteristic brain volume reductions in the hippocampus, olfactory bulbs, the cerebellar hemisphere, cerebellar white matter (WM) and cerebellar vermis WM, cingulate, occipital and frontal cortices, cerebellar flocculonodular WM, parietal region, endopiriform claustrum, and entorhinal cortex after irradiation with 5 Gy at P3. Irradiation at P10 induced significant volume reduction in the cerebellum, parietal region, cingulate region, and olfactory bulbs, whereas the reduction of the volume in the entorhinal, parietal, insular, and frontal cortices was demonstrated after irradiation at P21. Immunohistochemical study with cell division marker Ki67 and immature marker doublecortin (DCX) indicated the reduced cell division and genesis of new neurons in the subgranular zone of the dentate gyrus in the hippocampus after irradiation at all three postnatal days, but the reduction of total granule cells in the stratum granulosun was found after irradiation at P3 and P10.

CONCLUSIONS

The early life radiation exposure during different developmental stages induces varied brain pathophysiological changes which may be related to the development of neurological and neuropsychological disorders later in life.

Out-of-Field Hippocampus from Partial-Body Irradiated Mice Displays Changes in Multi-Omics Profile and Defects in Neurogenesis

The brain undergoes ionizing radiation exposure in many clinical situations, particularly during radiotherapy for brain tumors. The critical role of the hippocampus in the pathogenesis of radiation-induced neurocognitive dysfunction is well recognized. The goal of this study is to test the potential contribution of non-targeted effects in the detrimental response of the hippocampus to irradiation and to elucidate the mechanisms involved. C57Bl/6 mice were whole body (WBI) or partial body (PBI) irradiated with 0.1 or 2.0 Gy of X-rays or sham irradiated. PBI consisted of the exposure of the lower third of the mouse body, whilst the upper two thirds were shielded. Hippocampi were collected 15 days or 6 months post-irradiation and a multi-omics approach was adopted to assess the molecular changes in non-coding RNAs, proteins and metabolic levels, as well as histological changes in the rate of hippocampal neurogenesis. Notably, at 2.0 Gy the pattern of early molecular and histopathological changes induced in the hippocampus at 15 days following PBI were similar in quality and quantity to the effects induced by WBI, thus providing a proof of principle of the existence of out-of-target radiation response in the hippocampus of conventional mice. We detected major alterations in DAG/IP3 and TGF-β signaling pathways as well as in the expression of proteins involved in the regulation of long-term neuronal synaptic plasticity and synapse organization, coupled with defects in neural stem cells self-renewal in the hippocampal dentate gyrus. However, compared to the persistence of the WBI effects, most of the PBI effects were only transient and tended to decrease at 6 months post-irradiation, indicating important mechanistic difference. On the contrary, at low dose we identified a progressive accumulation of molecular defects that tended to manifest at later post-irradiation times. These data, indicating that both targeted and non-targeted radiation effects might contribute to the pathogenesis of hippocampal radiation-damage, have general implications for human health.

Whole brain proton irradiation in adult Sprague Dawley rats produces dose dependent and non-dependent cognitive, behavioral, and dopaminergic effects

Proton radiotherapy causes less off-target effects than X-rays but is not without effect. To reduce adverse effects of proton radiotherapy, a model of cognitive deficits from conventional proton exposure is needed. We developed a model emphasizing multiple cognitive outcomes. Adult male rats (10/group) received a single dose of 0, 11, 14, 17, or 20 Gy irradiation (the 20 Gy group was not used because 50% died). Rats were tested once/week for 5 weeks post-irradiation for activity, coordination, and startle. Cognitive assessment began 6-weeks post-irradiation with novel object recognition (NOR), egocentric learning, allocentric learning, reference memory, and proximal cue learning. Proton exposure had the largest effect on activity and prepulse inhibition of startle 1-week post-irradiation that dissipated each week. 6-weeks post-irradiation, there were no effects on NOR, however proton exposure impaired egocentric (Cincinnati water maze) and allocentric learning and caused reference memory deficits (Morris water maze), but did not affect proximal cue learning or swimming performance. Proton groups also had reduced striatal levels of the dopamine transporter, tyrosine hydroxylase, and the dopamine receptor D1, effects consistent with egocentric learning deficits. This new model will facilitate investigations of different proton dose rates and drugs to ameliorate the cognitive sequelae of proton radiotherapy.

NEUROENDOCRINE EFFECTS OF PRENATAL IRRADIATION FROM RADIOACTIVE IODINE (review)

BACKGROUND

Neuroendocrine effects of the prenatal radiation exposure from radioactive iodine in an event of nuclear power reactor accidents are a key issue in the field of radiation medicine and radiation safety because of a dramatic radiosensitivity of the developing organism.

OBJECTIVE

Review of contemporary epidemiological, clinical and experimental data on neuroendocrine effects of prenatal exposure to 131I.

OBJECT AND METHODS

Search in the PubMed/MEDLINE and Google Scholar abstract databases, along with a manual search for the relevant data sources.

RESULTS

Estimated absorbed doses of intrauterine thyroid irradiation from radioactive iodine were obtained based on ICRP Publication 88, both with estimates of effective radiation doses on embryo and fetus, and estimates of the brain equivalent doses upon exposure in utero. The latter ones are subject to updating. The evidence-based data has been presented regarding a radiation-associated reduction of head and chest circumference at birth, as well as a radiation-associated excess of goiter with large thyroid nodules, and possibly of thyroid cancer after a prenatal exposure to 131I radionuclides. Data on intrauterine brain damage are controversial, but most researchers share the view that there are cognitive and emotional-behavioral disorders due to prenatal and postnatal irradiation and psy- chosocial impacts. Incidence increase of non-cancerous endocrine disorders and degenerative vascular disease of retina was noted. An experimental model of intrauterine irradiation from 131I on Wistar rats was for the first time ever created, extrapolating the radioneuroembryological effects in rats to individuals prenatally exposed after the Chornobyl disaster. Late neuropsychiatric and endocrine effects may be resulted from the relatively short-term impact of ionizing radiation at a level previously been considered safe. The necessity of neuropsychiatric and endocrinological monitoring of individuals exposed prenatally to ionizing radiation after the Chornobyl catastrophe throughout their life is substantiated. Experimental animal studies are a key direction in the further research of radiation effects, especially associated with low radiation doses. Further experimental and clinical neuroradiobio- logical studies aimed at exploration of the effect of ionizing radiation on hippocampal neurogenesis are most rele- vant nowadays.

Irradiation-induced senescence of bone marrow mesenchymal stem cells aggravates osteogenic differentiation dysfunction via paracrine signaling

The role of cellular senescence induced by radiation in bone loss has attracted much attention. As one of the common complications of anticancer radiotherapy, irradiation-induced bone deterioration is common and clinically significant, but the pathological mechanism has not been elucidated. This study was performed to explore the cellular senescence and senescence-associated secretory phenotype (SASP) induction of bone marrow-derived mesenchymal stem cells (BMSCs) by irradiation and its role in osteogenic differentiation dysfunction. It was observed that irradiated BMSCs lost typical fibroblast-like morphology, exhibited suppressed viability and differentiation potential accompanied with senescence phenotypes, including an increase in senescence-associated β-galactosidase (SA-β-gal) staining-positive cells, and upregulated senescence-related genes p53/p21, whereas no changes happened to p16. Additionally, DNA damage γ-H2AX foci, G0/G1 phase of cell cycle arrest, and cellular and mitochondrial reactive oxygen species (ROS) increased in an irradiation dose-dependent manner. Meanwhile, the JAK1/STAT3 pathway was activated and accompanied by an increase in SASP secretion, such as IL-6, IL-8, and matrix metalloproteinase-9 (MMP9), whereas 0.8 μM JAK1 inhibitor (JAKi) treatment effectively inhibited the JAK pathway and SASP production. Furthermore, conditioned medium (CM) from irradiation-induced senescent (IRIS) BMSCs exhibited a markedly reduced ability in osteogenic differentiation and marker gene expression of osteoblasts, whereas CM with JAKi intervention may effectively improve these deterioration effects. In conclusion, irradiation could provoke BMSC senescence and SASP secretion and further aggravate osteogenic differentiation dysfunction via paracrine signaling, whereas SASP targeting may be a possible intervention strategy for alleviating irradiation-induced bone loss.

The Neuroprotective Effect of Amitriptyline on Radiation-Induced Impairment of Hippocampal Neurogenesis

The radioprotective effect of amitriptyline, an inhibitor of acid sphingomyelinase (ASMase), on radiation-induced impairment of hippocampal neurogenesis, loss of interneuron, and animal weight changes was investigated in BALB/c mice by immunostaining of biomarkers for cell division (Ki67), immature neurons (doublecortin or DCX), and interneurons (parvalbumin or PV) in the dentate gyrus (DG) of hippocampus. The results indicated that preirradiation (with 10 mg/kg, 2 times per day, for 7 consecutive days) or postirradiation (with 10 mg/kg, 2 times per day, for 14 consecutive days) treatment (pretreatment or posttreatment) with intraperitoneal injection of amitriptyline prevented the loss of newly generated neurons, proliferating cells, and interneurons in the subgranular zone of the DG. At the molecular level, pretreatment or posttreatment inhibited the expression of sphingomyelin phosphodiesterase 1 (SMPD1) gene which codes for ASMase. The pretreatment for 7 days also prevented radiation-induced weight loss from 2 to 3 weeks, but not within 1 week after irradiation. On the other hand, the posttreatment with amitriptyline for 14 days could improve animal weight gain from 4 to 6 weeks after irradiation. The present study suggests that amitriptyline may be a promising candidate radio-neuroprotective drug to improve radiation-induced impairment of hippocampal neurogenesis and relevant neurological and neuropsychological disorders.

Heat shock protein 70 increases cell proliferation, neuroblast differentiation, and the phosphorylation of CREB in the hippocampus

In the present study, we investigated the effects of heat shock protein 70 (HSP70) on novel object recognition, cell proliferation, and neuroblast differentiation in the hippocampus. To facilitate penetration into the blood–brain barrier and neuronal plasma membrane, we created a Tat-HSP70 fusion protein. Eight-week-old mice received intraperitoneal injections of vehicle (10% glycerol), control-HSP70, or Tat-HSP70 protein once a day for 21 days. To elucidate the delivery efficiency of HSP70 into the hippocampus, western blot analysis for polyhistidine was conducted. Polyhistidine protein levels were significantly increased in control-HSP70- and Tat-HSP70-treated groups compared to the control or vehicle-treated group. However, polyhistidine protein levels were significantly higher in the Tat-HSP70-treated group compared to that in the control-HSP70-treated group. In addition, immunohistochemical study for HSP70 showed direct evidences for induction of HSP70 immunoreactivity in the control-HSP70- and Tat-HSP70-treated groups. Administration of Tat-HSP70 increased the novel object recognition memory compared to untreated mice or mice treated with the vehicle. In addition, the administration of Tat-HSP70 significantly increased the populations of proliferating cells and differentiated neuroblasts in the dentate gyrus compared to those in the control or vehicle-treated group based on the Ki67 and doublecortin (DCX) immunostaining. Furthermore, the phosphorylation of cAMP response element-binding protein (pCREB) was significantly enhanced in the dentate gyrus of the Tat-HSP70-treated group compared to that in the control or vehicle-treated group. Western blot study also demonstrated the increases of DCX and pCREB protein levels in the Tat-HSP70-treated group compared to that in the control or vehicle-treated group. In contrast, administration of control-HSP70 moderately increased the novel object recognition memory, cell proliferation, and neuroblast differentiation in the dentate gyrus compared to that in the control or vehicle-treated group. These results suggest that Tat-HSP70 promoted hippocampal functions by increasing the pCREB in the hippocampus.

Radioprotective effect of epimedium on neurogenesis and cognition after acute radiation exposure

The radioprotective effect of herb epimedium (or yin yang huo) extract (5 g/kg, oral administration daily for 4 weeks) on neurogenesis and cognition after acute radiation exposure with 5.5 Gy was evaluated in Balb/c mice by behavioral tests and immunohistochemical study. The results indicated that epimedium extract could improve animal weight loss, locomotor activity and spatial learning and memory which are similar to pre-irradiation intraperitoneal injection (100 mg/kg) of amifostine phosphate, a well- known radioprotective drug. Immunohistochemical study showed that epimedium extract prevented the loss of proliferation cells, newly generated neurons, and interneurons in the hilus, in particular, the subgranular zone of the dentate gyrus. It suggests that herb epimedium may be a promising radio-neuro-protective drug to prevent radiation-induced neuropsychological disorders.

Dosimetric evaluation of four whole brain radiation therapy approaches with hippocampus and inner ear avoidance and simultaneous integrated boost for limited brain metastases

AIMS

To perform a dosimetric evaluation of four different simultaneous integrated boost whole brain radiotherapy modalities with hippocampus and inner ear avoidance in the treatment of limited brain metastases.

METHODS

Computed tomography/magnetic resonance imaging data of 10 patients with limited (1-5) brain metastases were used to replan step-and-shoot intensity-modulated radiotherapy (sIMRT), dynamic intensity-modulated radiation therapy (dIMRT), volumetric-modulated arc therapy (VMAT), and helical tomotherapy (Tomo). The prescribed doses of 40-50 Gy in 10 fractions and 30 Gy in 10 fractions were simultaneously delivered to the metastatic lesions and the whole-brain volume, respectively. The hippocampal dose met the RTOG 0933 criteria for hippocampal avoidance (Dmax ≤17 Gy, D100% ≤10 Gy). The inner ear dose was restrained to Dmean ≤15 Gy. Target coverage (TC), homogeneity index (HI), conformity index (CI), maximum dose (Dmax), minimum dose (Dmin) and dose to organs at risk (OARs) were compared.

RESULTS

All plans met the indicated dose restrictions. The mean percentage of planning target volume of metastases (PTVmets) coverage ranged from 97.1 to 99.4%. For planning target volume of brain (PTVbrain), Tomo provided the lowest average D2% (37.5 ± 2.8 Gy), the highest average D98% (25.2 ± 2.0 Gy), and the best TC (92.6% ± 2.1%) and CI (0.79 ± 0.06). The two fixed gantry IMRT modalities (step and shot, dynamic) provided similar PTVbrain dose homogeneity (both 0.76). Significant differences across the four approaches were observed for the maximum and minimum doses to the hippocampus and the maximum doses to the eyes, lens and optic nerves.

CONCLUSION

All four radiotherapy modalities produced acceptable treatment plans with good avoidance of the hippocampus and inner ear. Tomo obtained satisfactory PTVbrain coverage and the best homogeneity index.

TRIAL REGISTRATION

Clinicaltrials.gov, NCT03414944 . Registered 29 January 2018.

Depleting adult dentate gyrus neurogenesis increases cocaine-seeking behavior

The hippocampus is the main locus for adult dentate gyrus (DG) neurogenesis. A number of studies have shown that aberrant DG neurogenesis correlates with many neuropsychiatric disorders, including drug addiction. Although clear causal relationships have been established between DG neurogenesis and memory dysfunction or mood-related disorders, evidence of the causal role of DG neurogenesis in drug-seeking behaviors has not been established. Here we assessed the role of new DG neurons in cocaine self-administration using an inducible transgenic approach that selectively depletes adult DG neurogenesis. Our results show that transgenic mice with decreased adult DG neurogenesis exhibit increased motivation to self-administer cocaine and a higher seeking response to cocaine-related cues. These results identify adult hippocampal neurogenesis as a key factor in vulnerability to cocaine addiction.

Low dose or low dose rate ionizing radiation-induced health effect in the human

The extensive literature review on human epidemiological studies suggests that low dose ionizing radiation (LDIR) (≤100 mSv) or low dose rate ionizing radiation (LDRIR) (<6mSv/H) exposure could induce either negative or positive health effects. These changes may depend on genetic background, age (prenatal day for embryo), sex, nature of radiation exposure, i.e., acute or chronic irradiation, radiation sources (such as atomic bomb attack, fallout from nuclear weapon test, nuclear power plant accidents, ⁶⁰Co-contaminated building, space radiation, high background radiation, medical examinations or procedures) and radionuclide components and human epidemiological experimental designs. Epidemiological and clinical studies show that LDIR or LDRIR exposure may induce cancer, congenital abnormalities, cardiovascular and cerebrovascular diseases, cognitive and other neuropsychiatric disorders, cataracts and other eye and somatic pathology (endocrine, bronchopulmonary, digestive, etc). LDIR or LDRIR exposure may also reduce mutation and cancer mortality rates. So far, the mechanisms of LDIR- or LDRIR -induced health effect are poorly understood. Further extensive studies are still needed to clarify under what circumstances, LDIR or LDRIR exposure may induce positive or negative effects, which may facilitate development of new therapeutic approaches to prevent or treat the radiation-induced human diseases or enhance radiation-induced positive health effect.

The effect of brain-derived neurotrophic factor on radiation-induced neuron architecture impairment is associated with the NFATc4/3 pathway

Irradiation to developing brains results in progressive cognitive dysfunction. Changes in the morphology of mature neurons are thought to be related to impairments of cognitive function. However, little is known about the effects of radiation on neurite outgrowth of immature neurons. Therefore, we sought to evaluate the structural alterations of immature neurons following X-ray irradiation and determine potential strategies to reverse it. Our data revealed damage to the neurite outgrowths of cultured neurons after 2 Gy and 8 Gy irradiation at 1 d and 3 d, respectively. De-phosphorylation of nuclear factor of activated T-cells c4/3 (NFATc4/3) was inhibited post-irradiation. Extraneous brain-derived neurotrophic factor (BDNF) ameliorated impairment of neurite growth and activated the NFATc4/3 signaling pathway. These data indicate that BDNF confers neuroprotective effects against irradiation by modulating the NFATc4/3 pathway.

[Cognitive deficits following brain tumor radiation therapy]

Brain radiation is an important treatment option for malignant and benign brain diseases. The possible acute or chronic impact of radiation therapy on cognitive performance is important for daily functioning and quality of life. A detailed evaluation of cognitive impairment is important in the context of how to control disease progression. The susceptibility of the hippocampus to radiation-induced neuronal damage and its important role in memory highlight that therapeutic strategies require precision medicine.