Physiopathology of radiation-induced neurotoxicity

Delayed Reaction of Radiation on the Central Nervous System and Bone System in C57BL/6J Mice

The aim of this study was to provide a suitable mouse model of radiation-induced delayed reaction and identify potential targets for drug development related to the prevention and treatment of radiation injury. C57BL/6J mice were subjected to singular (109 cGy/min, 5 Gy*1) and fractional (109 cGy/min, 5 Gy*2) total body irradiation. The behavior and activity of mice were assessed 60 days after ionizing radiation (IR) exposure. After that, the pathological changes and mechanism of the mouse brain and femoral tissues were observed by HE, Nissl, Trap staining micro-CT scanning and RNA sequencing (RNA-Seq), and Western blot. The results show that singular or fractional IR exposure led to a decrease in spatial memory ability and activity in mice, and the cognitive and motor functions gradually recovered after singular 5 Gy IR in a time-dependent manner, while the fractional 10 Gy IR group could not recover. The decrease in bone density due to the increase in osteoclast number may be relative to the down-regulation of RUNX2, sclerostin, and beta-catenin. Meanwhile, the brain injury caused by IR exposure is mainly linked to the down-regulation of BNDF and Tau. IR exposure leads to memory impairment, reduced activity, and self-recovery, which are associated with time and dose. The mechanism of cognitive and activity damage was mainly related to oxidative stress and apoptosis induced by DNA damage. The damage caused by fractional 10 Gy TBI is relatively stable and can be used as a stable multi-organ injury model for radiation mechanism research and anti-radiation medicine screening.

Advances in treatments of patients with classical and emergent neurological toxicities of anticancer agents

The neurotoxicity associated to the anticancer treatments has received a growing body of interest in the recent years. The development of innovating therapies over the last 20years has led to the emergence of new toxicities. Their diagnosis and management can be challenging in the clinical practice and further research is warranted to improve the understanding of their pathogenic mechanisms. Conventional treatments as radiation therapy and chemotherapy are associated to well-known and under exploration emerging central nervous system (CNS) and peripheral nervous system (PNS) toxicities. The identification of the risk factors and a better understanding of their pathogeny through a "bench to bedside and back again" approach, are the first steps towards the development of toxicity mitigation strategies. New imaging techniques and biological explorations are invaluable for their diagnosis. Immunotherapies have changed the cancer treatment paradigm from tumor cell centered to immune modulation towards an efficient anticancer immune response. The use of the immune checkpoints inhibitors (ICI) and chimeric antigen receptor (CAR-T cells) lead to an increase in the incidence of immune-mediated toxicities and new challenges in the neurological patient's management. The neurological ICI-related adverse events (n-irAE) are rare but potentially severe and may present with both CNS and PNS involvement. The most frequent and well characterized, from a clinical and biological standpoint, are the PNS phenotypes: myositis and polyradiculoneuropathy, but the knowledge on CNS phenotypes and their treatments is expanding. The n-irAE management requires a good balance between dampening the autoimmune toxicity without impairing the anticancer immunity. The adoptive cell therapies as CAR-T cells, a promising anticancer strategy, trigger cellular activation and massive production of proinflammatory cytokines inducing frequent and sometime severe toxicity known as cytokine release syndrome and immune effector cell-associated neurologic syndrome. Their management requires a close partnership between oncologist-hematologists, neurologists, and intensivists. The oncological patient's management requires a multidisciplinary clinical team (oncologist, neurologist and paramedical) as well as a research team leading towards a better understanding and a better management of the neurological toxicities.

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.

Cumulative incidence and risk factors for radiation induced leukoencephalopathy in high grade glioma long term survivors

The incidence and risk factors associated with radiation-induced leukoencephalopathy (RIL) in long-term survivors of high-grade glioma (HGG) are still poorly investigated. We performed a retrospective research in our institutional database for patients with supratentorial HGG treated with focal radiotherapy, having a progression-free overall survival > 30 months and available germline DNA. We reviewed MRI scans for signs of leukoencephalopathy on T2/FLAIR sequences, and medical records for information on cerebrovascular risk factors and neurological symptoms. We investigated a panel of candidate single nucleotide polymorphisms (SNPs) to assess genetic risk. Eighty-one HGG patients (18 grade IV and 63 grade III, 50M/31F) were included in the study. The median age at the time of radiotherapy was 48 years old (range 18-69). The median follow-up after the completion of radiotherapy was 79 months. A total of 44 patients (44/81, 54.3%) developed RIL during follow-up. Twenty-nine of the 44 patients developed consistent symptoms such as subcortical dementia (n = 28), gait disturbances (n = 12), and urinary incontinence (n = 9). The cumulative incidence of RIL was 21% at 12 months, 42% at 36 months, and 48% at 60 months. Age > 60 years, smoking, and the germline SNP rs2120825 (PPARg locus) were associated with an increased risk of RIL. Our study identified potential risk factors for the development of RIL (age, smoking, and the germline SNP rs2120825) and established the rationale for testing PPARg agonists in the prevention and management of late-delayed radiation-induced neurotoxicity.

Low dose of carbon ion irradiation induces early delayed cognitive impairments in mice

People often encounter various sources of ionizing radiation, both in modern medicine and under various environmental conditions, such as space travel, nuclear power plants or in conditions of man-made disasters that may lead to long-term cognitive impairment. Whilst the effect of exposure to low and high doses of gamma and X-radiation on the central nervous system (CNS) has been well investigated, the consequences of protons and heavy ions irradiation are quite different and poorly understood. As for the assessment of long-term effects of carbon ions on cognitive abilities and neurodegeneration, very few data appeared in the literature. The main object of the research is to investigate the effects of accelerated carbon ions on the cognitive function. Experiments were performed on male SHK mice at an age of two months. Mice were irradiated with a dose of 0.7 Gy of accelerated carbon ions with an energy of 450 meV/n in spread-out Bragg peak (SOBP) on a U-70 particle accelerator (Protvino, Russia). Two months after the irradiation, mice were tested for total activity, spatial learning, as well as long- and short-term hippocampus-dependent memory. One month after the evaluation of cognitive activity, histological analysis of dorsal hippocampus was carried out to assess its morphological state and to reveal late neuronal degeneration. It was found that the mice irradiated with accelerated carbon ions develop an altered behavioral pattern characterized by anxiety and a shortage in hippocampal-dependent memory retention, but not in episodic memory. Nissl staining revealed a reduction in the number of cells in the dorsal hippocampus of irradiated mice, with the most pronounced reduction in cell density observed in the dentate gyrus (DG) hilus. Also, the length of the CA3 field of the dorsal hippocampus was significantly reduced, and the number of cells in it was moderately decreased. Experiments with the use of Fluoro-Jade B (FJB) staining revealed no FJB-positive regions in the dorsal hippocampus of irradiated and control animals 3 months after the irradiation. Thus, no morbid cells were detected in irradiated and control groups. The results obtained indicate that total irradiation with a low dose of carbon ions can produce a cognitive deficit in adult mice without evidence of neurodegenerative pathologic changes.

A longitudinal cohort study of childhood MMR vaccination and seizure disorder among American children

BACKGROUND

Measles (rubeola) is a highly contagious infectious disease with significant morbidity/mortality. Measles-Mumps-Rubella (MMR) is a live-attenuated vaccine used in the United States (US) to prevent measles. This retrospective longitudinal cohort study evaluated childhood MMR vaccination and the risk of a seizure episode and seizure disorder.

METHODS

The Independent Healthcare Research Database (IHRD) composed of records prospectively generated from Florida Medicaid was analyzed using SAS to identify persons continuously enrolled from birth for 120 months. Two cohorts were examined: 23,486 persons received at least one dose of MMR vaccine between 12 and 17 months (vaccinated) and 41,725 persons not receiving a measles-containing vaccine (unvaccinated). The daily incidence rate of an initial seizure episode (ICD-9 code: 780.3x) and seizure disorder (ICD-9 code: 345.xx) following an initial seizure episode diagnoses were examined using Cox proportional hazards ratio (HR) and time-trend models post-MMR vaccination compared to unvaccinated persons and in a self-controlled case-series (SCCS).

RESULTS

The daily incidence rate of an initial seizure episode diagnosed from 6 to 11 days post-MMR vaccination in comparison to 12 to17 months among unvaccinated persons was significantly increased (unadjusted HR = 5.73, p < 0.0001 and adjusted HR = 5.94, p < 0.0001) in HR models. The daily incidence rate of an eventual seizure disorder diagnosis among those diagnosed with an initial seizure episode from 6 to 11 days post-MMR vaccination was significantly increased (unadjusted HR = 17.7, p < 0.01 and adjusted HR = 17.4, p < 0.01) in comparison to the daily incidence rate of an eventual seizure disorder diagnosis among those diagnosed with an initial seizure episode from 12 to 17 months among unvaccinated persons. Time-trend analyses revealed a significantly increased rate ratio (RR) for an initial seizure episode (RR = 4.64, p < 0.0001) and seizure disorder (RR = 5.51, p < 0.0001) diagnoses. Time-trend SCCS analyses revealed a significantly increased daily incidence rate of an initial seizure episode (RR = 3.80, p < 0.0001) when comparing periods from 6 to 11 days post-MMR vaccination to 49-60 days post-MMR vaccination. The incidence rate of an eventual seizure disorder diagnosis among those with an initial seizure episode diagnosis from 6 to 11 days post-MMR vaccination compared to 49-60 days post-MMR vaccination was significantly increased (RR = 4.15, p < 0.01).

CONCLUSION

Seizure episode and seizure disorder are rare consequences of routine childhood MMR vaccination.

Whole-brain irradiation differentially modifies neurotransmitters levels and receptors in the hypothalamus and the prefrontal cortex

BACKGROUND

Whole-brain radiotherapy is a primary treatment for brain tumors and brain metastasis, but it also induces long-term undesired effects. Since cognitive impairment can occur, research on the etiology of secondary effects has focused on the hippocampus. Often overlooked, the hypothalamus controls critical homeostatic functions, some of which are also susceptible after whole-brain radiotherapy. Therefore, using whole-brain irradiation (WBI) in a rat model, we measured neurotransmitters and receptors in the hypothalamus. The prefrontal cortex and brainstem were also analyzed since they are highly connected to the hypothalamus and its regulatory processes.

METHODS

Male Wistar rats were exposed to WBI with 11 Gy (Biologically Effective Dose = 72 Gy). After 1 month, we evaluated changes in gamma-aminobutyric acid (GABA), glycine, taurine, aspartate, glutamate, and glutamine in the hypothalamus, prefrontal cortex, and brainstem according to an HPLC method. Ratios of Glutamate/GABA and Glutamine/Glutamate were calculated. Through Western Blott analysis, we measured the expression of GABAa and GABAb receptors, and NR1 and NR2A subunits of NMDA receptors. Changes were analyzed comparing results with sham controls using the non-parametric Mann-Whitney U test (p < 0.05).

RESULTS

WBI with 11 Gy induced significantly lower levels of GABA, glycine, taurine, aspartate, and GABAa receptor in the hypothalamus. Also, in the hypothalamus, a higher Glutamate/GABA ratio was found after irradiation. In the prefrontal cortex, WBI induced significant increases of glutamine and glutamate, Glutamine/Glutamate ratio, and increased expression of both GABAa receptor and NMDA receptor NR1 subunit. The brainstem showed no statistically significant changes after irradiation.

CONCLUSION

Our findings confirm that WBI can affect rat brain regions differently and opens new avenues for study. After 1 month, WBI decreases inhibitory neurotransmitters and receptors in the hypothalamus and, conversely, increases excitatory neurotransmitters and receptors in the prefrontal cortex. Increments in Glutamate/GABA in the hypothalamus and Glutamine/Glutamate in the frontal cortex indicate a neurochemical imbalance. Found changes could be related to several reported radiotherapy secondary effects, suggesting new prospects for therapeutic targets.

Exposure to Ionizing Radiation Causes Endoplasmic Reticulum Stress in the Mouse Hippocampus

It is well known that ionizing radiation-induced toxicity to normal tissue has functional consequences in the brain. However, the underlying molecular alterations have yet to be elucidated. We have previously reported cognitive impairments with concomitant changes in dendritic complexity, spine density and inflammation in mice at 6-24 weeks postirradiation. The goal of this study was to determine whether metabolic changes in the mouse hippocampus after whole-body (4 Gy) or cranial (9 Gy) X-ray irradiation might trigger some of the incipient changes contributing to the persisting pathology in the radiation-injured brain. Metabolomic and lipidomic profiling of hippocampal tissue revealed that radiation induced dyslipidemia in mice at two days and two weeks postirradiation. Strikingly, significant changes were also observed in metabolites of the hexosamine biosynthesis pathway, a finding that was further confirmed using orthogonal methodologies. We hypothesize that these changes in hexosamine metabolism could induce endoplasmic reticulum stress and contribute to radiation-induced cognitive impairments. Taken together, our results show that molecular phenotyping is a valuable approach to identify potentially detrimental pathway perturbations that manifest significantly earlier than gross structural and functional changes in the irradiated brain.

Once the Light Touch to the Brain: Cytotoxic Effects of Low-Dose Gamma-Ray, Laser Light, and Visible Light on Rat Neuronal Cell Culture

OBJECTIVE

We aimed to evaluate the effects of gamma-ray, laser light, and visible light, which neurons are commonly exposed to during treatment of various cranial diseases, on the viability of neurons.

MATERIALS AND METHODS

Neuronal cell culture was prepared from the frontal cortex of 9 newborn rats. Cultured cells were irradiated with gamma-ray for 1-10 min by (152)Eu, (241)Am, and (132)Ba isotopes, visible light for 1-160 min, and laser light for 0.2-2 seconds. The MTT tetrazolium reduction assay was used to assess the number of viable cells in the neuronal cell cultures. Wavelength dispersive X-ray fluorescence spectrometer was used to determine Na, K, and Ca levels in cellular fluid obtained from neuronal cell culture plaques.

RESULTS

Under low-dose radiation with (152)Eu, (241)Am, and (132)Ba isotopes, cell viability insignificantly decreased with time (p>0.05). On the other hand, exposure to visible light produced statistically significant decrease in cell viability at both short- (1-10 min) and long-term (20-160 min). Cell viability did not change with 2 seconds of laser exposure. Na, K, and Ca levels significantly decreased with gamma-ray and visible light. The level of oxidative stress markers significantly changed with gamma-ray.

CONCLUSION

In conclusion, while low dose gamma-ray has slight to moderate apoptotic effect in neuronal cell cultures by oxidative stress, long-term visible light induces remarkable apoptosis and cell death. Laser light has no significant effect on neurons. Further genetic studies are needed to clarify the chronic effect of visible light on neuronal development and functions.

Fractionated Radiation Exposure of Rat Spinal Cords Leads to Latent Neuro-Inflammation in Brain, Cognitive Deficits, and Alterations in Apurinic Endonuclease 1

Ionizing radiation causes degeneration of myelin, the insulating sheaths of neuronal axons, leading to neurological impairment. As radiation research on the central nervous system has predominantly focused on neurons, with few studies addressing the role of glial cells, we have focused our present research on identifying the latent effects of single/ fractionated -low dose of low/ high energy radiation on the role of base excision repair protein Apurinic Endonuclease-1, in the rat spinal cords oligodendrocyte progenitor cells’ differentiation. Apurinic endonuclease-1 is predominantly upregulated in response to oxidative stress by low- energy radiation, and previous studies show significant induction of Apurinic Endonuclease-1 in neurons and astrocytes. Our studies show for the first time, that fractionation of protons cause latent damage to spinal cord architecture while fractionation of HZE (²⁸Si) induce increase in APE1 with single dose, which then decreased with fractionation. The oligodendrocyte progenitor cells differentiation was skewed with increase in immature oligodendrocytes and astrocytes, which likely cause the observed decrease in white matter, increased neuro-inflammation, together leading to the observed significant cognitive defects.

Effects of expression level of DNA repair-related genes involved in the NHEJ pathway on radiation-induced cognitive impairment

Cranial radiation therapy can induce cognitive decline. Impairments of hippocampal neurogenesis are thought to be a paramountly important mechanism underlying radiation-induced cognitive dysfunction. In the mature nervous system, DNA double-strand breaks (DSBs) are mainly repaired by non-homologous end-joining (NHEJ) pathways. It has been demonstrated that NHEJ deficiencies are associated with impaired neurogenesis. In our study, rats were randomly divided into five groups to be irradiated by single doses of 0 (control), 0 (anesthesia control), 2, 10, and 20 Gy, respectively. The cognitive function of the irradiated rats was measured by open field, Morris water maze and passive avoidance tests. Real-time PCR was also used to detect the expression level of DNA DSB repair-related genes involved in the NHEJ pathway, such as XRCC4, XRCC5and XRCC6, in the hippocampus. The influence of different radiation doses on cognitive function in rats was investigated. From the results of the behavior tests, we found that rats receiving 20 Gy irradiation revealed poorer learning and memory, while no significant loss of learning and memory existed in rats receiving irradiation from 0-10 Gy. The real-time PCR and Western blot results showed no significant difference in the expression level of DNA repair-related genes between the 10 and 20 Gy groups, which may help to explain the behavioral results, i.e. DNA damage caused by 0-10 Gy exposure was appropriately repaired, however, damage induced by 20 Gy exceeded the body's maximum DSB repair ability. Ionizing radiation-induced cognitive impairments depend on the radiation dose, and more directly on the body's own ability to repair DNA DSBs via the NHEJ pathway.

Palmitic acid increases apoptosis of neural stem cells via activating c-Jun N-terminal kinase

Elevated plasma free fatty acid (FFA) level is common in many pathological conditions, including neurological disorders, and their deleterious effects on various cells have been well documented. However, it remains to be investigated whether elevated FFAs would have a direct effect on neural stem cells (NSCs). Here, we reported that palmitic acid (PA) impaired cell viability and increased apoptosis of NSCs significantly in a dose- and time-dependent manner. Increased protein levels of Bax and cleaved caspase 3 coupled with decreased expression of Bcl-2 were also observed in NSCs with increasing dose or time of PA treatment, whereas caspase 3 expression remained relatively unaltered. In parallel to this, the expression of phospho-c-Jun N-terminal kinase (p-JNK) in NSCs challenged with PA was increased significantly; however, JNK expression appeared stable. Remarkably, JNK inhibitor effectively reduced the apoptosis of NSCs induced by PA. The expression of phospho-p38 (p-p38), p38, phospho-extracellular regulated protein kinases 1/2 (p-EKR1/2) and EKR1/2 in NSCs was not affected by PA treatment. In consideration of the above, it is suggested that elevated plasma FFA level may induce apoptosis of NSCs in vivo, and that this might be one of possible underlying mechanisms for the cognitive disturbance in neurological disorders.

X-ray repair cross-complementing gene 1 Arg399Gln polymorphism and glioma risk among Asians: A meta-analysis based on 2 326 cases and 3 610 controls

OBJECTIVE:

Previous reports have demonstrated that X-ray repair cross-complementing gene 1 (XRCC1) Arg399Gln polymorphism is a possible risk factor for several cancers. Published data on the association of XRCC1 Arg399Gln polymorphism with glioma susceptibility have generated conflicting results. This study is designed to precisely estimate the relationship.

DATA RETRIEVAL:

A computer-based online retrieval of Medline, EMBASE, OVID, Sciencedirect, and Chinese National Knowledge Infrastructure was performed to search papers regarding association of XRCC1 Arg399Gln polymorphisms with glioma published up to April 2012.

SELECTION CRITERIA:

Two investigators selected data independently. Meta analysis was then performed for the selected studies using STATA 11.0 software after strict selection. Heterogeneity test, sensitivity analysis and publication bias assessments were then conducted.

MAIN OUTCOME MEASURES:

Association of XRCC1 Arg399Gln polymorphism with glioma risk.

RESULTS:

A total of nine case-controlled studies comprising 2 326 cases and 3 610 controls were selected for final analysis. The overall data failed to indicate a significant association of XRCC1 Arg399Gln polymorphism with glioma risk (Gln/Gln vs. Arg/Arg: odds ratio (OR) = 1.11; 95% confidence interval (CI) = 0.94–1.31; dominant model: OR = 1.06; 95%CI = 0.95–1.18; recessive model: OR = 1.04; 95%CI = 0.81–1.34). However, subgroup analysis regarding ethnicity showed an increased risk among Asians (Gln/Gln vs. Arg/Arg: OR = 1.70; 95%CI = 1.17–2.46; dominant model: OR = 1.40; 95%CI = 1.10–1.78; recessive model: OR = 1.46; 95%CI = 1.04–2.05) but not Caucasians or mixed ethnicities.

CONCLUSION:

XRCC1 Arg399Gln polymorphism might modify the susceptibility to glioma among Asians but not Caucasians. Further large and well-designed studies are needed to confirm this conclusion.

Early reduction of microglia activation by irradiation in a model of chronic glaucoma

Glaucoma is a neurodegenerative disease that results in the progressive decline and ultimate death of retinal ganglion cells (RGCs). While multiple risk factors are associated with glaucoma, the mechanisms leading to onset and progression of the disease remain unknown. Molecular analysis in various glaucoma models has revealed involvement of non-neuronal cell populations, including astrocytes, Mueller glia and microglia, at early stages of glaucoma. High-dose irradiation was reported to have a significant long-term protective effect in the DBA/2J (D2) mouse model of glaucoma, although the cellular and molecular basis for this effect remains unclear. In particular, the acute effects of irradiation on specific cell populations, including non-neuronal cells, in the D2 retina and nerve have not been assessed. Here we report that irradiation induces transient reduction in proliferating microglia within the optic nerve head and glial lamina within the first week post-irradiation. This was accompanied by reduced microglial activation, with no effect on astrocyte gliosis in those regions. At later stages we confirm that early high-dose irradiation of the mouse head results in improvement of axonal structural integrity and anterograde transport function, without reduction of intraocular pressure. Thus reduced microglial activation induced by irradiation at early stages is associated with reduced optic nerve and retinal neurodegeneration in the D2 mouse model of glaucoma.