Radiation-Induced Alterations in Mouse Brain Development Characterized by Magnetic Resonance Imaging

Sex chromosomes and hormones independently influence healthy brain development but act similarly after cranial radiation

The course of normal development and response to pathology are strongly influenced by biological sex. For instance, female childhood cancer survivors who have undergone cranial radiation therapy (CRT) tend to display more pronounced cognitive deficits than their male counterparts. Sex effects can be the result of sex chromosome complement (XX vs. XY) and/or gonadal hormone influence. The contributions of each can be separated using the four-core genotype mouse model (FCG), where sex chromosome complement and gonadal sex are decoupled. While studies of FCG mice have evaluated brain differences in adulthood, it is still unclear how sex chromosome and sex hormone effects emerge through development in both healthy and pathological contexts. Our study utilizes longitudinal MRI with the FCG model to investigate sex effects in healthy development and after CRT in wildtype and immune-modified Ccl2-knockout mice. Our findings in normally developing mice reveal a relatively prominent chromosome effect prepubertally, compared to sex hormone effects which largely emerge later. Spatially, sex chromosome and hormone influences were independent of one another. After CRT in Ccl2-knockout mice, both male chromosomes and male hormones similarly improved brain outcomes but did so more separately than in combination. Our findings highlight the crucial role of sex chromosomes in early development and identify roles for sex chromosomes and hormones after CRT-induced inflammation, highlighting the influences of biological sex in both normal brain development and pathology.

Imaging Assessment of Radiation Therapy-Related Normal Tissue Injury in Children: A PENTEC Visionary Statement

The Pediatric Normal Tissue Effects in the Clinic (PENTEC) consortium has made significant contributions to understanding and mitigating the adverse effects of childhood cancer therapy. This review addresses the role of diagnostic imaging in detecting, screening, and comprehending radiation therapy-related late effects in children, drawing insights from individual organ-specific PENTEC reports. We further explore how the development of imaging biomarkers for key organ systems, alongside technical advancements and translational imaging approaches, may enhance the systematic application of imaging evaluations in childhood cancer survivors. Moreover, the review critically examines knowledge gaps and identifies technical and practical limitations of existing imaging modalities in the pediatric population. Addressing these challenges may expand access to, minimize the risk of, and optimize the real-world application of, new imaging techniques. The PENTEC team envisions this document as a roadmap for the future development of imaging strategies in childhood cancer survivors, with the overarching goal of improving long-term health outcomes and quality of life for this vulnerable population.

A systematic review of normal tissue neurovascular unit damage following brain irradiation-Factors affecting damage severity and timing of effects

Background

Radiotherapy is key in the treatment of primary and secondary brain tumors. However, normal tissue is inevitably irradiated, causing toxicity and contributing to cognitive dysfunction. The relative importance of vascular damage to cognitive decline is poorly understood. Here, we systematically review the evidence for radiation-induced damage to the entire neurovascular unit (NVU), particularly focusing on establishing the factors that influence damage severity, and timing and duration of vascular effects relative to effects on neural tissue.

Methods

Using PubMed and Web of Science, we searched preclinical and clinical literature published between January 1, 1970 and December 1, 2022 and evaluated factors influencing NVU damage severity and timing of NVU effects resulting from ionizing radiation.

Results

Seventy-two rodents, 4 canines, 1 rabbit, and 5 human studies met inclusion criteria. Radiation increased blood-brain barrier (BBB) permeability, reduced endothelial cell number and extracellular matrix proteoglycans, reduced tight junction proteins, upregulated cellular adhesion molecule expression, reduced activity of glucose and BBB efflux transporters and activated glial cells. In the brain parenchyma, increased metalloproteinases 2 and 9 levels, demyelination, cell death, and inhibited differentiation were observed. Effects on the vasculature and neural compartment were observed across acute, delayed, and late timepoints, and damage extent was higher with low linear energy transfer radiation, higher doses, lower dose rates, broader beams, and in the presence of a tumor.

Conclusions

Irradiation of normal brain tissue leads to widespread and varied impacts on the NVU. Data indicate that vascular damage is in most cases an early effect that does not quickly resolve. More studies are needed to confirm sequence of damages, and mechanisms that lead to cognitive dysfunction.

Exercise promotes growth and rescues volume deficits in the hippocampus after cranial radiation in young mice

Human and animal studies suggest that exercise promotes healthy brain development and function, including promoting hippocampal growth. Childhood cancer survivors that have received cranial radiotherapy exhibit hippocampal volume deficits and are at risk of impaired cognitive function, thus they may benefit from regular exercise. While morphological changes induced by exercise have been characterized using magnetic resonance imaging (MRI) in humans and animal models, evaluation of changes across the brain through development and following cranial radiation is lacking. In this study, we used high-resolution longitudinal MRI through development to evaluate the effects of exercise in a pediatric mouse model of cranial radiation. Female mice received whole-brain radiation (7 Gy) or sham radiation (0 Gy) at an infant equivalent age (P16). One week after irradiation, mice were housed in either a regular cage or a cage equipped with a running wheel. In vivo MRI was performed prior to irradiation, and at three subsequent timepoints to evaluate the effects of radiation and exercise. We used a linear mixed-effects model to assess volumetric and cortical thickness changes. Exercise caused substantial increases in the volumes of certain brain regions, notably the hippocampus in both irradiated and nonirradiated mice. Volume increases exceeded the deficits induced by cranial irradiation. The effect of exercise and irradiation on subregional hippocampal volumes was also characterized. In addition, we characterized cortical thickness changes across development and found that it peaked between P23 and P43, depending on the region. Exercise also induced regional alterations in cortical thickness after 3 weeks of voluntary exercise, while irradiation did not substantially alter cortical thickness. Our results show that exercise has the potential to alter neuroanatomical outcomes in both irradiated and nonirradiated mice. This supports ongoing research exploring exercise as a strategy for improving neurocognitive development for children, particularly those treated with cranial radiotherapy.

Cross-translational models of late-onset cognitive sequelae and their treatment in pediatric brain tumor survivors

Pediatric brain tumor treatments have a high success rate, but survivors are at risk of cognitive sequelae that impact long-term quality of life. We summarize recent clinical and animal model research addressing pathogenesis or evaluating candidate interventions for treatment-induced cognitive sequelae. Assayed interventions encompass a broad range of approaches, including modifications to radiotherapy, modulation of immune response, prevention of treatment-induced cell loss or promotion of cell renewal, manipulation of neuronal signaling, and lifestyle/environmental adjustments. We further emphasize the potential of neuroimaging as a key component of cross-translation to contextualize laboratory research within broader clinical findings. This cross-translational approach has the potential to accelerate discovery to improve pediatric cancer survivors' long-term quality of life.

Protection from radiation-induced neuroanatomical deficits by CCL2-deficiency is dependent on sex

PURPOSE

Cranial radiation therapy for the treatment of paediatric brain tumours results in changes to brain development that are detectable with magnetic resonance imaging (MRI). We have previously demonstrated similar structural changes in both humans and mice. The goal of the current study was to examine the role of inflammation in this response. Since neuroanatomical volume deficits in paediatric survivors are more pronounced in females, we also evaluated possible dependence on sex.

EXPERIMENTAL DESIGN

Male mice deficient in the C-C chemokine ligand 2 gene (Ccl2; previously Mcp-1) have been shown by others to have a muted neuroinflammatory response after irradiation. We irradiated Ccl2^-/- (HOM; females[f]=12, males[m]=13), Ccl2^+/- (HET; f=13, m=16), and Ccl2^+/+ (WT; f=11, m=13) mice with a whole brain dose of 7 Gy during infancy. Control mice (with approximately equal groups sizes) were anaesthetized but not irradiated. In vivo MR images were acquired at 4 time points up to 3 months following irradiation, and deformation-based morphometry was used to identify volume differences.

RESULTS

Irradiation of WT mice resulted in a deficit in neuroanatomical growth with limited sex dependence. HOM and HET males were significantly protected from this radiation-induced damage, while HOM and HET females were not. We conclude that interventions aimed at mitigating the effects of cranial radiation therapy in paediatric cancer survivors by modulating inflammatory response will need to consider patient sex.

Multiple Irradiation Affects Cellular and Extracellular Components of the Mouse Brain Tissue and Adhesion and Proliferation of Glioblastoma Cells in Experimental System In Vivo

Intensive adjuvant radiotherapy (RT) is a standard treatment for glioblastoma multiforme (GBM) patients; however, its effect on the normal brain tissue remains unclear. Here, we investigated the short-term effects of multiple irradiation on the cellular and extracellular glycosylated components of normal brain tissue and their functional significance. Triple irradiation (7 Gy*3 days) of C57Bl/6 mouse brain inhibited the viability, proliferation and biosynthetic activity of normal glial cells, resulting in a fast brain-zone-dependent deregulation of the expression of proteoglycans (PGs) (decorin, biglycan, versican, brevican and CD44). Complex time-point-specific (24–72 h) changes in decorin and brevican protein and chondroitin sulfate (CS) and heparan sulfate (HS) content suggested deterioration of the PGs glycosylation in irradiated brain tissue, while the transcriptional activity of HS-biosynthetic system remained unchanged. The primary glial cultures and organotypic slices from triple-irradiated brain tissue were more susceptible to GBM U87 cells’ adhesion and proliferation in co-culture systems in vitro and ex vivo. In summary, multiple irradiation affects glycosylated components of normal brain extracellular matrix (ECM) through inhibition of the functional activity of normal glial cells. The changed content and pattern of PGs and GAGs in irradiated brain tissues are accompanied by the increased adhesion and proliferation of GBM cells, suggesting a novel molecular mechanism of negative side-effects of anti-GBM radiotherapy.

Spatiotemporal Mapping of Early Volume Loss in the Mouse Brain after Cranial Irradiation

Sequelae after pediatric cranial radiotherapy (CRT) result in long-term changes in brain structure. While past evidence indicates regional differences in brain volume change, it remains unclear how these manifest in the time course of change after CRT. In this study, we spatiotemporally characterized volume losses induced by cranial irradiation in a mouse model, with a dense sampling of measurements over the first week postirradiation. Wild-type mice received whole-brain irradiation (7 Gy) or sham irradiation (0 Gy) at 16 days of age. In vivo magnetic resonance imaging was performed at one time point before, and 2-4 time points postirradiation in each mouse, with a particular focus on sampling during the first week after cranial irradiation. Volume changes across the brain were measured, and the degree and timing of volume loss were quantified across structures from a predefined atlas. Volume measurements across the brain after cranial irradiation revealed a ∼2-day delay in which volume is not significantly altered, after which time volume change proceeds over the course of four days. Volume losses were 3% larger and emerged 40% slower in white matter than in gray matter. Large volume loss was also observed in the ventricles. Differences in the timing and magnitude of volume change between gray and white matter after cranial irradiation were observed. These results suggest differences in the mechanism and/or kinetics underlying the associated radio-response, which may have implications in development.

Metformin effects on brain development following cranial irradiation in a mouse model

BACKGROUND

Cranial radiation therapy (CRT) is a mainstay of treatment for malignant pediatric brain tumors and high-risk leukemia. Although CRT improves survival, it has been shown to disrupt normal brain development and result in cognitive impairments in cancer survivors. Animal studies suggest that there is potential to promote brain recovery after injury using metformin. Our aim was to evaluate whether metformin can restore brain volume outcomes in a mouse model of CRT.

METHODS

C57BL/6J mice were irradiated with a whole-brain radiation dose of 7 Gy during infancy. Two weeks of metformin treatment started either on the day of or 3 days after irradiation. In vivo magnetic resonance imaging was performed prior to irradiation and at 3 subsequent time points to evaluate the effects of radiation and metformin on brain development.

RESULTS

Widespread volume loss in the irradiated brain appeared within 1 week of irradiation with limited subsequent recovery in volume outcomes. In many structures, metformin administration starting on the day of irradiation exacerbated radiation-induced injury, particularly in male mice. Metformin treatment starting 3 days after irradiation improved brain volume outcomes in subcortical regions, the olfactory bulbs, and structures of the brainstem and cerebellum.

CONCLUSIONS

Our results show that metformin treatment has the potential to improve neuroanatomical outcomes after CRT. However, both timing of metformin administration and subject sex affect structure outcomes, and metformin may also be deleterious. Our results highlight important considerations in determining the potential benefits of metformin treatment after CRT and emphasize the need for caution in repurposing metformin in clinical studies.

Noninvasive Assessment of Neurodevelopmental Disorders after In Utero Irradiation in Mice: An In Vivo Anatomical and Diffusion MRI Study

In utero exposure to ionizing radiation can lead to cerebral alterations during adulthood. Using anatomical magnetic resonance imaging (MRI), it is possible to assess radiation-induced structural brain damage noninvasively. However, little is currently known about microstructure alterations in brain tissue. Therefore, the goal of this study was to establish, based on an original and robust pipeline of MRI image analysis, whether the long-term effects of in utero radiation exposure on brain tissue microstructure could be detected noninvasively. Pregnant C57BL/6N mice received a single dose of 1 Gy on gestation day 14.5, which led to behavioral impairments in adults. At 3 months old, in vivo MRI data were acquired from in utero irradiated and nonirradiated male mice. An MRI protocol was designed to assess the effects of radiation on the parameters of brain volume, non-Gaussian diffusion (ADC0, kurtosis and signature index) and anisotropic diffusion (fractional anisotropy and mean, axial, radial diffusivities and anisotropic signature index) in 10 key cerebral structures defined using an in-house atlas of the mouse brain. Based on the relative amplitude of these anatomical and microstructural changes, maps of the radiosensitivity of the brain to in utero irradiation were created. We observed microcephaly in irradiated mice with noticeably larger volume changes in the cortex and the corpus callosum. We also observed significantly lower ADC0, anisotropy fraction (sFA), radial diffusivity (sRD), as well as signature index (S-index and SI3) values, which are original markers sensitive to tissue microstructure alterations. All these changes together are in favor of a decreased cellular "imprint" and in some regions a reduced density in myelinated axons. A reduction in the number and complexity of myelinated axons was further revealed by myelin basic protein immunostaining. Combining anatomical and diffusion MRI is a promising approach to noninvasively investigate the radiosensitivity of local brain areas in adult mice after in utero irradiation in terms of microstructure.

Divergent effects of irradiation on brain cortical morphology in patients with nasopharyngeal carcinoma: one-year follow-up study using structural magnetic resonance imaging

Background

Increasing evidence indicates that radiotherapy (RT)-induced brain cortical deficits may play a critical role in developing radiation encephalopathy in patients with nasopharyngeal carcinoma (NPC). However, the evolutional processes of RT-induced cortical injury have not been sufficiently investigated. This study investigates RT-induced effects on cortical morphology using longitudinal structural magnetic resonance imaging (MRI) in NPC patients.

Methods

Using MRI-based morphometry with surface-based measures, we evaluated the longitudinal alterations of cortical volume (CV), cortical thickness (CT), and cortical surface area (CSA) in 104 NPC patients at pre-RT (n=104), within 3 months post-RT (n=92), 6 months post-RT (n=71), and 9-12 months post-RT (n=52). Twenty healthy controls were also evaluated in parallel. Linear mixed models were used to investigate the trajectories of RT-related changes in cortical brain morphology and its association with irradiation dose, with healthy controls data being used to construct a normal age-related benchmark. The level of statistical significance was set at P<0.05, corrected for multiple comparisons.

Results

The results showed that RT-related longitudinal alterations in cortical morphology underwent two diverse patterns during the first year of follow up in NPC patients. The temporal cortices (including the bilateral superior temporal gyrus, middle temporal gyrus, temporal pole, parahippocampal and fusiform gyrus, and the right inferior temporal and right transverse temporal gyrus), the basal occipital cortices (the right lingual gyrus and lateral occipital gyrus), and the basal frontal cortices (the right lateral orbitofrontal gyrus) showed time-dependent attenuation in cortical morphology indices. Furthermore, these effects on multiple cortices were dose-dependent, suggesting they were RT-associated. In contrast, in the left rostral middle frontal gyrus, there was a time-dependent increase in CT.

Conclusions

Our preliminary findings revealed divergent effects of irradiation on cortical brain morphology. These results contribute to a more comprehensive understanding of the underlying neural mechanisms of irradiation-related neurotoxic effects on cortical brain morphology and will help guide the investigation of critically neuroprotective strategies.

Multi-modality bedding platform for combined imaging and irradiation of mice

Preclinical imaging and irradiation yields valuable insights into clinically relevant research topics. While complementary imaging methods such as computed tomography (CT), magnetic resonance imaging (MRI), and positron emission tomography (PET) can be combined within single devices, this is technically demanding and cost-intensive. Similarly, bedding and setup solutions are often specific to certain devices and research questions. We present a bedding platform for mice that is compatible with various preclinical imaging modalities (combined PET/MRI, cone beam CT) and irradiation with photons and protons. It consists of a 3D-printed bedding unit (acrylonitrile butadiene styrene, ABS) holding the animal and features an inhalation anesthesia mask, jaw fixation, ear pins, and immobilization for the hind leg. It can be embedded on mounting adaptors for multi-modal imaging and into a transport box (polymethyl methacrylate, PMMA) for experiments outside dedicated animal facilities while maintaining the animal's hygiene status. A vital support unit provides heating, inhalation anesthesia, and a respiration monitor. We dosimetrically evaluated used materials in order to assess their interaction with incident irradiation. Proof-of-concept multi-modal imaging protocols were used on phantoms and mice. The measured attenuation of the bedding unit for 40/60/80/200 kV X-rays was less than 3%. The measured stopping-power-ratio of ABS was 0.951, the combined water-equivalent thickness of bedding unit and transport box was 4.2 mm for proton energies of 150 MeV and 200 MeV. Proof-of-concept imaging showed no loss of image quality. Imaging data of individual mice from different imaging modalities could be aligned rigidly. The presented bed aims to provide a platform for experiments related to both multi-modal imaging and irradiation, thus offering the possibility for image-guided irradiation which relies on precise imaging and positioning. The usage as a self-contained, stand-alone unit outside dedicated animal facilities represents an advantage over setups designed for specific devices.

The Acute and Early Effects of Whole-Brain Irradiation on Glial Activation, Brain Metabolism, and Behavior: a Positron Emission Tomography Study

Purpose

Radiotherapy is a frequently applied treatment modality for brain tumors. Concomitant irradiation of normal brain tissue can induce various physiological responses. The aim of this study was to investigate whether acute and early-delayed effects of brain irradiation on glial activation and brain metabolism can be detected with positron emission tomography (PET) and whether these effects are correlated with behavioral changes.

Procedures

Rats underwent 0-, 10-, or 25-Gy whole-brain irradiation. At 3 and 31 days post irradiation, 1-(2-chlorophenyl)-N-[¹¹C]methyl-(1-methylpropyl)-3-isoquinoline carboxamide ([¹¹C]PK11195) and 2-deoxy-2-[¹⁸F]fluoro-d-glucose ([¹⁸F]FDG) PET scans were acquired to detect changes in glial activation (neuroinflammation) and glucose metabolism, respectively. The open-field test (OFT) was performed on days 6 and 27 to assess behavioral changes.

Results

Twenty-five-gray-irradiated rats showed higher [¹¹C]PK11195 uptake in most brain regions than controls on day 3 (striatum, hypothalamus, accumbens, septum p < 0.05), although some brain regions had lower uptake (cerebellum, parietal association/retrosplenial visual cortex, frontal association/motor cortex, somatosensory cortex, p < 0.05). On day 31, several brain regions in 25-Gy-irradiated rats still showed significantly higher [¹¹C]PK11195 uptake than controls and 10-Gy-irradiated group (p < 0.05). Within-group analysis showed that [¹¹C]PK11195 uptake in individual brain regions of 25-Gy treated rats remained stable or slightly increased between days 3 and 31. In contrast, a significant reduction (p < 0.05) in tracer uptake between days 3 and 31 was found in all brain areas of controls and 10-Gy-irradiated animals. Moreover, 10-Gy treatment led to a significantly higher [¹⁸F]FDG uptake on day 3 (p < 0.05). [¹⁸F]FDG uptake decreased between days 3 and 31 in all groups; no significant differences between groups were observed anymore on day 31, except for increased uptake in the hypothalamus in the 10-Gy group. The OFT did not show any significant differences between groups.

Conclusions

Non-invasive PET imaging indicated that brain irradiation induces neuroinflammation and a metabolic flare, without causing acute or early-delayed behavioral changes.

Electronic supplementary material

The online version of this article (10.1007/s11307-020-01483-y) contains supplementary material, which is available to authorized users.

Radiation-induced hippocampal atrophy in patients with nasopharyngeal carcinoma early after radiotherapy: a longitudinal MR-based hippocampal subfield analysis

Increasing evidence indicates that radiation-induced injury to the hippocampus may play a critical role in neurocognitive dysfunction in patients with nasopharyngeal carcinoma (NPC). However, few studies have assessed RT-induced hippocampal structural alterations in these patients early after radiotherapy (RT). In this study, 58 NPC patients were longitudinally followed up prior to treatment initiation as well as 3 and 6 months after RT, respectively. Twenty comparable normal controls were recruited and followed up in parallel. A novel magnetic resonance imaging (MRI)-based automated method was used to label hippocampal subfields. The linear mixed model was employed to evaluate longitudinal changes in the volumes of the whole hippocampus and seven hippocampal subfields. Time-dependent volume reduction was observed in the bilateral hippocampus, as well as in the bilateral granule cell layer (GCL), bilateral cornu ammonis 1 (CA1), bilateral molecular layer (ML), and bilateral subiculum (SUB) in NPC patients, but not in controls. Moreover, volume deficits in the bilateral hippocampus, bilateral GCL, and right ML showed dose-dependent patterns, and high volume losses in the bilateral hippocampus, bilateral GCL, left SUB, and right ML were associated with a rapid decline in cognitive function. Our findings demonstrated that the hippocampal subfields were selectively injured by irradiation-related early neurotoxic effects, which might account for cognitive impairment in NPC patients at an early stage after RT. Further, structural MRI could serve as a potential noninvasive imaging biomarker for the early detection of radiation effects on the hippocampus in NPC patients after RT.

Evaluation of acute esophageal radiation-induced damage using magnetic resonance imaging: a feasibility study in mice

BACKGROUND

Thoracic and head and neck cancer radiation therapy (RT) can cause damage to nearby healthy organs such as the esophagus, causing acute radiation-induced esophageal damage (ARIED). A non-invasive method to detect and monitor ARIED can facilitate optimizing RT to avoid ARIED while improving local tumor control. Current clinical guidelines are limited to scoring the esophageal damage based on the symptoms of patients. Magnetic resonance imaging (MRI) is a non-invasive imaging modality that may potentially visualize radiation-induced organ damage. We investigated the feasibility of using T2-weighted MRI to detect and monitor ARIED using a two-phased study in mice.

METHODS

The first phase aimed to establish the optimal dose level at which ARIED is inducible and to determine the time points where ARIED is detectable. Twenty four mice received a single dose delivery of 20 and 40 Gy at proximal and distal spots of 10.0 mm (in diameter) on the esophagus. Mice underwent MRI and histopathology analysis with esophageal resection at two, three, and 4 weeks post-irradiation, or earlier in case mice had to be euthanized due to humane endpoints. In the second phase, 32 mice received a 40 Gy single dose and were studied at two, three, and 7 days post-irradiation. We detected ARIED as a change in signal intensity of the MRI images. We measured the width of the hyperintense area around the esophagus in all mice that underwent MRI prior to and after irradiation. We conducted a blind qualitative comparison between MRI findings and histopathology as the gold standard.

RESULTS/CONCLUSIONS

A dose of 40 Gy was needed to induce substantial ARIED. MRI detected ARIED as high signal intensity, visible from 2 days post-irradiation. Quantitative MRI analysis showed that the hyperintense area around the esophagus with severe ARIED was 1.41 mm wider than with no damage and MRI-only mice. The overall sensitivity and specificity were 56 and 43% respectively to detect any form of ARIED. However, in this study MRI correctly detected 100% of severe ARIED cases. Our two-phased preclinical study showed that MRI has the potential to detect ARIED as a change in signal intensity and width of enhancement around the esophagus.

Aberrant Brain Activity at Early Delay Stage Post-radiotherapy as a Biomarker for Predicting Neurocognitive Dysfunction Late-Delayed in Patients With Nasopharyngeal Carcinoma

Background: Increasing evidence indicates that early radiation-induced subtle cerebral changes may be the precursors to permanent brain dysfunction at the late-delayed (LDS) post-radiotherapy (RT) stage. In this study, we aim to track the RT-related longitudinal brain activity in nasopharyngeal carcinoma (NPC) patients and to determine whether early abnormal brain activity can predict late neurocognitive dysfunction after RT. Methods: Thirty-three NPC patients were finally included and longitudinally followed up at the following time points: prior to treatment initiation, early-delayed stage (EDS, 1-3 months), and LDS (six months) after RT. Fifteen comparable healthy controls (HCs) were finally included and followed up in parallel. Montreal Cognitive Assessment (MoCA) was used to assess the general cognitive function. Brain activity was recorded via resting-state fMRI and regional homogeneity (ReHo). A whole-brain voxel-wise-based one-way repeated-measure analysis of variance (ANOVA) was conducted to evaluate the longitudinal ReHo changes among the three time points for NPC patients and HCs, respectively. Results were reported at the significant level of a threshold of two-tailed voxel-wise P < 0.01 and cluster level P < 0.05 with Gaussian Random Field (GRF) correction. Finally, the efficacies of the aberrant ReHo at EDS for predicting the cognitive impairment at LDS in NPC patients were evaluated. Results: Significant differences were detected in ReHo among the three time points in NPC patients but not in HCs. Aberrant ReHo was distributed in the bilateral cerebellum, the right temporal lobe, and the left insular areas, which showed different dynamic changes patterns over time. Logistic regression model combining the mean ReHo, age, and irradiation dose on the bilateral temporal lobe had the highest diagnostic efficiency according to the area under the curve (AUC) score (AUC = 0.752, P = 0.023). Conclusions: The post-RT brain activity revealed by ReHo in NPC patients was dynamic, complex, and multifactorial. Furthermore, the combination of the aberrant ReHo at EDS, age, and irradiation dose may serve as a potential biomarker of the RT-induced cognitive impairments at LDS.

Human Mesenchymal Stem Cells Prevent Neurological Complications of Radiotherapy

Radiotherapy is a highly effective tool for the treatment of brain cancer. However, radiation also causes detrimental effects in the healthy tissue, leading to neurocognitive sequelae that compromise the quality of life of brain cancer patients. Despite the recognition of this serious complication, no satisfactory solutions exist at present. Here we investigated the effects of intranasal administration of human mesenchymal stem cells (hMSCs) as a neuroprotective strategy for cranial radiation in mice. Our results demonstrated that intranasally delivered hMSCs promote radiation-induced brain injury repair, improving neurological function. This intervention confers protection against inflammation, oxidative stress, and neuronal loss. hMSC administration reduces persistent activation of damage-induced c-AMP response element-binding signaling in irradiated brains. Furthermore, hMSC treatment did not compromise the survival of glioma-bearing mice. Our findings encourage the therapeutic use of hMSCs as a non-invasive approach to prevent neurological complications of radiotherapy, improving the quality of life of brain tumor patients.

Changes in cortical thickness and volume after cranial radiation treatment: A systematic review

Cognitive decline has a clear impact on quality of life in patients who have received cranial radiation treatment. The pathophysiological process is most likely multifactorial, with a possible role for decreased cortical thickness and volume. As radiotherapy treatment systems are becoming more sophisticated, precise sparing of vulnerable regions and tissue is possible. This allows radiation oncologists to make treatment more patient-tailored. A systematic search was performed to collect and review all available evidence regarding the effect of cranial radiation treatment on cortical thickness and volume. We searched the Pubmed, Embase and Cochrane databases, with an additional reference check in the Scopus database. Studies that examined cortical changes on MRI within patients as well as between treated and non-treated patients were included. The quality of the studies was assessed with a checklist specially designed for this review. No meta-analysis was performed due to the lack of randomised trials. Out of 1915 publications twenty-one papers were selected, of which fifteen observed cortical changes after radiation therapy. Two papers reported radiation-dependent decrease in cortical thickness within patients one year after radiation treatment, suggesting a clear relation between the two. However, study quality was considered mostly suboptimal, and there was great inhomogeneity between the included studies. This means that, although there has been increasing interest in the effects of radiation treatment on cortex morphology, no reliable conclusion can be drawn based on the currently available evidence. This calls for more research, preferably with a sufficiently large patient population, and adequate methodology.

Altered brain morphology after focal radiation reveals impact of off-target effects: implications for white matter development and neurogenesis

Background

Children with brain tumors treated with cranial radiation therapy (RT) often exhibit cognitive late effects, commonly associated with reduced white matter (WM) volume and decreased neurogenesis. The impact of radiation damage in particular regions or tissues on brain development as a whole has not been elucidated.

Methods

We delivered whole-brain or focal radiation (8 Gy single dose) to infant mice. Focal treatments targeted white matter (anterior commissure), neuronal (olfactory bulbs), or neurogenic (subventricular zone) regions. High-resolution ex vivo MRI was used to assess radiation-induced volume differences. Immunohistochemistry for myelin basic protein and doublecortin was performed to assess associated cellular changes within white matter and related to neurogenesis, respectively.

Results

Both whole-brain and focal RT in infancy resulted in volume deficits in young adulthood, with whole-brain RT resulting in the largest deficits. RT of the anterior commissure, surprisingly, showed no impact on its volume or on brain development as a whole. In contrast, RT of the olfactory bulbs resulted in off-target volume reduction in the anterior commissure and decreased subventricular zone neurogenesis. RT of the subventricular zone likewise produced volume deficits in both the olfactory bulbs and the anterior commissure. Similar off-target effects were found in the corpus callosum and parietal cortex.

Conclusions

Our results demonstrate that radiation damage locally can have important off-target consequences for brain development. These data suggest that WM may be less radiosensitive than volume change alone would indicate and have implications for region-sparing radiation treatments aimed at reducing cognitive late effects.

p53 Loss Mitigates Early Volume Deficits in the Brains of Irradiated Young Mice

PURPOSE

Pediatric cranial radiation therapy results in lasting changes in brain structure. Though different facets of radiation response have been characterized, the relative contributions of each to altered development is unclear. We sought to determine the role of radiation-induced programmed cell death, as mediated by the Trp53 (p53) gene, on neuroanatomic development.

METHODS AND MATERIALS

Mice having a conditional knockout of p53 (p53KO) or wildtype p53 (WT) were irradiated with a whole-brain dose of 7 Gy (IR; n = 30) or 0 Gy (sham; n = 28) at 16 days of age. In vivo magnetic resonance imaging was performed before irradiation and at 4 time points after irradiation, until 3 months posttreatment, followed by ex vivo magnetic resonance imaging and immunohistochemistry. The role of p53 in development was assessed at 6 weeks of age in another group of untreated mice (n = 37).

RESULTS

Neuroanatomic development in p53KO mice was normal. After cranial irradiation, alterations in neuroanatomy were detectable in WT mice and emerged through 2 stages: an early volume loss within 1 week and decreased growth through development. In many structures, the early volume loss was partially mitigated by p53KO. However, p53KO had a neutral or negative impact on growth; thus, p53KO did not widely improve volume at endpoint. Partial volume recovery was observed in the dentate gyrus and olfactory bulbs of p53KO-IR mice, with corresponding increases in neurogenesis compared with WT-IR mice.

CONCLUSIONS

Although p53 is known to play an important role in mediating radiation-induced apoptosis, this is the first study to look at the cumulative effect of p53KO through development after cranial irradiation across the entire brain. It is clear that apoptosis plays an important role in volume loss early after radiation therapy. This early preservation alone was insufficient to normalize brain development on the whole, but regions reliant on neurogenesis exhibited a significant benefit.

Association of Neuronal Injury in the Genu and Body of Corpus Callosum After Cranial Irradiation in Children With Impaired Cognitive Control: A Prospective Study

PURPOSE

Brain radiation is associated with functional deficits in children. The purpose of this study was to examine white matter integrity as measured by diffusion tensor imaging and associations with region-specific radiation dose and neuropsychological functioning in children treated with cranial irradiation.

METHODS AND MATERIALS

A total of 20 patients and 55 age- and sex-matched controls were included in the present study. Diffusion tensor imaging and neuropsychological assessments were conducted at baseline and 6, 15, and 27 months after treatment. The neuropsychological assessment included motor dexterity, working memory, and processing speed. White matter regions were contoured, and the apparent diffusion coefficient (ADC) and fractional anisotropy (FA) were recorded for each participant. Linear mixed effects regression models were used to prospectively compare the associations among ADC, FA, radiation dose to contoured structures, and performance on the neuropsychological assessments over time.

RESULTS

The mean prescription dose was 44 Gy (range 12-54). Across visits, compared with the controls, the patients showed a significantly increased ADC across all selected regions and alterations in FA in the dorsal midbrain and corpus callosum (genu, splenium, body). An increased radiation dose to the genu and body of the corpus callosum was associated with alterations in ADC and FA and reduced neuropsychological performance, most notably motor speed and processing.

CONCLUSIONS

These prospective data suggest that subcortical white matter, especially the genu and body of the corpus callosum, could be regions with increased susceptibility to radiation-induced injury, with implications for cognitive function.

MRI to Assess Neurological Function

This article describes a detailed set of protocols for mouse brain imaging using MRI. We focus primarily on measuring changes in neuroanatomy, and provide both instructions for mouse preparation and details on image acquisition, image processing, and statistics. Practical details as well as theoretical considerations are provided. © 2018 by John Wiley & Sons, Inc.

Longitudinal brain structural alterations in patients with nasopharyngeal carcinoma early after radiotherapy

Background and purpose

To investigate effects of radiotherapy on normal brain tissue using in vivo neuroimaging in patients with nasopharyngeal carcinoma (NPC).

Methods and materials

We used longitudinal MRI to monitor structural brain changes during standard radiotherapy in patients newly diagnosed with NPC. We assessed volumetric measures in 63 patients at 2–3 time points before and after radiotherapy, with 20 NPC-free participants as normal controls. Images were processed using validated software (FreeSurfer). Automated results were inspected visually for accuracy. We examined changes in volume of the whole brain, gray matter, white matter, and ventricles, as well as in cerebral volumes partitioned into temporal, frontal, parietal, and occipital lobes. A linear mixed model was used to evaluate longitudinal changes in these measurements. Statistical significance was evaluated at p < 0.05, which was corrected for multiple comparisons.

Results

Volumes of the gray matter, and bilateral temporal lobes decreased in a time-dependent manner, whereas ventricle volume showed a time-dependent increase after radiotherapy. No volume changes were detected in NPC patients before radiotherapy when compared normal controls. No volume changes were detected in the subcohort of patients after completion of induction chemotherapy but prior to initiation of radiotherapy. Changes of bilateral temporal lobe volume correlated with irradiation dose in this region. Expansion of the ventricles correlated with a reduction in cognition assessment.

Conclusions

We detected significant and progressive radiotherapy-associated structural changes in the brains of patients with NPC who were treated with standard radiotherapy, especially in the bilateral temporal lobe in which the effect was dose-dependent. Expansion of the ventricles can serve as an imaging marker for treatment-related reduction in cognitive function. Future studies with longer follow-ups are needed to evaluate morphometric changes long-term after radiotherapy.

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Time-dependent ventricle expansion in NPC patients post radiotherapy (RT)

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Time-dependent total gray matter and bilateral temporal lobe atrophy in NPC post-RT

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The bilateral temporal lobe had a pattern of dose-dependent atrophy.

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Longitudinal dilation of the ventricles correlated with reduction of cognition.

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Moreover, these findings cannot be explained by chemotherapy.

Repairing the brain with physical exercise: Cortical thickness and brain volume increases in long-term pediatric brain tumor survivors in response to a structured exercise intervention

There is growing evidence that exercise induced experience dependent plasticity may foster structural and functional recovery following brain injury. We examined the efficacy of exercise training for neural and cognitive recovery in long-term pediatric brain tumor survivors treated with radiation.

We conducted a controlled clinical trial with crossover of exercise training (vs. no training) in a volunteer sample of 28 children treated with cranial radiation for brain tumors (mean age = 11.5 yrs.; mean time since diagnosis = 5.7 yrs). The endpoints were anatomical T1 MRI data and multiple behavioral outcomes presenting a broader analysis of structural MRI data across the entire brain. This included an analysis of changes in cortical thickness and brain volume using automated, user unbiased approaches. A series of general linear mixed effects models evaluating the effects of exercise training on cortical thickness were performed in a voxel and vertex-wise manner, as well as for specific regions of interest. In exploratory analyses, we evaluated the relationship between changes in cortical thickness after exercise with multiple behavioral outcomes, as well as the relation of these measures at baseline.

Exercise was associated with increases in cortical thickness within the right pre and postcentral gyri. Other notable areas of increased thickness related to training were present in the left pre and postcentral gyri, left temporal pole, left superior temporal gyrus, and left parahippocampal gyrus. Further, we observed that compared to a separate cohort of healthy children, participants displayed multiple areas with a significantly thinner cortex prior to training and fewer differences following training, indicating amelioration of anatomical deficits. Partial least squares analysis (PLS) revealed specific patterns of relations between cortical thickness and various behavioral outcomes both after training and at baseline.

Overall, our results indicate that exercise training in pediatric brain tumor patients treated with radiation has a beneficial impact on brain structure. We argue that exercise training should be incorporated into the development of neuro-rehabilitative treatments for long-term pediatric brain tumor survivors and other populations with acquired brain injury. (ClinicalTrials.gov, NCT01944761)

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Exercise training in pediatric brain tumor patients treated with radiation results in changes in brain structure

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Exercise was associated with increased cortical thickness in several areas including motor and somatosensory cortex

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Fewer differences between patients and healthy controls in cortical thickness were seen following exercise training

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Specific patterns of relations between cortical thickness and behavior at a baseline and after exercise training were seen

Structural MRI research in patients with nasopharyngeal carcinoma following radiotherapy: A DTI and VBM study

The aim of the present study was to investigate the microstructural characteristics of the brain lobes following radiotherapy (RT) for patients with nasopharyngeal carcinoma (NPC) at distinct times. Diffusion tensor imaging (DTI) and 3D-T1-weighted imaging was performed in 70 age- and sex-matched subjects, 24 of whom were pre-treatment patients. The patients were divided into three groups, according to the time following completion of RT. Fractional anisotropy (FA) and gray matter (GM) volume were determined. The DTI data were analyzed using tract-based spatial statistics and the GM volume was analyzed using voxel-based morphometry (VBM). Compared with the pre-RT group, the mean FA values in the left parietal lobe white matter (WM) and right cerebellum decreased significantly in the post-RT 0-6 month group (P<0.05). In addition, the mean FA values in the right parietal lobe WM decreased significantly in the post-RT 6-12 month group (P<0.05), compared with the pre-RT group. The FA level in the right temporal lobe remained significantly decreased, compared with that in the pre-RT group (P<0.05) for 1 year after RT. Furthermore, compared with pre-RT group, the GM volume in the bilateral frontal lobe, right occipital lobe, left parietal lobe, right temporal lobe and left cerebellum decreased significantly in the post-RT 0-6 month group (P<0.05), and in the bilateral temporal lobe, parietal lobe, right frontal lobe and left cerebellum, the GM volume decreased significantly in the post-RT 6-12 month group (P<0.05). The GM volume in the right temporal lobe, bilateral frontal lobe and bilateral cerebellum remained significantly decreased compared with that in the pre-RT group (P<0.05) for 1 year after RT. A combination of DTI and VBM may be used to determine radiation-induced brain injury in patients treated for NPC.

Brain structure, working memory and response inhibition in childhood leukemia survivors

INTRODUCTION

Survival rates for children with acute lymphoblastic leukemia (ALL) approach 95%. At the same time, there is growing concern that chemotherapy causes alterations in brain development and cognitive abilities. We performed MRI measurements of white and gray matter volume to explore how variation in brain structure may be related to cognitive abilities in ALL survivors and healthy controls.

METHODS

The sample included 24 male ALL survivors who had completed contemporary treatment 3-11 years prior, and 21 age- and sex-matched controls. Participants were between 8 and 18 years old. Working memory and motor response inhibition were measured with the N-Back and Stop Signal Tasks (SST), respectively. Participants underwent 3T structural MRI to assess white and gray matter volumes overall, lobe-wise, and in cortical and atlas-identified subcortical structures. Mental health was assessed with the Child Behavioral Checklist.

RESULTS

ALL survivors performed more poorly on measures of working memory and response inhibition than controls. Frontal and parietal white matter, temporal and occipital gray matter volume, and volumes of subcortical white and gray matter structures were significantly reduced in ALL survivors compared with controls. Significant structure-function correlations were observed between working memory performance and volume of the amygdala, thalamus, striatum, and corpus callosum. Response inhibition was correlated with frontal white matter volume. No differences were found in psychopathology.

CONCLUSIONS

Compared with controls, a reduction in volume across brain regions and tissue types, was detectable in ALL survivors years after completion of therapy. These structural alterations were correlated with neurocognitive performance, particularly in working memory. Confirming these observations in a larger, more representative sample of the population is necessary. Additionally, establishing the time course of these changes-and the treatment, genetic, and environmental factors that influence them-may provide opportunities to identify at-risk patients, inform the design of treatment modifications, and minimize adverse cognitive outcomes.

Persistent Impact of In utero Irradiation on Mouse Brain Structure and Function Characterized by MR Imaging and Behavioral Analysis

Prenatal irradiation is known to perturb brain development. Epidemiological studies revealed that radiation exposure during weeks 8-15 of pregnancy was associated with an increased occurrence of mental disability and microcephaly. Such neurological deficits were reproduced in animal models, in which rodent behavioral testing is an often used tool to evaluate radiation-induced defective brain functionality. However, up to now, animal studies suggested a threshold dose of around 0.30 Gray (Gy) below which no behavioral alterations can be observed, while human studies hinted at late defects after exposure to doses as low as 0.10 Gy. Here, we acutely irradiated pregnant mice at embryonic day 11 with doses ranging from 0.10 to 1.00 Gy. A thorough investigation of the dose-response relationship of altered brain function and architecture following in utero irradiation was achieved using a behavioral test battery and volumetric 3D T2-weighted magnetic resonance imaging (MRI). We found dose-dependent changes in cage activity, social behavior, anxiety-related exploration, and spatio-cognitive performance. Although behavioral alterations in low-dose exposed animals were mild, we did unveil that both emotionality and higher cognitive abilities were affected in mice exposed to ≥0.10 Gy. Microcephaly was apparent from 0.33 Gy onwards and accompanied by deviations in regional brain volumes as compared to controls. Of note, total brain volume and the relative volume of the ventricles, frontal and posterior cerebral cortex, cerebellum, and striatum were most strongly correlated to altered behavioral parameters. Taken together, we present conclusive evidence for persistent low-dose effects after prenatal irradiation in mice and provide a better understanding of the correlation between their brain size and performance in behavioral tests.

Generation and Disease Model Relevance of a Manganese Enhanced Magnetic Resonance Imaging-Based NOD/scid-IL-2Rγc(null) Mouse Brain Atlas

Strain specific mouse brain magnetic resonance imaging (MRI) atlases provide coordinate space linked anatomical registration. This allows longitudinal quantitative analyses of neuroanatomical volumes and imaging metrics for assessing the role played by aging and disease to the central nervous system. As NOD/scid-IL-2Rγ(c)(null) (NSG) mice allow human cell transplantation to study human disease, these animals are used to assess brain morphology. Manganese enhanced MRI (MEMRI) improves contrasts amongst brain components and as such can greatly help identifying a broad number of structures on MRI. To this end, NSG adult mouse brains were imaged in vivo on a 7.0 Tesla MR scanner at an isotropic resolution of 100 μm. A population averaged brain of 19 mice was generated using an iterative alignment algorithm. MEMRI provided sufficient contrast permitting 41 brain structures to be manually labeled. Volumes of 7 humanized mice brain structures were measured by atlas-based segmentation and compared against non-humanized controls. The humanized NSG mice brain volumes were smaller than controls (p < 0.001). Many brain structures of humanized mice were significantly smaller than controls. We posit that the irradiation and cell grafting involved in the creation of humanized mice were responsible for the morphological differences. Six NSG mice without MnCl2 administration were scanned with high resolution T2-weighted MRI and segmented to test broad utility of the atlas.

4D MEMRI atlas of neonatal FVB/N mouse brain development

The widespread use of the mouse as a model system to study brain development has created the need for noninvasive neuroimaging methods that can be applied to early postnatal mice. The goal of this study was to optimize in vivo three- (3D) and four-dimensional (4D) manganese (Mn)-enhanced MRI (MEMRI) approaches for acquiring and analyzing data from the developing mouse brain. The combination of custom, stage-dependent holders and self-gated (motion-correcting) 3D MRI sequences enabled the acquisition of high-resolution (100-μm isotropic), motion artifact-free brain images with a high level of contrast due to Mn-enhancement of numerous brain regions and nuclei. We acquired high-quality longitudinal brain images from two groups of FVB/N strain mice, six mice per group, each mouse imaged on alternate odd or even days (6 3D MEMRI images at each day) covering the developmental stages between postnatal days 1 to 11. The effects of Mn-exposure, anesthesia and MRI were assessed, showing small but significant transient effects on body weight and brain volume, which recovered with time and did not result in significant morphological differences when compared to controls. Metrics derived from deformation-based morphometry (DBM) were used for quantitative analysis of changes in volume and position of a number of brain regions. The cerebellum, a brain region undergoing significant changes in size and patterning at early postnatal stages, was analyzed in detail to demonstrate the spatiotemporal characterization made possible by this new atlas of mouse brain development. These results show that MEMRI is a powerful tool for quantitative analysis of mouse brain development, with great potential for in vivo phenotype analysis in mouse models of neurodevelopmental diseases.

Neurocognitive Late Effects of Chemotherapy in Survivors of Acute Lymphoblastic Leukemia: Focus on Methotrexate

Childhood cancer survivors frequently experience long-lasting consequences of chemotherapy on health outcomes. Neurocognitive late effects of chemotherapy occur in 40 - 60% of acute lymphoblastic leukemia (ALL) survivors. These deficits affect mental health, school performance, job success, and are associated with poor quality of life, therefore presenting a clinical challenge for psychiatrists. However, not all cancer survivors are impacted by treatment in the same manner and emerging evidence suggests that genetic variation may modulate neurocognitive outcomes. Much like other complex psychopathologies, neurocognitive deficits in cancer survivors are the result of complex interactions between genetic and environmental variables. This review describes adverse neurocognitive outcomes observed in survivors of acute lymphoblastic leukemia (ALL) and discusses genetic variability in biochemical pathways targeted by chemotherapeutic agents as a possible mechanism contributing to psychopathology in ALL survivors.

Mouse cerebral magnetic resonance imaging fails to visualize brain volume changes after experimental subarachnoid hemorrhage

BACKGROUND

Brain atrophy after subarachnoid hemorrhage (SAH) has been detected in humans and might serve as a functional read-out parameter for neuropsychological deficits. To determine whether serial magnetic resonance imaging (MRI) can provide information on brain atrophy in animals as well, mice that had undergone experimental SAH were scanned repeatedly after the bleeding.

METHODS

Using a 7-T rodent MRI, six mice were evaluated for total hemispheric, cerebrospinal fluid (CSF) and hippocampal volumes on days 1, 2, 4, 21, 28, 42 and 60 after experimental SAH or sham operation, respectively.

RESULTS

Repeated MRI scanning demonstrated a very high reproducibility with minimum standard deviation. Nevertheless, no significant differences were found between the two groups concerning hemispherical volumes or hippocampal volumes. A transient but significant increase in CSF volume was detected on days 2 and 60 after SAH. Compared with the existing method, no MRI data on brain atrophy in mice after experimental SAH have been published.

CONCLUSION

Repeated brain MRI in mice after experimental SAH did not provide additional information on brain atrophy. Our data suggest that this is not due to a lack of sensitivity of the method. Despite all promising details about MRI, our results should initiate careful consideration (additional sequences/other questions) before its further use in this certain area, especially since it is expensive and associated with demanding logistics.

Diffusion tensor imaging of brain abnormalities induced by prenatal exposure to radiation in rodents

We assessed brain abnormalities in rats exposed prenatally to radiation (X-rays) using magnetic resonance imaging (MRI) and histological experiments. Pregnant rats were divided into 4 groups: the control group (n = 3) and 3 groups that were exposed to different radiation doses (0.5, 1.0, or 1.5 Gy; n = 3 each). Brain abnormalities were assessed in 32 neonatal male rats (8 per group). Ex vivo T2-weighted imaging and diffusion tensor imaging (DTI) were performed using 11.7-T MRI. The expression of markers of myelin production (Kluver-Barrera staining, KB), nonpyramidal cells (calbindin-D28k staining, CaBP), and pyramidal cells (staining of the nonphosphorylated heavy-chain neurofilament SMI-32) were histologically evaluated. Decreased brain volume, increased ventricle volume, and thinner cortices were observed by MRI in irradiated rats. However, no abnormalities in the cortical 6-layered structure were observed via KB staining in radiation-exposed rats. The DTI color-coded map revealed a dose-dependent reduction in the anisotropic signal (vertical direction), which did not represent reduced numbers of pyramidal cells; rather, it indicated a signal reduction relative to the vertical direction because of low nerve cell density in the entire cortex. We conclude that DTI and histological experiments are useful tools for assessing cortical and hippocampal abnormalities after prenatal exposure to radiation in rats.

Radiation-induced changes in normal-appearing gray matter in patients with nasopharyngeal carcinoma: a magnetic resonance imaging voxel-based morphometry study

INTRODUCTION

Evidence is accumulating that temporal lobe radiation necrosis in patients with nasopharyngeal carcinoma (NPC) after radiotherapy (RT) could involve gray matter (GM). The purpose of the study was to assess the radiation-induced GM volume differences between NPC patients who had and had not received RT and the effect of time after RT on GM volume differences in those patients who had received RT.

METHODS

We used magnetic resonance imaging voxel-based morphometry (VBM) to assess differences in GM volume between 30 NPC patients with normal-appearing whole-brain GM after RT and 15 control patients with newly diagnosed but not yet medically treated NPC. Correlation analyses were used to investigate the relationship between GM volume changes and time after RT.

RESULTS

Patients who had received RT had GM volume decreases in the bilateral superior temporal gyrus, left middle temporal gyrus, right fusiform gyrus, right precentral gyrus, and right inferior parietal lobule (p < 0.001, uncorrected, cluster size >100 voxels). Moreover, the correlation analysis indicated that regional GM volume loss in the left superior temporal gyrus, left middle temporal gyrus, and right fusiform gyrus were negatively related to the mean dose to the ipsilateral temporal lobe, respectively.

CONCLUSION

These results indicate that GM volume deficits in bilateral temporal lobes in patients who had received RT might be radiation-induced. Our findings might provide new insight into the pathogenesis of radiation-induced structural damage in normal-appearing brain tissue. Yet this is an exploratory study, whose findings should therefore be taken with caution.

Transplantation of enteric neural stem/progenitor cells into the irradiated young mouse hippocampus

Radiotherapy is an effective treatment for brain tumors but often results in cognitive deficits in survivors. Transplantation of embryonic or brain-derived neural stem/progenitor cells (BNSPCs) ameliorated cognitive impairment after irradiation (IR) in animal models. However, such an approach in patients requires a clinically relevant source of cells. We show for the first time the utilization of enteric neural stem/progenitor cells (ENSPCs) from the postnatal intestinal wall as a source of autologous cells for brain repair after injury caused by IR. Cells were isolated from the intestinal wall and propagated in vitro for 1 week. Differentiation assays showed that ENSPCs are multipotent and generated neurons, astrocytes, and myofibroblasts. To investigate whether ENSPCs can be used in vivo, postnatal day 9 mice were subjected to a single moderate irradiation dose (6 or 8 Gy). Twelve days later, mice received an intrahippocampal injection of syngeneic ENSPCs. Four weeks after transplantation, 0.5% and 1% of grafted ENSPCs were detected in the dentate gyrus of sham and irradiated animals, respectively, and only 0.1% was detected after 16 weeks. Grafted ENSPCs remained undifferentiated but failed to restore IR-induced loss of BNSPCs and the subsequent impaired growth of the dentate gyrus. We observed microglia activation, astrogliosis, and loss of granule neurons associated with grafted ENSPC clusters. Transplantation of ENSPCs did not ameliorate IR-induced impaired learning and memory. In summary, while autologous ENSPC grafting to the brain worked technically, even in the absence of immunosuppression, the protocols need to be modified to improve survival and integration.

A method for 3D immunostaining and optical imaging of the mouse brain demonstrated in neural progenitor cells

It is important to understand changes in cell distribution that occur as a part of disease progression. This is typically achieved using standard sectioning and immunostaining, however, many structures and cell distribution patterns are not readily appreciated in two-dimensions, including the distribution of neural stem and progenitor cells in the mouse forebrain. Three-dimensional immunostaining in the mouse brain has been hampered by poor penetration. For this reason, we have developed a method that allows for entire hemispheres of the mouse brain to be stained using commercially available antibodies. Brains stained for glial fibrillary acidic protein, doublecortin and nestin were imaged in three-dimensions using optical projection tomography and serial two-photon tomography. This staining method is simple, using a combination of heat, time and specimen preparation procedures readily available, so that it can be easily implemented without the need for specialized equipment, making it accessible to most laboratories.