Cellular response of the rat brain to single doses of (137)Cs γ rays does not predict its response to prolonged 'biologically equivalent' fractionated doses

Gamma radiation improves AD pathogenesis in APP/PS1 mouse model by potentiating insulin sensitivity

Alzheimer's disease (AD) is the largest unmet medical complication. The devastation caused by the disease can be assumed from the disease symptoms like speech impairment, loss of self-awareness, acute memory loss etc. The individuals suffering from AD completely depend on caregivers and have to bear the high cost of treatment which increases the socio-economic burden on the society. Recent studies have shown that radiation exposure can have therapeutic effects when given in suitable amount for a specific time period. Therefore, we investigated the role of gamma irradiation in AD pathogenesis. The effect of radiation on amelioration of disease progression was studied in AD transgenic mice model (APP/PS1). Our in-vivo studies using APP/PS1 mice demonstrated that a single dose of 4.0 Gy gamma irradiation improves AD associated behavioral impairment. Radiation exposure also increased the level of anti-oxidant enzymes and reduced the astrocyte activation in the brain of APP/PS1 mice. A significant reduction was observed in AD associated proteins (APP, pTau, BACE) and neurofibrillary tangle formations (NFTs). Exposure to a single dose of 4 Gy gamma radiation also increased glucose metabolic functionality in AD transgenic mouse model. The kinases involved in insulin signaling such as GSK, ERK and JNK were also found to be modulated. However, an increased level of GSK3β (ser 9) was observed, which could be responsible for downregulating ERK and JNK phosphorylation. This resulted in a decrease in neurofibrillary tangle formations and amyloid deposition. The reduced hyperphosphorylation of Tau can be attributed to the increased level of GSK3β (ser 9) downregulating ERK and JNK phosphorylation. Thus, a single dose of 4 Gy gamma irradiation was found to have therapeutic benefits in treating AD via potentiating insulin signaling in APP/PS1 transgenic mice.

Minimal difference between fractionated and single-fraction exposure in a murine model of radiation necrosis

Purpose

Despite the success of fractionation in clinical practice to spare healthy tissue, it remains common for mouse models used to study the efficacy of radiation therapy to use minimal or no fractionation. The goal of our study was to create a fractionated mouse model of radiation necrosis that we could compare to our single fraction model.

Methods

Precision X-Ray’s X-Rad 320 cabinet irradiator was used to irradiate the cerebrum of mice with four different fractionation schemes, while a 7 T Bruker magnetic resonance imaging (MRI) scanner using T2 and post-contrast T1 imaging was used to track the development of radiation necrosis over the span of six weeks.

Results

All four fractionation schemes with single fraction equivalent doses (SFED) less than 50 Gy for the commonly accepted alpha/beta ratio (α/β) value of 2–3 Gy produced radiation necrosis comparable to what would be achieved with single fraction doses of 80 and 90 Gy. This is surprising when previous work using single fractions of 50 Gy produced no visible radiation necrosis, with the results of this study showing fractionation not sparing brain tissue as much as expected.

Conclusion

Further interpretation of these results must take into consideration other studies which have shown a lack of sparing when fractionation has been incorporated, as well as consider factors such as the use of large doses per fraction, the time between fractions, and the limitations of using a murine model to analyze the human condition.

Chronic disturbance in the thalamus following cranial irradiation to the developing mouse brain

Better survival rates among pediatric brain tumor patients have resulted in an increased awareness of late side effects that commonly appear following cancer treatment. Radiation-induced changes in hippocampus and white matter are well described, but do not explain the full range of neurological late effects in childhood cancer survivors. The aim of this study was to investigate thalamus following cranial irradiation (CIR) to the developing brain. At postnatal day 14, male mice pups received a single dose of 8 Gy CIR. Cellular effects in thalamus were assessed using immunohistochemistry 4 months after CIR. Interestingly, the density of neurons decreased with 35% (p = 0.0431) and the density of astrocytes increased with 44% (p = 0.011). To investigate thalamic astrocytes, S100β⁺ cells were isolated by fluorescence-activated cell sorting and genetically profiled using next-generation sequencing. The phenotypical characterization indicated a disrupted function, such as downregulated microtubules’ function, higher metabolic activity, immature phenotype and degraded ECM. The current study provides novel insight into that thalamus, just like hippocampus and white matter, is severely affected by CIR. This knowledge is of importance to understand the late effects seen in pediatric brain tumor survivors and can be used to give them the best suitable care.

Risks of cognitive detriments after low dose heavy ion and proton exposures

Purpose: Heavy ion and proton brain irradiations occur during space travel and in Hadron therapy for cancer. Heavy ions produce distinct patterns of energy deposition in neuron cells and brain tissues compared to X-rays leading to large uncertainties in risk estimates. We make a critical review of findings from research studies over the last 25 years for understanding risks at low dose. Conclusions: A large number of mouse and rat cognitive testing measures have been reported for a variety of particle species and energies for acute doses. However, tissue reactions occur above dose thresholds and very few studies were performed at the heavy ion doses to be encountered on space missions (<0.04 Gy/y) or considered dose-rate effects, such that threshold doses are not known in rodent models. Investigations of possible mechanisms for cognitive changes have been limited by experimental design with largely group specific and not subject specific findings reported. Persistent oxidative stress and activated microglia cells are common mechanisms studied, while impairment of neurogenesis, detriments in neuron morphology, and changes to gene and protein expression were each found to be important in specific studies. Future research should focus on estimating threshold doses carried out with experimental designs aimed at understating causative mechanisms, which will be essential for extrapolating rodent findings to humans and chronic radiation scenarios, while establishing if mitigation are needed.

White Matter is the Predilection Site of Late-Delayed Radiation-Induced Brain Injury in Non-Human Primates

Fractionated whole-brain irradiation for the treatment of intracranial neoplasia causes progressive neurodegeneration and neuroinflammation. The long-term consequences of single-fraction high-dose irradiation to the brain are unknown. To assess the late effects of brain irradiation we compared transcriptomic gene expression profiles from nonhuman primates (NHP; rhesus macaques Macaca mulatta) receiving single-fraction total-body irradiation (TBI; n = 5, 6.75-8.05 Gy, 6-9 years prior to necropsy) to those receiving fractionated whole-brain irradiation (fWBI; n = 5, 40 Gy, 8 × 5 Gy fractions; 12 months prior to necropsy) and control comparators (n = 5). Gene expression profiles from the dorsolateral prefrontal cortex (DLPFC), hippocampus (HC) and deep white matter (WM; centrum semiovale) were compared. Stratified analyses by treatment and region revealed that radiation-induced transcriptomic alterations were most prominent in animals receiving fWBI, and primarily affected white matter in both TBI and fWBI groups. Unsupervised canonical and ontologic analysis revealed that TBI or fWBI animals demonstrated shared patterns of injury, including white matter neuroinflammation, increased expression of complement factors and T-cell activation. Both irradiated groups also showed evidence of impaired glutamatergic neurotransmission and signal transduction within white matter, but not within the dorsolateral prefrontal cortex or hippocampus. Signaling pathways and structural elements involved in extracellular matrix (ECM) deposition and remodeling were noted within the white matter of animals receiving fWBI, but not of those receiving TBI. These findings indicate that those animals receiving TBI are susceptible to neurological injury similar to that observed after fWBI, and these changes persist for years postirradiation. Transcriptomic profiling reaffirmed that macrophage/microglial-mediated neuroinflammation is present in radiation-induced brain injury (RIBI), and our data provide novel evidence that the complement system may contribute to the pathogenesis of RIBI. Finally, these data challenge the assumption that the hippocampus is the predilection site of injury in RIBI, and indicate that impaired glutamatergic neurotransmission may occur in white matter injury.

Modeling Reveals the Dependence of Hippocampal Neurogenesis Radiosensitivity on Age and Strain of Rats

Cognitive dysfunction following radiation treatment for brain cancers in both children and adults have been correlated to impairment of neurogenesis in the hippocampal dentate gyrus. Various species and strains of rodent models have been used to study radiation-induced changes in neurogenesis and these investigations have utilized only a limited number of doses, dose-fractions, age and time after exposures conditions. In this paper, we have extended our previous mathematical model of radiation-induced hippocampal neurogenesis impairment of C57BL/6 mice to delineate the time, age, and dose dependent alterations in neurogenesis of a diverse strain of rats. To the best of our knowledge, this is the first predictive mathematical model to be published about hippocampal neurogenesis impairment for a variety of rat strains after acute or fractionated exposures to low linear energy transfer (low LET) radiation, such as X-rays and γ-rays, which are conventionally used in cancer radiation therapy. We considered four compartments to model hippocampal neurogenesis and its impairment following radiation exposures. Compartments include: (1) neural stem cells (NSCs), (2) neuronal progenitor cells or neuroblasts (NB), (3) immature neurons (ImN), and (4) glioblasts (GB). Additional consideration of dose and time after irradiation dependence of microglial activation and a possible shift of NSC proliferation from neurogenesis to gliogenesis at higher doses is established. Using a system of non-linear ordinary differential equations (ODEs), characterization of rat strain and age-related dynamics of hippocampal neurogenesis for unirradiated and irradiated conditions is developed. The model is augmented with the description of feedback regulation on early and late neuronal proliferation following radiation exposure. Predictions for dose-fraction regimes compared to acute radiation exposures, along with the dependence of neurogenesis sensitivity to radiation on age and strain of rats are discussed. A major result of this work is predictions of the rat strain and age dependent differences in radiation sensitivity and sub-lethal damage repair that can be used for predictions for arbitrary dose and dose-fractionation schedules.

Upregulated epithelial junction expression represents a novel parameter of the epithelial radiation response to fractionated irradiation in oral mucosa

Purpose

During head and neck cancer treatment, the radiation response of the oral mucosa represents a frequent early side effect. Besides radiation-induced inhibition of proliferation, various other cellular responses occur. The radiation response of adherens and tight junction proteins was so far mostly investigated with large single-dose irradiation protocols, in vivo and in vitro. Therefore, the current study was initiated to investigate the impact of daily fractionated irradiation on the expression of adherens and tight junction proteins in vivo.

Materials and methods

Fractionation with 5 × 3 Gy/week (days 0–4, 7–11) was given to the snouts of mice. Groups of 5 animals per day were euthanized every second day between day 0 (unirradiated controls) and day 14, and their tongues subjected to histological processing. Adherens junction marker (β-catenin and E‑cadherin) and tight junction marker (claudin-1 and occludin) expression was analysed in the oral mucosa of unirradiated controls and during two weeks of fractionated irradiation.

Results

Adherens as well as tight junction marker proteins were rapidly and consistently upregulated in both the germinal as well as the functional layer of the oral mucosa. This represents a previously unknown parameter of the epithelial radiation response to clinically relevant fractionation protocols.

Conclusion

Fractionated irradiation significantly enhanced the expression of all proteins investigated. This study revealed a new parameter of the epithelial radiation response to fractionated irradiation.

Electronic supplementary material

The online version of this article (10.1007/s00066-018-1302-6) contains supplementary material, which is available to authorized users.

Design, construction, and in vivo feasibility of a positioning device for irradiation of mice brains using a clinical linear accelerator and intensity modulated radiation therapy

PURPOSE

The goal of this study was to design a positioning device that would allow for selective irradiation of the mouse brain with a clinical linear accelerator.

METHODS

We designed and fabricated an immobilization fixture that incorporates three functions: head stabilizer (through ear bars and tooth bar), gaseous anesthesia delivery and scavenging, and tissue mimic/bolus. Cohorts of five mice were irradiated such that each mouse in the cohort received a unique dose between 1000 and 3000 cGy. DNA damage immunohistochemistry was used to validate an increase in biological effect as a function of radiation dose. Mice were then followed with hematoxylin and eosin (H&E) and anatomical magnetic resonance imaging (MRI).

RESULTS

There was evidence of DNA damage throughout the brain proportional to radiation dose. Radiation-induced damage at the prescribed doses, as depicted by H&E, appeared to be constrained to the white matter consistent with radiological observation in human patients. The severity of the damage correlated with the radiation dose as expected.

CONCLUSIONS

We have designed and manufactured a device that allows us to selectively irradiate the mouse brain with a clinical linear accelerator. However, some off-target effects are possible with large prescription doses.

Changes in Imaging and Cognition in Juvenile Rats After Whole-Brain Irradiation

PURPOSE

In pediatric cancer survivors treated with whole-brain irradiation (WBI), long-term cognitive deficits and morbidity develop that are poorly understood and for which there is no treatment. We describe similar cognitive defects in juvenile WBI rats and correlate them with alterations in diffusion tensor imaging and magnetic resonance spectroscopy (MRS) during brain development.

METHODS AND MATERIALS

Juvenile Fischer rats received clinically relevant fractionated doses of WBI or a high-dose exposure. Diffusion tensor imaging and MRS were performed at the time of WBI and during the subacute (3-month) and late (6-month) phases, before behavioral testing.

RESULTS

Fractional anisotropy in the splenium of the corpus callosum increased steadily over the study period, reflecting brain development. WBI did not alter the subacute response, but thereafter there was no further increase in fractional anisotropy, especially in the high-dose group. Similarly, the ratios of various MRS metabolites to creatine increased over the study period, and in general, the most significant changes after WBI were during the late phase and with the higher dose. The most dramatic changes observed were in glutamine-creatine ratios that failed to increase normally between 3 and 6 months after either radiation dose. WBI did not affect the ambulatory response to novel open field testing in the subacute phase, but locomotor habituation was impaired and anxiety-like behaviors increased. As for cognitive measures, the most dramatic impairments were in novel object recognition late after either dose of WBI.

CONCLUSIONS

The developing brains of juvenile rats given clinically relevant fractionated doses of WBI show few abnormalities in the subacute phase but marked late cognitive alterations that may be linked with perturbed MRS signals measured in the corpus callosum. This pathomimetic phenotype of clinically relevant cranial irradiation effects may be useful for modeling, mechanistic evaluations, and testing of mitigation approaches.

The impact of high and low dose ionising radiation on the central nervous system

Responses of the central nervous system (CNS) to stressors and injuries, such as ionising radiation, are modulated by the concomitant responses of the brains innate immune effector cells, microglia. Exposure to high doses of ionising radiation in brain tissue leads to the expression and release of biochemical mediators of ‘neuroinflammation’, such as pro-inflammatory cytokines and reactive oxygen species (ROS), leading to tissue destruction. Contrastingly, low dose ionising radiation may reduce vulnerability to subsequent exposure of ionising radiation, largely through the stimulation of adaptive responses, such as antioxidant defences. These disparate responses may be reflective of non-linear differential microglial activation at low and high doses, manifesting as an anti-inflammatory or pro-inflammatory functional state. Biomarkers of pathology in the brain, such as the mitochondrial Translocator Protein 18 kDa (TSPO), have facilitated in vivo characterisation of microglial activation and ‘neuroinflammation’ in many pathological states of the CNS, though the exact function of TSPO in these responses remains elusive. Based on the known responsiveness of TSPO expression to a wide range of noxious stimuli, we discuss TSPO as a potential biomarker of radiation-induced effects.

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Ionising radiation can modulate responses of microglial cells in the CNS.

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High doses can induce ROS formation, oxidative stress and neuroinflammation.

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Low doses can mitigate tissue damage via antioxidant defences.

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TSPO as a potential biomarker and modulator of radiation induced effects in the CNS.

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Non-linear differential microglial activation to high and low doses is proposed.

Neurobehavioral radiation mitigation to standard brain cancer therapy regimens by Mn(III) n-butoxyethylpyridylporphyrin-based redox modifier

Combinations of radiotherapy (RT) and chemotherapy have shown efficacy toward brain tumors. However, therapy-induced oxidative stress can damage normal brain tissue, resulting in both progressive neurocognitive loss and diminished quality of life. We have recently shown that MnTnBuOE-2-PyP(5+) (Mn(III)meso-tetrakis(N-n-butoxyethylpyridinium -2-yl)porphyrin) rescued RT-induced white matter damage in cranially-irradiated mice. Radiotherapy is not used in isolation for treatment of brain tumors; temozolomide is the standard-of-care for adult glioblastoma, whereas cisplatin is often used for treatment of pediatric brain tumors. Therefore, we evaluated the brain radiation mitigation ability of MnTnBuOE-2-PyP(5+) after either temozolomide or cisplatin was used singly or in combination with 10 Gy RT. MnTnBuOE-2-PyP(5+) accumulated in brains at low nanomolar levels. Histological and neurobehavioral testing showed a drastic decrease (1) of axon density in the corpus callosum and (2) rotorod and running wheel performance in the RT only treatment group, respectively. MnTnBuOE-2-PyP(5+) completely rescued this phenotype in irradiated animals. In the temozolomide groups, temozolomide/ RT treatment resulted in further decreased rotorod responses over RT alone. Again, MnTnBuOE-2-PyP(5+) treatment rescued the negative effects of both temozolomide ± RT on rotorod performance. While the cisplatin-treated groups did not give similar results as the temozolomide groups, inclusion of MnTnBuOE-2-PyP(5+) did not negatively affect rotorod performance. Additionally, MnTnBuOE-2-PyP(5+) sensitized glioblastomas to either RT ± temozolomide in flank tumor models. Mice treated with both MnTnBuOE-2-PyP(5+) and radio-/chemo-therapy herein demonstrated brain radiation mitigation. MnTnBuOE-2-PyP(5+) may well serve as a normal tissue radio-/chemo-mitigator adjuvant therapy to standard brain cancer treatment regimens. Environ. Mol. Mutagen. 57:372-381, 2016. © 2016 Wiley Periodicals, Inc.

Analysis of radiation therapy in a model of triple-negative breast cancer brain metastasis

Most cancer patients with brain metastases are treated with radiation therapy, yet this modality has not yet been meaningfully incorporated into preclinical experimental brain metastasis models. We applied two forms of whole brain radiation therapy (WBRT) to the brain-tropic 231-BR experimental brain metastasis model of triple-negative breast cancer. When compared to sham controls, WBRT as 3 Gy × 10 fractions (3 × 10) reduced the number of micrometastases and large metastases by 87.7 and 54.5 %, respectively (both p < 0.01); whereas a single radiation dose of 15 Gy × 1 (15 × 1) was less effective, reducing metastases by 58.4 % (p < 0.01) and 47.1 % (p = 0.41), respectively. Neuroinflammation in the adjacent brain parenchyma was due solely to a reaction from metastases, and not radiotherapy, while adult neurogenesis in brains was adversely affected following both radiation regimens. The nature of radiation resistance was investigated by ex vivo culture of tumor cells that survived initial WBRT ("Surviving" cultures). The Surviving cultures surprisingly demonstrated increased radiosensitivity ex vivo. In contrast, re-injection of Surviving cultures and re-treatment with a 3 × 10 WBRT regimen significantly reduced the number of large and micrometastases that developed in vivo, suggesting a role for the microenvironment. Micrometastases derived from tumor cells surviving initial 3 × 10 WBRT demonstrated a trend toward radioresistance upon repeat treatment (p = 0.09). The data confirm the potency of a fractionated 3 × 10 WBRT regimen and identify the brain microenvironment as a potential determinant of radiation efficacy. The data also nominate the Surviving cultures as a potential new translational model for radiotherapy.