Whole brain radiation-induced vascular cognitive impairment: mechanisms and implications

Brain tumor-related epilepsy: an overview on neuropsychological, behavioral, and quality of life issues and assessment methodology

Brain tumor-related epilepsy (BTRE) is a rare disease in which brain tumor (BT) and epilepsy overlap simultaneously and can have a negative impact on a patient's neuropsychological, behavioral, and quality of life (QoL) spheres. In this review we (a) addressed the main neuropsychological, behavioral, and QoL issues that may occur in BTRE patients, (b) described how BT, BTRE, and their respective treatments can impact these domains, and (c) identified tools and standardized evaluation methodologies specific for BTRE patients. Neuropsychological disorders and behavioral issues can be direct consequences of BTRE and all related treatments, such as surgery, anti-cancer and anti-seizure medication, corticosteroids, etc., which can alter the structure of specific brain areas and networks, and by emotional aspects reactive to BTRE diagnosis, including the possible loss of autonomy, poor prognosis, and fear of death. Unfortunately, it seems there is a lack of uniformity in assessment methodologies, such as the administration of different batteries of neuropsychological tests, different times, frames, and purposes. Further research is needed to establish causality and deepen our understanding of the interplay between all these variables and our intervention in terms of diagnosis, treatment, psychosocial assessment, and their timing. We propose that the care of these patients to rely on the concepts of "BTRE-induced disability" and "biopsychosocial model" of BTRE, to prompt healthcare providers to handle and monitor BTRE-related psychological and social aspects, as to maintain the patient's best possible QoL.

Exploring Neuroprotection against Radiation-Induced Brain Injury: A Review of Key Compounds

Brain radiation is a crucial tool in neuro-oncology for enhancing local tumor control, but it can lead to mild-to-profound and progressive impairments in cognitive function. Radiation-induced brain injury is a significant adverse effect of radiotherapy for cranioencephalic tumors, primarily caused by indirect cellular damage through the formation of free radicals. This results in late neurotoxicity manifesting as cognitive impairment due to free radical production. The aim of this review is to highlight the role of different substances, such as drugs used in the clinical setting and antioxidants such as ascorbate, in reducing the neurotoxicity associated with radiation-induced brain injury. Currently, there is mainly preclinical and clinical evidence supporting the benefit of these interventions, representing a cost-effective and straightforward neuroprotective strategy.

Cognitive dysfunction induced by cranial radiotherapy: mechanisms and therapeutic methods

Cranial radiotherapy can damage normal brain tissues, inducing cognitive dysfunction in patients. Radiotherapy-induced cognitive dysfunction is associated with hippocampal injury, white matter damage and microvascular injury. In this study, the mechanisms of cognitive dysfunction induced by cranial radiotherapy and combined chemoradiotherapy are reviewed, and the advances in therapeutic methods for radiotherapy-induced brain injury are summarized. The mechanisms of radiotherapy-induced brain injury include a decline of neurogenesis, impairment of neurons and glial cells, vascular injury, oxidative stress and DNA damage, cell death, and inflammatory response. Disruption of the bloodbrain barrier (BBB) increases the exposure of the brain to chemotherapeutic agents, thus exacerbating radiotherapy-induced brain damage. The current methods used to prevent radiotherapy-induced brain injury mainly include precision radiotherapy, stem cell transplantation, and treatment with neuroprotective drugs. The combined application of precision radiotherapy and neuroprotective drugs, including antioxidants, anti-inflammatory agents and other drugs, might exert better neuroprotective effects. To resolve the issues of neuroprotective drugs, such as difficulty in crossing the BBB, nanoenzymes and drug delivery nano-systems could be applied in the future.

The Implications of Aging on Vascular Health

Vascular aging encompasses structural and functional changes in the vasculature, significantly contributing to cardiovascular diseases, which are the leading cause of death globally. The incidence and prevalence of these diseases increase with age, with most morbidity and mortality attributed to myocardial infarction and stroke. Diagnosing and intervening in vascular aging while understanding the mechanisms behind age-induced vascular phenotypic and pathophysiological alterations offers the potential for delaying and preventing cardiovascular mortality in an aging population. This review delves into various aspects of vascular aging by examining age-related changes in arterial health at the cellular level, including endothelial dysfunction, cellular senescence, and vascular smooth muscle cell transdifferentiation, as well as at the structural level, including arterial stiffness and changes in wall thickness and diameter. We also explore aging-related changes in perivascular adipose tissue deposition, arterial collateralization, and calcification, providing insights into the physiological and pathological implications. Overall, aging induces phenotypic changes that augment the vascular system's susceptibility to disease, even in the absence of traditional risk factors, such as hypertension, diabetes, obesity, and smoking. Overall, age-related modifications in cellular phenotype and molecular homeostasis increase the vulnerability of the arterial vasculature to structural and functional alterations, thereby accelerating cardiovascular risk. Increasing our understanding of these modifications is crucial for success in delaying or preventing cardiovascular diseases. Non-invasive techniques, such as measuring carotid intima-media thickness, pulse wave velocity, and flow-mediated dilation, as well as detecting vascular calcifications, can be used for the early detection of vascular aging. Targeting specific pathological mechanisms, such as cellular senescence and enhancing angiogenesis, holds promise for innovative therapeutic approaches.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Functional network disorganization and cognitive decline following fractionated whole-brain radiation in mice

Cognitive dysfunction following radiotherapy (RT) is one of the most common complications associated with RT delivered to the brain, but the precise mechanisms behind this dysfunction are not well understood, and to date, there are no preventative measures or effective treatments. To improve patient outcomes, a better understanding of the effects of radiation on the brain's functional systems is required. Functional magnetic resonance imaging (fMRI) has shown promise in this regard, however, compared to neural activity, hemodynamic measures of brain function are slow and indirect. Understanding how RT acutely and chronically affects functional brain organization requires more direct examination of temporally evolving neural dynamics as they relate to cerebral hemodynamics for bridging with human studies. In order to adequately study the underlying mechanisms of RT-induced cognitive dysfunction, the development of clinically mimetic RT protocols in animal models is needed. To address these challenges, we developed a fractionated whole-brain RT protocol (3Gy/day for 10 days) and applied longitudinal wide field optical imaging (WFOI) of neural and hemodynamic brain activity at 1, 2, and 3 months post RT. At each time point, mice were subject to repeated behavioral testing across a variety of sensorimotor and cognitive domains. Disruptions in cortical neuronal and hemodynamic activity observed 1 month post RT were significantly worsened by 3 months. While broad changes were observed in functional brain organization post RT, brain regions most impacted by RT occurred within those overlapping with the mouse default mode network and other association areas similar to prior reports in human subjects. Further, significant cognitive deficits were observed following tests of novel object investigation and responses to auditory and contextual cues after fear conditioning. Our results fill a much-needed gap in understanding the effects of whole-brain RT on systems level brain organization and how RT affects neuronal versus hemodynamic signaling in the cortex. Having established a clinically-relevant injury model, future studies can examine therapeutic interventions designed to reduce neuroinflammation-based injury following RT. Given the overlap of sequelae that occur following RT with and without chemotherapy, these tools can also be easily incorporated to examine chemotherapy-related cognitive impairment.

Whole brain irradiation-induced endothelial dysfunction in the mouse brain

Whole brain irradiation (WBI), also known as whole brain radiation therapy (WBRT), is a well-established treatment for multiple brain metastases and as a preventive measure to reduce the risk of recurrence after surgical removal of a cerebral metastasis. However, WBI has been found to lead to a gradual decline in neurocognitive function in approximately 50% of patients who survive the treatment, significantly impacting their overall quality of life. Recent preclinical investigations have shed light on the underlying mechanisms of this adverse effect, revealing a complex cerebrovascular injury that involves the induction of cellular senescence in various components of the neurovascular unit, including endothelial cells. The emergence of cellular senescence following WBI has been implicated in the disruption of the blood-brain barrier and impairment of neurovascular coupling responses following irradiation. Building upon these findings, the present study aims to test the hypothesis that WBI-induced endothelial injury promotes endothelial dysfunction, which mimics the aging phenotype. To investigate this hypothesis, we employed a clinically relevant fractionated WBI protocol (5 Gy twice weekly for 4 weeks) on young mice. Both the WBI-treated and control mice were fitted with a cranial window, enabling the assessment of microvascular endothelial function. In order to evaluate the endothelium-dependent, NO-mediated cerebral blood flow (CBF) responses, we topically administered acetylcholine and ATP, and measured the resulting changes using laser Doppler flowmetry. We found that the increases in regional CBF induced by acetylcholine and ATP were significantly diminished in mice subjected to WBI. These findings provide additional preclinical evidence supporting the notion that WBI induces dysfunction in cerebrovascular endothelial cells, which in turn likely contributes to the detrimental long-term effects of the treatment. This endothelial dysfunction resembles an accelerated aging phenotype in the cerebrovascular system and is likely causally linked to the development of cognitive impairment. By integrating these findings with our previous results, we have deepened our understanding of the lasting consequences of WBI. Moreover, our study underscores the critical role of cerebromicrovascular health in safeguarding cognitive function over the long term. This enhanced understanding highlights the importance of prioritizing cerebromicrovascular health in the context of preserving cognitive abilities.

An untapped window of opportunity for glioma: targeting therapy-induced senescence prior to recurrence

High-grade gliomas are primary brain tumors that are incredibly refractory long-term to surgery and chemoradiation, with no proven durable salvage therapies for patients that have failed conventional treatments. Post-treatment, the latent glioma and its microenvironment are characterized by a senescent-like state of mitotic arrest and a senescence-associated secretory phenotype (SASP) induced by prior chemoradiation. Although senescence was once thought to be irreversible, recent evidence has demonstrated that cells may escape this state and re-enter the cell cycle, contributing to tumor recurrence. Moreover, senescent tumor cells could spur the growth of their non-senescent counterparts, thereby accelerating recurrence. In this review, we highlight emerging evidence supporting the use of senolytic agents to ablate latent, senescent-like cells that could contribute to tumor recurrence. We also discuss how senescent cell clearance can decrease the SASP within the tumor microenvironment thereby reducing tumor aggressiveness at recurrence. Finally, senolytics could improve the long-term sequelae of prior therapy on cognition and bone marrow function. We critically review the senolytic drugs currently under preclinical and clinical investigation and the potential challenges that may be associated with deploying senolytics against latent glioma. In conclusion, senescence in glioma and the microenvironment are critical and potential targets for delaying or preventing tumor recurrence and improving patient functional outcomes through senotherapeutics.

The influence of physiological and pathological perturbations on blood-brain barrier function

The blood-brain barrier (BBB) is located at the interface between the vascular system and the brain parenchyma, and is responsible for communication with systemic circulation and peripheral tissues. During life, the BBB can be subjected to a wide range of perturbations or stresses that may be endogenous or exogenous, pathological or therapeutic, or intended or unintended. The risk factors for many diseases of the brain are multifactorial and involve perturbations that may occur simultaneously (e.g., two-hit model for Alzheimer's disease) and result in different outcomes. Therefore, it is important to understand the influence of individual perturbations on BBB function in isolation. Here we review the effects of eight perturbations: mechanical forces, temperature, electromagnetic radiation, hypoxia, endogenous factors, exogenous factors, chemical factors, and pathogens. While some perturbations may result in acute or chronic BBB disruption, many are also exploited for diagnostic or therapeutic purposes. The resultant outcome on BBB function depends on the dose (or magnitude) and duration of the perturbation. Homeostasis may be restored by self-repair, for example, via processes such as proliferation of affected cells or angiogenesis to create new vasculature. Transient or sustained BBB dysfunction may result in acute or pathological symptoms, for example, microhemorrhages or hypoperfusion. In more extreme cases, perturbations may lead to cytotoxicity and cell death, for example, through exposure to cytotoxic plaques.

Elimination of senescent cells by treatment with Navitoclax/ABT263 reverses whole brain irradiation-induced blood-brain barrier disruption in the mouse brain

Whole brain irradiation (WBI), a commonly employed therapy for multiple brain metastases and as a prophylactic measure after cerebral metastasis resection, is associated with a progressive decline in neurocognitive function, significantly impacting the quality of life for approximately half of the surviving patients. Recent preclinical investigations have shed light on the multifaceted cerebrovascular injury mechanisms underlying this side effect of WBI. In this study, we aimed to test the hypothesis that WBI induces endothelial senescence, contributing to chronic disruption of the blood-brain barrier (BBB) and microvascular rarefaction. To accomplish this, we utilized transgenic p16-3MR mice, which enable the identification and selective elimination of senescent cells. These mice were subjected to a clinically relevant fractionated WBI protocol (5 Gy twice weekly for 4 weeks), and cranial windows were applied to both WBI-treated and control mice. Quantitative assessment of BBB permeability and capillary density was performed using two-photon microscopy at the 6-month post-irradiation time point. The presence of senescent microvascular endothelial cells was assessed by imaging flow cytometry, immunolabeling, and single-cell RNA-sequencing (scRNA-seq). WBI induced endothelial senescence, which associated with chronic BBB disruption and a trend for decreased microvascular density in the mouse cortex. In order to investigate the cause-and-effect relationship between WBI-induced senescence and microvascular injury, senescent cells were selectively removed from animals subjected to WBI treatment using Navitoclax/ABT263, a well-known senolytic drug. This intervention was carried out at the 3-month post-WBI time point. In WBI-treated mice, Navitoclax/ABT263 effectively eliminated senescent endothelial cells, which was associated with decreased BBB permeability and a trend for increased cortical capillarization. Our findings provide additional preclinical evidence that senolytic treatment approaches may be developed for prevention of the side effects of WBI.

Measurements of cerebral microvascular blood flow, oxygenation, and morphology in a mouse model of whole-brain irradiation-induced cognitive impairment by two-photon microscopy and optical coherence tomography: evidence for microvascular injury in the cerebral white matter

Whole-brain irradiation (WBI, also known as whole-brain radiation therapy) is a mainstay treatment modality for patients with multiple brain metastases. It is also used as a prophylactic treatment for microscopic tumors that cannot be detected by magnetic resonance imaging. WBI induces a progressive cognitive decline in ~ 50% of the patients surviving over 6 months, significantly compromising the quality of life. There is increasing preclinical evidence that radiation-induced injury to the cerebral microvasculature and accelerated neurovascular senescence plays a central role in this side effect of WBI. To better understand this side effect, male C57BL/6 mice were first subjected to a clinically relevant protocol of fractionated WBI (5 Gy, two doses per week, for 4 weeks). Nine months post the WBI treatment, we applied two-photon microscopy and Doppler optical coherence tomography to measure capillary red-blood-cell (RBC) flux, capillary morphology, and microvascular oxygen partial pressure (PO2) in the cerebral somatosensory cortex in the awake, head-restrained, WPI-treated mice and their age-matched controls, through a cover-glass-sealed chronic cranial window. Thanks to the extended penetration depth with the fluorophore - Alexa680, measurements of capillary blood flow properties (e.g., RBC flux, speed, and linear density) in the cerebral subcortical white matter were enabled. We found that the WBI-treated mice exhibited a significantly decreased capillary RBC flux in the white matter. WBI also caused a significant reduction in capillary diameter, as well as a large (although insignificant) reduction in segment density at the deeper cortical layers (e.g., 600-700 μm), while the other morphological properties (e.g., segment length and tortuosity) were not obviously affected. In addition, we found that PO2 measured in the arterioles and venules, as well as the calculated oxygen saturation and oxygen extraction fraction, were not obviously affected by WBI. Lastly, WBI was associated with a significant increase in the erythrocyte-associated transients of PO2, while the changes of other cerebral capillary PO2 properties (e.g., capillary mean-PO2, RBC-PO2, and InterRBC-PO2) were not significant. Collectively, our findings support the notion that WBI results in persistent cerebral white matter microvascular impairment, which likely contributes to the WBI-induced brain injury and cognitive decline. Further studies are warranted to assess the WBI-induced changes in brain tissue oxygenation and malfunction of the white matter microvasculature as well.

Neurocognitive and radiological changes after cranial radiation therapy in humans and rodents: a systematic review

BACKGROUND

Radiation-induced brain injury is a common long-term side effect for brain cancer survivors, leading to a reduced quality of life. Although there is growing research pertaining to this topic, the relationship between cognitive and radiologically detected lesions of radiation-induced brain injury in humans remains unclear. Furthermore, clinically translatable similarities between rodent models and human findings are also undefined. The objective of this review is to then identify the current evidence of radiation-induced brain injury in humans and to compare these findings to current rodent models of radiation-induced brain injury.

METHODS

This review includes an examination of the current literature on cognitive and radiological characteristics of radiation-induced brain injury in humans and rodents. A thorough search was conducted on PubMed, Web of Science, and Scopus to identify studies that performed cognitive assessments and magnetic resonance imaging techniques on either humans or rodents after cranial radiation therapy. A qualitative synthesis of the data is herein reported.

RESULTS

A total of 153 studies pertaining to cognitively or radiologically detected radiation injury of the brain are included in this systematic review; 106 studies provided data on humans while 47 studies provided data on rodents. Cognitive deficits in humans manifest across multiple domains after brain irradiation. Radiological evidence in humans highlight various neuroimaging-detectable changes post-irradiation. It is unclear, however, whether these findings reflect ground truth or research interests. Additionally, rodent models do not comprehensively reproduce characteristics of cognitive and radiological injury currently identified in humans.

CONCLUSION

This systematic review demonstrates that associations between and within cognitive and radiological radiation-induced brain injuries often rely on the type of assessment. Well-designed studies that evaluate the spectrum of potential injury are required for a precise understanding of not only the clinical significance of radiation-induced brain injury in humans, but also how to replicate injury development in pre-clinical models.

Protective Potentials of Alpha-Lipoic Acid against Ionizing Radiation-Induced Brain Damage in Rats

Background

This study was aimed at determining the effects of alpha-lipoic acid on ionizing irradiation-induced oxidative damage and apoptosis in the brain of rats.

Methods

The animals were exposed to whole-brain X-radiation with a 15 Gy single dose in the absence or presence of alpha-lipoic acid (200 mg/kg body weight) pretreatment for one week. The rats were divided into four groups (5 rats in each group): vehicle control, alpha-lipoic acid alone (ALA), radiation alone (RAD), and radiation plus alpha-lipoic acid (RAD+ALA). In the next stage, malondialdehyde (MDA), nitric oxide, catalase (CAT), superoxide dismutase (SOD), and glutathione peroxidase (GPx) in the brain tissue of the rats were measured. Furthermore, the Western blot analysis technique was performed to assess the NOX2, NOX4, and caspase-3 protein expression levels.

Results

Twenty-four hours after the irradiation, MDA and nitric oxide levels in the irradiated rats were significantly higher than those in the control group (p < 0.001); however, the pretreatment with alpha-lipoic acid resulted in a significant reduction in these stress oxidative markers (p < 0.05). Moreover, a significant decrease in CAT, SOD, and GPx levels was observed in the radiation group alone compared to the control group (p < 0.01); in contrast, the activities of these antioxidant enzymes significantly increased in the radiation plus alpha-lipoic acid group in comparison to the radiation group alone (p < 0.05). The results of Western blot analysis revealed that NOX2, NOX4, and caspase-3 protein expressions significantly elevated in the irradiated rats compared to the control group (p < 0.001). The pretreatment with alpha-lipoic acid could significantly decrease the expression levels of NOX2, NOX4, and caspase-3 in comparison with the radiation group alone (p < 0.05).

Conclusion

According to the obtained findings, it can be mentioned that the alpha-lipoic acid pretreatment could mitigate the ionizing irradiation-induced oxidative damage and apoptosis in the brain of the rats.

Dose-dependent early white matter alterations in patients with brain metastases after radiotherapy

PURPOSE

Previous diffusion tensor imaging (DTI) studies have mainly focused on dose-dependent white matter (WM) alterations 1 month to 1 year after radiation therapy (RT) with a tract-average method. However, WM alterations immediately after RT are subtle, resulting in early WM alterations that cannot be detected by tract-average methods. Therefore, we performed a study with an along-tract method in patients with brain metastases to explore the early dose-response pattern of WM alterations after RT.

METHODS

Sixteen patients with brain metastases underwent DTI before and 1-3 days after brain RT. DTI metrics, such as fractional anisotropy (FA), axial diffusivity (AD), radial diffusivity (RD) and mean diffusivity (MD), were calculated. Along-tract statistics were then used to resample WM fibre streamlines and generate a WM skeleton fibre tract. DTI metric alterations (post_RT-pre_RT DTI metrics) and the planned doses (max or mean doses) were mapped to 18 WM tracts. A linear fixed model was performed to analyse the main effect of dose on DTI metric alterations.

RESULTS

AD alterations in the left hemispheric uncinated fasciculus (UNC_L) were associated with max doses, in which decreased AD alterations were associated with higher doses.

CONCLUSION

Our findings may provide pathological insight into early dose-dependent WM alterations and may contribute to the development of max dose-constrained RT techniques to protect brain microstructure in the UNC_L.

Strategies to overcome/penetrate the BBB for systemic nanoparticle delivery to the brain/brain tumor

Despite its prevalence in the management of peripheral tumors, compared to surgery and radiation therapy, chemotherapy is still a suboptimal intervention in fighting against brain cancer and cancer brain metastases. This discrepancy is mainly derived from the complicatedly physiological characteristic of intracranial tumors, including the presence of blood-brain barrier (BBB) and limited enhanced permeability and retention (EPR) effect attributed to blood-brain tumor barrier (BBTB), which largely lead to insufficient therapeutics penetrating to tumor lesions to produce pharmacological effects. Therefore, dependable methodologies that can boost the efficacy of chemotherapy for brain tumors are urgently needed. Recently, nanomedicines have shown great therapeutic potential in brain tumors by employing various transcellular strategies, paracellular strategies, and their hybrids, such as adsorptive-mediated transcytosis, receptor-mediated transcytosis, BBB disruption technology, and so on. It is compulsory to comprehensively summarize these practices to shed light on future directions in developing therapeutic regimens for brain tumors. In this review, the biological and pathological characteristics of brain tumors, including BBB and BBTB, are illustrated. After that, the emerging delivery strategies for brain tumor management are summarized into different classifications and supported with detailed examples. Finally, the potential challenges and prospects for developing and clinical application of brain tumor-oriented nanomedicine are discussed.

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.

Cerebral hemodynamic and metabolic dysregulation in the postradiation brain

Technological advances in the delivery of radiation and other novel cancer therapies have significantly improved the 5-year survival rates over the last few decades. Although recent developments have helped to better manage the acute effects of radiation, the late effects such as impairment in cognition continue to remain of concern. Accruing data in the literature have implicated derangements in hemodynamic parameters and metabolic activity of the irradiated normal brain as predictive of cognitive impairment. Multiparametric imaging modalities have allowed us to precisely quantify functional and metabolic information, enhancing the anatomic and morphologic data provided by conventional MRI sequences, thereby contributing as noninvasive imaging-based biomarkers of radiation-induced brain injury. In this review, we have elaborated on the mechanisms of radiation-induced brain injury and discussed several novel imaging modalities, including MR spectroscopy, MR perfusion imaging, functional MR, SPECT, and PET that provide pathophysiological and functional insights into the postradiation brain, and its correlation with radiation dose as well as clinical neurocognitive outcomes. Additionally, we explored some innovative imaging modalities, such as quantitative blood oxygenation level-dependent imaging, susceptibility-based oxygenation measurement, and T2-based oxygenation measurement, that hold promise in delineating the potential mechanisms underlying deleterious neurocognitive changes seen in the postradiation setting. We aim that this comprehensive review of a range of imaging modalities will help elucidate the hemodynamic and metabolic injury mechanisms underlying cognitive impairment in the irradiated normal brain in order to optimize treatment regimens and improve the quality of life for these patients.

Pathogenic mechanisms and therapeutic promise of phytochemicals and nanocarriers based drug delivery against radiotherapy-induced neurotoxic manifestations

Radiotherapy is one of the extensively used therapeutic modalities in glioblastoma and other types of cancers. Radiotherapy is either used as a first-line approach or combined with pharmacotherapy or surgery to manage and treat cancer. Although the use of radiotherapy significantly increased the survival time of patients, but its use has been reported with marked neuroinflammation and cognitive dysfunction that eventually reduced the quality of life of patients. Based on the preclinical and clinical investigations, the profound role of increased oxidative stress, nuclear translocation of NF-kB, production of proinflammatory cytokines such as TNF-α, IL-6, IL-β, increased level of MMPs, increased apoptosis, reduced angiogenesis, neurogenesis, and histological aberrations in CA1, CA2, CA3 and DG region of the hippocampus have been reported. Various pharmacotherapeutic drugs are being used as an adjuvant to counteract this neurotoxic manifestation. Still, most of these drugs suffer from systemic adverse effect, causes interference to ongoing chemotherapy, and exhibit pharmacokinetic limitations in crossing the blood-brain barrier. Therefore, various phytoconstituents, their nano carrier-based drug delivery systems and miRNAs have been explored to overcome the aforementioned limitations. The present review is focused on the mechanism and evidence of radiotherapy-induced neuroinflammation and cognitive dysfunction, pathological and molecular changes in the brain homeostasis, available adjuvants, their limitations. Additionally, the potential role and mechanism of neuroprotection of various nanocarrier based natural products and miRNAs have been discussed.

A Therapeutic Sheep in Metastatic Wolf's Clothing: Trojan Horse Approach for Cancer Brain Metastases Treatment

Early-stage brain metastasis of breast cancer (BMBC), due to the existence of an intact blood-brain barrier (BBB), is one of the deadliest neurologic complications. To improve the efficacy of chemotherapy for BMBC, a Trojan horse strategy-based nanocarrier has been developed by integrating the cell membrane of a brain-homing cancer cell and a polymeric drug depot. With the camouflage of a MDA-MB-231/Br cell membrane, doxorubicin-loaded poly (D, L-lactic-co-glycolic acid) nanoparticle (DOX-PLGA@CM) shows enhanced cellular uptake and boosted killing potency for MDA-MB-231/Br cells. Furthermore, DOX-PLGA@CM is equipped with naturally selected molecules for BBB penetration, as evidenced by its boosted capacity in entering the brain of both healthy and early-stage BMBC mouse models. Consequently, DOX-PLGA@CM effectively reaches the metastatic tumor lesions in the brain, slows down cancer progression, reduces tumor burden, and extends the survival time for the BMBC animal. Furthermore, the simplicity and easy scale-up of the design opens a new window for the treatment of BMBC and other brain metastatic cancers.

Low-level whole-brain radiation enhances theranostic potential of single-domain antibody fragments for human epidermal growth factor receptor type 2 (HER2)-positive brain metastases

Background

Single-domain antibody fragments (aka V_HH, ~ 13 kDa) are promising delivery systems for brain tumor theranostics; however, achieving efficient delivery of V_HH to intracranial lesions remains challenging due to the tumor–brain barrier. Here, we evaluate low-dose whole-brain irradiation as a strategy to increase the delivery of an anti- human epidermal growth factor receptor type 2 (HER2) V_HH to breast cancer-derived intracranial tumors in mice.

Methods

Mice with intracranial HER2-positive BT474BrM3 tumors received 10-Gy fractionated cranial irradiation and were evaluated by noninvasive imaging. Anti-HER2 V_HH 5F7 was labeled with ¹⁸F, administered intravenously to irradiated mice and controls, and PET/CT imaging was conducted periodically after irradiation. Tumor uptake of ¹⁸F-labeled 5F7 in irradiated and control mice was compared by PET/CT image analysis and correlated with tumor volumes. In addition, longitudinal dynamic contrast-enhanced MRI (DCE-MRI) was conducted to visualize and quantify the potential effects of radiation on tumor perfusion and permeability.

Results

Increased ¹⁸F-labeled 5F7 intracranial tumor uptake was observed with PET in mice receiving cranial irradiation, with maximum tumor accumulation seen approximately 12 days post initial radiation treatment. No radiation-induced changes in HER2 expression were detected by Western blot, flow cytometry, or on tissue sections. DCE-MRI imaging demonstrated transiently increased tumor perfusion and permeability after irradiation, consistent with the higher tumor uptake of ¹⁸F-labeled anti-HER2 5F7 in irradiated mice.

Conclusion

Low-level brain irradiation induces dynamic changes in tumor vasculature that increase the intracranial tumor delivery of an anti-HER2 V_HH, which could facilitate the use of radiolabeled V_HH to detect, monitor, and treat HER2-expressing brain metastases.

Tailoring of chitosan/diacrylated pluronic system as a versatile nanoplatform for the amelioration of radiation-induced cognitive dysfunction

Rutin (RUT) is a biologically active flavonoid that is reported to modulate radiation-induced brain dysfunctions. However, RUT's poor water solubility and low brain bioavailability limit its clinical use. To increase its brain bioavailability, RUT was loaded onto nanoplatforms based on chitosan/diacrylated pluronic (CS/DA-PLUR) nanogels synthesized by gamma radiation. The optimized formulation was investigated as a carrier system for RUT. Based on pilot experiments' results, the cranial radiation (CR) dose that induced cognitive dysfunction was selected. In the main experiment, rats were pre-treated orally with either free RUT or RUT-CS/DA-PLUR. Rats' cognitive and motor functions were assessed; 24 h later, rats were sacrificed, and the whole brain was separated for histopathological examination and biochemical estimation of brain content of acetylcholine esterase (AChE), neurotransmitters, oxidative stress markers, and interleukin-1β. CR produced prominent impairment in spatial and non-spatial learning memory, motor coordination, and muscular strength. Moreover, histopathological and biochemical alterations in brain contents of neurotransmitters, oxidative stress, and interleukin-1β were induced by CR. Conversely, RUT-CS/DA-PLUR, but not free RUT, successfully guarded against all the detrimental effects induced by CR. Based on the current findings, loading of RUT enhanced its bioavailability and therapeutic effectiveness by restoring the cognitive functions impaired by CR.

Functional role of brain-engrafted macrophages against brain injuries

BACKGROUND

Brain-resident microglia have a distinct origin compared to macrophages in other organs. Under physiological conditions, microglia are maintained by self-renewal from the local pool, independent of hematopoietic progenitors. Pharmacological depletion of microglia during whole-brain radiotherapy prevents synaptic loss and long-term recognition memory deficits. However, the origin or repopulated cells and the mechanisms behind these protective effects are unknown.

METHODS

CD45low/int/CD11b+ cells from naïve brains, irradiated brains, PLX5622-treated brains and PLX5622 + whole-brain radiotherapy-treated brains were FACS sorted and sequenced for transcriptomic comparisons. Bone marrow chimeras were used to trace the origin and long-term morphology of repopulated cells after PLX5622 and whole-brain radiotherapy. FACS analyses of intrinsic and exotic synaptic compartments were used to measure phagocytic activities of microglia and repopulated cells. In addition, concussive brain injuries were given to PLX5622 and brain-irradiated mice to study the potential protective functions of repopulated cells after PLX5622 + whole-brain radiotherapy.

RESULTS

After a combination of whole-brain radiotherapy and microglia depletion, repopulated cells are brain-engrafted macrophages that originate from circulating monocytes. Comparisons of transcriptomes reveal that brain-engrafted macrophages have an intermediate phenotype that resembles both monocytes and embryonic microglia. In addition, brain-engrafted macrophages display reduced phagocytic activity for synaptic compartments compared to microglia from normal brains in response to a secondary concussive brain injury. Importantly, replacement of microglia by brain-engrafted macrophages spare mice from whole-brain radiotherapy-induced long-term cognitive deficits, and prevent concussive injury-induced memory loss.

CONCLUSIONS

Brain-engrafted macrophages prevent radiation- and concussion-induced brain injuries and cognitive deficits.

Integrative Role of Hyperbaric Oxygen Therapy on Healthspan, Age-Related Vascular Cognitive Impairment, and Dementia

Growing life expectancy will contribute to the on-going shift towards a world population increasingly comprised of elderly individuals. This demographic shift is associated with a rising prevalence of age-related diseases, among all age-related pathologies it has become crucial to understand the age-associated cognitive changes that remain a major risk factor for the development of vascular cognitive impairment and dementia (VCID). Furthermore, age-related Alzheimer's disease and other neurogenerative diseases with vascular etiology are the most prominent contributing factors for the loss of cognitive function observed in aging. Hyperbaric Oxygen Therapy (HBOT) achieves physiologic effects by increasing oxygen tension (PO2), raising oxygen tissue levels, decreasing intracranial pressure and relieving cerebral edema. Many of the beneficial effects of HBOT exert their protective effects at the level of the microcirculation. Furthermore, the microcirculation's exquisite pervasive presence across every tissue in the body, renders it uniquely able to influence the local environment of most tissues and organs, including the brain. As such, treatments aimed at restoring aging-induced functional and structural alterations of the cerebral microcirculation may potentially contribute to the amelioration of a range of age-related pathologies including vascular cognitive impairment, Alzheimer's disease, and vascular dementias. Despite the presented evidence, the efficacy and safety of HBOT for the treatment of age-related vascular cognitive impairment and dementia remains understudied. The present review aims to examine the existing evidence indicative of a potential therapeutic role for HBOT-induced hyperoxia against age-related cerebromicrovascular pathologies contributing to cognitive impairment, dementia and decreased healthspan in the elderly.

Brain Damage and Patterns of Neurovascular Disorder after Ionizing Irradiation. Complications in Radiotherapy and Radiation Combined Injury

Exposure to ionizing radiation, mechanical trauma, toxic chemicals or infections, or combinations thereof (i.e., combined injury) can induce organic injury to brain tissues, the structural disarrangement of interactive networks of neurovascular and glial cells, as well as on arrays of the paracrine and systemic destruction. This leads to subsequent decline in cognitive capacity and decompensation of mental health. There is an ongoing need for improvement in mitigating and treating radiation- or combined injury-induced brain injury. Cranial irradiation per se can cause a multifactorial encephalopathy that occurs in a radiation dose- and time-dependent manner due to differences in radiosensitivity among the various constituents of brain parenchyma and vasculature. Of particular concern are the radiosensitivity and inflammation susceptibility of: 1. the neurogenic and oligodendrogenic niches in the subependymal and hippocampal domains; and 2. the microvascular endothelium. Thus, cranial or total-body irradiation can cause a plethora of biochemical and cellular disorders in brain tissues, including: 1. decline in neurogenesis and oligodendrogenesis; 2. impairment of the blood-brain barrier; and 3. ablation of vascular capillary. These changes, along with cerebrovascular inflammation, underlie different stages of encephalopathy, from the early protracted stage to the late delayed stage. It is evident that ionizing radiation combined with other traumatic insults such as penetrating wound, burn, blast, systemic infection and chemotherapy, among others, can exacerbate the radiation sequelae (and vice versa) with increasing severity of neurogenic and microvascular patterns of radiation brain damage.

Stem-Cell Therapy as a Potential Strategy for Radiation-Induced Brain Injury

Radiation therapy is a standard and effective non-surgical treatment for primary brain tumors and metastases. However, this strategy inevitably results in damage of normal brain tissue, causing severe complications, especially the late-delayed cognitive impairment. Due to the multifactorial and complex pathological effects of radiation, there is a lack of effective preventative and restorative treatments for the irradiated brain. Stem-cell therapy has held considerable promise for decades in the treatment of central nervous system (CNS) disorders because of its unique capacity for tissue repair and functional integrity. Currently, there is growing interest in using stem cells as a novel option to attenuate the adverse effects of irradiation. In the present review, we discuss recent studies evaluating stem-cell therapies for the irradiated brain and their therapeutic effects on ameliorating radiation-related brain injury as well as their potential challenges in clinical applications. We discuss these works in context of the pathogenesis of radiation-induced injury to CNS tissue in an attempt to elucidate the potential mechanisms of engrafted stem cells to reverse radiation-induced degenerative processes.

Altered properties of brain white matter structural networks in patients with nasopharyngeal carcinoma after radiotherapy

Previous neuroimaging studies revealed radiation-induced brain injury in patients with nasopharyngeal carcinoma (NPC) in the years after radiotherapy (RT). These injuries may be associated with structural and functional alterations. However, differences in the brain structural connectivity of NPC patients at different times after RT, especially in the early-delayed period, remain unclear. We acquired diffusion tensor imaging (DTI) data from three groups of NPC patients, 25 in the pre-RT (before RT) group, 22 in the early-delayed (1-6 months) period (post-RT-ED) group, and 33 in the late-delayed (>6 months) period (post-RT-LD) group. Then, we constructed brain white matter (WM) structural networks and used graph theory to compare their between-group differences. The NPC patients in the post-RT-ED group showed decreased global properties when compared with the pre-RT group. We also detected the nodes with between-group differences in nodal parameters. The nodes that differed between the post-RT-ED and pre-RT groups were mainly located in the default mode (DMN) and central executive networks (CEN); those that differed between the post-RT-LD and pre-RT groups were located in the limbic system; and those that differed between the post-RT-LD and post-RT-ED groups were mainly in the DMN. These findings may indicate that radiation-induced brain injury begins in the early-delayed period and that a reorganization strategy begins in the late-delayed period. Our findings may provide new insight into the pathogenesis of radiation-induced brain injury in normal-appearing brain tissue from the network perspective.

An Iatrogenic Model of Brain Small-Vessel Disease: Post-Radiation Encephalopathy

We studied 114 primitive cerebral neoplasia, that were surgically treated, and underwent radiotherapy (RT), and compared their results to those obtained by 190 patients diagnosed with subcortical vascular dementia (sVAD). Patients with any form of primitive cerebral neoplasia underwent whole-brain radiotherapy. All the tumor patients had regional field partial brain RT, which encompassed each tumor, with an average margin of 2.6 cm from the initial target tumor volume. We observed in our patients who have been exposed to a higher dose of RT (30–65 Gy) a cognitive and behavior decline similar to that observed in sVAD, with the frontal dysexecutive syndrome, apathy, and gait alterations, but with a more rapid onset and with an overwhelming effect. Multiple mechanisms are likely to be involved in radiation-induced cognitive impairment. The active site of RT brain damage is the white matter areas, particularly the internal capsule, basal ganglia, caudate, hippocampus, and subventricular zone. In all cases, radiation damage inside the brain mainly focuses on the cortical–subcortical frontal loops, which integrate and process the flow of information from the cortical areas, where executive functions are “elaborated” and prepared, towards the thalamus, subthalamus, and cerebellum, where they are continuously refined and executed. The active mechanisms that RT drives are similar to those observed in cerebral small vessel disease (SVD), leading to sVAD. The RT’s primary targets, outside the tumor mass, are the blood–brain barrier (BBB), the small vessels, and putative mechanisms that can be taken into account are oxidative stress and neuro-inflammation, strongly associated with the alteration of NMDA receptor subunit composition.

Single-cell RNA sequencing identifies senescent cerebromicrovascular endothelial cells in the aged mouse brain

Age-related phenotypic changes of cerebromicrovascular endothelial cells lead to dysregulation of cerebral blood flow and blood-brain barrier disruption, promoting the pathogenesis of vascular cognitive impairment (VCI). In recent years, endothelial cell senescence has emerged as a potential mechanism contributing to microvascular pathologies opening the avenue to the therapeutic exploitation of senolytic drugs in preclinical studies. However, difficulties with the detection of senescent endothelial cells in wild type mouse models of aging hinder the assessment of the efficiency of senolytic treatments. To detect senescent endothelial cells in the aging mouse brain, we analyzed 4233 cells in fractions enriched for cerebromicrovascular endothelial cells and other cells associated with the neurovascular unit obtained from young (3-month-old) and aged (28-month-old) C57BL/6 mice. We define 13 transcriptomic cell types by deep, single-cell RNA sequencing. We match transcriptomic signatures of cellular senescence to endothelial cells identified on the basis of their gene expression profile. Our study demonstrates that with advanced aging, there is an increased ratio of senescent endothelial cells (~ 10%) in the mouse cerebral microcirculation. We propose that our single-cell RNA sequencing-based method can be adapted to study the effect of aging on senescence in various brain cell types as well as to evaluate the efficiency of various senolytic regimens in multiple tissues.

Nicotinamide mononucleotide (NMN) supplementation promotes neurovascular rejuvenation in aged mice: transcriptional footprint of SIRT1 activation, mitochondrial protection, anti-inflammatory, and anti-apoptotic effects

Aging-induced structural and functional alterations of the neurovascular unit lead to impairment of neurovascular coupling responses, dysregulation of cerebral blood flow, and increased neuroinflammation, all of which contribute importantly to the pathogenesis of age-related vascular cognitive impairment (VCI). There is increasing evidence showing that a decrease in NAD+ availability with age plays a critical role in age-related neurovascular and cerebromicrovascular dysfunction. Our recent studies demonstrate that restoring cellular NAD+ levels in aged mice rescues neurovascular function, increases cerebral blood flow, and improves performance on cognitive tasks. To determine the effects of restoring cellular NAD+ levels on neurovascular gene expression profiles, 24-month-old C57BL/6 mice were treated with nicotinamide mononucleotide (NMN), a key NAD+ intermediate, for 2 weeks. Transcriptome analysis of preparations enriched for cells of the neurovascular unit was performed by RNA-seq. Neurovascular gene expression signatures in NMN-treated aged mice were compared with those in untreated young and aged control mice. We identified 590 genes differentially expressed in the aged neurovascular unit, 204 of which are restored toward youthful expression levels by NMN treatment. The transcriptional footprint of NMN treatment indicates that increased NAD+ levels promote SIRT1 activation in the neurovascular unit, as demonstrated by analysis of upstream regulators of differentially expressed genes as well as analysis of the expression of known SIRT1-dependent genes. Pathway analysis predicts that neurovascular protective effects of NMN are mediated by the induction of genes involved in mitochondrial rejuvenation, anti-inflammatory, and anti-apoptotic pathways. In conclusion, the recently demonstrated protective effects of NMN treatment on neurovascular function can be attributed to multifaceted sirtuin-mediated anti-aging changes in the neurovascular transcriptome. Our present findings taken together with the results of recent studies using mitochondria-targeted interventions suggest that mitochondrial rejuvenation is a critical mechanism to restore neurovascular health and improve cerebral blood flow in aging.

Pharmacological or genetic depletion of senescent astrocytes prevents whole brain irradiation-induced impairment of neurovascular coupling responses protecting cognitive function in mice

Whole brain irradiation (WBI, also known as whole brain radiation therapy or WBRT) is a mainstream therapy for patients with identifiable brain metastases and as a prophylaxis for microscopic malignancies. WBI accelerates brain aging, causing progressive cognitive dysfunction in ~ 50% of surviving patients, thus compromising quality of life. The mechanisms responsible for this WBI side effect remain obscure, and there are no effective treatments or prevention strategies. Here, we test the hypothesis that WBI induces astrocyte senescence, which contributes to impaired astrocytic neurovascular coupling (NVC) responses and the genesis of cognitive decline. To achieve this goal, we used transgenic p16-3MR mice, which allows the detection and selective elimination of senescent cells. We subjected these mice to a clinically relevant protocol of fractionated WBI (5 Gy twice weekly for 4 weeks). WBI-treated and control mice were tested for spatial memory performance (radial arm water maze), astrocyte-dependent NVC responses (whisker-stimulation-induced increases in cerebral blood flow, assessed by laser speckle contrast imaging), NVC-related gene expression, astrocytic release of eicosanoid gliotransmitters and the presence of senescent astrocytes (by flow cytometry, immunohistochemistry and gene expression profiling) at 6 months post-irradiation. WBI induced senescence in astrocytes, which associated with NVC dysfunction and impaired performance on cognitive tasks. To establish a causal relationship between WBI-induced senescence and NVC dysfunction, senescent cells were depleted from WBI-treated animals (at 3 months post-WBI) by genetic (ganciclovir treatment) or pharmacological (treatment with the BCL-2/BCL-xL inhibitor ABT263/Navitoclax, a known senolytic drug) means. In WBI-treated mice, both treatments effectively eliminated senescent astrocytes, rescued NVC responses, and improved cognitive performance. Our findings suggest that the use of senolytic drugs can be a promising strategy for preventing the cognitive impairment associated with WBI.

Mechanisms of Vascular Aging, A Geroscience Perspective: JACC Focus Seminar

Age-related pathological alterations of the vasculature have a critical role in morbidity and mortality of older adults. In epidemiological studies, age is the single most important cardiovascular risk factor that dwarfs the impact of traditional risk factors. To develop novel therapeutic interventions for prevention of age-related vascular pathologies, it is crucial to understand the cellular and molecular mechanisms of vascular aging. In this review, shared molecular mechanisms of aging are considered in terms of their contribution to the pathogenesis of macrovascular and microvascular diseases associated with old age. The role of cellular senescence in development of vascular aging phenotypes is highlighted, and potential interventions to prevent senescence and to eliminate senescent cells for prevention of vascular pathologies are presented. The evidence supporting a role for interorgan communication and circulating progeronic and antigeronic factors in vascular aging is discussed.

Assessment of age-related decline of neurovascular coupling responses by functional near-infrared spectroscopy (fNIRS) in humans

Preclinical studies provide strong evidence that age-related impairment of neurovascular coupling (NVC) plays a causal role in the pathogenesis of vascular cognitive impairment (VCI). NVC is a critical homeostatic mechanism in the brain, responsible for adjustment of local cerebral blood flow to the energetic needs of the active neuronal tissue. Recent progress in geroscience has led to the identification of critical cellular and molecular mechanisms involved in neurovascular aging, identifying these pathways as targets for intervention. In order to translate the preclinical findings to humans, there is a need to assess NVC in geriatric patients as an endpoint in clinical studies. Functional near-infrared spectroscopy (fNIRS) is a non-invasive neuroimaging technique that enables the investigation of local changes in cerebral blood flow, quantifying task-related changes in oxygenated and deoxygenated hemoglobin concentrations. In the present overview, the basic principles of fNIRS are introduced and the application of this technique to assess NVC in older adults with implications for the design of studies on the mechanistic underpinnings of VCI is discussed.

Endothelial dysfunction and angiogenesis impairment in the ageing vasculature

Ageing is the main risk factor for the development of cardiovascular diseases. A central mechanism by which ageing promotes vascular pathologies is compromising endothelial health. The age-related attenuation of endothelium-dependent dilator responses (endothelial dysfunction) associated with impairment of angiogenic processes and the subsequent pathological remodelling of the microcirculation contribute to compromised tissue perfusion and exacerbate functional decline in older individuals. This Review focuses on cellular, molecular, and functional changes that occur in the endothelium during ageing. We explore the links between oxidative and nitrative stress and the conserved molecular pathways affecting endothelial dysfunction and impaired angiogenesis during ageing. We also speculate on how these pathological processes could be therapeutically targeted. An improved understanding of endothelial biology in older patients is crucial for all cardiologists because maintenance of a competently functioning endothelium is critical for adequate tissue perfusion and long-term cardiac health.

Cognitive functioning following brain irradiation as part of cancer treatment: Characterizing better cognitive performance

OBJECTIVE

Although brain radiation therapy (RT) impacts cognitive function, little is known about the subset of survivors with minimal cognitive deficits. This study compares the characteristics of patients receiving brain irradiation as part of cancer treatment with minimal cognitive deficits to those with poorer cognitive functioning.

METHODS

Adults at least 6 months postbrain RT (N = 198) completed cognitive measures of attention, memory, and executive functions. Cognitive functioning was categorized into better- and poorer-performing groups, with better-performing survivors scoring no worse than 1.5 standard deviations below the published normative mean on all cognitive measures. Logistic regression was used to identify variables associated with better-performing group membership.

RESULTS

Approximately 25% of the sample met the criteria for the better-performing group. In unadjusted analyses, RT type (whole brain irradiation and partial brain irradiation), sedating medications, and fatigue were independently associated with cognition. Sociodemographic and other clinical characteristics were not significant. In adjusted analyses, only fatigue remained significantly associated with group membership (OR = 1.05, 95% CI = 1.01-1.09, P = .009).

CONCLUSIONS

There is a subgroup of survivors with minimal long-term cognitive deficits despite undergoing a full course of brain RT as part of cancer treatment. Lower fatigue had the strongest association with better cognitive performance. Interventions targeting cancer-related fatigue may help buffer the neurotoxic effects of brain RT.

The role of the immune system in brain metastasis

Metastatic brain tumors are the most common brain tumors in adults. With numerous successful advancements in systemic treatment of most common cancer types, brain metastasis is becoming increasingly important in the overall prognosis of cancer patients. Brain metastasis of peripheral tumor is the result of complex interplay of primary tumor, immune system and central nervous system microenvironment. Once formed, brain metastases hide behind the blood brain barrier and become inaccessible to chemotherapies that are otherwise successful in targeting systemic cancer. The approval of immune checkpoint inhibitors for several common cancers such as advanced melanoma and lung cancers brings with it the opportunity and obligation to further understand the mechanisms of immunosuppression by tumors that spread to the brain as well as the interaction between the brain environment and tumor microenvironment. In this review paper we define the central role of the immune system in the development of brain metastases. We performed a comprehensive review of the literature to outline the molecular mechanisms of immunosuppression used by tumors and how the immune system interacts with the central nervous system to facilitate brain metastasis. In particular we discuss the tumor-type-specific mechanisms of metastasis of cancers that preferentially metastasize to the brain as well as the therapies that effectively modulate the immune response, such as immune checkpoint inhibitors and vaccines.

Cognitive Decline Secondary to Therapeutic Brain Radiation-Similarities and Differences to Traumatic Brain Injury

Traumatic brain injury (TBI) resulting from forceful impacts on the torso and head has been of major interest because of the prevalence of such injuries in military personnel, contact sports and the elderly. Cognitive and behavioral changes associated with TBI are also seen following whole brain radiation treatment for cancer and chemotherapy for disseminated tumors. The biological mechanisms involved in the initiation of TBI from impact, radiation, and chemotherapy to loss of cognitive function have several shared characteristics including increases in blood brain barrier permeability, blood vessel density, increases in inflammatory and autoimmune responses, alterations in NMDA and glutamate receptor levels and release of proteins normally sequestered in the brain into the blood and spinal fluid. The development of therapeutic agents that mitigate the loss of cognition and development of behavioral disorders in patients experiencing radiation-induced injury may provide benefit to those with TBI when similar processes are involved on a cellular or molecular level. Increased collaborative efforts between the radiation oncology and the neurology and psychiatry communities may be of major benefit for the management of brain injury from varied environmental insults.

Efficacy of pre-operative stereotactic radiosurgery followed by surgical resection and correlative radiobiological analysis for patients with 1-4 brain metastases: study protocol for a phase II trial

BACKGROUND

Stereotactic radiosurgery (SRS) has emerged as a common adjuvant modality used with surgery for resectable brain metastases (BMs). However, the optimal sequence of the multi-modality therapy has not been established. The goal of the study is to evaluate 6-month local control utilizing pre-operative SRS followed by surgical resection for patients with 1-4 brain metastases.

METHODS

This prospective, single arm, phase II trial will recruit patients with up to 4 brain metastases and at least one resectable lesion. All lesions will be treated with SRS and symptomatic lesions will be resected within 1-4 days after SRS. Patients will be monitored for 6-month local control, in-brain progression free survival, distant in-brain failure, rate of leptomeningeal spread, radiation necrosis and overall survival. Additionally, we will also perform correlative radiobiological molecular studies to assess the effect of radiation dosing on the tumor tissue and clinical outcomes. We expect that pre-operative SRS to the gross tumor prior to surgical resection will improve local control and decrease leptomeningeal failure.

DISCUSSION

Our study is the second prospective trial to investigate the efficacy of pre-operative SRS in the treatment of multiple BMs. In addition, the correlative molecular studies will be the first to investigate early response of BMs at a cellular and genetic level in response to radiation doses and potentially provide molecular prognostic markers for local control and overall survival.

TRIAL REGISTRATION

Clinicaltrials.gov identifier: NCT03398694 (registration date: January 12, 2018).

Strategies to Preserve Cognition in Patients With Brain Metastases: A Review

Brain metastases are common to the natural history of many advanced malignancies. Historically, whole brain radiation therapy (WBRT) has played a key role in the management of brain metastases, especially for patients with multiple lesions. However, prospective trials have demonstrated consistent neurocognitive toxicities after WBRT, and various pharmacologic and anatomic strategies designed to mitigate these toxicities have been studied in recent years. Memantine, an NMDA receptor antagonist, taken during and after WBRT improved cognitive preservation in a randomized trial over placebo. Deliberate reductions in radiation dose to the hippocampus, via hippocampal-avoidance (HA)-WBRT, resulted in improved cognition over historic controls in a phase II trial, and follow-up randomized trials are now ongoing to evaluate cognitive outcomes with HA vs. conventional brain radiation techniques. Nevertheless, some of the most promising strategies currently available to reduce the cognitive effects of brain radiation may be found in efforts to avoid or delay WBRT administration altogether. Stereotactic radiosurgery (SRS), involving focused, high-dose radiation to central nervous system (CNS) lesions with maximal sparing of normal brain parenchyma, has become the standard for limited brain metastases (classically 1–3 or 4 lesions) in the wake of multiple randomized trials demonstrating equivalent survival and improved cognition with SRS alone compared to SRS plus WBRT. Today, there is growing evidence to support SRS alone for multiple (≥4) brain metastases, with comparable survival to SRS alone in patients with fewer lesions. In patients with small-cell lung cancer, the routine use of prophylactic cranial irradiation (PCI) for extensive-stage disease has been also been challenged following the results of a randomized trial supporting an alternative strategy of MRI brain surveillance and early salvage radiation for the development of brain metastases. Moreover, new systemic agents are demonstrating increasing CNS penetration and activity, with the potential to offer greater control of widespread and microscopic brain disease that was previously only achievable with WBRT. In this review, we endeavor to put these clinical data on cognition and brain metastases into historical context and to survey the evolving landscape of strategies to improve future outcomes.

The final frontier: Transient microglia reduction after cosmic radiation exposure mitigates cognitive impairments and modulates phagocytic activity

Microglia are the primary immune element within the brain, which are responsible for monitoring synapse function and neuron health. Exposure to cosmic radiation has the potential to cause long-term cognitive deficits in rodent models and therefore indicates a difficult challenge for future astronauts piloting interplanetary travel. Here, we discuss the potential of transient microglia depletion after the injury to ameliorate the harsh microenvironment of the brain and eliminate any potential long-term cognitive effects. Repopulation of microglia enables phagocytic phenotypes to be circumvented, via the reduction of Phagocytic and lysosomal markers, potentially being responsible for increased neuroprotection. Brief depletion of microglia after irradiation mitigated the development of any long-term memory deficits, comparable to healthy animals. Chronically, microglial levels were not affected by cosmic radiation followed by temporary microglia depletion. Following repopulation, improved recognition memory was paralleled by downregulated complement receptor C5aR. Preserved synapse function also demonstrated the therapeutic ability of microglia depletion as it corresponded with fewer phagocytic microglia phenotypes. The understanding of long-term radiation-induced cognitive impairments is vital for the protection of future astronauts and equally as important for current cancer patients. Temporary microglia depletion showed promise in preventing any deleterious cognitive impairments following exposure to elements of cosmic radiation, such as helium and high-charge nuclei.

miRNA-based therapeutic potential of stem cell-derived extracellular vesicles: a safe cell-free treatment to ameliorate radiation-induced brain injury

PURPOSE

This review compiles what is known about extracellular vesicles (EVs), their bioactive cargo, and how they might be used to treat radiation-induced brain injury. Radiotherapy (RT) is effective in cancer treatment, but can cause substantial damage to normal central nervous system tissue. Stem cell therapy has been shown to be effective in treating cognitive dysfunction arising from RT, but there remain safety concerns when grafting foreign stem cells into the brain (i.e. immunogenicity, teratoma). These limitations prompted the search for cell-free alternatives, and pointed to EVs that have been shown to have similar ameliorating effects in other tissues and injury models.

CONCLUSIONS

EVs are nano-scale and lipid-bound vesicles that readily pass the blood-brain barrier. Arguably the most important bioactive cargo within EVs are RNAs, in particular microRNAs (miRNA). A single miRNA can modulate entire gene networks and signalling within the recipient cell. Determining functionally relevant miRNA could lead to therapeutic treatments where synthetically-derived EVs are used as delivery vectors for miRNA. Stem cell-derived EVs can be effective in treating brain injury including radiation-induced cognitive deficits. Of particular interest are systemic modes of administration which obviate the need for invasive procedures.

Temporary microglia-depletion after cosmic radiation modifies phagocytic activity and prevents cognitive deficits

Microglia are the main immune component in the brain that can regulate neuronal health and synapse function. Exposure to cosmic radiation can cause long-term cognitive impairments in rodent models thereby presenting potential obstacles for astronauts engaged in deep space travel. The mechanism/s for how cosmic radiation induces cognitive deficits are currently unknown. We find that temporary microglia depletion, one week after cosmic radiation, prevents the development of long-term memory deficits. Gene array profiling reveals that acute microglia depletion alters the late neuroinflammatory response to cosmic radiation. The repopulated microglia present a modified functional phenotype with reduced expression of scavenger receptors, lysosome membrane protein and complement receptor, all shown to be involved in microglia-synapses interaction. The lower phagocytic activity observed in the repopulated microglia is paralleled by improved synaptic protein expression. Our data provide mechanistic evidence for the role of microglia in the development of cognitive deficits after cosmic radiation exposure.

The effect of carotid artery stenting on capillary transit time heterogeneity in patients with carotid artery stenosis

Introduction

Carotid revascularisation improves haemodynamic compromise in cerebral circulation as an additional benefit to the primary goal of reducing future thromboembolic risk. We determined the effect of carotid artery stenting on cerebral perfusion and oxygenation using a perfusion-weighted MRI algorithm that is based on assessment of capillary transit-time heterogeneity together with other perfusion and metabolism-related metrics.

Patients and methods

A consecutive series of 33 patients were evaluated by dynamic susceptibility contrast perfusion-weighted MRI prior to and within 24 h of the endovascular procedure. The level of relative change induced by stenting, and relationship of these changes with respect to baseline stenosis degree were analysed.

Results

Stenting led to significant increase in cerebral blood flow (p < 0.001), and decrease in cerebral blood volume (p = 0.001) and mean transit time (p < 0.001); this was accompanied by reduction in oxygen extraction fraction (p < 0.001) and capillary transit-time heterogeneity (p < 0.001), but an overall increase in relative capillary transit-time heterogeneity (RTH: CTH divided by MTT; p = 0.008). No significant change was observed with respect to cerebral metabolic rate of oxygen. The median volume of tissue with MTT > 2s decreased from 24 ml to 12 ml (p = 0.009), with CTH > 2s from 29 ml to 19 ml (p = 0.041), and with RTH < 0.9 from 61 ml to 39 ml (p = 0.037) following stenting. These changes were correlated with the baseline degree of stenosis.Discussion: Stenting improved the moderate stage of haemodynamic compromise at baseline in our cohort. The decreased relative transit-time heterogeneity, which increases following stenting, is probably a reflection of decreased functional capillary density secondary to chronic hypoperfusion induced by the proximal stenosis.Conclusion: Carotid artery stenting, is not only important for prophylaxis of future vascular events, but also is critical for restoration of microvascular function in the cerebral tissue.

Radiation-induced brain structural and functional abnormalities in presymptomatic phase and outcome prediction

Radiation therapy, a major method of treatment for brain cancer, may cause severe brain injuries after many years. We used a rare and unique cohort of nasopharyngeal carcinoma patients with normal-appearing brains to study possible early irradiation injury in its presymptomatic phase before severe, irreversible necrosis happens. The aim is to detect any structural or functional imaging biomarker that is sensitive to early irradiation injury, and to understand the recovery and progression of irradiation injury that can shed light on outcome prediction for early clinical intervention. We found an acute increase in local brain activity that is followed by extensive reductions in such activity in the temporal lobe and significant loss of functional connectivity in a distributed, large-scale, high-level cognitive function-related brain network. Intriguingly, these radiosensitive functional alterations were found to be fully or partially recoverable. In contrast, progressive late disruptions to the integrity of the related far-end white matter structure began to be significant after one year. Importantly, early increased local brain functional activity was predictive of severe later temporal lobe necrosis. Based on these findings, we proposed a dynamic, multifactorial model for radiation injury and another preventive model for timely clinical intervention. Hum Brain Mapp 39:407-427, 2018. © 2017 Wiley Periodicals, Inc.

A pilot study of neuropsychological functions, APOE and amyloid imaging in patients with gliomas

Brain tumor patients treated with radiotherapy (RT) often develop cognitive dysfunction, and recent studies suggest that the APOE ε-4 allele may influence cognitive outcome. The ε-4 allele is known to promote beta (β) amyloid deposition in the cortex, and preliminary evidence suggests that RT may be associated with this process. However, it is unknown whether β-amyloid accumulation contributes to treatment neurotoxicity. In this pilot study, we assessed neuropsychological functions and β-amyloid retention using ¹⁸F-florbetaben (FBB) PET in a subset of brain tumor patients who participated in our study of APOE polymorphisms and cognitive functions. Twenty glioma patients treated with conformal RT ± chemotherapy participated in the study: 6 were APOE ε-4 carriers and 14 were non-ε-4 carriers. Patients completed a neuropsychological re-evaluation (mean time interval = 5 years, SD = 0.83) and brain MRI and FBB PET scans. Wilcoxon signed-rank test comparisons between prior and current neuropsychological assessments showed a significant decline in attention (Brief Test of Attention, p = 0.018), and a near significant decline in verbal learning (Hopkins Verbal learning Test-Learning, p = 0.07). Comparisons by APOE status showed significant differences over time in attention/working memory (WAIS-III digits forward, p = 0.028 and digits backward, p = 0.032), with a decline among APOE ε-4 carriers. There were no significant differences in any of the FBB PET analyses between APOE ε-4 carriers and non-ε-4 carriers. The findings suggest that glioma patients may experience worsening in attention and executive functions several years after treatment, and that the APOE ε-4 allele may modulate cognitive decline, but independent of increased β-amyloid deposition.

Role of NADPH oxidase in radiation-induced pro-oxidative and pro-inflammatory pathways in mouse brain

PURPOSE

The present study was designed to investigate our hypothesis that NADPH oxidase plays a role in radiation-induced pro-oxidative and pro-inflammatory environments in the brain.

MATERIALS AND METHODS

C57BL/6 mice received either fractionated whole brain irradiation or sham-irradiation. The mRNA expression levels of pro-inflammatory mediators, such as TNF-α and MCP-1, were determined by quantitative real-time RT-PCR. The protein expression levels of TNF-α, MCP-1, NOX-2 and Iba1 were detected by immunofluorescence staining. The levels of ROS were visualized by in situ DHE fluorescence staining.

RESULTS

A significant up-regulation of mRNA and protein expression levels of TNF-α and MCP-1 was observed in irradiated mouse brains. Additionally, immunofluorescence staining of Iba1 showed a marked increase of microglial activation in mouse brain after irradiation. Moreover, in situ DHE fluorescence staining revealed that fractionated whole brain irradiation significantly increased production of ROS. Furthermore, a significant increase in immunoreactivity of NOX-2 was detected in mouse brain after irradiation. On the contrary, an enhanced ROS generation in mouse brain after irradiation was markedly attenuated in the presence of NOX inhibitors or NOX-2 neutralizing antibody.

CONCLUSIONS

These results suggest that NOX-2 may play a role in fractionated whole brain irradiation-induced pro-oxidative and pro-inflammatory pathways in mouse brain.

Heart in space: effect of the extraterrestrial environment on the cardiovascular system

National space agencies and private corporations aim at an extended presence of humans in space in the medium to long term. Together with currently suboptimal technology, microgravity and cosmic rays raise health concerns about deep-space exploration missions. Both of these physical factors affect the cardiovascular system, whose gravity-dependence is pronounced. Heart and vascular function are, therefore, susceptible to substantial changes in weightlessness. The altered cardiovascular function in space causes physiological problems in the postflight period. A compromised cardiovascular system can be excessively vulnerable to space radiation, synergistically resulting in increased damage. The space radiation dose is significantly lower than in patients undergoing radiotherapy, in whom cardiac damage is well-documented following cancer therapy in the thoracic region. Nevertheless, epidemiological findings suggest an increased risk of late cardiovascular disease even with low doses of radiation. Moreover, the peculiar biological effectiveness of heavy ions in cosmic rays might increase this risk substantially. However, whether radiation-induced cardiovascular effects have a threshold at low doses is still unclear. The main countermeasures to mitigate the effect of the space environment on cardiac function are physical exercise, antioxidants, nutraceuticals, and radiation shielding.

Prophylactic Cranial Irradiation (PCI) versus Active MRI Surveillance for Small Cell Lung Cancer: The Case for Equipoise

Prophylactic cranial irradiation (PCI) for SCLC offers a consistent reduction in the incidence of brain metastases at the cost of measurable toxicity to neurocognitive function and quality of life, in the setting of characteristic pathologic changes to the brain. The sequelae of PCI have historically been justified by the perception of an overall survival advantage specific to SCLC. This rationale has now been challenged by a randomized trial in extensive-stage SCLC demonstrating equivalent progression-free survival and a trend toward improved overall survival with PCI omission in the context of modern magnetic resonance imaging (MRI) staging and surveillance. In this article, we critically examine the randomized trials of PCI in extensive-stage SCLC and discuss their implications on the historical data supporting PCI for limited-stage SCLC from the pre-MRI era. Further, we review the toxicity of moderate doses of radiation to the entire brain that underlie the growing interest in active MRI surveillance and PCI omission. Finally, the evidence supporting prospective investigation of radiosurgery for limited brain metastases in SCLC is reviewed. Overall, our aim is to provide an evidence-based assessment of the debate over PCI versus active MRI surveillance and to highlight the need for contemporary trials evaluating optimal central nervous system management in SCLC.