Quantifying Cognitive Decrements Caused by Cranial Radiotherapy

With the exception of survival, cognitive impairment stemming from the clinical management of cancer is a major factor dictating therapeutic outcome. For many patients afflicted with CNS and non-CNS malignancies, radiotherapy and chemotherapy offer the best options for disease control. These treatments however come at a cost, and nearly all cancer survivors (~11 million in the US alone as of 2006) incur some risk for developing cognitive dysfunction, with the most severe cases found in patients subjected to cranial radiotherapy (~200,000/yr) for the control of primary and metastatic brain tumors1. Particularly problematic are pediatric cases, whose long-term survival plagued with marked cognitive decrements results in significant socioeconomic burdens2. To date, there are still no satisfactory solutions to this significant clinical problem

Sex-Specific Effects of a Wartime-Like Radiation Exposure on Cognitive Function.

Evaluating the risk for central nervous system (CNS) effects after whole-body or partial-body irradiation presents challenges due in part to the varied exposure scenarios in the context of occupational, accidental or wartime releases. Risk estimations are further complicated by the fact that robust changes in brain function are unlikely to manifest until significantly late post exposure times. Collectively, the current data regarding CNS radiation risk are conflicting in humans and a survey of the animal model data shows that it is similarly inconsistent. Due to the sparseness of such data, the current study was conducted using male and female mice to evaluate the brain for the delayed effects of a 2 Gy whole-body exposure to c rays starting six months postirradiation. Behavioral testing indicated sex-specific differences in the induction of anxiety-like behaviors and in the ability to abolish fear memories. Molecular analyses showed alterations in post-synaptic protein levels that might affect synaptic plasticity and increased levels of global DNA methylation, suggesting a potential epigenetic mechanism that might contribute to radiation-induced cognitive dysfunction. These data add to the understanding of the CNS response to whole-body irradiation and may lead to improved risk assessment and provide guidance in the development of effective radiation countermeasures to protect military personnel and civilians alike

Stem Cell Transplantation Strategies for the Restoration of Cognitive Dysfunction Caused by Cranial Radiotherapy

Radiotherapy often provides the only clinical recourse for those afflicted with primary or metastatic brain tumors. While beneficial, cranial irradiation can induce a progressive and debilitating decline in cognition that may, in part, be caused by the depletion of neural stem cells. Given the increased survival of patients diagnosed with brain cancer, quality of life in terms of cognitive health has become an increasing concern, especially in the absence of any satisfactory long-term treatments

Functional equivalence of stem cell and stem cell-derived extracellular vesicle transplantation to repair the irradiated brain.

Cranial radiotherapy, although beneficial for the treatment of brain tumors, inevitably leads to normal tissue damage that can induce unintended neurocognitive complications that are progressive and debilitating. Ionizing radiation exposure has also been shown to compromise the structural integrity of mature neurons throughout the brain, an effect believed to be at least in part responsible for the deterioration of cognitive health. Past work has shown that cranially transplanted human neural stem cells (hNSCs) or their extracellular vesicles (EVs) afforded long-term beneficial effects on many of these cognitive decrements. To provide additional insight into the potential neuroprotective mechanisms of cell-based regenerative strategies, we have analyzed hippocampal neurons for changes in structural integrity and synaptic remodeling after unilateral and bilateral transplantation of hNSCs or EVs derived from those same cells. Interestingly, hNSCs and EVs similarly afforded protection to host neurons, ameliorating the impact of irradiation on dendritic complexity and spine density for neurons present in both the ipsilateral and contralateral hippocampi 1 month following irradiation and transplantation. These morphometric improvements were accompanied by increased levels of glial cell-derived growth factor and significant attenuation of radiation-induced increases in postsynaptic density protein 95 and activated microglia were found ipsi- and contra-lateral to the transplantation sites of the irradiated hippocampus treated with hNSCs or hNSC-derived EVs. These findings document potent far-reaching neuroprotective effects mediated by grafted stem cells or EVs adjacent and distal to the site of transplantation and support their potential as therapeutic agents to counteract the adverse effects of cranial irradiation

Long-term cognitive effects of human stem cell transplantation in the irradiated brain

PURPOSE: Radiotherapy remains a primary treatment modality for the majority of central nervous system tumors, but frequently leads to debilitating cognitive dysfunction. Given the absence of satisfactory solutions to this serious problem, we have used human stem cell therapies to ameliorate radiation-induced cognitive impairment. Here, past studies have been extended to determine whether engrafted cells provide even longer-term benefits to cognition. MATERIALS AND METHODS: Athymic nude rats were cranially irradiated (10 Gy) and subjected to intrahippocampal transplantation surgery 2 days later. Human embryonic stem cells (hESC) or human neural stem cells (hNSC) were transplanted, and animals were subjected to cognitive testing on a novel place recognition task 8 months later. RESULTS: Grafting of hNSC was found to provide long lasting cognitive benefits over an 8-month post-irradiation interval. At this protracted time, hNSC grafting improved behavioral performance on a novel place recognition task compared to irradiated animals not receiving stem cells. Engrafted hESC previously shown to be beneficial following a similar task, 1 and 4 months after irradiation, were not found to provide cognitive benefits at 8 months. CONCLUSIONS: Our findings suggest that hNSC transplantation promotes the long-term recovery of the irradiated brain, where intrahippocampal stem cell grafting helps to preserve cognitive function

New Concerns for Neurocognitive Function during Deep Space Exposures to Chronic, Low Dose-Rate, Neutron Radiation.

As NASA prepares for a mission to Mars, concerns regarding the health risks associated with deep space radiation exposure have emerged. Until now, the impacts of such exposures have only been studied in animals after acute exposures, using dose rates ∼1.5×105 higher than those actually encountered in space. Using a new, low dose-rate neutron irradiation facility, we have uncovered that realistic, low dose-rate exposures produce serious neurocognitive complications associated with impaired neurotransmission. Chronic (6 month) low-dose (18 cGy) and dose rate (1 mGy/d) exposures of mice to a mixed field of neutrons and photons result in diminished hippocampal neuronal excitability and disrupted hippocampal and cortical long-term potentiation. Furthermore, mice displayed severe impairments in learning and memory, and the emergence of distress behaviors. Behavioral analyses showed an alarming increase in risk associated with these realistic simulations, revealing for the first time, some unexpected potential problems associated with deep space travel on all levels of neurological function