Physiological and cognitive changes after treatments of cyclophosphamide, methotrexate, and fluorouracil: implications of the gut microbiome and depressive-like behavior

Introduction

Chemotherapy-induced cognitive impairment colloquially referred to as chemobrain is a poorly understood phenomenon affecting a highly variable proportion of patients with breast cancer. Here we investigate the association between anxiety and despair-like behaviors in mice treated with cyclophosphamide, methotrexate, and fluorouracil (CMF) along with host histological, proteomic, gene expression, and gut microbial responses.

Methods

Forced swim and sociability tests were used to evaluate depression and despair-like behaviors. The tandem mass tag (TMT) proteomics approach was used to assess changes in the neural protein network of the amygdala and hippocampus. The composition of gut microbiota was assessed through 16S rRNA gene sequencing. Finally, quantitative reverse transcription polymerase chain reaction (qRT-PCR) was used to evaluate changes in intestinal gap junction markers.

Results and discussion

We observed that CMF induced social and despair-like behavior in mice 96 hours following treatment. Proteomic analysis identified changes in various proteins related to progressive neurological disease, working memory deficit, primary anxiety disorder, and gene expression revealing increases in NMDA and AMPA receptors in both the hippocampus and the amygdala because of CMF treatment. These changes finally, we observed immediate changes in the microbial population after chemotherapy treatment, with a notable abundance of Muribaculaceae and Romboutsia which may contribute to changes seen in the gut.

Sulforaphane's Multifaceted Potential: From Neuroprotection to Anticancer Action

Sulforaphane (SFN) is a naturally occurring compound found in cruciferous vegetables such as broccoli and cauliflower. It has been widely studied for its potential as a neuroprotective and anticancer agent. This review aims to critically evaluate the current evidence supporting the neuroprotective and anticancer effects of SFN and the potential mechanisms through which it exerts these effects. SFN has been shown to exert neuroprotective effects through the activation of the Nrf2 pathway, the modulation of neuroinflammation, and epigenetic mechanisms. In cancer treatment, SFN has demonstrated the ability to selectively induce cell death in cancer cells, inhibit histone deacetylase, and sensitize cancer cells to chemotherapy. SFN has also shown chemoprotective properties through inhibiting phase I metabolizing enzymes, modulating phase II xenobiotic-metabolizing enzymes, and targeting cancer stem cells. In addition to its potential as a therapeutic agent for neurological disorders and cancer treatment, SFN has shown promise as a potential treatment for cerebral ischemic injury and intracranial hemorrhage. Finally, the ongoing and completed clinical trials on SFN suggest potential therapeutic benefits, but more research is needed to establish its effectiveness. Overall, SFN holds significant promise as a natural compound with diverse therapeutic applications.

Effect of Sirt3 on hippocampal MnSOD activity, mitochondrial function, physiology, and cognition in an aged murine model

The NAD(+)-dependent deacetylase SIRT3 is a proven mitochondrial metabolic stress sensor. It has been linked to the regulation of the mitochondrial acetylome and activation of several metabolic enzymes (e.g., manganese superoxide dismutase [MnSOD]) to protect mitochondrial function and redox homeostasis, which are vital for survival, excitability, and synaptic signaling of neurons mediating short- and long-term memory formation as well as retention. Eighteen-month-old male and female wild-type (WT) and Sirt3-/- mice were behaviorally tested for hippocampus-dependent cognitive performance in a Morris water maze paradigm. Cognitive impairment was displayed during the probe trial by female and male Sirt3-/- mice but not WT mice. Upon sacrifice, brains were fixed, and morphological assessments were conducted on hippocampal tissues. Both female and male Sirt3-/- mice demonstrated impaired spatial memory retention implying that SIRT3 plays a role in long-term memory function. Golgi-staining studies revealed decreased dendritic arborization and dendritic length in the hippocampi of male Sirt3-/- compared to WT animals. Sirt3 deletion significantly increased NR1, NR2A, and NR2B expression in the hippocampus of female mice only. Enzymatic activity of MnSOD, a major mitochondrial deacetylation target of SIRT3, was significantly decreased in both female and male Sirt3-/- mice. Similarly, both female and male Sirt3-/- mice demonstrated a significant decrease in their respiratory control ratio during Complex I-driven respiration, which was apparent only in female Sirt3-/- mice during Complex II-driven respiration.

Chemotherapy induced oxidative stress in the ovary: drug-dependent mechanisms and potential interventions†

Cancer incidence and relative survival are expected to increase over the next few decades. With the majority of patients receiving combinatorial chemotherapy, an increasing proportion of patients experience long-term side effects from treatment-including reproductive disorders and infertility. A limited number of studies have examined mechanisms of single-agent chemotherapy-induced gonadotoxicity, with chemotherapy-induced oxidative stress being implicated in the loss of reproductive functions. Current methods of female fertility preservation are costly, invasive, only moderately successful, and seldom presented to cancer patients. The potential of antioxidants to alleviate chemotherapy has been overlooked at a time when it is becoming increasingly important to develop strategies to protect reproductive functions during chemotherapy. This review will summarize the importance of reactive oxygen species homeostasis in reproduction, chemotherapy-induced mitochondrial dysfunction in oocytes, chemotherapy-induced oxidative stress, and several promising natural adjuvants.

Effects of Simulated 5-Ion Galactic Cosmic Radiation on Function and Structure of the Mouse Heart

Missions into deep space will expose astronauts to the harsh space environment, and the degenerative tissue effects of space radiation are largely unknown. To assess the risks, in this study, male BALB/c mice were exposed to 500 mGy 5-ion simulated GCR (GCRsim) at the NASA Space Radiation Laboratory. In addition, male and female CD1 mice were exposed to GCRsim and administered a diet containing Transforming Growth Factor-beta (TGF-β)RI kinase (ALK5) inhibitor IPW-5371 as a potential countermeasure. An ultrasound was performed to investigate cardiac function. Cardiac tissue was collected to determine collagen deposition, the density of the capillary network, and the expression of the immune mediator toll-like receptor 4 (TLR4) and immune cell markers CD2, CD4, and CD45. In male BALB/c mice, the only significant effects of GCRsim were an increase in the CD2 and TLR4 markers. In male CD1 mice, GCRsim caused a significant increase in total collagens and a decrease in the expression of TLR4, both of which were mitigated by the TGF-β inhibitor diet. In female CD1 mice, GCRsim caused an increase in the number of capillaries per tissue area in the ventricles, which may be explained by the decrease in the left ventricular mass. However, this increase was not mitigated by TGF-β inhibition. In both male and female CD1 mice, the combination of GCRsim and TGF-β inhibition caused changes in left ventricular immune cell markers that were not seen with GCRsim alone. These data suggest that GCRsim results in minor changes to cardiac tissue in both an inbred and outbred mouse strain. While there were few GCRsim effects to be mitigated, results from the combination of GCRsim and the TGF-β inhibitor do point to a role for TGF-β in maintaining markers of immune cells in the heart after exposure to GCR.

Outcomes of the UAMS summer undergraduate research program to increase diversity in research and health professions

The University of Arkansas for Medical Sciences (UAMS) Summer Undergraduate Research Program (SURP) aims to increase diversity in research and health-related careers. The SURP provides underrepresented minority (URM) and disadvantaged students with research, mentoring, and networking experiences; real-life surgical observations; and simulated cardiovascular demonstrations. A postprogram survey was developed to assess program outcomes and explore ways of improving the program to stimulate URM and disadvantaged students' interest in research and health-related careers. This is a report of those postprogram survey findings. Using a survey research design, an online survey was emailed to participants (n = 88). Data were collected for 6 weeks beginning March 2020. There were 37 multiple-choice and open-ended questions regarding education, career choices, and program experiences. Responses were downloaded to statistical software for analyses. Quantitative data were analyzed using descriptive statistics. Major themes were identified for qualitative data. Responses were received from 44.3% (n = 39) of former SURP participants. Overall, 59% stated that the SURP influenced their career goals. When asked about mentor-mentee relationships, 69.3% responded that their interactions were excellent or good; 61.5% maintained contact with their mentor after the SURP. Finally, 79% indicated their SURP experience was excellent or good, and 84.6% would recommend the SURP to others. The SURP has been successful at providing URM and disadvantaged students with positive research experiences and long-term mentor-mentee relationships and has influenced educational and/or career goals. Programs that expose URM and disadvantaged students to basic, clinical, and/or translational research are beneficial for stimulating interest in research and health-related careers.NEW & NOTEWORTHY Mentor-mentee relationships were extremely beneficial as many of the former participants maintained contact with their summer mentor after the program ended. This assessment also revealed that exposing underrepresented and minority students to research has a long-lasting effect on career and educational goals.

Evaluating the effects of low-dose simulated galactic cosmic rays on murine hippocampal-dependent cognitive performance

Space exploration has advanced substantially over recent decades and plans to increase the duration of deep space missions are in preparation. One of the primary health concerns is potential damage to the central nervous system (CNS), resulting in loss of cognitive abilities and function. The majority of ground-based research on space radiation-induced health risks has been conducted using single particle simulations, which do not effectively model real-world scenarios. Thus, to improve the safety of space missions, we must expand our understanding of the effects of simulated galactic cosmic rays (GCRs) on the CNS. To assess the effects of low-dose GCR, we subjected 6-month-old male BALB/c mice to 50 cGy 5-beam simplified GCR spectrum (¹H, ²⁸Si, ⁴He, ¹⁶O, and ⁵⁶Fe) whole-body irradiation at the NASA Space Radiation Laboratory. Animals were tested for cognitive performance with Y-maze and Morris water maze tests 3 months after irradiation. Irradiated animals had impaired short-term memory and lacked spatial memory retention on day 5 of the probe trial. Glial cell analysis by flow cytometry showed no significant changes in oligodendrocytes, astrocytes, microglia or neural precursor cells (NPC's) between the sham group and GCR group. Bone marrow cytogenetic data showed a significant increase in the frequency of chromosomal aberrations after GCR exposure. Finally, tandem mass tag proteomics identified 3,639 proteins, 113 of which were differentially expressed when comparing sham versus GCR exposure (fold change > 1.5; p < 0.05). Our data suggest exposure to low-dose GCR induces cognitive deficits by impairing short-term memory and spatial memory retention.

Fractionated Proton Irradiation Does Not Impair Hippocampal-Dependent Short-Term or Spatial Memory in Female Mice

The environment outside the Earth's protective magnetosphere is a much more threatening and complex space environment. The dominant causes for radiation exposure, solar particle events and galactic cosmic rays, contain high-energy protons. In space, astronauts need healthy and highly functioning cognitive abilities, of which the hippocampus plays a key role. Therefore, understanding the effects of ¹H exposure on hippocampal-dependent cognition is vital for developing mitigative strategies and protective countermeasures for future missions. To investigate these effects, we subjected 6-month-old female CD1 mice to 0.75 Gy fractionated ¹H (250 MeV) whole-body irradiation at the NASA Space Radiation Laboratory. The cognitive performance of the mice was tested 3 months after irradiation using Y-maze and Morris water maze tests. Both sham-irradiated and ¹H-irradiated mice significantly preferred exploration of the novel arm compared to the familiar and start arms, indicating intact spatial and short-term memory. Both groups statistically spent more time in the target quadrant, indicating spatial memory retention. There were no significant differences in neurogenic and gliogenic cell counts after irradiation. In addition, proteomic analysis revealed no significant upregulation or downregulation of proteins related to behavior, neurological disease, or neural morphology. Our data suggests ¹H exposure does not impair hippocampal-dependent spatial or short-term memory in female mice.

Piperlongumine as a Neuro-Protectant in Chemotherapy Induced Cognitive Impairment

Advances in the early diagnosis and treatment have led to increases in breast cancer survivorship. Survivors report cognitive impairment symptoms such as loss of concentration and learning and memory deficits which significantly reduce the patient's quality of life. Additional therapies are needed to prevent these side effects and, the precise mechanisms of action responsible are not fully elucidated. However, increasing evidence points toward the use of neuroprotective compounds with antioxidants and anti-inflammatory properties as tools for conserving learning and memory. Here, we examine the ability of piperlongumine (PL), an alkaloid known to have anti-inflammatory and antioxidant effects, to play a neuroprotective role in 16-week-old female C57BL/6J mice treated with a common breast cancer regimen of doxorubicin, cyclophosphamide, and docetaxel (TAC). During social memory testing, TAC-treated mice exhibited impairment, while TAC/PL co-treated mice did not exhibit measurable social memory deficits. Proteomics analysis showed ERK1/2 signaling is involved in TAC and TAC/PL co-treatment. Reduced Nrf2 mRNA expression was also observed. mRNA levels of Gria2 were increased in TAC treated mice and reduced in TAC/PL co-treated mice. In this study, PL protects against social memory impairment when co-administered with TAC via multifactorial mechanisms involving oxidative stress and synaptic plasticity.

The Effects of 5-Fluorouracil/Leucovorin Chemotherapy on Cognitive Function in Male Mice

5-Fluorouracil (5-Fu) and leucovorin (LV) are often given in combination to treat colorectal cancer. 5-Fu/LV prevents cell proliferation by inhibiting thymidylate synthase, which catalyzes the conversion of deoxyuridine monophosphate to deoxythymidine monophosphate. While 5-Fu has been shown to cause cognitive impairment, the synergistic effect of 5-Fu with LV has not been fully explored. The present investigation was designed to assess how the combination of 5-Fu and LV affect cognition in a murine model. Six-month-old male mice were used in this study; 15 mice received saline injections and 15 mice received 5-Fu/LV injections. One month after treatment, the elevated plus maze, Y-maze, and Morris water maze behavioral tasks were performed. Brains were then extracted, cryosectioned, and stained for CD68 to assay microglial activation and with tomato lectin to assay the vasculature. All animals were able to locate the visible and hidden platform locations in the water maze. However, a significant impairment in spatial memory retention was observed in the probe trial after the first day of hidden-platform training (first probe trial) in animals that received 5-Fu/LV, but these animals showed spatial memory retention by day 5. There were no significant increases in inflammation as measured by CD68, but 5-Fu/LV treatment did modulate blood vessel morphology. Tandem mass tag proteomics analysis identified 6,049 proteins, 7 of which were differentially expressed with a p-value of <0.05 and a fold change of >1.5. The present data demonstrate that 5-Fu/LV increases anxiety and significantly impairs spatial memory retention.

Combined Mechanical and Enzymatic Dissociation of Mouse Brain Hippocampal Tissue

This neural dissociation protocol (an adaptation of the protocol accompanying a commercial adult brain dissociation kit) optimizes tissue processing in preparation for detailed downstream analysis such as flow cytometry or single-cell sequencing. Neural dissociation can be conducted via mechanical dissociation (such as using filters, chopping techniques, or pipette trituration), enzymatic digestion, or a combination thereof. The delicate nature of neuronal cells can complicate efforts to obtain the highly viable, true single-cell suspension with minimal cellular debris that is required for single-cell analysis. The data demonstrate that this combination of automated mechanical dissociation and enzymatic digestion consistently yields a highly viable (>90%) single-cell suspension, overcoming the aforementioned difficulties. While a few of the steps require manual dexterity, these steps lessen sample handling and potential cell loss. This manuscript details each step of the process to equip other laboratories to successfully dissociate small quantities of neural tissue in preparation for downstream analysis.

A Bibliometric Analysis of Cyclophosphamide, Methotrexate, and Fluorouracil Breast Cancer Treatments: Implication for the Role of Inflammation in Cognitive Dysfunction

Inflammation is considered one of the possible mechanisms behind long-term cognitive dysfunction persistent after chemotherapy treatment. The chemotherapy combination of cyclophosphamide, methotrexate, and fluorouracil (CMF) was one of the older methods of treating breast cancer patients. Decades later, these patients still report experiencing cognitive side effects. In this present bibliometric review, we applied the VOSviewer tool to describe the existing landscape on literature concerning inflammation as it relates to CMF and cognitive dysfunctions. As time progressed, we saw an increase in interest in the topic. By the mid-2010s there were approximately 1,000 publications per year. Terms related to the brain and CNS did not appear until the later years, and terms related to inflammation and breast cancer were very prevalent throughout the three decades. Also, in more recent years, inflammatory markers and plant-derived compounds used to alleviate side effects of the inflammatory response appeared in the search results. The USA remained the most prolific producer of CMF-, inflammation-, and cognitive dysfunction-related papers throughout the three decades followed by Asia and Europe. As research of cognitive dysfunction caused by inflammation due to chemotherapy treatment progresses, more opportunities emerge for therapeutic methods to improve the quality of life for long-term survivors.

Tocotrienols as an Anti-Breast Cancer Agent

In the past few years, breast cancer has become the most prevalent type of cancer. The majority of patients receive combinatorial chemotherapy treatments, which may result in increased risk of developing drug resistance, a reduced quality of life, and substantial side effects. Treatment modalities that could lessen the physical toll of standard treatments or act in synergy with chemotherapeutic treatments would benefit women worldwide. Research into tocotrienols has thus far demonstrated their potential to be such an agent, with tocotrienols surpassing the pharmacological potential of tocopherols. Further research using in vitro and preclinical breast cancer models to support clinical trials is needed. This review uses bibliometric analysis to highlight this gap in research and summarizes the current and future landscape of tocotrienols as an anti-breast cancer agent.

Development of polymorphic markers in the immune gene complex loci of cattle

The addition of cattle health and immunity traits to genomic selection indices holds promise to increase individual animal longevity and productivity, and decrease economic losses from disease. However, highly variable genomic loci that contain multiple immune-related genes were poorly assembled in the first iterations of the cattle reference genome assembly and underrepresented during the development of most commercial genotyping platforms. As a consequence, there is a paucity of genetic markers within these loci that may track haplotypes related to disease susceptibility. By using hierarchical assembly of bacterial artificial chromosome inserts spanning 3 of these immune-related gene regions, we were able to assemble multiple full-length haplotypes of the major histocompatibility complex, the leukocyte receptor complex, and the natural killer cell complex. Using these new assemblies and the recently released ARS-UCD1.2 reference, we aligned whole-genome shotgun reads from 125 sequenced Holstein bulls to discover candidate variants for genetic marker development. We selected 124 SNPs, using heuristic and statistical models to develop a custom genotyping panel. In a proof-of-principle study, we used this custom panel to genotype 1,797 Holstein cows exposed to bovine tuberculosis (bTB) that were the subject of a previous GWAS study using the Illumina BovineHD array. Although we did not identify any significant association of bTB phenotypes with these new genetic markers, 2 markers exhibited substantial effects on bTB phenotypic prediction. The models and parameters trained in this study serve as a guide for future marker discovery surveys particularly in previously unassembled regions of the cattle genome.

Early Effects of Cyclophosphamide, Methotrexate, and 5-Fluorouracil on Neuronal Morphology and Hippocampal-Dependent Behavior in a Murine Model

Breast cancer (BC) is the most common cancer among women. Fortunately, BC survival rates have increased because the implementation of adjuvant chemotherapy leading to a growing population of survivors. However, chemotherapy-induced cognitive impairments (CICIs) affect up to 75% of BC survivors and may be driven by inflammation and oxidative stress. Chemotherapy-induced cognitive impairments can persist 20 years and hinder survivors' quality of life. To identify early effects of CMF administration in mice, we chose to evaluate adult female mice at 2-week postchemotherapy. Mice received weekly IP administration of CMF (or saline) for 4 weeks, completed behavioral testing, and were sacrificed 2 weeks following their final CMF injection. Behavioral results indicated long-term memory (LTM) impairments postchemotherapy, but did not reveal short-term memory deficits. Dendritic morphology and spine data found increases in overall spine density within CA1 basal and CA3 basal dendrites, but no changes in DG, CA1 apical, or CA3 apical dendrites. Further analysis revealed decreases in arborization across the hippocampus (DG, CA1 apical and basal, CA3 apical and basal). These physiological changes within the hippocampus correlate with our behavioral data indicating LTM impairments following CMF administration in female mice 2-week postchemotherapy. Hippocampal cytokine analysis identified decreases in IL-1α, IL-1β, IL-3, IL-10, and TNF-α levels.

Effects of 16O charged-particle irradiation on cognition, hippocampal morphology and mutagenesis in female mice

The effects of radiation in space on human cognition are a growing concern for NASA scientists and astronauts as the possibility for long-duration missions to Mars becomes more tangible. Oxygen (¹⁶O) radiation is of utmost interest considering that astronauts will interact with this radiation frequently. ¹⁶O radiation is a class of galactic cosmic ray (GCR) radiation and also present within spacecrafts. Whole-body exposure to high linear energy transfer (LET) radiation has been shown to affect hippocampal-dependent cognition. To assess the effects of high-LET radiation, we gave 6-month-old female C57BL/6 mice whole-body exposure to ¹⁶O at 0.25 or 0.1 Gy at NASA's Space Radiation Laboratory. Three months following irradiation, animals were tested for cognitive performance using the Y-maze and Novel Object Recognition paradigms. Our behavioral data shows that ¹⁶O radiation significantly impairs object memory but not spatial memory. Also, dendritic morphology characterized by the Sholl analysis showed that ¹⁶O radiation significantly decreased dendritic branch points, ends, length, and complexity in 0.1 Gy and 0.25 Gy dosages. Finally, we found no significant effect of radiation on single nucleotide polymorphisms in hippocampal genes related to oxidative stress, inflammation, and immediate early genes. Our data suggest exposure to heavy ion ¹⁶O radiation modulates hippocampal neurons and induces behavioral deficits at a time point of three months after exposure in female mice.

Cognitive impairment resulting from treatment with docetaxel, doxorubicin, and cyclophosphamide

Breast cancer is the most commonly diagnosed cancer among women and it is estimated that about 30% of newly diagnosed cancers in women will be breast cancers. While advancements in treating breast cancer have led to an average 5-year survival rate of 90%, many survivors experience cognitive impairments as a result of chemotherapy treatment. Doxorubicin, cyclophosphamide, and docetaxel (TAC) are commonly administered as breast cancer treatments; however, there are few studies that have tested the cognitive effects of TAC. In the current study, 12-week-old female C57BL/6 mice received 4 weekly intraperitoneal injections of either saline or a combination therapy of doxorubicin and cyclophosphamide followed by 4 weekly docetaxel injections. Four weeks after the last injection, mice were tested for hippocampus-dependent cognitive performance in the Y-maze and the Morris water maze. During Y-maze testing, mice exposed to TAC exhibited impairment. During the water maze assessment, all animals were able to locate the visible and hidden platform locations. However, mice that received the TAC presented with a significant impairment in spatial memory retention on the probe trial days. TAC treatment significantly decreases the dendritic complexity of arborization in the dentate gyrus region of the hippocampus. In addition, comparative proteomic analysis revealed downregulation of proteins within key metabolic and signaling pathways associated with cognitive dysfunction, such as oxidative phosphorylation, ephrin signaling, and calcium signaling.

Implications of Breast Cancer Chemotherapy-Induced Inflammation on the Gut, Liver, and Central Nervous System

Breast Cancer is still one of the most common cancers today; however, with advancements in diagnostic and treatment methods, the mortality and survivorship of patients continues to decrease and increase, respectively. Commonly used treatments today consist of drug combinations, such as doxorubicin and cyclophosphamide; docetaxel, doxorubicin, and cyclophosphamide; or doxorubicin, cyclophosphamide, and paclitaxel. Although these combinations are effective at destroying cancer cells, there is still much to be understood about the effects that chemotherapy can have on normal organ systems such as the nervous system, gastrointestinal tract, and the liver. Patients can experience symptoms of cognitive impairments or “chemobrain”, such as difficulty in concentrating, memory recollection, and processing speed. They may also experience gastrointestinal (GI) distress symptoms such as diarrhea and vomiting, as well as hepatotoxicity and long term liver damage. Chemotherapy treatment has also been shown to induce peripheral neuropathy resulting in numbing, pain, and tingling sensations in the extremities of patients. Interestingly, researchers have discovered that this array of symptoms that cancer patients experience are interconnected and mediated by the inflammatory response.

Performance measures of racially underrepresented Ph.D. students in biomedical sciences: The UAMS IMSD Program Outcomes

The purpose of this study was to identify performance measures of racially underrepresented minority (RUM) Ph.D. trainees who needed additional training initiatives to assist with completing the UAMS biomedical science degree. A sample of 37 trainees in the 10-year NIH-NIGMS funded Initiative for Maximizing Student Development (IMSD) program at the University of Arkansas for Medical Sciences (UAMS) were examined. Descriptive statistics and correlations examined process measures (GRE scores, GPAs, etc.) and outcome measures (time-to-degree, publications, post-doctoral fellowship, etc.) While differences were found, there were no statistically significant differences between how these two groups (Historically Black Colleges and Universities (HBCUs) and Predominately White Institutions (PWIs)) of students performed over time as Ph.D. students. Graduates who scored lower on the verbal section of the GRE also had a higher final graduate school grade point average in graduates who received their undergraduate training from HBCUs. Of the graduates who received their undergraduate training from PWIs, graduates who scored lower on the quantitative section of the GRE had higher numbers of publications. These findings stimulate the need to 1) reduce reliance on the use of the GRE in admission committee decisions, 2) identify psychometrically valid indicators that tailored to assess outcome variables that are relevant to the careers of biomedical scientists, and 3) ensure the effective use of the tools in making admission decisions.

Consequences of space radiation on the brain and cardiovascular system

Staying longer in outer space will inevitably increase the health risks of astronauts due to the exposures to galactic cosmic rays and solar particle events. Exposure may pose a significant hazard to space flight crews not only during the mission but also later, when slow-developing adverse effects could finally become apparent. The body of literature examining ground-based outcomes in response to high-energy charged-particle radiation suggests differential effects in response to different particles and energies. Numerous animal and cellular models have repeatedly demonstrated the negative effects of high-energy charged-particle on the brain and cognitive function. However, research on the role of space radiation in potentiating cardiovascular dysfunction is still in its early stages. This review summarizes the available data from studies using ground-based animal models to evaluate the response of the brain and heart to the high-energy charged particles of GCR and SPE, addresses potential sex differences in these effects, and aims to highlight gaps in the current literature for future study.

Alzheimer amyloid-β- peptide disrupts membrane localization of glucose transporter 1 in astrocytes: implications for glucose levels in brain and blood

Alzheimer’s disease (AD) is associated with disturbances in blood glucose regulation, and type-2 diabetes elevates the risk for dementia. A role for amyloid-β peptide (Aβ) in linking these age-related conditions has been proposed, tested primarily in transgenic mouse lines that overexpress mutated amyloid precursor protein (APP). Because APP has its own impacts on glucose regulation, we examined the BRI-Aβ42 line (“Aβ₄₂-tg”), which produces extracellular Aβ_1–42 in the CNS without elevation of APP. We also looked for interactions with diet-induced obesity (DIO) resulting from a high-fat, high-sucrose (“western”) diet. Aβ₄₂-tg mice were impaired in both spatial memory and glucose tolerance. Although DIO induced insulin resistance, Aβ_1–42 accumulation did not, and the impacts of DIO and Aβ on glucose tolerance were merely additive. Aβ₄₂-tg mice exhibited no significant differences from wild-type in insulin production, body weight, lipidemia, appetite, physical activity, respiratory quotient, an-/orexigenic factors, or inflammatory factors. These negative findings suggested that the phenotype in these mice arose from perturbation of glucose excursion in an insulin-independent tissue. To wit, cerebral cortex of Aβ₄₂-tg mice had reduced glucose utilization, similar to human patients with AD. This was associated with insufficient trafficking of glucose transporter 1 to the plasma membrane in parenchymal brain cells, a finding also documented in human AD tissue. Together, the lower cerebral metabolic rate of glucose and diminished function of parenchymal glucose transporter 1 indicate that aberrant regulation of blood glucose in AD likely reflects a central phenomenon, resulting from the effects of Aβ on cerebral parenchyma, rather than a generalized disruption of hypothalamic or peripheral endocrinology. The involvement of a specific glucose transporter in this deficit provides a new target for the design of AD therapies.

Cranial irradiation impairs juvenile social memory and modulates hippocampal physiology

Cranial and craniospinal irradiation are the oldest central nervous system prophylaxis treatments considered for pediatric patients with acute lymphoblastic leukemia (ALL). However, survivors of childhood ALL that received cranial radiotherapy are at increased risk for deficits in neurocognitive skills. The continuous and dynamic response of normal tissue after irradiation has been identified as one of the causative factors for cognitive changes after cranial radiation therapy. The aim of our study was to investigate the radiation effects on social behavior and neuronal morphology in the hippocampus of adult mice. Twenty-oneday-old male C57BL/6 mice were irradiated with the small-animal radiation research platform (SARRP). Animals were given a single 10-Gy dose of radiation of X-ray cranial radiation. One month following irradiation, animals underwent behavioral testing in the Three-Chamber Sociability paradigm. Radiation affected social discrimination during the third stage eliciting an inability to discriminate between the familiar and stranger mouse, while sham successfully spent more time exploring the novel stranger. Proteomic analysis revealed dysregulation of metabolic and signaling pathways associated with neurocognitive dysfunction such as mitochondrial dysfunction, Rac 1 signaling, and synaptogenesis signaling. We observed significant decreases in mushroom spine density in the Cornu Ammonis 2 of the hippocampus, which is associated with sociability processing.

A Bibliometric Review of Publications on Oxidative Stress and Chemobrain: 1990-2019

Oxidative stress is considered one of the possible mechanisms behind chemobrain or the cognitive dysfunction persistent after chemotherapy treatment. Breast cancer patients have reported chemobrain symptoms since the 1990s. In this present bibliometric review, we employed the VOSviewer tool to describe the existing landscape on literature concerning oxidative stress, breast cancer chemotherapies, and chemobrain. As of 2019, 8799 papers were listed in the Web of Science database, with more than 900 papers published each year. As expected, terms relating to oxidative stress, mitochondria, breast cancer, and antioxidants have occurred very often in the literature throughout the years. In recent years, there has been an increase in the occurrence of terms related to nanomedicine. Only within the last decade do the keywords 'brain', 'blood-brain barrier', and 'central nervous system' appear, reflecting an increased interest in chemobrain. China has become the most prolific producer of oxidative stress and chemotherapy related papers in the last decade followed by the USA and India. In conclusion, the subject of oxidative stress as a mechanism behind chemotherapies' toxicities is an active area of research.

Assessing the Effects of Redox Modifier MnTnBuOE-2-PyP 5+ on Cognition and Hippocampal Physiology Following Doxorubicin, Cyclophosphamide, and Paclitaxel Treatment

Background: Chemotherapy treatment for breast cancer can induce cognitive impairments often involving oxidative stress. The brain, as a whole, is susceptible to oxidative stress due to its high-energy requirements, limited anaerobic respiration capacities, and limited antioxidant defenses. The goal of the current study was to determine if the manganese porphyrin superoxide dismutase mimetic MnTnBuOE-2-PyP (MnBuOE) could ameliorate the effects of doxorubicin, cyclophosphamide, and paclitaxel (AC-T) on mature dendrite morphology and cognitive function. Methods: Four-month-old female C57BL/6 mice received intraperitoneal injections of chemotherapy followed by subcutaneous injections of MnBuOE. Four weeks following chemotherapy treatment, mice were tested for hippocampus-dependent cognitive performance in the Morris water maze. After testing, brains were collected for Golgi staining and molecular analyses. Results: MnBuOE treatment preserved spatial memory during the Morris water-maze. MnBuOE/AC-T showed spatial memory retention during all probe trials. AC-T treatment significantly impaired spatial memory retention in the first and third probe trial (no platform). AC-T treatment decreased dendritic length in the Cornu Ammonis 1 (CA1) and dentate gyrus (DG) areas of the hippocampus while AC-T/MnBuOE maintained dendritic length. Comparative proteomic analysis revealed affected protein networks associated with cell morphology and behavior functions in both the AC-T and AC-T/MnBuOE treatment groups.

Effects of thioTEPA chemotherapy on cognition and motor coordination

Cancer survivorship has increased greatly as therapies have become more advanced and effective. Thus, we must now focus on improving the quality of life of patients after treatment. After chemotherapy, many patients experience chemotherapy-induced cognitive decline, indicating a need to investigate pathologies associated with this condition. In this study, we addressed cognitive impairment after thioTEPA treatment by assessing behavior and assaying cytokine production and the structure of dendrites in the hippocampus. Male mice were given three intraperitoneal injections of thioTEPA. Five weeks later, the mice underwent behavior testing, and brains were collected for Golgi staining and cytokine analysis. Behavior tests included y-maze and Morris water maze and licking behavioral task. Cytokines measured include: IL-1α, IL-1β, IL-2, IL-3, IL-4, IL-5, IL-10, IL-12p70, MCP-1, TNF-α, GMCSF, and RANTES. We observed decreased memory retention in behavioral tasks. Also, dendritic arborization and length were decreased after chemotherapy treatment. Finally, thioTEPA decreased cytokine production in animals treated with chemotherapy, compared to saline-treated controls. Here, we used a mouse model to correlate the decreases in dendritic complexity and inflammatory cytokine production with cognitive impairment after chemotherapy.

Late Effects of 16O-Particle Radiation on Female Social and Cognitive Behavior and Hippocampal Physiology

The radiation environment in space remains a major concern for manned space exploration, as there is currently no shielding material capable of fully protecting flight crews. Additionally, there is growing concern for the social and cognitive welfare of astronauts, due to prolonged radiation exposure and confinement they will experience on a mission to Mars. In this artice, we report on the late effects of ¹⁶O-particle radiation on social and cognitive behavior and neuronal morphology in the hippocampus of adult female mice. Six-month-old mice received ¹⁶O-particle whole-body irradiation at doses of either 0.25 or 0.1 Gy (600 MeV/n; 18-33 cGy/min) at the NASA's Space Radiation Laboratory in Upton, NY. At nine months postirradiation, the animals underwent behavioral testing in the three-chamber sociability, novel object recognition and Y-maze paradigms. Exposure to 0.1 or 0.25 Gy ¹⁶O significantly impaired object memory, a 0.25 Gy dose impaired social novelty learning, but neither dosage impaired short-term spatial memory. We observed significant decreases in mushroom spine density and dendrite morphology in the dentate gyrus, cornu ammonis 3, 2 and 1 of the hippocampus, which are critical areas for object novelty and sociability processing. Our data suggest exposure to ¹⁶O modulates hippocampal pyramidal and granular neurons and induces behavioral deficits at a time point of nine months after exposure in females.

Long-Term Changes in Cognition and Physiology after Low-Dose 16O Irradiation

Astronauts traveling to Mars will be exposed to high levels of ionizing radiation upon leaving low-Earth orbit. During prolonged space travel, astronauts are exposed to galactic cosmic rays (GCRs) composed of protons; oxygen molecules; and high energy, high mass charged particles. Notably, oxygen molecules can travel through the shielding of spacecraft, potentially impacting 25% of the hippocampus. The aim of the current study was to assess whether ¹⁶O-particle radiation induced a behavioral deficit and histological changes in mice. Mice were sent to the National Aeronautics and Space Administration (NASA) Space Radiation Laboratory at Brookhaven National Laboratory and exposed to particulate ¹⁶O radiation at doses of 0 and 0.05 Gy. Nine months after irradiation, the mice were tested for novel object recognition and in the Y-maze, after which the animals were sacrificed. The brains were then dissected along the midsagittal plane for Golgi staining. Exposure to 0.05 Gy significantly impaired novel object recognition. However, short term memory and exploratory activity in the Y-maze were not affected. Micromorphometric analysis revealed significant decreases in mushroom spine density in the dentate gyrus and cornu Ammonis-1 and -3 of the hippocampus. Sholl analysis revealed a significant decrease in dendritic complexity in the dentate gyrus. The present data provide evidence that space radiation has deleterious effects on mature neurons associated with hippocampal learning and memory.

Early effects of 16O radiation on neuronal morphology and cognition in a murine model

Astronauts exposed to high linear energy transfer radiation may experience cognitive injury. The pathogenesis of this injury is unknown but may involve glutamate receptors or modifications to dendritic structure and/or dendritic spine density and morphology. Glutamate is the major excitatory neurotransmitter in the central nervous system, where it acts on ionotropic and metabotropic glutamate receptors located at the presynaptic terminal and in the postsynaptic membrane at synapses in the hippocampus. Dendritic spines are sites of excitatory synaptic transmission, and changes in spine structure and dendrite morphology are thought to be morphological correlates of altered brain function associated with hippocampal-dependent learning and memory. The aim of the current study is to assess whether behavior, glutamate receptor gene expression, and dendritic structure in the hippocampus are altered in mice after early exposure to ¹⁶O radiation in mice. Two weeks post-irradiation, animals were tested for hippocampus-dependent cognitive performance in the Y-maze. During Y-maze testing, mice exposed to 0.1 Gy and 0.25 Gy radiation failed to distinguish the novel arm, spending approximately the same amount of time in all 3 arms during the retention trial. Exposure to ¹⁶O significantly reduced the expression of Nr1 and GluR1 in the hippocampus and modulated spine morphology in the dentate gyrus and cornu Ammon 1 within the hippocampus. The present data provide evidence that ¹⁶O radiation has early deleterious effects on mature neurons that are associated with hippocampal learning and memory.

Late effects of 1H irradiation on hippocampal physiology

NASA's Missions to Mars and beyond will expose flight crews to potentially dangerous levels of charged-particle radiation. Of all charged nuclei, ¹H is the most abundant charged particle in both the galactic cosmic ray (GCR) and solar particle event (SPE) spectra. There are currently no functional spacecraft shielding materials that are able to mitigate the charged-particle radiation encountered in space. Recent studies have demonstrated cognitive injuries due to high-dose ¹H exposures in rodents. Our study investigated the effects of ¹H irradiation on neuronal morphology in the hippocampus of adult male mice. 6-month-old mice received whole-body exposure to ¹H at 0.5 and 1 Gy (150 MeV/n; 0.35-0.55 Gy/min) at NASA's Space Radiation Laboratory in Upton, NY. At 9-months post-irradiation, we tested each animal's open-field exploratory performance. After sacrifice, we dissected the brains along the midsagittal plane, and then either fixed or dissected further and snap-froze them. Our data showed that exposure to 0.5 Gy or 1 Gy ¹H significantly increased animals' anxiety behavior in open-field testing. Our micromorphometric analyses revealed significant decreases in mushroom spine density and dendrite morphology in the Dentate Gyrus, Cornu Ammonis 3 and 1 of the hippocampus, and lowered expression of synaptic markers. Our data suggest ¹H radiation significantly increased exploration anxiety and modulated the dendritic spine and dendrite morphology of hippocampal neurons at a dose of 0.5 or 1 Gy.

Effects of Cyclophosphamide and/or Doxorubicin in a Murine Model of Postchemotherapy Cognitive Impairment

Postchemotherapy cognitive impairment, or PCCI, is a common complaint, particularly among breast cancer patients. However, the exact nature of PCCI appears complex. To model the human condition, ovariectomized C57BL/6J mice were treated intravenous weekly for 4 weeks with saline, 2 mg/kg doxorubicin (DOX), 50 mg/kg cyclophosphamide (CYP), or DOX + CYP. For the subsequent 10 weeks, mice were assessed on several behavioral tests, including those measuring spatial learning and memory. After sacrifice, hippocampal spine density and morphology in the dentate gyrus, CA1, and CA3 regions were measured. Additionally, hippocampal levels of total glutathione, glutathione disulfide, MnSOD, CuZnSOD, and cytokines were measured. Body weight decreased in all groups during treatment, but recovered post-treatment. Most behaviors were unaffected by drug treatment: Open field activity, motor coordination, grip strength, water maze and Barnes maze performance, buried food test performance, and novel object and object location recognition tests. There were some significant effects of CYP and DOX + CYP treatment during the initial test of home cage behavior, but these did not persist into the second and third test times. Density of stubby spines, but not mushroom or thin spines, in the dentate gyrus was significantly decreased in the DOX, CYP, and DOX + CYP treatment groups. There were no significant effects in the CA1 or CA3 regions. CuZnSOD levels were significantly increased in DOX + CYP-treated mice; other hippocampal antioxidant levels were unaffected. Most cytokines showed no treatment-related effects, but IL-1β, IL-6, and IL-12 were slightly reduced in mice treated with DOX + CYP. Although the animal model, route of exposure, and DOX and CYP doses used here were reflective of human exposure, there were only sporadic effects due to chemotherapeutic treatment.

Behavioral Effects of Focal Irradiation in a Juvenile Murine Model

Chemotherapy has been successfully used to reduce radiation dose and volume for most pediatric patients. However, because of the failure of chemotherapeutic agents to cross the blood-brain barrier and the lack of response of some brain tumors to these agents, radiation therapy is still used to treat many childhood cancers with CNS involvement. In this study, we investigated the radiation effects on cognition and dendritic structure in the hippocampus in juvenile male mice. Twenty-one-day-old male C57BL/6 mice were irradiated using the small animal radiation research platform (SARRP). Animals were exposed to either a 10 Gy single dose or 10 Gy × 2 fractionated doses of X-ray cranial radiation. Five weeks after irradiation, animals were tested for hippocampus-dependent cognitive performance in the Morris water maze. Significant impairment in spatial memory retention was observed in the probe trial after the first day of hidden-platform training (first probe trial) in animals that received either 10 Gy single-dose or 10 Gy × 2 fractionated doses. However, by day 5, mice that received a 10 Gy single dose showed spatial memory retention in the probe trials, whereas mice that received the 20 Gy fractionated doses remained impaired. During Y-maze testing, animals exposed to radiation were impaired; the irradiated mice were not able to distinguish among the three Y-maze arms and spent approximately the same amount of time in all three arms during the retention trial. Radiation significantly compromised the dendritic architecture and reduced spine density throughout the hippocampal trisynaptic network.

Changes in cognition and dendritic complexity following intrathecal methotrexate and cytarabine treatment in a juvenile murine model

Acute lymphoblastic leukemia (ALL) is the most prevalent childhood cancer and accounts for 26.8% of cancer diagnoses among children, worldwide-approximately 3000 children each year. While advancements in treating ALL have led to a remission rate of more than 90%, many survivors experience adverse neurocognitive and/or neurobehavioral effects as a result of intrathecal chemotherapy. Methotrexate (MTX) is commonly administered with cytosine arabinoside (AraC, cytarabine) during intrathecal chemotherapy for ALL. To date, few studies exist that test the cognitive effects of intrathecal injections of MTX/AraC on juvenile populations. The purpose of our study was to investigate the combined effects of MTX/AraC on cognition and dendritic structure in the hippocampus in juvenile male mice. Twenty, 21-day-old male C57BL/6 mice were used in this study; 10 mice received intrathecal MTX/AraC treatment, and 10 were given intrathecal saline injections. Five weeks after injections, we tested the animals' hippocampus-dependent cognitive performance in the Morris water maze. After the first day of hidden-platform training, we observed that the mice that received MTX/AraC treatment showed signs of significant impairment in spatial memory retention. MTX/AraC treatment significantly compromised the dendritic architecture and reduced mushroom spine density in the dorsal ganglion (DG), CA1, and CA3 areas of the hippocampus. The present data provided evidence that MTX/AraC compromised the dendritic architecture and impaired hippocampal dependent cognition. This could provide insight into chemotherapy-induced cognitive decline in juvenile patients treated for ALL.

Effects of 1H + 16O Charged Particle Irradiation on Short-Term Memory and Hippocampal Physiology in a Murine Model

Radiation from galactic cosmic rays (GCR) poses a significant health risk for deep-space flight crews. GCR are unique in their extremely high-energy particles. With current spacecraft shielding technology, some of the predominant particles astronauts would be exposed to are ¹H + ¹⁶O. Radiation has been shown to cause cognitive deficits in mice. The hippocampus plays a key role in memory and cognitive tasks; it receives information from the cortex, undergoes dendritic-dependent processing and then relays information back to the cortex. In this study, we investigated the effects of combined ¹H + ¹⁶O irradiation on cognition and dendritic structures in the hippocampus of adult male mice three months postirradiation. Six-month-old male C57BL/6 mice were irradiated first with ¹H (0.5 Gy, 150 MeV/n) and 1 h later with ¹⁶O (0.1 Gy, 600 MeV/n) at the NASA Space Radiation Laboratory (Upton, NY). Three months after irradiation, animals were tested for hippocampus-dependent cognitive performance using the Y-maze. Upon sacrifice, molecular and morphological assessments were performed on hippocampal tissues. During Y-maze testing, the irradiated mice failed to distinguish the novel arm, spending approximately the same amount of time in all three arms during the retention trial relative to sham-treated controls. Irradiated animals also showed changes in expression of glutamate receptor subunits and synaptic density-associated proteins. ¹H + ¹⁶O radiation compromised dendritic morphology in the cornu ammonis 1 and dentate gyrus within the hippocampus. These data indicate cognitive injuries due to ¹H + ¹⁶O at three months postirradiation.

Fine-mapping host genetic variation underlying outcomes to Mycobacterium bovis infection in dairy cows

BACKGROUND

Susceptibility to Mycobacterium bovis infection in cattle is governed in part by host genetics. However, cattle diagnosed as infected with M. bovis display varying signs of pathology. The variation in host response to infection could represent a continuum since time of exposure or distinct outcomes due to differing pathogen handling. The relationships between host genetics and variation in host response and pathological sequelae following M. bovis infection were explored by genotyping 1966 Holstein-Friesian dairy cows at 538,231 SNPs with three distinct phenotypes. These were: single intradermal cervical comparative tuberculin (SICCT) test positives with visible lesions (VLs), SICCT-positives with undetected visible lesions (NVLs) and matched controls SICCT-negative on multiple occasions.

RESULTS

Regional heritability mapping identified three loci associated with the NVL phenotype on chromosomes 17, 22 and 23, distinct to the region on chromosome 13 associated with the VL phenotype. The region on chromosome 23 was at genome-wide significance and candidate genes overlapping the mapped window included members of the bovine leukocyte antigen class IIb region, a complex known for its role in immunity and disease resistance. Chromosome heritability analysis attributed variance to six and thirteen chromosomes for the VL and NVL phenotypes, respectively, and four of these chromosomes were found to explain a proportion of the phenotypic variation for both the VL and NVL phenotype. By grouping the M. bovis outcomes (VLs and NVLs) variance was attributed to nine chromosomes. When contrasting the two M. bovis infection outcomes (VLs vs NVLs) nine chromosomes were found to harbour heritable variation. Regardless of the case phenotype under investigation, chromosome heritability did not exceed 8% indicating that the genetic control of bTB resistance consists of variants of small to moderate effect situated across many chromosomes of the bovine genome.

CONCLUSIONS

These findings suggest the host genetics of M. bovis infection outcomes is governed by distinct and overlapping genetic variants. Thus, variation in the pathology of M. bovis infected cattle may be partly genetically determined and indicative of different host responses or pathogen handling. There may be at least three distinct outcomes following M. bovis exposure in dairy cattle: resistance to infection, infection resulting in pathology or no detectable pathology.

Assessment of Hippocampal Dendritic Complexity in Aged Mice Using the Golgi-Cox Method

Dendritic spines are the protuberances from the neuronal dendritic shafts that contain  excitatory synapses. The morphological and branching variations of the neuronal dendrites within the hippocampus are implicated in cognition and memory formation. There are several approaches to Golgi staining, all of which have been useful for determining the morphological characteristics of dendritic arbors and produce a clear background. The present Golgi-Cox method, (a slight variation of the protocol that is provided with a commercial Golgi staining kit), was designed to assess how a relatively low dose of the chemotherapeutic drug 5-flurouracil (5-Fu) would affect dendritic morphology, the number of spines, and the complexity of arborization within the hippocampus. The 5-Fu significantly modulated the dendritic complexity and decreased the spine density throughout the hippocampus in a region-specific manner. The data presented show that the Golgi staining method effectively stained the mature neurons in the CA1, the CA3, and the dentate gyrus (DG) of the hippocampus. This protocol reports the details for each step so that other researchers can reliably stain tissue throughout the brain with high quality results and minimal troubleshooting.

28Si total body irradiation injures bone marrow hematopoietic stem cells via induction of cellular apoptosis

Long-term space mission exposes astronauts to a radiation environment with potential health hazards. High-energy charged particles (HZE), including ²⁸Si nuclei in space, have deleterious effects on cells due to their characteristics with high linear energy transfer and dense ionization. The influence of ²⁸Si ions contributes more than 10% to the radiation dose equivalent in the space environment. Understanding the biological effects of ²⁸Si irradiation is important to assess the potential health hazards of long-term space missions. The hematopoietic system is highly sensitive to radiation injury and bone marrow (BM) suppression is the primary life-threatening injuries after exposure to a moderate dose of radiation. Therefore, in the present study we investigated the acute effects of low doses of ²⁸Si irradiation on the hematopoietic system in a mouse model. Specifically, 6-month-old C57BL/6J mice were exposed to 0.3, 0.6 and 0.9Gy ²⁸Si (600MeV) total body irradiation (TBI). The effects of ²⁸Si TBI on BM hematopoietic stem cells (HSCs) and hematopoietic progenitor cells (HPCs) were examined four weeks after the exposure. The results showed that exposure to ²⁸Si TBI dramatically reduced the frequencies and numbers of HSCs in irradiated mice, compared to non-irradiated controls, in a radiation dose-dependent manner. In contrast, no significant changes were observed in BM HPCs regardless of radiation doses. Furthermore, irradiated HSCs exhibited a significant impairment in clonogenic ability. These acute effects of ²⁸Si irradiation on HSCs may be attributable to radiation-induced apoptosis of HSCs, because HSCs, but not HPCs, from irradiated mice exhibited a significant increase in apoptosis in a radiation dose-dependent manner. However, exposure to low doses of ²⁸Si did not result in an increased production of reactive oxygen species and DNA damage in HSCs and HPCs. These findings indicate that exposure to ²⁸Si irradiation leads to acute HSC damage.

Densely ionizing radiation affects DNA methylation of selective LINE-1 elements

Long Interspersed Nucleotide Element 1 (LINE-1) retrotransposons are heavily methylated and are the most abundant transposable elements in mammalian genomes. Here, we investigated the differential DNA methylation within the LINE-1 under normal conditions and in response to environmentally relevant doses of sparsely and densely ionizing radiation. We demonstrate that DNA methylation of LINE-1 elements in the lungs of C57BL6 mice is dependent on their evolutionary age, where the elder age of the element is associated with the lower extent of DNA methylation. Exposure to 5-aza-2'-deoxycytidine and methionine-deficient diet affected DNA methylation of selective LINE-1 elements in an age- and promoter type-dependent manner. Exposure to densely IR, but not sparsely IR, resulted in DNA hypermethylation of older LINE-1 elements, while the DNA methylation of evolutionary younger elements remained mostly unchanged. We also demonstrate that exposure to densely IR increased mRNA and protein levels of LINE-1 via the loss of the histone H3K9 dimethylation and an increase in the H3K4 trimethylation at the LINE-1 5'-untranslated region, independently of DNA methylation. Our findings suggest that DNA methylation is important for regulation of LINE-1 expression under normal conditions, but histone modifications may dictate the transcriptional activity of LINE-1 in response to exposure to densely IR.

Effect of behavioral testing on spine density of basal dendrites in the CA1 region of the hippocampus modulated by (56)Fe irradiation

A unique feature of the space radiation environment is the presence of high-energy charged particles, including (56)Fe ions, which can present a significant hazard to space flight crews during and following a mission. (56)Fe irradiation-induced cognitive changes often involve alterations in hippocampal function. These alterations might involve changes in spine morphology and density. In addition to irradiation, performing a cognitive task can also affect spine morphology. Therefore, it is often hard to determine whether changes in spine morphology and density are due to an environmental challenge or group differences in performance on cognitive tests. In this study, we tested the hypothesis that the ability of exploratory behavior to increase specific measures of hippocampal spine morphology and density is affected by (56)Fe irradiation. In sham-irradiated mice, exploratory behavior increased basal spine density in the CA1 region of the hippocampus and the enclosed blade of the dentate gyrus. These effects were not seen in irradiated mice. In addition, following exploratory behavior, there was a trend toward a decrease in the percent stubby spines on apical dendrites in the CA3 region of the hippocampus in (56)Fe-irradiated, but not sham-irradiated, mice. Other hippocampal regions and spine measures affected by (56)Fe irradiation showed comparable radiation effects in behaviorally naïve and cognitively tested mice. Thus, the ability of exploratory behavior to alter spine density and morphology in specific hippocampal regions is affected by (56)Fe irradiation.

Combined exposure to protons and (56)Fe leads to overexpression of Il13 and reactivation of repetitive elements in the mouse lung

Interest in deep space exploration underlines the needs to investigate the effects of exposure to combined sources of space radiation. The lung is a target organ for radiation, and exposure to protons and heavy ions as radiation sources may lead to the development of degenerative disease and cancer. In this study, we evaluated the pro-fibrotic and epigenetic effects of exposure to protons (150 MeV/nucleon, 0.1 Gy) and heavy iron ions ((56)Fe, 600 MeV/nucleon, 0.5 Gy) alone or in combination (protons on Day 1 and (56)Fe on Day 2) in C57BL/6 male mice 4 weeks after irradiation. Exposure to (56)Fe, proton or in combination, did not result in histopathological changes in the murine lung. At the same time, combined exposure to protons and (56)Fe resulted in pronounced molecular alterations in comparison with either source of radiation alone. Specifically, we observed a substantial increase in the expression of cytokine Il13, loss of expression of DNA methyltransferase Dnmt1, and reactivation of LINE-1, SINE B1 retrotransposons, and major and minor satellites. Given the deleterious potential of the observed effects that may lead to development of chronic lung injury, pulmonary fibrosis, and cancer, future studies devoted to the investigation of the long-term effects of combined exposures to proton and heavy ions are clearly needed.

Whole-body proton irradiation causes long-term damage to hematopoietic stem cells in mice

Space flight poses certain health risks to astronauts, including exposure to space radiation, with protons accounting for more than 80% of deep-space radiation. Proton radiation is also now being used with increasing frequency in the clinical setting to treat cancer. For these reasons, there is an urgent need to better understand the biological effects of proton radiation on the body. Such improved understanding could also lead to more accurate assessment of the potential health risks of proton radiation, as well as the development of improved strategies to prevent and mitigate its adverse effects. Previous studies have shown that exposure to low doses of protons is detrimental to mature leukocyte populations in peripheral blood, however, the underlying mechanisms are not known. Some of these detriments may be attributable to damage to hematopoietic stem cells (HSCs) that have the ability to self-renew, proliferate and differentiate into different lineages of blood cells through hematopoietic progenitor cells (HPCs). The goal of this study was to investigate the long-term effects of low-dose proton irradiation on HSCs. We exposed C57BL/6J mice to 1.0 Gy whole-body proton irradiation (150 MeV) and then studied the effects of proton radiation on HSCs and HPCs in the bone marrow (BM) 22 weeks after the exposure. The results showed that mice exposed to 1.0 Gy whole-body proton irradiation had a significant and persistent reduction of BM HSCs compared to unirradiated controls. In contrast, no significant changes were observed in BM HPCs after proton irradiation. Furthermore, irradiated HSCs and their progeny exhibited a significant impairment in clonogenic function, as revealed by the cobblestone area-forming cell (CAFC) and colony-forming cell assays, respectively. These long-term effects of proton irradiation on HSCs may be attributable to the induction of chronic oxidative stress in HSCs, because HSCs from irradiated mice exhibited a significant increase in NADPH oxidase 4 (NOX4) mRNA expression and reactive oxygen species (ROS) production. In addition, the increased production of ROS in HSCs was associated with a significant reduction in HSC quiescence and an increase in DNA damage. These findings indicate that exposure to proton radiation can lead to long-term HSC injury, probably in part by radiation-induced oxidative stress.

Targeted overexpression of mitochondrial catalase prevents radiation-induced cognitive dysfunction

AIMS

Radiation-induced disruption of mitochondrial function can elevate oxidative stress and contribute to the metabolic perturbations believed to compromise the functionality of the central nervous system. To clarify the role of mitochondrial oxidative stress in mediating the adverse effects of radiation in the brain, we analyzed transgenic (mitochondrial catalase [MCAT]) mice that overexpress human catalase localized to the mitochondria.

RESULTS

Compared with wild-type (WT) controls, overexpression of the MCAT transgene significantly decreased cognitive dysfunction after proton irradiation. Significant improvements in behavioral performance found on novel object recognition and object recognition in place tasks were associated with a preservation of neuronal morphology. While the architecture of hippocampal CA1 neurons was significantly compromised in irradiated WT mice, the same neurons in MCAT mice did not exhibit extensive and significant radiation-induced reductions in dendritic complexity. Irradiated neurons from MCAT mice maintained dendritic branching and length compared with WT mice. Protected neuronal morphology in irradiated MCAT mice was also associated with a stabilization of radiation-induced variations in long-term potentiation. Stabilized synaptic activity in MCAT mice coincided with an altered composition of the synaptic AMPA receptor subunits GluR1/2.

INNOVATION

Our findings provide the first evidence that neurocognitive sequelae associated with radiation exposure can be reduced by overexpression of MCAT, operating through a mechanism involving the preservation of neuronal morphology.

CONCLUSION

Our article documents the neuroprotective properties of reducing mitochondrial reactive oxygen species through the targeted overexpression of catalase and how this ameliorates the adverse effects of proton irradiation in the brain.

Delayed administration of alpha-difluoromethylornithine prevents hippocampus-dependent cognitive impairment after single and combined injury in mice

Radiation exposure due to radiological terrorism and military circumstances are a continuing threat for the civilian population. In an uncontrolled radiation event, it is likely that there will be other types of injury involved, including trauma. While radiation combined injury is recognized as an area of great significance, overall there is a paucity of information regarding the mechanisms underlying the interactions between irradiation and other forms of injury, or what countermeasures might be effective in ameliorating such changes. The objective of this study was to determine if difluoromethylornithine (DFMO) could reduce the adverse effects of single or combined injury if administered beginning 24 h after exposure. Eight-week-old C57BL/J6 young-adult male mice received whole-body cesium-137 ((137)Cs) irradiation with 4 Gy. Immediately after irradiation, unilateral traumatic brain injury was induced using a controlled cortical impact system. Forty-four days postirradiation, animals were tested for hippocampus-dependent cognitive performance in the Morris water maze. After cognitive testing, animals were euthanized and their brains snap frozen for immunohistochemical assessment of neuroinflammation (activated microglia) and neurogenesis in the hippocampal dentate gyrus. Our data show that single and combined injuries induced variable degrees of hippocampus-dependent cognitive dysfunction, and when given 24 h post trauma, DFMO treatment ameliorated those effects. Cellular changes including neurogenesis and numbers of activated microglia were generally not associated with the cognitive changes. Further analyses also revealed that DFMO increased hippocampal protein levels of the antioxidants thioredoxin 1 and peroxiredoxin 3 compared to vehicle treated animals. While the mechanisms responsible for the improvement in cognition after DFMO treatment are not yet clear, these results constitute a basis for further development of DFMO as a countermeasure for ameliorating the of risks for cognitive dysfunction in individuals subjected to trauma and radiation combined injury.

Long-term epigenetic effects of exposure to low doses of 56Fe in the mouse lung

Despite significant progress, the long-term health effects of exposure to high charge (Z) and energy (E) nuclei (HZEs) and the underlying mechanisms remain poorly understood. Mouse studies show that space missions can result in pulmonary pathological states. The goal of this study was to evaluate the pro-fibrotic and pro-carcinogenic effects of exposure to low doses of heavy iron ions ((56)Fe) in the mouse lung. Exposure to (56)Fe (600 MeV; 0.1, 0.2 and 0.4 Gy) resulted in minor pro-fibrotic changes, detected at the beginning of the fibrotic phase (22 weeks post exposure), which were exhibited as increased expression of chemokine Ccl3, and interleukin Il4. Epigenetic alterations were exhibited as global DNA hypermethylation, observed after exposure to 0.4 Gy. Cadm1, Cdh13, Cdkn1c, Mthfr and Sfrp1 were significantly hypermethylated after exposure to 0.1 Gy, while exposure to higher doses resulted in hypermethylation of Cdkn1c only. However, expression of these genes was not affected by any dose. Congruently with the observed patterns of global DNA methylation, DNA repetitive elements were hypermethylated after exposure to 0.4 Gy, with minor changes observed after exposure to lower doses. Importantly, hypermethylation of repetitive elements coincided with their transcriptional repression. The findings of this study will aid in understanding molecular determinants of pathological states associated with exposure to (56)Fe, as well as serve as robust biomarkers for the delayed effects of irradiation. Further studies are clearly needed to investigate the persistence and outcomes of molecular alterations long term after exposure.

Exposure to low-dose (56)Fe-ion radiation induces long-term epigenetic alterations in mouse bone marrow hematopoietic progenitor and stem cells

There is an increasing need to better understand the long-term health effects of high-linear energy transfer (LET) radiation due to exposure during space missions, as well as its increasing use in clinical treatments. Previous studies have indicated that exposure to (56)Fe heavy ions increases the incidence of acute myeloid leukemia (AML) in mice but the underlying molecular mechanisms remain elusive. Epigenetic alterations play a role in radiation-induced genomic instability and the initiation and progression of AML. In this study, we assessed the effects of low-dose (56)Fe-ion irradiation on epigenetic alterations in bone marrow mononuclear cells (BM-MNCs) and hematopoietic progenitor and stem cells (HPSCs). Exposure to (56)Fe ions (600 MeV, 0.1, 0.2 and 0.4 Gy) resulted in significant epigenetic alterations involving methylation of DNA, the DNA methylation machinery and expression of repetitive elements. Four weeks after irradiation, these changes were primarily confined to HPSCs and were exhibited as dose-dependent hypermethylation of LINE1 and SINE B1 repetitive elements [4.2-fold increase in LINE1 (P < 0.001) and 7.6-fold increase in SINE B1 (P < 0.01) after exposure to 0.4 Gy; n = 5]. Epigenetic alterations were persistent and detectable for at least 22 weeks after exposure, when significant loss of global DNA hypomethylation (1.9-fold, P < 0.05), decreased expression of Dnmt1 (1.9-fold, P < 0.01), and increased expression of LINE1 and SINE B1 repetitive elements (2.8-fold, P < 0.001 for LINE1 and 1.9-fold, P < 0.05 for SINE B1; n = 5) were observed after exposure to 0.4 Gy. In contrast, exposure to (56)Fe ions did not result in accumulation of increased production of reactive oxygen species (ROS) and DNA damage, exhibited as DNA strand breaks. Furthermore, no significant alterations in cellular senescence and apoptosis were detected in HPSCs after exposure to (56)Fe-ion radiation. These findings suggest that epigenetic reprogramming is possibly involved in the development of radiation-induced genomic instability and thus, may have a causative role in the development of AML.

Radiation exposure prior to traumatic brain injury induces responses that differ as a function of animal age

Purpose:

Uncontrolled radiation exposure due to radiological terrorism, industrial accidents or military circumstances is a continuing threat for the civilian population. Age plays a major role in the susceptibility to radiation; younger children are at higher risk of developing cognitive deterioration when compared to adults. Our objective was to determine if an exposure to radiation affected the vulnerability of the juvenile hippocampus to a subsequent moderate traumatic injury.

Materials and methods:

Three-week-old (juvenile) and eight-week-old young adult C57BL/J6 male mice received whole body cesium-137 (¹³⁷Cs) irradiation with 4 gray (Gy). One month later, unilateral traumatic brain injury was induced using a controlled cortical impact system. Two months post-irradiation, animals were tested for hippocampus-dependent cognitive performance in the Morris water-maze. After cognitive testing, animals were euthanized and their brains frozen for immunohistochemical assessment of activated microglia and neurogenesis in the hippocampal dentate gyrus.

Results:

All animals were able to learn the water maze task; however, treatment effects were seen when spatial memory retention was assessed. Animals that received irradiation as juveniles followed by a moderate traumatic brain injury one month later did not show spatial memory retention, i.e., were cognitively impaired. In contrast, all groups of animals that were treated as adults showed spatial memory retention in the probe trials.

Conclusion:

Although the mechanisms involved are not clear, our results suggest that irradiation enhanced a young animal's vulnerability to develop cognitive injury following a subsequent traumatic injury.

The phylogeny and population structure of Mycobacterium bovis in the British Isles

To further understand the epidemic of bovine tuberculosis in Great Britain, Northern Ireland and the Republic of Ireland, we identified 16 mutations that are phylogenetically informative for Mycobacterium bovis strains from these regions. We determined the status of these mutations among a collection of 501 strains representing the molecular diversity found in these three regions of the British Isles. The resulting linear phylogenies from each region were concordant, showing that the same lineage of M. bovis was present. The dominance of this lineage is unique within Europe, and suggests that in the past the populations were homogenous. Comparison of approximately 500 strains isolated in 2005 from each region by spoligotype and 5 locus VNTR profiling, revealed distinct differences in the genotype frequencies and sub-lineage makeup between each region. We concluded that whilst each region shared the same major phylogenetic lineage of M. bovis, more recent evolution had resulted in the development of region-specific populations. Regional differences in the M. bovis populations suggest that it may be possible to identify the movement of strains from one region to another.