Transient improvement in cognitive function and synaptic plasticity in rats following cancer chemotherapy

Phenyl-2-aminoethyl selenide ameliorates hippocampal long-term potentiation and cognitive deficits following doxorubicin treatment

Chemotherapy-induced memory loss ("chemobrain") can occur following treatment with the widely used chemotherapeutic agent doxorubicin (DOX). However, the mechanisms through which DOX induces cognitive dysfunction are not clear, and there are no commercially available therapies for its treatment or prevention. Therefore, the aim of this study was to determine the therapeutic potential of phenyl-2-aminoethyl selenide (PAESe), an antioxidant drug previously demonstrated to reduce cardiotoxicity associated with DOX treatment, against DOX-induced chemobrain. Four groups of male athymic NCr nude (nu/nu) mice received five weekly tail-vein injections of saline (Control group), 5 mg/kg of DOX (DOX group), 10 mg/kg PAESe (PAESe group), or 5 mg/kg DOX and 10 mg/kg PAESe (DOX+PAESe group). Spatial memory was evaluated using Y-maze and novel object location tasks, while synaptic plasticity was assessed through the measurement of field excitatory postsynaptic potentials from the Schaffer collateral circuit. Western blot analyses were performed to assess hippocampal protein and phosphorylation levels. In this model, DOX impaired synaptic plasticity and memory, and increased phosphorylation of protein kinase B (Akt) and extracellular-regulated kinase (ERK). Co-administration of PAESe reduced Akt and ERK phosphorylation and ameliorated the synaptic and memory deficits associated with DOX treatment.

Comparative evaluation of doxorubicin, cyclophosphamide, 5-fluorouracil, and cisplatin on cognitive dysfunction in rats: Delineating the role of inflammation of hippocampal neurons and hypothyroidism

Chemotherapeutic agents such as doxorubicin, cyclophosphamide, fluorouracil, and cisplatin are commonly used to treat a variety of cancers and often result in chemobrain, which manifests as difficulties in learning and memory processes that can persist in the years following treatment. The current study aims to evaluate the cognitive function following treatment with these agents and the underlying mechanisms using a rat model of neuroinflammation and possible implication of thyroid toxicity in chemotherapy induced cognitive dysfunction. Wistar female rats were treated with a single dose of doxorubicin (DOX, 25 mg/kg), 5-fluorouracil (5-FU, 100 mg/kg), cisplatin (8 mg/kg), and cyclophosphamide (CYP, 200 mg/kg) by intraperitoneal injection. The cognitive performance of rats was then evaluated in spatial memory tasks using the Y-maze, novel object recognition (NOR), and elevated plus maze (EPM) tests. Serum levels of thyroid hormones (T3, T4, FT3, and FT4) and thyroid stimulating hormone (TSH) were measured, followed by estimation of TNFα, IL-6, and IL-1β in the hippocampal tissue. Results revealed that all the chemotherapeutic agents produced impairment of cognitive function, and significant increase of pro-inflammatory cytokines such as TNFα, IL-6 and IL-1β in the hippocampal tissues. There was a significant reduction in thyroid hormones (T3, FT3, and T4) and an increase in thyroid stimulating hormone (TSH) in serum, which may also have contributed to the decline in cognitive function. In conclusion, DOX, 5-FU, CYP, and cisplatin produces impairment of spatial memory possibly by inflammation of hippocampal neurons and endocrine disruption (hypothyroidism) in rats.

Hippocampal neuroinflammation following combined exposure to cyclophosphamide and naproxen in ovariectomized mice

Aim: Cancer patients undergoing chemotherapy report cognitive changes collectively termed "chemo brain." Neuroinflammation is among the factors believed to contribute to "chemo brain" suggesting a potential beneficial role for anti-inflammatory drugs in cancer patients undergoing chemotherapy. We investigated whether the non-steroidal anti-inflammatory drug naproxen influenced hippocampal inflammation in non-tumor bearing female mice receiving the chemotherapy drug cyclophosphamide (CP).Materials and methods: Intact and ovariectomized C57BL/6 mice were used to examine potential role of ovarian hormones on neuroinflammation. The mice were placed on naproxen (375 ppm) or control diet, and a week later CP (100 mg/kg; i.p.) was administered every 3 days for 2 weeks. We analyzed hippocampal inflammatory biomarkers, anxiety-like behavior, spatial working memory, exploratory behavior, spontaneous locomotor activity and depression-like behavior.Results: CP produced significant effects on anti-inflammatory but not pro-inflammatory biomarkers. However, CP and naproxen in combination produced significant effects on both pro- and anti- inflammatory biomarkers. Naproxen and ovariectomy individually produced significant effects on pro- and anti-inflammatory biomarkers as well. Working memory and depression-like behavior were not significantly influenced by CP, naproxen or ovariectomy individually although CP and ovariectomy produced significant interaction effects on depression-like behavior. Exploratory behavior and locomotor activity showed significant effects of CP, and interaction between CP and naproxen was significant for locomotor activity.Conclusions: Ovariectomy, naproxen and a combination of CP and naproxen upregulate hippocampal pro- and anti- inflammatory biomarkers. None of the factors individually produce significant behavioral changes that could be consistent with chemo brain, although CP and ovariectomy in combination produced significant effects on depression-like behavior, a co-morbidity of chemo brain.

Chemobrain in Breast Cancer: Mechanisms, Clinical Manifestations, and Potential Interventions

Among the potential adverse effects of breast cancer treatment, chemotherapy-related cognitive impairment (CRCI) has gained increased attention in the past years. In this review, we provide an overview of the literature regarding CRCI in breast cancer, focusing on three main aspects. The first aspect relates to the molecular mechanisms linking individual drugs commonly used to treat breast cancer and CRCI, which include oxidative stress and inflammation, reduced neurogenesis, reduced levels of specific neurotransmitters, alterations in neuronal dendrites and spines, and impairment in myelin production. The second aspect is related to the clinical characteristics of CRCI in patients with breast cancer treated with different drug combinations. Data suggest the incidence rates of CRCI in breast cancer vary considerably, and may affect more than 50% of treated patients. Both chemotherapy regimens with or without anthracyclines have been associated with CRCI manifestations. While cross-sectional studies suggest the presence of symptoms up to 20 years after treatment, longitudinal studies confirm cognitive impairments lasting for at most 4 years after the end of chemotherapy. The third and final aspect is related to possible therapeutic interventions. Although there is still no standard of care to treat CRCI, several pharmacological and non-pharmacological approaches have shown interesting results. In summary, even if cognitive impairments derived from chemotherapy resolve with time, awareness of CRCI is crucial to provide patients with a better understanding of the syndrome and to offer them the best care directed at improving quality of life.

Research advances on how metformin improves memory impairment in "chemobrain"

Cognitive impairment caused by chemotherapy, referred to as “chemobrain,” is observed in approximately 70% of cancer survivors. However, it is not completely understood how chemotherapy induces cognitive dysfunction, and clinical treatment strategies for this problem are lacking. Metformin, used as a first-line treatment for type 2 diabetes mellitus, is reported to reduce the effects of chemobrain. Recently, several studies have examined the effect of metformin in rescuing chemobrain. This review discusses recent clinical/preclinical studies that addressed some mechanisms of chemobrain and evaluates the effect of metformin in rescuing chemobrain and its potential mechanisms of action.

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.

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.

Animal models of chemotherapy-induced cognitive decline in preclinical drug development

RATIONALE

Chemotherapy-induced cognitive impairment (CICI), chemobrain, and chemofog are the common terms for mental dysfunction in a cancer patient/survivor under the influence of chemotherapeutics. CICI is manifested as short/long term memory problems and delayed mental processing, which interferes with a person's day-to-day activities. Understanding CICI mechanisms help in developing therapeutic interventions that may alleviate the disease condition. Animal models facilitate critical evaluation to elucidate the underlying mechanisms and form an integral part of verifying different treatment hypotheses and strategies.

OBJECTIVES

A methodical evaluation of scientific literature is required to understand cognitive changes associated with the use of chemotherapeutic agents in different preclinical studies. This review mainly emphasizes animal models developed with various chemotherapeutic agents individually and in combination, with their proposed mechanisms contributing to the cognitive dysfunction. This review also points toward the analysis of chemobrain in healthy animals to understand the mechanism of interventions in absence of tumor and in tumor-bearing animals to mimic human cancer conditions to screen potential drug candidates against chemobrain.

RESULTS

Substantial memory deficit as a result of commonly used chemotherapeutic agents was evidenced in healthy and tumor-bearing animals. Spatial and episodic cognitive impairments, alterations in neurotrophins, oxidative and inflammatory markers, and changes in long-term potentiation were commonly observed changes in different animal models irrespective of the chemotherapeutic agent.

CONCLUSION

Dyscognition exists as one of the serious side effects of cancer chemotherapy. Due to differing mechanisms of chemotherapeutic agents with differing tendencies to alter behavioral and biochemical parameters, chemotherapy may present a significant risk in resulting memory impairments in healthy as well as tumor-bearing animals.

Sex-Specific Associations Between Chemotherapy, Chronic Conditions, and Neurocognitive Impairment in Acute Lymphoblastic Leukemia Survivors: A Report From the Childhood Cancer Survivor Study

BACKGROUND

The purpose was to examine associations between treatment and chronic health conditions with neurocognitive impairment survivors of acute lymphoblastic leukemia (ALL) treated with chemotherapy only.

METHODS

This cross-sectional study included 1207 ALL survivors (54.0% female; mean age 30.6 years) and 2273 siblings (56.9% female; mean age 47.6 years), who completed the Childhood Cancer Survivor Study Neurocognitive Questionnaire. Multivariable logistic regression compared prevalence of neurocognitive impairment between survivors and siblings by sex. Associations between neurocognitive impairment with treatment exposures and chronic conditions (graded according to Common Terminology Criteria for Adverse Events) were also examined. Statistical tests were 2-sided.

RESULTS

Relative to same-sex siblings, male and female ALL survivors reported increased prevalence of impaired task efficiency (males: 11.7% vs 16.9%; adjusted odds ratio [OR] = 1.89, 95% confidence interval [CI] = 1.31 to 2.74; females: 12.5% vs 17.6%; OR = 1.50, 95% CI = 1.07 to 2.14), as well as impaired memory (males: 11.6% vs 19.9%, OR = 1.89, CI = 1.31 to 2.74; females: 14.78% vs 25.4%, OR = 1.96, 95% CI = 1.43 to 2.70, respectively). Among male survivors, impaired task efficiency was associated with 2-4 neurologic conditions (OR = 4.33, 95% CI = 1.76 to 10.68) and with pulmonary conditions (OR = 4.99, 95% CI = 1.51 to 16.50), and impaired memory was associated with increased cumulative dose of intrathecal methotrexate (OR = 1.68, 95% CI = 1.16 to 2.46) and with exposure to dexamethasone (OR = 2.44, 95% CI = 1.19 to 5.01). In female survivors, grade 2-4 endocrine conditions were associated with higher risk of impaired task efficiency (OR = 2.19, 95% CI = 1.20 to 3.97) and memory (OR = 2.26, 95% CI = 1.31 to 3.92).

CONCLUSION

Neurocognitive impairment is associated with methotrexate, dexamethasone, and chronic health conditions in a sex-specific manner, highlighting the need to investigate physiological mechanisms and monitor impact through survivorship.

Stem cell therapies as a therapeutic option to counter chemo brain: a negative effect of cancer treatment

Chemo brain, a constellation of cognitive deficiencies followed by chemotherapy drugs, used to treat different types of cancers and adversely impacts the quality of life of a cancer survivor. The underlying mechanism of chemo brain remains vague, thus delaying the advancement of efficient treatments. Unfortunately, there is no US FDA approved medicine for chemo brain and often medicines considered for chemo brain are already the ones approved for other diseases. Nevertheless, researches exploring stem cell transplantation in different neurodegenerative diseases demonstrate that cellular transplantation could reverse chemotherapy-induced chemo brain. This review talks about the mechanism behind the cognitive impairments instigated by different chemotherapy drugs used in cancer treatment, and how stem cell therapy could be advantageous to overcome this disease.

Chemotherapy-induced cognitive impairment (CICI): An overview of etiology and pathogenesis

Many cancer patients treated with chemotherapy develop chemotherapy-induced cognitive impairment (CICI), often referred to as chemo-brain, which manifest during or post-treatment with variable degrees, onset and duration thereby affecting the patients' quality of life. Several chemotherapeutic agents have been studied to determine its possible association with cognitive impairment and to fully comprehend their contribution to CICI. A vast number of studies have emerged proposing several candidate underlying mechanisms and etiologies contributing to CICI such as direct neurotoxicity, BBB disruption, decreased hippocampal neurogenesis, white matter abnormalities, secondary neuro-inflammatory response and increased oxidative stress; however, the exact underlying mechanisms are still not well defined. This review summarizes CICI associated with most commonly used chemotherapeutic agents with emphasizes the possible underlying pathogenesis in both animal and clinical studies.

Spatial memory deficits after vincristine-induced lesions to the dorsal hippocampus

Vincristine is a commonly used cytostatic drug for the treatment of leukemia, neuroblastoma and lung cancer, which is known to have neurotoxic properties. The aim of this study was to assess the effects of vincristine, injected directly into the dorsal hippocampus, in spatial memory using the spatial cone field discrimination task. Long Evans rats were trained in the cone field, and after reaching training criterion received bilateral vincristine infusions into the dorsal hippocampus. Vincristine-treated animals presented unilateral or bilateral hippocampal lesions. Animals with bilateral lesions showed lower spatial working and reference memory performance than control animals, but task motivation was unaffected by the lesions. Working and reference memory of animals with unilateral lesions did not differ from animals with bilateral lesions and control animals. In sum, intrahippocampal injection of vincristine caused profound tissue damage in the dorsal hippocampus, associated with substantial cognitive deficits.

Chemotherapy and the pediatric brain

Survival rates of children with cancer are steadily increasing. This urges our attention to neurocognitive and psychiatric outcomes, as these can markedly influence the quality of life of these children. Neurobehavioral morbidity in childhood cancer survivors affects diverse aspects of cognitive function, which can include attention, memory, processing speed, intellect, academic achievement, and emotional health. Reasons for neurobehavioral morbidity are multiple with one major contributor being chemotherapy-induced central nervous system (CNS) toxicity. Clinical studies investigating the effects of chemotherapy on the CNS in children with cancer have reported causative associations with the development of leukoencephalopathies as well as smaller regional grey and white matter volumes, which have been found to correlate with neurocognitive deficits.Preclinical work has provided compelling evidence that chemotherapy drugs are potent neuro- and gliotoxins in vitro and in vivo and can cause brain injury via excitotoxic and apoptotic mechanisms. Furthermore, chemotherapy triggers DNA (deoxyribonucleic acid) damage directly or through increased oxidative stress. It can shorten telomeres and accelerate cell aging, cause cytokine deregulation, inhibit hippocampal neurogenesis, and reduce brain vascularization and blood flow. These mechanisms, when allowed to operate on the developing brain of a child, have high potential to not only cause brain injury, but also alter crucial developmental events, such as myelination, synaptogenesis, neurogenesis, cortical thinning, and formation of neuronal networks.This short review summarizes key publications describing neurotoxicity of chemotherapy in pediatric cancers and potential underlying pathomechanisms.

Chemotherapy and cognition: International cognition and cancer task force recommendations for harmonising preclinical research

Cancer survivors who undergo chemotherapy for non-CNS tumours often report substantial cognitive disturbances that adversely affect quality of life, during and after treatment. The neurotoxic effects of anti-cancer drugs have been confirmed in clinical and pre-clinical research. Work with animals has also identified a range of factors and underlying mechanisms that contribute to chemotherapy-induced cognitive impairment. However, there is a continuing need to develop standard cognitive testing procedures for validation and comparison purposes, broaden the search for biological and neurochemical mechanisms, and develop improved animal models for investigating the combined effects of treatment, the disease, and other potential factors (e.g., age, stress). In this paper, a working group, formed under the auspices of the International Cognition and Cancer Task Force, reviews the state of pre-clinical research, formulates strategic priorities, and provides recommendations to guide animal research that meaningfully informs clinical investigations.

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.

Compound K derived from ginseng: neuroprotection and cognitive improvement

The evidence for the neuroprotective and cognitive effects of compound K, a metabolite biotransformed from ginsenosides Rb1, Rb2, and Rc, is reviewed here. Compound K is more bioavailable than other ginsenosides and therefore has greater potential to exert bioactive functions in the body. Although the capability of compound K to cross the blood-brain barrier is not clear, it has been reported to have neuroprotective and cognition enhancing effects and decrease inflammatory biomarkers in animal models of Alzheimer's disease and cerebral ischemia. The plethora of potential health benefits of compound K warrants further research to evaluate its biochemical mechanisms and its ability to protect healthy populations from neurodegenerative diseases.

KU32 prevents 5-fluorouracil induced cognitive impairment

Chemotherapy induced cognitive impairment (i.e. chemobrain) involves acute and long-term deficits in memory, executive function, and processing speed. Animal studies investigating these cognitive deficits have had mixed results, potentially due to variability in the complexity of behavioral tasks across experiments. Further, common chemotherapy treatments such as 5-fluorouracil (5-FU) break down myelin integrity corresponding to hippocampal neurodegenerative deficits and mitochondrial dysfunction. There is little evidence, however, of pharmacological treatments that may target mitochondrial dysfunction. Using a differential reinforcement of low rates (DRL) task combining spatial and temporal components, the current study evaluated the preventative effects of the pharmacological agent KU32 on the behavior of rats treated with 5-FU (5-FU+Saline vs. 5FU+KU32). DRL performance was analyzed the day after the first set of injections (D1), the day after the second set of injections (D7) and the last day of the experiment (D14). The 5FU+KU32 group earned significantly more reinforcers on the DRL task at D7 and D14 than the 5FU+Saline group. Further, the 5FU+KU32 group showed significantly better temporal discrimination. The 5FU+KU32 showed within-group improvement in temporal discrimination from D7 to D14. No significant differences were observed in spatial discrimination, however, those in the 5FU+Saline group responded more frequently on T3 compared to the 5FU+KU32 group, highlighting temporal discrimination differences between groups. The current data suggest that KU32 shows promise in the prevention of chemotherapy induced impairments in temporal discrimination.

PET Evidence of the Effect of Donepezil on Cognitive Performance in an Animal Model of Chemobrain

A considerable number of patients with breast cancer complain of cognitive impairment after chemotherapy. In this study, we showed that donepezil enhanced memory function and increased brain glucose metabolism in a rat model of cognitive impairment after chemotherapy using behavioral analysis and positron emission tomography (PET). We found that chemotherapy affected spatial learning ability, reference memory, and working memory and that donepezil improved these cognitive impairments. According to PET analysis, chemotherapy reduced glucose metabolism in the medial prefrontal cortex and hippocampus, and donepezil increased glucose metabolism in the bilateral frontal lobe, parietal lobe, and hippocampus. Reduced glucose metabolism was more prominent after treatment with doxorubicin than cyclophosphamide. Our results demonstrated the neural mechanisms for cognitive impairment after chemotherapy and show that cognition was improved after donepezil intervention using both behavioral and imaging methods. Our results suggested that donepezil can be employed clinically for the treatment of cognitive deficits after chemotherapy.

Long-lasting impairments in adult neurogenesis, spatial learning and memory from a standard chemotherapy regimen used to treat breast cancer

The negative impact of chemotherapy on cognitive function in cancer patients has gained increasing attention in the last decade. Whilst the short-term acute effects on cognition are expected following chemotherapy, the persistence of such impairments in the long-term is still in question. This is despite clinical evidence indicating cognitive difficulties may persist well beyond treatment and affect quality of life. In the present study, we assessed the long-term (3 months) cognitive impact of chemotherapy in a mouse model intended to mimic the human female post-menopausal population receiving chemotherapy for breast cancer. Ovariectomized, female, C57BL/6J mice received two doses of Doxorubicin, Cyclophosphamide, and 5-Fluorouracil or saline vehicle (control), separated by one week. During this interval, mice received BrdU injections to label dividing cells. Results indicate a persistent impairment in learning and recall (1h, 24h and 48h) on the Morris water maze, reduced survival and differentiation of new neurons (BrdU+/NeuN+), and a persistent decline in proliferation of new cells (Ki67(+)) in the dentate gyrus. Locomotor activity, motor performance, and anxiety-like behavior were unaffected. We further evaluated the efficacy of a diet enriched in omega-3-fatty acids (DHA+EPA+DPA), in reversing long-term chemotherapy deficits but no rescue was observed. The model described produces long-term cognitive and cellular impairments from chemotherapy that mimic those observed in humans. It could be useful for identifying mechanisms of action and to test further the ability of lifestyle interventions (e.g., diet) for ameliorating chemotherapy-induced cognitive impairments.

Fasting, Circadian Rhythms, and Time-Restricted Feeding in Healthy Lifespan

Most animals alternate periods of feeding with periods of fasting often coinciding with sleep. Upon >24 hr of fasting, humans, rodents, and other mammals enter alternative metabolic phases, which rely less on glucose and more on ketone body-like carbon sources. Both intermittent and periodic fasting result in benefits ranging from the prevention to the enhanced treatment of diseases. Similarly, time-restricted feeding (TRF), in which food consumption is restricted to certain hours of the day, allows the daily fasting period to last >12 hr, thus imparting pleiotropic benefits. Understanding the mechanistic link between nutrients and the fasting benefits is leading to the identification of fasting-mimicking diets (FMDs) that achieve changes similar to those caused by fasting. Given the pleiotropic and sustained benefits of TRF and FMDs, both basic science and translational research are warranted to develop fasting-associated interventions into feasible, effective, and inexpensive treatments with the potential to improve healthspan.

Chemotherapy-induced neurotoxicity in pediatric solid non-CNS tumor patients: An update on current state of research and recommended future directions

Neurocognitive sequelae are known to be induced by cranial radiotherapy and central-nervous-system-directed chemotherapy in childhood Acute Lymphoblastic Leukemia (ALL) and brain tumor patients. However, less evidence exists for solid non-CNS-tumor patients. To get a better understanding of the potential neurotoxic mechanisms of non-CNS-directed chemotherapy during childhood, we performed a comprehensive literature review of this topic. Here, we provide an overview of preclinical and clinical studies investigating neurotoxicity associated with chemotherapy in the treatment of pediatric solid non-CNS tumors. Research to date suggests that chemotherapy has deleterious biological and psychological effects, with animal studies demonstrating histological evidence for neurotoxic effects of specific agents and human studies demonstrating acute neurotoxicity. Although the existing literature suggests potential neurotoxicity throughout neurodevelopment, research into the long-term neurocognitive sequelae in survivors of non-CNS cancers remains limited. Therefore, we stress the critical need for neurodevelopmental focused research in children who are treated for solid non-CNS tumors, since they are at risk for potential neurocognitive impairment.

Doxorubicin and cyclophosphamide induce cognitive dysfunction and activate the ERK and AKT signaling pathways

Chemotherapy is associated with long-term cognitive deficits in breast cancer survivors. Studies suggest that these impairments result in the loss of cognitive reserve and/or induce a premature aging of the brain. This study has been aimed to determine the potential underlying mechanisms that induce cognitive impairments by chemotherapeutic agents commonly used in breast cancer. Intact and ovariectomized (OVX) female rats were treated intravenously with either saline or a combination of cyclophosphamide (40 mg/kg) and doxorubicin (4 mg/kg). All subjects were tested for anxiety, locomotor activity, working, visual and spatial memory consecutively. Although anxiety and visual memory were not affected, chemotherapy significantly decreased locomotor activity and impaired working and spatial memory in female rats, independent of their hormonal status. The cognitive deficits observed are hippocampal dependent. Therefore, as a first step to identity the potential signaling pathways involved in this cognitive dysfunction, the protein levels of extracellular signal-regulated kinase 1/2 (Erk1/2), Akt (neuroprotectant) BDNF and (structural protein) PSD95 in hippocampal lysates were measured. Erk1/2 and Akt pathways are known to modulate synaptic plasticity, neuronal survival, aging and cancer. We found an increased activation of Erk1/2 and Akt as well as an increase in the protein levels of PSD95 in OVX female rodents. However, OVX females had a higher overall BDNF level, independent of chemotherapy. These studies provide additional evidence that commonly used chemotherapeutic agents affect cognitive function and impact synaptic plasticity/aging molecules which may be part of the underlying biology explaining cognitive change and can be potential therapeutic targets.

The long-term impact of oxaliplatin chemotherapy on rodent cognition and peripheral neuropathy

Chemotherapy treatment is associated with cognitive dysfunction in cancer survivors after treatment completion. The duration of these impairments is unclear. Therefore this paper aims to evaluate the lasting impact of varying doses of the chemotherapy oxaliplatin (OX) on cognition and peripheral neuropathy. In Experiment 1 rats were treated once a week for 3 weeks with either physiological saline (control) or 6 mg/kg OX i.p. and were assessed for peripheral neuropathy, using von Frey filaments, and cognitive function, using novel object and location recognition, up to 2 weeks after treatment completion. For Experiment 2 rats received 3 weekly i.p. injections of either physiological saline (control), 0.6 mg/kg, 2mg/kg or 6 mg/kg OX and assessed for peripheral neuropathy and cognitive function up to 11 months after treatment completion. Systemic OX treatment induced lasting effects on cognitive function at 11 months after treatment, and peripheral neuropathy at 1 month after treatment and these were dose dependent; higher doses of OX resulted in worse cognitive outcomes and more severe peripheral neuropathy.

Temporal profiles of synaptic plasticity-related signals in adult mouse hippocampus with methotrexate treatment

Methotrexate, which is used to treat many malignancies and autoimmune diseases, affects brain functions including hippocampal-dependent memory function. However, the precise mechanisms underlying methotrexate-induced hippocampal dysfunction are poorly understood. To evaluate temporal changes in synaptic plasticity-related signals, the expression and activity of N-methyl-D-aspartic acid receptor 1, calcium/calmodulin-dependent protein kinase II, extracellular signal-regulated kinase 1/2, cAMP responsive element-binding protein, glutamate receptor 1, brain-derived neurotrophic factor, and glial cell line-derived neurotrophic factor were examined in the hippocampi of adult C57BL/6 mice after methotrexate (40 mg/kg) intraperitoneal injection. Western blot analysis showed biphasic changes in synaptic plasticity-related signals in adult hippocampi following methotrexate treatment. N-methyl-D-aspartic acid receptor 1, calcium/calmodulin-dependent protein kinase II, and glutamate receptor 1 were acutely activated during the early phase (1 day post-injection), while extracellular signal-regulated kinase 1/2 and cAMP responsive element-binding protein activation showed biphasic increases during the early (1 day post-injection) and late phases (7–14 days post-injection). Brain-derived neurotrophic factor and glial cell line-derived neurotrophic factor expression increased significantly during the late phase (7–14 days post-injection). Therefore, methotrexate treatment affects synaptic plasticity-related signals in the adult mouse hippocampus, suggesting that changes in synaptic plasticity-related signals may be associated with neuronal survival and plasticity-related cellular remodeling.

Neurobehavioral consequences of small molecule-drug immunosuppression

60 years after the first successful kidney transplantation in humans, transplant patients have decent survival rates owing to a broad spectrum of immunosuppressive medication available today. Not only transplant patients, but also patients with inflammatory autoimmune diseases or cancer benefit from these life-saving immunosuppressive and anti-proliferative medications. However, this success is gained with the disadvantage of neuropsychological disturbances and mental health problems such as depression, anxiety and impaired quality of life after long-term treatment with immunosuppressive drugs. So far, surprisingly little is known about unwanted neuropsychological side effects of immunosuppressants and anti-proliferative drugs from the group of so called small molecule-drugs. This is partly due to the fact that it is difficult to disentangle whether and to what extent the observed neuropsychiatric disturbances are a direct result of the patient's medical history or of the immunosuppressive treatment. Thus, here we summarize experimental as well as clinical data of mammalian and human studies, with the focus on selected small-molecule drugs that are frequently employed in solid organ transplantation, autoimmune disorders or cancer therapy and their effects on neuropsychological functions, mood, and behavior. These data reveal the necessity to develop immunosuppressive and anti-proliferative drugs inducing fewer or no unwanted neuropsychological side effects, thereby increasing the quality of life in patients requiring long term immunosuppressive treatment. This article is part of a Special Issue entitled 'Neuroimmunology and Synaptic Function'.

Neurotoxicity of cancer chemotherapy

There is accumulating clinical evidence that chemotherapeutic agents induce neurological side effects, including memory deficits and mood disorders, in cancer patients who have undergone chemotherapeutic treatments. This review focuses on chemotherapy-induced neurodegeneration and hippocampal dysfunctions and related mechanisms as measured by in vivo and in vitro approaches. These investigations are helpful in determining how best to further explore the causal mechanisms of chemotherapy-induced neurological side effects and in providing direction for the future development of novel optimized chemotherapeutic agents.

Retracted: Involvement of insulin-like growth factor-1 in chemotherapy-related cognitive impairment

Here we examined the involvement of insulin-like growth factor 1 (IGF-1) on chemotherapy-induced cognitive impairment. Sixty-four ovariectomized female Sprague-Dawley rats were included in the study and given cyclophosphamide, methothrexate, and 5-fluorouracil (CMF) drug combination or saline (control). CMF was given once a week for 4 weeks. In one experiment, behavioral testing using the cued learning and spontaneous object recognition tasks were performed either: at the end of treatment or 4 weeks after treatment. In another experiment, rats from the chemotherapy and saline groups received either: continuous insulin-like growth factor 1 (IGF-1) or vehicle delivered subcutaneously via osmotic pump for 21 days (started the week after completion of therapy). Bromodeoxyuridine injections were given for 3 consecutive days starting at 2 weeks after completion of chemotherapy to assess the survival of proliferating cells. Increased levels of IGF-1 and activation of its receptor as well as increased activation of Akt and Erk1/2, its downstream signaling pathways was seen immediately after completion of chemotherapy but decreased 4 weeks after treatment. Behavioral testing showed CMF-induced cognitive impairment after completion of therapy and persisted for 4 weeks. We also found that giving IGF-1 significantly increased activation of its receptor, and the Akt and Erk1/2 pathways, and most importantly attenuated chemotherapy-induced cognitive impairment. CMF-induced neuronal apoptosis was also seen and the ratio of surviving cells that proliferate was higher compared to the number of apoptotic cells in the CMF rats given IGF-1. These results suggest that IGF-1 is involved in CMF-induced cognitive impairment by modulating cell death and cell proliferation.

Low-doses of cisplatin injure hippocampal synapses: a mechanism for 'chemo' brain?

Chemotherapy-related cognitive deficits are a major neurological problem, but the underlying mechanisms are unclear. The death of neural stem/precursor cell (NSC) by cisplatin has been reported as a potential cause, but this requires high doses of chemotherapeutic agents. Cisplatin is frequently used in modern oncology, and it achieves high concentrations in the patient's brain. Here we report that exposure to low concentrations of cisplatin (0.1μM) causes the loss of dendritic spines and synapses within 30min. Longer exposures injured dendritic branches and reduced dendritic complexity. At this low concentration, cisplatin did not affect NSC viability nor provoke apoptosis. However, higher cisplatin levels (1μM) led to the rapid loss of synapses and dendritic disintegration, and neuronal-but not NSC-apoptosis. In-vivo treatment with cisplatin at clinically relevant doses also caused a reduction of dendritic branches and decreased spine density in CA1 and CA3 hippocampal neurons. An acute increase in cell death was measured in the CA1 and CA3 neurons, as well as in the NSC population located in the subgranular zone of the dentate gyrus in the cisplatin treated animals. The density of dendritic spines is related to the degree of neuronal connectivity and function, and pathological changes in spine number or structure have significant consequences for brain function. Therefore, this synapse and dendritic damage might contribute to the cognitive impairment observed after cisplatin treatment.

Neural correlates of chemotherapy-related cognitive impairment

Cancer survivors frequently experience cognitive deficits following chemotherapy. The most commonly affected functions include memory, attention and executive control. The present paper reviews animal research and clinical studies including event-related potential (ERP) and neuroimaging investigations of chemotherapy-related changes of brain structure and function. In rodents, chemotherapeutic substances have been shown to damage neural precursor cells and white matter tracts and are associated with impairments of learning and memory. Structural and functional changes associated with chemotherapy have also been observed in humans. Structural imaging has revealed gray and white matter volume reductions and altered white matter microstructure. Functional studies using either ERPs or hemodynamic imaging have shown that chemotherapy alters the activation patterns of cortical networks involved in higher cognitive functions. Collectively, these findings support the existence of the "chemobrain" phenomenon beyond the patients' subjective reports. However, the rather small number of studies and methodological limitations of some of the pioneering investigations call for further research of high methodological quality, including larger numbers of subjects with appropriate controls to delineate the temporal and spatial pattern of chemotherapy-associated central nervous system (CNS) toxicity. Brain activation studies in humans might systematically vary task difficulty levels to distinguish between compensatory hyper-activations on the one hand and deficient recruitment of resources on the other hand. Integrative functions could be tested by connectivity analyses using both electrophysiological and hemodynamic measures. The ultimate goal should be the development of cognitive-behavioral and pharmacological interventions to reduce the cognitive side effects of the medically indispensable but neurotoxic chemotherapeutic treatments.

Why, After Chemotherapy, is it Necessary to Assess Memory Using Translational Testing?

As the number of cancer survivors rises, so does the importance of understanding what happens post-chemotherapy. The evidence is clear that chemotherapy affects not only cancer cells, but also healthy cells including neurons, leading to long-term cognitive dysfunction in a large portion of survivors. In order to understand the mechanism of action and in the hope of reducing the potential neurocognitive side effects of chemotherapy, pre-clinical testing should be used more effectively. However, the field is lacking translation from clinical studies to animal models. Spatial learning and memory paradigms based on the water maze, the most commonly used rodent model, are available for translational testing in humans and could overcome this weakness. There is an overwhelming need in the field to understand whether the water maze is an adequate model for post-chemotherapy impairments or whether other paradigms should be used. This is of great importance for the understanding of the mechanisms, side effects of new drugs, appropriate pharmacotherapy, and confounding factors related to chemotherapy treatment regiments. This review is very important to both basic scientists and clinicians determining how translational paradigms are critical to future cancer research, as well as what type of paradigms are appropriate in our technically advancing society.

[What's new concerning the chemobrain?]

Chemobrain, a subtle cognitive decline after chemotherapy in non-cerebral cancer, remains a debated issue, which has nevertheless been widely described for more than 15 years in the international literature. This phenomenon is almost unknown in France to experts, neurologists and oncologists. Experimental evidence from animal models and from human functional imagery is reliable but contrasts with the observations made during clinical studies. Indeed, in clinical practice, the difficulty in proving the occurrence of chemobrain may be explained by a large number of methodological skews. However, considering the International Cognition and Cancer Task Force (ICCTF) guidelines, we propose a methodology applicable in daily practice and capable of improving awareness of this phenomenon.

Cognitive impairments caused by oxaliplatin and 5-fluorouracil chemotherapy are ameliorated by physical activity

RATIONALE

Studies in women with breast cancer, and in animal models, have demonstrated that chemotherapy can have a negative impact on cognitive function. Which chemotherapy agents cause problems with cognition and the aetiology of the impairment is unknown. Furthermore, there is no proven treatment.

OBJECTIVES

This study aimed to evaluate the effects of 5-fluorouracil (5FU) and oxaliplatin (OX) chemotherapy agents commonly used to treat colorectal cancer on cognition in laboratory rodents. Furthermore, we assessed physical activity as a potential remedy for the observed chemotherapy-induced cognitive deficits.

RESULTS

In rodents, treatment with 5FU and OX alone impairs memory as measured by novel object recognition. But combined treatment appears to have greater detrimental effects on hippocampal-dependent tasks, contextual fear recall and spatial reference memory (water maze), yet had no effect on cued fear recall, a non-hippocampal task. These impairments were prevented by 4 weeks of wheel running overnight after 5FU/OX treatment. We found a significant interaction between chemotherapy and exercise: rats receiving both 5FU/OX and exercise had improved cognition relative to non-exercising 5FU/OX rats on novel object recognition and spatial reference memory.

CONCLUSIONS

The combination 5FU/OX had a significant impact on cognition. However, rats treated with 5FU/OX that exercised post chemotherapy had improved cognition relative to non-exercising rats. This suggests that physical activity may prove useful in ameliorating the cognitive impairments induced by 5FU/OX.

Chemotherapy-induced cognitive impairment is associated with decreases in cell proliferation and histone modifications

Background

In this study, we examined the effects of cyclophosphamide, methothrexate, and 5-Fluorouracil (CMF) drug combination on various aspects of learning and memory. We also examined the effects of CMF on cell proliferation and chromatin remodeling as possible underlying mechanisms to explain chemotherapy-associated cognitive dysfunction. Twenty-four adult female Wistar rats were included in the study and had minimitter implantation for continuous activity monitoring two weeks before the chemotherapy regimen was started. Once baseline activity data were collected, rats were randomly assigned to receive either CMF or saline injections given intraperitoneally. Treatments were given once a week for a total of 4 weeks. Two weeks after the last injection, rats were tested in the water maze for spatial learning and memory ability as well as discrimination learning. Bromodeoxyuridine (BrdU) injection was given at 100 mg/Kg intraperitoneally 4 hours prior to euthanasia to determine hippocampal cell proliferation while histone acetylation and histone deacetylase activity was measured to determine CMF effects on chromatin remodeling.

Results

Our data showed learning and memory impairment following CMF administration independent of the drug effects on physical activity. In addition, CMF-treated rats showed decreased hippocampal cell proliferation, associated with increased histone acetylation and decreased histone deacetylase activity.

Conclusions

These results suggest the negative consequences of chemotherapy on brain function and that anti-cancer drugs can adversely affect the self-renewal potential of neural progenitor cells and also chromatin remodeling in the hippocampus. The significance of our findings lie on the possible usefulness of animal models in addressing the clinical phenomenon of 'chemobrain.'

Preserved learning and memory following 5-fluorouracil and cyclophosphamide treatment in rats

Some patients experience enduring cognitive impairment after cancer treatment, a condition termed "chemofog". Animal models allow assessment of chemotherapy effects on learning and memory per se, independent of changes due to cancer itself or associated health consequences such as depression. The present study examined the long-term learning and memory effects of a chemotherapy cocktail used widely in the treatment of breast cancer, consisting of 5-fluorouracil (5FU) and cyclophosphamide (CYP). Eighty 5-month old male F344 rats received contextual and cued fear conditioning before treatment with saline, or a low or high dose drug cocktail (50mg/kg CYP and 75 mg/kg 5FU, or 75 mg/kg CYP and 120 mg/kg 5FU, i.p., respectively) every 30 days for 2 months. After a 2-month, no-drug recovery, both long-term retention and new task acquisition in the water maze and 14-unit T-maze were assessed. Neither dose of the CYP/5FU cocktail impaired retrograde fear memory despite marked toxicity documented by enduring weight loss and 50% mortality at the higher dose. Acquisition in the water maze and Stone maze was also normal relative to controls in rats treated with CYP/5FU. The results contribute to a growing literature suggesting that learning and memory mediated by the hippocampus can be relatively resistant to chemotherapy. Future investigation may need to focus on assessments of processing speed, executive function and attention, and the possible interactive contribution of cancer itself and aging to the post-treatment development of cognitive impairment.

Recent and remote spatial memory in mice treated with cytosine arabinoside

Clinical studies suggest that chemotherapy is associated with long-term cognitive impairment in some patients. A number of underlying mechanisms have been proposed, however, the etiology of chemotherapy-related cognitive dysfunction remains relatively unknown. As part of a multifaceted approach, animal models of chemotherapy-induced cognitive impairment are being developed. Thus far, the majority of animal studies have utilized a rat model, however, mice may prove particularly beneficial in studying genetic risk factors for developing chemotherapy-induced cognitive impairment. Various chemotherapy agents, including cytosine arabinoside (Ara-C), have been found to impair remote spatial memory in rats in the Morris water maze. The present study evaluated the effects of Ara-C on remote (30 d) spatial memory in mice. In addition, the possibility that time relative to chemotherapy treatment may modulate the effect of chemotherapy on spatial learning and/or recent (1 d) memory was explored. Male C57BL/6J mice received either Ara-C (275 mg/kg i.p. daily for 5 days) or saline. Spatial learning and memory was assessed using the Morris water maze. Half the mice performed a remote (30 d) memory version of the task and the other half performed a recent (1 d) memory version of the task. The experiment was designed such that the probe trial for the recent memory version occurred on the same day relative to chemotherapy treatment as the remote memory version. Despite significant toxic effects as assessed by weight loss, Ara-C treated mice performed as well as control mice during acquisition, recent memory, and remote memory portions of the task. As are some humans, C57BL/6J mice may be resistant to at least some aspects of chemotherapy induced cognitive decline.

Effects of repeated administration of chemotherapeutic agents tamoxifen, methotrexate, and 5-fluorouracil on the acquisition and retention of a learned response in mice

RATIONALE

A number of cancer chemotherapeutic agents have been associated with a loss of memory in breast cancer patients although little is known of the causality of this effect.

OBJECTIVES

To assess the potential cognitive effects of repeated exposure to chemotherapeutic agents, we administered the selective estrogen receptor modulator tamoxifen or the antimetabolite chemotherapy, methotrexate, and 5-fluorouracil, alone and in combination to mice and tested them in a learning and memory assay.

METHODS

Swiss-Webster male mice were injected with saline, 32 mg/kg tamoxifen, 3.2 or 32 mg/kg methotrexate, 75 mg/kg 5-fluorouracil, 3.2 or 32 mg/kg methotrexate in combination with 75 mg/kg 5-fluorouracil once per week for 3 weeks. On days 23 and 24, mice were tested for acquisition and retention of a nose-poke response in a learning procedure called autoshaping. In addition, the acute effects of tamoxifen were assessed in additional mice in a similar procedure.

RESULTS

The chemotherapeutic agents alone and in combination reduced body weight relative to saline treatment over the course of 4 weeks. Repeated treatment with tamoxifen produced both acquisition and retention effects relative to the saline-treated group although acute tamoxifen was without effect except at a behaviorally toxic dose. Repeated treatment with methotrexate in combination with 5-fluorouracil produced effects on retention, but the magnitude of these changes depended on the methotrexate dose.

CONCLUSIONS

These data demonstrate that repeated administration of tamoxifen or certain combination of methotrexate and 5-fluorouracil may produce deficits in the acquisition or retention of learned responses which suggest potential strategies for prevention or remediation might be considered in vulnerable patient populations.

Preserved learning and memory in mice following chemotherapy: 5-Fluorouracil and doxorubicin single agent treatment, doxorubicin-cyclophosphamide combination treatment

Clinical studies suggest that chemotherapy is associated with long-term cognitive impairment in some patients. A number of underlying mechanisms have been proposed, however, the etiology of chemotherapy-related cognitive dysfunction remains relatively unknown. As part of a multifaceted approach, animal models of chemotherapy induced cognitive impairment are being developed. Thus far, the majority of animal studies have utilized rats, however, mice may prove particularly beneficial in studying genetic risk factors for developing chemotherapy induced cognitive impairment. Thus, C57BL/6J mice were treated once a week for three weeks with saline, doxorubicin and cyclophosphamide (D&C), doxorubicin (Dox), or 5-fluorouracil (5-FU). Recent and remote contextual fear conditioning and novel object recognition (NOR) was assessed. Despite significant toxic effects as assessed by weight loss, the chemotherapy treated mice performed as well as control mice on all task. As are some humans, C57BL/6J mice may be resistant to at least some aspects of chemotherapy induced cognitive decline.

Cognitive impairment in humanized APP×PS1 mice is linked to Aβ(1-42) and NOX activation

Cognitive impairment in Alzheimer's disease (AD) is strongly associated with both extensive deposition of amyloid β peptides and oxidative stress, but the exact role of these indices in the development of dementia is not clear. This study was designed to determine the relationship between cognitive impairment, activation of the free radical producing enzyme NADPH oxidase (NOX), and progressive changes in Aβ deposition and solubility in humanized APP×PS1 knock-in mice of increasing age. Data show that cognitive performance and expression of key synaptic proteins were progressively decreased in aging APP×PS1 mice. Likewise, NOX activity and expression of the specific NOX subunit NOX4 were significantly increased in APP×PS1 mice in an age-dependent manner, and NOX activity and cognitive impairment shared a significant linear relationship. Data further show that age-dependent increases in Aβ(1-42) had a significant linear relationship with both NOX activity and cognitive performance in APP×PS1 knock-in mice. Collectively, these data show that NOX expression and activity are significantly upregulated with age in this humanized model of Aβ pathogenesis, and suggest that NOX-associated redox pathways are intimately linked to both the loss of cognitive function and the deposition of Aβ(1-42).

The effects of cyclophosphamide on hippocampal cell proliferation and spatial working memory in rat

Cyclophosphamide (CP) is a chemotherapy used in combinations that are associated with cognitive impairment. In the present study male Lister-hooded rats (n = 12) were used to investigate the effects of chronic administration of CP (30mg/kg, 7 i.v. doses, or an equivalent volume of saline) on performance in the novel location recognition (NLR) task and on the proliferation and survival of hippocampal cells. The survival of hippocampal cells dividing at the beginning of treatment was significantly reduced by CP. However, no difference was seen between CP treated and control groups for the number of cells proliferating 7 days after the final injection and both groups performed equally well in the NLR task. These results indicate that the given dose of CP acutely reduces the survival of newly born hippocampal cells. However, it does not have a longer term effect on spatial working memory or hippocampal proliferation, suggesting that CP is less neurotoxic than other chemotherapies with which it is used in combination.

Fluoxetine reverses the memory impairment and reduction in proliferation and survival of hippocampal cells caused by methotrexate chemotherapy

RATIONALE

Adjuvant cancer chemotherapy can cause long-lasting, cognitive deficits. It is postulated that these impairments are due to these drugs targeting neural precursors within the adult hippocampus, the loss of which has been associated with memory impairment.

OBJECTIVES

The present study investigates the effects of the chemotherapy, methotrexate (MTX) on spatial working memory and the proliferation and survival of the neural precursors involved in hippocampal neurogenesis, and the possible neuroprotective properties of the antidepressant fluoxetine.

METHODS

Male Lister hooded rats were administered MTX (75 mg/kg, two i.v. doses a week apart) followed by leucovorin rescue (i.p. 18 h after MTX at 6 mg/kg and at 26, 42 and 50 h at 3 mg/kg) and/or fluoxetine (10 mg/kg/day in drinking water for 40 days). Memory was tested using the novel location recognition (NLR) test. Using markers, cell proliferation (Ki67) and survival (bromodeoxyuridine/BrdU), in the dentate gyrus were quantified.

RESULTS

MTX-treated rats showed a cognitive deficit in the NLR task compared with the vehicle and fluoxetine-treated groups. Cognitive ability was restored in the group receiving both MTX and fluoxetine. MTX reduced both the number of proliferating cells in the SGZ and their survival. This was prevented by the co-administration of fluoxetine, which alone increased cell numbers.

CONCLUSIONS

These results demonstrate that MTX induces an impairment in spatial working memory and has a negative long-term effect on hippocampal neurogenesis, which is counteracted by the co-administration of fluoxetine. If translatable to patients, this finding has the potential to prevent the chemotherapy-induced cognitive deficits experienced by many cancer survivors.

Evaluation of multiple neurotoxic outcomes in cancer chemotherapy

Although it is now clear that cognitive dysfunction is a common accompaniment of cancer chemotherapy, its implications await further research and direction. Most of the clinical research relies on standard neuropsychological tests that were developed to diagnose stable traits. Cognitive dysfunction in patients undergoing treatment varies with time, however. Its dimensions will vary during the course of treatment, which generally consists of cycles of drug administration followed by recovery periods. To effectively determine the connection between chemotherapy and cognitive function requires neuropsychological tests based on performance, so that they can be administered repeatedly at specified times during the entire course of treatment and beyond. A number of computerized test batteries, many of which have been developed for environmental neurotoxicology, are now available that fit such criteria. Moreover, cognitive impairment is only one aspect of chemotherapy-induced neurotoxicity. A full appreciation of its scope requires assessment of sensory functions such as vision, audition and somatosensory properties and assessment of motor function. A program of research based on animal models is also essential. Only with animal models is it possible to determine dose-response relationships and to couple behavioral with mechanistic indices such as neuroplasticity. Animal behavior models play a vital role in environmental toxicology because, from them, it is possible to derive some index of exposure that limits adverse effects. However, as in human testing, it is critical to choose situations whose properties remain stable over long periods of time so as to trace the time course of neurotoxicity. Schedule-controlled operant behavior offers the most promising source of animal models.