Delayed administration of memantine prevents N-methyl-D-aspartate receptor-mediated neurotoxicity

Children's Oncology Group's 2023 blueprint for research: Behavioral science

As survival rates for childhood cancer have improved, there has been increasing focus on identifying and addressing adverse impacts of cancer and its treatment on children and their families during treatment and into survivorship. The Behavioral Science Committee (BSC) of the Children's Oncology Group (COG), comprised of psychologists, neuropsychologists, social workers, nurses, physicians, and clinical research associates, aims to improve the lives of children with cancer and their families through research and dissemination of empirically supported knowledge. Key achievements of the BSC include enhanced interprofessional collaboration through integration of liaisons into other key committees within COG, successful measurement of critical neurocognitive outcomes through standardized neurocognitive assessment strategies, contributions to evidence-based guidelines, and optimization of patient-reported outcome measurement. The collection of neurocognitive and behavioral data continues to be an essential function of the BSC, in the context of therapeutic trials that are modifying treatments to maximize event-free survival, minimize adverse outcomes, and optimize quality of life. In addition, through hypothesis-driven research and multidisciplinary collaborations, the BSC will also begin to prioritize initiatives to expand the systematic collection of predictive factors (e.g., social determinants of health) and psychosocial outcomes, with overarching goals of addressing health inequities in cancer care and outcomes, and promoting evidence-based interventions to improve outcomes for all children, adolescents, and young adults with cancer.

Memantine in the Prevention of Radiation-Induced Brain Damage: A Narrative Review

Simple Summary

Decline in cognitive function is a major problem for patients undergoing whole-brain radiotherapy (WBRT). Scientific interest has increased due to the high dropout rate of patients in the first months after WBRT and the early onset of cognitive decline. Therefore, the study of antiglutamatergic pharmacological prophylaxis and hippocampal-sparing WBRT techniques has been deepened based on the knowledge of the mechanisms of hyperglutamatergic neurotoxicity and the role of some hippocampal areas in cognitive decline. In order to provide a summary of the evidence in this field, and to foster future research in this setting, this literature review presents current evidence on the prevention of radiation-induced cognitive decline and particularly on the role of memantine.

Abstract

Preserving cognitive functions is a priority for most patients with brain metastases. Knowing the mechanisms of hyperglutamatergic neurotoxicity and the role of some hippocampal areas in cognitive decline (CD) led to testing both the antiglutamatergic pharmacological prophylaxis and hippocampal-sparing whole-brain radiotherapy (WBRT) techniques. These studies showed a relative reduction in CD four to six months after WBRT. However, the failure to achieve statistical significance in one study that tested memantine alone (RTOG 0614) led to widespread skepticism about this drug in the WBRT setting. Moreover, interest grew in the reasons for the strong patient dropout rates in the first few months after WBRT and for early CD onset. In fact, the latter can only partially be explained by subclinical tumor progression. An emerging interpretation of the (not only) cognitive impairment during and immediately after WBRT is the dysfunction of the limbic and hypothalamic system with its immune and hormonal consequences. This new understanding of WBRT-induced toxicity may represent the basis for further innovative trials. These studies should aim to: (i) evaluate in greater detail the cognitive effects and, more generally, the quality of life impairment during and immediately after WBRT; (ii) study the mechanisms producing these early effects; (iii) test in clinical studies, the modern and advanced WBRT techniques based on both hippocampal-sparing and hypothalamic-pituitary-sparing, currently evaluated only in planning studies; (iv) test new timings of antiglutamatergic drugs administration aimed at preventing not only late toxicity but also acute effects.

Memantine and its benefits for cancer, cardiovascular and neurological disorders

Memantine is a non-competitive N-methyl-D-aspartate (NMDA) receptor antagonist that was initially indicated for the treatment of moderate to severe Alzheimer's disease. It is now also considered for a variety of other pathologies in which activation of NMDA receptors apparently contributes to the pathogenesis and progression of disease. In addition to the central nervous system (CNS), NMDA receptors can be found in non-neuronal cells and tissues that recently have become an interesting research focus. Some studies have shown that glutamate signaling plays a role in cell transformation and cancer progression. In addition, these receptors may play a role in cardiovascular disorders. In this review, we focus on the most recent findings for memantine with respect to its pharmacological effects in a range of diseases, including inflammatory disorders, cardiovascular diseases, cancer, neuropathy, as well as retinopathy.

SARS-CoV-2 infection in patients with serious mental illness and possible benefits of prophylaxis with Memantine and Amantadine

Patients with serious mental illness are a high-risk category of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. Patients with schizophrenia are not participatory and have increased mortality and morbidity, patients with dementia cannot be cared for while depression, anxiety, bipolar tubing are associated with low immune status. Social stress is amplified by social isolation, amplifying depression and the mechanisms of decreased immunity. Hygiene measures and prophylactic behavior are impossible to put into practice in conditions of chronic mental illness. In coronavirus disease 2019 (COVID-19), the risk for severe development is associated with the presence of comorbidities and immune system deficiency. Prothrombotic status, cytokine storm and alveolar destruction are mechanisms that aggravate the evolution of patients, especially in the context in which they have dysfunction of the autonomic system. The activity of proinflammatory cytokines is accentuated by hyperglutamatergia, which potentiates oxidative stress and triggers the mechanisms of neural apoptosis by stimulating microglial activation. Activation of M1-type microglia has an important role in pathogenesis of major psychiatric disorders, such as major depression, schizophrenia or bipolar disorder, and may associate hippocampal atrophy and disconnection of cognitive structures. Memantine and Amantadine, N-methyl-D-aspartate (NMDA) glutamate receptor inhibitors, have demonstrated, through their pharmacological profile, psychotropic effects but also antiviral properties. In the conditions of the COVID-19 pandemic, based on these arguments, we suggest that they can be associated with the therapy with the basic psychotropics, Memantine or Amantadine, for the control of neuropsychiatric symptoms but also as adjuvants with antiviral action.

The search for novel targets in Alzheimer's disease-The 90s redux

Alzheimer's disease (AD) is a complex disease of the brain. Despite over 100 years of basic and clinical research, significantly intensified in the last three decades, the exact cause of this neurodegeneration is still an enigma. Based on neuroanatomical, experimental, and clinical findings, a series of hypotheses on AD pathogenesis have evolved. Among them, the "amyloid cascade hypothesis" has been most prominent. Clinical efforts targeting the biochemistry of amyloid β-protein (Aβ) as causal therapy have all failed so far, which may mean that the pathogenic mechanism of AD is less straightforward than initially thought. While there was good scientific reason to support this hypothesis before, the exclusive concentration on it may have impeded a more objective look and prevented the pursuit of alternative approaches to decipher the cause of AD. Here, a few key hypotheses of AD are summarized, and it is proposed that our view of the cause (or causes) of this detrimental disease be widened. This includes looking back, reactivating, and revisiting findings that were ignored over the last decades. Alternative and amyloid-independent ways to explain AD pathogenesis should receive more attention and are appearing.

Acute and chronic effects of single dose memantine after controlled cortical impact injury in adult rats

BACKGROUND

Altered glutamatergic neurotransmission after traumatic brain injury (TBI) contributes to excitotoxic cell damage and death. Prevention or suppression of such changes is a desirable goal for treatment of TBI. Memantine (3,5-dimethyl-1-adamantanamine), an uncompetitive NMDA receptor antagonist with voltage-dependent open channel blocking kinetics, was reported to be neuroprotective in preclinical models of excitotoxicity, brain ischemia, and in TBI when administered prophylactically, immediately, or within minutes after injury.

METHODS

The current study examined effects of memantine administered by single intraperitoneal injection to adult male rats at a more clinically relevant delay of one hour after moderate-severe controlled cortical impact (CCI) injury or sham surgery. Histopathology was assessed on days 1, 7, 21, and 90, vestibulomotor function (beam balance and beam walk) was assessed on days 1-5 and 71-75, and spatial memory (Morris water maze test, MWM) was assessed on days 14-21 and 83-90 after CCI injury or sham surgery.

RESULTS

When administered at 10 mg/kg, but not 2.5 or 5 mg/kg, memantine preserved cortical tissue and reduced neuronal degeneration 1 day after injury, and attenuated loss of synaptophysin immunoreactivity in the hippocampus 7 days after injury. No effects of 10 mg/kg memantine were observed on histopathology at 21 and 90 days after CCI injury or sham surgery, or on vestibulomotor function and spatial memory acquisition assessed during any of the testing periods. However, 10 mg/kg memantine resulted in trends for improved search strategy in the MWM memory retention probe trial.

CONCLUSIONS

Administration of memantine at a clinically-relevant delay after moderate-severe CCI injury has beneficial effects on acute outcomes, while more significant improvement on subacute and chronic outcomes may require repeated drug administration or its combination with another therapy.

Brain metastases: fractionated whole-brain radiotherapy

Brain metastases are the most common malignant adult intracranial tumors, occurring in approximately 10-30% of cancer patients, and generally lead to a poor prognosis. The incidence has been steadily rising, likely due to longer survival from newer systemic therapies and increased utilization of magnetic resonance imaging. Historically, whole-brain radiotherapy has been a standard of care for the management of patients with brain metastases. However, better understanding of both the acute and long-term toxicities associated with whole-brain radiotherapy has led to a more selective use of whole-brain radiotherapy. Herein we discuss the background and prognostication of brain metastases as well as the role of palliative whole-brain radiotherapy, as monotherapy and adjuvant use after resection or stereotactic radiosurgery. We also review refined whole-brain radiation techniques, potential neuroprotective drugs, and ongoing trials.

The Effects of Memantine on Glutamic Receptor-Associated Nitrosative Stress in a Traumatic Brain Injury Rat Model

BACKGROUND

The main aim of this study is to elucidate whether the neuroprotective effect of memantine, a noncompetitive N-methyl-d-aspartate receptor 2B (NR2B) antagonist, affects neuronal nitrosative stress, apoptosis, and NR2B expression and improves functional outcomes.

METHODS

Immediately after the onset of fluid percussion traumatic brain injury (TBI), anesthetized male Sprague-Dawley rats were divided into sham-operated, TBI + vehicle, and TBI + memantine groups. TBI rats were treated with a memantine intraperitoneal injection dose of 20 mg/kg intraperitoneally and then 1 mg/kg every 12 hours intraperitoneally for 6 doses. The motor function, proprioception, infarction volume, and neuronal apoptosis were then measured. Immunofluorescence was used to evaluate astrogliosis, microgliosis, nitrosative stress, and NR2A and NR2B expression in cortical cells. All the parameters were assessed 72 hours after TBI.

RESULTS

Compared with the sham-operated controls, the TBI-induced motor and proprioception deficits, and increased infraction volume after TBI were significantly attenuated by memantine therapy. The TBI-induced neuronal apoptosis, astrogliosis, and microgliosis, the numbers of neuronal NO synthase and 3-nitro-l-tyrosine expression in neurons, and inducible NO synthase expression in microglia and astrocyte cells in the ischemic cortex after TBI were significantly improved by memantine therapy. Simultaneously, without affecting the NR2A expression in neuronal cells, the NR2B expression significantly decreased after memantine therapy, as evaluated by an immunofluorescence stain.

CONCLUSIONS

Intraperitoneal injection of memantine in the acute stage may ameliorate TBI in rats by affecting NR2B expression and decreasing neuronal apoptosis and nitrosative stress in the injured cortex. These effects might represent 1 mechanism by which functional recovery occurred.

Neurocognitive aspects of brain metastasis

Brain metastases are common, occurring in approximately 20% of cancer patients. One of the biggest concerns for these patients and their families is neurocognitive decline. Neurocognitive issues in this patient population are complex and many patients have neurocognitive impairment due to systemic therapies even before they develop brain metastases. The development of brain metastases as well as the treatment of these tumors can cause decline in neurocognitive function. Diffuse treatments such as whole-brain radiotherapy are more frequently associated with neurocognitive decline than focal interventions such as radiosurgery, surgical resection, and implantable chemotherapy wafers. For patients with brain metastases treatment decisions require a multidisciplinary approach, balancing many factors including the neurocognitive impact of treatment and the disease process itself. Finally, to continue to advance the field there needs to be continued utilization, both off and on clinical trial, of performance-based clinical outcome assessments (i.e., neurocognitive tests) to objectively assess and measure the neurocognitive outcomes of these patients.

Memantine Reduced Cell Death, Astrogliosis, and Functional Deficits in an in vitro Model of Repetitive Mild Traumatic Brain Injury

Clinical studies suggest that athletes with a history of concussion may be at risk for additional mild traumatic brain injury (mTBI), and repetitive exposure to mTBI acutely increases risk for more significant and persistent symptoms and increases future risk for developing neurodegenerative diseases. Currently, symptoms of mTBI are managed with rest and pain medication; there are no drugs approved by the Food and Drug Administration (FDA) that target the biochemical pathology underlying mTBI to treat or prevent acute and long-term effects of repetitive mTBI. Memantine is an FDA-approved drug for treating Alzheimer's disease, and also was shown to be neuroprotective in rodents following a single, moderate to severe TBI. Therefore, we investigated the potential for memantine to mitigate negative outcomes from repetitive mild stretch injury in organotypical hippocampal slice cultures. Samples received two injuries 24 h apart; injury resulted in significant cell death, loss of long-term potentiation (LTP), and astrogliosis compared with naïve, uninjured samples. Delivery of 1.5 μM memantine 1 h following each stretch significantly reduced the effect of injury for all outcome measures, and did not alter those outcome measures that were unaffected by the injury. Therefore, memantine warrants further pre-clinical and clinical investigation for its therapeutic efficacy to prevent cognitive deficits and neuropathology from multiple mTBIs.

Intravitreal memantine retinal toxicity in rabbits

OBJECTIVE

To histologically evaluate whether the intravitreal application of memantine produces retinal toxicity in rabbits.

METHODS

A cross-sectional design, experimental, descriptive study was performed on 16 eyes of 16 New Zealand rabbits of 3 kg, divided in 4 groups of 4 rabbits. A dose of 70 ng/ml of intravitreal memantine was administered in Group A, a dose of 150 ng/ml in Group B, a dose of 400 ng/ml in Group C, and Group D received 1 ml of balanced salt solution. The injected eye of half of each group was enucleated 15 days after the injection, and the rest within 30 days after injection. Following enucleation, each eye was placed in 10% formaldehyde. Histopathological analysis was performed on all enucleated eyes. The animals were treated according to the guidelines of the Association for Research on Vision and Ophthalmology (ARVO).

RESULTS

Groups A, B and D did not show any histopathological changes after their enucleation at 15 and 30 days. Group C showed changes in the photoreceptor layer after enucleation at 15 and 30 days.

CONCLUSIONS

In our study, it was observed that memantine concentrations at 70 ng/ml and 150 ng/ml are safe when administered intravitreally; however, doses of 400 ng/ml produced retinal structural changes. This research should continue to assess its clinical usefulness.

Contemporary Review of the Management of Brain Metastasis with Radiation

Brain metastases are an important cause of morbidity and mortality, afflicting approximately 200,000 Americans annually. The prognosis for these patients is poor, with median survivals typically measured in months. In this review article, we present the standard treatment approaches with whole brain radiation and as well as novel approaches in the prevention of neurocognitive deficits.

Differentiation renders susceptibility to excitotoxicity in HT22 neurons

HT22 is an immortalized mouse hippocampal neuronal cell line that does not express cholinergic and glutamate receptors like mature hippocampal neurons in vivo. This in part prevents its use as a model for mature hippocampal neurons in memory-related studies. We now report that HT22 cells were appropriately induced to differentiate and possess properties similar to those of mature hippocampal neurons in vivo, such as becoming more glutamate-receptive and excitatory. Results showed that sensitivity of HT22 cells to glutamate-induced toxicity changed dramatically when comparing undifferentiated with differentiated cells, with the half-effective concentration for differentiated cells reducing approximately two orders of magnitude. Moreover, glutamate-induced toxicity in differentiated cells, but not undifferentiated cells, was inhibited by the N-methyl-D- aspartate receptor antagonists MK-801 and memantine. Evidently, differentiated HT22 cells expressed N-methyl-D-aspartate receptors, while undifferentiated cells did not. Our experimental findings indicated that differentiation is important for immortalized cell lines to render post-mitotic neuronal properties, and that differentiated HT22 neurons represent a better model of hippocampal neurons than undifferentiated cells.

Redox pioneer: Professor Stuart A. Lipton

[Figure: see text] Stuart A. Lipton, M.D., Ph.D. is recognized here as a Redox Pioneer because of his publication of four articles that have been cited more than 1000 times, and 96 reports which have been cited more than 100 times. In the redox field, Dr. Lipton is best known for his work on the regulation by S-nitrosylation of the NMDA-subtype of neuronal glutamate receptor, which provided early evidence for in situ regulation of protein activity by S-nitrosylation and a prototypic model of allosteric control by this post-translational modification. Over the past several years, Lipton's group has pioneered the discovery of aberrant protein nitrosylation that may contribute to a number of neurodegenerative disorders, including Alzheimer's disease, Parkinson's disease, Huntington's disease, and amyotrophic lateral sclerosis (Lou Gehrig's disease). In particular, the phenotypic effects of rare genetic mutations may be understood to be enhanced or mimicked by nitrosative (and oxidative) modifications of cysteines and thereby help explain common sporadic forms of disease. Thus, Lipton has contributed in a major way to the understanding that nitrosative stress may result from modifications of specific proteins and may operate in conjunction with genetic mutation to create disease phenotype. Lipton (collaborating with Jonathan S. Stamler) has also employed the concept of targeted S-nitrosylation to produce novel neuroprotective drugs that act at allosteric sites in the NMDA receptor. Lipton has won a number of awards, including the Ernst Jung Prize in Medicine, and is an elected fellow of the AAAS. Antioxid. Redox Signal. 19, 757-764.

Memantine for the prevention of cognitive dysfunction in patients receiving whole-brain radiotherapy: a randomized, double-blind, placebo-controlled trial

BACKGROUND

To determine the protective effects of memantine on cognitive function in patients receiving whole-brain radiotherapy (WBRT).

METHODS

Adult patients with brain metastases received WBRT and were randomized to receive placebo or memantine (20 mg/d), within 3 days of initiating radiotherapy for 24 weeks. Serial standardized tests of cognitive function were performed.

RESULTS

Of 554 patients who were accrued, 508 were eligible. Grade 3 or 4 toxicities and study compliance were similar in the 2 arms. There was less decline in delayed recall in the memantine arm at 24 weeks (P = .059), but the difference was not statistically significant, possibly because there were only 149 analyzable patients at 24 weeks, resulting in only 35% statistical power. The memantine arm had significantly longer time to cognitive decline (hazard ratio 0.78, 95% confidence interval 0.62-0.99, P = .01); the probability of cognitive function failure at 24 weeks was 53.8% in the memantine arm and 64.9% in the placebo arm. Superior results were seen in the memantine arm for executive function at 8 (P = .008) and 16 weeks (P = .0041) and for processing speed (P = .0137) and delayed recognition (P = .0149) at 24 weeks.

CONCLUSIONS

Memantine was well tolerated and had a toxicity profile very similar to placebo. Although there was less decline in the primary endpoint of delayed recall at 24 weeks, this lacked statistical significance possibly due to significant patient loss. Overall, patients treated with memantine had better cognitive function over time; specifically, memantine delayed time to cognitive decline and reduced the rate of decline in memory, executive function, and processing speed in patients receiving WBRT. RTOG 0614, ClinicalTrials.gov number CT00566852.

Enhancement of NMDA receptor-mediated excitatory postsynaptic currents by gp120-treated macrophages: implications for HIV-1-associated neuropathology

A plethora of prior studies has linked HIV-1-infected and immune activated brain mononuclear phagocytes (MP; blood borne macrophages and microglia) to neuronal dysfunction. These are modulated by N-methyl-D-aspartate receptor (NMDAR) antagonists and supporting their relevance for HIV-1-associated nervous system disease. The role of NMDAR subsets in HIV-1-induced neuronal injury, nonetheless, is poorly understood. To this end, we investigated conditioned media from HIV-1gp120-treated human monocyte-derived-macrophages (MDM) for its abilities to affect NMDAR-mediated excitatory postsynaptic currents (EPSC(NMDAR)) in rat hippocampal slices. Bath application of gp120-treated MDM-conditioned media (MCM) produced an increase of EPSC(NMDAR). In contrast, control (untreated) MCM had limited effects on EPSC(NMDAR). Testing NR2A NMDAR (NR2AR)-mediated EPSC (EPSC(NR2AR)) and NR2B NMDAR (NR2BR)-mediated EPSC (EPSC(NR2BR)) for MCM showed significant increased EPSC(NR2BR) when compared to EPSC(NR2AR) enhancement. When synaptic NR2AR-mediated EPSC was blocked by bath application of MK801 combined with low frequency stimulations, MCM retained its ability to enhance EPSC(NMDAR) evoked by stronger stimulations. This suggested that increase in EPSC(NMDAR) was mediated, in part, through extra-synaptic NR2BR. Further analyses revealed that the soluble factors with low (<3 kD) to medium (3-10 kD) molecular weight mediated the observed increases in EPSC(NMDAR). The link between activation of NR2BRs and HIV-1gp120 MCM for neuronal injury was demonstrated by NR2BR but not NR2AR blockers. Taken together, these results indicate that macrophage secretory products induce neuronal injury through extra-synaptic NR2BRs.

Future directions in treatment of brain metastases

BACKGROUND

Brain metastases affect up to 30% of patients with cancer. Management of brain metastases continues to evolve with ever increasing focus on cognitive preservation and quality of life. This manuscript reviews current state of brain metastases management and discusses various treatment controversies with focus on future clinical trials. Stereotactic radiosurgery (SRS) and whole-brain radiotherapy (WBRT) are discussed in context of multiple (4+ brain metastases) as well as new approaches combining radiation and targeted agents. A brief discussion of modified WBRT approaches, including hippocampal-avoidance WBRT (HA-WBRT) is included as well as a section on recently presented results of Radiation Therapy Oncology Group (RTOG) 0614, a randomized, double-blind, placebo-controlled trial of menantine for prevention of neurocognitive injury after WBRT.

METHODS

A search of selected studies relevant to management of brain metastases was performed in PubMed as well as in various published meeting abstracts. This data was collated and analyzed in context of contemporary management and future clinical trial plans. This data is presented in tabular form and discussed extensively in the text.

RESULTS

The published data demonstrate continued evolution of clinical trials and management strategies designed to minimize and/or prevent cognitive decline following radiation therapy management of brain metastases. Hippocampal avoidance whole-brain radiation therapy (HA-WBRT) and radiosurgery treatments for multiple brain metastases are discussed along with preliminary results of RTOG 0614, a trial of memantine therapy to prevent cognitive decline following WBRT. Trial results appear to support the use of memantine for prevention of cognitive decline.

CONCLUSIONS

Different management strategies for multiple brain metastases (>4 brain metastases) are currently being evaluated in prospective clinical trials to minimize the likelihood of cognitive decline following WBRT.

Glaucoma and Alzheimer’s disease in the elderly

Primary open angle glaucoma and Alzheimer’s disease have long been established as two separate pathological entities, primarily affecting the elderly. The progressive, irreversible course of both diseases has significant implications on an aging population. As the complex pathophysiology of the two diseases has progressively unraveled over the past two decades, common pathophysiological changes have also been elucidated. Some of these mechanisms have established a strong grounding, whilst others remain principally speculative. The mutual neuropathological changes in primary open angle glaucoma and Alzheimer’s disease have facilitated the development of neuroprotective strategies. While most of these strategies are still in the preclinical phase, they have shown great promise in experimental animal studies. Further understanding of the common pathophysiology of primary open angle glaucoma and Alzheimer’s disease and their timeline may have great implications on early diagnosis and effective therapeutic targeting.

Neuroprotection in glaucoma - Is there a future role?

In glaucoma, the major cause of global irreversible blindness, there is an urgent need for treatment modalities that directly target the RGCs. The discovery of an alternative therapeutic approach, independent of IOP reduction, is highly sought after, due to the indirect nature and limited effectiveness of IOP lowering therapy in preventing RGC loss. Several mechanisms have been implicated in initiating the apoptotic cascade in glaucomatous retinopathy and numerous drugs have been shown to be neuroprotective in animal models of glaucoma. These mechanisms and their potential treatment include excitotoxicity, protein misfolding, mitochondrial dysfunction, oxidative stress, inflammation and neurotrophin deprivation. All of these mechanisms ultimately lead to programmed cell death with loss of RGCs. In this article we summarize the mechanisms involved in glaucomatous disease, highlight the rationale for neuroprotection in glaucoma management and review current potential neuroprotective strategies targeting RGCs from the laboratory to the clinic.

Memantine treatment decreases levels of secreted Alzheimer's amyloid precursor protein (APP) and amyloid beta (A beta) peptide in the human neuroblastoma cells

Memantine, an uncompetitive NMDA receptor antagonist, is a FDA-approved drug used for the treatment of moderate-to-severe Alzheimer's disease (AD). Several studies have documented protective roles of memantine against amyloid beta (A beta) peptide-mediated damage to neurons in both in vitro and in vivo models. Memantine is also effective in reducing amyloid burden in the brain of APP transgenic mice. However, the exact mechanism by which memantine provides protection against A beta-mediated neurodegenerative cascade, including APP metabolism, remains to be elucidated. Herein, we investigated the effect of memantine on levels of the secreted form of A beta precursor protein (APP), secreted A beta and cell viability markers under short/acute conditions. We treated neuronal SK-N-SH cells with 10 microM memantine and measured levels of secreted total APP (sAPP), APP alpha isoform and A beta((1-40)) in a time dependent manner for up to 24h. Memantine significantly decreased the levels of the secreted form of sAPP, sAPP alpha and A beta((1-40)) compared to vehicle treated cells. This change started as early as 8h and continued for up to 24h of drug treatment. Unlike sAPP, a slight non-significant increase in total intracellular APP level was observed in 24-h treated memantine cells. Taken together, these results suggest a role for memantine in the transport or trafficking of APP molecules away from the site of their proteolytic cleavage by the secretase enzymes. Such a novel property of memantine warrants further study to define its therapeutic utility.

Memantine: a review of studies into its safety and efficacy in treating Alzheimer's disease and other dementias

Memantine is an uncompetitive N-methyl-D-aspartate receptor antagonist with moderate affinity. Its mechanism of action is neuroprotective and potentially therapeutic in several neuropsychiatric diseases. It has been approved by the FDA for the treatment of moderate to severe Alzheimer's disease (AD) either as a monotherapy or in combination with cholinesterase inhibitors. This review covers key studies of memantine's safety and efficacy in treating moderate to severe AD. It also covers current research into other dementias including but not exclusively mild AD and vascular dementia. Other studies on the efficacy of memantine for other neuropsychiatric diseases are discussed. Memantine is a safe and effective drug that merits further research on several topics. Clinicians should be aware of new studies and potential uses of memantine because of its safety and efficacy.

The effects of NMDA receptor antagonists over intestinal ischemia/reperfusion injury in rats

Intestinal ischemia/reperfusion causes severe injury and alters motility. N-methyl-D-aspartate (NMDA) receptor antagonists have been shown to reduce ischemia/reperfusion injury in the nervous system, and in other organs. In this study, we set out to investigate the effects of NMDA receptor antagonists over intestinal ischemia/reperfusion injury. Male Wistar rats were randomly divided into four groups: (1) a control, sham-operated group; (2) an intestinal ischemia/reperfusion group subjected to 45 min ischemia and 1h reperfusion; (3) a group treated with 10 mg/kg ketamine before ischemia/reperfusion; and (4) a group treated with 10 mg/kg memantine before ischemia/reperfusion. Intestinal samples were taken for histological evaluation. Serum levels of aspartate aminotransferase (AST), alanine aminotransferase (ALT), lactate dehydrogenase (LDH), malondialdehyde (MDA), total antioxidant capacity, tumor necrosis factor alpha (TNF-alpha), P-selectin and antithrombin III (ATIII) were measured. Intestinal transit time was determined to evaluate intestinal motility. Fecal pellet output and animal weight were also registered daily for 7 days post-ischemia. After reperfusion, AST, LDH, TNF-alpha and P-selectin levels were elevated, ATIII levels were depleted, and ALT levels were unchanged in serum. Additionally, levels of MDA were increased and total antioxidant capacity was reduced in serum, indicating oxidative stress. Intestinal mucosa showed severe injury. Ketamine, but not memantine, diminished these alterations. Intestinal motility and fecal pellet output were also altered after ischemia/reperfusion. Both drugs abolished the alterations in motility. In conclusion, ketamine's protective effects over ischemia/reperfusion do not appear to be NMDA mediated, but they could be playing a role in protecting the intestine against ischemia-induced functional changes.

Failure to improve the effect of thrombolysis by memantine in a rat embolic stroke model

OBJECTIVES

Partial and delayed recanalization is a regular finding after thrombolysis in stroke patients who may benefit from additional therapy with neuroprotectants. To translate this scenario into an experiment, memantine was combined with thrombolysis in an embolic stroke model and tissue outcome was assessed in terms of complete and incomplete damage.

METHODS

Tissue plasminogen activator (tPA, 5 mg/kg, b.w.) was administered 1.5 or 3.5 hours after embolic middle cerebral artery (MCA) occlusion in rats. In both groups, rats were assigned to additional therapy with memantine (10 mg/kg, i.p.) or saline injection. Ischemia and eventual reperfusion were continuously monitored by laser-Doppler flowmetry. Reperfusion was defined as a lasting increase in post-thrombolytic cerebral blood flow to >60% of baseline (complete) or to a lesser degree (partial). Experiments were terminated 6 hours post-occlusion to obtain quantitative histopathology.

RESULTS

tPA induced complete or partial recanalization in 54% of treated animals. Successful reperfusion reduced total ischemic lesion volume by 42% compared with non-reperfused animals (p<0.05), but increased significantly the percentage of scattered neuronal injury from 25.6 (non-reperfusion) to 36.3% (reperfusion, p<0.05). Memantine did not improve the effect of tPA-induced recanalization on infarct morphology whether applied at 1.5 or 3.5 hours post-occlusion.

DISCUSSION

We conclude from our experiments that add-on therapy with memantine did not alter the effect of thrombolysis in an embolic stroke model. Recanalization appears to be a prerequisite to confer neuroprotective effects.

Targeted Therapy for Brain Metastases: Improving the Therapeutic Ratio

Brain metastasis is the most common intracranial malignancy in adults. Improvements in modern imaging techniques are detecting previously occult brain metastases, and more effective therapies are extending the survival of patients with invasive cancer who have historically died from extracranial disease before developing brain metastasis. This combination of factors along with increased life expectancy has led to the increased diagnosis of brain metastases. Conventional treatment has been whole brain radiotherapy, which can improve symptoms, but potentially results in neurocognitive deficits. Several strategies to improve the therapeutic ratio are currently under investigation to either enhance the radiation effect, thereby preventing tumor recurrence or progression as well as reducing collateral treatment-related brain injury. In this review article, we discuss new directions in the management of brain metastases, including the role of chemical modifiers, novel systemic agents, and the management and prevention of neurocognitive deficits.

Pharmacological activation of mGlu2/3 metabotropic glutamate receptors protects retinal neurons against anoxic damage in the goldfish Carassius auratus

We examined the expression of mGlu2/3 metabotropic glutamate receptors in the retina of the goldfish Carassius auratus. mGlu2/3 receptors were expressed in all retinal layers internal to the photoreceptor layer, particularly in the outer and inner nuclear layers. Although the goldfish brain is able to tolerate prolonged periods of anoxia, we examined whether anoxia could induce retinal damage. Three hours of anoxia induced in the retina the development of apoptotic cell death, as assessed 48 h later by TUNEL staining. TUNEL-positive cells were particularly found in the inner and outer nuclear layers, and were also present in the ganglion cell layer. Pharmacological activation of mGlu2/3 receptors by systemic injection of LY379268 (0.5 mg/kg, i.p., 15 min before the onset of anoxia) substantially protected retinas against anoxia-induced cell death. In contrast, systemic injection of the mGlu2/3 receptor antagonist, LY341495 (1 mg/kg, i.p., 15 min before the onset of anoxia), significantly amplified cell death. Finally, as mGlu2/3 receptors are implicated in the control of extracellular glutamate concentrations, we examined the stimulation of glutamate release in isolated goldfish retinas. Depolarizing medium containing 30 mM KCl led to a significant increase in glutamate release, which was substantially reduced by LY379268. We conclude that activation of mGlu2/3 receptors may provide a major defensive mechanism against ischemic/anoxic retinal damage.

Memantine: a review of its use in Alzheimer's disease

Memantine (Ebixa, Axura, Namenda, Akatinol) is a moderate-affinity, uncompetitive, voltage-dependent, NMDA-receptor antagonist with fast on/off kinetics that inhibits excessive calcium influx induced by chronic overstimulation of the NMDA receptor. Memantine is approved in the US and the EU for the treatment of patients with moderate to severe dementia of the Alzheimer's type. In well designed clinical trials, oral memantine, as monotherapy or in addition to a stable dose of acetylcholinesterase inhibitors, was well tolerated during the treatment of mild to severe Alzheimer's disease for up to 52 weeks. Memantine generally modified the progressive symptomatic decline in global status, cognition, function and behaviour exhibited by patients with moderate to severe Alzheimer's disease in four 12- to 28-week trials. In patients with mild to moderate Alzheimer's disease, data from three 24-week trials are equivocal, although meta-analyses indicate beneficial effects on global status and cognition. Memantine is an effective pharmacotherapeutic agent, and currently the only approved option, for the treatment of moderate to severe Alzheimer's disease.

Paradigm shift in neuroprotection by NMDA receptor blockade: memantine and beyond

Neuroprotective drugs tested in clinical trials, particularly those that block N-methyl-D-aspartate-sensitive glutamate receptors (NMDARs), have failed miserably in large part because of intolerable side effects. However, one such drug, memantine, was recently approved by the European Union and the US FDA for the treatment of dementia following our group's discovery of its clinically tolerated mechanism of action. Here, we review the molecular basis for memantine efficacy in neurological diseases that are mediated, at least in part, by overactivation of NMDARs, producing excessive Ca(2+) influx through the receptor's associated ion channel and consequent free-radical formation.

Whole-brain radiotherapy in the management of brain metastasis

Brain metastases are an important cause of morbidity and mortality, afflicting nearly 170,000 Americans annually. The prognosis for these patients is poor, with median survival times measured in months. In this review article, we present the standard treatment approach of whole-brain radiotherapy and discuss new directions, including the role of chemical modifiers and the management and prevention of neurocognitive deficits.

Experimental and potential future therapeutic approaches for HIV-1 associated dementia targeting receptors for chemokines, glutamate and erythropoietin

Severe and debilitating neurological problems that include behavioral abnormalities, motor dysfunction and frank dementia can occur after infection with the human immunodeficiency virus-1 (HIV-1). Infected peripheral immune-competent cells, in particular macrophages, infiltrate the central nervous system (CNS) and provoke a neuropathological response involving all cell types in the brain. HIV-1 infection results in activation of chemokine receptors, inflammatory mediators, extracellular matrix-degrading enzymes and glutamate receptor-mediated excitotoxicity, all of which can trigger numerous downstream signaling pathways that result in disruption of neuronal and glial function. Despite many major improvements in the control of viral infection in the periphery, a truly effective therapy for HIV-1 associated dementia is currently not available. This review will discuss experimental and potentially future therapeutic strategies based on recently uncovered pathologic mechanisms contributing to neuronal damage induced by HIV-1.

Failures and successes of NMDA receptor antagonists: molecular basis for the use of open-channel blockers like memantine in the treatment of acute and chronic neurologic insults

Excitotoxicity, defined as excessive exposure to the neurotransmitter glutamate or overstimulation of its membrane receptors, has been implicated as one of the key factors contributing to neuronal injury and death in a wide range of both acute and chronic neurologic disorders. Excitotoxic cell death is due, at least in part, to excessive activation of N-methyl-D-aspartate (NMDA)-type glutamate receptors and hence excessive Ca2+ influx through the receptor's associated ion channel. Physiological NMDA receptor activity, however, is also essential for normal neuronal function; potential neuroprotective agents that block virtually all NMDA receptor activity will very likely have unacceptable clinical side effects. For this reason many NMDA receptor antagonists have disappointingly failed advanced clinical trials for a number of diseases including stroke and neurodegenerative disorders such as Huntington's disease. In contrast, studies in my laboratory were the first to show that memantine, an adamantane derivative, preferentially blocks excessive NMDA receptor activity without disrupting normal activity. Memantine does this through its action as an open-channel blocker; it enters the receptor-associated ion channel preferentially when it is excessively open, and, most importantly, its off-rate is relatively fast so that it does not substantially accumulate in the channel to interfere with normal synaptic transmission. Past clinical use for other indications has demonstrated that memantine is well tolerated, and it has recently been approved in both Europe and the USA for the treatment of dementia of the Alzheimer's type. Clinical studies of the safety and efficacy of memantine for other neurological disorders, including glaucoma and other forms of dementia, are currently underway. A series of second-generation memantine derivatives are currently in development and may prove to have even greater neuroprotective properties than does memantine. These second-generation drugs take advantage of the fact that the NMDA receptor has other modulatory sites, in addition to its ion channel, that could potentially be used for safe but effective clinical intervention.

Memantine: targeting glutamate excitotoxicity in Alzheimer's disease and other dementias

The management of dementia has changed since the development of new antidementia drugs. The benefits observed in Alzheimer's disease (AD) with selective cholinergic transmission treatments are mainly symptomatic, without clear evidence of neuroprotection. The hypothesis that glutamate-mediated neurotoxicity is involved in the pathogenesis of AD is finding increasingly more acceptance in the scientific community. Glutamate receptors are overactive, and N-methyl-D-aspartate (NMDA) receptor antagonists have therapeutic potential for the treatment of AD and other neurological disorders. Memantine is a noncompetitive NMDA antagonist that is considered a neuroprotective drug. Memantine's capacity has been demonstrated in preclinical studies, and it is considered a useful symptomatic treatment for AD. Memantine has been shown to benefit cognition, function, and global outcome in patients with moderate to severe AD, and it is currently approved by the US Food and Drug Administration (FDA) for the treatment of moderate to severe AD. Recently, memantine has also demonstrated efficacy in the initial stages of AD, although FDA authorization is pending. This review highlights the important pharmacological and clinical aspects of memantine, as well as some basic mechanisms mediating glutamatergic neurodegeneration.

The effects of memantine on lipid peroxidation following closed-head trauma in rats

Memantine is an uncompetitive N-methyl-D: -aspartate (NMDA) receptor antagonist. Unlike other NMDA antagonists, it has been used clinically for years for the treatment of Parkinson's disease, spasticity, and dementia without serious side effects. We aimed to investigate the therapeutic efficacy of memantine on a closed head trauma model. A total of 132 adult male Sprague-Dawley rats were randomly divided into four groups: sham-operated, control (closed head trauma), sham-vehicle (closed head trauma + saline), treatment (closed head trauma + memantine, 10 mg/kg, i.p.). A cranial impact was delivered to the skull, just in front of the coronal suture, over the left hemisphere, from the height of 7 cm. Saline or memantine were applied 15 min after trauma. Rats were euthanased 0.5, 1, 2, 6, 24, 48 h after trauma. Brain tissue samples were taken 5 mm away from the left frontal pole and also from the corresponding point of the contralateral hemispheres. Malondialdehyde activity (MDA) was considered to reflect the degree of lipid peroxidation. The MDA levels continued to increase for the first 2 h after the injury, then started to decrease gradually. Memantine treatment significantly reduced lipid peroxidation levels in the treatment group compared with other groups (P<0.01). The findings of the present study indicate that memantine provides beneficial effects after closed head trauma in rats.

An investigation of the neuroprotective effects of tetracycline derivatives in experimental models of retinal cell death

The purpose of this study was to determine the efficacy and putative mechanisms of action of tetracycline and minocycline in inhibiting retinal cell apoptosis after glutamate-induced excitotoxicity and trophic factor deprivation in a retinal cell line (E1A-NR.3) and in primary mixed retinal cell cultures. In addition, a differentiated PC-12 cell line was used to determine whether minocycline was neuroprotective after trophic withdrawal in a pure neuronal cell line devoid of glia. Results from this study demonstrated that minocycline, but not tetracycline, is protective in in vitro models of excitotoxicity-induced retinal cell apoptosis. Moreover, the protective effects provided by minocycline in retinal cells seemed independent of actions on N-methyl-D-aspartate receptors (NMDARs) and glutamate receptor-mediated Ca(2+) influx. Doses of the NMDAR antagonist MK-801 (dizocilpine) and minocycline that alone provided no significant neuroprotection resulted in enhanced retinal cell survival when applied concurrently, suggestive of distinct signaling pathways, and minocycline was without effect on glutamate-induced Ca(2+) influx, as assessed by calcium imaging. Minocycline was also neuroprotective after trophic factor withdrawal, producing a decrease in apoptosis and caspase-3 activation in both retinal cells and the PC-12 neuronal-like cell line. These results support a role for minocycline as a retinal neuroprotectant and demonstrate that the antiapoptotic actions of minocycline in retinal cells do not arise from the blockage of NMDARs or glutamate receptor-mediated Ca(2+) influx but do involve inhibition of caspase-3 activation. In addition, the survival-promoting actions of minocycline may arise via actions on both neuronal and non-neuronal cell targets.

The N-methyl-D-aspartate antagonist memantine retards progression of Huntington’s disease

According to the excitotoxicity hypothesis, neurotoxicity due to glutamate is regarded as potential factor in the progredient neurodegeneration of Huntington's disease (HD). Memantine, as a glutamate receptor antagonist, should counteract this mechanism. Its effectiveness (up to 30 mg/day) with regard to retardation of progression was thus examined in 27 HD patients in a two year, open and multicentre trial. The results suggest that memantine treatment of HD may be useful in terms of retardation of the progression of the disorder.

Memantine: an antiglutamatergic option for dementia

Alzheimer's disease (AD) is the most common form of dementia in occidental countries. Currently approved treatments for AD provide mainly symptomatic benefits without clear evidence of neuroprotection. N-methyl-D-aspartate (NMDA) receptor antagonists have therapeutic potential in several central nervous system disorders, including neuroprotective treatment in chronic neurodegenerative diseases, and symptomatic treatment in other neurologic diseases. Memantine, an NMDA antagonist, has been recently approved for the treatment of advanced AD. Due to its mechanism of action, memantine is considered a neuroprotective drug, whose utility has been demonstrated in preclinical studies. In addition, memantine is a useful symptomatic treatment for AD and vascular dementia. This paper reviews both aspects of memantine as well as some basic mechanisms mediating cognition and glutamatergic neurodegeneration.

The neuropharmacological basis for the use of memantine in the treatment of Alzheimer's disease

Memantine has been demonstrated to be safe and effective in the symptomatic treatment of Alzheimer's disease (AD). While the neurobiological basis for the therapeutic activity of memantine is not fully understood, the drug is not a cholinesterase inhibitor and, therefore, acts differently from current AD therapies. Memantine can interact with a variety of ligand-gated ion channels. However, NMDA receptors appear to be a key target of memantine at therapeutic concentrations. Memantine is an uncompetitive (channel blocking) NMDA receptor antagonist. Like other NMDA receptor antagonists, memantine at high concentrations can inhibit mechanisms of synaptic plasticity that are believed to underlie learning and memory. However, at lower, clinically relevant concentrations memantine can under some circumstances promote synaptic plasticity and preserve or enhance memory in animal models of AD. In addition, memantine can protect against the excitotoxic destruction of cholinergic neurons. Blockade of NMDA receptors by memantine could theoretically confer disease-modifying activity in AD by inhibiting the "weak" NMDA receptor-dependent excitotoxicity that has been hypothesized to play a role in the progressive neuronal loss that underlies the evolving dementia. Moreover, recent in vitro studies suggest that memantine abrogates beta-amyloid (Abeta) toxicity and possibly inhibits Abeta production. Considerable attention has focused on the investigation of theories to explain the better tolerability of memantine over other NMDA receptor antagonists, particularly those that act by a similar channel blocking mechanism such as dissociative anesthetic-like agents (phencyclidine, ketamine, MK-801). A variety of channel-level factors could be relevant, including fast channel-blocking kinetics and strong voltage-dependence (allowing rapid relief of block during synaptic activity), as well as reduced trapping (permitting egress from closed channels). These factors may allow memantine to block channel activity induced by low, tonic levels of glutamate--an action that might contribute to symptomatic improvement and could theoretically protect against weak excitotoxicity--while sparing synaptic responses required for normal behavioral functioning, cognition and memory.

Memantine

Memantine, an uncompetitive antagonist with moderate affinity for NMDA receptors, demonstrates voltage-dependency and relatively fast on/off receptor kinetics. Memantine 20 mg/day significantly slowed the rate of deterioration in outpatients with moderate to severe Alzheimer's disease in a 28-week US randomised, double-blind, placebo-controlled, multicentre study. Memantine 10 mg/day improved measures of dementia in care-dependent inpatients with Alzheimer's disease or vascular dementia in a 12-week randomised, double-blind study. Significantly more memantine than placebo recipients were responders according to Clinical Global Impression of Change scores and the Behavioural Rating Scale for Geriatric Patients Care Dependence subscale. Memantine 20 mg/day significantly improved cognition-related outcomes (cognitive subscale of the Alzheimer's Disease Assessment Scale) in patients with vascular dementia in two 28-week randomised, double-blind, placebo-controlled, multicentre trials. No statistically significant between-group difference was seen in other primary endpoints. Adverse events (incidence in memantine recipients greater than in placebo recipients) occurring in patients with moderately severe to severe dementia included diarrhoea, insomnia, dizziness, headache and hallucination.

Possible role for memantine in protecting retinal ganglion cells from glaucomatous damage

Glaucoma is a neurodegenerative disease typified by progressive loss of retinal ganglion cells (RGCs). Mild excitotoxicity has been implicated as one of the factors contributing to RGC death during the glaucomatous process. This type of excitotoxic cell death is due, at least in part, to somewhat excessive activation of N-methyl-D-aspartate (NMDA)-type glutamate receptors. NMDA-receptor activity, however, is also essential for normal neuronal function. This means that potential neuroprotective agents that block virtually all NMDA-receptor activity will have unacceptable clinical side effects. Studies in our laboratory have shown that the adamantane derivative, memantine, blocks only excessive NMDA-receptor activity without disrupting normal activity. Past clinical use has demonstrated that memantine is safe, and it has recently been approved in Europe for the treatment of Alzheimer's disease and vascular dementia. Clinical studies of the safety and efficacy of memantine in glaucoma are currently underway. A series of second-generation memantine derivatives called nitro-memantines are currently in development and may prove to have even greater neuroprotective properties than does memantine.

Group I metabotropic glutamate receptor inhibition selectively blocks a prolonged Ca(2+) elevation associated with age-dependent excitotoxicity

It has been recognized for some years that a prolonged Ca(2+) elevation that is predictive of impending cell death develops in cultured neurons following excitotoxic insult. In addition, neurons exhibit enhanced sensitivity to excitotoxic insult with increasing age in culture. However, little is known about the processes that selectively regulate the post-insult Ca(2+) elevation and therefore, it remains unclear whether it is associated specifically with age-dependent toxicity.Here, we tested the hypothesis that a group I metabotropic glutamate receptor antagonist selectively modulates the prolonged Ca(2+) elevation in direct association with its protective effects against excitotoxicity. Rat hippocampal cultures of two ages (8-9 and 21-28 days in vitro) were exposed to a 5-min glutamate insult (400 microM in younger and 10 microM in older cultures) sufficient to kill >50% of the neurons, and were treated with vehicle or the specific group I metabotropic glutamate receptor antagonist 1-aminoindan-1,5-dicarboxylic acid (AIDA; 1 mM), throughout and following the insult. Neuronal survival was quantified 24 h after insult. In parallel studies, neurons of similar age in culture were imaged ratiometrically with a confocal microscope during and for 60 min after the glutamate insult. A large post-insult Ca(2+) elevation was present in older but not most younger neurons. The N-methyl-D-aspartate receptor antagonist, MK-801, blocked the Ca(2+) elevation both during and following the insult. In contrast, AIDA blocked only the post-insult prolonged Ca(2+) elevation in older neurons. Moreover, AIDA was neuroprotective in older but not younger cultures. From these results we suggest that the post-insult Ca(2+) elevation is regulated differently from the Ca(2+) elevation during glutamate insult and is modulated by group I metabotropic glutamate receptors. Further, the prolonged Ca(2+) elevation appears to be directly linked to an age-dependent component of vulnerability.