Potential role of N-methyl-D-aspartate receptors as executors of neurodegeneration resulting from diverse insults: focus on memantine

Inflammatory signaling pathways in Alzheimer's disease: Mechanistic insights and possible therapeutic interventions

The complex pathophysiology of Alzheimer's disease (AD) poses challenges for the development of therapies. Recently, neuroinflammation has been identified as a key pathogenic mechanism underlying AD, while inflammation has emerged as a possible target for the management and prevention of AD. Several prior studies have demonstrated that medications modulating neuroinflammation might lessen AD symptoms, mostly by controlling neuroinflammatory signaling pathways such as the NF-κB, MAPK, NLRP3, etc, and their respective signaling cascade. Moreover, targeting these inflammatory modalities with inhibitors, natural products, and metabolites has been the subject of intensive research because of their anti-inflammatory characteristics, with many studies demonstrating noteworthy pharmacological capabilities and potential clinical applications. Therefore, targeting inflammation is considered a promising strategy for treating AD. This review comprehensively elucidates the neuroinflammatory mechanisms underlying AD progression and the beneficial effects of inhibitors, natural products, and metabolites in AD treatment.

Current nonstimulant medications for adults with attention-deficit/hyperactivity disorder

INTRODUCTION

Stimulants, including methylphenidate and amphetamines, are the first-line pharmacological treatment of ADHD in adults. However, in patients who do not respond or poorly tolerate stimulants, non-stimulant medications are usually recommended.

AREAS COVERED

The authors provide a narrative review of the literature on non-stimulant treatments for adult ADHD, including controlled and observational clinical studies conducted on adult samples. Atomoxetine has been extensively studied and showed significant efficacy in treating adult ADHD. Issues related to dosing, treatment duration, safety, and use in the case of psychiatric comorbidity are summarized. Among other compounds indicated for ADHD in adults, antidepressants sharing at least a noradrenergic or dopaminergic component, including tricyclic compounds, bupropion, and viloxazine, have shown demonstratable efficacy. Evidence is also available for antihypertensives, particularly guanfacine, as well as memantine, metadoxine, and mood stabilizers, while negative findings have emerged for galantamine, antipsychotics, and cannabinoids.

EXPERT OPINION

While according to clinical guidelines, atomoxetine may serve as the only second-line option in adults with ADHD, several other nonstimulant compounds may be effectively used in order to personalize treatment based on comorbid conditions and ADHD features. Nevertheless, further research is needed to identify and test more personalized treatment strategies for adults with ADHD.

Drug Development for Alzheimer's and Parkinson's Disease: Where Do We Go Now?

Neurodegenerative diseases (NDs) are a set of progressive, chronic, and incurable diseases characterized by the gradual loss of neurons, culminating in the decline of cognitive and/or motor functions. Alzheimer's disease (AD) and Parkinson's disease (PD) are the most common NDs and represent an enormous burden both in terms of human suffering and economic cost. The available therapies for AD and PD only provide symptomatic and palliative relief for a limited period and are unable to modify the diseases' progression. Over the last decades, research efforts have been focused on developing new pharmacological treatments for these NDs. However, to date, no breakthrough treatment has been discovered. Hence, the development of disease-modifying drugs able to halt or reverse the progression of NDs remains an unmet clinical need. This review summarizes the major hallmarks of AD and PD and the drugs available for pharmacological treatment. It also sheds light on potential directions that can be pursued to develop new, disease-modifying drugs to treat AD and PD, describing as representative examples some advances in the development of drug candidates targeting oxidative stress and adenosine A2A receptors.

Huannao Yicong decoction ameliorates cognitive deficits in APP/PS1/tau triple transgenic mice by interfering with neurotoxic interaction of Aβ-tau

ETHNOPHARMACOLOGICAL RELEVANCE

Huannao Yicong decoction (HYD) has been used in the study of AD for many years, which consists of Polygonum multiflorum Thunb., Panax ginseng C.A.Mey., Acorus gramineus Aiton, Coptis chinensis Franch., and Conioselinum acuminatum (Franch.) Lavrova. Previous studies have found that HYD could reduce β-Amyloid (Aβ) deposition and tau hyperphosphorylation which are the two critical pathological factors of AD. However, the mechanism of the neurotoxic interaction between Aβ and tau in AD remains unclear. Thus, the underlying mechanisms for HYD improving cognitive function of AD by interfering with the neurotoxic interaction between Aβ and tau remain to be explored.

AIM OF THE STUDY

The main objective of this study is to clarify the specific mechanisms of HYD on interfering with the neurotoxic interaction between Aβ and tau of AD both in vivo and in vitro.

MATERIALS AND METHODS

APP/PS1/tau triple transgenic mice were randomly divided into 4 groups, namely model group, memantine group, HYD low-dose group (HYD-L), and HYD high-dose group (HYD-H) with 28 mice in each group, while 28 C57BL/6J mice as the control group. Gavage was applied to all the mice daily for 24 weeks. SH-SY5Y model cells overexpressing Aβ and tau proteins as the intervention object in vitro experiments. Morris water maze was used to observe the learning and memory ability of APP/PS1/tau mice. Aβ deposition was detected by immunohistochemistry, and the levels of Aβ1-40 and Aβ1-42 were detected by enzyme-linked immunosorbent assay (ELISA). Neurofibrillary tangles (NFTs) were observed by silver staining and the levels of phosphorylated tau proteins were detected by Western blot. The GSK-3β and CDK-5 mRNA expression were detected by real-time polymerase chain reaction (RT-PCR). Besides, the levels of PSD95, GluR1, NR2A, and NR2B were detected by Western blot. Meanwhile, cell experiments were performed to further verify the effect of HYD on tau phosphorylation related kinases (GSK-3β, CDK-5, and PP2A), which further to clarify the mechanism of HYD intervention on the neurotoxic interaction between Aβ and tau.

RESULTS

HYD improved the learning and memory ability of APP/PS1/tau mice. HYD decreased the levels of Aβ1-40 and Aβ1-42 and inhibited tau hyperphosphorylation, which reduced Aβ deposition and NFTs forming. In addition, HYD inhibited the activity of kinases GSK-3β and CDK-5, and enhancing the activity of kinase PP2A. Moreover, HYD inhibited the overexpression of NR2A and NR2B, and increased the expression of GluR1 and postsynaptic density protein-95 (PSD95).

CONCLUSIONS

HYD can improve the cognitive deficits by interfering with the neurotoxic interaction between Aβ and tau. In addition, HYD can inhibit the overactivation of NMDARs and increase the levels of GluR1 and PSD95, which may play a role in alleviating neuronal excitotoxicity and improving synaptic function.

Differences in pharmacologic and demographic factors in male and female patients with vascular dementia, Alzheimer's disease, and mixed vascular dementia

Background

Increasing evidence suggests that demographic and pharmacologic factors may play a significant role in the epidemiology of dementia. Sex differences in prevalence also depend on dementia subtypes, such as Alzheimer's dementia (AD), vascular dementia (VaD), and mixed vascular-Alzheimer's dementia (MVAD). Therefore, studies are needed to investigate sex-specific differences, and identify potential therapeutic targets for both sexes.

Methods

Data was collected from the Prisma Health-Upstate Alzheimer's registry from 2016 to 2021 for 6,039 VaD patients, 9,290 AD patients, and 412 MVAD patients. A logistic regression was used to determine demographic and pharmacological factors associated with gender differences in patients with VaD, AD, and MVAD.

Results

In patients with VaD, African Americans (OR = 1.454, 95% CI, 1.257-1.682, p < 0.001) with increasing age (OR = 1.023, 95% CI, 1.017-1.029, p < 0.001), treated with aripiprazole (OR = 4.395, 95% CI, 2.880-6.707, p < 0.001), were associated with females, whereas patients treated with galantamine (OR = 0.228, 95% CI, 0.116-0.449, p < 0.001), memantine (OR = 0.662, 95% CI, 0.590-0.744, p < 0.001), with a history of tobacco (OR = 0.312, 95% CI, 0.278-0.349, p < 0.001), and ETOH (OR = 0.520, 95% CI, 0.452-0.598, p < 0.001) were associated with males. Among AD patients, African Americans (OR = 1.747, 95% CI, 1.486-2.053, p < 0.001), and Hispanics (OR = 3.668, 95% CI, 1.198-11.231, P = 0.023) treated with buspirone (OR = 1.541, 95% CI, 1.265-1.878, p < 0.001), and citalopram (OR = 1.790, 95% CI, 1.527-2.099, p < 0.001), were associated with females, whereas patients treated with memantine (OR = 0.882, 95% CI, 0.799-0.974, p = 0.013), and with a history of tobacco (OR = 0.247, 95% CI, 0.224-0.273, p < 0.001), and ETOH (OR = 0.627, 95% CI, 0.547-0.718, p < 0.001) were associated with male AD patients. In patients with MVAD, rivastigmine (OR = 3.293, 95% CI, 1.131-9.585, p = 0.029), memantine (OR = 2.816, 95% CI, 1.534-5.168, p < 0.001), and risperidone (OR = 10.515, 95% CI, 3.409-32.437, p < 0.001), were associated with females while patients with an increased length of stay (OR = 0.910, 95% CI, 0.828-1.000, p = 0.049), with a history of tobacco (OR = 0.148, 95% CI, 0.086-0.254, p < 0.001) and ETOH use (OR = 0.229, 95% CI, 0.110-0.477, p < 0.001) were more likely to be associated with males.

Conclusions

Our study revealed gender differences and similarities in the demographic and pharmacological factors of VaD, AD, and MVAD. Prospective studies are needed to determine the role of demographic and pharmacological factors in reducing sex-based disparities among VaD, AD, and MVAD patients.

Pharmacological Modulation of Glutamatergic and Neuroinflammatory Pathways in a Lafora Disease Mouse Model

Lafora disease (LD) is a fatal rare neurodegenerative disorder that affects young adolescents and has no treatment yet. The hallmark of LD is the presence of polyglucosan inclusions (PGs), called Lafora bodies (LBs), in the brain and peripheral tissues. LD is caused by mutations in either EPM2A or EPM2B genes, which, respectively, encode laforin, a glucan phosphatase, and malin, an E3-ubiquitin ligase, with identical clinical features. LD knockout mouse models (Epm2a - / - and Epm2b - / -) recapitulate PG body accumulation, as in the human pathology, and display alterations in glutamatergic transmission and neuroinflammatory pathways in the brain. In this work, we show the results of four pre-clinical trials based on the modulation of glutamatergic transmission (riluzole and memantine) and anti-neuroinflammatory interventions (resveratrol and minocycline) as therapeutical strategies in an Epm2b - / - mouse model. Drugs were administered in mice from 3 to 5 months of age, corresponding to early stage of the disease, and we evaluated the beneficial effect of the drugs by in vivo behavioral phenotyping and ex vivo histopathological brain analyses. The behavioral assessment was based on a battery of anxiety, cognitive, and neurodegenerative tests and the histopathological analyses included a panel of markers regarding PG accumulation, astrogliosis, and microgliosis. Overall, the outcome of ameliorating the excessive glutamatergic neurotransmission present in Epm2b - / - mice by memantine displayed therapeutic effectiveness at the behavioral levels. Modulation of neuroinflammation by resveratrol and minocycline also showed beneficial effects at the behavioral level. Therefore, our study suggests that both therapeutical strategies could be beneficial for the treatment of LD patients. A mouse model of Lafora disease (Epm2b-/-) was used to check the putative beneficial effect of different drugs aimed to ameliorate the alterations in glutamatergic transmission and/or neuroinflammation present in the model. Drugs in blue gave a more positive outcome than the rest.

(R,S)-ketamine and (2R,6R)-hydroxynorketamine differentially affect memory as a function of dosing frequency

A single subanesthetic infusion of ketamine can rapidly alleviate symptoms of treatment-resistant major depression. Since repeated administration is required to sustain symptom remission, it is important to characterize the potential untoward effects of prolonged ketamine exposure. While studies suggest that ketamine can alter cognitive function, it is unclear to what extent these effects are modulated by the frequency or chronicity of treatment. To test this, male and female adolescent (postnatal day [PD] 35) and adult (PD 60) BALB/c mice were treated for four consecutive weeks, either daily or thrice-weekly, with (R,S)-ketamine (30 mg/kg, intraperitoneal) or its biologically active metabolite, (2R,6R)-hydroxynorketamine (HNK; 30 mg/kg, intraperitoneal). Following drug cessation, memory performance was assessed in three operationally distinct tasks: (1) novel object recognition to assess explicit memory, (2) Y-maze to assess working memory, and (3) passive avoidance to assess implicit memory. While drug exposure did not influence working memory performance, thrice-weekly ketamine and daily (2R,6R)-HNK led to explicit memory impairment in novel object recognition independent of sex or age of exposure. Daily (2R,6R)-HNK impaired implicit memory in the passive-avoidance task whereas thrice-weekly (2R,6R)-HNK tended to improve it. These differential effects on explicit and implicit memory possibly reflect the unique mechanisms by which ketamine and (2R,6R)-HNK alter the functional integrity of neural circuits that subserve these distinct cognitive domains, a topic of clinical and mechanistic relevance to their antidepressant actions. Our findings also provide additional support for the importance of dosing frequency in establishing the cognitive effects of repeated ketamine exposure.

An Insight in Pathophysiological Mechanism of Alzheimer's Disease and its Management Using Plant Natural Products

Alzheimer's disease (AD) is an age-associated nervous system disorder and a leading cause of dementia worldwide. Clinically, it is described by cognitive impairment and pathophysiologically by deposition of amyloid plaques and neurofibrillary tangles in the brain and neurodegeneration. This article reviews the pathophysiology, course of neuronal degeneration, and the various possible hypothesis of AD progression. These hypotheses include amyloid cascade, tau hyperphosphorylation, cholinergic disruption, metal dysregulation, vascular dysfunction, oxidative stress, and neuroinflammation. There is an exponential increase in the occurrence of AD in the recent few years that indicate an urgent need to develop some effective treatment. Currently, only 2 classes of drugs are available for AD treatment, namely acetylcholinesterase inhibitor and NMDA receptor antagonist. Since AD is a complex neurological disorder and these drugs use a single target approach, alternatives are needed due to limited effectiveness and unpleasant side-effects of these drugs. Currently, plants have been used for drug development research especially because of their multiple sites of action and fewer side effects. Uses of some herbs and phytoconstituents for the management of neuronal disorders like AD have been documented in this article. Phytochemical screening of these plants shows the presence of many beneficial constituents like flavonoids, triterpenes, alkaloids, sterols, polyphenols, and tannins. These compounds show a wide array of pharmacological activities, such as anti-amyloidogenic, anticholinesterase, and antioxidants. This article summarizes the present understanding of AD progression and gathers biochemical evidence from various works on natural products that can be useful in the management of this disease.

The Role of Neurovascular System in Neurodegenerative Diseases

The neurovascular system (NVS), which consisted of neurons, glia, and vascular cells, is a functional and structural unit of the brain. The NVS regulates blood-brain barrier (BBB) permeability and cerebral blood flow (CBF), thereby maintaining the brain's microenvironment for normal functioning, neuronal survival, and information processing. Recent studies have highlighted the role of vascular dysfunction in several neurodegenerative diseases. This is not unexpected since both nervous and vascular systems are functionally interdependent and show close anatomical apposition, as well as similar molecular pathways. However, despite extensive research, the precise mechanism by which neurovascular dysfunction contributes to neurodegeneration remains incomplete. Therefore, understanding the mechanisms of neurovascular dysfunction in disease conditions may allow us to develop potent and effective therapies for prevention and treatment of neurodegenerative diseases. This review article summarizes the current research in the context of neurovascular signaling associated with neurodegenerative diseases, such as Alzheimer's disease (AD), Parkinson's disease (PD), amyotrophic lateral sclerosis (ALS), and Huntington's disease (HD). We also discuss the potential implication of neurovascular factor as a novel therapeutic target and prognostic marker in patients with neurodegenerative conditions. Graphical Abstract.

Therapeutic Approaches to Alzheimer's Type of Dementia: A Focus on FGF21 Mediated Neuroprotection

Neurodegenerative disorders are the most devastating disorder of the nervous system. The pathological basis of neurodegeneration is linked with dysfunctional protein trafficking, mitochondrial stress, environmental factors and aging. With the identification of insulin and insulin receptors in some parts of the brain, it has become evident that certain metabolic conditions associated with insulin dysfunction like Type 2 diabetes mellitus (T2DM), dyslipidemia, obesity etc., are also known to contribute to neurodegeneration mainly Alzheimer's Disease (AD). Recently, a member of the fibroblast growth factor (FGF) superfamily, FGF21 has proved tremendous efficacy in diseases like diabetes mellitus, obesity and insulin resistance (IR). Increased levels of FGF21 have been reported to exert multiple beneficial effects in metabolic syndrome. FGF21 receptors are present in certain areas of the brain involved in learning and memory. However, despite extensive research, its function as a neuroprotectant in AD remains elusive. FGF21 is a circulating endocrine hormone which is mainly secreted by the liver primarily in fasting conditions. FGF21 exerts its effects after binding to FGFR1 and co-receptor, β-klotho (KLB). It is involved in regulating energy via glucose and lipid metabolism. It is believed that aberrant FGF21 signalling might account for various anomalies like neurodegeneration, cancer, metabolic dysfunction etc. Hence, this review will majorly focus on FGF21 role as a neuroprotectant and potential metabolic regulator. Moreover, we will also review its potential as an emerging candidate for combating metabolic stress induced neurodegenerative abnormalities.

Alzheimer's disease: Neurotransmitters of the sleep-wake cycle

With aging, our sleeping pattern alters. Elderly often wake unrested because their sleep time and sleep efficacy is reduced. In Alzheimer's disease (AD) patients, these alterations are even more pronounced and may further aggravate cognitive decline. Therefore, sleep disturbances greatly impact self-care ability, caregiver exhaustion and institutionalization rate. Reestablishing an effective sleep-wake cycle in these patients still remains an unresolved challenge, partly because sleep physiology is quite complex and multiple neurotransmitter systems contribute to a single process. Gaining a better understanding of sleep physiology will be crucial for further research. Conjointly, animal models, along with a multidisciplinary approach, will be of great value to establish a common ground between AD and sleep disturbances and work towards a potential therapeutic application.

Prospective of managing impaired brain insulin signalling in late onset Alzheimers disease with excisting diabetic drugs

Late onset Alzheimer's disease (AD) is the most common cause of dementia among elderly. The exact cause of the disease is until now unknown and there is no complete cure for the disease. Growing evidence suggest that AD is a metabolic disorder associated with impairment in brain insulin signalling. These findings enriched the scope for the repurposing of diabetic drugs in AD management. Even though many of these drugs are moving in a positive direction in the ongoing clinical studies, the extent of the success has seen to influence by several properties of these drugs since they were originally designed to manage the peripheral insulin resistance. In depth understandings of these properties is hence highly significant to optimise the use of diabetic drugs in the clinical management of AD; which is the primary aim of the present review article.

Current advances of pharmacological properties of 7-chloro-4-(phenylselanyl) quinoline: Prevention of cognitive deficit and anxiety in Alzheimer's disease model

This study investigated the effect of 7-chloro-4-(phenylselanyl) quinoline (4-PSQ) at a dose of 1 mg/kg in memory impairment and anxiety in an Alzheimer's disease (AD) model induced by amyloid β-peptide (Aβ) (fragment 25-35) in mice. The involvement of acetylcholinesterase (AChE) activity and lipid peroxidation in hippocampus and cerebral cortex was evaluated. Male Swiss mice were pretreated with 4-PSQ (1 mg/kg, intragastrically (i.g.), daily) for fourteen days. Thirty minutes after the first treatment with 4-PSQ, the animals received a single injection of Aβ (3 nmol/3 μl/per site, intracerebroventricular (i.c.v.)). Mice were submitted to the behavioral tasks (open-field, elevated plus maze, Barnes maze, object recognition and location, and step-down inhibitory avoidance tests) from the fifth day onwards. On the fifteenth day, blood was removed for analysis of biochemical markers (glucose, triglycerides, urea, aspartate (AST) and alanine (ALT) aminotrasferases), and cerebral cortex and hippocampus for determination of AChE activity and thiobarbituric acid reactive species (TBARS) levels. Aβ caused memory impairment, anxiogenic behavior, increased AChE activity in the cerebral structures and TBARS levels in the cerebral cortex. 4-PSQ was effective to protect against behavioral changes, AChE activity and TBARS levels. In conclusion, 4-PSQ protected against learning and memory impairment and anxiety in a mouse model of AD induced by Aβ, and anticholinesterase and antioxidant actions are involved in the pharmacological effect of the compound.

Antioxidant and Neuroprotective Effects of N-((3,4-Dihydro-2H-benzo[h]chromen-2-yl)methyl)-4-methoxyaniline in Primary Cultured Rat Cortical Cells: Involvement of ERK-CREB Signaling

Excitotoxicity and oxidative stress play vital roles in the development of neurodegenerative disorders including Alzheimer's disease (AD). In the present study, we investigated the effect of N-((3,4-dihydro-2H-benzo[h]chromen-2-yl)methyl)-4-methoxyaniline (BL-M) on excitotoxic neuronal cell damage in primary cultured rat cortical cells, and compared to that of memantine, a non-competitive N-methyl-d-aspartate (NMDA) receptor antagonist clinically used to treat AD. We found that BL-M inhibited glutamate- or N-methyl-d-aspartate (NMDA)-induced excitotoxic cell damage. The IC50 value of BL-M against NMDA toxicity was comparable to that of memantine. BL-M potently inhibited intracellular reactive oxygen species generated by glutamate or NMDA. Additionally, it inhibited the formation of 1,1-diphenyl-2-picryl-hydrazyl radicals in vitro and lipid peroxidation in rat brain homogenates. In contrast, memantine showed minimal or negligible antioxidant activity. Western blotting and immunocytochemical analyses showed that BL-M, not memantine, increased the ERK1/2 phosphorylation and subsequent phosphorylation of cAMP response element-binding protein (CREB). The inhibition of NMDA toxicity by BL-M was dramatically reversed by U0126, a well-known MEK inhibitor, suggesting that ERK1/2-mediated CREB phosphorylation is required for the neuroprotective action. Collectively, in this study, we demonstrated the neuroprotective effect of a newly synthesized chromene derivative BL-M and its underlying action mechanism(s). In contrast to memantine, BL-M exhibited marked antioxidant activity. Furthermore, it enhanced the ERK-mediated phosphorylation of CREB, which plays a crucial neuroprotective role. Our findings suggest that BL-M may be beneficial for AD and other neurodegenerative disorders associated with excitotoxicity as well as oxidative stress.

Neurosteroids and oxysterols as potential therapeutic agents for glaucoma and Alzheimer's disease

Glaucoma is one of the most frequent causes of visual impairment worldwide and involves selective damage to retinal ganglion cells (RGCs) resulting in degeneration of neural pathways connecting retina to visual cortex. It is of interest that similarities in pathological changes have been described in Alzheimer's disease (AD), the most common cause of progressive memory loss and dementia in older people. Accumulation of amyloid-beta (Abeta) and hyperphosphorylated tau is thought to contribute to apoptotic neuronal death in Alzheimer's disease, and similar changes have been linked to apoptotic RGC death in glaucoma. Both glaucoma and Alzheimer's disease also suffer from a lack of effective treatments prompting a search for novel therapeutic interventions. Neurosteroids (NSs) (including oxysterols) are endogenous molecules synthesized in the nervous system from cholesterol that can modulate glutamate and GABA receptors, the primary mediators of fast excitatory and inhibitory neurotransmission in the brain, respectively. Because changes in the glutamate and GABA neurotransmitter systems contribute to the pathogenesis of AD and glaucoma, NSs are possible therapeutic targets for these disorders. In this review, we present recent evidence supporting pathological links between Alzheimer's disease and glaucoma, and focus on the possible role of NSs in these diseases and how NSs might be developed for therapeutic purposes.

Primary hippocampal neuronal cell death induction after acute and repeated paraquat exposures mediated by AChE variants alteration and cholinergic and glutamatergic transmission disruption

Paraquat (PQ) is a widely used non-selective contact herbicide shown to produce memory and learning deficits after acute and repeated exposure similar to those induced in Alzheimer's disease (AD). However, the complete mechanisms through which it induces these effects are unknown. On the other hand, cholinergic and glutamatergic systems, mainly in the hippocampus, are involved on learning, memory and cell viability regulation. An alteration of hippocampal cholinergic or glutamatergic transmissions or neuronal cell loss may induce these effects. In this regard, it has been suggested that PQ may induce cell death and affect cholinergic and glutamatergic transmission, which alteration could produce neuronal loss. According to these data, we hypothesized that PQ could induce hippocampal neuronal loss through cholinergic and glutamatergic transmissions alteration. To prove this hypothesis, we evaluated in hippocampal primary cell culture, the PQ toxic effects after 24h and 14 consecutive days exposure on neuronal viability and the cholinergic and glutamatergic mechanisms related to it. This study shows that PQ impaired acetylcholine levels and induced AChE inhibition and increased CHT expression only after 14days exposure, which suggests that acetylcholine levels alteration could be mediated by these actions. PQ also disrupted glutamate levels through induction of glutaminase activity. In addition, PQ induced, after 24h and 14days exposure, cell death on hippocampal neurons that was partially mediated by AChE variants alteration and cholinergic and gultamatergic transmissions disruption. Our present results provide new view of the mechanisms contributing to PQ neurotoxicity and may explain cognitive dysfunctions observed after PQ exposure.

Mechanisms of Alzheimer's Disease Pathogenesis and Prevention: The Brain, Neural Pathology, N-methyl-D-aspartate Receptors, Tau Protein and Other Risk Factors

The characteristic features of Alzheimer’s disease (AD) are the appearance of extracellular amyloid-beta (Aβ) plaques and neurofibrillary tangles in the intracellular environment, neuronal death and the loss of synapses, all of which contribute to cognitive decline in a progressive manner. A number of hypotheses have been advanced to explain AD. Abnormal tau phosphorylation may contribute to the formation of abnormal neurofibrillary structures. Many different structures are susceptible to AD, including the reticular formation, the nuclei in the brain stem (e.g., raphe nucleus), thalamus, hypothalamus, locus ceruleus, amygdala, substantia nigra, striatum, and claustrum. Excitotoxicity results from continuous, low-level activation of N-methyl-D-aspartate (NMDA) receptors. Premature synaptotoxicity, changes in neurotransmitter expression, neurophils loss, accumulation of amyloid β-protein deposits (amyloid/senile plaques), and neuronal loss and brain atrophy are all associated with stages of AD progression. Several recent studies have examined the relationship between Aβ and NMDA receptors. Aβ-induced spine loss is associated with a decrease in glutamate receptors and is dependent upon the calcium-dependent phosphatase calcineurin, which has also been linked to long-term depression.

Memantine in the Treatment of Executive Function Deficits in Adults With ADHD

OBJECTIVE

To evaluate the efficacy and safety of memantine hydrochloride as an adjunct to stimulant pharmacotherapy for treating executive function deficits (EFDs) in adults with ADHD.

METHOD

This was a 12-week, double-blind, placebo-controlled, randomized clinical trial of memantine added to open-label treatment with stimulant medication. Because of the small sample size, we considered a standardized mean difference (equivalent to effect size) of ≥0.5 and odds ratios ≥2 as indicators of trend improvements.

RESULTS

Twelve participants received memantine and 14 received a placebo. Trend improvements favoring memantine were observed on Behavior Rating Inventory of Executive Functions-Adult Inhibition and Self-Monitor subscales when compared with Placebo. No significant changes were noted on the Cambridge Neuropsychological Test Automated Battery.

CONCLUSION

Among adults with ADHD and EFDs, adjunct treatment with memantine to osmotic release oral system-methylphenidate (OROS-MPH) was associated with improvements in selective areas of executive functioning, supporting the need for further research.

Targeting Neuroinflammation to Treat Alzheimer's Disease

Over the past few decades, research on Alzheimer's disease (AD) has focused on pathomechanisms linked to two of the major pathological hallmarks of extracellular deposition of beta-amyloid peptides and intra-neuronal formation of neurofibrils. Recently, a third disease component, the neuroinflammatory reaction mediated by cerebral innate immune cells, has entered the spotlight, prompted by findings from genetic, pre-clinical, and clinical studies. Various proteins that arise during neurodegeneration, including beta-amyloid, tau, heat shock proteins, and chromogranin, among others, act as danger-associated molecular patterns, that-upon engagement of pattern recognition receptors-induce inflammatory signaling pathways and ultimately lead to the production and release of immune mediators. These may have beneficial effects but ultimately compromise neuronal function and cause cell death. The current review, assembled by participants of the Chiclana Summer School on Neuroinflammation 2016, provides an overview of our current understanding of AD-related immune processes. We describe the principal cellular and molecular players in inflammation as they pertain to AD, examine modifying factors, and discuss potential future therapeutic targets.

Alzheimer's disease: Targeting the Cholinergic System

Acetylcholine (ACh) has a crucial role in the peripheral and central nervous systems. The enzyme choline acetyltransferase (ChAT) is responsible for synthesizing ACh from acetyl-CoA and choline in the cytoplasm and the vesicular acetylcholine transporter (VAChT) uptakes the neurotransmitter into synaptic vesicles. Following depolarization, ACh undergoes exocytosis reaching the synaptic cleft, where it can bind its receptors, including muscarinic and nicotinic receptors. ACh present at the synaptic cleft is promptly hydrolyzed by the enzyme acetylcholinesterase (AChE), forming acetate and choline, which is recycled into the presynaptic nerve terminal by the high-affinity choline transporter (CHT1). Cholinergic neurons located in the basal forebrain, including the neurons that form the nucleus basalis of Meynert, are severely lost in Alzheimer’s disease (AD). AD is the most ordinary cause of dementia affecting 25 million people worldwide. The hallmarks of the disease are the accumulation of neurofibrillary tangles and amyloid plaques. However, there is no real correlation between levels of cortical plaques and AD-related cognitive impairment. Nevertheless, synaptic loss is the principal correlate of disease progression and loss of cholinergic neurons contributes to memory and attention deficits. Thus, drugs that act on the cholinergic system represent a promising option to treat AD patients.

Intrahippocampal Administration of Ibotenic Acid Induced Cholinergic Dysfunction via NR2A/NR2B Expression: Implications of Resveratrol against Alzheimer Disease Pathophysiology

Although several drugs revealed moderate amelioration of symptoms, none of them have sufficient potency to prevent or reverse the progression toward Alzheimer's disease (AD) pathology. Resveratrol (RSV), a polyphenolic compound has shown an outstanding therapeutic effect on a broad spectrum of diseases like age-associated neurodegeneration, inflammation etc. The present study was thus conducted to assess the therapeutic efficacy of RSV in ameliorating the deleterious effects of Ibotenic acid (IBO) in male Wistar rats. Stereotactic intrahippocampal administration of IBO (5 μg/μl) lesioned rats impairs cholinergic transmission, learning and memory performance that is rather related to AD and thus chosen as a suitable model to understand the drug efficacy in preventing AD pathophysiology. Since IBO is an agonist of glutamate, it is expected to exhibit an excitotoxic effect by altering glutamatergic receptors like NMDA receptor. The current study displayed significant alterations in the mRNA expression of NR2A and NR2B subunits of NMDA receptors, and further it is surprising to note that cholinergic receptors decreased in expression particularly α7-nAChR with increased m1AChR. RSV administration (20 mg/kg body weight, i.p.) significantly reduced these changes in IBO induced rats. Glutamatergic and cholinergic receptor alterations were associated with significant changes in the behavioral parameters of rats induced by IBO. While RSV improved spatial learning performance, attenuated immobility, and improvised open field activity in IBO induced rats. NR2B activation in the present study might mediate cell death through oxidative stress that form the basis of abnormal behavioral pattern in IBO induced rats. Interestingly, RSV that could efficiently encounter oxidative stress have significantly decreased stress markers viz., nitrite, PCO, and MDA levels by enhancing antioxidant status. Histopathological analysis displayed significant reduction in the hippocampal pyramidal layer thickness and live neurons in IBO induced rats, with slight pathological changes in the entorhinal cortex (EC) of rat brain, which was prevented on RSV administration. Our study thus concludes that RSV administration significantly ameliorated the deleterious effects in the IBO lesioned rat model for AD by alleviating cholinergic pathways, reducing oxidative stress and thereby improving spatial memory.

Nonsurgical therapy for hydrocephalus: a comprehensive and critical review

Pharmacological interventions have been tested experimentally and clinically to prevent hydrocephalus and avoid the need for shunting beginning in the 1950s. Clinical trials of varied quality have not demonstrated lasting and convincing protective effects through manipulation of cerebrospinal fluid production, diuresis, blood clot fibrinolysis, or manipulation of fibrosis in the subarachnoid compartment, although there remains some promise in the latter areas. Acetazolamide bolus seems to be useful for predicting shunt response in adults with hydrocephalus. Neuroprotection in the situation of established hydrocephalus has been tested experimentally beginning more recently. Therapies designed to modify blood flow or pulsation, reduce inflammation, reduce oxidative damage, or protect neurons are so far of limited success; more experimental work is needed in these areas. As has been recommended for preclinical studies in stroke and brain trauma, stringent conditions should be met for preclinical studies in hydrocephalus.

Purine nucleosides in neuroregeneration and neuroprotection

In the present review, we stress the importance of the purine nucleosides, adenosine and guanosine, in protecting the nervous system, both centrally and peripherally, via activation of their receptors and intracellular signalling mechanisms. A most novel part of the review focus on the mechanisms of neuronal regeneration that are targeted by nucleosides, including a recently identified action of adenosine on axonal growth and microtubule dynamics. Discussion on the role of the purine nucleosides transversally with the most established neurotrophic factors, e.g. brain derived neurotrophic factor (BDNF), glial derived neurotrophic factor (GDNF), is also focused considering the intimate relationship between some adenosine receptors, as is the case of the A2A receptors, and receptors for neurotrophins. This article is part of the Special Issue entitled 'Purines in Neurodegeneration and Neuroregeneration'.

Changing the face of kynurenines and neurotoxicity: therapeutic considerations

Kynurenines are the products of tryptophan metabolism. Among them, kynurenine and kynurenic acid are generally thought to have neuroprotective properties, while 3-hydroxykynurenine, 3-hydroxyanthranilic acid and quinolinic acid are considered neurotoxic. They participate in immunoregulation and inflammation and possess pro- or anti-excitotoxic properties, and their involvement in oxidative stress has also been suggested. Consequently, it is not surprising that kynurenines have been closely related to neurodegenerative diseases, such as Alzheimer's disease, Parkinson's disease, Huntington's disease, amyotrophic lateral sclerosis and multiple sclerosis. More information about the less-known metabolites, picolinic and cinnabarinic acid, evaluation of new receptorial targets, such as aryl-hydrocarbon receptors, and intensive research on the field of the immunomodulatory function of kynurenines delineated the high importance of this pathway in general homeostasis. Emerging knowledge about the kynurenine pathway provides new target points for the development of therapeutical solutions against neurodegenerative diseases.

Calcium dysregulation via L-type voltage-dependent calcium channels and ryanodine receptors underlies memory deficits and synaptic dysfunction during chronic neuroinflammation

Background

Chronic neuroinflammation and calcium (Ca⁺²) dysregulation are both components of Alzheimer’s disease. Prolonged neuroinflammation produces elevation of pro-inflammatory cytokines and reactive oxygen species which can alter neuronal Ca⁺² homeostasis via L-type voltage-dependent Ca⁺² channels (L-VDCCs) and ryanodine receptors (RyRs). Chronic neuroinflammation also leads to deficits in spatial memory, which may be related to Ca⁺² dysregulation.

Methods

The studies herein use an in vivo model of chronic neuroinflammation: rats were infused intraventricularly with a continuous small dose of lipopolysaccharide (LPS) or artificial cerebrospinal fluid (aCSF) for 28 days. The rats were treated with the L-VDCC antagonist nimodipine or the RyR antagonist dantrolene.

Results

LPS-infused rats had significant memory deficits in the Morris water maze, and this deficit was ameliorated by treatment with nimodipine. Synaptosomes from LPS-infused rats had increased Ca⁺² uptake, which was reduced by a blockade of L-VDCCs either in vivo or ex vivo.

Conclusions

Taken together, these data indicate that Ca⁺² dysregulation during chronic neuroinflammation is partially dependent on increases in L-VDCC function. However, blockade of the RyRs also slightly improved spatial memory of the LPS-infused rats, demonstrating that other Ca⁺² channels are dysregulated during chronic neuroinflammation. Ca⁺²-dependent immediate early gene expression was reduced in LPS-infused rats treated with dantrolene or nimodipine, indicating normalized synaptic function that may underlie improvements in spatial memory. Pro-inflammatory markers are also reduced in LPS-infused rats treated with either drug. Overall, these data suggest that Ca⁺² dysregulation via L-VDCCs and RyRs play a crucial role in memory deficits resulting from chronic neuroinflammation.

NMDARs in neurological diseases: a potential therapeutic target

N-methyl-D-aspartate ionotropic glutamate receptor (NMDARs) is a ligand-gated ion channel that plays a critical role in excitatory neurotransmission, brain development, synaptic plasticity associated with memory formation, central sensitization during persistent pain, excitotoxicity and neurodegenerative diseases in the central nervous system (CNS). Within iGluRs, NMDA receptors have been the most actively investigated for their role in neurological diseases, especially neurodegenerative pathologies such as Alzheimer's and Parkinson's diseases. It has been demonstrated that excessive activation of NMDA receptors (NMDARs) plays a key role in mediating some aspects of synaptic dysfunction in several CNS disorders, so extensive research has been directed on the discovery of compounds that are able to reduce NMDARs activity. This review discusses the role of NMDARs on neurological pathologies and the possible therapeutic use of agents that target this receptor. Additionally, we delve into the role of NMDARs in Alzheimer's and Parkinson's diseases and the receptor antagonists that have been tested on in vivo models of these pathologies. Finally, we put into consideration the importance of antioxidants to counteract oxidative capacity of the signaling cascade in which NMDARs are involved.

Riluzole partially rescues age-associated, but not LPS-induced, loss of glutamate transporters and spatial memory

Impaired memory may result from synaptic glutamatergic dysregulation related to chronic neuroinflammation. GLT1 is the primary excitatory amino acid transporter responsible for regulating extracellular glutamate levels in the hippocampus. We tested the hypothesis that if impaired spatial memory results from increased extracellular glutamate due to age or experimentally induced chronic neuroinflammation in the hippocampus, then pharmacological augmentation of the glutamate transporter GLT1 will attenuate deficits in a hippocampal-dependent spatial memory task. The profile of inflammation-related genes and proteins associated with normal aging, or chronic neuroinflammation experimentally-induced via a four-week LPS infusion into the IV(th) ventricle, were correlated with performance in the Morris water maze following treatment with Riluzole, a drug that can enhance glutamate clearance by increasing GLT1 expression. Age-associated inflammation was qualitatively different from LPS-induced neuro-inflammation in young rats. LPS produced a pro-inflammatory phenotype characterized by increased IL-1ß expression in the hippocampus, whereas aging was not associated with a strong central pro-inflammatory response but with a mixed peripheral immune phenotype. Riluzole attenuated the spatial memory impairment, the elevation of serum cytokines and the decrease in GLT1 gene expression in Aged rats, but had no effect on young rats infused with LPS. Our findings highlight the therapeutic potential of reducing glutamatergic function upon memory impairment in neurodegenerative diseases associated with aging.

Memantine and cholinesterase inhibitors: complementary mechanisms in the treatment of Alzheimer's disease

This review describes the preclinical mechanisms that may underlie the increased therapeutic benefit of combination therapy-with the N-methyl-D-aspartate receptor antagonist, memantine, and an acetylcholinesterase inhibitor (AChEI)-for the treatment of Alzheimer's disease (AD). Memantine, and the AChEIs target two different aspects of AD pathology. Both drug types have shown significant efficacy as monotherapies for the treatment of AD. Furthermore, clinical observations indicate that their complementary mechanisms offer superior benefit as combination therapy. Based on the available literature, the authors have considered the preclinical mechanisms that could underlie such a combined approach. Memantine addresses dysfunction in glutamatergic transmission, while the AChEIs serve to increase pathologically lowered levels of the neurotransmitter acetylcholine. In addition, preclinical studies have shown that memantine has neuroprotective effects, acting to prevent glutamatergic over-stimulation and the resulting neurotoxicity. Interrelations between the glutamatergic and cholinergic pathways in regions of the brain that control learning and memory mean that combination treatment has the potential for a complex influence on disease pathology. Moreover, studies in animal models have shown that the combined use of memantine and the AChEIs can produce greater improvements in measures of memory than either treatment alone. As an effective approach in the clinical setting, combination therapy with memantine and an AChEI has been a welcome advance for the treatment of patients with AD. Preclinical data have shown how these drugs act via two different, but interconnected, pathological pathways, and that their complementary activity may produce greater effects than either drug individually.

Comparison of behavioral effects of the NMDA receptor channel blockers memantine and ketamine in rats

Memantine and ketamine block N-methyl-D-aspartate (NMDA) receptors with similar affinity and kinetics, yet their behavioral consequences differ: e.g., memantine is used to alleviate symptoms of Alzheimer's disease, whereas ketamine reproduces symptoms of schizophrenia. The two drugs exhibit different pharmacokinetics, which may play a principal role in their differential behavioral effects. To gain insight into the drugs' behavioral consequences, we treated adult male rats acutely with varying doses (0-40 mg/kg i.p.) of memantine or ketamine and assessed exploratory behavior and spatial working memory. To examine the importance of pharmacokinetics, we assessed behavior either 15 or 45 min after drug administration. Both drugs decreased ambulation, fine movements, and rearing at the beginning of the exploratory activity test; however, at the end of the test, high doses of only memantine increased ambulation and fine movements. High doses of both drugs disrupted spontaneous alternation, a measure of working memory, but high doses of only memantine elicited perseverative behavior. Surprisingly, ketamine's effects were influenced by the delay between drug administration and testing no more frequently than were memantine's. Our findings show that, regardless of test delay, memantine and ketamine evoke similar behavioral effects at lower doses, consistent with NMDA receptors being both drugs' principal site of action, but can have divergent effects at higher doses. Our results suggest that the divergence of memantine's and ketamine's behavioral consequences is likely to result from differences in mechanisms of NMDA receptor antagonism or actions at other targets.

A pilot open label prospective study of memantine monotherapy in adults with ADHD

OBJECTIVES

Available pharmacotherapies treat some adults with ADHD inadequately. A small literature suggests that glutamate modulation could have effects on ADHD.

METHODS

Memantine, an N-methyl-d-aspartate (NMDA) receptor antagonist, was titrated to a maximum dose of 10 mg BID in 34 adult subjects aged 18-55 who met DSM-IV criteria for ADHD or ADHD NOS on structured interview. Twenty-eight subjects completed 12 weeks exposure. The Adult ADHD Investigator Symptom Report (AISRS), Clinical Global Impression (CGI), a neuropsychological battery sensitive to domains of executive function, and the CANTAB cognitive battery were administered. Paired t-tests compared treated and baseline scores.

RESULTS

At week 12, AISRS data showed reduction in total symptoms (-17.5, P < 0.001), inattentive symptoms (-10.6, P < 0.001), and hyperactive symptoms (-6.9, P < 0.01). A total of 44% of subjects had CGI ratings of much or very much improved. Cognitive performance improved in measures of attention, working memory, and other selected executive domains by weeks 6 and 12 (each P < 0.05); simple reaction time declined by week 12 (P < 0.05). There were no severe adverse events, but mild adverse events were common and six subjects discontinued due to adverse effects.

CONCLUSIONS

Memantine was largely well-tolerated and associated with improvement in ADHD symptoms and neuropsychological performance. Randomized studies are indicated to confirm whether memantine is a novel therapy for ADHD across the lifespan.

The potent effects of ginseng root extract and memantine on cognitive dysfunction in male albino rats

The study determined the maximum intraperitoneal (ip) scopolamine dose inducing memory impairment in rats (2 mg/kg) compared to 0.5 or 1 mg/kg dose. The effect reflected by significant increase from normal in the latency time required for rats to find the hidden platform in water maze task and acetylcholinesterase (AChE) activities in cortex, hippocampus and striatum. The dose-related histopathological effect via the hemorrhage, vacuolation and gliosis in cortex and hippocampus is assessed. Then the study investigated the potency of Panax ginseng root extract on scopolamine cognitive dysfunction rat model compared to memantine hydrochloride as reference Food and Drug Administration approved. Ginseng extract was administered at dose 100 or 200 mg/kg/day and memantine at 20 mg/kg/day orally for 2 weeks. All treatments showed improvement in the water maze task, however, ginseng (200 mg/kg) group acquired the advantage without statistical difference control. Scopolamine (2 mg/kg ip) group showed significant increase in AChE reactivity and glutamate level and reduced monoamines (norepinephrine, dopamine and serotonin) and γ-aminobutyric acid contents in cortex, hippocampus and striatum. Ginseng extract in a dose-dependent manner appears effective as memantine and can improve memory impairment through the retrieved homeostasis via neurotransmitter levels and AChE activities in rat brain areas with partial effect on the histological feature of the brain tissue.

Alzheimer's disease, β-amyloid, glutamate, NMDA receptors and memantine--searching for the connections

β-amyloid (Aβ) is widely accepted to be one of the major pathomechanisms underlying Alzheimer's disease (AD), although there is presently lively debate regarding the relative roles of particular species/forms of this peptide. Most recent evidence indicates that soluble oligomers rather than plaques are the major cause of synaptic dysfunction and ultimately neurodegeneration. Soluble oligomeric Aβ has been shown to interact with several proteins, for example glutamatergic receptors of the NMDA type and proteins responsible for maintaining glutamate homeostasis such as uptake and release. As NMDA receptors are critically involved in neuronal plasticity including learning and memory, we felt that it would be valuable to provide an up to date review of the evidence connecting Aβ to these receptors and related neuronal plasticity. Strong support for the clinical relevance of such interactions is provided by the NMDA receptor antagonist memantine. This substance is the only NMDA receptor antagonist used clinically in the treatment of AD and therefore offers an excellent tool to facilitate translational extrapolations from in vitro studies through in vivo animal experiments to its ultimate clinical utility.

Glutamate system, amyloid ß peptides and tau protein: functional interrelationships and relevance to Alzheimer disease pathology

Alzheimer disease is the most prevalent form of dementia globally and is characterized premortem by a gradual memory loss and deterioration of higher cognitive functions and postmortem by neuritic plaques containing amyloid ß peptide and neurofibrillary tangles containing phospho-tau protein. Glutamate is the most abundant neurotransmitter in the brain and is essential to memory formation through processes such as long-term potentiation and so might be pivotal to Alzheimer disease progression. This review discusses how the glutamatergic system is impaired in Alzheimer disease and how interactions of amyloid ß and glutamate influence synaptic function, tau phosphorylation and neurodegeneration. Interestingly, glutamate not only influences amyloid ß production, but also amyloid ß can alter the levels of glutamate at the synapse, indicating that small changes in the concentrations of both molecules could influence Alzheimer disease progression. Finally, we describe how the glutamate receptor antagonist, memantine, has been used in the treatment of individuals with Alzheimer disease and discuss its effectiveness.

On the promise of pharmacotherapies targeted at cognitive and neurodegenerative components of Down syndrome

Down syndrome (DS) is the phenotypic consequence of trisomy 21 and is the most common genetically defined cause of intellectual disability. The most complete, widely available, and well-studied animal model of DS is the Ts65Dn mouse. Recent preclinical successes in rescuing learning and memory deficits in Ts65Dn mice are legitimate causes for optimism that pharmacotherapies for cognitive deficits in DS might be within reach. This article provides a snapshot of potential pharmacotherapies for DS, with emphasis on our recent results showing that the N-methyl-D-aspartate receptor antagonist memantine can reverse learning and memory deficits in Ts65Dn mice. Because memantine has already been approved for the therapy of Alzheimer's dementia, we have been able to very rapidly translate these results into human research and are currently conducting a 16-week, randomized, double-blind, placebo-controlled evaluation of the efficacy, tolerability and safety of memantine hydrochloride on enhancing the cognitive abilities of young adults with DS. The design and current status of this clinical trial will be discussed, which will be followed by some speculation on the potential impact of this and future clinical trials in the field of DS.

Memantine: a treatment for Alzheimer’s disease with a new formulation

In nearly 20 years, aside from cholinesterase inhibitors, memantine is the only drug approved for the treatment of Alzheimer’s disease (AD). Memantine is an uncompetitive N-methyl-D-aspartate receptor antagonist that blocks pathological glutamate activity while permitting normal physiological function, thus preventing glutamate-induced excitotoxicity. Three Phase III pivotal trials demonstrated memantine’s efficacy in treating moderate-to-severe AD, which led to its initial approval by the EMA in 2002 and US FDA in 2003. The recommended target dose is 10 mg twice daily. The US FDA recently approved an extended-release (ER) formulation of memantine for once-daily 28-mg dosing. Memantine ER was evaluated in a 24-week placebo-controlled trial of patients with moderate-to-severe AD, which found significant benefits for cognition, global assessment, behavior and caregiver burden, but not function. The most common adverse events were headache, dizziness, diarrhea, hypertension, anxiety and influenza. Overall, memantine in all formulations has a favorable safety/tolerability profile and is safe to use with cholinesterase inhibitors. Memantine ER has yet to be evaluated against conventionally dosed immediate-release memantine.

Quantification of the Mg2+-induced potency shift of amantadine and memantine voltage-dependent block in human recombinant GluN1/GluN2A NMDARs

Clinically, amantadine and memantine are drugs whose therapeutic utility is linked to their ability to block N-methyl-D-aspartate receptors (NMDARs) in a voltage-dependent manner. Nevertheless many studies that have characterized the pharmacological actions of amantadine and memantine have done so in the absence of physiological levels of Mg(2+) ions. This study quantifies the extent to which Mg(2+) alters the potency of the block produced by both amantadine and memantine at human recombinant GluN1/GluN2A NMDARs. Human recombinant GluN1/GluN2A NMDARs were expressed in Xenopus laevis oocytes and two-electrode voltage-clamp recordings were made at -80, -60 and -40 mV to quantify amantadine and memantine block in the absence and presence of Mg(2+). Amantadine and memantine blocked human GluN1/GluN2A NMDARs in a voltage-dependent manner with IC(50) values (at -80 mV) of 49 ± 6 μM (n = 7) and 1.0 ± 0.3 μM (n = 7), respectively. In the presence of Mg(2+) (1mM) the equivalent IC(50) values were 165 ± 10 μM (n=6) and 6.6 ± 0.3 μM (n = 5). Similarly in the presence of amantadine or memantine the potency of Mg(2+) in blocking GluN1/GluN2A NMDARs was reduced. The decrease in the potencies of both amantadine and memantine in the presence of physiological concentrations of Mg(2+) indicates that other targets (e.g. α7-nicotinic acetylcholine receptors and 5-HT(3) receptors) in addition to NMDARs may well be sites of the therapeutic action of these channel blockers.

Alzheimer's disease: clinical trials and drug development

Alzheimer's disease is the most common cause of dementia in elderly people. Research into Alzheimer's disease therapy has been at least partly successful in terms of developing symptomatic treatments, but has also had several failures in terms of developing disease-modifying therapies. These successes and failures have led to debate about the potential deficiencies in our understanding of the pathogenesis of Alzheimer's disease and potential pitfalls in diagnosis, choice of therapeutic targets, development of drug candidates, and design of clinical trials. Many clinical and experimental studies are ongoing, but we need to acknowledge that a single cure for Alzheimer's disease is unlikely to be found and that the approach to drug development for this disorder needs to be reconsidered. Preclinical research is constantly providing us with new information on pieces of the complex Alzheimer's disease puzzle, and an analysis of this information might reveal patterns of pharmacological interactions instead of single potential drug targets. Several promising randomised controlled trials are ongoing, and the increased collaboration between pharmaceutical companies, basic researchers, and clinical researchers has the potential to bring us closer to developing an optimum pharmaceutical approach for the treatment of Alzheimer's disease.