Recent Advances in Medicinal Chemistry of Memantine Against Alzheimer's Disease.

Alzheimer's disease (AD) is a chronic progressive, age-related neurodegenerative brain disorder characterized by the irreversible decline of memory and other cognitive functions. It is one of the major health threat of the 21st century, which affects around 60% of the population over the age of 60 years. The problem of this disease is even more major because the existing pharmacotherapies only provide symptomatic relief without addressing the basic factors of the disease. It is characterized by the extracellular deposition of amyloid ß (Aß) to form senile plaques, and the intracellular hyperphosphorylation of tau to form neurofibrillary tangles (NFTs). Due to the complex pathophysiology of this disease, various hypotheses have been proposed, including the cholinergic, Aß, tau, oxidative stress, and the metal-ion hypothesis. Among these, the cholinergic and Aß hypotheses are the primary targets for addressing AD. Therefore, continuous advances have been made in developing potential cholinesterase inhibitors and N-methyl-D-aspartate (NMDA) receptor antagonists to delay disease progression and restore cholinergic neurotransmission. In this review article, we tried to comprehensively summarize the recent advancement in NMDA receptor antagonist (memantine) and their hybrid analogs as potential disease-modifying agents for the treatment of AD. Furthermore, we also depicted the design, rationale, and SAR analysis of the memantine-based hybrids used in the last decade for the treatment of AD.

Alzheimer Disease: Treatment of Cognitive and Functional Symptoms.

Alzheimer disease is a progressive, neurodegenerative disorder characterized by the accumulation of amyloid beta plaques and hyperphosphorylated tau proteins. Alzheimer disease affects cognitive function, leading to memory loss and impairment in activities of daily living. Approximately 6.9 million people in the United States 65 years and older live with Alzheimer disease, a number expected to double by 2060. Although there is no cure for Alzheimer disease, treatments are available to manage symptoms. Tools such as the Diagnostic and Statistical Manual of Mental Disorders, 5th ed., criteria aid in identifying major neurocognitive disorders. The evaluation involves a comprehensive medical history, cognitive examinations, and collateral information. Nonpharmacologic interventions focus on psychosocial approaches, with music, sensory stimulation, and validation therapies showing some evidence of reducing responsive behaviors. Pharmacologic management, such as acetylcholinesterase inhibitors (donepezil, galantamine, rivastigmine) and the N-methyl-d-aspartate receptor antagonist memantine, targets symptom relief and disease progression. Vitamin E does not improve cognition but may mitigate functional decline. Brexpiprazole has been approved in the United States for treating agitation associated with Alzheimer disease. Anti-amyloid monoclonal antibody treatments are approved for mild cognitive impairment and mild Alzheimer disease, but they are controversial and safety concerns exist. Ineffective therapies include ginkgo biloba, nonsteroidal anti-inflammatory drugs, omega-3 fatty acids, and statins.

Effect of long-term pharmacological treatments on Alzheimer disease: A systematic review and network meta-analysis.

BACKGROUND: To analyze and compare the pharmacological treatments for Alzheimer disease (AD), we will conduct a systematic review and network meta-analysis focusing on their efficacy and safety over a duration exceeding 1 year. METHODS: We searched the databases of PubMed, Scopus, EMBASE, Web of Science, the Cochrane Central Register of Controlled Trials, and CNKI until July 30, 2023, for randomized controlled trials (RCTs) evaluating pharmacological treatments for AD. RESULTS: Seventeen RCTs, comprising 7214 participants, investigated the efficacy of the following drugs: Donepezil, Rivastigmine, Galantamine, Memantine, Ginkgo biloba extract (EGb), Atorvastatin-calcium and Vitamin B in the treatment of AD. The network meta-analysis resulted indicated that placebo demonstrated greater effectiveness compared to Atorvastatin-calcium 80 mg (mean different [MD] = -6.93, confidence interval [CI] -11.57, -2.29) and Rivastigmine 12 mg (MD = -3.33, CI -6.56, -0.09). EGb120 mg exhibited a greater improvement in cognition compared to Atorvastatin-calcium 80 mg (MD = 7.77, CI 2.07, 13.46) and Rivastigmine 12 mg + EGb120 mg (MD = 9.92, CI 1.32, 17.22). EGb 120 mg emerged as the most efficient intervention for cognition, while placebo demonstrated the least harm over a period exceeding 1 year. CONCLUSIONS: In this network meta-analysis of studies of patients with AD and a follow-up period of at least 1 year, EGb 120 mg demonstrated cognitive benefits, while placebo posed the least harm for AD. More RCTs are required to address the uncertainty surrounding the efficacy of medication.

Impact of type 2 diabetes and its duration on incidence rates of dementia death and medication prescription in the Australian population during 2003-2016.

AIMS: To quantify rates of dementia treatment and death among Australians with type 2 diabetes relative to those without diabetes using linked national registries of Australia. METHODS: The study included 891,418 people with type 2 diabetes registered on the National Diabetes Services Scheme and a randomly sampled, population-based comparison group (n = 1,131,369). Outcomes included dementia death (all-cause dementia, Alzheimer's disease (AD) or vascular dementia), and first prescription of cholinesterase inhibitors or memantine. RESULTS: Excess dementia risk was observed in the diabetes group for the composite outcome of all-cause dementia death or dementia medication prescription but varied with age at diabetes diagnosis and its duration. At age 70, the rate of dementia death/medication prescription was ∼1.3 (95% CI 1.2, 1.3) and 1.1 (95% CI 1.1, 1.2) times higher in people with ten and five years of diabetes duration, respectively. Individual outcomes showed that diabetes was associated with a higher incidence of vascular dementia death, whereas an increased risk of AD death was only observed beyond âˆ¼10 years of diabetes duration. Further, the incidence of dementia medication prescription was lower among people with diabetes. CONCLUSIONS: A higher incidence of AD death in the setting of 10+ years of diabetes duration coupled with a lower incidence of AD treatment suggests an under-recognition of this dementia phenotype among people with type 2 diabetes.

Catatonia.

Catatonia is a neuropsychiatric disorder characterized by motor, affective and cognitive-behavioural signs, which lasts from hours to days. Intensive research over the past two decades has led to catatonia being recognized as an independent diagnosis in the International Classification of Diseases, 11th Revision (ICD-11) since 2022. Catatonia is found in 5-18% of inpatients on psychiatric units and 3.3% of inpatients on medical units. However, in an unknown number of patients, catatonia remains unrecognized and these patients are at risk of life-threatening complications. Hence, recognizing the symptoms of catatonia early is crucial to initiate appropriate treatment to achieve a favourable outcome. Benzodiazepines such as lorazepam and diazepam, electroconvulsive therapy, and N-methyl-D-aspartate antagonists such as amantadine and memantine, are the cornerstones of catatonia therapy. In addition, dopamine-modulating second-generation antipsychotics (for example, clozapine and aripiprazole) are effective in some patient populations. Early and appropriate treatment combined with new screening assessments has the potential to reduce the high morbidity and mortality associated with catatonia in psychiatric and non-psychiatric settings.

Acquired Risk Factors that Influence Risk for Dementia and Possibly Alzheimer Disease.

Various medicinal agents aimed at improving Alzheimer disease (AD) include cholinesterase inhibitors, memantine, aducanumab, and antioxidants. These medications are typically prescribed once AD is diagnosed in the clinical setting in order to slow progression. Though initiating treatment after being diagnosed with AD is important, significance should be placed on recognizing known acquired risk factors in order to potentially decrease the likelihood of developing dementia and perhaps specifically AD. This article summarizes the acquired factors that influence risk for dementia.

Impact of modifications to antidementia drug reimbursement in France: Analysis of the FRA-DEM cohort.

AIMS: Alzheimer's disease and related diseases (ADRD) is a progressive and inexorable disease. In France, acetylcholinesterase inhibitors and memantine were reimbursed for subjects with ADRD, until 2 modifications of their reimbursement rate (2012, 2018). We aimed to study the consequences of these measures on ADRD subjects' healthcare use. METHODS: We analysed data from the FRA-DEM cohort, including subjects with presumed incident ADRD identified since 2011 in the French health insurance system. We studied the healthcare use of subjects identified with incident ADRD in 2011, 2013, 2015, 2017 and 2019, notably the annual number of defined daily doses of various psychotropic groups. We performed 2 multivariate multinomial logistic regressions with the subcohort year as the dependent variable. RESULTS: In total, 165 120 subjects were included. A progressive decrease in exposure to antidementia drugs was observed between 2011 and 2019. Consultations with private neurologists or psychiatrists, and exposure to risperidone, antidepressants and benzodiazepines increased in the 2019 subcohort, following the 2018 reimbursement withdrawal. Meanwhile, the use of nursing/allied healthcare and emergency care increased over the subcohort years, whereas we observed a decrease in general practitioner consultations. CONCLUSION: These results suggest increases in private neurologist or psychiatrist consultations and exposure to recommended drugs after the reimbursement withdrawal, contrary to the fears expressed. However, antidementia drug exposure decreased long before the reimbursement modifications, probably due to the growing evidence of the modest effect of these drugs, and exposure to benzodiazepines increased after the reimbursement withdrawal.

Citicoline: A Cholinergic Precursor with a Pivotal Role in Dementia and Alzheimer's Disease.

Background: Citicoline is a naturally occurring compound with pleiotropic effects on neuronal function and cognitive processes. Objective: Based on previous studies, which shed light on the positive effects of citicoline 1 g when combined with acetylcholinesterase inhibitors (AChEIs) and/or memantine, we further investigated the benefits of citicoline in combination therapy in Alzheimer's disease and mixed dementia. Methods: We integrated the datasets of CITIMEM and CITIDEMAGE, increasing the overall sample size to enhance statistical power. We analyzed data from these two investigator-initiated studies involving 295 patients. The primary outcome was the assessment over time of the effects of combined treatment versus memantine given alone or AChEI plus memantine on cognitive functions assessed by Mini-Mental State Examination (MMSE). The secondary outcomes were the influence of combined treatment on daily life functions, mood, and behavioral symptoms assessed by activities of daily life (ADL) and instrumental ADL, Geriatric Depression Scale, and Neuropsychiatric Inventory Scale. One-hundred-forty-three patients were treated with memantine and/or AChEI (control group), and 152 patients were treated with memantine and/or AChEI plus citicoline 1 g/day orally (Citicoline group). Results: A significant difference in MMSE score was found in the average between the two groups of treatment at 6 and 12 months. Conclusions: This study confirmed the effectiveness of combined citicoline treatment in patients with mixed dementia and Alzheimer's disease, with a significant effect on the increase of MMSE score over time. The treated group also showed a significant reduction in the Geriatric Depression Scale and a significant increase in the instrumental ADL scale.

Geographic Variation of Antidementia and Antipsychotic Medication Use Among US Nursing Home Residents With Dementia.

BACKGROUND: Several antidementia medications have been approved for symptomatic treatment of cognitive and functional impairment due to Alzheimer disease. Antipsychotics are often prescribed off-label for behavioral symptoms. OBJECTIVE: The aim of this study was to describe the basis for regional variation in antidementia and antipsychotic medication use. SETTING: US nursing homes (n=9735), hospital referral regions (HRR; n=289). SUBJECTS: Long-stay residents with dementia (n=273,004). METHODS: Using 2018 Minimum Data Set 3.0 linked to Medicare data, facility information, and Dartmouth Atlas files, we calculated prevalence of use and separate multilevel logistic models [outcomes: memantine, cholinesterase inhibitor (ChEI), antipsychotic use] estimated adjusted odds ratios (aOR) and 95% CIs for resident, facility, and HRR characteristics. We then fit a series of cross-classified multilevel logistic models to estimate the proportional change in cluster variance (PCV). RESULTS: Overall, 20.9% used antipsychotics, 16.1% used memantine, and 23.3% used ChEIs. For antipsychotics, facility factors [eg, use of physical restraints (aOR: 1.08; 95% CI: 1.05-1.11) or poor staffing ratings (aOR: 1.10; 95% CI: 1.06-1.14)] were associated with more antipsychotic use. Nursing homes in HRRs with the highest health care utilization had greater antidementia drug use (aOR memantine: 1.68; 95% CI: 1.44-1.96). Resident/facility factors accounted for much regional variation in antipsychotics (PCV STATE : 27.80%; PCV HRR : 39.54%). For antidementia medications, HRR-level factors accounted for most regional variation (memantine PCV STATE : 37.44%; ChEI PCV STATE : 39.02%). CONCLUSION: Regional variations exist in antipsychotic and antidementia medication use among nursing home residents with dementia suggesting the need for evidence-based protocols to guide the use of these medications.

Cholinesterase inhibitors and memantine are associated with a reduced mortality in nursing home residents with dementia: a longitudinal observational study.

BACKGROUND: A large proportion of nursing home (NH) residents suffer from dementia and effects of conventional anti-dementia drugs on their health is poorly known. We aimed to investigate the associations between exposure to anti-dementia drugs and mortality among NH residents. METHODS: This retrospective longitudinal observational study involved 329 French NH and the residents admitted in these facilities since 2014 and having major neurocognitive disorder. From their electronic health records, we obtained their age, sex, level of dependency, Charlson comorbidity index, and Mini mental examination score at admission. Exposure to anti-dementia drugs was determined using their prescription into 4 categories: none, exposure to acetylcholinesterase inhibitors (AChEI) alone, exposure to memantine alone, exposure to AChEI and memantine. Survival until the end of 2019 was studied in the entire cohort by Cox proportional hazards. To alleviate bias related to prescription of anti-dementia drugs, we formed propensity-score matched cohorts for each type of anti-dementia drug exposure, and studied survival by the same method. RESULTS: We studied 25,358 NH residents with major neurocognitive disorder. Their age at admission was 87.1 + 7.1 years and 69.8% of them were women. Exposure to anti-dementia drugs occurred in 2,550 (10.1%) for AChEI alone, in 2,055 (8.1%) for memantine alone, in 460 (0.2%) for AChEI plus memantine, whereas 20,293 (80.0%) had no exposure to anti-dementia drugs. Adjusted hazard ratios for mortality were significantly reduced for these three groups exposed to anti-dementia drugs, as compared to reference group: HR: 0.826, 95%CI 0.769 to 0.888 for AChEI; 0.857, 95%CI 0.795 to 0.923 for memantine; 0.742, 95%CI 0.640 to 0.861 for AChEI plus memantine. Results were consistent in propensity-score matched cohorts. CONCLUSION: The use of conventional anti-dementia drugs is associated with a lower mortality in nursing home residents with dementia and should be widely used in this population.

Spectrum of NMDA Receptor Variants in Neurodevelopmental Disorders and Epilepsy.

N-methyl-D-aspartate receptors (NMDAR) are ligand-gated ion channels mediating excitatory neurotransmission and are important for normal brain development, cognitive abilities, and motor functions. Pathogenic variants in the Glutamate receptor Ionotropic N-methyl-D-aspartate (GRIN) genes (GRIN1, GRIN2A-D) encoding NMDAR subunits have been associated with a wide spectrum of neurodevelopmental disorders and epilepsies ranging from treatable focal epilepsies to devastating early-onset developmental and epileptic encephalopathies. Genetic variants in NMDA receptor genes can cause a range of complex alterations to receptor properties resulting in various degrees of loss-of-function, gain-of-function, or mixtures thereof. Understanding how genetic variants affect the function of the receptors, therefore, represents an important first step in the ongoing development towards targeted therapies. Currently, targeted treatment options for GRIN-related diseases are limited. However, treatment with memantine has been reported to significantly reduce seizure frequency in a few individuals with developmental and epileptic encephalopathies harboring de novo gain-of-function GRIN2A missense variants, and supplementary treatment with L-serine has been associated with improved motor and cognitive performance as well as reduced seizure frequency in patients with GRIN2B loss-of-function missense variants as well as GRIN2A and GRIN2B null variants.

Time-Dependent Long-Term Effect of Memantine following Repetitive Mild Traumatic Brain Injury.

Repetitive mild traumatic brain injury (rmTBI, e.g., sports concussions) may be associated with both acute and chronic symptoms and neurological changes. Despite the common occurrence of these injuries, therapeutic strategies are limited. One potentially promising approach is N-methyl-D-aspartate receptor (NMDAR) blockade to alleviate the effects of post-injury glutamatergic excitotoxicity. Initial pre-clinical work using the NMDAR antagonist, memantine, suggests that immediate treatment following rmTBI improves a variety of acute outcomes. It remains unclear (1) whether acute memantine treatment has long-term benefits and (2) whether delayed treatment following rmTBI is beneficial, which are both clinically relevant concerns. To test this, animals were subjected to rmTBI via a weight drop model with rotational acceleration (five hits in 5 days) and randomized to memantine treatment immediately, 3 months, or 6 months post-injury, with a treatment duration of one month. Behavioral outcomes were assessed at 1, 4, and 7 months post-injury. Neuropathological outcomes were characterized at 7 months post-injury. We observed chronic changes in behavior (anxiety-like behavior, motor coordination, spatial learning, and memory), as well as neuroinflammation (microglia, astrocytes) and tau phosphorylation (T231). Memantine treatment, either immediately or 6 months post-injury, appears to confer greater rescue of neuroinflammatory changes (microglia) than vehicle or treatment at the 3-month time point. Although memantine is already being prescribed chronically to address persistent symptoms associated with rmTBI, this study represents the first evidence of which we are aware to suggest a small but durable effect of memantine treatment in mild, concussive injuries. This effect suggests that memantine, although potentially beneficial, is insufficient to treat all aspects of rmTBI alone and should be combined with other therapeutic agents in a multi-therapy approach, with attention given to the timing of treatment.

Evaluating the efficacy and safety of Alzheimer's disease drugs: A meta-analysis and systematic review.

BACKGROUND: Alzheimer's disease (AD) is a progressive neurodegenerative disorder. Dementia severity was assessed mainly through cognitive function, psychobehavioral symptoms, and daily living ability. Currently, there are not many drugs that can be selected to treat mild to moderate AD, and the value of drugs remains controversial. OBJECTIVE: The aim of this study is to quantitatively evaluate the efficacy and safety of cholinesterase inhibitors (ChEIs), memantine, and sodium oligomannate (GV-971) in the treatment of patients with AD. Additionally, molecular docking analysis will be used to investigate the binding affinities of donepezil, galantamine, rivastigmine, and memantine with key receptor proteins associated with AD, including beta-amyloid (Abeta), microtubule-associated protein (MAP), apolipoprotein E4 (APOE4), and Mitofusin-2 (MFN2), to further validate the results of the meta-analysis. METHODS: We obtained clinical trials characterized by randomization, placebo control, and double-blinded methodologies concerning ChEIs, memantine, and GV-971. Statistical analysis was performed using Review Manager Version 5.4 software. Molecular docking was also conducted to evaluate the results. RESULTS: All drugs improved the cognitive function, with the effect value ranging from -1.23 (95% CI -2.17 to -0.30) for 20 mg memantine to -3.29 (95% CI -4.14 to -2.45) for 32 mg galantamine. Although 32 mg galanthamine and GV-971 did not improve the clinicians' Global Impression of Change scale, other drugs showed significant results compared with placebo. On NPI, only 10 mg of donepezil and 24 mg of galantamine had improvement effects. On ADCS/ADL, only 20 mg memantine and 900 mg GV-971 had no significant difference from the placebo. Donepezil 5 mg and GV-971 900 mg did not increase the drug withdrawal rates due to various reasons or adverse reactions when compared to the placebo. Donepezil demonstrated superior binding to the protein and exhibited greater efficacy compared to other drugs. CONCLUSION: ChEIs, memantine, and GV-971 all can slow the progression of AD but have different effects on respective assessments. Donepezil and GV-971 were relatively well tolerated.

Dementia Prevention and Treatment: A Narrative Review.

Importance: Dementia affects 10% of those 65 years or older and 35% of those 90 years or older, often with profound cognitive, behavioral, and functional consequences. As the baby boomers and subsequent generations age, effective preventive and treatment strategies will assume increasing importance. Observations: Preventive measures are aimed at modifiable risk factors, many of which have been identified. To date, no randomized clinical trial data conclusively confirm that interventions of any kind can prevent dementia. Nevertheless, addressing risk factors may have other health benefits and should be considered. Alzheimer disease can be treated with cholinesterase inhibitors, memantine, and antiamyloid immunomodulators, with the last modestly slowing cognitive and functional decline in people with mild cognitive impairment or mild dementia due to Alzheimer disease. Cholinesterase inhibitors and memantine may benefit persons with other types of dementia, including dementia with Lewy bodies, Parkinson disease dementia, vascular dementia, and dementia due to traumatic brain injury. Behavioral and psychological symptoms of dementia are best treated with nonpharmacologic management, including identifying and mitigating the underlying causes and individually tailored behavioral approaches. Psychotropic medications have minimal evidence of efficacy for treating these symptoms and are associated with increased mortality and clinically meaningful risks of falls and cognitive decline. Several emerging prevention and treatment strategies hold promise to improve dementia care in the future. Conclusions and Relevance: Although current prevention and treatment approaches to dementia have been less than optimally successful, substantial investments in dementia research will undoubtedly provide new answers to reducing the burden of dementia worldwide.

ATP1A2-related epileptic encephalopathy and movement disorder: Clinical features of three novel patients.

OBJECTIVE: Variants in the ATP1A2 gene exhibit a wide clinical spectrum, ranging from familial hemiplegic migraine to childhood epilepsies and early infantile developmental epileptic encephalopathy (EIDEE) with movement disorders. This study aims to describe the epileptology of three unpublished cases and summarize epilepsy features of the other 17 published cases with ATP1A2 variants and EIDEE. METHODS: Medical records of three novel patients with pathogenic ATP1A2 variants were retrospectively reviewed. Additionally, the PUBMED, EMBASE, and Cochrane databases were searched until December 2023 for articles on EIDEE with ATP1A2 variants, without language or publication year restrictions. RESULTS: Three female patients, aged 6 months-10 years, were investigated. Epilepsy onset occurred between 5 days and 2 years, accompanied by severe developmental delay, intellectual disability, drug-resistant epilepsy, severe movement disorder, and recurrent status epilepticus. All individuals had pathogenic variants of the ATP1A2 gene (ATP1A2 c.720_721del (p.Ile240MetfsTer9), ATP1A2c.3022C > T (p.Arg1008Trp), ATP1A2 c.1096G > T (p.Gly366Cys), according to ACMG criteria. Memantine was p) rescribed to three patients, one with a reduction in ictal frequency, one with improvement in gait pattern, coordination, and attention span, and another one in alertness without significant side effects. SIGNIFICANCE: This study reinforces the association between ATP1A2 variants and a severe phenotype. All patients had de novo variants, focal motor seizures with impaired awareness as the primary type of seizure; of the 11 EEGs recorded, 10 presented a slow background rhythm, 7 multifocal interictal epileptiform discharges (IED), predominantly temporal IEDs, followed by frontal IED, as well as ten ictal recordings, which showed ictal onset from the same regions mentioned above. Treatment with antiseizure medication was generally ineffective, but memantine showed moderate improvement. Prospective studies are needed to enlarge the phenotype and assess the efficacy of NMDA receptor antagonist therapies in reducing seizure frequency and improving quality of life.

Harnessing memantine in Alzheimer's disease therapy through inhibition of microtubule affinity-regulating kinase: Mechanistic insights.

Alzheimer's disease (AD) is one of the neurodegenerative disorder that primarily affects memory, thinking, and behavior, eventually leading to severe cognitive impairment. Therapeutic management of AD is urgently needed to improve the quality and lifestyle of patients. Tau phosphorylating kinases are considered attractive therapeutic targets. Microtubule affinity-regulating kinase 4 (MARK4) is directly linked with pathological phosphorylations of tau, highlighting its role in the therapeutic targeting of AD. The current manuscript shows the MARK4 inhibitory effect of Memantine (MEM), a drug used in treating AD. We have performed fluorescence based binding measurements, enzyme inhibition assay, docking and molecular dynamics (MD) simulations to understand the binding of of MARK4 and MEM and subsequent inhibition in the kinase activity. A 100 ns MD simulations provided a detailed analysis of MARK4-MEM complex and the role of potential critical residues in the binding. Finally, this study provides molecular insights into the therapeutic implication of MEM in AD therapeutics. We propose MEM effectively inhibits MARK4, it may be implicated in the development of targeted and efficient treatments for AD.

Combination strategy employing BACE1 inhibitor and memantine to boost cognitive benefits in Alzheimer's disease therapy.

RATIONALE: The ß-secretase BACE1 initiates amyloid-ß (Aß) generation and represents a long-standing prime therapeutic target for the treatment of Alzheimer's disease (AD). However, BACE1 inhibitors tested to date in clinical trials have yielded no beneficial outcomes. In fact, prior BACE1 inhibitor trials targeted at ~ 50-90% Aß reductions in symptomatic or prodromal AD stages have ended in the discontinuation due to futility and/or side effects, including cognitive worsening rather than expected improvement at the highest dose. OBJECTIVES: We tested whether a combination strategy with the selective BACE1 inhibitor GRL-8234 and the FDA-approved symptomatic drug memantine may provide synergistic cognitive benefits within their safe dose range. METHODS: The drug effects were evaluated in the advanced symptomatic stage of 5XFAD mice that developed extensive cerebral Aß deposition. RESULTS: Chronic combination treatment with 33.4-mg/kg GRL-8234 and 10-mg/kg memantine, but not either drug alone, rescued cognitive deficits in 5XFAD mice at 12 months of age (the endpoint after 60-day drug treatment), as assessed by the contextual fear conditioning, spontaneous alternation Y-maze and nest building tasks. Intact baseline performances of wild-type control mice on three cognitive paradigms demonstrated that combination treatment did not augment potential cognitive side effects of individual drugs. Biochemical and immunohistochemical examination showed that combination treatment did not synergistically reduce the ß-amyloidogenic processing of amyloid precursor protein or Aß levels in 5XFAD mouse brains. CONCLUSIONS: A combination strategy with BACE1 inhibitors and memantine may be able to increase the effectiveness of individual drugs within their safe dose range in AD therapy.