NMDA Receptor Antagonist Memantine Research Articles

Memantine as an Augmentation Therapy for Anxiety Disorders

Objective. Glutamate, an excitatory neurotransmitter in the central nervous system (CNS), may play a role in the development of anxiety. Memantine partially blocks N-methyl-D-aspartate (NMDA) receptors' glutamate channels located in the CNS. This paper evaluates memantine as an augmentation therapy for treatment of anxiety. Methods. 15 consecutive partially responding anxious patients were treated with adjunctive memantine for 10 weeks. Memantine was dosed 5–20 mg/day. Result. Memantine augmentation resulted in clinically relevant reduction in anxiety symptoms when compared to baseline. Forty percent of patients achieved remission (HAM-A ≥ 7). Memantine improved sleep quality. Mean dose was 14 mg/d (range 5–20 mg/d). Typical adverse events included nausea and headache. Conclusion. The NMDA receptor antagonist memantine may be an effective augmentation therapy in patients with treatment-resistant anxiety.

The NMDA receptor antagonist memantine impairs hippocampal plasticity during declarative learning

The NMDA receptor antagonist memantine impairs hippocampal plasticity during declarative learning

Exaggerated NMDA mediated LTD in a mouse model of Down syndrome and pharmacological rescuing by memantine

The Ts65Dn mouse is the best-studied animal model for Down syndrome. In the experiments described here, NMDA-mediated or mGluR-mediated LTD was induced in the CA1 region of hippocampal slices from Ts65Dn and euploid control mice by bath application of 20 µM NMDA for 3 min and 50 µM DHPG for 5 min, respectively. We found that Ts65Dn mice display exaggerated NMDA-induced, but not mGluR-induced, LTD in the CA1 region of the hippocampus compared with euploid control animals. In addition, this abnormal level of LTD can be pharmacologically rescued by the NMDA receptor antagonist memantine.

The “Aged Garlic Extract” (AGE) and One of its Active Ingredients S-Allyl-LCysteine (SAC) as Potential Preventive and Therapeutic Agents for Alzheimer's Disease (AD)

Alzheimer's disease (AD) is the most common form of dementia in the older people and 7(th) leading cause of death in the United States. Deposition of amyloid-beta (Aβ) plaques, hyperphosphorylation of microtubule associated protein tau (MAPT), neuroinflammation and cholinergic neuron loss are the major hallmarks of AD. Deposition of Aβ peptides, which takes place years before the clinical onset of the disease can trigger hyperphophorylation of tau proteins and neuroinflammation, and the latter is thought to be primarily involved in neuronal and synaptic damage seen in AD. To date, four cholinesterase inhibitors or ChEI (tacrine, rivastigmine, donepezil and galantamine) and a partial NMDA receptor antagonist (memantine) are the only approved treatment options for AD. However, these drugs fail to completely cure the disease, which warrants a search for newer class of targets that would eventually lead to effective drugs for the treatment of AD. In addition to selected pharmacological agents, botanical and medicinal plant extracts are also being investigated. Apart from its culinary use, garlic (Allium sativum) is being used to treat several ailments like cancer and diabetes. Herein we have discussed the effects of a specific 'Aged Garlic Extract' (AGE) and one of its active ingredients, S-allyl-L-cysteine (SAC) in restricting several pathological cascades related to the synaptic degeneration and neuroinflammatory pathways associated with AD. Thus, based on the reported positive preliminary results reviewed herein, further research is required to develop the full potential of AGE and/or SAC into an effective preventative strategy for AD.

Combination Therapy for Alzheimerʼs Disease

Alzheimer's disease (AD) is a progressive, degenerative brain disease. The mainstay of current management of patients with AD involves drugs that provide symptomatic therapy. Two classes of medications have been approved by the US FDA for the treatment of AD: the cholinesterase inhibitors (ChEIs), which include galantamine and rivastigmine (both approved for use in mild to moderate AD) and donepezil (approved for use in mild to severe AD); and the non-competitive NMDA receptor antagonist memantine (approved for use in moderate to severe AD). The European and Asian regulatory bodies have also approved ChEIs as monotherapy in mild to moderate AD. Future research directions are mostly focusing on disease modification and prevention. This review covers key studies of the efficacy, safety and tolerability of combination therapy in AD, defined as a combination of the NMDA receptor antagonist memantine with any of the ChEIs (donepezil, galantamine or rivastigmine) for the treatment of AD. Relevant studies were identified via a PubMed search. This review shows that combination therapy for AD seems to be safe, well tolerated and may represent the current gold standard for treatment of moderate to severe AD and possibly mild to moderate AD as well.

Oxidative insults to neurons and synapse are prevented by aged garlic extract and S-allyl-L-cysteine treatment in the neuronal culture and APP-Tg mouse model.

Alzheimer's disease (AD) is one of the most common forms of dementia in the elderly. In AD patients, β-amyloid peptide (Aβ) plaques and neurofibrillary tangles are common features observed in the CNS. Aβ deposition results in the production of reactive oxygen species (ROS) leading to the hyperphosphorylation of tau that are associated with neuronal damage. Cholinesterase inhibitors and a partial NMDA receptor antagonist (memantine) have been identified as potential treatment options for AD. However, clinical studies have found that these drugs fail to prevent the disease progression. From ancient times, garlic (Allium sativum) has been used to treat several diseases. By 'aging' of garlic, some adverse reactions of garlic can be eliminated. Recent findings suggest that 'aged garlic extract' (AGE) may be a therapeutic agent for AD because of its antioxidant and Aβ lowering properties. To date, the molecular properties of AGE have been sparsely studied in vitro or in vivo. The present study tested specific biochemical and molecular effects of AGE in neuronal and AD rodent models. Furthermore, we identified S-allyl-L-cysteine (SAC) as one of the most active chemicals responsible for the AGE-mediated effect(s). We observed significant neuroprotective and neurorescue properties of AGE and one of its ingredients, SAC, from ROS (H(2)O(2))-mediated insults to neuronal cells. Treatment of AGE and SAC were found to protect neuronal cells when they were independently co-treated with ROS. Furthermore, a novel neuropreservation effect of AGE was detected in that pre-treatment with AGE alone protected ∼ 80% neuronal cells from ROS-mediated damage. AGE was also found to preserve pre-synaptic protein synaptosomal associated protein of 25 kDa (SNAP25) from ROS-mediated insult. For example, treatment with 2% AGE containing diet and SAC (20 mg/kg of diet) independently increased (∼70%) levels of SNAP25 and synaptophysin in Alzheimer's amyloid precursor protein-transgenic mice, of which the latter was significantly decreased in AD. Taken together, the neuroprotective, including preservation of pre-synaptic proteins by AGE and SAC can be utilized in future drug development in AD.

Amyloid β peptide oligomers directly activate NMDA receptors

Amyloid beta (Aβ) oligomers accumulate in the brain tissue of Alzheimer disease patients and are related to disease pathogenesis. The precise mechanisms by which Aβ oligomers cause neurotoxicity remain unknown. We recently reported that Aβ oligomers cause intracellular Ca 2+ overload and neuronal death that can be prevented by NMDA receptor antagonists. This study investigated whether Aβ oligomers directly activated NMDA receptors (NMDARs) using NR1/NR2A and NR1/NR2B receptors that were heterologously expressed in Xenopus laevis oocytes. Indeed, Aβ oligomers induced inward non-desensitizing currents that were blocked in the presence of the NMDA receptor antagonists memantine, APV, and MK-801. Intriguingly, the amplitude of the responses to Aβ oligomers was greater for NR1/NR2A heteromers than for NR1/NR2B heteromers expressed in oocytes. Consistent with these findings, we observed that the increase in the cytosolic concentration of Ca 2+ induced by Aβ oligomers in cortical neurons is prevented by AP5, a broad spectrum NMDA receptor antagonist, but slightly attenuated by ifenprodil which blocks receptors with the NR2B subunit. Together, these results indicate that Aβ oligomers directly activate NMDA receptors, particularly those with the NR2A subunit, and further suggest that drugs that attenuate the activity of such receptors may prevent Aβ damage to neurons in Alzheimeŕs disease.

NMDA-Receptor Antagonist Memantine, Combined With Morphine, Decreases Pain of CRPS

NMDA-Receptor Antagonist Memantine, Combined With Morphine, Decreases Pain of CRPS

Subchronic memantine administration on spatial learning, exploratory activity, and nest-building in an APP/PS1 mouse model of Alzheimer’s disease

Glutamate neurotoxicity has been proposed to be involved in Alzheimer pathogenesis, with clinical data supporting succesful treatment with the NMDA receptor antagonist memantine. In the present study, the effects of subchronic memantine administration were assessed on spatial and non-spatial learning as well as exploratory activity and nest-building in APP/PS1 mutant mice. Memantine (10 mg/kg, i.p.) was better than placebo during the reversal phase of left-right discrimination, though equivalent to saline for Morris water maze and passive avoidance learning. The drug had no effect on non-learned behaviors in elevated plus-maze exploration and nest-building. These results support a specific action of the NMDA receptor antagonist on behavioral flexibility in mutant mice with amyloid pathology.

The Pharmacoeconomics of Cognitive Enhancers in Moderate to Severe Alzheimerʼs Disease

Alzheimer's disease is associated with a substantial economic impact on patients, their caregivers and society. Due to the current rise in the aging population, the prevalence and impact of Alzheimer's disease are expected to increase greatly. The cost of caring for someone with Alzheimer's disease is magnified in the more severe stages of the disease. There are four cognitive enhancers commonly used for the treatment of Alzheimer's disease: three cholinesterase inhibitors (donepezil, rivastigmine and galantamine) and one NMDA receptor antagonist (memantine). Of these, donepezil and memantine have been approved in many countries as pharmacological treatments for moderate to severe Alzheimer's disease, while donepezil, rivastigmine and galantamine are approved treatments for mild to moderate Alzheimer's disease. While cost effectiveness has been well studied in mild to moderate Alzheimer's disease, the cost-benefit information for drug therapy in moderate to severe Alzheimer's disease is less clear. This article reviews the pharmacoeconomic data available on these four drugs, with a specific focus on moderate to severe Alzheimer's disease, including economic burden, cost drivers, clinical outcomes and pharmacoeconomic studies. A key driver of the cost of Alzheimer's disease is the severity of the disease, indicating that the ability to stabilize the disease state is a potential source of cost savings. Drug therapies that can limit increases in behavioural problems and cognitive and functional impairment, and postpone institutionalization without an increase in longevity may serve to reduce the economic burden on Alzheimer's disease patients. The data suggest that, while the available, approved agents offer only modest improvements in clinical outcomes, they could be cost-effective treatments for moderate to severe Alzheimer's disease when viewed from the societal perspective. For memantine and donepezil, data are available that suggest that the cost of these drugs is offset by the clinical and societal benefits provided by slowing the progression of Alzheimer's disease. While there are few head-to-head comparison trials, the similarity in costs of the treatments and efficacy against placebo suggest that cost effectiveness will not be substantially different among treatments. More studies that examine longitudinal resource utilization and its relationship to drug treatment in the moderate to severe stages are needed to clarify cost benefit in this population and possibly differentiate between individual medications.

Memantine for patients with Parkinson's disease dementia or dementia with Lewy bodies: a randomised, double-blind, placebo-controlled trial

Previous studies have suggested that patients with Lewy-body-related dementias might benefit from treatment with the N-methyl D-aspartate receptor antagonist memantine, but further data are needed. Therefore, the efficacy and safety of memantine were investigated in patients with mild to moderate Parkinson's disease dementia (PDD) or dementia with Lewy bodies (DLB). Patients (≥50 years of age) with mild to moderate PDD or DLB were recruited from 30 specialist centres in Austria, France, Germany, the UK, Greece, Italy, Spain, and Turkey. They were randomly assigned to placebo or memantine (20 mg per day) according to a computer-generated list. Patients and all physicians who had contact with them were masked to treatment assignment. No primary endpoint was defined. Safety analyses were done for all patients who took at least one dose of memantine or placebo, and efficacy analyses were done for all patients who had at least one valid postbaseline assessment. This trial is registered with ClinicalTrials.gov, number NCT00855686. Of the 199 patients randomly assigned to treatment, 34 with DLB and 62 with PDD were given memantine, and 41 with DLB and 58 with PDD were given placebo. 159 (80%) patients completed the study: 80 in the memantine group and 79 in the placebo group. 93 patients treated with memantine and 97 patients treated with placebo were included in the efficacy analysis. At week 24, patients with DLB who received memantine showed greater improvement according to Alzheimer's disease cooperative study (ADCS)-clinical global impression of change scores than did those who received placebo (mean change from baseline 3·3 vs 3·9, respectively, difference -0·6 [95% CI -1·2 to -0·1]; p=0·023). No significant differences were noted between the two treatments in patients with PDD (3·6 with memantine vs 3·8 with placebo, -0·1 [-0·6 to 0·3]; p=0·576) or in the total population (3·5 with memantine vs 3·8 with placebo, -0·3 [-0·7 to 0·1]; p=0·120). Neuropsychiatric-inventory scores showed significantly greater improvement in the memantine group than in the placebo group (-4·3 vs 1·7, respectively, -5·9 [-11·6 to -0·2]; p=0·041) in patients with DLB, but not in those with PDD (-1·6 vs -0·1, respectively, -1·4 [-5·9 to 3·0]; p=0·522) or in the total patient population (-2·6 vs 0·4, respectively, -2·9 [-6·3 to 0·5]; p=0·092). In most of the cognitive test scores, ADCS-activities of daily living, and Zarit caregiver burden scores, there were no significant differences between the two treatment groups in any of the study populations. The incidence of adverse events and number of discontinuations due to adverse events were similar in the two groups. The most common serious adverse events were stroke (n=3 in memantine group), falls (n=2 in memantine group; n=1 in placebo group), and worsening of dementia (n=2 in memantine group). Memantine seems to improve global clinical status and behavioural symptoms of patients with mild to moderate DLB, and might be an option for treatment of these patients. Lundbeck.

Sustained calcium signalling and caspase-3 activation involve NMDA receptors in thymocytes in contact with dendritic cells

L-glutamate, the major excitatory neurotransmitter, also has a role in non-neuronal tissues and modulates immune responses. Whether NMDA receptor (NMDAR) signalling is involved in T-cell development is unknown. In this study, we show that mouse thymocytes expressed an array of glutamate receptors, including NMDARs subunits. Sustained calcium (Ca(2+)) signals and caspase-3 activation in thymocytes were induced by interaction with antigen-pulsed dendritic cells (DCs) and were inhibited by NMDAR antagonists MK801 and memantine. NMDARs were transiently activated, triggered the sustained Ca(2+) signal and were corecruited with the PDZ-domain adaptor postsynaptic density (PSD)-95 to thymocyte-DC contact zones. Although T-cell receptor (TCR) activation was sufficient for relocalization of NMDAR and PSD-95 at the contact zone, NMDAR could be activated only in a synaptic context. In these T-DC contacts, thymocyte activation occurred in the absence of exogenous glutamate, indicating that DCs could be a physiological source of glutamate. DCs expressed glutamate, glutamate-specific vesicular glutamate transporters and were capable of fast glutamate release through a Ca(2+)-dependent mechanism. We suggest that glutamate released by DCs could elicit focal responses through NMDAR-signalling in T cells undergoing apoptosis. Thus, synapses between T and DCs could provide a functional platform for coupling TCR activation and NMDAR signalling, which might reflect on T-cell development and modulation of the immune response.

Memantine reduces consumption of highly palatable food in a rat model of binge eating.

Excessive consumption of highly palatable food has been linked to the development of eating disorders and obesity, and can be modeled in non-food-deprived rats by offering them a limited (2-h daily) access to an optional dietary fat. Since the glutamatergic system has recently emerged as a viable target for binge-eating medication development, we compared the effects of subchronic treatment with glutamatergic receptor antagonists to the effects of a reference appetite-suppressing agent sibutramine on highly palatable food (lard) and normal chow intake. In three separate experiments, the consumption of a standard laboratory chow and lard were measured during 12 days of medication treatment and for 6 days afterwards. Generalized estimating equations analysis demonstrated that sibutramine (7.5 mg/kg, PO) significantly decreased lard consumption, with a concurrent increase in chow consumption. Sibutramine effects disappeared after treatment discontinuation. The NMDA receptor antagonist memantine (5 mg/kg, IP) significantly decreased lard consumption and increased chow consumption, comparable to effects of sibutramine; however, memantine’s effects persisted after treatment discontinuation. The effects of the mGluR5 antagonist MTEP (7.5 mg/kg, IP) on food consumption were in the same direction as seen with memantine, but the observed differences were not significant. In an additional control experiment, sibutramine and memantine reduced unlimited (24 h) chow intake during the treatment phase. Present results provide evidence that glutamatergic neurotransmission might be involved in the regulation of excessive consumption of highly palatable foods, and suggest that NMDA receptor may be an attractive target for developing obesity and disordered eating pharmacotherapies.

Oxymatrine Inhibits Development of Morphine-Induced Tolerance Associated With Decreased Expression of P-glycoprotein in Rats

The effect of oxymatrine on the development of tolerance to the antinociceptive effects of morphine was investigated in rats. The degree of tolerance was assessed using the tail-flick test before and after 6 days of twice daily administration of oxymatrine premorphine (10/20/30 mg/kg). High doses of oxymatrine inhibited the development of morphine tolerance (resembling the effect of 7.5 mg/kg of the NMDA receptor antagonist memantine) while also increasing the antinociceptive effects. A high dose of oxymatrine (30 mg/kg) also significantly inhibited the dramatic increase in expression of morphine-induced P-glycoprotein (P-gp), an ATP-dependent efflux pump acting at the blood-brain barrier, by Western blot analysis. Furthermore, these studies suggest that P-gp modulates the development of morphine tolerance while not affecting the magnitude of the analgesic effect of morphine. These results imply that oxymatrine prevention of the development of tolerance of morphine may be related to a considerable inhibition of P-gp expression. In contrast, the authors' data suggest that the mechanism of oxymatrine enhancement of morphine's analgesic effects is not associated with increase in the level of expression of P-gp. However, they believe that their findings can be used by researchers to develop therapies that will allow patients to take morphine without becoming tolerant of its benefits.

Effects of the Non‐Competitive NMDA Receptor Antagonist Memantine on the Volitional Consumption of Ethanol by Alcohol‐Preferring Rats

Potent N-methyl-d-aspartate (NMDA) receptor antagonists decrease volitional consumption of ethanol by rats. This study examined the effects of memantine, a low-affinity, open channel NMDA antagonist, on volitional consumption of ethanol by alcohol-preferring rats and potential locomotor, sedative and hypothermic effects. Volitional consumption of ethanol in a 24-hr two-choice paradigm was determined for male Myers' high-ethanol-preferring (mHEP) rats. Effects of memantine (0.3, 1.0, 3.0 and 10.0 mg/kg, i.p., b.i.d. [twice daily] for 3 days) or vehicle on volitional consumption of ethanol, proportion of ethanol to total fluids consumed, total fluid intake and consumption of food were observed. Potential sedating and locomotor effects of memantine (10.0 mg/kg, i.p., b.i.d.) were determined using an elevated plus maze and an Auto-Track Opto-Varimex activity monitoring system. Rectal temperature was measured to determine if memantine (10.0 mg/kg, i.p.) produces a hypothermic effect. The results indicate that memantine dose-dependently decreased the amount of ethanol and proportion of ethanol to total fluids consumed daily, reaching 48% and 24%, respectively, at the highest dose. These effects did not appear to be anti-caloric. Memantine (10.0 mg/kg) partially reversed both the sedation and the reductions in locomotor activity induced by ethanol. This dose did, however, produce a small, partially reversible hypothermic effect. In conclusion, memantine may decrease ethanol consumption with fewer side effects than other NMDA receptor antagonists, such as phencyclidine (PCP), MK 801 and ketamine.

Inhibition of calpain prevents NMDA‐induced cell death and β‐amyloid‐induced synaptic dysfunction in hippocampal slice cultures

Alzheimer's disease (AD) is a multifactorial, neurodegenerative disease, which is in part caused by an impairment of synaptic function, probably mediated by oligomeric forms of amyloid-beta (Abeta). While the Abeta pathology mainly affects the physiology of neurotransmission, neuronal decline is caused by excitotoxic cell death, which is mediated by the NMDA receptor. A comprehensive therapeutic approach should address both Abeta-induced synaptic deficits, as well as NMDA receptor-mediated neurodegeneration, via one molecular target. This study was designed to test whether calpain could be involved in both pathological pathways, which would offer a promising avenue for new treatments. Application of the specific, water-soluble calpain inhibitor A-705253 was used to inhibit calpain in hippocampal slice cultures. We examined whether inhibition of calpain would prevent Abeta-induced deficits in neurotransmission in CA1, as well as NMDA-induced neuronal cell death. A-705253 dose-dependently prevented excitotoxicity-induced neurodegeneration at low nanomolar concentrations, determined by propidium iodide histochemistry. Inhibition of the NMDA receptor similarly protected from neuronal damage. Caspase staining indicated that calpain inhibition was protective by reducing apoptosis. Electrophysiological analysis revealed that inhibition of calpain by A-705253 also fully prevented Abeta oligomer-induced deficits in neurotransmission. The protective effect of calpain was compared to the clinically available NMDA receptor antagonist memantine, which was also effective in this model. We suggest that inhibition of calpain exhibits a promising strategy to address several aspects of the pathology of AD that may go beyond the available therapeutic intervention by memantine.

GluN2B subunit-containing NMDA receptor antagonists prevent Aβ-mediated synaptic plasticity disruption in vivo

Currently, treatment with the relatively low-affinity NMDA receptor antagonist memantine provides limited benefit in Alzheimer's disease (AD). One probable dose-limiting factor in the use of memantine is the inhibition of NMDA receptor-dependent synaptic plasticity mechanisms believed to underlie certain forms of memory. Moreover, amyloid-beta protein (Abeta) oligomers that are implicated in causing the cognitive deficits of AD potently inhibit this form of plasticity. Here we examined if subtype-preferring NMDA receptor antagonists could preferentially protect against the inhibition of NMDA receptor-dependent plasticity of excitatory synaptic transmission by Abeta in the hippocampus in vivo. Using doses that did not affect control plasticity, antagonists selective for NMDA receptors containing GluN2B but not other GluN2 subunits prevented Abeta(1-42) -mediated inhibition of plasticity. Evidence that the proinflammatory cytokine TNFalpha mediates this deleterious action of Ass was provided by the ability of TNFalpha antagonists to prevent Abeta(1-42) inhibition of plasticity and the abrogation of a similar disruptive effect of TNFalpha using a GluN2B-selective antagonist. Moreover, at nearby synapses that were resistant to the inhibitory effect of TNFalpha, Abeta(1-42) did not significantly affect plasticity. These findings suggest that preferentially targeting GluN2B subunit-containing NMDARs may provide an effective means of preventing cognitive deficits in early Alzheimer's disease.

Model of methadone-induced hyperalgesia in rats and effect of memantine

Methadone used for opioid dependence therapy is associated with increased pain sensitivity. This study aimed to investigate whether methadone administration lowers nociceptive threshold in adult male Sprague-Dawley (SD) rats, and if this threshold could be altered by the NMDA receptor antagonist memantine. Rats were implanted with osmotic pumps delivering 1 mg/kg/day methadone (n = 6), or saline placebo (n = 6) (0.51 μl/h). A separate cohort of rats received either methadone 1 mg/kg/day (n = 8) or methadone 1 mg/kg/day with 20 mg/kg/day memantine (n = 8). Nociception was measured by the Hargreave's paw withdrawal test. Baseline nociception was measured on day 0 prior to osmotic pump implantation and was measured daily for the following 21 days. Osmotic pumps were removed following nociceptive testing on day 14. Methadone only treated rats had a mean paw withdrawal latency significantly lower than the corresponding values for saline on days 8, 9, 10, 11, 12, 14, and 17 (P < 0.05). At all other time points the mean paw withdrawal latency was not significantly different from saline (P > 0.05). Paw withdrawal latency of rats treated with methadone co-administered with memantine did not differ significantly compared to methadone only (P > 0.05). This demonstrates that methadone induces hyperalgesia in the SD rat yet this hyperalgesia resolves following discontinuation of methadone administration. Furthermore, memantine does not alter the development of methadone-induced hyperalgesia.

NMDA Receptor antagonist memantine suppresses DFP-induced oxidative/nitrosative stress and dendritic damage in rat brain

NMDA Receptor antagonist memantine suppresses DFP-induced oxidative/nitrosative stress and dendritic damage in rat brain

The excitotoxin quinolinic acid induces tau phosphorylation in human neurons.

Some of the tryptophan catabolites produced through the kynurenine pathway (KP), and more particularly the excitotoxin quinolinic acid (QA), are likely to play a role in the pathogenesis of Alzheimer's disease (AD). We have previously shown that the KP is over activated in AD brain and that QA accumulates in amyloid plaques and within dystrophic neurons. We hypothesized that QA in pathophysiological concentrations affects tau phosphorylation. Using immunohistochemistry, we found that QA is co-localized with hyperphosphorylated tau (HPT) within cortical neurons in AD brain. We then investigated in vitro the effects of QA at various pathophysiological concentrations on tau phosphorylation in primary cultures of human neurons. Using western blot, we found that QA treatment increased the phosphorylation of tau at serine 199/202, threonine 231 and serine 396/404 in a dose dependent manner. Increased accumulation of phosphorylated tau was also confirmed by immunocytochemistry. This increase in tau phosphorylation was paralleled by a substantial decrease in the total protein phosphatase activity. A substantial decrease in PP2A expression and modest decrease in PP1 expression were observed in neuronal cultures treated with QA. These data clearly demonstrate that QA can induce tau phosphorylation at residues present in the PHF in the AD brain. To induce tau phosphorylation, QA appears to act through NMDA receptor activation similar to other agonists, glutamate and NMDA. The QA effect was abrogated by the NMDA receptor antagonist memantine. Using PCR arrays, we found that QA significantly induces 10 genes in human neurons all known to be associated with AD pathology. Of these 10 genes, 6 belong to pathways involved in tau phosphorylation and 4 of them in neuroprotection. Altogether these results indicate a likely role of QA in the AD pathology through promotion of tau phosphorylation. Understanding the mechanism of the neurotoxic effects of QA is essential in developing novel therapeutic strategies for AD.