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

Ligand binding domain interface: A tipping point for pharmacological agents binding with GluN1/2A subunit containing NMDA receptors

N-methyl D-aspartate (NMDA) receptors play a crucial role in normal brain function, pathogenesis of neurodegenerative and psychiatric disorders. Functional tetra-heteromeric NMDA receptor contains two obligatory GluN1 subunits and two identical or different non-GluN1 subunits that evolve from six different genes including four GluN2 (A-D) and two GluN3 (A-B) subunits. Since NMDA receptors confer varied physiological properties and spatiotemporal distributions in the brain, pharmacological agents that target NMDA receptors with specific GluN2 subunits have significant potential for therapeutic applications. In the present work, by using electrophysiology techniques, we have studied the role of ligand binding domain (LBD) interactions in determining the effect of well-characterized pharmacological agents including agonists, competitive antagonists, channel blockers and an allosteric modulator. Remarkably, point mutations at the distal end (site-II&III) of GluN1 LBD interface increased memantine potency up to sevenfold when co-expressed with wild type GluN2A receptors but exhibit no effect on Mg²⁺ activity. Conversely, mutations at the proximal end (site-I) of the LBD interface did not affect the memantine but altered Zn²⁺ and Mg²⁺ potency towards opposite directions. These results indicate that GluN1/2A LBD interface interactions play a key role in determining channel function. Further, subtle changes in LBD interaction can be readily translated to the downstream extracellular vestibule of channel pore to adopt a conformation that may affect memantine, Zn²⁺ and Mg²⁺ binding. Further studies on NMDA receptor LBD to transmembrane domain signal propagation mechanisms will help develop GluN2 subunit selective biomolecules that can be used for the treatment of neurological and psychiatric disorders.

Cognitive Enhancer Effects of Low Memantine Doses Are Facilitated by an Alpha7 Nicotinic Acetylcholine Receptor Agonist in Scopolamine-Induced Amnesia in Rats

Alpha7 nicotinic acetylcholine receptors (nAChRs) play an important role in learning and memory and are promising targets for pharmacological cognitive enhancement. Memantine, an approved substance for Alzheimer's disease treatment, is an antagonist of the N-Methyl-D-aspartate receptor (NMDAR) and also acts as an alpha7 nAChR antagonist. Here, we tested the interaction between an alpha7 nAChR agonist (PHA-543613) and memantine. Efficacy of memantine, PHA-543613, and their co-administration were investigated on the spatial working memory of rats using the spontaneous alternation paradigm in T-maze. Scopolamine-induced transient amnesia was used to model cognitive impairment. First, the dose-response relationship was assessed for memantine, and its lowest effective dose was found to be 0.1 mg/kg. Then, co-administration treatments with subeffective doses of the alpha7 nAChR agonist PHA-543613 and different doses of memantine were tested. The co-administration of subeffective drug doses significantly improved memory performance of the rats and reversed scopolamine-induced deficits. Interestingly, a higher than effective (0.3 mg/kg) dose of memantine did not increase performance in monotreatment, only in co-administration with PHA-543613. However, the co-administration of PHA-543613 did not further increase the efficacy of the previously effective monotreatment doses of memantine. Thus, the efficacy of memantine monotreatment and its co-administration with PHA-543613 converged to create a common ceiling effect, with an additive interaction found in the behavioral effects. These results suggest that memantine and PHA-543613 may exert their cognitive enhancer effects on the same target, possibly on the alpha7 nAChRs. Results also suggest possible benefits of a combination therapy with memantine and alpha7 nAChR agonists.

The neuroprotective mechanism of cinnamaldehyde against amyloid-β in neuronal SHSY5Y cell line: The role of N-methyl-D-aspartate, ryanodine, and adenosine receptors and glycogen synthase kinase-3β

OBJECTIVE

Cinnamaldehyde may be responsible for some health benefits of cinnamon such as its neuroprotective effects. We aimed to investigate the cinnamaldehyde neuroprotective effects against amyloid beta (Aβ) in neuronal SHSY5Y cells and evaluate the contribution of N-methyl-D-aspartate (NMDA), ryanodine, and adenosine receptors and glycogen synthase kinase (GSK)-3β, to its neuroprotective effects.

MATERIALS AND METHODS

After seeding the cells in 96-well plates, adenosine (20, 40, 80, and 120 µM), NMDA (20, 40, 80, and 120 µM), and dantrolene (as a ryanodine receptor antagonist; 2, 4, 6, 8, and 16 µM) were added to the medium containing Aβ25-35 and/or cinnamaldehyde. The 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl tetrazolium bromide method was used to assess neurotoxicity and western blot to measure the GSK-3β protein level.

RESULTS

Cinnamaldehyde (15, 20, 23, and 25 μM) significantly reversed Aβ-induced toxicity in SHSY5Y neuronal cells. Adenosine (20, 40, 80 and 120 μM) inhibited the neuroprotective effects of cinnamaldehyde (15 μM). NMDA (20, 40, 80, and 120 μM) reduced cinnamaldehyde (15 and 23 μM) neuroprotective effects against Aβ neurotoxicity. Dantrolene (2, 4, 8, and 16 μM) significantly reduced cinnamaldehyde (15 μM) neuroprotective effects. Cinnamaldehyde (15 and 23 μM) suppressed the Aβ-induced increment of GSK-3β protein level.

CONCLUSION

NMDA and adenosine receptors suppression together with ryanodine receptors stimulation may be relevant to cinnamaldehyde neuroprotective effects against Aβ neurotoxicity. Moreover, the inhibition of GSK-3β may contribute to the cinnamaldehyde neuroprotection.

What are the links between hypoxia and Alzheimer's disease?

Alzheimer's disease (AD) is the most common neurodegenerative disease. Histological characterization of amyloid plaques and neurofibrillary tangles in the brains of AD patients, alongside genetic studies in individuals suffering the familial form of the disease, has fueled the accumulation of the amyloid-β protein as the initial pathological trigger of disease. Association studies have recently showed that cerebral hypoxia, via both genetic and epigenetic mechanisms, increase amyloid-β deposition by altering expression levels of enzymes involved in the production/degradation of the protein. Furthermore, hypoxia has also been linked to neuronal and glial-cell calcium dysregulation through formation of calcium-permeable pores, dysregulated glutamate signaling, and intracellular calcium-store dysfunction. Hypoxia has also been strongly linked to neuroinflammation; however, this relationship to AD has not been thoroughly discussed in the literature. Here, we highlight and organize critical research evidence showing that in both hypoxic and AD brains, there are similarities in terms of 1) the substances mediating/modulating the neuroinflammatory environment and 2) the immune cells that drive the formation of these substances.

Mechanism involved in insulin resistance via accumulation of β-amyloid and neurofibrillary tangles: link between type 2 diabetes and Alzheimer's disease

The pathophysiological link between type 2 diabetes mellitus (T2DM) and Alzheimer's disease (AD) has been suggested in several reports. Few findings suggest that T2DM has strong link in the development process of AD, and the complete mechanism is yet to be revealed. Formation of amyloid plaques (APs) and neurofibrillary tangles (NFTs) are two central hallmarks in the AD. APs are the dense composites of β-amyloid protein (Aβ) which accumulates around the nerve cells. Moreover, NFTs are the twisted fibers containing hyperphosphorylated tau proteins present in certain residues of Aβ that build up inside the brain cells. Certain factors contribute to the aetiogenesis of AD by regulating insulin signaling pathway in the brain and accelerating the formation of neurotoxic Aβ and NFTs via various mechanisms, including GSK3β, JNK, CamKII, CDK5, CK1, MARK4, PLK2, Syk, DYRK1A, PPP, and P70S6K. Progression to AD could be influenced by insulin signaling pathway that is affected due to T2DM. Interestingly, NFTs and APs lead to the impairment of several crucial cascades, such as synaptogenesis, neurotrophy, and apoptosis, which are regulated by insulin, cholesterol, and glucose metabolism. The investigation of the molecular cascades through insulin functions in brain contributes to probe and perceive progressions of diabetes to AD. This review elaborates the molecular insights that would help to further understand the potential mechanisms linking T2DM and AD.

Pharmacological and Electrophysiological Characterization of Novel NMDA Receptor Antagonists

This work reports the synthesis and pharmacological and electrophysiological evaluation of new N-methyl-d-aspartic acid receptor (NMDAR) channel blocking antagonists featuring polycyclic scaffolds. Changes in the chemical structure modulate the potency and voltage dependence of inhibition. Two of the new antagonists display properties comparable to those of memantine, a clinically approved NMDAR antagonist.

Therapeutic strategies and nano-drug delivery applications in management of ageing Alzheimer's disease

In recent years, the incidental rate of neurodegenerative disorders has increased proportionately with the aging population. Alzheimer's disease (AD) is one of the most commonly reported neurodegenerative disorders, and it is estimated to increase by roughly 30% among the aged population. In spite of screening numerous drug candidates against various molecular targets of AD, only a few candidates - such as acetylcholinesterase inhibitors are currently utilized as an effective clinical therapy. However, targeted drug delivery of these drugs to the central nervous system (CNS) exhibits several limitations including meager solubility, low bioavailability, and reduced efficiency due to the impediments of the blood-brain barrier (BBB). Current advances in nanotechnology present opportunities to overcome such limitations in delivering active drug candidates. Nanodrug delivery systems are promising in targeting several therapeutic moieties by easing the penetration of drug molecules across the CNS and improving their bioavailability. Recently, a wide range of nano-carriers, such as polymers, emulsions, lipo-carriers, solid lipid carriers, carbon nanotubes, metal based carriers etc., have been adapted to develop successful therapeutics with sustained release and improved efficacy. Here, we discuss few recently updated nano-drug delivery applications that have been adapted in the field of AD therapeutics, and future prospects on potential molecular targets for nano-drug delivery systems.

Dysregulation of Intracellular Calcium Signaling in Alzheimer's Disease

SIGNIFICANCE

Calcium (Ca²⁺) hypothesis of Alzheimer's disease (AD) gains popularity. It points to new signaling pathways that may underlie AD pathogenesis. Based on calcium hypothesis, novel targets for the development of potential AD therapies are identified. Recent Advances: Recently, the key role of neuronal store-operated calcium entry (nSOCE) in the development of AD has been described. Correct regulation of nSOCE is necessary for the stability of postsynaptic contacts to preserve the memory formation. Molecular identity of hippocampal nSOCE is defined. Perspective nSOCE-activating molecule, prototype of future anti-AD drugs, is described.

CRITICAL ISSUES

Endoplasmic reticulum Ca²⁺ overload happens in many but not in all AD models. The nSOCE targeting therapy described in this review may not be universally applicable.

FUTURE DIRECTIONS

There is a need to determine whether AD is a syndrome with one critical signaling pathway that initiates pathology, or it is a disorder with many different signaling pathways that are disrupted simultaneously or one after each other. It is necessary to validate applicability of nSOCE-activating therapy for the development of anti-AD medication. There is an experimental correlation between downregulated nSOCE and disrupted postsynaptic contacts in AD mouse models. Signaling mechanisms downstream of nSOCE which are responsible for the regulation of stability of postsynaptic contacts have to be discovered. That will bring new targets for the development of AD-preventing therapies. Antioxid. Redox Signal. 29, 1176-1188.

Multiple Rising Doses of Oral BI 425809, a GlyT1 Inhibitor, in Young and Elderly Healthy Volunteers: A Randomised, Double-Blind, Phase I Study Investigating Safety and Pharmacokinetics

Background and Objective

Schizophrenia and Alzheimer’s disease are characterised by abnormalities in glutamatergic pathways related to N-methyl-d-aspartate receptor hypofunction. Glycine is an N-methyl-d-aspartate receptor co-agonist; inhibition of glycine transporter 1 may improve N-methyl-d-aspartate receptor function. This phase I, randomised, two-part study evaluated the safety, tolerability and pharmacokinetic profile of BI 425809, a novel glycine transporter 1 inhibitor, in healthy male and female volunteers.

Methods

Part 1 evaluated BI 425809 10, 25, 50 or 75 mg once daily or 75 mg twice daily in young subjects, and 25 mg or 50 mg once daily in elderly subjects. Each dose group comprised 12 subjects who received BI 425809 (n = 9) or placebo (n = 3) for 14 days (day 1: single dose; days 4–14: multiple dosing). Part 2 compared pharmacokinetic profiles in 12 subjects who received a single dose of BI 425809 25 mg in the morning and evening.

Results

Pharmacokinetic profiles were similarly shaped for all dose groups. Median time to maximum plasma concentration was 3.0–4.5 h with steady state being reached between days 6 and 10. Pharmacokinetic parameters demonstrated dose linearity at the predicted therapeutic exposure range of BI 425809 ≤ 25 mg once daily, but increased less than dose proportionally for ≥ 50 mg once daily. All reported adverse events were of mild-to-moderate intensity, 51/84 (61%; part 1) subjects had one or more treatment-related adverse event, no serious adverse events occurred and no dose dependency was observed.

Conclusions

Pharmacokinetic properties support both morning and evening dosing. BI 425809 was generally well tolerated at all tested doses.

Clinicaltrials.gov identifier

NCT02337283.

Electronic supplementary material

The online version of this article (10.1007/s40261-018-0660-2) contains supplementary material, which is available to authorized users.

Current Therapeutic Molecules and Targets in Neurodegenerative Diseases Based on in silico Drug Design

Abstract: Background

As the number of elderly persons increases, neurodegenerative diseases are becoming ubiquitous. There is currently a great need for knowledge concerning management of old-age neurodegenerative diseases; the most important of which are: Alzheimer’s disease, Parkinson’s disease, Amyotrophic Lateral Sclerosis, and Huntington’s disease.

Objective

To summarize the potential of computationally predicted molecules and targets against neurodegenerative diseases.

Method

Review of literature published since 1997 against neurodegenerative diseases, utilizing as keywords: in silico, Alzheimer’s disease, Parkinson’s disease, Amyotrophic Lateral Sclerosis ALS, and Huntington’s disease was conducted.

Results and Conclusion

Due to the costs associated with experimentation and current ethical law, performing experiments directly on living organisms has become much more difficult. In this scenario, in silico techniques have been successful and have become powerful tools in the search to cure disease. Researchers use the Computer Aided Drug Design pipeline which: 1) generates 3-dimensional structures of target proteins through homology modeling 2) achieves stabilization through molecular dynamics simulation, and 3) exploits molecular docking through large compound libraries. Next generation sequencing is continually producing enormous amounts of raw sequence data while neuroimaging is producing a multitude of raw image data. To solve such pressing problems, these new tools and algorithms are required. This review elaborates precise in silico tools and techniques for drug targets, active molecules, and molecular docking studies, together with future prospects and challenges concerning possible breakthroughs in Alzheimer’s, Parkinson’s, Amyotrophic Lateral Sclerosis, and Huntington’s disease.

Exploring the potential of marine microbes in clinical management of Alzheimer's disease: A road map for bioprospecting and identifying promising isolates

Pervasiveness of Alzheimer's disease (AD) across the globe is on rise, devitalizing the essential brain functions of the afflicted individual. Multiple neurological pathways viz., cholinergic, amyloidogenic and tau protein pathways underlying the disease and interdependence make it more complex to develop effective treatment strategies. Existing drug treatments for Alzheimer's disease majorly belong to the class of cholinergic inhibitors which improve the behavioral symptoms. But there are no drugs that could arrest the disease progression. Inhibition of beta secretase enzyme could prevent the deposition of amyloid plaques in the neurons, thereby arresting the disease progression. Search for novel drugs to treat the underlying pathogenesis of the disease is pivotal in this day and age. The source of most active lead molecules discovered recently is from the nature. Marine ecosystem provides a plethora of pharmacologically lead molecules from various living organisms inhabiting the sea. Among all, marine microbes are the most under-explored and indispensable source of many bioactive metabolites. Studies have been reported on potent metabolites from marine microbes which could inhibit the key enzymes involved in the AD pathogenesis. The advancement in microbial bioprospecting and molecular biology techniques have eased the process of cultivation and identification of microbes, isolation of novel bioactive metabolites of clinical use. Exploring such marine natural resources for pharmacological lead molecules could give a breakthrough in the drug discovery domain for treating AD such debilitating diseases. In this review, a comprehensive account of bioprospecting methods and reports of marine microbial isolates are discussed.

Current Perspectives and Mechanisms of Relationship between Intestinal Microbiota Dysfunction and Dementia: A Review

BACKGROUND

Accumulating data suggest a crucial role of the intestinal microbiota in the development and progression of neurodegenerative diseases. More recently, emerging reports have revealed an association between intestinal microbiota dysfunctions and dementia, a debilitating multifactorial disorder, characterized by progressive deterioration of cognition and behavior that interferes with the social and professional life of the sufferer. However, the mechanisms of this association are not fully understood.

SUMMARY

In this review, I discuss recent data that suggest mechanisms of cross-talk between intestinal microbiota dysfunction and the brain that underlie the development of dementia. Potential therapeutic options for dementia are also discussed. The pleiotropic signaling of the metabolic products of the intestinal microbiota together with their specific roles in the maintenance of both the intestinal and blood-brain barriers as well as regulation of local, distant, and circulating immunocytes, and enteric, visceral, and central neural functions are integral to a healthy gut and brain.

KEY MESSAGES

Research investigating the effect of intestinal microbiota dysfunctions on brain health should focus on multiple interrelated systems involving local and central neuroendocrine, immunocyte, and neural signaling of microbial products and transmitters and neurohumoral cells that not only maintain intestinal, but also blood brain-barrier integrity. The change in intestinal microbiome/dysbiome repertoire is crucial to the development of dementia.

Hippocampal amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid GluA1 (AMPA GluA1) receptor subunit involves in learning and memory improvement following treatment with Centella asiatica extract in adolescent rats

INTRODUCTION

Centella asiatica is an herbal plant that contains phytochemicals that are widely believed to have positive effects on cognitive function. The adolescent stage is a critical development period for the maturation of brain processes that encompass changes in physical and psychological systems. However, the effect of C. asiatica has not been extensively studied in adolescents. The aim of this study was therefore to investigate the effects of a C. asiatica extract on the enhancement of learning and memory in adolescent rats.

METHODS

The locomotor activity, learning, and memory were assessed by using open field test and water T-maze test. This study also examined changes in neuronal cell morphology using cresyl violet and apoptosis staining. We also performed immunohistochemical study to analyse the expression of the glutamate AMPA receptor (α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid) GluA1 subunit and the GABA receptor (γ-Aminobutyric Acid) subtype GABA_A α1 subunit in the hippocampus of the same animals.

RESULTS

We found no significant changes in locomotor activity (p > 0.05). The water T-maze data showed that 30 mg/kg dose significantly (p < 0.05) improved learning, memory, and the memory consolidation phase but had no effect on reversal learning (p > 0.05). Histological data revealed no neuronal morphological changes. Immunohistochemical analysis revealed increased expression of the AMPA GluA1 receptor subunit but there was no effect on GABA_A receptor α1 subunit expression in the CA1 and CA2 subregions of the hippocampus.

CONCLUSIONS

The C. asiatica extract therefore improved hippocampus-dependent spatial learning and memory in a dose-dependent manner in rats through the GluA1-containing AMPA receptor in the CA1 and CA2 sub regions of the hippocampus.

The NMDA receptor antagonist Radiprodil reverses the synaptotoxic effects of different amyloid-beta (Aβ) species on long-term potentiation (LTP)

Aβ_1-42 is well accepted to be a primary early pathogenic agent in Alzheimer's disease (AD). However, other amyloid peptides are now gaining considerable attention as potential key participants in AD due to their proposed higher neuronal toxicity. Impairment of the glutamatergic system is also widely accepted to be associated with pathomechanisms underlying AD. There is ample evidence that Aβ_1-42 affects GLUN2B subunit containing N-methyl-D-aspartate receptor function and abolishes the induction of long term potentiation (LTP). In this study we show that different β-amyloid species, 1-42 Aβ_1-42 and 1-40 (Aβ_1-40) as well as post-translationally modified forms such as pyroglutamate-modified amyloid-(AβpE3) and nitrated Aβ (3NTyr10-Aβ), when applied for 90 min to murine hippocampal slices, concentration-dependently prevented the development of CA1-LTP after tetanic stimulation of the Schaffer collaterals with IC₅₀s of 2, 9, 2 and 35 nM, respectively whilst having no effect on baseline AMPA receptor mediated fEPSPs. Aβ_1-43 had no effect. Interestingly, the combination of all Aβ species did not result in any synergistic or additive inhibitory effect on LTP - the calculated pooled Aβ species IC₅₀ was 20 nM. A low concentration (10 nM) of the GLUN2B receptor antagonist Radiprodil restored LTP in the presence of Aβ_1-42, 3NTyr10-Aβ, Aβ_1-40, but not AβpE3. In contrast to AMPA receptor mediated fEPSPs, all different β-amyloid species tested at 50 nM supressed baseline NMDA-EPSC amplitudes. Similarly, all different Aβ species tested decreased spine density. As with LTP, Radiprodil (10 nM) reversed the synaptic toxicity of Aβ species but not that of AβpE3. These data do not support the enhanced toxic actions reported for some Aβ species such as AβpE3, nor synergistic toxicity of the combination of different Aβ species. However, whilst in our hands AβpE_3-42 was actually less toxic than Aβ_1-42, its effects were not reversed by Radiprodil indicating that the target receptors/subunits mediating such synaptotoxicity may differ between the different Aβ species tested.

Dysregulated Neurotransmission induces Trans-synaptic degeneration in reconstructed Neuronal Networks

Increasing evidence suggests that pathological hallmarks of chronic degenerative syndromes progressively spread among interconnected brain areas in a disease-specific stereotyped pattern. Functional brain imaging from patients affected by various neurological syndromes such as traumatic brain injury and stroke indicates that the progression of such diseases follows functional connections, rather than simply spreading to structurally adjacent areas. Indeed, initial damage to a given brain area was shown to disrupt the communication in related brain networks. Using cortico-striatal neuronal networks reconstructed in a microfluidic environment, we investigated the role of glutamate signaling in activity-dependent neuronal survival and trans-synaptic degeneration processes. Using a variety of neuronal insults applied on cortical neurons, we demonstrate that acute injuries such as axonal trauma, focal ischemia, or alteration of neuronal rhythms, lead to glutamate-dependent striatal neuron dysfunction. Interestingly, focal pro-oxidant insults or chronic alteration of spontaneous cortical rhythms provoked dysfunction of distant striatal neurons through abnormal glutamate GluN2B-NMDAR-mediated signaling at cortico-striatal synapses. These results indicate that focal alteration of cortical functions can initiate spreading of dysfunction along neuronal pathways in the brain, reminiscent of diaschisis-like processes.

Ceftriaxone Treatment for Neuronal Deficits: A Histological and MEMRI Study in a Rat Model of Dementia with Lewy Bodies

Dementia with Lewy bodies (DLB) is characterized by neuronal deficits and α-synuclein inclusions in the brain. Ceftriaxone (CEF), a β-lactam antibiotic, has been suggested as a therapeutic agent in several neurodegenerative disorders for its abilities to counteract glutamate-mediated toxicity and to block α-synuclein polymerization. By using manganese-enhanced magnetic resonance imaging (MEMRI) and immunohistochemistry, we measured the effects of CEF on neuronal activity and α-synuclein accumulation in the brain in a DLB rat model. The data showed that CEF corrected neuronal density and activity in the hippocampal CA1 area, suppressed hyperactivity in the subthalamic nucleus, and reduced α-synuclein accumulation, indicating that CEF is a potential agent in the treatment of DLB.

Calcium signaling in Alzheimer's disease & therapies

Alzheimer's disease (AD) is the most common type of dementia and is characterized by the accumulation of amyloid (Aβ) plaques and neurofibrillary tangles in the brain. Much attention has been given to develop AD treatments based on the amyloid cascade hypothesis; however, none of these drugs had good efficacy at improving cognitive functions in AD patients suggesting that Aβ might not be the disease origin. Thus, there are urgent needs for the development of new therapies that target on the proximal cause of AD. Cellular calcium (Ca²⁺) signals regulate important facets of neuronal physiology. An increasing body of evidence suggests that age-related dysregulation of neuronal Ca²⁺ homeostasis may play a proximal role in the pathogenesis of AD as disrupted Ca²⁺ could induce synaptic deficits and promote the accumulation of Aβ plaques and neurofibrillary tangles. Given that Ca²⁺ disruption is ubiquitously involved in all AD pathologies, it is likely that using chemical agents or small molecules specific to Ca²⁺ channels or handling proteins on the plasma membrane and membranes of intracellular organelles to correct neuronal Ca²⁺ dysregulation could open up a new approach to AD prevention and treatment. This review summarizes current knowledge on the molecular mechanisms linking Ca²⁺ dysregulation with AD pathologies and discusses the possibility of correcting neuronal Ca²⁺ disruption as a therapeutic approach for AD.

First in human evaluation of [18F]PK-209, a PET ligand for the ion channel binding site of NMDA receptors

Background

Efforts to develop suitable positron emission tomography (PET) tracers for the ion channel site of human N-methyl-d-aspartate (NMDA) receptors have had limited success. [¹⁸F]PK-209 is a GMOM derivative that binds to the intrachannel phencyclidine site with high affinity and selectivity. Primate PET studies have shown that the volume of distribution in the brain was reduced by administration of the NMDA receptor antagonist MK-801, consistent with substantial specific binding. The purpose of the present study was to evaluate [¹⁸F]PK-209 in 10 healthy humans by assessing test–retest reproducibility and binding specificity following intravenous S-ketamine administration (0.5 mg ∙ kg⁻¹). Five healthy subjects underwent a test–retest protocol, and five others a baseline-ketamine protocol. In all cases dynamic, 120-min PET scans were acquired together with metabolite-corrected arterial plasma input functions. Additional input functions were tested based on within-subject and population-average parent fractions.

Results

Best fits of the brain time-activity curves were obtained using an irreversible two-tissue compartment model with additional blood volume parameter. Mean test–retest variability of the net rate of influx K_i varied between 7 and 24% depending on the input function. There were no consistent changes in [¹⁸F]PK-209 PET parameters following ketamine administration, which may be a consequence of the complex endogenous ligand processes that affect channel gating.

Conclusions

The molecular interaction between [¹⁸F]PK-209 and the binding site within the NMDA receptor ion channel is insufficiently reproducible and specific to be a reliable imaging agent for its quantification.

Trial registration

EudraCT 2014-001735-36. Registered 28 April 2014

Curcumin derivatives and Aβ-fibrillar aggregates: An interactions' study for diagnostic/therapeutic purposes in neurodegenerative diseases

Several neurodegenerative diseases, like Alzheimer's (AD), are characterized by amyloid fibrillar deposition of misfolded proteins, and this feature can be exploited for both diagnosis and therapy design. In this paper, structural modifications of curcumin scaffold were examined in order to improve its bioavailability and stability in physiological conditions, as well as its ability to interfere with β-amyloid fibrils and aggregates. The acid-base behaviour of curcumin derivatives, their pharmacokinetic stability in physiological conditions, and in vitro ability to interfere with Aβ fibrils at different incubation time were investigated. The mechanisms governing these phenomena have been studied at atomic level by means of molecular docking and dynamic simulations. Finally, biological activity of selected curcuminoids has been investigated in vitro to evaluate their safety and efficiency in oxidative stress protection on hippocampal HT-22 mouse cells. Two aromatic rings, π-conjugated structure and H-donor/acceptor substituents on the aromatic rings showed to be the sine qua non structural features to provide interaction and disaggregation activity even at very low incubation time (2h). Computational simulations proved that upon binding the ligands modify the conformational dynamics and/or interact with the amyloidogenic region of the protofibril facilitating disaggregation. Significantly, in vitro results on hippocampal cells pointed out protection against glutamate toxicity and safety when administered at low concentrations (1 μM). On the overall, in view of its higher stability in physiological conditions with respect to curcumin, of his rapid binding to fibrillar aggregates and strong depolymerizing activity, phtalimmide derivative K2F21 appeared a good candidate for both AD diagnostic and therapeutic purposes.

Neurodegenerative diseases: model organisms, pathology and autophagy

A proteostasis view of neurodegeneration (ND) identifies protein aggregation as a leading causative reason for damage seen at the cellular and organ levels. While investigative therapies that aim at dissolving aggregates have failed, and the promises of silencing expression of ND associated pathogenic proteins or the deployment of engineered induced pluripotent stem cells (iPSCs) are still in the horizon, emerging literature suggests degrading aggregates through autophagy-related mechanisms hold the current potential for a possible cure. Macroautophagy (hereafter autophagy) is an intracellular degradative pathway where superfluous or unwanted cellular cargoes (such as peroxisomes, mitochondria, ribosomes, intracellular bacteria and misfolded protein aggregates) are wrapped in double membrane vesicles called autophagosomes that eventually fuses with lysosomes for their degradation. The selective branch of autophagy that deals with identification, capture and degradation of protein aggregates is called aggrephagy. Here, we cover the workings of aggrephagy detailing its selectivity towards aggregates. The diverse cellular adaptors that bridge the aggregates with the core autophagy machinery in terms of autophagosome formation are discussed. In ND, essential protein quality control mechanisms fail as the constituent components also find themselves trapped in the aggregates. Thus, although cellular aggrephagy has the potential to be upregulated, its dysfunction further aggravates the pathogenesis. This phenomenonwhen combined with the fact that neurons can neither dilute out the aggregates by cell division nor the dead neurons can be replaced due to low neurogenesis, makes a compelling case for aggrephagy pathway as a potential therapeutic option.

Inflammatory and oxidative mechanisms potentiate bifenthrin-induced neurological alterations and anxiety-like behavior in adult rats

Bifenthrin (BF) is a synthetic pyrethroid pesticide widely used in several countries to manage insect pests on diverse agricultural crops. Growing evidence indicates that BF exposure is associated with an increased risk of developing neurodegenerative disorders. However, the mechanisms by which BF induces neurological and anxiety alterations in the frontal cortex and striatum are not well known. The present in vivo study was carried out to determine whether reactive oxygen species (ROS)-mediated oxidative stress (OS) and neuroinflammation are involved in such alterations. Thirty-six Wistar rats were thus randomly divided into three groups and were orally administered with BF (0.6 and 2.1 mg/kg body weight, respectively) or the vehicle (corn oil), on a daily basis for 60 days. Results revealed that BF exposure in rats enhanced anxiety-like behavior after 60 days of treatment, as assessed with the elevated plus-maze test by decreases in the percentage of time spent in open arms and frequency of entries into these arms. BF-treated rats also exhibited increased oxidation of lipids and carbonylated proteins in the frontal cortex and striatum, and decreased glutathione levels and antioxidant enzyme activities including superoxide dismutase, catalase and glutathione peroxidase. Treatment with BF also increased protein synthesis and mRNA expression of the inflammatory mediators cyclooxygenase-2 (COX-2), microsomal prostaglandin synthase-1 (mPGES-1) and nuclear factor-kappaBp65 (NF-kBp65), as well as the production of tumor necrosis factor-α (TNF-α) and ROS. Moreover, BF exposure significantly decreased protein synthesis and mRNA expression of nuclear factor erythroid-2 (Nrf2) and acetylcholinesterase (AChE), as well as gene expression of muscarinic-cholinergic receptors (mAchR) and choline acetyltransferase (ChAT) in the frontal cortex and striatum. These data suggest that BF induced neurological alterations in the frontal cortex and striatum of rats, and that this may be associated with neuroinflammation and oxidative stress via the activation of Nrf2/NF-kBp65 pathways, which might promote anxiety-like behavior.

Neurotransmitter deficits from frontotemporal lobar degeneration

Frontotemporal lobar degeneration causes a spectrum of complex degenerative disorders including frontotemporal dementia, progressive supranuclear palsy and corticobasal syndrome, each of which is associated with changes in the principal neurotransmitter systems. We review the evidence for these neurochemical changes and propose that they contribute to symptomatology of frontotemporal lobar degeneration, over and above neuronal loss and atrophy. Despite the development of disease-modifying therapies, aiming to slow neuropathological progression, it remains important to advance symptomatic treatments to reduce the disease burden and improve patients' and carers' quality of life. We propose that targeting the selective deficiencies in neurotransmitter systems, including dopamine, noradrenaline, serotonin, acetylcholine, glutamate and gamma-aminobutyric acid is an important strategy towards this goal. We summarize the current evidence-base for pharmacological treatments and suggest strategies to improve the development of new, effective pharmacological treatments.

Analytical Strategy to Prioritize Alzheimer's Disease Candidate Genes in Gene Regulatory Networks Using Public Expression Data

Alzheimer’s disease (AD) progressively destroys cognitive abilities in the aging population with tremendous effects on memory. Despite recent progress in understanding the underlying mechanisms, high drug attrition rates have put a question mark behind our knowledge about its etiology. Re-evaluation of past studies could help us to elucidate molecular-level details of this disease. Several methods to infer such networks exist, but most of them do not elaborate on context specificity and completeness of the generated networks, missing out on lesser-known candidates. In this study, we present a novel strategy that corroborates common mechanistic patterns across large scale AD gene expression studies and further prioritizes potential biomarker candidates. To infer gene regulatory networks (GRNs), we applied an optimized version of the BC3Net algorithm, named BC3Net10, capable of deriving robust and coherent patterns. In principle, this approach initially leverages the power of literature knowledge to extract AD specific genes for generating viable networks. Our findings suggest that AD GRNs show significant enrichment for key signaling mechanisms involved in neurotransmission. Among the prioritized genes, well-known AD genes were prominent in synaptic transmission, implicated in cognitive deficits. Moreover, less intensive studied AD candidates (STX2, HLA-F, HLA-C, RAB11FIP4, ARAP3, AP2A2, ATP2B4, ITPR2, and ATP2A3) are also involved in neurotransmission, providing new insights into the underlying mechanism. To our knowledge, this is the first study to generate knowledge-instructed GRNs that demonstrates an effective way of combining literature-based knowledge and data-driven analysis to identify lesser known candidates embedded in stable and robust functional patterns across disparate datasets.

Diabetes and Alzheimer's Disease: Can Tea Phytochemicals Play a Role in Prevention?

Dementia and diabetes mellitus are prevalent disorders in the elderly population. While recognized as two distinct diseases, diabetes has more recently recognized as a significant contributor to risk for developing dementia, and some studies make reference to type 3 diabetes, a condition resulting from insulin resistance in the brain. Alzheimer's disease, the most common form of dementia, and diabetes, interestingly, share underlying pathological processes, commonality in risk factors, and, importantly, pathways for intervention. Tea has been suggested to possess potent antioxidant properties. It is rich in phytochemicals including, flavonoids, tannins, caffeine, polyphenols, boheic acid, theophylline, theobromine, anthocyanins, gallic acid, and finally epigallocatechin-3-gallate, which is considered to be the most potent active ingredient. Flavonoid phytochemicals, known as catechins, within tea offer potential benefits for reducing the risk of diabetes and Alzheimer's disease by targeting common risk factors, including obesity, hyperlipidemia, hypertension, cardiovascular disease, and stroke. Studies also show that catechins may prevent the formation of amyloid-β plaques and enhance cognitive functions, and thus may be useful in treating patients who have Alzheimer's disease or dementia. Furthermore, other phytochemicals found within tea offer important antioxidant properties along with innate properties capable of modulating intracellular neuronal signal transduction pathways and mitochondrial function.

Recent Progress in the Pharmacotherapy of Alzheimer's Disease

Alzheimer's disease is the most common major neurocognitive disorder with substantial social and economic impacts. This article is an update on current pharmacotherapy, advancements in biomarker use, and drugs in the pipeline for this disease. To date, no new drug has qualified to be added to the current therapeutic arsenal comprising cholinesterase inhibitors and the NMDA receptor antagonist memantine. Drugs in the pipeline include symptomatic therapies that are neurotransmitter-based, but mostly disease-modifying therapies. The latter have yielded disappointing results by focusing mainly on the two pathophysiological hallmarks of Alzheimer's disease: Aβ amyloid deposits and tau protein aggregates forming neurofibrillary tangles. These unsuccessful trials may have resulted from studying these drugs 'too late' relative to Alzheimer's disease onset, in addition to focusing only on the amyloid cascade. In fact, Alzheimer's disease is a complex multifactorial disease. Combining different biomarkers might enhance our ability to identify those patients most at risk of developing the disease, and better predict their conversion rates. Furthermore, adopting an integrative treatment approach by targeting additional pathophysiological pathways in Alzheimer's disease such as inflammation and oxidative stress could be the key to better outcomes in Alzheimer's disease pharmacotherapy research.

Neuronal pentraxin 1: A synaptic-derived plasma biomarker in Alzheimer's disease

Synaptic neurodegeneration is thought to be an early event initiated by soluble β-amyloid (Aβ) aggregates that closely correlates with cognitive decline in Alzheimer disease (AD). Apolipoprotein ε4 (APOE4) is the most common genetic risk factor for both familial AD (FAD) and sporadic AD; it accelerates Aβ aggregation and selectively impairs glutamate receptor function and synaptic plasticity. However, its molecular mechanisms remain elusive and these synaptic deficits are difficult to monitor. AD- and APOE4-dependent plasma biomarkers have been proposed, but synapse-related plasma biomarkers are lacking. We evaluated neuronal pentraxin 1 (NP1), a potential CNS-derived plasma biomarker of excitatory synaptic pathology. NP1 is preferentially expressed in brain and involved in glutamate receptor internalization. NP1 is secreted presynaptically induced by Aβ oligomers, and implicated in excitatory synaptic and mitochondrial deficits. Levels of NP1 and its fragments were increased in a correlated fashion in both brain and plasma of 7-8 month-old E4FAD mice relative to E3FAD mice. NP1 was also found in exosome preparations and reduced by dietary DHA supplementation. Plasma NP1 was higher in E4FAD+ (APOE4^+/+/FAD^+/-) relative to E4FAD- (non-carrier; APOE4^+/+/FAD^-/-) mice, suggesting NP1 is modulated by Aβ expression. Finally, relative to normal elderly, plasma NP1 was also elevated in patients with mild cognitive impairment (MCI) and elevated further in the subset who progressed to early-stage AD. In those patients, there was a trend towards increased NP1 levels in APOE4 carriers relative to non-carriers. These findings indicate that NP1 may represent a potential synapse-derived plasma biomarker relevant to early alterations in excitatory synapses in MCI and early-stage AD.

Excitotoxicity in the pathogenesis of neurological and psychiatric disorders: Therapeutic implications

Neurological and psychiatric disorders are leading contributors to the global disease burden, having a serious impact on the quality of life of both patients and their relatives. Although the molecular events underlying these heterogeneous diseases remain poorly understood, some studies have raised the idea of common mechanisms involved. In excitotoxicity, there is an excessive activation of glutamate receptors by excitatory amino acids, leading to neuronal damage. Thus, the excessive release of glutamate can lead to a dysregulation of Ca²⁺ homeostasis, triggering the production of free radicals and oxidative stress, mitochondrial dysfunction and eventually cell death. Although there is a consensus in considering excitotoxicity as a hallmark in most neurodegenerative diseases, increasing evidence points to the relevant role of this pathological mechanism in other illnesses affecting the central nervous system. Consequently, antagonists of glutamate receptors are used in current treatments or in clinical trials in both neurological and psychiatric disorders. However, drugs modulating other aspects of the excitotoxic mechanism could be more beneficial. This review discusses how excitotoxicity is involved in the pathogenesis of different neurological and psychiatric disorders and the promising strategies targeting the excitotoxic insult.

The Memory-Enhancing Effects of Liquiritigenin by Activation of NMDA Receptors and the CREB Signaling Pathway in Mice

Liquiritigenin (LQ) is a flavonoid that can be isolated from Glycyrrhiza radix. It is frequently used as a tranditional oriental medicine herbal treatment for swelling and injury and for detoxification. However, the effects of LQ on cognitive function have not been fully explored. In this study, we evaluated the memory-enhancing effects of LQ and the underlying mechanisms with a focus on the N-methyl-D-aspartic acid receptor (NMDAR) in mice. Learning and memory ability were evaluated with the Y-maze and passive avoidance tests following administration of LQ. In addition, the expression of NMDAR subunits 1, 2A, and 2B; postsynaptic density-95 (PSD-95); phosphorylation of Ca²⁺/calmodulin-dependent protein kinase II (CaMKII); phosphorylation of extracellular signal-regulated kinase 1/2 (ERK 1/2); and phosphorylation of cAMP response element binding (CREB) proteins were examined by Western blot. In vivo, we found that treatment with LQ significantly improved memory performance in both behavioral tests. In vitro, LQ significantly increased NMDARs in the hippocampus. Furthermore, LQ significantly increased PSD-95 expression as well as CaMKII, ERK, and CREB phosphorylation in the hippocampus. Taken together, our results suggest that LQ has cognition enhancing activities and that these effects are mediated, in part, by activation of the NMDAR and CREB signaling pathways.

Stress-Induced Synaptic Dysfunction and Neurotransmitter Release in Alzheimer's Disease: Can Neurotransmitters and Neuromodulators be Potential Therapeutic Targets?

The communication between neurons at synaptic junctions is an intriguing process that monitors the transmission of various electro-chemical signals in the central nervous system. Albeit any aberration in the mechanisms associated with transmission of these signals leads to loss of synaptic contacts in both the neocortex and hippocampus thereby causing insidious cognitive decline and memory dysfunction. Compelling evidence suggests that soluble amyloid-β (Aβ) and hyperphosphorylated tau serve as toxins in the dysfunction of synaptic plasticity and aberrant neurotransmitter (NT) release at synapses consequently causing a cognitive decline in Alzheimer's disease (AD). Further, an imbalance between excitatory and inhibitory neurotransmission systems induced by impaired redox signaling and altered mitochondrial integrity is also amenable for such abnormalities. Defective NT release at the synaptic junction causes several detrimental effects associated with altered activity of synaptic proteins, transcription factors, Ca2+ homeostasis, and other molecules critical for neuronal plasticity. These detrimental effects further disrupt the normal homeostasis of neuronal cells and thereby causing synaptic loss. Moreover, the precise mechanistic role played by impaired NTs and neuromodulators (NMs) and altered redox signaling in synaptic dysfunction remains mysterious, and their possible interlink still needs to be investigated. Therefore, this review elucidates the intricate role played by both defective NTs/NMs and altered redox signaling in synaptopathy. Further, the involvement of numerous pharmacological approaches to compensate neurotransmission imbalance has also been discussed, which may be considered as a potential therapeutic approach in synaptopathy associated with AD.

Toxoplasma gondii alters NMDAR signaling and induces signs of Alzheimer's disease in wild-type, C57BL/6 mice

BACKGROUND

Alzheimer's disease (AD) is a progressive neurodegenerative disease associated with cognitive decline and complete loss of basic functions. The ubiquitous apicomplexan parasite Toxoplasma gondii (T. gondii) infects up to one third of the world's population and is implicated in AD.

METHODS

We infected C57BL/6 wild-type male and female mice with 10 T. gondii ME49 cysts and assessed whether infection led to behavioral and anatomical effects using immunohistochemistry, immunofluorescence, Western blotting, cell culture assays, as well as an array of mouse behavior tests.

RESULTS

We show that T. gondii infection induced two major hallmarks of AD in the brains of C57BL/6 male and female mice: beta-amyloid (Aβ) immunoreactivity and hyperphosphorylated Tau. Infected mice showed significant neuronal death, loss of N-methyl-D-aspartate receptor (NMDAR) expression, and loss of olfactory sensory neurons. T. gondii infection also caused anxiety-like behavior, altered recognition of social novelty, altered spatial memory, and reduced olfactory sensitivity. This last finding was exclusive to male mice, as infected females showed intact olfactory sensitivity.

CONCLUSIONS

These results demonstrate that T. gondii can induce advanced signs of AD in wild-type mice and that it may induce AD in some individuals with underlying health problems.

An Improved Drugs Screening System Reveals that Baicalein Ameliorates the Aβ/AMPA/NMDA-Induced Depolarization of Neurons

The presence of amyloid-β (Aβ) plaque and tau protein hyperphosphorylation in brain tissue is the pathological hallmark of Alzheimer's disease (AD). At least some Aβ neurotoxicity is caused by the presence of excess glutamate that has been induced by Aβ accumulation. Memantine is currently the only NMDA receptor inhibitor approved for treating moderate-to-severe AD patients. We utilized primary cortical neurons and DiBAC4(3), a slow-response voltage sensitive fluorescence dye, to create a novel system for screening herbal medicines that allows the identification of pure compounds able to ameliorate Aβ-induced abnormal depolarization. The intensity of DiBAC4(3) fluorescence was increased when primary neurons were stimulated by Aβ; furthermore, pre-treatment with memantine abolished this change. Using this system, we identified six crude extracts made from herbal medicines that effectively alleviated this Aβ-induced abnormal depolarization. Among these herbal medicines, one pure compound, baicalein, which was known to be present in Scutellaria baricalensis and is known to improve memory using an AD mouse model, was identified by our assay. However, the compound's molecular mechanism remained unknown. We found that baicalein, in addition to inhibiting Aβ-induced depolarization, possibly functions as an antagonist of AMPA and NMDA receptors. Taken together, we have established a system/platform to identify herbal medicines that ameliorate Aβ-induced depolarization of neurons. Equally important, baicalein is a candidate drug with great potential for the treatment of AD patients.

Potential and Challenges for the Clinical Use of d-Serine As a Cognitive Enhancer

After 25 years of its discovery in the rat brain, d-serine is a recognized modulator of synaptic plasticity and cognitive processes through its actions on the NMDA-glutamate receptor. Importantly, cognitive impairment is a core feature of conditions, such as schizophrenia, Alzheimer's disease, depression, and aging, and is associated to disturbances in NMDA-glutamate receptors. The d-serine pathway has been associated with cognitive deficits and these conditions, and, for this reason, d-serine signaling is subject of intense research to probe its role in aiding diagnosis and therapy. Nevertheless, this has not resulted in new therapies being incorporated into clinical practice. Therefore, in this review we will address many questions that need to be solved by future studies, regarding d-serine pharmacokinetics, possible side effects, other strategies to modulate its levels, and combination with other therapies to increase its efficacy.

Activated forms of astrocytes with higher GLT-1 expression are associated with cognitive normal subjects with Alzheimer pathology in human brain

Although the cognitive impairment in Alzheimer's disease (AD) is believed to be caused by amyloid-β (Aβ) plaques and neurofibrillary tangles (NFTs), several postmortem studies have reported cognitive normal subjects with AD brain pathology. As the mechanism underlying these discrepancies has not been clarified, we focused the neuroprotective role of astrocytes. After examining 47 donated brains, we classified brains into 3 groups, no AD pathology with no dementia (N-N), AD pathology with no dementia (AD-N), and AD pathology with dementia (AD-D), which represented 41%, 21%, and 38% of brains, respectively. No differences were found in the accumulation of Aβ plaques or NFTs in the entorhinal cortex (EC) between AD-N and AD-D. Number of neurons and synaptic density were increased in AD-N compared to those in AD-D. The astrocytes in AD-N possessed longer or thicker processes, while those in AD-D possessed shorter or thinner processes in layer I/II of the EC. Astrocytes in all layers of the EC in AD-N showed enhanced GLT-1 expression in comparison to those in AD-D. Therefore these activated forms of astrocytes with increased GLT-1 expression may exert beneficial roles in preserving cognitive function, even in the presence of Aβ and NFTs.

The Level of NMDA Receptor in the Membrane Modulates Amyloid-β Association and Perforation

Alzheimer's disease is a neurodegenerative disorder that affects mostly the elderly. The main histopathological markers are the senile plaques formed by amyloid-β peptide (Aβ) aggregates that can perforate the plasma membrane of cells, increasing the intracellular calcium levels and releasing synaptic vesicles that finally lead to a delayed synaptic failure. Several membrane proteins and lipids interact with Aβ affecting its toxicity in neurons. Here, we focus on NMDA receptors (NMDARs) as proteins that could be modulating the association and neurotoxic perforation induced by Aβ on the plasma membrane. In fact, our results showed that decreasing NMDARs, using enzymatic or siRNA approaches, increased the association of Aβ to the neurons. Furthermore, overexpression of NMDARs also resulted in an enhanced association between NMDA and Aβ. Functionally, the reduction in membrane NMDARs augmented the process of membrane perforation. On the other hand, overexpressing NMDARs had a protective effect because Aβ was now unable to cause membrane perforation, suggesting a complex relationship between Aβ and NMDARs. Because previous studies have recognized that Aβ oligomers are able to increase membrane permeability and produce amyloid pores, the present study supports the conclusion that NMDARs play a critical protective role on Aβ actions in hippocampal neurons. These results could explain the lack of correlation between brain Aβ burden and clinically observed dementia.

Towards a Novel Class of Multitarget-Directed Ligands: Dual P2X7-NMDA Receptor Antagonists

Multi-target-directed ligands (MTDLs) offer new hope for the treatment of multifactorial complex diseases such as Alzheimer's Disease (AD). Herein, we present compounds aimed at targeting the NMDA and the P2X7 receptors, which embody a different approach to AD therapy. On one hand, we are seeking to delay neurodegeneration targeting the glutamatergic NMDA receptors; on the other hand, we also aim to reduce neuroinflammation, targeting P2X7 receptors. Although the NMDA receptor is a widely recognized therapeutic target in treating AD, the P2X7 receptor remains largely unexplored for this purpose; therefore, the dual inhibitor presented herein-which is open to further optimization-represents the first member of a new class of MTDLs.

Anti-neuroinflammatory effects of ethanolic extract of black chokeberry (Aronia melanocapa L.) in lipopolysaccharide-stimulated BV2 cells and ICR mice

BACKGROUND/OBJECTIVES

One of the mechanisms considered to be prevalent in the development of Alzheimer's disease (AD) is hyper-stimulation of microglia. Black chokeberry (Aronia melanocapa L.) is widely used to treat diabetes and atherosclerosis, and is known to exert anti-oxidant and anti-inflammatory effects; however, its neuroprotective effects have not been elucidated thus far.

MATERIALS/METHODS

We undertook to assess the anti-inflammatory effect of the ethanolic extract of black chokeberry friut (BCE) in BV2 cells, and evaluate its neuroprotective effect in the lipopolysaccharide (LPS)-induced mouse model of AD.

RESULTS

Following stimulation of BV2 cells by LPS, exposure to BCE significantly reduced the generation of nitric oxide as well as mRNA levels of numerous inflammatory factors such as inducible nitric oxide synthase (iNOS), cyclooxygenase 2 (COX-2), interleukin 1 beta (IL-1β), and tumor necrosis factor alpha (TNF-α). In addition, AD was induced in a mouse model by intraperitoneal injection of LPS (250 µg/kg), subsequent to which we investigated the neuroprotective effects of BCE (50 mg/kg) on brain damage. We observed that BCE significantly reduced tissue damage in the hippocampus by downregulating iNOS, COX-2, and TNF-α levels. We further identified the quinic acids in BCE using liquid chromatography-mass spectrometry (LCMS). Furthermore, we confirmed the neuroprotective effect of BCE and quinic acid on amyloid beta-induced cell death in rat hippocampal primary neurons.

CONCLUSIONS

Our findings suggest that black chokeberry has protective effects against the development of AD.

Memantine for the Treatment of Dementia: A Review on its Current and Future Applications

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by the presence in the brain of extracellular amyloid-β protein (Aβ) and intracellular neurofibrillary tangles composed of hyperphosphorylated tau protein. The N-Methyl-D-aspartate receptors (NMDAR), ionotropic glutamate receptor, are essential for processes like learning and memory. An excessive activation of NMDARs has been associated with neuronal loss. The discovery of extrasynaptic NMDARs provided a rational and physiological explanation between physiological and excitotoxic actions of glutamate. Memantine (MEM), an antagonist of extrasynaptic NMDAR, is currently used for the treatment of AD jointly with acetylcholinesterase inhibitors. It has been demonstrated that MEM preferentially prevents the excessive continuous extrasynaptic NMDAR disease activation and therefore prevents neuronal cell death induced by excitotoxicity without disrupting physiological synaptic activity. The problem is that MEM has shown no clear positive effects in clinical applications while, in preclinical stages, had very promising results. The data in preclinical studies suggests that MEM has a positive impact on improving AD brain neuropathology, as well as in preventing Aβ production, aggregation, or downstream neurotoxic consequences, in part through the blockade of extrasynaptic NMDAR. Thus, the focus of this review is primarily to discuss the efficacy of MEM in preclinical models of AD, consider possible combinations of this drug with others, and then evaluate possible reasons for its lack of efficacy in clinical trials. Finally, applications in other pathologies are also considered.