Memantine lowers amyloid-beta peptide levels in neuronal cultures and in APP/PS1 transgenic mice

Memantine: Updating a rare success story in pro-cognitive therapeutics

The great potential for NMDA receptor modulators as druggable targets in neurodegenerative disorders has been met with limited success. Considered one of the rare exceptions, memantine has consistently demonstrated restorative and prophylactic properties in many AD models. In clinical trials memantine slows the decline in cognitive performance associated with AD. Here, we provide an overview of the basic properties including pharmacological targets, toxicology and cellular effects of memantine. Evidence demonstrating reductions in molecular, physiological and behavioural indices of AD-like impairments associated with memantine treatment are also discussed. This represents both an extension and homage to Dr. Chris Parson's considerable contributions to our fundamental understanding of a success story in the AD treatment landscape.

Curcumin-derived carbon quantum dots: Dual actions in mitigating tau hyperphosphorylation and amyloid beta aggregation

The amyloid cascade and tau hypotheses both hold significant implications for the pathogenesis of Alzheimer's disease (AD). Curcumin shows potential by inhibiting the aggregation of amyloid beta (Aβ) and reducing tau hyperphosphorylation, however, its use is limited due to issues with solubility and bioavailability. Carbon dots, recognized for their high biocompatibility and optimal water solubility, have demonstrated the capability to inhibit either Aβ or tau aggregation. Nonetheless, their effects on tau hyperphosphorylation are yet to be extensively explored. This study aims to evaluate the water-soluble curcumin-derived carbon quantum dots (Cur-CQDs) synthesized via an eco-friendly method, designed to preserve the beneficial effects of curcumin while overcoming solubility challenges. The synthesis of Cur-CQDs involves a single-step dry heating process using curcumin, resulting in dots that exhibit negligible cytotoxicity to SH-SY5Y cells at the examined concentrations. Notably, Cur-CQDs have shown the ability to simultaneously mitigate Aβ aggregation and tau hyperphosphorylation. Therefore, it is suggested that Cur-CQDs may hold potential for AD treatment, a hypothesis deserving of further research.

Memantine protects the cultured rat hippocampal neurons treated by NMDA and amyloid β1-42

Alzheimer's disease (AD) is a devastating neurodegenerative condition with no effective treatments. Recent research highlights the role of NMDA receptors in AD development, as excessive activation of these receptors triggers excitotoxicity. Memantine, an NMDA receptor antagonist, shows promise in curbing excitotoxicity. What sets our study apart is our novel exploration of memantine's potential to protect hippocampal neurons from neurotoxicity induced by NMDA and amyloid β1-42, a hallmark of AD. To achieve this, we conducted a series of experiments using rat hippocampal cell cultures. We employed Hoechst and propidium iodide double staining to assess neuronal viability. Analyzing the viability of neurons in normal conditions compared to their status after 24 h of exposure to the respective agents revealed compelling results. The incubation of hippocampal neurons with NMDA or amyloid β1-42 led to a more than twofold increase in the number of apoptotic and necrotic neurons. However, when memantine was co-administered with NMDA or amyloid β1-42, we witnessed a notable augmentation in the number of viable cells. This unique approach not only suggests that memantine may act as a neuroprotective agent but also emphasizes the relevance of hippocampal neuron cultures as valuable models for investigating excitotoxicity and potential AD treatments.

Inhibition of NMDA Receptor Activation in the Rostral Ventrolateral Medulla by Amyloid-β Peptide in Rats

N-methyl-D-aspartate (NMDA) receptors, a subtype of ionotropic glutamate receptors, are important in regulating sympathetic tone and cardiovascular function in the rostral ventrolateral medulla (RVLM). Amyloid-beta peptide (Aβ) is linked to the pathogenesis of Alzheimer's disease (AD). Cerebro- and cardiovascular diseases might be the risk factors for developing AD. The present study examines the acute effects of soluble Aβ on the function of NMDA receptors in rats RVLM. We used the magnitude of increases in the blood pressure (pressor responses) induced by microinjection of NMDA into the RVLM as an index of NMDA receptor function in the RVLM. Soluble Aβ was applied by intracerebroventricular (ICV) injection. Aβ1-40 at a lower dose (0.2 nmol) caused a slight reduction, and a higher dose (2 nmol) showed a significant decrease in NMDA-induced pressor responses 10 min after administration. ICV injection of Aβ1-42 (2 nmol) did not affect NMDA-induced pressor responses in the RVLM. Co-administration of Aβ1-40 with ifenprodil or memantine blocked the inhibitory effects of Aβ1-40. Immunohistochemistry analysis showed a significant increase in the immunoreactivity of phosphoserine 1480 of GluN2B subunits (pGluN2B-serine1480) in the neuron of the RVLM without significant changes in phosphoserine 896 of GluN1 subunits (pGluN1-serine896), GluN1 and GluN2B, 10 min following Aβ1-40 administration compared with saline. Interestingly, we found a much higher level of Aβ1-40 compared to that of Aβ1-42 in the cerebrospinal fluid (CSF) measured using enzyme-linked immunosorbent assay 10 min following ICV administration of the same dose (2 nmol) of the peptides. In conclusion, the results suggest that ICV Aβ1-40, but not Aβ1-42, produced an inhibitory effect on NMDA receptor function in the RVLM, which might result from changes in pGluN2B-serine1480 (regulated by casein kinase II). The different elimination of the peptides in the CSF might contribute to the differential effects of Aβ1-40 and Aβ1-42 on NMDA receptor function.

Fundamental neurochemistry review: Glutamatergic dysfunction as a central mechanism underlying flavivirus-induced neurological damage

The Flaviviridae family comprises positive-sense single-strand RNA viruses mainly transmitted by arthropods. Many of these pathogens are especially deleterious to the nervous system, and a myriad of neurological symptoms have been associated with infections by Zika virus (ZIKV), West Nile virus (WNV), and Japanese encephalitis virus (JEV) in humans. Studies suggest that viral replication in neural cells and the massive release of pro-inflammatory mediators lead to morphological alterations of synaptic spine structure and changes in the balance of excitatory/inhibitory neurotransmitters and receptors. Glutamate is the predominant excitatory neurotransmitter in the brain, and studies propose that either enhanced release or impaired uptake of this amino acid contributes to brain damage in several conditions. Here, we review existing evidence suggesting that glutamatergic dysfunction-induced by flaviviruses is a central mechanism for neurological damage and clinical outcomes of infection. We also discuss current data suggesting that pharmacological approaches that counteract glutamatergic dysfunction show benefits in animal models of such viral diseases.

Development and Evaluation of Solid Lipid Nanoparticles for the Clearance of Aβ in Alzheimer's Disease

Aggregation of Amyloid-β (Aβ) leads to the formation and deposition of neurofibrillary tangles and plaques which is the main pathological hallmark of Alzheimer's disease (AD). The bioavailability of the drugs and their capability to cross the BBB plays a crucial role in the therapeutics of AD. The present study evaluates the Memantine Hydrochloride (MeHCl) and Tramiprosate (TMPS) loaded solid lipid nanoparticles (SLNs) for the clearance of Aβ on SHSY5Y cells in rat hippocampus. Molecular docking and in vitro Aβ fibrillation were used to ensure the binding of drugs to Aβ. The in vitro cell viability study showed that the M + T SLNs showed enhanced neuroprotection against SHSY5Y cells than the pure drugs (M + T PD) in presence of Aβ (80.35µM ± 0.455 µM) at a 3:1 molar ratio. The Box-Behnken Design (BBD) was employed to optimize the SLNs and the optimized M + T SLNs were further characterized by %drug entrapment efficiency (99.24 ± 3.24 of MeHCl and 89.99 ± 0.95 of TMPS), particle size (159.9 ± 0.569 nm), PDI (0.149 ± 0.08), Zeta potential (-6.4 ± 0.948 mV), Transmission Electron Microscopy (TEM), Atomic Force Microscopy (AFM) and in vitro drug release. The TEM & AFM analysis showed irregularly spherical morphology. In vitro release of SLNs was noted up to 48 h; whereas the pure drugs released completely within 3 hrs. M + T SLNs revealed an improved pharmacokinetic profile and a 4-fold increase in drug concentration in the brain when compared to the pure drug. Behavioral tests showed enhanced spatial memory and histological studies confirmed reduced Aβ plaques in rat hippocampus. Furthermore, the levels of Aβ decreased in AlCl₃-induced AD. Thus, all these noted results established that the M + T SLNs provide enhanced neuroprotective effects when compared to pure and individual drugs and can be a promising therapeutic strategy for the management of AD.

Effects of baicalein with memantine on aluminium chloride-induced neurotoxicity in Wistar rats

Alzheimer's disease is a progressive neurodegenerative condition. It is one of the most common 28 forms of dementia accounting for 60-80% of people suffering from dementia. There are very few medications that are approved for the treatment of Alzheimer's disease. Baicalein, belonging to the flavone subclass of flavonoids, has been reported to have a neuroprotective effect by reducing oxidative stress and neuroinflammation, inhibiting the AChE enzyme, and reducing amyloid protein aggregation and toxicity. Memantine is one of the most important drugs used for treating Alzheimer's disease. The purpose of this work was to study the effect of baicalein with memantine on aluminum chloride-induced neurotoxicity in Wistar rats. Aluminum chloride (100 mg/kg p.o.) was administered for 42 days in male Wistar rats to induce neurotoxicity. Baicalein alone (10 mg/kg) and a combination of baicalein (5 mg/kg and 10 mg/kg) with memantine (20 mg/kg) were administered for 42 days. Treatment of baicalein with memantine showed significant improvement in behavioral parameters. The combination reduced oxidative stress and the formation of β-Amyloid plaques and increased brain-derived neurotrophic factor (BDNF) expression. Based on findings, it can be concluded that treatment with baicalein and memantine may slow the progression of neurodegeneration in rats.

Antiglycoxidative properties of amantadine – a systematic review and comprehensive in vitro study

An important drug used in the treatment of Parkinson’s disease is amantadine. We are the first to perform a comprehensive study based on various glycation and oxidation factors, determining the impact of amantadine on protein glycoxidation. Sugars (glucose, fructose, galactose) and aldehydes (glyoxal, methylglyoxal) were used as glycation agents, and chloramine T was used as an oxidant. Glycoxidation biomarkers in albumin treated with amantadine were generally not different from the control group (glycation/oxidation factors), indicating that the drug did not affect oxidation and glycation processes. Molecular docking analysis did not reveal strong binding sites of amantadine on the bovine serum albumin structure. Although amantadine poorly scavenged hydroxyl radical and hydrogen peroxide, it had significantly lower antioxidant and antiglycation effect than all protein oxidation and glycation inhibitors. In some cases, amantadine even demonstrated glycoxidant, proglycation, and prooxidant properties. In summary, amantadine exhibited weak antioxidant properties and a lack of antiglycation activity.

HIV-Associated Insults Modulate ADAM10 and Its Regulator Sirtuin1 in an NMDA Receptor-Dependent Manner

Neurologic deficits associated with human immunodeficiency virus (HIV) infection impact about 50% of persons with HIV (PWH). These disorders, termed HIV-associated neurocognitive disorders (HAND), possess neuropathologic similarities to Alzheimer’s disease (AD), including intra- and extracellular amyloid-beta (Aβ) peptide aggregates. Aβ peptide is produced through cleavage of the amyloid precursor protein (APP) by the beta secretase BACE1. However, this is precluded by cleavage of APP by the non-amyloidogenic alpha secretase, ADAM10. Previous studies have found that BACE1 expression was increased in the CNS of PWH with HAND as well as animal models of HAND. Further, BACE1 contributed to neurotoxicity. Yet in in vitro models, the role of ADAM10 and its potential regulatory mechanisms had not been examined. To address this, primary rat cortical neurons were treated with supernatants from HIV-infected human macrophages (HIV/MDMs). We found that HIV/MDMs decreased levels of both ADAM10 and Sirtuin1 (SIRT1), a regulator of ADAM10 that is implicated in aging and in AD. Both decreases were blocked with NMDA receptor antagonists, and treatment with NMDA was sufficient to induce reduction in ADAM10 and SIRT1 protein levels. Furthermore, decreases in SIRT1 protein levels were observed at an earlier time point than the decreases in ADAM10 protein levels, and the reduction in SIRT1 was reversed by proteasome inhibitor MG132. This study indicates that HIV-associated insults, particularly excitotoxicity, contribute to changes of APP secretases by downregulating levels of ADAM10 and its regulator.

Glutamatergic transmission and receptor expression in the synucleinopathy h-α-synL62 mouse model: Effects of hydromethylthionine

The accumulation of alpha-synuclein (α-Syn) into Lewy bodies in cortical and subcortical regions has been linked to the pathogenesis of synucleinopathies such as Parkinson's disease (PD) and dementia with Lewy bodies (DLB). While there is a strong link between synuclein aggregates and the reduction in dopamine function in the emergence of PD, less is known about the consequences of α-Syn accumulation in glutamatergic neurons and how this could be exploited as a therapeutic target. Transgenic h-α-synL62 (L62) mice, in which synuclein aggregation is achieved through the expression of full-length human α-Syn fused with a signal sequence peptide, were used to characterise glutamatergic transmission using a combination of behavioural, immunoblotting, and histopathological approaches. The protein aggregation inhibitor hydromethylthionine mesylate (HMTM) alone, or in combination with the glutamatergic compounds 3-((2-Methyl-4-thiazolyl)ethynyl)pyridine hydrochloride (MTEP) and memantine, was used to target α-Syn aggregation. We show that accumulation of α-Syn aggregates in glutamatergic synapses affected synaptic protein expression including metabotropic glutamate receptor 5 (mGLUR5) levels and ratio of N-methyl-d-aspartate (NMDA) receptor subunits GluN1/GluN2A. The ratio of NMDA receptor subunits and levels of mGLUR5 were both normalised by HMTM in L62 mice. These alterations, however, did not affect glutamate release in synaptosomes derived from L62 mice or behavioural endpoints following pharmacological manipulations of glutamate functions. Our results confirm that HMTM acts in the L62 mouse model of PD as an inhibitor of pathological aggregation of synuclein and show that HMTM treatment normalises both the ratio of NMDA receptor subunits and mGLUR5 levels. These findings support the potential utility of HMTM as a disease-modifying treatment for PD aiming to reduce synuclein aggregation pathology.

Challenges and approaches of drugs such as Memantine, Donepezil, Rivastigmine and Aducanumab in the treatment, control and management of Alzheimer's disease

Alzheimer's disease (AD) is a kinds of neuropsychiatric illnesses that affect the central nervous system. In this disease, the accumulation of amyloid-beta increases, and phosphorylated tau (P-tau) protein, one of the ways to treat this disease is to reduce the accumulation of amyloid-beta. Various studies have demonstrated that pharmacological approaches have considerable effects in the treatment of AD, despite the side effects and challenges. Cholinesterase inhibitors and the NMDA receptor antagonist memantine are presently authorized therapies for AD. Memantine and Donepezil are the most common drugs for the prevention and therapy of AD with mechanisms such as lessened β-amyloid plaque, effect on N-Methyl-D-aspartate (NMDA) receptors. Diminution glutamate and elevated acetylcholine are some of the influences of medications administrated to treat AD, and drugs can also play a role in slowing the progression of cognitive and memory impairment. A new pharmacological approach and strategy is required to control the future of AD. This review appraises the effects of memantine, donepezil, rivastigmine, and aducanumab in clinical trials, in vitro and animal model studies that have explored how these drugs versus AD development and also discuss possible mechanisms of influence on the brain. Research in clinical trials has substantial findings that support the role of these medications in AD treatment and ameliorate the safety and efficacy of AD therapy, although more clinical trials are required to prove their effectiveness.

β-arrestin1 promotes tauopathy by transducing GPCR signaling, disrupting microtubules and autophagy

GPCRs regulator, β-arrestin1, is increased in FTLD-tau patients, is required for β2-adrenergic receptor and metabotropic glutamate receptor 2-induced tau phosphorylation, promotes tau aggregation by impairing autophagy, and destabilizes microtubule dynamics, whereas genetic reduction in β-arrestin1 mitigates tauopathy and cognitive impairments.

G protein–coupled receptors (GPCRs) have been shown to play integral roles in Alzheimer’s disease pathogenesis. However, it is unclear how diverse GPCRs similarly affect Aβ and tau pathogenesis. GPCRs share a common mechanism of action via the β-arrestin scaffolding signaling complexes, which not only serve to desensitize GPCRs by internalization, but also mediate multiple downstream signaling events. As signaling via the GPCRs, β2-adrenergic receptor (β2AR), and metabotropic glutamate receptor 2 (mGluR2) promotes hyperphosphorylation of tau, we hypothesized that β-arrestin1 represents a point of convergence for such pathogenic activities. Here, we report that β-arrestins are not only essential for β2AR and mGluR2-mediated increase in pathogenic tau but also show that β-arrestin1 levels are increased in brains of Frontotemporal lobar degeneration (FTLD-tau) patients. Increased β-arrestin1 in turn drives the accumulation of pathogenic tau, whereas reduced ARRB1 alleviates tauopathy and rescues impaired synaptic plasticity and cognitive impairments in PS19 mice. Biochemical and cellular studies show that β-arrestin1 drives tauopathy by destabilizing microtubules and impeding p62/SQSTM1 autophagy flux by interfering with p62 body formation, which promotes pathogenic tau accumulation.

Trait anxiety, a personality risk factor associated with Alzheimer's Disease

Alzheimer's disease (AD) is the most common neurodegenerative disease in elderly population and the leading cause of dementia worldwide. While senile plaques and neurofibrillary tangles have been proposed as the principal histopathologic hallmarks of AD, the exact etiology of this disease is still far from being clearly understood. AD has been recognized as pathological consequences of complex interactions among genetic, aging, medical, life style and psychosocial factors. Recently, the roles of neuroticism personality traits in AD incidence and progression have come into focus. More specifically, increasing evidence has further shown that the trait anxiety, one major component of neuroticism predicting the individual vulnerability in response to stress, is a risk factor for AD and may correlated with various AD pathologies. In this review, we summarized recent literature on the association of trait anxiety with AD. We also discussed the possible neuroendocrinological and neurochemical mechanisms of this association, which may provide clinical implications for AD diagnosis and therapy.

A review on advances of treatment modalities for Alzheimer's disease

Alzheimer's disease (AD) is a multifactorial neurodegenerative disease which is mainly characterized by progressive impairment in cognition, emotion, language and memory in older population. Considering the impact of AD, formulations of pharmaceutical drugs and cholinesterase inhibitors have been widely propagated, receiving endorsement by FDA as a form of AD treatment. However, these medications were gradually discovered to be ineffective in removing the root of AD pathogenesis but merely targeting the symptoms so as to improve a patient's cognitive outcome. Hence, a search for better disease-modifying alternatives is put into motion. Having a clear understanding of the neuroprotective mechanisms and diverse properties undertaken by specific genes, antibodies and nanoparticles is central towards designing novel therapeutic agents. In this review, we provide a brief introduction on the background of Alzheimer's disease, the biology of blood-brain barrier, along with the potentials and drawbacks associated with current therapeutic treatment avenues pertaining to gene therapy, immunotherapy and nanotherapy for better diagnosis and management of Alzheimer's disease.

New Evidence for P-gp-Mediated Export of Amyloid-β PEPTIDES in Molecular, Blood-Brain Barrier and Neuronal Models

Defective clearance mechanisms lead to the accumulation of amyloid-beta (Aβ) peptides in the Alzheimer’s brain. Though predominantly generated in neurons, little is known about how these hydrophobic, aggregation-prone, and tightly membrane-associated peptides exit into the extracellular space where they deposit and propagate neurotoxicity. The ability for P-glycoprotein (P-gp), an ATP-binding cassette (ABC) transporter, to export Aβ across the blood-brain barrier (BBB) has previously been reported. However, controversies surrounding the P-gp–Aβ interaction persist. Here, molecular data affirm that both Aβ₄₀ and Aβ₄₂ peptide isoforms directly interact with and are substrates of P-gp. This was reinforced ex vivo by the inhibition of Aβ₄₂ transport in brain capillaries from P-gp-knockout mice. Moreover, we explored whether P-gp could exert the same role in neurons. Comparison between non-neuronal CHO-APP and human neuroblastoma SK-N-SH cells revealed that P-gp is expressed and active in both cell types. Inhibiting P-gp activity using verapamil and nicardipine impaired Aβ₄₀ and Aβ₄₂ secretion from both cell types, as determined by ELISA. Collectively, these findings implicate P-gp in Aβ export from neurons, as well as across the BBB endothelium, and suggest that restoring or enhancing P-gp function could be a viable therapeutic approach for removing excess Aβ out of the brain in Alzheimer’s disease.

In Vitro Effects of (+)MK-801 (dizocilpine) and Memantine on β-Amyloid Peptides Linked to Alzheimer's Disease

An in vitro effect of (+)MK-801 (dizocilpine), an inhibitor of the glutamate/NMDA and nicotinic acetylcholine receptors, on the Aβ[1-42] and Aβ[1-40] peptides is described and compared to that of memantine. Memantine has been approved by the U.S. Food and Drug Administration for the treatment of mild-moderate Alzheimer's disease. Both compounds accelerated the formation of a β-sheet structure by Aβ[1-42], (+)MK-801 more rapidly than memantine, as observed in a thioflavin T fluorescence assay. The acceleration was followed by a decrease in the fluorescence signal that was not observed when the ligand was absent. Nuclear magnetic resonance spectra of the soluble peptides in the presence and absence of (+)MK-801 demonstrated that the monomeric form did not bind (+)MK-801 and that in the presence of (+)MK-801 the concentration of the monomeric form progressively decreased. Small angle X-ray scattering confirmed that the presence of (+)MK-801 resulted in a more rapid and characteristic transition to an insoluble form. These results suggest that (+)MK-801 and memantine accelerate the transition of Aβ[1-42] and Aβ[1-40] to ThT-negative insoluble forms.

Memantine and Ibuprofen pretreatment exerts anti-inflammatory effect against streptozotocin-induced astroglial inflammation via modulation of NMDA receptor-associated downstream calcium ion signaling

We had previously reported that neuroinflammation and memory impairment associated with intracerebroventricular streptozotocin (ICV STZ) injection in rats was due to glial activation and modulation of the N-methyl-D-aspartate (NMDA) receptor function. However, the exact role of the NMDA receptor and the molecules associated with downstream calcium ion signaling in STZ-induced astroglial activation is not known. Thus, in the present study, Memantine (an NMDA receptor antagonist) and Ibuprofen (an anti-inflammatory drug) were used as the pharmacological tool to investigate the molecular mechanisms involved in STZ-induced astroglial inflammation. We have studied the effect of STZ (100 μM) treatment for 24 h on NMDA receptor subunits (NR1, NR2A, and NR2B) expression and its associated calcium ion regulated molecules calcium/calmodulin-dependent protein kinase II subunit α (CaMKIIα), cyclic AMP-response element-binding (CREB) protein, Calpain, and Caspase 3. We have found a significant increase in the expression of NR1, NR2B, Calpain, and Caspase 3 expression, whereas a decrease in the level of NR2A, CaMKIIα, and CREB protein expression after 24 h of STZ treatment. These results indicate that STZ altered the NMDA receptor subunit expression and its downstream calcium (Ca²⁺) ion signaling molecules. We have also found that both Memantine (5 µM) and Ibuprofen (200 μM) significantly prevented the STZ-induced change in CaMKIIα, CREB, Calpain, and Caspase 3 expressions in C6 astrocytoma cells. Interestingly, only Memantine (and not Ibuprofen) was able to prevent the changes in NMDA receptor subunit expression in STZ-treated astrocytoma cells. STZ treatment also increased the level of glial fibrillary acidic protein (GFAP), tumor necrosis factor-alpha (TNF-α), inducible nitric oxide synthase (iNOS), and decreased the level of interleukin-10 (IL-10), indicating inflammatory condition, which was restored by both Memantine and Ibuprofen. These results suggest that both Memantine and Ibuprofen exert anti-inflammatory effect against STZ-induced astroglial activation and neuroinflammation via modulation of NMDA receptor-associated downstream calcium signaling cascade. However, only Memantine (not Ibuprofen) was able to revert STZ-induced changes in NMDA receptor subunit expression.

Chronic Memantine Treatment Ameliorates Behavioral Deficits, Neuron Loss, and Impaired Neurogenesis in a Model of Alzheimer's Disease

Memantine, a non-competitive NMDA receptor antagonist possessing neuroprotective properties, belongs to the small group of drugs which have been approved for the treatment of Alzheimer's disease (AD). While several preclinical studies employing different transgenic AD mouse models have described beneficial effects with regard to rescued behavioral deficits or reduced amyloid plaque pathology, it is largely unknown whether memantine might have beneficial effects on neurodegeneration. In the current study, we assessed whether memantine treatment has an impact on hippocampal neuron loss and associated behavioral deficits in the Tg4-42 mouse model of AD. We demonstrate that a chronic oral memantine treatment for 4 months diminishes hippocampal CA1 neuron loss and rescues learning and memory performance in different behavioral paradigms, such as Morris water maze or a novel object recognition task. Cognitive benefits of chronic memantine treatment were accompanied by an amelioration of impaired adult hippocampal neurogenesis. Taken together, our results demonstrate that memantine successfully counteracts pathological alterations in a preclinical mouse model of AD.

LY379268 Does Not Have Long-Term Procognitive Effects nor Attenuate Glutamatergic Signaling in AβPP/PS1 Mice

Chronically elevated basal glutamate levels are hypothesized to attenuate detection of physiological signals thereby inhibiting memory formation and retrieval, while inducing excitotoxicity-mediated neurodegeneration observed in Alzheimer's disease (AD). However, current medication targeting the glutamatergic system, such as memantine, shows limited efficacy and is unable to decelerate disease progression, possibly because it modulates postsynaptic N-methyl-D-aspartate receptors rather than glutamate release or clearance. To determine if decreasing presynaptic glutamate release leads to long-term procognitive effects, we treated AβPP/PS1 mice with LY379268 (3.0 mg/kg; i.p.), a metabotropic glutamate receptor (mGluR)2/3 agonist from 2-6 months of age when elevated glutamate levels are first observed but cognition is unaffected. C57BL/6J genetic background control mice and another cohort of AβPP/PS1 mice received normal saline (i.p.) as vehicle controls. After 6 months off treatment, mice receiving LY379268 did not show long-term improvement as assessed by the Morris water maze (MWM) spatial learning and memory paradigm. Following MWM, mice were isoflurane anesthetized and a glutamate selective microelectrode was used to measure in vivo basal and stimulus-evoked glutamate release and clearance independently from the dentate, CA3, and CA1 hippocampal subregions. Immunohistochemistry was used to measure hippocampal astrogliosis and plaque pathology. Similar to previous studies, we observed elevated basal glutamate, stimulus evoked glutamate release, and astrogliosis in AβPP/PS1 vehicle mice versus C57BL/6J mice. Treatment with LY379268 did not attenuate these responses nor diminish plaque pathology. The current study builds upon previous research demonstrating hyperglutamatergic hippocampal signaling in AβPP/PS1 mice; however, long-term therapeutic efficacy of LY379268 in AβPP/PS1 was not observed.

Effect of memantine on expression of Bace1-as and Bace1 genes in STZ-induced Alzheimeric rats

Recent studies have showed that the long non-coding RNAs (lncRNAs) expression is dysregulated in different neurodegenerative disorders like Alzheimer's disease (AD). In the present study, the effects of memantine on the level of Bace1-as and Bace1 genes' expression in streptozotocin (STZ)-induced Alzheimer's and memantine treated rats were investigated. The male Wistar rats were randomly divided into four groups: 1-Normal control, 2-Sham-operated control, 3- Alzheimer'scontrol rats (ICV-STZ), 4-Experimental group rats treated by memantine in a dose of 30 mg/kg/day for 28 days in ICV-STZ rats. The expression of Bace1-as and Bace1 genes was measured by quantitative-PCR in the brain and blood tissues. ELISA was used to analyze Bace1 and Aβ proteins. Expression of Bace1-as was significantly increased in the brain and blood tissues of the experimental group (p = 0.032 and p = 0.034, respectively). The expression of Bace1 gene showed no significant changes in the brain. Furthermore, the ELISA analysis revealed that Bace1 protein was significantly increased in the plasma of the Alzheimer's control group (p = 0.000) and in the brain tissue of the experimental group (p = 0.000). Additionally, Aβ levels had no significant changes between all groups studied. The Bace1 protein may be used as a prognostic biomarker in plasma, or before using memantine as a treatment. Furthermore, Bace1-as gene expression may play a role in monitoring the progression of AD.

Isolation, Characterization, and Possible Anti-Alzheimer's Disease Activities of Bisabolane-Type Sesquiterpenoid Derivatives and Phenolics from the Rhizomes of Curcuma longa

One new bisabolane-type sesquiterpenoid, together with four known bisabolane-type sesquiterpenoid derivatives and seven phenolics, was isolated from the rhizomes of Curcuma longa. Their structures were elucidated by extensive spectroscopic (IR, HR-ESI-MS, and NMR) data analysis. The possible anti-Alzheimer's disease (AD) activities of the isolated compounds were also evaluated using Caenorhabditis elegans AD pathological model, and 1β-hydroxybisabola-2,10-dien-4-one had the highest possible anti-AD activity.

β-Arrestin2 oligomers impair the clearance of pathological tau and increase tau aggregates

Multiple G protein-coupled receptors (GPCRs) are targets in the treatment of dementia, and the arrestins are common to their signaling. β-Arrestin2 was significantly increased in brains of patients with frontotemporal lobar degeneration (FTLD-tau), a disease second to Alzheimer's as a cause of dementia. Genetic loss and overexpression experiments using genetically encoded reporters and defined mutant constructs in vitro, and in cell lines, primary neurons, and tau P301S mice crossed with β-arrestin2-/- mice, show that β-arrestin2 stabilizes pathogenic tau and promotes tau aggregation. Cell and mouse models of FTLD showed this to be maladaptive, fueling a positive feedback cycle of enhanced neuronal tau via non-GPCR mechanisms. Genetic ablation of β-arrestin2 markedly ablates tau pathology and rescues synaptic plasticity defects in tau P301S transgenic mice. Atomic force microscopy and cellular studies revealed that oligomerized, but not monomeric, β-arrestin2 increases tau by inhibiting self-interaction of the autophagy cargo receptor p62/SQSTM1, impeding p62 autophagy flux. Hence, reduction of oligomerized β-arrestin2 with virus encoding β-arrestin2 mutants acting as dominant-negatives markedly reduces tau-laden neurofibrillary tangles in FTLD mice in vivo. Reducing β-arrestin2 oligomeric status represents a new strategy to alleviate tau pathology in FTLD and related tauopathies.

Eupulcherol A, a triterpenoid with a new carbon skeleton from Euphorbia pulcherrima, and its anti-Alzheimer's disease bioactivity

Eupulcherol A (1), a novel triterpenoid with an unprecedented carbon skeleton, was isolated from Euphorbia pulcherrima.

Effects of the drug combination memantine and melatonin on impaired memory and brain neuronal deficits in an amyloid-predominant mouse model of Alzheimer's disease

Objectives

Alzheimer's disease (AD) is a neurodegenerative disorder with no cure. Limited treatment options available today do not offer solutions to slow or stop any of the suspected causes. The current medications used for the symptomatic treatment of AD include memantine and acetylcholine esterase inhibitors. Some studies suggest that melatonin could also be used in AD patients due to its sleep-improving properties.

Methods

In this study, we evaluated whether a combination of memantine with melatonin, administered for 32 days in drinking water, was more effective than either drug alone with respect to Aβ aggregates, neuroinflammation and cognition in the double transgenic APP/PS1 (5xFAD) mouse model of AD.

Key findings

In this study, chronic administration of memantine with melatonin improved episodic memory in the object recognition test and reduced the number of amyloid aggregates and reactive microgliosis in the brains of 5xFAD mice. Although administration of memantine or melatonin alone also reduced the number of amyloid aggregates and inflammation in brain, this study shows a clear benefit of the drug combination, which had a significantly stronger effect in this amyloid-dominant mouse model of AD.

Conclusion

Our data suggest considerable potential for the use of memantine with melatonin in patients with AD.

Memantine, a Noncompetitive N-Methyl-D-Aspartate Receptor Antagonist, Attenuates Cerebral Amyloid Angiopathy by Increasing Insulin-Degrading Enzyme Expression

Sporadic cerebral amyloid angiopathy (CAA) is characterized by cerebrovascular amyloid beta (Aβ) deposits and causes cerebral hemorrhages and dementia in elderly people. Memantine is used in Alzheimer's disease to inhibit the glutamatergic system by blocking N-methyl-D-aspartate receptors. Its therapeutic effects in CAA are unclear, however. Here, we used APP23 transgenic mice (CAA model) to investigate whether memantine has direct therapeutic effects on cerebrovascular Aβ deposits. We treated APP23 mice and age-matched wild-type littermates with memantine at ages 6-18 months. We counted the numbers of vessels with Aβ and hemosiderin deposits. We measured soluble and insoluble Aβ40 and Aβ42 levels and levels of amyloid precursor protein (APP), APP-processing enzymes (α-, β-, γ-secretase), and Aβ-degrading enzymes (insulin-degrading enzyme [IDE], neprilysin). Memantine reduced cerebrovascular Aβ and hemosiderin deposits in APP23 mice. Compared with controls, memantine-treated APP23 mice had reduced Aβ40 levels and increased levels of hippocampal and vascular IDE. Our results suggest that memantine reduces cerebrovascular Aβ deposits by enhancing Aβ-cleaving IDE expression. The clinical availability of memantine may allow its use as a novel therapeutic agent in CAA.

Memantine Improves Cognitive Function and Alters Hippocampal and Cortical Proteome in Triple Transgenic Mouse Model of Alzheimer's Disease

Memantine is a non-competitive N-methyl-D-aspartate receptor (NMDAR) antagonist clinically approved for moderate-to-severe Alzheimer's disease (AD) to improve cognitive functions. There is no report about the proteomic alterations induced by memantine in AD mouse model yet. In this study, we investigated the protein profiles in the hippocampus and the cerebral cortex of AD-related transgenic mouse model (3×Tg-AD) treated with memantine. Mice (8-month) were treated with memantine (5 mg/kg/bid) for 4 months followed by behavioral and molecular evaluation. Using step-down passive avoidance (SDA) test, novel object recognition (NOR) test and Morris water maze (MWM) test, it was observed that memantine significantly improved learning and memory retention in 3xTg-AD mice. By using quantitative proteomic analysis, 3301 and 3140 proteins in the hippocampus and the cerebral cortex respectively were identified to be associated with AD abnormalities. In the hippocampus, memantine significantly altered the expression levels of 233 proteins, among which PCNT, ATAXIN2, TNIK, and NOL3 were up-regulated, and FLNA, MARK 2 and BRAF were down-regulated. In the cerebral cortex, memantine significantly altered the expression levels of 342 proteins, among which PCNT, PMPCB, CRK, and MBP were up-regulated, and DNM2, BRAF, TAGLN 2 and FRY1 were down-regulated. Further analysis with bioinformatics showed that memantine modulated biological pathways associated with cytoskeleton and ErbB signaling in the hippocampus, and modulated biological pathways associated with axon guidance, ribosome, cytoskeleton, calcium and MAPK signaling in the cerebral cortex. Our data indicate that memantine induces higher levels of proteomic alterations in the cerebral cortex than in the hippocampus, suggesting memantine affects various brain regions in different manners. Our study provides a novel view on the complexity of protein responses induced by memantine in the brain of AD.

Memantine ameliorates learning and memory disturbance and the behavioral and psychological symptoms of dementia in thiamine-deficient mice

Several studies have reported on the beneficial effects of memantine on behavioral and psychological symptoms of dementia (BPSD) in patients with Alzheimer's disease. However, the effects of memantine on BPSD-like behaviors in animals have not been well addressed. Here, the effects of memantine on memory disturbance and BPSD-like behaviors were evaluated in thiamine-deficient (TD) mice. Memantine (3 and 10 mg/kg, b.i.d.) was orally administered to ddY mice fed a TD diet for 22 days. During the treatment period, the forced swimming test, elevated plus-maze test, passive avoidance test, and locomotor activity test were performed. Neurotransmitter levels in the brain were analyzed after the treatment period. Daily oral administration of memantine ameliorated the memory disturbances, anxiety-like behavior, and depression-like behavior observed in TD mice. Memantine did not have a significant effect on monoamine levels, but increased glutamate levels in the hippocampus in TD mice. These results suggest that memantine prevents or suppresses the progression of BPSD-like behaviors that develop due to TD. This effect may be mediated in part by the enhancement of glutamatergic neuron activity in the hippocampus.

Memantine prodrug as a new agent for Alzheimer's Disease

Hydrogen sulphide has recently drawn much attention due to its potent anti-inflammatory and neuroprotective roles in brain functions. The purpose of the current study was to exploit these beneficial properties of H₂S to design a new agent for the treatment of Alzheimer's disease (AD). To pursue our aims, we replaced the free amine group of memantine with an isothiocyanate functionality as a putative H₂S-donor moiety. The new chemical entity, named memit, was then tested in vitro to determine whether it retains the pharmacological profile of the "native drug", while also providing a source of H₂S in the CNS. Indeed, Memit showed the ability to release H₂S through a cysteine-mediated mechanism, thus generating memantine. Moreover, the new hybrid molecule exerts protective effects against neuronal inflammation and induces a drastic fall in ROS production. In addition, memit was also able to reduce the Aβ(1-42) self-induced aggregation and exerted cytoprotective effect against Aβ oligomers-induced damage in both human neurons and rat microglia cells. Finally, similarly to memantine, the new compound promotes autophagy, a complex process required for cellular homeostasis in cell survival that results to be altered in neurodegenerative diseases. In conclusion, our study revealed that memit is a prodrug of memantine. Further in vivo studies will be necessary to fully investigate the synergic or cumulative effects due to the H₂S-releasing moiety and the native drug.

The role of LINC00094/miR-224-5p (miR-497-5p)/Endophilin-1 axis in Memantine mediated protective effects on blood-brain barrier in AD microenvironment

The dysfunction of the blood-brain barrier (BBB) is one of the main pathological features of Alzheimer's disease (AD). Memantine (MEM), an N-methyl-d-aspartate (NMDA) receptor antagonist, has been reported that been used widely for AD therapy. This study was performed to demonstrate the role of the MEM in regulating BBB permeability in AD microenvironment as well as its possible mechanisms. The present study showed that LINC00094 was dramatically increased in Abeta_1-42 -incubated microvascular endothelial cells (ECs) of BBB model in vitro. Besides, it was decreased in MEM-incubated ECs. Silencing LINC00094 significantly decreased BBB permeability, meanwhile up-regulating the expression of ZO-1, occludin and claudin-5. Furthermore, silencing LINC00094 enhance the effect of MEM on decreasing BBB permeability in AD microenvironment. The analysis of the mechanism demonstrated that reduction of LINC00094 inhibited Endophilin-1 expression by up-regulating miR-224-4p/miR-497-5p, promoted the expression of ZO-1, occludin and claudin-5, and ultimately alleviated BBB permeability in AD microenvironment. Taken together, the present study suggests that the MEM/LINC00094/miR-224-5p (miR-497-5p)/Endophilin-1 axis plays a crucial role in the regulation of BBB permeability in AD microenvironment. Silencing LINC00094 combined with MEM provides a novel target for the therapy of AD.

Diet-induced insulin resistance elevates hippocampal glutamate as well as VGLUT1 and GFAP expression in AβPP/PS1 mice

The symptomologies of Alzheimer's disease (AD) develop over decades suggesting modifiable lifestyle factors may contribute to disease pathogenesis. In humans, hyperinsulinemia associated with type 2 diabetes mellitus increases the risk for developing AD and both diseases share similar age-related etiologies including amyloidogenesis. Since we have demonstrated that soluble Aβ₄₂ elicits glutamate release, we wanted to understand how diet-induced insulin resistance alters hippocampal glutamate dynamics, which are important for memory formation and consolidation. Eight to twelve-week-old C57BL/6J and AβPP/PS1 mice were placed on either a low-fat diet or high-fat diet (HFD) for 8 months. A HFD led to significant weight increases as well as impaired insulin sensitivity, glucose tolerance, and learning in both C57BL/6J and AβPP/PS1 mice. AβPP/PS1 low-fat diet mice had elevated hippocampal basal as well as stimulus-evoked glutamate release that was further increased with consumption of a HFD. Immunohistochemistry indicated an increase in vesicular glutamate transporter 1 and glial fibrillary acidic protein density in hippocampal subregions corresponding with this elevated extracellular glutamate. While no differences in hippocampal plaque load were observed, the elevated astrogliotic response surrounding the plaques in AβPP/PS1 HFD mice may have been a compensatory mechanism to control plaque accumulation. These data support that AβPP/PS1 mice have chronically elevated extracellular glutamate that is exacerbated by a HFD and that modifiable lifestyle factors such as obesity-induced insulin resistance can contribute to AD pathogenesis. OPEN SCIENCE BADGES: This article has received a badge for *Open Materials* and for *Open Data* because it made the data publicly available. The data can be accessed at https://osf.io/5whvu (figures for data) and https://osf.io/gd5vf (materials and methods). The complete Open Science Disclosure form for this article can be found at the end of the article. More information about the Open Practices badges can be found at https://cos.io/our-services/open-science-badges/. Cover Image for this issue: doi: 10.1111/jnc.14490.

A role for astrocyte-derived amyloid β peptides in the degeneration of neurons in an animal model of temporal lobe epilepsy

Kainic acid, an analogue of the excitatory neurotransmitter glutamate, can trigger seizures and neurotoxicity in the hippocampus and other limbic structures in a manner that mirrors the neuropathology of human temporal lobe epilepsy (TLE). However, the underlying mechanisms associated with the neurotoxicity remain unclear. Since amyloid-β (Aβ) peptides, which are critical in the development of Alzheimer's disease, can mediate toxicity by activating glutamatergic NMDA receptors, it is likely that the enhanced glutamatergic transmission that renders hippocampal neurons vulnerable to kainic acid treatment may involve Aβ peptides. Thus, we seek to establish what role Aβ plays in kainic acid-induced toxicity using in vivo and in vitro paradigms. Our results show that systemic injection of kainic acid to adult rats triggers seizures, gliosis and loss of hippocampal neurons, along with increased levels/processing of amyloid precursor protein (APP), resulting in the enhanced production of Aβ-related peptides. The changes in APP levels/processing were evident primarily in activated astrocytes, implying a role for astrocytic Aβ in kainic acid-induced toxicity. Accordingly, we showed that treating rat primary cultured astrocytes with kainic acid can lead to increased Aβ production/secretion without any compromise in cell viability. Additionally, we revealed that kainic acid reduces neuronal viability more in neuronal/astrocyte co-cultures than in pure neuronal culture, and this is attenuated by precluding Aβ production. Collectively, these results indicate that increased production/secretion of Aβ-related peptides from activated astrocytes can contribute to neurotoxicity in kainic acid-treated rats. Since kainic acid administration can lead to neuropathological changes resembling TLE, it is likely that APP/Aβ peptides derived from astrocytes may have a role in TLE pathogenesis.

Pretreatment of glial cell-derived neurotrophic factor and geranylgeranylacetone ameliorates brain injury in Parkinson's disease by its anti-apoptotic and anti-oxidative property

The aim of the present study was to determine the combined effects of glial cell-derived neurotrophic factor (GDNF) and geranylgeranylacetone (GGA) on neuron apoptosis and oxidative stress in Parkinson's disease (PD). A mouse MPTP model of PD and cellular models of H₂ O₂ and MPP⁺ -treated PC12 cells were established. Swimming, pole, and traction tests were used to detect behavioral impairment. Tyrosine hydroxylase (TH) immunohistochemistry was used to evaluate the neuron loss. TUNEL and flow cytometer method were used to identify the neuron apoptosis. MDA levels and activities of antioxidant enzymes were used to detect the oxidative damage. The PD model of mice received GDNF and GGA exhibited a significant recovery in their swim, pole, and traction scores. Moreover, the combined treatment significantly reduced the neuron apoptosis in the substantia nigra (SN) of PD mice or in H₂ O₂ or MPP⁺ -induced PC12 cells compared with the single drug group. In addition, significant reduction of MDA levels and improvement of activities of CAT, SOD, and GSH-px were observed after GDNF and GGA treatment in the PD model and H₂ O₂ or MPP⁺ -induced PC12 cells. The combination of GDNF and GGA ameliorated neural apoptosis and oxidative damage in PD.

Peripheral and Central Effects of Memantine in a Mixed Preclinical Mice Model of Obesity and Familial Alzheimer's Disease

There is growing evidence that obesity associated with type 2 diabetes mellitus (T2DM) and aging are risk factors for the development of Alzheimer's disease (AD). However, the molecular mechanisms through which obesity interacts with β-amyloid (Aβ) to promote cognitive decline remains poorly understood. Memantine (MEM), a N-methyl-D-aspartate receptor antagonist, is currently used for the treatment of AD. Nonetheless, few studies have reported its effects on genetic preclinical models of this neurodegenerative disease exacerbated with high-fat diet (HFD)-induced obesity. Therefore, the present research aims to elucidate the effects of MEM on familial AD HFD-induced insulin resistance and learning and memory impairment. Furthermore, it aspires to determine the possible underlying mechanisms that connect AD to T2DM. Wild type and APPswe/PS1dE9 mice were used in this study. The animals were fed with either chow or HFD until 6 months of age, and they were treated with MEM-supplemented water (30 mg/kg) during the last 12 weeks. Our study demonstrates that MEM improves the metabolic consequences produced by HFD in this model of familial AD. Behavioural assessments confirmed that the treatment also improves animals learning abilities and decreases memory loss. Moreover, MEM treatment improves brain insulin signalling upregulating AKT, as well as cyclic adenosine monophosphate response element binding (CREB) expression, and modulates the amyloidogenic pathway, which, in turn, reduced the accumulation of Aβ. Moreover, this drug increases the activation of molecules involved with insulin signalling in the liver, such as insulin receptor substrate 2 (IRS2), which is a key protein regulating hepatic resistance to insulin. These results provide new insight into the role of MEM not only in the occurrence of AD treatment, but also in its potential application on peripheral metabolic disorders where Aβ plays a key role, as is the case of T2DM.

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.

Memantine-Loaded PEGylated Biodegradable Nanoparticles for the Treatment of Glaucoma

Glaucoma is a multifactorial neurodegenerative disease associated with retinal ganglion cells (RGC) loss. Increasing reports of similarities in glaucoma and other neurodegenerative conditions have led to speculation that therapies for brain neurodegenerative disorders may also have potential as glaucoma therapies. Memantine is an N-methyl-d-aspartate (NMDA) antagonist approved for Alzheimer's disease treatment. Glutamate-induced excitotoxicity is implicated in glaucoma and NMDA receptor antagonism is advocated as a potential strategy for RGC preservation. This study describes the development of a topical formulation of memantine-loaded PLGA-PEG nanoparticles (MEM-NP) and investigates the efficacy of this formulation using a well-established glaucoma model. MEM-NPs <200 nm in diameter and incorporating 4 mg mL^-1 of memantine were prepared with 0.35 mg mL^-1 localized to the aqueous interior. In vitro assessment indicated sustained release from MEM-NPs and ex vivo ocular permeation studies demonstrated enhanced delivery. MEM-NPs were additionally found to be well tolerated in vitro (human retinoblastoma cells) and in vivo (Draize test). Finally, when applied topically in a rodent model of ocular hypertension for three weeks, MEM-NP eye drops were found to significantly (p < 0.0001) reduce RGC loss. These results suggest that topical MEM-NP is safe, well tolerated, and, most promisingly, neuroprotective in an experimental glaucoma model.

Norcrassin A, a novel C16 tetranorditerpenoid, and bicrotonol A, an unusual dimeric labdane-type diterpenoid, from the roots of Croton crassifolius

Norcrassin A (1), a novel C₁₆ tetranorditerpenoid, featuring a new carbon skeleton, and bicrotonol A (2), an unusual dimeric labdane-type diterpenoid, were isolated from Croton crassifolius.

Four novel sesquiterpenoids with their anti-Alzheimer's disease activity from Nardostachys chinensis

Nardochinins A–D (1–4), four novel sesquiterpenoids, were isolated from Nardostachys chinensis. Nardochinin B (2) can significantly inhibit the Alzheimer's disease (AD) like symptom of worm paralysis.

Rose Essential Oil Delayed Alzheimer's Disease-Like Symptoms by SKN-1 Pathway in C. elegans

There are no effective medications for delaying the progress of Alzheimer's disease (AD), the most common neurodegenerative disease in the world. In this study, our results with C. elegans showed that rose essential oil (REO) significantly inhibited AD-like symptoms of worm paralysis and hypersensivity to exogenous 5-HT in a dose-dependent manner. Its main components of β-citronellol and geraniol acted less effectively than the oil itself. REO significantly suppressed Aβ deposits and reduced the Aβ oligomers to alleviate the toxicity induced by Aβ overexpression. Additionally, the inhibitory effects of REO on worm paralysis phenotype were abrogated only after skn-1 RNAi but not daf-16 and hsf-1 RNAi. REO markedly activated the expression of gst-4 gene, which further supported SKN-1 signaling pathway was involved in the therapeutic effect of REO on AD C. elegans. Our results provided direct evidence on REO for treating AD on an organism level and relative theoretical foundation for reshaping medicinal products of REO in the future.

Protective Effects of Memantine on Hydroquinone-Treated Human Retinal Pigment Epithelium Cells and Human Retinal Müller Cells

PURPOSE

Memantine (MEM) acts on the glutamatergic system by blocking N-methyl-d-aspartate (NMDA) glutamate receptors. The role that MEM plays in protecting retinal cells is unknown. Hydroquinone (HQ) is one of the cytotoxic components in cigarette smoke. In the present study, we tested whether pretreatment with MEM could protect against the cytotoxic effects of HQ on human retinal pigment epithelium cells (ARPE-19) and human retinal Müller cells (MIO-M1) in vitro.

METHODS

Cells were plated, pretreated for 6 h with 30 μM of MEM, and then exposed for 24 h to 200, 100, 50, and 25 μM of HQ while MEM was still present. Cell viability (CV), reactive oxygen species (ROS), mitochondrial membrane potential (ΔΨm), and lactate dehydrogenase (LDH) release assays were performed.

RESULTS

HQ-treated cells showed a dose-dependent decrease in CV and ΔΨm, but an increase in ROS production and LDH levels in both cell lines. MEM pretreatment reversed the CV in 50, 100, and 200 μM doses in ARPE-19 cells and at all HQ concentrations in MIO-M1 cells compared to HQ-treated cultures. ROS production was reversed in all HQ concentrations in both cell lines. ΔΨm was significantly increased after MEM pretreatment only in 50 μM HQ concentration for both cell lines. LDH levels were decreased at 50 and 25 μM HQ in ARPE-19 and MIO-M1 cells, respectively.

CONCLUSION

HQ-induced toxicity is concentration dependent in ARPE-19 and MIO-M1 cultures. MEM exerts protective effects against HQ-induced toxicity on human retinal pigment epithelial and Müller cells in vitro.

Memantine inhibits β-amyloid aggregation and disassembles preformed β-amyloid aggregates

Memantine, an uncompetitive glutamatergic N-methyl-d-aspartate (NMDA) receptor antagonist, is widely used as a medication for the treatment of Alzheimer's disease (AD). We previously reported that chronic treatment of AD with memantine reduces the amount of insoluble β-amyloid (Aβ) and soluble Aβ oligomers in animal models of AD. The mechanisms by which memantine reduces Aβ levels in the brain were evaluated by determining the effect of memantine on Aβ aggregation using thioflavin T and transmission electron microscopy. Memantine inhibited the formation of Aβ(1-42) aggregates in a concentration-dependent manner, whereas amantadine, a structurally similar compound, did not affect Aβ aggregation at the same concentrations. Furthermore, memantine inhibited the formation of different types of Aβ aggregates, including Aβs carrying familial AD mutations, and disaggregated preformed Aβ(1-42) fibrils. These results suggest that the inhibition of Aβ aggregation and induction of Aβ disaggregation may be involved in the mechanisms by which memantine reduces Aβ deposition in the brain.

Dianxianning improved amyloid β-induced pathological characteristics partially through DAF-2/DAF-16 insulin like pathway in transgenic C. elegans

Dianxianning (DXN) is a traditional Chinese formula, and has been approved in China for treating epilepsy since 1996. Here anti-Alzheimer's disease activity of DXN has been reported. DXN improved AD-like symptoms of paralysis and 5-HT sensitivity of transgenic Aβ1-42 C. elegans. In worms, DXN significantly increased Aβ monomers and decreased the toxic Aβ oligomers, thus reducing Aβ toxicity. DXN significantly suppressed the expression of hsp-16.2 induced by juglone, and up-regulated sod-3 expression. These results indicated that DXN increased stress resistance and protected C. elegans against oxidative stress. Furthermore, DXN could significantly promote DAF-16 nuclear translocation, but it did not activate SKN-1. The inhibitory effect of DXN on the Aβ toxicity was significantly reverted by daf-16 RNAi, rather than skn-1 RNAi or hsf-1 RNAi. These results indicated that DAF-16 is at least partially required for the anti-AD effect of DXN. In conclusion, DXN improved Aβ-induced pathological characteristics partially through DAF-2/DAF-16 insulin like pathway in transgenic worms. Together with our data obtained by Morris water maze test, the results showed that DXN markedly ameliorated cognitive performance impairment induced by scopolamine in mice. All the results support that DXN is a potential drug candidate to treat Alzheimer's diseases.

Ciproxifan improves cholinergic transmission, attenuates neuroinflammation and oxidative stress but does not reduce amyloid level in transgenic mice

AIM

The present study is aimed to investigate the ability of ciproxifan, a histamine H₃ receptor antagonist to inhibit β-amyloid (Aβ)-induced neurotoxicity in SK-N-SH cells and APP transgenic mouse model.

MATERIALS AND METHODS

In vitro studies was designed to evaluate the neuroprotective effects of ciproxifan in Aβ_25-35 - induced SK-N-SH cells. For the in vivo study, ciproxifan (1 and 3mg/kg, i.p.) was administrated to transgenic mice for 15days and behaviour was assessed using the radial arm maze (RAM). Brain tissues were collected to measure Aβ levels (Aβ_1-40 and Aβ_1-42), acetylcholine (ACh), acetylcholinesterase (AChE), nitric oxide (NO), lipid peroxidation (LPO), antioxidant activities, cyclooxygenases (COX) and cytokines (IL-1α, IL-1β and IL-6), while plasma was collected to measure TGF-1β.

RESULTS

The in vitro studies demonstrated neuroprotective effect of ciproxifan by increasing cell viability and inhibiting reactive oxygen species (ROS) in Aβ_25-35-induced SK-N-SH cells. Ciproxifan significantly improved the behavioural parameters in RAM. Ciproxifan however, did not alter the Aβ levels in APP transgenic mice. Ciproxifan increased ACh and showed anti-oxidant properties by reducing NO and LPO levels as well as enhancing antioxidant levels. The neuroinflammatory analysis showed that ciproxifan reduced both COX-1 and COX-2 activities, decreased the level of pro-inflammatory cytokines IL-1α, IL-1β and IL-6 and increased the level of anti-inflammatory cytokine TGF-1β.

CONCLUSION

This present study provides scientific evidence of the use of ciproxifan via antioxidant and cholinergic pathways in the management of AD.

Amelioration of cognitive impairments in APPswe/PS1dE9 mice is associated with metabolites alteration induced by total salvianolic acid

Purpose

Total salvianolic acid (TSA) is extracted from salvia miltiorrhiza; however, to date, there has been limited characterization of its effects on metabolites in Alzheimer’s disease model-APPswe/PS1dE9 mice. The main objective of this study was to investigate the metabolic changes in 7-month-old APPswe/PS1dE9 mice treated with TSA, which protects against learning and memory impairment.

Methods

APPswe/PS1dE9 mice were treated with TSA (30 mg/kg·d and 60 mg/kg·d, i.p.) and saline (i.p.) daily from 3.5 months old for 14 weeks; saline-treated (i.p.) WT mice were included as the controls. The effects of TSA on learning and memory were assessed by a series of behavioral tests, including the NOR, MWM and step-through tasks. The FBG and plasma lipid levels were subsequently assessed using the GOPOD and enzymatic color methods, respectively. Finally, the concentrations of Aβ42, Aβ40 and metabolites in the hippocampus of the mice were detected via ELISA and GC-TOF-MS, respectively.

Results

At 7 months of age, the APPswe/PS1dE9 mice treated with TSA exhibited an improvement in the preference index (PI) one hour after the acquisition phase in the NOR and the preservation of spatial learning and memory in the MWM. Treatment with TSA substantially decreased the LDL-C level, and 60 mg/kg TSA decreased the CHOL level compared with the plasma level of the APPswe/PS1dE9 group. The Aβ42 and Aβ40 levels in the hippocampus were decreased in the TSA-treated group compared with the saline-treated APPswe/PS1dE9 group. The regulation of metabolic pathways relevant to TSA predominantly included carbohydrate metabolism, such as sorbitol, glucose-6-phosphate, sucrose-6-phosphate and galactose, vitamin metabolism involved in cholecalciferol and ascorbate in the hippocampus.

Conclusions

TSA induced a remarkable amelioration of learning and memory impairments in APPswe/PS1dE9 mice through the regulation of Aβ42, Aβ40, carbohydrate and vitamin metabolites in the hippocampus and LDL-C and CHOL in the plasma.

New Insights into the Crosstalk between NMDARs and Iron: Implications for Understanding Pathology of Neurological Diseases

Both iron dyshomeostasis and N-methyl-D-aspartate receptors (NMDARs)-mediated neurotoxicity have been shown to have an important role in neurological diseases such as Parkinson’s disease (PD) and Alzheimer’s disease (AD). Evidence proved that activation of NMDARs could promote iron overload and iron-induced neurotoxicity by enhancing iron importer divalent metal transporter 1 (DMT1)-mediated iron uptake and iron releasing from lysosome. Also, iron overload could regulate NMDARs-mediated synaptic transmission. This indicates that there might be a possible relationship between iron and activation of NMDARs in neurological diseases. Understanding this interaction between iron and activation of NMDARs may provide new therapeutic avenues for a more targeted neurotherapeutic strategy for these diseases. Therefore, in this review article, we will describe the dysfunction of iron metabolism and NMDARs in neurological diseases including PD and AD, and summarize the new insight into the mechanisms underlying the interaction between iron and activation of NMDARs.

Memantine reduces the production of amyloid-β peptides through modulation of amyloid precursor protein trafficking

Memantine, an uncompetitive glutamatergic N-methyl-D-aspartate (NMDA) receptor antagonist, is widely used as medication for the treatment of Alzheimer's disease (AD). It has been reported that memantine reduces amyloid-β peptide (Aβ) levels in both neuronal cultures and in brains of animal models of AD. However, the underlying mechanism of these effects is unclear. Here we examined the effect of memantine on Aβ production. Memantine was administered to 9-month-old Tg2576 mice, a transgenic mouse model of AD, at 10 or 20mg/kg/day in drinking water for 1 month. Memantine significantly reduced the amounts of both CHAPS-soluble and CHAPS-insoluble Aβ in the brains of Tg2576 mice. Memantine at 10mg/kg/day for 1 month also reduced the levels of insoluble Aβ42 in the brains of aged F344 rats. Moreover, memantine reduced Aβ and sAPPβ levels in conditioned media from rat primary cortical cultures without affecting the enzymatic activities of α-secretase, β-secretase, or γ-secretase. Notably, in a cell-surface biotinylation assay, memantine increased the amount of amyloid precursor protein (APP) at the cell surface without changing the total amount of APP. Collectively, our results indicate that chronic treatment with memantine reduces the levels of Aβ both in AD models and in aged animals, and that memantine affects the endocytosis pathway of APP, which is required for β-secretase-mediated cleavage. This leads to a reduction in Aβ production. These results suggest that memantine reduces Aβ production and plaque deposition through the regulation of intracellular trafficking of APP.