Alzheimer's therapy targeting the β-secretase enzyme BACE1: Benefits and potential limitations from the perspective of animal model studies

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

RATIONALE

The β-secretase BACE1 initiates amyloid-β (Aβ) generation and represents a long-standing prime therapeutic target for the treatment of Alzheimer's disease (AD). However, BACE1 inhibitors tested to date in clinical trials have yielded no beneficial outcomes. In fact, prior BACE1 inhibitor trials targeted at ~ 50-90% Aβ reductions in symptomatic or prodromal AD stages have ended in the discontinuation due to futility and/or side effects, including cognitive worsening rather than expected improvement at the highest dose.

OBJECTIVES

We tested whether a combination strategy with the selective BACE1 inhibitor GRL-8234 and the FDA-approved symptomatic drug memantine may provide synergistic cognitive benefits within their safe dose range.

METHODS

The drug effects were evaluated in the advanced symptomatic stage of 5XFAD mice that developed extensive cerebral Aβ deposition.

RESULTS

Chronic combination treatment with 33.4-mg/kg GRL-8234 and 10-mg/kg memantine, but not either drug alone, rescued cognitive deficits in 5XFAD mice at 12 months of age (the endpoint after 60-day drug treatment), as assessed by the contextual fear conditioning, spontaneous alternation Y-maze and nest building tasks. Intact baseline performances of wild-type control mice on three cognitive paradigms demonstrated that combination treatment did not augment potential cognitive side effects of individual drugs. Biochemical and immunohistochemical examination showed that combination treatment did not synergistically reduce the β-amyloidogenic processing of amyloid precursor protein or Aβ levels in 5XFAD mouse brains.

CONCLUSIONS

A combination strategy with BACE1 inhibitors and memantine may be able to increase the effectiveness of individual drugs within their safe dose range in AD therapy.

Effect of salidroside on neuroprotection and psychiatric sequelae during the COVID-19 pandemic: A review

The coronavirus disease 2019 (COVID-19) pandemic has affected the mental health of individuals worldwide, and the risk of psychiatric sequelae and consequent mental disorders has increased among the general population, health care workers and patients with COVID-19. Achieving effective and widespread prevention of pandemic-related psychiatric sequelae to protect the mental health of the global population is a serious challenge. Salidroside, as a natural agent, has substantial pharmacological activity and health effects, exerts obvious neuroprotective effects, and may be effective in preventing and treating psychiatric sequelae and mental disorders resulting from stress stemming from the COVID-19 pandemic. Herein, we systematically summarise, analyse and discuss the therapeutic effects of salidroside in the prevention and treatment of psychiatric sequelae as well as its roles in preventing the progression of mental disorders, and fully clarify the potential of salidroside as a widely applicable agent for preventing mental disorders caused by stress; the mechanisms underlying the potential protective effects of salidroside are involved in the regulation of the oxidative stress, neuroinflammation, neural regeneration and cell apoptosis in the brain, the network homeostasis of neurotransmission, HPA axis and cholinergic system, and the improvement of synaptic plasticity. Notably, this review innovatively proposes that salidroside is a potential agent for treating stress-induced health issues during the COVID-19 pandemic and provides scientific evidence and a theoretical basis for the use of natural products to combat the current mental health crisis.

A Strategy for Allowing Earlier Diagnosis and Rigorous Evaluation of BACE1 Inhibitors in Preclinical Alzheimer's Disease

Given continued failure of BACE1 inhibitor programs at symptomatic and prodromal stages of Alzheimer's disease (AD), clinical trials need to target the earlier preclinical stage. However, trial design is complex in this population with negative diagnosis of classical hippocampal amnesia on standard memory tests. Besides recent advances in brain imaging, electroencephalogram, and fluid-based biomarkers, new cognitive markers should be established for earlier diagnosis that can optimize recruitment to BACE1 inhibitor trials in presymptomatic AD. Notably, accelerated long-term forgetting (ALF) is emerging as a sensitive cognitive measure that can discriminate between asymptomatic individuals with high risks for developing AD and healthy controls. ALF is a form of declarative memory impairment characterized by increased forgetting rates over longer delays (days to months) despite normal storage within the standard delays of testing (20-60 min). Therefore, ALF may represent a harbinger of preclinical dementia and the impairment of systems memory consolidation, during which memory traces temporarily stored in the hippocampus become gradually integrated into cortical networks. This review provides an overview of the utility of ALF in a rational design of next-generation BACE1 inhibitor trials in preclinical AD. I explore potential mechanisms underlying ALF and relevant early-stage biomarkers useful for BACE1 inhibitor evaluation, including synaptic protein alterations, astrocytic dysregulation and neuron hyperactivity in the hippocampal-cortical network. Furthermore, given the physiological role of the isoform BACE2 as an AD-suppressor gene, I also discuss the possible association between the poor selectivity of BACE1 inhibitors and their side effects (e.g., cognitive worsening) in prior clinical trials.

The Effect of a Novel Mica Nanoparticle, STB-MP, on an Alzheimer's Disease Patient-Induced PSC-Derived Cortical Brain Organoid Model

Alzheimer's disease (AD) is one of the most well-known neurodegenerative diseases, with a substantial amount of advancements in the field of neuroscience and AD. Despite such progress, there has been no significant improvement in AD treatments. To improve in developing a research platform for AD treatment, AD patient-derived induced pluripotent stem cell (iPSC) was employed to generate cortical brain organoids, expressing AD phenotypes, with the accumulation of amyloid-beta (Aβ) and hyperphosphorylated tau (pTau). We have investigated the use of a medical grade mica nanoparticle, STB-MP, as a treatment to decrease the expression of AD's major hallmarks. STB-MP treatment did not inhibit the expression of pTau; however, accumulated Aβ plaques were diminished in STB-MP treated AD organoids. STB-MP seemed to activate the autophagy pathway, by mTOR inhibition, and also decreased γ-secretase activity by decreasing pro-inflammatory cytokine levels. To sum up, the development of AD brain organoids successfully mimics AD phenotype expressions, and thus it could be used as a screening platform for novel AD treatment assessments.

Computational Studies Applied to Linalool and Citronellal Derivatives Against Alzheimer's and Parkinson's Disorders: A Review with Experimental Approach

Alzheimer's and Parkinson's are neurodegenerative disorders that affect a great number of people around the world, seriously compromising the quality of life of individuals, due to motor and cognitive damage. In these diseases, pharmacological treatment is used only to alleviate symptoms. This emphasizes the need to discover alternative molecules for use in prevention. Using Molecular Docking, this review aimed to evaluate the anti-Alzheimer's and anti-Parkinson's activity of linalool and citronellal, as well as their derivatives. Before performing Molecular Docking simulations, the compounds' pharmacokinetic characteristics were evaluated. For Molecular Docking, 7 chemical compounds derived from citronellal, and 10 compounds derived from linalool, and molecular targets involved in Alzheimer's and Parkinson's pathophysiology were selected. According to the Lipinski rules, the compounds under study presented good oral absorption and bioavailability. For toxicity, some tissue irritability was observed. For Parkinson-related targets, the citronellal and linalool derived compounds revealed excellent energetic affinity for α-Synuclein, Adenosine Receptors, Monoamine Oxidase (MAO), and Dopamine D1 receptor proteins. For Alzheimer disease targets, only linalool and its derivatives presented promise against BACE enzyme activity. The compounds studied presented high probability of modulatory activity against the disease targets under study, and are potential candidates for future drugs.

Effects of Donepezil Treatment on Brain Metabolites, Gut Microbiota, and Gut Metabolites in an Amyloid Beta-Induced Cognitive Impairment Mouse Pilot Model

Accumulated clinical and biomedical evidence indicates that the gut microbiota and their metabolites affect brain function and behavior in various central nervous system disorders. This study was performed to investigate the changes in brain metabolites and composition of the fecal microbial community following injection of amyloid β (Aβ) and donepezil treatment of Aβ-injected mice using metataxonomics and metabolomics. Aβ treatment caused cognitive dysfunction, while donepezil resulted in the successful recovery of memory impairment. The Aβ + donepezil group showed a significantly higher relative abundance of Verrucomicrobia than the Aβ group. The relative abundance of 12 taxa, including Blautia and Akkermansia, differed significantly between the groups. The Aβ + donepezil group had higher levels of oxalate, glycerol, xylose, and palmitoleate in feces and oxalate, pyroglutamic acid, hypoxanthine, and inosine in brain tissues than the Aβ group. The levels of pyroglutamic acid, glutamic acid, and phenylalanine showed similar changes in vivo and in vitro using HT-22 cells. The major metabolic pathways in the brain tissues and gut microbiota affected by Aβ or donepezil treatment of Aβ-injected mice were related to amino acid pathways and sugar metabolism, respectively. These findings suggest that alterations in the gut microbiota might influence the induction and amelioration of Aβ-induced cognitive dysfunction via the gut–brain axis. This study could provide basic data on the effects of Aβ and donepezil on gut microbiota and metabolites in an Aβ-induced cognitive impairment mouse model.

A TNF receptor 2 agonist ameliorates neuropathology and improves cognition in an Alzheimer's disease mouse model

Tumor necrosis factor-α (TNF-α) is a pleiotropic, proinflammatory cytokine related to different neurodegenerative diseases, including Alzheimer's disease (AD). Although the linkage between increased TNF-α levels and AD is widely recognized, TNF-α-neutralizing therapies have failed to treat AD. Previous research has associated this with the antithetic functions of the two TNF receptors, TNF receptor 1, associated with inflammation and apoptosis, and TNF receptor 2 (TNFR2), associated with neuroprotection. In our study, we investigated the effects of specifically stimulating TNFR2 with a TNFR2 agonist (NewStar2) in a transgenic Aβ-overexpressing mouse model of AD by administering NewStar2 in two different ways: centrally, via implantation of osmotic pumps, or systemically by intraperitoneal injections. We found that both centrally and systemically administered NewStar2 resulted in a drastic reduction in amyloid β deposition and β-secretase 1 expression levels. Moreover, activation of TNFR2 increased microglial and astrocytic activation and promoted the uptake and degradation of Aβ. Finally, cognitive functions were also improved after NewStar2 treatment. Our results demonstrate that activation of TNFR2 mitigates Aβ-induced cognitive deficits and neuropathology in an AD mouse model and indicates that TNFR2 stimulation might be a potential treatment for AD.

Casein Kinase 2 dependent phosphorylation of eIF4B regulates BACE1 expression in Alzheimer's disease

Alzheimer's disease (AD) is the most common age-related neurodegenerative disorder. Increased Aβ production plays a fundamental role in the pathogenesis of the disease and BACE1, the protease that triggers the amyloidogenic processing of APP, is a key protein and a pharmacological target in AD. Changes in neuronal activity have been linked to BACE1 expression and Aβ generation, but the underlying mechanisms are still unclear. We provide clear evidence for the role of Casein Kinase 2 in the control of activity-driven BACE1 expression in cultured primary neurons, organotypic brain slices, and murine AD models. More specifically, we demonstrate that neuronal activity promotes Casein Kinase 2 dependent phosphorylation of the translation initiation factor eIF4B and this, in turn, controls BACE1 expression and APP processing. Finally, we show that eIF4B expression and phosphorylation are increased in the brain of APPPS1 and APP-KI mice, as well as in AD patients. Overall, we provide a definition of a mechanism linking brain activity with amyloid production and deposition, opening new perspectives from the therapeutic standpoint.

Accelerated long-term forgetting is a BACE1 inhibitor-reversible incipient cognitive phenotype in Alzheimer's disease model mice

AIM

After the continued failure of β-secretase (BACE1) inhibitor clinical trials in prodromal as well as mild-to-moderate Alzheimer's disease (AD), they are shifting to further earlier or asymptomatic stages. The aim of this study is to explore a cognitive paradigm that allows us to more sensitively detect beneficial effects of BACE1 inhibitors in presymptomatic AD.

METHODS

GRL-8234 (33.4 mg/kg, ip), a small-molecule BACE1 inhibitor, was administered once daily for 28 days to the 5XAFD transgenic mouse model of AD. The contextual fear conditioning was used to evaluate the effects of GRL-8234 on memory deficits in 5XFAD mice at different ages.

RESULTS

Chronic administration of GRL-8234 to 5XFAD mice rescued their contextual memory deficits, when tested 1 day after training at 6-8 months but not at 12 months of age. Importantly, 4-month-old 5XFAD mice retain the ability to form contextual memory equivalent to wild-type controls, demonstrating that the standard method of 1-day memory assessment is not suitable for evaluating BACE1 inhibitor efficacy in ameliorating cognitive declines during earlier disease stages. Despite normal contextual memory formation, young 5XFAD mice showed faster forgetting when a longer delay (28 days) intervened between training and memory testing. Notably, GRL-8234 administered to 4-month-old 5XFAD mice during the 28-day delay reversed accelerated long-term forgetting almost completely back to wild-type control levels.

CONCLUSION

The results provide experimental evidence that accelerated long-term forgetting represents more sensitive memory testing that can help evaluate BACE1 inhibitor therapy in presymptomatic AD populations.

Cerebrovascular insufficiency and amyloidogenic signaling in Ossabaw swine with cardiometabolic heart failure

Individuals with heart failure (HF) frequently present with comorbidities, including obesity, insulin resistance, hypertension, and dyslipidemia. Many patients with HF experience cardiogenic dementia, yet the pathophysiology of this disease remains poorly understood. Using a swine model of cardiometabolic HF (Western diet+aortic banding; WD-AB), we tested the hypothesis that WD-AB would promote a multidementia phenotype involving cerebrovascular dysfunction alongside evidence of Alzheimer’s disease (AD) pathology. The results provide evidence of cerebrovascular insufficiency coupled with neuroinflammation and amyloidosis in swine with experimental cardiometabolic HF. Although cardiac ejection fraction was normal, indices of arterial compliance and cerebral blood flow were reduced, and cerebrovascular regulation was impaired in the WD-AB group. Cerebrovascular dysfunction occurred concomitantly with increased MAPK signaling and amyloidogenic processing (i.e., increased APP, BACE1, CTF, and Aβ40 in the prefrontal cortex and hippocampus) in the WD-AB group. Transcriptomic profiles of the stellate ganglia revealed the WD-AB group displayed an enrichment of gene networks associated with MAPK/ERK signaling, AD, frontotemporal dementia, and a number of behavioral phenotypes implicated in cognitive impairment. These provide potentially novel evidence from a swine model that cerebrovascular and neuronal pathologies likely both contribute to the dementia profile in a setting of cardiometabolic HF.

Inhibitory mechanism of O-methylated quercetins, highly potent β-secretase inhibitors isolated from Caragana balchaschensis (Kom.) Pojark

ETHNOPHARMACOLOGICAL RELEVANCE

Caragana has a standing history of implementation in Traditional Chinese Medicine (TCM). Most species of this genus have been explored for multi-functional purposes, such as promoting blood circulation and curing neuralgia, fatigue, migraine, arthritis, and vascular hypertension (Meng et al., 2009). Among them, the well-known species C. sinica showed the most promising potential to increase the expression of ADAM10 among 313 tested medicinal plants, which is one of the promising approach for the treatment of Alzheimer's disease (AD). (Schuck et al., 2015).

AIM OF THIS STUDY

The aim of this work is to explore β-secretase inhibitory activity of compounds isolated from the aerial part of endemic Caragana balchaschensis (Kom.) Pojark. We provided a full characterization of their inhibitory mechanisms, binding affinities, and binding modes.

MATERIALS AND METHODS

The isolation of quercetin derivatives was accomplished by various chromatographical approaches and their structures were annotated by spectroscopic analysis. The detailed kinetic behavior of β-secretase inhibitors was determined by estimation of kinetic parameters (K_m, V_max, K_I, and K_IS). Binding affinities (K_SV) and binding modes of inhibitors were elucidated by fluorescence quenching and molecular docking studies, respectively.

RESULTS

O-methylated quercetins (2-7) were significantly effective in β-secretase inhibition with IC₅₀ ranging from 1.2 to 6.5 μM. The most active one (6) was 20-fold effective than the mother skeleton, quercetin. The O-methyl motif was a critical factor in β-secretase inhibition: tri-O-methylated (1.2 μM) > di-O-methylated (3.5 μM) > mono-O-methylated (6.5 μM) > quercetin (25.2 μM). In the kinetic study, all quercetins (1-7) showed a noncompetitive inhibition, but glucoside ones (8 and 9) were mixed type I inhibitors. The binding affinities (K_SV) were agreed with inhibitory potencies. The O-methylated quercetins were annotated as the most natural abundant metabolites in the aerial part by LC-ESI-TOF/MS. Binding modes of inhibitors to enzyme were elucidated by molecular docking experiments.

CONCLUSION

This study disclosed that most of the major phenolic metabolites of the aerial part of C. balchaschensis are O-methylated quercetins, which have a significant inhibitory effect on β-secretase, which is a critical factor for AD.

CRISPR/Cas9 Technology as a Modern Genetic Manipulation Tool for Recapitulating of Neurodegenerative Disorders in Large Animal Models

BACKGROUND

Neurodegenerative diseases are often the consequence of alterations in structures and functions of the Central Nervous System (CNS) in patients. Despite obtaining massive genomic information concerning the molecular basis of these diseases and since the neurological disorders are multifactorial, causal connections between pathological pathways at the molecular level and CNS disorders development have remained obscure and need to be elucidated to a great extent.

OBJECTIVE

Animal models serve as accessible and valuable tools for understanding and discovering the roles of causative factors in the development of neurodegenerative disorders and finding appropriate treatments. Contrary to rodents and other small animals, large animals, especially non-human primates (NHPs), are remarkably similar to humans; hence, they establish suitable models for recapitulating the main human's neuropathological manifestations that may not be seen in rodent models. In addition, they serve as useful models to discover effective therapeutic targets for neurodegenerative disorders due to their similarity to humans in terms of physiology, evolutionary distance, anatomy, and behavior.

METHODS

In this review, we recommend different strategies based on the CRISPR-Cas9 system for generating animal models of human neurodegenerative disorders and explaining in vivo CRISPR-Cas9 delivery procedures that are applied to disease models for therapeutic purposes.

RESULTS

With the emergence of CRISPR/Cas9 as a modern specific gene-editing technology in the field of genetic engineering, genetic modification procedures such as gene knock-in and knock-out have become increasingly easier compared to traditional gene targeting techniques. Unlike the old techniques, this versatile technology can efficiently generate transgenic large animal models without the need to complicate lab instruments. Hence, these animals can accurately replicate the signs of neurodegenerative disorders.

CONCLUSION

Preclinical applications of CRISPR/Cas9 gene-editing technology supply a unique opportunity to establish animal models of neurodegenerative disorders with high accuracy and facilitate perspectives for breakthroughs in the research on the nervous system disease therapy and drug discovery. Furthermore, the useful outcomes of CRISPR applications in various clinical phases are hopeful for their translation to the clinic in a short time.

Agmatine ameliorates manifestation of depression-like behavior and hippocampal neuroinflammation in mouse model of Alzheimer's disease

Extensive clinical and experimental studies established that depression and mood disorders are highly prevalent neuropsychiatric conditions in Alzheimer's disease (AD). However, its neurochemical basis is not clearly understood. Thus, understanding the neural mechanisms involved in mediating the co-morbidity of depression and AD may be crucial in exploring new pharmacological treatments for this condition. The present study investigated the role of the agmatinergic system in β-amyloid (Aβ_β1-42) peptide-induced depression using forced swim test (FST) in mice. Following the 28th days of its administration, Aβ_1-42 peptide produced depression-like behavior in mice as evidenced by increased immobility time in FST and increased expression of pro-inflammatory cytokines like IL-6 and TNF-α compared to the control animals. The Aβ_1-42 peptide-induced depression and neuroinflammatory markers were significantly inhibited by agmatine -, moxonidine, 2-BFI and l-arginine by once-daily administration during day 8-27 of the protocol. The antidepressant-like effect of agmatine in Aβ_1-42 peptide in mice was potentiated by imidazoline receptor I₁ agonist, moxonidine and imidazoline receptor I₂ agonist 2-BFI at their sub-effective doses. On the other hand, it was completely blocked by imidazoline receptor I₁ antagonist, efaroxan and imidazoline receptor I₂ antagonist, idazoxan Also, agmatine levels were significantly reduced in brain samples of β-amyloid injected mice as compared to the control animals. In conclusion, the present study suggests the importance of endogenous agmatinergic system and imidazoline receptors system in β-amyloid induced a depressive-like behavior in mice. The data projects agmatine as a potential therapeutic target for the AD-associated depression and comorbidities.

Emerging Alternative Proteinases in APP Metabolism and Alzheimer's Disease Pathogenesis: A Focus on MT1-MMP and MT5-MMP

Processing of amyloid beta precursor protein (APP) into amyloid-beta peptide (Aβ) by β-secretase and γ-secretase complex is at the heart of the pathogenesis of Alzheimer’s disease (AD). Targeting this proteolytic pathway effectively reduces/prevents pathology and cognitive decline in preclinical experimental models of the disease, but therapeutic strategies based on secretase activity modifying drugs have so far failed in clinical trials. Although this may raise some doubts on the relevance of β- and γ-secretases as targets, new APP-cleaving enzymes, including meprin-β, legumain (δ-secretase), rhomboid-like protein-4 (RHBDL4), caspases and membrane-type matrix metalloproteinases (MT-MMPs/η-secretases) have confirmed that APP processing remains a solid mechanism in AD pathophysiology. This review will discuss recent findings on the roles of all these proteinases in the nervous system, and in particular on the roles of MT-MMPs, which are at the crossroads of pathological events involving not only amyloidogenesis, but also inflammation and synaptic dysfunctions. Assessing the potential of these emerging proteinases in the Alzheimer’s field opens up new research prospects to improve our knowledge of fundamental mechanisms of the disease and help us establish new therapeutic strategies.

BACE1 inhibitors: Current status and future directions in treating Alzheimer's disease

Alzheimer's disease (AD) is an irreversible, progressive neurodegenerative brain disorder with no current cure. One of the important therapeutic approaches of AD is the inhibition of β-site APP cleaving enzyme-1 (BACE1), which is involved in the rate-limiting step of the cleavage process of the amyloid precursor protein (APP) leading to the generation of the neurotoxic amyloid β (Aβ) protein after the γ-secretase completes its function. The produced insoluble Aβ aggregates lead to plaques deposition and neurodegeneration. BACE1 is, therefore, one of the attractive targets for the treatment of AD. This approach led to the development of potent BACE1 inhibitors, many of which were advanced to late stages in clinical trials. Nonetheless, the high failure rate of lead drug candidates targeting BACE1 brought to the forefront the need for finding new targets to uncover the mystery behind AD. In this review, we aim to discuss the most promising classes of BACE1 inhibitors with a description and analysis of their pharmacodynamic and pharmacokinetic parameters, with more focus on the lead drug candidates that reached late stages of clinical trials, such as MK8931, AZD-3293, JNJ-54861911, E2609, and CNP520. In addition, the manuscript discusses the safety concerns and insignificant physiological effects, which were highlighted for the most successful BACE1 inhibitors. Furthermore, the review demonstrates with increasing evidence that despite tremendous efforts and promising results conceived with BACE1 inhibitors, the latest studies suggest that their clinical use for treating Alzheimer's disease should be reconsidered. Finally, the review sheds light on alternative therapeutic options for targeting AD.

Exposure to fluoride aggravates the impairment in learning and memory and neuropathological lesions in mice carrying the APP/PS1 double-transgenic mutation

BACKGROUND

Alzheimer's disease (AD) is responsible for 60-70% of all cases of dementia. On the other hand, the tap water consumed by hundreds of millions of people has been fluoridated to prevent tooth decay. However, little is known about the influence of fluoride on the expression of APP and subsequent changes in learning and memory and neuropathological injury. Our aim here was to determine whether exposure to fluoride aggravates the neuropathological lesions in mice carrying the amyloid precursor protein (APP)/presenilin1 (PS1) double mutation.

METHODS

These transgenic or wide-type (WT) mice received 0.3 ml of a solution of fluoride (0.1 or 1 mg/ml, prepared with NaF) by intragastric administration once each day for 12 weeks. The learning and memory of these animals were assessed with the Morris water maze test. Senile plaques, ionized calcium binding adaptor molecule 1 (Iba-1), and complement component 3 (C3) expression were semi-quantified by immunohistochemical staining; the level of Aβ42 was detected by Aβ42 enzyme-linked immunosorbent assays (ELISAs); the levels of synaptic proteins and enzymes that cleave APP determined by Western blotting; and the malondialdehyde (MDA) content and activities of superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) measured by biochemical procedures.

RESULTS

The untreated APP mice exhibited a decline in learning and memory after 12 weeks of fluoride treatment, whereas treatment of these some animals with low or high levels of fluoride led to such declines after only 4 or 8 weeks, respectively. Exposure of APP mice to fluoride elevated the number of senile plaques and level of Aβ42, Iba-1, and BACE1, while reducing the level of ADAM10 in their brains. The lower levels of synaptic proteins and enhanced oxidative stress detected in the hippocampus of APP mice were aggravated to fluoride.

CONCLUSIONS

These findings indicate that exposure to fluoride, even at lower concentration, can aggravate the deficit in learning and memory and neuropathological lesions of the mice that express the high level of APP.

Molecular mechanisms underlying protective role of quercetin in attenuating Alzheimer's disease

Quercetin belongs to the flavonoids family, which is present in most of the plants including fruits, vegetables, green tea and even in red wine having antioxidant activities. It is available as a food supplement in the market and has physiological health effects. Quercetin has anti-inflammatory, anticancer and anti-prostate activities along with its beneficial effects on high cholesterol, kidney transplantation, asthma, diabetes, viral infections, pulmonary, schizophrenia and cardiovascular diseases. Quercetin possesses scavenging potential of hydroxyl radical (OH^-), hydrogen peroxide (H₂O₂), and superoxide anion (O₂^-). These reactive oxygen species (ROS) hampers lipid, protein, amino acids and deoxyribonucleic acid (DNA) processing leading to epigenetic alterations. Quercetin has the ability to combat these harmful effects. ROS plays a vital role in the progression of Alzheimer's disease (AD), and we propose that quercetin would be the best choice to overcome cellular and molecular signals in regulating normal physiological functions. However, data are not well documented regarding exact cellular mechanisms of quercetin. The neuroprotective effects of quercetin are mainly due to potential up- and/or down-regulation of cytokines via nuclear factor (erythroid-derived 2)-like 2 (Nrf2), Paraoxonase-2, c-Jun N-terminal kinase (JNK), Protein kinase C, Mitogen-activated protein kinase (MAPK) signalling cascades, and PI3K/Akt pathways. Therefore, the aim of the present review was to elaborate on the cellular and molecular mechanisms of the quercetin involved in the protection against AD.

Lack of β-amyloid cleaving enzyme-1 (BACE1) impairs long-term synaptic plasticity but enhances granule cell excitability and oscillatory activity in the dentate gyrus in vivo

BACE1 is a β-secretase involved in the cleavage of amyloid precursor protein and the pathogenesis of Alzheimer's disease (AD). The entorhinal cortex and the dentate gyrus are important for learning and memory, which are affected in the early stages of AD. Since BACE1 is a potential target for AD therapy, it is crucial to understand its physiological role in these brain regions. Here, we examined the function of BACE1 in the dentate gyrus. We show that loss of BACE1 in the dentate gyrus leads to increased granule cell excitability, indicated by enhanced efficiency of synaptic potentials to generate granule cell spikes. The increase in granule cell excitability was accompanied by prolonged paired-pulse inhibition, altered network gamma oscillations, and impaired synaptic plasticity at entorhinal-dentate synapses of the perforant path. In summary, this is the first detailed electrophysiological study of BACE1 deletion at the network level in vivo. The results suggest that BACE1 is important for normal dentate gyrus network function. This has implications for the use of BACE1 inhibitors as therapeutics for AD therapy, since BACE1 inhibition could similarly disrupt synaptic plasticity and excitability in the entorhinal-dentate circuitry.

Roasted Coffee Reduces β-Amyloid Production by Increasing Proteasomal β-Secretase Degradation in Human Neuroblastoma SH-SY5Y Cells

SCOPE

Epidemiological studies have shown that coffee consumption may be associated with a lower risk of developing several neurological disorders, including Alzheimer's disease (AD). Caffeine is a prominent candidate component underlying the preventive effects of coffee; however, the contribution of other constituents is unclear. To clarify this issue, the effect of roasting coffee beans on β-secretase (BACE1) expression in human neuroblastoma SH-SY5Y cells is investigated.

METHODS AND RESULTS

Coffee (2%) reduces Aβ accumulation in culture medium to 80% of control levels after 24 h. Accordingly, BACE1 expression is decreased to 70% of control levels at 12 h. Experiments using cycloheximide and MG132, a proteasome inhibitor, reveal that coffee enhanced BACE1 degradation through activation of proteasomal activity. Furthermore, coffee activates cAMP-dependent protein kinase, and consequently, phosphorylation of a serine residue of proteasome 26S subunit, non-ATPase 11 (PSMD11). Pyrocatechol, a strong antioxidant known as catechol or 1,2-dihydroxybenzene, produced from chlorogenic acid during roasting, also reduces BACE1 expression by activation of proteasomal activity. Furthermore, pyrocatechol reduces Aβ production in SH-SY5Y cells.

CONCLUSION

The data suggest that the roasting process may be crucial for the protective effects of coffee consumption in AD.

Knockdown of BACE1-AS by siRNA improves memory and learning behaviors in Alzheimer's disease animal model

Alzheimer's disease (AD) is a devastating neurodegenerative disease that causes progressive damage to neurons. Emerging evidence has demonstrated that long non-coding RNAs (lncRNAs) serve an important role in many neurological diseases, such as AD. β-secretase 1 (BACE1)-antisense transcript (BACE1-AS) was identified as a conserved non-coding antisense BACE1. Previous reports stated that BACE1-AS positively regulated BACE1 mRNA and subsequently BACE1 protein expression in vitro and in vivo. However, whether BACE1-AS is able to regulate memory and learning behaviors remains to be elucidated. In the present study, the role of lncRNA BACE1-AS on memory and learning was investigated. It was demonstrated that lncRNA BACE1-AS expression was highly expressed in blood samples from AD patients, and also upregulated in peripheral blood samples and hippocampi from an AD animal model. Knockdown of BACE1-AS by short interfering RNA increased the primary hippocampal neurons proliferation in vitro. Knockdown of BACE1-AS mediated by lentivirus in vivo improved the memory and learning behaviors of SAMP8 mice, inhibited BACE1 and amyloid precursor protein production, and phosphorylation of tau protein in hippocampi. Therefore, the present findings suggested that BACE1-AS may be a potential target for management of memory loss related diseases, such as AD.

Reduction of Aβ Generation by Schisandrin B through Restraining Beta-Secretase 1 Transcription and Translation

BACKGROUND Beta-secretase 1 (BACE1) is a rate-limiting enzyme in the generation of amyloid beta peptides, which are associated with Alzheimer's disease (AD). It has been reported that Schisandrin B could improve cognitive functions in animal models of AD, but the underlying mechanisms are not completely understood. MATERIAL AND METHODS In this research, in order to investigate the effects of Schisandrin B on amyloid-β (Aβ) metabolism and its mechanisms, amyloid precursor protein (APP) and its proteolytic products were determined by enzyme-linked immunosorbent assay (ELISA), western blotting, and RT-PCR after incubation of N2a/Swe cells with Schisandrin B. RESULTS The results indicated that Schisandrin B can significantly reduce the level of secretion of Aβ40 and Aβ42 secreted in N2a/Swe cells. Additionally, there was nonsignificant change in APP level after Schisandrin B treatment. Treatment of Schisandrin B dramatically reduced the mRNA and protein expression levels of BACE1. Moreover, Schisandrin B treatment resulted in a reduction of protein level of sAPPβ, an APP fragment cleavage by BACE1. CONCLUSIONS These results suggest that Schisandrin B inhibits the transcription and translation of BACE1, suppresses the activity of BACE1, and ultimately attenuates Aβ generation, which provides a novel mechanism for the regulation of Aβ metabolism by Schisandrin B.

Polyprenols mitigate cognitive dysfunction and neuropathology in the APP/PS1 mouse

Alzheimer's disease (AD) is a very common neurodegenerative disorder in the elderly and brings considerable financial and social problems worldwide. In this study, polyprenols were firstly evaluated the effects on the cognitive deficits and neuropathology in APP/PS1 mice model of AD. At 3 months old, the APP/PS1 mice were divided into model group; polyprenols low, middle, and high dosage group; and positive drug group. Age-matched wild-type mice were chosen in control group. The administration by oral gavage lasted 6 months. Polyprenols treatment significantly improved cognitive impairment of double transgenic mice compared with vehicle control treatment in behavioral tests. In addition, immunohistochemistry and enzyme-linked immunosorbent assay showed that there were significantly reductions in neuritic plaques and the level of hyperphosphorylated tau in brain of polyprenols-treated mice. Furthermore, we found that polyprenols treatment reduced the apoptotic cells in brain sections of 9-month-old APP/PS1 mice. These results reveal that polyprenols exert neuroprotective effects in APP/PS1 mice and could represent an effective treatment for AD.

BACE1 Function and Inhibition: Implications of Intervention in the Amyloid Pathway of Alzheimer's Disease Pathology

Alzheimer's disease (AD) is a fatal progressive neurodegenerative disorder characterized by increasing loss in memory, cognition, and function of daily living. Among the many pathologic events observed in the progression of AD, changes in amyloid β peptide (Aβ) metabolism proceed fastest, and precede clinical symptoms. BACE1 (β-secretase 1) catalyzes the initial cleavage of the amyloid precursor protein to generate Aβ. Therefore inhibition of BACE1 activity could block one of the earliest pathologic events in AD. However, therapeutic BACE1 inhibition to block Aβ production may need to be balanced with possible effects that might result from diminished physiologic functions BACE1, in particular processing of substrates involved in neuronal function of the brain and periphery. Potentials for beneficial or consequential effects resulting from pharmacologic inhibition of BACE1 are reviewed in context of ongoing clinical trials testing the effect of BACE1 candidate inhibitor drugs in AD populations.

Multi-Target Screening and Experimental Validation of Natural Products from Selaginella Plants against Alzheimer's Disease

Alzheimer's disease (AD) is a progressive and irreversible neurodegenerative disorder which is considered to be the most common cause of dementia. It has a greater impact not only on the learning and memory disturbances but also on social and economy. Currently, there are mainly single-target drugs for AD treatment but the complexity and multiple etiologies of AD make them difficult to obtain desirable therapeutic effects. Therefore, the choice of multi-target drugs will be a potential effective strategy inAD treatment. To find multi-target active ingredients for AD treatment from Selaginella plants, we firstly explored the behaviors effects on AD mice of total extracts (TE) from Selaginella doederleinii on by Morris water maze test and found that TE has a remarkable improvement on learning and memory function for AD mice. And then, multi-target SAR models associated with AD-related proteins were built based on Random Forest (RF) and different descriptors to preliminarily screen potential active ingredients from Selaginella. Considering the prediction outputs and the quantity of existing compounds in our laboratory, 13 compounds were chosen to carry out the in vitro enzyme inhibitory experiments and 4 compounds with BACE1/MAO-B dual inhibitory activity were determined. Finally, the molecular docking was applied to verify the prediction results and enzyme inhibitory experiments. Based on these study and validation processes, we explored a new strategy to improve the efficiency of active ingredients screening based on trace amount of natural product and numbers of targets and found some multi-target compounds with biological activity for the development of novel drugs for AD treatment.

Can brain impermeable BACE1 inhibitors serve as anti-CAA medicine?

Background

Cerebral amyloid angiopathy (CAA) is characterized by the deposition of ß-amyloid peptides (Aß) in and surrounding the wall of microvasculature in the central nervous system, together with parenchymal amyloid plaques collectively referred to as cerebral amyloidosis, which occurs in the brain commonly among the elderly and more frequently in patients with Alzheimer’s disease (AD). CAA is associated with vascular injury and may cause devastating neurological outcomes. No therapeutic approach is available for this lesion to date.

Main body

ß-Secretase 1 (BACE1) is the enzyme initiating Aß production. Brain permeable BACE1 inhibitors targeting primarily at the parenchymal plaque pathology are currently evaluated in clinical trials. This article presents findings in support of a role of BACE1 elevation in the development of CAA, in addition to plaque pathogenesis. The rationale, feasibility, benefit and strategic issues for developing BACE1 inhibitors against CAA are discussed. Brain impermeable compounds are considered preferable as they might exhibit sufficient anti-CAA efficacy without causing significant neuronal/synaptic side effects.

Conclusion

Early pharmacological intervention to the pathogenesis of CAA is expected to provide significant protection for cerebral vascular health and hence brain health. Brain impermeable BACE1 inhibitors should be optimized and tested as potential anti-CAA therapeutics.

KRICT-9 inhibits neuroinflammation, amyloidogenesis and memory loss in Alzheimer's disease models

Alzheimer's disease (AD) is one of the most common forms of dementia and is characterized by neuroinflammation and amyloidogenesis. Here we investigated the effects of KRICT-9 on neuroinflammation and amyloidogenesis in in vitro and in vivo AD models. We found that KRICT-9 decreased lipopolysaccharide (LPS)-induced inflammation in microglial BV-2 cells and astrocytes while reducing nitric oxide generation and expression of inflammatory marker proteins (iNOS and COX-2) as well as APP, BACE1, C99, Iba-1, and GFAP. KRICT-9 also inhibited β-secretase. Pull-down assays and docking model analyses indicated that KRICT-9 binds to the DNA binding domain of signal transducer and activator of transcription 3 (STAT3). KRICT-9 also decreased β-secretase activity and Aβ levels in tissues from LPS-induced mice brains, and it reversed memory impairment in mice. These experiments demonstrated that KRICT-9 protects against LPS-induced neuroinflammation and amyloidogenesis by inhibiting STAT3 activity. This suggests KRICT-9 or KRICT-9-inspired reagents could be used as therapeutic agents to treat AD.

APP mouse models for Alzheimer's disease preclinical studies

Animal models of human diseases that accurately recapitulate clinical pathology are indispensable for understanding molecular mechanisms and advancing preclinical studies. The Alzheimer's disease (AD) research community has historically used first‐generation transgenic (Tg) mouse models that overexpress proteins linked to familial AD (FAD), mutant amyloid precursor protein (APP), or APP and presenilin (PS). These mice exhibit AD pathology, but the overexpression paradigm may cause additional phenotypes unrelated to AD. Second‐generation mouse models contain humanized sequences and clinical mutations in the endogenous mouse App gene. These mice show Aβ accumulation without phenotypes related to overexpression but are not yet a clinical recapitulation of human AD. In this review, we evaluate different APP mouse models of AD, and review recent studies using the second‐generation mice. We advise AD researchers to consider the comparative strengths and limitations of each model against the scientific and therapeutic goal of a prospective preclinical study.

Forebrain depletion of Rheb GTPase elicits spatial memory deficits in mice

The precise molecular and cellular events responsible for age-dependent cognitive dysfunctions remain unclear. We report that Rheb (ras homolog enriched in brain) GTPase, an activator of mammalian target of rapamycin (mTOR), regulates memory functions in mice. Conditional depletion of Rheb selectively in the forebrain of mice obtained from crossing Rheb^f/f and CamKII^Cre results in spontaneous signs of age-related memory loss, that is, spatial memory deficits (T-maze, Morris water maze) without affecting locomotor (open-field test), anxiety-like (elevated plus maze), or contextual fear conditioning functions. Partial depletion of Rheb in forebrain was sufficient to elicit memory defects with little effect on the neuronal size, cortical thickness, or mammalian target of rapamycin activity. Rheb depletion, however, increased the levels of beta-site amyloid precursor protein cleaving enzyme 1 (BACE1), a protein elevated in aging and Alzheimer's disease. Overall, our study demonstrates that forebrain Rheb promotes aging-associated cognitive defects. Thus, molecular understanding of Rheb pathway in brain may provide new therapeutic targets for aging and/or Alzheimer's disease-associated memory deficits.

BACE1 RNAi Restores the Composition of Phosphatidylethanolamine-Derivates Related to Memory Improvement in Aged 3xTg-AD Mice

β-amyloid (Aβ) is produced by the β-secretase 1 (BACE1)-mediated enzymatic cleavage of the amyloid precursor protein through the amyloidogenic pathway, making BACE1 a therapeutic target against Alzheimer’s disease (AD). Alterations in lipid metabolism are a risk factor for AD by an unknown mechanism. The objective of this study was to determine the effect of RNA interference against BACE1 (shBACEmiR) on the phospholipid profile in hippocampal CA1 area in aged 3xTg-AD mice after 6 and 12 months of treatment compared to aged PS1KI mice. The shBACEmiR treatment induced cognitive function recovery and restored mainly the fatty acid composition of lysophosphatidylethanolamine and etherphosphatidylethanolamine, reduced the cPLA2’s phosphorylation, down-regulated the levels of arachidonic acid and COX2 in the hippocampi of 3xTg-AD mice. Together, our findings suggest, for the first time, that BACE1 silencing restores phospholipids composition which could favor the recovery of cellular homeostasis and cognitive function in the hippocampus of triple transgenic AD mice.

Ginsenoside Re reduces Aβ production by activating PPARγ to inhibit BACE1 in N2a/APP695 cells

Alzheimer's disease (AD) is a neurodegenerative disease characterized by β-amyloid protein (Aβ) deposition. Reducing the Aβ load may be a new perspective for AD treatment. Ginsenoside Re is an extract from Panax notoginseng, which is a well-known traditional Chinese medicine that has been used for the treatment of various diseases for years. Ginsenoside Re has been reported to decrease Aβ in Alzheimer's disease animal models, but the mechanism has not been fully elucidated. In the present study, we investigated the mechanism of ginsenoside Re. Our results showed that ginsenoside Re decreased the Aβ levels in N2a/APP695 cells. Aβ peptides are generated by β-secretase (β-site amyloid precursor protein cleaving enzyme 1 (BACE1)) and γ-secretase. We found that ginsenoside Re decreased the BACE1 mRNA and protein levels and inhibited BACE1 activity in the N2a/APP695 cells. Peroxisome proliferator-activated receptor-γ (PPARγ) is a transcription factor that regulates the activity of the BACE1 promoter, and activating PPARγ can inhibit BACE1. The results also showed that ginsenoside Re significantly increased the PPARγ protein and mRNA levels. These effects of ginsenoside Re on BACE1 could be effectively inhibited by the PPARγ antagonist GW9662. These findings indicate that ginsenoside Re inhibits BACE1 through activation of PPARγ, which ultimately reduces the generation of Aβ_1-40 and Aβ_1-42. Therefore, ginsenoside Re may be a promising agent for the modulation of Aβ-related pathology in AD.