Human aspartic protease memapsin 2 cleaves the beta-secretase site of beta-amyloid precursor protein

New Tetrahydroacridine Hybrids with Dichlorobenzoic Acid Moiety Demonstrating Multifunctional Potential for the Treatment of Alzheimer's Disease

A series of new tetrahydroacridine and 3,5-dichlorobenzoic acid hybrids with different spacers were designed, synthesized, and evaluated for their ability to inhibit both cholinesterase enzymes. Compounds 3a, 3b, 3f, and 3g exhibited selective butyrylcholinesterase (EqBuChE) inhibition with IC₅₀ values ranging from 24 to 607 nM. Among them, compound 3b was the most active (IC₅₀ = 24 nM). Additionally, 3c (IC₅₀ for EeAChE = 25 nM and IC₅₀ for EqBuChE = 123 nM) displayed dual cholinesterase inhibitory activity and was the most active compound against acetylcholinesterase (AChE). Active compound 3c was also tested for the ability to inhibit Aβ aggregation. Theoretical physicochemical properties of the compounds were calculated using ACD Labs Percepta and Chemaxon. A Lineweaver–Burk plot and docking study showed that 3c targeted both the catalytic active site (CAS) and the peripheral anionic site (PAS) of AChE. Moreover, 3c appears to possess neuroprotective activity and could be considered a free-radical scavenger. In addition, 3c did not cause DNA damage and was found to be less toxic than tacrine after oral administration; it also demonstrated little inhibitory activity towards hyaluronidase (HYAL), which may indicate that it possesses anti-inflammatory properties. The screening for new in vivo interactions between 3c and known receptors was realized by yeast three-hybrid technology (Y3H).

Biological Evaluation of Newly Synthesized Biaryl Guanidine Derivatives to Arrest β-Secretase Enzymatic Activity Involved in Alzheimer’s Disease

Proteases BACE1 (β-secretases) enzymes have been recognized as a promising target associated with Alzheimer's disease (AD). This study was carried out on the principles of molecular docking, chemical synthesis, and enzymatic inhibition of BACE1 enzymes via biaryl guanidine-based ligands. Based on virtual screening, thirteen different compounds were synthesized and subsequently evaluated via in vitro and in vivo studies. Among them, 1,3-bis(5,6-difluoropyridin-3-yl)guanidine (compound (9)) was found the most potent (IC₅₀ = 97 ± 0.91 nM) and active to arrest (99%) β-secretase enzymes (FRET assay). Furthermore, it was found to improve the novel object recognition test and Morris water maze test significantly (p < 0.05). Improved pharmacokinetic parameters, viz., Log P_o/w (1.76), Log S (-2.73), and better penetration to the brain (BBB permeation) with zero Lipinski violation, made it possible to hit the BACE1 as a potential therapeutic source for AD.

Proximity ligation assay reveals both pre- and postsynaptic localization of the APP-processing enzymes ADAM10 and BACE1 in rat and human adult brain

BACKGROUND

Synaptic degeneration and accumulation of amyloid β-peptides (Aβ) are hallmarks of the Alzheimer diseased brain. Aβ is synaptotoxic and produced by sequential cleavage of the amyloid precursor protein (APP) by the β-secretase BACE1 and by γ-secretase. If APP is instead cleaved by the α-secretase ADAM10, Aβ will not be generated. Although BACE1 is considered to be a presynaptic protein and ADAM10 has been reported to mainly localize to the postsynaptic density, we have previously shown that both ADAM10 and BACE1 are highly enriched in synaptic vesicles of rat brain and mouse primary hippocampal neurons.

RESULTS

Here, using brightfield proximity ligation assay, we expanded our previous result in primary neurons and investigated the in situ synaptic localization of ADAM10 and BACE1 in rat and human adult brain using both pre- and postsynaptic markers. We found that ADAM10 and BACE1 were in close proximity with both the presynaptic marker synaptophysin and the postsynaptic marker PSD-95. The substrate APP was also detected both pre- and postsynaptically. Subcellular fractionation confirmed that ADAM10 and BACE1 are enriched to a similar degree in synaptic vesicles and as well as in the postsynaptic density.

CONCLUSIONS

We show that the α-secretase ADAM10 and the β-secretase BACE1 are located in both the pre- and postsynaptic compartments in intact brain sections. These findings increase our understanding of the regulation of APP processing, thereby facilitating development of more specific treatment strategies.

BACE1 partial deletion induces synaptic plasticity deficit in adult mice

BACE1 is the first enzyme involved in APP processing, thus it is a strong therapeutic target candidate for Alzheimer's disease. The observation of deleterious phenotypes in BACE1 Knock-out (KO) mouse models (germline and conditional) raised some concerns on the safety and tolerability of BACE1 inhibition. Here, we have employed a tamoxifen inducible BACE1 conditional Knock-out (cKO) mouse model to achieve a controlled partial depletion of BACE1 in adult mice. Biochemical and behavioural characterization was performed at two time points: 4-5 months (young mice) and 12-13 months (aged mice). A ~50% to ~70% BACE1 protein reduction in hippocampus and cortex, respectively, induced a significant reduction of BACE1 substrates processing and decrease of Aβx-40 levels at both ages. Hippocampal axonal guidance and peripheral nerve myelination were not affected. Aged mice displayed a CA1 long-term potentiation (LTP) deficit that was not associated with memory impairment. Our findings indicate that numerous phenotypes observed in germline BACE1 KO reflect a fundamental role of BACE1 during development while other phenotypes, observed in adult cKO, may be absent when partially rather than completely deleting BACE1. However, we demonstrated that partial depletion of BACE1 still induces CA1 LTP impairment, supporting a role of BACE1 in synaptic plasticity in adulthood.

1-Benzylpyrrolidine-3-amine-based BuChE inhibitors with anti-aggregating, antioxidant and metal-chelating properties as multifunctional agents against Alzheimer's disease

Complex pathomechanism of Alzheimer's disease (AD) prompts researchers to develop multifunctional molecules in order to find effective therapy against AD. We designed and synthesized novel multifunctional ligands for which we assessed their activities towards butyrylcholinesterase, beta secretase, amyloid beta (Aβ) and tau protein aggregation as well as antioxidant and metal-chelating properties. All compounds showed dual anti-aggregating properties towards Aβ and tau protein in the in cellulo assay in Escherichia coli. Of particular interest are compounds 24b and 25b, which efficiently inhibit aggregation of Aβ and tau protein at 10 μM (24b: 45% for Aβ, 53% for tau; 25b: 49% for Aβ, 54% for tau). They display free radical scavenging capacity and antioxidant activity in ABTS and FRAP assays, respectively, and selectively chelate copper ions. Compounds 24b and 25b are also the most potent inhibitors of BuChE with IC₅₀ of 2.39 μM and 1.94 μM, respectively. Promising in vitro activities of the presented multifunctional ligands as well as their original scaffold are a very interesting starting point for further research towards effective anti-AD treatment.

Development of an Efficient Enzyme Production and Structure-Based Discovery Platform for BACE1 Inhibitors

BACE1 (Beta-site Amyloid Precursor Protein (APP) Cleaving Enzyme 1) is a promising therapeutic target for Alzheimer's Disease (AD). However, efficient expression, purification, and crystallization systems are not well described or detailed in the literature nor are approaches for treatment of enzyme kinetic data for potent inhibitors well described. We therefore developed a platform for expression and purification of BACE1, including protein refolding from E.coli inclusion bodies, in addition to optimizing a reproducible crystallization procedure of BACE1 bound with inhibitors. We also report a detailed approach to the proper analysis of enzyme kinetic data for compounds that exhibit either rapid-equilibrium or tight-binding mechanisms. Our methods allow for the purification of ∼15 mg of BACE1 enzyme from 1 L of culture which is higher than reported yields in the current literature. To evaluate the data analysis approach developed here, a well-known potent inhibitor and two of its derivatives were tested, analyzed, and compared. The inhibitory constants (K_i) obtained from the kinetic studies are in agreement with dissociation constants (K_d) that were also determined using isothermal titration calorimetry (ITC) experiments. The X-ray structures of these three compounds in complex with BACE1 were readily obtained and provide important insight into the structure and thermodynamics of the BACE1-inhibitor interactions.

Beta-Amyloid Increases the Expression Levels of Tid1 Responsible for Neuronal Cell Death and Amyloid Beta Production

Mitochondrial dysfunctions and oxidative stress play important roles in the early pathogenesis of Alzheimer's disease (AD), which also involves the aberrant expression levels of mitochondrial proteins. However, the molecular mechanisms underlying the aberrant expression levels of these proteins in the pathogenesis of AD are still not completely understood. Tid1 (DnaJA3/mtHsp40), a mammalian homolog of the Drosophila tumor suppressor Tid56, is reported to induce mitochondrial fragmentation associated with an increase in reactive oxygen species (ROS) levels, resulting in cell death in some cancer cells. However, the involvement of Tid1 in AD pathogenesis is as yet unknown. In this study, we found that the Tid1 protein levels were upregulated in the hippocampus of AD patients and Tg2576 mice. Our in vitro studies showed that Aβ42 increased the expression levels of Tid1 in primary rat cortical neurons. The knockdown of Tid1 protected against neuronal cell death induced by Aβ42, and Tid1-mediated neuronal cell death, was dependent on the increased ROS generation and caspase-3 activity. The overexpression of Tid1 in HEK293-APP cells increased the BACE1 levels, resulting in increased Aβ production. Conversely, Tid1 knockdown in HEK293-APP cells and primary cultured neurons decreased Aβ production through the reduction in the BACE1 levels. We also found that the overexpression of Tid1 activated c-Jun N-terminal kinase (JNK) leading to increased Aβ production. Taken together, our results suggest that upregulated Tid1 levels in the hippocampus of patients with AD and Tg2576 mice induce apoptosis and increase Aβ production, and Tid1 may therefore be a suitable target in therapeutic interventions for AD.

A short perspective on the long road to effective treatments for Alzheimer's disease

Globally, there are approximately 47 million people living with dementia, and about two thirds of those have Alzheimer's disease (AD). Age is the single biggest risk factor for the vast majority of sporadic AD cases, and because the world's population is aging, the number of people living with AD is set to rise dramatically over the coming decades. There are currently no disease-modifying treatments for AD, and the few symptomatic agents available have limited impact on the disease. Perhaps surprisingly, there is relatively little activity in the AD research and development field compared with other diseases with a high mortality burden, such as cancer. There is enormous economic incentive to discover and develop the first disease-modifying treatment, but previous failure has significantly reduced further industrial investment in this field. The short review looks at the historical path trodden to develop treatments and reflects on the journey down the road to truly effective treatments for people living with AD. LINKED ARTICLES: This article is part of a themed section on Therapeutics for Dementia and Alzheimer's Disease: New Directions for Precision Medicine. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.18/issuetoc.

Multiple BACE1 inhibitors abnormally increase the BACE1 protein level in neurons by prolonging its half-life

INTRODUCTION

There is keen interest in elucidating the biological mechanisms underlying recent failures of β-site amyloid precursor protein-cleaving enzyme-1 (BACE1) inhibitors in Alzheimer's disease trials.

METHODS

We developed a highly sensitive and specific immunoassay for BACE1 in cell lines and iPSC-derived human neurons to systematically analyze the effects of eight clinically relevant BACE1 inhibitors.

RESULTS

Seven of 8 inhibitors elevated BACE1 protein levels. Among protease inhibitors tested, the elevation was specific to BACE1 inhibitors. The inhibitors did not increase BACE1 transcription but extended the protein's half-life. BACE1 became elevated at concentrations below the IC₅₀ for amyloid β (Aβ).

DISCUSSION

Elevation of BACE1 by 7 of 8 BACE1 inhibitors raises new concerns about advancing such β-secretase inhibitors for AD. Chronic elevation could lead to intermittently uninhibited BACE1 when orally dosed inhibitors reach trough levels, abnormally increasing substrate processing. Compounds such as roburic acid that lower Aβ by dissociating β/γ secretase complexes are better candidates because they neither inhibit β- and γ-secretase nor increase BACE1 levels.

Characterization of Cerebrospinal Fluid BACE1 Species

The β-site amyloid precursor protein cleaving enzyme 1 (BACE1) is the main brain β-secretase responsible for the amyloidogenic processing of the amyloid precursor protein (APP). Previous studies have suggested that cerebrospinal fluid (CSF) β-secretase activity may be a candidate diagnostic biomarker for Alzheimer's disease (AD), but biochemical characterization of BACE1 protein in CSF is needed. CSF samples from 19 AD patients and 19 age-matched non-AD controls (n = 19) were classified according to their Aβ42, total tau, and P-tau CSF biomarker levels. We found that β-secretase activity was higher in the CSF of AD subjects than in that of the controls. We found that the majority of the β-secretase activity in the CSF, measured using a peptide substrate homologous to the BACE1 cleavage site, was not inhibited by specific BACE1 inhibitors. We defined enzymatic activity attributable specifically to BACE1 as the activity that was blocked by the specific inhibitors, which is still higher in AD subjects. BACE1 protein levels were characterized by lectin binding, immunoprecipitation, blue native-PAGE, and western blotting using antibodies against specific protein domains. BACE1 was found to be present in human CSF as a mature form of ~ 70 kDa that probably comprised truncated and full-length species, and also as an immature form of ~ 50 kDa that retains the prodomain. CSF-BACE1 was found to assemble into hetero-complexes containing distinct species. Immunoblotting with an antibody against the C-terminus of BACE1 revealed significantly higher levels of the 70-kDa full-length BACE1, while the 50 kDa immature form remained unaltered. When the 70-kDa species was probed with an antibody against the N-terminus of BACE1 (which does not discriminate between truncated and full-length forms), no increase in immunoreactivity was observed, suggesting that truncated forms of BACE1 do not increase in AD. In conclusion, the complexity of BACE1 species in CSF has to be taken into consideration when determining BACE1 activity and protein levels in CSF as biomarkers of AD.

Trafficking and proteolytic processing of amyloid precursor protein and secretases in Alzheimer's disease development: An up-to-date review

Alzheimer's disease (AD), which is predicted to affect 1 in 85 persons worldwide by 2050, results in progressive loss of neuronal functions, leading to impairments in memory and cognitive abilities. As being one of the major neuropathological hallmarks of AD, senile plaques mainly consist of amyloid-β (Aβ) peptides, which are derived from amyloid precursor protein (APP) via the sequential cleavage by β- and γ-secretases. Although the overproduction and accumulation of Aβ peptides are at the center of AD research, the new discoveries point out to the complexity of the disease development. In this respect, it is crucial to understand the processing and the trafficking of APP, the enzymes involved in its processing, the cleavage products and their therapeutic potentials. This review summarizes the salient features of APP processing focusing on APP, the canonical secretases as well as the novel secretases and the cleavage products with an update of the recent developments. We also discussed the intracellular trafficking of APP and secretases in addition to their potential in AD therapy.

Electroacupuncture Mitigates Hippocampal Cognitive Impairments by Reducing BACE1 Deposition and Activating PKA in APP/PS1 Double Transgenic Mice

Increased amyloid-β (Aβ) plaque deposition is thought to be the main cause of Alzheimer's disease (AD). β-Site amyloid precursor protein cleaving enzyme 1 (BACE1) is the key protein involved in Aβ peptide generation. Excessive expression of BACE1 might cause overproduction of neurotoxins in the central nervous system. Previous studies indicated that BACE1 initially cleaves the amyloid precursor protein (APP) and may subsequently interfere with physiological functions of proteins such as PKA, which is recognized to be closely associated with long-term potentiation (LTP) level and can effectively ameliorate cognitive impairments. Therefore, revealing the underlying mechanism of BACE1 in the pathogenesis of AD might have a significant impact on the future development of therapeutic agents targeting dementia. This study examined the effects of electroacupuncture (EA) stimulation on BACE1, APP, and p-PKA protein levels in hippocampal tissue samples. Memory and learning abilities were assessed using the Morris water maze test after EA intervention. Immunofluorescence, immunohistochemistry, and western blot were employed to assess the distribution patterns and expression levels of BACE1, APP, and p-PKA, respectively. The results showed the downregulation of BACE1 and APP and the activation of PKA by EA. In summary, EA treatment might reduce BACE1 deposition in APP/PS1 transgenic mice and regulate PKA and its associated substrates, such as LTP to change memory and learning abilities.

BACE1 Translation: At the Crossroads Between Alzheimer's Disease Neurodegeneration and Memory Consolidation

 Human life unfolds not only in time and space, but also in the recollection and interweaving of memories. Therefore, individual human identity depends fully on a proper access to the autobiographical memory. Such access is hindered under pathological conditions such as Alzheimer’s disease, which affects millions of people worldwide. Unfortunately, no effective cure exists to prevent this disorder, the impact of which will rise alarmingly within the next decades. While Alzheimer’s disease is largely considered to be the outcome of amyloid-β (Aβ) peptide accumulation in the brain, conceiving this complex disorder strictly as the result of Aβ-neurotoxicity is perhaps a too straight-line simplification. Instead, complementary to this view, the tableau of molecular disarrangements in the Alzheimer’s disease brain may be reflecting, at least in part, a loss of function phenotype in memory processing. Here we take BACE1 translation and degradation as a gateway to study molecular mechanisms putatively involved in the transition between memory and neurodegeneration. BACE1 participates in the excision of Aβ-peptide from its precursor holoprotein, but plays a role in synaptic plasticity too. Its translation is governed by eIF2α phosphorylation: a hub integrating cellular responses to stress, but also a critical switch in memory consolidation. Paralleling these dualities, the eIF2α-kinase HRI has been shown to be a nitric oxide-dependent physiological activator of hippocampal BACE1 translation. Finally, beholding BACE1 as a representative protease active in the CNS, we venture a new perspective on the cellular basis of memory, which may incorporate neurodegeneration in itself as a drift in memory consolidating systems.

Therapeutic potential of cyanobacterial pigment protein phycoerythrin: in silico and in vitro study of BACE1 interaction and in vivo Aβ reduction

Cyanobacteria are an immense source of innovative classes of pharmacologically active compounds exhibiting various biological activities ranging from antioxidants, antibiotics, anticancer, anti-inflammatory to anti-Alzheimer's disease. In the present study, we primarily targeted the inhibition of Beta-site amyloid precursor protein cleaving enzyme-1 (BACE1) by a naturally occurring cyanobacterial protein phycoerythrin (C-PE). BACE1 cleaves amyloid-β precursor protein (APP) and leads to accumulation of neurotoxic amyloid beta (Aβ) plaques in the brain, as an attribute of Alzheimer's disease (AD). Inhibition of BACE1 was measured in terms of their association and dissociation rate constants, thermodynamics of binding using surface plasmon resonance (SPR) and isothermal titration calorimetry (ITC). The kinetic parameters for enzyme activity were also measured using synthetic decapeptide as a substrate. We further validated the potential of PE by in-vivo histopathological staining of Aβ aggregate mutant Caenorhabditis elegans CL4176 by Thioflavin-T. The present studies pave the way for the application of naturally occurring C-PE as a putative therapeutic drug for the AD.

Resveratrol improves cognition and decreases amyloid plaque formation in Tg6799 mice

Alzheimer's disease (AD) is an irreversible, progressive neurodegenerative disorder of the central nervous system that causes severe cognitive impairment. One of the most significant pathological features of AD is the accumulation of β‑amyloid (Aβ) peptide in the brain. Resveratrol (Res) is a polyphenol derived from peanuts, red grapes and other plants, which has received increasing attention due to its neuroprotective features. Tg6799 mice are transgenic mice with five familial AD (FAD) mutations that are also known as 5XFAD mice. The present study aimed to investigate the effects of Res on Tg6799 mice. The transgenic mice were randomly divided into the Res treatment group and the vehicle control group, and were treated with 0.5% Res solution (60 mg/kg) or volume‑matched normal saline, respectively. Treatment was administered by oral gavage daily for 60 consecutive days. Res reduced amyloid plaque formation and the levels of Aβ42, and β‑secretase 1 levels were also significantly decreased. Furthermore, Res was able to reduce the expression of amyloid precursor protein and its cleavage products. The administration of Res to Tg6799 mice also improved their spatial working memory, as measured by the Y‑maze test, and rescued spatial memory deficits, as measured using the Morris water maze test; however, Res did not affect their motor function. In conclusion, this study suggested that Res may reduce Aβ‑induced neuronal damage, thus preventing memory loss.

Structure-Based Survey of the Binding Modes of BACE1 Inhibitors

BACE1 is a key aspartic protease that cleaves the amyloid precursor protein to generate of the amyloid peptide that is believed to be responsible for the Alzheimer's disease amyloid cascade. It is thus recognized as a promising therapeutic target for Alzheimer's disease treatment, and large efforts have been made in the discovery of novel BACE1 inhibitors. This Review presents a systematic mining of BACE1 inhibitors based on 354 crystal structures of the BACE1 catalytic domain in complex with ligands in the Protein Data Bank. A thorough exploration on the frequency as well as the patterns of residue-ligand interactions enables us to subdivide the ligand binding pocket into 10 subsites and then identify favorable substructures of ligands for each subsite. In addition, it is found that the assembly of subsites with an 8-like shape is responsible to bind all inhibitors and four major ligand binding modes are revealed. Thus, such a systematic survey deepens our understanding of the structural requirements for establishment of BACE1-ligand interactions that determine the affinity of a ligand to BACE1, which is pivotal for structure-based lead optimization and design of novel inhibitors.

Highly Selective and Potent Human β-Secretase 2 (BACE2) Inhibitors against Type 2 Diabetes: Design, Synthesis, X-ray Structure and Structure-Activity Relationship Studies

Herein we present the design, synthesis, and biological evaluation of potent and highly selective β-secretase 2 (memapsin 1, beta-site amyloid precursor protein cleaving enzyme 2, or BACE 2) inhibitors. BACE2 has been recognized as an exciting new target for type 2 diabetes. The X-ray structure of BACE1 bound to inhibitor 2 a {N³ -[(1S,2R)-1-benzyl-2-hydroxy-3-[[(1S,2S)-2-hydroxy-1-(isobutylcarbamoyl)propyl]amino]propyl]-5-[methyl(methylsulfonyl)amino]-N¹ -[(1R)-1-phenylpropyl]benzene-1,3-dicarboxamide} containing a hydroxyethylamine isostere was determined. Based on this structure, a computational docking study was performed which led to inhibitor 2 a-bound BACE2 models. These were used to optimize the potency and selectivity of inhibitors. A systematic structure-activity relationship study led to the identification of determinants of the inhibitors' potency and selectivity toward the BACE2 enzyme. Inhibitors 2 d [N³ -[(1S,2R)-1-benzyl-2-hydroxy-3-[[(1S,2S)-2-hydroxy-1-(isobutylcarbamoyl)pentyl]amino]propyl]-N¹ -methyl-N¹ -[(1R)-1-phenylpropyl]benzene-1,3-dicarboxamide; K_i =0.031 nm, selectivity over BACE1: ≈174 000-fold] and 3 l [N¹ -((2S,3R)-3-hydroxy-1-phenyl-4-((3-(trifluoromethyl)benzyl)amino)butan-2-yl)-N³ ,5-dimethyl-N³ -((R)-1-phenylethyl)isophthalamide; K_i =1.6 nm, selectivity over BACE1: >500-fold] displayed outstanding potency and selectivity. Inhibitor 3 l is nonpeptide in nature and may pave the way to the development of a new class of potent and selective BACE2 inhibitors with clinical potential.

Capillary electrophoresis integrated immobilized enzyme reactor for kinetic and inhibition assays of β-secretase as the Alzheimer's disease drug target

Capillary electrophoresis integrated immobilized enzyme reactors are becoming an increasingly popular alternative for enzyme kinetic and inhibition assays thanks to their unique set of features including cost effectiveness, repeated use of the enzyme, minuscule sample consumption, rapid analysis time and easy automation. In this work we present the development and application of a capillary electrophoresis integrated immobilized enzyme reactor based on magnetic particles for kinetic and inhibition studies of β-secretase, a key enzyme in the development of Alzheimer's disease and a promising drug target. We document the optimization of the immobilization procedure, characterization of immobilized β-secretase, optimization of a mutually compatible incubation protocol and separation method as well as the production of the capillary electrophoresis integrated immobilized enzyme reactor. The applicability of the capillary electrophoresis integrated immobilized enzyme reactor was demonstrated by kinetic assay with an unlabelled substrate and by inhibition assays using three structurally different reference inhibitors. The resulting kinetic and inhibition parameters clearly support the applicability of the herein presented method as well as document the fundamental phenomena which need to be taken in account when comparing the results to other methods.

Dual BACE1 and Cholinesterase Inhibitory Effects of Phlorotannins from Ecklonia cava-An In Vitro and in Silico Study

Alzheimer's disease (AD) is one of the most common neurodegenerative diseases with a multifactorial nature. β-Secretase (BACE1) and acetylcholinesterase (AChE), which are required for the production of neurotoxic β-amyloid (Aβ) and the promotion of Aβ fibril formation, respectively, are considered as prime therapeutic targets for AD. In our efforts towards the development of potent multi-target, directed agents for AD treatment, major phlorotannins such as eckol, dieckol, and 8,8'-bieckol from Ecklonia cava (E. cava) were evaluated. Based on the in vitro study, all tested compounds showed potent inhibitory effects on BACE1 and AChE. In particular, 8,8'-bieckol demonstrated the best inhibitory effect against BACE1 and AChE, with IC50 values of 1.62 ± 0.14 and 4.59 ± 0.32 µM, respectively. Overall, kinetic studies demonstrated that all the tested compounds acted as dual BACE1 and AChE inhibitors in a non-competitive or competitive fashion, respectively. In silico docking analysis exhibited that the lowest binding energies of all compounds were negative, and specifically different residues of each target enzyme interacted with hydroxyl groups of phlorotannins. The present study suggested that major phlorotannins derived from E. cava possess significant potential as drug candidates for therapeutic agents against AD.

BACE2, a conditional β-secretase, contributes to Alzheimer's disease pathogenesis

Deposition of amyloid-β protein (Aβ) to form neuritic plaques is the characteristic neuropathology of Alzheimer's disease (AD). Aβ is generated from amyloid precursor protein (APP) by β- and γ-secretase cleavages. BACE1 is the β-secretase and its inhibition induces severe side effects, whereas its homolog BACE2 normally suppresses Aβ by cleaving APP/Aβ at the θ-site (Phe20) within the Aβ domain. Here, we report that BACE2 also processes APP at the β site, and the juxtamembrane helix (JH) of APP inhibits its β-secretase activity, enabling BACE2 to cleave nascent APP and aggravate AD symptoms. JH-disrupting mutations and clusterin binding to JH triggered BACE2-mediated β-cleavage. Both BACE2 and clusterin were elevated in aged mouse brains, and enhanced β-cleavage during aging. Therefore, BACE2 contributes to AD pathogenesis as a conditional β-secretase and could be a preventive and therapeutic target for AD without the side effects of BACE1 inhibition.

Comprehensive review of mechanisms of pathogenesis involved in Alzheimer's disease and potential therapeutic strategies

AD is a progressive neurodegenerative disorder and a leading cause of dementia in an aging population worldwide. The enormous challenge which AD possesses to global healthcare makes it as urgent as ever for the researchers to develop innovative treatment strategies to fight this disease. An in-depth analysis of the extensive available data associated with the AD is needed for a more comprehensive understanding of underlying molecular mechanisms and pathophysiological pathways associated with the onset and progression of the AD. The currently understood pathological and biochemical manifestations include cholinergic, Aβ, tau, excitotoxicity, oxidative stress, ApoE, CREB signaling pathways, insulin resistance, etc. However, these hypotheses have been criticized with several conflicting reports for their involvement in the disease progression. Several issues need to be addressed such as benefits to cost ratio with cholinesterase therapy, the dilemma of AChE selectivity over BChE, BBB permeability of peptidic BACE-1 inhibitors, hurdles related to the implementation of vaccination and immunization therapy, and clinical failure of candidates related to newly available targets. The present review provides an insight to the different molecular mechanisms involved in the development and progression of the AD and potential therapeutic strategies, enlightening perceptions into structural information of conventional and novel targets along with the successful applications of computational approaches for the design of target-specific inhibitors.

Axonal organization defects in the hippocampus of adult conditional BACE1 knockout mice

β-Site APP (amyloid precursor protein) cleaving enzyme 1 (BACE1) is the β-secretase enzyme that initiates production of the toxic amyloid-β peptide that accumulates in the brains of patients with Alzheimer's disease (AD). Hence, BACE1 is a prime therapeutic target, and several BACE1 inhibitor drugs are currently being tested in clinical trials for AD. However, the safety of BACE1 inhibition is unclear. Germline BACE1 knockout mice have multiple neurological phenotypes, although these could arise from BACE1 deficiency during development. To address this question, we report that tamoxifen-inducible conditional BACE1 knockout mice in which the Bace1 gene was ablated in the adult largely lacked the phenotypes observed in germline BACE1 knockout mice. However, one BACE1-null phenotype was induced after Bace1 gene deletion in the adult mouse brain. This phenotype showed reduced length and disorganization of the hippocampal mossy fiber infrapyramidal bundle, the axonal pathway of dentate gyrus granule cells that is maintained by neurogenesis in the mouse brain. This defect in axonal organization correlated with reduced BACE1-mediated cleavage of the neural cell adhesion protein close homolog of L1 (CHL1), which has previously been associated with axon guidance. Although our results indicate that BACE1 inhibition in the adult mouse brain may avoid phenotypes associated with BACE1 deficiency during embryonic and postnatal development, they also suggest that BACE1 inhibitor drugs developed for treating AD may disrupt the organization of an axonal pathway in the hippocampus, an important structure for learning and memory.

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.

Understanding the Twisted Structure of Amyloid Fibrils via Molecular Simulations

Accumulation and aggregation of amyloid are associated with the pathogenesis of many human diseases, such as Alzheimer's disease and Type 2 diabetes mellitus. Therefore, a quantitative understanding of the molecular mechanisms causing different aggregated structures and biomechanical properties of amyloid fibrils could shed some light into the progression of these diseases. In this work, we develop coarse-grained molecular dynamics (CGMD) models to simulate the dynamic self-assembly of two types of amyloids (amylin and amyloid β (Aβ)). We investigate the structural and mechanical properties of different types of aggregated amyloid fibrils. Our simulations demonstrate that amyloid fibrils could result from longitudinal growth of protofilament bundles, confirming one of the hypotheses on the fibril formation. In addition, we find that the persistence length of amylin fibrils increases concurrently with their pitch length, suggesting that the bending stiffness of amylin fibrils becomes larger when the amylin fibrils are less twisted. Similar results are observed for Aβ fibrils. These findings quantify the connection between the structural and the biomechanical properties of the fibrils. The CGMD models developed in this work can be potentially used to examine efficacy of anti-aggregation drugs, which could help in developing new treatments.

Proteolytic ectodomain shedding of membrane proteins in mammals-hardware, concepts, and recent developments

Proteolytic removal of membrane protein ectodomains (ectodomain shedding) is a post-translational modification that controls levels and function of hundreds of membrane proteins. The contributing proteases, referred to as sheddases, act as important molecular switches in processes ranging from signaling to cell adhesion. When deregulated, ectodomain shedding is linked to pathologies such as inflammation and Alzheimer's disease. While proteases of the "a disintegrin and metalloprotease" (ADAM) and "beta-site APP cleaving enzyme" (BACE) families are widely considered as sheddases, in recent years a much broader range of proteases, including intramembrane and soluble proteases, were shown to catalyze similar cleavage reactions. This review demonstrates that shedding is a fundamental process in cell biology and discusses the current understanding of sheddases and their substrates, molecular mechanisms and cellular localizations, as well as physiological functions of protein ectodomain shedding. Moreover, we provide an operational definition of shedding and highlight recent conceptual advances in the field. While new developments in proteomics facilitate substrate discovery, we expect that shedding is not a rare exception, but rather the rule for many membrane proteins, and that many more interesting shedding functions await discovery.

A New Fluorogenic Small-Molecule Labeling Tool for Surface Diffusion Analysis and Advanced Fluorescence Imaging of β-Site Amyloid Precursor Protein-Cleaving Enzyme 1 Based on Silicone Rhodamine: SiR-BACE1

β-site APP-cleaving enzyme 1 (BACE1) is a major player in the pathogenesis of Alzheimer's disease. Structural and functional fluorescence microscopy offers a powerful approach to learn about the physiology and pathophysiology of this protease. Up to now, however, common labeling techniques require genetic manipulation, use large antibodies, or are not compatible with live cell imaging. Fluorescent small molecules that specifically bind to the protein of interest can overcome these limitations. Herein, we introduce SiR-BACE1, a conjugate of the BACE1 inhibitor S-39 and SiR647, as a novel fluorogenic, tag-free, and antibody-free label for BACE1. We present its chemical development, characterize its photophysical and pharmacologic properties, and evaluate its behavior in solution, in overexpression systems, and in native brain tissue. We demonstrate its applicability in confocal, stimulated emission depletion and dynamic single-molecule microscopy. The first functional studies with SiR-BACE1 on the surface mobility of BACE1 revealed a markedly confined diffusion pattern.

MixMD Probeview: Robust Binding Site Prediction from Cosolvent Simulations

Mixed-solvent molecular dynamics (MixMD) is a cosolvent simulation technique for identifying binding hotspots and specific favorable interactions on a protein's surface. MixMD studies have the ability to identify these biologically relevant sites by examining the occupancy of the cosolvent over the course of the simulation. However, previous MixMD analysis required a great deal of manual inspection to identify relevant sites. To address this limitation, we have developed MixMD Probeview as a plugin for the freely available, open-source version of the molecular visualization program PyMOL. MixMD Probeview incorporates two analysis procedures: (1) identifying and ranking whole binding sites and (2) identifying and ranking local maxima for each probe type. These functionalities were validated using four common benchmark proteins, including two with both active and allosteric sites. In addition, three different cosolvent procedures were compared to examine the impact of including more than one cosolvent in the simulations. For all systems tested, MixMD Probeview successfully identified known active and allosteric sites based on the total occupancy of neutral probe molecules. As an easy-to-use PyMOL plugin, we expect that MixMD Probeview will facilitate identification and analysis of binding sites from cosolvent simulations performed on a wide range of systems.

A gender dimorphism in up-regulation of BACE1 gene expression in schizophrenia

Schizophrenia has long been considered as a devastating brain disorder in which both genetic and environmental factors are involved. The BACE1 gene is one of the most important susceptibility genes for this disorder. However, the changes in BACE1 expression in schizophrenic patients compared with healthy subjects have not been evaluated yet. In this case-control study, we examined BACE1 expression in a group of 50 patients with schizophrenia and 50 healthy controls. The level of BACE1 gene expression was measured using Real-Time PCR. Substantial increase in gene expression was detected in the patients compared with normal individuals (P = 0.001). Furthermore, a gender dimorphism was observed in BACE1 gene expression in the patients in a way that the male patients manifested a statistically significant higher levels of BACE1 expression (P = 0.002). BACE1 might be implicated in the pathogenesis of schizophrenia. Besides, BACE1 physiology may be gender -based at some levels. Our findings warrant an investigation of BACE1 gene in a larger number of cases and controls.

Consequences of Rab GTPase dysfunction in genetic or acquired human diseases

Rab GTPases are important regulators of intracellular membrane trafficking in eukaryotes. Both activating and inactivating mutations in Rab genes have been identified and implicated in human diseases ranging from neurological disorders to cancer. In addition, altered Rab expression is often associated with disease prognosis. As such, the study of diseases associated with Rabs or Rab-interacting proteins has shed light on the important role of intracellular membrane trafficking in disease etiology. In this review, we cover recent advances in the field with an emphasis on cellular mechanisms.

BACE1 deletion in the adult mouse reverses preformed amyloid deposition and improves cognitive functions

This study uses mouse models to answer how BACE1 inhibitory drugs will be beneficial to Alzheimer’s patients. Hu et al. find that sequentially increased deletion of BACE1 in one adult Alzheimer’s mouse model reverses preexisting amyloid plaques and mitigates synaptic failures.

BACE1 initiates the generation of the β-amyloid peptide, which likely causes Alzheimer’s disease (AD) when accumulated abnormally. BACE1 inhibitory drugs are currently being developed to treat AD patients. To mimic BACE1 inhibition in adults, we generated BACE1 conditional knockout (BACE1^fl/fl) mice and bred BACE1^fl/fl mice with ubiquitin-Cre^ER mice to induce deletion of BACE1 after passing early developmental stages. Strikingly, sequential and increased deletion of BACE1 in an adult AD mouse model (5xFAD) was capable of completely reversing amyloid deposition. This reversal in amyloid deposition also resulted in significant improvement in gliosis and neuritic dystrophy. Moreover, synaptic functions, as determined by long-term potentiation and contextual fear conditioning experiments, were significantly improved, correlating with the reversal of amyloid plaques. Our results demonstrate that sustained and increasing BACE1 inhibition in adults can reverse amyloid deposition in an AD mouse model, and this observation will help to provide guidance for the proper use of BACE1 inhibitors in human patients.

Identification of rare RTN3 variants in Alzheimer's disease in Han Chinese

Reticulon 3 (RTN3) is a neuronally-expressed reticulon family protein that was previously shown to negatively regulate BACE1, a protease that is required for the generation of β-amyloid peptides (Aβ) from amyloid precursor protein. Despite biochemical and morphological evidence that supports a role of RTN3 in the formation of neuritic amyloid plaques, no systematic analyses of RTN3 mutations in patients with Alzheimer's disease (AD) have yet been reported. RTN3 were targeted sequenced in 154 sporadic early-onset and 285 late-onset AD patients. Luciferase reporter assay and kymographs were performed to analysis the expression of RNT3 and BACE1-RFP particle mobility on cells transfected with wild-type or variants RTN3 constructs. We identified heterozygous variants such as c.-8G > T, c.17C > A, c.42C > T, and c.116C > T from patients in the early-onset AD group and c.-8G > T, c.17C > A, from patients in the late-onset AD group. Such variants of RTN3 were not observed in control individuals. Further biochemical studies show that the RTN3 c.-8G > T variant in the 5'-untranslated region appears to cause reduced expression of RTN3. The RTN3 c.116 C > T variant causes a change of codon T39 to M39 (T39 M). Overexpression of RTN3 T39 M in cultured neurons led to impaired axonal transport of BACE1. The variants found in this study are likely genetic modifiers for RTN3-mediated formation of neuritic plaques in AD.

Effects of altered RTN3 expression on BACE1 activity and Alzheimer's neuritic plaques

Reticulon 3 (RTN3), which is a member of the reticulon family of proteins, has a biochemical function of shaping tubular endoplasmic reticulum. RTN3 has also been found to interact with β-site amyloid precursor protein cleaving enzyme 1 (BACE1), which initiates the generation of β-amyloid peptides (Aβ) from amyloid precursor protein. Aβ is the major proteinaceous component in neuritic plaques, which constitute one of the major pathological features in brains of Alzheimer's disease (AD) patients. Mice deficient in or overexpressing RTN3 have altered amyloid deposition through effects on BACE1 expression and activity. In this review, we will summarize the current findings concerning the role of RTN3 in AD pathogenesis and demonstrate that RTN3 protein levels act as age-dependent modulators of BACE1 activity and Aβ deposition during the pathogenic progression of AD.

Multi-functional neuroprotective activity of neohesperidin dihydrochalcone: a novel scaffold for Alzheimer's disease therapeutics identified via drug repurposing screening

Multi-target screening identifies neohesperidin dihydrochalcone for Alzheimer's disease therapeutics, which exhibits strong BACE1 and amyloid aggregation inhibition along with antioxidant activity.

Consequences of Rab GTPase dysfunction in genetic or acquired human diseases

Rab GTPases are important regulators of intracellular membrane trafficking in eukaryotes. Both activating and inactivating mutations in Rab genes have been identified and implicated in human diseases ranging from neurological disorders to cancer. In addition, altered Rab expression is often associated with disease prognosis. As such, the study of diseases associated with Rabs or Rab-interacting proteins has shed light on the important role of intracellular membrane trafficking in disease etiology. In this review, we cover recent advances in the field with an emphasis on cellular mechanisms.

Sequence, Structural Analysis and Metrics to Define the Unique Dynamic Features of the Flap Regions Among Aspartic Proteases

Aspartic proteases are a class of hydrolytic enzymes that have been implicated in a number of diseases such as HIV, malaria, cancer and Alzheimer's. The flap region of aspartic proteases is a characteristic unique structural feature of these enzymes; and found to have a profound impact on protein overall structure, function and dynamics. Flap dynamics also plays a crucial role in drug binding and drug resistance. Therefore, understanding the structure and dynamic behavior of this flap regions is crucial in the design of potent and selective inhibitors against aspartic proteases. Defining metrics that can describe the flap motion/dynamics has been a challenging topic in literature. This review is the first attempt to compile comprehensive information on sequence, structure, motion and metrics used to assess the dynamics of the flap region of different aspartic proteases in "one pot". We believe that this review would be of critical importance to the researchers from different scientific domains.

Resveratrol for Alzheimer's disease

The amyloid hypothesis suggests that the progressive accumulation and deposition of central nervous system (CNS) amyloid with aging is the proximate cause of Alzheimer's disease (AD). Thus, targeting molecular mechanisms of aging may be a viable treatment approach. Caloric restriction prevents diseases of aging, including AD, in animal models, perhaps by activation of sirtuins. The sirtuins (e.g., mammalian SIRT1) are deacetylases that link energy balance (NAD+ /NADH) to regulation of gene transcription. Resveratrol is a potent activator of SIRT1, and thus may mimic caloric restriction to prevent diseases of aging. We conducted a randomized, double-blind, placebo-controlled, phase II trial of resveratrol for individuals with mild-to-moderate AD. Resveratrol (1) is detectable in cerebrospinal fluid (at low nanomolar levels), (2) is safe and well tolerated, (3) alters AD biomarker trajectories, (4) preserves blood-brain barrier integrity, and (5) modulates the CNS immune response. Further studies are needed to determine the safety and efficacy of resveratrol and the validity of this approach in the treatment and prevention of AD and other diseases of aging.

Role of BACE1 in Alzheimer's synaptic function

Alzheimer's disease (AD) is the most common age-dependent disease of dementia, and there is currently no cure available. This hallmark pathologies of AD are the presence of amyloid plaques and neurofibrillary tangles. Although the exact etiology of AD remains a mystery, studies over the past 30 have shown that abnormal generation or accumulation of β-amyloid peptides (Aβ) is likely to be a predominant early event in AD pathological development. Aβ is generated from amyloid precursor protein (APP) via proteolytic cleavage by β-site APP cleaving enzyme 1 (BACE1). Chemical inhibition of BACE1 has been shown to reduce Aβ in animal studies and in human trials. While BACE1 inhibitors are currently being tested in clinical trials to treat AD patients, it is highly important to understand whether BACE1 inhibition will significantly impact cognitive functions in AD patients. This review summarizes the recent studies on BACE1 synaptic functions. This knowledge will help to guide the proper use of BACE1 inhibitors in AD therapy.

Beta-secretase inhibitors in phase I and phase II clinical trials for Alzheimer's disease

INTRODUCTION

BACE 1 is a protease that cleaves the transmembrane amyloid precursor protein and generates amyloid-β peptides that accumulate in AD brains. No known mutations are identified in the gene encoding BACE1 in AD. However, enzyme levels are elevated in AD and a single residue mutation in amyloid precursor protein protects against protein cleavage by BACE1, suggesting BACE involvement in disease pathogenesis. Drugs that can inhibit BACE1 would theoretically prevent Aβ accumulation and halt AD onset and progression. Areas covered: This review discusses clinical developments of BACE1 inhibitors and focuses on what is learned about these inhibitors as a potential treatment. Expert opinion: BACE1 inhibition as a therapeutic strategy to improve cognition in AD has been challening. Brain-penetrant BACE1 inhibitors have been developed and clinical trials are underway, both safety and efficacy are questionable. Several clinical trials suggest that BACE1 inhibition and other immunotherapies to reduce brain Aβ are insufficient to improve cognition in AD. This may be due to the emphasis on the amyloid hypothesis despite big failures. We may have to seriously consider shifting attention to therapeutic strategies other than BACE1 inhibition or reduction of Aβ alone and pay more attention to simultaneous clearance of tau and Aβ.