Beta-secretase as a target for the treatment of Alzheimer's disease

A Comprehensive Review on Potential Molecular Drug Targets for the Management of Alzheimer's Disease

Alzheimer's disease (AD) is an onset and incurable neurodegenerative disorder that has been linked to various genetic, environmental, and lifestyle factors. Recent research has revealed several potential targets for drug development, such as the prevention of Aβ production and removal, prevention of tau hyperphosphorylation, and keeping neurons alive. Drugs that target numerous ADrelated variables have been developed, and early results are encouraging. This review provides a concise map of the different receptor signaling pathways associated with Alzheimer's Disease, as well as insight into drug design based on these pathways. It discusses the molecular mechanisms of AD pathogenesis, such as oxidative stress, aging, Aβ turnover, thiol groups, and mitochondrial activities, and their role in the disease. It also reviews the potential drug targets, in vivo active agents, and docking studies done in AD and provides prospects for future drug development. This review intends to provide more clarity on the molecular processes that occur in Alzheimer's patient's brains, which can be of use in diagnosing and preventing the condition.

Selective Inhibition of Human Monoamine Oxidase B by 5-hydroxy-2-methyl-chroman-4-one Isolated from an Endogenous Lichen Fungus Daldinia fissa

Inhibitory activities against monoamine oxidases (MAOs) and cholinesterases (ChEs) and antioxidant activity were evaluated for 195 extracts from Ukraine-derived endogenous lichen fungi (ELF). Among them, an ELF13 (identified as Daldinia fissa) extract showed the highest inhibitory activity against MAO-B, and 5-hydroxy-2-methyl-chroman-4-one (HMC) was isolated as a ~ 4-fold selective inhibitor of MAO-B (IC₅₀ = 3.23 µM) compared to MAO-A (IC₅₀ = 13.97 µM). HMC is a reversible competitive inhibitor with a K_i value of 0.896 µM. No cytotoxicity was observed in normal and cancer cells at 50 µM of HMC. HMC showed blood–brain barrier permeability and high gastrointestinal absorption in silico pharmacokinetics. The docking simulation results showed that the binding affinity of HMC for MAO-B (−7.3 kcal/mol) was higher than that of MAO-A (−6.1 kcal/mol) and that HMC formed a hydrogen bond interaction with Cys172 of MAO-B (distance: 3.656 Å), whereas no hydrogen bonding was predicted with MAO-A. These results suggest that HMC can be considered a candidate for the treatment of neurodegenerative diseases, such as Alzheimer’s disease and Parkinson’s disease.

Revealing the cholinergic inhibition mechanism of Alzheimer's by galantamine: a metadynamics simulation study

Galantamine is one of the approved drugs based on the cholinergic hypothesis for the symptomatic treatment of mild to moderate Alzheimer's disease (AD). The etiology of AD is not fully known; however, the reported cholinergic hypothesis suggests the inadequate synthesis of the neurotransmitter acetylcholine (ACh) is responsible for this disease. The crystal structure of galantamine bound human acetylcholinesterase (hAChE) has been reported; however, the inhibition mechanism of hAChE by galantamine is not well understood. A Well-tempered metadynamics (WTMtD) simulation study has been performed with the crystal structure of galantamine bound hAChE. The reported mechanism for the degradation of ACh is suggested through a proton transfer process from a carboxylic group of Glu334 to the hydroxyl group of Ser203, which attacks ACh for the degradation to acetic acid and choline. Such proton transfer process is lowered in the presence of galantamine due to the separation of catalytic triad inside the gorge of AChE as observed with WTMtD. A docking study has been performed to examine the ACh's binding with the catalytic triad of galantamine bound hAChE. The docking results reveal that the approach of ACh to the catalytic triad is interrupted due to the galantamine's presence in the gorge of the enzyme.

Computational modelling of potent β-secretase (BACE1) inhibitors towards Alzheimer's disease treatment

Researchers have identified the β-amyloid precursor protein cleaving enzyme 1 (BACE1) in the multifactorial pathway of Alzheimer's disease (AD) as a drug target. The design and development of molecules to inhibit BACE1 as a potential cure for AD thus remained significant. Herein, we simulated two potent BACE1 inhibitors (AM-6494 and CNP-520) to understand their binding affinity at the atomistic level. AM-6494 is a newly reported potent BACE1 inhibitor with an IC₅₀ value of 0.4 nM in vivo and now picked for preclinical considerations. Umibecestat (CNP-520), which was discontinued at human trials lately, was considered to enable a reasonable evaluation of our results. Using density functional theory (DFT) and Our Own N-layered Integrated molecular Orbital and Molecular Mechanics (ONIOM), we achieved the aim of this investigation. These computational approaches enabled the prediction of the electronic properties of AM-6494 and CNP-520 plus their binding energies when complexed with BACE1. For AM-6494 and CNP-520 interaction with protonated BACE1, the ONIOM calculation gave binding free energy of -62.849 and -33.463 kcal/mol, respectively. In the unprotonated model, we observed binding free energy of -59.758 kcal/mol in AM-6494. Taken together thermochemistry of the process and molecular interaction plot, AM-6494 is more favourable than CNP-520 towards the inhibition of BACE1. The protonated model gave slightly better binding energy than the unprotonated form. However, both models could sufficiently describe ligand binding to BACE1 at the atomistic level. Understanding the detailed molecular interaction of these inhibitors could serve as a basis for pharmacophore exploration towards improved inhibitor design.

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.

Multi-Target β-Protease Inhibitors from Andrographis paniculata: In Silico and In Vitro Studies

Natural products derived from plants play a vital role in the discovery of new drug candidates, and these are used for novel therapeutic drug development. Andrographis paniculata and Spilanthes paniculata are used extensively as medicinal herbs for the treatment of various ailments, and are reported to have neuroprotective properties. β-amyloid is a microscopic brain protein whose significant aggregation is detected in mild cognitive impairment and Alzheimer’s disease (AD) brains. The accumulation of β-amyloid disrupts cell communication and triggers inflammation by activating immune cells, leading to neuronal cell death and cognitive disabilities. The proteases acetylcholinesterase (AChE), butyrylcholinesterase (BChE), and beta secretase-1 (BACE-1) have been reported to be correlated with the synthesis and growth of β-amyloid plaques in the brains of AD patients. In the present study, the phenolic compounds from A. paniculata and S. paniculata that have been reported in the literature were selected for the current investigation. Furthermore, we employed molecular docking and molecular dynamics studies of the phenolic compounds with the proteins AChE, BChE, and BACE-1 in order to evaluate the binding characteristics and identify potent anti-amyloid agents against the neurodegenerative diseases such as AD. In this investigation, we predicted three compounds from A. paniculata with maximum binding affinities with cholinesterases and BACE-1. The computational investigations predicted that these compounds follow the rule of five. We further evaluated these molecules for in vitro inhibition activity against all the enzymes. In the in vitro investigations, 3,4-di-o-caffeoylquinic acid (5281780), apigenin (5280443), and 7-o-methylwogonin (188316) were found to be strong inhibitors of AChE, BChE, and BACE-1. These findings suggest that these compounds can be potent multi-target inhibitors of the proteases that might cumulatively work and inhibit the initiation and formation of β-amyloid plaques, which is a prime cause of neurotoxicity and dementia. According to our knowledge, these findings are the first report on natural compounds isolated from A. paniculata as multi-target potent inhibitors and anti-amyloid agents.

Revealing the mechanistic pathway of cholinergic inhibition of Alzheimer's disease by donepezil: a metadynamics simulation study

Donepezil, an acetylcholinesterase inhibitor, is an approved drug for the symptomatic treatment of Alzheimer's disease (AD). The mechanistic pathway for the inhibition mechanism of acetylcholinesterase (AChE) by donepezil is not well explored. We report for the first time, the inhibition mechanism of AChE by the donepezil drug molecule for the hydrolysis of acetylcholine (ACh) with docking and well-tempered metadynamics (WTMtD) simulations with a human acetylcholinesterase (hAChE) crystal structure (). This study explored the orientation of the donepezil drug molecule inside the gorge of AChE. The 1D free energy surface obtained from WTMtD simulation studies reveals that the orientation of donepezil in the crystal donepezil (-87.25 kJ mol^-1) is energetically more favored than the other orientation of donepezil (-74.74 kJ mol^-1) for inhibition of AChE. The free energy landscape computation for the two sets of CVs further corroborates the 1D free energy surface. The WTMtD simulation performed with the crystal structure of donepezil bound hAChE gives the conformation of donepezil at Basin-I as similar to the conformation of donepezil observed in the crystal structure (). The WTMtD simulations further reveal that the bridged water molecules are more ordered near the catalytic triad of AChE to deter the nucleophilicity of Ser203 through intermolecular hydrogen bonding when donepezil approaches near to the active site gorge of AChE. The presence of donepezil near the active site of AChE can inhibit its approach for ACh hydrolysis; this is revealed through the docking study, where the drug molecule inside the active gorge of hAChE restricts the approach of ACh to Ser203 for the hydrolysis process.

Highlights in BACE1 Inhibitors for Alzheimer's Disease Treatment

Alzheimer's disease (AD) is a severe neurodegenerative disorder and the most common type of dementia in the elderly. The clinical symptoms of AD include a progressive loss of memory and impairment of cognitive functions interfering with daily life activities. The main neuropathological features consist in extracellular amyloid-β (Aβ) plaque deposition and intracellular Neurofibrillary tangles (NFTs) of hyperphosphorylated Tau. Understanding the pathophysiological mechanisms that underlie neurodegeneration in AD is essential for rational design of neuroprotective agents able to prevent disease progression. According to the "Amyloid Cascade Hypothesis" the critical molecular event in the pathogenesis of AD is the accumulation of Aβ neurotoxic oligomers. Since the proteolytic processing of Amyloid Precursor Protein (APP) by β-secretase (beta-site APP cleaving enzyme 1, BACE1) is the rate-limiting step in the production of Aβ, this enzyme is considered a major therapeutic target and BACE1 inhibitors have the potential to be disease-modifying drugs for AD treatment. Therefore, intensive efforts to discover and develop inhibitors that can reach the brain and effectively inhibit BACE1 have been pursued by several groups worldwide. The aim of this review is to highlight the progress in the discovery of potent and selective small molecule BACE1 inhibitors over the past decade.

Cyclic cis-Locked Phospho-Dipeptides Reduce Entry of AβPP into Amyloidogenic Processing Pathway

The cis/trans isomerization of X-Pro peptide bonds in proteins in some instances acts as a molecular switch in biological pathways. Our prior work suggests that the cis isomer of the phospho-Thr668-Pro669 motif, located in the cytoplasmic domain of the amyloid-β protein precursor (AβPP), is correlated with an increase in amyloidogenic processing of AβPP and production of amyloid-beta (Aβ), the neurotoxic peptide fragment in Alzheimer's disease (AD). We designed a 100% cis-locked cyclic dipeptide composed of cyclized phospho-Thr-Pro (pCDP) as a mimic for this putative pathological conformation, and three phosphate-blocked derivatives (pCDP-diBzl, pCDP-Bzl, and pCDP-diPOM). Two H4 neuroglioma cell lines were established as AD cell models for use in testing these compounds: H4-AβPP695 for stable overexpression of wild-type AβPP695, and H4-BACE1 for stable overexpression of β-site AβPP cleaving enzyme-1 (BACE1). The level of the secreted AβPP fragment resulting from BACE1 activity, sAβPPβ, served as a key proxy for amyloidogenic processing, since cleavage of AβPP by BACE1 is a requisite first step in Aβ production. Of the compounds tested, pCDP-diBzl decreased sAβPPβ levels in both cell lines, while pCDP-diPOM decreased sAβPPβ levels in only H4-BACE1 cells, all with similar dose-dependences and patterns of proteolytic AβPP fragments. Enzymatic assays showed that none of the pCDP derivatives directly inhibit BACE1 catalytic activity. These results suggest a model in which pCDP-diBzl and pCDP-diPOM act at a common point to inhibit entry of AβPP into the amyloidogenic AβPP processing pathway but through different targets, and provide important insights for the development of novel AD therapeutics.

2-Substituted-thio-N-(4-substituted-thiazol/1H-imidazol-2-yl)acetamides as BACE1 inhibitors: Synthesis, biological evaluation and docking studies

In this work, a series of 2-substituted-thio-N-(4-substituted-thiazol/1H-imidazol-2-yl)acetamide derivatives were developed as β-secretase (BACE-1) inhibitors. Supported by docking study, a small library of derivatives were designed, synthesized and biologically evaluated in vitro. In addition, the selected compounds were tested with affinity (K_D) towards BACE-1, blood brain barrier (BBB) permeability and cytotoxicity. The studies revealed that the most potent analog 41 (IC₅₀ = 4.6 μM) with high predicted BBB permeability and low cellular cytotoxicity, could serve as a good lead structure for further optimization.

Paradigm shift redefining molecular, metabolic and structural events in Alzheimer's disease involves a proposed contribution by transition metals. Defined lengthy preclinical stage provides new hope to circumvent advancement of disease- and age-related neurodegeneration

It is estimated that 5.5 Million North Americans suffer from varying degrees of Alzheimer's disease (AD) and by the year 2050 it may be one in 85 people globally (100 Million). It will be shown that heavy metal toxicity plays a significant role in sporadic AD. Although current literature speaks to involvement of metal ions (via Fenton reaction), studies and reviewers have yet to link cellular events including known structural changes such as amyloid plaque development to this metal toxicity the way it is proposed here. Contrary to the current AD model which positions BACE1 (β-secretase) as an aberrant or AD-advancing enzyme, it is proposed herein that the neuron's protective counteraction to this metal toxicity is, in fact, a justified increase in BACE1 activity and amyloid precursor protein (APP) processing to yield more secreted APP (sAPP) and β-amyloid peptide in response to metal toxicity. This new perspective which justifies a functional role for APP, BACE1 enzyme activity and the peptide products from this activity may at first appear to be counterintuitive. Compelling evidence, however, is presented and a mechanism is shown herein that validate BACE1 recruitment and the resulting β-amyloid protein as strategic countermeasures serving the cell effectively against neuro-impeding disease. It is proposed that β-amyloid peptide chelates and sequesters free heavy metals in the extracellular medium to aggregate as amyloid plaque while unchelated β-amyloid migrates across the cell membrane to chelate intracellular free divalent metals. The sequestered intracellular metal is subsequently chaperoned as a metallo-peptide to cross the plasma membrane and aggregate as amyloid plaques extracellularly. The BACE1 countermeasure is not genetic or metabolic aberration; and this novel conclusion demonstrates that it must not be inhibited as currently targeted. APP, BACE1, β-amyloid peptide, and sAPP play positive roles against the preclinical oxidative load that predates AD symptoms for as long as 20 years. A healthy neuron may tolerate free metal toxicity, such as iron in the case of injury-induced amyloid, for as long as twenty years due to this very BACE1 activity. In later stages, the uncontrolled metals and ROS are compounded by other factors which together overcome this BACE1/β-amyloid protein countermeasure. This results in a sudden increase in IL-1 leading to Tau's hyperphosphorylation as cited and eventually to Tau dissociation from the microtubule cytoskeleton interrupting cell trafficking. At this later stage of AD the β-amyloid protein which once served as a vehicle to escort toxic metals to the extracellular medium and a trap to form a relatively benign extraneuronal disposal site is no longer translocated due to interruption of trafficking and now accumulates intracellularly facilitating hyper-oxidative ROS levels and contributes to irreversible neuron apoptosis.

Pistagremic acid, a novel β-secretase enzyme (BACE1) inhibitor from Pistacia integerrima Stewart

A new triterpenic compound named pistagremic acid (PA) was once again isolated from Pistaciaintegerrima. The β-secretase inhibition study was carried out. Compound PA was found significantly active against β-secretase enzyme (BACE1) with IC50 value of 350 ± 2 nM in comparison to the standard inhibitors [Asn670, Sta671, Val672]-amyloid-β/A4 precursor protein 770 fragment 662-675 (IC50 = 290.71 ± 1 nM). The selectivity of this compound was also evaluated against the acetylcholinesterase and butyrylcholinesterase enzymes. Interestingly compound PA was found to be inactive against them and showed selectivity towards β-secretase enzyme (BACE1).

New type of BACE1 siRNA delivery to cells

BACKGROUND

Small interfering RNA (siRNA) gene therapy is a new molecular approach in the search for an efficient therapy for Alzheimer disease (AD), based on the principle of RNA interference. Reducing BACE activity can have great therapeutic potential for the treatment of AD. In this study, receptor-mediated delivery was used to deliver opioid peptide-conjugated BACE 1 to INR-32 human neuroblastoma cells.

MATERIAL AND METHODS

An INR-32 human neuroblastoma cell line was stably transfected to express the APP cDNA coding fragment containing the predicted sites for cleavage by α, β, or γ-secretase. This was then treated with BACE 1 siRNA to silence BACE gene expression. BACE gene transcription and translation was determined using BACE-1 siRNA cross-linked with opioid peptide, together with RT-PCR, Western blot analysis, and ELISA.

RESULTS

Receptor-mediated delivery was used to introduce BACE1 siRNA to the APP - INR 32 human neuroblastoma cells. Decreased BACE mRNA and protein expression were observed after the cells were transfected with BACE1 siRNA.

CONCLUSIONS

Delivery of BACE1 siRNA appears to specifically reduce the cleavage of APP by inhibiting BACE1 activity.

Molecular investigations of protriptyline as a multi-target directed ligand in Alzheimer's disease

Alzheimer's disease (AD) is a complex neurodegenerative disorder involving multiple cellular and molecular processes. The discovery of drug molecules capable of targeting multiple factors involved in AD pathogenesis would greatly facilitate in improving therapeutic strategies. The repositioning of existing non-toxic drugs could dramatically reduce the time and costs involved in developmental and clinical trial stages. In this study, preliminary screening of 140 FDA approved nervous system drugs by docking suggested the viability of the tricyclic group of antidepressants against three major AD targets, viz. Acetylcholinesterase (AChE), β-secretase (BACE-1), and amyloid β (Aβ) aggregation, with one member, protriptyline, showing highest inhibitory activity. Detailed biophysical assays, together with isothermal calorimetry, fluorescence quenching experiments, kinetic studies and atomic force microscopy established the strong inhibitory activity of protriptyline against all three major targets. The molecular basis of inhibition was supported with comprehensive molecular dynamics simulations. Further, the drug inhibited glycation induced amyloid aggregation, another important causal factor in AD progression. This study has led to the discovery of protriptyline as a potent multi target directed ligand and established its viability as a promising candidate for AD treatment.

From the dual function lead AP2238 to AP2469, a multi-target-directed ligand for the treatment of Alzheimer's disease

The development of drugs with different pharmacological properties appears to be an innovative therapeutic approach for Alzheimer's disease. In this article, we describe a simple structural modification of AP2238, a first dual function lead, in particular the introduction of the catechol moiety performed in order to search for multi-target ligands. The new compound AP2469 retains anti-acetylcholinesterase (AChE) and beta-site amyloid precursor protein cleaving enzyme (BACE)1 activities compared to the reference, and is also able to inhibit Aβ₄₂ self-aggregation, Aβ₄₂ oligomer-binding to cell membrane and subsequently reactive oxygen species formation in both neuronal and microglial cells. The ability of AP2469 to interfere with Aβ₄₂ oligomer-binding to neuron and microglial cell membrane gives this molecule both neuroprotective and anti-inflammatory properties. These findings, together with its strong chain-breaking antioxidant performance, make AP2469 a potential drug able to modify the course of the disease.

L655,240, acting as a competitive BACE1 inhibitor, efficiently decreases β-amyloid peptide production in HEK293-APPswe cells

AIM

To identify a small molecule L655,240 as a novel β-secretase (BACE1) inhibitor and to investigate its effects on β-amyloid (Aβ) generation in vitro.

METHODS

Fluorescence resonance energy transfer (FRET) was used to characterize the inhibitory effect of L655,240 on BACE1. Surface plasmon resonance (SPR) technology-based assay was performed to study the binding affinity of L655,240 for BACE1. The selectivity of L655,240 toward BACE1 over other aspartic proteases was determined with enzymatic assay. The effects of L655,240 on Aβ40, Aβ42, and sAPPβ production were studied in HEK293 cells stably expressing APP695 Swedish mutant(K595N/M596L) (HEK293-APPswe cells). The activities of BACE1, γ-secretase and α-secretase were assayed, and both the mRNA and protein levels of APP and BACE1 were evaluated using real-time PCR (RT-PCR) and Western blot analysis.

RESULTS

L655,240 was determined to be a competitive, selective BACE1 inhibitor (IC(50)=4.47±1.37 μmol/L), which bound to BACE1 directly (K(D)=17.9±0.72 μmol/L). L655,240 effectively reduced Aβ40, Aβ42, and sAPPβ production by inhibiting BACE1 without affecting the activities of γ-secretase and α-secretase in HEK293-APPswe cells. L655,240 has no effect on APP and BACE1 mRNA or protein levels in HEK293-APPswe cells.

CONCLUSION

The small molecule L655,240 is a novel BACE1 inhibitor that can effectively decreases Aβ production in vitro, thereby highlighting its therapeutic potential for the treatment of Alzheimer's disease.

Beneficial effect of antibodies against β- secretase cleavage site of APP on Alzheimer's-like pathology in triple-transgenic mice

The toxicity of amyloid β and tau, the two hallmark proteins in Alzheimer's disease (AD), has been extensively studied individually. Recently new data suggest their possible interactions and synergistic effects in the disease. In this study, we investigate the ability of antibodies against the β secretase cleavage site on APP, named BBS1, to affect tau pathology, besides their well established effect on intracellular Aβ and amyloid load. For this purpose we treated the triple transgenic mice model of AD (3x Tg-AD) with mAb BBS1 intracerebroventricularly, using mini osmotic pumps for one month. The experimental data demonstrated reduction in total and phosphorylated tau levels, explained by significant reduction in GSK3β which phosphorylates tau on sites recognized by antibodies against PHF1 and AT-8. The treatment increased the cognitive capabilities and reduced the brain inflammation levels which accompany AD pathology. The data showing that tau pathology was significantly reduced by BBS1 antibodies suggest a close interaction between tau and Aβ in the development of AD, and may serve as an efficient novel immunotherapy against both hallmarks of this disease.

In silico design and search for acetylcholinesterase inhibitors in Alzheimer's disease with a suitable pharmacokinetic profile and low toxicity

Alzheimer's disease is a complex neurodegenerative disorder of the central nervous system, characterized by amyloid-β deposits, τ-protein aggregation, oxidative stress and reduced levels of acetylcholine in the brain. One pharmacological approach is to restore acetylcholine level by inhibiting acetylcholinesterase (AChE) with reversible inhibitors, such as galanthamine, thus helping to improve the cognitive symptoms of the disease. In order to design new galanthamine derivatives and search for novel, potential inhibitors with improved interactions, as well as a suitable pharmacokinetic profile and low toxicity, several molecular modeling techniques were applied. These techniques included the investigation of AChE-drug complexes (1QT1 and 1ACJ Protein Data Bank codes), ligand-binding sites calculation within the active site of the enzyme, pharmacophore perception of galanthamine derivatives, virtual screening, toxicophorical analysis and estimation of pharmacokinetics properties. A total of four galanthamine derivatives having a N-alkyl-phenyl chain were designed, since the tertiary amine substituents could reach the peripheral anionic site that is not occupied by galanthamine. In addition, 12 drug-like compounds from the Ilibdiverse database were selected by virtual screening as novel, hypothetical AChE inhibitors. The toxicophorical analysis revealed that only four proposed inhibitors have chemical groups able to develop mutagenicity and chromosome damage. The remaining compounds showed only mild or none toxicophorical alerts. At least three screened compounds presented theoric parameters consistent with good oral bioavailability. The designed molecules have the potential to become new lead compounds that might guide the design of drugs with optimized pharmacodynamic and pharmacokinetic properties in order to improve the treatment of Alzheimer's disease by creating new pharmacotherapeutic options.

BACE1 inhibitory activity of fungal endophytic extracts from Malaysian medicinal plants

BACKGROUND

BACE1 was found to be the major β-secretase in neurons and its appearance and activity were found to be elevated in the brains of AD patients. Fungal endophytic extracts for BACE1 inhibitory activity and cytotoxicity against PC-12 (a rat pheochromocytoma with neuronal properties) and WRL68 (a non-tumorigenic human hepatic) were investigated.

METHODS

Endophytes were isolated from plants collected from Kuala Pilah, Negeri Sembilan and the National Park, Pahang and the extracts were tested for BACE1 inhibition. For investigation of biological activity, the pure endophytic cultures were cultivated for 14 days on PDA plates at 28°C and underwent semipolar extraction with ethyl acetate.

RESULTS

Of 212 endophytic extracts (1000 μg/ml), 29 exhibited more than 90% inhibition of BACE1 in the preliminary screening. Four extracts from isolates HAB16R13, HAB16R14, HAB16R18 and HAB8R24 identified as Cytospora rhizophorae were the most active with IC(50(BACE1)) values of less than 3.0 μg/ml. The most active extract HAB16R13 was shown to non-competitively inhibit BACE1 with K(i) value of 10.0 μg/ml. HAB16R13 was considered non-potent against PC-12 and WRL68 (IC(50(CT))) of 60.0 and 40.0 μg/ml, respectively).

CONCLUSIONS

This first report on endophytic fungal extract with good BACE1 inhibitory activity demonstrates that more extensive study is required to uncover the potential of endophytes.

Current therapeutic options for Alzheimer's disease

Alzheimer's disease (AD) is the most common neurodegenerative disease in the developed world. The increasing life expectancy in the last years has led to an increase in the prevalence of this age-related condition and has posed an important medical and social challenge for developed societies. The mainstays of current therapy for AD rely on the cholinergic hypothesis developed more than 20 years ago. These compounds, known as acetylcholinesterase inhibitors (AChEIs), inhibit the cholinesterases and aim at improving the brain synaptic availability of acetylcholine. These drugs have been approved for the treatment of AD based on pivotal clinical trials showing modest symptomatic benefit on cognitive, behavioral, and global measures. Memantine, an NMDA antagonist, has been recently included as a therapeutic option for AD. Memantine can be combined safely with AChEIs for an additional symptomatic benefit. During the last years our understanding of the mechanisms underlying the pathogenesis of AD has markedly expanded. Several putative neuroprotective drugs are thoroughly investigated and many of them have reached the clinical arena. It can be anticipated that some of these drugs will be able to slow/prevent the progression of this condition in the near future.

Flavonoids lower Alzheimer's Aβ production via an NFκB dependent mechanism

Alzheimer's disease (AD) is characterized by the brain accumulation of Aβ peptides and by the presence of neurofibrillary tangles. Aβ is believed to play an important role in AD and it has been shown that certain flavonoids can affect Aβ production. Recently, it was suggested that the Aβ lowering properties of flavonoids are mediated by a direct inhibition the β-secretase (BACE-1) activity, the rate limiting enzyme responsible for the production of Aβ peptides. Westernblots and ELISAs were employed to monitor the impact of flavonoids on amyloid precursor protein processing and Aβ production. A cell free chemoluminescent assay using human recombinant BACE-1 was used to assess the effect of flavonoids on BACE-1 activity. The effect of flavonoids on NFκB activation was determined by using a stable NFκB luciferase reporter cell line. Molecular docking simulations were performed to predict the binding of flavonoids to the BACE-1 catalytic site. Real time quantitative PCR was used to determine the effect of flavonoids on BACE-1 transcription. We show in a cell free assay that flavonoids are only weak inhibitors of BACE-1 activity. Docking simulation studies with different BACE-1 structures also suggest that flavonoids are poor BACE-1 inhibitors as they appear to adopt various docking poses in the active site pocket and have weak docking scores that differ as a function of the BACE-1 structures studied. Moreover, a weak correlation was observed between the effect of flavonoids on Aβ production in vitro and their ability to lower BACE-1 activity suggesting that the Aβ lowering properties of flavonoids in whole cells are not mediated via direct inhibition of BACE-1 activity. We found however a strong correlation between the inhibition of NFκB activation by flavonoids and their Aβ lowering properties suggesting that flavonoids inhibit Aβ production in whole cells via NFκB related mechanisms. As NFκB has been shown to regulate BACE-1 expression, we show that NFκB lowering flavonoids inhibit BACE-1 transcription in human neuronal SH-SY5Y cells. Altogether, our data suggest that flavonoids inhibit Aβ and sAPPβ production by regulating BACE-1 expression and not by directly inhibiting BACE-1 activity.

Identification of beta-secretase (BACE1) substrates using quantitative proteomics

β-site APP cleaving enzyme 1 (BACE1) is a transmembrane aspartyl protease with a lumenal active site that sheds the ectodomains of membrane proteins through juxtamembrane proteolysis. BACE1 has been studied principally for its role in Alzheimer's disease as the β-secretase responsible for generating the amyloid-β protein. Emerging evidence from mouse models has identified the importance of BACE1 in myelination and cognitive performance. However, the substrates that BACE1 processes to regulate these functions are unknown, and to date only a few β-secretase substrates have been identified through candidate-based studies. Using an unbiased approach to substrate identification, we performed quantitative proteomic analysis of two human epithelial cell lines stably expressing BACE1 and identified 68 putative β-secretase substrates, a number of which we validated in a cell culture system. The vast majority were of type I transmembrane topology, although one was type II and three were GPI-linked proteins. Intriguingly, a preponderance of these proteins are involved in contact-dependent intercellular communication or serve as receptors and have recognized roles in the nervous system and other organs. No consistent sequence motif predicting BACE1 cleavage was identified in substrates versus non-substrates. These findings expand our understanding of the proteins and cellular processes that BACE1 may regulate, and suggest possible mechanisms of toxicity arising from chronic BACE1 inhibition.

Do CSF total tau, phosphorylated tau, and beta-amyloid 42 help to predict progression of mild cognitive impairment to Alzheimer's disease? A systematic review and meta-analysis of the literature

The search for biomarkers as a diagnostic aid to the identification of patients in pre-dementia stages is a fast growing research area. In view of the low specificity attained with the clinically based diagnostic criteria, including those for mild cognitive impairment (MCI), biomarker information will add precision to the incipient dementia diagnostic work-up, particularly Alzheimer's disease (AD). We present a systematic review of the literature and meta-analysis of the most relevant publications about the role of CSF biomarkers in the identification of patients with probable Alzheimer's disease at pre-dementia stages. A total of 16 studies were included in the systematic review, five of which were suitable for meta-analysis. We compared the standard mean differences (SMD) of beta-amyloid 42 (Abeta42), total tau (T-tau) and phosphorylated tau (P-tau) for 130, 169 and 123 patients with MCI who converted to AD (MCI-AD) and 142, 157 and 130 controls, respectively. We conclude that when a clinical diagnosis of MCI is made at baseline assessment, low CSF levels of Abeta42 (SMD: -1.57, CI 95% [-2.30 to -0.84], P < 0.001), along with high T-tau (SMD: 1.52, CI 95% [1.25 to 1.79], P < 0.001), and high P-tau (SMD: 1.75, CI 95% [0.99 to 2.51], P < 0.001), help to predict the conversion to Alzheimer's disease as compared to controls subjects.

Assessment of neuroprotection in the retina with DARC

Currently, assessment of new drug efficacy in glaucoma relies on conventional perimetry to monitor visual field changes. However, visual field defects cannot be detected until 20-40% of retinal ganglion cells (RGCs), the key cells implicated in the development of irreversible blindness in glaucoma, have been lost. We have recently developed a new, noninvasive real-time imaging technology, which is named DARC (detection of apoptosing retinal cells), to visualize single RGC undergoing apoptosis, the earliest sign of glaucoma. Utilizing fluorescently labeled annexin 5 and confocal laser scanning ophthalmoscopy, DARC enables evaluation of treatment effectiveness by monitoring RGC apoptosis in the same living eye over time. Using DARC, we have assessed different neuroprotective therapies in glaucoma-related animal models and demonstrated DARC to be a useful tool in screening neuroprotective strategies. DARC will potentially provide a meaningful clinical end point that is based on the direct assessment of the RGC death process, not only being useful in assessing treatment efficacy, but also leading to the early identification of patients with glaucoma. Clinical trials of DARC in glaucoma patients are due to start in 2008.

Development and characterization of beta-secretase monolithic micro-immobilized enzyme reactor for on-line high-performance liquid chromatography studies

beta-Site APP cleavage enzyme 1 (BACE-1) is a transmembrane aspartyl protease that cleaves the amyloid-beta precursor protein (APP), which is abundant in neurons. BACE-1 is required for the generation of amyloid-beta (Abeta) peptides implicated in the pathogenesis of Alzheimer's disease (AD). It is widely believed that halting the production of Abeta peptide, by inhibition of BACE-1, is an attractive therapeutic modality for the treatment of Alzheimer's disease. BACE-1 has never been immobilized before. In the present study, for the first time, human recombinant beta-secretase micro-immobilised enzyme reactor (hrBACE-1-micro-IMER) was prepared by using an in situ immobilisation procedure on an ethylendiamine monolithic convective interaction media (EDA-CIM) disk. The activity and kinetic parameters of the hrBACE-1-micro-IMER were investigated by insertion in a HPLC system with fluorescent and mass detection. The micro-IMER was characterized in terms of units of immobilised hrBACE-1 and best mobile phase conditions for activity, by using as substrate casein-FITC and JMV2236, a peptide mimicking the Swedish-mutated APP (amyloid precursor protein) sequence. The characterization of the hrBACE-1-micro-IMER in terms of number of enzymatic active units after covalent linking to the solid matrix was performed by using the JMV2236 peptide as substrate in a HPLC-MS system. JMV2236 was injected into the hrBACE-1-micro-IMER and enzymatically cleaved; the product of the enzymatic cleavage and the remaining non-cleaved substrate were collected on a C18 column trap and switched to the LC-electrospray ionization MS system for kinetic constants determination. Inhibition studies were carried out. The effect of donepezil and pepstatin A, as BACE-1 inhibitors, was evaluated by simultaneous injection of the compounds with the peptidic substrate. The relative IC(50) values were found in agreement with that derived by the conventional fluorescence method, confirming the applicability of this new IMER for on-line inhibition studies. The main advantages of the hrBACE-1-micro-IMER approach over the conventional methods were found to be the increased enzyme efficiency, stability and the decreased time of analysis.

Multi-target-directed coumarin derivatives: hAChE and BACE1 inhibitors as potential anti-Alzheimer compounds

The complex etiology of Alzheimer's disease (AD) prompts scientists to develop multifunctional compounds to combat causes and symptoms of such neurodegeneration. To this aim we designed, synthesized, and tested a series of compounds by introducing halophenylalkylamidic functions on the scaffold of AP2238, which is a dual binding site acetylcholinesterase inhibitor. The inhibitory activity was successfully extended to the beta-site amyloid precursor protein cleavage enzyme, leading to the discovery of a potent inhibitor of this enzyme (3) and affording multifunctional compounds (2, 6, 8) for the treatment of AD.

Targeting amyloid-beta in glaucoma treatment

The development of the devastating neurodegenerative condition, Alzheimer's disease, is strongly associated with amyloid-beta (Abeta) deposition, neuronal apoptosis, and cell loss. Here, we provide evidence that implicates these same mechanisms in the retinal disease glaucoma, a major cause of irreversible blindness worldwide, previously associated simply with the effects of intraocular pressure. We show that Abeta colocalizes with apoptotic retinal ganglion cells (RGC) in experimental glaucoma and induces significant RGC apoptosis in vivo in a dose- and time-dependent manner. We demonstrate that targeting different components of the Abeta formation and aggregation pathway can effectively reduce glaucomatous RGC apoptosis in vivo, and finally, that combining treatments (triple therapy) is more effective than monotherapy. Our work suggests that targeting the Abeta pathway provides a therapeutic avenue in glaucoma management. Furthermore, our work demonstrates that the combination of agents affecting multiple stages in the Abeta pathway may be the most effective strategy in Abeta-related diseases.

Beta-secretase (BACE1)-inhibiting stilbenoids from Smilax Rhizoma

In the course of searching for BACE1 (beta-secretase) inhibitors from natural products, the ethyl acetate soluble fraction of Smilax Rhizoma (the dried rhizomes of Smilax china L.) showed potent inhibitory activity. The active compounds were identified as a trans/cis-resveratrol mixture, oxyresveratrol, veraphenol, and cis-scirpusin A. They were shown to non-competitively inhibit BACE1 with the Ki values of 5.4 x 10(-6), 5.4 x 10(-6), 3.4 x 10(-6), and 5.4 x 10(-6)M and IC(50) values of 1.5 x 10(-5), 7.6 x 10(-6), 4.2 x 10(-6), and 1.0 x 10(-5)M, respectively. The active compounds were less inhibitory to alpha-secretase (TACE) and other serine proteases such as chymotrypsin, trypsin, and elastase, suggesting that they were relatively specific inhibitors of BACE1.

Identification of inhibitors using a cell-based assay for monitoring Golgi-resident protease activity

Noninvasive real-time quantification of cellular protease activity allows monitoring of enzymatic activity and identification of activity modulators within the protease's natural milieu. We developed a protease activity assay based on differential localization of a recombinant reporter consisting of a Golgi retention signal and a protease cleavage sequence fused to alkaline phosphatase (AP). When expressed in mammalian cells, this protein localizes to Golgi bodies and, on protease-mediated cleavage, AP translocates to the extracellular medium where its activity is measured. We used this system to monitor the Golgi-associated protease furin, a pluripotent enzyme with a key role in tumorigenesis, viral propagation of avian influenza, ebola, and HIV as well as in activation of anthrax, pseudomonas, and diphtheria toxins. This technology was adapted for high-throughput screening of 39,000-compound small molecule libraries, leading to identification of furin inhibitors. Furthermore, this strategy was used to identify inhibitors of another Golgi protease, the beta-site amyloid precursor protein (APP)-cleaving enzyme (BACE). BACE cleavage of the APP leads to formation of the Abeta peptide, a key event that leads to Alzheimer's disease. In conclusion, we describe a customizable noninvasive technology for real-time assessment of Golgi protease activity used to identify inhibitors of furin and BACE.

Lithium decreases secretion of Abeta1-42 and C-truncated species Abeta1-37/38/39/40 in chicken telencephalic cultures but specifically increases intracellular Abeta1-38

We studied endogenous amyloid precursor protein (APP) processing and amyloid beta (Abeta) peptide formation in primary chicken telencephalic neurons, because their Abeta peptide sequence is identical to humans. As detected by quantitative Abeta-SDS-PAGE/immunoblot, Abeta peptides 1-40/42 and three additional C-truncated species, namely Abeta1-37/38/39 were regularly released into the supernatant. The highly conserved Abeta quintet strongly resembles the pattern of Abeta peptides found in human cerebrospinal fluid. Furthermore, the C-terminally shorter Abeta peptides 1-33/34 could be readily detected. Recent evidence indicates that lithium specifically inhibits secretion of the amyloidogenic Abeta1-42 peptide in cultured permanent cells transfected with human APP. We therefore investigated the effect of lithium on Abeta peptide secretion as well as intracellular Abeta peptides in our untransfected primary cell culture system. Our data shows that lithium leads to a dose-dependent reduction of Abeta1-37/38/39/40/42 secretion. Surprisingly, intracellular analysis revealed that lithium specifically increases a band comigrating with synthetic Abeta1-38 while Abeta1-40 and Abeta1-42 remained almost unaffected. These results demonstrate for the first time that lithium treatment decreases Abeta peptide secretion in primary chicken neuronal cells but specifically elevates intracellular Abeta1-38. Therefore, we conclude that there are two independent mechanisms of lithium in intra- and extracellular Abeta peptide production.

BACE1, a major determinant of selective vulnerability of the brain to amyloid-beta amyloidogenesis, is essential for cognitive, emotional, and synaptic functions

A transmembrane aspartyl protease termed beta-site APP cleavage enzyme 1 (BACE1) that cleaves the amyloid-beta precursor protein (APP), which is abundant in neurons, is required for the generation of amyloid-beta (Abeta) peptides implicated in the pathogenesis of Alzheimer's disease (AD). We now demonstrate that BACE1, enriched in neurons of the CNS, is a major determinant that predisposes the brain to Abeta amyloidogenesis. The physiologically high levels of BACE1 activity coupled with low levels of BACE2 and alpha-secretase anti-amyloidogenic activities in neurons is a major contributor to the accumulation of Abeta in the CNS, whereas other organs are spared. Significantly, deletion of BACE1 in APPswe;PS1DeltaE9 mice prevents both Abeta deposition and age-associated cognitive abnormalities that occur in this model of Abeta amyloidosis. Moreover, Abeta deposits are sensitive to BACE1 dosage and can be efficiently cleared from the CNS when BACE1 is silenced. However, BACE1 null mice manifest alterations in hippocampal synaptic plasticity as well as in performance on tests of cognition and emotion. Importantly, memory deficits but not emotional alterations in BACE1(-/-) mice are prevented by coexpressing APPswe;PS1DeltaE9 transgenes, indicating that other potential substrates of BACE1 may affect neural circuits related to emotion. Our results establish BACE1 and APP processing pathways as critical for cognitive, emotional, and synaptic functions, and future studies should be alert to potential mechanism-based side effects that may occur with BACE1 inhibitors designed to ameliorate Abeta amyloidosis in AD.

Current Pharmacotherapy for Alzheimer's Disease

Alzheimer's disease (AD) is an age-related neurodegenerative disease that affects approximately 4.5 million people in the United States. The mainstays of current pharmacotherapy for AD are compounds aimed at increasing the levels of acetylcholine in the brain, thereby facilitating cholinergic neurotransmission through inhibition of the cholinesterases. These drugs, known as acetylcholinesterase inhibitors (AChEIs), were first approved by the U.S. Food and Drug Administration (FDA) in 1995 based on clinical trials showing modest symptomatic benefit on cognitive, behavioral, and global measures. In 2004 the FDA approved memantine, an NMDA antagonist, for treating dementia symptoms in moderate to severe AD cases. In clinical practice, memantine may be co-administered with an AChEI, although neither drug individually or in combination affects the underlying pathophysiology of dementia. Dementia in AD results from progressive synaptic loss and neuronal death. As knowledge of the mechanisms responsible for neurodegeneration in AD increases, it is anticipated that neuroprotective drugs to slow or prevent neuronal dysfunction and death will be developed to complement current symptomatic treatments.

A PNA-DNA hybridization chip approach for the detection of beta-secretase activity

Developed was the addressable chip technology based on the PNA-DNA complementary hybridization equipped with short seven-mer PNA-encoded peptides that can be a versatile scaffold to monitor on-chip immunoassays. We also developed and validated a methodology to perform beta-secretase enzyme assay with a highly sensitive fashion, resulting that a peptide substrate tethering dual fluorescent probes allowed us to detect beta-secretase activity 10 times more sensitively than assays in solution.

Post-translational processing of beta-secretase in Alzheimer's disease

Beta-amyloid is released into the brains of Alzheimer's patients, where it aggregates and causes damage to neurons. It is cleaved proteolytically from a large transmembrane glycoprotein amyloid precursor protein by a membrane-bound protease, known as beta-secretase identified previously as the acid protease, Asp-2. We have shown previously that beta-secretase is up-regulated by increased intracellular cholesterol, and down-regulated by cholesterol biosynthesis inhibition. Here we show using mass spectrometry that discrete changes in the glycosylation and palmitoylation of beta-secretase occur when cells expressing it are treated with statins.

β-Secretase (BACE1) inhibitors from Sanguisorbae Radix

In the course of screening anti-dementia agents from natural products, two beta-secretase (BACE1) inhibitors were isolated from the ethyl acetate soluble fraction of Sanguisorbae Radix by the activity-guided purification using silica gel, Sephadex LH-20, and RP-HPLC. They were identified as 1,2,3-trigalloyl-4,6-hexahydroxydiphenoyl-beta-D-glucopyranoside (Tellimagrandin II, 1) and 1,2,3,4,6-pentagalloyl-beta-D-glucopyranoside (2) and were shown to non-competitively inhibit beta-secretase (BACE1) with the IC50 values of 3.10x10(-6) M and 3.76x10(-6) M, respectively. The Ki values of 1 and 2 were 6.84x10(-6) M and 5.13x10(-6) M. They were less inhibitory to alphasecretase (TACE) and other serine proteases such as chymotrypsin, trypsin, and elastase, suggesting that they were relatively specific inhibitors of BACE1.

A Computational Positron Emission Tomography Simulation Model for Imaging ?-Amyloid in Mice

PURPOSE

We aimed to develop a computational simulation model for beta-amyloid (Abeta) positron emission tomography (PET) imaging.

PROCEDURES

Model parameters were set to reproduce levels of Abeta within the PDAPP mouse. Pharmacokinetic curves of virtual tracers were computed and a PET detector simulator was configured for a commercially available preclinical PET-imaging system.

RESULTS

We modeled the effects of Abeta therapy and tracer affinity on the ability to differentiate Abeta levels by PET. Varying affinity had a significant effect on the ability to quantitate Abeta. Further, PET tracers for Abeta monomers were more sensitive to the therapeutic reduction in Abeta levels than total brain amyloid. Following therapy, the decrease in total brain Abeta corresponded to the slow rate of change in total amyloid load as expected.

CONCLUSIONS

We have developed a first proof-of-concept Abeta-PET simulation model that will be a useful tool in the interpretation of preclinical Abeta imaging data and tracer development.

Alzheimer's beta-secretase cleaves a glycosyltransferase as a physiological substrate

Alzheimer's beta-secretase (BACE1) is a membrane-bound protease that cleaves the amyloid precursor protein (APP) in the trans-Golgi network, an initial step in the pathogenesis of Alzheimer's disease. Although BACE1 is distributed among various tissues including brain, its physiological substrate other than APP have not been identified. We have recently found that when BACE1 was overexpressed in COS cells together with alpha2,6-sialyltransferase (ST6Gal I), the secretion of ST6Gal I markedly increased, suggesting that BACE1 cleaves ST6Gal I as a physiological substrate. Thus BACE1 is the first identified protease that is responsible for the cleavage and secretion of glycosyltransferases.

Rational design and synthesis of selective BACE-1 inhibitors

An effective approach for enhancing the selectivity of beta-site amyloid precursor protein cleaving enzyme (BACE 1) inhibitors is developed based on the unique features of the S1' pocket of the enzyme. A series of low molecular weight (<600) compounds were synthesized with different moieties at the P1' position. The selectivity of BACE 1 inhibitors versus cathepsin D and renin was enhanced 120-fold by replacing the hydrophobic propyl group with a hydrophilic propionic acid group.

AATF protects neural cells against oxidative damage induced by amyloid beta-peptide

Extensive loss of neurons and synapses in vulnerable regions of the brain is one of the most important pathological features of Alzheimer's disease (AD). Increased oxidative stress has been shown to contribute to the neurodegenerative process in AD. Aggregation of amyloid beta-peptide (Abeta) in amyloid plaques is one of the defining features of Alzheimer's disease. Indeed, Abeta has been shown to induce oxidative stress and apoptosis in many in vivo and in vitro models of AD. We now report that AATF (apoptosis-antagonizing transcription factor), a leucine zipper protein initially identified as an interaction partner of DAP like kinase (Dlk, a member of the pro-apoptotic Death-Associated Protein kinase family), is expressed in cortical neurons and in neural PC12 cells. Abeta induces alterations in AATF expression in cortical neurons. Inhibition of AATF induction sensitizes neurons to Abeta toxicity. Overexpression of AATF suppressed superoxide production, inhibited peroxynitrite formation and membrane lipid peroxidation, and protected against Abeta-induced apoptosis in PC12 cells. These results suggest that AATF is a novel neuroprotective factor and it may protect against Abeta-induced apoptosis through its effects on suppressing the production of reactive oxygen species (ROS). AATF may therefore represent a potential candidate for therapeutic intervention of neurodegeneration in both sporadic and familial forms of AD.

[Current status and perspectives on the development of therapeutic agents for Alzheimer's disease]

Acetylcholinesterase inhibitors have beneficial effects to improve the cognitive impairment in patients with mild to moderate Alzheimer's disease (AD). In addition, a channel blocker of N-methyl-D-aspartate receptor, memantine hydrochloride, was approved as a therapeutic agent for patients with moderate to severe AD in both EU countries in 2002 and USA in 2003, while the clinical development is still ongoing in Japan. In contrast, the pharmacotherapy for a prime cure against AD is not available in the market, although there has been a worldwide search for novel compounds. The most plausible mechanism for the treatment of AD is the reduction of the amyloid beta-peptide (Abeta) plaques, one of the pathological markers of AD, in the brain. For this purpose, the inhibitors of beta-secretase and gamma-secretase, which cleave amyloid precursor protein (APP) to release Abeta, has been developed to interfere with APP processing. The beta-sheet breaker and metal chelators for the breakdown of aggregated Abeta have also been synthesized as well as the immunotherapeutic approach using Abeta vaccine. On the other hand, some nonsteroidal anti-inflammatory drugs, such as ibuprofen and sulindac, noncompetitively inhibited Abeta production but not Notch cleavage. The development of Abeta-lowering drugs is highly expected for the treatment of AD.

Inhibition of tumor necrosis factor-alpha-converting enzyme by a selective antagonist protects brain from focal ischemic injury in rats

Tumor necrosis factor alpha (TNFalpha) is an immunomodulatory and proinflammatory cytokine implicated in neuroinflammation and neuronal damage in response to cerebral ischemia. Tumor necrosis factor-alpha converting enzyme (TACE or ADAM17) is a key sheddase that releases TNFalpha from its inactive cell-bound precursor. Using a selective small molecule inhibitor of TACE, DPH-067517, we tested the hypothesis that inhibition of TNFalpha formation might have a salutary effect in ischemic stroke induced by embolic occlusion of the middle cerebral artery (MCAO). DPH-067517 selectively inhibited TACE enzyme activity in vitro (K(i) = 2.8 nM), and effectively suppressed ischemia-induced increase in soluble TNFalpha in brain tissue after systemic administration. DPH-067517 (3 and 30 mg/kg, i.p. administered 15 min before MCAO) produced 43% (n = 8, p = 0.16) and 58% (n = 8, p < 0.05) reduction in infarct size and 36% (p < 0.05) and 23% (p < 0.05) reduction in neurological deficits, respectively. The salutary effect of DPH-067517 in ischemic brain injury was also observed when the first dose was administrated 60 min after the onset of ischemia. Inhibition of TACE had no effect on apoptosis measured by levels of active caspase-3 expression and DNA fragmentation. Our data suggest that inhibition of TACE might be a potential therapeutic strategy for neuroprotection after focal ischemic stroke.

Efficient inhibition of β-secretase gene expression in HEK293 cells by tRNAVal-driven and CTE-helicase associated hammerhead ribozymes

The beta-amyloid peptide (Abeta) is a major component of toxic amyloid plaques found in the brains of patients with Alzheimer's disease. Abeta is liberated by sequential cleavage of amyloid precursor protein (APP) by beta- and gamma-secretases. The level of Abeta depends directly on the hydrolytic activity of beta-secretase. Therefore, beta-secretase is an excellent target for drug design. An approach based on RNA-cleaving ribozymes was developed to control expression of beta-secretase. Two sites of mRNA coding beta-site APP cleaving enzyme were chosen as target sequences for endogenously delivered ribozymes. The ribozyme cassette was designed to constitute a catalytic hammerhead core and substrate recognition arms, flanked at the 5'-terminus by tRNAVal and at the 3'-terminus by constitutive transport element sequences. Ribozyme cassettes were cloned into a pUC19 plasmid and used for transient transfection of HEK293 cells. We demonstrate that such ribozymes efficiently inhibit beta-secretase gene expression at both the mRNA (up to 95%) and the protein (up to 90%) levels. Inhibition of beta-site APP cleaving enzyme activity directly influences the intra- and extracellular population of Abeta peptide. Therefore, such ribozymes may be considered as molecular tools for silencing the beta-secretase activity, and further, as therapeutic agents for anti-amyloid treatment.