Small molecule beta-amyloid inhibitors that stabilize protofibrillar structures in vitro improve cognition and pathology in a mouse model of Alzheimer's disease

Synergistic activity of nootropic herbs as potent therapeutics for Alzheimer's disease: A cheminformatics, pharmacokinetics, and system pharmacology approach

Background

Alzheimer's disease (AD) is a progressive neurodegenerative disorder, which subdues over 55 million people and finding a cure, still remains disenchanting. Indian medicinal herbs notably, Withania somnifera, Bacopa monnieri, Curcuma longa, and Clitoria ternatea are traditionally utilized for their memory-enhancing properties.

Objective

We computationally investigated the therapeutic potential of four nootropic herbs by uncovering the molecular mechanisms underlying their treatment for AD.

Methods

Cheminformatics, pharmacokinetics, and system pharmacology studies were carried out to predict the phytocompounds drug-like properties, protein targets, targets functional association and enrichment analysis. A comparative study was performed with phytocompounds and FDA-approved drugs. Investigation on the expression of protein targets in the hippocampus and entorhinal cortex of the AD brain was performed. Network was constructed to depict the interaction between phytocompounds, drugs, and molecular targets.

Results

Through comparative analysis, we found that the phytocompounds shared common targets with both FDA drugs and drugs under clinical trials. We identified potential active compounds notably, Withaferin A, Withanolide-D, Withanolide-E, Withanolide-G, and Humulene epoxide II, that can combat AD. Interestingly, the enzyme inhibition scores of the identified drugs were much higher than FDA-approved drugs. In addition, regulatory proteins such as AβPP, acetylcholinesterase, BACE1, and PTPN1 were the targets of 8, 16, 9, and 22 phytocompounds, respectively. Nonetheless, AR and CYP19A, were the primary targets of most phytocompounds.

Conclusions

Herbal medicines can synergistically stimulate multiple protein targets, rendering a holistic and integrative treatment, encouraging a promising avenue to treat AD.

Current biomarkers and treatment strategies in Alzheimer disease: An overview and future perspectives

Alzheimer's disease (AD), a progressive degenerative disorder first identified by Alois Alzheimer in 1907, poses a significant public health challenge. Despite its prevalence and impact, there is currently no definitive ante mortem diagnosis for AD pathogenesis. By 2050, the United States may face a staggering 13.8 million AD patients. This review provides a concise summary of current AD biomarkers, available treatments, and potential future therapeutic approaches. The review begins by outlining existing drug targets and mechanisms in AD, along with a discussion of current treatment options. We explore various approaches targeting Amyloid β (Aβ), Tau Protein aggregation, Tau Kinases, Glycogen Synthase kinase-3β, CDK-5 inhibitors, Heat Shock Proteins (HSP), oxidative stress, inflammation, metals, Apolipoprotein E (ApoE) modulators, and Notch signaling. Additionally, we examine the historical use of Estradiol (E2) as an AD therapy, as well as the outcomes of Randomized Controlled Trials (RCTs) that evaluated antioxidants (e.g., vitamin E) and omega-3 polyunsaturated fatty acids as alternative treatment options. Notably, positive effects of docosahexaenoic acid nutriment in older adults with cognitive impairment or AD are highlighted. Furthermore, this review offers insights into ongoing clinical trials and potential therapies, shedding light on the dynamic research landscape in AD treatment.

Targets, trials and tribulations in Alzheimer therapeutics

Alzheimer's disease (AD) is a progressive neurodegenerative disorder characterized by abnormal accumulation of extracellular amyloid beta senile plaques and intracellular neurofibrillary tangles in the parts of the brain responsible for cognition. The therapeutic burden for the management of AD relies solely on cholinesterase inhibitors that provide only symptomatic relief. The urgent need for disease-modifying drugs has resulted in intensive research in this domain, which has led to better understanding of the disease pathology and identification of a plethora of new pathological targets. Currently, there are over a hundred and seventy clinical trials exploring disease modification, cognitive enhancement, and reduction of neuro-psychiatric complications. However, the path to developing safe and efficacious AD therapeutics has not been without challenges. Several clinical trials have been terminated in advanced stages due to lack of therapeutic translation or increased incidence of adverse events. This review presents an in-depth look at the various therapeutic targets of AD and the lessons learnt during their clinical assessment. Comprehensive understanding of the implication of modulating various aspects of Alzheimer brain pathology is crucial for development of drugs with potential to halt disease progression in Alzheimer therapeutics.

Past, present and future of therapeutic strategies against amyloid-β peptides in Alzheimer's disease: a systematic review

Alzheimer's disease (AD) is the most prevalent neurodegenerative disease in ageing, affecting around 46 million people worldwide but few treatments are currently available. The etiology of AD is still puzzling, and new drugs development and clinical trials have high failure rates. Urgent outline of an integral (multi-target) and effective treatment of AD is needed. Accumulation of amyloid-β (Aβ) peptides is considered one of the fundamental neuropathological pillars of the disease, and its dyshomeostasis has shown a crucial role in AD onset. Therefore, many amyloid-targeted therapies have been investigated. Here, we will systematically review recent (from 2014) investigational, follow-up and review studies focused on anti-amyloid strategies to summarize and analyze their current clinical potential. Combination of anti-Aβ therapies with new developing early detection biomarkers and other therapeutic agents acting on early functional AD changes will be highlighted in this review. Near-term approval seems likely for several drugs acting against Aβ, with recent FDA approval of a monoclonal anti-Aβ oligomers antibody -aducanumab- raising hopes and controversies. We conclude that, development of oligomer-epitope specific Aβ treatment and implementation of multiple improved biomarkers and risk prediction methods allowing early detection, together with therapies acting on other factors such as hyperexcitability in early AD, could be the key to slowing this global pandemic.

Concise syntheses and some biological activities of dl-2,5-di-O-methyl-chiro-inositol, dl-1,4-di-O-methyl-scyllo-inositol, and dl-1,6-dibromo-1,6-dideoxy-2,5-di-O-methyl-chiro-inositol

The regio- and stereospecific synthesis of O-methyl-chiro-inositols and O-methyl-scyllo-inositol was achieved, starting from p-benzoquinone. After preparing dimethoxy conduritol-B as a key compound, regiospecific bromination of the alkene moiety of dimethoxy conduritol-B and acid-catalyzed ring opening of dimethoxydiacetate conduritol-B epoxide with Ac₂ O afforded the desired new chiro-inositol derivatives and scyllo-inositol derivative, respectively. Spectroscopic methods were employed for the characterization of all synthesized compounds. The novel inositols (11-17) had effective inhibition profiles against human carbonic anhydrase isoenzymes I and II (hCA I and II) and acetylcholinesterase (AChE). The novel inositols 11-17 were found to be effective inhibitors against AChE, hCA I, and hCA II enzymes. K_i values were calculated in the range of 87.59 ± 7.011 to 237.95 ± 17.75 μM for hCA I, 65.08 ± 12.39 to 538.98 ± 61.26 μM for hCA II, and 193.28 ± 43.13 to 765.08 ± 209.77 μM for AChE, respectively. Also, due to the inhibitory effects of the novel inositols 11-17 against the tested enzymes, these novel inositols are potential drug candidates to treat some diseases such as glaucoma, epilepsy, leukemia, and Alzheimer's disease.

Nanocarriers for effective nutraceutical delivery to the brain

Neurodegenerative disorders are common among aging populations around the globe. Most are characterized by loss of neurons, protein aggregates, oxidative stress, mitochondrial damage, neuroinflammation among others. Although symptomatic treatment using conventional pharmacotherapy has been widely employed, their therapeutic success is limited due to varied reasons. In the need to identify an alternative approach, researchers successfully demonstrated the therapeutic utility of plant-derived nutraceuticals in cell and animal models of neurodegenerative conditions. However, most nutraceuticals failed during clinical trials in humans owing to their poor bioavailability in vivo and limited permeability across the blood brain barrier (BBB). The current emphasis is therefore on the improved delivery of nutraceuticals to the brain. In this regard, development of nanoparticle conjugated nutraceuticals to enhance bioavailability and therapeutic efficacy in the brain has gained attention. Here, we review the research advances in nanoparticles conjugated nutraceuticals applied in neurodegenerative disorders and discuss their advantages and limitations, clinical trials and toxicity concerns.

New Insights Into the Pathogenesis of Alzheimer's Disease

Alzheimer's disease (AD), a common neurodegenerative disease in the elderly and the most prevalent cause of dementia, is characterized by progressive cognitive impairment. The prevalence of AD continues to increase worldwide, becoming a great healthcare challenge of the twenty-first century. In the more than 110 years since AD was discovered, many related pathogenic mechanisms have been proposed, and the most recognized hypotheses are the amyloid and tau hypotheses. However, almost all clinical trials targeting these mechanisms have not identified any effective methods to treat AD. Scientists are gradually moving away from the simple assumption, as proposed in the original amyloid hypothesis, to new theories of pathogenesis, including gamma oscillations, prion transmission, cerebral vasoconstriction, growth hormone secretagogue receptor 1α (GHSR1α)-mediated mechanism, and infection. To place these findings in context, we first reviewed the neuropathology of AD and further discussed new insights in the pathogenesis of AD.

Investigating the efficacy of a combination Aβ-targeted treatment in a mouse model of Alzheimer's disease

Amyloid-beta peptide (Aβ) plays a critical role in the pathogenesis of Alzheimer's disease (AD). Here, we explored the use of a combination treatment to reduce amyloid load through microglial phagocytosis in a mouse model of AD. We hypothesized that using an initial treatment of magnetic resonance image guided focused ultrasound (MRIgFUS) to transiently increase the blood-brain barrier (BBB) permeability and enhance the delivery of an Aβ-antibody (BAM-10), followed by scyllo-inositol treatment would result in accelerated clearance. TgCRND8 mice expressing both Swedish (KM670/671NL) and Indiana (V717F) APP mutations under the hamster prion (PrP) promoter at 5 months of age were either treated with scyllo-inositol or received an initial MRIgFUS treatment delivering BAM-10 prior to scyllo-inositol treatment for one month. Treated animals and untreated TgCRND8 littermates were then sacrificed at 6 months of age, and their brains were processed for immunohistochemistry and immunofluorescence. Amyloid load was quantified and analyzed through immunohistochemical staining. Astrocyte and microglial activation were quantified and analyzed through immunofluorescent staining. We found that both the scyllo-inositol treatment and combination treatment, MRIgFUS/BAM10+scyllo-inositol, significantly reduced amyloid load and astrocyte activation in the hippocampus and the cortex. Furthermore, in both treatment paradigms microglial activation and phagocytosis was increased in comparison to the untreated mice. There were no differences detected between the two treatment paradigms. We propose that the 30-day scyllo-inositol treatment saturated the early benefit of the MRIgFUS/BAM-10 treatment. In the future, multiple FUS treatments combined with BAM-10 throughout the duration of scyllo-inositol treatment may lead to more effective amyloid clearance.

Inhibition of amyloid oligomerization into different supramolecular architectures by small molecules: mechanistic insights and design rules

Protein misfolding and aggregation have been associated with several human disorders, including Alzheimer’s, Parkinson’s and Huntington’s diseases, as well as senile systemic amyloidosis and Type II diabetes. However, there is no current disease-modifying therapy available for the treatment of these disorders. In spite of extensive academic, pharmaceutical, medicinal and clinical research, a complete mechanistic model for this family of diseases is still lacking. In this review, we primarily discuss the different types of small molecular entities which have been used for the inhibition of the aggregation process of different amyloidogenic proteins under diseased conditions. These include small peptides, polyphenols, inositols, quinones and their derivatives, and metal chelator molecules. In recent years, these groups of molecules have been extensively studied using in vitro, in vivo and computational models to understand their mechanism of action and common structural features underlying the process of inhibition. A salient feature found to be instrumental in the process of inhibition is the balance between the aromatic unit that functions as the amyloid recognition unit and the hydrophilic amyloid breaker unit. The establishment of structure–function relationship for amyloid-modifying therapies by the various functional entities should serve as an important step toward the development of efficient therapeutics.

Hematoxylin Inhibits Amyloid β-Protein Fibrillation and Alleviates Amyloid-Induced Cytotoxicity

Accumulation and aggregation of amyloid β-protein (Aβ) play an important role in the pathogenesis of Alzheimer's disease. There has been increased interest in finding new anti-amyloidogenic compounds to inhibit Aβ aggregation. Herein, thioflavin T fluorescent assay and transmission electron microscopy results showed that hematoxylin, a natural organic molecule extracted from Caesalpinia sappan, was a powerful inhibitor of Aβ42 fibrillogenesis. Circular dichroism studies revealed hematoxylin reduced the β-sheet content of Aβ42 and made it assemble into antiparallel arrangement, which induced Aβ42 to form off-pathway aggregates. As a result, hematoxylin greatly alleviated Aβ42-induced cytotoxicity. Molecular dynamics simulations revealed the detailed interactions between hematoxylin and Aβ42. Four binding sites of hematoxylin on Aβ42 hexamer were identified, including the N-terminal region, S8GY10 region, turn region, and C-terminal region. Notably, abundant hydroxyl groups made hematoxylin prefer to interact with Aβ42 via hydrogen bonds. This also contributed to the formation of π-π stacking and hydrophobic interactions. Taken together, the research proved that hematoxylin was a potential agent against Aβ fibrillogenesis and cytotoxicity.

The "Other" Inositols and Their Phosphates: Synthesis, Biology, and Medicine (with Recent Advances in myo-Inositol Chemistry)

Cell signaling via inositol phosphates, in particular via the second messenger myo-inositol 1,4,5-trisphosphate, and phosphoinositides comprises a huge field of biology. Of the nine 1,2,3,4,5,6-cyclohexanehexol isomers, myo-inositol is pre-eminent, with "other" inositols (cis-, epi-, allo-, muco-, neo-, L-chiro-, D-chiro-, and scyllo-) and derivatives rarer or thought not to exist in nature. However, neo- and d-chiro-inositol hexakisphosphates were recently revealed in both terrestrial and aquatic ecosystems, thus highlighting the paucity of knowledge of the origins and potential biological functions of such stereoisomers, a prevalent group of environmental organic phosphates, and their parent inositols. Some "other" inositols are medically relevant, for example, scyllo-inositol (neurodegenerative diseases) and d-chiro-inositol (diabetes). It is timely to consider exploration of the roles and applications of the "other" isomers and their derivatives, likely by exploiting techniques now well developed for the myo series.

Anti-amyloidogenic properties of some phenolic compounds

A family of 21 polyphenolic compounds consisting of those found naturally in danshen and their analogues were synthesized and subsequently screened for their anti-amyloidogenic activity against the amyloid beta peptide (Aβ₄₂) of Alzheimer’s disease. After 24 h incubation with Aβ₄₂, five compounds reduced thioflavin T (ThT) fluorescence, indicative of their anti-amyloidogenic propensity (p < 0.001). TEM and immunoblotting analysis also showed that selected compounds were capable of hindering fibril formation even after prolonged incubations. These compounds were also capable of rescuing the yeast cells from toxic changes induced by the chemically synthesized Aβ₄₂. In a second assay, a Saccharomyces cerevisiae AHP1 deletant strain transformed with GFP fused to Aβ₄₂ was treated with these compounds and analyzed by flow cytometry. There was a significant reduction in the green fluorescence intensity associated with 14 compounds. We interpret this result to mean that the compounds had an anti-amyloid-aggregation propensity in the yeast and GFP-Aβ₄₂ was removed by proteolysis. The position and not the number of hydroxyl groups on the aromatic ring was found to be the most important determinant for the anti-amyloidogenic properties.

Interactions between misfolded protein oligomers and membranes: A central topic in neurodegenerative diseases?

The deposition of amyloid material has been associated with many different diseases. Although these diseases are very diverse the amyloid material share many common features such as cross-β-sheet structure of the backbone of the proteins deposited. Another common feature of the aggregation process for a wide variety of proteins is the presence of prefibrillar oligomers. These oligomers are linked to the cytotoxicity occurring during the aggregation of proteins. These prefibrillar oligomers interact extensively with lipid membranes and in some cases leads to destabilization of lipid membranes. This interaction is however highly dependent on the nature of both the oligomer and the lipids. Anionic lipids are often required for interaction with the lipid membrane while increased exposure of hydrophobic patches from highly dynamic protein oligomers are structural determinants of cytotoxicity of the oligomers. To explore the oligomer lipid interaction in detail the interaction between oligomers of α-synuclein and the 4th fasciclin-1 domain of TGFBIp with lipid membranes will be examined here. For both proteins the dynamic species are the ones causing membrane destabilization and the membrane interaction is primarily seen when the lipid membranes contain anionic lipids. Hence the dynamic nature of oligomers with exposed hydrophobic patches alongside the presence of anionic lipids could be essential for the cytotoxicity observed for prefibrillar oligomers in general. This article is part of a Special Issue entitled: Lipid-protein interactions.

Role of cerebrospinal fluid biomarkers in clinical trials for Alzheimer's disease modifying therapies

Until now, a disease-modifying therapy (DMT) that has an ability to slow or arrest Alzheimer's disease (AD) progression has not been developed, and all clinical trials involving AD patients enrolled by clinical assessment alone also have not been successful. Given the growing consensus that the DMT is likely to require treatment initiation well before full-blown dementia emerges, the early detection of AD will provide opportunities to successfully identify new drugs that slow the course of AD pathology. Recent advances in early detection of AD and prediction of progression of the disease using various biomarkers, including cerebrospinal fluid (CSF) Aβ_1-42, total tau and p-tau₁₈₁ levels, and imagining biomarkers, are now being actively integrated into the designs of AD clinical trials. In terms of therapeutic mechanisms, monitoring these markers may be helpful for go/no-go decision making as well as surrogate markers for disease severity or progression. Furthermore, CSF biomarkers can be used as a tool to enrich patients for clinical trials with prospect of increasing statistical power and reducing costs in drug development. However, the standardization of technical aspects of analysis of these biomarkers is an essential prerequisite to the clinical uses. To accomplish this, global efforts are underway to standardize CSF biomarker measurements and a quality control program supported by the Alzheimer's Association. The current review summarizes therapeutic targets of developing drugs in AD pathophysiology, and provides the most recent advances in the

Inhibiting toxic aggregation of amyloidogenic proteins: a therapeutic strategy for protein misfolding diseases

BACKGROUND

The deposition of self-assembled amyloidogenic proteins is associated with multiple diseases, including Alzheimer's disease, Parkinson's disease and type 2 diabetes mellitus. The toxic misfolding and self-assembling of amyloidogenic proteins are believed to underlie protein misfolding diseases. Novel drug candidates targeting self-assembled amyloidogenic proteins represent a potential therapeutic approach for protein misfolding diseases.

SCOPE OF REVIEW

In this perspective review, we provide an overview of the recent progress in identifying inhibitors that block the aggregation of amyloidogenic proteins and the clinical applications thereof.

MAJOR CONCLUSIONS

Compounds such as polyphenols, certain short peptides, and monomer- or oligomer-specific antibodies, can interfere with the self-assembly of amyloidogenic proteins, prevent the formation of oligomers, amyloid fibrils and the consequent cytotoxicity.

GENERAL SIGNIFICANCE

Some inhibitors have been tested in clinical trials for treating protein misfolding diseases. Inhibitors that target the aggregation of amyloidogenic proteins bring new hope to therapy for protein misfolding diseases.

Protection against the synaptic targeting and toxicity of Alzheimer's-associated Aβ oligomers by insulin mimetic chiro-inositols

Alzheimer's disease (AD) is a progressive dementia that correlates highly with synapse loss. This loss appears due to the synaptic accumulation of toxic Aβ oligomers (ADDLs), which damages synapse structure and function. Although it has been reported that oligomer binding and toxicity can be prevented by stimulation of neuronal insulin signaling with PPARγ agonists, these agonists have problematic side effects. We therefore investigated the therapeutic potential of chiro-inositols, insulin-sensitizing compounds safe for human consumption. Chiro-inositols have been studied extensively for treatment of diseases associated with peripheral insulin resistance, but their insulin mimetic function in memory-relevant central nervous system (CNS) cells is unknown. Here we demonstrate that mature cultures of hippocampal neurons respond to d-chiro-inositol (DCI), pinitol (3-O-methyl DCI), and the inositol glycan INS-2 (pinitol β-1-4 galactosamine) with increased phosphorylation in key upstream components in the insulin-signaling pathway (insulin receptor, insulin receptor substrate-1, and Akt). Consistent with insulin stimulation, DCI treatment promotes rapid withdrawal of dendritic insulin receptors. With respect to neuroprotection, DCI greatly enhances the ability of insulin to prevent ADDL-induced synapse damage (EC(50) of 90 nM). The mechanism comprises inhibition of oligomer binding at synapses and requires insulin/IGF signaling. DCI showed no effects on Aβ oligomerization. We propose that inositol glycans and DCI, a compound already established as safe for human consumption, have potential as AD therapeutics by protecting CNS synapses against Aβ oligomers through their insulin mimetic activity.

True and apparent inhibition of amyloid fibril formation

A possible therapeutic strategy for amyloid diseases involves the use of small molecule compounds to inhibit protein assembly into insoluble aggregates. According to the recently proposed Crystallization-Like Model, the kinetics of amyloid fibrillization can be retarded by decreasing the frequency of new fibril formation or by decreasing the elongation rate of existing fibrils. To the compounds that affect the nucleation and/or the growth steps we call true inhibitors. An apparent inhibition mechanism may however result from the alteration of thermodynamic properties such as the solubility of the amyloidogenic protein. Apparent inhibitors markedly influence protein aggregation kinetics measured in vitro, yet they are likely to lead to disappointing results when tested in vivo. This is because cells and tissues media are in general much more buffered against small variations in composition than the solutions prepared in lab. Here we show how to discriminate between true and apparent inhibition mechanisms from experimental data on protein aggregation kinetics. The goal is to be able to identify false positives much earlier during the drug development process.

Discovery and structure activity relationship of small molecule inhibitors of toxic β-amyloid-42 fibril formation

Increasing evidence implicates Aβ peptides self-assembly and fibril formation as crucial events in the pathogenesis of Alzheimer disease. Thus, inhibiting Aβ aggregation, among others, has emerged as a potential therapeutic intervention for this disorder. Herein, we employed 3-aminopyrazole as a key fragment in our design of non-dye compounds capable of interacting with Aβ42 via a donor-acceptor-donor hydrogen bond pattern complementary to that of the β-sheet conformation of Aβ42. The initial design of the compounds was based on connecting two 3-aminopyrazole moieties via a linker to identify suitable scaffold molecules. Additional aryl substitutions on the two 3-aminopyrazole moieties were also explored to enhance π-π stacking/hydrophobic interactions with amino acids of Aβ42. The efficacy of these compounds on inhibiting Aβ fibril formation and toxicity in vitro was assessed using a combination of biophysical techniques and viability assays. Using structure activity relationship data from the in vitro assays, we identified compounds capable of preventing pathological self-assembly of Aβ42 leading to decreased cell toxicity.

Inhibition of amyloid-beta peptide aggregation rescues the autophagic deficits in the TgCRND8 mouse model of Alzheimer disease

scyllo-Inositol (SI) is an endogenous inositol stereoisomer known to inhibit aggregation and fibril formation of the amyloid-beta peptide (Aβ). Human clinical trials using SI to treat Alzheimer disease (AD) patients have shown potential benefits. In light of the growing therapeutic potential of SI, the objective of our study was to gain a more thorough understanding of the mechanism of action. In addition to Aβ plaques, a prominent pathological feature of AD is the extensive accumulation of autophagic vacuoles (AVs) suggesting dysfunction in this degradation pathway. Using the TgCRND8 mouse model for AD, we examined SI treatment effects on various components of the autophagic pathway. Autophagy impairment in TgCRND8 mice occurs in the latter stages of the pathway where AV-lysosome fusion and lysosomal degradation take place. SI treatment attenuated this impairment with a decrease in the size and the number of accumulated AVs. We propose that the beneficial effects of SI-Aβ interactions may resolve autophagic deficiencies in the AD brains.

Biochemistry of amyloid β-protein and amyloid deposits in Alzheimer disease

Progressive cerebral deposition of the amyloid β-protein (Aβ) in brain regions serving memory and cognition is an invariant and defining feature of Alzheimer disease. A highly similar but less robust process accompanies brain aging in many nondemented humans, lower primates, and some other mammals. The discovery of Aβ as the subunit of the amyloid fibrils in meningocerebral blood vessels and parenchymal plaques has led to innumerable studies of its biochemistry and potential cytotoxic properties. Here we will review the discovery of Aβ, numerous aspects of its complex biochemistry, and current attempts to understand how a range of Aβ assemblies, including soluble oligomers and insoluble fibrils, may precipitate and promote neuronal and glial alterations that underlie the development of dementia. Although the role of Aβ as a key molecular factor in the etiology of Alzheimer disease remains controversial, clinical trials of amyloid-lowering agents, reviewed elsewhere in this book, are poised to resolve the question of its pathogenic primacy.

Aβ(1-42) assembly in the presence of scyllo-inositol derivatives: identification of an oxime linkage as important for the development of assembly inhibitors

To identify a lead skeleton structure for optimization of scyllo-inositol-based inhibitors of amyloid-beta peptide (Aβ) aggregation, we have synthesized aldoxime, hydroxamate, carbamate, and amide linked scyllo-inositol derivatives. These structures represent backbones that can be readily expanded into a wide array of derivatives. They also provide conservative modifications of the scyllo-inositol backbone, as they maintain the display of the equatorial polar atoms, preserving the stereochemical requirement necessary for maximum inhibition of Aβ(1-42) fiber formation. In addition, a reliable work plan for screening derivatives was developed in order to preferentially identify a backbone(s) structure that prevents fibrillogenesis and stabilizes nontoxic small molecular weight oligomers, as we have previously reported for scyllo-inositol. In the present studies, we have adapted a high throughput ELISA-based oligomerization assay followed by atomic force microscopy to validate the results screen compounds. The lead compounds were then tested for toxicity and ability to rescue Aβ(1-42) induced toxicity in vitro and the affinity of the compounds for Aβ(1-42) compared by mass spectrometry. The data to suggest that compounds must maintain a planar conformation to exhibit activity similar to scyllo-inositol and that the oxime derivative represents the lead backbone for future development.

Hippocampal metabolites and memory performances in patients with amnestic mild cognitive impairment and Alzheimer's disease

In patients with amnestic mild cognitive impairment (aMCI) and Alzheimer's disease (AD), previous studies have reported the decrease of N-acetylaspartate (NAA) concentration and the increase of myo-inositol (MI) concentration using proton magnetic resonance spectroscopy (1H-MRS). However, it remains to be investigated what aspects of cognition these metabolite changes reflect. In this study we evaluated the correlations between the subtests of Wechsler Memory Scale-Revised (WMS-R) and the concentrations of NAA and MI. The study group was composed of 42 patients with aMCI and 67 patients with AD. 1H-MR spectra with a single voxel-point resolved spectroscopy (PRESS) at a short echo time were acquired from the bilateral hippocampi and posterior cingulate gyrus. Positive correlations were shown between the NAA concentration in the left hippocampus and verbal memory, visual memory, general memory, attention and delayed recall; and furthermore, between the NAA concentration in the right hippocampus and verbal memory and general memory. Negative correlations were shown between the MI concentration in the left hippocampus and verbal memory, general memory, and delayed recall, and between the MI concentration in the right hippocampus and verbal memory. There was no significant correlation between any subtest of WMS-R and these two metabolite concentrations in the posterior cingulate gyrus. These findings suggest that bilateral, especially left hippocampal NAA and MI concentrations are associated with memory dysfunction observed in patients with aMCI and AD. In contrast, NAA and MI concentrations in the posterior cingulate gyrus may be less related to memory function than those in the hippocampus.

Oligomeric intermediates in amyloid formation: structure determination and mechanisms of toxicity

Oligomeric intermediates are non-fibrillar polypeptide assemblies that occur during amyloid fibril formation and that are thought to underlie the aetiology of amyloid diseases, such as Alzheimer's disease, Parkinson's disease and Huntington's disease. Focusing primarily on the oligomeric states formed from Alzheimer's disease β-amyloid (Aβ) peptide, this review will make references to other polypeptide systems, highlighting common principles or sequence-specific differences. The covered topics include the structural properties and polymorphism of oligomers, the biophysical mechanism of peptide self-assembly and its role for pathogenicity in amyloid disease. Oligomer-dependent toxicity mechanisms will be explained along with recently emerging possibilities of interference.

Inhibition of amyloid formation

Amyloid is aggregated protein in the form of insoluble fibrils. Amyloid deposition in human tissue-amyloidosis-is associated with a number of diseases including all common dementias and type II diabetes. Considerable progress has been made to understand the mechanisms leading to amyloid formation. It is, however, not yet clear by which mechanisms amyloid and protein aggregates formed on the path to amyloid are cytotoxic. Strategies to prevent protein aggregation and amyloid formation are nevertheless, in many cases, promising and even successful. This review covers research on intervention of amyloidosis and highlights several examples of how inhibition of protein aggregation and amyloid formation has been achieved in practice. For instance, rational design can provide drugs that stabilize a native folded state of a protein, protein engineering can provide new binding proteins that sequester monomeric peptides from aggregation, small molecules and peptides can be designed to block aggregation or direct it into non-cytotoxic paths, and monoclonal antibodies have been developed for therapies towards neurodegenerative diseases based on inhibition of amyloid formation and clearance.

Establishing the links between Aβ aggregation and cytotoxicity in vitro using biophysical approaches

Aggregation and fibril formation of the amyloid-β (Aβ) peptides play a pivotal role in the pathogenesis of Alzheimer's disease (AD). The missing links on the pathway to Aβ oligomerization, fibril formation, and neurotoxicity in AD remain the identity of the toxic Aβ species and mechanism(s) of their toxicity. Such information is crucial for the development of mechanism-based therapeutics to treat AD and tools to diagnose and/or monitor the disease progression. Herein, we describe a simple approach that combines standard biophysical methods with cell biology assays to correlate the aggregation state of Aβ peptides with their cytotoxicity in vitro. The individual assays are well-established, commonly used, rely on easily accessible materials and can be performed within 24 h.

A cell factory of Bacillus subtilis engineered for the simple bioconversion of myo-inositol to scyllo-inositol, a potential therapeutic agent for Alzheimer's disease

BACKGROUND

A stereoisomer of inositol, scyllo-inositol, is known as a promising therapeutic agent for Alzheimer's disease, since it prevents the accumulation of beta-amyloid deposits, a hallmark of the disease. However, this compound is relatively rare in nature, whereas another stereoisomer of inositol, myo-inositol, is abundantly available.

RESULTS

Bacillus subtilis possesses a unique inositol metabolism involving both stereoisomers. We manipulated the inositol metabolism in B. subtilis to permit the possible bioconversion from myo-inositol to scyllo-inositol. Within 48 h of cultivation, the engineered strain was able to convert almost half of 10 g/L myo-inositol to scyllo-inositol that accumulated in the culture medium.

CONCLUSIONS

The engineered B. subtilis serves as a prototype of cell factory enabling a novel and inexpensive supply of scyllo-inositol.

Sodium/myo-Inositol transporters: substrate transport requirements and regional brain expression in the TgCRND8 mouse model of amyloid pathology

Inositol stereoisomers, myo- and scyllo-inositol, are known to enter the brain and are significantly elevated following oral administration. Elevations in brain inositol levels occur across a concentration gradient as a result of active transport from the periphery. There are two sodium/myo-inositol transporters (SMIT1, SMIT2) that may be responsible for regulating brain inositol levels. The goals of this study were to determine the effects of aging and Alzheimer's disease (AD)-like amyloid pathology on transporter expression, to compare regional expression and to analyze substrate requirements of the inositol transporters. QPCR was used to examine expression of the two transporters in the cortex, hippocampus and cerebellum of TgCRND8 mice, a mouse model of amyloid pathology, in comparison to non-transgenic littermates. In addition, we examined the structural features of inositol required for active transport, utilizing a cell-based competitive uptake assay. Disease pathology did not alter transporter expression in the cortex or hippocampus (p>0.005), with only minimal effects of aging observed in the cerebellum (SMIT1: F_2,26 = 12.62; p = 0.0002; SMIT2: F_2,26 = 8.71; p = 0.0015). Overall, brain SMIT1 levels were higher than SMIT2, however, regional differences were observed. For SMIT1, at 4 and 6 months cerebellar SMIT1 levels were significantly higher than cortical and hippocampal levels (p<0.05). For SMIT2, at all three ages both cortical and cerebellar SMIT2 levels were significantly higher than hippocampal levels (p<0.05) and at 4 and 6 months of age, cerebellar SMIT2 levels were also significantly higher than cortical levels (p<0.05). Inositol transporter levels are stably expressed as a function of age, and expression is unaltered with disease pathology in the TgCRND8 mouse. Given the fact that scyllo-inositol is currently in clinical trials for the treatment of AD, the stable expression of inositol transporters regardless of disease pathology is an important finding.

Novel insights for the treatment of Alzheimer's disease

The development of treatments for Alzheimer's disease (AD) is currently shifting away from the correction of neurotransmitter abnormalities and from attempts to remove the pathognomonic protein deposits. Drug discovery is heading towards novel types of pharmacological interventions which are aimed at more central and upstream pathophysiological events. The large number of upcoming treatment targets can be grouped into two major categories. The first category consists of antecedents of beta amyloid peptide (Aβ) and TAU deposition including Aβ production, degradation and clearance, TAU hyperphosphorylation and aggregation. The second consists of protectors against neuronal dysfunction and premature death such as mitochondrial functioning, nerve growth and regeneration, and neuronal membrane integrity. It is hoped that some of these strategies will not only have larger symptomatic effects than the currently available drugs but also an impact on the underlying neurodegeneration. Since the novel treatments will be typically administered over years they must meet high standards of safety, drug-drug compatibility, and tolerability. Probably the most important target groups for novel treatments are carriers of mutations causing AD, and individuals with minor cognitive impairment representing a pre-dementia stage of the disease. To minimise incorrect case identifications, drug development must be paralleled by improved diagnostic techniques. Novel pharmacological strategies may be cost-effective if disability and need of full-time care can be postponed or prevented without prolonging time lived with dementia or extending survival. We are uncertain whether the advent of novel disease-retarding strategies will revolutionise the management of AD. Symptomatic treatments will continue to be needed, and psychosocial approaches will retain an essential role in supporting affected individuals and their families.

Drug development for Alzheimer's disease: recent progress

Alzheimer's disease, the most common cause of dementia, is characterized by two major pathological hallmarks: amyloid plaques and neurofibrillary tangles. Based on these two indicators, an amyloid cascade hypothesis was proposed, and accordingly, most current therapeutic approaches are now focused on the removal of β-amyloid peptides (Aβ from the brain. Additionally, strategies for blocking tau hyperphosphorylation and aggregation have been suggested, including the development of drugs that can block the formation of tangles. However, there are no true disease-modifying drugs in the current market, though many drugs based on theories other than Aβ and tau pathology are under development. The purpose of this review was to provide information on the current development of AD drugs and to discuss the issues related to drug development.

Abeta42 neurotoxicity is mediated by ongoing nucleated polymerization process rather than by discrete Abeta42 species

The identification of toxic Aβ species and/or the process of their formation is crucial for understanding the mechanism(s) of Aβ neurotoxicity in Alzheimer disease and also for the development of effective diagnostic and therapeutic interventions. To elucidate the structural basis of Aβ toxicity, we developed different procedures to isolate Aβ species of defined size and morphology distribution, and we investigated their toxicity in different cell lines and primary neurons. We observed that crude Aβ42 preparations, containing a monomeric and heterogeneous mixture of Aβ42 oligomers, were more toxic than purified monomeric, protofibrillar fractions, or fibrils. The toxicity of protofibrils was directly linked to their interactions with monomeric Aβ42 and strongly dependent on their ability to convert into amyloid fibrils. Subfractionation of protofibrils diminished their fibrillization and toxicity, whereas reintroduction of monomeric Aβ42 into purified protofibril fractions restored amyloid formation and enhanced their toxicity. Selective removal of monomeric Aβ42 from these preparations, using insulin-degrading enzyme, reversed the toxicity of Aβ42 protofibrils. Together, our findings demonstrate that Aβ42 toxicity is not linked to specific prefibrillar aggregate(s) but rather to the ability of these species to grow and undergo fibril formation, which depends on the presence of monomeric Aβ42. These findings contribute significantly to the understanding of amyloid formation and toxicity in Alzheimer disease, provide novel insight into mechanisms of Aβ protofibril toxicity, and important implications for designing anti-amyloid therapies.