Genes and mechanisms involved in beta-amyloid generation and Alzheimer's disease

Relationship Between Chronic Noise Exposure, Cognitive Impairment, and Degenerative Dementia: Update on the Experimental and Epidemiological Evidence and Prospects for Further Research

Degenerative dementia, of which Alzheimer's disease is the most common form, is characterized by the gradual deterioration of cognitive function. The events that trigger and promote degenerative dementia are not clear, and treatment options are limited. Experimental and epidemiological studies have revealed chronic noise exposure (CNE) as a potential risk factor for cognitive impairment and degenerative dementia. Experimental studies have indicated that long-term exposure to noise might accelerate cognitive dysfunction, amyloid-β deposition, and tau hyperphosphorylation in different brain regions such as the hippocampus and cortex. Epidemiological studies are increasingly examining the possible association between external noise exposure and dementia. In this review, we sought to construct a comprehensive summary of the relationship between CNE, cognitive dysfunction, and degenerative dementia. We also present the limitations of existing evidence as a guide regarding important prospects for future research.

Hippocampal Deficits in Amyloid-β-Related Rodent Models of Alzheimer's Disease

Alzheimer's disease (AD) is a progressive neurodegenerative disease that is the most common cause of dementia. Symptoms of AD include memory loss, disorientation, mood and behavior changes, confusion, unfounded suspicions, and eventually, difficulty speaking, swallowing, and walking. These symptoms are caused by neuronal degeneration and cell loss that begins in the hippocampus, and later in disease progression spreading to the rest of the brain. While there are some medications that alleviate initial symptoms, there are currently no treatments that stop disease progression. Hippocampal deficits in amyloid-β-related rodent models of AD have revealed synaptic, behavioral and circuit-level defects. These changes in synaptic function, plasticity, neuronal excitability, brain connectivity, and excitation/inhibition imbalance all have profound effects on circuit function, which in turn could exacerbate disease progression. Despite, the wealth of studies on AD pathology we don't yet have a complete understanding of hippocampal deficits in AD. With the increasing development of in vivo recording techniques in awake and freely moving animals, future studies will extend our current knowledge of the mechanisms underpinning how hippocampal function is altered in AD, and aid in progression of treatment strategies that prevent and/or delay AD symptoms.

Activities of mitochondrial respiratory chain complexes in platelets of patients with Alzheimer's disease and depressive disorder

We analyzed activities of complex I, II, III, and IV, and citrate synthase (CS) in patients with major depressive disorder (MDD) or Alzheimer's disease (AD) presenting with or without depression. Associations of these parameters with disease or disease severity were observed in both AD and MDD; however, mean values of mitochondrial parameters were significantly altered in AD but not in MDD. Potential mitochondrial dysfunction in MDD seems not to be caused by disturbed activity of CS or respiratory complexes. In AD, a decrease in the activity of CS and complex IV may cause mitochondrial dysfunction, whereas an increase in activities of other mitochondrial complexes or their ratios to CS may be an adaptive response. The data indicate that comorbid depression in AD is associated with increased complex II activity. The mitochondrial parameters measured can be included in the panel of biomarkers of AD.

Plasma amyloid beta levels and platelet mitochondrial respiration in patients with Alzheimer's disease

OBJECTIVES

Altered amyloid metabolism and mitochondrial dysfunction play key roles in the development of Alzheimer's disease (AD). We asked whether an association exists between disturbed platelet mitochondrial respiration and the plasma concentrations of Aβ₄₀ and Aβ₄₂ in patients with AD.

DESIGN AND METHODS

Plasma Aβ₄₀ and Aβ₄₂ concentrations and mitochondrial respiration in intact and permeabilized platelets were measured in 50 patients with AD, 15 patients with vascular dementia and 25 control subjects. A pilot longitudinal study was performed to monitor the progression of AD in a subgroup 11 patients with AD.

RESULTS

The mean Aβ₄₀, Aβ₄₂ and Aβ₄₂/Aβ₄₀ levels were not significantly altered in patients with AD compared with controls. The mitochondrial respiratory rate in intact platelets was significantly reduced in patients with AD compared to controls, particularly the basal respiratory rate, maximum respiratory capacity, and respiratory reserve; however, the flux control ratio for basal respiration was increased. A correlation between the plasma Aβ₄₂ concentration and mitochondrial respiration in both intact and permeabilized platelets differs in controls and patients with AD.

CONCLUSIONS

Based on our data, (1) mitochondrial respiration in intact platelets, but not the Aβ level itself, may be included in a panel of biomarkers for AD; (2) dysfunctional mitochondrial respiration in platelets is not explained by changes in plasma Aβ concentrations; and (3) the association between mitochondrial respiration in platelets and plasma Aβ levels differs in patients with AD and controls. The results supported the hypothesis that mitochondrial dysfunction is the primary factor contributing to the development of AD.

A systematic approach for identifying shared mechanisms in epilepsy and its comorbidities

Cross-sectional epidemiological studies have shown that the incidence of several nervous system diseases is more frequent in epilepsy patients than in the general population. Some comorbidities [e.g. Alzheimer's disease (AD) and Parkinson's disease] are also risk factors for the development of seizures; suggesting they may share pathophysiological mechanisms with epilepsy. A literature-based approach was used to identify gene overlap between epilepsy and its comorbidities as a proxy for a shared genetic basis for disease, or genetic pleiotropy, as a first effort to identify shared mechanisms. While the results identified neurological disorders as the group of diseases with the highest gene overlap, this analysis was insufficient for identifying putative common mechanisms shared across epilepsy and its comorbidities. This motivated the use of a dedicated literature mining and knowledge assembly approach in which a cause-and-effect model of epilepsy was captured with Biological Expression Language. After enriching the knowledge assembly with information surrounding epilepsy, its risk factors, its comorbidities, and anti-epileptic drugs, a novel comparative mechanism enrichment approach was used to propose several downstream effectors (including the GABA receptor, GABAergic pathways, etc.) that could explain the therapeutic effects carbamazepine in both the contexts of epilepsy and AD. We have made the Epilepsy Knowledge Assembly available at https://www.scai.fraunhofer.de/content/dam/scai/de/downloads/bioinformatik/epilepsy.bel and queryable through NeuroMMSig at http://neurommsig.scai.fraunhofer.de. The source code used for analysis and tutorials for reproduction are available on GitHub at https://github.com/cthoyt/epicom.

PSEN1 gene polymorphisms in Caucasian Alzheimer's disease: A meta-analysis

BACKGROUND

A meta-analysis was performed to assess PSEN1 gene polymorphisms (rs1800839 and rs17125721) in Alzheimer's disease (AD) risk.

METHODS

A systematic electronic search was performed across databases to retrieve studies published before 31 January 2017. The association between the selected PSEN1 polymorphisms and AD was based on five genetic models using DerSimonian and Laird's method or Mantel-Haenszel's method.

RESULTS

A total of 14 case-controlled studies were included. Results showed that rs1800839 polymorphism was significantly associated with AD in allelic OR=0.85 (95% CI [0.72-1.00]) and dominant OR=0.82 (95% CI [0.69-0.98]) genetic models, respectively. However, an insignificant association was found for rs17125721 polymorphism in all genetic models.

CONCLUSIONS

Meta-analysis of PSEN1 gene suggests that the rs1800839 polymorphism has potential influence on AD among Caucasians.

AZD3293: A Novel, Orally Active BACE1 Inhibitor with High Potency and Permeability and Markedly Slow Off-Rate Kinetics

A growing body of pathological, biomarker, genetic, and mechanistic data suggests that amyloid accumulation, as a result of changes in production, processing, and/or clearance of brain amyloid-β peptide (Aβ) concentrations, plays a key role in the pathogenesis of Alzheimer’s disease (AD). Beta-secretase 1 (BACE1) mediates the first step in the processing of amyloid-β protein precursor (AβPP) to Aβ peptides, with the soluble N terminal fragment of AβPP (sAβPPβ) as a direct product, and BACE1 inhibition is an attractive target for therapeutic intervention to reduce the production of Aβ. Here, we report the in vitro and in vivo pharmacological profile of AZD3293, a potent, highly permeable, orally active, blood-brain barrier (BBB) penetrating, BACE1 inhibitor with unique slow off-rate kinetics. The in vitro potency of AZD3293 was demonstrated in several cellular models, including primary cortical neurons. In vivo in mice, guinea pigs, and dogs, AZD3293 displayed significant dose- and time-dependent reductions in plasma, cerebrospinal fluid, and brain concentrations of Aβ₄₀, Aβ₄₂, and sAβPPβ. The in vitro potency of AZD3293 in mouse and guinea pig primary cortical neuronal cells was correlated to the in vivo potency expressed as free AZD3293 concentrations in mouse and guinea pig brains. In mice and dogs, the slow off-rate from BACE1 may have translated into a prolongation of the observed effect beyond the turnover rate of Aβ. The preclinical data strongly support the clinical development of AZD3293, and patients with AD are currently being recruited into a combined Phase 2/3 study to test the disease-modifying properties of AZD3293.

Protein-Induced Pluripotent Stem Cells Ameliorate Cognitive Dysfunction and Reduce Aβ Deposition in a Mouse Model of Alzheimer's Disease

Transplantation of stem cells into the brain attenuates functional deficits in the central nervous system via cell replacement, the release of specific neurotransmitters, and the production of neurotrophic factors. To identify patient‐specific and safe stem cells for treating Alzheimer's disease (AD), we generated induced pluripotent stem cells (iPSCs) derived from mouse skin fibroblasts by treating protein extracts of embryonic stem cells. These reprogrammed cells were pluripotent but nontumorigenic. Here, we report that protein‐iPSCs differentiated into glial cells and decreased plaque depositions in the 5XFAD transgenic AD mouse model. We also found that transplanted protein‐iPSCs mitigated the cognitive dysfunction observed in these mice. Proteomic analysis revealed that oligodendrocyte‐related genes were upregulated in brains injected with protein‐iPSCs, providing new insights into the potential function of protein‐iPSCs. Taken together, our data indicate that protein‐iPSCs might be a promising therapeutic approach for AD. Stem Cells Translational Medicine2017;6:293–305

Artificial Neural Networks Link One-Carbon Metabolism to Gene-Promoter Methylation in Alzheimer's Disease

BACKGROUND

There is increasing interest in DNA methylation studies in Alzheimer's disease (AD), but little is still known concerning the relationship between gene-promoter methylation and circulating biomarkers of one-carbon metabolism in patients.

OBJECTIVE

To detect the connections among circulating folate, homocysteine (hcy) and vitamin B12 levels and promoter methylation levels of PSEN1, BACE1, DNMT1, DNMT3A, DNMT3B, and MTHFR genes in blood DNA.

METHODS

We applied a data mining system called Auto Contractive Map to an existing database of 100 AD and 100 control individuals.

RESULTS

Low vitamin B12 was linked to the AD condition, to low folates, and to high hcy. Low PSEN1 methylation was linked to low folate levels as well as to low promoter methylation of BACE1 and DNMTs genes. Low hcy was linked to controls, to high folates and vitamin B12, as well as to high methylation levels of most of the studied genes.

CONCLUSIONS

The present pilot study suggests that promoter methylation levels of the studied genes are linked to circulating levels of folates, hcy, and vitamin B12.

Advances in development of fluorescent probes for detecting amyloid-β aggregates

With accumulating evidence suggesting that amyloid-β (Aβ) deposition is a good diagnostic biomarker for Alzheimer's disease (AD), the discovery of active Aβ probes has become an active area of research. Among the existing imaging methods, optical imaging targeting Aβ aggregates (fibrils or oligomers), especially using near-infrared (NIR) fluorescent probes, is increasingly recognized as a promising approach for the early diagnosis of AD due to its real time detection, low cost, lack of radioactive exposure and high-resolution. In the past decade, a variety of fluorescent probes have been developed and tested for efficiency in vitro, and several probes have shown efficacy in AD transgenic mice. This review classifies these representative probes based on their chemical structures and functional modes (dominant solvent-dependent mode and a novel solvent-independent mode). Moreover, the pharmaceutical characteristics of these representative probes are summarized and discussed. This review provides important perspectives for the future development of novel NIR Aβ diagnostic probes.

Regulated proteolysis of NOTCH2 and NOTCH3 receptors by ADAM10 and presenilins

In mammals, there are four NOTCH receptors and five Delta-Jagged-type ligands regulating many aspects of embryonic development and adult tissue homeostasis. NOTCH proteins are type I transmembrane receptors that interact with ligands on adjacent cells and are activated by regulated intramembrane proteolysis (RIP). The activation mechanism of NOTCH1 receptors upon ligand binding is well understood and requires cleavage by ADAM10 metalloproteases prior to intramembranous cleavage by γ-secretase. How the other human NOTCH receptor homologues are activated upon ligand binding is not known. Here, we dissect the proteolytic activation mechanism of the NOTCH2 and NOTCH3 receptors. We show that NOTCH2 and NOTCH3 signaling can be triggered by both Delta-Jagged-type ligands and requires ADAM10 and presenilin-1 or -2. Importantly, we did not find any role for the highly related ADAM17/TACE (tumor necrosis factor alpha-converting enzyme) protease in ligand-induced NOTCH2 or NOTCH3 signaling. These results demonstrate that canonical ligand-induced proteolysis of the NOTCH1, -2, and -3 receptors strictly depends on consecutive cleavage of these receptors by ADAM10 and the presenilin-containing γ-secretase complex, leading to transcriptional activation.

Population PKPD modeling of BACE1 inhibitor-induced reduction in Aβ levels in vivo and correlation to in vitro potency in primary cortical neurons from mouse and guinea pig

PURPOSE

The aims were to quantify the in vivo time-course between the oral dose, the plasma and brain exposure and the inhibitory effect on Amyloid β (Aβ) in brain and cerebrospinal fluid, and to establish the correlation between in vitro and in vivo potency of novel β-secretase (BACE1) inhibitors.

METHODS

BACE1-mediated inhibition of Aβ was quantified in in vivo dose- and/or time-response studies and in vitro in SH-SY5Y cells, N2A cells, and primary cortical neurons (PCN). An indirect response model with inhibition on Aβ production rate was used to estimate unbound in vivo IC 50 in a population pharmacokinetic-pharmacodynamic modeling approach.

RESULTS

Estimated in vivo inhibitory potencies varied between 1 and 1,000 nM. The turnover half-life of Aβ40 in brain was predicted to be 0.5 h in mouse and 1 h in guinea pig. An excellent correlation between PCN and in vivo potency was observed. Moreover, a strong correlation in potency was found between human SH-SY5Y cells and mouse PCN, being 4.5-fold larger in SH-SY5Y cells.

CONCLUSION

The strong in vivo-in vitro correlation increased the confidence in using human cell lines for screening and optimization of BACE1 inhibitors. This can optimize the design and reduce the number of preclinical in vivo effect studies.

Notch signaling in the brain: in good and bad times

Notch signaling is an evolutionarily conserved pathway, which is fundamental for neuronal development and specification. In the last decade, increasing evidence has pointed out an important role of this pathway beyond embryonic development, indicating that Notch also displays a critical function in the mature brain of vertebrates and invertebrates. This pathway appears to be involved in neural progenitor regulation, neuronal connectivity, synaptic plasticity and learning/memory. In addition, Notch appears to be aberrantly regulated in neurodegenerative diseases, including Alzheimer's disease and ischemic injury. The molecular mechanisms by which Notch displays these functions in the mature brain are not fully understood, but are currently the subject of intense research. In this review, we will discuss old and novel Notch targets and molecular mediators that contribute to Notch function in the mature brain and will summarize recent findings that explore the two facets of Notch signaling in brain physiology and pathology.

The calcium-sensing receptor: a novel Alzheimer's disease crucial target?

Alzheimer's disease (AD) is the most common human neurodegenerative ailment, the most prevalent (>95%) late-onset type of which has a still uncertain etiology. The progressive decline of cognitive functions, dementia, and physical disabilities of AD is caused by synaptic losses that progressively disconnect key neuronal networks in crucial brain areas, like the hippocampus and temporoparietal cortex, and critically impair language, sensory processing, memory, and conscious thought. AD's two main hallmarks are fibrillar amyloid-β (fAβ) plaques in extracellular spaces and intracellular accumulation of fAβ peptides and neurofibrillary tangles (NFTs). It is still undecided whether either or both these AD hallmarks cause or result from the disease. Recently, the dysregulation of calcium homeostasis has been advanced as a novel cause of AD. In this case, a suitable candidate of AD driver would be the Aβ peptides-binding/activated calcium-sensing receptor (CaSR), whose intracellular signalling is triggered by Aβ peptides. In this review, we briefly discuss CaSR's roles in normal adult human astrocytes (NAHAs) and their possible impacts on AD.

Neuronal autophagy and neurodegenerative diseases

Autophagy is a dynamic cellular pathway involved in the turnover of proteins, protein complexes, and organelles through lysosomal degradation. The integrity of postmitotic neurons is heavily dependent on high basal autophagy compared to non-neuronal cells as misfolded proteins and damaged organelles cannot be diluted through cell division. Moreover, neurons contain the specialized structures for intercellular communication, such as axons, dendrites and synapses, which require the reciprocal transport of proteins, organelles and autophagosomes over significant distances from the soma. Defects in autophagy affect the intercellular communication and subsequently, contributing to neurodegeneration. The presence of abnormal autophagic activity is frequently observed in selective neuronal populations afflicted in common neurodegenerative diseases, such as Alzheimer's disease, Parkinson's disease, Huntington's disease and amyotrophic lateral sclerosis. These observations have provoked controversy regarding whether the increase in autophagosomes observed in the degenerating neurons play a protective role or instead contribute to pathogenic neuronal cell death. It is still unknown what factors may determine whether active autophagy is beneficial or pathogenic during neurodegeneration. In this review, we consider both the normal and pathophysiological roles of neuronal autophagy and its potential therapeutic implications for common neurodegenerative diseases.

Novel BACE1 inhibitors possessing a 5-nitroisophthalic scaffold at the P2 position

Recently, we reported substrate-based pentapeptidic BACE1 inhibitors possessing a hydroxymethylcarbonyl isostere as a substrate transition-state mimic. These inhibitors showed potent inhibitory activities in enzymatic and cell assays. We also designed and synthesized non-peptidic and small-sized inhibitors possessing a heterocyclic scaffold at the P(2) position. By studying the structure-activity relationship of these inhibitors, we found that the σ-π interaction of an inhibitor with the BACE1-Arg235 side chain played a key role in the inhibition mechanism. Hence, we optimized the inhibitors with a focus on their P(2) regions. In this Letter, a series of novel BACE1 inhibitors possessing a 5-nitroisophthalic scaffold at the P(2) position are described along with the results of the related structure-activity relationship study. These small-sized inhibitors are expected improved membrane permeability and bioavailability.

Mechanisms of neural and behavioral dysfunction in Alzheimer's disease

This review critically examines progress in understanding the link between Alzheimer's disease (AD) molecular pathogenesis and behavior, with an emphasis on the impact of amyloid-β. We present the argument that the AD research field requires more multifaceted analyses into the impacts of Alzheimer's pathogenesis which combine simultaneous molecular-, circuit-, and behavior-level approaches. Supporting this argument is a review of particular research utilizing similar, "systems-level" methods in mouse models of AD. Related to this, a critique of common physiological and behavioral models is made-highlighting the likely usefulness of more refined and specific tools in understanding the relationship between candidate molecular pathologies and behavioral dysfunction. Finally, we propose challenges for future research which, if met, may greatly extend our current understanding of how AD molecular pathology impacts neural network function and behavior and possibly may lead to refinements in disease therapeutics.

Design of pentapeptidic BACE1 inhibitors with carboxylic acid bioisosteres at P1' and P4 positions

We previously reported potent BACE1 inhibitors KMI-420 and KMI-570 possessing a hydroxymethylcarbonyl isostere as a substrate transition-state mimic. Acidic moieties at the P(1)(') and P(4) positions of KMI inhibitors are thought to be unfavorable in terms of membrane permeability across the blood-brain barrier. Herein, we replaced acidic moieties at the P(4) position with hydrogen bond accepting groups and acidic moieties at the P(1)(') position with less acidic and similar molecular-size moieties (carboxylic acid or tetrazole bioisosteres). These inhibitors exhibited improved BACE1 inhibitory activities and a thorough quantitative structure-activity relationship study was performed.

Divergent pathways mediate spine alterations and cell death induced by amyloid-beta, wild-type tau, and R406W tau

Alzheimer's disease is characterized by synaptic alterations and neurodegeneration. Histopathological hallmarks represent amyloid plaques composed of amyloid-beta (Abeta) and neurofibrillary tangles containing hyperphosphorylated tau. To determine whether synaptic changes and neurodegeneration share common pathways, we established an ex vivo model using organotypic hippocampal slice cultures from amyloid precursor protein transgenic mice combined with virus-mediated expression of EGFP-tagged tau constructs. Confocal high-resolution imaging, algorithm-based evaluation of spines, and live imaging were used to determine spine changes and neurodegeneration. We report that Abeta but not tau induces spine loss and shifts spine shape from mushroom to stubby through a mechanism involving NMDA receptor (NMDAR), calcineurin, and GSK-3beta activation. In contrast, Abeta alone does not cause neurodegeneration but induces toxicity through phosphorylation of wild-type (wt) tau in an NMDAR-dependent pathway. We show that GSK-3beta levels are elevated in APP transgenic cultures and that inhibiting GSK-3beta activity or use of phosphorylation-blocking tau mutations prevented Abeta-induced toxicity of tau. FTDP-17 tau mutants are differentially affected by Abeta. While R406W tau shows increased toxicity in the presence of Abeta, no change is observed with P301L tau. While blocking NMDAR activity abolishes toxicity of both wt and R406W tau, the inhibition of GSK-3beta only protects against toxicity of wt tau but not of R406W tau induced by Abeta. Tau aggregation does not correlate with toxicity. We propose that Abeta-induced spine pathology and tau-dependent neurodegeneration are mediated by divergent pathways downstream of NMDAR activation and suggest that Abeta affects wt and R406W tau toxicity by different pathways downstream of NMDAR activity.

Design of potent aspartic protease inhibitors to treat various diseases

In this retrospective, personal review covering our research from the late 1980s until 2007, we outline nearly two-decade worth of our own work on several aspartic protease inhibitors including those affecting renin, HIV-1 protease, plasmepsins, beta-secretase, and HTLV-I protease and we report on aspartic protease inhibitors as potential drugs to treat hypertension, AIDS, malaria, Alzheimer's disease and adult T-cell leukemia, HTLV-I associated myelopathy / tropical spastic paraparesis, and various, respectively, associated diseases. Herein, we describe our methods for rational substrate-based drug design of peptidomimetics that potently inhibit the activity of renin, HIV-1 protease, plasmepsins, beta-secretase, and HTLV-I protease accordingly, using an appropriately selected inhibitory residue that contained a hydroxymethylcarbonyl isostere. Although this non-hydrolyzable isostere mimics the transition state that is formed during protein cleavage of a substrate, the isostere-containing inhibitor is not cleaved. We highlight our optimization studies in which we used various techniques and tools such as truncation studies, natural and non-natural amino acid substitution studies, various moieties to promote chemical and pharmacological stability, X-ray crystallography, computer-assisted docking and dynamic simulations, quantitative structure-activity relationship studies, and various other methods that this review can barely mention.

What determines the molecular composition of abnormal protein aggregates in neurodegenerative disease?

Abnormal protein aggregates, in the form of either extracellular plaques or intracellular inclusions, are an important pathological feature of the majority of neurodegenerative disorders. The major molecular constituents of these lesions, viz., beta-amyloid (Abeta), tau, and alpha-synuclein, have played a defining role in the diagnosis and classification of disease and in studies of pathogenesis. The molecular composition of a protein aggregate, however, is often complex and could be the direct or indirect consequence of a pathogenic gene mutation, be the result of cell degeneration, or reflect the acquisition of new substances by diffusion and molecular binding to existing proteins. This review examines the molecular composition of the major protein aggregates found in the neurodegenerative diseases including the Abeta and prion protein (PrP) plaques found in Alzheimer's disease (AD) and prion disease, respectively, and the cellular inclusions found in the tauopathies and synucleinopathies. The data suggest that the molecular constituents of a protein aggregate do not directly cause cell death but are largely the consequence of cell degeneration or are acquired during the disease process. These findings are discussed in relation to diagnosis and to studies of to disease pathogenesis.

β-Secretase inhibitors: Modification at the P4 position and improvement of inhibitory activity in cultured cells

Recently, we reported potent and small-sized beta-secretase (BACE1) inhibitors KMI-570 and KMI-684 in which we replaced carboxylic acid groups at the P(1)(') position of KMI-420 and KMI-429, respectively, with tetrazole derivatives as carboxylic acid bioisosteres. These modifications improved significantly BACE1 inhibitory activity and chemical stability. In this study, the acidic tetrazole ring of the P(4) position of KMI-420 and KMI-570, respectively, was replaced with various hydrogen bond acceptor groups. We found BACE1 inhibitor KMI-574 that exhibited potent inhibitory activity in cultured cells as well as in vitro enzymatic assay.

Design and synthesis of potent β-secretase (BACE1) inhibitors with carboxylic acid bioisosteres

Recently, we reported potent and small-sized beta-secretase (BACE1) inhibitors KMI-420 and KMI-429 in which we replaced the Glu residue at the P4 position of KMI-260 and KMI-360, respectively, with a 1H-tetrazole-5-carbonyl DAP (L-alpha,beta-diaminopropionic acid) residue. At the P1' position, these compounds contain one or two carboxylic acid groups, which are unfavorable for crossing the blood-brain barrier. Herein, we report BACE1 inhibitors with P1' carboxylic acid bioisosteres in order to develop practical anti-Alzheimer's disease drugs. Among them, tetrazole ring-containing compounds, KMI-570 (IC50=4.8 nM) and KMI-684 (IC50=1.2 nM), exhibited significantly potent BACE1 inhibitory activities.

Progressive neuronal loss and behavioral impairments of transgenic C57BL/6 inbred mice expressing the carboxy terminus of amyloid precursor protein

The beta-secretase cleaved Abeta-bearing carboxy-terminal fragments (betaCTFs) of amyloid precursor protein (APP) in neural cells have been suggested to be cytotoxic. However, the functional significance of betaCTFs in vivo remains elusive. We created a transgenic mouse line Tg-betaCTF99/B6 expressing the human betaCTF99 in the brain of inbred C57BL/6 strain. Tg-betaCTF99/B6 mouse brain at 12-16 months showed severely down-regulated calbindin, phospho-CREB, and Bcl-xL expression and up-regulated phospho-JNK, Bcl-2, and Bax expression. Neuronal cell density in the Tg-betaCTF99/B6 cerebral cortex at 16-18 months was lower than that of the non-transgenic control, but not at 5 months. At 11-14 months, Tg-betaCTF99/B6 mice displayed cognitive impairments and increased anxiety, which were not observed at 5 months. These results suggest that increased betaCTF99 expression is highly detrimental to the aging brain and that it produces a progressive and age-dependent AD-like pathogenesis.

Working memory impairment in a transgenic amyloid precursor protein TgCRND8 mouse model of Alzheimer's disease

The most profound deficits observed in Alzheimer's disease (AD) are in domains of episodic and working memory systems. Transgenic (Tg) mice expressing mutated human amyloid precursor protein (APP) genes offer a model to study the effect of AD pathology on cognition. We reported previously that APP TgCRND8 mice showed deficits in a reference and working memory evaluated in a Morris water-maze test. In this study, we evaluated the working memory of TgCRND8 mice comparing two training paradigms in a six-arm radial water maze. In the first paradigm, the exploration of the maze was constrained, forcing the mice to use a spatial mapping strategy. In the second paradigm, mice were unconstrained in their exploration of the maze. TgCRND8 mice proved to be significantly impaired in spatial working memory in both paradigms as compared with their non-transgenic littermates. The analysis of data revealed that forcing mice to use a spatial strategy during training caused only a moderate improvement in the performance of all mice. However, unconstrained exploration of the maze not only resulted in a fast learning in control mice, but also facilitated the development of a chaining strategy in spatially impaired TgCRND8 mice. In conclusion, TgCRND8 mice showed impairment in spatial working memory but retained a plasticity to choose alternative search strategies.

Design and synthesis of highly active Alzheimer’s β-secretase (BACE1) inhibitors, KMI-420 and KMI-429, with enhanced chemical stability

Recently, we reported potent and small-sized BACE1 inhibitors KMI-358 and KMI-370 in which the Glu residue is replaced by a beta-N-oxalyl-DAP (l-alpha,beta-diaminopropionyl) residue at the P(4) position. The beta-N-oxalyl-DAP group is important for enhancing BACE1 inhibitory activity, but these inhibitors isomerized to alpha-N-oxalyl-DAP derivatives in solvents. Hence, we used a tetrazole moiety as a bioisostere of the free carboxylic acid of the oxalyl group. KMI-420 and KMI-429, containing a tetrazole ring, showed improved stability and potent enzyme inhibitory activity.

Nilvadipine antagonizes both Abeta vasoactivity in isolated arteries, and the reduced cerebral blood flow in APPsw transgenic mice

The development of Alzheimer's disease (AD) is generally thought to correlate with cerebral accumulation of Abeta. It has previously been shown that Abeta peptides enhance vasoconstriction in isolated arteries and oppose certain vasorelaxants. Moreover, exogenous application of Abeta peptides causes cerebral vasoconstriction in rodents and in transgenic mouse models of AD that overexpress Abeta there is reduced cerebral blood flow. In the present study, we investigated the effect of nilvadipine, a dihydropyridine-type calcium channel blocker, on Abeta induced vasoconstriction in isolated arteries and in vivo on cerebral blood flow (CBF) of an AD transgenic mouse model overexpressing Abeta (Tg APPsw line 2576). Nilvadipine completely inhibited the vasoactivity elicited by Abeta in rat aortae and in human middle cerebral arteries. The effect of a short treatment duration (2 weeks) with nilvadipine on regional CBF was investigated in 13-month-old Tg APPsw mice and control littermates using a laser Doppler imager. Additionally, CBF was also measured in 20-month-old Tg APPsw mice and control littermates that were chronically treated with nilvadipine for 7 months. Untreated Tg APPsw mice showed a reduction of regional CBF compared to their untreated control littermates. Nilvadipine restored cortical perfusion levels in Tg APPsw to values similar to those observed in control littermates without notably affecting the CBF of control mice. All together, these data suggest that nilvadipine might be useful for the treatment of oligemia associated with AD.

A novel recombinant adeno-associated virus vaccine reduces behavioral impairment and beta-amyloid plaques in a mouse model of Alzheimer's disease

Memory impairment progressing to dementia is the main clinical symptom of Alzheimer's disease (AD). Deposition of the amyloid-beta peptide (Abeta) in brain, particularly its 42-amino acid isoform (Abeta42), has been shown to play a primary and crucial role in the pathogenesis of AD. In this study we have developed a recombinant adeno-associated virus (AAV) vaccine against AD. This vaccine could express CB-Abeta42 (cholera toxin B subunit and Abeta42 fusion protein) in vivo. A single administration of the AAV-CB-Abeta42 vaccine induced a prolonged, strong production of Abeta-specific serum IgG in transgenic mice that overexpressed the London mutant of amyloid precursor protein (APP/V717I), and resulted in improved ability of memory and cognition, decreased Abeta deposition in the brain, and a resultant decrease in plaque-associated astrocytosis. Our results extended the immunological approaches for the treatment and prevention of AD to an oral, intranasal, or intramuscular route that might be better tolerated in human patients than repetitive parental immunizations in the presence of adjuvant. AAV has attracted tremendous interest as a promising vector for gene delivery. Our results raised the possibility that AAV-CB-Abeta42 vector immunization may provide the basis of a novel and promising Alzheimer's disease vaccination program.

Uptake and pathogenic effects of amyloid beta peptide 1-42 are enhanced by integrin antagonists and blocked by NMDA receptor antagonists

Many synapses contain two types of receptors - integrins and N-methyl-D-aspartate (NMDA) receptors - that have been implicated in peptide internalization. The present studies tested if either class is involved in the uptake of the 42-residue form of amyloid beta peptide (Abeta1-42), an event hypothesized to be of importance in the development of Alzheimer's disease. Cultured hippocampal slices were exposed to Abeta1-42 for 6 days in the presence or absence of soluble Gly-Arg-Gly-Asp-Ser-Pro, a peptide antagonist of Arg-Gly-Asp (RGD)-binding integrins, or the disintegrin echistatin. Abeta uptake, as assessed with immunocytochemistry, occurred in 42% of the slices incubated with Abeta peptide alone but in more than 80% of the slices co-treated with integrin antagonists. Uptake was also found in a broader range of hippocampal subfields in RGD-treated slices. Increased sequestration was accompanied by two characteristics of early stage Alzheimer's disease: elevated concentrations of cathepsin D immunoreactivity and activation of microglia. The selective NMDA receptor antagonist D-(-)-2-amino-5-phosphonovalerate completely blocked internalization of Abeta, up-regulation of cathepsin D, and activation of microglia. Our results identify two classes of receptors that cooperatively regulate the internalization of Abeta1-42 and support the hypothesis that characteristic pathologies of Alzheimer's disease occur once critical intraneuronal Abeta concentrations are reached.

Dementia epidemiology

Determining the incidence and prevalence of dementia is an inexact science. Dementia is difficult to define and detect in the population. Even with the difficulties of determining prevalence and incidence, it is clear that dementia causes a substantial burden on our society. Problems with diagnostic inaccuracy and insidious disease onset influence our ability to observe risk factor associations; factors related to survival may be mistaken for risk/protective factors. Current studies suggest that factors influencing brain development or cognitive reserve may delay the onset of AD, perhaps through a protective mechanism or a delay in diagnosis caused by improved performance on cognitive tests. The recent identification of genes that cause dementia suggests that these genes or their biochemical pathways may be involved in the pathogenesis of nonfamilial cases. The contribution of genes that cause disease in and of themselves may be smaller than that of genes that act to metabolize or potentiate environmental exposures. The interaction between gene and environment should be increasingly well studied in the future. Epidemiology must take advantage of these molecular advances. The tasks of public health and epidemiology should still involve prevention, the nonrandom occurrence of disease, and its environmental context in addition to heredity. The tools to address these tasks should continue to be refined.

Neuropathology of Alzheimer's disease and other dementias

Clinical differentiation of neurodegenerative diseases that produce dementia is imprecise. Neuropathology offers the only way to make a definite diagnosis. The CNS autopsy is also important for clinical quality control and for providing tissue that furthers research into these disabling disorders. This brief article summarizes the major neuropathologic features of largely sporadic disorders that present with late-life dementia. The common causes of dementia discussed are Alzheimer's disease, Lewy body disease, and vascular dementia; less common disorders described are dementia lacking distinctive histopathology, Pick's disease, progressive supranuclear palsy, corticobasal degeneration, and Creutzfeldt-Jakob disease.

Prostate apoptosis response-4 enhances secretion of amyloid beta peptide 1-42 in human neuroblastoma IMR-32 cells by a caspase-dependent pathway

Prostate apoptosis response-4 (Par-4) is a leucine zipper protein that promotes neuronal cell death in Alzheimer's disease (AD). Neuronal degeneration in AD may result from extracellular accumulation of amyloid beta peptide (Abeta) 1-42. To examine the effect of Par-4 on Abeta secretion and to reconcile amyloid/apoptosis hypotheses of AD, we generated IMR-32 cell lines that overexpress Par-4 and/or its leucine zipper domain. Overexpression of Par-4 did not significantly affect levels of the endogenously expressed beta amyloid precursor protein but drastically increased the Abeta(1-42)/Abeta(total) ratio in the conditioned media about 6-8 h after trophic factor withdrawal. Time course analysis of caspase activation reveals that Par-4 overexpression exacerbated caspase activation, which is detectable within 2 h after trophic factor withdrawal. Furthermore, inhibition of caspase activity by the broad spectrum caspase inhibitor BD-fmk significantly attenuated the Par-4-induced increase in Abeta 1-42 production. In addition, the effects of Par-4 on secretion of Abeta 1-42 were consistently blocked by co-expression of the leucine zipper domain, indicating that the effect of Par-4 on Abeta secretion may require its interaction with other protein(s). These results suggest that Par-4 increases secretion of Abeta 1-42 largely through a caspase-dependent pathway after apoptotic cascades are initiated.

Sequence, genomic structure and tissue expression of Human BRI3, a member of the BRI gene family

The BRI3 gene is a member of the BRI gene family, made up of at least three different genes (BRI1-3). Previous studies established the cDNA sequence and structure of the human and mouse BRI1 and BRI2 genes and we recently reported that mutations in the BRI2 isoform, located on chromosome 13, are associated with dementia in humans. In the present work, we determine the complete cDNA sequence and genomic organization of the human BRI3 gene. BRI3 codes for a polypeptide of 267 amino acids, with a Mr of 30 KDa and a pI of 8.47. The amino acid sequence is 43.7% identical to the sequence of the human BRI2, and 38.3% identical to that of human BRI1, with the highest percentage of amino acid identity being concentrated on the C-terminal half of the molecules. In Northern blots, BRI3 cDNA hybridizes only one message of approximately 2.1 kilobases, which is predominantly present in the human brain. The BRI3 gene is localized on chromosome 2 and consists of six exons spanning more than 20 kb. Homology search of EST data banks retrieved a Caenorhabditis briggsae homolog of BRI, indicating that the BRI gene belongs to a strongly conserved gene family. These studies, aimed at characterizing the members of the BRI gene family, may provide valuable clues to the understanding of their normal function and how mutations in BRI2 can cause neurodegeneration and dementia similar to Alzheimer's disease.

A beta peptide immunization reduces behavioural impairment and plaques in a model of Alzheimer's disease

Much evidence indicates that abnormal processing and extracellular deposition of amyloid-beta peptide (A beta), a proteolytic derivative of the beta-amyloid precursor protein (betaAPP), is central to the pathogenesis of Alzheimer's disease (reviewed in ref. 1). In the PDAPP transgenic mouse model of Alzheimer's disease, immunization with A beta causes a marked reduction in burden of the brain amyloid. Evidence that A beta immunization also reduces cognitive dysfunction in murine models of Alzheimer's disease would support the hypothesis that abnormal A beta processing is essential to the pathogenesis of Alzheimer's disease, and would encourage the development of other strategies directed at the 'amyloid cascade'. Here we show that A beta immunization reduces both deposition of cerebral fibrillar A beta and cognitive dysfunction in the TgCRND8 murine model of Alzheimer's disease without, however, altering total levels of A beta in the brain. This implies that either a approximately 50% reduction in dense-cored A beta plaques is sufficient to affect cognition, or that vaccination may modulate the activity/abundance of a small subpopulation of especially toxic A beta species.

Par-4 induces cholinergic hypoactivity by suppressing ChAT protein synthesis and inhibiting NGF-inducibility of ChAT activity

Profound reductions in choline acetyl-transferase (ChAT) activity are reliable markers for cholinergic hypoactivity associated with cognitive function deficit in Alzheimer's disease (AD). Par-4 (prostate apoptosis response-4) is a novel mediator of neuronal apoptosis associated with the pathogenesis of AD. Par-4 contains a leucine zipper domain (Leu.zip) that presumably mediates protein-protein interactions critical for its functions in apoptosis. Par-4 activity can be effectively blocked by overexpression of Leu. zip because it exerts a dominant negative action possibly by competitively blocking the interaction of Par-4 with other proteins. Whether Par-4 participates in regulation of cholinergic signaling has not been determined. We report that overexpression of Par-4 results in apoptotic and non-apoptotic reductions in ChAT activity in transfected PC12 cells following exposure to a toxic concentration (50 microM) of aggregated amyloid beta peptide 1-42 (Abeta 1-42) and a non-toxic concentration (1 microM) of soluble Abeta 1-42, respectively. Non-apoptotic reduction in ChAT activity induced by Par-4 can be completely blocked by co-overexpression of Leu.zip, indicating that enhanced Par-4 activity is a necessary event for cholinergic hypoactivity in PC12 cells. Further studies found that Par-4 induces non-apoptotic reduction in ChAT activity by: (1) reducing ChAT protein levels following exposure to non-toxic concentration of Abeta, and (2) blocking the cellular capability to increase ChAT activity following exposure to nerve growth factor (NGF). The role of Par-4 in inducing cholinergic hypoactivity may have significant implications in the understanding and the treatment of memory impairment in AD.