Evidence for high affinity choline transport in synaptosomes prepared from hippocampus and neocortex of patients with Alzheimer's disease

Mortality of alzheimer's disease in Italy from 1980 to 2015

OBJECTIVE

To evaluate mortality for Alzheimer's Disease (AD) in Italy over more than three decades (1980-2015) and discuss the possible role of general and specific contributing factors.

METHODS

Mortality data were extracted by the Italian National Institute of Statistics: crude mortality rates were computed for sex and age, considering the whole country and its five main geographical sub-areas. Rates were standardized in two ways: directly (annual mortality rates AMRs) and indirectly (standardized mortality rates, SMRs). SMRs were then used to evaluate geographical differences; to study mortality trend, AMRs and joinpoint linear regression analysis were used.

RESULTS

Considering the entire period and the whole country, mortality rates were similar for females and males and for geographical regions, with the exception of the older age groups where mortality for AD in females slightly prevailed. In these older patients, a steep increase of mortality was seen starting from the current century. The increase in male mortality mirrored the national trend in North-West and Central Italy, but not in North-East, South, and the Islands, where it did not surge until the mid to late 1990s.

CONCLUSIONS

the general increase of mortality is in line with international data and it reflects the increasing prevalence of the disease, likely due to increasing longevity, and to improvements in diagnostic accuracy. In addition, the accuracy of death certificate compilation could account for both geographical and temporal differences. Currently available drugs for AD do not seem to have an impact on mortality rates.

To evaluate the effect of endothelin receptor agonist IRL-1620 alone and in combination with donepezil in modulating neurodegeneration elicited by amyloid-β in rats

BACKGROUND

The development of efficient therapies for Alzheimer''s disease is essential since it is a serious public health problem. This investigation sought to ascertain any potential synergistic benefits of treating Alzheimer's disease with IRL-1620 monotherapy in addition to Donepezil. Additionally, the effect of IRL-1620 was evaluated using different doses (5 μg/kg,7 μg/kg, and 9 μg/kg). The study further assessed neurobehavioral, biochemical, molecular, and histopathological parameters to evaluate the efficacy of both IRL1620 by its own and in association with Donepezil. Fifty-eight adult male Wistar rats were allocated to eight experimental groups. A dose-ranging study of IRL-1620 was conducted using different doses administered via intravenous injection. Alzheimer's disease was induced by Aβ administration, and treatment arms included disease Control (Sham), Donepezil monotherapy, and combination treatment with IRL-1620 5 μg/kg (Dose selected from the dose-ranging study). The treatment using IRL-1620 (9 μg/kg) intravenously and Donepezil (1 mg/kg orally) both on its own and in addition substantially enhanced memory in comparison with the control group (p < 0.05). Dose of IRL-1620 (9 μg/kg) intravenously, escape latency decreased and the time spent in the target quadrant was considerably increased, and they further benefited from combination therapy. Moreover, IRL-1620 (9 μg/kg) intravenously and combination treatment reduced lipid peroxidation and acetylcholinesterase levels while increasing antioxidant enzyme levels. Immunohistochemistry and molecular analysis revealed enhanced expression of neurotrophic factors with combination treatment. The combination of IRL-1620 and Donepezil showed significant improvements in memory and neurobehavioral parameters (p < 0.05). Alzheimer's disease in male Wistar rats. These results indicate to the probable therapeutic advantages of IRL-1620 and Donepezil in the management of Alzheimer's disease. The combination treatment exhibited enhanced effects compared to monotherapy, highlighting its potential promising therapeutic approach. Additional research is required to understand the mechanisms behind these synergistic benefits and to establish the ideal dosage and duration of therapy for therapeutic applications.

Potential Cardiologic Protective Effects of Acetylcholinesterase Inhibitors in Patients With Mild to Moderate Dementia

In patients with mild to moderate dementia, acetylcholinesterase inhibitors (AChE-I) are used to improve cognitive functions, but bradycardia, conduction abnormalities, and hypotension are possible side effects because of the peripheral muscarinic M2 receptor stimulation. This study aimed to evaluate the main cardiologic clinical outcomes in patients with dementia who are on AChE-I. In this retrospective, monocentric, observational cohort study, 2 groups were considered: (1) patients with dementia because of the typical and atypical forms of Alzheimer disease treated with AChE-I and (2) cognitively unimpaired, matched control group. The primary end point was a composite of cardiovascular death, nonfatal acute myocardial infarction, myocardial revascularization, occurrence of stroke and/or transient ischemic attacks, and hospitalization for heart failure occurring during a mean of 3.1 years of follow-up. The secondary end points were each individual component of the primary end point, total mortality, noncardiovascular death, and incidence of pacemaker implant. Each group included 221 patients who were homogeneous in terms of age, gender, and main cardiovascular risk factors. Major adverse cardiovascular events occurred in 24 patients with dementia (2.1 per 100 patient-years) compared with 56 in control group (5.0 per 100 patient-years), p = 0.036. Even if not significant, the difference was mainly driven by myocardial revascularization (3.2% vs 6.8%) and hospitalization for heart failure (4.5% vs 14.5%). As expected, noncardiovascular mortality was significantly higher in the treatment group (13.6% vs 2.7% p = 0.006). No significant difference between the groups was observed in terms of other secondary outcomes. In conclusion, in patients with dementia, the use of AChE-I may be protective for cardiovascular outcomes, especially in reducing heart failure hospitalization and myocardial revascularization.

Alzheimer's disease as a synaptopathy: Evidence for dysfunction of synapses during disease progression

The synapse has consistently been considered a vulnerable and critical target within Alzheimer's disease, and synapse loss is, to date, one of the main biological correlates of cognitive decline within Alzheimer's disease. This occurs prior to neuronal loss with ample evidence that synaptic dysfunction precedes this, in support of the idea that synaptic failure is a crucial stage within disease pathogenesis. The two main pathological hallmarks of Alzheimer's disease, abnormal aggregates of amyloid or tau proteins, have had demonstrable effects on synaptic physiology in animal and cellular models of Alzheimer's disease. There is also growing evidence that these two proteins may have a synergistic effect on neurophysiological dysfunction. Here, we review some of the main findings of synaptic alterations in Alzheimer's disease, and what we know from Alzheimer's disease animal and cellular models. First, we briefly summarize some of the human evidence to suggest that synapses are altered, including how this relates to network activity. Subsequently, animal and cellular models of Alzheimer's disease are considered, highlighting mouse models of amyloid and tau pathology and the role these proteins may play in synaptic dysfunction, either in isolation or examining how the two pathologies may interact in dysfunction. This specifically focuses on neurophysiological function and dysfunction observed within these animal models, typically measured using electrophysiology or calcium imaging. Following synaptic dysfunction and loss, it would be impossible to imagine that this would not alter oscillatory activity within the brain. Therefore, this review also discusses how this may underpin some of the aberrant oscillatory patterns seen in animal models of Alzheimer's disease and human patients. Finally, an overview of some key directions and considerations in the field of synaptic dysfunction in Alzheimer's disease is covered. This includes current therapeutics that are targeted specifically at synaptic dysfunction, but also methods that modulate activity to rescue aberrant oscillatory patterns. Other important future avenues of note in this field include the role of non-neuronal cell types such as astrocytes and microglia, and mechanisms of dysfunction independent of amyloid and tau in Alzheimer's disease. The synapse will certainly continue to be an important target within Alzheimer's disease for the foreseeable future.

A Review of the Recent Advances in Alzheimer's Disease Research and the Utilization of Network Biology Approaches for Prioritizing Diagnostics and Therapeutics

Alzheimer's disease (AD) is a polygenic multifactorial neurodegenerative disease that, after decades of research and development, is still without a cure. There are some symptomatic treatments to manage the psychological symptoms but none of these drugs can halt disease progression. Additionally, over the last few years, many anti-AD drugs failed in late stages of clinical trials and many hypotheses surfaced to explain these failures, including the lack of clear understanding of disease pathways and processes. Recently, different epigenetic factors have been implicated in AD pathogenesis; thus, they could serve as promising AD diagnostic biomarkers. Additionally, network biology approaches have been suggested as effective tools to study AD on the systems level and discover multi-target-directed ligands as novel treatments for AD. Herein, we provide a comprehensive review on Alzheimer's disease pathophysiology to provide a better understanding of disease pathogenesis hypotheses and decipher the role of genetic and epigenetic factors in disease development and progression. We also provide an overview of disease biomarkers and drug targets and suggest network biology approaches as new tools for identifying novel biomarkers and drugs. We also posit that the application of machine learning and artificial intelligence to mining Alzheimer's disease multi-omics data will facilitate drug and biomarker discovery efforts and lead to effective individualized anti-Alzheimer treatments.

Loss of Cholinergic Receptor Muscarinic 1 (CHRM1) Protein in the Hippocampus and Temporal Cortex of a Subset of Individuals with Alzheimer’s Disease, Parkinson’s Disease, or Frontotemporal Dementia: Implications for Patient Survival

Background: Dysfunction of cholinergic neurotransmission is a hallmark of Alzheimer’s disease (AD); forming the basis for using acetylcholine (ACh) esterase (AChE) inhibitors to mitigate symptoms of ACh deficiency in AD. The Cholinergic Receptor Muscarinic 1 (CHRM1) is highly expressed in brain regions impaired by AD. Previous analyses of postmortem AD brains revealed unaltered CHRM1 mRNA expression compared to normal brains. However, the CHRM1 protein level in AD and other forms of dementia has not been extensively studied. Reduced expression of CHRM1 in AD patients may explain the limited clinical efficacy of AChE inhibitors. Objective: To quantify CHRM1 protein in the postmortem hippocampus and temporal cortex of AD, Parkinson’s disease (PD), and frontotemporal dementia (FTD) patients. Methods: Western blotting was performed on postmortem hippocampus (N = 19/73/7/9: unaffected/AD/FTD/PD) and temporal cortex (N = 9/74/27: unaffected/AD/PD) using a validated anti-CHRM1 antibody. Results: Quantification based on immunoblotting using a validated anti-CHRM1 antibody revealed a significant loss of CHRM1 protein level (<50%) in the hippocampi (78% AD, 66% PD, and 85% FTD) and temporal cortices (56% AD and 42% PD) of dementia patients. Loss of CHRM1 in the temporal cortex was significantly associated with early death (<65–75 years) for both AD and PD patients. Conclusion: Severe reduction of CHRM1 in a subset of AD and PD patients can explain the reported low efficacy of AChE inhibitors as a mitigating treatment for dementia patients. Based on this study, it can be suggested that future research should prioritize therapeutic restoration of CHRM1 protein levels in cholinergic neurons.

Synaptosome microRNAs regulate synapse functions in Alzheimer's disease

MicroRNAs (miRNAs) are found in nerve terminals, synaptic vesicles, and synaptosomes, but it is unclear whether synaptic and cytosolic miRNA populations differ in Alzheimer's disease (AD) or if synaptosomal miRNAs affect AD synapse activity. To address these questions, we generated synaptosomes and cytosolic fractions from postmortem brains of AD and unaffected control (UC) samples and analyzed them using a global Affymetrix miRNAs microarray platform. A group of miRNAs significantly differed (P < 0.0001) with high fold changes variance (+/- >200-fold) in their expressions in different comparisons: (1) UC synaptosome vs UC cytosol, (2) AD synaptosomes vs AD cytosol, (3) AD cytosol vs UC cytosol, and (4) AD synaptosomes vs UC synaptosomes. MiRNAs data analysis revealed that some potential miRNAs were consistently different across sample groups. These differentially expressed miRNAs were further validated using AD postmortem brains, brains of APP transgenic (Tg2576), Tau transgenic (P301L), and wild-type mice. The miR-501-3p, miR-502-3p, and miR-877-5p were identified as potential synaptosomal miRNAs upregulated with disease progression based on AD Braak stages. Gene Ontology Enrichment and Ingenuity Pathway Analysis of synaptosomal miRNAs showed the involvement of miRNAs in nervous system development, cell junction organization, synapse assembly formation, and function of GABAergic synapse. This is the first description of synaptic versus cytosolic miRNAs in AD and their significance in synapse function.

Allosteric Binding Sites of Ab Peptides on the Acetylcholine Synthesizing Enzyme ChAT as Deduced by In Silico Molecular Modeling

The native function of amyloid-β (Aβ) peptides is still unexplored. However, several recent reports suggest a prominent role of Aβ peptides in acetylcholine homeostasis. To clarify this role of Aβ, we have reported that Aβ peptides at physiological concentrations can directly enhance the catalytic efficiency of the key cholinergic enzyme, choline acetyltransferase (ChAT), via an allosteric interaction. In the current study, we further aimed to elucidate the underlying ChAT-Aβ interaction mechanism using in silico molecular docking and dynamics analysis. Docking analysis suggested two most probable binding clusters on ChAT for Aβ40 and three for Aβ42. Most importantly, the docking results were challenged with molecular dynamic studies of 100 ns long simulation in triplicates (100 ns × 3 = 300 ns) and were analyzed for RMSD, RMSF, RoG, H-bond number and distance, SASA, and secondary structure assessment performed together with principal component analysis and the free-energy landscape diagram, which indicated that the ChAT-Aβ complex system was stable throughout the simulation time period with no abrupt motion during the evolution of the simulation across the triplicates, which also validated the robustness of the simulation study. Finally, the free-energy landscape analysis confirmed the docking results and demonstrated that the ChAT-Aβ complexes were energetically stable despite the unstructured nature of C- and N-terminals in Aβ peptides. Overall, this study supports the reported in vitro findings that Aβ peptides, particularly Aβ42, act as endogenous ChAT-Potentiating-Ligand (CPL), and thereby supports the hypothesis that one of the native biological functions of Aβ peptides is the regulation of acetylcholine homeostasis.

Targeting the M1 muscarinic acetylcholine receptor in Alzheimer's disease

Alzheimer's disease (AD) remains a major cause of morbidity and mortality worldwide, and despite extensive research, only a few drugs are available for management of the disease. One strategy has been to up-regulate cholinergic neurotransmission to improve cognitive function, but this approach has dose-limiting adverse effects. To avoid these adverse effects, new drugs that target specific receptor subtypes of the cholinergic system are needed, and the M1 subtype of muscarinic acetylcholine receptor (M1-mAChR) has been shown to be a good target for this approach. By using several strategies, M1-mAChR ligands have been developed and trialled in preclinical animal models and in human studies, with varying degrees of success. This article reviews the different approaches to targeting the M1-mAChR in AD and discusses the advantages and limitations of these strategies. The factors to consider in targeting the M1-mAChR in AD are also discussed.

Drug Design Targeting the Muscarinic Receptors and the Implications in Central Nervous System Disorders

There is substantial evidence that cholinergic system function impairment plays a significant role in many central nervous system (CNS) disorders. During the past three decades, muscarinic receptors (mAChRs) have been implicated in various pathologies and have been prominent targets of drug-design efforts. However, due to the high sequence homology of the orthosteric binding site, many drug candidates resulted in limited clinical success. Although several advances in treating peripheral pathologies have been achieved, targeting CNS pathologies remains challenging for researchers. Nevertheless, significant progress has been made in recent years to develop functionally selective orthosteric and allosteric ligands targeting the mAChRs with limited side effect profiles. This review highlights past efforts and focuses on recent advances in drug design targeting these receptors for Alzheimer’s disease (AD), schizophrenia (SZ), and depression.

Multifaceted Alzheimer's Disease: Building a Roadmap for Advancement of Novel Therapies

Alzheimer's disease (AD) is one of the most prevailing neurodegenerative disorders of elderly humans associated with cognitive damage. Biochemical, epigenetic, and pathophysiological factors all consider a critical role of extracellular amyloid-beta (Aß) plaques and intracellular neurofibrillary tangles (NFTs) as pathological hallmarks of AD. In an endeavor to describe the intricacy and multifaceted nature of AD, several hypotheses based on the roles of Aß accumulation, tau hyperphosphorylation, impaired cholinergic signaling, neuroinflammation, and autophagy during the initiation and advancement of the disease have been suggested. However, in no way do these theories have the potential of autonomously describing the pathophysiological alterations located in AD. The complex pathological nature of AD has hindered the recognition and authentication of successful biomarkers for the progression of its diagnosis and therapeutic strategies. There has been a significant research effort to design multi-target-directed ligands for the treatment of AD, an approach which is developed by the knowledge that AD is a composite and multifaceted disease linked with several separate but integrated molecular pathways.

The Biology and Pathobiology of Glutamatergic, Cholinergic, and Dopaminergic Signaling in the Aging Brain

The elderly population is growing worldwide, with important health and socioeconomic implications. Clinical and experimental studies on aging have uncovered numerous changes in the brain, such as decreased neurogenesis, increased synaptic defects, greater metabolic stress, and enhanced inflammation. These changes are associated with cognitive decline and neurobehavioral deficits. Although aging is not a disease, it is a significant risk factor for functional worsening, affective impairment, disease exaggeration, dementia, and general disease susceptibility. Conversely, life events related to mental stress and trauma can also lead to accelerated age-associated disorders and dementia. Here, we review human studies and studies on mice and rats, such as those modeling human neurodegenerative diseases, that have helped elucidate (1) the dynamics and mechanisms underlying the biological and pathological aging of the main projecting systems in the brain (glutamatergic, cholinergic, and dopaminergic) and (2) the effect of defective glutamatergic, cholinergic, and dopaminergic projection on disabilities associated with aging and neurodegenerative disorders, such as Alzheimer's and Parkinson's diseases. Detailed knowledge of the mechanisms of age-related diseases can be an important element in the development of effective ways of treatment. In this context, we briefly analyze which adverse changes associated with neurodegenerative diseases in the cholinergic, glutaminergic and dopaminergic systems could be targeted by therapeutic strategies developed as a result of our better understanding of these damaging mechanisms.

Epigenetic plasticity and redox regulation of neural stem cell state and fate

The neural stem cells (NSCs) are essential for normal brain development and homeostasis. The cell state (i.e. quiescent versus activated) and fate (i.e. the cell lineage of choice upon differentiation) of NSCs are tightly controlled by various redox and epigenetic regulatory mechanisms. There is an increasing appreciation that redox and epigenetic regulations are intimately linked, but how this redox-epigenetics crosstalk affects NSC activity remains poorly understood. Another unresolved topic is whether the NSCs actually contribute to brain ageing and neurodegenerative diseases. In this review, we aim to 1) distill concepts that underlie redox and epigenetic regulation of NSC state and fate; 2) provide examples of the redox-epigenetics crosstalk in NSC biology; and 3) highlight potential redox- and epigenetic-based therapeutic opportunities to rescue NSC dysfunctions in ageing and neurodegenerative diseases.

Sigma ligands as potent inhibitors of Aβ and AβOs in neurons and promising therapeutic agents of Alzheimer's disease

Alzheimer's disease (AD) is an age-related neurodegenerative disease and characterized by dementia, memory decline, loss of learning and cognitive disorder. The main pathological features of AD are the deposition of amyloid plaques and the formation of neurofibrillary tangles (NFTs) in the brain. The current anti-AD drugs have shown unsatisfactory therapeutic results. Due to the complications and unclear pathogenesis, AD is still irreversible and incurable. Among several hypotheses proposed by the academic community, the amyloid cascade is widely recognized by scholars and supported by a large amount of evidences. However, controversy over pathogenic factors has also been ongoing. Increasing evidence has shown that amyloid-β (Aβ) and especially amyloid-β oligomers (AβOs) are highly neurotoxic and pathogenic agents that damage neurons, mediate various receptors in the downstream pathways, and ultimately lead to learning and cognitive dysfunction. However, efforts in developing inhibitors of Aβ or amyloid-β precursor protein (APP) have all failed to yield good clinical results. More recently, it has been demonstrated that sigma receptors, including sigma-1 and sigma-2 subtypes, may play critical roles in the regulation of binding and metabolism of AβOs in neuron cells and the pathophysiology of AD. Thus, sigma receptor ligands are being recognized as promising therapeutic agents for treating or ameliorating AD. This article will review the pathophysiology of AD and highlight the sigma ligands that display the capability of preventing or even reversing Aβ- and AβOs-induced neurotoxicity and blocking the signal transduction caused by AβOs.

The role of synaptic microRNAs in Alzheimer's disease

Structurally and functionally active synapses are essential for neurotransmission and for maintaining normal synaptic and cognitive functions. Researchers have found that synaptic dysfunction is associated with the onset and progression of neurodegenerative diseases, such as Alzheimer's disease (AD), and synaptic dysfunction is even one of the main physiological hallmarks of AD. MiRNAs are present in small, subcellular compartments of the neuron such as neural dendrites, synaptic vesicles, and synaptosomes are known as synaptic miRNAs. Synaptic miRNAs involved in governing multiple synaptic functions that lead to healthy brain functioning and synaptic activity. However, the precise role of synaptic miRNAs has not been determined in AD progression. This review emphasizes the presence of miRNAs at the synapse, synaptic compartments and roles of miRNAs in multiple synaptic functions. We focused on synaptic miRNAs alteration in AD, and how the modulation of miRNAs effect the synaptic functions in AD. We also discussed the impact of synaptic miRNAs in AD progression concerning the synaptic ATP production, mitochondrial function, and synaptic activity.

Relationships between Mitochondrial Dysfunction and Neurotransmission Failure in Alzheimer's Disease

Besides extracellular deposition of amyloid beta and formation of phosphorylated tau in the brains of patients with Alzheimer's disease (AD), the pathogenesis of AD is also thought to involve mitochondrial dysfunctions and altered neurotransmission systems. However, none of these components can describe the diverse cognitive, behavioural, and psychiatric symptoms of AD without the pathologies interacting with one another. The purpose of this review is to understand the relationships between mitochondrial and neurotransmission dysfunctions in terms of (1) how mitochondrial alterations affect cholinergic and monoaminergic systems via disruption of energy metabolism, oxidative stress, and apoptosis; and (2) how different neurotransmission systems drive mitochondrial dysfunction via increasing amyloid beta internalisation, oxidative stress, disruption of mitochondrial permeabilisation, and mitochondrial trafficking. All these interactions are separately discussed in terms of neurotransmission systems. The association of mitochondrial dysfunctions with alterations in dopamine, norepinephrine, and histamine is the prospective goal in this research field. By unfolding the complex interactions surrounding mitochondrial dysfunction in AD, we can better develop potential treatments to delay, prevent, or cure this devastating disease.

Synaptosome as a tool in Alzheimer's disease research

Synapse dysfunction is an integral feature of Alzheimer's disease (AD) pathophysiology. In fact, prodromal manifestation of structural and functional deficits in synapses much prior to appearance of overt pathological hallmarks of the disease indicates that AD might be considered as a degenerative disorder of the synapses. Several research instruments and techniques have allowed us to study synaptic function and plasticity and their alterations in pathological conditions, such as AD. One such tool is the biochemically isolated preparations of detached and resealed synaptic terminals, the "synaptosomes". Because of the preservation of many of the physiological processes such as metabolic and enzymatic activities, synaptosomes have proved to be an indispensable ex vivo model system to study synapse physiology both when isolated from fresh or cryopreserved tissues, and from animal or human post-mortem tissues. This model system has been tremendously successful in the case of post-mortem tissues because of their accessibility relative to acute brain slices or cultures. The current review details the use of synaptosomes in AD research and its potential as a valuable tool in furthering our understanding of the pathogenesis and in devising and testing of therapeutic strategies for the disease.

The antioxidant 2,3-dichloro,5,8-dihydroxy,1,4-naphthoquinone inhibits acetyl-cholinesterase activity and amyloid β42 aggregation: A dual target therapeutic candidate compound for the treatment of Alzheimer's disease

Alzheimer's disease is characterized by amyloid β aggregation and cholinergic neurodegeneration. In the present study, pure DDN (2,3-dichloro-5,8-dihydroxy-1,4-naphthoquinone) was examined, for the first time, for its dual potential as inhibitor of acetylcholinesterase (AChE) and Aβ₄₂ aggregation. Such investigation was encouraged by the in vitro high antioxidant potential of DDN. Indeed, it revealed interesting antioxidant activity with IC₅₀ values of 9.8 and 4.3 µM for ABTS and reducing power, respectively. The ability of DDN to counteract Aβ₄₂ aggregation was evaluated by thioflavine-T assay. Strong inhibition of Aβ₄₂ aggregation of more than 90% at 25 µM was measured. Moreover, results showed that DDN inhibited AChE (IC₅₀ = 14.5 µM). To better understand the interactions between DDN and AChE, molecular docking was performed. Obtained data predicted a high interaction characterized by hydrogen bonding at TYR337 as for galanthamine (positive control). Several residues involved in AChE hydrophobic interactions were similarly implicated in binding of this domain to DDN (ASP74, THR83, and TYR124). All these data would be useless if DDN could not pass the blood-brain barrier. So, DDN was loaded into alginate microspheres to enhance its stability and bioavailability. Thereafter, drug release profiles were assessed using immersion cell apparatus.

Acetylcholinesterase and Butyrylcholinesterase – Important Enzymes of Human Body

The serine hydrolases and proteases are a ubiquitous group of enzymes that is fundamental to many critical lifefunctions. Human tissues have two distinct cholinesterase activities: acetylcholinesterase and butyrylcholinesterase. Acetylcholinesterase functions in the transmission of nerve impulses, whereas the physiological function of butyrylcholinesterase remains unknown. Acetylcholinesterase is one of the crucial enzymes in the central and peripheral nerve system. Organophosphates and carbamates are potent inhibitors of serine hydrolases and well suited probes for investigating the chemical reaction mechanism of the inhibition. Understanding the enzyme’s chemistry is essential in preventing and/or treating organophosphate and carbamate poisoning as well as designing new medicaments for cholinergic-related diseases like as Alzheimer’s disease.

Rollercoaster ride of kynurenines: steering the wheel towards neuroprotection in Alzheimer's disease

INTRODUCTION

Alzheimer's disease (AD) is associated with cerebral cognitive deficits exhibiting two cardinal hallmarks: accruement of extracellular amyloid plaques and intracellular neurofibrillary tangles composed of hyperphosphorylated tau protein. The currently accessible therapeutic armamentarium merely provides symptomatic relief. Therefore, the cry for prospective neuroprotective strategies seems to be the need of the hour. Areas covered: This review comprehensively establishes correlation between kynurenine pathway (KP) metabolites and AD with major emphasis on its two functionally contrasting neuroactive metabolites i.e. kynurenic acid (KYNA) and quinolinic acid (QUIN) and enlists various clinical studies which hold a potential for future therapeutics in AD. Also, major hypotheses of AD and mechanisms underlying them have been scrutinized with the aim to brush up the readers with basic pathology of AD. Expert opinion: KP is unique in itself as it holds two completely different domains i.e. neurotoxic QUIN and neuroprotective KYNA and disrupted equilibrium between the two has a hand in neurodegeneration. KYNA has long been demonstrated to be neuroprotective but lately being disparaged for cognitive side effects. But we blaze a trail by amalgamating the pharmacological mechanistic studies of KYNA in kinship with α7nAChRs, NMDARs and GABA which lends aid in favour of KA.

Soluble Aβ42 Acts as Allosteric Activator of the Core Cholinergic Enzyme Choline Acetyltransferase

Two major questions in the field of Alzheimer-type dementia remain elusive. One is the native function of amyloid-β (Aβ) peptides and the other is an early deficit in the central cholinergic network. Nevertheless, recent evidence suggests that Aβ peptides are involved in the regulation of acetylcholine (ACh) homeostasis either by allosteric activation of ACh-degrading cholinesterases or by inhibiting the high-affinity choline uptake transporter. In the current study, we report that Aβ peptides, in particular Aβ42, allosterically enhances the catalytic rate of the core-cholinergic enzyme choline acetyltransferase (ChAT), responsible for biosynthesis of ACh. Detailed in vitro enzyme kinetic analysis indicated that both soluble Aβ40 and Aβ42 enhanced the catalytic efficiency of ChAT by ∼21% and 26% at physiological concentration ranges found in human cerebrospinal fluid (CSF). Further analyses indicated that activation of ChAT by Aβ was highly specific. Intriguingly, Aβ42 exhibited an EC₅₀ of activation potency at 10-fold lower concentrations compared to Aβ40. The activation was persistent even in the presence of a physiological Aβ 40/42 mixture ratio, expected in human CSF. In conclusion, we report for the first time that Aβ42 peptide acts as allosteric enhancers of ACh-biosynthesizing enzyme ChAT. Together with two previous observations, this points to a complex molecular cross-talk between Aβ and the enzymatic machinery involved in maintaining cellular, synaptic and extra-synaptic ACh homeostasis, warranting further investigation.

Blockage of High-Affinity Choline Transporter Increases Visceral Hypersensitivity in Rats with Chronic Stress

Background

Visceral hypersensitivity is a common feature of irritable bowel syndrome. Cholinergic system involves in the development of visceral hypersensitivity, and high-affinity choline transporter (CHT1) is of crucial importance in choline uptake system. However, involvement of CHT1 in visceral hypersensitivity remains unknown. The research aimed to study the CHT1 expression in dorsal root ganglions (DRGs) and the role of CHT1 in visceral hypersensitivity.

Methods

Repetitive water avoidance stress (WAS) was used to induce visceral hypersensitivity in rats. Colorectal distension (CRD) was determined, and the abdominal withdrawal reflex (AWR) and threshold intensity data were recorded to measure the visceral sensitivity. After intraperitoneal injection of hemicholinium-3 (HC-3), the specific inhibitor of CHT1, CRD data were also recorded. The CHT1 expression of DRGs was investigated by Western blotting, immunohistochemistry, and quantitative RT-PCR. Acetylcholine levels in the DRGs were detected by the assay kit.

Results

Repetitive WAS increased the AWR score of CRD at high distension pressure and decreased the mean threshold of rats. The CHT1 expression and acetylcholine concentration of DRG were significantly increased in WAS rats. After the administration of HC-3, the AWR score in WAS group was significantly increased at higher distension pressure while the threshold intensity was significantly reduced compared to the normal saline group. Acetylcholine concentration was significantly lower than the normal saline rats.

Conclusion

Our research firstly reports that CHT1 is overexpressed in noninflammatory visceral hypersensitivity, and blockage of CHT1 can enhance the visceral hypersensitivity. CHT1 may play an inhibitory role in visceral hypersensitivity.

CRISPR/Cas9-Correctable mutation-related molecular and physiological phenotypes in iPSC-derived Alzheimer's PSEN2 N141I neurons

Basal forebrain cholinergic neurons (BFCNs) are believed to be one of the first cell types to be affected in all forms of AD, and their dysfunction is clinically correlated with impaired short-term memory formation and retrieval. We present an optimized in vitro protocol to generate human BFCNs from iPSCs, using cell lines from presenilin 2 (PSEN2) mutation carriers and controls. As expected, cell lines harboring the PSEN2^N141I mutation displayed an increase in the Aβ42/40 in iPSC-derived BFCNs. Neurons derived from PSEN2^N141I lines generated fewer maximum number of spikes in response to a square depolarizing current injection. The height of the first action potential at rheobase current injection was also significantly decreased in PSEN2^N141I BFCNs. CRISPR/Cas9 correction of the PSEN2 point mutation abolished the electrophysiological deficit, restoring both the maximal number of spikes and spike height to the levels recorded in controls. Increased Aβ42/40 was also normalized following CRISPR/Cas-mediated correction of the PSEN2^N141I mutation. The genome editing data confirms the robust consistency of mutation-related changes in Aβ42/40 ratio while also showing a PSEN2-mutation-related alteration in electrophysiology.

Targeting the Cholinergic System to Develop a Novel Therapy for Huntington's Disease

In this review, we outline the role of the cholinergic system in Huntington’s disease, and briefly describe the dysfunction of cholinergic transmission, cholinergic neurons, cholinergic receptors and cholinergic survival factors observed in post-mortem human brains and animal models of Huntington’s disease. We postulate how the dysfunctional cholinergic system can be targeted to develop novel therapies for Huntington’s disease, and discuss the beneficial effects of cholinergic therapies in pre-clinical and clinical studies.

The Study of Postmortem Human Synaptosomes for Understanding Alzheimer's Disease and Other Neurological Disorders: A Review

Synaptic dysfunction is thought to play important roles in the pathophysiology of many neurological diseases, including Alzheimer’s disease, Parkinson’s disease, and schizophrenia. Over the past few decades, there have been systematic efforts to collect postmortem brain tissues via autopsies, leading to the establishment of dozens of human brain banks around the world. From cryopreserved human brain tissues, it is possible to isolate detached-and-resealed synaptic terminals termed synaptosomes, which remain metabolically and enzymatically active. Synaptosomes have become important model systems for studying human synaptic functions, being much more accessible than ex vivo brain slices or primary neuronal cultures. Here we review recent advances in the establishment of human brain banks, the isolation of synaptosomes, their biological activities, and various analytical techniques for investigating their biochemical and ultrastructural properties. There are unique insights to be gained by directly examining human synaptosomes, which cannot be substituted by animal models. We will also discuss how human synaptosome research has contributed to better understanding of neurological disorders, especially Alzheimer’s disease.

Cholinergic neurodegeneration in an Alzheimer mouse model overexpressing amyloid-precursor protein with the Swedish-Dutch-Iowa mutations

Alzheimer's disease (AD) is a chronic neurodegenerative disorder that is mainly characterized by beta-amyloid (Aβ) plaque deposition, Tau pathology and dysfunction of the cholinergic system causing memory impairment. The aim of the present study was to examine (1) anxiety and cognition, (2) Aβ plaque deposition and (3) degeneration of cholinergic neurons in the nucleus basalis of Meynert (nbM) and cortical cholinergic innervation in an Alzheimer mouse model (APP_SweDI; overexpressing amyloid precursor protein (APP) with the Swedish K670N/M671L, Dutch E693Q, and Iowa D694N mutations). Our results show that 12-month-old APP_SweDI mice were more anxious and had more memory impairment. A large number of Aβ plaques were already visible at the age of 6 months and increased with age. A significant decrease in cholinergic neurons was seen in the transgenic mouse model in comparison to the wild-type mice, identified by immunohistochemistry against choline acetyltransferase (ChAT) and p75 neurotrophin receptor as well as by in situ hybridization. Moreover, a significant decrease in cortical cholinergic fiber density was found in the transgenic mice as compared to the wild-type. In the cerebral cortex of APP_SweDI mice, swollen cholinergic varicosities were seen in the vicinity of Aβ plaques. In conclusion, the present study shows that in an AD mouse model (APP_SweDI mice) a high Aβ plaque load in the cortex causes damage to cholinergic axons in the cortex, followed by subsequent retrograde-induced cell death of cholinergic neurons and some forms of compensatory processes. This degeneration was accompanied by enhanced anxiety and impaired cognition.

Amyloid cascade hypothesis: Pathogenesis and therapeutic strategies in Alzheimer's disease

Alzheimer's disease is an irreversible, progressive neurodegenerative disorder. Various therapeutic approaches are being used to improve the cholinergic neurotransmission, but their role in AD pathogenesis is still unknown. Although, an increase in tau protein concentration in CSF has been described in AD, but several issues remains unclear. Extensive and accurate analysis of CSF could be helpful to define presence of tau proteins in physiological conditions, or released during the progression of neurodegenerative disease. The amyloid cascade hypothesis postulates that the neurodegeneration in AD caused by abnormal accumulation of amyloid beta (Aβ) plaques in various areas of the brain. The amyloid hypothesis has continued to gain support over the last two decades, particularly from genetic studies. Therefore, current research progress in several areas of therapies shall provide an effective treatment to cure this devastating disease. This review critically evaluates general biochemical and physiological functions of Aβ directed therapeutics and their relevance.

Insulin Regulates the Activity of the High-Affinity Choline Transporter CHT

Studies in humans and animal models show that neuronal insulin resistance increases the risk of developing Alzheimer’s Disease (AD), and that insulin treatment may promote memory function. Cholinergic neurons play a critical role in cognitive and attentional processing and their dysfunction early in AD pathology may promote the progression of AD pathology. Synthesis and release of the neurotransmitter acetylcholine (ACh) is closely linked to the activity of the high-affinity choline transporter protein (CHT), but the impact of insulin receptor signaling and neuronal insulin resistance on these aspects of cholinergic function are unknown. In this study, we used differentiated SH-SY5Y cells stably-expressing CHT proteins to study the effect of insulin signaling on CHT activity and function. We find that choline uptake activity measured after acute addition of 20 nM insulin is significantly lower in cells that were grown for 24 h in media containing insulin compared to cells grown in the absence of insulin. This coincides with loss of ability to increase phospho-Protein Kinase B (PKB)/Akt levels in response to acute insulin stimulation in the chronic insulin-treated cells. Inhibition of phosphatidylinositol-4,5-bisphosphate 3-kinase (PI3-kinase) in cells significantly lowers phospho-PKB/Akt levels and decreases choline uptake activity. We show total internal reflection microscopy (TIRF) imaging of the dynamic movement of CHT proteins in live cells in response to depolarization and drug treatments. These data show that acute exposure of depolarized cells to insulin is coupled to transiently increased levels of CHT proteins at the cell surface, and that this is attenuated by chronic insulin exposure. Moreover, prolonged inhibition of PI3-kinase results in enhanced levels of CHT proteins at the cell surface by decreasing their rate of internalization.

Regulation of the high-affinity choline transporter activity and trafficking by its association with cholesterol-rich lipid rafts

The sodium-coupled, hemicholinium-3-sensitive, high-affinity choline transporter (CHT) is responsible for transport of choline into cholinergic nerve terminals from the synaptic cleft following acetylcholine release and hydrolysis. In this study, we address regulation of CHT function by plasma membrane cholesterol. We show for the first time that CHT is concentrated in cholesterol-rich lipid rafts in both SH-SY5Y cells and nerve terminals from mouse forebrain. Treatment of SH-SY5Y cells expressing rat CHT with filipin, methyl-β-cyclodextrin (MβC) or cholesterol oxidase significantly decreased choline uptake. In contrast, CHT activity was increased by addition of cholesterol to membranes using cholesterol-saturated MβC. Kinetic analysis of binding of [(3)H]hemicholinium-3 to CHT revealed that reducing membrane cholesterol with MβC decreased both the apparent binding affinity (KD) and maximum number of binding sites (Bmax ); this was confirmed by decreased plasma membrane CHT protein in lipid rafts in cell surface protein biotinylation assays. Finally, the loss of cell surface CHT associated with lipid raft disruption was not because of changes in CHT internalization. In summary, we provide evidence that CHT association with cholesterol-rich rafts is critical for transporter function and localization. Alterations in plasma membrane cholesterol cholinergic nerve terminals could diminish cholinergic transmission by reducing choline availability for acetylcholine synthesis. The sodium-coupled choline transporter CHT moves choline into cholinergic nerve terminals to serve as substrate for acetylcholine synthesis. We show for the first time that CHT is concentrated in cholesterol-rich lipid rafts, and decreasing membrane cholesterol significantly reduces both choline uptake activity and cell surface CHT protein levels. CHT association with cholesterol-rich rafts is critical for its function, and alterations in plasma membrane cholesterol could diminish cholinergic transmission by reducing choline availability for acetylcholine synthesis.

Transmitter deficits in Alzheimer's disease

The pattern of neurotransmitter pathway losses in Alzheimer's disease are reviewed. Deficits of the cholinergic pathway from the nucleus basalis, the noradrenergic pathway from the locus coeruleus and the serotoninergic pathway from the raphe nuclei are established. Cortical somatostatin interneurons are affected and dopaminergic neurons may be affected although these may be late or secondary phenomena in the disease process. Other neuronal systems, particularly in the hippocampus and temporal cortex, are also damaged. However, the disease is not one of generalised neuronal atrophy since some neurons are selectively spared. The established pathway-specific losses are discussed in relation to the clinical symptomatology and the pathology of the disorder. The biochemical and histological findings are compared with similar measurements made on tissues from other dementing disorders in an attempt to trace features common to dementias. Finally, as an addendum, a hypothesis is briefly outlined which attempts to explain the common features of the affected neurons and the pathogenesis of the disorder.

Therapeutic approaches to age-associated neurocognitive disorders

The United Nations projects that the number of individuals with dementia in developed countries alone will be approximately 36,7 million by the year 2050. International recognition of the significant emotional and economic burden of Alzheimer's disease has been matched by a dramatic increase in the development of pharmacological and nonpharmacological approaches to this illness in the past decade. Changing demographics have underscored the necessity to develop similar approaches for the remediation of the cognitive impairment associated with more benign syndromes, such as mild cognitive impairment (MCI) and age-associated cognitive decline (AACD). The present article aims to provide an overview of the most current therapeutic approaches to age-associated neurocognitive disorders. Additionally, it discusses the conceptual and methodological issues that surround the design, implementation, and interpretation of such approaches.

Axo-axonal interaction in autonomic regulation of the cerebral circulation

Noradrenaline (NE) and acetylcholine (ACh) released from the sympathetic and parasympathetic neurones in cerebral blood vessels were suggested initially to be the respective vasoconstricting and dilating transmitters. Both substances, however, are extremely weak post-synaptic transmitters. Compelling evidence indicates that nitric oxide (NO) which is co-released with ACh from same parasympathetic nerves is the major transmitter for cerebral vasodilation, and its release is inhibited by ACh. NE released from the sympathetic nerve, acting on presynaptic β2-adrenoceptors located on the neighbouring parasympathetic nitrergic nerves, however, facilitates NO release with enhanced vasodilation. This axo-axonal interaction mediating NE transmission is supported by close apposition between sympathetic and parasympathetic nerve terminals, and has been shown in vivo at the base of the brain and the cortical cerebral circulation. This result reveals the physiological need for increased regional cerebral blood flow in 'fight-or-flight response' during acute stress. Furthermore, α7- and α3β2-nicotinic ACh receptors (nAChRs) on sympathetic nerve terminals mediate release of NE, leading to cerebral nitrergic vasodilation. α7-nAChR-mediated but not α3β2-nAChR-mediated cerebral nitrergic vasodilation is blocked by β-amyloid peptides (Aβs). This may provide an explanation for cerebral hypoperfusion seen in patients with Alzheimer's disease. α7- and α3β2-nAChR-mediated nitrergic vasodilation is blocked by cholinesterase inhibitors (ChEIs) which are widely used for treating Alzheimer's disease, leading to possible cerebral hypoperfusion. This may contribute to the limitation of clinical use of ChEIs. ChEI blockade of nAChR-mediated dilation like that by Aβs is prevented by statins pretreatment, suggesting that efficacy of ChEIs may be improved by concurrent use of statins.

Oral tremor induced by galantamine in rats: a model of the parkinsonian side effects of cholinomimetics used to treat Alzheimer's disease

Anticholinesterases are the most common treatment for Alzheimer's disease, and, in recent years, a new group of cholinesterase inhibitors (i.e. rivastigmine, galantamine, and donepezil) has become available. Although these drugs improve cognitive symptoms, they also can induce or exacerbate parkinsonian symptoms, including tremor. The present studies were conducted to determine if galantamine induces tremulous jaw movements, a rodent model of parkinsonian tremor, and to investigate whether these oral motor impairments can be reversed by co-administration of adenosine A(2A) antagonists. The first experiment demonstrated that systemic injections of galantamine (0.75-6.0 mg/kg I.P.) induced a dose-related increase in tremulous jaw movements in rats. In a second study, co-administration of the muscarinic antagonist scopolamine (0.0156-0.25 mg/kg I.P.) produced a dose dependent suppression of tremulous jaw movements induced by a 3.0 mg/kg dose of galantamine, indicating that galantamine induces these tremulous oral movements through actions on muscarinic acetylcholine receptors. In two additional studies, analyses of freeze-frame video and electromyographic activity recorded from the lateral temporalis muscle indicated that the local frequency of these galantamine-induced jaw movements occurs in the 3-7 Hz frequency range that is characteristic of parkinsonian tremor. In the final experiment, the adenosine A(2A) antagonist MSX-3 significantly attenuated the tremulous jaw movements induced by the 3.0mg/kg dose of galantamine, which is consistent with the hypothesis that co-administration of adenosine A(2A) antagonists may be beneficial in reducing parkinsonian motor impairments induced by anticholinesterase treatment.

Neurotherapeutic applications of nanoparticles in Alzheimer's disease

A rapid increase in incidence of neurodegenerative disorders has been observed with the aging of the population. Alzheimer's disease (AD) is the most common neurodegenerative disorder among the elderly. It is characterized by memory dysfunction, loss of lexical access, spatial and temporal disorientation and impairment of judgement clinically. Unfortunately, clinical development of drugs for the symptomatic and disease-modifying treatment of AD has resulted in both promise and disappointment. Indeed, a large number of drugs with differing targets and mechanisms of action were investigated with only a few of them being clinically available. The targeted drug delivery to the central nervous system (CNS), for the diagnosis and treatment of neurodegenerative disorders such as AD, is restricted due to the limitations posed by the blood-brain barrier (BBB) as well as due to opsonization by plasma proteins in the systemic circulation and peripheral side-effects. Over the last decade, nanoparticle-mediated drug delivery represents one promising strategy to successfully increase the CNS penetration of several therapeutic moieties. Different nanocarriers are being investigated to treat and diagnose AD by delivering at a constant rate a host of therapeutics over times extending up to days, weeks or even months. This review provides a concise incursion on the current pharmacotherapies for AD besides reviewing and discussing the literature on the different drug molecules that have been successfully encapsulated in nanoparticles (NPs). Some of them have been shown to cross the BBB and have been tested either for diagnosis or treatment of AD. Finally, the route of NPs administration and the future prospects will be discussed.

Cortical M1 receptor concentration increases without a concomitant change in function in Alzheimer's disease

Although the M(1) muscarinic receptor is a potential therapeutic target for Alzheimer's disease (AD) based on its wide spread distribution in brain and its association with learning and memory processes, whether its receptor response is altered during the onset of AD remains unclear. A novel [(35)S]GTPgammaS binding/immunocapture assay was employed to evaluated changes in M(1) receptor function in cortical tissue samples harvested from people who had no cognitive impairment (NCI), mild cognitive impairment (MCI), or AD. M(1) function was stable across clinical groups. However, [(3)H]-oxotremorine-M radioligand binding studies revealed that the concentration of M(1) cortical receptors increased significantly between the NCI and AD groups. Although M(1) receptor function did not correlate with cognitive function based upon mini-mental status examination (MMSE) or global cognitive score (GCS), functional activity was negatively correlated with the severity of neuropathology determined by Braak staging and NIA-Reagan criteria for AD. Since M(1) agonists have the potential to modify the pathologic hallmarks of AD, as well as deficits in cognitive function in animal models of this disease, the present findings provide additional support for targeting the M(1) receptor as a potential therapeutic for AD.

The history of the cholinergic hypothesis

The cholinergic hypothesis of cognitive impairment and Alzheimer's disease has been for decades a "polar star" for studies on dementia and neurodegenerative diseases. Aim of the present article is to briefly summarize its birth and its evolution throughout years and discoveries. Putting the cholinergic hypothesis in an historical perspective, allows to appreciate the enormous amount of experimental and clinical research that it has stimulated over years and the impressive extent of knowledge generated by this research. While some of the assumptions at the basis of its original formulation are disputable in the light of recent developments, the cholinergic hypothesis has, however, constituted an invaluable stimulus to better understand not only the anatomy and the biochemistry of the cholinergic systems of brain connections but also its developmental biology, its complex relationships with trophic factors, its role in cognitive functions. Thus, rather than being consigned to history, the cholinergic hypothesis will likely contribute to further understanding dementia and neurodegenerative diseases and will hopefully be integrated in novel therapies and treatments.

Acetylcholine receptors in dementia and mild cognitive impairment

PURPOSE

To clarify whether changes in the cholinergic transmission occur early in the course of Alzheimer's disease (AD), we carried out positron emission tomography (PET) with the radioligand 2-[(18)F]F-A-85380, which is supposed to be specific for alpha4beta2 nicotinic acetylcholine receptors (nAChRs).

METHOD

We included patients with moderate to severe AD and patients with amnestic mild cognitive impairment (MCI), presumed to present preclinical AD.

RESULTS

Both patients with AD and MCI showed significant reductions in alpha4beta2 nAChRs in brain regions typically affected by AD pathology. These findings indicate that a reduction in alpha4beta2 nAChRs occurs during early symptomatic stages of AD. The alpha4beta2 nAChR availability in these regions correlated with the severity of cognitive impairment, indicating a stage sensitivity of the alpha4beta2 nAChR status.

CONCLUSION

Together, our results provide evidence for the potential of 2-[(18)]F-A-85380 nAChR PET in the diagnosis of patients at risk for AD. Because of the extraordinary long acquisition time with 2-[(18)F]F-A-85380, we developed the new alpha4beta2 nAChR-specific radioligands (+)- and (-)-[(18)F]norchloro-fluoro-homoepibatidine (NCFHEB) and evaluated them preclinically. (-)-[(18)F]NCFHEB shows twofold higher brain uptake and significantly shorter acquisition times. Therefore, (-)-[(18)F]NCFHEB should be a suitable radioligand for larger clinical investigations.

Should One Use Medications in Combination With Cognitive Training? If So, Which Ones?

In this article, we review current research regarding diagnosis of cognitive impairment in nondemented adults and discuss why medications and cognitive training together may be more beneficial than either alone. We also review potential cognitive enhancers and future research challenges. There are major reasons for such research: (a) Large numbers of older adults without dementia but with cognitive problems are not treatable with current cognitive training techniques; (b) some medications offer a rationale (i.e., cognitive enhancement) and some evidence that they might be a useful adjunct; and (c) there are unanswered questions about which population to target, which medications to use, how to administer them, and issues regarding tolerance and use of appropriate (active) placebo controls. As the number of cognitively impaired older adults grows, it is likely that there will be pressure to treat more broadly with both medications and cognitive training.

Cholinesterase inhibitor blockade and its prevention by statins of sympathetic alpha7-nAChR-mediated cerebral nitrergic neurogenic vasodilation

Cholinesterase inhibitors (ChEIs) have been used to treat Alzheimer's disease (AD). The efficacy of these drugs, however, is less than satisfactory. The possibility that ChEIs may have effects unrelated to ChE activity, such as negatively modulate neuronal nicotinic acetylcholine receptors (nAChRs) was evaluated. Since alpha7-nAChRs on cerebral perivascular sympathetic neurons mediate cerebral parasympathetic-nitrergic vasodilation, effects of physostigmine, neostigmine, and galantamine on alpha7-nAChR-mediated dilation in isolated porcine basilar arterial rings denuded of endothelium was examined using in vitro tissue bath technique. The results indicated that these ChEIs blocked vasodilation induced by choline (0.3 mmol/L), nicotine (0.1 mmol/L), and transmural nerve stimulation (TNS). The ChEI inhibition of dilation induced by TNS but not by choline or nicotine was prevented by atropine (0.1 micromol/L) pretreatment. Furthermore, using confocal microscopy, significant calcium influx induced by choline and nicotine in cultured porcine superior cervical ganglion (SCG) cells was attenuated by ChEIs. In alpha7-nAChR-expressed Xenopus oocytes, nicotine-induced inward currents were attenuated by alpha-bungarotoxin and ChEIs. Moreover, ChEI inhibition of nicotine- and choline-induced dilation was prevented by pretreatment with mevastatin and lovastatin (10 micromol/L), which did not affect ChEI inhibition of TNS-induced relaxation. These findings suggest that ChEIs inhibit the alpha7-nAChRs located on postganglionic sympathetic nerve terminals of SCG origin, causing a decreased release of nitric oxide in the neighboring nitrergic nerves and cerebral vasodilation. Inhibition of alpha7-nAChRs leading to a potential cerebral hypoperfusion may contribute to the limitation of ChEIs and question the validity of using a ChEI alone in treating AD. The efficacy of ChEIs may be improved by concurrent use of statins.

Down-regulation of vesicular glutamate transporters precedes cell loss and pathology in Alzheimer's disease

Alzheimer's disease (AD) is characterized pathologically by plaques, tangles, and cell and synapse loss. As glutamate is the principle excitatory neurotransmitter of the CNS, the glutamatergic system may play an important role in AD. An essential step in glutamate neurotransmission is the concentration of glutamate into synaptic vesicles before release from the presynaptic terminal. Recently a group of proteins responsible for uptake has been identified - the vesicular glutamate transporters (VGLUTs). The generation of antibodies has facilitated the study of glutamatergic neurones. Here, we used antibodies to the VGLUTs together with immunohistochemistry and western blotting to investigate the status of glutamatergic neurones in temporal, parietal and occipital cortices of patients with AD; these regions were chosen to represent severely, moderately and mildly affected regions at the end stage of the disease. There was no change in expression of the synaptic markers in relation to total protein in the temporal cortex, but a significant reduction in synaptophysin and VGLUT1 was found in both the parietal and occipital cortices. These changes were found to relate to the number of tangles in the temporal cortex. There were no correlations with either mental test score or behaviour syndromes, with the exception of depression.

The "ins" and "outs" of the high-affinity choline transporter CHT1

Maintenance of acetylcholine (ACh) synthesis depends on the activity of the high-affinity choline transporter (CHT1), which is responsible for the reuptake of choline from the synaptic cleft into presynaptic neurons. In this review, we discuss the current understanding of mechanisms involved in the cellular trafficking of CHT1. CHT1 protein is mainly found in intracellular organelles, such as endosomal compartments and synaptic vesicles. The presence of CHT1 at the plasma membrane is limited by rapid endocytosis of the transporter in clathrin-coated pits in a mechanism dependent on a dileucine-like motif present in the carboxyl-terminal region of the transporter. The intracellular pool of CHT1 appears to constitute a reserve pool of transporters, important for maintenance of cholinergic neurotransmission. However, the physiological basis of the presence of CHT1 in intracellular organelles is not fully understood. Current knowledge about CHT1 indicates that stimulated and constitutive exocytosis, in addition to endocytosis, will have major consequences for regulating choline uptake. Future investigations of CHT1 trafficking should elucidate such regulatory mechanisms, which may aid in understanding the pathophysiology of diseases that affect cholinergic neurons, such as Alzheimer's disease.

Altered generation of spontaneous oscillations in Alzheimer's disease

Slowing of spontaneous alpha oscillations and an anterior shift of a source of alpha activity (8-13 Hz) have been consistently reported in the EEG studies of Alzheimer's disease (AD). It is unknown whether these changes are associated with a gradual shift in location and frequency of existing sources or rather with the involvement of a new set of oscillators. We addressed this question by applying source modeling (minimum current estimates, MCE) to spontaneous alpha activity recorded with a 306-channel MEG system from eleven non-medicated AD patients with mild to moderate cognitive impairment and twelve age-matched controls during the eyes-closed session. AD patients had predominant lower alpha band sources in the temporal regions, whereas in the controls, robust alpha sources were found near the parieto-occipital sulcus. Activation within the parieto-occipital region was significantly weaker, and activation in the right temporal area was significantly enhanced in the AD patients. These results suggest an increased temporal-lobe contribution coinciding with parieto-occipital deficits. We propose that MCE, which provides simultaneous mapping of several oscillatory sources, might be useful for detecting neurophysiological abnormalities associated with AD in combination with other neuropsychological and neurological measures.