Cholinergic modulation of the cerebral metabolic response to citalopram in Alzheimer's disease

Review of Alzheimer's disease drugs and their relationship with neuron-glia interaction

Alzheimer's disease (AD) is the most common cause of dementia worldwide. Because Alzheimer's disease has no known treatment, sufferers and their caregivers must concentrate on symptom management. Astrocytes and microglia are now known to play distinct physiological roles in synaptic function, the blood-brain barrier, and neurovascular coupling. Consequently, the search for drugs that can slow the degenerative process in dementia sufferers continues because existing drugs are designed to alleviate the symptoms of Alzheimer's disease. Drugs that address pathological changes without interfering with the normal function of glia, such as eliminating amyloid-beta deposits, are prospective treatments for neuroinflammatory illnesses. Because neuron-astrocytes-microglia interactions are so complex, developing effective, preventive, and therapeutic medications for AD will necessitate novel methodologies and strategic targets. This review focused on existing medications used in treating AD amongst which include Donepezil, Choline Alphoscerate, Galantamine, Dextromethorphan, palmitoylethanolamide, citalopram, resveratrol, and solanezumab. This review summarizes the effects of these drugs on neurons, astrocytes, and microglia interactions based on their pharmacokinetic properties, mechanism of action, dosing, and clinical presentations.

The Identification of Alzheimer's Disease Using Functional Connectivity Between Activity Voxels in Resting-State fMRI Data

Background: Alzheimer’s disease (AD) is a common neurodegenerative disease occurring in the elderly population. The effective and accurate classification of AD symptoms by using functional magnetic resonance imaging (fMRI) has a great significance for the clinical diagnosis and prediction of AD patients. Methods: Therefore, this paper proposes a new method for identifying AD patients from healthy subjects by using functional connectivities (FCs) between the activity voxels in the brain based on fMRI data analysis. Firstly, independent component analysis is used to detect the activity voxels in the fMRI signals of AD patients and healthy subjects; Secondly, the FCs between the common activity voxels of the two groups are calculated, and then the FCs with significant differences are further identified by statistical analysis between them; Finally, the classification of AD patients from healthy subjects is realized by using FCs with significant differences as the feature samples in support vector machine. Results: The results show that the proposed identification method can obtain higher classification accuracy, and the FCs between activity voxels within prefrontal lobe as well as those between prefrontal and parietal lobes play an important role in the prediction of AD patients. Furthermore, we also find that more brain regions and much more voxels in some regions are activity in AD group compared with health control group. Conclusion: It has a great potential value for the AD pathogenesis mechanism study.

Established amyloid-β pathology is unaffected by chronic treatment with the selective serotonin reuptake inhibitor paroxetine

INTRODUCTION

Treatment with selective serotonin reuptake inhibitors has been suggested to mitigate amyloid-β (Aβ) pathology in Alzheimer's disease, in addition to an antidepressant mechanism of action.

METHODS

We investigated whether chronic treatment with paroxetine, a selective serotonin reuptake inhibitor, mitigates Aβ pathology in plaque-bearing double-transgenic amyloid precursor protein (APP)swe/presenilin 1 (PS1)ΔE9 mutants. In addition, we addressed whether serotonin depletion affects Aβ pathology. Treatments were assessed by measurement of serotonin transporter occupancy and high-performance liquid chromatography. The effect of paroxetine on Aβ pathology was evaluated by stereological plaque load estimation and Aβ42/Aβ40 ratio by enzyme-linked immunosorbent assay.

RESULTS

Contrary to our hypothesis, paroxetine therapy did not mitigate Aβ pathology, and depletion of brain serotonin did not exacerbate Aβ pathology. However, chronic paroxetine therapy increased mortality in APPswe/PS1ΔE9 transgenic mice.

DISCUSSION

Our results question the ability of selective serotonin reuptake inhibitor therapy to ameliorate established Aβ pathology. The severe adverse effect of paroxetine may discourage its use for disease-modifying purposes in Alzheimer's disease.

The emerging role of PET imaging in dementia

A compelling need in the field of neurodegenerative diseases is the development and validation of biomarkers for early identification and differential diagnosis. The availability of positron emission tomography (PET) neuroimaging tools for the assessment of molecular biology and neuropathology has opened new venues in the diagnostic design and the conduction of new clinical trials. PET techniques, allowing the in vivo assessment of brain function and pathology changes, are increasingly showing great potential in supporting clinical diagnosis also in the early and even preclinical phases of dementia. This review will summarize the most recent evidence on fluorine-18 fluorodeoxyglucose-, amyloid -, tau -, and neuroinflammation - PET tools, highlighting strengths and limitations and possible new perspectives in research and clinical applications. Appropriate use of PET tools is crucial for a prompt diagnosis and target evaluation of new developed drugs aimed at slowing or preventing dementia.

Pharmacological Therapy for Apathy in Alzheimer’s Disease: A Systematic Review and Meta-Analysis

Introduction:Apathy is highly prevalent in Alzheimer’s disease (AD), but whether pharmacotherapy is effective in managing apathy is unclear.Methods:To assess the efficacy of pharmacotherapy for apathy in AD we searched for randomized controlled trials (RCT) and aggregate data reporting on apathy in several search engines, reference lists of articles, and reviews. Demographic characteristics and relevant data were extracted to assess apathy.Results:Fifteen RCTs’ were examined, and 11 were used in aggregate meta-analytic statistics. Drugs included were cholinesterase inhibitors, memantine, and psycho-stimulants. We found no significant treatment effect in favour of any of the drugs, and the effect-size estimates under a random effect model were heterogeneous. Most RCTs had a high attrition rate and used the NPI apathy subscale to measure apathy.Conclusion:The lack of an effect could be explained by methodological limitations, publication bias, and heterogeneity.

G-protein coupled receptors as therapeutic targets for neurodegenerative and cerebrovascular diseases

Neurodegenerative and cerebrovascular diseases are frequent in elderly populations and comprise primarily of dementia (mainly Alzheimer's disease) Parkinson's disease and stroke. These neurological disorders (NDs) occur as a result of neurodegenerative processes and represent one of the most frequent causes of death and disability worldwide with a significant clinical and socio-economic impact. Although NDs have been characterized for many years, the exact molecular mechanisms that govern these pathologies or why they target specific individuals and specific neuronal populations remain unclear. As research progresses, many similarities appear which relate these diseases to one another on a subcellular level. Discovering these similarities offers hope for therapeutic advances that could ameliorate the conditions of many diseases simultaneously. G-protein coupled receptors (GPCRs) are the most abundant receptor type in the central nervous system and are linked to complex downstream pathways, manipulation of which may have therapeutic application in many NDs. This review will highlight the potential use of neurotransmitter GPCRs as emerging therapeutic targets for neurodegenerative and cerebrovascular diseases.

Identifying patients with Alzheimer's disease using resting-state fMRI and graph theory

OBJECTIVE

Study of brain network on the basis of resting-state functional magnetic resonance imaging (fMRI) has provided promising results to investigate changes in connectivity among different brain regions because of diseases. Graph theory can efficiently characterize different aspects of the brain network by calculating measures of integration and segregation.

METHOD

In this study, we combine graph theoretical approaches with advanced machine learning methods to study functional brain network alteration in patients with Alzheimer's disease (AD). Support vector machine (SVM) was used to explore the ability of graph measures in diagnosis of AD. We applied our method on the resting-state fMRI data of twenty patients with AD and twenty age and gender matched healthy subjects. The data were preprocessed and each subject's graph was constructed by parcellation of the whole brain into 90 distinct regions using the automated anatomical labeling (AAL) atlas. The graph measures were then calculated and used as the discriminating features. Extracted network-based features were fed to different feature selection algorithms to choose most significant features. In addition to the machine learning approach, statistical analysis was performed on connectivity matrices to find altered connectivity patterns in patients with AD.

RESULTS

Using the selected features, we were able to accurately classify patients with AD from healthy subjects with accuracy of 100%.

CONCLUSION

Results of this study show that pattern recognition and graph of brain network, on the basis of the resting state fMRI data, can efficiently assist in the diagnosis of AD.

SIGNIFICANCE

Classification based on the resting-state fMRI can be used as a non-invasive and automatic tool to diagnosis of Alzheimer's disease.

Deep Brain Stimulation Influences Brain Structure in Alzheimer's Disease

BACKGROUND

Deep Brain Stimulation (DBS) is thought to improve the symptoms of selected neurological disorders by modulating activity within dysfunctional brain circuits. To date, there is no evidence that DBS counteracts progressive neurodegeneration in any particular disorder.

OBJECTIVE/HYPOTHESIS

We hypothesized that DBS applied to the fornix in patients with Alzheimer's Disease (AD) could have an effect on brain structure.

METHODS

In six AD patients receiving fornix DBS, we used structural MRI to assess one-year change in hippocampal, fornix, and mammillary body volume. We also used deformation-based morphometry to identify whole-brain structural changes. We correlated volumetric changes to hippocampal glucose metabolism. We also compared volumetric changes to those in an age-, sex-, and severity-matched group of AD patients (n = 25) not receiving DBS.

RESULTS

We observed bilateral hippocampal volume increases in the two patients with the best clinical response to fornix DBS. In one patient, hippocampal volume was preserved three years after diagnosis. Overall, mean hippocampal atrophy was significantly slower in the DBS group compared to the matched AD group, and no matched AD patients demonstrated bilateral hippocampal enlargement. Across DBS patients, hippocampal volume change correlated strongly with hippocampal metabolism and with volume change in the fornix and mammillary bodies, suggesting a circuit-wide effect of stimulation. Deformation-based morphometry in DBS patients revealed local volume expansions in several regions typically atrophied in AD.

CONCLUSION

We present the first in-human evidence that, in addition to modulating neural circuit activity, DBS may influence the natural course of brain atrophy in a neurodegenerative disease.

Inter-modality relationship constrained multi-modality multi-task feature selection for Alzheimer's Disease and mild cognitive impairment identification

Previous studies have demonstrated that the use of integrated information from multi-modalities could significantly improve diagnosis of Alzheimer's Disease (AD). However, feature selection, which is one of the most important steps in classification, is typically performed separately for each modality, which ignores the potentially strong inter-modality relationship within each subject. Recent emergence of multi-task learning approach makes the joint feature selection from different modalities possible. However, joint feature selection may unfortunately overlook different yet complementary information conveyed by different modalities. We propose a novel multi-task feature selection method to preserve the complementary inter-modality information. Specifically, we treat feature selection from each modality as a separate task and further impose a constraint for preserving the inter-modality relationship, besides separately enforcing the sparseness of the selected features from each modality. After feature selection, a multi-kernel support vector machine (SVM) is further used to integrate the selected features from each modality for classification. Our method is evaluated using the baseline PET and MRI images of subjects obtained from the Alzheimer's Disease Neuroimaging Initiative (ADNI) database. Our method achieves a good performance, with an accuracy of 94.37% and an area under the ROC curve (AUC) of 0.9724 for AD identification, and also an accuracy of 78.80% and an AUC of 0.8284 for mild cognitive impairment (MCI) identification. Moreover, the proposed method achieves an accuracy of 67.83% and an AUC of 0.6957 for separating between MCI converters and MCI non-converters (to AD). These performances demonstrate the superiority of the proposed method over the state-of-the-art classification methods.

Neuropsychiatric symptoms in Alzheimer's disease: past progress and anticipation of the future

Neuropsychiatric symptoms (NPS) in Alzheimer's disease (AD) are widespread and disabling. This has been known since Dr. Alois Alzheimer's first case, Frau Auguste D., presented with emotional distress and delusions of infidelity/excessive jealousy, followed by cognitive symptoms. Being cognizant of this, in 2010 the Alzheimer's Association convened a research roundtable on the topic of NPS in AD. A major outcome of the roundtable was the founding of a Professional Interest Area (PIA) within the International Society to Advance Alzheimer's Research and Treatment (ISTAART). The NPS-PIA has prepared a series of documents that are intended to summarize the literature and provide more detailed specific recommendations for NPS research. This overview paper is the first of these living documents that will be updated periodically as the science advances. The overview is followed by syndrome-specific synthetic reviews and recommendations prepared by NPS-PIA workgroups on depression, apathy, sleep, agitation, and psychosis.

Fluorodeoxyglucose positron emission tomography in semantic dementia after 6 months of memantine: an open-label pilot study

OBJECTIVES

To follow up on the increases we reported in normalized metabolic activity in salience network hubs from a 2-month open-label study of memantine in frontotemporal dementia (FTD).

METHODS

We repeated fluorodeoxyglucose positron emission tomography (FDG-PET) after 6 months of drug use and subjected the data to Statistical Parametrical Mapping (SPM) analysis to reveal clusters of significant change from baseline. We also sought correlations between changes in behavioral disturbances on the Frontal Behavioral Inventory (FBI) and the PET signal.

RESULTS

Recruitment of one progressive nonfluent aphasia and one behavioral variant FTD precluded statistical analysis for any FTD subtype other than semantic dementia (SD). The baseline-to-6-month interval showed increased normalized metabolic activity in the left orbitofrontal cortex (p < 0.002) for five participants with SD. The 2-6-month interval revealed a late increase in normalized metabolic activity in the left insula (p < 0.013), right insula (p < 0.009), and left anterior cingulate (p < 0.005). The right anterior cingulate showed both an initial increase and a delayed further increase (2-6 months, p < 0.016). FBI scores worsened by 43.3%. One participant with SD opted not to continue memantine beyond 2 months yet showed similar FDG-PET increases.

CONCLUSIONS

Increases in normalized cortical metabolic activity in salience network hubs were sustained in SD over a 6-month period. Because one participant without medication also showed these changes, further investigation is recommended through a double-blind, placebo-controlled study with FDG-PET as an outcome measure.

Potentially procholinergic effects of medications commonly used in older adults

BACKGROUND

Older adults are susceptible to a variety of illnesses, many of which can be treated with medications that may need to be used for the long term. Considerable attention has been paid to drugs that, in addition to their intended function, may have an anticholinergic effect that results in undesirable side effects, including impairment in cognition. Cholinesterase inhibitors are used as procholinergic drugs to improve cognitive dysfunction in Alzheimer's disease. We hypothesized that some of the drugs commonly used by older adults might, in addition to their intended function, also have procholinergic effects by virtue of inhibiting cholinesterases.

OBJECTIVE

To determine the potential procholinergic nature of some of the commonly used drugs by examining their cholinesterase inhibiting properties.

METHODS

The Ellman spectrophotometric method was used with human acetylcholinesterase and butyrylcholinesterase, in the absence and presence of increasing concentrations of each test drug. To compare inhibition potencies, from enzyme kinetic data, we determined half maximal inhibitory concentration (IC(50) values) for each cholinesterase by each drug.

RESULTS

Of the 28 drugs examined, over half (17/28) inhibited one or both of the human cholinesterases. The inhibition potencies were often within 1 to 2 orders of magnitude of reversible cholinesterase inhibitors currently used to treat Alzheimer's disease. These included trazodone, quetiapine, risperidone, indapamide, and perindopril.

CONCLUSIONS

Many drugs used by older adults for other reasons have potentially clinically relevant procholinergic effects. The effect of cumulative cholinesterase inhibition merits clinical evaluation.

Synergistic inhibition of butyrylcholinesterase by galantamine and citalopram

BACKGROUND

Many persons with Alzheimer's disease (AD) treated with galantamine appear to receive additional cognitive benefit from citalopram. Both drugs inhibit acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE). These enzymes co-regulate acetylcholine catabolism. In AD brain, AChE is diminished while BuChE is not, suggesting BuChE inhibition may be important in raising acetylcholine levels. BuChE is subject to activation at high acetylcholine levels reached at the synaptic cleft. The present study explores one way combining galantamine and citalopram could be beneficial in AD.

METHODS

Spectrophotometric studies of BuChE catalysis in the absence or presence of galantamine or citalopram or both, were performed using the Ellman method. Data analysis involved expansion of our previous equation describing BuChE catalysis.

RESULTS

Galantamine almost completely inhibited BuChE at low substrate concentrations (V(S)=43.6 μM/min; V(S(gal))=0.34 μM/min) without influencing the substrate-activated form of the enzyme (V(SS)=64.0 μM/min;V(SS(gal))=62.3 μM/min). Conversely, citalopram inhibited both un-activated (V(S)=43.6 μM/min; V(S(cit))=10.2 μM/min) and substrate-activated (V(SS)=64.0 μM/min; V(SS(cit))=47.3 μM/min) forms of BuChE. Combined galantamine and citalopram increased inhibition of un-activated BuChE (V(S)=43.6 μM/min; V(S(gal)(cit))=2.73 μM/min) and substrate-activated form (V(SS)=64.0 μM/min; V(SS(gal)(cit))=42.2 μM/min).

CONCLUSION

Citalopram and galantamine produce a combined inhibition of BuChE that is considered to be synergistic.

GENERAL SIGNIFICANCE

Clinical benefit from combined galantamine and citalopram may be related to a synergistic inhibition of BuChE, facilitating cholinergic neurotransmission. This emphasizes the importance of further study into use of drug combinations in AD treatment.

REVIEW: Apathy diagnosis, assessment, and treatment in Alzheimer's disease

Apathy is defined as a disorder of motivation. There is wide acknowledgement that apathy is an important behavioral syndrome in Alzheimer's disease and in various neuropsychiatric disorders. In light of recent research and the renewed interest in the correlates and impacts of apathy and in its treatments, it is important to develop criteria for apathy that will be widely accepted, have clear operational steps, and be easy to apply in clinical practice and in research settings. Meeting these needs was the focus for a task force that included members of the European Psychiatric Association, the European Alzheimer's Disease Consortium and experts from Europe, Australia and North America.

Escitalopram attenuates posterior cingulate activity during self-evaluation in healthy volunteers

Medial cortex is critically involved in self-referential processing. Little is known about how selective serotonin reuptake inhibitors (SSRIs) affect medial cortical activity during self-assessment. We hypothesized that a 3-week oral course of escitalopram,10 mg/day, would alter activity related to self-referential processing in medial cortex. Fifteen healthy females performed a self-assessment task during functional magnetic resonance imaging on two occasions--once after 3 weeks of placebo and once at the end of 3 weeks of escitalopram. Task conditions involved responding "yes" or "no" to whether various positive and negative adjectives described the subject (i.e., "self" evaluation trials) or the subject's best friend (i.e., "other" evaluation trials), whereas the comparison condition involved responding whether the valence of various adjectives was positive or negative (i.e., "word" evaluation trials). Behaviorally after escitalopram, subjects less frequently endorsed that negative adjectives described themselves. Three main neuroimaging results were observed: (1) increased activation in medial prefrontal cortex and posterior cingulate related to self minus word evaluation trials, (2) increased activation in posterior cingulate related to escitalopram minus placebo for self and word evaluation trials, and (3) drug by task interactions in the insula, cerebellum and prefrontal cortex. These results show that SSRIs change medial cortical activity and may alter self-evaluation.

The use of PET in Alzheimer disease

In Alzheimer disease (AD), which is the most common cause of dementia, the underlying disease pathology most probably precedes the onset of cognitive symptoms by many years. Thus, efforts are underway to find early diagnostic markers as well as disease-modifying treatments for this disorder. PET enables various brain systems to be monitored in living individuals. In patients with AD, PET can be used to investigate changes in cerebral glucose metabolism, various neurotransmitter systems, neuroinflammation, and the protein aggregates that are characteristic of the disease, notably the amyloid deposits. These investigations are helping to further our understanding of the complex pathophysiological mechanisms that underlie AD, as well as aiding the early and differential diagnosis of the disease in the clinic. In the future, PET studies will also be useful for identifying new therapeutic targets and monitoring treatment outcomes. Amyloid imaging could be useful as early diagnostic marker of AD and for selecting patients for anti-amyloid-beta therapy, while cerebral glucose metabolism could be a suitable PET marker for monitoring disease progression. For the near future, multitracer PET studies are unlikely to be used routinely in the clinic for AD, being both burdensome and expensive; however, such studies are very informative in a research context.

Beyond the cholinergic hypothesis: do current drugs work in Alzheimer's disease?

Alzheimer's disease (AD) is a neurodegenerative disease characterized by memory and cognitive loss, and represents the leading cause of dementia in elderly people. Besides the complex biochemical processes involved in the neuronal degeneration (formation of senile plaques containing Abeta peptides, and development of neurofibrillary tangles), other molecular and neurochemical alterations, like cholinergic deficit due to basal forebrain degeneration, also occur. Because acetylcholine has been demonstrated to be involved in cognitive processes, the idea to increase acetylcholine levels to restore cognitive deficits has gained interest (the so-called cholinergic hypothesis). This has led to the development of drugs able to prevent acetylcholine hydrolysis (acetylcholinesterase inhibitors). However, the analysis of clinical efficacy of these drugs in alleviating symptoms of dementia showed unsatisfactory results. Despite such critical opinions on the efficacy of these drugs, it should be said that acetylcholinesterase inhibitors, and for some aspects memantine also, improve memory and other cognitive functions throughout most of the duration of the disease. The pharmacological activity of these drugs suggests an effect beyond the mere increase of acetylcholine levels. These considerations are in agreement with the idea that cognitive decline is the result of a complex and not fully elucidated interplay among different neurotransmitters. The role of each of the neurotransmitters implicated has to be related to a cognitive process and as a consequence to its decline. The current review aims to highlight the positive role of cholinergic drugs in alleviating cognitive deficits during wake as well as sleep. Moreover, we suggest that future therapeutic approaches have to be developed to restore the complex interplay between acetylcholine and other neurotransmitters systems, such as dopamine, serotonin, noradrenaline, or glutamate, that are likely involved in the progressive deterioration of several cognitive functions such as attention, memory, and learning.

Antidepressants are a rational complementary therapy for the treatment of Alzheimer's disease

There is a high prevalence rate (30-50%) of Alzheimer's disease (AD) and depression comorbidity. Depression can be a risk factor for the development of AD or it can be developed secondary to the neurodegenerative process. There are numerous documented diagnosis and treatment challenges for the patients who suffer comorbidity between these two diseases. Meta analysis studies have provided evidence for the safety and efficacy of antidepressants in treatment of depression in AD patients. Preclinical and clinical studies show the positive role of chronic administration of selective serotonin reuptake inhibitor (SSRI) antidepressants in hindering the progression of the AD and improving patient performance. A number of clinical studies suggest a beneficial role of combinatorial therapies that pair antidepressants with FDA approved AD drugs. Preclinical studies also demonstrate a favorable effect of natural antidepressants for AD patients. Based on the preclinical studies there are a number of plausible antidepressants effects that may modulate the progression of AD. These effects include an increase in neurogenesis, improvement in learning and memory, elevation in the levels of neurotrophic factors and pCREB and a reduction of amyloid peptide burden. Based on this preclinical and clinical evidence, antidepressants represent a rational complimentary strategy for the treatment of AD patients with depression comorbidity.

Nitric oxide in cell survival: a janus molecule

Nitric oxide (NO), plays multiple roles in the nervous system. In addition to regulating proliferation, survival and differentiation of neurons, NO is involved in synaptic activity, neural plasticity, and memory function. Nitric oxide promotes survival and differentiation of neural cells and exerts long-lasting effects through regulation of transcription factors and modulation of gene expression. Signaling by reactive nitrogen species is carried out mainly by targeted modifications of critical cysteine residues in proteins, including S-nitrosylation and S-oxidation, as well as by lipid nitration. NO and other reactive nitrogen species are also involved in neuroinflammation and neurodegeneration, such as in Alzheimer disease, amyotrophic lateral sclerosis, Parkinson disease, multiple sclerosis, Friedreich ataxia, and Huntington disease. Susceptibility to NO and peroxynitrite exposure may depend on factors such as the intracellular reduced glutathione and cellular stress resistance signaling pathways. Thus, neurons, in contrast to astrocytes, appear particularly vulnerable to the effects of nitrosative stress. This article reviews the current understanding of the cytotoxic versus cytoprotective effects of NO in the central nervous system, highlighting the Janus-faced properties of this small molecule. The significance of NO in redox signaling and modulation of the adaptive cellular stress responses and its exciting future perspectives also are discussed.