Role of the immune system in the pathogenesis, prevention and treatment of Alzheimer's disease

Peripheral inflammation is associated with brain atrophy and cognitive decline linked to mild cognitive impairment and Alzheimer's disease

Inflammation is an important factor in Alzheimer's disease (AD). An NMR measurement in plasma, glycoprotein acetyls (GlycA), captures the overall level of protein production and glycosylation implicated in systemic inflammation. With its additional advantage of reducing biological variability, GlycA might be useful in monitoring the relationship between peripheral inflammation and brain changes relevant to AD. However, the associations between GlycA and these brain changes have not been fully evaluated. Here, we performed Spearman's correlation analyses to evaluate these associations cross-sectionally and determined whether GlycA can inform AD-relevant longitudinal measurements among participants in the Alzheimer's Disease Neuroimaging Initiative (n = 1506), with additional linear models and stratification analyses to evaluate the influences of sex or diagnosis status and confirm findings from Spearman's correlation analyses. We found that GlycA was elevated in AD patients compared to cognitively normal participants. GlycA correlated negatively with multiple concurrent regional brain volumes in females diagnosed with late mild cognitive impairment (LMCI) or AD. Baseline GlycA level was associated with executive function decline at 3-9 year follow-up in participants diagnosed with LMCI at baseline, with similar but not identical trends observed in the future decline of memory and entorhinal cortex volume. Results here indicated that GlycA is an inflammatory biomarker relevant to AD pathogenesis and that the stage of LMCI might be relevant to inflammation-related intervention.

Tau and neuroinflammation in Alzheimer's disease: interplay mechanisms and clinical translation

Alzheimer's Disease (AD) contributes to most cases of dementia. Its prominent neuropathological features are the extracellular neuritic plaques and intercellular neurofibrillary tangles composed of aggregated β-amyloid (Aβ) and hyperphosphorylated tau protein, respectively. In the past few decades, disease-modifying therapy targeting Aβ has been the focus of AD drug development. Even though it is encouraging that two of these drugs have recently received accelerated US Food and Drug Administration approval for AD treatment, their efficacy or long-term safety is controversial. Tau has received increasing attention as a potential therapeutic target, since evidence indicates that tau pathology is more associated with cognitive dysfunction. Moreover, inflammation, especially neuroinflammation, accompanies AD pathological processes and is also linked to cognitive deficits. Accumulating evidence indicates that inflammation has a complex and tight interplay with tau pathology. Here, we review recent evidence on the interaction between tau pathology, focusing on tau post-translational modification and dissemination, and neuroinflammatory responses, including glial cell activation and inflammatory signaling pathways. Then, we summarize the latest clinical trials targeting tau and neuroinflammation. Sustained and increased inflammatory responses in glial cells and neurons are pivotal cellular drivers and regulators of the exacerbation of tau pathology, which further contributes to its worsening by aggravating inflammatory responses. Unraveling the precise mechanisms underlying the relationship between tau pathology and neuroinflammation will provide new insights into the discovery and clinical translation of therapeutic targets for AD and other tau-related diseases (tauopathies). Targeting multiple pathologies and precision therapy strategies will be the crucial direction for developing drugs for AD and other tauopathies.

Poor Oral Health as a Risk Factor for Dementia in a Swedish Population: A Cohort Study with 40 Years of Follow-Up

BACKGROUND

Whether poor oral health is associated with dementia risk remains unclear.

OBJECTIVE

We conducted a cohort study of 14,439 participants who were followed up for up to 40 years in Uppsala County, central Sweden, aiming to explore the association between poor oral health, namely the number of tooth loss, dental plaque status, and oral mucosal lesions, and the risk of dementia.

METHODS

We used Cox proportional hazards regression model to derive cause-specific hazard ratios (HR) and corresponding 95% confidence intervals (CI), while adjusting for baseline potential confounders as well as a time-varying covariate, Charlson's Comorbidity Index score.

RESULTS

Dementia risk was substantially higher among those with a higher number of tooth loss; compared to the group with tooth loss 0-10, the HRs were 1.21 (95% CI: 1.02, 1.42), 1.17 (95% CI: 0.97, 1.40), and 1.30 (95% CI: 1.09, 1.54) respectively for groups with increasing number of tooth loss. There was some evidence of dose-risk association in this study, with a HR of 1.10 (1.04, 1.18) comparing adjacent groups (ptrend = 0.001). In a stratified analysis by attained age, tooth loss was more pronouncedly associated with the risk of dementia onset before age 80 (those with 21-32 versus 0-10 lost teeth, HR = 1.82, (95% CI: 1.32, 2.51); HR = 1.22 (95% CI: 1.10, 1.35) comparing adjacent groups, ptrend < 0.001).

CONCLUSION

In summary, there are some indications that poor oral health, as indicated by more tooth loss, is positively associated with an increased risk of dementia, especially for dementia onset before age 80.

Identification of Two CDK5R1-Related Subtypes and Characterization of Immune Infiltrates in Alzheimer's Disease Based on an Integrated Bioinformatics Analysis

Background

Alzheimer's disease (AD) is a neurodegenerative disorder and the major cause of senile dementia. The Reelin pathway has been involved in both learning and AD pathogenesis. However, the specific Reelin-related gene signature during the pathological process remains unknown.

Methods

Reelin-related gene (CDK5R1) expression was analyzed using the GEO datasets. The relevant genes of CDK5R1 were identified using differential expression analysis and weighted gene correlation network analysis (WGCNA) based on the GSE43850 dataset. ConsensusClusterPlus analysis was applied to identify subtypes (C1 and C2) of AD. The CIBERSORT algorithm was used to assess the immune cell infiltration between the two AD subtypes.

Results

CDK5R1 was downregulated in AD. 244 differentially expressed CDK5R1-related genes (DECRGs) between the two subgroups were mainly enriched in GABAergic synapse, neuroactive ligand-receptor interaction, synapse organization, neurotransmitter transport, etc. Furthermore, the GSVA results indicated that immune-related pathways were significantly enriched in the C1 subgroup. Interestingly, 10 Reelin pathway-related genes (CRK, DAB2IP, LRP8, RELN, STAT5A, CDK5, CDK5R1, DAB1, FYN, and SH3KBP1) were abnormally expressed between the two subgroups. The proportion of T cell gamma delta, monocytes, macrophage M2, and dendritic cells activated decreased from C1 to C2, while the proportion of plasma cells, T cell follicular helper, and NK cells activated increased.

Conclusion

Two CDK5R1-related subtypes of AD were identified, helping us to better understand the role of CDK5R1 in the pathological process of AD.

Pathophysiological mechanisms explaining the association between low skeletal muscle mass and cognitive function

Low skeletal muscle mass is associated with cognitive impairment and dementia in older adults. This review describes the possible underlying pathophysiological mechanisms: systemic inflammation, insulin metabolism, protein metabolism, and mitochondrial function. We hypothesize that the central tenet in this pathophysiology is the dysfunctional myokine secretion consequent to minimal physical activity. Myokines, such as fibronectin type III domain containing 5/irisin and cathepsin B, are released by physically active muscle and cross the blood–brain barrier. These myokines upregulate local neurotrophin expression such as brain-derived neurotrophic factor (BDNF) in the brain microenvironment. BDNF exerts anti-inflammatory effects that may be responsible for neuroprotection. Altered myokine secretion due to physical inactivity exacerbates inflammation and impairs muscle glucose metabolism, potentially affecting the transport of insulin across the blood–brain barrier. Our working model also suggests other underlying mechanisms. A negative systemic protein balance, commonly observed in older adults, contributes to low skeletal muscle mass and may also reflect deficient protein metabolism in brain tissues. As a result of age-related loss in skeletal muscle mass, decrease in the abundance of mitochondria and detriments in their function lead to a decrease in tissue oxidative capacity. Dysfunctional mitochondria in skeletal muscle and brain result in the excessive production of reactive oxygen species, which drives tissue oxidative stress and further perpetuates the dysfunction in mitochondria. Both oxidative stress and accumulation of mitochondrial DNA mutations due to aging drive cellular senescence. A targeted approach in the pathophysiology of low muscle mass and cognition could be to restore myokine balance by physical activity.

Oral Health Status in Older People with Dementia: A Case-Control Study

Dementia is characterized by a range of cognitive defects with impaired activities of daily living that have implications for patient oral health. Objectives. A case-control study was made of the impact of dementia upon oral health. A total of 152 patients were included: 69 with dementia and 83 controls from the region of Murcia (Spain). The Global Deterioration Scale (GDS) was used to classify the patients and an oral exploration was carried out. Odds ratios (ORs) and confidence intervals (CIs) were estimated using regression models. The patients with more severe disease were significantly more likely to have fewer natural teeth (OR 11.00, 95%CI 1.28–23.22; p = 0.001), a higher plaque index (p = 0.001), and a greater bleeding index (p = 0.001) than the control group. These findings suggest that older adults with dementia have deficient oral health. A higher bleeding index increases the risk of deterioration of cognitive function. The oral hygiene and health of older people with dementia need to be improved.

Tetrachlorobisphenol A induced immunosuppression and uterine injury in mice

Tetrachlorobisphenol A (TCBPA) is used as flame retardant, and it has been widely detected in the environmental and human samples. TCBPA is an endocrine disrupting chemical, but its effects on the immune system remains poorly understood. Here the effects of TCBPA on immune system were studied using combined in vivo and in vitro assays. Results showed that TCBPA could suppress the immune response in BALB/c mice via reducing the ratio of CD3⁺ T lymphocytes to regulatory T cells. Moreover, TCBPA exposure significantly induced the increasing secretion of four pro-inflammatory cytokines (IL-2, IL-12, IFN-γ, and TNF-α) and four anti-inflammatory cytokines (IL-4, IL-5, IL-10, GM-CSF) in mice serum. Interestingly, uterine edema was observed in over 80% TCBPA-treated mice after 14- day exposure. TCBPA was detected in 18.6% serum samples of 150 female volunteers in this study. Therefore, our findings provided evidence that TCBPA exposure may cause adverse outcomes on immune system and uterus, suggesting that environmental exposure of TCBPA, as well as its adverse effects on human health should be of concern.

Current Strategies and Novel Drug Approaches for Alzheimer Disease

Alzheimer's Disease (AD) is a chronic, devastating dysfunction of neurons in the brain leading to dementia. It mainly arises due to neuronal injury in the cerebral cortex and hippocampus area of the brain and is clinically manifested as a progressive mental failure, disordered cognitive functions, personality changes, reduced verbal fluency and impairment of speech. The pathology behind AD is the formation of intraneuronal fibrillary tangles, deposition of amyloid plaque and decline in choline acetyltransferase and loss of cholinergic neurons. Tragically, the disease cannot be cured, but its progression can be halted. Various cholinesterase inhibitors available in the market like Tacrine, Donepezil, Galantamine, Rivastigmine, etc. are being used to manage the symptoms of Alzheimer's disease. The paper's objective is to throw light not only on the cellular/genetic basis of the disease, but also on the current trends and various strategies of treatment including the use of phytopharmaceuticals and nutraceuticals. Enormous literature survey was conducted and published articles of PubMed, Scifinder, Google Scholar, Clinical Trials.org and Alzheimer Association reports were studied intensively to consolidate the information on the strategies available to combat Alzheimer's disease. Currently, several strategies are being investigated for the treatment of Alzheimer's disease. Immunotherapies targeting amyloid-beta plaques, tau protein and neural pathways are undergoing clinical trials. Moreover, antisense oligonucleotide methodologies are being approached as therapies for its management. Phytopharmaceuticals and nutraceuticals are also gaining attention in overcoming the symptoms related to AD. The present review article concludes that novel and traditional therapies simultaneously promise future hope for AD treatment.

Tetrahydroxystilbene glycoside antagonizes β-amyloid-induced inflammatory injury in microglia cells by regulating PU.1 expression

Inhibiting β-amyloid (Aβ)-induced microglial activation is proposed as an effective strategy for the treatment of Alzheimer’s disease. Tetrahydroxystilbene glycoside (TSG) is the main active ingredient of Polygonum multiflorum and has a wide range of biological properties, including antiinflammation. Here, we focused on the function and regulatory mechanism of TSG in Aβ-induced N9 and BV2 cells. The results showed that Aβ treatment induced the activation of microglia cells and the production of inflammatory molecules, including inducible nitric oxide synthase, nitric oxide, cyclooxygenase 2, and prostaglandin E2, which were significantly inhibited by TSG pretreatment. Furthermore, we found Aβ exposure increased the levels of microglial M1 markers, interleukin (IL)-1β, IL-6, and tumor necrosis factor α, and the pretreatment of TSG suppressed the increase of M1 markers and enhanced the levels of M2 markers, including IL-10, brain-derived neurotrophic factor, glial cell-derived neurotrophic factor, and arginase-1. PU.1 overexpression was found to eradicate the anti-inflammatory effects of TSG in Aβ-induced microglial cells. Taken together, these findings indicate that TSG attenuates Aβ-induced microglial activation and polarizes microglia towards M2 phenotype, which may be closely associated with the regulation of PU.1.

Identification of Alzheimer's Disease-Related Genes Based on Data Integration Method

Alzheimer disease (AD) is the fourth major cause of death in the elderly following cancer, heart disease and cerebrovascular disease. Finding candidate causal genes can help in the design of Gene targeted drugs and effectively reduce the risk of the disease. Complex diseases such as AD are usually caused by multiple genes. The Genome-wide association study (GWAS), has identified the potential genetic variants for most diseases. However, because of linkage disequilibrium (LD), it is difficult to identify the causative mutations that directly cause diseases. In this study, we combined expression quantitative trait locus (eQTL) studies with the GWAS, to comprehensively define the genes that cause Alzheimer disease. The method used was the Summary Mendelian randomization (SMR), which is a novel method to integrate summarized data. Two GWAS studies and five eQTL studies were referenced in this paper. We found several candidate SNPs that have a strong relationship with AD. Most of these SNPs overlap in different data sets, providing relatively strong reliability. We also explain the function of the novel AD-related genes we have discovered.

Relationship Between Alzheimer's Disease and the Immune System: A Meta-Analysis of Differentially Expressed Genes

Alzheimer's disease (AD), a neurodegenerative diseases (neuro-diseases) which is prevalent in the elderly and seriously affects the lives of individuals. Many studies have discussed the relationship between immune system and AD pathogenesis. Here, the meta-analysis of differentially expressed (DE) genes based on microarray data was conducted to study the association between AD and immune system. 9519 target genes of hippocampus in 146 subjects (73 AD cases and 73 controls) from 4 microarray data sets were compiled and DE genes with p < 1.00E - 04 were selected to conduct the pathway-analysis. The results indicated that the DE genes were significantly enriched in the neuro-diseases as well as the immune system pathways.

Immunosenescence of Natural Killer Cells, Inflammation, and Alzheimer's Disease

Alzheimer's disease (AD) represents the most common cause of dementia in the elderly. AD is a neurodegenerative disorder characterized by progressive memory loss and cognitive decline. Although the aetiology of AD is not clear, both environmental factors and heritable predisposition may contribute to disease occurrence. In addition, inflammation and immune system alterations have been linked to AD. The prevailing hypothesis as cause of AD is the deposition in the brain of amyloid beta peptides (Aβ). Although Aβ have a role in defending the brain against infections, their accumulation promotes an inflammatory response mediated by microglia and astrocytes. The production of proinflammatory cytokines and other inflammatory mediators such as prostaglandins and complement factors favours the recruitment of peripheral immune cells further promoting neuroinflammation. Age-related inflammation and chronic infection with herpes virus such as cytomegalovirus may also contribute to inflammation in AD patients. Natural killer (NK) cells are innate lymphoid cells involved in host defence against viral infections and tumours. Once activated NK cells secrete cytokines such as IFN-γ and TNF-α and chemokines and exert cytotoxic activity against target cells. In the elderly, changes in NK cell compartment have been described which may contribute to the lower capacity of elderly individuals to respond to pathogens and tumours. Recently, the role of NK cells in the immunopathogenesis of AD is discussed. Although in AD patients the frequency of NK cells is not affected, a high NK cell response to cytokines has been described together with NK cell dysregulation of signalling pathways which is in part involved in this altered behaviour.

Tooth loss as a risk factor for dementia: systematic review and meta-analysis of 21 observational studies

BACKGROUND

Tooth loss is suggested to be associated with an increased risk of dementia in many studies. But the relationship between tooth loss and dementia is not yet fully understood. This systematic review and meta-analysis aimed to determine the relative effect of tooth loss on dementia risk.

METHODS

An electronic search of PubMed, Scopus, Embase, and Web of Knowledge was conducted in March 2018 to identify relevant observational studies with the English language restriction. Studies were included if they assessed the relationship between tooth loss and risk of dementia. Study quality was detected by the modified Downs and Black scale. Odds risks (ORs) were pooled using a random-effects model in the crude model.

RESULTS

The literature search initially yielded 1574 articles, and 21 observational studies published between 1994 and 2017 were finally included for the analyses. The crude results with random-effects model showed that patients with multiple tooth loss had higher incidence of dementia (OR 2.62, 95% CI 1.90-3.61, P < 0.001, I² = 90.40%). The association remained noted when only adjusted results were pooled from 18 studies (OR 1.55, 95% CI 1.41-1.70, P = 0.13, I² = 28.00%). Meta-regression analysis showed that study design explained about 16.52% of heterogeneity in the crude model. The overall quality rating scores of studies ranged from 11 to 16.

CONCLUSIONS

Findings from this review evidenced that tooth loss is positively associated with an increased risk of dementia in adults. Future well-designed longitudinal researches examining the direct and indirect relationship between tooth loss and dementia risk are encouraged.

Serum Homocysteine and Behavioral and Psychological Symptoms of Dementia: Is There Any Correlation in Alzheimer's Disease?

Background

There are studies showing the relation between serum B12, folate and Behavioral and Psychological symptoms of Dementia (BPSD) in Alzheimer's disease (AD). Serum levels of these vitamins do not reflect actual disease status and therefore checking the serum Homocysteine level is considered a better test. Homocysteine has been found to be associated with cognitive impairment and various psychiatric disorders.

Purpose

This study was planned to identify the correlation between serum homocysteine levels and BPSD in AD patients.

Methods

AD patients (n = 18) and healthy controls (n = 18) were included in the study. Diagnosis of AD was confirmed using International Classification Disease-10. AD patients were assessed using Mini Mental Status Examination (MMSE), Clinical Dementia Rating scale (CDR), Global Deterioration scale (GDS), and Neuropsychiatric inventory (NPI). Healthy controls were assessed on MMSE and Mini International Neuropsychiatric Interview. Serum homocysteine, vitamin B12, and folate levels were measured in all study subjects.

Results

Patients with AD had statistically significant higher serum levels of homocysteine as compared to the control group, while the levels of vitamin B12 and folate did not differ significantly. There was statistically significant positive correlation of serum homocysteine levels with total NPI score as well as with NPI sub-domains particularly delusion, agitation/aggression, and depression/dysphoria. Serum homocysteine levels did not correlate significantly with MMSE, CDR, and GDS scores.

Conclusion

Correlation was observed between serum homocysteine levels and behavioral and psychological symptoms of AD. There is a possibility of etiological role, but the underlying pathophysiological mechanisms need to be elucidated. Whether patients will benefit or not with supplements of vitamin B12 and folate requires further research. This was a cross-sectional study and findings should not be generalized. Further prospective longitudinal studies with a large number of patients are needed.

Proteomics Analysis of Blood Serums from Alzheimer's Disease Patients Using iTRAQ Labeling Technology

Alzheimer' disease (AD) is the most common form of dementia affecting up to 6% of the population over the age of 65. In order to discover differentially expressed proteins that might serve as potential biomarkers, the serums from AD patients and healthy controls were compared and analyzed using the proteomics approach of isobaric tagging for relative and absolute quantitation (iTRAQ). For the first time, AD biomarkers in serums are investigated in the Han Chinese population using iTRAQ labeled proteomics strategy. Twenty-two differentially expressed proteins were identified and out of which nine proteins were further validated with more sample test. Another three proteins that have been reported in the literature to be potentially associated with AD were also investigated for alteration in expression level. Functions of those proteins were mainly related to the following processes: amyloid-β (Aβ) metabolism, cholesterol transport, complement and coagulation cascades, immune response, inflammation, hemostasis, hyaluronan metabolism, and oxidative stress. These results support current views on the molecular mechanism of AD. For the first time, differential expression of zinc-alpha-2-glycoprotein (AZGP1), fibulin-1 (FBLN1), platelet basic protein (PPBP), thrombospondin-1 (THBS1), S100 calcium-binding protein A8 (S100A8), and S100 calcium-binding protein A9 (S100A9) were detected in the serums of AD patients compared with healthy controls. These proteins might play a role in AD pathophysiology and serve as potential biomarkers for AD diagnosis. Specifically, our results strengthened the crucial role of Aβ metabolism and blood coagulation in AD pathogenesis and proteins related to these two processes may be used as peripheral blood biomarkers for AD.

Review: Impact of Helicobacter pylori on Alzheimer's disease: What do we know so far?

BACKGROUND

Helicobacter pylori has changed radically gastroenterologic world, offering a new concept in patients' management. Over time, more medical data gave rise to diverse distant, extragastric manifestations and interactions of the "new" discovered bacterium. Special interest appeared within the field of neurodegenerative diseases and particularly Alzheimer's disease, as the latter and Helicobacter pylori infection are associated with a large public health burden and Alzheimer's disease ranks as the leading cause of disability. However, the relationship between Helicobacter pylori infection and Alzheimer's disease remains uncertain.

METHODS

We performed a narrative review regarding a possible connection between Helicobacter pylori and Alzheimer's disease. All accessible relevant (pre)clinical studies written in English were included. Both affected pathologies were briefly analyzed, and relevant studies are discussed, trying to focus on the possible pathogenetic role of this bacterium in Alzheimer's disease.

RESULTS

Data stemming from both epidemiologic studies and animal experiments seem to be rather encouraging, tending to confirm the hypothesis that Helicobacter pylori infection might influence the course of Alzheimer's disease pleiotropically. Possible main mechanisms may include the bacterium's access to the brain via the oral-nasal-olfactory pathway or by circulating monocytes (infected with Helicobacter pylori due to defective autophagy) through disrupted blood-brain barrier, thereby possibly triggering neurodegeneration.

CONCLUSIONS

Current data suggest that Helicobacter pylori infection might influence the pathophysiology of Alzheimer's disease. However, further large-scale randomized controlled trials are mandatory to clarify a possible favorable effect of Helicobacter pylori eradication on Alzheimer's disease pathophysiology, before the recommendation of short-term and cost-effective therapeutic regimens against Helicobacter pylori-related Alzheimer's disease.

Serum Soluble Tumor Necrosis Factor-Related Apoptosis-Inducing Ligand Levels in Older Subjects with Dementia and Mild Cognitive Impairment

BACKGROUND

The tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) has been involved in both physiological and pathological conditions, including vascular pathologies and pathologies of the central nervous system. Nonetheless, the knowledge about the role of systemic TRAIL in patients affected by different types of dementia and mild cognitive impairment (MCI) is still limited.

OBJECTIVE

We assessed serum TRAIL levels in a large cohort of older individuals (n = 644) including patients with late-onset Alzheimer's disease (LOAD), vascular dementia (VAD), 'mixed' dementia (MIX), MCI, and healthy controls.

METHODS

Circulating TRAIL was measured by ELISA.

RESULTS

At univariate analysis, TRAIL levels were higher in VAD, MIX, and MCI patients compared with LOAD patients and controls. Using the multiple linear regression model, we found that TRAIL levels were associated with VAD and MCI, but not MIX, independent of potential confounding factors.

CONCLUSION

The finding of high levels of circulating TRAIL in VAD and MCI seems to suggest that both of these conditions are characterized by a significant vascular damage with respect to LOAD.

Cyclooxygenase-2 gene polymorphisms and risk of Alzheimer's disease: A meta-analysis

PURPOSE

Cyclooxygenase-2 (COX-2) is one of the key enzymes in the synthesis of prostaglandins, and plays a pivotal role in inflammatory response. Recent studies have suggested cyclooxygenase-2 is involved in the pathogenesis of Alzheimer's disease (AD). However, the relationship between COX-2 gene polymorphisms (-765G>C rs20417, -1195A>G rs689466) and Alzheimer's disease risk is not conclusive. We conducted a meta-analysis to systematically examine and to clarify the association between the two SNPs and AD risk.

METHODS

PubMed, EMBASE, Web of Science, Cochrane Library and CBMdisc were searched in July 2015 to identify eligible studies. Odds ratio (OR) and 95% confidence intervals (95% CI) were used to assess the strength of association.

RESULTS

A total of 7 case-control studies about COX-2 rs20417 polymorphisms and AD risk, and 3 studies about COX-2 rs689466 and AD risk were included in this meta-analysis. For rs20417 (-765G>C), there was a significant association between rs20417 and AD, and the risk for AD decreased in all gene models (C allele versus G allele: OR=0.570 CI 0.484-0.672; CC+GC versus GG: OR=0.568 CI 0.470-0.686; CC versus GC+GG: OR=0.357, CI 0.217-0.587; CC versus GG: OR=0.311, CI 0.189-0.514; GC versus GG: OR=0.613 CI 0.503-0.746).

CONCLUSION

C-allele of rs20417 (-765G>C) polymorphism was associated with reduced risk of AD, and might be a protective factor. Because of the limit sample and heterogeneity, the association between rs689466 polymorphism and AD risk should be treated with caution. To further confirm this relationship, larger-scale and better-designed studies should be conducted in the future.

Tormentic acid reduces inflammation in BV-2 microglia by activating the liver X receptor alpha

Tormentic acid (TA) has been reported to have anticancer, anti-inflammatory and anti-atherogenic properties. However, the effects of TA on neuroinflammation have not been reported. In this study, we investigated whether TA inhibited lipopolysaccharide (LPS)-induced inflammatory response in BV2 microglia cells. BV2 microglia cells were treated with TA for 1h before exposure to LPS. The expression of inducible nitric oxide synthase (iNOS), Cyclooxygenase-2 (COX-2), Nuclear factor κB (NF-κB) and liver X receptor alpha (LXRα) was detected by western blotting. The expression of cytokines Tumor necrosis factor-alpha (TNF-α) and interleukin 1beta (IL-1β) was detected by enzyme-linked immunosorbent assays (ELISA). Results showed that TA inhibited nitric oxide (NO), prostaglandin E2 (PGE2) production by inhibiting iNOS and COX-2 expression. TA also inhibited LPS-induced inflammatory cytokines TNF-α and IL-1β expression. Furthermore, TA could activate LXRα and inhibit LPS-induced NF-κB activation. Knowdown of LXRα reversed the anti-inflammatory effects of TA. In conclusion, our results indicate that TA exerts an anti-inflammatory effect on LPS-stimulated BV2 microglia cells by activating LXRα.

Positive and negative effects of prostaglandins in Alzheimer's disease

The aim of this review was to clarify the role of prostaglandins and prostaglandin receptors in the immunopathology of Alzheimer's disease. A PubMed search was done using the key word, 'Alzheimer's disease' in combination with the term 'prostaglandins'. Articles from the past 10 years were preferentially selected but important ones from the past 20 years were also included according to the authors' judgment. Alzheimer's disease is characterized by pathological hallmarks such as extracellular deposition of the amyloid β-peptide, the appearance of intracellular neurofibrillary tangles, extensive neuronal loss and synaptic changes in the cerebral cortex and hippocampus. These processes induce inflammatory pathways by activating microglia, astrocytes and infiltrating leukocytes that produce inflammatory mediators including cytokines and prostaglandins.Prostaglandins are small lipid mediators derived from arachidonic acid by multi-enzymatic pathways in which cyclooxygenases and phospholipases are the rate-limiting enzymes. In the central nervous system, prostaglandins exhibit either neurotoxic or neuroprotective effects by acting on specific G-protein-coupled receptors that have different subfamilies and differences in their selective agonists, tissue distribution and signal transduction cascades. Further studies on the role of prostaglandins in Alzheimer's disease may contribute to clarification of their neuroprotective actions, which may lead to the development of successful therapeutic strategies.

Serum homocysteine levels are correlated with behavioral and psychological symptoms of Alzheimer's disease

PURPOSE

Homocysteine has been associated with cognitive impairment and various psychiatric symptoms. This study was designed to clarify whether a relationship exists between the serum levels of homocysteine and the behavioral and psychological symptoms of dementia.

METHODS

Patients with Alzheimer's disease (n=77) and control subjects (n=37) were included in this study. History taking, physical examination, and cognitive assessment were carried out as part of the investigation for the diagnosis of Alzheimer's disease based on the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition. The Mini-Mental State Examination, Global Deterioration Scale, Clinical Dementia Rating, and the Korean version of the Neuropsychiatric Inventory were applied to all patients. The patients' serum homocysteine, folate, and vitamin B12 levels were measured.

RESULTS

Patients with Alzheimer's disease had statistically significantly lower Mini-Mental State Examination scores and higher serum homocysteine levels compared to the control subjects. Mean serum folate and vitamin B12 concentration were significantly lower in patients with Alzheimer's disease compared to control subjects. A statistically significant positive correlation was found between the serum homocysteine levels and the Neuropsychiatric Inventory subdomains, including delusion, agitation/aggression, depression/dysphoria, elation/euphoria, apathy/indifference, and disinhibition. No statistically significant correlation was found between the serum homocysteine concentration and the Mini-Mental State Examination, Global Deterioration Scale, or Clinical Dementia Rating.

CONCLUSION

Associations between the serum homocysteine levels and behavioral and psychological symptoms of dementia were observed, raising the possibility of an etiological role. However, the correlations between the folate or vitamin B12 levels and the Neuropsychiatric Inventory scores were not significant. The pathophysiological mechanisms underlying these findings remain to be elucidated. This was a cross-sectional study and the findings should be confirmed by repetitive, prospective longitudinal studies in a larger group of patients with neurodegenerative disorders.

Vitamin D insufficiency in psychiatric inpatients

OBJECTIVE

The extraskeletal effects of vitamin D have gained increasing attention with the discovery of receptors in a variety of organ systems. Previous work has identified associations between vitamin D insufficiency and a variety of mental illnesses, including affective, cognitive, and psychotic spectrum disorders. We attempted to determine the point prevalence of vitamin D insufficiency among psychiatric inpatients and determine if there was a relationship between vitamin D insufficiency and specific diagnoses and pharmacological treatments.

METHODS

This was a retrospective chart review of all adult patients (N=544) admitted to the psychiatric ward of a community hospital in central Illinois between December, 2010 and June, 2011.

RESULTS

The mean vitamin D level on admission was 22.3 ng/mL, with a range of 4-79.2 ng/mL. The incidence of vitamin D insufficiency (defined as levels < 30 ng/mL) was 75%. Of those with insufficient levels of vitamin D, only 37% received treatment. Vitamin D insufficiency was not correlated with age, gender, month of admission, length of stay, score on the Global Assessment of Functioning (GAF) scale at admission, diagnosis, or psychotropic medication usage.

CONCLUSIONS

Vitamin D insufficiency is highly prevalent in psychiatric inpatients. It is unclear whether this is the result of severe mental illness and resultant social isolation, or if vitamin D has a regulatory role on upstream genes involved in neural networks that influence affect, cognition, and perception.

Pathways towards an effective immunotherapy for Parkinson's disease

Immunizations that target specific types of immune responses are used commonly to prevent microbial infections. However, a range of immune responses may prove necessary to combat the ravages of neurodegenerative diseases. The goal is to eliminate the 'root' cause of neurodegenerative disorders, misfolded aggregated proteins, while harnessing adaptive immune responses to promote neural repair. However, immunization strategies used to elicit humoral immune responses against aberrant brain proteins have yielded mixed success. While specific proteins can be cleared, the failures in halting disease progression revolve, in measure, around adaptive immune responses that promote autoreactive T cells and, as such, induce a meningoencephalitis, accelerating neurodegeneration. Thus, alternative approaches for protein clearance and neural repair are desired. To this end, our laboratories have sought to transform autoreactive adaptive immune responses into regulatory neuroprotective cells in Parkinson's disease. In this context, induction of immune responses against modified brain proteins serves to break immunological tolerance, while eliciting adaptive immunity to facilitate neuronal repair. How to harness the immune response in the setting of Parkinson's disease requires a thorough understanding of the role of immunity in human disease and the ways to modify such immune responses to elicit therapeutic gain. These are discussed in this review.

Amyloid-specific T-cells differentiate Alzheimer's disease from Lewy body dementia

Alzheimer's disease and dementia with Lewy bodies are the most common neurodegenerative dementias in old age. Accurate diagnosis of these conditions has important clinical implications because they tend to be confounded. In the brain of Alzheimer's disease patients amyloid-beta is produced in excess and deposited as plaques, forming the hallmark of this condition. Lymphocytes have been implicated in the process of amyloid-beta removal and inflammation occurrence. Here we investigated peripheral amyloid-beta1-42-specific T-cells by multicolor flow cytometry to simultaneously detect and characterize activation markers and cell signaling proteins (phospho-protein kinase C) in patients with Alzheimer's disease or Lewy body dementia and in healthy controls. Results indicate that only Alzheimer's disease patients display small subsets of peripheral amyloid-beta1-42-specific T-cells, characterized by bright expression of phosphorylated-protein kinase C-delta or -zeta whose significance although discussed, is far from being understood. The identification of such subsets, anyhow, may strongly contribute to distinguish Alzheimer's disease from dementia with Lewy bodies, opening possible new routes to early therapeutic strategies.

Serum level of endogenous secretory receptor for advanced glycation end products and other factors in type 2 diabetic patients with mild cognitive impairment

OBJECTIVE

Determine the serum levels of endogenous secretory receptor for advanced glycation end products (esRAGEs) in patients with type 2 diabetes and mild cognitive impairment (MCI) and in control patients with type 2 diabetes but no MCI, and examine the relationship of esRAGE and MCI with other clinical factors.

RESEARCH DESIGN AND METHODS

A total of 101 patients with type 2 diabetes who were hospitalized in the Department of Endocrinology at Fujian Provincial Hospital between January 2010 and January 2011 were enrolled. There were 58 patients with MCI and 43 patients without MCI (control). Serum levels of esRAGE were measured using an enzyme-linked immunosorbent assay (ELISA). Other clinical parameters were also measured.

RESULTS

Type 2 diabetic patients with MCI had a longer duration of diabetes; elevated HbA(1c), total cholesterol (CHOL), LDL cholesterol (LDL-C), triglyceride (TG), intima-media thickness, C-reactive protein (CRP), and brachial-ankle pulse wave velocity (ba-PWV); and lower ankle brachial index (ABI) and esRAGE relative to the control group. Among patients with MCI, the Montreal Cognitive Assessment (MoCA) score was positively correlated with serum esRAGE but negatively correlated with CHOL. Spearman rank correlation analysis indicated that esRAGE was positively correlated with MoCA score and ABI but negatively correlated with ba-PWV, CHOL, TG, and CRP in all subjects.

CONCLUSIONS

Our results suggest that esRAGE may be a potential protective factor for dyslipidemia, atherosclerosis, and MCI in patients with type 2 diabetes.

Role of interleukin 6 and alpha-globulins in differentiating Alzheimer and vascular dementias

BACKGROUND

Inflammatory mechanisms and immune activation have been hypothesized to play a role in the pathogenesis of age-associated diseases, including Alzheimer's disease.

PURPOSE

The evaluation of inflammatory markers in patients with dementia, and to determine whether these markers can be used to differentiate between vascular dementia (VD) and Alzheimer's dementia (AD).

PATIENTS AND METHODS

Twenty demented patients (10 AD and 10 VD) and 20 non-demented controls were subjected to clinical evaluation, MRI brain scans and laboratory tests, including interleukin (IL) 6, C-reactive protein and serum protein electrophoresis.

RESULTS

The results of this study revealed that serum levels of IL-6 and C-reactive protein were significantly elevated among patients with both types of dementia compared to normal elderly subjects. Although the mean IL-6 level was higher in patients with AD compared to patients with VD, this difference was not significant. The cutoff value at which the serum level of IL-6 gave maximum sensitivity and specificity was 14.25 pg/ml. Moreover, α₁- and α₂-globulins were able to discriminate between AD and VD (being significantly higher in AD).

CONCLUSION

IL-6 levels could be used to differentiate dementia from normal aging. Moreover, α₁- and α₂-globulins could differentiate between AD and VD. It can be concluded that inflammation plays an important role in both types of dementia.

Relationship of tooth loss to mild memory impairment and cognitive impairment: findings from the Fujiwara-kyo study

Background

This cross-sectional study investigated the relationship between the number of remaining teeth to mild memory impairment (MMI), which is a preclinical stage of dementia, and to cognitive impairment.

Methods

The subjects were aged 65 years or older and were grouped according to their score for the Mini-Mental State Examination (MMSE), the three-word delayed recall test in the MMSE, and the Geriatric Depression Scale into the control group (n = 3,696), the MMI group (n = 121), and the low MMSE score (23 or lower) group (n = 214). We collected data on the number of remaining teeth, the length of the edentulous period, health-related lifestyle, medical history, blood pressure, height, and body weight. Fasting venous blood samples were also obtained.

Results

Multiple logistic regression analysis, adjusted for depressive symptoms, age, sex, length of education, and other explanatory variables, revealed that the odds ratios of 0-10 remaining teeth to 22-32 remaining teeth were 1.679 (95% CI 1.073-2.627) for MMI and 2.177 (95% CI 1.510-3.140) for a low MMSE score. A significant relationship was also found between the length of the edentulous period and the risk of a low MMSE score (odds ratio 3.102, 95% CI 1.432-6.720) (15 years or more/less than 15 years).

Conclusions

Our findings suggest that tooth loss is associated with cognitive function.

[Premature immunosenescence: a pathogenetic factor in Alzheimer's disease?]

While the familial form of Alzheimer's disease (AD) is known to be entirely inherited, the etiopathogenesis of the most common late-onset form of Alzheimer's disease still remains unresolved. Among various factors, aging seems to be one of the most prominent risk factors. Moreover, a large body of evidence points to the contribution of immunological alterations in AD. The involvement of inflammatory factors in the etiopathology has been widely discussed. Moreover, an impairment of certain immune responses in AD has been observed. Presumably, premature immunosenescence may lead to inadequate immune reactions. Against this background, the development of different immunotherapeutic strategies seems to be a promising challenge for future research.

Adaptive immune regulation of glial homeostasis as an immunization strategy for neurodegenerative diseases

Neurodegenerative diseases, notably Alzheimer's and Parkinson's diseases, are amongst the most devastating disorders afflicting the elderly. Currently, no curative treatments or treatments that interdict disease progression exist. Over the past decade, immunization strategies have been proposed to combat disease progression. Such strategies induce humoral immune responses against misfolded protein aggregates to facilitate their clearance. Robust adaptive immunity against misfolded proteins, however, accelerates disease progression, precipitated by induced effector T cell responses that lead to encephalitis and neuronal death. Since then, mechanisms that attenuate such adaptive neurotoxic immune responses have been sought. We propose that shifting the balance between effector and regulatory T cell activity can attenuate neurotoxic inflammatory events. This review summarizes advances in immune regulation to achieve a homeostatic glial response for therapeutic gain. Promising new ways to optimize immunization schemes and measure their clinical efficacy are also discussed.

Noradrenaline activation of neurotrophic pathways protects against neuronal amyloid toxicity

Degeneration of locus coeruleus (LC) noradrenergic forebrain projection neurons is an early feature of Alzheimer's disease. The physiological consequences of this phenomenon are unclear, but observations correlating LC neuron loss with increased Alzheimer's disease pathology in LC projection sites suggest that noradrenaline (NA) is neuroprotective. To investigate this hypothesis, we determined that NA protected both hNT human neuronal cultures and rat primary hippocampal neurons from amyloid-beta (Abeta(1-42) and Abeta(25-35)) toxicity. The noradrenergic co-transmitter galanin was also effective at preventing Abeta-induced cell death. NA inhibited Abeta(25-35)-mediated increases in intracellular reactive oxygen species, mitochondrial membrane depolarization, and caspase activation in hNT neurons. NA exerted its neuroprotective effects in these cells by stimulating canonical beta(1) and beta(2) adrenergic receptor signaling pathways involving the activation of cAMP response element binding protein and the induction of endogenous nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF). Treatment with functional blocking antibodies for either NGF or BDNF blocked NA's protective actions against Abeta(1-42) and Abeta(25-35) toxicity in primary hippocampal and hNT neurons, respectively. Taken together, these data suggest that the neuroprotective effects of noradrenergic LC afferents result from stimulating neurotrophic NGF and BDNF autocrine or paracrine loops via beta adrenoceptor activation of the cAMP response element binding protein pathway.

Decreased serum brain-derived neurotrophic factor levels in elderly korean with dementia

OBJECTIVE

The primary purpose of this study was to investigate the differences in the serum brain-derived neurotrophic factor (BDNF) level between elderly Korean people over 65 years with and without dementia.

METHODS

171 individuals over 65 years were enrolled in this study. Screening for cognitive impairments was carried out using the Mini-Mental Status Examination-Korean version (MMSE-KC). One hundred thirty-two subjects scored below 1.5 standard deviations (SD) of the mean MMSE-KC score, and these were evaluated using the Consortium to Establish a Registry for Alzheimer's Disease, Korean version (CERAD-K) and the Geriatric Depression Scale (GDS). The Clinical Dementia Rating Scale (CDRS) and the Diagnostic and Statistical Manual of Mental Disorders, fourth edition (DSM-IV) diagnostic criteria were used for further evaluation. Subjects with a CDRS score of 1 or higher were classified as having Alzheimer's disease (AD), and subjects with a CDRS score of 0.5 were classified as having a mild cognitive impairment (MCI). Subjects with a CDRS score of 0 were classified as having aging-associated cognitive decline (AACD). Serum BDNF levels were analyzed using the enzyme-linked immunosorbent assay (ELISA) method.

RESULTS

The serum BDNF levels were significantly lower in the subjects with MCI and AD compared with the healthy controls (p<0.01). A significant correlation was found between the total MMSE-KC score and serum BDNF level (r=0.295; p<0.01). However, no significant correlation was observed between the severity of MMSE-KC and the total GDS score. A significant difference was found in the total score of GDS between the AACD group and subjects with AD (p<0.05).

CONCLUSION

This study suggested that BDNF might be involved in the pathophysiology of cognitive decline in elderly people.

Increase of SCF plasma concentration during donepezil treatment of patients with early Alzheimer's disease

Alzheimer's disease (AD) can be treated with inhibitors of the enzyme acetylcholinesterase (AChE). There is evidence that AChE inhibitors promote neuroprotective effects and neurogenesis in the central nervous system (CNS). However, the mechanisms by which AChE inhibitors mediate these effects are still not well understood. One possible mechanism could be the up-regulation of haematopoietic growth factors (HGFs), also known to promote neuroprotective effects and to stimulate neurogenesis in the CNS. In the present study we investigated the impact of a 15-month treatment with the AChE inhibitor donepezil on blood levels of the HGFs stem cell factor (SCF), stromal cell-derived factor 1 (SDF-1), granulocyte colony- stimulating factor (G-CSF) and vascular endothelial growth factor (VEGF) in 19 patients with AD and 45 age-matched healthy controls. Before treatment with donepezil we found in AD patients significantly decreased SCF plasma concentrations (661.1+/-40.0 pg/ml) compared to healthy controls (997.7+/-33.7 pg/ml, p<0.001) but no significant differences between both groups concerning blood levels of SDF-1, G-CSF and VEGF. After 15 months' treatment SCF plasma levels increased significantly in the AD patients (764.5+/-41.5 pg/ml, p=0.016). In addition, we found a significant positive correlation between SCF plasma levels at baseline and changes of cognitive functions over the 15-month period (r=0.521, p=0.022). For the other HGFs we were unable to show a significant impact of donepezil treatment. Our findings indicate that donepezil treatment of AD patients is associated with an up-regulation of SCF plasma levels, which may contribute to neuroprotection and neurogenesis in the CNS.

Development of vaccination approaches for the treatment of neurological diseases

Several progressive neurodegenerative diseases share a common pathology: the accumulation of misfolded proteins within cells or neuropil of the brain. Characteristically, these misfolded proteins form organized beta-sheet-containing assemblies that have optical and biochemical properties of amyloid. Thus, the brain amyloidoses, Alzheimer's disease (AD), Parkinson's disease, and the prionoses or transmissible spongioform encelphalopathies (TSEs) all manifest putatively pathogenic misfolded proteins, suggesting that these proteins or their precursors may be targets for therapeutics development efforts. Two different biological approaches, both predicated on vaccination, are discussed in this monograph as preclinical approaches for the treatment of AD and a TSE. Herein, I first describe an active vaccination approach that exploits immune shaping to engender a prophylactic T(H)2 response to Abeta in AD mouse models. Second, I describe a passive vaccination strategy whereby recombinant adeno-associated virus vectored delivery of anti-prion single-chain fragment variable antibodies attenuates disease progression and promotes life extension in a mouse TSE model.

CD 4+ T cells in the pathobiology of neurodegenerative disorders

CD4+ T cells orchestrate innate and adaptive immunity. In the central nervous system they modulate immune responses including cell trafficking and glial neuroregulatory functions through an array of soluble molecules cell-cell interactions affecting tissue homeostasis. During disease their roles evolve to an auto-aggressive or, alternatively, protective phenotype. How such a balance is struck in the setting of neurodegenerative disorders may reflect a dichotomy between regulatory T cell, anti-inflammatory and neuroprotective activities versus effector T cell inflammation and neurodegeneration. Interestingly, such roles may show commonalities amongst neurodegenerative diseases. Herein we focus on strategies to modulate such CD4+ T cell responses for therapeutic gain.

Human misfolded truncated tau protein promotes activation of microglia and leukocyte infiltration in the transgenic rat model of tauopathy

It has been hypothesized that misfolded tau protein could be a mediator of the inflammatory response in human tauopathies. Here we show that neurodegenerative lesions caused by human truncated tau promote inflammatory response manifested by upregulation of immune-molecules (CD11a,b, CD18, CD4, CD45 and CD68) and morphological activation of microglial cells in a rat model of tauopathy. In parallel, the innate immune brain response promotes activation of MHC class II positive blood-borne leukocytes and their influx into the brain parenchyma. These findings have important consequences for the rationale drug development of effective inflammation-based therapeutic strategies for human tauopathies.

Toll-like receptors in Alzheimer's disease

Alzheimer's disease (AD) is characterized by the formation of insoluble deposits of beta-amyloid (Abeta) within the parenchyma of the brain. These deposits are associated with a robust microglia-mediated inflammatory response. Recent work has demonstrated that Toll-like receptors (TLRs) participate in this inflammatory response. This chapter reviews the mechanisms whereby TLRs contribute to the induction of a microglial inflammatory response to promote AD pathogenesis. Specifically, the involvement of CD14 and the TLRs in microglial activation is delineated. The TLR-mediated microglial response has beneficial roles in stimulating phagocytosis as well as detrimental roles in the Abeta-stimulated release of neurotoxic products.

Th1 responses to beta-amyloid in young humans convert to regulatory IL-10 responses in Down syndrome and Alzheimer's disease

A beta(1-42)-specific antibodies and T-cell proliferation point to the existence of a memory response to A beta(1-42) in humans. Using ELISPOT, we studied A beta(1-42)-specific T cells in individuals of various ages, and in subjects with Trisomy 21 or Alzheimer's disease. We show for the first time that A beta(1-42)-specific Th1-type T-cell memory is present in young humans, producing high levels of IFN-gamma and IL-2. With increasing age, the production of IFN-gamma and IL-2 decreases but is not discontinued in healthy subjects and is accompanied by a sharp rise in CD4(+) T-cell-derived regulatory IL-10 production. In contrast, individuals with Trisomy 21 and with Alzheimer's disease produce IL-10 only in the absence of any effector cytokine. This signifies a switch from a Th1 effector to an IL-10 mediated regulatory response.

Inflammation as a potential mediator for the association between periodontal disease and Alzheimer's disease

Periodontal disease (PDD) is associated with increased risk of cardiovascular disease, cerebrovascular disease, and mortality in many studies, while other studies have begun to suggest an association of PDD with Alzheimer's disease (AD). This paper discusses how infectious pathogens and systemic infection may play a role in AD. The roles of infection and inflammation are addressed specifically with regard to known AD pathologic lesions including senile plaques, neuron death, neurofibrillary tangles, and cerebrovascular changes. A testable model of proposed pathways between periodontal infection and AD is presented including three possible mechanisms: a) direct effects of infectious pathogens, b) inflammatory response to pathogens, and c) the effects on vascular integrity. The role of gene polymorphisms is discussed, including apolipoprotein (APOE) varepsilon4 as a pro-inflammatory and pro-infection genotype.

Serum brain-derived neurotrophic factor is associated with cognitive function in healthy older adults

Cognitive decline is common in older adults, even in the absence of significant medical or neurological conditions. Recent work implicates serum levels of brain-derived neurotrophic factor in age-related cognitive decline, though no study has directly examined this possibility. A total of 35 older adults without neurological history underwent fasting blood draw and completed a brief neuropsychological test battery during a single session. After adjusting for demographic and medical confounds, higher serum brain-derived neurotrophic factor levels were associated with better performance on the Mini-Mental State Examination (r = .36) and short form of the Boston Naming Test (r = .39). These findings extend work from Alzheimer disease and vascular dementia samples and indicate that higher brain-derived neurotrophic factor levels are associated with better neuropsychological function in healthy older adults. The exact mechanisms for this relationship are unknown and require further examination.