Maximizing the potential of plasma amyloid-beta as a diagnostic biomarker for Alzheimer's disease

Effects of a staged integral art-based cognitive intervention (SIACI) program in older adults with cognitive impairments: protocol for a randomized controlled trial

Background

Given the aging population worldwide and the COVID-19 pandemic, which has been found to be associated with a deterioration in Alzheimer’s disease (AD) symptoms, investigating methods to prevent or delay cognitive decline in preclinical AD and AD itself is important. The trial described in this protocol aims to evaluate the effects of a staged integral art-based cognitive intervention (SIACI) in older adults with CIs (preclinical AD [SCD or MCI] and mild AD), in order to gather evidence on the effects of SIACI on cognition and psychological/psychosocial health gains and determine the mechanisms.

Methods

The planned study is a single-center, parallel-arm, randomized controlled trial with allocation concealment and outcome assessor blinding. A total of 88 participants will be randomized to two groups: (i) an intervention group that receives the 16-week, 24-session SIACI program and (ii) a waitlist control group (which will receive the SIACI program after completing the follow-up assessment). Global cognitive function, specific domains of cognition (memory, language, executive function, and visuospatial skills), and other health-related outcomes (quality of life, anxiety, depression, sleep quality, and physical activity level) will be measured at baseline, immediately after the intervention, and at the 6-month follow-up. Blood biomarkers, event-related potential (ERP)-P300, and magnetic resonance imaging (MRI) data will be collected at baseline and immediately after the intervention to explore the mechanisms of SIACI.

Discussion

The trial will elucidate the immediate and long-term effects of SIACI based on neuropsychological testing and blood biomarkers, and neuroscience involving ERP-P300 and MRI parameters will make it possible to explore the mechanisms of SIACI in older adults with CIs. The results will provide evidence on the effectiveness of an AT-based cognitive intervention, which may delay or even halt cognitive decline in preclinical AD and AD itself.

Trial registration

ChiCTR, ChiCTR2100044959. Registered 03 April 2021.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12877-022-02961-4.

Amyloidogenic Nanoplaques in Blood Serum of Patients with Alzheimer's Disease Revealed by Time-Resolved Thioflavin T Fluorescence Intensity Fluctuation Analysis

BACKGROUND

Biomarkers are central to current research on molecular mechanisms underlying Alzheimer's disease (AD). Their further development is of paramount importance for understanding pathophysiological processes that eventually lead to disease onset. Biomarkers are also crucial for early disease detection, before clinical manifestation, and for development of new disease modifying therapies.

OBJECTIVE

The overall aim of this work is to develop a minimally invasive method for fast, ultra-sensitive and cost-effective detection of structurally modified peptide/protein self-assemblies in the peripheral blood and in other biological fluids. Specifically, we focus here on using this method to detect structured amyloidogenic oligomeric aggregates in the blood serum of apparently healthy individuals and patients in early AD stage, and measure their concentration and size.

METHODS

Time-resolved detection of Thioflavin T (ThT) fluorescence intensity fluctuations in a sub-femtoliter observation volume element was used to identify in blood serum ThT-active structured amyloidogenic oligomeric aggregates, hereafter called nanoplaques, and measure with single-particle sensitivity their concentration and size.

RESULTS

The concentration and size of structured amyloidogenic nanoplaques are significantly higher in the blood serum of individuals diagnosed with AD than in control subjects.

CONCLUSION

A new method with the ultimate, single-particle sensitivity was successfully developed. The proposed approach neither relies on the use of immune-based probes, nor on the use of radiotracers, signal-amplification or protein separation techniques, and provides a minimally invasive test for fast and cost-effective early determination of structurally modified peptides/proteins in the peripheral blood, as shown here, but also in other biological fluids.

Effect of memantine on expression of Bace1-as and Bace1 genes in STZ-induced Alzheimeric rats

Recent studies have showed that the long non-coding RNAs (lncRNAs) expression is dysregulated in different neurodegenerative disorders like Alzheimer's disease (AD). In the present study, the effects of memantine on the level of Bace1-as and Bace1 genes' expression in streptozotocin (STZ)-induced Alzheimer's and memantine treated rats were investigated. The male Wistar rats were randomly divided into four groups: 1-Normal control, 2-Sham-operated control, 3- Alzheimer'scontrol rats (ICV-STZ), 4-Experimental group rats treated by memantine in a dose of 30 mg/kg/day for 28 days in ICV-STZ rats. The expression of Bace1-as and Bace1 genes was measured by quantitative-PCR in the brain and blood tissues. ELISA was used to analyze Bace1 and Aβ proteins. Expression of Bace1-as was significantly increased in the brain and blood tissues of the experimental group (p = 0.032 and p = 0.034, respectively). The expression of Bace1 gene showed no significant changes in the brain. Furthermore, the ELISA analysis revealed that Bace1 protein was significantly increased in the plasma of the Alzheimer's control group (p = 0.000) and in the brain tissue of the experimental group (p = 0.000). Additionally, Aβ levels had no significant changes between all groups studied. The Bace1 protein may be used as a prognostic biomarker in plasma, or before using memantine as a treatment. Furthermore, Bace1-as gene expression may play a role in monitoring the progression of AD.

The Level of Plasma Amyloid-β40 Is Correlated with Peripheral Transport Proteins in Cognitively Normal Adults: A Population-Based Cross-Sectional Study

BACKGROUND

Transport proteins, soluble low-density lipoprotein receptor-related protein-1 (sLRP1), and soluble receptor of advanced glycation end products (sRAGE), play an important role in the clearance of plasma amyloid-β (Aβ). However, their relationship is not clear.

OBJECTIVE

The aim was to explore the relationship between plasma levels of sLRP1, sRAGE, and Aβ in a cross-sectional study.

METHODS

A total of 1,185 cognitively normal participants (age above 40) from a village in the suburbs of Xi'an, China were enrolled from October 8, 2014 to March 30, 2015. Plasma Aβ40, Aβ42, sLRP1, and sRAGE were tested using a commercial ELISA. Apolipoprotein E (APOE) genotyping was conducted using PCR and sequencing. The relationship between plasma levels of sLRP1, sRAGE, and Aβ was analyzed using Pearson's correlation analysis and multiple linear regression.

RESULTS

In the total population, Log sLRP1 and Log sRAGE were positively correlated with plasma Aβ40 (r= 0.103, p < 0.001; r= 0.064, p = 0.027, respectively), but neither were associated with plasma Aβ42. After multivariable adjustment in the regression model, Log sLRP1 and Log sRAGE were still positively related with plasma Aβ40 (β= 2.969, p < 0.001; β= 1.936, p = 0.017, respectively) but not Aβ42. Furthermore, the positive correlations between transport proteins and plasma Aβ40 remained significant only in APOEɛ4 non-carriers after Pearson's analysis and multiple regression analysis after stratification by gene status.

CONCLUSION

The concentrations of plasma sLRP1 and sRAGE had a significant impact on the level of plasma Aβ40 in cognitively normal adults, especially in APOEɛ4 non-carriers. However, the mechanism by which the transport proteins are involved in peripheral Aβ clearance and the relationship between transporters and amyloid burden in the brain needs further validation.

Toward Exosome-Based Neuronal Diagnostic Devices

Targeting exosome for liquid biopsy has gained significant attention for its diagnostic and therapeutic potential. For detecting neuronal disease diagnosis such as Alzheimer's disease (AD), the main technique for identifying AD still relies on positron-emission tomography (PET) imaging to detect the presence of amyloid-β (Aβ). While the detection of Aβ in cerebrospinal fluid has also been suggested as a marker for AD, the lack of quantitative measurements has compromised existing assays. In cerebrospinal fluid, in addition to Aβ, T-Tau, and P-Tau, alpha-synuclein has been considered a biomarker of neurodegeneration. This review suggests that and explains how the exosome can be used as a neuronal diagnostic component. To this end, we summarize current progress in exosome preparation/isolation and quantification techniques and comment on the outlooks for neuronal exosome-based diagnostic techniques.

Peripheral Biomarkers for Early Detection of Alzheimer's and Parkinson's Diseases

Neurological disorders are found to be influencing the peripheral tissues outside CNS. Recent developments in biomarkers for CNS have emerged with various diagnostic and therapeutic shortcomings. The role of central biomarkers including CSF-based and molecular imaging-based probes are still unclear for early diagnosis of major neurological diseases. Current trends show that early detection of neurodegenerative diseases with non-invasive methods is a major focus of researchers, and the development of biomarkers aiming peripheral tissues is in demand. Alzheimer's and Parkinson's diseases are known for the progressive loss in neural structures or functions, including the neural death. Various dysfunctions of metabolic and biochemical pathways are associated with early occurrence of neuro-disorders in peripheral tissues including skin, blood cells, and eyes. This article reviews the peripheral biomarkers explored for early detection of Alzheimer's and Parkinson's diseases including blood cells, skin fibroblast, proteomics, saliva, olfactory, stomach and colon, heart and peripheral nervous system, and others. Graphical Abstract.

Sleep Deprivation Induced Plasma Amyloid-β Transport Disturbance in Healthy Young Adults

BACKGROUND

Sleep is an important physiological process and beneficial in the removal of brain metabolites and functional recovery. Prior studies have shown that sleep disorders are significant risk factors for Alzheimer's disease (AD).

OBJECTIVE

The present study was designed to characterize the effect of short-term total sleep deprivation (TSD) on plasma amyloid-β (Aβ) concentrations.

METHODS

A clinical trial was conducted between March 1, 2016, and April 1, 2016. Twenty volunteers (age 27.3±3.4 years) with normal cognitive function and sleeping habits were recruited from the local population. Participants underwent 24 h of TSD. Periprocedural blood samples were collected to compare the changes of plasma Aβ42, Aβ40, low-density lipoprotein receptor-related protein (sLRP-1), soluble receptors for advanced glycation end products (sRAGE), and serum superoxide dismutase (SOD) and malonaldehyde (MDA).

RESULTS

TSD increased morning plasma Aβ40 levels by 32.6% (p < 0.001) and decreased the Aβ42/Aβ40 ratio by 19.3% (p < 0.001). A positive relationship was found between TSD duration and plasma Aβ40 level (r = 0.51, p < 0.001) and Aβ40/Aβ42 ratio (r = 0.25, p = 0.003). Plasma concentrations of sLRP1 (p = 0.018) and sRAGE (p = 0.001) decreased significantly after TSD. Aβ40 and Aβ42 plasma concentrations correlated with plasma levels of sLRP1 and sRAGE. Serum SOD decreased after TSD (p = 0.005), whereas serum MDA was increased (p = 0.001).

CONCLUSION

Sleep deprivation can lead to an elevation of plasma Aβ40 and decrease of the Aβ42/Aβ40 ratio. The underlying mechanisms may be related to increased oxidative stress and impaired peripheral Aβ clearance as pathomechanisms of AD.

Heparan sulfate proteoglycans mediate Aβ-induced oxidative stress and hypercontractility in cultured vascular smooth muscle cells

BACKGROUND

Substantial evidence suggests that amyloid-β (Aβ) species induce oxidative stress and cerebrovascular (CV) dysfunction in Alzheimer's disease (AD), potentially contributing to the progressive dementia of this disease. The upstream molecular pathways governing this process, however, are poorly understood. In this report, we examine the role of heparan sulfate proteoglycans (HSPG) in Aβ-induced vascular smooth muscle cell (VSMC) dysfunction in vitro.

RESULTS

Our results demonstrate that pharmacological depletion of HSPG (by enzymatic degradation with active, but not heat-inactivated, heparinase) in primary human cerebral and transformed rat VSMC mitigates Aβ(1-40⁻) and Aβ(1-42⁻)induced oxidative stress. This inhibitory effect is specific for HSPG depletion and does not occur with pharmacological depletion of other glycosaminoglycan (GAG) family members. We also found that Aβ(1-40) (but not Aβ(1-42)) causes a hypercontractile phenotype in transformed rat cerebral VSMC that likely results from a HSPG-mediated augmentation in intracellular Ca(2+) activity, as both Aβ(1-40⁻)induced VSMC hypercontractility and increased Ca(2+) influx are inhibited by pharmacological HSPG depletion. Moreover, chelation of extracellular Ca(2+) with ethylene glycol tetraacetic acid (EGTA) does not prevent the production of Aβ(1-40⁻) or Aβ(1-42⁻)mediated reactive oxygen species (ROS), suggesting that Aβ-induced ROS and VSMC hypercontractility occur through different molecular pathways.

CONCLUSIONS

Taken together, our data indicate that HSPG are critical mediators of Aβ-induced oxidative stress and Aβ(1-40⁻)induced VSMC dysfunction.

Oral glucose tolerance testing to modulate plasma amyloid levels: A novel biomarker

INTRODUCTION

Plasma levels of amyloid-beta (Aβ) do not correlate well with different stages of Alzheimer's disease (AD) in cross-sectional studies. Measuring the changes in Aβ plasma levels with an acute intervention may be more sensitive to distinguishing individuals in earlier stages of AD (mild cognitive impairment; MCI) from normal controls.

METHODS

57 participants (18 with AD/MCI and 39 cognitively normal controls) underwent oral glucose tolerance testing (OGTT). Blood samples were obtained over a 2 hour time period. Changes in plasma Aβ40 and42 levels were measured from either baseline or 5 minutes to the 10 minute time point.

RESULTS

Compared to normal controls, subjects with AD/MCI had significantly less change (Δ) in plasma levels for both Aβ40(-3.13(40.93)pg/ml vs. 41.34(57.16)pg/ml;p=0.002) and Aβ42(-0.15(3.77)pg/ml vs. 5.64(10.65)pg/ml; p=0.004).

DISCUSSION

OGTT combined with measures of plasma Aβ40 and 42 is potentially useful in distinguishing aging individuals who are in different stages of AD.

Women with the Alzheimer's risk marker ApoE4 lose Aβ-specific CD4⁺ T cells 10-20 years before men

Adaptive immunity to self-antigens causes autoimmune disorders, such as multiple sclerosis, psoriasis and type 1 diabetes; paradoxically, T- and B-cell responses to amyloid-β (Aβ) reduce Alzheimer's disease (AD)-associated pathology and cognitive impairment in mouse models of the disease. The manipulation of adaptive immunity has been a promising therapeutic approach for the treatment of AD, although vaccine and anti-Aβ antibody approaches have proven difficult in patients, thus far. CD4(+) T cells have a central role in regulating adaptive immune responses to antigens, and Aβ-specific CD4(+) T cells have been shown to reduce AD pathology in mouse models. As these cells may facilitate endogenous mechanisms that counter AD, an evaluation of their abundance before and during AD could provide important insights. Aβ-CD4see is a new assay developed to quantify Aβ-specific CD4(+) T cells in human blood, using dendritic cells derived from human pluripotent stem cells. In tests of >50 human subjects Aβ-CD4see showed an age-dependent decline of Aβ-specific CD4(+) T cells, which occurs earlier in women than men. In aggregate, men showed a 50% decline in these cells by the age of 70 years, but women reached the same level before the age of 60 years. Notably, women who carried the AD risk marker apolipoproteinE-ɛ4 (ApoE4) showed the earliest decline, with a precipitous drop between 45 and 52 years, when menopause typically begins. Aβ-CD4see requires a standard blood draw and provides a minimally invasive approach for assessing changes in Aβ biology that may reveal AD-related changes in physiology by a decade. Furthermore, CD4see probes can be modified to target any peptide, providing a powerful new tool to isolate antigen-specific CD4(+) T cells from human subjects.

Reverse engineering of Alzheimer's disease based on biomarker pathways analysis

Alzheimer's disease (AD) poses an increasingly profound problem to society, yet progress toward a genuine understanding of the disease remains worryingly slow. Perhaps, the most outstanding problem with the biology of AD is the question of its mechanistic origins, that is, it remains unclear wherein the molecular failures occur that underlie the disease. We demonstrate how molecular biomarkers could help define the nature of AD in terms of the early biochemical events that correlate with disease progression. We use a novel panel of biomolecules that appears in cerebrospinal fluid of AD patients. As changes in the relative abundance of these molecular markers are associated with progression to AD from mild cognitive impairment, we make the assumption that by tracking their origins we can identify the biochemical conditions that predispose their presence and consequently cause the onset of AD. We couple these protein markers with an analysis of a series of genetic factors and together this hypothesis essentially allows us to redefine AD in terms of the molecular pathways that underlie the disease.

Vitamin D2-enriched button mushroom (Agaricus bisporus) improves memory in both wild type and APPswe/PS1dE9 transgenic mice

Vitamin D deficiency is widespread, affecting over 30% of adult Australians, and increasing up to 80% for at-risk groups including the elderly (age>65). The role for Vitamin D in development of the central nervous system is supported by the association between Vitamin D deficiency and incidence of neurological and psychiatric disorders including Alzheimer's disease (AD). A reported positive relationship between Vitamin D status and cognitive performance suggests that restoring Vitamin D status might provide a cognitive benefit to those with Vitamin D deficiency. Mushrooms are a rich source of ergosterol, which can be converted to Vitamin D2 by treatment with UV light, presenting a new and convenient dietary source of Vitamin D2. We hypothesised that Vitamin D2-enriched mushrooms (VDM) could prevent the cognitive and pathological abnormalities associated with dementia. Two month old wild type (B6C3) and AD transgenic (APPSwe/PS1dE9) mice were fed a diet either deficient in Vitamin D2 or a diet which was supplemented with VDM, containing 1±0.2 µg/kg (∼54 IU/kg) vitamin D2, for 7 months. Effects of the dietary intervention on memory were assessed pre- and post-feeding. Brain sections were evaluated for amyloid β (Aβ) plaque loads and inflammation biomarkers using immuno-histochemical methods. Plasma vitamin D metabolites, Aβ40, Aβ42, calcium, protein and cholesterol were measured using biochemical assays. Compared with mice on the control diet, VDM-fed wild type and AD transgenic mice displayed improved learning and memory, had significantly reduced amyloid plaque load and glial fibrillary acidic protein, and elevated interleukin-10 in the brain. The results suggest that VDM might provide a dietary source of Vitamin D2 and other bioactives for preventing memory-impairment in dementia. This study supports the need for a randomised clinical trial to determine whether or not VDM consumption can benefit cognitive performance in the wider population.

Oral glucose loading modulates plasma β-amyloid level in alzheimer's disease patients: potential diagnostic method for Alzheimer's disease

BACKGROUND

Although plasma β-amyloid (Aβ) has been suggested to be a noninvasive diagnostic biomarker for Alzheimer's disease (AD), its significance and validity have been inconclusive. Thus, it is quite important to establish a novel diagnostic method related to plasma Aβ.

METHODS

As our previous animal studies demonstrated a relation of glucose with plasma Aβ, we examined the effect of glucose loading on plasma Aβ levels in AD patients. After fasting, an oral glucose load was administered to AD patients and non-AD dementia patients, and subsequently, blood glucose, plasma insulin, and plasma Aβ levels were measured.

RESULTS

The plasma levels of baseline blood glucose, plasma insulin, and plasma Aβ were not different between the two groups. However, immediately after glucose loading, a significant increase in plasma Aβ40 and Aβ42 levels was observed in AD patients, whereas a mild decrease in plasma Aβ40 and Aβ42 levels was detected in non-AD dementia patients.

CONCLUSION

The present study clearly demonstrated a different response in plasma Aβ40 and Aβ42 levels after glucose loading between AD and non-AD dementia patients, which is consistent with our previous animal studies. These findings suggest a novel diagnostic tool for AD using the elevation of plasma Aβ level after glucose loading, although further studies are necessary.

Potential blood biomarker for disease severity in the Taiwanese population with Alzheimer's disease

The identification of blood biomarkers for Alzheimer's disease (AD) could contribute for improvement in early diagnosis. To define AD biomarkers, we compared serum/plasma levels of amyloid β (Aβ), tau, cytokines, and biometals between AD and non-AD groups. Cognitive impairment was assessed by Mini-Mental Status Examination (MMSE) and Clinical Dementia Rating scales. Plasma concentrations of total Aβ, Aβ(42), tumor necrosis factor α (TNF-α), and interleukin 6 were quantified by immunoassays. Serum biometal concentrations were determined using flame atomic absorption spectrometry. We found that serum zinc (Zn) was lower in patients with AD. After controlling for age, the MMSE score correlated with both TNF-α and total Aβ levels in the AD group, while the MMSE score correlated with iron only in the non-AD group. Our finding that blood Zn, TNF-α, and total Aβ are possible biomarkers for AD diagnosis and prognosis validates the pervious publication on potential biomarker in the Taiwanese population.

Plasma neopterin level as a marker of peripheral immune activation in amnestic mild cognitive impairment and Alzheimer's disease

OBJECTIVE

Alterations of the immune system play important roles in Alzheimer's disease (AD). The primary purpose of this study was to compare the plasma levels of neopterin, a marker of cellular immune activity, in amnestic mild cognitive impairment (aMCI), early (mild to moderate) AD, and cognitively normal controls. In addition, the correlation of plasma neopterin with interferon-gamma (IFN-γ) and interleukin-6 (IL-6) was also examined.

METHODS

Plasma samples from patients with mild-to-moderate AD (N = 34), aMCI (N = 27), and cognitively normal controls (N = 30) were obtained from the Johns Hopkins Alzheimer's Disease Research Center. Plasma neopterin, IFN-γ, and IL-6 levels were measured using commercially available ELISAs. Multiple linear regression was performed to study differences in the baseline neopterin levels between normal, aMCI, and AD patients. Pearson correlation coefficients were estimated for neopterin and IFN-γ and IL-6 levels. All analyses were conducted using SAS (SAS Institute, Inc., Cary, NC) and GraphPad Prism version 5.00 for Window (GraphPad Software, San Diego, CA, USA).

RESULTS

AD subjects had significantly higher neopterin values compared with aMCI (β = 0.202, p = 0.004) and normal (β = 0.263, p = 0.0004) subjects. There was no statistically significant difference between normal and aMCI subjects. Significant associations between neopterin and IFN-γ (r = 0.41, p < 0.0001) and IL-6 (r = 0.35, p = 0.0006) levels were found.

CONCLUSIONS

Our study demonstrates that peripheral immune response may be stronger in later stages of AD pathophysiology, when dementia has developed.

Meta-analysis of plasma amyloid-β levels in Alzheimer's disease

Plasma amyloid-β (Aβ) levels have been proposed as biomarkers of Alzheimer's disease (AD), but studies have produced inconsistent results. We present a meta-analytic review of cross-sectional studies that examined plasma Aβ levels in AD and cognitively normal subjects, and longitudinal studies that used baseline plasma Aβ levels to predict conversion from normal cognition to AD. Medline and EMBASE databases were searched to generate an initial list of relevant studies, and selected authors approached for additional data. Twelve cross- sectional studies (n = 1483) and seven longitudinal (n = 3920) met the inclusion criteria for meta-analysis. Random effects model was used to calculate the weighted mean difference (WMD) by Review Manager Version 4.2. In longitudinal studies, cognitively normal individuals who converted to AD had higher baseline Aβ1-40 and Aβ1-42 levels (WMD: 10.29, z = 3.80, p = 0.0001 and WMD: 8.01, z = 2.76, p = 0.006, respectively), and non-significantly increased Aβ1-42/Aβ1-40 ratio (WMD: 0.03, z = 1.65, p = 0.10). In cross sectional studies, compared to cognitively normal individuals, AD patients had marginally but non-significantly lower Aβ1-42 levels (WMD:-2.84, z = 1.73, p = 0.08), but Aβ1-40 levels were not significantly different (WMD: 3.43, z = 0.40, p = 0.69). Our systematic review suggests a model of differential longitudinal changes in plasma Aβ levels in cognitively stable individuals versus those who go on to develop AD dementia. Baseline Aβ1-40 and Aβ1-42 levels in cognitively normal elderly individuals might be predictors of higher rates of progression to AD, and should be further explored as potential biomarkers.

BACE1 as a potential biomarker for Alzheimer's disease

The diagnosis of Alzheimer's disease (AD) relies principally on clinical criteria for probable and possible AD as defined by the NINCDS-ADRDRA. The field is desperately lacking of biological markers to assist with AD diagnosis and verification of treatment efficacy. According to the Consensus Report of the Working Group on Molecular and Biochemical Markers of Alzheimer's Disease, in order to qualify as a biomarker the sample in question must adhere to certain basic requirements, including the ability to: reflect AD pathology and differentiate it from other dementia with an 80% sensitivity; be reliable and reproducible; be easy to perform and analyze; remain relatively inexpensive. Beta secretases are crucial enzymes in the pathogenesis of AD. Given its primary role in brain amyloidogenesis and its ubiquitous expression, one may consider measuring peripheral BACE1 levels and activity as biomarkers of AD, like performed in the brain and cerebrospinal fluid. However, very little is known about the periphery and whether peripheral BACE1 is involved in AD pathogenesis or mirrors AD progression. Moreover, no investigation has focused on the possibility of monitoring peripheral BACE1 to assess the efficiency of BACE1 inhibitors during the course of clinical trials. Part of the problem may be attributed to the lack of sensitive molecular tools which are absolutely necessary to use BACE1 as a biomarker. In this review we evaluate the progress and feasibility of developing BACE1 as a biomarker for AD in different tissues.

Biomarkers in Alzheimer's disease drug development

Developing new therapies for Alzheimer's disease (AD) is critically important to avoid the impending public health disaster imposed by this common disorder. Means must be found to prevent, delay the onset, or slow the progression of AD. These goals will be achieved by identifying disease-modifying therapies and testing them in clinical trials. Biomarkers play an increasingly important role in AD drug development. In preclinical testing, they assist in decisions to develop an agent. Biomarkers in phase I provide insights into toxic responses and drug metabolism and in Phase II proof-of-concept trials they facilitate go/no-go decisions and dose finding. Biomarkers can play a role in identifying presymptomatic patients or specific patient subgroups. They can provide evidence of target engagement before clinical changes can be expected. Brain imaging can serve as a primary outcome in Phase II trials and as a key secondary outcome in Phase III trials. Magnetic resonance imaging is currently best positioned for use in large multicenter clinical trials. Cerebrospinal fluid (CSF) measures of amyloid beta protein (Aβ), tau protein, and hyperphosphorylated tau (p-tau) protein are sensitive and specific to the diagnosis of AD and may serve as inclusion criteria and possibly as outcomes in clinical trials targeting relevant pathways. Plasma measures of Aβ are of limited diagnostic value but may provide important information as a measure of treatment response. A wide variety of measures of detectable products of cellular processes are being developed as possible biomarkers accessible in the cerebrospinal fluid and plasma or serum. Surrogate markers that can function as outcomes in pivotal trials and reliably predict clinical outcomes are needed to facilitate primary prevention trials of asymptomatic persons where clinical measures may be of limited value. Fit-for-purpose biomarkers are increasingly available to guide AD drug development decisions.

Neurodegenerative processes in Alzheimer’s disease: an overview of pathogenesis with strategic biomarker potential

Since Alzheimer’s disease (AD) is the leading cause of senile dementia in the USA, affecting 15% of people over the age of 65 years and almost 50% of those aged over 85 years, the need for an adequate and early diagnosis as well as preventative measure against disease onset and progression is increasing. Epidemiological and molecular studies suggest that AD has multiple etiologies, including genetic mutations, genetic variations affecting susceptibility and environmental factors. All these aspects can promote the formation and the accumulation of insoluble amyloid-β and hyperphosphorylated tau. Since the disease is multifactorial and clinical diagnosis is highly exclusive, the need for a sensitive, specific and reliable biomarker for the disease is crucial. While amyloid and amyloid-related compounds may be useful biomarkers in the early diagnosis of AD, the multitude of other characteristic features of AD presented in this article may be similarly appropriate. For example, genetic mutations play a role in a subset of AD patients (often with early disease onset and more severe disease progression), and genetic analysis could thus play a role in disease diagnosis. Similarly, oxidative damage to various proteins, nucleic acids and other cellular compounds, probably arising from mitochondrial abnormalities, is found early in the disease and may provide certain biochemical signatures of disease. Ultimately, specific assays for genetic, protein and oxidative profiles and mitochondrial abnormalities, as well as those for amyloid-β and its immunological response, may serve as a relevant group of biomarkers that could be informative to individuals regarding risk of disease, as well as for indicators of the progression of disease. Correspondingly, new developments in treatment options will probably be available.

Comparison of conventional ELISA with electrochemiluminescence technology for detection of amyloid-β in plasma

Plasma amyloid-β (Aβ) level could be useful as a non-invasive biomarker in Alzheimer's disease research. We compared a multiplex electrochemiluminescence detection method with a well established ELISA method for plasma Aβ quantification. Compared to the ELISA method, the electrochemiluminescence detection method demonstrates a statistically significant, but modest correlation. The reasons for this may include the differences in the affinities of antibodies, and purity and source of Aβ peptides used as standards. However, the advantages of electrochemiluminescence detection technology include short processing time and small sample volume. This comparison demonstrates the need for a further study in optimizing this system.

Plasma beta-amyloid as potential biomarker of Alzheimer disease: possibility of diagnostic tool for Alzheimer disease

Alzheimer disease (AD), which is characterized by progressive cognitive and behavioral deficit, is the most common form of dementia. The incidence of AD is increasing at an alarming rate, and has become a major public health concern in many countries. It is well known that the onset of AD is preceded by a long preclinical period. It is thus critical to establish diagnostic biomarkers that can predict the risk of developing AD prior to clinical manifestation of dementia, for effective prevention and early intervention. With the emergence of potential promising approaches to treat AD targeting the beta-amyloid (Abeta) pathway, such as gamma-secretase inhibitors and vaccine therapy, there is an urgent need for such diagnostic markers. Although cerebrospinal fluid (CSF) Abeta and tau protein levels are candidate biomarkers for AD, the invasive sampling procedure with associated complications limits their use in routine clinical practice. Plasma Abeta has been suggested as an inexpensive and non-invasive biomarker for AD. Although most previous cross-sectional studies on plasma Abeta level in humans failed to show a significant difference between individuals with AD compared to healthy older adults, many strategies are under investigation to improve the diagnostic potential of plasma Abeta. One promising approach is to modify the plasma Abeta level using some potential modulators. It is possible that a difference in plasma Abeta level might be unmasked by evaluating the response to stimulation by a modulator. Anti-Abeta antibody and Abeta binding proteins have been reported to be such modulators of plasma Abeta. In addition, the glucometabolic or hormonal status appears to modulate the plasma Abeta level. Our recent study has shown the possibility that glucose loading could be a novel simple strategy to modulate the plasma Abeta level, making it better suited for early diagnosis. This review summarizes the utility and limitations of current biomarkers of AD and discusses future strategies to improve the diagnostic potential of plasma Abeta.

Biomarkers in Alzheimer's disease: past, present and future

Epidemiological and molecular studies suggest that Alzheimer's disease (AD) has multiple etiologies including genetic mutations, genetic variations affecting susceptibility and environmental factors. These aspects can promote the formation and accumulation of insoluble amyloid-beta and hyperphosphorylated tau. Since the disease is multifactorial and clinical diagnosis is highly exclusive, the need for a sensitive, specific and reliable biomarker is crucial. The concept of a biomarker implies sensitivity and specificity relative to the condition being considered. For clinical practice, AD diagnosis has been based on adherence to clinical criteria such as the NINCDS/ADRDA and DSM-IV. A more recent set of diagnostic criteria proposed incorporates imaging findings into the diagnosis of AD. In this article, we consider the most studied candidates or group of candidates for AD biomarkers, including pathological processes and proteins (amyloid-beta, tau, oxidative stress, mitochondrial/metabolic changes and cell-cycle processes), or autoantibodies thereto, as well as genetic factors.

Soluble amyloid-beta, effect on cerebral arteriolar regulation and vascular cells

Background

Evidence indicates that soluble forms of amyloid-β (Aβ) are vasoactive, which may contribute to cerebrovascular dysfunction noted in patients with Alzheimer's Disease and cerebral amyloid angiopathy. The effects of soluble Aβ on penetrating cerebral arterioles - the vessels most responsible for controlling cerebrovascular resistance - have not been studied.

Results

Freshly dissolved Aβ_1-40 and Aβ_1-42, but not the reverse peptide Aβ_40-1 constricted isolated rat penetrating arterioles and diminished dilation to adenosine tri-phosphate (ATP). Aβ_1-42 also enhanced ATP-induced vessel constriction. Aβ_1-40 diminished arteriolar myogenic response, and an anti-Aβ antibody reduced Aβ_1-40 induced arteriolar constriction. Prolonged Aβ exposure in vessels of Tg2576 mice resulted in a marked age-dependent effect on ATP-induced vascular responses. Vessels from 6 month old Tg2576 mice had reduced vascular responses whereas these were absent from 12 month old animals. Aβ_1-40 and Aβ_1-42 acutely increased production of reactive oxygen species (ROS) in cultured rat cerebro-microvascular cells. The radical scavenger MnTBAP attenuated this Aβ-induced oxidative stress and Aβ_1-40-induced constriction in rat arterioles.

Conclusions

Our results suggest that soluble Aβ_1-40 and Aβ_1-42 directly affect the vasomotor regulation of isolated rodent penetrating arterioles, and that ROS partially mediate these effects. Once insoluble Aβ deposits are present, arteriolar reactivity is greatly diminished.

Dissociated amyloid-beta antibody levels as a serum biomarker for the progression of Alzheimer's disease: a population-based study

With an ever growing population of aged individuals who are at risk of developing Alzheimer disease (AD), there is an urgent need for a sensitive, specific, and preferably non-invasive diagnostic standard of disease progression. Mainstream thinking suggests that early intervention is key to maximizing the opportunity for a successful treatment regimen in AD and, as such, an early and accurate means of diagnosis is essential. In this study, we applied a recently described antibody-antigen dissociation technique to samples obtained as part of a population-based analysis of the prevalence of AD. Stratified sampling and random selection strategies were combined to obtain a representative population for screening of individuals older than 55 years. Serum antibodies to amyloid-beta (Abeta)(1-42) were measured before and after antigen dissociation. The difference between the two measurements was indicated as the dissociation delta (Delta). Our analyses showed that the levels of dissociated antibody in AD patients were always significantly different from controls and that levels of Abeta antibody after dissociation, but not those of non-dissociated antibody, correlated negatively (p<0.05) with both duration of the disease and age in the AD patients. Moreover, the change in concentration of Abeta antibody from pre- to post-dissociation (i.e., the dissociation Delta) directly reflected the progression of AD in terms of both time since diagnosis and age of the patients, with a lower dissociation Delta indicating a more advanced stage of AD. Ultimately, these data suggest that dissociated Abeta antibody levels are of significant diagnostic value at the onset of the neurodegenerative process and, thereafter, may be a useful biomarker for disease progression.

Elevation of plasma beta-amyloid level by glucose loading in Alzheimer mouse models

With the emergence of a promising approach to treat Alzheimer disease (AD) targeting the beta-amyloid (Abeta) pathway, it is necessary to establish new diagnostic biomarkers that enable the antemortem diagnosis of AD. Although plasma Abeta has been suggested as a non-invasive biomarker, its significance has been inconclusive. Thus, it is important to improve the diagnostic potential of plasma Abeta. One of the potential approaches is to modify plasma Abeta level using various modulators. In this study, we evaluated the influence of glucometabolic status on plasma Abeta level in two lines of AD transgenic mouse. The present study demonstrated that plasma Abeta level rapidly increased after glucose loading. More importantly, the magnitude of the increase in plasma Abeta was significantly larger in AD transgenic mice than in wild-type littermates. These findings might provide a novel diagnostic tool for AD using the elevation of plasma Abeta level after glucose loading.