A systematic review and meta-analysis of plasma amyloid 1-42 and tau as biomarkers for Alzheimer's disease

Tau: a biomarker of Huntington's disease

Developing effective treatments for patients with Huntington's disease (HD)-a neurodegenerative disorder characterized by severe cognitive, motor and psychiatric impairments-is proving extremely challenging. While the monogenic nature of this condition enables to identify individuals at risk, robust biomarkers would still be extremely valuable to help diagnose disease onset and progression, and especially to confirm treatment efficacy. If measurements of cerebrospinal fluid neurofilament levels, for example, have demonstrated use in recent clinical trials, other proteins may prove equal, if not greater, relevance as biomarkers. In fact, proteins such as tau could specifically be used to detect/predict cognitive affectations. We have herein reviewed the literature pertaining to the association between tau levels and cognitive states, zooming in on Alzheimer's disease, Parkinson's disease and traumatic brain injury in which imaging, cerebrospinal fluid, and blood samples have been interrogated or used to unveil a strong association between tau and cognition. Collectively, these areas of research have accrued compelling evidence to suggest tau-related measurements as both diagnostic and prognostic tools for clinical practice. The abundance of information retrieved in this niche of study has laid the groundwork for further understanding whether tau-related biomarkers may be applied to HD and guide future investigations to better understand and treat this disease.

Methodological flaws in"diagnostic accuracy of blood biomarkers for Alzheimer's disease and amnestic mild cognitive impairment: A meta-analysis"

We read with interest the review by Chen et al. They intended to examine the diagnostic accuracy of blood-based biomarkers for detecting Alzheimer's disease and amnestic mild cognitive impairment. We believe that there were substantial methodological flaws in their meta-analysis. These methodological flaws included no comprehensive literature search details, neglect of the negative result research, no prespecified cut-off values, erroneous data input in their meta-analysis, and the issue of prevalence determined by the included studies. These factors potentially contributed to overestimation of the discriminative accuracy of blood-based biomarkers. Subsequently, the conclusion that blood-based biomarkers are effective tools for detecting Alzheimer's disease is debatable without correction of these methodological flaws and providing robust and trustworthy estimates.

Advances in sample preparation and HPLC-MS/MS methods for determining amyloid-β peptide in biological samples: a review

Alzheimer's disease (AD), a neurological disorder, is a major public health concern and the most common form of dementia. Its typical symptoms include memory loss, confusion, changes in personality, and cognitive impairment, which result in patients gradually losing independence. Over the last decades, some studies have focused on searching for effective biomarkers as early diagnostic indicators of AD. Amyloid-β (Aβ) peptides have been consolidated as reliable AD biomarkers and have been incorporated into modern diagnostic research criteria. However, quantitative analysis of Aβ peptides in biological samples remains a challenge because both the sample and the physical-chemical properties of these peptides are complex. During clinical routine, Aβ peptides are measured in the cerebrospinal fluid by immunoassays, but the availability of a specific antibody is critical-in some cases, an antibody may not exist, or its specificity may be inadequate, leading to low sensitivity and false results. HPLC-MS/MS has been reported as a sensitive and selective method for determining different fragments of Aβ peptides in biological samples simultaneously. Developments in sample preparation techniques (preconcentration platforms) such as immunoprecipitation, 96-well plate SPME, online SPME, and fiber-in-tube SPME have enabled not only effective enrichment of Aβ peptides present at trace levels in biological samples, but also efficient exclusion of interferents from the sample matrix (sample cleanup). This high extraction efficiency has provided MS platforms with higher sensitivity. Recently, methods affording LLOQ values as low as 5 pg mL^-1 have been reported. Such low LLOQ values are adequate for quantifying Aβ peptides in complex matrixes including cerebrospinal fluid (CSF) and plasma samples. This review summarizes the advances in mass spectrometry (MS)-based methods for quantifying Aβ peptides and covers the period 1992-2022. Important considerations regarding the development of the HPLC-MS/MS method such as the sample preparation step, optimization of the HPLC-MS/MS parameters, and matrix effects are described. Clinical applications, difficulties related to analysis of plasma samples, and future trends of these MS/MS-based methods are also discussed.

Evaluation of Cognitive and Physical Function Among Older Adults by Their Physical Activity: A Cross-Sectional Kasama Study, Japan

BACKGROUND

The amyloid-β1-42 (Aβ42) level is a biomarker that is widely used to evaluate individual cognitive dysfunction early in neurodegenerative diseases, as well as differentiate between normal cognitive function, mild cognitive impairment, Alzheimer's disease, and vascular cognitive impairment.

OBJECTIVE

Our cross-sectional study evaluated the association between daily exercise and physical and cognitive function and Aβ42 levels among a subsample of 325 older adults from the Kasama Study.

METHODS

Participants (age: 74.5 [range 65-90] years) were classified into three exercise groups: the dual-task (DEG, n = 128), single-task (SEG, n = 122), and non-exercise (NEG, n = 75) groups. The main outcomes were the plasma Aβ42 levels and the scores of the five cognitive (5-COG) tests and five cognition-related physical function (5-PHYS) tests.

RESULTS

The Aβ42 levels and 5-COG and 5-PHYS scores were higher in the SEG and DEG than in the NEG. The Aβ42 levels were higher in the DEG than in the NEG (p = 0.008).

CONCLUSIONS

Physical activities such as regular exercise may benefit older adults, improving their cognitive and physical function.

Western Agarose Native GeELution (WANGEL) with beta-amyloid and tau: Novel method to elute proteins or peptides using native agarose gels followed by Lumipulse assay

Alzheimer´s disease is characterized by hyperphosphorylated tau neurofibrillary tangles and beta-amyloid plaques. Both molecules can be easily measured in human fluids or tissue extracts by immunoassays. However, the different molecular weight species can only be differentiated on Western Blot gels. Analysis of native proteins from polyacrylamide gels is also not well characterized. Hence, we developed a modified method to elute proteins or peptides from native agarose gels. Initially, full-length tau (60 kDa) and beta-amyloid(42) (4 kDa) were separated on a Western Blot gel and eluted from native agarose gels (WANGEL) using an elution system inside a polypropylene tube. The eluates were analyzed with the Lumipulse immunoassay. Both molecules were successfully eluted into 1% agarose gels to the cathode and were detected in the eluate. Additionally, tau was eluted from mouse cortical extracts, but was below the detection limit when eluted from human cerebrospinal fluid. Beta-amyloid(40) was eluted from CSF extracts and detected by Lumipulse. In cortical extracts taken from transgenic mice (APP_SweDI) beta-amyloid(42) was detectable as a native peptide and small oligomeric aggregates. Taken together, our novel WANGEL method enables fast, easy and cheap elution of protein/peptides from polyacrylamide/agarose gels with a subsequent analysis by Lumipulse immunoassay.

Three bullet points:•

Beta-amyloid and tau are major hallmarks in Alzheimer´s disease and are established cerebrospinal fluid biomarkers.

•

Lumipulse is a method to measure beta-amyloid and tau in cerebrospinal fluid in the pg/mL range.

•

Western Blot and our novel combined native agarose method (WANGEL) allows an easy and fast determination of the molecular size in combination with Lumipulse.

Amylin and Secretases in the Pathology and Treatment of Alzheimer's Disease

Alzheimer’s disease remains a prevailing neurodegenerative condition which has an array physical, emotional, and financial consequences to patients and society. In the past decade, there has been a greater degree of investigation on therapeutic small peptides. This group of biomolecules have a profile of fundamentally sound characteristics which make them an intriguing area for drug development. Among these biomolecules, there are four modulatory mechanisms of interest in this review: alpha-, beta-, gamma-secretases, and amylin. These protease-based biomolecules all have a contributory role in the amyloid cascade hypothesis. Moreover, the involvement of various biochemical pathways intertwines these peptides to have shared regulators (i.e., retinoids). Further clinical and translational investigation must occur to gain a greater understanding of its potential application in patient care. The aim of this narrative review is to evaluate the contemporary literature on these protease biomolecule modulators and determine its utility in the treatment of Alzheimer’s disease.

Glucose-lowering drugs, cognition, and dementia: The clinical evidence

Type 2 diabetes mellitus (T2DM) is an important risk factor for dementia. The possibility to mitigate this risk by controlling T2DM is compelling; however, different glucose-lowering drugs have different effects on the brain by virtue of their different mechanisms of action. The clinical and epidemiological data appear mixed, warranting careful critical evaluation of the human studies. Here we examine the evidence in the context of dementia prevention and treatment, both for people with and without T2DM. We discuss the evidence on this scaffold of research directions, identifying methodological complexities in the extant literature (e.g. comparator discrepancies, changes in the therapeutic landscape), and the implications of different outcome measures (e.g. neuropsychological). We consider possible implications of cerebrovascular protection vs. effects on progression of neurodegenerative proteinopathy, and we present a research roadmap for glucose-lowering drugs in cognitive neurology, including neuroimaging, and fluid biomarkers. We conclude that there is great potential to advance personalized strategies to prevent and treat dementia with glucose-lowering drugs.

Traditional East Asian Herbal Medicine Treatment for Alzheimer's Disease: A Systematic Review and Meta-Analysis

Alzheimer's disease (AD) is a leading progressive neurodegenerative disease worldwide, and its treatment is a challenging clinical problem. This review was conducted to evaluate the efficacy and safety of herbal medicine for AD treatment. The PubMed, CENTRAL, EMBASE, CNKI, OASIS, KTKP, and CiNii databases were searched until June 2020 for randomized controlled trials (RCTs) on herbal medicine for AD, and a meta-analysis of 57 RCTs was conducted. For cognitive function, herbal medicine significantly improved the Mini-Mental State Examination (MMSE) and AD Assessment Scale-Cognitive Subscale (ADAS-cog) scores compared with conventional medicine. The MMSE scores showed no significant difference between the groups treated with herbal medicine and donepezil; however, herbal medicine significantly lowered the ADAS-cog score. Acori Graminei Rhizoma-containing and Cnidii Rhizoma-containing herbal medicine significantly improved the MMSE and ADAS-cog scores compared with conventional medicine. Ginseng Radix-containing herbal medicine showed a positive, but not statistically significant, tendency toward improving the MMSE score compared with conventional medicine. Herbal medicine with conventional medicine significantly improved the MMSE, ADAS-cog, and Montreal Cognitive Assessment (MoCA) scores compared with conventional medicine, and herbal medicine with donepezil also significantly improved these scores compared with donepezil. Acori Graminei Rhizoma or Cnidii Rhizoma-containing herbal medicine with conventional medicine significantly improved the MMSE and ADAS-cog scores compared with conventional medicine. Ginseng Radix-containing herbal medicine + conventional medicine significantly improved the MMSE score, but not the ADAS-cog score, compared with conventional medicine. For behavioral and psychological symptoms of dementia, the Neuropsychiatry Inventory (NPI) score was not significantly different between herbal and conventional medicines. Herbal medicine with conventional medicine significantly improved the NPI and Behavioral Pathology in Alzheimer's Disease Rating Scale scores compared with conventional medicine. The NPI score showed no significant difference between the groups treated with herbal medicine and placebo. Furthermore, herbal medicine with conventional medicine significantly lowered plasma amyloid beta levels compared with conventional medicine alone. Herbal medicine, whether used alone or as an adjuvant, may have beneficial effects on AD treatment. However, owing to the methodological limitations and high heterogeneity of the included studies, concrete conclusions cannot be made.

Out with the old, in with the new: Could plasma exchange be used to fill a therapeutic gap in neurology?

The global tally of neurological disorders is exponentially rising and yet effective therapies for most remain evasive. There is a great deal of research into novel small molecules, immunotherapies and gene therapies to fill this therapeutic gap. We believe greater focus on plasma exchange as a research and clinical tool may provide useful insight into pathological mechanisms and effective treatment strategies. Plasma exchange has been traditionally used to treat antibody-mediated neurological diseases, such as myasthenia gravis and neuromyelitis optica, but there could be much wider future potential uses in neurology. Plasma exchange is not antibody specific, as it also removes a variety of other plasma-soluble factors, including age-related and disease-associated neurotoxic proteins, such as fibrinogen and amyloid. As research develops into the role of blood-brain barrier and immunological alterations in diseases not typically regarded as immune-driven, interest in neurotoxic plasma proteins grows. Here, we highlight that plasma exchange may have uses outside of antibody-mediated neurological diseases, by removing neurotoxic proteins from the systemic circulation.

Performance of the plasma Aβ42/Aβ40 ratio, measured with a novel HPLC-MS/MS method, as a biomarker of amyloid PET status in a DPUK-KOREAN cohort

Background

We assessed the feasibility of plasma Aβ42/Aβ40 determined using a novel liquid chromatography-mass spectrometry method (LC-MS) as a useful biomarker of PET status in a Korean cohort from the DPUK Study.

Methods

A total of 580 participants belonging to six groups, Alzheimer’s disease dementia (ADD, n = 134), amnestic mild cognitive impairment (aMCI, n = 212), old controls (OC, n = 149), young controls (YC, n = 15), subcortical vascular cognitive impairment (SVCI, n = 58), and cerebral amyloid angiopathy (CAA, n = 12), were included in this study. Plasma Aβ40 and Aβ42 were quantitated using a new antibody-free, LC-MS, which drastically reduced the sample preparation time and cost. We performed receiver operating characteristic (ROC) analysis to develop the cutoff of Aβ42/Aβ40 and investigated its performance predicting centiloid-based PET positivity (PET+).

Results

Plasma Aβ42/Aβ40 were lower for PET+ individuals in ADD, aMCI, OC, and SVCI (p < 0.001), but not in CAA (p = 0.133). In the group of YC, OC, aMCI, and ADD groups, plasma Aβ42/Aβ40 predicted PET+ with an area under the ROC curve (AUC) of 0.814 at a cutoff of 0.2576. When adding age, APOE4, and diagnosis, the AUC significantly improved to 0.912.

Conclusion

Plasma Aβ42/Aβ40, as measured by this novel LC-MS method, showed good discriminating performance based on PET positivity.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13195-021-00911-7.

Change in the plasma proteome associated with canine cognitive dysfunction syndrome (CCDS) in Thailand

BACKGROUND

Canine cognitive dysfunction syndrome (CCDS) is a progressive neurodegenerative disorder found in senior dogs. Due to the lack of biological markers, CCDS is commonly underdiagnosed. The aim of this study was to identify potential plasma biomarkers using proteomics techniques and to increase our understanding of the pathogenic mechanism of the disease. Plasma amyloid beta 42 (Aβ₄₂) has been seen to be a controversial biomarker for CCDS. Proteomics analysis was performed for protein identification and quantification.

RESULTS

Within CCDS, ageing, and adult dogs, 87 proteins were identified specific to Canis spp. in the plasma samples. Of 87 proteins, 48 and 41 proteins were changed in the ageing and adult groups, respectively. Several distinctly expressed plasma proteins identified in CCDS were involved in complement and coagulation cascades and the apolipoprotein metabolism pathway. Plasma Aβ₄₂ levels considerably overlapped within the CCDS and ageing groups. In the adult group, the Aβ₄₂ level was low compared with that in the other groups. Nevertheless, plasma Aβ₄₂ did not show a correlation with the Canine Cognitive Dysfunction Rating scale (CCDR) score in the CCDS group (p = 0.131, R² = 0.261).

CONCLUSIONS

Our present findings suggest that plasma Aβ₄₂ does not show potential for use as a diagnostic biomarker in CCDS. The nano-LC-MS/MS data revealed that the predictive underlying mechanism of CCDS was the co-occurrence of inflammation-mediated acute phase response proteins and complement and coagulation cascades that partly functioned by apolipoproteins and lipid metabolism. Some of the differentially expressed proteins may serve as potential predictor biomarkers along with Aβ₄₂ in plasma for improved CCDS diagnosis. Further study in larger population-based cohort study is required in validation to define the correlation between protein expression and the pathogenesis of CCDS.

Pharmacokinetics and Pharmacodynamics of LY2599666, a PEG-Linked Antigen Binding Fragment that Targets Soluble Monomer Amyloid-β

LY2599666 is a humanized, affinity-optimized monoclonal antibody antigen-binding fragment linked to a PEG molecule and targets soluble amyloid-β (Aβ) monomers. This first-in-human dose ascending study assessed pharmacokinetics (PK) (measured as serum free LY2599666 concentration) and pharmacodynamic (PD) effects (measured as plasma total soluble Aβ40 and Aβ42) after a single subcutaneous (SC) dose of 10, 25, 100, and 200 mg LY2599666 in healthy subjects. As LY2599666 binds to multiple soluble Aβ monomers, a two-target mediated drug disposition model (TMDD) was developed to simultaneously fit serum LY2599666 concentration and Aβ monomer levels. Four Alzheimer's disease patients completed 25 mg once-weekly dosing of LY2599666 for 12 weeks. In addition, single cerebrospinal fluid samples were collected to assess penetration capability across the blood-brain barrier. PK and PD data collected from the multiple dose cohort aligned with model predictions, suggesting the established TMDD model predicted suppression of soluble Aβ40 and Aβ42 in plasma after SC dosing of LY2599666.

Evidence-based umbrella review of 162 peripheral biomarkers for major mental disorders

The literature on non-genetic peripheral biomarkers for major mental disorders is broad, with conflicting results. An umbrella review of meta-analyses of non-genetic peripheral biomarkers for Alzheimer's disease, autism spectrum disorder, bipolar disorder (BD), major depressive disorder, and schizophrenia, including first-episode psychosis. We included meta-analyses that compared alterations in peripheral biomarkers between participants with mental disorders to controls (i.e., between-group meta-analyses) and that assessed biomarkers after treatment (i.e., within-group meta-analyses). Evidence for association was hierarchically graded using a priori defined criteria against several biases. The Assessment of Multiple Systematic Reviews (AMSTAR) instrument was used to investigate study quality. 1161 references were screened. 110 met inclusion criteria, relating to 359 meta-analytic estimates and 733,316 measurements, on 162 different biomarkers. Only two estimates met a priori defined criteria for convincing evidence (elevated awakening cortisol levels in euthymic BD participants relative to controls and decreased pyridoxal levels in participants with schizophrenia relative to controls). Of 42 estimates which met criteria for highly suggestive evidence only five biomarker aberrations occurred in more than one disorder. Only 15 meta-analyses had a power >0.8 to detect a small effect size, and most (81.9%) meta-analyses had high heterogeneity. Although some associations met criteria for either convincing or highly suggestive evidence, overall the vast literature of peripheral biomarkers for major mental disorders is affected by bias and is underpowered. No convincing evidence supported the existence of a trans-diagnostic biomarker. Adequately powered and methodologically sound future large collaborative studies are warranted.

Plasma levels of Interleukin 18 but not amyloid-β or Tau are elevated in female depressive patients

BACKGROUND

Depression is associated with inflammation and Alzheimer's disease (AD). However, detailed molecular mechanisms linking mood, neuroinflammation and AD remain unclear. Although changes in peripheral inflammatory factors such as Interleukin 18 (IL18), and AD-associated amyloid-β (Aβ) peptides have been linked to depression, a solid relationship between these factors in depressive disorder has yet to be established. This study aims to further determine whether plasma IL18, Aβ40, Aβ42, and the AD-associated tangle component Tau, as well as IL18 single nucleotide polymorphisms (SNPs) may be biomarkers for depression.

METHODS

We measured plasma IL18, Aβ40, Aβ42, and Tau in 64 depressive patients and 75 healthy controls, and characterized genotypes of three IL18 SNPs (rs187238, rs1946518 and rs1946519) in these subjects. Comparisons between depressive patients and controls were carried out in males, in females or in combination. Regression analyses were conducted to examine the correlation between these parameters.

RESULTS

We found that none of the plasma levels of IL18, Aβ40, Aβ42, and Tau, the ratio of Aβ42/Aβ40, and the genotypes of IL18 SNPs were significantly different between combined depressive patients and combined healthy controls, or between male depressive patients and male controls. However, IL18 levels were less in females than in males in healthy people and were significantly increased in female depressive patients compared to female controls. Moreover, IL18 and standardized IL18 were correlated with standardized Aβ42/Aβ40 ratio and standardized Tau in depressive patients.

CONCLUSIONS

Plasma IL18 may be a potential biomarker for depression in women.

Advance in Plasma AD Core Biomarker Development: Current Findings from Immunomagnetic Reduction-Based SQUID Technology

New super-sensitive biomarker assay platforms for measuring Alzheimer's disease (AD) core pathological markers in plasma have recently been developed and tested. Research findings from these technologies offer promising evidence for identifying the earliest stages of AD and correlating them with brain pathological progression. Here, we review findings using immunomagnetic reduction, one of these ultrasensitive technologies. The principles, technology and assays developed, along with selected published findings will be discussed. The major findings from this technology were significant increases of amyloid beta (Aβ) 42 and total tau (t-tau) levels in subjects clinically diagnosed with early AD when compared with cognitively normal control (NC) subjects. The composite marker of the product of Aβ42 and t-tau discriminated subjects with early AD from NC subjects with high accuracy. The potential of this technology for the purpose of early or preclinical disease stage detection has yet to be explored in subjects who have also been assessed with brain imaging and cerebrospinal fluid AD core biomarker measurements.

Plasma Oligomeric Beta Amyloid in Alzheimer's Disease with History of Agent Orange Exposure

BACKGROUND AND PURPOSE

During the Vietnam War, many Korean soldiers were exposed to Agent Orange. Until now, there existed only limited evidence of association between exposure to Agent Orange and Alzheimer's disease (AD). The main pathological feature of AD is brain amyloidosis. To explore the pathophysiological characteristic of AD with Agent Orange exposure, we compared newly developed amyloid beta (Aβ) oligomer levels in plasma between AD with Agent Orange exposure and without exposure.

METHODS

We recruited 48 AD patients with Agent Orange exposure and 66 AD patients without Agent Orange. Using the Multimer Detection System technique, which was based on an enzyme-linked immunosorbent assay, we measured Aβ oligomers in the plasma of study subjects.

RESULTS

Compared to normal control patients, plasma Aβ oligomer levels were higher in AD patients regardless of history of Agent Orange exposure. However, AD patients with Agent Orange exposure showed higher plasma Aβ oligomer levels than AD patients without Agent Orange.

DISCUSSION

This study showed higher plasma Aβ oligomer levels in AD patients with Agent Orange exposure compared to AD patients without Agent Orange. This finding suggests the possibility of a different pathophysiology of AD patients with Agent Orange exposure from AD patients without Agent Orange.

Two novel blood-based biomarker candidates measuring degradation of tau are associated with dementia: A prospective study

BACKGROUND

Truncated tau appears to be specifically related to disease pathology and recent studies have shown the presence and elevation of several truncated tau species in Cerebrospinal fluid (CSF) of subjects with Alzheimer's disease (AD); however, the relevance of truncated Tau measurements in blood is still being studied.

OBJECTIVE

The aim of the current study was to assess the longitudinal associations between baseline levels of two novel blood biomarker candidates measuring truncated tau, Tau-A and Tau-C, and the risk of incident dementia and AD in elderly women.

METHODS

Using solid phase competitive ELISA, two tau fragments were detected in serum of 5,309 women from the Prospective Epidemiological Risk Factor study. The study was an observational, prospective study of Danish postmenopausal women. Subjects were followed with registry-linkage for up to 15 years (median follow-up time 13.7 years). Cox regression was used to assess the utility of the biomarker candidates in relation to dementia and AD.

RESULTS

High levels of Tau-A and Tau-C (above the median) in blood were associated with lower risk of dementia and AD (Tau-A: Dementia HR[95% CI] = 0.85[0.70-1.04]; AD 0.71[0.52-0.98] and Tau-C: Dementia 0.84[0.70-1.00]; AD 0.78[0.60-1.03]). Tau-C gave a very modest increase in the AUC in a 5-year prediction horizon as compared to a reference model with age and education, while a combination of the two did not improve their predictive capacity.

CONCLUSIONS

Measurement of tau in serum is feasible. The serological tau turnover profile may be related to the diagnosis and development of dementia and AD. The exact processing and profile in serum in relation to cognitive disorders remains to be further assessed to provide simple non-invasive tests to identify subjects with progressive cognitive disorders.

Plasma Aβ analysis using magnetically-labeled immunoassays and PET 18F-florbetapir binding in non-demented patients with major depressive disorder

An increased level of brain amyloid deposition and a decreased level of cerebral spinal fluid (CSF) Aβ42 are currently considered reliable biomarkers of Alzheimer’s disease (AD); however, the usefulness of plasma Aβ levels are not well-established. This study investigated the relationships between plasma Aβ levels and cerebral amyloidosis in 36 non-demented patients with major depressive disorder (MDD). All participants underwent ¹⁸F-florbetapir PET imaging and provided a blood sample at the same time for immunomagnetic reduction assay to measure the plasma levels of Aβ40 and Aβ42. We found inverse associations of the plasma Aβ42 level and the Aβ42/Aβ40 ratio, and a positive association of the plasma Aβ40 level, with cerebral amyloid deposition in the precuneus, parietal and posterior cingulate cortex. Subgroup analyses in subjects with higher ¹⁸F-florbetapir uptake values or MDD with amnestic mild cognitive impairment revealed more pervasive relationships of plasma Aβ measures with ¹⁸F-florbetapir binding across the brain regions examined. The study suggested that regional brain amyloid deposition in terms of ¹⁸F-florbetapir PET uptake had weak-to-moderate associations with plasma Aβ42 and Aβ40 levels, and the Aβ42/Aβ40 ratio. Validation in a larger population of subjects of known cerebral amyloidosis status is needed. Careful interpretation of plasma data is warranted.

Oligomeric forms of amyloid-β protein in plasma as a potential blood-based biomarker for Alzheimer's disease

Background

Soluble amyloid-β (Aβ) oligomers are the major toxic substances associated with the pathology of Alzheimer’s disease (AD). The ability to measure Aβ oligomer levels in the blood would provide simple and minimally invasive tools for AD diagnostics. In the present study, the recently developed Multimer Detection System (MDS) for AD, a new enzyme-linked immunosorbent assay for measuring Aβ oligomers selectively, was used to detect Aβ oligomers in the plasma of patients with AD and healthy control individuals.

Methods

Twenty-four patients with AD and 37 cognitively normal control individuals underwent extensive clinical evaluations as follows: blood sampling; detailed neuropsychological tests; brain magnetic resonance imaging; cerebrospinal fluid (CSF) measurement of Aβ42, phosphorylated tau protein (pTau), and total tau protein (tTau); and ¹¹C-Pittsburgh compound B (PIB) positron emission tomography. Pearson’s correlation analyses between the estimations of Aβ oligomer levels by MDS and other conventional AD biomarkers (CSF Aβ₄₂, pTau, and tTau, as well as PIB standardized uptake value ratio [PIB SUVR]) were conducted. ROC analyses were used to compare the diagnostic performance of each biomarker.

Results

The plasma levels of Aβ oligomers by MDS were higher in patients with AD than in normal control individuals, and they correlated well with conventional AD biomarkers (levels of Aβ oligomers by MDS vs. CSF Aβ₄₂, r = −0.443; PIB SUVR, r = 0.430; CSF pTau, r = 0.530; CSF tTau, r = 0.604). The sensitivity and specificity of detecting plasma Aβ oligomers by MDS for differentiating AD from the normal controls were 78.3% and 86.5%, respectively. The AUC for plasma Aβ oligomers by MDS was 0.844, which was not significantly different from the AUC of other biomarkers (p = 0.250).

Conclusions

Plasma levels of Aβ oligomers could be assessed using MDS, which might be a simple, noninvasive, and accessible assay for evaluating brain amyloid deposition related to AD pathology.

Electronic supplementary material

The online version of this article (doi:10.1186/s13195-017-0324-0) contains supplementary material, which is available to authorized users.

Study on Analysis of Peripheral Biomarkers for Alzheimer's Disease Diagnosis

Many factors are involved in Alzheimer’s disease (AD) pathology including tau phosphorylation, amyloid β protein (Aβ) accumulation, lipid dysregulation, oxidative stress, and inflammation. The markers of these pathological processes in cerebral spinal fluid are used currently for AD diagnosis. However, peripheral biomarkers are the need of the hour for large population screening for AD. The main objective of the present study is to evaluate the peripheral levels of redox markers, lipid peroxidation (LPO) indicators, and pathological markers in AD patients. Blood was collected from AD patients (n = 45), controls (n = 45), and analyzed for pathological markers of AD including Aβ42 and tau, LPO, and redox indicators. Plasma Aβ42 was significantly (P < 0.001) elevated while total tau was decreased in AD compared to controls. Hydroxynonenal (HNE) and malondialdehyde (MDA) were higher (P < 0.001) in AD patients pointing the enhanced LPO in AD pathology. Receiver operating characteristic curve (ROC) analysis indicated that HNE is a better indicator of LPO compared to MDA. Plasma glutathione (GSH) level was significantly (P < 0.001) low while oxidized glutathione (GSSG) level was higher (P < 0.001) in AD patients with corresponding decrease in GSH/GSSG ratio (P < 0.001). ROC analysis indicated that GSH/GSSG ratio can be used as reliable indicator for redox imbalance in AD with a cutoff value of <8.73 (sensitivity 91.1%, specificity 97.8%). Correlation analysis revealed a positive correlation for both HNE and MDA with Aβ42 and a negative correlation with total tau. Negative correlation was observed between GSH/GSSG ratio and LPO markers. While oxidative stress has been implicated in pathology of various neurodegenerative disorders, the present study pinpoints the direct link between LPO and Aβ production in plasma of AD patients. Normally, at low amyloid concentration in body fluids, this peptide shown to function as a strong metal chelating antioxidant. However, when the Aβ production enhanced as in AD, through gain of functional transformation, Aβ evolves into prooxidant, thereby enhancing oxidative stress and LPO. Altered redox status with enhanced LPO observed in AD blood could contribute to the oxidation and S-glutathionylation proteins, which has to be addressed in future studies.

Repetitive head impact exposure and later-life plasma total tau in former National Football League players

Introduction

Blood protein analysis of total tau (t-tau) may be a practical screening biomarker for chronic traumatic encephalopathy (CTE), a neurodegenerative tauopathy associated with repetitive head impact (RHI) exposure. We examined plasma t-tau in symptomatic former National Football League (NFL) players compared with controls and the relationship between RHI exposure and later-life plasma t-tau.

Methods

Ninety-six former NFL players (age 40–69) and 25 same-age controls underwent blood draw to determine plasma t-tau levels. The cumulative head impact index (CHII) quantified RHI exposure. Subjects completed measures of clinical function.

Results

A higher CHII predicted greater plasma t-tau in the former NFL players (P = .0137). No group differences in plasma t-tau emerged, but a concentration ≥3.56 pg/mL was 100% specific to former NFL players. Plasma t-tau did not predict clinical function.

Discussion

Greater RHI exposure predicted higher later-life plasma t-tau concentrations, and further study on plasma t-tau as a candidate screening biomarker for CTE is warranted.