The study of Alzheimer’s disease biomarkers

Alzheimer’s disease (AD) is by far the most common dementing illness of late life and is increasing with the ever-growing number of older adults, in particular, in developed countries. The disease is often referred to as the “Long-Goodbye” because the person with the illness slowly becomes lost to everyone a long time before the body finally gives out. Being able to detect AD earlier on during the course of the disease offers better prospects for the future, for AD individuals, their families and friends as well as on the economy, as a whole. Unfortunately, such a detection technique is not yet, available. However, there are a number of promising biological markers (biomarkers) that correlate well with clinical cognitive tests of individuals and/or postmortem histopathological manifestations of the disease, especially when at least two markers are used for the diagnosis. Biosensors are tools that combine a biochemical binding element to a signal conversion unit and are already being used in the study of some AD biomarkers. However, their use in clinical diagnosis remains a challenge. Introduction of nanotechnology leading to nanobiosensors has several potential advantages over other clinical and/or existing analytical tools, including increased assay speed, flexibility, reduced cost of diagnostic testing, potential to deliver molecular diagnostic tools to family general practitioners, and other health care systems. Even more important, nano-based assays have the potential to detect target proteins at attomolar concentration level. They are, therefore, being increasingly exploited for the detection of early metabolic changes associated with diseases. Because brain damage is irreversible, the use of nanotechnology is particularly important in AD and other neurodegenerative disorders. Nanosensors can also facilitate and enable pointofcare-testing (POCT). This article reviews the basic biochemical processes that lead to AD pathology, current biomarkers for AD, and the current role of nanosensor technology for the study of AD biomarkers. Furthermore, it discusses the huge potential of nanosensing to deliver new molecular diagnostic strategies to AD research.     

The effect of aging on brain barriers and the consequences for Alzheimer’s disease development

Life expectancy has increased in most developed countries, which has led to an increase in the proportion of elderly people in the world’s population. However, this increase in life expectancy is not accompanied by a lengthening of the health span since aging is characterized with progressive deterioration in cellular and organ functions. The brain is particularly vulnerable to disease, and this is reflected in the onset of age-related neurodegenerative diseases such as Alzheimer’s disease. Research shows that dysfunction of two barriers in the central nervous system (CNS), the blood–brain barrier (BBB) and the blood–cerebrospinal fluid (CSF) barrier (BCSFB), plays an important role in the progression of these neurodegenerative diseases. The BBB is formed by the endothelial cells of the blood capillaries, whereas the BCSFB is formed by the epithelial cells of the choroid plexus (CP), both of which are affected during aging. Here, we give an overview of how these barriers undergo changes during aging and in Alzheimer’s disease, thereby disturbing brain homeostasis. Studying these changes is needed in order to gain a better understanding of the mechanisms of aging at the brain barriers, which might lead to the development of new therapies to lengthen the health span (including mental health) and reduce the chances of developing Alzheimer’s disease.     

Mathematical model on Alzheimer’s disease

Background

Alzheimer disease (AD) is a progressive neurodegenerative disease that destroys memory and cognitive skills. AD is characterized by the presence of two types of neuropathological hallmarks: extracellular plaques consisting of amyloid β-peptides and intracellular neurofibrillary tangles of hyperphosphorylated tau proteins. The disease affects 5 million people in the United States and 44 million world-wide. Currently there is no drug that can cure, stop or even slow the progression of the disease. If no cure is found, by 2050 the number of alzheimer’s patients in the U.S. will reach 15 million and the cost of caring for them will exceed $ 1 trillion annually.

Results

The present paper develops a mathematical model of AD that includes neurons, astrocytes, microglias and peripheral macrophages, as well as amyloid β aggregation and hyperphosphorylated tau proteins. The model is represented by a system of partial differential equations. The model is used to simulate the effect of drugs that either failed in clinical trials, or are currently in clinical trials.

Conclusions

Based on these simulations it is suggested that combined therapy with TNF- α inhibitor and anti amyloid β could yield significant efficacy in slowing the progression of AD.

     

A genome-wide association study of Alzheimer’s disease using random forests and enrichment analysis

Alzheimer??s disease (AD) is a serious neurodegenerative disorder and its cause remains largely elusive. In past years, genome-wide association (GWA) studies have provided an effective means for AD research. However, the univariate method that is commonly used in GWA studies cannot effectively detect the biological mechanisms associated with this disease. In this study, we propose a new strategy for the GWA analysis of AD that combines random forests with enrichment analysis. First, backward feature selection using random forests was performed on a GWA dataset of AD patients carrying the apolipoprotein gene (APOE?4) and 1058 susceptible single nucleotide polymorphisms (SNPs) were detected, including several known AD-associated SNPs. Next, the susceptible SNPs were investigated by enrichment analysis and significantly-associated gene functional annotations, such as ??alternative splicing??, ??glycoprotein??, and ??neuron development??, were successfully discovered, indicating that these biological mechanisms play important roles in the development of AD in APOE?4 carriers. These findings may provide insights into the pathogenesis of AD and helpful guidance for further studies. Furthermore, this strategy can easily be modified and applied to GWA studies of other complex diseases.     

A qualitative model for aggregation and diffusion of \beta -amyloid in Alzheimer’s disease

In this paper we present a mathematical model for the aggregation and diffusion of A $\beta $ amyloid in the brain affected by Alzheimer’s disease, at the early stage of the disease. The model is based on a classical discrete Smoluchowski aggregation equation modified to take diffusion into account. We also describe a numerical scheme and discuss the results of the simulations in the light of the recent biomedical literature.     

Elton’s hypothesis revisited: an experimental test using cogongrass

In the 1950s Charles Elton hypothesized that more diverse communities should be less susceptible to invasion by exotic species (biodiversity–invasibility hypothesis). The biodiversity–invasibility hypothesis postulates that species-rich communities are less vulnerable to invasion because vacant niches are less common and the intensity of interspecific competition is more severe. Field studies were conducted at two sites, a logged site and an unlogged site in Santa Rosa County, Florida, U.S.A, to test Elton’s hypothesis using cogongrass (Imperata cylindrica), a non-indigenous grass invading large areas of the Southeastern United States. The logged site was under 17-year-old loblolly pine prior to clear cutting. The unlogged site, a longleaf pine forest, was at the Blackwater River State Forest. Both the logged site and unlogged site showed no significant relationship between the rate of cogongrass spread and native plant species richness, functional richness, and cover of the invaded community. Increased species or functional richness may increase the use of resources; however, the extensive rhizome/root network possessed by cogongrass and its ability to thrive under shade may allow for its persistence in a diverse community. The results from both the logged and unlogged sites do not support the general hypothesis of Elton that invasion resistance and compositional stability increase with diversity. Biodiversity does not appear to be an important factor for cogongrass invasion in the southern United States. Extrinsic factors in this study prevent the ability to draw a defined causal relationship between native plant diversity and invasibility. Underlying reasons for why no relationship was observed may be simply due to the tremendous competitive ability of cogongrass or the narrow range of species richness, functional richness and cover observed in our study.     

Proteomic studies of cerebrospinal fluid biomarkers of Alzheimer’s disease: an update

Introduction: Alzheimer’s disease (AD) is a neurodegenerative disease affecting the brain. Today there are three cerebrospinal fluid (CSF) biomarkers, amyloid-β consisting of 42 amino acids (Aβ42), total-tau (t-tau) and phosphorylated-tau (p-tau), which combined have sensitivity and specificity figures around 80%. However, pathological studies have shown that comorbidity is a common feature in AD and that the three currently used CSF biomarkers do not optimally reflect the activity of the disease process. Thus, additional markers are needed.

Areas covered: In the present review, we screened PubMed for articles published the last five years (2012–2017) for proteomic studies in CSF with the criteria that AD had to be included as one of the diagnostic groups. Based on inclusion criteria, 28 papers were included reporting in total 224 biomarker-data that were altered in AD compared to control. Both mass spectrometry and multi-panel immunoassays were considered as proteomic studies.

Expert commentary: A large number of pilot studies have been reported but so far there is a lack of replicated findings and to date no CSF biomarker discovered in proteomic studies has reached the clinic to aid in the diagnostic work-up of patients with cognitive impairment.     

New approaches for the treatment of Alzheimer’s disease

Alzheimer’s disease (AD) is the most prevalent chronic neurodegenerative disease. Current approved therapies are symptomatic treatments having some effect on cognitive function. Therapies that target β-amyloid (Aβ) have been the focus of efforts to develop a disease modification treatment for AD but these approaches have failed to show any clinical benefit so far. Beyond the ‘Aβ hypothesis’, there are a number of newer approaches to treat AD with neuroinflammation emerging as a very active area of research based on risk gene analysis. This short review will summarize approved drug therapies, recent clinical trials and new approaches for the treatment of AD.     

Immunotherapy for Alzheimer’s disease: hoops and hurdles

Alzheimer’s disease (AD) is the most common form of dementia, afflicting more than 30 million people worldwide. Currently, there is no cure or way to prevent this devastating disease. Extracellular plaques, containing various forms of amyloid-β protein (Aβ), and intracellular neurofibrillary tangles (NFTs), composed of hyper-phosphorylated tau protein, are two major pathological hallmarks of the AD brain. Aggregation, deposition, and N-terminal modification of Aβ protein and tau phosphorylation and aggregation are thought to precede the onset of cognitive decline, which is better correlated with tangle formation and neuron loss. Active and passive vaccines against various forms of Aβ have shown promise in pre-clinical animal models. However, translating these results safely and effectively into humans has been challenging. Recent clinical trials showed little or no cognitive efficacy, possibly due to the fact that the aforementioned neurodegenerative processes most likely pre-existed in the patients well before the start of immunotherapy. Efforts are now underway to treat individuals at risk for AD prior to or in the earliest stages of cognitive decline with the hope of preventing or delaying the onset of the disease. In addition, efforts to immunize against tau and other AD-related targets are underway.     

Plasma lipoproteome in Alzheimer’s disease: a proof-of-concept study

Background

Although total plasma lipoproteome consists of proteins that have shown promises as biomarkers that can identify Alzheimer’s disease (AD), effect sizes are modest. The objective of this study is to provide initial proof-of-concept that the plasma lipoproteome more likely differ between AD cases and controls when measured in individual plasma lipoprotein fractions than when measured as total in immunodepleted plasma.

Methods

We first developed a targeted proteomics method based on selected reaction monitoring (SRM) and liquid chromatography and tandem mass spectrometry for measurement of 120 tryptic peptides from 79 proteins that are commonly present in plasma lipoproteins. Then in a proof-of concept case–control study of 5 AD cases and 5 sex- and age-matched controls, we applied the targeted proteomic method and performed relatively quantification of 120 tryptic peptides in plasma lipoprotein fractions (fractionated by sequential gradient ultracentrifugation) and in immunodepleted plasma (of albumin and IgG). Unadjusted p values from two-sample t-tests and overall fold change was used to evaluate a peptide relative difference between AD cases and controls, with lower p values (<?0.05) or greater fold differences (>?1.05 or?<?0.95) suggestive of greater peptide/protein differences.

Results

Within-day and between-days technical precisions (mean %CV [SD] of all SRM transitions) of the targeted proteomic method were 3.95% (2.65) and 9.31% (5.59), respectively. Between-days technical precisions (mean % CV [SD]) of the entire plasma lipoproteomic workflow including plasma lipoprotein fractionation was 27.90% (14.61). Ten tryptic peptides that belonged to 5 proteins in plasma lipoproteins had unadjusted p values?<?0.05, compared to no peptides in immunodepleted plasma. Furthermore, 27, 32, 17, and 20 tryptic peptides in VLDL, IDL, LDL and HDL, demonstrated overall peptide fold differences?>?1.05 or?<?0.95, compared to only 6 tryptic peptides in immunodepleted plasma. The overall comparisons, therefore, suggested greater peptide/protein differences in plasma lipoproteome when measured in individual plasma lipoproteins than as total in immunodepleted plasma. Specifically, protein complement C3’s peptide IHWESASLLR, had unadjusted p values of 0.00007, 0.00012, and 0.0006 and overall 1.25, 1.17, 1.14-fold changes in VLDL, IDL, and LDL, respectively. After positive False Discovery Rate (pFDR) adjustment, the complement C3 peptide IHWESASLLR in VLDL remained statistically different (adjusted p value?<?0.05).

Discussion

The findings may warrant future studies to investigate plasma lipoproteome when measured in individual plasma lipoprotein fractions for AD diagnosis.

     

Cryogenic solid state NMR studies of fibrils of the Alzheimer’s disease amyloid-β peptide: perspectives for DNP

Dynamic Nuclear Polarization solid-state NMR holds the potential to enable a dramatic increase in sensitivity by exploiting the large magnetic moment of the electron. However, applications to biological solids are hampered in uniformly isotopically enriched biomacromolecules due to line broadening which yields a limited spectral resolution at cryogenic temperatures. We show here that high magnetic fields allow to overcome the broadening of resonance lines often experienced at liquid nitrogen temperatures. For a fibril sample of the Alzheimer’s disease β-amyloid peptide, we find similar line widths at low temperature and at room temperature. The presented results open new perspectives for structural investigations in the solid-state.     

Quantitative assessment of the effect of ABCA1 gene polymorphism on the risk of Alzheimer’s disease

ATP-binding cassette transporter A1 (ABCA1) is a membrane-associated protein which has attracted considerable attention as a candidate gene for Alzheimer’s disease (AD) based on its function as a key factor in lipid metabolism by mediating cellular cholesterol efflux, the rate-limiting step in the production of nascent high-density lipoprotein (HDL) particles. The relationship between ABCA1 common variations (R219 K rs2230806, I883 M rs4149313 and R1587 K rs2230808) and AD has been reported in various ethnic groups; however, these studies have yielded contradictory results. To investigate this inconsistency, we performed a meta-analysis of 13 studies involving a total of 12,248 subjects to evaluate the effect of ABCA1 on genetic susceptibility for AD. Overall, the summary OR of AD was 1.01 (95 % CI: 0.93–1.10; P = 0.77), 1.10 (95 % CI: 0.96–1.26; P = 0.16), and 1.08 (95 % CI: 0.96–1.23; P = 0.21) for R219 K, I883 M and R1587 K polymorphism, respectively. No significant results were observed in dominant and recessive when compared with wild genotype for these polymorphisms. In the stratified analyses by ethnicity and sample size, no evidence of any gene-disease association was obtained. In conclusion, the present meta-analysis does not support the notion that common SNPs on ABCA1 is a major genetic risk factor for AD.     

Therapeutic and pharmacokinetic characterizations of an anti-amyloidogenic bis-styrylbenzene derivative for Alzheimer’s disease treatment

Alzheimer’s disease drug discovery regarding exploration into the molecules and processes has focused on the intrinsic causes of the brain disorder correlated with the accumulation of amyloid-β. An anti-amyloidogenic bis-styrylbenzene derivative, KMS80013, showed excellent oral bioavailability (F = 46.2%), facilitated brain penetration (26%, iv) in mouse and target specific in vivo efficacy in acute AD mouse model attenuating the cognitive deficiency in Y-maze test. Acute toxicity (LD₅₀ >2000 mg/kg) and hERG channel inhibition (14% at 10 μM) results indicated safety of KMS80013.     

Pushing the boundaries of brain organoids to study Alzheimer’s disease

Progression of Alzheimer’s disease (AD) entails deterioration or aberrant function of multiple brain cell types, eventually leading to neurodegeneration and cognitive decline. Defining how complex cell–cell interactions become dysregulated in AD requires novel human cell-based in vitro platforms that could recapitulate the intricate cytoarchitecture and cell diversity of the human brain. Brain organoids (BOs) are 3D self-organizing tissues that partially resemble the human brain architecture and can recapitulate AD-relevant pathology. In this review, we highlight the versatile applications of different types of BOs to model AD pathogenesis, including amyloid-β and tau aggregation, neuroinflammation, myelin breakdown, vascular dysfunction, and other phenotypes, as well as to accelerate therapeutic development for AD.