Alzheimer's disease (AD) is the most common form of dementia, and the pathological changes of senile plaques (SPs) and neurofibrillary tangles (NFTs) in AD brains are well described. Clinically, a diagnosis remains a postmortem one, hampering both accurate and early diagnosis as well as research into potential new treatments. Visual deficits have long been noted in AD patients, and it is becoming increasingly apparent that histopathological changes already noted in the brain also occur in an extension of the brain; the retina. Due to the optically transparent nature of the eye, it is possible to image the retina at a cellular level noninvasively and thus potentially allow an earlier diagnosis as well as a way of monitoring progression and treatment effects. Transgenic animal models expressing amyloid precursor protein (APP) presenilin (PS) and tau mutations have been used successfully to recapitulate the pathological findings of AD in the brain. This paper will cover the ocular abnormalities that have been detected in these transgenic AD animal models.
Neurofibrillary tangles (NFT) and amyloid plaques are hallmark neuropathological features
of Alzheimer’s disease (AD). There is some debate as to which neuropathological feature
comes first in the disease process, with early autopsy studies suggesting that NFT develop first,
and more recent neuroimaging studies supporting the early role of amyloid beta (Aβ)
deposition. Cerebrospinal fluid (CSF) biomarkers of Aβ42 and hyperphosphorylated
tau (p-tau) have been shown to serve as in vivo proxy measures of amyloid plaques and NFT,
respectively. The aim of this study was to examine the association between CSF biomarkers and rate
of atrophy in the precuneus and hippocampus. These regions were selected because the precuneus
appears to be affected early and severely by Aβ deposition, and the hippocampus similarly by
NFT pathology. We predicted (1) baseline Aβ42 would be related to accelerated
rate of cortical thinning in the precuneus and volume loss in the hippocampus, with the latter
relationship expected to be weaker, (2) baseline p-tau181p would be related to
accelerated rate of hippocampal atrophy and cortical thinning in the precuneus, with the latter
relationship expected to be weaker. Using all ADNI cohorts, we fitted separate linear mixed-effects
models for changes in hippocampus and precuneus longitudinal outcome measures with baseline CSF
biomarkers modeled as predictors. Results partially supported our hypotheses: Both baseline
p-tau181p and Aβ42 were associated with hippocampal atrophy over time.
Neither p-tau181p nor Aβ42 were significantly related to cortical
thinning in the precuneus over time. However, follow-up analyses demonstrated that having abnormal
levels of both Aβ42 and p-tau181p was associated with an accelerated
rate of atrophy in both the hippocampus and precuneus. Results support early effects of Aβ
in the Alzheimer’s disease process, which are less apparent than and perhaps dependent on
p-tau effects as the disease progresses. However, amyloid deposition alone may be insufficient for
emergence of significant morphometric changes and clinical symptoms.
Biomarkers; Beta Amyloid; Phosphorylated Tau; MRI; Alzheimer’s Disease; Hippocampus; Precuneus
Alzheimer's disease (AD) is associated with a cascade of pathological events involving formation of amyloid-based neuritic plaques and tau-based neurofibrillary tangles, changes in brain structure and function, and eventually, cognitive impairment and functional disability. The precise sequence of when each of these disease markers becomes abnormal is not yet clearly understood. The present study systematically tested the relationship between classes of biomarkers according to a proposed model of temporal sequence (Jack et al., 2010). We examined temporal relations among four classes of biomarkers: CSF Aβ, CSF tau, neuroimaging variables (hippocampal volume, ventricular volume, FDG PET), and cognitive variables (memory and executive function). Random effects modeling of longitudinal data obtained from the Alzheimer's Disease Neuroimaging Initiative (ADNI) was used to test hypotheses that putative earlier markers of AD predicted change in later markers, and that intervening markers reduced effects of earlier on later markers. Specifically, we hypothesized that CSF tau would explain CSF Aβ's relation to neuroimaging and cognitive variables, and neuroimaging variables would explain tau's relation to cognitive variables. Consistent with hypotheses, results indicated that CSF Aβ effects on cognition change were substantially attenuated by CSF tau and measures of brain structure and function, and CSF tau effects on cognitive change were attenuated by neuroimaging variables. Contrary to hypotheses, CSF Aβ and CSF tau were observed to have independent effects on neuroimaging and CSF tau had a direct effect on baseline cognition independent of brain structure and function. These results have implications for clarifying the temporal sequence of AD changes and corresponding biomarkers.
Beta Amyloid; Tau; Memory; Executive Functions; Neuroimaging
Alzheimer's disease (AD) is the most common form of dementia that affects several million people worldwide. The major neuropathological hallmarks of AD are the presence of extracellular amyloid plaques that are composed of Aβ40 and Aβ42 and intracellular neurofibrillary tangles (NFT), which is composed of hyperphosphorylated protein Tau. While the amyloid plaques and NFT could define the disease progression involving neuronal loss and dysfunction, significant cognitive decline occurs before their appearance. Although significant advances in neuroimaging techniques provide the structure and physiology of brain of AD cases, the biomarker studies based on cerebrospinal fluid (CSF) and plasma represent the most direct and convenient means to study the disease progression. Biomarkers are useful in detecting the preclinical as well as symptomatic stages of AD. In this paper, we discuss the recent advancements of various biomarkers with particular emphasis on CSF biomarkers for monitoring the early development of AD before significant cognitive dysfunction.
Alzheimer’s disease (AD) is the most common type of dementia, comprising 60–80% of all reported cases, and currently affects 5.2 million Americans. AD is characterized pathologically by the accumulation of senile plaques (SPs), neurofibrillary tangles (NFTs), and synapse loss. The early stages of memory loss associated with AD have been studied in a condition known as amnestic mild cognitive impairment (MCI), arguably the earliest form of AD. In spite of extensive research across a variety of disciplines the cause of AD remains elusive. Proteomics techniques have helped to advance knowledge about AD by identifying irregularities in protein expression and post-translational modifications (PTMs) in AD brain. Glycosylation is a less studied PTM with regards to AD and MCI. This PTM is important to study because glycosylation is involved in proper protein folding, protein anchoring to cell membranes, and the delivery of proteins to organelles, and these processes are impaired in AD. Concanavalin-A (Con-A) binds to N-linked glycoproteins, but hydrophobic sites on non-glycoproteins are also known to bind Con-A. To our knowledge, the present study is the first to examine Con-A-associated brain proteins in MCI and AD with focus on the hippocampus and inferior parietal lobule (IPL) brain regions. Proteins found in AD hippocampus with altered levels are glutamate dehydrogenase (GDH), glial fibrillary acidic protein (GFAP), tropomyosin 3 (TPM3), Rab GDP-dissociation inhibitor XAP-4 (XAP4), and heat shock protein 90 (HSP90). Proteins found with altered levels in AD IPL are α-enolase, γ-enolase, and XAP-4. MCI hippocampal proteins with altered levels are dihydropyrimidase-2 (DRP2), glucose-regulated protein 78 (GRP-78), protein phosphatase related protein Sds-22 (Sds22), and GFAP and the only protein found with altered levels in MCI IPL was β-synuclein. These results are discussed with reference to biochemical and pathological alterations in and progression of AD.
Diffusion tensor imaging (DTI) is a sophisticated MRI-based neuroimaging technique that enables in vivo quantification of differences in molecular diffusion at the cellular level. Owing to the highly directional architecture of white matter (WM), DTI is providing important clues of the structure and geometric organization of this neural compartment. Since DTI can detect changes even in the case of radiologically “normal” appearing WM, researchers are using the technique for the study of WM integrity at the initial stages of the most common neurodegenerative disorders. Along with a well characterized cortical pathology (neuritic plaques and intracellular neurofibrillary tangles), WM changes have been also demonstrated in Alzheimer’s disease (AD). However, these changes had been for years found nonliable in the onset and progress of AD, basically due to lack of incriminatory evidence. The use of novel tools such as DTI has enabled the anatomical distribution of WM microstructural damage in the prodromal stages of AD to be gauged and determined, granting a long-delayed protagonic role to WM in the natural history of this highly prevalent neurodegenerative condition.
diffusion; DTI; white matter; Alzheimer’s disease; aging; anisotropy
Alzheimer’s disease (AD) is the most common form of dementia in the elderly. Classic symptoms of the disease include memory loss and confusion associated with the hallmark neuro-pathologic lesions of neurofibrillary tangles (NFT) and senile plaques (SP) and their sequelae, gray matter atrophy. Volumetric assessment methods measure tissue atrophy, which typically follows early biochemical changes. An alternate MRI contrast mechanism to visualize the early pathological changes is T1ρ (or “T-1-rho”), the spin lattice relaxation time constant in the rotating frame, which determines the decay of the transverse magnetization in the presence of a “spin-lock” radio-frequency field. Macromolecular changes (in plaques and tangles) that accompany early AD are expected to alter bulk water T1ρ relaxation times. In this work, we measure T1ρ MRI on patients with clinically diagnosed AD, MCI and in age-matched ognitively normal control subjects in order to compare T1ρ values with changes in brain volume in the same regions of the brain and demonstrate that T1ρ can potentially constitute an important biomarker of AD.
T1rho; spin-lock imaging; Alzheimer’s Disease
Alzheimer's disease (AD) is a dementing neurological disorder that results in progressive memory loss and cognitive decline thought to be associated with buildup of amyloid plaques and neurofibrillary tangles in the brain. Vascular Dementia (VaD) is another common dementing disorder characterized by decreased brain perfusion. Together, AD and VaD constitute mixed dementia, an extremely common type of dementia associated with aging. Neuroimaging research suggests that brain vascular atrophy results in mild cognitive impairment (MCI), a possible precursor for AD. Additionally, literature suggests that attention to cardiovascular risk factors such as hypertension could reduce or delay the incidence of mixed dementia. Furthermore, foods and beverages rich in natural antioxidant flavanoids (i.e. epicatechin and catechin) are currently being advocated as possible preventative agents for a number of pathological conditions ranging from coronary heart disease to dementia. Experimental evidence is mounting that oxidative stress is involved in the pathophysiology of AD, and numerous studies are indicating that polyphenolic antioxidants found in fruits and vegetables can be useful in countering this and blocking neuronal death. More specifically, several cocoa studies suggest that daily intake of cocoa flavanols leads to cardiovascular benefits including vasodilatation via a nitric oxide mechanism and increased brain perfusion. The following text will consider an important question that thus arises regarding the potential of flavanols as effective agents for the prevention and delay of the onset of brain vascular atrophy and subsequently MCI and AD. It will also review the molecular mechanisms through which flavanols operate to accomplish their protective effects.
Brain vascular atrophy; mild cognitive impairment; Alzheimer's disease; flavanols; oxidative stress; antioxidants
Cognitive impairment, including dementia, is commonly seen in those afflicted with Parkinson disease (PD), particularly at advanced disease stages. Pathologically, PD with dementia (PD-D) is most often associated with the presence of cortical Lewy bodies, as is the closely related dementia with Lewy bodies (DLB). Both PD-D and DLB are also frequently complicated by the presence of neurofibrillary tangles and amyloid plaques, features most often attributed to Alzheimer disease. Biomarkers are urgently needed to differentiate among these disease processes and predict dementia in PD as well as monitor responses of patients to new therapies. A few clinical assessments, along with structural and functional neuroimaging, have been utilized in the last few years with some success in this area. Additionally, a number of other strategies have been employed to identify biochemical/molecular biomarkers associated with cognitive impairment and dementia in PD, e.g., targeted analysis of candidate proteins known to be important to PD pathogenesis and progression in cerebrospinal fluid or blood. Finally, interesting results are emerging from preliminary studies with unbiased and high throughput genomic, proteomic and metabolomic techniques. The current findings and perspectives of applying these strategies and techniques are reviewed in this article, together with potential areas of advancement.
Parkinson disease; dementia; mild cognitive impairment; biomarker; cerebrospinal fluid; proteomics; genomics; and metabolomics
Alzheimer’s disease (AD) is the most common form of dementia in the elderly, and it is characterized by progressive impairment in multiple cognitive domains of sufficient severity to interfere with individuals’ daily living activities. Historically, the diagnosis of AD has been based on the identification of a clinical syndrome, and accuracy studies of the current clinical criteria conducted in referral clinics have shown high sensitivity for AD. However, the identification of the disease is still not perfect, and there is growing evidence that the use of biomarkers will increase our ability to better indentify the underlying biology of AD, especially in its early stages. These biomarkers will improve the detection of the patients suitable for research studies and drug trials, and they will contribute to a better management of the disease in the clinical practice. In this review, we discuss the most studied biomarkers in AD: cerebrospinal fluid proteins, structural magnetic resonance imaging, functional neuroimaging techniques, and amyloid imaging.
Alzheimer’s disease; mild cognitive impairment; biomarker; cerebrospinal fluid; magnetic resonance imaging; positron emission tomography
Aggregation of amyloid beta peptide into senile plaques and hyperphosphorylated tau protein into neurofibrillary tangles in the brain are the pathological hallmarks of Alzheimer’s disease. Despite over a century of research into these lesions, the exact relationship between pathology and neurotoxicity has yet to be fully elucidated. In order to study the formation of plaques and tangles and their effects on the brain, we have applied multiphoton in vivo imaging of transgenic mouse models of Alzheimer’s disease. This technique allows longitudinal imaging of pathological aggregation of proteins and the subsequent changes in surrounding neuropil neurodegeneration and recovery after therapeutic interventions.
Alzheimer; tau; plaque; multiphoton; in vivo imaging
Peripheral biomarkers of Alzheimer's disease (AD) reflecting early neuropathological change are critical to the development of treatments for this condition. The most widely used indicator of AD pathology in life at present is neuroimaging evidence of brain atrophy. We therefore performed a proteomic analysis of plasma to derive biomarkers associated with brain atrophy in AD. Using gel based proteomics we previously identified seven plasma proteins that were significantly associated with hippocampal volume in a combined cohort of subjects with AD (N = 27) and MCI (N = 17). In the current report, we validated this finding in a large independent cohort of AD (N = 79), MCI (N = 88) and control (N = 95) subjects using alternative complementary methods—quantitative immunoassays for protein concentrations and estimation of pathology by whole brain volume. We confirmed that plasma concentrations of five proteins, together with age and sex, explained more than 35% of variance in whole brain volume in AD patients. These proteins are complement components C3 and C3a, complement factor-I, γ-fibrinogen and alpha-1-microglobulin. Our findings suggest that these plasma proteins are strong predictors of in vivo AD pathology. Moreover, these proteins are involved in complement activation and coagulation, providing further evidence for an intrinsic role of these pathways in AD pathogenesis.
Over the past two decades, it has become increasingly apparent that Alzheimer’s disease neuropathology is characterized by activated microglia (brain resident macrophages) as well as the classic features of amyloid plaques and neurofibrillary tangles. The intricacy of microglial biology has also become apparent, leading to a heightened research interest in this particular cell type. Over the years a number of different microglial cell culturing techniques have been developed to study either primary mammalian microglia, or immortalized cell lines. Each microglial system has advantages and disadvantages and should be selected for its appropriateness in a particular research context. This review summarizes several of the most common microglial cell culture systems currently being employed in Alzheimer’s research including primary microglia; BV2 and N9 retroviral immortalized microglia; human immortalized microglia (HMO6); and spontaneously immortalized rodent microglial lines (EOC lines and HAPI cells). Particularities of cell culture requirements and characteristics of microglial behavior, especially in response to applied inflammogen stimuli, are compared and discussed across these cell types.
Alzheimer’s disease; Microglia; Cell culture; Nitric oxide; Cytokines
The diagnostic guidelines of Alzheimer’s disease (AD) have recently been updated to include brain imaging and cerebrospinal fluid (CSF) biomarkers, with the aim of increasing the certainty of whether a patient has an ongoing AD neuropathologic process or not. The CSF biomarkers total tau (T-tau), hyperphosphorylated tau (P-tau) and the 42 amino acid isoform of amyloid β (Aβ42) reflect the core pathologic features of AD, which are neuronal loss, intracellular neurofibrillary tangles and extracellular senile plaques. Since the pathologic processes of AD start decades before the first symptoms, these biomarkers may provide means of early disease detection. The updated guidelines identify three different stages of AD: preclinical AD, mild cognitive impairment (MCI) due to AD and AD with dementia. In this review, we aim to summarize the CSF biomarker data available for each of these stages. We also review results from blood biomarker studies. In summary, the core AD CSF biomarkers have high diagnostic accuracy both for AD with dementia and to predict incipient AD (MCI due to AD). Longitudinal studies on healthy elderly and recent cross-sectional studies on patients with dominantly inherited AD mutations have also found biomarker changes in cognitively normal at-risk individuals. This will be important if disease-modifying treatment becomes available, given that treatment will probably be most effective early in the disease. An important prerequisite for this is trustworthy analyses. Since measurements vary between studies and laboratories, standardization of analytical as well as pre-analytical procedures will be essential. This process is already initiated. Apart from filling diagnostic roles, biomarkers may also be utilized for prognosis, disease progression, development of new treatments, monitoring treatment effects and for increasing the knowledge about pathologic processes coupled to the disease. Hence, the search for new biomarkers continues. Several candidate biomarkers have been found in CSF, and although biomarkers in blood have been harder to find, some recent studies have presented encouraging results. But before drawing any major conclusions, these results need to be verified in independent studies.
Alzheimer’s disease; Cerebrospinal fluid; Blood; Biomarker; Amyloid β; Total tau; Phosphorylated tau; Diagnosis; Disease stages
Alzheimer’s disease (AD) is an age-dependent neurodegenerative disorder and the most common cause of dementia. The early stages of AD are characterized by short-term memory loss. Once the disease progresses, patients experience difficulties in sense of direction, oral communication, calculation, ability to learn, and cognitive thinking. The median duration of the disease is 10 years. The pathology is characterized by deposition of amyloid beta peptide (so-called senile plaques) and tau protein in the form of neurofibrillary tangles. Currently, two classes of drugs are licensed by the European Medicines Agency for the treatment of AD, ie, acetylcholinesterase inhibitors for mild to moderate AD, and memantine, an N-methyl-D-aspartate receptor antagonist, for moderate and severe AD. Treatment with acetylcholinesterase inhibitors or memantine aims at slowing progression and controlling symptoms, whereas drugs under development are intended to modify the pathologic steps leading to AD. Herein, we review the clinical features, pharmacologic properties, and cost-effectiveness of the available acetylcholinesterase inhibitors and memantine, and focus on disease-modifying drugs aiming to interfere with the amyloid beta peptide, including vaccination, passive immunization, and tau deposition.
Alzheimer’s disease; acetylcholinesterase inhibitors; memantine; disease-modifying drugs; diagnosis; treatment
Because the pathologic processes that underlie Alzheimer's disease (AD) appear to start 10 to 20 years before symptoms develop, there is currently intense interest in developing techniques to accurately predict which individuals are most likely to become symptomatic. Several AD risk prediction strategies - including identification of biomarkers and neuroimaging techniques and development of risk indices that combine traditional and non-traditional risk factors - are being explored. Most AD risk prediction strategies developed to date have had moderate prognostic accuracy but are limited by two key issues. First, they do not explicitly model mortality along with AD risk and, therefore, do not differentiate individuals who are likely to develop symptomatic AD prior to death from those who are likely to die of other causes. This is critically important so that any preventive treatments can be targeted to maximize the potential benefit and minimize the potential harm. Second, AD risk prediction strategies developed to date have not explored the full range of predictive variables (biomarkers, imaging, and traditional and non-traditional risk factors) over the full preclinical period (10 to 20 years). Sophisticated modeling techniques such as hidden Markov models may enable the development of a more comprehensive AD risk prediction algorithm by combining data from multiple cohorts. As the field moves forward, it will be critically important to develop techniques that simultaneously model the risk of mortality as well as the risk of AD over the full preclinical spectrum and to consider the potential harm as well as the benefit of identifying and treating high-risk older patients.
Given the predicted increase in prevalence of Alzheimer’s disease (AD) in coming decades, early detection and intervention in persons with the pre-dementia condition known as Mild Cognitive Impairment (MCI) is of paramount importance. Recent years have seen remarkable advances in the application of neuroimaging and other biomarkers to the study of MCI. The article reviews the most recent developments in the use of MRI to characterize brain changes and to prognosticate clinical outcome of MCI patients. The review begins with description of methods and findings in structural MRI research, delineating findings regarding both gross atrophy and microstructural brain changes in MCI. Second, we describe the most recent findings regarding brain function in MCI, enumerating findings from functional MRI and brain perfusion studies. Third, we will make recommendations regarding the current clinical use of MRI in identification of MCI.As a conclusion, we will look to the future of neuroimaging as a tool in early AD detection.
Alzheimer’s disease; Mild Cognitive Impairment; MRI
Cerebrospinal fluid (CSF) biomarkers of Alzheimer’s disease (AD) are currently being considered for inclusion in revised diagnostic criteria for research and/or clinical purposes to increase the certainty of ante-mortem diagnosis. Establishing biomarker validity requires demonstration that the assays are true markers of underlying disease pathology (e.g., amyloid plaques and/or neurofibrillary tangles) in living individuals.
We compared the performances of the two most commonly used platforms, INNOTEST® ELISA and INNO-BIA AlzBio3 for measurement of CSF amyloid-beta (Aβ) and tau(s), for identifying the presence of amyloid plaques in a research cohort (n=103). Values obtained for CSF Aβ1-42, total tau and phosphorylated tau181 (p-tau181) using the two assay platforms were compared to brain amyloid load as assessed by positron emission tomography using the amyloid imaging agent, Pittsburgh Compound B (PIB).
Research volunteers who are cognitively normal or have very mild to moderate AD dementia.
The two assay platforms yielded different (~2–6-fold) absolute values for the various analytes, but relative values were highly correlated. CSF Aβ1-42 correlated inversely, and tau and p-tau181 correlated positively, with the amount of cortical PIB binding, albeit to differing degrees. Both assays yielded similar patterns of CSF biomarker correlations with amyloid load. The ratios of total tau/Aβ1-42 and p-tau181/Aβ1-42 outperformed any single analyte, including Aβ1-2, in discriminating individuals with versus without cortical amyloid.
The INNOTEST® and INNO-BIA CSF platforms performed equally well in identifying individuals with underlying amyloid plaque pathology. Differences in absolute values, however, point to the need for assay-specific diagnostic cut-point values.
Alzheimer’s disease; amyloid; biomarkers; cerebrospinal fluid; imaging (PET, MRI) in dementias; Pittsburgh Compound B
Alzheimer's Disease (AD) is the most frequent form of dementia and represents one of the main causes of disability among older subjects. Up to now, the diagnosis of AD has been made according to clinical criteria. However, the use of such criteria does not allow an early diagnosis, as pathological alterations may be apparent many years before the clear-cut clinical picture. An early diagnosis is even more valuable to develop new treatments, potentially interfering with the pathogenetic process. During the last decade, several neuroimaging and cerebrospinal fluid (CSF) parameters have been introduced to allow an early and accurate detection of AD patients, and, recently, they have been included among research criteria for AD diagnosis. However, their use in clinical practice suffers from limitations both in accuracy and availability. The increasing amount of knowledge about peripheral biomarkers will possibly allow the future identification of reliable and easily available diagnostic tests.
Alzheimer’s disease (AD), the most devastating chronic neurodegenerative disease in adults, causes dementia and eventually, death of the affected individuals. Clinically, AD is characterized as late-onset, age-dependent cognitive decline due to loss of neurons in cortex and hippocampus. The pathologic corollary of these symptoms is the formation of senile plaques and neurofibrillary tangles. Senile plaques are formed due to accumulation of oligomeric amyloid beta (Aβ) forming fibrillary plaques. This occurs due to the amyloidogenic processing of the amyloid precursor protein (APP) by various secretases. On the other hand, neurofibrillary tangles are formed due to hyperphosphorylation of cytoskeleton proteins like tau and neurofilament. Both are hyperphosphorylated by cyclin-dependent kinase-5 (Cdk5) and are part of the paired helical filament (PHF), an integral part of neurofibrillary tangles. Unlike other cyclin-dependent kinases, Cdk5 plays a very important role in the neuronal development. Cdk5 gets activated by its neuronal activators p35 and p39. Upon stress, p35 and p39 are cleaved by calpain resulting in truncated products as p25 and p29. Association of Cdk5/p25 is longer and uncontrolled causing aberrant hyperphosphorylation of various substrates of Cdk5 like APP, tau and neurofilament, leading to neurodegenerative pathology like AD. Additionally recent evidence has shown increased levels of p25, Aβ, hyperactivity of Cdk5, phosphorylated tau and neurofilament in human AD brains. This review briefly describes the above-mentioned aspects of involvement of Cdk5 in the pathology of AD and at the end summarizes the advances in Cdk5 as a therapeutic target.
Cyclin dependent kinase 5 (Cdk5); Hyperphosphorylation; Neurodegeneration; Alzheimer’s disease; Plaques; Tangles
Alzheimer's disease is a chronic, age-related neurodegenerative disorder. Neurofibrillary tangles are among the pathological hallmarks of Alzheimer's disease. Neurofibrillary tangles consist of abnormal protein fibers known as paired helical filaments. The accumulation of paired helical filaments is one of the most characteristic cellular changes in Alzheimer's disease. Tau protein, a microtubule-associated protein, is the major component of paired helical filaments. Tau in paired helical filaments is hyperphosphorylated, truncated, and aggregated. What triggers the formation of paired helical filaments is not known, but neuroinflammation could play a role. Neuroinflammation is an active process detectable in the earliest stages of Alzheimer's disease. The neuronal toxicity associated with inflammation makes it a potential risk factor in the pathogenesis of Alzheimer's disease. Determining the sequence of events that lead to this devastating disease has become one of the most important goals for the prevention and treatment of Alzheimer's disease. In this review, we focus on the pathological properties of tau thought to play a role in neurofibrillary tangle formation and summarize how central nervous system inflammation might be a critical contributor to the pathology of Alzheimer's disease. A better understanding of the mechanisms that cause neurofibrillary tangle formation is of clinical importance for developing therapeutic strategies to prevent and treat Alzheimer's disease. One of the major challenges facing us is singling out neuroinflammation as a therapeutic target for the prevention of Alzheimer's disease neurodegeneration. The challenge is developing therapeutic strategies that prevent neurotoxicity linked to inflammation without compromising its neuroprotective role.
aggregation; Alzheimer's disease; inflammation; neurofibrillary tangles; tau protein
Alzheimer's disease is the most common form of dementia affecting millions of individuals worldwide. It is currently diagnosed only via clinical assessments and confirmed by postmortem brain pathology. The development of validated biomarkers for Alzheimer's disease is essential to improve diagnosis and accelerate the development of new therapies. Biochemical and neuroimaging markers could facilitate diagnosis, predict AD progression from a pre-AD state of mild cognitive impairment (MCI), and be used to monitor efficacies of disease-modifying therapies. Cerebrospinal fluid (CSF) levels of Aβ40, Aβ42, total tau, and phosphorylated tau have diagnostic values in AD. Measurements of the above CSF markers in combination are useful in predicting the risk of progression from MCI to AD. New potential biomarkers are emerging, and CSF or plasma marker profiles may eventually become part of the clinician's toolkit for accurate AD diagnosis and management. These biomarkers along with clinical assessment, neuropsychological testing, and neuroimaging could achieve a much higher diagnostic accuracy for AD and related disorders in the future.
Alzheimer's disease (AD) is an age-related neurodegenerative disease characterized clinically by cognitive decline and pathologically by the accumulation of amyloid-β-containing senile plaques and neurofibrillary tangles. A great deal of attention has focused on amyloid-β as the major pathogenic mechanisms with the ultimate goal of using amyloid-β lowering therapies as an avenue of treatment. Unfortunately, nearly a quarter century later, no tangible progress has been offered, whereas spectacular failure tends to be the most compelling. We have long contended, as has substantial literature, that proteinaceous accumulations are simply downstream and, often, endstage manifestations of disease. Their overall poor correlation with the level of dementia, and their presence in the cognitively intact is evidence that is often ignored as an inconvenient truth. Current research examining amyloid oligomers, therefore, will add copious details to what is, in essence, a reductionist distraction from upstream pleiotrophic processes such as oxidative stress, cell cycle dysfunction, and inflammation. It is now long overdue that the neuroscientists avoid the pitfall of perseverating on “proteinopathies” and recognize that the continued targeting of end stage lesions in the face of repeated failure, or worse, is a losing proposition.
Alzheimer's disease; amyloid; amyloid-β protein precursor (AβPP) processing; antioxidant; cellular toxicity; oligomers; oxidative stress
While neurodegenerative diseases are characterized by steady degeneration over relatively long timelines, it is widely believed that the early stages are the most promising for therapeutic intervention, before irreversible neuronal loss occurs. Developing a therapeutic response requires a precise measure of disease progression. However, since the early stages are for the most part asymptomatic, obtaining accurate measures of disease progression is difficult. Longitudinal databases of hundreds of subjects observed during several years with tens of validated biomarkers are becoming available, allowing the use of computational methods. We propose a widely applicable statistical methodology for creating a disease progression score (DPS), using multiple biomarkers, for subjects with a neurodegenerative disease. The proposed methodology was evaluated for Alzheimer’s disease (AD) using the publicly available AD Neuroimaging Initiative (ADNI) database, yielding an Alzheimer’s DPS or ADPS score for each subject and each time-point in the database. In addition, a common description of biomarker changes was produced allowing for an ordering of the biomarkers. The Rey Auditory Verbal Learning Test delayed recall was found to be the earliest biomarker to become abnormal. The group of biomarkers comprising the volume of the hippocampus and the protein concentration amyloid beta and Tau were next in the timeline, and these were followed by three cognitive biomarkers. The proposed methodology thus has potential to stage individuals according to their state of disease progression relative to a population and to deduce common behaviors of biomarkers in the disease itself.
Neurodegenerative diseases; Alzheimer’s disease; biomarkers; disease progression score
The introduction of biological markers in the clinical management of Alzheimer's disease (AD) will not only improve diagnosis relating to early detection of neuropathology with underlying molecular mechanisms, but also provides tools for the assessment of objective treatment benefits. In this review, we identify a number of in vivo neurochemistry and neuroimaging techniques, which can reliably assess aspects of physiology, pathology, chemistry, and neuroanatomy of AD, and hold promise as meaningful biomarkers in the early diagnostic process, as well as for the tracking of disease-modifying pharmacological effects. These neurobiological measures appear to relate closely to pathophysiological, neuropathological, and clinical data, such as hyperphosphorylation of tau, abeta metabolism, lipid peroxidation, pattern and rate of atrophy, loss of neuronal integrity, and functional and cognitive decline, as well as risk of future decline. As a perspective, the important role of biomarkers in the development of innovative drug treatments for AD and the related regulatory process is discussed.
Alzheimer's disease; Alzheimer's Disease Neuroimaging Initiative; biomarker; drug development; disease modification; diagnosis