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Editorial commentary for jnnp-2016-313476.R1: association between naturally occurring antiamyloid β autoantibodies and medial temporal lobe atrophy in Alzheimer's disease
Abstract
The pathophysiology of Alzheimer's disease (AD) is thought to involve the accumulation and deposition of amyloid β (Aβ) peptide in the form of plaques. It is well known that decreased cerebrospinal fluid (CSF) Aβ42 concentrations occur early in AD. Besides this, τ protein becomes hyperphosphorylated (P-τ), getting unstable and unable to bind the microtubules and finally disintegrating into neurofibrillary tangles.
The neuropathological process leads to a characteristic pattern of brain damage starting in the medial temporal lobe (MTL) that can be viewed and measured with structural MRI. Both CSF biomarkers (Aβ and P-τ) and MTL atrophy have been accepted as biomarkers of AD, supporting the diagnosis of AD even in preclinical stages.1 There is some correlation between MRI findings and CSF biomarkers. On one hand, atrophy of the MTL is a diagnostic marker for AD at the mild cognitive impairment stage, although this is not a such …
... These data suggest that reduction of Aβ in the periphery is not sufficient to reduce brain Aβ levels and that BACE is not the rate-limiting enzyme for Aβ processing in the brain (Georgievska et al., 2015). Recent research suggests that CSF naturally occurring antibodies against Aβ seem to have a protective effect for AD, while serum naturally occurring antibodies against Aβ do not seem to have any effect (Kimura et al., 2017;Menendez Gonzalez, 2017a). In line with this, Piazza et al. (2013) reported the first evidence about the participation of natural anti-Aβ autoantibodies in cerebral amyloid-related angiopathy (CAA) and the possible elimination mechanism of soluble Aβ in the CSF by antibodies. ...
Although immunotherapies against the amyloid-β (Aβ) peptide tried so date failed to prove sufficient clinical benefit, Aβ still remains the main target in Alzheimer's disease (AD). This article aims to show the rationale of a new therapeutic strategy: clearing Aβ from the CSF continuously (the "CSF-sink" therapeutic strategy). First, we describe the physiologic mechanisms of Aβ clearance and the resulting AD pathology when these mechanisms are altered. Then, we review the experiences with peripheral Aβ-immunotherapy and discuss the related hypothesis of the mechanism of action of "peripheral sink." We also present Aβ-immunotherapies acting on the CNS directly. Finally, we introduce alternative methods of removing Aβ including the "CSF-sink" therapeutic strategy. As soluble peptides are in constant equilibrium between the ISF and the CSF, altering the levels of Aβ oligomers in the CSF would also alter the levels of such proteins in the brain parenchyma. We conclude that interventions based in a "CSF-sink" of Aβ will probably produce a steady clearance of Aβ in the ISF and therefore it may represent a new therapeutic strategy in AD.
Atrophy in the medial temporal lobe (MTA) is being used as a criterion to support a diagnosis of Alzheimer’s disease (AD). There are several structural neuroimaging approaches for quantifying MTA, including semiquantitative visual rating scales, volumetry (3D), planimetry (2D), and linear measures (1D). Current applications of structural neuroimaging in Alzheimer’s disease clinical trials (ADCTs) incorporate it as a tool for improving the selection of subjects for enrollment or for stratification, for tracking disease progression, or providing evidence of target engagement for new therapeutic agents. It may also be used as a surrogate marker, providing evidence of disease-modifying effects. However, despite the widespread use of volumetric magnetic resonance imaging (MRI) in ADCTs, there are some important challenges and limitations, such as difficulties in the interpretation of results, limitations in translating results into clinical practice, and reproducibility issues, among others. Solutions to these issues may arise from other methodologies that are able to link the results of volumetric MRI from trials with conventional MRIs performed in routine clinical practice (linear or planimetric methods). Also of potential benefit are automated volumetry, using indices for comparing the relative rate of atrophy of different regions instead of absolute rates of atrophy, and combining structural neuroimaging with other biomarkers. In this review, authors present the existing structural neuroimaging approaches for MTA quantification. They then discuss solutions to the limitations of the different techniques as well as the current challenges of the field. Finally, they discuss how the current advances in AD neuroimaging can help AD diagnosis.
Amyloid-β (Aβ) immunotherapy has recently begun to gain considerable attention as a potentially promising therapeutic approach to reducing the levels of Aβ in the Central Nervous System (CNS) of patients with Alzheimer's Disease (AD). Despite extensive preclinical evidence showing that immunization with Aβ(1-42) peptide can prevent or reverse the development of the neuropathological hallmarks of AD, in 2002, the clinical trial of AN-1792, the first trial involving an AD vaccine, was discontinued at Phase II when a subset of patients immunized with Aβ(1-42) developed meningoencephalitis, thereby making it necessary to take a more refined and strategic approach towards developing novel Aβ immunotherapy strategies by first constructing a safe and effective vaccine. This review describes the rational basis in modern clinical trials that have been designed to overcome the many challenges and known hurdles inherent to the search for effective AD immunotherapies. The precise delimitation of the most appropriate targets for AD vaccination remains a major point of discussion and emphasizes the need to target antigens in proteins involved in the early steps of the amyloid cascade. Other obstacles that have been clearly defined include the need to avoid unwanted anti-Aβ/APP Th1 immune responses, the need to achieve adequate responses to vaccination in the elderly and the need for precise monitoring. Novel strategies have been implemented to overcome these problems including the use of N-terminal peptides as antigens, the development of DNA based epitope vaccines and vaccines based on passive immunotherapy, recruitment of patients at earlier stages with support of novel biomarkers, the use of new adjuvants, the use of foreign T cell epitopes and viral-like particles and adopting new efficacy endpoints. These strategies are currently being tested in over 10,000 patients enrolled in one of the more than 40 ongoing clinical trials, most of which are expected to report final results within two years.
A lot of research on biomarkers for Alzheimer is being done in the last few decades. The aim of these studies is to find some method to ease the diagnosis of Alzheimers as early as possible. Such methods are a range of blood or CSF tests on one hand and several types of neuroimaging scans on the other. Many of the images coming both from laboratory and neuroimaging are very visual and illustrative. These images, accompanied by a short description, can perfectly explain the main results and usefulness of every biomarker. The objective of this book would be to summarize the most important studies made in this field. Few publications have systematically compiled results on this topic and only one as an atlas. Readers would be interested in this publication because it allows reviewing the current status of research by handily visualizing the results.
Background Naturally occurring autoantibodies against amyloid β (Aβ) peptide exist in the serum and cerebrospinal fluid (CSF) of healthy individuals. Recently, it was reported that administration of intravenous immunoglobulin at the mild cognitive impairment (MCI) stage of Alzheimer's disease (AD) reduces brain atrophy.
Objective To examine the association between naturally occurring anti-Aβ autoantibodies and brain atrophy in patients with cognitive impairment.
Methods Serum and CSF levels of anti-Aβ autoantibodies and CSF biomarkers were evaluated in 68 patients with cognitive impairment, comprising 44 patients with AD, 19 patients with amnestic MCI and five patients with non-Alzheimer's dementia. The degree of brain atrophy was assessed using the voxel-based specific regional analysis system for AD, which targets the volume of interest (VOI) in medial temporal structures, including the whole hippocampus, entorhinal cortex and amygdala.
Results CSF levels of anti-Aβ autoantibodies were inversely correlated with the extent and severity of VOI atrophy, and the ratio of VOI/grey matter atrophy in patients with AD, but not in MCI or non-AD patients. Serum levels of anti-Aβ autoantibodies were not associated with these parameters in any of the patient groups.
Conclusions These results indicate that CSF levels of naturally occurring anti-Aβ autoantibodies are inversely associated with the degree of the VOI atrophy in patients with AD. Although the mechanism is unclear, CSF levels of naturally occurring anti-Aβ autoantibodies may be implicated in the progression of atrophy of the whole hippocampus, entorhinal cortex and amygdala, in AD.
Alzheimer's disease (AD) so far did not have promising treatment. The accurate and early diagnosis is still a major issue. For this purpose, biomarkers related to the diagnosis, clinical course, and other aims has been reported.
During the past decade, a conceptual shift occurred in the field of Alzheimer’s disease (AD)
considering the disease as a continuum. Thanks to evolving biomarker research and substantial discoveries,
it is now possible to identify the disease even at the preclinical stage before the occurrence
of the first clinical symptoms. This preclinical stage of AD has become a major research focus as the
field postulates that early intervention may offer the best chance of therapeutic success. To date, very
little evidence is established on this “silent” stage of the disease. A clarification is needed about the
definitions and lexicon, the limits, the natural history, the markers of progression, and the ethical
consequence of detecting the disease at this asymptomatic stage. This article is aimed at addressing
all the different issues by providing for each of them an updated review of the literature and evidence,
with practical recommendations.
Objective:
To capitalize on data from different clinical series to compare sensitivity and specificity of individual biomarkers for predicting mild cognitive impairment (MCI) progression to Alzheimer's disease (AD).
Methods:
Medial temporal atrophy, cortical hypometabolism, and cerebrospinal fluid biomarkers were assessed in 18 patients with mild cognitive impairment (MCI) with prodromal AD (pAD; conversion time, 26 ± 12 months) and 18 stable MCI (sMCI) patients from the Translational Outpatient Memory Clinic cohort, as well as in 24 pAD patients (conversion time, 36 ± 12 months) and 33 sMCI patients from the Alzheimer's Disease Neuroimaging Initiative cohort. Medial temporal atrophy was measured by manual, semi-automated, and automated hippocampal volumetry; cortical hypometabolism was measured using several indices of AD-related hypometabolism pattern; and cerebrospinal fluid markers were amyloid β (Aβ)42 and total tau protein concentrations. For each biomarker, sensitivity for pAD, specificity for sMCI, and diagnostic accuracy were computed.
Results:
Sensitivity to predict MCI conversion to AD in the Alzheimer's Disease Neuroimaging Initiative and Translational Outpatient Memory Clinic cohorts was 79% and 94% based on Aβ42, 46% and 28% based on hippocampal volumes, 33% to 66% and 56% to 78% based on different hypometabolism indices, and 46% and 61% based on total tau levels, respectively. Specificity to exclude sMCI was 27% and 50% based on Aβ42, 76% and 94% based on hippocampal volumes, 58% to 67% and 55% to 83% based on different hypometabolism indices, and 61% and 83% based on total tau levels, respectively.
Conclusions:
Current findings suggest that Aβ42 concentrations and hippocampal volumes may be used in combination to best identify pAD.
Hippocampal atrophy as assessed by magnetic resonance imaging (MRI) and abnormal cerebrospinal fluid (CSF) biomarkers are supportive features for the diagnosis of Alzheimer's disease (AD) and are assumed to be indirect pathological markers of the disease. In AD patients, antemortem MRI hippocampal volumes (HVs) correlate with the density of neurofibrillary tangles (but not with senile plaques) at autopsy suggesting that HVs may better correlate with CSF tau and hyperphosphorylated tau (P-tau) levels than CSF amyloid beta protein (Aβ)(42) level. Here, we tested this hypothesis in a well-defined AD group. Patients were selected according to the New Research Criteria for AD, including specific episodic memory deficit and CSF AD profile (defined as abnormal ratio of Aβ(42):tau). MRI was performed within 6 months of lumbar puncture. HVs were obtained using automated segmentation software. Thirty-six patients were included. Left HV correlated with CSF tau (R = -0.53) and P-tau (R = -0.56) levels. Mean HVs correlated with the CSF P-tau level (R = -0.52). No correlation was found between any brain measurement and CSF Aβ(42) level. The CSF tau and P-tau levels, but not the CSF Aβ(42) level, correlated with HV, suggesting that CSF tau markers reflect the neuronal loss associated with the physiopathological process of AD.
Translational outpatient memory clinic Working Group
- A Prestia
- A Caroli
- K Herholz
Prestia A, Caroli A, Herholz K, et al., Translational
outpatient memory clinic Working Group, Alzheimer's
Disease Neuroimaging Initiative. Diagnostic accuracy of