A novel panel of cerebrospinal fluid biomarkers for the differential diagnosis of Alzheimer's disease versus normal aging and frontotemporal dementia

Identification and validation of novel cerebrospinal fluid biomarkers for staging early Alzheimer's disease

BACKGROUND

Ideally, disease modifying therapies for Alzheimer disease (AD) will be applied during the 'preclinical' stage (pathology present with cognition intact) before severe neuronal damage occurs, or upon recognizing very mild cognitive impairment. Developing and judiciously administering such therapies will require biomarker panels to identify early AD pathology, classify disease stage, monitor pathological progression, and predict cognitive decline. To discover such biomarkers, we measured AD-associated changes in the cerebrospinal fluid (CSF) proteome.

METHODS AND FINDINGS

CSF samples from individuals with mild AD (Clinical Dementia Rating [CDR] 1) (n = 24) and cognitively normal controls (CDR 0) (n = 24) were subjected to two-dimensional difference-in-gel electrophoresis. Within 119 differentially-abundant gel features, mass spectrometry (LC-MS/MS) identified 47 proteins. For validation, eleven proteins were re-evaluated by enzyme-linked immunosorbent assays (ELISA). Six of these assays (NrCAM, YKL-40, chromogranin A, carnosinase I, transthyretin, cystatin C) distinguished CDR 1 and CDR 0 groups and were subsequently applied (with tau, p-tau181 and Aβ42 ELISAs) to a larger independent cohort (n = 292) that included individuals with very mild dementia (CDR 0.5). Receiver-operating characteristic curve analyses using stepwise logistic regression yielded optimal biomarker combinations to distinguish CDR 0 from CDR>0 (tau, YKL-40, NrCAM) and CDR 1 from CDR<1 (tau, chromogranin A, carnosinase I) with areas under the curve of 0.90 (0.85-0.94 95% confidence interval [CI]) and 0.88 (0.81-0.94 CI), respectively.

CONCLUSIONS

Four novel CSF biomarkers for AD (NrCAM, YKL-40, chromogranin A, carnosinase I) can improve the diagnostic accuracy of Aβ42 and tau. Together, these six markers describe six clinicopathological stages from cognitive normalcy to mild dementia, including stages defined by increased risk of cognitive decline. Such a panel might improve clinical trial efficiency by guiding subject enrollment and monitoring disease progression. Further studies will be required to validate this panel and evaluate its potential for distinguishing AD from other dementing conditions.

Granins as disease-biomarkers: translational potential for psychiatric and neurological disorders

The identification of biomarkers represents a fundamental medical advance that can lead to an improved understanding of disease pathogenesis, and holds the potential to define surrogate diagnostic and prognostic endpoints. Because of the inherent difficulties in assessing brain function in patients and objectively identifying neurological and cognitive/emotional symptoms, future application of biomarkers to neurological and psychiatric disorders is extremely desirable. This article discusses the biomarker potential of the granin family, a group of acidic proteins present in the secretory granules of a wide variety of endocrine, neuronal and neuroendocrine cells: chromogranin A (CgA), CgB, Secretogranin II (SgII), SgIII, HISL-19 antigen, 7B2, NESP55, VGF and ProSAAS. Their relative abundance, functional significance, and secretion into the cerebrospinal fluid (CSF), saliva, and the general circulation have made granins tractable targets as biomarkers for many diseases of neuronal and endocrine origin, recently impacting diagnosis of a number of neurological and psychiatric disorders including amyotrophic lateral sclerosis (ALS), Alzheimer's disease, frontotemporal dementia, and schizophrenia. Although research has not yet validated the clinical utility of granins as surrogate endpoints for the progression or treatment of neurological or psychiatric disease, a growing body of experimental evidence indicates that the use of granins as biomarkers might be of great potential clinical interest. Advances that further elucidate the mechanism(s) of action of granins, coupled with improvements in biomarker technology and direct clinical application, should increase the translational effectiveness of this family of proteins in disease diagnosis and drug discovery.

Proteomic investigations of the ventriculo-lumbar gradient in human CSF

Cerebrospinal fluid (CSF) is an ideal biological material in which to search for new biomarkers for improved diagnosis of neurological diseases. During a lumbar puncture between 5 and 15 mL of CSF are obtained. Previous studies have assessed the ventriculo-lumbar concentration gradient of a number of specific proteins. In the present study we took a proteomics approach to investigate the possible concentration gradient of a panel of proteins and peptides in the CSF of 16 patients with neurodegenerative diseases. Using two different mass spectrometry techniques, matrix assisted laser desorption ionization time of flight (MALDI-TOF) and surface enhanced laser desorption ionization time of flight (SELDI-TOF), we found that only one of the investigated proteins, apolipoprotein CI, was significantly decreased between the 1st and the 10th mL of CSF. Furthermore, we confirmed previous results showing a significant decrease in albumin concentration from the first to the last CSF aliquots. In conclusion, we found a significant gradient effect for only two of the measured proteins. However, a standardized procedure for CSF collection for diagnostic and research purposes is crucial to allow comparisons of results between patient groups and between laboratories. This is especially important since CSF is usually collected at several centres and variation in sampled CSF due to pre-analytical factors could complicate the interpretation of the results.

Primary progressive aphasia: clinicopathological correlations

Primary progressive aphasia (PPA) is a disorder of declining language that is a frequent presentation of neurodegenerative diseases such as frontotemporal lobar degeneration. Three variants of PPA are recognized: progressive nonfluent aphasia, semantic dementia, and logopenic progressive aphasia. In an era of etiology-specific treatments for neurodegenerative conditions, determining the histopathological basis of PPA is crucial. Clinicopathological correlations in PPA emphasize the contributory role of dementia with Pick bodies and other tauopathies, TDP-43 proteinopathies, and Alzheimer disease. These data suggest an association between a specific PPA variant and an underlying pathology, although many cases of PPA are associated with an unexpected pathology. Neuroimaging and biofluid biomarkers are now emerging as important adjuncts to clinical diagnosis. There is great hope that the addition of biomarker assessments to careful clinical examination will enable accurate diagnosis of the pathology associated with PPA during a patient's life, and that such findings will serve as the basis for clinical trials in this spectrum of disease.

Glycoproteomics in neurodegenerative diseases

Protein glycosylation regulates protein function and cellular distribution. Additionally, aberrant protein glycosylations have been recognized to play major roles in human disorders, including neurodegenerative diseases. Glycoproteomics, a branch of proteomics that catalogs and quantifies glycoproteins, provides a powerful means to systematically profile the glycopeptides or glycoproteins of a complex mixture that are highly enriched in body fluids, and therefore, carry great potential to be diagnostic and/or prognostic markers. Application of this mass spectrometry-based technology to the study of neurodegenerative disorders (e.g., Alzheimer's disease and Parkinson's disease) is relatively new, and is expected to provide insight into the biochemical pathogenesis of neurodegeneration, as well as biomarker discovery. In this review, we have summarized the current understanding of glycoproteins in biology and neurodegenerative disease, and have discussed existing proteomic technologies that are utilized to characterize glycoproteins. Some of the ongoing studies, where glycoproteins isolated from cerebrospinal fluid and human brain are being characterized in Parkinson's disease at different stages versus controls, are presented, along with future applications of targeted validation of brain specific glycoproteins in body fluids.

An update on clinical proteomics in Alzheimer's research

Alzheimer's disease (AD) is a pathologically complex and aetiologically multifactorial dementing disorder affecting millions of people worldwide. The pathological brain changes are assumed to occur decades prior to the onset of clinical symptoms. The diagnosis of early AD remains problematic and is mainly based on clinical and neuropsychological findings after the onset of symptoms. Currently available drugs are able to delay the symptom progression of the disease but not to attenuate the progression of pathological brain changes. Many studies exploring AD proteomes have been conducted as the middle of 1990s as a consequence of recent advances in the development of both gel-based and gel-free proteomics approaches. It is hoped that proteomics can contribute to improving the understanding, diagnosis, and follow-up of the progression of AD. In this review, we summarise the present status of proteome alterations, with emphasis on quantitative approaches, in AD brain, CSF and blood, and their relevance to dementia research.

Biomarkers for Alzheimer disease in cerebrospinal fluid, urine, and blood

Alzheimer disease is the most common cause of dementia, yet its clinical diagnosis remains uncertain until an eventual postmortem histopathology examination. Currently, therapy for patients with Alzheimer disease only treats the symptoms; however, it is anticipated that new disease-modifying drugs will soon become available.Diagnostic tools for detecting Alzheimer disease at an incipient stage that can reliably differentiate the disease from other forms of dementia are of key importance for optimal treatment. Biomarkers have the potential to aid in a correct diagnosis, and great progress has been made in the discovery and development of potentially useful biomarkers in recent years. This includes single protein biomarkers in the cerebrospinal fluid, as well as multi-component biomarkers, and biomarkers based on gene expression. Novel biomarkers that use blood and urine, the more easily available clinical samples, are also being discovered and developed. The plethora of potential biomarkers currently being investigated may soon provide biomarkers that fulfill different functions, not only for diagnostic purposes but also for drug development and to follow disease progression.

Proteomics of human neurodegenerative diseases

The technology, experimental approaches, and bioinformatics that support proteomic research are evolving rapidly. The application of these new capabilities to the study of neurodegenerative diseases is providing insight into the biochemical pathogenesis of neurodegeneration as well as fueling major efforts in biomarker discovery. Here, we review the fundamentals of commonly used proteomic approaches and the outcomes of these investigations with autopsy and cerebrospinal fluid samples from patients with neurodegenerative diseases.

Why do so many drugs for Alzheimer's disease fail in development? Time for new methods and new practices?

Alzheimer's disease (AD) drug developments and clinical trials (CT) remain vulnerable to problems that undermine research validity. Investigations of CT methods reveal how numerous factors decrease active drug-placebo group differences and increase variance, thereby reducing power to reach statistical significance for outcome measure differences in AD CTs. Such factors include, amongst many, inaccuracy, imprecision, bias, failures to follow or lack of operational protocols for applying CT methods, inter-site variance, and lack of homogeneous sampling using disorder criteria. After a review of the literature and survey of a sample of AD and Mild Cognitive Impairment (MCI) CTs, the authors question whether problems of human error preclude AD researchers from continuing their dependence on rated outcome measures for CTs. The authors propose that the realities of AD, especially a probable irreversible progression of neuropathology prior to onset of clinical symptoms or signs capable of differentiating persons at risk for AD from normal aged, require AD investigators and clinicians to privilege biomarkers and encourage their development as surrogate targets for preventive AD treatment developments, testing, and use in clinical practice.

Biomarkers for cognitive impairment and dementia in elderly people

The threat of a looming pandemic of dementia in elderly people highlights the compelling need for the development and validation of biomarkers that can be used to identify pre-clinical and prodromal stages of disease in addition to fully symptomatic dementia. Although predictive risk factors and correlative neuroimaging measures will have important roles in these efforts, this Review describes recent progress in the discovery, validation, and standardisation of molecular biomarkers--small molecules and macromolecules whose concentration in the brain or biological fluids can aid diagnosis at different stages of the more common dementing diseases and in the assessment of disease progression and response to therapeutics. An approach that efficiently combines independent information from risk-factor assessment, neuroimaging measures, and biomarkers might soon guide clinicians in the early diagnosis and management of cognitive impairment in elderly people.