Protein-Based Biomarkers in Cerebrospinal Fluid and Blood for Alzheimer’s Disease

Advanced Overview of Biomarkers and Techniques for Early Diagnosis of Alzheimer's Disease

The development of early non-invasive diagnosis methods and identification of novel biomarkers are necessary for managing Alzheimer's disease (AD) and facilitating effective prognosis and treatment. AD has multi-factorial nature and involves complex molecular mechanism, which causes neuronal degeneration. The primary challenges in early AD detection include patient heterogeneity and lack of precise diagnosis at the preclinical stage. Several cerebrospinal fluid (CSF) and blood biomarkers have been proposed to show excellent diagnosis ability by identifying tau pathology and cerebral amyloid beta (Aβ) for AD. Intense research endeavors are being made to develop ultrasensitive detection techniques and find potent biomarkers for early AD diagnosis. To mitigate AD worldwide, understanding various CSF biomarkers, blood biomarkers, and techniques that can be used for early diagnosis is imperative. This review attempts to provide information regarding AD pathophysiology, genetic and non-genetic factors associated with AD, several potential blood and CSF biomarkers, like neurofilament light, neurogranin, Aβ, and tau, along with biomarkers under development for AD detection. Besides, numerous techniques, such as neuroimaging, spectroscopic techniques, biosensors, and neuroproteomics, which are being explored to aid early AD detection, have been discussed. The insights thus gained would help in finding potential biomarkers and suitable techniques for the accurate diagnosis of early AD before cognitive dysfunction.

The Association of Blood-Based Inflammatory Factors IL-1β, TGF-β and CRP with Cognitive Function in Alzheimer's Disease and Mild Cognitive Impairment

OBJECTIVE

Many patients suffer from dementia in its most common form, Alzheimer's disease (AD). In this study, the levels of IL-1β, TGF-β and CRP, which are involved in the inflammatory response in Alzheimer's disease and its mild cognitive impairment (MCI), were measured and analyzed.

METHODS

Seventy nine subjects participated in this study (mean age: 75.56 years, female: 54.3%, AD: 26, MCI: 28, normal: 25). The overall cognitive function of the subjects and the severity of the disease stage were assessed using the Mini-Mental State Examination (MMSE-K), the Clinical Dementia Rating (CDR), the Global Deterioration Scale (GDS) and the Geriatric Depression Scale-Korean (GDS-K).

RESULTS

It was observed that patients with AD had significantly higher levels of IL-1β and TGF-β than the patients with MCI and normal controls. In addition, the MCI group showed a statistically significantly higher TGF-β concentration than the normal group.

CONCLUSION

These results suggest that IL-1β and TGF-β may be useful biological markers for patients with Alzheimer's disease.

Dysregulation of stress systems and nitric oxide signaling underlies neuronal dysfunction in Alzheimer's disease

Stress is a multimodal response involving the coordination of numerous body systems in order to maximize the chance of survival. However, long term activation of the stress response results in neuronal oxidative stress via reactive oxygen and nitrogen species generation, contributing to the development of depression. Stress-induced depression shares a high comorbidity with other neurological conditions including Alzheimer's disease (AD) and dementia, often appearing as one of the earliest observable symptoms in these diseases. Furthermore, stress and/or depression appear to exacerbate cognitive impairment in the context of AD associated with dysfunctional catecholaminergic signaling. Given there are a number of homologous pathways involved in the pathophysiology of depression and AD, this article will highlight the mechanisms by which stress-induced perturbations in oxidative stress, and particularly NO signaling, contribute to neurodegeneration.

Plasma Protein Biomarkers for the Prediction of CSF Amyloid and Tau and [18F]-Flutemetamol PET Scan Result

Background: Blood biomarkers may aid in recruitment to clinical trials of Alzheimer's disease (AD) modifying therapeutics by triaging potential trials participants for amyloid positron emission tomography (PET) or cerebrospinal fluid (CSF) Aβ and tau tests. Objective: To discover a plasma proteomic signature associated with CSF and PET measures of AD pathology. Methods: Liquid chromatography-tandem mass spectrometry (LC-MS/MS) based proteomics were performed in plasma from participants with subjective cognitive decline (SCD), mild cognitive impairment (MCI), and AD, recruited to the Amsterdam Dementia Cohort, stratified by CSF Tau/Aβ42 (n = 50). Technical replication and independent validation were performed by immunoassay in plasma from SCD, MCI, and AD participants recruited to the Amsterdam Dementia Cohort with CSF measures (n = 100), MCI participants enrolled in the GE067-005 study with [18F]-Flutemetamol PET amyloid measures (n = 173), and AD, MCI and cognitively healthy participants from the EMIF 500 study with CSF Aβ42 measurements (n = 494). Results: 25 discovery proteins were nominally associated with CSF Tau/Aβ42 (P < 0.05) with associations of ficolin-2 (FCN2), apolipoprotein C-IV and fibrinogen β chain confirmed by immunoassay (P < 0.05). In the GE067-005 cohort, FCN2 was nominally associated with PET amyloid (P < 0.05) replicating the association with CSF Tau/Aβ42. There were nominally significant associations of complement component 3 with PET amyloid, and apolipoprotein(a), apolipoprotein A-I, ceruloplasmin, and PPY with MCI conversion to AD (all P < 0.05). In the EMIF 500 cohort FCN2 was trending toward a significant relationship with CSF Aβ42 (P ≈ 0.05), while both A1AT and clusterin were nominally significantly associated with CSF Aβ42 (both P < 0.05). Conclusion: Associations of plasma proteins with multiple measures of AD pathology and progression are demonstrated. To our knowledge this is the first study to report an association of FCN2 with AD pathology. Further testing of the proteins in larger independent cohorts will be important.

Mechanism involved in insulin resistance via accumulation of β-amyloid and neurofibrillary tangles: link between type 2 diabetes and Alzheimer's disease

The pathophysiological link between type 2 diabetes mellitus (T2DM) and Alzheimer's disease (AD) has been suggested in several reports. Few findings suggest that T2DM has strong link in the development process of AD, and the complete mechanism is yet to be revealed. Formation of amyloid plaques (APs) and neurofibrillary tangles (NFTs) are two central hallmarks in the AD. APs are the dense composites of β-amyloid protein (Aβ) which accumulates around the nerve cells. Moreover, NFTs are the twisted fibers containing hyperphosphorylated tau proteins present in certain residues of Aβ that build up inside the brain cells. Certain factors contribute to the aetiogenesis of AD by regulating insulin signaling pathway in the brain and accelerating the formation of neurotoxic Aβ and NFTs via various mechanisms, including GSK3β, JNK, CamKII, CDK5, CK1, MARK4, PLK2, Syk, DYRK1A, PPP, and P70S6K. Progression to AD could be influenced by insulin signaling pathway that is affected due to T2DM. Interestingly, NFTs and APs lead to the impairment of several crucial cascades, such as synaptogenesis, neurotrophy, and apoptosis, which are regulated by insulin, cholesterol, and glucose metabolism. The investigation of the molecular cascades through insulin functions in brain contributes to probe and perceive progressions of diabetes to AD. This review elaborates the molecular insights that would help to further understand the potential mechanisms linking T2DM and AD.

Proteomic Analysis of Protein Expression Throughout Disease Progression in a Mouse Model of Alzheimer's Disease

Alzheimer's disease (AD) is the most common cause of dementia. Mice in the transgenic AβPPswe/PS1dE9 mouse line express a chimeric mouse/human amyloid-β protein precursor (Mo/HuAβPP695swe) and mutant human presenilin 1 (PS1-dE9) associated with early-onset AD. Knowing the protein expression in these mice may offer better understanding of the pathological changes in AD. In this study, we used two-dimensional gel electrophoresis combined with mass spectrometry techniques to compare protein expression in AβPPswe/PS1dE9 mice with age-matched wild-type mice throughout the disease progression. We identified 15 proteins that were significantly different between the AβPPswe/PS1dE9 mice and age-matched controls and also changed with disease development. Among those, the expression levels of the following proteins in AβPPswe/PS1dE9 mice were at least 1.5 times higher than those in normal mice: DCC-interacting protein 13-beta, serum albumin, creatine kinase B-type, heat shock 70 kDa protein 1A, T-complex protein 1 subunit beta, adenylate kinase isoenzyme 1, pyruvate dehydrogenase E1 component subunit beta mitochondrial, and V-type proton ATPase catalytic subunit A. Levels of the following proteins in AβPPswe/PS1dE9 mice were at least 1.5 times lower than those in normal mice: dihydropyrimidinase-related protein 2, actin cytoplasmic 2, isoform 1 of V-type proton ATPase catalytic subunit, tubulin alpha-1C chain, F-actin-capping protein subunit alpha-2, ubiquitin carboxyl-terminal hydrolase isozyme L1, and actin cytoplasmic 1. These proteins are involved in regulating various cellular functions, including cytoskeletal structure, energy metabolism, synaptic components, and protein degradation. These findings indicate altered protein expression in the pathogenesis of AD and illuminate novel therapeutic avenues for treatment in AD.

The Immune System and Neuroinflammation as Potential Sources of Blood-Based Biomarkers for Alzheimer's Disease, Parkinson's Disease, and Huntington's Disease

Neurodegenerative diseases are characterized by a loss of neurons that leads to cognitive and behavioral dysfunction. Alzheimer's disease (AD) is the most common neurodegenerative disorder affecting millions of people in the United States and worldwide, followed by Parkinson's disease (PD). While some early onset forms of AD and PD are hereditary, the sporadic or late-onset cases are believed to result from lifestyle and environmental factors. On the contrary, Huntington's disease (HD) is a neurodegenerative disease solely caused by mutations in the gene for huntingtin protein. The disease mechanisms at play for all three disorders remain elusive, hampering efforts to develop effective therapeutic interventions. In light of this, the discovery of robust biomarkers is crucial in order to identify people at risk for AD and PD, preferably before symptoms arise. For all three diseases, the identification of biomarkers would not only allow development of treatments but also evaluation and adjustment of these with disease progression. It is now understood that neuroinflammation plays a crucial role in neurodegenerative diseases, along with subsequent immune activation. Therefore, research is actively ongoing to discover and evaluate inflammatory and immune-related biomarkers. Recent progress in this area for AD, PD, and HD is presented here.