Incremental Value of CSF Biomarkers in Clinically Diagnosed AD and Non-AD Dementia

Targeting amyloid proteins for clinical diagnosis of neurodegenerative diseases

Abnormal aggregation and accumulation of pathological amyloid proteins such as amyloid-β, Tau, and α-synuclein play key pathological roles and serve as histological hallmarks in different neurodegenerative diseases (NDs) such as Alzheimer's disease (AD) and Parkinson's disease (PD). In addition, various post-translational modifications (PTMs) have been identified on pathological amyloid proteins and are subjected to change during disease progression. Given the central role of amyloid proteins in NDs, tremendous efforts have been made to develop amyloid-targeting strategies for clinical diagnosis and molecular classification of NDs. In this review, we summarize two major strategies for targeting amyloid aggregates, with a focus on the trials in AD diagnosis. The first strategy is a positron emission tomography (PET) scan of protein aggregation in the brain. We mainly focus on introducing the development of small-molecule PET tracers for specifically recognizing pathological amyloid fibrils. The second strategy is the detection of PTM biomarkers on amyloid proteins in cerebrospinal fluid and plasma. We discuss the pathological roles of different PTMs in diseases and how we can use the PTM profile of amyloid proteins for clinical diagnosis. Finally, we point out the potential technical challenges of these two strategies, and outline other potential strategies, as well as a combination of multiple strategies, for molecular diagnosis of NDs.

Clinical usefulness of cerebrospinal fluid biomarkers in Alzheimer's disease

BACKGROUND

Alzheimer's disease (AD) is a complex disease that shares clinical features with other dementias. It is important to establish a specific and reliable diagnosis. Nowadays, AD diagnosis is based on cerebrospinal fluid (CSF) biomarkers. However, the corresponding cut-offs differ amongst studies. This study aims to evaluate the CSF biomarkers in the AD differential diagnosis.

METHODS

Clinical relevant biomarkers (amyloid β42 (Aβ42), t-Tau, p-Tau, amyloid β40 (Aβ40), neurofilament light chain (NfL)) were determined in CSF samples from participants classified as AD (n = 124) and non-AD (n = 148) patients from the Neurology Unit. They were included and evaluated consecutively (August 2018-October 2020). The clinical utility of these biomarkers was evaluated by AUC-ROC curves and the corresponding cut-off points were defined.

RESULTS

The results showed satisfactory accuracy (AUC-ROC 0.91 for Aβ42, 0.890 for t-Tau and 0.933 for p-Tau); whilst Aβ40 and NfL did not show good discriminatory capacity (AUC-ROC 0.557 and 0.738, respectively). The ratios Aβ42/Aβ40 and t-Tau/Aβ42 improved the diagnosis indices of each individual biomarker, with AUC-ROC of 0.980 and 0.971, respectively. Also, elevated levels of NfL were found in the frontotemporal dementia group compared with the other participant groups.

CONCLUSIONS

The ratio Aβ42/Aβ40 showed the highest discriminating capacity between AD and non-AD patients and might be useful in clinical practice. Regarding NfL, it is not a specific biomarker for AD; however, it might be helpful for the differential diagnosis of frontotemporal dementia. Nevertheless, further analysis in an external cohort is required in order to validate these results.

Correlation between Cerebrospinal Fluid Core Alzheimer's Disease Biomarkers and β-Amyloid PET in Chinese Dementia Population

The current diagnoses of Alzheimer's disease (AD) mainly rely on such measures as amyloid-β (Aβ) and tau neuropathology biomarkers in vivo via cerebrospinal fluid (CSF) and positron emission tomography (PET) imaging, which had been systematically studied in Caucasian individuals, whereas diagnostic performances of these approaches in Chinese dementia population still remain unclear. This study investigated the associations between the levels of CSF core AD biomarkers, including phosphorylated tau (p-Tau181), total tau (t-Tau), Aβ42, and Aβ40 measured by the single-molecule array (Simoa) and cerebral Aβ deposition status assessed by ¹⁸F-Florbetapir PET (Aβ PET), and evaluated the predictive values of CSF core AD biomarkers in discriminating Aβ PET status in a clinical dementia cohort of the Chinese population, which consisted of patients with mild cognitive impairment (MCI), AD dementia, and non-Alzheimer's dementia disease (Non-ADD). Global standard uptake value ratios (SUVRs) were calculated by Aβ PET, which was divided into positive (Aβ+) and negative (Aβ-) through visual analysis. CSF p-Tau181 and p-Tau181/t-Tau ratio were positively correlated with the global SUVR, while CSF Aβ42 and Aβ42/Aβ40 ratio were negatively correlated with the global SUVR. CSF Aβ40 has the highest predictive value in discriminating the MCI group from the AD group, while CSF p-Tau181 was applied to discriminate the AD group from the non-ADD group. CSF Aβ42/Aβ40 ratio, as the optimal predictive factor, was combined with APOE ε4 status rather than age and education, which could improve the predictive ability in differentiating the Aβ+ group from the Aβ- group. The results reveal the universal applicability of CSF core AD biomarkers and Aβ PET imaging in Chinese dementia population, which is helpful in clinical practice and drug trials in China.

Mass Spectrometry for Neurobiomarker Discovery: The Relevance of Post-Translational Modifications

Neurodegenerative diseases are incurable, heterogeneous, and age-dependent disorders that challenge modern medicine. A deeper understanding of the pathogenesis underlying neurodegenerative diseases is necessary to solve the unmet need for new diagnostic biomarkers and disease-modifying therapy and reduce these diseases’ burden. Specifically, post-translational modifications (PTMs) play a significant role in neurodegeneration. Due to its proximity to the brain parenchyma, cerebrospinal fluid (CSF) has long been used as an indirect way to measure changes in the brain. Mass spectrometry (MS) analysis in neurodegenerative diseases focusing on PTMs and in the context of biomarker discovery has improved and opened venues for analyzing more complex matrices such as brain tissue and blood. Notably, phosphorylated tau protein, truncated α-synuclein, APP and TDP-43, and many other modifications were extensively characterized by MS. Great potential is underlying specific pathological PTM-signatures for clinical application. This review focuses on PTM-modified proteins involved in neurodegenerative diseases and highlights the most important and recent breakthroughs in MS-based biomarker discovery.