Preanalytical Stability of CSF Total and Oligomeric Alpha-Synuclein

Molecular Biomarkers of Neurodegenerative Disorders: A Practical Guide to Their Appropriate Use and Interpretation in Clinical Practice

Neurodegenerative disorders (NDs) represent a group of different diseases characterized by the progressive degeneration and death of the nervous system's cells. The diagnosis is challenging, especially in the early stages, due to no specific clinical signs and symptoms. In this context, laboratory medicine could support clinicians in detecting and differentiating NDs. Indeed, biomarkers could indicate the pathological mechanisms underpinning NDs. The ideal biofluid for detecting the biomarkers of NDs is cerebrospinal fluid (CSF), which has limitations, hampering its widespread use in clinical practice. However, intensive efforts are underway to introduce high-sensitivity analytical methods to detect ND biomarkers in alternative nonivasive biofluid, such as blood or saliva. This study presents an overview of the ND molecular biomarkers currently used in clinical practice. For some diseases, such as Alzheimer's disease or multiple sclerosis, biomarkers are well established and recommended by guidelines. However, for most NDs, intensive research is ongoing to identify reliable and specific biomarkers, and no consensus has yet been achieved.

[Biobanking in clinical trials involving multiple sclerosis patients]

Investigation of multiple sclerosis (MS) pathogenesis requires sophisticated analytical tools of precision medicine, such as omics research, which include genomics, microbiomics and metabolomics (proteomics, lipidomics and glycomics). Such sensitive methods are based on careful preanalytical work with biomaterials to maintain quality and obtain objective results. Implementation of biobanking as a universal method for working with biomaterials will help to standardize the stages of research, compare different scientific team's results. Collaboration of MS researchers with large biobanks can also help to conduct multicenter and long-term prospective studies, to include a wide number of patients. In this article, we analyze the experience of biobanking practice technologies in studies of MS patients and share the experience of partnership between the Center for MS of the Tomsk Region and the Bank of Biological Material of the Siberian State Medical University.

Charting the Next Road Map for CSF Biomarkers in Alzheimer's Disease and Related Dementias

Clinical prediction of underlying pathologic substrates in people with Alzheimer's disease (AD) dementia or related dementia syndromes (ADRD) has limited accuracy. Etiologic biomarkers - including cerebrospinal fluid (CSF) levels of AD proteins and cerebral amyloid PET imaging - have greatly modernized disease-modifying clinical trials in AD, but their integration into medical practice has been slow. Beyond core CSF AD biomarkers (including beta-amyloid 1-42, total tau, and tau phosphorylated at threonine 181), novel biomarkers have been interrogated in single- and multi-centered studies with uneven rigor. Here, we review early expectations for ideal AD/ADRD biomarkers, assess these goals' future applicability, and propose study designs and performance thresholds for meeting these ideals with a focus on CSF biomarkers. We further propose three new characteristics: equity (oversampling of diverse populations in the design and testing of biomarkers), access (reasonable availability to 80% of people at risk for disease, along with pre- and post-biomarker processes), and reliability (thorough evaluation of pre-analytical and analytical factors influencing measurements and performance). Finally, we urge biomarker scientists to balance the desire and evidence for a biomarker to reflect its namesake function, indulge data- as well as theory-driven associations, re-visit the subset of rigorously measured CSF biomarkers in large datasets (such as Alzheimer's disease neuroimaging initiative), and resist the temptation to favor ease over fail-safe in the development phase. This shift from discovery to application, and from suspended disbelief to cogent ingenuity, should allow the AD/ADRD biomarker field to live up to its billing during the next phase of neurodegenerative disease research.

Identifying clinically useful biomarkers in neurodegenerative disease through a collaborative approach: the NeuroToolKit

BACKGROUND

Alzheimer's disease (AD) is a complex and heterogeneous disease, which requires reliable biomarkers for diagnosis and monitoring disease activity. Preanalytical protocol and technical variability associated with biomarker immunoassays makes comparability of biomarker data across multiple cohorts difficult. This study aimed to compare cerebrospinal fluid (CSF) biomarker results across independent cohorts, including participants spanning the AD continuum.

METHODS

Measured on the NeuroToolKit (NTK) prototype panel of immunoassays, 12 CSF biomarkers were evaluated from three cohorts (ALFA+, Wisconsin, and Abby/Blaze). A correction factor was applied to biomarkers found to be affected by preanalytical procedures (amyloid-β1-42, amyloid-β1-40, and alpha-synuclein), and results between cohorts for each disease stage were compared. The relationship between CSF biomarker concentration and cognitive scores was evaluated.

RESULTS

Biomarker distributions were comparable across cohorts following correction. Correlations of biomarker values were consistent across cohorts, regardless of disease stage. Disease stage differentiation was highest for neurofilament light (NfL), phosphorylated tau, and total tau, regardless of the cohort. Correlation between biomarker concentration and cognitive scores was comparable across cohorts, and strongest for NfL, chitinase-3-like protein-1 (YKL40), and glial fibrillary acidic protein.

DISCUSSION

The precision of the NTK enables merging of biomarker datasets, after correction for preanalytical confounders. Assessment of multiple cohorts is crucial to increase power in future studies into AD pathogenesis.

Global, in situ analysis of the structural proteome in individuals with Parkinson's disease to identify a new class of biomarker

Parkinson's disease (PD) is a prevalent neurodegenerative disease for which robust biomarkers are needed. Because protein structure reflects function, we tested whether global, in situ analysis of protein structural changes provides insight into PD pathophysiology and could inform a new concept of structural disease biomarkers. Using limited proteolysis-mass spectrometry (LiP-MS), we identified 76 structurally altered proteins in cerebrospinal fluid (CSF) of individuals with PD relative to healthy donors. These proteins were enriched in processes misregulated in PD, and some proteins also showed structural changes in PD brain samples. CSF protein structural information outperformed abundance information in discriminating between healthy participants and those with PD and improved the discriminatory performance of CSF measures of the hallmark PD protein α-synuclein. We also present the first analysis of inter-individual variability of a structural proteome in healthy individuals, identifying biophysical features of variable protein regions. Although independent validation is needed, our data suggest that global analyses of the human structural proteome will guide the development of novel structural biomarkers of disease and enable hypothesis generation about underlying disease processes.

Diagnostic Utility of Cerebrospinal Fluid α-Synuclein in Creutzfeldt-Jakob Disease: A Systematic Review and Meta-Analysis

BACKGROUND

Creutzfeldt-Jakob disease (CJD) can be difficult to distinguish clinically from some non-prion neurological diseases. Previous studies have reported markedly increased levels of α-synuclein in cerebrospinal fluid (CSF) of CJD patients, indicating that it is a potential diagnostic biomarker.

OBJECTIVE

The aim of this study was to assess the diagnostic power of CSF α-synuclein in discriminating CJD from non-prion disorders.

METHODS

The Ovid MEDLINE, Cochrane, and Embase databases were searched for articles published on or before February 25, 2022, using the search term (prion diseases OR Creutzfeldt-Jakob syndrome) AND (synuclein OR α-synuclein). The difference in CSF α-synuclein levels between CJD and non-prion diseases was calculated using random-effects models (I2 > 50%) or fixed-effects models (I2 < 50%) in terms of standardized mean difference (SMD) and 95% confidence interval (CI). The publication bias was estimated using funnel plots and the Egger's test.

RESULTS

Ten studies were included in this study. The concentrations of CSF α-synuclein were significantly higher in CJD patients compared to total non-prion controls (SMD = 1.98, 95% CI 1.60 to 2.36, p < 0.00001), tauopathies (SMD = 1.34, 95% CI 0.99 to 1.68, p < 0.00001), synucleinopathies (SMD = 1.78, 95% CI 1.11 to 2.44, p < 0.00001), or Alzheimer's (SMD = 1.14, 95% CI 0.95 to 1.33, p < 0.00001). CSF α-synuclein could distinguish CJD from non-prion diseases with overall sensitivity of 89% (95% CI 80-95%), specificity of 92% (95% CI 86-95%), and AUC of 0.96 (95% CI: 0.94-0.97).

CONCLUSION

CSF α-synuclein has excellent diagnostic value in discriminating CJD from non-prion neurological diseases. Given the high heterogeneity among the included studies, further studies are needed to confirm its clinical utility.

Opportunities and challenges of alpha-synuclein as a potential biomarker for Parkinson's disease and other synucleinopathies

Parkinson’s disease (PD), the second most common progressive neurodegenerative disease, develops and progresses for 10–15 years before the clinical diagnostic symptoms of the disease are manifested. Furthermore, several aspects of PD pathology overlap with other neurodegenerative diseases (NDDs) linked to alpha-synuclein (aSyn) aggregation, also called synucleinopathies. Therefore, there is an urgent need to discover and validate early diagnostic and prognostic markers that reflect disease pathophysiology, progression, severity, and potential differences in disease mechanisms between PD and other NDDs. The close association between aSyn and the development of pathology in synucleinopathies, along with the identification of aSyn species in biological fluids, has led to increasing interest in aSyn species as potential biomarkers for early diagnosis of PD and differentiate it from other synucleinopathies. In this review, we (1) provide an overview of the progress toward mapping the distribution of aSyn species in the brain, peripheral tissues, and biological fluids; (2) present comparative and critical analysis of previous studies that measured total aSyn as well as other species such as modified and aggregated forms of aSyn in different biological fluids; and (3) highlight conceptual and technical gaps and challenges that could hinder the development and validation of reliable aSyn biomarkers; and (4) outline a series of recommendations to address these challenges. Finally, we propose a combined biomarker approach based on integrating biochemical, aggregation and structure features of aSyn, in addition to other biomarkers of neurodegeneration. We believe that capturing the diversity of aSyn species is essential to develop robust assays and diagnostics for early detection, patient stratification, monitoring of disease progression, and differentiation between synucleinopathies. This could transform clinical trial design and implementation, accelerate the development of new therapies, and improve clinical decisions and treatment strategies.

Quantitative detection of α-Synuclein and Tau oligomers and other aggregates by digital single particle counting

The pathological hallmark of neurodegenerative diseases is the formation of toxic oligomers by proteins such as alpha-synuclein (aSyn) or microtubule-associated protein tau (Tau). Consequently, such oligomers are promising biomarker candidates for diagnostics as well as drug development. However, measuring oligomers and other aggregates in human biofluids is still challenging as extreme sensitivity and specificity are required. We previously developed surface-based fluorescence intensity distribution analysis (sFIDA) featuring single-particle sensitivity and absolute specificity for aggregates. In this work, we measured aSyn and Tau aggregate concentrations of 237 cerebrospinal fluid (CSF) samples from five cohorts: Parkinson's disease (PD), dementia with Lewy bodies (DLB), Alzheimer's disease (AD), progressive supranuclear palsy (PSP), and a neurologically-normal control group. aSyn aggregate concentration discriminates PD and DLB patients from normal controls (sensitivity 73%, specificity 65%, area under the receiver operating curve (AUC) 0.68). Tau aggregates were significantly elevated in PSP patients compared to all other groups (sensitivity 87%, specificity 70%, AUC 0.76). Further, we found a tight correlation between aSyn and Tau aggregate titers among all patient cohorts (Pearson coefficient of correlation r = 0.81). Our results demonstrate that aSyn and Tau aggregate concentrations measured by sFIDA differentiate neurodegenerative disease diagnostic groups. Moreover, sFIDA-based Tau aggregate measurements might be particularly useful in distinguishing PSP from other parkinsonisms. Finally, our findings suggest that sFIDA can improve pre-clinical and clinical studies by identifying those individuals that will most likely respond to compounds designed to eliminate specific oligomers or to prevent their formation.

Detection and assessment of alpha-synuclein in Parkinson disease

PURPOSE

Different studies have reported varying alpha-synuclein values in the cerebrospinal fluid (CSF), serum, and plasma, making determination of the alpha-synuclein cutoff value for Parkinson's disease difficult and rendering identifying the cause of variation essential.

METHOD

We searched PubMed from inception to June 2021 and identified 76 eligible studies. Included studies reported data on total, phosphorylated, and oligomeric alpha-synuclein in the CSF, serum, or plasma from individuals with Parkinson's disease and healthy controls. The mean or median alpha-synuclein values from the included studies were summarized and categorized through laboratory assays to visualize potential trends.

RESULTS

The enzyme-linked immunosorbent assay (ELISA) is the most common assay used to determine alpha-synuclein concentrations. Less common assays include Luminex, single molecule arrays, electrochemiluminescence, and immunomagnetic reduction (IMR). IMR is a single-antibody and wash-free immunoassay designed for determining the extremely low concentration of bio-molecules. For patients with Parkinson's disease, the median or mean testing values ranged from 60.9 to 55,000 pg/mL in the CSF, 0.446 to 1,777,100 pg/mL in plasma, and 0.0292 to 38,200,000 pg/mL in serum. The antibody selection was diverse between studies. The tendency of distribution was more centralized among studies that used the same kit. Studies adopting specific antibodies or in-house assays contribute to the extreme values. Only a few studies on phosphorylated and oligomeric alpha-synuclein were included.

CONCLUSION

The type of assay and antibody selection in the laboratory played major roles in the alpha-synuclein variation. Studies that used the same assay and kit yielded relatively unanimous results. Furthermore, IMR may be a promising assay for plasma and serum alpha-synuclein quantification. A consensus on sample preparation and testing protocol unification is warranted in the future.

Cerebrospinal fluid hemoglobin levels as markers of blood contamination: relevance for α-synuclein measurement

OBJECTIVES

Cerebrospinal fluid α-synuclein (CSF α-syn) represents a possible biomarker in Parkinson's disease (PD) diagnosis. CSF blood contamination can introduce a bias in α-syn measurement. To date, CSF samples with a red blood cells (RBC) count >50 RBC × 10⁶/L or haemoglobin (Hb) concentration >200 μg/L are excluded from biomarker studies. However, investigations for defining reliable cut-off values are missing.

METHODS

We evaluated the effect of blood contamination on CSF α-syn measurement by a systematic approach in a cohort of 42 patients with different neurological conditions who underwent lumbar puncture (LP) for diagnostic reasons. CSF samples were spiked with whole blood and serially diluted to 800, 400, 200, 100, 75, 50, 25, 5, 0 RBC × 10⁶/L. CSF α-syn and Hb levels were measured by ELISA.

RESULTS

In neat CSF, the average concentration of α-syn was 1,936 ± 636 ng/L. This value increased gradually in spiked CSF samples, up to 4,817 ± 1,456 ng/L (+149% α-syn variation) in samples with 800 RBC × 10⁶/L. We established different cut-offs for discriminating samples with α-syn level above 5, 10, and 20% variation, corresponding to a Hb (RBC) concentration of 1,569 μg/L (37 RBC × 10⁶/L), 2,082 μg/L (62 RBC × 10⁶/L), and 3,118 μg/L (87 RBC × 10⁶/L), respectively.

CONCLUSIONS

Our data show the high impact of CSF blood contamination on CSF α-syn levels, highlighting the measurement of Hb concentration as mandatory when assessing CSF α-syn. The thresholds we calculated are useful to classify CSF samples for blood contamination, considering as reliable only those showing a Hb concentration <1,569 μg/L.