Rethinking the reliability and accuracy of biomarkers in CNS-originating EVs for Parkinson's disease and multiple system atrophy

Differences in Blood and Cerebrospinal Fluid Between Parkinson's Disease and Related Diseases

It is difficult to distinguish Parkinson's disease (PD) in the early stage from those of various disorders including atypical Parkinson's syndrome (APS), vascular parkinsonism (VP), and even essential tremor (ET), because of the overlap of symptoms. Other, more challenging problems will arise when Parkinson's disease develops into Parkinson's disease dementia (PDD) in the middle and late stages. At this time, the differential diagnosis of PDD and DLB becomes thorny. These complicate the diagnostic process for PD, which traditionally heavily relies on symptomatic assessment and treatment response. Recent advances have identified several biomarkers in the blood and cerebrospinal fluid (CSF), including α-synuclein, lysosomal enzymes, fatty acid-binding proteins, and neurofilament light chain, whose concentration differs in PD and the related diseases. However, not all these molecules can effectively discriminate PD from related disorders. This review advocates for a paradigm shift toward biomarker-based diagnosis to effectively distinguish between PD and similar conditions. These biomarkers may reflect the diversity that exist among different diseases and provide an effective way to accurately understand their mechanisms. This review focused on blood and CSF biomarkers of PD that may have differential diagnostic value and the related molecular measurement methods with high diagnostic performance due to emerging technologies.

Plasma versus serum for extracellular vesicle (EV) isolation: A duel for reproducibility and accuracy for CNS-originating EVs biomarker analysis

Blood-derived extracellular vesicles (EVs) are a popular source of biomarkers for central nervous system (CNS) diseases, but inconsistencies in isolation and analysis hinder their clinical translation. This review summarizes recent studies that investigate the impact of different anticoagulated plasma and serum on the yield, purity, and molecular content of EVs. Specifically, the studies compare ethylenediaminetetraacetic acid (EDTA), citrate, heparin plasma, and serum and highlight the risk of contamination from platelet-derived EVs. Here, I offer practical guidelines for standardizing EV isolation and analysis, recommending the use of plasma anticoagulated with acid-citrate-dextrose (ACD) or citrate followed by EDTA and heparin, subgroup analyses for samples from different biobank repositories, and avoiding serum and plasma-to-serum transformation. Other factors like illness, age, gender, meal timing, exercise, circadian timing, and arm pressure during blood draw can alter EV signatures. Yet, how these variables interact with different anticoagulated plasma or serum samples is unclear, necessitating further research. Furthermore, whether the changes are dependent on the isolation or quantification methodology remains an area of investigation. Importantly, the perspective emphasizes the need for consistency in experimental methodologies to improve the reproducibility and clinical applicability of CNS-originating EV biomarker studies. The proposed guidelines, along with ongoing efforts to standardize blood sample handling and collection, may facilitate the development of more reliable and informative CNS-originating EV biomarkers for diagnosis, prognosis, and treatment monitoring of CNS diseases.