Extracellular vesicles (EV), by nomenclature not uniformly defined, are nanoparticles surrounded by a lipid bilayer and released by various cell types, lacking the ability to replicate1. This diverse group includes exosomes, a subpopulation of EV of endosomal origin, typically ranging from approximately 40 nm to 160 nm in diameter2. Detectable in numerous body fluids3, EVs facilitate intercellular communication by transferring various active biomolecules such as proteins, mRNA, microRNA, and lipids. Thus, EV provide information about their cell of origin through cell-specific surface markers and biomolecules, with their properties strongly influenced by the condition of the parent cell and its environment4. These characteristics have led to a growing interest in the potential role of EV as biomarkers, particularly in the context of cardiovascular diseases.
Numerous in vitro and in vivo studies have demonstrated that myocardial hypoxic stress leads to an increased release of EV5,6,7. Contemporary research on EV cargo has largely focused on EV-bound microRNA, which has the potential to serve as a biomarker in the diagnosis of various cardiovascular diseases8,9,10. In contrast, evidence on the circulating EV proteome remains relatively scarce, with even fewer studies investigating plasma EV in cardiovascular patients. In two comprehensive studies on plasma-derived EV from patients suffering myocardial infarction, the authors identified a specific ischemia-induced EV proteome profile with potential diagnostic relevance6,11.
The methodological processing of EV has historically proven challenging, and currently, there is no definitive recommendation for the optimal approach to EV isolation, characterization, and quantification. Commonly used methods for EV isolation include differential ultracentrifugation, density-gradient centrifugation, and filtration methods such as size-exclusion chromatography1. According to current consensus guidelines, the characterization of EV isolates should include evidence of at least three typical EV surface protein markers, such as tetraspanins or annexins, combined with an imaging modality1. To examine EV cargo at the protein level, antibody-based methods such as Western blot or ELISA are most frequently utilized.
Given the methodological challenges associated with the isolation and processing of circulating EV, this protocol presents a comprehensive pathway from patient recruitment and sample collection to subsequent EV isolation, characterization, and quantification of plasma EV isolates. Additionally, this study showcases a workflow for the immediate isolation of plasma-derived EV from patients presenting to the emergency department (Chest Pain Unit) at a tertiary care center in southwestern Germany, followed by the label-free analysis of disease-specific plasma EV proteome using liquid chromatography-tandem mass spectrometry (LC-MS/MS). The aim is to facilitate a high-throughput analysis to identify differentially enriched EV-bound proteins across a large cohort of patients with diverse ischemic, congenital, or (auto-)immune cardiovascular diseases at the initial diagnosis and throughout disease progression and/or resolution. This proteomic screening approach seeks to identify patterns of EV-specific protein enrichment associated with distinct disease pathways, with the ultimate goal of uncovering novel EV-bound protein biomarkers to enhance current diagnostics and therapeutic monitoring in cardiovascular disease.