Urinary Extracellular Vesicles as Potential Source of Acute Kidney Injury Biomarkers for Liquid Biopsy

Acute kidney injury (AKI), characterized by sudden loss of excretory kidney function, affects approximately 15% of hospitalized patients. When maladaptive repair occurs, AKI frequently progresses to chronic kidney disease (CKD). Traditional diagnostic methods, including estimated glomerular filtration rate (eGFR), hinder early detection, while kidney biopsy, though the gold standard, is invasive and impractical for routine use. Recently, liquid biopsy has emerged as a promising alternative. In this scenario, extracellular vesicles (EVs)—cell-secreted nanovesicles—are crucial for detecting disease-related proteins. Urinary EVs (uEVs), reflecting molecular signatures from various kidney regions, offer valuable biomarkers for kidney diseases. However, their small size hampers surface protein detection by standard flow cytometry, requiring bead-based assays. In this study, we aimed to assess a uEV bead-based cytofluorimetric analysis using a novel membrane-sensing peptide (MSP) that binds EVs based on lipid curvature. After validating the peptide’s ability to isolate uEVs, we analyzed surface biomarkers in 49 AKI patients followed for three months post-discharge. By comparing this flow cytometry-based approach with a commercial kit, our goal was to identify a clinically translatable method for monitoring AKI-to-CKD progression. Profiling uEVs with the commercial kit revealed significant differences in marker expression between AKI patients and controls. Notably, stage-specific embryonic antigen-4 (SSEA-4), upregulated in patients with improved renal function three months post-discharge, showed promise as a prognostic biomarker for AKI-to-CKD transition. Using MSP-beads to capture uEVs, we confirmed a decrease in CD24 in AKI patients, though no markers for AKI-to-CKD transition were identified. This study highlights the potential of uEV surface biomarkers in AKI-to-CKD progression, revealing SSEA-4 as a promising candidate. Further research should focus on refining the MSP-bead assay, validating its effectiveness in larger cohorts.