Urinary extracellular vesicles levels of n-3 and n-6 polyunsaturated fatty acids in children with steroid-sensitive nephrotic syndrome: a pilot study

Background: Urine extracellular vesicles (uEVs) are a useful source of non-invasive biomarkers for the diagnosis of kidney diseases. This study aims to characterize the fatty acid (FA) profile of uEVs in children with steroid-sensitive nephrotic syndrome (SSNS) during the active phase of the disease and remission, and to evaluate their association with a pro-inflammatory milieu. Methods: We enrolled 35 SSNS children at different clinical stages, 10 SRNS children with proteinuria, and 14 healthy controls, and collected urine samples. uEVs were isolated by ultracentrifugation and characterized by Western blot, Nanoparticle Tracking Analysis, and Transmission Electron Microscopy. Lipid composition was evaluated by gas chromatography. Results: An increase in omega-3 fatty acids was observed in uEVs isolated from SSNS with proteinuria (above 0.2 mg/mg) (p < 0.01) or in remission (p < 0.05) compared to controls. The α-Linolenic acid (ALA) pathway changed in SSNS children compared to healthy controls. In detail, ALA was upregulated in SSNS patients at remission (p < 0.01 vs. CTRL). Its downstream products, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), were upregulated during remission (p < 0.01 vs. CTRL) and active disease phase (p < 0.05 vs. CTRL), respectively. A higher EPA/DHA ratio was detected in remission compared to the active disease phase (p < 0.05). Moreover, a reduction of linoleic acid (LA) was detected in SSNS at remission (p < 0.05 vs. active SSNS and SRNS) along with a lower linoleic acid/arachidonic acid ratio (LA/AA) (p < 0.01). Short-term prednisone treatment in relapsing patients did not significantly change the overall FA profile in uEVs. Conclusions: This study provides the first evidence that uEV-associated FAs are differentially modulated in uEVs isolated from SSNS, compared to healthy children. Distinct lipid signatures characterize SSNS across disease stages and from SRNS. The reduction of pro-inflammatory lipid mediators during remission in SSNS children supports their potential as biomarkers of disease activity and treatment response for INS patients. Future longitudinal studies are needed to verify the prognostic value of these findings.