Assessment of tubular-derived extracellular vesicles in association with urinary tubular markers, inflammatory mediators and disease activity in lupus nephritis

Introduction: Lupus nephritis (LN) is a complication of systemic lupus erythematosus (SLE), a chronic inflammatory autoimmune disease, which can involve renal damage via immune complex deposition, leading to cellular stress and local production of inflammatory mediators. In this context, tubular cells can release extracellular vesicles (EVs) containing bioactive molecules to enhance the LN development. Objective: To evaluate associations between urinary inflammatory mediators, disease activity and tubular-derived EVs in patients with SLE. Methods: This observational cross-sectional study is conducted at Hospital Universitário Antonio Pedro/UFF, approved by the Ethics and Research Committee/UFF (60747722.2.0000.5243). Groups were defined according SLEDAI-2K and R-SLEDAI indexes: inactive LES (SLEDAI-2K =0), active SLE (SLEDAI-2K ≥1), and LN (SLEDAI-2K ≥1 and R-SLEDAI ≥4). Urinary tubular biomarkers were assessed according to commercial multiplex assays and kidney injury molecule-1 (KIM-1) was assessed by ELISA. Urinary EVs (uEV) were isolated by differential centrifugation and tubular-derived uEVs were identified by nanoscale flow cytometry (Annexin V and anti-megalin/LRP2). Results: 46 patients were included, 8 (17.4%) were inactive SLE, 19 (41.3%) were active SLE, and 19 (41.3%) with LN. LN patients presented higher count of tubular uEVs (p=0.02). Also, moderate positive correlations were observed between tubular uEVs and SLEDAI-2K (r=0.5, p=0.009), R-SLEDAI (r=0.4, p=0.01), and KIM-1 (r=0.7, p=0.02) in LN patients. uEVs also presented a strong negative correlation with EGF (r=-0.9, p=0.0007) and clusterin (r=-0.7, p=0.03). Lastly, the same group presented higher urinary levels of IL-6 when compared to inactive SLE (p=0.01) Conclusion: Our results suggest that tubular-derived urinary EVs are associated with disease activity, markers of tubular injury and inflammatory mediators in LN, reinforcing their potential as noninvasive biomarkers of renal involvement in SLE.