Sickle cell anemia (SCA) is characterized by renal manifestations, such as glomerular hyperfiltration, proteinuria and tubular dysfunction. Extracellular vesicles (EV) are cell membrane-derived particles that mediate intercellular communication, modulating physiological functions as well as inflammatory and immune responses. They reflect the state of their cell of origin and are studied as biomarkers in various diseases. In this context, studies show that changes in plasma EVs have been associated with disease severity in SCD, but data on urinary EVs (uEVs), mainly released by kidney cells, in this population remain scarce. Therefore, uEVs emerge as promising biomarkers of kidney injury, since they allow an earlier detection of renal damage.

To characterize and quantify uEVs in sickle cell anemia patients, and to evaluate its association with renal function parameters.

This is a cross-sectional analytical study involving adults with SCA followed up at the Hospital Universitário Antonio Pedro/UFF Hematology Outpatient Clinic. Pregnant women and patients with chronic kidney disease stage 4/5 were excluded. Urine and peripheral blood samples were collected and the laboratory analyses including estimated glomerular filtrations rate (eGFR), urea, creatinine, albumin/creatinine ratios (ACR), and protein/creatinine ratios (UPCR) were performed. Twelve non-SCA individuals were included as controls. uEVs were isolated by differential centrifugation and characterized by size (100-900nm) and origin by nanoscale flow cytometry. Total uEVs were characterized by positivity to Annexin-V, podocyte-derived uEVs were double-positive for Annexin-V and podoplanin, proximal tubular-derived uEVs presented positivity for both Annexin-V and megalin.

A total of 17 individuals (82.4% women) with SCA were included in the study. The median age was 37 years (IQR: 26-46 years). In relation to renal function parameters, we obtained an eGFR rate with a median of 125.0 (IQR: 118.5–133.0 mL/min/1.73 m²), with 10 (58.8%) participants presenting values that may suggest glomerular hyperfiltration. The medians for urea and serum creatinine were within the normal range, however, 15 (88.2%) participants presented albuminuria (> 50 mg/g) and 5 (29.4%) presented proteinuria (>200 mg/g). Patients with SCA had a higher count of total uEVs (P = 0.0001) and podocyte-derived uEVs (P = 0.0001) when compared to the control group. When comparing patients with and without glomerular hyperfiltration, we observed a higher tubular-derived uEV count (P = 0.015) in patients without hyperfiltration and a downward trend in the podocyte- derived EVs count (P = 0.086) in the population with hyperfiltration. No differences were observed regarding uEVs count according to proteinuria or albuminuria.

Although some classical markers of renal function remain within the normal range in our cohort in SCA patients, higher counts of urinary EVs may indicate some degree of kidney cellular dysfunction, especially in podocytes. Thus, our data show that SCA patients present a higher release of uEVs and the presence of hyperfiltration may be associated with lower count of uEVs.