Urine soluble urokinase plasminogen activator receptor as a potential biomarker of lupus nephritis activity

There is a lack of non-invasive biomarkers to identify lupus nephritis (LN). Soluble urokinase plasminogen activator receptor (suPAR) is a sensitive biomarker of ongoing inflammation and a potential marker of podocyte dysfunction. The aim of this study was to assess urine and plasma suPAR in LN. 14 systemic lupus erythematosus (SLE) patients with newly diagnosed LN, 8 active SLE patients (SLEDAI >8) without LN and 31 healthy individuals were enrolled. Urine and plasma samples were taken before the initiation of LN induction therapy, and monthly thereafter. Global and renal disease activity were defined using the SLEDAI-2K and the SLEDAI-2K renal domain score, respectively. suPAR concentrations were measured with the suPARnostic Flex ELISA assay. Urine and plasma suPAR levels were elevated in SLE patients with active LN compared with resolved LN and healthy controls. Urine suPAR levels were comparable to healthy controls in active SLE without LN. Urine and plasma suPAR levels were higher before than after the initiation of LN induction therapy. Prospective follow-up measurements also suggested that urine suPAR levels raised again in patients with a relapse of LN according to SLEDAI-2K renal domain score, whereas plasma suPAR levels did not correlate with renal disease activity. Urine suPAR is a promising LN activity biomarker, given its isolated elevation in urine in active LN and pronounced decrease with LN improvement.