Urinary clusterin-a novel urinary biomarker associated with pediatric lupus renal histopathologic features and renal survival

Background Lupus nephritis (LN) is a major risk factor for systemic lupus erythematous (SLE)-related morbidity and mortality. With the aim of bypassing renal biopsy, we analyzed urinary biomarkers for their ability to predict renal histopathologic features and end-stage kidney disease (ESKD). Methods Urinary albumin, beta 2-microglobulin (B2M), cystatin C, kidney injury molecule-1 (KIM-1), monocyte chemoattractant protein 1 (MCP-1), clusterin, calbindin, interleukin-18 (IL-18), neutrophil gelatinase-associated lipocalin (NGAL), trefoil factor 3 (TFF3), osteopontin, and glutathione S-transferase pi (GST-pi) levels were measured at time of renal biopsy. Renal histopathologies were carefully reviewed. Results Urine from 60 pediatric SLE cases with LN, 29 without and 22 healthy controls were collected. Median age at SLE diagnosis was 12.92 years (range = 4.27-17.30 years) and 10 cases progressed to ESKD during a period of 4.12 +/- 2.17 years. Urinary albumin and clusterin were significantly elevated (p = 0.035 and 0.048, respectively) in patients with tubulointerstitial renal lesions. Urinary clusterin among all urinary markers, performed best at predicting ESKD with cutoff of 0.61 x 10(-4) (AUC = 0.804; p = 0.002). Interestingly, elevation of urinary clusterin likely resulted from local over-expression in tubulointerstitial tissue since the level of serum clusterin was not concomitantly higher (p = 0.424). Conclusion Urinary biomarkers are emerging as non-invasive indicators for lupus-related renal histopathology and renal outcome prediction in pediatric SLE patients. Urinary clusterin, a newly identified biomarker, is an indicator that shows an association with tubulointerstitial renal lesions and demonstrates the best ability to predict ESKD.