Evaluation and validation of biomarkers in granulomatosis with polyangiitis and microscopic polyangiitis

Background. Studies in anti-neutrophil cytoplasm antibody (ANCA)-associated vasculitis (AAV) have revealed promising biomarkers. The aim of our study was to validate the most encouraging markers of granulomatosis with polyangiitis and microscopic polyangiitis identified by literature search and to create biomarker panels. Methods. A systematic literature review was performed and we identified 161 marker molecules that were ranked by their quantitative differential expression between active and inactive disease. Enzyme-linked immunosorbent assays were used to validate the results in a cross-sectional cohort of patients with renal involvement. Active vasculitis as assessed by the Birmingham Vasculitis Score version 3 (BVAS v3) was defined as BVAS v3 >= 1 and inactive disease as BVAS v3 = 0. Statistical analysis was performed with SPSS version 21 and the Salford Predictive Modeler 7.0 was used to generate a predictive biomarker panel. Results. The review indicated abundant expression of sC5bC9, C3a, C5a and monocyte chemotactic protein (MCP)-1 in urine, whereas granulocyte macrophage colony-stimulating factor, C-reactive protein (CRP), soluble fms-like tyrosine kinase-1, interleukin-17A (IL-17A), C5a, hyaluronan, C3a and interleukin-18 binding protein (IL-18BP) were identified to be highly diverse in active and inactive disease in blood samples. Our cross-sectional analysis revealed significant up-regulation of CRP, C5a, C3a, IL-18BP in blood and C5a and MCP-1 in urine samples during active AAV (all P < 0.05). Creation of a biomarker panel comprising CRP and urinary MCP-1 yielded a sensitivity and specificity of 76% (area under the curve 0.89). Conclusions. We identified promising biomarkers in a literature-based review that were in part corroborated as has been shown for CRP, C3a, C5a, IL-18BP in blood and MCP-1 and C5a in urine samples. Moreover, we propose a biomarker panel comprising CRP and urinary MCP-1 in patients with AAV and renal involvement. Further investigations to confirm our preliminary results are clearly warranted, including the reliability to predict disease relapses.