Background/Purpose: Targeted proteomics, which involves quantitative analysis of targeted proteins using selected reaction monitoring (SRM) mass spectrometry, has emerged as a new methodology for discovery of clinical biomarkers. The aim of this study was to identify circulating biomarkers for prediction of disease activity and organ involvement in antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) by using targeted serum proteomics.

Methods: We selected the targeted candidates by an experiment-based approach in which we conducted MS-based serum proteomic profiling of AAV patients before and after treatment. We further selected 87 endothelium-related proteins, which were expected to be present in blood, based on information from publicly available databases. A large-scale SRM assay targeting 135 biomarker candidates was established using a triple quadrupole mass spectrometer coupled with nano-flow liquid chromatography. Target proteins in serum samples from patients in the active and remission (6 months after treatment) stages were quantified using the established assays. Identified marker candidates were further validated by ELISA using serum samples (n=169) collected in a large-cohort Japanese study (RemIT-JAV-RPGN study).

Results: The following proteins were identified as biomarkers for discriminating patients with highly active AAV from those in remission or healthy controls: tenascin C (TNC), C-reactive protein (CRP), tissue inhibitor of metalloproteinase 1 (TIMP1), leucine-rich alpha-2-glycoprotein 1, S100A8/A9, CD93, matrix metalloproteinase 9, and transketolase (TKT). Of these, TIMP1 was the best-performing marker of disease activity, allowing distinction between non-remission (mildly active AAV) and remission. The serum levels of TKT and CD93 were higher in patients with renal involvement than in those without, and predicted renal outcome. The serum level of TNC was elevated significantly in patients with lung infiltration. AAV severity was associated with markers reflecting organ involvement (TKT, CD93 and TNC) rather than inflammation.

Conclusion: We have identified promising biomarkers of disease activity and severity and organ involvement in AAV with targeted proteomics approach using serum samples collected in a large-cohort Japanese study. Especially, our analysis demonstrated the effectiveness of TIMP1 as a marker of AAV activity. In addition, we identified TKT and CD93 as novel markers for evaluation of renal involvement and renal outcome in AAV.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/identification-of-circulating-biomarkers-of-disease-activity-and-organ-involvement-in-anca-associated-vasculitis-by-targeted-proteomics/