Association of Serum Calprotectin (S100A8/A9) Level With Disease Relapse in Proteinase 3-Antineutrophil Cytoplasmic Antibody-Associated Vasculitis

Abstract

Objective: S100A8/A9 (calprotectin) has shown promise as a biomarker for predicting relapse in antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV). This study was undertaken to investigate serum S100A8/A9 level as a biomarker for predicting future relapse in a large cohort of patients with severe AAV.

Methods: Serum levels of S100A8/A9 were measured at baseline and months 1, 2, and 6 following treatment initiation in 144 patients in the Rituximab in ANCA-Associated Vasculitis trial (cyclophosphamide/azathioprine versus rituximab [RTX] for induction of remission) in whom complete remission was attained.

Results: Patients were divided into 4 groups: proteinase 3 (PR3)-ANCA with relapse (n = 37), PR3-ANCA without relapse (n = 56), myeloperoxidase (MPO)-ANCA with relapse (n = 6), and MPO-ANCA without relapse (n = 45). Serum S100A8/A9 level decreased in all groups during the first 6 months of treatment. The percentage reduction from baseline to month 2 was significantly different between patients who experienced a relapse and those who did not in the PR3-ANCA group (P = 0.046). A significantly higher risk of relapse was associated with an increase in S100A8/A9 level between baseline and month 2 (P = 0.0043) and baseline and month 6 (P = 0.0029). Subgroup analysis demonstrated that patients treated with RTX who had increased levels of S100A8/A9 were at greatest risk of future relapse (P = 0.028).

Conclusion: An increase in serum S100A8/A9 level by month 2 or 6 compared to baseline identifies a subgroup of PR3-ANCA patients treated with RTX who are at higher risk of relapse by 18 months. Since RTX is increasingly used for remission induction in PR3-ANCA-positive patients experiencing a relapse, S100A8/A9 level may assist in identifying those patients requiring more intensive or prolonged treatment.

Figure 1

Graphs to demonstrate the % change in serum S100A8/A9. (i) Demonstrates the absolute values of serum S100A8/A9 at each time point in all patients (n=144): baseline, month 1, month 2 and month 6 with significant decreases in the value compared to baseline [all p<0.0001] (ii) shows the results comparing the % change in the PR3-ANCA patients serum levels at month 2 compared to baseline. The median change in serum S100A8/A9 at month 2 compared to baseline was a decrease of 10% in the relapsing groups (IQR −59% to +60%), and a decrease of 31% in the non-relapsing group (IQR −60 to −9%)(p=0.046)[Mann-Whitney U-paired t-test].(iii) Graph demonstrates the % change in PR3-ANCA patients divided into 4 groups (RTX relapse and non-relapse, CYC relapse and non-relapse). The % change in S100A8/A9 is baseline compared to month 1 (M1), month 2 (M2) and month 6 (M6).

Figure 2

Graphs (i) and (ii) are Kaplan-Meier survival curves of the PR3-ANCA patients remaining relapse-free. Times in days represents the duration of complete remission. The data has been adjusted for multiple comparisons and significance defined as p<0.025. The patients are divided into 2 groups: those with a decrease (solid line) and those who had an increase (dotted line) in serum S100A8/A9 between the following time-points: (i) Baseline to month 2 data: (ii) Baseline to month 6. The numbers represent those patients remaining relapse free during follow-up. There is a significant difference in relapse-free survival, with those patients increasing serum S100A8/A9 having a significantly lower relapse-free survival. (i) baseline to month 2 (p= 0.0043), (ii) baseline to month 6 (p=0.0029). Numbers at risk included.

Figure 3

Relapse-free survival divided into the trial treatment groups of all the patients. The x-axis demonstrates days follow-up from 6 months. The patients are divided into 4 groups depending on treatment arm and relapse status. [Blue solid line= patients treated with rituximab with an increase in S100S8/A9][blue dotted line= patients treated with rituximab with no increase in S100A8/A9][black solid line= patients treated with cyclophosphamide with an increase in S100S8/A9][black dotted line= patients treated with cyclophosphamide with no increase in S100A8/A9]. The numbers on the graph represent the number of patients free of relapses categorized into treatment arm and whether there was an increase or decrease in S100A8/A9. Patients treated with rituximab who increased S100A8/A9 demonstrate significantly more relapses than patients with a decrease in S100A8/A9.(i) baseline to month 2 (p=0.006) (ii) baseline to month 6 (p=0.028).