Interference of tumor necrosis factor inhibitor treatments on soluble tumor necrosis factor receptor 2 levels in rheumatoid arthritis

Abstract

Objective: Soluble Tumor Necrosis Factor Receptor II (sTNFR2) is used as a biomarker to study cardiovascular disease (CVD) in diverse populations. TNF inhibitors (TNFi's) are a common treatment for inflammatory conditions. The objective of this study was to examine whether TNFi use impacts measured sTNFR2 levels.

Methods: We studied blood samples from a cohort of RA patients with clinical data and high sensitivity-C-reactive protein (hsCRP) measurements. To assess for interference, we tested the entire cohort for the expected positive correlation between sTNFR2 and TNFi using Pearson correlations. We then performed Pearson correlations between sTNFR2 and TNFi and sequentially removed subjects on adalimumab, etanercept, and infliximab; if interference was occurring, no correlation would be observed between hsCRP and sTNFR2, and correlation would be restored by removing subjects on the treatment causing the interference.

Results: We studied 190 subjects, 84.2% female, 73.4% anti-CCP positive. All subjects with sTNFR2 level exceeding measurable level were on etanercept. The expected positive correlation between hsCRP and sTNFR2 was not observed when assessing the entire cohort, r = 0.05, p = 0.51. However, the expected correlation was restored only after excluding subjects on etanercept, r = 0.46, p < 0.0001, and not adalimumab or infliximab. ELISA for sTNFR2 was performed using etanercept only and demonstrated direct binding to sTNFR2.

Conclusions: Our data identified interference between etanercept and the TNFR2 assay. Of the TNFi's, only etanercept has a TNF-binding domain modeled after TNFR2. These data should be considered when designing studies using sTNFR2 in populations where etanercept is a treatment option.

Keywords: Biomarker; Cardiovascular; High sensitivity C-reactive protein (hsCRP); Inflammation; Rheumatoid arthritis; Tumor necrosis factor inhibitor (TNFi).

Fig. 1

Correlation between plasma sTNFR2, hsCRP, and from subjects on different TNFi's. Scatter plots of the 190 RA subjects illustrate influence of etanercept (A), adalimumab (B), and infliximab (C) on the correlation between hsCRP and sTNFR2. Both hsCRP and sTNFR2 levels are on a natural logarithm scale. (A–C) Blue triangles and orange circles represent subjects on and not on the corresponding TNFi. Green solid lines represent linear regression smooth for all subjects; Count (N), Pearson correlation (r) and p-value are shown in the bottom right table in green. Orange dotted lines represent linear regression smooth for subjects not on the corresponding TNFi; Count (N), Pearson correlation (r) and p-value are shown in the bottom right table in orange.

Fig. 2

Correlation between etanercept concentration and ELISA results for sTNFR2 detection, log10 transformed.

Fig. 3

Schematic illustration of interaction between sTNFR2 and etanercept binding to the sTNFR2 assay. ELISA test showing A) sTNFR2 and B) etanercept binding to the monoclonal TNFR2 antibody. sTNFR2 and etanercept share the same soluble extracellular TNFR2 portion (colored in red), which is recognized by the monoclonal TNFR2 antibody.

Fig. s1