Rheumatoid arthritis (RA) is an inflammatory autoimmune disease characterized by increasingly severe joint inflammation and degeneration. It is also not widely understood at the molecular level, which limits the efficacy of current treatment choices as well as new drug discovery and development. Robust biomarkers are particularly needed, as the current measurements used (C-reactive protein levels and erythrocyte sedimentation rate) are non-specific for RA.
The protein matrix metalloproteinase 3 (MMP-3), which plays a role in cartilage and bone degradation, is associated with RA and has been suggested as a potential biomarker for early disease onset. However, MMP-3 levels do not consistently correlate to clinical response in early disease.
To address the need for better biomarkers, Atsuko Murota and his team at the Keio University School of Medicine used the SOMAscan assay to find novel markers associated with both MMP-3 and RA. The Murota team also sought to identify new biomarkers associated with RA disease status, including response to treatment.
The study was done in two phases.
Phase 1: Screening for RA-associated proteins
Murota’s team used the SOMAscan assay to identify proteins in serum from subjects in three groups:
- People with untreated RA (n = 28)
- People with primary Sjögren’s syndrome (pSS), an autoimmune disease (n = 30)
- Healthy controls with no history of autoimmune disease (n = 30)
The team measured protein levels in each subject’s serum, validating the SOMAscan results with a series of traditional immunoassays. They found 10 proteins in the serum of RA subjects were elevated more than 1.5-fold over healthy controls and more than 1.2-fold over pSS patients. On further examination, only the cytokine interleukin 16 (IL-16) was significantly increased in untreated patients with RA compared to both pSS patients and healthy controls. IL-16 is a proinflammatory cytokine associated with a number of immune-mediated disorders, and was shown in this study to be closely associated with MMP-3 and the most characteristic protein biomarker of RA.
Phase 2: Correlating IL-16 levels with clinical outcomes
The researchers then engaged a second set of subjects to determine whether or not IL-16 levels changed with treatment. They recruited people in three groups:
- Subjects with untreated RA and osteoarthritis as controls
- Methotrexate-naïve subjects treated with methotrexate during the study (n = 28)
- Subjects treated with a combination of methotrexate and a biologic: abatacept (n = 11), tocilizumab (n = 7) or infliximab (n = 22)
Clinical and laboratory assessments for each subject were made at baseline and then after 12 weeks of treatment (with various therapeutic agents or placebo). The team confirmed that IL-16 expression was associated with clinical response during the early treatment phase of RA. IL-16 decreased in all treated subjects except those treated with infliximab.
The significance of IL-16 in the pathogenesis of RA is not yet understood, and more studies (with more subjects) are required to determine the role that IL-16 plays in this disease. However, the fact that this team has demonstrated its unambiguous association with RA is a promising start, and offers a potentially robust biomarker for monitoring disease progression and treatment.
- Murota A et al. (2016) Serum Proteomic Analysis Identifies Interleukin 16 as a Biomarker for Clinical Response during Early Treatment of Rheumatoid Arthritis. Cytokine 78:87–93. doi: 10.1016/j.cyto.2015.12.002