Abstract
Objective Myeloid-related proteins (MRP) 8/14 belong to a family of calcium-binding proteins produced by myeloid cells. Baseline serum levels of MRP8/14 have been shown to predict response to biologicals in rheumatoid arthritis (RA). Because methotrexate (MTX) is the first-line therapy in RA, we studied whether MRP8/14 levels can predict response to MTX.
Methods Patients with active RA disease who were naive to disease-modifying antirheumatic drugs were enrolled. All patients were treated with MTX only, to a maximum of 25 mg/week or the maximal tolerated dose. At 4 months, the European League Against Rheumatism response was assessed. All patients who needed rescue therapy after 2 months or who did not respond at 4 months were classified as nonresponders.
Results Ninety patients were enrolled, of whom 3 discontinued MTX within 4–6 weeks, so 87 patients were analyzed [74 women, median (interquartile range; IQR) for the Disease Activity Score at 28 joints (DAS28) was 4.43 (4.1–5.1)]. The median (IQR) serum MRP8/14 level at baseline was 19.95 μg/ml (11.49–39.06). The serum MRP8/14 had good correlation with DAS28-C-reactive protein (CRP; r = 0.35, p = 0.001). The MRP8/14 levels fell significantly after 4 months of treatment (10.28 μg/ml, 5.95–16.05, p < 0.001). Among 87 patients, 69 were responders. The median (IQR) baseline level of MRP8/14 was higher among responders compared with nonresponders: 23.99 μg/ml (15.39–42.75) versus 9.58 μg/ml (6.11–24.93, p = 0.00250). The levels declined in the responders, from 23.99 μg/ml (15.39–42.75) to 10.41 μg/ml (5.83–15.61, p < 0.001), but not in the nonresponders, from 9.58 μg/ml (6.11–24.93) to 9.19 μg/ml (7.74–21.96, p = 0.687). Receiver-operation characteristic analysis showed that MRP8/14 was a better predictor of response than CRP and erythrocyte sedimentation rate, especially with early disease onset (< 1-yr duration).
Conclusion MRP8/14 is a good marker of disease activity in RA, and higher levels predict response to MTX.
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