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.
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.
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).
MRP8/14 is a good marker of disease activity in RA, and higher levels predict response to MTX.