Peptidylarginine deiminase 4 (PAD4) activity in early rheumatoid arthritis

Objectives: Peptidylarginine deiminases (PADs) are a family of calcium-dependent enzymes catalysing the conversion of arginine residues to citrulline, which may constitute a risk factor in rheumatoid arthritis (RA) pathogenesis. We investigated PAD activation by serum (PAD_Act) in early RA, and the associations between PAD activation and disease characteristics, treatment response, and progression of radiographic damage.Method: Sera from disease-modifying anti-rheumatic drug (DMARD)-naïve early RA patients (n = 225), classified according to the 2010 American College of Rheumatology/European League Against Rheumatism criteria, and healthy controls (n = 63) were analysed for PAD4 activating capacity at 0, 3, 12, and 24 months using a high-performance liquid chromatography fluorometric method. Associations for PAD_Act were evaluated by Mann-Whitney U and chi-squared tests. Changes in PAD_Act levels were compared using the Wilcoxon signed-rank test.Results: PAD_Act positivity occurred in 42% (n = 95) of the patients and was more prevalent in anti-citrullinated protein antibody (ACPA)-positive vs ACPA-negative patients (47% vs 20%, p = 0.002), but not in rheumatoid factor (RF)-positive vs RF-negative patients (44% vs 38%, p = 0.49). PAD_Act-positive were younger than PAD_Act-negative patients [mean ± sd 48.7 ± 13.5 vs 53.2 ± 13.7 years, p = 0.011]. Median [25th, 75th percentile] PAD_Act levels were higher in patients than in controls (8768 [7491, 11 393] vs 7046 [6347, 7906], p < 0.0001) and decreased after initiation of DMARD treatment, but were not associated with treatment response or progression of radiographic damage after 2 years of follow-up.Conclusion: Serum capacity to activate PAD4 was associated with ACPA and RF positivity and earlier disease onset in early RA patients, and decreased after initiation of DMARD treatment, indicating that anti-PAD treatment could potentially be beneficial in RA.