Myeloperoxidase and oxidative stress in rheumatoid arthritis

Myeloperoxidase and oxidative stress in rheumatoid arthritis

Objective. To determine whether MPO contributes to oxidative stress and disease activity in rheumatoid arthritis ( RA) and whether it produces hypochlorous acid in SF.


Methods. Plasma and where possible SF were collected from 77 RA patients while 120 healthy controls supplied plasma only. MPO and protein carbonyls were measured by ELISAs. 3-Chlorotyrosine in proteins and allantoin in plasma were measured by mass spectrometry.

Results. Plasma Myeloperoxidase concentrations were significantly higher in patients with RA compared with healthy controls [10.8 ng/ml, inter-quartile range (IQR): 7.2–14.2; P < 0.05], but there was no significant difference in plasma MPO protein concentrations between RA patients with high disease activity (HDA; DAS-28 >3.2) and those with low disease activity (LDA; DAS-28 ≤3.2) (HDA 27.9 ng/ml, 20.2–34.1 vs LDA 22.1 ng/ml, 16.9–34.9; P > 0.05). There was a significant relationship between plasma MPO and DAS-28 (r = 0.35; P = 0.005). Plasma protein carbonyls and allantoin were significantly higher in patients with RA compared with the healthy controls. MPO protein was significantly higher in SF compared with plasma (median 624.0 ng/ml, IQR 258.4–2433.0 vs 30.2 ng/ml, IQR 25.1–50.9; P < 0.0001). The MPO present in SF was mostly active. 3-Chlorotyrosine, a specific biomarker of hypochlorous acid, was present in proteins from SF and related to the concentration of MPO (r = 0.69; P = 0.001). Protein carbonyls in SF were associated with MPO protein concentration (r = 0.40; P = 0.019) and 3-chlorotyrosine (r = 0.66; P = 0.003).

Conclusion. MPO is elevated in patients with RA and promotes oxidative stress through the production of hypochlorous acid.

Lisa K. Stamp1, Irada Khalilova2, Joanna M. Tarr3, Revathy Senthilmohan2, Rufus Turner2, Richard C. Haigh3,4, Paul G. Winyard3 and Anthony J. Kettle2


+ Author Affiliations

1Department of Medicine, 2Department of Pathology, University of Otago Christchurch, Christchurch, New Zealand, 3Peninsula Medical School, University of Exeter and 4Royal Devon and Exeter Foundation Trust, Exeter, UK.

Correspondence to: Lisa K. Stamp, Department of Medicine, University of Otago, Christchurch, PO Box 4345, Christchurch 8140, New Zealand. E-mail: lisa.stamp@cdhb.govt.nz