Antibodies against 4 Atypical Post-Translational Protein Modifications in Patients with Rheumatoid Arthritis.

Lorena Rodríguez-Martínez,Paloma Herbello-Hermelo,Antonio Moreda-Piñeiro,Antonio Mera-Varela,Carmen Pena,Eva Pérez-Pampín,Sámer Amhaz-Escanlar,Antonio González,Javier Rodriguez-Garcia,Cristina Regueiro

doi:10.3390/diagnostics12020352

Abstract

Patients with rheumatoid arthritis (RA) show autoantibodies against post-translational protein modifications (PTMs), such as anti-citrullinated protein antibodies. However, the range of recognized PTMs is unknown. Here, we addressed four PTMs: chlorination, non-enzymatic glycation, nitration, and homocysteinylation, identified as targets of atypical RA autoantibodies in studies whose protocols we have followed. The modified antigens included collagen type II, an extract of synovial proteins and a selection of peptides. We interpreted the results according to the optical density (OD) obtained in an enzyme-linked immunosorbent assay ( ELISA) with the modified antigen and the corrected OD obtained after subtracting the reactivity against the unmodified antigen. The results showed evidence of specific antibodies against glycated collagen type II, as the corrected ODs were higher in the 182 patients with RA than in the 164 healthy controls (p = 0.0003). However, the relevance of these antibodies was doubtful because the magnitude of the specific signal was small (median OD = 0.072 vs. 0.027, respectively). There were no specific antibodies against any of the other three PTMs. Therefore, our results showed that the four PTMs are not inducing a significant autoantibody response in patients with RA. These results indicated that the repertoire of PTM autoantigens in RA is restricted.

Highlights

Rheumatoid arthritis (RA) is a chronic autoimmune disease of complex etiology and pathogenesis [1]
We aimed to explore four atypical anti-protein modifications (PTMs) antibodies that have been described in rheumatoid arthritis (RA) as recognizing the following PTM: protein chlorination by hypochlorous acid [11,13], which is one of the reactive oxygen species found in arthritic joints; protein non-enzymatic glycation and formation of advanced glycation end products (AGEs) by ribose [11,13,14]; the tyrosine nitration of peptides or, more broadly, the nitration of proteins by peroxynitrite [10,11], which is a reactive nitrogen species increased in inflamed joints; and the homocysteinylation by a metabolite of homocysteine, homocysteine-thiolactone [9,12]
We considered the 182 RA patients with samples taken less than two years after symptom onset as an early RA subset (ERA), whereas the remaining 143 RA patients formed an established RA subset

Summary

Introduction

Rheumatoid arthritis (RA) is a chronic autoimmune disease of complex etiology and pathogenesis [1]. It is characterized by inflammation at multiple joints leading to pain, morning stiffness, joint swelling, and functional disability. Well established autoantigens include the malondialdehyde and malondialdehyde-acetaldehyde adduct containing proteins, the antibodies against these are less specific for RA [4,5]. All of these PTMs affect many proteins and take place in many tissues in a variety of physiological and pathological situations. The identity of the proteins that are modified is less important for the binding of the autoantibodies than the PTM itself, meaning that the patient can sera bind multiple different peptides with the same PTM [4,6,7,8]

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Conclusion