Anti-carbamylated protein antibodies: a specific hallmark for rheumatoid arthritis. Comparison to conditions known for enhanced carbamylation; renal failure, smoking and chronic inflammation

Antibodies that target carbamylated proteins (anti-CarP antibodies) have been described as a biomarker in rheumatoid arthritis (RA).1 However, little is known about the factors that predispose to the production of anti-CarP antibodies. Carbamylation is a posttranslational modification resulting from the conversion of lysines into homocitrullines that requires the presence of cyanate. There are several conditions in which the concentration of cyanate (and therefore carbamylation) is increased, such as renal failure, chronic inflammation and heavy smoking.2–4 We therefore addressed the question whether conditions of enhanced carbamylation could result in the induction of anti-CarP antibodies. To investigate this, we determined the presence of anti-CarP antibodies in serum samples from patients with renal failure,5 inflammatory bowel disease (IBD)6 and in heavy smokers with or without chronic obstructive pulmonary disease (COPD)7 (see table 1). The presence of anti-CarP antibodies in healthy controls and patients with RA was used as a comparison.1 ,8 The collection of these cohorts was approved by the Leiden University Medical Center ethics committee and informed consent …