Israel Medical Association Journal

Background: The parasympathetic system and its main neurotransmitter, acetylcholine, contributes to homeostasis of inflammation. Cholinergic dysregulation is thought to contribute to the pathogenesis of inflammatory rheumatic diseases. Cholinesterase activity in patients with psoriatic arthritis (PsA) has not been investigated.

Objectives: To compare the cholinesterase activity in patients with PsA and immunocompetent controls and to explore the correlation between cholinergic status (CS) and PsA disease activity.

Methods: Serum acetylcholinesterase (AChE) and total cholinesterase activity were measured in patients with PsA (n=88) and matched controls (n=84). Cholinergic activity before and 3–6 months after the initiation of a biologic treatment was evaluated in seven patients with PsA.

Results: The levels of AChE and CS were similar in both PsA patients and controls. PsA patients treated with biologics had significantly lower levels of AChE and CS compared to patients treated with non-biologics: 447.4 vs. 526 substrate hydrolyzed/min/ml, P = 0.005, and 1360.9 vs. 1536, P = 0.029, respectively. We found an association between C-reactive protein levels, AChE activity (r = 0.291, P = 0.008), and cholinergic status (r = 0.247, P = 0.026) in patients with PsA but not in controls. No correlation between AChE activity, cholinergic status, and the indices of PsA disease activity was found. After initiating or switching biologic treatment in 7 patients, AChE levels remained stable.

Conclusions: We demonstrated similar cholinesterase activity in patients with psoriatic arthritis and controls, highlighting a potential effect of biologic treatment on cholinergic activity in patients with PsA.

The major autoantigens in the inflamed synovium in rheumatoid arthritis (RA) are citrullinated peptides. Citrullinated peptides are employed in diagnostic kits for detection of anti-citrullinated protein antibodies (ACPA), a serological marker with high specificity and sensitivity in the diagnosis of RA, and have been included in the new ACR/EULAR classification criteria for RA. ACPA-positive RA patients suffer from an erosive and more aggressive disease compared to ACPA-negative patients. In view of the mounting indications that ACPA plays a seminal role in the pathogenesis of RA, it might be valuable to pursue a specific treatment aiming ACPA as a target. We found that citrullinated peptides, which contain a unique amino acid, citrulline, alter the protein structure within the connective tissue, leading to tolerance breakdown and triggering the autoimmune response in RA. However, with different doses and routes of administration, citrullinated peptides can promote immune tolerance rather than induction of disease.