Role and Function of A2A and A3 Adenosine Receptors in Patients with Ankylosing Spondylitis, Psoriatic Arthritis and Rheumatoid Arthritis

Rheumatoid arthritis (RA), ankylosing spondylitis (AS) and psoriatic arthritis (PsA) are chronic inflammatory rheumatic diseases that affect joints, causing debilitating pain and disability. Adenosine receptors (ARs) play a key role in the mechanism of inflammation, and the activation of A(2A) and A(3)AR subtypes is often associated with a reduction of the inflammatory status. The aim of this study was to investigate the involvement of ARs in patients suffering from early-RA (ERA), RA, AS and PsA. Messenger RNA (mRNA) analysis and saturation binding experiments indicated an upregulation of A(2A) and A(3)ARs in lymphocytes obtained from patients when compared with healthy subjects. A(2A) and A(3)AR agonists inhibited nuclear factor kappa-light-chain-enhancer of activated B cells (NF-kappa B) activation and reduced inflammatory cytokines release, such as tumor necrosis factor-alpha (TNF-alpha), interleukin (IL)-1 beta and IL-6. Moreover, A(2A) and A(3)AR activation mediated a reduction of metalloproteinases (MMP)-1 and MMP-3. The effect of the agonists was abrogated by selective antagonists demonstrating the direct involvement of these receptor subtypes. Taken together, these data confirmed the involvement of ARs in chronic autoimmune rheumatic diseases highlighting the possibility to exploit A(2A) and A(3)ARs as therapeutic targets, with the aim to limit the inflammatory responses usually associated with RA, AS and PsA.