The
adenosine pathway is a powerful evolutionarily selected mechanism aimed at a fine modulation of inflammatory responses and protection of tissues from
injuries.
Adenosine exerts its modulatory effects via interaction with
G protein-coupled receptors, designated as A(1), A(2A), A(2B) and A(3). In this regard, extracellular
adenosine concentrations are critical in determining its ability of regulating several biological functions. The levels achieved by
adenosine in close proximity of its receptors are strictly regulated by a variety of dynamic mechanisms, including intracellular and extracellular biosynthesis, transport and metabolism, based on tissue energy status. In this context, the catabolic
enzyme adenosine deaminase (ADA) represents a critical checkpoint in the regulation of extracellular
adenosine levels and, consequently, in the control of receptor stimulation, thus playing a pivotal role in the modulation of purinergic responses to several pathophysiological events, such as chronic
pulmonary diseases,
rheumatoid arthritis,
inflammatory bowel diseases and
sepsis. This article reviews current data on the role played by ADA in the regulation of immune system activity through its modulation of
adenosine pathways. Particular attention has been paid to the involvement of ADA in the pathophysiology of relevant inflammatory diseases. In addition, the interest in designing and developing novel
ADA inhibitors, as new tools potentially useful for the therapeutic management of inflammatory disorders, has been discussed.