Role of adenosine receptors in the treatment of asthma and chronic obstructive pulmonary disease: recent developments.

Adenosine is a naturally occurring purine nucleoside with a ubiquitous presence in human tissue, where it plays a key role in many biological processes such as energy generation and protein metabolism. It has been shown that adenosine induces bronchoconstriction in asthmatic and chronic obstructive pulmonary disease (COPD) patients, but not in normal airways. Four different G-protein-coupled adenosine receptors have been described, namely adenosine A(1), A(2A), A(2B) and A(3) receptors. The main mechanism of adenosine-induced bronchoconstriction appears to involve the release of inflammatory mediators from mast cells via activation of the A(2B) receptor. However, adenosine can also act on A(1), A(2A) and A(3) receptors. In recent years there has been an increasing interest in the role of adenosine receptors in asthma and COPD, since it is now clear that they play an important role in the pathophysiology of asthma and COPD. Adenosine receptors are involved in the production and release of a variety of mediators from inflammatory and structural cells. A therapeutic potential for adenosine receptor modulation has even been anticipated. This review focuses on the role of adenosine and adenosine receptors in the treatment of asthma and COPD.