Adenosine signaling in airways: toward a promising antiasthmatic approach.

Adenosine participates to asthma physiopathology by signaling through more than just one receptor subtype. Defining the role of each receptor is complicated by evidence that often results obtained on rodents do not coincide with human studies, but what emerges is that an important condition to establish hyperresponsiveness to adenosine in any species of sensitized animals is the exposure to allergen; this feature appears to be very similar to the human situation, since allergic humans regularly undergo exposure to allergen. Furthermore, A₂B in humans, but A₃ receptor in rodents, would mediate, indirectly, the bronchoconstriction in response to adenosine and would play the main role in adenosine-induced airway inflammation and airway hyperreactivity. On the other hand, A₁ receptor over-expressed on asthmatic airways would mediate a direct adenosine bronchoconstrictor effect. Antagonists and agonists to adenosine receptors have been considered as antiasthmatic drugs but often their development has been limited by unwanted effects. Preventing adenosine accumulation in airways should be considered as a novel promising antiasthmatic strategy.