The extracellular concentration of
adenosine in the brain increases dramatically during
ischemia.
Adenosine A(2A) receptor is expressed in neurons and glial cells and in inflammatory cells (lymphocytes and granulocytes). Recently,
adenosine A(2A) receptor emerged as a potential therapeutic attractive target in
ischemia.
Ischemia is a multifactorial pathology characterized by different events evolving in the time. After
ischemia the early massive increase of extracellular
glutamate is followed by activation of resident immune cells, that is, microglia, and production or activation of
inflammation mediators. Proinflammatory
cytokines, which upregulate
cell adhesion molecules, exert an important role in promoting recruitment of leukocytes that in turn promote expansion of the inflammatory response in ischemic tissue. Protracted
neuroinflammation is now recognized as the predominant mechanism of secondary
brain injury progression. A(2A) receptors present on central cells and on blood cells account for important effects depending on the time-related evolution of the pathological condition. Evidence suggests that A(2A) receptor antagonists provide early protection via centrally mediated control of excessive excitotoxicity, while A(2A) receptor agonists provide protracted protection by controlling massive blood cell infiltration in the hours and days after
ischemia. Focus on inflammatory responses provides for
adenosine A(2A) receptor agonists a wide therapeutic time-window of hours and even days after
stroke.