Contribution of adenosine A2 receptors and cyclic adenosine monophosphate to protective ischemic preconditioning of sinusoidal endothelial cells against storage/reperfusion injury in rat livers

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Abstract
A brief period of liver ischemia decreases sinusoidal endothelial cell killing after cold liver storage and improves graft survival after liver transplantation, a phenomenon called ischemic preconditioning. In this study, we investigated the mechanism of sinusoidal endothelial cell protection after ischemic preconditioning. Livers were preconditioned by 5 minutes of ischemia and 5 minutes of reperfusion. Subsequently, livers were stored for 30 hours in cold University of Wisconsin (UW) solution and reperfused briefly with physiological buffer containing Trypan blue. Ischemic preconditioning decreased sinusoidal endothelial cell killing after storage/reperfusion, as assessed by Trypan blue staining of nonparenchymal cells. Adenosine A2 receptor blockade prevented the protective effect of ischemic preconditioning. By contrast, adenosine A1 receptor blockade did not prevent protective ischemic preconditioning. Other rat livers were treated with adenosine A1 and A2 receptor agonists or dibutyryl-cyclic adenosine monophosphate (DB-cAMP) before storage. The adenosine A2 receptor agonist, CGS-21680, and DB-cAMP decreased sinusoidal endothelial cell killing to the same extent as ischemic preconditioning, but the adenosine A1 receptor agonist, 2-chloro-N 6-cyclopentyladenosine (CCPA), had no effect. The adenosine A2 agonist and prostaglandin E2, another agent that preconditions sinusoidal endothelial cells against storage/reperfusion injury, but not the adenosine A1 agonist, increased cAMP levels in cultured sinusoidal endothelial cells. In conclusion, an adenosine A2 receptor pathway coupled to increased cAMP mediates sinusoidal endothelial cell protection by ischemic preconditioning.

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