Protection from ischemic liver injury by activation of A2Aadenosine receptors during reperfusion: inhibition of chemokine induction

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Abstract
Ischemia-reperfusion (I/R) injury occurs as a result of restoring blood flow to previously hypoperfused vessels or after tissue transplantation and is characterized by inflammation and microvascular occlusion. We report here that 4-{3-[6-amino-9-(5-ethylcarbamoyl-3,4-dihydroxy-tetrahydro-furan-2-yl)-9H-purin-2-yl]-prop-2-ynyl}-cyclohexanecarboxylic acid methyl ester (ATL146e), a selective agonist of the A2A adenosine receptor (A2AAR), profoundly protects mouse liver from I/R injury when administered at the time of reperfusion, and protection is blocked by the antagonist ZM241385. ATL146e lowers liver damage by 90% as assessed by serum glutamyl pyruvic transaminase and reduces hepatic edema and MPO. Most protection remains if ATL146e treatment is delayed for 1 h but disappears when delayed for 4 h after the start of reperfusion. In mice lacking the A2AAR gene, protection by ATL1465e is lost and ischemic injury of short duration is exacerbated compared with wild-type mice, suggesting a protective role for endogenous adenosine. I/R injury causes induction of hepatic transcripts for IL-1α, IL-1ÎČ, IL-1Ra, IL-6, IL-10, IL-18, INF-ÎČ, INF-Îł, regulated on activation, normal T cell expressed, and presumably secreted (RANTES), major intrinsic protein (MIP)-1α, MIP-2, IFN-Îł-inducible protein (IP)-10, and monocyte chemotactic protein (MCP)-1 that are suppressed by administering ATL146e to wild-type but not to A2AAR knockout mice. RANTES, MCP-1, and IP-10 are notable as induced chemokines that are chemotactic to T lymphocytes. The induction of cytokines may contribute to transient lymphopenia and neutrophilia that occur after liver I/R injury. We conclude that most damage after hepatic ischemia occurs during reperfusion and can be blocked by A2AAR activation. We speculate that inhibition of chemokine and cytokine production limits inflammation and contributes to tissue protection by the A2AAR agonist ATL146e.