In Vivo Hypoxic Preconditioning Protects From Warm Liver Ischemia-Reperfusion Injury Through the Adenosine A2B Receptor

Abstract

BACKGROUND Liver ischemia(I)/reperfusion(R) injury(I) is a known risk factor for the postoperative outcome of patients undergoing liver surgery/transplantation. Attempts to protect from organ damage require multidisciplinary strategies and are of emerging interest in view of patients with higher age and ASA-status. Ischemic preconditioning has been successfully applied to prevent from IRI during liver resections/transplantation. Since even short periods of ischemia during preconditioning inevitably lead to hypoxia and formation of anti-inflammatory/ cytoprotective acting adenosine, we reasoned that short non-ischemic hypoxia also protects against hepatic IRI. METHODS Mice underwent hypoxic preconditioning(HPC) by breathing 10%-oxygen for 10 minutes, followed by 10 minutes of 21%-oxygen prior to left-liver-lobe-ischemia(45 min) and reperfusion(4 hrs). The interactions of hypoxia->adenosine->adenosine-receptors were tested by pharmacologic antagonism at adenosine receptor(AR) sites in wild type mice and in mice with genetic deletions at the A1-;A2A-;A2B- and A3-ARs. Hepatocellular damage, inflammation and metabolic effects were quantified by enzyme activities, cytokines, liver-myeloperoxidase(MPO), blood adenosine and tissue-adenosinemonophosphate(AMP), respectively. RESULTS Hepatoprotection by HPC was significant in wild type and A1-, A2A-and A3 AR-knock-out mice as quantified by lower ALT serum activities, cytokine levels, histological damage-scores, tissue-myeloperoxidase-concentrations and as well as preserved AMP-concentrations. Protection by HPC was blunted in mice pretreated with the A2B-AR-antagonist MRS1754 or in A2B-AR“knock-outs”. CONCLUSION Because liver protective effects of HPC are negated when the A2B receptor is non-functional, the "hypoxia->adenosine->A2B receptor" pathway plays a critical role in the prevention of warm ischemia reperfusion injury in vivo. Hypoxic activation of this pathway warrants use of selective A2B-AR-agonists or even intermittent hypoxia (e.g. in deceased organ donors) to protect from liver ischemia/reperfusion injury.

RETRACTED: Signaling through hepatocellular A2B adenosine receptors dampens ischemia and reperfusion injury of the liver

“…Other studies identified a previously unknown binding site for the hypoxia-inducible factor (HIF) within the promoter region of human Adora2b (28). Moreover, consistent with the our findings, a recent study in hypoxic preconditioning of the liver found liver protection via Adora2b signaling (29). Indeed, the finding that adenosine signaling can dampen hypoxic inflammation goes back to several landmark papers from the research laboratory of Michael Sitkovsky, that provided the first genetic in vivo evidence for adenosine receptor signaling in dampening inflammation (30) or inflammatory hypoxia (31).…”

Purinergic Signaling and Blood Vessels in Health and Disease

“…Hepatic ischemia-reperfusion injury induces expression of A 2B receptors early after partial portal occlusion and A 2B receptor activation has a protective effect (Zimmerman et al, 2011). Hypoxic preconditioning in vivo was reported to protect against liver ischemia-reperfusion injury via A 2B receptors (Choukèr et al, 2012). Ischemia-driven expression of 59-nucleotidase/CD73 leads to increased adenosine production conferring tissue protection during liver ischemia-reperfusion (Hart et al, 2008b).…”

I drink for my liver, Doc: emerging evidence that coffee prevents cirrhosis

“…The receptor that seems to be mainly responsible for adenosine protection is A 2b AR 47, 48 . A 1 AR was also shown to have a protective effect against ethanol-induced hepatotoxicity 49 and to protect against alpha-naphthylisothiocyanate-induced cholestatic liver injury induced by DPCPX (a specific A 1 AR antagonist) in A 1 AR deficient mice 50 .…”