Transient limb ischemia induces remote preconditioning and remote postconditioning in humans by a KATP channel-dependent mechanism

Background - Transient limb ischemia administered before a prolonged ischemic insult has systemic protective effects against ischemia-reperfusion (IR) injury ( remote ischemic preconditioning [RIPC]). It has been demonstrated that protection from IR can be achieved by brief periods of ischemia applied at a remote site during an injurious ischemic event ( remote postconditioning [RPostC]). Using an in vivo model of endothelial IR injury, we sought to determine whether RPostC occurred in humans and whether it shared mechanistic similarities with RIPC. Methods and Results - Endothelial function was assessed by flow-mediated dilation before and after IR ( 20 minutes of arm ischemia followed by reperfusion). RIPC was induced by conditioning cycles of 5 minutes of ischemia and reperfusion on the contralateral arm or leg before IR. For RPostC induction, conditioning cycles were administered during the ischemic phase of IR. Oral glibenclamide was used to determine the dependence of RIPC and RPostC on K(ATP) channels. IR caused a significant reduction in flow-mediated dilation in healthy volunteers ( baseline, 9.3 +/- 1.2% versus post-IR, 3.3 +/- 0.7%; P < 0.0001) and patients with atherosclerosis ( baseline, 5.5 +/- 0.6% versus post-IR, 2.3 +/- 0.5%; P < 0.01). This reduction was prevented by RIPC (post-IR+RIPC: healthy volunteers, 7.2 +/- 0.5% [P < 0.0001 versus post-IR]; patients, 4.5 +/- 0.3% [P < 0.01 versus post-IR]) and RPostC (post-IR+RPostC: 8.0 +/- 0.5%; P < 0.0001 versus post-IR). The protective effects of RIPC and RPostC were blocked by glibenclamide. Conclusions - This study demonstrates for the first time in humans that RPostC can be induced by transient limb ischemia and is as effective as RIPC in preventing endothelial IR injury. RIPC and RPostC share mechanistic similarities, with protection being dependent on KATP channel activation. These results suggest that remote conditioning stimuli could be protective in patients with acute ischemia about to undergo therapeutic reperfusion.