Transient limb ischemia induces remote preconditioning and remote postconditioning in humans by a K(ATP)-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.


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 K(ATP) channel activation. These results suggest that remote conditioning stimuli could be protective in patients with acute ischemia about to undergo therapeutic reperfusion.
Loukogeorgakis
Stavros P
SP
Vascular Physiology Unit, Institute of Child Health, University College London, 34 Great Ormond St, London, WC1N 3JE, UK. s.loukogeorgakis@ich.ucl.ac.uk
Williams
Rupert
R
Panagiotidou
Anna T
AT
Kolvekar
Shyamsunder K
SK
Donald
Ann
A
Cole
Tim J
TJ
Yellon
Derek M
DM
Deanfield
John E
JE
MacAllister
Raymond J
RJ
D000328:Adult; D000368:Aged; D050197:Atherosclerosis / Q000503:physiopathology; D001916:Brachial Artery / Q000503:physiopathology*; D004730:Endothelium, Vascular / Q000187:drug effects / Q000503:physiopathology; D005260:Female; D005542:Forearm / Q000098:blood supply*; D005905:Glyburide / Q000494:pharmacology; D018056:Hemorheology / Q000187:drug effects; D006801:Humans; D006940:Hyperemia / Q000503:physiopathology; D007511:Ischemia / Q000503:physiopathology / Q000628:therapy*; D019194:Ischemic Preconditioning / Q000379:methods*; D007866:Leg / Q000098:blood supply*; D008297:Male; D008875:Middle Aged; D009928:Organ Specificity; D026902:Potassium Channel Blockers / Q000494:pharmacology; D015221:Potassium Channels / Q000187:drug effects / Q000502:physiology*; D011955:Receptors, Drug / Q000187:drug effects / Q000502:physiology*; D015427:Reperfusion Injury / Q000503:physiopathology / Q000517:prevention & control*; D013997:Time Factors; D014664:Vasodilation / Q000187:drug effects / Q000502:physiology
D026902:Potassium Channel Blockers; D015221:Potassium Channels; D011955:Receptors, Drug; C067662:glibenclamide receptor; D005905:Glyburide