The mechanism of Intralipid®-mediated cardioprotection complex IV inhibition by the active metabolite, palmitoylcarnitine, generates reactive oxygen species and activates reperfusion injury salvage kinases.
BACKGROUND
Intralipid® administration at reperfusion elicits protection against myocardial ischemia-reperfusion injury. However, the underlying mechanisms are not fully understood.


METHODS
Sprague-Dawley rat hearts were exposed to 15 min of ischemia and 30 min of reperfusion in the absence or presence of Intralipid® 1% administered at the onset of reperfusion. In separate experiments, the reactive oxygen species (ROS) scavenger N-(2-mercaptopropionyl)-glycine was added either alone or with Intralipid®. Left ventricular work and activation of Akt, STAT3, and ERK1/2 were used to evaluate cardioprotection. ROS production was assessed by measuring the loss of aconitase activity and the release of hydrogen peroxide using Amplex Red. Electron transport chain complex activities and proton leak were measured by high-resolution respirometry in permeabilized cardiac fibers. Titration experiments using the fatty acid intermediates of Intralipid® palmitoyl-, oleoyl- and linoleoylcarnitine served to determine concentration-dependent inhibition of complex IV activity and mitochondrial ROS release.


RESULTS
Intralipid® enhanced postischemic recovery and activated Akt and Erk1/2, effects that were abolished by the ROS scavenger N-(2-mercaptopropionyl)glycine. Palmitoylcarnitine and linoleoylcarnitine, but not oleoylcarnitine concentration-dependently inhibited complex IV. Only palmitoylcarnitine reached high tissue concentrations during early reperfusion and generated significant ROS by complex IV inhibition. Palmitoylcarnitine (1 µM), administered at reperfusion, also fully mimicked Intralipid®-mediated protection in an N-(2-mercaptopropionyl)-glycine -dependent manner.


CONCLUSIONS
Our data describe a new mechanism of postconditioning cardioprotection by the clinically available fat emulsion, Intralipid®. Protection is elicited by the fatty acid intermediate palmitoylcarnitine, and involves inhibition of complex IV, an increase in ROS production and activation of the RISK pathway.
Postdoctoral Fellow, Cardiovascular Research Centre, University of Alberta, Edmonton, AB, Canada.
Phing-How
PH
Lou
Research Associate, Department of Anesthesiology & Pain Medicine, University of Alberta, Edmonton, AB, Canada.
Eliana
E
Lucchinetti
Research Associate, Department of Anesthesiology & Pain Medicine, University of Alberta, Edmonton, AB, Canada.
Liyan
L
Zhang
Research Associate, Department of Clinical Chemistry, University Children's Hospital Zurich, Zurich, Switzerland.
Andreas
A
Affolter
Professor, Institute of Pharmacology and Toxicology, University of Zurich, Zurich, Switzerland.
Marcus C
MC
Schaub
Research Associate, Department of Pharmacology, University of Alberta, Edmonton, AB, Canada.
Manoj
M
Gandhi
Head of the Department of Clinical Chemistry, University Children's Hospital Zurich, Zurich, Switzerland.
Martin
M
Hersberger
Undergraduate student, Campus Saint-Jean, University of Alberta, Edmonton, AB, Canada.
Blair E
BE
Warren
Assistant Professor, Campus Saint-Jean, University of Alberta, Edmonton, AB, Canada.
Hélène
H
Lemieux
Assistant Professor and Director of Coppin Center for Organic Synthesis, Coppin State University, Baltimore, Maryland, United States of America.
Hany F
HF
Sobhi
Professor, Department of Pharmacology, University of Alberta, Edmonton, AB, Canada.
Alexander S
AS
Clanachan
Professor, Department of Anesthesiology & Pain Medicine, University of Alberta, Edmonton, AB, Canada.
Michael
M
Zaugg
D000818:Animals; D002316:Cardiotonic Agents / Q000494:pharmacology*; D002331:Carnitine / Q000031:analogs & derivatives / Q000378:metabolism; D003576:Electron Transport Complex IV / Q000037:antagonists & inhibitors* / Q000378:metabolism; D004655:Emulsions / Q000494:pharmacology; D006321:Heart / Q000187:drug effects; D020935:MAP Kinase Signaling System / Q000187:drug effects; D008297:Male; D008929:Mitochondria, Heart / Q000187:drug effects / Q000378:metabolism; D015428:Myocardial Reperfusion Injury / Q000378:metabolism*; D010172:Palmitoylcarnitine / Q000378:metabolism*; D010743:Phospholipids / Q000494:pharmacology*; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D017382:Reactive Oxygen Species / Q000378:metabolism*; D013024:Soybean Oil / Q000494:pharmacology*; D016277:Ventricular Function, Left / Q000187:drug effects
D002316:Cardiotonic Agents; D004655:Emulsions; D010743:Phospholipids; D017382:Reactive Oxygen Species; C116917:acylcarnitine; C545823:soybean oil, phospholipid emulsion; D010172:Palmitoylcarnitine; D013024:Soybean Oil; D003576:Electron Transport Complex IV; D051057:Proto-Oncogene Proteins c-akt; D002331:Carnitine