The Mechanism of Intralipid®-Mediated Cardioprotection Complex IV Inhibition by the Active Metabolite, Palmitoylcarnitine, Generates Reactive Oxygen Species and Activates Reperfusion Injury Salvage Kinases

Abstract

BackgroundIntralipid® administration at reperfusion elicits protection against myocardial ischemia-reperfusion injury. However, the underlying mechanisms are not fully understood.MethodsSprague-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.ResultsIntralipid® 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.ConclusionsOur 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.

The Third American Society of Regional Anesthesia and Pain Medicine Practice Advisory on Local Anesthetic Systemic Toxicity

“…25 Coupled with the observation that infused lipid emulsion activates cardioprotective pathways, this provides an additional mechanism of postconditioning benefit to the local anesthetic-toxic heart. 26,27 The explanations behind these purported benefits are discussed in detail in the supporting article. 10…”

The Mechanisms Underlying Lipid Resuscitation Therapy

“…24 The activation of Akt and inhibition of GSK-3β contribute to prevention of opening of the mPTP; this effect is consistent with studies showing that ILE attenuates IR injury. 112,116,117 Lou et al 118 proposed a mechanism of protection by ILE in IR injury based on accumulation of palmitoylcarnitine, which slightly uncouples mitochondria at complex IVand releases a burst of ROS, which signal RISK activation. Reactive oxygen species can oxidize and inactivate phosphatase and tensin homolog, which leads to hyperphosphorylation of prosurvival kinases, 119 making this a plausible but incompletely tested hypothesis.…”

“…124,125 Lipid also modifies signaling in many pathways while functioning as a metabolic fuel. Lipid activates Akt, Erk1/2, and GSK-3b after IR injury, 112,[116][117][118] as well as AMPK in peripheral tissues, 126 and can drive cardiac hypertrophy. 127 Long-term lipid treatment activates PKCy and PKCδ via diacylglycerol to promote insulin resistance.…”

MRI Investigation of New Approach to Improve the Recovery of Myocardial Ischemia Reperfusion Injury by Treatment with Intralipid<sup>®</sup>

“…Based on these results, we hypothesize that Intralipid ® has the potential to derail MØs and change the trafficking of MØs in inflammatory heart diseases. Intralipid ® has been shown to protect hearts against ischemic reperfusion injury to reduce infarct size after ischemic insult [21]- [23]. The cardioprotective mechanisms of Intralipid ® are not totally understood.…”

“…The cardioprotective mechanisms of Intralipid ® are not totally understood. It has been shown that Intralipid ® can inhibit mitochondrial permeability transition pore opening [24] and reduce mitochondrial superoxide production, and increase pro-survival kinases such as Akt and GSK-3 [23] among other effects [4] [6] [7] [25] [26]. However, the effect of Intralipid ® on post-MI inflammatory MØs has not been investigated.…”