Infarct-remodelled hearts with limited oxidative capacity boost fatty acid oxidation after conditioning against ischaemia/reperfusion injury

miR-133a-A Potential Target for Improving Cardiac Mitochondrial Health and Regeneration After Injury

ABSTRACT

The various roles of muscle secretory factors and myokines have been well studied, but in recent decades, the role of myocyte-specific microRNAs (myomiRs) has gained momentum. These myomiRs are known to play regulatory roles in muscle health in general, both skeletal muscle and cardiac muscle. In this review, we have focused on the significance of a myomiR termed miR-133a in cardiovascular health. The available literature supports the claim that miR-133a could be helpful in the healing process of muscle tissue after injury. The protective function could be due to its regulatory effect on muscle or stem cell mitochondrial function. In this review, we have shed light on the protective mechanisms offered by miR-133a. Most of the beneficial effects are due to the presence of miR-133a in circulation or tissue-specific expression. We have also reviewed the potential mechanisms by which miR-133a could interact with cell surface receptors and also transcriptional mechanisms by which they offer cardioprotection and regeneration. Understanding these mechanisms will help in finding an ideal strategy to repair cardiac tissue after injury.

Cardioprotective effects of empagliflozin after ischemia and reperfusion in rats

The Sodium Glucose Co-Transporter-2 inhibitor, empagliflozin (EMPA), reduces mortality and hospitalisation for heart failure following myocardial infarction irrespective of diabetes status. While the findings suggest an inherent cardioprotective capacity, the mechanism remains unknown. We studied infarct size (IS) ex-vivo in isolated hearts exposed to global IR injury and in-vivo in rats subjected to regional myocardial ischemia reperfusion (IR) injury, in whom we followed left ventricular dysfunction for 28 days. We compared rats that were given EMPA orally for 7 days before, EMPA 1.5 h before IR injury and at onset of reperfusion and continued orally during the follow-up period. We used echocardiography, high resolution respirometry, microdialysis and plasma levels of β-hydroxybutyrate to assess myocardial performance, mitochondrial respiration and intermediary metabolism, respectively. Pretreatment with EMPA for 7 days reduced IS in-vivo (65 ± 7% vs. 46 ± 8%, p < 0.0001 while administration 1.5 h before IR, at onset of reperfusion or ex-vivo did not. EMPA alleviated LV dysfunction irrespective of the reduction in IS. EMPA improved mitochondrial respiration and modulated myocardial interstitial metabolism while the concentration of β-hydroxybutyric acid was only transiently increased without any association with IS reduction. EMPA reduces infarct size and yields cardioprotection in non-diabetic rats with ischemic LV dysfunction by an indirect, delayed intrinsic mechanism that also improves systolic function beyond infarct size reduction. The mechanism involves enhanced mitochondrial respiratory capacity and modulated myocardial metabolism but not hyperketonemia.

Panax quinquefolium saponin Optimizes Energy Homeostasis by Modulating AMPK-Activated Metabolic Pathways in Hypoxia-Reperfusion Induced Cardiomyocytes

OBJECTIVE

To investigate the effects and underlying mechanisms of Panax quinquefolium saponin (PQS) on energy deficiency in hypoxia-reperfusion (H/R) induced cardiomyocytes.

METHODS

The H/R injury involved hypoxia for 3 h and then reperfusion for 2 h. Cardiomyocytes recruited from neonatal rat ventricular myocytes (NRVMs) were randomly divided into control, H/R, H/R+compound C (C.C), H/R+PQS, and H/R+C. C+PQS groups. BrdU assay, lactase dehydrogenase (LDH) leakage and early apoptosis rate were evaluated to assess cell damages. Contents of high energy phosphate compounds were conducted to detect the energy production. Protein expression levels of adenosine monophosphate-activated protein kinase a (AMPKα), glucose transporter 4 (GLUT4), phosphate fructose kinase 2 (PFK2), fatty acid translocase/cluster of differentiation 36 (FAT/CD36), and acetyl CoA carboxylase 2 (ACC2) in the regulatory pathways were measured by Western blotting. Immunofluorescence staining of GLUT4 and FAT/CD36 was used to observe the mobilization of metabolic transporters.

RESULTS

PQS (50 mg/L) pretreatment significantly alleviated H/R-induced inhibition of NRVMs viability, up-regulation of LDH leakage, acceleration of early apoptosis, and reduction of energy production (P<0.05). Compared with the H/R group, up-regulated expression of AMPKα, GLUT4, PFK2, FAT/CD36 and ACC2 were observed, and more GLUT4 and FAT/CD36 expressions were detected on the membrane in the H/R+PQS group (P<0.05). These effects of PQS on H/R-induced NRVMs were eliminated in the H/R+C.C+PQS group (P<0.05).

CONCLUSION

PQS has prominent advantages in protecting NRVMs from H/R-induced cell damages and energy metabolic disorders, by activation of AMPKα-mediated GLUT4-PFK2 and FAT/CD36-ACC2 pathways.

Intralipid Increases Nitric Oxide Release from Human Endothelial Cells During Oxidative Stress

BACKGROUND

Intralipid (ILP), a lipid emulsion, protects organs against ischemia/reperfusion (IR) injury. We hypothesized that ILP activates endothelial nitric oxide synthase (eNOS) and increases NO release from endothelial cells (ECs) through a fatty-acid translocase cluster of differentiation (CD36) mediated endocytotic mechanism, acting as a potentially protective paracrine signal during oxidative stress.

METHODS

Human umbilical-vein ECs were exposed to 1% ILP for 2 hours followed by oxidative stress with 0.2-mM hydrogen peroxide for 2 hours. Western blots were conducted with anti-CD36, dynamin-2, src-kinase-1, eNOS, and phospho-eNOS; equal protein loading was confirmed with β-actin. CD36 immunoprecipitation was probed for caveolin-1 to determine if CD36 and caveolin-1 were complexed on the cell membrane. NO was measured by fluorescence of ECs.

RESULTS

ILP caused a 227% increase in CD36 expression vs controls. Immunoprecipitation indicated a CD36/caveolin-1 complex on ECs' membrane with exposure to ILP. Dynamin-2 increased 52% and src-kinase-1 340% after ILP treatment vs control cells. eNOS phosphorylation was confirmed by a 63% increase in the phospho-eNOS/eNOS ratio in ILP-treated cells, and NO fluorescence increased 102%.

CONCLUSION

ILP enters ECs via endocytosis by a CD36/caveolin-1 cell membrane receptor complex, which in turn is pulled into the cell by dynamin-2 activity. Upregulation of src-kinase-1 and eNOS phosphorylation suggest downstream mediators. Subsequent NO release from ECs serve as a paracrine signal to neighboring cells for protection against IR injury. Student t-test was utilized for single comparisons and analysis of variance with Bonferroni-Dunn post hoc modification for multiple comparisons; P < .05 was considered statistically significant.

Myocardial ischaemia reperfusion injury: the challenge of translating ischaemic and anaesthetic protection from animal models to humans

Myocardial ischaemia reperfusion injury is the leading cause of death in patients with cardiovascular disease. Interventions such as ischaemic pre and postconditioning protect against myocardial ischaemia reperfusion injury. Certain anaesthesia drugs and opioids can produce the same effects, which led to an initial flurry of excitement given the extensive use of these drugs in surgery. The underlying mechanisms have since been extensively studied in experimental animal models but attempts to translate these findings to clinical settings have resulted in contradictory results. There are a number of reasons for this such as dose response, the intensity of the ischaemic stimulus applied, the duration of ischaemia and lost or diminished cardioprotection in common co-morbidities such as diabetes and senescence. This review focuses on current knowledge regarding myocardial ischaemia reperfusion injury and cardioprotective interventions both in experimental animal studies and in clinical trials.

Postconditioning with Intralipid emulsion protects against reperfusion injury in post-infarct remodeled rat hearts by activation of ROS-Akt/Erk signaling

The clinically used lipid emulsion Intralipid (ILE) reduces ischemia reperfusion injury in healthy rodent hearts. We tested whether ILE is cardioprotective in postinfarct remodeled hearts. Post-infarct remodeled and sham Sprague-Dawley rat hearts were perfused in working mode and subjected to ischemia (15 minutes) and reperfusion (30 minutes). Left ventricular (LV) work was measured in hearts that were untreated or that received ILE (1%) postconditioning administered at the onset of reperfusion, or the reactive oxygen species (ROS) scavenger N-(2-mercaptopropionyl)-glycine (10 μM) alone or in combination with ILE. Mitochondrial O₂ consumption was measured in LV muscle fibers. Acetyl CoA production was calculated from the oxidation of [U-¹⁴C]glucose and [9,10-³H]palmitate. ROS production was assessed by loss of aconitase activity as well as by release of hydrogen peroxide. Phosphorylation of Akt, Erk1/2, and STAT3 were used to evaluate protection signaling. Remodeled hearts exhibited LV dysfunction and signs of hypertrophy consistent with significant postinfarct remodeling. ILE postconditioning enhanced the recovery of postischemic LV function in remodeled hearts, preserved energy metabolism in mitochondria, accelerated palmitate oxidation and acetyl CoA production, and activated Akt/Erk/STAT3 in a ROS-dependent manner. Protection by ILE postconditioning evolved rapidly within the first minutes of reperfusion without evidence of additional cardiotonic effects due to provision of supplementary energy substrates potentially released from ILE during reperfusion. ILE represents a novel and clinically feasible cardioprotective strategy that is highly effective in remodeled hearts. Our data provide a rationale for the clinical evaluation of ILE postconditioning where ILE is administered as a bolus at the onset of reperfusion.

Lysophosphatidic Acid Pretreatment Attenuates Myocardial Ischemia/Reperfusion Injury in the Immature Hearts of Rats

The cardioprotection of the immature heart during cardiac surgery remains controversial due to the differences between the adult heart and the newborn heart. Lysophosphatidic acid (LPA) is a small bioactive molecule with diverse functions including cell proliferation and survival via its receptor: LPA₁–LPA₆. We previously reported that the expressions of LPA₁ and LPA₃ in rat hearts were much higher in immature hearts and then declined rapidly with age. In this study, we aimed to investigate whether LPA signaling plays a potential protective role in immature hearts which had experienced ischemia/reperfusion (I/R) injury. The results showed that in Langendorff-perfused immature rat hearts (2 weeks), compared to I/R group, LPA pretreatment significantly enhanced the cardiac function, attenuated myocardial infarct size and CK-MB release, decreased myocardial apoptosis and increased the expression of pro-survival signaling molecules. All these effects could be abolished by Ki16425, an antagonist to LPA₁ and LPA₃. Similarly, LPA pretreatment protected H9C2 from hypoxia-reoxygenation (H/R) induced apoptosis and necrosis in vitro. The mechanisms underlying the anti-apoptosis effects were related to activation of the phosphatidylinositol 3-kinase (PI3K)/protein kinas B (AKT) signaling pathways as well as phosphorylation of the downstream effector of AKT, glycogen synthase kinase 3 beta (GSK3β), through LPA₁ and/or LPA₃. What's more, we found that LPA preconditioning increased glucose uptake of H9C2 subjected to H/R by the activation of AMP-Activated Protein Kinase (AMPK) but not the translocation of GLUT4. In conclusion, our study indicates that LPA is a potent survival factor for immature hearts against I/R injuries and has the potential therapeutic function as a cardioplegia additive for infantile cardiac surgery.

Pre-ischaemic mitochondrial substrate constraint by inhibition of malate-aspartate shuttle preserves mitochondrial function after ischaemia-reperfusion

KEY POINTS

Pre-ischaemic administration of aminooxiacetate (AOA), an inhibitor of the malate-aspartate shuttle (MAS), provides cardioprotection against ischaemia-reperfusion injury. The underlying mechanism remains unknown. We examined whether transient inhibition of the MAS during ischaemia and early reperfusion by AOA treatment could prevent mitochondrial damage at later reperfusion. The AOA treatment preserved mitochondrial respiratory capacity with reduced mitochondrial oxidative stress during late reperfusion to the same extent as ischaemic preconditioning (IPC). However, AOA treatment, but not IPC, reduced the myocardial interstitial concentration of tricarboxylic acid cycle intermediates at the onset of reperfusion. The results obtained in the present study demonstrate that metabolic regulation by inhibition of the MAS at the onset of reperfusion may be beneficial for the preservation of mitochondrial function during late reperfusion in an IR-injured heart.

ABSTRACT

Mitochondrial dysfunction plays a central role in ischaemia-reperfusion (IR) injury. Pre-ischaemic administration of aminooxyacetate (AOA), an inhibitor of the malate-aspartate shuttle (MAS), provides cardioprotection against IR injury, although the underlying mechanism remains unknown. We hypothesized that a transient inhibition of the MAS during ischaemia and early reperfusion could preserve mitochondrial function at later phase of reperfusion in the IR-injured heart to the same extent as ischaemic preconditioning (IPC), which is a well-validated cardioprotective strategy against IR injury. In the present study, we show that pre-ischaemic administration of AOA preserved mitochondrial complex I-linked state 3 respiration and fatty acid oxidation during late reperfusion in IR-injured isolated rat hearts. AOA treatment also attenuated the excessive emission of mitochondrial reactive oxygen species during state 3 with complex I-linked substrates during late reperfusion, which was consistent with reduced oxidative damage in the IR-injured heart. As a result, AOA treatment reduced infarct size after reperfusion. These protective effects of MAS inhibition on the mitochondria were similar to those of IPC. Intriguingly, the protection of mitochondrial function by AOA treatment appears to be different from that of IPC because AOA treatment, but not IPC, downregulated myocardial tricarboxilic acid (TCA)-cycle intermediates at the onset of reperfusion. MAS inhibition thus preserved mitochondrial respiratory capacity and decreased mitochondrial oxidative stress during late reperfusion in the IR-injured heart, at least in part, via metabolic regulation of TCA cycle intermediates in the mitochondria at the onset of reperfusion.

Testosterone Replacement Modulates Cardiac Metabolic Remodeling after Myocardial Infarction by Upregulating PPARα

Despite the importance of testosterone as a metabolic hormone, its effects on myocardial metabolism in the ischemic heart remain unclear. Myocardial ischemia leads to metabolic remodeling, ultimately resulting in ATP deficiency and cardiac dysfunction. In the present study, the effects of testosterone replacement on the ischemic heart were assessed in a castrated rat myocardial infarction model established by ligating the left anterior descending coronary artery 2 weeks after castration. The results of real-time PCR and Western blot analyses showed that peroxisome proliferator-activated receptor α (PPARα) decreased in the ischemic myocardium of castrated rats, compared with the sham-castration group, and the mRNA expression of genes involved in fatty acid metabolism (the fatty acid translocase CD36, carnitine palmitoyltransferase I, and medium-chain acyl-CoA dehydrogenase) and glucose transporter-4 also decreased. A decline in ATP levels in the castrated rats was accompanied by increased cardiomyocyte apoptosis and fibrosis and impaired cardiac function, compared with the sham-castration group, and these detrimental effects were reversed by testosterone replacement. Taken together, our findings suggest that testosterone can modulate myocardial metabolic remodeling by upregulating PPARα after myocardial infarction, exerting a protective effect on cardiac function.

PPARs: Protectors or Opponents of Myocardial Function?

Over 5 million people in the United States suffer from the complications of heart failure (HF), which is a rapidly expanding health complication. Disorders that contribute to HF include ischemic cardiac disease, cardiomyopathies, and hypertension. Peroxisome proliferator-activated receptors (PPARs) are members of the nuclear receptor family. There are three PPAR isoforms: PPARα, PPARγ, and PPARδ. They can be activated by endogenous ligands, such as fatty acids, as well as by pharmacologic agents. Activators of PPARs are used for treating several metabolic complications, such as diabetes and hyperlipidemia that are directly or indirectly associated with HF. However, some of these drugs have adverse effects that compromise cardiac function. This review article aims to summarize the current basic and clinical research findings of the beneficial or detrimental effects of PPAR biology on myocardial function.

Low T3 State Is Correlated with Cardiac Mitochondrial Impairments after Ischemia Reperfusion Injury: Evidence from a Proteomic Approach

Mitochondria are major determinants of cell fate in ischemia/reperfusion injury (IR) and common effectors of cardio-protective strategies in cardiac ischemic disease. Thyroid hormone homeostasis critically affects mitochondrial function and energy production. Since a low T3 state (LT3S) is frequently observed in the post infarction setting, the study was aimed to investigate the relationship between 72 h post IR T3 levels and both the cardiac function and the mitochondrial proteome in a rat model of IR. The low T3 group exhibits the most compromised cardiac performance along with the worst mitochondrial activity. Accordingly, our results show a different remodeling of the mitochondrial proteome in the presence or absence of a LT3S, with alterations in groups of proteins that play a key role in energy metabolism, quality control and regulation of cell death pathways. Overall, our findings highlight a relationship between LT3S in the early post IR and poor cardiac and mitochondrial outcomes, and suggest a potential implication of thyroid hormone in the cardio-protection and tissue remodeling in ischemic disease.

TIMP3 interplays with apelin to regulate cardiovascular metabolism in hypercholesterolemic mice

OBJECTIVE

Tissue inhibitor of metalloproteinase 3 (TIMP3) is an extracellular matrix (ECM) bound protein, which has been shown to be downregulated in human subjects and experimental models with cardiometabolic disorders, including type 2 diabetes mellitus, hypertension and atherosclerosis. The aim of this study was to investigate the effects of TIMP3 on cardiac energy homeostasis during increased metabolic stress conditions.

METHODS

ApoE(-/-)TIMP3(-/-) and ApoE(-/-) mice on a C57BL/6 background were subjected to telemetric ECG analysis and experimental myocardial infarction as models of cardiac stress induction. We used Western blot, qRT-PCR, histology, metabolomics, RNA-sequencing and in vivo phenotypical analysis to investigate the molecular mechanisms of altered cardiac energy metabolism.

RESULTS

ApoE(-/-)TIMP3(-/-) revealed decreased lifespan. Telemetric ECG analysis showed increased arrhythmic episodes, and experimental myocardial infarction by left anterior descending artery (LAD) ligation resulted in increased peri-operative mortality together with increased scar formation, ventricular dilatation and a reduction of cardiac function after 4 weeks in the few survivors. Hearts of ApoE(-/-)TIMP3(-/-) exhibited accumulation of neutral lipids when fed a chow diet, which was exacerbated by a high fat, high cholesterol diet. Metabolomics analysis revealed an increase in circulating markers of oxidative stress with a reduction in long chain fatty acids. Using whole heart mRNA sequencing, we identified apelin as a putative modulator of these metabolic defects. Apelin is a regulator of fatty acid oxidation, and we found a reduction in the levels of enzymes involved in fatty acid oxidation in the left ventricle of ApoE(-/-)TIMP3(-/-) mice. Injection of apelin restored the hitherto identified metabolic defects of lipid oxidation.

CONCLUSION

TIMP3 regulates lipid metabolism as well as oxidative stress response via apelin. These findings therefore suggest that TIMP3 maintains metabolic flexibility in the heart, particularly during episodes of increased cardiac stress.

Late Post-Conditioning with Sevoflurane after Cardiac Surgery--Are Surrogate Markers Associated with Clinical Outcome?

Introduction

In a recent randomized controlled trial our group has demonstrated in 102 patients that late post-conditioning with sevoflurane performed in the intensive care unit after surgery involving extracorporeal circulation reduced damage to cardiomyocytes exposed to ischemia reperfusion injury. On the first post-operative day the sevoflurane patients presented with lower troponin T values when compared with those undergoing propofol sedation. In order to assess possible clinical relevant long-term implications in patients enrolled in this study, we performed the current retrospective analysis focusing on cardiac and non-cardiac events during the first 6 months after surgery.

Methods

All patients who had successfully completed the late post-conditioning trial were included into this follow-up. Our primary and secondary endpoints were the proportion of patients experiencing cardiac and non-cardiac events, respectively. Additionally, we were interested in assessing therapeutic interventions such as initiation or change of drug therapy, interventional treatment or surgery.

Results

Of 102 patients analyzed in the primary study 94 could be included in this follow-up. In the sevoflurane group (with 41 patients) 16 (39%) experienced one or several cardiac events within 6 months after cardiac surgery, in the propofol group (with 53 patients) 19 (36%, p=0.75). Four patients (9%) with sevoflurane vs. 7 (13%) with propofol sedation had non-cardiac events (p=0.61). While a similar percentage of patients suffered from cardiac and/or non-cardiac events, only 12 patients in the sevoflurane group compared to 20 propofol patients needed a therapeutic intervention (OR: 0.24, 95% CI: 0.04-1.43, p=0.12). A similar result was found for hospital admissions: 2 patients in the sevoflurane group had to be re-admitted to the hospital compared to 8 in the propofol group (OR 0.23, 95% CI: 0.04-1.29, p=0.10).

Conclusions

Sevoflurane does not seem to provide protection with regard to the occurrence of cardiac and non-cardiac events in the 6-month period following cardiac surgery with the use of extracorporeal circulation. However, there was a clear trend towards fewer interventions (less need for treatment, fewer hospital admissions) associated with sevoflurane post-conditioning in patients experiencing any event. Such results might encourage launching large multicenter post-conditioning trials with clinical outcome defined as primary endpoint.

Loss of Intralipid®- but not sevoflurane-mediated cardioprotection in early type-2 diabetic hearts of fructose-fed rats: importance of ROS signaling

BACKGROUND

Insulin resistance and early type-2 diabetes are highly prevalent. However, it is unknown whether Intralipid® and sevoflurane protect the early diabetic heart against ischemia-reperfusion injury.

METHODS

Early type-2 diabetic hearts from Sprague-Dawley rats fed for 6 weeks with fructose were exposed to 15 min of ischemia and 30 min of reperfusion. Intralipid® (1%) was administered at the onset of reperfusion. Peri-ischemic sevoflurane (2 vol.-%) served as alternative protection strategy. Recovery of left ventricular function was recorded and the activation of Akt and ERK 1/2 was monitored. Mitochondrial function was assessed by high-resolution respirometry and mitochondrial ROS production was measured by Amplex Red and aconitase activity assays. Acylcarnitine tissue content was measured and concentration-response curves of complex IV inhibition by palmitoylcarnitine were obtained.

RESULTS

Intralipid® did not exert protection in early diabetic hearts, while sevoflurane improved functional recovery. Sevoflurane protection was abolished by concomitant administration of the ROS scavenger N-2-mercaptopropionyl glycine. Sevoflurane, but not Intralipid® produced protective ROS during reperfusion, which activated Akt. Intralipid® failed to inhibit respiratory complex IV, while sevoflurane inhibited complex I. Early diabetic hearts exhibited reduced carnitine-palmitoyl-transferase-1 activity, but palmitoylcarnitine could not rescue protection and enhance postischemic functional recovery. Cardiac mitochondria from early diabetic rats exhibited an increased content of subunit IV-2 of respiratory complex IV and of uncoupling protein-3.

CONCLUSIONS

Early type-2 diabetic hearts lose complex IV-mediated protection by Intralipid® potentially due to a switch in complex IV subunit expression and increased mitochondrial uncoupling, but are amenable to complex I-mediated sevoflurane protection.

Modulation of membrane lipid composition and homeostasis in salmon hepatocytes exposed to hypoxia and perfluorooctane sulfonamide, given singly or in combination

The relative importance of environmental hypoxia due to global climate change on organismal ability to adapt to chemical insult and/or mechanisms of these responses is not well understood. Therefore, we have studied the effects of combined exposure to perfluorooctane sulfonamide (PFOSA) and chemically induced hypoxia on membrane lipid profile and homeostasis. Primary salmon hepatocytes were exposed to PFOSA at 0, 25 and 50 µM singly or in combination with either cobalt chloride (CoCl2: 0 and 150 µM) or deferroxamine (DFO: 0 and 100 µM) for 24 and 48 h. CoCl2 and DFO were used to induce cellular hypoxia because these two chemicals have been commonly used in animal experiments for this purpose and have been shown to increase hypoxia-inducible factor 1-alpha (HIF-1α) and vascular endothelial growth factor (VEGF) levels. Fatty acid (FA) profiles were determined by GC-MS, while gene expression patterns were determined by quantitative PCR. Hypoxic condition was confirmed with time-related increases of HIF-1α mRNA levels in CoCl2 and DFO exposed cells. In general, significant alterations of genes involved in lipid homeostasis were predominantly observed after 48 h exposure. Gene expression analysis showed that biological responses related to peroxisome proliferation (peroxisome proliferator-activated receptors (PPARs) and acyl coenzyme A (ACOX)) and FA desaturation (Δ5- and Δ6-desaturases: FAD5 and FAD6, respectively) and elongation (FAE) were elevated slightly by single exposure (i.e. either PFOSA, CoCl2 or DFO exposure alone), and these responses were potentiated in combined exposure conditions. Principal component analysis (PCA) showed a clustering of peroxisome proliferation responses at transcript levels and FA desaturation against membrane FAs levels whose changes were explained by PFOSA and chemically induced hypoxia exposures. Overall, our data show that most of the observed responses were stronger in combined stressor exposure conditions, compared to individual stressor exposure. In general, our data show that hypoxia may, singly or in combination with PFOSA produce deleterious health, physiological and developmental consequences through the alteration of membrane lipid profile in organisms.

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.