Diabetic Rat Hearts Show More Favorable Metabolic Adaptation to Omegaven Containing High Amounts of n3 Fatty Acids Than Intralipid Containing n6 Fatty Acids.

BACKGROUND: While Omegaven, an omega-3 (n3) fatty acid-based lipid emulsion, fosters insulin signaling in healthy hearts, it is unknown whether beneficial metabolic effects occur in insulin-resistant diabetic hearts. METHODS: Diabetic hearts from fructose-fed Sprague-Dawley rats were perfused in the working mode for 90 minutes in the presence of 11 mM glucose and 1.2 mM palmitate bound to albumin, the first 30 minutes without insulin followed by 60 minutes with insulin (50 mU/L). Hearts were randomly allocated to Intralipid (25 and 100 µM), Omegaven (25 and 100 µM), or no emulsion (insulin alone) for 60 minutes. Glycolysis, glycogen synthesis, and glucose oxidation were measured with the radioactive tracers [5-H]glucose and [U-C]glucose. Central carbon metabolites, acyl-coenzyme A species (acyl-CoAs), ketoacids, purines, phosphocreatine, acylcarnitines, and acyl composition of phospholipids were measured with mass spectrometry. RESULTS: Diabetic hearts showed no response to insulin with regard to glycolytic flux, consistent with insulin resistance. Addition of either lipid emulsion did not alter this response but unexpectedly increased glucose oxidation (ratio of treatment/baseline, ie, fold change): no insulin 1.3 (0.3) [mean (standard deviation)], insulin alone 1.4 (0.4), insulin + 25 µM Intralipid 1.8 (0.5), insulin + 100 µM Intralipid 2.2 (0.4), P < .001; no insulin 1.3 (0.3), insulin alone 1.4 (0.4), insulin + 25 µM Omegaven 2.3 (0.5) insulin + 100 µM Omegaven 1.9 (0.4), P < .001. Intralipid treatment led to accumulation of acylcarnitines as a result of the released linoleic acid (C18:2-n6) and enhanced its integration into phospholipids, consistent with incomplete or impaired ß-oxidation necessitating a compensatory increase in glucose oxidation. Accumulation of acylcarnitines was also associated with a higher nicotinamide adenine dinucleotide reduced/oxidized (NADH/NAD) ratio, which inhibited pyruvate dehydrogenase (PDH), and resulted in excess lactate production. In contrast, Omegaven-treated hearts showed no acylcarnitine accumulation, low malonyl-CoA concentrations consistent with activated ß-oxidation, and elevated PDH activity and glucose oxidation, together indicative of a higher metabolic rate possibly by substrate cycling. CONCLUSIONS: Omegaven is the preferred lipid emulsion for insulin-resistant diabetic hearts.

Lipid Emulsion Containing High Amounts of n3 Fatty Acids (Omegaven) as Opposed to n6 Fatty Acids (Intralipid) Preserves Insulin Signaling and Glucose Uptake in Perfused Rat Hearts.

BACKGROUND: It is currently unknown whether acute exposure to n3 fatty acid-containing fish oil-based lipid emulsion Omegaven as opposed to the n6 fatty acid-containing soybean oil-based lipid emulsion Intralipid is more favorable in terms of insulin signaling and glucose uptake in the intact beating heart. METHODS: Sprague-Dawley rat hearts were perfused in the working mode for 90 minutes in the presence of 11 mM glucose and 1.2 mM palmitate bound to albumin, the first 30 minutes without insulin followed by 60 minutes with insulin (50 mU/L). Hearts were randomly allocated to 100 µM Intralipid, 100 µM Omegaven, or no emulsion (insulin treatment alone) for 60 minutes. Glycolysis and glycogen synthesis were measured with the radioactive tracer [5-H]glucose, and glucose uptake was calculated. Phosphorylation of protein phosphatase 2A (PP2A), protein kinase Akt, and phosphofructokinase (PFK)-2 was measured by immunoblotting. Glycolytic metabolites were determined by enzymatic assays. Mass spectrometry was used to establish acylcarnitine profiles. Nuclear factor κB (NFκB) nuclear translocation served as reactive oxygen species (ROS) biosensor. RESULTS: Insulin-mediated glucose uptake was decreased by Intralipid (4.9 ± 0.4 vs 3.7 ± 0.3 µmol/gram dry heart weight [gdw]·min; P = .047) due to both reduced glycolysis and glycogen synthesis. In contrast, Omegaven treatment did not affect insulin-mediated glycolysis or glycogen synthesis and thus preserved glucose uptake (5.1 ± 0.3 vs 4.9 ± 0.4 µmol/gdw·min; P = .94). While Intralipid did not affect PP2A phosphorylation status, Omegaven resulted in significantly enhanced tyrosine phosphorylation and inhibition of PP2A. This was accompanied by increased selective threonine phosphorylation of Akt and the downstream target PFK-2 at S483. PFK-1 activity was increased when compared with Intralipid as measured by the ratio of fructose 1,6-bisphosphate to fructose 6-phosphate (Omegaven 0.60 ± 0.11 versus Intralipid 0.47 ± 0.09; P = .023), consistent with increased formation of fructose 2,6-bisphosphate by PFK2, its main allosteric activator. Omegaven lead to accumulation of acylcarnitines and fostered a prooxidant response as evidenced by NFκB nuclear translocation and activation. CONCLUSIONS: Omegaven as opposed to Intralipid preserves glucose uptake via the PP2A-Akt-PFK pathway in intact beating hearts. n3 fatty acids decelerate ß-oxidation causing accumulation of acylcarnitine species and a prooxidant response, which likely inhibits redox-sensitive PP2A and thus preserves insulin signaling and glucose uptake.

Enhanced myocardial protection in cardiac donation after circulatory death using Intralipid® postconditioning in a porcine model.

PURPOSE: Intralipid® (ILE), a clinically used lipid emulsion, reduces ischemia-reperfusion (IR) injury in healthy and infarct-remodelled rat hearts. We tested whether ILE is also cardioprotective in large porcine hearts in the context of the donation after circulatory death (DCD) model, where human hearts are procured for transplantation after cardiac arrest and thus are exposed to significant IR injury. METHODS: After induction of anesthesia, surgical preparation, termination of ventilator support, and cardiac arrest, hearts of female pigs were procured following a 15 min standoff period, with an optimized normokalemic crystalloid adenosine-lidocaine cardioplegia. Hearts were then randomly allocated to ex vivo reperfusion (38°C) in the absence (control) or presence of 1% ILE. All hearts were perfused with blood and Krebs-Henseleit solution (1:1) for 30 min in Langendorff mode and for an additional 30 min in working mode to assess mechanical function. Left ventricular (LV) biopsies were obtained after five minutes of reperfusion and LV tissue was preserved at the end of reperfusion for biochemical analyses and immunohistochemistry. RESULTS: Intralipid® postconditioning reduced cell membrane damage as assessed by the mean (standard deviation) leakage of myocardial glutathione disulfide (39 (9) nmol·mg-1 protein vs 19 (7) nmol·mg-1 protein; P = 0.006), protected LV tissue from protein carbonylation (3.4 [0.6] nmol·mg-1 protein vs 5.3 [0.9] nmol·mg-1 protein; P = 0.006), decreased myeloperoxidase activity (35 [8] nmol·min-1·mg-1 protein vs 75 [11] nmol·min-1·mg-1 protein; P < 0.001), and increased inotropy (maximum rate of rise of LV pressure 2001 [345] mmHg·sec-1vs 1584 [192] mmHg·sec-1; P = 0.044). Intralipid® postconditioning triggered reactive oxygen species signalling at early reperfusion and activated protection signalling (Akt, signal transducer and activator of transcription 3, and glycogen synthase kinase 3ß) in LV tissue, recapitulating all features of ILE-mediated protection reported in small rodent hearts. CONCLUSIONS: Our data show that ILE postconditioning elicits protection signalling in large mammalian hearts while mimicking clinical conditions, and is capable of enhancing protection of DCD hearts.

Differential Effects of Anesthetics and Opioid Receptor Activation on Cardioprotection Elicited by Reactive Oxygen Species-Mediated Postconditioning in Sprague-Dawley Rat Hearts.

BACKGROUND: Despite an array of cardioprotective interventions identified in preclinical models of ischemia-reperfusion (IR) injury, successful clinical translation has not been achieved. This study investigated whether drugs routinely used in clinical anesthesia influence cardioprotective effectiveness by reducing effects of reactive oxygen species (ROS), upstream triggers of cardioprotective signaling. Effects of propofol, sevoflurane, or remifentanil were compared on postischemic functional recovery induced by ROS-mediated postconditioning with Intralipid. METHODS: Recovery of left ventricular (LV) work, an index of IR injury, was measured in isolated Sprague-Dawley rat hearts subjected to global ischemia (20 minutes) and reperfusion (30 minutes). Hearts were either untreated or were treated with postconditioning with Intralipid (1%, throughout reperfusion). Propofol (10 µM), sevoflurane (2 vol%), remifentanil (3 nM), or combinations thereof were administered peri-ischemically (before and during IR). The effects of anesthetics on ROS production were measured in LV cardiac fibers by Amplex Red assay under phosphorylating and nonphosphorylating conditions. RESULTS: Recovery of LV work (expressed as percentage of the preischemic value ± standard deviation) in untreated hearts was poor (20% ± 7%) and was improved by Intralipid postconditioning (58% ± 8%, P = .001). In the absence of Intralipid postconditioning, recovery of LV work was enhanced by propofol (28% ± 9%, P = .049), sevoflurane (49% ± 5%, P < .001), and remifentanil (51% ± 6%, P < .001). The benefit of Intralipid postconditioning was abolished by propofol (33% ± 10%, P < .001), but enhanced by sevoflurane (80% ± 7%, P < .001) or remifentanil (80% ± 9%, P < .001). ROS signaling in LV fibers was abolished by propofol, but unaffected by sevoflurane or remifentanil. We conclude that propofol abolishes ROS-mediated Intralipid postconditioning by acting as a ROS scavenger. Sevoflurane and remifentanil are protective per se and provide additive cardioprotection to ROS-mediated cardioprotection. CONCLUSIONS: These divergent effects of routinely used drugs in clinical anesthesia may influence the translatability of cardioprotective therapies such as Intralipid postconditioning.

Alterations in fatty acid metabolism and sirtuin signaling characterize early type-2 diabetic hearts of fructose-fed rats.

Despite the fact that skeletal muscle insulin resistance is the hallmark of type-2 diabetes mellitus (T2DM), inflexibility in substrate energy metabolism has been observed in other tissues such as liver, adipose tissue, and heart. In the heart, structural and functional changes ultimately lead to diabetic cardiomyopathy. However, little is known about the early biochemical changes that cause cardiac metabolic dysregulation and dysfunction. We used a dietary model of fructose-induced T2DM (10% fructose in drinking water for 6 weeks) to study cardiac fatty acid metabolism in early T2DM and related signaling events in order to better understand mechanisms of disease. In early type-2 diabetic hearts, flux through the fatty acid oxidation pathway was increased as a result of increased cellular uptake (CD36), mitochondrial uptake (CPT1B), as well as increased ß-hydroxyacyl-CoA dehydrogenase and medium-chain acyl-CoA dehydrogenase activities, despite reduced mitochondrial mass. Long-chain acyl-CoA dehydrogenase activity was slightly decreased, resulting in the accumulation of long-chain acylcarnitine species. Cardiac function and overall mitochondrial respiration were unaffected. However, evidence of oxidative stress and subtle changes in cardiolipin content and composition were found in early type-2 diabetic mitochondria. Finally, we observed decreased activity of SIRT1, a pivotal regulator of fatty acid metabolism, despite increased protein levels. This indicates that the heart is no longer capable of further increasing its capacity for fatty acid oxidation. Along with increased oxidative stress, this may represent one of the earliest signs of dysfunction that will ultimately lead to inflammation and remodeling in the diabetic heart.

Hearts lacking plasma membrane KATP channels display changes in basal aerobic metabolic substrate preference and AMPK activity.

Cardiac ATP-sensitive K+ (KATP) channels couple changes in cellular metabolism to membrane excitability and are activated during metabolic stress, although under basal aerobic conditions, KATP channels are thought to be predominately closed. Despite intense research into the roles of KATP channels during metabolic stress, their contribution to aerobic basal cardiac metabolism has not been previously investigated. Hearts from Kir6.2+/+ and Kir6.2-/- mice were perfused in working mode, and rates of glycolysis, fatty acid oxidation, and glucose oxidation were measured. Changes in activation/expression of proteins regulating metabolism were probed by Western blot analysis. Despite cardiac mechanical function and metabolic efficiency being similar in both groups, hearts from Kir6.2-/- mice displayed an approximately twofold increase in fatty acid oxidation and a 0.45-fold reduction in glycolytic rates but similar glucose oxidation rates compared with hearts from Kir6.2+/+ mice. Kir6.2-/- hearts also possessed elevated levels of activated AMP-activated protein kinase (AMPK), higher glycogen content, and reduced mitochondrial density. Moreover, activation of AMPK by isoproterenol or diazoxide was significantly blunted in Kir6.2-/- hearts. These data indicate that KATP channel ablation alters aerobic basal cardiac metabolism. The observed increase in fatty acid oxidation and decreased glycolysis before any metabolic insult may contribute to the poor recovery observed in Kir6.2-/- hearts in response to exercise or ischemia-reperfusion injury. Therefore, KATP channels may play an important role in the regulation of cardiac metabolism through AMPK signaling.NEW & NOTEWORTHY In this study, we show that genetic ablation of plasma membrane ATP-sensitive K+ channels results in pronounced changes in cardiac metabolic substrate preference and AMP-activated protein kinase activity. These results suggest that ATP-sensitive K+ channels may play a novel role in regulating metabolism in addition to their well-documented effects on ionic homeostasis during periods of stress.

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.

Myocardial mechanical dysfunction following endotoxemia: role of changes in energy substrate metabolism.

Cardiovascular depression due to endotoxemia remains a major cause of mortality in intensive care patients. To determine whether drug-induced alterations in cardiac metabolism may be a viable strategy to reduce endotoxemia-mediated cardiac dysfunction, we assessed endotoxemia-induced changes in glucose and fatty acid metabolism under aerobic and post-ischemic conditions. Endotoxemia was induced in male Sprague-Dawley rats by lipopolysaccharide (Escherichia coli 0111:B4c, 4 mg/kg, i.p.) 6 h prior to heart removal for ex vivo assessment of left ventricular (LV) work and rates of glucose metabolism (glucose uptake, glycogen synthesis, glycolysis and glucose oxidation) and palmitate oxidation. Under aerobic conditions, endotoxemic hearts had impaired LV function as judged by echocardiography in vivo (% ejection fraction, 66.0 ± 3.2 vs 78.0 ± 2.1, p < 0.05) or by LV work ex vivo (2.14 ± 0.16 vs 3.28 ± 0.16, Joules min(-1) g dry wt(-1), p < 0.05). However, rates of glucose uptake, glycogen synthesis, glycolysis, and glucose oxidation were not altered. Palmitate oxidation was lower in endotoxemic hearts in proportion to the decreased workload, thus metabolic efficiency was unaffected. In hearts reperfused following global ischemia, untreated hearts had impaired recovery of LV work (52.3 ± 9.4 %) whereas endotoxemic hearts had significantly higher recovery (105.6 ± 11.3 %, p < 0.05). During reperfusion, fatty acid oxidation, acetyl CoA production and metabolic efficiency were similar in both groups. As impaired cardiac function appeared unrelated to depression of energy substrate oxidation, it is unlikely that drug-induced acceleration of fatty acid oxidation will improve mechanical function. The beneficial repartitioning of glucose metabolism in reperfused endotoxemic hearts may contribute to the cardioprotected phenotype.

Unraveling Interactions Between Anesthetics and the Endothelium: Update and Novel Insights.

The vascular endothelium is one of the largest organs in the body and consists of a single layer of highly specialized cells with site-specific morphology and functions. Endothelial cells play a vital role in the regulation of vascular tone in arterial, venous, microvascular, and lymphatic vascular beds. The endothelium also coordinates angiogenesis and controls cell adhesion, fluid homeostasis, and both innate and adaptive immunity. Fundamental research has shown that general and local anesthetics markedly modulate the biological activities of endothelial cells under aerobic and ischemia-reperfusion conditions, making the endothelium an important target of anesthetics in the cardiovascular system. Halogenated volatile anesthetics provide significant anti-inflammatory actions and protect the endothelium against ischemia-reperfusion injury, despite their inhibiting effects on endothelium-dependent vasorelaxation. They provide not only acute but also potential long-term, beneficial effects. Although many effects of IV anesthetics on endothelial function are controversial, or completely unexplored, propofol and opioids appear to have the most favorable profile with respect to the preservation of endothelial function. Some opioids and ketamine have stereoselective effects on the endothelium. Finally, there is experimental evidence to suggest important effects of anesthetics on the regulation of vascular permeability, proliferation of stem cells, including endothelial progenitor cells, and promotion or inhibition of tumor growth, potentially related to alterations in angiogenesis. However, most of these findings are from in vitro experiments and await confirmation in an in vivo setting. Thus, the clinical implications of these interactions remain uncertain.

Tolerance to ischaemic injury in remodelled mouse hearts: less ischaemic glycogenolysis and preserved metabolic efficiency.

AIMS: Post-infarction remodelled failing hearts have reduced metabolic efficiency. Paradoxically, they have increased tolerance to further ischaemic injury. This study was designed to investigate the metabolic mechanisms that may contribute to this phenomenon and to examine the relationship between ischaemic tolerance and metabolic efficiency during post-ischaemic reperfusion. METHODS AND RESULTS: Male C57BL/6 mice were subjected to coronary artery ligation (CAL) or SHAM surgery. After 4 weeks, in vivo mechanical function was assessed by echocardiography, and then isolated working hearts were perfused in this sequence: 45 min aerobic, 15 min global no-flow ischaemia, and 30 min aerobic reperfusion. Left ventricular (LV) function, metabolic rates, and metabolic efficiency were measured. Relative to SHAM, both in vivo and in vitro CAL hearts had depressed cardiac function under aerobic conditions (45 and 36%, respectively), but they had a greater recovery of LV function during post-ischaemic reperfusion (67 vs. 49%, P < 0.05). While metabolic efficiency (LV work per ATP produced) was 50% lower during reperfusion of SHAM hearts, metabolic efficiency in CAL hearts did not decrease. During ischaemia, glycogenolysis was 28% lower in CAL hearts, indicative of lower ischaemic proton production. There were no differences in mitochondrial abundance, calcium handling proteins, or key metabolic enzymes. CONCLUSION: Compared with SHAM, remodelled CAL hearts are more tolerant to ischaemic injury and undergo no further deterioration of metabolic efficiency during reperfusion. Less glycogen utilization in CAL hearts during ischaemia may contribute to increased ischaemic tolerance by limiting ischaemic proton production that may improve ion homeostasis during early reperfusion.

Propofol (Diprivan®) and Intralipid® exacerbate insulin resistance in type-2 diabetic hearts by impairing GLUT4 trafficking.

BACKGROUND: The IV anesthetic, propofol, when administered as fat emulsion-based formulation (Diprivan) promotes insulin resistance, but the direct effects of propofol and its solvent, Intralipid, on cardiac insulin resistance are unknown. METHODS: Hearts of healthy and type-2 diabetic rats (generated by fructose feeding) were aerobically perfused for 60 minutes with 10 µM propofol in the formulation of Diprivan or an equivalent concentration of its solvent Intralipid (25 µM) ± insulin (100 mU•L). Glucose uptake, glycolysis, and glycogen metabolism were measured using [H]glucose. Activation of Akt, GSK3ß, AMPK, ERK1/2, p38MAPK, S6K1, JNK, protein kinase Cθ (PKCθ), and protein kinase CCßII (PKCßII) was determined using immunoblotting. GLUT4 trafficking and phosphorylations of insulin receptor substrate-1 (IRS-1) at Ser307(h312), Ser1100(h1101), and Tyr608(hTyr612) were measured. Mass spectrometry was used to determine acylcarnitines, phospholipids, and sphingolipids. RESULTS: Diprivan and Intralipid reduced insulin-induced glucose uptake and redirected glucose to glycogen stores in diabetic hearts. Reduced glucose uptake was accompanied by lower GLUT4 trafficking to the sarcolemma. Diprivan and Intralipid inactivated GSK3ß but activated AMPK and ERK1/2 in diabetic hearts. Only Diprivan increased phosphorylation of Akt(Ser473/Thr308) and translocated PKCθ and PKCßII to the sarcolemma in healthy hearts, whereas it activated S6K1 and p38MAPK and translocated PKCßII in diabetic hearts. Furthermore, only Diprivan phosphorylated IRS-1 at Ser1100(h1101) in healthy and diabetic hearts. JNK expression, phosphorylation of Ser307(h312) of IRS-1, and PKCθ expression and translocation were increased, whereas GLUT4 expression was reduced in insulin-treated diabetic hearts. Phosphatidylglycerol, phosphatidylethanolamine, and C18-sphingolipids accumulated in Diprivan-perfused and Intralipid-perfused diabetic hearts. CONCLUSIONS: Propofol and Intralipid promote insulin resistance predominantly in type-2 diabetic hearts.

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.

Propofol ameliorates hyperglycemia-induced cardiac hypertrophy and dysfunction via heme oxygenase-1/signal transducer and activator of transcription 3 signaling pathway in rats.

OBJECTIVES: Heme oxygenase-1 is inducible in cardiomyocytes in response to stimuli such as oxidative stress and plays critical roles in combating cardiac hypertrophy and injury. Signal transducer and activator of transcription 3 plays a pivotal role in heme oxygenase-1-mediated protection against liver and lung injuries under oxidative stress. We hypothesized that propofol, an anesthetic with antioxidant capacity, may attenuate hyperglycemia-induced oxidative stress in cardiomyocytes via enhancing heme oxygenase-1 activation and ameliorate hyperglycemia-induced cardiac hypertrophy and apoptosis via heme oxygenase-1/signal transducer and activator of transcription 3 signaling and improve cardiac function in diabetes. DESIGN: Treatment study. SETTING: Research laboratory. SUBJECTS: Sprague-Dawley rats. INTERVENTIONS: In vivo and in vitro treatments. MEASUREMENTS AND MAIN RESULTS: At 8 weeks of streptozotocin-induced type 1 diabetes in rats, myocardial 15-F2t-isoprostane was significantly increased, accompanied by cardiomyocyte hypertrophy and apoptosis and impaired left ventricular function that was coincident with reduced heme oxygenase-1 activity and signal transducer and activator of transcription 3 activation despite an increase in heme oxygenase-1 protein expression as compared to control. Propofol infusion (900 µg/kg/min) for 45 minutes significantly improved cardiac function with concomitantly enhanced heme oxygenase-1 activity and signal transducer and activator of transcription activation. Similar to the changes seen in diabetic rat hearts, high glucose (25 mmol/L) exposure for 48 hours led to cardiomyocyte hypertrophy and apoptosis, both in primary cultured neonatal rat cardiomyocytes and in H9c2 cells compared to normal glucose (5.5 mmol/L). Hypertrophy was accompanied by increased reactive oxygen species and malondialdehyde production and caspase-3 activity. Propofol, similar to the heme oxygenase-1 inducer cobalt protoporphyrin, significantly increased cardiomyocyte heme oxygenase-1 and p-signal transducer and activator of transcription protein expression and heme oxygenase-1 activity and attenuated high-glucose-mediated cardiomyocyte hypertrophy and apoptosis and reduced reactive oxygen species and malondialdehyde production (p < 0.05). These protective effects of propofol were abolished by heme oxygenase-1 inhibition with zinc protoporphyrin and by heme oxygenase-1 or signal transducer and activator of transcription 3 gene knockdown. CONCLUSIONS: Heme oxygenase-1/signal transducer and activator of transcription 3 signaling plays a critical role in propofol-mediated amelioration of hyperglycemia-induced cardiomyocyte hypertrophy and apoptosis, whereby propofol improves cardiac function in diabetic rats.

Chronic treatment with metformin suppresses toll-like receptor 4 signaling and attenuates left ventricular dysfunction following myocardial infarction.

Acute treatment with metformin has a protective effect in myocardial infarction by suppression of inflammatory responses due to activation of AMP-activated protein kinase (AMPK). In the present study, the effect of chronic pre-treatment with metformin on cardiac dysfunction and toll-like receptor 4 (TLR4) activities following myocardial infarction and their relation with AMPK were assessed. Male Wistar rats were randomly assigned to one of 5 groups (n=6): normal control and groups were injected isoproterenol after chronic pre-treatment with 0, 25, 50, or 100mg/kg of metformin twice daily for 14 days. Isoproterenol (100mg/kg) was injected subcutaneously on the 13th and 14th days to induce acute myocardial infarction. Isoproterenol alone decreased left ventricular systolic pressure and myocardial contractility indexed as LVdp/dtmax and LVdp/dtmin. The left ventricular dysfunction was significantly lower in the groups treated with 25 and 50mg/kg of metformin. Metfromin markedly lowered isoproterenol-induced elevation in the levels of TLR4 mRNA, myeloid differentiation protein 88 (MyD88), tumor necrosis factor-alpha (TNF-α), and interleukin 6 (IL-6) in the heart tissues. Similar changes were also seen in the serum levels of TNF-α and IL-6. However, the lower doses of 25 and 50mg/kg were more effective than 100mg/kg. Phosphorylated AMPKα (p-AMPK) in the myocardium was significantly elevated by 25mg/kg of metformin, slightly by 50mg/kg, but not by 100mg/kg. Chronic pre-treatment with metformin reduces post-myocardial infarction cardiac dysfunction and suppresses inflammatory responses, possibly through inhibition of TLR4 activities. This mechanism can be considered as a target to protect infarcted myocardium.

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.

Anesthetic cardioprotection in clinical practice from proof-of-concept to clinical applications.

In 2007, the American Heart Association (AHA) recommended (class IIa, level of evidence B) in their guidelines on Perioperative Cardiovascular Evaluation and Care for Noncardiac Surgery volatile anesthetics as first choice for general anesthesia in hemodynamically stable patients at risk for myocardial ischemia. This recommendation was based on results from patients undergoing coronary artery bypass grafting (CABG) surgery and thus subject to criticism. However, since a "good anesthetic" often resembles a piece of art in the complex perioperative environment, and is difficult to highly standardize, it seems unlikely that large-scale randomized control trials in noncardiac surgical patients will be performed in the near future to tackle this question. There is growing evidence that ether-derived volatile anesthetics and opioids provide cardioprotection in patients undergoing CABG surgery. Since 2011, the American College of Cardiology Foundation/AHA have recommended a "volatile-based anesthesia" for these procedures (class IIa, level of evidence A). It is very likely that volatile anesthetics and opioids also protect hearts of noncardiac surgical patients. However, age, diabetes and myocardial remodeling diminish the cardioprotective benefits of anesthetics. In patients at risk for perioperative cardiovascular complications, it is essential to abandon the use of "anti-conditioning" drugs (sulfonylureas and COX-2 inhibitors) and probably glitazones. There is significant interference in cardioprotection between sevoflurane and propofol, which should not be used concomitantly during anesthesia if possible. Any type of ischemic "conditioning" appears to exhibit markedly reduced protection or completely loses protection in the presence of volatile anesthetics and/or opioids.

Early mitochondrial dysfunction in glycolytic muscle, but not oxidative muscle, of the fructose-fed insulin-resistant rat.

Although evidence that type 2 diabetes mellitus (T2DM) is accompanied by mitochondrial dysfunction in skeletal muscle has been accumulating, a causal link between mitochondrial dysfunction and the pathogenesis of the disease remains unclear. Our study focuses on an early stage of the disease to determine whether mitochondrial dysfunction contributes to the development of T2DM. The fructose-fed (FF) rat was used as an animal model of early T2DM. Mitochondrial respiration and acylcarnitine species were measured in oxidative (soleus) and glycolytic [extensor digitorum longus (EDL)] muscle. Although FF rats displayed characteristic signs of T2DM, including hyperglycemia, hyperinsulinemia, and hypertriglyceridemia, mitochondrial content was preserved in both muscles from FF rats. The EDL muscle had reduced complex I and complex I and II respiration in the presence of pyruvate but not glutamate. The decrease in pyruvate-supported respiration was due to a decrease in pyruvate dehydrogenase activity. Accumulation of C14:1 and C14:2 acylcarnitine species and a decrease in respiration supported by long-chain acylcarnitines but not acetylcarnitine indicated dysfunctional ß-oxidation in the EDL muscle. In contrast, the soleus muscle showed preserved mitochondrial respiration, pyruvate dehydrogenase activity, and increased fatty acid oxidation, as evidenced by overall reduced acylcarnitine levels. Aconitase activity, a sensitive index of reactive oxygen species production in mitochondria, was reduced exclusively in EDL muscle, which showed lower levels of the antioxidant enzymes thioredoxin reductase and glutathione peroxidase. Here, we show that the glycolytic EDL muscle is more prone to an imbalance between energy supply and oxidation caused by insulin resistance than the oxidative soleus muscle.