Cardiac preconditioning by volatile anesthetic agents: a defining role for altered mitochondrial bioenergetics

Effects of sevoflurane on left ventricular function by speckle-tracking echocardiography in coronary bypass patients: A randomized trial

The present study aimed to dynamically observe the segmental and global myocardial movements of the left ventricle during coronary artery bypass grafting by transesophageal speckle-tracking echocardiography, and to assess the effect of sevoflurane on cardiac function. Sixty-four patients scheduled for the off-pump coronary artery bypass grafting were randomly divided into a sevoflurane-based anesthesia (AS) group and a propofol-based total intravenous anesthesia (AA) group. The AS group demonstrated a higher absolute value of left ventricular global longitudinal strain than that of the AA group at both T 1 (after harvesting all grafts and before coronary anastomosis) and T 2 (30 min after completing all coronary anastomoses) ( P < 0.05). Moreover, strain improvement in the segment with the highest preoperative strain was significantly reduced in the AS group, compared with the AA group at both T 1 and T 2 ( P < 0.01). The flow of the left internal mammary artery-left anterior descending artery graft was superior, and the postoperative concentration of troponin T decreased rapidly in the AS group, compared with the AA group ( P < 0.05). Compared with total intravenous anesthesia, sevoflurane resulted in a significantly higher global longitudinal strain, stroke volume, and cardiac output. Sevoflurane also led to an amelioration in the condition of the arterial graft. Furthermore, sevoflurane significantly reduced strain improvement in the segmental myocardium with a high preoperative strain value. The findings need to be replicated in larger studies.

Induction of JAK2/STAT3 pathway contributes to protective effects of different therapeutics against myocardial ischemia/reperfusion

Insufficiency in coronary blood supply results in myocardial ischemia and consequently, various clinical syndromes and irreversible injuries. Myocardial damage occurs as a result of two processes during acute myocardial infarction (MI): ischemia and subsequent reperfusion. According to the available evidence, oxidative stress, excessive inflammation reaction, reactive oxygen species (ROS) generation, and apoptosis are crucial players in the pathogenesis of myocardial ischemia/reperfusion (IR) injury. There is emerging evidence that Janus tyrosine kinase 2 (JAK2) signal transducer and activator of the transcription 3 (STAT3) pathway offers cardioprotection against myocardial IR injury. This article reviews therapeutics that exert cardioprotective effects against myocardial IR injury through induction of JAK2/STAT3 pathway.

Argon preconditioning enhances postischaemic cardiac functional recovery following cardioplegic arrest and global cold ischaemia

OBJECTIVES

Previous studies demonstrated that preconditioning with argon gas provided a marked reduction in inflammation and apoptosis and increased myocardial contractility in the setting of acute myocardial ischaemia-reperfusion (IR). There is substantial evidence that myocardial IR injury following cardioplegic arrest is associated with the enhancement of apoptosis and inflammation, which is considered to play a role in cardiac functional impairment. Therefore, the present study was designed to clarify whether preconditioning with argon gas enhances recovery of cardiac function following cardioplegic arrest.

METHODS

Sprague-Dawley rats were anaesthetized and ventilated and allocated to (i) the control group (control IR, n = 10) and (ii) the in vivo group (argon IR), which received 3 cycles of argon (50% argon, 21% oxygen and 29% nitrogen, n = 10) administered for 5 min interspersed with 5 min of a gas mixture (79% nitrogen and 21% oxygen). The hearts were excised and then evaluated in an erythrocyte-perfused isolated working heart system. Cold ischaemia (4°C) for 60 min was induced by histidine-tryptophan-ketoglutarate cardioplegia, followed by 40 min of reperfusion. Cardiac functional parameters were assessed. In left ventricular tissue samples, the expressions of extracellular-regulated kinase (ERK1/2), AKT serine/threonine kinase (Akt), jun N-terminal kinase (JNK), endothelial nitric oxide synthase (eNOS) and HMGB1: high-mobility group box 1 (HMGB1) protein were assessed by western blot, and high-energy phosphates were evaluated by high-performance liquid chromatography.

RESULTS

At the end of reperfusion, the rats preconditioned with argon showed significantly enhanced recovery of cardiac output (101 ± 6% vs 87 ± 11%; P < 0.01), stroke volume (94 ± 4% vs 80 ± 11%; P = 0.001), external heart work (100 ± 6% vs 81 ± 13%; P < 0.001) and coronary flow (90 ± 13% vs 125 ± 21%; P < 0.01) compared with the control IR group. These results were accompanied by a significant increase in the levels of myocardial phosphocreatine (23.71 ± 2.07 µmol/g protein vs the control IR group, 13.50 ± 4.75; P = 0.001) and maintained adenosine triphosphate levels (13.62 ±1.89 µmol/g protein vs control IR group adenosine triphosphate: 10.08 ± 1.94 µmol/g; P = 0.017). Additionally, preconditioning with argon markedly reduced the activation of JNK (0.11 ± 0.01 vs 0.25 ± 0.03; P = 0.005) and the expression of HMGB1 protein (0.52 ± 0.04 vs 1.5 ± 0.10; P < 0.001) following reperfusion.

CONCLUSIONS

Preconditioning with argon enhanced cardiac functional recovery in rat hearts arrested with histidine-tryptophan-ketoglutarate cardioplegia, thereby representing a potential novel cardioprotective approach in cardiac surgery.

Short-term consumption of Ilex paraguariensis extracts protects isolated hearts from ischemia/reperfusion injury and contradicts exercise-mediated cardioprotection

Perfusion of hearts with extracts of Ilex paraguariensis (IP/mate) appears to reduce ischemia/reperfusion (I/R) injury. To determine if oral consumption of IP/mate can provide similar cardioprotection, short-term consumption was investigated alone or in association with exercise in rats. Animals were grouped into control (C), IP/mate consumption (M), exercise (E), and exercise with mate (E+M). M and E+M groups consumed IP/mate (1 g·kg^-1 body weight in 1 mL water) by gavage. E and E+M groups swam 7× per week for 30 min carrying an additional 5% of body weight. After 1 week, hearts were tested ex vivo to measure left ventricle developed pressure (LVDP), systolic and end diastolic pressure (LVSP/LVEDP), maximum velocity of contraction and relaxation (dP/dt+ and dP/dt-) during I/R and infarction size. In addition, cardiac tissue was analyzed for oxidative stress by lipid peroxidation and protein carbonyl levels along with activity of catalase and superoxide dismutase (SOD). LVDP was higher in hearts from M and E groups as well as decreased infarction sizes than others. At the end of reperfusion, dP/dt+ was increased in E and M and dP/dt- was higher in M. LVSP was higher in M and E compared with C. Protein carbonyl and thiobarbituric acid reactive substances levels were higher in M while SOD activity was increased in E. No differences were observed in other activities. The results suggest that short-term consumption of IP/mate has protective effects on heart I/R injury similar to exercise, but the combination of these interventions appears to contradict the beneficial adaptations from exercise.

Neuroprotective effects of 2,4-dinitrophenol in an acute model of Parkinson's disease

Neurons depend on mitochondria for homeostasis and survival, and thus, mitochondrial dysfunction has been implicated in neurodegenerative diseases, including Parkinson's disease (PD). Increasing evidence indicates the mitochondrial uncoupler, 2,4-dinitrophenol (DNP), protects neurons against neurodegeneration and enhances neural plasticity. Here, the authors evaluated the protective effects of intraperitoneally (i.p.) administered low dose DNP in an acute mouse model of PD. Mice were administered DNP (1 or 5mg/kg) for 12 consecutive days, and then on day 13, MPTP (20mg/kg, i.p.) was administered four times (with 2h intervals between injections) to induce PD. It was found that MPTP-induced motor dysfunction was ameliorated in the DNP-treated mice versus vehicle-treated controls. Additionally, DNP effectively attenuated dopaminergic neuronal loss observed in MPTP treated mice. Moreover, in primary cultured neurons, DNP at 10μM, but not at 100μM, prevented MPP⁺-induced cell death and mitochondrial membrane potential (MMP) reduction. In addition, DNP was observed to cause the nuclear translocation of Nrf2 in primary neurons. Taken together, these findings of the present study suggest that DNP protects dopaminergic neurons against neurodegeneration and maintains MMP integrity in PD by activating adaptive stress responses.

Acute exhaustive aerobic exercise training impair cardiomyocyte function and calcium handling in Sprague-Dawley rats

Introduction

Recent data from long-distance endurance participants suggest that cardiac function is impaired after completion. Existing data further indicate that right ventricular function is more affected than left ventricular function. The cellular mechanisms underpinning cardiac deterioration are limited and therefore the aim of this study was to examine cardiomyocyte and molecular responses of the right and left ventricle to an acute bout of exhaustive endurance exercise.

Materials and methods

Male Sprague-Dawley rats were assigned to sedentary controls or acute exhaustive endurance exercise consisting of a 120 minutes long forced treadmill run. The contractile function and Ca²⁺ handling properties in isolated cardiomyocytes, protein expression levels of sarcoplasmic reticulum Ca²⁺-ATPase and phospholamban including two of its phosphorylated states (serine 16 and threonine 17), and the mitochondrial respiration in permeabilized cardiac muscle fibers were analyzed.

Results

The exercise group showed a significant reduction in cardiomyocyte fractional shortening (right ventricle 1 Hz and 3 Hz p<0.001; left ventricle 1 Hz p<0.05), intracellular Ca²⁺ amplitude (right ventricle 1 and 3 Hz p<0.001; left ventricle 1 Hz p<0.01 and 3 Hz p<0.05) and rate of diastolic Ca²⁺ decay (right ventricle 1 Hz p<0.001 and 3 Hz p<0.01; left ventricle 1 and 3 Hz p<0.01). Cardiomyocyte relaxation during diastole was only significantly prolonged at 3 Hz in the right ventricle (p<0.05) compared to sedentary controls. We found an increase in phosphorylation of phospholamban at serine 16 and threonine 17 in the left (p<0.05), but not the right, ventricle from exhaustively exercised animals. The protein expression levels of sarcoplasmic reticulum Ca²⁺-ATPase and phospholamban was not changed. Furthermore, we found a reduction in maximal oxidative phosphorylation and electron transport system capacities of mitochondrial respiration in the right (p<0.01 and p<0.05, respectively), but not the left ventricle from rats subjected to acute exhaustive treadmill exercise.

Conclusion

Acute exhaustive treadmill exercise is associated with impairment of cardiomyocyte Ca²⁺ handling and mitochondrial respiration that causes depression in both contraction and diastolic relaxation of cardiomyocytes.

Controlled Reperfusion Strategies Improve Cardiac Hemodynamic Recovery after Warm Global Ischemia in an Isolated, Working Rat Heart Model of Donation after Circulatory Death (DCD)

Aims: Donation after circulatory death (DCD) could improve cardiac graft availability, which is currently insufficient to meet transplant demand. However, DCD organs undergo an inevitable period of warm ischemia and most cardioprotective approaches can only be applied at reperfusion (procurement) for ethical reasons. We investigated whether modifying physical conditions at reperfusion, using four different strategies, effectively improves hemodynamic recovery after warm ischemia.

Methods and Results: Isolated hearts of male Wistar rats were perfused in working-mode for 20 min, subjected to 27 min global ischemia (37°C), and 60 min reperfusion (n = 43). Mild hypothermia (30°C, 10 min), mechanical postconditioning (MPC; 2x 30 s reperfusion/30 s ischemia), hypoxia (no O₂, 2 min), or low pH (pH 6.8–7.4, 3 min) was applied at reperfusion and compared with controls (i.e., no strategy). After 60 min reperfusion, recovery of left ventricular work (developed pressure^*heart rate; expressed as percent of pre-ischemic value) was significantly greater for mild hypothermia (62 ± 7%), MPC (65 ± 8%) and hypoxia (61 ± 11%; p < 0.05 for all), but not for low pH (45 ± 13%), vs. controls (44 ± 7%). Increased hemodynamic recovery was associated with greater oxygen consumption (mild hypothermia, MPC) and coronary perfusion (mild hypothermia, MPC, hypoxia), and with reduced markers of necrosis (mild hypothermia, MPC, hypoxia) and mitochondrial damage (mild hypothermia, hypoxia).

Conclusions: Brief modifications in physical conditions at reperfusion, such as hypothermia, mechanical postconditioning, and hypoxia, improve post-ischemic hemodynamic function in our model of DCD. Cardioprotective reperfusion strategies applied at graft procurement could improve DCD graft recovery and limit further injury; however, optimal clinical approaches remain to be characterized.

Effect of Propofol, Sevoflurane and Desflurane on Systemic Redox Balance

We studied the effects of Propofol, Desflurane, and Sevoflurane on the systemic redox balance in patients undergoing laparohysterectomy. We measured blood concentration of glutathione (GSH), plasma antioxidant capacity (Trolox Equivalent Antioxidant Capacity-TEAC), and lipid peroxidation products (malondialdehyde (aMDA) and 4-hydroxynonenal (aHNE) protein adducts). Sixty patients were randomly placed into three groups of twenty people each. In Group P anesthesia was induced with Propofol 2 mg/kg and maintained with 12–10–8 mg/kg/min; in Groups S and D anesthesia was induced with 3 mg/kg Sodium Thiopental and maintained with 2% Sevoflurane and 6% Desflurane, respectively. Blood samples were collected prior to induction (T0bas), 60min and 24h postoperatively (T160' and T224 h). In Group P, GSH increased on T160' (p<0.02) and returned to baseline on T24h, while TEAC remained unmodified; in Groups S, GSH and TEAC decreased on T160' (p<0.01 vs. T0bas, p<0.03 vs. T0bas, respectively); in Group D, on T160' there was a slight decrease of GSH and TEAC. The levels of aMDA slightly decreased throughout the study periods in Group P, increased in Group D, and remained stable in Group S. Propofol showed antioxidant properties, while Sevoflurane and Desflurane seemed to shift the redox balance towards oxidation, yet without inducing overt oxidative damage.

Hyperbaric oxygen preconditioning ameliorates hypoxia-ischemia brain damage by activating Nrf2 expression in vivo and in vitro

The present study aimed to investigate whether hyperbaric oxygen preconditioning (HBO-PC) could ameliorate hypoxia-ischemia brain damage (HIBD) by an increase of Nrf2 expression. P7 Sprague-Dawley rats (aged 7 d, n = 195) were used in two in vivo experiments, including BO-PC exposure experiments in non-HIBD models and treatment experiments in HIBD models. 2,3,5-triphenyltetrazolium chloride (TTC) staining, Nissl Staining, and TUNEL staining were performed. And expressions of Nrf2, HO-1, and GSTs were measured. For in vitro studies, oxygen-glucose deprivation cells were established. Morphological and apoptotic staining and gene silencing of Nrf2 by siRNA transfection were investigated. For exposure experiments, HBO-PC for longer time increased the expression of Nrf2 significantly. And for treatment experiments, HBO-PC treatment significantly decreased infarction area, lessened neuronal injury, reduced apoptosis, and increased both the expression of Nrf2 and activities of its downstream proteins. Cytology tests confirmed effects of HBO-PC treatments. Besides, Nrf2 siRNA significantly reduced protective effects of HBO-PC. These observations demonstrated that an up-regulation of Nrf2 by HBO-PC might play an important role in the generation of tolerance against HIBD.

Sevoflurane

Sevoflurane has been available for clinical practice for about 20 years. Nowadays, its pharmacodynamic and pharmacokinetic properties together with its absence of major adverse side effects on the different organ systems have made this drug accepted worldwide as a safe and reliable anesthetic agent for clinical practice in various settings.

Nitrite Confers Preconditioning and Cytoprotection After Ischemia/Reperfusion Injury Through the Modulation of Mitochondrial Function

SIGNIFICANCE

Nitrite is now recognized as an intrinsic signaling molecule that mediates a number of biological processes. One of the most reproducible effects of nitrite is its ability to mediate cytoprotection after ischemia/reperfusion (I/R). This robust phenomenon has been reproduced by a number of investigators in varying animal models focusing on different target organs. Furthermore, nitrite's cytoprotective versatility is highlighted by its ability to mediate delayed preconditioning and remote conditioning in addition to acute protection.

RECENT ADVANCES

In the last 10 years, significant progress has been made in elucidating the mechanisms underlying nitrite-mediated ischemic tolerance.

CRITICAL ISSUES

The mitochondrion, which is essential to both the progression of I/R injury and the protection afforded by preconditioning, has emerged as a major subcellular target for nitrite. This review will outline the role of the mitochondrion in I/R injury and preconditioning, review the accumulated preclinical studies demonstrating nitrite-mediated cytoprotection, and finally focus on the known interactions of nitrite with mitochondria and their role in the mechanism of nitrite-mediated ischemic tolerance.

FUTURE DIRECTIONS

These studies set the stage for current clinical trials testing the efficacy of nitrite to prevent warm and cold I/R injury.

Mortality associated with using medetomidine and ketamine for general anesthesia in pregnant and nonpregnant Wistar rats

Medetomidine and ketamine are injectable drugs that can be used in combination to induce general anesthesia in rats. After noticing a high incidence of morbidity and mortality in pregnant Wistar rats given medetomidine and ketamine for anesthesia, the authors further investigated the effects of this combination of anesthetic drugs in both pregnant and nonpregnant Wistar rats. The time to recumbency and the duration of general anesthesia were similar between pregnant and nonpregnant rats. Pregnancy status did not affect the rats' pulse rate, respiratory rate, rectal temperature, oxygen saturation or perfusion index during 2 h of anesthesia. Pregnant rats had significantly lower blood glucose concentrations than nonpregnant rats at all time points, though blood glucose concentrations increased in both groups. The mortality rate was ∼15% both for nonpregnant rats and for pregnant rats. Researchers using medetomidine and ketamine to anesthetize Wistar rats should carefully monitor the rats in order to minimize mortality.

Mitochondrial targets for volatile anesthetics against cardiac ischemia-reperfusion injury

Mitochondria are critical modulators of cell function and are increasingly recognized as proximal sensors and effectors that ultimately determine the balance between cell survival and cell death. Volatile anesthetics (VA) are long known for their cardioprotective effects, as demonstrated by improved mitochondrial and cellular functions, and by reduced necrotic and apoptotic cell death during cardiac ischemia and reperfusion (IR) injury. The molecular mechanisms by which VA impart cardioprotection are still poorly understood. Because of the emerging role of mitochondria as therapeutic targets in diseases, including ischemic heart disease, it is important to know if VA-induced cytoprotective mechanisms are mediated at the mitochondrial level. In recent years, considerable evidence points to direct effects of VA on mitochondrial channel/transporter protein functions and electron transport chain (ETC) complexes as potential targets in mediating cardioprotection. This review furnishes an integrated overview of targets that VA impart on mitochondrial channels/transporters and ETC proteins that could provide a basis for cation regulation and homeostasis, mitochondrial bioenergetics, and reactive oxygen species (ROS) emission in redox signaling for cardiac cell protection during IR injury.

Isoflurane modulates cardiac mitochondrial bioenergetics by selectively attenuating respiratory complexes

Mitochondrial dysfunction contributes to cardiac ischemia-reperfusion (IR) injury but volatile anesthetics (VA) may alter mitochondrial function to trigger cardioprotection. We hypothesized that the VA isoflurane (ISO) mediates cardioprotection in part by altering the function of several respiratory and transport proteins involved in oxidative phosphorylation (OxPhos). To test this we used fluorescence spectrophotometry to measure the effects of ISO (0, 0.5, 1, 2mM) on the time-course of interlinked mitochondrial bioenergetic variables during states 2, 3 and 4 respiration in the presence of either complex I substrate K(+)-pyruvate/malate (PM) or complex II substrate K(+)-succinate (SUC) at physiological levels of extra-matrix free Ca(2+) (~200nM) and Na(+) (10mM). To mimic ISO effects on mitochondrial functions and to clearly delineate the possible ISO targets, the observed actions of ISO were interpreted by comparing effects of ISO to those elicited by low concentrations of inhibitors that act at each respiratory complex, e.g. rotenone (ROT) at complex I or antimycin A (AA) at complex III. Our conclusions are based primarily on the similar responses of ISO and titrated concentrations of ETC. inhibitors during state 3. We found that with the substrate PM, ISO and ROT similarly decreased the magnitude of state 3 NADH oxidation and increased the duration of state 3 NADH oxidation, ΔΨm depolarization, and respiration in a concentration-dependent manner, whereas with substrate SUC, ISO and ROT decreased the duration of state 3 NADH oxidation, ΔΨm depolarization and respiration. Unlike AA, ISO reduced the magnitude of state 3 NADH oxidation with PM or SUC as substrate. With substrate SUC, after complete block of complex I with ROT, ISO and AA similarly increased the duration of state 3 ΔΨm depolarization and respiration. This study provides a mechanistic understanding in how ISO alters mitochondrial function in a way that may lead to cardioprotection.

Nitrite activates protein kinase A in normoxia to mediate mitochondrial fusion and tolerance to ischaemia/reperfusion

AIMS

Nitrite (NO2(-)), a dietary constituent and nitric oxide (NO) oxidation product, mediates cardioprotection after ischaemia/reperfusion (I/R) in a number of animal models when administered during ischaemia or as a pre-conditioning agent hours to days prior to the ischaemic episode. When present during ischaemia, the reduction of nitrite to bioactive NO by deoxygenated haem proteins accounts for its protective effects. However, the mechanism of nitrite-induced pre-conditioning, a normoxic response which does not appear to require reduction of nitrite to NO, remains unexplored.

METHODS AND RESULTS

Using a model of hypoxia/reoxygenation (H/R) in cultured rat H9c2 cardiomyocytes, we demonstrate that a transient (30 min) normoxic nitrite treatment significantly attenuates cell death after a hypoxic episode initiated 1 h later. Mechanistically, this protection depends on the activation of protein kinase A, which phosphorylates and inhibits dynamin-related protein 1, the predominant regulator of mitochondrial fission. This results morphologically, in the promotion of mitochondrial fusion and functionally in the augmentation of mitochondrial membrane potential and superoxide production. We identify AMP kinase (AMPK) as a downstream target of the mitochondrial reactive oxygen species (ROS) generated and show that its oxidation and subsequent phosphorylation are essential for cytoprotection, as scavenging of ROS prevents AMPK activation and inhibits nitrite-mediated protection after H/R. The protein kinase A-dependent protection mediated by nitrite is reproduced in an intact isolated rat heart model of I/R.

CONCLUSIONS

These data are the first to demonstrate nitrite-dependent normoxic modulation of both mitochondrial morphology and function and reveal a novel signalling pathway responsible for nitrite-mediated cardioprotection.

Effects of sevoflurane postconditioning on cell death, inflammation and TLR expression in human endothelial cells exposed to LPS

Background

Sevoflurane is an anesthetic agent which also participates in protective mechanisms in sepsis, likely due to anti-inflammatory properties. A key tissue in sepsis is the endothelium, which expresses TLR2 and TLR4 receptors, known regulators of inflammatory mechanisms and potential therapeutic targets for this pathology. In this context, we explored the effect of sevoflurane postconditioning in an in vitro sepsis model.

Methods

Primary cultures of human umbilical vein endothelial cells were used for two different experiments. In the first set, cultures were placed in an airtight incubation chamber and exposed to different concentrations of sevoflurane (0,1,3 or 7% vol,) for 1 hour. In the second set, lipopolysaccharide from Escherichia coli 0111:B4 (1 μg/mL) was added to culture medium for 3 hours and cells were subsequently exposed to sevoflurane (0,1,3 or 7% vol,) for 1 hour as explained before. In both cases, cell viability was measured by MTT and Trypan blue assays, TLR2 and TLR4 expression were analyzed by flow cytometry, and TNFα and IL-6 levels were quantified in cell culture media by an immunoassay immediately after exposure, at 6 and 24 hours.

Results

Exposure to 3% sevoflurane decreased TLR2 at 24 hours and TLR4 at 6 and 24 hours (both p<0.05), whereas exposure to 7% decreased TLR4 expression at 6 hours (p<0.05). Both 3 and 7% sevoflurane decreased TNF-α and IL-6 levels at 24 hours (both p<0.05). In LPS-stimulated cultures, exposure to 3% sevoflurane was cytoprotective at 6 and 24 hours (p<0.05) compared with control, and decreased TLR2 and TLR4 expression at 24 hours (p<0.05); whereas 7% decreased TLR4 expression at 24 hours (p<0.05). Both 3% and 7% sevoflurane decreased TNF-α and IL-6 levels at 24 hours (both p<0.05).

Conclusions

Postconditioning with the halogenated anesthetic agent sevoflurane after LPS stimulation shows a cytoprotective effect in an in vitro model, decreasing cell death and reducing TLR2 and TLR4 expression as well as levels of the inflammatory mediators TNF-α and IL-6 in human endothelial cells.

Complex I and ATP synthase mediate membrane depolarization and matrix acidification by isoflurane in mitochondria

Short application of the volatile anesthetic isoflurane at reperfusion after ischemia exerts strong protection of the heart against injury. Mild depolarization and acidification of the mitochondrial matrix are involved in the protective mechanisms of isoflurane, but the molecular basis for these changes is not clear. In this study, mitochondrial respiration, membrane potential, matrix pH, matrix swelling, ATP synthesis and -hydrolysis, and H(2)O(2) release were assessed in isolated mitochondria. We hypothesized that isoflurane induces mitochondrial depolarization and matrix acidification through direct action on both complex I and ATP synthase. With complex I-linked substrates, isoflurane (0.5mM) inhibited mitochondrial respiration by 28 ± 10%, and slightly, but significantly depolarized membrane potential and decreased matrix pH. With complex II- and complex IV-linked substrates, respiration was not changed, but isoflurane still decreased matrix pH and depolarized mitochondrial membrane potential. Depolarization and matrix acidification were attenuated by inhibition of ATP synthase with oligomycin, but not by inhibition of mitochondrial ATP- and Ca(2+)-sensitive K(+) channels or uncoupling proteins. Isoflurane did not induce matrix swelling and did not affect ATP synthesis and hydrolysis, but decreased H(2)O(2) release in the presence of succinate in an oligomycin- and matrix pH-sensitive manner. Isoflurane modulated H(+) flux through ATP synthase in an oligomycin-sensitive manner. Our results indicate that isoflurane-induced mitochondrial depolarization and acidification occur due to inhibition of the electron transport chain at the site of complex I and increased proton flux through ATP synthase. K(+) channels and uncoupling proteins appear not to be involved in the direct effects of isoflurane on mitochondria.

Metabotropic actions of the volatile anaesthetic sevoflurane increase protein kinase M synthesis and induce immediate preconditioning protection of rat hippocampal slices

Anaesthetic preconditioning occurs when a volatile anaesthetic, such as sevoflurane, is administered before a hypoxic or ischaemic insult; this has been shown to improve neuronal recovery after the insult. We found that sevoflurane-induced preconditioning in the rat hippocampal slice enhances the hypoxic hyperpolarization of CA1 pyramidal neurons, delays and attenuates their hypoxic depolarization, and increases the number of neurons that recover their resting and action potentials after hypoxia. These altered electrophysiological effects and the improved recovery corresponded with an increase in the amount of a constitutively active, atypical protein kinase C isoform found in brain, protein kinase M zeta (PKMζ). A selective inhibitor of this kinase, zeta inhibitory peptide (ZIP), blocked the increase in the total amount of PKMζ protein and the amount of the activated form of this kinase, phospho-PKMζ (p-PKMζ); it also blocked the altered electrophysiological effects and the improved recovery. We found that both cycloheximide, a general protein synthesis inhibitor, and rapamycin, a selective inhibitor of the mTOR pathway for regulating protein synthesis, blocked the increase in p-PKMζ, the electrophysiological changes, and the improved recovery due to sevoflurane-induced preconditioning. Glibenclamide, a KATP channel blocker, when present only during the hypoxia, prevented the enhanced hyperpolarization, the delayed and attenuated hypoxic depolarization, and the improved recovery following sevoflurane-induced preconditioning. To examine the function of persistent PKMζ and KATP channel activity after the preconditioning was established, we administered 4% sevoflurane for 30 min and then discontinued it for 30 min before 10 min of hypoxia. When either tolbutamide, a KATP channel blocker, or ZIP were administered at least 15 min after the washout of sevoflurane, there was little recovery compared with sevoflurane alone. Thus, continuous KATP channel and PKMζ activity are required to maintain preconditioning protection. We conclude that sevoflurane induces activation of the mTOR pathway, increasing the new protein synthesis of PKMζ, which is constitutively phosphorylated to its active form, leading to an increased KATP channel-induced hyperpolarizaton. This hyperpolarization delays and attenuates the hypoxic depolarization, improving the recovery of neurons following hypoxia. Thus, sevoflurane acts via a metabotropic pathway to improve recovery following hypoxia.

Cockayne syndrome group B protein prevents the accumulation of damaged mitochondria by promoting mitochondrial autophagy

Cells from Cockayne syndrome patients and a mouse model of the disease show increased metabolism as a result of impaired autophagy-mediated removal of damaged mitochondria.

Cockayne syndrome (CS) is a devastating autosomal recessive disease characterized by neurodegeneration, cachexia, and accelerated aging. 80% of the cases are caused by mutations in the CS complementation group B (CSB) gene known to be involved in DNA repair and transcription. Recent evidence indicates that CSB is present in mitochondria, where it associates with mitochondrial DNA (mtDNA). We report an increase in metabolism in the CSB^m/m mouse model and CSB-deficient cells. Mitochondrial content is increased in CSB-deficient cells, whereas autophagy is down-regulated, presumably as a result of defects in the recruitment of P62 and mitochondrial ubiquitination. CSB-deficient cells show increased free radical production and an accumulation of damaged mitochondria. Accordingly, treatment with the autophagic stimulators lithium chloride or rapamycin reverses the bioenergetic phenotype of CSB-deficient cells. Our data imply that CSB acts as an mtDNA damage sensor, inducing mitochondrial autophagy in response to stress, and that pharmacological modulators of autophagy are potential treatment options for this accelerated aging phenotype.

Low concentrations of methamphetamine can protect dopaminergic cells against a larger oxidative stress injury: mechanistic study

Mild stress can protect against a larger insult, a phenomenon termed preconditioning or tolerance. To determine if a low intensity stressor could also protect cells against intense oxidative stress in a model of dopamine deficiency associated with Parkinson disease, we used methamphetamine to provide a mild, preconditioning stress, 6-hydroxydopamine (6-OHDA) as a source of potentially toxic oxidative stress, and MN9D cells as a model of dopamine neurons. We observed that prior exposure to subtoxic concentrations of methamphetamine protected these cells against 6-OHDA toxicity, whereas higher concentrations of methamphetamine exacerbated it. The protection by methamphetamine was accompanied by decreased uptake of both [(3)H] dopamine and 6-OHDA into the cells, which may have accounted for some of the apparent protection. However, a number of other effects of methamphetamine exposure suggest that the drug also affected basic cellular survival mechanisms. First, although methamphetamine preconditioning decreased basal pERK1/2 and pAkt levels, it enhanced the 6-OHDA-induced increase in these phosphokinases. Second, the apparent increase in pERK1/2 activity was accompanied by increased pMEK1/2 levels and decreased activity of protein phosphatase 2. Third, methamphetamine upregulated the pro-survival protein Bcl-2. Our results suggest that exposure to low concentrations of methamphetamine cause a number of changes in dopamine cells, some of which result in a decrease in their vulnerability to subsequent oxidative stress. These observations may provide insights into the development of new therapies for prevention or treatment of PD.

Sevoflurane preconditioning reverses impairment of hippocampal long-term potentiation induced by myocardial ischaemia-reperfusion injury

BACKGROUND AND OBJECTIVE

We sought to test whether a transient myocardial ischaemia can induce impairment of hippocampal long-term potentiation (LTP) and whether sevoflurane preconditioning can provide robust protective effects on this neurological impairment.

METHODS

Wistar rats were subjected to a transient coronary artery occlusion for 30 min. Sevoflurane preconditioning was performed by exposure to 1.0 minimum alveolar concentration of sevoflurane for 1 h and washout for 30 min before myocardial ischaemia. Hippocampal LTP was evaluated during a 7-day observation period. The expressions of haem oxygenase-1 mRNA, tumour necrosis factor-alpha mRNA and interleukin-1beta mRNA in the hippocampus were analysed by quantitative reverse transcription-PCR.

RESULTS

LTP was significantly inhibited 1 and 3 days after the transient myocardial ischaemia in the control group when compared with the animals subjected to a sham operation without coronary occlusion, and the LTP recovered to a normal magnitude 7 days later. Sevoflurane preconditioning remarkably reversed the transient inhibition of LTP observed at 1 and 3 days after myocardial ischaemia. Compared with the sham animals, the expressions of haem oxygenase-1 mRNA, tumour necrosis factor-alpha mRNA and interleukin-1beta mRNA in the hippocampus of the control rats were significantly increased during the early stage after myocardial ischaemia (1-3 days), and the increases of these cytokines were attenuated by sevoflurane pretreatment.

CONCLUSION

Sevoflurane preconditioning induced neuroprotection against impairment of hippocampal LTP resulting from myocardial ischaemia and reperfusion.

Sevoflurane postconditioning protects isolated rat hearts against ischemia-reperfusion injury: the role of radical oxygen species, extracellular signal-related kinases 1/2 and mitochondrial permeability transition pore

The roles of reactive oxygen species (ROS), extracellular signal-regulated kinase 1/2 (ERK 1/2) and mitochondrial permeability transition pore (mPTP) in sevoflurane postconditioning induced cardioprotection against ischemia-reperfusion injury in Langendorff rat hearts were investigated. When compared with the unprotected hearts subjected to 30 min of ischemia followed by 1 h of reperfusion, exposure of 3% sevoflurane during the first 15 min of reperfusion significantly improved functional recovery, decreased infarct size, reduced lactate dehydrogenase and creatine kinase-MB release, and reduced myocardial malondialdehyde production. However, these protective effects were abolished in the presence of either ROS scavenger N-acetylcysteine or ERK 1/2 inhibitor PD98059, and accompanied by prevention of ERK 1/2 phosphorylation and elimination of inhibitory effect on mPTP opening. These findings suggested that sevoflurane postconditioning protected isolated rat hearts against ischemia-reperfusion injury via the recruitment of the ROS-ERK 1/2-mPTP signaling cascade.

Anaesthesia and myocardial ischaemia/reperfusion injury

Anaesthetists are confronted on a daily basis with patients with coronary artery disease, myocardial ischaemia, or both during the perioperative period. Therefore, prevention and ultimately adequate therapy of perioperative myocardial ischaemia and its consequences are the major challenges in current anaesthetic practice. This review will focus on the translation of the laboratory evidence of anaesthetic-induced cardioprotection into daily clinical practice.

Effects of desflurane and propofol on electrophysiological parameters during and recovery after hypoxia in rat hippocampal slice CA1 pyramidal cells

Cerebral ischemia is a major cause of death and disability and may be a complication of neurosurgery. Certain anesthetics may improve recovery after ischemia and hypoxia by altering electrophysiological changes during the insult. Intracellular recordings were made from CA1 pyramidal cells in hippocampal slices from adult rats. Desflurane or propofol was applied 10 min before and during 10 min of hypoxia (95% nitrogen, 5% carbon dioxide). None of the untreated CA1 pyramidal neurons, 46% of the 6% desflurane- and 38% of the 12% desflurane-treated neurons recovered their resting and action potentials 1 h after hypoxia (P<0.05). Desflurane (6% or 12%) enhanced the hypoxic hyperpolarization (4.9 or 4.7 vs. 2.6 mV), increased the time until the rapid depolarization (441 or 390 vs. 217 s) and reduced the level of depolarization at 10 min of hypoxia (-13.5 or -13.0 vs. -0.6 mV); these changes may be part of the mechanism of its protective effect. Either chelerythrine (5 microM), a protein kinase C inhibitor, or glybenclamide (5 microM), a K(ATP) channel blocker, prevented the protective effect and the electrophysiological changes with 6% desflurane. Propofol (33 or 120 microM) did not improve recovery (0 or 0% vs. 0%) 1 h after 10 min of hypoxia; it did not significantly enhance the hypoxic hyperpolarization (3.6 or 3.1 vs. 2.6 mV) or increase the latency of the rapid depolarization (282 or 257 vs. 217 s). The average depolarization at 10 m of hypoxia with 33 microM propofol (-4.1 mV) was slightly but significantly different from that in untreated hypoxic tissue (-0.6 mV). Desflurane but not propofol improved recovery of the resting and action potentials in hippocampal slices after hypoxia, this improvement correlated with enhanced hyperpolarization and attenuated depolarization of the membrane potential during hypoxia. Our results demonstrate differential effects of anesthetics on electrophysiological changes during hypoxia.

Levosimendan facilitates weaning from cardiopulmonary bypass in patients undergoing coronary artery bypass grafting with impaired left ventricular function

BACKGROUND

Levosimendan is a compound with vasodilatory and inotropic properties. Experimental data suggest effective reversal of stunning and cardioprotective properties.

METHODS

This prospective, randomized, placebo-controlled, double-blind study included 60 patients with 3-vessel coronary disease and left ventricular ejection fraction (LVEF) of less than 0.50. Levosimendan administration (12 microg/kg bolus, followed by an infusion of 0.2 microg/kg/min) was started immediately after induction anesthesia. Predefined strict hemodynamic criteria were used to assess the success of weaning. If weaning was not successful, CPB was reinstituted and an epinephrine infusion was started. If the second weaning attempt failed, intraaortic balloon pumping (IABP) was instituted.

RESULTS

The groups had comparable demographics. The mean (standard deviation) preoperative LVEF was 0.36 (0.8) in both groups. The baseline cardiac index was 1.8 (0.3) L/min/m(2) in the levosimendan group and 1.9 (0.4) L/min/m(2) in the placebo group. The mean duration of CPB to primary weaning attempt was 104 (25) minutes in the levosimendan and 109 (22) minutes in the placebo group. Primary weaning was successful in 22 patients (73%) in the levosimendan group and in 10 (33%) in the placebo group (p = 0.002). The odds ratio for failure in primary weaning was 0.182 (95% confidence interval, 0.060 to 0.552). Four patients in the placebo group failed the second weaning and underwent IABP compared with none in the levosimendan group (p = 0.112).

CONCLUSIONS

Levosimendan significantly enhanced primary weaning from CPB compared with placebo in patients undergoing 3-vessel on-pump coronary artery bypass grafting. The need for additional inotropic or mechanical therapy was decreased.

In vivo cardioprotection by S-nitroso-2-mercaptopropionyl glycine

The reversible S-nitrosation and inhibition of mitochondrial complex I is a potential mechanism of cardioprotection, recruited by ischemic preconditioning (IPC), S-nitrosothiols, and nitrite. Previously, to exploit this mechanism, the mitochondrial S-nitrosating agent S-nitroso-2-mercaptopropionyl glycine (SNO-MPG) was developed, and protected perfused hearts and isolated cardiomyocytes against ischemia-reperfusion (IR) injury. In the present study, the murine left anterior descending coronary artery (LAD) occlusion model of IR injury was employed, to determine the protective efficacy of SNO-MPG in vivo. Intraperitoneal administration of 1 mg/kg SNO-MPG, 30 min prior to occlusion, significantly reduced myocardial infarction and improved EKG parameters, following 30 min occlusion plus 2 or 24 h reperfusion. SNO-MPG protected to the same degree as IPC, and notably was also protective when administered at reperfusion. Cardioprotection was accompanied by increased mitochondrial protein S-nitrosothiol content, and inhibition of complex I, both of which were reversed after 2 h reperfusion. Finally, hearts from mice harboring a heterozygous mutation in the complex I NDUSF4 subunit were refractory to protection by either SNO-MPG or IPC, suggesting that a fully functional complex I, capable of reversible inhibition is critical for cardioprotection. Overall, these results are consistent with a role for mitochondrial S-nitrosation and complex I inhibition in the cardioprotective mechanism of IPC and SNO-MPG in vivo.

Mitochondrial iron accumulation with age and functional consequences

During the aging process, an accumulation of non-heme iron disrupts cellular homeostasis and contributes to the mitochondrial dysfunction typical of various neuromuscular degenerative diseases. Few studies have investigated the effects of iron accumulation on mitochondrial integrity and function in skeletal muscle and liver tissue. Thus, we isolated liver mitochondria (LM), as well as quadriceps-derived subsarcolemmal mitochondria (SSM) and interfibrillar mitochondria (IFM), from male Fischer 344 x Brown Norway rats at 8, 18, 29 and 37 months of age. Non-heme iron content in SSM, IFM and LM was significantly higher with age, reaching a maximum at 37 months of age. The mitochondrial permeability transition pore (mPTP) was more susceptible to the opening in aged mitochondria containing high levels of iron (i.e. SSM and LM) compared to IFM. Furthermore, mitochondrial RNA oxidation increased significantly with age in SSM and LM, but not in IFM. Levels of mitochondrial RNA oxidation in SSM and LM correlated positively with levels of mitochondrial iron, whereas a significant negative correlation was observed between the maximum Ca(2+) amounts needed to induce mPTP opening and iron contents in SSM, IFM and LM. Overall, our data suggest that age-dependent accumulation of mitochondrial iron may increase mitochondrial dysfunction and oxidative damage,thereby enhancing the susceptibility to apoptosis.

Differential increase of mitochondrial matrix volume by sevoflurane in isolated cardiac mitochondria

BACKGROUND

Mitochondrial (m) adenosine triphosphate sensitive potassium (K(ATP)) channel opening has been reported to trigger and/or mediate cardioprotection by volatile anesthetics. However, the effects of volatile anesthetics on mitochondrial function are not well understood. Prevention of mitochondrial matrix volume (MMV) contraction during ischemia may contribute to cardioprotection against ischemia/reperfusion injury. We investigated whether sevoflurane increases MMV and if this increase is mediated by mK(ATP) channel opening.

METHODS

Mitochondria from fresh guinea pig hearts were isolated and diluted in buffer that included oligomycin and ATP to inhibit ATP synthesis. Changes in MMV by diazoxide, a known mK(ATP) channel opener, and by different sevoflurane concentrations, were measured by light absorption at 520 nm in the absence or presence of the mK(ATP) channel blocker, 5-hydroxydecanoate.

RESULTS

Compared with control, 30-300 microM sevoflurane (approximately 0.2-2.1 vol %) increased MMV by 30%-55%, which was similar to the effect of diazoxide. These increases were blocked by 5-hydroxydecanoate. Higher sevoflurane concentration (1000 microM; 7.1 vol %), however, had no effect on MMV.

CONCLUSIONS

In clinically relevant concentrations, sevoflurane increases MMV via mK(ATP) channel opening. Preservation of mitochondrial integrity may contribute to the cardioprotective effects of sevoflurane against ischemia/reperfusion injury. Impaired mitochondrial function at supraclinical anesthetic concentrations may explain the observed biphasic response. These findings add to our understanding of the intracellular mechanisms of volatile anesthetics as cardioprotective drugs.

Ischemic preconditioning: from molecular mechanisms to therapeutic opportunities

Ischemia/reperfusion (I/R) injury is a major contributory factor to cardiac dysfunction and infarct size that determines patient prognosis after acute myocardial infarction. Considerable interest exists in harnessing the heart's endogenous capacity to resist I/R injury, known as ischemic preconditioning (IPC). The IPC research has contributed to uncovering the pathophysiology of I/R injury on a molecular and cellular basis and to invent potential therapeutic means to combat such damage. However, the translation of basic research findings learned from IPC into clinical practice has often been inadequate because the majority of basic research findings have stemmed from young and healthy animals. Few if any successful implementations of IPC have occurred in the diseased hearts that are the primary target of viable therapies activating cardioprotective mechanisms to limit cardiac dysfunction and infarct size. Therefore, the first purpose of this review is to facilitate understanding of pathophysiology of I/R injury and the mechanisms of cardioprotection afforded by IPC in the normal heart. Then I focus on the problems and opportunities for successful bench-to-bedside translation of IPC in the diseased hearts.

Isoflurane Activates Human Cardiac Mitochondrial Adenosine Triphosphate-Sensitive K+ Channels Reconstituted in Lipid Bilayers

BACKGROUND

Activation of the mitochondrial adenosine triphosphate (ATP)-sensitive K+ channel (mitoK(ATP)) has been proposed as a critical step in myocardial protection by isoflurane-induced preconditioning in humans and animals. Recent evidence suggests that reactive oxygen species (ROS) may mediate isoflurane-mediated myocardial protection. In this study, we examined the direct effect of isoflurane and ROS on human cardiac mitoK(ATP) channels reconstituted into the lipid bilayers.

METHODS

Inner mitochondrial membranes were isolated from explanted human left ventricles not suitable for heart transplantation and fused into lipid bilayers in symmetrical potassium glutamate solution (150 mM). ATP-sensitive K+ currents were recorded before and after exposure to isoflurane and H2O2 under voltage clamp.

RESULTS

The human mitoK(ATP) was identified by its sensitivity to inhibition by ATP and 5-hydroxydecanoate. Addition of isoflurane (0.8 mM) increased the open probability of the mitoK(ATP) channels, either in the presence or absence of ATP inhibition (0.5 mM). The isoflurane-mediated increase in K+ currents was completely inhibited by 5-hydroxydecanoate. Similarly, H2O2 (200 microM) was able to activate the mitoK(ATP) previously inhibited by ATP.

CONCLUSIONS

These data confirm that isoflurane, as well as ROS, directly activates reconstituted human cardiac mitoK(ATP) channel in vitro, without apparent involvement of cytosolic protein kinases, as commonly proposed. Activation of the mitoK(ATP) channel may contribute to the myocardial protective effect of isoflurane in the human heart.

Neuroprotective antioxidant STAZN protects against myocardial ischemia/reperfusion injury

BACKGROUND

Protecting the myocardium from ischemia-reperfusion injury has significant potential to reduce the complications of myocardial infarction and interventional revascularization procedures. Reperfusion damage is thought to result, in part, from oxidative stress. Here we use a novel method of percutaneous coronary occlusion to show that the potent antioxidant and neuroprotective free-radical scavenger, stilbazulenyl nitrone (STAZN), confers marked cardioprotection when given immediately prior to reperfusion.

METHODS AND RESULTS

Physiologically controlled male Sprague-Dawley rats were anesthetized with isoflurane, paralyzed with pancuronium and mechanically ventilated. A guide wire was introduced via the femoral artery and advanced retrogradely via the aorta into the left coronary artery under fluoroscopic guidance. Rats with established coronary ischemia (85 min after occlusion) were given STAZN 3.5 mg/kg or its vehicle 5 min before and 2 h after reperfusion, and were subjected to functional and histopathologic studies at 3 days. Ischemia-associated Q wave amplitude was reduced by 73% in STAZN-treated rats (P=0.01), while infarct-related ejection fraction, fractional shortening and severe regional wall-motion impairments were improved by 48%, 54% and 37%, respectively, relative to vehicle-treated controls (P=0.05). Total myocardial infarct volume in STAZN-treated rats was correspondingly reduced by 43% (P<0.05), representing a sparing of 14% of the total left ventricular myocardium.

CONCLUSIONS

STAZN, a second-generation azulenyl nitrone with potent neuroprotective efficacy in brain ischemia, is also a rapidly acting and highly effective cardioprotective agent in acute coronary ischemia. Our results suggest the potential for clinical benefit in the setting of acute coronary syndromes.

Volatile anesthetic-induced cardiac preconditioning

Pharmacological preconditioning with volatile anesthetics, or anesthetic-induced preconditioning (APC), is a phenomenon whereby a brief exposure to volatile anesthetic agents protects the heart from the potentially fatal consequences of a subsequent prolonged period of myocardial ischemia and reperfusion. Although not completely elucidated, the cellular and molecular mechanisms of APC appear to mimic those of ischemic preconditioning, the most powerful endogenous cardioprotective mechanism. This article reviews recently accumulated evidence underscoring the importance of mitochondria, reactive oxygen species, and K(ATP) channels in cardioprotective signaling by volatile anesthetics. Moreover, the article addresses current concepts and controversies regarding the specific roles of the mitochondrial and the sarcolemmal K(ATP) channels in APC.

Relationship between oxidative stress, lipid peroxidation, and ultrastructural damage in patients with coronary artery disease undergoing cardioplegic arrest/reperfusion

OBJECTIVE

In animal models, formation of oxidants during postischemic reperfusion may exert deleterious effects ("oxidative stress"). Cardioplegic arrest/reperfusion during cardiac surgery might similarly induce oxidative stress. However, the phenomenon has not been precisely characterized in patients, and therefore the role of antioxidant therapy at cardiac surgery is a matter of debate. Thus, we wanted to ascertain whether the relationship between oxidant formation and development of myocardial injury also translates to the situation of patients subjected to cardioplegic arrest.

METHODS

In 24 patients undergoing coronary artery bypass, trans-cardiac blood samples and myocardial biopsies were taken before cardioplegic arrest and again following reperfusion.

RESULTS

Cardiac glutathione release (marker of oxidant production) was negligible at baseline (0.02+/-0.04 micromol/L), but it increased 15 min into reperfusion (1.10+/-0.40 micromol/L; p<0.05); concomitantly, myocardial concentration of the antioxidant ubiquinol decreased from 144.5+/-52.0 to 97.6+/-82.0 nmol/g (p<0.05). Although these changes document cardiac exposure to oxidants, they were not accompanied by evidence of injury. Neither coronary sinus blood nor cardiac biopsies showed increased lipid peroxide concentrations. Furthermore, electron microscopy showed no major ultrastructural alterations. Finally, full recovery of left ventricular systolic and diastolic function was observed.

CONCLUSIONS

Careful investigation reveals that while oxidant production does occur during cardiac surgery in patients with chronic ischemic heart disease, cardiac oxidative stress may not progress through membrane damage and irreversible injury.

Sevoflurane immediate preconditioning alters hypoxic membrane potential changes in rat hippocampal slices and improves recovery of CA1 pyramidal cells after hypoxia and global cerebral ischemia

Pretreatment with anesthetics before but not during hypoxia or ischemia can improve neuronal recovery after the insult. Sevoflurane, a volatile anesthetic agent, improved neuronal recovery subsequent to 10 min of global cerebral ischemia when it was present for 1 h before the ischemia. The mean number of intact hippocampal cornus ammonis 1 (CA1) pyramidal neurons in rats subjected to cerebral ischemia without any pretreatment was 17+/-5 (neurons/mm+/-S.D.) 6 weeks after the ischemia; naïve, non-ischemic rats had 177+/-5 neurons/mm. Rats pretreated with either 2% or 4% sevoflurane had 112+/-57 or 150+/-15 CA1 pyramidal neurons/mm respectively (P<0.01) 6 weeks after global cerebral ischemia. In order to examine the mechanisms of protection we used hypoxia to generate energy deprivation. Intracellular recordings were made from CA1 pyramidal neurons in rat hippocampal slices; the recovery of resting and action potentials after hypoxia was used as an indicator of neuronal survival. Pretreatment with 4% sevoflurane for 15 min improved neuronal recovery 1 h after the hypoxia; 90% of the sevoflurane-pretreated neurons recovered while none (0%) of the untreated neurons recovered. Pretreatment with sevoflurane enhanced the hypoxic hyperpolarization(-6.4+/-0.6 vs. -3.3+/-0.3 mV) and reduced the final level of the hypoxic depolarization (-39+/-6 vs. -0.3+/-2 mV) during hypoxia. Chelerythrine (5 muM), a protein kinase C/protein kinase M inhibitor, blocked both the improved recovery (10%) and the electrophysiological changes with 4% sevoflurane preconditioning. Two percent sevoflurane for 15 min before hypoxia did not improve recovery (0% recovery both groups) and did not enhance the hypoxic hyperpolarization or reduce the final depolarization during hypoxia. However if 2% sevoflurane was present for 1 h before the hypoxia then there was significantly improved recovery, enhanced hypoxic hyperpolarization, and reduced final depolarization. Thus we conclude that sevoflurane preconditioning improves recovery in both in vivo and in vitro models of energy deprivation and that preconditioning enhances the hypoxic hyperpolarization and reduces the hypoxic depolarization. Anesthetic preconditioning may protect neurons from ischemia by altering the electrophysiological changes a neuron undergoes during energy deprivation.

Preterminal gasping during hypoxic cardiac arrest increases cardiac function in immature rats

Newborn animals are more resistant to anoxia than older animals, partly due to an increased tolerance of the immature heart to anoxia. Newborn animals also have a more robust preterminal gasp. We investigated the relationship between gasping and cardiac function in immature and maturing rats exposed to anoxia. Immature postnatal day 7 (PND7) rats (n = 13) and maturing PND17 rats (n = 13) were exposed to 100% nitrogen (anoxia) for 10 min. Echocardiography was used to calculate cardiac contractility (CC) by left ventricular shortening fraction and cardiac output (CO) from Doppler velocity recordings of pulmonary artery blood flow. In a separate group of PND7 rats, CC and CO were recorded after the paralytic agent pancuronium was used to prevent gasping. Anoxia decreased CC and CO in PND7 and PND17 rats, followed by a partial and transient recovery. Gasping preceded recovery of CO and was required to sustain CO. Gasping in PND7 rats lasted longer (541 s versus 351 s, p < 0.01) and resulted in a greater recovery of CC and CO. Anoxia-induced gasping and the associated recovery of cardiac function were abolished by paralysis. Thus, anoxia-induced gasping transiently improves cardiac function, and more robust gasping in immature rats is associated with increased cardiac anoxic tolerance.

Myocardial preconditioning and cardioprotection by volatile anaesthetics

The biological bases and the clinical applications of ischaemic and anaesthetic preconditioning are reviewed. Ischaemic preconditioning is an endogenous defensive phenomenon of the myocardium in which brief periods of ischaemia followed by reperfusion reduce the infarct size induced by longer ischaemic stimuli; both an early and a late phase may be distinguished. In the early phase, the mediators released activate ATP-dependent potassium channels and kinase cascade; these enzymes migrating at the level of various subcellular structures phosphorylate some end-effectors responsible for cardioprotection. Several molecules that are involved in the regulation of cell death during ischaemia-reperfusion injury have been proposed for such a role, including mitochondrial ATP-dependent potassium channels, connexins and cytoskeletal and mitochondrial proteins. In the late phase, the triggers and mediators themselves, plus nitric oxide, are responsible for the genetic reprogramming providing a protective effect via ex-novo synthesis of proteins. Volatile halogenated anaesthetics may induce a particular sort of pharmacological preconditioning, anaesthetic preconditioning, which presents some differences in the biochemical signalling mechanism but is able to give protection comparable to the ischaemic form. Anaesthetic preconditioning presents obvious advantages compared to ischaemic preconditioning, and researchers have tried to take advantage of this in the clinical setting, in cardiac surgical patients, in neuroprotection and to prolong the survival of organs destined for transplantation.

Exercise by lifelong voluntary wheel running reduces subsarcolemmal and interfibrillar mitochondrial hydrogen peroxide production in the heart

Evidence suggests that mitochondrial dysfunction and oxidant production, in association with an accumulation of oxidative damage, contribute to the aging process. Regular physical activity can delay the onset of morbidity, increase mean lifespan, and reduce the risk of developing several pathological states. No studies have examined age-related changes in oxidant production and oxidative stress in both subsarcolemmal (SSM) and interfibrillar (IFM) mitochondria in combination with lifelong exercise. Therefore, we investigated whether long-term voluntary wheel running in Fischer 344 rats altered hydrogen peroxide (H2O2) production, antioxidant defenses, and oxidative damage in cardiac SSM and IFM. At 10–11 wk of age, rats were randomly assigned to one of two groups: sedentary and 8% food restriction (sedentary; n = 20) or wheel running and 8% food restriction (runners; n = 20); rats were killed at 24 mo of age. After the age of 6 mo, running activity was maintained at an average of 1,145 ± 248 m/day. Daily energy expenditure determined by doubly labeled water technique showed that runners expended on average ∼70% more energy per day than the sedentary rats. Long-term voluntary wheel running significantly reduced H2O2production from both SSM (−10.0%) and IFM (−9.6%) and increased daily energy expenditure (kJ/day) significantly in runners compared with sedentary controls. Additionally, MnSOD activity was significantly lowered in SSM and IFM from wheel runners, which may reflect a reduction in mitochondrial superoxide production. Activities of the other major antioxidant enzymes (glutathione peroxidase and catalase) and glutathione levels were not altered by wheel running. Despite the reduction in mitochondrial oxidant production, no significant differences in oxidative stress levels (4-hydroxy-2-nonenal-modified proteins, protein carbonyls, and malondialdehyde) were detected between the two groups. The health benefits of chronic exercise may be, at least partially, due to a reduction in mitochondrial oxidant production; however, we could not detect a significant reduction in several selected parameters of oxidative stress.

Increasing Heart Size and Age Attenuate Anesthetic Preconditioning in Guinea Pig Isolated Hearts

Anesthetic preconditioning (APC) reduces myocardial ischemia/reperfusion injury. Recent investigations have reported that older hearts are not susceptible to APC. We investigated if increasing heart size with age determines the susceptibility to APC in young guinea pigs. Langendorff-prepared guinea pig hearts of different weights (1.1-2.2 g) and ages (2-7 wks) were exposed to 1.3 mM sevoflurane for 15 min followed by 30 min washout (APC; n = 20) before 30 min global ischemia and 120 min reperfusion. Control hearts (n = 20) were not subject to APC. Left ventricular pressure was measured isovolumetrically and infarct size was determined by triphenyltetrazolium staining. Functional data were not different between groups at the beginning of the experiments nor did they correlate with heart weight or age. At 120 min reperfusion, left ventricular pressure, coronary flow, and tissue viability showed significant negative correlations with increasing heart weight and age in APC but not in control hearts; i.e., APC improved function and attenuated infarct size better in smaller/younger hearts than in larger/older hearts. Thus, increasing age and heart size attenuate the susceptibility for APC even in younger guinea pigs. This may have important implications for further basic science research and the possible clinical applicability of APC in humans.

The influence of mitochondrial KATP-channels in the cardioprotection of preconditioning and postconditioning by sevoflurane in the rat in vivo

Volatile anesthetics induce myocardial preconditioning and can also protect the heart when given at the onset of reperfusion-a practice recently termed "postconditioning." We investigated the role of mitochondrial KATP (mKATP)-channels in sevoflurane-induced cardioprotection for both preconditioning and postconditioning alone and whether there is a synergistic effect of both. Rats were subjected to 25 min of coronary artery occlusion followed by 120 min of reperfusion. Infarct size was determined by triphenyltetrazolium staining. The following protocols were used: 1) preconditioning (S-Pre, n = 10, achieved by 2 periods of 5 min sevoflurane administration (1 MAC) followed by 10 min of washout); 2) sevoflurane postconditioning (1 MAC of sevoflurane given for 2 min at the beginning of reperfusion; S-Post, n = 10); 3) administration before and after ischemia (S-Pre + S-Post, n = 10). Protocols 1-3 were repeated in the presence of 5-hydroxydecanoate (5HD), a specific mKATP-channel-blocker (S-Pre + S-Post + 5HD, S-Pre + 5HD: n = 10; S-Post + 5HD: n = 9). Nine rats served as untreated controls (CON) or received 5HD alone (5HD, n = 10). Both S-Pre (23% +/- 13% of the area at risk, mean +/- sd) and S-Post (18% +/- 5%) reduced infarct size compared with CON (49% +/- 11%, both P < 0.05). S-Pre + S-Post resulted in a larger reduction of infarct size (12% +/- 5%, P = 0.054 versus S-Pre) compared with administration before or after ischemia alone. 5HD diminished the protection in all three sevoflurane treated groups (S-Pre + 5HD, 35% +/- 12%; S-Post + 5HD, 44% +/- 12%; S-Pre + S-Post + 5HD, 46% +/- 14%;) but given alone had no effect on infarct size (41% +/- 13%). Sevoflurane preconditioning and postconditioning protects against myocardial ischemia-reperfusion injury. The combination of preconditioning and postconditioning provides additive cardioprotection and is mediated, at least in part, by mKATP-channels.

Reactive oxygen species as mediators of cardiac injury and protection: the relevance to anesthesia practice

Reactive oxygen species (ROS) are central to cardiac ischemic and reperfusion injury. They contribute to myocardial stunning, infarction and apoptosis, and possibly to the genesis of arrhythmias. Multiple laboratory studies and clinical trials have evaluated the use of scavengers of ROS to protect the heart from the effects of ischemia and reperfusion. Generally, studies in animal models have shown such effects. Clinical trials have also shown protective effects of scavengers, but whether this protection confers meaningful clinical benefits is uncertain. Several IV anesthetic drugs act as ROS scavengers. In contrast, volatile anesthetics have recently been demonstrated to generate ROS in the heart, most likely because of inhibitory effects on cardiac mitochondria. ROS are involved in the signaling cascade for cardioprotection induced by brief exposure to a volatile anesthetic (termed "anesthetic preconditioning"). ROS, therefore, although injurious in large quantities, can have a paradoxical protective effect within the heart. In this review we provide background information on ROS formation and elimination relevant to anesthetic and adjuvant drugs with particular reference to the heart. The sources of ROS, the means by which they induce cardiac injury or activate protective signaling pathways, the results of clinical studies evaluating ROS scavengers, and the effects of anesthetic drugs on ROS are each discussed.

Cardioprotection by volatile anesthetics

Preconditioning describes a very powerful endogenous mechanism by which the heart may be protected against ischemia and reperfusion injury. Transient administration of a volatile anesthetic before a prolonged ischemic episode reduces myocardial infarct size to a degree comparable to that observed during ischemic preconditioning. Many components of the signal transduction pathways responsible for cardioprotection are shared by anesthetic and ischemic preconditioning. Exposure to volatile anesthetics generates small "triggering" quantities of reactive oxygen species (ROS) by directly interacting with the mitochondrial electron transport chain or indirectly through a signaling cascade in which G-protein-coupled receptors, protein kinases, and mitochondrial ATP-sensitive potassium (K(ATP)) channels play important roles. Several clinical studies also suggest that preconditioning by volatile anesthetics exerts beneficial effects in patients undergoing cardiac surgery. This review summarizes some of the recent major developments in the understanding of cardioprotection by volatile anesthetics.

Cardioprotection with volatile anesthetics: mechanisms and clinical implications

Cardiac surgery and some noncardiac procedures are associated with a significant risk of perioperative cardiac morbid events. Experimental data indicate that clinical concentrations of volatile general anesthetics protect the myocardium from ischemia and reperfusion injury, as shown by decreased infarct size and a more rapid recovery of contractile function on reperfusion. These anesthetics may also mediate protective effects in other organs, such as the brain and kidney. Recently, a number of reports have indicated that these experimentally observed protective effects may also have clinical implications in cardiac surgery. However, the impact of the use of volatile anesthetics on outcome measures, such as postoperative mortality and recovery in cardiac and noncardiac surgery, is yet to be determined.

Integrated pharmacological preconditioning and memory of cardioprotection: role of protein kinase C and phosphatidylinositol 3-kinase

Although protein kinase C (PKC) and phosphatidylinositol 3 (PI3)-kinase are implicated in cardioprotective signal transduction mediated by ischemic preconditioning, their role in pharmacological preconditioning (PPC) has not been determined. Cultured neonatal rat cardiomyocytes (CMCs) were subjected to simulated ischemia for 2 h followed by 15 min of reoxygenation. PPC of CMCs consisted of administration of 50 microM adenosine, 50 microM diazoxide, and 50 microM S-nitroso-N-acetylpenicillamine (SNAP), each alone or in combination, for 15 min followed by 30 min of washout before simulated ischemia. Although PKC-epsilon and PI3-kinase were significantly activated during treatment with adenosine, activation of these kinases dissipated after washout. In contrast, PPC combined with adenosine, diazoxide, and SNAP elicited sustained activation of PKC-epsilon and PI-3 kinase after washout. The combined-PPC, but not the single-PPC, protocol conferred antiapoptotic and antinecrotic effects after reoxygenation. The PKC inhibitor chelerythrine (5 microM) or the PI3-kinase inhibitor LY-294002 (10 microM) given during the washout period partially blocked the activation of PKC-epsilon and PI3-kinase mediated by the combined-PPC protocol, whereas combined addition of chelerythrine and LY-294002 completely inhibited activation of PKC-epsilon and PI3-kinase. Chelerythrine or LY-294002 partially blocked antiapoptotic and antinecrotic effects mediated by the combined-PPC protocol, whereas combined addition of chelerythrine and LY-294002 completely abrogated antiapoptotic and antinecrotic effects. These results suggest that the combined-PPC protocol confers cardioprotective memory through sustained and interdependent activation of PKC and PI3-kinase.

Cardioprotective anesthesia in patients undergoing coronary surgery: fact or fiction?

The use of volatile anesthetics in patients undergoing coronary artery bypass grafting resulted in a shorter length of stay (LOS) in the intensive care unit, shorter LOS in the hospital, and a decreased need for prolonged intensive care. Volatile anesthetics exert cardioprotective effects by anesthetic preconditioning in patients at risk of myocardial ischemia. Sarcolemmal and mitochondrial ATP-dependent potassium channels are the key for anesthetic preconditioning. However, no clinical study has shown that the perioperative use of volatile anesthetics in patients undergoing coronary surgery contributes to a reduced perioperative mortality. For the first time, the study from De Hert and colleagues clearly demonstrates that inhalational anesthesia results in a reduced perioperative cardiac morbidity. In the authors opinion, cardioprotection by activation of ATP-dependent potassium channels will become part of any cardiac revascularization procedure in the future.

Anesthetic preconditioning: the role of free radicals in sevoflurane-induced attenuation of mitochondrial electron transport in Guinea pig isolated hearts

Cardioprotection by anesthetic preconditioning (APC) can be abolished by nitric oxide (NO*) synthase inhibitors or by reactive oxygen species (ROS) scavengers. We previously reported attenuated mitochondrial electron transport (ET) and increased ROS generation during preconditioning sevoflurane exposure as part of the triggering mechanism of APC. We hypothesized that NO* and other ROS mediate anesthetic-induced ET attenuation. Cardiac function and reduced nicotinamide adenine dinucleotide (NADH) fluorescence, an index of mitochondrial ET, were measured online in 68 Langendorff-prepared guinea pig hearts. Hearts underwent 30 min of global ischemia and 120 min of reperfusion. Before ischemia, hearts were temporarily perfused with superoxide dismutase, catalase, and glutathione to scavenge ROS or N(G)-nitro-L-arginine-methyl-ester (L-NAME) to inhibit NO* synthase in the presence or absence of 1.3 mM sevoflurane (APC). APC temporarily increased NADH before ischemia, i.e., it attenuated mitochondrial ET. Both this NADH increase and the cardioprotection by APC on reperfusion were prevented by superoxide dismutase, catalase, and glutathione and by N(G)-nitro-L-arginine-methyl-ester. Thus, ROS and NO*, or reaction products including peroxynitrite, mediate sevoflurane-induced ET attenuation. This may lead to a positive feedback mechanism with augmented ROS generation to trigger APC secondary to altered mitochondrial function.

Age‐associated increases in oxidative stress and antioxidant enzyme activities in cardiac interfibrillar mitochondria: implications for the mitochondrial theory of aging

Mitochondrial dysfunction and the accumulation of oxidative damage to macromolecules are believed to play key roles in the aging process. Characterization of age-related changes to cardiac mitochondria has been complicated by the fact that two distinct populations of mitochondria exist in the myocardium: subsarcolemmal mitochondria (SSM) and interfibrillar mitochondria (IFM). We investigated whether differences in hydrogen peroxide production (H2O2) and oxidative stress existed between cardiac SSM and IFM isolated from young (6 mo) and old (24 mo) male Fischer-344 rats. There was a significant increase in oxidative stress levels (4-hydroxy-2-nonenal-modified proteins, protein carbonyls, and malondialdehyde) in IFM with age. In contrast, only protein carbonyls were elevated in SSM with age. Significant age-related increases in MnSOD, GPX, and CAT activities were detected in IFM, while in SSM, MnSOD, and GPX activities increased with age and CAT activity declined. These increases in antioxidant enzyme activity likely occurred in response to increased mitochondrial production of superoxide and hydrogen peroxide. Indeed, SSM produced more H2O2 with age, while the increase in IFM was not significant, but this may be due to the higher antioxidant enzyme activity observed in IFM compared with SSM. Finally, reduced glutathione levels were significantly lower in IFM compared with SSM in both young and old rats, while glutathione reductase activity was not different with age or mitochondrial subpopulations, indicating increased consumption of glutathione. The accumulation of oxidant-induced damage in IFM may be a major contributing factor to the age-related alterations in myocardial function. Our results emphasize the importance of studying both mitochondrial populations when attempting to elucidate the contribution of mitochondrial dysfunction to myocardial aging.

ATP-dependent potassium channels as a key target for the treatment of myocardial and vascular dysfunction

PURPOSE OF REVIEW

The aim of this review is to highlight the most recent and interesting articles on the physiologic properties and functions of ATP-dependent potassium channels in the cardiovascular system and on the role of the potassium channel openers for the treatment of cardiovascular dysfunction.

RECENT FINDINGS

The initial efforts in the development of potassium channel openers focused on the management of systemic hypertension. Lately, the range of possible indications for potassium channel openers has increased to include pulmonary hypertension and stable angina pectoris. The discovery of a connection between the mitochondrial ATP-dependent potassium channels and the phenomenon of cardiac preconditioning created potential new uses for potassium channel openers in myocardial ischemia, inn unstable angina, in preoperative and perioperative settings, and for the preservation of organs for transplant.

SUMMARY

The most recent data on the physiologic roles of sarcolemmal and mitochondrial ATP-dependent potassium channels and the pharmacology of potassium channel openers in the cardiovascular system are summarized and discussed. Finally, the effects of potassium channel opener drugs including minoxidil, nicorandil, pinacidil, bimakalin, and levosimendan, a dual-action potassium channel opener and calcium sensitizer with inodilator and cardioprotective activity, are discussed.