Delayed cardioprotection by isoflurane: role of K(ATP) channels

Risk assessment of occupational exposure to anesthesia Isoflurane in the hospital and veterinary settings

Despite the modern ventilation and waste anesthetic gas (WAG) scavenging systems, occupational exposure to common volatile anesthesia, isoflurane, can occur in the hospital and veterinary settings, but limited information exists on potential exposure and health risk of isoflurane. We assessed exposure dose rates and risks among clinicians and veterinary professionals from occupational exposure to isoflurane. Through a critical review of open literature (1965 to 2020), we summarized potential adverse effects and exposure scenarios of isoflurane among the professional groups, including anesthetists, nurses, operating room personnel, researchers, and/or veterinarians. Deterministic United States National Research Council/Environmental Protection Agency's risk assessment framework (hazard identification, dose-response relationship, exposure assessment and risk characterization) was used to compute inhalation Reference Doses (RfDs), Average Daily Doses (ADDs), and Hazard Quotient (HQ) values-an established measure of non-carcinogenic (systemic) risks-from exposure to isoflurane to workers in hospital and veterinary settings. We identified the central nervous system as the main target for isoflurane, and that isoflurane has dose-dependent effects on cardiac hemodynamics, can impair pulmonary functions and potentially cross the utero-placental barrier leading to congenital malformation in fetus. Based on the modelled RfDs (range 0.8003-7.55 mg/kg-day) and ADDs (range 0.071-1.9617 mg/kg-day), we estimated 56 different HQ values, of which 5 HQs were higher than 1 (range 1.099-2.4512) under high exposure scenarios. Our results suggest a significant non-carcinogenic risk from isoflurane exposures among workers in the occupational settings. The findings underscore the need to significantly minimize isoflurane release to protect workers' health in the hospital and veterinary environments.

MiR-21-5p but not miR-1-3p expression is modulated by preconditioning in a rat model of myocardial infarction

Isoflurane (Iso) preconditioning (PC) is known to be cardioprotective against ischemia/reperfusion (I/R) injury. It was previously shown that microRNA-21-5p (miR-21-5p) is regulated by Iso-PC. It is unclear, if expression of cardiac enriched miR-1-3p is also affected by Iso-PC, and associated with activation of HIF1α (hypoxia-inducible factor 1-alpha).  Male Wistar rats (n = 6–8) were randomly assigned to treatment with or without 1 MAC Iso for 30 min, followed by 25 min of regional myocardial ischemia, with 120 min reperfusion. At the end of reperfusion, myocardial expression of miR-1-3p, miR-21-5p and mRNAs of two HIF-1α-dependent genes, VEGF (vascular endothelial growth factor) and HO-1 (heme oxygenase-1), were determined by quantitative PCR. Protein expression of a miR-21 target gene, PDCD4 (programmed cell death protein 4), was assessed by western blot analysis. Infarct sizes were analyzed with triphenyltetrazoliumchloride staining. MiR-21-5p expression was increased by Iso, whereas expression of miR-1-3p was not altered. The expression of VEGF but not HO-1 was induced by Iso. Iso-PC reduced infarct sizes compared to untreated controls. No regulation of miRNA and mRNA expression was detected after I/R. PDCD4 protein expression was not affected after Iso exposure. Expression of miR-21-5p, in contrast to miR-1-3p, is altered during this early time point of Iso-PC. HIF1α signaling seems to be involved in miR-21-5p regulation.

Sevoflurane Preconditioning Confers Delayed Cardioprotection by Upregulating AMP-Activated Protein Kinase Levels to Restore Autophagic Flux in Ischemia-Reperfusion Rat Hearts

Background

Volatile anesthetic preconditioning confers delayed cardioprotection against ischemia/reperfusion injury (I/R). AMP-activated protein kinase (AMPK) takes part in autophagy activation. Furthermore, autophagic flux is thought to be impaired after I/R. We hypothesized that delayed cardioprotection can restore autophagic flux by activating AMPK.

Material/Methods

All male rat hearts underwent 30-min ischemia and 120-min reperfusion with or without sevoflurane exposure. AMPK inhibitor compound C (250 μg/kg, iv) was given at the reperfusion period. Autophagic flux blocker chloroquine (10 mg/kg, ip) was administrated 1 h before the experiment. Myocardial infarction, nicotinamide adenine dinucleotide (NAD⁺) content, and cytochrome c were measured. To evaluate autophagic flux, the markers of microtubule-associated protein 1 light chain 3 (LC3) I and II, P62 and Beclin 1, and lysosome-associated membrane protein-2 (LAMP 2) were analyzed.

Results

The delayed cardioprotection enhanced post-ischemic AMPK activation, reduced infarction, CK-MB level, NAD⁺ content loss and cytochrome c release, and compound C blocked these effects. Sevoflurane restored impaired autophagic flux through a lower ratio of LC3II/LC3I, downregulation of P62 and Beclin 1, and higher expression in LAMP 2. Consistently, compound C inhibited these changes of autophagy flux. Moreover, chloroquine pretreatment abolished sevoflurane-induced infarct size reduction, CK-MB level, NAD⁺ content loss, and cytochrome c release, with concomitant increase the ratios of LC3II/LC3I and levels of P62 and Beclin 1, but p-AMPK expression was not downregulated by chloroquine.

Conclusions

Sevoflurane exerts a delayed cardioprotective effects against myocardial injury in rats by activation of AMPK and restoration of I/R-impaired autophagic flux.

Cardioprotection with halogenated gases: how does it occur?

Numerous studies have studied the effect of halogenated agents on the myocardium, highlighting the beneficial cardiac effect of the pharmacological mechanism (preconditioning and postconditioning) when employed before and after ischemia in patients with ischemic heart disease. Anesthetic preconditioning is related to the dose-dependent signal, while the degree of protection is related to the concentration of the administered drug and the duration of the administration itself. Triggers for postconditioning and preconditioning might have numerous pathways in common; mitochondrial protection and a decrease in inflammatory mediators could be the major biochemical elements. Several pathways have been identified, including attenuation of NFκB activation and reduced expression of TNFα, IL-1, intracellular adhesion molecules, eNOS, the hypercontraction reduction that follows reperfusion, and antiapoptotic activating kinases (Akt, ERK1/2). It appears that the preconditioning and postconditioning triggers have numerous similar paths. The key biochemical elements are protection of the mitochondria and reduction in inflammatory mediators, both of which are developed in various ways. We have studied this issue, and have published several articles on cardioprotection with halogenated gases. Our results confirm greater cardioprotection through myocardial preconditioning in patients anesthetized with sevoflurane compared with propofol, with decreasing levels of troponin and N-terminal brain natriuretic peptide prohormone. The difference between our studies and previous studies lies in the use of sedation with sevoflurane in the postoperative period. The results could be related to a prolonged effect, in addition to preconditioning and postconditioning, which could enhance the cardioprotective effect of sevoflurane in the postoperative period. With this review, we aim to clarify the importance of various mechanisms involved in preconditioning and postconditioning with halogenated gases, as supported by our studies.

Coronary Sinus Isoflurane Concentration in Cardiac Surgery

OBJECTIVE

Volatile anesthetic agents such as isoflurane may be associated with fewer adverse myocardial events compared with total intravenous anesthesia in cardiac surgery. The authors aimed to determine whether reasonable isoflurane concentrations at tissue level were being achieved to protect the myocardium using this agent. The isoflurane concentration in myocardium has never been measured. The primary aim was to sample coronary sinus (CS) blood and measure its isoflurane concentration. Secondary aims were to determine whether the CS blood concentration would equilibrate with the arterial blood concentration and the relationship of CS blood concentration with oxygenator exhaust isoflurane concentrations during cardiopulmonary bypass (CPB).

DESIGN

Prospective, observational study.

SETTING

Single-center university hospital.

PARTICIPANTS

The study comprised 23 patients undergoing cardiac surgery using CPB and isoflurane.

MEASUREMENTS AND MAIN RESULTS

Shortly after initiation of CPB and insertion of a CS retrograde cardioplegia catheter but before aortic cross-clamping, CS blood was aspirated, followed by radial artery blood, which then were analyzed for isoflurane with gas chromatography and mass spectrometry. The oxygenator exhaust isoflurane level was measured with an anesthetic gas analyzer. The mean arterial and CS isoflurane concentrations were 87.7 ± 50.1 and 73.0 ± 42.9 μg/mL, respectively. There was a significant mean difference of 14.7 μg/mL (95% confidence interval 6.7-22.8) between CS and arterial isoflurane concentrations. Oxygenator exhaust isoflurane levels were correlated positively with those in the CS blood (r = 0.68, p < 0.001) and arterial blood (r = 0.72, p < 0.001).

CONCLUSIONS

This was the first study in which CS blood was sampled and measured for isoflurane concentration. The CS isoflurane concentration could be estimated from the isoflurane concentration in the oxygenator exhaust gas. However, the value of this relationship is limited because the CS isoflurane concentration does not accurately represent its myocardial levels during CPB.

Caveolin-1/-3: therapeutic targets for myocardial ischemia/reperfusion injury

Myocardial ischemia/reperfusion (I/R) injury is a major cause of morbidity and mortality worldwide. Caveolae, caveolin-1 (Cav-1), and caveolin-3 (Cav-3) are essential for the protective effects of conditioning against myocardial I/R injury. Caveolins are membrane-bound scaffolding proteins that compartmentalize and modulate signal transduction. In this review, we introduce caveolae and caveolins and briefly describe the interactions of caveolins in the cardiovascular diseases. We also review the roles of Cav-1/-3 in protection against myocardial ischemia and I/R injury, and in conditioning. Finally, we suggest several potential research avenues that may be of interest to clinicians and basic scientists. The information included, herein, is potentially useful for the design of future studies and should advance the investigation of caveolins as therapeutic targets.

KATP Channels in the Cardiovascular System

KATP channels are integral to the functions of many cells and tissues. The use of electrophysiological methods has allowed for a detailed characterization of KATP channels in terms of their biophysical properties, nucleotide sensitivities, and modification by pharmacological compounds. However, even though they were first described almost 25 years ago (Noma 1983, Trube and Hescheler 1984), the physiological and pathophysiological roles of these channels, and their regulation by complex biological systems, are only now emerging for many tissues. Even in tissues where their roles have been best defined, there are still many unanswered questions. This review aims to summarize the properties, molecular composition, and pharmacology of KATP channels in various cardiovascular components (atria, specialized conduction system, ventricles, smooth muscle, endothelium, and mitochondria). We will summarize the lessons learned from available genetic mouse models and address the known roles of KATP channels in cardiovascular pathologies and how genetic variation in KATP channel genes contribute to human disease.

The second window of desflurane-induced preconditioning is mediated by STAT3: role of Pim-1 kinase

BACKGROUND

Late ischemic preconditioning is mediated via nuclear transcription factor signal transducer and activator of transcription 3 (STAT3). Pim-1 kinase reduces infarct size in cardiomyocytes and is regulated by STAT3. We tested the hypothesis that late desflurane-induced preconditioning (DES-SWOP) is mediated via STAT3 and Pim-1.

METHODS

After institutional approval, pentobarbital-anesthetized male C57BL/6 mice were subjected to 45 min coronary artery occlusion (CAO) and 3 h reperfusion. Control animals received no additional intervention. Desflurane was administered 48 h before CAO either alone or in combination with the janus kinase/STAT3 inhibitor AG-490 (40 μg/g i.p., 20 min before desflurane administration) or the Pim-1 kinase inhibitor II (PIM-Inh.II, 10 μg/g i.p., 15 min before CAO). Infarct size (IS) and area at risk were determined with triphenyltetrazolium chloride and Evans blue, respectively. Additionally, cytosolic and nuclear fractions were separated at two different time points and expression of STAT3, phospho-STAT3(Ser727) , phospho-STAT3(Tyr705) , Pim-1, Bad and phospho-Bad(Ser112) were determined by Western Blot analysis. Data were analyzed with one-way or two-way ANOVA and post hoc Duncan test and are presented as mean ± SEM.

RESULTS

IS was 47 ± 2% (n = 7-8 per group) in control animals (CON). DES-SWOP reduced myocardial infarct size to 23 ± 4%* (*P < 0.05 vs. CON). AG-490 alone did not affect myocardial infarct size (44 ± 7%), but abolished DES-SWOP (44 ± 4%). Blockade of Pim-1 did not affect the protection by DES-SWOP (34 ± 4%*). Desflurane reduced cytosolic content and enhanced nuclear content of phospho-STAT(S) (er727) . After 48 h, desflurane enhanced Pim-1 activity, whereas Pim-1 expression remained unchanged.

CONCLUSION

These data suggest that DES-SWOP is mediated by activation and nuclear translocation of STAT3. The impact of Pim-1 in DES-SWOP signaling remains unclear.

Remote Limb Ischemic Preconditioning: A Neuroprotective Technique in Rodents

Sublethal ischemia protects tissues against subsequent, more severe ischemia through the upregulation of endogenous mechanisms in the affected tissue. Sublethal ischemia has also been shown to upregulate protective mechanisms in remote tissues. A brief period of ischemia (5-10 min) in the hind limb of mammals induces self-protective responses in the brain, lung, heart and retina. The effect is known as remote ischemic preconditioning (RIP). It is a therapeutically promising way of protecting vital organs, and is already under clinical trials for heart and brain injuries. This publication demonstrates a controlled, minimally invasive method of making a limb - specifically the hind limb of a rat - ischemic. A blood pressure cuff developed for use in human neonates is connected to a manual sphygmomanometer and used to apply 160 mmHg pressure around the upper part of the hind limb. A probe designed to detect skin temperature is used to verify the ischemia, by recording the drop in skin temperature caused by pressure-induced occlusion of the leg arteries, and the rise in temperature which follows release of the cuff. This method of RIP affords protection to the rat retina against bright light-induced damage and degeneration.

Isoflurane protects the myocardium against ischemic injury via the preservation of mitochondrial respiration and its supramolecular organization

BACKGROUND

Isoflurane has been demonstrated to limit myocardial ischemic injury. This effect is hypothesized to be mediated in part via effects on mitochondria. We investigated the hypothesis that isoflurane maintains mitochondrial respiratory chain functionality, in turn limiting mitochondrial damage and mitochondrial membrane disintegration during myocardial ischemic injury.

METHODS

Mice (9-12 weeks of age) received isoflurane (1.0 minimum alveolar concentration) 36 hours before a 30-minute coronary artery occlusion that was followed by 24 hours of reperfusion. Cardiac mitochondria were isolated at a time point corresponding to 4 hours of reperfusion. 2,3,5-Triphenyltetrazoliumchloride staining was used to determine myocardial infarct size. Mitochondrial respiratory chain functionality was investigated using blue native polyacrylamide gel electrophoresis, as well as specific biochemical assays. Mitochondrial lipid peroxidation was quantified via the formation of malondialdehyde; mitochondrial membrane integrity was assessed by Ca-induced swelling. Protein identification was achieved via liquid chromatography mass spectrometry/mass spectrometry.

RESULTS

Thirty-one mice were studied. Mice receiving isoflurane displayed a reduced myocardial infarct size (P = 0.0011 versus ischemia/reperfusion [I/R]), accompanied by a preserved activity of respiratory complex III (P = 0.0008 versus I/R). Isoflurane stabilized mitochondrial supercomplexes consisting of oligomers from complex III/IV (P = 0.0086 versus I/R). Alleviation of mitochondrial damage after isoflurane treatment was further demonstrated as decreased malondialdehyde formation (P = 0.0019 versus I/R) as well as a diminished susceptibility to Ca-induced swelling (P = 0.0010 versus I/R).

CONCLUSIONS

Our findings support the hypothesis that isoflurane protects the heart from ischemic injury by maintaining the in vivo functionality of the mitochondrial respiratory chain. These effects may result in part from the preservation of mitochondrial supramolecular organization and minimized oxidative damage, circumventing the loss of mitochondrial membrane integrity.

Anaesthetics as cardioprotectants: translatability and mechanism

The pharmacological conditioning of the heart with anaesthetics, such as volatile anaesthetics or opioids, is a phenomenon whereby a transient exposure to an anaesthetic agent protects the heart from the harmful consequences of myocardial ischaemia and reperfusion injury. The cellular and molecular mechanisms of anaesthetic conditioning appear largely to mimic those of ischaemic pre- and post-conditioning. Progress has been made on the understanding of the underlying mechanisms although the order of events and the specific targets of anaesthetics that trigger protection are not always clear. In the laboratory, the protection afforded by certain anaesthetics against cardiac ischaemia and reperfusion injury is powerful and reproducible but this has not necessarily translated into similarly robust clinical benefits. Indeed, clinical studies and meta-analyses delivered variable results when comparing in the laboratory setting protective and non-protective anaesthetics. Reasons for this include underlying conditions such as age, obesity and diabetes. Animal models for disease or ageing, human cardiomyocytes derived from stem cells of patients and further clinical studies are employed to better understand the underlying causes that prevent a more robust protection in patients.

Anaesthetics as cardioprotectants: translatability and mechanism

The pharmacological conditioning of the heart with anaesthetics, such as volatile anaesthetics or opioids, is a phenomenon whereby a transient exposure to an anaesthetic agent protects the heart from the harmful consequences of myocardial ischaemia and reperfusion injury. The cellular and molecular mechanisms of anaesthetic conditioning appear largely to mimic those of ischaemic pre- and post-conditioning. Progress has been made on the understanding of the underlying mechanisms although the order of events and the specific targets of anaesthetics that trigger protection are not always clear. In the laboratory, the protection afforded by certain anaesthetics against cardiac ischaemia and reperfusion injury is powerful and reproducible but this has not necessarily translated into similarly robust clinical benefits. Indeed, clinical studies and meta-analyses delivered variable results when comparing in the laboratory setting protective and non-protective anaesthetics. Reasons for this include underlying conditions such as age, obesity and diabetes. Animal models for disease or ageing, human cardiomyocytes derived from stem cells of patients and further clinical studies are employed to better understand the underlying causes that prevent a more robust protection in patients.

Ventricular hypertrophy blocked delayed anesthetic cardioprotection in rats by alteration of iNOS/COX-2 signaling

The aim of the current study was to determine whether ventricular hypertrophy affects the delayed isoflurane preconditioning against myocardial ischemia-reperfusion (IR) injury. Transverse aortic constriction (TAC) was performed on male Sprague-Dawley rats to induce left ventricular (LV) hypertrophy, then sham-operated or hypertrophied rat hearts were subjected to isoflurane preconditioning (2.1% v/v, 1 h). 24 h after exposure, the hearts were isolated and perfused retrogradely by the Langendorff for 30 min (equilibration) followed by 40 min of ischemia and then 120 min of reperfusion. The hemodynamics, infarct size, apoptosis, nitric oxide synthase (NOS), cyclooxygenase-2 (COX-2), Cleaved Caspase-3 and production of NO were determined. We found that the hemodynamic parameters were all markedly improved during the reperfusion period and the myocardial infarct size and apoptosis was significantly reduced by delayed isoflurane preconditioning in sham-operated rats. However, such cardiac improvement induced by delayed isoflurane preconditioning was not observed in hypertrophied hearts. The expression of iNOS, COX-2 and NO was markedly enhanced, whereas Cleaved Caspase-3 activity was inhibited by delayed isoflurane preconditioning in sham-operated rats, a phenomenon was not found in TAC-control groups pretreated with isoflurane. Our results demonstrated that ventricular hypertrophy abrogated isoflurane-induced delayed cardioprotection by alteration of iNOS/COX-2 pathway.

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.

The changes of technetium-99m-labeled annexin-V in delayed anesthetic preconditioning during myocardial ischemia/reperfusion

This study was designed to use real-time imaging to test the hypothesis that delayed cardiac protection induced by volatile anesthetics inhibits apoptosis. Rats were divided into two groups. One group was exposed to 120 min of 33 % O2 [control group (CON group)] and the other group was exposed to 2.5 % sevoflurane in 33 % O2 for 120 min [sevoflurane group (SEVO group)]. Both groups were allowed to return to their cages for 24 h. After 24 h recovery, all rats underwent 30 min myocardial ischemia by occluding coronary artery followed by 2 h of reperfusion. After reperfusion, technetium-99m-labeled annexin-V was administered intravenously to identify apoptosis. Left ventricular samples were obtained to measure infarct size and radionuclide imaging and caspase-3. Radionuclide imaging indicated that apoptosis was reduced in SEVO group (0.78 % ± 0.82) when compared with the CON group (1.15 % ± 0.61), and the infarct size was also decreased in the SEVO group (40 % ± 7). The transferase dUTP nick end labeling (TUNEL)-positive cardiomyocytes in the SEVO group (16 % ± 6) were significantly decreased in the peri-infarct zone when compared with the CON group (28 % ± 4). After reperfusion, caspase-3 expression was significantly blunted in the SEVO group than in CON group (50 % ± 11 vs. 68 % ± 10, p < 0.05). This study used technetium-99m-labeled annexin-V of real-time imaging to detect cardiomyocyte apoptosis and the results were confirmed by the TUNEL assay and caspase-3 expression. We concluded that delayed volatile anesthetic preconditioning (APC) protects against I/R in vivo. The method of technetium-99m-labeled annexin-V of real-time imaging can be used to detect cardiomyocyte apoptosis in delayed APC during ischemia/reperfusion.

Hypotension due to Kir6.1 gain-of-function in vascular smooth muscle

Background

K_ATP channels, assembled from pore‐forming (Kir6.1 or Kir6.2) and regulatory (SUR1 or SUR2) subunits, link metabolism to excitability. Loss of Kir6.2 results in hypoglycemia and hyperinsulinemia, whereas loss of Kir6.1 causes Prinzmetal angina–like symptoms in mice. Conversely, overactivity of Kir6.2 induces neonatal diabetes in mice and humans, but consequences of Kir6.1 overactivity are unknown.

Methods and Results

We generated transgenic mice expressing wild‐type (WT), ATP‐insensitive Kir6.1 [Gly343Asp] (GD), and ATP‐insensitive Kir6.1 [Gly343Asp,Gln53Arg] (GD‐QR) subunits, under Cre‐recombinase control. Expression was induced in smooth muscle cells by crossing with smooth muscle myosin heavy chain promoter–driven tamoxifen‐inducible Cre‐recombinase (SMMHC‐Cre‐ER) mice. Three weeks after tamoxifen induction, we assessed blood pressure in anesthetized and conscious animals, as well as contractility of mesenteric artery smooth muscle and K_ATP currents in isolated mesenteric artery myocytes. Both systolic and diastolic blood pressures were significantly reduced in GD and GD‐QR mice but normal in mice expressing the WT transgene and elevated in Kir6.1 knockout mice as well as in mice expressing dominant‐negative Kir6.1 [AAA] in smooth muscle. Contractile response of isolated GD‐QR mesenteric arteries was blunted relative to WT controls, but nitroprusside relaxation was unaffected. Basal K_ATP conductance and pinacidil‐activated conductance were elevated in GD but not in WT myocytes.

Conclusions

K_ATP overactivity in vascular muscle can lead directly to reduced vascular contractility and lower blood pressure. We predict that gain of vascular K_ATP function in humans would lead to a chronic vasodilatory phenotype, as indeed has recently been demonstrated in Cantu syndrome.

Microarray analyses of genes regulated by isoflurane anesthesia in vivo: a novel approach to identifying potential preconditioning mechanisms

BACKGROUND

Although general anesthetics are recognized for their potential to render patients unconscious during surgery, exposure can also lead to long-term outcomes of both cellular damage and protection. As regards the latter, delayed anesthetic preconditioning is an evolutionarily conserved physiological response that has the potential for protecting against ischemic injury in a number of tissues. Although it is known that delayed preconditioning requires de novo protein synthesis, knowledge of anesthetic-regulated genes is incomplete. In this study, we used the conserved nature of preconditioning to analyze differentially regulated genes in 3 different rat tissues. We hypothesized that by selecting those genes regulated in multiple tissues, we could develop a focused list of gene candidates potentially involved in delayed anesthetic preconditioning.

METHODS

Young adult male Sprague-Dawley rats were anesthetized with a 2% isoflurane/98% air mixture for 90 minutes. Immediately after anesthetic exposure, animals were euthanized and liver, kidney, and heart were removed and total RNA was isolated. Differential gene expression was determined using rat oligonucleotide gene arrays. Array data were analyzed to select for genes that were significantly regulated in multiple tissues.

RESULTS

All 3 tissues showed differentially regulated genes in response to a clinically relevant exposure to isoflurane. Analysis of coordinately regulated genes yielded a focused list of 34 potential gene candidates with a range of ontologies including regulation of inflammation, modulation of apoptosis, regulation of ion gradients, and maintenance of energy pathways.

CONCLUSIONS

Through using an analysis approach focusing on coordinately regulated genes, we were able to generate a focused list of interesting gene candidates with potential to enable future preconditioning studies.

Pretreatment with xenon protected immature rabbit heart from ischaemia/reperfusion injury by opening of the mitoKATP channel

BACKGROUND

The noble gas anaesthetic, xenon has previously been shown to protect the adult myocardium from ischaemia/reperfusion (I/R) injury, however its effect on immature myocardium is unclear. The aim of this study was to investigate the effect of xenon on the isolated immature heart.

METHODS

Isolated, immature (2-3weeks old) New Zealand rabbit hearts were perfused with Krebs-Henseleit buffer via Langendorff-mode. After 20min of baseline equilibration, hearts were pretreated with 75% xenon, 75% xenon+100μM diazoxide, or 75% xenon+100μM 5-hydroxydecanoate, and then subjected to 1h of global ischaemia and 3h of reperfusion.

RESULTS

Pretreatment with 75% xenon significantly improved cardiac function (P<0.01 vs. the I/R group, respectively), limited myocardial infarct size (20.83±2.16%, P<0.01 vs. 35.82±2.14% of the I/R group), reduced cardiac enzyme release (CK-MB, 1.00±0.19IU/L, P<0.01 vs. 0.44±0.14IU/L of the I/R group; LDH, 6.15±1.06IU/L P<0.01 vs. 3.49±0.37IU/L of the I/R group) and decreased apoptosis (6.17±0.56%, P<0.01 vs. 11.31±0.93% of the I/R group). In addition, the mitochondrial structure changes caused by I/R injury were largely prevented by 75% xenon pretreatment (1.37±0.16, P<0.01 vs. 2.32±0.13 of the I/R group). The mitochondrial adenosine triphosphate-sensitive potassium (mitoKATP) channel opener diazoxide did not influence the effect of xenon, but the specific mitoKATP channel blocker 5-hydroxydecanoate completely abolished this effect.

CONCLUSIONS

Our study demonstrated that pretreatment with 75% xenon protected immature heart from I/R injury, and this protection was probably mediated by preservation of myocardial mitochondria and opening of mitoKATP channel.

Age-associated differences in gene expression in response to delayed anesthetic preconditioning

Evidence suggests that the protective benefits of anesthetic preconditioning (APC) are significantly attenuated in the aged myocardium. In this study, we investigated the effect of aging on gene expression in delayed APC. Hearts from Fischer 344 rats, age 4 or 24 months, were divided into five groups: control; ischemia/reperfusion (I/R); and delayed APC at 6, 12, and 24 h. Whole-genome array was studied using Affymetrix Rat Genome 230 2.0 array. Data were analyzed for significant ≥2.0-fold changes in gene expression. Microarray results were confirmed by quantitative real-time reverse transcription-polymerase chain reaction. Of the 28,000 genes represented on the Affymetrix Rat Genome 230 2.0 Microarray chip, 24 transcripts in 6 h APC, 28 in 12 h APC, and 28 in 24 h APC group displayed significant up-regulation in mRNA levels, and 70 transcripts in 6 h APC, 101 in 12 h APC, and 82 in 24 h APC displayed significant down-regulation in young rat hearts. These altered genes fall into functional categories of cell defense/death, cell structure, gene expression/protein synthesis, inflammatory response/growth/remodeling, and signaling/communication. Although alterations for some genes were in common, the numbers of changed genes in old rats were markedly and consistently lower than the young rats. Twenty-four hour delayed APC also significantly reduced infarct size and improved myocardial left ventricular function in young hearts, effects that were not observed in old rat hearts. We concluded that delayed APC profoundly and differentially affected gene expression profiles of the cardiomyocyte in an age-associated pattern. The impaired genomic response to delayed APC could underlie the loss of the protective benefits of preconditioning in aged hearts.

Effect of HEMADO on Level of CK-MB and LDH Enzymes after Ischemia/Reperfusion Injury in Isolated Rat Heart

INTRODUCTION

Ischemia/Reperfusion (IR) injury mainly causes the increase of enzymes involved in myocytes injury including CK-MB (creatine kinase-MB) isoenzyme and LDH (lactate dehydrogenase). Leakage of CK-MB isoenzyme and LDH from myocardial tissues to blood is indicator of acute myocardial infarction. The aim of this study was to assess the effect of HEMADO on IR injury and its relationship with mitochondrial ATP-sensitive K+ channels (mitoKATP) in rat heart.

METHODS

Twenty eight male Wistar rats (250-300g) were divided into four groups (seven members in each group): control (without ischemia), I/R (with ischemia+without HEMADO), ischemia received HEMADO (HEMADO), ischemia received HEMADO and 5-HD (5-hydroxydecanoate, specific mitoKATP channel blocker) (HEMADO+5-HD). The animals were anesthetized and the hearts were quickly removed and mounted on Langendorff apparatus and perfused by Krebs-Henseleit solution under constant pressure and temperature of 37ºC. After 20 minutes of stabilization, ischemic groups were exposed to 40 minutes of global ischemia and consecutive 90 minutes of reperfusion.

RESULTS

IR injury increased the level of LDH and CK-MB in the collected coronary flow during 5 minutes since start of reperfusion. HEMADO reduced the enzymes' levels and using 5-HD abolished the effect of HEMADO.

CONCLUSION

Our findings indicated that HEMADO could protect the heart against ischemia-reperfusion injury by decreasing the CK-MB and LDH levels. The cardioprotective effect of HEMADO may be mediated in part by mitoKATP.

Nitric oxide has no obligatory role in isoflurane late preconditioning against myocardial stunning

AIMS

Isoflurane has been demonstrated to produce late preconditioning against myocardial stunning. We tested the hypothesis that this effect is dependent upon an increased production of nitric oxide.

MAIN METHODS

Studies were performed in 18 conscious dogs, chronically instrumented to measure coronary blood flow and myocardial wall thickening (WT). In Group 1 (control; n=7), a 10-min coronary occlusion was produced followed by reperfusion; WT was monitored until full recovery. In Group 2 (n=6), the same occlusion-reperfusion protocol was performed 24h after inhalation of 1 MAC isoflurane (1.4% in O(2)) for 60 min. In Group 3 (n=5), the late anti-stunning effect of isoflurane was evaluated following non-selective inhibition of NOS with N-nitro-l-arginine (l-NA, 30 mg/kg on 3 days beginning 1 day prior to isoflurane). Expression of eNOS and iNOS protein was measured by Western blotting.

KEY FINDINGS

Two to 3h of reperfusion was required for recovery of WT following isoflurane (Group 2). In contrast, without isoflurane (Group 1), WT remained markedly reduced (30% below baseline) at this time point and required more than 6h of reperfusion for recovery. Treatment with l-NA (Group 3) did not alter time-course of recovery of WT following isoflurane. Isoflurane caused an increased expression of eNOS, but not of iNOS.

SIGNIFICANCE

Isoflurane produced late preconditioning against myocardial stunning. Although this effect was associated with an up-regulation of eNOS, its persistence following l-NA suggested that an increased production of nitric oxide did not play an obligatory role.

Caveolins: targeting pro-survival signaling in the heart and brain

The present review discusses intracellular signaling moieties specific to membrane lipid rafts (MLRs) and the scaffolding proteins caveolin and introduces current data promoting their potential role in the treatment of pathologies of the heart and brain. MLRs are discreet microdomains of the plasma membrane enriched in gylcosphingolipids and cholesterol that concentrate and localize signaling molecules. Caveolin proteins are necessary for the formation of MLRs, and are responsible for coordinating signaling events by scaffolding and enriching numerous signaling moieties in close proximity. Specifically in the heart and brain, caveolins are necessary for the cytoprotective phenomenon termed ischemic and anesthetic preconditioning. Targeted overexpression of caveolin in the heart and brain leads to induction of multiple pro-survival and pro-growth signaling pathways; thus, caveolins represent a potential novel therapeutic target for cardiac and neurological pathologies.

The role of Volatile Anesthetics in Cardioprotection: a systematic review

This review evaluates the mechanism of volatile anesthetics as cardioprotective agents in both clinical and laboratory research and furthermore assesses possible cardiac side effects upon usage. Cardiac as well as non-cardiac surgery may evoke perioperative adverse events including: ischemia, diverse arrhythmias and reperfusion injury. As volatile anesthetics have cardiovascular effects that can lead to hypotension, clinicians may choose to administer alternative anesthetics to patients with coronary artery disease, particularly if the patient has severe preoperative ischemia or cardiovascular instability. Increasing preclinical evidence demonstrated that administration of inhaled anesthetics - before and during surgery - reduces the degree of ischemia and reperfusion injury to the heart. Recently, this preclinical data has been implemented clinically, and beneficial effects have been found in some studies of patients undergoing coronary artery bypass graft surgery. Administration of volatile anesthetic gases was protective for patients undergoing cardiac surgery through manipulation of the potassium ATP (K_ATP) channel, mitochondrial permeability transition pore (mPTP), reactive oxygen species (ROS) production, as well as through cytoprotective Akt and extracellular-signal kinases (ERK) pathways. However, as not all studies have demonstrated improved outcomes, the risks for undesirable hemodynamic effects must be weighed against the possible benefits of using volatile anesthetics as a means to provide cardiac protection in patients with coronary artery disease who are undergoing surgery.

A murine closed-chest model of myocardial ischemia and reperfusion

Surgical trauma by thoracotomy in open-chest models of coronary ligation induces an immune response which modifies different mechanisms involved in ischemia and reperfusion. Immune response includes cytokine expression and release or secretion of endogenous ligands of innate immune receptors. Activation of innate immunity can potentially modulate infarct size. We have modified an existing murine closed-chest model using hanging weights which could be useful for studying myocardial pre- and postconditioning and the role of innate immunity in myocardial ischemia and reperfusion. This model allows animals to recover from surgical trauma before onset of myocardial ischemia. Volatile anesthetics have been intensely studied and their preconditioning effect for the ischemic heart is well known. However, this protective effect precludes its use in open chest models of coronary artery ligation. Thus, another advantage could be the use of the well controllable volatile anesthetics for instrumentation in a chronic closed-chest model, since their preconditioning effect lasts up to 72 hours. Chronic heart diseases with intermittent ischemia and multiple hit models are other possible applications of this model. For the chronic closed-chest model, intubated and ventilated mice undergo a lateral blunt thoracotomy via the 4th intercostal space. Following identification of the left anterior descending a ligature is passed underneath the vessel and both suture ends are threaded through an occluder. Then, both suture ends are passed through the chest wall, knotted to form a loop and left in the subcutaneous tissue. After chest closure and recovery for 5 days, mice are anesthetized again, chest skin is reopened and hanging weights are hooked up to the loop under ECG control. At the end of the ischemia/reperfusion protocol, hearts can be stained with TTC for infarct size assessment or undergo perfusion fixation to allow morphometric studies in addition to histology and immunohistochemistry.

Endothelial nitric oxide synthase mediates the first and inducible nitric oxide synthase mediates the second window of desflurane-induced preconditioning

OBJECTIVES

Nitric oxide synthases (NOSs) mediate the first window of anesthetic-induced preconditioning (APC). The authors tested the hypothesis that endothelial NOS (eNOS) mediates the first window and inducible NOS (iNOS) mediates the second window of APC.

DESIGN

Randomized, prospective, blinded laboratory investigation.

SETTING

Experimental laboratory.

PARTICIPANTS

Mice.

INTERVENTIONS

Mice were subjected to a 45-minute coronary artery occlusion (CAO) and a 180-minute reperfusion. C57BL/6 mice received desflurane, 1.0 minimum alveolar concentration, for 30 minutes or 12, 24, 48, or 96 hours before CAO. In eNOS(-/-) and iNOS(-/-) mice, desflurane was given 30 minutes and 48 hours before CAO. In the control groups, no desflurane was administered. Myocardial infarct size (IS) was determined after staining with Evans blue and triphenyltetrazolium chloride.

MEASUREMENTS AND MAIN RESULTS

The second window of APC was detectable at 48 hours but not at 12, 24, and 96 hours after preconditioning. In the control groups, IS was not different among the wild-type (50 ± 10%), eNOS(-/-) (52 ± 14%), and iNOS(-/-) (46 ± 10%) mice. The IS decreased significantly (p < 0.05) when desflurane was administered 30 minutes (10 ± 6%) or 48 hours (16 ± 7%) before CAO in wild-type mice, 48 hours (21 ± 13%) before CAO in eNOS(-/-) mice, and 30 minutes (13 ± 6%) before CAO in iNOS(-/-) mice. Desflurane given 30 minutes before CAO in eNOS(-/-) mice (60 ± 10%) and 48 hours before CAO in iNOS(-/-) mice (48 ± 21%) did not decrease the IS significantly compared with controls.

CONCLUSIONS

Endothelial NOS and iNOS work independently to mediate the first and second windows of APC, respectively. Endothelial NOS is not necessary to trigger the second window of APC.

Impaired diastolic function and disruption of the force-frequency relationship in the right ventricle of newborn pigs resuscitated with 100% oxygen

BACKGROUND

Resuscitation with 100% oxygen increases oxidative stress and is detrimental for organ function.

OBJECTIVE

To study the effects of resuscitation with 100% oxygen compared to room-air on myocardial function.

METHODS

Twenty-eight newborn pigs underwent global hypoxia (8% oxygen/N2) until base excess reached -20 mmol/l. The animals were randomized into two groups and resuscitated with either 100% or room air for 30 min. Myocardial tissue Doppler velocities and acceleration of the mitral and tricuspid valve annuli during systole and diastole were assessed before global hypoxia and after resuscitation together with troponin I.

RESULTS

Peak early diastolic velocity (E') and acceleration (pEac) in the septum and pEac in the lateral tricuspid valve annulus were lower after resuscitation with 100% oxygen, suggesting impaired diastolic relaxation in the right ventricle. Lower systolic velocities and acceleration in the right ventricle relative to heart rate indicate disruption of the right ventricular force-frequency relationship after resuscitation with 100% oxygen. Troponins were higher in the 100% oxygen group, suggesting increased myocardial damage in this group.

CONCLUSION

Resuscitation with 100% oxygen compared to room air induces diastolic dysfunction, disrupts the systolic force-frequency relationship and increases myocardial damage in the newborn pig.

Isoflurane late preconditioning against myocardial stunning is associated with enhanced antioxidant defenses

BACKGROUND

We tested the hypothesis that an upregulation of antioxidant proteins [Cu-Zn superoxide dismutase (SOD), Mn SOD, catalase, glutathione peroxidase, and glutathione peroxidase] plays a role in the delayed protection against myocardial stunning produced by isoflurane preconditioning (ISOPC). Findings were compared with late ischemic PC (IPC).

METHODS

Fourteen mongrel dogs were chronically instrumented to measure coronary blood flow and myocardial wall thickening (WT) in conscious state. In Group 1, dogs underwent IPC, induced by a 10-min coronary artery occlusion (CAO); after 24 h of reperfusion, they were subjected to a second 10-min ischemia CAO-reperfusion. In Group 2 (ISOPC), dogs inhaled one minimum alveolar concentration (MAC) ISO (1.4% in O(2)) for 60 min, allowed to recover for 24 h, and then subjected to CAO ischemia-reperfusion. Recovery of WT following the initial 10-min CAO in Group 1 served as control response for both ISOPC and IPC. Expression and activity of antioxidant proteins were measured using Western blotting and spectrophotometric techniques, respectively.

RESULTS

Two to three hours of reperfusion were required for recovery of WT following either ISOPC or IPC; in contrast, without PC, WT remained markedly reduced (30% below baseline) at this time point and required more than 6 h of reperfusion for recovery. Neither IPC nor ISOPC affected expression of Cu-Zn SOD, Mn SOD, or catalase. However, ISOPC increased activity of Mn SOD (+40%), catalase (+39%), glutathione peroxidase (+37%), and glutathione reductase (+93%) (P < 0.05); IPC had similar effects.

CONCLUSION

ISOPC had powerful, delayed anti-stunning effect that was associated with an enhancement of endogenous antioxidant defenses.

Enhanced charge-independent mitochondrial free Ca(2+) and attenuated ADP-induced NADH oxidation by isoflurane: Implications for cardioprotection

Modulation of mitochondrial free Ca(2+) ([Ca(2+)](m)) is implicated as one of the possible upstream factors that initiates anesthetic-mediated cardioprotection against ischemia-reperfusion (IR) injury. To unravel possible mechanisms by which volatile anesthetics modulate [Ca(2+)](m) and mitochondrial bioenergetics, with implications for cardioprotection, experiments were conducted to spectrofluorometrically measure concentration-dependent effects of isoflurane (0.5, 1, 1.5, 2mM) on the magnitudes and time-courses of [Ca(2+)](m) and mitochondrial redox state (NADH), membrane potential (ΔΨ(m)), respiration, and matrix volume. Isolated mitochondria from rat hearts were energized with 10mM Na(+)- or K(+)-pyruvate/malate (NaPM or KPM) or Na(+)-succinate (NaSuc) followed by additions of isoflurane, 0.5mM CaCl(2) (≈200nM free Ca(2+) with 1mM EGTA buffer), and 250μM ADP. Isoflurane stepwise: (a) increased [Ca(2+)](m) in state 2 with NaPM, but not with KPM substrate, despite an isoflurane-induced slight fall in ΔΨ(m) and a mild matrix expansion, and (b) decreased NADH oxidation, respiration, ΔΨ(m), and matrix volume in state 3, while prolonging the duration of state 3 NADH oxidation, respiration, ΔΨ(m), and matrix contraction with PM substrates. These findings suggest that isoflurane's effects are mediated in part at the mitochondrial level: (1) to enhance the net rate of state 2 Ca(2+) uptake by inhibiting the Na(+)/Ca(2+) exchanger (NCE), independent of changes in ΔΨ(m) and matrix volume, and (2) to decrease the rates of state 3 electron transfer and ADP phosphorylation by inhibiting complex I. These direct effects of isoflurane to increase [Ca(2+)](m), while depressing NCE activity and oxidative phosphorylation, could underlie the mechanisms by which isoflurane provides cardioprotection against IR injury at the mitochondrial level.

Volatile anesthetics protect cancer cells against tumor necrosis factor-related apoptosis-inducing ligand-induced apoptosis via caveolins

BACKGROUND

Volatile anesthetics have a dual effect on cell survival dependent on caveolin expression. The effect of volatile anesthetics on cancer cell survival and death after anesthetic exposure has not been well investigated. The authors examined the effects of isoflurane exposure on apoptosis and its regulation by caveolin-1 (Cav-1).

METHODS

The authors exposed human colon cancer cell lines to isoflurane and proapoptotic stimuli and assessed what role Cav-1 plays in cell protection. They evaluated apoptosis using assays for nucleosomal fragmentation, cleaved caspase 3 expression, and caspase activity assays. To test the mechanism, they used pharmacologic inhibitors (i.e., pertussis toxin) and assessed changes in glycolysis.

RESULTS

Apoptosis as measured by nucleosomal fragmentation was enhanced by isoflurane (1.2% in air) in HT29 (by 64% relative to control, P < 0.001) and decreased in HCT116 (by 23% relative to control, P < 0.001) cells. Knockdown of Cav-1 in HCT116 cells increased the sensitivity to apoptotic stimuli but not with scrambled small interfering RNA (siRNA) treatment (19.7 ± 0.4 vs. 20.0 ± 0.6, P = 0.7786 and 19.7 ± 0.5 vs. 16.3 ± 0.4, P = 0.0012, isoflurane vs. control in Cav-1 small interfering RNA vs. scrambled small interfering RNA treated cells, respectively). The protective effect of isoflurane with various exposure times on apoptosis was enhanced in HT29 cells overexpressing Cav-1 (P < 0.001 by two-way ANOVA). Pertussis toxin effectively blocked the antiapoptotic effect of isoflurane exhibited by Cav-1 in all cell lines. Cav-1 cells had increased glycolysis with isoflurane exposure; however, in the presence of tumor necrosis factor-related apoptosis-inducing ligand, this increase in glycolysis was maintained in HT29-Cav-1 but not control cells.

CONCLUSION

Brief isoflurane exposure leads to resistance against apoptosis via a Cav-1-dependent mechanism.

Delayed preconditioning by sevoflurane elicits changes in the mitochondrial proteome in ischemia-reperfused rat hearts

BACKGROUND

Delayed myocardial preconditioning by volatile anesthetics involves changes in DNA transcription and translation. Mitochondria play a central role in myocardial ischemia/reperfusion (I/R) injury and in ischemic or pharmacologic preconditioning. In this study, we investigated whether there are alterations in myocardial mitochondrial protein expression after volatile anesthetic preconditioning (APC) to examine the underlying mechanisms of delayed cardioprotection.

METHODS

Thirty-six Sprague-Dawley rats were randomly assigned to 1 of 3 groups (n = 12 for each group). Rats in the delayed APC group were exposed to sevoflurane (2.5% for 60 minutes) 24 hours before myocardial ischemia was induced. Myocardial ischemia in the I/R and APC groups was induced by left coronary artery occlusion for 30 minutes, followed by 120 minutes of reperfusion. The control group received no treatment. The mitochondria fractions were prepared by differential centrifugation with density gradient isolation for proteomic analysis. Two-dimensional gel electrophoresis and matrix-assisted laser desorption/ionization with time-of-flight mass spectrometry was used to identify differences in the protein expression from mitochondria of the rat hearts.

RESULTS

Fifteen differentially expressed mitochondrial proteins between the APC group and I/R group were identified and the expression patterns of 2 of the proteins were confirmed by Western blot analysis. These proteins were associated with mitochondrial substrate metabolism, respiration, and adenosine triphosphate (ATP)/adenosine diphosphate transport. The modifications of the mitochondrial proteome suggest an enhanced capacity of mitochondria to maintain myocardial ATP levels after I/R injury.

CONCLUSION

Delayed sevoflurane myocardial preconditioning induces mitochondrial proteome remodeling, which mainly involves proteins that are related to ATP generation and transport. Therefore, proteomic changes related to bioenergetic balance may be the mechanistic basis of delayed anesthetic myocardial preconditioning.

Genetic influences on survival time after severe hemorrhage in inbred rat strains

To find a genetic basis for differential ability to survive severe hemorrhage, we previously showed eightfold differences in survival times among inbred rat strains. We assumed that rat strains had similar normalized blood volumes (NBV; ml/100 g body wt). As NBV might vary among strains and constitute one genetic variable affecting survival time to hemorrhage, in experiment 1 of the current studies we first measured total blood volumes and calculated NBV in specific inbred rat strains (Brown Norway/Medical College of Wisconsin, BN; Dark Agouti, DA; Fawn Hooded Hypertensive, FHH; Lewis, LEW; and Dahl Salt-Sensitive, SS) previously found to be divergent in survival time. NBV differed by 20% (P < 0.01; BN > SS > FHH = LEW = DA) and had a heritability (h(2)) of 0.56. Hence, differential survival times in our previously published study might reflect strain-dependent differences in NBV. Then studies were conducted wherein rats were catheterized and, ∼24 h later, 47% of their blood volume was removed; these rats were observed for a maximum of 4 h. In experiment 2, blood volumes were measured the day prior to hemorrhage. Percent survival and survival time did not differ among strains. To obviate possible confounding effects of blood volume determination, in experiment 3 the average NBV for each strain was used to determine hemorrhage volumes. Percent survival (P < 0.01) and survival times (P < 0.001) were different with DA demonstrating the best (62.5%, 190 ± 29 min) and BN the worst (0%, 52 ± 5 min) survival responses. These data indicate that both blood volume and survival time after hemorrhage in rats are heritable quantitative traits, and continue to suggest that genetic assessment of these phenotypes might lead to novel therapeutics to improve survival to hemorrhage.

Peroxisome-proliferator-activated receptor γ mediates the second window of anaesthetic-induced preconditioning

The second window of anaesthetic-induced preconditioning (APC) is afforded by the interplay of multiple signalling pathways, whereas a similar protective response is mediated by peroxisome-proliferator-activated receptor γ (PPARγ) agonists. However, a possible role of this nuclear receptor during APC has not been studied to date. We investigated the hypothesis that the second window of APC is mediated by the activation of PPARγ. New Zealand White rabbits (n = 48) were subjected to 30 min of coronary artery occlusion followed by 3 h of reperfusion. The animals received desflurane (1.0 minimal alveolar concentration), the PPARγ antagonist GW9662, as well as the combined application of both, respectively, 24 h prior to coronary artery occlusion. Infarct size was determined gravimetrically; tissue levels of 15-deoxy-(12,14)-prostaglandin J(2) (15d-PGJ(2)) and nitrite/nitrate (NO(x)), as well as PPAR DNA binding were measured using specific assays. Data are presented as means ± s.e.m. Desflurane led to a reduced myocardial infarct size (41.7 ± 2.5 versus 61.8 ± 2.8%, P < 0.05), accompanied by significantly increased PPAR DNA binding (289.9 ± 33 versus 102.9 ± 18 relative light units, P < 0.05), as well as elevated tissue levels of 15d-PGJ(2) (224.4 ± 10.2 versus 116.9 ± 14.2 pg ml(-1), P < 0.05) and NO(x) (14.9 ± 0.7 versus 5.4 ± 0.7 μm, P < 0.05). Pharmacological inhibition of PPARγ abolished these protective effects, resetting the infarct size (56.5 ± 2.9%), as well as PPAR DNA-binding activity (91.2 ± 31 relative light units) and NO(x) tissue levels (5.9 ± 0.9 μm) back to control levels. Desflurane governs a second window of APC by increasing the production of 15d-PGJ(2), subsequently activating PPARγ, resulting in a diminished myocardial infarct size by increasing the downstream availability of NO.

Role of caveolin-3 and glucose transporter-4 in isoflurane-induced delayed cardiac protection

BACKGROUND

Caveolae are small, flask-like invaginations of the plasma membrane. Caveolins are structural proteins found in caveolae that have scaffolding properties to allow organization of signaling. The authors tested the hypothesis that delayed cardiac protection induced by volatile anesthetics is caveolae or caveolin dependent.

METHODS

An in vivo mouse model of ischemia-reperfusion injury with delayed anesthetic preconditioning (APC) was tested in wild-type, caveolin-1 knockout, and caveolin-3 knockout mice. Mice were exposed to 30 min of oxygen or isoflurane and allowed to recover for 24 h. After 24 h recovery, mice underwent 30-min coronary artery occlusion followed by 2 h of reperfusion at which time infarct size was determined. Biochemical assays were also performed in excised hearts.

RESULTS

Infarct size as a percent of the area at risk was reduced by isoflurane in wild-type (24.0 +/- 8.8% vs. 45.1 +/- 10.1%) and caveolin-1 knockout mice (27.2 +/- 12.5%). Caveolin-3 knockout mice did not show delayed APC (41.5 +/- 5.0%). Microscopically distinct caveolae were observed in wild-type and caveolin-1 knockout mice but not in caveolin-3 knockout mice. Delayed APC increased the amount of caveolin-3 protein but not caveolin-1 protein in discontinuous sucrose-gradient buoyant fractions. In addition, glucose transporter-4 was increased in buoyant fractions, and caveolin-3/glucose transporter-4 colocalization was observed in wild-type and caveolin-1 knockout mice after APC.

CONCLUSIONS

These results show that delayed APC involves translocation of caveolin-3 and glucose transporter-4 to caveolae, resulting in delayed protection in the myocardium.

Mechanism of cardiac preconditioning with volatile anaesthetics

In recent years, there has been increased interest in the mechanisms involved in anaesthetic-induced cardioprotection. It is not thoroughly understood how volatile anaesthetics protect the myocardium from ischaemia or reperfusion injury, but the overall mechanism is likely to be multifactorial. This review examines the recent experimental and clinical research underlying the cellular and molecular mechanisms involved in anaesthetic-induced preconditioning. A variety of intracellular signalling pathways have been implicated in the protective phenomenon. Ischaemic preconditioning and anaesthetic-induced preconditioning share similar molecular mechanisms, including activation of guanine nucleotide-binding proteins, triggering of second messenger pathways, activation of multiple kinases, mediation of nitric oxide formation and reactive oxygen species release, maintenance of intracellular and/or mitochondrial Ca2+ homeostasis and moderation of the opening of adenosine-triphosphate-sensitive potassium channels. A more thorough understanding of the multiple signalling steps and the ultimate cytoprotective mechanisms underlying anaesthetic-induced preconditioning may lead to improvements in the management of ischaemia and/or reperfusion injury.

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.

Is survival time after hemorrhage a heritable, quantitative trait?: an initial assessment

Enhancing survival to hemorrhage of both civilian and military patients is a major emphasis for trauma research. Previous observations in humans and outbred rats show differential survival to similar levels of hemorrhage. In an initial attempt to determine potential genetic components of such differential outcomes, survival time after a controlled hemorrhage was measured in 15 inbred strains of rats. Anesthetized rats were catheterized, and approximately 24 h later, 55% of the calculated blood volume was removed during a 26-min period from conscious unrestrained animals. Rats were observed for a maximum of 6 h. Survival time was 7.7-fold longer in the longest-lived strain (Brown Norway/Medical College of Wisconsin; 306 +/- 36 min; mean +/- SEM) than in the shortest-lived strain (DA; 40 +/- 5 min; P < or = 0.01). Mean survival times for the remaining inbred strains ranged from 273 +/- 44 to 49 +/- 4 min (Dahl-Salt Sensitive > Brown Norway > Munich Wistar Fromter> Dahl-Salt Resistant > Copenhagen > Noble > Spontaneous-hypertensive > Lewis > BDIX > Fawn Hooded Hypertensive > FISCHER 344 > Black agouti > PVG). The variance in the hazard of death attributable to different strains was estimated to be 1.22 log-hazard units, corresponding to a heritability of approximately 48%. Graded and divergent survival times to hemorrhage in inbred rat strains are remarkable and suggest multiple genetic components for this characteristic. However, this interpretation of differential responses to hemorrhage may be confounded by potential strain-associated differences related to the surgical preparation. Identification of inbred strains divergent in survival time to hemorrhage provides the opportunity for future use of these strains to identify genes associated with this complex response.

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.

Molecular evidence of late preconditioning after sevoflurane inhalation in healthy volunteers

BACKGROUND

Late preconditioning by volatile anesthetics evolves in response to transcriptional changes. We hypothesized that sevoflurane inhalation would modify the transcriptome in human blood and modulate the expression of adhesion molecules in white blood cells consistent with the occurrence of a late preconditioning phase.

METHODS

Five healthy male subjects inhaled sevoflurane at an end-tidal concentration of 0.5%-1.0% for 60 min. Venous blood samples were collected at baseline, after 15 and 60 min of inhalation, and 6, 24, 48, and 72 h thereafter and immediately processed for flow cytometry and mRNA extraction and hybridization to Affymetrix U133 Plus 2.0 microarrays. Data were analyzed using Significance Analysis of Microarray and Gene Set Enrichment Analysis and confirmed by real-time reverse transcription polymerase chain reaction. L-selectin (CD62L) and beta2-integrin (CD11b) expression was determined on granulocytes and monocytes using flow cytometry.

RESULTS

Sevoflurane inhalation rapidly and markedly altered gene expression in white blood cells. Key transcripts potentially involved in late preconditioning or organ protection including paraoxonase, 12-lipoxygenase, heat shock protein 40, chemokine ligand 5, and phosphodiesterase 5A were regulated in response to sevoflurane. Sevoflurane further decreased transcripts involved in peroxisome proliferator-activated receptor gamma coactivator-1alpha (PGC-1alpha) signaling and fatty acid oxidation. Reduced L-selectin (CD62L) expression on granulocytes accompanied with increased resistance to inflammatory activation was present at 24 to 48 h after sevoflurane exposure.

CONCLUSIONS

Sevoflurane at subanesthetic concentrations modifies blood transcriptome and decreases the expression of the proinflammatory L-selectin (CD62L), consistent with a "second window of protection" in humans.

Preconditioning and protection against ischaemia-reperfusion in non-cardiac organs: a place for volatile anaesthetics?

There is an increasing body of evidence that volatile anaesthetics protect myocardium against ischaemic insult by a mechanism termed 'anaesthetic preconditioning'. Anaesthetic preconditioning and ischaemic preconditioning share several common mechanisms of action. Since ischaemic preconditioning has been demonstrated in organs other than the heart, anaesthetic preconditioning might also apply in these organs and have significant clinical applications in surgical procedures carrying a high risk of ischaemia-reperfusion injury. After a brief review on myocardial preconditioning, experimental and clinical data on preconditioning in non-cardiac tissues will be presented. Potential benefits of anaesthetic preconditioning during non-cardiac surgery will be addressed.

General anesthesia delays the inflammatory response and increases survival for mice with endotoxic shock

Anesthesia is an indispensable component of any operative procedure. In this study, we demonstrate that continuous isoflurane anesthesia for 1 h after a lethal dose (20 mg/kg of body weight) of Escherichia coli lipopolysaccharide (LPS) results in a significant increase in survival of C57BL/6J (B6) mice in comparison with survival of nonanesthetized mice. Protection by anesthesia correlates with a delay in plasma LPS circulation, resulting in a delayed inflammatory response, particularly DNA binding activity of NF-kappaB and serum levels of tumor necrosis factor alpha, interleukin-6 (IL-6), and IL-10. Disparate classes of anesthetic agents produce the same effects on the inflammatory response, which is also independent of the inbred mouse strain used. These results suggest that anesthesia has an important impact on the outcome from endotoxemia. Moreover, the immunomodulatory effects of anesthetics should be considered when interpreting data from experimental animal models.

Volatile anesthetics evoke prolonged changes in the proteome of the left ventricule myocardium: defining a molecular basis of cardioprotection?

BACKGROUND

Volatile anesthetics can alter cardiac gene and protein expression. Of those underlying molecular changes in gene and protein expression in the myocardium after exposure to volatile anesthetics that have been identified, some of them have been related to cardioprotection.

METHODS

We used two-dimensional gel electrophoresis and mass spectrometry to identify changes in the protein expression of the left ventricle myocardium of anesthesized rats. We maintained anesthesia for 3 h using isoflurane, sevoflurane or desflurane, respectively, at 1.0 minimum alveolar concentration (MAC) and dissected the left ventricular myocardium either immediately or 72 h after the end of anesthesia.

RESULTS

We found changes of at least twofold in 106 proteins of the more than 1.600 protein spots discriminated in each gel. These differentially expressed proteins are associated with functions in glycolysis, mitochondrial respiration and stress response. No obvious difference could be observed between the patterns of differential expression of the three volatile anesthetics.

CONCLUSION

We provide the first study of post-anesthetic protein expression profiles associated with three common volatile anesthetics. These volatile anesthetics promote a distinct change in the myocardial protein expression profile, whereby changes in the expression pattern still exist 72 h after anesthesia. These proteome changes are closely related to cardioprotection and ischemic preconditioning, indicating a common functional signaling of volatile anesthestics.

Isoflurane induces second window of preconditioning through upregulation of inducible nitric oxide synthase in rat heart

The second window of preconditioning (SWOP) induced by inhalation of volatile anesthetics has been documented in the rat heart and is triggered by nitric oxide synthase (NOS), but involvement of NOS in the mediator phase of isoflurane-induced SWOP has not been demonstrated. We tested the hypothesis that isoflurane-induced SWOP is mediated through upregulation of inducible NOS (iNOS). Rats inhaled 0.75 minimum alveolar concentration (MAC) isoflurane, 1.5 MAC isoflurane, or O2 for 2 h. After 24, 48, 72, and 96 h, the isolated heart was perfused with buffer and subjected to 30 min of ischemia followed by 2 h of reperfusion. Inhalation of 0.75 and 1.5 MAC isoflurane significantly limited infarct size after ischemia-reperfusion 24–72 h after isoflurane inhalation. The maximum effect was obtained 48 h after inhalation of 1.5 MAC isoflurane. Postischemic left ventricular function was improved only 48 h after inhalation of 1.5 MAC isoflurane. iNOS expression and activity in the heart were increased 24–72 h after inhalation of 1.5 MAC isoflurane; this increase was less pronounced after inhalation of 0.75 MAC isoflurane. A selective iNOS inhibitor, 1400W (10 μM), abolished iNOS activation and cardioprotection induced 48 h after inhalation of 1.5 MAC isoflurane. These results suggest that isoflurane inhalation induces SWOP after 24–72 h through overexpression and activation of iNOS in the rat heart.

Anesthesia-specific protection from endotoxic shock is not mediated through the vagus nerve

BACKGROUND

We have shown recently that volatile anesthetics significantly decrease inflammatory cytokine production and dramatically increase survival among rodents challenged with lipopolysaccharide (LPS). Because acetylcholine's interaction with nicotine receptors on tissue macrophages during vagus nerve stimulation has been implicated in the modulation of LPS-stimulated tumor necrosis factor alpha (TNF-alpha) production, we hypothesized that the mechanism of anesthetic immunoprotection is mediated through the vagus nerve.

METHODS

Male Sprague-Dawley rats underwent bilateral cervical vagotomy (n = 20) or sham operation (n = 6). Twenty-four hours postoperatively, vagotomized rats were randomized into 3 groups: LPS injection (V+LPS, n = 6), LPS injection followed by 60 minutes of isoflurane anesthesia (V+LPS+ISO, n = 7), or saline injection (V+S, n = 7). Sham animals were also given LPS (Sham+LPS). A sublethal dose of LPS (8 mg/kg) was used. Blood samples were collected via cardiac puncture 90 minutes after LPS or saline injection, and plasma was isolated for the measurement of cytokines by enzyme-linked immunosorbent assay. Statistical differences between groups were detected by 1-way analysis of variance.

RESULTS

Serum TNF-alpha was reduced significantly and interleukin (IL)-6 was abrogated completely among V+LPS+ISO rats, compared with both V+LPS and Sham+LPS animals (P < or = .05 for all). In contrast, levels of the anti-inflammatory cytokine IL-10 were similar among all LPS groups.

CONCLUSIONS

Isoflurane anesthesia administered simultaneously with the injection of LPS decreases serum production of TNF-alpha and IL-6 despite bilateral transection of the vagus nerve. Isoflurane-mediated attenuation of proinflammatory cytokine production occurs via a mechanism other than modulation of vagal output.