Wolfgang Schlack

Isoflurane Preconditions Myocardium against Infarction via Release of Free Radicals

Background Isoflurane exerts cardioprotective effects that mimic the ischemic preconditioning phenomenon. Generation of free radicals is implicated in ischemic preconditioning. The authors investigated whether isoflurane-induced preconditioning may involve release of free radicals. Methods Sixty-one &agr;-chloralose–anesthetized rabbits were instrumented for measurement of left ventricular (LV) pressure (tip-manometer), cardiac output (ultrasonic flowprobe), and myocardial infarct size (triphenyltetrazolium staining). All rabbits were subjected to 30 min of occlusion of a major coronary artery and 2 h of subsequent reperfusion. Rabbits of all six groups underwent a treatment period consisting of either no intervention for 35 min (control group, n = 11) or 15 min of isoflurane inhalation (1 minimum alveolar concentration end-tidal concentration) followed by a 10-min washout period (isoflurane group, n = 12). Four additional groups received the radical scavenger N-(2-mercaptoproprionyl)glycine (MPG; 1 mg · kg−1 · min−1) or Mn(III)tetrakis(4-benzoic acid)porphyrine chloride (MnTBAP; 100 &mgr;g · kg−1 · min−1) during the treatment period with (isoflurane + MPG; n = 11; isoflurane + MnTBAP, n = 9) or without isoflurane inhalation (MPG, n = 11; MnTBAP, n = 7). Results Hemodynamic baseline values were not significantly different between groups (LV pressure, 97 ± 17 mmHg [mean ± SD]; cardiac output, 228 ± 61 ml/min). During coronary artery occlusion, LV pressure was reduced to 91 ± 17% of baseline and cardiac output to 94 ± 21%. After 2 h of reperfusion, recovery of LV pressure and cardiac output was not significantly different between groups (LV pressure, 83 ± 20%; cardiac output, 86 ± 23% of baseline). Infarct size was reduced from 49 ± 17% of the area at risk in controls to 29 ± 19% in the isoflurane group (P = 0.04). MPG and MnTBAP themselves had no effect on infarct size (MPG, 50 ± 14%; MnTBAP, 56 ± 15%), but both abolished the preconditioning effect of isoflurane (isoflurane + MPG, 50 ± 24%, P = 0.02; isoflurane + MnTBAP, 55 ± 10%, P = 0.001). Conclusion Isoflurane-induced preconditioning depends on the release of free radicals.

The noble gas xenon induces pharmacological preconditioning in the rat heart in vivo via induction of PKC-ɛ and p38 MAPK

1 Xenon is an anesthetic with minimal hemodynamic side effects, making it an ideal agent for cardiocompromised patients. We investigated if xenon induces pharmacological preconditioning (PC) of the rat heart and elucidated the underlying molecular mechanisms. 2 For infarct size measurements, anesthetized rats were subjected to 25 min of coronary artery occlusion followed by 120 min of reperfusion. Rats received either the anesthetic gas xenon, the volatile anesthetic isoflurane or as positive control ischemic preconditioning (IPC) during three 5‐min periods before 25‐min ischemia. Control animals remained untreated for 45 min. To investigate the involvement of protein kinase C (PKC) and p38 mitogen‐activated protein kinase (MAPK), rats were pretreated with the PKC inhibitor calphostin C (0.1 mg kg−1) or the p38 MAPK inhibitor SB203580 (1 mg kg−1). Additional hearts were excised for Western blot and immunohistochemistry. 3 Infarct size was reduced from 50.9±16.7% in controls to 28.1±10.3% in xenon, 28.6±9.9% in isoflurane and to 28.5±5.4% in IPC hearts. Both, calphostin C and SB203580, abolished the observed cardioprotection after xenon and isoflurane administration but not after IPC. Immunofluorescence staining and Western blot assay revealed an increased phosphorylation and translocation of PKC‐ɛ in xenon treated hearts. This effect could be blocked by calphostin C but not by SB203580. Moreover, the phosphorylation of p38 MAPK was induced by xenon and this effect was blocked by calphostin C. 4 In summary, we demonstrate that xenon induces cardioprotection by PC and that activation of PKC‐ɛ and its downstream target p38 MAPK are central molecular mechanisms involved. Thus, the results of the present study may contribute to elucidate the beneficial cardioprotective effects of this anesthetic gas.

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.

Xenon administration during early reperfusion reduces infarct size after regional ischemia in the rabbit heart in vivo.

The noble gas xenon can be used as an anesthetic gas with many of the properties of the ideal anesthetic. Other volatile anesthetics protect myocardial tissue against reperfusion injury. We investigated the effects of xenon on reperfusion injury after regional myocardial ischemia in the rabbit. Chloralose-anesthetized rabbits were instrumented for measurement of aortic pressure, left ventricular pressure, and cardiac output. Twenty-eight rabbits were subjected to 30 min of occlusion of a major coronary artery followed by 120 min of reperfusion. During the first 15 min of reperfusion, 14 rabbits inhaled 70% xenon/30% oxygen (Xenon), and 14 rabbits inhaled air containing 30% oxygen (Control). Infarct size was determined at the end of the reperfusion period by using triphenyltetrazolium chloride staining. Xenon reduced infarct size from 51% ± 3% of the area at risk in controls to 39% ± 5% (P < 0.05). Infarct size in relation to the area at risk size was smaller in the xenon-treated animals, indicated by a reduced slope of the regression line relating infarct size to the area at risk size (Control: 0.70 ± 0.08, r = 0.93; Xenon: 0.19 ± 0.09, r = 0.49, P < 0.001). In conclusion, inhaled xenon during early reperfusion reduced infarct size after regional ischemia in the rabbit heart in vivo. Implications Xenon might be a suitable volatile anesthetic in an ischemia-reperfusion situation.

Molecular Mechanisms Transducing the Anesthetic, Analgesic, and Organ-protective Actions of Xenon

The anesthetic properties of xenon have been known for more than 50 yr, and the safety and efficacy of xenon inhalational anesthesia has been demonstrated in several recent clinical studies. In addition, xenon demonstrates many favorable pharmacodynamic and pharmacokinetic properties, which could be used in certain niche clinical settings such as cardiopulmonary bypass. This inert gas is capable of interacting with a variety of molecular targets, and some of them are also modulated in anesthesia-relevant brain regions. Besides these anesthetic and analgesic effects, xenon has been shown to exert substantial organoprotective properties, especially in the brain and the heart. Several experimental studies have demonstrated a reduction in cerebral and myocardial infarction after xenon application. Whether this translates to a clinical benefit must be determined because preservation of myocardial and cerebral function may outweigh the significant cost of xenon administration. Clinical trials to assess the impact of xenon in settings with a high probability of injury such as cardiopulmonary bypass and neonatal asphyxia should be designed and underpinned with investigation of the molecular targets that transduce these effects.

Ketamine, but Not S (+)-ketamine, Blocks Ischemic Preconditioning in Rabbit Hearts In Vivo

BackgroundKetamine blocks KATP channels in isolated cells and abolishes the cardioprotective effect of ischemic preconditioning in vitro. The authors investigated the effects of ketamine and S (+)-ketamine on ischemic preconditioning in the rabbit heart in vivo. MethodsIn 46 &agr;-chloralose–anesthetized rabbits, left ventricular pressure (tip manometer), cardiac output (ultrasonic flow probe), and myocardial infarct size (triphenyltetrazolium staining) at the end of the experiment were measured. All rabbits were subjected to 30 min of occlusion of a major coronary artery and 2 h of subsequent reperfusion. The control group underwent the ischemia–reperfusion program without preconditioning. Ischemic preconditioning was elicited by 5-min coronary artery occlusion followed by 10 min of reperfusion before the 30 min period of myocardial ischemia (preconditioning group). To test whether ketamine or S (+)-ketamine blocks the preconditioning-induced cardioprotection, each (10 mg kg−1) was administered 5 min before the preconditioning ischemia. To test any effect of ketamine itself, ketamine was also administered without preconditioning at the corresponding time point. ResultsHemodynamic baseline values were not significantly different between groups [left ventricular pressure, 107 ± 13 mmHg (mean ± SD); cardiac output, 183 ± 28 ml/min]. During coronary artery occlusion, left ventricular pressure was reduced to 83 ± 14% of baseline and cardiac output to 84 ± 19%. After 2 h of reperfusion, functional recovery was not significantly different among groups (left ventricular pressure, 77 ± 19%; cardiac output, 86 ± 18%). Infarct size was reduced from 45 ± 16% of the area at risk in controls to 24 ± 17% in the preconditioning group (P = 0.03). The administration of ketamine had no effect on infarct size in animals without preconditioning (48 ± 18%), but abolished the cardioprotective effects of ischemic preconditioning (45 ± 19%, P = 0.03). S (+)-ketamine did not affect ischemic preconditioning (25 ± 11%, P = 1.0). ConclusionsKetamine, but not S (+)-ketamine blocks the cardioprotective effect of ischemic preconditioning in vivo.

Desflurane Preconditioning Induces Time-dependent Activation of Protein Kinase C Epsilon and Extracellular Signal-regulated Kinase 1 and 2 in the Rat Heart In Vivo

Background:Activation of protein kinase C epsilon (PKC-&egr;) and extracellular signal-regulated kinase 1 and 2 (ERK1/2) are important for cardioprotection by preconditioning. The present study investigated the time dependency of PKC-&egr; and ERK1/2 activation during desflurane-induced preconditioning in the rat heart. Methods:Anesthetized rats were subjected to regional myocardial ischemia and reperfusion, and infarct size was measured by triphenyltetrazoliumchloride staining (percentage of area at risk). In three groups, desflurane-induced preconditioning was induced by two 5-min periods of desflurane inhalation (1 minimal alveolar concentration), interspersed with two 10-min periods of washout. Three groups did not undergo desflurane-induced preconditioning. The rats received 0.9% saline, the PKC blocker calphostin C, or the ERK1/2 inhibitor PD98059 with or without desflurane preconditioning (each group, n = 7). Additional hearts were excised at four different time points with or without PKC or ERK1/2 blockade: without further treatment, after the first or the second period of desflurane-induced preconditioning, or at the end of the last washout phase (each time point, n = 4). Phosphorylated cytosolic PKC-&egr; and ERK1/2, and membrane translocation of PKC-&egr; were determined by Western blot analysis (average light intensity). Results:Desflurane significantly reduced infarct size from 57.2 ± 4.7% in controls to 35.2 ± 16.7% (desflurane-induced preconditioning, mean ± SD, P < 0.05). Both calphostin C and PD98059 abolished this effect (58.8 ± 13.2% and 64.2 ± 15.4% respectively, both P < 0.05 versus desflurane-induced preconditioning). Cytosolic phosphorylated PKC-&egr; reached its maximum after the second desflurane-induced preconditioning and returned to baseline after the last washout period. Both calphostin C and PD98059 inhibited PKC-&egr; activation. ERK1/2 phosphorylation reached its maximum after the first desflurane-induced preconditioning and returned to baseline after the last washout period. Calphostin C had no effect on ERK1/2 phosphorylation. Conclusions:Both, PKC and ERK1/2 mediate desflurane-induced preconditioning. PKC-&egr; and ERK1/2 are both activated in a time dependent manner during desflurane-induced preconditioning, but ERK1/2 activation during desflurane-induced preconditioning is not PKC dependent. Moreover, ERK1/2 blockade abolished PKC-&egr; activation, suggesting ERK-dependent activation of PKC-&egr; during desflurane-induced preconditioning.

Adenosine A2-receptor activation at reperfusion reduces infarct size and improves myocardial wall function in dog heart

Reestablishment of blood supply to ischemic myocardium leads to biochemical and cellular changes which are believed to reduce the amount of potentially salvageable myocardium (reperfusion injury). In this situation, adenosine is known to have myocardial protective properties. Activation of adenosine A2-receptors may account for most of the beneficial effects of adenosine in reperfusion injury because A2-receptor activation mediates vasodilation, inhibits neutrophil adhesion to vascular endothelium and diminishes generation of free radicals by neutrophils, thus acting on some of the key mechanisms of reperfusion injury such as postischemic vascular dysfunction and neutrophil-mediated damage. Therefore, we investigated the effect of an intracoronary A2-agonist, CGS 21680, on regional postischemic myocardial function (measured as wall thickening) and infarct size [determined by triphenyltetrazolium chloride (TTC) staining]. Fourteen anesthetized open-chest dogs underwent 1-h left anterior descending artery (LAD) occlusion and 6-h reperfusion and were randomly assigned to receive intracoronary CGS 21680 or to serve as control. The drug was infused for 60 min starting 5 min before reperfusion with a concentration of 10 -7 M at a rate of 10 ml/min under anoxic conditions. The infusion was then continued for the first 55 min of reperfusion with 10 -6 M at a rate of 1 ml/min. Intracoronary infusion of CGS 21680 led to significant improvement in regional wall function in postischemic myocardium (p < 0.05 vs. control). Thickening fraction (percentage of baseline) increased from −13.1 ± 13.7% (mean ± SD) during occlusion to 15.3 ± 29.8% at 30 min of reperfusion in the CGS 21680 treatment group and remained at this level throughout the reperfusion period. In the control group, thickening fraction was - 23.7 ± 16.2% during occlusion and did not recover during reperfusion. A significant reduction in infarct size was noted in the treatment group (11.5 ± 7.9% of area at risk) as compared with the control group (28.6 ± 11.4%, p < 0.05). These findings support the hypothesis that the protective effect of adenosine on reperfusion injury is not due to replenishment of the nucleoside pool but rather is induced by stimulation of the adenosine A2-receptor.

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.

Hyperglycaemia blocks sevoflurane-induced postconditioning in the rat heart in vivo: cardioprotection can be restored by blocking the mitochondrial permeability transition pore

BACKGROUND Recent studies showed that hyperglycaemia (HG) blocks anaesthetic-induced preconditioning. The influence of HG on anaesthetic-induced postconditioning (post) has not yet been determined. We investigated whether sevoflurane (Sevo)-induced postconditioning is blocked by HG and whether the blockade could be reversed by inhibiting the mitochondrial permeability transition pore (mPTP) with cyclosporine A (CsA). METHODS Chloralose-anaesthetized rats (n=7-11 per group) were subjected to 25 min coronary artery occlusion followed by 120 min reperfusion. Postconditioning was achieved by administration of 1 or 2 MAC sevoflurane for the first 5 min of early reperfusion. HG was induced by infusion of glucose 50% (G 50) for 35 min, starting 5 min before ischaemia up to 5 min of reperfusion. CsA (5 or 10 mg kg(-1)) was administered i.v. 5 min before the onset of reperfusion. At the end of the experiments, hearts were excised for infarct size measurements. RESULTS Infarct size (% of area at risk) was reduced from 51.4 (5.0)% [mean (sd)] in controls to 32.7 (12.8)% after sevoflurane postconditioning (Sevo-post) (P<0.05). This infarct size reduction was completely abolished by HG [51.1 (13.2)%, P<0.05 vs Sevo-post], but was restored by administration of sevoflurane with CsA [35.2 (5.2)%, P<0.05 vs HG+Sevo-post]. Increased concentrations of sevoflurane or CsA alone could not restore cardioprotection in a state of HG [Sevo-post2, 54.1 (12.6)%, P>0.05 vs HG+Sevo-post; CsA10, 58.8 (11.3)%, P>0.05 vs HG+CsA]. CONCLUSIONS Sevoflurane-induced postconditioning is blocked by HG. Inhibition of the mPTP with CsA is able to reverse this loss of cardioprotection.