Jacob Raphael

Volatile anesthetic preconditioning attenuates myocardial apoptosis in rabbits after regional ischemia and reperfusion via Akt signaling and modulation of Bcl-2 family proteins

We tested whether isoflurane preconditioning inhibits cardiomyocyte apoptosis and evaluated the role of the phosphatidylinositol-3-kinase (PI3K)/Akt pathway in anesthetic preconditioning and determined whether PI3K/Akt signaling modulates the expression of pro- and antiapoptotic proteins in anesthetic preconditioning. Six-month-old New Zealand rabbits subjected to 40 min of myocardial ischemia followed by 180 min of reperfusion were assigned to the following groups: ischemia-reperfusion (I/R), isoflurane preconditioning and isoflurane plus PI3K inhibitors, wortmannin and 2-(4-morpholinyl)-8-phenyl-4H-l-benzopyran-4-one (LY294002) (0.6 and 0.3 mg/kg i.v., respectively). Sham-operated, wortmannin + I/R, wortmannin + sham, LY294002 + I/R, and LY294002 + sham groups were also included. Infarct size was assessed by triphenyltetrazolium chloride staining. Apoptosis was evaluated by terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling and activated caspase-3 assays. Akt phosphorylation, Bax, Bcl-2, Bad, and phosphorylated Bad (phospho-Bad) expression was assessed by immunoblotting. Isoflurane preconditioning reduced infarct size compared with the I/R group: 22 ± 4 versus 41 ± 5% (p < 0.05). The percentage of apoptotic cells decreased in the isoflurane group (3.8 ± 1.2%) compared with the I/R group (12.4 ± 1.6%; p < 0.05). These results were also confirmed by the activated caspase-3 assay. Wortmannin and LY294002 inhibited the effects of isoflurane. Myocardial infarction increased to 44 ± 3 and 45 ± 2% and the percentage of apoptotic cells was 11.9 ± 2.1 and 11.7 ± 3.3%, respectively. Akt phosphorylation and Bcl-2 and phospho-Bad expression increased after isoflurane preconditioning, whereas Bax expression decreased. These effects were inhibited by wortmannin and LY294002. The data indicate that isoflurane preconditioning reduces infarct size and myocardial apoptosis after I/R. Activation of PI3K and modulation of the expression of pro- and antiapoptotic proteins may play a role in isoflurane-induced myocardial protection.

Isoflurane Preconditioning Decreases Myocardial Infarction in Rabbits via Up-regulation of Hypoxia Inducible Factor 1 That Is Mediated by Mammalian Target of Rapamycin

Background:Volatile anesthetics are known to protect the heart against ischemia-reperfusion injury. The authors tested whether anesthetic preconditioning with isoflurane is mediated via activation of the transcription factor hypoxia inducible factor 1 (HIF-1) and evaluated the role of mammalian target of rapamycin signaling in this process. Methods:New Zealand White rabbits subjected to 40 min of regional myocardial ischemia, followed by 180 min of reperfusion, were assigned to the following groups: ischemia and reperfusion (I/R) only, isoflurane (1 minimal alveolar concentration) preconditioning, and isoflurane preconditioning in the presence of the mammalian target of rapamycin inhibitor rapamycin (0.25 mg/kg). Sham-operated, isoflurane + sham, rapamycin + sham, rapamycin + I/R, and dimethyl sulfoxide + I/R groups were also included. Creatine kinase-MB levels were assessed as an indicator of myocardial damage, and infarct size was evaluated by triphenyl tetrazolium chloride staining. HIF-1&agr; expression and DNA binding were assessed by Western blotting and electrophoretic mobility shift analysis, respectively. Results:Isoflurane preconditioning reduced infarct size compared with the I/R group: 26 ± 4% versus 44 ± 6% (P < 0.05). Creatine kinase-MB concentrations in the preconditioned animals (103 ± 8% above baseline) were lower than in the I/R group (243 ± 12% above baseline; P < 0.05). Rapamycin inhibited the cardioprotective effect of isoflurane: myocardial infarction increased to 44 ± 4% and creatine kinase-MB level increased to 254 ± 9% above baseline. HIF-1&agr; protein expression and DNA binding activity increased after isoflurane preconditioning compared with the ischemia group. These effects were also inhibited by rapamycin. Conclusions:The current results indicate that isoflurane-induced myocardial protection involves activation of the HIF-1 pathway that is mediated by the mammalian target of rapamycin.

Hyperglycemia inhibits anesthetic-induced postconditioning in the rabbit heart via modulation of phosphatidylinositol-3-kinase/Akt and endothelial nitric oxide synthase signaling.

Hyperglycemia is known to inhibit ischemic and anesthetic preconditioning. We tested whether hyperglycemia inhibits anesthetic postconditioning with isoflurane and whether this effect is mediated via phosphatidylinositol-3-kinase/Akt and nitric oxide signaling. New Zealand white rabbits subjected to 40 minutes of myocardial ischemia, followed by 3 hours of reperfusion were assigned to the following groups: ischemia and reperfusion (I/R), isoflurane (1 minimal alveolar concentration) postconditioning, and isoflurane postconditioning with hyperglycemia (15% dextrose in water infusion). A control group of hyperglycemia + I/R was also included. Levels of MB fraction of creatine kinase (CK-MB) were assessed as an indicator of myocardial damage, and infarct size was evaluated. Akt, iNOS, and endothelial nitric oxide synthase (eNOS) expression was assessed by immunoblotting. Determination of nitrite and nitrate levels in the myocardium was also performed. Isoflurane postconditioning reduced infarct size compared with the I/R group: 25% ± 4% versus 49% ± 5% (P < 0.01). CK-MB concentrations in the postconditioned animals (124% ± 14% above baseline levels) were lower than those in the I/R group (236% ± 9% above baseline levels; P < 0.01). Hyperglycemia inhibited the cardioprotective effect of isoflurane: myocardial infarction size was 46% ± 4% and CK-MB increased to 241% ± 11% above baseline. Phosphorylated Akt and eNOS protein expression increased after isoflurane postconditioning compared with the I/R group. These effects were also inhibited by hyperglycemia. iNOS expression, however, did not change significantly within the various experimental groups. There were increased tissue levels of nitrite and nitrate (NOx) in the postconditioning group. This was also blocked by hyperglycemia. Our results suggest that hyperglycemia inhibits cardioprotection provided by isoflurane postconditioning. This effect seems to be mediated via modulation Akt and eNOS.

Flumazenil mimics whereas midazolam abolishes ischemic preconditioning in a rabbit heart model of ischemia-reperfusion.

Background:The goal of the current study was to assess the effects of flumazenil, a benzodiazepine receptor antagonist, in limiting infarct size and in reducing hydroxyl free radical production. Methods:After intravenous salicylate (100 mg/kg) administration, rabbits were subjected to 40 min of regional myocardial ischemia and 2 h of reperfusion. In one group, flumazenil (0.05 mg/kg) and, in another, midazolam (0.05 mg/kg) was administered 15 min before 40 min of ischemia. Ischemic preconditioning (IP) was elicited by 5 min of ischemia followed by 10 min of reperfusion (before the 40-min ischemia period). In two other groups, midazolam was added to flumazenil and IP. Infarct size was determined using triphenyl tetrazolium chloride staining. The authors quantified the hydroxyl-mediated conversion of salicylate to its 2,3- and 2,5-dihydroxybenzoate derivatives during reperfusion by high-performance liquid chromatography coupled with electrochemical detection. Results are expressed as mean ± SEM. Results:Flumazenil, like IP, significantly decreased infarct size (23 ± 4 and 22 ± 5%, respectively, vs. 57 ± 6% in control group; P < 0.01). Midazolam inhibited the effects of flumazenil and IP. Flumazenil and IP significantly limited the increase in the normalized concentrations of 2,3- and 2,5-dihydroxybenzoic acids. With midazolam, however, the increase was comparable to that of the control group. 5-Hydroxydecanoate, a selective mitochondrial adenosine triphosphate–sensitive K+ channel blocker, given with flumazenil, abolished the protection obtained with the latter. Conclusions:Flumazenil mimics preconditioning to decrease infarct size and hydroxyl radical production during reperfusion. Midazolam, however, abolishes these effects. Blockade of benzodiazepine receptors is upstream to the mitochondrial adenosine triphosphate–sensitive K+ channels in the preconditioning cascade.

Ischemic preconditioning decreases the reperfusion-related formation of hydroxyl radicals in a rabbit model of regional myocardial ischemia and reperfusion: The role of KATP channels

The objective of this study was to assess the effects of ischemic preconditioning (IP) on hydroxyl free radical production in an in vivo rabbit model of regional ischemia and reperfusion. Another goal was to determine whether KATP channels are involved in these effects. The hearts of anesthetized and mechanically ventilated New Zealand White rabbits were exposed through a left thoracotomy. After IV salicylate (100 mg/kg) administration, all animals underwent a 30-min stabilization period followed by 40 min of regional ischemia and 2 h of reperfusion. In the IP group, IP was elicited by 5 min of ischemia followed by 10 min of reperfusion (prior to the 40-min ischemia period). Glibenclamide, a KATP channel blocker, was administered prior to the preconditioning stimulus. Infarct size was measured by 2,3,5-triphenyl tetrazolium chloride (TTC) staining. We quantified the hydroxyl-mediated conversion of salicylate to its 2,3 and 2,5-dihydroxybenzoate derivatives during reperfusion by high performance liquid chromatography coupled with electro-chemical detection. IP was evidenced by reduced infarct size compared to control animals: 22% vs. 58%, respectively. Glibenclamide inhibited this cardioprotective effect and infarct size was 53%. IP limited the increase in 2,3 and 2,5-dihydroxybenzoic acid to 24.3 and 23.8% above baseline, respectively. Glibenclamide abrogated this effect and the increase in 2,3 and 2,5-dihydroxybenzoic acid was 94.3 and 85% above baseline levels, respectively, similar to the increase in the control group. We demonstrated that IP decreased the formation of hydroxyl radicals during reperfusion. The fact that glibenclamide inhibited this effect, indicates that KATP channels play a key role in this cardioprotective effect of IP.

Activation of Adenosine Triphosphate-regulated Potassium Channels during Reperfusion Restores Isoflurane Postconditioning-induced Cardiac Protection in Acutely Hyperglycemic Rabbits.

Background:Hyperglycemia is known to inhibit myocardial anesthetic postconditioning. The authors tested whether activation of adenosine triphosphate–regulated potassium (KATP) channels would restore anesthetic postconditioning during acute hyperglycemia. Methods:Rabbits subjected to 40-min myocardial ischemia and 3-h reperfusion (ischemia–reperfusion [I/R]) were assigned to groups (n = 10 in each group) with or without isoflurane postconditioning (2.1% for 5 min) in the presence or absence of hyperglycemia and/or the KATP channel agonist diazoxide. Creatine kinase MB fraction and infarct size were measured. Phosphorylated protein kinase B (Akt) and endothelial nitric oxide synthase (eNOS) were assessed. Oxidative stress was evaluated by measuring malondialdehyde, and apoptosis was assessed by dUTP nick-end labeling and activated caspase-3. Results:Postconditioning significantly reduced myocardial infarct size (26 ± 4% in the isoflurane [ISO] group vs. 53 ± 2% in the I/R group; P = 0.007); whereas, hyperglycemia inhibited this effect (infarct size: 47 ± 2%, P = 0.02 vs. the ISO group). Phosphorylated and eNOS levels increased, whereas malondialdehyde and myocardial apoptosis were significantly lower after isoflurane postconditioning compared with I/R. These effects were inhibited by acute hyperglycemia. Diazoxide restored the protective effect of isoflurane in the hyperglycemic animals (infarct size: 29 ± 2%; P = 0.01 vs. the I/R group), reduced malondialdehyde levels and myocardial apoptosis, but did not affect the expression of phosphorylated Akt or eNOS. Conclusions:KATP channel activation restored anesthetic postconditioning-induced myocardial protection under acute hyperglycemia. This effect occurred without increasing Akt or eNOS phosphorylation, suggesting that KATP channels are located downstream to Akt and eNOS in the pathway of isoflurane-induced myocardial postconditioning.