Late Preconditioning Research Articles

Late Exercise Preconditioning Regulates BNP Increasing to Assist the Cardioprotection via Up-Regulation of NPR-A and Down-Regulation of NPR-C in Rat Myocardium

Late Exercise Preconditioning Regulates BNP Increasing to Assist the Cardioprotection via Up-Regulation of NPR-A and Down-Regulation of NPR-C in Rat Myocardium

Autocrine Bradykinin Release Promotes Ischemic Preconditioning-Induced Cytoprotection in Bovine Aortic Endothelial Cells.

The aims of this study were to assess whether ischemic preconditioning (PC) induces bradykinin (Bk) synthesis in bovine aortic endothelial cells (bAECs) and, if so, to explore the molecular mechanisms by which this peptide provides cytoprotection against hypoxia. PC was induced by exposing bAECs to three cycles of 15 min of hypoxia followed by 15 min of reoxygenation. Bk synthesis peaked in correspondence to the early and late phases of PC (10−12 M and 10−11 M, respectively) and was abolished by a selective tissue kallikrein inhibitor, aprotinin. Stimulation with exogenous Bk at concentrations of 10−12 M and 10−11 M reduced the cell death induced by 12 h of hypoxia by 50%. Pretreatment with HOE−140, a Bk receptor 2 (BKR2) inhibitor, in bAECs exposed to 12 h of hypoxia, abrogated the cytoprotective effect of early and late PC, whereas des-Arg-HOE-140, a Bk receptor 1 (BKR1) inhibitor, affected only the late PC. In addition, we found that PC evoked endocytosis and the recycling of BKR2 during both the early and late phases, and that inhibition of these pathways affected PC-mediated cytoprotection. Finally, we evaluated the activation of PKA and Akt in the presence or absence of BKR2 inhibitor. HOE-140 abrogated PKA and Akt activation during both early and late PC. Consistently, BKR2 inhibition abolished cross-talk between PKA and Akt in PC. In bAECs, Bk-synthesis evoked by PC mediates the protection against both apoptotic and necrotic hypoxia-induced cell death in an autocrine manner, by both BKR2- and BKR1-dependent mechanisms.

Late cardiac perconditioning by phenylephrine in an isolated rat heart model is mediated by mitochondrial potassium channels

The present study was designed to investigate the effect of early and late administration of phenylephrine during ischemia against regional ischemia–reperfusion injuries in an isolated rat heart model. All animals were randomly divided into experimental groups: (I) IR (Ischemic/ reperfusion): the hearts underwent 35 min of regional ischemia followed by 60 min of reperfusion; (II) 5HD-IR-0: the hearts were perfused for 5 min with 5HD (5-hydroxydecanoate, specific mKATP channel blocker, 100 µM) at the onset of regional ischemia; (III) 5HD-IR-20: the hearts were perfused for 5 min with 5HD 20 min after regional ischemia; (IV) PE-IR-10: the hearts were perfused for 5 min with phenylephrine 10 min after regional ischemia; (V) PE-IR-30: the hearts were perfused for 5 min with phenylephrine (100 µM) 30 min after regional ischemia; (VI) PE-5HD-IR-10 group: the hearts were perfused for 5 min with 5HD at the onset of regional ischemia after which phenylephrine was administrated as in group IV; and (VII) PE-5HD-IR-30: the hearts were perfused for 5 min with 5HD 20 min after the ischemia and then phenylephrine was administrated as in group V. The hemodynamic parameters were recorded throughout the experiment. Ischemia-induced arrhythmias, myocardial infarct size (IS), creatin kinase-MB isoenzyme (CK-MB), plasma lactate dehydrogenase (LDH) activities, and coronary blood flow (CBF) were measured in all animals. Perfusion of phenylephrine 30 min after the regional ischemia curtailed the myocardial infarct size, reduced CK-MB, and improved cardiac function and CBF. Administration of 5HD 30 min after the ischemia abolished cardioprotective effects of phenylephrine in the late phase. These results suggest the involvement of mKATP in the mechanism of phenylephrine-induced late preconditioning.

Extended Second Window of Protection of Sevoflurane-induced Preconditioning

Late preconditioning (LPC) can be induced by volatile anesthetics and initiates cardioprotection against ischemia/reperfusion injury for 3-4 days. We investigated the possibility to extend the time window of sevoflurane-induced LPC by repeated sevoflurane administration. An in vivo rat model of regional myocardial ischemia/reperfusion injury was used. Myocardial infarct size was determined by triphenyltetrazolium chloride staining at the end of the experiment. In the first series of experiments, male Wistar rats were randomized to 5 groups (each n = 8). Control animals were not treated further. Animals in the preconditioning groups inhaled sevoflurane for 60 minutes (1 MAC) 24, 48, 72, and 96 hours, respectively, before myocardial ischemia. Based on the findings of the first experimental series, another 6 groups of animals were investigated. Again, control animals were left untreated; all other animals received a second sevoflurane stimulus 72 hours after the first sevoflurane treatment, and myocardial ischemia was induced 24, 48, 72, and 96 hours, respectively, after the second sevoflurane treatment to investigate, whether the cardioprotective effect could be extended. Sevoflurane reduced infarct size after 24, 48, and 72 hours (each P < 0.05 vs. control) but not after 96 hours. The repeated administration of sevoflurane 72 hours after the first stimulus extended the time window of protection for additional 72 hours (each P < 0.05 vs. control). There was no myocardial protection 4 days after the second preconditioning stimulus. The time window of sevoflurane-induced LPC can be extended by an additional sevoflurane stimulus up to 72 hours after the initial sevoflurane exposure.

Low-Dose Endotoxin Induces Late Preconditioning, Increases Peroxynitrite Formation, and Activates STAT3 in the Rat Heart

Administration of low-dose endotoxin (lipopolysaccharide, LPS) 24 h before a lethal ischemia induces pharmacological late preconditioning. The exact mechanism of this phenomenon is not clear. Here we aimed to investigate whether low-dose LPS exerts late effects on peroxynitrite formation and activation of Akt, Erk, and STAT3 in the heart. Male Wistar rats were injected with LPS (S. typhimurium; 0.5 mg/kg i.p.) or saline. Twenty-four hours later, hearts were isolated, perfused for 10 min, and then used for biochemical analyses. LPS pretreatment enhanced cardiac formation of the peroxynitrite marker 3-nitrotyrosine. LPS pretreatment also increased cardiac levels of the peroxynitrite precursor nitric oxide (NO) and superoxide. The activities of Ca2+-independent NO synthase and xanthine oxidoreductase increased in LPS-pretreated hearts. LPS pretreatment resulted in significantly enhanced phosphorylation of STAT3 and non-significantly increased phosphorylation of Akt without affecting the activation of Erk. In separate experiments, isolated working hearts were subjected to 30 min global ischemia and 20 min reperfusion. LPS pretreatment significantly improved ischemia-reperfusion-induced deterioration of cardiac function. We conclude that LPS pretreatment enhances cardiac peroxynitrite formation and activates STAT3 24 h later, which may contribute to LPS-induced late preconditioning.

A review on Late phase ischemic preconditioning.

A review on Late phase ischemic preconditioning.

Role of Endogenous Opioid System in Ischemic-Induced Late Preconditioning.

BackgroundOpioid receptors (OR) are involved in myocardial late preconditioning (LPC) induced by morphine and δ1-opioid receptor (δ1-OR) agonists. The role of OR in ischemic-induced LPC is unknown. We investigated whether 1) OR are involved in the trigger and/or mediation phase of LPC and 2) a time course effect on the expression of different opioid receptors and their endogenous ligands exists.MethodsMale Wistar rats were randomly allocated to four groups (each group n = 8). Awake animals were ischemic preconditioned by a 5 minutes coronary occlusion. 24 hours later, anesthetized animals underwent 25 minutes coronary occlusion followed by 2 hours of reperfusion. The role of OR was investigated by treatment with intraperitoneal naloxone (Nal) 10 minutes prior to LPC (Nal-LPC; trigger phase) or 10 min prior to sustained ischemia (LPC-Nal; mediation phase).ResultsLPC reduced infarct size from 61±10% in controls to 25±9% (P<0.001). Naloxone during trigger or mediation phase completely abolished LPC-induced cardioprotection (59±9% and 62±9%; P<0.001 vs. LPC). 8, 12 and 24 hours after the ischemic stimulus, expression of δ-OR in the heart was increased, whereas μ-opioid receptor (μ-OR) and κ-opioid receptor (κ-OR) were not. Plasma concentrations of β-endorphin and leu-enkephalin but not dynorphin were increased by LPC.ConclusionIschemic LPC is triggererd and mediated by OR. Expression of δ-OR and plasma levels of endogenous opioid peptides are increased after ischemic LPC.

Exercise preconditioning of myocardial infarct size in dogs is triggered by calcium.

We showed that exercise induces early and late myocardial preconditioning in dogs and that these effects are mediated through nicotinamide adenine dinucleotide phosphate reduced form (NADPH) oxidase activation. As the intracoronary administration of calcium induces preconditioning and exercise enhances the calcium inflow to the cell, we studied if this effect of exercise triggers exercise preconditioning independently of its hemodynamic effects. We analyzed in 81 dogs the effect of blocking sarcolemmal L-type Ca channels with a low dose of verapamil on early and late preconditioning by exercise, and in other 50 dogs, we studied the effect of verapamil on NADPH oxidase activation in early exercise preconditioning. Exercise reduced myocardial infarct size by 76% and 52% (early and late windows respectively; P < 0.001 both), and these effects were abolished by a single low dose of verapamil given before exercise. This dose of verapamil did not modify the effect of exercise on metabolic and hemodynamic parameters. In addition, verapamil blocked the activation of NADPH oxidase during early preconditioning. The protective effect of exercise preconditioning on myocardial infarct size is triggered, at least in part, by calcium inflow increase to the cell during exercise and, during the early window, is mediated by NADPH oxidase activation.

Endoplasmic reticulum stress-dependent activation of ATF3 mediates the late phase of ischemic preconditioning

Ischemic preconditioning (PC) is an adaptive response to transient myocardial ischemia that protects the heart from subsequent ischemia/reperfusion (I/R) injury. However, the mechanisms underlying its cardioprotective effects remain unclear. Myocardium of adult male C57/BL6 mice, preconditioned by 6cycles of 4minute coronary occlusion and reperfusion, showed nuclear translocation of ATF3 and ATF6 and PERK phosphorylation 30min after PC. The abundance of ER proteins, ATF3 and ATF4 was increased 24h after PC; however, there was no evidence of IRE-1 activation in WT or ER-stress activated indicator (ERAI) mice expressing XBP-1-Venus fusion protein. PC-induced nuclear translocation of ATF3 was attenuated in transgenic mice with cardiac-restricted overexpression of inducible ATF6. Ischemic PC increased the abundance of inducible nitric oxide synthase, cyclooxygenase-2, heme oxygenase-1 and aldose reductase to levels similar between WT and ATF3-null hearts; however, the increase in IL-6 and ICAM-1 was exaggerated in ATF3-null hearts. Genetic deletion of ATF3 did not increase infarct size in non-preconditioned hearts but abolished the cardioprotective effects of PC. Larger infarct size in preconditioned ATF3-null hearts was associated with greater neutrophil infiltration in the myocardium, but no ATF3-dependent changes in the total or relative abundance of inflammatory monocytes were observed. Ischemic PC activates the unfolded protein response (UPR) and the activation of ATF3 by ER stress is essential for the cardioprotective effects of late PC.

Helium Induces Preconditioning in Human Endothelium In Vivo

Helium protects myocardium by inducing preconditioning in animals. We investigated whether human endothelium is preconditioned by helium inhalation in vivo. Forearm ischemia-reperfusion (I/R) in healthy volunteers (each group n = 10) was performed by inflating a blood pressure cuff for 20 min. Endothelium-dependent and endothelium-independent responses were measured after cumulative dose-response infusion of acetylcholine and sodium nitroprusside, respectively, at baseline and after 15 min of reperfusion using strain-gauge, venous occlusion plethysmography. Helium preconditioning was applied by inhalation of helium (79% helium, 21% oxygen) either 15 min (helium early preconditioning [He-EPC]) or 24 h before I/R (helium late preconditioning). Additional measurements of He-EPC were done after blockade of endothelial nitric oxide synthase. Plasma levels of cytokines, adhesion molecules, and cell-derived microparticles were determined. Forearm I/R attenuated endothelium-dependent vasodilation (acetylcholine) with unaltered endothelium-independent response (sodium nitroprusside). Both He-EPC and helium late preconditioning attenuated I/R-induced endothelial dysfunction (max increase in forearm blood flow in response to acetylcholine after I/R was 180 ± 24% [mean ± SEM] without preconditioning, 573 ± 140% after He-EPC, and 290 ± 32% after helium late preconditioning). Protection of helium was comparable to ischemic preconditioning (max forearm blood flow 436 ± 38%) and was not abolished after endothelial nitric oxide synthase blockade. He-EPC did not affect plasma levels of cytokines, adhesion molecules, or microparticles. Helium is a nonanesthetic, nontoxic gas without hemodynamic side effects, which induces early and late preconditioning of human endothelium in vivo. Further studies have to investigate whether helium may be an instrument to induce endothelial preconditioning in patients with cardiovascular risk factors.

The COX-2/PGI2 Receptor Axis Plays an Obligatory Role in Mediating the Cardioprotection Conferred by the Late Phase of Ischemic Preconditioning

BackgroundPharmacologic studies with cyclooxygenase-2 (COX-2) inhibitors suggest that the late phase of ischemic preconditioning (PC) is mediated by COX-2. However, nonspecific effects of COX-2 inhibitors cannot be ruled out, and the selectivity of these inhibitors for COX-2 vs. COX-1 is only relative. Furthermore, the specific prostaglandin (PG) receptors responsible for the salubrious actions of COX-2-derived prostanoids remain unclear.ObjectiveTo determine the role of COX-2 and prostacyclin receptor (IP) in late PC by gene deletion.MethodsCOX-2 knockout (KO) mice (COX-2−/−), prostacyclin receptor KO (IP−/−) mice, and respective wildtype (WT, COX-2+/+ and IP+/+) mice underwent sham surgery or PC with six 4-min coronary occlusion (O)/4-min R cycles 24 h before a 30-min O/24 h R.ResultsThere were no significant differences in infarct size (IS) between non-preconditioned (non-PC) COX-2+/+, COX-2−/−, IP+/+, and IP−/− mice, indicating that neither COX-2 nor IP modulates IS in the absence of PC. When COX-2−/− or IP−/− mice were preconditioned, IS was not reduced, indicating that the protection of late PC was completely abrogated by deletion of either the COX-2 or the IP gene. Administration of the IP selective antagonist, RO3244794 to C57BL6/J (B6) mice 30 min prior to the 30-min O had no effect on IS. When B6 mice were preconditioned 24 h prior to the 30-min O, IS was markedly reduced; however, the protection of late PC was completely abrogated by pretreatment of RO3244794.ConclusionsThis is the first study to demonstrate that targeted disruption of the COX-2 gene completely abrogates the infarct-sparing effect of late PC, and that the IP, downstream of the COX-2/prostanoid pathway, is a key mediator of the late PC. These results provide unequivocal molecular genetic evidence for an essential role of the COX-2/PGI2 receptor axis in the cardioprotection afforded by the late PC.

Effects of noble gas conditioning on Caveolin expression in the rat heart in vivo

Caveolins are structural scaffolding proteins that allow for organization of signalling molecules in caveolae, membrane invaginations enriched in lipids. Caveolin‐3 (Cav‐3) is a heart specific isoform that is modulated by volatile anesthetics and is required for cardiac protection. We hypothesized that the cardioprotective noble gases Helium (He) and Xenon (Xe) also influence the enrichment of Cav‐3 to caveolae in vivo. Sprague‐ Dawley rats underwent 25 minutes of myocardial ischemia and 2 hours of reperfusion. Rats where left untreated (Con) or underwent different preconditioning (PC) protocols: in He late PC (HeLPC), rats inhaled He for 3×5 min a day before the experiment, the He postconditioning (HePost) group inhaled 70% He for 15 min at the onset of reperfusion. The Xe‐PC rats inhaled 70% Xe for 3×5 min before ischemia. Hearts were processed for sucrose density gradient centrifugation to purify caveolae. Cav‐3 and 1 expression were determined by immunoblotting. HeLPC and HePost increased Cav‐3 localization from 0.2±0.1 in Con to 0.4±0.1 and 0.4±0.2 (arbitrary units), respectively, in buoyant caveolar fractions indicative of increased caveolae formation. Xe‐PC had no effect on Cav‐3 localization. We found no effect on Cav‐1 localization.These data suggest that He might exert its cardioprotective effect by augmenting Cav‐3 localization to caveolae to further enhance cardioprotective signaling.

A murine model of inducible, cardiac-specific deletion of STAT3: Its use to determine the role of STAT3 in the upregulation of cardioprotective proteins by ischemic preconditioning

Pharmacological studies have shown that signal transducers and activators of transcription (STATs) are necessary for the delayed cardioprotection of ischemic preconditioning (PC). However, pharmacologic STAT inhibitors are not specific; furthermore, the individual role of STAT3 in late PC remains unknown. The objectives of the study were (i) to create an inducible, cardiac-specific STAT3 knockout mouse; (ii) to verify whether STAT3 deletion has any adverse effects in the short term (~ 1 month); and (iii) to use this novel tool to evaluate the role of STAT3 in the PC-induced upregulation of cardioprotective and anti-apoptotic proteins. We created an inducible, cardiomyocyte-restricted STAT3 deficient mouse ( MCM TG: STAT3 flox/flox ) by interbreeding STAT3 flox/flox mice and tamoxifen-inducible MCM TG mice. Treatment of MCM TG: STAT3 flox/flox mice with tamoxifen resulted in deletion of STAT3 specifically in cardiac myocytes, concomitant with abrogation of ischemic PC-induced Tyr-705 and Ser-727 phosphorylation of STAT3 and increased STAT3 DNA-binding activity. In vehicle-treated MCM TG: STAT3 flox/flox mice, ischemic PC increased the expression of cardioprotective (COX-2 and HO-1) and anti-apoptotic (e.g., Mcl-1, Bcl-x L, c-FLIP L, c-FLIP S) proteins 24 h later; in contrast, in tamoxifen-treated MCM TG: STAT3 flox/flox mice this increase was completely absent. Deletion of STAT3 had no apparent adverse effects on LV structure or function after 35 days. We have developed a novel inducible, cardiomyocyte-restricted STAT3 deficient mouse that can be used to specifically interrogate the role of this transcription factor in cardiovascular pathophysiology in vivo. Our data demonstrate, for the first time, that recruitment of STAT3 plays an obligatory role in the upregulation of cardioprotective and anti-apoptotic proteins and suggest that STAT3 activation is important in inhibiting both the death receptor pathway (which is modulated by c-FLIP L and c-FLIP S) and the mitochondrial pathway (which is mediated by Mcl-1 and Bcl-x L).

Hypoxia Induces Late Preconditioning in the Rat Heart In Vivo

Although hypoxic late preconditioning (LPC) limits ischemia-reperfusion injury in vitro, its cardioprotective effect is not established in vivo. In part 1, rats were exposed to 4 h of hypoxia (16%, 12%, 8% oxygen) before 24 h of reoxygenation. In part 2, normoxic rats received early preconditioning with sevoflurane (1 minimum alveolar concentration [MAC] for 3 × 5 min), continuous administration of 1 MAC sevoflurane, or 11 mg · kg · h propofol. Thereafter, all rats underwent 25 min of regional myocardial ischemia and 120 min of reperfusion. After reperfusion, hearts were excised for infarct staining. The expression of protein kinase C (PKC)α and PKCε was assessed by Western blot analysis and the expression of heme oxygenase-1 and vascular endothelial growth factor by reverse transcriptase polymerase chain reaction. In normoxic control rats, infarct size was 62 ± 6% of the area at risk. Hypoxic LPC reduced infarct size (LPC16: 36 ± 11%, LPC12: 38 ± 10%, LPC8: 39 ± 11%; each P < 0.001) to approximately the same magnitude as sevoflurane-preconditioning (40 ± 8%; P < 0.001). Combined LPC16 and sevoflurane preconditioning was not superior to either substance alone. Continuous sevoflurane or propofol was not protective. The PKC inhibitor calphostin C abolished the cardioprotective effects of LPC16. PKCε, but not PKCα, expression was increased 6 and 28 h after hypoxic LPC. Heme oxygenase-1 and vascular endothelial growth factor were transiently up-regulated after 6 h. Hypoxic LPC at 8%, 12%, and 16% oxygen reduces infarct size in the rat heart in vivo. This effect is as powerful as sevoflurane-preconditioning. PKCε is a key player in mediating hypoxic LPC.

Late Cardiac Preconditioning by Exercise in Dogs Is Mediated by Mitochondrial Potassium Channels

We previously showed that exercise induces myocardial preconditioning in dogs and that early preconditioning is mediated through mitochondrial adenosine triphosphate-sensitive potassium channels. We decided to study if late preconditioning by exercise is also mediated through these channels. Forty-eight dogs, surgically instrumented and trained to run daily, were randomly assigned to 4 groups: (1) Nonpreconditioned dogs: under anesthesia, the coronary artery was occluded during 1 hour and then reperfused during 4.5 hours. (2) Late preconditioned dogs: similar to group 1, but the dogs run on the treadmill for 5 periods of 5 minutes each, 24 hours before the coronary occlusion. (3) Late preconditioned dogs plus 5-hydroxydecanoate (5HD): similar to group 2, but 5HD was administered before the coronary occlusion. (4) Nonpreconditioned dogs plus 5HD: similar to group 1, but 5HD was administered before the coronary occlusion. Infarct size (percent of the risk region) decreased by effect of exercise by 56% (P < 0.05), and this effect was abolished with 5HD. 5HD by itself did not modify infarct size. Exercise did not induce myocardial ischemia, and the hemodynamics during ischemia-reperfusion period did not differ among groups. These effects were independent of changes in collateral flow to the ischemic region. We concluded that late cardiac preconditioning by exercise is mediated through mitochondrial adenosine triphosphate-sensitive potassium channels.

Role of iNOS and peroxynitrite–matrix metalloproteinase-2 signaling in myocardial late preconditioning in rats

We have previously shown that the inhibition of myocardial nitric oxide (NO) and peroxynitrite-matrix metalloproteinase (MMP) signaling by early preconditioning (PC) is involved in its cardioprotective effect. Therefore, in the present study, we investigated the role of NO and peroxynitrite-MMP signaling in the development of late PC. PC was performed by five consecutive cycles of 4-min coronary occlusion and 4-min reperfusion in anesthetized rats in vivo. Twenty-four hours later, hearts were subjected to a 30-min coronary occlusion followed by 180-min reperfusion to measure infarct size. In separate experiments, heart tissue was sampled to measure biochemical parameters before and 3, 6, 12, or 24 h after the PC protocol, respectively. Late PC decreased infarct size, increased cardiac inducible NO synthase (iNOS) activity and gene expression, and decreased SOD activity at 24 h significantly compared with sham-operated controls. Late PC increased cardiac superoxide levels significantly at 24 h; however, it did not change cardiac NO levels. Cardiac peroxynitrite levels were significantly decreased. Downstream cellular targets of peroxynitrite, MMP-2 and MMP-9 activities were decreased in the late PC group at 24 h compared with the sham-operated group. To verify if PC-induced inhibition of MMPs had a causative role in the reduction of infarct size, in separate experiments, we measured infarct size after the pharmacological inhibition of MMPs by ilomastat and found a significant reduction of infarct size compared with the vehicle-treated group. In conclusion, this is the first demonstration that the inhibition of cardiac peroxynitrite-MMP signaling contributes to cardioprotection by late PC and that pharmacological inhibition of MMPs is able to reduce infarct size in vivo. Furthermore, increased expression of iNOS may play a role in the development of late PC; however, increased iNOS activity does not lead to increased NO production in late PC.

Ferilnic nirate produces delayed preconditioning against myocardial ischemia and reperfusion injury in rats

To determine whether ferilnic nirate (FLNT) can precondition the rat heart against myocardial ischemia/reperfusion (I/R) damage and its mechanism, two groups of experiments were conducted. In the first group of experiments, rats were divided among four treatment groups: sham group; solvent with I/R (I/R control group); FLNT pretreatment with I/R (I/R FLNT group); and late ischemic preconditioning group (LPC group). In the second group of experiments without I/R, rats were divided into two treatment groups: control group and FLNT group. The results indicated that myocardial infarct size and the levels of creatine kinase and lactate dehydrogenase in the sera of the I/R FLNT group were significantly lower and the level of nitric oxide molecule and Mn-containing superoxide dismutase were significantly elevated in the heart tissue compared with I/R control group. The protein expression ratio of Bcl-2/Bax in heart tissue was significantly elevated in the I/R FLNT group. These results demonstrate FLNT is able to precondition rat hearts against myocardial ischemia/reperfusion damage to a similar level as that achieved via the late phase of ischemic preconditioning. The mechanism may involve the up-regulation of nitric oxide and the strengthening of anti-oxidant and anti-apoptosis cellular functions.

Cross-Talk Between PKA and Akt Protects Endothelial Cells From Apoptosis in the Late Ischemic Preconditioning

The aim of this study was to explore the molecular mechanisms involved in late preconditioning-induced cell protection in endothelial cells. Preconditioning (PC) was induced by exposing bovine aortic endothelial cells (BAECs) to 3 cycles of 15 minutes of hypoxia followed by 15 minutes of reoxygenation. A 12-hour period of hypoxia induced cell death in 60% of BAECs (48+/-5% apoptosis, 12+/-4% necrosis). Early and late PC decreased hypoxia-induced apoptotic (25+/-5% and 28+/-4%, respectively) and necrotic (6+/-3%, and 8+/-2%, respectively) cell death. Consistently, hypoxia-induced caspase-3 cleavage was reduced by PC. Pretreatment with H89 (protein kinase A [PKA] inhibitor), LY294002 (phosphatidyl-inositol-3-kinase [PI3K] inhibitor), and N-acetyl-cysteine (antioxidant) abrogated late PC-induced cell protection, whereas inhibition of protein kinase C by Go6983, and of nitric oxide synthesis by L-NAME,1400W and bovine eNOS siRNA did not. In addition, in early and late PC, PKA physically interacted with the phosphorylated form of Akt, suggesting that PKA is required for Akt phosphorylation. Expression of PKA and Akt dominant negative mutants inhibited ischemic late PC-induced protection, indicating that these kinases play a key role in late PC-mediated cell protection. Late ischemic PC protects BAECs against hypoxia through PKA- and PI3K-dependent activation of Akt.

Helium-induced late preconditioning in the rat heart in vivo

A recent study showed that the noble gas helium induces early myocardial preconditioning. Cyclooxygenase-2 (COX-2) has been shown to be an important mediator in the signal transduction of late preconditioning. In the present study, we investigated whether helium induces late preconditioning in a concentration-dependent, time-dependent, or in both manner and whether COX-2 activity, mitochondrial function, or both are involved. The study was performed in male Wistar rats and consisted of two parts. In part 1, late preconditioning was achieved by administration of 70%, 50%, 30%, and 10% helium for 15 min 24 h before ischaemia/reperfusion (I/R). Based on the findings of part 1, in additional experiments 30% helium was administered subsequently three and two days before I/R. Furthermore, additional rats were pretreated with the COX-2 inhibitor NS-398 (5 mg kg(-1)) with and without 30% helium. Additional experiments were performed for mitochondrial analysis. Helium concentrations of 70%, 50%, and 30% but not 10% reduced infarct size [He-LPC 70: 37(13)%, He-LPC 50: 34(16)%, He-LPC 30: 40(9)%; each P<0.05 vs 55(8)%, He-LPC 10: 53(4)%; P>0.05 vs CONTROL]. Repeated administration of helium did not further enhance cardioprotection. NS-398 completely abolished cardioprotection by 30% helium [He-LPC 30+NS-398: 57(9)%; P<0.05 vs He-LPC 30] but had itself no effect on infarct size [NS-398: 55(9)%; P>0.05 vs CONTROL]. There were no differences in mitochondrial function after helium preconditioning. Helium induces late preconditioning. Cardioprotection is already maximal with administration of one cycle of 30% helium and is abolished by functional blockade of COX-2 activity.

A Novel Role of MicroRNA in Late Preconditioning

MicroRNAs (miRNAs) are noncoding RNAs of 18 to 24 nucleotides that are involved in posttranscriptional regulation of protein expression. Their role in ischemic preconditioning (IPC) is currently unknown. We hypothesized that miRNAs induced after IPC in the heart may create a preconditioned phenotype through upregulating proteins including endothelial nitric oxide synthase (eNOS)/inducible nitric oxide synthase (iNOS) and heat shock protein (HSP)70, which are implicated in the late-phase protection of IPC. miRNAs were extracted from hearts of ICR mice following IPC. The purified miRNAs were injected in vivo into the left ventricular wall of mice, and, 48 hours later, the hearts were subjected to regional ischemia/reperfusion injury by left anterior descending artery ligation for 30 minutes followed by reperfusion for 24 hour. IPC caused no changes in miRNA-23b and miRNA-483 whereas miRNA-1, miRNA-21and miRNA-24 were significantly increased. The IPC-miRNA treatment caused an increase in eNOS mRNA and protein, whereas iNOS was not changed. HSF-1 (heat shock transcription factor 1) and HSP70 were also increased with IPC-miRNA treatment versus control. Moreover, injection of IPC-miRNA protected the hearts against ischemia/reperfusion injury, as shown by a reduction of infarct size as compared with saline or non-IPC miRNA-treated control. We conclude that IPC-induced miRNAs trigger cardioprotection similar to the delayed phase of IPC, possibly through upregulating eNOS, HSP70, and the HSP70 transcription factor HSF-1.