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1.  Targeting Cardiac Mast Cells: Pharmacological Modulation of the Local Renin-Angiotensin System 
Current Pharmaceutical Design  2011;17(34):3744-3752.
Enhanced production of angiotensin II and excessive release of norepinephrine in the ischemic heart are major causes of arrhythmias and sudden cardiac death. Mast cell-dependent mechanisms are pivotal in the local formation of angiotensin II and modulation of norepinephrine release in cardiac pathophysiology. Cardiac mast cells increase in number in myocardial ischemia and are located in close proximity to sympathetic neurons expressing angiotensin AT1- and histamine H3-receptors. Once activated, cardiac mast cells release a host of potent pro-inflammatory and pro-fibrotic cytokines, chemokines, preformed mediators (e.g., histamine) and proteases (e.g., renin). In myocardial ischemia, angiotensin II (formed locally from mast cell-derived renin) and histamine (also released from local mast cells) respectively activate AT1- and H3-receptors on sympathetic nerve endings. Stimulation of angiotensin AT1-receptors is arrhythmogenic whereas H3-receptor activation is cardioprotective. It is likely that in ischemia/reperfusion the balance may be tipped toward the deleterious effects of mast cell renin, as demonstrated in mast cell-deficient mice, lacking mast cell renin and histamine in the heart. In these mice, no ventricular fibrillation occurs at reperfusion following ischemia, as opposed to wild-type hearts which all fibrillate. Preventing mast cell degranulation in the heart and inhibiting the activation of a local reninangiotensin system, hence abolishing its detrimental effects on cardiac rhythmicity, appears to be more significant than the loss of histamine-induced cardioprotection. This suggests that therapeutic targets in the treatment of myocardial ischemia, and potentially congestive heart failure and hypertension, should include prevention of mast cell degranulation, mast cell renin inhibition, local ACE inhibition, ANG II antagonism and H3-receptor activation.
PMCID: PMC3298860  PMID: 22103845
arrhythmias; cardiac renin-angiotensin system; histamine H3-receptors; mast-cell renin; myocardial ischemia-reperfusion; norepinephrine; sensory and sympathetic nerve endings; sodium-proton exchanger
2.  Cardiac mast cell–derived renin promotes local angiotensin formation, norepinephrine release, and arrhythmias in ischemia/reperfusion 
Journal of Clinical Investigation  2006;116(4):1063-1070.
Having identified renin in cardiac mast cells, we assessed whether its release leads to cardiac dysfunction. In Langendorff-perfused guinea pig hearts, mast cell degranulation with compound 48/80 released Ang I–forming activity. This activity was blocked by the selective renin inhibitor BILA2157, indicating that renin was responsible for Ang I formation. Local generation of cardiac Ang II from mast cell–derived renin also elicited norepinephrine release from isolated sympathetic nerve terminals. This action was mediated by Ang II-type 1 (AT1) receptors. In 2 models of ischemia/reperfusion using Langendorff-perfused guinea pig and mouse hearts, a significant coronary spillover of renin and norepinephrine was observed. In both models, this was accompanied by ventricular fibrillation. Mast cell stabilization with cromolyn or lodoxamide markedly reduced active renin overflow and attenuated both norepinephrine release and arrhythmias. Similar cardioprotection was observed in guinea pig hearts treated with BILA2157 or the AT1 receptor antagonist EXP3174. Renin overflow and arrhythmias in ischemia/reperfusion were much less prominent in hearts of mast cell–deficient mice than in control hearts. Thus, mast cell–derived renin is pivotal for activating a cardiac renin-angiotensin system leading to excessive norepinephrine release in ischemia/reperfusion. Mast cell–derived renin may be a useful therapeutic target for hyperadrenergic dysfunctions, such as arrhythmias, sudden cardiac death, myocardial ischemia, and congestive heart failure.
PMCID: PMC1421347  PMID: 16585966
3.  Activation of aldehyde dehydrogenase 2 (ALDH2) confers cardioprotection in protein kinase C epsilon (PKCε) knockout mice 
Acute administration of ethanol can reduce cardiac ischemia/reperfusion injury. Previous studies demonstrated that the acute cytoprotective effect of ethanol on the myocardium is mediated by protein kinase C epsilon (PKCε). We recently identified aldehyde dehydrogenase 2 (ALDH2) as an PKCε substrate, whose activation is necessary and sufficient to confer cardioprotection in vivo. ALDH2 metabolizes cytotoxic reactive aldehydes, such as 4-hydroxy-2-nonenal (4-HNE), which accumulate during cardiac ischemia/reperfusion. Here, we used a combination of PKCε knockout mice and a direct activator of ALDH2, Alda-44, to further investigate the interplay between PKCε and ALDH2 in cardioprotection. We report that ethanol preconditioning requires PKCε, whereas direct activation of ALDH2 reduces infarct size in both wild type and PKCε knockout hearts. Our data suggest that ALDH2 is downstream of PKCε in ethanol preconditioning and that direct activation of ALDH2 can circumvent the requirement of PKCε to induce cytoprotection. We also report that in addition to ALDH2 activation, Alda-44 prevents 4-HNE induced inactivation of ALDH2 by reducing the formation of 4-HNE-ALDH2 protein adducts. Thus, Alda-44 promotes metabolism of cytotoxic reactive aldehydes that accumulate in ischemic myocardium. Taken together, our findings suggest that direct activation of ALDH2 may represent a method of harnessing the cardioprotective effect of ethanol without the side effects associated with alcohol consumption.
PMCID: PMC2837767  PMID: 19913552
4.  Remote ischemic preconditioning of cardiomyocytes inhibits the mitochondrial permeability transition pore independently of reduced calcium‐loading or sarcKATP channel activation 
Physiological Reports  2014;2(11):e12231.
Ischemic preconditioning (IPC) inhibits Ca2+‐loading during ischemia which contributes to cardioprotection by inhibiting mechanical injury due to hypercontracture and biochemical injury through mitochondrial permeability transition (MPT) pores during reperfusion. However, whether remote‐IPC reduced Ca2+‐loading during ischemia and its subsequent involvement in inhibiting MPT pore formation during reperfusion has not been directly shown. We have developed a cellular model of remote IPC to look at the impact of remote conditioning on Ca2+‐regulation and MPT pore opening during simulated ischemia and reperfusion, using fluorescence microscopy. Ventricular cardiomyocytes were isolated from control rat hearts, hearts preconditioned with three cycles of ischemia/reperfusion or naïve myocytes remotely conditioned with effluent collected from preconditioned hearts. Both conventional‐IPC and remote‐IPC reduced the loss of Ca2+‐homeostasis and contractile function following reenergization of metabolically inhibited cells and protected myocytes against ischemia/reperfusion injury. However, only conventional‐IPC reduced the Ca2+‐loading during metabolic inhibition and this was independent of any change in sarcKATP channel activity but was associated with a reduction in Na+‐loading, reflecting a decrease in Na/H exchanger activity. Remote‐IPC delayed opening of the MPT pores in response to ROS, which was dependent on PKCε and NOS‐signaling. These data show that remote‐IPC inhibits MPT pore opening to a similar degree as conventional IPC, however, the contribution of MPT pore inhibition to protection against reperfusion injury is independent of Ca2+‐loading in remote IPC. We suggest that inhibition of the MPT pore and not Ca2+‐loading is the common link in cardioprotection between conventional and remote IPC.
Remote ischemic preconditioning (IPC) provides a similar level of protection against ischemia–reperfusion injury to that of conventional‐IPC. This study shows that unlike conventional‐IPC, this was independent of any reduction in Na or Ca2+‐loading during the simulated ischemic event but results from a direct PKCε‐dependent inhibition of the mitochondrial permeability transition pore.
PMCID: PMC4255825  PMID: 25428953
Ca2+‐Loading; ischemic preconditioning; MPT pore; remote ischemic preconditioning; sodium/hydrogen exchanger
5.  Possible involvement of caveolin in attenuation of cardioprotective effect of ischemic preconditioning in diabetic rat heart 
Nitric oxide (NO) has been noted to produce ischemic preconditioning (IPC)-mediated cardioprotection. Caveolin is a negative regulator of NO, which inhibits endothelial nitric oxide synthase (eNOS) by making caveolin-eNOS complex. The expression of caveolin is increased during diabetes mellitus (DM). The present study was designed to investigate the involvement of caveolin in attenuation of the cardioprotective effect of IPC during DM in rat.
Experimental DM was induced by single dose of streptozotocin (50 mg/Kg, i.p,) and animals were used for experiments four weeks later. Isolated heart was mounted on Langendorff's apparatus, and was subjected to 30 min of global ischemia and 120 min of reperfusion. IPC was given by four cycles of 5 min of ischemia and 5 min of reperfusion with Kreb's-Henseleit solution (K-H). Extent of injury was measured in terms of infarct size by triphenyltetrazolium chloride (TTC) staining, and release of lactate dehydrogenase (LDH) and creatin kinase-MB (CK-MB) in coronary effluent. The cardiac release of NO was noted by measuring the level of nitrite in coronary effluent.
IPC- induced cardioprotection and release of NO was significantly decreased in diabetic rat heart. Pre-treatment of diabetic rat with daidzein (DDZ) a caveolin inhibitor (0.2 mg/Kg/s.c), for one week, significantly increased the release of NO and restored the attenuated cardioprotective effect of IPC. Also perfusion of sodium nitrite (10 μM/L), a precursor of NO, significantly restored the lost effect of IPC, similar to daidzein in diabetic rat. Administration of 5-hydroxy deaconate (5-HD), a mito KATP channel blocker, significantly abolished the observed IPC-induced cardioprotection in normal rat or daidzein and sodium nitrite perfused diabetic rat heart alone or in combination.
Thus, it is suggested that attenuation of the cardioprotection in diabetic heart may be due to decrease the IPC mediated release of NO in the diabetic myocardium, which may be due to up -regulation of caveolin and subsequently decreased activity of eNOS.
PMCID: PMC3142229  PMID: 21745415
6.  Role of phosphoinositide 3-kinase IA (PI3K-IA) activation in cardioprotection induced by ouabain preconditioning 
Acute myocardial infarction, the clinical manifestation of ischemia-reperfusion (IR) injury, is a leading cause of death worldwide. Like ischemic preconditioning (IPC) induced by brief episodes of ischemia and reperfusion, ouabain preconditioning (OPC) mediated by Na/K-ATPase signaling protects the heart against IR injury. Class I PI3K activation is required for IPC, but its role in OPC has not been investigated. While PI3K-IB is critical to IPC, studies have suggested that ouabain signaling is PI3K-IA-specific. Hence, a pharmacological approach was used to test the hypothesis that OPC and IPC rely on distinct PI3K-I isoforms. In Langendorff-perfused mouse hearts, OPC was initiated by 4 min of ouabain 10 μM and IPC was triggered by 4 cycles of 5 min ischemia and reperfusion prior to 40 min of global ischemia and 30 min of reperfusion. Without affecting PI3K-IB, ouabain doubled PI3K-IA activity and Akt phosphorylation at Ser473. IPC and OPC significantly preserved cardiac contractile function and tissue viability as evidenced by left ventricular developed pressure and end-diastolic pressure recovery, reduced lactate dehydrogenase release, and decreased infarct size. OPC protection was blunted by the PI3K-IA inhibitor PI-103, but not by the PI3K-IB inhibitor AS-604850. In contrast, IPC-mediated protection was not affected by PI-103 but was blocked by AS-604850, suggesting that PI3K-IA activation is required for OPC while PI3K-IB activation is needed for IPC. Mechanistically, PI3K-IA activity is required for ouabain-induced Akt activation but not PKCε translocation. However, in contrast to PKCε translocation which is critical to protection, Akt activity was not required for OPC. Further studies shall reveal the identity of the downstream targets of this new PI3K IA-dependent branch of OPC. These findings may be of clinical relevance in patients at risk for myocardial infarction with underlying diseases and/or medication that could differentially affect the integrity of cardiac PI3K-IA and IB pathways.
PMCID: PMC4827870  PMID: 25575882
preconditioning; PI3K; ischemia-reperfusion injury; Na/K-ATPase
7.  Isoflurane Preconditioning Confers Cardioprotection by Activation of ALDH2 
PLoS ONE  2013;8(2):e52469.
The volatile anesthetic, isoflurane, protects the heart from ischemia/reperfusion (I/R) injury. Aldehyde dehydrogenase 2 (ALDH2) is thought to be an endogenous mechanism against ischemia-reperfusion injury possibly through detoxification of toxic aldehydes. We investigated whether cardioprotection by isoflurane depends on activation of ALDH2.Anesthetized rats underwent 40 min of coronary artery occlusion followed by 120 min of reperfusion and were randomly assigned to the following groups: untreated controls, isoflurane preconditioning with and without an ALDH2 inhibitor, the direct activator of ALDH2 or a protein kinase C (PKCε) inhibitor. Pretreatment with isoflurane prior to ischemia reduced LDH and CK-MB levels and infarct size, while it increased phosphorylation of ALDH2, which could be blocked by the ALDH2 inhibitor, cyanamide. Isolated neonatal cardiomyocytes were treated with hypoxia followed by reoxygenation. Hypoxia/reoxygenation (H/R) increased cardiomyocyte apoptosis and injury which were attenuated by isoflurane and forced the activation of ALDH2. In contrast, the effect of isoflurane-induced protection was almost abolished by knockdown of ALDH2. Activation of ALDH2 and cardioprotection by isoflurane were substantially blocked by the PKCε inhibitor. Activation of ALDH2 by mitochondrial PKCε plays an important role in the cardioprotection of isoflurane in myocardium I/R injury.
PMCID: PMC3585331  PMID: 23468836
8.  Loss of ischaemic preconditioning in ovariectomized rat hearts: possible involvement of impaired protein kinase C ε phosphorylation 
Cardiovascular Research  2008;79(3):387-394.
The aims of this study were to determine whether chronic oestrogen withdrawal influences the development of ischaemic preconditioning (IPC) in female hearts, to investigate the mechanism whereby IPC is impaired, and to assess whether direct activation of protein kinase C (PKC) can mimic IPC in female hearts with chronic oestrogen depletion.
Methods and results
We performed Sham-operation (Sham) or bilateral ovariectomy on 16-week-old Sprague–Dawley female rats. Ovariectomized rats were randomized to subcutaneous implantation of 17β-estradiol (OxE) or placebo (OxP) pellets. Four weeks later, isolated, perfused hearts were subjected to 30 min of ischaemia followed by 120 min of reperfusion with or without three cycles of 5 min ischaemia/5 min reperfusion. The cardioprotective effect of IPC was completely lost in the OxP group. Western immunoblots revealed that in the OxP group, IPC failed to translocate PKCε to the membranous fraction and that phosphorylation of PKCε (Ser729) and phosphoinositide-dependent kinase (PDK) 1 (Ser241) was impaired. Oestrogen replacement restored the IPC effect, the translocation and phosphorylation of PKCε, and the phosphorylation of PDK1. In the OxP group, pre-treatment with a PKCε selective activator peptide (Ψ–εRACK) mimicked the IPC effect. Pre-treatment with a phosphatidylinositol-3 kinase inhibitor before IPC abrogated the translocation and phosphorylation of PKCε in the Sham group.
The cardioprotective effect of IPC is lost in female hearts with chronic oestrogen withdrawal and this is due, at least in part, to impaired translocation and phosphorylation of PKCε. Selective activation of PKCε-mediated signalling can fully restore the IPC effect in a manner analogous to oestrogen replacement.
PMCID: PMC2492728  PMID: 18390563
Oestrogen; Gender; Myocardial infarction; Protein kinase C; Reperfusion injury
Journal of molecular and cellular cardiology  2013;64:10.1016/j.yjmcc.2013.08.005.
It is believed that the diabetic myocardium is refractory to cardioprotection by ischemic preconditioning (IPC) mainly because of impaired insulin signaling to posphatidylinositol 3-kinase (PI3K) and protein kinase B (PKB or Akt). However, human as well as animal studies have clearly showed that hearts of type 2 diabetic humans and animals may exhibit increased signaling through PI3K-Akt but yet are resistant to cardioprotection by IPC or ischemic post-conditioning. Therefore, this study was designed to determine whether activation of insulin signaling prior to IPC is detrimental for cardioprotection and to assess the role of insulin receptors (IRs) and Akt in mediating this effect. Wild-type (WT) hearts, hearts lacking IRs or hearts expressing an active form of Akt (myrAkt1) were perfused ex vivo using a Langendorff preparation and were subjected to IPC (3 cycles of 5 min ischemia followed by 5 min reflow before 30 min no flow ischemia and then by 45 min reperfusion) in the presence or absence of 1 nmol/L insulin. Interestingly, whereas insulin was protective against I/R (30 min no flow ischemia and 45 min reperfusion), it completely abolished cardioprotection by IPC in WT hearts but not in mice lacking insulin receptors (IRs) in cardiomyocytes (CIRKO) or in all cardiac cells (TIRKO). The suppression of IPC-mediated cardioprotection was mediated through downstream signaling to Akt and Gsk3β. In addition, transgenic induction of Akt in the heart was sufficient to abrogate IPC even when insulin was absent, further confirming the involvement of Akt in insulin’s suppression of cardioprotection by IPC. These data provide evidence that excessive insulin signaling to Akt is detrimental for cardioprotection by IPC and could explain the failure of the diabetic myocardium to precondition.
PMCID: PMC3835741  PMID: 23994159
insulin; cardioprotection; insulin signaling; ischemia; reperfusion
10.  The alpha1 isoform of soluble guanylate cyclase regulates cardiac contractility but is not required for ischemic preconditioning 
Basic Research in Cardiology  2011;106(4):635-643.
Nitric oxide (NO)-dependent soluble guanylate cyclase (sGC) activation is an important component of cardiac signal transduction pathways, including the cardioprotective signaling cascade induced by ischemic preconditioning (IPC). The sGCα subunit, which binds to the common sGCβ1 subunit, exists in two different isoforms, sGCα1 and sGCα2, but their relative physiological roles remain unknown. In the present study, we studied Langendorff-perfused isolated hearts of genetically engineered mice lacking functional sGCα1 (sGCα1KO mice), which is the predominant isoform in the heart. Our results show that the loss of sGCα1 has a positive inotropic and lusitropic effect on basal cardiac function, indicating an important role for sGCα1 in regulating basal myocardial contractility. Surprisingly, IPC led to a similar 35–40% reduction in infarct size and concomitant protein kinase Cε (PKCε) phosphorylation in both wild-type (WT) and sGCα1KO hearts subjected to 40 min of global ischemia and reperfusion. Inhibition of the activation of all sGC isoforms by 1H-[1,2,4]oxadiazolo[4,3-a]quinoxaline-1-one (ODQ, 10 μmol/L) completely abolished the protection by IPC in WT and sGCα1KO hearts. NO-stimulated cGMP production was severely attenuated in sGCα1KO hearts compared to WT hearts, indicating that the sGCα2 isoform only produces minute amounts of cGMP after NO stimulation. Taken together, our results indicate that although sGCα1 importantly regulates cardiac contractility, it is not required for cardioprotection by IPC. Instead, our results suggest that possibly only minimal sGC activity, which in sGCα1KO hearts is provided by the sGCα2 isoform, is sufficient to transduce the cardioprotective signal induced by IPC via phosphorylation of PKCε.
PMCID: PMC3375061  PMID: 21394564
Soluble guanylate cyclase; Ischemic preconditioning; Isolated heart; Contractility; Nitric oxide
11.  Mitochondrial import of PKCε is mediated by HSP90: a role in cardioprotection from ischaemia and reperfusion injury 
Cardiovascular Research  2010;88(1):83-92.
Protein kinase C epsilon (PKCε) is critical for cardiac protection from ischaemia and reperfusion (IR) injury. PKCε substrates that mediate cytoprotection reside in the mitochondria. However, the mechanism enabling mitochondrial translocation and import of PKCε to enable phosphorylation of these substrates is not known. Heat shock protein 90 (HSP90) is a cytoprotective protein chaperone that participates in mitochondrial import of a number of proteins. Here, we investigated the role of HSP90 in mitochondrial import of PKCε.
Methods and results
Using an ex vivo perfused rat heart model of IR, we found that PKCε translocates from the cytosol to the mitochondrial fraction following IR. Immunogold electron microscopy and mitochondrial fractionation demonstrated that following IR, mitochondrial PKCε is localized within the mitochondria, on the inner mitochondrial membrane. Pharmacological inhibition of HSP90 prevented IR-induced interaction between PKCε and the translocase of the outer membrane (Tom20), reduced mitochondrial import of PKCε, and increased necrotic cell death by ∼70%. Using a rational approach, we designed a 7-amino acid peptide activator of PKCε, derived from an HSP90 homologous sequence located in the C2 domain of PKCε (termed ψεHSP90). Treatment with this peptide (conjugated to the cell permeating TAT protein-derived peptide, TAT47–57) increased PKCε–HSP90 protein–protein interaction, enhanced mitochondrial translocation of PKCε, increased phosphorylation and activity of an intra-mitochondrial PKCε substrate, aldehyde dehydrogenase 2, and reduced cardiac injury in ex vivo and in vivo models of myocardial infarction.
Our results suggest that HSP90-mediated mitochondrial import of PKCε plays an important role in the protection of the myocardium from IR injury.
PMCID: PMC2936125  PMID: 20558438
Protein kinase C epsilon; Mitochondria; Protein–protein interaction; Ischaemia reperfusion; Heat shock protein 90
12.  A kallidin-like peptide is a protective cardiac kinin, released by ischaemic preconditioning of rat heart 
British Journal of Pharmacology  2005;146(7):952-957.
Bradykinin is thought to play a major role among the endogenous cardioprotective candidates of ischaemic preconditioning (IPC). Little attention has been paid to the fact that in the tissue kallidin (KAL), rather than bradykinin might be the physiological mediator of the kallikrein–kinin system. In order to evaluate the importance of one or the other peptide the release and effect of both kinins has been investigated in isolated rat hearts following IPC.Bradykinin- and a KAL-like peptide were measured in the effluent of the rat isolated Langendorff heart with two different specific radioimmunoassays. The creatine kinase activity in the effluent was judged as degree of cardiac injury caused by ischaemia.During IPC, which consists of three 5 min no-flow and 5 min reperfusion cycles prior to the 30 min ischaemia, the bradykinin level in the effluent did not change significantly (15.4–19.4 pg ml−1). In the control group the bradykinin levels were 15.9–16.6 pg ml−1.During IPC KAL-like peptide (Arg1-, instead of Lys1-KAL), which has recently been verified by mass spectrometry, displays 5.8-fold higher levels in the effluent and significantly increases in the same time interval from 90.4 to 189 pg ml−1.After 30 min ischaemia the bradykinin levels in the IPC group were not significantly different to those of the control group (18.7 vs 14.4 pg ml−1). The KAL-like peptide levels in the IPC group vs the control group were 105 vs 86.1 pg ml−1.By the 30 min ischaemia the creatine kinase activity in the IPC group increased from 0.367 to 8.93 U l−1 (before and 10–30 min after ischaemia). In the control group during the same time period the creatine kinase levels increased from 0.277 to 34.9 U l−1. The low increase in creatine kinase activity following IPC was taken as equivalent of the cardioprotective action. A KAL antibody or HOE140 (kinin B2-receptor antagonist) completely abolished this beneficial effect of IPC (36.6 and 53.0 U l−1) when added to the perfusion medium during the reperfusion cycles of IPC prior to the 30 min ischaemia.Our data suggest that in rat hearts KAL-like peptide rather than bradykinin is the physiological compound activated by IPC and acting via the cardiac kinin B2-receptor. Thus, endogenously generated KAL-like peptide seems to play a major role in the cardioprotection of IPC.
PMCID: PMC1751226  PMID: 16231012
Myocardial ischaemic preconditioning; isolated perfused rat hearts; bradykinin; kallidin-like peptide; HOE140; kallidin antiserum; creatine kinase activity
13.  Protein Kinase C Protects Preconditioned Rabbit Hearts by Increasing Sensitivity of Adenosine A2b-Dependent Signaling During Early Reperfusion 
Although protein kinase C (PKC) plays a key role in ischemic preconditioning (IPC), the actual mechanism of that protection is unknown. We recently found that protection from IPC requires activation of adenosine receptors during early reperfusion. We, therefore, hypothesized PKC might act to increase the heart’s sensitivity to adenosine. IPC limited infarct size in isolated rabbit hearts subjected to 30-min regional ischemia/2-h reperfusion and IPC’s protection was blocked by the PKC inhibitor chelerythrine given during early reperfusion revealing involvement of PKC at reperfusion. Similarly chelerythrine infused in the early reperfusion period blocked the increased phosphorylation of the protective kinases Akt and ERK1/2 observed after IPC. Infusing phorbol 12-myristate 13-acetate (PMA), a PKC activator, during early reperfusion mimicked IPC’s protection. As expected, the protection triggered by PMA at reperfusion was blocked by chelerythrine, but surprisingly it was also blocked by MRS1754, an adenosine A2b receptor–selective antagonist, suggesting that PKC was somehow facilitating signaling from the A2b receptors. NECA [5′-(N-ethylcarboxamido) adenosine], a potent but not selective A2b receptor agonist, increased phosphorylation of Akt and ERK1/2 in a dose-dependent manner. Pretreating hearts with PMA or brief preconditioning ischemia had no effect on phosphorylation of Akt or ERK1/2 per se, but markedly lowered the threshold for NECA to induce their phosphorylation. BAY 60-6583, a highly selective A2b agonist, also caused phosphorylation of ERK 1/2 and Akt. MRS1754 prevented phosphorylation induced by BAY 60-6583. BAY 60-6583 limited infarct size when given to ischemic hearts at reperfusion. These results suggest that activation of cardiac A2b receptors at reperfusion is protective, but because of the very low affinity of the receptors endogenous cardiac adenosine is unable to trigger their signaling. We propose that the key protective event in IPC occurs when PKC increases the heart’s sensitivity to adenosine so that endogenous adenosine can activate A2b-dependent signaling.
PMCID: PMC2729547  PMID: 17632123
adenosine A2b receptors; BAY 60-6583; NECA; preconditioning; protein kinase C
14.  Angiotensin II and ischemic preconditioning synergize to improve mitochondrial function while showing additive effects on ventricular post-ischemic recovery 
Recent studies indicate that the cardioprotective effects of ischemic preconditioning (IPC) against sustained ischemia/reperfusion (IR) can be replicated by angiotensin II (Ang II). However, it is not clear whether IPC and Ang II-induced preconditioning (APC) act through similar mechanisms or synergize to enhance cardioprotection. In this study, Langendorff-perfused rat hearts were subjected to IPC, APC or their combination (IPC/APC) followed by IR. IPC and less potently APC, significantly increased the percent recovery of the left ventricular developed-pressure, the first derivative of developed pressure and the rate pressure product compared to control. Furthermore, the post-ischemic recovery of the heart was significantly higher for IPC/APC compared to IPC or APC. The improvements in cardiac function by IPC, APC and IPC/APC were associated with similar reductions in LDH release and infarct size. However, a significant improvement in mitochondrial respiration was observed with IPC/APC. The post-ischemic recovery observed with APC and IPC/APC was inhibited by treatment with losartan, an Ang II type-1 receptor blocker, during the preconditioning phase but not by chelerythrine, a pan-PKC inhibitor. Both drugs, however, abolished the enhanced mitochondrial respiration by IPC/APC. Altogether, these results indicate that APC and IPC interact through mechanisms that enhance cardioprotection by affecting cardiac function and mitochondrial respiration.
PMCID: PMC4126876  PMID: 24705171
Preconditioning; Angiotensin II; Mitochondria; Cardioprotection; Ischemia-Reperfusion
15.  Notch signaling activation contributes to cardioprotection provided by ischemic preconditioning and postconditioning 
Notch signaling is known to be activated following myocardial ischemia, but its role in cardioprotection provided by ischemic preconditioning (IPC) and ischemic postconditioning (IPost) remains unclear.
Lentiviral vectors were constructed to overexpress or knockdown N1ICD in H9c2 cardiomyocyte and rat heart exposed to ischemia reperfusion injury (IRI), IPC or IPost.
Notch1 signaling was activated during myocardial IPC and IPost, and could enhance cell viability and inhibit apoptosis. Furthermore, activated Notch1 signaling stabilized mitochondrial membrane potential and reduced reactive oxygen species induced by IRI. The cardioprotection provided by activated Notch1 signaling resembled that of IPC and IPost, which was related to Stat3 activation and regulation of apoptosis related proteins. Furthermore, in langendorff heart perfusion model, activated Notch1 signaling restored cardiac function, decreased lactate dehydrogenase release and limited infarct size after myocardial ischemia. Conclusions: Notch1 signaling is activated and mediates cardioprotection provided by IPC and Ipost. Notch1 signaling may represent a potential new pharmacologic mimic for cardioprotection of ischemic heart disease.
PMCID: PMC3853230  PMID: 24098939
Notch signaling; Mitochondrial permeability transition pore; Stat3, Ischemic preconditioning; Ischemic postconditioning
16.  Preconditionin effects of dexmedetomidine on myocardial ischemia/reperfusion injury in rats 
Background: Preconditioning might protect the myocardium against ischemia/ reperfusion injury by reducing infarct size and preventing arrhythmias. Dexmedetomidine (DEX) is a highly selective α2-agonist used for sedoanalgesia in daily anesthetic practice. The cardioprotective effects of DEX on infarct size and on the incidence of arrhythmias observed after regional ischemia/reperfusion injury in vivo have not been reported.
Objective: The aim of this study was to determine whether DEX exhibits a preconditioning effect and reduces infarct size and the incidence and duration of arrhythmias in a regional cardiac ischemia/reperfusion model in rats.
Methods: Adult male Sprague-Dawley rats were anesthetized with sodium thiopental and mechanically ventilated (0.9 mL/100 g at 60 strokes/min) through a cannula inserted into the trachea after tracheotomy. Cardiac ischemia was then produced by ligating the left main coronary artery for 30 minutes, followed by a reperfusion period of 120 minutes. Blood pressure (BP) and heart rate (HR) were monitored and echocardiograms (ECGs) were performed. Arrhythmia was scored based on incidence and duration. The animals were randomly divided into 3 groups. The ischemic preconditioning (IPC) group underwent 5 minutes of ischemia followed by 5 minutes of reperfusion before the 30-minute ischemia/120-minute reperfusion period. In the DEX group, intraperitoneal (IP) DEX 1 mL (100 μg/kg) was administered 30 minutes before the ischemia/ reperfusion period. In the control group, IP saline 1 mL was administered 30 minutes before the ischemia/reperfusion period. After reperfusion, the heart was excised, demarcated with saline and ethanol to identify the occluded and nonoccluded myocardium, and cut into slices ~2 mm thick, that were then stained and placed between 2 glass plates. The risk zone and the infarct zone were compared between groups. The investigator assessing the infarcts was blinded to the study group.
Results: Twenty-one adult (aged 4-6 months) male Sprague-Dawley rats weighing 280 to 360 g were included in the study; 7 rats were assigned to each group. BP, HR, and ECG readings were not significantly different between groups and did not change during the study. Arrythmias occurred during ischemia and reperfusion in all groups. The duration of the arrhythmias was significantly shorter and the arrhythmia score was significantly lower in the IPC group (all, P<0.05), compared with the control group; however, they were not significantly different in the DEX group. During the ischemic period, duration of ventricular tachycardia (VT) and ventricular premature contractions (VPC) in the DEX group was significantly longer than that observed in the IPC group (all, P<0.05). The duration of VPC was also significantly shorter than that observed in the control group (both, P<0.05). Duration of VT during the reperfusion period in the DEX group was significantly longer than that observed in both IPC and control groups (both, P<0.05). The mean (SD) percentage of damage was significantly lower in the IPC group (44.1% [2.0%]) and the DEX group (26.7% [2.0%]) compared with the control group (69.0% [3.0%]; both, P<0.05). The percentage of damage in the DEX group was also significantly lower compared with the IPC group (P<0.05).
Conclusions: This small, experimental in vivo study found that DEX was associated with reduced infarct size in ischemia/reperfusion injury in regional ischemia in this rat model but had no effect on the incidence of arrhythmias. Future studies are needed to clarify these findings.
PMCID: PMC3969917  PMID: 24692794
dexmedetomidine; preconditioning; cardiac ischemia/reperfusion
17.  Ouabain triggers preconditioning through activation of the Na+,K+-ATPase signaling cascade in rat hearts 
Cardiovascular research  2006;73(3):488-496.
Because ouabain activates several pathways that are critical to cardioprotective mechanisms such as ischemic preconditioning, we tested if this digitalis compound could protect the heart against ischemia-reperfusion injury through activation of the Na+,K+-ATPase/c-Src receptor complex.
Methods and Results
In Langendorff-perfused rat hearts, a short (4 min) administration of ouabain 10 μM followed by an 8-minute washout before 30 minutes of global ischemia and reperfusion improved cardiac function, decreased lactate dehydrogenase release and reduced infarct size by 40%. Western blot analysis revealed that ouabain activated the cardioprotective phospholipase Cγ1/protein kinase Cε (PLC-γ1/PKCε) pathway. Pre-treatment of the hearts with the Src kinase family inhibitor 4-amino-5-(4-chlorophenyl)-7-(t-butyl)pyrazolol[3,4-d]pyrimidine (PP2) blocked not only ouabain-induced activation of PLC-γ1/PKCε pathway, but also cardiac protection. This protection was also blocked by a PKCε translocation inhibitor peptide (PKCε TIP).
Short exposure to a low concentration of ouabain protects the heart against ischemia/reperfusion injury. This effect of ouabain on the heart is most likely due to the activation of the Na+,K+-ATPase/c-Src receptor complex and subsequent stimulation of key mediators of preconditioning, namely PLC-γ1 and PKCε.
PMCID: PMC1852501  PMID: 17157283
18.  Ischemic preconditioning reduces endoplasmic reticulum stress and upregulates hypoxia inducible factor-1α in ischemic kidney: the role of nitric oxide 
Although recent studies indicate that renal ischemic preconditioning (IPC) protects the kidney from ischemia-reperfusion (I/R) injury, the precise protective mechanism remains unclear. In the current study, we investigated whether early IPC could upregulate hypoxia inducible transcription factor-1α (HIF-1α) expression and could reduce endoplasmic reticulum (ER) stress after renal I/R and whether pharmacological inhibition of nitric oxide (NO) production would abolish these protective effects.
Kidneys of Wistar rats were subjected to 60 min of warm ischemia followed by 120 min of reperfusion (I/R group), or to 2 preceding cycles of 5 min ischemia and 5 min reperfusion (IPC group), or to intravenously injection of NG-nitro-L-arginine methylester (L-NAME, 5 mg/kg) 5 min before IPC (L-NAME+IPC group). The results of these experimental groups were compared to those of a sham-operated group. Sodium reabsorption rate, creatinine clearance, plasma lactate dehydrogenase (LDH) activity, tissues concentrations of malonedialdehyde (MDA), HIF-1α and nitrite/nitrate were determined. In addition, Western blot analyses were performed to identify the amounts of Akt, endothelial nitric oxide synthase (eNOS) and ER stress parameters.
IPC decreased cytolysis, lipid peroxidation and improved renal function. Parallely, IPC enhanced Akt phosphorylation, eNOS, nitrite/nitrate and HIF-1α levels as compared to I/R group. Moreover, our results showed that IPC increased the relative amounts of glucose-regulated protein 78 (GRP78) and decreased those of RNA activated protein kinase (PKR)-like ER kinase (PERK), activating transcription factor 4 (ATF4) and TNF-receptor-associated factor 2 (TRAF2) as judged to I/R group. However, pre treatment with L-NAME abolished these beneficial effects of IPC against renal I/R insults.
These findings suggest that early IPC protects kidney against renal I/R injury via reducing oxidative and ER stresses. These effects are associated with phosphorylation of Akt, eNOS activation and NO production contributing thus to HIF-1α stabilization. The beneficial impact of IPC was abolished when NO production is inhibited before IPC application.
PMCID: PMC3398272  PMID: 22252226
kidney; ischemia-reperfusion; ischemic preconditioning; Akt; eNOS, HIF1-α; ER stress
19.  AMPK-Regulated and Akt-Dependent Enhancement of Glucose Uptake Is Essential in Ischemic Preconditioning-Alleviated Reperfusion Injury 
PLoS ONE  2013;8(7):e69910.
Ischemic preconditioning (IPC) is a potent form of endogenous protection. However, IPC-induced cardioprotective effect is significantly blunted in insulin resistance-related diseases and the underlying mechanism is unclear. This study aimed to determine the role of glucose metabolism in IPC-reduced reperfusion injury.
Normal or streptozotocin (STZ)-treated diabetic rats subjected to 2 cycles of 5 min ischemia/5 min reperfusion prior to myocardial ischemia (30 min)/reperfusion (3 h). Myocardial glucose uptake was determined by 18F-fluorodeoxyglucose-positron emission tomography (PET) scan and gamma-counter biodistribution assay.
IPC exerted significant cardioprotection and markedly improved myocardial glucose uptake 1 h after reperfusion (P<0.01) as evidenced by PET images and gamma-counter biodistribution assay in ischemia/reperfused rats. Meanwhile, myocardial translocation of glucose transporter 4 (GLUT4) to plasma membrane together with myocardial Akt and AMPK phosphorylation were significantly enhanced in preconditioned hearts. Intramyocardial injection of GLUT4 siRNA markedly decreased GLUT4 expression and blocked the cardioprotection of IPC as evidence by increased myocardial infarct size. Moreover, the PI3K inhibitor wortmannin significantly inhibited activation of Akt and AMPK, reduced GLUT4 translocation, glucose uptake and ultimately, depressed IPC-induced cardioprotection. Furthermore, IPC-afforded antiapoptotic effect was markedly blunted in STZ-treated diabetic rats. Exogenous insulin supplementation significantly improved glucose uptake via co-activation of myocardial AMPK and Akt and alleviated ischemia/reperfusion injury as evidenced by reduced myocardial apoptosis and infarction size in STZ-treated rats (P<0.05).
The present study firstly examined the role of myocardial glucose metabolism during reperfusion in IPC using direct genetic modulation in vivo. Augmented glucose uptake via co-activation of myocardial AMPK and Akt in reperfused myocardium is essential to IPC-alleviated reperfusion injury. This intrinsic metabolic modulation and cardioprotective capacity are present in STZ-treated hearts and can be triggered by insulin.
PMCID: PMC3724784  PMID: 23922853
20.  Aldehyde dehydrogenase 2 in cardiac protection: a new therapeutic target? 
Trends in cardiovascular medicine  2009;19(5):158-164.
Mitochondrial aldehyde dehydrogenase 2 (ALDH2) is emerging as a key enzyme involved in cytoprotection in the heart. ALDH2 mediates both the detoxification of reactive aldehydes such as acetaldehyde and 4-hydroxy-2-nonenal (4-HNE) and the bioactivation of nitroglycerin (GTN) to nitric oxide (NO). In addition, chronic nitrate treatment results in ALDH2 inhibition and contributes to nitrate tolerance. Our lab recently identified ALDH2 to be a key mediator of endogenous cytoprotection. We reported that ALDH2 is phosphorylated and activated by the survival kinase protein kinase C epsilon (PKCε) and found a strong inverse correlation between ALDH2 activity and infarct size. We also identified a small molecule ALDH2 activator (Alda-1) which reduces myocardial infarct size induced by ischemia/reperfusion in vivo. In this review, we discuss evidence that ALDH2 is a key mediator of endogenous survival signaling in the heart, suggest possible cardioprotective mechanisms mediated by ALDH2, and discuss potential clinical implications of these findings.
PMCID: PMC2856486  PMID: 20005475
We applied a combined proteomic and metabolomic approach to obtain novel mechanistic insights in PKCε-mediated cardioprotection. Mitochondrial and cytosolic proteins from control and transgenic hearts with constitutively active or dominant negative PKCε were analyzed using difference in-gel electrophoresis (DIGE). Among the differentially expressed proteins were creatine kinase, pyruvate kinase, lactate dehydrogenase, and the cytosolic isoforms of aspartate amino transferase and malate dehydrogenase, the two enzymatic components of the malate aspartate shuttle, which is required for the import of reducing equivalents from glycolysis across the inner mitochondrial membrane. These enzymatic changes appeared to be dependent on PKCε activity, as they were not observed in mice expressing inactive PKCε. High-resolution proton nuclear magnetic resonance (1H-NMR) spectroscopy confirmed a pronounced effect of PKCε activity on cardiac glucose and energy metabolism: normoxic hearts with constitutively active PKCε had significantly lower concentrations of glucose, lactate, glutamine and creatine, but higher levels of choline, glutamate and total adenosine nucleotides. Moreover, the depletion of cardiac energy metabolites was slower during ischemia/reperfusion injury and glucose metabolism recovered faster upon reperfusion in transgenic hearts with active PKCε. Notably, inhibition of PKCε resulted in compensatory phosphorylation and mitochondrial translocation of PKCδ. Taken together, our findings are the first evidence that PKCε activity modulates cardiac glucose metabolism and provide a possible explanation for the synergistic effect of PKCδ and PKCε in cardioprotection.
PMCID: PMC3661410  PMID: 19027023
proteomics; metabolism; cardioprotection; protein kinase C
22.  Acute Hyperglycemia Abolishes Ischemic Preconditioning by Inhibiting Akt Phosphorylation: Normalizing Blood Glucose before Ischemia Restores Ischemic Preconditioning 
This study examined the hypothesis that acute hyperglycemia (HG) blocks ischemic preconditioning (IPC) by inhibiting Akt phosphorylation. Brief HG of approximately 400 mg/dL was induced in C57BL/6 mice via intraperitoneal injection of 20% dextrose (2 g/kg). All mice underwent 40 min LAD occlusion and 60 min reperfusion. The IPC protocol was 2 cycles of 5 min ischemia and 5 min reperfusion prior to index ischemia. Results. In control mice, infarct size (IF) was 51.7 ± 2.0 (% risk region). Preconditioning reduced IF by 50% to 25.8 ± 3.2 (P < 0.05 versus control). In HG mice, IF was significantly exacerbated to 58.1 ± 2.3. However, the effect of IPC completely disappeared in HG mice. Normalization of blood glucose with insulin 5 min before IPC recovered the cardioprotective effect. Administration of CCPA before index ischemia mimicked IPC effect. The cardioprotective effect of CCPA, not its chronotropic effect, completely disappeared in HG mice. Phosphorylation of cardiac tissue Akt before index ischemia was enhanced by IPC or CCPA but was significantly inhibited by HG in both groups. Normalization of glucose with insulin reversed the inhibition of Akt phosphorylation by HG. Conclusion. HG abolishes the cardioprotective effect of preconditioning by inhibiting Akt phosphorylation. Normalization of blood glucose with insulin suffices to recover the cardioprotective effect of preconditioning.
PMCID: PMC3858874  PMID: 24371503
23.  Regulatory T cells contribute to the protective effect of ischemic preconditioning in the kidney 
Kidney international  2010;77(9):771-780.
Ischemia-reperfusion is a major cause of acute kidney injury and inflammation has been well-established as a detrimental process in the pathogenesis of kidney ischemia reperfusion injury (IRI). The kidney has the ability to be preconditioned by a non-lethal period of ischemia, rendering the kidney refractory to further ischemia-induced dysfunction (ischemic preconditioning: IPC). Regulatory T (Treg) cells are lymphocytes that suppress immune responses. We hypothesized that IPC is partially mediated by Treg cells. To test this, a model of delayed IPC was used by subjecting mice to 24 min of bilateral renal IRI or sham surgery on day 0, then 28 min IRI on day 7 (IPC = IRI/IRI; non-IPC = Sham/IRI). IPC significantly inhibited the accumulation of neutrophils and macrophages, tubular necrosis and loss of kidney function induced by IRI. The initial 24 min IRI caused a significant increase in kidney CD4+CD25+FoxP3+ and CD4+CD25+IL-10+ Treg cells at 7 days of reperfusion. Use of a Treg cell-depleting antibody (PC61) in preconditioned mice reversed the effect of IPC on kidney neutrophil accumulation and partially inhibited the functional and histological protection of IPC. Adoptive transfer of Treg cells, prior to IR, in naïve mice, mimicked the protective and anti-inflammatory effects of IPC on the kidney. These results demonstrate that suppression of inflammation and a significant fraction of kidney protection, imparted by delayed IPC, is mediated by Treg cells.
PMCID: PMC2912287  PMID: 20164824
24.  Evidence that the acute phase of ischemic preconditioning does not require signaling by the A2B adenosine receptor 
Ischemic preconditioning (IPC) is a protective phenomenon in which brief ischemia renders the myocardium resistant to subsequent ischemic insults. Here, we used A2BAR gene knock-out (A2BKO)/β-galactosidase reporter gene knock-in mice and the A2BAR antagonist ATL-801 to investigate the potential involvement of the A2BAR in IPC, focusing on the acute phase of protection. Cardioprotection provided by acute IPC elicited by two 3-min occlusion/3-min reperfusion cycles was readily apparent in an isolated, Langendorff-perfused mouse heart model in studies using hearts from A2BKO mice. IPC equivalently improved the recovery of contractile function following 20 min of global ischemia and 45 min of reperfusion in both WT and A2BKO hearts by ~30–40%, and equivalently decreased the release of cardiac tropinin I during the reperfusion period (from 5,969±925 to 1,595±674 ng/g and 4,376±739 to 2,278±462 ng/g using WT and A2BKO hearts, respectively). Similarly, the infarct size-reducing capacity of acute IPC in an in vivo model of infarction was fully manifest in experiments using A2BKO mice, as well as in experiments using rats pretreated with ATL-801. We did observe, however, a marked reduction in infarct size in rats following administration of the selective A2BAR agonist BAY 60-658 (~25% reduction at a dose of 1.0 mg/kg). While supportive of its concept as a cardioprotective receptor, these experiments indicate that the mechanism of the early phase of IPC is not dependent on signaling by the A2BAR. We present the idea that the A2BAR may contribute to the later stages of IPC dependent on the induction of stress-responsive genes.
PMCID: PMC2958103  PMID: 20797398
25.  Limb ischemic preconditioning protects against contrast-induced nephropathy via renalase 
EBioMedicine  2016;9:356-365.
Clinical trials shows that remote ischemic preconditioning (IPC) can protect against contrast induced nephropathy (CIN) in risky patients, however, the exact mechanism is unclear. In this study, we explored whether renalase, an amine oxidase that has been previously shown to mediate reno-protection by local IPC, would also mediate the same effect elicited by remote IPC in animal model. Limb IPC was performed for 24 h followed by induction of CIN. Our results indicated that limb IPC prevented renal function decline, attenuated tubular damage and reduced oxidative stress and inflammation in the kidney. All those beneficial effects were abolished by silencing of renalase with siRNA. This suggests that similar to local IPC, renalase is also critically involved in limb IPC-elicited reno-protection. Mechanistic studies showed that limb IPC increased TNFα levels in the muscle and blood, and up-regulated renalase and phosphorylated IκBα expression in the kidney. Pretreatment with TNFα antagonist or NF-κB inhibitor, largely blocked renalase expression. Besides, TNFα preconditioning increased expression of renal renalase in vivo and in vitro, and attenuated H2O2 induced apoptosis in renal tubular cells. Collectively, our results suggest that limb IPC-induced reno-protection in CIN is dependent on increased renalase expression via activation of the TNFα/NF-κB pathway.
•Limb ischemic preconditioning (IPC) leads to renalase upregulation in kidney tissue.•Renalase is critically involved in limb IPC-elicited renal protection in contrast induced nephropathy.•Limb IPC induces renalase upregulation via activation of the tumor necrosis factor α (TNFα)/ nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) pathway.
Renalase, a kidney-secreted protein, serves as extracellular pro-survival signals and has been reported to participate in the local ischemic preconditioning (IPC) induced renal protection against ischemia-reperfusion injury. Whether renalase contributes to the beneficial effects of limb IPC on contrast induced nephropathy (CIN) remains unknown. This study revealed that limb IPC induced reno-protection in CIN was at least in part dependent on increased renalase expression, which is evidenced by our observations that knockdown of renalase abolished reno-protective effects conferred by limb IPC. The upregulation of renalase elicited by limb IPC may be mediated by activation of TNFα/NF-κB pathway.
PMCID: PMC4972520  PMID: 27333047
Limb ischemic preconditioning; Contrast induced nephropathy; Renalase; TNFα

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