Preconditioning In Heart Research Articles

Nitric oxide is involved in the cardioprotection of neonatal rat hearts, but not in neonatal ischemic postconditioning.

The cardioprotective effect of ischemic preconditioning (IPC) and ischemic postconditioning (IPoC) in adult hearts is mediated by nitric oxide (NO). During the early developmental period, rat hearts exhibit higher resistance to ischemia-reperfusion (I/R) injury, contain higher levels of serum nitrates, and their resistance cannot be further increased by IPC or IPoC. NOS blocker (L-NAME) lowers their high resistance. Wistar rat hearts (postnatal Days 1 and 10) were perfused according to Langendorff and exposed to 40 min of global ischemia followed by reperfusion with or without IPoC. NO and reactive oxygen species donors (DEA-NONO, SIN-1) and L-NAME were administered. Tolerance to ischemia decreased between Days 1 and 10. DEA-NONO (low concentrations) significantly increased tolerance to I/R injury on both Days 1 and 10. SIN-1 increased tolerance to I/R injury on Day 10, but not on Day 1. L-NAME significantly reduced resistance to I/R injury on Day 1, but actually increased resistance to I/R injury on Day 10. Cardioprotection by IPoC on Day 10 was not affected by either NO donors or L-NAME. It can be concluded that resistance of the neonatal heart to I/R injury is NO dependent, but unlike in adult hearts, cardioprotective interventions, such as IPoC, are most likely NO independent.

Donor heart preconditioning during orthotopic transplantation

Background. To date, there are about 500 patients in the heart transplant waiting list in Ukraine. The study included 20 donors for orthotopic heart transplantation. Their average age was 32.3 years. The study evaluated the preparation of the donor heart in terms of its protection against ischemia-reperfusion injury during transplantation and the effect of donor heart preconditioning in a recipient after orthotopic heart transplantation. Тhe purpose was to evaluate the effectiveness of donor heart preconditioning for increasing myocardial resistance to ischemia-reperfusion injury and its preparation for orthotopic transplantation. Materials and methods. The work is based on the results of 20 donors who were diagnosed with brain death and authorized for the use of transplantation of human anatomical materials. Then changes in the main biochemical parameters (lactate, troponin, acid-base balance, creatinine clearance, blood glucose) and the functional state of systemic hemodynamics (blood pressure, heart rate, central venous pressure, ejection fraction, cardiac index) were analyzed at the time of donor heart explantation. Results. It was found that in 100 % of donors, norepinephrine was used for inotropic support, in 40 % — dobutamine and in 25 % — dopamine. Lactate levels were higher than normal in 75 % of cases and troponin levels were increased in all donors, indicating a possible microcirculatory dysfunction that led to a deterioration in donor preconditioning and enhanced ischemia-reperfusion injury to the transplant. According to the correlation coefficient between time and cardiac index, there was a tendency to the deterioration in the donor’s condition depending on the time of making a decision about heart transplantation before heart explantation. Conclusions. The study showed that in 100 % of donors, norepinephrine was used for inotropic support — more often than dobutamine or dopamine. Lactate levels were higher than normal in 75 % of donors and troponin levels were increased in all donors, indicating a possible microcirculatory dysfunction that led to a deterioration in donor preconditioning and increased ischemia-reperfusion injury to the transplant. According to the correlation coefficient between time indicators and cardiac index, it is noted that the longer the time of authorization for orthotopic heart transplantation, the greater the deterioration in the donor’s condition, which is expressed in a decreased myocardial contractility. Based on the correlation coefficient between time indicators and troponin, it was concluded that the growth of troponin complexes was observed with an increase in the time of making a decision for obtaining permission to transplant human anatomical materials, which indicated the onset of ischemic changes in the myocardium.

GJA1-20k and Mitochondrial Dynamics.

Connexin 43 (Cx43) is the primary gap junction protein of mammalian heart ventricles and is encoded by the gene Gja1 which has a single coding exon and therefore cannot be spliced. We previously identified that Gja1 mRNA undergoes endogenous internal translation initiated at one of several internal AUG (M) start codons, generating N-terminal truncated protein isoforms that retain the C-terminus distal to the start site. GJA1-20k, whose translation initiates at mRNA M213, is usually the most abundant isoform in cells and greatly increases after ischemic and metabolic stress. GJA1-20k consists of a small segment of the last transmembrane domain and the complete C-terminus tail of Cx43, with a total size of about 20 kDa. The original role identified for GJA1-20k is as an essential subunit that facilitates the trafficking of full-length Cx43 hexameric hemichannels to cell-cell contacts, generating traditional gap junctions between adjacent cells facilitating, in cardiac muscle, efficient spread of electrical excitation. GJA1-20k deficient mice (generated by a M213L substitution in Gja1) suffer poor electrical coupling between cardiomycytes and arrhythmogenic sudden death two to 4 weeks after their birth. We recently identified that exogenous GJA1-20k expression also mimics the effect of ischemic preconditioning in mouse heart. Furthermore, GJA1-20k localizes to the mitochondrial outer membrane and induces a protective and DRP1 independent form of mitochondrial fission, preserving ATP production and generating less reactive oxygen species (ROS) under metabolic stress, providing powerful protection of myocardium to ischemic insult. In this manuscript, we focus on the detailed roles of GJA1-20k in mitochondria, and its interaction with the actin cytoskeleton.

Involvement of Estrogen Receptor and Mitochondrial KATP Channels in Cardioprotective Effect of Remote Aortic Preconditioning in Isolated Rat Heart

The present study was designed to investigate the role of estrogen receptor and KATP channel in cardioprotective effect of remote aortic preconditioning in rat heart. Remote preconditioning is a phenomenon in which brief episodes of ischemia and reperfusion to remote organs protect the target organ against sustained ischemia/ reperfusion induced injury. Protective effects of remote aortic preconditioning are well established in the heart, but their mechanisms still remain to be elucidated. Remote aortic preconditioning in rats was produced by introducing four episodes of ischemia and reperfusion, each comprising of 5 min occlusion and 5 min reperfusion, through abdominal aorta. Perfused rat heart was isolated and subjected to global ischemia for 30 min followed by reperfusion for 120 min. The degree of cardiac injury was assessed by analysing the level of lactate dehydrogenase, creatin kinase, reactive oxygen species and nitrite in coronary effluent. Myocardial infarct size was also estimated macroscopically using tetrazolium tri chloride staining. Ethylinestradiol (10 μg/kg, orally) as estrogen receptor agonist was noted to reproduce remote aortic preconditioning mediated cardioprotection in ovariectomized rat. However, administration of glibenclamide along with or prior to ethylinestradiol abolished cardioprotection. Moreover, glibenclamide a KATP channel blocker, abolish cardioprotective effect of remote aortic preconditioning with daidzein a caveolin inhibitor (0.2 mg/kg subcutaneous). Ethylinestradiol significantly increased the release of nitric oxide and restored the attenuated cardioprotective effect of remote aortic preconditioning. These data provide the evidence that estrogen receptor activation involved in cardioprotective effect of remote aortic preconditioning-mediated trough opening of KATP channels.

A Tangy Twist Review on Hog-Plum: <i>Spondias pinnata</i> (L.f.) Kurz

<em>Spondias pinnata</em> (L.f.) Kurz., belongs to the Anacardiaceae family, generally referred to as Indian Hog plum, a deciduous, glabrous tree with a healthy fruit to eat. Hog plum is a mild deciduous tree plant of high nutritional value, stubby calories and abundant in vegetable proteins, zinc, chitin, starch, vitamins and minerals. Traditional use of various parts of <em>S. pinnata</em> includes diarrhea, dysentery, stomach troubles, hyperacidity, wounds, sprain, rheumatism, gonorrhoea, tuberculosis, aphrodisiac, arrow poison antidote, dyspepsia, dysentery, ring worms, abscess painful joints, refrigerant, tonic, antiseptic, astringent, mental disorders, tuberculosis, vomiting and many more. A number of pharmacological activities were reported from several extracts of <em>S. pinnata</em> and its parts that include hypoglycemic, anti-cancer, ulcer-protective, antidiarrhoeal, anti-microbial, hepatoprotective, thrombolytic, anti-inflammatory, antiarthritic, analgesic, antipyretic, antihypertensive, anthelmintic, diuretic and laxative, anti-tuberculosis, cytotoxic, antioxidant, anti-hyperlipidemic, ischemia reperfusion injury and preconditioning of heart, anxiolytic, reduce side effects of chemotherapy, ameliorating, platelet aggregation inhibitory activity and acute and sub-chronic toxicity. A few phytochemicals were detailed on this plant. The chemical components of <em>S. pinnata</em> include different amino acids, carbohydrates, terpenoids, flavonoids, polysaccharides, steroids and so on. Various solvent extract and their gas chromatography-mass spectrometry analysis have confirmed the structures of a number of important phytoconstituents. Hence this review can be a good reference for researchers who would undertake further investigation about <em>S. pinnata</em>.

Effluent from ischemic preconditioned hearts confers cardioprotection independent of the number of preconditioning cycles.

Coronary effluent collected from ischemic preconditioning (IPC) treated hearts induces myocardial protection in non-ischemic-preconditioned hearts. So far, little is known about the number of IPC cycles required for the release of cardioprotective factors into the coronary effluent to successfully induce cardioprotection. This study investigated the cardioprotective potency of effluent obtained after various IPC cycles in the rat heart. Experiments were performed on isolated hearts of male Wistar rats, mounted onto a Langendorff system and perfused with Krebs-Henseleit buffer. In a first part, effluent was taken before (Con) and after each IPC cycle (Eff 1, Eff 2, Eff 3). IPC was induced by 3 cycles of 5 min of global myocardial ischemia followed by 5 minutes of reperfusion. In a second part, hearts of male Wistar rats were randomized to four groups (each group n = 4–5) and underwent 33 min of global ischemia followed by 60 min of reperfusion. The previously obtained coronary effluent was administered for 10 minutes before ischemia as a preconditioning stimulus. Infarct size was determined at the end of reperfusion by triphenyltetrazoliumchloride (TTC) staining. Infarct size with control effluent was 54±12%. Effluent obtained after IPC confers a strong infarct size reduction independent of the number of IPC cycles (Eff 1: 27±5%; Eff 2: 35±7%; Eff 3: 35±8%, each P<0.05 vs. Con). Effluent extracted after one cycle IPC is comparably protective as after two or three cycles IPC.

Long-chain free fatty acids inhibit ischaemic preconditioning of the isolated rat heart.

We recently reported that non-preconditioned hearts from diet-induced obese rats showed, compared to controls, a significant reduction in infarct size after ischaemia/reperfusion, whilst ischaemic preconditioning was without effect. In view of the high circulating FFA concentration in diet rats, the aims of the present study were to: (i) compare the effect of palmitate on the preconditioning potential of hearts from age-matched controls and diet rats (ii) elucidate the effects of substrate manipulation on ischaemic preconditioning. Substrate manipulation was done with dichloroacetate (DCA), which enhances glucose oxidation and decreases fatty acid oxidation. Isolated hearts from diet rats, age-matched controls or young rats, were perfused in the working mode using the following substrates: glucose (10mM); palmitate (1.2mM)/3% albumin) + glucose (10mM) (HiFA + G); palmitate (1.2mM/3% albumin) (HiFA); palmitate (0.4mM/3% albumin) + glucose(10mM) (LoFA + G); palmitate (0.4mM/3% albumin) (LoFA). Hearts were preconditioned with 3 × 5min ischaemia/reperfusion, followed by 35min coronary ligation and 60min reperfusion for infarct size determination (tetrazolium method) or 20min global ischaemia/10 or 30min reperfusion for Western blotting (ERKp44/42, PKB/Akt). Preconditioning of glucose-perfused hearts from age-matched control (but not diet) rats reduced infarct size, activated ERKp44/42 and PKB/Akt and improved functional recovery during reperfusion (ii) perfusion with HiFA + G abolished preconditioning and activation of ERKp44/42 (iii) DCA pretreatment largely reversed the harmful effects of HiFA. Hearts from non-preconditioned diet rats exhibited smaller infarcts, but could not be preconditioned, regardless of the substrate. Similar results were obtained upon substrate manipulation of hearts from young rats. Abolishment of preconditioning in diet rats may be due to altered myocardial metabolic patterns resulting from changes in circulating FA. The harmful effects of HiFA were attenuated by stimulation of glycolysis and inhibition of FA oxidation.

Diabetic animal fed with high-fat diet prevents the protective effect of myocardial ischemic preconditioning effect in isolated rat heart perfusion model.

Diabetic heart (diabetes mellitus [DM]) has been shown to attenuate the beneficial effect of ischemic preconditioning (IPC) in rat heart. But the effect of IPC on diabetic rat heart that develops myopathy remains unclear. This study was designed to test the impact of IPC on diabetic cardiomyopathy (DCM) rat heart. Male Wistar rats were grouped as (a) normal, (b) DM (streptozotocin: 65 mg/kg; fed with normal diet), and (c) DCM (streptozotocin: 65 mg/kg; fed with high-fat diet). Isolated rat hearts from each group were randomly subjected to (a) normal perfusion, (b) ischemia-reperfusion (I/R), and (c) IPC procedure. At the end of the perfusion experiments, hearts were analyzed for injury, contractile function, mitochondrial activity, and oxidative stress. The results obtained from hemodynamics, cardiac injury markers, and caspase-3 activity showed that DCM rat displayed prominent I/R-associated cardiac abnormalities than DM rat heart. But the deteriorated physiological performance and cardiac injury were not recovered in both DM and DCM heart by IPC procedure. Unlike normal rat heart, IPC did not reverse mitochondrial dysfunction (determined by electron transport chain enzymes activity, ATP level, and membrane integrity, expression levels of genes like PGC-1ɑ, GSK3β, complex I, II, and V) in DCM and DM rat heart. The present study demonstrated that IPC failed to protect I/R-challenged DCM rat heart, and the underlying pathology was associated with deteriorated mitochondrial function.

Impact of hyperglycemia on myocardial ischemia\u2013reperfusion susceptibility and ischemic preconditioning in hearts from rats with type 2 diabetes

BackgroundThe mechanisms underlying increased mortality in patients with diabetes and admission hyperglycemia after an acute coronary syndrome may involve reduced capacity for cardioprotection. We investigated the impact of hyperglycemia on exogenously activated cardioprotection by ischemic preconditioning (IPC) in hearts from rats with type 2 diabetes mellitus (T2DM) that were endogenously cardioprotected by an inherent mechanism, and the involvement of myocardial glucose uptake (MGU) and myocardial O-linked β-N-acetylglucosamine (O-GlcNAc).Methods and resultsIn isolated, perfused rat hearts subjected to ischemia–reperfusion, infarct size (IS) was overall larger during hyper- ([Glucose] = 22 mmol/L]) than normoglycemia ([Glucose] = 11 mmol/L]) (p < 0.001). IS was smaller in 12-week old Zucker diabetic fatty rats with recent onset T2DM (fa/fa) than in rats without T2DM (fa/+) (n = 8 in each group) both during hyperglycemia (p < 0.05) and normoglycemia (p < 0.05). IPC (2 × 5 min cycles) reduced IS during normo- (p < 0.01 for both groups) but not during hyperglycemia independently of the presence of T2DM. During hyperglycemia, an intensified IPC stimulus (4 × 5 min cycles) reduced IS only in hearts from animals with T2DM (p < 0.05). IPC increased MGU and O-GlcNAc levels during reperfusion in animals with and without T2DM at normoglycemia (MGU: p < 0.05, O-GlcNAc: p < 0.01 for both groups) but not during hyperglycemia. Intensified IPC at hyperglycemia increased MGU (p < 0.05) and O-GlcNAc levels (p < 0.05) only in hearts from animals with T2DM.ConclusionWhile the effect of IPC is reduced during hyperglycemia in rats without T2DM, endogenous cardioprotection in animals with T2DM is not influenced by hyperglycemia and the capacity for exogenous cardioprotection by IPC is preserved. MGU and O-GlcNAc levels are increased by exogenously induced cardioprotection by IPC but not by endogenous cardioprotection in animals with T2DM reflecting different underlying mechanisms by exogenous and endogenous cardioprotection.

Ciliary neurotrophic factor stimulates cardioprotection and the proliferative activity in the adult zebrafish heart

Unlike mammals, adult zebrafish can regenerate their hearts after injury via proliferation of cardiomyocytes. The cell-cycle entry of zebrafish cardiac cells can also be stimulated through preconditioning by thoracotomy, a chest incision without myocardial damage. To identify effector genes of heart preconditioning, we performed transcriptome analysis of ventricles from thoracotomized zebrafish. This intervention led to enrichment of cardioprotective factors, epithelial-to-mesenchymal transition genes, matrix proteins and components of LIFR/gp130 signaling. We identified that inhibition of the downstream signal transducer of the LIFR/gp130 pathway through treatment with Ruxolitinib, a specific JAK1/2 antagonist, suppressed the cellular effects of preconditioning. Activation of LIFR/gp130 signaling by a single injection of the ligand Cilliary Neurotrophic Factor, CNTF, was sufficient to trigger cardiomyocyte proliferation in the intact heart. In addition, CNTF induced other pro-regenerative processes, including expression of cardioprotective genes, activation of the epicardium, enhanced intramyocardial Collagen XII deposition and leucocyte recruitment. These effects were abrogated by the concomitant inhibition of the JAK/STAT activity. Mutation of the cntf gene suppressed the proliferative response of cardiomyocytes after thoracotomy. In the regenerating zebrafish heart, CNTF injection prior to ventricular cryoinjury improved the initiation of regeneration via reduced cell apoptosis and boosted cardiomyocyte proliferation. Our findings reveal the molecular effectors of preconditioning and demonstrate that exogenous CNTF exerts beneficial regenerative effects by rendering the heart more resilient to injury and efficient in activation of the proliferative programs.

The impact of sex and myocardial ischemic preconditioning on immunohistochemical markers of acute myocardial infarction.

The immunohistochemical detection of dityrosine, troponins I (cTNI) and T (cTnT), and connexin 43 has been proposed as a tool for the diagnosis of myocardial infarction with short survival times. Results of clinical and experimental studies reveal that gender and/or ischemic preconditioning of the heart may have an influence on severity and magnitude of myocardial infarction. To clarify the question, if the above-mentioned markers are influenced by sex or ischemic preconditioning, experiments on isolated rat hearts using the Langendorff technique were performed. Using the hearts of 12 male and 12 female Wistar rats a local ischemia was induced through ligation of the left coronary artery. Furthermore, 12 male rat hearts underwent ischemic preconditioning of the heart by stopping the perfusion of the whole heart for 30min and subsequently reperfusing the heart for another 60min, before inducing local ischemia. The perfusion time after ligation varied from 10 to 60min. A control group was comprised out of 6 male and 2 female rat hearts. These were placed in the Langendorff system for 60min without further manipulation or received ischemic preconditioning without subsequent local ischemia or were excised without being mounted on the Langendorff system at all. All hearts were fixed in formalin and stained immunohistochemically. Depletion of the marker cTnT appeared to be less in females when compared to male hearts, for all other markers tested, no apparent difference in staining results were seen when comparing male and female rat hearts. Male rat hearts with ischemic preconditioning showed no difference compared to male rat hearts without ischemic preconditioning when stained fort dityrosine. Connexin 43 staining was less pronounced in hearts with ischemic preconditioning, whereas cTnI as well as cTnT depletion was more pronounced in preconditioned hearts. The presented findings indicate to some extent the vulnerability of the investigated markers for the influencing factors tested.

Non-ischemic heart preconditioning.

Ischemic heart conditioning has been shown to protect the organ against ischemia/reperfusion injury. Animal studies have revealed that the heart can also be conditioned by non-ischemic procedures, namely physical exercise and tachycardia. Long and short term endurance training, sprint training, resistance or interval training and even one bout of exercise induce cardiac preconditioning, which is manifested by a reduction in post ischemia/reperfusion infarct size, ventricular arrhythmia and improved heart function. Several factors contribute to the exercise-induced heart preconditioning, among which the most important can be: increased activity of the anti-radical defense system, opioids, interleukin-6, nitric oxide, ATP dependent potassium channels, heat shock protein 72 and sphingosine-1-phosphate. A few studies have also shown that one bout of exercise in patients with stable angina increases tolerated workload. According to some data obtained in swine and dogs, stimulated tachycardia before ischemia/reperfusion reduces the infarct size. Future studies are needed to fully clarify the mechanisms responsible for exercise- or tachycardia-induced heart preconditioning against ischemia/reperfusion. It may lead to the development of new treatment modes of the disease.

Possible role of mitochondrial K-ATP channel and nitric oxide in protection of the neonatal rat heart

Cardioprotective effect of ischemic preconditioning (IPC) and ischemic postconditioning (IPoC) in adult hearts is mediated by mitochondrial-K-ATP channels and nitric oxide (NO). During early developmental period, rat hearts exhibit higher resistance to ischemia–reperfusion (I/R) injury and their resistance cannot be further increased by IPC or IPoC. Therefore, we have speculated, whether mechanisms responsible for high resistance of neonatal heart may be similar to those of IPC and IPoC. To test this hypothesis, rat hearts isolated on days 1, 4, 7, and 10 of postnatal life were perfused according to Langendorff. Developed force (DF) of contraction was measured. Hearts were exposed to 40 min of global ischemia followed by reperfusion up to the maximum recovery of DF. IPoC was induced by 5 cycles of 10-s ischemia. Mito-K-ATP blocker (5-HD) was administered 5 min before ischemia and during first 20 min of reperfusion. Another group of hearts was isolated for biochemical analysis of 3-nitrotyrosine, and serum samples were taken to measure nitrate levels. Tolerance to ischemia did not change from day 1 to day 4 but decreased on days 7 and 10. 5-HD had no effect either on neonatal resistance to I/R injury or on cardioprotective effect of IPoC on day 10. Significant difference was found in serum nitrate levels between days 1 and 10 but not in tissue 3-nitrotyrosine content. It can be concluded that while there appears to be significant difference of NO production, mito-K-ATP and ROS probably do not play role in the high neonatal resistance to I/R injury.

THE EVOLVING CONCEPT OF CAVEOLINS AND INTERMEDIARY ROLE IN VARIOUS MECHANISMS VIA BIOMOLECULAR PATHWAYS

Caveolins are integral membrane proteins which consist of caveolae, present in plasma membrane. Many researchers have reported the role of caveolae in major physiological conduits of the mammalian cells, including cholesterol homeostasis, transcytosis and endocytosis. Caveolin also play a role in ischemic preconditioning of heart, postmenopausal women, brain microvessels, cancer progression and Alzheimer’s disease. Attenuation of myocardial protection in diabetic heart may be due to decrease in the ischemic preconditioning mediated release of nitric oxide, upregulation of caveolin and consequently decrease in activity of endothelial nitric oxide synthase (eNOS). Caveolin alogwith integral membrane proteins overexpress in a huge range of tumor entities, while hormonal changes cause variation in caveolin expression. Under ovariectomy conditions, eNOS inhibitory action occurs because of interaction between eNOS and caveolin. Some new concepts explain that multiple proteins, including caveolin-1 alter trans-membrane flux of fatty acid and play role in fatty acid uptake. Caveolin can be useful in the controlling of cardiovascular system (CVS) and brain disease using various predicaments. New intermediate steps have been discovered which correlate various mechanisms of ischemic preconditioning, cardiopotection and eNOS in the field of cardiovascular research.

Pharmacological preconditioning with gemfibrozil preserves cardiac function after heart transplantation

While heart transplantation (HTX) is the definitive therapy of heart failure, donor shortage is emerging. Pharmacological activation of soluble guanylate cyclase (sGC) and increased cGMP-signalling have been reported to have cardioprotective properties. Gemfibrozil has recently been shown to exert sGC activating effects in vitro. We aimed to investigate whether pharmacological preconditioning of donor hearts with gemfibrozil could protect against ischemia/reperfusion injury and preserve myocardial function in a heterotopic rat HTX model. Donor Lewis rats received p.o. gemfibrozil (150 mg/kg body weight) or vehicle for 2 days. The hearts were explanted, stored for 1 h in cold preservation solution, and heterotopically transplanted. 1 h after starting reperfusion, left ventricular (LV) pressure-volume relations and coronary blood flow (CBF) were assessed to evaluate early post-transplant graft function. After 1 h reperfusion, LV contractility, active relaxation and CBF were significantly (p < 0.05) improved in the gemfibrozil pretreated hearts compared to that of controls. Additionally, gemfibrozil treatment reduced nitro-oxidative stress and apoptosis, and improved cGMP-signalling in HTX. Pharmacological preconditioning with gemfibrozil reduces ischemia/reperfusion injury and preserves graft function in a rat HTX model, which could be the consequence of enhanced myocardial cGMP-signalling. Gemfibrozil might represent a useful tool for cardioprotection in the clinical setting of HTX surgery soon.

The Question of the End Effector of Ischemic Preconditioning of the Heart

The Question of the End Effector of Ischemic Preconditioning of the Heart

Adenosine A1 receptor activation increases myocardial protein S-nitrosothiols and elicits protection from ischemia-reperfusion injury in male and female hearts.

Nitric oxide (NO) plays an important role in cardioprotection, and recent work from our group and others has implicated protein S-nitrosylation (SNO) as a critical component of NO-mediated protection in different models, including ischemic pre- and post-conditioning and sex-dependent cardioprotection. However, studies have yet to examine whether protein SNO levels are similarly increased with pharmacologic preconditioning in male and female hearts, and whether an increase in protein SNO levels, which is protective in male hearts, is sufficient to increase baseline protection in female hearts. Therefore, we pharmacologically preconditioned male and female hearts with the adenosine A1 receptor agonist N6-cyclohexyl adenosine (CHA). CHA administration prior to ischemia significantly improved functional recovery in both male and female hearts compared to baseline in a Langendorff-perfused heart model of ischemia-reperfusion injury (% of preischemic function ± SE: male baseline: 37.5±3.4% vs. male CHA: 55.3±3.2%; female baseline: 61.4±5.7% vs. female CHA: 76.0±6.2%). In a separate set of hearts, we found that CHA increased p-Akt and p-eNOS levels. We also used SNO-resin-assisted capture with LC-MS/MS to identify SNO proteins in male and female hearts, and determined that CHA perfusion induced a modest increase in protein SNO levels in both male (11.4%) and female (12.3%) hearts compared to baseline. These findings support a potential role for protein SNO in a model of pharmacologic preconditioning, and provide evidence to suggest that a modest increase in protein SNO levels is sufficient to protect both male and female hearts from ischemic injury. In addition, a number of the SNO proteins identified with CHA treatment were also observed with other forms of cardioprotective stimuli in prior studies, further supporting a role for protein SNO in cardioprotection.

Distinct effects of inflammation on preconditioning and regeneration of the adult zebrafish heart.

The adult heart is able to activate cardioprotective programmes and modifies its architecture in response to physiological or pathological changes. While mammalian cardiac remodelling often involves hypertrophic expansion, the adult zebrafish heart exploits hyperplastic growth. This capacity depends on the responsiveness of zebrafish cardiomyocytes to mitogenic signals throughout their entire life. Here, we have examined the role of inflammation on the stimulation of cell cycle activity in the context of heart preconditioning and regeneration. We used thoracotomy as a cardiac preconditioning model and cryoinjury as a model of cardiac infarction in the adult zebrafish. First, we performed a spatio-temporal characterization of leucocytes and cycling cardiac cells after thoracotomy. This analysis revealed a concomitance between the infiltration of inflammatory cells and the stimulation of the mitotic activity. However, decreasing the immune response using clodronate liposome injection, PLX3397 treatment or anti-inflammatory drugs surprisingly had no effect on the re-entry of cardiac cells into the cell cycle. In contrast, reducing inflammation using the same strategies after cryoinjury strongly impaired cardiac cell mitotic activity and the regenerative process. Taken together, our results show that, while the immune response is not necessary to induce cell-cycle activity in intact preconditioned hearts, inflammation is required for the regeneration of injured hearts in zebrafish.

Effects of wortmannin on cardioprotection exerted by ischemic preconditioning in rat hearts subjected to ischemia-reperfusion.

Ischemic preconditioning (IPC) is one of the most powerful interventions to reduce ischemia-reperfusion injury. The aim of the present study was to investigate the involvement of the phosphatidylinositol-3-kinases (PI3Ks) family in cardioprotection exerted by IPC and the relationship between preservation of mitochondrial morphology and ATP synthesis capacity. In this regard, macroautophagy (autophagy) is considered a dynamic process involved in the replacement of aged or defective organelles under physiological conditions. IPC consisted of four 5-min cycles of ischemia-reperfusion followed by sustained ischemia. Wortmannin (W), a PI3K family inhibitor, was added to the perfusion medium to study the involvement of autophagy in the beneficial effects of IPC. In the present study, LC3-II/I expression was significantly increased in the IPC group when compared with the control group. The hearts subjected to IPC showed greater degradation of p62 than control groups, establishing the existence of an autophagic flow. Electron microscopy showed that IPC preserves the structural integrity of mitochondria after ischemia and at the end of reperfusion. Moreover, hearts subjected to IPC exhibited increased mitochondrial ATP synthesis. The beneficial effects of IPC were abolished by W in all trials of this study, abolishing the differences between the IPC and control groups. These results suggest that IPC could partly reduce injury by ischemia-reperfusion (I/R) by decreasing mitochondrial damage and promoting autophagy. Since W is a nonspecific inhibitor of the PI3Ks family, further research is required to confirm participation of PI3K in the response to IPC.

Studies of Ischemic Preconditioning Mechanisms in Langendorff Rat Heart Model the Impact of Phosphocreatin Kinase and ATP Sensitive Potasium Channels Pharmachological Openers and Blockers on Cardioprotection

Abstract Ischemic preconditioning (IPC) induced by administration of brief episodes of ischemia-reperfusion represents a protective mechanism of the heart against prolonged episodes of ischemia. Although the mechanism of ischemic preconditioning has been extensively studied, however, until now it is insufficient elucidated. Using a Langendorff rat heart model with 45 minutes ischemia followed by 120 minute reperfusion we aimed to evaluate the role of Phosphocreatin Kinase-C (PCK) in ischemic rat myocardium and demonstration of its involvment in the path of pharmachological preconditioning (PP) by using PKC activators 1,2-dioctanoyl-sn-glycerol (DOG) and inhibitors chelerythrine (CHE) and evaluation of the role of K ATP channels in pharmachological preconditioning (PP) mechanism by administration of a K ATP channel opener (Cromakalim) (CRK) or by blocking the opening of K ATP channels with glibenclamide(GLB). The activators of PCK(DOG) and of K ATP channel (CRK) limited the infarct size when perfused before lethal ischemia, mimicking the ischemic preconditioning in rat heart When activator of PCK DOG + GLB, a K ATP channel inhibitor were coperfused before the lethal ischemia, there was an increase in myocardial infarct size, expressed as a percentage of the area at risk, versus control, the cardioprotective effect of DOG being abolished by GLB. The same results were obtained when CHE the inhibitor of PCK was coperfused with CRK the activator of K ATP channel. The effect of CHE and GLB perfused at the beginning of IPC resulted in loss of protection accompanied by a significant increase in infarct size area. The finding that treatment with a DOG PKC activator and CRK activator of K ATP channel gives a similar degree of protection against infarction as that seen after ischemic preconditioning and that this protection can be blocked by CHE a PCK pharmachological inhibitor provides support for the hypothesis that PKC plays a pivotal role in ischemic preconditioning. Our data may have a significance in pharmachological preconditioning (PP) with decrease in infarct size as an end point.