Differential role of PI3K/Akt pathway in the infarct size limitation and antiarrhythmic protection in the rat heart

Camphene as a Protective Agent in Myocardial Ischemia/Reperfusion Injury

Myocardial ischemia/reperfusion injury (I/R) and the resulting heart failure is one of the main causes of mortality and morbidity worldwide. Camphene has been shown to have anti-inflammatory and hypolipidemic properties; however, its role in the protection of the heart from ischemia and reperfusion has not been investigated. The cardioprotective role of camphene and the mechanism that mediates its action against I/R injury was evaluated in the present study. A single dose of camphene was administered in adult rats prior to ex vivo I/R induction. Infarct size was measured using 2,3,5-triphenyltetrazolium chloride (TTC) staining and cardiomyocyte injury was assessed by determining the release of the enzyme lactate dehydrogenase (LDH). Camphene pretreatment provided significant protection reducing myocardial infarct size and cell death after I/R. The effect was correlated with the reduction in oxidative stress as evidenced by the determination of protein carbonylation, GSH/GSSG ratio, the increase in mitochondrial content as determined by CS activity, and the modulation of antioxidant defense mechanisms (expression of Nrf2 and target genes and activities of CAT, MnSOD, and GR). Furthermore, ferroptosis was decreased, as demonstrated by downregulation of GPx4 expression and reduction in lipid peroxidation. The results suggest that camphene can protect the heart against I/R injury by maintaining redox homeostasis and can hold therapeutic potential for mitigating the detrimental effects of I/R in the heart.

The Research Progress of Trastuzumab-Induced Cardiotoxicity in HER-2-Positive Breast Cancer Treatment

In recent years, the incidence of breast cancer has been increasing on an annual basis. Human epidermal growth factor receptor-2 (HER-2) is overexpressed in 15-20% human breast cancers, which is associated with poor prognosis and a high recurrence rate. Trastuzumab is the first humanized monoclonal antibody against HER-2. The most significant adverse effect of trastuzumab is cardiotoxicity, which has become an important factor in limiting the safe use of the drug. Unfortunately, the mechanism causing this cardiotoxicity is still not completely understood, and the use of preventive interventions remains controversial. This article focuses on trastuzumab-induced cardiotoxicity, reviewing the clinical application, potential cardiotoxicity, mechanism and discussing the potential interventions through summarizing related researches over the past tens of years.

The effect of adaptation to hypoxia on cardiac tolerance to ischemia/reperfusion

The acute myocardial infarction (AMI) and sudden cardiac death (SCD), both associated with acute cardiac ischemia, are one of the leading causes of adult death in economically developed countries. The development of new approaches for the treatment and prevention of AMI and SCD remains the highest priority for medicine. A study on the cardiovascular effects of chronic hypoxia (CH) may contribute to the development of these methods. Chronic hypoxia exerts both positive and adverse effects. The positive effects are the infarct-reducing, vasoprotective, and antiarrhythmic effects, which can lead to the improvement of cardiac contractility in reperfusion. The adverse effects are pulmonary hypertension and right ventricular hypertrophy. This review presents a comprehensive overview of how CH enhances cardiac tolerance to ischemia/reperfusion. It is an in-depth analysis of the published data on the underlying mechanisms, which can lead to future development of the cardioprotective effect of CH. A better understanding of the CH-activated protective signaling pathways may contribute to new therapeutic approaches in an increase of cardiac tolerance to ischemia/reperfusion.

Impact of Maturation on Myocardial Response to Ischemia and the Effectiveness of Remote Preconditioning in Male Rats

Aging attenuates cardiac tolerance to ischemia/reperfusion (I/R) associated with defects in protective cell signaling, however, the onset of this phenotype has not been completely investigated. This study aimed to compare changes in response to I/R and the effects of remote ischemic preconditioning (RIPC) in the hearts of younger adult (3 months) and mature adult (6 months) male Wistar rats, with changes in selected proteins of protective signaling. Langendorff-perfused hearts were exposed to 30 min I/120 min R without or with prior three cycles of RIPC (pressure cuff inflation/deflation on the hind limb). Infarct size (IS), incidence of ventricular arrhythmias and recovery of contractile function (LVDP) served as the end points. In both age groups, left ventricular tissue samples were collected prior to ischemia (baseline) and after I/R, in non-RIPC controls and in RIPC groups to detect selected pro-survival proteins (Western blot). Maturation did not affect post-ischemic recovery of heart function (Left Ventricular Developed Pressure, LVDP), however, it increased IS and arrhythmogenesis accompanied by decreased levels and activity of several pro-survival proteins and by higher levels of pro-apoptotic proteins in the hearts of elder animals. RIPC reduced the occurrence of reperfusion-induced ventricular arrhythmias, IS and contractile dysfunction in younger animals, and this was preserved in the mature adults. RIPC did not increase phosphorylated protein kinase B (p-Akt)/total Akt ratio, endothelial nitric oxide synthase (eNOS) and protein kinase Cε (PKCε) prior to ischemia but only after I/R, while phosphorylated glycogen synthase kinase-3β (GSK3β) was increased (inactivated) before and after ischemia in both age groups coupled with decreased levels of pro-apoptotic markers. We assume that resistance of rat heart to I/R injury starts to already decline during maturation, and that RIPC may represent a clinically relevant cardioprotective intervention in the elder population.

Cardioprotective Effects of PPARβ/δ Activation against Ischemia/Reperfusion Injury in Rat Heart Are Associated with ALDH2 Upregulation, Amelioration of Oxidative Stress and Preservation of Mitochondrial Energy Production

Accumulating evidence support the cardioprotective properties of the nuclear receptor peroxisome proliferator activated receptor β/δ (PPARβ/δ); however, the underlying mechanisms are not yet fully elucidated. The aim of the study was to further investigate the mechanisms underlying PPARβ/δ-mediated cardioprotection in the setting of myocardial ischemia/reperfusion (I/R). For this purpose, rats were treated with PPARβ/δ agonist GW0742 and/or antagonist GSK0660 in vivo and hearts were subjected to ex vivo global ischemia followed by reperfusion. PPARβ/δ activation improved left ventricular developed pressure recovery, reduced infarct size (IS) and incidence of reperfusion-induced ventricular arrhythmias while it also up-regulated superoxide dismutase 2, catalase and uncoupling protein 3 resulting in attenuation of oxidative stress as evidenced by the reduction in 4-hydroxy-2-nonenal protein adducts and protein carbonyl formation. PPARβ/δ activation also increased both mRNA expression and enzymatic activity of aldehyde dehydrogenase 2 (ALDH2); inhibition of ALDH2 abrogated the IS limiting effect of PPARβ/δ activation. Furthermore, upregulation of PGC-1α and isocitrate dehydrogenase 2 mRNA expression, increased citrate synthase activity as well as mitochondrial ATP content indicated improvement in mitochondrial content and energy production. These data provide new mechanistic insight into the cardioprotective properties of PPARβ/δ in I/R pointing to ALDH2 as a direct downstream target and suggesting that PPARβ/δ activation alleviates myocardial I/R injury through coordinated stimulation of the antioxidant defense of the heart and preservation of mitochondrial function.

Preconditioning of Caenorhabditis elegans to anoxic insult by inactivation of cholinergic, GABAergic and muscle activity

For most metazoans, oxygen deprivation leads to cell dysfunction and if severe, death. Sublethal stress prior to a hypoxic or anoxic insult ("preconditioning") can protect cells from subsequent oxygen deprivation. The molecular mechanisms by which sublethal stress can buffer against a subsequent toxic insult and the role of the nervous system in the response are not well understood. We studied the role of neuronal activity preconditioning to oxygen deprivation in Caenorhabditis elegans. Animals expressing the histamine gated chloride channels (HisCl1) in select cell populations were used to temporally and spatially inactivate the nervous system or tissue prior to an anoxic insult. We find that inactivation of the nervous system for 3 h prior to the insult confers resistance to a 48-h anoxic insult in 4th-stage larval animals. Experiments show that this resistance can be attributed to loss of activity in cholinergic and GABAergic neurons as well as in body wall muscles. These observations indicate that the nervous system activity can mediate the organism's response to anoxia.

The involvement of protein kinases in the cardioprotective effect of chronic hypoxia

The purpose of this review is to analyze the involvement of protein kinases in the cardioprotective mechanism induced by chronic hypoxia. It has been reported that chronic intermittent hypoxia contributes to increased expression of the following kinases in the myocardium: PKCdelta, PKCalpha, p-PKCepsilon, p-PKCalpha, AMPK, p-AMPK, CaMKII, p-ERK1/2, p-Akt, PI3-kinase, p-p38, HK-1, and HK-2; whereas, chronic normobaric hypoxia promotes increased expression of the following kinases in the myocardium: PKCepsilon, PKCbetaII, PKCeta, CaMKII, p-ERK1/2, p-Akt, p-p38, HK-1, and HK-2. However, CNH does not promote enhanced expression of the AMPK and JNK kinases. Adaptation to hypoxia enhances HK-2 association with mitochondria and causes translocation of PKCdelta, PKCbetaII, and PKCeta to the mitochondria. It has been shown that PKCdelta, PKCepsilon, ERK1/2, and MEK1/2 are involved in the cardioprotective effect of chronic hypoxia. The role of other kinases in the cardioprotective effect of adaptation to hypoxia requires further research.

Intermittent hypoxia reduces infarct size in rats with acute myocardial infarction: a systematic review and meta-analysis

Background

To determine whether intermittent hypoxia (IH) can reduce the infarct size (IS) after acute myocardial infarction (AMI) in rats.

Methods

Articles were identified in PubMed, EMBASE and the Web of Science and were included if they evaluated the effect of IH on the changes in the infarcted area after AMI in rats.

Results

A preliminary search identified 3633 articles and 29 data sets from 23 articles (12 in vivo, 16 in vitro). The IS decreased after AMI in IH rats both in vitro (SMD -1.46, 95% CI [− 2.37, − 0.55]; I² = 85.6%, P = 0.000) and in vivo (SMD -1.43, 95% CI [− 2.05, − 0.82], I² = 73.6%, P = 0.000). Sensitivity analysis indicated that IH had a strong protective effect against myocardial infarction, and the hypoxia concentration was significantly correlated with the change in IS after AMI.

Conclusion

IH can reduce IS after AMI in rats. This effect of IH may be related to the dose of hypoxia, and the oxygen concentration may be one of the most important influencing factors.

Factor Xa Inhibition with Apixaban Does Not Influence Cardiac Remodelling in Rats with Heart Failure After Myocardial Infarction

Background

Heart failure (HF) is considered to be a prothrombotic condition and it has been suggested that coagulation factors contribute to maladaptive cardiac remodelling via activation of the protease-activated receptor 1 (PAR1). We tested the hypothesis that anticoagulation with the factor Xa (FXa) inhibitor apixaban would ameliorate cardiac remodelling in rats with HF after myocardial infarction (MI).

Methods and Results

Male Sprague-Dawley rats were either subjected to permanent ligation of the left ascending coronary artery (MI) or sham surgery. The MI and sham animals were randomly allocated to treatment with placebo or apixaban in the chow (150 mg/kg/day), starting 2 weeks after surgery. Cardiac function was assessed using echocardiography and histological and molecular markers of cardiac hypertrophy were assessed in the left ventricle (LV). Apixaban resulted in a fivefold increase in anti-FXa activity compared with vehicle, but no overt bleeding was observed and haematocrit levels remained similar in apixaban- and vehicle-treated groups. After 10 weeks of treatment, LV ejection fraction was 42 ± 3% in the MI group treated with apixaban and 37 ± 2 in the vehicle-treated MI group (p > 0.05). Both vehicle- and apixaban-treated MI groups also displayed similar degrees of LV dilatation, LV hypertrophy and interstitial fibrosis. Histological and molecular markers for pathological remodelling were also comparable between groups, as was the activity of signalling pathways downstream of the PAR1 receptor.

Conclusion

FXa inhibition with apixaban does not influence pathological cardiac remodelling after MI. These data do not support the use of FXa inhibitor in HF patients with the aim to amend the severity of HF.

Voluntary exercise may activate components of pro-survival risk pathway in the rat heart and potentially modify cell proliferation in the myocardium

Although physical exercise is known to reduce size of infarction, incidence of ventricular arrhythmias, and to improve heart function, molecular mechanisms of this protection are not fully elucidated. We explored the hypothesis that voluntary running, similar to adaptive interventions, such as ischemic or remote preconditioning, may activate components of pro-survival (RISK) pathway and potentially modify cell proliferation. Sprague-Dawley adult male rats freely exercised for 23 days in cages equipped with running wheels, while sedentary controls were housed in standard cages. After 23 days, left ventricular (LV) myocardial tissue samples were collected for the detection of expression and activation of RISK proteins (WB). The day before, a marker of cell proliferation 5-bromo-2'-deoxyuridine (BrdU) was given to all animals to detect its incorporation into DNA of the LV cells (ELISA). Running increased phosphorylation (activation) of Akt, as well as the levels of PKC? and phospho-ERK1/2, whereas BrdU incorporation into DNA was unchanged. In contrast, exercise promoted pro-apoptotic signaling - enhanced Bax/Bcl-2 ratio and activation of GSK-3ß kinase. Results suggest that in the rat myocardium adapted to physical load, natural cardioprotective processes associated with physiological hypertrophy are stimulated, while cell proliferation is not modified. Up-regulation of pro-apoptotic markers indicates potential induction of cell death mechanisms that might lead to maladaptation in the long-term.

Participation of opioid receptors in the cytoprotective effect of chronic normobaric hypoxia

We studied the role of the delta, micro, and kappa opioid receptor (OR) subtypes in the cardioprotective effect of chronic continuous normobaric hypoxia (CNH) in the model of acuteanoxia-reoxygenation of isolated cardiomyocytes. Adaptation of rats to CNH was performed by their exposure to atmosphere containing 12% of O(2) for 21 days. Anoxia-reoxygenation of cardiomyocytes isolated from normoxiccontrol rats caused the death of 51 % of cells and lactate dehydrogenase (LDH) release. Adaptation of rats to CNH resulted in the anoxia/reoxygenation-induced cardiomyocyte death of only 38 %, and reduced the LDH release by 25 %. Pre-incubation of the cells with either the non-selective OR (opioid receptor) blocker naloxone (300 nM/l), the delta OR antagonist TIPP(psi) (30 nM/l), the selective delta(2) OR antagonist naltriben (1 nM/l) or the micro OR antagonist CTAP (100 nM/l) for 25 minutes before anoxia abolished the reduction of cell death and LDH release afforded by CNH. The antagonist of delta(1) OR BNTX (1 nM/l) or the kappa OR antagonist nor-binaltorphimine (3 nM/l) did not influence the cytoprotective effects of CNH. Taken together, the cytoprotective effect of CNH is associated with the activation of the delta(2) and micro OR localized on cardiomyocytes.

Potential markers and metabolic processes involved in the mechanism of radiation-induced heart injury

Irradiation of normal tissues leads to acute increase in reactive oxygen/nitrogen species that serve as intra- and inter-cellular signaling to alter cell and tissue function. In the case of chest irradiation, it can affect the heart, blood vessels, and lungs, with consequent tissue remodelation and adverse side effects and symptoms. This complex process is orchestrated by a large number of interacting molecular signals, including cytokines, chemokines, and growth factors. Inflammation, endothelial cell dysfunction, thrombogenesis, organ dysfunction, and ultimate failing of the heart occur as a pathological entity - "radiation-induced heart disease" (RIHD) that is major source of morbidity and mortality. The purpose of this review is to bring insights into the basic mechanisms of RIHD that may lead to the identification of targets for intervention in the radiotherapy side effect. Studies of authors also provide knowledge about how to select targeted drugs or biological molecules to modify the progression of radiation damage in the heart. New prospective studies are needed to validate that assessed factors and changes are useful as early markers of cardiac damage.

Past and current perspective on new therapeutic targets for Type-II diabetes

Loss of pancreatic β-cell function is a hallmark of Type-II diabetes mellitus (DM). It is a chronic metabolic disorder that results from defects in both insulin secretion and insulin action. Recently, United Kingdom Prospective Diabetes Study reported that Type-II DM is a progressive disorder. Although, DM can be treated initially by monotherapy with oral agent; eventually, it may require multiple drugs. Additionally, insulin therapy is needed in many patients to achieve glycemic control. Pharmacological approaches are unsatisfactory in improving the consequences of insulin resistance. Single therapeutic approach in the treatment of Type-II DM is unsuccessful and usually a combination therapy is adopted. Increased understanding of biochemical, cellular and pathological alterations in Type-II DM has provided new insight in the management of Type-II DM. Knowledge of underlying mechanisms of Type-II DM development is essential for the exploration of novel therapeutic targets. Present review provides an insight into therapeutic targets of Type-II DM and their role in the development of insulin resistance. An overview of important signaling pathways and mechanisms in Type-II DM is provided for the better understanding of disease pathology. This review includes case studies of drugs that are withdrawn from the market. The experience gathered from previous studies and knowledge of Type-II DM pathways can guide the anti-diabetic drug development toward the discovery of clinically viable drugs that are useful in Type-II DM.

Naproxen and Diclofenac Attenuate Atorvastatin-induced Preconditioning of the Myocardium

Statins reduce infarct size (IS) in ischemia-reperfusion injury of the myocardium. Inhibition of cyclooxygenase-2 (COX-2) attenuates this benefit. We investigated the effect of two widely used non-selective non-steroidal anti-inflammatory drugs (NSAIDs) with different degree of anti-COX-2 activity on atorvastatin-mediated preconditioning. Wistar rats received oral atorvastatin (10 mg∙kg^-1∙day^-1), naproxen (10 mg∙kg^-1∙day^-1), diclofenac (8 mg∙kg^-1∙day^-1), atorvastatin+naproxen, atorvastatin+diclofenac or water for three days. Hearts were then excised and perfused in the Langendorff system. Area at risk (AR) and IS were determined after 30 min of regional ischemia and 120 min of reperfusion. Atorvastatin reduced IS by 51.3% compared with controls (14.7 ± 3.9% vs. 30.2 ± 4.6% of the AR; P < 0.001). Naproxen and diclofenac alone did not alter IS compared to control. Diclofenac completely abrogated atorvastatin-mediated protection of the myocardium. Naproxen significantly attenuated but did not eliminate the IS reducing the effect of atorvastatin when compared with controls (P = 0.038). The difference in IS between the atorvastatin+naproxen group and the atorvastatin+diclofenac group showed a strong trend in reaching statistical significance (P = 0.058), but was not found to be significant. Our results suggest relatively small, but noticeable differences among non-selective NSAIDs in their potential to attenuate statin-mediated preconditioning.

Modification of Caffeic Acid with Pyrrolidine Enhances Antioxidant Ability by Activating AKT/HO-1 Pathway in Heart

Overproduction of free radicals during ischemia/reperfusion (I/R) injury leads to an interest in using antioxidant therapy. Activating an endogenous antioxidant signaling pathway is more important due to the fact that the free radical scavenging behavior in vitro does not always correlate with a cytoprotection effect in vivo. Caffeic acid (CA), an antioxidant, is a major phenolic constituent in nature. Pyrrolidinyl caffeamide (PLCA), a derivative of CA, was compared with CA for their antioxidant and cytoprotective effects. Our results indicate that CA and PLCA exert the same ability to scavenge DPPH in vitro. In response to myocardial I/R stress, PLCA was shown to attenuate lipid peroxydation and troponin release more than CA. These responses were accompanied with a prominent elevation in AKT and HO-1 expression and a preservation of mnSOD expression and catalase activity. PLCA also improved cell viability and alleviated the intracellular ROS level more than CA in cardiomyocytes exposed to H₂O₂. When inhibiting the AKT or HO-1 pathways, PLCA lost its ability to recover mnSOD expression and catalase activity to counteract with oxidative stress, suggesting AKT/HO-1 pathway activation by PLCA plays an important role. In addition, inhibition of AKT signaling further abolished HO-1 activity, while inhibition of HO-1 signaling attenuated AKT expression, indicating cross-talk between the AKT and HO-1 pathways. These protective effects may contribute to the cardiac function improvement by PLCA. These findings provide new insight into therapeutic approaches using a modified natural compound against oxidative stress from myocardial injuries.

Participation of heart mitochondria in myocardial protection against ischemia/reperfusion injury: benefit effects of short-term adaptation processes

Acute streptozotocin diabetes mellitus (DM) as well as remote ischemic preconditioning (RPC) has shown a favorable effect on the postischemic-reperfusion function of the myocardium. Cardioprotective mechanisms offered by these experimental models involve the mitochondria with the changes in functional properties of membrane as the end-effector. The aim was to find out whether separate effects of RPC and DM would stimulate the mechanisms of cardioprotection to a maximal level or whether RPC and DM conditions would cooperate in stimulation of cardioprotection. Experiments were performed on male Wistar rats divided into groups: control, DM, RPC and DM treated by RPC (RPC+DM). RPC protocol of 3 cycles of 5-min hind limb ischemia followed by 5-min reperfusion was used. Ischemic-reperfusion injury was induced by 30-min ischemia followed by 40-min reperfusion of the hearts in Langendorff mode. Mitochondria were isolated by differential centrifugation, infarct size assessed by staining with 1 % 2,3,5-triphenyltetrazolium chloride, mitochondrial membrane fluidity with a fluorescent probe DPH, CoQ(9) and CoQ(10) with HPLC. Results revealed that RPC as well as DM decreased the infarct size and preserved mitochondrial function by increasing the mitochondrial membrane fluidity. Both used models separately offered a sufficient protection against ischemic-reperfusion injury without an additive effect of their combination.

Impaired PI3K/Akt Signaling as a Potential Cause of Failure to Precondition Rat Hearts Under Conditions of Simulated Hyperglycemia

The aim of the study was to evaluate the impact of simulated acute hyperglycemia (HG) on PI3K/Akt signaling in preconditioned and non-preconditioned isolated rat hearts perfused with Krebs-Henseleit solution containing normal (11 mmol/l) or elevated (22 mmol/l) glucose subjected to ischemia-reperfusion. Ischemic preconditioning (IP) was induced by two 5-min cycles of coronary occlusion followed by 5-min reperfusion. Protein levels of Akt, phosphorylated (activated) Akt (P-Akt), as well as contents of BAX protein were assayed (Western blotting) in cytosolic fraction of myocardial tissue samples taken prior to and after 30-min global ischemia and 40-min reperfusion. In “normoglycemic” conditions (NG), IP significantly increased P-Akt at the end of long-term ischemia, while reperfusion led to its decrease together with the decline of BAX levels as compared to non-preconditioned hearts. On the contrary, under HG conditions, P-Akt tended to decline in IP-hearts after long-term ischemia, and it was significantly higher after reperfusion than in non-preconditioned controls. No significant influence of IP on BAX levels at the end of I/R was observed under HG conditions. It seems that high glucose may influence IP-induced activation of Akt and its downstream targets, as well as maintain persistent Akt activity that may be detrimental for the heart under above conditions.

Molecular changes induced by repeated restraint stress in the heart: the effect of oxytocin receptor antagonist atosiban

Even though stress belongs to the most common lifestyle risk factors of cardiovascular diseases, there are only limited data on direct influence of stressors on the heart. The aim of the present study was to explore selected protein signaling pathways in response to repeated immobilization stress in the heart tissue. Effects of simultaneous treatment with atosiban, an oxytocin receptor antagonist, on stress-induced changes in the heart were also investigated. Male Wistar rats were exposed to repeated immobilization (2 h daily, lasting 2 weeks). The results showed increased phosphorylation of Akt kinase, enhanced levels of Bcl-2, and decreased levels of cleaved caspase-3 in the left ventricle in response to chronic stress independently of the treatment. Exposure to restraint led to the rise of HSP-90 and p53 in vehicle-treated rats only. Stress failed to modify MMP-2 activity and ultrastructure of the heart tissue. Treatment with the oxytocin/vasopressin receptor antagonist atosiban reversed stress-induced rise in HSP-90 and p53 proteins. In conclusion, our data demonstrate that repeated restraint stress induces Akt kinase activation and this is associated with elevation of anti-apoptotic proteins (Bcl-2) and down-regulation of pro-apoptotic proteins (cleaved caspase-3). These findings suggest that activation of pro-survival anti-apoptotic Akt kinase pathway plays an important role in molecular mechanisms underlying responses and adaptation of the rat heart to repeated stress exposure. The results further indicate a regulatory role of oxytocin/vasopressin in the control of stress-induced activation in HSP-90 and related proteins.

Involvement of PKCε in Cardioprotection Induced by Adaptation to Chronic Continuous Hypoxia

Continuous normobaric hypoxia (CNH) renders the heart more tolerant to acute ischemia/reperfusion injury. Protein kinase C (PKC) is an important component of the protective signaling pathway, but the contribution of individual PKC isoforms under different hypoxic conditions is poorly understood. The aim of this study was to analyze the expression of PKCε after the adaptation to CNH and to clarify its role in increased cardiac ischemic tolerance with the use of PKCε inhibitory peptide KP-1633. Adult male Wistar rats were exposed to CNH (10 % O2, 3 weeks) or kept under normoxic conditions. The protein level of PKCε and its phosphorylated form was analyzed by Western blot in homogenate, cytosolic and particulate fractions; the expression of PKCε mRNA was measured by RT-PCR. The effect of KP-1633 on cell viability and lactate dehydrogenase (LDH) release was analyzed after 25-min metabolic inhibition followed by 30-min re-energization in freshly isolated left ventricular myocytes. Adaptation to CNH increased myocardial PKCε at protein and mRNA levels. The application of KP-1633 blunted the hypoxia-induced salutary effects on cell viability and LDH release, while control peptide KP-1723 had no effect. This study indicates that PKCε is involved in the cardioprotective mechanism induced by CNH.

Quercetin improves postischemic recovery of heart function in doxorubicin-treated rats and prevents doxorubicin-induced matrix metalloproteinase-2 activation and apoptosis induction

Quercetin (QCT) is flavonoid that possesses various biological functions including anti-oxidative and radical-scavenging activities. Moreover, QCT exerts some preventive actions in treatment of cardiovascular diseases. The aim of present study was to explore effects of prolonged administration of QCT on changes induced by repeated application of doxorubicin (DOX) in rat hearts. We focused on the ultrastructure of myocardium, matrix metalloproteinases (MMPs), biometric parameters, and apoptosis induction. Our aim was also to examine effects of QCT on ischemic tolerance in hearts exposed to chronic effects of DOX, and to determine possible mechanisms underlying effects of QCT. Our results showed that QCT prevented several negative chronic effects of DOX: (I) reversed DOX-induced blood pressure increase; (II) mediated improvement of deleterious effects of DOX on ultrastructure of left ventricle; (III) prevented DOX-induced effects on tissue MMP-2 activation; and (iv) reversed effects of DOX on apoptosis induction and superoxide dismutase inhibition. Moreover, we showed that rat hearts exposed to effects of QCT were more resistant to ischemia/reperfusion injury. Effects of QCT on modulation of ischemic tolerance were linked to Akt kinase activation and connexin-43 up-regulation. Taken together, these results demonstrate that prolonged treatment with QCT prevented negative chronic effects of DOX on blood pressure, cellular damage, MMP-2 activation, and apoptosis induction. Moreover, QCT influenced myocardial responses to acute ischemic stress. These facts bring new insights into mechanisms of QCT action on rat hearts exposed to the chronic effects of DOX.

TM-1-1DP exerts protective effect against myocardial ischemia reperfusion injury via AKT-eNOS pathway

Coronary heart disease remains a leading cause of death in the world. The demand on targeting therapy to reduce myocardial ischemia/reperfusion (I/R) injury is still urgent. The pathogenesis of I/R-induced myocardial injury is complicated. Reactive oxygen species (ROS) generation and inflammatory response activation participate in the development of I/R injury. Cell death occurs and finally leads to myocardial infarction. A newly phenolic aporphine alkaloid derivative, TM-1-1DP, was synthesized in our team. We aimed to investigate the effect of novel compound on myocardial I/R injury. Rats were subjected to 1-h coronary artery occlusion and followed by 2-h reperfusion. Adult rat cardimoycyte was isolated for the cell study, and H2O2 was added into culture medium to induce ROS stress. As compared to the sham group, TM-1-1DP-treated rats had better cardiac performance in association with less infarct size and cardiac injury markers after myocardial I/R. The protective effect is associated with the inhibition of inflammatory response, cell death-related pathway (caspase-3 and TNF-α), and the activation of AKT-eNOS pathway. The finding was further coincided with the cell study. TM-1-1DP treatment significantly alleviated ROS production and improved cell viability in cardiomyocyte after H2O2 exposure. The action of TM-1-1DP is via a nitric oxide (NO)-dependent manner, since NOS inhibitor, L-NAME, abolished the protective effect. We provide a new insight into this therapeutic potential for phenolic aporphine alkaloid in myocardial I/R.

Hypoxic Conditioning as a New Therapeutic Modality

Preconditioning refers to a procedure by which a single noxious stimulus below the threshold of damage is applied to the tissue in order to increase resistance to the same or even different noxious stimuli given above the threshold of damage. Hypoxic preconditioning relies on complex and active defenses that organisms have developed to counter the adverse consequences of oxygen deprivation. The protection it confers against ischemic attack for instance as well as the underlying biological mechanisms have been extensively investigated in animal models. Based on these data, hypoxic conditioning (consisting in recurrent exposure to hypoxia) has been suggested a potential non-pharmacological therapeutic intervention to enhance some physiological functions in individuals in whom acute or chronic pathological events are anticipated or existing. In addition to healthy subjects, some benefits have been reported in patients with cardiovascular and pulmonary diseases as well as in overweight and obese individuals. Hypoxic conditioning consisting in sessions of intermittent exposure to moderate hypoxia repeated over several weeks may induce hematological, vascular, metabolic, and neurological effects. This review addresses the existing evidence regarding the use of hypoxic conditioning as a potential therapeutic modality, and emphasizes on many remaining issues to clarify and future researches to be performed in the field.

Upregulation of genes involved in cardiac metabolism enhances myocardial resistance to ischemia/reperfusion in the rat heart

Genes encoding enzymes involved in fatty acids (FA) and glucose oxidation are transcriptionally regulated by peroxisome proliferator-activated receptors (PPAR), members of the nuclear receptor superfamily. Under conditions associated with O(2) deficiency, PPAR-alpha modulates substrate switch (between FA and glucose) aimed at the adequate energy production to maintain basic cardiac function. Both, positive and negative effects of PPAR-alpha activation on myocardial ischemia/reperfusion (I/R) injury have been reported. Moreover, the role of PPAR-mediated metabolic shifts in cardioprotective mechanisms of preconditioning (PC) is relatively less investigated. We explored the effects of PPAR-alpha upregulation mimicking a delayed "second window" of PC on I/R injury in the rat heart and potential downstream mechanisms involved. Pretreatment of rats with PPAR-alpha agonist WY-14643 (WY, 1 mg/kg, i.p.) 24 h prior to I/R reduced post-ischemic stunning, arrhythmias and the extent of lethal injury (infarct size) and apoptosis (caspase-3 expression) in isolated hearts exposed to 30-min global ischemia and 2-h reperfusion. Protection was associated with remarkably increased expression of PPAR-alpha target genes promoting FA utilization (medium-chain acyl-CoA dehydrogenase, pyruvate dehydrogenase kinase-4 and carnitine palmitoyltransferase I) and reduced expression of glucose transporter GLUT-4 responsible for glucose transport and metabolism. In addition, enhanced Akt phosphorylation and protein levels of eNOS, in conjunction with blunting of cardioprotection by NOS inhibitor L-NAME, were observed in the WY-treated hearts.

CONCLUSIONS

upregulation of PPAR-alpha target metabolic genes involved in FA oxidation may underlie a delayed phase PC-like protection in the rat heart. Potential non-genomic effects of PPAR-alpha-mediated cardioprotection may involve activation of prosurvival PI3K/Akt pathway and its downstream targets such as eNOS and subsequently reduced apoptosis.

The effect of uraemia on the duration of arrhythmias in the context of cardioprotective ischaemic conditioning strategies

BACKGROUND

Sudden cardiac death is a leading cause of death in patients with chronic kidney disease and end stage renal disease. Ischaemic conditioning strategies confer profound myocardial protection and, in the absence of uraemia, have been reported to reduce myocardial dysrhythmias. Recent data confirms that ischaemic conditioning can protect the uraemic heart. However, the effect of uraemia on myocardial arrhythmogenesis in the context of ischaemia-reperfusion injury and whether ischaemic conditioning can modulate this is unknown.

OBJECTIVE

We investigated the effect of underling chronic uraemia on the duration of arrhythmias in the context of cardioprotective ischaemic conditioning strategies.

METHODS

We examined the effect of chronic uraemia on arrhythmias occurring in the context of myocardial ischaemia-reperfusion injury and the ability of ischaemic preconditioning (IPC), remote ischaemic preconditioning (RIPC) and ischaemic postconditioning (iPOST) to suppress arrhythmogenesis in uraemic and non-uraemic animals.

RESULTS

IPC led to a reduction in the frequency and duration of arrhythmias occurring during ischaemia and reperfusion. Neither RIPC nor iPOST affected the duration or frequency of ischaemic or reperfusion arrhythmias. Underlying uraemia did not alter the frequency or duration of ischaemic arrhythmias in any of the experiments however it was associated with a reduction in reperfusion arrhythmia duration in the IPC and iPOST experiments.

CONCLUSIONS

These studies demonstrate that underlying chronic uraemia does not reduce the threshold for arrhythmia timing or duration resulting from myocardial ischaemia-reperfusion and underlying uraemia did not alter the effects of these cardioprotective ischaemic conditioning strategies in the context of arrhythmia duration.

SUMMARY

This novel work in a rodent model of chronic uraemia establishes that underlying uraemia does not increase the susceptibility to myocardial ischaemia-reperfusion induced arrhythmias. When compared with the non-uraemic heart, the uraemic heart has a similar response to the effects of ischaemic conditioning strategies in terms of their effect on arrhythmia timing and duration.

Impact of the phosphatidylinositide 3-kinase signaling pathway on the cardioprotection induced by intermittent hypoxia

BACKGROUND

Exposure to intermittent hypoxia (IH) may enhance cardiac function and protects heart against ischemia-reperfusion (I/R) injury. To elucidate the underlying mechanisms, we developed a cardioprotective IH model that was characterized at hemodynamic, biochemical and molecular levels.

METHODS

Mice were exposed to 4 daily IH cycles (each composed of 2-min at 6-8% O2 followed by 3-min reoxygenation for 5 times) for 14 days, with normoxic mice as controls. Mice were then anesthetized and subdivided in various subgroups for analysis of contractility (pressure-volume loop), morphology, biochemistry or resistance to I/R (30-min occlusion of the left anterior descending coronary artery (LAD) followed by reperfusion and measurement of the area at risk and infarct size). In some mice, the phosphatidylinositide 3-kinase (PI3K) inhibitor wortmannin was administered (24 µg/kg ip) 15 min before LAD.

RESULTS

We found that IH did not induce myocardial hypertrophy; rather both contractility and cardiac function improved with greater number of capillaries per unit volume and greater expression of VEGF-R2, but not of VEGF. Besides increasing the phosphorylation of protein kinase B (Akt) and the endothelial isoform of NO synthase with respect to control, IH reduced the infarct size and post-LAD proteins carbonylation, index of oxidative damage. Administration of wortmannin reduced the level of Akt phosphorylation and worsened the infarct size.

CONCLUSION

We conclude that the PI3K/Akt pathway is crucial for IH-induced cardioprotection and may represent a viable target to reduce myocardial I/R injury.

Redox signaling in pathophysiology of hypertension

Reactive oxygen species (ROS) are products of normal cellular metabolism and derive from various sources in different cellular compartments. Oxidative stress resultant from imbalance between ROS generation and antioxidant defense mechanisms is important in pathogenesis of cardiovascular diseases, such as hypertension, heart failure, atherosclerosis, diabetes, and cardiac hypertrophy. In this review we focus on hypertension and address sources of cellular ROS generation, mechanisms involved in regulation of radical homeostasis, superoxide dismutase isoforms in pathophysiology of hypertension; as well as radical intracellular signaling and phosphorylation processes in proteins of the affected cardiovascular tissues. Finally, we discuss the transcriptional factors involved in redox-sensitive gene transcription and antioxidant response, as well as their roles in hypertension.

Proteomic mechanisms of cardioprotection during mammalian hibernation in woodchucks, Marmota monax

Mammalian hibernation is a unique strategy for winter survival in response to limited food supply and harsh climate, which includes resistance to cardiac arrhythmias. We previously found that hibernating woodchucks (Marmota monax) exhibit natural resistance to Ca2+ overload-related cardiac dysfunction and nitric oxide (NO)-dependent vasodilation, which maintains myocardial blood flow during hibernation. Since the cellular/molecular mechanisms mediating the protection are less clear, the goal of this study was to investigate changes in the heart proteome and reveal related signaling networks that are involved in establishing cardioprotection in woodchucks during hibernation. This was accomplished using isobaric tags for a relative and absolute quantification (iTRAQ) approach. The most significant changes observed in winter hibernation compared to summer non-hibernation animals were upregulation of the antioxidant catalase and inhibition of endoplasmic reticulum (ER) stress response by downregulation of GRP78, mechanisms which could be responsible for the adaptation and protection in hibernating animals. Furthermore, protein networks pertaining to NO signaling, acute phase response, CREB and NFAT transcriptional regulations, protein kinase A and α-adrenergic signaling were also dramatically upregulated during hibernation. These adaptive mechanisms in hibernators may provide new directions to protect myocardium of non-hibernating animals, especially humans, from cardiac dysfunction induced by hypothermic stress and myocardial ischemia.

Delayed cardioprotective effects of WY-14643 are associated with inhibition of MMP-2 and modulation of Bcl-2 family proteins through PPAR-α activation in rat hearts subjected to global ischaemia–reperfusion

Peroxisome proliferator-activated receptors (PPARs) are ligand-activated transcription factors regulating cardiac lipid metabolism and energy homeostasis. Although the activation of PPARs has been implicated in cardioprotection, the molecular mechanisms are largely unexplored. In this study, we aimed to investigate the effect of the PPAR-α agonist WY-14643 (WY), mimicking a delayed effect of preconditioning in rat hearts exposed to acute ischaemia–reperfusion (I/R) 24 h later, and to define whether antioxidative and antiapoptotic mechanisms are involved. Treatment with WY markedly attenuated post-ischaemic contractile dysfunction (as evidenced by the reduced infarct size), the higher left ventricular developed pressure (LVDP) recovery, and the decreased occurrence of arrhythmias. These effects were abolished in the presence of the PPAR-α antagonist MK886. Heme oxygenase-1, a key antioxidative enzyme implicated in cytoprotection, was upregulated in response to WY at baseline, but was markedly reduced after I/R, indicating reduced oxidative stress. WY treatment was also associated with decreased mRNA levels and enzymatic activity of matrix metalloproteinase-2, and increased ratios of Bcl-2:Bax proteins. These results indicate that PPAR-α activation by its selective ligand WY may confer delayed preconditioning-like protection in rat hearts subjected to I/R by modulating oxidative stress, activation of matrix metalloproteinase-2, and expression of Bcl-2 and Bax.

The impact of lifestyle-related risk factors on cardiac response to ischemia and possibilities to restore impaired ischemic tolerance

Risk factors (RF) of cardiovascular diseases associated with modern lifestyle, such as stress, chronically increased blood pressure, hyperglycemia and dyslipidemia have a negative impact on the heart exposed to ischemia: they may facilitate its lethal injury (myocardial infarction) and occurrence of sudden death due to ventricular arrhythmias. On the other hand, some stressful stimuli related to RF including reactive oxygen species, transient episodes of ischemia (hypoxia), high glucose and other may play a dual role in the pathogenesis of ischemia/reperfusion (I/R) injury (IRI). Besides their deleterious effects, these factors may trigger adaptive processes in the heart resulting in greater resistance against IRI, which is also a characteristic feature of the female myocardium. However, sensitivity to ischemia is increasing with age in both genders. Current research indicates that comorbidity related to lifestyle may impair the cardiac response to acute ischemia not only by interference with pathophysiological mechanisms of IRI per se, but via suppression of intrinsic protective mechanisms in the heart and its ability to tolerate the ischemic challenges, although the role of RF has not been unequivocally proven. Moreover, even pathologically altered myocardium need not completely lose its adaptive potential. In addition, increased ischemic tolerance can be induced by the pleiotropic (independent of the primary) effects of some hypolipidemic and antidiabetic drugs, even in the diseased myocardium. This review addresses the issue of the impact of RF on cellular cardioprotective mechanisms and the possibilities to restore adaptive potential in subjects challenged with several RF. Reactivation of adaptive processes in the myocardium taking into consideration gender and age can contribute to optimalization of antiischemic therapy.

DPP4 deficiency exerts protective effect against H2O2 induced oxidative stress in isolated cardiomyocytes

Apart from the antihyperglycemic effects, DPP4 inhibitors and GLP-1 molecules are involved in the preservation of cardiac functions. We have demonstrated that DPP4-deficient rats possess resistance to endotoxemia and ischemia/reperfusion stress. However, whether the decrease of DPP4 activity simply augmented the GLP-1 signaling or that such decrease resulted in a change of cellular function remain unclear. Accordingly, we investigated the responses of H₂O₂-induced oxidative stress in adult wild-type and DPP4-deficient rats isolated cardiomyocytes. The coadministration of GLP-1 or DPP4 inhibitor was also performed to define the mechanisms. Cell viability, ROS concentration, catalase activity, glucose uptake, prosurvival, proapoptotic signaling, and contractile function were examined after cells exposed to H₂O₂. DPP4-deficient cardiomyocytes were found to be resistant to H₂O₂-induced cell death via activating AKT signaling, enhancing glucose uptake, preserving catalase activity, diminishing ROS level and proapoptotic signaling. GLP-1 concentration-dependently improved cell viability in wild-type cardiomyocyte against ROS stress, and the ceiling response concentration (200 nM) was chosen for studies. GLP-1 was shown to decrease H₂O₂-induced cell death by its receptor-dependent AKT pathway in wild-type cardiomyocytes, but failed to cause further activation of AKT in DPP4-deficient cardiomyocytes. Acute treatment of DPP4 inhibitor only augmented the protective effect of low dose GLP-1, but failed to alter fuel utilization or ameliorate cell viability in wild-type cardiomyocytes after H₂O₂ exposure. The improvement of cell viability after H₂O₂ exposure was correlated with the alleviation of cellular contractile dysfunction in both DPP4-deficient and GLP-1 treated wild-type cardiomyocytes. These findings demonstrated that GLP-1 receptor-dependent pathway is important and exert protective effect in wild-type cardiomyocyte. Long term loss of DPP4 activity increased the capability against ROS stress, which was more than GLP-1 dependent pathway.

PPAR-alpha activation as a preconditioning-like intervention in rats in vivo confers myocardial protection against acute ischaemia–reperfusion injury: involvement of PI3K–Akt

Peroxisome proliferator-activated receptors (PPAR) regulate the expression of genes involved in lipid metabolism, energy production, and inflammation. Their role in ischaemia–reperfusion (I/R) is less clear, although research indicates involvement of PPARs in some forms of preconditioning. This study aimed to explore the effects of PPAR-α activation on the I/R injury and potential cardioprotective downstream mechanisms involved. Langendorff-perfused hearts of rats pretreated with the selective PPAR-α agonist WY-14643 (WY, pirinixic acid; 3 mg·(kg body mass)·day–1; 5 days) were subjected to 30 min ischaemia – 2 h reperfusion with or without the phosphatidylinositol 3-kinase (PI3K)–Akt inhibitor wortmannin for the evaluation of functional (left ventricular developed pressure, LVDP) recovery, infarct size (IS), and reperfusion-induced arrhythmias. A 2-fold increase in baseline PPAR-α mRNA levels (qPCR) in the WY-treated group and higher post-I/R PPAR-α levels compared with those in untreated controls were accompanied by similar changes in the expression of PPAR-α target genes PDK4 and mCPT-1, regulating glucose and fatty acid metabolism, and by enhanced Akt phosphorylation. Post-ischaemic LVDP restoration in WY-treated hearts reached 60% ± 9% of the pre-ischaemic values compared with 24% ± 3% in the control hearts (P < 0.05), coupled with reduced IS and incidence of ventricular fibrillation that was blunted by wortmannin. Results indicate that PPAR-α up-regulation may confer preconditioning-like protection via metabolic effects. Downstream mechanisms of PPAR-α-mediated cardioprotection may involve PI3K–Akt activation.

Preconditioning approach in stem cell therapy for the treatment of infarcted heart

Nearly two decades of research in regenerative medicine have been focused on the development of stem cells as a therapeutic option for treatment of the ischemic heart. Given the ability of stem cells to regenerate the damaged tissue, stem-cell-based therapy is an ideal approach for cardiovascular disorders. Preclinical studies in experimental animal models and clinical trials to determine the safety and efficacy of stem cell therapy have produced encouraging results that promise angiomyogenic repair of the ischemically damaged heart. Despite these promising results, stem cell therapy is still confronted with issues ranging from uncertainty about the as-yet-undetermined "ideal" donor cell type to the nonoptimized cell delivery strategies to harness optimal clinical benefits. Moreover, these lacunae have significantly hampered the progress of the heart cell therapy approach from bench to bedside for routine clinical applications. Massive death of donor cells in the infarcted myocardium during acute phase postengraftment is one of the areas of prime concern, which immensely lowers the efficacy of the procedure. An overview of the published data relevant to stem cell therapy is provided here and the various strategies that have been adopted to develop and optimize the protocols to enhance donor stem cell survival posttransplantation are discussed, with special focus on the preconditioning approach.

Ginsenoside-Rg1 enhances angiogenesis and ameliorates ventricular remodeling in a rat model of myocardial infarction

Ginsenoside-Rg1 (Rg1) has been used in the traditional Chinese medicine for over 2,000 years. The present study was performed to test our hypothesis that Rg1 provides pro-angiogenic and anti-fibrotic benefits in the ischemic myocardium in a rat model of myocardial infarction. The expression of vascular endothelial growth factor (VEGF) and phosphorylation/activation of PI3K, Akt, and p38 MAPK signaling pathways were examined in human umbilical vein endothelial cells and in the myocardial samples of rats. In addition, the expression levels of TNF-α and collagen I level, the number of newly formed blood vessels, the extent of myocardial fibrosis, and left ventricular function were measured in vivo. Our results demonstrated that administration of Rg1 increased VEGF expression levels, activated PI3K/Akt, and inhibited p38 MAPK in vitro and in vivo. Furthermore, Rg1 increased the density of newly formed vessels, decreased TNF-α and collagen I expression levels and area of myocardial fibrosis, and improved left ventricle function in vivo. PI3K inhibitor LY294002 significantly attenuated Rg1-enhanced VEGF expression and capillary density. As well, inhibition of p38 MAPK slightly increased VEGF expression in vitro and in vivo, increased capillary density, and decreased TNF-α and collagen I expression levels and area of myocardial fibrosis in vivo. Rg1-induced activation of PI3K/Akt also contributed to the downregulation of p38 MAPK. Thus, Rg1 is effective in promoting angiogenesis and attenuating myocardial fibrosis, resulting in ameliorated left ventricular function. The possible mechanisms may involve activation of PI3K/Akt, inhibition of p38 MAPK, and cross talk between the two signaling pathways.

Environmental and genetic preconditioning for long-term anoxia responses requires AMPK in Caenorhabditis elegans

Background

Preconditioning environments or therapeutics, to suppress the cellular damage associated with severe oxygen deprivation, is of interest to our understanding of diseases associated with oxygen deprivation. Wildtype C. elegans exposed to anoxia enter into a state of suspended animation in which energy-requiring processes reversibly arrest. C. elegans at all developmental stages survive 24-hours of anoxia exposure however, the ability of adult hermaphrodites to survive three days of anoxia significantly decreases. Mutations in the insulin-like signaling receptor (daf-2) and LIN-12/Notch (glp-1) lead to an enhanced long-term anoxia survival phenotype.

Methodology/Principal Findings

In this study we show that the combined growth environment of 25°C and a diet of HT115 E. coli will precondition adult hermaphrodites to survive long-term anoxia; many of these survivors have normal movement after anoxia treatment. Animals fed the drug metformin, which induces a dietary-restriction like state in animals and activates AMPK in mammalian cell culture, have a higher survival rate when exposed to long-term anoxia. Mutations in genes encoding components of AMPK (aak-2, aakb-1, aakb-2, aakg-2) suppress the environmentally and genetically induced long-term anoxia survival phenotype. We further determine that there is a correlation between the animals that survive long-term anoxia and increased levels of carminic acid staining, which is a fluorescent dye that incorporates in with carbohydrates such as glycogen.

Conclusions/Significance

We conclude that small changes in growth conditions such as increased temperature and food source can influence the physiology of the animal thus affecting the responses to stress such as anoxia. Furthermore, this supports the idea that metformin should be further investigated as a therapeutic tool for treatment of oxygen-deprived tissues. Finally, the capacity for an animal to survive long bouts of severe oxygen deprivation is likely dependent on specific subunits of the heterotrimeric protein AMPK and energy stores such as carbohydrates.

Testosterone-down-regulated Akt pathway during cardiac ischemia/reperfusion: a mechanism involving BAD, Bcl-2 and FOXO3a

BACKGROUND

Lower levels of myocardial Akt activity in males are associated with a higher incidence of heart failure and worsened cardiac function after ischemia/reperfusion (I/R). While Akt activation by estrogen provides cardioprotection in females, no information exists regarding the effect of testosterone on the myocardial Akt pathway following I/R. We hypothesized that following I/R: (1) endogenous testosterone will decrease myocardial Akt activation in male hearts; (2) endogenous testosterone will mediate downstream signals of Akt, including Bad, Bcl-2, and FOXO3a; (3) administration of exogenous testosterone will recapitulate negative effects on the Akt pathway in castrated male hearts.

METHODS AND RESULTS

Rat hearts from age-matched adult males, females, castrated males, males with androgen receptor blocker-flutamide, castrated males with chronic 5α-dihydrotestosterone (DHT) implantation, or acute testosterone infusion (ATI) (n = 9/group) were subjected to I/R (Langendorff). Castration or flutamide treatment significantly up-regulated myocardial Akt activation, increased downstream apoptosis-regulatory molecules p-Bad, Bcl-2, p-FOXO3a, but reduced Fas-L, consistent with decreased myocardial injury in male hearts following I/R. ATI administration, but not chronic DHT, reversed these effects on Akt signaling associated with further exacerbated cardiac dysfunction in castrated males. Notably, lower levels of MnSOD were observed in male hearts, and castration or flutamide treatment restored myocardial MnSOD expression to the levels of females in male hearts after I/R.

CONCLUSION

Our study represents the initial evidence of testosterone-induced down-regulation of the Akt pathway in male hearts following I/R, thereby mediating cardiac injury through decreased p-Bad, reduced ratio of Bcl-2/Bax in the cytoplasm, and increased FOXO3a in the nucleus.

Protein Kinases as Drug Development Targets for Heart Disease Therapy

Protein kinases are intimately integrated in different signal transduction pathways for the regulation of cardiac function in both health and disease. Protein kinase A (PKA), Ca²⁺-calmodulin-dependent protein kinase (CaMK), protein kinase C (PKC), phosphoinositide 3-kinase (PI3K) and mitogen-activated protein kinase (MAPK) are not only involved in the control of subcellular activities for maintaining cardiac function, but also participate in the development of cardiac dysfunction in cardiac hypertrophy, diabetic cardiomyopathy, myocardial infarction, and heart failure. Although all these kinases serve as signal transducing proteins by phosphorylating different sites in cardiomyocytes, some of their effects are cardioprotective whereas others are detrimental. Such opposing effects of each signal transduction pathway seem to depend upon the duration and intensity of stimulus as well as the type of kinase isoform for each kinase. In view of the fact that most of these kinases are activated in heart disease and their inhibition has been shown to improve cardiac function, it is suggested that these kinases form excellent targets for drug development for therapy of heart disease.

Phosphorylation of phosphatidylinositol-3-kinase-protein kinase B and extracellular signal-regulated kinases 1/2 mediate reoxygenation-induced cardioprotection during hypoxia

In vivo exposure to chronic hypoxia (CH) depresses myocardial performance and tolerance to ischemia, but daily reoxyenation during CH (CHR) confers cardioprotection. To elucidate the underlying mechanism, we tested the role of phosphatidylinositol-3-kinase-protein kinase B (Akt) and p42/p44 extracellular signal-regulated kinases (ERK1/2), which are known to be associated with protection against ischemia/reperfusion (I/R). Male Sprague-Dawley rats were maintained for two weeks under CH (10% O(2)) or CHR (as CH but with one-hour daily exposure to room air). Then, hearts were either frozen for biochemical analyses or Langendorff-perfused to determine performance (intraventricular balloon) and tolerance to 30-min global ischemia and 45-min reperfusion, assessed as recovery of performance after I/R and infarct size (tetrazolium staining). Additional hearts were perfused in the presence of 15 micromol/L LY-294002 (inhibitor of Akt), 10 micromol/L UO-126 (inhibitor of ERK1/2) or 10 micromol/L PD-98059 (less-specific inhibitor of ERK1/2) given 15 min before ischemia and throughout the first 20 min of reperfusion. Whereas total Akt and ERK1/2 were unaffected by CH and CHR in vivo, in CHR hearts the phosphorylation of both proteins was higher than in CH hearts. This was accompanied by better performance after I/R (heart rate x developed pressure), lower end-diastolic pressure and reduced infarct size. Whereas the treatment with LY-294002 decreased the phosphorylation of Akt only, the treatment with UO-126 decreased ERK1/2, and that with PD-98059 decreased both Akt and ERK1/2. In all cases, the cardioprotective effect led by CHR was lost. In conclusion, in vivo daily reoxygenation during CH enhances Akt and ERK1/2 signaling. This response was accompanied by a complex phenotype consisting in improved resistance to stress, better myocardial performance and lower infarct size after I/R. Selective inhibition of Akt and ERK1/2 phosphorylation abolishes the beneficial effects of the reoxygenation. Therefore, Akt and ERK1/2 have an important role to mediate cardioprotection by reoxygenation during CH in vivo.

Changes in PPAR gene expression and myocardial tolerance to ischaemia: relevance to pleiotropic effects of statins

Peroxisome proliferator-activated receptors (PPAR), which are key transcriptional regulators of lipid metabolism and energy production, have been suggested to play an important role in myocardial ischaemia-reperfusion (I/R) injury. Their role in cardioprotection, however, is not yet fully elucidated. Statins have shown beneficial effects on I/R damage beyond lipid lowering, and some of their cardioprotective cholesterol-independent effects may be related to the regulation of PPAR. To clarify this issue, we explored a potential link between a response to I/R and changes in cardiac PPARalpha protein and gene expression in simvastatin-treated normocholesterolaemic rats. After 5 days of treatment with simvastatin (10 mg/kg per day, p.o.), Langendorff-perfused hearts were subjected to 30 min regional ischaemia (occlusion of the left anterior descending coronary artery) or global ischaemia and 2 h reperfusion for the evaluation of the infarct size (triphenyltetrazolium chloride and planimetry; as percentage of risk area), ischaemic arrhythmias, and postischaemic contractile recovery. Baseline PPARalpha mRNA and protein levels were increased by 3-fold and 2-fold, respectively, in simvastatin-treated hearts compared with the untreated controls. Simvastatin-treated hearts exhibited smaller size of infarction (11.5% +/- 0.4% vs. 33.7% +/- 4% in controls; p < 0.01), improved postischaemic contractile recovery, and lower severity of arrhythmias during ischaemia and early reperfusion. Enhanced resistance to I/R injury was associated with preservation of mRNA and protein levels of PPARalpha in contrast to their marked downregulation in controls. In conclusion, statin-induced changes in the expression of PPARalpha may contribute to attenuation of myocardial I/R injury and thus suggest the involvement of cardioprotective mechanisms independent of inhibition of HMG-CoA reductase.

Preconditioning and stem cell survival

The harsh ischemic and cytokine-rich microenvironment in the infarcted myocardium, infiltrated by the inflammatory and immune cells, offers a significant challenge to the transplanted donor stem cells. Massive cell death occurs during transplantation as well as following engraftment which significantly lowers the effectiveness of the heart cell therapy. Various approaches have been adopted to overcome this problem nevertheless with multiple limitations with each of these current approaches. Cellular preconditioning and reprogramming by physical, chemical, genetic, and pharmacological manipulation of the cells has shown promise and "prime" the cells to the "state of readiness" to withstand the rigors of lethal ischemia in vitro as well as posttransplantation. This review summarizes the past and present novel approaches of ischemic preconditioning, pharmacological and genetic manipulation using preconditioning mimetics, recombinant growth factor protein treatment, and reprogramming of stem cells to overexpress survival signaling molecules, microRNAs, and trophic factors for intracrine, autocrine, and paracrine effects on cytoprotection.

Mitochondrial KATP opening confers protection against lethal myocardial injury and ischaemia-induced arrhythmias in the rat heart via PI3K/Akt-dependent and -independent mechanismsThis article is one of a selection of papers published in a special issue on Advances in Cardiovascular Research

Opening of mitochondrial KATP channels (mitoKATP) has been reported to underlie protection against ischaemia–reperfusion injury induced by ischaemic preconditioning (I-PC); however, the molecular mechanisms of its antiarrhythmic effect have not been fully elucidated. We explored the involvement of phosphatidylinositol 3-kinase (PI3K)/Akt in the PC-like effect of mitoKATP opener diazoxide with particular regard to its role in protection against ischaemia-induced arrhythmias. Langendorff-perfused rat hearts were subjected to 30 min LAD occlusion with or without a prior 15 min of perfusion with diazoxide (50 µmol/L) given either alone (D-PC) or in combination with the PI3K/Akt inhibitor wortmannin (100 nmol/L). In an additional protocol, ischaemia was followed by 2 h reperfusion for infarct size (IS) determination (tetrazolium staining). The total number of premature ventricular complexes over the whole period of ischaemia, episodes of ventricular tachycardia and its duration were significantly lower in the D-PC group than in the non-preconditioned controls (158 ± 20, 2 ± 0.6 and 4.6 ± 1.8 s vs. 551 ± 61, 11 ± 2 and 42 ± 8 s, respectively; p < 0.05), concomitant with a 62% reduction in the size of infarction. Wortmannin modified neither arrhythmogenesis nor IS in the non-preconditioned hearts. Bracketing of diazoxide with wortmannin did not reverse the antiarrhythmic protection, whereas the IS-limiting effect was blunted. The results indicate that in contrast with the positive role of PI3K/Akt in protection against lethal myocardial injury, its activity is not involved in suppression of ischaemia-induced arrhythmias conferred by mitoKATP opening in the rat heart.

Pharmacological preconditioning in type 2 diabetic rat hearts: the roles of mitochondrial ATP-sensitive potassium channels and the phosphatidylinositol 3-kinase-Akt pathway

PURPOSE

The authors examined whether olprinone, a phosphodiesterase type 3 inhibitor, or isoflurane, a volatile anesthetic, could protect the heart against myocardial infarction in type 2 diabetic rats and whether the underlying mechanisms involve protein kinase C (PKC), mitochondrial ATP-sensitive potassium (m-K(ATP)) channels, or the phosphatidylinositol 3-kinase (PI3K)-Akt pathway.

METHODS

All rats underwent 30 min of coronary artery occlusion followed by 2 h of reperfusion. Wistar rats received isoflurane or olprinone before ischemia with or without the PKC inhibitor chelerythrine (CHE), the m-K(ATP) channel blocker 5-hydroxydecanoic acid (5HD), or the PI3K-Akt inhibitor LY294002 (LY). Goto-Kakizaki (GK) rats were randomly assigned to receive isoflurane or olprinone. In another group, GK rats received LY before the olprinone.

RESULTS

In the Wistar rats, both isoflurane (38 +/- 11%) and olprinone (40 +/- 11%) reduced infarct size as compared to the control group (59 +/- 8%). In the GK rats, olprinone (41 +/- 9%) but not isoflurane (53 +/- 11%) reduced infarct size as compared to the GK control group (58 +/- 14%). The beneficial effects of olprinone were blocked by LY (58 +/- 14%). In the Wistar rats, CHE, 5HD, and LY prevented isoflurane-induced reductions of infarct size. On the other hand, LY but not CHE or 5HD prevented olprinone-induced reductions of infarct size.

CONCLUSIONS

Olprinone but not isoflurane protects the heart against myocardial infarction in type 2 diabetic rats. The olprinone-induced cardioprotective effect is mediated by the PI3K-Akt pathway but not PKC or m-K(ATP) channels.