Cardioprotection in stunned and hibernating myocardium

The Impact of Coronary Ischemia Assessment on Outcomes in Those With Scar-Dependent Ventricular Tachycardia

BACKGROUND

Guidance and outcomes of coronary ischemia assessment (IA) in those with structural heart disease (SHD), presenting with monomorphic ventricular tachycardia (MMVT) is unclear.

OBJECTIVES

To assess the impact of IA on arrhythmic and non-arrhythmic outcomes in those with SHD.

METHODS

Patients presenting with MMVT over a 6-year period to a tertiary center were retrospectively analyzed. Propensity score-matched analysis was performed comparing those undergoing IA to those who did not. The primary endpoint was a composite of VT recurrence, appropriate ICD therapy, heart failure hospitalization, and death. Secondary analysis of the individual components of the composite was performed. Kaplan-Meier, univariate and multivariate analysis was performed to compare the two groups and derive predictors of poor outcomes.

RESULTS

Two hundred and seventeen patients (57.6% ICM) were analyzed. 55.8% underwent IA. Following propensity score-matching, 120 patients remained. At 12 months, freedom from the primary endpoint was 68.3% of those undergoing IA versus 43.3% who did not, p < 0.001, multivariate HR 0.56 (0.34-0.92). This was driven by a reduction in all-cause mortality, with a 12-month survival of 98.3% in those undergoing IA versus 86.5% in those not undergoing IA (p < 0.01). Coronary intervention was associated with a significantly higher event-free 12-month survival compared to those who did not undergo intervention (82.4% vs 51.5%, respectively, p = 0.01).

CONCLUSIONS

Patients with SHD presenting MMVT who undergo an IA have significantly improved freedom from VT recurrence, appropriate ICD therapies, HF hospitalization, and death compared to those who do not, driven by a reduction in mortality.

Connexin 43 modulates reverse electron transfer in cardiac mitochondria from inducible knock-out Cx43Cre-ER(T)/fl mice by altering the coenzyme Q pool

Succinate accumulates during myocardial ischemia and is rapidly oxidized during reperfusion, leading to reactive oxygen species (ROS) production through reverse electron transfer (RET) from mitochondrial complex II to complex I, and favoring cell death. Given that connexin 43 (Cx43) modulates mitochondrial ROS production, we investigated whether Cx43 influences RET using inducible knock-out Cx43Cre-ER(T)/fl mice. Oxygen consumption, ROS production, membrane potential and coenzyme Q (CoQ) pool were analyzed in subsarcolemmal (SSM, expressing Cx43) and interfibrillar (IFM) cardiac mitochondria isolated from wild-type Cx43fl/fl mice and Cx43Cre-ER(T)/fl knock-out animals treated with 4-hydroxytamoxifen (4OHT). In addition, infarct size was assessed in isolated hearts from these animals submitted to ischemia-reperfusion (IR), and treated or not with malonate, a complex II inhibitor attenuating RET. Succinate-dependent ROS production and RET were significantly lower in SSM, but not IFM, from Cx43-deficient animals. Mitochondrial membrane potential, a RET driver, was similar between groups, whereas CoQ pool (2.165 ± 0.338 vs. 4.18 ± 0.55 nmol/mg protein, p < 0.05) and its reduction state were significantly lower in Cx43-deficient animals. Isolated hearts from Cx43Cre-ER(T)/fl mice treated with 4OHT had a smaller infarct size after IR compared to Cx43fl/fl, despite similar concentration of succinate at the end of ischemia, and no additional protection by malonate. Cx43 deficiency attenuates ROS production by RET in SSM, but not IFM, and was associated with a decrease in CoQ levels and a change in its redox state. These results may partially explain the reduced infarct size observed in these animals and their lack of protection by malonate.

FICD deficiency protects mice from hypertrophy-induced heart failure via BiP-mediated activation of the UPR ER and ER-phagy

Cardiomyocytes require the HSP70 chaperone BiP to maintain proteostasis in the endoplasmic reticulum (ER) following cardiac stress. The adenylyl transferase (AMPylase) FICD is increasingly recognized to regulate BiP activity through the post-translational addition of an adenosine monophosphate moiety to BiP surface residues. However, the physiological impact of FICD-mediated BiP regulation in the context of cardiovascular health is unknown. Here, we find that FICD deficiency prevents pressure overload-associated heart failure, hypertrophy, and fibrosis, and that FICD knockout mice maintain normal cardiac function after cardiac pressure overload. At a cellular level, we observe that FICD-mediated BiP AMPylation blunts the induction of the unfolded protein response (UPR ER ) and impairs BiP interaction with FAM134B, an ER-phagy receptor, thus limiting ER-phagy induction under stress. In contrast, FICD loss significantly increases BiP-dependent UPR ER induction and ER-phagy in stressed cardiomyocytes. We also uncover cell type-specific consequences of FICD activity in response to ER stress, positioning FICD as a critical proteostasis regulator in cardiac tissue. Our results highlight a novel regulatory paradigm controlling stress resilience in cardiomyocytes and offer a rationale to consider FICD as a therapeutic target to treat cardiac hypertrophy.

Promising influences of gingerols against metabolic syndrome: A mechanistic review

Metabolic syndrome is an inflammatory disorder characterized by diabetes, obesity, atherosclerosis, and hypertension. Globally, this disease is increasing, especially in developed countries. Supposedly, herbal treatments for this disease likely have fewer adverse effects than chemical medications. Thus, they can be suitable options among the available chemical treatments. Ginger has been used as a spice and medicinal plant in traditional medicine and cooking. This herbal compound and its derivatives, such as 6-gingerol, have shown promising effects on various molecular aspects of metabolic syndrome. In this study, we reviewed and discussed the significant impacts of gingerol, a derivative of ginger, on metabolic syndrome through various mechanisms. The benefits of 6-gingerol include its effects on AMP-activated protein kinase (AMPK), which prevent diabetes, lipid regulating effect (peroxisome proliferator-activated receptors, PPARs), as well as its effects on enzymes and proteins preventing hyperlipidemia caused by a high-fat diet. In addition, 6-gingerol has anti-atherosclerosis and anti-hypertension effects through several molecular mechanisms. The current review will discuss various effects of 6-gingerol on molecular pathways involved in diabetes, obesity, atherosclerosis, and hypertension as characterizing features of metabolic syndrome and suggests that 6-gingerol can be a potential treatment agent for metabolic syndrome and shed light on a higher requirement for more pre-clinical and clinical investigations.

Dose-dependent effects of perfluorocarbon-based blood substitute on cardiac function in myocardial ischemia-reperfusion injury

The main goal of this study was to investigate the cardioprotective properties in terms of effects on cardiodynamics of perfluorocarbon emulsion (PFE) in ex vivo-induced ischemia-reperfusion injury of an isolated rat heart. The first part of the study aimed to determine the dose of 10% perfluoroemulsion (PFE) that would show the best cardioprotective effect in rats on ex vivo-induced ischemia-reperfusion injury of an isolated rat heart. Depending on whether the animals received saline or PFE, the animals were divided into a control or experimental group. They were also grouped depending on the applied dose (8, 12, 16 ml/kg body weight) of saline or PFE. We observed the huge changes in almost all parameters in the PFE groups in comparison with IR group without any pre-treatment. Calculated in percent, dp/dt max was the most changed parameter in group treated with 8 mg/kg, while the dp/dt min, SLVP, DLVP, HR, and CF were the most changed in group treated with 16 mg/kg 10 h before ischemia. The effects of 10% PFE are more pronounced if there is a longer period of time from application to ischemia, i.e., immediate application of PFE before ischemia (1 h) gave the weakest effects on the change of cardiodynamics of isolated rat heart. Therefore, the future of PFE use is in new indications and application methods, and PFE can also be referred to as antihypoxic and antiischemic blood substitute with mild membranotropic effects.

Diagnosis of coronary artery rethrombosis after effective systemic thrombolytic therapy in patients with ST-segment elevation myocardial infarction

The aim of the study was to evaluate the diagnostic significance of ST-segment re-elevation episodes registered with telemetric ECG monitoring in patients with ST-segment elevation myocardial infarction (STEMI) treated with thrombolytic therapy (TLT). The study included 117 patients with STEMI following effective TLT. The elective coronary angiography followed by percutaneous coronary interventions was performed in the interval from 3 to 24 hours after a successful systemic TLT. Before and after cardiac catheterization, the telemetric ECG monitoring was performed using AstroCard Telemetry system (Meditec, Russia). During the study, two groups of patients were formed. Group 1 included 85 patients (72.6%) without new ST-segment deviations on telemetry. 77 patients (90.6%) had no recurrent coronary artery thrombosis at angiography. Eight patients (9.4%) from group 1 were diagnosed with thrombosis of the infarct-related coronary artery. Group 2 included 32 patients (27.4%) who underwent TLT and then had ST-segment re-elevation episodes of 1 mV or more in the infarct-related leads, lasting for at least 1 minute. In group 2, in 27 of 32 patients (84.4%), thrombosis of the infarct-related coronary artery was confirmed (p<0.01 compared with group 1). In 71.9% cases, the recurrent ischemic episodes were asymptomatic ('painless myocardial ischemia') (p<0.01). Thus, in patients with STEMI and successful TLT, re-elevation of ST-segment during remote ECG monitoring is strongly related to angiographically documented coronary artery thrombotic reocclusion. The absence of chest pain during recurrent myocardial ischemia requires continuous ECG telemetry to select patients for the rescue percutaneous coronary interventions at an earlier stage.

In Vitro Models of the Blood-Brain Barrier

Traditional in vitro models can replicate many essential features of drug transport/permeability across the blood-brain barrier (BBB) but are not entirely projecting in vivo central nervous system (CNS) uptake. Species differences fail to translate experimental therapeutics from the research laboratory to the clinic. Improved in vitro modeling of human BBB is vital for both CNS drug discovery and delivery. High-end human BBB models fabricated by microfluidic technologies offer some solutions to this problem. BBB's complex physiological microenvironment has been established by increasing device complexity in terms of multiple cells, dynamic conditions, and 3D designs. It is now possible to predict the therapeutic effects of a candidate drug and identify new druggable targets by studying multicellular interactions using the advanced in vitro BBB models. This chapter reviews the current as well as an ideal in vitro model of the BBB.

Cardioprotective Effect of Stem-Leaf Saponins From Panax notoginseng on Mice With Sleep Derivation by Inhibiting Abnormal Autophagy Through PI3K/Akt/mTOR Pathway

Sleep deprivation (SD) may lead to serious myocardial injury in cardiovascular diseases. Saponins extracted from the roots of Panax notoginseng, a traditional Chinese medicine beneficial to blood circulation and hemostasis, are the main bioactive components exerting cardiovascular protection in the treatment of heart disorders, such as arrhythmia, ischemia and reperfusion injury, and cardiac hypertrophy. This study aimed to explore the protective effect of stem-leaf saponins from Panax notoginseng (SLSP) on myocardial injury in SD mice. SD was induced by a modified multi-platform method. Cardiac morphological changes were assessed by hematoxylin and eosin (H&E) staining. Heart rate and ejection fraction were detected by specific instruments. Serum levels of atrial natriuretic peptide (ANP) and lactate dehydrogenase (LDH) were measured with biochemical kits. Transmission electron microscopy (TEM), immunofluorescent, and Western blotting analysis were used to observe the process and pathway of autophagy and apoptosis in heart tissue of SD mice. In vitro, rat H9c2 cells pretreated with rapamycin and the effect of SLSP were explored by acridine orange staining, transient transfection, flow cytometry, and Western blotting analysis. SLSP prevented myocardial injury, such as morphological damage, accumulation of autophagosomes in heart tissue, abnormal high heart rate, serum ANP, and serum LDH induced by SD. In addition, it reversed the expressions of proteins involved in the autophagy and apoptosis and activated PI3K/Akt/mTOR signaling pathway that is disturbed by SD. On H9c2 cells induced by rapamycin, SLSP could markedly resume the abnormal autophagy and apoptosis. Collectively, SLSP attenuated excessive autophagy and apoptosis in myocardial cells in heart tissue induced by SD, which might be acted through activating PI3K/Akt/mTOR signaling pathway.

Identification and Quantification of Glutathionylated Cysteines under Ischemic Stress

Ischemia reperfusion injury contributes to adverse cardiovascular diseases in part by producing a burst of reactive oxygen species that induce oxidations of many muscular proteins. Glutathionylation is one of the major protein cysteine oxidations that often serve as molecular mechanisms behind the pathophysiology associated with ischemic stress. Despite the biological significance of glutathionylation in ischemia reperfusion, identification of specific glutathionylated cysteines under ischemic stress has been limited. In this report, we have analyzed glutathionylation under oxygen-glucose deprivation (OGD) or repletion of nutrients after OGD (OGD/R) by using a clickable glutathione approach that specifically detects glutathionylated proteins. Our data find that palmitate availability induces a global level of glutathionylation and decreases cell viability during OGD/R. We have then applied a clickable glutathione-based proteomic quantification strategy, which enabled the identification and quantification of 249 glutathionylated cysteines in response to palmitate during OGD/R in the HL-1 cardiomyocyte cell line. The subsequent bioinformatic analysis found 18 glutathionylated cysteines whose genetic variants are associated with muscular disorders. Overall, our data report glutathionylated cysteines under ischemic stress that may contribute to adverse outcomes or muscular disorders.

Cardiometabolism as an Interlocking Puzzle between the Healthy and Diseased Heart: New Frontiers in Therapeutic Applications

Cardiac metabolism represents a crucial and essential connecting bridge between the healthy and diseased heart. The cardiac muscle, which may be considered an omnivore organ with regard to the energy substrate utilization, under physiological conditions mainly draws energy by fatty acids oxidation. Within cardiomyocytes and their mitochondria, through well-concerted enzymatic reactions, substrates converge on the production of ATP, the basic chemical energy that cardiac muscle converts into mechanical energy, i.e., contraction. When a perturbation of homeostasis occurs, such as an ischemic event, the heart is forced to switch its fatty acid-based metabolism to the carbohydrate utilization as a protective mechanism that allows the maintenance of its key role within the whole organism. Consequently, the flexibility of the cardiac metabolic networks deeply influences the ability of the heart to respond, by adapting to pathophysiological changes. The aim of the present review is to summarize the main metabolic changes detectable in the heart under acute and chronic cardiac pathologies, analyzing possible therapeutic targets to be used. On this basis, cardiometabolism can be described as a crucial mechanism in keeping the physiological structure and function of the heart; furthermore, it can be considered a promising goal for future pharmacological agents able to appropriately modulate the rate-limiting steps of heart metabolic pathways.

Independent Functional Outcomes after Prolonged Coma following Cardiac Arrest: A Mechanistic Hypothesis

OBJECTIVE

Survivors of prolonged (>2 weeks) post-cardiac arrest (CA) coma are expected to remain permanently disabled. We aimed to investigate 3 outlier patients who ultimately achieved independent functional outcomes after prolonged post-CA coma to identify electroencephalographic (EEG) markers of their recovery potential. For validation purposes, we also aimed to evaluate these markers in an independent cohort of post-CA patients.

METHODS

We identified 3 patients with late recovery from coma (17-37 days) following CA who recovered to functionally independent behavioral levels. We performed spectral power analyses of available EEGs during prominent burst suppression patterns (BSP) present in all 3 patients. Using identical methods, we also assessed the relationship of intraburst spectral power and outcomes in a prospectively enrolled cohort of post-CA patients. We performed chart reviews of common clinical, imaging, and EEG prognostic variables and clinical outcomes for all patients.

RESULTS

All 3 patients with late recovery from coma lacked evidence of overwhelming cortical injury but demonstrated prominent BSP on EEG. Spectral analyses revealed a prominent theta (~4-7Hz) feature dominating the bursts during BSP in these patients. In the prospective cohort, similar intraburst theta spectral features were evident in patients with favorable outcomes; patients with BSP and unfavorable outcomes showed either no features, transient burst features, or decreasing intraburst frequencies with time.

INTERPRETATION

BSP with theta (~4-7Hz) peak intraburst spectral power after CA may index a recovery potential. We discuss our results in the context of optimizing metabolic substrate availability and stimulating the corticothalamic system during recovery from prolonged post-CA coma. ANN NEUROL 2020;87:618-632.

Clinical significance of chronic myocardial ischemia in coronary artery disease patients

Myocardial ischemia is considered the cornerstone of the treatment of patients with coronary artery disease (CAD). Although the deleterious effects of myocardial infarction, the maximum expression of ischemia, have been extensively studied and described, the clinical effects of chronic, documented myocardial ischemia are not completely clarified. The first studies that compared therapies for coronary disease focused on the presence of anatomical features and assessed ischemia based on the interpretation of the findings of obstructive atherosclerotic lesions. They suggested that revascularization interventions did not confer any clinical advantage over medical therapy (MT), in terms of cardiac or overall death. Other retrospective studies that were dedicated to assessing the impact of documented stress-induced ischemia on cardiovascular outcomes have suggested a prognostic impact of chronic ischemia. However, this has been questioned in recent studies. Moreover, the previous understanding that chronic ischemia could lead to worsening of ventricular function was not confirmed in a recent study. Thus, the prognostic significance of stress-induced ischemia has been questioned. Regarding treatment options, although some previous analyses have suggested that interventional therapies would reduce cardiovascular events in CAD patients with documented ischemia, recent post-hoc studies and metanalysis have shown distinct results. In this review article, the authors discuss myocardial ischemia, the different responses of the myocardium to ischemic insults, ischemic preconditioning, and the main findings of recent studies about the clinical aspects and treatment of patients with chronic, documented myocardial ischemia.

Phosphomimetic-mediated in vitro rescue of hypertrophic cardiomyopathy linked to R58Q mutation in myosin regulatory light chain

Myosin regulatory light chain (RLC) phosphorylation is important for cardiac muscle mechanics/function as well as for the Ca²⁺ -troponin/tropomyosin regulation of muscle contraction. This study focuses on the arginine to glutamine (R58Q) substitution in the human ventricular RLC (MYL2 gene), linked to malignant hypertrophic cardiomyopathy in humans and causing severe functional abnormalities in transgenic (Tg) R58Q mice, including inhibition of cardiac RLC phosphorylation. Using a phosphomimic recombinant RLC variant where Ser-15 at the phosphorylation site was substituted with aspartic acid (S15D) and placed in the background of R58Q, we aimed to assess whether we could rescue/mitigate R58Q-induced structural/functional abnormalities in vitro. We show rescue of several R58Q-exerted adverse phenotypes in S15D-R58Q-reconstituted porcine cardiac muscle preparations. A low level of maximal isometric force observed for R58Q- versus WT-reconstituted fibers was restored by S15D-R58Q. Significant beneficial effects were also observed on the V_max of actin-activated myosin ATPase activity in S15D-R58Q versus R58Q-reconstituted myosin, along with its binding to fluorescently labeled actin. We also report that R58Q promotes the OFF state of myosin, both in reconstituted porcine fibers and in Tg mouse papillary muscles, thereby stabilizing the super-relaxed state (SRX) of myosin, characterized by a very low ATP turnover rate. Experiments in S15D-R58Q-reconstituted porcine fibers showed a mild destabilization of the SRX state, suggesting an S15D-mediated shift in disordered-relaxed (DRX)↔SRX equilibrium toward the DRX state of myosin. Our study shows that S15D-phosphomimic can be used as a potential rescue strategy to abrogate/alleviate the RLC mutation-induced phenotypes and is a likely candidate for therapeutic intervention in HCM patients.

Stress response protein GJA1-20k promotes mitochondrial biogenesis, metabolic quiescence, and cardioprotection against ischemia/reperfusion injury

Connexin 43 (Cx43), a product of the GJA1 gene, is a gap junction protein facilitating intercellular communication between cardiomyocytes. Cx43 protects the heart from ischemic injury by mechanisms that are not well understood. GJA1 mRNA can undergo alternative translation, generating smaller isoforms in the heart, with GJA1-20k being the most abundant. Here, we report that ischemic and ischemia/reperfusion (I/R) injuries upregulate endogenous GJA1-20k protein in the heart, which targets to cardiac mitochondria and associates with the outer mitochondrial membrane. Exploring the functional consequence of increased GJA1-20k, we found that AAV9-mediated gene transfer of GJA1-20k in mouse hearts increases mitochondrial biogenesis while reducing mitochondrial membrane potential, respiration, and ROS production. By doing so, GJA1-20k promotes a protective mitochondrial phenotype, as seen with ischemic preconditioning (IPC), which also increases endogenous GJA1-20k in heart lysates and mitochondrial fractions. As a result, AAV9-GJA1-20k pretreatment reduces myocardial infarct size in mouse hearts subjected to in vivo ischemic injury or ex vivo I/R injury, similar to an IPC-induced cardioprotective effect. In conclusion, GJA1-20k is an endogenous stress response protein that induces mitochondrial biogenesis and metabolic hibernation, preconditioning the heart against I/R insults. Introduction of exogenous GJA1-20k is a putative therapeutic strategy for patients undergoing anticipated ischemic injury.

Connexins and Nitric Oxide Inside and Outside Mitochondria: Significance for Cardiac Protection and Adaptation

Irreversible myocardial damage happens in the presence of prolonged and severe ischemia. Several phenomena protect the heart against myocardial infarction and other adverse outcomes of ischemia and reperfusion (IR), namely: hibernation related to stunned myocardium, ischemic preconditioning (IPC), ischemic post-conditioning, and their pharmacological surrogates. Ischemic preconditioning consists in the induction of a brief IR to reduce damage of the tissue caused by prolonged and severe ischemia. Nitric oxide (NO) signaling plays an essential role in IPC. Nitric oxide-sensitive guanylate cyclase/cyclic guanosine-3′,5′-monophosphate (cGMP)-dependent protein kinase type I-signaling pathway protects against the IR injury during myocardial infarction. Mitochondrial ATP-sensitive and Ca²⁺-activated K⁺ channels are involved in NO-mediated signaling in IPC. Independently of the cGMP-mediated induction of NO production, S-nitrosation represents a regulatory molecular mechanism similar to phosphorylation and is essential for IPC. Unlike conditioning phenomena, the mechanistic basis of myocardial stunning and hibernation remains poorly understood. In this review article, we hypothesize that the disruption of electrical syncytium of the myocardium may underly myocardial stunning and hibernation. Considering that the connexins are the building blocks of gap junctions which represent primary structural basis of electrical syncytium, we discuss data on the involvement of connexins into myocardial conditioning, stunning, and hibernation. We also show how NO-mediated signaling is involved in myocardial stunning and hibernation. Connexins represent an essential element of adaptation phenomena of the heart at the level of both the cardio- myocytes and the mitochondria. Nitric oxide targets mitochondrial connexins which may affect electrical syncytium continuum in the heart. Mitochondrial connexins may play an essential role in NO-dependent mechanisms of myocardial adaptation to ischemia.

Preservation of Functional Microvascular Bed Is Vital for Long-Term Survival of Cardiac Myocytes Within Large Transmural Post-Myocardial Infarction Scar

This study was aimed to understand the mechanism of persistent cardiac myocyte (CM) survival in myocardial infarction (MI) scars. A transmural MI was induced in 12-month-old Sprague-Dawley rats by permanent coronary artery ligation. The hearts were collected 3 days, 1, 2, 4, 8, and 12 weeks after MI and evaluated with histology, immunohistochemistry, and quantitative morphometry. Vasculature patency was assessed in 4-, 8-, and 12-week-old scars by infusion of 15-micron microspheres into the left ventricle before euthanasia. The infarcted/scarred area has a small continually retained population of surviving CMs in subendocardial and subepicardial regions. Surprisingly, whereas the transverse area of subepicardial CMs remained relatively preserved or even enlarged over 12 post-MI weeks, subendocardial CMs underwent progressive atrophy. Nevertheless, the fractional volume of viable CMs remained comparable in mature scars 4, 8, and 12 weeks after MI (3.6 ± 0.4%, 3.4 ± 0.5%, and 2.5 ± 0.3%, respectively). Despite the opposite dynamics of changes in size, CMs of both regions displayed sarcomeres and gap junctions. Most importantly, surviving CMs were always accompanied by patent microvessels linked to a venous network composed of Thebesian veins, intramural sinusoids, and subepicardial veins. Our findings reveal that long-term survival of CMs in transmural post-MI scars is sustained by a local microcirculatory bed.

Ischemia/Reperfusion

Ischemic disorders, such as myocardial infarction, stroke, and peripheral vascular disease, are the most common causes of debilitating disease and death in westernized cultures. The extent of tissue injury relates directly to the extent of blood flow reduction and to the length of the ischemic period, which influence the levels to which cellular ATP and intracellular pH are reduced. By impairing ATPase-dependent ion transport, ischemia causes intracellular and mitochondrial calcium levels to increase (calcium overload). Cell volume regulatory mechanisms are also disrupted by the lack of ATP, which can induce lysis of organelle and plasma membranes. Reperfusion, although required to salvage oxygen-starved tissues, produces paradoxical tissue responses that fuel the production of reactive oxygen species (oxygen paradox), sequestration of proinflammatory immunocytes in ischemic tissues, endoplasmic reticulum stress, and development of postischemic capillary no-reflow, which amplify tissue injury. These pathologic events culminate in opening of mitochondrial permeability transition pores as a common end-effector of ischemia/reperfusion (I/R)-induced cell lysis and death. Emerging concepts include the influence of the intestinal microbiome, fetal programming, epigenetic changes, and microparticles in the pathogenesis of I/R. The overall goal of this review is to describe these and other mechanisms that contribute to I/R injury. Because so many different deleterious events participate in I/R, it is clear that therapeutic approaches will be effective only when multiple pathologic processes are targeted. In addition, the translational significance of I/R research will be enhanced by much wider use of animal models that incorporate the complicating effects of risk factors for cardiovascular disease. © 2017 American Physiological Society. Compr Physiol 7:113-170, 2017.

Caveolin-3 plays a critical role in autophagy after ischemia-reperfusion

Autophagy is a dynamic recycling process responsible for the breakdown of misfolded proteins and damaged organelles, providing nutrients and energy for cellular renovation and homeostasis. Loss of autophagy is associated with cardiovascular diseases. Caveolin-3 (Cav-3), a muscle-specific isoform, is a structural protein within caveolae and is critical to stress adaptation in the heart. Whether Cav-3 plays a role in regulating autophagy to modulate cardiac stress responses remains unknown. In the present study, we used HL-1 cells, a cardiac muscle cell line, with stable Cav-3 knockdown (Cav-3 KD) and Cav-3 overexpression (Cav-3 OE) to study the impact of Cav-3 in regulation of autophagy. We show that traditional stimulators of autophagy (i.e., rapamycin and starvation) result in upregulation of the process in Cav-3 OE cells while Cav-3 KD cells have a blunted response. Cav-3 coimmunoprecipitated with beclin-1 and Atg12, showing an interaction of caveolin with autophagy-related proteins. In the heart, autophagy may be a major regulator of protection from ischemic stress. We found that Cav-3 KD cells have a decreased expression of autophagy markers [beclin-1, light chain (LC3-II)] after simulated ischemia and ischemia-reperfusion (I/R) compared with WT, whereas OE cells showed increased expression. Moreover, Cav-3 KD cells showed increased cell death and higher level of apoptotic proteins (cleaved caspase-3 and cytochrome c) with suppressed mitochondrial function in response to simulated ischemia and I/R, whereas Cav-3 OE cells were protected and had preserved mitochondrial function. Taken together, these results indicate that autophagy regulates adaptation to cardiac stress in a Cav-3-dependent manner.

A major miss in prognostication after cardiac arrest: Burst suppression and brain healing

We report a case with therapeutic hypothermia after cardiac arrest where meaningful recovery far exceeded anticipated negative endpoints following cardiac arrest with loss of brainstem reflexes and subsequent status epilepticus. This man survived and recovered after an out-of-hospital cardiac arrest followed by a 6-week coma with absent motor responses and 5 weeks of burst suppression. Standard criteria suggested no chance of recovery. His recovery may relate to the effect of burst-suppression on EEG to rescue neurons near neuronal cell death. Further research to understand the mechanisms of therapeutic hypothermia and late restoration of neuronal functional capacity may improve prediction and aid end-of-life decisions after cardiac arrest.

6-Gingerol induces autophagy to protect HUVECs survival from apoptosis

6-Gingerol, the major pharmacologically-active component of ginger, has the potential to prevent heart disease. However, the mechanisms are not well understood. In this study, the protective effect of 6-gingerol against hydrogen peroxide-induced apoptosis in human umbilical vein endothelial cells (HUVECs) was investigated. Apoptosis was detected by Hoechst 33342 and Flow cytometry analysis. To further elucidate the crosstalk between apoptosis and autophagy, we tested the expression of autophagy related proteins, LC3B, Bcl-2, Beclin1, AKT, p-AKT, mechanistic target of rapamycin (mTOR), and p-mTOR. Furthermore, mitochondrial membrane potential and the intracellular generation of reactive oxygen species (ROS) were also investigated. Our data revealed that 6-gingerol significantly reduced apoptosis by inducing autophagy. It has been demonstrated that 6-gingerol suppressed the phosphatidylinositol 3-kinase (PI3K)/AKT/mTOR signaling pathway, increased the expression of Beclin1 to promote autophagy, and increased Bcl-2 expression to inhibit apoptosis. In addition, the damage of mitochondrial was protected, and ROS level was decreased by 6-gingerol. These firmly indicate 6-gingerol has a strong protective ability against the apoptosis caused by oxidative stress in HUVECs, and the mechanism may relate to the induction of autophagy. Our data suggest 6-gingerol may be beneficial in the prevention of atherosclerosis.

Pathobiology of Ischemic Heart Disease: Past, Present and Future

This review provides a perspective on knowledge of ischemic heart disease (IHD) obtained from the contemporary era of research which began in the 1960s and has continued to the present day. Important discoveries have been made by basic and translational scientists and clinicians. Pathologists have contributed significantly to insights obtained from experimental studies and clinicopathological studies in humans. The review also provides a perspective for future directions in research in IHD aimed at increasing basic knowledge and developing additional therapeutic options for patients with IHD.

Molecular targets for anti-oxidative protection of green tea polyphenols against myocardial ischemic injury

Ischemic heart disease is the leading cause of death worldwide. An improved understanding of the mechanisms involved in myocardial injury would allow intervention downstream in the pathway where certain drugs including natural products could be efficiently applied to target the end effectors of the cell death pathway. Green tea polyphenols (GTPs) have potent anti-oxidative capabilities, which may account for their beneficial effects in preventing oxidative stress associated with ischemia injury. Although studies have provided convincing evidence to support the protective effects of GTPs in cardiovascular system, the potential end effectors that mediate cardiac protection are only beginning to be addressed. Proteomics analyses widely used to identify the protein targets for many cardiovascular diseases have advanced the discovery of the signaling mechanism for GTPs-mediated cardio-protection. This review focuses on putative triggers, mediators, and end effectors for the GTPs-mediated cardio-protection signaling pathways engaged in myocardial ischemia crisis, allowing a promising natural product to be used for ameliorating oxidative stress associated with ischemic heart diseases.

Overexpression of microRNA-99a attenuates heart remodelling and improves cardiac performance after myocardial infarction

MicroRNAs are involved in the regulation of various cellular processes, including cell apoptosis and autophagy. Expression of microRNA-99a (miR-99a) is reduced in apoptotic neonatal mice ventricular myocytes (NMVMs) subjected to hypoxia. We hypothesize that miR-99a might restore cardiac function after myocardial infarction (MI) by up-regulation of myocyte autophagy and apoptosis. We observed down-regulated miR-99a expression in NMVMs exposed to hypoxia using TaqMan quantitative reverse transcriptase-polymerase chain reaction analysis (RT-PCR). We also observed that miR-99a overexpression decreased hypoxia-mediated apoptosis in cultured NMVMs. To investigate whether overexpression of miR-99a in vivo could improve cardiac function in ischaemic heart, adult C57/BL6 mice undergoing MI were randomized into two groups and were intra-myocardially injected with lenti-99a-green fluorescent protein (GFP) or lenti-GFP (control). Four weeks after MI, lenti-99a-GFP group showed significant improvement in both left ventricular (LV) function and survival ratio, as compared to the lenti-GFP group. Histological analysis, western blotting analysis and electron microscopy revealed decreased cellular apoptosis and increased autophagy in cardiomyocytes of lenti-99a-GFP group. Furthermore, western blotting analysis showed inhibited mammalian target of rapamycin (mTOR) expression in the border zones of hearts in miR-99a-treated group. Our results demonstrate that miR-99a overexpression improves both cardiac function and survival ratio in a murine model of MI by preventing cell apoptosis and increasing autophagy via an mTOR/P70/S6K signalling pathway. These findings suggest that miR-99a plays a cardioprotective role in post-infarction LV remodelling and increased expression of miR-99a may have a therapeutic potential in ischaemic heart disease.

Organs-on-a-chip: a new tool for drug discovery

INTRODUCTION

The development of emerging in vitro tissue culture platforms can be useful for predicting human response to new compounds, which has been traditionally challenging in the field of drug discovery. Recently, several in vitro tissue-like microsystems, also known as 'organs-on-a-chip', have emerged to provide new tools for better evaluating the effects of various chemicals on human tissue.

AREAS COVERED

The aim of this article is to provide an overview of the organs-on-a-chip systems that have been recently developed. First, the authors introduce single-organ platforms, focusing on the most studied organs such as liver, heart, blood vessels and lung. Later, the authors briefly describe tumor-on-a-chip platforms and highlight their application for testing anti-cancer drugs. Finally, the article reports a few examples of other organs integrated in microfluidic chips along with preliminary multiple-organs-on-a-chip examples. The article also highlights key fabrication points as well as the main application areas of these devices.

EXPERT OPINION

This field is still at an early stage and major challenges need to be addressed prior to the embracement of these technologies by the pharmaceutical industry. To produce predictive drug screening platforms, several organs have to be integrated into a single microfluidic system representative of a humanoid. The routine production of metabolic biomarkers of the organ constructs, as well as their physical environment, have to be monitored prior to and during the delivery of compounds of interest to be able to translate the findings into useful discoveries.

Change in paternal grandmothers' early food supply influenced cardiovascular mortality of the female grandchildren

BACKGROUND

This study investigated whether large fluctuations in food availability during grandparents' early development influenced grandchildren's cardiovascular mortality. We reported earlier that changes in availability of food - from good to poor or from poor to good - during intrauterine development was followed by a double risk of sudden death as an adult, and that mortality rate can be associated with ancestors' childhood availability of food. We have now studied transgenerational responses (TGR) to sharp differences of harvest between two consecutive years' for ancestors of 317 people in Överkalix, Sweden.

RESULTS

The confidence intervals were very wide but we found a striking TGR. There was no response in cardiovascular mortality in the grandchild from sharp changes of early exposure, experienced by three of the four grandparents (maternal grandparents and paternal grandfathers). If, however, the paternal grandmother up to puberty lived through a sharp change in food supply from one year to next, her sons' daughters had an excess risk for cardiovascular mortality (HR 2.69, 95% confidence interval 1.05-6.92). Selection or learning and imitation are unlikely explanations. X-linked epigenetic inheritance via spermatozoa seemed to be plausible, with the transmission, limited to being through the father, possibly explained by the sex differences in meiosis.

CONCLUSION

The shock of change in food availability seems to give specific transgenerational responses.

Regulation of cellular gas exchange, oxygen sensing, and metabolic control

Cells must continuously monitor and couple their metabolic requirements for ATP utilization with their ability to take up O2 for mitochondrial respiration. When O2 uptake and delivery move out of homeostasis, cells have elaborate and diverse sensing and response systems to compensate. In this review, we explore the biophysics of O2 and gas diffusion in the cell, how intracellular O2 is regulated, how intracellular O2 levels are sensed and how sensing systems impact mitochondrial respiration and shifts in metabolic pathways. Particular attention is paid to how O2 affects the redox state of the cell, as well as the NO, H2S, and CO concentrations. We also explore how these agents can affect various aspects of gas exchange and activate acute signaling pathways that promote survival. Two kinds of challenges to gas exchange are also discussed in detail: when insufficient O2 is available for respiration (hypoxia) and when metabolic requirements test the limits of gas exchange (exercising skeletal muscle). This review also focuses on responses to acute hypoxia in the context of the original "unifying theory of hypoxia tolerance" as expressed by Hochachka and colleagues. It includes discourse on the regulation of mitochondrial electron transport, metabolic suppression, shifts in metabolic pathways, and recruitment of cell survival pathways preventing collapse of membrane potential and nuclear apoptosis. Regarding exercise, the issues discussed relate to the O2 sensitivity of metabolic rate, O2 kinetics in exercise, and influences of available O2 on glycolysis and lactate production.

Hypothermia may attenuate ischemia/reperfusion-induced cardiomyocyte death by reducing autophagy

OBJECTIVE

We sought to assess the effect of therapeutic hypothermia on the autophagy that occurred in ischemia-reperfused (IR) H9c2 cardiomyocytes.

METHODS

In control studies, the H9c2 cells at a density of 1 × 10(5) per culture dish in six-well plate were exposed to normoxic culture medium at 37 °C for 12h. All assays contained appropriate controls and were performed in triplicate and repeated on three separately initiated cultures. In hypothermia-treated group, the ischemic and hypoxic cells were maintained in a 32 °C incubation. The trypan blue exclusion method was used to assess the cell viability. Autophagy was evaluated by determining both the microtubule-associated protein 1 light chain 3 [LC3] levels and punctuate distribution of the autophagic vesicle associated form [LC3-II].

RESULTS

The results were mean ± standard error of mean of triplicates. The viable cell percentage for control group, IR group, and IR group treated with hypothermia at the start of ischemia, or reperfusion were 100% ± 9%, 20% ± 1%, 32% ± 3%, and 41% ± 3%, respectively. The cell death in I/R H9c2 cells was positively associated with increased LC3 levels and punctuate distribution of (LC3-II). Mild hypothermia adopted at the start of ischemia or reperfusion significantly reduced both the cell death and the autophagy in H9c2 cells.

CONCLUSION

Our data indicate that in H9c2, IR stimulates cell autophagy and causes cell death, which can be attenuated by mild hypothermia. Our results, if further confirmed in vivo, may have important clinical implications during IR injury.

Cell-based vasculogenic studies in preclinical models of chronic myocardial ischaemia and hibernation

INTRODUCTION

Coronary artery disease commonly leads to myocardial ischaemia and hibernation. Relevant preclinical models of these conditions are essential to evaluate new therapeutic options such as cell-based vasculogenic therapies.

AREAS COVERED

In this article, the authors first review basic concepts of myocardial ischaemia/hibernation and relevant techniques to assess myocardial viability. Then, preclinical models of chronic myocardial ischaemia and hibernation, induced by devices such as ameroid constrictors, Delrin stenosis, hydraulic occluders, and coils/stents are described. Lastly, the authors discuss cell-based vasculogenic therapy, and summarise studies conducted in large animal models of chronic myocardial ischaemia and hibernation.

EXPERT OPINION

Approximately one-third of patients with viable myocardium do not undergo revascularisation; however, this population is at high risk for cardiac events and would surely benefit from effective cell-based therapy. Because of the modest benefits in clinical studies, preclinical models accurately representing clinical myocardial ischemia/hibernation are necessary to better understand and appropriately direct regenerative therapy research.

Potentially neuroprotective gene modulation in an in vitro model of mild traumatic brain injury

In this study, we investigated the hypothesis that mild traumatic brain injury (mTBI) triggers a controlled gene program as an adaptive response finalized to neuroprotection, similar to that found in hibernators and in ischemic preconditioning. A stretch injury device was used to produce an equi-biaxial strain field in rat organotypic hippocampal slice cultures at a specified Lagrangian strain of 10 % and a constant strain rate of 20 s(-1). After 24 h from injury, propidium iodide staining, HPLC analysis of metabolites and microarray analysis of cDNA were performed to evaluate cell viability, cell energy state and gene expression, respectively. Compared to control cultures, 10 % stretch injured cultures showed no change in viability, but demonstrated a hypometabolic state (decreased ATP, ATP/ADP, and nicotinic coenzymes) and a peculiar pattern of gene modulation. The latter was characterized by downregulation of genes encoding for proteins of complexes I, III, and IV of the mitochondrial electron transport chain and of ATP synthase; downregulation of transcriptional and translational genes; downregulation and upregulation of genes controlling the synthesis of glutamate and GABA receptors, upregulation of calmodulin and calmodulin-binding proteins; proper modulation of genes encoding for proapoptotic and antiapoptotic proteins. These results support the hypothesis that, following mTBI, a hibernation-type response is activated in non-hibernating species. Unlike in hibernators and ischemic preconditioning, this adaptive gene programme, aimed at achieving maximal neuroprotection, is not triggered by decrease in oxygen availability. It seems rather activated to avoid increase in oxidative/nitrosative stress and apoptosis during a transient period of mitochondrial malfunctioning.

Acute myocardial infarction and thyroid function: new pathophysiological and therapeutic perspectives

In the post-reperfusion era, molecular and genetic mechanisms of cardioprotection and regeneration represent new therapeutic challenges to limit infarct size and minimize post-ischemic remodeling after acute myocardial infarction (AMI). Activation of cell survival mechanisms can be promoted by the administration of external drugs, stimulation of internal mechanisms, and genetic manipulation to delete or replace pathological genes or enhance gene expression. Among internal cardiovascular regulatory mechanisms, thyroid hormones (THs) may play a fundamental role. TH has a critical role in cardiovascular development and homeostasis in both physiological and pathological conditions. In experimental AMI, TH has been shown to affect cardiac contractility, left ventricular (LV) function, and remodeling. Several experimental studies have clearly shown that THs participate in the regulation of molecular mechanisms of angiogenesis, cardioprotection, cardiac metabolism, and ultimately myocyte regeneration, changes that can reverse left ventricular remodeling by favorably improving myocyte shape and geometry of LV cavity, thus improving systolic and diastolic performance. This review is focused on the role of thyroid on AMI evolution and on the potential novel option of thyroid-related treatment of AMI.

Myocardial viability: what we knew and what is new

Some patients with chronic ischemic left ventricular dysfunction have shown significant improvements of contractility with favorable long-term prognosis after revascularization. Several imaging techniques are available for the assessment of viable myocardium, based on the detection of preserved perfusion, preserved glucose metabolism, intact cell membrane and mitochondria, and presence of contractile reserve. Nuclear cardiology techniques, dobutamine echocardiography and positron emission tomography are used to assess myocardial viability. In recent years, new advances have improved methods of detecting myocardial viability. This paper summarizes the pathophysiology, methods, and impact of detection of myocardial viability, concentrating on recent advances in such methods. We reviewed the literature using search engines MIDLINE, SCOUPS, and EMBASE from 1988 to February 2012. We used key words: myocardial viability, hibernation, stunning, and ischemic cardiomyopathy. Recent studies showed that the presence of viable myocardium was associated with a greater likelihood of survival in patients with coronary artery disease and LV dysfunction, but the assessment of myocardial viability did not identify patients with survival benefit from revascularization, as compared with medical therapy alone. This topic is still debatable and needs more evidence.

Activities of some caspase cascade enzymes and myocardial contractility in experimental left ventricular focal ischemia

Focal left ventricular ischemia was modeled in male Chinchilla rabbits. Activities of caspase-3 and caspase-8 in the left and right ventricular myocardium and myocardial contractility were studied after 1, 3, and 5 days. Caspase-3 activity increased significantly in the left ventricular peri-infarction zone and right ventricular myocardium, while caspase-8 activity did not differ from the control. Left ventricular contractility decreased significantly and the hemodynamic load of the right ventricle sharply increased. These results attest to induction of the internal (mitochondrial) pathway of apoptosis in myocardial cells most likely caused by left ventricular hypoxia and right ventricular overload.

Proteomic analysis of effluents from perfused human heart for transplantation: identification of potential biomarkers for ischemic heart damage

Background

Biomarkers released from the heart at early stage of ischemia are very important to diagnosis of ischemic heart disease and salvage myocytes from death. Known specific markers for blood tests including CK-MB, cardiac troponin T (cTnT) and cardiac troponin I (cTnI) are released after the onset of significant necrosis instead of early ischemia. Thus, they are not good biomarkers to diagnose myocardial injury before necrosis happens. Therefore, in this study, we performed proteomic analysis on effluents from perfused human hearts of donors at different ischemic time.

Results

After global ischemia for 0 min, 30 min and 60 min at 4°C, effluents from five perfused hearts were analyzed respectively, by High performance liquid chromatography-Chip-Mass spectrometry (HPLC-Chip-MS) system. Total 196 highly reliable proteins were identified. 107 proteins were identified at the beginning of ischemia, 174 and 175 proteins at ischemic 30 min and ischemic 60 min, respectively. With the exception of cardiac troponin I and T, all known biomarkers for myocardial ischemia were detected in our study. However, there were four glycolytic enzymes and two targets of matrix metalloproteinase released significantly from the heart when ischemic time was increasing. These proteins were L-lactate dehydrogenase B(LDHB), glyceraldehyde-3-phosphate dehydrogenase, glucose-6-phosphate isomerase (GPI), phosphoglycerate mutase 2 (PGAM2), gelsolin and isoform 8 of titin. PGAM2, LDHB and titin were measured with enzyme-linked immunosorbent assays kits. The mean concentrations of LDHB and PGAM2 in samples showed an increasing trend when ischemic time was extending. In addition, 33% identified proteins are involved in metabolism. Protein to protein interaction network analysis showed glycolytic enzymes, such as isoform alpha-enolase of alpha-enolase, isoform 1 of triosephosphate isomerase and glyceraldehyde-3-phosphate dehydrogenase, had more connections than other proteins in myocardial metabolism during ischemia.

Conclusion

It is the first time to use effluents of human perfused heart to study the proteins released during myocardial ischemia by HPLC-Chip-MS system. There might be many potential biomarkers for mild ischemic injury in myocardium, especially isoform 8 of titin and M-type of PGAM2 that are more specific in the cardiac tissue than in the others. Furthermore, glycolysis is one of the important conversions during early ischemia in myocardium. This finding may provide new insight into pathology and biology of myocardial ischemia, and potential diagnostic and therapeutic biomarkers.

Cell biology of ischemia/reperfusion injury

Disorders characterized by ischemia/reperfusion (I/R), such as myocardial infarction, stroke, and peripheral vascular disease, continue to be among the most frequent causes of debilitating disease and death. Tissue injury and/or death occur as a result of the initial ischemic insult, which is determined primarily by the magnitude and duration of the interruption in the blood supply, and then subsequent damage induced by reperfusion. During prolonged ischemia, ATP levels and intracellular pH decrease as a result of anaerobic metabolism and lactate accumulation. As a consequence, ATPase-dependent ion transport mechanisms become dysfunctional, contributing to increased intracellular and mitochondrial calcium levels (calcium overload), cell swelling and rupture, and cell death by necrotic, necroptotic, apoptotic, and autophagic mechanisms. Although oxygen levels are restored upon reperfusion, a surge in the generation of reactive oxygen species occurs and proinflammatory neutrophils infiltrate ischemic tissues to exacerbate ischemic injury. The pathologic events induced by I/R orchestrate the opening of the mitochondrial permeability transition pore, which appears to represent a common end-effector of the pathologic events initiated by I/R. The aim of this treatise is to provide a comprehensive review of the mechanisms underlying the development of I/R injury, from which it should be apparent that a combination of molecular and cellular approaches targeting multiple pathologic processes to limit the extent of I/R injury must be adopted to enhance resistance to cell death and increase regenerative capacity in order to effect long-lasting repair of ischemic tissues.

Reversible alteration of calcium dynamics in cardiomyocytes during acute hypoxia transient in a microfluidic platform

Heart disease is the leading cause of mortality in western countries. Apart from congenital and anatomical alterations, ischemia is the most common agent causing myocardial damage. During ischemia, a sudden decrease in oxygen concentration alters cardiomyocyte function and compromises cell survival. The calcium handling machinery, which regulates the main functional features of a cardiomyocyte, is heavily compromised during acute hypoxic events. Alterations in calcium dynamics have been linked to both short- and long-term consequences of ischemia, ranging from arrhythmias to heart failure. In this perspective, we aimed at investigating the calcium dynamics in functional cardiomyocytes during the early phase of a hypoxic event. For this purpose, we developed a microfluidic system specifically designed for controlling fast oxygen concentration dynamics through a gas micro-exchanger allowing in line analysis of intracellular calcium concentration by confocal microscopy. Experimental results show that exposure of Fluo-4 loaded neonatal rat cardiomyocytes to hypoxic conditions induced changes in intracellular Ca(2+) transients. Such behavior was reversible and was detected for hypoxic levels below 5% of oxygen partial pressure. The observed changes in Ca(2+) dynamics were mimicked using specific L-type Ca(2+) channel antagonists, suggesting that alterations in calcium channel function occur at low oxygen levels. Reversible alteration in ion channel function, that takes place in response to changes in cellular oxygen, might represent an adaptive mechanism of cardiopreservation during ischemia.

A new state of cardiac myosin with very slow ATP turnover: a potential cardioprotective mechanism in the heart

The mechanisms that control cardiac contractility are complex. Recent work we conducted in vertebrate skeletal muscle identified a new state of myosin, the super-relaxed state (SRX), which had a very low metabolic rate. To determine whether this state also exists in cardiac muscle we used quantitative epi-fluorescence to measure single nucleotide turnovers by myosin in bundles of relaxed permeable rabbit ventricle cells. We measured two turnover times--one compatible with the normal relaxed state, and one much slower which was shown to arise from myosin heads in the SRX. In both skeletal and cardiac muscle, the SRX appears to play a similar role in relaxed cells, providing a state with a very low metabolic rate. However, in active muscle the properties of the SRX differ dramatically. We observed a rapid transition of myosin heads out of the SRX in active skeletal fibers, whereas the population of the SRX remained constant in active cardiac cells. This property allows the SRX to play a very different role in cardiac muscle than in skeletal muscle. The SRX could provide a mechanism for decreasing the metabolic load on the heart, being cardioprotective, particularly in time of stress such as ischemia.

Interventricular heterogeneity in rat heart responses to hypoxia: the tuning of glucose metabolism, ion gradients, and function

The matching of energy supply and demand under hypoxic conditions is critical for sustaining myocardial function. Numerous reports indicate that basal energy requirements and ion handling may differ between the ventricles. We hypothesized that ventricular response to hypoxia shows interventricular differences caused by the heterogeneity in glucose metabolism and expression and activity of ion transporters. Thus we assessed glucose utilization rate, ATP, sodium and potassium concentrations, Na, K-ATPase activity, and tissue reduced:oxidized glutathione (GSH/GSSG) content in the right and left ventricles before and after the exposure of either the whole animals or isolated blood-perfused hearts to hypoxia. The hypoxia-induced boost in glucose utilization was more pronounced in the left ventricle compared with the right one. ATP levels in the right ventricle of hypoxic heart were lower than those in the left ventricle. Left ventricular sodium content was higher, and hydrolytic Na, K-ATPase activity was reduced compared with the right ventricle. Administration of the Na, K-ATPase blocker ouabain caused rapid increase in the right ventricular Na(+) and elimination of the interventricular Na(+) gradients. Exposure of the hearts to hypoxia made the interventricular heterogeneity in the Na(+) distribution even more pronounced. Furthermore, systemic hypoxia caused oxidative stress that was more pronounced in the right ventricle as revealed by GSH/GSSG ratios. On the basis of these findings, we suggest that the right ventricle is more prone to hypoxic damage, as it is less efficient in recruiting glucose as an alternative fuel and is particularly dependent on the efficient Na, K-ATPase function.

c-Jun N-terminal kinase (JNK-1) confers protection against brief but not extended ischemia during acute myocardial infarction

Brief periods of ischemia do not damage the heart and can actually protect against reperfusion injury caused by extended ischemia. It is not known what causes the transition from protection to irreversible damage as ischemia progresses. c-Jun N-terminal kinase-1 (JNK-1) is a stress-regulated kinase that is activated by reactive oxygen and thought to promote injury during severe acute myocardial infarction. Because some reports suggest that JNK-1 can also be protective, we hypothesized that the function of JNK-1 depends on the metabolic state of the heart at the time of reperfusion, a condition that changes progressively with duration of ischemia. Mice treated with JNK-1 inhibitors or transgenic mice wherein the JNK-1 gene was ablated were subjected to 5 or 20 min of ischemia followed by reperfusion. When JNK-1 was inactive, ischemia of only 5 min duration caused massive apoptosis, infarction, and negative remodeling that was equivalent to or greater than extended ischemia. Conversely, when ischemia was extended JNK-1 inactivation was protective. Mechanisms of the JNK-1 switch in function were investigated in vivo and in cultured cardiac myocytes. In vitro there was a comparable switch in the function of JNK-1 from protective when ATP levels were maintained during hypoxia to injurious when reoxygenation followed glucose and ATP depletion. Both apoptotic and necrotic death pathways were affected and responded reciprocally to JNK-1 inhibitors. JNK-1 differentially regulated Akt phosphorylation of the regulatory sites Ser-473 and Thr-450 and the catalytic Thr-308 site in vivo. The studies define a novel role for JNK-1 as a conditional survival kinase that protects the heart against brief but not protracted ischemia.

Green tea extract given before regional myocardial ischemia-reperfusion in rats improves myocardial contractility by attenuating calcium overload

There is evidence for a negative correlation between green tea consumption and cardiovascular diseases. The aim of the present study was to examine whether green tea extract (GTE) given before regional myocardial ischemia could improve depression of myocardial contractility by preventing cytosolic Ca(2+) overload. Regional ischemia-reperfusion (IR) was induced in rats by ligating the left anterior descending branch for 20 min, then releasing the ligature. Ligation induced ventricular arrhythmias in rats without GTE pretreatment, but decreased arrhythmogenesis was seen in rats pretreated 30 min earlier with GTE (400 mg/kg). During reperfusion, arrhythmias only occurred during the initial 5 min, and GTE pretreatment had no effect. After overnight recovery, serum cTnI levels were greatly increased in control post-IR rats but only slightly elevated in GTE-pretreated post-IR rats. Myocardial contractility measured by echocardiography was still depressed after 3 days in control post-IR rats, but not in GTE-pretreated post-IR rats. No myocardial ischemic injury was seen in post-IR rats with or without GTE pretreatment. Using freshly isolated single heart myocytes, GTE was found to attenuate the post-IR injury-associated cytosolic Ca(2+) overload and modulate changes in the levels and distribution of myofibril, adherens junction, and gap junction proteins. In summary, GTE pretreatment protects cardiomyocytes from IR injury by preventing cytosolic Ca(2+) overload, myofibril disruption, and alterations in adherens and gap junction protein expression and distribution.

Proteomic analysis of heat shock-induced protection in acute pancreatitis

Acute pancreatitis is an inflammatory disease of the pancreas, which can result in serious morbidity or death. Acute pancreatitis severity can be reduced in experimental models by preconditioning animals with a short hyperthermia prior to disease induction. Heat shock proteins 27 and 70 are key effectors of this protective effect. In this study, we performed a comparative proteomic analysis using a combination of liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis and isobaric tagging to investigate changes in pancreatic proteins expression that were associated with thermal stress, both in healthy rats and in a model of caerulein-induced pancreatitis. In agreement with previous studies, we observed modulation of heat shock and inflammatory proteins expression in response to heat stress or pancreatitis induction. We also identified numerous other proteins, whose pancreatic level changed following pancreatitis induction, when acute pancreatitis severity was reduced by prior thermal stress, or in healthy rats in response to hyperthermia. Interestingly, we showed that the expression of various proteins associated with the secretory pathway was modified in the different experimental models, suggesting that modulation of this process is involved in the protective effect against pancreatic tissue damage.

Is detection of hibernating myocardium necessary in deciding revascularization in systolic heart failure?

Although the prognosis of systolic heart failure, also called heart failure with reduced ejection fraction, has improved with advances in therapy, the prognosis remains poor in patients who become refractory to such therapies. That cardiac transplantation improves the quality of life and survival of such patients has been established, but it is available to a very small number of patients. Thus, newer pharmacologic and nonpharmacologic therapies for patients with refractory systolic heart failure are being explored. Because chronic ischemic heart disease is the most common cause of systolic heart failure, potential exists for revascularization therapy. Although revascularization can be performed with low procedural mortality, improvement in left ventricular function, relief of symptoms, and long-term prognosis appear to be related to the presence and extent of viable ischemic hibernating myocardium. In conclusion, the detection of hibernating myocardium is highly desirable before revascularization treatment is undertaken.

Hibernating myocardium: pathophysiology, diagnosis, and treatment

Comprehensive management of patients with chronic ischemic disease is a critically important component of clinical practice. Cardiac myocytes have the potential to adapt to limited flow conditions by adjusting contractile function, reducing metabolism, conserving resources, and preserving myocardial integrity to cope with an oxygen and (or) nutrition shortage. A prime metabolic feature of cardiac myocytes affected by chronic ischemia is the return to a fetal gene pattern with predominance of carbohydrates as the substrate for energy. Structural adaptation with multiple intracellular changes is part of the remodeling process in hibernating myocardium. Transmural heterogeneity, which defines the pattern of injury in ventricular cardiomyocytes and the response to chronic ischemia, is a multifactorial process originating from functional, metabolic, and flow differences in subendocardial and subepicardial regions. Autophagy is typically activated in hibernating myocardium and has been identified as a prosurvival mechanism. Chronic ischemia is associated with changes in the number, size, and distribution of gap junctions and may give rise to conduction disturbances and arrhythmogenesis. Differentiation between viable and nonviable myocardium by assessing sensitivity of inotropic reserve is a crucial diagnostic tool that is correlated with the prognosis and outcome for improved contractility after restoration of blood perfusion in afflicted myocardium.Reliable and accurate diagnosis of ischemic, scar, and viable tissues is critical for recover strategies. Although early surgical reinstitution of blood flow is most effective in restoring physiologic function of the hibernating myocardium, several new approaches offer promising alternatives. Among others, vascular endothelial growth factor and fibroblast growth factor-2 (FGF-2), especially its lo-FGF-2 isoform, have been shown to be effective in rapid neovascularization. Substances such as statins, resveratrol, some hormones, and omega-3 fatty acids can improve recovery effect in chronically underperfused hearts. For patients with drug-refractory ischemia, intramyocardial transplantation of stem cells into predefined areas of the heart can enhance vascularization and have beneficial effects on cardiac function. This review of ischemic injury, its heterogeneity, accurate diagnosis, and newer methods of treatment, shows there is much information and tremendous hope for better management of patients with coronary heart disease.