Calcium/calmodulin-dependent protein kinase II mediates cardioprotection of intermittent hypoxia against ischemic-reperfusion-induced cardiac dysfunction

Enhanced KCl-mediated contractility and Ca2+ sensitization in porcine collateral-dependent coronary arteries persist after exercise training

We have previously reported enhanced Ca²⁺ sensitivity of coronary arteries that is dependent upon collateral circulation for their blood supply. For the current study, we hypothesized that small collateral-dependent arteries would exhibit an enhanced KCl-mediated contractile response attributable to Ca²⁺ sensitization and increased Ca²⁺ channel current. Ameroid constrictors were surgically placed around the left circumflex (LCX) artery of female Yucatan miniature swine. Eight weeks postoperatively, pigs were randomized into sedentary or exercise-trained (treadmill run; 5 days/wk; 14 wk) groups. Small coronary arteries (150-300 μm luminal diameter) were isolated from myocardial regions distal to the collateral-dependent LCX and the nonoccluded left anterior descending arteries. Contractile tension and simultaneous measures of both tension and intracellular free Ca²⁺ levels (fura-2) were measured in response to increasing concentrations of KCl. In addition, whole cell Ca²⁺ currents were also obtained. Chronic occlusion enhanced contractile responses to KCl and increased Ca²⁺ sensitization in collateral-dependent compared with nonoccluded arteries of both sedentary and exercise-trained pigs. In contrast, smooth muscle cell Ca²⁺ channel current was not altered by occlusion or exercise training. Ca²⁺/calmodulin-dependent protein kinase II (CaMKII; inhibited by KN-93, 0.3-1 μM) contributed to the enhanced contractile response in collateral-dependent arteries of sedentary pigs, whereas both CaMKII and Rho-kinase (inhibited by hydroxyfasudil, 30 μM or Y27632, 10 μM) contributed to increased contraction in exercise-trained animals. Taken together, these data suggest that chronic occlusion leads to enhanced contractile responses to KCl in collateral-dependent coronary arteries via increased Ca²⁺ sensitization, a response that is further augmented with exercise training.NEW & NOTEWORTHY Small coronary arteries distal to chronic occlusion displayed enhanced contractile responses, which were further augmented after exercise training and attributable to enhanced calcium sensitization without alterations in calcium channel current. The calcium sensitization mediators Rho-kinase and CaMKII significantly contributed to enhanced contraction in collateral-dependent arteries of exercise-trained, but not sedentary, pigs. Exercise-enhanced contractile responses may increase resting arterial tone, creating an enhanced coronary flow reserve that is accessible during periods of increased metabolic demand.

Phosphoproteomic analysis identifies phospho-Threonine-17 site of phospholamban important in low molecular weight isoform of fibroblast growth factor 2-induced protection against post-ischemic cardiac dysfunction

RATIONALE

Among its many biological roles, fibroblast growth factor 2 (FGF2) protects the heart from dysfunction and damage associated with an ischemic attack. Our laboratory demonstrated that its protection against myocardial dysfunction occurs by the low molecular weight (LMW) isoform of FGF2, while the high molecular weight (HMW) isoforms are associated with a worsening in post-ischemic recovery of cardiac function. LMW FGF2-mediated cardioprotection is facilitated by activation of multiple kinases, including PKCalpha, PKCepsilon, and ERK, and inhibition of p38 and JNK.

OBJECTIVE

Yet, the substrates of those kinases associated with LMW FGF2-induced cardioprotection against myocardial dysfunction remain to be elucidated.

METHODS AND RESULTS

To identify substrates in LMW FGF2 improvement of post-ischemic cardiac function, mouse hearts expressing only LMW FGF2 were subjected to ischemia-reperfusion (I/R) injury and analyzed by a mass spectrometry (MS)-based quantitative phosphoproteomic strategy. MS analysis identified 50 phosphorylation sites from 7 sarcoendoplasmic reticulum (SR) proteins that were significantly altered in I/R-treated hearts only expressing LMW FGF2 compared to those hearts lacking FGF2. One of those phosphorylated SR proteins identified was phospholamban (PLB), which exhibited rapid, increased phosphorylation at Threonine-17 (Thr17) after I/R in hearts expressing only LMW FGF2; this was further validated using Selected Reaction Monitoring-based MS workflow. To demonstrate a mechanistic role of phospho-Thr17 PLB in LMW FGF2-mediated cardioprotection, hearts only expressing LMW FGF2 and those expressing only LMW FGF2 with a mutant PLB lacking phosphorylatable Thr17 (Thr17Ala PLB) were subjected to I/R. Hearts only expressing LMW FGF2 showed significantly improved recovery of cardiac function following I/R (p < 0.05), and this functional improvement was significantly abrogated in hearts expressing LMW FGF2 and Thr17Ala PLB (p < 0.05).

CONCLUSION

The findings indicate that LMW FGF2 modulates intracellular calcium handling/cycling via regulatory changes in SR proteins essential for recovery from I/R injury, and thereby protects the heart from post-ischemic cardiac dysfunction.

Prevalence of Undiagnosed Obstructive Sleep Apnea Among Patients Hospitalized for Cardiovascular Disease and Associated In-Hospital Outcomes: A Scoping Review

BACKGROUND

Obstructive sleep apnea (OSA) is associated with long-term cardiovascular morbidity and is highly prevalent in patients with cardiovascular disease (CVD). The objectives of this scoping review were to determine the prevalence of OSA inpatients hospitalized for CVD and to map the range of in-hospital outcomes associated with OSA.

METHODS

We searched MEDLINE(R), Embase, and Cochrane Databases for articles published from 1946-2018. We included studies involving non-surgical adults with OSA or at high risk of OSA who were hospitalized for CVD. The outcomes were considered as in-hospital if they were collected from admission up to 30 days post-discharge from hospital.

RESULTS

After the screening of 4642 articles, 26 studies were included for qualitative synthesis. Eligible studies included patients presenting with acute coronary syndromes (n = 19), congestive heart failure (n = 6), or any cardiovascular disease (n = 1). The pooled prevalence of OSA in cardiac inpatients was 48% (95% CI: 42-53). The in-hospital outcomes reported were mortality (n = 4), length of stay (n = 8), left ventricular ejection fraction (n = 8), peak troponin (n = 7), peak B-type natriuretic peptide (n = 4), and composite cardiovascular complications (n = 2).

CONCLUSIONS

OSA is highly prevalent in the cardiac inpatient population. The outcomes reported included mortality, cardiac function, cardiac biomarkers, and resource utilization. There are significant knowledge gaps regarding the effect of treatment and OSA severity on these outcomes. The findings from this review serve to inform further areas of research on the management of OSA among patients with CVD.

Iron-deficiency anemia reduces cardiac contraction by downregulating RyR2 channels and suppressing SERCA pump activity

Iron deficiency is present in ~50% of heart failure (HF) patients. Large multicenter trials have shown that treatment of iron deficiency with i.v. iron benefits HF patients, but the underlying mechanisms are not known. To investigate the actions of iron deficiency on the heart, mice were fed an iron-depleted diet, and some received i.v. ferric carboxymaltose (FCM), an iron supplementation used clinically. Iron-deficient animals became anemic and had reduced ventricular ejection fraction measured by magnetic resonance imaging. Ca2+ signaling, a pathway linked to the contractile deficit in failing hearts, was also significantly affected. Ventricular myocytes isolated from iron-deficient animals produced smaller Ca2+ transients from an elevated diastolic baseline but had unchanged sarcoplasmic reticulum (SR) Ca2+ load, trigger L-type Ca2+ current, or cytoplasmic Ca2+ buffering. Reduced fractional release from the SR was due to downregulated RyR2 channels, detected at protein and message levels. The constancy of diastolic SR Ca2+ load is explained by reduced RyR2 permeability in combination with right-shifted SERCA activity due to dephosphorylation of its regulator phospholamban. Supplementing iron levels with FCM restored normal Ca2+ signaling and ejection fraction. Thus, 2 Ca2+-handling proteins previously implicated in HF become functionally impaired in iron-deficiency anemia, but their activity is rescued by i.v. iron supplementation.

Cardioprotection by intermittent hypoxia conditioning: evidence, mechanisms, and therapeutic potential

The calibrated application of limited-duration, cyclic, moderately intense hypoxia-reoxygenation increases cardiac resistance to ischemia-reperfusion stress. These intermittent hypoxic conditioning (IHC) programs consistently produce striking reductions in myocardial infarction and ventricular tachyarrhythmias after coronary artery occlusion and reperfusion and, in many cases, improve contractile function and coronary blood flow. These IHC protocols are fundamentally different from those used to simulate sleep apnea, a recognized cardiovascular risk factor. In clinical studies, IHC improved exercise capacity and decreased arrhythmias in patients with coronary artery or pulmonary disease and produced robust, persistent, antihypertensive effects in patients with essential hypertension. The protection afforded by IHC develops gradually and depends on β-adrenergic, δ-opioidergic, and reactive oxygen-nitrogen signaling pathways that use protein kinases and adaptive transcription factors. In summary, adaptation to intermittent hypoxia offers a practical, largely unrecognized means of protecting myocardium from impending ischemia. The myocardial and perhaps broader systemic protection provided by IHC clearly merits further evaluation as a discrete intervention and as a potential complement to conventional pharmaceutical and surgical interventions.

RNA SEQ Analysis Indicates that the AE3 Cl-/HCO3- Exchanger Contributes to Active Transport-Mediated CO2 Disposal in Heart

Loss of the AE3 Cl⁻/HCO₃⁻ exchanger (Slc4a3) in mice causes an impaired cardiac force-frequency response and heart failure under some conditions but the mechanisms are not known. To better understand the functions of AE3, we performed RNA Seq analysis of AE3-null and wild-type mouse hearts and evaluated the data with respect to three hypotheses (CO₂ disposal, facilitation of Na⁺-loading, and recovery from an alkaline load) that have been proposed for its physiological functions. Gene Ontology and PubMatrix analyses of differentially expressed genes revealed a hypoxia response and changes in vasodilation and angiogenesis genes that strongly support the CO₂ disposal hypothesis. Differential expression of energy metabolism genes, which indicated increased glucose utilization and decreased fatty acid utilization, were consistent with adaptive responses to perturbations of O₂/CO₂ balance in AE3-null myocytes. Given that the myocardium is an obligate aerobic tissue and consumes large amounts of O₂, the data suggest that loss of AE3, which has the potential to extrude CO₂ in the form of HCO₃⁻, impairs O₂/CO₂ balance in cardiac myocytes. These results support a model in which the AE3 Cl⁻/HCO₃⁻ exchanger, coupled with parallel Cl⁻ and H⁺-extrusion mechanisms and extracellular carbonic anhydrase, is responsible for active transport-mediated disposal of CO₂.

Early administration of nifedipine protects against angiotensin II-induced cardiomyocyte hypertrophy through regulating CaMKII-SERCA2a pathway and apoptosis in rat cardiomyocytes

The calcium channel blocker (CCB), nifedipine, is a more effective treatment for early- than late-stage cardiac hypertrophy. We investigated the effects of early- and late-stage nifedipine administration on calcium homeostasis, CaMKII (Ca(2+) /calmodulin-dependent protein kinase II) activity and apoptosis of cardiomyocytes under hypertrophic stimulation with angiotensin II (AngII). Primary rat cardiomyocytes were divided into five treatment groups: AK, AngII plus the CaMKII inhibitor, KN-93; AN-1 (early-stage), AngII plus nifedipine × 48 h; AN-2 (late-stage), AngII × 48 h, then AngII plus nifedipine × 48 h; C, untreated; and A, AngII × 48 h. The t1/2β [time required for intracellular Ca(2+) concentration ([Ca(2+) ]i) to decline to one half of the peak value] decreased; however, CaMKII and SERCA2a (sarcoplasmic reticulum Ca(2+) -ATPase 2a) activities increased in the AN-1 group compared with the AK group. In the AN-2 group compared with the AN-1 group, CaMKII activity, t1/2α [time required for [Ca(2+) ]i to increase from the bottom to one half of peak value], t1/2β, and apoptosis increased. These results indicate that the timing of CCB administration affects the calcium concentration and apoptosis of hypertrophic cardiomyocytes through the CaMKII-SERCA2a signalling pathway, thereby influencing the drug's protective activity against cardiomyocyte hypertrophy.

Left ventricular deformation associated with cardiomyocyte Ca(2+) transients delay in early stage of low-dose of STZ and high-fat diet induced type 2 diabetic rats

Background

In the early stage of diabetes, the cardiac ejection fraction is preserved, despite the existence of the subclinical cardiac dysfunction to some extent. However, the detailed phenotype of this dysfunction and the underlying mechanism remain unclear. To improve our understanding of this issue, we used low-dose STZ and high-fat diet to induce type 2 diabetic models in rats. The effects and the mechanism associated with the early stages of the disease were analyzed.

Methods

The type 2 diabetic mellitus (T2DM) in SD rats were induced through 30 mg/kg STZ and high-fat diet. Two-dimensional spackle-tracking echocardiography (STE) and the dobutamine test were performed to examine the cardiac function. Calcium transients of left ventricular myocytes were detected and the related intracellular signalling factors were analyzed by western blotting.

Results

After 6-weeks, T2DM rats in left ventricular (LV) diastole showed decreased global and segment strain(S) levels (P < 0.05), both in the radial and circumferential directions. Strain rate (Sr) abatement occurred in three segments in the radial and circumferential directions (P < 0.05), and the radial global Sr also decreased (P < 0.05). In the systolic LV, radial Sr was reduced, except the segment of the anterior septum, and the Sr of the lateral wall and post septum decreased in the circumferential direction (P < 0.05). Conventional M-mode echocardiography failed to detect significant alterations of cardiac performance between the two groups even after 12 weeks, and the decreased ejection fraction (EF%), fractional shortening (FS%) and end-systolic diameters (ESD) could be detected only under stress conditions induced by dobutamine (P < 0.05). In terms of calcium transients in cardiac myocytes, the T_peak in model rats at 6 weeks was not affected, while the T_decay1/2 was higher than that of the controls (P < 0.05), and both showed a dose-dependent delay after isoproterenol treatment (P < 0.05). Western blot analysis showed that in 6-week T2DM rats, myocardial p-PLB expression was elevated, whereas p-CaMKII, p-AMPK and Sirt1 were significantly down-regulated (P < 0.05).

Conclusion

A rat model of T2DM was established by low dose STZ and a high-fat diet. LV deformation was observed in the early stages of T2DM in association with the delay of Ca²⁺ transients in cardiomyocytes due to the decreased phosphorylation of CaMKII. Myocardial metabolism remodeling might contribute to the early LV function and calcium transportation abnormalities.

Alterations in left ventricular function during intermittent hypoxia: Possible involvement of O-GlcNAc protein and MAPK signaling

Obstructive sleep apnea, characterized by recurrent episodes of hypoxia [intermittent hypoxia (IH)], has been identified as a risk factor for cardiovascular diseases. The O-linked β-N-acetylglucosamine (O-GlcNAc) modification (O-GlcNAcylation) of proteins has important regulatory implications on the pathophysiology of cardiovascular disorders. In this study, we examined the role of O-GlcNAcylation in cardiac architecture and left ventricular function following IH. Rats were randomly assigned to a normoxia and IH group (2 min 21% O₂; 2 min 6–8% O₂). Left ventricular function, myocardial morphology and the levels of signaling molecules were then measured. IH induced a significant increase in blood pressure, associated with a gradually abnormal myocardial architecture. The rats exposed to 2 or 3 weeks of IH presented with augmented left ventricular systolic and diastolic function, which declined at week 4. Consistently, the O-GlcNAc protein and O-GlcNAcase (OGA) levels in the left ventricular tissues steadily increased following IH, reaching peak levels at week 3. The O-GlcNAc transferase (OGT), extracellular signal-regulated kinase 1/2 (ERK1/2) and the p38 mitogen-activated protein kinase (p38 MAPK) phosphorylation levels were affected in an opposite manner. The phosphorylation of calcium/calmodulin-dependent protein kinase II (CaMKII) remained unaltered. In parallel, compared with exposure to normoxia, 4 weeks of IH augmented the O-GlcNAc protein, OGT, phosphorylated ERK1/2 and p38 MAPK levels, accompanied by a decrease in OGA levels and an increase in the levels of myocardial nuclear factor-κB (NF-κB), inflammatory cytokines, caspase-3 and cardiomyocyte apoptosis. Taken together, our suggest a possible involvement of O-GlcNAc protein and MAPK signaling in the alterations of left ventricular function and cardiac injury following IH.

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.

ROS generated during early reperfusion contribute to intermittent hypobaric hypoxia-afforded cardioprotection against postischemia-induced Ca(2+) overload and contractile dysfunction via the JAK2/STAT3 pathway

Moderate enhanced reactive oxygen species (ROS) during early reperfusion trigger the cardioprotection against ischemia/reperfusion (I/R) injury, while the mechanism is largely unknown. Janus kinase 2 (JAK2)/signal transducer and activator of transcription 3 (STAT3) contributes to the cardioprotection but whether it is activated by ROS and how it regulates Ca(2+) homeostasis remain unclear. Here we investigated whether the ROS generated during early reperfusion protect the heart/cardiomyocyte against I/R-induced Ca(2+) overload and contractile dysfunction via the activation of JAK2/STAT3 signaling pathway by using a cardioprotective model of intermittent hypobaric hypoxia (IHH) preconditioning. IHH improved the postischemic recovery of myocardial contractile performance in isolated rat I/R hearts as well as Ca(2+) homeostasis and cell contraction in simulated I/R cardiomyocytes. Meanwhile, IHH enhanced I/R-increased STAT3 phosphorylation at tyrosine 705 in the nucleus and reversed I/R-suppressed STAT3 phosphorylation at serine 727 in the nucleus and mitochondria during reperfusion. Moreover, IHH improved I/R-suppressed sarcoplasmic reticulum (SR) Ca(2+)-ATPase 2 (SERCA2) activity, enhanced I/R-increased Bcl-2 expression, and promoted the co-localization and interaction of Bcl-2 with SERCA2 during reperfusion. These effects were abolished by scavenging ROS with N-(2-mercaptopropionyl)-glycine (2-MPG) and/or by inhibiting JAK2 with AG490 during the early reperfusion. Furthermore, IHH-improved postischemic SERCA2 activity and Ca(2+) homeostasis as well as cell contraction were reversed after Bcl-2 knockdown by short hairpin RNA. In addition, the reversal of the I/R-suppressed mitochondrial membrane potential by IHH was abolished by 2-MPG and AG490. These results indicate that during early reperfusion the ROS/JAK2/STAT3 pathways play a crucial role in (i) the IHH-maintained intracellular Ca(2+) homeostasis via the improvement of postischemic SERCA2 activity through the increase of SR Bcl-2 and its interaction with SERCA2; and (ii) the IHH-improved mitochondrial function.

Therapeutic potential of intermittent hypoxia: a matter of dose

Intermittent hypoxia (IH) has been the subject of considerable research in recent years, and triggers a bewildering array of both detrimental and beneficial effects in multiple physiological systems. Here, we review the extensive literature concerning IH and its impact on the respiratory, cardiovascular, immune, metabolic, bone, and nervous systems. One major goal is to define relevant IH characteristics leading to safe, protective, and/or therapeutic effects vs. pathogenesis. To understand the impact of IH, it is essential to define critical characteristics of the IH protocol under investigation, including potentially the severity of hypoxia within episodes, the duration of hypoxic episodes, the number of hypoxic episodes per day, the pattern of presentation across time (e.g., within vs. consecutive vs. alternating days), and the cumulative time of exposure. Not surprisingly, severe/chronic IH protocols tend to be pathogenic, whereas any beneficial effects are more likely to arise from modest/acute IH exposures. Features of the IH protocol most highly associated with beneficial vs. pathogenic outcomes include the level of hypoxemia within episodes and the number of episodes per day. Modest hypoxia (9-16% inspired O2) and low cycle numbers (3-15 episodes per day) most often lead to beneficial effects without pathology, whereas severe hypoxia (2-8% inspired O2) and more episodes per day (48-2,400 episodes/day) elicit progressively greater pathology. Accumulating evidence suggests that "low dose" IH (modest hypoxia, few episodes) may be a simple, safe, and effective treatment with considerable therapeutic potential for multiple clinical disorders.

Adiponectin regulates SR Ca(2+) cycling following ischemia/reperfusion via sphingosine 1-phosphate-CaMKII signaling in mice

The adipocyte-secreted hormone adiponectin (APN) exerts protective effects on the heart under stress conditions. Recent studies have demonstrated that APN induces a marked Ca(2+) influx in skeletal muscle. However, whether APN modulates [Ca(2+)]i activity, especially [Ca(2+)]i transients in cardiomyocytes, is still unknown. This study was designed to determine whether APN modulates [Ca(2+)]i transients in cardiomyocytes. Adult male wild-type (WT) and APN knockout (APN KO) mice were subjected to myocardial ischemia/reperfusion (I/R, 30min/30min) injury. CaMKII-PLB phosphorylation and SR Ca(2+)-ATPase (SERCA2) activity were downregulated in I/R hearts of WT mice and further decreased in those of APN KO mice. Both the globular domain of APN and full-length APN significantly reversed the decrease in CaMKII-PLB phosphorylation and SERCA2 activity in WT and APN KO mice. Interestingly, compared with WT littermates, single myocytes isolated from APN KO mice had remarkably decreased [Ca(2+)]i transients, cell shortening, and a prolonged Ca(2+) decay rate. Further examination revealed that APN enhances SERCA2 activity via CaMKII-PLB signaling. In in vivo and in vitro experiments, both APN receptor 1/2 and S1P were necessary for the APN-stimulated CaMKII-PLB-SERCA2 activation. In addition, S1P activated CaMKII-PLB signaling in neonatal cardiomyocytes in a dose dependent manner and improved [Ca(2+)]i transients in APN KO myocytes via the S1P receptor (S1PR1/3). Further in vivo experiments revealed that pharmacological inhibition of S1PR1/3 and SERCA2 siRNA suppressed APN-mediated cardioprotection during I/R. These data demonstrate that S1P is a novel regulator of SERCA2 that activates CaMKII-PLB signaling and mediates APN-induced cardioprotection.

Ca²⁺/calmodulin-dependent protein kinase II contributes to hypoxic ischemic cell death in neonatal hippocampal slice cultures

We have recently shown that p38MAP kinase (p38MAPK) stimulates ROS generation via the activation of NADPH oxidase during neonatal hypoxia-ischemia (HI) brain injury. However, how p38MAPK is activated during HI remains unresolved and was the focus of this study. Ca²⁺/calmodulin-dependent protein kinase II (CaMKII) plays a key role in brain synapse development, neural transduction and synaptic plasticity. Here we show that CaMKII activity is stimulated in rat hippocampal slice culture exposed to oxygen glucose deprivation (OGD) to mimic the condition of HI. Further, the elevation of CaMKII activity, correlated with enhanced p38MAPK activity, increased superoxide generation from NADPH oxidase as well as necrotic and apoptotic cell death. All of these events were prevented when CaMKII activity was inhibited with KN93. In a neonatal rat model of HI, KN93 also reduced brain injury. Our results suggest that CaMKII activation contributes to the oxidative stress associated with neural cell death after HI.

Intermittent hypobaric hypoxia applicability in myocardial infarction prevention and recovery

Intermittent hypobaric hypoxia (IHH) has been the focus of important research in cardioprotection, and it has been associated with several mechanisms. Intermittent hypobaric hypoxia inhibits prolyl hydroxylases (PHD) activity, increasing the stabilization of hypoxia-inducible factor-1 (HIF-1) and activating crucial adaptative genes. It has been hence suggested that IHH might be a simple intervention, which may offer a thoughtful benefits to patients with acute myocardial infarction and no complications. Nevertheless, several doubts exist as to whether IHH is a really safe technique, with little to no complications in post-myocardial infarction patients. Intermittent hypobaric hypoxia might produce instead unfavourable changes such as impairment of vascular hemodynamics and hypertensive response, increased risk of hemoconcentration and thrombosis, cardiac rhythm perturbations, coronary artery disease and heart failure, insulin resistance, steatohepatitis and even high-altitude pulmonary oedema in susceptible or nonacclimatized patients. Although intermittent and chronic exposures seem effective in cardioprotection, IHH safety issues have been mostly overlooked, so that assorted concerns should be raised about the opportunity to use IHH in the post-myocardial infarction period. Several IHH protocols used in some studies were also aggressive, which would hamper their widespread introduction within the clinical practice. As such, further research is needed before IHH can be widely advocated in myocardial infarction prevention and recovery.

Berbamine increases myocardial contractility via a Ca2+-independent mechanism

Berbamine (BM), a natural compound derived from Berberis vulgaris L, has been reported to inhibit cardiac contractile function at higher concentrations. Here, we report that BM had concentration-dependent biphasic effects on myocardial contraction in Langendorff-perfused rat hearts, that is, at lower concentrations (30-100 nM), it displayed positive inotropic and lusitropic effects, whereas at a higher concentration of 1 μM, it caused a negative inotropic effect after an initially weak increase. These effects were further confirmed in cardiomyocytes isolated from the left ventricles of rats. Moreover, the increased cell shortening by BM at concentrations from 0.1 to 100 nM was not associated with an alteration of intracellular Ca transients. Consistently, at 30 nM, BM shifted the cell shortening--Ca transient relationship curve induced by cumulative elevation of extracellular Ca concentration to the left. Furthermore, BM significantly increased membrane-bound but not filament-bound protein kinase C epsilon (PKCε) in the isolated hearts and cardiomyocytes. Such a translocation was inhibited by PKCε-specific inhibitor PKCε V1-2 concomitant with the abolishment of the BM-induced increase in contraction. These findings reveal the positive inotropic effect of BM in the myocardium and demonstrate that BM increases myocardial contractility by increasing myofilament Ca sensitivity via a PKCε-dependent signaling pathway.

Mitochondrial energy metabolism plays a critical role in the cardioprotection afforded by intermittent hypobaric hypoxia

Intermittent hypobaric hypoxia (IHH) is an effective protective strategy against myocardial ischaemia-reperfusion (I/R) injury, but the precise mechanisms are far from clear. To understand the overall effects of IHH on the myocardial proteins during I/R, we analysed functional performance and the protein expression profile in isolated hearts from normoxic rats and from rats adapted to IHH (5000 m, 4 h day(-1), 4 weeks) following I/R injury (30 min/45 min). Intermittent hypobaric hypoxia significantly improved the postischaemic recovery of left ventricular function compared with the recovery in time-matched normoxic control hearts. Two-dimensional electrophoresis with matrix-assisted laser desorption/ionization and time-of-flight mass spectrometric analysis was then used to assess protein alterations in left ventricles from normoxic and IHH groups, with or without I/R. The expressions of 16 proteins changed by over fivefold; nine of these proteins are involved in energy metabolism. Immunoblot and real-time PCR analysis confirmed the IHH-increased expressions of the ATP synthase subunit β, mitochondrial aldehyde dehydrogenase and heat shock protein 27 in left ventricles. Furthermore, IHH significantly attenuated the reduction of myocardial ATP content, mitochondrial ATP synthase activity, membrane potential and respiratory control ratios due to I/R. In addition, inhibition of mitochondrial ATP synthase by oligomycin (1 μmol l(-1)) abolished the IHH-induced improvements in three parameters: postischaemic recovery of left ventricular function, mitochondrial membrane potential and respiratory control ratios. These results suggest that an improvement in mitochondrial energy metabolism makes an important contribution to the cardioprotection afforded by IHH against postischaemic myocardial dysfunction.

CaMKII in the cardiovascular system: sensing redox states

The multifunctional Ca(2+)- and calmodulin-dependent protein kinase II (CaMKII) is now recognized to play a central role in pathological events in the cardiovascular system. CaMKII has diverse downstream targets that promote vascular disease, heart failure, and arrhythmias, so improved understanding of CaMKII signaling has the potential to lead to new therapies for cardiovascular disease. CaMKII is a multimeric serine-threonine kinase that is initially activated by binding calcified calmodulin (Ca(2+)/CaM). Under conditions of sustained exposure to elevated Ca(2+)/CaM, CaMKII transitions into a Ca(2+)/CaM-autonomous enzyme by two distinct but parallel processes. Autophosphorylation of threonine-287 in the CaMKII regulatory domain "traps" CaMKII into an open configuration even after Ca(2+)/CaM unbinding. More recently, our group identified a pair of methionines (281/282) in the CaMKII regulatory domain that undergo a partially reversible oxidation which, like autophosphorylation, prevents CaMKII from inactivating after Ca(2+)/CaM unbinding. Here we review roles of CaMKII in cardiovascular disease with an eye to understanding how CaMKII may act as a transduction signal to connect pro-oxidant conditions into specific downstream pathological effects that are relevant to rare and common forms of cardiovascular disease.

In vitro studies of early cardiac remodeling: impact on contraction and calcium handling

Cardiac remodeling, hypertrophy, and alterations in calcium signaling are changes of the heart that often lead to failure. After a hypertrophic stimulus, the heart progresses through a state of compensated hypertrophy which over time leads to decompensated hypertrophy or failure. It is at this point that a cardiac transplant is required for survival making early detection imperative. Current experimental systems used to study the remodeling of the heart include in vivo systems (the whole body), isolated organ and sub-organ tissue, and the individual cardiac muscle cells and organelles.. During pathological remodeling there is a derangement in the intracellular calcium handling processes. These derangements are thought to lead to a dysregulation of contractile output. Hence, understanding the mechanism between remodeling and dysregulation is of great interest in the cardiac field and will ultimately help in the development of future treatment and early detection. This review will center on changes in contraction and calcium handling in early cardiac remodeling, with a specific focus on findings in two different in vitro model systems: multicellular and individual cell preparations.

Chronic intermittent hypoxia caused by obstructive sleep apnea may play an important role in explaining the morbidity-mortality paradox of obesity

Obesity has reached global pandemic that threatens the health of millions of people and is associated with numerous morbidities such as hypertension, type II diabetes mellitus, dyslipidemia, cor pulmonale, gallbladder disease, obstructive sleep apnea (OSA), certain cancers, osteoarthritis, increased surgical risk and postoperative complications, lower extremity venous and/or lymphatic problems, pulmonary embolism, stroke/cerebrovascular diseases and coronary arterial disease. Despite all these adverse associations, numerous studies and meta-analyses have documented an "obesity paradox" in which overweight and obese population with established cardiovascular disease have a better prognosis than do their lean counterparts. There are potential and plausible explanations offered by literature for these puzzling data; however, it still remains uncertain whether this phenomenon is attributable to a real protective effect of high body fat mass. In recent years, the survival advantage of patients with OSA, combined with the potential cardioprotective effects of chronic intermittent hypoxia, raise the possibility that apneas during sleep may activate preconditioning-like cardioprotective effect. Chronic intermittent hypoxia, one of the physiological markers of OSA, is characterized by transient periods of oxygen desaturation followed by reoxygenation, and is a major cause of its systemic harmful (oxidative stress, inflammation, sympathetic activity, vasculature remodelling and endothelial dysfunction) and/or protective (preconditioning-like cardioprotective) effects. Since many OSA subjects are obese, and obesity is an independent risk factor for many comorbidities associated with OSA; and also most OSA has never been diagnosed in obese patients, we hypothesed that the chronic intermittent hypoxia caused by OSA in obese patients may be one of the underlying mechanisms in morbi-mortality paradox of obesity.