Effects of ischemia and reperfusion on isolated ventricular myocytes from young adult and aged Fischer 344 rat hearts

Long-term effects of primary graft dysfunction after heart transplantation

BACKGROUND

We studied the incidence of primary graft dysfunction (PGD), its impact on in-hospital and follow-up outcomes and searched for independent risk factors.

METHODS

During an 18-year period, 508 individuals underwent heart transplantation at our institution. Patients were diagnosed with none, mild, moderate or severe PGD according to ISHLT criteria.

RESULTS

Thirty-eight patients (7.5%) met the ISHLT criteria for mild PGD, 92 (18.1%) for moderate PGD and 23 (4.5%) for severe PGD. Patients were classified into none/mild PGD (77.4%) and moderate/severe PGD (22.6%) groups. In-hospital mortality was 12.4% (7.8% for none/mild PGD and 28.7% for moderate/severe PGD; p < .001). Survival at 1, 5, and 15 years was 85.5 ± 1.9% versus 67.2 ± 4.5%, 80 ± 2.2% versus 63.5 ± 4.7%, and 60.4 ± 3.6% versus 45.9 ± 8.4%, respectively (p < .001). Excluding the events occurring during the first month of follow-up, survival was comparable between the two groups (93.1 ± 1.4% vs. 94.7 ± 2.6 at 1 year and 65.6 ± 3.8% vs. 70.4 ± 10.4% at 15 years, respectively; p = .88). Upon multivariate logistic regression analysis preoperative mechanical circulatory support (odds ratio [OR] = 5.86) and preoperative intra-aortic balloon pump (IABP) (OR = 9.58) were independently associated with moderate/severe PGD.

CONCLUSIONS

Our results confirm that PGD is associated with poor in-hospital outcome. The poor outcome does not extend beyond the first month of follow-up, with comparable survival between patients with none/mild PGD and moderate/severe PGD in the short and long-term. Mechanical circulatory support and preoperative IABP were found to be independent risk factors for moderate/severe PGD.

Age- and gender-related differences in the del Nido cardioprotection protocol

BACKGROUND

The evidence regarding the impact of patient's age and gender on del Nido cardioplegia cadioprotection capability in adults is strongly limited.

METHODS

A group of 75 patients undergoing aortic valve replacement (AVR) with del Nido cardioplegia was divided into Group 1 (male) and Group 2 (female). Creatine kinase (CK-MB isoenzyme) and high sensitivity troponin T (hs-TnT) values at 24 hours and 48 hours, occurrence of cardiac activity during crossclamp and ventricular fibrillation (VF) during reperfusion were compared. The impact of age on hs-TnT,CK-MB, VF during reperfusion and cardiac activity during crossclamp was investigated using regression models.

RESULTS

No difference between the groups was reported in 24-hour CK-MB (median 15.57 ng/ml; IQR 12.13-22.82 ng/mL vs 13.97; 12.09-17.147 ng/mL; p= .168), 48-hour CK-MB (6.19; 4.22-7.71 ng/mL vs 6.07;4.56-7.06 ng/mL; p= .707), 24-hour hs-TnT (259.2; 172.0-376.9 pg/mL vs 193.0; 167.8-351 pg/mL.1; p= .339), 48-hour hs-TnT (169.1; 124.9-293.0 pg/mL vs 159.2; 123.12-211.77 pg/mL; p= .673), VF during reperfusion (25% vs 18,5%; p= .774) and cardiac activity during arrest (39.6% vs 37.1%; p= 1.0). Values of CK-MB at 24 hours, hs-TnT at 24 hours and hs-TnT at 48 hours were not dependent on age. The CK-MB at 48 hours was dependent on age (p=.039). Probit regression failed to reveal the impact of patients' age on post-clamp VF occurrence ( p=.11) or electrical activity during arrest (p=.57) .

CONCLUSIONS

Basing on study results, it can be hypothesised that the del Nido cardioplegia provides adequate myocardial protection in AVR patients regardless of age and gender.

H3K14 hyperacetylation‑mediated c‑Myc binding to the miR‑30a‑5p gene promoter under hypoxia postconditioning protects senescent cardiomyocytes from hypoxia/reoxygenation injury

Our previous study reported that microRNA (miR)‑30a‑5p upregulation under hypoxia postconditioning (HPostC) exert a protective effect on aged H9C2 cells against hypoxia/reoxygenation injury via DNA methyltransferase 3B‑induced DNA hypomethylation at the miR‑30a‑5p gene promoter. This suggests that miR‑30a‑5p may be a potential preventative and therapeutic target for ischemic heart disease in aged myocardium. The present study aimed to investigate the underlying mechanisms of miR‑30a‑5p transcription in aged myocardium in ischemic heart disease. Cardiomyocytes were treated with 8 mg/ml D‑galactose for 9 days, and then exposed to hypoxic conditions. Cell viability was determined using a cell viability assay. Expression levels of histone deacetylase 2 (HDAC2), LC3B‑II/I, beclin‑1 and p62 were detected via reverse transcription‑quantitative PCR and western blotting. Chromatin immunoprecipitation‑PCR and luciferase reporter assays were performed to evaluate the effect of c‑Myc binding and activity on the miR‑30a‑5p promoter in senescent cardiomyocytes following HPostC. It was found that HPostC enhanced the acetylation levels of H3K14 at the miR‑30a‑5p gene promoter in senescent cardiomyocytes, which attributed to the decreased expression of HDAC2. In addition, c‑Myc could positively regulate miR‑30a‑5p transcription to inhibit senescent cardiomyocyte autophagy. Mechanically, it was observed that increased H3K14 acetylation level exposed to romidepsin facilitated c‑Myc binding to the miR‑30a‑5p gene promoter region, which led to the increased transcription of miR‑30a‑5p. Taken together, these results demonstrated that HDAC2‑mediated H3K14 hyperacetylation promoted c‑Myc binding to the miR‑30a‑5p gene promoter, which contributed to HPostC senescent cardioprotection.

Age, Sex and Overall Health, Measured As Frailty, Modify Myofilament Proteins in Hearts From Naturally Aging Mice

We investigated effects of age, sex and frailty on contractions, calcium transients and myofilament proteins to determine if maladaptive changes associated with aging were sex-specific and modified by frailty. Ventricular myocytes and myofilaments were isolated from middle-aged (~12 mos) and older (~24 mos) mice. Frailty was assessed with a non-invasive frailty index. Calcium transients declined and slowed with age in both sexes, but contractions were largely unaffected. Actomyosin Mg-ATPase activity increased with age in females but not males; this could maintain contractions with smaller calcium transients in females. Phosphorylation of myosin-binding protein C (MyBP-C), desmin, tropomyosin and myosin light chain-1 (MLC-1) increased with age in males, but only MyBP-C and troponin-T increased in females. Enhanced phosphorylation of MyBP-C and MLC-1 could preserve contractions in aging. Interestingly, the age-related decline in Hill coefficients (r = −0.816; p = 0.002) and increase in phosphorylation of desmin (r = 0.735; p = 0.010), tropomyosin (r = 0.779; p = 0.005) and MLC-1 (r = 0.817; p = 0.022) were graded by the level of frailty in males but not females. In these ways, cardiac remodeling at cellular and subcellular levels is graded by overall health in aging males. Such changes may contribute to heart diseases in frail older males, whereas females may be resistant to these effects of frailty.

Ischemia Enhances the Acute Stretch-Induced Increase in Calcium Spark Rate in Ventricular Myocytes

Introduction: In ventricular myocytes, spontaneous release of calcium (Ca²⁺) from the sarcoplasmic reticulum via ryanodine receptors (“Ca²⁺ sparks”) is acutely increased by stretch, due to a stretch-induced increase of reactive oxygen species (ROS). In acute regional ischemia there is stretch of ischemic tissue, along with an increase in Ca²⁺ spark rate and ROS production, each of which has been implicated in arrhythmogenesis. Yet, whether there is an impact of ischemia on the stretch-induced increase in Ca²⁺ sparks and ROS has not been investigated. We hypothesized that ischemia would enhance the increase of Ca²⁺ sparks and ROS that occurs with stretch.

Methods: Isolated ventricular myocytes from mice (male, C57BL/6J) were loaded with fluorescent dye to detect Ca²⁺ sparks (4.6 μM Fluo-4, 10 min) or ROS (1 μM DCF, 20 min), exposed to normal Tyrode (NT) or simulated ischemia (SI) solution (hyperkalemia [15 mM potassium], acidosis [6.5 pH], and metabolic inhibition [1 mM sodium cyanide, 20 mM 2-deoxyglucose]), and subjected to sustained stretch by the carbon fiber technique (~10% increase in sarcomere length, 15 s). Ca²⁺ spark rate and rate of ROS production were measured by confocal microscopy.

Results: Baseline Ca²⁺ spark rate was greater in SI (2.54 ± 0.11 sparks·s⁻¹·100 μm⁻²; n = 103 cells, N = 10 mice) than NT (0.29 ± 0.05 sparks·s⁻¹·100 μm⁻²; n = 33 cells, N = 9 mice; p < 0.0001). Stretch resulted in an acute increase in Ca²⁺ spark rate in both SI (3.03 ± 0.13 sparks·s⁻¹·100 μm⁻²; p < 0.0001) and NT (0.49 ± 0.07 sparks·s⁻¹·100 μm⁻²; p < 0.0001), with the increase in SI being greater than NT (+0.49 ± 0.04 vs. +0.20 ± 0.04 sparks·s⁻¹·100 μm⁻²; p < 0.0001). Baseline rate of ROS production was also greater in SI (1.01 ± 0.01 normalized slope; n = 11, N = 8 mice) than NT (0.98 ± 0.01 normalized slope; n = 12, N = 4 mice; p < 0.05), but there was an acute increase with stretch only in SI (+12.5 ± 2.6%; p < 0.001).

Conclusion: Ischemia enhances the stretch-induced increase of Ca²⁺ sparks in ventricular myocytes, with an associated enhancement of stretch-induced ROS production. This effect may be important for premature excitation and/or in the development of an arrhythmogenic substrate in acute regional ischemia.

Early Graft Dysfunction Following Heart Transplant: Prevention and Management

Heart transplant can be considered as the “gold standard” treatment for end-stage heart failure, with nearly 5.7 million adults in the United States carrying a diagnosis of heart failure. According to the International Society for Heart and Lung Transplantation registry, nearly 3300 orthotopic heart transplants were performed in 2016 in North America. In spite of significant improvements in overall perioperative care of heart transplant recipients for the past few decades, the risk of 30-day mortality remains 5% to 10%, primarily related to early failure of the allograft. Early graft dysfunction (EGD) occurs within 24 hours after transplant, manifesting as left ventricular dysfunction, right ventricular dysfunction, or biventricular dysfunction. EGD is further classified into primary and secondary graft dysfunction. This review focus on describing overall incidences of EGD, potential risk factors associated with EGD, perioperative preventive measures, and various management options.

Aging Exacerbates Ischemia-Reperfusion-Induced Mitochondrial Respiration Impairment in Skeletal Muscle

Cycles of ischemia-reperfusion (IR) that occur during peripheral arterial disease (PAD) are associated with significant morbi-mortality, and aging is an irreversible risk factor of PAD. However, the effects of advanced age on IR-induced skeletal muscle mitochondrial dysfunction are not well known. Young and aged mice were therefore submitted to hindlimb IR (2 h ischemia followed by 2 h reperfusion). Skeletal muscle mitochondrial respiration, calcium retention capacity (CRC) and reactive oxygen species (ROS) production were determined using high resolution respirometry, spectrofluorometry and electronic paramagnetic resonance. IR-induced impairment in mitochondrial respiration was enhanced in old animals (V_ADP; from 33.0 ± 2.4 to 18.4 ± 3.8 and 32.8 ± 1.3 to 5.9 ± 2.7 pmol/s/mg wet weight; −44.2 ± 11.4% vs. −82.0 ± 8.1%, in young and aged mice, respectively). Baseline CRC was lower in old animals and IR similarly decreased the CRC in both groups (from 11.8 ± 0.9 to 4.6 ± 0.9 and 5.5 ± 0.9 to 2.1 ± 0.3 µmol/mg dry weight; −60.9 ± 7.3 and −60.9 ± 4.6%, in young and aged mice, respectively). Further, IR-induced ROS production tended to be higher in aged mice. In conclusion, aging exacerbated the deleterious effects of IR on skeletal muscle mitochondrial respiration, potentially in relation to an increased oxidative stress.

Conditioning-induced cardioprotection: Aging as a confounding factor

The aging process induces a plethora of changes in the body including alterations in hormonal regulation and metabolism in various organs including the heart. Aging is associated with marked increase in the vulnerability of the heart to ischemia-reperfusion injury. Furthermore, it significantly hampers the development of adaptive response to various forms of conditioning stimuli (pre/post/remote conditioning). Aging significantly impairs the activation of signaling pathways that mediate preconditioning-induced cardioprotection. It possibly impairs the uptake and release of adenosine, decreases the number of adenosine transporter sites and down-regulates the transcription of adenosine receptors in the myocardium to attenuate adenosine-mediated cardioprotection. Furthermore, aging decreases the expression of peroxisome proliferator-activated receptor gamma co-activator 1-alpha (PGC-1α) and subsequent transcription of catalase enzyme which subsequently increases the oxidative stress and decreases the responsiveness to preconditioning stimuli in the senescent diabetic hearts. In addition, in the aged rat hearts, the conditioning stimulus fails to phosphorylate Akt kinase that is required for mediating cardioprotective signaling in the heart. Moreover, aging increases the concentration of Na⁺ and K⁺, connexin expression and caveolin abundance in the myocardium and increases the susceptibility to ischemia-reperfusion injury. In addition, aging also reduces the responsiveness to conditioning stimuli possibly due to reduced kinase signaling and reduced STAT-3 phosphorylation. However, aging is associated with an increase in MKP-1 phosphorylation, which dephosphorylates (deactivates) mitogen activated protein kinase that is involved in cardioprotective signaling. The present review describes aging as one of the major confounding factors in attenuating remote ischemic preconditioning-induced cardioprotection along with the possible mechanisms.

Cardiovascular aging: the unveiled enigma from bench to bedside

: The rapid increase in the median age of the world's population requires particular attention towards older and more fragile people. Cardiovascular risk factors, time and comorbidities play a vicious role in the development of heart failure, both with reduced and preserved ejection fraction, in the elderly. Understanding the mechanisms underlying the pathophysiological processes observed with aging is pivotal to target those patients and their therapeutic needs properly. This review aims to investigate and to dissect the main pathways leading to the aging cardiomyopathy, helping to understand the relationship from bench to bedside of the clinical phenotype.

Myocardial susceptibility to ischaemia/reperfusion in obesity: a re-evaluation of the effects of age

Background

Reports on the effect of age and obesity on myocardial ischaemia/reperfusion (I/R) injury and ischaemic preconditioning are contradictory. The aim of this study was to re-evaluate the effects of age and diet-induced obesity (DIO) on myocardial I/R injury and preconditioning potential.

Methods

Four groups of Wistar male rats were used: age-matched controls (AMC) receiving standard rat chow for (i) 16 weeks and (ii) 16 months respectively; DIO rats receiving a sucrose-supplemented diet for (iii) 16 weeks and (iv) 16 months respectively. The ages of groups (i) and (iii) were 22 weeks (“young”) and groups (ii) and (iv) 17 months (“middle-aged”) at time of experimentation. Isolated perfused working hearts were subjected to 35 min regional ischaemia/1 h reperfusion. Endpoints were infarct size (tetrazolium staining) and functional recovery. Hearts were preconditioned by 3 × 5 min ischaemia/5 min reperfusion. Results were processed using GraphPad Prism statistical software.

Results

Age did not affect baseline heart function before induction of ischaemia and I/R damage as indicated by infarct size and similar values were obtained in hearts from both age groups. Age also had no effect on functional recovery of hearts during reperfusion after regional ischaemia in AMC rats, but cardiac output during reperfusion was better in hearts from middle-aged than young DIO rats.

The diet reduced infarct size in hearts from young rats (% of area at risk: AMC: 32.4 ± 3.6; DIO: 20.7 ± 2.9, p < 0.05), with no differences in hearts from middle-aged rats (AMC: 24.6 ± 4.6; DIO: 28.3 ± 13.5, p = NS). Compared to their respective AMC, diet-induced obesity had no significant effect on functional recovery of hearts from both age groups after exposure to regional ischaemia.

When exposed to the more severe stress of global ischaemia, the functional recovery potential of middle-aged DIO rats appeared to be impeded compared to hearts of young DIO rats, while age had no effect on the functional recovery of AMC hearts.

Preconditioning reduced infarct size in hearts from young control rats and both middle-aged groups, but not from young DIO rats. Age had a significant effect on functional recovery in preconditioning: it was improved in hearts from young control and DIO rats, but depressed in both middle-aged groups.

Conclusions

The data showed that middle-age and obesity had no effect on baseline myocardial function and did not increase susceptibility to I/R damage upon exposure to regional ischaemia. On the contrary, obesity reduced I/R damage in young rats. Preconditioned aging hearts showed a decreased infarct size, but a reduction in functional recovery.

Regulation of gap junction conductance by calcineurin through Cx43 phosphorylation: implications for action potential conduction

Cardiac arrhythmias are associated with raised intracellular [Ca²⁺] and slowed action potential conduction caused by reduced gap junction (GJ) electrical conductance (Gj). Ventricular GJs are composed of connexin proteins (Cx43), with Gj determined by Cx43 phosphorylation status. Connexin phosphorylation is an interplay between protein kinases and phosphatases but the precise pathways are unknown. We aimed to identify key Ca²⁺-dependent phosphorylation sites on Cx43 that regulate cardiac gap junction conductance and action potential conduction velocity. We investigated the role of the Ca²⁺-dependent phosphatase, calcineurin. Intracellular [Ca²⁺] was raised in guinea-pig myocardium by a low-Na solution or increased stimulation. Conduction velocity and Gj were measured in multicellular strips. Phosphorylation of Cx43 serine residues (S365 and S368) and of the intermediary regulator I1 at threonine35 was measured by Western blot. Measurements were made in the presence and absence of inhibitors to calcineurin, I1 or protein phosphatase-1 and phosphatase-2.Raised [Ca²⁺]_i decreased Gj, reduced Cx43 phosphorylation at S365 and increased it at S368; these changes were reversed by calcineurin inhibitors. Cx43-S368 phosphorylation was reversed by the protein kinase C inhibitor chelerythrine. Raised [Ca²⁺]_i also decreased I1 phosphorylation, also prevented by calcineurin inhibitors, to increase activity of the Ca²⁺-independent phosphatase, PPI. The PP1 inhibitor, tautomycin, prevented Cx43-365 dephosphorylation, Cx43-S368 phosphorylation and Gj reduction in raised [Ca²⁺]_i. PP2A had no role. Conduction velocity was reduced by raised [Ca²⁺]_i and reversed by calcineurin inhibitors. Reduced action potential conduction and Gj in raised [Ca²⁺] are regulated by calcineurin-dependent Cx43-S365 phosphorylation, leading to Cx43-S368 dephosphorylation. The calcineurin action is indirect, via I1 dephosphorylation and subsequent activation of PP1.

Male and female hypertrophic rat cardiac myocyte functional responses to ischemic stress and β-adrenergic challenge are different

Background

Cardiac hypertrophy is the most potent cardiovascular risk factor after age, and relative mortality risk linked with cardiac hypertrophy is greater in women. Ischemic heart disease is the most common form of cardiovascular pathology for both men and women, yet significant differences in incidence and outcomes exist between the sexes. Cardiac hypertrophy and ischemia are frequently occurring dual pathologies. Whether the cellular (cardiomyocyte) mechanisms underlying myocardial damage differ in women and men remains to be determined. In this study, utilizing an in vitro experimental approach, our goal was to examine the proposition that responses of male/female cardiomyocytes to ischemic (and adrenergic) stress may be differentially modulated by the presence of pre-existing cardiac hypertrophy.

Methods

We used a novel normotensive custom-derived hypertrophic heart rat (HHR; vs control strain normal heart rat (NHR)). Cardiomyocyte morphologic and electromechanical functional studies were performed using microfluorimetric techniques involving simulated ischemia/reperfusion protocols.

Results

HHR females exhibited pronounced cardiac/cardiomyocyte enlargement, equivalent to males. Under basal conditions, a lower twitch amplitude in female myocytes was prominent in normal but not in hypertrophic myocytes. The cardiomyocyte Ca²⁺ responses to β-adrenergic challenge differed in hypertrophic male and female cardiomyocytes, with the accentuated response in males abrogated in females—even while contractile responses were similar. In simulated ischemia, a marked and selective elevation of end-ischemia Ca²⁺ in normal female myocytes was completely suppressed in hypertrophic female myocytes—even though all groups demonstrated similar shifts in myocyte contractile performance. After 30 min of simulated reperfusion, the Ca²⁺ desensitization characterizing the male response was distinctively absent in female cardiomyocytes.

Conclusions

Our data demonstrate that cardiac hypertrophy produces dramatically different basal and stress-induced pathophenotypes in female- and male-origin cardiomyocytes. The lower Ca²⁺ operational status characteristic of female (vs male) cardiomyocytes comprising normal hearts is not exhibited by myocytes of hypertrophic hearts. After ischemia/reperfusion, availability of activator Ca²⁺ is suppressed in female hypertrophic myocytes, whereas sensitivity to Ca²⁺ is blunted in male hypertrophic myocytes. These findings demonstrate that selective intervention strategies should be pursued to optimize post-ischemic electromechanical support for male and female hypertrophic hearts.

Electronic supplementary material

The online version of this article (doi:10.1186/s13293-016-0084-8) contains supplementary material, which is available to authorized users.

The Use of Lidocaine Containing Cardioplegia in Surgery for Adult Acquired Heart Disease

BACKGROUND

Del Nido cardioplegia, a crystalloid-based solution with lidocaine as a key element, is given as a single dose and has been used successfully in congenital cardiac surgery.

HYPOTHESIS

We retrospectively compared a lidocaine containing "modified del Nido" solution with our standard whole blood cardioplegia to investigate its safety and efficacy in adult cardiac surgery.

METHODS

From June 1, 2013 to December 30, 2013, we used a single dose of lidocaine containing cardioplegia (LC group) in 92 consecutive operations. Propensity matching analysis was undertaken to compare the outcomes of such patients with those who underwent their surgery by the same surgeon using standard whole blood cardioplegia (WB group), n = 396. Propensity score matching yielded 79 pairs of patients.

RESULTS

After propensity matching, LC and WB groups were similar in baseline operative characteristics including cross-clamp time (LC: 65 minutes [range 54 to 89] vs. WB: 70 minutes [54 to 86], p = 0.993). Postoperative outcomes were similar including inotropic requirements (30.4% [24/72] vs. 25.3% [20/72], p < 0.60), median ventilation time (4.7 hours vs. 5.3, p < 0.74) and median length of stay was seven days for both groups (p < 0.82). Despite higher median postoperative, 24-hour CK-MB levels LC group (LC:22.3 ng/ml, range [15.6 to 40.3] vs. WB:18.4 ng/ml [13.9 to 28.2], p = 0.040), operative and one-year mortality were comparable among study groups (both p > 0.798).

CONCLUSIONS

Lidocaine containing cardioplegia appears to be safe in adults undergoing cardiac procedure when administered for the first 60 minutes of aortic cross clamping. Higher CK-MB levels did not translate into adverse clinical outcomes.

Altered FoF1 ATP synthase and susceptibility to mitochondrial permeability transition pore during ischaemia and reperfusion in aging cardiomyocytes

Aging is a major determinant of the incidence and severity of ischaemic heart disease. Preclinical information suggests the existence of intrinsic cellular alterations that contribute to ischaemic susceptibility in senescent myocardium, by mechanisms not well established. We investigated the role of altered mitochondrial function in the adverse effect of aging. Isolated perfused hearts from old mice (> 20 months) displayed increased ischaemia-reperfusion injury as compared to hearts from adult mice (6 months) despite delayed onset of ischaemic rigor contracture. In cardiomyocytes from aging hearts there was a more rapid decline of mitochondrial membrane potential (Δψm) as compared to young ones, but ischaemic rigor shortening was also delayed. Transient recovery of Δψm observed during ischaemia, secondary to the reversal of mitochondrial FoF1 ATP synthase to ATPase mode, was markedly reduced in aging cardiomyocytes. Proteomic analysis demonstrated increased oxidation of different subunits of ATP synthase. Altered bionergetics in aging cells was associated with reduced mitochondrial calcium uptake and more severe cytosolic calcium overload during ischaemia-reperfusion. Despite attenuated ROS burst and mitochondrial calcium overload, mitochondrial permeability transition pore (mPTP) opening and cell death was increased in reperfused aged cells. In vitro studies demonstrated a significantly reduced calcium retention capacity in interfibrillar mitochondria from aging hearts. Our results identify altered FoF1 ATP synthase and increased sensitivity of mitochondria to undergo mPTP opening as important determinants of the reduced tolerance to ischaemia-reperfusion in aging hearts. Because ATP synthase has been proposed to conform mPTP, it is tempting to hypothesise that oxidation of ATP synthase underlie both phenomena.

Mitochondria-targeted ROS scavenger improves post-ischemic recovery of cardiac function and attenuates mitochondrial abnormalities in aged rats

Mitochondria-generated reactive oxygen species (ROS) play a crucial role in the pathogenesis of aging and age-associated diseases. In this study, we evaluated the effects of XJB-5-131 (XJB), a mitochondria-targeted ROS and electron scavenger, on cardiac resistance to ischemia-reperfusion (IR)-induced oxidative stress in aged rats. Male adult (5-month old, n=17) and aged (29-month old, n=19) Fischer Brown Norway (F344/BN) rats were randomly assigned to the following groups: adult (A), adult+XJB (AX), aged (O), and aged+XJB (OX). XJB was administered 3 times per week (3mg/kg body weight, IP) for four weeks. At the end of the treatment period, cardiac function was continuously monitored in excised hearts using the Langendorff technique for 30 min, followed by 20 min of global ischemia, and 60-min reperfusion. XJB improved post-ischemic recovery of aged hearts, as evidenced by greater left ventricular developed-pressures and rate-pressure products than the untreated, aged-matched group. The state 3 respiration rates at complexes I, II and IV of mitochondria isolated from XJB-treated aged hearts were 57% (P<0.05), 25% (P<0.05) and 28% (P<0.05), respectively, higher than controls. Ca(2+)-induced swelling, an indicator of permeability transition pore opening, was reduced in the mitochondria of XJB-treated aged rats. In addition, XJB significantly attenuated the H2O2-induced depolarization of the mitochondrial inner membrane as well as the total and mitochondrial ROS levels in cultured cardiomyocytes. This study underlines the importance of mitochondrial ROS in aging-induced cardiac dysfunction and suggests that targeting mitochondrial ROS may be an effective therapeutic approach to protect the aged heart against IR injury.

Ang-(1-7) offers cytoprotection against ischemia-reperfusion injury by restoring intracellular calcium homeostasis

Accumulating evidence indicates that angiotensin-(1-7) [Ang-(1-7)] offers protective effects against ischemia-reperfusion (I/R) induced arrhythmias and contractile dysfunction, which are related to disturbances of intracellular calcium homeostasis. However, whether or not Ang-(1-7) regulates intracellular calcium in I/R is not clear. To shed light on this issue, we carried out studies with a cellular model of simulated I/R in isolated rat ventricular myocytes and measured calcium transients using laser scanning confocal microscopy. Our results showed that Ang-(1-7) had no effects on the calcium transient in myocytes superfused with normal solution; however, in myocytes of simulated I/R, Ang-(1-7) significantly attenuated the increased diastolic intracellular Ca during reperfusion, restored the decreased peak Ca of calcium transient during ischemia, and reversed the decreased amplitude of calcium transient throughout the I/R periods. Additionally, Ang-(1-7) significantly suppressed the reactive oxygen species production in I/R, especially during the ischemic phase. These data indicated that Ang-(1-7) affords significant cytoprotective effects through directly improving calcium homeostasis independent of its anti-oxidative action. Most notably, the effects of Ang-(1-7) on intracellular Ca dynamics manifests only in the diseased states, that is, I/R. This unique property suggests that upregulation of Ang-(1-7) expression and/or activation of the Ang-(1-7)/Mas signaling cascade is a highly desirable strategy for the treatment of myocardial impairment induced by I/R.

Sex differences in SR Ca(2+) release in murine ventricular myocytes are regulated by the cAMP/PKA pathway

Previous studies have shown that ventricular myocytes from female rats have smaller contractions and Ca(2+) transients than males. As cardiac contraction is regulated by the cyclic adenosine monophosphate (cAMP)/protein kinase A (PKA) pathway, we hypothesized that sex differences in cAMP contribute to differences in Ca(2+) handling. Ca(2+) transients (fura-2) and ionic currents were measured simultaneously (37°C, 2Hz) in ventricular myocytes from adult male and female C57BL/6 mice. Under basal conditions, diastolic Ca(2+), sarcoplasmic reticulum (SR) Ca(2+) stores, and L-type Ca(2+) current did not differ between the sexes. However, female myocytes had smaller Ca(2+) transients (26% smaller), Ca(2+) sparks (6% smaller), and excitation-contraction coupling gain in comparison to males (23% smaller). Interestingly, basal levels of intracellular cAMP were lower in female myocytes (0.7±0.1 vs. 1.7±0.2fmol/μg protein; p<0.001). Importantly, PKA inhibition (2μM H-89) eliminated male-female differences in Ca(2+) transients and gain, as well as Ca(2+) spark amplitude. Western blots showed that PKA inhibition also reduced the ratio of phospho:total RyR2 in male hearts, but not in female hearts. Stimulation of cAMP production with 10μM forskolin abolished sex differences in cAMP levels, as well as differences in Ca(2+) transients, sparks, and gain. To determine if the breakdown of cAMP differed between the sexes, phosphodiesterase (PDE) mRNA levels were measured. PDE3 expression was similar in males and females, but PDE4B expression was higher in female ventricles. The inhibition of cAMP breakdown by PDE4 (10μM rolipram) abolished differences in Ca(2+) transients and gain. These findings suggest that female myocytes have lower levels of basal cAMP due, in part, to higher expression of PDE4B. Lower cAMP levels in females may attenuate PKA phosphorylation of Ca(2+) handling proteins in females, and may limit positive inotropic responses to stimulation of the cAMP/PKA pathway in female hearts.

Efficacy of selective NCX inhibition by ORM-10103 during simulated ischemia/reperfusion

In this study we evaluated the effects of selective Na+/Ca2+ exchanger (NCX) inhibition by ORM-10103 on the [Ca2+]i transient (CaT), action potential (AP), and cell viability in isolated canine ventricular cardiomyocytes exposed to a simulated ischemia/reperfusion protocol performed either alone (modeling moderate low-flow ischemia) or with simultaneous strophantidine challenge (modeling more severe low-flow ischemia). CaTs were monitored using a Ca2+-sensitive fluorescent dye, APs were recorded by intracellular microelectrodes, and anaerobic shifts in cellular metabolism were verified via monitoring native NADH fluorescence. Simulated ischemia increased the NADH fluorescence, reduced the amplitudes of the AP and CaT and induced membrane depolarization. APs moderately shortened, CaTs prolonged. Diastolic [Ca2+]i ([Ca2+]iD) level increased significantly during ischemia and further elevated following strophantidine application. Reperfusion normalized the NADH level, the amplitude of the AP and duration of the [Ca2+]i transient, but only partially restored action potential triangulation and the amplitude of the CaT. [Ca2+]iD decreased in untreated, but further increased in strophantidine-treated cells. 10 µM ORM-10103 significantly reduced the ischemic [Ca2+]i raise in both untreated and strophantidine-treated cells. During reperfusion ORM-10103 decreased [Ca2+]i and eliminated its diastolic elevation in untreated and strophantidine-treated cardiomyocytes. Following the application of ORM-10103 the detrimental effect of ischemia/reperfusion on cell viability and the reperfusion-induced increase in AP and CaT variabilities were substantially reduced, but ischemia-induced shifts in AP morphology were barely influenced. In conclusion, selective NCX inhibition by ORM-10103 is highly effective against ischemia/reperfusion induced pathologic alterations in [Ca2+]i homeostasis, however, it fails to normalize untoward arrhythmogenic changes in AP morphology.

Cardiac contraction, calcium transients, and myofilament calcium sensitivity fluctuate with the estrous cycle in young adult female mice

This study established conditions to induce regular estrous cycles in female C57BL/6J mice and investigated the impact of the estrous cycle on contractions, Ca2+ transients, and underlying cardiac excitation-contraction (EC)-coupling mechanisms. Daily vaginal smears from group-housed virgin female mice were stained to distinguish estrous stage (proestrus, estrus, metestrus, diestrus). Ventricular myocytes were isolated from anesthetized mice. Contractions and Ca2+ transients were measured simultaneously (4 Hz, 37°C). Interestingly, mice did not exhibit regular cycles unless they were exposed to male pheromones in bedding added to their cages. Field-stimulated myocytes from mice in estrus had larger contractions (∼2-fold increase), larger Ca2+ transients (∼1.11-fold increase), and longer action potentials (>2-fold increase) compared with other stages. Larger contractions and Ca2+ transients were not observed in estrus myocytes voltage-clamped with shorter action potentials. Voltage-clamp experiments also demonstrated that estrous stage had no effect on Ca2+ current, EC-coupling gain, diastolic Ca2+, sarcoplasmic reticulum (SR) Ca2+ content, or fractional release. Although contractions were largest in estrus, myofilament Ca2+ sensitivity was lowest (EC50 values ∼1.15-fold higher) in conjunction with increased phosphorylation of myosin binding protein C in estrus. Contractions were enhanced in ventricular myocytes from mice in estrus because action potential prolongation increased SR Ca2+ release. These findings demonstrate that cyclical changes in reproductive hormones associated with the estrous cycle can influence myocardial electrical and contractile function and modify Ca2+ homeostasis. However, such changes are unlikely to occur in female mice housed in groups under conventional conditions, since these mice do not exhibit regular estrous cycles.

The Na+/Ca2+ exchange inhibitor SEA0400 limits intracellular Ca2+ accumulation and improves recovery of ventricular function when added to cardioplegia

Background

The Na⁺/Ca²⁺ exchange inhibitor SEA0400 prevents myocardial injury in models of global ischemia and reperfusion. We therefore evaluated its potential as a cardioplegia additive.

Methods

Isolated rat cardiomyocytes were exposed to hypoxia (45 min) followed by reperfusion. During hypoxia, cells were protected using cardioplegia with (n = 25) or without (n = 24) SEA0400 (1 μM), or were not protected with cardioplegia (hypoxic control, n = 8). Intracellular Ca²⁺ levels were measured using Ca²⁺ sensitive dye (fura-2 AM). Isolated rat hearts were arrested using cardioplegia with (n = 7) or without (n = 6) SEA0400 (1 μM) then reperfused after 45 min of ischemia. Left ventricular (LV) function, troponin release, and mitochondrial morphology were evaluated.

Results

Cardiomyocytes exposed to hypoxia without cardioplegia had poor survival (13%). Survival was significantly improved when cells were protected with cardioplegia containing SEA0400 (68%, p = 0.009); cardioplegia without SEA0400 was associated with intermediate survival (42%). Cardiomyocytes exposed to hypoxia alone had a rapid increase in intracellular Ca²⁺ (305 ± 123 nM after 20 minutes of ischemia). Increases in intracellular Ca²⁺ were reduced in cells arrested with cardioplegia without SEA0400; however cardioplegia containing SEA0400 was associated with the lowest intracellular Ca²⁺ levels (110 ± 17 vs. 156 ± 42 nM after 45 minutes of ischemia, p = 0.004). Hearts arrested with cardioplegia containing SEA0400 had better recovery of LV work compared to cardioplegia without SEA0400 (23140 ± 2264 vs. 7750 ± 929 mmHg.μl, p = 0.0001). Troponin release during reperfusion was lower (0.6 ± 0.2 vs. 2.4 ± 0.5 ng/mL, p = 0.0026), and there were more intact (41 ± 3 vs. 22 ± 5%, p < 0.005), and fewer disrupted mitochondria (24 ± 2 vs. 33 ± 3%, p < 0.05) in the SEA0400 group.

Conclusions

SEA0400 added to cardioplegia limits accumulation of intracellular Ca²⁺ during ischemic arrest in isolated cardiomyocytes and prevents myocardial injury and improves recovery of LV function in isolated hearts.

The impact of ovariectomy on calcium homeostasis and myofilament calcium sensitivity in the aging mouse heart

This study determined whether deficiency of ovarian estrogen starting very early in life promoted age-associated Ca(2+) dysregulation and contractile dysfunction in isolated ventricular myocytes. Myocytes were isolated from anesthetized C57BL/6 female mice. Animals received an ovariectomy or sham-operation at one month and were aged to ~24 months. Excitation-contraction coupling parameters were compared in fura-2 loaded myocytes (37°C). While Ca(2+) transients were larger and faster in field-stimulated myocytes from ovariectomized mice, ovariectomy had no effect on peak fractional shortening. Similarly, ovariectomy had no effect on fractional shortening measured in vivo by echocardiography (values were 60.5 ± 2.9 vs. 60.3 ± 2.5% in sham and ovariectomized, respectively; n=5 mice/group). Ovariectomy did decrease myofilament Ca(2+) sensitivity, as evidenced by a 26% increase in the Ca(2+) required to activate actomyosin MgATPase in ovariectomized hearts. Larger Ca(2+) transients were attributable to a 48% increase in peak Ca(2+) current, along with an increase in the amplitude, width and frequency of Ca(2+) sparks measured in fluo-4 loaded myocytes. These changes in Ca(2+) handling were not due to increased expression of Ca(2+) channels (Cav1.2), sarcoplasmic reticulum Ca(2+) ATPase (SERCA2) or Na(+)-Ca(2+) exchanger in ovariectomized hearts. However, ovariectomy increased sarcoplasmic reticulum Ca(2+) stores by ~90% and promoted spontaneous Ca(2+) release from the sarcoplasmic reticulum when compared to sham controls. These observations demonstrate that long-term ovariectomy promotes intracellular Ca(2+) dysregulation, reduces myofilament Ca(2+) sensitivity and increases spontaneous Ca(2+) release in the aging female heart.

Ischemia/Reperfusion injury protection by mesenchymal stem cell derived antioxidant capacity

Mesenchymal stem cell (MSC) transplantation after ischemia/reperfusion (I/R) injury reduces infarct size and improves cardiac function. We used mouse ventricular myocytes (VMs) in an in vitro model of I/R to determine the mechanism by which MSCs prevent reperfusion injury by paracrine signaling. Exposure of mouse VMs to an ischemic challenge depolarized their mitochondrial membrane potential (Ψmito), increased their diastolic Ca(2+), and significantly attenuated cell shortening. Reperfusion of VMs with Ctrl tyrode or MSC-conditioned tyrode (ConT) resulted in a transient increase of the Ca(2+) transient amplitudes in all cells. ConT-reperfused cells exhibited a decreased number early after depolarization (EADs) (ConT: 6.3% vs. Ctrl: 28.4%) and prolonged survival (ConT: 58% vs. Ctrl: 33%). Ψmito rapidly recovered in Ctrl as well as ConT-treated VMs on reperfusion; however, in Ctrl solution, an exaggerated hyperpolarization of Ψmito was determined that preceded the collapse of Ψmito. The ability of ConT to attenuate the hyperpolarization of Ψmito was suppressed on inhibition of the PI3K/Akt signaling pathway or IK,ATP. However, protection of Ψmito was best mimicked by the reactive oxygen species (ROS) scavenger mitoTEMPO. Analysis of ConT revealed a significant antioxidant capacity that was linked to the presence of extracellular superoxide dismutase (SOD3) in ConT. In conclusion, MSC ConT protects VMs from simulated I/R injury by its SOD3-mediated antioxidant capacity and by delaying the recovery of Ψmito through Akt-mediated opening of IK,ATP. These changes attenuate reperfusion-induced ROS production and prevent the opening of the permeability transition pore and arrhythmic Ca(2+) release.

Interactions of GSK-3β with mitochondrial permeability transition pore modulators during preconditioning: age-associated differences

Anesthetic preconditioning (APC) and ischemic preconditioning (IPC) are lost with normal aging. Here, we investigated age-related difference between phosphoglycogen synthase kinase-3beta (pGSK-3β) and pGSK-3β with modulators of mitochondrial permeability transition pore, including adenine nucleotide translocase (ANT), cyclophilin-D, or voltage-dependent anion channel. APC or IPC significantly increased pGSK-3β in the young groups in both the cytosol and the mitochondria and also significantly increased pGSK-3β in co-immunoprecipitates with ANT. Importantly, the level of cyclophilin-D in co-immunoprecipitates with ANT was significantly decreased in the young APC and IPC groups, but not in old rats. We also found that APC or IPC significantly prolonged mitochondrial permeability transition pore opening time in the young cardiomyocytes under oxidative stress, but not in the elderly. Attenuation of APC or IPC protection in the aging heart is associated with failure to reduce ANT-cyclophilin-D interactions and to decreased pGSK-3β responsiveness of ANT, critical modulators of mitochondrial permeability transition pore.

Chronic Tempol treatment restores pharmacological preconditioning in the senescent rat heart

Cardioprotective effects of anesthetic preconditioning and cyclosporine A (CsA) are lost with aging. To extend our previous work and address a possible mechanism underlying age-related differences, we investigated the role of oxidative stress in the aging heart by treating senescent animals with the oxygen free radical scavenger Tempol. Old male Fischer 344 rats (22–24 mo) were randomly assigned to control or Tempol treatment groups for 2 or 4 wk (T×2wk and T×4wk, respectively). Rats received isoflurane 30 min before ischemia-reperfusion injury or CsA just before reperfusion. Myocardial infarction sizes were significantly reduced by isoflurane or CsA in the aged rats treated with Tempol (T×4wk) compared with old control rats. In other experiments, young (4–6 mo) and old rats underwent either chronic Tempol or vehicle treatment, and the levels of myocardial protein oxidative damage, antioxidant enzymes, mitochondrial Ca2+ uptake, cyclophilin D protein, and mitochondrial permeability transition pore opening times were measured. T×4wk significantly increased MnSOD enzyme activity, GSH-to-GSSH ratios, MnSOD protein level, mitochondrial Ca2+ uptake capacity, reduced protein nitrotyrosine levels, and normalized cyclophilin D protein expression in the aged rat heart. T×4wk also significantly prolonged mitochondrial permeability transition pore opening times induced by reactive oxygen species in old cardiomyocytes. Our studies demonstrate that 4 wk of Tempol pretreatment restores anesthetic preconditioning and cardioprotection by CsA in the old rat and that this is associated with decreased oxidative stress and improved mitochondrial function. Our results point to a new protective strategy for the ischemic myocardium in the high-risk older population.

Contribution of caveolin-1 to ventricular nitric oxide in age-related adaptation to hypovolemic state

Our previous results have shown that hypovolemic state induced by acute hemorrhage in young anesthetized rats triggers heterogeneous and dynamic nitric oxide synthase (NOS) activation, modulating the cardiovascular response. Involvement of the nitric oxide pathway is both isoform-specific and time-dependent. The aim of the present study was to investigate changes in activity and protein levels of the different NOS forms, changes in the abundance of caveolin-1 during hypovolemic state and caveolin-1/eNOS association using young and middle-aged rats. Therefore, we studied (i) changes in NOS activity and protein levels and (ii) caveolin-1 abundance, as well as its association with endothelial NOS (eNOS) in ventricles from young and middle-aged rats during hypovolemic state. We used 2-month (young) and 12-month (middle-aged) old male Sprague-Dawley rats. Animals were divided into two groups (n=14/group): (a) sham; (b) hemorrhaged animals (20% blood loss). With advancing age, we observed an increase in ventricle NOS activity accompanied by a decrease in eNOS and caveolin-1 protein levels, but increased inducible NOS (iNOS). We also observed that aging is associated with caveolin-1 dissociation from eNOS. Myocardia from young and middle-aged rats subjected to hemorrhage-induced hypovolemia exhibited an increase in NOS activity and protein levels with a reduction in caveolin-1 abundance, accompanied by a greater dissociation between eNOS and its regulatory protein. Further, an increase in iNOS protein levels after blood loss was observed only in middle-aged rats. Our evidence suggests that aging and acute hemorrhage contribute to the development of upregulation in NOS activity. Our findings demonstrate that specific expression patterns of ventricular NOS isoforms, alterations in the amount of caveolin-1 and caveolin-1/eNOS interaction are involved in aged-related adjustment to hypovolemic state.

Ratiometric imaging of calcium during ischemia-reperfusion injury in isolated mouse hearts using Fura-2

Background

We present an easily implementable method for measuring Fura-2 fluorescence from isolated mouse hearts using a commercially available switching light source and CCD camera. After calibration, it provides a good estimate of intracellular [Ca²⁺] with both high spatial and temporal resolutions, permitting study of changes in dispersion of diastolic [Ca²⁺], Ca²⁺ transient dynamics, and conduction velocities in mouse hearts. In a proof-of-principle study, we imaged isolated Langendorff-perfused mouse hearts with reversible regional myocardial infarctions.

Methods

Isolated mouse hearts were perfused in the Landendorff-mode and loaded with Fura-2. Hearts were then paced rapidly and subjected to 15 minutes of regional ischemia by ligation of the left anterior descending coronary artery, following which the ligation was removed to allow reperfusion for 15 minutes. Fura-2 fluorescence was recorded at regular intervals using a high-speed CCD camera. The two wavelengths of excitation light were interleaved at a rate of 1 KHz with a computer controlled switching light source to illuminate the heart.

Results

Fura-2 produced consistent Ca²⁺ transients from different hearts. Ligating the coronary artery rapidly generated a well defined region with a dramatic rise in diastolic Ca²⁺ without a significant change in transient amplitude; Ca²⁺ handling normalized during reperfusion. Conduction velocity was reduced by around 50% during ischemia, and did not recover significantly when monitored for 15 minutes following reperfusion.

Conclusions

Our method of imaging Fura-2 from isolated whole hearts is capable of detecting pathological changes in intracellular Ca²⁺ levels in cardiac tissue. The persistent change in the conduction velocities indicates that changes to tissue connectivity rather than altered intracellular Ca²⁺ handling may be underlying the electrical instabilities commonly seen in patients following a myocardial infarction.

H-89 decreases the gain of excitation-contraction coupling and attenuates calcium sparks in the absence of beta-adrenergic stimulation

This study used the selective protein kinase A (PKA) inhibitor H-89 (N-[2-(p-Bromocinnamylamino)ethyl]-5-isoquinolinesulfonamide) to determine the role of basal PKA activity in modulating cardiac excitation-contraction coupling in the absence of β-adrenergic stimulation. Basal intracellular cyclic AMP (cAMP) levels measured in isolated murine ventricular myocytes with an enzyme immunoassay were increased upon adenylyl cyclase activation (forskolin; 1 and 10 μM) or phosphodiesterase inhibition (3-isobutyl-1-methylxanthine, IBMX; 300 μM). Forskolin and IBMX also caused concentration-dependent increases in peak Ca(2+) transients (fura-2) and cell shortening (edge-detector) measured simultaneously in field-stimulated myocytes (37 °C). Similar effects were seen upon application of dibutyryl cAMP. In voltage-clamped myocytes, H-89 (2 μM) decreased basal Ca(2+) transients, contractions and underlying Ca(2+) currents. H-89 also decreased diastolic Ca(2+) and the gain of excitation-contraction coupling (Ca(2+) release/Ca(2+) current), especially at negative membrane potentials. This was independent of alterations in sarcoplasmic reticulum (SR) Ca(2+) loading, as SR stores were unchanged by PKA inhibition. H-89 also decreased the frequency, amplitude and width of spontaneous Ca(2+) sparks measured in quiescent myocytes (loaded with fluo-4), but increased time-to-peak. Thus, H-89 suppressed SR Ca(2+) release by decreasing Ca(2+) current and by reducing the gain of excitation-contraction coupling, in part by decreasing the size of individual Ca(2+) release units. These data suggest that basal PKA activity enhances SR Ca(2+) release in the absence of ß-adrenergic stimulation. This may depress contractile function in models such as aging, where the cAMP/PKA pathway is altered due to low basal cAMP levels.

N-n-Butyl haloperidol iodide inhibits the augmented Na+/Ca2+ exchanger currents and L-type Ca2+ current induced by hypoxia/reoxygenation or H2O2 in cardiomyocytes

N-n-butyl haloperidol iodide (F(2)), a novel quaternary ammonium salt derivative of haloperidol, was reported to antagonize myocardial ischemia/reperfusion injuries. To investigate its mechanisms, we characterized the effects of F(2) on Na(+)/Ca(2+) exchanger currents (I(NCX)) and the L-type Ca(2+) channel current (I(Ca,L)) of cardiomyocytes during either hypoxia/reoxygenation or exposure to H(2)O(2). Using whole-cell patch-clamp techniques, the I(NCX) and I(Ca,L) were recorded from isolated rat ventricular myocytes. Exposure of cardiomyocytes to hypoxia/reoxygenation or H(2)O(2) enhanced the amplitude of the inward and outward of I(NCX) and I(Ca,L). F(2) especially inhibited the outward current of Na(+)/Ca(2+) exchanger, as well as the I(Ca,L), in a concentration-dependent manner. F(2) inhibits cardiomyocyte I(NCX) and I(Ca,L) after exposure to hypoxia/reoxygenation or H(2)O(2) to antagonize myocardial ischemia/reperfusion injury by inhibiting Ca(2+) overload.

Primary graft failure after heart transplantation

Primary graft failure (PGF) is a devastating complication that occurs in the immediate postoperative period following heart transplantation. It manifests as severe ventricular dysfunction of the donor graft and carries significant mortality and morbidity. In the last decade, advances in pharmacological treatment and mechanical circulatory support have improved the outlook for heart transplant recipients who develop this complication. Despite these advances in treatment, PGF is still the leading cause of death in the first 30 days after transplantation. In today's climate of significant organ shortages and growing waiting lists, transplant units worldwide have increasingly utilised "marginal donors" to try and bridge the gap between "supply and demand." One of the costs of this strategy has been an increased incidence of PGF. As the threat of PGF increases, the challenges of predicting and preventing its occurrence, as well as the identification of more effective treatment modalities, are vital areas of active research and development.

Age-associated differences in the inhibition of mitochondrial permeability transition pore opening by cyclosporine A

BACKGROUND

Inhibiting mitochondrial permeability transition pore (mPTP) opening is a key protection of the myocardium from ischemia/reperfusion (I/R) injury. Here, we investigated age-associated differences in the ability of cyclosporine A (CsA) to protect the heart and to modulate mPTP opening during I/R injury in vivo and its opening induced by reactive oxygen species (ROS) in vitro.

METHODS

Fischer 344 male rats were assigned from their respective age groups, young or old groups, to (1) I/R or (2) I/R+CsA. All animals were subjected to 30 min of ischemia following 120 min of reperfusion to determine myocardial infarct size in vivo. To measure mPTP opening in vivo, left ventricular tissues were collected 10 min after reperfusion and nicotinamide adenine dinucleotide (NAD(+)) levels were measured. In parallel experiments, rat ventricular myocytes were prepared from young and old hearts, loaded with tetramethylrhodamine ethylester and then subjected to oxidative stress in the presence or absence of CsA, and the mPTP opening time was measured using laser scanning confocal microscopy.

RESULTS

CsA reduced myocardial infarct size in young I/R rats. Whereas CsA failed to significantly affect myocardial infarct size in old I/R rats, NAD(+) levels were better preserved in young CsA-treated rats, but this relative improvement was not observed in old rats. CsA also significantly prolonged the time necessary to induce mPTP opening in young cardiomyocytes, but not in cardiomyocytes isolated from the old rats.

CONCLUSIONS

mPTP regulation is dysfunctional in the aged myocardium and this could account for loss of cardioprotection with aging.

Cardioprotection of the aged rat heart by GSK-3beta inhibitor is attenuated: age-related changes in mitochondrial permeability transition pore modulation

It is well established that inhibition of glycogen synthase kinase (GSK)-3β in the young adult myocardium protects against ischemia-reperfusion (I/R) injury through inhibition of mitochondrial permeability transition pore (mPTP) opening. Here, we investigated age-associated differences in the ability of GSK-3β inhibitor [SB-216763 (SB)] to protect the heart and to modulate mPTP opening during I/R injury. Fischer 344 male rats were assigned from their respective young or old age groups. Animals were subjected to 30 min ischemia following 120 min reperfusion to determine myocardial infarction (MI) size in vivo. Ischemic tissues were collected 10 min after reperfusion for nicotinamide adenine dinucleotide (NAD(+)) measurements and immunoblotting. In parallel experiments, ventricular myocytes isolated from young or old rats were exposed to oxidative stress through generation of reactive oxygen species (ROS), and mPTP opening times were measured by using confocal microscopy. Our results showed that SB decreased MI in young SB-treated rats compared with young untreated I/R animals, whereas SB failed to significantly affect MI in the old animals. SB also significantly increased GSK-3β phosphorylation in young rats, but phosphorylation levels were already highly elevated in old control groups. There were no significant differences observed between SB-treated and untreated old animals. NAD(+) levels were better maintained in young SB-treated animals compared with the young untreated group during I/R, but this relative improvement was not observed in old animals. SB also significantly prolonged the time to mPTP opening induced by ROS in young cardiomyocytes, but not in aged cardiomyocytes. These results demonstrate that this GSK-3β inhibitor fails to protect the aged myocardium in response to I/R injury or prevent mPTP opening following a rise in ROS and suggest that healthy aging alters mPTP regulation by GSK-3β.

N-n-butyl haloperidol iodide preserves cardiomyocyte calcium homeostasis during hypoxia/ischemia

AIMS

N-n-Butyl haloperidol iodide (F(2)) is a novel compound derived from haloperidol. In our previous work, F(2) was found to be an L-type calcium channel blocker which played a protective role in rat heart ischemic-reperfusion injury in a dose-dependent manner. In the current study, we aimed to investigate the effects and some possible mechanisms of F(2) on calcium transients in hypoxic/ischemic rat cardiac myocytes.

METHODS AND RESULTS

Calcium transients' images of rat cardiac myocytes were recorded during simulated hypoxia, using a confocal calcium imaging system. The amplitude, rising time from 25% to 75% (RT25-75), decay time from 75% to 25% (DT75-25) of calcium transients, and resting [Ca(2+)](i) were extracted from the images by self-coding programs. In this study, hypoxia produced a substantial increase in diastolic [Ca(2+)](i) and reduced the amplitude of calcium transients. Both RT25-75 and DT75-25 of Ca(2+) transients were significantly prolonged. And F(2) could reduce the increase in resting [Ca(2+)](i)and the prolongation of RT25-75 and DT75-25 of Ca(2+) transients during hypoxia. F(2) also inhibited the reduction in amplitude of calcium transients which was caused by 30-min hypoxia. The activity of SERCA2a (sarcoplasmic reticulum Ca(2+)-ATPase, determined by test kits) decreased after 30-min ischemia, and intravenous F(2) in rats could ameliorate the decreased activity of SERCA2a. The inward and outward currents of NCX (recorded by whole-cell patch-clamp analysis) were reduced during 10-min hypoxia, and F(2) further inhibited the outward currents of NCX during 10-min hypoxia. All these data of SERCA2a and NCX might be responsible for the changes in calcium transients during hypoxia.

CONCLUSION

Our data suggest that F(2) reduced changes in calcium transients that caused by hypoxia/ischemia, which was regarded to be a protective role in calcium homeostasis of ventricular myocytes, probably via changing the function of SERCA2a.

Sex differences in mechanisms of cardiac excitation-contraction coupling in rat ventricular myocytes

Components of excitation-contraction (E-C) coupling were compared in ventricular myocytes isolated from 3-mo-old male and female rats. Ca2+ concentrations (fura-2) and cell shortening (edge detector) were measured simultaneously (37°C). Membrane potential and ionic currents were measured with microelectrodes. Action potentials were similar in male and female myocytes, but contractions were smaller and slower in females. In voltage-clamped cells, peak contractions were smaller in females than in males (5.1 ± 0.7% vs. 7.7 ± 0.8% diastolic length, P < 0.05). Similarly, Ca2+ transients were smaller in females than in males and the rate of rise of the Ca2+ transient was slower in females. Despite smaller contractions and Ca2+ transients in females, Ca2+ current density was similar in both groups. Sarcoplasmic reticulum Ca2+ content, assessed with caffeine, did not differ between the sexes. However, E-C coupling gain (rate of Ca2+ release/Ca2+ current) was smaller in females than in males (157.0 ± 15.6 vs. 338.4 ± 54.3 (nM/s)/(pA/pF), P < 0.05). To determine whether the reduced gain in female cells was due to changes in unitary Ca2+ release, spontaneous Ca2+ sparks were evaluated (fluo-4, 37°C). Spark frequencies and widths were similar in both groups, but spark amplitudes were smaller in females than in males (0.56 ± 0.01 vs. 0.64 ± 0.01 ΔF/F0, P < 0.05). Spark durations also were shorter in females than in males (full duration at half-maximum = 14.86 ± 0.17 vs. 16.25 ± 0.27 ms, P < 0.05). These observations suggest that decreases in the size and duration of Ca2+ sparks contributes to the decrease in E-C coupling gain in female myocytes. Thus, differences in cardiac contractile function arise, in part, from differences in unitary Ca2+ release between the sexes.

Isoflurane protects cardiomyocytes and mitochondria by immediate and cytosol-independent action at reperfusion

BACKGROUND AND PURPOSE

The volatile anaesthetic isoflurane protects the heart from ischaemia and reperfusion (I/R) injury when applied at the onset of reperfusion [anaesthetic postconditioning (APoC)]. However, the mechanism of APoC-mediated protection is unknown. In this study, we examined the effect of APoC on mitochondrial bioenergetics, mitochondrial matrix pH (pH(m)) and cytosolic pH (pH(i)), and intracellular Ca(2+).

EXPERIMENTAL APPROACH

Cardiac mitochondria from Wistar rats were isolated after in vivo I/R with or without APoC (1.4%-vol isoflurane, 1 minimum alveolar concentration), and mitochondrial permeability transition pore (mPTP) opening, mitochondrial membrane potential (DeltaPsi(m)), and oxygen consumption were assessed. In isolated cardiomyocytes and isolated mitochondria I/R injury was produced in vitro, with or without APoC (0.5 mM isoflurane). Intracellular Ca(2+), pH(m), pH(i) and DeltaPsi(m) were monitored with SNARF-1, TMRE and fluo-4, respectively. Myocyte survival was assessed when APoC was induced at pH 7.4 and 7.8. In isolated mitochondria oxygen consumption and ATP synthesis were measured.

KEY RESULTS

In vivo APoC protected against mPTP opening, slowed mitochondrial respiration and depolarized mitochondria. APoC decreased the number of hypercontracted cardiomyocytes at pH 7.4, but not at pH 7.8. APoC attenuated intracellular Ca(2+) accumulation, maintained lower pH(m), and preserved DeltaPsi(m) during reoxygenation. Isoflurane did not affect the regulation of cytosolic pH. In mitochondria, APoC preserved ATP production rate and respiration.

CONCLUSIONS AND IMPLICATIONS

At reperfusion, APoC inhibited mitochondrial respiration, depolarized mitochondria and acidified pH(m). These events may lead to inhibition of mPTP opening and, consequently, to preserved DeltaPsi(m) and ATP synthesis. This reduces intracellular Ca(2+) overload and cell death.

Age-associated changes in excitation-contraction coupling are more prominent in ventricular myocytes from male rats than in myocytes from female rats

We evaluated effects of age on components of excitation-contraction (EC) coupling in ventricular myocytes from male and female rats to examine sex differences in mechanisms responsible for age-related contractile dysfunction. Myocytes were isolated from anesthetized young adult (approximately 3 mo) and aged (approximately 24 mo) Fischer 344 rats. Ca(2+) concentrations and contractions were measured simultaneously (37 degrees C, 2 Hz). Fractional shortening declined with age in males (6.7 +/- 0.6% to 2.4 +/- 0.4%; P < 0.05), as did peak Ca(2+) transients (47.7 +/- 4.6 to 28.1 +/- 2.1 nM; P < 0.05) and Ca(2+) current densities (-7.7 +/- 0.7 to -6.2 +/- 0.5 pA/pF; P < 0.05). Although sarcoplasmic reticulum (SR) Ca(2+) content was similar regardless of age in males, EC coupling gain declined significantly with age to 55.8 +/- 7.8% of values in younger males. In contrast with results in males, contraction and Ca(2+) transient amplitudes were unaffected by age in females. Ca(2+) current density declined with age in females (-7.5 +/- 0.5 to -5.1 +/- 0.7 pA/pF; P < 0.05), but SR Ca(2+) content actually increased dramatically (49.0 +/- 7.5 to 147.3 +/- 28.5 nM; P < 0.05). Even so, EC coupling gain was not affected by age in female myocytes. Age also promoted hypertrophy of male myocytes more than female myocytes. Age and sex differences in EC coupling were largely maintained when conditioning pulse frequency was increased to 4 Hz. Contractions, Ca(2+) transients, and EC coupling gain were also smaller in young females than in young males. Thus age-dependent changes are more prominent in myocytes from males than females. Increased SR Ca(2+) content may compensate for reduced Ca(2+) current to preserve contractile function in aged females, which may limit the detrimental effects of age on cardiac contractile function.

Acidosis and ischemia increase cellular Ca2+ transient alternans and repolarization alternans susceptibility in the intact rat heart

Cardiac cellular Ca(2+) transient (CaT) alternans and electrocardiographic T-wave alternans (TWA) often develop in myocardial ischemia, but the mechanisms for this relationship have not been elucidated. Acidosis is a major component of ischemia, but there is no direct evidence linking acidosis-induced cellular CaT alternans to ischemia-induced CaT alternans and TWA in whole heart. We used laser-scanning confocal microscopy to measure intracellular Ca(2+) (Ca(i)(2+)) cycling in individual myocytes of fluo-4 AM-loaded rat hearts and simultaneously recorded pseudo-ECGs to investigate changes in CaTs and late-phase repolarization, respectively, during baseline and rapid pacing under control and either globally acidic or globally ischemic conditions. Acidosis (hypercapnia; pH 6.6) increased diastolic Ca(i)(2+) levels, prolonged CaT duration, and shifted to slower heart rates both the development of pacing-induced acidosis-induced CaT alternans (both concordant and discordant) and of repolarization alternans (RPA, a measure of TWA in rat ECGs). The magnitudes of these shifts were equivalent for both CaT alternans and RPA, suggesting a close association between them. Nearly identical results were found in low-flow global ischemia. Additionally, ischemic preconditioning reduced the increased propensity for CaT alternans and RPA development and was mimicked by preconditioning by acidosis alone. Our results demonstrate that global acidosis or ischemia modifies Ca(i)(2+) cycling in myocytes such that the diastolic Ca(i)(2+) rises and the cellular CaT duration is prolonged, causing spatially concordant as well as spatially discordant cellular CaT alternans to develop at slower heart rates than in controls. Since RPA also developed at slower heart rates, our results suggest that acidosis is a major contributor to CaT alternans, which underlies the proarrhythmic state induced by myocardial ischemia and therefore may play a role in its modulation and prevention.

Hypoxia inducible factor-1 improves the actions of positive inotropic agents in stunned cardiac myocytes

1. In the present study, we tested hypothesis that upregulation of hypoxia-inducible factor-1 (HIF-1) would improve the actions of positive inotropic agents in cardiac myocytes after simulated ischaemia-reperfusion (I/R). 2. Hypoxia-inducible factor-1α was upregulated with deferoxamine (150 mg/kg per day for 2 days). Rabbit cardiac myocytes were subjected to simulated ischaemia (15 min, 95% N(2)-5% CO2) and reperfusion (re-oxygenation) and compared with control myocytes. Cell contraction and calcium transients were measured at baseline and after forskolin (10(-7) and 10(-6) mol/L) or ouabain (10(-5) and 10(-4) mol/L). 3. Under control conditions, high-dose forskolin and ouabain increased percentage shortening by 20 and 18%, respectively. Deferoxamine-treated control myocytes responded similarly. In stunned myocytes, forskolin and ouabain did not significantly increase shortening (increases of 8% and 9%, respectively). Deferoxamine restored the effects of forskolin (+26%) and ouabain (+28%) in stunning. The results for maximum shortening and relaxation rates were similar. The increased calcium transients caused by forskolin and ouabain were also depressed in stunned myocytes, but were maintained by HIF-1 upregulation. 4. These results suggest that simulated I/R impaired the functional and calcium transient effects of positive inotropic agents. Upregulation of HIF-1 protects cardiac myocyte function after I/R by maintaining calcium release.

Loss of cardioprotection with ageing

Not only the prevalence, but also the mortality due to ischaemic cardiovascular disease is higher in older than in young humans, and the demographic shift towards an ageing population will further increase the prevalence of age-related cardiovascular disease. In order to develop strategies aimed to limit reversible and irreversible myocardial damage in older patients, there is a need to better understand age-induced alterations in protein expression and cell signalling. Cardioprotective phenomena such as ischaemic and pharmacological pre and postconditioning attenuate ischaemia/reperfusion injury in young hearts. Whether or not pre and postconditioning are still effective in aged organs, animals, or patients, i.e. under conditions where such cardioprotection is most relevant, is still a matter of debate; most studies suggest a loss of protection in aged hearts. The present review discusses changes in protein expression and cell signalling important to ischaemia/reperfusion injury with myocardial ageing. The efficacy of cardioprotective manoeuvres, e.g. ischaemic pre and postconditioning in aged organs and animals will be discussed, and the development of strategies aimed to antagonize the age-induced loss of protection will be addressed.

Simulated ischemia-induced preconditioning of isolated ventricular myocytes from young adult and aged Fischer-344 rat hearts

The impact of ischemic preconditioning (IPC) on contraction, Ca(2+) homeostasis, and cell survival was compared in isolated ventricular myocytes from young adult ( approximately 3 mo) and aged ( approximately 24 mo) male Fischer-344 rats. Myocytes were field stimulated at 4 Hz (37 degrees C). Contraction (edge detector) and intracellular Ca(2+) (fura-2) were measured simultaneously. Viability was assessed with trypan blue. All cells were exposed to 30 min of simulated ischemia followed by reperfusion. Some cells were preconditioned by exposure to 5 min of simulated ischemia before prolonged ischemia. Pretreatment with IPC abolished postischemic contractile depression, inhibited diastolic contracture, and increased Ca(2+) transient amplitudes in reperfusion in young adult and aged cells. IPC did not affect the modest rise in diastolic Ca(2+) in ischemia in young adult myocytes. However, IPC abolished the marked rise in diastolic Ca(2+) observed in ischemia and early reperfusion in aged myocytes. IPC also suppressed mechanical alternans in ischemia in aged cells, but younger myocytes showed little evidence of mechanical alternans whether or not cells were preconditioned. IPC markedly improved cell viability in reperfusion in young adult but not aged cells. These results suggest that IPC augments the recovery of contractile function in reperfusion by increasing Ca(2+) transient amplitudes in ventricular myocytes from young adult and aged rats. IPC reduced diastolic Ca(2+) accumulation in ischemia in aged myocytes, which may diminish the severity of mechanical alternans in aged cells. Nonetheless, the efficacy of IPC is compromised in aging, as IPC did not improve survival of aged myocytes exposed to ischemia and reperfusion.