Recovery Of Rate-pressure Product Research Articles

Cardioprotective effects of losartan and diminazene against the ischemia/reperfusion injury in hyperthyroidism rats.

Hyperthyroidism is a condition where the thyroid gland produces high levels of thyroid hormone. Heart diseases are one of the main complications of hyperthyroidism. Several studies have shown that losartan (LOS) and diminazene aceturate (DIZE) possess cardioprotection effects against cardiac hypertrophy, ischemic heart disease, and heart failure. The research aimed to investigate the cardioprotection of LOS, DIZE, and their combination in the case of levothyroxine (LT4)-induced cardiomyopathy in rats. Hyperthyroidism was induced by LT4 in drinking water (12mg/L) for 28 days. LOS (10mg/kg, orally) and/or DIZE (15mg/kg, subcutaneously) were administrated in rats with hyperthyroidism for 28 days. Decreased serum creatine kinase myoglobin and lactate dehydrogenase levels and cardiac hypertrophy by DIZE and combination therapy in hyperthyroidism rats have been reported. Cardiac hemodynamic findings showed that DIZE and its combination with LOS decreased the LT4-mediated left ventricular developed pressure (LVDP), rate pressure product (RPP), and RPP recovery percentage. Elevated cardiac oxidative stress and inflammation were confirmed by decreasing cardiac superoxide dismutase (SOD) activity and increasing the total oxidative stress and tumor necrosis factor-alpha (TNF-α) levels. SOD activity and TNF-α level were reversed by LOS and DIZE administration, respectively. Generally, DIZE and combination therapy with LOS improved cardiac dysfunction caused by hyperthyroidism in rats, whereas LOS alone has not been able to effectively respond to this dysfunction.

Imatinib attenuates reperfusion injury in a rat model of acute myocardial infarction

Following an acute myocardial infarction, reperfusion of an occluded coronary artery is often accompanied by microvascular injury, leading to worse long-term prognosis. Experimental studies have revealed the potential of tyrosine-kinase inhibitor imatinib to reduce vascular leakage in various organs. Here, we examined the potential of imatinib to attenuate microvascular injury in a rat model of myocardial reperfusion injury. Isolated male Wistar rat hearts (n = 20) in a Langendorff system and male Wistar rats (n = 37) in an in vivo model were randomly assigned to imatinib or placebo and subjected to ischaemia and reperfusion. Evans-blue/Thioflavin-S/TTC staining and Cardiac Magnetic Resonance Imaging were performed to assess the extent of reperfusion injury. Subsequently, in vivo hearts were perfused ex vivo with a vascular leakage tracer and fluorescence and electron microscopy were performed. In isolated rat hearts, imatinib reduced global infarct size, improved end-diastolic pressure, and improved rate pressure product recovery compared to placebo. In vivo, imatinib reduced no-reflow and infarct size with no difference between imatinib and placebo for global cardiac function. In addition, imatinib showed lower vascular resistance, higher coronary flow, and less microvascular leakage in the affected myocardium. At the ultrastructural level, imatinib showed higher preserved microvascular integrity compared to placebo. We provide evidence that low-dose imatinib can reduce microvascular injury and accompanying myocardial infarct size in a rat model of acute myocardial infarction. These data warrant future work to examine the potential of imatinib to reduce reperfusion injury in patients with acute myocardial infarction.

Abstract P1047: Imatinib Attenuates Reperfusion Injury In A Rat Model Of Acute Myocardial Infarction

Background: Reperfusion of an occluded coronary artery is often accompanied by injury of the microvasculature (MVI), which portends a worse long term prognosis after an acute myocardial infarction (AMI). In previous experimental studies, the tyrosine-kinase inhibitor imatinib has shown to reduce vascular leakage and therefore could have a potential role to prevent MVI. This study aims to provide a potential therapeutic approach using imatinib to attenuate reperfusion injury. Methods: First, 16 isolated male Wistar rat hearts were randomly assigned to 10 μM imatinib or placebo and subjected to 40 min of global ischemia followed by 120 min of reperfusion ex vivo in a Langendorff setup. Global infarct size and mechanical function were assessed. Second, 25 male Wistar rats were randomly assigned to 30 mg/kg imatinib or placebo intravenously and subjected to 45 min of left anterior descending coronary artery ligation followed by 180 min of reperfusion in vivo. Cardiovascular magnetic resonance imaging was performed to assess infarct size and cardiac function. Subsequently, hearts were perfused ex vivo with a fluorescent vascular leakage tracer and used for fluorescence- and electron microscopy. Results: In isolated hearts, imatinib reduced global infarct size (imatinib 36.2±7.9 vs placebo 50.0±8.0% infarcted area/total area, p<0.01), improved end diastolic pressure (imatinib 44.2±8.0 vs placebo 59.5±13.5 mmHg, p<0.05) and rate pressure product recovery (imatinib 39.0±6.8 vs placebo 26.2±7.6% of baseline, p<0.05). In vivo, imatinib reduced infarct size (imatinib 12.6±8.8 vs placebo 25.6±9.3% infarcted area/left ventricle, p<0.01), but did not improve global cardiac function. At the end of reperfusion, imatinib showed lower vascular resistance, higher coronary flow and less microvascular leakage (all p<0.05). At the ultrastructural level, imatinib showed better preserved microvascular integrity compared to placebo. Conclusion: This study provides evidence that imatinib attenuates reperfusion injury in an ex vivo and in vivo AMI rat model, mainly by protection of the coronary microcirculation. These data warrant future work to examine the potential of imatinib to reduce reperfusion injury in patients with AMI.

Protective effects of trehalose preconditioning on cardiac and coronary endothelial function through eNOS signaling pathway in a rat model of ischemia-reperfusion injury.

Coronary endothelial dysfunction is a major cause of ischemia-reperfusion (I/R) injury. Trehalose, a natural disaccharide, has been reported to ameliorate endothelial dysfunction during aging by activating endothelial nitric oxide synthase (eNOS); however, its role in I/R injury is unknown. This study evaluated the effects of trehalose preconditioning on cardiac and coronary endothelial function after I/R. Langendorff-perfused rat hearts underwent 30min of global ischemia followed by 80min of reperfusion with or without trehalose preconditioning. Rate pressure product (RPP) and coronary flow (CF) were measured during reperfusion. Perivascular edema was assessed by hematoxylin and eosin staining. Myocardial oxidative stress and apoptosis were evaluated by immunohistochemistry and TUNEL staining, respectively. eNOS dimerization was determined by western blotting. An eNOS inhibitor was used to examine the role of eNOS. Trehalose preconditioning showed a higher recovery rate after I/R as indicated by high RPP (control vs. trehalose, 28 ± 6% vs. 46 ± 9%; P = 0.017, Cohen's d = 2.3) and CF values (35 ± 10% vs. 55 ± 9%; P = 0.025, d = 1.7). Furthermore, trehalose preconditioning reduced perivascular edema, myocardial oxidative stress, and apoptosis. The eNOS dimerization ratio was increased by trehalose (1.2 ± 0.2 vs. 1.6 ± 0.2; P = 0.023, d = 2.1), which was associated with the recovery of RPP and CF. These effects of trehalose were abolished by the eNOS inhibitor. Trehalose preconditioning showed protective effects on cardiac and coronary endothelial function after I/R through the eNOS signaling pathway.

Recovery of rate-pressure product and cardiac mortality in coronary artery disease patients with type 2 diabetes

AimsTo investigate prognostic significance of post-exercise recovery of rate-pressure product (RPP) in patients with stable coronary artery disease (CAD) and type 2 diabetes (T2D). MethodsPatients with angiographically documented CAD and T2D (n = 697) underwent symptom-limited bicycle exercise test. Exercise capacity (EC), heart rate, blood pressure and RPP responses to peak exercise and recovery (2′ and 5′ after cessation of exercise) were analyzed. Cardiac death was the primary and sudden cardiac death (SCD) secondary endpoint. ResultsDuring a median follow-up of 76 months, 49 cardiac deaths (7.0%) and 28 SCDs (4.0%) were observed. The recovery of RPP at 5′ was the strongest univariate predictor of cardiac death (hazard ratio [HR]: 2.55 per SD decrease, 95%CI: 1.82–3.58, p < 0.001) and SCD (HR: 2.34, 95%CI: 1.51–3.62, p < 0.001). In multivariate analysis, it remained significantly associated to cardiac death and SCD without (HR: 1.66, 95%CI: 1.14–2.41, p < 0.01 and HR: 1.75, 95%CI: 1.08–2.85, p < 0.05, respectively) and with additional adjustment for EC and peak RPP (HR: 1.45, 95%CI: 1.09–1.92, p < 0.05 and HR: 1.52, 95%CI: 1.01–2.27, p < 0.05, respectively). ConclusionsThe recovery of RPP after exercise is a potent predictor of cardiac death in patients with CAD and T2D. It provides significant prognostic information beyond EC and peak RPP.

Critical role of angiotensin II type 2 receptors in the control of mitochondrial and cardiac function in angiotensin II-preconditioned rat hearts.

Angiotensin II preconditioning (APC) involves an angiotensin II type 1 receptor (AT1-R)-dependent translocation of PKCε and survival kinases to the mitochondria leading to cardioprotection after ischemia-reperfusion (IR). However, the role that mitochondrial AT1-Rs and angiotensin II type 2 receptors (AT2-Rs) play in APC is unknown. We investigated whether pretreatment of Langendorff-perfused rat hearts with losartan (L, AT1-R blocker), PD 123,319 (PD, AT2-R blocker), or their combination (L + PD) affects mitochondrial AT1-R, AT2-R, PKCε, PKCδ, Akt, PKG-1, MAPKs (ERK1/2, JNK, p38), mitochondrial respiration, cardiac function, and infarct size (IS). The results indicate that expression of mitochondrial AT1-Rs and AT2-Rs were enhanced by APC 1.91-fold and 2.32-fold, respectively. Expression of AT2-R was abolished by PD but not by L, whereas the AT1-R levels were abrogated by both blockers. The AT1-R response profile to L and PD was also shared by PKCε, Akt, MAPKs, and PKG-1, but not by PKCδ. A marked increase in state 3 (1.84-fold) and respiratory control index (1.86-fold) of mitochondria was observed with PD regardless of L treatment. PD also enhanced the post-ischemic recovery of rate pressure product (RPP) by 74% (p < 0.05) compared with APC alone. Losartan, however, inhibited the (RPP) by 44% (p < 0.05) before IR and reduced the APC-induced increase of post-ischemic cardiac recovery by 73% (p < 0.05). Finally, L enhanced the reduction of IS by APC through a PD-sensitive mechanism. These findings suggest that APC upregulates angiotensin II receptors in mitochondria and that AT2-Rs are cardioprotective through their permissive action on AT1-R signaling and the suppression of cardiac function.

Critical role of angiotensin II type 2 receptors in the control of mitochondrial and cardiac function in angiotensin II‐preconditioned rat hearts

Angiotensin II preconditioning (APC) involves an angiotensin II type 1 receptor (AT1‐R)‐dependent translocation of PKCɛ and survival kinases to the mitochondria leading to cardioprotection after ischemia‐reperfusion (IR). However, the role that mitochondrial AT1‐Rs and angiotensin II type 2 receptors (AT2‐Rs) play in APC is unknown. We investigated whether pretreatment of Langendorff‐perfused rat hearts with losartan (L, AT1‐R blocker), PD 123,319 (PD, AT2‐R blocker) or their combination (L+PD), affects mitochondrial AT1‐R, AT2‐R, PKCɛ, PKCδ, Akt, PKG‐1, MAPKs (ERK1/2, JNK, p38), mitochondrial respiration, and cardiac function. The results indicate that expression of mitochondrial AT1‐Rs and AT2‐Rs were enhanced by APC 1.91‐fold and 2.32‐fold, respectively. Expression of AT2‐R was abolished by PD but not by L, whereas the AT1‐R levels were abrogated by both blockers. The AT1‐R response profile to L and PD was also shared by PKCɛ, Akt, MAPKs, and PKG‐1, but not by PKCδ. A marked increase in state 3 (1.84‐fold) and respiratory control index (1.86‐fold) of mitochondria was observed with PD regardless of L treatment. PD also enhanced the post‐ischemic recovery of RPP by 74% (p&lt;0.05) compared with APC alone. Losartan, however, inhibited the rate pressure product (RPP) by 44% (p&lt;0.05) before IR and reduced the APC‐induced increase of post‐ischemic cardiac recovery by 73% (p&lt;0.05). These findings suggest that APC upregulates angiotensin II receptors in mitochondria and that AT2‐Rs have a permissive effect on AT1‐R‐dependent signaling and suppress mitochondrial respiration and cardiac function. These results support a critical role of mitochondrial AT2‐Rs in the control of cardiac function in APC.Support or Funding InformationSupported by the National Institutes of Health (NIH) Research Centers in Minority Institutions (RCMI) Program grant No. G12M007600, National Heart, Lung, and Blood Institute (NHLBI) grant SC1HL118669 (SJ), and the University of Puerto Rico.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Does p53 Inhibition Suppress Myocardial Ischemia-Reperfusion Injury?

p53 is well known as a regulator of apoptosis and autophagy. In addition, a recent study showed that p53 is a modulator of the opening of the mitochondrial permeability transition pore (mPTP), a trigger event of necrosis, but the role of p53 in necrosis induced by myocardial ischemia-reperfusion (I/R) remains unclear. The aim of this study was to determine the role of p53 in acute myocardial I/R injury in perfused mouse hearts. In male C57BL6 mice between 12 and 15 weeks of age, 2 types of p53 inhibitors were used to suppress p53 function during I/R: pifithrin-α, an inhibitor of transcriptional functions of p53, and pifithrin-μ, an inhibitor of p53 translocation from the cytosol to mitochondria. Neither infusion of these inhibitors before ischemia nor infusion for the first 30-minute period of reperfusion reduced infarct size after 20-minute ischemia/120-minute reperfusion. Infarct sizes were similar in p53 heterozygous knockout mice (p53+/-) and wild-type mice (WT), but recovery of rate pressure product (RRP) 120 minutes after reperfusion was higher in p53+/- than in WT. The protein expression of p53 in WT was negligible under baseline conditions, during ischemia, and at 10 minutes after the start of reperfusion, but it became detectable at 120 minutes after reperfusion. In conclusion, upregulation of p53 during the late phase of reperfusion plays a significant role in contractile dysfunction after reperfusion, although p53 is not involved in cardiomyocyte necrosis during ischemia or in the early phase of reperfusion.

Cardioprotection in mice with a knock-in mutation in Cyclophilin D (CypD-C202S): a site of S-nitrosylation

Our previous study in mouse embryonic fibroblasts showed that cysteine 202 of cyclophilin D (CyPD) is necessary for redox stress-induced activation of the mitochondrial permeability transition pore (mPTP). To further investigate the essential function of this cysteine residue in situ, we used CRISPR to develop a knock-in mouse model (C57BL/6N strain), where CyPD cysteine 202 was mutated to a serine (C202S-KI). The amount of total CyPD expressed in the CyPD C202S-KI did not differ compared to the wild-type (WT). However, the CyPD C202S-KI mouse hearts elicit a significant cardioprotective effect against ischemia-reperfusion (I/R) injury in the Langendorff perfused heart model. After 20 min of global ischemia followed by 90 min of reperfusion, the post-ischemic recovery of rate pressure product (RPP= heart rate x LVDP) was 45.0±4.2% in CyPD WT and 59.6±4.0% in CyPD C202S-KI mice (p=0.0455). Myocardial infarct size was decreased in CyPD C202S-KI mouse hearts versus CyPD WT mice (24.5±4.7% vs 49.8±2.7%, p=0.0095). Isolated heart mitochondria from CyPD C202-KI mice had a higher calcium retention capacity compared to CyPD WT mice (213.3±16.67 vs 140.0±20.82 umol Ca+2/g protein, p=0.0371). However, in contrast to CyPD knockout mice which exhibit more pronounced cardiac hypertrophy in response to pressure overload stimulation than control mice, CyPD C202S-KI mice developed a comparable level of hypertrophy to their WT littermate in an angiotensin II-induced hypertrophy model delivered by implanted osmotic minipumps. In conclusion, these results show that mutated CyPD C202S affords cardioprotection against I/R injury, suggesting that the redox-modification of cysteine 202 might play an important role in the regulation of CyPD and its downstream targets such as mPTP.

Sex-dependent effects of sleep deprivation on myocardial sensitivity to ischemic injury

Sleep deprivation is associated with increased risk of myocardial infarction. However, it is unknown whether the effects of sleep deprivation are limited to increasing the likelihood of experiencing a myocardial infarction or if sleep deprivation also increases the extent of myocardial injury. In this study, rats were deprived of paradoxical sleep for 96 h using the platform-over-water method. Control rats were subjected to the same condition except the control platform was large enough for the rats to sleep. Hearts from sleep deprived and control rats were subjected to 20 min ischemia on a Langendorff isolated heart system. Infarct size and post ischemic recovery of contractile function were unaffected by sleep deprivation in male hearts. In contrast, hearts from sleep-deprived females exhibited significantly larger infarcts than hearts from control females. Post ischemic recovery of rate pressure product and + dP/dT were significantly attenuated by sleep deprivation in female hearts, and post ischemic recovery of end diastolic pressure was significantly elevated in hearts from sleep deprived females compared to control females, indicating that post ischemic recovery of both systolic and diastolic function were worsened by sleep deprivation. These data provide evidence that sleep deprivation increases the extent of ischemia-induced injury in a sex-dependent manner.

Abstract 105: Increased Myocardial Sensitivity to Ischemic Injury in an Animal Model of Posttraumatic Stress Disorder

Background: Posttraumatic stress disorder (PTSD) is a psychological disorder characterized by the formation of traumatic memories following exposure to a life threatening event. In addition to psychological manifestations, PTSD promotes atherosclerosis and increases the incidence of myocardial infarction. However, it is unknown whether the effects of PTSD are limited to increasing the incidence of myocardial infarction or if PTSD also increases infarct severity. Therefore, we used an animal model of PTSD to determine whether posttraumatic stress influences infarct size and postischemic recovery of cardiac contractile function. Methods: Rats were subjected to a well-established animal model of PTSD that is based on predator exposure and psychosocial stress (Zoladz et al., Stress 11:259-281). Rats subjected to this model exhibit many PTSD-like characteristics including the formation of traumatic memories, increased anxiety, increased startle reflex, hypertension, and alterations in the hypothalamic-pituitary adrenal axis. Male rats (7 weeks of age) were either subjected to psychosocial stress (n = 9) or continuously housed in their home cages (n = 8) for 31 days. Hearts were subsequently isolated and subjected to 20 minutes of ischemia and 2 hours reperfusion on a Langendorff isolated heart system. Results: Stressed rats exhibited significantly elevated corticosterone concentrations and anxiety-like behavior in the elevated plus maze. Infarct sizes were significantly larger in hearts from stressed rats (44.7 ± 1.7 % of area at risk) compared to nonstressed rats (31.0 ± 5.4 % of area at risk). Consistent with increased myocardial injury, postischemic recovery of rate pressure product (stressed = 16,922 ± 1,554 mmHg*bpm; nonstressed = 26,407 ± 2,977 mmHg*bpm) and +dP/dT (stressed = 1,901 ± 189 mmHg/sec; nonstressed =3,259 ± 498 mmHg/sec) were significantly attenuated in hearts from stressed rats. Furthermore, postischemic end diastolic pressure was significantly elevated in hearts from stressed (57 ± 6 mmHg) compared to nonstressed (32 ± 7 mmHg) rats. Conclusion: This animal model suggests that PTSD may make the myocardium more sensitive to ischemic injury through a mechanism that is independent from its ability to promote atherosclerosis.

Acute BH4 depletion leads to a loss of myocardial protection conferred by cardiac‐specific overexpression of inducible nitric oxide synthase in mice (547.11)

Many studies have shown that cardiac overexpression of NOS enzymes can lead to myocardial protection against ischemia/reperfusion (I/R) injury. However, none of these studies experiment with modulating BH4 levels. Because adequate BH4 levels lead iNOS to produce nitric oxide and inadequate BH4 levels lead iNOS to produce damaging superoxide, we hypothesized that depletion of BH4 in a model of constitutive iNOS expression would lead to a loss of iNOS function and diminished recovery of post‐ischemic myocardial contractility. The study involved two groups of iNOS TG mice: untreated mice and treated mice. Treated mice received 21 days of BH4 depletion diet using food with GTP cyclohydrolase inhibitor 2,4‐舃Diamino‐舃6‐舃hydroxypyrimidine (DAHP). The 21 day DAHP treatment led to a roughly 65% myocardial depletion of BH4 as measured by HPLC. Hearts from these two groups were used in isolated heart experiments and were subjected to 30’ of ischemia and 60’ of reperfusion. Compared to untreated mice, DAHP‐treated mice had significantly less recovery of rate pressure product, left ventricular developed pressure, and significantly more elevated end diastolic pressure at 30 and 60’ of reperfusion. This work shows the importance of adequate BH4 levels in protection against myocardial I/R, especially in the context of NOS overexpression.Grant Funding Source: 00000784

Luteolinidin, a naturally occurring flavonoid, decreases ischemia/reperfusion injury through inhibition of CD38 and preservation of NADPH and BH4 (547.14)

CD38, a consumer of NAD+ and NADP+, is activated in I/R, leading to depletion of myocardial NADP(H) and consequently, lower eNOS function due to low levels of cofactor NADPH. Isolated hearts were subjected to two treatments: pre‐ischemic luteolinidin (25μM) infusion or vehicle control infusion (empty liposomes). In vehicle‐treated hearts at 30’ ischemia and 30’ reperfusion, NADPH and BH4 were depleted by 67% and 64% respectively. With 3’ of luteolinidin infusion (25μM), these numbers changed to 23% and 32% for NADPH and BH4, respectively, representing an impressive 44% salvage of NADPH, and a 32% salvage of BH4 compared to vehicle‐treated hearts. This NADPH and BH4 salvage was manifested physiologically as an increased loss of coronary flow (CF) in response to eNOS inhibitor L‐NAME (1mM) at 30’ reperfusion. Moreover, we found in luteolinidin‐treated hearts more post‐ischemic recovery of rate pressure product, left ventricular developed pressure and CF, and, a less elevated end diastolic pressure. This work suggests that inhibition of CD38 with luteolinidin is beneficial in I/R as measured by parameters of post‐ischemic endothelial and contractile function. The work also suggests that that post‐ischemic NADPH and BH4 levels are related, possibly through modulation of dihydrofolate reductase activity by NADPH levels.Grant Funding Source: Supported by 00000784

Lipid emulsion pretreatment has different effects on mepivacaine and bupivacaine cardiac toxicity in an isolated rat heart model

The use of lipid emulsions to reduce cardiac toxicity of local anaesthetics (LAs) has shown success in experimental studies and some clinical cases, and thus has been implemented in clinical practice. However, lipid treatment is usually given after the occurrence of neurological or cardiovascular symptoms of systemic intoxication. The aim of this study was to determine if pretreatment with lipid emulsion reduces cardiac toxicity produced by bupivacaine or mepivacaine. Isolated rat hearts were perfused with or without lipid emulsion (0.25 ml kg(-1) min(-1)) before administration of equipotent doses of bupivacaine (250 µM) or mepivacaine (1000 µM). Haemodynamic parameters and times from start of perfusion LA to a 1 min period of asystole and recovery were determined. Pretreatment with lipid emulsion extended the time until occurrence of asystole and decreased times to recovery in bupivacaine-induced cardiac toxicity but not in mepivacaine-induced cardiac toxicity compared with control. Lipid pretreatment impaired rate-pressure product recovery in mepivacaine-intoxicated hearts. This study confirms that pretreatment with a lipid emulsion reduces cardiac toxicity of LAs. The efficacy of pretreatment with lipid emulsion was LA-dependent, so pharmacokinetic properties, such as lipophilicity, might influence the effects of lipid emulsion pretreatment.

Clinically-relevant consecutive treatment with isoproterenol and adenosine protects the failing heart against ischaemia and reperfusion.

BackgroundConsecutive treatment of normal heart with a high dose of isoproterenol and adenosine (Iso/Ade treatment), confers strong protection against ischaemia/reperfusion injury. In preparation for translation of this cardioprotective strategy into clinical practice during heart surgery, we further optimised conditions for this intervention using a clinically-relevant dose of Iso and determined its cardioprotective efficacy in hearts isolated from a model of surgically-induced heart failure.MethodsIsolated Langendorff-perfused rat hearts were treated sequentially with 5 nM Iso and 30 μM Ade followed by different durations of washout prior to 30 min global ischaemia and 2 hrs reperfusion. Reperfusion injury was assessed by measuring haemodynamic function, lactate dehydrogenase (LDH) release and infarct size. Protein kinase C (PKC) activity and glycogen content were measured in hearts after the treatment. In a separate group of hearts, Cyclosporine A (CsA), a mitochondria permeability transition pore (MPTP) inhibitor, was added with Iso/Ade. Failing hearts extracted after 16 weeks of ligation of left coronary artery in 2 months old rats were also subjected to Iso/Ade treatment followed by ischaemia/reperfusion.ResultsRecovery of the rate pressure product (RPP) in Iso/Ade-treated hearts was significantly higher than in controls. Thus in Iso/Ade treated hearts with 5 nM Iso and no washout period, RPP recovery was 76.3 ± 6.9% of initial value vs. 28.5 ± 5.2% in controls. This was associated with a 3 fold reduction in LDH release irrespective to the duration of the washout period. Hearts with no washout of the drugs (Ade) had least infarct size, highest PKC activity and also showed reduced glycogen content. Cardioprotection with CsA was not additive to the effect of Iso/Ade treatment. Iso/Ade treatment conferred significant protection to failing hearts. Thus, RPP recovery in failing hearts subjected to the treatment was 69.0 ± 16.3% while in Control hearts 19.7 ± 4.0%. LDH release in these hearts was also 3 fold lower compared to Control.ConclusionsConsecutive Iso/Ade treatment of normal heart can be effective at clinically-relevant doses and this effect appears to be mediated by glycogen depletion and inhibition of MPTP. This intervention protects clinically relevant failing heart model making it a promising candidate for clinical use.

Abstract 18164: The Effect of Sex Chromosomes on Myocardial Ischemia/Reperfusiong Injury

Introduction: Sex differences in susceptibility to ischemia/reperfusion(I/R) injury have been demonstrated both in basic and clinical settings. Female hearts show better functional recovery after I/R injury compared with males. Most of these sex differences in I/R settings have been attributed to sex hormones. Here we used two unique mouse models (four core genotypes mice and XY* mice) to investigate the role of sex chromosomes on cardiac I/R injury. Methods: We used two unique mouse models of “four core genotypes” (FCG) (XX mice with ovaries or testes and XY mice with ovaries and testes) and XY* (mice with one X chromosome (XO or XY) or with two X chromosomes (XX or XXY). All mice were gonadectomized at day75 and used 30 days after gonadectomy to eliminate the effects of gonadal hormones. Isolated hearts were subjected to 30 min global normothermic ischemia followed by 60 min reperfusion to measure heart function and infarct size. There were 4-7 mice per group. Two way ANOVA was used for statistical analysis. P&lt;0.05 was considered statistically significant. Values are expressed as mean± SE. Results: In both FCG and XY* models, the cardiac function was similar among all groups before ischemia. However postischemic function of XX mice was significantly lower than XY, irrespective of gonadal sex (recovery of rate pressure product (RPP): 31.2±5.7% in XX females and 44.7±8.8% in XX males vs. 56.6±5.8% in XY females and 67.2±10.1% in XY males, p&lt;0.01). Infarct size was also markedly larger in XX mice than XY (52.4±4.7% in female-XX and 49.4±7.6% in male-XX vs. 33.2±5.6% in female-XY and 30.5±5.5% in male-XY, p&lt;0.05). In XY* mice, functional recovery of mice with two copies of the X chromosome was significantly lower than mice with a single copy(recovery of RPP=34.0±10.3% XX females and 28.0±12.1% in XXY males vs. 60.3±13.5% in XO females and 60.5±13.8% in XO males, p&lt;0.05). Infarct size was also markedly larger in mice with two X chromosomes (41.4±8.9% in XX females and 46.3±9.5% in XXY males) than mice with one X chromosome (23.7±3.9% in XO females and 26.6±6.9% in XO males, p&lt;0.05). Conclusion: Irrespective of gonadal sex, the number of X chromosomes in gonadectomized mice plays a key role in susceptibility to myocardial I/R injury regardless of the presence or absence of the Y chromosome.

Hexokinase cellular trafficking in ischemia–reperfusion and ischemic preconditioning is altered in type I diabetic heart

Diabetes mellitus (DM) has been reported to alter the cardiac response to ischemia-reperfusion (IR). In addition, cardioprotection induced by ischemic preconditioning (IPC) is often impaired in diabetes. We have previously shown that the subcellular localisation of the glycolytic enzyme hexokinase (HK) is causally related to IR injury and IPC protective potential. Especially the binding of HK to mitochondria and prevention of HK solubilisation (HK detachment from mitochondria) during ischemia confers cardioprotection. It is unknown whether diabetes affects HK localisation during IR and IPC as compared to non-diabetes. In this study we hypothesize that DM alters cellular trafficking of hexokinase in response to IR and IPC, possibly explaining the altered response to IR and IPC in diabetic heart. Control (CON) and type I diabetic (DM) rat hearts (65 mg/kg streptozotocin, 4 weeks) were isolated and perfused in Langendorff-mode and subjected to 35 min I and 30 min R with or without IPC (3 times 5 min I). Cytosolic and mitochondrial fractions were obtained at (1) baseline, i.e. after IPC but before I, (2) 35 min I, (3) 5 min R and (4) 30 min R. DM improved rate-pressure product recovery (RPP; 71 ± 10 % baseline (DM) versus 9 ± 1 % baseline (CON) and decreased contracture (end-diastolic pressure: 24 ± 8 mmHg (DM) vs 77 ± 4 mmHg (CON)) after IR as compared to control, and was associated with prevention of HK solubilisation at 35 min I. IPC improved cardiac function in CON but not in DM hearts. IPC in CON prevented HK solubilisation at 35 min I and at 5 min R, with a trend for increased mitochondrial HK. In contrast, the non-effective IPC in DM was associated with solubilisation of HK and decreased mitochondrial HK at early reperfusion and a reciprocal behaviour at late reperfusion. We conclude that type I DM significantly altered cellular HK translocation patterns in the heart in response to IR and IPC, possibly explaining altered response to IR and IPC in diabetes.

Mild hypothermia during global cardiac ischemia opens a window of opportunity to develop heart donation after cardiac death

Although heart donation after cardiac death (DCD) could greatly improve graft availability, concerns regarding warm ischemic damage typically preclude transplantation. Improving tolerance to warm ischemia may thus open a window of opportunity for DCD hearts. We investigated the hypothesis that, compared with normothermia, mild hypothermia (32°C) initiated after ischemic onset improves cardiac functional recovery upon reperfusion. Isolated, working hearts from adult, male Wistar rats underwent global, no-flow ischemia, and reperfusion (n=28). After ischemic onset, temperature was maintained at either 37°C for 20 or 30min or reduced to 32°C for 40, 50, or 60min. Recovery was measured after 60-min reperfusion. Following normothermic ischemia, recovery of rate-pressure product (RPP; per cent of preischemic value) was almost complete after 20-min ischemia (97±9%), whereas no recovery was detectable after 30-min ischemia. After mildly hypothermic ischemia (32°C), RPP also recovered well after 40min (86±4%). Markers of metabolism and necrosis were similar in 37°C/20min and 32°C/40min groups. Simple reduction in cardiac temperature by a few degrees after the onset of global ischemia dramatically prolongs the interval during which the heart remains resistant to functional deterioration. Preservation of hemodynamic function is associated with improved metabolic recovery and reduced necrosis. The application of mild hypothermia may be a simple first step towards development of clinical protocols for DCD heart recovery.

Abstract 19807: Increased Triacylglycerol Synthesis in the Heart Improves Functional Recovery After Ischemia

Accumulation of cardiac lipids has been associated with cardiac dysfunction in diabetes and obesity while increased muscle lipid storage in athletes is associated with improved function. We have previously shown that cardiac specific overexpression of diacylglycerol acyltransferase 1 (MHC-DGAT1), the rate limiting enzyme for triacylglycerol (TAG) synthesis, enhances TAG synthesis, reduces ceramide formation, and rescues lipotoxic cardiomyopathy. Using MHC-DGAT1 mice, we tested whether increased TAG synthesis and storage affected cardiac responses to ischemia-reperfusion. A doubling of cardiac TAG content in MHC-DGAT1 (P&lt;0.05; n=4) was not associated with in-vivo cardiac dysfunction or heart size. With dynamic 13C NMR spectroscopy we found a 70% increase of incorporation of 13C labeled fatty acids (FA) into the cardiac TAG pool in MHC-DGAT1 hearts. In isolated Langendorff perfused hearts, rate pressure product (RPP), was similar in MHC-DGAT1 and control (CON) hearts at baseline (BL). When subjected to 25min of no-flow ischemia (ISC), end diastolic pressure rose equivalently in both groups. However, recovery of RPP during reperfusion (REP) was significantly improved in MHC-DGAT1 compared to CON (51±6% vs 28±6%; n=5-6). At the end of REP, 13C NMR spectroscopy of heart extracts suggested decreased exogenous FA oxidation with no change in glucose oxidation in MHC-DGAT1 hearts. Cardiac TAGs, measured in freeze-clamped hearts, remained unchanged in CON during BL, at end ISC, and at end REP (n=3 per time point). Interestingly, despite ~2-fold increase in TAG in MHC-DGAT1 at BL, TAG content depleted to levels similar to CON at end ISC and REP, inferring accelerated TAG lipolysis in MHC-DGAT1 during the ischemic period. Non-esterified fatty acid (NEFA) concentration was not different between the groups at any time point. In conclusion, these results suggest that ischemia-induced activation of lipolysis in MHC-DGAT1 hearts improves functional recovery, in part, by increasing the oxidation of endogenous lipids during reperfusion. These data also suggest a potential secondary role of endogenous lipids to act as signaling molecules to modulate cardiac function.

South Asians Have Elevated Postexercise Blood Pressure and Myocardial Oxygen Consumption Compared to Europeans Despite Equivalent Resting Pressure

BackgroundStroke mortality rate is higher in South Asians than in Europeans, despite equivalent or lower resting blood pressure (BP). Elevated recovery BP after exercise predicts stroke, independently of resting values. We hypothesized that South Asians would have adverse postexercise hemodynamics and sought explanations for this.Methods and ResultsA population-based sample of 147 European and 145 South Asian middle-aged men and women performed the Dundee 3-minute step test. Cardiovascular risk factors were measured. BP, heart rate, and rate–pressure product, a measure of myocardial oxygen consumption, were compared. With 90% power and 5% significance, we could detect a difference of 0.38 of a standard deviation in any outcome measure. Resting systolic BP was similar in South Asians (144 mm Hg) and Europeans (142 mm Hg) (P=0.2), as was exercise BP (P=0.4). However, recovery systolic BP at 3 minutes after exercise was higher in South Asians by 4.3 mm Hg (95% confidence interval [CI], 0.2 to 8.3 mm Hg; P=0.04). This effect persisted when adjusted for exercise BP and work effort (5.4 mm Hg [95% CI, 2.2 to 8.7 mm Hg; P=0.001]). Adjustment for baroreflex insensitivity and greater aortic stiffness in South Asians contributes greatly to attenuating this ethnic difference (1.9 mm Hg [95% CI, −0.9 to 4.6 mm Hg; P=0.4]). Similarly, rate–pressure product recovery after exercise was impaired in South Asians by 735 mm Hg/min (95% CI, 137 to 1334 mm Hg/min; P=0.02); again, adjustment for baroreflex insensitivity and aortic stiffness attenuated this difference (261 mm Hg/min [95% CI, −39 to 561 mm Hg/min; P=0.3]).ConclusionPostexercise recovery of BP and rate–pressure product is impaired in South Asians compared to Europeans even though resting and exercise BP are similar. This is associated with the autonomic dysfunction and aortic stiffness in South Asians. (J Am Heart Assoc. 2012;1:e000281 doi: 10.1161/JAHA.111.000281.)