Amrinone preconditioning in the isolated perfused rabbit heart

Comparison of Enoximone, Amrinone, or Levosimendan Enriched St. Thomas’ Hospital Cardioplegic Solutions Used for Myocardial Preservation in Isolated Guinea Pig Hearts

Myocardial contractile function after cardioplegic arrest is often depressed and an ideal cardioplegic solution has not been developed yet. The aim of this study was to assess the efficacy of phosphodiesterase III inhibitors, amrinone and enoximone, and levosimendan, a novel Ca2+ sensitizing agent, on recovery of hearts after normothermic cardioplegic arrest when added to the St. Thomas’ hospital cardioplegic solution. In the control group, isolated guinea pig hearts were perfused in Langendorff apparatus and arrested with standard St. Thomas’ solution. In other groups, amrinone (10-5 mol.L-1), levosimendan (10-5 mol.L-1), or enoximone (10-4 mol.L-1) were added to the cardioplegic solution. In all hearts, intraventricular pressure, +dp/dtmax, -dp/dtmax, area under pressure-time curve, heart rate, coronary flow, lactate dehydrogenase and creatine kinase enzyme leakage, and oxygen consumption were measured. In the enoximone group, contractility force and +dp/dtmax, were found to be significantly high in the reperfusion and inotropic periods in comparison with other groups (p<0.05). -dp/dtmax and area under contractility-time curve values were significantly high in inotropic period in enoximone group (p<0.05). No statistically significant difference was noted in other groups. Cardioplegic solution enrichment with enoximone augmented mechanic functions in reperfusion period. No positive effect of amrinone or levosimendan was observed in this study.

Cyclic nucleotide phosphodiesterase 3A1 protects the heart against ischemia-reperfusion injury

Phosphodiesterase 3A (PDE3A) is a major regulator of cAMP in cardiomyocytes. PDE3 inhibitors are used for acute treatment of congestive heart failure, but are associated with increased incidence of arrhythmias and sudden death with long-term use. We previously reported that chronic PDE3A downregulation or inhibition induced myocyte apoptosis in vitro. However, the cardiac protective effect of PDE3A has not been demonstrated in vivo in disease models. In this study, we examined the role of PDE3A in regulating myocardial function and survival in vivo using genetically engineered transgenic mice with myocardial overexpression of the PDE3A1 isozyme (TG). TG mice have reduced cardiac function characterized by reduced heart rate and ejection fraction (52.5±7.8% vs. 83.9±4.7%) as well as compensatory expansion of left ventricular diameter (4.19±0.19mm vs. 3.10±0.18mm). However, there was no maladaptive increase of fibrosis and apoptosis in TG hearts compared to wild type (WT) hearts, and the survival rates also remained the same. The diminution of cardiac contractile function is very likely attributed to a decrease in beta-adrenergic receptor (β-AR) response in TG mice. Importantly, the myocardial infarct size (4.0±1.8% vs. 24.6±3.8%) and apoptotic cell number (1.3±1.0% vs. 5.6±1.5%) induced by ischemia/reperfusion (I/R) injury were significantly attenuated in TG mice. This was associated with decreased expression of inducible cAMP early repressor (ICER) and increased expression of anti-apoptotic protein BCL-2. To further verify the anti-apoptotic effects of PDE3A1, we performed in vitro apoptosis study in isolated adult TG and WT cardiomyocytes. We found that the apoptotic rates stimulated by hypoxia/reoxygenation or H2O2 were indeed significantly reduced in TG myocytes, and the differences between TG and WT myocytes were completely reversed in the presence of the PDE3 inhibitor milrinone. These together indicate that PDE3A1 negatively regulates β-AR signaling and protects against I/R injury by inhibiting cardiomyocyte apoptosis.

Pivotal effects of phosphodiesterase inhibitors on myocyte contractility and viability in normal and ischemic hearts

Phosphodiesterases (PDEs) are enzymes that degrade cellular cAMP and cGMP and are thus essential for regulating the cyclic nucleotides. At least 11 families of PDEs have been identified, each with a distinctive structure, activity, expression, and tissue distribution. The PDE type-3, -4, and -5 (PDE3, PDE4, PDE5) are localized to specific regions of the cardiomyocyte, such as the sarcoplasmic reticulum and Z-disc, where they are likely to influence cAMP/cGMP signaling to the end effectors of contractility. Several PDE inhibitors exhibit remarkable hemodynamic and inotropic properties that may be valuable to clinical practice. In particular, PDE3 inhibitors have potent cardiotonic effects that can be used for short-term inotropic support, especially in situations where adrenergic stimulation is insufficient. Most relevant to this review, PDE inhibitors have also been found to have cytoprotective effects in the heart. For example, PDE3 inhibitors have been shown to be cardioprotective when given before ischemic attack, whereas PDE5 inhibitors, which include three widely used erectile dysfunction drugs (sildenafil, vardenafil and tadalafil), can induce remarkable cardioprotection when administered either prior to ischemia or upon reperfusion. This article provides an overview of the current laboratory and clinical evidence, as well as the cellular mechanisms by which the inhibitors of PDE3, PDE4 and PDE5 exert their beneficial effects on normal and ischemic hearts. It seems that PDE inhibitors hold great promise as clinically applicable agents that can improve cardiac performance and cell survival under critical situations, such as ischemic heart attack, cardiopulmonary bypass surgery, and heart failure.

Cardioprotection induced by olprinone, a phosphodiesterase III inhibitor, involves phosphatidylinositol-3-OH kinase-Akt and a mitochondrial permeability transition pore during early reperfusion

PURPOSE

Ischemic preconditioning is mediated by the activation of phosphatidylinositol-3-OH kinase-Akt (PI3K-Akt) and by the inhibition of the opening of a mitochondrial permeability transition pore (mPTP) during early reperfusion. Preischemic administration of the phosphodiesterase type III inhibitor olprinone protects the myocardium against infarction, but its mechanism has not been fully clarified. We hypothesized that this olprinone-induced cardioprotective effect was mediated by the activation of PI3K-Akt and by the inhibition of mPTP during early reperfusion.

METHODS

Pentobarbital-anesthetized rats (n = 42) subjected to 30-min coronary occlusion followed by 2-h reperfusion, received olprinone (20 microg.kg(-1)) or saline (control) in the preischemic phase in the presence or absence of the PI3K-Akt inhibitor wortmannin (0.6 mg.kg(-1)) or the mPTP opener atractyloside (5 mg.kg(-1)) before 5 min of reperfusion. The myocardial infarct size was expressed as a percentage of the area at risk. All values were expressed as means +/- SD. Statistical comparisons within groups were made using repeated-measures analysis of variance (ANOVA), followed by a paired t-test, and comparisons among groups were analyzed using a two-way ANOVA, followed by the Tukey-Kramer test.

RESULTS

Mean arterial pressure and heart rate showed no significant differences within or among groups. The preischemic administration of olprinone significantly reduced the infarct size (12 +/- 4%) as compared with that in the control group (43 +/- 4%). Wortmannin or atractyloside abolished the protective effect of olprinone (42 +/- 11% or 41 +/- 10%).

CONCLUSION

The olprinone-induced cardioprotective effect could be exerted via the activation of PI3K-Akt and the inhibition of mPTP during early reperfusion.

Milrinone administered before ischemia or just after reperfusion, attenuates myocardial stunning in anesthetized swine

PURPOSE

We assessed the dose or timing effect of milrinone administered against myocardial stunning in 37 anesthetized open-chest swine.

METHODS

All swine were subjected to 12-min ischemia followed by reperfusion to produce myocardial stunning. Group A (n = 12) received saline in place of milrinone both before and after ischemia. Group B (n = 9) and C (n = 9) received intravenous milrinone at a rate of 5 microg/kg/min for 10 min followed by 0.5 microg/kg/min for 10 min and 10 microg/kg/min for 10 min followed by 1 microg/kg/min for 10 min, respectively, until 30 min before coronary occlusion. Group D (n = 7) received the same dose of milrinone as group B starting 1 min after reperfusion. Myocardial contractility was assessed by percentage segment shortening (%SS).

RESULTS

Five swine in group A and two swine in groups B and C each had ventricular fibrillation or tachycardia after reperfusion, and were thus excluded from further analysis. The percentage changes of %SS from the baseline 90 min after reperfusion in groups B, C, and D were 78 +/- 9%, 82 +/- 13%, and 79 +/- 7%, respectively, which were significantly higher than those in group A (43 +/- 13%).

CONCLUSION

We conclude that milrinone administered before ischemia or just after reperfusion attenuates myocardial stunning.

beta1-Adrenoreceptor activation contributes to ischemia-reperfusion damage as well as playing a role in ischemic preconditioning

Protein kinase A (PKA) activation has been implicated in early-phase ischemic preconditioning. We recently found that during ischemia PKA activation causes inactivation of cytochrome-c oxidase (CcO) and contributes to myocardial damage due to ischemia-reperfusion. It may be that beta-adrenergic stimulation during ischemia via endogenous catecholamine release activates PKA. Thus beta-adrenergic stimulation may mediate both myocardial protection and damage during ischemia. The present studies were designed to determine the role of the beta(1)-adrenergic receptor (beta(1)-AR) in myocardial ischemic damage and ischemic preconditioning. Langendorff-perfused rabbit hearts underwent 30-min ischemia by anterior coronary artery ligation followed by 2-h reperfusion. Occlusion-reperfusion damage was evaluated by delineating the nonperfused volume of myocardium at risk and volume of myocardial necrosis after 2-h reperfusion. In some hearts ischemic preconditioning was accomplished by two 5-min episodes of global low-flow ischemia separated by 10 min before coronary occlusion-reperfusion. Orthogonal electrocardiograms were recorded, and coronary flow was monitored by a drip count. Three hearts from each experimental group were used to determine mitochondrial CcO and aconitase activities. Two-hour reperfusion after occlusion caused an additional decrease in CcO activity vs. that after 30-min occlusion alone. Blocking the beta(1)-AR during occlusion-reperfusion reversed CcO activity depression and preserved myocardium at risk for necrosis. Similarly, mitochondrial aconitase activity exhibited a parallel response after occlusion-reperfusion as well as for the other interventions. Furthermore, classic ischemic preconditioning had no effect on CcO depression. However, blocking the beta(1)-AR during preconditioning eliminated the cardioprotection. If the beta(1)-AR was blocked after preconditioning, the myocardium was preserved. Interestingly, in both of the latter cases the depression in CcO activity was reversed. Thus the beta(1)-AR plays a dual role in myocardial ischemic damage. Our findings may lead to therapeutic strategies for preserving myocardium at risk for infarction, especially in coronary reperfusion intervention.

Effect of Combining Phosphodiesterase III Inhibitors With St Thomas Hospital’s Solution Used as Transplantation Preservative Solution in Isolated Rat Hearts

Improved preservation of the harvested heart with attenuation of the reperfusion injury is important for successful outcomes of cardiac transplantations. The most commonly used cardioplegic solution, to prevent ischemic changes has been St Thomas' Hospital cardioplegic solution (STHCS). However, it is neither ideal nor sufficient to prevent myocardial ischemia and reperfusion injury. Phosphodiesterase inhibitors can attenuate the damage due to the injuries of ischemia and reperfusion. In this study we sought to enrich STHCS with a phosphodiesterase inhibitor to improve preservation of cardiac functions. The harvested hearts of 24 rats were divided into four groups. All hearts were mounted on a Langendorff perfusion system. After a stabilization period, cardiac arrest was maintained by STHCS. The hearts were stored in STHCS alone or with milrinone, amrinone, or enoximone for 6 hours. The reperfusion was maintained using a modified Tyrode's solution. All hearts were compared for their preischemic and postischemic left ventricular developed pressure, +dp/dtmax, -dp/dtmax, duration of systole, ejection time, and time to reach peak systolic pressure. Coronary effluent was collected for lactate dehydrogenase (LDH) measurements. The initial values for all metrics were comparable between the groups. During the postreperfusion period, all hearts showed lower peak systolic pressures than the initial values. Although the amrinone group seemed to have higher values, the 25-minute result was at the border of significance and the 30-minute value, significantly higher. All hearts showed far lower results of maximum changes in contractility during the time period (+dp/dtmax) versus the initial values; comparisons between groups were not significant. For the parameter of maximum changes in relaxation during the time period (-dp/dtmax), while other hearts showed lower results, the amrinone group displayed values comparable to the initial ones after 20 minutes. Comparisons between groups were insignificant. While other hearts had comparable values for time of systole, the hearts applied with milrinone reached these values after 15 minutes. Group comparison for time of ejection revealed that the results at 5-minute postreperfusion were higher in the enoximone and the amrinone groups than the milrinone group. Postreperfusion 5-minute results were higher in the enoximone and the amrinone groups than the milrinone group for time to reach peak systolic pressure. LDH levels were lowest in the amrinone group. In conclusion, our study revealed that adding phosphodiesterase inhibitors to STHCS improved peak systolic pressure and maximum changes in relaxation during the time period (-dp/dtmax, mm Hg/s). It also decreased the LDH leakage, which corresponded to the degree of ischemic tissue damage. Amrinone seemed to result in more favorable results, which may be attributed to its additional effects on inflammation, including those on cytokines and leukocyte aggregation.

Anaesthetics and cardiac preconditioning. Part II. Clinical implications

There is compelling evidence that preconditioning occurs in humans. Experimental studies with potential clinical implications as well as clinical studies evaluating ischaemic, pharmacological and anaesthetic cardiac preconditioning in the perioperative setting are reviewed. These studies reveal promising results. However, there are conflicting reports on the efficacy of preconditioning in the diseased and aged myocardium. In addition, many anaesthetics and a significant number of perioperatively administered drugs affect the activity of cardiac sarcolemmal and mitochondrial K(ATP) channels, the end-effectors of cardiac preconditioning, and thereby markedly modulate preconditioning effects in myocardial tissue. Although these modulatory effects on K(ATP) channels have been investigated almost exclusively in laboratory investigations, they may have potential implications in clinical medicine. Important questions regarding the clinical utility and applicability of perioperative cardiac preconditioning remain unresolved and need more experimental work and randomized controlled clinical trials.

Repetitive preischemic infusion of phosphodiesterase III inhibitor olprinone elicits cardioprotective effects in the failing heart after myocardial infarction

Beta-adrenergic (BA) signaling including cAMP-protein kinase A (PKA) pathway has been implicated in the mechanism of ischemic preconditioning (IPC). However, effect of IPC on the failing heart, in which BA signaling is supposed to be altered, is left to be determined. To assess a role of BA signaling in IPC, levels of beta2-adrenergic receptor (B2AR) mRNA were quantified by real time RT-PCR, and in vivo intracardiac function was evaluated in post-MI heart. The effect of IPC on post-MI heart was then determined with an isolated heart perfusion system. Finally, cardioprotective effect of repetitive preischemic infusion of phosphodiesterase III inhibitor olprinone (30 microM), which is known to increase myocardial cAMP levels, was evaluated with/without PKA inhibitor H-89 (2 microM). B2AR mRNA levels in post-MI heart were significantly reduced compared to non-MI heart. IPC was not effective in post-MI heart. Repetitive preischemic infusion of olprinone increased peak developed pressure (94.6 +/- 6.3 vs. 62.8 +/- 4.9%, OLP vs. control, p < 0.05) and decreased infect size (15.2 +/- 0.4 vs. 33.5 +/- 2.5%, OLP vs. control, p < 0.01). These effects were abolished by H-89. These results may indicate that repetitive preischemic infusion of olprinone mimics IPC through cAMP-PKA pathway in post-MI heart, and that BA signaling plays a crucial role in IPC response.

Left ventricular mechanical unloading restores Beta-2-adrenergic receptor mRNA expression and decreases susceptibility to ischemia and reperfusion in the failing heart

OBJECTIVES

Left ventricular (LV) mechanical unloading is known to reduce the hemodynamic demands of failing LV, resulting in improved myocyte contractility. This study was designed to examine effects of LV unloading on beta-adrenergic receptor (BAR) expression and ischemic susceptibility to ischemia reperfusion.

METHODS

Five groups were studied: group 1 [unloading myocardial infarction (MI), n = 6], MI hearts 2 weeks after coronary ligation subjected to LV unloading by heterotopic heart transplantation for 2 weeks; group 2 (2-week MI, n = 6), MI hearts left for 2 weeks without unloading; group 3 (4-week MI, n = 6), MI hearts left for 4 weeks without unloading; group 4 (control, n = 6), normal (non-MI) hearts as a control with no interventions, and group 5 (unloading control, n = 5), normal (non-MI) hearts subjected to LV unloading for 2 weeks. Then, all hearts were isolated and subjected to 20 min of global ischemia and 60 min of reperfusion on Langendorff apparatus. LV pressures and coronary flow were measured throughout the experiment. Either total BAR density or beta(2)-adrenergic receptor (B2AR) mRNA expression in the noninfarcted myocardium was determined by radioligand binding assays or real-time quantitative RT-PCR, respectively.

RESULTS

LV unloading improved postischemic functional recovery (unloading MI vs. 2-week MI vs. 4-week MI: 74 +/- 6 vs. 54 +/- 5 vs. 51 +/- 4%; p < 0.05 vs. unloading MI). LV unloading restored B2AR mRNA expression (unloading MI vs. 2-week MI vs. 4-week MI: 4.78 +/- 0.21 vs. 2.80 +/- 0.19 vs. 2.24 +/- 0.17 x 10(7) copy/microg total RNA; p < 0.05 vs. unloading MI).

CONCLUSION

LV mechanical unloading restored B2AR mRNA expression and improved postischemic functional recovery.