Pharmacologic preconditioning of estrogen by activation of the myocardial adenosine triphosphate-sensitive potassium channel in patients undergoing coronary angioplasty

Rapid estrogen actions on ion channels: A survey in search for mechanisms

A survey of nearly two hundred reports shows that rapid estrogenic actions can be detected across a range of kinds of estrogens, a range of doses, on a wide range of tissue, cell and ion channel types. Striking is the fact that preparations of estrogenic agents that do not permeate the cell membrane almost always mimic the actions of the estrogenic agents that do permeate the membrane. All kinds of estrogens, ranging from natural ones, through receptor modulators, endocrine disruptors, phytoestrogens, agonists, and antagonists to novel G-1 and STX, have been reported to be effective. For actions on specific types of ion channels, the possibility of opposing actions, in different cases, is the rule, not the exception. With this variety there is no single, specific action mechanism for estrogens per se, although in some cases estrogens can act directly or via some signaling pathways to affect ion channels. We infer that estrogens can bind a large number of substrates/receptors at the membrane surface. As against the variety of subsequent routes of action, this initial step of the estrogen's binding action is the key.

Molecular aspects of ischaemic postconditioning

Preconditioning, a well established phenomenon had been used since 1980s to attenuate ischaemia-reperfusion induced injury. However, inability to predict the onset of ischaemia in clinical settings led to the discovery of a new concept of postconditioning (PoCo), in 2000s whereby brief repetitive cycles of ischaemia with intermittent reperfusion followed by prolonged ischaemia-elicited tissue protection. There is an impressive array of molecular mechanisms contributing to PoCo-mediated tissue-protection, which include triggers like adenosine (ADO), opioid, erythropoietin (EPO), endogenous nitric-oxide, reactive oxygen species, acetylcholine, tissue factors, pro-inflammatory cytokines and bradykinin; mediators like reperfusion injury salvage kinase pathways including phosphoinositide-3-kinase, extra-cellular signal regulated kinase(1/2) pathway, protein kinase G and protein kinase C; end-effectors like mitochondrial permeability transition pore and mitochondrial potassium ATP channel. The clinical applicability of PoCo has been extended with the use of PoCo mimetic agents like insulin, glucagon like peptide, EPO, statins and ADO before reperfusion in patients with ischaemia reperfusion injury. Remote PoCo has also emerged as a new concept; however, considerable research is required for understanding its molecular mechanisms. In this review, an exhaustive attempt has been made to unearth some molecular aspects of PoCo.

Reperfusion injury salvage kinase signalling: taking a RISK for cardioprotection

Following an acute myocardial infarction (AMI), early coronary artery reperfusion remains the most effective means of limiting the eventual infarct size. The resultant left ventricular systolic function is a critical determinant of the patient's clinical outcome. Despite current myocardial reperfusion strategies and ancillary antithrombotic and antiplatelet therapies, the morbidity and mortality of an AMI remain significant, with the number of patients developing cardiac failure increasing, necessitating the development of novel strategies for cardioprotection which can be applied at the time of myocardial reperfusion to reduce myocardial infarct size. In this regard, the Reperfusion Injury Salvage Kinase (RISK) Pathway, the term given to a group of pro-survival protein kinases (including Akt and Erk1/2), which confer powerful cardioprotection, when activated specifically at the time of myocardial reperfusion, provides an amenable pharmacological target for cardioprotection. Preclinical studies have demonstrated that an increasing number of agents including insulin, erythropoietin, adipocytokines, adenosine, volatile anesthetics natriuretic peptides and 'statins', when administered specifically at the time of myocardial reperfusion, reduce myocardial infarct size through the activation of the RISK pathway. This recruits various survival pathways that include the inhibition of mitochondrial permeability transition pore opening. Interestingly, the RISK pathway is also recruited by the cardioprotective phenomena of ischemic preconditioning (IPC) and postconditioning (IPost), enabling the use of pharmacological agents which target the RISK pathway, to be used at the time of myocardial reperfusion, as pharmacological mimetics of IPC and IPost. This article reviews the origins and evolution of the RISK pathway, as part of a potential common cardioprotective pathway, which can be activated by an ever-expanding list of agents administered at the time of myocardial reperfusion, as well as by IPC and IPost. Preliminary clinical studies have demonstrated myocardial protection with several of these pharmacological activators of the RISK pathway in AMI patients undergoing PCI. Through the use of appropriately designed clinical trials, guided by the wealth of existing preclinical data, the administration of pharmacological agents which are known to activate the RISK pathway, when applied as adjuvant therapy to current myocardial reperfusion strategies for patients presenting with an AMI, should lead to improved clinical outcomes in this patient group.

Effect of pravastatin on left ventricular mass in the two-kidney, one-clip hypertensive rats

We have demonstrated that myocardial ATP-sensitive potassium (KATP) channels are implicated in the development of cardiac hypertrophy in hyperlipidemic rabbits. We investigated the effect of pravastatin on development of ventricular hypertrophy in male normolipidemic Wistar rats with two-kidney, one-clip (2K1C) hypertension and whether the attenuated hypertrophic effect was via activation of KATPchannels. Twenty-four hours after the left renal artery was clipped, rats were treated with one of the following therapies for 8 wk: vehicle, nicorandil (an agonist of KATPchannels), pravastatin, glibenclamide (an antagonist of KATPchannels), hydralazine, nicorandil plus glibenclamide, or pravastatin plus glibenclamide. Systolic blood pressure, relative left ventricular (LV) weight, and cardiomyocyte sizes significantly increased in vehicle-treated 2K1C rats compared with those in sham-operated rats. Treatment with either nicorandil or pravastatin significantly attenuated LV hypertrophy/body weight compared with the vehicle, which was further confirmed by downregulation of LV atrial natriuretic peptide mRNA. Nicorandil-induced effects were abolished by administering glibenclamide. Similarly, pravastatin-induced beneficial effects were reversed by the addition of glibenclamide, implicating KATPchannels as the relevant target. A dissociation between the effects of blood pressure and cardiac structure was noted because pravastatin and hydralazine reduced arterial pressure similarly. These results suggest a crucial role of cardiac KATPchannel system in the development of ventricular hypertrophy in the 2K1C hypertensive rats. Pravastatin is endowed with cardiac antihypertrophic properties probably through activation of KATPchannels, independent of lipid and hemodynamic changes.

Pharmacological postconditioning with the phytoestrogen genistein

Estrogens are known to activate the phosphatidyl-inosityl 3-kinase (PI3K)/Akt pathway, which is central in the cardioprotection afforded by ischemic postconditioning. Therefore, our goal was to investigate whether a phytoestrogen, genistein, could induce a pharmacological postconditioning and to investigate potential mechanisms. We used low doses of genistein in order to avoid tyrosine kinases inhibition. Thus, pentobarbital-anesthetized rabbits underwent a coronary artery occlusion followed by 4 h of reperfusion. Prior to reperfusion, they randomly received an i.v. injection of either saline (Control), 100 or 1000 microg/kg of genistein (Geni(100) and Geni(1000), respectively), and 10 or 100 microg/kg of 17beta-estradiol (17beta(10) and 17beta(100), respectively). Infarct size (IS, % area at risk) was significantly reduced in Gen(100), Gen(1000) and 17beta(100) but not in 17beta(10) (6+/-2, 16+/-5, 12+/-3 and 29+/-7%, respectively) vs. Control (35+/-4%). A significant decrease in the percentage of TUNEL-positive nuclei within infarcted area was observed in Gen(100) and 17beta(100) vs. Controls. The estrogen receptor antagonist fulvestrant (1 mg/kg i.v.) and the PI3K inhibitor wortmaninn (0.6 mg/kg) abolished the cardioprotective effect of genistein. Western blots also demonstrated an increase in Akt posphorylation in Gen(100). In the same group, in vitro mitochondrial swelling studies demonstrated a significant inhibition of calcium-induced opening of mitochondrial transition pore vs. Controls. In conclusion, genistein exerts pharmacological postconditioning with a similar potency as 17beta-estradiol through a pathway involving activation of the estrogen receptor, of PI3K/Akt and mitochondrial preservation. Therefore, genistein should not be only considered as an inhibitor of tyrosine kinase but also as a cardioprotective estrogen.

The Effect of the Phytoestrogen Genistein on Myocardial Protection, Preconditioning and Oxidative Stress

INTRODUCTION

We have previously shown that estrogen administered in ovariectomized female rabbits significantly reduce myocardial infarct size. We now investigated whether the phytoestrogen genistein similarly protects ischemic myocardium and whether this is associated with its antioxidant properties. In addition, we examined whether genistein abolishes preconditioning, since at high doses, it inhibits tyrosine kinase.

MATERIALS AND METHODS

We studied five groups of New Zealand white female rabbits. Group A (n = 12) were normal controls, group B (n = 14) were ovariectomized 4 weeks prior to the experiment, group C (n = 10) were ovariectomized and treated with genistein (0.2 mg kg(-1) day(-1) subcutaneously) for 4 weeks before the experiment, group D (n = 12) had intact gonads and were treated with genistein (0.2 mg kg(-1) day(-1) subcutaneously) for 4 weeks before the experiment and group E (n = 8) were ovariectomized 4 weeks prior to the experiment and treated with a single dose of genistein (0.2 mg kg(-1) day(-1) subcutaneously) just prior to the experiment. All animals underwent 30 min of heart ischemia and 120 min of reperfusion, with (subgroup I) or without (subgroup II) preconditioning. Malondialdehyde (MDA) concentration just before the experiment was determined.

RESULTS

We found significant differences between the groups-p < 0.0001 in factorial ANOVA. The groups with preconditioning had significant smaller infarcts compared to those without-AI vs AII (10.66 +/- 1.42% vs 43.22 +/- 2.67%), BI vs BII (18.53 +/- 2.36% vs 43.05 +/- 8.37%), CI vs CII (10.17 +/- 2.07% vs 44.5 +/- 5.47%), DI vs DII (14.98 +/- 2.36% vs 37.79 +/- 3.92%) and EI vs EII (17.11 +/- 3.24% vs 42.08 +/- 3.42%), p < 0.0005. Ovariectomy was not associated with larger myocardial infarctions-AII vs BII, p = NS. Genistein, for 4 weeks, did not protect ischemic myocardium in either ovariectomized or non-ovariectomized animals-BII vs CII and AII vs DII, p = NS. There was no significant difference between the preconditioned animals, with intact gonads or ovariectomized (AI vs BI, p = NS), ovariectomized with or without genistein (BI vs CI, p = NS) and non-ovariectomized whether treated with genistein or not (AI vs DI, p = NS). A single dose of genistein did not offer any protection (EII vs BII, p = NS), nor did it modify the preconditioning effect (EI vs BI, p = NS). We found no significant difference in MDA plasma levels between the groups.

CONCLUSION

Genistein, at this dose, does not reduce infarct size per se nor abolishes the protection induced by preconditioning, in both ovariectomized and non-ovariectomized animals. Preconditioning offers myocardial protection in animals with intact gonads as well as estrogen deprived; bilateral ovariectomy, at least during short-term, is not associated with larger myocardial infarcts compared to control animals. In addition estrogen deprivation, during short term, as well as genistein do not modify oxidative stress.

A phase of increased ST elevation during coronary occlusion following ischemic preconditioning

ATP-sensitive potassium channels are opened during the course of ischemic preconditioning (IP). As experimental data suggest that opening of sarcolemmal ATP-sensitive potassium channels underlie ST elevation during myocardial ischemia, one would expect to observe increased ST elevation during ischemia following IP. However, clinical studies have reported IP to attenuate ST elevation during repeated brief coronary occlusions. The objective of this study was to characterize the temporal course of ST elevation during coronary occlusion following IP. Twenty-eight closed-chest pigs were subject to catheter-based left anterior descending coronary artery occlusion/ reperfusion for 45/120 minutes. Thirteen animals were preconditioned by two occlusion/reperfusion cycles of 10/30 minutes. Fifteen pigs served as controls. The electrocardiographic ST vector magnitude was continuously monitored. IP reduced the infarct size normalized for area at risk (IP 9.6 +/- 15.8%; control 71.2 +/- 14.7%; p < 0.001). IP increased the time between coronary artery occlusion and appearance of significant rise in ST vector magnitude from 51 +/- 17 to 94 +/- 33 seconds (p < 0.01). IP reduced the rise in ST vector magnitude after 120 seconds of occlusion from 202 +/- 85 microV to 68 +/- 28 microV (p < 0.001) and increased the rise in ST vector magnitude after 600 seconds from 265 +/- 106 microV to 427 +/- 232 microV (p < 0.001).

CONCLUSION

Ischemic preconditioning reduced and delayed early ST elevation during subsequent coronary artery occlusion, but increased late ST elevation. Thus, ischemic preconditioning causes a dynamic and critically time-dependent biphasic pattern of ST elevation during repeated coronary occlusions.

Cardiac Preconditioning during Percutaneous Coronary Interventions

Ischemic preconditioning (PC) is a polygenic defensive cellular adaptive phenomenon of the heart to ischemic stress, whereby the heart changes its phenotype to become more resistant to subsequent ischemia. Early and late of PC represent two chronologically and pathophysiologically distinct phases of this phenomenon, which can be recruited pharmacologically. We represent a post hoc analysis examining the late PC-mimetic effects of nitroglycerin (NTG) on peri-procedural myocardial necrosis during percutaneous coronary intervention (PCI). A group of 66 patients presenting with angina were randomized, 24 h prior to a scheduled PCI for single obstructive CAD, to a 4 h pretreatment with intravenous NTG or saline. Measurements of electrocardiographic ST-segment shifts, echocardiographic regional wall motion and angina scores demonstrated that NTG pre-treatment preconditioned the heart by rendering it resistant to ischemia during balloon inflations. NTG-pretreated patients exhibited trends towards lower average peak CK (131.1 vs. 188.6 U/L, P = 0.38) and CK-MB levels (7.1 vs. 12.6 ng/ml, P = 0.40). NTG, however, had no significant impact on the incidence of post-procedural MI or any cardiac enzyme elevation. The exploitation of ischemic and pharmacological PC may prove a useful strategy to confer cardioprotection during high-risk PCI and is worth exploring.

Propyl paraben inhibits voltage-dependent sodium channels and protects cardiomyocytes from ischemia-reperfusion injury

The effects of propyl paraben, an antimicrobial preservative, on voltage-dependent sodium current and myocardial ischemia-reperfusion injury were investigated in isolated adult rat cardiomyocytes. Whole cell voltage-clamp recording showed that propyl paraben reversibly blocked the voltage-gated sodium channel both in concentration- and voltage-dependent manners. Propyl paraben (500 microM but not 100 microM) significantly shifted the steady-state inactivation of the sodium channel toward the hyperpolarizing direction at the V(1/2) point. Consistent with the above result, the propidium iodide (PI) uptake test revealed that pretreatment with 500 microM but not 100 microM of propyl paraben significantly reduced cell death induced by 45 min of sustained ischemia followed by 15 h of reperfusion (42.37 +/- 7.01% of cell viability in control and 71.05 +/- 7.06% in the propyl paraben group), suggesting that propyl paraben can protect myocytes from ischemia-reperfusion injury. These results indicate a possible correlation between the inhibition of sodium current and cardioprotection against ischemia-reperfusion injury.

Differential role of K(ATP) channels activated by conjugated estrogens in the regulation of myocardial and coronary protective effects

BACKGROUND

We have demonstrated that estrogen can reduce myocardial injury in ischemia-reperfusion via activation of ATP-sensitive potassium (K(ATP)) channels. We sought to determine whether the protective effect of estrogen extends to epicardial coronary artery with attenuated vasoconstriction in patients after angioplasty by activation of such channels.

METHODS AND RESULTS

The study was designed to prospectively investigate 41 consecutive patients scheduled for elective coronary angioplasty. Pretreatment with estrogen limited myocardial ischemia during coronary occlusion and attenuated postangioplasty coronary vasoconstriction at the dilated and distal segments. An inhibitor of K(ATP) channels, glibenclamide, did not affect coronary vasomotor response, although it abolished the beneficial effect of estrogen on myocardial ischemia. Patients to whom estrogen was administered after the second balloon deflation experienced a similar magnitude of myocardial ischemia as controls but showed significantly attenuated vasoconstriction compared with controls (P=0.0001). Endothelin-1 levels from the great cardiac vein rose significantly from 1.9+/-0.4 to 3.1+/-0.6 pg/mL (P=0.001) 15 minutes after angioplasty in the control group; this was attenuated after estrogen was administered. Significant correlation was found between the changes in coronary vasomotion of the dilated segment and endothelin-1 levels (r=0.65, P<0.0001).

CONCLUSIONS

These results demonstrate that estrogen is protective against both myocardial ischemia and coronary vasoconstriction through different mechanisms. The myocardial effect of estrogen was abolished by glibenclamide, which suggests that the cardioprotective effect of estrogen may result from activation of K(ATP) channels. In contrast, estrogen-induced attenuated vasoconstriction is associated with an attenuated release of endothelin-1, independent of K(ATP) activation.