Delayed myocardial preconditioning by alpha1-adrenoceptors involves inhibition of apoptosis

Mitigation of dexamethasone-induced nephrotoxicity by modulating the activity of adrenergic receptors: Implication of Wnt/β-arrestin2/β-catenin pathway

The present study aimed to investigate the role of α and β-adrenergic receptors (βARs) in mediation or modulation of the dexamethasone-induced nephrotoxicity by using different pharmacological interventions. Nephrotoxicity was induced by subcutaneous injection of dexamethasone (10 mg/kg) for 7 days in Wistar albino rats. Eight groups were used: control; dexamethasone; carvedilol; phenylephrine; carvedilol and phenylephrine; propranolol; doxazosin; propranolol and doxazosin. At the end of experiment, rats were euthanized and blood, urine and kidney samples were collected. Serum and urinary creatinine and urinary total protein levels were measured. Also, the renal tissue levels of diacylglycerol (DAG); Akt kinase activity, malondialdehyde (MDA), NADPH oxidase 2 (NOX2), transforming growth factor-β (TGF-β), Wnt3A and β-catenin were recorded. Furthermore, histopathological and β-arrestin2-immunohistochemical examinations of renal tissues were performed. Results: Dexamethasone induced glomerular damage, proteinuria, renal oxidative stress and upregulated the renal Wnt/β-arrestin2/β-catenin pathway and the profibrotic signals. Blocking the α1 and βARs by carvedilol reduced the dexamethasone-induced nephrotoxicity. Pre-injection of phenylephrine did not reduce the reno-protective action of carvedilol. Blocking the βARs only by propranolol reduced the dexamethasone-induced nephrotoxicity to the same extent of carvedilol group. Blocking the α1ARs only by doxazosin reduced dexamethasone-induced nephrotoxicity to a higher extent than other treatments. However, combined use of propranolol and doxazosin did not synergize the reno-protective effects of doxazosin. Conclusion: Dexamethasone induces nephrotoxicity, possibly, by upregulating the Wnt/β-arrestin2/β-catenin pathway. Blocking either α1ARs or βARs can effectively protect against the dexamethasone-induced nephrotoxicity. However, combined blocking of α1ARs and βARs does not synergize the reno-protective effects.

Hurdles to Cardioprotection in the Critically Ill

Cardiovascular disease is the largest contributor to worldwide mortality, and the deleterious impact of heart failure (HF) is projected to grow exponentially in the future. As heart transplantation (HTx) is the only effective treatment for end-stage HF, development of mechanical circulatory support (MCS) technology has unveiled additional therapeutic options for refractory cardiac disease. Unfortunately, despite both MCS and HTx being quintessential treatments for significant cardiac impairment, associated morbidity and mortality remain high. MCS technology continues to evolve, but is associated with numerous disturbances to cardiac function (e.g., oxidative damage, arrhythmias). Following MCS intervention, HTx is frequently the destination option for survival of critically ill cardiac patients. While effective, donor hearts are scarce, thus limiting HTx to few qualifying patients, and HTx remains correlated with substantial post-HTx complications. While MCS and HTx are vital to survival of critically ill cardiac patients, cardioprotective strategies to improve outcomes from these treatments are highly desirable. Accordingly, this review summarizes the current status of MCS and HTx in the clinic, and the associated cardiac complications inherent to these treatments. Furthermore, we detail current research being undertaken to improve cardiac outcomes following MCS/HTx, and important considerations for reducing the significant morbidity and mortality associated with these necessary treatment strategies.

Clinical translation of myocardial conditioning

Rapid admission and acute interventional treatment combined with modern antithrombotic pharmacologic therapy have improved outcomes in patients with ST elevation myocardial infarction. The next major target to further advance outcomes needs to address ischemia-reperfusion injury, which may contribute significantly to the final infarct size and hence mortality and postinfarction heart failure. Mechanical conditioning strategies including local and remote ischemic pre-, per-, and postconditioning have demonstrated consistent cardioprotective capacities in experimental models of acute ischemia-reperfusion injury. Their translation to the clinical scenario has been challenging. At present, the most promising mechanical protection strategy of the heart seems to be remote ischemic conditioning, which increases myocardial salvage beyond acute reperfusion therapy. An additional aspect that has gained recent focus is the potential of extended conditioning strategies to improve physical rehabilitation not only after an acute ischemia-reperfusion event such as acute myocardial infarction and cardiac surgery but also in patients with heart failure. Experimental and preliminary clinical evidence suggests that remote ischemic conditioning may modify cardiac remodeling and additionally enhance skeletal muscle strength therapy to prevent muscle waste, known as an inherent component of a postoperative period and in heart failure. Blood flow restriction exercise and enhanced external counterpulsation may represent cardioprotective corollaries. Combined with exercise, remote ischemic conditioning or, alternatively, blood flow restriction exercise may be of aid in optimizing physical rehabilitation in populations that are not able to perform exercise practice at intensity levels required to promote optimal outcomes.

α1A-Adrenergic receptor prevents cardiac ischemic damage through PKCδ/GLUT1/4-mediated glucose uptake

While α(1)-adrenergic receptors (ARs) have been previously shown to limit ischemic cardiac damage, the mechanisms remain unclear. Most previous studies utilized low oxygen conditions in addition to ischemic buffers with glucose deficiencies, but we discovered profound differences if the two conditions are separated. We assessed both mouse neonatal and adult myocytes and HL-1 cells in a series of assays assessing ischemic damage under hypoxic or low glucose conditions. We found that α(1)-AR stimulation protected against increased lactate dehydrogenase release or Annexin V(+) apoptosis under conditions that were due to low glucose concentration not to hypoxia. The α(1)-AR antagonist prazosin or nonselective protein kinase C (PKC) inhibitors blocked the protective effect. α(1)-AR stimulation increased (3)H-deoxyglucose uptake that was blocked with either an inhibitor to glucose transporter 1 or 4 (GLUT1 or GLUT4) or small interfering RNA (siRNA) against PKCδ. GLUT1/4 inhibition also blocked α(1)-AR-mediated protection from apoptosis. The PKC inhibitor rottlerin or siRNA against PKCδ blocked α(1)-AR stimulated GLUT1 or GLUT4 plasma membrane translocation. α(1)-AR stimulation increased plasma membrane concentration of either GLUT1 or GLUT4 in a time-dependent fashion. Transgenic mice overexpressing the α(1A)-AR but not α(1B)-AR mice displayed increased glucose uptake and increased GLUT1 and GLUT4 plasma membrane translocation in the adult heart while α(1A)-AR but not α(1B)-AR knockout mice displayed lowered glucose uptake and GLUT translocation. Our results suggest that α(1)-AR activation is anti-apoptotic and protective during cardiac ischemia due to glucose deprivation and not hypoxia by enhancing glucose uptake into the heart via PKCδ-mediated GLUT translocation that may be specific to the α(1A)-AR subtype.

Molecular basis of cardioprotection: signal transduction in ischemic pre-, post-, and remote conditioning

Reperfusion is mandatory to salvage ischemic myocardium from infarction, but reperfusion per se contributes to injury and ultimate infarct size. Therefore, cardioprotection beyond that by timely reperfusion is needed to reduce infarct size and improve the prognosis of patients with acute myocardial infarction. The conditioning phenomena provide such cardioprotection, insofar as brief episodes of coronary occlusion/reperfusion preceding (ischemic preconditioning) or following (ischemic postconditioning) sustained myocardial ischemia with reperfusion reduce infarct size. Even ischemia/reperfusion in organs remote from the heart provides cardioprotection (remote ischemic conditioning). The present review characterizes the signal transduction underlying the conditioning phenomena, including their physical and chemical triggers, intracellular signal transduction, and effector mechanisms, notably in the mitochondria. Cardioprotective signal transduction appears as a highly concerted spatiotemporal program. Although the translation of ischemic postconditioning and remote ischemic conditioning protocols to patients with acute myocardial infarction has been fairly successful, the pharmacological recruitment of cardioprotective signaling has been largely disappointing to date.

Cardiac alpha1-adrenergic receptors: novel aspects of expression, signaling mechanisms, physiologic function, and clinical importance

Adrenergic receptors (AR) are G-protein-coupled receptors (GPCRs) that have a crucial role in cardiac physiology in health and disease. Alpha1-ARs signal through Gαq, and signaling through Gq, for example, by endothelin and angiotensin receptors, is thought to be detrimental to the heart. In contrast, cardiac alpha1-ARs mediate important protective and adaptive functions in the heart, although alpha1-ARs are only a minor fraction of total cardiac ARs. Cardiac alpha1-ARs activate pleiotropic downstream signaling to prevent pathologic remodeling in heart failure. Mechanisms defined in animal and cell models include activation of adaptive hypertrophy, prevention of cardiac myocyte death, augmentation of contractility, and induction of ischemic preconditioning. Surprisingly, at the molecular level, alpha1-ARs localize to and signal at the nucleus in cardiac myocytes, and, unlike most GPCRs, activate "inside-out" signaling to cause cardioprotection. Contrary to past opinion, human cardiac alpha1-AR expression is similar to that in the mouse, where alpha1-AR effects are seen most convincingly in knockout models. Human clinical studies show that alpha1-blockade worsens heart failure in hypertension and does not improve outcomes in heart failure, implying a cardioprotective role for human alpha1-ARs. In summary, these findings identify novel functional and mechanistic aspects of cardiac alpha1-AR function and suggest that activation of cardiac alpha1-AR might be a viable therapeutic strategy in heart failure.

Effect of HEMADO on Level of CK-MB and LDH Enzymes after Ischemia/Reperfusion Injury in Isolated Rat Heart

INTRODUCTION

Ischemia/Reperfusion (IR) injury mainly causes the increase of enzymes involved in myocytes injury including CK-MB (creatine kinase-MB) isoenzyme and LDH (lactate dehydrogenase). Leakage of CK-MB isoenzyme and LDH from myocardial tissues to blood is indicator of acute myocardial infarction. The aim of this study was to assess the effect of HEMADO on IR injury and its relationship with mitochondrial ATP-sensitive K+ channels (mitoKATP) in rat heart.

METHODS

Twenty eight male Wistar rats (250-300g) were divided into four groups (seven members in each group): control (without ischemia), I/R (with ischemia+without HEMADO), ischemia received HEMADO (HEMADO), ischemia received HEMADO and 5-HD (5-hydroxydecanoate, specific mitoKATP channel blocker) (HEMADO+5-HD). The animals were anesthetized and the hearts were quickly removed and mounted on Langendorff apparatus and perfused by Krebs-Henseleit solution under constant pressure and temperature of 37ºC. After 20 minutes of stabilization, ischemic groups were exposed to 40 minutes of global ischemia and consecutive 90 minutes of reperfusion.

RESULTS

IR injury increased the level of LDH and CK-MB in the collected coronary flow during 5 minutes since start of reperfusion. HEMADO reduced the enzymes' levels and using 5-HD abolished the effect of HEMADO.

CONCLUSION

Our findings indicated that HEMADO could protect the heart against ischemia-reperfusion injury by decreasing the CK-MB and LDH levels. The cardioprotective effect of HEMADO may be mediated in part by mitoKATP.

Time course analysis of cardiac pacing-induced gene expression changes in the canine heart

Rapid right ventricular pacing in anesthetized dogs results in marked protection against ischemia and reperfusion-induced ventricular arrhythmias, 24 h later. We have previous evidence that this protection associates with altered expression of genes, encoding proteins involved in the delayed cardioprotection. However, the sequence of transcriptional changes occurring between the pacing stimulus and the test ischemia has not yet been elucidated. Thus, we designed studies in which the expression of 29 genes was examined by real-time PCR at various time intervals, i.e., immediately (0 h), 6, 12, and 24 h after short periods (4 times 5 min) of rapid (240 beats min(-1)) right ventricular pacing in the canine. Sham-operated dogs (the pacing electrode was introduced but the dogs were not paced) served as controls. Compared with these dogs, pacing induced an early up-regulation of genes which encode, for example, HSP90, MnSOD, ERK1, PKCε, Bcl2, and sGC; all these somehow relate to the early phase of the protection. These genes remained either up-regulated or, after a transient lower expression (around 6 h), were up-regulated again, suggesting their involvement in the delayed protection. There were also some genes which down-regulated soon after the pacing stimulus (e.g., Bax, Casp3, Casp9, MMP9, GSK3β), and showed also low expression 24 h later. Genes encoding eNOS and iNOS, as well as Cx43 were only up-regulated 12 h after pacing. We conclude that cardiac pacing induces time-dependent changes in gene expression, and the sequence of these changes is important in the development of the delayed protection.

Cardiac and neuroprotection regulated by α(1)-adrenergic receptor subtypes

Sympathetic nervous system regulation by the α(1)-adrenergic receptor (AR) subtypes (α(1A), α(1B), α(1D)) is complex, whereby chronic activity can be either detrimental or protective for both heart and brain function. This review will summarize the evidence that this dual regulation can be mediated through the different α(1)-AR subtypes in the context of cardiac hypertrophy, heart failure, apoptosis, ischemic preconditioning, neurogenesis, locomotion, neurodegeneration, cognition, neuroplasticity, depression, anxiety, epilepsy, and mental illness.

Alpha-1-adrenergic receptors: targets for agonist drugs to treat heart failure

Evidence from cell, animal, and human studies demonstrates that α1-adrenergic receptors mediate adaptive and protective effects in the heart. These effects may be particularly important in chronic heart failure, when catecholamine levels are elevated and β-adrenergic receptors are down-regulated and dysfunctional. This review summarizes these data and proposes that selectively activating α1-adrenergic receptors in the heart might represent a novel and effective way to treat heart failure. This article is part of a special issue entitled "Key Signaling Molecules in Hypertrophy and Heart Failure."

Molecular Biology of Apoptosis in Ischemia and Reperfusion

This study reviews the current understanding of the mechanisms that mediate the complex processes involved in apoptosis secondary to ischemia and reperfusion (I/R) and is not intended as a complete literature review of apoptosis. Several biochemical reactions trigger a cascade of events, which activate caspases. These caspases exert their effect through downstream proteolysis until the final effector caspases mediate the nuclear features characteristic of apoptosis, DNA fragmentation and condensation. Within the context of ischemia, the hypoxic environment initiates the expression of several genes involved in inflammation, the immune response, and apoptosis. Many of these same genes are activated during reperfusion injury in response to radical oxygen species generation. It is plausible that inhibition of specific apoptotic pathways via inactivation or downregulation of those genes responsible for the initiation of inflammation, immune response, and apoptosis may provide promising molecular targets for ameliorating reperfusion injury in I/R-related processes. Such inhibitory mechanisms are discussed in this review. Important targets in I/R-related pathologies include the brain during stroke, the heart during myocardial infarction, and the organs during harvesting and/or storage for transplantation. In addition, we present data from our ongoing research of specific signal transduction-related elements and their role in ischemia/reperfusion injury. These data address the potential therapeutic application of anti-inflammatory and anti-ischemic compounds in the prevention of I/R damage.

Acidic pre-conditioning suppresses apoptosis and increases expression of Bcl-xL in coronary endothelial cells under simulated ischaemia

Ischaemic pre-conditioning has a powerful protective potential against ischaemia-induced cell death, and acidosis is an important featur of ischaemia and can lead to apoptosis. Here we tested whether pre-conditioning with acidosis, that is, acidic pre-conditioning (APC), may protect coronary endothelial cells (EC) against apoptosis induced by simulated ischaemia. For pre-conditioning, EC were exposed fo 40 min. to acidosis (pH 6.4) followed by a 14-hrs recovery period (pH 7.4) and finally treated for 2 hrs with simulated ischaemia (glucose-free anoxia at pH 6.4). Cells undergoing apoptosis were visualized by chromatin staining or by determination of caspase-3 activit Simulated ischaemia in untreated EC increased caspase-3 activity and the number of apoptotic cell (31.3 ± 1.3%versus 3.9 ± 0.6% in control). APC significantly reduced the rate of apoptosis (14.2 ± 1.3%) and caspase-3 activity. Western blot analysis exploring the under lying mechanism leading to this protection revealed suppression of the endoplasmic reticulum- (reduced cleavage of caspase-12) and mitochondria-mediated (reduced cytochrome C release) pathways of apoptosis. These effects were associated with an over-expression of the anti-apoptotic protein Bcl-xL 14 hrs after APC, whereas no effect on the expression of Bcl-2, Bax, Bak, procaspase-12, reticulum-localized chaperones (GRP78, calreticulin), HSP70, HSP32 and HSP27 could be detected. Knock-down of Bcl-xL by siRNA-treatment prevented the protective effect of APC. In conclusion, short acidic pre-treatment can protect EC against ischaemic apoptosis. The mechanism of this protection consists of suppression of the endoplasmic reticulum- and mitochondria-mediated pathways. Over-expression of the anti apoptotic protein Bcl-xL is responsible for the increased resistance to apoptosis during ischaemic insult.

Obligatory role of cardiac nerves and alpha1-adrenergic receptors for the second window of ischemic preconditioning in conscious pigs

We tested the hypothesis that cardiac nerves may mediate ischemic preconditioning. Pigs were chronically instrumented to measure aortic, left atrial and left ventricular pressures, and regional myocardial function (wall thickening). Hemodynamic variables, area at risk, and tissue blood flows (radioactive microspheres) were similar among groups. Myocardial infarct size following 60 minutes coronary artery occlusion and 4 days reperfusion, expressed as a fraction of the area at risk, was 42+/-4.0%, in innervated pigs and similar in pigs with regional cardiac denervation (CD, 41+/-2.5%). Infarct size in innervated pigs during the first window of preconditioning (first window) was markedly reduced (6+/-1.8%, P<0.01), as it was in the second window of preconditioning (second window) (16+/-3.3%, P<0.01). Although infarct size was still reduced in pigs with CD and first window preconditioning (9+/-1.8%, P<0.01), the protective effects of second window were abrogated in pigs with CD resulting in an infarct size of 38+/-5.6%. In another group of innervated pigs during pharmacological alpha(1)-adrenergic receptor (AR) blockade, infarct size was also not reduced during the second window (48+/-3.2%). Additionally, Western blot analysis of inducible nitric oxide synthase and cyclooxygenase-2 proteins demonstrated significant (P<0.05) upregulation following the second window in innervated pigs, but not in pigs with CD or alpha(1)-AR blockade. Thus, the mechanism of protection during the second window, but not the first window, appears to be dependent on cardiac nerves and alpha(1)-AR stimulation.

Cardiomyocyte apoptosis and ischemic preconditioning in open heart operations

BACKGROUND

The aim of the present study was to ascertain the percentage of left apical myocardial apoptosis in three-vessel coronary artery bypass grafting patients quantitatively and the impact of ischemic preconditioning.

METHODS

Twenty-one patients with three-vessel disease who had elective coronary artery bypass grafting were randomized in a ratio of 2:1 to ischemic preconditioning (n = 14) or a control group (n = 7). The ischemic preconditioning protocol was established by two cycles of ascending aorta occlusion for 2 minutes followed by 3 minutes of reperfusion. Myocardial samples from the apex of the left ventricle were taken using a Tru-Cut needle before aortic cross-clamping and immediately after declamping. The percentage of apoptosis was analyzed by TUNEL methods. Data on hemodynamics and biochemical markers were collected.

RESULTS

Low levels of myocardial apoptosis were found before the operation (0.01% +/- 0.00%). During the early reperfusion period, the percentage of myocardial apoptotic cells significantly increased (0.15% +/- 0.05%, p = 0.008). Ischemic preconditioning significantly improved cardiac index and right ventricular ejection fraction recovery after the operation (p = 0.036 and 0.001 respectively, repeated measure) but had no effect on myocardial apoptosis before and after the operation (0.01 +/- 0.00 versus 0.01 +/- 0.00, p = 0.658 and 0.12% +/- 0.04% versus 0.23% +/- 0.14%, p = 0.302).

CONCLUSIONS

Cardioplegic myocardial ischemia during open heart operation was associated with induction of cardiomyocyte apoptosis in humans. Attenuation of postoperative cardiac dysfunction by ischemic preconditioning appeared to be independent of apoptosis.

Effects of ACE inhibition on myocardial apoptosis in an ischemia-reperfusion rat heart model

Myocardial ischemia-reperfusion injury involves necrosis and apoptosis. The inhibition of angiotensin-converting enzyme (ACE) has been reported to suppress infarct size. In this study, it was investigated whether an ACE inhibitor affected myocardial apoptosis and apoptosis-related proteins in rats with experimental myocardial infarction. Anesthetized Sprague-Dawley rats were divided into four groups. Group I underwent 30 minutes of left coronary artery occlusion followed by 24 hours of reperfusion (control group); Group II underwent oral administration of the ACE inhibitor quinapril (10 mg/kg/day) before coronary occlusion (quinapril group); Group III underwent administration of the bradykinin B(2)-receptor antagonist Hoe 140 (250 microg/kg/day, subcutaneously) with quinapril (quinapril + Hoe 140 group); and Group IV underwent administration of Hoe 140 alone (Hoe 140 group). After reperfusion, myocardial infarct size was determined by triphenyltetrazolium chloride staining. Myocardial apoptosis was detected immunohistologically using terminal deoxynucleotidyl transferase-mediated nick end labeling staining and DNA electrophoresis. Myocardial caspase-3 activation was analyzed by Western blot and the expressions of Bcl-xL and Bax proteins were detected immunohistochemically. Quinapril significantly reduced the ratio of myocardial infarct size in the ischemic area at risk. In addition, quinapril significantly suppressed the incidence of apoptotic myocytes around the necrotic region (from 18.9 +/- 0.8% to 8.6 +/- 1.0%; P < 0.0001), the intensity of DNA ladder formation, and the activation of caspase-3. Hoe 140 attenuated these protective effects of quinapril. In the immunohistochemical study, Bax and Bcl-xL were expressed in myocytes, and ischemia-reperfusion abolished both proteins in the center region of ischemia. The Bax staining was equally observed among all groups. However, Bcl-xL staining remained in the ischemic area widely after quinapril treatment. In addition, Hoe 140 also depleted this effect of quinapril. These results suggest that inhibition of ACE reduces myocardial infarction and apoptosis via the bradykinin B(2) receptor in part. The antiapoptotic effect of the ACE inhibitor is attributed to the changing expression of Bcl-xL.

Alpha-adrenergic receptor stimulation produces late preconditioning through inducible nitric oxide synthase in mouse heart

Inducible nitric oxide synthase (iNOS) mediates late preconditioning (PC) induced by ischemia and pharmacological agents. Since alpha -adrenoceptor (alpha -AR) stimulation is one of the key triggers of PC, we hypothesized that activation of this receptor may induce delayed cardioprotective effect via iNOS-sensitive mechanisms. Adult male ICR mice were treated i.p. with either vehicle/inhibitors or phenylephrine (10 mg/kg) and subjected to 30 min of global ischemia and 30 min reperfusion in Langendorff mode 24 h later. 5-Methyl-urapidil (3 mg/kg) and chloroethylclonidine (3 mg/kg) were injected 15 min prior to phenylephrine to block alpha -AR(1A) and alpha -AR(1B) receptors respectively. S-Methylisothiourea (3 mg/kg), an iNOS inhibitor, was given 60 min prior to ischemia in phenylephrine-pretreated mice. Preischemic NO(x) was measured using a chemoluminescence reaction. Phenylephrine treatment reduced infarct size from 31.10 +/- 0.79% (vehicle) to 14.24 +/- 0.84% (P<0.001). Chloroethylclonidine blocked the effect of phenylephrine (infarct size 31.31 +/- 1.69%) but 5-methyl-urapidil (17.72 +/- 1.25%) did not. Phenylephrine-induced delayed cardioprotection was abolished by S-methylisothiourea and absent in iNOS knockout mice. Baseline NO(x) content was significantly increased in phenylephrine and 5-methyl-urapidil+phenylephrine treated hearts, but remained at baseline levels in hearts treated with chloroethylclonidine, 5-methyl-urapidil or S-methylisothiourea. Western blot analysis revealed a 1.8-fold increase in iNOS with phenylephrine, which was inhibited by chloroethylclonidine but not by 5-methyl-urapidil. We conclude that phenylephrine-induced delayed PC is mediated by selective activation of alpha-AR(1B). Enhanced iNOS expression concomitant with increased NO synthesis, as well as pharmacological blockade and absence of cardioprotection in iNOS knockout mice suggests an essential role of NO in phenylephrine triggered late PC.

Apoptosis in the ischemic reperfused myocardium

Recovery of the myocardium from an ischemic event depends on the reperfusion of the ischemic area. Resumed blood flow to the tissue restores the metabolic substrates necessary for energy production and cell survival. Paradoxically, ischemic reperfusion (I/R) can result in further damage to the myocardium (I/R injury) through an acute inflammatory response mediated by cytokines, neutrophils, macrophages, and reactive oxygen species. These events can trigger cardiomyocyte death through either necrosis or apoptosis. This report will focus on the apoptosis process, which is an organized, active, and gene-directed process of cell self-destruction that can be initiated by intracellular genetic programs, or second messenger pathways inside the cell upon extracellular stimulation by signaling molecules or stress. Awareness of the apoptotic process in cardiomyocytes and endothelial cells is relevant to myocardial preservation during cardiopulmonary bypass compared with off-pump cornary artery bypass procedures. Pharmacological interventions of the signaling pathways that control apoptosis provide an opportunity for new therapeutic approaches to reduce I/R injury in the heart. This review of apoptosis will introduce the perfusionist to apoptosis in the I/R heart, discuss some of the metabolic pathways that initiate it, and report on developing strategies to prevent it.

Bcl-2/Bax protein expression in heart, slow-twitch and fast-twitch muscles in young rats growing under chronic hypoxia conditions

We have studied the magnitude of apoptosis in heart, slow-twitch skeletal muscle (soleus) and fast-twitch skeletal muscle (gastrocnemius) of rats exposed to 3 weeks in vivo chronic hypoxia. Apoptosis was evaluated biochemically by DNA laddering and by TUNEL and annexin V-staining. The expression of Bax and Bcl-2 proteins was determined by immunohistochemistry and Western blotting. Western blot analysis revealed only a slight difference in Bax expression among the different tissues under normoxic and hypoxic conditions; therefore we can consider that Bax protein is constitutively expressed in muscle tissues. However a singular pattern of Bcl-2 expression was observed among the different tissues under normoxic conditions. Bcl-2 protein was more expressed in fast-twitch glycolytic muscles than in slow-twitch or oxidative muscles with a highest value found in gastrocnemius (4926 +/- 280 AU), followed by soleus (2138 +/- 200 AU) and a very low expression was displayed in the heart muscle (543 +/- 50 AU). After exposure to hypoxia for 21 days (10% O2), Bcl-2 protein expression markedly increased, (44%) in gastrocnemius, (323%) in soleus and (1178%) in heart, with significant differences (p < 0.05 student t-test), reaching a similar threshold of expression in both types of muscles. Furthermore, no sign of apoptosis was detected by TUNEL assay, annexin V-binding assay or DNA electrophoresis analysis. The latter suggested some indiscriminate fragmentations of DNA without apoptosis. In conclusion, we postulate that these protein modifications could represent a adaptative mechanism allowing a better protection against the lack of oxygen in oxidative muscles by preventing apoptosis.

Protecting the myocardium from ischemic injury: a critical role for alpha(1)-adrenoreceptors?

Ischemic preconditioning (IPC) refers to the ability of short periods of ischemia to make the myocardium more resistant to a subsequent ischemic insult. It is the most powerful form of endogenous protection against myocardial infarction and has been demonstrated in all species evaluated to date. However, the cellular mechanisms that drive IPC remain poorly understood. This hypothesis describes an important role for alpha(1)-adrenoreceptors in mediating IPC and discusses the underlying mechanisms by which this is likely achieved. alpha(1)-Adrenoreceptors are present in the myocardium of all mammalian species, and several lines of evidence suggest that they play an important role in mediating IPC. During periods of myocardial hypoxia/ischemia, cardiomyocytes have to rely solely on anaerobic glycolysis for energy production; for this, the cells have to depend on increased glucose entry inside the cell as well as increased glycolysis. Stimulation of alpha(1)-adrenoreceptors increases glucose transport inside the cardiomyocytes by translocating glucose transporter (GLUT)-1 and GLUT-4 from the cytoplasm to the plasma membrane, enhances glycogenolysis by activating phosphorylase kinase, increases the rate of glycolysis by activating the enzyme phosphofructokinase, reduces intracellular acidity produced during excessive glycolysis by activating the Na(+)/H(+) exchanger, and inhibits apoptosis by increasing the levels of the antiapoptotic protein Bcl-2. Myocardial ischemia produces an increase in the expression of alpha(1)-adrenoreceptors in cardiomyocytes, as well as increases the levels of its agonist norepinephrine by several fold. During ischemic states, upregulation of alpha(1)-adrenoreceptors and increase in norepinephrine release could be a powerful adaptive mechanism that drives IPC. An understanding into the role of alpha(1)-adrenoreceptors in mediating IPC could not only point to newer treatments for limiting myocardial damage during myocardial infarction or heart surgery, but could also help in avoiding the use of alpha(1)-antagonists in patients with ischemic heart disease.

Cell death in the heart

The role of apoptosis in cardiac disease remains controversial. Much of the apoptosis detected, by chemical or molecular means, reflects inflammatory reaction and responding blood cells rather than myocytes, though their apoptosis in situ may exacerbate a bad situation, and their direct action against myocytes has not been excluded definitely. Myocyte apoptosis may reflect end-stage cardiac failure rather than causing it. If this is the case, then preventing apoptosis so that the cells can undergo necrosis does not accomplish much. Apoptosis is a consistent and important finding in many forms of cardiovascular disease. As determined by ultra-structure, apoptosis is common in cardiomyocytes, fibroblasts, vascular endothelial cells, and smooth muscle cells in cardiovascular disease of many origins. (62) Even though smooth muscle cells in atheromatous plaques appear to be necrotic,l it is likely that this is an evolved situation of apoptotic cells that were not removed. Given the prevalence of apoptotic processes in diseased heart and the very limited capacity of this organ to repair itself, (56) it is appropriate and justified to continue to explore the significance of apoptosis in cardiac disease and, above all, to explore the use of antiapoptotic agents in acute situations. Researchers must pay explicit attention to how they document cell death and in what tissues or cells it occurs. Otherwise, clinicians risk being deluded by preservation of morphology in nonfunctional cells and by confusion of what happened and where death occurred in the sequence of causality. Cell death in the heart is a matter of substantial theoretical and practical concern. A major problem in analyzing it is that, although apoptosis may be demonstrated easily in myocytes, particularly embryonic myocytes, under conditions of culture, interpretation is much more complex in an intact organ. The first issue is one of timing. In situations of severe, acute loss of cells, such as in an infarct, apoptotic cells may not be cleared rapidly and may progress to a more oncotic or necrotic morphology. Second, in situations of inflammation, biochemical or molecular techniques may confound apoptosis of inflammatory cells with apoptosis of myocytes. Third, priorities in the sequence of apoptosis differ between large, generally nonmitotic cells with massive cytoplasm (as differentiated myocytes) and small mitotic cells in culture, which usually are studied. The appearance and many markers of physiological cell death may differ from the most widely recognized forms of apoptosis, including late collapse of the nucleus and primacy of lysosomal or other proteases as opposed to caspases. Investigators should always strive to establish multiple criteria for apoptosis, with good documentation of timing and cell type. When these factors are taken into consideration, it seems that aggressive action against apoptosis may be of value in acute situations, such as infarct, in which buying short increments of time may reduce damage. In more chronic situations, much of the apoptosis detected derives from invading lymphocytes, mast cells, or other cells relating to inflammation. The apoptosis of these cells may exacerbate an already difficult situation, and intervention may prove of value. Otherwise, apoptosis of myocytes is more typically an end-stage situation, and it is more fruitful to alleviate the problem before this stage is reached.

Neonatal mouse cardiac myocytes exhibit cardioprotection induced by hypoxic and pharmacologic preconditioning and by transgenic overexpression of human Cu/Zn superoxide dismutase

Although mouse models have been increasingly used for studies of cardiac pathophysiology, there is little information regarding cultured murine cardiac myocytes. Accordingly, we have developed a cell culture model of neonatal mouse cardiac myocytes by modifying a protocol used to prepare neonatal rat myocytes. The principal change is the substitution of cytosine arabinoside for bromodeoxyuridine to prevent fibroblast proliferation. Neonatal murine myocytes exhibited persistent spontaneous contraction and were viable for up to 14 days in culture. By flow cytometry 85% of the cells were cardiac myocytes. In sparse cultures (average cell density 259 cells/mm(2)), both hypoxic preconditioning (n=5) and phenylephrine pretreatment (n=8) produced significant protection of cardiac myocytes from cell death during a prolonged period of severe hypoxia (<0.5% O(2)for 18-20 h, both P<0.05). The phenylephrine effect was inhibited by the alpha(1)-adrenoceptor antagonist prazosin (n=4, P<0.05) and by an xi PKC peptide antagonist (xi V1-2) coupled to a TAT peptide (n=5, P<0. 05). Interestingly, the mixed alpha(1)- and beta -adrenoceptor agonist norepinephrine, which stimulates hypertrophy as measured by(14)[C]phenylalanine incorporation in neonatal rat cardiac myocytes, did not cause hypertrophy in mouse myocytes, suggesting that the signaling pathways for myocardial protection and hypertrophy are likely to be both divergent and species specific. In cardiac myocytes prepared from transgenic mice either homozygous or heterozygous for human Cu/Zn superoxide dismutase, there was protection from cell death (n=3) and restoration of(14)[C]phenyl- alanine uptake (n=4) during prolonged hypoxia (1% O(2)for 3 days, both P<0.05). We conclude that this cellular model, which is relatively simple to prepare, can be used for in-vitro examination of cardiac protection induced by preconditioning agents, various transgenes, and potentially by targeted gene deletions.

Phenylephrine protects neonatal rat cardiomyocytes from hypoxia and serum deprivation-induced apoptosis

Previous studies have shown that alpha-adrenergic activation reduces myocardial damages caused by ischemia/reperfusion. However, the molecular mechanisms of how alpha-adrenergic activation protects the myocardium are not completely understood. The objective of this study was to test the hypothesis that alpha-adrenergic activation protects the myocardium by, at least in part, inhibiting apoptosis in cardiomyocytes. The current data has shown that apoptosis in neonatal rat cardiomyocytes, induced by 24 h treatment with hypoxia (95% N2 and 5% CO2) and serum deprivation, was inhibited by co-treatment with phenylephrine. Pre-treatment with phenylephrine for 24 h also protected cardiomyocytes against subsequent 24 h treatment with hypoxia and serum deprivation. Exposure of cardiomyocytes to phenylephrine for up to 9 days under normoxic conditions did not cause apoptosis. The phenylephrine-mediated cytoprotection was blocked by an alpha-adrenergic antagonist, phentolamine. beta-adrenergic activation with isoproterenol did not protect cardiomyocytes against hypoxia and serum deprivation-induced apoptosis. Under hypoxic conditions, phenylephrine prevented the down-regulation of Bcl-2 and Bcl-X mRNA/protein and induced hypertrophic growth. Phenylephrine-mediated protection was abrogated by the phosphatidylinositol 3-kinase (PI 3-kinase) inhibitor wortmannin and was mimicked by the caspase-9 peptidic inhibitor LEHD-fmk. These results suggest that alpha-adrenergic activation protects cardiomyocytes against hypoxia and serum deprivation-induced apoptosis through regulating the expression of mitochondrion-associated apoptosis regulatory genes, preventing activation of mitochondrial damage-induced apoptosis pathway (cytochrome C-caspase-9), and activating hypertrophic growth.

Expression of active alpha(1B)-adrenergic receptors in the heart does not alleviate ischemic reperfusion injury

Ischemic preconditioning reduces infarct size and improves cardiac function in various species, including mice. The mechanism for ischemic preconditioning protection is not entirely clear and activation of alpha(1B)-adrenergic receptors (AR) is believed to be involved. Transgenic mice expressing constitutively active mutant alpha(1B)-AR in the heart have enhanced alpha(1B)-AR activity and therefore can be used to test the role of alpha(1B)-AR in ischemic preconditioning. Wild-type and transgenic mice were subjected to 30- or 40-min periods of left coronary artery occlusion followed by 60-min reperfusion, or ischemic preconditioning prior to sustained ischemia-reperfusion. Risk and infarct zones were determined by staining with Evans blue and triphenyltetrazolium, respectively, and quantitated digitally. Infarct zone and infarct size were not different between wild-type and transgenic mice, nor was the extent of reduction in infarct size by preconditioning ischemia (wild-type mice: 45+/-3 to 18+/-3%, transgenic mice: 46+/-3 to 19+/-2% of the left ventricle, both P<0.01). Ventricular function was similar between wild-type and transgenic mice with or without ischemia-reperfusion injury. In conclusion, enhanced alpha(1B)-AR activity by cardiac-specific expression of constitutively active mutant alpha(1B)-AR in mice does not mimic ischemic preconditioning to protect against ischemia-reperfusion injury.

Bcl-x and Bax regulate mouse primordial germ cell survival and apoptosis during embryogenesis

Restricted germ cell loss through apoptosis is initiated in the fetal gonad around embryonic day 13.5 (E13.5) as part of normal germ cell development. The mechanism of this germ cell attrition is unknown. We show that Bcl-x plays a crucial role in maintaining the survival of mouse germ cells during gonadogenesis. A bcl-x hypomorphic mouse was generated through the introduction of a neomycin (neo) gene into the promoter of the bcl-x gene by homologous recombination. Mice that contained two copies of the hypomorphic allele had severe reproductive defects attributed to compromised germ cell development. Males with two mutant alleles lacked spermatogonia and were sterile; females showed a severely reduced population of primordial and primary follicles and exhibited greatly impaired fertility. Primordial germ cells (PGCs) in bcl-x hypomorph mice migrated to the genital ridge by E12.5 but were depleted by E15.5, a time when Bcl-x and Bax were present. Two additional bcl-x transcripts were identified in fetal germ cells more than 300 bp upstream of previously reported start sites. Insertion of a neo cassette led to a down-regulation of the bcl-x gene at E12.5 in the hypomorph. Bax was detected by immunohistochemistry in germ cells from bcl-x hypomorph and control testes at E12.5 and E13.5. Bcl-x function was restored, and animals of both genders were fertile after removal of the neo selection cassette using Cre-mediated recombination. Alternatively, the loss of Bcl-x function in the hypomorph was corrected by the deletion of both copies of the bax gene, resulting in a restoration of germ cell survival. These findings demonstrate that the balance of Bcl-x and Bax control PGC survival and apoptosis.

Unresolved issues regarding the role of apoptosis in the pathogenesis of ischemic injury and heart failure

Apoptosis is "suicidal" programmed cell death followed by necrosis, i.e. cellular degradation. This review presents a critical evaluation of the methods used for detection of apoptosis and on data regarding the role of apoptosis in ischemia and heart failure.

METHODS

DNA laddering by electrophoresis and the TUNEL method in histology for the final stage of apoptosis, Annexin V labeling, evidence of caspase activation, cleavage of substrates, measurements of mitochondrial pro-apoptotic and anti-apoptotic factors (Bcl-2, Bax and others) and determination of the mitochondrial transitional pore potential. Much work has been carried out regarding the mechanism and the importance of apoptosis in ischemia and heart failure but many issues still remain unsolved: (1)Time needed for completion of apoptosis from stimulus to DNA fragmentation? (2)Importance of mitochondrial pathway considering the fact that cardiomyocytes contain the highest volume density of mitochondria of all mammalian cells (25% in humans, 37% in mice)? (3)Means of removal of dead cells, disconnection at the intercalated disc from neighbouring myocytes, time frame of this process? (4)Reversibility of apoptosis? (5)Differences between physiological (postnatal differentiation of the conduction system) v pathological apoptotic cell death? (6)Why do cells, under ischemic conditions, die by either apoptosis or oncosis? (7)Is apoptosis an epiphenomenon or a true cause of heart failure? (8)Quantification of the rate of apoptosis in different pathophysiological situations? Clarification of these unresolved issues will then allow an estimation of the importance of apoptosis in cardiac pathophysiology and, if necessary because the role of apoptosis has been established, the development of new therapeutic concepts.