Oxidative stress developed during open heart surgery induces apoptosis: reduction of apoptotic cell death by ebselen, a glutathione peroxidase mimic

A prospective cohort study of dynamic cell-free DNA elevation during cardiac surgery with cardiopulmonary bypass

Cardiac surgery and cardiopulmonary bypass (CPB) are associated with a systemic inflammatory reaction that occasionally induces a life-threatening organ dysfunction caused by the dysregulated host response to the damage-associated molecular patterns (DAMPs). In severe inflammation, cell-free DNA (cfDNA) and histones are released by inflammatory cells and damaged tissue and act as DAMPs. We sought to characterize the changes in circulating cell-free DNA (cfDNA) levels during CPB. Primary outcomes were renal failure, ventilation time (>18 hr), length of stay (LOS) in the intensive care unit (ICU) (>48hr), hospital LOS (>15 days), and death. We looked for associations with blood tests and comparison to standard scores. In a prospective cohort study, we enrolled 71 patients undergoing non-emergent coronary artery bypass grafting. Blood was drawn at baseline, 20 and 40 minutes on CPB, after cross-clamp removal, and 30 minutes after chest closure. cfDNA was measured by our fast fluorescent method. Baseline cfDNA levels [796 (656–1063) ng/ml] increased during surgery, peaked after cross-clamp removal [2403 (1981–3357) ng/ml] and returned to baseline at recovery. The difference in cfDNA from 20 to 40 minutes on CPB (ΔcfDNA 40–20) inversely correlated with peripheral vascular disease (PVD), longer ventilation time, and longer ICU and hospital length of stay (LOS). Receiver operating characteristic (ROC) curve of ΔcfDNA 40–20 for long ICU-LOS (>48hr) was with an area under the curve (AUC) of 0.738 (p = 0.022). ROC AUC of ΔcfDNA 40–20 to long Hospital LOS (>15 days) was 0.787 (p = 0.006). Correction for time on CPB in a multivariate logistic regression model improved ROC-AUC to 0.854 (p = 0.003) and suggests that ΔcfDNA 40–20 is an independent risk factor. To conclude, of measured parameters, including STS and Euroscore, the predictive power of ΔcfDNA 40–20 was the highest. Thus, measurement of ΔcfDNA 40–20 may enable early monitoring of patients at higher risk. Further studies on the mechanism behind the negative association of ΔcfDNA 40–20 with PVD and outcomes are warranted.

Mechanisms of ebselen as a therapeutic and its pharmacology applications

Ebselen is a synthetic organoselenium radical scavenger compound that possesses glutathione peroxidase-like activity and its own unique bioactivity by reacting with thiols, hydroperoxides and peroxynitrites. Owing to its high affinity toward several essential reactions, ebselen protects cellular components from oxidative and free radical damage, and it has been employed as a useful tool for studying redox-related mechanisms. Based on numerous in vitro and in vivo research, mechanisms are proposed to understand the biomedical and molecular actions of ebselen in health and disease, and it is currently under clinical trials for the prevention and treatment of various human disorders. Based on these outstanding discoveries, this review summarizes the current understanding of the biochemical and molecular characteristics, pharmacological applications and future directions of ebselen.

Ebselen rescues oxidative-stress-suppressed osteogenic differentiation of bone-marrow-derived mesenchymal stem cells via an antioxidant effect and the PI3K/Akt pathway

BACKGROUND

Patients with metabolic bone diseases often have high risk of titanium implant failure due to compromised bone regeneration ability. Clinical evidence indicates that the poor osteogenic ability is partly because of excessive oxidative stress. To date, specific treatments for these patients are urgently needed. Ebselen, a non-toxic organoselenium compound, is reported to be a potent antioxidant agent. In this study, we hypothesized that ebselen exerted protective effects on osteogenic differentiation of bone-marrow-derived mesenchymal stem cells (BMSCs) under oxidative stress.

METHODS

BMSCs were isolated from SD rats, and their morphology and multiple differentiation abilities were characterized. Proliferation rates of BMSCs treated with different concentrations of ebselen were analyzed. Then BMSCs were pretreated by hydrogen peroxide (H₂O₂), after which ebselen at different concentrations (0, 1, 5, 10 μM) was added, alkaline phosphatase (ALP) activity, mineralization and osteogenic-related protein levels were evaluated and an optimum concentration of ebselen was selected. Subsequently, intracellular reactive oxygen species (ROS) generation and the role of the PI3K/AKT pathway were also investigated.

RESULTS

Ebselen within a proper range could promote the proliferation of BMSCs. H₂O₂-induced oxidative stress suppressed osteogenic differentiation of BMSCs, which was verified by the decrease in ALP activity, calcium deposition, Runx2 and β-catenin expression. However, ebselen could alleviate osteogenic dysfunction of BMSCs. We also observed that ebselen reduced ROS accumulation in H₂O₂-pretreated BMSCs. Moreover, the pro-osteogenic effects afforded by ebselen were almost abolished by the Akt inhibitor.

CONCLUSION

We concluded that ebselen could attenuate osteogenic dysfunction of BMSCs induced by H₂O₂ through an antioxidant effect and the activation of the PI3K/Akt pathway, suggesting that ebselen has a potential therapeutic effect for patients with metabolic bone diseases.

Ebselen protects rat hearts against myocardial ischemia-reperfusion injury

Ebselen is an organoselenium compound that has demonstrated potent antioxidant and anti-inflammatory effects in previous studies. The present study was conducted to evaluate the effect of ebselen on myocardial ischemia-reperfusion (I/R) injury in a rat model and to elucidate the related mechanisms. Myocardial infarct size was assessed using triphenyltetrazolium chloride staining. Myocardial injury was evaluated according to the histopathological and ultrastructural alterations of rat hearts and the serum activity levels of cardiac enzymes, including creatine kinase (CK), CK-MB isoenzyme and lactate dehydrogenase (LDH). Cardiomyocyte apoptosis was detected using the terminal dUTP nick end-labelling (TUNEL) assay. In addition, the expression of apoptosis-associated proteins was measured using western blot analysis. In heart tissue specimens the activity of superoxide dismutase (SOD) and glutathione peroxidase (GPx), and levels of malondialdehyde (MDA) and protein carbonyl (PC) were also detected. The results indicated that ebselen reduced I/R-induced increase in myocardial infarct size and prevented the I/R-induced decreases in ejection fraction and fractional shortening. Further of note, ebselen improved I/R-induced rat heart injury. This was indicated by attenuation of histological and ultrastructural changes; reduction of serum CK, CK-MB and LDH activity levels; and decreased cell apoptosis on TUNEL staining, which was verified by decreased expression of cleaved (C)-Caspase-8, C-Caspase-3, B-cell lymphoma 2 (Bcl-2)-associated X protein and C-PARP, and increased expression of Bcl-2. Additionally, SOD and GPx activity levels were significantly higher, while MDA and PC levels were significantly lower in the ebselen + I/R group compared with in the I/R group. In conclusion, the present results suggested that ebselen serves an important role in protecting against myocardial I/R injury. The underlying mechanism may involve suppression of cardiomyocyte apoptosis and promotion of antioxidant activity.

Saffron (Crocus sativus) pretreatment confers cardioprotection against ischemia-reperfusion injuries in isolated rabbit heart

Restoration of blood flow to the ischemic myocardium is imperative to avoid demise of cardiomyocytes, but is paradoxically associated with irreversible damage to cardiac tissues due to the excessive generation of reactive oxygen species (ROS). We have previously reported that saffron, a natural antioxidant, attenuated ischemia-reperfusion (IR) injuries in vitro; however, its role in a meaningful cardiac recovery remains unknown. Here, we show that saffron supplement (oral administration for 6 weeks) reduced myocardial damage and restored cardiac function in an IR model of rabbit hearts. This was evidenced by improved left ventricle pressure, heart rate and coronary flow, and left ventricle end diastolic pressure (LVEDP) in IR hearts (isolated from rabbits pre-exposed to saffron (S/IR)). Electrophysiological recordings revealed a significant decline in both premature ventricle contraction and ventricle tachycardia/fibrillation in S/IR compared to IR hearts. This was paralleled by increased expression of the contractile proteins α-actinin and Troponin C in the myocardium of S/IR hearts. Histological examination combined to biochemical analysis indicated that hearts pre-exposed to saffron exhibited reduced infarct size, lower lipid peroxidation, with increased glutathione peroxidase activity, and oxidation of nitro blue tetrazolium (by reactive oxygen species). Furthermore, in contrast with IR hearts, saffron pretreatment induced restoration of the phosphorylation level of the survival proteins Akt and 4EBP1 and reduced activity of p38. Collectively, our data demonstrate that the natural antioxidant saffron plays a pivotal role in halting IR-associated cardiac injuries and emerges as a novel preventive tool for ischemic heart disease.

Histidine-tryptophan-ketoglutarate solution with added ebselen augments myocardial protection in neonatal porcine hearts undergoing ischemia/reperfusion

Whether modified histidine-tryptophan-ketoglutarate (HTK) solution offers myocardial protection to newborn heart has not been documented. The purpose of this study was to compare myocardial protection using HTK added by ebselen with HTK in a piglet model of cardiopulmonary bypass (CPB). Fifteen piglets were randomly assigned to three groups: the control group (C group, n = 5), HTK solution group (HTK group, n = 5), and HTK added by 10 nM ebselen group (HTK+E group, n = 5). Animals in the two experimental groups were placed on hypothermic CPB, after which the ascending aorta had been clamped for 2 h. The control animals underwent normothermic CPB without cardiac arrest. Myocardial antioxidant activities, myocytes apoptosis and mitochondrial structures, as well as the release of cytochrome c and the expression of Bax, Bcl-2, and HSP72 protein in myocardium were measured. Increased myocardial superoxide dismutase (SOD) and Mn-SOD activities, decreased TUNEL-positive cells, and reduced release of cytochrome c were noted in the HTK+E group compared with those in the HTK group (P = 0.021, P = 0.020, P = 0.045, and P = 0.010, respectively). The Bax/Bcl-2 ratio in the HTK group was significantly higher than that in the C group (P = 0.024). The expression of HSP72 protein and mRNA in the HTK+E group was higher than that in the HTK group (P = 0.039 and P = 0.035, respectively). Mitochondrial score under electron microscope in the HTK+E group was lower than that in the HTK group (P = 0.047). Improved antioxidant defense, reduced myocytes apoptosis, and better preserved mitochondrial structure were observed in the HTK+E group. Ebselen added to HTK provides better myocardioprotection to HTK solution for the neonatal heart.

Alpha lipoic acid attenuates inflammatory response during extracorporeal circulation

Aim

Extracorporeal circulation (ECC) of blood during cardiopulmonary surgery has been shown to stimulate various pro-inflammatory molecules such as cytokines and chemokines. The biochemical oxidation/reduction pathways of a-lipoic acid suggest that it may have antioxidant properties.

Methods

In this study we aimed to evaluate only patients with coronary heart disease and those planned for coronary artery bypass graft operation. Blood samples were obtained from the patients before the operation (P1) and one (P2), four (P3), 24 (P4) and 48 hours (P5) after administration of a-lipoic acid (LA). The patients were divided into two groups, control and LA treatment group. Levels of interleukin-6 (IL-6) and -8 (IL-8), complement 3 (C3) and 4 (C4), anti-streptolysin (ASO), C-reactive protein (CRP) and haptoglobin were assessed in the blood samples.

Results

Cytokine IL-6 and IL-8 levels were significantly higher after surgery. Compared with the control groups, LA significantly decreased IL-6 and IL-8 levels in a time-dependent manner. CRP levels did not show significant variation in the first three time periods. CRP levels were higher after surgery, especially in the later periods. These results demonstrate that CRP formation depends on cytokine release. C3 and C4 levels were significantly higher after surgery than in the pre-operative period. LA treatment decreased C3 and C4 levels. Therefore, LA administration may be useful for the treatment of diseases and processes where excessive cytokine release could cause oxidative damage.

Conclusions

Our findings suggest a possible benefit of using LA during cardiac surgery to reduce cytokine levels.

Role of NADPH oxidase isoforms NOX1, NOX2 and NOX4 in myocardial ischemia/reperfusion injury

Myocardial reperfusion injury is mediated by several processes including increase of reactive oxygen species (ROS). The aim of the study is to identify potential sources of ROS contributing to myocardial ischemia-reperfusion injury. For this purpose, we investigated myocardial ischemia/reperfusion pathology in mice deficient in various NADPH oxidase isoforms (Nox1, Nox2, Nox4, as well as Nox1/2 double knockout). Following 30min of ischemia and 24h of reperfusion, a significant decrease in the size of myocardial infarct was observed in Nox1-, Nox2- and Nox1/Nox2-, but not in Nox4-deficient mice. However, no protection was observed in a model of chronic ischemia, suggesting that NOX1 and NOX2-mediated oxidative damage occurs during reperfusion. Cardioprotective effect of Nox1 and Nox2 deficiencies was associated with decrease of neutrophil invasion, but, on the other hand an improved reperfusion injury was also observed in isolated perfused hearts (Langendorff model) suggesting that inflammatory cells were not the major source of oxidative damage. A decrease in global post-reperfusion oxidative stress was clearly detected in Nox2-, but not in Nox1-deficient hearts. Analysis of key signaling pathways during reperfusion suggests distinct cardioprotective patterns: increased phosphorylation was seen for Akt and Erk in Nox1-deficient mice and for Stat3 and Erk in Nox2-deficient mice. Consequently, NOX1 and NOX2 represent interesting drug targets for controlling reperfusion damage associated with revascularization in coronary disease.

An insight into the protection of rat liver against ischemia/reperfusion injury by 2-selenium-bridged beta-cyclodextrin

AIM

The reperfusion following liver ischemia results in the damage and apoptosis of hepatocytes. The aim of this study was to investigate the possible effects and mechanism of a new synthesized glutathione peroxidase (GPX) mimic, 2-selenium-bridged beta-cyclodextrin (2-SeCD), on rat liver ischemia-reperfusion (I/R) injury.

METHODS

Male Wistar rats (n = 32) were randomly divided into four groups: I. sham-operated group, II. I/R group, III. I/R +2-SeCD group, IV. I/R + Ebselen group. Hepatic I/R was administered by 90 min of ischemia and 12 h of reperfusion. Liver tissues were collected at the end of reperfusion period for measurement of various biochemical parameters.

RESULTS

The serum aspartate aminotransferase (AST), alanine aminotransferase (ALT) activity and tissue malondialdehyde, myeloperoxidase levels were increased in I/R group, while the increase was significantly reduced by 2-SeCD treatment. The glutathione level, depressed by I/R, was elevated back to normal levels by treatment with 2-SeCD. Severe hepatic damage were observed by light and transmission electron microscopy whilst pretreatment with 2-SeCD resulted in tissue and cellular preservation. Furthermore, 2-SeCD reduced cytochrome c release from mitochondria and subsequent DNA fragmentation by regulating Bcl-2/Bax expression ratio. RESULTS suggested that 2-SeCD was more effective than ebselen in the reversal of the alteration in tissue structural and biochemical parameters caused by I/R injury.

CONCLUSION

2-selenium-bridged beta-cyclodextrin playes an important role in the protection of liver against I/R injury and this treatment may be a novel pharmacological agent for liver surgery.

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.

RAGE modulates myocardial injury consequent to LAD infarction via impact on JNK and STAT signaling in a murine model

The receptor for advanced glycation end-products (RAGE) has been implicated in the pathogenesis of ischemia-reperfusion (I/R) injury in the isolated perfused heart. To test the hypothesis that RAGE-dependent mechanisms modulated responses to I/R in a murine model of transient occlusion and reperfusion of the left anterior descending coronary artery (LAD), we subjected male homozygous RAGE−/− mice and their wild-type age-matched littermates to 30 min of occlusion of the LAD followed by reperfusion. At 48 h of reperfusion, hematoxylin and eosin staining revealed significantly larger infarct size in wild-type versus RAGE−/− mice. Contractile function, as evaluated by echocardiography 48 h after reperfusion, revealed that fractional shortening was significantly higher in RAGE−/− versus wild-type mice. Plasma levels of creatine kinase were markedly decreased in RAGE−/− versus wild-type animals. Integral to the impact of RAGE deletion on diminished myocardial damage after infarction was significantly decreased apoptosis in the heart, as assessed by TUNEL staining, release of cytochrome c, and caspase-3 activity. Experiments investigating the impact of RAGE on early signaling pathways influencing myocardial ischemic injury revealed attenuation of JNK and STAT5 phosphorylation in RAGE−/− mouse hearts versus robust activation observed in wild-type mice upon ischemia and reperfusion. Solidifying the link to RAGE, these experiments revealed that infarction stimulated the rapid production of advanced glycation end-products in the heart. Thus, we tested the effect of ligand decoy soluble RAGE (sRAGE). Administration of sRAGE protected the myocardium from ischemic damage, similar to the effects observed in RAGE−/− mouse hearts. Taken together, these data implicate RAGE and its ligands in the pathogenesis of I/R injury and identify JNK and STAT signal transduction as central downstream effector pathways of the ligand-RAGE axis in the heart subjected to I/R injury.

Phosphoregulation of Signal Transduction Pathways in Ischemia and Reperfusion

Ischemia/reperfusion (I/R) injury triggered by pathogenic processes, such as organ transplant dysfunction, stroke, myocardial infarction, and shock, stimulate both immune and inflammatory pathways. Inflammatory cell activation and cytotoxic cytokine expression are associated with reperfusion injury. The activation of these inflammatory mediators initiates several interconnected downstream cascades regulated by phosphorylation and dephosphorylation reactions. These complex phosphorylation-dependent signal transduction pathways ultimately initiate nuclear transcription of inflammatory as well as anti-inflammatory genes to repair and assist in the recovery of damaged cells. Radical oxygen species (ROS) production, under ischemic conditions, initiates a cascade of events regulated by phosphorylation/dephosphorylation reactions and inflammatory gene expression. This is a review of the current understanding of the phosphoregulatory mechanisms that mediate the complex processes of signal transduction secondary to I/R injury. The rationale for inhibiting or activating signaling pathways as a promising molecular target for ameliorating reperfusion injury in I/R-related diseases, such as stroke, myocardial infarction, and storage for transplantation, is discussed on the basis of a new understanding of the mechanisms modulating phosphoregulatory pathways. In addition, we present part of our ongoing research in this field with phosphoregulatory signal transduction and its potential application.

Phytosphingosine in combination with ionizing radiation enhances apoptotic cell death in radiation-resistant cancer cells through ROS-dependent and -independent AIF release

The use of chemical modifiers as radiosensitizers in combination with low-dose irradiation may increase the therapeutic effect on cancer by overcoming a high apoptotic threshold. Here, we showed that phytosphingosine treatment in combination with γ-radiation enhanced apoptotic cell death of radiation-resistant human T-cell lymphoma in a caspase-independent manner. Combination treatment induced an increase in intracellular reactive oxygen species (ROS) level, mitochondrial relocalization of B-cell lymphoma-2(Bcl-2)-associated X protein (Bax), poly-adenosine diphosphate (ADP)-ribose polymerase 1 (PARP-1) activation, and nuclear translocation of apoptosis-inducing factor (AIF). siRNA targeting of AIF effectively protected cells from the combination treatment-induced cell death. An antioxidant, N-acetyl-L-cysteine (NAC), inhibited Bax relocalization and AIF translocation but not PARP-1 activation. Moreover, transfection of Bax-siRNA significantly inhibited AIF translocation. Pretreatment of PARP-1 inhibitor, DPQ (3,4-dihydro-5-[4-(1-piperidinyl)-butoxy]-1(2H)-isoquinolinone), or PARP-1-siRNA also partially attenuated AIF translocation, whereas the same treatment did not affect intracellular ROS level and Bax redistribution. Taken together, these results demonstrate that enhancement of cell death of radiation-resistant cancer cells by phytosphingosine treatment in combination with γ-radiation is mediated by nuclear translocation of AIF, which is in turn mediated both by ROS-dependent Bax relocalization and ROS-independent PARP-1 activation. The molecular signaling pathways that we elucidated in this study may provide potential drug targets for radiation sensitization of cancers refractive to radiation therapy. (Blood. 2005;105:1724-1733)

Attenuation of antioxidative capacity enhances reperfusion injury in aged rat myocardium after MI/R

Mortality due to ischemic cardiovascular diseases is significantly higher in elderly than in young adults. Myocardial ischemia-reperfusion (MI/R) can induce oxidative stress and an inflammatory response. We hypothesized that increased vulnerability of aged myocardium to reperfusion injury could be caused by decreased antioxidative capacity, rather than increased oxidant production, after MI/R. Aged (20-mo-old) and young (4-mo-old) male F344BN rats were subjected to 30 min of myocardial ischemia by ligation of the left main coronary artery followed by release of the ligature and 4 h of reperfusion. Four experimental groups were studied: young sham-operated rats, aged sham-operated rats, young rats subjected to MI/R, and aged rats subjected to MI/R. MI/R significantly increased infiltrated leukocyte number and myeloperoxidase (MPO) activity in perinecrotic areas of hearts of young rats compared with aged MI/R rats. These changes in infiltrated leukocyte number and MPO activity were associated with an increase in superoxide generation in perinecrotic areas from hearts of young rats compared with aged rats. Plasma levels of TNF-alpha and IL-1beta were significantly higher in young than in aged MI/R rats. However, plasma 8-hydroxy-2'-deoxyguanosine levels and creatine kinase activity were increased in aged compared with young MI/R rats. Increased reperfusion damage in aged rats was associated with a significant decrease in plasma ratio of GSH to GSSG. Our results suggest that enhanced ischemia-reperfusion injury in aged rat hearts may be related to reduced antioxidative capacity, rather than increased reactive oxygen species production. These findings contribute to a better understanding of effects of aging on oxidative stress and inflammatory responses of the heart after MI/R.

Myocardial apoptosis prevention by radical scavenging in patients undergoing cardiac surgery

BACKGROUND

Reactive oxygen-derived species, including those generated during myocardial ischemia and reperfusion induced by cardioplegia, have been suggested to be involved in myocardial apoptosis induction. The purpose of our study was to investigate (1) whether cardioplegic arrest initiates apoptosis in the hearts of cardiac surgery patients and (2) whether reactive oxygen-derived species scavenging with N-acetylcysteine attenuates myocardial apoptosis initiation.

METHODS

In transmural left ventricular biopsy samples collected before and at the end of cardiopulmonary bypass, we densitometrically determined cardiac myocyte staining intensity for active caspases-3 and -7, the apoptosis signal pathway central effector enzymes. The left ventricular biopsy samples had been obtained from 36 coronary artery bypass graft patients randomized in a double-blind fashion to receive either N-acetylcysteine (100 mg/kg into cardiopulmonary bypass prime followed by infusion at 20 mg.kg(-1).h(-1); n = 18) or placebo (n = 18).

RESULTS

The change in left ventricular cardiac myocyte staining (end of cardiopulmonary bypass minus before cardiopulmonary bypass) differed significantly between groups for both measures: caspase-3, -3.1 +/- 4.5 gray units (mean +/- SD; N-acetylcysteine group) versus 7.1 +/- 8.1 gray units (placebo); 95% confidence interval, 6.4 to 14.4; P <.0001; caspase-7, -5.1 +/- 6.1 gray units (N-acetylcysteine) versus 5.1 +/- 5.7 gray units (placebo); 95% confidence interval, 6.3 to 15.0; P <.0001. Clinical outcome did not differ between N-acetylcysteine and placebo.

CONCLUSIONS

Our data show that cardioplegic arrest initiates the apoptosis signal cascade in human left ventricular cardiac myocytes. This apoptosis induction can effectively be prevented by N-acetylcysteine.

Apoptosis and heart failure: mechanisms and therapeutic implications

A large volume of experimental data supports the presence of apoptosis in failing hearts. Apoptosis in many types of cells results from exposure to cytotoxic cytokines or damaging agents. Cytotoxic cytokines such as tumor necrosis factor (TNF)-alpha or Fas ligand (FasL) bind to their receptors to activate caspase-8, while damaging agents can cause mitochondrial release of cytochrome c, which can initiate activation of caspase-9. Caspase-8 or -9 can activate a cascade of caspases. The p53 protein is often required for damaging agent-induced apoptosis. An imbalance of proapoptotic factors versus prosurvival factors in the bcl-2 family precedes the activation of caspases. Given these typical changes of apoptosis found in many cell types, the apoptotic pathway in cardiomyocytes is somewhat unconventional since in vivo experimental data reveal that apoptosis does not appear to be controlled by TNF-alpha, FasL, p53 or decrease of bcl-2. In vitro and in vivo studies suggest the importance of mitochondria and activation of caspases in cell death occurring in failing hearts. Oxidants, excessive nitric oxide, angiotensin II and catecholamines have been shown to trigger apoptotic death of cardiomyocytes. Eliminating these inducers reduces apoptosis and reverses the loss of contractile function in many cases, indicating the feasibility of the pharmacological application of antioxidants, nitric oxide synthetase inhibitors, ACE inhibitors, angiotensin II receptor antagonists and adrenergic receptor antagonists. Most inducers of apoptosis initiate a cascade of signaling events, including activation of the p38 mitogen-activated protein kinase. Small molecule inhibitors of p38 have been shown to be capable of preventing apoptosis and loss of contractile function associated with ischemia and reperfusion. Although further experimental work is needed, several studies have already indicated the beneficial effect of caspase inhibitors against cell loss and features of heart failure in vitro and in vivo. These studies indicate the importance of inhibiting apoptosis in therapeutic interventions against heart failure.

The basic biology of apoptosis and its implications for cardiac function and viability

Apoptosis or programed cell death is a continuous process of destruction of nonfunctional cells. It is a physiologic process whereby the body disposes of unwanted cells by self-destruction and is our utmost defense against damaged cells. There are several pathways leading to programed cell death. Apoptosis is seen in failing, infarcted, and hibernating human hearts, and during open heart surgery. Apoptosis appears to be induced by myocardial ischemia-reperfusion injury and this is reduced by ischemic preconditioning. Antiapoptotic interventions may be a future target for myocardial protection.