Diazoxide triggers cardioprotection against apoptosis induced by oxidative stress

Diazoxide attenuates DOX-induced cardiotoxicity in cultured rat myocytes

Doxorubicin (DOX)-induced cardiotoxicity is a well known clinical problem, and many investigations have been made of its possible amelioration. We have investigated whether diazoxide (DIA), an agonist at mitochondrial ATP-sensitive potassium channels (mitoKATP), could reverse DOX-induced apoptotic myocardial cell loss, in cultured rat cardiomyocytes. The role of certain proteins in this pathway was also studied. The rat cardiomyocyte cell line (H9c2) was treated with DOX, and also co-treated with DOX and DIA, for 24 h. Distribution of actin filaments, mitochondrial membrane potential, superoxide dismutase (SOD) activity, total oxidant and antioxidant status (TOS and TAS, respectively), and some protein expressions, were assessed. DOX significantly decreased SOD activity, increased ERK1/2 protein levels, and depolarised the mitochondrial membrane, while DIA co-treatment inhibited such changes. DIA co-treatment ameliorated DOX-induced cytoskeletal changes via F-actin distribution and mitoKATP structure. Co-treatment also decreased ERK1/2 and cytochrome c protein levels. Cardiomyocyte loss due to oxidative stress-mediated apoptosis is a key event in DOX-induced cytotoxicity. DIA had protective effects on DOX-induced cardiotoxicity, via mitoKATP integrity, especially with elevated SUR2A levels; but also by a cascade including SOD/AMPK/ERK1/2. Therefore, DIA may be considered a candidate agent for protecting cardiomyocytes against DOX chemotherapy.

KATP channels are regulators of programmed cell death and targets for the creation of novel drugs against ischemia/reperfusion cardiac injury

BACKGROUND

The use of percutaneous coronary intervention (PCI) in patients with ST-segment elevation myocardial infarction (STEMI) is associated with a mortality rate of 5%-7%. It is clear that there is an urgent need to develop new drugs that can effectively prevent cardiac reperfusion injury. ATP-sensitive K+ (KATP ) channel openers (KCOs) can be classified as such drugs.

RESULTS

KCOs prevent irreversible ischemia and reperfusion injury of the heart. KATP channel opening promotes inhibition of apoptosis, necroptosis, pyroptosis, and stimulation of autophagy. KCOs prevent the development of cardiac adverse remodeling and improve cardiac contractility in reperfusion. KCOs exhibit antiarrhythmic properties and prevent the appearance of the no-reflow phenomenon in animals with coronary artery occlusion and reperfusion. Diabetes mellitus and a cholesterol-enriched diet abolish the cardioprotective effect of KCOs. Nicorandil, a KCO, attenuates major adverse cardiovascular event and the no-reflow phenomenon, reduces infarct size, and decreases the incidence of ventricular arrhythmias in patients with acute myocardial infarction.

CONCLUSION

The cardioprotective effect of KCOs is mediated by the opening of mitochondrial KATP (mitoKATP ) and sarcolemmal KATP (sarcKATP ) channels, triggered free radicals' production, and kinase activation.

The effect of adaptation to hypoxia on cardiac tolerance to ischemia/reperfusion

The acute myocardial infarction (AMI) and sudden cardiac death (SCD), both associated with acute cardiac ischemia, are one of the leading causes of adult death in economically developed countries. The development of new approaches for the treatment and prevention of AMI and SCD remains the highest priority for medicine. A study on the cardiovascular effects of chronic hypoxia (CH) may contribute to the development of these methods. Chronic hypoxia exerts both positive and adverse effects. The positive effects are the infarct-reducing, vasoprotective, and antiarrhythmic effects, which can lead to the improvement of cardiac contractility in reperfusion. The adverse effects are pulmonary hypertension and right ventricular hypertrophy. This review presents a comprehensive overview of how CH enhances cardiac tolerance to ischemia/reperfusion. It is an in-depth analysis of the published data on the underlying mechanisms, which can lead to future development of the cardioprotective effect of CH. A better understanding of the CH-activated protective signaling pathways may contribute to new therapeutic approaches in an increase of cardiac tolerance to ischemia/reperfusion.

Dexmedetomidine attenuates H2O2-induced neonatal rat cardiomyocytes apoptosis through mitochondria- and ER-medicated oxidative stress pathways

Dexmedetomidine (DEX), an α2 adrenoceptor agonist, has sedative and analgesic properties and myocardial protective effects. However, the mechanism underlying the protective effects of DEX on the myocardium remain unclear. The present study aimed to determine whether DEX serves an important role on cardioprotection through the endoplasmic reticulum (ER)- and mitochondria-mediated apoptosis signaling pathways. Neonatal rat cardiomyocytes (NRCMs) were cultured and divided four groups: i) Normal culture medium with 10% fetal bovine serum (control group); ii) H₂O₂ at 500 µM (H₂O₂ group); iii) DEX at 5 µM (DEX group); and iv) H₂O₂ plus DEX (H₂O₂ + DEX group). The levels of apoptosis and oxidative stress of NRCMs were investigated by ELISA, western blotting, flow cytometry and cell immunofluorescence. DEX significantly suppressed H₂O₂-induced apoptosis, and increased activity of caspases 3, 8 and 9 of NRCMs. DEX inhibited mitochondria-mediated oxidative stress and apoptosis, as evidenced by decreased levels of reactive oxygen species and lactic dehydrogenase, alleviated mitochondrial membrane potential depolarization, and increased Bcl-2-associated X protein/B-cell lymphoma 2 ratio. In addition, DEX decreased the activity of caspase 12, and the expression levels of glucose-regulated protein 78 kDa and serine/threonine-protein kinase/endoribonuclease IRE1, three major signaling molecules involved in the ER stress-mediated apoptosis pathway. Preventive treatment with DEX alleviates cardiomyocyte against H₂O₂-induced oxidative stress injury through attenuating the mitochondria- and ER-mediated apoptosis pathways.

Propofol attenuates H2O2-induced oxidative stress and apoptosis via the mitochondria- and ER-medicated pathways in neonatal rat cardiomyocytes

Previous studies have shown that propofol, an intravenous anesthetic commonly used in clinical practice, protects the myocardium from injury. Mitochondria- and endoplasmic reticulum (ER)-mediated oxidative stress and apoptosis are two important signaling pathways involved in myocardial injury and protection. The present study aimed to test the hypothesis that propofol could exert a cardio-protective effect via the above two pathways. Cultured neonatal rat cardiomyocytes were treated with culture medium (control group), H₂O₂ at 500 μM (H₂O₂ group), propofol at 50 μM (propofol group), and H₂O₂ plus propofol (H₂O₂ + propofol group), respectively. The oxidative stress, mitochondrial membrane potential (ΔΨm) and apoptosis of the cardiomyocytes were evaluated by a series of assays including ELISA, flow cytometry, immunofluorescence microscopy and Western blotting. Propofol significantly suppressed the H₂O₂-induced elevations in the activities of caspases 3, 8, 9 and 12, the ratio of Bax/Bcl-2, and cell apoptosis. Propofol also inhibited the H₂O₂-induced reactive oxygen species (ROS) generation, lactic dehydrogenase (LDH) release and mitochondrial transmembrane potential (ΔΨm) depolarization, and restored the H₂O₂-induced reductions of glutathione (GSH) and superoxide dismutase (SOD). In addition, propofol decreased the expressions of glucose-regulated protein 78 kDa (Grp78) and inositol-requiring enzyme 1α (IRE1α), two important signaling molecules in the ER-mediated apoptosis pathway. Propofol protects cardiomyocytes from H₂O₂-induced injury by inhibiting the mitochondria- and ER-mediated apoptosis signaling pathways.

Mitochondria-Targeted Antioxidants: Future Perspectives in Kidney Ischemia Reperfusion Injury

Kidney ischemia/reperfusion injury emerges in various clinical settings as a great problem complicating the course and outcome. Ischemia/reperfusion injury is still an unsolved puzzle with a great diversity of investigational approaches, putting the focus on oxidative stress and mitochondria. Mitochondria are both sources and targets of ROS. They participate in initiation and progression of kidney ischemia/reperfusion injury linking oxidative stress, inflammation, and cell death. The dependence of kidney proximal tubule cells on oxidative mitochondrial metabolism makes them particularly prone to harmful effects of mitochondrial damage. The administration of antioxidants has been used as a way to prevent and treat kidney ischemia/reperfusion injury for a long time. Recently a new method based on mitochondria-targeted antioxidants has become the focus of interest. Here we review the current status of results achieved in numerous studies investigating these novel compounds in ischemia/reperfusion injury which specifically target mitochondria such as MitoQ, Szeto-Schiller (SS) peptides (Bendavia), SkQ1 and SkQR1, and superoxide dismutase mimics. Based on the favorable results obtained in the studies that have examined myocardial ischemia/reperfusion injury, ongoing clinical trials investigate the efficacy of some novel therapeutics in preventing myocardial infarct. This also implies future strategies in preventing kidney ischemia/reperfusion injury.

The effect of mitochondrial ATP-sensitive potassium channels on apoptosis of chick embryo cecal cells by Eimeria tenella

The objective of this study was to investigate the effect of mitochondrial ATP-sensitive potassium (mitoKATP) channels on apoptosis induced by Eimeria tenella. At 24, 48, 72, 96 and 120 h after Eimeria tenella infection, TUNEL assays and translation of phosphatidyl serines to the host cell plasma membrane surface showed that diazoxide-treated chick embryo cecal cells underwent less apoptosis (P <0.05), while light microscopy showed that infection rates of treated cells were higher (P <0.01) than untreated cells. Caspase 9 and caspase 3 of infected cells were activated less (P <0.01) in diazoxide-treated cells than untreated cells. These results indicate that opening mitoKATP channels can protect chick embryo cecal cells from mitochondria-dependent apoptosis induced by Eimeria tenella by inhibiting activations of caspase 9 and caspase 3.

Diazoxide attenuates autoimmune encephalomyelitis and modulates lymphocyte proliferation and dendritic cell functionality

Activation of mitochondrial ATP-sensitive potassium (KATP) channels is postulated as an effective mechanism to confer cardio and neuroprotection, especially in situations associated to oxidative stress. Pharmacological activation of these channels inhibits glia-mediated neuroinflammation. In this way, diazoxide, an old-known mitochondrial KATP channel opener, has been proposed as an effective and safe treatment for different neurodegenerative diseases, demonstrating efficacy in different animal models, including the experimental autoimmune encephalomyelitis (EAE), an animal model for Multiple Sclerosis. Although neuroprotection and modulation of glial reactivity could alone explain the positive effects of diazoxide administration in EAE mice, little is known of its effects on the immune system and the autoimmune reaction that triggers the EAE pathology. The aim of the present work was to study the effects of diazoxide in autoimmune key processes related with EAE, such as antigen presentation and lymphocyte activation and proliferation. Results show that, although diazoxide treatment inhibited in vitro and ex-vivo lymphocyte proliferation from whole splenocytes it had no effect in isolated CD4(+) T cells. In any case, treatment had no impact in lymphocyte activation. Diazoxide can also slightly decrease CD83, CD80, CD86 and major histocompatibility complex class II expression in cultured dendritic cells, demonstrating a possible role in modulating antigen presentation. Taken together, our results indicate that diazoxide treatment attenuates autoimmune encephalomyelitis pathology without immunosuppressive effect.

Extracts from Astragalus membranaceus limit myocardial cell death and improve cardiac function in a rat model of myocardial ischemia

ETHNOPHARMACOLOGICAL RELEVANCE

The root of Astragalus membranaceus, known as "huang-qi", is one of the most widely used Chinese herbal medicines for the prevention and treatment of myocardial ischemic diseases. However, the mechanisms governing its therapeutic effects are largely unknown.

AIMS OF THE STUDY

The aims of the present study were to investigate the cardioprotective effect of the root extract of Astragalu membranaceus (EAM) in myocardial ischemia and to explore its underlying mechanisms in ROS-mediated signaling cascade in vivo and in vitro.

MATERIALS AND METHODS

The saponins in EAM were analyzed using HPLC. The tests for the cardioprotective effects of EAM and its mechanisms were performed in vivo and in vitro. In vivo, the rat model of persistent myocardial ischemia was produced by occlusion of the left anterior descending (LAD) coronary artery. In vitro, the cardiomyocyte model of oxidative stress was mimicked by the direct free radical donor, H2O2.

RESULTS

In vivo, the increased myocardial infarct size and the increased serum levels of lactate dehydrogenase (LDH), creatine kinase isoform MB (CK-MB), and cardiac troponin (cTnI) were significantly decreased by pre-treatment with EAM. Moreover, cardiac function, as assessed by±dP/dt, left ventricular developed pressure (LVDP), and left ventricular end-diastolic pressure (LVEDP), was dramatically improved. An oxidative stress biomarker, malondialdehyde (MDA), was reduced, and the antioxidant enzyme superoxide dismutase (SOD) was induced. In vitro, H2O2-triggered myocardial cell death and cytoplasm Ca(2+) overload were blocked by treatment with EAM. Furthermore, the KATP channel blocker (5-HD, glibenclamide) blocked the anti-apoptotic protective effect of EAM on cardiomyocytes injured by H2O2.

CONCLUSIONS

The cardioprotection of EAM was manifested as a protection of tissue structure and as a decrease in serum markers of ischemic injury. The mechanisms underlying the EAM-mediated protective effects may involve improving cardiac function, attenuating the oxidative injury via a decrease in MDA, a maintenance in SOD, and a reduction in free radical-induced myocardial cell injury. Additionally, EAM enhanced the myocardial cell viability via arresting the influx of Ca(2+) to block cell death and opening mitochondrial KATP channels to reduce cell apoptosis.

Skeletal muscle post-conditioning by diazoxide, anti-oxidative and anti-apoptotic mechanisms

Pretreatment with diazoxide, K(ATP) channel opener, increases tissue tolerance against ischemia reperfusion (IR) injury. In clinical settings pretreatment is rarely an option therefore we evaluated the effect of post-ischemic treatment with diazoxide on skeletal muscle IR injury. Rats were treated with either saline, diazoxide (K(ATP) opener; 40 mg/kg) or 5-hydroxydecanoate (5-HD; mitochondrial K(ATP) inhibitor; 40 mg/kg) after skeletal muscle ischemia (3 h) and reperfusion (6, 24 or 48 h). Tissue contents of malondialdehyde (MDA), superoxide dismutase (SOD) and catalase (CAT) activities, Bax and Bcl-2 protein expression and muscle histology were determined. Apoptosis was examined (24 and 48 h) after ischemia. IR induced severe histological damage, increased MDA content and Bax expression (24 and 48 h; p < 0.01) and decreased CAT and SOD activities (6 and 24 h, p < 0.01 and 48 h, p < 0.05), with no significant effect on Bcl-2 expression. Diazoxide reversed IR effects on MDA (6 and 24 h; p < 0.05), SOD (6 and 24 h; p < 0.01) and CAT (6 and 48 h, p < 0.05 and 24 h p < 0.01) and tissue damage. Diazoxide also decreased Bax (24 and 48 h; p < 0.05) and increased Bcl-2 protein expression (24 and 48 h; p < 0.01). Post-ischemic treatment with 5-HD had no significant effect on IR injury. Number of apoptotic nuclei in IR and 5-HD treated groups significantly increased (p < 0.001) while diazoxide decreased apoptosis (p < 0.01). The results suggested that post-ischemic treatment with diazoxide decrease oxidative stress in acute phase which modulates expression of apoptotic proteins in the late phase of reperfusion injury. Involvement of KATP channels in this effect require further evaluations.

Inhibitors of succinate: quinone reductase/Complex II regulate production of mitochondrial reactive oxygen species and protect normal cells from ischemic damage but induce specific cancer cell death

Succinate:quinone reductase (SQR) of Complex II occupies a unique central point in the mitochondrial respiratory system as a major source of electrons driving reactive oxygen species (ROS) production. It is an ideal pharmaceutical target for modulating ROS levels in normal cells to prevent oxidative stress-induced damage or alternatively,increase ROS in cancer cells, inducing cell death.The value of drugs like diazoxide to prevent ROS production,protecting normal cells, whereas vitamin E analogues promote ROS in cancer cells to kill them is highlighted. As pharmaceuticals these agents may prevent degenerative disease and their modes of action are presently being fully explored. The evidence that SDH/Complex II is tightly coupled to the NADH/NAD+ ratio in all cells,impacted by the available supplies of Krebs cycle intermediates as essential NAD-linked substrates, and the NAD+-dependent regulation of SDH/Complex II are reviewed, as are links to the NAD+-dependent dehydrogenases, Complex I and the E3 dihiydrolipoamide dehydrogenase to produce ROS. This review collates and discusses diverse sources of information relating to ROS production in different biological systems, focussing on evidence for SQR as the main source of ROS production in mitochondria, particularly its relevance to protection from oxidative stress and to the mitochondrial-targeted anti cancer drugs (mitocans) as novel cancer therapies [corrected].

Heat shock protein 90 mediates anti-apoptotic effect of diazoxide by preventing the cleavage of Bid in hypothermic preservation rat hearts

BACKGROUND

Successful organ preservation is the premise for clinical organ transplantation. The present study investigated whether heat shock protein 90 (Hsp90) is important in the anti-apoptotic effect of diazoxide in hypothermic preservation rat hearts.

METHODS

Isolated rat hearts were preserved in Celsior solution, with or without diazoxide, for 3 to 9 hours, followed by 60 minutes of reperfusion. Cell apoptosis was assessed by terminal deoxynucleotide transferase-mediated deoxy uridine triphosphate nick-end labeling. The left ventricular developed pressure (LVDP) was recorded. Expression of Hsp90 protein and cleavage of Bid were detected by Western blot and polymerase chain reaction.

RESULTS

After hypothermic preservation for 3 to 9 hours, the LVDP recovery rate significantly decreased and cardiomyocyte apoptosis index increased in a time-dependent manner. When compared with the 9-hour preservation group, Celsior solution supplemented with diazoxide significantly enhanced the LVDP recovery rate and decreased the apoptosis index. The cleavage of Bid increased after 9 hours of hypothermic preservation, which was inhibited by Celsior solution supplemented with diazoxide. Hypothermic preservation of rat hearts for 9 hours decreased the expression of Hsp90, whereas diazoxide supplementation significantly increased the expression of Hsp90. The Hsp90 inhibitor 17-allylamino-17-demethoxy-geldanamycin inhibited the diazoxide-induced decrease in cleavage of Bid, improvement of cardiac function, and decrease of apoptosis. Hsp90 inhibitor had no effect on the diazoxide-induced increase of total Cx43 protein expression in hearts preserved 9 hours, but inhibited the diazoxide-induced increase of mitochondrial Cx43 protein level.

CONCLUSION

Hsp90 might mediate diazoxide-induced cardioprotection against apoptosis in hypothermic preservation heart by preventing the cleavage of Bid.

Noninvasive delayed limb ischemic preconditioning attenuates myocardial ischemia-reperfusion injury in rats by a mitochondrial K(ATP) channel-dependent mechanism

We previously demonstrated in rats that noninvasive delayed limb ischemic preconditioning (LIPC) induced by three cycles of 5-min occlusion and 5-min reperfusion of the left hind limb per day for three days confers the same cardioprotective effect as local ischemic preconditioning of the heart, but the mechanism has not been studied in depth. The aim of this project was to test the hypothesis that delayed LIPC enhances myocardial antioxidative ability during ischemia-reperfusion by a mitochondrial K(ATP) channel (mito K(ATP))-dependent mechanism. Rats were randomized to five groups: ischemia-reperfusion (IR)-control group, myocardial ischemic preconditioning (MIPC) group, LIPC group, IR-5HD group and LIPC-5HD group. The MIPC group underwent local ischemic preconditioning induced by three cycles of 5-min occlusion and 5-min reperfusion of the left anterior descending coronary arteries. The LIPC and LIPC-5HD groups underwent LIPC induced by three cycles of 5-min occlusion and 5-min reperfusion of the left hind limb using a modified blood pressure aerocyst per day for three days. All rats were subjected to myocardial ischemia-reperfusion injury. The IR-5HD and LIPC-5HD groups received the mito K(ATP) channel blocker 5-hydroxydecanoate Na (5-HD) before and during the myocardial ischemia-reperfusion injury. Compared with the IR-control group, both the LIPC and MIPC groups showed an amelioration of ventricular arrhythmia, reduced myocardial infarct size, increased activities of total superoxide dismutase, manganese-superoxide dismutase (Mn-SOD) and glutathione peroxidase, increased expression of Mn-SOD mRNA and decreased xanthine oxidase activity and malondialdehyde concentration. These beneficial effects of LIPC were prevented by 5-HD. In conclusion, delayed LIPC offers similar cardioprotection as local IPC. These results support the hypothesis that the activation of mito K(ATP) channels enhances myocardial antioxidative ability during ischemia-reperfusion, thereby contributing, at least in part, to the anti-arrhythmic and anti-infarct effects of delayed LIPC.

Single channel studies of the ATP-regulated potassium channel in brain mitochondria

Mitochondrial potassium channels in the brain have been suggested to have an important role in neuroprotection. The single channel activity of mitochondrial potassium channels was measured after reconstitution of the purified inner membrane from rat brain mitochondria into a planar lipid bilayer. In addition to a large conductance potassium channel that was described previously, we identified a potassium channel that has a mean conductance of 219 +/- 15 pS. The activity of this channel was inhibited by ATP/Mg(2+) and activated by the potassium channel opener BMS191095. Channel activity was not influenced either by 5-hydroxydecanoic acid, an inhibitor of mitochondrial ATP-regulated potassium channels, or by the plasma membrane ATP-regulated potassium channel blocker HMR1098. Likewise, this mitochondrial potassium channel was unaffected by the large conductance potassium channel inhibitor iberiotoxin or by the voltage-dependent potassium channel inhibitor margatoxin. The amplitude of the conductance was lowered by magnesium ions, but the opening ability was unaffected. Immunological studies identified the Kir6.1 channel subunit in the inner membrane from rat brain mitochondria. Taken together, our results demonstrate for the first time the single channel activity and properties of an ATP-regulated potassium channel from rat brain mitochondria.

17 beta-estradiol modulates expression of low-voltage-activated Ca(V)3.2 T-type calcium channel via extracellularly regulated kinase pathway in cardiomyocytes

T-type Ca(2+) channel current (I(Ca,T)) plays an important role for spontaneous pacemaker activity and is involved in the progression of structural heart diseases. Estrogens are of importance for the regulation of growth and differentiation and function in a wide array of target tissues, including those in the cardiovascular system. The aim of this study was to elucidate the short-term and long-term effects of 17beta-estradiol (E(2)) on I(Ca,T) in cardiomyocytes. We employed in vivo and in vitro techniques to clarify E(2)-mediated modulation of heart rate (HR) in ovariectomized rats and I(Ca,T) in cardiomyocytes. Ovariectomy increased HR and E(2) supplement reduced HR in ovariectomized rats. Slowing of E(2)-induced HR was consistent with the deceleration of automaticity in E(2)-treated neonatal cardiomyocytes. Short-term application of E(2) did not have significant effects on I(Ca,T), whereas in cardiomyocytes treated with 10 nm E(2) for 24 h, estrogen receptor-independent down-regulation of peak I(Ca,T) and declination of Ca(V)3.2 mRNA were observed. Expression of a cardiac-specific transcription factor Csx/Nkx2.5 was also suppressed by E(2) treatment for 24 h. On the other hand, expression of Ca(V)3.1 mRNA was unaltered by E(2) treatment in this study. An ERK-1/2, 5 inhibitor, PD-98059, abolished the effects of E(2) on I(Ca,T) and Ca(V)3.2 mRNA as well as Csx/Nkx2.5 mRNA. These findings indicate that E(2) decreases Ca(V)3.2 I(Ca,T) through activation of ERK-1/2, 5, which is mediated by the suppression of Csx/Nkx2.5-dependent transcription, suggesting a genomic effect of E(2) as a negative chronotropic factor in the heart.

Diazoxide-mediated growth inhibition in human lung cancer cells via downregulation of beta-catenin-mediated cyclin D1 transcription

Treatment of various types of cells with the mitochondrial ATP-sensitive K(+) channel opener, diazoxide, preconditions cells to subsequent injuries and inhibits apoptosis. However, the role and mechanism(s) of diazoxide in solid tumor cell growth are largely unknown. Here we demonstrate that diazoxide inhibited the proliferation of lung cancer cells as well as the transcription of cell cycle-related protein Cyclin D1. Cyclin D1 overexpression inhibited the negative role of diazoxide in cell cycle progression. We further explored the mechanisms by which diazoxide affected Cyclin D1 transcription and found that the beta-catenin transcription factor was downregulated by diazoxide, with a corresponding decrease in Cyclin D1 promoter activity. Taken together, these results suggest that diazoxide inhibits lung cancer cell proliferation via downregulation of Cyclin D1 transcription, which may have important therapeutic implications in lung cancer patients.

Role of sarcolemmal ATP-sensitive potassium channel in oxidative stress-induced apoptosis: mitochondrial connection

From time of their discovery, sarcolemmal ATP-sensitive K+ (sarcK ATP) channels were thought to have an important protective role in the heart during stress whereby channel opening protects the heart from stress-induced Ca2+ overload and resulting damage. In contrast, some recent studies indicate that sarcK ATP channel closing can lead to cardiac protection. Also, the role of the sarcK ATP channel in apoptotic cell death is unclear. In the present study, the effects of channel inhibition on apoptosis and the specific interaction between the sarcK ATP channel and mitochondria were investigated. Apoptotic cell death of cultured HL-1 and neonatal cardiomyocytes following exposure to oxidative stress was significantly increased in the presence of sarcK ATP channel inhibitor HMR-1098 as evidenced by terminal deoxynucleotidyltransferase-mediated dUTP nick end labeling and caspase-3,7 assays. This was paralleled by an increased release of cytochrome c from mitochondria to cytosol, suggesting activation of the mitochondrial death pathway. sarcK ATP channel inhibition during stress had no effect on Bcl-2, Bad, and phospho-Bad, indicating that the increase in apoptosis cannot be attributed to these modulators of the apoptotic pathway. However, monitoring of mitochondrial Ca2+ with rhod-2 fluorescent indicator revealed that mitochondrial Ca2+ accumulation during stress is potentiated in the presence of HMR-1098. In conclusion, this study provides novel evidence that opening of sarcK ATP channels, through a specific Ca2+-related interaction with mitochondria, plays an important role in preventing cardiomyocyte apoptosis and mitochondrial damage during stress.

Amelioration of oxidative mitochondrial DNA damage and deletion after renal ischemic injury by the KATP channel opener diazoxide

Renal ischemia was induced in the rat by constriction of the renal artery for 45 min, and the ability of the ATP-sensitive K(+) (K(ATP)) channel opener diazoxide (DZ) to ameliorate renal ischemia-reperfusion (I/R) injury was evaluated. In this model, blood urea nitrogen and creatinine were elevated 2 days after I/R injury but returned closer to normal levels by 7 days after reperfusion. Histological staining for reactive oxygen species (ROS) was clearly positive and oxidized DNA, detected by the presence of the stable adduct 8-hydroxy-2'-deoxyguanosine, was clearly present in the cytoplasm of tubular cells after 1 h of reperfusion and declined 7 days after reperfusion. This finding was confirmed by ELISA, which detected 8-hydroxy-2'-deoxyguanosine in the mitochondrial fraction of kidney homogenates. Despite evidence of improved function measured by blood urea nitrogen and creatinine 7 days after reperfusion, the early changes in tubules were alarming. Mitochondrial DNA showed the common deletion, and the number of TdT-mediated dUTP nick-end label-positive tubular cells increased. Activation of caspase-3 continued, and abnormal levels of ROS were found in the mitochondrial fraction of cellular homogenates. Treatment with DZ before ischemia reduced or prevented the acute and subacute deleterious effects associated with renal I/R injury. We conclude that excess production of ROS by mitochondria on reperfusion is a major upstream event in renal reperfusion injury and that DZ functioned by preventing ROS accumulation in the mitochondria after I/R injury, thereby reducing oxidative stress as measured by the presence of oxidized mitochondrial DNA and features of apoptosis.

Plasma concentration of Fas/Fas ligand and left ventricular function in response to metoprolol in conjunction with standard treatment

Recent studies suggest that cardiac myocyte apoptosis contributes to the progress of CHF (congestive heart failure). In the present study, we tested the hypothesis that metoprolol in conjunction with the standard treatment regime for CHF [an ACE (angiotensin-converting enzyme) inhibitor, diuretics and digoxin] may significantly reduce the plasma concentrations of the apoptotic mediators sFas (soluble Fas) and sFasL (soluble Fas ligand) in patients with CHF. An ELISA was used to determine the plasma concentrations of sFas and sFasL in 106 patients with stable CHF at recruitment. Echocardiography was performed at baseline and after 1 year of treatment with metoprolol in conjunction with the standard treatment regime for CHF (i.e. an ACE inhibitor, diuretics and digoxin). The dose of metoprolol was doubled on a biweekly basis up to 50 mg twice a day or maintained at the maximum tolerated dose. Data after 1 year were available for 92 patients and were analysed. The plasma concentrations of sFas and sFasL in patients with CHF decreased significantly (P<0.01) after 1 year of treatment with metoprolol in conjunction with the standard treatment regime compared with at baseline (5.4±0.2 compared with 3.2±0.1 ng/ml respectively for sFas, and 52.1±2.3 compared with 26.7±1.0 pg/ml respectively for sFasL). Compared with baseline, after 1 year of treatment with metoprolol in conjunction with the standard treatment regime there were significant improvements in LV (left ventricular) ejection fraction (from 32.6±0.9 to 51.5±0.8%; P<0.01), LV end-diastolic dimension (from 69.8±0.6 to 57.7±0.3 mm; P<0.01), LV end-systolic dimension (from 53.9±0.6 to 40.5±0.5 mm; P<0.01), LV end-diastolic volume (from 254.7±5.0 to 164.1±2.2 ml; P<0.01) and LV end-systolic volume (from 142.0±4.2 to 72.2±2.0 ml; P<0.01). In addition, the distance walked in a 6-min walk test increased markedly (P<0.01) from 260.3±5.2 m at baseline to 440.9±5.7 m after 1 year of treatment. In conclusion, we have demonstrated that metoprolol in conjunction with an ACE inhibitor, diuretics and digoxin in patients with CHF can lead to a reverse in LV remodelling potentially through its anti-apoptotic effects.

Diazoxide-induced cardioprotection via ΔΨm loss depending on timing of application

Although the role of mitochondrial ATP-sensitive potassium (mitoKATP) channels in cardioprotection is widely accepted, it remains unclear when their opening is critical for protection. We tested the hypothesis that the mitoKATP channel acts as a trigger or mediator of protection against apoptosis through loss of mitochondrial inner membrane potential (DeltaPsim). Exposure of neonatal rat cardiomyocytes to H2O2 (0.5 mmol/L) resulted in apoptosis associated with severe DeltaPsim loss. Pretreatment with diazoxide (20 to 100 micromol/L) prevented H2O2-induced apoptosis and DeltaPsim loss at 2 but not 18 h after exposure, while the latter was prevented by cotreatment with diazoxide. Lack of protection by pretreatment with diazoxide was observed in cardiomyocytes cultured in a medium containing H2O2 for 2 h and then not containing for 16 h. The slopes of the regression lines of the relationship between the proportion of apoptotic cells and DeltaPsim loss (y = -0.89 vs. -0.42) and the proportion of cells with high side scatter signal differed between cardiomyocytes exposed H2O2 for 2 and 18 h. Diazoxide per se caused a transient DeltaPsim loss (within 30 min) with a recovery followed by persistent DeltaPsim loss (after 6 h). Inhibition of the former by 5-hydroxydecanoate (5-HD, 0.5 mmol/L) abolished protection of pretreatment with diazoxide (trigger phase), while that of the latter prevented the protection of cotreatment with diazoxide (mediator phase). Our results suggest that mitoKATP channels act as a trigger and mediator of cardioprotection through a transient or persistent DeltaPsim loss depending on phenotypic consequence in response to oxidants.

The mitochondrial K-ATP channel opener, diazoxide, prevents ischemia-reperfusion injury in the rabbit spinal cord

Paraplegia resulting from ischemia is a catastrophic complication of thoracoabdominal aortic surgery. The current study was designed to investigate the effects of diazoxide (DZ) on mitochondrial structure, neurological function, DNA damage-repair, and apoptosis in spinal cord ischemia-reperfusion injury. Rabbits were subjected to 30 minutes of spinal cord ischemia and reperfusion (1 hour) with or without diazoxide (n = 6 in each group) by clamping and releasing the infrarenal aorta. The neurological functional score was significantly improved in the DZ-treated ischemia-reperfusion injury group. Electron microscopic studies demonstrated that mitochondrial damage in the spinal cord after injury was significantly reduced by DZ. Mitochondrial superoxide and hydrogen peroxide levels were also markedly decreased in the DZ-treated injury group compared with the untreated group. DZ decreased levels of the oxidative DNA damage product 8-oxoG and increased levels of the DNA repair enzyme OGG-1. Furthermore, DZ inhibited apoptosis via caspase-dependent and -independent pathways. These studies indicate for the first time that the mitochondrial K-ATP channel opener diazoxide improves neurological function after spinal cord ischemia and reperfusion by diminishing levels of reactive oxygen species, decreasing DNA oxidative damage, and inhibiting caspase-dependent and -independent apoptotic pathways while preserving mitochondrial structure.

Mitochondrial potassium channels: from pharmacology to function

Mitochondrial potassium channels, such as ATP-regulated or large conductance Ca2+ -activated and voltage gated channels were implicated in cytoprotective phenomenon in different tissues. Basic effects of these channels activity include changes in mitochondrial matrix volume, mitochondrial respiration and membrane potential, and generation of reactive oxygen species. In this paper, we describe the pharmacological properties of mitochondrial potassium channels and their modulation by channel inhibitors and potassium channel openers. We also discuss potential side effects of these substances.

Nitric oxide-cGMP-protein kinase G signaling pathway induces anoxic preconditioning through activation of ATP-sensitive K+ channels in rat hearts

Nitric oxide (NO) plays an important role in anoxic preconditioning to protect the heart against ischemia-reperfusion injuries. The present work was performed to study better the NO-cGMP-protein kinase G (PKG) signaling pathway in the activation of both sarcolemmal and mitochondrial ATP-sensitive K+ (KATP) channels during anoxic preconditioning (APC) and final influence on reducing anoxia-reperfusion (A/R)-induced cardiac damage in rat hearts. The upstream regulating elements controlling NO-cGMP-PKG signal-induced KATP channel opening that leads to cardioprotection were investigated. The involvement of both inducible and endothelial NO synthases (iNOS and eNOS) in the progression of this signaling pathway was followed. Final cellular outcomes of ischemia-induced injury after different preconditioning in the form of lactate dehydrogenase release, DNA strand breaks, and malondialdehyde formation as indexes of cell injury and lipid peroxidation, respectively, were investigated. The lactate dehydrogenase and malondialdehyde values decreased in the groups that underwent preconditioning periods with specific mitochondrial KATP channels opener diazoxide (100 microM), nonspecific mitochondrial KATP channels opener pinacidil (50 microM), S-nitroso-N-acetylpenicillamine (SNAP, 300 microM), or beta-phenyl-1,N2-etheno-8-bromoguanosine-3',5'-cyclicmonophosphorothioate, Sp-isomer (10 microM) before the A/R period. Preconditioning with SNAP significantly reduced the DNA damage. The effect was blocked by glibenclamide (50 microM), 5-hydroxydecanoate (100 microM), NG-nitro-L-arginine methyl ester (200 microM), and beta-phenyl-1,N2-etheno-8-bromoguanosine-3',5'-cyclic monophosphorothioate, Rp-isomer (1 microM). The results suggest iNOS, rather than eNOS, as the major contributing NO synthase during APC treatment. Moreover, the PKG shows priority over NO as the upstream regulator of NO-cGMP-PKG signal-induced KATP channel opening that leads to cardioprotection during APC treatment.

Subunit composition of ATP-sensitive potassium channels in mitochondria of rat hearts

Mitochondrial ATP-sensitive potassium (mitoKATP) channels play a pivotal role in early and late ischemic preconditioning, but the subunit composition of mitoKATP channels remains unclear. In this study, we investigated the subunit composition of mitoKATP channels in rat hearts using confocal microscopy, immunofluorescence, and Western blot analysis. The green fluorescent probe glibenclamide-BODIPY was colocalized with the red fluorescent mitochondrial marker MitroTracker Red in isolated ventricular myocytes and in ventricular myocyte mitochondria, indicating the presence of sulfonylurea receptors (SURs) in the mitochondria. Anti-Kir6.1, anti-Kir6.2, and anti-SUR2 immunofluorescence was colocalized with that of MitoTracker Red in isolated mitochondria, suggesting that Kir6.1, Kir6.2, and SUR2 subunits are present in the mitochondria. Similarly, Kir6.1 (approximately 46 kDa), Kir6.2 (approximately 46 and approximately 40 kDa), and SUR2 (approximately 140 kDa) proteins were found to be expressed in mitochondria using Western blot analysis. By contrast, SUR1 was not present in mitochondria. These results suggest that mitoKATP channels in rat hearts might comprise a combination of Kir6.1, Kir6.2, and SUR2 subunits.

Responses in extracellular and intracellular calcium and magnesium in aldosteronism

We hypothesized the hypercalciuria and hypermagnesuria that accompany aldosteronism could be pharmacologically attenuated to prevent shifts in extracellular and intracellular levels of these divalent cations and the adverse outcomes associated with them. Accordingly, rats administered aldosterone/salt treatment (ALDOST) were cotreated with either hydrochlorothiazide (Hctz), to selectively reabsorb urinary Ca2+, or with Hctz plus spironolactone (Hctz+Spi), where Spi retards the excretion of these cations in both urine and feces. We monitored urinary excretion and responses in extracellular and intracellular Ca2+ and Mg2+, together with indices of oxi/nitrosative stress in plasma and ventricular tissue. At 4 weeks ALDOST we found the following: (1) hypercalciuria was reduced by Hctz and normalized by Hctz+Spi, and this combination, unlike Hctz alone, also rescued hypermagnesuria; (2) the decrease in plasma-ionized [Ca2+]o was not seen with Hctz or Hctz+Spi, whereas Spi cotreatment protected against a decline in [Mg2+]o; (3) the Ca2+ loading of peripheral blood mononuclear cells and cardiac tissue was not seen with Hctz+Spi; and (4) the induction of oxi/nitrosative stress, expressed as reduced plasma alpha1-antiproteinase activity and activation of gp91(phox) subunit of NADPH oxidase in inflammatory cells invading intramural coronary arteries of the right and left ventricles, together with vascular fibrosis, was completely prevented by Spi cotreatment. In rats with aldosteronism, cotreatment with Hctz+Spi more effectively (vis-à-vis Hctz alone) protects against adverse iterations in extracellular and intracellular concentrations of Ca2+ and Mg2+, as well as the appearance of oxi/nitrosative stress to prevent the proinflammatory vascular phenotype.

Apoptosis and oncosis in acute coronary syndromes: assessment and implications

The rational design of therapeutic interventions for protection of ischemic myocardium from ultimate death requires an understanding of the mechanistic basis of cardiomyocyte (CM) cell death, its timing and the tools for its quantification. Until recently, CM cell death following ischemia and/or reperfusion was considered to involve necrosis or 'accidental cell death' from very early on. Collective evidence over the past decade indicates that early CM cell death after myocardial ischemia and post-ischemic reperfusion involves apoptosis with cell shrinkage and drop-out, and/or oncosis with cell swelling followed by necrosis. This paradigm shift suggests that different approaches for cardioprotection are required. Oncologists, pathologists, anatomists and basic scientists who have studied apoptosis over the last three decades separated physiological apoptosis from inappropriate apoptosis in pathological states. Until recently, cardiologists resisted the concepts of CM apoptosis and regeneration. Cumulative evidence indicating that apoptosis in the heart may occur in different cell types, spread from one cell type to another, and occur in bursts, may have profound implications for therapies aimed at protection of ischemic myocardium by targeting CM apoptosis in acute coronary syndromes. This review focuses on a critique of the methods used for the assessment of CM apoptosis and the implications of CM apoptosis in acute coronary syndromes.

mitoKATP channel activation in the postanoxic developing heart protects E-C coupling via NO-, ROS-, and PKC-dependent pathways

Whereas previous studies have shown that opening of the mitochondrial ATP-sensitive K+ (mitoKATP) channel protects the adult heart against ischemia-reperfusion injury, it remains to be established whether this mechanism also operates in the developing heart. Isolated spontaneously beating hearts from 4-day-old chick embryos were subjected to 30 min of anoxia followed by 60 min of reoxygenation. The chrono-, dromo-, and inotropic disturbances, as well as alterations of the electromechanical delay (EMD), reflecting excitation-contraction (E-C) coupling, were investigated. Production of reactive oxygen species (ROS) in the ventricle was determined using the intracellular fluorescent probe 2′,7′-dichlorofluorescin (DCFH). Effects of the specific mitoKATP channel opener diazoxide (Diazo, 50 μM) or the blocker 5-hydroxydecanoate (5-HD, 500 μM), the nitric oxide synthase (NOS) inhibitor NG-nitro-l-arginine methyl ester (l-NAME, 50 μM), the antioxidant N-(2-mercaptopropionyl)glycine (MPG, 1 mM), and the PKC inhibitor chelerythrine (Chel, 5 μM) on oxidative stress and postanoxic functional recovery were determined. Under normoxia, the baseline parameters were not altered by any of these pharmacological agents, alone or in combination. During the first 20 min of postanoxic reoxygenation, Diazo doubled the peak of ROS production and, interestingly, accelerated recovery of ventricular EMD and the PR interval. Diazo-induced ROS production was suppressed by 5-HD, MPG, or l-NAME, but not by Chel. Protection of ventricular EMD by Diazo was abolished by 5-HD, MPG, l-NAME, or Chel, whereas protection of the PR interval was abolished by l-NAME exclusively. Thus pharmacological opening of the mitoKATP channel selectively improves postanoxic recovery of cell-to-cell communication and ventricular E-C coupling. Although the NO-, ROS-, and PKC-dependent pathways also seem to be involved in this cardioprotection, their interrelation in the developing heart can differ markedly from that in the adult myocardium.

Mechanisms by which KATP channel openers produce acute and delayed cardioprotection

Mitochondria are being increasingly studied for their critical role in cell survival. Multiple diverse signaling pathways have been shown to converge on the K+-sensitive ATP channels as the effectors of cytoprotection against necrosis and apoptosis. The role of potassium channel openers in regulation and transformation of cell membrane excitability, action potential and electrolyte transfer has been extensively studied. Cardiac mitoK(ATP) channels are the key effectors in cardioprotection during ischemic preconditioning, as yet with an undefined mechanism. They have been hypothesized to couple myocardial metabolism with membrane electrical activity and provide an excellent target for drug therapy. A number of K(ATP) channel openers have been characterized for their beneficial effects on the myocardium against ischemic injury. This review updates recent progress in understanding the physiological role of K(ATP) channels in cardiac protection induced by preconditioning and highlights relevant questions and controversies in the light of published data.

Estrogen inhibits hyperthermia-induced expression of heat-shock protein 72 and cardioprotection against ischemia/reperfusion injury in female rat heart

There is still controversy as to whether estrogen inhibits or enhances heat-shock protein (HSP72) expression in the heart. To evaluate the gender difference, whole-body hyperthermia (HT, 43 degrees C for 20 min) or normothermia (NT, 37 degrees C for 20 min) was applied to both male and female rats. Twenty-four hours after each thermo-treatment, the heart was isolated for either Western blot analysis or isolated-perfused heart experiments. Induction of HSP72 expression and post-ischemic recovery of left ventricular (LV) function was pronounced in male than in female heart. To evaluate the effect of estrogen, female rats received ovariectomy. One week after the operation, ovariectomized rats were treated with 17beta-estradiol in a single administration of 4, 40, or 400 mug/kg or vehicle (placebo) intraperitoneally (IP), followed by HT or NT at 6 h after the administration. In the placebo-treated ovariectomized female, HT-induced cardiac HSP72 expression was more remarkable with better LV functional recovery than sham-operated gonadally intact female. Treatment with 17beta-estradiol reduced HT-induced cardiac HSP72 overexpression and abolished better LV functional recovery observed in placebo-treated ovariectomized female. Inhibition of HT-induced HSP72 expression was in association with the inhibition of activation of heat-shock factor 1 (HSF1). In cultured rat neonatal cardiomyocytes, prior exposure to H(2)O(2)-induced HSP72 expression and rendered protection against hypoxia/reoxygenation, which was attenuated by the treatment with 17beta-estradiol. The washout of 17beta-estradiol for 48 h recovered the H(2)O(2)-induced HSP72 expression and tolerance against hypoxia/reoxygenation. Our results suggest that the male heart is more sensitive than gonadally intact female heart in terms of response to HT to express HSP72 in association with protection against ischemic insult. This observation may be due to the inhibitory effects of estrogen on HSP72 expression at a transcriptional level.

Prostacyclin attenuates oxidative damage of myocytes by opening mitochondrial ATP-sensitive K+ channels via the EP3 receptor

Prostacyclin (PGI2) and the PGE family alleviate myocardial ischemia-reperfusion injury and limit oxidative damage. The cardioprotective effects of PGI2 have been traditionally ascribed to activation of IP receptors. Recent advances in prostanoid research have revealed that PGI2 can bind not only to IP, but also to EP, receptors, suggesting cross talk between PGI2 and PGEs. The mechanism(s) whereby PGI2 protects myocytes from oxidative damage and the specific receptors involved remain unknown. Thus fresh isolated adult rat myocytes were exposed to 200 microM H2O2 with or without carbaprostacyclin (cPGI2), IP-selective agonists, and ONO-AE-248 (an EP3-selective agonist). Cell viability was assessed by trypan blue exclusion after 30 min of H2O2 superfusion. cPGI2 and ONO-AE-248 significantly improved cell survival during H2O2 superfusion; IP-selective agonists did not. The protective effect of cPGI2 and ONO-AE-248 was completely abrogated by pretreatment with 5-hydroxydecanoate or glibenclamide. In the second series of experiments, the mitochondrial ATP-sensitive K+ (K(ATP)) channel opener diazoxide (Dx) reversibly oxidized flavoproteins in control myocytes. Exposure to prostanoid analogs alone had no effect on flavoprotein fluorescence. A second application of Dx in the presence of cPGI2 or ONO-AE-248 significantly increased flavoprotein fluorescence compared with Dx alone, but IP-selective agonists did not. This study demonstrates that PGI2 analogs protect cardiac myocytes from oxidative stress mainly via activation of EP3. The data also indicate that activation of EP3 receptors primes the opening of mitochondrial K(ATP) channels and that this mechanism is essential for EP3-dependent protection.

Androgen receptors containing expanded polyglutamine tracts exhibit progressive toxicity when stably expressed in the neuroblastoma cell line, SH-SY 5Y

The pathogenesis of X-linked spinal and bulbar muscular atrophy (SBMA) has been traced to an expansion of repeated glutamine (Gln) residues within the amino terminus of the human androgen receptor (AR). To examine the mechanisms by which these expanded repeat ARs (Exp-ARs) are toxic to neurons, we have established and characterized a cell culture model by stably transfecting SH-SY 5Y neuroblastoma cells with cDNAs containing either normal AR (81 series; 23 Glns) or Exp-AR (902 series; 56 Glns). At a low passage number, no differences in cell morphology, growth properties, or susceptibility to toxic insults were observed between clones expressing normal AR or Exp-AR. Initially, both types of cultures were found to express similar levels of specific hormone binding in monolayer binding assays. Immunohistochemical studies demonstrated the vast majority of both the normal AR and Exp-AR were localized to the nucleus in the absence and presence of androgen. As the 902 series of clones were propagated, the Exp-AR content in the cells appeared to decline progressively. However, this decrease actually reflects a gradual disappearance of the Exp-AR cell population. No such selection occurred during the propagation of cells expressing the normal AR. This selection against cells expressing physiological levels of Exp-AR occurs in the absence of intracellular aggregates and suggests that mechanisms other than those involving the formation of aggregates underlie the observed toxicity of Exp-ARs.

Regulation and critical role of potassium homeostasis in apoptosis

Programmed cell death or apoptosis is broadly responsible for the normal homeostatic removal of cells and has been increasingly implicated in mediating pathological cell loss in many disease states. As the molecular mechanisms of apoptosis have been extensively investigated a critical role for ionic homeostasis in apoptosis has been recently endorsed. In contrast to the ionic mechanism of necrosis that involves Ca(2+) influx and intracellular Ca(2+) accumulation, compelling evidence now indicates that excessive K(+) efflux and intracellular K(+) depletion are key early steps in apoptosis. Physiological concentration of intracellular K(+) acts as a repressor of apoptotic effectors. A huge loss of cellular K(+), likely a common event in apoptosis of many cell types, may serve as a disaster signal allowing the execution of the suicide program by activating key events in the apoptotic cascade including caspase cleavage, cytochrome c release, and endonuclease activation. The pro-apoptotic disruption of K(+) homeostasis can be mediated by over-activated K(+) channels or ionotropic glutamate receptor channels, and most likely, accompanied by reduced K(+) uptake due to dysfunction of Na(+), K(+)-ATPase. Recent studies indicate that, in addition to the K(+) channels in the plasma membrane, mitochondrial K(+) channels and K(+) homeostasis also play important roles in apoptosis. Investigations on the K(+) regulation of apoptosis have provided a more comprehensive understanding of the apoptotic mechanism and may afford novel therapeutic strategies for apoptosis-related diseases.