Mitochondrial permeability transition pore as a target for cardioprotection in the human heart

After an episode of myocardial ischemia, opening of the mitochondrial permeability transition pore (mPTP), at the onset of reperfusion, is a critical determinant of myocyte death. We investigated the role of the mPTP as a target for cardioprotection in the human heart. We subjected human atrial tissue, harvested from patients undergoing cardiac surgery, to a period of lethal hypoxia and investigated the effect of suppressing mPTP opening at the onset of reoxygenation. We found that suppressing mPTP opening at the onset of reoxygenation with known mPTP inhibitors cyclosporin A (CsA, 0.2 micromol/l) and sanglifehrin A (SfA, 1.0 micromol/l) 1) improved recovery of baseline contractile function from 29.4 +/- 2.0% under control conditions to 48.7 +/- 2.2% with CsA and 46.1 +/- 2.3% with SfA (P < 0.01) and 2) improved cell survival from 62.8 +/- 5.3% under hypoxic control conditions to 91.4 +/- 4.1% with CsA and 87.2 +/- 6.2% with SfA (P < 0.001). Furthermore, with a cell model in which oxidative stress was used to induce mPTP opening in human atrial myocytes, we demonstrated directly that CsA and SfA mediated their cardioprotective effects by inhibiting mPTP opening, as evidenced by an extension in the time required to induce mPTP opening from 116 +/- 8 s under control conditions to 189 +/- 10 s with CsA and 183 +/- 12 s with SfA (P < 0.01). We report that suppressing mPTP opening at the onset of reoxygenation protects human myocardium against lethal hypoxia-reoxygenation injury. This suggests that, in the human heart, the mPTP is a viable target for cardioprotection.     

Mitochondrial targeted cyclophilin D protects cells from cell death by peptidyl prolyl isomerization

Cyclophilin D (CyPD) is thought to sensitize opening of the mitochondrial permeability transition pore (mPTP) based on the findings that cyclosporin A (CsA), a pseudo-CyPD substrate, hyperpolarizes the mitochondrial membrane potential (DeltaPsi) and inhibits apoptosis. We provide evidence that contrasts with this model. Using live cell imaging and two photon microscopy, we report that overexpression of CyPD desensitizes HEK293 and rat glioma C6 cells to apoptotic stimuli. By site-directed mutagenesis of CyPD that compromises peptidyl-prolyl cis-trans isomerase (PPIase) activity, we demonstrate that the mechanism involved in this protective effect requires PPIase activity. Furthermore, we show that, under resting conditions, DeltaPsi is hyperpolarized in CyPD wild type-overexpressing cells but not in cells overexpressing mutant forms of CyPD that lack PPIase activity. Finally, in glutathione S-transferase (GST) pull-down assays, we demonstrate that CyPD binding to the adenine nucleotide translocator (ANT), which is considered to be the core component of the mPTP, is not affected by the loss of PPIase activity. Collectively, our data suggest that CyPD should be viewed as a cell survival-signaling molecule and indicate a protective role of CyPD against apoptosis that is mediated by one or more targets other than the ANT.     

1-Phenyl-2-decanoylamino-3-morpholino-1-propanol (PDMP) facilitates curcumin-induced melanoma cell apoptosis by enhancing ceramide accumulation, JNK activation, and inhibiting PI3K/AKT activation

The majority of metastatic melanomas are resistant to different chemotherapeutic agents, consequently, the search for novel anti-melanoma agents and adjuvant is urgent. Here, we found that 1-phenyl-2-decanoylamino-3-morpholino-1-propanol (PDMP), an inhibitor of glycosphingolipid biosynthesis, enhanced curcumin-induced cell growth inhibition and apoptosis in two melanoma cell lines (WM-115 and B16). PDMP facilitated curcumin-induced ceramide accumulation; the latter contributed to melanoma cell apoptosis. PDMP also dramatically enhanced curcumin-induced c-Jun N-terminal kinase activation, which was important to melanoma cell apoptosis. Meanwhile, curcumin plus PDMP treatment largely inhibited the activation of pro-survival PI3K/AKT signal pathway. In conclusion, PDMP-sensitized curcumin-induced melanoma cell growth inhibition and apoptosis in vitro due to changes of multiple signal events. Combining PDMP with curcumin may represent a new therapeutic intervention against melanoma.     

Is mPTP the gatekeeper for necrosis, apoptosis, or both?

Permeabilization of the mitochondrial membranes is a crucial step in apoptosis and necrosis. This phenomenon allows the release of mitochondrial death factors, which trigger or facilitate different signaling cascades ultimately causing the execution of the cell. The mitochondrial permeability transition pore (mPTP) has long been known as one of the main regulators of mitochondria during cell death. mPTP opening can lead to matrix swelling, subsequent rupture of the outer membrane, and a nonspecific release of intermembrane space proteins into the cytosol. While mPTP was purportedly associated with early apoptosis, recent observations suggest that mitochondrial permeabilization mediated by mPTP is generally more closely linked to events of late apoptosis and necrosis. Mechanisms of mitochondrial membrane permeabilization during cell death, involving three different mitochondrial channels, have been postulated. These include the mPTP in the inner membrane, and the mitochondrial apoptosis-induced channel (MAC) and voltage-dependent anion-selective channel (VDAC) in the outer membrane. New developments on mPTP structure and function, and the involvement of mPTP, MAC, and VDAC in permeabilization of mitochondrial membranes during cell death are explored. This article is part of a Special Issue entitled Mitochondria: the deadly organelle.     

Sanglifehrin A acts as a potent inhibitor of the mitochondrial permeability transition and reperfusion injury of the heart by binding to cyclophilin-D at a different site from cyclosporin A

Cyclosporin A (CsA) inhibits opening of the mitochondrial permeability transition pore (MPTP), a critical event in some forms of necrotic and apoptotic cell death, by binding to cyclophilin D (CyP-D) and inhibiting its peptidyl-prolyl cis-trans isomerase (PPIase) activity. Sanglifehrin A (SfA), like CsA, exerts its immunosuppressive action by binding to cyclophilin A but at a different site from CsA, and unlike the latter, SfA does not inhibit calcineurin activity. Here we demonstrate that SfA inhibits the PPIase activity of CyP-D (K(0.5) 2 nm) and acts as a potent inhibitor of MPTP opening under both energized and de-energized conditions. However, unlike CsA, the dose-response curve for inhibition by SfA is sigmoidal rather than hyperbolic, suggesting a multimeric structure for the MPTP with cooperativity between subunits. Furthermore, SfA does not prevent CyP-D binding to submitochondrial particles or detergent-solubilized adenine nucleotide translocase (ANT), implying that CyP-D binding to the ANT does not require PPIase activity but pore opening does. Once bound to the MPTP, SfA is not readily dissociated, and inhibition of pore opening is maintained following extensive washing. To investigate the potential of SfA as an inhibitor of cell death in vivo, we used the Langendorff perfused rat heart. SfA caused a time-dependent inhibition of the MPTP that was maintained on mitochondrial isolation to a greater extent than was CsA inhibition. We demonstrate that SfA, like CsA, improves the recovery of left ventricular developed pressure during reperfusion after 30 min of global ischemia and greatly reduces lactate dehydrogenase release, implying inhibition of necrotic damage. Because SfA does not inhibit calcineurin activity, our data suggest that it may be more desirable than CsA for protecting tissues recovering from ischemic episodes and for studying the role of the MPTP in cell death.     

Pre-clinical evaluation of cinobufotalin as a potential anti-lung cancer agent

Lung cancer is a major cause of cancer-related mortality in the United States and around the world. Due to the pre-existing or acquired chemo-resistance, the current standard chemotherapy regimens only show moderate activity against lung cancer. In the current study, we explored the potential anti-lung cancer activity of cinobufotalin in vivo and in vitro, and studied the underlying mechanisms. We demonstrated that cinobufotalin displayed considerable cytotoxicity against lung cancer cells (A549, H460 and HTB-58 lines) without inducing significant cell apoptosis. Our data suggest that mitochondrial protein cyclophilin D (Cyp-D)-dependent mitochondrial permeability transition pore (mPTP) opening mediates cinobufotalin-induced non-apoptotic death of lung cancer cells. The Cyp-D inhibitor cyclosporine A (CsA), the mPTP blocker sanglifehrin A (SfA), and Cyp-D shRNA-silencing significantly inhibited cinobufotalin-induced mitochondrial membrane potential (MMP) reduction and A549 cell death (but not apoptosis). Using a mice xenograft model, we found that cinobufotalin inhibited A549 lung cancer cell growth in vivo. Thus, cinobufotalin mainly induces Cyp-D-dependent non-apoptotic death in cultured lung cancer cells. The results of this study suggest that cinobufotalin might be further investigated as a novel anti-lung cancer agent.     

Modulation of mitochondrial permeability transition pore affects multidrug resistance in human hepatocellular carcinoma cells

Multidrug resistance (MDR) is a critical problem in the chemotherapy of cancers. Human hepatocellular carcinoma (HCC) responds poorly to chemotherapy owing to its potent MDR. Chemotherapeutic drugs primarily act by inducing apoptosis of cancer cells, and defects in apoptosis may result in MDR. Mitochondrial permeability transition (mPT) is implicated as an important event in the control of cell death or survival and mPT represents a target for the development of cytotoxic drugs. This study aimed to investigate the effects of selective opener (Atractyloside glycoside, ATR) and inhibitor (Cyclosporine A, CsA) of mitochondrial permeability transition pore (mPTP) on a CDDP-resistant HCC cell line (SK-Hep1 cells). In this study, a stable MDR phenotype characterization of SK-Hep1 cell line (SK-Hep1/CDDP cells) was established and used to investigate the role of mPTP in MDR. Results suggested that ATR accelerated the decrease of mitochondrial membrane potential (ΔΨm), reduced the Bax activity, and increased the apoptosis of SK-Hep1/CDDP cells; while CsA inhibited mPTP opening, reduced and delayed the decline of mitochondrial membrane potential, and increased the Bax activity, leading to increased tolerance of SK-Hep1/CDDP cells to apoptosis induction. However, mPTP activity had no effect on the expression of MDR1 in cells,meanwhile the P-gp translocation to mitochondria was increased, and functionally activated. In conclusion, selective modulation of mPTP can affect MDR in human HCC cells. Therefore, activation of mPTP may provide a new strategy to sensitize cancer cells to chemotherapeutic drugs and to reverse the MDR in cancer cells.     

Curcumin induces Apaf-1-dependent,p21-mediated caspase activation and apoptosis

Previous studies have demonstrated that curcumin induces mitochondria-mediated apoptosis. However, understanding of the molecular mechanisms underlying curcumin-induced cell death remains limited. In this study, we demonstrate that curcumin treatment of cancer cells caused dose- and time-dependent caspase-3 activation, which is required for apoptosis as confirmed using the pan caspase inhibitor, z-VAD. Knockdown experiments and knockout cells excluded a role of caspase-8 in curcumin-induced caspase-3 activation. In contrast, Apaf-1 deficiency or silencing inhibited the activity of caspase-3, pointing to a requisite role of Apaf-1 in curcumin-induced apoptotic cell death. Curcumin treatment led to Apaf-1 upregulation both at the protein and mRNA levels. Cytochrome c release from mitochondria to the cytosol in curcumin-treated cells was associated with upregulation of proapoptotic proteins such as Bax, Bak, Bid, and Bim. Crosslinking experiments demonstrated Bax oligomerization during curcumin-induced apoptosis, suggesting that induced expression of Bax, Bid, and Bim causes Bax-channel formation on the mitochondrial membrane. The release of cytochrome c was unaltered in p53-deficient cells, whereas absence of p21 blocked cytochrome c release, caspase activation, and apoptosis. Importantly, p21-deficiency resulted in reduced expression of Apaf-1 during curcumin treatment, indicating a requirement of p21 in Apaf-1 dependent caspase activation and apoptosis. Together, our findings demonstrate that Apaf-1, Bax, and p21 as novel potential targets for curcumin or curcumin-based anticancer agents.     

The role of the mitochondrial permeability transition pore in heart disease

Like Dr. Jeckyll and Mr. Hyde, mitochondria possess two distinct persona. Under normal physiological conditions they synthesise ATP to meet the energy needs of the beating heart. Here calcium acts as a signal to balance the rate of ATP production with ATP demand. However, when the heart is overloaded with calcium, especially when this is accompanied by oxidative stress, mitochondria embrace their darker side, and induce necrotic cell death of the myocytes. This happens acutely in reperfusion injury and chronically in congestive heart failure. Here calcium overload, adenine nucleotide depletion and oxidative stress combine forces to induce the opening of a non-specific pore in the mitochondrial membrane, known as the mitochondrial permeability transition pore (mPTP). The molecular nature of the mPTP remains controversial but current evidence implicates a matrix protein, cyclophilin-D (CyP-D) and two inner membrane proteins, the adenine nucleotide translocase (ANT) and the phosphate carrier (PiC). Inhibition of mPTP opening can be achieved with inhibitors of each component, but targeting CyP-D with cyclosporin A (CsA) and its non-immunosuppressive analogues is the best described. In animal models, inhibition of mPTP opening by either CsA or genetic ablation of CyP-D provides strong protection from both reperfusion injury and congestive heart failure. This confirms the mPTP as a promising drug target in human cardiovascular disease. Indeed, the first clinical trials have shown CsA treatment improves recovery after treatment of a coronary thrombosis with angioplasty.     

MST1 activation by curcumin mediates JNK activation,Foxo3a nuclear translocation and apoptosis in melanoma cells

Different groups including ours have shown that curcumin induces melanoma cell apoptosis, here we focused the role of mammalian Sterile 20-like kinase 1 (MST1) in it. We observed that curcumin activated MST1-dependent apoptosis in cultured melanoma cells. MST1 silencing by RNA interference (RNAi) suppressed curcumin-induced cell apoptosis, while MST1 over-expressing increased curcumin sensitivity. Meanwhile, curcumin induced reactive oxygen species (ROS) production in melanoma cells, and the ROS scavenger, N-acetyl-cysteine (NAC), almost blocked MST1 activation to suggest that ROS might be required for MST1 activation by curcumin. c-Jun N-terminal protein kinase (JNK) activation by curcumin was dependent on MST1, since MST1 inhibition by RNAi or NAC largely inhibited curcumin-induced JNK activation. Further, curcumin induced Foxo3 nuclear translocation and Bim-1 (Foxo3 target gene) expression in melanoma cells, such an effect by curcumin was inhibited by MST1 RNAi. In conclusion, we suggested that MST1 activation by curcumin mediates JNK activation, Foxo3a nuclear translocation and apoptosis in melanoma cells.     

Curcumin induces apoptosis in human gastric carcinoma AGS cells and colon carcinoma HT-29 cells through mitochondrial dysfunction and endoplasmic reticulum stress

In the present study, we investigate the effect of curcumin, a major active component isolated from rhizomes of Curcuma longa, on the cytotoxicity of three human carcinoma cell lines (AGS, HT-29 and MGC803) in gastrointestinal tract and a normal gastric epithelial cell line GES-1, and the mechanism of curcumin-induced apoptosis. The results indicated that curcumin inhibited the gastrointestinal carcinoma cell growth in a dose-dependent manner and cytotoxicity was more towards the gastric carcinoma cell AGS and colon carcinoma cell HT-29 compared to normal gastric cell GES-1, and increased externalization of phosphatidylserine residue was observed by Annexin V/PI staining in the two cell lines. Treatment of AGS and HT-29 cells with curcumin enhanced the cleavage of procaspase-3, -7, -8 and -9. Meanwhile, curcumin induced endoplasmic reticulum (ER) stress and mitochondrial dysfunction as evidenced by up-regulation of CCAAT/enhancer binding protein homologous protein (CHOP), phosphorylation of JNK and down-regulation of SERCA2ATPase, release of cytochrome c, decrease of Bcl-2 and reduction of mitochondrial membrane potential in both AGS and HT-29 cells. Overexpression of bax, total JNK, phospho-FADD and total FADD were also observed in curcumin-treated HT-29 cells. Moreover, curcumin decreased cytosolic and ER Ca²⁺, but increased mitochondrial Ca²⁺ in the two cell lines. 2-Aminoethoxydiphenyl borate, an antagonist of inositol 1, 4, 5-triphosphate receptor, partly blocked curcumin-induced cytosolic Ca²⁺ decrease in AGS and HT-29 cells. Additionally, carbonyl cyanide m-chlorophenylhydrazone, an inhibitor of mitochondrial Ca²⁺ uptake, reversed curcumin-triggered AGS and HT-29 cells growth inhibition. siRNA to CHOP markedly reduced curcumin-induced apoptosis. These results suggest that curcumin can impact on ER stress and mitochondria functional pathways in AGS and HT-29 cells, death receptor pathway was also involved in curcumin-treated HT-29 cells, thus identifying specific well-defined molecular mechanisms that may be targeted by therapeutic strategies.     

Dynamin‐related protein 1‐mediated mitochondrial fission contributes to IR‐783‐induced apoptosis in human breast cancer cells

IR‐783 is a kind of heptamethine cyanine dye that exhibits imaging, cancer targeting and anticancer properties. A previous study reported that its imaging and targeting properties were related to mitochondria. However, the molecular mechanism behind the anticancer activity of IR‐783 has not been well demonstrated. In this study, we showed that IR‐783 inhibits cell viability and induces mitochondrial apoptosis in human breast cancer cells. Exposure of MDA‐MB‐231 cells to IR‐783 resulted in the loss of mitochondrial membrane potential (MMP), adenosine triphosphate (ATP) depletion, mitochondrial permeability transition pore (mPTP) opening and cytochrome c (Cyto C) release. Furthermore, we found that IR‐783 induced dynamin‐related protein 1 (Drp1) translocation from the cytosol to the mitochondria, increased the expression of mitochondrial fission proteins mitochondrial fission factor (MFF) and fission‐1 (Fis1), and decreased the expression of mitochondrial fusion proteins mitofusin1 (Mfn1) and optic atrophy 1 (OPA1). Moreover, knockdown of Drp1 markedly blocked IR‐783‐mediated mitochondrial fission, loss of MMP, ATP depletion, mPTP opening and apoptosis. Our in vivo study confirmed that IR‐783 markedly inhibited tumour growth and induced apoptosis in an MDA‐MB‐231 xenograft model in association with the mitochondrial translocation of Drp1. Taken together, these findings suggest that IR‐783 induces apoptosis in human breast cancer cells by increasing Drp1‐mediated mitochondrial fission. Our study uncovered the molecular mechanism of the anti‐breast cancer effects of IR‐783 and provided novel perspectives for the application of IR‐783 in the treatment of breast cancer.     

Curcumin induces small cell lung cancer NCI-H446 cell apoptosis via the reactive oxygen species-mediated mitochondrial pathway and not the cell death receptor pathway

Curcumin (diferuloylmethane), an active component of the spice turmeric, induces apoptosis in several types of malignancies. However, little is known about its anticancer activity in small cell lung cancer (SCLC). SCLC represents a highly malignant and particularly aggressive form of cancer, with early and widespread metastases and a poor prognosis. In this study, we found that curcumin does not activate caspase-8 cleavage or alter the expression of apoptotic receptors FAS and TRAIL in NCI-H446 cells, suggesting that curcumin-induced apoptosis is not associated with death receptor-mediated pathways in these cells. Instead, curcumin caused apoptosis by increasing Bax expression while decreasing the expression of Bcl-2 and Bcl-xL. Curcumin induced a rapid decrease in mitochondrial membrane potential and the release of cytochrome c into the cytosol, followed by activation of caspase-9 and caspase-3. In addition, curcumin-induced apoptosis was accompanied by an increase of intracellular reactive oxygen species (ROS) level. These results indicated that a ROS-mediated mitochondrial pathway played an important role in the process of curcumin-induced apoptosis of human SCLC NCI-H446 cells.     

Mitochondrial permeability transition pore opening induces the initial process of renal calcium crystallization

Renal tubular cell injury induced by oxidative stress via mitochondrial collapse is thought to be the initial process of renal calcium crystallization. Mitochondrial collapse is generally caused by mitochondrial permeability transition pore (mPTP) opening, which can be blocked by cyclosporine A (CsA). Definitive evidence for the involvement of mPTP opening in the initial process of renal calcium crystallization, however, is lacking. In this study, we examined the physiological role of mPTP opening in renal calcium crystallization in vitro and in vivo. In the in vitro study, cultured renal tubular cells were exposed to calcium oxalate monohydrate (COM) crystals and treated with CsA (2 μM). COM crystals induced depolarization of the mitochondrial membrane potential and generated oxidative stress as evaluated by Cu-Zn SOD and 4-HNE. Furthermore, the expression of cytochrome c and cleaved caspase 3 was increased and these effects were prevented by CsA. In the in vivo study, Sprague-Dawley rats were administered 1% ethylene glycol (EG) to generate a rat kidney stone model and then treated with CsA (2.5, 5.0, and 10.0 mg/kg/day) for 14 days. EG administration induced renal calcium crystallization, which was prevented by CsA. Mitochondrial collapse was demonstrated by transmission electron microscopy, and oxidative stress was evaluated by measuring Cu-Zn SOD, MDA, and 8-OHdG generated by EG administration, all of which were prevented by CsA. Collectively, our results provide compelling evidence for a role of mPTP opening and its associated mitochondrial collapse, oxidative stress, and activation of the apoptotic pathway in the initial process of renal calcium crystallization.     

Curcumin induces apoptosis through mitochondrial hyperpolarization and mtDNA damage in human hepatoma G2 cells

Curcumin, a major pigment of turmeric, is a natural antioxidant possessing a variety of pharmacological activities and therapeutic properties. But its mechanisms are unknown. In our previous study, we found that a 2-h exposure to curcumin induced DNA damage to both the mitochondrial DNA (mtDNA) and the nuclear DNA (nDNA) in HepG2 cells and that mtDNA damage was more extensive than nDNA damage. Therefore, experiments were initiated to evaluate the role of mtDNA damage in curcumin-induced apoptosis. The results demonstrated that HepG2 cells challenged with curcumin for 1 h showed a transient elevation of the mitochondrial membrane potential (DeltaPsim), followed by cytochrome c release into the cytosol and disruption of DeltaPsim after 6 h exposure to curcumin. Apoptosis was detected by Hoechst 33342 and annexin V/PI assay after 10 h treatment. Interestingly, the expression of Bcl-2 remained unchanged. A resistance to apoptosis for the corresponding rho0 counterparts confirmed a critical dependency for mitochondria during the induction of apoptosis in HepG2 cells mediated by curcumin. The effects of PEG-SOD in protecting against curcumin-induced cytotoxicity suggest that curcumin-induced cytotoxicity is directly dependent on superoxide anion O2- production. These data suggest that mitochondrial hyperpolarization is a prerequisite for curcumin-induced apoptosis and that mtDNA damage is the initial event triggering a chain of events leading to apoptosis in HepG2 cells.     

Curcumin Induces Apoptosis in Human Melanoma Cells through a Fas Receptor/Caspase-8 Pathway Independent of p53

In this study, we investigated the molecular pathways targeted by curcumin during apoptosis of human melanoma cell lines. We found that curcumin caused cell death in eight melanoma cell lines, four with wild-type and four with mutant p53. We demonstrate that curcumin-induced apoptosis is both dose- and time-dependent. We found that curcumin did not induce p53, suggesting that curcumin activates other apoptosis pathways. Our data show that curcumin activates caspases-3 and -8 but not caspase-9, supporting the rationale that apoptosis occurs via a membrane-mediated mechanism. Both a caspase-8 and broad-based caspase inhibitor, but not a caspase-9 specific inhibitor, suppressed curcumin-induced cell death. To further support our hypothesis that curcumin induces activation of a death receptor pathway, we show that curcumin induces Fas receptor aggregation in a FasL-independent manner and that low-temperature incubation, previously shown to inhibit receptor aggregation, prevented curcumin-induced cell death. Moreover, we demonstrate that expression of dominant negative FADD significantly inhibited curcumin-induced cell death. In addition, our results indicate that curcumin also blocks the NF-kappaB cell survival pathway and suppresses the apoptotic inhibitor, XIAP. Since melanoma cells with mutant p53 are strongly resistant to conventional chemotherapy, curcumin may overcome the chemoresistance of these cells and provide potential new avenues for treatment.     

Mitochondrial permeability transition relevance for apoptotic triggering in the post-ischemic heart

Dysfunction of mitochondrial calcium homeostasis transforms this cation from a key regulator of mitochondrial function, into a death effector during post-ischemic reperfusion. High intramitochondrial calcium and prevailing cellular conditions favor the opening of the mitochondrial permeability transition pore (mPTP), that induces mitochondrial swelling and provides a mechanism for cytochrome c release, a hallmark signal protein of the mitochondrial apoptosis pathway; indeed, a second mechanism induced by pro-apoptotic BAX protein, could account for cytochrome c leak in the post-ischemic heart. The present study was undertaken to determine which one of these mechanisms triggers the mitochondrial apoptosis pathway in the reperfused heart. To accomplish this goal we prevented the opening of the mPTP in such hearts, by diminishing calcium overload with Ru360, a specific mitochondrial calcium uniporter inhibitor. We found that mPTP opening in reperfused hearts increased along with reperfusion time and concurs with cytochrome c release from mitochondria. Maximal cytochrome c release correlated with mitochondrial dysfunction and complete NAD+ deletion. Fully inserted BAX was detected early after reperfusion and remained unchanged during the evaluated reperfusion times. Remarkably, heart perfusion with Ru360, inhibited mPTP opening and BAX docking into the mitochondrial membranes, suggesting a mPTP upstream role on BAX migration/insertion.     

Curcumin induces Apaf-1-dependent,p21-mediated caspase activation and apoptosis

Previous studies have demonstrated that curcumin induces mitochondria-mediated apoptosis. However, understanding of the molecular mechanisms underlying curcumin-induced cell death remains limited. In this study, we demonstrate that curcumin treatment of cancer cells caused dose- and time-dependent caspase 3 activation, which is required for apoptosis as confirmed using the pan-caspase inhibitor, z-VAD. Knockdown experiments and knockout cells excluded a role for caspase 8 in curcumin-induced caspase 3 activation. In contrast, Apaf-1 deficiency or silencing inhibited the activity of caspase 3, pointing to a requisite role of Apaf-1 in curcumin-induced apoptotic cell death. Curcumin treatment led to Apaf-1 upregulation, both at the protein and mRNA levels. Cytochrome c release from mitochondria to the cytosol in curcumin-treated cells was associated with upregulation of pro-apoptotic proteins, such as Bax, Bak, Bid and Bim. Cross-linking experiments demonstrated Bax oligomerization during curcumin-induced apoptosis, suggesting that induced expression of Bax, Bid and Bim causes Bax channel formation on the mitochondrial membrane. The release of cytochrome c was unaltered in p53-deficient cells, whereas absence of p21 blocked cytochrome c release, caspase activation and apoptosis. Importantly, p21 deficiency resulted in reduced expression of Apaf-1 during curcumin treatment, indicating a requirement for p21 in Apaf-1-dependent caspase activation and apoptosis. Together, our findings identify Apaf-1, Bax and p21 as novel potential targets for curcumin or curcumin-based anticancer agents.Key words: curcumin, mitochondria, cytochrome c, Apaf-1, caspase, p21     

Fas-independent mitochondrial damage triggers cardiomyocyte death after ischemia-reperfusion

The Fas/Fas ligand and mitochondria pathways have been involved in cell death in several cell types. We combined the genetic inactivation of the Fas receptor (lpr mice), on the one hand, to the pharmacological inhibition of the mitochondrial permeability transition pore (mPTP), on the other hand, to investigate which of these pathways is predominantly activated during prolonged ischemia-reperfusion. Anesthetized C57BL/6JICO (control) and C57BL/6-lpr mice were pretreated with either saline or cyclosporin A (CsA; 40 mg/kg, 3 times a day), an inhibitor of the mPTP, and underwent 25 min of ischemia and 24 h of reperfusion. After 24 h of reperfusion, hearts were harvested: infarct size was assessed by 2,3,5-triphenyltetrazolium chloride staining, myocardial apoptosis by caspase 3 activity, and mitochondrial permeability transition by Ca2+-induced mPTP opening using a potentiometric approach. Infarct size was comparable in untreated control and lpr mice, ranging from 77 +/- 5% to 83 +/- 3% of the area at risk. CsA significantly reduced infarct size in control and lpr hearts. Control and lpr hearts exhibited comparable increase in caspase 3 activity that averaged 57 +/- 18 and 49 +/- 5 pmol x min(-1) x mg(-1), respectively. CsA treatment significantly reduced caspase 3 activity in control and lpr hearts. The Ca2+ overload required to open the mPTP was decreased to a similar extent in lpr and controls. CsA significantly attenuated Ca2+-induced mPTP opening in both groups. Our results suggest that the Fas pathway likely plays a minor role, whereas mitochondria are preferentially involved in mice cardiomyocyte death after a lethal ischemia-reperfusion injury.