Mitochondrial intermembrane junctional complexes and their role in cell death

Long-chain ceramide is a potent inhibitor of the mitochondrial permeability transition pore

The sphingolipid ceramide has been implicated in mediating cell death that is accompanied by mitochondrial functional alterations. Moreover, ceramide has been shown to accumulate in mitochondria upon induction of apoptotic processes. In this study, we sought to evaluate the effects of natural, highly hydrophobic long-chain ceramides on mitochondrial function in vitro. Ceramide in a dodecane/ethanol delivery system inhibited the opening of the mitochondrial permeability transition pore (PTP) induced by either oxidative stress, SH group cross-linking, or high Ca2+ load, suggesting that the inhibitory point is at a level at which major PTP regulatory pathways converge. Moreover, ceramide had no effect on well known mitochondrial components that modulate PTP activity, such as cyclophilin D, voltage-dependent anion channel, adenine nucleotide transporter, and ATP synthase. The inhibitory effect of ceramide on PTP was not stereospecific, nor was there a preference for ceramide over dihydroceramide. However, the effect of ceramide on PTP was significantly influenced by the fatty acid moiety chain length. These studies are the first to show that long-chain ceramide can influence PTP at physiologically relevant concentrations, suggesting that it is the only known potent natural inhibitor of PTP. These results suggest a novel mechanism of ceramide regulation of mitochondrial function.

Cellular functions of cardiolipin in yeast

Cardiolipin (CL), the signature lipid of mitochondria, plays a critical role in mitochondrial function and biogenesis. The availability of yeast mutants blocked in CL synthesis has facilitated studies of the biological role of this lipid. Perturbation of CL synthesis leads to growth defects not only during respiratory growth but also under conditions in which respiration is not essential. CL was shown to play a role in mitochondrial protein import, cell wall biogenesis, aging and apoptosis, ceramide synthesis, and translation of electron transport chain components. The genetic disorder Barth syndrome (BTHS) is caused by mutations in the tafazzin gene resulting in decreased total CL levels, accumulation of monolysocardiolipin (MLCL), and decreased unsaturated fatty acyl species of CL. The variation in clinical presentation of BTHS indicates that other physiological factors play a significant role in modifying the phenotype resulting from tafazzin deficiency. Elucidating the functions of CL is expected to shed light on the role of this important lipid in BTHS and other disorders of mitochondrial dysfunction.

Diallyl trisulfide (DATS) effectively attenuated oxidative stress-mediated liver injury and hepatic mitochondrial dysfunction in acute ethanol-exposed mice

The protective effects of diallyl trisulfide (DATS) on acute ethanol-induced liver injury were investigated. Mice were pretreated with DATS (30mg/kgbw) for 7d before being exposed to ethanol (4.8g/kgbw). The biochemical indices (aspartate amino transferase, AST; alanine amino transferase, ALT; triglyceride, TG) were examined to evaluate the protective effects. Mitochondria were isolated for the mitochondrial permeability transition (MPT), membrane potential (DeltaPsi(m)) and adenosine nucleotide pool assay. The lipid peroxidation (malondialdehyde, MDA), non-enzymatic antioxidant (glutathione, GSH) and enzymatic antioxidants (superoxide dismutase, SOD; catalase, CAT; glutathione reductase, GR; glutathione peroxidase, GSH-Px) were measured both in the liver homogenate and isolated mitochondria. Acute ethanol exposure resulted in the significant increase of the ALT, AST and TG levels and hepatic mitochondria dysfunction shown as MPT, and the decreases of DeltaPsi(m), ATP and energy charge (EC). However, DATS pretreatment dramatically attenuated these adverse effects. Beside this, DATS was found to significantly inhibit the increase of the hepatic and mitochondrial MDA levels, which were decreased by 33.3% (P<0.01) and 39.0% (P<0.01), respectively. In addition, DATS pretreatment markedly suppressed the ethanol-induced decrease of the hepatic GSH level and increased the mitochondrial GSH level. Moreover, the activities of the hepatic antioxidant enzymes (SOD, CAT, and GR) and the mitochondrial antioxidant enzymes (SOD, GR, and GSH-Px) were significantly boosted. Thus, we concluded that DATS dramatically attenuated acute ethanol-induced liver injury and mitochondrial dysfunction. The increase of the hepatic and mitochondrial GSH levels and the elevation of the antioxidant enzymes activities should account for the preventive effects.

Hydroxysafflor yellow A inhibits rat brain mitochondrial permeability transition pores by a free radical scavenging action

Hydroxysafflor yellow A (HSYA), the major and most active antioxidant from Carthamus tinctorius L., has been clinically prescribed in China to treat patients with cerebral ischemia, but the detailed mechanism is not known. This study examines the effect of HSYA on mitochondrial permeability transition pores (mtPTP) in the rat brain. HSYA at 10-80 micromol.l(-1) inhibited Ca(2+)- and H(2)O(2)-induced swelling of mitochondria isolated from rat brains. The addition of Ca(2+) generated reactive oxygen species (ROS) in isolated mitochondria. HSYA (10-80 micromol.l(-1)) inhibited Ca(2+)-induced generation of ROS. At the same time, HSYA significantly improved mitochondrial energy metabolism, enhanced ATP levels and the respiratory control ratio. These results suggest that HSYA inhibits the opening of mtPTP by a free radical scavenging action in the brain, and this may contribute to the neuroprotective effect of HSYA.

Mitochondria in cancer cells: what is so special about them?

The past decade has revealed a new role for the mitochondria in cell metabolism--regulation of cell death pathways. Considering that most tumor cells are resistant to apoptosis, one might question whether such resistance is related to the particular properties of mitochondria in cancer cells that are distinct from those of mitochondria in non-malignant cells. This scenario was originally suggested by Otto Warburg, who put forward the hypothesis that a decrease in mitochondrial energy metabolism might lead to development of cancer. This review is devoted to the analysis of mitochondrial function in cancer cells, including the mechanisms underlying the upregulation of glycolysis, and how intervention with cellular bioenergetic pathways might make tumor cells more susceptible to anticancer treatment and induction of apoptosis.

Increased mitochondrial calcium coexists with decreased reperfusion injury in postconditioned (but not preconditioned) hearts

Ca(2+) is the main trigger for mitochondrial permeability transition pore opening, which plays a key role in cardiomyocyte death after ischemia-reperfusion. We investigated whether a reduced accumulation of mitochondrial Ca(2+) might explain the attenuation of lethal reperfusion injury by postconditioning. Anesthetized New Zealand White rabbits underwent 30 min of ischemia, followed by either 240 (infarct size protocol) or 60 (mitochondria protocol) min of reperfusion. They received either no intervention (control), preconditioning by 5-min ischemia and 5-min reperfusion, postconditioning by four cycles of 1-min reperfusion and 1-min ischemia at the onset of reflow, or pharmacological inhibition of the transition pore opening by N-methyl-4-isoleucine-cyclosporin (NIM811; 5 mg/kg iv) given at reperfusion. Area at risk and infarct size were assessed by blue dye injection and triphenyltetrazolium chloride staining. Mitochondria were isolated from the risk region for measurement of 1) Ca(2+) retention capacity (CRC), and 2) mitochondrial content of total (atomic absorption spectrometry) and ionized (potentiometric technique) calcium concentration. CRC averaged 0.73 +/- 0.16 in control vs. 4.23 +/- 0.17 mug Ca(2+)/mg proteins in shams (P < 0.05). Postconditioning, preconditioning, or NIM811 significantly increased CRC (P < 0.05 vs. control). In the control group, total and free mitochondrial calcium significantly increased to 2.39 +/- 0.43 and 0.61 +/- 0.10, respectively, vs. 1.42 +/- 0.09 and 0.16 +/- 0.01 mug Ca(2+)/mg in sham (P < 0.05). Surprisingly, whereas total and ionized mitochondrial Ca(2+) decreased in preconditioning, it significantly increased in postconditioning and NIM811 groups. These data suggest that retention of calcium within mitochondria may explain the decreased reperfusion injury in postconditioned (but not preconditioned) hearts.

Involvement of both mitochondrial- and death receptor-dependent apoptotic pathways regulated by Bcl-2 family in sodium fluoride-induced apoptosis of the human gingival fibroblasts

Sodium fluoride (NaF) has been shown to be cytotoxic and produces inflammatory responses in humans. However, the cellular mechanisms underlying the NaF-induced cytotoxicity in periodontal tissues are unclear. This study examined whether or not NaF induces apoptosis in human gingival fibroblasts (HGF), and its underlying mechanisms by monitoring various apoptosis-associated processes. NaF reduced the cell viability of HGF in a dose- and time-dependent manner. NaF increased TUNEL-positive cell and induced apoptosis with concomitant chromatin condensation and DNA fragmentation in HGF. In addition, NaF increased the level of cytochrome c released from the mitochondria into the cytosol, enhanced the caspase-9, -8 and -3 activities, the cleavage of poly (ADP-ribose) polymerase (PARP), and up-regulated the voltage-dependent anion channel (VDAC) 1. However, NaF did not affect the production of reactive oxygen species (ROS) which is a strong apoptotic inducer. Furthermore, NaF up-regulated the Fas-ligand (Fas-L), a ligand of death receptor. Bcl-2, a member of the anti-apoptotic Bcl-2 family, was down-regulated, whereas the expression of Bax, a member of the pro-apoptotic Bcl-2 family, was unaffected in the NaF-treated HGF. These results suggest that NaF induces apoptosis in HGF through both the mitochondria-mediated pathways regulated by the Bcl-2 family and death receptor-mediated pathway.

Effect of magnesium on calcium-induced depolarisation of mitochondrial transmembrane potential

An effect of magnesium on calcium-induced depolarisation of mitochondrial transmembrane potential (DeltaPsi(m)) was investigated. Depending on the presence of Mg(2+), addition of Ca(2+) to suspension of isolated rat heart mitochondria induced either reversible depolarisation or irreversible collapse of succinate-driven DeltaPsi(m). Irreversible collapse of DeltaPsi(m), observed in the absence of Mg(2+), was insensitive to Ca(2+) chelation, inhibition of Ca(2+) uptake and increased efflux of Ca(2+) from mitochondrial matrix. Based on these data, opening of mPTP in a high-conductance mode is considered to be a major cause of the Ca(2+)-induced irreversible collapse of DeltaPsi(m) in the absence of Mg(2+). Involvement of mPTP in the process of Ca(2+)-induced collapse of DeltaPsi(m) was further supported by protective effect of both CsA and ADP. Reversible collapse of DeltaPsi(m), observed in the presence of Mg(2+), was sensitive to EGTA, ADP; and inhibition of Ca(2+) uptake and increased efflux of Ca(2+) from mitochondrial matrix. This may represent selective induction of a low-conductance permeability pathway. Presented results indicate important role of Mg(2+) in the process of Ca(2+)-induced depolarisation of DeltaPsi(m) mainly through discrimination between low- and high-conductance modes of mPTP. Minor effect of Mg(2+) on Ca(2+)-induced depolarisation of DeltaPsi(m) was observed at the level of stimulation of DeltaPsi(m) generation and inhibition of mitochondrial Ca(2+) uptake.

The interplay between pro-death and pro-survival signaling pathways in myocardial ischemia/reperfusion injury: apoptosis meets autophagy

INTRODUCTION

Programmed cell death of cardiac myocytes occurs following a bout of ischemia/reperfusion (I/R), which results in reduced function of the heart. Numerous studies, including in vivo, have shown that cell death occurs via necrosis and apoptosis following I/R. Recently, autophagy has emerged as a powerful mediator of programmed cell death, either opposing or enhancing apoptosis, or acting as an alternative form of programmed cell death distinct from apoptosis.

AIM

Here we review the apoptotic and autophagic signaling pathways, their influences on each other, and we discuss the relevance of autophagy in the heart.

Chaperones as Parts of Organelle Networks

The efficiency, divergence, and specificity of virtually all intracellular metabolic and signalling pathways largely depend on their compartmentalized organization. A corollary of the requirement of compartmentalization is the dynamic structural partition of the intracellular space by endomembrane systems. A branch of these membranes communicate with the extracellular space through the endo- and exocytotic processes. Others, like the mitochondrial and endoplasmic reticulum networks accomplish a further role, being fundamental for the maintenance of cellular energy balance and for determination of cell fate under stress conditions. Recent structural and functional studies revealed that the interaction of these networks and the connectivity state of mitochondria controls metabolic flow, protein transport, intracellular Ca2+ signalling, and cell death. Moreover, reflecting the fact that the above processes are accomplished in a microdomain between collaborating organelle membranes, the existence of macromolecular complexes at their contact sites have also been revealed. Being not only assistants of nascent protein folding, chaperones are proposed to participate in assembling and maintaining the function of the above complexes. In this chapter we discuss recently found examples of such an assembly of protein interactions driven by chaperone proteins, and their role in regulating physiological and pathological processes.

Preconditioning and postconditioning: united at reperfusion

Despite current optimal treatment, the morbidity and mortality of coronary heart disease (CHD), the leading cause of death worldwide, remains significant, paving the way for the development of novel cardioprotective therapies. Two potential strategies for protecting the heart are ischemic preconditioning (IPC) and ischemic postconditioning (IPost), which describe the cardioprotection obtained from applying transient episodes of myocardial ischemia and reperfusion either before or after the index ischemic event, respectively. Much progress has been made in elucidating the signal transduction pathway, which underlies their protection. Intriguingly, it is the first few minutes of myocardial reperfusion following the index ischemic period, which appear crucial to both IPC- and IPost-induced protection. Emerging evidence suggests that they appear to recruit a similar signaling pathway at time of myocardial reperfusion, comprising cell-surface receptors, a diverse array of protein kinase cascades including the reperfusion injury salvage kinase (RISK) pathway, redox signaling, and the mitochondrial permeability transition pore (mPTP). The common signaling pathway that appears to unite these 2 cardioprotective strategies at the time of reperfusion is the subject of this review. Importantly, this common cardioprotective pathway can be activated at the time of myocardial reperfusion in the clinical setting using pharmacological agents to target the essential signaling components, which should lead to the development of novel treatment strategies for improving the clinical outcomes of patients with CHD.

Inhibition of mitochondrial permeability transition improves functional recovery and reduces mortality following acute myocardial infarction in mice

Inhibition of mitochondrial permeability transition pore (mPTP) opening by cyclosporin A or ischemic postconditioning attenuates lethal reperfusion injury. Its impact on major post-myocardial infarction events, including worsening of left ventricular (LV) function and death, remains unknown. We sought to determine whether pharmacological or postconditioning-induced inhibition of mPTP opening might improve functional recovery and survival following myocardial infarction in mice. Anesthetized mice underwent 25 min of ischemia and 24 h (protocol 1) or 30 days (protocol 2) of reperfusion. At reperfusion, they received no intervention (control), postconditioning (3 cycles of 1 min ischemia-1 min reperfusion), or intravenous injection of the mPTP inhibitor Debio-025 (10 mg/kg). At 24 h of reperfusion, mitochondria were isolated from the region at risk for assessment of the Ca(2+) retention capacity (CRC). Infarct size was measured by triphenyltetrazolium chloride staining. At 30 days of reperfusion, mortality and LV contractile function (echocardiography) were evaluated. Postconditioning and Debio-025 significantly improved Ca(2+) retention capacity (132 +/- 13 and 153 +/- 31 vs. 53 +/- 16 nmol Ca(2+)/mg protein in control) and reduced infarct size to 35 +/- 4 and 32 +/- 7% of area at risk vs. 61 +/- 6% in control (P < 0.05). At 30 days, ejection fraction averaged 74 +/- 6 and 77 +/- 6% in postconditioned and Debio-025 groups, respectively, vs. 62 +/- 12% in the control group (P < 0.05). At 30 days, survival was improved from 58% in the control group to 92 and 89% in postconditioned and Debio-025 groups, respectively. Inhibition of mitochondrial permeability transition at reperfusion improves functional recovery and mortality in mice.

Mitochondrial medicine: pharmacological targeting of mitochondria in disease

Mitochondria play a central role in cell life and death and are known to be important in a wide range of diseases including the cancer, diabetes, cardiovascular disease, and the age-related neurodegenerative diseases. The unique structural and functional characteristics of mitochondria enable the selective targeting of drugs designed to modulate the function of this organelle for therapeutic gain. This review discusses mitochondrial drug targeting strategies and a variety of novel mitochondrial drug targets including the electron transport chain, mitochondrial permeability transition, Bcl-2 family proteins and mitochondrial DNA. Mitochondrial drug-targeting strategies will open up avenues for manipulating mitochondrial functions and allow for selective protection or eradication of cells for therapeutic gain in a variety of diseases.

Necrosis and apoptosis: sequence of liver damage following reperfusion after 60 min ischemia in rats

This study evaluated the time-dependent modes of cell death that occur during the course of reperfusion after 60 min ischemia. The serum ALT level increased immediately after reperfusion, peaked at 6 h and then declined gradually thereafter. This was supported by the H&E staining of the liver tissues taken at 2 h reperfusion, which revealed massive peri-portal necrosis. The succinate driven mitochondrial-swelling rate, release of cytochrome c into the cytoplasm, increase in caspase-3 activity and TUNEL stained tissue were measured to determine the changes in the biochemical markers of apoptosis. The biochemical markers of apoptosis increased by 2 h of reperfusion, peaked at 6 h and remained elevated throughout the 24 h reperfusion period. Cyclosporin A, an inhibitor of the mitochondrial permeability transition (MPT), inhibited MPT opening, the release of cytochrome c and caspase-3 activation. This indicates that necrotic death occurs particularly in the peri-portal region in the initial period of reperfusion, and delayed apoptotic death occurs primarily in the peri-central region in the liver tissues undergoing I/R.

Ethanol induced mitochondria injury and permeability transition pore opening: Role of mitochondria in alcoholic liver disease

AIM: To observe changes of mitochondria and investigate the effect of ethanol on mitochondrial perme-ability transition pore (PTP), mitochondrial membrane potential (MMP, ΔΨm) and intracellular calcium concentration in hepatocytes by establishing an animal model of alcoholic liver disease (ALD).

METHODS: Fourty adult male Wistar rats were randomly divided into two groups, the model group (20) was administered alcohol intragastrically plus an Oliver oil diet to establish an ALD model, and the control group (20) was given an equal amount of normal saline. The ultramicrostructural changes of mitochondria were observed under electron microscopy. Mitochondria of liver was extracted, and patency of PTP, mitochondrial membrane potential (ΔΨm), mitochondrial mass and intracellular calcium concentration of isolated hepacytes were detected by flow cytometry using rhodamine123 (Rh123), Nonyl-Acridine Orange and calcium fluorescent probe Fluo-3/AM, respectively.

RESULTS: Membrane and cristae were broken or disappeared in mitochondria in different shapes under electron microscopy. Some mitochondria showed U shape or megamitochondrion. In the model group, liver mitochondria PTP was broken, and mitochondria swelled, the absorbance at 450 nm, A540 decreased (0.0136 ± 0.0025 vs 0.0321 ± 0.0013, model vs control, P < 0.01); mitochondria transmembrane potential (239.4638 ±12.7263 vs 377.5850 ± 16.8119, P < 0.01) was lowered; mitochondrial mass (17.4350 ± 1.9880 vs 31.6738 ± 3.4930, P < 0.01); and [Ca²⁺]i was increased in liver cells (7.0020 ± 0.5008 vs 10.2050 ± 0.4701, P < 0.01).

CONCLUSION: Chronic alcohol intake might lead to broken mitochondria PTP, decreased mitochondria membrane potential and injury, and elevated intracellular Ca²⁺ production. Ethanol-induced chondriosome injury may be an important mechanism of alcoholic diseases.

Mitochondria, metabolic disturbances, oxidative stress and the kynurenine system, with focus on neurodegenerative disorders

The mitochondria have several important functions in the cell. A mitochondrial dysfunction causes an abatement in ATP production, oxidative damage and the induction of apoptosis, all of which are involved in the pathogenesis of numerous disorders. This review focuses on mitochondrial dysfunctions and discusses their consequences and potential roles in the pathomechanism of neurodegenerative disorders. Other pathogenetic factors are also briefly surveyed. The second part of the review deals with the kynurenine metabolic pathway, its alterations and their potential association with cellular energy impairment in certain neurodegenerative diseases. During energy production, most of the O(2) consumed by the mitochondria is reduced fully to water, but 1-2% of the O(2) is reduced incompletely to give the superoxide anion (O(2)(-)). If the function of one or more respiratory chain complexes is impaired for any reason, the enhanced production of free radicals further worsens the mitochondrial function by causing oxidative damage to macromolecules, and by opening the mitochondrial permeability transition pores thereby inducing apoptosis. These high-conductance pores offer a pathway which can open in response to certain stimuli, leading to the induction of the cells' own suicide program. This program plays an essential role in regulating growth and development, in the differentiation of immune cells, and in the elimination of abnormal cells from the organism. Both failure and exaggeration of apoptosis in a human body can lead to disease. The increasing amount of superoxide anions can react with nitric oxide to yield the highly toxic peroxynitrite anion, which can destroy cellular macromolecules. The roles of oxidative, nitrative and nitrosative damage are discussed. Senescence is accompanied by a higher degree of reactive oxygen species production, and by diminished functions of the endoplasmic reticulum and the proteasome system, which are responsible for maintenance of the normal protein homeostasis of the cell. In the event of a dysfunction of the endoplasmic reticulum, unfolded proteins aggregate in it, forming potentially toxic deposits which tend to be resistant to degradation. Cells possess adaptive mechanisms with which to avoid the accumulation of incorrectly folded proteins. These involve molecular chaperones that fold proteins correctly, and the ubiquitin proteasome system which degrades misfolded, unwanted proteins. Both the endoplasmic reticulum and the ubiquitin proteasome system fulfill cellular protein quality control functions. The kynurenine system: Tryptophan is metabolized via several pathways, the main one being the kynurenine pathway. A central compound of the pathway is kynurenine (KYN), which can be metabolized in two separate ways: one branch furnishing kynurenic acid, and the other 3-hydroxykynurenine and quinolinic acid, the precursors of NAD. An important feature of kynurenic acid is the fact that it is one of the few known endogenous excitatory amino acid receptor blockers with a broad spectrum of antagonistic properties in supraphysiological concentrations. One of its recently confirmed sites of action is the alpha7-nicotinic acetylcholine receptor and interestingly, a more recently identified one is a higher affinity positive modulatory binding site at the AMPA receptor. Kynurenic acid has proven to be neuroprotective in several experimental settings. On the other hand, quinolinic acid is a specific agonist at the N-methyl-d-aspartate receptors, and a potent neurotoxin with an additional and marked free radical-producing property. There are a number of neurodegenerative disorders whose pathogenesis has been demonstrated to involve multiple imbalances of the kynurenine pathway metabolism. These changes may disturb normal brain function and can add to the pathomechanisms of the diseases. In certain disorders, there is a quinolinic acid overproduction, while in others the alterations in brain kynurenic acid levels are more pronounced. A more precise knowledge of these alterations yields a basis for getting better therapeutic possibilities. The last part of the review discusses metabolic disturbances and changes in the kynurenine metabolic pathway in Parkinson's, Alzheimer's and Huntington's diseases.

Mitochondrial channelopathies in aging

Defects in ion channels (channelopathies) are increasingly found in a large spectrum of human pathologies including aging. Mutations in genes encoding ion channel proteins, which disrupt channel function, are the most commonly identified cause of channelopathies. Mutations in associated proteins, alterations in the expression of ion channels, or changes in the activity of non-mutated channel genes or associated proteins can also produce acquired channelopathies. Mitochondria, the powerhouse of the cells, are considered to be the most important cellular organelles to contribute to aging mainly because of their role in the production of reactive oxygen species in the initiation of apoptotic cell remodeling and in efficient ATP synthesis. During the past 50 years, multiple ion channels or transporters have been found in mitochondria, and the relationship between the activity of these channels and cellular aging, as well as the overall cellular biological function, has been intensively studied in a number of cell types and animal models. In this review, we discuss the better characterized mitochondrial ion channels whose dysfunction (mitochondrial channelopathies) may affect or accelerate the aging processes. These channels include the mitochondrial ATP-sensitive potassium channel (mitoK(ATP)), Ca(2+) transporters, voltage-dependent anion channel, and the mitochondrial permeability transition pore (mitoPTP).

Regulation of cytochrome C peroxidase activity by nitric oxide and laser irradiation

Apoptosis can be induced by activation of so-called "death receptors" (extrinsic pathway) or multiple apoptotic factors (intrinsic pathway), which leads to release of cytochrome c from mitochondria. This event is considered to be a point of no return in apoptosis. One of the most important events in the development of apoptosis is the enhancement of cytochrome c peroxidase activity upon its interaction with cardiolipin, which modifies the active center of cytochrome c. In the present work, we have investigated the effects of nitric oxide on the cytochrome c peroxidase activity when cytochrome c is bound to cardiolipin or sodium dodecyl sulfate. We have observed that cytochrome c peroxidase activity, distinctly increased due to the presence of anionic lipids, is completely suppressed by nitric oxide. At the same time, nitrosyl complexes of cytochrome c, produced in the interaction with nitric oxide, demonstrated sensitivity to laser irradiation (441 nm) and were photolyzed during irradiation. This decomposition led to partial restoration of cytochrome c peroxidase activity. Finally, we conclude that nitric oxide and laser irradiation may serve as effective instruments for regulating the peroxidase activity of cytochrome c, and, probably, apoptosis.

Upregulation of nitric oxide synthase II contributes to apoptotic cell death in the hippocampal CA3 subfield via a cytochrome c/caspase-3 signaling cascade following induction of experimental temporal lobe status epilepticus in the rat

Status epilepticus results in preferential neuronal cell loss in the hippocampus. We evaluated the hypothesis that the repertoire of intracellular events in the vulnerable hippocampal CA3 subfield after induction of experimental temporal lobe status epilepticus entails upregulation of nitric oxide synthase II (NOS II), followed by the release of mitochondrial cytochrome c that triggers the cytosolic caspase-3 cascade, leading to apoptotic cell death. In Sprague-Dawley rats, significant and temporally correlated upregulation of NOS II (3-24h), but not NOS I or II expression, enhanced cytosolic translocation of cytochrome c (days 1 and 3), augmented activated caspase-3 in cytosol (days 1, 3 and 7) and DNA fragmentation (days 1, 3 and 7) was detected bilaterally in the hippocampal CA3 subfield after elicitation of sustained seizure activity by microinjection of kainic acid into the unilateral CA3 subfield. Application bilaterally into the hippocampal CA3 subfield of a selective NOS II inhibitor, S-methylisothiourea, significantly blunted these apoptotic events; a selective NOS I inhibitor, N(omega)-propyl-l-arginine or a potent NOS III inhibitor, N(5)-(1-iminoethyl)-l-ornithine was ineffective. We conclude that upregulation of NOS II contributes to apoptotic cell death in the hippocampal CA3 subfield via a cytochrome c/caspase-3 signaling cascade following the induction of experimental temporal lobe status epilepticus.

Dual effect of thapsigargin on cell death in porcine aortic smooth muscle cells

A sustained increase in the cytosolic Ca(2+) concentration ([Ca(2+)](i)) can cause cell death. In this study, we found that, in cultured porcine aortic smooth muscle cells, endoplasmic reticulum (ER) stress, triggered by depletion of Ca(2+) stores by thapsigargin (TG), induced an increase in the [Ca(2+)](i) and cell death. However, the TG-induced death was not related to the [Ca(2+)](i) increase but was mediated by targeting of activated Bax to mitochondria and the opening of mitochondrial permeability transition pores (PTPs). Once the mitochondrial PTPs had opened, several events, including collapse of the mitochondrial membrane potential, cytochrome c release, and caspase-3 activation, occurred and the cells died. TG-induced cell death was completely inhibited by the pan-caspase inhibitor Z-VAD-fmk and was enhanced by the Ca(2+) chelator 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA), suggesting the existence of a Ca(2+)-dependent anti-apoptotic mechanism. After TG treatment, Ca(2+)-sensitive mitogen-activated protein kinase (MAPK) activation was induced and acted as a downstream effector of phosphatidylinositol 3-kinase (PI 3-kinase). The protective effect of Z-VAD-fmk on TG-induced cell death was reversed by BAPTA, PD-098059 (an MAPK kinase inhibitor), or LY-294002 (a PI 3-kinase inhibitor). Taken together, our data indicate that ER stress simultaneously activate two pathways, the mitochondrial caspase-dependent death cascade and the Ca(2+)-dependent PI 3-kinase/MAPK anti-apoptotic machinery. The Bax activation and translocation, but not the [Ca(2+)](i) increase, may activate mitochondrial PTPs, which, in turn, causes activation of caspases and cell death, whereas Ca(2+)-dependent MAPK activation counteracts death signaling; removal of Ca(2+) activated a second caspase-independent death pathway.

Epigallocatechin gallate inhibits nitric oxide-induced apoptosis in rat PC12 cells

Nitric oxide (NO) is associated with many pathophysiology of the central nervous system including brain ischemia, neurodegeneration and inflammation. Epigallocatechin gallate (EGCG) is a major compound of green tea polyphenol that has shown the protective activity against neuronal diseases. This study examined the effect of EGCG on NO-induced cell death in PC12 cells. The administration of sodium nitroprusside (SNP), a NO donor, decreased the cell viability and induced apoptosis showing characterization such as cell shrinkage and chromatin condensation as well as subG1 fraction of cell cycles. EGCG inhibited the cytotoxicity and apoptotic morphogenic changes induced by SNP. EGCG attenuated the production of reactive oxygen species (ROS) by SNP, and ameliorated the SNP-induced Bax to Bcl-2 expression ratio leading to apoptosis. In addition, EGCG prevented the release of cytochrome c from the mitochondria into the cytosol as well as the upregulation of the voltage-dependent anion channel (VDAC), a cytochrome c releasing channel, in the mitochondria of SNP-treated cells. EGCG abrogated the activation of caspase-9, caspase-8 and caspase-3 induced by SNP. These results demonstrate that EGCG has a protective effect against SNP-induced apoptosis in PC12 cells by scavenging ROS and modulating the signal molecules associated with cytochrome c, caspases, VDAC and the Bcl-2 family. These findings suggest that EGCG might be a natural neuroprotective substance.

Mitochondria: a target for cancer therapy

Mitochondria, the cells powerhouses, are essential for maintaining cell life, and they also play a major role in regulating cell death, which occurs upon permeabilization of their membranes. Once mitochondrial membrane permeabilization (MMP) occurs, cells die either by apoptosis or necrosis. Key factors regulating MMP include calcium, the cellular redox status (including levels of reactive oxygen species) and the mobilization and targeting to mitochondria of Bcl-2 family members. Contemporary approaches to targeting mitochondria in cancer therapy use strategies that either modulate the action of Bcl-2 family members at the mitochondrial outer membrane or use specific agents that target the mitochondrial inner membrane and the mitochondrial permeability transition (PT) pore. The aim of this review is to describe the major mechanisms regulating MMP and to discuss, with examples, mitochondrial targeting strategies for potential use in cancer therapy.

Novel lipid transfer property of two mitochondrial proteins that bridge the inner and outer membranes

This study provides evidence of a novel function for mitochondrial creatine kinase (MtCK) and nucleoside diphosphate kinase (NDPK-D). Both are basic peripheral membrane proteins with symmetrical homo-oligomeric structure, which in the case of MtCK was already shown to allow crossbridging of lipid bilayers. Here, different lipid dilution assays clearly demonstrate that both kinases also facilitate lipid transfer from one bilayer to another. Lipid transfer occurs between liposomes mimicking the lipid composition of mitochondrial contact sites, containing 30 mol % cardiolipin, but transfer does not occur when cardiolipin is replaced by phosphatidylglycerol. Ubiquitous MtCK, but not NDPK-D, shows some specificity in the nature of the lipids transferred and it is not active with phosphatidylcholine alone. MtCK can undergo reversible oligomerization between dimeric and octameric forms, but only the octamer can bridge membranes and promote lipid transfer. Cytochrome c, another basic mitochondrial protein known to bind to anionic membranes but not crosslinking them, is also incapable of promoting lipid transfer. The lipid transfer process does not involve vesicle fusion or loss of the internal contents of the liposomes.

The role of the mitochondrial permeability transition in cell death

The mitochondrial permeability transition (MPT) is a non-selective inner membrane permeabilization that occurs in response to increased calcium load and redox stress. Currently, two models of the MPT exist including the, largely hypothetical, native proteinaceous pore model and the oxidized inner membrane protein model which may reflect the extremes in a continuum of changes that occur to the inner membrane prior to its permeabilization. Here I discuss evidence that the MPT per se leads to necrosis, but not cytochrome c release and apoptosis. However, data also suggest that signaling crosstalk between the MPT and Bcl-2 family proteins occurs indicating an important role for the MPT in apoptosis.

The permeability transition pore complex in cancer cell death

The permeability transition pore (PTP) is a multi-protein complex at contact sites of the inner with the outer mitochondrial membrane. Research over the past years has led to the concept that the PTP occupies a central role in cell death induction. Numerous apoptosis signals convert this protein aggregate into an unspecific pore, thus activating mitochondria for the cellular self-destruction process. Here, we describe the evidence for this and the various approaches being undertaken to elucidate its subunit composition and mode of regulation. In particular, we review data that indicate a role of specific PTP subunits for apoptosis inhibition during tumorigenesis.

Cholinergic-receptor-independent dysfunction of mitochondrial respiratory chain enzymes, reduced mitochondrial transmembrane potential and ATP depletion underlie necrotic cell death induced by the organophosphate poison mevinphos

Our current understanding of the nature of cell death that is associated with fatal organophosphate poisoning and the underlying cellular mechanisms is surprisingly limited. Taking advantage of the absence in an in vitro system of acetylcholinesterase, the pharmacological target of organophosphate compounds, the present study evaluated the hypothesis that the repertoire of cholinergic receptor-independent cellular events that underlie fatal organophosphate poisoning entails induction of mitochondrial dysfunction, followed by bioenergetic failure that leads to necrotic cell death because of ATP depletion. Pheochromocytoma PC12 cells incubated with the organophosphate pesticide mevinphos (0.4 or 4mumol) for 1 or 3h underwent a dose-related and time-dependent loss of cell viability that was not reversed by muscarinic (atropine) or nicotinic (mecamylamine) blockade. This was accompanied by depressed NADH cytochrome c reductase, succinate cytochrome c reductase or cytochrome c oxidase activity in the mitochondrial respiratory chain, reduced mitochondrial transmembrane potential, decreased ATP concentration, elevated ADP/ATP ratio, increased lactate dehydrogenase release and necrotic cell death. We conclude that Mev induces cholinergic receptor-independent necrotic cell death by depressing the activity of Complexes I to IV in the mitochondrial respiratory chain, eliciting reduction in mitochondrial transmembrane potential, depleting intracellular ATP contents and damaging cell membrane integrity.

Modulation of electron transport protects cardiac mitochondria and decreases myocardial injury during ischemia and reperfusion

Mitochondria are increasingly recognized as lynchpins in the evolution of cardiac injury during ischemia and reperfusion. This review addresses the emerging concept that modulation of mitochondrial respiration during and immediately following an episode of ischemia can attenuate the extent of myocardial injury. The blockade of electron transport and the partial uncoupling of respiration are two mechanisms whereby manipulation of mitochondrial metabolism during ischemia decreases cardiac injury. Although protection by inhibition of electron transport or uncoupling of respiration initially appears to be counterintuitive, the continuation of mitochondrial oxidative phosphorylation in the pathological milieu of ischemia generates reactive oxygen species, mitochondrial calcium overload, and the release of cytochrome c. The initial target of these deleterious mitochondrial-driven processes is the mitochondria themselves. Consequences to the cardiomyocyte, in turn, include oxidative damage, the onset of mitochondrial permeability transition, and activation of apoptotic cascades, all favoring cardiomyocyte death. Ischemia-induced mitochondrial damage carried forward into reperfusion further amplifies these mechanisms of mitochondrial-driven myocyte injury. Interruption of mitochondrial respiration during early reperfusion by pharmacologic blockade of electron transport or even recurrent hypoxia or brief ischemia paradoxically decreases cardiac injury. It increasingly appears that the cardioprotective paradigms of ischemic preconditioning and postconditioning utilize modulation of mitochondrial oxidative metabolism as a key effector mechanism. The initially counterintuitive approach to inhibit mitochondrial respiration provides a new cardioprotective paradigm to decrease cellular injury during both ischemia and reperfusion.

A wave of reactive oxygen species (ROS)-induced ROS release in a sea of excitable mitochondria

Once considered simply as the main source of ATP, mitochondria are now implicated in the control of many additional aspects of cell physiology, such as calcium signaling, and pathology, as in injury incurred on ischemia and subsequent reperfusion (I/R). Mitochondrial respiration is ordinarily accompanied by low-level ROS production, but they can respond to elevated ROS concentrations by increasing their own ROS production, a phenomenon termed ROS-induced ROS release (RIRR). Two modes of RIRR have been described. In the first mode of RIRR, enhanced ROS leads to mitochondrial depolarization via activation of the MPTP, yielding a short-lived burst of ROS originating from the mitochondrial electron transport chain (ETC). The second mode of RIRR is MPTP independent but is regulated by the mitochondrial benzodiazepine receptor (mBzR). Increased ROS in the mitochondrion triggers opening of the inner mitochondrial membrane anion channel (IMAC), resulting in a brief increase in ETC-derived ROS. Both modes of RIRR have been shown to transmit localized mitochondrial perturbations throughout the cardiac cell in the form of oscillations or waves but are kinetically distinct and may involve different ROS that serve as second messengers. In this review, we discuss the mechanisms of these different modes of RIRR.

Hypoxia and Reoxygenation: a Possible Mechanism for Placental Oxidative Stress in Preeclampsia

Preeclampsia is a human pregnancy-specific disorder that is diagnosed by the new appearance of hypertension and proteinuria after 20 weeks' gestation. It is a leading cause of perinatal morbidity and mortality, and the only intervention that effectively reverses the syndrome is delivery. Oxidative stress of the placenta is considered to be a key intermediary step in the pathogenesis of preeclampsia, but the cause for the stress remains unknown. Hypoxia-reoxygenation (H/R) injury, as a result of intermittent placental perfusion secondary to deficient trophoblast invasion of the endometrial arteries, is a possible mechanism. In this review, we present evidence to show that there is a plausible basis from which to assume that blood flow in the intervillous space will be intermittent in all normal pregnancies. The intermittency will be exacerbated by impaired conversion of the spiral arteries, or by the presence of atherotic changes that reduce their caliber as seen in preeclampsia. Placental oxidative stress can be the consequences of fluctuations in oxygen concentrations after H/R through the actions of reactive oxygen species. On this basis, there will be a complete spectrum of placental changes among the normal, the late onset and the early onset preeclamptic states. Viewing the syndrome as a continuum of H/R insults provides new insight into the pathophysiology of pregnancy that will hope fully lead to improved clinical interventions.

Heat shock protein 60 in rostral ventrolateral medulla reduces cardiovascular fatality during endotoxaemia in the rat

The rostral ventrolateral medulla (RVLM) is the origin of a 'life-and-death' signal that reflects central cardiovascular regulatory failure during brain stem death. Using an experimental endotoxaemia model, we evaluated the hypothesis that the 60 kDa heat shock protein 60 (HSP60) reduces cardiovascular fatality during brain stem death via an anti-apoptotic action in the RVLM. In Sprague-Dawley rats maintained under propofol anaesthesia, proteomic or Western blot analysis revealed a progressive augmentation of HSP60 expression in the RVLM after intravenous administration of Escherichia coli lipopolysaccharide (30 mg kg(-1)). Pretreatment with a microinjection of actinomycin D or cycloheximide into bilateral RVLM significantly blunted this HSP60 increase, whereas real-time PCR showed progressive augmentation of hsp60 mRNA. Intriguingly, superimposed on the augmented expression was a progressive decline in mitochondrial, or elevation in cytosolic, HSP60 in ventrolateral medulla. Loss-of-function manipulations in the RVLM using anti-HSP60 antiserum or antisense hsp60 oligonucleotide exacerbated mortality by potentiating the cardiovascular depression during experimental endotoxaemia, alongside intensified nucleosomal DNA fragmentation, elevated cytoplasmic histone-associated DNA fragments or augmented cytochromec-caspase-3 cascade of apoptotic signalling in the RVLM. Immunoprecipitation coupled with immunoblot analysis further revealed a progressive increase in the complex formed between HSP60 and mitochondrial or cytosolic Bax or mitochondrial Bcl-2 during endotoxaemia, alongside a dissociation of the cytosolic HSP60-Bcl-2 complex. We conclude that HSP60 redistributed from mitochondrion to cytosol in the RVLM confers neuroprotection against fatal cardiovascular depression during endotoxaemia via reduced activation of the cytochrome c-caspase-3 cascade of apoptotic signalling through enhanced interactions with mitochondrial or cytosolic Bax or Bcl-2.

Direct interaction and reciprocal regulation between ASK1 and calcineurin-NFAT control cardiomyocyte death and growth

The calcium-calmodulin-activated protein phosphatase calcineurin functions as a key mediator of diverse biologic processes, including differentiation, apoptosis, growth, and adaptive responses, in part through dephosphorylation and activation of nuclear factor of activated T-cell (NFAT) transcription factors. Apoptosis signal-regulating kinase 1 (ASK1) is an upstream component of the mitogen-activated protein kinases that serves as a pivotal regulator of cytokine-, oxidative-, and stress-induced cell death. Here, we performed a yeast two-hybrid screen with calcineurin B as bait, which identified ASK1 as a direct physical interacting partner. The C-terminal 218 amino acids of ASK1 were sufficient to mediate interaction with calcineurin B in yeast, as well as in mammalian cell lysates. Importantly, endogenous calcium binding B subunit (CnB) protein interacted with endogenous ASK1 protein in cardiomyocytes at baseline, suggesting that the interaction observed in yeast was of potential biologic relevance. Indeed, calcineurin directly dephosphorylated ASK1 at serine 967 using purified proteins or mammalian cell lysates. Dephosphorylation of ASK1 serine 967 by calcineurin promoted its disassociation from 14-3-3 proteins, resulting in ASK1 activation. Calcineurin and ASK1 cooperatively enhanced cardiomyocyte apoptosis, while expression of a dominant negative ASK1 blocked calcineurin-induced apoptosis. Mouse embryonic fibroblasts deficient in ask1 were also partially resistant to calcineurin- or ionomycin-induced apoptosis. Finally, ASK1 negatively regulated calcineurin-NFAT signaling indirectly through c-Jun NH2-terminal kinase (JNK)- and p38-mediated phosphorylation of NFAT, which blocked calcineurin- and agonist-dependent hypertrophic growth of cardiomyocytes. Thus, ASK1 and calcineurin-NFAT constitute a feedback regulatory circuit in which calcineurin positively regulates ASK1 through direct dephosphorylation, while ASK1 negatively regulates calcineurin-NFAT signaling through p38- and JNK-mediated NFAT phosphorylation.

The mechanism by which the mitochondrial ATP-sensitive K+ channel opening and H2O2 inhibit the mitochondrial permeability transition

Myocardial infarction is a manifestation of necrotic cell death as a result of opening of the mitochondrial permeability transition (MPT). Receptor-mediated cardioprotection is triggered by an intracellular signaling pathway that includes phosphatidylinositol 3-kinase, endothelial nitric-oxide synthase, guanylyl cyclase, protein kinase G (PKG), and the mitochondrial K(ATP) channel (mitoK(ATP)). In this study, we explored the pathway that links mitoK(ATP) with the MPT. We confirmed previous findings that diazoxide and activators of PKG or protein kinase C (PKC) inhibited MPT opening. We extended these results and showed that other K(+) channel openers as well as the K(+) ionophore valinomycin also inhibited MPT opening and that this inhibition required reactive oxygen species. By using isoform-specific peptides, we found that the effects of K(ATP) channel openers, PKG, or valinomycin were mediated by a PKCepsilon. Activation of PKCepsilon by phorbol 12-myristate 13-acetate or H(2)O(2) resulted in mitoK(ATP)-independent inhibition of MPT opening, whereas activation of PKCepsilon by PKG or the specific PKCepsilon agonist psiepsilon receptor for activated C kinase caused mitoK(ATP)-dependent inhibition of MPT opening. Exogenous H(2)O(2) inhibited MPT, because of its activation of PKCepsilon, with an IC(50) of 0.4 (+/-0.1) microm. On the basis of these results, we propose that two different PKCepsilon pools regulate this signaling pathway, one in association with mitoK(ATP) and the other in association with MPT.

Discovering novel chemical inhibitors of human cyclophilin A: virtual screening, synthesis, and bioassay

Cyclophilin A (CypA) is a member of cyclophilins, a family of the highly homologous peptidyl prolyl cis-trans isomerases (PPIases), which can bind to cyclosporin A (CsA). CypA plays critical roles in various biological processes, including protein folding, assembly, transportation, regulation of neuron growth, and HIV replication. The discovery of CypA inhibitor is now of a great special interest in the treatment of immunological disorders. In this study, a series of novel small molecular CypA inhibitors have been discovered by using structure-based virtual screening in conjunction with chemical synthesis and bioassay. The SPECS_1 database containing 85,000 small molecular compounds was searched by virtual screening against the crystal structure of human CypA. After SPR-based binding affinity assay, 15 compounds were found to show binding affinities to CypA at submicro-molar or micro-molar level (compounds 1-15). Seven compounds were selected as the starting point for the further structure modification in considering binding activity, synthesis difficulty, and structure similarity. We thus synthesized 40 new small molecular compounds (1-6, 15, 16a-q, 17a-d, and 18a-l), and four of which (compounds 16b, 16h, 16k, and 18g) showed high CypA PPIase inhibition activities with IC50s of 2.5-6.2 microM. Pharmacological assay indicated that these four compounds demonstrated somewhat inhibition activities against the proliferation of spleen cells.

Adaptive responses of vertebrate neurons to anoxia--matching supply to demand

Oxygen depleted environments are relatively common on earth and represent both a challenge and an opportunity to organisms that survive there. A commonly observed survival strategy to this kind of stress is a lowering of metabolic rate or metabolic depression. Whether metabolic rate is at a normal or a depressed level the supply of ATP (glycolysis and oxidative phosphorylation) must match the cellular demand for ATP (protein synthesis and ion pumping), a condition that must of course be met for long-term survival in hypoxic and anoxic environments. Underlying a decrease in metabolic rate is a corresponding decrease in both ATP supply and ATP demand pathways setting a new lower level for ATP turnover. Both sides of this equation can be actively regulated by second messenger pathways but it is less clear if they are regulated differentially or even sequentially with the onset of anoxia. The vertebrate brain is extremely sensitive to low oxygen levels yet some species can survive in oxygen depleted environments for extended periods and offer a working model of brain survival without oxygen. Hypoxia tolerant vertebrate brain will be the primary focus of this review; however, we will draw upon research involving hypoxia/ischemia tolerance mechanisms in liver and heart to offer clues to how brain can tolerate anoxia. The issue of regulating ATP supply or demand pathways will also be addressed with a focus on ion channel arrest being a significant mechanism to reduce ATP demand and therefore metabolic rate. Furthermore, mitochondria are ideally situated to serve as cellular oxygen sensors and mediator of protective mechanisms such as ion channel arrest. Therefore, we will also describe a mitochondria based mechanism of ion channel arrest involving ATP-sensitive mitochondrial K(+) channels, cytosolic calcium and reaction oxygen species concentrations.

Decreased ANT content in Zucker fatty rats: relevance for altered hepatic mitochondrial bioenergetics in steatosis

Mitochondria from Zucker fatty (ZF) rats (a model for fatty liver disease) showed a delay in the repolarization after a phosphorylative cycle and a decrease on state 3 respiration, suggesting alterations at the phosphorylative system level. The ATPase activity showed no differences between control and ZF rats, implying alterations in other components of the phosphorylative system. A pronounced depletion in the content of the adenine nucleotide translocator (ANT) was observed by Western blotting, while no alterations were found in the mitochondrial voltage-dependent anion channel content. These data suggest that hepatic accumulation of fat impairs mitochondrial function, reflecting the loss of oxidative phosphorylation capacity caused by a decrease in the ANT content.

Mitochondrial creatine kinase in human health and disease

Mitochondrial creatine kinase (MtCK), together with cytosolic creatine kinase isoenzymes and the highly diffusible CK reaction product, phosphocreatine, provide a temporal and spatial energy buffer to maintain cellular energy homeostasis. Mitochondrial proteolipid complexes containing MtCK form microcompartments that are involved in channeling energy in form of phosphocreatine rather than ATP into the cytosol. Under situations of compromised cellular energy state, which are often linked to ischemia, oxidative stress and calcium overload, two characteristics of mitochondrial creatine kinase are particularly relevant: its exquisite susceptibility to oxidative modifications and the compensatory up-regulation of its gene expression, in some cases leading to accumulation of crystalline MtCK inclusion bodies in mitochondria that are the clinical hallmarks for mitochondrial cytopathies. Both of these events may either impair or reinforce, respectively, the functions of mitochondrial MtCK complexes in cellular energy supply and protection of mitochondria form the so-called permeability transition leading to apoptosis or necrosis.

Patch clamp reveals powerful blockade of the mitochondrial permeability transition pore by the D2‐receptor agonist pramipexole

The dopamine-D2-agonist pramipexole (PPX) was tested for blocking mitochondrial permeability transition (PT) in order to give a possible explanation for its neuroprotective effect seen in PPX-treated Parkinson's disease patients. Patch-clamp techniques for studying single-channel currents in the inner mitochondrial membrane and large-amplitude swelling of energized mitochondria were used to study PPX action on the permeability transition pore (PTP), a key player in the mitochondrial route of the apoptotic cascade. Identity of the PTP was proven by measuring the concentration-response relation for cyclosporin A-blockade (IC50=26 nM). PPX inhibits the PTP reversibly with an IC50 of 500 nM, which is close to the values determined earlier as plasma concentrations after PPX medication in patients. Interaction of PPX with the PTP is further supported by demonstrating that it abolished Ca2+-triggered swelling in functionally intact mitochondria. Blockade of the PTP by PPX was attenuated by increasing concentrations of inorganic phosphate and by acidification. We suggest that PPX could exert part of its neuroprotective effect by inhibition of the PTP and thus, probably, blocking of the mitochondrial pathway of the apoptosis cascade.

Involvement of apoptosis in malathion-induced cytotoxicity in a grass carp (Ctenopharyngodon idellus) cell line

We investigated the role of apoptosis in malathion-induced cytotoxicity in the grass carp (Ctenopharyngodon idellus) cell line ZC-7901. Fish cells were treated with different concentrations of malathion (0.62-95 mg/L), and the IC(50) ranged from 37.94+/-1.93 mg/L for 12 h to 3.04+/-0.27 mg/L for 72 h by the MTT assay. Apoptosis was detected by confocal laser scanning microscopy, transmission electron microscopy, TUNEL reaction, DNA laddering and a flow cytometric PI staining assay. The results demonstrated that apoptosis was involved in the cytotoxic effect of malathion, and that malathion-induced apoptosis occurred in a dose- and time-dependent manner. In addition, the induction of apoptosis by malathion was accompanied by mitochondrial membrane potential (DeltaPsi(m)) disruption, intracellular Ca(2+) elevation, generation of reactive oxygen species (ROS) and ATP depletion. Our investigation suggested that malathion exerts its cytotoxic effects by the induction of apoptosis via a direct effect on the mitochondria.

Mitochondrial membrane permeabilization: the sine qua non for cell death

Mitochondria are essential for maintaining cell life but they also play a role in regulating cell death, which occurs when their membranes become permeabilized. Mitochondria possess two distinct membrane systems including an outer membrane in close communication with the cytosol and an inner membrane involved in energy transduction. Outer membrane permeabilization is regulated by Bcl-2 family proteins, which control the release of proteins from the mitochondrial intermembrane space; these proteins then activate apoptosis. Inner membrane permeabilization is regulated by the mitochondrial permeability transition (MPT), which is activated by calcium and oxidative stress and leads to bioenergetic failure and necrosis. The purpose of this review is to discuss the biochemical mechanisms regulating mitochondrial membrane permeabilization; this is crucial to our understanding of the role of cell death in diseases such as cancer and the neurodegenerative diseases.

New insights on brain stem death: From bedside to bench

As much as brain stem death is currently the clinical definition of death in many countries and is a phenomenon of paramount medical importance, there is a dearth of information on its mechanistic underpinnings. A majority of the clinical studies are concerned only with methods to determine brain stem death. Whereas a vast amount of information is available on the cellular and molecular mechanisms of cell death, rarely are these studies directed specifically towards the understanding of brain stem death. This review presents a framework for translational research on brain stem death that is based on systematically coordinated clinical and laboratory efforts that center on this phenomenon. It begins with the identification of a novel clinical marker from patients that is related specifically to brain stem death. After realizing that this "life-and-death" signal is related to the functional integrity of the brain stem, its origin is traced to the rostral ventrolateral medulla (RVLM). Subsequent laboratory studies on this neural substrate in animal models of brain stem death provide credence to the notion that both "pro-life" and "pro-death" programs are at work during the progression towards death. Those programs (mitochondrial functions, nitric oxide, peroxynitrite, superoxide anion, coenzyme Q10, heat shock proteins and ubiquitin-proteasome system) hitherto identified from the RVLM are presented, along with their cellular and molecular mechanisms. It is proposed that outcome of the interplay between the "pro-life" and "pro-death" programs (dying) in this neural substrate determines the final fate of the individual (being dead). Thus, identification of additional programs in the RVLM and delineation of their regulatory mechanisms should shed new lights on future directions for clinical management of life-and-death.

Effect of sphingosine on Ca2+ entry and mitochondrial potential of Jurkat T cells--interaction with Bcl2

Triggers of Jurkat T cell apoptosis include sphingosine and ceramide. Sphingosine and ceramide further inhibit capacitative Ca2+ entry (ICRAC), an effect leading to inactivation but not death of Jurkat T cells. Mitochondria are key organelles in the machinery leading to apoptosis and on the other hand have been shown to participate in the regulation of Ca2+ entry. The present experiments were performed to explore whether treatment of Jurkat T cells with sphingosine leads to apoptosis and reduced Ca2+ entry and whether those effects are sensitive to expression of the antiapoptotic protein Bcl2, localized in the outer mitochondrial membrane. Exposure of Jurkat T cells to 10 microM spingosine was according to DiOC6 fluorescence followed by mitochondrial depolarization and according to Fura-red/Fluo-3 fluorescence followed by decreased capacitative Ca2+ entry. Mitochondrial depolarization was significantly delayed in cells overexpressing wild type Bcl2 or Bcl2 targeted to the mitochondrial membrane, whereas no significant influence on mitochondrial depolarization was observed in cells expressing Bcl2 lacking the membrane targeting motif or Bcl2 targeted to the endoplasmatic reticulum. In contrast to mitochondrial potential, the blunting of capacitative Ca2+ entry following sphingosine treatment was not sensitive to mitochondrial Bcl2 expression. In conclusion sphingosine exposure leads to both, mitochondrial depolarization and inhibition of capacitative Ca2+ entry. Mitochondrial Bcl2 reverses the effect on mitochondria but not on Ca2+ entry and thus leads to dissociation of those two sequelae of sphingosine treatment.

Effects of decreasing mitochondrial volume on the regulation of the permeability transition pore

The permeability transition pore (PTP) is a Ca(2+)-sensitive mitochondrial inner membrane channel involved in several models of cell death. Because the matrix concentration of PTP regulatory factors depends on matrix volume, we have investigated the role of the mitochondrial volume in PTP regulation. By incubating rat liver mitochondria in media of different osmolarity, we found that the Ca(2+) threshold required for PTP opening dramatically increased when mitochondrial volume decreased relative to the standard condition. This shrinkage-induced PTP inhibition was not related to the observed changes in protonmotive force, or pyridine nucleotide redox state and persisted when mitochondria were depleted of adenine nucleotides. On the other hand, mitochondrial volume did not affect PTP regulation when mitochondria were depleted of Mg(2+). By studying the effects of Mg(2+), cyclosporin A (CsA) and ubiquinone 0 (Ub(0)) on PTP regulation, we found that mitochondrial shrinkage increased the efficacy of Mg(2+) and Ub(0) at PTP inhibition, whereas it decreased that of CsA. The ability of mitochondrial volume to alter the activity of several PTP regulators represents a hitherto unrecognized characteristic of the pore that might lead to a new approach for its pharmacological modulation.

Nitric oxide applications prior and simultaneous to potentially excitotoxic NMDA-evoked calcium transients: Cell death or survival

Nitric oxide (NO) is a molecule that plays a prominent role in neurotoxic as well as neuroprotective pathways. Here, we investigated the effects of NO on potentially excitotoxic glutamate-induced intracellular calcium ([Ca2+]i) dynamics. Our hypothesis was that pre- and coexposure to NO in conjunction with glutamate receptor stimulation modulates [Ca2+]i responses differentially. [Ca2+]i transients, assessed by the fluorescent cytosolic Ca2+ indicator dye fluo-4, were elicited in mouse striatal neurons by consecutive NMDA applications (200 microM for 100 s each). Subgroups of neuronal cultures were additionally exposed to a NO donor (S-nitroso-N-acetyl-d,l-penicillamine, SNAP, 50-500 microM), either by pre- (for 6 h prior to NMDA) or cotreatment (for 30 min during NMDA). Pretreatment with NO led to dramatically decreased NMDA-evoked [Ca2+]i rises in comparison to controls (NMDA alone). Annexin V/propidium iodide staining showed consistently that NO pretreatment is protective against NMDA-induced cell death. In contrast, NO/NMDA cotreatment caused a potentiation of [Ca2+]i rises, whereby the duration of [Ca2+]i transients following NMDA application was prolonged and remained at an increased plateau level. Simultaneous application of the mitochondrial permeability transition pore (mtPTP) blocker cyclosporin A (2 microM) during the NO/NMDA cotreatment prevented the deregulation of [Ca2+]i. The observed [Ca2+]i deregulation was accompanied by a decrease in the mitochondrial membrane potential as indicated by tetramethylrhodamine methylester (TMRM) fluorescence. These findings suggest that NO can act in a protective way due to preconditioning or can have a possibly detrimental impact in case of acute release. They provide a possible explanation for the ambivalence of NO in neurodegenerative processes where glutamate receptor stimulation and mitochondrial [Ca2+]i sequestration are causally involved.

Malonate induces cell death via mitochondrial potential collapse and delayed swelling through an ROS-dependent pathway

1. Herein we study the effects of the mitochondrial complex II inhibitor malonate on its primary target, the mitochondrion. 2. Malonate induces mitochondrial potential collapse, mitochondrial swelling, cytochrome c (Cyt c) release and depletes glutathione (GSH) and nicotinamide adenine dinucleotide coenzyme (NAD(P)H) stores in brain-isolated mitochondria. 3. Although, mitochondrial potential collapse was almost immediate after malonate addition, mitochondrial swelling was not evident before 15 min of drug presence. This latter effect was blocked by cyclosporin A (CSA), Ruthenium Red (RR), magnesium, catalase, GSH and vitamin E. 4. Malonate added to SH-SY5Y cell cultures produced a marked loss of cell viability together with the release of Cyt c and depletion of GSH and NAD(P)H concentrations. All these effects were not apparent in SH-SY5Y cells overexpressing Bcl-xL. 5. When GSH concentrations were lowered with buthionine sulphoximine, cytoprotection afforded by Bcl-xL overexpression was not evident anymore. 6. Taken together, all these data suggest that malonate causes a rapid mitochondrial potential collapse and reactive oxygen species production that overwhelms mitochondrial antioxidant capacity and leads to mitochondrial swelling. Further permeability transition pore opening and the subsequent release of proapoptotic factors such as Cyt c could therefore be, at least in part, responsible for malonate-induced toxicity.

Porin and cytochrome oxidase containing contact sites involved in the oxidation of cytosolic NADH

Cytochrome c (cyto-c) added to isolated mitochondria promotes the oxidation of extra-mitochondrial NADH and the reduction of molecular oxygen associated to the generation of an electrochemical membrane potential available for ATP synthesis. The electron transport pathway activated by exogenous cyto-c molecules is completely distinct from the one catalyzed by the respiratory chain. Dextran sulfate (500 kDa), known to interact with porin (the voltage-dependent anion channel), other than to inhibit the release of ATP synthesized inside the mitochondria, greatly decreases the activity of exogenous NADH/cyto-c system of intact mitochondria but has no effect on the reconstituted system made of mitoplasts and external membrane preparations. The results obtained are consistent with the existence of specific contact sites containing cytochrome oxidase and porin, as components of the inner and the outer membrane respectively, involved in the oxidation of cytosolic NADH. The proposal is put forward that the bi-trans-membrane electron transport chain activated by cytosolic cyto-c becomes, in physio-pathological conditions: (i) functional in removing the excess of cytosolic NADH; (ii) essential for cell survival in the presence of an impairment of the first three respiratory complexes; and (iii) an additional source of energy at the beginning of apoptosis.

Mechanisms of benzarone and benzbromarone-induced hepatic toxicity

Treatment with benzarone or benzbromarone can be associated with hepatic injury. Both drugs share structural similarities with amiodarone, a well-known mitochondrial toxin. Therefore, we investigated the hepatotoxicity of benzarone and benzbromarone as well as the analogues benzofuran and 2-butylbenzofuran. In isolated rat hepatocytes, amiodarone, benzarone, and benzbromarone (20 micromol/L) decreased mitochondrial membrane potential by 23%, 54% or 81%, respectively. Benzofuran and 2-butylbenzofuran had no effect up to 100 micromol/L. In isolated rat liver mitochondria, amiodarone, benzarone, and benzbromarone, but not benzofuran, decreased state 3 oxidation and respiratory control ratios for L-glutamate (50% decrease of respiratory control ratio at [micromol/L]: amiodarone, 12.9; benzarone, 10.8; benzbromarone, <1). Amiodarone, benzarone, and benzbromarone, but not benzofuran, also uncoupled oxidative phosphorylation. Mitochondrial beta-oxidation was decreased by 71%, 87%, and 58% with 100 micromol/L amiodarone or benzarone and 50 micromol/L benzbromarone, respectively, but was unaffected by benzofuran, whereas ketogenesis was not affected. 2-Butylbenzofuran weakly inhibited state 3 oxidation and beta-oxidation only at 100 micromol/L. In the presence of 100 micromol/L amiodarone, benzarone or benzbromarone, reactive oxygen species production was increased, mitochondrial leakage of cytochrome c was induced in HepG2 cells, and permeability transition was induced in isolated rat liver mitochondria. At the same concentrations, amiodarone, benzarone, and benzbromarone induced apoptosis and necrosis of isolated rat hepatocytes. In conclusion, hepatotoxicity associated with amiodarone, benzarone, and benzbromarone can at least in part be explained by their mitochondrial toxicity and the subsequent induction of apoptosis and necrosis. Side chains attached to the furan moiety are necessary for rendering benzofuran hepatotoxic.

Effects of cyclophilin A on cell proliferation and gene expressions in human vascular smooth muscle cells and endothelial cells

BACKGROUND

Cyclophilin A (CypA) is a cytosolic protein which involves many biological functions including immune modulation, cell growth, tumorigenesis, and vascular disease. The objective of this study was to determine the effect of CypA on cell proliferation and several gene expressions in human endothelial cells and vascular smooth muscle cells.

METHODS

Human coronary artery endothelial cells (HCAEC), human lung microvascular endothelial cells (HMVEC-L), and human aorta smooth muscle cells (HAoSMC) were used in this study. Cells were treated with 10 nM CypA for 24 h. The cell proliferation was determined by [3H]thymidine incorporation. The mRNA levels of 13 genes including CD147 (receptor for CypA), PDGF-BB, endothelin-1 (ET-1), vascular endothelial growth factor receptor-1 (VEGFR-1), VEGFR-2, VEGFR-3, neuropilin-1 (NRP-1), NRP-2, eNOS, iNOS, nNOS, ICAM-1, and PECAM-1 were semiquantitatively determined by real time RT-PCR as standardized with a house keeping gene beta-actin.

RESULTS

CypA significantly increased cell proliferation of HAoSMC and HMVEC-L by 31% and 45%, respectively, as compared to controls, but had no effect on HCAEC. Blocking CD147 did not affect the mitogenic action of CypA. In addition, CypA also significantly increased the mRNA expression of CD147 by 43% and VEGFR-2 by 65% in HAoSMCs (P < 0.05, t test). HAoSMCs expressed much higher CD147 and neuropilin-1 (NRP-1) mRNA than HMVECs-L and HCAECs (P < 0.017, ANOVA). Furthermore, CypA increased ET-1 mRNA by 22% and VEGFR-1 mRNA by 23% in HMVECs-L, but had limited effects on HCAECs. HMVECs-L had much higher expressions of PDGF-BB, ET-1, VEGFR-2, VEGFR-1, VEGFR-3, and NRP-2 than HAoSMCs and HCAECs (P < 0.017, ANOVA). By contrast, HCAECs had much higher ICAM-1 mRNA levels than HMVECs-L and HAoSMCs (P < 0.017, ANOVA).

CONCLUSIONS

These data demonstrate that CypA has a mitogenic effect on HAoSMCs and HMVECs-L, but not HCAECs. CD147 may not mediate the action of CypA. In addition, CypA substantially alters the mRNA levels of several key genes in human vascular cells, indicating potential multifunctional roles of CypA in vascular system. Furthermore, this study provides several new aspects of gene expressions in vascular cells.

Metformin inhibits mitochondrial permeability transition and cell death: a pharmacological in vitro study

Metformin, a drug widely used in the treatment of Type II diabetes, has recently received attention owing to new findings regarding its mitochondrial and cellular effects. In the present study, the effects of metformin on respiration, complex 1 activity, mitochondrial permeability transition, cytochrome c release and cell death were investigated in cultured cells from a human carcinoma-derived cell line (KB cells). Metformin significantly decreased respiration both in intact cells and after permeabilization. This was due to a mild and specific inhibition of the respiratory chain complex 1. In addition, metformin prevented to a significant extent mitochondrial permeability transition both in permeabilized cells, as induced by calcium, and in intact cells, as induced by the glutathione-oxidizing agent t-butyl hydroperoxide. This effect was equivalent to that of cyclosporin A, the reference inhibitor. Finally, metformin impaired the t-butyl hydroperoxide-induced cell death, as judged by Trypan Blue exclusion, propidium iodide staining and cytochrome c release. We propose that metformin prevents the permeability transition-related commitment to cell death in relation to its mild inhibitory effect on complex 1, which is responsible for a decreased probability of mitochondrial permeability transition.