Release of cytochrome c from liver mitochondria during permeability transition

Mechanistic insights into Retama raetam's anti-proliferative and pro-apoptotic effects in A549 lung cancer cells: targeting PI3K/Akt pathway and ROS production

Lung cancer, particularly non-small cell lung cancer (NSCLC), is a leading cause of cancer-related deaths worldwide. This study investigates the molecular mechanisms behind the anti-cancer effects of the tropical desert plant Retama raetam (R. raetam) on the A549 NSCLC cell line. The research examined R. raetam's anti-proliferative effects, cytotoxicity, apoptosis, reactive oxygen species (ROS) generation, mitochondrial membrane potential, and cell morphology in NSCLC A549 and L-132 cells. In addition, the influence of R. raetam on DNA fragmentation, apoptotic signaling, and PI3K/Akt pathways for its anti-cancer mechanism was examined. Our results indicated that R. raetam's effects were dose- and time-dependent to exhibit anti-proliferative effects on A549 cells. R. raetam treatment promoted apoptotic cell death cycle arrest, increased apoptotic cells, depolarized the mitochondrial membrane, and induced morphological alterations in cells and nuclei. It also inhibited A549 cell migration (P < 0.05), colonization, and invasiveness. Moreover, the study demonstrated that R. raetam treatment resulted in the upregulation of Bax expression, downregulation of Bcl-2 expression, and apoptotic fragmented DNA in A549 cells. The top five bioactive compounds derived from R. raetam exhibited molecular interactions that inhibit PIK3CA and AKT1. This inhibition leads to an increased frequency of apoptosis and subsequent death of cancer cells. Additionally, R. raetam extract induced an increase in ROS formation and cytochrome c levels, indicating that its toxic effects on A549 cells involve both ROS-dependent cytotoxicity through the disruption of mitochondrial transmembrane potential ΔΨm and ROS-independent cell cycle arrest through downregulation BCL-2, PARP, E-Cadherin, PI3K, and Akt expressions pathways.

Mitochondrial Dysfunction and Permeability Transition in Neonatal Brain and Lung Injuries

This review discusses the potential mechanistic role of abnormally elevated mitochondrial proton leak and mitochondrial bioenergetic dysfunction in the pathogenesis of neonatal brain and lung injuries associated with premature birth. Providing supporting evidence, we hypothesized that mitochondrial dysfunction contributes to postnatal alveolar developmental arrest in bronchopulmonary dysplasia (BPD) and cerebral myelination failure in diffuse white matter injury (WMI). This review also analyzes data on mitochondrial dysfunction triggered by activation of mitochondrial permeability transition pore(s) (mPTP) during the evolution of perinatal hypoxic-ischemic encephalopathy. While the still cryptic molecular identity of mPTP continues to be a subject for extensive basic science research efforts, the translational significance of mitochondrial proton leak received less scientific attention, especially in diseases of the developing organs. This review is focused on the potential mechanistic relevance of mPTP and mitochondrial dysfunction to neonatal diseases driven by developmental failure of organ maturation or by acute ischemia-reperfusion insult during development.

Mitochondrial Dysfunction and Oxidative Stress Caused by Cryopreservation in Reproductive Cells

Mitochondria, fundamental organelles in cell metabolism, and ATP synthesis are responsible for generating reactive oxygen species (ROS), calcium homeostasis, and cell death. Mitochondria produce most ROS, and when levels exceed the antioxidant defenses, oxidative stress (OS) is generated. These changes may eventually impair the electron transport chain, resulting in decreased ATP synthesis, increased ROS production, altered mitochondrial membrane permeability, and disruption of calcium homeostasis. Mitochondria play a key role in the gamete competence to facilitate normal embryo development. However, iatrogenic factors in assisted reproductive technologies (ART) may affect their functional competence, leading to an abnormal reproductive outcome. Cryopreservation, a fundamental technology in ART, may compromise mitochondrial function leading to elevated intracellular OS that decreases sperm and oocytes' competence and the dynamics of fertilization and embryo development. This article aims to review the role played by mitochondria and ROS in sperm and oocyte function and the close, biunivocal relationships between mitochondrial damage and ROS generation during cryopreservation of gametes and gonadal tissues in different species. Based on current literature, we propose tentative hypothesis of mechanisms involved in cryopreservation-associated mitochondrial dysfunction in gametes, and discuss the role played by antioxidants and other agents to retain the competence of cryopreserved reproductive cells and tissues.

Progesterone induces apoptosis by activation of caspase-8 and calcitriol via activation of caspase-9 pathways in ovarian and endometrial cancer cells in vitro

Previously we have shown inhibition of endometrial cancer cell growth with progesterone and calcitriol. However, the mechanisms by which the two agents attenuate proliferation have not been well characterized yet. Herein, we investigated how progesterone and calcitriol induce apoptosis in cancer cells. DNA fragmentation was upregulated by progesterone and calcitriol in ovarian and endometrial cancer cells. Time-dependent treatment of ovarian cancer cells, ES-2, and TOV-21G with progesterone enhanced caspase -8 activity after 12 h, whereas OV-90, TOV-112D, HEC-1A, and HEC-59 cells showed increased activity after 24 h. Caspase 9 activity was increased in all cell lines after 24 h treatment with calcitriol. Pretreatment of cancer cells with a caspase-8 inhibitor (z-IETD-fmk) or caspase-9 inhibitor (Z-LEHD-fmk) significantly attenuated progesterone and calcitriol induced caspase-8 and caspase-9 expression, respectively. The expression of FasL, Fas, FAD, and pro-caspase-8, which constitute the death-inducing signaling complex (DISC), was upregulated in progesterone treated cancer cells. Knockdown of FAS or FADD with specific siRNAs significantly blocked progesterone-induced caspase-8. Cleavage of the BID was not affected by caspase-8 activation suggesting the absence of cross-talk between caspase-8 and caspase-9 pathways. Calcitriol treatment decreased mitochondrial membrane potential and increased the release of cancer cytochrome C. These findings indicate that progesterone induces apoptosis through activation of caspase-8 and calcitriol through caspase-9 activation in cancer cells. A combination of progesterone-calcitriol activates both extrinsic and intrinsic apoptotic pathways in cancer cells.

Physiopathology of the Permeability Transition Pore: Molecular Mechanisms in Human Pathology

Mitochondrial permeability transition (MPT) is the sudden loss in the permeability of the inner mitochondrial membrane (IMM) to low-molecular-weight solutes. Due to osmotic forces, MPT is paralleled by a massive influx of water into the mitochondrial matrix, eventually leading to the structural collapse of the organelle. Thus, MPT can initiate outer-mitochondrial-membrane permeabilization (MOMP), promoting the activation of the apoptotic caspase cascade and caspase-independent cell-death mechanisms. The induction of MPT is mostly dependent on mitochondrial reactive oxygen species (ROS) and Ca²⁺, but is also dependent on the metabolic stage of the affected cell and signaling events. Therefore, since its discovery in the late 1970s, the role of MPT in human pathology has been heavily investigated. Here, we summarize the most significant findings corroborating a role for MPT in the etiology of a spectrum of human diseases, including diseases characterized by acute or chronic loss of adult cells and those characterized by neoplastic initiation.

Composite mathematical modeling of calcium signaling behind neuronal cell death in Alzheimer's disease

Background

Alzheimer’s disease (AD) is a progressive neurological disorder, recognized as the most common cause of dementia affecting people aged 65 and above. AD is characterized by an increase in amyloid metabolism, and by the misfolding and deposition of β-amyloid oligomers in and around neurons in the brain. These processes remodel the calcium signaling mechanism in neurons, leading to cell death via apoptosis. Despite accumulating knowledge about the biological processes underlying AD, mathematical models to date are restricted to depicting only a small portion of the pathology.

Results

Here, we integrated multiple mathematical models to analyze and understand the relationship among amyloid depositions, calcium signaling and mitochondrial permeability transition pore (PTP) related cell apoptosis in AD. The model was used to simulate calcium dynamics in the absence and presence of AD. In the absence of AD, i.e. without β-amyloid deposition, mitochondrial and cytosolic calcium level remains in the low resting concentration. However, our in silico simulation of the presence of AD with the β-amyloid deposition, shows an increase in the entry of calcium ions into the cell and dysregulation of Ca ²⁺ channel receptors on the Endoplasmic Reticulum. This composite model enabled us to make simulation that is not possible to measure experimentally.

Conclusions

Our mathematical model depicting the mechanisms affecting calcium signaling in neurons can help understand AD at the systems level and has potential for diagnostic and therapeutic applications.

Electronic supplementary material

The online version of this article (10.1186/s12918-018-0529-2) contains supplementary material, which is available to authorized users.

Metformin-Induced Mitochondrial Complex I Inhibition: Facts, Uncertainties, and Consequences

Metformin is the most widely prescribed drug to treat patients with type II diabetes, for whom retrospective studies suggest that metformin may have anticancer properties. However, in experiments performed with isolated cells, authors have reported both pro- and anti-apoptotic effects of metformin. The exact molecular mechanism of action of metformin remains partly unknown despite its use for over 60 years and more than 17,000 articles in PubMed. Among the various widely recognized or recently proposed targets, it has been reported consistently that metformin is capable of inhibiting mitochondrial respiratory chain Complex I. Since most of the effects of metformin have been replicated by other inhibitors of Complex I, it has been suggested that the mechanism of action of metformin involved the inhibition of Complex I. However, compared to conventional Complex I inhibitors, the metformin-induced inhibition of Complex I has unique characteristics. Among these, the most original one is that the concentrations of metformin required to inhibit Complex I are lower in intact cells than in isolated mitochondria. Experiments with isolated mitochondria or Complex I were generally performed using millimolar concentrations of metformin, while plasma levels remain in the micromolar range in both human and animal studies, highlighting that metformin concentration is an important issue. In order to explain the effects in animals based on observations in cells and mitochondria, some authors proposed a direct effect of the drug on Complex I involving an accumulation of metformin inside the mitochondria while others proposed an indirect effect (the drug no longer having to diffuse into the mitochondria). This brief review attempts to: gather arguments for and against each hypothesis concerning the mechanism by which metformin inhibits Complex I and to highlight remaining questions about the toxicity mechanism of metformin for certain cancer cells.

Calcium uptake and cytochrome c release from normal and ischemic brain mitochondria

At abnormally elevated levels of intracellular Ca²⁺, mitochondrial Ca²⁺ uptake may compromise mitochondrial electron transport activities and trigger membrane permeability changes that allow for release of cytochrome c and other mitochondrial apoptotic proteins into the cytosol. In this study, a clinically relevant canine cardiac arrest model was used to assess the effects of global cerebral ischemia and reperfusion on mitochondrial Ca²⁺ uptake capacity, Ca²⁺ uptake-mediated inhibition of respiration, and Ca²⁺-induced cytochrome c release, as measured in vitro in a K⁺-based medium in the presence of Mg²⁺, ATP, and NADH-linked oxidizable substrates. Maximum Ca²⁺ uptake by frontal cortex mitochondria was significantly lower following 10 min cardiac arrest compared to non-ischemic controls. Mitochondria from ischemic brains were also more sensitive to the respiratory inhibition associated with accumulation of large levels of Ca²⁺. Cytochrome c was released from brain mitochondria in vitro in a Ca²⁺-dose-dependent manner and was more pronounced following both 10 min of ischemia alone and following 24 h reperfusion, in comparison to mitochondria from non-ischemic Shams. These effects of ischemia and reperfusion on brain mitochondria could compromise intracellular Ca²⁺ homeostasis, decrease aerobic and increase anaerobic cerebral energy metabolism, and potentiate the cytochrome c-dependent induction of apoptosis, when re-oxygenated mitochondria are exposed to abnormally high levels of intracellular Ca²⁺.

Exercise-induced rhabdomyolysis mechanisms and prevention: A literature review

Exercise-induced rhabdomyolysis (exRML), a pathophysiological condition of skeletal muscle cell damage that may cause acute renal failure and in some cases death. Increased Ca²⁺ level in cells along with functional degradation of cell signaling system and cell matrix have been suggested as the major pathological mechanisms associated with exRML. The onset of exRML may be exhibited in athletes as well as in general population. Previous studies have reported that possible causes of exRML were associated with excessive eccentric contractions in high temperature, abnormal electrolytes balance, and nutritional deficiencies possible genetic defects. However, the underlying mechanisms of exRML have not been clearly established among health professionals or sports medicine personnel. Therefore, we reviewed the possible mechanisms and correlated prevention of exRML, while providing useful and practical information for the athlete and general exercising population.

Imeglimin prevents human endothelial cell death by inhibiting mitochondrial permeability transition without inhibiting mitochondrial respiration

Imeglimin is the first in a new class of oral glucose-lowering agents, having recently completed its phase 2b trial. As Imeglimin did show a full prevention of β-cell apoptosis, and since angiopathy represents a major complication of diabetes, we studied Imeglimin protective effects on hyperglycemia-induced death of human endothelial cells (HMEC-1). These cells were incubated in several oxidative stress environments (exposure to high glucose and oxidizing agent tert-butylhydroperoxide) which led to mitochondrial permeability transition pore (PTP) opening, cytochrome c release and cell death. These events were fully prevented by Imeglimin treatment. This protective effect on cell death occurred without any effect on oxygen consumption rate, on lactate production and on cytosolic redox or phosphate potentials. Imeglimin also dramatically decreased reactive oxygen species production, inhibiting specifically reverse electron transfer through complex I. We conclude that Imeglimin prevents hyperglycemia-induced cell death in HMEC-1 through inhibition of PTP opening without inhibiting mitochondrial respiration nor affecting cellular energy status. Considering the high prevalence of macrovascular and microvascular complications in type 2 diabetic subjects, these results together suggest a potential benefit of Imeglimin in diabetic angiopathy.

HS-543 induces apoptosis of Imatinib-resistant chronic myelogenous leukemia with T315I mutation

Chronic myeloid leukemia (CML) is characterized by a constitutive activation of Bcr-Abl tyrosine kinase. Bcr-Abl/T315I is the predominant mutation that causes resistance to Imatinib. In the present study, we synthesized a novel Bcr-Abl inhibitor, HS-543, and investigated its effect on cell survival or apoptosis in CML cells bearing Bcr-Abl/T315I (BaF3/T315I) or wild-type Bcr-Abl (BaF3/WT). HS-543 showed anti-proliferative effects in the BaF3/WT cells as well as the BaF3/T315I cells with resistance to Imatinib and strongly inhibited the Bcr-Abl signaling pathway in a dose-dependent manner. Furthermore, it significantly increased the sub G₁ phase associated with early apoptosis, with increased levels of cleaved PARP and cleaved caspase-3, as well as the TUNEL-positive apoptotic cells. In addition, we found that HS-543 induced apoptosis with the loss of mitochondrial membrane potential by decreasing the expression of Mcl-1 and survivin, together with increasing that of Bax. In BaF3/T315I xenograft models, HS-543 significantly delayed tumor growth, unlike Imatinib. Our results demonstrate that HS-543 exhibits the induction of apoptosis and anti-proliferative effect by blocking the Bcr-Abl signaling pathway in the T315I-mutated Bcr-Abl cells with resistance to Imatinib. We suggest that HS-543 may be a novel promising agent to target Bcr-Abl and overcome Imatinib resistance in CML patients.

Respective effects of oxygen and energy substrate deprivation on beta cell viability

Deficit in oxygen and energetic substrates delivery is a key factor in islet loss during islet transplantation. Permeability transition pore (PTP) is a mitochondrial channel involved in cell death. We have studied the respective effects of oxygen and energy substrate deprivation on beta cell viability as well as the involvement of oxidative stress and PTP opening. Energy substrate deprivation for 1h followed by incubation in normal conditions led to a cyclosporin A (CsA)-sensitive-PTP-opening in INS-1 cells and human islets. Such a procedure dramatically decreased INS-1 cells viability except when transient removal of energy substrates was performed in anoxia, in the presence of antioxidant N-acetylcysteine (NAC) or when CsA or metformin inhibited PTP opening. Superoxide production increased during removal of energy substrates and increased again when normal energy substrates were restored. NAC, anoxia or metformin prevented the two phases of oxidative stress while CsA prevented the second one only. Hypoxia or anoxia alone did not induce oxidative stress, PTP opening or cell death. In conclusion, energy substrate deprivation leads to an oxidative stress followed by PTP opening, triggering beta cell death. Pharmacological prevention of PTP opening during islet transplantation may be a suitable option to improve islet survival and graft success.

The mitochondrial permeability transition pore and cancer: molecular mechanisms involved in cell death

Since its discovery in the 1970s, the mitochondrial permeability transition (MPT) has been proposed to be a strategic regulator of cell death. Intense research efforts have focused on elucidating the molecular components of the MPT because this knowledge may help to better understand and treat various pathologies ranging from neurodegenerative and cardiac diseases to cancer. In the case of cancer, several studies have revealed alterations in the activity of the mitochondrial permeability transition pore (mPTP) and have determined its regulatory mechanism; these studies have also suggested that suppression of the activity of the mPTP, rather than its inactivation, commonly occurs in solid neoplasms. This review focuses on the most recent advances in understanding mPTP regulation in cancer and highlights the ability of the mPTP to impede the mechanisms of cell death.

Methyl protodioscin induces G2/M cell cycle arrest and apoptosis in A549 human lung cancer cells

Background:

Methyl protodioscin (MPD) is a furostanol bisglycoside with antitumor properties. It has been shown to reduce proliferation, cause cell cycle arrest.

Objective:

The present study elucidates the mechanism underlying MPD's apoptotic effects, using the A549 human lung cancer cell line.

Materials and Methods:

The human pulmonary adenocarcinoma cell line A549 was obtained from the Cell Bank of the Animal Experiment Center, North School Region, Sun Yat-Sen University. All of the cells were grown in RPMI 1640 supplemented with 10% fetal calf serum (Hyclone, Logan, UT, USA), penicillin (10,000 U/l), and streptomycin (100 mg/l) at 37°C in a 5% CO₂ humidified atmosphere. The induction of apoptosis was observed in flow cytometry and fluorescent staining experiments.

Results:

MPD showed growth inhibitory effects in A549 cells in a dose- and time-dependent manner. The significant G2/M cell cycle arrest and apoptotic effect were also seen in A549 cells treated with MPD. MPD-induced apoptosis was accompanied by a significant reduction of mitochondrial membrane potential, release of mitochondrial cytochrome c to cytosol, activation of caspase-3, downregulation of Bcl-2, p-Bad, and upregulation of Bax.

Conclusion:

Our results show that the induction of apoptosis by MPD involves multiple molecular pathways and strongly suggest that Bcl-2 family proteins signaling pathways. In addition, mitochondrial membrane potential, mitochondrial cytochrome c and caspase-3 were also closely associated with MPD-induced apoptotic process in human A549 cells.

Dietary Isothiocyanates Modify Mitochondrial Functions through Their Electrophilic Reaction

We found that both benzyl isothiocyanate (ITC) and phenyl ITC inhibited respiration in the mitochondria in an electrophilic reaction-dependent manner. ITC-induced mitochondrial swelling and cytochrome c release were prevented by cyclosporin A, indicating that they are mediated through the ITC moiety-dependent reaction to critical thiol groups for the opening of membrane permeability transition-dependent pores.

Apoptotic effects of curcumin on human osteosarcoma U2OS cells

OBJECTIVE

 Curcumin, an active ingredient derived from the rhizome of the plant, Curcuma longa, has antioxidant, anti-inflammatory and anti-cancer activities. The aims of this study were to examine whether curcumin can induce apoptosis in an osteosarcoma cell line.

METHODS

Curcumin-induced apoptosis in human osteosarcoma U2OS cells was investigated using morphological analysis, marked nuclear condensation and fragmentation of chromatin, which were observed by Hoechst 33258 staining and DNA ladder formation. The U2OS cells were treated with or without curcumin. Cell viability was assessed by the 3-(4,5-Dimethylthiazol-2-yl)-2,5-Diphenyltetrazolium (MTT) method. Cell-cycle, apoptosis and apoptosis-related proteins in U2OS cells were evaluated by flow cytometry and western blotting.

RESULTS

Curcumin showed growth inhibitory effects on U2OS cells in a dose-and time-dependent manner, inducing significant G1 arrest and apoptosis in U2OS cells. This curcumin-induced apoptosis in U2OS cells was accompanied by up-regulation of Bax, Bak, and p-Bad and down-regulation of Bcl-2, but no effect on the levels of Bcl-X(L) or Bad proteins was noted. Moreover, curcumin treatment resulted in a significant reduction of mitochondrial membrane potential and increase in the concentrations of mitochondrial cytochrome C and caspase-3.

CONCLUSION

Multiple molecular pathways are involved in curcumin-induced apoptosis of human U2OS cells. These include pro-and anti-apoptotic Bcl-2 family proteins, mitochondrial membrane potential, mitochondrial cytochrome C and caspase-3.

Effects of α-mangostin on apoptosis induction of human colon cancer

AIM: To investigate the effect of α-mangostin on the growth and apoptosis induction of human colon cancer cells.

METHODS: The three colorectal adenocarcinoma cell lines tested (COLO 205, MIP-101 and SW 620) were treated with α-mangostin to determine the effect on cell proliferation by MTT assay, cell morphology, chromatin condensation, cell cycle analysis, DNA fragmentation, phosphatidylserine exposure and changing of mitochondrial membrane potential. The molecular mechanisms of α-mangostin mediated apoptosis were further investigated by Western blotting analysis including activation of caspase cascade, cytochrome c release, Bax, Bid, p53 and Bcl-2 modifying factor.

RESULTS: The highest inhibitory effect of α-mangostin on cell proliferation of COLO 205, MIP-101 and SW 620 were 9.74 ± 0.85 μg/mL, 11.35 ± 1.12 μg/mL and 19.6 ± 1.53 μg/mL, respectively. Further study showed that α-mangostin induced apoptotic cell death in COLO 205 cells as indicated by membrane blebbing, chromatin condensation, DNA fragmentation, cell cycle analysis, sub-G1 peak (P < 0.05) and phosphatidylserine exposure. The executioner caspase, caspase-3, the initiator caspase, caspase-8, and caspase-9 were expressed upon treatment with α-mangostin. Further studies of apoptotic proteins were determined by Western blotting analysis showing increased mitochondrial cytochrome c release, Bax, p53 and Bmf as well as reduced mitochondrial membrane potential (P < 0.05). In addition, up-regulation of tBid and Fas were evident upon treatment with α-mangostin (P < 0.01).

CONCLUSION: α-Mangostin may be effective as an anti-cancer agent that induced apoptotic cell death in COLO 205 via a link between extrinsic and intrinsic pathways.

AMPK-associated signaling to bridge the gap between fuel metabolism and hepatocyte viability

The adenosine monophosphate-activated protein kinase (AMPK) and p70 ribosomal S6 kinase-1 pathway may serve as a key signaling flow that regulates energy metabolism; thus, this pathway becomes an attractive target for the treatment of liver diseases that result from metabolic derangements. In addition, AMPK emerges as a kinase that controls the redox-state and mitochondrial function, whose activity may be modulated by antioxidants. A close link exists between fuel metabolism and mitochondrial biogenesis. The relationship between fuel metabolism and cell survival strongly implies the existence of a shared signaling network, by which hepatocytes respond to challenges of external stimuli. The AMPK pathway may belong to this network. A series of drugs and therapeutic candidates enable hepatocytes to protect mitochondria from radical stress and increase cell viability, which may be associated with the activation of AMPK, liver kinase B1, and other molecules or components. Consequently, the components downstream of AMPK may contribute to stabilizing mitochondrial membrane potential for hepatocyte survival. In this review, we discuss the role of the AMPK pathway in hepatic energy metabolism and hepatocyte viability. This information may help identify ways to prevent and/or treat hepatic diseases caused by the metabolic syndrome. Moreover, clinical drugs and experimental therapeutic candidates that directly or indirectly modulate the AMPK pathway in distinct manners are discussed here with particular emphasis on their effects on fuel metabolism and mitochondrial function.

Ubiquinone analogs: a mitochondrial permeability transition pore-dependent pathway to selective cell death

BACKGROUND

Prolonged opening of the mitochondrial permeability transition pore (PTP) leads to cell death. Various ubiquinone analogs have been shown to regulate PTP opening but the outcome of PTP regulation by ubiquinone analogs on cell fate has not been studied yet.

METHODOLOGY/PRINCIPAL FINDINGS

The effects of ubiquinone 0 (Ub(0)), ubiquinone 5 (Ub(5)), ubiquinone 10 (Ub(10)) and decyl-ubiquinone (DUb) were studied in freshly isolated rat hepatocytes, cultured rat liver Clone-9 cells and cancerous rat liver MH1C1 cells. PTP regulation by ubiquinones differed significantly in permeabilized Clone-9 and MH1C1 cells from that previously reported in liver mitochondria. Ub(0) inhibited PTP opening in isolated hepatocytes and Clone-9 cells, whereas it induced PTP opening in MH1C1 cells. Ub(5) did not affect PTP opening in isolated hepatocytes and MH1C1 cells, but it induced PTP opening in Clone-9 cells. Ub(10) regulated PTP in isolated hepatocytes, whereas it did not affect PTP opening in Clone-9 and MH1C1 cells. Only DUb displayed the same effect on PTP regulation in the three hepatocyte lines tested. Despite such modifications in PTP regulation, competition between ubiquinones still occurred in Clone-9 and MH1C1 cells. As expected, Ub(5) induced a PTP-dependent cell death in Clone-9, while it did not affect MH1C1 cell viability. Ub(0) induced a PTP-dependent cell death in MH1C1 cells, but was also slightly cytotoxic in Clone-9 by an oxidative stress-dependent mechanism.

CONCLUSIONS/SIGNIFICANCE

We found that various ubiquinone analogs regulate PTP in different ways depending on the cell studied. We took advantage of this unique property to develop a PTP opening-targeted strategy that leads to cell death specifically in cells where the ubiquinone analog used induces PTP opening, while sparing the cells in which it does not induce PTP opening.

Antioxidant and mitochondrial protective effects of oxidized metabolites of oltipraz

IMPORTANCE OF THE FIELD

Comprehensive studies indicate that oltipraz exerts cancer chemopreventive effects. Oltipraz has other therapeutic potentials, which include anti-fibrotic effect, inhibition of insulin resistance, mitochondrial protection and cytoprotective effect against oxidative stress. Although antioxidant mechanisms may account for its cancer chemopreventive effect, details on the molecular mechanism still remain to be clarified.

AREAS COVERED IN THIS REVIEW

Two major metabolic pathways of oltipraz include oxidative desulfuration of the thione to yield 4-methyl-5-(pyrazin-2-yl)-3H-1,2-dithiol-3-one and molecular rearrangement to 7-methyl-6,8-bis(methylthio)H-pyrrolo[1,2-a]pyrazine. In addition to the diverse pharmacological effects of oltipraz, the oxidized metabolites may have distinct biological effects on cell survival. The AMP-activated protein kinase pathway has been recognized as a key cascade for mitochondrial protection and cell survival events, which can be activated by the oxidized metabolites of oltipraz.

WHAT THE READER WILL GAIN

In this review, the metabolic activation of oltipraz and the role of the cell signaling pathways in regulating the expression of Phase II genes and antioxidant activity are discussed with particular reference to their effects on mitochondrial protection and cell survival.

TAKE HOME MESSAGE

In terms of therapeutic potential, the findings reviewed here demonstrate a therapeutic potential for oxidized metabolite of oltipraz and offer comparison of antioxidant capacity between metabolites and parent compound.

Post-conditioning reduces infarct size in an open-chest porcine acute ischemia-reperfusion model

BACKGROUND

Timely reperfusion is a prerequisite for myocardial salvage; however, re-oxygenation of the ischemic myocardium initiates reperfusion injury. Post-conditioning diminishes the detrimental aftermath of an acute myocardial infarction through alleviation of reperfusion injury. Ischemic post-conditioning consists of a series of brief interruptions in the coronary blood supply that has to be applied within the first minutes after re-establishing the coronary flow.

METHODS

Sixteen female mixed Danish Landrace and Yorkshire pigs weighing 20 kg were included. The heart was exposed through a midline sternotomy. A snare was positioned around the left anterior descending coronary artery downstream of the second diagonal branch. After randomization to either no treatment (control group) or treatment by ischemic post-conditioning (post-conditioning group), the pigs underwent 45 min of ischemia and 180 min of reperfusion. The post-conditioning group had a post-conditioning algorithm applied consisting of 15 s of reperfusion alternating with 15 s of re-occlusion repeated 10 times.

RESULTS

The groups were comparable with regard to body weight, hemodynamics and the size of the area at risk. The post-conditioning group had an absolute reduction in infarct size of 18.1% [confidence interval (CI): 6.2: 30.0%] compared with the control group (P=0.0056). In the post-conditioning group, infarction developed in 39.6+/-12.0% (1 SD) of the area at risk compared with 57.8+/-10.2% (1 SD) in the control group.

CONCLUSION

When ischemic post-conditioning was applied at reperfusion, we found an absolute reduction in infarct size of 18.1% presumably attributable to a diminished reperfusion injury. The model we have developed is suitable for further studies of this promising intervention.

Nortriptyline protects mitochondria and reduces cerebral ischemia/hypoxia injury

BACKGROUND AND PURPOSE

Nortriptyline, an antidepressant, was identified as a strong inhibitor of mitochondrial permeability transition by our screening of a library of 1040 drugs. Because mitochondrial permeability transition and consequent mitochondrial dysfunction have been implicated in acute neuronal death, we proposed to investigate the possible neuroprotective effects of nortriptyline in cerebral ischemia.

METHODS

The effects of nortriptyline were first studied in oxygen/glucose deprivation-induced death of primary cerebrocortical neurons, a cellular model of cerebral ischemia. Mitochondrial membrane potential, mitochondrial factor release, and caspase 3 activation were evaluated after its treatment. Nortriptyline was also studied in a mouse model, which was established by occlusion of the middle cerebral artery. The infarct volume, neurological function, and biochemical events were examined in the absence or the presence of nortriptyline.

RESULTS

Nortriptyline inhibits oxygen/glucose deprivation-induced cell death, loss of mitochondrial membrane potential, downstream release of mitochondrial factors, and activation of caspase 3 in primary cerebrocortical neurons. Furthermore, it decreases infarct size and improves neurological scores after middle cerebral artery occlusion in mice.

CONCLUSIONS

The ability of nortriptyline to inhibit mitochondrial factor release and caspase activation and further protect the animals correlates to its inhibitory effect on mitochondrial permeability transition in isolated mitochondria. This study indicated that nortriptyline is neuroprotective against cerebral ischemia. It also suggested mitochondrial permeability transition might be a valuable therapeutic target for acute neurodegeneration.

Minocycline, a possible neuroprotective agent in Leber’s hereditary optic neuropathy (LHON): Studies of cybrid cells bearing 11778 mutation

Leber's hereditary optic neuropathy (LHON) is a retinal neurodegenerative disorder caused by mitochondrial DNA point mutations. Complex I of the respiratory chain affected by the mutation results in a decrease in ATP and an increase of reactive oxygen species production. Evaluating the efficacy of minocycline in LHON, the drug increased the survival of cybrid cells in contrast to the parental cells after thapsigargin-induced calcium overload. Similar protection was observed by treatment with cyclosporine A, a blocker of the mitochondrial permeability transition pore (mPTP). Ratiometric Ca(2+) imaging reveals that acetylcholine/thapsigargin triggered elevation of the cytosolic calcium concentration is alleviated by minocycline and cyclosporine A. The mitochondrial membrane potential of LHON cybrids was significantly conserved and the active-caspase-3/procaspase-3 ratio was decreased in both treatments. Our observations show that minocycline inhibits permeability transition induced by thapsigargin in addition to its antioxidant effects. In relation with its high safety profile, these results would suggest minocycline as a promising neuroprotective agent in LHON.

Sorbitol-induced apoptosis of human leukemia is mediated by caspase activation and cytochrome c release

It has been reported that sorbitol induces apoptosis in several cancer cell lines. However, the molecular mechanism underlying the sorbitol-induced apoptotic process is not yet clearly understood. In the present study, the intracellular signaling pathways of sorbitol-induced apoptosis in human K562 cells were investigated using both morphological analysis and DNA fragmentation technique. In this study, we demonstrated that sorbitol-induced apoptosis in human K562 cells is a concentration- and time-dependent manner. This sorbitol-induced apoptosis in human K562 cells was also accompanied by the up-regulation of Bax, and down-regulation of p-Bcl-2, but no effect on the levels of Bcl-X(L). Moreover, the sorbitol treatment resulted in a significant reduction of mitochondria membrane potential, increase in the release of mitochondrial cytochrome c (cyt c), and activation of caspase 3. Furthermore, treatment with caspase 3 inhibitor (z-DEVD-fmk) was capable of preventing the sorbitol-induced caspase 3 activity and cell death. These results clearly demonstrate that the induction of apoptosis by sorbitol involves multiple cellular/molecular pathways and strongly suggest that pro- and anti-apoptotic Bcl-2 family proteins, mitochondrial membrane potential, mitochondrial cyt c, and caspase 3, they all participate in sorbitol-induced apoptotic process in human K562 cells.

Construction of hybrid bilayer membrane (HBM) Biochips and characterization of the cooperative binding between cytochrome-c and HBM

We constructed multi-channel hybrid bilayer membrane (HBM) biochips and characterized them by surface plasmon resonance imaging. Each channel in the biochip was prepared using vesicles with different proportions of negative, neutral, and positive lipids. The HBM surfaces were tested by interaction with two globular proteins that recognize surfaces covered with opposite charges. Spots modified with the same HBM show responses within a relative standard deviation of 10% or smaller. These devices were also used to study in detail the interaction between cytochrome-c (cyt-c) and HBMs. Cooperative binding between cyt-c and negative HBMs was demonstrated. Using an adaptation of the Hill model, we calculated a Hill coefficient of 5 and a 10-fold increase in the binding constant with the increase in cyt-c concentration. We propose that this treatment can be used to evaluate the cooperative binding of surface proteins to membranes.

The syndrome of rhabdomyolysis: Pathophysiology and diagnosis

Rhabdomyolysis is defined as a pathological condition of skeletal muscle cell damage leading to the release of toxic intracellular material into the blood circulation. Its major causes include trauma, ischemia, drugs, toxins, metabolic disorders, and infections. The pathophysiological hallmark of the syndrome is an increase in intracellular free ionized calcium due to either cellular energy depletion, or direct plasma membrane rupture. The increased intracellular calcium activates several proteases, intensifies skeletal muscle cell contractility, induces mitochondrial dysfunction, and increases the production of reactive oxygen species, ultimately resulting in skeletal muscle cell death. Clinically, the syndrome presents with severe muscular pain, weakness and myoglobinuria. Increased myoglobin and creatine phosphokinase as a consequence of muscular cell death are the major laboratory findings, which, in combination with the clinical presentation, lead the clinician to the final diagnosis of the syndrome.

ATP-induced apoptotic cell death in porcine ovarian theca cells through P2X7 receptor activation

Folliculogenesis modulation via distinct neurotransmitters is a well-documented phenomenon. Intraovarian purinergic signaling mechanisms have been identified previously in different species. However, the molecular elements involved and the physiological role of this purinergic signaling remain to be elucidated. Here, studies using RT-PCR amplification, immunoblotting, and immunofluorescence microscopy showed that murine and porcine ovaries express the P2X7 subtype receptor, a cationic receptor-channel operated by ATP. Using immunofluorescence it was demonstrated that P2X7 protein expression, in both mouse and pig, occurs specifically in the theca cells from antral follicles. Isolated porcine theca cells maintained in primary cultures and tested with 1 mM ATP or 250 microM Bz-ATP, a specific agonist of P2X7, responded with an increase in intracellular calcium concentration, as demonstrated in cells loaded with fluo-4 as calcium indicator. This strongly suggested that P2X7 receptors in theca cells are functional. Moreover, application for 24 hr of 1 mM ATP or 250 microM Bz-ATP induced apoptotic cell death as indicated by the DNA fragmentation pattern, positive TUNEL test, and annexin V binding. This ATP effect was antagonized by 300 microM PPADS and 200 microM oxidized ATP. Also, addition of 5 mM EGTA in the external medium to chelate free Ca++ decreased death cell to 24% of that produced by 200 microM Bz-ATP, suggesting that Ca++ influx participates in the phenomenon. The highly specific and functional expression of P2X7 receptors in theca cells suggest a role for ATP in modulating follicular physiology.

Cytotoxic and apoptotic effects of prenylflavonoid artonin B in human acute lymphoblastic leukemia cells

AIM

To investigate the anticancer effects and molecular mechanism of artonin B on the human acute lymphoblastic leukemia CCRF-CEM cells compared with other prenylflavonoid compounds.

METHODS

The effects of four prenylflavonoids on the growth of CCRF-CEM and HaCa cells were studied by 3-(4,5)-2,5-diphenyl-tetrazolium bromide (MTT) assay. Apoptosis were detected through Hoechst 33258 staining. The effect of artonin B on the cell cycle of CCRF-CEM cells were studied by propidium iodide method. The change in mitochondrial membrane potential was detected by rohdamine 123 staining. The cytochrome c release and caspase 3 activity were checked by immunoassay kits, respectively. The expression of Bcl-2 family proteins was detected by Western blot.

RESULTS

Our data revealed that artonin B strongly induced human CCRF-CEM leukemia cell death in a dose- and time-dependent manner by MTT assay, but not on normal epithelia cells (HaCa cells). Artonin B-induced cell death was considered to be apoptotic by observing the typical apoptotic morphological change by Hoechst 33258 staining. The induction of human CCRF-CEM leukemia cancer cell death was caused by an induction of apoptosis through mitochondrial membrane potential change, cytochrome c release, sub-G1 proportion increase, downregulation of Bcl-2 expression, upregulation of Bax and Bak expression and activation of caspase 3 pathways.

CONCLUSION

These results clearly demonstrated that artonin B is able to inhibit proliferation by induction of hypoploid cells and cell apoptosis. Moreover, the anticancer effects of artonin B were related to mitochondrial pathway and caspase 3 activation in human CCRF-CEM leukemia cells.

Ca(2+) rise within a narrow window of concentration prevents functional injury of mitochondria exposed to hypoxia/reoxygenation by increasing antioxidative defence

Injury of liver by ischaemia crucially involves mitochondrial damage. The role of Ca(2+) in mitochondrial damage is still unclear. We investigated the effect of low micromolar Ca(2+) concentrations on respiration, membrane permeability, and antioxidative defence in liver mitochondria exposed to hypoxia/reoxygenation. Hypoxia/reoxygenation caused decrease in state 3 respiration and in the respiratory control ratio. Liver mitochondria were almost completely protected at about 2 microM Ca(2+). Below and above 2 microM Ca(2+), mitochondrial function was deteriorated, as indicated by the decrease in respiratory control ratio. Above 2 microM Ca(2+), the mitochondrial membrane was permeabilized, as demonstrated by the sensitivity of state 3 respiration to NADH. Below 2 microM Ca(2+), the nitric oxide synthase inhibitor nitro-l-arginine methylester had a protective effect. The activities of the manganese superoxide dismutase and glutathione peroxidase after hypoxia showed maximal values at about 2 microM Ca(2+). We conclude that Ca(2+) exerts a protective effect on mitochondria within a narrow concentration window, by increasing the antioxidative defence.

Bcl-2 sensitive mitochondrial potassium accumulation and swelling in apoptosis

During etoposide-induced apoptosis in HL-60 cells, cytochrome c release was associated with mitochondrial swelling caused by increased mitochondrial potassium uptake. The mitochondrial permeability transition was also observed; however, it was not the primary cause of mitochondrial swelling. Potassium uptake and swelling of mitochondria were blocked by bcl-2 overexpression. As a result, cytochrome c release was reduced, and apoptosis delayed. Residual cytochrome c release in the absence of swelling in bcl-2 expressing cells could be due to observed Bax translocation into mitochondria. This study suggests several novel aspects of apoptotic signaling: (1) potassium related swelling of mitochondria; (2) inhibition of mitochondrial potassium uptake by bcl-2; (3) co-existence within one system of multiple mechanisms of cytochrome c release: mitochondrial swelling and swelling-independent permeabilization of the outer mitochondrial membrane.

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.

Cytochrome c is released in a single step during apoptosis

Release of cytochrome c from mitochondria is a central event in apoptotic signaling. In this study, we utilized a cytochrome c fusion that binds fluorescent biarsenical ligands (cytochrome c-4CYS (cyt. c-4CYS)) as well as cytochrome c-green fluorescent protein (cyt. c-GFP) to measure its release from mitochondria in different cell types during apoptosis. In single cells, the kinetics of cyt. c-4CYS release was indistinguishable from that of cyt. c-GFP in apoptotic cells expressing both molecules. Lowering the temperature by 7 degrees C did not affect this corelease, but further separated cytochrome c release from the subsequent decrease in mitochondrial membrane potential (DeltaPsi(m)). Cyt. c-GFP rescued respiration in cells lacking endogenous cytochrome c, and the duration of cytochrome c release was approximately 5 min in a variety of cell types induced to die by various forms of cellular stress. In addition, we could observe no evidence of caspase-dependent amplification of cytochrome c release or changes in DeltaPsi(m) preceding the release of cyt. c-GFP. We conclude that there is a general mechanism responsible for cytochrome c release that proceeds in a single step that is independent of changes in DeltaPsi(m).

Cytochrome C release from CNS mitochondria and potential for clinical intervention in apoptosis-mediated CNS diseases

Apoptosis is critical for normal development and tissue homeostasis. However, its abnormal occurrence has been implicated in a number of disorders, including neurodegenerative diseases and stroke. Translocation of cytochrome c (Cyt c) from mitochondria to the cytoplasm is a key step in the initiation and/or amplification of apoptosis. Here we discuss Cyt c release in apoptosis with its impact on the CNS and review our studies of Cyt c release from isolated rat brain mitochondria in response to several insults. Calcium-induced Cyt c release, as occurs in neurons during stroke and ischemia, involves rupture of the mitochondrial outer membrane (MOM) and can be blocked by inhibitors of the mitochondrial permeability transition (mPT). Thus, inhibitors of the mPT have shown efficacy in animal models of ischemia. In contrast, proapoptotic proteins, such as BID, BAX, and BAK, induce Cyt c release independently of the mPT without lysing the MOM. Several inhibitors of BAX-induced Cyt c release have shown promise in models of CNS apoptosis. Because of their distinct mechanisms for Cyt c release, both the mPT and proapoptotic proteins should be targeted for effective clinical intervention in CNS disorders involving apoptosis.

MnSOD in mouse heart: acute responses to ischemic preconditioning and ischemia-reperfusion injury

Manganese superoxide dismutase (MnSOD) is one of the main antioxidant enzymes that protects the heart against ischemia-reperfusion (I/R) injury. Ischemic preconditioning (IPC) is a short period of ischemia-reperfusion that reduces subsequent prolonged I/R injury. Although MnSOD localizes in mitochondria, the immediate subcellular distribution of MnSOD in heart after IPC and I/R has not been studied. In a Langendorff mouse heart model, IPC significantly improved cardiac function and reduced the infarction size induced by I/R. Immunoblotting and double immunostaining in fresh preparations revealed that I/R resulted in an increase in cytosolic MnSOD content accompanied by the release of cytochrome c. In contrast, IPC increased mitochondrial MnSOD and reduced cytosolic MnSOD and cytochrome c release induced by I/R. We found that compared with freshly prepared fractions, the freeze-thaw approach results in mitochondrial integrity disruption and release of large amounts of MnSOD into the cytosol along with mitochondrial markers even in the absence of I/R. In contrast, fresh preparations exhibit early MnSOD release into the cytosol after I/R that is prevented by IPC and cyclosporin A administration.

The powerhouse takes control of the cell: is the mitochondrial permeability transition a viable therapeutic target against neuronal dysfunction and death?

Stroke and neurodegenerative disease exert an increasing large toll on human health at the levels both of the individual and of society. As an example of each, in the United States, stroke is the major single cause of overall morbidity and mortality, and the financial costs of Alzheimer's disease alone dwarfs the entire federal medical research budget. It has been long recognized that mitochondrial energy production is essential for the second to second functions of the central nervous system (CNS), and that severe mitochondrial impairment is incompatible with normal cerebral function. The last decade, however, has brought a growing understanding that mitochondria play an even greater role than previously suspected. Increased understanding of the role of mitochondria in antioxidant defense and calcium homeostasis further solidified the importance of mitochondria in CNS function--just as increased understanding of mitochondrial roles in calcium-mediated toxicity and production of reactive species further exemplified the Janus role of mitochondria--as mediators of CNS dysfunction. Perhaps most unexpected, however, was the evidence that mitochondria serve as the dominant integrators, checkpoints, and amplifiers of the cell death signals in the CNS. The mechanism of propagation of cell death cascades by mitochondria remains controversial. In this review, we focus on the evidence that supports the involvement of an event termed the mitochondrial permeability transition that (i) occurs (patho)physiologically; (ii) occurs in the CNS, and; (iii) is a potential target for pharmaceutical intervention against CNS dysfunction, injury, and cell loss resulting from stroke, trauma, and neurodegenerative disease.

Cell cycle specific induction of apoptosis and necrosis by paclitaxel in the leukemic U937 cells

Induction of cell apoptosis and necrosis by paclitaxel was investigated in human leukemic U937 cells. To explore whether paclitaxel induces both apoptosis and necrosis in different cell cycle stages, we synchronized the cells in G1, S and G2/M stages by counterflow centrifugal elutriation (CCE). The Annexin V and PI analysis revealed that, after paclitaxel treatment, the cells in G1 and S stages died predominantly through apoptosis, whereas G2/M-stage cells died through both apoptosis and necrosis. These phenomena were verified by a trypan blue exclusion assay and by detection of the release of lactose dehydrogenase (LDH). Paclitaxel treatment significantly decreased viability in G2/M cells and led these cells to release more LDH than other cells. These treated cells also released certain substances that inhibited cell growth. These results strongly suggest that the cell membrane of the treated G2/M-cells is disrupted, leading to the leakage of LDH and cell growth inhibitory substances out of cell. Furthermore, the typical events of apoptosis, such as the release of cytochrome c and the decrease of mitochondria membrane potential, occur primarily in S stage rather than in the G2/M stages. These results suggest that paclitaxel induces typical apoptosis in the G1- and S- cells, but it induces both apoptosis and necrosis in G2/M-phase cells.

Induction of apoptosis by electrotransfer of positively charged proteins as Cytochrome C and Histone H1 into cells

Cytochrome C (Cyt. C) is a mitochondrial protein inducing apoptosis when it is accumulated in the cytosol by a currently unknown mechanism, but regulated by the bcl-2 family of proteins. The linker Histone H1 is another basic protein with highly conservative structure, composition, and equal molecular weight, not changed during the evolution. An attempt was made to understand better the apoptotic processes by electroloading of leukemic cells, such as K562, HL-60, and SKW3, and human lymphocytes with positively charged proteins, such as Cyt. C, Histone H1, and methylated BSA albumin (mBSA). The triggering apoptotic processes followed by MTT test, FACS analysis, and DNA fragmentation after the electrotransfer of these proteins into the cells were observed. Histone H1 and mBSA induce the release of Cyt. C from rat liver mitochondria. Cytochrome C release was higher when mitochondria were in "high-energy" state. It is supposed that release of Cyt. C from mitochondria is due to the mechanical rupture of the outer mitochondrial membrane, rich in negatively charged groups, predominately due to cardiolipin. The reason for the morphological rupture of the outer mitochondial membrane could be the rigidification and segregation of the membrane and the destroyed membrane asymmetries of both monolayers in the presence of positively charged proteins at higher linear charges such as Histone H1. We suggested that Histone H1, at a given moment of activated signaling for apoptosis, could be not transported to the nucleus and could lead to the release of Cyt. C from the mitochondria in the cytoplasm. It is temping to speculate that Histone H1 has other physiological extranuclear functions involved in apoptosis.

Clinically approved heterocyclics act on a mitochondrial target and reduce stroke-induced pathology

Substantial evidence indicates that mitochondria are a major checkpoint in several pathways leading to neuronal cell death, but discerning critical propagation stages from downstream consequences has been difficult. The mitochondrial permeability transition (mPT) may be critical in stroke-related injury. To address this hypothesis, identify potential therapeutics, and screen for new uses for established drugs with known toxicity, 1,040 FDA-approved drugs and other bioactive compounds were tested as potential mPT inhibitors. We report the identification of 28 structurally related drugs, including tricyclic antidepressants and antipsychotics, capable of delaying the mPT. Clinically achievable doses of one drug in this general structural class that inhibits mPT, promethazine, were protective in both in vitro and mouse models of stroke. Specifically, promethazine protected primary neuronal cultures subjected to oxygen-glucose deprivation and reduced infarct size and neurological impairment in mice subjected to middle cerebral artery occlusion/reperfusion. These results, in conjunction with new insights provided to older studies, (a) suggest a class of safe, tolerable drugs for stroke and neurodegeneration; (b) provide new tools for understanding mitochondrial roles in neuronal cell death; (c) demonstrate the clinical/experimental value of screening collections of bioactive compounds enriched in clinically available agents; and (d) provide discovery-based evidence that mPT is an essential, causative event in stroke-related injury.

Alveolar cell death in hyperoxia-induced lung injury

Exposure to high oxygen concentration causes direct oxidative cell damage through increased production of reactive oxygen species. In vivo oxygen-induced lung injury is well characterized in rodents and has been used as a valuable model of human respiratory distress syndrome. Hyperoxia-induced lung injury can be considered as a bimodal process resulting (1) from direct oxygen toxicity and (2) from the accumulation of inflammatory mediators within the lungs. Both apoptosis and necrosis have been described in alveolar cells (mainly epithelial and endothelial) during hyperoxia. While the in vitro response to oxygen seems to be cell type-dependent in tissue cultures, it is still unclear which are the death mechanisms and pathways implicated in vivo. Even though it is not yet possible to distinguish unequivocally between apo-ptosis, necrosis, or other intermediate form(s) of cell death, a great variety of strategies has been shown to prevent alveolar damage and to increase animal survival during hyperoxia. In this review, we summarize the different cell death pathways leading to alveolar damage during hyperoxia, with particular attention to the pivotal role of mitochondria. In addition, we discuss the different protective mechanisms potentially interfering with alveolar cell death.

The peripheral benzodiazepine receptor ligand PK11195 overcomes different resistance mechanisms to sensitize AML cells to gemtuzumab ozogamicin

The antibody-targeted therapeutic, gemtuzumab ozogamicin (GO, Mylotarg), is approved for treatment of relapsed acute myeloid leukemia (AML). We previously showed that AML blasts from GO refractory patients frequently express the drug transporters P-glycoprotein (Pgp) and/or multidrug resistance protein (MRP). We also previously reported that inhibition of drug transport by the Pgp modulator, cyclosporine A (CSA), can increase GO sensitivity in Pgp(+) AML cells and that the peripheral benzodiazepine receptor ligand, PK11195, sensitizes AML cells to standard chemotherapeutics both by inhibiting Pgp-mediated efflux and by promoting mitochondrial apoptosis. We now show that PK11195 also can overcome multiple resistance mechanisms to increase GO sensitivity in AML cells, including resistance associated with expression of drug transporters and/or antiapoptotic proteins. PK11195 substantially increases GO cytotoxicity in AML cells from many different cell lines and primary patient samples, often more effectively than CSA. We also show that PK11195 is nontoxic in NOD/SCID mice and can sensitize xenografted human AML cells to GO. Since PK11195 is well tolerated in humans as a single agent, its further study as a multifunctional chemosensitizer for anti-AML therapies, including GO-based therapies, is warranted.

Opening of the mitochondrial permeability transition pore induces reactive oxygen species production at the level of the respiratory chain complex I

We have investigated the consequences of permeability transition pore (PTP) opening on the rate of production of reactive oxygen species in isolated rat liver mitochondria. We found that PTP opening fully inhibited H(2)O(2) production when mitochondria were energized both with complex I or II substrates. Because PTP opening led to mitochondrial pyridine nucleotide depletion, H(2)O(2) production was measured again in the presence of various amounts of NADH. PTP opening-induced H(2)O(2) production began when NADH concentration was higher than 50 microm and reached a maximum at over 300 microm. At such concentrations of NADH, the maximal H(2)O(2) production was 4-fold higher than that observed when mitochondria were permeabilized with the channel-forming antibiotic alamethicin, indicating that the PTP opening-induced H(2)O(2) production was not due to antioxidant depletion. Moreover, PTP opening decreased rotenone-sensitive NADH ubiquinone reductase activity, whereas it did not affect the NADH FeCN reductase activity. We conclude that PTP opening induces a specific conformational change of complex I that (i) dramatically increases H(2)O(2) production so long as electrons are provided to complex I, and (ii) inhibits the physiological pathway of electrons inside complex I. These data allowed the identification of a novel consequence of permeability transition that may partly account for the mechanism by which PTP opening induces cell death.

Over-Expressed Bcl-2 Cannot Suppress Apoptosis via the Mitochondria in Buprenorphine Hydrochloride-Treated NG108-15 Cells

We previously reported that the morphine alkaloid derivative buprenorphine hydrochloride (Bph) induces rapid apoptosis in NG108-15 nerve cells accompanied by the activation of caspase-3. Here, we found this kind of apoptosis was also accompanied by rapid loss of the mitochondrial membrane potential, followed by the efflux of cytochrome c from the mitochondria to the cytosol and the activation of caspases-9 and -3. Together, these results strongly suggested the Bph death signal was routed through the mitochondrial pathway in NG108-15 cells. In these cells, serum-starvation induces a different apoptosis, which we exploited to investigate Bcl-2's role as an apoptosis inhibitor. We made an NG108-15 transfectant, Bcl-2(P2), that stably expressed human Bcl-2, and used it to test Bcl-2's effect on the serum-starvation-induced apoptosis in NG108-15 cells. Cell viability, DNA-ladder formation, and efflux of cytochrome c from the mitochondria were all detected, showing that the human Bcl-2 functioned normally in the Bcl-2(P2) cells. Although the apoptotic events tested were identical in the parental cells and transformants, Bcl-2 expression completely failed to inhibit Bph-induced apoptosis in the Bcl-2(P2) cells.

Induction of apoptosis without redox catastrophe by thioredoxin-inhibitory compounds

The dithiol-reducing thioredoxin/thioredoxin reductase system normally maintains the reduced state of key enzymes responsible for the cell's anti-oxidant defences. We therefore addressed the question of whether AW 464--a novel thioredoxin inhibitor--as well as broad spectrum dithiol ligands diamide and phenylarsine oxide are able to induce and execute a regular apoptotic sequence of events without overwhelming the cell's ability to detoxify reactive oxygen species. All three agents were found to target the thioredoxin system in a cell-free assay. In HL-60 leukaemia cells, they were also found to induce Bak activation, cytochrome c release from mitochondria, decreasing Delta Psi m, chromatin condensation, phosphatidyl serine exposure and Tdt-sensitive DNA nicks. At the onset of apoptosis there was no evidence of increases in oxygen free radicals or peroxide in cells treated with AW 464 or diamide. Phenylarsine oxide induced both free radicals and hydrogen peroxide, but this did not appear to interfere with apoptosis. We conclude that pharmacological targeting of thioredoxin can induce a well-orchestrated apoptotic programme.

Dietary ginger constituents, galanals A and B, are potent apoptosis inducers in Human T lymphoma Jurkat cells

The effects of the constituents isolated from ginger species including curcumin, 6-gingerol and labdane-type diterpene compounds on cell proliferation and the induction of apoptosis in the cultured human T lymphoma Jurkat cells were studied. Among the tested compounds, galanals A and B, isolated from the flower buds of a Japanese ginger, myoga (Zingiber mioga Roscoe), showed the most potent cytotoxic effect. Exposure of Jurkat human T-cell leukemia cells to galanals resulted in the induction of apoptotic cell death characterized by DNA fragmentation and caspase-3 activation. The mitochondrial damage pathway was suggested to be involved in galanal-induced apoptosis because the treatment of cells with galanals induced mitochondrial transmembrane potential (DeltaPsim) alteration and cytochrome c release. The anti-apoptotic Bcl-2 protein was downregulated by the galanal treatment together with enhancement of the Bax expression. In conclusion, the results from this study provide biological evidence that ginger-specific constituents other than curcuminoids are potential anticancer agents.

Cytochrome c, released from cerebellar granule cells undergoing apoptosis or excytotoxic death, can generate protonmotive force and drive ATP synthesis in isolated mitochondria

In rat cerebellar granule cells, cytochrome c release takes place during glutamate toxicity and apoptosis due to deprivation of depolarising levels of potassium. We show that, as in necrosis, the released cytochrome c present in the cytosolic fraction obtained from cerebellar granule cells undergoing apoptosis can operate as a reactive oxygen species (ROS) scavenger and as a respiratory substrate. The capability of the cytosolic fraction containing cytochrome c, obtained from cerebellar granule cells undergoing either necrosis or apoptosis, to energise coupled mitochondria isolated by the same cells is also investigated. We show that, in both cases, the cytosolic fraction containing cytochrome c, added to mitochondria, can cause proton ejection, and membrane potential generation and can drive ATP synthesis and export in the extramitochondrial phase, as photometrically measured via the ATP detecting system. Cytochrome c, separated immunologically from the cytosolic fraction of apoptotic cells when added to mitochondria, is found to cause proton ejection to generate membrane potential and to drive ATP synthesis and export in a manner not sensitive to the further addition of the cytosolic fraction depleted of cytochrome c, which failed to do this. In the light of these findings we propose that in apoptosis the released cytochrome c can contribute to provide ATP required for the cell programmed death to occur.

Quantitation of cytochrome c release from rat liver mitochondria

The apoptogenic protein cytochrome c can be quantitated by reverse-phase HPLC, but this method is not utilized by those who investigate mechanisms of cell death. Here, we extend the sensitivity of the method to exceed that available from immunogenic approaches and report specific procedures for applying the method to preparations of intact mitochondria, and to supernatants and pellets that arise from mitochondrial incubations. The detection limit corresponds to 0.6% of total cytochrome c found in 100 microg of rat liver mitochondrial protein, or to all of the cytochrome c that is expected in approximately 6000 hepatocytes. A single determination can be completed in 20 min, compared to a time scale of days for Western blotting methods, or hours for ELISA-based methods. The procedures are illustrated by experiments that determine the amount of cytochrome c released following the mitochondrial permeability transition as a function of medium ionic strength, and by long-term incubations of intact mitochondria in the presence and absence of an exogenous oxidizable substrate. Swelling and the release of adenylate kinase activity have been determined simultaneously to show how the data can be applied to evaluate the role of outer membrane disruption in mechanisms that release cytochrome c.