Role of reactive oxygen species and cardiolipin in the release of cytochrome c from mitochondria

Overexpression of Catalase Diminishes Oxidative Cysteine Modifications of Cardiac Proteins

Reactive protein cysteine thiolates are instrumental in redox regulation. Oxidants, such as hydrogen peroxide (H₂O₂), react with thiolates to form oxidative post-translational modifications, enabling physiological redox signaling. Cardiac disease and aging are associated with oxidative stress which can impair redox signaling by altering essential cysteine thiolates. We previously found that cardiac-specific overexpression of catalase (Cat), an enzyme that detoxifies excess H₂O₂, protected from oxidative stress and delayed cardiac aging in mice. Using redox proteomics and systems biology, we sought to identify the cysteines that could play a key role in cardiac disease and aging. With a ‘Tandem Mass Tag’ (TMT) labeling strategy and mass spectrometry, we investigated differential reversible cysteine oxidation in the cardiac proteome of wild type and Cat transgenic (Tg) mice. Reversible cysteine oxidation was measured as thiol occupancy, the ratio of total available versus reversibly oxidized cysteine thiols. Catalase overexpression globally decreased thiol occupancy by ≥1.3 fold in 82 proteins, including numerous mitochondrial and contractile proteins. Systems biology analysis assigned the majority of proteins with differentially modified thiols in Cat Tg mice to pathways of aging and cardiac disease, including cellular stress response, proteostasis, and apoptosis. In addition, Cat Tg mice exhibited diminished protein glutathione adducts and decreased H₂O₂ production from mitochondrial complex I and II, suggesting improved function of cardiac mitochondria. In conclusion, our data suggest that catalase may alleviate cardiac disease and aging by moderating global protein cysteine thiol oxidation.

Canine parvovirus NS1 induced apoptosis involves mitochondria, accumulation of reactive oxygen species and activation of caspases

The non-structural protein (NS1) of parvoviruses plays an important role in viral replication and is thought to be responsible for inducing cell death. However, the detailed mechanism and the pathways involved in canine parvovirus type 2 NS1 (CPV2.NS1) induced apoptosis are not yet known. In the present study, we report that expression of CPV2.NS1 in HeLa cells arrests cells in G1 phase of the cell cycle and the apoptosis is mitochondria mediated as indicated by mitochondrial depolarization, release of cytochrome-c and activation of caspase 9. Treatment of cells with caspase 9 inhibitor Z-LEHD-FMK reduced the induction of apoptosis significantly. We also report that expression of CPV2.NS1 causes accumulation of reactive oxygen species (ROS) and treatment with an antioxidant reduces the ROS levels and the extent of apoptosis. Our results provide an insight into the mechanism of CPV2.NS1 induced apoptosis, which might prove valuable in developing NS1 protein as an oncolytic agent.

Distribution and dynamics of OXPHOS complexes in the bacterial cytoplasmic membrane

Oxidative phosphorylation (OXPHOS) is an essential process for most living organisms mostly sustained by protein complexes embedded in the cell membrane. In order to thrive, cells need to quickly respond to changes in the metabolic demand or in their environment. An overview of the strategies that can be employed by bacterial cells to adjust the OXPHOS outcome is provided. Regulation at the level of gene expression can only provide a means to adjust the OXPHOS outcome to long-term trends in the environment. In addition, the actual view is that bioenergetic membranes are highly compartmentalized structures. This review discusses what is known about the spatial organization of OXPHOS complexes and the timescales at which they occur. As exemplified with the commensal gut bacterium Escherichia coli, three levels of spatial organization are at play: supercomplexes, membrane microdomains and polar assemblies. This review provides a particular focus on whether dynamic spatial organization can fine-tune the OXPHOS through the definition of specialized functional membrane microdomains. Putative mechanisms responsible for spatio-temporal regulation of the OXPHOS complexes are discussed. This article is part of a Special Issue entitled Organization and dynamics of bioenergetic systems in bacteria, edited by Conrad Mullineaux.

Controlled H2O2 release via long-lived electron-hole separation mediated to induce tumor cell apoptosis

Flexible films of polytungstate (PT) as active ingredients were fabricated in PDMS as a "band-Aid" to achieve controllable H₂O₂ release. In these different systems of an amorphous PT building block, the lengthened lifetime (bleaching process) of photo-electron-hole separation is attributed to the electron trapping of the PT network and the existence of hole scavengers. The hole scavengers further prevent recombination of electrons and holes, so that the long-lived photoelectron could provide sustainable reactive oxygen species (ROS) by trapped electrons. Transient absorption illustrates the kinetic competition between the process of photohole induced bleaching and coloration induced by weak irradiation, which suggests that the hole scavenger is vital for ROS generation. The signals of electron spin resonance further confirm the existence of ROS. The profiles of controllable H₂O₂ with various release efficiency were obtained via fluorescence studies. The results indicate that the H₂O₂ release efficiency is related to both the hole scavenger and the tungstate cluster. The released H₂O₂ on the responses of tumor cells were evaluated. Compared with a cancer drug, the controllable and reversible released H₂O₂ delivery is highly efficient in preventing the proliferation and inducing apoptosis of A375 melanoma cells.

Cytochrome c release from rat liver mitochondria is compromised by increased saturated cardiolipin species induced by sucrose feeding

Cytochrome c release from mitochondria has been described to be related to reactive oxygen species (ROS) generation. With ROS generation being increased in fatty liver from sucrose-fed (SF) rats, we hypothesized that cytochrome c release might be positively associated with H2O2 generation from SF mitochondria. Surprisingly, cytochrome c release from mitochondria of SF liver was found to be significantly lower compared with control (C) mitochondria oxidizing pyruvate/malate or succinate. Exposure of mitochondria to exogenous superoxide radical generated by the xanthine/xanthine oxidase system elicits a dose-response cytochrome c release in both control and SF mitochondria, but cytochrome c release remains lower in SF mitochondria compared with C mitochondria. Furthermore, the addition of ebselen, PEG-catalase, or catalase, a H2O2 scavenger, significantly reduces cytochrome c release from C and SF mitochondria. Our results suggest that both intra- and extramitochondrial H2O2 are involved in cytochrome c release, but the persisting difference between C and SF levels can be attributed to the differences in cardiolipin compositions. Indeed, the ratio of palmitic acid-rich cardiolipin species was found to be increased in lipid membrane from SF mitochondria compared with C mitochondria, whereas that of linoleic acid-rich cardiolipin species was found decreased. In addition, the content of tafazzin, a protein responsible for cardiolipin remodeling, was decreased in SF mitochondria. Therefore, we conclude that the changes observed in the composition of cardiolipin molecular species in SF mitochondria may be involved in cytochrome c interaction with mitochondrial inner membrane lipid and in its reduced release from SF mitochondria.

Translocator protein (TSPO) role in aging and Alzheimer's disease

Cellular damage and deregulated apoptotic cell death lead to functional impairment, and a main consequence of these events is aging. Cellular damage is initiated by different stress/risk factors such as oxidative stress, inflammation, and heavy metals. These stress/risk factors affect the cellular homeostasis by altering methylation status of several aging and Alzheimer’s disease associated genes; these effects can be manifested immediately after exposure to stress and at later stages of life. However, when cellular damage exceeds certain threshold levels apoptosis is initiated. This review discusses the stress factors involved in cellular damage and the role and potential of TSPO-mediated cell death in aging as well as in Alzheimer’s disease, which is also characterized by extensive cell death. Mitochondrial-mediated apoptotic death through the release of cytochrome c is regulated by TSPO, and increased expression of this protein is observed in both elderly people and in patients with Alzheimer’s disease. TSPO forms and mediates opening of the mitochondrial membrane pore, mPTP and oxidizes cardiolipin, and these events lead to the leakage of apoptotic death mediators, such as cytochrome c, resulting in cell death. However, TSPO has many proposed functions and can also increase steroid synthesis, which leads to inhibition of inflammation and inhibition of the release of apoptotic factors, thereby decreasing cell damage and promoting cell survival. Thus, TSPO mediates apoptosis and decreases the cell damage, which in turn dictates the process of aging as well as the functionality of organs such as the brain. TSPO modulation with ligands in the Alzheimer’s disease mouse model showed improvement in behavioral symptoms, and studies in Drosophila species showed increased cell survival and prolonged lifespan in flies after TSPO inhibition. These data suggest that since effects/signs of stress can manifest at any time, prevention through change in lifestyle and TSPO modulation could be potential strategies for altering both the aging process and the progression of Alzheimer’s disease.

Elephantopus scaber induces apoptosis through ROS-dependent mitochondrial signaling pathway in HCT116 human colorectal carcinoma cells

ETHNOPHARMACOLOGICAL RELEVANCE

Elephantopus scaber also known as Elephant's foot (Asteraceae family) has a plethora of traditional applications including dysuria, diarrhea, dysentery, leukemia and cancer. This study aimed to investigate the apoptosis inducing effects of E. scaber and the underlying mechanisms in HCT116 colorectal cell line.

METHODS

The MTT assay was used to determine the IC50 values on cancer cell lines by the ethanol, hexane, ethyl acetate and water fractions. Apoptosis was detected by cell morphologic observation through Hoechst 33342/PI dual staining, phosphatidylserine externalization by Annexin V/PI staining and DNA fragmentation by TUNEL assay. The caspase activity, Bcl-2 family and p53 proteins were determined by flow cytometric analysis. The cleaved PARP protein expression was assessed by western blot analysis

RESULTS

The ethanol extract of E. scaber and its fractions significantly inhibited the growth of HCT116 and HT-29 cells and induced apoptosis. The E. scaber ethyl acetate fraction (ESEAF) was the most potent on HCT116 cell line with the IC50 value of 1.42 ± 0.10 µg/mL. The induction of apoptosis was marked by nuclear shrinkage accompanied with chromatin condensation, DNA fragmentation and phosphatidylserine externalization. The results showed that ESEAF-induced apoptosis was associated with an upregulation of proapoptotic Bax, elevation of Bax/Bcl-2 ratio, dissipation of mitochondrial membrane potential, activation of caspase-3 and cleavage of poly (ADP-ribose) polymerase (PARP). In addition, a compromised mitochondrial membrane potential and overproduction of ROS demonstrated the involvement of the mitochondrial signaling pathway. Mechanistic studies further revealed that ESEAF caused the augmentation of the intracellular ROS, subsequently incited the increase in p53 protein expression and led to oligomerization of Bax, depolarization of mitochondrial membrane potential and caspases cascade (caspase-3/7 and -9) in a time-dependent manner. The attenuation of intracellular ROS level by N-acetyl-l-cysteine (NAC) preserved the integrity of mitochondrial membrane and rescued the cells from cell death. Furthermore, caspase cascade results in the cleavage of PARP which ultimately activated DNA fragmentation and eventually apoptosis.

CONCLUSION

Taken together, cumulative evidences in this study suggest that ESEAF induces apoptosis through ROS-dependent mitochondrial signaling pathway and holds potential therapeutic effect for colorectal cancer.

Molecular mechanisms of apoptosis and cell selectivity of zinc dithiocarbamates functionalized with hydroxyethyl substituents

In the solid state each of three binuclear zinc dithiocarbamates bearing hydroxyethyl groups, {Zn[S2CN(R)CH2CH2OH]2}2 for R = iPr (1), CH2CH2OH (2), and Me (3), and an all alkyl species, [Zn(S2CNEt2)2]2 (4), features a centrosymmetric {ZnSCS}2 core with a step topology; both 1 and 3 were isolated as monohydrates. All compounds were broadly cytotoxic, specifically against human cancer cell lines compared with normal cells, with greater potency than cisplatin. Notably, some selectivity were indicated with 2 being the most potent against human ovarian carcinoma cells (cisA2780), and 4 being more cytotoxic toward multidrug resistant human breast carcinoma cells (MCF-7R), human colon adenocarcinoma cells (HT-29), and human lung adenocarcinoma epithelial cells (A549). Based on human apoptosis PCR-array analysis, caspase activities, DNA fragmentation, cell apoptotic assays, intracellular reactive oxygen species (ROS) measurements and human topoisomerase I inhibition, induction of apoptosis in HT-29 cells is demonstrated via both extrinsic and intrinsic pathways. Compounds 2-4 activate the p53 gene while 1 activates both p53 and p73. Cell cycle arrest at the S and G2/M phases correlates with inhibition of HT-29 cell growth. Cell invasion is also inhibited by 1-4 which is correlated with down-regulation of NF-κB.

Cytocompatibility of direct water synthesized cadmium selenide quantum dots in colo-205 cells

Cadmium selenide quantum dots (CdSe QDs), inorganic semiconducting nanocrystals, are alluring increased attraction due to their highly refined chemistry, availability, and super tunable optical properties suitable for many applications in different research areas, such as photovoltaics, light-emitting devices, environmental sciences, and nanomedicine. Specifically, they are being widely used in bio-imaging in contrast to organic dyes due to their high brightness and improved photo-stability, and their ability to tune their absorption and emission spectra upon changing the crystal size. The production of CdSe QDs is mostly assisted by trioctylphosphine oxide compound, which acts as solvent or solubilizing agent and renders the QDs soluble in organic compounds (such as toluene, chloroform, and hexane) that are highly toxic. To circumvent the toxicity-related factor in CdSe QDs, we report the synthesis of CdSe QDs capped with thioglycolic acid (TGA) in an aqueous medium, and their biocompatibility in colo-205 cancer cells. In this study, the [Cd²⁺]/[TGA] ratio was adjusted to 11:1 and the Se concentration (10 and 15 mM) was monitored in order to evaluate its influence on the optical properties and cytocompatibility. QDs resulted to be quite stable in water (after purification) and RPMI cell medium and no precipitation was observed for long contact times, making them appealing for in vitro experiments. The spectroscopy analysis, advanced electron microscopy, and X-ray diffractometry studies indicate that the final products were successfully formed exhibiting an improved optical response. Colo-205 cells being exposed to different concentrations of TGA-capped CdSe QDs for 12, 24, and 48 h with doses ranging from 0.5 to 2.0 mM show high tolerance reaching cell viabilities as high as 93 %. No evidence of cellular apoptotic pathways was observed as pointed out by our Annexin V assays at higher concentrations. Moreover, confocal microscopy analysis conducted to evaluate the intracellular uptake of TGA-CdSe QDs reveal that the TGA-CdSe QDs were uniformly distributed within the cytosolic side of cell membranes. Our results also suggest that under controlled conditions, direct water-soluble TGA-CdSe QDs can be potentially employed for bio-imaging colo-205 cancer cells with minimal adverse effects.

Normothermic liver preservation: a new paradigm?

Despite increasing donor numbers, waiting lists and pre-transplant mortality continue to grow in many countries. The number of donor organs suitable for liver transplantation is restricted by cold preservation and ischemia-reperfusion injury (IRI). Transplantation of marginal donor organs has led to renewed interest in new techniques which have the potential to improve the quality of preservation, assess the quality of the organ and allow repair of the donor organ prior to transplantation. If successful, such techniques would not only improve the outcome of currently transplanted marginal livers, but also increase the donor pool. Experimental evidence suggests that preservation under near physiological conditions of temperature and oxygenation abrogates IRI. Normothermic perfusion maintains the organ in a physiological state, avoiding the depletion of cellular energy and the accumulation of waste products, which occurs with static cold storage. It enables viability assessment prior to transplantation thereby reducing the risk of transplanting inherently marginal organs. Here we review the use of normothermic machine perfusion as a means of organ preservation.

Wilson's disease: a comprehensive review of the molecular mechanisms

Wilson’s disease (WD), also known as hepatolenticular degeneration, is an autosomal recessive inherited disorder resulting from abnormal copper metabolism. Reduced copper excretion causes an excessive deposition of the copper in many organs such as the liver, central nervous system (CNS), cornea, kidney, joints, and cardiac muscle where the physiological functions of the affected organs are impaired. The underlying molecular mechanisms for WD have been extensively studied. It is now believed that a defect in P-type adenosine triphosphatase (ATP7B), the gene encoding the copper transporting P-type ATPase, is responsible for hepatic copper accumulation. Deposited copper in the liver produces toxic effects via modulating several molecular pathways. WD can be a lethal disease if left untreated. A better understanding of the molecular mechanisms causing the aberrant copper deposition and organ damage is the key to developing effective management approaches.

Down-regulation of deacetylase HDAC6 inhibits the melanoma cell line A375.S2 growth through ROS-dependent mitochondrial pathway

Previous studies have shown that histone deacetylase 6 (HDAC6) plays critical roles in many cellular processes related to cancer. However, its biological roles in the development of melanoma remain unexplored. Our aim was to investigate whether HDAC6 has a biological role in human melanoma development and to understand its underlying mechanism. In the present study, HDAC6 expression was up-regulated in melanoma tissues and cell lines. Knockdown of HDAC6 significantly inhibited the proliferation and colony formation ability of A375.S2 cells, promoted cell arrest at G0/G1 phase and apoptosis. Additionally, western blotting assay showed that HDAC6 silencing suppressed Bcl-2 level and enhanced Bax level, then activated caspase-9 and caspase-3, and further activated the release of cytochrome c from mitochondria to cytoplasm, finally induced cell apoptosis involving the mitochondrial pathway. Knockdown of HDAC6 triggered a significant generation of ROS and disruption of mitochondrial membrane potential (MMP). Furthermore, ROS inhibitor, NAC reduced HDAC6 siRNA-induced ROS production, and blocked HDAC6 siRNA-induced loss of MMP and apoptosis. NAC also significantly blocked HDAC6 siRNA-induced mtDNA copy number decrease and mitochondrial biogenesis and degradation imbalance. In conclusion, the results showed that knockdown of HDAC6 induced apoptosis in human melanoma A375.S2 cells through a ROS-dependent mitochondrial pathway.

ROS signaling during granzyme B-mediated apoptosis

Reactive oxygen species (ROS) are involved in cell signaling, aging, and death and play a role in carcinogenesis. However, whether ROS are bystanders or active effectors of apoptosis was unclear until recently. New evidence shows that the killer lymphocyte protease granzyme B activates a conserved biochemical pathway centered on respiratory chain disruption to trigger mitocentric ROS-dependent apoptosis.

Bmi1 regulates auditory hair cell survival by maintaining redox balance

Reactive oxygen species (ROS) accumulation are involved in noise- and ototoxic drug-induced hair cell loss, which is the major cause of hearing loss. Bmi1 is a member of the Polycomb protein family and has been reported to regulate mitochondrial function and ROS level in thymocytes and neurons. In this study, we reported the expression of Bmi1 in mouse cochlea and investigated the role of Bmi1 in hair cell survival. Bmi1 expressed in hair cells and supporting cells in mouse cochlea. Bmi1^−/− mice displayed severe hearing loss and patched outer hair cell loss from postnatal day 22. Ototoxic drug-induced hair cells loss dramatically increased in Bmi1^−/− mice compared with that in wild-type controls both in vivo and in vitro, indicating Bmi1^−/− hair cells were significantly more sensitive to ototoxic drug-induced damage. Cleaved caspase-3 and TUNEL staining demonstrated that apoptosis was involved in the increased hair cell loss of Bmi1^−/− mice. Aminophenyl fluorescein and MitoSOX Red staining showed the level of free radicals and mitochondrial ROS increased in Bmi1^−/− hair cells due to the aggravated disequilibrium of antioxidant–prooxidant balance. Furthermore, the antioxidant N-acetylcysteine rescued Bmi1^−/− hair cells from neomycin injury both in vitro and in vivo, suggesting that ROS accumulation was mainly responsible for the increased aminoglycosides sensitivity in Bmi1^−/− hair cells. Our findings demonstrate that Bmi1 has an important role in hair cell survival by controlling redox balance and ROS level, thus suggesting that Bmi1 may work as a new therapeutic target for the prevention of hair cell death.

RECOMBINANT BCL-XL ATTENUATES VASCULAR HYPERPERMEABILITY IN A RAT MODEL OF HEMORRHAGIC SHOCK

Following hemorrhagic shock (HS), vascular hyperpermeability, that is, the leakage of fluid, nutrients and proteins into the extravascular space occurs primarily due to the disruption of the endothelial cell–cell adherens junctional complex. Studies from our laboratory demonstrate that activation of the mitochondria-mediated ‘intrinsic’ apoptotic signaling cascade has a significant role in modulating HS-induced hyperpermeability. Here we report the novel use of recombinant Bcl-xL, an anti-apoptotic protein, to control HS-induced vascular hyperpermeability. Our results corroborate involvement of vascular hyperpermeability and apoptotic signaling. HS (the mean arterial pressure (MAP) was reduced to 40 mm Hg for 60 min followed by resuscitation to 90 mm Hg for 60 min) in rats resulted in vascular hyperpermeability as determined by intravital microscopy. Treatment of Bcl-xL (2.5 µg/ml of rat blood in non-lipid cationic polymer, i.v.) before, during and even after HS attenuated or reversed HS-induced vascular hyperpermeability significantly (P<0.05). Conversely, treatment using Bcl-xL inhibitors, 2-methoxy antimycin (2-OMeAA) and ABT 737, significantly increased vascular hyperpermeability compared with sham (P<0.05). Bcl-xL treatment also decreased the amount of fluid volume required to maintain a MAP of 90 mm Hg during resuscitation (P<0.05). HS resulted in an increased mitochondrial reactive oxygen species formation, reduction of ΔΨm, mitochondrial release of cytochrome c and significant activation of caspase-3 (P<0.05). All of these effects were significantly inhibited by Bcl-xL pre-treatment (P<0.05). Our results show that recombinant Bcl-xL is effective against HS-induced vascular hyperpermeability that appears to be mediated through the preservation of ΔΨm and subsequent prevention of caspase-3 activation.

Lipid analogues as potential drugs for the regulation of mitochondrial cell death

The mitochondrion plays an important role in the production of energy as ATP, the regulation of cell viability and apoptosis, and the biosynthesis of major structural and regulatory molecules, such as lipids. During ATP production, reactive oxygen species are generated that alter the intracellular redox state and activate apoptosis. Mitochondrial dysfunction is a well-recognized component of the pathogenesis of diseases such as cancer. Understanding mitochondrial function, and how this is dysregulated in disease, offers the opportunity for the development of drug molecules to specifically target such defects. Altered energy metabolism in cancer, in which ATP production occurs largely by glycolysis, rather than by oxidative phosphorylation, is attributable in part to the up-regulation of cell survival signalling cascades. These pathways also regulate the balance between pro- and anti-apoptotic factors that may determine the rate of cell death and proliferation. A number of anti-cancer drugs have been developed that target these factors and one of the most promising groups of agents in this regard are the lipid-based molecules that act directly or indirectly at the mitochondrion. These molecules have emerged in part from an understanding of the mitochondrial actions of naturally occurring fatty acids. Some of these agents have already entered clinical trials because they specifically target known mitochondrial defects in the cancer cell.

The mitochondrial voltage-dependent anion channel 1 in tumor cells

VDAC1 is found at the crossroads of metabolic and survival pathways. VDAC1 controls metabolic cross-talk between mitochondria and the rest of the cell by allowing the influx and efflux of metabolites, ions, nucleotides, Ca2+ and more. The location of VDAC1 at the outer mitochondrial membrane also enables its interaction with proteins that mediate and regulate the integration of mitochondrial functions with cellular activities. As a transporter of metabolites, VDAC1 contributes to the metabolic phenotype of cancer cells. Indeed, this protein is over-expressed in many cancer types, and silencing of VDAC1 expression induces an inhibition of tumor development. At the same time, along with regulating cellular energy production and metabolism, VDAC1 is involved in the process of mitochondria-mediated apoptosis by mediating the release of apoptotic proteins and interacting with anti-apoptotic proteins. The engagement of VDAC1 in the release of apoptotic proteins located in the inter-membranal space involves VDAC1 oligomerization that mediates the release of cytochrome c and AIF to the cytosol, subsequently leading to apoptotic cell death. Apoptosis can also be regulated by VDAC1, serving as an anchor point for mitochondria-interacting proteins, such as hexokinase (HK), Bcl2 and Bcl-xL, some of which are also highly expressed in many cancers. By binding to VDAC1, HK provides both a metabolic benefit and apoptosis-suppressive capacity that offer the cell a proliferative advantage and increase its resistance to chemotherapy. Thus, these and other functions point to VDAC1 as an excellent target for impairing the re-programed metabolism of cancer cells and their ability to evade apoptosis. Here, we review current evidence pointing to the function of VDAC1 in cell life and death, and highlight these functions in relation to both cancer development and therapy. In addressing the recently solved 3D structures of VDAC1, this review will point to structure-function relationships of VDAC as critical for deciphering how this channel can perform such a variety of roles, all of which are important for cell life and death. Finally, this review will also provide insight into VDAC function in Ca2+ homeostasis, protection against oxidative stress, regulation of apoptosis and involvement in several diseases, as well as its role in the action of different drugs. We will discuss the use of VDAC1-based strategies to attack the altered metabolism and apoptosis of cancer cells. These strategies include specific siRNA able to impair energy and metabolic homeostasis, leading to arrested cancer cell growth and tumor development, as well VDAC1-based peptides that interact with anti-apoptotic proteins to induce apoptosis, thereby overcoming the resistance of cancer cell to chemotherapy. Finally, small molecules targeting VDAC1 can induce apoptosis. VDAC1 can thus be considered as standing at the crossroads between mitochondrial metabolite transport and apoptosis and hence represents an emerging cancer drug target. This article is part of a Special Issue entitled: Membrane channels and transporters in cancers.

Granzyme B-induced mitochondrial ROS are required for apoptosis

Caspases and the cytotoxic lymphocyte protease granzyme B (GB) induce reactive oxygen species (ROS) formation, loss of transmembrane potential and mitochondrial outer membrane permeabilization (MOMP). Whether ROS are required for GB-mediated apoptosis and how GB induces ROS is unclear. Here, we found that GB induces cell death in an ROS-dependent manner, independently of caspases and MOMP. GB triggers ROS increase in target cell by directly attacking the mitochondria to cleave NDUFV1, NDUFS1 and NDUFS2 subunits of the NADH: ubiquinone oxidoreductase complex I inside mitochondria. This leads to mitocentric ROS production, loss of complex I and III activity, disorganization of the respiratory chain, impaired mitochondrial respiration and loss of the mitochondrial cristae junctions. Furthermore, we have also found that GB-induced mitocentric ROS are necessary for optimal apoptogenic factor release, rapid DNA fragmentation and lysosomal rupture. Interestingly, scavenging the ROS delays and reduces many of the features of GB-induced death. Consequently, GB-induced ROS significantly promote apoptosis.

Effects of partial inhibition of respiratory complex I on H2O 2 production by isolated brain mitochondria in different respiratory states

The aim of this work was to characterize the effects of partial inhibition of respiratory complex I by rotenone on H2O2 production by isolated rat brain mitochondria in different respiratory states. Flow cytometric analysis of membrane potential in isolated mitochondria indicated that rotenone leads to uniform respiratory inhibition when added to a suspension of mitochondria. When mitochondria were incubated in the presence of a low concentration of rotenone (10 nm) and NADH-linked substrates, oxygen consumption was reduced from 45.9 ± 1.0 to 26.4 ± 2.6 nmol O2 mg(-1) min(-1) and from 7.8 ± 0.3 to 6.3 ± 0.3 nmol O2 mg(-1) min(-1) in respiratory states 3 (ADP-stimulated respiration) and 4 (resting respiration), respectively. Under these conditions, mitochondrial H2O2 production was stimulated from 12.2 ± 1.1 to 21.0 ± 1.2 pmol H2O2 mg(-1) min(-1) and 56.5 ± 4.7 to 95.0 ± 11.1 pmol H2O2 mg(-1) min(-1) in respiratory states 3 and 4, respectively. Similar results were observed when comparing mitochondrial preparations enriched with synaptic or nonsynaptic mitochondria or when 1-methyl-4-phenylpyridinium ion (MPP(+)) was used as a respiratory complex I inhibitor. Rotenone-stimulated H2O2 production in respiratory states 3 and 4 was associated with a high reduction state of endogenous nicotinamide nucleotides. In succinate-supported mitochondrial respiration, where most of the mitochondrial H2O2 production relies on electron backflow from complex II to complex I, low rotenone concentrations inhibited H2O2 production. Rotenone had no effect on mitochondrial elimination of micromolar concentrations of H2O2. The present results support the conclusion that partial complex I inhibition may result in mitochondrial energy crisis and oxidative stress, the former being predominant under oxidative phosphorylation and the latter under resting respiration conditions.

Oxygen metabolism in human placenta mitochondria

Due to the high metabolic demands of the placental tissue during gestation, we decide to analyzed the mitochondrial bioenergetic functions in the human term placenta. Different mitochondrial morphological parameters, membrane potential and cardiolipin content were determined by flow cytometry. Oxygen uptake, hydrogen peroxide production and cytochrome P450 content, were also measured. Some apoptotic mitochondrial proteins were also analyzed by western blot. Two isolated mitochondrial fractions were observed: large/heavy and small/light with different functional characteristics. Oxygen uptake showed a respiratory control (RC) of 3.4 ± 0.3 for the heavy mitochondria, and 1.1 ± 0.4 for light mitochondria, indicating a respiratory dysfunction in the light fraction. Good levels of polarization were detected in the heavy fraction, meanwhile the light population showed a collapsed ΔΨm. Increased levels of cytochrome P450, higher levels of hydrogen peroxide, and low cardiolipin content were described for the light fraction. Three pro-apoptotic proteins p53, Bax, and cytochrome c were found increased in the heavy mitochondrial fraction; and deficient in the light fraction. The heavy mitochondrial fraction showed an improved respiratory function. This mitochondrial fraction, being probably from cytotrophoblast cells showed higher content of proteins able to induce apoptosis, indicating that these cells can effectively execute an apoptotic program in the presence of a death stimulus. Meanwhile the light and small organelles probably from syncytiotrophoblast, with a low oxygen metabolism, low level of ΔΨm, and increased hydrogen peroxide production, may not actively perform an apoptotic process due to their deficient energetic level. This study contributes to the characterization of functional parameters of human placenta mitochondria in order to understand the oxygen metabolism during the physiological process of gestation.

Recent advances in mitochondrial turnover during chronic muscle disuse

Chronic muscle disuse, such as that resulting from immobilization, denervation, or prolonged physical inactivity, produces atrophy and a loss of mitochondria, yet the molecular relationship between these events is not fully understood. In this review we attempt to identify the key regulatory steps mediating the loss of muscle mass and the decline in mitochondrial content and function. An understanding of common intracellular signaling pathways may provide much-needed insight into the possible therapeutic targets for treatments that will maintain aerobic energy metabolism and preserve muscle mass during disuse conditions.

Stabilization of apoptotic cells: generation of zombie cells

Apoptosis is characterized by degradation of cell components but plasma membrane remains intact. Apoptotic microtubule network (AMN) is organized during apoptosis forming a cortical structure beneath plasma membrane that maintains plasma membrane integrity. Apoptotic cells are also characterized by high reactive oxygen species (ROS) production that can be potentially harmful for the cell. The aim of this study was to develop a method that allows stabilizing apoptotic cells for diagnostic and therapeutic applications. By using a cocktail composed of taxol (a microtubule stabilizer), Zn²⁺ (a caspase inhibitor) and coenzyme Q₁₀ (a lipid antioxidant), we were able to stabilize H460 apoptotic cells in cell cultures for at least 72 h, preventing secondary necrosis. Stabilized apoptotic cells maintain many apoptotic cell characteristics such as the presence of apoptotic microtubules, plasma membrane integrity, low intracellular calcium levels and mitochondrial polarization. Apoptotic cell stabilization may open new avenues in apoptosis detection and therapy.

Cardiolipin plays a role in KCN-induced necrosis

Cardiolipin (CL) is a unique anionic, dimeric phospholipid found almost exclusively in the inner mitochondrial membrane and is essential for the function of numerous enzymes that are involved in mitochondrial energy metabolism. While the role of cardiolipin in apoptosis is well established, its involvement in necrosis is enigmatic. In the present study, KCN-induced necrosis in U937 cells was used as an experimental model to assess the role of CL in necrosis. KCN addition to U937 cells induced reactive oxygen species (ROS) formation, while the antioxidants inhibited necrosis, indicating that ROS play a role in KCN-induced cell death. Further, CL oxidation was confirmed by the monomer green fluorescence of 10-N-nonyl acridine orange (NAO) and by TLC. Utilizing the red fluorescence of the dimeric NAO, redistribution of CL in mitochondrial membrane during necrosis was revealed. We also showed that the catalytic activity of purified adenosine triphosphate (ATP) synthase complex, known to be modulated by cardiolipin, decreased following KCN treatment. All these events occurred at an early phase of the necrotic process prior to rupture of the cell membrane. Furthermore, CL-deficient HeLa cells were found to be resistant to KCN-induced necrosis as compared with the wild type cells. We suggest that KCN, an effective reversible inhibitor of cytochrome oxidase and thereby of the respiratory chain leads to ROS increase, which in turn oxidizes CL (amongst other membrane phospholipids) and leads to mitochondrial membrane lipid reorganization and loss of CL symmetry. Finally, the resistance of CL-deficient cells to necrosis further supports the notion that CL, which undergoes oxidation during necrotic cell death, is an integral part of the milieu of events taking place in mitochondria leading to membrane disorganization and mitochondrial dysfunction.

Mitochondrial protection restores renal function in swine atherosclerotic renovascular disease

AIMS

The mechanisms responsible for renal injury in atherosclerotic renovascular disease (ARVD) are incompletely understood, and few therapeutic options are available to reverse it. We hypothesized that chronic renal damage involves mitochondrial injury, and that mitochondrial protection would reduce renal fibrosis and dysfunction in ARVD pigs.

METHODS AND RESULTS

Domestic pigs were studied after 10 weeks of ARVD or sham, treated for the last 4 weeks with daily subcutaneous injections (5 days/week) of vehicle or Bendavia (0.1 mg/kg), a tetrapeptide that preserves cardiolipin content in the mitochondrial inner membrane. Single-kidney haemodynamics and function were studied using fast-computer tomography, oxygenation using blood oxygen level-dependent magnetic resonance imaging, microvascular architecture, oxidative stress, and fibrosis ex vivo. Cardiolipin content was assessed using mass spectrometry and staining. Renal endothelial function was studied in vivo and ex vivo. In addition, swine renal artery endothelial cells incubated with tert-butyl hydroperoxide were also treated with Bendavia. Stenotic-kidney renal blood flow (RBF) and glomerular filtration rate (GFR) decreased in ARVD + Vehicle compared with normal (318.8 ± 61.0 vs. 553.8 ± 82.8 mL/min and 48.0 ± 4.0 vs. 84.0 ± 3.8 mL/min, respectively) associated with loss of cardiolipin, intra-renal microvascular rarefaction, and hypoxia. Bendavia restored cardiolipin content in ARVD and improved vascular density, oxygenation, RBF (535.1 ± 24.9 mL/min), and GFR (86.6 ± 11.2 mL/min). Oxidative stress and fibrosis were ameliorated, and renovascular endothelial function normalized both in vivo and in vitro.

CONCLUSION

Preservation of mitochondrial cardiolipin attenuated swine stenotic-kidney microvascular loss and injury, and improved renal oxygenation, haemodynamics, and function. These observations implicate mitochondrial damage in renal deterioration in chronic experimental ARVD, and position the mitochondria as a central therapeutic target.

Vam3, a resveratrol dimer, inhibits cigarette smoke-induced cell apoptosis in lungs by improving mitochondrial function

AIM

To investigate the effects of Vam3 (a resveratrol dimer extracted from Vitis amurensis Rupr) on cigarette smoke (CS)-induced cell apoptosis in lungs in vitro and in vivo and the underlying mechanisms of action.

METHODS

Human bronchial epithelial cell line BEAS-2B was exposed to cigarette smoke condensate (CSC, 300 mg/L), and cell apoptosis was determined using flow cytometry and Hoechst staining. Mitochondrial membrane potential was examined with TMRE staining. ROS and ceramide levels were detected with DCFH-DA fluorescence and HPLC-MS/MS, respectively. Cytochrome c release was detected using immunofluorescence. Caspase-9 and neutral sphingomyelinase 2 expression was measured with Western blotting. The breast carcinoma cell line MCF7 stably expressing GFP-tagged Bax was used to elucidate the role of mitochondria in CS-induced apoptosis. For in vivo study, male mice were exposed to CS for 5 min twice a day for 4 weeks. The mice were orally administered Vam3 (50 mg·kg(-1)·d(-1)) or resveratrol (30 mg·kg(-1)·d(-1)) each day 1 h before the first CS exposure.

RESULTS

Pretreatment of BEAS-2B cells with Vam3 (5 μmol/L) or resveratrol (5 μmol/L) significantly suppressed CSC-induced apoptosis, and prevented CSC-induced Bax level increase in the mitochondria, mitochondrial membrane potential loss, cytochrome c release and caspase-9 activation. Furthermore, pretreatment of BEAS-2B cells with Vam3 or resveratrol significantly suppressed CSC-stimulated intracellular ceramide production, and CSC-induced upregulation of neutral sphingomyelinase 2, the enzyme responsible for ceramide production in bronchial epithelial cells. Similar results were obtained in C6-pyridinium ceramide-induced apoptosis of GFP-Bax-stable MCF7 cells in vitro, and in the lungs of CS-exposed mice that were treated with oral administration of Vam3 or resveratrol.

CONCLUSION

Vam3 protects bronchial epithelial cells from CS-induced apoptosis in vitro and in vivo by preventing mitochondrial dysfunction.

Cardiolipin and mitochondrial function in health and disease

Cardiolipin (CL) is a unique phospholipid that is almost exclusively localized at the level of the inner mitochondrial membrane (IMM), where it is biosynthesized. This phospholipid is associated with membranes which are designed to generate an electrochemical gradient that is used to produce ATP. Such membranes include the bacterial plasma membrane and IMM. This ubiquitous and intimate association between CL and energy-transducing membranes suggests an important role for CL in mitochondrial bioenergetic processes. CL has been shown to interact with a number of IMM proteins, including the respiratory chain complexes and substrate carriers. Moreover, CL is involved in different stages of the mitochondrial apoptosis process as well as in mitochondrial membrane stability and dynamics. Alterations in CL structure, content, and acyl chain composition have been associated with mitochondrial dysfunction in multiple tissues in several physiopathological conditions and aging. In this review, we provide an overview of the roles of CL in mitochondrial function and bioenergetics in health and disease.

Cardiolipin asymmetry, oxidation and signaling

Cardiolipins (CLs) are ancient and unusual dimeric phospholipids localized in the plasma membrane of bacteria and in the inner mitochondrial membrane of eukaryotes. In mitochondria, two types of asymmetries--trans-membrane and molecular--are essential determinants of CL functions. In this review, we describe CL-based signaling mitochondrial pathways realized via modulation of trans-membrane asymmetry and leading to externalization and peroxidation of CLs in mitophagy and apoptosis, respectively. We discuss possible mechanisms of CL translocations from the inner leaflet of the inner to the outer leaflet of the outer mitochondrial membranes. We present redox reaction mechanisms of cytochrome c-catalyzed CL peroxidation as a required stage in the execution of apoptosis. We also emphasize the significance of CL-related metabolic pathways as new targets for drug discovery. Finally, a remarkable diversity of polyunsaturated CL species and their oxidation products have evolved in eukaryotes vs. prokaryotes. This diversity--associated with CL molecular asymmetry--is presented as the basis for mitochondrial communications language.

Structural and metabolic changes in Atp7b-/- mouse liver and potential for new interventions in Wilson's disease

Wilson's disease (WD) is caused by ATP7B mutations and results in copper accumulation and toxicity in liver and brain tissues. The specific mechanisms underlying copper toxicity are still poorly understood. Mouse models have revealed new insights into pathomechanisms of hepatic WD. Mitochondrial damage is observed in livers of WD patients and in mouse models; copper induces fragmentation of mitochondrial membrane lipids, particularly cardiolipin, with deleterious effects on both mitochondrial integrity and function. Copper accumulation also induces chronic inflammation in WD livers, which is followed by regeneration in parts of the liver and occasionally neoplastic proliferation. Gene expression studies using microarrays have aided our understanding of the molecular basis of these changes. Copper overload alters cholesterol biosynthesis in hepatocytes resulting in reduced liver and serum cholesterol. Experiments are currently underway to elucidate the link between copper and cholesterol metabolism. These findings may facilitate the development of specific therapies to ameliorate WD progression.

Technical feasibility of liver transplantation without cold storage

PURPOSE

The success of liver transplantation (LT) is accompanied by an increased need for organs. The wider use of older donors and marginal organs with risk factors such as steatosis has lead to a new interest to improve the outcome with marginal organs. We herewith report a novel technique for LT with in situ preparation and immediate warm-ischemia liver transplantation (WI-LT). The aim of our study was to demonstrate the technical feasibility and report the transplant course.

METHODS

Six patients underwent WI-LT at our institution. Hepatectomies during procurement and LT were both performed in parallel by different surgical teams. Technical factors and postoperative allograft function were analyzed.

RESULTS

All six WI-LTs were performed without intraoperative complications with a mean warm-ischemia time (WIT) of 29.0 min. No patient developed primary non-function or required retransplantation. Mean alanine aminotransferase (194.0 ± 170.4 U/l) and aspartate aminotransferase (316.3 ± 222.1 U/l) values on the first postoperative day were low, indicating a low ischemia/reperfusion injury and an excellent liver function.

CONCLUSIONS

These results demonstrate that WI-LT is a safe and technically feasible approach for LT with possibly reduced IRI and an excellent postoperative allograft quality. WI-LT may therefore be considered in individual patients especially with extended criteria donors to eventually improve postoperative allograft quality.

Lipid Replacement Therapy: a natural medicine approach to replacing damaged lipids in cellular membranes and organelles and restoring function

Lipid Replacement Therapy, the use of functional oral supplements containing cell membrane phospholipids and antioxidants, has been used to replace damaged, usually oxidized, membrane glycerophospholipids that accumulate during aging and in various clinical conditions in order to restore cellular function. This approach differs from other dietary and intravenous phospholipid interventions in the composition of phospholipids and their defense against oxidation during storage, ingestion, digestion and uptake as well as the use of protective molecules that noncovalently complex with phospholipid micelles and prevent their enzymatic and bile disruption. Once the phospholipids have been taken in by transport processes, they are protected by several natural mechanisms involving lipid receptors, transport and carrier molecules and circulating cells and lipoproteins until their delivery to tissues and cells where they can again be transferred to intracellular membranes by specific and nonspecific transport systems. Once delivered to membrane sites, they naturally replace and stimulate removal of damaged membrane lipids. Various chronic clinical conditions are characterized by membrane damage, mainly oxidative but also enzymatic, resulting in loss of cellular function. This is readily apparent in mitochondrial inner membranes where oxidative damage to phospholipids like cardiolipin and other molecules results in loss of trans-membrane potential, electron transport function and generation of high-energy molecules. Recent clinical trials have shown the benefits of Lipid Replacement Therapy in restoring mitochondrial function and reducing fatigue in aged subjects and patients with a variety of clinical diagnoses that are characterized by loss of mitochondrial function and include fatigue as a major symptom. This Article is Part of a Special Issue Entitled: Membrane Structure and Function: Relevance in the Cell's Physiology, Pathology and Therapy.

Conformational change of mitochondrial complex I increases ROS sensitivity during ischemia

AIMS

Myocardial ischemia/reperfusion (I/R) is associated with mitochondrial dysfunction and subsequent cardiomyocyte death. The generation of excessive quantities of reactive oxygen species (ROS) and resultant damage to mitochondrial enzymes is considered an important mechanism underlying reperfusion injury. Mitochondrial complex I can exist in two interconvertible states: active (A) and deactive or dormant (D). We have studied the active/deactive (A/D) equilibrium in several tissues under ischemic conditions in vivo and investigated the sensitivity of both forms of the heart enzyme to ROS.

RESULTS

We found that in the heart, t½ of complex I deactivation during ischemia was 10 min, and that reperfusion resulted in the return of A/D equilibrium to its initial level. The rate of superoxide generation by complex I was higher in ischemic samples where content of the D-form was higher. Only the D-form was susceptible to inhibition by H2O2 or superoxide, whereas turnover-dependent activation of the enzyme resulted in formation of the A-form, which was much less sensitive to ROS. The mitochondrial-encoded subunit ND3, most likely responsible for the sensitivity of the D-form to ROS, was identified by redox difference gel electrophoresis.

INNOVATION

A combined in vivo and biochemical approach suggests that sensitivity of the mitochondrial system to ROS during myocardial I/R can be significantly affected by the conformational state of complex I, which may therefore represent a new therapeutic target in this setting.

CONCLUSION

The presented data suggest that transition of complex I into the D-form in the absence of oxygen may represent a key event in promoting cardiac injury during I/R.

Cardiolipin remodeling in diabetic heart

Cardiolipin, a signature phospholipid of mitochondria, is predominantly present in the mitochondrial inner membrane and plays an important role in keeping optimal mitochondrial function. In addition to the cardiolipin content, the composition of four fatty acid chain is thought determine cardiolipin biological function. These acyl chains of cardiolipin are dynamically remodeled via tafazzin, monolysocardiolipin acyltransferase, and acyl-CoA lysocardiolipin acyltransferase especially in the heart under pathological conditions. The major species of cardiolipin in the normal heart, tetralinoleoyl cardiolipin, is dramatically decreased in the diabetic heart, but other species, typically those containing long fatty acyl chains, are increased. This remodeling of cardiolipin has detrimental effects on mitochondrial function and thereafter cardiac function. Approaches for manipulating cardiolipin acyl chains have been examined including via molecular biology and through supplementation of linoleic acid. The efficiency of cardiolipin remodeling and functional improvement is still under investigation.

The role of mitochondria-derived reactive oxygen species in hyperthermia-induced platelet apoptosis

A combination of hyperthermia with radiotherapy and chemotherapy for various solid tumors has been practiced clinically. However, hyperthermic therapy has side effects, such as thrombocytopenia. Up to now, the pathogenesis of hyperthermia-induced thrombocytopenia remains unclear. Previous studies have shown that hyperthermia induces platelet apoptosis. However, the signaling pathways and molecular mechanisms involved in hyperthermia-induced platelet apoptosis have not been determined. Here we show that hyperthermia induced intracellular reactive oxygen species (ROS) production and mitochondrial ROS generation in a time-dependent manner in platelets. The mitochondria-targeted ROS scavenger Mito-TEMPO blocked intracellular ROS and mitochondrial ROS generation. By contrast, inhibitors of reduced nicotinamide adenine dinucleotide phosphate (NADPH) oxidase, nitric oxide synthase, cyclooxygenase and lipoxygenase did not. Furthermore, Mito-TEMPO inhibited hyperthermia-induced malonyldialdehyde production and cardiolipin peroxidation. We also showed that hyperthermia-triggered platelet apoptosis was inhibited by Mito-TEMPO. Furthermore, Mito-TEMPO ameliorated hyperthermia-impaired platelet aggregation and adhesion function. Lastly, hyperthermia decreased platelet manganese superoxide dismutase (MnSOD) protein levels and enzyme activity. These data indicate that mitochondrial ROS play a pivotal role in hyperthermia-induced platelet apoptosis, and decreased of MnSOD activity might, at least partially account for the enhanced ROS levels in hyperthermia-treated platelets. Therefore, determining the role of mitochondrial ROS as contributory factors in platelet apoptosis, is critical in providing a rational design of novel drugs aimed at targeting mitochondrial ROS. Such therapeutic approaches would have potential clinical utility in platelet-associated disorders involving oxidative damage.

Neuroglobin overexpression inhibits oxygen-glucose deprivation-induced mitochondrial permeability transition pore opening in primary cultured mouse cortical neurons

Neuroglobin (Ngb) is an endogenous neuroprotective molecule against hypoxic/ischemic brain injury, but the underlying mechanisms remain largely undefined. Our recent study revealed that Ngb can bind to voltage-dependent anion channel (VDAC), a regulator of mitochondria permeability transition (MPT). In this study we examined the role of Ngb in MPT pore (mPTP) opening following oxygen-glucose deprivation (OGD) in primary cultured mouse cortical neurons. Co-immunoprecipitation (Co-IP) and immunocytochemistry showed that the binding between Ngb and VDAC was increased after OGD compared to normoxia, indicating the OGD-enhanced Ngb-VDAC interaction. Ngb overexpression protected primary mouse cortical neurons from OGD-induced neuronal death, to an extent comparable to mPTP opening inhibitor, cyclosporine A (CsA) pretreatment. We further measured the role of Ngb in OGD-induced mPTP opening using Ngb overexpression and knockdown approaches in primary cultured neurons, and recombinant Ngb exposure to isolated mitochondria. Same as CsA pretreatment, Ngb overexpression significantly reduced OGD-induced mPTP opening markers including mitochondria swelling, mitochondrial NAD(+) release, and cytochrome c (Cyt c) release in primary cultured neurons. Recombinant Ngb incubation significantly reduced OGD-induced NAD(+) release and Cyt c release from isolated mitochondria. In contrast, Ngb knockdown significantly increased OGD-induced neuron death, and increased OGD-induced mitochondrial NAD(+) release and Cyt c release as well, and these outcomes could be rescued by CsA pretreatment. In summary, our results demonstrated that Ngb overexpression can inhibit OGD-induced mPTP opening in primary cultured mouse cortical neurons, which may be one of the molecular mechanisms of Ngb's neuroprotection.

Substrate-specific impairment of mitochondrial respiration in permeabilized fibers from patients with coronary heart disease versus valvular disease

High-resolution respirometry of permeabilized myocardial fibers offers reliable insights concerning the integrated mitochondrial function while using small amounts of cardiac tissue. The aim of the present study was to assess the respiratory function in permeabilized fibers of human right atrial appendages harvested from patients with coronary heart disease (CHD) (n = 6) versus patients with valvular disease (n = 5) and preserved ejection fraction that underwent non-emergency cardiac surgery. Human bundle samples (1-3 mg wet weight) permeabilized with saponin were transferred into the 2 ml Oxygraph-2 k chambers to measure complex I(CI) and II (CII)-dependent respiration, respectively. The following values (expressed in pmol/s mg) were obtained for CI-dependent respiration: oxidative phosphorylation (OXPHOS), 35.65 ± 1.10 versus 42.43 ± 1.08, electron transport system (ETS), 37.87 ± 1.72 versus. 46.58 ± 1.85, and respiratory control ratio (RCR, calculated as the ratio between OXPHOS and LEAK states), 2.43 ± 0.09 versus 2.73 ± 0.068 (p < 0.05). In conclusion, in patients with CHD we showed a significant decline for the OXPHOS capacity, ETS and RCR for mitochondria energized with CI (but not with CII) substrates. These observations are suggestive for an early impairment of complex I supported respiration in ischemic heart disease, as previously demonstrated in the setting of experimental ischemia/reperfusion in several animal species.

Cardiolipin-mediated cellular signaling

This review focuses on recent studies showing that cardiolipin (CL), a unique mitochondrial phospholipid, regulates many cellular functions and signaling pathways, both inside and outside the mitochondria. Inside the mitochondria, CL is a critical target of mitochondrial generated reactive oxygen species (ROS) and regulates signaling events related to apoptosis and aging. CL deficiency causes perturbation of signaling pathways outside the mitochondria, including the PKC-Slt2 cell integrity pathway and the high osmolarity glycerol (HOG) pathway, and is a key player in the cross-talk between the mitochondria and the vacuole. Understanding these connections may shed light on the pathology of Barth syndrome, a disorder of CL remodeling.

Changes in the mitochondrial permeability transition pore in aging and age-associated diseases

Aging is a biological process associated with impairment of mitochondrial bioenergetic function, increased oxidative stress, attenuated ability to respond to stresses and increased risk in contracting age-associated diseases. When mitochondria are subjected to oxidative stress, accompanied by calcium overload and ATP depletion, they undergo "a permeability transition", characterized by sudden induced change of the inner mitochondrial membrane permeability for water as well as for low-molecular weight solutes (≤1.5kDa), resulting in membrane depolarization and uncoupling of oxidative phosphorylation. Research interest in the entity responsible for this phenomenon, the "mitochondrial permeability transition pore" (MPTP) has dramatically increased after demonstration that it plays a key role in the life and death decision in cells. The molecular structure and identity of MPTP is not yet known, although the pore is thought to exist as multiprotein complex. Some evidence indicate that the sensitivity of mitochondria to Ca(2+)-induced MPTP opening increases with aging; however the basis of this difference is unknown. Changes in MPTP structure and/or function may have important implications in the aging process and aged-associated diseases. This article examines data relevant to this issue. The important role of a principal lipidic counter-partner of the MPTP, cardiolipin, will also be discussed.

The nitric oxide donor sodium nitroprusside requires the 18 kDa Translocator Protein to induce cell death

Various studies have shown that several lethal agents induce cell death via the mitochondrial 18 kDa Translocator Protein (TSPO). In this study we tested the possibility that nitric oxide (NO) is the signaling component inducing the TSPO to initiate cell death process. Cell viability assays included Trypan blue uptake, propidium iodide uptake, lactate dehydrogenase release, and DNA fragmentation. These assays showed that application of the specific TSPO ligand PK 11195 reduced these parameters for the lethal effects of the NO donor sodium nitroprusside (SNP) by 41, 27, 40, and 42 %, respectively. TSPO silencing by siRNA also reduced the measured lethal effects of SNP by 50 % for all of these four assays. With 2,3-bis[2-methoxy-4-nitro-5-sulphophenyl]-2H-tetrazolium-5-carboxyanilide (XTT) changes in metabolic activity were detected. PK 11195 and TSPO knockdown fully prevented the reductions in XTT signal otherwise induced by SNP. Collapse of the mitochondrial membrane potential was studied with the aid of JC-1 (5,5',6,6'-tetrachloro-1,1',3,3'-tetraethyl-benzimidazolylcarbocyanine chloride). PK 11195 and TSPO knockdown reduced, respectively by 36 and 100 %, the incidence of collapse of the mitochondrial membrane potential otherwise induced by SNP. 10-N-Nonyl-Acridine Orange (NAO) was used to detect mitochondrial reactive oxygen species generation due to SNP. PK 11195 and TSPO knockdown reduced this effect of SNP by 65 and 100 %, respectively. SNP did not affect TSPO protein expression and binding characteristics, and also did not cause TSPO S-nitrosylation. However, β-actin and various other proteins (not further defined) were S-nitrosylated. In conclusion, TSPO is required for the lethal and metabolic effects of the NO donor SNP, but TSPO itself is not S-nitrosylated.

VDAC1: from structure to cancer therapy

Here, we review current evidence pointing to the function of VDAC1 in cell life and death, and highlight these functions in relation to cancer. Found at the outer mitochondrial membrane, VDAC1 assumes a crucial position in the cell, controlling the metabolic cross-talk between mitochondria and the rest of the cell. Moreover, its location at the boundary between the mitochondria and the cytosol enables VDAC1 to interact with proteins that mediate and regulate the integration of mitochondrial functions with other cellular activities. As a metabolite transporter, VDAC1 contributes to the metabolic phenotype of cancer cells. This is reflected by VDAC1 over-expression in many cancer types, and by inhibition of tumor development upon silencing VDAC1 expression. Along with regulating cellular energy production and metabolism, VDAC1 is also a key protein in mitochondria-mediated apoptosis, participating in the release of apoptotic proteins and interacting with anti-apoptotic proteins. The involvement of VDAC1 in the release of apoptotic proteins located in the inter-membranal space is discussed, as is VDAC1 oligomerization as an important step in apoptosis induction. VDAC also serves as an anchor point for mitochondria-interacting proteins, some of which are also highly expressed in many cancers, such as hexokinase (HK), Bcl2, and Bcl-xL. By binding to VDAC, HK provides both metabolic benefit and apoptosis-suppressive capacity that offers the cell a proliferative advantage and increases its resistance to chemotherapy. VDAC1-based peptides that bind specifically to HK, Bcl2, or Bcl-xL abolished the cell’s abilities to bypass the apoptotic pathway. Moreover, these peptides promote cell death in a panel of genetically characterized cell lines derived from different human cancers. These and other functions point to VDAC1 as a rational target for the development of a new generation of therapeutics.

Susceptibility of mitochondrial electron-transport complexes to oxidative damage. Focus on cytochrome c oxidase

Reactive oxygen species (ROS) are associated with a number of mitochondrial disorders. These include: ischemia/reperfusion injury, Parkinson's disease, Alzheimer's disease, neurodegenerative diseases, and other age-related degenerative changes. ROS can be generated at numerous sites within the cell, but the mitochondrial electron transport chain is recognized as the major source of intracellular ROS. Two mitochondrial electron-transfer complexes are major sources of ROS: complex I and complex III. Oxidative damage to either of these complexes, or to electron transport complexes that are in close proximity to these ROS sources, e.g., cytochrome c oxidase, would be expected to inhibit electron transport. Such inhibition would lead to increased electron leakage and more ROS production, much like the well-known effect of adding electron transport inhibitors. Recent studies reveal that ROS and lipid peroxidation products are effective inhibitors of the electron-transport complexes. In some cases, inactivation of enzymes correlates with chemical modification of only a small number of unusually reactive amino acids. In this article, we review current knowledge of ROS-induced alterations within three complexes: (1) complex IV; (2) complex III; and (3) complex I. Our goal is to identify "hot spots" within each complex that are easily chemically modified and could be responsible for ROS-induced inhibition of the individual complexes. Special attention has been placed on ROS-induced damage to cardiolipin that is tightly bound to each of the inner membrane protein complexes. Peroxidation of the bound cardiolipin is thought to be particularly important since its close proximity and long residence time on the protein make it an especially effective reagent for subsequent ROS-induced damage to these proteins.