The Ca2+ -induced pore opening in mitochondria energized by succinate-ferricyanide electron transport

Vulnerability to a Metabolic Challenge Following Perinatal Asphyxia Evaluated by Organotypic Cultures: Neonatal Nicotinamide Treatment

The hypothesis of enhanced vulnerability following perinatal asphyxia was investigated with a protocol combining in vivo and in vitro experiments. Asphyxia-exposed (AS) (by 21 min water immersion of foetuses containing uterine horns) and caesarean-delivered control (CS) rat neonates were used at P2-3 for preparing triple organotypic cultures (substantia nigra, neostriatum and neocortex). At DIV 18, cultures were exposed to different concentrations of H₂O₂ (0.25-45 mM), added to the culture medium for 18 h. After a 48-h recovery period, the cultures were either assessed for cell viability or for neurochemical phenotype by confocal microscopy. Energy metabolism (ADP/ATP ratio), oxidative stress (GSH/GSSG) and a modified ferric reducing/antioxidant power assay were applied to homogenates of parallel culture series. In CS cultures, the number of dying cells was similar in substantia nigra, neostriatum and neocortex, but it was several times increased in AS cultures evaluated under the same conditions. A H₂O₂ challenge led to a concentration-dependent increase in cell death (>fourfold after 0.25 mM of H₂O₂) in CS cultures. In AS cultures, a significant increase in cell death was only observed after 0.5 mM of H₂O₂. At higher than 1 mM of H₂O₂ (up to 45 mM), cell death increased several times in all cultures, but the effect was still more prominent in CS than in AS cultures. The cell phenotype of dying/alive cells was investigated in formalin-fixed cultures exposed to 0 or 1 mM of H₂O₂, co-labelling for TUNEL (apoptosis), MAP-2 (neuronal phenotype), GFAP (astroglial phenotype) and TH (tyrosine hydroxylase; for dopamine phenotype), counterstaining for DAPI (nuclear staining), also evaluating the effect of a single dose of nicotinamide (0.8 nmol/kg, i.p. injected in 100 μL, 60 min after delivery). Perinatal asphyxia produced a significant increase in the number of DAPI/TUNEL cells/mm³, in substantia nigra and neostriatum. One millimolar of H₂0₂ increased the number of DAPI/TUNEL cells/mm³ by ≈twofold in all regions of CS and AS cultures, an effect that was prevented by neonatal nicotinamide treatment. In substantia nigra, the number of MAP-2/TH-positive cells/mm³ was decreased in AS compared to CS cultures, also by 1 mM of H₂0₂, both in CS and AS cultures, prevented by nicotinamide. In agreement, the number of MAP-2/TUNEL-positive cells/mm³ was increased by 1 mM H₂O₂, both in CS (twofold) and AS (threefold) cultures, prevented by nicotinamide. The number of MAP-2/TH/TUNEL-positive cells/mm³ was only increased in CS (>threefold), but not in AS (1.3-fold) cultures. No TH labelling was observed in neostriatum, but 1 mM of H₂O₂ produced a strong increase in the number of MAP-2/TUNEL-positive cells/mm³, both in CS (>2.9-fold) and AS (>fourfold), decreased by nicotinamide. In neocortex, H₂O₂ increased the number of MAP-2/TUNEL-positive cells/mm³, both in CS and AS cultures (≈threefold), decreased by nicotinamide. The ADP/ATP ratio was increased in AS culture homogenates (>sixfold), compared to CS homogenates, increased by 1 mM of H₂0₂, both in CS and AS homogenates. The GSH/GSSG ratio was significantly decreased in AS, compared to CS cultures. One millimolar of H₂O₂ decreased that ratio in CS and AS homogenates. The present results demonstrate that perinatal asphyxia induces long-term changes in metabolic pathways related to energy and oxidative stress, priming cell vulnerability with both neuronal and glial phenotype. The observed effects were region dependent, being the substantia nigra particularly prone to cell death. Nicotinamide administration in vivo prevented the deleterious effects observed after perinatal asphyxia in vitro, a suitable pharmacological strategy against the deleterious consequences of perinatal asphyxia.

Impact of mitochondria on nitrite metabolism in HL-1 cardiomyocytes

Apart from ATP synthesis mitochondria have many other functions, one being nitrite reductase activity. Nitric oxide (NO) released from nitrite has been shown to protect the heart from ischemia/reperfusion (I/R) injury in a cGMP-dependent manner. However, the exact impact of mitochondria on the release of NO from nitrite in cardiomyocytes is not completely understood. Besides mitochondria, a number of non-mitochondrial metalloproteins have been suggested to facilitate this process. The aim of this study was to investigate the impact of mitochondria on the bioactivation of nitrite in HL-1 cardiomyocytes. The levels of nitrosyl complexes of hemoglobin (NO-Hb) and cGMP levels were measured by electron spin resonance spectroscopy and enzyme immunoassay. In addition the formation of free NO was determined by confocal microscopy as well as intracellular nitrite and S-nitrosothiols by chemoluminescence analysis. NO was released from nitrite in cell culture in an oxygen-dependent manner. Application of specific inhibitors of the respiratory chain, p450, NO synthases (NOS) and xanthine oxidoreductase (XOR) showed that all four enzymatic systems are involved in the release of NO, but more than 50% of NO is released via the mitochondrial pathway. Only NO released by mitochondria activated cGMP synthesis. Cardiomyocytes co-cultured with red blood cells (RBC) competed with RBC for nitrite, but free NO was detected only in HL-1 cells suggesting that RBC are not a source of NO in this model. Apart from activation of cGMP synthesis, NO formed in HL-1 cells diffused out of the cells and formed NO-Hb complexes. In addition nitrite was converted by HL-1 cells to S-nitrosyl complexes. In HL-1 cardiomyocytes, several enzymatic systems are involved in nitrite reduction to NO but only the mitochondrial pathway of NO release activates cGMP synthesis. Our data suggest that this pathway may be a key regulator of myocardial contractility especially under hypoxic conditions.

Mitochondria from Dipodascus (Endomyces) magnusii and Yarrowia lipolytica yeasts did not undergo a Ca²⁺-dependent permeability transition even under anaerobic conditions

In this study we used tightly-coupled mitochondria from Yarrowia lipolytica and Dipodascus (Endomyces) magnusii yeasts. The two yeast strains are good alternatives to Saccharomyces cerevisiae, being aerobes containing well structured mitochondria (thus ensuring less structural limitation to observe their appreciable swelling) and fully competent respiratory chain with three invariantly functioning energy conservation points, including Complex I, that can be involved in induction of the canonical Ca²⁺/P(i)-dependent mitochondrial permeability transition (mPTP pore) with an increased open probability when electron flux increases(Fontaine et al. J Biol Chem 273: 25734–25740, 1998; Bernardi et al. FEBS J 273:2077–2099, 2006). High amplitude swelling and collapse of the membrane potential were used as parameters for demonstrating pore opening. Previously (Kovaleva et al. J Bioenerg Biomembr 41:239–249, 2009; Kovaleva et al. Biochemistry (Moscow) 75: 297–303, 2010) we have shown that mitochondria from Y.lipolytica and D. magnusii were very resistant to the Ca²⁺overload combined with varying concentrations of P(i),palmitic acid, SH-reagents, carboxyatractyloside (an inhibitor of ADP/ATP translocator), as well as depletion of intramitochondrial adenine nucleotide pools, deenergization of mitochondria, and shifting to acidic pH values in the presence of high [P(i)]. Here we subjected yeast mitochondria to other conditions known to induce an mPTP in animal and plant mitochondria, namely to Ca²⁺ overload under hypoxic conditions (anaerobiosis). We were unable to observe Ca²⁺-induced high permeability of the inner membrane of D. magnusii and Y. lipolytica yeast mitochondria under anaerobic conditions, thus suggesting that an mPTP-like pore, if it ever occurs in yeast mitochondria, is not coupled with the Ca²⁺ uptake. The results provide the first demonstration of ATP-dependent energization of yeast mitochondria under conditions of anaerobiosis.

Myoglobin causes oxidative stress, increase of NO production and dysfunction of kidney's mitochondria

Rhabdomyolysis or crush syndrome is a pathology caused by muscle injury resulting in acute renal failure. The latest data give strong evidence that this syndrome caused by accumulation of muscle breakdown products in the blood stream is associated with oxidative stress with primary role of mitochondria. In order to evaluate the significance of oxidative stress under rhabdomyolysis we explored the direct effect of myoglobin on renal tubules and isolated kidney mitochondria while measuring mitochondrial respiratory control, production of reactive oxygen and nitrogen species and lipid peroxidation. In parallel, we evaluated mitochondrial damage under myoglobinurea in vivo. An increase of lipid peroxidation products in kidney mitochondria and release of cytochrome c was detected on the first day of myoglobinuria. In mitochondria incubated with myoglobin we detected respiratory control drop, uncoupling of oxidative phosphorylation, an increase of lipid peroxidation products and stimulated NO synthesis. Mitochondrial pore inhibitor, cyclosporine A, mitochondria-targeted antioxidant (SkQ1) and deferoxamine (Fe-chelator and ferryl-myoglobin reducer) abrogated these events. Similar effects (oxidative stress and mitochondrial dysfunction) were revealed when myoglobin was added to isolated renal tubules. Thus, rhabdomyolysis can be considered as oxidative stress-mediated pathology with mitochondria to be the primary target and possibly the source of reactive oxygen and nitrogen species. We speculate that rhabdomyolysis-induced kidney damage involves direct interaction of myoglobin with mitochondria possibly resulting in iron ions release from myoglobin's heme, which promotes the peroxidation of mitochondrial membranes. Usage of mitochondrial permeability transition blockers, Fe-chelators or mitochondria-targeted antioxidants, may bring salvage from this pathology.

Testing hypotheses of aging in long-lived mice of the genus Peromyscus: association between longevity and mitochondrial stress resistance, ROS detoxification pathways, and DNA repair efficiency

In the present review we discuss the potential use of two long-lived mice of the genus Peromyscus--the white-footed mouse (P. leucopus) and the deer mouse (P. maniculatus) maximum lifespan potential approximately 8 years for both--to test predictions of theories about aging from the oxidative stress theory, mitochondrial theory and inflammatory theory. Previous studies have shown that P. leucopus cells exhibit superior antioxidant defense mechanisms and lower cellular production of reactive oxygen species (ROS) than do cells of the house mouse, Mus musculus (maximum lifespan approximately 3.5 years). We present new data showing that mitochondria in P. leucopus cells produce substantially less ROS than mitochondria in M. musculus cells, and that P. leucopus mitochondria exhibit superior stress resistance to those of M. musculus. We also provide evidence that components of the DNA repair system (e.g., pathways involved in repair of DNA damage induced by gamma-irradiation) are likely to be more efficient in P. leucopus than in M. musculus. We propose that mitochondrial stress resistance, ROS detoxification pathways and more efficient DNA repair contribute to the previously documented resistance of P. leucopus cells toward oxidative stress-induced apoptosis. The link between these three pathways and species longevity is discussed.

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.

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Comparative kinetic analysis reveals that inducer-specific ion release precedes the mitochondrial permeability transition

Relationships among the multiple events that precede the mitochondrial membrane permeability transition (MPT) are not yet clearly understood. A combination of newly developed instrumental and computational approaches to this problem is described. The instrumental innovation is a high-resolution digital apparatus for the simultaneous, real-time measurement of four mitochondrial parameters as indicators of the respiration rate, membrane potential, calcium ion transport, and mitochondrial swelling. A computational approach is introduced that tracks the fraction of mitochondria that has undergone pore opening. This approach allows multiple comparisons on a single time scale. The validity of the computational approach for studying complex mitochondrial phenomena was evaluated with mitochondria undergoing an MPT induced by Ca(2+), phenylarsine oxide or alamethicin. Selective ion leaks were observed that precede the permeability transition and that are inducer specific. These results illustrate the occurrence of inducer-specific sequential changes associated with the induction of the permeability transition. Analysis of the temporal relationship among the multiple mitochondrial parameters of isolated mitochondria should provide insights into the mechanisms underlying these responses.

Reactive oxygen and nitrogen species: Friends or foes?

Chemical and physiological functions of molecular oxygen and reactive oxygen species (ROS) and existing equilibrium between pools of pro-oxidants and anti-oxidants providing steady state ROS level vital for normal mitochondrial and cell functioning are reviewed. The presence of intracellular oxygen and ROS sensors is postulated and few candidates for this role are suggested. Possible involvement of ROS in the process of fragmentation of mitochondrial reticulum made of long mitochondrial filaments serving in the cell as "electric cables", as well as the role of ROS in apoptosis and programmed mitochondrial destruction (mitoptosis) are reviewed. The critical role of ROS in destructive processes under ischemia/reoxygenation and ischemic preconditioning is discussed. Mitochondrial permeability transition gets special consideration as a possible component of the apoptotic cascade, resulting in excessive "ROS-induced ROS release".

Minocycline inhibits cytochrome c release and delays progression of amyotrophic lateral sclerosis in mice

Minocycline mediates neuroprotection in experimental models of neurodegeneration. It inhibits the activity of caspase-1, caspase-3, inducible form of nitric oxide synthetase (iNOS) and p38 mitogen-activated protein kinase (MAPK). Although minocycline does not directly inhibit these enzymes, the effects may result from interference with upstream mechanisms resulting in their secondary activation. Because the above-mentioned factors are important in amyotrophic lateral sclerosis (ALS), we tested minocycline in mice with ALS. Here we report that minocycline delays disease onset and extends survival in ALS mice. Given the broad efficacy of minocycline, understanding its mechanisms of action is of great importance. We find that minocycline inhibits mitochondrial permeability-transition-mediated cytochrome c release. Minocycline-mediated inhibition of cytochrome c release is demonstrated in vivo, in cells, and in isolated mitochondria. Understanding the mechanism of action of minocycline will assist in the development and testing of more powerful and effective analogues. Because of the safety record of minocycline, and its ability to penetrate the blood-brain barrier, this drug may be a novel therapy for ALS.

Occurrence and characteristics of the mitochondrial permeability transition in plants

The behavior of purified potato mitochondria toward the main effectors of the animal mitochondrial permeability transition has been studied by light scattering, fluorescence, SDS-polyacrylamide gel electrophoresis, and immunoblotting techniques. The addition of Ca(2+) induces a phosphate-dependent swelling that is fully inhibited by cyclosporin A if dithioerythritol is present. Mg(2+) cannot be substituted for Ca(2+) but competes with it. Disruption of the outer membrane and release of several proteins, including cytochrome c, occur upon completion of swelling. Ca(2+)-induced swelling is delayed and its rate is decreased when pH is shifted from 7.4 to 6.6. It is accelerated by diamide, phenylarsine oxide, and linolenic acid. In the absence of Ca(2+), however, linolenic acid (< or =20 microm) rapidly dissipates the succinate-driven membrane potential while having no effect on mitochondrial volume. Anoxic conditions favor in vitro swelling and the concomitant release of cytochrome c and of other proteins in a pH-dependent way. These data indicate that the classical mitochondrial permeability transition occurs also in plants. This may have important implications for our understanding of cell stress and death processes.

The permeability transition pore induced under anaerobic conditions in mitochondria energized with ATP

The role of oxygen in the induction of mitochondrial permeability transitions was studied. Oxygen consumption, swelling, membrane potential and calcium transport were recorded simultaneously in isolated rat liver mitochondria. Oxygen depletion was accomplished by saturating the medium with N2 and allowing either mitochondrial respiration or glucose/glucose oxidase to consume the residual oxygen. Upon anaerobiosis, mitochondria were supplemented with 500 microM ATP to support succinate-driven membrane potential. Under these conditions, 100 microM Ca2+ induced cyclosporin A-sensitive permeability transitions. To eliminate the possible inhibition of permeability transition by high concentrations of adenine nucleotides, anaerobic mitochondria were also energized by the combination of 20 microM ADP and phosphoenolpyruvate/pyruvate kinase. These mitochondria also underwent Ca2+-induced permeability transition. Under both of these conditions, namely the addition of ATP as a single or through actions of pyruvate kinase, the respiratory components were totally reduced. Thus, oxygen is not a necessary factor for mitochondria to undergo permeability transitions.

Imaging the permeability pore transition in single mitochondria

In mitochondria the opening of a large proteinaceous pore, the "mitochondrial permeability transition pore" (MTP), is known to occur under conditions of oxidative stress and matrix calcium overload. MTP opening and the resulting cellular energy deprivation have been implicated in processes such as hypoxic cell damage, apoptosis, and neuronal excitotoxicity. Membrane potential (delta psi(m)) in single isolated heart mitochondria was measured by confocal microscopy with a voltage-sensitive fluorescent dye. Measurements in mitochondrial populations revealed a gradual loss of delta psi(m) due to the light-induced generation of free radicals. In contrast, the depolarization in individual mitochondria was fast, sometimes causing marked oscillations of delta psi(m). Rapid depolarizations were accompanied by an increased permeability of the inner mitochondrial membrane to matrix-entrapped calcein (approximately 620 Da), indicating the opening of a large membrane pore. The MTP inhibitor cyclosporin A significantly stabilized delta psi(m) in single mitochondria, thereby slowing the voltage decay in averaged recordings. We conclude that the spontaneous depolarizations were caused by repeated stochastic openings and closings of the transition pore. The data demonstrate a much more dynamic regulation of membrane permeability at the level of a single organelle than predicted from ensemble behavior of mitochondrial populations.