The participation of pyridine nucleotides redox state and reactive oxygen in the fatty acid-induced permeability transition in rat liver mitochondria

Metabolic activation of 2,4,6-trinitrotoluene; a case for ROS-induced cell damage

The explosive compound 2,4,6-trinitrotoluene (TNT) is well known as a major component of munitions. In addition to its potential carcinogenicity and mutagenicity in humans, recent reports have highlighted TNT toxicities in diverse organisms due to its occurrence in the environment. These toxic effects have been linked to the intracellular metabolism of TNT, which is generally characterised by redox cycling and the generation of noxious reactive molecules. The reactive intermediates formed, such as nitroso and hydroxylamine compounds, also interact with oxygen molecules and cellular components to cause macromolecular damage and oxidative stress. The current review aims to highlight the crucial role of TNT metabolism in mediating TNT toxicity, via increased generation of reactive oxygen species. Cellular proliferation of reactive species results in depletion of cellular antioxidant enzymes, DNA and protein adduct formation, and oxidative stress. While TNT toxicity is well known, its ability to induce oxidative stress, resulting from its reductive activation, suggests that some of its toxic effects may be caused by its reactive metabolites. Hence, further research on TNT metabolism is imperative to elucidate TNT-induced toxicities.

Mitochondrial calcium transport and the redox nature of the calcium-induced membrane permeability transition

Mitochondria possess a Ca²⁺ transport system composed of separate Ca²⁺ influx and efflux pathways. Intramitochondrial Ca²⁺ concentrations regulate oxidative phosphorylation, required for cell function and survival, and mitochondrial redox balance, that participates in a myriad of signaling and damaging pathways. The interaction between Ca²⁺ accumulation and redox imbalance regulates opening and closing of a highly regulated inner membrane pore, the membrane permeability transition pore (PTP). In this review, we discuss the regulation of the PTP by mitochondrial oxidants, reactive nitrogen species, and the interactions between these species and other PTP inducers. In addition, we discuss the involvement of mitochondrial redox imbalance and PTP in metabolic conditions such as atherogenesis, diabetes, obesity and in mtDNA stability.

Lipid-Mediated Modulation of Intracellular Ion Channels and Redox State: Physiopathological Implications

Significance: Ion channels play an important role in the regulation of organelle function within the cell, as proven by increasing evidence pointing to a link between altered function of intracellular ion channels and different pathologies ranging from cancer to neurodegenerative diseases, ischemic damage, and lysosomal storage diseases. Recent Advances: A link between these pathologies and redox state as well as lipid homeostasis and ion channel function is in the focus of current research. Critical Issues: Ion channels are target of modulation by lipids and lipid messengers, although in most cases the mechanistic details have not been clarified yet. Ion channel function importantly impacts production of reactive oxygen species (ROS), especially in the case of mitochondria and lysosomes. ROS, in turn, may modulate the function of intracellular channels triggering thereby a feedback control under physiological conditions. If produced in excess, ROS can be harmful to lipids and may produce oxidized forms of these membrane constituents that ultimately affect ion channel function by triggering a "circulus vitiosus." Future Directions: The present review summarizes our current knowledge about the contribution of intracellular channels to oxidative stress and gives examples of how these channels are modulated by lipids and how this modulation may affect ROS production in ROS-related diseases. Future studies need to address the importance of the regulation of intracellular ion channels and related oxidative stress by lipids in various physiological and pathological contexts. Antioxid. Redox Signal. 28, 949-972.

Central role of mitochondria in drug-induced liver injury

A frequent mechanism for drug-induced liver injury (DILI) is the formation of reactive metabolites that trigger hepatitis through direct toxicity or immune reactions. Both events cause mitochondrial membrane disruption. Genetic or acquired factors predispose to metabolite-mediated hepatitis by increasing the formation of the reactive metabolite, decreasing its detoxification, or by the presence of critical human leukocyte antigen molecule(s). In other instances, the parent drug itself triggers mitochondrial membrane disruption or inhibits mitochondrial function through different mechanisms. Drugs can sequester coenzyme A or can inhibit mitochondrial β-oxidation enzymes, the transfer of electrons along the respiratory chain, or adenosine triphosphate (ATP) synthase. Drugs can also destroy mitochondrial DNA, inhibit its replication, decrease mitochondrial transcripts, or hamper mitochondrial protein synthesis. Quite often, a single drug has many different effects on mitochondrial function. A severe impairment of oxidative phosphorylation decreases hepatic ATP, leading to cell dysfunction or necrosis; it can also secondarily inhibit ß-oxidation, thus causing steatosis, and can also inhibit pyruvate catabolism, leading to lactic acidosis. A severe impairment of β-oxidation can cause a fatty liver; further, decreased gluconeogenesis and increased utilization of glucose to compensate for the inability to oxidize fatty acids, together with the mitochondrial toxicity of accumulated free fatty acids and lipid peroxidation products, may impair energy production, possibly leading to coma and death. Susceptibility to parent drug-mediated mitochondrial dysfunction can be increased by factors impairing the removal of the toxic parent compound or by the presence of other medical condition(s) impairing mitochondrial function. New drug molecules should be screened for possible mitochondrial effects.

Brain mitochondria from rats treated with sulforaphane are resistant to redox-regulated permeability transition

Oxidative stress promotes Ca2+-dependent opening of the mitochondrial inner membrane permeability transition pore (PTP), causing bioenergetic failure and subsequent cell death in many paradigms, including those related to acute brain injury. One approach to pre-conditioning against oxidative stress is pharmacologic activation of the Nrf2/ARE pathway of antioxidant gene expression by agents such as sulforaphane (SFP). This study tested the hypothesis that administration of SFP to normal rats increases resistance of isolated brain mitochondria to redox-sensitive PTP opening. SFP or DMSO vehicle was administered intraperitoneally to adult male rats at 10 mg/kg 40 h prior to isolation of non-synaptic brain mitochondria. Mitochondria were suspended in medium containing a respiratory substrate and were exposed to an addition of Ca2+ below the threshold for PTP opening. Subsequent addition of tert-butyl hydroperoxide (tBOOH) resulted in a cyclosporin A-inhibitable release of accumulated Ca2+ into the medium, as monitored by an increase in fluorescence of Calcium Green 5N within the medium, and was preceded by a decrease in the autofluorescence of mitochondrial NAD(P)H. SFP treatment significantly reduced the rate of tBOOH-induced Ca2+ release but did not affect NAD(P)H oxidation or inhibit PTP opening induced by the addition of phenylarsine oxide, a direct sulfhydryl oxidizing agent. SFP treatment had no effect on respiration by brain mitochondria and had no effect on PTP opening or respiration when added directly to isolated mitochondria. We conclude that SFP confers resistance of brain mitochondria to redox-regulated PTP opening, which could contribute to neuroprotection observed with SFP.

Plasma and liver proteomic analysis of 3Z-3-[(1H-pyrrol-2-yl)-methylidene]-1-(1-piperidinylmethyl)-1,3-2H-indol-2-one-induced hepatotoxicity in Wistar rats

3Z-3-[(1H-pyrrol-2-yl)-methylidene]-1-(1-piperidinylmethyl)-1,3-2H-indol-2-one (Z24), a synthetic anti-angiogenic compound, inhibits the growth and metastasis of certain tumors. Previous works have shown that Z24 induces hepatotoxicity in rodents. We examined the hepatotoxic mechanism of Z24 at the protein level and looked for potential biomarkers. We used 2-DE and MALDI-TOF/TOF MS to analyze alternatively expressed proteins in rat liver and plasma after Z24 administration. We also examined apoptosis in rat liver and measured levels of intramitochondrial ROS and NAD(P)H redox in liver cells. We found that 22 nonredundant proteins in the liver and 11 in the plasma were differentially expressed. These proteins were involved in several important metabolic pathways, including carbohydrate, lipid, amino acid, and energy metabolism, biotransformation, apoptosis, etc. Apoptosis in rat liver was confirmed with the terminal deoxynucleotidyl transferase dUTP-nick end labeling assay. In mitochondria, Z24 increased the ROS and decreased the NAD(P)H levels. Thus, inhibition of carbohydrate aerobic oxidation, fatty acid beta-oxidation, and oxidative phosphorylation is a potential mechanism of Z24-induced hepatotoxicity, resulting in mitochondrial dysfunction and apoptosis-mediated cell death. In addition, fetub protein and argininosuccinate synthase in plasma may be potential biomarkers of Z24-induced hepatotoxicity.

Mitochondrial involvement in drug-induced liver injury

Mitochondrial dysfunction is a major mechanism of liver injury. A parent drug or its reactive metabolite can trigger outer mitochondrial membrane permeabilization or rupture due to mitochondrial permeability transition. The latter can severely deplete ATP and cause liver cell necrosis, or it can instead lead to apoptosis by releasing cytochrome c, which activates caspases in the cytosol. Necrosis and apoptosis can trigger cytolytic hepatitis resulting in lethal fulminant hepatitis in some patients. Other drugs severely inhibit mitochondrial function and trigger extensive microvesicular steatosis, hypoglycaemia, coma, and death. Milder and more prolonged forms of drug-induced mitochondrial dysfunction can also cause macrovacuolar steatosis. Although this is a benign liver lesion in the short-term, it can progress to steatohepatitis and then to cirrhosis. Patient susceptibility to drug-induced mitochondrial dysfunction and liver injury can sometimes be explained by genetic or acquired variations in drug metabolism and/or elimination that increase the concentration of the toxic species (parent drug or metabolite). Susceptibility may also be increased by the presence of another condition, which also impairs mitochondrial function, such as an inborn mitochondrial cytopathy, beta-oxidation defect, certain viral infections, pregnancy, or the obesity-associated metabolic syndrome. Liver injury due to mitochondrial dysfunction can have important consequences for pharmaceutical companies. It has led to the interruption of clinical trials, the recall of several drugs after marketing, or the introduction of severe black box warnings by drug agencies. Pharmaceutical companies should systematically investigate mitochondrial effects during lead selection or preclinical safety studies.

Oligomeric BAX induces mitochondrial permeability transition and complete cytochrome c release without oxidative stress

In the present study, we investigated the mechanism of cytochrome c release from isolated brain mitochondria induced by recombinant oligomeric BAX (BAX(oligo)). We found that BAX(oligo) caused a complete release of cytochrome c in a concentration- and time-dependent manner. The release was similar to those induced by alamethicin, which causes maximal mitochondrial swelling and eliminates barrier properties of the OMM. BAX(oligo) also produced large amplitude mitochondrial swelling as judged by light scattering assay and transmission electron microscopy. In addition, BAX(oligo) resulted in a strong mitochondrial depolarization. ATP or a combination of cyclosporin A and ADP, inhibitors of the mPT, suppressed BAX(oligo)-induced mitochondrial swelling and depolarization as well as cytochrome c release but did not influence BAX(oligo) insertion into the OMM. Both BAX(oligo)- and alamethicin-induced cytochrome c releases were accompanied by inhibition of ROS generation, which was assessed by measuring mitochondrial H(2)O(2) release with an Amplex Red assay. The mPT inhibitors antagonized suppression of ROS generation caused by BAX(oligo) but not by alamethicin. Thus, BAX(oligo) resulted in a complete cytochrome c release from isolated brain mitochondria in the mPT-dependent manner without involvement of oxidative stress by the mechanism requiring mitochondrial remodeling and permeabilization of the OMM.

Redox status of thioredoxin-1 (TRX1) determines the sensitivity of human liver carcinoma cells (HepG2) to arsenic trioxide-induced cell death

Intracellular redox homeostasis plays a critical role in determining tumor cells' sensitivity to drug-induced apoptosis. Here we investigated the role of thioredoxin-1 (TRX1), a key component of redox regulation, in arsenic trioxide (As(2)O(3))-induced apoptosis. Over-expression of wild-type TRX1 in HepG(2) cells led to the inhibition of As(2)O(3)-induced cytochrome c (cyto c) release, caspase activation and apoptosis, and down-regulation of TRX1 expression by RNAi sensitized HepG(2) cells to As(2)O(3)-induced apoptosis. Interestingly, mutation of the active site of TRX1 from Cys(32/35) to Ser(32/35) converted this molecule from an apoptotic protector to an apoptotic promoter. In an effort to understand the mechanisms of this conversion, we used isolated mitochondria from mouse liver and found that recombinant wild-type TRX1 could protect mitochondria from the apoptotic changes. In contrast, the mutant form of TRX1 alone elicited mitochondria-related apoptotic changes, including the mitochondrial permeability transition pore (mPTP) opening, loss of mitochondrial membrane potential, and cyto c release from mitochondria. These apoptotic effects were inhibited by cyclosporine A (CsA), indicating that mutant TRX1 targeted to mPTP. Alteration of TRX1 from its reduced form to oxidized form in vivo by 2,4-dinitrochlorobenzene (DNCB), a specific inhibitor of TRX reductase, also sensitized HepG(2) cells to As(2)O(3)-induced apoptosis. These data suggest that TRX1 plays a central role in regulating apoptosis by blocking cyto c release, and inactivation of TRX1 by either mutation or oxidization of the active site cysteines may sensitize tumor cells to As(2)O(3)-induced apoptosis.

Interrelated influence of superoxides and free fatty acids over mitochondrial uncoupling in skeletal muscle

Mitochondrial uncoupling protein 3 (UCP(3))-mediated uncoupling has been postulated to depend on several factors, including superoxides, free fatty acids (FFAs), and fatty acid hydroperoxides and/or their derivatives. We investigated whether there is an interrelation between endogenous mitochondrial superoxides and fatty acids in inducing skeletal muscle mitochondrial uncoupling, and we speculated on the possible involvement of UCP(3) in this process. In the absence of FFAs, no differences in proton-leak kinetic were detected between succinate-energized mitochondria respiring in the absence or presence of rotenone, despite a large difference in complex I superoxide production. The addition of either arachidic acid or arachidonic acid induced an increase in proton-leak kinetic, with arachidonic acid having the more marked effect. The uncoupling effect of arachidic acid was independent of the presence of GDP, rotenone and vitamin E, while that of arachidonic acid was dependent on these factors. These data demonstrate that FFA and O(2-) play interrelated roles in inducing mitochondrial uncoupling, and we hypothesize that a likely formation of mitochondrial fatty acid hydroperoxides is a key event in the arachidonic acid-induced GDP-dependent inhibition of mitochondrial uncoupling.

Ischemic preconditioning enhances fatty acid-dependent mitochondrial uncoupling

This study tests the hypothesis that ischemic preconditioning (IP) changes fatty acid (FA)-dependent uncoupling between mitochondrial respiration and oxidative phosphorylation. We found that IP does not alter mitochondrial membrane integrity or FA levels, but enhances membrane potential decreases when FA are present, in an ATP-sensitive manner. FA hydroperoxides had equal effects in control and preconditioned mitochondria, and GTP did not abrogate the IP effect, suggesting uncoupling proteins were not involved. Conversely, thiol reductants and atractyloside, which inhibits the adenine nucleotide translocator, eliminated the differences in responses to FA. Together, our results suggest that IP leads to thiol oxidation and activation of the adenine nucleotide translocator, resulting in enhanced FA transport and mild mitochondrial uncoupling.

Synthesis and in vitro photodynamic activities of water-soluble fluorinated tetrapyridylporphyrins as tumor photosensitizers

A series of water-soluble fluorinated cationic porphyrins were designed, synthesized, and characterized. In vitro photocytotoxicity of these compounds was evaluated by MTT assay on HeLa cells. Their photocytotoxicity was dependent on the positions of the cations and the fluorines in the pyridine ring, and 5,10,15,20-tetrakis-(N-methyl-2-fluoro-pyridin-3-yl)-porphyrin (8) showed the most potent photo-induced cytotoxicity without photobleaching. PDT-induced ROS inside HeLa cells was measured with flow cytometry using ROS-sensitive fluorometric probe, 2,7-dichlorofluororescin (DCF), which revealed high correlations of ROS with cellular cytotoxicity. FACS analysis shows that PDT with porphyrin 8 induced apoptosis in HeLa cells. In summary, efficient generation of ROS, biological effectiveness, and good photostability of porphyrin 8 indicate its potential application in photodynamic therapy (PDT) in the near future.

Mathematical model of mitochondrial ionic homeostasis: three modes of Ca2+ transport

Mitochondria play an important role in regulation of Ca2+ homeostasis in a cell. Here we present a mathematical model of mitochondrial ion transport and use this model to analyse different modes of Ca2+ uptake by mitochondria. The model includes transport of H+, Ca2+, K+, inorganic phosphate and oxidative substrates across the inner mitochondrial membrane harboring permeability transition pore (PTP). The detailed description of ion fluxes is based on the experimental ion kinetics in isolated mitochondria. Using the model we show that the kinetics of Ca2+ uptake by mitochondria is regulated by the total amount of Ca2+ in the system and the rate of Ca2+ infusion. Varying these parameters we find three different modes of ion transport. When the total amount of Ca2+ is below 140 nmol Ca2+/mg protein, all available Ca2+ is accumulated in the matrix without activation of the PTP. Between 140 and 160 nmol Ca2+/mg protein, accumulation of Ca2+ generates periodic opening and closure of the PTP and oscillations of ion fluxes. Higher levels of Ca2+ (> 160 nmol Ca2+/mg protein) result in a permanently open PTP, membrane depolarization and loss of small ions from the matrix. We show that in the intermediate range of Ca2+ concentrations the rate of Ca2+ infusion regulates the PTP state, so that slow Ca2+ infusion does not lead to PTP opening, while fast Ca2+ infusion results in an oscillatory state.

Regulation of human male germ cell death by modulators of ATP production

The understanding of testicular physiology, pathology, and male fertility issues requires knowledge of male germ cell death and energy production. Here, we induced human male germ cell apoptosis (detected by Southern blot analysis of DNA fragmentation, TUNEL, activation of caspases-3 and -9, and electron microscopy) by incubating seminiferous tubule segments under hormone- and serum-free conditions. Inhibitors of complexes I to IV of mitochondrial respiration, exposure to anoxia, and inhibition of F0F1-ATPase (with oligomycin) decreased the ATP levels (analyzed by HPLC) and suppressed apoptosis at 4 h. Uncoupler 2,4-dinitrophenol (DNP) and oligomycin combination also suppressed death at 4 h, as did the DNP alone. Inhibition of glycolysis by 2-deoxyglucose neither suppressed nor further induced apoptosis nor altered the antiapoptotic effects of the mitochondrial inhibitors. Furthermore, Fas system activation did not modify the effects of mitochondrial modulators. After 24 h, delayed male germ cell apoptosis was observed despite the presence of the mitochondrial inhibitors. We conclude that the mitochondrial ATP production machinery plays an important role in regulating in vitro-induced primary pathways of human male germ apoptosis. The ATP synthesized by the F0F1-ATPase seems to be the crucial death regulator, rather than any of the complexes (I-IV) alone, the functional electron transport chain, or the membrane potential. We also conclude that there seem to be secondary pathways of human testicular cell apoptosis that do not require mitochondrial ATP production. The present study emphasizes the role of the main catabolic pathways in the complex network of regulating events of male germ cell life and death.

The Anti-Inflammatory Drug, Nimesulide (4-Nitro-2-phenoxymethane-sulfoanilide), Uncouples Mitochondria and Induces Mitochondrial Permeability Transition in Human Hepatoma Cells: Protection by Albumin

Like other nonsteroidal anti-inflammatory drugs, nimesulide (4-nitro-2-phenoxymethane-sulfoanilide) triggers hepatitis in a few recipients. Although nimesulide has been shown to uncouple mitochondrial respiration and cause hepatocyte necrosis in the absence of albumin, mechanisms for cell death are incompletely understood, and comparisons with human concentrations are difficult because 99% of nimesulide is albumin-bound. We studied the effects of nimesulide, with or without a physiological concentration of albumin, in isolated rat liver mitochondria or microsomes and in human hepatoma cells. Nimesulide did not undergo monoelectronic nitro reduction in microsomes. In mitochondria incubated without albumin, nimesulide (50 microM) decreased the mitochondrial membrane potential (DeltaPsim), increased basal respiration, and potentiated the mitochondrial permeability transition (MPT) triggered by calcium preloading. In HUH-7 cells incubated for 24 h without albumin, nimesulide (1 mM) decreased the DeltaPsim and cell NADPH and increased the glutathione disulfide/reduced glutathione ratio and cell peroxides; nimesulide triggered MPT, ATP depletion, high cell calcium, and caused mostly necrosis, with rare apoptotic cells. Coincubation with either cyclosporin A (an MPT inhibitor) or the combination of fructose-1,6-diphosphate (a glycolysis substrate) and oligomycin (an ATPase inhibitor) prevented the decrease in DeltaPsim, ATP depletion, and cell death. A physiological concentration of albumin abolished the effects of nimesulide on isolated mitochondria or HUH-7 cells. In conclusion, the weak acid, nimesulide, uncouples mitochondria and triggers MPT and ATP depletion in isolated mitochondria or hepatoma cells incubated without albumin. However, in the presence of albumin, only a fraction of the drug enters cells or organelles, and uncoupling and toxicity are not observed.

SOD2 overexpression: enhanced mitochondrial tolerance but absence of effect on UCP activity

We have created P1 artificial chromosome transgenic mice expressing the human mitochondrial superoxide dismutase 2 (SOD2) and thus generated mice with a physiologically controlled augmentation of SOD2 expression leading to increased SOD2 enzyme activities and lowered superoxide levels. In the transgenic mice, effects on mitochondrial function such as enhanced oxidative capacity and greater resistance against inducers of mitochondrial permeability were observed. Superoxide in the mitochondrial matrix has been proposed to activate uncoupling proteins (UCPs), thus providing a feedback mechanism that will lower respiratory chain superoxide production by increasing a proton leak across the inner mitochondrial membrane. However, UCP1 and UCP3 activities and mitochondrial ATP production rates were not altered in isolated mitochondria from SOD2 transgenic mice, despite lowered superoxide levels. Globally, the transgenic mice displayed normal resting metabolic rates, indicating an absence of effect on any UCP activities, and normal oxygen consumption responses after norepinephrine injection. These results strongly suggest that endogenously generated matrix superoxide does not regulate UCP activity and in vivo energy expenditure.

Eugenol isolated from the essential oil of Eugenia caryophyllata induces a reactive oxygen species-mediated apoptosis in HL-60 human promyelocytic leukemia cells

Eugenol is a major component of essential oil isolated from the Eugenia caryophyllata (Myrtaceae), which has been widely used as a herbal drug. In this study, we investigated the effects of eugenol on the cytotoxicity, induction of apoptosis, and the putative pathways of its actions in human promyelocytic leukemia cells (HL-60) under the standard laboratory illumination. Eugenol-treated HL-60 cells displayed features of apoptosis including DNA fragmentation and formation of DNA ladders in agarose gel electrophoresis. We observed that eugenol transduced the apoptotic signal via ROS generation, thereby inducing mitochondrial permeability transition (MPT), reducing anti-apoptotic protein bcl-2 level, inducing cytochrome c release to the cytosol, and subsequent apoptotic cell death. Taken together, the present study demonstrated that ROS plays a critical role in eugenol-induced apoptosis in HL-60, and this is the first report on the mechanism of the anticancer effect of eugenol.

Inhibition Mechanisms of Mitochondrial Permeability Transition by 4-Hydroxytamoxifen: Protection of NAD(P)H and Thiol Group Oxidation

Abstract The effects of 4-hydroxytamoxifen (OHTAM) on the mitochondrial permeability transition (MPT) induced by Ca(2+) plus peroxynitrite (ONOO(-)) or phenylarsine oxide (PhAsO) were studied to clarify its mechanisms of MPT inhibition. Ca(2+) plus ONOO(-) induced mitochondrial swelling, membrane potential (Delta Psi) depolarization, and Ca(2+) release. OHTAM, when preincubated with mitochondria, prevents those events, and if added after their induction this drug promotes a time-dependent reversal of Delta Psi depolarization and Ca(2+) release associated with MPT induction, because these events are also inhibited by cyclosporine A (CyA). Preincubation with OHTAM also inhibits thiol group oxidation associated with the MPT promoted by ONOO(-) and allows the NAD(P)(+) to recover their reduced state faster and in a higher extension. The mitochondrial swelling and Ca(2+) release after MPT induction with Ca(2+) plus PhAsO are inhibited by OHTAM; similarly to CyA, the oxidation of NAD(P)H induced by this combination is also inhibited. According to these data, the MPT inhibition by OHTAM may be related to its antioxidant capacity and the binding to target protein components of the MPT, preventing the oxidation of NAD(P)H and thiol groups, an event that increases the sensitivity to MPT induction.

Quinine inhibits mitochondrial ATP-regulated potassium channel from bovine heart

The mitochondrial ATP-regulated potassium (mitoK(ATP) channel has been suggested as trigger and effector in myocardial ischemic preconditioning. However, molecular and pharmacological properties of the mitoK(ATP) channel remain unclear. In the present study, single-channel activity was measured after reconstitution of the inner mitochondrial membrane from bovine ventricular myocardium into bilayer lipid membrane. After incorporation, a potassium-selective current was recorded with mean conductance of 103 +/- 9 pS in symmetrical 150 mM KCl. Single-channel activity of this reconstituted protein showed properties of the mitoK(ATP) channel: it was blocked by 500 microM ATP/Mg, activated by the potassium-channel opener diazoxide at 30 microM, inhibited by 50 microM glibenclamide or 150 microM 5-hydroxydecanoic acid, and was not affected by the plasma membrane ATP-regulated potassium-channel blocker HMR1098 at 100 microM. We observed that the mitoK(ATP) channel was blocked by quinine in the micromolar concentration range. The inhibition by quinine was additionally verified with the use of 86Rb+ flux experiments and submitochondrial particles. Quinine inhibited binding of the sulfonylurea derivative [3H]glibenclamide to the inner mitochondrial membrane. We conclude that quinine inhibits the cardiac mitoK(ATP) channel by acting on the mitochondrial sulfonylurea receptor.

Protection of tamoxifen against oxidation of mitochondrial thiols and NAD(P)H underlying the permeability transition induced by prooxidants

The effects of tamoxifen (TAM) were studied on the mitochondrial permeability transition (MPT) induced by the prooxidant tert-butyl hydroperoxide (t-BuOOH) or the thiol cross-linker phenylarsine oxide (PhAsO), in the presence of Ca2+, in order to clarify the mechanisms involved in the MPT inhibition by this drug. The combination of Ca2+ with t-BuOOH or PhAsO induces mitochondrial swelling and depolarization of membrane potential (deltapsi). These events are inhibited by cyclosporine A (CyA), suggesting the inhibition of the MPT. The pre-incubation of mitochondria with TAM also prevents those events and induces a time-dependent reversal of deltapsi depolarization following MPT induction, similarly to CyA. Moreover, TAM inhibits the Ca2+ release and the oxidation of NAD(P)H and protein thiol (-SH) groups promoted by t-BuOOH plus Ca2+. On the other hand, the MPT induced by PhAsO plus Ca2+ does not induce -SH groups oxidation, supporting the notion that MPT induction by this compound is not mediated by the oxidation of specific membrane proteins groups. However, TAM also inhibits the PhAsO induced MPT, suggesting that this drug may inhibit this phenomenon by inhibiting PhAsO binding to -SH vicinal groups, implicated in the MPT induction. These data indicate that the MPT inhibition by TAM may be related to its antioxidant capacity in preventing the oxidation of NAD(P)H and -SH groups or by blocking these groups, since the oxidation of these groups increases the sensitivity of mitochondria to the MPT induction. Additionally, they suggest an MPT-independent pathway for TAM-induced apoptosis and a potential ER-independent mechanism for the effectiveness of this drug in the cancer therapy and prevention.

Glutamate-cysteine ligase attenuates TNF-induced mitochondrial injury and apoptosis

Glutathione (GSH) is important in free radical scavenging, maintaining cellular redox status, and regulating cell survival in response to a wide variety of toxicants. The rate-limiting enzyme in GSH synthesis is glutamate-cysteine ligase (GCL), which is composed of catalytic (GCLC) and modifier (GCLM) subunits. To determine whether increased GSH biosynthetic capacity enhances cellular resistance to tumor necrosis factor-alpha- (TNF-alpha-) induced apoptotic cell death, we have established several mouse liver hepatoma (Hepa-1) cell lines overexpressing GCLC and/or GCLM. Cells overexpressing GCLC alone exhibit modest increases in GCL activity, while cells overexpressing both subunits have large increases in GCL activity. Importantly, cells overexpressing both GCL subunits exhibit increased resistance to TNF-induced apoptosis as judged by a loss of redox potential; mitochondrial membrane potential; translocation of cytochrome c to the cytoplasm; and activation of caspase-3, caspase-8, and caspase-9. Analysis of the effects of TNF on these parameters indicates that maintaining mitochondrial integrity mediates this protective effect in GCL-overexpressing cells.

Endogenously generated hydrogen peroxide is required for execution of melphalan-induced apoptosis as well as oxidation and externalization of phosphatidylserine

Hydrogen peroxide (H(2)O(2)) is generated endogenously during execution of both intrinsic as well as extrinsic apoptotic programs suggesting that it may function as a secondary messenger in apoptotic pathways. In the present study, we investigated the role of endogenously generated H(2)O(2) by using two cell lines-HL-60 cells and its subclone, H(2)O(2) resistant HP100 cells overexpressing catalase (CAT). With the exception of CAT, we found no differences in the expression of other primary antioxidant enzymes (Cu/Zn-superoxide dismutase, Mn-superoxide dismutase, and glutathione peroxidase) or apoptosis-related proteins (Bcl-2 and Bax) in HP100 cells as compared with the parental HL-60 cells. Production of H(2)O(2) was readily detectable as early as 1 h after melphalan (Mel) exposure of HL-60 cells but not HP-100 cells. Biomarkers of apoptosis, such as release of cytochrome c, disruption of mitochondrial transmembrane potential, caspase-3 activation, and chromatin condensation, became apparent much later, 3 h and onward after Mel treatment of HL-60 cells. The emergence of essentially all biomarkers of apoptosis was dramatically delayed in HP100 cells as compared with HL-60 cells. A relatively minor phospholipid species, phosphatidylserine (PS), was markedly oxidized 3 h after Mel treatment in HL-60 cells (but not in HP100 cells) where it was significantly inhibited by exogenously added CAT. The two most abundant classes of membrane phospholipids, phosphatidylcholine and phosphatidyletanolamine, did not undergo any significant oxidation. PS oxidation took place 3 h after exposure of HL-60 cells to Mel and paralleled the appearance of cytochrome c in the cytosol. Neither cytochrome c release nor PS oxidation occurred in Mel-treated HP100 cells, indicating that both endogenous H(2)O(2) and cytochrome c were essential for selective PS oxidation detected in HL-60 cells. Mel-induced PS oxidation was also associated with externalization of PS on the surface of HL-60 cells. Given that 3-amino-1,2,4-triazole, a CAT inhibitor, suppressed the resistance of HP100 cells to apoptosis, production of reactive oxygen species, PS oxidation, and PS externalization induced by Mel, the results from the present study suggest that H(2)O(2) is critical for triggering the Mel-induced apoptotic program as well as PS oxidation and externalization.

Mechanisms of enhanced apoptosis in HL-60 cells by UV-irradiated n-3 and n-6 polyunsaturated fatty acids

We examined the effects of arachidonic acid (AA), eicosapentaenoic acid (EPA), and their ultraviolet (UV)-irradiated products on HL-60 cells and isolated mitochondria to explore the following four obscure points in the mechanism of polyunsaturated fatty acids (PUFAs)-induced apoptosis: (i). the role of reactive oxygen species, (ii). the interaction of PUFAs and their metabolites with mitochondria in situ, (iii). the cyclosporine A (CsA)-sensitivity in PUFA-induced membrane permeability transition, (iv). the specificity of oxidized n-3 PUFAs in the induction of apoptosis in cancer cells. UV-oxidized PUFAs contained conjugated dienes and thiobarbituric acid reactive substances (TBARS). The apoptotic effects of PUFAs on HL-60 cells were increased by UV-irradiation whereas the swelling effect of PUFAs on isolated mitochondria was decreased. Both oxidized n-3 and n-6 PUFAs induced increased depolarization, ferricytochrome c release, the activation of various caspases, and DNA-fragmentation in a CsA-insensitive mechanism concomitant with a slight increase in the value of TBARS in cells. Furthermore, there were no significant differences in the mechanism of apoptosis induced by either oxidized AA or oxidized EPA. On the basis of these results, it was concluded that both oxidized n-3 or n-6 PUFAs induced apoptosis in HL-60 cells by a similar mechanism in a CsA-insensitive manner and also that oxidized products of PUFAs, but not the cellular oxidation process itself, play an important role in the mechanism of apoptosis in HL-60 cells.

Cinnamaldehyde induces apoptosis by ROS-mediated mitochondrial permeability transition in human promyelocytic leukemia HL-60 cells

Cinnamaldehyde is an active compound isolated from the stem bark of Cinnamomum cassia, a traditional oriental medicinal herb, which has been shown to inhibit tumor cell proliferation. In this study, we investigated the effects of cinnamaldehyde on the cytotoxicity, induction of apoptosis and the putative pathways of its actions in human promyelocytic leukemia cells. Using apoptosis analysis, measurement of reactive oxygen species (ROS), and assessment of mitochondrial membrane potentials (DeltaPsim), we show that cinnamaldehyde is a potent inducer of apoptosis and that it transduces the apoptotic signal via ROS generation, thereby inducing mitochondrial permeability transition (MPT) and cytochrome c release to the cytosol. ROS production, mitochondrial alteration, and subsequent apoptotic cell death in cinnamaldehyde-treated cells were blocked by the antioxidant N-acetylcystein. Taken together, our data indicate that cinnamaldehyde induces the ROS-mediated mitochondrial permeability transition and resultant cytochrome c release. This is the first report on the mechanism of the anticancer effect of cinnamaldehyde.

Appetizing rancidity of apoptotic cells for macrophages: oxidation, externalization, and recognition of phosphatidylserine

Programmed cell death (apoptosis) functions as a mechanism to eliminate unwanted or irreparably damaged cells ultimately leading to their orderly phagocytosis in the absence of calamitous inflammatory responses. Recent studies have demonstrated that the generation of free radical intermediates and subsequent oxidative stress are implicated as part of the apoptotic execution process. Oxidative stress may simply be an unavoidable yet trivial byproduct of the apoptotic machinery; alternatively, intermediates or products of oxidative stress may act as essential signals for the execution of the apoptotic program. This review is focused on the specific role of oxidative stress in apoptotic signaling, which is realized via phosphatidylserine-dependent pathways leading to recognition of apoptotic cells and their effective clearance. In particular, the mechanisms involved in selective phosphatidylserine oxidation in the plasma membrane during apoptosis and its association with disturbances of phospholipid asymmetry leading to phosphatidylserine externalization and recognition by macrophage receptors are at the center of our discussion. The putative importance of this oxidative phosphatidylserine signaling in lung physiology and disease are also discussed.

A study on permeability transition pore opening and cytochrome c release from mitochondria, induced by caspase-3 in vitro

We recently described that there is a feedback amplification of cytochrome c release from mitochondria by caspases. Here we investigated how caspases impact on mitochondria to induce cytochrome c release and found that recombinant caspase-3 induced opening of permeability transition pore and reduction of membrane potential in vitro. These events were inhibited by Bcl-xL, cyclosporin A and z-VAD.fmk. Moreover, caspase-3 stimulated the rate of mitochondrial state 4 respiration, superoxide production and NAD(P)H oxidation in a Bcl-xL- and cyclosporin A-inhibitable manner. These results suggest that caspase-3 induces cytochrome c release by inducing permeability transition pore opening which is associated with changes in mitochondrial respiration and redox potential.

Oxidative stress in Ca(2+)-induced membrane permeability transition in brain mitochondria

Mitochondrial permeability transition (PT) is a non-selective inner membrane permeabilization, typically promoted by the accumulation of excessive quantities of Ca(2+) ions in the mitochondrial matrix. This phenomenon may contribute to neuronal cell death under some circumstances, such as following brain trauma and hypoglycemia. In this report, we show that Ca(2+)-induced brain mitochondrial PT was stimulated by Na(+) (10 mM) and totally prevented by the combination of ADP and cyclosporin A. Removal of Ca(2+) from the mitochondrial suspension by EGTA or inhibition of Ca(2+) uptake by ruthenium red partially reverted the dissipation of the membrane potential associated with PT. Ca(2+)-induced brain mitochondrial PT was significantly inhibited by the antioxidant catalase, indicating the participation of reactive oxygen species in this process. An increased detection of reactive oxygen species, measured through dichlorodihydrofluorescein oxidation, was observed after mitochondrial Ca(2+) uptake. Ca(2+)-induced dichlorodihydrofluorescein oxidation was enhanced by Na(+) and prevented by ADP and cyclosporin A, indicating that PT enhances mitochondrial oxidative stress. This could be at least in part a consequence of the extensive depletion in NAD(P)H that accompanied this Ca(2+)-induced mitochondrial PT. NADPH is known to maintain the antioxidant function of the glutathione reductase/peroxidase and thioredoxin reductase/peroxidase systems. In addition, the occurrence of mitochondrial PT was associated with membrane lipid peroxidation. We conclude that PT further increases Ca(2+)-induced oxidative stress in brain mitochondria leading to secondary damage such as lipid peroxidation.

Dynamics of intracellular calcium and free radical production during ischemia in pyramidal neurons

Biochemical cascades initiated by oxidative stress and excitotoxic intracellular calcium rises are thought to converge on mitochondrial dysfunction. We investigated the contribution of mitochondrial dysfunction to free radical (FR) overproduction in rat CA1 pyramidal neurons of organotypic slices subjected to a hypoxic-hypoglycemic insult. Ischemia-induced FR generation was decreased by the mitochondrial complex I blocker, rotenone, indicating that mitochondria are the principal source of ischemic FR production. Measurements of mitochondrial calcium with the mitochondrial calcium probe dihydroRhod-2, revealed that FR production during and after the anoxic episode correlates with the accumulation of mitochondrial calcium. However, the mitochondrial calcium uptake inhibitor Ru360 did not prevent FR generation during ischemia and attenuated it to some degree during reoxygenation. On the other hand, the mitochondrial permeability transition blocker cyclosporinA (CsA) completely arrested both ischemic FR generation and mitochondrial calcium overload, and prevented deterioration of neuronal intrinsic membrane properties. CsA had no effect on the accumulation of intracellular calcium during ischemia-reperfusion. Nicotinamide, a blocker of NAD+ hydrolysis, reproduced the CsA effects on FR generation, mitochondrial calcium accumulation and cytoplasmic calcium increases. These observations suggest that a major determinant of ischemic FR generation in pyramidal neurons is the uncoupling of the mitochondrial respiratory chain, which may be associated with the mitochondrial permeability transition.

Platelet-activating factor (PAF) enhances apoptosis induced by ultraviolet radiation in corneal epithelial cells through cytochrome c-caspase activation

PURPOSE

To examine the role of platelet-activating factor (PAF) on apoptosis of corneal epithelial cells exposed to radiation.

METHODS

Rabbit corneal epithelial (RCE) and human corneal epithelial (HCE) cells were exposed to UVC radiation and then to carbamyl PAF (cPAF) for different increments of time. The PAF antagonist BN50739 was added 30 min before cPAF. The caspase inhibitors Ac-DEVD-CHO and Ac-YVAD-CHO were added 1 h before, and the phospholipase A(2) (PLA(2)) inhibitor MAFP was added 3 h before UVC irradiation. FITC-dUTP TUNEL and DAPI staining were performed to assess the percentage of apoptotic cells. DNA ladder analysis was used to investigate apoptosis induced by different intensities of UVC (50-600 J/m(2)) with or without cPAF. Caspase activation and release of cytochrome c from mitochondria to cytosol were determined by Western blot.

RESULTS

While only 2.7% of RCE cells were DAPI positive in controls incubated for 12 h, 44% of cells were stained positive 4 h after irradiation; these values increased to 63% in the presence of cPAF. Cells incubated with cPAF alone were similar to controls. TUNEL staining and DNA laddering showed also increased in apoptosis after PAF treatment of UV-irradiated cells and BN50739 blocked the effect of cPAF. cPAF increased caspase-3 activation induced by UV irradiation in HCE cells. Cytochrome c release from mitochondria to cytosol was observed 30 min after irradiation. cPAF almost doubled the release of cytochrome c at 30 min and 1 h. Here, too, BN50739 blocked the PAF effect. No release of cytochrome c by PAF was seen in non-irradiated cells, even at higher concentrations. MAFP caused a decrease in cytochrome c release from UV-treated cells, and caused an even greater inhibition of cytochrome c release in cells stimulated with PAF.

CONCLUSIONS

PAF increases RCE and HCE apoptosis caused by UV irradiation by stimulating PLA(2), producing an early release of cytocrome c from mitochondria and activating caspase-3 by a receptor-mediated mechanism. This accelerating effect of PAF on the apoptotic cascade only occurred when corneal epithelial cells had been previously damaged by UV radiation.

Reactive Oxygen Species and Mitochondria Mediate the Induction of Apoptosis in Human Hepatoma HepG2 Cells by the Rodent Peroxisome Proliferator and Hepatocarcinogen, Perfluorooctanoic Acid

We have previously shown that one of the most potent rodent hepatocarcinogens, perfluorooctanoic acid (PFOA), induces apoptosis in human HepG2 cells in a dose- and time-dependent manner. In this study we have investigated the involvement of reactive oxygen species (ROS), mitochondria, and caspase-9 in PFOA-induced apoptosis. Treatment with 200 and 400 microM PFOA was found to cause a dramatic increase in the cellular content of superoxide anions and hydrogen peroxide after 3 h. Measurement of the mitochondrial transmembrane potential (Delta Psi(m)) after PFOA treatment showed a dissipation of Delta Psi(m) at 3 h. Caspase-9 activation was seen at 5 h after treatment with 200 microM PFOA. In order to evaluate the importance of these events in PFOA-induced apoptosis, cells were cotreated with PFOA and N-acetylcysteine (NAC), a precursor of glutathione, or Cyclosporin A (CsA), an inhibitor of mitochondrial permeability transition pore (MPT pore). NAC reduced Delta Psi(m) dissipation, caspase 9 activation, and apoptosis, indicating a role for PFOA-induced ROS. In addition, CsA also reduced Delta Psi(m) dissipation, caspase 9 activation, and apoptosis, indicating a role for PFOA-induced opening of the MPT pore. In summary, we have delineated a ROS and mitochondria-mediated pathway for induction of apoptosis by PFOA.

Mitochondrial permeability transition and oxidative stress

Mitochondrial permeability transition (MPT) is a non-selective inner membrane permeabilization that may precede necrotic and apoptotic cell death. Although this process has a specific inhibitor, cyclosporin A, little is known about the nature of the proteinaceous pore that results in MPT. Here, we review data indicating that MPT is not a consequence of the opening of a pre-formed pore, but the consequence of oxidative damage to pre-existing membrane proteins.

Costunolide induces apoptosis by ROS-mediated mitochondrial permeability transition and cytochrome C release

Costunolide is an active compound isolated from the root of Saussurea lappa Clarks, a Chinese medicinal herb, and is considered a therapeutic candidate for various types of cancers. Nevertheless, the pharmacological pathways of costunolide are still unknown. In this study, we investigate the effects of costunolide on the induction of apoptosis in HL-60 human leukemia cells and its putative pathways of action. Using apoptosis analysis, measurement of reactive oxygen species (ROS), and assessment of mitochondrial membrane potentials, we show that costunolide is a potent inducer of apoptosis, and facilitates its activity via ROS generation, thereby inducing mitochondrial permeability transition (MPT) and cytochrome c release to the cytosol. ROS production, mitochondrial alteration, and subsequent apoptotic cell death in costunolide-treated cells were blocked by the antioxidant N-acetylcystein (NAC). Cyclosporin A, a permeability transition inhibitor, also inhibited mitochondrial permeability transition and apoptosis. Our data indicate that costunolide induces the ROS-mediated mitochondrial permeability transition and resultant cytochrome c release. This is the first report on the mechanism of the anticancer effect of costunolide.

Activation of ion-conducting pathways in the inner mitochondrial membrane - an unrecognized activity of fatty acid?

The effect of non-esterified myristate (C14:0) or dodecyl sulfate was studied on passive swelling of rat liver mitochondria suspended in hypotonic alkaline KCl medium in the absence of the potassium ionophore valinomycin. Both compounds rapidly initiated large-amplitude swelling. However, they failed to initiate swelling when the mitochondria were suspended in hypotonic alkaline sucrose medium. In contrast to myristate or dodecyl sulfate, the non-ionic detergent Triton X-100 initiated swelling of mitochondria in both of the media. The following findings indicate that the inner mitochondrial membrane (IMM) is permeabilized by myristate to K+ and Cl- in a specific manner. (i) Swelling initiated by myristate did not respond to cyclosporin A, (ii) the protonophoric uncoupler FCCP was unable to mimic the myristate effect on swelling, and (iii) myristate-induced Cl- -permeation (measured with KCl medium plus valinomycin) was inhibited by N,N'-dicyclohexylcarbodiimide, quinine or ATP. Myristate- or dodecyl sulfate-initiated swelling was paralleled by the lowering of endogenous Mg2+ content. Both effects, stimulation of swelling and depletion of endogenous Mg2+ are correlated with each other. Similar effects have been reported previously for the carboxylic divalent cation ionophore calcimycin (A23187). The A23187-induced swelling has identical inhibiting characteristics on Cl- -permeation with respect to N,N'-dicyclohexylcarbodiimide, quinine and ATP as the myristate-stimulated swelling. Therefore, we conclude that non-esterified fatty acids increase the permeability of mitochondria to K+ and Cl- at alkaline pH by activating Mg2+-dependent ion-conducting pathways in IMM.

Arachidonic acid causes cytochrome c release from heart mitochondria

Arachidonic acid interaction with heart mitochondria is known to cause uncoupling as well as inhibition of pyruvate + malate and succinate-supported respiration. Here we present experiments showing that arachidonic acid causes cytochrome c release from Ca(2+)-loaded heart mitochondria. We have also measured mitochondrial matrix swelling and found a fairly good correlation between the two processes, as revealed by the same arachidonic acid concentration dependence and by the same susceptibility toward different free fatty acid species. The effects produced by arachidonic acid are not related to its protonophoric activity since, under the experimental conditions used, saturating concentrations of FCCP did not cause any effect.

The redox state of endogenous pyridine nucleotides can determine both the degree of mitochondrial oxidative stress and the solute selectivity of the permeability transition pore

Acetoacetate, an NADH oxidant, stimulated the ruthenium red-insensitive rat liver mitochondrial Ca(2+) efflux without significant release of state-4 respiration, disruption of membrane potential (Deltapsi) or mitochondrial swelling. This process is compatible with the opening of the currently designated low conductance state of the permeability transition pore (PTP) and, under our experimental conditions, was associated with a partial oxidation of the mitochondrial pyridine nucleotides. In contrast, diamide, a thiol oxidant, induced a fast mitochondrial Ca(2+) efflux associated with a release of state-4 respiration, a disruption of Deltapsi and a large amplitude mitochondrial swelling. This is compatible with the opening of the high conductance state of the PTP and was associated with extensive oxidation of pyridine nucleotides. Interestingly, the addition of carbonyl cyanide p-(trifluoromethoxy)phenylhydrazone to the acetoacetate experiment promoted a fast shift from the low to the high conductance state of the PTP. Both acetoacetate and diamide-induced mitochondrial permeabilization were inhibited by exogenous catalase. We propose that the shift from a low to a high conductance state of the PTP can be promoted by the oxidation of NADPH. This impairs the antioxidant function of the glutathione reductase/peroxidase system, strongly strengthening the state of mitochondrial oxidative stress.

Copper sensitizes the mitochondrial permeability transition to carboxytractyloside and oleate

Addition of 5 microM copper to rat kidney mitochondria enhances the effect of carboxyatractyloside and oleate on pore opening, in a cyclosporin A-sensitive fashion. The effects of the pair copper-carboxyatractyloside were observed on matrix Ca2+ efflux, mitochondrial swelling and on the transmembrane electric gradient. The effect of Cu2+ emphasizes the importance of membrane thiol groups located, probably, in the ADP/ATP translocase (ANT), on permeability transition. It was also found that Cu2+ does not block the fluorescent label of ANT by eosin 5-maleimide, but abolishes the inhibition by CAT on the labeling. This suggests that the binding of Cu2+ to cysteine residues of ANT promotes a conformational change in the carrier, strengthening the effect of CAT and oleate on membrane leakage.