Nitric oxide interacts with mitochondrial complex III producing antimycin-like effects

The effect of NO between cytochromes b and c of the mitochondrial respiratory chain were studied using submitochondrial particles (SMP) from bovine heart and GSNO and SPER-NO as NO sources. Succinate-cytochrome c reductase (complex II-III) activity (222 ± 4 nmol/min. mg protein) was inhibited by 51% in the presence of 500 μM GSNO and by 48% in the presence of 30 μM SPER-NO, in both cases at ~1.25 μM NO. Neither GSNO nor SPER-NO were able to inhibit succinate-Q reductase activity (complex II; 220 ± 9 nmol/min. mg protein), showing that NO affects complex III. Complex II-III activity was decreased (36%) when SMP were incubated with l-arginine and mtNOS cofactors, indicating that this effect is also produced by endogenous NO. GSNO (500 μM) reduced cytochrome b562 by 71%, in an [O2] independent manner. Hyperbolic increases in O2(•-) (up to 1.3 ± 0.1 nmol/min. mg protein) and H2O2 (up to 0.64 ± 0.05 nmol/min. mg protein) productions were observed with a maximal effect at 500 μM GSNO. The O2(•-)/H2O2 ratio was 1.98 in accordance with the stoichiometry of the O2(•-) disproportionation. Moreover, H2O2 production was increased by 72-74% when heart coupled mitochondria were exposed to 500 μM GSNO or 30 μM SPER-NO. SMP incubated in the presence of succinate showed an EPR signal (g=1.99) compatible with a stable semiquinone. This EPR signal was increased not only by antimycin but also by GSNO and SPER-NO. These signals were not modified under N2 atmosphere, indicating that they are not a consequence to the effect of NOx species on complex III area. These results show that NO interacts with ubiquinone-cytochrome b area producing antimycin-like effects. This behaviour comprises the inhibition of electron transfer, the interruption of the oxidation of cytochromes b, and the enhancement of [UQH(•)]ss which, in turn, leads to an increase in O2(•-) and H2O2 mitochondrial production rates.

ATP Binding and Hydrolysis Properties of ABCB10 and Their Regulation by Glutathione

ABCB10 (ATP binding cassette sub-family B10) is a mitochondrial inner-membrane ABC transporter. ABCB10 has been shown to protect the heart from the impact of ROS during ischemia-reperfusion and to allow for proper hemoglobin synthesis during erythroid development. ABC transporters are proteins that increase ATP binding and hydrolysis activity in the presence of the transported substrate. However, molecular entities transported by ABCB10 and its regulatory mechanisms are currently unknown. Here we characterized ATP binding and hydrolysis properties of ABCB10 by using the 8-azido-ATP photolabeling technique. This technique can identify potential ABCB10 regulators, transported substrates and amino-acidic residues required for ATP binding and hydrolysis. We confirmed that Gly497 and Lys498 in the Walker A motif, Glu624 in the Walker B motif and Gly602 in the C-Loop motif of ABCB10 are required for proper ATP binding and hydrolysis activity, as their mutation changed ABCB10 8-Azido-ATP photo-labeling. In addition, we show that the potential ABCB10 transported entity and heme precursor delta-aminolevulinic acid (dALA) does not alter 8-azido-ATP photo-labeling. In contrast, oxidized glutathione (GSSG) stimulates ATP hydrolysis without affecting ATP binding, whereas reduced glutathione (GSH) inhibits ATP binding and hydrolysis. Indeed, we detectABCB10 glutathionylation in Cys547 and show that it is one of the exposed cysteine residues within ABCB10 structure. In all, we characterize essential residues for ABCB10 ATPase activity and we provide evidence that supports the exclusion of dALA as a potential substrate directly transported by ABCB10. Last, we show the first molecular mechanism by which mitochondrial oxidative status, through GSH/GSSG, can regulate ABCB10.

Mitochondrial chloride channels: electrophysiological characterization and pH induction of channel pore dilation

Physiological and pathological functions of mitochondria are highly dependent on the properties and regulation of mitochondrial ion channels. There is still no clear understanding of the molecular identity, regulation, and properties of anion mitochondrial channels. The inner membrane anion channel (IMAC) was assumed to be equivalent to mitochondrial centum picosiemens (mCS). However, the different properties of IMAC and mCS channels challenges this opinion. In our study, we characterized the single-channel anion selectivity and pH regulation of chloride channels from purified cardiac mitochondria. We observed that channel conductance decreased in the order: Cl⁻ > Br⁻ > I⁻ > chlorate ≈ formate > acetate, and that gluconate did not permeate under control conditions. The selectivity sequence was Br⁻ ≥ chlorate ≥ I⁻ ≥ Cl⁻ ≥ formate ≈ acetate. Measurement of the concentration dependence of chloride conductance revealed altered channel gating kinetics, which was demonstrated by prolonged mean open time value with increasing chloride concentration. The observed mitochondrial chloride channels were in many respects similar to those of mCS, but not those of IMAC. Surprisingly, we observed that acidic pH increased channel conductance and that an increase of pH from 7.4 to 8.5 reduced it. The gluconate current appeared and gradually increased when pH decreased from pH 7.0 to 5.6. Our results indicate that pH regulates the channel pore diameter in such a way that dilation increases with more acidic pH. We assume this newly observed pH-dependent anion channel property may be involved in pH regulation of anion distribution in different mitochondrial compartments.

Mitochondrial DAMPs increase endothelial permeability through neutrophil dependent and independent pathways

Trauma and sepsis can cause acute lung injury (ALI) and Acute Respiratory Distress Syndrome (ARDS) in part by triggering neutrophil (PMN)-mediated increases in endothelial cell (EC) permeability. We had shown that mitochondrial (mt) damage-associated molecular patterns (DAMPs) appear in the blood after injury or shock and activate human PMN. So we now hypothesized that mitochondrial DAMPs (MTD) like mitochondrial DNA (mtDNA) and peptides might play a role in increased EC permeability during systemic inflammation and proceeded to evaluate the underlying mechanisms. MtDNA induced changes in EC permeability occurred in two phases: a brief, PMN-independent ‘spike’ in permeability was followed by a prolonged PMN-dependent increase in permeability. Fragmented mitochondria (MTD) caused PMN-independent increase in EC permeability that were abolished with protease treatment. Exposure to mtDNA caused PMN-EC adherence by activating expression of adherence molecule expression in both cell types. Cellular activation was manifested as an increase in PMN calcium flux and EC MAPK phosphorylation. Permeability and PMN adherence were attenuated by endosomal TLR inhibitors. EC lacked formyl peptide receptors but were nonetheless activated by mt-proteins, showing that non-formylated mt-protein DAMPs can activate EC. Mitochondrial DAMPs can be released into the circulation by many processes that cause cell injury and lead to pathologic endothelial permeability. We show here that mitochondria contain multiple DAMP motifs that can act on EC and/or PMN via multiple pathways. This can enhance PMN adherence to EC, activate PMN-EC interactions and subsequently increase systemic endothelial permeability. Mitochondrial DAMPs may be important therapeutic targets in conditions where inflammation pathologically increases endothelial permeability.

Peroxynitrite formation in nitric oxide-exposed submitochondrial particles: detection, oxidative damage and catalytic removal by Mn-porphyrins

Peroxynitrite (ONOO(-)) formation in mitochondria may be favored due to the constant supply of superoxide radical (O(2)(∙-)) by the electron transport chain plus the facile diffusion of nitric oxide ((∙)NO) to this organelle. Herein, a model system of submitochondrial particles (SMP) in the presence of succinate plus the respiratory inhibitor antimycin A (to increase O(2)(∙-) rates) and the (∙)NO-donor NOC-7 was studied to directly establish and quantitate peroxynitrite by a multiplicity of methods including chemiluminescence, fluorescence and immunochemical analysis. While all the tested probes revealed peroxynitrite at near stoichiometric levels with respect to its precursor radicals, coumarin boronic acid (a probe that directly reacts with peroxynitrite) had the more straightforward oxidation profile from O(2)(∙-)-forming SMP as a function of the (∙)NO flux. Interestingly, immunospintrapping studies verified protein radical generation in SMP by peroxynitrite. Substrate-supplemented SMP also reduced Mn(III)porphyrins (MnP) to Mn(II)P under physiologically-relevant oxygen levels (3-30 μM); then, Mn(II)P were capable to reduce peroxynitrite and protect SMP from the inhibition of complex I-dependent oxygen consumption and protein radical formation and nitration of membranes. The data directly support the formation of peroxynitrite in mitochondria and demonstrate that MnP can undergo a catalytic redox cycle to neutralize peroxynitrite-dependent mitochondrial oxidative damage.

Localization of the site of oxygen radical generation inside the complex I of heart and nonsynaptic brain mammalian mitochondria

Mitochondrial production of oxygen radicals seems to be involved in many diseases and aging. Recent studies clearly showed that a substantial part of the free radical generation of rodent mitochondria comes from complex I. It is thus important to further localize the free radical generator site within this respiratory complex. In this study, superoxide production by heart and nonsynaptic brain submitochondrial particles from up to seven mammalian species, showing different longevities, were studied under different conditions. The results, taking together, show that rotenone stimulates NADH-supported superoxide generation, confirming that complex I is a source of oxygen radicals in mammals, in general. The rotenone-stimulated NADH-supported superoxide production of the heart and nonsynaptic brain mammalian submitochondrial particles was inhibited both by p-chloromercuribenzoate and by ethoxyformic anhydride. These results localize the complex I oxygen radical generator between the ferricyanide and the ubiquinone reduction site, making iron-sulfur centers possible candidates, although unstable semiquinones can not be discarded. The results also indicate that the previously described inverse correlation between rates of mitochondrial oxygen radical generation and mammalian longevity operates through mechanisms dependent on the presence of intact functional mitochondria.

Leishmania major ascorbate peroxidase overexpression protects cells against reactive oxygen species-mediated cardiolipin oxidation

Heme peroxidases are a class of multifunctional redox-active proteins found in all organisms. We recently cloned, expressed, and characterized an ascorbate peroxidase from Leishmania major (LmAPX) that was capable of detoxifying hydrogen peroxide. Localization studies using green fluorescent protein fusions revealed that LmAPX was localized within the mitochondria by its N-terminal signal sequence. Subcellular fractionation analysis of the cell homogenate by the Percoll density-gradient method and subsequent Western blot analysis with anti-LmAPX antibody further confirmed the mitochondrial localization of mature LmAPX. Submitochondrial fractionation analysis showed that the mature enzyme (~3.6 kDa shorter than the theoretical value of the whole gene) was present in the intermembrane space side of the inner membrane. Moreover, expression of the LmAPX gene was increased by treatment with exogenous H(2)O(2), indicating that LmAPX was induced by oxidative stress. To investigate the biological role of LmAPX we generated Leishmania cells overexpressing LmAPX in the mitochondria. Flow-cytometric analysis, thin-layer chromatography, and IC(50) measurements suggested that overexpression of LmAPX caused depletion of the mitochondrial ROS burden and conferred a protection against mitochondrial cardiolipin oxidation and increased tolerance to H(2)O(2). These results suggest that the single-copy LmAPX gene plays a protective role against oxidative damage.

Molecular modeling and experimental evidence for hypericin as a substrate for mitochondrial complex III; mitochondrial photodamage as demonstrated using specific inhibitors

The effect of hypericin photoactivation on mitochondria of human prostate carcinoma cells was studied using a range of mitochondrial inhibitors. Oligomycin significantly enhanced hypericin phototoxicity while atractyloside and antymicin A conferred a significant protection. Use of myxothiazol did not affect cell survival following hypericin photoactivation. These results signify a protective role for F(1)F(0)-ATP synthase running in reverse mode, and a significant photodamage at the quinone-reducing site of mitochondrial complex III. In light of these results, we performed molecular modeling of hypericin binding to complex III. This revealed three binding sites, two of which coincided with the quinol-oxidizing and quinone-reducing centers. Using submitochondrial particles we examined hypericin as a possible substrate of complex III and compared this to its natural substrate, ubiquinone-10. Our results demonstrate uniquely that hypericin is an efficient substrate for complex III, and this activity is inhibited by myxothiazol and antimycin A. We further demonstrated that hypericin photosensitization completely inactivated complex III with ubiquinone as substrate. The ability to enhance HYP potency by inhibition of F(1)F(0)-ATP synthase or depress HYP efficacy by inhibition at the Qi site of complex III provides a potential to increase the therapeutic index of HYP and amplify its PDT action in tumor cells.

Effect of storage temperature on the activity of submitochondrial particles

The submitochondrial particle (SMP) assay employs processed mammalian mitchondria to assess the toxicity of chemical contaminants in aqueous solutions. Particles and associated reagents are commercially available to support two individual procedures, the electron transfer (ETr) and reverse electron transfer (RET) assays. The objective of the present study was to assess the effect of storage temperature on SMP activity. One RET and one ETr assay were conducted with sodium dodecylsulfate on each of two vials of particles stored at -20 and -80 degrees C at periodic intervals over a six-month span. Results demonstrated that SMP could remain active in either assay through six months of storage at either temperature. However, there were isolated vials of particles stored at -20 degrees C that exhibited unacceptable reductions in activity for both the ETr and the RET assays that were not related to storage duration. These results were used to develop guidance in assessing the acceptability of particle activity in SMP assays.

Mitochondrial production of reactive oxygen species: role of complex I and quinone analogues

Mitochondrial reactive oxygen species (ROS) are mainly produced by the respiratory chain enzymes. The sites for ROS production in mitochondrial respiratory chain are normally ascribed to the activity of Complex I and III. The presence of specific inhibitors modulates reactive oxygen species production in Complex I: inhibitors such as rotenone induce a strong ROS increase, while inhibitors such as stigmatellin prevent it. We have investigated the effect of hydrophilic quinones on Complex I ROS production in presence of different inhibitors. Some short chain quinones are Complex I inhibitors (CoQ2, idebenone and its derivatives), while CoQ1, decylubiquinone~ (DB) and duroquinone (DQ) are good electron acceptors from Complex I. Our results show that the ability of short chain quinones to induce an oxidative stress depends on the site of interaction with Complex I and on their physical-chemical characteristics. We can conclude that hydrophilic quinones may enhance oxidative stress by interaction with the electron escape sites on Complex I while more hydrophobic quinones can be reduced only at the physiological quinone reducing site without reacting with molecular oxygen.

Inhibition of anion channels derived from mitochondrial membranes of the rat heart by stilbene disulfonate--DIDS

The objective of this work was to characterize in more detail the inhibition effect of diisothiocyanatostilbene-2',2-disulfonic acid (DIDS) on anion channels isolated from the rat heart mitochondria. The channels reconstituted into a planar lipid membrane displayed limited powers of discrimination between anions and cations and the ion conductance measured under asymmetric (250/50 mM KCl, cis/trans) and symmetric (150 mM KCl) conditions was approximately 100 pS. DIDS caused a dramatic decrease in the channel activity (IC(50) = 11.7 +/- 3.1 microM) only when it was added to the cis side of a planar lipid membrane. The inhibition was accompanied by the significant prolongation of closings and the shortening of openings within the burst as well as gaps between bursts were prolonged and durations of bursts were reduced. The blockade was complete and irreversible when concentration of DIDS was increased up to 200 microM. Our data indicate that DIDS is an allosteric blocker of mitochondrial anion channels and this specific effect could be used as a tool for reliable identification of anion channels on the functional level.

Fine-tuning the amphiphilicity: a crucial parameter in the design of potent alpha-phenyl-N-tert-butylnitrone analogues

A new series of hydrophilic, lipophilic, and amphiphilic alpha-phenyl-N-tert-butylnitrone (PBN) derivatives were synthesized to explore the relationship between their hydrophilic-lipophilic properties and antioxidant potency. Very potent protective effects of amphiphilic lactobionamide and tris(hydroxymethyl)aminomethane PBN derivatives were observed in mitochondrial preparations, in cell cultures, and in rotifers exposed to unspecific and mitochondria targeted oxidotoxins.

Acute and chronic vitamin A supplementation at therapeutic doses induces oxidative stress in submitochondrial particles isolated from cerebral cortex and cerebellum of adult rats

Vitamin A is an essential micronutrient to the normal brain function. However, there is an increasing concern regarding the use of vitamin A at high doses even therapeutically. Here, we show that acute and chronic vitamin A supplementation induces oxidative stress to submitochondrial particles (SMP) isolated from rat cerebral cortex and cerebellum. Both chronic and acute vitamin A supplementation at therapeutic (1000 IU/kg or 2500 IU/kg) or excessive (4500 IU/kg or 9000 IU/kg) doses induced lipid peroxidation, protein carbonylation, and oxidation of protein thiol groups in cerebral cortex and cerebellum SMP. Furthermore, vitamin A supplementation induced an increase in the superoxide (O(2)(-)) anion production, indicating an uncoupling in the electron transfer chain (ETC). Locomotory and exploratory activity, which are associated to cerebral cortex and cerebellum, also were affected by both acute and chronic vitamin A supplementation. Vitamin A induced a decrease in both locomotory and exploratory behavior. Together, these results show that vitamin A could be toxic at the sub cellular level, inducing mitochondrial dysfunction and altering cerebral cortex and/or cerebellum-dependent behavior.

Melatonin protects against rotenone-induced oxidative stress in a hemiparkinsonian rat model

In the present study, we evaluated the effect of melatonin, a well-known free radical scavenger and neuroprotector, against rotenone-induced oxidative stress in a hemiparkinsonian rat model. The effect of melatonin on glutathione (GSH) depletion caused by unilateral, intranigral infusion of rotenone was investigated employing a spectrofluorimetric procedure. We also studied the effect of melatonin on rotenone-induced changes in the antioxidant enzymes superoxide dismutase (SOD) and catalase in the cytosolic fractions of substantia nigra (SN), employing spectrophotometric procedures. Rotenone-induced hydroxyl radicals (*OH) in the isolated mitochondria, as measured employing a sensitive HPLC-electrochemical method, were significantly scavenged by melatonin. Melatonin treatment restored the rotenone-induced decrease in GSH level and changes in antioxidant enzyme (SOD and catalase) activities in the SN. Our results strongly indicate melatonin's beneficial use in Parkinson's disease therapy as an antioxidant.

The AAA+ protein ATAD3 has displacement loop binding properties and is involved in mitochondrial nucleoid organization

Many copies of mammalian mitochondrial DNA contain a short triple-stranded region, or displacement loop (D-loop), in the major noncoding region. In the 35 years since their discovery, no function has been assigned to mitochondrial D-loops. We purified mitochondrial nucleoprotein complexes from rat liver and identified a previously uncharacterized protein, ATAD3p. Localization studies suggested that human ATAD3 is a component of many, but not all, mitochondrial nucleoids. Gene silencing of ATAD3 by RNA interference altered the structure of mitochondrial nucleoids and led to the dissociation of mitochondrial DNA fragments held together by protein, specifically, ones containing the D-loop region. In vitro, a recombinant fragment of ATAD3p bound to supercoiled DNA molecules that contained a synthetic D-loop, with a marked preference over partially relaxed molecules with a D-loop or supercoiled DNA circles. These results suggest that mitochondrial D-loops serve to recruit ATAD3p for the purpose of forming or segregating mitochondrial nucleoids.

Methods to determine the status of mitochondrial ATP synthase assembly

The adenosine triphosphate (ATP) synthase (F1-F0 complex) of the mitochondrial inner membrane is responsible for making nearly all of the ATP utilized by eukaryotic organisms. The enzyme is an oligomer of more than 20 different subunits, 14 of which are essential for its catalytic activity. The other subunits function in the regulation and structure of the complex. Subunits essential for catalytic activity make up the proton pore, the bulk of the F1 headpiece, and the two stalks that physically and functionally couple the catalytic and proton-translocating activities of the ATP synthase. Saccharomyces cerevisiae provides an excellent model system for studying mutations that affect assembly of the complex because of the ability of this organism to survive on the ATP produced from fermentation in the absence of mitochondrial respiration or oxidative phosphorylation. Studies of such mutants have been instrumental in identifying novel molecular chaperones that act at discrete steps of F1-F0 assembly. Here, we describe some experimental approaches useful in assessing the status of F1-F0 assembly.

Mitochondria and neuronal activity

Mitochondria are central for various cellular processes that include ATP production, intracellular Ca(2+) signaling, and generation of reactive oxygen species. Neurons critically depend on mitochondrial function to establish membrane excitability and to execute the complex processes of neurotransmission and plasticity. While much information about mitochondrial properties is available from studies on isolated mitochondria and dissociated cell cultures, less is known about mitochondrial function in intact neurons in brain tissue. However, a detailed description of the interactions between mitochondrial function, energy metabolism, and neuronal activity is crucial for the understanding of the complex physiological behavior of neurons, as well as the pathophysiology of various neurological diseases. The combination of new fluorescence imaging techniques, electrophysiology, and brain slice preparations provides a powerful tool to study mitochondrial function during neuronal activity, with high spatiotemporal resolution. This review summarizes recent findings on mitochondrial Ca(2+) transport, mitochondrial membrane potential (DeltaPsi(m)), and energy metabolism during neuronal activity. We will first discuss interactions of these parameters for experimental stimulation conditions that can be related to the physiological range. We will then describe how mitochondrial and metabolic dysfunction develops during pathological neuronal activity, focusing on temporal lobe epilepsy and its experimental models. The aim is to illustrate that 1) the structure of the mitochondrial compartment is highly dynamic in neurons, 2) there is a fine-tuned coupling between neuronal activity and mitochondrial function, and 3) mitochondria are of central importance for the complex behavior of neurons.

The inhibitor protein (IF1) promotes dimerization of the mitochondrial F1F0-ATP synthase

The effect of increased expression or reconstitution of the mitochondrial inhibitor protein (IF1) on the dimer/monomer ratio (D/M) of the rat liver and bovine heart F1F0-ATP synthase was studied. The 2-fold increased expression of IF1 in AS-30D hepatoma mitochondria correlated with a 1.4-fold increase in the D/M ratio of the ATP synthase extracted with digitonin as determined by blue native electrophoresis and averaged densitometry analyses. Removal of IF1 from rat liver or bovine heart submitochondrial particles increased the F1F0-ATPase activity and decreased the D/M ratio of the ATP synthase. Reconstitution of recombinant IF1 into submitochondrial particles devoid of IF1 inhibited the F1F0-ATPase activity by 90% and restored partially the D/M ratio of the whole F1F0 complex as revealed by blue native electrophoresis and subsequent SDS-PAGE or glycerol density gradient centrifugation. Thus, the inhibitor protein promotes or stabilizes the dimeric form of the intact F1F0-ATP synthase. A possible location of the IF1 protein in the dimeric structure of the rat liver F1F0 complex is proposed. According to crystallographic and electron microscopy analyses, dimeric IF1 could bridge the F1-F1 part of the dimeric F1F0-ATP synthase in the inner mitochondrial membrane.

Kinetics of integrated electron transfer in the mitochondrial respiratory chain: random collisions vs. solid state electron channeling

Recent evidence, mainly based on native electrophoresis, has suggested that the mitochondrial respiratory chain is organized in the form of supercomplexes, due to the aggregation of the main respiratory chain enzymatic complexes. This evidence strongly contrasts the previously accepted model, the Random Diffusion Model, largely based on kinetic studies, stating that the complexes are randomly distributed in the lipid bilayer of the inner membrane and functionally connected by lateral diffusion of small redox molecules, i.e., coenzyme Q and cytochrome c. This review critically examines the experimental evidence, both structural and functional, pertaining to the two models and attempts to provide an updated view of the organization of the respiratory chain and of its kinetic consequences. The conclusion that structural respiratory assemblies exist is overwhelming, whereas the expected functional consequence of substrate channeling between the assembled enzymes is controversial. Examination of the available evidence suggests that, although the supercomplexes are structurally stable, their kinetic competence in substrate channeling is more labile and may depend on the system under investigation and the assay conditions.

Increased oxidative stress in submitochondrial particles after chronic amphetamine exposure

Previous studies have suggested that reactive oxygen species (ROS) production may play a role in the pathophysiology of many neuropsychiatric disorders, such as bipolar disorder (BD) and schizophrenia (SCZ). In addition, there is an emerging body of data indicating that BD and SCZ may be associated with mitochondrial dysfunction. We studied the effects of acute and chronic d-amphetamine on ROS production in submitochondrial particles of rat brain. Male Wistar rats were divided in two experimental groups: acute and chronic treatment. In the acute treatment, rats received one single IP injection of d-amphetamine (1, 2 or 4 mg/kg) or saline (control group). In the chronic treatment, rats received one daily IP injection of d-amphetamine (1, 2 or 4 mg/kg) or saline for 7 days. Locomotor activity was assessed with the open field task, and thiobarbituric acid reactive substances (TBARS) and superoxide production were measured in submitochondrial particles of the prefrontal cortex and hippocampus. Both acute and chronic amphetamine treatment increased locomotor behavior. Chronic amphetamine exposure induced a 3- to 6-fold increase of TBARS and a 1.5- to 2-fold increase of superoxide production in submitochondrial particles of prefrontal cortex and hippocampus (P < 0.05). No effects on superoxide or TBARS were observed with acute treatment. These findings suggest that amphetamine-induced mitochondrial ROS generation may be a useful model to investigate the hypothesis of altered brain energy metabolism associated with BD and SCZ. Further studies assessing the effects of mood stabilizers and antipsychotics in preventing mitochondrial oxidative stress are necessary.

K+-independent actions of diazoxide question the role of inner membrane KATP channels in mitochondrial cytoprotective signaling

Activation by diazoxide and inhibition by 5-hydroxydecanoate are the hallmarks of mitochondrial ATP-sensitive K+ (K(ATP)) channels. Opening of these channels is thought to trigger cytoprotection (preconditioning) through the generation of reactive oxygen species. However, we found that diazoxide-induced oxidation of the widely used reactive oxygen species indicator 2',7'-dichlorodihydrofluorescein in isolated liver and heart mitochondria was observed in the absence of ATP or K+ and therefore independent of K(ATP) channels. The response was blocked by stigmatellin, implying a role for the cytochrome bc1 complex (complex III). Diazoxide, though, did not increase hydrogen peroxide (H2O2) production (quantitatively measured with Amplex Red) in intact mitochondria, submitochondrial particles, or purified cytochrome bc1 complex. We confirmed that diazoxide inhibited succinate oxidation, but it also weakly stimulated state 4 respiration even in K+-free buffer, excluding a role for K(ATP) channels. Furthermore, we have shown previously that 5-hydroxydecanoate is partially metabolized, and we hypothesized that fatty acid metabolism may explain the ability of this putative mitochondrial K(ATP) channel blocker to inhibit diazoxide-induced flavoprotein fluorescence, commonly used as an assay of K(ATP) channel activity. Indeed, consistent with our hypothesis, we found that decanoate inhibited diazoxide-induced flavoprotein oxidation. Taken together, our data question the "mitochondrial K(ATP) channel" hypothesis of preconditioning. Diazoxide did not evoke superoxide (which dismutates to H2O2) from the respiratory chain by a direct mechanism, and the stimulatory effects of this compound on mitochondrial respiration and 2',7'-dichlorodihydrofluorescein oxidation were not due to the opening of K(ATP) channels.

PINK1 protein in normal human brain and Parkinson's disease

Parkinson's disease is a common incurable neurodegenerative disease whose molecular aetiology remains unclear. The identification of Mendelian genes causing rare familial forms of Parkinson's disease has revealed novel proteins and pathways that are likely to be relevant in the pathogenesis of sporadic Parkinson's disease. Recently, mutations in a novel gene, PINK1, encoding a 581 amino acid protein with both mitochondrial targeting and serine/threonine kinase domains, were identified as a cause of autosomal recessive parkinsonism. This provided important evidence for the role of the mitochondrial dysfunction and kinase pathways in neurodegeneration. In this study, we report the first characterization of the PINK1 protein in normal human and sporadic Parkinson's brains, in addition to Parkinson's cases with heterozygous PINK1 mutations. The possible role of the PINK1 protein was also assessed in a number of neurodegenerative diseases characterized by proteinaceous inclusions. For these studies, rabbit polyclonal antibodies were raised against two peptide sequences within the N-terminal hydrophilic loops of PINK1 protein. Using immunohistochemistry and western blotting we were able to demonstrate that PINK1 is a ubiquitous protein expressed throughout the human brain and it is found in all cell types showing a punctate cytoplasmic staining pattern consistent with mitochondrial localization. Fractionation studies of human and rat brain confirm that PINK1 is localized to the mitochondrial membranes. In addition, we show that PINK1 is detected in a proportion of Lewy bodies in cases of sporadic Parkinson's disease and Parkinson's disease associated with heterozygous mutations in the PINK1 gene, which are clinically and pathologically indistinguishable from the sporadic cases. PINK1 was absent in cortical Lewy bodies, in neurofibrillary tangles in Alzheimer's disease, progressive supranuclear palsy and corticobasal degeneration, and in the glial and neuronal alpha-synuclein positive inclusions in multiple system atrophy. These studies provide for the first time in vivo morphological and biochemical evidence to support a mitochondrial localization of PINK1 and underpin the significance of mitochondrial dysfunction in the pathogenesis of nigral cell degeneration in Parkinson's disease.

Topography and chemical reactivity of the active-inactive transition-sensitive SH-group in the mitochondrial NADH:ubiquinone oxidoreductase (Complex I)

The spatial arrangement and chemical reactivity of the activation-dependent thiol in the mitochondrial Complex I was studied using the membrane penetrating N-ethylmaleimide (NEM) and non-penetrating anionic 5,5'-dithiobis-(2-nitrobenzoate) (DTNB) as the specific inhibitors of the enzyme in mitochondria and inside-out submitochondrial particles (SMP). Both NEM and DTNB rapidly inhibited the de-activated Complex I in SMP. In mitochondria NEM caused rapid inhibition of Complex I, whereas the enzyme activity was insensitive to DTNB. In the presence of the channel-forming antibiotic alamethicin, mitochondrial Complex I became sensitive to DTNB. Neither active nor de-activated Complex I in SMP was inhibited by oxidized glutathione (10 mM, pH 8.0, 75 min). The data suggest that the active/de-active transition sulfhydryl group of Complex I which is sensitive to inhibition by NEM is located at the inner membrane-matrix interface. These data include the sidedness dependency of inhibition, effect of pH, ionic strength, and membrane bilayer modification on enzyme reactivity towards DTNB and its neutral analogue.

Acrolein is a mitochondrial toxin: effects on respiratory function and enzyme activities in isolated rat liver mitochondria

Acrolein is an air pollutant from cigarette smoking and other pollutions and also a by-product of lipid peroxidation. Studies have demonstrated that acrolein causes cytotoxicity and genotoxicity, including liver damage and death of hepatocytes. However, the toxic effects and the underlying mechanisms of acrolein on mitochondria, especially, on liver mitochondria, have not been well studied. In the present study, we investigated the toxic effects and mechanisms of acrolein on mitochondria isolated from rat liver by examining mitochondrial respiration, dehydrogenases, complex I, II, III, IV and V, permeability transition, and protein oxidation. Acrolein incubation (10-1000 microM, or 0.02-2 micromol/mg protein) with mitochondria caused dose-dependent inhibition of NADH- and succinate-linked mitochondrial respiration chain, change of mitochondrial permeability transition, increase in protein carbonyls, and selective enzyme inhibition of mitochondrial complex I, II, pyruvate dehydrogenase, alpha-ketoglutarate dehydrogenase, but no effects on mitochondrial complex III, IV, V and malate dehydrogenase. These results suggest that acrolein is a mitochondrial toxin and that mitochondrial dysfunction caused by acrolein may play an important role in acrolein toxicity such as hepatotoxicity and also smoking-related diseases.

Differential gel electrophoresis and transgenic mitochondrial calcium reporters demonstrate spatiotemporal filtering in calcium control of mitochondria

Mitochondria must adjust both their intracellular location and their metabolism in order to balance their output to the needs of the cell. Here we show by the proteomic technique of time series difference gel electrophoresis that a major result of neuroendocrine stimulation of the Drosophila renal tubule is an extensive remodeling of the mitochondrial matrix. By generating Drosophila that were transgenic for both luminescent and fluorescent mitochondrial calcium reporters, it was shown that mitochondrial calcium tracked the slow (minutes) but not the rapid (<1 s) changes in cytoplasmic calcium and that this resulted in both increased mitochondrial membrane polarization and elevated cellular ATP levels. The selective V-ATPase inhibitor, bafilomycin, further enhanced ATP levels, suggesting that the apical plasma membrane V-ATPase is a major consumer of ATP. Both the mitochondrial calcium signal and the increase in ATP were abolished by the mitochondrial calcium uniporter blocker Ru360. By using both mitochondrial calcium imaging and the potential sensing dye JC-1, the apical mitochondria of principal cells were found to be selectively responsive to neuropeptide signaling. As the ultimate target is the V-ATPase in the apical plasma membrane, this selective activation of mitochondria is clearly adaptive. The results highlight the dynamic nature and both spatial and temporal heterogeneity of calcium signaling possible in differentiated, organotypic cells and provide a new model for neuroendocrine control of V-ATPase.

Generation of superoxide by the mitochondrial Complex I

Superoxide production by inside-out coupled bovine heart submitochondrial particles, respiring with succinate or NADH, was measured. The succinate-supported production was inhibited by rotenone and uncouplers, showing that most part of superoxide produced during succinate oxidation is originated from univalent oxygen reduction by Complex I. The rate of the superoxide (O2*-)) production during respiration at a high concentration of NADH (1 mM) was significantly lower than that with succinate. Moreover, the succinate-supported O2*- production was significantly decreased in the presence of 1 mM NADH. The titration curves, i.e., initial rates of superoxide production versus NADH concentration, were bell-shaped with the maximal rate (at 50 microM NADH) approaching that seen with succinate. Both NAD+ and acetyl-NAD+ inhibited the succinate-supported reaction with apparent Ki's close to their Km's in the Complex I-catalyzed succinate-dependent energy-linked NAD+ reduction (reverse electron transfer) and NADH:acetyl-NAD+ transhydrogenase reaction, respectively. We conclude that: (i) under the artificial experimental conditions the major part of superoxide produced by the respiratory chain is formed by some redox component of Complex I (most likely FMN in its reduced or free radical form); (ii) two different binding sites for NADH (F-site) and NAD+ (R-site) in Complex I provide accessibility of the substrates-nucleotides to the enzyme red-ox component(s); F-site operates as an entry for NADH oxidation, whereas R-site operates in the reverse electron transfer and univalent oxygen reduction; (iii) it is unlikely that under the physiological conditions (high concentrations of NADH and NAD+) Complex I is responsible for the mitochondrial superoxide generation. We propose that the specific NAD(P)H:oxygen superoxide (hydrogen peroxide) producing oxidoreductase(s) poised in equilibrium with NAD(P)H/NAD(P)+ couple should exist in the mitochondrial matrix, if mitochondria are, indeed, participate in ROS-controlled processes under physiologically relevant conditions.

Mitochondrial membrane dynamics, cristae remodelling and apoptosis

Mitochondria form a highly dynamic reticular network in living cells, and undergo continuous fusion/fission events and changes in ultrastructural architecture. Although significant progress has been made in elucidating the molecular events underlying these processes, their relevance to normal cell function remains largely unexplored. Emerging evidence, however, suggests an important role for mitochondrial dynamics in cellular apoptosis. The mitochondria is at the core of the intrinsic apoptosis pathway, and provides a reservoir for protein factors that induce caspase activation and chromosome fragmentation. Additionally, mitochondria modulate Ca2+ homeostasis and are a source of various metabolites, including reactive oxygen species, that have the potential to function as second messengers in response to apoptotic stimuli. One of the mitochondrial factors required for activation of caspases in most intrinsic apoptotic pathways, cytochrome c, is largely sequestered within the intracristae compartment, and must migrate into the boundary intermembrane space in order to allow passage across the outer membrane to the cytosol. Recent evidence argues that inner mitochondrial membrane dynamics regulate this process. Here, we review the contribution of mitochondrial dynamics to the intrinsic apoptosis pathway, with emphasis on the inner membrane.

Mitochondrial free radical generation and lifespan control in the fungal aging model Podospora anserina

In the filamentous fungus Podospora anserina a central role of mitochondria in the control of aging has been repeatedly demonstrated. Interestingly, impairments in cytochrome c oxidase (COX) activity induce an enhancement in the expression of the quinol-oxygen alternative oxidoreductase (AOX) correlating with an extension of lifespan. This effect is thought to be determined by a reduction of the free radical generation in mitochondria. In the current investigation we have analyzed the electron transport chain composition of P. anserina and the superoxide generation rate in wild type s and in mutant grisea, a long-lived mutant with complex IV deficiency. Here we report that, similarly to other fungi, mitochondrial respiration in P. anserina is a combination of standard and alternative routes. A switch in the COX/AOX respiration balance affects the mitochondrial free radical generation. Lower mitochondrial rates of superoxide generation were found in the long-lived mutant, supporting the central role of mitochondrial free radical generation in the lifespan control of P. anserina. The question of how the activity of the alternative respiratory pathway influences the rate of free radical generation in P. anserina mitochondria is discussed.

Tamoxifen and estradiol interact with the flavin mononucleotide site of complex I leading to mitochondrial failure

This study evaluated the action of tamoxifen and estradiol on the function of isolated liver mitochondria. We observed that although tamoxifen and estradiol per se did not affect mitochondrial complexes II, III, or IV, complex I is affected, this effect being more drastic (except for state 4 of respiration) when mitochondria were coincubated with both drugs. Furthermore, using two respiratory chain inhibitors, rotenone and diphenyliodonium chloride, we identified the flavin mononucleotide site of complex I as the target of tamoxifen and/or estradiol action(s). Tamoxifen (25 microm) per se induced a significant increase in hydrogen peroxide production and state 4 of respiration. Additionally, a significant decrease in respiratory control ratio, transmembrane, and depolarization potentials were observed. Estradiol per se decreased carbonyl cyanide p-trifluoromethoxyphenylhydrazone (FCCP)-stimulated respiration, state 3 of respiration, and respiratory control ratio and increased lag phase of repolarization. With the exception of state 4 of respiration whose increase induced by tamoxifen was reversed by the presence of estradiol, the effects of tamoxifen were highly exacerbated when estradiol was present. We observed that 10 microm tamoxifen in the presence of estradiol affected mitochondria significantly by decreasing FCCP-stimulated respiration, state 3 of respiration, respiratory control ratio, and ADP depolarization and increasing the lag phase of repolarization. All of the deleterious effects induced by 25 microm tamoxifen were highly exacerbated in the presence of estradiol. Furthermore, we observed that the effects of both compounds were independent of estrogen receptors because the pure estrogen antagonist ICI 182,780 did not interfere with tamoxifen and/or estradiol detrimental effects. Altogether, our data provide a mechanistic explanation for the multiple cytotoxic effects of tamoxifen including its capacity to destroy tamoxifen-resistant breast cancer cells in the presence of estradiol. This new piece of information provides a basis for the development of new and promising anticancer therapeutic strategies.

Change in mitochondrial membrane potential is the key mechanism in early warm hepatic ischemia-reperfusion injury

The mitochondrion has been proposed to be both a target and a perpetuator of hepatic ischemia-reperfusion (IR) injury because of its reactive oxygen species (ROS) formation. Our hypothesis is that subcellular derangement in mitochondrial function is one of the earliest steps leading to the early IR-mediated loss of hepatocellular integrity. Under chloralhydrate anesthesia (36 mg/kg BW), Sprague-Dawley rats (n=7) were subjected to 40 min of warm hepatic lobular ischemia followed by 60 min reperfusion. Rats (n=7) without hepatic IR were used as controls. The fluorochromes rhodamine 123 and bisbenzimide were administered intravenously for observation of changes in mitochondrial membrane potential and hepatocellular viability, respectively. Intravital fluorescence microscopy (IVFM) was performed prior to ischemia and at 15, 45, and 60 min after reperfusion in the experimental group and at corresponding time points in the control group. A parallel relationship between mitochondrial membrane potential and cell viability as reflected in a concomitant reduction in nuclear and cytoplasmic fluorescence intensity during IR was demonstrated (r2=0.76, P<0.05). The diminution in fluorescence intensities also correlated significantly with the elevation in plasma transaminase activities (r2>0.90, P<0.05). Our data suggested that alteration in mitochondrial membrane potential is a critical subcellular event leading to hepatocellular damage in the early phase of hepatic IR injury.

Mitochondrial leader sequence--plasmid DNA conjugates delivered into mammalian cells by DQAsomes co-localize with mitochondria

In the last decade the increase in therapeutic strategies aimed at mitochondrial targets has resulted in the need for novel delivery systems for the selective delivery of drugs and DNA into mitochondria. In this study, we have continued our efforts towards the development of the first mitochondriotropic drug and DNA delivery system (DQAsomes). Prepared from derivatives of the self-assembling mitochondriotropic bola-amphiphile dequalinium chloride, these vesicles bind and transport DNA to mitochondria in living mammalian cells where upon they have been shown to release the DNA on contact with mitochondrial membranes. We present data to demonstrate that oligonucleotides as well as plasmid DNA conjugated to a mitochondrial leader sequence (MLS) co-localize with mitochondria when delivered into mammalian cells by DQAsomes. In contrast to a commercially available DNA delivery vector, our vesicles appear to have a pronounced specificity for mitochondria. Further, the data strongly suggest that linear conjugates might be better suited to delivery into mitochondria and that in the absence of a mitochondria specific vector, the presence of a MLS-peptide conjugated to the DNA is alone not sufficient to direct the accumulation of DNA at mitochondria.

Cyc2p, a Membrane-bound Flavoprotein Involved in the Maturation of Mitochondrial c-Type Cytochromes

Mitochondrial apocytochrome c and c1 are converted to their holoforms in the intermembrane space by attachment of heme to the cysteines of the CXXCH motif through the activity of assembly factors cytochrome c heme lyase and cytochrome c1 heme lyase (CCHL and CC1HL). The maintenance of apocytochrome sulfhydryls and heme substrates in a reduced state is critical for the ligation of heme. Factors that control the redox chemistry of the heme attachment reaction to apocytochrome c are known in bacteria and plastids but not in mitochondria. We have explored the function of Cyc2p, a candidate redox cytochrome c assembly component in yeast mitochondria. We show that Cyc2p is required for the activity of CCHL toward apocytochrome c and c1 and becomes essential for the heme attachment to apocytochrome c1 carrying a CAPCH instead of CAACH heme binding site. A redox function for Cyc2p in the heme lyase reaction is suggested from 1) the presence of a noncovalently bound FAD molecule in the C-terminal domain of Cyc2p, 2) the localization of Cyc2p in the inner membrane with the FAD binding domain exposed to the intermembrane space, and 3) the ability of recombinant Cyc2p to carry the NADPH-dependent reduction of ferricyanide. We postulate that, in vivo, Cyc2p interacts with CCHL and is involved in the reduction of heme prior to its ligation to apocytochrome c by CCHL.

Acute glutathione depletion restricts mitochondrial ATP export in cerebellar granule neurons

Decreases in GSH pools detected during ischemia sensitize neurons to excitotoxic damage. Thermodynamic analysis predicts that partial GSH depletion will cause an oxidative shift in the thiol redox potential. To investigate the acute bioenergetic consequences, neurons were exposed to monochlorobimane (mBCl), which depletes GSH by forming a fluorescent conjugate. Neurons transfected with redox-sensitive green fluorescent protein showed a positive shift in thiol redox potential synchronous with the formation of the conjugate. Mitochondria within neurons treated with mBCl for 1 h failed to hyperpolarize upon addition of oligomycin to inhibit their ATP synthesis. A decreased ATP turnover was confirmed by monitoring neuronal oxygen consumption in parallel with mitochondrial membrane potential (Deltapsi(m)) and GSH-mBCl formation. mBCl progressively decreased cell respiration, with no effect on mitochondrial proton leak or maximal respiratory capacity, suggesting adequate glycolysis and a functional electron transport chain. This approach to "state 4" could be mimicked by the adenine nucleotide translocator inhibitor bongkrekic acid, which did not further decrease respiration when administered after mBCl. The cellular ATP/ADP ratio was decreased by mBCl, and consistent with mitochondrial ATP export failure, respiration could not respond to an increased cytoplasmic ATP demand by plasma membrane Na(+) cycling; instead, mitochondria depolarized. More prolonged mBCl exposure induced mitochondrial failure, with Deltapsi(m) collapse followed by cytoplasmic Ca(2+) deregulation. The initial bioenergetic consequence of neuronal GSH depletion in this model is thus an inhibition of ATP export, which precedes other forms of mitochondrial dysfunction.

Identification of tyrosine-phosphorylated proteins of the mitochondrial oxidative phosphorylation machinery

The role of some serine/threonine kinases in the regulation of mitochondrial physiology is now well established, but little is known about mitochondrial tyrosine kinases. We showed that tyrosine phosphorylation of rat brain mitochondrial proteins was increased by in vitro addition of ATP and H2O2, and also during in situ ATP production at state 3, and maximal reactive oxygen species production. The Src kinase inhibitor PP2 decreased tyrosine phosphorylation and respiratory rates at state 3. We found that the 39-kDa subunit of complex I was tyrosine phosphorylated, and we identified putative tyrosine-phosphorylated subunits for the other complexes. We also have strong evidence that the FoF1-ATP synthase alpha chain is probably tyrosine-phosphorylated, but demonstrated that the beta chain is not. The tyrosine phosphatase PTP 1B was found in brain but not in muscle, heart or liver mitochondria. Our results suggest that tyrosine kinases and phosphatases are involved in the regulation of oxidative phosphorylation.

Possible involvement of glutamic and/or aspartic acid residue(s) and requirement of mitochondrial integrity for the protective effect of creatine against inhibition of cardiac mitochondrial respiration by methylglyoxal

We had previously shown that creatine exerted a protective effect against inhibition of cardiac mitochondrial respiration by methylglyoxal (SinhaRoy S, Biswas S, Ray M, Ray S. Biochem J 372: 661-669,2003). In the present study, we have investigated the mechanism of this protective effect by specific amino acid modifying reagent and by several compounds, which are structurally related to creatine. The results show that the compounds, which contain guanidine group such as arginine and guanidinopropionic acid, exert a protective effect, which is quantitatively similar to creatine. This result suggests the presence of carboxylic acid(s) such as glutamic and/or aspartic acid(s) in the creatine-binding site, which has been further supported by experiments with N-ethyl-5-phenyl isoxazolium-3'-sulfonate a reagent known to modify these amino acids. Both polarographic and spectrophotometric assays were performed with NADH as respiratory substrate by using a) submitochondrial particles by sonication, b) freeze-thawed mitochondria and c) mitochondria permeabilized by alamethicin treatment. The results of these studies as compared to that of intact mitochondria indicate that structural integrity of mitochondria is essential for the protective effect of creatine.

Study on the toxicity of phenolic and phenoxy herbicides using the submitochondrial particle assay

A simple and rapid in vitro toxicological assay, utilizing submitochondrial particles (SMP), has been used to evaluate the toxic effects of fifteen herbicides belonging to the phenol and phenoxyalkanoic acid chemical classes. The SMP assay allows the quantitative evaluation of the toxicity of compounds with different mechanisms of action: uncouplers, inhibitors of the enzyme complexes involved in reverse electron transfer and in oxidative phosphorylation and chemicals that alter the membrane structure. The two groups of herbicides showed different levels of toxicity. For phenol derivatives, EC50 values ranged from 0.16 microM (ioxynil) to 6.7 microM (2,4-dinitrophenol), whereas for phenoxy herbicides EC50 values ranged from 21 microM (2,4,5-trichlorophenoxyacetic acid, 2,4,5-T) to 110 microM (4-chloro-2-methylphenoxyacetic acid, MCPA). On the average, the toxicity of phenolic compounds is greater than that of phenoxyalkanoic acids by two orders of magnitude. Quantitative structure-activity relationships (QSAR) were developed between EC50 values and various molecular descriptors. The results suggest the existence of different mechanisms of action for the two classes of compounds. The findings obtained for phenolic herbicides are consistent with a protonophoric uncoupling mechanism, whereas for phenoxy herbicides a non-specific mode of action at membrane level can be hypothesized.

Involvement of phospholipid, biomembrane integrity, and NO peroxidase activity in the NO catabolism by cytochrome c oxidase

The physiological regulation of mitochondrial respiration by NO has been reported to result from the reversible binding of NO to the two-electron reduced binuclear center (Fe(2+)(a3)-Cu(1+)(B)) of cytochrome c oxidase (CcO). Although the role of CcO and its derived catalytic intermediates in the catabolism of NO has been documented, little has been established for the enzyme in its fully oxidized state (Fe(3+)(a3)-Cu(2+)(B)). We report: (1) CcO, in its fully oxidized state, represents the major component of the mitochondrial electron transport chain for NO consumption as controlled by the binding of NO to its binuclear center. Phospholipid enhances NO consumption by fully oxidized CcO, whereas the consumption of NO is slowed down by membrane structure and membrane potential when CcO is embedded in the phospholipid bilayer. (2) In the presence of H(2)O(2), CcO was shown to serve as a mitochondria-derived NO peroxidase. A CcO-derived protein radical intermediate was induced and involved in the modulation of NO catabolism.

Release of the mitochondrial enzyme carbamoyl phosphate synthase under septic conditions

To identify sepsis-related dysregulations of protein expression in the liver, we used a baboon model of acute endotoxemia and performed comparative proteome analysis. Treatment with lipopolysaccharide (LPS) was followed by an early but long-lasting (5-48 h) generation of N-terminal fragments of carbamoyl phosphate synthase-1 (CPS-1), an abundant enzyme of the hepatic urea cycle, which is normally located in the mitochondrial matrix. In addition, we developed a new sandwich immunoassay to determine circulating CPS-1 in human and baboons. We found CPS-1 to be induced by LPS and to be released into the circulation of healthy humans and baboons as early as 4 to 5 h after stimulation. Similarly, CPS-1 levels increased after injection of gram-positive bacteria in another baboon model. Enhanced CPS-1 levels were also detected in serum of patients with sepsis. Our data demonstrate fragmentation of CPS-1 in the liver and early increase in circulating CPS-1 levels under septic conditions. We suggest that circulating CPS-1 might serve as a novel serum marker indicating mitochondrial impairment of the liver and/or the small intestine in critically ill patients.

Analysis of mitochondrial generation and release of reactive oxygen species

BACKGROUND

Reactive oxygen species (ROS) are mainly produced in mitochondria and are important contributors to many forms of cell death. ROS also function as second messengers within the cell and may constitute a signaling pathway from mitochondria to the cytoplasm and nucleus. The aim of the present study was to develop a protocol to detect changes in intra- and extramitochondrial releases of ROS, which could be used to analyze the role of mitochondria in cell signaling and cell death.

METHODS

Fluorescence-based assays were used to measure (a) total production of ROS, (b) intramitochondrial ROS, (c) extramitochondrial hydrogen peroxide, and (d) superoxide outside inverted (inside-out) submitochondrial particles. ROS generation in the samples was increased or decreased by the addition of different substrates, enzymes, and inhibitors of the electron transport chain.

RESULTS

The individual assays used were sensitive to increased (e.g., after addition of antimycin A; increased signal) and decreased (ROS scavenging; decreased signal) levels of ROS. In combination, the assays provided information about mitochondrial ROS generation and release dynamics from small samples of isolated mitochondria.

CONCLUSIONS

The combination of fluorescent techniques described is a useful tool to study the role of ROS in cell death and in cellular redox signaling.

Gender dimorphism in rat liver mitochondrial oxidative metabolism and biogenesis

In the present study, we have investigated gender differences in rat liver mitochondrial oxidative metabolism. Total mitochondrial population (M) as well as the heavy (M1), medium (M3), and light (M8) mitochondrial fractions obtained by means of differential centrifugation steps at 1,000, 3,000, and 8,000 g, respectively, were isolated. Electron microscopic analysis was performed and mitochondrial protein content and cardiolipin levels, mitochondrial O(2) flux, ATP synthase activity, mitochondrial membrane potential, and mitochondrial transcription factor A (TFAM) protein levels were measured in each sample. Our results indicate that mitochondria from females have higher protein content and higher cardiolipin levels, greater respiratory and phosphorylative capacities, and more-energized mitochondria in respiratory state 3. Moreover, protein levels of TFAM were four times greater in females than in males. Gender differences in the aforementioned parameters were more patent in the isolated heavy M1 and M3 mitochondrial fractions. The present study demonstrates that gender-related differences in liver mitochondrial function are due mainly to a higher capacity and efficiency of substrate oxidation, likely related to greater mitochondrial machinery in females than in males, which is in accord with greater mitochondrial differentiation in females.

Mitochondrial localization of cellular prion protein (PrPC) invokes neuronal apoptosis in aged transgenic mice overexpressing PrPC

Recent studies suggest that the disease isoform of prion protein (PrPSc) is non-neurotoxic in the absence of cellular isoform of prion protein (PrPC), indicating that PrPC may participate directly in the neurodegenerative damage by itself. Meanwhile, transgenic mice harboring a high-copy-number of wild-type mouse (Mo) PrPC develop a spontaneous neurological dysfunction in an age-dependent manner, even without inoculation of PrPSc and thus, investigations of these aged transgenic mice may lead to the understanding how PrPC participate in the neurotoxic property of PrP. Here we demonstrate mitochondria-mediated neuronal apoptosis in aged transgenic mice overexpressing wild-type MoPrPC (Tg(MoPrP)4053/FVB). The aged mice exhibited an aberrant mitochondrial localization of PrPC concomitant with decreased proteasomal activity, while younger littermates did not. Such aberrant mitochondrial localization was accompanied by decreased mitochondrial manganese superoxide dismutase (Mn-SOD) activity, cytochrome c release into the cytosol, caspase-3 activation, and DNA fragmentation, most predominantly in hippocampal neuronal cells. Following cell culture studies confirmed that decrease in the proteasomal activity is fundamental for the PrPC-related, mitochondria-mediated apoptosis. Hence, the neurotoxic property of PrPC could be explained by the mitochondria-mediated neuronal apoptosis, at least in part.

Role of the novel metallopeptidase Mop112 and saccharolysin for the complete degradation of proteins residing in different subcompartments of mitochondria

Mitochondria harbor a conserved proteolytic system that mediates the complete degradation of organellar proteins. ATP-dependent proteases, like a Lon protease in the matrix space and m- and i-AAA proteases in the inner membrane, degrade malfolded proteins within mitochondria and thereby protect the cell against mitochondrial damage. Proteolytic breakdown products include peptides and free amino acids, which are constantly released from mitochondria. It remained unclear, however, whether the turnover of malfolded proteins involves only ATP-dependent proteases or also oligopeptidases within mitochondria. Here we describe the identification of Mop112, a novel metallopeptidase of the pitrilysin family M16 localized in the intermembrane space of yeast mitochondria. This peptidase exerts important functions for the maintenance of the respiratory competence of the cells that overlap with the i-AAA protease. Deletion of MOP112 did not affect the stability of misfolded proteins in mitochondria, but resulted in an increased release from the organelle of peptides, generated upon proteolysis of mitochondrial proteins. We find that the previously described metallopeptidase saccharolysin (or Prd1) exerts a similar function in the intermembrane space. The identification of peptides released from peptidase-deficient mitochondria by mass spectrometry indicates a dual function of Mop112 and saccharolysin: they degrade peptides generated upon proteolysis of proteins both in the intermembrane and matrix space and presequence peptides cleaved off by specific processing peptidases in both compartments. These results suggest that the turnover of mitochondrial proteins is mediated by the sequential action of ATP-dependent proteases and oligopeptidases, some of them localized in the intermembrane space.

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

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

Reactivation of the alternative oxidase of Yarrowia lipolytica by nucleoside monophosphates

The study of the effect of nucleoside phosphates on the activity of cyanide-resistant oxidase in the mitochondria and submitochondrial particles of Yarrowia lipolytica showed that adenosine monophosphate (5'-AMP, AMP) did not stimulate the respiration of intact mitochondria. The incubation of mitochondria at room temperature (25 degrees C) for 3-5 h or their treatment with ultrasound, phospholipase A, and the detergent Triton X-100 at a low temperature inactivated the cyanide-resistant alternative oxidase. The inactivated alternative oxidase could be reactivated with AMP. The reactivating effect of AMP was enhanced by azolectin. Some other nucleoside phosphates also showed reactivating ability in the following descending order: AMP = GMP > GDP > GTP > MP > IMP. The apparent K(m) values for AMP in reactivation of the alternative oxidase of submitochondrial particles or mitochondria treated with Triton X-100 and incubated at 25 degrees C were calculated. Physiological aspects of activation of the alternative oxidase are discussed in connection with the impairment of electron transfer through the cytochrome pathway.

Mitochondrial permeability transition in cardiomyocyte apoptosis during acute graft rejection

Evidence indicates that acute cardiac graft rejection is associated with cardiomyocyte apoptosis. Mitochondrial permeability transition (MPT) induces apoptotic cell death. We sought to determine whether MPT might play a role in cardiomyocyte apoptosis in the rat model of heterotopic cardiac transplantation. Syngenic and allogenic transplantations were performed, and both native and grafted hearts were harvested 3 or 5 d after transplantation for detection of acute rejection, assessment of Ca(2+)-induced MPT, and myocardial apoptosis by TUNEL staining and caspase 3 activity. Allogenic grafts developed severe acute rejection at day 5 with concomitant cardiomyocyte apoptosis (apoptotic index: 7.1 +/- 1.0% vs. 1.0 +/- 0.2% in syngenic hearts, and caspase 3 activity: 38 +/- 25 vs. 5 +/- 9 nmol/mg, in allogenic vs. syngenic grafts, respectively). At day 5, Ca(2+)-induced MPT was dramatically altered in allogenic when compared with syngenic grafts (mean Ca(2+) overload averaged 0 +/- 20 vs. 280 +/- 30 microM in allogenic and syngenic grafts, respectively). NIM811, a nonimmunosuppressive derivative of cyclosporin A (CsA), that specifically inhibits the MPT pore, did not alter acute rejection, but significantly delayed Ca(2+)-induced MPT pore opening, attenuated caspase 3 activity and cardiomyocyte apoptosis in allogenic grafts. This suggests that mitochondrial permeability transition pore opening may play an important role in cardiomyocyte apoptosis associated with acute cardiac graft rejection.

[Activation of the alternative oxidase of Yarrowia lipolytica by adenosine 5'-monophosphate]

The study of the effect of nucleoside phosphates on the activity of cyanide-resistant oxidase in the mitochondria and the submitochondrial particles of Yarrowia lipolytica showed that adenosine monophosphate (5'-AMP, AMP) did not stimulate the respiration of the intact mitochondria. The incubation of the mitochondria at room temperature (25 degrees C) for 3-5 h or their treatment with ultrasound, phospholipase A, and detergent Triton X-100 at a low temperature inactivated the cyanide-resistant alternative oxidase. The inactivated alternative oxidase could be reactivated by AMP. The reactivating effect of AMP was enhanced by azolectin. Some other nucleoside phosphates also showed reactivating ability in the following descending order. AMP = GMP > GDP > GTP > XMP > IMP. The apparent reaction rate constant Km for AMP upon the reactivation of the alternative oxidase of mitochondria treated with Triton X-100 or incubated at 25 degrees C was 12.5 and 20 microM, respectively. The Km for AMP upon the reactivation of the alternative oxidase of submitochondrial particles was 15 microM. During the incubation of yeast cells under conditions promoting the development of alternative oxidase, the content of adenine nucleotides (AMP, ADP, and ATP) in the cells and their respiration tended to decrease. The subsequent addition of cyanide to the cells activated their respiration, diminished the intracellular content of ATP three times, and augmented the content of AMP five times. These data suggest that the stimulation of cell respiration by cyanide may be due to the activation of alternative oxidase by AMP.

Aspects, mechanism, and biological relevance of mitochondrial protein nitration sustained by mitochondrial nitric oxide synthase

The goal of this study was to explore the occurrence of nitrated proteins in mitochondria given that these organelles are endowed with a mitochondrial nitric oxide (NO·) synthase and considering the important role that mitochondria have in energy metabolism. Our hypothesis is that nitration of proteins constitutes a posttranslational modification by which NO· exhibits long-term effects above and beyond those bioregulatory ones mediated through the interaction with cytochrome c oxidase. Our studies are aimed at understanding the mechanisms underlying the nitration of proteins in mitochondria and the biological significance of such a process in the cellular milieu. On promoting a sustained NO· production by mitochondria, we investigated various aspects of protein nitration. Among them, the localization of nitrated proteins in mitochondrial subfractions, the identification of nitrated proteins through proteomic approaches, the characterization of affected pathways, and depiction of a target sequence. The biological relevance was analyzed by considering the turnover of native and nitrated proteins. In this regard, mitochondrial dysfunction, ensuing nitrative stress, may be envisioned as the result of accumulation of nitrated proteins, resulting from an overproduction of endogenous NO· (this study), a failure in the proteolytic system to catabolize modified proteins, or a combination of both. Finally, this study allows one to gain understanding on the mechanism and nitrating species underlying mitochondrial protein nitration.

Functional cooperation and separation of translocators in protein import into mitochondria, the double-membrane bounded organelles

Nearly all mitochondrial proteins are synthesized in the cytosol and subsequently imported into mitochondria with the aid of translocators: the TOM complex in the outer membrane, and the TIM23 and TIM22 complexes in the inner membrane. The TOM complex and the TIM complexes cooperate to achieve efficient transport of proteins to the matrix or into the inner membrane and several components, including Tom22, Tim23, Tim50 and small Tim proteins, mediate functional coupling of the two translocator systems. The TOM complex can be disconnected from the TIM systems and their energy sources (ATP and DeltaPsi), however, using alternative mechanisms to achieve vectorial protein translocation across the outer membrane