Oxidatively damaged proteins of heart mitochondrial electron transport complexes

The on-off switches of the mitochondrial uncoupling proteins

Mitochondrial uncoupling proteins disengage substrate oxidation from ADP phosphorylation by dissipating the proton electrochemical gradient that is required for ATP synthesis. In doing this, the archetypal uncoupling protein, UCP1, mediates adaptive thermogenesis. By contrast, its paralogues UCP2 and UCP3 are not thought to mediate whole body thermogenesis in mammals. Instead, they have been implicated in a variety of physiological and pathological processes, including protection from oxidative stress, negative regulation of glucose sensing systems and the adaptation of fatty acid oxidation capacity to starving. Although much work has been devoted to how these proteins are activated, little is known of the mechanisms that reverse this activation.

Substrate-specific derangements in mitochondrial metabolism and redox balance in the atrium of the type 2 diabetic human heart

OBJECTIVES

The aim of this study was to determine the impact of diabetes on oxidant balance and mitochondrial metabolism of carbohydrate- and lipid-based substrates in myocardium of type 2 diabetic patients.

BACKGROUND

Heart failure represents a major cause of death among diabetic patients. It has been proposed that derangements in cardiac metabolism and oxidative stress may underlie the progression of this comorbidity, but scarce evidence exists in support of this mechanism in humans.

METHODS

Mitochondrial oxygen (O(2)) consumption and hydrogen peroxide (H(2)O(2)) emission were measured in permeabilized myofibers prepared from samples of the right atrial appendage obtained from nondiabetic (n = 13) and diabetic (n = 11) patients undergoing nonemergent coronary artery bypass graft surgery.

RESULTS

Mitochondria in atrial tissue of type 2 diabetic individuals show a sharply decreased capacity for glutamate and fatty acid-supported respiration, in addition to an increased content of myocardial triglycerides, as compared to nondiabetic patients. Furthermore, diabetic patients show an increased mitochondrial H(2)O(2) emission during oxidation of carbohydrate- and lipid-based substrates, depleted glutathione, and evidence of persistent oxidative stress in their atrial tissue.

CONCLUSIONS

These findings are the first to directly investigate the effects of type 2 diabetes on a panoply of mitochondrial functions in the human myocardium using cellular and molecular approaches, and they show that mitochondria in diabetic human hearts have specific impairments in maximal capacity to oxidize fatty acids and glutamate, yet increased mitochondrial H(2)O(2) emission, providing insight into the role of mitochondrial dysfunction and oxidative stress in the pathogenesis of heart failure in diabetic patients.

Importance of the bioenergetic reserve capacity in response to cardiomyocyte stress induced by 4-hydroxynonenal

Mitochondria play a critical role in mediating the cellular response to oxidants formed during acute and chronic cardiac dysfunction. It is widely assumed that, as cells are subjected to stress, mitochondria are capable of drawing upon a 'reserve capacity' which is available to serve the increased energy demands for maintenance of organ function, cellular repair or detoxification of reactive species. This hypothesis further implies that impairment or depletion of this putative reserve capacity ultimately leads to excessive protein damage and cell death. However, it has been difficult to fully evaluate this hypothesis since much of our information about the response of the mitochondrion to oxidative stress derives from studies on mitochondria isolated from their cellular context. Therefore the goal of the present study was to determine whether 'bioenergetic reserve capacity' does indeed exist in the intact myocyte and whether it is utilized in response to stress induced by the pathologically relevant reactive lipid species HNE (4-hydroxynonenal). We found that intact rat neonatal ventricular myocytes exhibit a substantial bioenergetic reserve capacity under basal conditions; however, on exposure to pathologically relevant concentrations of HNE, oxygen consumption was increased until this reserve capacity was depleted. Exhaustion of the reserve capacity by HNE treatment resulted in inhibition of respiration concomitant with protein modification and cell death. These data suggest that oxidized lipids could contribute to myocyte injury by decreasing the bioenergetic reserve capacity. Furthermore, these studies demonstrate the utility of measuring the bioenergetic reserve capacity for assessing or predicting the response of cells to stress.

Mitochondrial permeability transition pore opening as a promising therapeutic target in cardiac diseases

In addition to their central role in ATP synthesis, mitochondria play a critical role in cell death. Oxidative stress accompanied by calcium overload, ATP depletion, and elevated phosphate levels induces mitochondrial permeability transition (MPT) with formation of nonspecific MPT pores (MPTP) in the inner mitochondrial membrane. Pore opening results in mitochondrial dysfunction with uncoupled oxidative phosphorylation and ATP hydrolysis, ultimately leading to cell death. For the past 20 years, three proteins have been accepted as key structural components of the MPTP: adenine nucleotide translocase (ANT) in the inner membrane, cyclophilin D (CyP-D) in the matrix, and the voltage-dependent anion channel (VDAC) in the outer membrane. However, most recent studies have questioned the molecular identity of the pores. Genetic studies have eliminated the VDAC as an essential component of MPTP and attributed a regulatory (rather than structural) role to ANT. Currently, the phosphate carrier appears to play a crucial role in MPTP formation. MPTP opening has been examined extensively in cardiac pathological conditions, including ischemia/reperfusion as well as heart failure. Accordingly, MPTP is accepted as a therapeutic target for both pharmacological and conditional strategies to block pore formation by direct interaction with MPTP components or indirectly by decreasing MPTP inducers. Inhibition of MPTP opening by reduction of CyP-D activity by nonimmunosuppressive analogs of cyclosporine A or sanglifehrin A, as well as attenuation of reactive oxygen species accumulation through mitochondria-targeted antioxidants, is the most promising. This review outlines our current knowledge of the structure and function of the MPTP and describes possible approaches for cardioprotection.

Huperzine A protects isolated rat brain mitochondria against beta-amyloid peptide

Our previous work in cells and animals showed that mitochondria are involved in the neuroprotective effect of huperzine A (HupA). In this study, the effects of HupA on isolated rat brain mitochondria were investigated. In addition to inhibiting the Abeta(25-35) (40 microM)-induced decrease in mitochondrial respiration, adenosine 5'-triphosphate (ATP) synthesis, enzyme activity, and transmembrane potential, HupA (0.01 or 0.1 microM) effectively prevented Abeta-induced mitochondrial swelling, reactive oxygen species increase, and cytochrome c release. More interestingly, administration of HupA to isolated mitochondria promoted the rate of ATP production and blocked mitochondrial swelling caused by normal osmosis. These results indicate that HupA protects mitochondria against Abeta at least in part by preserving membrane integrity and improving energy metabolism. These direct effects on mitochondria further extend the noncholinergic functions of HupA.

Mitochondrial reactive oxygen species production in excitable cells: modulators of mitochondrial and cell function

The mitochondrion is a major source of reactive oxygen species (ROS). Superoxide (O(2)(*-)) is generated under specific bioenergetic conditions at several sites within the electron-transport system; most is converted to H(2)O(2) inside and outside the mitochondrial matrix by superoxide dismutases. H(2)O(2) is a major chemical messenger that, in low amounts and with its products, physiologically modulates cell function. The redox state and ROS scavengers largely control the emission (generation scavenging) of O(2)(*-). Cell ischemia, hypoxia, or toxins can result in excess O(2)(*-) production when the redox state is altered and the ROS scavenger systems are overwhelmed. Too much H(2)O(2) can combine with Fe(2+) complexes to form reactive ferryl species (e.g., Fe(IV) = O(*)). In the presence of nitric oxide (NO(*)), O(2)(*-) forms the reactant peroxynitrite (ONOO(-)), and ONOOH-induced nitrosylation of proteins, DNA, and lipids can modify their structure and function. An initial increase in ROS can cause an even greater increase in ROS and allow excess mitochondrial Ca(2+) entry, both of which are factors that induce cell apoptosis and necrosis. Approaches to reduce excess O(2)(*-) emission include selectively boosting the antioxidant capacity, uncoupling of oxidative phosphorylation to reduce generation of O(2)(*-) by inducing proton leak, and reversibly inhibiting electron transport. Mitochondrial cation channels and exchangers function to maintain matrix homeostasis and likely play a role in modulating mitochondrial function, in part by regulating O(2)(*-) generation. Cell-signaling pathways induced physiologically by ROS include effects on thiol groups and disulfide linkages to modify posttranslationally protein structure to activate/inactivate specific kinase/phosphatase pathways. Hypoxia-inducible factors that stimulate a cascade of gene transcription may be mediated physiologically by ROS. Our knowledge of the role played by ROS and their scavenging systems in modulation of cell function and cell death has grown exponentially over the past few years, but we are still limited in how to apply this knowledge to develop its full therapeutic potential.

High-throughput liquid-liquid fractionation of multiple protein post-translational modifications

Post-translational protein modifications have contributed significantly to the identification of macromolecular biomarkers of biological processes. We have modified a two-dimensional HPLC system (Beckman Coulter PF2D ProteomeLab) to create proteome maps of post-translational protein modifications. This system resolves complex protein mixtures by anion exchange chromatofocusing in the first dimension and hydrophobicity (reverse phase chromatography) in the second dimension. The simultaneous identification of multiple protein modifications, accomplished by incorporating a photo diode array (PDA) detector into the PF2D system, facilitates the simultaneous production of three-dimensional proteome maps and visualization of both unmodified and post-translationally modified (PTM) proteins at their signature wavelengths within the proteome. We describe procedures for the simultaneous resolution of proteome maps, the identification of proteins modified by nitration, carbonylation, and phosphorylation, and proteins with unique spectra such as the heme containing proteins.

Multiple measures of functionality exhibit progressive decline in a parallel, stochastic fashion in Drosophila Sod2 null mutants

Oxidative damage has been proposed as an important factor in the progression of pathological and non-pathological age-related functional declines. Here, we examine functional deterioration in short-lived flies mutant for the mitochondrial antioxidant Manganese Superoxide Dismutase (Sod2). We find that the decline of several functional measures of aging occurs, in an accelerated fashion, in Sod2 mutants. Olfactory behavior, locomotor ability and cardiac performance were all seen to decline rapidly in Sod2 mutants. On average, functional declines in Sod2 mutants occur in a pattern similar to that seen in late-life Drosophila with a normal complement of Sod2. In longitudinal experiments, however, we find that functional failures occur in every possible sequence in Sod2 mutants. Significantly, failure of these functional measures is not irreversible, as spontaneous functional recovery was sometimes observed. These findings support a model where ROS-related damage strikes at multiple organ systems in parallel, rather than a "chain of dominos" model, in which primary organ failure contributes to the deterioration of further organ systems.

Is mitochondrial dysfunction a cause of insulin resistance?

Insulin resistance is a key defect associated with obesity and type-2 diabetes. The precise factors that lead to insulin resistance have not been elucidated fully, but there is a strong association between insulin resistance and inappropriate lipid accumulation in insulin-target tissues. Over the past decade, several studies have reported changes in markers of mitochondrial metabolism in insulin-resistant individuals. These observations have led to the theory that compromised mitochondrial oxidative function, particularly in skeletal muscle, causes excess lipid deposition and the development of insulin resistance. Here, we review the latest findings regarding the link between mitochondrial metabolism and insulin action and, in particular, highlight several recent studies that call into question the cause-and-effect relationship between mitochondrial dysfunction and insulin resistance.

Theoretical and experimental studies of tyrosyl hydroperoxide formation in the presence of H-bond donors

Oxidative damage to biomolecules such as lipids, proteins, nucleotides, and sugars has been implicated in the pathogenesis of various diseases. Superoxide radical anion (O 2 (*-)) addition to nitrones bearing an amide N-H has been shown to be more favored as compared to other nitrones [ Villamena, F. A. , ( 2007) J. Am. Chem. Soc. 129, 8177- 8191 ]. It has also been demonstrated by others [ Winterbourn, C. C. , ( 2004) Biochem. J. 381, 241- 248 ] that O 2 (*-) addition to tyrosine to form hydroperoxide is favored in the presence of basic amino groups, but the mechanism for this observation remains obscure. We, therefore, hypothesized that the alpha-effect resulting from the interaction of O 2 (*-) with N-H can play a crucial role in the enhancement of hydroperoxide formation. Understanding this phenomenon is important in the elucidation of mechanisms leading to oxidative stress in cellular systems. Computational (at the PCM/B3LYP/6-31+G**//B3LYP/6-31G level of theory) as well as experimental studies were carried out to shed insights into the effect of amide or amino N-H on the enhancement (or stabilization) of hydroperoxide formation in tyrosine. H-bond interaction of amino acid group with O 2 (*-) results in the perturbation of the spin and charge densities of O 2 (*-). A similar phenomenon has been predicted for non-amino acids bearing H-bond donor groups. Using the FOX assay, tyrosyl hydroperoxide formation was enhanced in the presence of H-bond donors from amino acids and non-amino acids. The role of H-bonding in either stabilizing the hydroperoxide adduct or facilitating O 2 (*-) addition via an alpha-effect was further theoretically investigated, and results show that the latter mechanism is more thermodynamically preferred. This study provides new mechanistic insights in the initiation of oxidative modification to tyrosyl radical.

Age-related alterations in oxidatively damaged proteins of mouse skeletal muscle mitochondrial electron transport chain complexes

Age-associated mitochondrial dysfunction is a major source of reactive oxygen species (ROS) and oxidative modification to proteins. Mitochondrial electron transport chain (ETC) complexes I and III are the sites of ROS production and we hypothesize that proteins of the ETC complexes are primary targets of ROS-mediated modification which impairs their structure and function. The pectoralis, primarily an aerobic red muscle, and quadriceps, primarily an anaerobic white muscle, have different rates of respiration and oxygen-carrying capacity, and hence, different rates of ROS production. This raises the question of whether these muscles exhibit different levels of oxidative protein modification. Our studies reveal that the pectoralis shows a dramatic age-related decline in almost all complex activities that correlates with increased oxidative modification. Similar complex proteins were modified in the quadriceps, at a significantly lower level with less change in enzyme and ETC coupling function. We postulate that mitochondrial ROS causes damage to specific ETC subunits which increases with age and leads to further mitochondrial dysfunction. We conclude that physiological characteristics of the pectoralis vs quadriceps may play a role in age-associated rate of mitochondrial dysfunction and in the decline in tissue function.

Astaxanthin protects mesangial cells from hyperglycemia-induced oxidative signaling

Astaxanthin (ASX) is a carotenoid that has potent protective effects on diabetic nephropathy in mice model of type 2 diabetes. In this study, we investigated the protective mechanism of ASX on the progression of diabetic nephropathy using an in vitro model of hyperglycemia, focusing on mesangial cells. Normal human mesangial cells (NHMCs) were cultured in the medium containing normal (5 mM) or high (25 mM) concentrations of D-glucose. Reactive oxygen species (ROS) production, the activation of nuclear transcription factors such as nuclear factor kappa B (NFkappaB) and activator protein-1 (AP-1), and the expression/production of transforming growth factor-beta 1 (TGFbeta(1)) and monocyte chemoattractant protein-1 (MCP-1) were evaluated in the presence or absence of ASX. High glucose (HG) exposure induced significant ROS production in mitochondria of NHMCs, which resulted in the activation of transcription factors, and subsequent expression/production of cytokines that plays an important role in the mesangial expansion, an important event in the pathogenesis of diabetic nephropathy. ASX significantly suppressed HG-induced ROS production, the activation of transcription factors, and cytokine expression/production by NHMCs. In addition, ASX accumulated in the mitochondria of NHMCs and reduced the production of ROS-modified proteins in mitochondria. ASX may prevent the progression of diabetic nephropathy mainly through ROS scavenging effect in mitochondria of mesangial cells and thus is expected to be very useful for the prevention of diabetic nephropathy.

Is the failing heart out of fuel or a worn engine running rich? A study of mitochondria in old spontaneously hypertensive rats

Hypertension now affects about 600 million people worldwide and is a leading cause of death in the Western world. The spontaneously hypertensive rat (SHR), provides a useful model to investigate hypertensive heart failure (HF). The SHR model replicates the clinical progression of hypertension in humans, wherein early development of hypertension is followed by a long stable period of compensated cardiac hypertrophy that slowly progresses to HF. Although the hypertensive failing heart generally shows increased substrate preference towards glucose and impaired mitochondrial function, the cause-and-effect relationship between these characteristics is incompletely understood. To explore these pathogenic processes, we compared cardiac mitochondrial proteomes of 20-month-old SHR and Wistar-Kyoto controls by iTRAQ-labelling combined with multidimensional LC/MS/MS. Of 137 high-scoring proteins identified, 79 differed between groups. Changes were apparent in several metabolic pathways, chaperone and antioxidant systems, and multiple subunits of the oxidative phosphorylation complexes were increased (complexes I, III and IV) or decreased (complexes II and V) in SHR heart mitochondria. Respiration assays on skinned fibres and isolated mitochondria showed markedly lower respiratory capacity on succinate. Enzyme activity assays often also showed mismatches between increased protein expression and activities suggesting elevated protein expression may be compensatory in the face of pathological stress.

Mitochondria and ageing in Drosophila

Studies in different organisms have revealed that ageing is a complex process involving a tight regulation of gene expression. Among other features, ageing organisms generally display an increased oxidative stress and a decreased mitochondrial function. The increase in oxidative stress can be attributable to reactive oxygen species, which are mainly produced by mitochondria as a by-product of energy metabolism. Consistent with these data, mitochondria have been suggested to play a significant role in lifespan determination. The fruitfly Drosophila melanogaster is a well-suited organism to study ageing as it is relatively short-lived, mainly composed of post-mitotic cells, has sequenced nuclear and mitochondrial genomes, and multiple genetic tools are available. It has been used in genome-wide studies to unveil the molecular signature of ageing, in different feeding and dietary restriction protocols and in overexpression and down-regulation studies to examine the effect of specific compounds or genes/proteins on lifespan. Here we review the various features linking mitochondria and ageing in Drosophila melanogaster.

High membrane potential promotes alkenal-induced mitochondrial uncoupling and influences adenine nucleotide translocase conformation

Mitochondria generate reactive oxygen species, whose downstream lipid peroxidation products, such as 4-hydroxynonenal, induce uncoupling of oxidative phosphorylation by increasing proton leak through mitochondrial inner membrane proteins such as the uncoupling proteins and adenine nucleotide translocase. Using mitochondria from rat liver, which lack uncoupling proteins, in the present study we show that energization (specifically, high membrane potential) is required for 4-hydroxynonenal to activate proton conductance mediated by adenine nucleotide translocase. Prolonging the time at high membrane potential promotes greater uncoupling. 4-Hydroxynonenal-induced uncoupling via adenine nucleotide translocase is prevented but not readily reversed by addition of carboxyatractylate, suggesting a permanent change (such as adduct formation) that renders the translocase leaky to protons. In contrast with the irreversibility of proton conductance, carboxyatractylate added after 4-hydroxynonenal still inhibits nucleotide translocation, implying that the proton conductance and nucleotide translocation pathways are different. We propose a model to relate adenine nucleotide translocase conformation to proton conductance in the presence or absence of 4-hydroxynonenal and/or carboxyatractylate.

Age-related alterations in oxidatively damaged proteins of mouse heart mitochondrial electron transport chain complexes

Mitochondrially generated ROS increase with age and are a major factor that damages proteins by oxidative modification. Accumulation of oxidatively damaged proteins has been implicated as a causal factor in the age-associated decline in tissue function. Mitochondrial electron transport chain (ETC) complexes I and III are the principle sites of ROS production, and oxidative modifications to their complex subunits inhibit their in vitro activity. We hypothesize that mitochondrial complex subunits may be primary targets for modification by ROS, which may impair normal complex activity. This study of heart mitochondria from young, middle-aged, and old mice reveals that there is an age-related decline in complex I and V activity that correlates with increased oxidative modification to their subunits. The data also show a specificity for modifications of the ETC complex subunits, i.e., several proteins have more than one type of adduct. We postulate that the electron leakage from ETC complexes causes specific damage to their subunits and increased ROS generation as oxidative damage accumulates, leading to further mitochondrial dysfunction, a cyclical process that underlies the progressive decline in physiologic function of the aged mouse heart.

Role of mitochondrial dysfunction in insulin resistance

Insulin resistance is characteristic of obesity, type 2 diabetes, and components of the cardiometabolic syndrome, including hypertension and dyslipidemia, that collectively contribute to a substantial risk for cardiovascular disease. Metabolic actions of insulin in classic insulin target tissues (eg, skeletal muscle, fat, and liver), as well as actions in nonclassic targets (eg, cardiovascular tissue), help to explain why insulin resistance and metabolic dysregulation are central in the pathogenesis of the cardiometabolic syndrome and cardiovascular disease. Glucose and lipid metabolism are largely dependent on mitochondria to generate energy in cells. Thereby, when nutrient oxidation is inefficient, the ratio of ATP production/oxygen consumption is low, leading to an increased production of superoxide anions. Reactive oxygen species formation may have maladaptive consequences that increase the rate of mutagenesis and stimulate proinflammatory processes. In addition to reactive oxygen species formation, genetic factors, aging, and reduced mitochondrial biogenesis all contribute to mitochondrial dysfunction. These factors also contribute to insulin resistance in classic and nonclassic insulin target tissues. Insulin resistance emanating from mitochondrial dysfunction may contribute to metabolic and cardiovascular abnormalities and subsequent increases in cardiovascular disease. Furthermore, interventions that improve mitochondrial function also improve insulin resistance. Collectively, these observations suggest that mitochondrial dysfunction may be a central cause of insulin resistance and associated complications. In this review, we discuss mechanisms of mitochondrial dysfunction related to the pathophysiology of insulin resistance in classic insulin-responsive tissue, as well as cardiovascular tissue.

Age-related increases in oxidatively damaged proteins of mouse kidney mitochondrial electron transport chain complexes

Mitochondrial dysfunction generates reactive oxygen species (ROS) which damage essential macromolecules. Oxidative modification of proteins, DNA, and lipids has been implicated as a major causal factor in the age-associated decline in tissue function. Mitochondrial electron transport chain complexes I and III are the principal sites of ROS production, and oxidative modifications to the complex subunits inhibit their in vitro activity. Therefore, we hypothesize that mitochondrial complex subunits may be primary targets for oxidative damage by ROS which may impair normal complex activity by altering their structure/function leading to mitochondrial dysfunction associated with aging. This study of kidney mitochondria from young, middle-aged, and old mice reveals that there are functional decreases in complexes I, II, IV, and V between aged compared to young kidney mitochondria and these functional declines directly correlate with increased oxidative modification to particular complex subunits. We postulate that the electron leakage from complexes causes specific damage to their subunits and increased ROS generation as oxidative damage accumulates, leading to further mitochondrial dysfunction, a cyclical process that underlies the progressive decline in physiologic function seen in aged mouse kidney. In conclusion, increasing mitochondrial dysfunction may play a key role in the age-associated decline in tissue function.

Identification of carbonylated proteins from enriched rat skeletal muscle mitochondria using affinity chromatography-stable isotope labeling and tandem mass spectrometry

We describe a strategy for the identification of carbonylated proteins from complex protein mixtures that combines biotin hydrazide labeling of protein carbonyl groups, avidin affinity chromatography, multiplexed iTRAQ reagent stable isotope labeling, and analysis using pulsed Q dissociation (PQD) operation on an LTQ linear ion trap mass spectrometer. This strategy provided the ability to distinguish biotin hydrazide labeled, avidin purified, carbonylated proteins from non-carbonylated background proteins with affinity for the avidin column, derived from a control sample. Applying this strategy to the identification of crudely enriched rat skeletal muscle mitochondrial protein isolates, we generated a catalogue of over 200 carbonylated proteins by virtue of their quantitative enrichment compared to the control sample. The catalogue contains many mitochondrial localized proteins shown to be susceptible to carbonyl modification for the first time, including numerous transmembrane proteins involved in oxidative phosphorylation. Other oxidative modifications (e.g. nitrosylation, hydroxylation) were also identified on many of the carbonylated proteins, providing further evidence of the susceptibility of these proteins to oxidative damage. The results also demonstrate the utility of PQD operation on the LTQ instrument for quantitative analysis of iTRAQ reagent-labeled peptide mixtures, as well as the quantitative reproducibility of the avidin-affinity enrichment method.

The Cytotoxic lipid peroxidation product 4-hydroxy-2-nonenal covalently modifies a selective range of proteins linked to respiratory function in plant mitochondria

Plants encounter a variety of environmental stresses that affect their cellular machinery and that they adapt to on a daily basis. Lipid peroxidation is one consequence, at the cellular level, of such stresses and yields cytotoxic lipid aldehydes, including 4-hydroxy-2-nonenal (HNE), that react with specific sites in proteins, leading to diverse changes in protein function and/or stability. We have assessed the sensitivity of plant mitochondrial proteins to HNE modification, using one-dimensional and two-dimensional denaturing PAGE and blue native-PAGE coupled to immunological detection and tandem mass spectrometry identification. A select range of proteins was modified by exogenous application of HNE to mitochondria isolated from Arabidopsis cell cultures. These included a number of proteins that directly interact with the ubiquinone pool, as well as a number of soluble matrix proteins. Mitochondria isolated from cell cultures following hydrogen peroxide, antimycin A, or menadione treatment had significantly reduced respiratory capacity and elevated levels of HNE adduction to specific subsets of proteins. Targets identified included the proteins affected by direct application of HNE but also some new proteins, including a number of matrix dehydrogenases, the inner membrane adenine nucleotide translocator, and the outer membrane voltage-dependent anion channel. Degradation products of some proteins were also found to be HNE adducted, suggesting a link between HNE adduction and protein turnover. Some of the major enzyme complexes that were HNE adducted did not show demonstrable changes in their maximal activity measured with artificial acceptors, but changes did occur in associations between respiratory chain complexes following stress treatments.

Mitochondrial-nuclear cross-talk in the aging and failing heart

HYPOTHESIS

Damage to heart mitochondrial structure and function occur with aging, and in heart failure (HF). However, the extent of mitochondrial dysfunction, the expression of mitochondrial and nuclear genes, and their cross-talk is not known.

OBSERVATIONS

Several observations have suggested that somatic mutations in mitochondrial DNA (mtDNA), induced by reactive oxygen species (ROS), appear to be the primary cause of energy decline, and that the generation of ROS is mainly the product of the mitochondrial respiratory chain. The free radical theory of aging, that could also be applied to HF, and in particular the targeting of mtDNA is supported by a plurality of observations from both animal and clinical studies showing decreased mitochondrial function, increased ROS levels and mtDNA mutations in the aging heart.

DISCUSSION

Aging and HF with their increased ROS-induced defects in mtDNA, including base modifications and frequency of mtDNA deletions, might be expected to cause increased errors or mutations in mtDNA-encoded enzyme subunits, resulting in impaired oxidative phosphorylation and defective electron transport chain (ETC) activity which in turn creates more ROS. These events in both the aging and failing heart involve substantial nuclear-mitochondrial interaction, which is further illustrated in the progression of myocardial apoptosis. In this review the cross-talk between the nucleus and the mitochondrial organelle will be examined based on a number of animal and clinical studies, including our own.

The role of nitric oxide in muscle fibers with oxidative phosphorylation defects

NO has been pointed as an important player in the control of mitochondrial respiration, especially because of its inhibitory effect on cytochrome c oxidase (COX). However, all the events involved in this control are still not completely elucidated. We demonstrate compartmentalized abnormalities on nitric oxide synthase (NOS) activity on muscle biopsies of patients with mitochondrial diseases. NOS activity was reduced in the sarcoplasmic compartment in COX deficient fibers, whereas increased activity was found in the sarcolemma of fibers with mitochondrial proliferation. We observed increased expression of neuronal NOS (nNOS) in patients and a correlation between nNOS expression and mitochondrial content. Treatment of skeletal muscle culture with an NO donor induced an increase in mitochondrial content. Our results indicate specific roles of NO in compensatory mechanisms of muscle fibers with mitochondrial deficiency and suggest the participation of nNOS in the signaling process of mitochondrial proliferation in human skeletal muscle.

Mitochondrial respiration is decreased in skeletal muscle of patients with type 2 diabetes

We tested the hypothesis of a lower respiratory capacity per mitochondrion in skeletal muscle of type 2 diabetic patients compared with obese subjects. Muscle biopsies obtained from 10 obese type 2 diabetic and 8 obese nondiabetic male subjects were used for assessment of 3-hydroxy-Acyl-CoA-dehydrogenase (HAD) and citrate synthase activity, uncoupling protein (UCP)3 content, oxidative stress measured as 4-hydroxy-2-nonenal (HNE), fiber type distribution, and respiration in isolated mitochondria. Respiration was normalized to citrate synthase activity (mitochondrial content) in isolated mitochondria. Maximal ADP-stimulated respiration (state 3) with pyruvate plus malate and respiration through the electron transport chain (ETC) were reduced in type 2 diabetic patients, and the proportion of type 2X fibers were higher in type 2 diabetic patients compared with obese subjects (all P < 0.05). There were no differences in respiration with palmitoyl-l-carnitine plus malate, citrate synthase activity, HAD activity, UCP3 content, or oxidative stress measured as HNE between the groups. In the whole group, state 3 respiration with pyruvate plus malate and respiration through ETC were negatively associated with A1C, and the proportion of type 2X fibers correlated with markers of insulin resistance (P < 0.05). In conclusion, we provide evidence for a functional impairment in mitochondrial respiration and increased amount of type 2X fibers in muscle of type 2 diabetic patients. These alterations may contribute to the development of type 2 diabetes in humans with obesity.

Characterization of canine mitochondrial protein expression in natural and induced forms of idiopathic dilated cardiomyopathy

OBJECTIVE

To map canine mitochondrial proteins and identify qualitative and quantitative differences in heart mitochondrial protein expression between healthy dogs and dogs with naturally occurring and induced dilated cardiomyopathy (DCM).

SAMPLE POPULATION

Left ventricle samples were obtained from 7 healthy dogs, 7 Doberman Pinschers with naturally occurring DCM, and 7 dogs with induced DCM.

PROCEDURES

Fresh and frozen mitochondrial fractions were isolated from the left ventricular free wall and analyzed by 2-dimensional electrophoresis. Protein spots that increased or decreased in density by >or= 2-fold between groups were analyzed by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry or quadrupole selecting, quadrupole collision cell, time-of-flight mass spectrometry.

RESULTS

Within narrow pH gradients of control canine heart mitochondrial samples, a total of 1,528 protein spots were revealed. Forty subunits of heart mitochondrial proteins that differ significantly from control tissues were altered in tissue specimens from dogs with naturally occurring and induced forms of DCM. The most affected heart mitochondrial proteins in both groups were those of oxidative phosphorylation (55%). Upregulation of manganese superoxide dismutase was suggestive of heart oxidative injury in tissue specimens from dogs with both forms of DCM. Evidence of apoptosis was associated with overexpression of the heart mitochondrial voltage-dependent anion channel-2 protein and endonuclease G in tissue specimens from dogs with induced DCM.

CONCLUSIONS AND CLINICAL RELEVANCE

Alterations of heart mitochondrial proteins related to oxidative phosphorylation dysfunction were more prevalent in tissue specimens from dogs with induced or naturally occurring DCM, compared with those of control dogs.

Coenzyme Q10 in cardiovascular disease

In this review we summarise the current state of knowledge of the therapeutic efficacy and mechanisms of action of CoQ(10) in cardiovascular disease. Our conclusions are: 1. There is promising evidence of a beneficial effect of CoQ(10) when given alone or in addition to standard therapies in hypertension and in heart failure, but less extensive evidence in ischemic heart disease. 2. Large scale multi-centre prospective randomised trials are indicated in all these areas but there are difficulties in funding such trials. 3. Presently, due to the notable absence of clinically significant side effects and likely therapeutic benefit, CoQ(10) can be considered a safe adjunct to standard therapies in cardiovascular disease.

Cardiovascular effects of pulmonary exposure to single-wall carbon nanotubes

BACKGROUND

Engineered nanosized materials, such as single-wall carbon nanotubes (SWCNT), are emerging as technologically important in different industries.

OBJECTIVE

The unique physical characteristics and the pulmonary toxicity of SWCNTs raised concerns that respiratory exposure to these materials may be associated with cardiovascular adverse effects.

METHODS

In these studies we evaluated aortic mitochondrial alterations by oxidative stress assays, including quantitative polymerase chain reaction of mitochondrial (mt) DNA and plaque formation by morphometric analysis in mice exposed to SWCNTs.

RESULTS

A single intrapharyngeal instillation of SWCNTs induced activation of heme oxygenase-1 (HO-1), a marker of oxidative insults, in lung, aorta, and heart tissue in HO-1 reporter transgenic mice. Furthermore, we found that C57BL/6 mice, exposed to SWCNT (10 and 40 mug/mouse), developed aortic mtDNA damage at 7, 28, and 60 days after exposure. mtDNA damage was accompanied by changes in aortic mitochondrial glutathione and protein carbonyl levels. Because these modifications have been related to cardiovascular diseases, we evaluated whether repeated exposure to SWCNTs (20 mug/mouse once every other week for 8 weeks) stimulates the progression of atherosclerosis in ApoE(-/-) transgenic mice. Although SWCNT exposure did not modify the lipid profiles of these mice, it resulted in accelerated plaque formation in ApoE(-/-) mice fed an atherogenic diet. Plaque areas in the aortas, measured by the en face method, and in the brachiocephalic arteries, measured histopathologically, were significantly increased in the SWCNT-treated mice. This response was accompanied by increased mtDNA damage but not inflammation.

CONCLUSIONS

Taken together, the findings are of sufficient significance to warrant further studies to evaluate the systemic effects of SWCNT under workplace or environmental exposure paradigms.

Mitochondrial dynamics generate equal distribution but patchwork localization of respiratory Complex I

Highly dynamic mitochondrial morphology is a prerequisite for fusion and fission. Mitochondrial fusion may represent a rescue mechanism for impaired mitochondria by exchanging constituents (proteins, lipids and mitochondrial DNA) and thus maintaining functionality. Here we followed for the first time the dynamics of a protein complex of the respiratory chain during fusion and fission. HeLa cells with differently labelled respiratory Complex I were fused and the dynamics of Complex I were investigated. The mitochondrial proteins spread throughout the whole mitochondrial population within 3 to 6 h after induction of cell fusion. Mitochondria of fused cells displayed a patchy substructure where the differently labelled proteins occupied separate and distinct spaces. This patchy appearance was already--although less pronounced--observed within single mitochondria before fusion, indicating a specific localization of Complex I with restricted diffusion within the inner membrane. These findings substantiate the view of a homogenous mitochondrial population due to constantly rearranging mitochondria, but also indicate the existence of distinct inner mitochondrial sub-compartments for respiratory chain complexes.

Structural Requirements for Optimized Delivery, Inhibition of Oxidative Stress, and Antiapoptotic Activity of Targeted Nitroxides

Suppression of mitochondrial production of reactive oxygen species is a promising strategy against intrinsic apoptosis typical of degenerative diseases. Stable nitroxide radicals such as 4-hydroxy-2,2,6,6-tetramethyl piperidine-1-oxyl (TEMPOL) and its analogs combine several important features, including recycleability, electron acceptance from respiratory complexes, superoxide dismutase mimicry, and radical scavenging. Although successful in antioxidant protection, their effective concentrations are too high for successful in vivo applications. Recently (J Am Chem Soc 127:12460, 2005), we reported that 4-amino 2,2,6,6-tetramethyl-1-piperidinyloxy, covalently conjugated to a five-residue segment of gramicidin S (GS), was integrated into mitochondria and blocked actinomycin D (ActD)-induced superoxide generation and apoptosis. Using a model of ActD-induced apoptosis in mouse embryonic cells, we screened a library of nitroxides to explore structure-activity relationships between their antioxidant/antiapoptotic properties and chemical composition and three-dimensional (3D) structure. High hydrophobicity and effective mitochondrial integration are necessary but not sufficient for high antiapoptotic/antioxidant activity of a nitroxide conjugate. By designing conformationally preorganized peptidyl nitroxide conjugates and characterizing their 3D structure experimentally (circular dichroism and NMR) and theoretically (molecular dynamics), we established that the presence of the beta-turn/beta-sheet secondary structure is essential for the desired activity. Monte Carlo simulations in model lipid membranes confirmed that the conservation of the d-Phe-Pro reverse turn in hemi-GS analogs ensures the specific positioning of the nitroxide moiety at the mitochondrial membrane interface and maximizes their protective effects. These new insights into the structure-activity relationships of nitroxide-peptide and -peptide isostere conjugates are instrumental for development of new mechanism-based therapeutically effective agents.

Protective role of 3-nitro-N-methyl-salicylamide on isolated rat heart during 4 hours of cold storage and reperfusion

OBJECTIVE

Cardiac ischemia/reperfusion (I/R) injury, a necessary consequence of transplantation, is probably related to the formation of reactive oxygen species (ROS). The ROS burst within the first moments of reperfusion is associated with injury, continuously generate O2- at about 3% to 5% of total O2 consumption owing to electron leak by mitochondrial oxidoreductases, especially complexes I and III. 3-nitro-N-methyl-salicylamide (NNMS) displays inhibitory effects on succinate-cytochrome C reductase, but also reduces effects on creation of O2- radical and H2O2 by isolated rat mitochondria. Presumably NNMS inhibits electron leakage from the mitochondrial respiratory chain. We investigated effect of NNMS on heart protection after hypothermic ischemia.

METHODS

A Langendorff-prepared rat heart model was employed after the heart had been preserved for 4 hours under hypothermic conditions of ischemia with subsequent reperfusion/rewarming for 60 minutes.

RESULTS

The group of hearts treated with NNMS showed increased recovery of heart function compared with a group of mEC. The lactate dehydrogenase (LDH) activity in coronary flow (CF) by hearts treated with NNMS was lower than that with mECs, as was the content of malonedialdehyde (MDA) and conjugated diene (CD).

CONCLUSIONS

NNMS improved heart physiology after reperfusion following 4 hours of hypothermic ischemia.

Huperzine A attenuates mitochondrial dysfunction in beta-amyloid-treated PC12 cells by reducing oxygen free radicals accumulation and improving mitochondrial energy metabolism

We observed previously that huperzine A (HupA), a selective acetylcholinesterase inhibitor, can counteract neuronal apoptosis and cell damage induced by several neurotoxic substances, and that this neuroprotective action somehow involves the mitochondria. We investigated the ability of HupA to reduce mitochondrial dysfunction in neuron-like rat pheochromocytoma (PC12) cells exposed in culture to the amyloid beta-peptide fragment 25-35 (Abeta(25-35)). After exposure to 1 microM Abeta(25-35) for various periods, cells exhibited a rapid decline of ATP levels and obvious disruption of mitochondrial membrane homeostasis and integrity as determined by characteristic morphologic alterations, reduced membrane potential, and decreased activity of ion transport proteins. In addition, Abeta(25-35) treatment also led to inhibition of key enzyme activities in the electron transport chain and the tricarboxylic acid cycle, as well as an increase of intracellular reactive oxygen species (ROS). Pre-incubation with HupA for 2 hr not only attenuated these signs of cellular stress caused by Abeta, but also enhanced ATP concentration and decreased ROS accumulation in unharmed normal cells. Those results indicate that HupA protects mitochondria against Abeta-induced damages, at least in part by inhibiting oxidative stress and improving energy metabolism, and that these protective effects reduce the apoptosis of neuronal cells exposed to this toxic peptide.

Detection and analysis of protein–protein interactions in organellar and prokaryotic proteomes by native gel electrophoresis: (Membrane) protein complexes and supercomplexes

It is an essential and challenging task to unravel protein-protein interactions in their actual in vivo context. Native gel systems provide a separation platform allowing the analysis of protein complexes on a rather proteome-wide scale in a single experiment. This review focus on blue-native (BN)-PAGE as the most versatile and successful gel-based approach to separate soluble and membrane protein complexes of intricate protein mixtures derived from all biological sources. BN-PAGE is a charge-shift method with a running pH of 7.5 relying on the gentle binding of anionic CBB dye to all membrane and many soluble protein complexes, leading to separation of protein species essentially according to their size and superior resolution than other fractionation techniques can offer. The closely related colorless-native (CN)-PAGE, whose applicability is restricted to protein species with intrinsic negative net charge, proved to provide an especially mild separation capable of preserving weak protein-protein interactions better than BN-PAGE. The essential conditions determining the success of detecting protein-protein interactions are the sample preparations, e.g. the efficiency/mildness of the detergent solubilization of membrane protein complexes. A broad overview about the achievements of BN- and CN-PAGE studies to elucidate protein-protein interactions in organelles and prokaryotes is presented, e.g. the mitochondrial protein import machinery and oxidative phosphorylation supercomplexes. In many cases, solubilization with digitonin was demonstrated to facilitate an efficient and particularly gentle extraction of membrane protein complexes prone to dissociation by treatment with other detergents. In general, analyses of protein interactomes should be carried out by both BN- and CN-PAGE.

Endurance training limits the functional alterations of heart rat mitochondria submitted to in vitro anoxia-reoxygenation

BACKGROUND

Studies analysing the effect of endurance training on heart mitochondrial function submitted to in vitro anoxia-reoxygenation (A-R) are missing. The present study aimed to investigate the effect of moderate endurance treadmill training (14 weeks) against rat heart mitochondrial dysfunction induced by in vitro A-R.

METHODS

Respiratory parameters (state 3, state 4, ADP/O and respiratory control ratio-RCR) and oxidative damage markers (carbonyl groups and malondialdehyde) were determined in isolated mitochondria before and after 1 min anoxia followed by 4 min reoxygenation. Levels of heat shock protein 60 kDa (HSP60) and 70 kDa (HSP70) were measured before A-R in mitochondria and whole muscle homogenate, respectively.

RESULTS

A-R significantly impaired the rate of state 3 and state 4 respiration, as well as the RCR and ADP/O in the sedentary group. However, mitochondrial state 3 respiration was significantly higher in trained than in the sedentary group both before and after A-R. The impairments in RCR, ADP/O ratio and state 4 induced by A-R in sedentary group were significantly attenuated in endurance-trained group. The inhibition of state 4 induced by GDP was significantly higher in trained than in sedentary group. Oxidative modifications of mitochondrial proteins and phospholipids were found in sedentary group after A-R, although limited in trained group. Increased levels of mitochondrial HSP60 and tissue HSP70 accompanied the lower decrease in the respiratory function after A-R observed in trained group.

CONCLUSION

We therefore concluded that endurance training limited the impairments on rat heart mitochondria caused by the oxidant insult inflicted by in vitro A-R.

UCP1 and Defense against Oxidative Stress

Uncoupling proteins have been ascribed a role in defense against oxidative stress, particularly by being activated by products of oxidative stress such as 4-hydroxy-2-nonenal (HNE). We have investigated here the ability of HNE to activate UCP1. Using brown fat mitochondria from UCP1+/+ and UCP1-/- mice to allow for identification of UCP1-dependent effects, we found that HNE could neither (re)activate purine nucleotide-inhibited UCP1, nor induce additional activation of innately active UCP1. The aldehyde nonenal had a (re)activating effect only if converted to the corresponding fatty acid by aldehyde dehydrogenase; the presence of a carboxyl group was thus an absolute requirement for (re)activation. The UCP1-dependent proton leak was not increased by HNE but HNE changed basal proton leak characteristics in a UCP1-independent manner. In agreement with the in vitro results, we found, as compared with UCP1+/+ mice, no increase in HNE/protein adducts in brown fat mitochondria isolated from UCP1-/- mice, irrespective of whether they were adapted to thermoneutral temperature (30 degrees C) or to the cold (4 degrees C). The absence of oxidative damage in UCP1-/- mitochondria was not due to enhanced activity of antioxidant enzymes. Thus, HNE did not affect UCP1 activity, and UCP1 would appear not to be physiologically involved in defense against oxidative stress. Additionally, it was concluded that at least in brown adipose tissue, conditions of high mitochondrial membrane potential, high oxygen tension, and high substrate supply do not necessarily lead to increased oxidative damage.

Energy deficiency in the failing heart: linking increased reactive oxygen species and disruption of oxidative phosphorylation rate

Heart failure is a complex syndrome of numerous dysfunctional components which converge to cause chronic progressive failure of ventricular contractile function and maintenance of cardiac output demand. The aim of this brief review is to highlight some of the mounting evidence indicating that augmented superoxide, related reactive oxygen species and other free radicals contribute to the oxidative stress evident during the progression of heart failure. While much of the source of increased reactive oxygen species is mitochondrial, there are other intracellular sources, which together are highly reactive with functional and structural cellular lipids and proteins. Bioenergetic defects limiting ATP synthesis in the failing myocardium relate not only to post-translational modification of electron transport respiratory chain proteins but also to perturbation of Krebs Cycle enzyme-dependent synthesis of NADH. Accumulation of pathological levels of lipid peroxides relate to dysfunction in the intrinsic capacity to clear and renew dysfunctional proteins. This review also features key limitations of human heart failure studies and potential clinical therapies that target the elevated oxidative stress that is a hallmark of human heart failure.

Protein carbonylation, cellular dysfunction, and disease progression

Carbonylation of proteins is an irreversible oxidative damage, often leading to a loss of protein function, which is considered a widespread indicator of severe oxidative damage and disease-derived protein dysfunction. Whereas moderately carbonylated proteins are degraded by the proteasomal system, heavily carbonylated proteins tend to form high-molecular-weight aggregates that are resistant to degradation and accumulate as damaged or unfolded proteins. Such aggregates of carbonylated proteins can inhibit proteasome activity. Alarge number of neurodegenerative diseases are directly associated with the accumulation of proteolysis-resistant aggregates of carbonylated proteins in tissues. Identification of specific carbonylated protein(s) functionally impaired and development of selective carbonyl blockers should lead to the definitive assessment of the causative, correlative or consequential role of protein carbonylation in disease onset and/or progression, possibly providing new therapeutic approaches.

Decreased complex II respiration and HNE-modified SDH subunit in diabetic heart

Several lines of research suggest that mitochondria play a role in the etiopathogenesis of diabetic cardiomyopathy, although the mechanisms involved are still debated. In the present study, we report that State 3 oxygen consumption decreases by approximately 35% with glutamate and by approximately 30% with succinate in mitochondria from diabetic rat hearts compared to controls. In these mitochondria the enzymatic activities of complex I and complex II are also decreased to a comparable extent. Western blot analysis of mitochondrial protein pattern using antibodies recognizing proteins modified by the lipid peroxidation product 4-hydroxynonenal indicates the FAD-containing subunit of succinate dehydrogenase as one of the targets of this highly reactive aldehyde. In rats diabetic for 6 or 12 weeks, insulin supplementation for 2 weeks decreases the level of protein modified by 4-hydroxynonenal and restores mitochondrial respiration and enzyme activity to control level. Taken together, these results: (1) indicate that 4-hydroxynonenal is endogenously produced within diabetic mitochondria and forms an adduct with selective mitochondrial proteins, (2) identify one of these proteins as a subunit of succinate dehydrogenase, and (3) provide strong evidence that insulin treatment can reverse and ameliorate free radical damage and mitochondrial function under diabetic conditions.

Reactive species and early manifestation of insulin resistance in type 2 diabetes

The early stages of type 2 diabetes mellitus are characterized by the development of insulin resistance (IRe) in muscle cells and adipocytes with the concomitant loss of beta-cell compensation. We have extensively reviewed the literature related to metabolic and signalling pathways of reactive oxygen species (ROS) in regard to the coordinated development of oxidative stress and IRe. We considered the hypothesis that oxidative stress leads to IRe in muscle cells and adipocytes, but found that the data are more consistent with the hypothesis that the cellular mechanisms that protect against oxidative stress per se are capable of creating an ROS-dependent insulin-resistant state. Furthermore, ROS-induced mitochondrial dysfunction can lead to disruptions of lipid metabolism, increasing the intracellular lipid content, and, in addition, contribute to lipid-dependent IRe in myocytes. Together, these two ROS-activated pathways to IRe can contribute to a global state of profound resistance to insulin action. Therapeutic strategies should, therefore, be directed towards reducing insulin resistance without an increase in ROS production or concentration. Pharmacological or other approaches to IRe that result in the activation of mitochondrial biogenesis in particular could be highly beneficial in the prevention or treatment of both insulin resistance and type 2 diabetes.

Differential impact of environmental stresses on the pea mitochondrial proteome

Exposure to adverse environmental conditions causes oxidative stress in many organisms, leading either to disease and debilitation or to response and tolerance. Mitochondria are a key site of oxidative stress and of cellular response and play important roles in cell survival. We analyzed the response of mitochondria in pea (Pisum sativum) plants to the common stresses associated with drought, cold, and herbicides. These treatments all altered photosynthetic and respiratory rates of pea leaves to various extents, but only herbicides significantly increased lipid peroxidation product accumulation. Mitochondria isolated from the stressed pea plants maintained their electron transport chain activity, but changes were evident in the abundance of uncoupling proteins, non-phosphorylating respiratory pathways, and oxidative modification of lipoic acid moieties on mitochondrial proteins. These data suggest that herbicide treatment placed a severe oxidative stress on mitochondria, whereas chilling and particularly drought were milder stresses. Detailed analysis of the soluble proteome of mitochondria by gel electrophoresis and mass spectrometry revealed differential degradation of key matrix enzymes during treatments with chilling being significantly more damaging than drought. Differential induction of heat shock proteins and specific losses of other proteins illustrated the diversity of response to these stresses at the protein level. Cross-species matching was required for mass spectrometry identification of nine proteins because only a limited number of pea cDNAs have been sequenced, and the full pea genome is not available. Blue-native separation of intact respiratory chain complexes revealed little if any change in response to environmental stresses. Together these data suggest that although many of the molecular events identified by chemical stresses of mitochondria from a range of model eukaryotes are also apparent during environmental stress of plants, their extent and significance can vary substantially.

Metal-catalyzed oxidation induces carbonylation of peroxisomal proteins and loss of enzymatic activities

Peroxisomes are involved in oxidative metabolic reactions and have the capacity to generate large amounts of reactive oxygen species that could damage biomolecules including their own resident proteins. The purpose of this study was to determine whether peroxisomal proteins are susceptible to oxidation and whether oxidative damage affects their enzymatic activity. Peroxisomal proteins were subjected to metal-catalyzed oxidation (MCO) with CuCl(2)/ascorbate and derivatized with 2,4-dinitrophenylhydrazine which allowed for spectrophotometric quantification of carbonylation. Immunochemical detection of carbonylated peroxisomal proteins, resolved by gel electrophoresis and detected with anti-DNP antibodies, revealed five oxidatively modified proteins with the following molecular weights: 80, 66, 62, 55, and 50 kDa. The proteins at 66, 62, and 55 kDa were identified as malate synthase (MS), isocitrate lyase, and catalase (CAT), respectively. MS and CAT were estimated to contain 2-3 mol of carbonyl/mol of protein as a result of MCO. Enzymatic assays revealed varying degrees of activity loss. Isocitrate lyase and malate synthase showed significant loss of activity while catalase and malate dehydrogenase were less inhibited by carbonylation. Our findings show that peroxisomal proteins are vulnerable to MCO damage and thus may also be affected by in vivo exposure to reactive oxygen species.

Acetogenins from Annonaceae: recent progress in isolation, synthesis and mechanisms of action

The aim of the present review is to summarise the knowledge about newly isolated acetogenins (ACGs) in the last six years. It will also report the total syntheses that have allowed either the confirmation or the revision of some structures, together with the biological activities and mechanism of action of such interesting natural products. In fact, of the 417 isolated compounds reviewed, over 176 have been added during the period from 1998 to 2004.

Proteomic identification of 3-nitrotyrosine-containing rat cardiac proteins: effects of biological aging

Proteomic techniques were used to identify cardiac proteins from whole heart homogenate and heart mitochondria of Fisher 344/Brown Norway F1 rats, which suffer protein nitration as a consequence of biological aging. Soluble proteins from young (5 mo old) and old (26 mo old) animals were separated by one- and two-dimensional gel electrophoresis. One- and two-dimensional Western blots with an anti-nitrotyrosine antibody show an age-related increase in the immunoresponse of a few specific proteins, which were identified by nanoelectrospray ionization-tandem mass spectrometry (NSI-MS/MS). Complementary proteins were immunoprecipitated with an immobilized anti-nitrotyrosine antibody followed by NSI-MS/MS analysis. A total of 48 proteins were putatively identified. Among the identified proteins were alpha-enolase, alpha-aldolase, desmin, aconitate hydratase, methylmalonate semialdehyde dehydrogenase, 3-ketoacyl-CoA thiolase, acetyl-CoA acetyltransferase, GAPDH, malate dehydrogenase, creatine kinase, electron-transfer flavoprotein, manganese-superoxide dismutase, F1-ATPase, and the voltage-dependent anion channel. Some contaminating blood proteins including transferrin and fibrinogen beta-chain precursor showed increased levels of nitration as well. MS/MS analysis located nitration at Y105 of the electron-transfer flavoprotein. Among the identified proteins, there are important enzymes responsible for energy production and metabolism as well as proteins involved in the structural integrity of the cells. Our results are consistent with age-dependent increased oxidative stress and with free radical-dependent damage of proteins. Possibly the oxidative modifications of the identified proteins contribute to the age-dependent degeneration and functional decline of heart proteins.