Qualitative determination of superoxide release at both sides of the mitochondrial inner membrane by capillary electrophoretic analysis of the oxidation products of triphenylphosphonium hydroethidine

Detection of superoxide radical in all biological systems by Thin Layer Chromatography

The study presents a new method that detects O₂^•-, via quantification of 2-hydroxyethidium (2-ΟΗ-Ε⁺) as low as ∼30 fmoles by High-Performance Thin Layer Chromatography (HPTLC). The method isolates 2-ΟΗ-Ε⁺ after its extraction by the anionic detergent SDS (at 18-fold higher than its CMC) together with certain organic/inorganic reagents, and its HPTLC-separation from di-ethidium (di-Ε⁺) and ethidium (Ε⁺). Quantification of 2-OH-E⁺ is based on its ex/em maxima at 290/540 nm, and of di-E⁺ and E⁺ at 295/545 nm. The major innovations of the present method are the development of protocols for (i) efficient extraction (by SDS) and (ii) sensitive quantification (by HPTLC) for 2-OH-E⁺ (as well as di-E⁺ and E⁺) from most biological systems (animals, plants, cells, subcellular compartments, fluids). The method extracts 2-ΟΗ-Ε⁺ (by neutralizing the strong binding between its quaternary N⁺ and negatively charged sites on phospholipids, DNA etc) together with free HE, while protects both from biological oxidases, and also extracts/quantifies total proteins (hydrophilic and hydrophobic) for expressing O₂^•- levels per protein quantity. The method also uses SDS (at 80-fold lower than its CMC) to extract/remove/wash 2-ΟΗ-Ε⁺ from cell/organelle exterior membrane sites, for more accurate internal content quantification. The new method is applied on indicative biological systems: (1) artificially stressed (mouse organs and liver mitochondria and nuclei, ±exposed to paraquat, a known O₂^•- generator), and (2) physiologically stressed (cauliflower plant, exposed to light/dark).

4-Hydroxyphenylpyruvate Dioxygenase-Like Protein Promotes Pancreatic Cancer Cell Progression and Is Associated With Glutamine-Mediated Redox Balance

Tumor cells develop a series of metabolic reprogramming mechanisms to meet the metabolic needs for tumor progression. As metabolic hubs in cells, mitochondria play a significant role in this process, including energy production, biosynthesis, and redox hemostasis. In this study, we show that 4-hydroxyphenylpyruvate dioxygenase-like protein (HPDL), a previously uncharacterized protein, is positively associated with the development of pancreatic ductal adenocarcinoma (PDAC) and disease prognosis. We found that overexpression of HPDL in PDAC cells promotes tumorigenesis in vitro, whereas knockdown of HPDL inhibits cell proliferation and colony formation. Mechanistically, we found that HPDL is a mitochondrial intermembrane space localized protein that positively regulates mitochondrial bioenergetic processes and adenosine triphosphate (ATP) generation in a glutamine dependent manner. Our results further reveal that HPDL protects cells from oxidative stress by reprogramming the metabolic profile of PDAC cells toward glutamine metabolism. In short, we conclude that HPDL promotes PDAC likely through its effects on glutamine metabolism and redox balance.

Roles of Reactive Oxygen Species in Cardiac Differentiation, Reprogramming, and Regenerative Therapies

Reactive oxygen species (ROS) have been implicated in mechanisms of heart development and regenerative therapies such as the use of pluripotent stem cells. The roles of ROS mediating cell fate are dependent on the intensity of stimuli, cellular context, and metabolic status. ROS mainly act through several targets (such as kinases and transcription factors) and have diverse roles in different stages of cardiac differentiation, proliferation, and maturation. Therefore, further detailed investigation and characterization of redox signaling will help the understanding of the molecular mechanisms of ROS during different cellular processes and enable the design of targeted strategies to foster cardiac regeneration and functional recovery. In this review, we focus on the roles of ROS in cardiac differentiation as well as transdifferentiation (direct reprogramming). The potential mechanisms are discussed in regard to ROS generation pathways and regulation of downstream targets. Further methodological optimization is required for translational research in order to robustly enhance the generation efficiency of cardiac myocytes through metabolic modulations. Additionally, we highlight the deleterious effect of the host's ROS on graft (donor) cells in a paracrine manner during stem cell-based implantation. This knowledge is important for the development of antioxidant strategies to enhance cell survival and engraftment of tissue engineering-based technologies. Thus, proper timing and level of ROS generation after a myocardial injury need to be tailored to ensure the maximal efficacy of regenerative therapies and avoid undesired damage.

Rotenone protects against β-cell apoptosis and attenuates type 1 diabetes mellitus

Type 1 diabetes mellitus (T1DM) is caused by pancreatic β-cell dysfunction and apoptosis, with consequent severe insulin deficiency. Thus, β-cell protection may be a primary target in the treatment of T1DM. Evidence has demonstrated that defective mitochondrial function plays an important role in pancreatic β-cell dysfunction and apoptosis; however, the fundamental effect of mitochondrial complex I action on β-cells and T1DM remains unclear. In the current study, the pancreas protective effect of complex I inhibitor rotenone (ROT) and its potential mechanism were assessed in a streptozotocin (STZ)-induced mouse model of T1DM and in cultured mouse pancreatic β-cell line, Min6. ROT treatment exerted a hypoglycemic effect, restored the insulin level, and decreased inflammation and cell apoptosis in the pancreas. In vitro experiments also showed that ROT decreased STZ- and inflammatory cytokines-induced β-cell apoptosis. These protective effects were accompanied by attenuation of reactive oxygen species, increased mitochondrial membrane potential, and upregulation of transcriptional coactivator PPARα coactivator 1α (PGC-1α)-controlled mitochondrial biogenesis. These findings suggest that mitochondrial complex I inhibition may represent a promising strategy for β-cell protection in T1DM.

Interaction of nitric oxide with the components of the plant mitochondrial electron transport chain

Mitochondria are not only major sites for energy production but also participate in several alternative functions, among these generation of nitric oxide (NO), and its different impacts on this organelle, is receiving increasing attention. The inner mitochondrial membrane contains the chain of protein complexes, and electron transfer via oxidation of various organic acids and reducing equivalents leads to generation of a proton gradient that results in energy production. Recent evidence suggests that these complexes are sources and targets for NO. Complex I and rotenone-insensitive NAD(P)H dehydrogenases regulate hypoxic NO production, while complex I also participates in the formation of a supercomplex with complex III under hypoxia. Complex II is a target for NO which, by inhibiting Fe-S centres, regulates reactive oxygen species (ROS) generation. Complex III is one of the major sites for NO production, and the produced NO participates in the phytoglobin-NO cycle that leads to the maintenance of the redox level and limited energy production under hypoxia. Expression of the alternative oxidase (AOX) is induced by NO under various stress conditions, and evidence exists that AOX can regulate mitochondrial NO production. Complex IV is another major site for NO production, which can also be linked to ATP generation via the phytoglobin-NO cycle. Inhibition of complex IV by NO can prevent oxygen depletion at the frontier of anoxia. The NO production and action on various complexes play a major role in NO signalling and energy metabolism.

Redox Control of Skeletal Muscle Regeneration

Skeletal muscle shows high plasticity in response to external demand. Moreover, adult skeletal muscle is capable of complete regeneration after injury, due to the properties of muscle stem cells (MuSCs), the satellite cells, which follow a tightly regulated myogenic program to generate both new myofibers and new MuSCs for further needs. Although reactive oxygen species (ROS) and reactive nitrogen species (RNS) have long been associated with skeletal muscle physiology, their implication in the cell and molecular processes at work during muscle regeneration is more recent. This review focuses on redox regulation during skeletal muscle regeneration. An overview of the basics of ROS/RNS and antioxidant chemistry and biology occurring in skeletal muscle is first provided. Then, the comprehensive knowledge on redox regulation of MuSCs and their surrounding cell partners (macrophages, endothelial cells) during skeletal muscle regeneration is presented in normal muscle and in specific physiological (exercise-induced muscle damage, aging) and pathological (muscular dystrophies) contexts. Recent advances in the comprehension of these processes has led to the development of therapeutic assays using antioxidant supplementation, which result in inconsistent efficiency, underlying the need for new tools that are aimed at precisely deciphering and targeting ROS networks. This review should provide an overall insight of the redox regulation of skeletal muscle regeneration while highlighting the limits of the use of nonspecific antioxidants to improve muscle function. Antioxid. Redox Signal. 27, 276-310.

A lifelong competitive training practice attenuates age-related lipid peroxidation

The effect of exercise-induced oxidative stress on health and aging is not clearly explained. This study examined the effects of habitual sport practice, age, and submaximal exercise on the blood markers of oxidative stress, muscle damage, and antioxidant response. Seventy-two healthy men were grouped by their habitual sport practice: inactive (<1.5 h/week), recreational (3-8 h/week), and trained athletes (>8 h/week), and further divided by age: young (18-25 years), adult (40-55 years), and senior (>55 years). Blood samples were collected at rest and after submaximal effort. Hydroperoxides and superoxide dismutase, glutathione peroxidase, and catalase activities were measured by spectrophotometry. Nuclear DNA damage was analyzed by comet assay. The alpha-actin release was analyzed by Western blot. Alpha-tocopherol, retinol, and coenzyme-Q10 were quantified by high-performance liquid chromatography analysis. Data was analyzed through a factorial ANOVA and the Bonferroni post hoc test. Lipid peroxidation increased significantly with age and submaximal effort (p < 0.05). However, the trained athlete group presented lower lipid peroxidation compared with the recreational group (MD = 2.079, SED = 0.58, p = 0.002) and inactive group (MD = 1.979, SED = 0.61, p = 0.005). Trained athletes showed significant higher alpha-actin levels (p < 0.001) than the other groups. Recreational group showed lower nuclear DNA damage than trained athletes (MD = 3.681, SED = 1.28, p = 0.015). Nevertheless, the inactive group presented significantly higher superoxide dismutase and catalase (p < 0.05) than the other groups. Data suggested that habitual competitive training practice could prevent age-related increases of plasma lipid peroxidation, which, according with our results, cannot be entirely attributed to blood antioxidant defense systems.

'Mitochondrial energy imbalance and lipid peroxidation cause cell death in Friedreich's ataxia'

Friedreich's ataxia (FRDA) is an inherited neurodegenerative disease. The mutation consists of a GAA repeat expansion within the FXN gene, which downregulates frataxin, leading to abnormal mitochondrial iron accumulation, which may in turn cause changes in mitochondrial function. Although, many studies of FRDA patients and mouse models have been conducted in the past two decades, the role of frataxin in mitochondrial pathophysiology remains elusive. Are the mitochondrial abnormalities only a side effect of the increased accumulation of reactive iron, generating oxidative stress? Or does the progressive lack of iron-sulphur clusters (ISCs), induced by reduced frataxin, cause an inhibition of the electron transport chain complexes (CI, II and III) leading to reactive oxygen species escaping from oxidative phosphorylation reactions? To answer these crucial questions, we have characterised the mitochondrial pathophysiology of a group of disease-relevant and readily accessible neurons, cerebellar granule cells, from a validated FRDA mouse model. By using live cell imaging and biochemical techniques we were able to demonstrate that mitochondria are deregulated in neurons from the YG8R FRDA mouse model, causing a decrease in mitochondrial membrane potential (▵Ψm) due to an inhibition of Complex I, which is partially compensated by an overactivation of Complex II. This complex activity imbalance leads to ROS generation in both mitochondrial matrix and cytosol, which results in glutathione depletion and increased lipid peroxidation. Preventing this increase in lipid peroxidation, in neurons, protects against in cell death. This work describes the pathophysiological properties of the mitochondria in neurons from a FRDA mouse model and shows that lipid peroxidation could be an important target for novel therapeutic strategies in FRDA, which still lacks a cure.

ALS-linked misfolded SOD1 species have divergent impacts on mitochondria

Approximately 20 % of familial Amyotrophic Lateral Sclerosis (ALS) is caused by mutations in superoxide dismutase (SOD1), which leads to misfolding of the SOD1 protein, resulting in a toxic gain of function. Several conformation-restricted antibodies have been generated that specifically recognize misfolded SOD1 protein, and have been used as therapeutics in pre-clinical models. Misfolded SOD1 selectively associates with spinal cord mitochondria in SOD1 rodent models. Using the SOD1(G93A) rat model, we find that SOD1 conformational specific antibodies AMF7-63 and DSE2-3H1 labeled a fibrillar network concentrated in the anterior horn; while A5C3, B8H10, C4F6 and D3H5 labeled motor neurons as well as puncta in the neuropil. There is a time-dependent accumulation of misfolded SOD1 at the surface of spinal cord mitochondria with AMF7-63-labeled mitochondria having increased volume in contrast to a mitochondrial subset labeled with B8H10. In spinal cord homogenates and isolated mitochondria, AMF7-63, DSE2-3H1 and B8H10 detect misfolded SOD1 aggregates. SOD1 that lacks its metal cofactors has an increased affinity for naïve mitochondria and misfolded SOD1 antibodies B8H10 and DSE2-3H1 readily detect demetalated mutant and wild-type SOD1. Together, these data suggest that multiple non-native species of misfolded SOD1 may exist, some of which are associated with mitochondrial damage. Conformational antibodies are invaluable tools to identify and characterize the variation in misfolded SOD1 species with regards to biochemical characteristics and toxicity. This information is highly relevant to the further development of these reagents as therapeutics.

A tutorial on oxidative stress and redox signaling with application to exercise and sedentariness

Oxidative stress has been shown to play a role in the etiology of several chronic diseases, including cardiovascular disease, diabetes mellitus, and cancer. Free radicals and, most prominently, the superoxide radical, result from oxidative metabolism and several enzyme-catalyzed reactions, and endogenous cellular antioxidants dismutate many reactive oxygen species (ROS). Under certain conditions, ROS production can outpace dismutation (e.g., long-term sedentariness and positive energy balance) and the result is oxidative stress, with proteins, lipids, and DNA the most common targets of radicals. However, the molecules that contribute to oxidative stress also appear to participate in vital cell signaling activity that supports health and stimulates favorable adaptations to exercise training, such that inhibiting ROS formation prevents common adaptations to training. Furthermore, researchers have recently suggested that some proteins are not as readily formed when the redox state of the cell is insufficiently oxidative. Exercise training appears to optimize the redox environment by dramatically enhancing the capacity of the cell to neutralize ROS while regularly creating oxidative environments in which membrane and secretory proteins can be synthesized. The role that exercise plays in enhancing management of ROS likely explains many of the associated health benefits.

Immunodetection of outer membrane proteins by flow cytometry of isolated mitochondria

Methods to detect and monitor mitochondrial outer membrane protein components in animal tissues are vital to study mitochondrial physiology and pathophysiology. This protocol describes a technique where mitochondria isolated from rodent tissue are immunolabeled and analyzed by flow cytometry. Mitochondria are isolated from rodent spinal cords and subjected to a rapid enrichment step so as to remove myelin, a major contaminant of mitochondrial fractions prepared from nervous tissue. Isolated mitochondria are then labeled with an antibody of choice and a fluorescently conjugated secondary antibody. Analysis by flow cytometry verifies the relative purity of mitochondrial preparations by staining with a mitochondrial specific dye, followed by detection and quantification of immunolabeled protein. This technique is rapid, quantifiable and high-throughput, allowing for the analysis of hundreds of thousands of mitochondria per sample. It is applicable to assess novel proteins at the mitochondrial surface under normal physiological conditions as well as the proteins that may become mislocalized to this organelle during pathology. Importantly, this method can be coupled to fluorescent indicator dyes to report on certain activities of mitochondrial subpopulations and is feasible for mitochondria from the central nervous system (brain and spinal cord) as well as liver.

MnSOD overexpression reduces fibrosis and pro-apoptotic signaling in the aging mouse heart

Contractility of the heart is impaired with advancing age via mechanical remodeling, as myocytes are lost through apoptosis and collagenous fibers accumulate. Exercise training confers protection against fibrosis and apoptosis in the aging heart, but the mechanisms remain poorly understood. We recently reported that exercise training elevates Mn isoform of superoxide dismutase (MnSOD) in the aging heart, concomitant with reduction in oxidative stress and fibrosis. Here, we tested the hypothesis that overexpression of MnSOD would be causal in protection against fibrosis and apoptosis in the aging heart. Hearts were extracted from young (8 months) wild-type, young mice overexpressing the Sod2 (MnSOD) gene, old (28 months) wild-type, and old transgenic mice. Left ventricle MnSOD protein levels were elevated in young mice overexpressing the Sod2 (MnSOD) gene and old transgenic mice. MnSODTg mice exhibited lower oxidative stress (total hydroperoxides, 4-hydroxynonenal, and 8-isoprostane) in the old group. Age-related cardiac remodeling and fibrosis was mitigated in MnSOD Tg mice with reductions in extramyocyte space (-65%), collagen-I, and transforming growth factor-β. Pro-apoptotic markers Bax (-38%) and caspase-3 cleavage (-41%) were reduced and apoptosis (terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling-positive nuclei, DNA laddering) was mitigated in MnSOD Tg hearts compared with old wild-type. We conclude that MnSOD elevation is indeed protective against oxidative stress, fibrosis, and apoptosis in the aging heart.

The mitochondria-targeted antioxidant MitoQ extends lifespan and improves healthspan of a transgenic Caenorhabditis elegans model of Alzheimer disease

β-Amyloid (Aβ)-induced toxicity and oxidative stress have been postulated to play critical roles in the pathogenic mechanism of Alzheimer disease (AD). We investigated the in vivo ability of a mitochondria-targeted antioxidant, MitoQ, to protect against Aβ-induced toxicity and oxidative stress in a Caenorhabditis elegans model overexpressing human Aβ. Impairment of electron transport chain (ETC) enzymatic activity and mitochondrial dysfunction are early features of AD. We show that MitoQ extends lifespan, delays Aβ-induced paralysis, ameliorates depletion of the mitochondrial lipid cardiolipin, and protects complexes IV and I of the ETC. Despite its protective effects on lifespan, healthspan, and ETC function, we find that MitoQ does not reduce DCFDA fluorescence, protein carbonyl levels or modulate steadystate ATP levels or oxygen consumption rate. Moreover, MitoQ does not attenuate mitochondrial DNA (mtDNA) oxidative damage. In agreement with its design, the protective effects of MitoQ appear to be targeted specifically to the mitochondrial membrane and our findings suggest that MitoQ may have therapeutic potential for Aβ- and oxidative stress-associated neurodegenerative disorders, particularly AD.

Novel insights into the antiproliferative effects and synergism of quercetin and menadione in human leukemia Jurkat T cells

The flavonoid quercetin and menadione (vitamin K3) are known as potent apoptogens in human leukemia Jurkat T cells. We explored some underlying mechanisms and the potential relevance of the combination quercetin-menadione for clinical applications. In acute treatments, quercetin manifested a strong antioxidant character, but induced a transient loss of Δψm, likely mediated by opening of the mitochondrial permeability transition pore. After removal of quercetin, persistent mitochondrial hyperpolarization was generated via stimulation of respiratory Complex I. In contrast, menadione-induced Δψm dissipation was only partially and transiently reversed after menadione removal. Results indicate that Ca(2+) release is a necessary event in quercetin-induced cell death and that the survival response to quercetin is delineated within 1h from exposure. Depending on dose, the two agents exhibited either antagonistic or synergistic effects in reducing clonogenicity of Jurkat cells. 24-h combinatorial regimens at equimolar concentrations of 10-15 μM, which are compatible with a clinically achievable (and safe) scheme, reduced cell viability at efficient rates. Altogether, these findings support the idea that the combination quercetin-menadione could improve the outcome of conventional leukemia therapies, and warrant the utility of additional studies to investigate the therapeutic effects of this combination in different cellular or animal models for leukemia.

Recent advances in 2D and 3D in vitro systems using primary hepatocytes, alternative hepatocyte sources and non-parenchymal liver cells and their use in investigating mechanisms of hepatotoxicity, cell signaling and ADME

This review encompasses the most important advances in liver functions and hepatotoxicity and analyzes which mechanisms can be studied in vitro. In a complex architecture of nested, zonated lobules, the liver consists of approximately 80 % hepatocytes and 20 % non-parenchymal cells, the latter being involved in a secondary phase that may dramatically aggravate the initial damage. Hepatotoxicity, as well as hepatic metabolism, is controlled by a set of nuclear receptors (including PXR, CAR, HNF-4α, FXR, LXR, SHP, VDR and PPAR) and signaling pathways. When isolating liver cells, some pathways are activated, e.g., the RAS/MEK/ERK pathway, whereas others are silenced (e.g. HNF-4α), resulting in up- and downregulation of hundreds of genes. An understanding of these changes is crucial for a correct interpretation of in vitro data. The possibilities and limitations of the most useful liver in vitro systems are summarized, including three-dimensional culture techniques, co-cultures with non-parenchymal cells, hepatospheres, precision cut liver slices and the isolated perfused liver. Also discussed is how closely hepatoma, stem cell and iPS cell-derived hepatocyte-like-cells resemble real hepatocytes. Finally, a summary is given of the state of the art of liver in vitro and mathematical modeling systems that are currently used in the pharmaceutical industry with an emphasis on drug metabolism, prediction of clearance, drug interaction, transporter studies and hepatotoxicity. One key message is that despite our enthusiasm for in vitro systems, we must never lose sight of the in vivo situation. Although hepatocytes have been isolated for decades, the hunt for relevant alternative systems has only just begun.

Mitochondrial damage revealed by immunoselection for ALS-linked misfolded SOD1

Mutant superoxide dismutase 1 (SOD1) selectively associates with spinal cord mitochondria in rodent models of SOD1-mediated amyotrophic lateral sclerosis. A portion of mutant SOD1 exists in a non-native/misfolded conformation that is selectively recognized by conformational antibodies. Misfolded SOD1 is common to all mutant SOD1 models, is uniquely found in areas affected by the disease and is considered to mediate toxicity. We report that misfolded SOD1 recognized by the antibody B8H10 is present in greater abundance in mitochondrial fractions of SOD1(G93A) rat spinal cords compared with oxidized SOD1, as recognized by the C4F6 antibody. Using a novel flow cytometric assay, we detect an age-dependent deposition of B8H10-reactive SOD1 on spinal cord mitochondria from both SOD1(G93A) rats and SOD1(G37R) mice. Mitochondrial damage, including increased mitochondrial volume, excess superoxide production and increased exposure of the toxic BH3 domain of Bcl-2, tracks positively with the presence of misfolded SOD1. Lastly, B8H10 reactive misfolded SOD1 is present in the lysates and mitochondrial fractions of lymphoblasts derived from ALS patients carrying SOD1 mutations, but not in controls. Together, these results highlight misfolded SOD1 as common to two ALS rodent animal models and familial ALS patient lymphoblasts with four different SOD1 mutations. Studies in the animal models point to a role for misfolded SOD1 in mitochondrial dysfunction in ALS pathogenesis.

Capillary electrophoretic analysis of hydroxyl radicals produced by respiring mitochondria

Here, we report the use of a capillary electrophoretic method with laser-induced fluorescence detection to evaluate hydroxyl radicals produced by respiring mitochondria. The probe, hydroxyphenylfluorescein (HPF), is separated from the product, fluorescein, in under 5 min with zeptomole and attomole limits of detection for fluorescein and HPF, respectively. Purification of the probe with a C-18 SPE column is necessary to reduce the fluorescein impurity in the probe stock solution from 0.4% to less than 0.001%. HPF was responsive to hydroxyl radicals produced by isolated mitochondria from L6 cells, and this signal was blunted when DMSO was added to scavenge hydroxyl radicals and when carbonyl cyanide m-chlorophenylhydrazone was added to depolarize the mitochondria. The method was used to compare hydroxyl radical levels in mitochondria isolated from brown adipose tissue of lean and obese mice. Mitochondria from obese mice produced significantly more hydroxyl radicals than those from lean mice.

Methods for assessing mitochondrial function in diabetes

A growing body of research is investigating the potential contribution of mitochondrial function to the etiology of type 2 diabetes. Numerous in vitro, in situ, and in vivo methodologies are available to examine various aspects of mitochondrial function, each requiring an understanding of their principles, advantages, and limitations. This review provides investigators with a critical overview of the strengths, limitations and critical experimental parameters to consider when selecting and conducting studies on mitochondrial function. In vitro (isolated mitochondria) and in situ (permeabilized cells/tissue) approaches provide direct access to the mitochondria, allowing for study of mitochondrial bioenergetics and redox function under defined substrate conditions. Several experimental parameters must be tightly controlled, including assay media, temperature, oxygen concentration, and in the case of permeabilized skeletal muscle, the contractile state of the fibers. Recently developed technology now offers the opportunity to measure oxygen consumption in intact cultured cells. Magnetic resonance spectroscopy provides the most direct way of assessing mitochondrial function in vivo with interpretations based on specific modeling approaches. The continuing rapid evolution of these technologies offers new and exciting opportunities for deciphering the potential role of mitochondrial function in the etiology and treatment of diabetes.

Protein carbonylation and adipocyte mitochondrial function

Carbonylation is the covalent, non-reversible modification of the side chains of cysteine, histidine, and lysine residues by lipid peroxidation end products such as 4-hydroxy- and 4-oxononenal. In adipose tissue the effects of such modifications are associated with increased oxidative stress and metabolic dysregulation centered on mitochondrial energy metabolism. To address the role of protein carbonylation in the pathogenesis of mitochondrial dysfunction, quantitative proteomics was employed to identify specific targets of carbonylation in GSTA4-silenced or overexpressing 3T3-L1 adipocytes. GSTA4-silenced adipocytes displayed elevated carbonylation of several key mitochondrial proteins including the phosphate carrier protein, NADH dehydrogenase 1α subcomplexes 2 and 3, translocase of inner mitochondrial membrane 50, and valyl-tRNA synthetase. Elevated protein carbonylation is accompanied by diminished complex I activity, impaired respiration, increased superoxide production, and a reduction in membrane potential without changes in mitochondrial number, area, or density. Silencing of the phosphate carrier or NADH dehydrogenase 1α subcomplexes 2 or 3 in 3T3-L1 cells results in decreased basal and maximal respiration. These results suggest that protein carbonylation plays a major instigating role in cytokine-dependent mitochondrial dysfunction and may be linked to the development of insulin resistance in the adipocyte.

Detailed analysis of apoptosis and delayed luminescence of human leukemia Jurkat T cells after proton irradiation and treatments with oxidant agents and flavonoids

Following previous work, we investigated in more detail the relationship between apoptosis and delayed luminescence (DL) in human leukemia Jurkat T cells under a wide variety of treatments. We used menadione and hydrogen peroxide to induce oxidative stress and two flavonoids, quercetin, and epigallocatechin gallate, applied alone or in combination with menadione or H₂O₂. 62 MeV proton beams were used to irradiate cells under a uniform dose of 2 or 10 Gy, respectively. We assessed apoptosis, cell cycle distributions, and DL. Menadione, H₂O₂ and quercetin were potent inducers of apoptosis and DL inhibitors. Quercetin decreased clonogenic survival and the NAD(P)H level in a dose-dependent manner. Proton irradiation with 2 Gy but not 10 Gy increased the apoptotic rate. However, both doses induced a substantial G₂/M arrest. Quercetin reduced apoptosis and prolonged the G₂/M arrest induced by radiation. DL spectroscopy indicated that proton irradiation disrupted the electron flow within Complex I of the mitochondrial respiratory chain, thus explaining the massive necrosis induced by 10 Gy of protons and also suggested an equivalent action of menadione and quercetin at the level of the Fe/S center N2, which may be mediated by their binding to a common site within Complex I, probably the rotenone-binding site.

Oxidants, antioxidants, and the beneficial roles of exercise-induced production of reactive species

This review offers an overview of the influence of reactive species produced during exercise and their effect on exercise adaptation. Reactive species and free radicals are unstable molecules that oxidize other molecules in order to become stable. Although they play important roles in our body, they can also lead to oxidative stress impairing diverse cellular functions. During exercise, reactive species can be produced mainly, but not exclusively, by the following mechanisms: electron leak at the mitochondrial electron transport chain, ischemia/reperfusion and activation of endothelial xanthine oxidase, inflammatory response, and autooxidation of catecholamines. Chronic exercise also leads to the upregulation of the body's antioxidant defence mechanism, which helps minimize the oxidative stress that may occur after an acute bout of exercise. Recent studies show a beneficial role of the reactive species, produced during a bout of exercise, that lead to important training adaptations: angiogenesis, mitochondria biogenesis, and muscle hypertrophy. The adaptations occur depending on the mechanic, and consequently biochemical, stimulus within the muscle. This is a new area of study that promises important findings in the sphere of molecular and cellular mechanisms involved in the relationship between oxidative stress and exercise.

Measurement of H2O2 within living Drosophila during aging using a ratiometric mass spectrometry probe targeted to the mitochondrial matrix

Hydrogen peroxide (H(2)O(2)) is central to mitochondrial oxidative damage and redox signaling, but its roles are poorly understood due to the difficulty of measuring mitochondrial H(2)O(2) in vivo. Here we report a ratiometric mass spectrometry probe approach to assess mitochondrial matrix H(2)O(2) levels in vivo. The probe, MitoB, comprises a triphenylphosphonium (TPP) cation driving its accumulation within mitochondria, conjugated to an arylboronic acid that reacts with H(2)O(2) to form a phenol, MitoP. Quantifying the MitoP/MitoB ratio by liquid chromatography-tandem mass spectrometry enabled measurement of a weighted average of mitochondrial H(2)O(2) that predominantly reports on thoracic muscle mitochondria within living flies. There was an increase in mitochondrial H(2)O(2) with age in flies, which was not coordinately altered by interventions that modulated life span. Our findings provide approaches to investigate mitochondrial ROS in vivo and suggest that while an increase in overall mitochondrial H(2)O(2) correlates with aging, it may not be causative.

Chemical cytometry quantitates superoxide levels in the mitochondrial matrix of single myoblasts

Triphenylphosphonium hydroethidine (TPP-HE) is a membrane-permeable probe that reacts with superoxide and forms hydroxytriphenylphosphonium ethidium (OH-TPP-E(+)), a fluorescent product that has been previously used in qualitative measurements of superoxide production. In order to develop quantitative methods to measure superoxide, it is necessary to take into consideration the principles that drive TPP-HE accumulation into various subcellular compartments. In the mitochondria matrix, TPP-HE accumulation depends on the mitochondrial membrane potential, which varies from cell to cell. Here we address this issue by including rhodamine 123 (R123) as an internal mitochondrial membrane potential calibrant in chemical cytometry experiments. After loading with TPP-HE and R123, a single cell is lysed within a separation capillary and its contents are separated and detected by micellar electrokinetic capillary chromatography with laser-induced fluorescence detection (MEKC-LIF). Using theoretical arguments, we show that the ratio [OH-TPP-E(+)]/[R123] is adequate to obtain a relative quantitation of mitochondrial matrix superoxide levels for each analyzed cell. We applied this method to single skeletal muscle myoblasts and determined that the steady state superoxide levels in the mitochondrial matrix is approximately (0.29 +/- 0.10) x 10(-12) M. The development of this quantitative method is a critical step toward establishing the importance of reactive oxygen species in biological systems, including those relevant to aging and disease.

Asymmetric superoxide release inside and outside the mitochondria in skeletal muscle under conditions of aging and disuse

Superoxide released from mitochondria forms reactive oxygen species that can cause severe oxidative damage and have been associated with aging- and disuse-induced muscle dysfunction. Superoxide is released to both the exterior and the matrix of mitochondria, where oxidative damage is not necessarily the same. This complicates determining the role of mitochondrial superoxide in eliciting oxidative stress in skeletal muscle. A newly developed capillary electrophoretic method analyzes hydroxytriphenylphosphonium ethidium, a superoxide-specific product of triphenylphosphonium hydroethidine, released to outside the mitochondria (supernatant) and retained in the matrix (pellet). In this study, we investigated the mitochondrial superoxide production of soleus (type I) and semimembranosus (type II) muscles of Fischer 344 rats affected by aging (13 vs. 26 mo) and disuse (hindlimb unloading). In agreement with previous studies, overall superoxide production increased with aging and disuse. On the other hand, the new experimental method revealed that superoxide production outside the mitochondria of the soleus does not show a significant age-related increase. Another observation was that the superoxide production increase in the matrix occurs earlier (7 days of disuse) compared with the outside mitochondria (14 days of disuse) in both muscle types. These findings indicate that superoxide release is complex as it occurs asymmetrically at both sides of the mitochondrial inner membrane, and that such release has muscle type and temporal specificity. These findings are important to refine current concepts on oxidative stress associated with muscle aging and disuse.

Analysis of superoxide production in single skeletal muscle fibers

Due to their high energetic profile, skeletal muscle fibers are prone to damage by endogenous reactive oxygen species (ROS), thereby causing alterations in muscle function. Unfortunately, the complexity of skeletal muscle makes it difficult to measure and understand ROS production by fibers since other components (e.g., extracellular collagen and vascular vessels) may also generate ROS. Single cell imaging techniques are promising approaches to monitor ROS production in single muscle fibers, but usually the detection schemes for ROS are not specific. Single cell analysis by capillary electrophoresis (aka chemical cytometry) has the potential to separate and detect specific ROS reporters, but the approach is only suitable for small spherical cells that fit within the capillary lumen. Here, we report a novel method for the analysis of superoxide in single fibers maintained in culture for up to 48 h. Cultured muscle fibers in individual nanoliter-volume wells were treated with triphenylphosphonium hydroethidine (TPP-HE), which forms the superoxide specific reporter hydroxytriphenylphosphonium ethidium (OH-TPP-E(+)). After lysis of each fiber in their corresponding nanowell, the contents of each well were processed and analyzed by micellar electrokinetic capillary chromatography with laser-induced fluorescence detection (MEKC-LIF) making it possible to detect superoxide found in single fibers. Superoxide basal levels as well as changes due to fiber treatment with the scavenger, tiron, and the inducer, antimycin A, were easily monitored demonstrating the feasibility of the method. Future uses of the method include parallel single-fiber measurements aiming at comparing pharmacological treatments on the same set of fibers and investigating ROS production in response to muscle disease, disuse, exercise, and aging.

Downregulation of adipose glutathione S-transferase A4 leads to increased protein carbonylation, oxidative stress, and mitochondrial dysfunction

OBJECTIVE

Peripheral insulin resistance is linked to an increase in reactive oxygen species (ROS), leading in part to the production of reactive lipid aldehydes that modify the side chains of protein amino acids in a reaction termed protein carbonylation. The primary enzymatic method for lipid aldehyde detoxification is via glutathione S-transferase A4 (GSTA4) dependent glutathionylation. The objective of this study was to evaluate the expression of GSTA4 and the role(s) of protein carbonylation in adipocyte function.

RESEARCH DESIGN AND METHODS

GSTA4-silenced 3T3-L1 adipocytes and GSTA4-null mice were evaluated for metabolic processes, mitochondrial function, and reactive oxygen species production. GSTA4 expression in human obesity was evaluated using microarray analysis.

RESULTS

GSTA4 expression is selectively downregulated in adipose tissue of obese insulin-resistant C57BL/6J mice and in human obesity-linked insulin resistance. Tumor necrosis factor-alpha treatment of 3T3-L1 adipocytes decreased GSTA4 expression, and silencing GSTA4 mRNA in cultured adipocytes resulted in increased protein carbonylation, increased mitochondrial ROS, dysfunctional state 3 respiration, and altered glucose transport and lipolysis. Mitochondrial function in adipocytes of lean or obese GSTA4-null mice was significantly compromised compared with wild-type controls and was accompanied by an increase in superoxide anion.

CONCLUSIONS

These results indicate that downregulation of GSTA4 in adipose tissue leads to increased protein carbonylation, ROS production, and mitochondrial dysfunction and may contribute to the development of insulin resistance and type 2 diabetes.

Hydroethidine- and MitoSOX-derived red fluorescence is not a reliable indicator of intracellular superoxide formation: another inconvenient truth

Hydroethidine (HE; or dihydroethidium) is the most popular fluorogenic probe used for detecting intracellular superoxide radical anion. The reaction between superoxide and HE generates a highly specific red fluorescent product, 2-hydroxyethidium (2-OH-E(+)). In biological systems, another red fluorescent product, ethidium, is also formed, usually at a much higher concentration than 2-OH-E(+). In this article, we review the methods to selectively detect the superoxide-specific product (2-OH-E(+)) and the factors affecting its levels in cellular and biological systems. The most important conclusion of this review is that it is nearly impossible to assess the intracellular levels of the superoxide-specific product, 2-OH-E(+), using confocal microscopy or other fluorescence-based microscopic assays and that it is essential to measure by HPLC the intracellular HE and other oxidation products of HE, in addition to 2-OH-E(+), to fully understand the origin of red fluorescence. The chemical reactivity of mitochondria-targeted hydroethidine (Mito-HE, MitoSOX red) with superoxide is similar to the reactivity of HE with superoxide, and therefore, all of the limitations attributed to the HE assay are applicable to Mito-HE (or MitoSOX) as well.

Effectiveness of Novel Borane-Phosphine Complexes In Inhibiting Cell Death Depends on the Source of Superoxide Production Induced by Blockade of Mitochondrial Electron Transport

Central neurons undergo cell death after axotomy. One of the signaling pathways for this process is oxidative modification of one or more critical sulfhydryls in association with superoxide generation within mitochondria. Agents that reduce oxidized sulfhydryls are neuroprotective of axotomized retinal ganglion cells, and we hypothesized that this occurs via reversal of the effects of mitochondrial-produced superoxide. To study this, we measured the ability of the novel borane-phosphine complex drugs bis(3-propionic acid methyl ester)phenylphosphine borane complex (PB1) and (3-propionic acid methyl ester)diphenylphosphine borane complex (PB2) to inhibit the death of neuron-like RGC-5 cells induced by perturbation of the mitochondrial electron transport chain. We found that borane-phosphine complexes prevent neuronal cell death from superoxide produced by the redox-cycling agent menadione and the complex III inhibitor antimycin A, which produce superoxide towards the cytoplasm and matrix, but not the complex I inhibitor rotenone, which produces superoxide in the matrix alone. The ability of these disulfide reductants to prevent cell death may be predicted by the topology of superoxide production with respect to the mitochondrial matrix and extramitochondrial space.