Teaching the fundamentals of electron transfer reactions in mitochondria and the production and detection of reactive oxygen species

Catalyst-free Click PEGylation reveals substantial mitochondrial ATP synthase sub-unit alpha oxidation before and after fertilisation

Using non-reducing Western blotting to assess protein thiol redox state is challenging because most reduced and oxidised forms migrate at the same molecular weight and are, therefore, indistinguishable. While copper catalysed Click chemistry can be used to ligate a polyethylene glycol (PEG) moiety termed Click PEGylation to mass shift the reduced or oxidised form as desired, the potential for copper catalysed auto-oxidation is problematic. Here we define a catalyst-free trans-cyclooctene-methyltetrazine (TCO-Tz) inverse electron demand Diels Alder chemistry approach that affords rapid (k ~2000 M-1 s-1), selective and bio-orthogonal Click PEGylation. We used TCO-Tz Click PEGylation to investigate how fertilisation impacts reversible mitochondrial ATP synthase F1-Fo sub-unit alpha (ATP-α-F1) oxidation-an established molecular correlate of impaired enzyme activity-in Xenopus laevis. TCO-Tz Click PEGylation studies reveal substantial (~65%) reversible ATP-α-F1 oxidation at evolutionary conserved cysteine residues (i.e., C244 and C294) before and after fertilisation. A single thiol is, however, preferentially oxidised likely due to greater solvent exposure during the catalytic cycle. Selective reduction experiments show that: S-glutathionylation accounts for ~50-60% of the reversible oxidation observed, making it the dominant oxidative modification type. Intermolecular disulphide bonds may also contribute due to their relative stability. Substantial reversible ATP-α-F1 oxidation before and after fertilisation is biologically meaningful because it implies low mitochondrial F1-Fo ATP synthase activity. Catalyst-free TCO-Tz Click PEGylation is a valuable new tool to interrogate protein thiol redox state in health and disease.

Hydrogen sulfide, reactive sulfur species and coping with reactive oxygen species

Life began in a ferruginous (anoxic and Fe²⁺ dominated) world around 3.8 billion years ago (bya). Hydrogen sulfide (H₂S) and other sulfur molecules from hydrothermal vents and other fissures provided many key necessities for life's origin including catalytic platforms (primordial enzymes) that also served as primitive boundaries (cell walls), substrates for organic synthesis and a continuous source of energy in the form of reducing equivalents. Anoxigenic photosynthesis oxidizing H₂S followed within a few hundred million years and laid the metabolic groundwork for oxidative photosynthesis some half-billion years later that slightly and episodically increased atmospheric oxygen around 2.3 bya. This oxidized terrestrial sulfur to sulfate which was washed to the sea where it was reduced creating vast euxinic (anoxic and sulfidic) areas. It was in this environment that eukaryotic cells appeared around 1.5 bya and where they evolved for nearly 1 billion additional years. Oxidative photosynthesis finally oxidized the oceans and around 0.6 bya oxygen levels in the atmosphere and oceans began to rise toward present day levels. This is purported to have been a life-threatening event due to the prevalence of reactive oxygen species (ROS) and thus necessitated the elaboration of chemical and enzymatic antioxidant mechanisms. However, these antioxidants initially appeared around the time of anoxigenic photosynthesis suggesting a commitment to metabolism of reactive sulfur species (RSS). This review examines these events and suggests that many of the biological attributes assigned to ROS may, in fact, be due to RSS. This is underscored by observations that ROS and RSS are chemically similar, often indistinguishable by analytical methods and the fact that the bulk of biochemical and physiological experiments are performed in unphysiologically oxic environments where ROS are artifactually favored over RSS.

Cerium- and Iron-Oxide-Based Nanozymes in Tissue Engineering and Regenerative Medicine

Nanoparticulate materials displaying enzyme-like properties, so-called nanozymes, are explored as substitutes for natural enzymes in several industrial, energy-related, and biomedical applications. Outstanding high stability, enhanced catalytic activities, low cost, and availability at industrial scale are some of the fascinating features of nanozymes. Furthermore, nanozymes can also be equipped with the unique attributes of nanomaterials such as magnetic or optical properties. Due to the impressive development of nanozymes during the last decade, their potential in the context of tissue engineering and regenerative medicine also started to be explored. To highlight the progress, in this review, we discuss the two most representative nanozymes, namely, cerium- and iron-oxide nanomaterials, since they are the most widely studied. Special focus is placed on their applications ranging from cardioprotection to therapeutic angiogenesis, bone tissue engineering, and wound healing. Finally, current challenges and future directions are discussed.

Increased reactive oxygen species production and maintenance of membrane potential in VDAC-less Neurospora crassa mitochondria

The highly abundant voltage-dependent anion-selective channel (VDAC) allows transit of metabolites across the mitochondrial outer membrane. Previous studies in Neurospora crassa showed that the LoPo strain, expressing 50% of normal VDAC levels, is indistinguishable from wild-type (WT). In contrast, the absence of VDAC (ΔPor-1), or the expression of an N-terminally truncated variant VDAC (ΔN2-12porin), is associated with deficiencies in cytochromes b and aa₃ of complexes III and IV and concomitantly increased alternative oxidase (AOX) activity. These observations led us to investigate complex I and complex II activities in these strains, and to explore their mitochondrial bioenergetics. The current study reveals that the total NADH dehydrogenase activity is similar in mitochondria from WT, LoPo, ΔPor-1 and ΔN2-12porin strains; however, in ΔPor-1 most of this activity is the product of rotenone-insensitive alternative NADH dehydrogenases. Unexpectedly, LoPo mitochondria have increased complex II activity. In all mitochondrial types analyzed, oxygen consumption is higher in the presence of the complex II substrate succinate, than with the NADH-linked (complex I) substrates glutamate and malate. When driven by a combination of complex I and II substrates, membrane potentials (Δψ) and oxygen consumption rates (OCR) under non-phosphorylating conditions are similar in all mitochondria. However, as expected, the induction of state 3 (phosphorylating) conditions in ΔPor-1 mitochondria is associated with smaller but significant increases in OCR and smaller decreases in Δψ than those seen in wild-type mitochondria. High ROS production, particularly in the presence of rotenone, was observed under non-phosphorylating conditions in the ΔPor-1 mitochondria. Thus, the absence of VDAC is associated with increased ROS production, in spite of AOX activity and wild-type OCR in ΔPor-1 mitochondria.

Xanthine oxidase-mediated oxidative stress promotes cancer cell-specific apoptosis

The natural compound Alternol was shown to induce profound oxidative stress and apoptotic cell death preferentially in cancer cells. In this study, a comprehensive investigation was conducted to understand the mechanism for Alternol-induced ROS accumulation responsible for apoptotic cell death. Our data revealed that Alternol treatment moderately increased mitochondrial superoxide formation rate, but it was significantly lower than the total ROS positive cell population. Pre-treatment with mitochondria-specific anti-oxidant MitoQ, NOX or NOS specific inhibitors had no protective effect on Alternol-induced ROS accumulation and cell death. However, XDH/XO inhibition by specific small chemical inhibitors or gene silencing reduced total ROS levels and protected cells from apoptosis induced by Alternol. Further analysis revealed that Alternol treatment significantly enhanced XDH oxidative activity and induced a strong protein oxidation-related damage in malignant but not benign cells. Interestingly, benign cells exerted a strong spike in anti-oxidant SOD and catalase activities compared to malignant cells after Alternol treatment. Cell-based protein-ligand engagement and in-silicon docking analysis showed that Alternol interacts with XDH protein on the catalytic domain with two amino acid residues away from its substrate binding sites. Taken together, our data demonstrate that Alternol treatment enhances XDH oxidative activity, leading to ROS-dependent apoptotic cell death.

Isopsoralen ameliorates H2O2-induced damage in osteoblasts via activating the Wnt/β-catenin pathway

Osteoporosis is a disease with a worldwide prevalence that involves a severe loss of bone mineral density and decreased microarchitecture, which increases the risk of bone fracture. The present study evaluated the effects of isopsoralen on osteoblastic OB-6 cells following hydrogen peroxide (H₂O₂)-induced damage and investigated the molecular mechanisms involved in this process. For in vitro experiments, OB-6 osteoblasts were treated with H₂O₂ or H₂O₂ + isopsoralen then the cell viability, apoptosis, reactive oxygen species (ROS) production and calcium accumulation were determined. Results demonstrated that treatment with H₂O₂ reduced cell viability, runt-related transcription factor 2 (RUNX2) and osteocalcin (OCN) expression levels, and calcium deposition, whilst markedly increasing cell apoptosis and ROS production. However, isopsoralen (1 µM) provided significant protection against H₂O₂-induced alterations in osteoblasts. In addition, isopsoralen effectively upregulated protein expression of tankyrase and β-catenin which are the main transductors of the Wnt/β-catenin pathway. Of note, the protective effects of isopsoralen against H₂O₂-induced damage were attenuated in OB-6 cells treated with tankyrase inhibitor XAV-939. In conclusion, the present findings provided evidence that isopsoralen attenuated oxidative stress-induced injury in osteoblasts via the Wnt/β-catenin signaling pathway.

Mitochondrial Morphofunction in Mammalian Cells

Significance: In addition to their classical role in cellular ATP production, mitochondria are of key relevance in various (patho)physiological mechanisms including second messenger signaling, neuro-transduction, immune responses and death induction. Recent Advances: Within cells, mitochondria are motile and display temporal changes in internal and external structure ("mitochondrial dynamics"). During the last decade, substantial empirical and in silico evidence was presented demonstrating that mitochondrial dynamics impacts on mitochondrial function and vice versa. Critical Issues: However, a comprehensive and quantitative understanding of the bidirectional links between mitochondrial external shape, internal structure and function ("morphofunction") is still lacking. The latter particularly hampers our understanding of the functional properties and behavior of individual mitochondrial within single living cells. Future Directions: In this review we discuss the concept of mitochondrial morphofunction in mammalian cells, primarily using experimental evidence obtained within the last decade. The topic is introduced by briefly presenting the central role of mitochondria in cell physiology and the importance of the mitochondrial electron transport chain (ETC) therein. Next, we summarize in detail how mitochondrial (ultra)structure is controlled and discuss empirical evidence regarding the equivalence of mitochondrial (ultra)structure and function. Finally, we provide a brief summary of how mitochondrial morphofunction can be quantified at the level of single cells and mitochondria, how mitochondrial ultrastructure/volume impacts on mitochondrial bioreactions and intramitochondrial protein diffusion, and how mitochondrial morphofunction can be targeted by small molecules.

Proliferating tumor cells mimick glucose metabolism of mature human erythrocytes

Mature human erythrocytes are dependent on anerobic glycolysis, i.e. catabolism (oxidation) of one glucose molecule to produce two ATP and two lactate molecules. Proliferating tumor cells mimick mature human erythrocytes to glycolytically generate two ATP molecules. They deliberately avoid or switch off their respiration, i.e. tricarboxylic acid (TCA) cycle and oxidative phosphorylation (OXPHOS) machinery and consequently dispense with the production of additional 36 ATP molecules from one glucose molecule. This phenomenon is named aerobic glycolysis or Warburg effect. The present review deals with the fate of a glucose molecule after entering a mature human erythrocyte or a proliferating tumor cell and describes why it is useful for a proliferating tumor cell to imitate a mature erythrocyte. Blood consisting of plasma and cellular components (99% of the cells are erythrocytes) may be regarded as a mobile organ, constantly exercising a direct interaction with other organs. Therefore, the use of drugs, which influences the biological activity of erythrocytes, has an immediate effect on the entire organism.

Abbreviations: TCA: tricarboxylic acid cycle; OXPHOS: oxidative phosphorylation; GSH: reduced state of glutathione; NFκB: Nuclear factor of kappa B; PKB (Akt): protein kinase B; NOS: nitric oxide synthase; IgG: immune globulin G; H₂S: hydrogen sulfide; slanDCs: Human 6-sulfo LacNAc-expressing dendritic cells; IL-8: interleukin-8; LPS: lipopolysaccharide; ROS: reactive oxygen species; PPP: pentose phosphate pathway; NADPH: nicotinamide adenine dinucleotide phosphate hydrogen; R5P: ribose-5-phophate; NAD: nicotinamide adenine dinucleotide; FAD: flavin adenine dinucleotide; O₂^●−: superoxide anion; G6P: glucose 6-phosphate; HbO₂: Oxyhemoglobin; GAPDH: glyceraldehyde-3-phosphate dehydrogenase; GAP: glyceraldehyde-3-phosphate; 1,3-BPG: 1,3-bis-phosphoglycerate; 2,3-BPG: 2,3-bisphosphoglycerte; PGAM1: phosphoglycerate mutase 1; 3-PG: 3-phosphoglycerate; 2-PG: 2-phosphoglycerate; MIPP1: Multiple inositol polyphosphate phosphatase; mTORC1: mammalian target of rapamycin complex 1; Ru5P: ribulose 5-phosphate; ox-PPP: oxidative branch of pentose phosphate pathway; PGK: phosphoglycerate kinase; IFN-γ: interferon-γ; LDH: lactate dehydrogenase; STAT3: signal transducer and activator of transcription 3; Rheb: Ras homolog enriched in Brain; H₂O₂: hydrogen peroxide; ROOH: lipid peroxide; SOD: superoxide dismutase; MRC: mitochondrial respiratory chain; MbFe²⁺-O₂: methmyoglobin; RNR: ribonucleotide reductase; PRPP: phosphoribosylpyrophosphate; PP_i: pyrophosphate; GSSG: oxidized state of glutathione; non-ox-PPP: non-oxidative branch of pentose phosphate pathway; RPI: ribose-5-phosphate isomerase; RPE: ribulose 5-phosphate 3-epimerase; X5P: xylulose 5-phosphate; TK: transketolase; TA: transaldolase; F6P: fructose-6-phosphate; AR2: aldose reductase 2; SD: sorbitol dehydrogenase; HK: hexokinase; MG: mehtylglyoxal; DHAP: dihydroxyacetone phosphate; TILs: tumor-infiltrating lymphocytes; MCTs: monocarboxylate transporters; pHi: intracellular pH; Hif-1α: hypoxia-induced factor 1; NHE1: sodium/H⁺ (Na⁺/H⁺) antiporter 1; V-ATPase: vacuolar-type proton ATPase; CAIX: carbonic anhydrase; CO₂: carbon dioxide; HCO₃⁻: bicarbonate; NBC: sodium/bicarbonate (Na⁺/HCO₃⁻) symporter; pHe: extracellular pH; GLUT-1: glucose transporter 1; PGK-1: phosphoglycerate kinase 1

Mitochondria-coupled glucose phosphorylation develops after birth to modulate H2 O2 release and calcium handling in rat brain

The adult brain is a high-glucose and oxygen-dependent organ, with an extremely organized network of cells and large energy-consuming synapses. To reach this level of organization, early stages in development must include an efficient control of cellular events and regulation of intracellular signaling molecules and ions such as hydrogen peroxide (H₂ O₂ ) and calcium (Ca²⁺ ), but in cerebral tissue, these mechanisms of regulation are still poorly understood. Hexokinase (HK) is the first enzyme in the metabolism of glucose and, when bound to mitochondria (mtHK), it has been proposed to have a role in modulation of mitochondrial H₂ O₂  generation and Ca²⁺ handling. Here, we have investigated how mtHK modulates these signals in the mitochondrial context during postnatal development of the mouse brain. Using high-resolution respirometry, western blot analysis, spectrometry and resorufin, and Calcium Green fluorescence assays with brain mitochondria purified postnatally from day 1 to day 60, we demonstrate that brain HK increases its coupling to mitochondria and to oxidative phosphorylation to induce a cycle of ADP entry/ATP exit of the mitochondrial matrix that leads to efficient control over H₂ O₂ generation and Ca²⁺ uptake during development until reaching plateau at day 21. This contrasts sharply with the antioxidant enzymes, which do not increase as mitochondrial H₂ O₂ generation escalates. These results suggest that, as its use of glucose increases, the brain couples HK to mitochondria to improve glucose metabolism, redox balance and Ca²⁺ signaling during development, positioning mitochondria-bound hexokinase as a hub for intracellular signaling control.

GATA-1 isoforms differently contribute to the production and compartmentation of reactive oxygen species in the myeloid leukemia cell line K562

Maintenance of a balanced expression of the two isoforms of the transcription factor GATA‐1, the full‐length protein (GATA‐1_FL) and a shorter isoform (GATA‐1 _S), contributes to control hematopoiesis, whereas their dysregulation can alter the differentiation/proliferation potential of hematopoietic precursors thereby eventually leading to a variety of hematopoietic disorders. Although it is well established that these isoforms play opposite roles in these remarkable processes, most of the molecular pathways involved remain unknown.

Here, we demonstrate that GATA‐1_FL and GATA‐1_S are able to differently influence intracellular redox states and reactive oxygen species (ROS) compartmentation in the erythroleukemic K562 cell line, thus shedding novel mechanistic insights into the processes of cell proliferation and apoptosis resistance in myeloid precursors. Furthermore, given the role played by ROS signaling as a strategy to escape apoptosis and evade cell‐mediated immunity in myeloid cells, this study highlights a mechanism through which aberrant expression of GATA‐1 isoforms could play a role in the leukemogenic process.

An old medicine as a new drug to prevent mitochondrial complex I from producing oxygen radicals

Findings

Here, we demonstrate that OP2113 (5-(4-Methoxyphenyl)-3H-1,2-dithiole-3-thione, CAS 532-11-6), synthesized and used as a drug since 1696, does not act as an unspecific antioxidant molecule (i.e., as a radical scavenger) but unexpectedly decreases mitochondrial reactive oxygen species (ROS/H₂O₂) production by acting as a specific inhibitor of ROS production at the I_Q site of complex I of the mitochondrial respiratory chain. Studies performed on isolated rat heart mitochondria also showed that OP2113 does not affect oxidative phosphorylation driven by complex I or complex II substrates. We assessed the effect of OP2113 on an infarct model of ex vivo rat heart in which mitochondrial ROS production is highly involved and showed that OP2113 protects heart tissue as well as the recovery of heart contractile activity.

Conclusion / Significance

This work represents the first demonstration of a drug authorized for use in humans that can prevent mitochondria from producing ROS/H₂O₂. OP2113 therefore appears to be a member of the new class of mitochondrial ROS blockers (S1QELs) and could protect mitochondrial function in numerous diseases in which ROS-induced mitochondrial dysfunction occurs. These applications include but are not limited to aging, Parkinson’s and Alzheimer's diseases, cardiac atrial fibrillation, and ischemia-reperfusion injury.

Rare ginsenosides ameliorate lipid overload-induced myocardial insulin resistance via modulating metabolic flexibility

BACKGROUND

Rare ginsenosides are found in ginseng and notoginseng, two medicinal plants widely used in China for treatment of cardiovascular diseases and type 2 diabetes. However, their pharmacological studies regarding myocardial fuel metabolism and insulin signaling are not clear.

PURPOSE

To explore the effect of a rare ginsenoside-standardized extract (RGSE), derived from steamed notoginseng, on cardiac fuel metabolism and insulin signaling.

STUDY DESIGN

We used palmitic acid (PA) to treat H9c2 cells in vitro and high fat diet (HFD) to mice to induce insulin resistance in vivo.

METHODS

In vitro, differentiated H9c2 cells were pretreated with RGSE, metformin, mildronate or dichloroacetate (DCA) and stimulated with PA. In vivo, mice were fed with HFD and received RGSE, metformin or DCA for 6 weeks. Protein expression was determined by Western blotting. Mitochondrial membrane potential (Δψm), glucose uptake and reactive oxygen species (ROS) production were measured by fluorescence labeling. Other assessments including oxygen consumption rate (OCR) were also performed.

RESULTS

RGSE prevented PA-induced decrease in pyruvate dehydrogenase (PDH) activity and increase in carnitine palmitoyltransferase 1 (CPT1) expression, and ameliorated insulin-mediated glucose uptake and utilization in H9c2 cells. Metformin and mildronate exhibited similar effects. In vivo, RGSE counteracted HFD-induced increase in myocardial expression of p-PDH and CPT1 and ameliorated cardiac insulin signaling. Metformin and DCA also showed beneficial effects. Further study showed that RGSE decreased OCR and mitochondrial complex I activity in PA-treated H9c2 cells, reduced ROS production and relieved mitochondrial oxidative stress, thus decreased serine phosphorylation in IRS-1.

CONCLUSION

RGSE ameliorated myocardial insulin sensitivity under conditions of lipid overload, which was tightly associated with the decrease in mitochondrial oxidative stress via modulating glucose and fatty acid oxidation.

Human serum albumin attenuates global cerebral ischemia/reperfusion-induced brain injury in a Wnt/β-Catenin/ROS signaling-dependent manner in rats

This study sought to clarify the role and underlying mechanisms of human serum albumin (HSA) therapy in global cerebral ischemia/reperfusion (GCI/R)-induced brain damage in rats. Five groups of adult male Wistar rats (n = 12 per group) were created as follows: sham operation (Sham), global cerebral ischemia/reperfusion (GCI/R), HSA treatment (GCI/R + HSA), Dickkopf-1 (DDK1) treatment (GCI/R + DDK1), and DDK1 plus HSA treatment (GCI/R + DKK1 + HSA). The GCI/R injury model was created using the modified Pusinelli four-vessel occlusion method. After 24 h, rats were evaluated using neurological scoring, Nissl staining, and brain tissue water content. The mRNA expression of Wnt, GSK3β, and β-Catenin in the brain were detected by quantitative real time polymerase chain reaction. The protein expression of β-Catenin and GSK-3β were investigated by western blot and immunohistochemical analysis in the presence and absence of the Wnt/β-Catenin antagonist, DKK-1. Complex I activity and ROS content were also measured. After 24 h of reperfusion, the behavior score and brain tissue water content in the GCI/R + HSA group were lower than that in the GCI/R group. In addition, the degree of neuronal injury was significantly reduced in the GCI/R + HSA group (P < 0.05). The ROS content was significantly decreased and Complex I activity was markedly raised in the GCI/R + HSA group compared to the GCI/R group (P < 0.05). Further, GSK-3β expression in the GCI/R + HSA group was lower than that in the GCI/R group, while the Wnt and β-catenin expression were increased. These effects were reversed by DKK1. Taken together, we showed that HSA attenuates GCI/R-induced brain damage and may be neuroprotective via regulation of the Wnt/β-catenin/ROS signaling pathway.

Ca2+-Induced Mitochondrial ROS Regulate the Early Embryonic Cell Cycle

While it is appreciated that reactive oxygen species (ROS) can act as second messengers in both homeostastic and stress response signaling pathways, potential roles for ROS during early vertebrate development have remained largely unexplored. Here, we show that fertilization in Xenopus embryos triggers a rapid increase in ROS levels, which oscillate with each cell division. Furthermore, we show that the fertilization-induced Ca²⁺ wave is necessary and sufficient to induce ROS production in activated or fertilized eggs. Using chemical inhibitors, we identified mitochondria as the major source of fertilization-induced ROS production. Inhibition of mitochondrial ROS production in early embryos results in cell-cycle arrest, in part, via ROS-dependent regulation of Cdc25C activity. This study reveals a role for oscillating ROS levels in early cell cycle regulation in Xenopus embryos.

Elucidation of in vitro cellular steps induced by antitumor treatment with plasma-activated medium

Numerous studies have reported cold atmospheric plasma cytotoxic activities in various cancer cell lines, either by direct exposure to non-thermal plasma or indirectly by activating a medium (plasma-activated medium, PAM) prior to cell treatment. We suggested the use of in vitro 3D tumor model spheroids to determine the potential of PAM for cancer therapy at the tissue scale, especially in human tumor tissue. This work aimed to better understand the effect of PAM on human colorectal tumor spheroids by describing the in vitro-induced-cell death kinetics and associated mechanisms to further improve its therapeutic potential. Tumor spheroid growth was delayed depending on contact time with PAM. Medium osmolarity was increased by activation with low temperature Helium plasma jet but it did not fully explain the observed growth delay. PAM impaired tumor cell viability through intracellular ATP depletion, leading within hours to both cell apoptosis and necrosis as well as mitochondrial oxidative stress. When successive treatments were spaced over time, cumulative effects on the growth delay of spheroids were observed. Taken together, these results demonstrated that plasma-activated liquids may represent a novel and efficient therapeutic method for the treatment of tumors, especially when successive treatments are applied.

Mitoflash biogenesis and its role in the autoregulation of mitochondrial proton electrochemical potential

Individual mitochondria undergo an intermittent, all-or-none electrochemical excitation termed “mitoflash.” Feng et al. show that mitoflash occurs following build-up of mitochondrial electrochemical potential and may serve to autoregulate mitochondrial proton electrochemical potential.

Respiring mitochondria undergo an intermittent electrical and chemical excitation called mitochondrial flash (mitoflash), which transiently uncouples mitochondrial respiration from ATP production. How a mitoflash is generated and what specific role it plays in bioenergetics remain incompletely understood. Here, we investigate mitoflash biogenesis in isolated cardiac mitochondria by varying the respiratory states and substrate supply and by dissecting the involvement of different electron transfer chain (ETC) complexes. We find that robust mitoflash activity occurs once mitochondria are electrochemically charged by state II/IV respiration (i.e., no ATP synthesis at Complex V), regardless of the substrate entry site (Complex I, Complex II, or Complex IV). Inhibiting forward electron transfer abolishes, while blocking reverse electron transfer generally augments, mitoflash production. Switching from state II/IV to state III respiration, to allow for ATP synthesis at Complex V, markedly diminishes mitoflash activity. Intriguingly, when mitochondria are electrochemically charged by the ATPase activity of Complex V, mitoflashes are generated independently of ETC activity. These findings suggest that mitoflash biogenesis is mechanistically linked to the build up of mitochondrial electrochemical potential rather than ETC activity alone, and may functionally counteract overcharging of the mitochondria and hence serve as an autoregulator of mitochondrial proton electrochemical potential.

Lag Phase Is a Dynamic, Organized, Adaptive, and Evolvable Period That Prepares Bacteria for Cell Division

Lag is a temporary period of nonreplication seen in bacteria that are introduced to new media. Despite latency being described by Müller in 1895, only recently have we gained insights into the cellular processes characterizing lag phase. This review covers literature to date on the transcriptomic, proteomic, metabolomic, physiological, biochemical, and evolutionary features of prokaryotic lag. Though lag is commonly described as a preparative phase that allows bacteria to harvest nutrients and adapt to new environments, the implications of recent studies indicate that a refinement of this view is well deserved. As shown, lag is a dynamic, organized, adaptive, and evolvable process that protects bacteria from threats, promotes reproductive fitness, and is broadly relevant to the study of bacterial evolution, host-pathogen interactions, antibiotic tolerance, environmental biology, molecular microbiology, and food safety.

The role of NO-cGMP pathway inhibition in vascular endothelial-dependent smooth muscle relaxation disorder of AT1-AA positive rats: protective effects of adiponectin

Angiotensin II type 1 receptor autoantibodies (AT1-AA) cause endothelial-dependent smooth muscle relaxation disorder. It is well understood that impairment of the NO-cGMP signaling pathway is one of the mechanisms of endothelial-dependent smooth muscle relaxation disorder. However, it is still unclear whether AT1-AA induces endothelial-dependent smooth muscle relaxation disorder via the impairment of the NO-cGMP signaling pathway. In addition, adiponectin exerts vascular endothelial protection through the NO-cGMP signaling pathway. Therefore, the purpose of this investigation was to assess the mechanism of vascular endothelial-dependent smooth muscle relaxation disorder induced by AT1-AA and the role of adiponectin in attenuating this dysregulation. Serum endothelin-1 (ET-1), adiponectin and AT1-AA were detected by enzyme-linked immunosorbent assay. In preeclamptic patients, there was an increased level of AT1-AA, which was positively correlated with ET-1 and negatively correlated with adiponectin, as elevated levels of ET-1 suggested endothelial injury. AT1-AA-positive animal models were actively immunized with the second extracellular loop of the angiotensin II type 1 receptor (AT1R-ECII) for eight weeks. In thoracic aortas of AT1-AA positive rats, ET-1 was elevated, endothelium-dependent vasodilation was decreased. Paradoxically, as the upstream element of the NO-cGMP signaling pathway, NO production was not decreased but increased, and the ratio of p-VASP/VASP, an established biochemical endpoint of NO-cGMP signaling pathway, was reduced. Moreover, the levels of nitrotyrosine and gp91phox which indicate the presence of peroxynitrite (ONOO^-) and superoxide anion (O₂·^-) were increased. Pretreatment with the ONOO^- scavenger FeTMPyP or O₂·^-scavenger Tempol normalized vasorelaxation. Key enzymes responsible for NO synthesis were also assessed. iNOS protein expression was increased, but p-eNOS(Ser1177)/eNOS was reduced. Preincubation with the iNOS inhibitor 1400 W or eNOS agonist nebivolol restored vasorelaxation. Further experiments showed levels of p-AMPKα (Thr172)/AMPKα, which controls iNOS expression and eNOS activity, to have been reduced. Furthermore, levels of the upstream component of AMPK, adiponectin, was reduced in sera of AT1-AA positive rats and supplementation of adiponectin significantly decreased ET-1 contents, improved endothelial-dependent vasodilation, reduced NO production, elevated p-VASP/VASP, inhibited protein expression of nitrotyrosine and gp91phox, reduced iNOS overexpression, and increased eNOS phosphorylation at Ser1177 in the thoracic aorta of AT1-AA positive rats. These results established that impairment NO-cGMP pathway may aggravate the endothelial-dependent smooth muscle relaxation disorder in AT1-AA positive rats and adiponectin improved endothelial-dependent smooth muscle relaxation disorder by enhancing NO-cGMP pathway. This discovery may shed a novel light on clinical treatment of vascular diseases associated with AT1-AA.

Effects of zearalenone and its derivatives on the synthesis and secretion of mammalian sex steroid hormones: A review

Zearalenone (ZEA), a non-steroidal estrogen mycotoxin produced by several species of Fusarium fungi, can be metabolized into many other derivatives by microorganisms, plants, animals and humans. It can affect mammalian reproductive capability by impacting the synthesis and secretion of sex hormones, including testosterone, estradiol and progesterone. This review summarizes the mechanisms in which ZEA and its derivatives disturb the synthesis and secretion of sex steroid hormones. Because of its structural analogy to estrogen, ZEA and its derivatives can exert a variety of estrogen-like effects and engage in estrogen negative feedback regulation, which can result in mediating the production of follicle-stimulating hormone (FSH) and luteinizing hormone (LH) in the pituitary gland. ZEA and its derivatives can ultimately reduce the number of Leydig cells and granulosa cells by inducing oxidative stress, endoplasmic reticulum (ER) stress, cell cycle arrest, cell apoptosis, and cell regeneration delay. Additionally, they can disrupt the mitochondrial structure and influence mitochondrial functions through overproduction of reactive oxygen species (ROS) and aberrant autophagy signaling ways. Finally, ZEA and its derivatives can disturb the expressions and activities of the related steroidogenic enzymes through cross talking between membrane and nuclear estrogen receptors.

Redox regulation of motile cilia in airway disease

Motile cilia on airway cells are necessary for clearance of mucus-trapped particles out of the lung. Ciliated airway epithelial cells are uniquely exposed to oxidants through trapping of particles, debris and pathogens in mucus and the direct exposure to inhaled oxidant gases. Dynein ATPases, the motors driving ciliary motility, are sensitive to the local redox environment within each cilium. Several redox-sensitive cilia-localized proteins modulate dynein activity and include Protein Kinase A, Protein Kinase C, and Protein Phosphatase 1. Moreover, cilia are rich in known redox regulatory proteins and thioredoxin domain-containing proteins that are critical in maintaining a balanced redox environment. Importantly, a nonsense mutation in TXNDC3, which contains a thioredoxin motif, has recently been identified as disease-causing in Primary Ciliary Dyskinesia, a hereditary motile cilia disease resulting in impaired mucociliary clearance. Here we review current understanding of the role(s) oxidant species play in modifying airway ciliary function. We focus on oxidants generated in the airways, cilia redox targets that modulate ciliary beating and imbalances in redox state that impact health and disease. Finally, we review disease models such as smoking, asthma, alcohol drinking, and infections as well as the direct application of oxidants that implicate redox balance as a modulator of cilia motility.

VAS2870 Inhibits Histamine-Induced Calcium Signaling and vWF Secretion in Human Umbilical Vein Endothelial Cells

In this study, we investigated the effects of NAD(P)H oxidase (NOX) inhibitor VAS2870 (3-benzyl-7-(2-benzoxazolyl)thio-1,2,3-triazolo[4,5-d]pyrimidine) on the histamine-induced elevation of free cytoplasmic calcium concentration ([Ca²⁺]_i) and the secretion of von Willebrand factor (vWF) in human umbilical vein endothelial cells (HUVECs) and on relaxation of rat aorta in response to histamine. At 10 μM concentration, VAS2870 suppressed the [Ca²⁺]_i rise induced by histamine. Inhibition was not competitive, with IC50 3.64 and 3.22 μM at 1 and 100 μM concentrations of histamine, respectively. There was no inhibition of [Ca²⁺]_i elevation by VAS2870 in HUVECs in response to the agonist of type 1 protease-activated receptor SFLLRN. VAS2870 attenuated histamine-induced secretion of vWF and did not inhibit basal secretion. VAS2870 did not change the degree of histamine-induced relaxation of rat aortic rings constricted by norepinephrine. We suggest that NOX inhibitors might be used as a tool for preventing thrombosis induced by histamine release from mast cells without affecting vasorelaxation.

Signaling and Regulation Through the NAD+ and NADP+ Networks

SIGNIFICANCE

NAD⁺ and NADP⁺ are important cosubstrates in redox reactions and participate in regulatory networks operating in adjustment of metabolic pathways. Moreover, NAD⁺ is a cosubstrate in post-translational modification of proteins and is involved in DNA repair. NADPH is indispensable for reductive syntheses and the redox chemistry involved in attaining and maintaining correct protein conformation. Recent Advances: Within a couple of decades, a wealth of information has been gathered on NAD(H)⁺/NADP(H) redox imaging, regulatory role of redox potential in assembly of spatial protein structures, and the role of ADP-ribosylation of regulatory proteins affecting both gene expression and metabolism. All these have a bearing also on disease, healthy aging, and longevity.

CRITICAL ISSUES

Knowledge of the signal propagation pathways of NAD⁺-dependent post-translational modifications is still fragmentary for explaining the mechanism of cellular stress effects and nutritional state on these actions. Evaluation of the cosubstrate and regulator roles of NAD(H) and NADP(H) still suffers from some controversies in experimental data.

FUTURE DIRECTIONS

Activating or inhibiting interventions in NAD⁺-dependent protein modifications for medical purposes has shown promise, but restraining tumor growth by inhibiting DNA repair in tumors by means of interference in sirtuins is still in the early stage. The same is true for the use of this technology in improving health and healthy aging. New genetically encoded specific NAD and NADP probes are expected to modernize the research on redox biology.

Cysteine Switches and the Regulation of Mitochondrial Bioenergetics and ROS Production

Mitochondria are dynamic organelles that perform a number of interconnected tasks that are elegantly intertwined with the regulation of cell functions. This includes the provision of ATP, reactive oxygen species (ROS), and building blocks for the biosynthesis of macromolecules while also serving as signaling platforms for the cell. Although the functions executed by mitochondria are complex, at its core these roles are, to a certain degree, fulfilled by electron transfer reactions and the establishment of a protonmotive force (PMF). Indeed, mitochondria are energy conserving organelles that extract electrons from nutrients to establish a PMF, which is then used to drive ATP and NADPH production, solute import, and many other functions including the propagation of cell signals. These same electrons extracted from nutrients are also used to produce ROS, pro-oxidants that can have potentially damaging effects at high levels, but also serve as secondary messengers at low amounts. Mitochondria are also enriched with antioxidant defenses, which are required to buffer cellular ROS. These same redox buffering networks also fulfill another important role; regulation of proteins through the reversible oxidation of cysteine switches. The modification of cysteine switches with the antioxidant glutathione, a process called protein S-glutathionylation, has been found to play an integral role in controlling various mitochondrial functions. In addition, recent findings have demonstrated that disrupting mitochondrial protein S-glutathionylation reactions can have some dire pathological consequences. Accordingly, this chapter focuses on the role of mitochondrial cysteine switches in the modulation of different physiological functions and how defects in these pathways contribute to the development of disease.

AVE 0991 attenuates oxidative stress and neuronal apoptosis via Mas/PKA/CREB/UCP-2 pathway after subarachnoid hemorrhage in rats

Oxidative stress and neuronal apoptosis have been demonstrated to be key features in early brain injury (EBI) after subarachnoid hemorrhage (SAH). Previous studies have indicated that Mas receptor activation initiates an anti-oxidative and anti-apoptotic role in the brain. However, whether Mas activation can attenuate oxidative stress and neuronal apoptosis after SAH remains unknown. To investigate the beneficial effect of Mas on oxidative stress injury and neuronal apoptosis induced by SAH, a total of 196 rats were subjected to an endovascular perforation model of SAH. AVE 0991 (AVE), a selective agonist of Mas, was administered intranasally 1 h after SAH induction. A779, a selective inhibitor of Mas, and small interfering ribonucleic acid (siRNA) for UCP-2 were administered by intracerebroventricular (i.c.v) injection at 1 h and 48 h before SAH induction respectively. Neurological tests, immunofluorescence, TUNEL, Fluoro-Jade C, DHE staining, and Western blot experiments were performed. We found that Mas activation with AVE significantly improved neurobehavioral scores and reduced oxidative stress and neuronal apoptosis in SAH+AVE group compared with SAH+vehicle group. Moreover, AVE treatment significantly promoted phosphorylation of CREB and the expression UCP-2, as well as upregulated expression of Bcl-2 and downregulation of Romo-1 and Bax. The protective effects of AVE were reversed by i.c.v injection of A779 and UCP-2 siRNA in SAH+AVE+A779 and SAH+AVE+UCP-2 siRNA groups, respectively. In conclusion, our data provides evidence that Mas activation with AVE reduces oxidative stress injury and neuronal apoptosis through Mas/PKA/p-CREB/UCP-2 pathway after SAH. Furthermore, our study indicates that Mas may be a novel therapeutic treatment target in early brain injury of SAH.

Respiratory Membrane Protein Complexes Convert Chemical Energy

The invention of a biological membrane which is used as energy storage system to drive the metabolism of a primordial, unicellular organism represents a key event in the evolution of life. The innovative, underlying principle of this key event is respiration. In respiration, a lipid bilayer with insulating properties is chosen as the site for catalysis of an exergonic redox reaction converting substrates offered from the environment, using the liberated Gibbs free energy (ΔG) for the build-up of an electrochemical H⁺ (proton motive force, PMF) or Na⁺ gradient (sodium motive force, SMF) across the lipid bilayer. Very frequently , several redox reactions are performed in a consecutive manner, with the first reaction delivering a product which is used as substrate for the second redox reaction, resulting in a respiratory chain. From today's perspective, the (mostly) unicellular bacteria and archaea seem to be much simpler and less evolved when compared to multicellular eukaryotes. However, they are overwhelmingly complex with regard to the various respiratory chains which permit survival in very different habitats of our planet, utilizing a plethora of substances to drive metabolism. This includes nitrogen, sulfur and carbon compounds which are oxidized or reduced by specialized, respiratory enzymes of bacteria and archaea which lie at the heart of the geochemical N, S and C-cycles. This chapter gives an overview of general principles of microbial respiration considering thermodynamic aspects, chemical reactions and kinetic restraints. The respiratory chains of Escherichia coli and Vibrio cholerae are discussed as models for PMF- versus SMF-generating processes, respectively. We introduce main redox cofactors of microbial respiratory enzymes, and the concept of intra-and interelectron transfer. Since oxygen is an electron acceptor used by many respiratory chains, the formation and removal of toxic oxygen radicals is described. Promising directions of future research are respiratory enzymes as novel bacterial targets, and biotechnological applications relying on respiratory complexes.

Action of Hydrogen Peroxide on Synaptic Transmission at the Mouse Neuromuscular Junction

Hydrogen peroxide (H₂O₂) is one of the reactive oxygen species (ROS), endogenously produced during metabolism, which acts as a second messenger. In skeletal muscles, hypoxia- or hyperthermia-induced increase in H₂O₂ might affect synaptic transmission by targeting the most redox-sensitive presynaptic compartment (Giniatullin et al., 2006). However, the effects of H₂O₂ as a signal molecule have not previously been studied in different patterns of the synaptic activity. Here, using optical and microelectrode recording of synaptic vesicle exocytosis, we studied the use-dependent action of low concentrations of H₂O₂ and other oxidants in the mouse neuromuscular junction. We found that: (i) H₂O₂ at low micromole concentrations inhibited both spontaneous and evoked transmitter releases from the motor nerve terminals in a use-dependent manner, (ii) the antioxidant N-acetylcysteine (NAC) eliminated these depressant effects, (iii) the influence of H₂O₂ was not associated with lipid oxidation suggesting a pure signaling action, (iv) the intracellular oxidant Chloramine-T or (v) the glutathione depletion produced similar to H₂O₂ depressant effects. Taken together, our data revealed the effective inhibition of neurotransmitter release by ROS, which was proportional to the intensity of synaptic activity at the neuromuscular junction. The combination of various oxidants suggested an intracellular location for redox-sensitive sites responsible for modulation of the synaptic transmission in the skeletal muscle.

When safeguarding goes wrong: Impact of oxidative stress on protein homeostasis in health and neurodegenerative disorders

Cellular redox status is an established player in many different cellular functions. The buildup of oxidants within the cell is tightly regulated to maintain a balance between the positive and negative outcomes of cellular oxidants. Proteins are highly sensitive to oxidation, since modification can cause widespread unfolding and the formation of toxic aggregates. In response, cells have developed highly regulated systems that contribute to the maintenance of both the global redox status and protein homeostasis at large. Changes to these systems have been found to correlate with aging and age-related disorders, such as neurodegenerative pathologies. This raises intriguing questions as to the source of the imbalance in the redox and protein homeostasis systems, their interconnectivity, and their role in disease progression. Here we focus on the crosstalk between the redox and protein homeostasis systems in neurodegenerative diseases, specifically in Alzheimer's, Parkinson's, and ALS. We elaborate on some of the main players of the stress response systems, including the master regulators of oxidative stress and the heat shock response, Nrf2 and Hsf1, which are essential features of protein folding, and mediators of protein turnover. We illustrate the elegant mechanisms used by these components to provide an immediate response, including protein plasticity controlled by redox-sensing cysteines and the recruitment of naive proteins to the redox homeostasis array that act as chaperons in an ATP-independent manner.

Protein S-glutathionylation: The linchpin for the transmission of regulatory information on redox buffering capacity in mitochondria

Protein S-glutathionylation reactions are a ubiquitous oxidative modification required to control protein function in response to changes in redox buffering capacity. These reactions are rapid and reversible and are, for the most part, enzymatically mediated by glutaredoxins (GRX) and glutathione S-transferases (GST). Protein S-glutathionylation has been found to control a range of cell functions in response to different physiological cues. Although these reactions occur throughout the cell, mitochondrial proteins seem to be highly susceptible to reversible S-glutathionylation, a feature attributed to the unique physical properties of this organelle. Indeed, mitochondria contain a number of S-glutathionylation targets which includes proteins involved in energy metabolism, solute transport, reactive oxygen species (ROS) production, proton leaks, apoptosis, antioxidant defense, and mitochondrial fission and fusion. Moreover, it has been found that conjugation and removal of glutathione from proteins in mitochondria fulfills a number of important physiological roles and defects in these reactions can have some dire pathological consequences. Here, we provide an updated overview on mitochondrial protein S-glutathionylation reactions and their importance in cell functions and physiology.

Placental mitochondrial adaptations in preeclampsia associated with progression to term delivery

Preeclampsia is a devastating pregnancy disorder. Severity varies widely, and while severe preeclampsia often requires pre-term delivery, women with mild preeclampsia may reach term with minor interventions. The mechanisms that mediate disease severity are poorly understood, but may include adaptive processes by the placenta. We aimed to establish whether in pregnancies that reached term and those that delivered pre-term, the placental response to preeclampsia was intrinsically different, and explore potential adaptive mechanisms. Hydrogen peroxide production and antioxidant activity were increased in term preeclamptic placentae, whereas pre-term preeclamptic placentae had reduced hydrogen peroxide production and reduced function of the antioxidant system superoxide dismutase compared to control placentae. Markers of mitochondrial fission/fusion, apoptosis and the expression level of mitochondrial complexes were differentially disrupted in term compared to pre-term preeclamptic placentae. Mitochondrial respiration and content were increased in term preeclamptic placentae, but mitochondria had a lower respiratory reserve capacity. Mitochondrial respiration and hydrogen peroxide production were increased in healthy term placentae after in vitro hypoxia/reoxygenation. Placentae from preeclamptic pregnancies that reached term showed multiple adaptions that were not present in pre-term preeclamptic placentae. Increased antioxidant activity, and expression of markers of mitochondrial fusion and apoptotic suppression, may relate to salvaging damaged mitochondria. Increased mitochondrial respiration may allow ongoing tissue function even with reduced respiratory efficiency in term preeclamptic pregnancies. Response after in vitro hypoxia/reoxygenation suggests that disruption of oxygen supply is key to placental mitochondrial adaptations. Reactive oxygen species signalling in term preeclamptic placentae may be at a level to trigger compensatory antioxidant and mitochondrial responses, allowing tissue level maintenance of function when there is organelle level dysfunction.

Biochemical re-programming of human dermal stem cells to neurons by increasing mitochondrial membrane potential

Stem cells are generally believed to contain a small number of mitochondria, thus accounting for their glycolytic phenotype. We demonstrate here, however, that despite an indispensable glucose dependency, human dermal stem cells (hDSCs) contain very numerous mitochondria. Interestingly, these stem cells segregate into two distinct subpopulations. One exhibits high, the other low-mitochondrial membrane potentials (_Δψ_m). We have made the same observations with mouse neural stem cells (mNSCs) which serve here as a complementary model to hDSCs. Strikingly, pharmacologic inhibition of phosphoinositide 3-kinase (PI3K) increased the overall _Δψ_m, decreased the dependency on glycolysis and led to formation of TUJ1 positive, electrophysiologically functional neuron-like cells in both mNSCs and hDSCs, even in the absence of any neuronal growth factors. Furthermore, of the two, it was the _Δψ_m-high subpopulation which produced more mitochondrial reactive oxygen species (ROS) and showed an enhanced neuronal differentiation capacity as compared to the _Δψ_m-low subpopulation. These data suggest that the _Δψ_m-low stem cells may function as the dormant stem cell population to sustain future neuronal differentiation by avoiding excessive ROS production. Thus, chemical modulation of PI3K activity, switching the metabotype of hDSCs to neurons, may have potential as an autologous transplantation strategy for neurodegenerative diseases.

Promoting the treatment of crude oil alkane pollution through the study of enzyme activity

Microbes appear to play a key role in bioremediation of petroleum hydrocarbons pollution and little attention has been paid to the enzyme activity in the process of alkane bioremediation. Oil field bacterium identified as Pseudomonas synxantha LSH-7' was chosen as the tested strain. Periodically collected samples were analyzed by GC-FID (Gas Chromatography- Flame Ionization Detector) and RT-qPCR (Quantitative-Real-Time-PCR). GC-FID results showed this bacterial strain has great degradation ability on crude oil n-alkanes and RT-qPCR data indicated the differences between the three genes expression including AlkB-, Cytochromes P450-, and almA- related when grown on different-chain alkanes. Meanwhile, enzyme activity like alkane hydroxylase, alcohol dehydrogenase, dehydrogenase, protease, phosphatase, catalase and lipase were measured. Extracellular alkane hydroxylase was induced in a higher degree than intracellular in the early incubation time, alcohol dehydrogenase increased/decreased along with alkane hydroxylase, and the pH of the medium obviously decreased. Other enzymes were also described including dehydrogenase activity that reached a highest point that was slower than alcohol dehydrogenase, protease activity started multiplying after a period of culture while biomass was immediately increased, catalase activity dramatically enhanced in the presence of alkanes, phosphatase activity was closely linked to pH approximately but lipase activity was found to be moderate.

Cytoprotective and antioxidant properties of organic selenides for the myelin-forming cells, oligodendrocytes

Here a new series of twenty-one organoselenides, of potential protective activity, were synthesized and tested for their intrinsic cytotoxicity, anti-apoptotic and antioxidant capacities in oligodendrocytes. Most of the organoselenides were able to decrease the ROS levels, revealing antioxidant properties. Compounds 5b and 7b showed a high glutathione peroxidase (GPx)-like activities, which were 1.5 folds more active than ebselen. Remarkably, compound 5a diminished the formation of the oligodendrocytes SubG1 peak in a concentration-dependent manner, indicating its anti-apoptotic properties. Furthermore, based on the SwissADME web interface, we performed an in-silico structure-activity relationship to explore the drug-likeness of these organoselenides, predicting the pharmacokinetic parameters for compounds of interest that could cross the blood-brain barrier. Collectively, we present new organoselenide compounds with cytoprotective and antioxidant properties that can be considered as promising drug candidates for myelin diseases.

Oxidative Stress and Cardiac Remodeling: An Updated Edge

Background:

A common phenotype associated with heart failure is the development of cardiac hypertrophy. Cardiac hypertrophy occurs in response to stress, such as hypertension, coro-nary vascular disease, or myocardial infarction. The most critical pathophysiological conditions in-volved may include dilated hypertrophy, fibrosis and contractile malfunction. The intricate pathophys-iological mechanisms of cardiac hypertrophy have been the core of several scientific studies, which may help in opening a new avenue in preventive and curative procedures.

Objectives:

To our knowledge from the literature, the development of cardiac remodeling and hyper-trophy is multifactorial. Thus, in this review, we will focus and summarize the potential role of oxida-tive stress in cardiac hypertrophy development.

Conclusion:

Oxidative stress is considered a major stimulant for the signal transduction in cardiac cells pathological conditions, including inflammatory cytokines, and MAP kinase. The understanding of the pathophysiological mechanisms which are involved in cardiac hypertrophy and remodeling process is crucial for the development of new therapeutic plans, especially that the mortality rates re-lated to cardiac remodeling/dysfunction remain high

CFTR prevents neuronal apoptosis following cerebral ischemia reperfusion via regulating mitochondrial oxidative stress

The cystic fibrosis transmembrane conductance regulator (CFTR) is linked to cell apoptosis and abundantly expressed in brain tissue. Mitochondrial oxidative stress plays a key role in activating apoptotic pathway following cerebral ischemia reperfusion (IR) injury. Reduced glutathione (GSH) is exclusively synthesized in cytosol but distributed in mitochondria. In the present study, we investigated whether CFTR affected mitochondrial oxidative stress via regulating GSH and thereby protected neurons against apoptosis following cerebral IR. Brains were subjected to global IR by four-vessel occlusion and CFTR activator forskolin (FSK) was used in vivo. CFTR silence was performed in vitro for neurons by RNA interference. We found that FSK suppressed neuronal apoptosis whereas CFTR silence enhanced neuronal apoptosis. FSK prevented the elevations in reactive oxygen species (ROS) and caspase activities while FSK inhibited the reductions in complex I activity and mitochondrial GSH level following IR. FSK decreased mitochondrial oxidative stress partially and preserved mitochondrial function. On the contrary, CFTR silence exaggerated mitochondrial dysfunction. CFTR loss increased hydrogen peroxide (H₂O₂) level and decreased GSH level in mitochondria. Importantly, we showed that CFTR was located on mitochondrial membrane. GSH transport assay suggested that GSH decrease may be a consequence not a reason for mitochondrial oxidative stress mediated by CFTR disruption. Our results highlight the central role of CFTR in the pathogenesis of cerebral IR injury. CFTR regulates neuronal apoptosis following cerebral IR via mitochondrial oxidative stress-dependent pathway. The mechanism of CFTR-mediated mitochondrial oxidative stress needs further studies. KEY MESSAGES: CFTR activation protects brain tissue against IR-induced apoptosis and oxidative stress. CFTR disruption enhances H₂O₂-induced neuronal apoptosis and CFTR loss leads to mitochondrial oxidative stress. CFTR regulates IR-induced neuronal apoptosis via mitochondrial oxidative stress. CFTR may be a potential therapeutic target to cerebral IR damage.

Characterization of the impact of glutaredoxin-2 (GRX2) deficiency on superoxide/hydrogen peroxide release from cardiac and liver mitochondria

Mitochondria are critical sources of hydrogen peroxide (H2O2), an important secondary messenger in mammalian cells. Recent work has shown that O2•-/H2O2 emission from individual sites of production in mitochondria is regulated by protein S-glutathionylation. Here, we conducted the first examination of O2•-/H2O2 release rates from cardiac and liver mitochondria isolated from mice deficient for glutaredoxin-2 (GRX2), a matrix-associated thiol oxidoreductase that facilitates the S-glutathionylation and deglutathionylation of proteins. Liver mitochondria isolated from mice heterozygous (GRX2+/-) and homozygous (GRX2-/-) for glutaredoxin-2 displayed a significant decrease in O2•-/H2O2 release when oxidizing pyruvate or 2-oxoglutarate. The genetic deletion of the Grx2 gene was associated with increased protein expression of pyruvate dehydrogenase (PDH) but not 2-oxoglutarate dehydrogenase (OGDH). By contrast, O2•-/H2O2 production was augmented in cardiac mitochondria from GRX2+/- and GRX2-/- mice metabolizing pyruvate or 2-oxoglutarate which was associated with decreased PDH and OGDH protein levels. ROS production was augmented in liver and cardiac mitochondria metabolizing succinate. Inhibitor studies revealed that OGDH and Complex III served as high capacity ROS release sites in liver mitochondria. By contrast, Complex I and Complex III were found to be the chief O2•-/H2O2 emitters in cardiac mitochondria. These findings identify an essential role for GRX2 in regulating O2•-/H2O2 release from mitochondria in liver and cardiac tissue. Our results demonstrate that the GRX2-mediated regulation of O2•-/H2O2 release through the S-glutathionylation of mitochondrial proteins may play an integral role in controlling cellular ROS signaling.

Cobra neurotoxin produces central analgesic and hyperalgesic actions via adenosine A1 and A2A receptors

Cobra neurotoxin, a short-chain peptide isolated from snake venom of Naja naja atra, showed both a central analgesic effect and a hyperalgesic effect in mice tests. In order to explore mechanisms, a hypothesis is put forward that cobra neurotoxin takes effect through adenosine receptor pathway. The central effects of cobra neurotoxin were evaluated using the hot plate test (a model of acute pain) and the spinal cord injury (a model of central pain) in mice and using A₁ receptor antagonist (DPCPX) and A_2A receptor antagonist (ZM241385); behaviors were scored and signal molecules such as reactive oxygen species and adenosine triphosphate levels and mitogen-activated protein kinases/extracellular signal-regulated protein kinase expression were measured. Low dose of cobra neurotoxin (25 µg/kg) had analgesic effects which were inhibited by DPCPX, while high dose of cobra neurotoxin (100 µg/kg) had hyperalgesic effects which were blocked by ZM241385. Cobra neurotoxin reduced reactive oxygen species and increased adenosine triphosphate in brain tissues, and extracellular signal-regulated protein kinase expression was markedly inhibited by cobra neurotoxin. Cobra neurotoxin may take effect through mitogen-activated protein kinases/extracellular signal-regulated protein kinase pathway inhibition by activating adenosine A₁Rs and cause changes of reactive oxygen species and adenosine triphosphate through feedback mechanisms. Overdose cobra neurotoxin further activates the adenosine A_2ARs to generate pain sensitization. This research proposes a new central analgesic mechanism of cobra neurotoxin and discloses dual regulation of pain.

Oxygen-dependence of mitochondrial ROS production as detected by Amplex Red assay

The initial rates of superoxide plus hydrogen peroxide (ROS) generation by intact or permeabilized rat heart mitochondria and coupled inside-out bovine heart submitochondrial particles (SMP) oxidizing NAD-dependent substrates, NADH, and succinate were measured by detecting resorufin formation in the Amplex Red assay at various oxygen concentrations. Linear dependences of the initial rates on oxygen concentration within the range of ~125-750 μM were found for all significant mitochondrial generators, i.e. the respiratory complexes and ammonium-stimulated dihydrolipoamide dehydrogenase. At lower oxygen concentrations upon its decrease from air saturation level to zero, the time-course of resorufin formation by SMP catalyzing coupled oxidation of succinate (the total ROS production by respiratory complexes II and III and by the reverse electron transfer (RET)-mediated by complex I) also corresponds to the linear dependence on oxygen with the same first-order rate constant determined in the initial rate studies. Prolonged incubation of SMP generating succinate-supported complex I-mediated ROS affected neither their NADH oxidase nor ROS generating activity. In contrast to SMP significant deviation from the first-order oxygen dependence in the time-course kinetics during coupled oxidation of succinate by intact mitochondria was evident. Complex I catalyzes the NADH:resorufin oxidoreductase reaction resulting in formation of colorless reduced resorufin. Hydrogen peroxide oxidizes reduced resorufin in the presence of peroxidase, thus showing its dihydroresorufin peroxidase activity. Combined NADH:resorufin reductase and dihydroresorufin peroxidase activities result in underestimation of the amount of hydrogen peroxide generated by mitochondria. We conclude that only initial rates of the mitochondrial ROS production, not the amount of resorufin accumulated, should be taken as the reliable measure of the mitochondrial ROS-generating activity, because of the cycling of the oxidized and reduced resorufin during Amplex Red assays fed by NADH and other possible reductant(s) present in mitochondria.

Circadian rhythms in mitochondrial respiration

Many physiological processes are regulated with a 24-h periodicity to anticipate the environmental changes of daytime to nighttime and vice versa. These 24-h regulations, commonly termed circadian rhythms, among others control the sleep-wake cycle, locomotor activity and preparation for food availability during the active phase (daytime for humans and nighttime for nocturnal animals). Disturbing circadian rhythms at the organ or whole-body level by social jetlag or shift work, increases the risk to develop chronic metabolic diseases such as type 2 diabetes mellitus. The molecular basis of this risk is a topic of increasing interest. Mitochondria are essential organelles that produce the majority of energy in eukaryotes by converting lipids and carbohydrates into ATP through oxidative phosphorylation. To adapt to the ever-changing environment, mitochondria are highly dynamic in form and function and a loss of this flexibility is linked to metabolic diseases. Interestingly, recent studies have indicated that changes in mitochondrial morphology (i.e., fusion and fission) as well as generation of new mitochondria are dependent on a viable circadian clock. In addition, fission and fusion processes display diurnal changes that are aligned to the light/darkness cycle. Besides morphological changes, mitochondrial respiration also displays diurnal changes. Disturbing the molecular clock in animal models leads to abrogated mitochondrial rhythmicity and altered respiration. Moreover, mitochondrial-dependent production of reactive oxygen species, which plays a role in cellular signaling, has also been linked to the circadian clock. In this review, we will summarize recent advances in the study of circadian rhythms of mitochondria and how this is linked to the molecular circadian clock.

The Good, the Bad, and the Ugly of ROS: New Insights on Aging and Aging-Related Diseases from Eukaryotic and Prokaryotic Model Organisms

Aging is associated with the accumulation of cellular damage over the course of a lifetime. This process is promoted in large part by reactive oxygen species (ROS) generated via cellular metabolic and respiratory pathways. Pharmacological, nonpharmacological, and genetic interventions have been used to target cellular and mitochondrial networks in an effort to decipher aging and age-related disorders. While ROS historically have been viewed as a detrimental byproduct of normal metabolism and associated with several pathologies, recent research has revealed a more complex and beneficial role of ROS in regulating metabolism, development, and lifespan. In this review, we summarize the recent advances in ROS research, focusing on both the beneficial and harmful roles of ROS, many of which are conserved across species from bacteria to humans, in various aspects of cellular physiology. These studies provide a new context for our understanding of the parts ROS play in health and disease. Moreover, we highlight the utility of bacterial models to elucidate the molecular pathways by which ROS mediate aging and aging-related diseases.

Oxidative Stress and Cardiac Remodeling: An Updated Edge

BACKGROUND

A common phenotype associated with heart failure is the development of cardiac hypertrophy. Cardiac hypertrophy occurs in response to stress, such as hypertension, coronary vascular disease, or myocardial infarction. The most critical pathophysiological conditions involved may include dilated hypertrophy, fibrosis and contractile malfunction. The intricate pathophysiological mechanisms of cardiac hypertrophy have been the core of several scientific studies, which may help in opening a new avenue in preventive and curative procedures.

OBJECTIVES

To our knowledge from the literature, the development of cardiac remodeling and hypertrophy is multifactorial. Thus, in this review, we will focus and summarize the potential role of oxidative stress in cardiac hypertrophy development.

CONCLUSION

Oxidative stress is considered a major stimulant for the signal transduction in cardiac cells pathological conditions, including inflammatory cytokines, and MAP kinase. The understanding of the pathophysiological mechanisms which are involved in cardiac hypertrophy and remodeling process is crucial for the development of new therapeutic plans, especially that the mortality rates related to cardiac remodeling/dysfunction remain high.

Simultaneous Measurement of Superoxide/Hydrogen Peroxide and NADH Production by Flavin-containing Mitochondrial Dehydrogenases

It has been reported that mitochondria can contain up to 12 enzymatic sources of reactive oxygen species (ROS). A majority of these sites include flavin-dependent respiratory complexes and dehydrogenases that produce a mixture of superoxide (O2^●-) and hydrogen peroxide (H2O2). Accurate quantification of the ROS-producing potential of individual sites in isolated mitochondria can be challenging due to the presence of antioxidant defense systems and side reactions that also form O2^●-/H2O2. Use of nonspecific inhibitors that can disrupt mitochondrial bioenergetics can also compromise measurements by altering ROS release from other sites of production. Here, we present an easy method for the simultaneous measurement of H2O2 release and nicotinamide adenine dinucleotide (NADH) production by purified flavin-linked dehydrogenases. For our purposes here, we have used purified pyruvate dehydrogenase complex (PDHC) and α-ketoglutarate dehydrogenase complex (KGDHC) of porcine heart origin as examples. This method allows for an accurate measure of native H2O2 release rates by individual sites of production by eliminating other potential sources of ROS and antioxidant systems. In addition, this method allows for a direct comparison of the relationship between H2O2 release and enzyme activity and the screening of the effectiveness and selectivity of inhibitors for ROS production. Overall, this approach can allow for the in-depth assessment of native rates of ROS release for individual enzymes prior to conducting more sophisticated experiments with isolated mitochondria or permeabilized muscle fiber.

Oncogene-Driven Metabolic Alterations in Cancer

Cancer is the leading cause of human deaths worldwide. Understanding the biology underlying the evolution of cancer is important for reducing the economic and social burden of cancer. In addition to genetic aberrations, recent studies demonstrate metabolic rewiring, such as aerobic glycolysis, glutamine dependency, accumulation of intermediates of glycolysis, and upregulation of lipid and amino acid synthesis, in several types of cancer to support their high demands on nutrients for building blocks and energy production. Moreover, oncogenic mutations are known to be associated with metabolic reprogramming in cancer, and these overall changes collectively influence tumor-microenvironment interactions and cancer progression. Accordingly, several agents targeting metabolic alterations in cancer have been extensively evaluated in preclinical and clinical settings. Additionally, metabolic reprogramming is considered a novel target to control cancers harboring un-targetable oncogenic alterations such as KRAS. Focusing on lung cancer, here, we highlight recent findings regarding metabolic rewiring in cancer, its association with oncogenic alterations, and therapeutic strategies to control deregulated metabolism in cancer.

Measurement of Mitochondrial ROS Formation

Reactive oxygen species (ROS) are involved in both physiological and pathological processes. This widely accepted concept is based more on the effects of antioxidant interventions than on reliable assessments of rates and sites of intracellular ROS formation. This argument applies also to mitochondria that are generally considered the major site for ROS formation, especially in skeletal and cardiac myocytes.Detection of oxidative modifications of intracellular or circulating molecules is frequently used as a marker of ROS formation. However, this approach provides limited information on spatiotemporal aspects of ROS formation that have to be defined in order to elucidate the role of ROS in a given pathophysiological condition. This information can be obtained by means of fluorescent probes that allow monitoring ROS formation in cell-free extracts and isolated cells. Thus, this approach can be used to characterize ROS formation in both isolated mitochondria and mitochondria within intact cells. This chapter describes three major examples of the use of fluorescent probes for monitoring mitochondrial ROS formation. Detailed methods description is accompanied by a critical analysis of the limitations of each technique, highlighting the possible sources of errors in performing the assay and results interpretation.

An adverse outcome pathway for parkinsonian motor deficits associated with mitochondrial complex I inhibition

Epidemiological studies have observed an association between pesticide exposure and the development of Parkinson's disease, but have not established causality. The concept of an adverse outcome pathway (AOP) has been developed as a framework for the organization of available information linking the modulation of a molecular target [molecular initiating event (MIE)], via a sequence of essential biological key events (KEs), with an adverse outcome (AO). Here, we present an AOP covering the toxicological pathways that link the binding of an inhibitor to mitochondrial complex I (i.e., the MIE) with the onset of parkinsonian motor deficits (i.e., the AO). This AOP was developed according to the Organisation for Economic Co-operation and Development guidelines and uploaded to the AOP database. The KEs linking complex I inhibition to parkinsonian motor deficits are mitochondrial dysfunction, impaired proteostasis, neuroinflammation, and the degeneration of dopaminergic neurons of the substantia nigra. These KEs, by convention, were linearly organized. However, there was also evidence of additional feed-forward connections and shortcuts between the KEs, possibly depending on the intensity of the insult and the model system applied. The present AOP demonstrates mechanistic plausibility for epidemiological observations on a relationship between pesticide exposure and an elevated risk for Parkinson's disease development.

Complex II phosphorylation is triggered by unbalanced redox homeostasis in cells lacking complex III

A marked stimulation of complex II enzymatic activity was detected in cybrids bearing a homoplasmic MTCYB microdeletion causing disruption of both the activity and the assembly of complex III, but not in cybrids harbouring another MTCYB mutation affecting only the complex III activity. Moreover, complex II stimulation was associated with SDHA subunit tyrosine phosphorylation. Despite the lack of detectable hydrogen peroxide production, up-regulation of the levels of mitochondrial antioxidant defenses revealed a significant redox unbalance. This effect was also supported by the finding that treatment with N-acetylcysteine dampened the complex II stimulation, SDHA subunit tyrosine phosphorylation, and levels of antioxidant enzymes. In the absence of complex III, the cellular amount of succinate, but not fumarate, was markedly increased, indicating that enhanced activity of complex II is hampered due to the blockage of respiratory electron flow. Thus, we propose that complex II phosphorylation and stimulation of its activity represent a molecular mechanism triggered by perturbation of mitochondrial redox homeostasis due to severe dysfunction of respiratory complexes. Depending on the site and nature of the damage, complex II stimulation can either bypass the energetic deficit as an efficient compensatory mechanism, or be ineffectual, leaving cells to rely on glycolysis for survival.

Succinate dehydrogenase: Prospect for neurodegenerative diseases

Onset of Alzheimer's, Parkinson's and Huntington's diseases as neurodegenerative disorders is increased by age. Alleviation of clinical symptoms and protection of neurons against degeneration are the main aspects of researches to establish new therapeutic strategies. Many studies have shown that mitochondria play crucial roles in high energy demand tissues like brain. Impairments in mitochondrial activity and physiology can makes neurons vulnerable to stress and degeneration. Succinate dehydrogenase (SDH) connects tricarboxylic cycle to the electron transport chain. Therefore, dysfunction of the SDH could impair mitochondrial activity, ATP generation and energy hemostasis in the cell. Exceed lipid synthesis, induction of the excitotoxicity in neurodegenerative disorders could be controlled by SDH through direct and indirect mechanism. In addition, mutation in SDH correlates with the onset of neurodegenerative disorders. Therefore, SDH could behave as a key regulator in neuroprotection. This review will present recent findings which are about SDH activity and related pathways which could play important roles in neuronal survival. Additionally, we will discuss about all possibilities which candidate SDH as a neuroprotective agent.

Mitochondrial ROS control of cancer

Mitochondria serves a primary role in energy maintenance but also function to govern levels of mitochondria-derived reactive oxygen species (mROS). ROS have long been established to play a critical role in tumorigenesis and are now considered to be integral to the regulation of diverse signaling networks that drive proliferation, tumor cell survival and malignant progression. mROS can damage DNA, activate oncogenes, block the function of tumor suppressors and drive migratory signaling. The mitochondrion's oxidant scavenging systems including SOD2, Grx2, GPrx, Trx and TrxR are key of the cellular redox tone. These mitochondrial antioxidant systems serve to tightly control the levels of the primary ROS signaling species, H2O2. The coordinated control of mROS levels is also coupled to the activity of the primary H2O2 consuming enzymes of the mitochondria which are reliant on the epitranscriptomic control of selenocysteine incorporation. This review highlights the interplay between these many oncogenic signaling networks, mROS and the H2O2 emitting and consuming capacity of the mitochondria.

Para-hydroxyphenylpyruvate inhibits the pro-inflammatory stimulation of macrophage preventing LPS-mediated nitro-oxidative unbalance and immunometabolic shift

Targeting metabolism is emerging as a promising therapeutic strategy for modulation of the immune response in human diseases. In the presented study we used the lipopolysaccharide (LPS)-mediated activation of RAW 264.7 macrophage-like cell line as a model to investigate changes in the metabolic phenotype and to test the effect of p-hydroxyphenylpyruvate (pHPP) on it. pHPP is an intermediate of the PHE/TYR catabolic pathway, selected as analogue of the ethyl pyruvate (EP), which proved to exhibit antioxidant and anti-inflammatory activities. The results obtained show that LPS-priming of RAW 264.7 cell line to the activated M1 state resulted in up-regulation of the inducible nitric oxide synthase (iNOS) expression and consequently of NO production and in release of the pro-inflammatory cytokine IL-6. All these effects were prevented dose dependently by mM concentrations of pHPP more efficiently than EP. Respirometric and metabolic flux analysis of LPS-treated RAW 264.7 cells unveiled a marked metabolic shift consisting in downregulation of the mitochondrial oxidative phosphorylation and upregulation of aerobic glycolysis respectively. The observed respiratory failure in LPS-treated cells was accompanied with inhibition of the respiratory chain complexes I and IV and enhanced production of reactive oxygen species. Inhibition of the respiratory activity was also observed following incubation of human neonatal fibroblasts (NHDF-neo) with sera from septic patients. pHPP prevented all the observed metabolic alteration caused by LPS on RAW 264.7 or by septic sera on NHDF-neo. Moreover, we provide evidence that pHPP is an efficient reductant of cytochrome c. On the basis of the presented results a working model, linking pathogen-associated molecular patterns (PAMPs)-mediated immune response to mitochondrial oxidative metabolism, is put forward along with suggestions for its therapeutic control.

Markers and Biomarkers of Endothelium: When Something Is Rotten in the State

Endothelium is a community of endothelial cells (ECs), which line the blood and lymphatic vessels, thus forming an interface between the tissues and the blood or lympha. This strategic position of endothelium infers its indispensable functional role in controlling vasoregulation, haemostasis, and inflammation. The state of endothelium is simultaneously the cause and effect of many diseases, and this is coupled with modifications of endothelial phenotype represented by markers and with biochemical profile of blood represented by biomarkers. In this paper, we briefly review data on the functional role of endothelium, give definitions of endothelial markers and biomarkers, touch on the methodological approaches for revealing biomarkers, present an implicit role of endothelium in some toxicological mechanistic studies, and survey the role of reactive oxygen species (ROS) in modulation of endothelial status.