Ascorbate stabilization is stimulated in rho(0)HL-60 cells by CoQ10 increase at the plasma membrane

New Insights on the Uptake and Trafficking of Coenzyme Q

Coenzyme Q (CoQ) is an essential lipid with many cellular functions, such as electron transport for cellular respiration, antioxidant protection, redox homeostasis, and ferroptosis suppression. Deficiencies in CoQ due to aging, genetic disease, or medication can be ameliorated by high-dose supplementation. As such, an understanding of the uptake and transport of CoQ may inform methods of clinical use and identify how to better treat deficiency. Here, we review what is known about the cellular uptake and intracellular distribution of CoQ from yeast, mammalian cell culture, and rodent models, as well as its absorption at the organism level. We discuss the use of these model organisms to probe the mechanisms of uptake and distribution. The literature indicates that CoQ uptake and distribution are multifaceted processes likely to have redundancies in its transport, utilizing the endomembrane system and newly identified proteins that function as lipid transporters. Impairment of the trafficking of either endogenous or exogenous CoQ exerts profound effects on metabolism and stress response. This review also highlights significant gaps in our knowledge of how CoQ is distributed within the cell and suggests future directions of research to better understand this process.

Capsaicin has potent anti-oxidative effects in vivo through a mechanism which is non-receptor mediated

Capsaicin (8-methyl-N-vanillyl-trans-6-nonenamide) is the active ingredient of chilli peppers and is responsible for the characteristic pungency. The ubiquitous human consumption of chilli peppers indicates their influence on human health. The effect of capsaicin through sensory neurons via TRPV1 activation has been well studied, but its non-neuronal effects are still not extensively explored. The purpose of this study was to investigate the in vivo antioxidant effect of capsaicin on erythrocytes of male Wistar rats. Markers of oxidative stress in blood were determined by assessing the plasma total antioxidant potential, activity of plasma membrane redox system, intracellular glutathione (GSH) level, ROS level, protein oxidation and lipid peroxidation. Results of this study suggest a significant protective effect of capsaicin against oxidative stress by enhancing FRAP, GSH level, PMRS activity and ameliorating ROS, MDA, PCO and AOPP.

Regulation of coenzyme Q biosynthesis pathway in eukaryotes

Coenzyme Q (CoQ, ubiquinone/ubiquinol) is a ubiquitous and unique molecule that drives electrons in mitochondrial respiratory chain and an obligatory step for multiple metabolic pathways in aerobic metabolism. Alteration of CoQ biosynthesis or its redox stage are causing mitochondrial dysfunctions as hallmark of heterogeneous disorders as mitochondrial/metabolic, cardiovascular, and age-associated diseases. Regulation of CoQ biosynthesis pathway is demonstrated to affect all steps of proteins production of this pathway, posttranslational modifications and protein-protein-lipid interactions inside mitochondria. There is a bi-directional relationship between CoQ and the epigenome in which not only the CoQ status determines the epigenetic regulation of many genes, but CoQ biosynthesis is also a target for epigenetic regulation, which adds another layer of complexity to the many pathways by which CoQ levels are regulated by environmental and developmental signals to fulfill its functions in eukaryotic aerobic metabolism.

The effect of hyperbaric oxygen on mitochondrial and glycolytic energy metabolism: the caloristasis concept

We present new data on the effects of HBOT on human kidney (HK-2) cell metabolism using a SeaHorse XF Analyzer to evaluate separately the state of mitochondrial and glycolytic energy metabolism. The data are discussed in the context of the concept of cellular caloristasis networks. The information on the changes in cellular energy metabolism stimulated by HBOT presented here provides new insights into the cellular energy state and mitochondrial environment in which sHSPs function. These data will be useful in forming testable hypotheses about the functions of translocated sHSPs in human mitochondria responding to stressors.

Glucose-dependent trans-plasma membrane electron transport and p70S6k phosphorylation in skeletal muscle cells

The reduction of extracellular oxidants by intracellular electrons is known as trans-plasma membrane electron transport (tPMET). The goal of this study was to characterize a role of tPMET in the sensing of glucose as a physiological signal. tPMET from C2C12 myotubes was monitored using a cell-impermeable extracellular electron acceptor, water-soluble tetrazolium salt-1 (WST-1). Superoxide dismutase in the incubation medium or exposure to an NADPH oxidase (NOX) isoform 1/4 inhibitor suppressed WST-1 reduction by 70%, suggesting a role of NOXs in tPMET. There was a positive correlation between medium glucose concentration and WST-1 reduction, suggesting that tPMET is a glucose-sensing process. WST-1 reduction was also decreased by an inhibitor of the pentose phosphate pathway, dehydroepiandrosterone. In contrast, glycolytic inhibitors, 3PO and sodium fluoride, did not affect WST-1 reduction. Thus, it appears that glucose uptake and processing in the pentose phosphate pathway drives NOX-dependent tPMET. Western blot analysis demonstrated that p70^S6k phosphorylation is glucose-dependent, while the phosphorylation of AKT and MAPK did not differ in the presence or absence of glucose. Further, phosphorylation of p70^S6k was dependent upon NOX enzymes. Finally, glucose was required for full stimulation of p70^S6k by insulin, again in a fashion prevented by NOX inhibition. Taken together, the data suggest that muscle cells have a novel glucose-sensing mechanism dependent on NADPH production and NOX activity, culminating in increased p70^S6k phosphorylation.

How Supraphysiological Oxygen Levels in Standard Cell Culture Affect Oxygen-Consuming Reactions

Most mammalian tissue cells experience oxygen partial pressures in vivo equivalent to 1–6% O₂ (i.e., physioxia). In standard cell culture, however, headspace O₂ levels are usually not actively regulated and under these conditions are ~18%. This drives hyperoxia in cell culture media that can affect a wide variety of cellular activities and may compromise the ability of in vitro models to reproduce in vivo biology. Here, we review and discuss some specific O₂-consuming organelles and enzymes, including mitochondria, NADPH oxidases, the transplasma membrane redox system, nitric oxide synthases, xanthine oxidase, and monoamine oxidase with respect to their sensitivities to O₂ levels. Many of these produce reactive oxygen and/or nitrogen species (ROS/RNS) as either primary end products or byproducts and are acutely sensitive to O₂ levels in the range from 1% to 18%. Interestingly, many of them are also transcriptional targets of hypoxia-inducible factors (HIFs) and chronic cell growth at physioxia versus 18% O₂ may alter their expression. Aquaporins, which facilitate hydrogen peroxide diffusion into and out of cells, are also regulated by HIFs, indicating that O₂ levels may affect intercellular communication via hydrogen peroxide. The O₂ sensitivities of these important activities emphasize the importance of maintaining physioxia in culture.

Measuring Trans-Plasma Membrane Electron Transport by C2C12 Myotubes

Trans-plasma membrane electron transport (tPMET) plays a role in protection of cells from intracellular reductive stress as well as protection from damage by extracellular oxidants. This process of transporting electrons from intracellular reductants to extracellular oxidants is not well defined. Here we present spectrophotometric assays by C2C12 myotubes to monitor tPMET utilizing the extracellular electron acceptors: water-soluble tetrazolium salt-1 (WST-1) and 2,6-dichlorophenolindophenol (DPIP or DCIP). Through reduction of these electron acceptors, we are able to monitor this process in a real-time analysis. With the addition of enzymes such as ascorbate oxidase (AO) and superoxide dismutase (SOD) to the assays, we can determine which portion of tPMET is due to ascorbate export or superoxide production, respectively. While WST-1 was shown to produce stable results with low background, DPIP was able to be re-oxidized after the addition of AO and SOD, which was demonstrated with spectrophotometric analysis. This method demonstrates a real-time, multi-well, quick spectrophotometric assay with advantages over other methods used to monitor tPMET, such as ferricyanide (FeCN) and ferricytochrome c reduction.

Coenzyme Q and Its Role in the Dietary Therapy against Aging

Coenzyme Q (CoQ) is a naturally occurring molecule located in the hydrophobic domain of the phospholipid bilayer of all biological membranes. Shortly after being discovered, it was recognized as an essential electron transport chain component in mitochondria where it is particularly abundant. Since then, more additional roles in cell physiology have been reported, including antioxidant, signaling, death prevention, and others. It is known that all cells are able to synthesize functionally sufficient amounts of CoQ under normal physiological conditions. However, CoQ is a molecule found in different dietary sources, which can be taken up and incorporated into biological membranes. It is known that mitochondria have a close relationship with the aging process. Additionally, delaying the aging process through diet has aroused the interest of scientists for many years. These observations have stimulated investigation of the anti-aging potential of CoQ and its possible use in dietary therapies to alleviate the effects of aging. In this context, the present review focus on the current knowledge and evidence the roles of CoQ cells, its relationship with aging, and possible implications of dietary CoQ in relation to aging, lifespan or age-related diseases.

Brassica foods as a dietary source of vitamin C: a review

Brassica genus includes known horticultural vegetables with major economical importance worldwide, and involves vegetables of economical importance being part of the diet and source of oils for industry in many countries. Brassicales own a broad array of health-promoting compounds, emphasized as healthy rich sources of vitamin C. The adequate management of pre- and postharvest factors including crop varieties, growth conditions, harvesting, handling, storage, and final consumer operations would lead to increase or preserve of the vitamin C content or reduced losses by interfering in the catalysis mechanisms that remains largely unknown, and should be reviewed. Likewise, the importance of the food matrix on the absorption and metabolism of vitamin C is closely related to the range of the health benefits attributed to its intake. However, less beneficial effects were derived when purified compounds were administered in comparison to the ingestion of horticultural products such as Brassicas, which entail a closely relation between this food matrix and the bioavailability of its content in vitamin C. This fact should be here also discussed. These vegetables of immature flowers or leaves are used as food stuffs all over the world and represent a considerable part of both western and non-Western diets, being inexpensive crops widely spread and reachable to all social levels, constituting an important source of dietary vitamin C, which may work synergistically with the wealth of bioactive compounds present in these foods.

The regulation of coenzyme q biosynthesis in eukaryotic cells: all that yeast can tell us

Coenzyme Q (CoQ) is a mitochondrial lipid, which functions mainly as an electron carrier from complex I or II to complex III at the mitochondrial inner membrane, and also as antioxidant in cell membranes. CoQ is needed as electron acceptor in β-oxidation of fatty acids and pyridine nucleotide biosynthesis, and it is responsible for opening the mitochondrial permeability transition pore. The yeast model has been very useful to analyze the synthesis of CoQ, and therefore, most of the knowledge about its regulation was obtained from the Saccharomyces cerevisiae model. CoQ biosynthesis is regulated to support 2 processes: the bioenergetic metabolism and the antioxidant defense. Alterations of the carbon source in yeast, or in nutrient availability in yeasts or mammalian cells, upregulate genes encoding proteins involved in CoQ synthesis. Oxidative stress, generated by chemical or physical agents or by serum deprivation, modifies specifically the expression of some COQ genes by means of stress transcription factors such as Msn2/4p, Yap1p or Hsf1p. In general, the induction of COQ gene expression produced by metabolic changes or stress is modulated downstream by other regulatory mechanisms such as the protein import to mitochondria, the assembly of a multi-enzymatic complex composed by Coq proteins and also the existence of a phosphorylation cycle that regulates the last steps of CoQ biosynthesis. The CoQ biosynthetic complex assembly starts with the production of a nucleating lipid such as HHB by the action of the Coq2 protein. Then, the Coq4 protein recognizes the precursor HHB acting as the nucleus of the complex. The activity of Coq8p, probably as kinase, allows the formation of an initial pre-complex containing all Coq proteins with the exception of Coq7p. This pre-complex leads to the synthesis of 5-demethoxy-Q6 (DMQ6), the Coq7p substrate. When de novo CoQ biosynthesis is required, Coq7p becomes dephosphorylated by the action of Ptc7p increasing the synthesis rate of CoQ6. This critical model is needed for a better understanding of CoQ biosynthesis. Taking into account that patients with CoQ10 deficiency maintain to some extent the machinery to synthesize CoQ, new promising strategies for the treatment of CoQ10 deficiency will require a better understanding of the regulation of CoQ biosynthesis in the future.

Sirtuin activation: a role for plasma membrane in the cell growth puzzle

For more than 20 years, the observation that impermeable oxidants can stimulate cell growth has not been satisfactorily explained. The discovery of sirtuins provides a logical answer to the puzzle. The NADH-dependent transplasma membrane electron transport system, which is stimulated by growth factors and interventions such as calorie restriction, can transfer electrons to external acceptors and protect against stress-induced apoptosis. We hypothesize that the activation of plasma membrane electron transport contributes to the cytosolic NAD(+) pool required for sirtuin to activate transcription factors necessary for cell growth and survival.

Trans-plasma membrane electron transport in mammals: functional significance in health and disease

Trans-plasma membrane electron transport (t-PMET) has been established since the 1960s, but it has only been subject to more intensive research in the last decade. The discovery and characterization at the molecular level of its novel components has increased our understanding of how t-PMET regulates distinct cellular functions. This review will give an update on t-PMET, with particular emphasis on how its malfunction relates to some diseases, such as cancer, abnormal cell death, cardiovascular diseases, aging, obesity, neurodegenerative diseases, pulmonary fibrosis, asthma, and genetically linked pathologies. Understanding these relationships may provide novel therapeutic approaches for pathologies associated with unbalanced redox state.

Inhibition of trans-plasma membrane electron transport: a potential anti-leukemic strategy

The recently demonstrated reliance of glycolytic cancer cells on trans-plasma membrane electron transport (tPMET) for survival raises the question of its suitability as a target for anticancer drug development. In this study, the effects of several new and known compounds on proliferation, tPMET activity and NAD(P)H intrinsic fluorescence in human myelogenous leukemic cell lines were investigated. The whole data confirm the importance of tPMET in leukemic cell survival and suggest this activity as a new potential anti-leukemic target.

Is coenzyme Q a key factor in aging?

Coenzyme Q (Q) is a key component for bioenergetics and antioxidant protection in the cell. During the last years, research on diseases linked to Q-deficiency has highlighted the essential role of this lipid in cell physiology. Q levels are also affected during aging and neurodegenerative diseases. Therefore, therapies based on dietary supplementation with Q must be considered in cases of Q deficiency such as in aging. However, the low bioavailability of dietary Q for muscle and brain obligates to design new mechanisms to increase the uptake of this compound in these tissues. In the present review we show a complete picture of the different functions of Q in cell physiology and their relationship to age and age-related diseases. Furthermore, we describe the problems associated with dietary Q uptake and the mechanisms currently used to increase its uptake or even its biosynthesis in cells. Strategies to increase Q levels in tissues are indicated.

CYB5R3: a key player in aerobic metabolism and aging?

Aging results from a complex and not completely understood chain of processes that are associated with various negative metabolic consequences and ultimately leads to senescence and death. The intracellular ratio of pyridine nucleotides (NAD⁺/NADH), has been proposed to be at the center stage of age-related biochemical changes in organisms, and may help to explain the observed influence of calorie restriction and energy-sensitive proteins on lifespan in model organisms. Indeed, the NAD⁺/NADH ratios affect the activity of a number of proteins, including sirtuins, which have gained prominence in the aging field as potential mediators of the beneficial effects of calorie restriction and mediating lifespan. Here we review the activities of a redox enzyme (NQR1 in yeast and CYB5R3 in mammals) that also influences the NAD⁺/NADH ratio and may play a regulatory role that connects aerobic metabolism with aging.

Cell survival from chemotherapy depends on NF-kappaB transcriptional up-regulation of coenzyme Q biosynthesis

BACKGROUND

Coenzyme Q (CoQ) is a lipophilic antioxidant that is synthesized by a mitochondrial complex integrated by at least ten nuclear encoded COQ gene products. CoQ increases cell survival under different stress conditions, including mitochondrial DNA (mtDNA) depletion and treatment with cancer drugs such as camptothecin (CPT). We have previously demonstrated that CPT induces CoQ biosynthesis in mammal cells.

METHODOLOGY/PRINCIPAL FINDINGS

CPT activates NF-kappaB that binds specifically to two kappaB binding sites present in the 5'-flanking region of the COQ7 gene. This binding is functional and induces both the COQ7 expression and CoQ biosynthesis. The inhibition of NF-kappaB activation increases cell death and decreases both, CoQ levels and COQ7 expression induced by CPT. In addition, using a cell line expressing very low of NF-kappaB, we demonstrate that CPT was incapable of enhancing enhance both CoQ biosynthesis and COQ7 expression in these cells.

CONCLUSIONS/SIGNIFICANCE

We demonstrate here, for the first time, that a transcriptional mechanism mediated by NF-kappaB regulates CoQ biosynthesis. This finding contributes new data for the understanding of the regulation of the CoQ biosynthesis pathway.

Mechanisms underlying caloric restriction and lifespan regulation: implications for vascular aging

This review focuses on the emerging evidence that attenuation of the production of reactive oxygen species and inhibition of inflammatory pathways play a central role in the antiaging cardiovascular effects of caloric restriction. Particular emphasis is placed on the potential role of the plasma membrane redox system in caloric restriction-induced pathways responsible for sensing oxidative stress and increasing cellular oxidative stress resistance. We propose that caloric restriction increases bioavailability of NO, decreases vascular reactive oxygen species generation, activates the Nrf2/antioxidant response element pathway, inducing reactive oxygen species detoxification systems, exerts antiinflammatory effects, and, thereby, suppresses initiation/progression of vascular disease that accompany aging.

The importance of plasma membrane coenzyme Q in aging and stress responses

The plasma membrane of eukaryotic cells is the limit to interact with the environment. This position implies receiving stress signals that affects its components such as phospholipids. Inserted inside these components is coenzyme Q that is a redox compound acting as antioxidant. Coenzyme Q is reduced by diverse dehydrogenase enzymes mainly NADH-cytochrome b(5) reductase and NAD(P)H:quinone reductase 1. Reduced coenzyme Q can prevent lipid peroxidation chain reaction by itself or by reducing other antioxidants such as alpha-tocopherol and ascorbate. The group formed by antioxidants and the enzymes able to reduce coenzyme Q constitutes a plasma membrane redox system that is regulated by conditions that induce oxidative stress. Growth factor removal, ethidium bromide-induced rho degrees cells, and vitamin E deficiency are some of the conditions where both coenzyme Q and its reductases are increased in the plasma membrane. This antioxidant system in the plasma membrane has been observed to participate in the healthy aging induced by calorie restriction. Furthermore, coenzyme Q regulates the release of ceramide from sphingomyelin, which is concentrated in the plasma membrane. This results from the non-competitive inhibition of the neutral sphingomyelinase by coenzyme Q particularly by its reduced form. Coenzyme Q in the plasma membrane is then the center of a complex antioxidant system preventing the accumulation of oxidative damage and regulating the externally initiated ceramide signaling pathway.

Up-regulation of plasma membrane-associated redox activities in neuronal cells lacking functional mitochondria

Mitochondria-deficient cells (rho(o) cells) survive through enhanced glycolytic metabolism in the presence of pyruvate and uridine. The plasma membrane redox system (PMRS) contains several NAD(P)H-related enzymes and plays a key role in maintaining the levels of NAD(+)/NADH and reduced coenzyme Q. In this study, rho(o) cells were used to investigate how the PMRS is regulated under conditions of mitochondrial dysfunction. rho(o) cells exhibited a lower oxygen consumption rate and higher levels of lactate than parental cells, and were more sensitive to glycolysis inhibitors (2-deoxyglucose and iodoacetamide) than control cells. However, they were more resistant to H(2)O(2), consistent with increased catalase activity and decreased oxidative damage (protein carbonyls and nitrotyrosine). PM-associated redox enzyme activities were enhanced in rho(o) cells compared to those in control cells. Our data suggest that all PMRS enzymes and biomarkers tested are closely related to the ability of the PMs to maintain redox homeostasis. These results illustrate that an up-regulated PM redox activity can protect cells from oxidative stress as a result of an improved antioxidant capacity, and suggest a mechanism by which neurons adapt to conditions of impaired mitochondrial function.

Calorie restriction up-regulates the plasma membrane redox system in brain cells and suppresses oxidative stress during aging

The plasma membrane (PM) contains redox enzymes that provide electrons for energy metabolism and recycling of antioxidants such as coenzyme Q and alpha-tocopherol. Brain aging and neurodegenerative disorders involve impaired energy metabolism and oxidative damage, but the involvement of the PM redox system (PMRS) in these processes is unknown. Caloric restriction (CR), a manipulation that protects the brain against aging and disease, increased activities of PMRS enzymes (NADH-ascorbate free radical reductase, NADH-quinone oxidoreductase 1, NADH-ferrocyanide reductase, NADH-coenzyme Q10 reductase, and NADH-cytochrome c reductase) and antioxidant levels (alpha-tocopherol and coenzyme Q10) in brain PM during aging. Age-related increases in PM lipid peroxidation, protein carbonyls, and nitrotyrosine were attenuated by CR, levels of PMRS enzyme activities were higher, and markers of oxidative stress were lower in cultured neuronal cells treated with CR serum compared with those treated with ad libitum serum. These findings suggest important roles for the PMRS in protecting brain cells against age-related increases in oxidative and metabolic stress.

The plasma membrane redox system in aging

Oxidative stress over time leads to the accumulation of damaged macromolecules and to profound physiological changes that are associated with several age-related diseases. The plasma membrane redox system (PMRS) appears to attenuate oxidative stress acting as a compensatory mechanism during the aging process. The PMRS appears to play a protective role during mitochondrial dysfunction to provide cells with a survival mechanism by lowering oxidative stress. The PMRS accomplishes this by producing more NAD(+) for glycolytic ATP production via transfer of electrons from intracellular reducing equivalents to extracelluar acceptors. Ubiquinone and alpha-tocopherol are key antioxidant molecules in the plasma membrane that are affected by aging and can be up-regulated by dietary interventions such as calorie restriction (CR). Up-regulation of PMRS activity leads to cell survival and membrane homeostasis under stress conditions and during calorie restriction. Further studies of the PMRS may provide not only additional information on the mechanisms involved in aging and CR, but may provide therapeutic targets for the prevention and treatment of age-related diseases.

Coenzyme Q-dependent functions of plasma membrane in the aging process

Coenzyme Q (Q) is reduced in plasma membrane and mitochondria by NAD(P)H-dependent reductases providing reducing equivalents to maintain both respiratory chain and antioxidant protection. Reactive oxygen species (ROS) are accumulated in the aging process originating mainly in mitochondria but also in other membranes, such as plasma membrane partially by the loss of electrons from the semiquinone. The reduction of Q by NAD(P)H-dependent reductases in plasma membrane is responsible for providing its antioxidant capacity, preventing both the lipid peroxidation chain and the activation of the ceramide-dependent apoptosis pathway. Both Q content and its reductases are decreased in plasma membrane of aging mammals. Calorie restriction, which extends mammal life span, increases the content of Q in the plasma membrane and also activates Q reductases in this membrane. Both lipid peroxidation and ceramide production are decreased in the plasma membrane in calorie-restricted animals. Plasma membrane is, then, an important cellular component to control the aging process through its concentration and redox state of Q.

Mouse liver plasma membrane redox system activity is altered by aging and modulated by calorie restriction

Caloric restriction (CR) is known as the only non-genetic method proven to slow the rate of aging and extend lifespan in animals. Free radicals production emerges from normal metabolic activity and generates the accumulation of oxidized macromolecules, one of the main characteristics of aging. Due to its central role in cell bioenergetics, a great interest has been paid to CR-induced modifications in mitochondria, where CR has been suggested to decrease reactive oxygen species production. The plasma membrane contains a trans-membrane redox system (PMRS) that provides electrons to recycle lipophilic antioxidants, such as α-tocopherol and coenzyme Q (CoQ), and to modulate cytosolic redox homeostasis. In the present study, we have investigated age differences in the PMRS in mouse liver and their modulation by CR. Aging induced a decrease in the ratio of CoQ10/CoQ9 and α-tocopherol in liver PM from AL-fed mice that was attenuated by CR. CoQ-dependent NAD(P)H dehydrogenases highly increased in CR old mice liver PMs. On the other hand, the CoQ-independent NADH-FCN reductase activity increased in AL-fed animals; whereas, in mice under CR this activity did not change during aging. Our results suggest that liver PMRS activity changes during aging and that CR modulates these changes. By this mechanism CR maintains a higher antioxidant capacity in liver PM of old animals by increasing the activity of CoQ-dependent reductases. Also, the putative role of PMRS in the modulation of redox homeostasis of cytosol is implicated.

Specificity of coenzyme Q10 for a balanced function of respiratory chain and endogenous ubiquinone biosynthesis in human cells

Coenzyme Q (Q) is an obligatory component of both respiratory chain and uncoupling proteins. Also, Q acts as an antioxidant in cellular membranes. Several neurodegenerative diseases are associated with modifications of Q10 levels. For these reasons, therapies based on Q supplementation in the diet are currently studied in order to mitigate the symptoms of these diseases. However, the incorporation of exogenous Q also affects aging process in nematodes probably affecting reactive oxygen species (ROS) production. The aim of the present work is to clarify if supplementation with both Q10 and Q6 isoforms affects mitochondrial Q10 content, respiratory chain activity and ROS levels in human cells. Cells incorporated exogenously added Q10 and Q6 isoforms into mitochondria that produced changes in mitochondrial activity depending on the side chain length. Supplementation with Q10, but not with Q6, increased mitochondrial Q-dependent activities. However, Q6 affected the mitochondrial membrane potential, ROS production, and increased the protein levels of both catalase and Mn-superoxide dismutase (Mn-SOD). Also, Q6 induced a transient decrease in endogenous mitochondrial Q10 levels by increasing its catabolism. These results show that human cells supplemented with Q6 undergo a mitochondrial impairment, which is not observed with Q10 supplementation.

Calorie restriction attenuates age-related alterations in the plasma membrane antioxidant system in rat liver

Aging is associated with increased production of reactive oxygen species and oxidation-induced damage to intracellular structures and membranes. Caloric restriction (CR) is the only non-genetic method proven to extend lifespan in mammals. Although the mechanisms of CR remain to be clearly elucidated, reductions in oxidative stress have been shown to increase lifespan in several model systems. Oxidative stress can be attenuated by CR. Mitochondria and plasma membrane (PM) are normal sources of free radicals. The PM has a trans-membrane redox system that provides electrons to recycle lipophilic antioxidants, such as alpha-tocopherol and coenzyme Q (CoQ). The idea developed in this study is that the PM is intimately involved in cellular physiology controlling the relationship of the cell to its environment. PM is the key for protecting cellular integrity during aging. Specifically, we have investigated age-related alterations and the effects of CR in the trans-PM redox (antioxidant) system in rat liver. We found that age-related declines in the ratio of CoQ(10)/CoQ(9) and alpha-tocopherol in liver PM were attenuated by CR compared to those fed ad libitum (AL). CoQ-dependent NAD(P)H dehydrogenases were increased in CR old rat liver PMs. As a consequence, the liver PM of CR old rats was more resistant to oxidative stress-induced lipid peroxidation than AL rats. Thus, our results suggest that CR induces a higher capacity to oxidize NAD(P)H in the PM of old rat livers and as a result, a higher resistance to oxidative stress-induced damage.

Mitochondrial gene-knockout (rho0) cells: a versatile model for exploring the secrets of trans-plasma membrane electron transport

Plasma membrane electron transport (tPMET) pathways have been identified in all living cells, and a wide variety of tools have been used to study these processes. In our laboratory we have used the cell-impermeable tetrazolium dye WST-1, together with the mitochondrial gene knockout (rho0) cell model, to investigate one of these pathways. We have shown that growth of HL60rho0 cells is dependent on oxygen, and that these cells consume oxygen at the cell surface. Similarities in inhibition profiles between non-mitochondrial oxygen consumption and WST-1 reduction suggest that both systems share a common tPMET pathway. In support of this, oxygen was shown to compete with the intermediate electron acceptor that mediates WST-1 reduction, for reducing electrons. The observation that tPMET activity is higher in rho0 cells compared to their mitochondrially-competent counterparts was shown to be the result of competition between the mitochondrial and plasma membrane electron transport systems for intracellular reducing equivalents. Elevated rates of dye reduction appear to be mediated through increased expression of the key components of tPMET, which include the cell surface NADH oxidase, CNOX. These findings have played a critical role in shaping our current understanding of the mechanisms of this particular pathway of tPMET.

Ethidium bromide stimulated hyper laccase production from bird's nest fungus Cyathus bulleri

AIMS

Effect of ethidium bromide, a DNA intercalating agent, on laccase production from Cyathus bulleri was studied.

METHODS AND RESULTS

The bird's nest fungus, Cyathus bulleri was grown on 2% (w/v) malt extract agar (MEA) supplemented with 1.5 microg ml(-1) of the phenanthridine dye ethidium bromide (EtBr) for 7 d and when grown subsequently in malt extract broth (MEB), produced a 4.2-fold increase in laccase production as compared to the untreated fungus. The fungal cultures following a single EtBr treatment, when regrown on MEA devoid of EtBr, produced a sixfold increase in laccase in MEB. However, on subsequent culturing on MEA in the absence of EtBr, only a 2.5-fold increase in laccase production could be maintained. In another attempt, the initial EtBr-treated cultures, when subjected to a second EtBr treatment (1.5 microg ml(-1)) on MEA for 7 d, produced a 1.4-fold increase in laccase production in MEB.

CONCLUSIONS

The white-rot fungus Cyathus bulleri, when treated with EtBr at a concentration of 1.5 microg ml(-1) and regrown on MEA devoid of EtBr, produced a sixfold increase in laccase production in MEB.

SIGNIFICANCE AND THE IMPACT OF THE STUDY

The variable form of C. bulleri capable of hyper laccase production can improve the economic feasibility of environmentally benign processes involving use of fungal laccases in cosmetics (including hair dyes), food and beverages, clinical diagnostics, pulp and paper industry, industrial effluent treatment, animal biotechnology and biotransformations.

Mitochondrial complex I inhibitor rotenone induces apoptosis through enhancing mitochondrial reactive oxygen species production

Inhibition of mitochondrial respiratory chain complex I by rotenone had been found to induce cell death in a variety of cells. However, the mechanism is still elusive. Because reactive oxygen species (ROS) play an important role in apoptosis and inhibition of mitochondrial respiratory chain complex I by rotenone was thought to be able to elevate mitochondrial ROS production, we investigated the relationship between rotenone-induced apoptosis and mitochondrial reactive oxygen species. Rotenone was able to induce mitochondrial complex I substrate-supported mitochondrial ROS production both in isolated mitochondria from HL-60 cells as well as in cultured cells. Rotenone-induced apoptosis was confirmed by DNA fragmentation, cytochrome c release, and caspase 3 activity. A quantitative correlation between rotenone-induced apoptosis and rotenone-induced mitochondrial ROS production was identified. Rotenone-induced apoptosis was inhibited by treatment with antioxidants (glutathione, N-acetylcysteine, and vitamin C). The role of rotenone-induced mitochondrial ROS in apoptosis was also confirmed by the finding that HT1080 cells overexpressing magnesium superoxide dismutase were more resistant to rotenone-induced apoptosis than control cells. These results suggest that rotenone is able to induce apoptosis via enhancing the amount of mitochondrial reactive oxygen species production.

DPI induces mitochondrial superoxide-mediated apoptosis

The iodonium compounds diphenyleneiodonium (DPI) and diphenyliodonium (IDP) are well-known phagocyte NAD(P)H oxidase inhibitors. However, it has been shown that at high concentrations they can inhibit the mitochondrial respiratory chain as well. Since inhibition of the mitochondrial respiratory chain has been shown to induce superoxide production and apoptosis, we investigated the effect of iodonium compounds on mitochondria-derived superoxide and apoptosis. Mitochondrial superoxide production was measured on both cultured cells and isolated rat-heart submitochondrial particles. Mitochondria function was examined by monitoring mitochondrial membrane potential. Apoptotic pathways were studied by measuring cytochrome c release and caspase 3 activation. Apoptosis was characterized by detecting DNA fragmentation on agarose gel and measuring propidium iodide- (PI-) stained subdiploid cells using flow cytometry. Our results showed that DPI could induce mitochondrial superoxide production. The same concentration of DPI induced apoptosis by decreasing mitochondrial membrane potential and releasing cytochrome c. Addition of antioxidants or overexpression of MnSOD significantly reduced DPI-induced mitochondrial damage, cytochrome c release, caspase activation, and apoptosis. These observations suggest that DPI can induce apoptosis via induction of mitochondrial superoxide. DPI-induced mitochondrial superoxide production may prove to be a useful model to study the signaling pathways of mitochondrial superoxide.

Uptake of exogenous coenzyme Q and transport to mitochondria is required for bc1 complex stability in yeast coq mutants

Coenzyme Q (Q) is an essential component of the mitochondrial respiratory chain in eukaryotic cells but also is present in other cellular membranes where it acts as an antioxidant. Because Q synthesis machinery in Saccharomyces cerevisiae is located in the mitochondria, the intracellular distribution of Q indicates the existence of intracellular Q transport. In this study, the uptake of exogenous Q(6) by yeast and its transport from the plasma membrane to mitochondria was assessed in both wild-type and in Q-less coq7 mutants derived from four distinct laboratory yeast strains. Q(6) supplementation of medium containing ethanol, a non-fermentable carbon source, rescued growth in only two of the four coq7 mutant strains. Following culture in medium containing dextrose, the added Q(6) was detected in the plasma membrane of each of four coq7 mutants tested. This detection of Q(6) in the plasma membrane was corroborated by measuring ascorbate stabilization activity, as catalyzed by NADH-ascorbate free radical reductase, a transmembrane redox activity that provides a functional assay of plasma membrane Q(6). These assays indicate that each of the four coq7 mutant strains assimilate exogenous Q(6) into the plasma membrane. The two coq7 mutant strains rescued by Q(6) supplementation for growth on ethanol contained mitochondrial Q(6) levels similar to wild type. However, the content of Q(6) in mitochondria from the non-rescued strains was only 35 and 8%, respectively, of that present in the corresponding wild-type parental strains. In yeast strains rescued by exogenous Q(6), succinate-cytochrome c reductase activity was partially restored, whereas non-rescued strains contained very low levels of activity. There was a strong correlation between mitochondrial Q(6) content, succinate-cytochrome c reductase activity, and steady state levels of the cytochrome c(1) polypeptide. These studies show that transport of extracellular Q(6) to the mitochondria operates in yeast but is strain-dependent. When Q biosynthesis is disrupted in yeast strains with defects in the intracellular transport of exogenous Q, the bc(1) complex is unstable. These results indicate that delivery of exogenous Q(6) to mitochondria is required fore activity and stability of the bc(1) complex in yeast coq mutants.

Ascorbic acid: much more than just an antioxidant

Vitamin C (ascorbic acid (AA)) is very popular for its antioxidant properties. Consequently, many other important aspects of this multifaceted molecule are often underestimated or even ignored. In the present paper, we have tried to bring to the foreground some of these aspects, including the peculiarities of the AA biosynthetic pathway in different organisms, the remarkable function of AA as a co-substrate of many important dioxygenases, the role of AA-regenerating enzymes and the known pathways of AA catabolism, as well as the intriguing function of AA in gene expression.

Dual role of plasma membrane electron transport systems in defense

Because oxidative stress is one of the main sources of severe cellular damage, cells have different defense weapons against reactive oxygen species. Ubiquitous plasma membrane redox systems play a role in defense against oxidative stress damage. On the other hand, a tightly controlled and localized production of reactive oxygen species by a plasma membrane NADPH oxidase can be used as a potent microbicidal weapon. This dual, prooxidant and antioxidant role of plasma membrane electron transport systems in defense is studied and discussed.

A dietary source of coenzyme Q is essential for growth of long-lived Caenorhabditis elegans clk-1 mutants

Mutations in the clk-1 gene of the nematode Caenorhabditis elegans result in slowed development, sluggish adult behaviors, and an increased lifespan. CLK-1 is a mitochondrial polypeptide with sequence and functional conservation from human to yeast. Coq7p, the Saccharomyces cerevisiae homologue, is essential for ubiquinone (coenzyme Q or Q) synthesis and therefore respiration. However, based on assays of respiratory function, it has been reported that the primary defect in the C. elegans clk-1 mutants is not in Q biosynthesis. How do the clk-1 mutant worms have essentially normal rates of respiration, when biochemical studies in yeast suggest a Q deficiency? Nematodes are routinely fed Escherichia coli strains containing a rich supply of Q. To study the Q synthesized by C. elegans, we cultured worms on an E. coli mutant that lacks Q and found that clk-1 mutants display early developmental arrest from eggs, or sterility emerging from dauer stage. Provision of Q-replete E. coli rescues these defects. Lipid analysis showed that clk-1 worms lack the nematode Q(9) isoform and instead contain a large amount of a metabolite that is slightly more polar than Q(9). The clk-1 mutants also have increased levels of Q(8), the E. coli isoform, and rhodoquinone-9. These results show that the clk-1 mutations result in Q auxotrophy evident only when Q is removed from the diet, and that the aging and developmental phenotypes previously described are consistent with altered Q levels and distribution.

A dietary source of coenzyme Q is essential for growth of long-lived Caenorhabditis elegans clk-1 mutants

Mutations in the clk-1 gene of the nematode Caenorhabditis elegans result in slowed development, sluggish adult behaviors, and an increased lifespan. CLK-1 is a mitochondrial polypeptide with sequence and functional conservation from human to yeast. Coq7p, the Saccharomyces cerevisiae homologue, is essential for ubiquinone (coenzyme Q or Q) synthesis and therefore respiration. However, based on assays of respiratory function, it has been reported that the primary defect in the C. elegans clk-1 mutants is not in Q biosynthesis. How do the clk-1 mutant worms have essentially normal rates of respiration, when biochemical studies in yeast suggest a Q deficiency? Nematodes are routinely fed Escherichia coli strains containing a rich supply of Q. To study the Q synthesized by C. elegans, we cultured worms on an E. coli mutant that lacks Q and found that clk-1 mutants display early developmental arrest from eggs, or sterility emerging from dauer stage. Provision of Q-replete E. coli rescues these defects. Lipid analysis showed that clk-1 worms lack the nematode Q(9) isoform and instead contain a large amount of a metabolite that is slightly more polar than Q(9). The clk-1 mutants also have increased levels of Q(8), the E. coli isoform, and rhodoquinone-9. These results show that the clk-1 mutations result in Q auxotrophy evident only when Q is removed from the diet, and that the aging and developmental phenotypes previously described are consistent with altered Q levels and distribution.

Genetic evidence for a multi-subunit complex in the O-methyltransferase steps of coenzyme Q biosynthesis

Coq3 O-methyltransferase carries out both O-methylation steps in coenzyme Q (ubiquinone) biosynthesis. The degree to which Coq3 O-methyltransferase activity and expression are dependent on the other seven COQ gene products has been investigated. A panel of yeast mutant strains harboring null mutations in each of the genes required for coenzyme Q biosynthesis (COQ1-COQ8) have been prepared. Mitochondria have been isolated from each member of the yeast coq mutant collection, from the wild-type parental strains and from respiratory deficient mutants harboring deletions in ATP2 or COR1 genes. These latter strains constitute Q-replete, respiratory deficient controls. Each of these mitochondrial preparations has been analyzed for COQ3-encoded O-methyltransferase activity and steady state levels of Coq3 polypeptide. The findings indicate that the presence of the other COQ gene products is required to observe normal levels of O-methyltransferase activity and the Coq3 polypeptide. However, COQ3 steady state RNA levels are not decreased in any of the coq mutants, relative to either wild-type or respiratory deficient control strains, suggesting either a decreased rate of translation or a decreased stability of the Coq3 polypeptide. These data are consistent with the involvement of the Coq polypeptides (or the Q-intermediates formed by the Coq polypeptides) in a multi-subunit complex. It is our hypothesis that a deficiency in any one of the COQ gene products results in a defective complex in which the Coq3 polypeptide is rendered unstable.

Functions of vitamin C as a mediator of transmembrane electron transport in blood cells and related cell culture models

Vitamin C (ascorbic acid) is an important physiological antioxidant. Within cells, it is practically always present in the reduced form. Several enzymatic and nonenzymatic mechanisms have been reported to maintain this status. In the extracellular environment, oxidation of ascorbate leads to loss of vitamin because the oxidized form, dehydroascorbic acid, is unstable under physiological conditions. The intermediate ascorbate free radical, although rather long-lived for a free radical, quickly disproportionates into the two other forms, also leading to loss of vitamin. Protection from loss can only be achieved by cellular regeneration mechanisms, i.e., by uptake of dehydroascorbic acid and either storage or recycling, and by plasma-membrane mediated reduction of extracellular free radical or dehydroascorbic acid. Moreover, intracellular ascorbate can also serve as an electron donor for transmembrane reduction of external electron acceptors. However, the physiological significance of this function is as yet unknown. The results presented in the literature are sometimes conflicting as to the relative contributions of these different possibilities, which seem to differ in different cell types. In this short review, the various pathways of regeneration of ascorbate and their relative contributions to the avoidance of vitamin loss in plasma or cell culture medium are discussed.

Genetic evidence for coenzyme Q requirement in plasma membrane electron transport

Plasma membranes isolated from wild-type Saccharomyces cerevisiae crude membrane fractions catalyzed NADH oxidation using a variety of electron acceptors, such as ferricyanide, cytochrome c, and ascorbate free radical. Plasma membranes from the deletion mutant strain coq3delta, defective in coenzyme Q (ubiquinone) biosynthesis, were completely devoid of coenzyme Q6 and contained greatly diminished levels of NADH-ascorbate free radical reductase activity (about 10% of wild-type yeasts). In contrast, the lack of coenzyme Q6 in these membranes resulted in only a partial inhibition of either the ferricyanide or cytochrome-c reductase. Coenzyme Q dependence of ferricyanide and cytochrome-c reductases was based mainly on superoxide generation by one-electron reduction of quinones to semiquinones. Ascorbate free radical reductase was unique because it was highly dependent on coenzyme Q and did not involve superoxide since it was not affected by superoxide dismutase (SOD). Both coenzyme Q6 and NADH-ascorbate free radical reductase were rescued in plasma membranes derived from a strain obtained by transformation of the coq3delta strain with a single-copy plasmid bearing the wild type COQ3 gene and in plasma membranes isolated form the coq3delta strain grown in the presence of coenzyme Q6. The enzyme activity was inhibited by the quinone antagonists chloroquine and dicumarol, and after membrane solubilization with the nondenaturing detergent Zwittergent 3-14. The various inhibitors used did not affect residual ascorbate free radical reductase of the coq3delta strain. Ascorbate free radical reductase was not altered significantly in mutants atp2delta and cor1delta which are also respiration-deficient but not defective in ubiquinone biosynthesis, demonstrating that the lack of ascorbate free radical reductase in coq3delta mutants is related solely to the inability to synthesize ubiquinone and not to the respiratory-defective phenotype. For the first time, our results provide genetic evidence for the participation of ubiquinone in NADH-ascorbate free radical reductase, as a source of electrons for transmembrane ascorbate stabilization.

Coenzyme Q6 and iron reduction are responsible for the extracellular ascorbate stabilization at the plasma membrane of Saccharomyces cerevisiae

Yeast plasma membrane contains an electron transport system that maintains ascorbate in its reduced form in the apoplast. Reduction of ascorbate free radical by this system is comprised of two activities, one of them dependent on coenzyme Q6 (CoQ6). Strains with defects in CoQ6 synthesis exhibit decreased capacity for ascorbate stabilization compared with wild type or with atp2 or cor1 respiratory-deficient mutant strains. Both CoQ6 content in plasma membranes and ascorbate stabilization were increased during log phase growth. The addition of exogenous CoQ6 to whole cells resulted in its incorporation in the plasma membrane, produced levels of CoQ6 in the coq3 mutant strain that were 2-fold higher than in the wild type, and increased ascorbate stabilization activity in both strains, although it was higher in the coq3 mutant than in wild type. Other antioxidants, such as benzoquinone or alpha-tocopherol, did not change ascorbate stabilization. The CoQ6-independent reduction of ascorbate free radical was not due to copper uptake, pH changes or to the presence of CoQ6 biosynthetic intermediates, but decreased to undetectable levels when coq3 mutant strains were cultured in media supplemented with ferric iron. Plasma membrane CoQ6 levels were unchanged by either the presence or absence of iron in wild type, atp2, or cor1 strains. Ascorbate stabilization appears to be a function of the yeast plasma membrane, which is partially based on an electron transfer chain in which CoQ6 is the central electron carrier, whereas the remainder is independent of CoQ6 and other antioxidants but is dependent on the iron-regulated ferric reductase complex.

Multifunctional plasma membrane redox systems

All the biological membranes contain oxidoreduction systems actively involved in their bioenergetics. Plasma membrane redox systems seem to be ubiquitous and they have been related to several important functions, including not only their role in cell bioenergetics, but also in cell defense through the generation of reactive oxygen species, in iron uptake, in the control of cell growth and proliferation and in signal transduction. In the last few years, an increasing number of mechanistic and molecular studies have deeply widened our knowledge on the function of these plasma membrane redox systems. The aim of this review is to summarize what is currently known about the components and physiological roles of these systems.