The NADH oxidase activity of the plasma membrane of synaptosomes is a major source of superoxide anion and is inhibited by peroxynitrite

Structural Features of Cytochrome b5–Cytochrome b5 Reductase Complex Formation and Implications for the Intramolecular Dynamics of Cytochrome b5 Reductase

Membrane cytochrome b₅ reductase is a pleiotropic oxidoreductase that uses primarily soluble reduced nicotinamide adenine dinucleotide (NADH) as an electron donor to reduce multiple biological acceptors localized in cellular membranes. Some of the biological acceptors of the reductase and coupled redox proteins might eventually transfer electrons to oxygen to form reactive oxygen species. Additionally, an inefficient electron transfer to redox acceptors can lead to electron uncoupling and superoxide anion formation by the reductase. Many efforts have been made to characterize the involved catalytic domains in the electron transfer from the reduced flavoprotein to its electron acceptors, such as cytochrome b₅, through a detailed description of the flavin and NADH-binding sites. This information might help to understand better the processes and modifications involved in reactive oxygen formation by the cytochrome b₅ reductase. Nevertheless, more than half a century since this enzyme was first purified, the one-electron transfer process toward potential electron acceptors of the reductase is still only partially understood. New advances in computational analysis of protein structures allow predicting the intramolecular protein dynamics, identifying potential functional sites, or evaluating the effects of microenvironment changes in protein structure and dynamics. We applied this approach to characterize further the roles of amino acid domains within cytochrome b₅ reductase structure, part of the catalytic domain, and several sensors and structural domains involved in the interactions with cytochrome b₅ and other electron acceptors. The computational analysis results allowed us to rationalize some of the available spectroscopic data regarding ligand-induced conformational changes leading to an increase in the flavin adenine dinucleotide (FAD) solvent-exposed surface, which has been previously correlated with the formation of complexes with electron acceptors.

Melatonin: Regulation of Biomolecular Condensates in Neurodegenerative Disorders

Biomolecular condensates are membraneless organelles (MLOs) that form dynamic, chemically distinct subcellular compartments organizing macromolecules such as proteins, RNA, and DNA in unicellular prokaryotic bacteria and complex eukaryotic cells. Separated from surrounding environments, MLOs in the nucleoplasm, cytoplasm, and mitochondria assemble by liquid-liquid phase separation (LLPS) into transient, non-static, liquid-like droplets that regulate essential molecular functions. LLPS is primarily controlled by post-translational modifications (PTMs) that fine-tune the balance between attractive and repulsive charge states and/or binding motifs of proteins. Aberrant phase separation due to dysregulated membrane lipid rafts and/or PTMs, as well as the absence of adequate hydrotropic small molecules such as ATP, or the presence of specific RNA proteins can cause pathological protein aggregation in neurodegenerative disorders. Melatonin may exert a dominant influence over phase separation in biomolecular condensates by optimizing membrane and MLO interdependent reactions through stabilizing lipid raft domains, reducing line tension, and maintaining negative membrane curvature and fluidity. As a potent antioxidant, melatonin protects cardiolipin and other membrane lipids from peroxidation cascades, supporting protein trafficking, signaling, ion channel activities, and ATPase functionality during condensate coacervation or dissolution. Melatonin may even control condensate LLPS through PTM and balance mRNA- and RNA-binding protein composition by regulating N6-methyladenosine (m6A) modifications. There is currently a lack of pharmaceuticals targeting neurodegenerative disorders via the regulation of phase separation. The potential of melatonin in the modulation of biomolecular condensate in the attenuation of aberrant condensate aggregation in neurodegenerative disorders is discussed in this review.

Oxidative Stress and NADPH Oxidase: Connecting Electromagnetic Fields, Cation Channels and Biological Effects

Electromagnetic fields (EMFs) disrupt the electrochemical balance of biological membranes, thereby causing abnormal cation movement and deterioration of the function of membrane voltage-gated ion channels. These can trigger an increase of oxidative stress (OS) and the impairment of all cellular functions, including DNA damage and subsequent carcinogenesis. In this review we focus on the main mechanisms of OS generation by EMF-sensitized NADPH oxidase (NOX), the involved OS biochemistry, and the associated key biological effects.

β-Carotene and its physiological metabolites: Effects on oxidative status regulation and genotoxicity in in vitro models

Carotenoids are ubiquitously distributed in nature, β-carotene being the most frequently found carotenoid in the human diet. In the human body, β-carotene is absorbed, distributed and metabolized by enzymatic and/or non-enzymatic oxidant cleavage into several metabolites. Despite the broadly accepted biological value of β-carotene, it has also been considered a double-edged sword, mainly due to its potential antioxidant versus pro-oxidant behaviour. In this sense, the aim of this work was to scrutinize the antioxidant or pro-oxidant potential of β-carotene and its metabolites, namely trans-β-apo-8'-carotenal and β-ionone. Several parameters were evaluated in this study, viz. their effects on reactive species production, both in human whole blood and neutrophils; their effects on lipid peroxidation, in the absence and presence of peroxynitrite anion (ONOO^-) or hydrogen peroxide (H₂O₂), using a synaptosomal model; and finally, their putative genotoxic effects in the human hepatic HepG2 cell line. In general, depending on the cellular model and conditions tested, β-carotene and its metabolites revealed antioxidant effects to varying degrees without significant pro-oxidant or genotoxic effects.

Cellular and Molecular Mechanisms of Recessive Hereditary Methaemoglobinaemia Type II

Cytochrome b5 reductase 3 (CYB5R3) is a membrane-bound NADH-dependent redox enzyme anchored to the mitochondrial outer membrane, endoplasmic reticulum, and plasma membrane. Recessive hereditary methaemoglobinaemia (RHM) type II is caused by CYB5R3 deficiency and is an incurable disease characterized by severe encephalopathy with mental retardation, microcephaly, generalized dystonia, and movement disorders. Currently, the etiology of type II RHM is poorly understood and there is no treatment for encephalopathy associated with this disease. Defective CYB5R3 leads to defects in the elongation and desaturation of fatty acids and cholesterol biosynthesis, which are conventionally linked with neurological disorders of type II RHM. Nevertheless, this abnormal lipid metabolism cannot explain all manifestations observed in patients. Current molecular and cellular studies indicate that CYB5R3 deficiency has pleiotropic tissue effects. Its localization in lipid rafts of neurons indicates its role in interneuronal contacts and its presence in caveolae of the vascular endothelial membrane suggests a role in the modulation of nitric oxide diffusion. Its role in aerobic metabolism and oxidative stress in fibroblasts, neurons, and cardiomyocytes has been reported to be due to its ability to modulate the intracellular ratio of NAD⁺/NADH. Based on the new molecular and cellular functions discovered for CYB5R3 linked to the plasma membrane and mitochondria, the conventional conception that the cause of type II RHM is a lipid metabolism disorder should be revised. We hypothesized that neurological symptoms of the disease could be caused by disorders in the synapse, aerobic metabolism, and/or vascular homeostasis rather than in disturbances of lipid metabolism.

Purified NADH-cytochrome b5 reductase is a novel superoxide anion source inhibited by apocynin: sensitivity to nitric oxide and peroxynitrite

Cytochrome b5 reductase (Cb5R) is a pleiotropic flavoprotein that catalyzes multiple one-electron reduction reactions with various redox partners in cells. In earlier work from our laboratory, we have shown its implication in the generation of reactive oxygen species (ROS), primarily a superoxide anion overshoot peak, which plays a major role as a triggering event for the acceleration of apoptosis in cerebellar granule neurons in culture. However, the results obtained in that work did not allow us to exclude the possibility that this superoxide anion production could be derived from Cb5R acting in concert with other cellular components. In this work, we have purified Cb5R from pig liver and we have experimentally shown that this enzyme catalyzed NADH-dependent production of superoxide anion, assayed with cytochrome c and nitroblue tetrazolium as detection reagents for this particular ROS. The basic kinetic parameters for this novel NADH-dependent activity of Cb5R at 37°C are Vmax = 3.0 ± 0.5 μmol/min/mg of purified Cb5R and KM(NADH) = 2.8 ± 0.3 μM NADH. In addition, we report that apocynin, a widely used inhibitor of nonmitochondrial ROS production in mammalian cell cultures and tissues, is a potent inhibitor of purified Cb5R activity at the concentrations used in the experiments done with cell cultures. In the presence of apocynin the KM(NADH) value of Cb5R increases, and docking simulations indicate that apocynin can bind to a site near to or partially overlapping the NADH binding site of Cb5R. Other ROS, such as nitric oxide and peroxynitrite, have inhibitory effects on purified Cb5R, providing the basis for a feedback cellular protection mechanism through modulation of excessive extramitochondrial superoxide anion production by Cb5R. Both kinetic assays and docking simulations suggest that nitric oxide-induced nitrosylation (including covalent adduction of nitroso functional groups) of Cb5R cysteines and peroxynitrite-induced tyrosine nitration and cysteine oxidation modified the conformation of the NADH binding domain leading to a decreased affinity of Cb5R for NADH.

Bioluminescent detection of peroxynitrite with a boronic acid-caged luciferin

Peroxynitrite, a highly reactive biological oxidant, is formed under pathophysiologic conditions from the diffusion-limited reaction of nitric oxide and superoxide radical anion. Peroxynitrite has been implicated as the mediator of nitric oxide toxicity in many diseases and as an important signaling disrupting molecule (L. Liaudet et al., Front. Biosci.14, 4809-4814, 2009) [1]. Biosensors effective at capturing peroxynitrite in a specific and fast enough manner for detection, along with readouts compatible with in vivo studies, are lacking. Here we report that the boronic acid-based bioluminescent system PCL-1 (peroxy-caged luciferin-1), previously reported as a chemoselective sensor for hydrogen peroxide (G.C. Van de Bittner et al., Proc. Natl. Acad. Sci. USA107, 21316-21321, 2010) [2], reacts with peroxynitrite stoichiometrically with a rate constant of 9.8±0.3×10(5)M(-1)s(-1) and a bioluminescence detection limit of 16nM, compared to values of 1.2±0.3M(-1)s(-1) and 231nM for hydrogen peroxide. Further, we demonstrate bioluminescent detection of peroxynitrite in the presence of physiological competitors: carbon dioxide, glutathione, albumin, and catalase. We also demonstrate the utility of this method to assess peroxynitrite formation in mammalian cells by measuring peroxynitrite generated under normal culture conditions after stimulation of macrophages with bacterial endotoxin lipopolysaccharide. Thus, the PCL-1 method for measuring peroxynitrite generation shows superior selectivity over other oxidants under in vivo conditions.

Stimulation and clustering of cytochrome b5 reductase in caveolin-rich lipid microdomains is an early event in oxidative stress-mediated apoptosis of cerebellar granule neurons

The apoptosis of cerebellar granule neurons (CGN) induced by low potassium in the extracellular medium is a model of neuronal apoptosis where an overshot of reactive oxygen species (ROS) triggers the neuronal death. In this work, using dihydroethidium and L-012 as specific dyes for superoxide anion detection we show that this ROS overshot can be accounted by an increased release of superoxide anion to the extracellular medium. The amplitude and time course of the increase of superoxide anion observed early during apoptosis correlated with the increase of the content of soluble cytochrome b(5), a substrate of the NADH-dependent oxidase activity of the cytochrome b(5) reductase associated with lipid rafts in CGN. Western blotting and immunofluorescence microscopy approaches, including fluorescence energy transfer, pointed out an enhanced clustering of cytochrome b(5) reductase within caveolins-rich lipid rafts microdomains. Protein/protein docking analysis suggests that cytochrome b(5) reductase can form complexes with caveolins 1α, 1β and 2, playing electrostatic interactions a major role in this association. In conclusion, our results indicate that overstimulation of cytochrome b(5) reductase associated with lipid rafts can account for the overshot of plasma membrane-focalized superoxide anion production that triggers the entry of CGN in the irreversible phase of apoptosis. This article is part of a Special Issue entitled: Proteomics: The clinical link.

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.

Peroxynitrite-mediated oxidative modifications of myosin and implications on structure and function

Abstract The peroxynitrite-induced functional impairment of myosin was studied in different reaction conditions, known to alter the oxidative chemistry of peroxynitrite, to better understand the molecular mechanisms of this interaction. It is shown that peroxynitrite is able to enhance the basal MgATPase activity up to 2-fold while inhibiting the actin-stimulated ATPase activity of myosin and that the extent of these functional alterations is dependent on the reaction medium. The observed changes in the stimulation of the MgATPase activity correlate with the extent of carbonyl formation in myosin. The enzyme inhibition is more potent in conditions where the efficiency of tyrosine nitration and peroxynitrite reactivity towards sulphydryls are lower. Together with the observation that reversion of sulphydryl oxidation did not lead to the recovery of myosin functional and structural impairments, these results point out to the importance of protein carbonylation as a post-translational modification in the peroxynitrite-induced myosin functional impairment.

Radio frequency electromagnetic radiation (RF-EMR) from GSM (0.9/1.8GHz) mobile phones induces oxidative stress and reduces sperm motility in rats

INTRODUCTION

Mobile phones have become indispensable in the daily lives of men and women around the globe. As cell phone use has become more widespread, concerns have mounted regarding the potentially harmful effects of RF-EMR from these devices.

OBJECTIVE

The present study was designed to evaluate the effects of RF-EMR from mobile phones on free radical metabolism and sperm quality.

MATERIALS AND METHODS

Male albino Wistar rats (10-12 weeks old) were exposed to RF-EMR from an active GSM (0.9/1.8 GHz) mobile phone for 1 hour continuously per day for 28 days. Controls were exposed to a mobile phone without a battery for the same period. The phone was kept in a cage with a wooden bottom in order to address concerns that the effects of exposure to the phone could be due to heat emitted by the phone rather than to RF-EMR alone. Animals were sacrificed 24 hours after the last exposure and tissues of interest were harvested.

RESULTS

One hour of exposure to the phone did not significantly change facial temperature in either group of rats. No significant difference was observed in total sperm count between controls and RF-EMR exposed groups. However, rats exposed to RF-EMR exhibited a significantly reduced percentage of motile sperm. Moreover, RF-EMR exposure resulted in a significant increase in lipid peroxidation and low GSH content in the testis and epididymis.

CONCLUSION

Given the results of the present study, we speculate that RF-EMR from mobile phones negatively affects semen quality and may impair male fertility.

Clustering of plasma membrane-bound cytochrome b5 reductase within 'lipid raft' microdomains of the neuronal plasma membrane

Plasma membrane redox centres play a major role in neuronal defence against oxidative stress and survival. In cerebellar granule neurons in culture (CGN) a large pool of the flavoproteins are associated with the plasma membrane, and the intensity of CGN green/orange autofluorescence correlated with the levels of expression of cytochrome b(5) reductase. Regionalization of cytochrome b(5) reductase in the plasma membrane of CGN by fluorescence resonance energy transfer points out the close proximity between cytochrome b(5) reductase and the 'lipid raft' markers cholera toxin B and caveolin-2. This study unravels that membrane-bound cytochrome b(5) reductase is largely enriched at interneuronal contact sites in the neuronal soma and associated with 'lipid rafts' of the CGN plasma membrane. We also show that cytochrome b(5) reductase makes a large contribution to the NADH oxidase activity and to the red-shifted flavine fluorescence of purified rat brain synaptic plasma membranes. In conclusion, membrane-bound cytochrome b(5) reductase forms a large mesh of redox centres associated with the neuronal plasma membrane.

Vanadium and cadmium in vivo effects in teleost cardiac muscle: metal accumulation and oxidative stress markers

Several biological studies associate vanadium and cadmium with the production of reactive oxygen species (ROS), leading to lipid peroxidation and antioxidant enzymes alterations. The present study aims to analyse and compare the oxidative stress responses induced by an acute intravenous exposure (1 and 7 days) to a sub-lethal concentration (5 mM) of two vanadium solutions, containing different vanadate n-oligomers (n=1-5 or n=10), and a cadmium solution on the cardiac muscle of the marine teleost Halobatrachus didactylus (Lusitanian toadfish). It was observed that vanadium is mainly accumulated in mitochondria (1.33+/-0.26 microM), primarily when this element was administrated as decameric vanadate, than when administrated as metavanadate (432+/-294 nM), while the highest content of cadmium was found in cytosol (365+/-231 nM). Indeed, decavanadate solution promotes stronger increases in mitochondrial antioxidant enzymes activities (catalase: +120%; superoxide dismutase: +140%) than metavanadate solution. On contrary, cadmium increases cytosolic catalase (+111%) and glutathione peroxidases (+50%) activities. It is also observed that vanadate oligomers induce in vitro prooxidant effects in toadfish heart, with stronger effects induced by metavanadate solution. In summary, vanadate and cadmium are differently accumulated in blood and cardiac subcellular fractions and induced different responses in enzymatic antioxidant defence mechanisms. In the present study, it is described for the first time the effects of equal doses of two different metals intravenously injected in the same fish species and upon the same exposure period allowing to understand the mechanisms of vanadate and cadmium toxicity in fish cardiac muscle.

Reduction of ascorbate free radical by the plasma membrane of synaptic terminals from rat brain

Synaptic plasma membranes (SPMV) decrease the steady state ascorbate free radical (AFR) concentration of 1mM ascorbate in phosphate/EDTA buffer (pH 7), due to AFR recycling by redox coupling between ascorbate and the ubiquinone content of these membranes. In the presence of NADH, but not NADPH, SPMV catalyse a rapid recycling of AFR which further lower the AFR concentration below 0.05 microM. These results correlate with the nearly 10-fold higher NADH oxidase over NADPH oxidase activity of SPMV. SPMV has NADH-dependent coenzyme Q reductase activity. In the presence of ascorbate the stimulation of the NADH oxidase activity of SPMV by coenzyme Q(1) and cytochrome c can be accounted for by the increase of the AFR concentration generated by the redox pairs ascorbate/coenzyme Q(1) and ascorbate/cytochrome c. The NADH:AFR reductase activity makes a major contribution to the NADH oxidase activity of SPMV and decreases the steady-state AFR concentration well below the micromolar concentration range.

A possible role of oxidative stress in the switch mechanism of the cell death mode from apoptosis to necrosis--studies on rho0 cells

Apoptosis is induced not only during morphogenesis and embryogenesis but also under various pathological conditions, especially related to oxidative stress. Apoptotic cells are phagocytized by neighboring cells while necrotic cells cause local and general reactions sometimes lethal to our bodies. Data have been accumulated to demonstrate that the switch of the cell death mode from apoptosis to necrosis does occur. However, detailed mechanisms involved in the switch mechanism remain unsolved although decreases in the intracellular level of ATP and a burst in the cellular level of reactive oxygen species (ROS) have been proposed. Recently, we have shown that the population of apoptotic cells reaches maximum in human osteosarcoma 143B cells treated for 6h with menadione (MEN) while necrotic cells become predominant at 9h of the treatment. In the present study we have attempted to clarify the role of cellular ATP in the switch mechanism using rho(0) cells derived from human osteosarcoma rho+ cells. Results are summarized as follows: (1) Apoptotic and necrotic changes in rho(0) cells are much faster than rho+ cells after the treatment with MEN. (2) Cellular level of ATP in rho(0) cells remains essentially in the same level before and after the MEN-treatment while intracellular levels of superoxide continuously increase after the MEN-treatment. (3) rho+ cells treated with MEN in the presence of antimycin A plus oligomycin show similar changes to those of MEN-treated rho(0) cells. (4) MEN-induced increases in the cellular level of superoxide are distinctly suppressed by inhibitors of NADPH oxidase. These results suggest that the intracellular level of superoxide may be a key factor directly related to the switch mechanism from apoptosis to necrosis, and that decreases in cellular level of ATP accelerate both apoptotic and necrotic changes of the cells.

Regionalization of plasma membrane-bound flavoproteins of cerebellar granule neurons in culture by fluorescence energy transfer imaging

Flavoproteins are components of plasma membrane redox chains, which have been suggested to play major roles in neuronal activity and survival. We found that the red/orange autofluorescence of mature primary cultures of cerebellar granule neurons (8-9 days in vitro) was largely quenched by millimolar concentrations of dithionite added to the extracellular medium, and pointed out that nearly 50% of this autofluorescence was due to plasma membrane-bound flavoproteins. We report in this work that the lipophilic neuronal plasma membrane markers N-(3-triethylammoniumpropyl)-4-(4-(4-(diethylamino)phenyl)butadienyl)-pyridinium dibromide (RH-414) and N-(3-triethylammoniumpropyl)-4-(6-(4-(diethylamino)phenyl)hexatrienyl)pyridinium dibromide (FM4-64) can form fluorescence energy transfer donor-acceptor pairs with flavoproteins with calculated R (0) values between 3.7 and 4.2 nm. The quantification of the efficiency of fluorescence energy transfer with different concentrations of acceptor dyes has been worked out with re-suspended neurons. Using quantitative images of the neurons in culture, acquired with a CCD camera attached to an epifluorescence microscope, regionalization of the plasma membrane-bound flavoproteins of cerebellar granule neurons has been achieved from the quenching by dithionite of the fluorescence of the acceptor dye. The results unraveled that plasma membrane-bound flavoproteins are largely enriched in interneuronal contact sites forming clusters of 0.5-1 microm diameter size, which appears largely regionalized in the neuron's cell body.

A potent sorbitol dehydrogenase inhibitor exacerbates sympathetic autonomic neuropathy in rats with streptozotocin-induced diabetes

We have developed an animal model of diabetic sympathetic autonomic neuropathy which is characterized by neuroaxonal dystrophy (NAD), an ultrastructurally distinctive axonopathy, in chronic streptozotocin (STZ)-diabetic rats. Diabetes-induced alterations in the sorbitol pathway occur in sympathetic ganglia and therapeutic agents which inhibit aldose reductase or sorbitol dehydrogenase improve or exacerbate, respectively, diabetes-induced NAD. The sorbitol dehydrogenase inhibitor SDI-711 (CP-470711, Pfizer) is approximately 50-fold more potent than the structurally related compound SDI-158 (CP 166,572) used in our earlier studies. Treatment with SDI-711 (5 mg/kg/day) for 3 months increased ganglionic sorbitol (26-40 fold) and decreased fructose content (20-75%) in control and diabetic rats compared to untreated animals. SDI-711 treatment of diabetic rats produced a 2.5- and 4-5-fold increase in NAD in the SMG and ileal mesenteric nerves, respectively, in comparison to untreated diabetics. Although SDI-711 treatment of non-diabetic control rat ganglia increased ganglionic sorbitol 40-fold (a value 8-fold higher than untreated diabetics), the frequency of NAD remained at control levels. Levels of ganglionic sorbitol pathway intermediates in STZ-treated rats (a model of type 1 diabetes) and Zucker Diabetic Fatty rats (ZDF, a genetic model of type 2 diabetes) were comparable, although STZ-diabetic rats develop NAD and ZDF-diabetic rats do not. SDI failed to increase diabetes-related ganglionic NGF above levels seen in untreated diabetics. Initiation of Sorbinil treatment for the last 4 months of a 9 month course of diabetes, substantially reversed the frequency of established NAD in the diabetic rat SMG without affecting the metabolic severity of diabetes. These findings indicate that sorbitol pathway-linked metabolic alterations play an important role in the development of NAD, but sorbitol pathway activity, not absolute levels of sorbitol or fructose per se, may be most critical to its pathogenesis.

The switch mechanism of the cell death mode from apoptosis to necrosis in menadione-treated human osteosarcoma cell line 143B cells

Time-dependent changes in the cell death mode from apoptosis to necrosis were studied in cultured 143B cells treated with menadione, an anti-cancerous drug, excluding a possible involvement of "secondary necrosis." The population of apoptotic cells judged by FITC-Annexin V and propidium iodide (PI) double staining reached its maximum at 6 hours after 100 microM menadione treatment followed by an abrupt decrease thereafter, while that of necrotic cells continuously increased reaching 90% at 24 hours. Electron microscopically, cells attached to the culture dish at 6 hours after the treatment consisted of two different types of cells: cells with typical apoptotic features occupying the major population and those with condensed nuclei and swollen cytoplasm. Cells attached to the culture dish at 8 hours after the treatment consisted exclusively of those with condensed nuclei and swollen cytoplasm. Mitochondria in these cells showed various structural changes: those swollen to various degrees with deposition of flocculent densities, or those with highly condensed matrix. Distinct decreases both in intracellular levels of ATP and caspase-3-like activities and remarkable elevations of intracellular levels of superoxide, which were partly suppressed by NAD(P)H oxidase inhibitors, occurred at 6 hours after the treatment. These results may suggest that distinct increases of the intracellular level of superoxide derived from plasma membrane NAD(P)H oxidase besides that from mitochondria have triggered the transition of cell death mode from apoptosis to necrosis. Transition of highly condensed mitochondria to extremely swollen ones may reflect necrotic processes in menadione-treated cells. The present study strongly suggests that time-dependent study is essential using the electron microscopic technique to analyze detailed processes in the changes of the cell death mode.

Release of reactive oxygen and nitrogen species from contracting skeletal muscle cells

A number of studies have indicated that exercise is associated with an increased oxidative stress in skeletal muscle tissue, but the nature of the increased oxidants and sites of their generation have not been clarified. The generation of extracellular reactive oxygen and nitrogen species has been studied in myotubes derived from an immortalized muscle cell line (H-2k(b) cells) that were stimulated to contract by electrical stimulation in culture. Cells were stimulated to contract with differing frequencies of electrical stimulation. Both induced release of superoxide anion and nitric oxide into the extracellular medium and caused an increase in extracellular hydroxyl radical activity. Increasing frequency of stimulation increased the nitric oxide generation and hydroxyl radical activity, but had no significant effect on the superoxide released. Additions of inhibitors of putative generating pathways indicated that contraction-induced NO release was primarily from neuronal NO synthase enzymes and that the superoxide released is likely to be generated by a plasma membrane-located, flavoprotein oxidoreductase system. The data also indicate that peroxynitrite is generated in the extracellular fluid of muscle during contractile activity.

Kaempferol blocks oxidative stress in cerebellar granule cells and reveals a key role for reactive oxygen species production at the plasma membrane in the commitment to apoptosis

Micromolar concentrations of the flavonoid kaempferol were found to efficiently block cerebellar granule cell (CGC) death through low K+-induced apoptosis, as demonstrated by prevention of the activation of caspase-3, internucleosomal DNA fragmentation, and chromatin condensation, without a significant rise in intracellular free Ca2+ concentration. Half of the maximum protection against CGC apoptosis was attained with 8 +/- 2 microM kaempferol. Reactive oxygen species (ROS) were monitored with 2',7'-dichlorodihydrofluorescein diacetate. Quantitative analysis of intracellularly and extracellularly oriented ROS production up to 3 h from the onset of low K+-induced CGC apoptosis was carried out with acquired digital fluorescence microscopy images of CGC in culture plates using a CCD camera, and also with fluorescence measurements of resuspended CGCs. In both cases, nearly 90% of ROS production by CGCs during the early stages (up to 3 h) after induction of low-K+ apoptosis occurs at the plasma membrane. Kaempferol, at concentrations that blocked CGC apoptosis, has been found to be a particularly potent blocker of extracellularly oriented ROS production by CGCs, and to inhibit the ascorbate-dependent NADH oxidase and superoxide anion production activities of the neuronal plasma membrane redox chain.

Inhibition of oxidative stress produced by plasma membrane NADH oxidase delays low-potassium-induced apoptosis of cerebellar granule cells

From 1 to 3 h after the onset of cerebellar granule cells (CGC) apoptosis in a low-K+(5 mm KCl) medium there was a large decay of NADH and a 2.5-fold increase of the rate of reactive oxygen species (ROS) production (measured using CGC loaded with dichlorodihydrofluorescein). During the same time period, the ascorbate-dependent NADH oxidase activity, which accounted for more than 90% of both total NADH oxidase activity and NADH-dependent *O2- production of CGC lysates, increased 2.5- to threefold. The stimulation of the ascorbate-dependent NADH oxidase activity by oxidized cytochrome c, 2.5-fold at saturation with a K(0.5) of 4-5 microm cytochrome c, can at least partially explain this activation. The plasma membrane ascorbate-dependent NADH oxidase activity accounted for more than 70% of the total activity (both in terms of NADH oxidase and *O2- release) of CGC lysates. 4-Hydroxyquinazoline (4-HQ), which was found to block this apoptotic process, prevented the increase of ROS production. 4-HQ protection against cell viability loss and DNA fragmentation correlated with the inhibition by 4-HQ of the ascorbate-dependent NADH oxidase activity of CGC lysates, showing the same K(0.5)-value (4-5 mm 4-HQ). The efficient blockade of CGC apoptosis by addition of superoxide dismutase to the medium further supports the neurotoxic role of *O2- overproduction by the plasma membrane ascorbate-dependent NADH oxidase.