Diphenylene iodonium as an inhibitor of the NADPH oxidase complex of bovine neutrophils. Factors controlling the inhibitory potency of diphenylene iodonium in a cell-free system of oxidase activation

Regulation of respiratory complex I assembly by FMN cofactor targeting

Respiratory complex I plays a crucial role in the mitochondrial electron transport chain and shows promise as a therapeutic target for various human diseases. While most studies focus on inhibiting complex I at the Q-site, little is known about inhibitors targeting other sites within the complex. In this study, we demonstrate that diphenyleneiodonium (DPI), a N-site inhibitor, uniquely affects the stability of complex I by reacting with its flavin cofactor FMN. Treatment with DPI blocks the final stage of complex I assembly, leading to the complete and reversible degradation of complex I in different cellular models. Growing cells in medium lacking the FMN precursor riboflavin or knocking out the mitochondrial flavin carrier gene SLC25A32 results in a similar complex I degradation. Overall, our findings establish a direct connection between mitochondrial flavin homeostasis and complex I stability and assembly, paving the way for novel pharmacological strategies to regulate respiratory complex I.

NOX-2 Inhibitors may be Potential Drug Candidates for the Management of COVID-19 Complications

COVID-19 is an RNA virus that attacks the targeting organs, which express angiotensin- converting enzyme-2 (ACE-2), such as the lungs, heart, renal system, and gastrointestinal tract. The virus that enters the cell by endocytosis triggers ROS production within the confines of endosomes via a NOX-2 containing NADPH-oxidase. Various isoforms of NADPH oxidase are expressed in airways and alveolar epithelial cells, endothelial and vascular smooth muscle cells, and inflammatory cells, such as alveolar macrophages, monocytes, neutrophils, and Tlymphocytes. The key NOX isoform expressed in macrophages and neutrophils is the NOX-2 oxidase, whereas, in airways and alveolar epithelial cells, it appears to be NOX-1 and NOX-2. The respiratory RNA viruses induce NOX-2-mediated ROS production in the endosomes of alveolar macrophages. The mitochondrial and NADPH oxidase (NOX) generated ROS can enhance TGF-β signaling to promote fibrosis of the lungs. The endothelium-derived ROS and platelet-derived ROS, due to activation of the NADPH-oxidase enzyme, play a crucial role in platelet activation. It has been observed that NOX-2 is generally activated in COVID-19 patients. The post-COVID complications like pulmonary fibrosis and platelet aggregation may be due to the activation of NOX-2. NOX-2 inhibitors may be a useful drug candidate to prevent COVID-19 complications like pulmonary fibrosis and platelet aggregation.

The NADPH Oxidase Inhibitors Apocynin and Diphenyleneiodonium Protect Rats from LPS-Induced Pulmonary Inflammation

Inflammation is the body's response to insults, for instance, lung inflammation is generally caused by pathogens or by exposure to pollutants, irritants and toxins. This process involves many inflammatory cells such as epithelial cells, monocytes, macrophages and neutrophils. These cells produce and release inflammatory mediators such as pro-inflammatory cytokines, lipids and reactive oxygen species (ROS). Lung epithelial cells and phagocytes (monocytes, macrophages and neutrophils) produce ROS mainly by the NADPH oxidase NOX1 and NOX2, respectively. The aim of this study was to investigate the effects of two NADPH oxidase inhibitors, apocynin and diphenyleneiodonium (DPI), on lipopolysaccharide (LPS)-induced lung inflammation in rats. Our results showed that apocynin and DPI attenuated the LPS-induced morphological and histological alterations of the lung, reduced edema and decreased lung permeability. The evaluation of oxidative stress markers in lung homogenates showed that apocynin and DPI inhibited LPS-induced NADPH oxidase activity, and restored superoxide dismutase (SOD) and catalase activity in the lung resulting in the reduction in LPS-induced protein and lipid oxidation. Additionally, apocynin and DPI decreased LPS-induced MPO activity in bronchoalveolar liquid and lung homogenates, TNF-α and IL-1β in rat plasma. NADPH oxidase inhibition could be a new therapeutic strategy for the treatment of inflammatory lung diseases.

A noncanonical response to replication stress protects genome stability through ROS production, in an adaptive manner

Cells are inevitably challenged by low-level/endogenous stresses that do not arrest DNA replication. Here, in human primary cells, we discovered and characterized a noncanonical cellular response that is specific to nonblocking replication stress. Although this response generates reactive oxygen species (ROS), it induces a program that prevents the accumulation of premutagenic 8-oxoguanine in an adaptive way. Indeed, replication stress-induced ROS (RIR) activate FOXO1-controlled detoxification genes such as SEPP1, catalase, GPX1, and SOD2. Primary cells tightly control the production of RIR: They are excluded from the nucleus and are produced by the cellular NADPH oxidases DUOX1/DUOX2, whose expression is controlled by NF-κB, which is activated by PARP1 upon replication stress. In parallel, inflammatory cytokine gene expression is induced through the NF-κB-PARP1 axis upon nonblocking replication stress. Increasing replication stress intensity accumulates DNA double-strand breaks and triggers the suppression of RIR by p53 and ATM. These data underline the fine-tuning of the cellular response to stress that protects genome stability maintenance, showing that primary cells adapt their responses to replication stress severity.

Integrated regulation of periclinal cell division by transcriptional module of BZR1-SHR in Arabidopsis roots

The timing and extent of cell division are crucial for the correct patterning of multicellular organism. In Arabidopsis, root ground tissue maturation involves the periclinal cell division of the endodermis to generate two cell layers: endodermis and middle cortex. However, the molecular mechanism underlying this pattern formation remains unclear. Here, we report that phytohormone brassinosteroid (BR) and redox signal hydrogen peroxide (H₂ O₂ ) interdependently promote periclinal division during root ground tissue maturation by regulating the activity of SHORT-ROOT (SHR), a master regulator of root growth and development. BR-activated transcription factor BRASSINAZOLE RESISTANT1 (BZR1) directly binds to the promoter of SHR to induce its expression, and physically interacts with SHR to increase the transcripts of RESPIRATORY BURST OXIDASE HOMOLOGs (RBOHs) and elevate the levels of H₂ O₂ , which feedback enhances the interaction between BZR1 and SHR. Additionally, genetic analysis shows that SHR is required for BZR1-promoted periclinal division, and BZR1 enhances the promoting effects of SHR on periclinal division. Together, our finding reveals that the transcriptional module of BZR1-SHR fine-tunes periclinal division during root ground tissue maturation in response to hormone and redox signals.

Pharmacological intervention in oxidative stress as a therapeutic target in neurological disorders

OBJECTIVES

Oxidative stress is a major cellular burden that triggers reactive oxygen species (ROS) and antioxidants that modulate signalling mechanisms. Byproducts generated from this process govern the brain pathology and functions in various neurological diseases. As oxidative stress remains the key therapeutic target in neurological disease, it is necessary to explore the multiple routes that can significantly repair the damage caused due to ROS and consequently, neurodegenerative disorders (NDDs). Nicotinamide adenine dinucleotide phosphate (NADPH) oxidase is the critical player of oxidative stress that can also be used as a therapeutic target to combat NDDs.

KEY FINDINGS

Several antioxidants signalling pathways are found to be associated with oxidative stress and show a protective effect against stressors by increasing the release of various cytoprotective enzymes and also exert anti-inflammatory response against this oxidative damage. These pathways along with antioxidants and reactive species can be the defined targets to eliminate or reduce the harmful effects of neurological diseases.

SUMMARY

Herein, we discussed the underlying mechanism and crucial role of antioxidants in therapeutics together with natural compounds as a pharmacological tool to combat the cellular deformities cascades caused due to oxidative stress.

ROS regulated reversible protein phase separation synchronizes plant flowering

How aerobic organisms exploit inevitably generated but potentially dangerous reactive oxygen species (ROS) to benefit normal life is a fundamental biological question. Locally accumulated ROS have been reported to prime stem cell differentiation. However, the underlying molecular mechanism is unclear. Here, we reveal that developmentally produced H₂O₂ in plant shoot apical meristem (SAM) triggers reversible protein phase separation of TERMINATING FLOWER (TMF), a transcription factor that times flowering transition in the tomato by repressing pre-maturation of SAM. Cysteine residues within TMF sense cellular redox to form disulfide bonds that concatenate multiple TMF molecules and elevate the amount of intrinsically disordered regions to drive phase separation. Oxidation triggered phase separation enables TMF to bind and sequester the promoter of a floral identity gene ANANTHA to repress its expression. The reversible transcriptional condensation via redox-regulated phase separation endows aerobic organisms with the flexibility of gene control in dealing with developmental cues.

Oxidative damage mechanism in Saccharomyces cerevisiae cells exposed to tetrachlorobisphenol A

Tetrachlorobisphenol A (TCBPA) can promote intracellular reactive oxygen species (ROS) accumulation. However, limited attention has been given to mechanisms underlying TCBPA exposure-associated ROS accumulation. Here, such mechanisms were explored in the simple eukaryotic model organism Saccharomyces cerevisiae exposed to multiple concentrations of TCBPA. Addition of diphenyleneiodonium, a specific inhibitor of NADPH oxidase, blocked TCBPA treatment-associated intracellular ROS accumulation. NADPH oxidase can be activated by calcineurin, mitogen-activated protein kinase (MAPK), and tyrosine kinase. Therefore, corresponding specific inhibition respectively on these three kinases was performed and results suggested that the Ca²⁺ signaling pathway, MAPK pathway, and tyrosine kinase pathway all contributed to the TCBPA exposure-associated intracellular ROS accumulation. In addition, TCBPA exposure-associated up-regulation of genes involved in ROS production and down-regulation of catalase promoted ROS accumulation in S. cerevisiae. To sum up, our current results provide insights into the understanding of TCBPA exposure-associated ROS accumulation.

Sources of Vascular Nitric Oxide and Reactive Oxygen Species and Their Regulation

Nitric oxide (NO) is a small free radical with critical signaling roles in physiology and pathophysiology. The generation of sufficient NO levels to regulate the resistance of the blood vessels and hence the maintenance of adequate blood flow is critical to the healthy performance of the vasculature. A novel paradigm indicates that classical NO synthesis by dedicated NO synthases is supplemented by nitrite reduction pathways under hypoxia. At the same time, reactive oxygen species (ROS), which include superoxide and hydrogen peroxide, are produced in the vascular system for signaling purposes, as effectors of the immune response, or as byproducts of cellular metabolism. NO and ROS can be generated by distinct enzymes or by the same enzyme through alternate reduction and oxidation processes. The latter oxidoreductase systems include NO synthases, molybdopterin enzymes, and hemoglobins, which can form superoxide by reduction of molecular oxygen or NO by reduction of inorganic nitrite. Enzymatic uncoupling, changes in oxygen tension, and the concentration of coenzymes and reductants can modulate the NO/ROS production from these oxidoreductases and determine the redox balance in health and disease. The dysregulation of the mechanisms involved in the generation of NO and ROS is an important cause of cardiovascular disease and target for therapy. In this review we will present the biology of NO and ROS in the cardiovascular system, with special emphasis on their routes of formation and regulation, as well as the therapeutic challenges and opportunities for the management of NO and ROS in cardiovascular disease.

Respiratory burst oxidase homologue-dependent H2 O2 and chloroplast H2 O2 are essential for the maintenance of acquired thermotolerance during recovery after acclimation

Thermotolerance is improved by heat stress (HS) acclimation, and the thermotolerance level is "remembered" by plants. However, the underlying signalling mechanisms remain largely unknown. Here, we showed NADPH oxidase-mediated H₂ O₂ (NADPH-H₂ O₂ ), and chloroplast-H₂ O₂ promoted the sustained expression of HS-responsive genes and programmed cell death (PCD) genes, respectively, during recovery after HS acclimation. When spraying the NADPH oxidase inhibitor, diphenylene iodonium, after HS acclimation, the NADPH-H₂ O₂ level significantly decreased, resulting in a decrease in the expression of HS-responsive genes and the loss of maintenance of acquired thermotolerance (MAT). In contrast, compared with HS acclimation, NADPH-H₂ O₂ declined but chloroplast-H₂ O₂ further enhanced during recovery after HS over-acclimation, resulting in the reduced expression of HS-responsive genes and substantial production of PCD. Notably, the further inhibition of NADPH-H₂ O₂ after HS over-acclimation also inhibited chloroplast-H₂ O₂ , alleviating the severe PCD and surpassing the MAT of HS over-acclimation treatment. Due to the change in subcellular H₂ O₂ after HS acclimation, the tomato seedlings maintained a constant H₂ O₂ level during recovery, resulting in stable and lower total H₂ O₂ levels during a tester HS challenge conducted after recovery. We conclude that tomato seedlings increase their MAT by enhancing NADPH-H₂ O₂ content and controlling chloroplast-H₂ O₂ production during recovery, which enhances the expression of HS-responsive genes and balances PCD levels, respectively.

Supramolecular Encapsulation and Bioactivity Modulation of a Halonium Ion by Cucurbit[ n]uril ( n = 7, 8)

This is the first time that cucurbit[7]uril and cucurbit[8]uril have been demonstrated to serve as synthetic receptors for a halonium guest species, diphenyleneiodonium, modulating its bioactivities and alleviating its cardiotoxicity, which further expands the onium family of guest molecules for the cucurbit[ n]uril family and provides new insights for halonium-cucurbit[ n]uril host-guest chemistry and its potential applications in pharmaceutical chemistry.

Hydrogen peroxide positively regulates brassinosteroid signaling through oxidation of the BRASSINAZOLE-RESISTANT1 transcription factor

Hydrogen peroxide (H₂O₂) is an important signaling molecule in plant developmental processes and stress responses. However, whether H₂O₂-mediated signaling crosstalks with plant hormone signaling is largely unclear. Here, we show that H₂O₂ induces the oxidation of the BRASSINAZOLE-RESISTANT1 (BZR1) transcription factor, which functions as a master regulator of brassinosteroid (BR) signaling. Oxidative modification enhances BZR1 transcriptional activity by promoting its interaction with key regulators in the auxin-signaling and light-signaling pathways, including AUXIN RESPONSE FACTOR6 (ARF6) and PHYTOCHROME INTERACTING FACTOR4 (PIF4). Genome-wide analysis shows that H₂O₂-dependent regulation of BZR1 activity plays a major role in modifying gene expression related to several BR-mediated biological processes. Furthermore, we show that the thioredoxin TRXh5 can interact with BZR1 and catalyzes its reduction. We conclude that reversible oxidation of BZR1 connects H₂O₂-mediated and thioredoxin-mediated redox signaling to BR signaling to regulate plant development.

Hydrogen peroxide and brassinosteroids (BR) both regulate plant development and stress responses. Here Tian et al. show that hydrogen peroxide can trigger oxidation of the BR-responsive BZR1 transcription factor and promote its transcriptional activity, thereby linking BR and redox signaling.

Exogenous Hydrogen Peroxide Contributes to Heme Oxygenase-1 Delaying Programmed Cell Death in Isolated Aleurone Layers of Rice Subjected to Drought Stress in a cGMP-Dependent Manner

Hydrogen peroxide (H2O2) is a reactive oxygen species (ROS) that plays a dual role in plant cells. Here, we discovered that drought (20% polyethylene glycol-6000, PEG)-triggered decreases of HO-1 transcript expression and HO activity. However, exogenous H2O2 contributed toward the increase in HO-1 gene expression and activity of the enzyme under drought stress. Meanwhile, the HO-1 inducer hematin could mimic the effects of the H2O2 scavengers ascorbic acid (AsA) and dimethylthiourea (DMTU) and the H2O2 synthesis inhibitor diphenyleneiodonium (DPI) for scavenging or diminishing drought-induced endogenous H2O2. Conversely, the zinc protoporphyrin IX (ZnPPIX), an HO-1-specific inhibitor, reversed the effects of hematin. We further analyzed the endogenous H2O2 levels and HO-1 transcript expression levels of aleurone layers treated with AsA, DMTU, and DPI in the presence of exogenous H2O2 under drought stress, respectively. The results showed that in aleurone layers subjected to drought stress, when the endogenous H2O2 level was inhibited, the effect of exogenous H2O2 on the induction of HO-1 was enhanced. Furthermore, exogenous H2O2-activated HO-1 effectively enhanced amylase activity. Application of 8-bromoguanosine 3',5'-cyclic guanosine monophosphate (8-Br-cGMP) (the membrane permeable cGMP analog) promoted the effect of exogenous H2O2-delayed PCD of aleurone layers in response to drought stress. More importantly, HO-1 delayed the programmed cell death (PCD) of aleurone layers by cooperating with nitric oxide (NO), and the delayed effect of NO on PCD was achieved via mediation by cGMP under drought stress. In short, in rice aleurone layers, exogenous H2O2 (as a signaling molecule) triggered HO-1 and delayed PCD via cGMP which possibly induced amylase activity under drought stress. In contrast, as a toxic by-product of cellular metabolism, the drought-generated H2O2 promoted cell death.

Regulation of SIRT3 signal related metabolic reprogramming in gastric cancer by Helicobacter pylori oncoprotein CagA

Injection of the Helicobacter pylori cytotoxin-associated gene A (CagA) is closely associated with the development of chronic gastritis and gastric cancer. Individuals infected with H. pylori possessing the CagA protein produce more reactive oxygen species (ROS) and show an increased risk of developing gastric cancer. Sirtuins (SIRTs) are nicotinamide adenine dinucleotide (NAD⁺)-dependent deacetylases and mitochondrial SIRT3 is known to be a tumor suppressor via its ability to suppress ROS and hypoxia inducible factor 1α (HIF-1α). However, it is unclear whether increased ROS production by H. pylori is regulated by SIRT3 followed by HIF-1α regulation and whether intracellular CagA acts as a regulator thereof. In this study, we investigated correlations among SIRT3, ROS, and HIF-1α in H. pylori-infected gastric epithelial cells. We observed that SIRT3-deficient AGS cells induce HIF-1α protein stabilization and augmented transcriptional activity under hypoxic conditions. In CagA⁺H. pylori infected cells, CagA protein localized to mitochondria where it subsequently suppressed SIRT3 proteins. CagA⁺H. pylori infection also increased HIF-1α activity through the ROS production induced by the downregulated SIRT3 activity, which is similar to the hypoxic condition in gastric epithelial cells. In contrast, overexpression of SIRT3 inhibited the HIF-1α protein stabilization and attenuated the increase in HIF-1α transcriptional activity under hypoxic conditions. Moreover, CagA⁺H. pylori attenuated HIF-1α stability and decreased transcriptional activity in SIRT3-overexpressing gastric epithelial cells. Taken together, these findings provide valuable insights into the potential role of SIRT3 in CagA⁺H. pylori-mediated gastric carcinogenesis and a possible target for cancer prevention via inhibition of HIF-1α.

NADPH oxidase in brain injury and neurodegenerative disorders

Oxidative stress is a common denominator in the pathology of neurodegenerative disorders such as Alzheimer’s disease, Parkinson’s disease, Huntington’s disease, amyotrophic lateral sclerosis, and multiple sclerosis, as well as in ischemic and traumatic brain injury. The brain is highly vulnerable to oxidative damage due to its high metabolic demand. However, therapies attempting to scavenge free radicals have shown little success. By shifting the focus to inhibit the generation of damaging free radicals, recent studies have identified NADPH oxidase as a major contributor to disease pathology. NADPH oxidase has the primary function to generate free radicals. In particular, there is growing evidence that the isoforms NOX1, NOX2, and NOX4 can be upregulated by a variety of neurodegenerative factors. The majority of recent studies have shown that genetic and pharmacological inhibition of NADPH oxidase enzymes are neuroprotective and able to reduce detrimental aspects of pathology following ischemic and traumatic brain injury, as well as in chronic neurodegenerative disorders. This review aims to summarize evidence supporting the role of NADPH oxidase in the pathology of these neurological disorders, explores pharmacological strategies of targeting this major oxidative stress pathway, and outlines obstacles that need to be overcome for successful translation of these therapies to the clinic.

Nox Inhibitors & Therapies: Rational Design of Peptidic and Small Molecule Inhibitors

Oxidative stress-related diseases underlie many if not all of the major leading causes of death in United States and the Western World. Thus, enormous interest from both academia and pharmaceutical industry has been placed on the development of agents which attenuate oxidative stress. With that in mind, great efforts have been placed in the development of inhibitors of NADPH oxidase (Nox), the major enzymatic source of reactive oxygen species and oxidative stress in many cells and tissue. The regulation of a catalytically active Nox enzyme involves numerous protein-protein interactions which, in turn, afford numerous targets for inhibition of its activity. In this review, we will provide an updated overview of the available Nox inhibitors, both peptidic and small molecules, and discuss the body of data related to their possible mechanisms of action and specificity towards each of the various isoforms of Nox. Indeed, there have been some very notable successes. However, despite great commitment by many in the field, the need for efficacious and well-characterized, isoform-specific Nox inhibitors, essential for the treatment of major diseases as well as for delineating the contribution of a given Nox in physiological redox signalling, continues to grow.

Selective Targeting of Heme Protein in Cytochrome P450 and Nitric Oxide Synthase by Diphenyleneiodonium

Cytochrome P450 (CYP) enzymes mediate mixed-function oxidation reactions important in drug metabolism. The aromatic heterocyclic cation, diphenyleneiodonium (DPI), binds flavin in cytochrome P450 reductase and inhibits CYP-mediated activity. DPI also inhibits CYP by directly interacting with heme. Herein, we report that DPI effectively inhibits a number of CYP-related monooxygenase reactions including NADPH oxidase, a microsomal enzyme activity that generates hydrogen peroxide in the absence of metabolizing substrates. Inhibition of monooxygenase by DPI was time and concentration dependent with IC50's ranging from 0.06 to 1.9 μM. Higher (4.6-23.9 μM), but not lower (0.06-1.9 μM), concentrations of DPI inhibited electron flow via cytochrome P450 reductase, as measured by its ability to reduce cytochrome c and mediate quinone redox cycling. Similar results were observed with inducible nitric oxide synthase (iNOS), an enzyme containing a C-terminal reductase domain homologous to cytochrome P450 reductase that mediates reduction of cytochrome c, and an N-terminal heme-thiolate oxygenase domain mediating nitric oxide production. Significantly greater concentrations of DPI were required to inhibit cytochrome c reduction by iNOS (IC50 = 3.5 µM) than nitric oxide production (IC50 = 0.16 µM). Difference spectra of liver microsomes, recombinant CYPs, and iNOS demonstrated that DPI altered heme-carbon monoxide interactions. In the presence of NADPH, DPI treatment of microsomes and iNOS yielded a type II spectral shift. These data indicate that DPI interacts with both flavin and heme in CYPs and iNOS. Increased sensitivity for inhibition of CYP-mediated metabolism and nitric oxide production by iNOS indicates that DPI targets heme moieties within the enzymes.

The quest for selective nox inhibitors and therapeutics: challenges, triumphs and pitfalls

SIGNIFICANCE

Numerous studies in animal models and human subjects corroborate that elevated levels of reactive oxygen species (ROS) play a pivotal role in the progression of multiple diseases. As a major source of ROS in many organ systems, the NADPH oxidase (Nox) has become a prime target for therapeutic development.

RECENT ADVANCES

In recent years, intense efforts have been dedicated to the development of pan- and isoform-specific Nox inhibitors as opposed to antioxidants that proved ineffective in clinical trials. Over the past decade, an array of compounds has been proposed in an attempt to fill this void.

CRITICAL ISSUES

Although many of these compounds have proven effective as Nox enzyme family inhibitors, isoform specificity has posed a formidable challenge to the scientific community. This review surveys the most prominent Nox inhibitors, and discusses potential isoform specificity, known mechanisms of action, and shortcomings. Some of these inhibitors hold substantial promise as targeted therapeutics.

FUTURE DIRECTIONS

Increased insight into the mechanisms of action and regulation of this family of enzymes as well as atomic structures of key Nox subunits are expected to give way to a broader spectrum of more potent, efficacious, and specific molecules. These lead molecules will assuredly serve as a basis for drug development aimed at treating a wide array of diseases associated with increased Nox activity.

Visualization of phagosomal hydrogen peroxide production by a novel fluorescent probe that is localized via SNAP-tag labeling

Hydrogen peroxide (H2O2), a member of reactive oxygen species (ROS), plays diverse physiological roles including host defense and cellular signal transduction. During ingestion of invading microorganisms, professional phagocytes such as macrophages release H2O2 specifically into the phagosome to direct toxic ROS toward engulfed microbes. Although H2O2 is considered to exert discrete effects in living systems depending on location of its production, accumulation, and consumption, there have been limitations of techniques for probing this oxygen metabolite with high molecular specificity at the subcellular resolution. Here we describe the development of an O(6)-benzylguanine derivative of 5-(4-nitrobenzoyl)carbonylfluorescein (NBzF-BG), a novel H2O2-specific fluorescent probe; NBzF-BG is covalently and selectively conjugated with the SNAP-tag protein, leading to formation of the fluorophore-protein conjugate (SNAP-NBzF). SNAP-NBzF rapidly reacts with H2O2 and thereby shows a 9-fold enhancement in fluorescence. When SNAP-tag is expressed in HEK293T cells and RAW264.7 macrophages as a protein C-terminally fused to the transmembrane domain of platelet-derived growth factor receptor (PDGFR), the tag is presented on the outside of the plasma membrane; conjugation of NBzF-BG with the cell surface SNAP-tag enables detection of H2O2 added exogenously. We also demonstrate molecular imaging of H2O2 that is endogenously produced in phagosomes of macrophages ingesting IgG-coated latex beads. Thus, NBzF-BG, combined with the SNAP-tag technology, should be useful as a tool to measure local production of H2O2 in living cells.

Nitroarachidonic acid prevents NADPH oxidase assembly and superoxide radical production in activated macrophages

Nitration of arachidonic acid (AA) to nitroarachidonic acid (AANO2) leads to anti-inflammatory intracellular activities during macrophage activation. However, less is known about the capacity of AANO2 to regulate the production of reactive oxygen species under proinflammatory conditions. One of the immediate responses upon macrophage activation involves the production of superoxide radical (O2(•-)) due to the NADPH-dependent univalent reduction of oxygen to O2(•-) by the phagocytic NADPH oxidase isoform (NOX2), the activity of NOX2 being the main source of O2(•-) in monocytes/macrophages. Because the NOX2 and AA pathways are connected, we propose that AANO2 can modulate macrophage activation by inhibiting O2(•-) formation by NOX2. When macrophages were activated in the presence of AANO2, a significant inhibition of NOX2 activity was observed as evaluated by cytochrome c reduction, luminol chemiluminescence, Amplex red fluorescence, and flow cytometry; this process also occurs under physiological mimic conditions within the phagosomes. AANO2 decreased O2(•-) production in a dose- (IC50=4.1±1.8 μM AANO2) and time-dependent manner. The observed inhibition was not due to a decreased phosphorylation of the cytosolic subunits (e.g., p40(phox) and p47(phox)), as analyzed by immunoprecipitation and Western blot. However, a reduction in the migration to the membrane of p47(phox) was obtained, suggesting that the protective actions involve the prevention of the correct assembly of the active enzyme in the membrane. Finally, the observed in vitro effects were confirmed in an in vivo inflammatory model, in which subcutaneous injection of AANO2 was able to decrease NOX2 activity in macrophages from thioglycolate-treated mice.

Effects of iodonium-class flavin dehydrogenase inhibitors on growth, reactive oxygen production, cell cycle progression, NADPH oxidase 1 levels, and gene expression in human colon cancer cells and xenografts

Iodonium-class flavoprotein dehydrogenase inhibitors have been demonstrated to possess antiproliferative potential and to inhibit reactive oxygen production in human tumor cells, although the mechanism(s) that explains the relationship between altered cell growth and the generation of reactive oxygen species (ROS) remains an area of active investigation. Because of the ability of these compounds to inhibit the activity of flavoprotein-containing epithelial NADPH oxidases, we chose to examine the effects of several iodonium-class flavoprotein inhibitors on human colon cancer cell lines that express high, functional levels of a single such oxidase (NADPH oxidase 1, or Nox1). We found that diphenyleneiodonium (DPI), di-2-thienyliodonium (DTI), and iodonium diphenyl inhibited the growth of Caco2, HT-29, and LS-174T colon cancer cells at concentrations (10-250nM for DPI, 0.5-2.5μM for DTI, and 155nM to 10μM for iodonium diphenyl) substantially lower than needed for DU145 human prostate cancer cells, which do not possess functional NADPH oxidase activity. Drug treatment was associated with decreased H2O2 production and diminished intracellular ROS levels, lasting up to 24h, after short-term (1-h) exposure to the iodonium analogs. Decreased tumor cell proliferation was caused, in part, by a profound block in cell cycle progression at the G1/S interface in both LS-174T and HT-29 cells exposed to either DPI or DTI; and the G1 block was produced, for LS-174T cells, by upregulation of p27 and a drug concentration-related decrease in the expression of cyclins D1, A, and E that was partially prevented by exogenous H2O2. Not only did DPI and DTI decrease intracellular ROS, they both also significantly decreased the mRNA expression levels of Nox1, potentially contributing to the prolonged reduction in tumor cell reactive oxygen levels. We also found that DPI and DTI significantly decreased the growth of both HT-29 and LS-174T human tumor xenografts, at dose levels that produced peak plasma concentrations similar to those utilized for our in vitro experiments. These findings suggest that iodonium analogs have therapeutic potential for NADPH oxidase-containing human colon cancers in vivo and that at least part of their antineoplastic mechanism of action may be related to targeting Nox1.

Activation of conventional protein kinase C (PKC) is critical in the generation of human neutrophil extracellular traps

Background

Activation of NADPH oxidase is required for neutrophil extracellular trap (NET) formation. Protein kinase C (PKC) is an upstream mediator of NADPH oxidase activation and thus likely to have a role in NET formation.

Methods

Pharmacological inhibitors were used to block PKC activity in neutrophils harvested from healthy donor blood.

Results

Pan PKC inhibition with Ro-31-8220 (p<0.001), conventional PKC inhibition with Go 6976 (p<0.001) and specific PKCβ inhibition with LY333531 (p<0.01) blocked NET formation in response to PMA. Inhibition of novel and atypical PKC had no effect. LY333531 blocked NET induction by the diacylglycerol analogue OAG (conventional PKC activator) (p<0.001).

Conclusions

Conventional PKCs have a prominent role in NET formation. Furthermore PKCβ is the major isoform implicated in NET formation.

A comparative study of iron uptake mechanisms in marine microalgae: iron binding at the cell surface is a critical step

We investigated iron uptake mechanisms in five marine microalgae from different ecologically important phyla: the diatoms Phaeodactylum tricornutum and Thalassiosira pseudonana, the prasinophyceae Ostreococcus tauri and Micromonas pusilla, and the coccolithophore Emiliania huxleyi. Among these species, only the two diatoms were clearly able to reduce iron, via an inducible (P. tricornutum) or constitutive (T. pseudonana) ferrireductase system displaying characteristics similar to the yeast (Saccharomyces cerevisiae) flavohemoproteins proteins. Iron uptake mechanisms probably involve very different components according to the species, but the species we studied shared common features. Regardless of the presence and/or induction of a ferrireductase system, all the species were able to take up both ferric and ferrous iron, and iron reduction was not a prerequisite for uptake. Iron uptake decreased with increasing the affinity constants of iron-ligand complexes and with increasing ligand-iron ratios. Therefore, at least one step of the iron uptake mechanism involves a thermodynamically controlled process. Another step escapes to simple thermodynamic rules and involves specific and strong binding of ferric as well as ferrous iron at the cell surface before uptake of iron. Binding was paradoxically increased in iron-rich conditions, whereas uptake per se was induced in all species only after prolonged iron deprivation. We sought cell proteins loaded with iron following iron uptake. One such protein in O. tauri may be ferritin, and in P. tricornutum, Isip1 may be involved. We conclude that the species we studied have uptake systems for both ferric and ferrous iron, both involving specific iron binding at the cell surface.

Relationship of proton motive force and the F(0)F (1)-ATPase with bio-hydrogen production activity of Rhodobacter sphaeroides: effects of diphenylene iodonium, hydrogenase inhibitor, and its solvent dimethylsulphoxide

Rhodobacter sphaeroides MDC 6521 was able to produce bio-hydrogen (H(2)) in anaerobic conditions under illumination. In this study the effects of the hydrogenase inhibitor-diphenylene iodonium (Ph(2)I) and its solvent dimethylsulphoxide (DMSO) on growth characteristics and H(2) production by R. sphaeroides were investigated. The results point out the concentration dependent DMSO effect: in the presence of 10 mM DMSO H(2) yield was ~6 fold lower than that of the control. The bacterium was unable to produce H(2) in the presence of Ph(2)I. In order to examine the mediatory role of proton motive force (∆p) or the F(0)F(1)-ATPase in H(2) production by R. sphaeroides, the effects of Ph(2)I and DMSO on ∆p and its components (membrane potential (∆ψ) and transmembrane pH gradient), and ATPase activity were determined. In these conditions ∆ψ was of -98 mV and the reversed ∆pH was +30 mV, resulting in ∆p of -68 mV. Ph(2)I decreased ∆ψ in concentrations of 20 μM and higher; lower concentrations of Ph(2)I as DMSO had no valuable effect on ∆ψ. The R. sphaeroides membrane vesicles demonstrated significant ATPase activity sensitive to N,N'-dicyclohexylcarbodiimide. The 10-20 μM Ph(2)I did not affect the ATPase activity, whereas 40 μM Ph(2)I caused a marked inhibition (~2 fold) in ATPase activity. The obtained results provide novel evidence on the involvement of hydrogenase and the F(0)F(1)-ATPase in H(2) production by R. sphaeroides. Moreover, these data indicate the role of hydrogenase and the F(0)F(1)-ATPase in ∆p generation. In addition, DMSO might increase an interaction of nitrogenase with CO(2), decreasing nitrogenase activity and affecting H(2) production.

Mechanism of all-trans-retinal toxicity with implications for stargardt disease and age-related macular degeneration

Compromised clearance of all-trans-retinal (atRAL), a component of the retinoid cycle, increases the susceptibility of mouse retina to acute light-induced photoreceptor degeneration. Abca4(-/-)Rdh8(-/-) mice featuring defective atRAL clearance were used to examine the one or more underlying molecular mechanisms, because exposure to intense light causes severe photoreceptor degeneration in these animals. Here we report that bright light exposure of Abca4(-/-)Rdh8(-/-) mice increased atRAL levels in the retina that induced rapid NADPH oxidase-mediated overproduction of intracellular reactive oxygen species (ROS). Moreover, such ROS generation was inhibited by blocking phospholipase C and inositol 1,4,5-trisphosphate-induced Ca(2+) release, indicating that activation occurs upstream of NADPH oxidase-mediated ROS generation. Because multiple upstream G protein-coupled receptors can activate phospholipase C, we then tested the effects of antagonists of serotonin 2A (5-HT(2A)R) and M(3)-muscarinic (M(3)R) receptors and found they both protected Abca4(-/-)Rdh8(-/-) mouse retinas from light-induced degeneration. Thus, a cascade of signaling events appears to mediate the toxicity of atRAL in light-induced photoreceptor degeneration of Abca4(-/-)Rdh8(-/-) mice. A similar mechanism may be operative in human Stargardt disease and age-related macular degeneration.

Nicotine- and tar-free cigarette smoke induces cell damage through reactive oxygen species newly generated by PKC-dependent activation of NADPH oxidase

We examined cytotoxic effects of nicotine/tar-free cigarette smoke extract (CSE) on C6 glioma cells. The CSE induced plasma membrane damage (determined by lactate dehydrogenase leakage and propidium iodide uptake) and cell apoptosis {determined by MTS [3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium] reduction activity and DNA fragmentation}. The cytotoxic activity decayed with a half-life of approximately 2 h at 37°C, and it was abolished by N-acetyl-L-cysteine and reduced glutathione. The membrane damage was prevented by catalase and edaravone (a scavenger of (•)OH) but not by superoxide dismutase, indicating involvement of (•)OH. In contrast, the CSE-induced cell apoptosis was resistant to edaravone and induced by authentic H(2)O(2) or O(2)(-) generated by the xanthine/xanthine oxidase system, indicating involvement of H(2)O(2) or O(2)(-) in cell apoptosis. Diphenyleneiodonium [NADPH oxidase (NOX) inhibitor] and bisindolylmaleimide I [BIS I, protein kinase C (PKC) inhibitor] abolished membrane damage, whereas they partially inhibited apoptosis. These results demonstrate that 1) a stable component(s) in the CSE activates PKC, which stimulates NOX to generate reactive oxygen species (ROS), causing membrane damage and apoptosis; 2) different ROS are responsible for membrane damage and apoptosis; and 3) part of the apoptosis is caused by oxidants independently of PKC and NOX.

Oxygen activation at the plasma membrane: relation between superoxide and hydroxyl radical production by isolated membranes

Production of reactive oxygen species (hydroxyl radicals, superoxide radicals and hydrogen peroxide) was studied using EPR spin-trapping techniques and specific dyes in isolated plasma membranes from the growing and the non-growing zones of hypocotyls and roots of etiolated soybean seedlings as well as coleoptiles and roots of etiolated maize seedlings. NAD(P)H mediated the production of superoxide in all plasma membrane samples. Hydroxyl radicals were only produced by the membranes of the hypocotyl growing zone when a Fenton catalyst (FeEDTA) was present. By contrast, in membranes from other parts of the seedlings a low rate of spontaneous hydroxyl radical formation was observed due to the presence of small amounts of tightly bound peroxidase. It is concluded that apoplastic hydroxyl radical generation depends fully, or for the most part, on peroxidase localized in the cell wall. In soybean plasma membranes from the growing zone of the hypocotyl pharmacological tests showed that the superoxide production could potentially be attributed to the action of at least two enzymes, an NADPH oxidase and, in the presence of menadione, a quinone reductase.

Programmed cell death of the megagametophyte during post-germinative growth of white spruce (Picea glauca) seeds is regulated by reactive oxygen species and the ubiquitin-mediated proteolytic system

The megagametophyte of white spruce (Picea glauca) seeds undergoes programmed cell death following seed germination. This process is characterized by distinct morphological and biochemical features, such as DNA fragmentation and the induction of proteases. Biphasic production of hydrogen peroxide was detected in the megagametophyte following seed germination. ROS scavengers or inhibitors of ROS production decreased caspase-like protease activity and slowed the progression of cell death. One catalase (CAT) of white spruce reacted with antibodies directed against cotton-seed CAT. The corresponding CAT gene was cloned and compared with the catalase genes of other plant species. The activity of the white spruce CAT enzyme was stimulated by tyrosine phosphorylation. The phosphorylated CAT was subjected to ubiquitination and degraded by the proteasome. Furthermore, the proteasome inhibitor MG132 inhibited the degradation of CAT and delayed cell death. These results suggest that the interplay of CAT and the ubiquitin-mediated proteolytic system is critical in the control of ROS production and subsequent cell death.

Stimulation of reactive oxygen species and collagen synthesis by angiotensin II in cardiac fibroblasts

Superoxide anion generated by NAD(P)H-oxidase has an important role in the pathogenesis of cardiovascular diseases and scavenging superoxide anion can be considered as a reasonable therapeutic strategy. In hypertensive heart diseases there is a mutual reinforcement of reactive oxygen species (ROS) and angiotensin II (ANG II). ANG II increases the NAD(P)H-dependent superoxide anion production and the intracellular generation of ROS in cardiac fibroblasts and apocynin, a membrane NAD(P)H oxidase inhibitor, abrogates this rise. ANG II also stimulates the collagen production, the collagen I and III content and mRNA expression in cardiac fibroblasts and apocynin abolishes this induction. In this review we demonstrate that scavenging superoxide anion by tempol or EUK-8 or administration of PEG-superoxide dismutase (SOD) inhibits collagen production in cardiac fibroblasts. On the contrary increasing superoxide anion formation by inhibition of SOD stimulates collagen production. A vital role of SOD and the generated ROS can be suggested in the regulation and organization of collagen in cardiac fibroblasts. Specific pharmacological intervention with SOD mimetics can probably be an alternative approach for reducing myocardial fibrosis.

In vivo cell wall loosening by hydroxyl radicals during cress seed germination and elongation growth

Loosening of cell walls is an important developmental process in key stages of the plant life cycle, including seed germination, elongation growth, and fruit ripening. Here, we report direct in vivo evidence for hydroxyl radical ((*)OH)-mediated cell wall loosening during plant seed germination and seedling growth. We used electron paramagnetic resonance spectroscopy to show that (*)OH is generated in the cell wall during radicle elongation and weakening of the endosperm of cress (Lepidium sativum; Brassicaceae) seeds. Endosperm weakening precedes radicle emergence, as demonstrated by direct biomechanical measurements. By (3)H fingerprinting, we showed that wall polysaccharides are oxidized in vivo by the developmentally regulated action of apoplastic (*)OH in radicles and endosperm caps: the production and action of (*)OH increased during endosperm weakening and radicle elongation and were inhibited by the germination-inhibiting hormone abscisic acid. Both effects were reversed by gibberellin. Distinct and tissue-specific target sites of (*)OH attack on polysaccharides were evident. In vivo (*)OH attack on cell wall polysaccharides were evident not only in germinating seeds but also in elongating maize (Zea mays; Poaceae) seedling coleoptiles. We conclude that plant cell wall loosening by (*)OH is a controlled action of this type of reactive oxygen species.

Impaired insulin secretion by diphenyleneiodium associated with perturbation of cytosolic Ca2+ dynamics in pancreatic beta-cells

Pancreatic islets express the superoxide-producing nicotinamide adenine dinucleotide phosphate (NADPH) oxidase system, but its role remains unknown. To address this, we studied the mechanisms of impaired insulin secretion induced by diphenyleneiodium (DPI), an NADPH oxidase inhibitor. We investigated the effects of DPI on glucose- and nonfuel-stimulated insulin secretion, islet glucose metabolism, and intracellular Ca2+ concentration ([Ca2+]i) dynamics in rat islets and beta-cell line RINm5F cells. DPI did not affect insulin secretion at 3.3 mm glucose but totally suppressed insulin secretion stimulated by 16.7 mm glucose (percentage of control, 9.2 +/- 1.2%; P <0.001). DPI also inhibited insulin release by high K+-induced membrane depolarization (percentage of control, 36.0 +/- 5.3%; P <0.01) and protein kinase C activation (percentage of control, 30.2 +/- 10.6% in the presence of extracellular Ca2+, P <0.01; percentage of control, 42.0 +/- 4.7% in the absence of extracellular Ca2+, P <0.01). However, DPI had no effect on mastoparan-induced insulin secretion at 3.3 and 16.7 mm glucose under Ca2+-free conditions. DPI significantly suppressed islet glucose oxidation and ATP content through its known inhibitory action on complex I in the mitochondrial respiratory chain. On the other hand, DPI altered [Ca2+]i dynamics in response to high glucose and membrane depolarization, and DPI per se dose-dependently increased [Ca2+]i. The DPI-induced [Ca2+]i rise was associated with a transient increase in insulin secretion and was attenuated by removal of extracellular Ca2+, by L-type voltage-dependent Ca2+ channel blockers, by mitochondrial inhibitors, or by addition of 0.1 or 1.0 microm H2O2 exogenously. Our results showed that DPI impairment of insulin secretion involved altered Ca2+ signaling, suggesting that NADPH oxidase may modulate Ca2+ signaling in beta-cells.

Origin of cadmium-induced reactive oxygen species production: mitochondrial electron transfer versus plasma membrane NADPH oxidase

* Cadmium (Cd(2+)) is an environmental pollutant that causes increased reactive oxygen species (ROS) production. To determine the site of ROS production, the effect of Cd(2+) on ROS production was studied in isolated soybean (Glycine max) plasma membranes, potato (Solanum tuberosum) tuber mitochondria and roots of intact seedlings of soybean or cucumber (Cucumis sativus). * The effects of Cd(2+) on the kinetics of superoxide (O2*-), hydrogen peroxide (H(2)O(2)) and hydroxyl radical ((*OH) generation were followed using absorption, fluorescence and spin-trapping electron paramagnetic resonance spectroscopy. * In isolated plasma membranes, Cd(2+) inhibited O2*- production. This inhibition was reversed by calcium (Ca(2+)) and magnesium (Mg(2+)). In isolated mitochondria, Cd(2+) increased and H(2)O(2) production. In intact roots, Cd(2+) stimulated H(2)O(2) production whereas it inhibited O2*- and (*)OH production in a Ca(2+)-reversible manner. * Cd(2+) can be used to distinguish between ROS originating from mitochondria and from the plasma membrane. This is achieved by measuring different ROS individually. The immediate ( Collapse

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MESH Headings

• Cadmium Chloride/toxicity
• Calcium Chloride/pharmacology
• Cell Fractionation
• Cell Membrane/drug effects
• Cell Membrane/enzymology
• Cucumis sativus/drug effects
• Cucumis sativus/metabolism
• Electron Transport/drug effects
• Environmental Exposure
• Environmental Pollutants/toxicity
• Hypocotyl/drug effects
• Hypocotyl/metabolism
• Kinetics
• Magnesium Chloride/pharmacology
• Mitochondria/drug effects
• Mitochondria/metabolism
• NADPH Oxidases/antagonists & inhibitors
• Oxidative Stress
• Plant Roots/drug effects
• Plant Roots/metabolism
• Plants/drug effects
• Reactive Oxygen Species/chemistry
• Reactive Oxygen Species/metabolism
• Solanum tuberosum/drug effects
• Solanum tuberosum/metabolism
• Glycine max/drug effects
• Glycine max/metabolism

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Affiliation(s)

Eiri Heyno CEA, iBiTecS, CNRS URA 2096, Service de Bioénergétique Biologie Structurale et Mécanisme, 91191 Gif-sur-Yvette Cedex, France
Cornelia Klose Institut für Biologie II, Universität Freiburg, Schänzlestr. 1, 79104 Freiburg, Germany
Anja Krieger-Liszkay CEA, iBiTecS, CNRS URA 2096, Service de Bioénergétique Biologie Structurale et Mécanisme, 91191 Gif-sur-Yvette Cedex, France

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Naphthoquinone-dependent generation of superoxide radicals by quinone reductase isolated from the plasma membrane of soybean

Using a tetrazolium-based assay, a NAD(P)H oxidoreductase was purified from plasma membranes prepared from soybean (Glycine max) hypocotyls. The enzyme, a tetramer of 85 kD, produces O2(.-) by a reaction that depended on menadione or several other 1,4-naphthoquinones, in apparent agreement with a classification as a one-electron-transferring flavoenzyme producing semiquinone radicals. However, the enzyme displayed catalytic and molecular properties of obligatory two-electron-transferring quinone reductases of the DT-diaphorase type, including insensitivity to inhibition by diphenyleneiodonium. This apparent discrepancy was clarified by investigating the pH-dependent reactivity of menadionehydroquinone toward O2 and identifying the protein by mass spectrometry and immunological techniques. The enzyme turned out to be a classical NAD(P)H:quinone-acceptor oxidoreductase (EC 1.6.5.2, formerly 1.6.99.2) that reduces menadione to menadionehydroquinone and subsequently undergoes autoxidation at pH > or = 6.5. Autoxidation involves the production of the semiquinone as an intermediate, creating the conditions for one-electron reduction of O2. The possible function of this enzyme in the generation of O2(.-) and H2O2 at the plasma membrane of plants in vivo is discussed.

NOX enzymes as novel targets for drug development

The members of the NOX/DUOX family of NADPH oxidases mediate such physiologic functions as host defense, cell signaling, and thyroid hormone biosynthesis through the generation of reactive oxygen species (ROS), including superoxide anion and hydrogen peroxide. Moreover, ROS are involved in a broad range of fundamental biochemical and cellular processes, and data accumulated in recent years indicate that the NOX enzymes comprise one of the most important biological sources of ROS. Given the high biochemical reactivity of ROS, it is not surprising that they have been implicated in a wide variety of pathologies and diseases. Prominent among the settings that feature ROS-mediated tissue injury are disorders associated with inflammation, aging, and progressive degenerative changes in cells and organ systems, and it appears that essentially no organ system is exempt. Among the disorders currently believed to be mediated at least in part by NOX-derived ROS are hypertension, aortic aneurysm, myocardial infarction (and other ischemia-reperfusion disorders), pulmonary fibrosis and hypertension, amyotropic lateral sclerosis, Alzheimer's disease, Parkinson's disease, ischemic stroke, diabetic nephropathy, and renal cell carcinoma. Several small-molecule and peptide inhibitors of the NOX enzymes have been useful in experimental studies, but issues of specificity, potency, and toxicity militate against any of the existing published compounds as candidates for drug development. Given the broad array of disease targets documented in recent work, the time is here for vigorous efforts to develop clinically useful inhibitors of the NOX enzymes. As most (though not all) NOX-related diseases appear to be mediated by a single member of the NOX family, agents with isoform specificity will be preferred, although broadly active NOX inhibitors may prove to be useful in some settings.

Volume-sensitive NADPH oxidase activity and taurine efflux in NIH3T3 mouse fibroblasts

Reactive oxygen species (ROS) are produced in NIH3T3 fibroblasts during hypotonic stress, and H(2)O(2) potentiates the concomitant release of the organic osmolyte taurine (Lambert IH. J Membr Biol 192: 19-32, 2003). The increase in ROS production [5-(and-6)-carboxy-2', 7'-dichlorodihydrofluorescein diacetate fluorescence] is detectable after a reduction in the extracellular osmolarity from 335 mosM (isotonic) to 300 mosM and reaches a maximal value after a reduction to 260 mosM. The swelling-induced ROS production is reduced by the flavoprotein inhibitor diphenylene iodonium chloride (25 microM) but is unaffected by the nitric oxide synthase inhibitor N omega-nitro-l-arginine methyl ester, indicating that the volume-sensitive ROS production is NADPH oxidase dependent. NIH3T3 cells express the NADPH oxidase components: p22 phox, a NOX4 isotype; p47 phox; and p67 phox (real-time PCR). Exposure to the Ca2+-mobilizing agonist ATP (10 microM) potentiates the release of taurine but has no effect on ROS production under hypotonic conditions. On the other hand, addition of the protein kinase C (PKC) activator phorbol 12-myristate 13-acetate (PMA, 100 nM) or the lipid messenger lysophosphatidic acid (LPA, 10 nM) potentiates the swelling-induced taurine release as well as the ROS production. Overexpression of Rac1 or p47 phox or p47 phox knockdown [small interfering (si)RNA] had no effect on the swelling-induced ROS production or taurine release. NOX4 knockdown (siRNA) impairs the increase in the ROS production and the concomitant taurine release following osmotic exposure. It is suggested that a NOX4 isotype plus p22 phox account for the swelling-induced increase in the ROS production in NIH3T3 cells and that the oxidase activity is potentiated by PKC and LPA but not by Ca2+.

Regulation of normal cell cycle progression by flavin-containing oxidases

Mechanisms underlying the role of reactive oxygen species (ROS) generated by flavin-containing oxidases in regulating cell cycle progression were examined in human and rodent fibroblasts. Incubation of confluent cell cultures with nontoxic/nonclastogenic concentrations of the flavoprotein inhibitor, diphenyleneiodonium (DPI), reduced nicotinamide adenine dinucleotide phosphate (NAD(P)H) oxidase activity and basal ROS levels, but increased proteolysis of cyclin D1, p21(Waf1) and phospho-p38(MAPK). When these cells were allowed to proliferate by subculture in DPI-free medium, an extensive G(1) delay was observed with concomitant activation of p53/p21(Waf1) signaling and reduced phosphorylation of mitogen-activated kinases. Compensation for decreased oxidant generation by simultaneous exposure to DPI and nontoxic doses of the ROS generators, gamma-radiation or t-butyl-hydroperoxide, attenuated the G(1) delay. Whereas the DPI-induced G(1) checkpoint was completely dependent on PHOX91, ATM and WAF1, it was only partially dependent on P53. Interestingly, G(1) to S progression was not affected when another flavin-containing enzyme, nitric oxide synthase, was inhibited nor was it associated with changes in mitochondrial membrane potential. Proliferating cells treated with DPI also experienced a significant but attenuated delay in G(2). We propose that ATM performs a critical function in mediating normal cellular proliferation that is regulated by nonphagocytic NAD(P)H oxidase enzymes activity, which may serve as a novel target for arresting cancer cells in G(1).

Activation and inactivation of the volume-sensitive taurine leak pathway in NIH3T3 fibroblasts and Ehrlich Lettre ascites cells

Hypotonic exposure provokes the mobilization of arachidonic acid, production of ROS, and a transient increase in taurine release in Ehrlich Lettre cells. The taurine release is potentiated by H2O2 and the tyrosine phosphatase inhibitor vanadate and reduced by the phospholipase A2 (PLA2) inhibitors bromoenol lactone (BEL) and manoalide, the 5-lipoxygenase (5-LO) inhibitor ETH-615139, the NADPH oxidase inhibitor diphenyl iodonium (DPI), and antioxidants. Thus, swelling-induced taurine efflux in Ehrlich Lettre cells involves Ca2+-independent (iPLA2)/secretory PLA2 (sPLA2) plus 5-LO activity and modulation by ROS. Vanadate and H2O2 stimulate arachidonic acid mobilization and vanadate potentiates ROS production in Ehrlich Lettre cells and NIH3T3 fibroblasts under hypotonic conditions. However, vanadate-induced potentiation of the volume-sensitive taurine efflux is, in both cell types, impaired in the presence of BEL and DPI and following restoration of the cell volume. Thus, potentiation of the volume-sensitive taurine efflux pathway following inhibition of tyrosine phosphatase activity reflects increased arachidonic acid mobilization and ROS production for downstream signaling. Vanadate delays the inactivation of volume-sensitive taurine efflux in NIH3T3 cells, and this delay is impaired in the presence of DPI. Vanadate has no effect on the inactivation of swelling-induced taurine efflux in Ehrlich Lettre cells. It is suggested that increased tyrosine phosphorylation of regulatory components of NADPH oxidase leads to increased ROS production and a subsequent delay in inactivation of the volume-sensitive taurine efflux pathway and that NADPH oxidase or antioxidative capacity differ between NIH3T3 and Ehrlich Lettre cells.

Reactive oxygen species generation by the ethylene-bis-dithiocarbamate (EBDC) fungicide mancozeb and its contribution to neuronal toxicity in mesencephalic cells

Previous in vitro studies in our laboratory have shown that mancozeb (MZ) and maneb (MB), both widely used EBDC fungicides, are equipotent neurotoxicants that produce cell loss in mesencephalic dopaminergic and GABAergic cells after an acute 24h exposure. Mitochondrial uncoupling and inhibition were associated with fungicide exposure. Inhibition of mitochondrial respiration is known to increase free radical production. Here the mechanism(s) of neuronal damage associated with MZ exposure was further explored by determining the role that reactive oxygen species (ROS) played in toxicity. Damage to mesencephalic dopamine and GABA cell populations were significantly attenuated when carried out in the presence of ascorbate or SOD, indicative of a free radical-mediated contribution to toxicity. ROS generation monitored by hydrogen peroxide (H(2)O(2)) production using Amplex Red increased in a dose-dependent manner in response to MZ. Inhibition of intracellular catalase with aminotriazole had little effect on H(2)O(2) generation, whereas exogenously added catalase significantly reduced H(2)O(2) production, demonstrating a large extracellular contribution to ROS generation. Conversely, cells preloaded with the ROS indicator dye DCF showed significant MZ-induced ROS production, demonstrating an increase in intracellular ROS. Both the organic backbone of MZ as well as its associated Mn ion, but not Zn ion, were responsible and required for H(2)O(2) generation. The functionally diverse NADPH oxidase inhibitors, diphenylene iodonium chloride, apocynin, and 4-(2-aminoethyl)benzene-sulfonyl fluoride hydrochloride significantly attenuated H(2)O(2) production by MZ. In growth medium lacking cells, MZ produced little H(2)O(2), but enhanced H(2)O(2) generation when added with xanthine plus xanthine oxidase whereas, in cultured cells, allopurinol partially attenuated H(2)O(2) production by MZ. Minocycline, an inhibitor of microglial activation, modestly reduced H(2)O(2) formation in mesencephalic cells. In contrast, neuronal-enriched cultures or cultures treated with MAC-1-SAP to kill microglia, did not show an attenuation of ROS production. These findings demonstrate that Mn-containing EBDC fungicides such as MZ and MB can produce robust ROS generation that likely occurs via redox cycling with extracellular and intracellular oxidases. The findings further show that microglia may contribute to but are not required for ROS production by MZ.

Chemiluminescent picture of diphenyleneiodonium-inhibited NADPH oxidase: a bimodal process and its logistic-exponential model-based description

A chemiluminescence (CL) study of diphenyleneiodonium-inhibited NADPH oxidase was performed on a cellular system containing neutrophils stimulated by phorbol myristate acetate, indicating a complex bimodal structure of CL processes corresponding to different stages of the inhibition. The complex structure of these processes was described by a superposition of two logistic-exponential (LE) models, characterizing these processes as bimodal ones. To determine the mechanistic foundation of the LE model-described processes, a generalized form of the second-order dynamic system of CL reactions, the solution to which corresponds to the LE model, was constructed. The diphenyleneiodonium effects on neutrophil NADPH oxidase were separated from the total bimodal CL of the whole measurement system by the use of difference CL processes. These difference processes were also found to be bimodal; thus, inhibitor-induced reduction of CL could be described by a second-order dynamic system. The rate constants and initial concentrations in this dynamic system were determined by the least squares method applied to numerical solutions approximating the difference processes. Using interrelations between the parameters of the dynamic system, cooperative effects in the inhibitor reactions with NADPH oxidase were found and described quantitatively. Other evidences of cooperativity were obtained from integral characteristics of the CL reduction process, i.e. dose-response and progress curves, determined by numerical integration of the LE models constituting the superposition. On this basis, it was also possible to detect a specific binding of the inhibitor to the enzyme. Finally, putative reaction mechanisms suggested by the model obtained were considered and compared with those known at present.

The NOX family of ROS-generating NADPH oxidases: physiology and pathophysiology

For a long time, superoxide generation by an NADPH oxidase was considered as an oddity only found in professional phagocytes. Over the last years, six homologs of the cytochrome subunit of the phagocyte NADPH oxidase were found: NOX1, NOX3, NOX4, NOX5, DUOX1, and DUOX2. Together with the phagocyte NADPH oxidase itself (NOX2/gp91(phox)), the homologs are now referred to as the NOX family of NADPH oxidases. These enzymes share the capacity to transport electrons across the plasma membrane and to generate superoxide and other downstream reactive oxygen species (ROS). Activation mechanisms and tissue distribution of the different members of the family are markedly different. The physiological functions of NOX family enzymes include host defense, posttranlational processing of proteins, cellular signaling, regulation of gene expression, and cell differentiation. NOX enzymes also contribute to a wide range of pathological processes. NOX deficiency may lead to immunosuppresion, lack of otoconogenesis, or hypothyroidism. Increased NOX activity also contributes to a large number or pathologies, in particular cardiovascular diseases and neurodegeneration. This review summarizes the current state of knowledge of the functions of NOX enzymes in physiology and pathology.

Xanthine oxidoreductase is a regulator of adipogenesis and PPARgamma activity

In an effort to identify novel candidate regulators of adipogenesis, gene profiling of differentiating 3T3-L1 preadipocytes was analyzed using a novel algorithm. We report here the characterization of xanthine oxidoreductase (XOR) as a novel regulator of adipogenesis. XOR lies downstream of C/EBPbeta and upstream of PPARgamma, in the cascade of factors that control adipogenesis, and it regulates PPARgamma activity. In vitro, knockdown of XOR inhibits adipogenesis and PPARgamma activity while constitutive overexpression increases activity of the PPARgamma receptor in both adipocytes and preadipocytes. In vivo, XOR -/- mice demonstrate 50% reduction in adipose mass versus wild-type littermates while obese ob/ob mice exhibit increased concentrations of XOR mRNA and urate in the adipose tissue. We propose that XOR is a novel regulator of adipogenesis and of PPARgamma activity and essential for the regulation of fat accretion. Our results identify XOR as a potential therapeutic target for metabolic abnormalities beyond hyperuricemia.