NOX-dependent Reactive Oxygen Species Research Articles

NMDA Receptor Activation Increases Free Radical Production through Nitric Oxide and NOX2

Reactive oxygen species (ROS) and nitric oxide (NO) participate in NMDA receptor signaling. However, the source(s) of the ROS and their role in the increase in cerebral blood flow (CBF) induced by NMDA receptor activation have not been firmly established. NADPH oxidase generates ROS in neurons, but there is no direct evidence that this enzyme is present in neurons containing NMDA receptors, or that is involved in NMDA receptor-dependent ROS production and CBF increase. We addressed these questions using a combination of in vivo and in vitro approaches. We found that the CBF and ROS increases elicited by topical application of NMDA to the mouse neocortex were both dependent on neuronal NO synthase (nNOS), cGMP, and the cGMP effector kinase protein kinase G (PKG). In mice lacking the NADPH oxidase subunit NOX2, the ROS increase was not observed, but the CBF increase was still present. Electron microscopy of the neocortex revealed NOX2 immunolabeling in postsynaptic somata and dendrites that also expressed the NMDA receptor NR1 subunit and nNOS. In neuronal cultures, the NMDA-induced increase in ROS was mediated by NADPH oxidase through NO, cGMP and PKG. We conclude that NADPH oxidase in postsynaptic neurons generates ROS during NMDA receptor activation. However, NMDA receptor-derived ROS do not contribute to the CBF increase. The findings establish a NOX2-containing NADPH oxidase as a major source of ROS produced by NMDA receptor activation, and identify NO as the critical link between NMDA receptor activity and NOX2-dependent ROS production.

Na+/H+exchanger-1 inhibitors decrease myocardial superoxide production via direct mitochondrial action

The possibility of a direct mitochondrial action of Na(+)/H(+) exchanger-1 (NHE-1) inhibitors decreasing reactive oxygen species (ROS) production was assessed in cat myocardium. Angiotensin II and endothelin-1 induced an NADPH oxidase (NOX)-dependent increase in anion superoxide (O(2)(-)) production detected by chemiluminescence. Three different NHE-1 inhibitors [cariporide, BIIB-723, and EMD-87580] with no ROS scavenger activity prevented this increase. The mitochondria appeared to be the source of the NOX-dependent ROS released by the "ROS-induced ROS release mechanism" that was blunted by the mitochondrial ATP-sensitive potassium channel blockers 5-hydroxydecanoate and glibenclamide, inhibition of complex I of the electron transport chain with rotenone, and inhibition of the permeability transition pore (MPTP) by cyclosporin A. Cariporide also prevented O(2)(-) production induced by the opening of mK(ATP) with diazoxide. Ca(2+)-induced swelling was evaluated in isolated mitochondria as an indicator of MPTP formation. Cariporide decreased mitochondrial swelling to the same extent as cyclosporin A and bongkrekic acid, confirming its direct mitochondrial action. Increased O(2)(-) production, as expected, stimulated ERK1/2 and p90 ribosomal S6 kinase phosphorylation. This was also prevented by cariporide, giving additional support to the existence of a direct mitochondrial action of NHE-1 inhibitors in preventing ROS release. In conclusion, we report a mitochondrial action of NHE-1 inhibitors that should lead us to revisit or reinterpret previous landmark observations about their beneficial effect in several cardiac diseases, such as ischemia-reperfusion injury and cardiac hypertrophy and failure. Further studies are needed to clarify the precise mechanism and site of action of these drugs in blunting MPTP formation and ROS release.

Differential vascular functions of Nox family NADPH oxidases

Reactive oxygen species have been implicated in the initiation and progression of atherosclerosis. Reactive oxygen species can oxidize lipoproteins, limit the vascular availability of antiatherosclerotic nitric oxide and promote vascular expression of cytokines and adhesion molecules. Nox proteins of the NADPH oxidase family are prominent sources of vascular reactive oxygen species, and Nox protein-dependent reactive oxygen species production has been linked to atherogenesis. Recently, significant progress has been made in the understanding of differences among the Nox proteins. Nox proteins exhibit cell-specific expression patterns and divergent molecular mechanisms controlling activity have been identified for individual Nox proteins. These aspects may relate to cellular activation, differentiation, proliferation, angiogenesis and gene expression, and may also be modulated by the functional states of the vessel such as endothelial dysfunction: in quiescent vessels, Nox proteins contribute to signal transduction and to the physiological responses to growth factors such as vascular endothelial growth factor or thrombin. Excessive Nox-dependent reactive oxygen species formation in vascular disease such as hyperlipidemia or diabetes, however, largely contributes to vascular dysfunction resulting in defective angiogenesis and inflammatory activation. Reactive oxygen species, specifically generated by individual Nox proteins, act as secondary messengers. Selective inhibition of Nox proteins might be a novel approach to prevent and treat cardiovascular diseases.

Peroxisome proliferator activated receptor γ agonists suppress TNFα-induced ICAM-1 expression by endothelial cells in a manner potentially dependent on inhibition of reactive oxygen species

In this study, we investigated the anti-inflammatory effect of various peroxisome proliferator activated receptor gamma (PPARγ) agonists (15-deoxy-Δ12,14-prostaglandin J 2, troglitazone, rosiglitazone, ciglitazone) on human aortic endothelial cells. Pretreatment with PPARγ agonists abrogated tumor necrosis factor α (TNFα)-induced expression of intercellular adhesion molecule-1 (ICAM-1) and subsequent monocytic adhesion by endothelial cells. Because reactive oxygen species (ROS) have been reported to play important roles in pro-inflammatory signal transduction, the involvement of ROS was investigated as a potential mechanism of anti-inflammatory effect of PPARγ ligands. Consistent with previous reports in other cell types, blockade of TNFα-induced ROS by treatment with N-acetylcysteine, diphenylene iodonium or NADPH oxidase 4 (NOX4) siRNA suppressed TNFα-induced ICAM-1 expression and subsequent monocytic adhesion, indicating that TNFα mediates pro-inflammatory signals via NOX4-dependent ROS generation in human endothelial cells. Finally, pretreatment with PPARγ agonists significantly suppressed TNFα-induced increases of intracellular ROS. Our results collectively suggest that PPARγ agonists might exert an anti-inflammatory effect on endothelial cells in a ROS-dependent manner.

NOX4 activity is determined by mRNA levels and reveals a unique pattern of ROS generation

NOX4 is an enigmatic member of the NOX (NADPH oxidase) family of ROS (reactive oxygen species)-generating NADPH oxidases. NOX4 has a wide tissue distribution, but the physiological function and activation mechanisms are largely unknown, and its pharmacology is poorly understood. We have generated cell lines expressing NOX4 upon tetracycline induction. Tetracycline induced a rapid increase in NOX4 mRNA (1 h) followed closely (2 h) by a release of ROS. Upon tetracycline withdrawal, NOX4 mRNA levels and ROS release decreased rapidly (<24 h). In membrane preparations, NOX4 activity was selective for NADPH over NADH and did not require the addition of cytosol. The pharmacological profile of NOX4 was distinct from other NOX isoforms: DPI (diphenyleneiodonium chloride) and thioridazine inhibited the enzyme efficiently, whereas apocynin and gliotoxin did not (IC(50)>100 muM). The pattern of NOX4-dependent ROS generation was unique: (i) ROS release upon NOX4 induction was spontaneous without need for a stimulus, and (ii) the type of ROS released from NOX4-expressing cells was H(2)O(2), whereas superoxide (O(2)(-)) was almost undetectable. Probes that allow detection of intracellular O(2)(-) generation yielded differential results: DHE (dihydroethidium) fluorescence and ACP (1-acetoxy-3-carboxy-2,2,5,5-tetramethylpyrrolidine) ESR measurements did not detect any NOX4 signal, whereas a robust signal was observed with NBT. Thus NOX4 probably generates O(2)(-) within an intracellular compartment that is accessible to NBT (Nitro Blue Tetrazolium), but not to DHE or ACP. In conclusion, NOX4 has a distinct pharmacology and pattern of ROS generation. The close correlation between NOX4 mRNA and ROS generation might hint towards a function as an inducible NOX isoform.

NADPH oxidase-dependent reactive oxygen species formation required for root hair growth depends on ROP GTPase

Reactive oxygen species (ROS) production by an NADPH oxidase (NOX) encoded by AtrbohC/RHD2 is required for root hair growth in Arabidopsis thaliana. ROP (RHO of plants) GTPases are also required for normal root hair growth and have been proposed to regulate ROS production in plants. Therefore, the role of ROP GTPase in NOX-dependent ROS formation by root hairs was investigated. Plants overexpressing wild-type ROP2 (ROP2 OX), constitutively active (CA-rop2), or dominant negative (DN-rop2) rop2 mutant proteins were used. Superoxide formation by root hairs was detected by superoxide dismutase-sensitive nitroblue tetrazolium reduction, and ROS production in the root hair differentiation zone was detected by dihydrofluorescein diacetate oxidation. Both probes showed that ROS production was increased in ROP2 OX and CA-rop2 plants, and decreased in DN-rop2 plants, relative to wild-type plants. When CA-rop2 was expressed in the NOX loss-of-function rhd2-1 mutant, ROS formation and root hair growth were impaired, suggesting that RHD2 is required for this ROP2-dependent ROS formation.

Les Nox/Duox : une nouvelle famille de NADPH oxydases

Reactive oxygen species (ROS) generated by the NADPH oxidases are conventionally thought to be cytotoxic and mutagenic and at high levels induce an oxidative stress response. The phagocyte NADPH oxidase catalyzes the NADPH-dependent reduction of molecular oxygen to generate superoxide O2-., which can dismute to generate ROS species. Together, these ROS participate in host defence by killing or damaging invading microbes. Flavocytochrome b558 is the catalytic core of the phagocyte NADPH oxidase and consists of a large glycoprotein gp91phox or Nox-2 and a small protein p22phox. The other components of the NADPH oxidase are cytosolic proteins, namely p67phox, p47phox, p40phox and Rac. A defect in any of the genes encoding gp91phox, p22phox, p67phox or p47phox results in chronic granulomatous disease, a genetic disorder characterized by severe and recurrent infections. Evidence is rapidly accumulating that low level of ROS were produced by NADPH oxidase homologs in non-phagocytic cells. To date, six human homologs (Nox-1, Nox-3, Nox-4, Nox-5, Duox-1 and Duox-2) have been recently identified in a variety of non-phagocytic cells. The identification of Nox-1 was quickly followed by the cloning of Nox-3, Nox-4, and Nox-5. In parallel, two very large members of the Nox family were discovered, namely Duox-1 and Duox-2, initially also referred to as thyroid oxidases. The physiological functions of Nox-dependent ROS generation are in progress and still require detailed characterization. Activation mechanisms and tissue distribution of the different members of the Nox family are very different, suggesting distinct physiological functions. Nox family enzymes are likely to be involved in a variety of physiological events including cell proliferation, host defence, differentiation, apoptosis, senescence and activation of growth-related signaling pathways. An increase and a decrease in the function of Nox enzymes can contribute to a wide range of pathological processes.

A Transverse Tubule NADPH Oxidase Activity Stimulates Calcium Release from Isolated Triads via Ryanodine Receptor Type 1 S -Glutathionylation

We report here the presence of an NADPH oxidase (NOX) activity both in intact and in isolated transverse tubules and in triads isolated from mammalian skeletal muscle, as established by immunochemical, enzymatic, and pharmacological criteria. Immunohistochemical determinations with NOX antibodies showed that the gp91(phox) membrane subunit and the cytoplasmic regulatory p47(phox) subunit co-localized in transverse tubules of adult mice fibers with the alpha1s subunit of dihydropyridine receptors. Western blot analysis revealed that isolated triads contained the integral membrane subunits gp91(phox) and p22(phox), which were markedly enriched in isolated transverse tubules but absent from junctional sarcoplasmic reticulum vesicles. Isolated triads and transverse tubules, but not junctional sarcoplasmic reticulum, also contained varying amounts of the cytoplasmic NOX regulatory subunits p47(phox) and p67(phox). NADPH or NADH elicited superoxide anion and hydrogen peroxide generation by isolated triads; both activities were inhibited by NOX inhibitors but not by rotenone. NADH diminished the total thiol content of triads by one-third; catalase or apocynin, a NOX inhibitor, prevented this effect. NADPH enhanced the activity of ryanodine receptor type 1 (RyR1) in triads, measured through [3H]ryanodine binding and calcium release kinetics, and increased significantly RyR1 S-glutathionylation over basal levels. Preincubation with reducing agents or NOX inhibitors abolished the enhancement of RyR1 activity produced by NADPH and prevented NADPH-induced RyR1 S-glutathionylation. We propose that reactive oxygen species generated by the transverse tubule NOX activate via redox modification the neighboring RyR1 Ca2+ release channels. Possible implications of this putative mechanism for skeletal muscle function are discussed.