Chronic intermittent hypoxia increases rat sternohyoid muscle NADPH oxidase expression with attendant modest oxidative stress

Chronic intermittent hypoxia (CIH) causes upper airway muscle dysfunction. We hypothesized that the superoxide generating NADPH oxidase (NOX) is upregulated in CIH-exposed muscle causing oxidative stress. Adult male Wistar rats were exposed to intermittent hypoxia (5% O2 at the nadir for 90 s followed by 210 s of normoxia), for 8 h per day for 14 days. The effect of CIH exposure on the expression of NOX subunits, total myosin and 4-hydroxynonenal (4-HNE) protein adducts in sternohyoid muscle was determined by western blotting and densitometry. Sternohyoid protein free thiol and carbonyl group contents were determined by 1D electrophoresis using specific fluorophore probes. Aconitase and glutathione reductase activities were measured as indices of oxidative stress. HIF-1α content and key oxidative and glycolytic enzyme activities were determined. Contractile properties of sternohyoid muscle were determined ex vivo in the absence and presence of apocynin (putative NOX inhibitor). We observed an increase in NOX 2 and p47 phox expression in CIH-exposed sternohyoid muscle with decreased aconitase and glutathione reductase activities. There was no evidence, however, of increased lipid peroxidation or protein oxidation in CIH-exposed muscle. CIH exposure did not affect sternohyoid HIF-1α content or aldolase, lactate dehydrogenase, or glyceraldehyde-3-phosphate dehydrogenase activities. Citrate synthase activity was also unaffected by CIH exposure. Apocynin significantly increased sternohyoid force and power. We conclude that CIH exposure upregulates NOX expression in rat sternohyoid muscle with concomitant modest oxidative stress but it does not result in a HIF-1α-dependent increase in glycolytic enzyme activity. Constitutive NOX activity decreases sternohyoid force and power. Our results implicate NOX-dependent reactive oxygen species in CIH-induced upper airway muscle dysfunction which likely relates to redox modulation of key regulatory proteins in excitation-contraction coupling.

Defective localization of the NADPH phagocyte oxidase to Salmonella-containing phagosomes in tumor necrosis factor p55 receptor-deficient macrophages

Tumor necrosis factor receptor (TNFR) p55-knockout (KO) mice are susceptible profoundly to Salmonella infection. One day after peritoneal inoculation, TNFR-KO mice harbor 1,000-fold more bacteria in liver and spleen than wild-type mice despite the formation of well organized granulomas. Macrophages from TNFR-KO mice produce abundant quantities of reactive oxygen and nitrogen species in response to Salmonella but nevertheless exhibit poor bactericidal activity. Treatment with IFN-γ enhances killing by wild-type macrophages but does not restore the killing defect of TNFR-KO cells. Bactericidal activity of macrophages can be abrogated by a deletion in the gene encoding TNFα but not by saturating concentrations of TNF-soluble receptor, suggesting that intracellular TNFα can regulate killing of Salmonella by macrophages. Peritoneal macrophages from TNFR-KO mice fail to localize NADPH oxidase-containing vesicles to Salmonella-containing vacuoles. A TNFR-KO mutation substantially restores virulence to an attenuated mutant bacterial strain lacking the type III secretory system encoded by Salmonella pathogenicity island 2 (SPI2), suggesting that TNFα and SPI2 have opposing actions on a common pathway of vesicular trafficking. TNFα–TNFRp55 signaling plays a critical role in the immediate innate immune response to an intracellular pathogen by optimizing the delivery of toxic reactive oxygen species to the phagosome.

NADPH oxidases as regulators of tumor angiogenesis : current and emerging concepts

Significance Reactive oxygen species (ROS) such as superoxide, hydrogen peroxide, and peroxynitrite are generated ubiquitously by all mammalian cells and have been understood for many decades as inflicting cell damage and as causing cancer by oxidation and nitration of macromolecules, including DNA, RNA, proteins, and lipids. Recent Advances A current concept suggests that ROS can also promote cell signaling pathways triggered by growth factors and transcription factors that ultimately regulate cell proliferation, differentiation, and apoptosis, all of which are important hallmarks of tumor cell proliferation and angiogenesis. Moreover, an emerging concept indicates that ROS regulate the functions of immune cells that infiltrate the tumor environment and stimulate angiogenesis, such as macrophages and specific regulatory T cells. Critical Issues In this article, we highlight that the NADPH oxidase family of ROS-generating enzymes are the key sources of ROS and, thus, play an important role in redox signaling within tumor, endothelial, and immune cells thereby promoting tumor angiogenesis. Future Directions Knowledge of these intricate ROS signaling pathways and identification of the culprit NADPH oxidases is likely to reveal novel therapeutic opportunities to prevent angiogenesis that occurs during cancer and which is responsible for the revascularization after current antiangiogenic treatment.

Modulação das vias de sinalização intracelulares pelo sistema NAD(P)H oxidase em melanoma humano

Evidências têm mostrado que as espécies reativas de oxigênio (ROS) geradas pela NAD(P)H oxidase são importantes moduladores de diversas funções celulares como migração, crescimento, proliferação e sobrevivência. Estudos recentes demonstraram o envolvimento da atividade da NAD(P)H oxidase no crescimento e sobrevivência de células de melanoma. Neste trabalho, investigamos o efeito da inibição da NAD(P)H oxidase por difenileneiodônio (DPI) sobre o crescimento das células de melanoma humano MV3 e observamos que este composto reduziu o crescimento destas células em aproximadamente 50%. A inibição da NAD(P)H oxidase induziu mudanças no formato celular, com arredondamento, diminuição do espraiamento e descolamento celular. Esta redução foi acompanhada por um rearranjo do citoesqueleto de actina, diminuição da fosforilação no resíduo Tyr397 da quinase de adesão focal (FAK) e redução na associação de FAK com actina e com a tirosina quinase c-Src. Isto indica que a inibição da geração de ROS está modulando negativamente vias de sinalização ativadas por integrinas, o que freqüentemente conduz a um tipo particular de morte celular conhecida por anoikis. Comprovando a ocorrência deste fenômeno, observamos que a inibição da atividade da NAD(P)H oxidase aumentou a apoptose das células de melanoma e induziu a ativação da caspase-3. Nossos resultados mostram ainda que a inibição da viabilidade celular por DPI foi revertida com o pré-tratamento das células MV3 com um inibidor de tirosina fosfatases (ortovanadato de sódio). Em resumo, este estudo mostra que a geração de ROS por NAD(P)H oxidase está envolvida nos mecanismos de sobrevivência em células de melanoma, uma vez que afetam as vias de sinalização dependentes de FAK-Src, através da inibição da atividade de proteína tirosina fosfatases.

Functional effect of the C242T polymorphism in the NAD(P)H oxidase p22phox gene on vascular superoxide production in atherosclerosis.

BACKGROUND:

Increased superoxide anion production increases oxidative stress and reduces nitric oxide bioactivity in vascular disease states. NAD(P)H oxidase is an important source of superoxide in human blood vessels, and some studies suggest a possible association between polymorphisms in the NAD(P)H oxidase CYBA gene and atherosclerosis; however, no functional data address this hypothesis. We examined the relationships between the CYBA C242T polymorphism and direct measurements of superoxide production in human blood vessels.

METHODS AND RESULTS:

Vascular NAD(P)H oxidase activity was determined in human saphenous veins obtained from 110 patients with coronary artery disease and identified risk factors. Immunoblotting, reverse-transcription polymerase chain reaction, and DNA sequencing showed that p22phox protein, mRNA, and 242C/T allelic variants are expressed in human blood vessels. Vascular superoxide production, both basal and NADH-stimulated, was highly variable between patients, but the presence of the CYBA 242T allele was associated with significantly reduced vascular NAD(P)H oxidase activity, independent of other clinical risk factors for atherosclerosis.

CONCLUSIONS:

Association of the CYBA 242T allele with reduced NAD(P)H oxidase activity in human blood vessels suggests that genetic variation in NAD(P)H oxidase components may play a significant role in modulating superoxide production in human atherosclerosis.

Attenuation of urokinase activity during experimental ischaemia protects the cerebral barrier from damage through regulation of matrix metalloproteinase-2 and NAD(P)H oxidase

Ischaemic injury impairs the integrity of the blood-brain barrier (BBB). In this study, we investigated the molecular causes of this defect with regard to the putative correlations among NAD(P)H oxidase, plasminogen-plasmin system components, and matrix metalloproteinases. Hence, the activities of NAD(P)H oxidase, matrix metalloproteinase-2, urokinase-type plasminogen activator (uPA), and tissue-type plasminogen activator (tPA), and superoxide anion levels, were assessed in human brain microvascular endothelial cells (HBMECs) exposed to oxygen-glucose deprivation (OGD) alone or OGD followed by reperfusion (OGD + R). The integrity of an in vitro model of BBB comprising HBMECs and astrocytes was studied by measuring transendothelial electrical resistance and the paracellular flux of albumin. OGD with or without reperfusion (OGD ± R) radically perturbed barrier function while concurrently enhancing uPA, tPA and NAD(P)H oxidase activities and superoxide anion release in HBMECs. Pharmacological inactivation of NAD(P)H oxidase attenuated OGD ± R-mediated BBB damage through modulation of matrix metalloproteinase-2 and tPA, but not uPA activity. Overactivation of NAD(P)H oxidase in HBMECs via cDNA electroporation of its p22-phox subunit confirmed the involvement of tPA in oxidase-mediated BBB disruption. Interestingly, blockade of uPA or uPA receptor preserved normal BBB function by neutralizing both NAD(P)H oxidase and matrix metalloproteinase-2 activities. Hence, selective targeting of uPA after ischaemic strokes may protect cerebral barrier integrity and function by concomitantly attenuating basement membrane degradation and oxidative stress.

Association of NAD(P)H Oxidase with Glucose-Induced Insulin Secretion by Pancreatic beta-Cells

We previously described the presence of nicotinamide adenine dinucleotide phosphate reduced form [NAD(P)H] oxidase components in pancreatic beta-cells and its activation by glucose, palmitic acid, and proinflammatory cytokines. In the present study, the importance of the NAD(P)H oxidase complex for pancreatic beta-cell function was examined. Rat pancreatic islets were incubated in the presence of glucose plus diphenyleneiodonium, a NAD(P)H oxidase inhibitor, for 1 h or with the antisense oligonucleotide for p47(PHOX) during 24 h. Reactive oxygen species (ROS) production was determined by a fluorescence assay using 2,7-dichlorodihydrofluorescein diacetate. Insulin secretion, intracellular calcium responses, [U-(14)C] glucose oxidation, and expression of glucose transporter-2, glucokinase and insulin genes were examined. Antisense oligonucleotide reduced p47(PHOX) expression [an important NAD(P)H oxidase cytosolic subunit] and similarly to diphenyleneiodonium also blunted the enzyme activity as indicated by reduction of ROS production. Suppression of NAD(P)H oxidase activity had an inhibitory effect on intracellular calcium responses to glucose and glucose-stimulated insulin secretion by isolated islets. NAD(P)H oxidase inhibition also reduced glucose oxidation and gene expression of glucose transporter-2 and glucokinase. These findings indicate that NAD(P)H oxidase activation plays an important role for ROS production by pancreatic beta-cells during glucose-stimulated insulin secretion. The importance of this enzyme complex for the beta-cell metabolism and the machinery involved in insulin secretion were also shown. (Endocrinology 150: 2197-2201, 2009)

Angiotensin II induces superoxide generation via NAD(P)H oxidase activation in isolated rat pancreatic islets

Angiotensin II (Ang II) controls blood pressure, electrolyte balance, cell growth and vascular remodeling. Ang II activates NAD(P)H oxidase in several tissues with important function in the control of insulin secretion. Considering the concomitant occurrence of hypertension, insulin resistance and pancreatic B cell secretion impairment in the development of type II diabetes the aim of the present study was to evaluate the effect of ANG II on NAD(P)H oxidase activation in isolated pancreatic islets. We found that ANGII-induced superoxide generation via NAD(P)H oxidase activation and increased protein and mRNA levels of NAD(P)H oxidase subunits (p47(PHOX) and gp91(PHOX)). (C) 2008 Elsevier B.V. All rights reserved.

NAD(P)H Oxidase Participates in the Palmitate-Induced Superoxide Production and Insulin Secretion by Rat Pancreatic Islets

Nicotinamide adenine dinucleotide phosphate [NAD(P)H] oxidase complex has been shown to be involved in the process of glucose-stimulated insulin secretion (GSIS). In this study, we examined the effect of palmitic acid on superoxide production and insulin secretion by rat pancreatic islets and the mechanism involved. Rat pancreatic islets were incubated during 1 h with 1 mM palmitate, 1% fatty acid free-albumin, 5.6 or 10 mM glucose and in the presence of inhibitors of NAD(P)H oxidase (DPI-diphenyleneiodonium), PKC (calphostin C) and carnitine palmitoyl transferase-I (CPT-I) (etomoxir). Superoxide content was determined by hydroethidine assays. Palmitate increased superoxide production in the presence of 5.6 and 10 mM glucose. This effect was dependent on activation of PKC and NAD(P)H oxidase. Palmitic acid oxidation was demonstrated to contribute for the fatty acid induction of superoxide production in the presence of 5.6 mM glucose. In fact, palmitate caused p47(PHOX) translocation to plasma membrane, as shown by immunohistochemistry. Exposure to palmitate for 1 h up-regulated the protein content of p47(PHOX) and the mRNA levels of p22(PHOX), gp91(PHOX), p47(PHOX), proinsulin and the G protein-coupled receptor 40 (GPR40). Fatty acid stimulation of insulin secretion in the presence of high glucose concentration was reduced by inhibition of NAD(P)H oxidase activity. In conclusion, NAD(P)H oxidase is an important source of superoxide in pancreatic islets and the activity of NAD(P)H oxidase is involved in the control of insulin secretion by palmitate. J. Cell. Physiol. 226: 1110-1117, 2011. (C) 2010 Wiley-Liss, Inc.

Oleic Acid Modulates Metabolic Substrate Channeling during Glucose-Stimulated Insulin Secretion via NAD(P)H Oxidase

Positive acute effects of fatty acids (FA) on glucose-stimulated insulin secretion (GSIS) and reactive oxygen species (ROS) formation have been reported. However, those studies mainly focused on palmitic acid actions, and reports on oleic acid (OA) are scarce. In this study, the effect of physiological OA levels on beta-cell function and the mechanisms involved were investigated. Analyses of insulin secretion, FA and glucose oxidation, and ROS formation showed that, at high glucose concentration, OA treatment increases GSIS in parallel with increased ROS content. At high glucose, OA oxidation was increased, accompanied by a suppression of glucose oxidation. Using approaches for protein knockdown of FA receptor G protein-coupled receptor 40 (GPR40) and of p47(PHOX), a reduced nicotinamide adenine dinucleotide phosphate [NAD(P) H] oxidase component, we observed that GPR40 does not mediate OA effects on ROS formation and GSIS. However, in p47(PHOX) knockdown islets, OA-induced ROS formation and the inhibitory effect of OA on glucose metabolism was abolished. Similar results were obtained by pharmacological inhibition of protein kinase C, a known activator of NAD(P) H oxidase. Thus, ROS derived from OA metabolism via NAD(P) H oxidase are an inhibitor of glucose oxidation. Put together, these results indicate that OA acts as a modulator of glucose oxidation via ROS derived from its own metabolism in beta-cells. (Endocrinology 152: 3614-3621, 2011)

Effects of glucocorticoids on vascular NADPH oxidases and endothelial NO synthase

Glukokortikoide (GCs) stellen wichtige Hormone in der Regulation der metabolischen Homöostase dar. Synthetische GCs, wie Dexamethasone (DEX), spielen eine essentielle Rolle in der Behandlung inflammatorischer Krankheiten. Jedoch sind unter einer Dexamethason-Therapie zahlreiche Nebenwirkungen bekannt, so z.B. auch die Entwicklung einer Hypertonie, in deren Pathogenese oxidativer Stress eine entscheidende Rolle spielt. Obwohl sich in den vergangenen Jahren zahlreiche Studien zum Ziel setzten die GC-induzierte Hypertonie (GC-HT) aufzuklären, sind die genauen Mechanismen bis heute unklar. Eine erhöhte Expression von NADPH Oxidasen (Nox) und eine Entkopplung der endothelialen NO Synthase (eNOS), die Hauptquellen reaktiver Sauerstoffspezies (ROS) im vaskulären System, tragen maßgeblich zur Pathogenese kardiovaskulärer Erkrankungen bei. Daher ist eine Beteiligung dieser Enzyme in GC-induziertem oxidativen Stress sehr wahrscheinlich. Folglich wurde die Hypothese aufgestellt, dass NADPH Oxidasen und eine entkoppelte eNOS die vielversprechendsten unter den zahlreichen involvierten pro- und anti-oxidativen Enzymen sind. Mit Fokus auf die oben genannten Systeme wurde in der vorliegenden Studie der Effekt von DEX mit Hilfe von in vivo (WKY Ratten) ebenso wie in vitro Experimenten (A7r5 und EA.hy 926 Zellen) untersucht. Dabei zeigte sich, dass Nox1, Nox4 und p22phox durch DEX unterschiedlich reguliert wurden. Nox1 wurde hoch-, Nox4 hingegen herunterreguliert, während p22phox unverändert blieb. Die Modufikation schien hierbei auf transkriptioneller und post-transkriptioneller Ebene stattzufinden. Durch die gegensätzliche Regulation von Nox1 und Nox4 bleibt die Nettowirkung der verschiedenen Nox Isoformen unklar. Immer mehr Studien bringen vaskulären oxidativen Stress mit der Pathogenese einer GC-HT in Zusammenhang, welche letztendlich zu einer verminderten Bioverfügbarkeit von Stickstoffmonoxid (NO) führt. Durch die eNOS produziertes NO stellt einen essentiellen Schutzfaktor der Blutgefäße dar. Eine verminderte NO-Bioverfügbarkeit könnte die Folge einer eNOS-Entkopplung darstellen, ausgelöst durch oxidativen Stress. Da die Verfügbarkeit von Tetrahydrobiopterin (BH4) entscheident ist für die Aktivität und enzymatische Kopplung der eNOS, beschäftigt sich die vorliegende Arbeit mit GC-induzierten Veränderungen in der BH4-Versorgung. Die Behandlung von EA.hy 926 Zellen mit DEX führte zu einer zeit- und konzentrationsabhängigen Herunterregulation von eNOS auf mRNA- und Proteinebene. Gleichzeitig wurde die Phosphorylierung an Serine1177 vermindert. Als maßgeblicher “Kopplungs-Schalter” kann BH4 endogen über zwei verschiedene Signalwege synthetisiert werden, welche durch die Enzyme GCH1 und DHFR reguliert werden. DEX führte zu einer zeit- und konzentrationsabhängigen Herunterregulation von BH4, BH2 und Biopterin, wobei ebenso das BH4 / BH2 -Verhältnis vermindert wurde. Beide Enzyme, GCH1 genauso wie DHFR, wurden auf mRNA- und Proteinebene herunterreguliert, was auf einen Effekt von GCs auf beide rnBH4-produzierenden Signalwege schließen lässt. Nach Behandlung mit DEX wurde die Produktion von NO in Endothelzellen maßgeblich vermindert. In ROS-Messungen zeigte sich eine Tendenz hin zu einer eNOS-Entkopplung, jedoch war es mit unserem experimentellen Aufbau nicht möglich, diese endgültig zu beweisen.rnZusammenfassend lässt sich sagen, dass die Behandlung mit GCs zu Veränderungen in beiden untersuchten Systemen, den NADPH Oxidasen ebenso wie dem eNOS-NO System, führte. DEX erhöhte die Expression von Nox1 in glatten Muskelzellen und reduzierte die Nox4-Expression in Endothelzellen. Gleichzeitig verminderte DEX die Verfügbarkeit von BH4 und inhibierte die Phosphorylierung / Aktivität von eNOS. Mithilfe weiterer Studien muss die endgültige Beteiligung von NADPH Oxidasen und einer eNOS-Entkopplung an oxidativem Stress in GC-HT abschließend aufgeklärt werden.rn