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.

Inhibition of phase-1 biotransformation and cytostatic effects of diphenyleneiodonium on hepatoblastoma cell line HepG2 and a CYP3A4-overexpressing HepG2 cell clone

Cell-based in vitro liver models are an important tool in the development and evaluation of new drugs in pharmacological and toxicological drug assessment. Hepatic microsomal enzyme complexes, consisting of cytochrome P450 oxidoreductase (CPR) and cytochrome P450 monooxygenases (CYPs), play a decisive role in catalysing phase-1 biotransformation of pharmaceuticals and xenobiotics. For a comprehensive understanding of the phase-1 biotransformation of drugs, the availability of well-characterized substances for the targeted modulation of in vitro liver models is essential. In this study, we investigated diphenyleneiodonium (DPI) for its ability to inhibit phase-1 enzyme activity and further its toxicological profile in an in vitro HepG2 cell model with and without recombinant expression of the most important drug metabolization enzyme CYP3A4.

Aim of the study was to identify effective DPI concentrations for CPR/CYP activity modulation and potentially associated dose and time dependent hepatotoxic effects. The cells were treated with DPI doses up to 5,000nM (versus vehicle control) for a maximum of 48 h and subsequently examined for CYP3A4 activity as well as various toxicological relevant parameters such as cell morphology, integrity and viability, intracellular ATP level, and proliferation. Concluding, the experiments revealed a time- and concentration-dependent DPI mediated partial and complete inhibition of CYP3A4 activity in CYP3A4 overexpressing HepG2-cells (HepG2-CYP3A4). Other cell functions, including ATP synthesis and consequently the proliferation were negatively affected in both in vitro cell models. Since neither cell integrity nor cell viability were reduced, the effect of DPI in HepG2 can be assessed as cytostatic rather than cytotoxic.

Effect of Diphenyleneiodonium Chloride on Intracellular Reactive Oxygen Species Metabolism with Emphasis on NADPH Oxidase and Mitochondria in Two Therapeutically Relevant Human Cell Types

Reactive oxygen species (ROS) have recently been recognized as important signal transducers, particularly regulating proliferation and differentiation of cells. Diphenyleneiodonium (DPI) is known as an inhibitor of the nicotinamide adenine dinucleotide phosphate oxidase (NOX) and is also affecting mitochondrial function. The aim of this study was to investigate the effect of DPI on ROS metabolism and mitochondrial function in human amniotic membrane mesenchymal stromal cells (hAMSCs), human bone marrow mesenchymal stromal cells (hBMSCs), hBMSCs induced into osteoblast-like cells, and osteosarcoma cell line MG-63. Our data suggested a combination of a membrane potential sensitive fluorescent dye, tetramethylrhodamine methyl ester (TMRM), and a ROS-sensitive dye, CM-H2DCFDA, combined with a pretreatment with mitochondria-targeted ROS scavenger MitoTEMPO as a good tool to examine effects of DPI. We observed critical differences in ROS metabolism between hAMSCs, hBMSCs, osteoblast-like cells, and MG-63 cells, which were linked to energy metabolism. In cell types using predominantly glycolysis as the energy source, such as hAMSCs, DPI predominantly interacted with NOX, and it was not toxic for the cells. In hBMSCs, the ROS turnover was influenced by NOX activity rather than by the mitochondria. In cells with aerobic metabolism, such as MG 63, the mitochondria became an additional target for DPI, and these cells were prone to the toxic effects of DPI. In summary, our data suggest that undifferentiated cells rather than differentiated parenchymal cells should be considered as potential targets for DPI.

An ultralow dose of the NADPH oxidase inhibitor diphenyleneiodonium (DPI) is an economical and effective therapeutic agent for the treatment of colitis-associated colorectal cancer

Long-term inflammatory stimulation is considered one of the most important causes of colorectal cancer. Diphenyleneiodonium (DPI), an NADPH oxidase inhibitor, can inhibit a variety of inflammatory responses. However, the systemic toxicity of DPI limits its clinical application. Whether DPI can inhibit colitis-associated colorectal cancer (CAC) at ultralow concentrations remains unknown.

Methods: CAC was induced by azoxymethane (AOM) injection followed by treatment with dextran sulfate sodium (DSS), and DPI was intraperitoneally injected (i.p.) in the first cycle for 21 days. Colon tissue was collected and analyzed by western blotting. Immune cell infiltration and macrophage polarization were examined by immunohistochemistry, immunofluorescence, or real-time polymerase-chain reaction (PCR). Reactive oxygen species (ROS) production was measured by flow cytometry.

Results: Ultralow dose DPI significantly ameliorated the DSS-induced colitis and attenuated the colon tumorigenesis in the mouse model of AOM/ DSS-induced CAC. Mechanistically, an ultralow dose of DPI inhibited the production of pro-inflammatory cytokines, (tumor necrosis factor (TNF)-α and interleukin (IL)-6), reduced the macrophage infiltration and classical polarization, and induced the ROS generation. These effects were found to be related to the inhibition of the phosphorylation of signal transducer and activator of transcription 3 (STAT3), mitogen-activated protein kinase (MAPK), and nuclear factor kappa B (NF -κB).

Conclusion: The present study revealed that an ultralow dose of DPI, with no significant systemic toxicity involved, may be an effective way to prevent the occurrence and development of CAC.

Diphenyleneiodonium chloride synergizes with diazoxide to enhance protection against amyloid β induced neurotoxicity

We examined synergistic effects of inhibiting reactive oxygen species generated from the mitochondria and from nicotinamide adenine dinucleotide phosphate oxidase on neurotoxicity. Primary hippocampal neurons were exposed to amyloid β, and the cells were treated with diazoxide or/and diphenyleneiodonium chloride. We found that the cell viability was decreased significantly after exposure to amyloid β for 72 h with higer reactive oxygen species and malondialdehyde levels, higher caspase-3 and cleaved caspase-3 levels and lower B-cell lymphoma 2 (Bcl-2) level. Both diazoxide and diphenyleneiodonium increased cell viability by inhibiting the increase in reactive oxygen species and caspase-3 activity as well as the decrease in Bcl-2 induced by amyloid β. The combination of diazoxide and diphenyleneiodonium exhibited better protective effects compared to a single treatment. In conclusion, the activation of a mitochondrial potassium channel in combination with the inhibitor of nicotinamide adenine dinucleotide phosphate oxidase exhibit synergistic protective effects against amyloid β neurotoxicity.

Reactive oxygen species are involved in eosinophil extracellular traps release and in airway inflammation in asthma

In asthma, there are high levels of inflammatory mediators, reactive oxygen species (ROS), and eosinophil extracellular traps (EETs) formation in airway. Here, we attempted to investigate the ROS involvement in EETs release and airway inflammation in OVA-challenged mice. Before the intranasal challenge with ovalbumin (OVA), animals were treated with two ROS inhibitors, N-acetylcysteine (NAC) or diphenyleneiodonium (DPI). We showed that NAC treatment reduced inflammatory cells in lung. DPI and NAC treatments reduced eosinophil peroxidase (EPO), goblet cells hyperplasia, proinflammatory cytokines, NFκB p65 immunocontent, and oxidative stress in lung. However, only the NAC treatment improved mitochondrial energy metabolism. Moreover, the treatments with DPI and NAC reduced EETs release in airway. This is the first study to show that ROS are needed for EETs formation in asthma. Based on our results, NAC and DPI treatments can be an interesting alternative for reducing airway inflammation, mitochondrial damage, and EETs release in asthma.

Dipenyleneiodonium Induces Growth Inhibition of Toxoplasma gondii through ROS Induction in ARPE-19 Cells

Based on the reactive oxygen species (ROS) regulatory properties of diphenyleneiodonium (DPI), we investigated the effects of DPI on host-infected T. gondii proliferation and determined specific concentration that inhibit the intracellular parasite growth but without severe toxic effect on human retinal pigment epithelial (ARPE-19) cells. As a result, it is observed that host superoxide, mitochondria superoxide and H₂O₂ levels can be increased by DPI, significantly, followed by suppression of T. gondii infection and proliferation. The involvement of ROS in anti-parasitic effect of DPI was confirmed by finding that DPI effect on T. gondii can be reversed by ROS scavengers, N-acetyl-L-cysteine and ascorbic acid. These results suggest that, in ARPE-19 cell, DPI can enhance host ROS generation to prevent T. gondii growth. Our study showed DPI is capable of suppressing T. gondii growth in host cells while minimizing the un-favorite side-effect to host cell. These results imply that DPI as a promising candidate material for novel drug development that can ameliorate toxoplasmosis based on ROS regulation.

Protective effects of diphenyleneiodonium, an NADPH oxidase inhibitor, on lipopolysaccharide-induced acute lung injury

NADPH oxidase (NOX) plays an important role in inflammatory response by producing reactive oxygen species (ROS). The inhibition of NOX has been shown to induce anti-inflammatory effects in a few experimental models. The aim of this study was to investigate the effects of diphenyleneiodonium (DPI), a NOX inhibitor, on lipopolysaccharide (LPS)-induced acute lung injury (ALI) in a rat model. Sprague-Dawley rats were intraperitoneally administered by DPI (5 mg/kg) 30 minutes after intratracheal instillation of LPS (3 mg/kg). After 6 hours, bronchoalveolar lavage fluid (BALF) and lung tissue were collected. The NOX activity in lung tissue was significantly increased in LPS-treated rats. It was significantly attenuated by DPI. DPI-treated rats showed significant reduction in the intracellular ROS, the number of inflammatory cells, and cytokines (TNF-α and IL-6) in BALF compared with LPS-treated rats. In lung tissue, DPI-treated rats showed significantly decreased malondialdehyde content and increased activity of glutathione peroxidase and superoxide dismutase compared with LPS-treated rats. Lung injury score, myeloperoxidase activity, and inducible nitric oxide synthase expression were significantly decreased in DPI-treated rats compared with LPS-treated animals. Western blotting analysis demonstrated that DPI significantly suppressed LPS-induced activation of NF-κB and ERK1/2 and SAPK/JNK in MAPK pathway. Our results suggest that DPI may have protective effects on LPS-induced ALI thorough anti-oxidative and anti-inflammatory effects which may be due to inactivation of the NF-κB, ERK1/2, and SAPK/JNK pathway. These results suggest the therapeutic potential of DPI as an anti-inflammatory agent in ALI.

Involvement of nitric oxide in enhanced germination and seedling growth of magnetoprimed maize seeds

Nitric oxide (NO) is a highly reactive gaseous free radical, which in plants was found to stimulate seed germination and ending of dormancy. Experiments were conducted to study the effect of NO inhibitors sodium tungstate (ST) and Nω-nitro-L-arginine methyl ester hydrochloride (L-NAME), NADPH oxidase inhibitor diphenyleneiodonium (DPI) and NO donor sodium nitroprusside (SNP) on untreated and magnetoprimed maize (Zea mays var: GSF-2) seeds. Treatment of maize seeds with these inhibitors inhibited germination related parameters like seedling length, fresh weight, dry weight and vigour indices and α-amylase activity of maize seeds under laboratory conditions, whereas NO donor (SNP) promoted all these parameters. Among 3 different inhibitors used ST was most effective and showed an inhibition in seedling length of 67% and 71% at 1 mM concentration for untreated (UT) and magnetically treated (MT) seeds respectively. Data presented here indicate the involvement of nitric oxide in enhanced germination and seedling growth of magnetoprimed maize seeds. ROS are continuosly produced by the cells of germinating seeds and play a positive role in germination of magnetoprimed maize seeds. ROS inhibitor (DPI) inhibited seedling length by 34% and 40% for control and MT seeds respectively. α-amylase activity was also inhibited by all the 3 inhibitors used. It is concluded that NO inhibitors and ROS inhibitor inhibited magnetic field induced promotion of seedling parameters and α- amylase activity of maize seeds.

NADPH oxidase inhibitor, diphenyleneiodonium prevents necroptosis in HK-2 cells

The aim of the present study was to investigate the protective effect of the NADPH oxidase inhibitor, diphenyleneiodonium (DPI) against necroptosis in renal tubular epithelial cells. A necroptosis model of HK-2 cells was established using tumor necrosis factor-α, benzyloxycarbonyl-Val-Ala-Asp-fluoromethylketone and antimycin A (collectively termed TZA), as in our previous research. The necroptosis inhibitor, necrostatin-1 (Nec-1) or the NADPH oxidase inhibitor, DPI were administered to the necroptosis model. Production of reactive oxygen species (ROS) was detected by dichlorodihydrofluorescein diacetate in the different groups, and the manner of cell death was identified by flow cytometry. Western blot analysis was used to determine the levels of phosphorylation of receptor-interacting protein kinase 3 (RIP-3) and mixed lineage kinase domain-like (MLKL), which are essential to necroptosis. The results revealed that TZA increased the percentages of propidium iodide-positive HK-2 cells from 1.22±0.69 to 8.98±0.73% (P<0.001), and augmented the phosphorylation of RIP-3 and MLKL. ROS levels were increased in the TZA group compared with the control group (27.74±1.60×10⁴ vs. 18.51±1.10×10⁴, respectively; P<0.001), and could be inhibited by Nec-1 (TZA + Nec-1 group, 22.90±2.22×10⁴ vs. TZA group, 27.74±1.60×10⁴; P=0.01). DPI decreased ROS production (TZA + DPI group, 22.13±1.86×10⁴ vs. TZA group, 27.74±1.60×10⁴; P<0.001) and also reduced the proportions of necrosis in the necroptosis model (TZA + DPI group, 4.40±1.51% vs. TZA group, 8.98±0.73%; P<0.001). Phosphorylated RIP-3 and MLKL were also decreased by DPI treatment. The results indicate that ROS production increases in HK-2 cells undergoing necroptosis, and that the NADPH oxidase inhibitor, DPI may protect HK-2 cells from necroptosis via inhibition of ROS production.

Diphenyleneiodonium Inhibits Apoptotic Cell Death of Gastric Epithelial Cells Infected with Helicobacter pylori in a Korean Isolate

NADPH oxidase produces a large amount of reactive oxygen species (ROS) in Helicobacter pylori (H. pylori)-induced gastric epithelial cells. Even though ROS mediate apoptotic cell death, direct involvement of NADPH oxidase on H. pylori-induced apoptosis remains unclear. Besides, H. pylori isolates show a high degree of genetic variability. The predominant genotype of H. pylori in Korea has been reported as cagA⁺, vacA s1b, m2, iceA genotype. Present study aims to investigate whether NADPH oxidase-generated ROS mediate apoptosis in human gastric epithelial AGS cells infected with H. pylori in a Korean isolate. AGS cells were pretreated with or without an NADPH oxidase inhibitor diphenyleneiodonium (DPI) and cultured in the presence of H. pylori at a bacterium/cell ratio of 300:1. Cell viability, hydrogen peroxide level, DNA fragmentation, and protein levels of p53, Bcl-2, and Bax were determined. Results showed that H. pylori inhibited cell viability with the density of H. pylori added to the cells. Inhibition of NADPH oxidase by DPI suppressed H. pylori-induced cell death, increased hydrogen peroxide, DNA fragmentation, and the ratio of Bax/Bcl-2, and p53 induction in AGS cells dose-dependently. The results suggest that targeting NADPH oxidase may prevent the development of gastric inflammation associated with H. pylori infection by suppressing abnormal apoptotic cell death of gastric epithelial cells.

Dual oxidase regulates neutrophil recruitment in allergic airways

Enhanced reactive oxygen species production in allergic airways is well described and correlates with increased airway contractions, inflammatory cell infiltration, goblet cell metaplasia, and mucus hypersecretion. There is also an abundance of interleukin-4/interleukin-13 (IL-4/IL-13)- or interleukin-5-secreting cells that are thought to be central to the pathogenesis of allergic asthma. We postulated that the dual oxidases (DUOX1 and DUOX2), members of the nicotinamide adenine dinucleotide phosphate oxidase family that release hydrogen peroxide (H2O2) in the respiratory tract, are critical proteins in the pathogenesis of allergic airways. DUOX activity is regulated by cytokines, including IL-4 and IL-13, and DUOX-mediated H2O2 influences several important features of allergic asthma: mucin production, IL-8 secretion, and wound healing. The objective of this study was to establish the contribution of DUOXs to the development of allergic asthma in a murine model. To accomplish this goal, we utilized a DUOXA-deficient mouse model (Duoxa(-/-)) that lacked maturation factors for both DUOX1 and DUOX2. Our results are the first to demonstrate evidence of DUOX protein and DUOX functional activity in murine airway epithelium. We also demonstrate that DUOXA maturation factors are required for airway-specific H2O2 production and localization of DUOX to cilia of fully differentiated airway epithelial cells. We compared wild-type and Duoxa(-/-) mice in an ovalbumin exposure model to determine the role of DUOX in allergic asthma. In comparison to DUOX-intact mice, Duoxa(-/-) mice had reduced mucous cell metaplasia and lower levels of TH2 cytokine levels in bronchoalveolar fluid. In addition, increased airway resistance in response to methacholine was observed in Duoxa(+/+) mice, as expected, but was absent in Duoxa(-/-) mice. Surprisingly, Duoxa(-/-) mice had decreased influx of neutrophils in bronchoalveolar fluid and lung tissue sections associated with a lower level of the chemotactic cytokine IL-6. These findings suggest that DUOX-derived H2O2 has an important role in signaling neutrophils into allergic airways.

Nrf2 deficiency induces oxidative stress and promotes RANKL-induced osteoclast differentiation

Nuclear factor-erythroid 2-related factor 2 (Nrf2) is a redox-sensitive transcription factor that regulates the expression of a variety of antioxidant and detoxification genes through an antioxidant-response element. Nrf2 has been shown to protect several types of cells against the acute and chronic injury that accompanies oxidative stress, but its role in osteoclasts remains unclear. In this study, we investigated the role of Nrf2 in osteoclast (OC) differentiation, a process in which reactive oxygen species (ROS) are generated and then participate, using Nrf2-knockout mice. Receptor activator of nuclear factor κB ligand (RANKL)-induced OC differentiation, actin ring formation, and osteoclastic bone resorption were substantially promoted in Nrf2-deficient OC precursor cells compared to wild-type cells. Under both unstimulated and RANKL-stimulated conditions, Nrf2 loss led to an increase in the intracellular ROS level and the oxidized-to-reduced glutathione ratio and a defect in the production of numerous antioxidant enzymes and glutathione. Moreover, pretreatment with N-acetylcysteine or diphenyleneiodonium significantly reduced the OC differentiation and decreased the intracellular ROS level in both Nrf2-deficient and wild-type cells. Pretreatment with sulforaphane and curcumin also inhibited the OC differentiation by activating Nrf2 in part. Nrf2 deficiency promoted the RANKL-induced activation of mitogen-activated protein kinases, including c-Jun N-terminal kinase, extracellular signal-regulated kinase, and p38; the induction of c-Fos; and the consequent induction of nuclear factor of activated T cells, cytoplasmic 1, a pivotal determinant of OC differentiation. Our results suggest that Nrf2 probably inhibits RANKL-induced OC differentiation by regulating the cellular redox status by controlling the expression of oxidative response genes, findings that might form the basis of a new strategy for treating inflammatory bone diseases.

NADPH oxidase inhibitor diphenyleneiodonium and reduced glutathione mitigate ethephon-mediated leaf senescence, H2O2 elevation and senescence-associated gene expression in sweet potato (Ipomoea batatas)

Ethephon, an ethylene releasing compound, promoted leaf senescence, H2O2 elevation, and senescence-associated gene expression in sweet potato. It also affected the glutathione and ascorbate levels, which in turn perturbed H2O2 homeostasis. The decrease of reduced glutathione and the accumulation of dehydroascorbate correlated with leaf senescence and H2O2 elevation at 72h in ethephon-treated leaves. Exogenous application of reduced glutathione caused quicker and significant increase of its intracellular level and resulted in the attenuation of leaf senescence and H2O2 elevation. A small H2O2 peak produced within the first 4h after ethephon application was also eliminated by reduced glutathione. Diphenyleneiodonium (DPI), an NADPH oxidase inhibitor, delayed leaf senescence and H2O2 elevation at 72h, and its influence was effective only within the first 4h after ethephon treatment. Ethephon-induced senescence-associated gene expression was repressed by DPI and reduced glutathione at 72h in pretreated leaves. Leaves treated with l-buthionine sulfoximine, an endogenous glutathione synthetase inhibitor, did enhance senescence-associated gene expression, and the activation was strongly repressed by reduced glutathione. In conclusion, ethephon-mediated leaf senescence, H2O2 elevation and senescence-associated gene expression are all alleviated by reduced glutathione and NADPH oxidase inhibitor DPI. The speed and the amount of intracellular reduced glutathione accumulation influence its effectiveness of protection against ethephon-mediated effects. Reactive oxygen species generated from NADPH oxidase likely serves as an oxidative stress signal and participates in ethephon signaling. The possible roles of NADPH oxidase and reduced glutathione in the regulation of oxidative stress signal in ethephon are discussed.

Expression of Pisum sativum PsAO3 gene, which encodes an aldehyde oxidase utilizing abscisic aldehyde, is induced under progressively but not rapidly imposed drought stress

Aldehyde oxidase (AO; EC 1.2.3.1) catalyzes the final step of abscisic acid (ABA) biosynthesis, which is the oxidation of abscisic aldehyde (ABAld) to ABA. Gene expression analyses indicate that the stress-induced Pisum sativum PsAOγ isoform, which effectively uses ABAld as a substrate, is encoded by the PsAO3 gene. PsAO3 was heterologously expressed in Pichia pastoris and the recombinant PsAO3 protein revealed substrate preferences highly similar to the native PsAOγ protein present in the pea leaves and roots. Both proteins prefer indole-3-aldehyde and naphthaldehyde as substrates, although high activities against abscisic aldehyde and citral were also observed. The Km values of PsAO3 for naphthaldehyde and abscisic aldehyde (4.6 and 5.1 μM, respectively) were the lowest among the substrates tested. PsAO3 activity was almost completely inhibited by potassium cyanide, diphenyleneiodonium, and methanol. Rapidly imposed drought stress did not increase the level of PsAO3 mRNA or activity of any AO isoform, although an enhanced ABA accumulation and induction of PsNCED2 and -3 (9-cis-epoxycarotenoid dioxygenase; EC 1.13.11.51) expression, both in the pea roots and leaves, was observed. During a progressively induced drought, the level of PsAO3 transcript and PsAOγ activity increased significantly in the roots and leaves, whereas ABA accumulation occurred only in the leaves where it was accompanied by induction of the PsNCED3 expression. Therefore, we suppose that next to NCED, also AO (mainly PsAOγ) might be involved in regulation of the drought-induced ABA synthesis. However, while the "constitutive activity" of PsAOγ is sufficient for the fast generation of ABA under rapid drought stress, the enhanced PsAOγ activity is required for the progressive and long-term ABA accumulation in the leaves under progressive drought stress.

Lipopolysaccharides elicit an oxidative burst as a component of the innate immune system in the seagrass Thalassia testudinum

This study represents the first report characterizing the biological effects of a lipopolysaccharide (LPS) immune modulator on a marine vascular plant. LPS was shown to serve as a strong elicitor of the early defense response in the subtropical seagrass Thalassia testudinum Banks ex König and was capable of inducing an oxidative burst identified at the single cell level. The formation of reactive oxygen species (ROS), detected by a redox-sensitive fluorescent probe and luminol-based chemiluminescence, included a diphenyleneiodonium sensitive response, suggesting the involvement of an NADPH oxidase. A 900 bp cDNA fragment coding for this enzyme was sequenced and found to encode a NAD binding pocket domain with extensive homology to the Arabidopsis thaliana rbohF (respiratory burst oxidase homolog) gene. The triggered release of ROS occurred at 20 min post-elicitation and was dose-dependent, requiring a minimal threshold of 50 μg/mL LPS. Pharmacological dissection of the early events preceding ROS emission indicated that the signal transduction chain of events involved extracellular alkalinization, G-proteins, phospholipase A2, as well as K(+), Ca(2+), and anion channels. Despite exclusively thriving in a marine environment, seagrasses contain ROS-generating machinery and signal transduction components that appear to be evolutionarily conserved with the well-characterized defense response systems found in terrestrial plants.

Subsets of human type 2 macrophages show differential capacity to produce reactive oxygen species

Reactive oxygen species (ROS) produced by macrophages have recently been shown to have immunosuppressive properties and induce regulatory T cells. Here we investigated the ROS producing capacity of well-defined human Mph2 subsets and studied the contribution of ROS in the Mph-T cell interaction. Mph were generated from monocytes using M-CSF (Mph2), IL-4 (Mph2a), or IL-10 (Mph2c). Upon PMA stimulation, Mph2 and Mph2c showed a high ROS producing capacity, whereas this was low for Mph2a. Mph2 and Mph2c displayed a reduced T cell stimulatory capacity compared to Mph2a. Addition of the ROS inhibitor DPI decreased the T cell proliferation and IFN-γ production. When testing directly on Mph, DPI dose-dependently decreased the IL-10 and IL-12p40 production of CD40L-stimulated Mph2 subsets. In conclusion, the ROS producing capacity is different among human Mph type-2 subsets. In all cases, DPI suppressed T cell proliferation and cytokine production, indicating a ROS-dependent mechanism of T cell activation.

Oxidative stress induced by P2X7 receptor stimulation in murine macrophages is mediated by c-Src/Pyk2 and ERK1/2

BACKGROUND

Activation of ATP-gated P2X7 receptors (P2X7R) in macrophages leads to production of reactive oxygen species (ROS) by a mechanism that is partially characterized. Here we used J774 cells to identify the signaling cascade that couples ROS production to receptor stimulation.

METHODS

J774 cells and mP2X7-transfected HEK293 cells were stimulated with Bz-ATP in the presence and absence of extracellular calcium. Protein inhibitors were used to evaluate the physiological role of various kinases in ROS production. In addition, phospho-antibodies against ERK1/2 and Pyk2 were used to determine activation of these two kinases.

RESULTS

ROS generation in either J774 or HEK293 cells (expressing P2X7, NOX2, Rac1, p47phox and p67phox) was strictly dependent on calcium entry via P2X7R. Stimulation of P2X7R activated Pyk2 but not calmodulin. Inhibitors of MEK1/2 and c-Src abolished ERK1/2 activation and ROS production but inhibitors of PI3K and p38 MAPK had no effect on ROS generation. PKC inhibitors abolished ERK1/2 activation but barely reduced the amount of ROS produced by Bz-ATP. In agreement, the amount of ROS produced by PMA was about half of that produced by Bz-ATP.

CONCLUSIONS

Purinergic stimulation resulted in calcium entry via P2X7R and subsequent activation of the PKC/c-Src/Pyk2/ERK1/2 pathway to produce ROS. This signaling mechanism did not require PI3K, p38 MAPK or calmodulin.

GENERAL SIGNIFICANCE

ROS is generated in order to kill invading pathogens, thus elucidating the mechanism of ROS production in macrophages and other immune cells allow us to understand how our body copes with microbial infections.

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.

The involvement of reactive oxygen species (ROS) in the cell cycle activation (G(0)-to-G(1) transition) of plant cells

Reactive oxygen species (ROS) are involved in various cellular processes in plants. Among those, resistance to abiotic stress, defence mechanisms and cell expansion have been intensively studied during the last years. We recently demonstrated that ROS, in concert with auxin, have a role in cell cycle activation of differentiated leaf cells.1 In this addendum we provide further evidence to show that oxidative stress/ROS accelerate auxin-mediated cell cycle entry (G(0)-to-G(1)) and may have a positive effect on the plant cell cycle machinery. A generalized model for concentration-dependent synergistic effect of auxin and ROS on differentiated plant cells is also shown.

Endothelium-independent relaxation of aortic rings by the nitric oxide synthase inhibitor diphenyleneiodonium

1. The flavoprotein binder diphenyleneiodonium (DPI) is a potent, irreversible inhibitor of nitric oxide synthase (NOS), but produces only a transient pressor response following systemic administration to animals, despite evidence of persistent NOS inhibition. To characterize further the effects of DPI on vascular tone, isometric tension was recorded from rat isolated aortic rings mounted between steel wires in an organ bath. 2. The NOS inhibitor NG-nitro-L-arginine methyl ester (L-NAME, 1 mM) initiated an additional contraction of prostaglandin F2 alpha-preconstricted rings with endothelium which was sustained throughout the period of L-NAME exposure (+234 +/- 39% at 15 min). In contrast, addition of DPI (5 microM) to rings with endothelium produced a transient initial contraction (+111 +/- 27% at 2 min) followed by a more sustained relaxation (-27 +/- 19% at 15 min, P < 0.001 vs L-NAME). 3. The contraction to DPI was also observed in rings without endothelium, was abolished by L-NAME pretreatment, and was unaffected by the alpha-adrenoreceptor inhibitor prazosin. Relaxation in response to DPI was not inhibited by endothelium removal or by pretreatment with either L-NAME or with the ATP-sensitive potassium channel blocker glibenclamide. 4. The endothelium-independent relaxation to DPI was inhibited at 23 degrees C and its time course was delayed by pretreatment with the guanylate cyclase inhibitor methylene blue. 5. Thus, in addition to a transient initial contraction due to NOS inhibition, DPI produces an endothelium-independent, temperature-dependent relaxation which appears in part due to activation of guanylate cyclase. This relaxant effect of DPI may explain the transient nature of its pressor effect in vivo despite sustained NOS inhibition.