The superoxide-forming enzymatic system of phagocytes

A Descriptive Review of the Action Mechanisms of Berberine, Quercetin and Silymarin on Insulin Resistance/Hyperinsulinemia and Cardiovascular Prevention

Insulin resistance (IR) and the associated hyperinsulinemia are early pathophysiological changes which, if not well treated, can lead to type 2 diabetes, endothelial dysfunction and cardiovascular disease. While diabetes care is fairly well standardized, the prevention and treatment of IR lacks a single pharmaceutical approach and many lifestyle and dietary interventions have been proposed, including a wide range of food supplements. Among the most interesting and well-known natural remedies, alkaloid berberine and the flavonol quercetin have particular relevance in the literature, while silymarin-the active principle of the Silybum marianum thistle-was traditionally used for lipid metabolism disorders and to sustain liver function. This review describes the major defects of insulin signaling leading to IR and the main properties of the three mentioned natural substances, their molecular targets and synergistic action mechanisms. The actions of berberine, quercetin and silymarin are partially superimposable as remedies against reactive oxygen intermediates generated by a high-lipid diet and by NADPH oxidase, which is triggered by phagocyte activation. Furthermore, these compounds inhibit the secretion of a battery of pro-inflammatory cytokines, modulate intestinal microbiota and are especially able to control the various disorders of the insulin receptor and post-receptor signaling systems. Although most of the evidence on the effects of berberine, quercetin and silymarin in modulating insulin resistance and preventing cardiovascular disease derive from experimental studies on animals, the amount of pre-clinical knowledge strongly suggests the need to investigate the therapeutic potential of these substances in human pathology.

Neuroprotective Potentials of Flavonoids: Experimental Studies and Mechanisms of Action

Neurological and neurodegenerative diseases, particularly those related to aging, are on the rise, but drug therapies are rarely curative. Functional disorders and the organic degeneration of nervous tissue often have complex causes, in which phenomena of oxidative stress, inflammation and cytotoxicity are intertwined. For these reasons, the search for natural substances that can slow down or counteract these pathologies has increased rapidly over the last two decades. In this paper, studies on the neuroprotective effects of flavonoids (especially the two most widely used, hesperidin and quercetin) on animal models of depression, neurotoxicity, Alzheimer's disease (AD) and Parkinson's disease are reviewed. The literature on these topics amounts to a few hundred publications on in vitro and in vivo models (notably in rodents) and provides us with a very detailed picture of the action mechanisms and targets of these substances. These include the decrease in enzymes that produce reactive oxygen and ferroptosis, the inhibition of mono-amine oxidases, the stimulation of the Nrf2/ARE system, the induction of brain-derived neurotrophic factor production and, in the case of AD, the prevention of amyloid-beta aggregation. The inhibition of neuroinflammatory processes has been documented as a decrease in cytokine formation (mainly TNF-alpha and IL-1beta) by microglia and astrocytes, by modulating a number of regulatory proteins such as Nf-kB and NLRP3/inflammasome. Although clinical trials on humans are still scarce, preclinical studies allow us to consider hesperidin, quercetin, and other flavonoids as very interesting and safe dietary molecules to be further investigated as complementary treatments in order to prevent neurodegenerative diseases or to moderate their deleterious effects.

NADPH Oxidases (NOX): An Overview from Discovery, Molecular Mechanisms to Physiology and Pathology

The reactive oxygen species (ROS)-producing enzyme NADPH oxidase (NOX) was first identified in the membrane of phagocytic cells. For many years, its only known role was in immune defense, where its ROS production leads to the destruction of pathogens by the immune cells. NOX from phagocytes catalyzes, via one-electron trans-membrane transfer to molecular oxygen, the production of the superoxide anion. Over the years, six human homologs of the catalytic subunit of the phagocyte NADPH oxidase were found: NOX1, NOX3, NOX4, NOX5, DUOX1, and DUOX2. Together with the NOX2/gp91phox component present in the phagocyte NADPH oxidase assembly itself, the homologs are now referred to as the NOX family of NADPH oxidases. NOX are complex multidomain proteins with varying requirements for assembly with combinations of other proteins for activity. The recent structural insights acquired on both prokaryotic and eukaryotic NOX open new perspectives for the understanding of the molecular mechanisms inherent to NOX regulation and ROS production (superoxide or hydrogen peroxide). This new structural information will certainly inform new investigations of human disease. As specialized ROS producers, NOX enzymes participate in numerous crucial physiological processes, including host defense, the post-translational processing of proteins, cellular signaling, regulation of gene expression, and cell differentiation. These diversities of physiological context will be discussed in this review. We also discuss NOX misregulation, which can contribute to a wide range of severe pathologies, such as atherosclerosis, hypertension, diabetic nephropathy, lung fibrosis, cancer, or neurodegenerative diseases, giving this family of membrane proteins a strong therapeutic interest.

Development of a caffeic acid–phthalimide hybrid compound for NADPH oxidase inhibition

NADPH oxidases are pharmacological targets for the treatment of inflammation-based diseases. This work presents the synthesis and study of a caffeic acid/phthalimide hybrid compound (C2) as a potential inhibitor of NADPH oxidases. Throughout the study, we have compared compound C2 with its precursor caffeic acid (C1). The redox properties were compared using three different antioxidant methodologies and showed that C2 was slightly less effective than C1, a well-established and robust antioxidant. However, C2 was three-fold more effective than albumin (used as a model protein). This chemical feature was decisive for the higher efficiency of C2 as an inhibitor of the release of superoxide anions by stimulated neutrophils and enzymatic activity of cell-free NADPH oxidase. Docking simulation studies were performed using the crystal structure of the recombinant dehydrogenase domain of the isoform NOX5 of C. stagnale, which retains the FAD cofactor (PDB: 5O0X). Considering that C2 could bind at the FAD redox site of NOX5, studies were conducted by comparing the interactions and binding energies of C1 and C2. The binding energies were −50.30 (C1) and −74.88 (C2) (kJ mol⁻¹), which is in agreement with the higher efficacy of the latter as an NADPH oxidase inhibitor. In conclusion, incorporating the phthalimide moiety into caffeic acid was decisive for its effectiveness as an NADPH oxidase inhibitor.

The incorporation of the phthalimide moiety into caffeic acid was decisive for its effectiveness as an NADPH oxidase inhibitor.

Hesperidin and SARS-CoV-2: New Light on the Healthy Function of Citrus Fruits

Among the many approaches to Coronavirus disease 2019 (COVID-19) prevention, the possible role of nutrition has so far been rather underestimated. Foods are very rich in substances, with a potential beneficial effect on health, and some of these could have an antiviral action or be important in modulating the immune system and in defending cells from the oxidative stress associated with infection. This short review draws the attention on some components of citrus fruits, and especially of the orange (Citrus sinensis), well known for its vitamin and flavonoid content. Among the flavonoids, hesperidin has recently attracted the attention of researchers, because it binds to the key proteins of the Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Several computational methods, independently applied by different researchers, showed that hesperidin has a low binding energy, both with the coronavirus "spike" protein, and with the main protease that transforms the early proteins of the virus (pp1a and ppa1b) into the complex responsible for viral replication. The binding energy of hesperidin to these important components is lower than that of lopinavir, ritonavir, and indinavir, suggesting that it could perform an effective antiviral action. Furthermore, both hesperidin and ascorbic acid counteract the cell damaging effects of the oxygen free radicals triggered by virus infection and inflammation. There is discussion about the preventive efficacy of vitamin C, at the dose achievable by the diet, but recent reviews suggest that this substance can be useful in the case of strong immune system burden caused by viral disease. Computational methods and laboratory studies support the need to undertake apposite preclinical, epidemiological, and experimental studies on the potential benefits of citrus fruit components for the prevention of infectious diseases, including COVID-19.

Quartz Disrupts Iron Homeostasis in Alveolar Macrophages To Impact a Pro-Inflammatory Effect

The biological response of bronchial epithelial cells to particles is associated with a sequestration of cell metal by the particle surface and a subsequent disruption in host iron homeostasis. The macrophage is the cell type resident in the respiratory tract that is most likely to make initial contact with inhaled particles. We tested the postulates that (1) silica, a prototypical particle, disrupts iron homeostasis in alveolar macrophages (AMs); and (2) the altered iron homeostasis results in both an oxidative stress and pro-inflammatory effects. Human AMs (1.0 × 10⁶/mL) demonstrated an increased import of iron following particle exposure with nonheme iron concentrations of 0.57 ± 0.03, 1.72 ± 0.09, 0.88 ± 0.09, and 3.21 ± 0.11 ppm in cells exposed for 4 h to media, 500 μM ferric ammonium citrate (FAC), 100 μg/mL silica, and both silica and FAC, respectively. Intracellular ferritin concentrations and iron release were similarly increased after AM exposure to FAC and silica. Silica increased oxidant generation by AMs measured using both dichlorofluorescein diacetate fluorescence and reduction of nitroblue tetrazolium salt. Concentrations of interleukin (IL)-1β, IL-6, IL-8, and tumor necrosis factor-α in macrophage supernatant increased following 100 μg/mL silica exposure for 24 h. Treatment of AMs with 500 μM FAC decreased both oxidant generation and cytokine release associated with silica exposure, supporting a dependence of these effects on sequestration of cell metal by the particle surface. We conclude that (1) silica exposure disrupts iron homeostasis resulting in increased import, accumulation, and release of the metal; and (2) the altered iron homeostasis following silica exposure impacts oxidant generation and pro-inflammatory effects.

Investigating Dynamic Molecular Events in Melanoma Cell Nucleus During Photodynamic Therapy by SERS

Photodynamic therapy (PDT) involves the uptake of photosensitizers by cancer cells and the irradiation of a light with a specific wavelength to trigger a series of photochemical reactions based on the generation of reactive oxygen, leading to cancer cell death. PDT has been widely used in various fields of biomedicine. However, the molecular events of the cancer cell nucleus during the PDT process are still unclear. In this work, a nuclear-targeted gold nanorod Raman nanoprobe combined with surface-enhanced Raman scattering spectroscopy (SERS) was exploited to investigate the dynamic intranuclear molecular changes of B16 cells (a murine melanoma cell line) treated with a photosensitizer (Chlorin e6) and the specific light (650 nm). The SERS spectra of the cell nucleus during the PDT treatment were recorded in situ and the spectroscopic analysis of the dynamics of the nucleus uncovered two main events in the therapeutic process: the protein degradation and the DNA fragmentation. We expect that these findings are of vital significance in having a better understanding of the PDT mechanism acting on the cancer cell nucleus and can further help us to design and develop more effective therapeutic platforms and methods.

Duox1 Regulates Primary B Cell Function under the Influence of IL-4 through BCR-Mediated Generation of Hydrogen Peroxide

Engagement of the BCR with Ags triggers signaling pathways for commitment of B lymphocyte responses that can be regulated, in part, by reactive oxygen species. To investigate the functional relevance of reactive oxygen species produced in primary B cells, we focused on the role of the hydrogen peroxide generator Duox1 in stimulated splenic B cells under the influence of the TH2 cytokine IL-4. We found that H2O2 production in wild type (WT) and Nox2-deficient CD19+ B cells was boosted concomitantly with enhanced expression of Duox1 following costimulation with BCR agonists together with IL-4, whereas stimulated Duox1-/- cells showed attenuated H2O2 release. We examined whether Duox1-derived H2O2 contributes to proliferative activity and Ig isotype production in CD19+ cells upon BCR stimulation. Duox1-/- CD19+ B cells showed normal responses of Ig production but a higher rate of proliferation than WT or Nox2-deficient cells. Furthermore, we demonstrated that the H2O2 scavenger catalase mimics the effect of Duox1 deficiency by enhancing proliferation of WT CD19+ B cells in vitro. Results from immunized mice reflected the in vitro observations: T cell-independent Ag induced increased B cell expansion in germinal centers from Duox1-/- mice relative to WT and Nox2-/- mice, whereas immunization with T cell-dependent or -independent Ag elicited normal Ig isotype secretion in the Duox1 mutant mice. These observations, obtained both by in vitro and in vivo approaches, strongly suggest that Duox1-derived hydrogen peroxide negatively regulates proliferative activity but not Ig isotype production in primary splenic CD19+ B cells.

Effects of homœopathic preparations of organic acids and minerals on the oxidative metabolism of human neutrophils

A number of different potencies of commercially available homœopathic preparations in saline solution were tested for their ability to regulate the oxidative metabolism (superoxide production) and adhesion function of human neutrophils in vitro. 15% to 30% inhibition of oxidative metabolism was caused by Sulphur 6x, Manganum phosphoricum 6x and 8x, and Magnesium phosphoricum 6x and 8x. Phosphorus slightly reduced superoxide production, with varying results in a series of experiments. Using Magnesium phosphoricum and Phosphorus, small inhibitory effects (8–11%) were noted event at high potencies. Among the organic acids, a group (Acidum malicum 4x and Acidum fumaricum 4x) enhanced superoxide production, while others either inhibited the response (Acidum citricum and Acidum succinicum, 3x and 4x) or had no effect (Acidum α-ketoglutaricum and Acidum cis-aconitum). Attempts to reproduce these effects using solutions prepared in the laboratory confirmed the inhibitory effects of Manganum phosphoricum 6x and of organic acids in the 3x, while other data indicated that critical factors in the methodology of preparation may affect the results.

Se@SiO2 nanocomposites suppress microglia-mediated reactive oxygen species during spinal cord injury in rats

Selenium (Se) is an essential trace element with strong antioxidant activity, showing a great prospect in the treatment of spinal cord injury (SCI). However, the narrow gap between the beneficial and toxic effects has limited its further clinical application. In this experiment, we used porous Se@SiO2 nanocomposites (Se@SiO2) modified by nanotechnology as a new means of release control to investigate the anti-oxidative effect in SCI. In vitro Se@SiO2 toxicity, anti-oxidative and anti-inflammatory effects on microglia were assayed. In vivo we investigated the protective effect of Se@SiO2 to SCI rats. Neurological function was evaluated by Basso, Beattie and Bresnahan (BBB). The histopathological analysis, microglia activation, oxidative stress, inflammatory factors (TNF-α, IL-1β and IL-6) and apoptosis were detected at 3 and 14 days after SCI. The favorable biocompatibility of Se@SiO2 suppressed microglia activation, which is known to be associated with oxidative stress and inflammation in vivo and in vitro. In addition, Se@SiO2 improved the rat neurological function and reduced apoptosis via caspase-3, Bax and Bcl-2 pathways in SCI. Se@SiO2 was able to treat SCI and reduce oxidative stress, inflammation and apoptosis induced by microglia activation, which may provide a novel and safe strategy for clinical application.

Possible Involvement of Nitric Oxide and Peroxynitrite in Nasal Polyposis

Background

Nitric oxide (NO) is implicated in inflammation. Its role in the pathogenesis of nasal polyposis is not clear.

Methods

The expression of inducible NO synthase (iNOS), and the production of peroxynitrite represented by the formation of 3-nitrotyrosine (3-NT) were examined by immunohisto-chemistry in nasal polyps. The contents of superoxide dismutases (SODs) in nasal polyps and nasal mucosa were assessed by Western blot analyses.

Results

iNOS expression and 3-NT accumulation were noted in mucosal epithelium, vascular endothelium, and interstitial cells of nasal polyps. In comparison with our previous study on the nasal mucosa from patients with rhinitis, the stromal cells of the nasal polyp had higher labeling intensity for both iNOS and 3-NT. The polyp showed similar levels of CuZnSOD and MnSOD as those of nasal mucosa.

Conclusions

The iNOS/NO system may be important in the pathophysiology of nasal polyposis. The increased peroxynitrite may result from increased iNOS expression but is not related to decreased SODs.

Ehrlichia chaffeensis and Its Invasin EtpE Block Reactive Oxygen Species Generation by Macrophages in a DNase X-Dependent Manner

The obligatory intracellular pathogen Ehrlichia chaffeensis lacks most genes that confer resistance to oxidative stress but can block reactive oxygen species (ROS) generation by host monocytes-macrophages. Bacterial and host molecules responsible for this inhibition have not been identified. To infect host cells, Ehrlichia uses the C terminus of its surface invasin, entry-triggering protein of Ehrlichia (EtpE; EtpE-C), which directly binds the mammalian cell surface receptor glycosylphosphatidylinositol-anchored protein DNase X. We investigated whether EtpE-C binding to DNase X blocks ROS production by mouse bone marrow-derived macrophages (BMDMs). On the basis of a luminol-dependent chemiluminescence assay, E. chaffeensis inhibited phorbol myristate acetate (PMA)-induced ROS generation by BMDMs from wild-type, but not DNase X^−/−, mice. EtpE-C is critical for inhibition, as recombinant EtpE-C (rEtpE-C)-coated latex beads, but not recombinant N-terminal EtpE-coated or uncoated beads, inhibited PMA-induced ROS generation by BMDMs from wild-type mice. DNase X is required for this inhibition, as none of these beads inhibited PMA-induced ROS generation by BMDMs from DNase X^−/− mice. Previous studies showed that E. chaffeensis does not block ROS generation in neutrophils, a cell type that is a potent ROS generator but is not infected by E. chaffeensis. Human and mouse peripheral blood neutrophils did not express DNase X. Our findings point to a unique survival mechanism of ROS-sensitive obligate intramonocytic bacteria that involves invasin EtpE binding to DNase X on the host cell surface. This is the first report of bacterial invasin having such a subversive activity on ROS generation.

Ehrlichia chaffeensis preferentially infects monocytes-macrophages and causes a life-threatening emerging tick-transmitted infectious disease called human monocytic ehrlichiosis. Ehrlichial infection, and hence the disease, depends on the ability of this bacterium to avoid or overcome powerful microbicidal mechanisms of host monocytes-macrophages, one of which is the generation of ROS. Our findings reveal that an ehrlichial surface invasin, EtpE, not only triggers bacterial entry but also blocks ROS generation by host macrophages through its host cell receptor, DNase X. As ROS sensitivity is an Achilles’ heel of this group of pathogens, understanding the mechanism by which E. chaffeensis rapidly blocks ROS generation suggests a new approach for developing effective anti-infective measures. The discovery of a ROS-blocking pathway is also important, as modulation of ROS generation is important in a variety of ailments and biological processes.

Alcohol, Aldehyde, and Ketone Liberation and Intracellular Cargo Release through Peroxide-Mediated α-Boryl Ether Fragmentation

α-Boryl ethers, carbonates, and acetals, readily prepared from the corresponding alcohols that are accessed through ketone diboration, react rapidly with hydrogen peroxide to release alcohols, aldehydes, and ketones through the collapse of hemiacetal intermediates. Experiments with α-boryl acetals containing a latent fluorophore clearly demonstrate that cargo can be released inside cells in the presence of exogenous or endogenous hydrogen peroxide. These experiments show that this protocol can be used for drug activation in an oxidative environment without generating toxic byproducts.

Sensing Glucose in Urine and Serum and Hydrogen Peroxide in Living Cells by Use of a Novel Boronate Nanoprobe Based on Surface-Enhanced Raman Spectroscopy

Hydrogen peroxide (H2O2) is known as a key molecule in a variety of biological processes, as well as a crucial byproduct in many enzymatic reactions. Therefore, being able to selectively and sensitively detect H2O2 is not only important in monitoring, estimating, and decoding H2O2 relevant physiological pathways but also very helpful in developing enzymatic-based biosensors for other analytes of interest. Herein, we report a plasmonic probe for H2O2 based on 3-mercaptophenylboronic acid (3-MPBA) modified gold nanoparticles (AuNPs) which is coupled with surface-enhanced Raman scattering (SERS) to yield a limit of detection (LOD) of 70 nM. Our probe quantifies both exogenous and endogenous H2O2 levels in living cells and can further be coupled with glucose oxidase (GOx) to achieve quantitative and selective detection of glucose in artificial urine and human serum.

High Spatial Resolution Imaging of Endogenous Hydrogen Peroxide in Living Cells by Solid-State Fluorescence

Herein, we describe selective imaging of hydrogen peroxide using a precipitating dye conjugated to a boronic acid-based immolative linker. We achieved visualization of endogenous hydrogen peroxide in phagosomes by solid-state two-photon fluorescence imaging in living cells with exceptionally high spatial resolution.

The Pathophysiology of Phagocytes

No survey of clinically important immunological phenomena would be complete without consideration of the functions of phagocytic cells. They play a pivotal role in the immune response by kiling microbes, by presenting antigens to lymphocytes and by serving as supportive, accessory cells to lymphocytes, at least partly by releasing soluble factors. The phagocytes of the body, professional and non professional, consist of two specialized groups of cells: granulocytes, which can be mobilized rapidly and which reach inflamed sites quickly and in large numbers, and which are highly efficient at dealing with many types of injury and infection but which have no capacity for differentiation and live only a short time; and the mononuclear phagocyte system consisting partly of motile cells which respond initially more slowly than neutrophils but which can differentiate in sites of inflammation into cells which are more efficient in various functions than the cells from which they originated. Many mononuclear phagocytes are fixed cells located in tissues where they act as trays or filters for material circulating through the tissue. Phagocytes, which usually function as the primary defender in infections, have also been implicated as effector cells in several conditions characterized by a destructive inflammatory response.

Carbazole-based two-photon fluorescent probe for selective imaging of mitochondrial hydrogen peroxide in living cells and tissues

The two-photon imaging in living cells and tissue demonstrated that the prepared probe possessed high specificity for mitochondrial H₂O₂.

Simultaneous fluorescence visualization of mitochondrial hydrogen peroxide and zinc ions in live cells and in vivo

We have developed two new fluorescent probes termedM-H2O2andM-Znfor simultaneous imaging of hydrogen peroxide and zinc ions in mitochondria.

Protective role of carbon dioxide (CO2) in generation of reactive oxygen species

The results testify to the fact that CO2 is a powerful inhibitor of reactive oxygen species (ROS) generation by cells (blood phagocytes and alveolar macrophages of 96 people and cells of inner organs and tissue phagocytes (of liver, brain, myocardium, lungs, kidneys, stomach, and skeleton muscles), as well as by mitochondria of the liver of 186 white mice and human tissues. Generation of ROS was determined using various methods with CO2 directly acting on the cells and bioptates and indirectly on the organism as a whole. CO2 in the concentration of 5.1% (P = 37.5 mmHg), 8.2% (P = 60.0 mmHg), and 20% (P = 146.0 mmHg) in a mixture with air (total pressure = 730 mmHg) inhibits the basal ROS generation by phagocytes on the average by 3.52, 5.69, and 10.03 times, respectively (p < 0.05), and the stimulated by corpuscular particles: (a) zymosan by 3.24, 4.43, and 7.95 times; (b)SiO2: by 2.99, 3.24, and 5.76 times (p < 0.05). This is confirmed by the feet that CO2, along with inhibiting the O2 (-) generation by cells of the various organs, including the liver, as a rule, by 2.19-4.7 times, p < 0.01 or <0.001 induces simultaneously a decrease in the O2 (-) generation by mitochondria isolated from the liver (by 1.91-3.2 times, p < 0.001). The mechanism of CO2 influence is realized, in part, by inhibition of NADPH-oxidase activity. Taken into consideration proven role of CO2 in different pathophysiological conditions, (such as endoarteritis, bronchial asthma, and infectious diseases), present findings may be of clinical interest in terms of potential implementation of CO2 donors as adjuvant therapeutics in these diseases.

Pooling and Analysis of Published in Vitro Data: A Proof of Concept Study for the Grouping of Nanoparticles

The study aim was to test the applicability of pooling of nanomaterials-induced in vitro data for identifying the toxic capacity of specific (SiO₂, TiO₂, ZnO, CuO, CeO₂ and carbon nanotubes, [CNT]) nanoparticles (NP) and to test the usefulness for grouping purposes. Publication selection was based on specific criteria regarding experimental conditions. Two relevant biological endpoints were selected; generation of intracellular reactive oxygen species (ROS) and viability above 90%. The correlations of the ROS ratios with the NP parameters' size, concentration, and exposure time were analysed. The obtained data sets were then analysed with multiple regression analysis of variance (ANOVA) and the Tukey post-hoc test. The results show that this method is applicable for the selected metal oxide NP, but might need reconsideration and a larger data set for CNT. Several statistically significant correlations and results were obtained, thus validating the method. Furthermore, the relevance of the combination of ROS release with a cell viability test was shown. The data also show that it is advisable to compare ROS production of professional phagocytic with non-phagocytic cells. In conclusion, this is the first systematic analysis showing that pooling of available data into groups is a useful method for evaluation of data regarding NP induced toxicity in vitro.

Inhibition of the phospholipase A2 activity of peroxiredoxin 6 prevents lung damage with exposure to hyperoxia

Lung injury associated with hyperoxia reflects in part the secondary effects of pulmonary inflammation and the associated production of reactive oxygen species due to activation of NADPH oxidase, type 2 (NOX2). Activation of NOX2 requires the phospholipase A2 (PLA2) activity of peroxiredoxin 6 (Prdx6). Therefore, we evaluated whether blocking Prdx6 PLA2 activity using the inhibitor MJ33 would be protective in a mouse model of acute lung injury resulting from hyperoxic exposure. Mice were treated with an intraperitoneal injection of MJ33 (2.5nmol/g body weight) at the start of exposure (zero time) and at 48h during continuous exposure to 100% O2 for 80h. Treatment with MJ33 reduced the number of neutrophils and the protein content in the fluid obtained by bronchoalveolar lavage, inhibited the increase in lipid peroxidation products in lung tissue, decreased the number of apoptotic cells in the lung, and decreased the perivascular edema associated with the 80h exposure to hyperoxia. Thus, blocking Prdx6 PLA2 activity by MJ33 significantly protected lungs against damage from hyperoxia, presumably by preventing the activation of NOX2 and the amplification of lung injury associated with inflammation. These findings demonstrate that MJ33, a potent inhibitor of Prdx6 PLA2 activity, can protect mouse lungs against the manifestations of acute lung injury due to oxidative stress.

Temporal changes in hepatic antioxidant enzyme activities after ischemia and reperfusion in a rat liver ischemia model

This study investigated the hypothesis that administration of tilapia fish oil diet would attenuate warm liver ischemia/reperfusion injury (IRI) and whether fish oil modulates prooxidant/antioxidant status. Male Wistar rats were subjected to 30 min of approximately 70% hepatic ischemia followed by 1, 12, and 24 h reperfusion. Rats were randomly divided into three groups: sham-operated group (SO), control–warm hepatic ischemia (WI) group, and Oil–WI group given tilapia oil for 3 weeks followed by liver IRI. Aspartate aminotransferase (AST) and alanine aminotransferase (ALT) levels were measured in the plasma. Levels of thiobarbituric acid reactive substances (TBARS) and antioxidant enzymes as superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPx) activities were measured in liver fractions.

In the sham group, there was no enzymatic or histological change. I/R caused significant increase in serum AST, ALT, and tissue TBARS levels. As compared to the control group, animals treated with tilapia oil experienced a significant decrease ( p < 0.05) in AST and ALT levels in reperfusion periods. Tissue TBARS levels in Oil–WI group were significantly ( p < 0.05) reduced as compared to control group at 60 min after reperfusion. After ischemia, 1, 12, and 24 h of reperfusion, CAT, SOD, and GPx values were the lowest in the Oil–WI group and highest in the control group and were statistically significant ( p < 0.05). Histological analysis also revealed that fish oil provided some protection compared with the control group.

Tilapia oil exerts a protective effect during the early phase of reperfusion, and it modulates prooxidant/antioxidant status of rat liver subjected to warm IRI.

Comparative study of β-glucan induced respiratory burst measured by nitroblue tetrazolium assay and real-time luminol-enhanced chemiluminescence assay in common carp (Cyprinus carpio L.)

The respiratory burst is an important feature of the immune system. The increase in cellular oxygen uptake that marks the initiation of the respiratory burst is followed by the production of reactive oxygen species (ROS) such as superoxide anion and hydrogen peroxide which plays a role in the clearance of pathogens and tissue regeneration processes. Therefore, the respiratory burst and associated ROS constitute important indicators of fish health status. This paper compares two methods for quantitation of ROS produced during the respiratory burst in common carp: the widely used, single-point measurement based on the intracellular reduction of nitroblue tetrazolium (NBT) and a real-time luminol-enhanced assay based on the detection of native chemiluminescence. Both assays allowed for detection of dose-dependent changes in magnitude of the respiratory burst response induced by β-glucans in head kidney cells of carp. However, whereas the NBT assay was shown to detect the production of only superoxide anions, the real-time luminol-enhanced assay could detect the production of both superoxide anions and hydrogen peroxide. Only the chemiluminescence assay could reliably record the production of ROS on a real-time scale at frequent and continual time intervals for time course experiments, providing more detailed information on the respiratory burst response. The real-time chemiluminescence assay was used to measure respiratory burst activity in macrophage and neutrophilic granulocyte-enriched head kidney cell fractions and total head kidney cell suspensions and proved to be a fast, reliable, automated multiwell microplate assay to quantitate fish health status modulated by β-glucans.

Molecular mechanisms involved in the bidirectional relationship between diabetes mellitus and periodontal disease

Both diabetes and periodontitis are chronic diseases. Diabetes has many adverse effects on the periodontium, and conversely periodontitis may have deleterious effects further aggravating the condition in diabetics. The potential common pathophysiologic pathways include those associated with inflammation, altered host responses, altered tissue homeostasis, and insulin resistance. This review examines the relationship that exists between periodontal diseases and diabetes mellitus with a focus on potential common pathophysiologic mechanisms.

Carp head kidney leukocytes display different patterns of oxygen radical production after stimulation with PAMPs and DAMPs

Wound healing and tissue regeneration are essential mechanisms to ensure the survival and health of any organism. Despite this, only a few studies have been devoted to study tissue regeneration during wound healing in fish. Reactive oxygen species (ROS), in particular hydrogen peroxide, play an important dual role both for promoting tissue repair, but also for eradication of pathogens. This study aims at dissecting the contribution of PAMPs (using β-glucan) and DAMPs in the respiratory burst response of carp head kidney-derived leukocytes, and address their contribution to wound healing processes. Consistent with a pathogen eradication strategy, ROS responses to PAMP stimulation (β-glucan) was fast, vigorous and highly dominated by production of superoxide anion. In contrast, stimulation with DAMPs led to a slow, subtle but long-lasting production of oxygen radicals dominated by hydrogen peroxide. Using an in vitro model of scratch-wounded CCB fibroblast cell cultures and a novel PhotoID proliferation assay, stimulation with low and continuous levels of hydrogen peroxide (5 μM) led to a slight increase in the percentage of wound recovery and thus promoted wound closure. In contrast, high doses of hydrogen peroxide (300 μM) impaired fibroblast scratch-wound recovery and caused cell death. These results elucidate the capacity of hydrogen peroxide to influence the fate of tissue regeneration through the establishment of environments suitable for promoting either tissue regeneration or oxidative stress and thereby potential tissue damage. Direct in vitro stimulation with β-glucans did not impact fibroblast scratch-wound recovery, which further suggests that interaction with tissue-resident leukocytes or other components of the fish immune system are required to induce fibroblast proliferation and thus for the accelerated wound healing promoted by β-glucan stimulation.

Regulation of alveolar macrophage p40phox: hierarchy of activating kinases and their inhibition by PGE2

PGE(2), produced in the lung during infection with microbes such as Klebsiella pneumoniae, inhibits alveolar macrophage (AM) antimicrobial functions by preventing H(2)O(2) production by NADPH oxidase (NADPHox). Activation of the NADPHox complex is poorly understood in AMs, although in neutrophils it is known to be mediated by kinases including PI3K/Akt, protein kinase C (PKC) δ, p21-activated protein kinase (PAK), casein kinase 2 (CK2), and MAPKs. The p40phox cytosolic subunit of NADPHox has been recently recognized to function as a carrier protein for other subunits and a positive regulator of oxidase activation, a role previously considered unique to another subunit, p47phox. The regulation of p40phox remains poorly understood, and the effect of PGE(2) on its activation is completely undefined. We addressed these issues in rat AMs activated with IgG-opsonized K. pneumoniae. The kinetics of kinase activation and the consequences of kinase inhibition and silencing revealed a critical role for a PKCδ-PAK-class I PI3K/Akt1 cascade in the regulation of p40phox activation upon bacterial challenge in AMs; PKCα, ERK, and CK2 were not involved. PGE(2) inhibited the activation of p40phox, and its effects were mediated by protein kinase A type II, were independent of interactions with anchoring proteins, and were directed at the distal class I PI3K/Akt1 activation step. Defining the kinases that control AM p40phox activation and that are the targets for inhibition by PGE(2) provides new insights into immunoregulation in the infected lung.

Local oxidative and nitrosative stress increases in the microcirculation during leukocytes-endothelial cell interactions

Leukocyte-endothelial cell interactions and leukocyte activation are important factors for vascular diseases including nephropathy, retinopathy and angiopathy. In addition, endothelial cell dysfunction is reported in vascular disease condition. Endothelial dysfunction is characterized by increased superoxide (O₂^•−) production from endothelium and reduction in NO bioavailability. Experimental studies have suggested a possible role for leukocyte-endothelial cell interaction in the vessel NO and peroxynitrite levels and their role in vascular disorders in the arterial side of microcirculation. However, anti-adhesion therapies for preventing leukocyte-endothelial cell interaction related vascular disorders showed limited success. The endothelial dysfunction related changes in vessel NO and peroxynitrite levels, leukocyte-endothelial cell interaction and leukocyte activation are not completely understood in vascular disorders. The objective of this study was to investigate the role of endothelial dysfunction extent, leukocyte-endothelial interaction, leukocyte activation and superoxide dismutase therapy on the transport and interactions of NO, O₂^•− and peroxynitrite in the microcirculation. We developed a biotransport model of NO, O₂^•− and peroxynitrite in the arteriolar microcirculation and incorporated leukocytes-endothelial cell interactions. The concentration profiles of NO, O₂^•− and peroxynitrite within blood vessel and leukocytes are presented at multiple levels of endothelial oxidative stress with leukocyte activation and increased superoxide dismutase accounted for in certain cases. The results showed that the maximum concentrations of NO decreased ∼0.6 fold, O₂^•− increased ∼27 fold and peroxynitrite increased ∼30 fold in the endothelial and smooth muscle region in severe oxidative stress condition as compared to that of normal physiologic conditions. The results show that the onset of endothelial oxidative stress can cause an increase in O₂^•− and peroxynitrite concentration in the lumen. The increased O₂^•− and peroxynitrite can cause leukocytes priming through peroxynitrite and leukocytes activation through secondary stimuli of O₂^•− in bloodstream without endothelial interaction. This finding supports that leukocyte rolling/adhesion and activation are independent events.

Periodontitis and risk of diabetes mellitus

Diabetes mellitus (DM) is a complex disease with varying degrees of systemic and oral complications. The periodontium is also a target for diabetic damage. Diabetes is a pandemic in both developed and developing countries. In recent years, a link between periodontitis and diabetes mellitus has been postulated. The oral cavity serves as a continuous source of infectious agents that could further worsen the diabetic status of the patient and serve as an important risk factor deterioration of diabetes mellitus. The present review highlights the relationship between diabetes mellitus and periodontitis. The potential mechanisms involved in the deterioration of diabetic status and periodontal disease are also discussed.

Aging, Neurodegenerative Disease and the Brain

L'eorganisation anatomique et chimique du cerveau humain subit de nombreux changements au cours du vieillissement. Certains neurons meurent, d'autres s'atrophient et ily a une réduction marquée du nombre de synapses dans des régions spécifiques du cerveau. Des diminutions du métabolisme du glucose et des effets pré- et post-synaptiques des neurotransmetteurs ont aussi été rapportées. À l'exception de certaines structures sous-corticales, il existe cependant une controverse quant à la sévérité des changements dans l'ensemble du cerveau. De plus, les effets du vieillissement sont très variables d'une région du cerveau à l'autre ainsi que d'un individu à l'autre. Certains phénomènes observès dans le vieillissement normal, tels la perte des neurones dopaminergique de la substance noire et celle des neurones cholinergiques du prosencé;phale basal, apparaissent sous une forme grandement exacerbées dans diverses pathologies neurodégénératives comme les maladies de Parkinson et d'Alzeimer. Les faibles altérations qui surviennent au niveau de ces systémes lors du vieillissement normal pourraient étre responsables des troubles d'équilibre, de la pauvreté de mouvement et des pertes de mémoires que l'on observent chez les gens âgés. Cependant, l'inflammation chronique du cerveau semble être une caractéristique typique des individus atteints de maladies neurodégénératives. L'hypothèse voulant que cette inflammation puisse être ralentie par un traitement avec des agents anti-inflammatoires a été supportée par les résultats de 19 études épidémiologiques ainsi que par un essai clinique de moindre envergure. Cependant, d'Autres études cliniques devront ètre réalisées et une attention particulière devra être portée aux effets secondaires de la thérapie anti-inflammatoire conventionnelle afin d'en arriver à une conclusion définitive.

Evaluation of therapeutic effects of astaxanthin on impairments in salivary secretion

The involvement of reactive oxygen species (ROS) in the pathophysiology of Sjögren's syndrome (SS), an autoimmune disorder, and irradiation-induced impairments in salivary secretion has been reported. Meanwhile, the strong antioxidant astaxanthin (Ast) has been suggested to have therapeutic effects on various diseases. In the present study, we examined the ROS scavenging capacity of Ast using a human salivary gland epithelial cell line (HSY) and investigated the effects of Ast on salivary secretion in a mouse model of irradiation-induced salivary gland dysfunction. Furthermore, we performed a clinical study of Ast in six SS patients and six normal individuals, quantifying the volume of saliva secretion and the level of oxidative stress markers in the saliva. Ast partially suppressed hydrogen peroxide-induced ROS in HSY cells. The mouse model demonstrated that the pre-administration of Ast resulted in the suppression of irradiation-induced hyposalivation. Furthermore, the administration of Ast appeared to increase salivary output in both the SS and normal groups. The level of oxidative stress marker, hexanoyl-lysine, in the saliva was reduced after Ast intake. These results suggest that Ast might act as an ROS scavenger, providing benefits to SS patients with impaired salivary secretion.

Electron spin resonance and spin trapping technique provide direct evidence that edaravone prevents acute ischemia–reperfusion injury of the liver by limiting free radical-mediated tissue damage

A novel free radical scavenger, 3-methyl-1-phenyl-2-pyrazolin-5-one (edaravone), is used for the treatment of acute ischemic stroke and is protective in several animal models of organ injury. We tested whether edaravone is protective against acute liver warm ischemia/reperfusion injury in the rat by acting as a radical scavenger. When edaravone was administered prior to ischemia and at the time of initiation of the reperfusion, liver injury was markedly reduced. Production of oxidants in the liver in this model was assessed in vivo by spin-trapping/electron spin resonance (ESR) spectroscopy. Ischemia/reperfusion caused an increase in free radical adducts rapidly, an effect markedly blocked by edaravone. Furthermore, edaravone treatment blunted ischemia/reperfusion-induced elevation in pro-inflammatory cytokines, infiltration of leukocytes and lipid peroxidation in the liver. These results demonstrate that edaravone is an effective blocker of free radicals in vivo in the liver after ischemia/reperfusion, leading to prevention of organ injury by limiting the deleterious effects of free radicals.

Antioxidant Lignans from the Fruits of Broussonetia papyrifera

Nine new lignans, chushizisins A-I (1-9), and three known lignans, threo-1-(4-hydroxy-3-methoxyphenyl)-2-{4-[(E)-3-hydroxy-1-propenyl]-2-methoxyphenoxy}-1,3-propanediol (10), erythro-1-(4-hydroxy-3-methoxyphenyl)-2-{4-[(E)-3-hydroxy-1-propenyl]-2-methoxyphenoxy}-1,3-propanediol (11), and 3-[2-(4- hydroxyphenyl)-3-hydroxymethyl-2,3-dihydro-1-benzofuran-5-yl]propan-1-ol (12), were isolated from the fruits of Broussonetia papyrifera. Their structures were elucidated using spectroscopic methods. Compounds 1, 5, 6, 8, 9, and 11 exhibited antioxidant activities against H(2)O(2)-induced impairment in PC12 cells, while compounds 1, 2, 4, 7, and 11 showed DPPH radical-scavenging activities with IC(50) values of 236.8, 156.3, 273.9, 281.1, and 60.9 microM, respectively.

Calcium influx-dependent differential actions of superoxide and hydrogen peroxide on microvessel permeability

Our previous study demonstrated that reactive oxygen species (ROS) released from activated blood cells contribute significantly to the increased microvessel permeability during inflammation. This study aims to define the individual roles of hydrogen peroxide (H(2)O(2)) and superoxide in ROS-induced increases in permeability and endothelial intracellular Ca(2+) concentration ([Ca(2+)](i)) in individually perfused rat mesenteric venules. Microvessel permeability was determined by measuring hydraulic conductivity (L(p)). Endothelial [Ca(2+)](i) was measured in fura-2 AM-loaded microvessels. Perfusing microvessels with superoxide generated by hypoxanthine and xanthine oxidase (HX/XO) induced immediate and transient increases in L(p). The mean peak value, which occurred within 5 min of HX/XO exposure, was 4.3 +/- 0.6 times that of the control. In contrast, the perfusion of H(2)O(2) (100 and 500 microM) caused no immediate increases in L(p). A significant L(p) increase, 3.6 +/- 0.6 times the control value, occurred 30 min after the perfusion of H(2)O(2) at 500 microM. The perfusion of H(2)O(2) at 100 or 500 microM for 1 h increased L(p) to 6.6 +/- 0.9 and 11.3 +/- 3.6 times the control value, respectively. The increased endothelial [Ca(2+)](i) in HX/XO or H(2)O(2) perfused vessels was correlated with the time course of the increases in L(p). Inhibiting Ca(2+) influx by LaCl(3) prevented the permeability increase induced by HX/XO or H(2)O(2). These results demonstrated differential actions of superoxide and H(2)O(2) on microvessel permeability and endothelial [Ca(2+)](i). Superoxide-induced permeability increases were immediate and transient, whereas H(2)O(2)-induced permeability increases were progressive, demonstrating concentration and time dependence. Ca(2+) influx plays an essential role in both superoxide and H(2)O(2)-induced permeability increases.

IFATS collection: Selenium induces improvement of stem cell behaviors in human adipose-tissue stromal cells via SAPK/JNK and stemness acting signals

In the present study, the potential of selenium to enhance stem cell behavior through improvement of human adipose tissue-derived stromal cells (ATSCs) and the associated molecular mechanism was evaluated. Selenium-induced improvement in stem cell behavior of human ATSCs caused expression of several genes, indicating downregulated mature cell marker proteins coupled with increased cell growth and telomerase activities after the overexpression of Rex1, Nanog, OCT4, SOX2, KLF4, and c-Myc. Also, selenium-treated ATSCs significantly downregulated p53 and p21 tumor suppressor gene products. Selenium induced active growth and growth enhanced by the activation of signal proteins in ATSCs via the inhibition of reactive oxygen species-mediated phospho-stress-activated protein kinase/c-Jun N-terminal protein kinase activation. The selenium-induced activation of extracellular regulated kinases 1/2 and Akt in ATSCs resulted in a subsequent induction of the expression of stemness transcription factors, particularly Rex1, Nanog, and Oct4, along with definitive demethylation on regulatory regions of Rex-1, Nanog, and Oct4. The results of our small interfering RNA knockdown experiment showed that Rex1 plays a major role in the proliferation of selenium-induced ATSCs. Selenium-treated ATSCs also exhibited more profound differentiation into mesodermal and neural lineages. We performed a direct comparison of gene expression profiles in control ATSCs and selenium-treated ATSCs and delineated specific members of important growth factor, signaling, cell adhesion, and transcription factor families. The observations of improved life span and multipotency of selenium-treated ATSCs clearly indicate that selenium-treated ATSCs represent an extraordinarily useful candidate cell source for tissue regeneration. Disclosure of potential conflicts of interest is found at the end of this article.

NADPH oxidase: recent evidence for its role in erectile dysfunction

Important roles for reactive oxygen species (ROS) in physiology and pathophysiology have been increasingly recognized. Under normal conditions, ROS serve as signaling molecules in the regulation of cellular functions. However, enhanced ROS production as a result of the activation of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase contributes significantly to the pathogeneses of vascular diseases. Although it has become evident that increased ROS is associated with erectile dysfunction (ED), the sources of ROS in the penis remain largely unknown. In recent years, emergent evidence suggests the possible role of NADPH oxidase in inducing ED. In this review, we examine the relationship between ROS and ED in different disease models and discuss the current evidence basis for NADPH oxidase-derived ROS in ED.

An ICT-based approach to ratiometric fluorescence imaging of hydrogen peroxide produced in living cells

We present the synthesis, properties, and biological applications of Peroxy Lucifer 1 (PL1), a new fluorescent probe for imaging hydrogen peroxide produced in living cells by a ratiometric response. PL1 utilizes a chemoselective boronate-based switch to detect hydrogen peroxide by modulation of internal charge transfer (ICT) within a 1,8-naphthalimide dye. PL1 features high selectivity for hydrogen peroxide over similar reactive oxygen species, including superoxide, and nitric oxide, and a 65 nm shift in emission from blue-colored fluorescence to green-colored fluorescence upon reaction with peroxide. Two-photon confocal microscopy experiments in live macrophages show that PL1 can ratiometrically visualize localized hydrogen peroxide bursts generated in living cells at immune response levels.

Selenium attenuates ROS-mediated apoptotic cell death of injured spinal cord through prevention of mitochondria dysfunction; in vitro and in vivo study

The primary objective of this study was to determine the possible apoptotic cell death preventive effects of the antioxidant selenium using an experimental rat spinal cord injury (SCI) model and cultured spinal cord-derived neural progenitor cells (NPCs). Sodium selenite treatment exerted a profound preventive effect on apoptotic cell death, including p-P38, p-SAPK/JNK, caspases, and PARP activity, and ameliorated astrogliosis and hypomyelination, which occurs in regions of active cell death in the spinal cords of SCI rats. The foremost protective effect of selenite in SCI would therefore be manifested in the suppression of acute secondary apoptotic cell death. However, selenite does not appear to exert an anti-inflammatory function associated with active microglia and macrophage propagation or infiltration into the lesion site. Selenite-mediated neuroprotection has been linked to selenite's attenuation or inhibition of p38 mitogen-activated protein kinase, pSAPK/JNK, and Bax activation in in vitro and in vivo SCI lesion sites. Selenite also attenuated cell death via the prevention of cytochrome c release, caspase activation, and ROS accumulation in the cytosol. Also, our study showed that selenite administered immediately after SCI significantly diminishes functional deficits. The selenite-treated group recovered hind limb reflexes more rapidly, and a higher percentage of these rats regained responses to a greater degree than was seen in the untreated injured rats. Our data indicate that the therapeutic outcome of selenite is most likely the consequence of its comprehensive apoptotic cell death blocking effects, resulting in the protection of white matter, oligodendrocytes, and neurons, and the inhibition of astrogliosis. The finding that the administration of selenite prevents secondary pathological events in traumatic spinal cord injuries, and promotes the recovery of motor function in an animal model. Its efficacy may facilitate the development of novel drug targets for the treatment of SCI.

Iptakalim protects PC12 cell against H2O2-induced oxidative injury via opening mitochondrial ATP-sensitive potassium channel

The final common pathway in the demise of dopaminergic neurons in Parkinson's disease may involve oxidative stress and excitotoxicity. In this study, we examined the neuroprotective effects of a novel ATP-sensitive potassium channel (K(ATP)) opener, iptakalim (IPT), against H(2)O(2)-induced cytotoxicity in rat dopaminergic PC12 cells. Pretreatment with IPT could attenuate increased extracellular glutamate levels and inhibit calcium influxing induced by H(2)O(2). Moreover, IPT regulated the expressions of bcl-2 and bax which were responsible for inhibiting apoptosis in PC12 cells. These protective effects of IPT were abolished by selective mitoK(ATP) channel blocker 5-hydroxydecanoate. Therefore, IPT can protect PC12 cells against H(2)O(2)-induced oxidative injury via activating mitoK(ATP) channel.

Detection of superoxide anion generation by equine spermatozoa

OBJECTIVE

To identify the generation of the superoxide anion by equine spermatozoa.

SAMPLE POPULATION

Multiple ejaculates collected from 3 Thoroughbred stallions.

PROCEDURES

Induced superoxide production by reduced nicotinamide adenine dinucleotides (NAD[P]H; ie, reduced nicotinamide adenine dinucleotide [NADH] and reduced nicotinamide adenine dinucleotide phosphate [NADPH]) was measured by use of a nitroblue tetrazolium (NBT) reduction assay on whole spermatozoa and a cytochrome c reduction assay on isolated membrane fractions of spermatozoa. Localization of superoxide generation was determined by use of NBT cytochemistry.

RESULTS

A dose-dependent increase in NBT reduction was found in the presence of NADPH, which was inhibited by superoxide dismutase (SOD). The flavoprotein inhibitor, diphenyleneiodonium (DPI; 5 or 15 microM), significantly decreased NBT reduction. Cytochrome c reduction by plasma membranes of spermatozoa was significantly higher in the presence of NADPH than in its absence. Cytochemical staining of equine spermatozoa in the presence of NADPH and NADH revealed diaphorase labeling in the spermatozoon midpiece and head. This staining was inhibited by DPI and SOD.

CONCLUSIONS AND CLINICAL RELEVANCE

Results of our study indicate that superoxide generation is associated with a membrane-associated NAD(P)H oxidase present in equine spermatozoa, although mitochondrial generation of superoxide is also detected. This oxidase may play a role in cell signaling or may also contribute to cytopathic effects associated with oxidative stress in equine spermatozoa.