Involvement of reactive oxygen species produced via NADPH oxidase in tyrosine phosphorylation in human B- and T-lineage lymphoid cells

Monitoring in real time and far-red imaging of H2O2 dynamics with subcellular resolution

Monitoring H2O2 dynamics in conjunction with key biological interactants is critical for elucidating the physiological outcome of cellular redox regulation. Optogenetic hydrogen peroxide sensor with HaloTag with JF635 (oROS-HT635) allows fast and sensitive chemigenetic far-red H2O2 imaging while overcoming drawbacks of existing red fluorescent H2O2 indicators, including oxygen dependency, high pH sensitivity, photoartifacts and intracellular aggregation. The compatibility of oROS-HT635 with blue-green-shifted optical tools allows versatile optogenetic dissection of redox biology. In addition, targeted expression of oROS-HT635 and multiplexed H2O2 imaging enables spatially resolved imaging of H2O2 targeting the plasma membrane and neighboring cells. Here we present multiplexed use cases of oROS-HT635 with other green fluorescence reporters by capturing acute and real-time changes in H2O2 with intracellular redox potential and Ca2+ levels in response to auranofin, an inhibitor of antioxidative enzymes, via dual-color imaging. oROS-HT635 enables detailed insights into intricate intracellular and intercellular H2O2 dynamics, along with their interactants, through spatially resolved, far-red H2O2 imaging in real time.

The Role of NADPH Oxidase 2 in Leukocytes

NADPH oxidase (NOX) family members are major resources of intracellular reactive oxygen species (ROS). In the immune system, ROS derived from phagocytic NOX (NOX2) participate in both pathogen clearance and signaling transduction. The role of NOX2 in neutrophils and macrophages has been well studied as mutations in NOX2 subunits cause chronic granulomas disease (CGD). NOX2 is expressed across a wide range of immune cells and recent reports have demonstrated that NOX2-derived ROS play important roles in other immune cells during an immune response. In this review, we summarize current knowledge of functions of NADPH oxidase 2 in each subset of leukocytes, as well as associations of NOX2 deficiency with diseases associated specifically with autoimmunity and immune deficiency. We also discuss important knowledge gaps as well as potential future directions for NOX2 research.

Far-red and sensitive sensor for monitoring real time H2O2 dynamics with subcellular resolution and in multi-parametric imaging applications

H2O2 is a key oxidant in mammalian biology and a pleiotropic signaling molecule at the physiological level, and its excessive accumulation in conjunction with decreased cellular reduction capacity is often found to be a common pathological marker. Here, we present a red fluorescent Genetically Encoded H2O2 Indicator (GEHI) allowing versatile optogenetic dissection of redox biology. Our new GEHI, oROS-HT, is a chemigenetic sensor utilizing a HaloTag and Janelia Fluor (JF) rhodamine dye as fluorescent reporters. We developed oROS-HT through a structure-guided approach aided by classic protein structures and recent protein structure prediction tools. Optimized with JF635, oROS-HT is a sensor with 635 nm excitation and 650 nm emission peaks, allowing it to retain its brightness while monitoring intracellular H2O2 dynamics. Furthermore, it enables multi-color imaging in combination with blue-green fluorescent sensors for orthogonal analytes and low auto-fluorescence interference in biological tissues. Other advantages of oROS-HT over alternative GEHIs are its fast kinetics, oxygen-independent maturation, low pH sensitivity, lack of photo-artifact, and lack of intracellular aggregation. Here, we demonstrated efficient subcellular targeting and how oROS-HT can map inter and intracellular H2O2 diffusion at subcellular resolution. Lastly, we used oROS-HT with other green fluorescence reporters to investigate the transient effect of the anti-inflammatory agent auranofin on cellular redox physiology and calcium levels via multi-parametric, dual-color imaging.

Roles of reactive oxygen species in inflammation and cancer

Reactive oxygen species (ROS) constitute a spectrum of oxygenic metabolites crucial in modulating pathological organism functions. Disruptions in ROS equilibrium span various diseases, and current insights suggest a dual role for ROS in tumorigenesis and the immune response within cancer. This review rigorously examines ROS production and its role in normal cells, elucidating the subsequent regulatory network in inflammation and cancer. Comprehensive synthesis details the documented impacts of ROS on diverse immune cells. Exploring the intricate relationship between ROS and cancer immunity, we highlight its influence on existing immunotherapies, including immune checkpoint blockade, chimeric antigen receptors, and cancer vaccines. Additionally, we underscore the promising prospects of utilizing ROS and targeting ROS modulators as novel immunotherapeutic interventions for cancer. This review discusses the complex interplay between ROS, inflammation, and tumorigenesis, emphasizing the multifaceted functions of ROS in both physiological and pathological conditions. It also underscores the potential implications of ROS in cancer immunotherapy and suggests future research directions, including the development of targeted therapies and precision oncology approaches. In summary, this review emphasizes the significance of understanding ROS-mediated mechanisms for advancing cancer therapy and developing personalized treatments.

Far-red and sensitive sensor for monitoring real time H2O2 dynamics with subcellular resolution and in multi-parametric imaging applications

H2O2 is a key oxidant in mammalian biology and a pleiotropic signaling molecule at the physiological level, and its excessive accumulation in conjunction with decreased cellular reduction capacity is often found to be a common pathological marker. Here, we present a red fluorescent Genetically Encoded H2O2 Indicator (GEHI) allowing versatile optogenetic dissection of redox biology. Our new GEHI, oROS-HT, is a chemigenetic sensor utilizing a HaloTag and Janelia Fluor (JF) rhodamine dye as fluorescent reporters. We developed oROS-HT through a structure-guided approach aided by classic protein structures and recent protein structure prediction tools. Optimized with JF635, oROS-HT is a sensor with 635 nm excitation and 650 nm emission peaks, allowing it to retain its brightness while monitoring intracellular H2O2 dynamics. Furthermore, it enables multi-color imaging in combination with blue-green fluorescent sensors for orthogonal analytes and low auto-fluorescence interference in biological tissues. Other advantages of oROS-HT over alternative GEHIs are its fast kinetics, oxygen-independent maturation, low pH sensitivity, lack of photo-artifact, and lack of intracellular aggregation. Here, we demonstrated efficient subcellular targeting and how oROS-HT can map inter and intracellular H2O2 diffusion at subcellular resolution. Lastly, we used oROS-HT with the green fluorescent calcium indicator Fluo-4 to investigate the transient effect of the anti-inflammatory agent auranofin on cellular redox physiology and calcium levels via multi-parametric, dual-color imaging.

Reactive oxygen species: The signal regulator of B cell

Reactive oxygen species (ROS) are indispensable for determining the fate of immune cells in both physiological and pathogenic environments, thus stimulating the interest of immunologists and clinicians. B cells are essential in maintaining immune homeostasis, and studies have indicated that ROS affect the maturation, activation and differentiation of B cells by controlling the signaling molecules in various molecular pathways. In the present review, we aimed to summarize the biological properties of ROS and the mechanisms by which ROS regulate B cell signaling pathways. We propose that ROS and their mediated signal transduction can be a new approach for manipulating B cell immune functions.

Prostaglandin E2 blocks menadione-induced apoptosis through the Ras/Raf/Erk signaling pathway in promonocytic leukemia cell lines

Altered oxidative stress has long been observed in cancer cells, and this biochemical property of cancer cells represents a specific vulnerability that can be exploited for therapeutic benefit. The major role of an elevated oxidative stress for the efficacy of molecular targeted drugs is under investigation. Menadione is considered an attractive model for the study of oxidative stress, which can induce apoptosis in human leukemia HL-60 cell lines. Prostaglandin E(2) (PGE(2)) via its receptors not only promotes cell survival but also reverses apoptosis and promotes cancer progression. Here, we present evidence for the biological role of PGE(2) as a protective agent of oxidative stress-induced apoptosis in monocytic cells. Pretreatment of HL-60 cells with PGE(2) markedly ameliorated the menadione-induced apoptosis and inhibited the degradation of PARP and lamin B. The EP(2) receptor antagonist AH6809 abrogated the inhibitory effect of PGE(2), suggesting the role of the EP(2)/cAMP system. The PKA inhibitor H89 also reversed apoptosis and decreased the PKA activity that was elevated 10-fold by PGE(2). The treatment of HL-60 cells with NAC or zinc chloride showed a similar protective effect as with PGE(2) on menadione-treated cells. Furthermore, PGE(2) activated the Ras/Raf/MEK pathway, which in turn initiated ERK activation, and ultimately protected menadione-induced apoptosis. These results imply that PGE(2) via cell survival pathways may protect oxidative stress-induced apoptosis in monocytic cells. This study warrants further pre-clinical investigation as well as application towards leukemia clinics.

Modulation of CD40-activated B lymphocytes by N-acetylcysteine involves decreased phosphorylation of STAT3

B lymphocyte activation, maturation and reshaping require the interaction of its receptor CD40 with its ligand CD154, which is expressed on activated T lymphocytes. Metabolism in activated B lymphocytes is also characterized with several REDOX changes including fluctuation of Reactive Oxygen Species (ROS). Herein, we first confirm that stimulation of human peripheral blood B lymphocyte with CD154 increases intracellular ROS level. Then, by treatments with two well-known antioxidants, N-acetylcysteine (NAC) and Trolox, we further investigate the influence of REDOX fluctuation in CD40-activated B lymphocyte homeostasis in long term culture (13 days). Treatments with NAC increase viability, decrease proliferation and Ig secretion and enhance homoaggregation of B lymphocytes while Trolox only induces a marginal increase of their Ig secretion. The NAC-induced homoaggregation phenotype is paralleled with increased expressions of CD54, CD11a, CD27 and CD38. Mechanistically, a 24h exposure of B lymphocytes with NAC is sufficient to show strong inhibition of STAT3 phosphorylation. Besides, the treatment of B lymphocytes with the STAT3 inhibitor VI increases viability and decreases proliferation and secretion as in NAC-treated cells thus showing a role for STAT3 in these NAC-induced phenotypes. This study done in a human-based model provides new findings on how REDOX fluctuations may modulate CD40-activated B lymphocytes during immune response and provide additional hints on NAC its immunomodulatory functions.

Adenosine A(2A) receptor activation limits chronic granulomatous disease-induced hyperinflammation

Chronic granulomatous disease (CGD) is caused by defects in the NADPH oxidase complex and is characterized by an increased susceptibility to infection. Other significant complications of CGD include autoimmunity and non-infectious hyperinflammatory disorders. We show that a gp91(phox) deficiency leads to the development of phenotypically altered T lymphocytes in mice and that this abnormal, hyperactive phenotype can be modulated by activation of the adenosine A(2A) receptor. T cells isolated from CGD mice produce significantly higher levels of the pro-inflammatory cytokines IFN-γ, IL-2, TNF-α, IL-4 and IL-13 than do WT cells after TCR-mediated activation; treatment with the selective adenosine A(2A) receptor agonist, CGS21680, potently inhibits this response. Additionally, the over exuberant inflammatory response elicited by thioglycollate challenge in gp91(phox) deficient mice is attenuated by CGS21680. These data suggest that treatment with A(2A)R agonists may be an effective therapy by which to regulate the immune system hyperactivity that results from a gp91(phox) deficiency.

Aberrant reactive oxygen and nitrogen species generation in rheumatoid arthritis (RA): causes and consequences for immune function, cell survival, and therapeutic intervention

The infiltration and persistence of hematopoietic immune cells within the rheumatoid arthritis (RA) joint results in elevated levels of pro-inflammatory cytokines, increased reactive oxygen (ROS) and -nitrogen (RNS) species generation, that feeds a continuous self-perpetuating cycle of inflammation and destruction. Meanwhile, the controlled production of ROS is required for signaling within the normal physiological reaction to perceived "foreign matter" and for effective apoptosis. This review focuses on the signaling pathways responsible for the induction of the normal immune response and the contribution of ROS to this process. Evidence for defects in the ability of immune cells in RA to regulate the generation of ROS and the consequence for their immune function and for RA progression is considered. As the hypercellularity of the rheumatoid joint and the associated persistence of hematopoietic cells within the rheumatoid joint are symptomatic of unresponsiveness to apoptotic stimuli, the role of apoptotic signaling proteins (specifically Bcl-2 family members and the tumor suppressor p53) as regulators of ROS generation and apoptosis are considered, evaluating evidence for their aberrant expression and function in RA. We postulate that ROS generation is required for effective therapeutic intervention.

Mitochondrial concept of leukemogenesis: key role of oxygen-peroxide effects

Background and hypothesis

The high sensitivity of hematopoietic cells, especially stem cells, to radiation and to pro-oxidative and other leukemogenic agents is related to certain of their morphological and metabolic features. It is attributable to the low (minimal) number of active mitochondria and the consequently slow utilization of O₂ entering the cell. This results in an increased intracellular partial pressure of O₂ (pO₂) and increased levels of reactive oxygen (ROS) and nitrogen (RNS) species, and a Δ(PO – AO) imbalance between the pro-oxidative (PO) and antioxidative (AO) constituents.

Proposed mechanism

Because excessive O₂ is toxic, we suggest that hematopoietic cells exist in a kind of unstable dynamic balance. This suggestion is based on the idea that mitochondria not only consume O₂ in the process of ATP production but also constitute the main anti-oxygenic stage in the cell's protective antioxidative system. Variations in the mitochondrial base capacity (quantity and quality of mitochondria) constitute an important and highly efficient channel for regulating the oxidative stress level within a cell.

The primary target for leukemogenic agents is the few mitochondria within the hematopoietic stem cell. Disturbance and weakening of their respiratory function further enhances the initial pro-oxidative state of the cell. This readily results in peroxygenation stress, creating the necessary condition for inducing leukemogenesis. We propose that this is the main cause of all related genetic and other disorders in the cell. ROS, RNS and peroxides act as signal molecules affecting redox-sensitive transcription factors, enzymes, oncogenes and other effectors. Thereby, they influence the expression and suppression of many genes, as well as the course and direction of proliferation, differentiation, leukemogenesis and apoptosis.

Differentiation of leukemic cells is blocked at the precursor stage. While the transformation of non-hematopoietic cells into tumor cells starts during proliferation, hematopoietic cells become leukemic at one of the interim stages in differentiation, and differentiation does not continue beyond that point. Proliferation is switched to differentiation and back according to a trigger principle, again involving ROS and RNS. When the leukemogenic Δ_L(PO – AO) imbalance decreases in an under-differentiated leukemia cell to the differentiation level Δ_D(PO – AO), the cell may continue to differentiate to the terminal stage.

Conclusion

The argument described in this article is used to explain the causes of congenital and children's leukemia, and the induction of leukemia by certain agents (vitamin K3, benzene, etc.). Specific research is required to validate the proposals made in this article. This will require accurate and accessible methods for measuring and assessing oxidative stress in different types of cells in general, and in hematopoietic cells in particular, in their different functional states.

Oxidation of mitochondrial peroxiredoxin 3 during the initiation of receptor-mediated apoptosis

It is hypothesized that activation of death receptors disrupts the redox homeostasis of cells and that this contributes to the induction of apoptosis. The redox status of the peroxiredoxins, which are extremely sensitive to increases in H2O2 and disruption of the thioredoxin system, were monitored in Jurkat T lymphoma cells undergoing Fas-mediated apoptosis. The only detectable change during the early stages of apoptosis was oxidation of mitochondrial peroxiredoxin 3. Increased H2O2 triggers peroxiredoxin overoxidation to a sulphinic acid; however during apoptosis peroxiredoxin 3 was captured as a disulfide, suggesting impairment of the thioredoxin system responsible for maintaining peroxiredoxin 3 in its reduced form. Peroxiredoxin 3 oxidation was an early event, occurring within the same timeframe as increased mitochondrial oxidant production, caspase activation and cytochrome c release. It preceded other major apoptotic events including mitochondrial permeability transition and phosphatidylserine exposure, and glutathione depletion, global thiol protein oxidation and protein carbonylation. Peroxiredoxin 3 oxidation was also observed in U937 cells stimulated with TNF-alpha. We hypothesize that the selective oxidation of peroxiredoxin 3 leads to an increase in mitochondrial H2O2 and that this may influence the progression of apoptosis.

Extracellular calcium sensing promotes human B-cell activation and function

Calcium is a second messenger for many signaling pathways in B cells, but its role as a receptor ligand has not been well characterized. However, pulses of free calcium were found to cause the rapid release of internal calcium stores in normal human B cells. This response appeared to be mediated by a cell surface protein with receptor properties as it could be blocked by pretreatment with trypsin and with kinase and phospholipase Cgamma inhibitors. The calcium receptor on B cells was not the conventional calcium-sensing receptor (CaSR) since B cells did not express CaSR and calcium-induced responses could not be blocked by specific CaSR inhibitors. B-cell responses to extracellular calcium activated phosphoinositide-3 kinase/AKT, calcineurin, extracellular signal regulated kinase, p38 mitogen-activated protein kinase, protein kinase C, Ca(2+)/calmodulin kinase II, and nuclear factor-kappaB signaling pathways, and resulted in transcription of the early response gene, CD83. This extracellular calcium sensor enhanced B-cell responses to Toll-like receptor, B-cell receptor, and cytokine receptor agonists. These findings suggest a means by which B cells prepare to engage in immune responses by responding to calcium fluctuations in their environment.

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

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

Cross-linking of MHC class II molecules interferes with phorbol 12,13-dibutyrate-induced differentiation of resting B cells by inhibiting Rac-associated ROS-dependent ERK/p38 MAP kinase pathways leading to NF-kappaB activation

In addition to their essential role in antigen presentation, major histocompatibility complex (MHC) class II molecules have been described as the receptor associated with signal transduction regulating B-cell function. In previous experiments, we found that cross-linking of MHC class II molecules with corresponding anti-MHC class II antibodies inhibited NF-kappaB-activated signaling pathways associated with the proliferation and differentiation of the LPS-stimulated primary and resting B-cell line, 38B9. We also found that exposure to the anti-MHC class II antibody reduced the production of ROS, which function as secondary signal transducers, in the phorbol 12,13-dibutyrate (PDBU)-treated (but not in the LPS-treated) resting B-cell line. In this study, we investigated the molecular mechanisms in the ROS-associated signaling pathway leading to PDBU-induced NF-kappaB activation that results in B-cell differentiation and speculated that the signaling pathway was inhibited by exposure to the anti-MHC class II antibody. We also found that this inhibition was mediated through down-regulation of the activated Rac/ROS-associated ERK/p38 MAPK signaling pathway in PDBU-treated 38B9 cells. Collectively, these findings suggest that ROS-associated molecules are involved in MHC class II-associated negative signal transduction in resting B cells.

Patients with Chronic Granulomatous Disease Have a Reduced Peripheral Blood Memory B Cell Compartment

In this study, we have identified an altered B cell compartment in patients with chronic granulomatous disease (CGD), a disorder of phagocyte function, characterized by pyogenic infections and granuloma formation caused by defects in NADPH activity. This is characterized by an expansion of CD5-expressing B cells, and profound reduction in B cells expressing the memory B cell marker, CD27. Both findings were independent of the age, genotype, and clinical status of the patients, and were not accompanied by altered CD5 and CD27 expression on T cells. Focusing on CD27-positive B cells, considered to be memory cells based on somatically mutated Ig genes, we found that the reduction was not caused by CD27 shedding or abnormal retention of CD27 protein inside the cell. Rather, it was determined that CD27-negative B cells were, appropriately, CD27 mRNA negative, consistent with a naive phenotype, whereas CD27-positive B cells contained abundant CD27 mRNA and displayed somatic mutations, consistent with a memory B cell phenotype. Thus, it appears that CGD is associated with a significant reduction in the peripheral blood memory B cell compartment, but that the basic processes of somatic mutation and expression of CD27 are intact. X-linked carriers of CGD revealed a significant correlation between the percentage of CD27-positive B cells and the percentage of neutrophils with normal NADPH activity, reflective of the degree of X chromosome lyonization. These results suggest a role for NADPH in the process of memory B cell formation, inviting further exploration of secondary Ab responses in CGD patients.

p40phox: The last NADPH oxidase subunit

The phagocytic NADPH-oxidase is a multiprotein system activated during the inflammatory response to produce superoxide anion (O2-), which is the substrate for formation of additional reactive oxygen species (ROS). The importance of this system for innate immunity is established by chronic granulomatous disease (CGD), a primary immunodeficiency caused by defects in the NADPH oxidase. In this review, we present and discuss recent knowledge about p40phox, the last NADPH oxidase component to be identified. Furthermore, its interaction with cellular pathways outside of the NADPH oxidase is discussed. Described in this review is evidence that p40phox participates in NADPH oxidase dynamics within cells, what is known about its role in the oxidase, the possibility that p40phox participates in non-NADPH oxidase processes in phagocytic and non-phagocytic cells and whether p40phox could mediate a similar function in other NADPH oxidases. An improved understanding of p40phox should provide new insights about NADPH oxidase, the physiology of phagocytic cells and the innate immune system.

Fc epsilon RI signaling of mast cells activates intracellular production of hydrogen peroxide: role in the regulation of calcium signals

Earlier studies, including our own, revealed that activation of mast cells is accompanied by production of reactive oxygen species (ROS) that help to mediate the release of the inflammatory mediators, including histamine and eicosanoids. However, little is known about the mechanisms of ROS production, including the species of oxidants produced. In this study we show that in both the RBL-2H3 mast cell line and bone marrow-derived mast cells, FcepsilonRI cross-linking stimulates intracellular oxidative burst, including hydrogen peroxide (H(2)O(2)) production, as defined with the oxidant-sensitive dyes dichlorofluorescein and scopoletin and the selective scavenger ebselen (2-phenyl-1,2-benzisoselenazol-3(2H)-one). The oxidative burst was observed immediately after stimulation and was most likely due to an NAD(P)H oxidase. Experiments using selective pharmacological inhibitors demonstrated that activation of tyrosine kinases and phosphatidylinositol-3-kinase is required for induction of the oxidative burst. Blockade of the oxidative burst by diphenyleneiodonium impaired the release of preformed granular mediators, such as histamine and beta-hexosaminidase, and the secretion of newly synthesized leukotriene C(4), whereas selective scavenging H(2)O(2) by ebselen impaired leukotriene C(4) secretion, but not degranulation. Sustained elevation of cytosolic calcium through store-operated calcium entry was totally abolished when ROS production was blocked. In contrast, selective depletion of H(2)O(2) caused a considerable decrease and delay of the calcium response. Finally, tyrosine phosphorylation of phospholipase Cgamma and the linker for activation of T cells, an event required for calcium influx, was suppressed by diphenyleneiodonium and ebselen. These studies demonstrate that activation of the intracellular oxidative burst is an important regulatory mechanism of mast cell responses.

Ceramide induces a loss in cytosolic peroxide levels in mononuclear cells

Ceramide (a sphingolipid) and reactive oxygen species are each partly responsible for intracellular signal transduction in response to a variety of agents. It has been reported that ceramide and reactive oxygen species are intimately linked and show reciprocal regulation [Liu, Andreieu-Abadie, Levade, Zhang, Obeid and Hannun (1998) J. Biol. Chem. 273, 11313-11320]. Utilizing synthetic, short-chain ceramide to mimic the cellular responses to fluctuations in natural endogenous ceramide formation or using stimulation of CD95 to induce ceramide formation, we found that the principal redox-altering property of ceramide is to lower the [peroxide](cyt) (cytosolic peroxide concentration). Apoptosis of Jurkat T-cells, primary resting and phytohaemagglutinin-activated human peripheral blood T-lymphocytes was preceded by a loss in [peroxide](cyt), as measured by the peroxide-sensitive probe 2',7'-dichlorofluorescein diacetate (also reflected in a lower rate of superoxide dismutase-inhibitable cytochrome c reduction), and this was not associated with a loss of membrane integrity. Where growth arrest of U937 monocytes was observed without a loss of membrane integrity, the decrease in [peroxide](cyt) was of a lower magnitude when compared with that preceding the onset of apoptosis in T-cells. Furthermore, decreasing the cytosolic peroxide level in U937 monocytes before the application of synthetic ceramide by pretreatment with either of the antioxidants N -acetyl cysteine or glutathione conferred apoptosis. However, N -acetyl cysteine or glutathione did not affect the kinetics or magnitude of ceramide-induced apoptosis of Jurkat T-cells. Therefore the primary redox effect of cellular ceramide accumulation is to lower the [peroxide](cyt) of both primary and immortalized cells, the magnitude of which dictates the cellular response.

Diminished T cell numbers in patients with chronic granulomatous disease

Chronic granulomatous disease is a neutrophil disorder in which phagocytic cells fail to produce a respiratory burst. Five genetic types of chronic granulomatous disease have been described and in each case the clinical manifestations relate to the inability to effectively kill catalase-positive organisms. It is classically described as a pure disorder of intracellular killing, with preservation of other aspects of phagocytic function such as migration and phagocytosis and normal function of nonmyeloid cells. This article describes a heretofore unrecognized feature of chronic granulomatous disease. Fifty-three patients with chronic granulomatous disease and 42 age-matched controls were studied by flow cytometry. Total T cell numbers and CD4 and CD8 T cell numbers were compared between patients and controls. Patients with chronic granulomatous disease had diminished T cell numbers compared to controls after 3 years of age. The difference increased with age. It is not known whether diminished T cell numbers influence the susceptibility to infections in these patients, but T cell effects could represent a significant cofactor for infection.

Effects of N-acetylcysteine on macrophage and lymphocyte functions in a mouse model of premature ageing

In previous studies, we have observed that mice of the same strain and age show striking interindividual differences in behavior when exposed to a T-maze test. The animals that take longer to explore a T-shaped maze ("slow" animals) show high levels of emotionality/anxiety in other standard behavioral tests, prematurely aged immune functions, and a shorter life span, in comparison to "fast" mice. In these slow mice, which are a model of premature immunosenescence, the immune functions were improved after the ingestion of the thiolic antioxidant thioproline in the diet. In the present work, we studied the effects in vivo (0.1% w/w, for 4 weeks) and in vitro (0.001, 0.01, 0.1, 1, and 2.5 mM) of the thiolic antioxidant N-acetylcysteine (NAC) on different functions of peritoneal macrophages and lymphocytes from slow and fast adult Swiss mice. The results showed an improvement of all the functions studied, namely adherence to substrate, directed migration or chemotaxis, phagocytosis, and reactive oxygen species (ROS) production, after in vivo and in vitro treatment with NAC. The effect of this antioxidant was stronger in the cells from the slow than in those from the fast mice.

Blockade of superoxide generation prevents high-affinity immunoglobulin E receptor-mediated release of allergic mediators by rat mast cell line and human basophils

BACKGROUND

Previous studies have shown that rat peritoneal mast cells and mast cell model rat basophilic leukaemia (RBL-2H3) cells generate intracellular reactive oxygen species (ROS) in response to antigen challenge. However, the physiological significance of the burst of ROS is poorly understood.

OBJECTIVE

The present study was undertaken to investigate the role of superoxide anion in mediator release in rat and human cell systems.

METHODS

RBL-2H3 cells were directly stimulated with anti-rat FcepsilonRI alpha-subunit monoclonal antibody (mAb). For the analysis of human cell system, leucocytes were isolated by dextran sedimentation from healthy volunteers or from patients, and challenged either with anti-human FcepsilonRI mAb or with the relevant antigens. Superoxide generation was determined by chemiluminescence-based methods. The releases of histamine and leukotrienes (LT)s were determined by enzyme-linked immunosorben assay (ELISA).

RESULTS

Cross-linking of FcepsilonRI on RBL-2H3 cells or on human leucocytes from healthy donors by the anti-FcepsilonRI mAb resulted in a rapid generation of superoxide anion, as determined by chemiluminescence using superoxide-specific probes. Similarly, leucocytes from patients generated superoxide anion in response to the challenge with the relevant allergen but not with the irrelevant allergen. Furthermore, diphenyleneiodonium (DPI), a well-known inhibitor of flavoenzymes suppressed the superoxide generation and the release of histamine and LTC4 induced by the anti-FcepsilonRI mAb or by allergen in parallel.

CONCLUSION

These results indicate that both RBL-2H3 cells and human basophils generate superoxide anion upon FcepsilonRI cross-linking either by antibody or by allergen challenge and that blockade of the generation prevents the release of allergic mediators. The findings strongly support the role of superoxide generation in the activation of mast cells and basophils under both physiological and pathological conditions. The findings suggest that drugs regulating the superoxide generation have potential therapeutic use for allergic disorders.

Signalling apoptosis: a radical approach

Reactive oxygen species (ROS) are frequently associated with cytotoxicity, often being described as damaging, harmful or toxic. It is generally assumed that, under pathological circumstances, ROS elicit wide-spread and random acts of oxidation. This passive attack of cellular components by ROS, in conditions where oxidative stress is the initiating stimulus for apoptosis, is assumed to simply trigger cell death as a result of cumulative oxidative damage. However, accumulating evidence now suggests that ROS may act as signalling molecules for the initiation and execution of the apoptotic death programme in many, if not all, current models of apoptotic cell death. Signalling by ROS would not appear to be random, as previously assumed, but targeted at specific metabolic and signal transduction cellular components. There is also evidence that the enzymatic generation of ROS may not simply be an unwanted by-product of the primary reaction catalysed, but that ROS may be used as signalling molecules to regulate cellular processes including apoptosis. This view of ROS as signalling molecules (as opposed to toxic metabolites) has been further bolstered by the findings that cellular antioxidants such as glutathione and thioredoxin not only serve to regulate ROS levels but also act as reversible redox modifiers of enzyme function. This review will attempt to delineate the involvement of ROS in apoptosis in light of these recent discoveries and provide evidence for a crucial role for ROS in the initiation and execution of the death process.

Oxidant-dependent phosphorylation of p40phox in B lymphocytes

As with the neutrophil NADPH oxidase, the B lymphocyte NADPH oxidase consists of a membrane-bound flavocytochrome b and regulatory factors including Rac and the cytosolic phox protein triad p67phox, p47phox, and p40phox. Here we demonstrate by phosphoamino acid analysis and the use of the potent PKC inhibitor GFX that, in response to stimulation of B lymphocytes with sodium orthovanadate and H(2)O(2), the p40phox component of the cytosolic phox triad is selectively phosphorylated on serine and threonine residues by a PKC-type protein kinase. The pattern of p40phox phosphorylation was closely related to the kinetics of tyrosine phosphorylation of PKC-delta, the main PKC isotype of B lymphocytes. Blocking H(2)O(2)-dependent tyrosine phosphorylation of PKC by genistein resulted in inhibition of p40phox phosphorylation. The correlation between the tyrosine phosphorylation of PKC-delta and the serine/threonine phosphorylation of p40phox, together with the inhibition of p40phox phosphorylation by rottlerin, a selective inhibitor of PKC-delta, makes the activated PKC-delta a likely candidate in the process of the oxidant-dependent phosphorylation of p40phox in B cells.

cAMP potentiates H(2)O(2)-induced ERK1/2 phosphorylation without the requirement for MEK1/2 phosphorylation

In Jurkat T lymphocytes, hydrogen peroxide (H(2)O(2)) potentiates the phosphorylation level of extracellular signal-regulated kinase 1 and 2 (ERK1/2) caused by T cell receptor (TCR) stimulation with anti-CD3 and anti-CD28 or anti-CD3 alone. Submillimolar concentrations of H(2)O(2)-induced phosphorylation of ERK1/2 and MAP/ERK kinase 1 and 2 (MEK1/2) without antigenic stimulation. H(2)O(2) also induced the electrophoretic mobility shift of Lck from 56 to 60 kDa. The MEK inhibitor, PD98059 attenuated ERK1/2 and MEK1/2 phosphorylation, as well as the migration shift of Lck induced by H(2)O(2). The phospholipase C (PLC) inhibitor, U73122, and EGTA reduced the phosphorylation of both ERK1/2 and MEK1/2 induced by H(2)O(2). Interestingly, an increase of intracellular cAMP level with forskolin or 8-(4-chlorophenylthio)-cAMP augmented ERK1/2 phosphorylation by H(2)O(2), while inhibiting MEK1/2 phosphorylation by H(2)O(2). These results demonstrate an alternative pathway that results in augmentation of ERK1/2 phosphorylation without concomitant MEK1/2 phosphorylation in T cells.

Diphenyleneiodonium prevents reactive oxygen species generation, tyrosine phosphorylation, and histamine release in RBL-2H3 mast cells

Mast cells play a central role in immediate allergic reactions mediated by immunoglobulin E. It has recently been reported that mast cells generate intracellular reactive oxygen species (ROS) in response to stimulation with divergent physiologically relevant stimulants. However, the physiological role of ROS is poorly understood. Here we demonstrate that mast cell model rat basophilic leukemia (RBL-2H3) cells generate ROS in response to antigen and the calcium-ionophore A23187 via activation of diphenyleneiodonuim (DPI)-sensitive enzyme and that blockade of ROS generation by DPI suppresses histamine release induced by either stimulant. Increased tyrosine phosphorylation of pp125(FAK) and a 77-kDa protein coprecipitating specifically with the kinase occurred in parallel with the secretion, and blockade of ROS generation by DPI also suppressed the tyrosine phosphorylation of both proteins. These findings suggest that ROS generated by a flavoenzyme-dependent mechanism may be involved in histamine release through the pp125(FAK) pathway.

Epigallocatechin gallate inhibits histamine release from rat basophilic leukemia (RBL-2H3) cells: role of tyrosine phosphorylation pathway

Some tea polyphenolic compounds including (-)-epigallocatechin gallate (EGCG) have been shown to inhibit histamine release from mast cells through poorly understood mechanisms. By using a mast cell model rat basophilic leukemia (RBL-2H3) cells we explored the mechanism of the inhibition. EGCG inhibited histamine release from RBL-2H3 cells in response to antigen or the calcium-ionophore A23187, while (-)-epicatechin (EC) had little effect. Increased tyrosine phosphorylation of several proteins including approximately 120 kDa proteins occurred in parallel with the secretion induced by either stimulation. EGCG also inhibited tyrosine phosphorylation of the approximately 120-kDa proteins induced by either stimulation, whereas EC did not. The tyrosine kinase-specific inhibitor piceatannol inhibited the secretion and tyrosine phosphorylation of these proteins induced by either stimulation also. Further analysis showed that the focal adhesion kinase pp125(FAK) was one of the approximately 120-kDa proteins. These findings suggest that EGCG prevents histamine release from mast cells mainly by inhibiting tyrosine phosphorylation of proteins including pp125(FAK).

Role of reactive oxygen species and phosphatidylinositol 3-kinase in cardiomyocyte differentiation of embryonic stem cells

Cardiotypic development in embryonic stem cell-derived embryoid bodies may be regulated by reactive oxygen species (ROS). ROS were generated by a NADPH oxidase-like enzyme which was transiently expressed during the time course of embryoid body development. Incubation with either H(2)O(2) or menadione enhanced cardiomyogenesis, whereas the radical scavengers trolox, pyrrolidinedithiocarbamate and N-acetylcysteine exerted inhibitory effects. The phosphatidylinositol 3-kinase (PI-3-kinase) inhibitors LY294002 and wortmannin abolished cardiac commitment and downregulated ROS in embryoid bodies. Coadministration of LY294002 with prooxidants resumed cardiomyocyte differentiation, indicating a role for PI-3-kinase in the regulation of the intracellular redox state.