Nox3 regulation by NOXO1, p47phox, and p67phox

NADPH Oxidase 3: Beyond the Inner Ear

Reactive oxygen species (ROS) were formerly known as mere byproducts of metabolism with damaging effects on cellular structures. The discovery and description of NADPH oxidases (Nox) as a whole enzyme family that only produce this harmful group of molecules was surprising. After intensive research, seven Nox isoforms were discovered, described and extensively studied. Among them, the NADPH oxidase 3 is the perhaps most underrated Nox isoform, since it was firstly discovered in the inner ear. This stigma of Nox3 as "being only expressed in the inner ear" was also used by me several times. Therefore, the question arose whether this sentence is still valid or even usable. To this end, this review solely focuses on Nox3 and summarizes its discovery, the structural components, the activating and regulating factors, the expression in cells, tissues and organs, as well as the beneficial and detrimental effects of Nox3-mediated ROS production on body functions. Furthermore, the involvement of Nox3-derived ROS in diseases progression and, accordingly, as a potential target for disease treatment, will be discussed.

NADPH Oxidases: From Molecular Mechanisms to Current Inhibitors

NADPH oxidases (NOXs) form a family of electron-transporting membrane enzymes whose main function is reactive oxygen species (ROS) generation. Strong evidence suggests that ROS produced by NOX enzymes are major contributors to oxidative damage under pathologic conditions. Therefore, blocking the undesirable actions of these enzymes is a therapeutic strategy for treating various pathological disorders, such as cardiovascular diseases, inflammation, and cancer. To date, identification of selective NOX inhibitors is quite challenging, precluding a pharmacologic demonstration of NOX as therapeutic targets in vivo. The aim of this Perspective is to furnish an updated outlook about the small-molecule NOX inhibitors described over the last two decades. Structures, activities, and in vitro/in vivo specificity are discussed, as well as the main biological assays used.

Identification of an inhibitor for atherosclerotic enzyme NOX-1 to inhibit ROS production

Background

NOX-1 overexpression has been observed in various studies, persons with diabetes or cardiovascular conditions. NOX-1 orchestrates the disease pathogenesis of various cardiovascular conditions such as atherosclerotic plaque development and is a very crucial biomarker. Therefore, this study was carried out to deduce the three-dimensional modelled structure of NOX-1 using DeepMind AlphaFold-2 to find meaningful insight into the structural biology. Extensive in silico approaches have been used to determine the active pocket, virtually screen large chemical space to identify potential inhibitors. The role of the key amino acid residues was also deduced using alanine scanning mutagenesis contributing to the catalytic process and to the overall stability of NOX-1.

Results

The modelled structure of NOX-1 protein was validated using ERRAT. The ERRAT statistics with 9 amino acids sliding window have shown a confidence score of 96.937%. According to the Ramachandran statistics, 96.60% of the residues lie within the most favoured region, and 2.80% of residues lie in the additionally allowed region, which gives an overall of 99.4% residues in the three quadrants in the plot. GKT-831 which is a referral drug in this study has shown a GOLD interaction score of 62.12 with respect to the lead molecule zinc000059139266 which has shown a higher GOLD score of 78.07. Alanine scanning mutagenesis studies has shown that Phe201, Leu98 and Leu76 are found to be the key interacting residues in hydrophobic interactions. Similarly, Tyr324, Arg287 and Cys73 are major amino acid residues in the hydrogen bond interactions.

Conclusions

NOX-1 overexpression leads to heightened ROS production resulting in catastrophic outcomes. The modelled structure of NOX-1 has a good stereochemistry with respect to Ramachandran plot. The lead molecule zinc000059139266 has shown to have a very high interaction score of 78.07 compared to the referral drug GKT-831 with a score of 62.12. There is an excellent scope for the lead molecule to progress further into in vitro and in vivo studies.

Redox-dependent Igfbp2 signaling controls Brca1 DNA damage response to govern neural stem cell fate

Neural stem cell (NSC) maintenance and functions are regulated by reactive oxygen species (ROS). However, the mechanisms by which ROS control NSC behavior remain unclear. Here we report that ROS-dependent Igfbp2 signaling controls DNA repair pathways which balance NSC self-renewal and lineage commitment. Ncf1 or Igfbp2 deficiency constrains NSCs to a self-renewing state and prevents neurosphere formation. Ncf1-dependent oxidation of Igfbp2 promotes neurogenesis by NSCs in vitro and in vivo while repressing Brca1 DNA damage response genes and inducing DNA double-strand breaks (DDSBs). By contrast, Ncf1^-/- and Igfbp2^-/- NSCs favor the formation of oligodendrocytes in vitro and in vivo. Notably, transient repression of Brca1 DNA repair pathway genes induces DDSBs and is sufficient to rescue the ability of Ncf1^-/- and Igfbp2^-/- NSCs to lineage-commit to form neurospheres and neurons. NSC lineage commitment is dependent on the oxidizable cysteine-43 residue of Igfbp2. Our study highlights the role of DNA damage/repair in orchestrating NSC fate decisions downstream of redox-regulated Igfbp2.

Role of NADPH Oxidases in Blood-Brain Barrier Disruption and Ischemic Stroke

NADPH oxidases (Nox) are one of the main sources of reactive oxygen species (ROS) in the central nervous system (CNS). While these enzymes have been shown to be involved in physiological regulation of cerebral vascular tone, excessive ROS produced by Nox1-5 play a critical role in blood–brain barrier (BBB) dysfunction in numerous neuropathologies. Nox-derived ROS have been implicated in mediating matrix metalloprotease (MMP) activation, downregulation of junctional complexes between adjacent brain endothelial cells and brain endothelial cell apoptosis, leading to brain microvascular endothelial barrier dysfunction and consequently, increases in BBB permeability. In this review, we will highlight recent findings on the role played by these enzymes in BBB disruption induced by ischemic stroke.

Nicotinamide Adenine Dinucleotide Phosphate Oxidases Are Everywhere in Brain Disease, but Not in Huntington's Disease?

Huntington’s disease (HD) is an inherited neurodegenerative disorder characterized by neuronal loss and tissue atrophy mainly in the striatum and cortex. In the early stages of the disease, impairment of neuronal function, synaptic dysfunction and white matter loss precedes neuronal death itself. Relative to other neurodegenerative diseases such as Alzheimer’s and Parkinson’s disease and Amyotrophic Lateral Sclerosis, where the effects of either microglia or NADPH oxidases (NOXs) are recognized as important contributors to disease pathogenesis and progression, there is a pronounced lack of information in HD. This information void contrasts with evidence from human HD patients where blood monocytes and microglia are activated well before HD clinical symptoms (PET scans), and the clear signs of oxidative stress and inflammation in post mortem HD brain. Habitually, NOX activity and oxidative stress in the central nervous system (CNS) are equated with microglia, but research of the last two decades has carved out important roles for NOX enzyme function in neurons. Here, we will convey recent information about the function of NOX enzymes in neurons, and contemplate on putative roles of neuronal NOX in HD. We will focus on NOX-produced reactive oxygen species (ROS) as redox signaling molecules in/among neurons, and the specific roles of NOXs in important processes such as neurogenesis and lineage specification, neurite outgrowth and growth cone dynamics, and synaptic plasticity where NMDAR-dependent signaling, and long-term depression/potentiation are redox-regulated phenomena. HD animal models and induced pluripotent stem cell (iPSC) studies have made it clear that the very same physiological processes are also affected in HD, and we will speculate on possible roles for NOX in the pathogenesis and development of disease. Finally, we also take into account the limited information on microglia in HD and relate this to any contribution of NOX enzymes.

The role of NADPH oxidases in infectious and inflammatory diseases

Nicotinamide adenine dinucleotide phosphate (NADPH) oxidases (NOX) are enzymes that generate superoxide or hydrogen peroxide from molecular oxygen utilizing NADPH as an electron donor. There are seven enzymes in the NOX family: NOX1-5 and dual oxidase (DUOX) 1-2. NOX enzymes in humans play important roles in diverse biological functions and vary in expression from tissue to tissue. Importantly, NOX2 is involved in regulating many aspects of innate and adaptive immunity, including regulation of type I interferons, the inflammasome, phagocytosis, antigen processing and presentation, and cell signaling. DUOX1 and DUOX2 play important roles in innate immune defenses at epithelial barriers. This review discusses the role of NOX enzymes in normal physiological processes as well as in disease. NOX enzymes are important in autoimmune diseases like type 1 diabetes and have also been implicated in acute lung injury caused by infection with SARS-CoV-2. Targeting NOX enzymes directly or through scavenging free radicals may be useful therapies for autoimmunity and acute lung injury where oxidative stress contributes to pathology.

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.

The double-edged roles of ROS in cancer prevention and therapy

Reactive oxygen species (ROS) serve as cell signaling molecules generated in oxidative metabolism and are associated with a number of human diseases. The reprogramming of redox metabolism induces abnormal accumulation of ROS in cancer cells. It has been widely accepted that ROS play opposite roles in tumor growth, metastasis and apoptosis according to their different distributions, concentrations and durations in specific subcellular structures. These double-edged roles in cancer progression include the ROS-dependent malignant transformation and the oxidative stress-induced cell death. In this review, we summarize the notable literatures on ROS generation and scavenging, and discuss the related signal transduction networks and corresponding anticancer therapies. There is no doubt that an improved understanding of the sophisticated mechanism of redox biology is imperative to conquer cancer.

NLRC3-like 1 inhibits NOD1-RIPK2 pathway via targeting RIPK2

Both NLRC3 and NOD1 belong to regulatory NLR subfamily based on their best-characterized function. In mammals, NLRC3 was reported to function by attenuating signaling cascades initiated by other families of PRRs. In teleosts, multiple NLRC3-like genes were identified through transcriptome sequencing. However, the functions of many NLRC3-like genes, especially the fish-specific NLRC3-like genes, remain unclear. In the present study, we report the functional characterization of a novel category of NLRC3-like proteins (named as NLRC3-like 1) from the zebrafish, which consists of a fish-specific FISNA, a conserved NACHT and five C-terminal LRRs domains. The expression of zebrafish NLRC3-like 1 was inducible in response to Edwardsiella piscicida infection. During bacterial infection, the in vitro and in vivo studies revealed that zebrafish NLRC3-like 1 overexpression facilitated bacterial growth and dissemination, together with the decreased survival rate of zebrafish larvae infected with E. piscicida. The attenuated response by zebrafish NLRC3-like 1 in response to bacterial infection were characterized by the impaired expression of antibacterial genes, proinflammatory cytokines and Nox genes. Furthermore, zebrafish NLRC3-like 1 interacted with the adaptor protein RIPK2 of NODs signaling via the FISNA (Fish-specific NACHT associated domain) and NACHT domains. However, the interaction between zebrafish NLRC3-like 1 and RIPK2 inhibited the assembly of the NOD1-RIPK2 complex. Importantly, zebrafish NLRC3-like 1 inhibited NOD1-mediated antibacterial activity, NF-κB and MAPK pathways and proinflammatory cytokine production. All together, these results firstly demonstrate that zebrafish NLRC3-like 1 inhibits NOD1-RIPK2 antibacterial pathway via targeting the adaptor protein RIPK2.

Curcumin alleviates oxidative stress and inhibits apoptosis in diabetic cardiomyopathy via Sirt1-Foxo1 and PI3K-Akt signalling pathways

Diabetes is a disorder of glucose metabolism, and over 90% are type 2 diabetes. Diabetic cardiomyopathy (DCM) is one of the type 2 diabetes complications, usually accompanied by changes in myocardial structure and function, together with cardiomyocyte apoptosis. Our study investigated the effect of curcumin on regulating oxidative stress (OS) and apoptosis in DCM. In vivo, diabetes was induced in an experimental rat model by streptozoticin (STZ) together with high‐glucose and high‐fat (HG/HF) diet feeding. In vitro, H9c2 cardiomyocytes were cultured with high‐glucose and saturated free fatty acid palmitate. Curcumin was orally or directly administered to rats or cells, respectively. Streptozoticin ‐induced diabetic rats showed metabolism abnormalities and elevated markers of OS (superoxide dismutase [SOD], malondialdehyde [MDA], gp91^phox, Cyt‐Cyto C), enhanced cell apoptosis (Bax/Bcl‐2, Cleaved caspase‐3, TUNEL‐positive cells), together with reduced Akt phosphorylation and increased Foxo1 acetylation. Curcumin attenuated the myocardial dysfunction, OS and apoptosis in the heart of diabetic rats. Curcumin treatment also enhanced phosphorylation of Akt and inhibited acetylation of Foxo1. These results strongly suggest that apoptosis was increased in the heart of diabetic rats, and curcumin played a role in diabetic cardiomyopathy treatment by modulating the Sirt1‐Foxo1 and PI3K‐Akt pathways.

The NADPH Oxidase Family and Its Inhibitors

Significance: The oxidative stress, resulting from an imbalance in the production and scavenging of reactive oxygen species (ROS), is known to be involved in the development and progression of several pathologies. The excess of ROS production is often due to an overactivation of nicotinamide adenine dinucleotide phosphate (NADPH) oxidases (NOX) and for this reason these enzymes became promising therapeutic targets. However, even if NOX are now well characterized, the development of new therapies is limited by the lack of highly isoform-specific inhibitors. Recent Advances: In the past decade, several groups and laboratories have screened thousands of molecules to identify new specific inhibitors with low off-target effects. These works have led to the characterization of several new potent NOX inhibitors; however, their specificity varies a lot depending on the molecules. Critical Issues: Here, we are reviewing more than 25 known NOX inhibitors, focusing mainly on the newly identified ones such as APX-115, NOS31, Phox-I1 and 2, GLX7013114, and GSK2795039. To have a better overall view of these molecules, the inhibitors were classified according to their specificity, from pan-NOX inhibitors to highly isoform-specific ones. We are also presenting the use of these compounds both in vitro and in vivo. Future Directions: Several of these new molecules are potent and very specific inhibitors that could be good candidates for the development of new drugs. Even if the results are very promising, most of these compounds were only validated in vitro or in mice models and further investigations will be required before using them as potential therapies.

Oxidative Stress in Pulmonary Fibrosis

Oxidative stress has been linked to various disease states as well as physiological aging. The lungs are uniquely exposed to a highly oxidizing environment and have evolved several mechanisms to attenuate oxidative stress. Idiopathic pulmonary fibrosis (IPF) is a progressive age-related disorder that leads to architectural remodeling, impaired gas exchange, respiratory failure, and death. In this article, we discuss cellular sources of oxidant production, and antioxidant defenses, both enzymatic and nonenzymatic. We outline the current understanding of the pathogenesis of IPF and how oxidative stress contributes to fibrosis. Further, we link oxidative stress to the biology of aging that involves DNA damage responses, loss of proteostasis, and mitochondrial dysfunction. We discuss the recent findings on the role of reactive oxygen species (ROS) in specific fibrotic processes such as macrophage polarization and immunosenescence, alveolar epithelial cell apoptosis and senescence, myofibroblast differentiation and senescence, and alterations in the acellular extracellular matrix. Finally, we provide an overview of the current preclinical studies and clinical trials targeting oxidative stress in fibrosis and potential new strategies for future therapeutic interventions. © 2020 American Physiological Society. Compr Physiol 10:509-547, 2020.

Function of NADPH Oxidases in Diabetic Nephropathy and Development of Nox Inhibitors

Several recent studies have reported that reactive oxygen species (ROS), superoxide anion and hydrogen peroxide (H₂O₂), play important roles in various cellular signaling networks. NADPH oxidase (Nox) isozymes have been shown to mediate receptor-mediated ROS generation for physiological signaling processes involved in cell growth, differentiation, apoptosis, and fibrosis. Detectable intracellular levels of ROS can be induced by the electron leakage from mitochondrial respiratory chain as well as by activation of cytochrome p450, glucose oxidase and xanthine oxidase, leading to oxidative stress. The up-regulation and the hyper-activation of NADPH oxidases (Nox) also likely contribute to oxidative stress in pathophysiologic stages. Elevation of the renal ROS level through hyperglycemia-mediated Nox activation results in the oxidative stress which induces a damage to kidney tissues, causing to diabetic nephropathy (DN). Nox inhibitors are currently being developed as the therapeutics of DN. In this review, we summarize Nox-mediated ROS generation and development of Nox inhibitors for therapeutics of DN treatment.

NOX2-derived reactive oxygen species in immune cells exacerbates salt-sensitive hypertension

Previous studies utilizing the SSp67phox-/- rat have demonstrated the importance of systemic NADPH oxidase NOX2-derived reactive oxygen species (ROS) production in the pathogenesis of Dahl Salt-Sensitive (SS) hypertension and renal damage. It is established that the immune system contributes to the development of SS hypertension and our laboratory has observed an enrichment of NOX2 subunits in infiltrating T cells. However, the contribution of immune cell-derived ROS in SS hypertension remains unknown. To assess the role of ROS in immune cells, SSp67phox-/- rats underwent total body irradiation and received bone marrow transfer from either SS (+SS) or SSp67phox-/- (+SSp67phox-/-) donor rats. Demonstrated in a respiratory burst assay, response to phorbol 12-myristate 13-acetate stimulus (135 μM) was 10.2-fold greater in peritoneal macrophages isolated from +SS rats compared to nonresponsive + SSp67phox-/- cells, validating that + SS rats were capable of producing NOX2-derived ROS in cells of hematopoietic origin. After 3 weeks of high salt challenge, there was an exacerbated increase in mean arterial pressure in +SS rats compared to + SSp67phox-/- control rats (176.1 ± 4.7 vs 147.9 ± 8.4 mmHg, respectively), which was accompanied by a significant increase in albuminuria (168.3 ± 23.7 vs 107.0 ± 20.4 mg/day) and renal medullary protein cast formation (33.2 ± 4.7 vs 8.1 ± 3.5%). Interestingly, upon analysis of renal immune cells, there was trending increase of CD11b/c + monocytes and macrophages in the kidney of +SS rats (4.7 ± 0.4 vs 3.5 ± 0.5 × 106 cells/kidney, +SS vs + SSp67phox-/-, p = 0.06). These data altogether demonstrate that immune cell production of NOX2-derived ROS is sufficient to exacerbate Dahl SS hypertension, renal damage, and renal inflammation.

Carcinogenesis and Reactive Oxygen Species Signaling: Interaction of the NADPH Oxidase NOX1-5 and Superoxide Dismutase 1-3 Signal Transduction Pathways

SIGNIFICANCE

Reduction/oxidation (redox) balance could be defined as an even distribution of reduction and oxidation complementary processes and their reaction end products. There is a consensus that aberrant levels of reactive oxygen species (ROS), commonly observed in cancer, stimulate primary cell immortalization and progression of carcinogenesis. However, the mechanism how different ROS regulate redox balance is not completely understood. Recent Advances: In the current review, we have summarized the main signaling cascades inducing NADPH oxidase NOX1-5 and superoxide dismutase (SOD) 1-3 expression and their connection to cell proliferation, immortalization, transformation, and CD34+ cell differentiation in thyroid, colon, lung, breast, and hematological cancers.

CRITICAL ISSUES

Interestingly, many of the signaling pathways activating redox enzymes or mediating the effect of ROS are common, such as pathways initiated from G protein-coupled receptors and tyrosine kinase receptors involving protein kinase A, phospholipase C, calcium, and small GTPase signaling molecules.

FUTURE DIRECTIONS

The clarification of interaction of signal transduction pathways could explain how cells regulate redox balance and may even provide means to inhibit the accumulation of harmful levels of ROS in human pathologies.

Intersecting Stories of the Phagocyte NADPH Oxidase and Chronic Granulomatous Disease

Neutrophils serve as the circulating cells that respond early and figure prominently in human host defense to infection and in inflammation in other settings. Optimal oxidant-dependent antimicrobial activity by neutrophils relies on the ability of stimulated phagocytes to utilize a multicomponent NADPH oxidase to generate oxidants. The frequent, severe, and often fatal infections experienced by individuals with chronic granulomatous disease (CGD), an inherited disorder in which one of the NADPH oxidase components is absent or dysfunctional, underscore the link between a functional phagocyte NADPH oxidase and robust host protection against microbial infection.The history of the discovery and characterization of the normal neutrophil NADPH oxidase and the saga of recognizing CGD and its underlying causes together illustrate how the observations of astute clinicians and imaginative basic scientists synergize to forge new understanding of both basic cell biology and pathogenesis of human disease.In this chapter, we review the events in the stepwise evolution of our understanding of the phagocyte NADPH oxidase, both in the context of normal human neutrophil function and in the setting of CGD. The phagocyte oxidase complex employs a heterodimeric transmembrane protein composed of gp91phox and p22phox to relay electrons from NADPH to molecular oxygen, while other cofactors contribute to localization and regulation of the activity of the assembled oxidase. The b-type cytochrome gp91phox, also known as NOX2, serves as the catalytic component of this multicomponent enzyme complex. Although many of the features of the composition and regulation of the phagocyte oxidase may apply as well to NOX2 expressed in non-phagocytes and to other members of the NOX protein family, exceptions exist and pose special challenges to investigators exploring the biology of NADPH oxidases.

Insights into the NOX NADPH Oxidases Using Heterologous Whole Cell Assays

Assays based on ectopic expression of NOX NADPH oxidase subunits in heterologous mammalian cells are an important approach for investigating features of this family of enzymes. These model systems have been used to analyze the biosynthesis and functional domains of NOX enzyme components as well as their regulation and cellular activities. This chapter provides an overview of the basic principles and applications of heterologous whole cell assays in studying NOX NADPH oxidases.

The defense and signaling role of NADPH oxidases in eukaryotic cells : Review

This short review article summarizes what is known clinically and biochemically about the seven human NADPH oxidases. Emphasis is put on the connection between mutations in the catalytic and regulatory subunits of Nox2, the phagocyte defense enzyme, with syndromes like chronic granulomatous disease, as well as a number of chronic inflammatory diseases. These arise paradoxically from a lack of reactive oxygen species production needed as second messengers for immune regulation. Both Nox2 and the six other human NADPH oxidases display signaling functions in addition to the functions of these enzymes in specialized biochemical reactions, for instance, synthesis of the hormone thyroxine. NADPH oxidases are also needed by Saccharomyces cerevisiae cells for the regulation of the actin cytoskeleton in times of stress or developmental changes, such as pseudohyphae formation. The article shows that in certain cancer cells Nox4 is also involved in the re-structuring of the actin cytoskeleton, which is required for cell mobility and therefore for metastasis.

Identification and Characterization of a Novel NADPH Oxidase 1 (Nox1) Inhibitor That Suppresses Proliferation of Colon and Stomach Cancer Cells

Reactive oxygen species (ROS) generated by reduced nicotinamide adenine dinucleotide phosphate (NADPH) oxidase (Nox)1 mediate cellular signalings involved in normal physiological processes, and aberrant control of Nox1 has been implicated in the pathogenesis of various diseases. Therefore, Nox1 could have great potential as a therapeutic target. Here, we identified a novel Nox1 inhibitor, NOS31 secreted from Stretomyces sp. and analyzed its chemical structure. Furthermore, NOS31 was found to selectively inhibit Nox1-mediated ROS generation, with only a marginal effect on other Nox isoforms (Nox2-5) and no ROS scavenging activity. This compound blocked both Nox organizer 1 (NOXO1)/Nox activator 1 (NOXA1)-dependent and phorbol 12-myristate 13-acetate-stimulated Nox1-mediated ROS production in colon cancer cells. NOS31 inhibited the proliferation of several colon carcinoma and gastric cancer cell lines that upregulate the Nox1 system, whereas it had no appreciable effect on normal cells with low levels of Nox1. The finding suggests that NOS31 is a unique, potent Nox1 inhibitor of microbial origin and raises its possibility as a therapeutic agent for inhibiting gastrointestinal cancer cell growth.

Organizers and activators: Cytosolic Nox proteins impacting on vascular function

NADPH oxidases of the Nox family are important enzymatic sources of reactive oxygen species (ROS) in the cardiovascular system. Of the 7 members of the Nox family, at least three depend for their activation on specific cytosolic proteins. These are p47phox and its homologue NoxO1 and p67phox and its homologue NoxA1. Also the Rho-GTPase Rac is important but as this protein has many additional functions, it will not be covered here. The Nox1 enzyme is preferentially activated by the combination of NoxO1 with NoxA1, whereas Nox2 gains highest activity with p47phox together with p67phox. As p47phox, different to NoxO1 contains an auto inhibitory region it has to be phosphorylated prior to complex formation. In the cardio-vascular system, all cytosolic Nox proteins are expressed but the evidence for their contribution to ROS production is not well established. Most data have been collected for p47phox, whereas NoxA1 has basically not yet been studied. In this article the specific aspects of cytosolic Nox proteins in the cardiovascular system with respect to Nox activation, their expression and their importance will be reviewed. Finally, it will be discussed whether cytosolic Nox proteins are suitable pharmacological targets to tamper with vascular ROS production.

Rare NOX3 Variants Confer Susceptibility to Agranulocytosis During Thyrostatic Treatment of Graves' Disease

Agranulocytosis is a rare and serious adverse effect of antithyroid drugs, with unknown etiology. The present study aimed to uncover genetic susceptibility and underlying mechanisms of antithyroid drug-induced agranulocytosis (ATDAC). We studied two independent families with familial Graves' disease, of which several members developed ATDAC. In addition, six sporadic ATDAC patients with Graves' disease were investigated. Whole exome sequencing analysis of affected and unaffected family members was performed to identify genetic susceptibility variants for ATDAC, followed by functional characterization of primary granulocytes from patients and unrelated healthy controls. Whole exome sequencing, cosegregation analysis, and stringent selection criteria of candidate gene variants identified NOX3 as a genetic factor related to ATDAC. Functional studies revealed increased apoptosis of methimazole-treated granulocytes from patients carrying NOX3 variants. In conclusion, genetic variants in NOX3 may confer susceptibility to antithyroid drug-induced apoptosis of granulocytes. These findings contribute to the understanding of the mechanisms underlying ATDAC.

Central Nervous System Injury and Nicotinamide Adenine Dinucleotide Phosphate Oxidase: Oxidative Stress and Therapeutic Targets

Injury to the central nervous system (CNS) includes both traumatic brain and spinal cord injury (TBI and SCI, respectively). These injuries, which are heterogeneous and, therefore, difficult to treat, result in long-lasting functional, cognitive, and behavioral deficits. Severity of injury is determined by multiple factors, and is largely mediated by the activity of the CNS inflammatory system, including the primary CNS immune cells, microglia. The nicotinamide adenine dinucleotide phosphate (NADPH) oxidase (NOX) family of enzymes is a primary source of reactive oxygen species (ROS), key inflammatory mediators after CNS injury. ROS play a central role in inflammation, contributing to cytokine translation and release, microglial polarization and activation, and clearance of damaged tissue. NOX has been suggested as a potential therapeutic target in CNS trauma, as inhibition of this enzyme family modulates inflammatory cell response and ROS production. The purpose of this review is to understand how the different NOX enzymes function and what role they play in the scope of CNS trauma.

Nox Inhibitors & Therapies: Rational Design of Peptidic and Small Molecule Inhibitors

Oxidative stress-related diseases underlie many if not all of the major leading causes of death in United States and the Western World. Thus, enormous interest from both academia and pharmaceutical industry has been placed on the development of agents which attenuate oxidative stress. With that in mind, great efforts have been placed in the development of inhibitors of NADPH oxidase (Nox), the major enzymatic source of reactive oxygen species and oxidative stress in many cells and tissue. The regulation of a catalytically active Nox enzyme involves numerous protein-protein interactions which, in turn, afford numerous targets for inhibition of its activity. In this review, we will provide an updated overview of the available Nox inhibitors, both peptidic and small molecules, and discuss the body of data related to their possible mechanisms of action and specificity towards each of the various isoforms of Nox. Indeed, there have been some very notable successes. However, despite great commitment by many in the field, the need for efficacious and well-characterized, isoform-specific Nox inhibitors, essential for the treatment of major diseases as well as for delineating the contribution of a given Nox in physiological redox signalling, continues to grow.

The Cytosolic NADPH Oxidase Subunit NoxO1 Promotes an Endothelial Stalk Cell Phenotype

OBJECTIVE

Reactive oxygen species generated by nicotinamide adenine dinucleotide phosphate (NADPH) oxidases contribute to angiogenesis and vascular repair. NADPH oxidase organizer 1 (NoxO1) is a cytosolic protein facilitating assembly of constitutively active NADPH oxidases. We speculate that NoxO1 also contributes to basal reactive oxygen species formation in the vascular system and thus modulates angiogenesis.

APPROACH AND RESULTS

A NoxO1 knockout mouse was generated, and angiogenesis was studied in cultured cells and in vivo. Angiogenesis of the developing retina and after femoral artery ligation was increased in NoxO1(-/-) when compared with wild-type animals. Spheroid outgrowth assays revealed greater angiogenic capacity of NoxO1(-/-) lung endothelial cells (LECs) and a more tip-cell-like phenotype than wild-type LECs. Usually signaling by the Notch pathway switches endothelial cells from a tip into a stalk cell phenotype. NoxO1(-/-) LECs exhibited attenuated Notch signaling as a consequence of an attenuated release of the Notch intracellular domain on ligand stimulation. This release is mediated by proteolytic cleavage involving the α-secretase ADAM17. For maximal activity, ADAM17 has to be oxidized, and overexpression of NoxO1 promoted this mode of activation. Moreover, the activity of ADAM17 was reduced in NoxO1(-/-) LECs when compared with wild-type LECs.

CONCLUSIONS

NoxO1 stimulates α-secretase activity probably through reactive oxygen species-mediated oxidation. Deletion of NoxO1 attenuates Notch signaling and thereby promotes a tip-cell phenotype that results in increased angiogenesis.

NOX2 As a Target for Drug Development: Indications, Possible Complications, and Progress

SIGNIFICANCE

NOX2 is important for host defense, and yet is implicated in a large number of diseases in which inflammation plays a role in pathogenesis. These include acute and chronic lung inflammatory diseases, stroke, traumatic brain injury, and neurodegenerative diseases, including Alzheimer's and Parkinson's Diseases.

RECENT ADVANCES

Recent drug development programs have targeted several NOX isoforms that are implicated in a variety of diseases. The focus has been primarily on NOX4 and NOX1 rather than on NOX2, due, in part, to concerns about possible immunosuppressive side effects. Nevertheless, NOX2 clearly contributes to the pathogenesis of many inflammatory diseases, and its inhibition is predicted to provide a novel therapeutic approach.

CRITICAL ISSUES

Possible side effects that might arise from targeting NOX2 are discussed, including the possibility that such inhibition will contribute to increased infections and/or autoimmune disorders. The state of the field with regard to existing NOX2 inhibitors and targeted development of novel inhibitors is also summarized.

FUTURE DIRECTIONS

NOX2 inhibitors show particular promise for the treatment of inflammatory diseases, both acute and chronic. Theoretical side effects include pro-inflammatory and autoimmune complications and should be considered in any therapeutic program, but in our opinion, available data do not indicate that they are sufficiently likely to eliminate NOX2 as a drug target, particularly when weighed against the seriousness of many NOX2-related indications. Model studies demonstrating efficacy with minimal side effects are needed to encourage future development of NOX2 inhibitors as therapeutic agents.

Evolution of NADPH Oxidase Inhibitors: Selectivity and Mechanisms for Target Engagement

SIGNIFICANCE

Oxidative stress, an excess of reactive oxygen species (ROS) production versus consumption, may be involved in the pathogenesis of different diseases. The only known enzymes solely dedicated to ROS generation are nicotinamide adenine dinucleotide phosphate (NADPH) oxidases with their catalytic subunits (NOX). After the clinical failure of most antioxidant trials, NOX inhibitors are the most promising therapeutic option for diseases associated with oxidative stress.

RECENT ADVANCES

Historical NADPH oxidase inhibitors, apocynin and diphenylene iodonium, are un-specific and not isoform selective. Novel NOX inhibitors stemming from rational drug discovery approaches, for example, GKT137831, ML171, and VAS2870, show improved specificity for NADPH oxidases and moderate NOX isoform selectivity. Along with NOX2 docking sequence (NOX2ds)-tat, a peptide-based inhibitor, the use of these novel small molecules in animal models has provided preliminary in vivo evidence for a pathophysiological role of specific NOX isoforms.

CRITICAL ISSUES

Here, we discuss whether novel NOX inhibitors enable reliable validation of NOX isoforms' pathological roles and whether this knowledge supports translation into pharmacological applications. Modern NOX inhibitors have increased the evidence for pathophysiological roles of NADPH oxidases. However, in comparison to knockout mouse models, NOX inhibitors have limited isoform selectivity. Thus, their use does not enable clear statements on the involvement of individual NOX isoforms in a given disease.

FUTURE DIRECTIONS

The development of isoform-selective NOX inhibitors and biologicals will enable reliable validation of specific NOX isoforms in disease models other than the mouse. Finally, GKT137831, the first NOX inhibitor in clinical development, is poised to provide proof of principle for the clinical potential of NOX inhibition.

NOX Modifiers-Just a Step Away from Application in the Therapy of Airway Inflammation?

SIGNIFICANCE

NADPH oxidase (NOX) enzymes, which are widely expressed in different airway cell types, not only contribute to the maintenance of physiological processes in the airways but also participate in the pathogenesis of many acute and chronic diseases. Therefore, the understanding of NOX isoform regulation, expression, and the manner of their potent inhibition might lead to effective therapeutic approaches.

RECENT ADVANCES

The study of the role of NADPH oxidases family in airway physiology and pathophysiology should be considered as a work in progress. While key questions still remain unresolved, there is significant progress in terms of our understanding of NOX importance in airway diseases as well as a more efficient way of using NOX modifiers in human settings.

CRITICAL ISSUES

Agents that modify the activity of NADPH enzyme components would be considered useful tools in the treatment of various airway diseases. Nevertheless, profound knowledge of airway pathology, as well as the mechanisms of NOX regulation is needed to develop potent but safe NOX modifiers.

FUTURE DIRECTIONS

Many compounds seem to be promising candidates for development into useful therapeutic agents, but their clinical potential is yet to be demonstrated. Further analysis of basic mechanisms in human settings, high-throughput compound scanning, clinical trials with new and existing molecules, and the development of new drug delivery approaches are the main directions of future studies on NOX modifiers. In this article, we discuss the current knowledge with regard to NOX isoform expression and regulation in airway inflammatory diseases as well as the aptitudes and therapeutic potential of NOX modifiers.

NADPH oxidases and cancer

The mechanism by which reactive oxygen species (ROS) are produced by tumour cells remained incompletely understood until the discovery over the last 15 years of the family of NADPH oxidases (NOXs 1–5 and dual oxidases DUOX1/2) which are structural homologues of gp91phox, the major membrane-bound component of the respiratory burst oxidase of leucocytes. Knowledge of the roles of the NOX isoforms in cancer is rapidly expanding. Recent evidence suggests that both NOX1 and DUOX2 species produce ROS in the gastrointestinal tract as a result of chronic inflammatory stress; cytokine induction (by interferon-γ, tumour necrosis factor α, and interleukins IL-4 and IL-13) of NOX1 and DUOX2 may contribute to the development of colorectal and pancreatic carcinomas in patients with inflammatory bowel disease and chronic pancreatitis, respectively. NOX4 expression is increased in pre-malignant fibrotic states which may lead to carcinomas of the lung and liver. NOX5 is highly expressed in malignant melanomas, prostate cancer and Barrett's oesophagus-associated adenocarcinomas, and in the last it is related to chronic gastro-oesophageal reflux and inflammation. Over-expression of functional NOX proteins in many tissues helps to explain tissue injury and DNA damage from ROS that accompany pre-malignant conditions, as well as elucidating the potential mechanisms of NOX-related damage that contribute to both the initiation and the progression of a wide range of solid and haematopoietic malignancies.

BcNoxD, a putative ER protein, is a new component of the NADPH oxidase complex in Botrytis cinerea

NADPH oxidases (Nox) are major enzymatic producer of reactive oxygen species (ROS). In fungi these multi-enzyme complexes are involved in sexual differentiation and pathogenicity. However, in contrast to mammalian systems, the composition and recruitment of the fungal Nox complexes are unresolved. Here we introduce a new Nox component, the membrane protein NoxD in the grey mold fungus Botrytis cinerea. It has high homology to the ER protein Pro41 from Sordaria macrospora, similar functions to the catalytic Nox subunit BcNoxA in differentiation and pathogenicity, and shows similarities to phagocytic p22phox. BcNoxA and BcNoxD interact with each other. Both proteins are involved in pathogenicity, fusion of conidial anastomosis tubes (CAT) and formation of sclerotia and conidia. These data support our earlier view based on localization studies, for an ER-related function of the Nox complex. We present the first evidence that some functions of the BcNoxA complex are indeed linked to the ER, while others clearly require export from the ER.

Nox family NADPH oxidases: Molecular mechanisms of activation

NADPH oxidases of the Nox family are important enzymatic sources of reactive oxygen species (ROS). Numerous homologue-specific mechanisms control the activity of this enzyme family involving calcium, free fatty acids, protein-protein interactions, intracellular trafficking, and posttranslational modifications such as phosphorylation, acetylation, or sumoylation. After a brief review on the classic pathways of Nox activation, this article will focus on novel mechanisms of homologue-specific activity control and on cell-specific aspects which govern Nox activity. From these findings of the recent years it must be concluded that the activity control of Nox enzymes is much more complex than anticipated. Moreover, depending on the cellular activity state, Nox enzymes are selectively activated or inactivated. The complex upstream signaling aspects of these events make the development of "intelligent" Nox inhibitors plausible, which selectively attenuate disease-related Nox-mediated ROS formation without altering physiological signaling ROS. This approach might be of relevance for Nox-mediated tissue injury in ischemia-reperfusion and inflammation and also for chronic Nox overactivation as present in cancer initiation and cardiovascular disease.

NADPH oxidases: an overview from structure to innate immunity-associated pathologies

Oxygen-derived free radicals, collectively termed reactive oxygen species (ROS), play important roles in immunity, cell growth, and cell signaling. In excess, however, ROS are lethal to cells, and the overproduction of these molecules leads to a myriad of devastating diseases. The key producers of ROS in many cells are the NOX family of NADPH oxidases, of which there are seven members, with various tissue distributions and activation mechanisms. NADPH oxidase is a multisubunit enzyme comprising membrane and cytosolic components, which actively communicate during the host responses to a wide variety of stimuli, including viral and bacterial infections. This enzymatic complex has been implicated in many functions ranging from host defense to cellular signaling and the regulation of gene expression. NOX deficiency might lead to immunosuppression, while the intracellular accumulation of ROS results in the inhibition of viral propagation and apoptosis. However, excess ROS production causes cellular stress, leading to various lethal diseases, including autoimmune diseases and cancer. During the later stages of injury, NOX promotes tissue repair through the induction of angiogenesis and cell proliferation. Therefore, a complete understanding of the function of NOX is important to direct the role of this enzyme towards host defense and tissue repair or increase resistance to stress in a timely and disease-specific manner.

Nox4: a hydrogen peroxide-generating oxygen sensor

Nox4 is an oddity among members of the Nox family of NADPH oxidases [seven isoenzymes that generate reactive oxygen species (ROS) from molecular oxygen] in that it is constitutively active. All other Nox enzymes except for Nox4 require upstream activators, either calcium or organizer/activator subunits (p47(phox), NOXO1/p67(phox), and NOXA1). Nox4 may also be unusual as it reportedly releases hydrogen peroxide (H₂O₂) in contrast to Nox1-Nox3 and Nox5, which release superoxide, although this result is controversial in part because of possible membrane compartmentalization of superoxide, which may prevent detection. Our studies were undertaken (1) to identify the Nox4 ROS product using a membrane-free, partially purified preparation of Nox4 and (2) to test the hypothesis that Nox4 activity is acutely regulated not by activator proteins or calcium, but by cellular pO₂, allowing it to function as an O₂ sensor, the output of which is signaling H₂O₂. We find that approximately 90% of the electron flux through isolated Nox4 produces H₂O₂ and 10% forms superoxide. The kinetic mechanism of H₂O₂ formation is consistent with a mechanism involving binding of one oxygen molecule, which is then sequentially reduced by the heme in two one-electron reduction steps first to form a bound superoxide intermediate and then H₂O₂; kinetics are not consistent with a previously proposed internal superoxide dismutation mechanism involving two oxygen binding/reduction steps for each H₂O₂ formed. Critically, Nox4 has an unusually high Km for oxygen (∼18%), similar to the values of known oxygen-sensing enzymes, compared with a Km of 2-3% for Nox2, the phagocyte NADPH oxidase. This allows Nox4 to generate H₂O₂ as a function of oxygen concentration throughout a physiological range of pO2 values and to respond rapidly to changes in pO₂.

Oxidative Stress and the Use of Antioxidants in Stroke

Transient or permanent interruption of cerebral blood flow by occlusion of a cerebral artery gives rise to an ischaemic stroke leading to irreversible damage or dysfunction to the cells within the affected tissue along with permanent or reversible neurological deficit. Extensive research has identified excitotoxicity, oxidative stress, inflammation and cell death as key contributory pathways underlying lesion progression. The cornerstone of treatment for acute ischaemic stroke remains reperfusion therapy with recombinant tissue plasminogen activator (rt-PA). The downstream sequelae of events resulting from spontaneous or pharmacological reperfusion lead to an imbalance in the production of harmful reactive oxygen species (ROS) over endogenous anti-oxidant protection strategies. As such, anti-oxidant therapy has long been investigated as a means to reduce the extent of injury resulting from ischaemic stroke with varying degrees of success. Here we discuss the production and source of these ROS and the various strategies employed to modulate levels. These strategies broadly attempt to inhibit ROS production or increase scavenging or degradation of ROS. While early clinical studies have failed to translate success from bench to bedside, the combination of anti-oxidants with existing thrombolytics or novel neuroprotectants may represent an avenue worthy of clinical investigation. Clearly, there is a pressing need to identify new therapeutic alternatives for the vast majority of patients who are not eligible to receive rt-PA for this debilitating and devastating disease.

NADPH oxidases in lung health and disease

SIGNIFICANCE

The evolution of the lungs and circulatory systems in vertebrates ensured the availability of molecular oxygen (O2; dioxygen) for aerobic cellular metabolism of internal organs in large animals. O2 serves as the physiologic terminal acceptor of mitochondrial electron transfer and of the NADPH oxidase (Nox) family of oxidoreductases to generate primarily water and reactive oxygen species (ROS), respectively.

RECENT ADVANCES

The purposeful generation of ROS by Nox family enzymes suggests important roles in normal physiology and adaptation, most notably in host defense against invading pathogens and in cellular signaling.

CRITICAL ISSUES

However, there is emerging evidence that, in the context of chronic stress and/or aging, Nox enzymes contribute to the pathogenesis of a number of lung diseases.

FUTURE DIRECTIONS

Here, we review evolving functions of Nox enzymes in normal lung physiology and emerging pathophysiologic roles in lung disease.

The quest for selective nox inhibitors and therapeutics: challenges, triumphs and pitfalls

SIGNIFICANCE

Numerous studies in animal models and human subjects corroborate that elevated levels of reactive oxygen species (ROS) play a pivotal role in the progression of multiple diseases. As a major source of ROS in many organ systems, the NADPH oxidase (Nox) has become a prime target for therapeutic development.

RECENT ADVANCES

In recent years, intense efforts have been dedicated to the development of pan- and isoform-specific Nox inhibitors as opposed to antioxidants that proved ineffective in clinical trials. Over the past decade, an array of compounds has been proposed in an attempt to fill this void.

CRITICAL ISSUES

Although many of these compounds have proven effective as Nox enzyme family inhibitors, isoform specificity has posed a formidable challenge to the scientific community. This review surveys the most prominent Nox inhibitors, and discusses potential isoform specificity, known mechanisms of action, and shortcomings. Some of these inhibitors hold substantial promise as targeted therapeutics.

FUTURE DIRECTIONS

Increased insight into the mechanisms of action and regulation of this family of enzymes as well as atomic structures of key Nox subunits are expected to give way to a broader spectrum of more potent, efficacious, and specific molecules. These lead molecules will assuredly serve as a basis for drug development aimed at treating a wide array of diseases associated with increased Nox activity.

P21-activated kinase in inflammatory and cardiovascular disease

P-21 activated kinases, or PAKs, are serine-threonine kinases that serve a role in diverse biological functions and organ system diseases. Although PAK signaling has been the focus of many investigations, still our understanding of the role of PAK in inflammation is incomplete. This review consolidates what is known about PAK1 across several cell types, highlighting the role of PAK1 and PAK2 in inflammation in relation to NADPH oxidase activation. This review explores the physiological functions of PAK during inflammation, the role of PAK in several organ diseases with an emphasis on cardiovascular disease, and the PAK signaling pathway, including activators and targets of PAK. Also, we discuss PAK1 as a pharmacological anti-inflammatory target, explore the potentials and the limitations of the current pharmacological tools to regulate PAK1 activity during inflammation, and provide indications for future research. We conclude that a vast amount of evidence supports the idea that PAK is a central molecule in inflammatory signaling, thus making PAK1 itself a promising prospective pharmacological target.

Ebselen and congeners inhibit NADPH oxidase 2-dependent superoxide generation by interrupting the binding of regulatory subunits

NADPH oxidases (Nox) are a primary source of reactive oxygen species (ROS), which function in normal physiology and, when overproduced, in pathophysiology. Recent studies using mice deficient in Nox2 identify this isoform as a novel target against Nox2-implicated inflammatory diseases. Nox2 activation depends on the binding of the proline-rich domain of its heterodimeric partner p22phox to p47phox. A high-throughput screen that monitored this interaction via fluorescence polarization identified ebselen and several of its analogs as inhibitors. Medicinal chemistry was performed to explore structure-activity relationships and to optimize potency. Ebselen and analogs potently inhibited Nox1 and Nox2 activity but were less effective against other isoforms. Ebselen also blocked translocation of p47phox to neutrophil membranes. Thus, ebselen and its analogs represent a class of compounds that inhibit ROS generation by interrupting the assembly of Nox2-activating regulatory subunits.

Nox4 redox regulation of PTP1B contributes to the proliferation and migration of glioblastoma cells by modulating tyrosine phosphorylation of coronin-1C

Glioblastoma multiforme is a common primary brain tumor in adults and one of the most devastating human cancers. Reactive oxygen species (ROS) generated by NADPH oxidase (Nox) 4 have recently been a focus of attention in the study of glioblastomas, but the molecular mechanisms underlying the actions of Nox4 remain elusive. In this study, we demonstrated that silencing of Nox4 expression by Nox4-targeted siRNA suppressed cell growth and motility of glioblastoma U87 cells, indicating the involvement of Nox4. Furthermore, Nox4-derived ROS oxidized and inactivated protein tyrosine phosphatase (PTP):1B: PTP1B in its active form downregulates cell proliferation and migration. By affinity purification with the substrate-trapping mutant of PTP1B, tyrosine-phosphorylated coronin-1C was identified as a substrate of PTP1B. Its tyrosine phosphorylation level was suppressed by Nox4 inhibition, suggesting that tyrosine phosphorylation of coronin-1C is regulated by the Nox4-PTP1B pathway. Finally, ablation of coronin-1C attenuated the proliferative and migratory activity of the cells. Collectively, these findings reveal that Nox4-mediated redox regulation of PTP1B serves as a modulator, in part through coronin-1C, of the growth and migration of glioblastoma cells, and provide new insight into the mechanistic aspect of glioblastoma malignancy.

Characterization of NADPH oxidase 5 expression in human tumors and tumor cell lines with a novel mouse monoclonal antibody

Reactive oxygen species generated by NADPH oxidase 5 (Nox5) have been implicated in physiological and pathophysiological signaling pathways, including cancer development and progression. However, because immunological tools are lacking, knowledge of the role of Nox5 in tumor biology has been limited; the expression of Nox5 protein across tumors and normal tissues is essentially unknown. Here, we report the characterization and use of a mouse monoclonal antibody against a recombinant Nox5 protein (bp 600-746) for expression profiling of Nox5 in human tumors by tissue microarray analysis. Using our novel antibody, we also report the detection of endogenous Nox5 protein in human UACC-257 melanoma cells. Immunofluorescence, confocal microscopy, and immunohistochemical techniques were employed to demonstrate Nox5 localization throughout UACC-257 cells, with perinuclear enhancement. Tissue microarray analysis revealed, for the first time, substantial Nox5 overexpression in several human cancers, including those of prostate, breast, colon, lung, brain, and ovary, as well as in malignant melanoma and non-Hodgkin lymphoma; expression in most nonmalignant tissues was negative to weak. This validated mouse monoclonal antibody will promote further exploration of the functional significance of Nox5 in human pathophysiology, including tumor cell growth and proliferation.

C-terminal truncation of Noxa1 greatly enhances its ability to activate Nox2 in a pure reconstitution system

Noxa1 activates Nox2 together with Noxo1 and Rac in a pure reconstitution system, but the resulting activity is considerably lower than that induced by p67(phox) and p47(phox). In this study, we found that C-terminal-truncated forms of Noxa1 exhibited higher activities than full-length Noxa1. Of the truncations examined, Noxa1(1-225) showed the highest ability for activation. Kinetic studies revealed that Noxa1(1-225) had a threefold higher Vmax value than full-length Noxa1 with a similar EC50 value. The affinities of Noxo1 and RacQ61L were not much altered by the truncation. Conversely, the affinity of FAD for the Nox2 complex was enhanced after the truncation. In the absence of Noxo1, Noxa1(1-225) showed much higher activity with a lower EC50 than full-length Noxa1. Noxa1(1-225) showed comparable activity to that of p67(phox) with either Noxo1 or p47(phox), although the stability was lower than that with p67(phox) and p47(phox). These findings indicate that the role of the C-terminal half of Noxa1 is autoinhibition. The data suggest a two-step autoinhibition mechanism, comprising self-masking to interrupt the binding to the oxidase, and holding of the activation domain in a suboptimal position to the oxidase. This study reveals that when both types of inhibition are released, Noxa1 achieves high-level superoxide production.

Noise-induced changes in expression levels of NADPH oxidases in the cochlea

NADPH oxidases are enzymes that transport electrons across the plasma membrane and generate superoxide radical from molecular oxygen. The current study investigated the expression and distribution of NOX/DUOX members of the NADPH oxidase family (NOX1-5 and DUOX1-2) in the rat cochlea and their regulation in response to noise. Wistar rats (8-10 weeks) were exposed for 24 h to band noise (8-12 kHz) at moderate (100 dB) or traumatic (110 dB) sound pressure levels (SPL). Animals exposed to ambient noise (45-55 dB SPL) served as controls. Immunohistochemistry demonstrated predominant expression of all NOX/DUOX isoforms in the sensory and supporting cells of the organ of Corti, with very limited immunoexpression in the lateral wall tissues and spiral ganglion neurons. Noise exposure induced up-regulation of NOX1 and DUOX2 in the cochlea, whereas NOX3 was down-regulated. A significant reduction in the intensity of NOX3 immunolabeling was observed in the inner sulcus region of the cochlea after exposure to noise. Post-exposure inhibition of NADPH oxidases by Diphenyleneiodonium (DPI), a broadly selective NADPH oxidase inhibitor, mitigated noise-induced hearing loss.

CONCLUSION

Noise-induced up-regulation of NOX1 and DUOX2 could be linked to cochlear injury. In contrast, down-regulation of NOX3 may represent an endogenous protective mechanism to reduce oxidative stress in the noise-exposed cochlea. Inhibition of NADPH oxidases is potentially a novel pathway for therapeutic management of noise-induced hearing loss.

NADPH Oxidase as a Therapeutic Target for Neuroprotection against Ischaemic Stroke: Future Perspectives

Oxidative stress caused by an excess of reactive oxygen species (ROS) is known to contribute to stroke injury, particularly during reperfusion, and antioxidants targeting this process have resulted in improved outcomes experimentally. Unfortunately these improvements have not been successfully translated to the clinical setting. Targeting the source of oxidative stress may provide a superior therapeutic approach. The NADPH oxidases are a family of enzymes dedicated solely to ROS production and pre-clinical animal studies targeting NADPH oxidases have shown promising results. However there are multiple factors that need to be considered for future drug development: There are several homologues of the catalytic subunit of NADPH oxidase. All have differing physiological roles and may contribute differentially to oxidative damage after stroke. Additionally, the role of ROS in brain repair is largely unexplored, which should be taken into consideration when developing drugs that inhibit specific NADPH oxidases after injury. This article focuses on the current knowledge regarding NADPH oxidase after stroke including in vivo genetic and inhibitor studies. The caution required when interpreting reports of positive outcomes after NADPH oxidase inhibition is also discussed, as effects on long term recovery are yet to be investigated and are likely to affect successful clinical translation.

Reactive oxygen species production in the phagosome: impact on antigen presentation in dendritic cells

SIGNIFICANCE

The NADPH oxidase 2 (NOX2) is known to play a major role in innate immunity for several decades. Phagocytic cells provide host defense by ingesting microbes and destroy them by different mechanisms, including the generation of reactive oxygen species (ROS) by NOX2, a process known as oxidative burst. The phagocytic pathway of dendritic cells (DCs), highly adapted to antigen processing, has been shown to display remarkable differences compared to other phagocytes. Contrary to macrophages and neutrophils, the main function of DC phagosomes is antigen presentation rather than pathogen killing or clearance of cell debris.

RECENT ADVANCES

In the last few years, it became clear that NOX2 is also involved in the establishment of adaptive immunity. Several studies support the idea of a relationship between antigen presentation and the level of antigen degradation, the latter one being regulated by the pH and ROS within phagosomes.

CRITICAL ISSUES

The regulation of phagosomal pH exerted by NOX2, and thereby of the efficacy of antigen cross-presentation in DCs, represents a clear illustration of how NOX2 can influence CD8(+) T lymphocyte responses. In this review, we want to put emphasis on the relationship between ROS generation and antigen processing and presentation, since there is growing evidence that the low levels of ROS generated by DCs play an important role in these processes.

FUTURE DIRECTIONS

In the next years, it will be interesting to unravel possible mechanisms involved and to find other possible connections between NOX family members and adaptive immune responses.

Toward understanding the genetic basis of adaptation to high-elevation life in poikilothermic species: a comparative transcriptomic analysis of two ranid frogs, Rana chensinensis and R. kukunoris

BACKGROUND

Understanding how organisms adapt to high-elevation environments at a genome scale provides novel insights into the process of adaptive evolution. Previous studies have mainly focused on endothermic organisms, while poikilothermic species may have evolved different mechanisms to cope with high-elevation environments. In this context, we sequenced transcriptomes of a pair of closely related anuran species, Rana chensinensis and R. kukunoris, which inhabit respective low- and high-elevation habitats. By comparing the two transcriptomes, we identified candidate genes that may be involved in high-elevation adaption in poikilothermic species.

RESULTS

Over 66 million sequence reads from each transcriptome were generated. A total of 41,858 and 39,293 transcripts for each species were obtained by de novo assembly. By comparing the orthologous transcripts, we identified 125 protein-coding genes that have likely experienced strong positive selection (Ka/Ks>1). In addition, 335 genes that may bear a signature of positive selection (1≥Ka/Ks>0.5) were also recognized. By considering their functions, fourteen candidate genes were determined to be likely involved in high-elevation adaptation, including two CYP genes, USP-1, and several others.

CONCLUSIONS

We identified a set of candidate genes that may have promoted adaptation of R. kukunoris to its high-elevation environment. These include several genes that have previously been associated with oxygen binding, response to UV radiation, and repair of free radical injury. Detailed molecular, physiological, and phenotypic studies are required to better understand the roles of these genes in improving the performance of R. kukunoris in a high-elevation environment. We have evidence for both convergent and divergent evolution between endothermic and poikilothemic species, but additional research across a wide range of organisms will be necessary to comprehend the complexity of high-elevation adaptation.