Current Pharmaceutical Design - Volume 21, Issue 41, 2015

The family of NADPH oxidase (Nox) proteins plays an integral role in the homeostatic functions of the cell, including gene expression, cell migration, proliferation, senescence and inflammation. There are currently 4 isoforms (Nox1, 2, 4 and 5) that are expressed across all cell types of the vascular system and play an important role in many physiological processes such as endothelial function, vascular tone and angiogenesis. The balance between Nox derived reactive oxygen species production and their elimination by dismutase enzymes is a critical finely tuned process. It is when this balance is shifted in disease states, either leading to an over- or under-production of reactive oxygen species that vascular injury develops. To date, Nox isoforms have been linked to the development of many vascular diseases including hypertension, atherosclerosis and stroke. The contribution of each isoform to the pathophysiology of vascular disease appears to be a matter of debate with most studies suggesting that Nox1 oxidase and Nox2 oxidase play deleterious roles, whereas Nox4 oxidase potentially plays a protective role in the vasculature. This review will discuss the current knowledge on the role of Nox derived oxidative stress in the pathophysiology of various vascular diseases including hypertension and atherosclerosis.

Experimental and clinical studies provided evidence that formation of intra-platelet reactive oxidant species (ROS) is implicated in the process of thrombosis. Animal models demonstrated that enhanced ROS formation was associated with serious thrombotic complications and death. In recent years, nutritional and therapeutic approaches were tested to modulate ROS mediated thrombus formation. The use of a nutritional approach stems from the observation that foods rich in antioxidant elements, such as polyphenols, were able to modulate ROS formation. Similarly, some drugs used for different diseases (i.e. statins) showed the ability to modulate oxidative stress. Aim of this review is to summarize current evidences supporting the role of nutrients rich in polyphenols, such as olive oil and cocoa, and of some drugs, such as statins as antiplatelet agents interfering with the Nicotinamide Adenine Dinucleotide Phosphate (NADPH) Oxidase signaling. Indeed, for nutrients and statins, the antiplatelet activity seems to be dependent, at least in part, upon the inhibition of platelet NADPH oxidase–derived ROS formation, resulting in down-regulation of isoprostanes, which are pro-aggregating molecules, and up-regulation of nitric oxide, which is a platelet inhibitor.

Reactive oxygen species (ROS) contribute to the pathogenesis of cardiovascular disease, including hypertension, atherosclerosis, cardiac hypertrophy, heart failure and restenosis. Thiol proteins and thiol oxidoreductases are key players in cell signaling, and their altered expression and/or activity has been associated with a disrupture in cardiac and vascular homeostasis. Protein disulfide isomerase (PDI) is a thiol oxidoreductase member of the thioredoxin family that has multiple roles in cellular function. Originally discovered in the endoplasmic reticulum (ER), PDI is essential for protein folding. However, it can also be found in the cytosol and closely associated with the surface of platelets, smooth muscle cells, neutrophils and endothelial cells. On the cell surface, PDI is imperative for platelet aggregation and transnitrosation, which are related to thrombosis and control of vascular tone by nitric oxide, respectively. Furthermore, PDI signaling contributes to redox-dependent events such as smooth muscle cell migration induced by PDGF and TNFα-dependent angiogenesis. Studies from our group have shown that intracellular PDI regulates the expression and activity of the NADPH oxidase family of proteins (Nox), which are enzymes dedicated to ROS generation. PDI acts as a new organizer of leukocyte Nox2 by redox dependently associating with p47phox and controlling its recruitment to the plasma membrane, an essential step for assembly of the active enzyme. Such multiple effects of PDI suggest that specific targeting of this oxidoreductase could represent a new approach in the treatment of vascular disease. In this review, we present a novel role for PDI as an adaptor protein involved in redox processes and Nox signaling and propose PDI as a potential therapeutic target in the treatment of atherosclerosis, thrombosis and hypertension.

Liver fibrosis is a pathological consequence of chronic liver diseases and results from the progressive accumulation of altered extracellular matrix, highly enriched in type I and III fibrillar collagens. In advanced stages, fibrosis leads to cirrhosis, defined by abnormal liver architecture and altered vascularization. Clinical consequences of cirrhosis are failure in the synthetic function of the liver, portal hypertension, high susceptibility to infection and high risk to develop hepatocellular carcinoma (HCC). The TGF-β family of cytokines plays essential roles in many cellular processes, including growth inhibition, cell migration and invasion, extracellular matrix remodelling and immune suppression, being involved in the maintenance of tissue homeostasis. However, TGF-βs are often continuously overexpressed in disease states, such as fibrosis, inflammation and cancer, and they play pivotal roles in the sequence of events leading to end-stage of chronic liver diseases. Reactive oxygen species (ROS) are critical intermediates in liver physiology and pathology. When the equilibrium between ROS generation and the antioxidant defence of the cell is disrupted, it results in an oxidative stress process. The NADPH oxidase (NOX) family has emerged in the last years as important source of ROS in liver pathologies. Interestingly, NOXes mediate TGF-β actions in liver cells, such as regulation of hepatocyte growth and death, as well as activation of hepatic stellate cells to myofibroblasts, key executers of the fibrotic process. In this review we will update the relevant and differential roles of NOX isoforms during liver fibrosis and hepatocarcinogenesis, their cross-talk with the TGF-β pathway and their potential as therapeutic targets for these diseases.

Inner ear pathologies are associated with major morbidity and loss of life quality in affected patients. In many of these conditions, production of reactive oxygen-species (ROS) is thought to be a key pathological mechanism. While the sources of ROS are complex (including for example mitochondria), there is increasing evidence that activation of NOX enzymes, in particular NOX3, plays a key role. NOX3 is a multi-subunit NADPH oxidase, functionally and structurally closely related to NOX1 and NOX2. In both the vestibular and the cochlear compartments of the inner ear, high levels of NOX3 mRNA are expressed. In NOX3 mutant mice, the vestibular function is perturbed due to a lack of otoconia, while only minor alterations of hearing have been documented. However, there is increasing evidence that activation of NOX3 through drugs, noise and probably also aging, leads to hearing loss. Thus, NOX3 is an interesting target to treat and prevent inner ear pathologies and a few first animal models based on drug - or molecular therapy have been reported. So far however, there are no specific NOX3 inhibitors with a documented penetration into the inner ear. Nevertheless, certain antioxidants and non-specific NOX inhibitors diminish hearing loss in animal models. Development of small molecules inhibitors or molecular strategies against NOX3 could improve specificity and efficiency of redox-targeted treatments. In this review, we will discuss arguments for the involvement of NOX3 in inner ear pathologies and therapeutic approaches to target NOX3 activity.

Pathological angiogenesis in the retina is a leading cause of serious vision loss in potentially blinding eye diseases, including proliferative diabetic retinopathy, retinopathy of prematurity and the wet form of agerelated macular degeneration. Hypoxia is thought to be the driver of pathological angiogenesis, and transcription factors such as hypoxia-inducible factor (HIF) and vascular endothelial growth factor (VEGF) are key mediators in these processes. Current treatments employ either laser photocoagulation or intravitreal injection of therapeutic antibodies for VEGF, in order to arrest the growth of leaky blood vessels in the avascular vitreous cavity and to restore visual acuity. However, all such therapeutic approaches are limited by low or variable efficacy, and the inconvenience, risk and financial burden of such treatments, which need to be given frequently. The lack of noninvasive and efficacious therapy has therefore driven the search for alternative strategies. We have been interested in the roles of reactive oxygen species (ROS), such as superoxide and hydrogen peroxide, which when produced intracellularly at low concentration can act as second messengers to regulate physiological and pathological angiogenesis. Accumulating evidence suggests NADPH oxidase-dependent ROS are involved in regulation of the angiogenic signalling pathways of HIF and VEGF. Suppressing pathological neovascularisation in the retina by manipulating such redox mechanisms appears to be an attractive and clinically translatable therapeutic strategy to treat proliferative neovascular eye diseases. Here we provide a brief overview of the roles of NADPH oxidase in the sensing and regulation processes involving HIF and VEGF that contribute to the development of pathological angiogenesis in the retina.

The NADPH oxidases (NOX) represent a family of 7 related transmembrane enzymes that share a basic structural paradigm and the common ability to utilize NADPH to synthesize superoxide and other reactive oxygen species (ROS). NOX isoforms are distinguished from each other by their amino acid sequences, expression levels in different cell types, the mechanisms of enzyme activation and the type of ROS that are generated. NOX5 was the last NOX family member to be identified and in the past decade and a half we have gained significant insights into how NOX5 produces ROS, the cell types where it is expressed and the functional significance of NOX5 in health and disease. The objective of this review is to highlight accumulated and recent knowledge of the genetic and enzymatic regulation of NOX5 and the importance of NOX5 in human physiology and pathophysiology.

Nox generated ROS, particularly those derived from Nox1, Nox2 and Nox4, have emerged as important regulators of the actin cytoskeleton and cytoskeleton-supported cell functions, such as migration and adhesion. The effects of Nox-derived ROS on cytoskeletal remodeling may be largely attributed to the ability of ROS to directly modify proteins that constitute or are associated with the cytoskeleton. Additionally, Nox-derived ROS may participate in signaling pathways governing cytoskeletal remodeling. In addition to these more extensively studied signaling pathways involving Nox-derived ROS, there also exist redox sensitive pathways for which the source of ROS is unclear. ROS from as of yet undetermined sources play a role in modifying, and thus regulating, the activity of several proteins critical for remodeling of the actin cytoskeleton. In this review we discuss ROS sensitive targets that are likely to affect cytoskeletal dynamics, as well as the potential involvement of Nox proteins.

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.