Redox Pathogenesis in Rheumatic Diseases

Despite being some of the most anecdotally well-known roads to pathogenesis, the mechanisms governing autoimmune rheumatic diseases are not yet fully understood. The overactivation of the cellular immune system and the characteristic development of autoantibodies have been linked to oxidative stress. Typical clinical manifestations, such as joint swelling and deformities and inflammation of the skin and internal organs, have also been connected directly or indirectly to redox mechanisms. The differences in generation and restraint of oxidative stress provide compelling evidence for the broad variety in pathology among rheumatic diseases and explain some of the common triggers and discordant manifestations in these diseases. Growing evidence of redox mechanisms in pathogenesis has provided a broad array of new potential therapeutic targets. Here, we explore the mechanisms by which oxidative stress is generated, explore its roles in autoimmunity and end-organ damage, and discuss how individual rheumatic diseases exhibit unique features that offer targets for therapeutic interventions.

Oxidative Stress Induced by Reactive Oxygen Species (ROS) and NADPH Oxidase 4 (NOX4) in the Pathogenesis of the Fibrotic Process in Systemic Sclerosis: A Promising Therapeutic Target

Numerous clinical and research investigations conducted during the last two decades have implicated excessive oxidative stress caused by high levels of reactive oxygen species (ROS) in the development of the severe and frequently progressive fibrotic process in Systemic Sclerosis (SSc). The role of excessive oxidative stress in SSc pathogenesis has been supported by the demonstration of increased levels of numerous biomarkers, indicative of cellular and molecular oxidative damage in serum, plasma, and other biological fluids from SSc patients, and by the demonstration of elevated production of ROS by various cell types involved in the SSc fibrotic process. However, the precise mechanisms mediating oxidative stress development in SSc and its pathogenetic effects have not been fully elucidated. The participation of the NADPH oxidase NOX4, has been suggested and experimentally supported by the demonstration that SSc dermal fibroblasts display constitutively increased NOX4 expression and that reduction or abrogation of NOX4 effects decreased ROS production and the expression of genes encoding fibrotic proteins. Furthermore, NOX4-stimulated ROS production may be involved in the development of certain endothelial and vascular abnormalities and may even participate in the generation of SSc-specific autoantibodies. Collectively, these observations suggest NOX4 as a novel therapeutic target for SSc.

Prominence of IL6, IGF, TLR, and Bioenergetics Pathway Perturbation in Lung Tissues of Scleroderma Patients With Pulmonary Fibrosis

Scleroderma-associated pulmonary fibrosis (SSc-PF) and idiopathic pulmonary fibrosis (IPF) are two of many chronic fibroproliferative diseases that are responsible for nearly 45% of all deaths in developed countries. While sharing several pathobiological characteristics, they also have very distinct features. Currently no effective anti-fibrotic treatments exist that can halt the progression of PF or reverse it. Our goal is to uncover potential gene targets for the development of anti-fibrotic therapies efficacious in both diseases, and those specific to SSc-PF, by identifying universal pathways and molecules driving fibrosis in SSc-PF and IPF tissues as well as those unique to SSc-PF. Using DNA microarray data, a meta-analysis of the differentially expressed (DE) genes in SSc-PF and IPF lung tissues (diseased vs. normal) was performed followed by a full systems level analysis of the common and unique transcriptomic signatures obtained. Protein-protein interaction networks were generated to identify hub proteins and explore the data using the centrality principle. Our results suggest that therapeutic strategies targeting IL6 trans-signaling, IGFBP2, IGFL2, and the coagulation cascade may be efficacious in both SSc-PF and IPF. Further, our data suggest that the expression of matrikine-producing collagens is also perturbed in PF. Lastly, an overall perturbation of bioenergetics, specifically between glycolysis and fatty acid metabolism, was uncovered in SSc-PF. Our findings provide insights into potential targets for the development of anti-fibrotic therapies that could be effective in both IPF and SSc-PF.

Implication of oxidative stress in the pathogenesis of systemic sclerosis via inflammation, autoimmunity and fibrosis

Systemic sclerosis is an autoimmune disorder characterized by inflammation and a progressive fibrosis affecting the skin and visceral organs. Over the last two decades, it became clear that oxidative stress plays a key role in its pathogenesis. In this review, we highlighted the role of ROS in the various pathological components of systemic sclerosis, namely the inflammatory, the autoimmune and the fibrotic processes. We also discussed how these pathological processes can induce ROS overproduction, thus maintaining a vicious circle. Finally, we summarized the therapeutic approaches targeting oxidative stress tested in systemic sclerosis, in cells, animal models and patients.

Oxidative/nitrative stress in the pathogenesis of systemic sclerosis: are antioxidants beneficial?

Systemic sclerosis (SSc) is a multisystem autoimmune disease: characterised from the clinical side by progressive vasculopathy and fibrosis of the skin and different organs and from the biochemical side by fibroblast deregulation with excessive production of collagen and increased expression of nicotinamide adenine dinucleotide phosphate oxidase 4 (NOX4). The latter contributes to an overproduction of reactive oxygen species that through an autocrine loop maintains NOX4 in a state of activation. Reactive oxygen and nitrogen species are implicated in the origin and perpetuation of several clinical manifestations of SSc having vascular damage in common; attempts to dampen oxidative and nitrative stress through different agents with antioxidant properties have not translated into a sustained clinical benefit. Objective of this narrative review is to describe the origin and clinical implications of oxidative and nitrative stress in SSc, with particular focus on the central role of NOX4 and its interactions, to re-evaluate the antioxidant approaches so far used to limit disease progression, to appraise the complexity of antioxidant treatment and to touch on novel pathways elements of which may represent specific treatment targets in the not so distant future.

NADPH oxidase, oxidative stress and fibrosis in systemic sclerosis

Systemic sclerosis (SSc) is an autoimmune disease characterized by damage of small vessels, immune abnormalities and exaggerated production of extracellular matrix. The etiology of the disease is unknown and the pathogenesis ill defined. However, there is consistent evidence that oxidative stress contributes to the establishment and progression of the disease. This review examines the most relevant research regarding the involvement of free radicals and of nicotinamide adenine dinucleotide phosphate oxidases (NADPH oxidases; NOX) in the pathogenesis of systemic sclerosis.

Pulmonary function tests as outcomes for systemic sclerosis interstitial lung disease

Interstitial lung disease (ILD) is the leading cause of morbidity and mortality in systemic sclerosis (SSc). We performed a systematic review to characterise the use and validation of pulmonary function tests (PFTs) as surrogate markers for systemic sclerosis-associated interstitial lung disease (SSc-ILD) progression.Five electronic databases were searched to identify all relevant studies. Included studies either used at least one PFT measure as a longitudinal outcome for SSc-ILD progression (i.e. outcome studies) and/or reported at least one classical measure of validity for the PFTs in SSc-ILD (i.e. validation studies).This systematic review included 169 outcome studies and 50 validation studies. Diffusing capacity of the lung for carbon monoxide (DLCO) was cumulatively the most commonly used outcome until 2010 when it was surpassed by forced vital capacity (FVC). FVC (% predicted) was the primary endpoint in 70.4% of studies, compared to 11.3% for % predicted DLCO Only five studies specifically aimed to validate the PFTs: two concluded that DLCO was the best measure of SSc-ILD extent, while the others did not favour any PFT. These studies also showed respectable validity measures for total lung capacity (TLC).Despite the current preference for FVC, available evidence suggests that DLCO and TLC should not yet be discounted as potential surrogate markers for SSc-ILD progression.

Review: Metabolic Control of Immune System Activation in Rheumatic Diseases

Metabolic pathways mediate lineage specification within the immune system through the regulation of glucose utilization, a process that generates energy in the form of ATP and synthesis of amino acids, nucleotides, and lipids to enable cell growth, proliferation, and survival. CD4+ T cells, a proinflammatory cell subset, preferentially produce ATP through glycolysis, whereas cells with an antiinflammatory lineage, such as memory and regulatory T cells, favor mitochondrial ATP generation. In conditions of metabolic stress or a shortage of nutrients, cells rely on autophagy to secure amino acids and other substrates, while survival depends on the sparing of mitochondria and maintenance of a reducing environment. The pentose phosphate pathway acts as a key gatekeeper of inflammation by supplying ribose‐5‐phosphate for cell proliferation and NADPH for antioxidant defenses. Increased lysosomal catabolism, accumulation of branched amino acids, glutamine, kynurenine, and histidine, and depletion of glutathione and cysteine activate the mechanistic target of rapamycin (mTOR), an arbiter of lineage development within the innate and adaptive immune systems. Mapping the impact of susceptibility genes to metabolic pathways allows for better understanding and therapeutic targeting of disease‐specific expansion of proinflammatory cells. Therapeutic approaches aimed at glutathione depletion and mTOR pathway activation appear to be safe and effective for treating lupus, while an opposing intervention may be of benefit in rheumatoid arthritis. Environmental sources of origin for metabolites within immune cells may include microbiota and plants. Thus, a better understanding of the pathways of immunometabolism could provide new insights into the pathogenesis and treatment of the rheumatic diseases.

Role of cellular senescence and NOX4-mediated oxidative stress in systemic sclerosis pathogenesis

Systemic sclerosis (SSc) is a systemic autoimmune disease characterized by progressive fibrosis of skin and numerous internal organs and a severe fibroproliferative vasculopathy resulting frequently in severe disability and high mortality. Although the etiology of SSc is unknown and the detailed mechanisms responsible for the fibrotic process have not been fully elucidated, one important observation from a large US population study was the demonstration of a late onset of SSc with a peak incidence between 45 and 54 years of age in African-American females and between 65 and 74 years of age in white females. Although it is not appropriate to consider SSc as a disease of aging, the possibility that senescence changes in the cellular elements involved in its pathogenesis may play a role has not been thoroughly examined. The process of cellular senescence is extremely complex, and the mechanisms, molecular events, and signaling pathways involved have not been fully elucidated; however, there is strong evidence to support the concept that oxidative stress caused by the excessive generation of reactive oxygen species may be one important mechanism involved. On the other hand, numerous studies have implicated oxidative stress in SSc pathogenesis, thus, suggesting a plausible mechanism in which excessive oxidative stress induces cellular senescence and that the molecular events associated with this complex process play an important role in the fibrotic and fibroproliferative vasculopathy characteristic of SSc. Here, recent studies examining the role of cellular senescence and of oxidative stress in SSc pathogenesis will be reviewed.

Relationship between redox status and cell fate in immunity and autoimmunity

SIGNIFICANCE

The signaling function of redox molecules is essential for an efficient and proper execution of a large number of cellular processes, contributing to the maintenance of cell homeostasis. Excessive oxidative stress is considered as playing an important role in the pathogenesis of autoimmune diseases by enhancing inflammation and breaking down the immunological tolerance through protein structural modifications that induce the appearance of neo/cryptic epitopes.

RECENT ADVANCES

There is a complex reciprocal relationship between oxidative stress and both apoptosis and autophagy, which is essential to determine cell fate. This is especially relevant in the context of autoimmune disorders in which apoptosis and autophagy play a crucial pathogenic role.

CRITICAL ISSUES

In this review, we describe the latest developments with regard to the involvement of redox molecules in the initiation and progression of autoimmune disorders, focusing on their role in cell fate regulation. We also discuss new therapeutic approaches that target oxidative stress in the treatment of these disorders. The administration of antioxidants is scarcely studied in autoimmunity, and future analyses are needed to assess its beneficial effects in preventing or ameliorating these diseases.

FUTURE DIRECTIONS

Deciphering the intricate relationships between oxidative stress and both apoptosis and autophagy in the context of autoimmunity could be critical in elucidating key pathogenic mechanisms and could lead to novel interventions for the clinical management of autoimmune diseases.

N-acetylcysteine attenuates subcutaneous administration of bleomycin-induced skin fibrosis and oxidative stress in a mouse model of scleroderma

BACKGROUND

Several lines of evidence suggest that the generation of reactive oxygen species (ROS) is of major importance in the pathogenesis of scleroderma, and thus antioxidant therapy may be useful for patients with an impaired oxidative defence mechanism.

AIM

To examine the effect of N-acetylcysteine (NAC) on skin fibrosis and oxidative stress in a bleomycin (BLM)-induced mouse model of scleroderma.

METHODS

We used this mouse model to evaluate the effect of NAC on skin fibrosis and oxidative stress. Skin fibrosis was evaluated by histopathological examination and hydroxyproline content. To measure lipid peroxidation, we used a thiobarbituric acid-reactive species, malondialdehyde (MDA). Oxidative protein damage (carbonyl content) and the activities of catalase (CAT) and superoxide dismutase (SOD) were determined to evaluate oxidative stress in the skin tissue.

RESULTS

Treatment with NAC attenuated the skin fibrosis induced by BLM, significantly reducing the MDA and protein carbonyl content in these mice. SOD activity in BLM-only mice and BLM plus NAC-treated mice was increased compared with control mice. However, there was no significant difference in skin SOD activity of mice treated with both BLM and NAC compared with those treated with BLM only. In addition, CAT activity was not altered in the BLM plus NAC mice.

CONCLUSIONS

NAC treatment attenuates skin fibrosis in a BLM-induced mouse model of scleroderma, and this is associated with diminished oxidative stress. The results suggest that NAC may be a potential therapeutic agent for patients with scleroderma.

Impact of Immunity in Autism Spectrum Disorders

Autism spectrum disorders (ASDs) are childhood psychopathologies characterized by having difficulties in social interaction, verbal and non-verbal communication as well as sensor motor movements. Evidence suggests that in ASDs environmental toxicant exposure, genetic and mitochondrial dysfunction are involved associated with abnormal immune response with allergic problems and elevated serum IgE. ASDs present the major cytokine and chemokine dysfunction in CNS and is mediated by an increase of pro-inflammatory cytokine levels in the brain, such as TNF, IL-1, IFN-γ, IL-6, IL-8 and others. Mast cells, which are also implicated in ASDs, are worsened by stress and produce proinflammatory cytokines and can be stimulated by neurotensin in the brain and gut, contributing also to the inflammatory response. However, the exact etiology of ASDs remains largely unknown.

Focal adhesion kinase and reactive oxygen species contribute to the persistent fibrotic phenotype of lesional scleroderma fibroblasts

OBJECTIVE

Fibrotic diseases such as SSc (systemic sclerosis, scleroderma) are characterized by the abnormal presence of the myofibroblast, a specialized type of fibroblast that overexpresses the highly contractile protein α-smooth muscle actin. Myofibroblasts display excessive adhesive properties and hence exert a potent mechanical force. We aim to identify the precise contribution of adhesive signalling, which requires integrin-mediated activation of focal adhesion kinase (FAK)/src, to fibrogenic gene expression in normal and fibrotic SSc fibroblasts.

METHODS

We subject either FAK wild-type and knockout fibroblasts or normal and SSc fibroblasts treated with FAK/src inhibitors to real-time polymerase chain, western blot, cell migration and collagen gel contraction analyses.

RESULTS

FAK operates downstream of both integrin β1 and reactive oxygen species (ROS) to promote the expression of genes involved in matrix production and remodelling, including CCN2, α-smooth muscle actin and type I collagen. Blocking either FAK/src with PP2 or ROS with N-acetyl cysteine alleviates the elevated contractile and migratory capability of lesional SSc dermal fibroblasts.

CONCLUSIONS

Excessive adhesive signalling is intimately involved with the fibrotic phenotype of lesional SSc fibroblasts; blocking adhesive signalling or ROS generation may be beneficial in controlling the fibrosis observed in SSc.