**4.1 Oxidative stress in rheumatoid arthritis**

RA is one of the conditions that induces OS. A fivefold increase in mitochondrial ROS production in whole blood and monocytes of RA patients–compared with healthy subjects–suggests that OS is a pathogenic hallmark in RA. Free radicals are indirectly implicated in joint damage because they also play a role as secondary messengers in inflammatory and immune cellular response in RA. T-cell exposure to increased OS becomes refractory to several stimuli including those for growth and death and may perpetuate the abnormal immune response [33]. On the other hand, free radicals can degrade directly the joint cartilage, attacking its proteoglycan and inhibiting its synthesis [34]. Oxidative damage of hyaluronic acid and lipoperoxidation products and oxidation of low-density lipoproteins and carbonyl increment resulting from protein oxidation have been demonstrated in RA. Increased levels of 4-HNE have been assessed in serum (or plasma) and synovial fluid of patients with RA [35, 36]. Peroxidative damage induced by free radicals has been demonstrated to play a role in the pathogenesis not only of RA but also of systemic lupus erythematosus, progressive systemic sclerosis, diabetes mellitus type 1, and myasthenia gravis. Increased OS has been associated with increased lipid peroxidation in these patients. Lipid peroxidation occurs as a result of increased OS stemming from deranged pro-oxidant/antioxidant balance and represents an important pathogenic process in the oxygen toxicity. As a result of lipid peroxidation increases in the levels of conjugated dienes, isoprostanes, 4-HNE, and malondialdehyde have been demonstrated [37]. Study of Basu et al. [38] has shown that blood and synovial fluid from patients with various rheumatic diseases have high levels of both free radical-mediated F2-isoprostanes and the cyclooxygenasederived PGF2 metabolite. This suggests that both oxidative injury and inflammation play a part to various degrees in these chronic inflammatory diseases. The measuring of arachidonic acid metabolites in body fluids opens unique opportunities for studying the role of lipid peroxidation [38]. ROS-induced genotoxic events have also been linked to mutation of p53 in RA-derived fibroblast-like synoviocytes [39]. Furthermore, it has been suggested that antioxidants systems, either enzymatic or not, are impaired in RA. Low levels of glutathione [40], tocopherols, β-carotene, and retinols and low activities of glutathione reductase and superoxide dismutase have been observed in patients with RA [41]. In a recent study, RA patients were, as usually, sub-grouped according to the presence or absence of rheumatoid factor, disease activity score, and disease duration. In addition, RA patients and healthy controls were evaluated for the oxidant-antioxidant status by monitoring ROS production, biomarkers of lipid peroxidation, protein oxidation, and DNA damage. The endogenous levels of enzymatic and nonenzymatic antioxidants were also measured. RA patients showed a marked increase in ROS formation, lipid peroxidation, protein oxidation, DNA damage, and decrease in the activity of antioxidant defense system leading to OS, which obviously contributes to tissue damage and to the

## *Impact of Oxidative Stress on Inflammation in Rheumatoid and Adjuvant Arthritis: Damage… DOI: http://dx.doi.org/10.5772/intechopen.89480*

chronicity of the disease [42]. Oxidative modification of proteins has been shown to elicit antibodies in a variety of diseases including systemic lupus erythematosus (SLE), alcoholic liver disease, diabetes mellitus, and finally RA. Oxidative stress processes enhance the reactivity of the adaptive response. Oxidation of carbohydrates increased the antibody response to coadministered coantigens. In addition, the use of the Schiff base-forming agent Tucaresol during immunization with protein antigen increased T-cell-dependent immune response. Direct modification of protein antigen has been shown to be required for the enhancement of the immune response [43]. In SLE, oxidatively modified DNA and low-density lipoproteins (LDL) are present and induce a premature atherosclerosis. In an animal model of SLE, immunization with 4-hydroxy-2-nonenal (HNE)-modified autoantigens accelerated epitope spreading. Pentosidine, an advanced glycation end product (AGE), and AGE-modified IgG have correlated with RA disease activity. Oxidatively modified glutamic acid decarboxylase is important in type 1 diabetes mellitus. Oxidative modification induced fragmentation of scleroderma-specific autoantigens and seems to be responsible for the production of autoantibodies. Growing evidence for the involvement of oxidative damage in autoimmunity is pointing to the administration of antioxidants could be a viable untried alternative for preventing or ameliorating autoimmune disease [37]. OS occurring during inflammation can cause proteins to become nonenzymatically damaged by glyoxidation. This process results in the generation of AGE. The immunoglobulin molecule can also undergo similar glyoxidation to generate AGE-IgG. In inflammatory arthritis, they have shown that antibodies to AGE-IgG are specifically associated with RA, whereas the actual formation of AGE-IgG is related to the intensity of the systemic inflammatory response [44].

Studies focusing on direct detection of ROS and RNS found all these biomarkers elevated in RA patients suggesting an active OS. The redox status of neutrophils sourced from SF was measured by flow cytometry in terms of total ROS and hydroxyl radicals. Neutrophils a major cellular component of the SF of RA patients and their levels of ROS correlated strongly with protein carbonylation and lipid peroxidation. In patients with RA, the strong correlation between DAS28 score, levels of ROS, and markers of oxidative damage suggests that measurement of OS could serve as a marker for monitoring disease severity [45]. In another study, RA patients had significantly higher levels of ROS (O2-, H2O2) than controls. Significant differences where monitored in serum levels of NO in patients with high activity of disease. More intensive response in samples with higher disease activity suggests that oxidative/nitrosative stress markers may be valuable in evaluating the RA progression and helpful in elucidating the mechanisms of disease pathogenesis [46]. The chronic OS in the RA synovium increases ROS production in the cellular oxidative phosphorylation and induces repetitive cycles of hypoxia/reoxygenation. The hypoxia in RA joints whose origin is a consequence of the rapid cellular proliferation induced by the inflammatory response, however, precedes inflammation at least in an animal arthritis model [47]. From the "danger model," in which the synoviocyte is an impaired cell, this sequence of events could be happening in the human disease [48]. Activated phagocytic cells can also enhance this OS during oxidative burst. Kundu et al. [49] showed neutrophils as most important phagocytes responsible for elevating OS in synovial infiltrates and peripheral blood of RA patients: The basal levels of total ROS, superoxide, and hydroxyl radicals were significantly increased in neutrophils from peripheral blood and synovial infiltrate. Furthermore, raised levels of superoxide in neutrophils of synovial infiltrate showed a positive correlation with NADPH oxidase activity in synovial fluid. However, there was no major increase in the RNS generated in monocytes from both sources.

cysteines and GSH. This process is called as glutathionylation, which regulates signaling proteins and transcription factors [32]. Inflammatory stimuli induce the release of PRDX2, a ubiquitous redox-active intracellular enzyme. PRDX2 is a redox-dependent inflammatory mediator, which activates macrophages to produce and release TNF-α. During intracellular oxidative stress GSH binds with PRDX2 and

this protein glutathionylation occurs before or during PRDX2 release, and glutathionylated PRDX2 regulates immunity. PRDX2 is a part of inflammatory cascade and is able to induce TNF-α release. This study showed that PRDX2 and thioredoxin from macrophages could alter the redox balance of cell surface recep-

RA is one of the conditions that induces OS. A fivefold increase in mitochondrial

ROS production in whole blood and monocytes of RA patients–compared with healthy subjects–suggests that OS is a pathogenic hallmark in RA. Free radicals are indirectly implicated in joint damage because they also play a role as secondary messengers in inflammatory and immune cellular response in RA. T-cell exposure to increased OS becomes refractory to several stimuli including those for growth and death and may perpetuate the abnormal immune response [33]. On the other hand, free radicals can degrade directly the joint cartilage, attacking its proteoglycan and inhibiting its synthesis [34]. Oxidative damage of hyaluronic acid and lipoperoxidation products and oxidation of low-density lipoproteins and carbonyl increment resulting from protein oxidation have been demonstrated in RA. Increased levels of 4-HNE have been assessed in serum (or plasma) and synovial fluid of patients with RA [35, 36]. Peroxidative damage induced by free radicals has been demonstrated to play a role in the pathogenesis not only of RA but also of systemic lupus erythematosus, progressive systemic sclerosis, diabetes mellitus type 1, and myasthenia gravis. Increased OS has been associated with increased lipid peroxidation in these patients. Lipid peroxidation occurs as a result of increased OS stemming from deranged pro-oxidant/antioxidant balance and represents an important pathogenic process in the oxygen toxicity. As a result of lipid peroxida-

tion increases in the levels of conjugated dienes, isoprostanes, 4-HNE, and

malondialdehyde have been demonstrated [37]. Study of Basu et al. [38] has shown that blood and synovial fluid from patients with various rheumatic diseases have high levels of both free radical-mediated F2-isoprostanes and the cyclooxygenasederived PGF2 metabolite. This suggests that both oxidative injury and inflammation play a part to various degrees in these chronic inflammatory diseases. The measuring of arachidonic acid metabolites in body fluids opens unique opportunities for studying the role of lipid peroxidation [38]. ROS-induced genotoxic events have also been linked to mutation of p53 in RA-derived fibroblast-like synoviocytes [39]. Furthermore, it has been suggested that antioxidants systems, either enzymatic or not, are impaired in RA. Low levels of glutathione [40], tocopherols, β-carotene, and retinols and low activities of glutathione reductase and superoxide dismutase have been observed in patients with RA [41]. In a recent study, RA patients were, as usually, sub-grouped according to the presence or absence of rheumatoid factor, disease activity score, and disease duration. In addition, RA patients and healthy controls were evaluated for the oxidant-antioxidant status by monitoring ROS production, biomarkers of lipid peroxidation, protein oxidation, and DNA damage. The endogenous levels of enzymatic and nonenzymatic antioxidants were also measured. RA patients showed a marked increase in ROS formation, lipid peroxidation, protein oxidation, DNA damage, and decrease in the activity of antioxidant defense system leading to OS, which obviously contributes to tissue damage and to the

tors and enable the induction of inflammatory process [28].

**4.1 Oxidative stress in rheumatoid arthritis**

*Animal Models in Medicine and Biology*

**200**
