**3. Rat adjuvant arthritis**

Animal models of arthritis play an important role in unraveling mechanisms of chronic inflammation in rheumatoid synovial tissue. They are used extensively to study new treatment strategies for RA. AA can be induced by intradermal or footpad injection of heat-killed mycobacterial species, preferably in a fine suspension in a mineral or vegetable oil (CFA). The disease is restricted to susceptible rodents, mostly certain rat strains, such as Lewis, Buffalo, Sprague-Dawley, and Wistar rats [20]. Following AA induction with CFA, rats not only develop arthritis but also systemic features of inflammation, such as uveitis, inflammation of the gastrointestinal tract, and a loss in body weight that starts 24–48 h before the clinical onset of arthritis. AA is a symmetric polyarthritis, affecting primarily the peripheral joints. The affected joints are red, swollen, and painful. The onset of overt clinical arthritis is seen 10–14 days following the induction of AA with CFA (**Figures 2** and **3**). The first histopathological signs of arthritis, an accumulation of mononuclear cells in connective tissues adjacent to periosteal surfaces, are already manifested 6 days after disease induction. Approximately 10 days after disease induction, the first radiological signs of inflammation become visible: localized osteoporosis, with erosive lesions, and periosteal reaction. The synovial infiltrate leads to pannus formation, resulting in cartilage deformation, and severe destruction of the joint [21]. An important component of the disease process is the trafficking of arthritogenic leukocytes into the target organ. The synovial cellular infiltrate during the initial phase of inflammation in AA consists primarily of mononuclear cells (mostly monocytes, macrophages, and T cells) and relatively fewer neutrophils [22]. The arthritogenic T cells migrate into the synovium before the appearance of clinical signs of the disease [23]. Data in AA suggesting that

immune-stimulatory DNA sequences (ISS) may be a critical factor contributing to the chronicity of inflammation in chronic autoimmune arthritis. ISS can stimulate the expression of co-stimulatory molecules and the production of cytokines such as IL-12, TNF-α, and interferons by macrophages, dendritic cells, B cells, and NK cells

*Changes in body mass during development of adjuvant-induced arthritis. Co, control healthy rats; AIA,*

*Impact of Oxidative Stress on Inflammation in Rheumatoid and Adjuvant Arthritis: Damage…*

Inflammation is a natural defense mechanism against pathogens. It occurs in many pathogenic diseases (microbial and viral infections, exposure to allergens, radiation and toxic chemicals, autoimmune diseases, etc.). Chronic diseases linked with higher production of ROS result in OS and variety of protein oxidations [27]. Furthermore, some oxidized proteins trigger a release of inflammatory signal molecules, and peroxiredoxin 2 (PRDX2), which has been recognized as an inflammatory signal [28]. Relationship between OS and inflammation has been documented by many authors. Evidences indicated that OS plays a pathogenic role in chronic inflammatory diseases. Damage of OS such as oxidized proteins, glycated products, and lipid peroxidation results in neuron degenerations mostly reported in brain disorders [29]. ROS generated in brain tissues can modulate synaptic and nonsynaptic communication between neurons that result in neuro-inflammation and cell death and then in neurodegeneration and memory loss [29]. Tripeptide glutathione (GSH) is an intracellular thiol antioxidant; lower level of this GSH causes higher ROS production, which results in imbalanced immune response, inflammation, and susceptibility to infection [30]. A study was conducted on the role of GSH and its oxidized form and their regulatory function and gene expressions beyond free radical scavenging activities linked with GSH. GSH is involved in the redox regulation of immune system [31] through disulfide bounds between protein

[24] and are capable of skewing an immune response toward a strong and prolonged Th1 type of immunity [25]. AA has been used in the evaluation of nonsteroidal inflammatory drugs, such as phenylbutazone and aspirin during the early 1960s, and later in cyclooxygenase-2 inhibitors such as celecoxib. AA in rats shares many features with human arthritis, including genetic linkage, synovial CD4

+ cells, and T-cell dependence [26].

**Figure 3.**

**199**

*adjuvant-induced arthritic rats.*

*DOI: http://dx.doi.org/10.5772/intechopen.89480*

**4. Oxidative stress and inflammation**

#### **Figure 2.**

*Changes in hind paw volume during development of adjuvant-induced arthritis. Co, control healthy rats; AIA, adjuvant-induced arthritic rats.*

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

#### **Figure 3.**

TNF-α participates positively in the phosphorylation of kinase kappa inhibitor, allowing NF-κB dimers (p50 and p65 portions) to migrate to the nucleus and then bind to promoters of pro-inflammatory genes [19] and stimulate the NADPH oxidase activation. Increased cytokine production driven by NF-κB can enhance expression of vascular adhesion molecules that attract leucocytes into the joint as

Animal models of arthritis play an important role in unraveling mechanisms of chronic inflammation in rheumatoid synovial tissue. They are used extensively to study new treatment strategies for RA. AA can be induced by intradermal or footpad injection of heat-killed mycobacterial species, preferably in a fine suspension in a mineral or vegetable oil (CFA). The disease is restricted to susceptible rodents, mostly certain rat strains, such as Lewis, Buffalo, Sprague-Dawley, and Wistar rats [20]. Following AA induction with CFA, rats not only develop arthritis but also systemic features of inflammation, such as uveitis, inflammation of the gastrointestinal tract, and a loss in body weight that starts 24–48 h before the clinical onset of arthritis. AA is a symmetric polyarthritis, affecting primarily the peripheral joints. The affected joints are red, swollen, and painful. The onset of overt clinical arthritis is seen 10–14 days following the induction of AA with CFA (**Figures 2** and **3**). The first histopathological signs of arthritis, an accumulation of mononuclear cells in connective tissues adjacent to periosteal surfaces, are already manifested 6 days after disease induction. Approximately 10 days after disease induction, the first radiological signs of inflammation become visible: localized osteoporosis, with erosive lesions, and periosteal reaction. The synovial infiltrate leads to pannus formation, resulting in cartilage deformation, and severe destruction of the joint [21]. An important component of the disease process is the trafficking of arthritogenic leukocytes into the target organ. The synovial cellular infiltrate during the initial phase of inflammation in AA consists primarily of mononuclear cells (mostly monocytes, macrophages, and T cells) and relatively fewer neutrophils [22]. The arthritogenic T cells migrate into the synovium before the appearance of clinical signs of the disease [23]. Data in AA suggesting that

*Changes in hind paw volume during development of adjuvant-induced arthritis. Co, control healthy rats; AIA,*

well as MMPs.

**Figure 2.**

**198**

*adjuvant-induced arthritic rats.*

**3. Rat adjuvant arthritis**

*Animal Models in Medicine and Biology*

*Changes in body mass during development of adjuvant-induced arthritis. Co, control healthy rats; AIA, adjuvant-induced arthritic rats.*

immune-stimulatory DNA sequences (ISS) may be a critical factor contributing to the chronicity of inflammation in chronic autoimmune arthritis. ISS can stimulate the expression of co-stimulatory molecules and the production of cytokines such as IL-12, TNF-α, and interferons by macrophages, dendritic cells, B cells, and NK cells [24] and are capable of skewing an immune response toward a strong and prolonged Th1 type of immunity [25]. AA has been used in the evaluation of nonsteroidal inflammatory drugs, such as phenylbutazone and aspirin during the early 1960s, and later in cyclooxygenase-2 inhibitors such as celecoxib. AA in rats shares many features with human arthritis, including genetic linkage, synovial CD4 + cells, and T-cell dependence [26].

## **4. Oxidative stress and inflammation**

Inflammation is a natural defense mechanism against pathogens. It occurs in many pathogenic diseases (microbial and viral infections, exposure to allergens, radiation and toxic chemicals, autoimmune diseases, etc.). Chronic diseases linked with higher production of ROS result in OS and variety of protein oxidations [27]. Furthermore, some oxidized proteins trigger a release of inflammatory signal molecules, and peroxiredoxin 2 (PRDX2), which has been recognized as an inflammatory signal [28]. Relationship between OS and inflammation has been documented by many authors. Evidences indicated that OS plays a pathogenic role in chronic inflammatory diseases. Damage of OS such as oxidized proteins, glycated products, and lipid peroxidation results in neuron degenerations mostly reported in brain disorders [29]. ROS generated in brain tissues can modulate synaptic and nonsynaptic communication between neurons that result in neuro-inflammation and cell death and then in neurodegeneration and memory loss [29]. Tripeptide glutathione (GSH) is an intracellular thiol antioxidant; lower level of this GSH causes higher ROS production, which results in imbalanced immune response, inflammation, and susceptibility to infection [30]. A study was conducted on the role of GSH and its oxidized form and their regulatory function and gene expressions beyond free radical scavenging activities linked with GSH. GSH is involved in the redox regulation of immune system [31] through disulfide bounds between protein

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

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

*Impact of Oxidative Stress on Inflammation in Rheumatoid and Adjuvant Arthritis: Damage…*

*DOI: http://dx.doi.org/10.5772/intechopen.89480*

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

response [44].

both sources.

**201**
