## 3 Oxidative Stress Biomarkers Involved in Psoriasis Inflammation
### Catalase (CAT)  
Catalase (CAT) is an essential antioxidant enzyme found in nearly all oxygen-exposed living organisms, serving to protect cells from the damaging effects of ROS by breaking down hydrogen peroxide (H\({}_{2}\)O\({}_{2}\)) into water (H\({}_{2}\)O) and oxygen (O\({}_{2}\)) [56; 57]. With a heme group in its active site, catalase facilitates the conversion of hydrogen peroxide, preventing its accumulation and subsequent oxidative damage to cellular components such as proteins, lipids, and DNA [57]. Catalase protects the mitochondria and the cell by regulating the amounts of H\({}_{2}\)O\({}_{2}\), thereby preventing oxidative stress and promoting optimal mitochondrial function. Deficiencies in catalase activity or expression have been associated with increased susceptibility to oxidative stress, mitochondrial DNA damage and various diseases, highlighting its crucial role in cellular defense mechanisms [58]. Psoriasis is characterized by increased oxidative stress, which refers to an imbalance between the generation of damaging ROS and the body's antioxidant defenses. The uneven distribution causes oxidative harm to cellular structures, intensifying inflammation and playing a role in the formation of psoriatic lesions. Catalase, as a key component of the body's antioxidant defense system, plays a vital role in mitigating the impact of oxidative stress by catalyzing the breakdown of hydrogen peroxide, thereby preventing the accumulation of reactive oxygen species and protecting skin cells from oxidative damage [57]. Maintaining optimal catalase activity is essential in psoriasis to mitigate the harmful effects of oxidative stress, thereby preserving skin integrity and reducing disease progression. A study assessed the plasma levels of CAT in 100 psoriasis patients and 100 healthy controls resulted in a significant reduction in CAT activity (\(p<0.05\)) among individuals with psoriasis, suggesting the presence of oxidative stress in the condition [35]. A study aimed to assess the redox imbalance and protein changes in lymphocytes of individuals diagnosed with psoriasis vulgaris (PsV) or psoriatic arthritis (PsA) [59]. The findings indicated a more pronounced transition towards circumstances that promote oxidation in lymphocytes of individuals with psoriatic arthritis (PsA). This was characterized by elevated levels of reactive oxygen species and reduced catalase activity in comparison to patients with PsV and healthy individuals [59]. Subsequently, research was conducted to evaluate the level of oxidative stress in individuals with psoriasis by quantifying the presence of malondialdehydehyde (MDA) in their blood serum as an oxidant, as well as assessing the activity of erythrocyte CAT as an antioxidant [60]. The study found that psoriasis patients had significantly lower erythrocyte catalase activity (\(p<0.001\)) compared to the control group [60]. These findings imply that oxidative stress plays a role in the development of psoriasis. The link between CAT gene expression and psoriasis was also investigated. The catalase gene in humans was discovered and described by [PERSON] et al. in 1986 [61]. It is located on chromosome 11, specifically on band p13, and consists of 13 exons and 12 introns. The presence of regulatory components inside it allows for the modulation of its expression in response to different cellular signals, such as oxidative stress. Comprehending these regulatory processes is essential for interpreting the function of catalase in disorders like psoriasis. A study observed the quantification of CAT gene expression was conducted using real-time PCR, following the methodology outlined by [PERSON] et al. (2018). The study by [PERSON] et al. (2018) discovered a significant reduction in the expression of the catalase gene (\(p=0.02\)) in psoriasis patients, suggesting that catalase may play a part in the redox imbalance linked to psoriasis.