## 4 Oxidative Stress Parameters Involved in Psoriasis Inflammation
### Oxidative Stress Index (OSI)  
The oxidative stress index (OSI) is a ratio that compares the level of oxidative stress, which is represented by total oxidant status (TOS), to the total antioxidant capacity, which is represented by total antioxidant status (TAS) [68]. Oxidative stress plays a significant role in promoting inflammation in psoriasis. The presence of ROS can activate inflammatory pathways, trigger immune responses, and contribute to the development of psoriatic lesions. Therefore, monitoring OSI levels can help assess the degree of oxidative stress-induced inflammation in psoriasis patients. Measurement of the OSI provides valuable information about the overall redox status and oxidative burden experienced by cells and tissues. In conditions associated with increased oxidative stress, such as psoriasis, the OSI may be elevated, reflecting an imbalance where the production of oxidants surpasses the body's ability to neutralize them, contributing to the pathogenesis and progression of the disease [53]. On the other hand, a lower OSI score denotes a more advantageous equilibrium in which antioxidant defenses are more effective in counteracting oxidative stress [53]. The OSI offers a quantitative measure of the equilibrium between antioxidant defenses and oxidative stress. The OSI value is calculated according to the following formula: OSI (arbitrary unit) = TOS (umol H\({}_{2}\)O\({}_{2}\) Eq\(\backslash\)L)\(\backslash\)TAS (umol Trolo Eq\(\backslash\)L) \(\times\) 100 [68]. Studies have shown that psoriasis patients often exhibit higher OSI values compared to healthy individuals. A study evaluated redox balance parameters and oxidative stress biomarkers in plaque psoriasis patients compared to healthy controls [53]. The OSI values in unstimulated and stimulated saliva, as well as plasma of psoriatic patients, were significantly higher (\(p\leq 0.001\)), suggesting potential diagnostic biomarkers for plaque psoriasis [53]. The OSI was then used in a study to measure oxidative stress in psoriatic patients. The results showed that psoriasis patients had significantly higher levels of the OSI (\(p<0.001\)) than controls, and that these levels positively correlated with the severity and duration of the disease. This suggests that psoriasis may be related to increased reactive oxygen species and decreased antioxidant activity [69]. In addition, a study looked at OSI and inflammatory markers in people with psoriasis vulgaris. The findings showed that psoriasis patients had significantly higher baseline levels of OSI than controls and that OSI and sialic acids significantly correlated with the severity of the disease [70]. Additionally, after 12 weeks of therapy, a significant decline in the OSI and inflammatory markers was seen, indicating a possible link between oxidative stress, inflammation, and the pathogenesis of psoriasis [70]. In individuals with psoriasis, monitoring OSI levels can assist in assessing the severity, course, and responsiveness to therapy of the condition. Treatment options may change if the link between OSI and psoriasis is understood. Sporiasis patients may have less inflammation and better results with therapies targeted at lowering oxidative stress and restablishing antioxidant balance. To control OSI levels and lessen oxidative stress in psoriasis, lifestyle changes, dietary changes, and antioxidant supplements may be taken into consideration. In summary, the OSI is a helpful biomarker for assessing antioxidant state and oxidative stress in biological systems, providing information on the pathophysiology of oxidative stress-related diseases and potential targets for therapeutic intervention. Total oxidant status (TOS) and total antioxidant status (TAS) stand as pivotal parameters in evaluating the redox equilibrium within biological systems, shedding light on the interplay between antioxidant defenses and oxidative stress.