## 4 Oxidative Stress Parameters Involved in Psoriasis Inflammation
### Oxidative Stress Index (OSI)
TOS serves as a comprehensive measure that reflects the overall oxidative stress level in biological samples by quantifying the total concentration of oxidant molecules and free radicals present in the system, while TAS measures the overall antioxidant capacity of a biological sample, reflecting the cumulative activity of antioxidants present in the system [70]. In the context of psoriasis, disturbances in the equilibrium between TOS and TAS have been implicated in disease pathogenesis and progression. TOS quantifies the oxidative burden within biological systems, reflecting the levels of oxidant molecules, including ROS and reactive nitrogen species (RNS). The heightened generation of ROS and oxidative stress in psoriatic lesions, stemming from immunological dysregulation and inflammatory processes, is mirrored in elevated TOS levels [53]. Studies consistently demonstrate higher TOS levels in psoriasis patients, indicative of increased oxidative stress and the accumulation of oxidant molecules capable of causing cellular damage [4; 53]. In patients with plaque psoriasis, significantly higher values of TOS and OSI were observed in nasal washings (NWS), sweat washings (SWS), and plasma compared to the control group, along with a faster rate of ROS production in NWS and SWS [53]. Psoriasis patients have higher levels of TOS due to several factors, including abnormal immune cell activation, increased synthesis of inflammatory cytokines, and compromised antioxidant defenses. Conversely, TAS represents the cumulative capacity of endogenous and exogenous antioxidants to neutralize oxidant molecules and maintain redox homeostasis. Antioxidants scavenge free radicals, inhibit lipid peroxidation, and repair oxidative damage, thereby mitigating the detrimental effects of oxidative stress [2; 71]. Psoriasis is characterized by alterations in TAS levels, reflecting changes in antioxidant capacity and redox balance. Decreased TAS levels may indicate compromised antioxidant defenses, rendering cells more susceptible to oxidative damage and exacerbating inflammation and tissue injury in psoriatic lesions [2; 71]. The study evaluated TAS in individuals with psoriasis and showed that TAS levels were reduced but were not statistically significant before or after methotrexate (MTX) medication [72]. TAS was measured in 20 healthy controls and 55 psoriasis patients based on severity, and the results showed that TAS levels were lower in all psoriasis groups than in the control group [71]. These results emphasize the involvement of antioxidant defense systems in the pathophysiology of the disease and point to a possible correlation between decreased TAS and the severity of psoriasis. The delicate balance between antioxidant defenses and oxidative stress is reflected in the link between TOS and TAS dynamics in psoriasis. Imbalances favoring higher TOS and/or lower TAS exacerbate the severity of the illness by prolonging oxidative damage and inflammation in psoriatic lesions. Understanding the interplay between TOS and TAS dynamics provides insights into the underlying mechanisms driving psoriasis pathogenesis. In a study on 40 psoriatic patients, [PERSON] et al. observed elevated levels of TOS, highly sensitive C-reactive protein (hs-CRP), total sialic acids [16], and protein-bound sialic acid (PBSA) at baseline, along with decreased of TAS, correlating positively with PASI scores [70]. Following a 12-week treatment with MTX, reductions in TOS, hs-CRP, TSA, and PBSA were noted alongside an increase in TAS levels, indicating potential therapeutic efficacy in modulating oxidative stress parameters in psoriasis [70]. In contrast, a study observed that TOS levels between the patient and control groups demonstrated a significant disparity, while TAS levels did not significantly differ between the two groups. This observation was made in a study involving fifty psoriasis patients who were not receiving systemic medication and forty-five healthy volunteers [73].