SOD2 and rheumatoid arthritis: On the contrary, 50% or 100% OA and RA SF induced a significant increase in superoxide anion production (p < 0.01, p < 0.001), as well as in the gene expression of SOD-2 (p < 0.05, p < 0.01) and NRF2 (p < 0.05, p < 0.01) gene expression (Figure 4A–F).