Fig. 2

Intracellular concentration of H₂O₂, ROS levels, and OS. a Estimated ranges of H₂O₂ concentration concerning OS cellular responses. The intracellular physiological range of H₂O₂ boasts a wide span from 1 to 100 nM, and cellular proliferation, differentiation, migration, and angiogenesis rely heavily on that appropriate range. High concentrations of H₂O₂ trigger cellular adaptive stress responses. Even higher levels result in inflammatory responses, growth retardation, tumor growth, metastasis, and cell death through different mechanisms. Green and orange coloring stands for principally eustress and distress responses, respectively. It is estimated that a 100-fold concentration gradient, which varies with cell type, the location inside cells, and the activity of enzymatic sinks, gives a rough orientation from extracellular to intracellular [18, 279]. b Imbalance between oxidants and antioxidants causes OS and influences tumorigenesis. Excessive ROS generation leads to prooxidative/antioxidative imbalance and OS, which could be detrimental and result in cellular dysfunction or cell death. For tumor cells, a higher generation of ROS and an elevated redox state are crucial for tumorigenesis. In addition, tumor cells are able to increase the antioxidant levels to alleviate the cytotoxic effect of ROS and counteract OS-induced cell death