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. 2020 Nov 27;2020:8874304. doi: 10.1155/2020/8874304

Figure 1.

Figure 1

NADPH oxidase system and antioxidative stress. NADPH oxidase system contains NOX2 and NOX4. TBHQ activates Nrf2, then Nrf2 negatively regulates NOX2, and NOX2 can produce ROS, and Nrf2 can also directly reduce ROS. Under homeostasis, NOX4 produces hydrogen peroxide and superoxide which both oxidize cysteine sensor and cysteine sensor activate Nrf2; then, Nrf2 inhibits the transcription of NOX4, making NOX4 under homeostasis, forming a positive feedback loop. However, with upregulation of NOX4, the homeostasis and feedback loop mentioned above are destroyed, creating a prooxidative environment; then, ROS and MDA will increase, and MDA can indirectly reflect ROS. In addition, NOX4 consumes and inhibits antioxidases including SOD. NADPH: nicotinamide adenine dinucleotide phosphate; TBHQ: tert-butyl hydroquinone; Nrf2: nuclear factor E2 related factor 2; ROS: reactive oxygen species; SOD: superoxide dismutase; MDA: malondialdehyde; NOX: NADPH oxidase.