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Fig. 2 | Molecular Cancer

Fig. 2

From: Antioxidants in brain tumors: current therapeutic significance and future prospects

Fig. 2

Oxidative stress-related biomarkers in the brain. The mitochondrion is considered to be the major intracellular production house of ROS. Several enzymes, such as NOX, XO, and uncoupled form of NOS can trigger O2•− production. NOS also catalyze the metabolic reaction of amino acid to produce NO. NO reacts with O2•− and produces ONOO•−, a RNS. O2•− is converted into H2O2 by the action of SOD, which subsequently produces OH•−. H2O2 also yields HOCl by the action of MPO, which again yields O2•− and highly active Cl−. These highly active free radicals deplete GSH and endorse oxidative damages to cellular lipids, proteins, and DNA, resulting in aberrant levels of some specific biochemical markers in the blood circulation. Thus, these specific biochemical markers could serve as potential OS-related biomarkers. Red arrows indicate downstream events and red lines indicate inhibition. 4-HNE, 4-hydroxynonenal; 8-iso-PGF2α, 8-Epi-prostaglandin F2alpha; 8-OHdG, 8-hydroxydeoxyguanosine; DNA, deoxyribonucleic acid; H2O2, hydrogen peroxide; HOCl, hypochlorous acid; Keap1, Kelch-like ECH-associated protein 1; MDA, malondialdehyde; MPO, myeloperoxidase; NO, nitric oxide; NOS, nitric oxide synthase; NOX, NADPH oxidase; Nrf-2, nuclear factor erythroid 2-related factor 2; O2•−, superoxide; OH•−, hydroxyl radical; ONOO•−, peroxynitrite; ROS, reactive oxygen species; SOD, superoxide dismutase; TBARS, thiobarbituric acid reactive substances; XO, xanthine oxidase

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