Type of AT Name Role in redox homeostasis Prooxidant role (cytotoxic effect) Enzymatic SOD Catalyzes dismutation of superoxide radical to form oxygen and hydrogen peroxide None observed so far. GPx and GSH Scavenges hydroxyl radical and prevents LPO cellular damage, with GSH as electron donor. Regenerates Vit C and E to their active form. None observed so far. Non enzymatic α-tocopherol (Vit. E) Free radical chain-breaking molecule inhibiting LPO by capturing electrons and converting into α-tocopheroxyl. In clinical studies massive doses (3000 mg/day) have not been found toxic. Ascorbic acid (Vit. C) Scavenges ROS, protecting of mtDNA. It also restores oxidized α-tocopheroxyl to its AT form. Mega doses: renal stone, iron overload, destruction of B12 in the gut. Polyphenols Scavenges FR, reduces hydroperoxides. More clinical studies needed. Melatonin FR scavenger (OH.), prevents LPO. Its metabolites (c-3OHM and AFMK) also have AT action. Protects and stimulates enzymatic AT. No toxicity or adverse effects have been found at high doses in pregnant rats. SOD: superoxide dismutase, GPx: Glutathione peroxidase, GSH: Glutathione, AT: Antioxidant, FR: free radicals, LPO: lipid peroxidation.

Table 1:Summary of antioxidants (AT) and their role in redox homeostasis and oxidative stress