Antioxidant Systems

Antioxidant systems refer to a complex network of molecules and enzymes that work together to counteract harmful reactive oxygen species (ROS) and reactive nitrogen species (RNS) in biological systems. These systems play a crucial role in maintaining cellular redox balance and preventing oxidative stress. They are broadly classified into enzymatic antioxidants (like SOD, CAT, GPx, APX, MDAR, DHAR, GR, GSTs, PRX) and non-enzymatic antioxidants (like Vitamin C, Vitamin E, Glutathione, Coenzyme Q, Carotenes, Trace elements). Antioxidant systems operate as an integrated network through cooperative cycles (e.g., water-water cycle, ascorbate-glutathione cycle) where antioxidants can regenerate each other, and through compartmentalization where different systems operate in specific cellular locations (e.g., peroxisomes, cytosol, mitochondria, chloroplasts). Understanding these systems is crucial for developing therapeutic strategies to combat oxidative stress-related diseases.

Antioxidants operate through various mechanisms. Primary (Chain-breaking) antioxidants actively inhibit oxidation reactions by scavenging ROS/RNS, interrupting radical chain reactions by donating hydrogen atoms to free radicals (e.g., α-tocopherol protecting against lipid peroxidation). Secondary (Preventive) antioxidants act indirectly through mechanisms such as chelation of transition metal ions, anti-inflammatory effects, inhibition of enzymes like NADPH oxidase and xanthine oxidase, regulation of redox-sensitive signal transduction pathways, inhibition of PARP-1 polymerase, and activation of transcription factors like Nrf2 leading to activation of endogenous antioxidant enzymes.