First line defence antioxidants-superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GPX): Their fundamental role in the entire antioxidant defence grid

The body encloses a complex antioxidant defence grid that relies on endogenous enzymatic and non-enzymatic antioxidants. These molecules collectively act against free radicals to resist their damaging effects to vital biomolecules and ultimately body tissues. Based on their response to general free radical invasion, they can be categorized into first, second, third and even fourth line defense antioxidants. The role and effectiveness of the first line defense antioxidants which basically include superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GPX) is important and indispensable in the entire defense strategy of antioxidants, especially in reference to super oxide anion radical (*O2) which is perpetually generated in normal body metabolism, particularly through the mitochondrial energy production pathway (MEPP). A lot has been published concerning antioxidants and their significance in preventing oxidative stress and the attendant cellular damage, howbeit with paucity of awareness on the fundamental role of SOD, CAT and GPX. The present review tends to articulate important information on SOD, CAT and GPX as first line defense antioxidant enzymes.