Antioxidant

Antioxidant cells are continuously exposed to intra- and extracellular oxidant molecules. Although these oxidants are involved in many cellular processes, they are primarily responsible for cellular damage. Cells maintain an interacting network of molecules called antioxidants to control these compounds. Antioxidants can scavenge rampaging free radicals by donating electrons before free radicals interact with vital cellular molecules, thus reducing or limiting their capacity to damage. When coined, the term antioxidant defined a group of chemical compounds that prevented oxygen consumption. The term is now used in a broad sense. Nowadays, antioxidants mean a group of compounds, including electron donor, hydrogen donor, synergist, singlet oxygen quencher, peroxide decomposer, enzyme inhibitor, radical scavenger (reactive oxygen and nitrogen species (ROS/RNS)), and metal-chelating agents. Antioxidants usually use two general mechanisms to perform their roles. In the first mechanism, antioxidants share electrons with the free radicals present in the system. This is called the chain termination mechanism. In a second mechanism, antioxidants quench chain reaction initiators and thus stop the beginning of the chain reaction.

Generally, cells maintain non-enzymatic and enzymatic antioxidants function in the extracellular and intracellular environment for these mechanisms to neutralize these reactive molecules. The primary antioxidants are glutathione, ubiquinol, uric acid, vitamins, etc. Most of these are formed during regular body metabolism. However, vitamins, eg, vitamin C (ascorbic acid), B-carotene and vitamin E (α-tocopherol), need to be present in the diet. There are a few endogenous protein enzymes that act as a part of the antioxidant system. For example, superoxide dismutases (SODs) are enzymes that catalyze the breakdown of the superoxide anion into oxygen and hydrogen peroxide. Another major enzyme, Catalase, involves the breakdown of hydrogen peroxide, cellular byproducts to water and oxygen. Another mentionable scheme of the body is the glutathione system, which includes glutathione, glutathione peroxidases, glutathione S-transferases and glutathione reductase. Among the components, glutathione peroxidase catalyzes the breakdown of hydrogen peroxide and organic hydroperoxides. Other components of this system are used to recycle the glutathione between its oxidized and reduced forms. Any imbalances in the oxidant-antioxidant system are responsible for several human diseases. [MM Towhidul Islam]