Antioxidant Enzymes and their Role in Preventing Cell Damage (original) (raw)

2020, Acta Scientifci Nutritional Health

Oxidative stress (OS) is a cellular phenomenon or condition which occurs as a result of physiological imbalance between the levels of antioxidants and oxidants (free radicals or reactive species) in favour of oxidants. In other words, oxidative/nitrosative stress is the result of disequilibrium in oxidant/antioxidant which reveals from continuous increase of reactive oxygen species (ROS) and reactive nitrogen species (RNS) production [1]. ROS is a collective term used for a group of oxidants, which are either free radicals or molecular species capable of generating free radicals [2]. These free radicals, which can be found as oxygen derived (ROS) or nitrogen derived (RNS) have rather high reactivity and short life. Generally, ROS/RNS are generated as by-products of cellular metabolism and ionizing radiation. Therefore, different reactive species are involved in cellular oxidative stress and oxidative damage. The common name for these reactive species is "free radicals". Free radicals are defined as "any chemical species capable of independent existence that contains one or more unpaired electrons". Reactive oxygen species (ROS), such as superoxide anion (O 2 •−), nitric oxide (NO•) hydrogen peroxide (H 2 O 2), and hydroxyl radical (HO•), consist of radical and non-radical oxygen species formed by the partial reduction of oxygen. The accumulation of ROS in cells may cause damage of nucleic acids, proteins, lipids and may cause cell death and trigger oxidative stress which yield to the development and progression of several diseases. Furthermore, ROS may promote tumour metastasis through gene activation. It is important to emphasize that equilibrium between the production and elimination of toxic levels of ROS is sustained by enzymatic and nonenzymatic antioxidants. When oxidative stress arises as a consequence of high level of ROS, a defence system promotes the regulation and expression of several nonenzymatic and enzymatic antioxidant. To cope with potentially damaging ROS, aerobic tissues contain endogenously produced antioxidant enzymes such as superoxide dismutase (SOD), glutathione peroxidase (GPx), and catalase and several exogenously acquired radical-scavenging substances such as vitamins E and C, carotenoids and tocopherols. Afterward, both zinc and selenium are intimately involved in protecting the body against oxidant stress. In addition, it was reveal that supplementation with exogenous antioxidants or boosting of endogenous antioxidants is a promising method of countering the undesirable effects of oxidative stress on the human body.