A variety of oxidative reactions occur continuously within our cells in a dynamic environment. One common type of reaction – reduction oxidation or redox reaction– plays a vital role in maintaining cellular functions. During these reactions, one couple loses electrons (becomes oxidised) and another gains the same electrons(becomes reduced). As a result, our cells have to maintain a delicate redox balance between the various macromolecules that comprise them.
These pro-oxidants, which are referred to as reactive oxygen species (ROS) and reactive nitrogen species (RNS), mainly originate from the oxygen metabolism in the mitochondria. They are signalling molecules that can trigger various systems, but can cause damage to the cell if produced in excess.
On the other hand, antioxidant systems are represented by exogenous molecules (vitamins, polyphenols) that have ROS scavenging activities and endogenous systems (mainly enzymes such as superoxide dismutase, catalase, glutathione peroxidase and thioredoxin reductase). Selenium (Se) is part of this second group as it is a constituent of a small group of enzymes (Figure 1).