Essential trace element selenium and redox regulation: its metabolism, physiological function, and related diseases

The essential trace element selenium plays a significant role in redox homeostasis in the human body. Selenium is very reactive and has a potent toxicity; however, the living body cleverly utilizes its reactivity for redox reactions. The biological function of selenium is mainly mediated by selenoproteins, which contain selenocysteine, a cysteine analogue that possesses selenium instead of sulphur. Twenty-five types of human selenoproteins have been identified, including glutathione peroxidase (GPX; for the reduction of hydrogen peroxide and lipid hydroperoxide) and thioredoxin reductase (for redox regulation). Selenoprotein P (SELENOP), which is a major selenoprotein in the plasma, is mainly synthesized in the liver and secreted into the plasma. As a multifunctional protein with selenium-transporting activity, GPX-like activity, and metal-binding properties, SELENOP plays a vital role in selenium metabolism and redox regulation. This review focuses on the relationship between selenium metabolism and redox regulation, particularly on the physiological role of selenoproteins and the pathophysiological implications of its disorder. Furthermore, the significant roles of selenium in infectious diseases and its utility for phylaxis are discussed.