Selenium

Selenium is an essential mineral for all animals including humans. It is found in amino acids selenocysteine and selenomethionine, which usually forms active sites in selenoproteins. In humans, 25 selenoproteins have been identified, and most of them function as important antioxidant enzymes and play important roles in the detoxification of reactive oxygen species (ROS). Selenoproteins are critical for normal physiology. Dysregulation and malfunction of selenoproteins are associated with numerous human diseases, mostly cancers. The selenium levels are found to be associated with frequency of multiple cancer types, by clinical studies and experimental data. In addition, multiple forms of small selenium compounds, such as inorganic selenite and selenate and organic selenomethionine, Se-methyl-selenocysteine, and methyl-selenic acid, have been applied clinically for cancer prevention and treatment. These small selenium molecules share distinct function and mechanisms in the cellular signaling and effects. In this chapter, mechanisms involved in small selenium molecule cellular metabolism, regulation of cancer cell signaling, and their application in the cancer prevention and therapies are discussed.