Metabolism of Selenium/Selenocystine and Their Roles in the Prevention and Treatment of Human Cancer
Selenium and sulfur share many common chemical properties. There are many biologically active selenium analogues of naturally occurring sulfur compounds. Based on the structural similarities, some of these selenium compounds are known to be taken up by transporters involved in uptake of cognate sulfur-containing substrates. In a similar way, they share some of the common metabolic transformations. Selenium compounds are unique in their redox chemistry in comparison to their sulfur counterparts. Such distinct chemical properties result in the unique biological activities of selenium. While selenium functions as an antioxidant at low doses, high doses elicit pro-oxidant effects. Manifestation of these dual biological functions is exploited in cancer chemoprevention as well as in prospective cancer therapy. Efficacy of these selenium compounds is attributed towards their notable differences in the metabolic pathways and their modes and mechanisms of actions.