Selenometabolomics: Identification of selenometabolites and specification of their biological significance by complementary use of elemental and molecular mass spectrometry

Selenium (Se) shows ambivalent characteristics in animals and plants. It is an essential element in animals but becomes severely toxic when the amount ingested exceeds the required level. Meanwhile, Se is not essential in plants although some plants are Se hyperaccumulators. As Se changes into several chemical forms when metabolized, the identification of selenometabolites is considered to correspond to the depiction of the metabolic chart of Se. Hence, we are very much interested in unveiling selenometabolomes, i.e., the entirety of selenometabolites. Speciation with elemental and molecular mass spectrometry coupled with separation techniques has significantly contributed to the discovery of selenometabolomes. At the same time, speciation has highlighted some metabolites required for solid verification of the metabolic chart. The aim of this article is to review currently proposed Se metabolic pathways in animals and plants and to point out ambiguous selenometabolites from the viewpoint of speciation.