| The biochemistry and pharmacology of selenium are subjects of intense current interest, particularly from the viewpoint of public health. Selenium has long been recognized as a “dietary antioxidant” and more recently as an anticarcinogenic agent, and its role as an essential component of the active sites of selenoenzymes such as glutathione peroxidase and mammalian thioredoxin reductase is well established. Evidence is now emerging that, at least in the case of cancer, the antitumorigenic effect of selenium supplementation arises at least in part from enhanced production of specific selenium-containing metabolites, not just from maximal expression of selenoenzymes. Yet there is a dearth of structure-level information extant regarding selenium-containing metabolites in humans. Thus, it is clear that investigations of the chemical nature and levels of selenium metabolites in biological samples and of their metabolic fates are needed.; In an effort to speciate and identify low molecular weight organoselenium metabolites in human urine, a new method was developed utilizing High Performance Liquid Chromatography in conjunction with Inductively Coupled Plasma/Mass Spectrometry (ICP/MS) and Electrospray Ioninization/Triple Quadruple Mass Spectrometry (ESI/MS-MS). Using this method, two organoselenium metabolites in selenium-supplemented human urine, selenocystamine and selenomethionine, were positively identified. Another new approach, exact mass determination of unknown organoselenium compounds in biological matrices using Surface-Assisted Laser Desorption Ionization/High Resolution Time-of-Flight/Mass Spectrometry (SALDI/TOF-MS) was investigated. A new method to prepare SALDI substrates by aerosol deposition was developed. In addition, effects of sample treatments and storage conditions on selenium speciation profiles were studied. Furthermore, signal suppression in ESI/MS and its dependence on matrix interference were investigated, and improvement on the performance of the Sciex API III Ionspray mass spectrometer was made. Overall, this research has provided in-depth understanding of mass spectral techniques in the analysis of low molecular weight organoselenium compounds and enabled their metabolic studies in complex biological matrices. |
