Element selective characterization of stability and reactivity of selenium species in selenized yeast

Abstract

The concerted application of element specific atomic spectral detection for chromatographic eluent monitoring allows previously unexploited qualitative and quantitative analytical concepts to be developed for the determination of selenium species. Selenium speciation is vital in order to better understand its metabolism and biological significance in clinical chemistry, biology, toxicology, and nutrition. Fluoroacid ion pair HPLC with ICP-MS detection and GC derivatization with atomic emission detection (AED) together aid analysis and elucidation of reaction pathways of selenium compounds in high selenium enriched yeast, as used widely in nutritional and clinical cancer preventative studies. Comparisons between currently produced and archived selenized yeasts show major differences in speciation. The formation of selenomethionine selenoxide and the identification of Se-S bonded S-(selenomethyl)-cysteine in archived nutritional yeast may be important for short and long term stability and nutritional activity studies.

Speciation of selenium dietary supplements; formation of S-(methylseleno)cysteine and other selenium compounds

“…1 shows the HPLC-ICP-MS chromatogram of the Life Extension Super Selenium Complex capsules. Comparisons with results for selenium supplements utilizing these HPLC conditions [40,51,52] confirm the peak identifications and show a complex selenium speciation including inorganic and organic compounds. The former (selenate and selenite) are quantifiable since the both elute after the void volume and no other anionic selenium species have ever been observed under these conditions.…”

“…In 2004, we reported [51] the presence of a sulfur-selenium amino acid, S-(methylseleno)cysteine, in archived selenized yeast samples from the Clark study [42]. Its presence was subsequently confirmed by GC-AED [52] and 77 Se NMR [59].…”

“…The operating conditions with a cross flow nebulizer and Scott spray chamber were as follows: RF power 1100 W, plasma Ar flow rate 15 L min −1 , nebulizer Ar flow rate 0.98 L min −1 , auxiliary gas flow rate 1.20 L min −1 , methane collision cell gas 0.6 mL min −1 , isotopes monitored 78 Se, 80 Se, 72 Ge, dwell time 80 ms [52]. The HPLC system which utilized a 5-m Symmetry Shield TM RP-C 8 column (3.9 mm × 15 cm) (Waters Corporation, Milford, MA) and an ion-pairing mobile phase of 0.1% heptafluorobutanoic acid (HFBA), 1% methanol and 99% water (v/v) was described previously [40,51].…”

“…Most dramatically the SELECT trial that utilized l-selenomethionine as the active supplement, was terminated in 2008 following a conclusion that there had been no demonstrable beneficial effect on prevention of prostate cancer and there was a possible indication of increased incidence of diabetes [50]. Since selenized yeast, as employed by Clark et al and in most supplements, was not tested in the SELECT study, it is conceivable that this difference proved important and that other selenium species observed in the 'Clark' yeast were germane to those results [51,52]. Alternatively Rayman et al have argued that the null results of SELECT are explainable by the fact that the candidate subjects already had optimal selenoprotein concentration/activity (notably selenoprotein P) and the results of SELECT tell nothing regarding effects of selenium on advanced cancer or on men of low Se status [53][54][55].…”

Identification and Synthesis of a Novel Selenium−Sulfur Amino Acid Found in Selenized Yeast: Rapid Indirect Detection NMR Methods for Characterizing Low-Level Organoselenium Compounds in Complex Matrices

“…Analysis of archived samples of selenized yeast from the Clark trials showed that two additional Se compounds were sometimes present, in some cases in amounts together approaching or exceeding the level of 1. One of these unidentified compounds corresponds in retention time and mass spectral fragmentation to the hydrate of selenomethionine Se-oxide (2, MeSe(OH) 2 CH 2 CH 2 CH(NH 2 )CO 2 H) (16)(17)(18)(19).…”