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

Abstract

a b s t r a c tSpeciation of selenium is of interest because it is both essential and toxic to humans, depending on the species and the amount ingested. Following indications that selenium supplementation could reduce the incidence of some cancers, selenium-enriched yeast and other materials have been commercialized as supplements. Most dramatically however, the SELECT trial that utilized l-selenomethionine as the active supplement was terminated in 2008 and there is much debate regarding both the planning and the results of efficacy studies. Further, since dietary supplements are not regulated as pharmaceuticals, there are concerns about the quality, storage conditions, stability and selenium content in selenium supplements. Enzymatic hydrolysis enabled selenium speciation profiles to be obtained by high performance liquid chromatography with inductively coupled plasma mass spectrometry (HPLC-ICP-MS) and following derivatization gas chromatography with atomic emission detection (GC-AED). Coated fiber solid phase microextraction (SPME) was used to extract volatile selenium species for determination by GC-AED and GC-MS. Similar speciation patterns were observed between yeast-based supplements subject to extended storage and those heated briefly at elevated temperatures. All the yeast-based supplements and one yeast-free supplement formed S-(methylseleno)cysteine on heating. Evidence was obtained in support of the hypotheses that S-(methylseleno)cysteine is formed from a reaction between dimethyldiselenide and cysteine or cystine.

Supplementation of cultivated mushroom species with selenium: bioaccumulation and speciation study

“…Introduction of any new product potentially used to supplement Se requires chemical speciation to assess Se bioavailability. Although most dietary selenium is absorbed efficiently, the retention of organic forms is higher than that of inorganic forms [35][36][37][38]. The high level of Se org found in fruiting bodies of investigated mushrooms indicates that P. eryngii or P. ostreatus grown on substrates supplemented with Se may represent a sufficient bioavailable source of Se.…”

Selenium species in selenium fortified dietary supplements

“…In 25 preparations, Se(IV) and selenium-organic compounds were found; in 15, Se(VI) and selenium-organic compounds were observed; in nine, selenium occurred as both Se(IV) and Se(VI) as well as in inorganic compounds. It should be, however, be noted that, in terms of potential selenium bioavailability, the occurrence of inorganic compounds is less favorable than selenium-organic compounds (Amoako et al 2009). In other studies of selenium dietary supplements, the authors found both inorganic forms Se(IV) and, predominantly, Se(VI), as well as selenium-organic compounds, mainly as selenomethionine with traces of selenocysteine (Hsieh & Jiang, 2013).…”

“…In this study, the selenium content in organic compounds was determined without determining the particular organic forms: selenomethionine Se-O, S-(methylseleno)cysteine, selenomethionine (Amoako et al, 2009). In view of contradictory opinion on the significance of particular selenium-organic compounds (selenomethionine versus Se-(methyl)selenocysteine) in cancer prevention (Infante et al, 2004), determination of total selenium-organic compounds allows for assessment of general bioactive properties.…”

Determination of Inorganic Selenium Species in Dietary Supplements by Hyphenated Analytical System HPLC-HG-AAS

“…In all dietary supplement products, selenium was present mainly in the form of organic species (Amoako et al 2009;Alzate et al 2007;Infante et al 2005;Dumont et al 2005). In two samples (samples 1 and 5), no inorganic selenium species were detected.…”