Abstract
Selenium (Se) shows biologically ambivalent characteristics in animals. It is an essential element but becomes severely toxic when the amount ingested exceeds the adequate intake level. Its biological, nutritional, and toxicological effects are strongly dependent on its chemical form. In this study, we evaluated the toxicity and bioavailability of nine naturally occurring Se compounds, or the so-called bioselenocompounds, in vivo and in vitro. Selenite and selenocystine showed higher toxicity than the other bioselenocompounds in vitro. In an in vitro membrane permeability study using Caco-2 cells, selenomethionine and Se-methylselenocysteine were more efficiently transported than the other bioselenocompounds. The effect of bioselenocompounds on nutritional availability was quantitatively determined from the recovery of serum selenoproteins in Se-deficient rats by speciation analysis. In contrast to the in vitro study, there were no significant differences in the assimilation of Se into serum selenoproteins among the bioselenocompounds, including selenoamino acids, selenosugar, and inorganic Se species, such as selenite, selenate, and selenocyanate, except trimethylselenonium ion. These results indicate that animals can equally assimilate both inorganic and organic naturally occurring selenocompounds except trimethylselenonium ion, which is the urinary metabolite of excess Se. We confirmed that the bioselenocompounds except trimethylselenonium ion had equivalent nutritional availabilities.
Highlights
Selenium (Se) is an essential trace element in animals, including humans, and exists in selenoproteins as selenocysteine (SeCys)
Se deficiency is often reported in patients who receive total parental nutrition (TPN) and sick children who are given special milk for specific metabolic diseases [3]
Quantitative methods indicated no significant differences in bioavailability among the bioselenocompounds except TMSe+ (Figure 4), the in vitro experiment showed that the permeability of MeSeCys and SeMet was significantly larger than that of the other Se species
Summary
Selenium (Se) is an essential trace element in animals, including humans, and exists in selenoproteins as selenocysteine (SeCys). Quantitative methods indicated no significant differences in bioavailability among the bioselenocompounds except TMSe+ (Figure 4), the in vitro experiment showed that the permeability of MeSeCys and SeMet was significantly larger than that of the other Se species. In addition to MeSeCys from plants, i.e., vegetables, cereals, nuts, and fruits, and SeCys in selenoproteins in animals, i.e., meat and fish, selenoneine, (2S)-3-(2-selenoxo-2,3-dihydro-1H-imidazol4-yl)-2-(trimethylazaniumyl)propanoate (2-selenyl-Nα,Nα,Nα-trimethyl-L-histidine), which is the major Se metabolite in marine animals, is a possible nutritional source of Se for people who are ichthyophagous [25]. According to the findings of this study, selenoneine would be the most preferable source of Se because it is a monomeric amino acid and contains non-methylated Se in its molecule These structural features are expected to result in increased absorption, metabolism, and assimilation into selenoproteins. These results indicate that SeCN− is a suitable inorganic Se form that is economical and safe for Se supplementation
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