Selenosugars Are the Major Selenometabolites in Liver of Turkeys Fed High Selenium
Abstract Objectives Liver and other tissues accumulate selenium (Se) when animals are supplemented with high dietary Se as inorganic Se. Because the nature of this accumulated Se is not well characterized, we studied selenometabolomics in Se-deficient, Se-adequate, and high-Se liver. Methods Turkey poults were fed 0, 0.4, and 5 μg Se/g diet as Na2SeO3 in a Se-deficient (0.005 μg Se/g) diet for 28 days, and the effects of Se status determined using HPLC-ICP-MS and HPLC-ESI-MS/MS. Results In liver from turkeys fed a true Se-deficient diet and supplemented with inorganic Se (selenite), no selenomethionine (SeMet) was detected showing that the turkey cannot synthesize SeMet de novo from inorganic Se. Selenocysteine (Sec) was also below the level of detection in Se-deficient turkey liver, as expected in animals with negligible selenoprotein levels. Sec content in liver of turkeys fed high Se only doubled compared with Se-adequate liver, indicating that the 6-fold incryscease in liver Se in these birds was not due to increases in selenoproteins. What increased dramatically in high Se liver were the low molecular weight (MW) selenometabolites, glutathione-, cysteine- and methyl- conjugates of the selenosugar, seleno-N-acetyl galactosamine (SeGalNac). In addition, size-exclusion chromatography and followup analysis demonstrated that a substantial amount of Se in Se-adequate liver was present as selenosugars decorating general proteins via mixed-disulfide links, in addition to Sec-containing selenoproteins. In high-Se liver, these “selenosugar-decorated” proteins comprised ∼50% of the Se in the water-soluble fraction, in addition to the low MW selenometabolites. Conclusions In Se-adequate liver, far more Se is present as the selenosugar moiety, mostly decorating general proteins, than is present as Sec in selenoproteins. With high Se supplementation, increased selenosugar formation occurs, further increasing selenosugar-decorated proteins, but also increasing selenosugar linked to low MW thiols, leading to the formation of methyl-SeGalNac. This suggested pathway, underlying adaptation to high Se status in animals, needs further investigation including study of the potential of selenosugar compounds as biomarkers of high Se status. Funding Sources USDA, Hatch project 1,004,389, and by the Wisconsin Alumni Foundation, Selenium Nutrition Research Fund 12,046,295.
