Metabolism of 76Se-methylselenocysteine compared with that of 77Se-selenomethionine and 82Se-selenite

Se-Methylated selenoamino acids, Se-methylselenocysteine (MeSeCys) and selenomethionine (SeMet), are chemically inert storage forms of selenium in selenium-accumulators, and a nutritional and supplemental source. The metabolic pathway for MeSeCys was precisely traced by referring to those for SeMet and selenite by applying a new tracer method involving multiple homo-elemental stable isotopes. Male Wistar rats were depleted of endogenous natural abundance selenium with a single Se-enriched isotope, and then Se-76-MeSeCys, Se-77-SeMet and Se-82- selenite were orally administered simultaneously at 25 mu g Se/kg body weight each. Organs and body fluids were obtained at 3, 6, 9 and 12 h, and I and 2 days later, and subjected to speciation analysis. The main characteristics of the metabolism were as follows-, MeSeCys was incorporated into selenoprotein P slightly more than or at a comparable level to that of SeMet but less than that of selenite. MeSeCys and SeMet but not selenite was taken up by organs in their intact forms. MeSeCys and SeMet were delivered specifically to the pancreas and present in a form bound to an identical or similar protein. Trimethylselenonium (TMSe) was only produced from MeSeCys, i.e., not from SeMet or selenite, in the kidneys. Both selenosugars A and B of MeSeCys, SeMet and selenite origin were detected in the liver but only selenosugar B in the kidneys. These results suggest that MeSeCys can be a similar or better selenium source than SeMet, and supplies methylselenol much more efficiently in organs than SeMet and selenite. TMSe was produced much efficiently from MeSeCys than from SeMet and selenite, suggesting a role of methylselenol through the beta-lyase reaction in the metabolism of Se-niethylated selenoamino acids. (c) 2006 Elsevier Inc. All rights reserved.