Characterization of the Pharmacokinetics of Oral Selenium Compounds in Humans Before and Following Supplementation

Study Summary

The chemopreventive efficacy of Se was tested in a 10-year human intervention trial; total and lung cancer mortality, total cancer incidence, colorectal cancer and prostate cancer incidence decreased. This study is designed to compare, via stable isotope tracer studies the kinetics of inorganic and organic Se before and following two years of oral supplementation with L-selenomethionine, to measure forms of Se in the plasma (extracellular Se-dependent glutathione peroxidase \[GSHPx\], selenoprotein-P \[SeP\], albumin-bound Se \[AlbSe\] and nonprotein-bound low molecular weight \[LMWSe\] fractions), and to determine the effects of supplementation on the ecology of the hindgut microflora. The forms of Se were chosen to resemble the metabolism of the principal forms of Se in mixed American diets. Sodium selenite, an inorganic form, is metabolized by reduction to selenide which is then either used in the co-translational synthesis of SeCys in specific Se-containing proteins (e.g., glutathione peroxidases, diodinases, selenoproteins P and W), or is converted to methylated excretion products; in this sense it resembles the food form selenocysteine (SeCys) which is metabolized to the selenide level. Selenomethionine (SeMet), an organic form, is a major form of Se in many foods, particularly those of plan origin. In addition to being metabolized to selenide, SeMet also enters the metabolic protein pool by competing with the sulfur-containing amino acid, methionine. A study is proposed to assess the impact of selenium (Se) supplementation on its metabolism in humans. A pilot study will be conducted to test recruitment strategies and sample collection, preparation and analysis and to assess the detectability of two stable isotopes given together. Four subjects will receive two 300 ug oral doses consisting of 150 ug of the stable isotope 76Se as selenite and 150 ug of the stable isotope 74Se as selenomethionine on study days one and twelve. Subjects will be followed for six w