Use of Stable Isotopic Selenium As a Tracer to Follow Incorporation of Selenium into Selenoproteins

Abstract

Abstract

Stable isotopes of selenium (Se) have been used in human studies to measure Se absorption, retention and excretion. The purpose of this study was to examine whether stable Se could also be used to follow the incorporation of Se into selenoproteins and whether selenoproteins are labeled with stable isotopes the same way they are with radioactive Se. Rats fed either a Se-deficient or a high-Se diet were injected with either a radioactive (⁷⁵Se) or a stable isotope of Se (⁷⁷Se), and the liver cytosol was chromatographed on Sephadex G-200. Compared with ⁷⁵Se, a greater percentage of ⁷⁷Se was incorporated into cytosol, but the distribution and the effect of dietary Se was similar for both isotopes. New Zealand long-eared rabbits were also injected with either ⁷⁷Se or ⁷⁵Se, and the plasma was chromatographed. More of the ⁷⁵Se was incorporated into the plasma, but again the patterns of incorporation were similar for both isotopes. Plasma from a male subject who ingested 60 μg of ⁷⁷Se was chromatographed, and the stable Se was detected in column fractions and showed a distribution similar to that observed for rabbit plasma. Finally, a polyacrylamide gel electrophoresis (PAGE) method was developed that allowed loading of sufficient protein to analyze for ⁷⁷Se in individual protein fractions. The distribution of ⁷⁷Se and ⁷⁵Se in rabbit plasma was similar. Human plasma was electrophoresed by a similar method and peaks of 56 and 23 kDa were detected. These data show that stable isotopes of Se can be used for selenoprotein production in the same way as radioactive isotopes. They also show that, when physiological amounts of stable Se are ingested by humans, the isotope can be detected in blood-borne proteins separated by column chromatography and PAGE. [P.S.E.B.M. 1995, Vol 210]