Synthesis of [77Se]-methylselenocysteine when preparing sauerkraut in the presence of [77Se]-selenite. Metabolic transformation of [77Se]-methylselenocysteine in Wistar rats determined by LC–IDA–ICP–MS

The use of enriched Se isotopes as tracers has provided important information on Se metabolism. However, selenium isotopes are expensive and difficult to obtain. A simple and cheap strategy based on the production of [77Se]-methylselenocysteine ([77Se]-MeSeCys) when preparing sauerkraut in the presence of [77Se]-selenite was developed. The resulting [77Se]-MeSeCys was used for evaluating the metabolic transformation of MeSeCys in Wistar rats, by feeding them with an AIN-93 M diet containing 20 % sauerkraut enriched in [77Se]-MeSeCys. Organs (liver, kidney, brain, testicles, and heart) were obtained after seven days of treatment and subjected to total selenium and selenium-speciation analysis by high-performance liquid chromatography coupled with isotope-dilution-analysis inductively-coupled-plasma mass spectrometry (HPLC–IDA–ICP–MS). Analysis of 77Se-labeled organs revealed a prominent increase (more than 100 % Se-level enhancement) of selenium in the kidney and heart, whereas in the liver selenium concentration only increased by up to 20 % and it remained constant in the brain and testicles. 77Se-enriched-sauerkraut supplementation does not alter the concentration of other essential elements in comparison to controls except for in the heart and kidney, in which selenium was positively correlated with Mg, Zn, Cu, and Mo. HPLC–ICP–MS analysis of hydrolyzed extracts after carbamidomethylation of the 77Se-labeled organs revealed the presence of [77Se]-SeCys and an unknown Se-containing peak, the identity of which could not be verified by electrospray-ionization (ESI)-MS–MS. Low amounts of [77Se]-MeSeCys were found in 77Se-labeled liver and kidney extracts, suggesting the incorporation of this selenium species in its intact form.