Preferential organ distribution of methylselenol source Se-methylselenocysteine relative to methylseleninic acid

It has been proposed that Se-methylselenocysteine (MeSeCys) and methylseleninic acid (MSAIV) are efficiently transformed through the β-lyase and reduction reactions, respectively, into methylselenol, the assumed biologically active selenometabolite responsive for the anti-carcinogenicity and anti-oxidant actions of selenium. The bioavailability and distribution of the two selenium sources in major organs/tissues were compared under exactly identical conditions. Namely, labeled selenium sources 76Se-MeSeCys and 77Se-MSAIV, at a single oral dose of 10 μg Se/kg body weight each, were administered simultaneously to rats that had been depleted of natural abundance selenium with a single isotope 78Se. The same dose of 82Se-selenite was also administered as a reference selenium source. The distributions of the three labeled selenium isotopes were determined 3 h after the administration in 13 organs/tissues/blood. MeSeCys was taken up more efficiently by most organs, especially the pancreas and duodenum, than MSAIV and selenite, the latter two sources being taken up similarly to each other except for in the kidney, liver, and spleen, where the three labeled isotopes were detected at comparable concentrations. The labeled selenium in the liver supernatant was speciated by HPLC inductively coupled argon plasma-mass spectrometry (ICP-MS), and it was suggested that MeSeCys was delivered in its intact form to organs, and then transformed into methylselenol. In addition to the known properties of that MeSeCys is chemically more stable than MSAIV and is a naturally occurring edible product, and that MeSeCys produces methylselenol much more efficiently than a homologous selenoamino acid selenomethionine, the present study revealed that MeSeCys is more efficiently distributed than MSAIV in its intact form, and then produces methylselenol, suggesting that MeSeCys is the best methylselenol source in most organs/tissues.