Speciation analysis of selenium metabolites in urine and breath by HPLC- and GC-inductively coupled plasma-MS after administration of selenomethionine and methylselenocysteine to rats.

Selenium is an essential trace element found in vegetables as selenomethionine (SeMet) and methylselenocysteine (MeSeCys). In the present study, we used stable isotopes of Se to investigate differences between how SeMet and MeSeCys are metabolized, using methylseleninic acid (MSA) as a reference methylselenol source. A mixture containing (76)Se-SeMet, (77)Se-MeSeCys, and (82)Se-MSA (each 25 microg Se/kg b.w.) was orally administered to rats, and then, speciation analyses of Se in urine and exhaled gas were conducted using HPLC-inductively coupled plasma (ICP)-MS and GC-ICP-MS, respectively. The proportions of (76)Se-, (77)Se-, and (82)Se-selenosugar (Se-sugar) to total urinary Se metabolites originating from each tracer were very similar, while the proportion of (77)Se-tirmethylselenonium (TMSe) was much less than that of(76)Se- and (82)Se-TMSe in urine, suggesting that(77)Se-SeMet is less efficiently metabolized to TMSe. Similarly, there was significantly less (77)Se-dimethylselenide (DMSe) originating from (77)Se-SeMet than(76)Se- and (82)Se-DMSe originating from (76)Se-MeSeCys and (82)Se-MSA in exhaled gas. It is generally accepted that DMSe and TMSe are metabolites of methylselenol, a putative metabolic intermediate in Se metabolism. Methylselenol is believed to be responsible for the cancer chemoprevention effects of Se. These results suggest that MeSeCys is converted to methylselenol more efficiently than is SeMet and that urinary TMSe and exhaled DMSe might be useful biomarkers for the generation of cancer chemopreventive forms of Se.