The group of researchers used HPLC/ICP MS for their speciation studies and carried out mass balance studies for quality assurance. Trimethylselenonium ion, a commonly reported urine metabolite generally thought to be produced as a way of excreting excess, potentially toxic selenium, could not be detected in normal (unsupplemented) human urine and in human urine collected after supplementation with selenite or selenomethionine. With respect to the obtained detection limit of 1 µg Se/L for TMSe, the group concluded that if at all present, this compound would account for < 0.5 % of the total selenium in those urine samples containing the highest selenium concentrations. This result is in accordance with recent results of the research group at the Danish University of Pharmaceutical Science but questions results obtained in some earlier studies.

 

 

The major Se species found in background urine were two selenosugars, namely methyl-2-acetamido-2-deoxy-1-seleno-ß-D-galactopyranoside (selenosugar 1) and its deacylated analog methyl-2-amino-2-deoxy-1-seleno-ß-D-galactopyranoside (selenosugar 3) (see below).

 

selenosugar 1	selenosugar 3

 

By spiking experiments it was confirmed that these non-identified species were not selenite, selenate, selenocystamine or trimethylselenonium. The researcher believe that the relative quantities of selenosugars 1 and 3 are dose-dependent, and thus might be relevant to a possible detoxification pathway for selenium. A possible explanation may involve transformation of excess selenium to selenosugar 1, which is then deacylated to selenosugar 3. At normal levels both species are present at similar  concentrations, but at high exposure the deacylation steps is overloaded leading to a large excess of selenosugar 1. Both selenosugars were about a factor of 1,000 less toxic than selenite a finding that may reassure people on selenium supplements, that excess ingested selenium is excreted as nontoxic metabolites.

 

Selenomethionine was a significant species (20%) in the urine when DL-selenomethionine was ingested. It was speculated that unchanged selenomethionine results from the D-selenomethione in the ingested mixture, reflecting the selectivity for L-selenomethionine of enzymes involved in metabolism. This may be another hint, that naturally occuring "L" compounds, for example from selenized yeast, are better suited for Se-supplementation.

 

 

 Doris Kuehnelt, Norbert Kienzl, Pedro Traar, Nam Hoang Le, Kevin A. Francesconi, Takafumi Ochi, Selenium metabolites in human urine after ingestion of selenite, L-selenomethionine, or DL-selenomethionine: a quantitative case study by HPLC/ICP MS, Anal. Bioanal. Chem., 383/2 (2005) 235-246

 

 

 Related Studies

 

 

 K. T. Suzuki, Y. Ogra, Metabolic pathway for selenium in the body: speciation by HPLC-ICP MS with enriched Se, Food Addit. Contam., 19/10 (2002) 974-983.

 

 Yasumitsu Ogra, Kazuya Ishiwata, Hiromitsu Takayama, Norio Aimi, Kazuo T. Suzuki, Identification of a novel selenium metabolite, Se-methyl-N-acetylseleno-hexosamine, in rat urine by HPLC-ICP MS and -electrospray ionization tandem mass spectrometry, J. Chromatogr. B, 767/2 (2002) 301-312

 

 Y. Kobayashi, Y. Ogra, K. Ishiwata, H. Takayama, N. Aimi, K.T. Suzuki, Selenosugars are key and urinary metabolites for selenium excretion within the required to low-toxic range, Proc. Natl. Acad. Sci. U.S.A., 99 (2002) 15932-36

 

 Yasumitsu Ogra, Toshitake Hatano, Masayoshi Ohmichi, Kazuo T. Suzuki, Oxidative production of monomethylated selenium from the major urinary selenometabolite, selenosugar, J. Anal. At. Spectrom., 18/10 (2003) 1252-1255.

 

 V. Díaz Huerta, J. Szpunar, R. Lobinski, M. L. Fernández Sánchez, A. Sanz-Medel, Sample preparation for identification of selenocompounds in urine by electrospray-MS/MS, J. Anal. At. Spectrom., 18/12 (2003) 1471-1476

 

 Kevin A. Francesconi, Florence Pannier, Selenium Metabolites in Urine: A Critical Overview of Past Work and Current Status, Clin. Chem. (Winston-Salem, N.C.), 50 (2004) 2240-2253.

 

 Bente Gammelgaard, Lars Bendahl, Selenium speciation in human urine samples by LC- and CE-ICP-MS-separation and identification of selenosugars, J. Anal. At. Spectrom., 19/1 (2004) 135-142

 

 Lars Bendahl, Bente Gammelgaard, Separation and identification of Se-methylseleno-galactosamine - a new metabolite in basal human urine - by HPLC-ICP-MS and CE-nano-ESI-(MS)2, J. Anal. At. Spectrom., 19 (2004) 950-957

 

 Pedro Traar, Ferdinand Belaj, Kevin A. Francesconi, Synthesis of Methyl 2-Acetamido-2-deoxy-1-seleno-ß-d-gluco- and galacto-pyranoside: Selenium Metabolites in Human Urine, Aust. J. Chem., 57/11 (2004) 1051-1053

 

 Kazuo T. Suzuki, Metabolomics of Selenium: Se Metabolites Based on Speciation Studies, J. Health Sci., 51/2 (2005) 107-114