Human urinary excretion and metabolism of 82Se-enriched selenite and selenate determined by LC-ICP-MS

Abstract

Urinary excretion of selenium after ingestion of isotope labeled selenite and selenate was studied in seven healthy volunteers, 4 men and 3 women (age 28-50 years). An aqueous solution containing 330 μL (82)Se-selenate (corresponding to 74.3 μg (82)Se) was given orally and urine samples were subsequently collected during the following 24 hours. The scheme was repeated four weeks later with a 280 μL (82)Se-selenite solution (corresponding to 74.4 μg (82)Se). The amount of total Se in the urine samples was determined by inductively coupled mass spectrometry. The mean total urinary excretion of (82)Se following (82)Se-selenate administration was 33.7% (range 15.6-42.5%) while the mean total excretion of (82)Se after (82)Se-selenite administration was 3.2% (range 2.8-3.9%) of the ingested amount. LC-ICPMS analysis of the urine samples showed that the majority of the selenium excreted after selenate ingestion was unchanged selenate for 6 of the individuals while one individual had metabolized a fraction (approx. 20%) of the selenate to selenosugar. Ingestion of 10 times larger doses of selenite in two individuals resulted in 13-23% excretion primarily excreted as selenosugar. These results show that the human metabolic pathways of selenite and selenate are different and indicate that not all selenate, although well absorbed, may be available for the beneficial health effects.

Human metabolism and renal excretion of selenium compounds after oral ingestion of sodium selenate dependent on trimethylselenium ion (TMSe) status

“…Another conformity with the study of Gammelgaard et al (2012) was the particular case of one subject showing a clear increased elimination of SeSug1 with a maximum 6 h after ingestion like the subject of subgroup III in the present study. Due to the fact that Gammelgaard et al (2012) used isotope-labeled selenate, they proved the conversion of selenate to SeSug1.…”

“…In accordance with the observation of lower amounts of total selenium eliminated by TMSe eliminators, the investigation of Gammelgaard et al (2012) showed also one subject with a distinct lower elimination of 82 Se. The TMSe status was unfortunately not tested in their study.…”

“…However, the speciation analysis of a study of Gammelgaard et al (2012) and the present study revealed that the main elimination product is selenate itself. Gammelgaard et al (2012) showed in a study of seven subjects that after an oral dosage of 74.3 μg 82 Se-labeled selenate 25.7 ± 7.7 % is excreted completely via urine within the first 24 h. These results are confirmed by the present results. Consequently, the main portion of selenate was eliminated without metabolism and does not supply the general selenide pool.…”

“…Due to the fact that Gammelgaard et al (2012) used isotope-labeled selenate, they proved the conversion of selenate to SeSug1. The subject in their study eliminated 6.9 % of the supplemented dose via urine, which is in good accordance with the results of the present study.…”

Human metabolism and renal excretion of selenium compounds after oral ingestion of sodium selenite and selenized yeast dependent on the trimethylselenium ion (TMSe) status

“…methyl-2-acetamido-2-desoxy-1-seleno-β-d-glucopyranoside (SeSug2) and methyl-2-amino-2-desoxy-1-seleno-β-d-galactopyranoside (SeSug3) have been detected in human urine, from which SeSug1 is the most important one Gammelgaard and Bendahl 2004;Gammelgaard et al 2003Gammelgaard et al , 2005Gammelgaard et al , 2012Kuehnelt et al 2005). Another pathway is the elimination after methylation in the form of dimethylselenide via breath (Kremer et al 2005) or trimethylselenium ion via urine (Gammelgaard et al 2000;Kuehnelt et al 2006;Lu et al 2012;Marchante-Gayón et al 2001).…”