Detection, Identification, and Quantification of Selenoproteins in a Candidate Human Plasma Standard Reference Material

To understand the effect of Se supplementation on health, it is critical to accurately assess the Se status in the human body by measuring reliable biomarkers. The preferred biomarkers of the Se status are selenoprotein P (SelP) and glutathione peroxidase 3 (GPx3) along with selenoalbumin (SeAlb), but there is still a real need for reference methods and reference materials to validate their measurements. Therefore, this work presents a systematic approach to provide quality control data in selenoprotein measurements. This approach combines online isotope dilution affinity liquid chromatography (LC) coupled to inductively coupled plasma mass spectrometry (ICPMS), laser ablation ICPMS, and tandem mass spectrometry (MS/MS) to identify and quantify SelP, GPx3, and SeAlb in a human plasma reference material SRM 1950. Quantitative determinations of SelP, GPO, and SeAlb were 50.2 +/- 4.3, 23.6 +/- 1.3, and 28.2 +/- 2.6 ng g(-1) as Se, respectively. The subsequent identification of the selenoproteins included nine SelP peptides, including two selenopeptides and nine GPx3 peptides, while albumin was identified with a protein coverage factor >95%. The structural elucidation of selenoproteins in the target Se affinity fractions in SRM 1950 provides information needed for method validation and quality control measurements of selenoproteins and therefore the selenium status in human plasma.