Selenium speciation in paired serum and cerebrospinal fluid samples of sheep

This study was performed to characterise selenium (Se) and Se species in cerebrospinal fluid (CSF) of sheep and its relation to the respective Se concentrations in serum. Paired samples from 10 adult sheep were used for the study. Five sheep were fed a diet with a marginal Se concentration of <0.05 mg Se/kg diet dry weight (dw, Se–), and five animals were fed the same diet supplemented with sodium selenite revealing a concentration of 0.2 mg Se/kg diet dw (Se+). The feeding strategy was conducted for two years; The results on metabolic effects were published previously. At the end of the feeding period, paired samples of serum and CSF were collected and analysed using ion exchange chromatography inductively coupled plasma–dynamic reaction cell–mass spectrometry (IEC-ICP-DRC-MS) technique for total Se concentration and concentrations of Se species. Albumin concentrations were analysed additionally.The feeding strategy caused significant differences (p < 0.01) in serum Se concentrations with 33.1 ± 5.11 μg Se/l in the Se– group and 96.5 ± 18.3 μg Se/l in the Se+ group, respectively. The corresponding total Se concentrations in CSF were 4.38 ± 1.02 μg Se/l and 6.13 ± 1.64 μg Se/l in the Se– and the Se+ group, respectively, missing statistical significance (p = 0.077). IEC-ICP-DRC-MS technique was able to differentiate the Se species selenoprotein P-bound Se (SePP), selenomethionine, glutathione peroxidase-bound Se (Se-GPx), selenocystine, thioredoxin reductase-bound Se, ovine serum albumin-bound Se (Se-OSA), SeIV and SeVI in ovine serum and CSF. Quantitatively, SePP is the main selenoprotein in ovine serum followed by Se-GPx. The CSF/blood ratio of albumin (QAlbumin) reflected a physiological function of the blood-CSF barrier in all sheep. QSe-species were higher than QAlbumin both feeding groups, supporting the hypothesis of local production of Se species in the brain. Significant positive regression lines for CSF vs. serum were found for albumin and Se-OSA only, suggesting a role of albumin to convey Se across the blood-CSF barrier. The ovine model, together with the IEC-ICP-DRC-MS technique to characterise the Se species, might be a worthwhile model for further studies as repeated sample collection as well as modification of the nutritional status is feasible and effective.