Selenium speciation studies in cancer patients to evaluate the responses of biomarkers of selenium status to different selenium compounds

Abstract This work presents the first systematic comparison of selenium (Se) speciation in plasma from cancer patients treated orally with three Se compounds (sodium selenite, SS; L-selenomethionine, SeMet; or Se-methylselenocysteine, MSC) at 400 µg/day for 28 days. The primary goal was to investigate how these chemical forms of Se affect the plasma Se distribution, aiming to identify the most effective Se compound for optimal selenoprotein expression. This was achieved using methodology based on HPLC-ICP-MS after sample preparation/fractionation approaches. Measurements of total Se in plasma samples collected before and after 4 weeks of treatment showed that median total Se levels increased significantly from 89.6 to 126.4 µg kg−1 Se (p < 0.001), particularly when SeMet was administered (190.4 µg kg−1 Se). Speciation studies showed that the most critical differences between treated and baseline samples were seen for selenoprotein P (SELENOP) and selenoalbumin after administration with MSC (p = 5.8 × 10−4) and SeMet (p = 6.8 × 10−5), respectively. Notably, selenosugar-1 was detected in all low-molecular-weight plasma fractions following treatment, particularly with MSC. Two different chromatographic approaches and spiking experiments demonstrated that about 45% of that increase in SELENOP levels (to ~ 8.8 mg L−1) with SeMet is likely due to the non-specific incorporation of SeMet into the SELENOP affinity fraction. To the authors’ knowledge, this has not been reported to date. Therefore, SELENOP is probably part of both the regulated (55%) and non-regulated (45%) Se pools after SeMet administration, whereas SS and MSC mainly contribute to the regulated one. Graphical abstract Supplementary information The online version contains supplementary material available at 10.1007/s00216-024-05141-y.


Measurement Conditions
Total Se analysis-Spectrum mode, ICP-MS/MS   Table S4.Validation of the double-AF-ICP-MS Se speciation methodology by the analysis of the NIST SRM 1950 human plasma.Mean, expanded uncertainty U (expressed as µg kg -1 Se, k=2) and relative expanded uncertainty U r (%, k=2) of the different Se-species measured during 4 independent batches (at least 4 injections per batch).Expected IDA values and corresponding obtained recovery (%).

Table S3 .
Total Se concentrations in the HMW ultrafiltered plasma fractions by ICP-MS at baseline (v2) and after 4 weeks of administration (v4) expressed as µg kg -1 Se: mean ± expanded uncertainty (2 independent measurements per sample, k=2), median, interquartile range (IQR) in all study subjects (n = 23) and in the randomised groups (SS, SeMet and MSC).Results of the comparison of the two-time points expressed as increase of Se (ΔSe, %) and p-value (paired t-test).And results of Pearson correlation analysis (correlation coefficient, r) between total Se in the whole plasma by ICP-MS (Table1) and in the HMW ultrafiltration one.LMW calculated is calculated indirectly by the subtraction of Se in the HMW pool from total plasma Se, expressed as percentage relative to total content.p < 0.01 (**), and p < 0.001 (***).
Value obtained by double species-specific IDA in combination with HPLC-ICP-MS/MS at the peptide level(26) b c Reference value determined by IDA-ICP-MS by NIST (k=2.2)

Table S5 .
Levels of Se bound to SeALB obtained by double AF-ICP-MS at baseline (v2) and after 4 weeks of administration (v4) expressed as µg kg -1 Se: mean ± expanded uncertainty (2 independent measurements per sample, k=2), median, interquartile range (IQR) in all study subjects (n = 23) and in the randomised groups (SS, SeMet and MSC).Results of the comparison of the two-time points expressed as increase of Se (ΔSe, %) and p-value (paired t-test).And results of Pearson correlation analysis (correlation coefficient, r) between total Se by ICP-MS (Table1) and double AF-ICP-MS.p < 0.01 (**), and p < 0.001 (***).

Table S6 .
Levels of Se bound to GPX3 obtained by double AF-ICP-MS at baseline (v2) and after 4 weeks of administration (v4) expressed as µg kg -1 Se: mean ± expanded uncertainty (2 independent measurements per sample, k=2), median, interquartile range (IQR) in all study subjects (n = 23) and in the randomised groups (SS, SeMet and MSC).Results of the comparison of the two-time points expressed as increase of Se (ΔSe, %) and p-value (paired t-test).And results of Pearson correlation analysis (correlation coefficient, r) between total Se by ICP-MS (Table1) and double AF-ICP-MS.p < 0.01 (**), and p < 0.001 (***).