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

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.

Demethylation of Methylmercury in Bird, Fish, and Earthworm.

Toxicity of methylmercury (MeHg) to wildlife and humans results from its binding to cysteine residues of proteins, forming MeHg-cysteinate (MeHgCys) complexes that hinder biological functions. MeHgCys complexes can be detoxified in vivo, yet how this occurs is unknown. We report that MeHgCys complexes are transformed into selenocysteinate [Hg(Sec)4] complexes in multiple animals from two phyla (a waterbird, freshwater fish, and earthworms) sampled in different geographical areas and contaminated by different Hg sources. In addition, high energy-resolution X-ray absorption spectroscopy (HR-XANES) and chromatography-inductively coupled plasma mass spectrometry of the waterbird liver support the binding of Hg(Sec)4 to selenoprotein P and biomineralization of Hg(Sec)4 to chemically inert nanoparticulate mercury selenide (HgSe). The results provide a foundation for understanding mercury detoxification in higher organisms and suggest that the identified MeHgCys to Hg(Sec)4 demethylation pathway is common in nature.

Stable isotope labelling and FPLC-ICP-SFMS for the accurate determination of clinical iron status parameters in human serum.

Iron is involved in the function of all living cells and, in fact, many diseases arise from imbalances in iron homeostasis. Therefore, the development of analytical methodologies to improve and automate the measurement of clinical indices of iron status has increased tremendously over the years. This work describes the development of two complementary methodologies to evaluate transferrin (Tf) saturation, total iron-binding capacity (TIBC), unsaturated iron-binding capacity (UIBC) and serum iron based on the use of iron-selective monitoring by inductively coupled plasma mass spectrometry (ICP-MS). The first methodology is based on the saturation of transferrin (Tf) with natural Fe3+ followed by separation of the different sialoforms in an anion exchange column (Mono-Q) to quantify the iron in each Tf sialoform and total Tf by ICP-MS using post-column isotope dilution analysis. In the second part, the saturation is done with an iron tracer (57Fe) and the application of pattern deconvolution analysis permits the direct quantification of the Tf saturation, the serum iron and the unsaturated iron-binding capacity. These strategies are validated by using a reference serum certified for total Tf and tested also in serum samples from individuals suffering from hemochromatosis and Fe-supplemented patients. The results obtained for all the parameters related to Fe status were in good agreement with those obtained by clinical tests. The use of stable isotope labelling in connection with the on-line coupling of fast protein liquid chromatography (FPLC) to ICP-MS allows the accurate determination of several parameters of great clinical relevance in iron homeostasis by means of two independent chromatographic runs. The main advantage of the proposed methodology is the number of parameters that can be simultaneously obtained.