XFM and HERFD-XAS studies of selenium in tissues and whole blood from mice supplemented with potentially therapeutic selenocompounds

Selenium nanoparticles (SeNPs) and selenoneine (SeN) are prospective nutritional supplements and therapeutic agents postulated to counteract Se deficiency and alleviate oxidative stress induced by various pathological conditions. X-ray fluorescence microscopy (XFM) and high energy resolution fluorescence detected X-ray absorption spectroscopy (HERFD-XAS) investigated Se distribution and speciation in mice fed supranutritional doses of SeNPs (10 mg Se/kg in feed) and SeN (5 mg Se/kg in feed). Mice fed control and SeNP diets showed equivalent Se distributions in the liver and testes, however, Se concentrations were elevated in the renal tubules of mice supplemented with SeNPs. Negligible differences in the composition of selenospecies were detected in tissues from mice fed SeNPs and control diets. Mice supplemented with SeN exhibited significant elevations in Se across all analysed tissues. Se Kα1 HERFD-XAS data revealed reduced SeN as the predominant selenospecies in tissues and blood from mice fed the SeN diet. Characterisation of the SeN-enriched feed showed that SeN was initially present in both the oxidised dimer and reduced monomer forms. These results support the hypothesised in vivo reduction of SeN and subsequent bioaccumulation in the blood and various tissues. The present findings highlight marked differences in the bioavailability and utilisation of these purported therapeutic selenocompounds.