Analytical methods for the quantification of selenium species in biological matrix: Where are we?

Objective: Over the years, scientific investigations have proven the importance of selenium as an essential element for mammals, emphasizing its activity against many diseases and even its prophylactic effects. It is also established now that a malconsumption of selenium can be harmful. Therefore, the nature and the concentration of selenium and its derivatives found in the diet, the body, and even in the environment, for example, in the soil, should be determined carefully. Methods: In this review, analytical methods for speciation and determination of selenium concentrations in biological samples are summarized. Results: Methods ranging from routine to cutting-edge are explored, focusing on their analytical characteristics, such as specificity for discrete selenium species, sensitivity, accuracy, reproducibility, and skills required. Conclusion: There are already numerous studies regarding the analysis of selenium species. Beyond the method employed for actual measurements, we propose to review the preanalytic steps for sample handling in biological matrices, which directly affect results that will be more accurate with careful pretreatment. Furthermore, to reach better outcomes in terms of the identification of selenium species, different combinations of techniques might be the answer. We highlight here the last and the cutting-edge methods to identify and quantify selenium such as, high-performance liquid chromatography combined to inductively coupled plasma mass spectrometry (HPLC-ICP-MS), hydride generation atomic absorption spectrometry (HG-AAS), hydride-generation combined to atomic fluorescence spectrometry (HG-AFS), or to inductively coupled plasma optical emission spectrometry (HG-ICP-OES). This review emphasizes the importance of such investigations and the need to achieve reliable, safe, and effective quantification and methods of determination.

Association of Urinary and Dietary Selenium and of Serum Selenium Species with Serum Alanine Aminotransferase in a Healthy Italian Population

The trace element selenium is of considerable interest due to its toxic and nutritional properties, which markedly differ according to the dose and the chemical form. It has been shown that excess selenium intake increases the risk of type 2 diabetes and, possibly, other metabolic diseases like hyperlipidemia and non-alcoholic fatty liver disease (NAFLD). For the latter, however, epidemiologic evidence is still limited. We carried out a cross-sectional study recruiting 137 healthy blood donors living in Northern Italy and assessed their exposure to selenium through different methods and measuring serum selenium species. We performed linear and spline regression analyses to assess the relation of selenium and its forms with serum alanine aminotransferase (ALT) levels, a marker of NAFLD. Urinary selenium levels were positively and somewhat linearly correlated with ALT (beta regression coefficient (β) 0.11). Conversely, the association of dietary selenium intake with ALT was positive up to 100 µg/day and null above that amount (β 0.03). Total serum selenium was inversely associated with ALT up to 120 µg/L, and slightly positive above that amount. Concerning the different serum selenium species, ALT positively correlated with two organic forms, selenocysteine (β 0.27) and glutathione peroxidase-bound selenium (β 0.09), showed a U-shaped relation with the inorganic tetravalent form, selenite, and an inverse association with human serum albumin-bound selenium (β −0.56). Our results suggest that overall exposure to selenium, and more specifically to some of its chemical forms, is positively associated with ALT, even at levels so far generally considered to be safe. Our findings add to the evidence suggesting that low-dose selenium overexposure is associated with NAFLD.