Mercury binding to selenoproteins and age-related depletion of bioavailable selenium in long-finned pilot whales

Selenoproteins-particularly glutathione peroxidase (GPx) and selenoprotein P (SelP)-are essential for redox regulation and selenium (Se) homeostasis. However, the influence of aging and mercury (Hg) exposure on these proteins in marine mammals remains inadequately characterized. In this study, we examined liver, brain, kidney, and muscle tissues from 21 stranded long-finned pilot whales (Globicephala melas), aged 1 to 36 years, using double-affinity high-performance liquid chromatography (AF-HPLC) coupled with inductively coupled plasma tandem mass spectrometry (ICP-MS/MS) to fractionate Se and Hg within selenoprotein-containing fractions. Age-dependent increases in total Hg and Se were observed across all tissues, alongside significant reductions (p < 0.05) in bioavailable selenoproteins-specifically those fractions associated with GPx and SelP-in brain and muscle. Although direct Hg-protein binding was not assessed, co-elution of Hg with Se-containing fractions suggests Hg association with selenoproteins, potentially compromising enzymatic function. These findings indicate a reduction in antioxidant capacity, with SelP potentially facilitating Hg transport into neural tissues, thereby increasing neurotoxic risk in older individuals. Our results underscore the age-related vulnerability of marine mammals to oxidative stress and highlight the need for mechanistic studies to clarify the biochemical basis of HgSe interactions.