154 - Selenoneine: Potential Key Role in Mercury Detoxification Mechanisms in Seabirds

Seabirds are principally exposed to selenium (Se) and mercury (Hg) through their marine diet. In long-lived and top predator seabirds, such as the giant petrel, extremely high concentrations of Hg and Se are found (reaching up to 1000 µg.g-1). Recently, tiemannite (HgSe), which is considered the end-product of methylmercury (MeHg) demethylation, has been found in different tissues of seabirds, such as brain, liver, muscle and kidneys. The biomineralization of HgSe nanoparticles (NPs) represents the final stage of an efficient MeHg detoxification mechanism which is not yet fully elucidated. One of the remaining questions is the identification of reactive bio-organic Se compounds involved in such process. In this work, the speciation of Se by hyphenated techniques (HPLC-ICP-MS/ESI-MS) was used to investigate Se compounds in the water-soluble fraction of seabirds tissues. A set of 8 giant petrel (Macronectes sp.) individuals of a wide age range from the Southern Ocean was studied. Selenoneine (C9H15N3O2Se, 2-selenyl-Nα,Nα,Nα-trimethyl-L-histidine), a Se-analogue of ergothioneine, was identified as the major water-soluble Se compound in the tissues (brain, liver, muscle, kidneys, testis and blood) of this wild avian species. The levels of selenoneine found in giant petrels are the highest reported in animal tissues until now, with values reaching up to 88 μg Se g−1. The highest proportion of selenoneine versus total Se was found in the brain tissues (83% ± 5%). This suggests that selenoneine could plays a crucial role in protecting the nervous system against Hg toxicity. Consistently, the dramatic decrease of selenoneine (from 68 to 3%) with increasing total Hg concentrations in liver (95% of Hg as HgSe) strongly supports the hypothesis of its crucial role in Hg detoxification.

Authors: Khouloud El Hanafi