Selenoneine and ergothioneine in beluga skin and tissues as key antioxidants in the Inuit diet.

As a result of their unique traditional diet, Inuit living in Nunavik (northern Quebec) exhibit among the highest blood concentrations of antioxidants selenoneine and ergothioneine worldwide. While beluga skin consumption has been identified as the main dietary source of selenoneine, potentially affording protection against methylmercury toxicity, little is known regarding the presence of ergothioneine, its sulphur isologue, in wild foods consumed by Inuit. We used isotope-dilution liquid chromatography-tandem mass spectrometry to quantify concentrations of selenoneine, ergothioneine and their metabolites in various organs and tissues obtained from 14 adult beluga whales (Delphinapterus leucas) harvested by Quaqtaq hunters in 2018-2019. We found the highest concentrations in the skin, with an average of 17.2 µg/g selenoneine and 78.6 µg/g ergothioneine - the highest ergothioneine concentration reported to date in the marine biome. We also obtained evidence of transplacental transfer of both antioxidants. Selenoneine and ergothioneine displayed outwardly increasing concentrations across skin layers and immunofluorescence staining revealed the primary location of the ergothioneine transporter in the basal epidermal layer. The combined accumulation of these antioxidants in the skin epidermis may suggest a protective role against UV photodamage and may help protect both belugas and Inuit against physical and chemical stressors of the northern environment.