Selenoneine is a major selenium species in beluga skin and red blood cells of Inuit from Nunavik

Nunavimmiut (Inuit of Nunavik, Northern Quebec, Canada) exhibit a high selenium (Se) status because oftheir frequent consumption of marine mammal foods. Indirect evidence from our previous studies hadsuggested that selenoneineea novel selenocompoundemay be accumulating in the blood of Nuna-vimmiut. We used a liquid-chromatography/inductively coupled tandem mass spectrometry (LC-ICP-MS/MS) method to measure concentrations of selenoneine and its methylated metabolite Se-methylselenoneine in archived red blood cells (RBC) obtained from 210 Nunavimmiut living in com-munities along the Hudson Strait, where marine mammal hunting and consumption are most frequent inNunavik. This method was adapted to quantify selenoneine and its methylated metabolite in belugamattaaq, an Inuit delicacy consisting of the skin with the underlying layer of fat and the major dietarysource of Se for Nunavimmiut. Total selenium concentration was also measured in RBC and belugamattaaq samples by isotope dilution ICP-MS/MS. The median selenoneine concentration in RBC was413mg Se/L (range¼3.20e3230mg Se/L), representing 54% (median) of total Se content (range¼1.6e91%). Quantification of selenoneine infive beluga mattaaq samples (skin layer) from Nunavik revealed amedian concentration of 1.8mg Se/g wet wt (range¼1.2e7.4mg Se/g), constituting 54% (median) of thetotal Se content (range¼44e74%). Se-methylselenoneine was also detected in Inuit RBC but not inbeluga mattaaq, suggesting that selenoneine undergoes methylation in humans. Selenoneine may protect Nunavimmiut from methylmecury toxicity by increasing its demethylation in RBC and in turndecreasing its distribution to target organs.