L’objectif principal de cette étude était de vérifier les niveaux circulants des sélénoprotéines et du mercure associé dans le plasma d’adultes inuits du Nunavik, chez qui le statut en sélénium et les concentrations du mercure sont élevés. Pour ce faire, une méthode analytique combinant une séparation par chromatographie d’affinité couplée à la spectrométrie de masse à plasma induit avec une quantification par dilution isotopique a été développée. L’application de cette méthode à l’ensemble des échantillons plasmatiques nous a permis de quantifier avec précision les concentrations des sélénoprotéines et d’avoir une meilleure évaluation du statut en sélénium chez les Inuits du Nunavik. De plus, la quantification du signal du mercure associé aux sélénoprotéines nous a permis de vérifier la possibilité d’une interaction entre ces deux entités.
Ainsi, les espèces plasmatiques de sélénoprotéines (GPx3, SelP et SeAlb) ont été séparées et quantifiées dans 852 échantillons. Nos résultats indiquent que le sélénium plasmatique, en moyenne chez les Inuits du Nunavik, est incorporé à plus de 50% dans la SelP alors que le reste est partagé entre les deux autres sélénoprotéines. Cette distribution du sélénium n’était pas différente de celles retrouvées dans d’autres populations dont le statut en sélénium était comparable. Ceci indique que les sélénoprotéines sont maintenues à un équilibre lorsque le statut en sélénium plasmatique est élevé, à l’exception de la SeAlb qui varie selon le statut de la SeMet.
Nous avons pu aussi quantifier le mercure plasmatique qui représentait 15% du mercure total. Ce mercure n’était pas totalement libre dans le plasma et était associé aux pics de sélénoprotéines lors de la séparation chromatographique. Ces résultats suggèrent que le mercure se lie aux sélénoprotéines plasmatiques, probablement par affinité aux groupements sélénols. Toutefois, cette liaison diminue la biodisponibilité du mercure mais ne permet pas de prouver un quelconque antagonisme entre le mercure et les sélénoprotéines.
Les analyses sanguines effectuées nous ont permis de comparer les niveaux sanguins du sélénium avec ceux du plasma. Nous avons été surpris de l’écart existant entre les valeurs sanguines et plasmatiques dans cette population. En effet, nos résultats démontrent que la relation entre le sélénium plasmatique et sanguin était non-linéaire et que le sélénium dans le sang continuait à augmenter alors qu’il atteignait un plateau dans le plasma. Cette observation était semblable à ce qui a été rapporté par Hansen et al en 2004 chez les Inuits du Groenland alors que chez les Brésiliens d’Amazonie, une relation linéaire était observée. Nous pensons que cette différence entre les Inuits et les Brésiliens réside dans l’espèce de sélénium consommée. De ce fait, nous supposons que l’alimentation traditionnelle des Inuits contient une ou plusieurs formes de sélénium qui sont redirigées vers les cellules sanguines où elles sont stockées. De plus, on se basant sur les données de Yamashita, nous supposons aussi que le sélénium dans les cellules sanguines est sous forme de sélénonéine.
Enfin, au terme de cette étude il devient clair de mentionner que pour mieux caractériser le statut en sélénium dans une population comme celle des Inuits du Nunavik, une spéciation dans la fraction cellulaire sanguine s’impose. Cette dernière va nous permettre de mieux comprendre l’effet que peut avoir une alimentation riche en sélénium sur la santé des Inuits et donnera plus de détails quant aux interactions que peut avoir le sélénium avec les différents contaminants environnementaux, principalement le mercure.
57
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