Participation of b0,+ and B0,+ systems in the transport of mercury bound to cysteine in intestinal cells

Abstract

The main source of exposure to mercury (Hg) as divalent inorganic Hg [Hg(II)] and methylmercury (CH₃Hg) is the diet, in which complexes with the amino acid cysteine (Hg–Cys) may be found. The present study explores the participation of the b^0,+ and B^0,+ amino acid transporters in the intestinal transport of mercuric conjugates with cysteine [Hg(II)–Cys and CH₃Hg–Cys], using Caco-2 cells as a model of the intestinal epithelium. For this purpose, the effects of b^0,+ and B^0,+ gene silencing upon Hg(II)–Cys and CH₃Hg–Cys uptake were evaluated. In addition, after treatment with Hg–Cys complexes, we evaluated the differential expression of b^0,+ and B^0,+ and of transporters belonging to the LAT and y⁺LAT systems, which have also been described as possible participants in the Hg–Cys transport. The results show that b^0,+ and B^0,+ silencing reduces intracellular accumulation of Hg(II)–Cys (39 ± 8%) and CH₃Hg–Cys (16 ± 3%), respectively. These results, together with the existing literature, suggest that these transporters are involved in the transport of Hg–Cys in intestinal cells. On the other hand, the differential expression studies reflect an increase in LAT and y⁺LAT transporters after treatment with Hg–Cys, which could indicate their participation in the cellular elimination of such complexes, as has been previously suggested.