IngentaConnect Transport measurements across Caco-2 monolayers of different orga...

Abstract:

The transport and uptake of the most common Se compounds, selenate (SeO ₄ ²⁻ ), selenite (SeO ₃ ²⁻ ), selenomethionine, and selenocystine, were investigated using confluent monolayers of Caco-2 cells, a human carcinoma cell line. Comparative measurements were performed in the absorptive (apical to basolateral side) and exsorptive (basolateral to apical side) directions. Apparent permeability coefficients (P _app), calculated from transport experiments in the absorptive direction, showed increasing values in the following rank order: about 1×10⁻⁶ cm/s ≤ mannitol ≤ SeO ₃ ²⁻ ≤ selenocystine < selenomethionine < SeO ₄ ²⁻ ≤ about 16×10⁻⁶ cm/s. The ratios of the P _app measured in the absorptive versus exsorptive directions indicated that only the organic forms presented a net polarized transport (P _app ratio ≫1), suggesting the presence of a transcellular pathway. No significant excretion was observed. The transport of selenomethionine was inhibited by its sulfur analog, methionine, suggesting a common transport mechanism. In contrast, an inhibition of the transport of selenocystine by cysteine was not observed. From the two substrates tested, sulfate and thiosulfate, only thiosulfate inhibited the transport of SeO ₄ ²⁻ . This effect was also observed for SeO ₃ ²⁻ (i.e., was unspecific), which questioned the assertion of a common transport for sulfate and SeO ₄ ²⁻ and may confirm the paracellular pathway of SeO ₄ ²⁻ suggested by the P _app ratio of about 1. The addition of glutathione (GSH) in large excess had no consequence on the passage of SeO ₃ ²⁻ but strongly increased the uptake (about fourfold). The liquid chromatography — mass spectrometry (LC-MS) data showed that, in the ionic condition of incubation medium, GSH promptly reduced SeO ₃ ²⁻ (≤2 min) in its elemental form Se⁰, which cannot ascribe to selenodiglutathione a direct role in the effect of GSH.

Keywords: Selenium; selenite; selenate; selenocystine; selenomethionine; glutathione; Caco-2 cells

Document Type: Research article

DOI: 10.1385/BTER:83:3:191

Affiliations: 1: Laboratory of Pharmacology and Toxicology, University Hospital, 4 rue Larrey, 49033, Angers cedex 01, France,

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Transport measurements across Caco-2 monolayers of different organic and inorganic selenium: Influence of sulfur compounds