Functions of GI-GPx: lessons from selenium-dependent expression and intracellular localization.

Gastro intestinal glutathione peroxidase (GI-GPx) is one of the four distinct mammalian selenoperoxidases. It had been reported to be restricted to the gastrointestinal tract but has more recently been identified also in human liver and some tumor cell lines. GI-GPx ranks high in the hierarchy of selenoproteins. The GI-GPx mRNA rather increases than decreases in selenium deficiency. GI-GPx protein responds poorly to selenium deprivation and increases fast upon resupplementation. Putative biological roles of GI-GPx, e.g. protection against food-born hydroperoxides, redox-regulation of proliferation or apoptosis, and modulation of mucosal immunity, are discussed in the light of cellular and subcellular distribution, transcriptional regulation and observations with k.o. mice.

Gastrointestinal glutathione peroxidase prevents transport of lipid hydroperoxides in CaCo-2 cells.

BACKGROUND & AIMS: Gastrointestinal glutathione peroxidase (GI-GPx), 1 of the 4 types of selenium-dependent glutathione peroxidases, is expressed exclusively in the gastrointestinal system and has therefore been suggested to function as a barrier against the absorption of dietary hydroperoxides. METHODS: The selenium-dependent expression of GI-GPx and cytosolic GPx (cGPx) was analyzed by Western blotting. Transport of 13-hydroperoxy octadecadienoic acid (13-HPODE) was investigated in a CaCo-2 cell monolayer modulated in GI-GPx and cGPx by selenium restriction or repletion. Localization of GI-GPx in rat intestine was visualized by immunohistochemistry. RESULTS: Low but significant GI-GPx levels were detected in selenium-deficient CaCo-2 cells and in the gastrointestinal tract of selenium-deficient rats, whereas cGPx was completely absent. Selenium supplementation of CaCo-2 cells resulted in a 5-fold increase of GI-GPx protein, whereas total GPx activity increased by a factor of 13, with most of the GPx activity under selenium-adequate conditions being cGPx. Irrespective of the selenium status, 13-HPODE did not reach the basolateral side of an intact CaCo-2 cell monolayer. Depending on the selenium status, hydroperoxides damaged the monolayer as evidenced by loss of transepithelial resistance and paracellular diffusion of lucifer yellow. Only under these conditions was unmetabolized 13-HPODE detectable at the basolateral side. CONCLUSIONS: Low GI-GPx levels, as present in selenium deficiency, suffice to prevent transport of 13-HPODE. GI-GPx may thus function as a barrier against hydroperoxide absorption. cGPx contributes to balance major oxidative challenge.