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

Background ge Aims: Gastrointestinal glutathione peroxidase (Gl-GPx), 1 of the 4 types of selenium-dependent glutathione peroxidases, is expressed exc lusively in the gastrointestinal system and has therefore been suggested to function as a barrier against the absorption of dietary hydroperoxides. Me thods: The selenium-dependent expression of Gl-GPx and cytosolic GPx (cGPx) was analyzed by Western blotting. Transport of 13-hydroperoxy octadecadien oic acid (13-HPODE) was investigated in a CaCo-2 cell monolayer modulated i n Gl-GPx and cGPx by selenium restriction or repletion. Localization of Gl- GPx in rat intestine was visualized by immunohistochemistry, Results: Low b ut significant Gl-GPx levels were detected in selenium-deficient CaCo-2 cel ls and in the gastrointestinal tract of selenium-deficient rats, whereas cG Px was completely absent. Selenium supplementation of CaCo-2 cells resulted in a 5-fold increase of Gl-GPx protein, whereas total GPx activity increas ed 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 n ot reach the basolateral side of an intact CaCo-2 cell monolayer, Depending on the selenium status, hydroperoxides damaged the monolayer as evidenced by toss of transepithelial resistance and paracellular diffusion of lucifer yellow, Only under these conditions was unmetabolized 13-HPODE detectable at the basolateral side. Conclusions: Low Gl-GPx levels, as present in sele nium deficiency, suffice to prevent transport of 13-HPODE. Gl-GPx may thus function as a barrier against hydroperoxide absorption, cGPx contributes to balance major oxidative challenge.