Assessment of the lupin seed glucose-lowering protein intestinal absorption by using in vitro and ex vivo models

A lupin seed glycoprotein, termed γ-conglutin, has previously been found to display insulin-mimetic activity in myocyte models and reduce plasma glucose concentration when orally administered to both rats and humans. To envisage the possible metabolic fate of this bioactive protein, we used in vitro cell and ex vivo tissue models to monitor its transit through the intestinal barrier. Caco-2 cell monolayers and rat intestinal everted sacs were treated with purified γ-conglutin and the protein was immuno-assayed by chemi-luminescence-enhanced Western blotting. The in vitro approach showed that the intact protein can transit from the apical to the basolateral side of the cell monolayers. The unmodified lupin protein was also detected inside the intestinal everted sacs. Proper controls of cell monolayer and sac integrity ruled out the possibility of protein passive leakage.