Involvement of the PI3K/AKT pathway in the hypoglycemic effects of saponins from Helicteres isora

Aim of the studySaponins from Helicteres isora have previously been shown to exert antidiabetic effects. The present study explored the underlying mechanisms in C2C12 skeletal muscle cells.Materials and methodsC2C12 cells were incubated with saponins and sapogenin followed by Western blotting and immunofluorescence analysis.ResultsWestern blotting revealed that incubation with saponins (100 μg/ml) and sapogenin (100 μg/ml) induced the phosphorylation of the phosphatidylinositol-3-kinase (PI3K) as well as of the downstream targets protein kinase B/Akt (at Ser473) and glycogen synthase kinase GSK-3α/β (at Ser21/9) in a time-dependent manner. In contrast, no phosphorylation of the AMP-sensitive kinase AMPK (at Thr172) was observed. Within 48 h saponins/sapogenin treatment further increased the protein abundance of the insulin-sensitive glucose transporter Glut4. Confocal microscopy confirmed that saponins/sapogenin treatment stimulated Akt phosphorylation and revealed that the treatment was followed by translocation of Glut4 into the cell membrane of C2C12 muscle cells.ConclusionsSaponins and sapogenin activate the PI3K/Akt pathway thus leading to phosphorylation and inactivation of GSK-3α/β with subsequent stimulation of glycogen synthesis as well as increase of Glut4-dependent glucose transport across the cell membrane.