Honokiol and magnolol stimulate glucose uptake by activating PI3K-dependent Akt in L6 myotubes

Honokiol and magnolol, ingredients of Magnolia officinalis, which is used in traditional Chinese and Japanese medicines, have been reported to have antioxidant, anticancer, and antiangiogenic effects. Effects of these compounds on glucose metabolism in adipocytes have also been reported. However, their effects on skeletal muscle glucose uptake and the underlying molecular mechanisms are still unknown. Here, we investigated the direct effects and signaling pathways activated by honokiol and magnolol in skeletal muscle cells using L6 myotubes. We found that honokiol and magnolol dose-dependently acutely stimulated glucose uptake without synergistic effects of combined administration in L6 myotubes. Treatment with honokiol and magnolol also stimulated glucose transporter-4 translocation to the cell surface. Honokiol- and magnolol-stimulated glucose uptake was blocked by the phosphatidylinositol-3 kinase inhibitor, wortmannin. Both honokiol and magnolol stimulated Akt phosphorylation, a key element in the insulin signaling pathway, which was completely inhibited by wortmannin. These results suggest that honokiol and magnolol might have beneficial effects on glucose metabolism by activating the insulin signaling pathway.