Improvement of palmitate-induced insulin resistance in C2C12 skeletal muscle cells using Platycodon grandiflorum seed extracts

Platycodon grandiflorum seeds (PGSE) and P. grandiflorum root extracts (PGRE) were prepared and their effect on glucose uptake were evaluated in C2C12 myotubes. PGSE had significantly higher total phenolic and flavonoid contents than PGRE (P < 0.05), whereas crude saponin contents did not differ significantly between extracts. IC50 values of PGSE and PGRE for α-glucosidase were 0.269 and 1.47 mg/mL, respectively. PGSE treatments led to greater glucose uptake-promoting effects than PGRE treatments in normal and palmitate-treated C2C12 myotubes and luteolin was identified as an active PGSE compound. The insulin signaling molecules and insulin-independent AMP kinase were significantly activated by PGSE treatments and GLUT4 translocation on the plasma membrane was increased by 1.7 fold in palmitate-treated C2C12 myotubes. Based on the α-glucosidase inhibitory activity and glucose uptake promoting effects of PGSE in insulin-resistant muscle cells, these extract have a great potential to be developed as an anti-diabetic agent.