EGCG and quercetin protected INS-1 cells in oxidative stress via different mechanisms.

EGCG and quercetin are known as beneficial dietary flavonoid for various diseases including diabetes mellitus. But it is not certain whether they could protect pancreatic beta cell directly. We performed this study to test both EGCG and quercetin could directly protect beta cell line under oxidative stress, and verify the action mechanisms. The protective effect of quercetin on INS-1 cells against oxidative stress was concentration dependent, but EGCG showed specific concentration zone for the protection. The protective effect of EGCG was more pronounced in pre-treatment before oxidative stress, while quercetin showed dramatic improvement of viability in simultaneous incubation with H2O2. In EGCG pre-treatment, antioxidant enzymes and activity were decreased, but the phosphorylated PI3K and Akt were significantly increased. PI3K inhibitor significantly reduced cell viability in EGCG pre-treatment. In conclusion, EGCG and quercetin have protective effect on INS-1 cells against oxidative stress through both antioxidant effect and anti-apoptosis signaling. In EGCG, pre-treatment make its effect better by the enhancement of anti-apoptosis signaling. Quercetin protected INS-1 cells more in simultaneous incubation via strong antioxidant defense.