Akt is also a key antiapoptotic effector of cellular growth factors [35]. PI3K activation by growth factors leads to Akt activation, which is an important player in survival pathway [36]. Some studies have shown

that Akt suppresses apoptosis signaling via BCL2 induction [27], and p-p53 inhibition through MDM2 activation [37]. Previously, KRG was shown to upregulate PI3K/Akt signaling and to inhibit apoptosis via Bortezomib in vitro the regulation of BCL2 and caspase-3 expression, thus protecting endothelial cells from starvation [38]. Moreover, Panax notoginseng saponins inhibit ischemia-induced apoptosis by stimulating PI3K/Akt signaling in cardiomyocytes [39]. However, the mechanism by which KRG activates PI3K/Akt signal via ER-β under oxidative stress in brain cells has been unclear until now. In this study,

we demonstrated that KRG increases PI3K/Akt signaling via upregulation of ER-β, thus inhibiting apoptosis through p-p53 and caspase-3 downregulation and BCL2 induction in oxidatively stressed brain cells. Excitotoxicity SCH727965 molecular weight is the pathological process caused by neurotransmitter glutamate such as n-methyl-d-aspartate (NMDA) and kainic acid [40]. These excitotoxins bind to glutamate receptor and result in increase of intracellular Ca2+. Subsequently, overload of intracellular Ca2+ stimulates activation of enzymes comprising calpains, which are the ubiquitously expressed family of Ca2+-dependent proteases Alanine-glyoxylate transaminase [40]; thus these enzymes can damage

cellular structures such as cytoskeleton, and are important for apoptosis and necrosis. Estrogen induced ER-α inhibited excitotoxicity via downregulating calpain expression [41]. In addition, ER-β play an important role in estrogenic neuroprotection against NMDA-induced excitotoxicity [42]. Red ginseng extract was reported to have neuroprotective activity against kainic acid-induced excitotoxicity in vitro and in vivo by inhibition of ROS level [40]. Moreover, ginsenoside Rg3 exhibited neuroprotection against homocysteine-induced excitotoxicity via inhibition of homocysteine-mediated NMDA receptor activation [43]. Our results showed that KRG increases ER-β expression and provides ER-β mediated-neuroprotection. Taken together, KRG-induced ER-β seems to play some role in protection against excitotoxicity. However, further studies are necessary for elucidation of the underlying mechanism. Ginsenosides are structurally similar to glucocorticoids or estrogens. In agreement, ginsenosides Re and Rg1 are functional ligands of the glucocorticoid receptor, whereas ginsenosides Rb1 and Rh1 are functional ligands of the ER [44]. Ginseng was also shown to activate ER in breast cancer cells in vitro but not in vivo [19]. Previously, we found that the ER-α expression was not affected in vitro by oxidative stress nor by KRG treatment, thus ERα would not be predicted to play a major role in oxidative stress in the brain [17].