Protective effects of kaempferol, quercetin, and its glycosides on amyloid beta-induced neurotoxicity in C6 glial cell

Alzheimer’s disease (AD) is a common neurodegenerative disease. Oxidative stress by amyloid beta peptide (Aβ) of neuronal cell is the most cause of AD. In the present study, protective effects of several flavonoids such as kaempferol (K), kaempferol-3-O-glucoside (KG), quercetin (Q) and quercetin3-β-D-glucoside (QG) from Aβ25-35 were investigated using C6 glial cell. Treatment of Aβ25-35 to C6 glial cell showed decrease of cell viability, while treatment of flavonoids such as Q and QG increased cell viability. In addition, treatment of flavonoids declined reactive oxygen species (ROS) production compared with Aβ25-35induced control. The ROS production was increased by treatment of Aβ25-35 to 133.39%, while KG and QG at concentration of 1 μM decreased ROS production to 107.44 and 113.10%, respectively. To study mechanisms of protective effect of these flavonoids against Aβ25-35, the protein expression related to inflammation under Aβ25-35-induced C6 glial cell was investigated. The results showed that C6 glial cell under Aβ25-35-induced oxidative stress up-regulated inflammation-related protein expressions. However, treatment of flavonoids led to reduction of protein expression such as inducible nitric oxide synthase, cyclooxygenase-2 and interleukin-1β. Especially, treatment of KG and QG decreased more effectively inflammation-related protein expression than its aglycones, K and Q. Therefore, the present results indicated that K, Q and its glycosides attenuated Aβ25-35-induced neuronal oxidative stress and inflammation.