Neuroprotective biflavonoids of Chamaecyparis obtusa leaves against glutamate-induced oxidative stress in HT22 hippocampal cells

•Fifteen phenolic compounds were isolated from Chamaecyparis obtusa.•3, 4 and 9 showed protective effects in glutamate-injured HT22 cells.•The reduced activities of antioxidant enzymes induced by glutamate were preserved by 3, 4 or 9.•The reduced content of GSH, and the increased production of ROS by glutamate were attenuated by 3, 4 or 9.•The phosphorylated ERK1/2 proteins increased by glutamate was prevented by 3, while unaffected by 4. Four biflavonoids (1–4), five flavonoids glycosides (5–9), two catechins (10, 11), two lignans (12–13), neolignan glycoside (14) and phenylpropanoid glycoside (15) were isolated from the leaves of Chamaecyparis obtusa (Cupressaceae). Neuroprotective effects of the isolated compounds were evaluated employing HT22 mouse hippocampal cells, a model system to study glutamate-induced oxidative stress. The glutamate injured HT22 cells were protected significantly by amentoflavone (3), ginkgetin (4) and (−)-epitaxifolin 3-O-β-D-xylopyranoside (9). The reduced activities of antioxidant enzymes, superoxide dismutase (SOD), glutathione reductase (GR) in response to high concentration of glutamate were preserved by pre-treatment of 3, 4 or 9, while the activities of glutathione peroxidase (Gpx) and catalase (CAT) were little affected. The reduced content of GSH induced by glutamate was also recovered by 3, 4 or 9 in accommodation with the decrease in ROS production. In addition, the phosphorylation of ERK1/2 induced by glutamate insult was clearly prevented by 3, while little changed by 4. Taken together, amentoflavone (3), ginkgetin (4) and (−)-epitaxifolin 3-O-β-D-xylopyranoside (9) derived from C. obtusa could protect HT22 neuronal cells against glutamate-induced oxidative damage through preserving antioxidant enzymes activities and/or inhibiting ERK1/2 activation.