Four carotenoids from Pittosporum tobira protect primary cultured rat cortical cells from glutamate-induced toxicity.

We observed that an aqueous extract of this medicinal plant exhibited significant neuroprotection against glutamate-induced toxicity in primary cultured rat cortical cells from methanol extracts of the seeds of P. tobira. To further clarify the underlying neuroprotective mechanism(s) of this observed effect, we isolated and identified various active fractions and components. By using such fractionation procedures, four known carotenoids compounds--tobiraxanthins A1, A2, A3, and B--were isolated from the n-hexane fraction of methanol extracts from the seeds of P. tobira. Among these four compounds, tobiraxanthins B exhibited significant neuroprotective activity against glutamate-induced neurotoxicity, as indicated by a cell viability of approximately 50%, at concentrations ranging from 0.1 microM to 10 microM. These findings indicate that, the neuroprotective effects of P. tobira might be due to the inhibition of glutamate-induced toxicity by carotenoids present in the plant.