We have previously shown that six propolins, A-F, could be isolated from Taiwanese
propolis (TP) and that they exerted a broad spectrum of
biological activities. Recently, we isolated a seventh compound,
propolin G. Its chemical structure has been identified by NMR and fast atom bombardment-mass spectrometry spectra and was found to be identical to a known compound,
nymphaeol C. We used high-performance liquid chromatography to determine the relative contents of propolins C, D, F, and G in TP collected in various seasons and regions and found them to be relatively higher in TPs collected from May to July than from September to October. In our present study, we were interested in the various
biological activities of TP extract as well as in
propolin G as a pure compound. We found that
propolin G could efficiently induce apoptosis in
brain cancer cell lines (
glioma and
glioblastoma). The apoptosis might have been through a mitochondrial- and
caspase-dependent pathway. This result demonstrated that the TP collection season was more an important factor than the geographical region.
Propolis has been suggested to possess a potent
antioxidant activity. We further evaluated the
antioxidant property of
propolin G using DPPH (1,2-diphenyl-2-picryhydrazyl). Our results indicate that
propolin G does possess
free radical scavenging activity. We also evaluated the neuroprotective action of
propolin G, TP, and BP (Brazilian
propolis) extracts against oxidative stress in rat primary cortical neurons. Our data demonstrate that
propolin G and TP extracts have a marked
neuroprotective effect that is greater than BP extract. In conclusion, the isolation and characterization of
propolin G from TP have demonstrated for the first time that this compound is a potent inducer of apoptosis in
brain cancer cells and that this compound and TP extract exhibit a protective effect against oxidative stress in rat cortical neurons.