Acylated
oleanane-type
triterpene saponins, namely chakasaponins I (1) and II (2),
floratheasaponin A (3), and their analogs, together with catechins-including (-)-
epigallocatechin 3-O-gallate (4),
flavonoids, and
caffeine-have been isolated as characteristic functional constituents from the extracts of "
tea flower", the flower buds of Camellia sinensis (Theaceae), which have common components with that of the leaf part. These isolates exhibited antiproliferative activities against human digestive tract
carcinoma HSC-2, HSC-4, MKN-45, and Caco-2 cells. The antiproliferative activities of the
saponins (1-3, IC50 = 4.4-14.1, 6.2-18.2, 4.5-17.3, and 19.3-40.6 µM, respectively) were more potent than those of catechins,
flavonoids, and
caffeine. To characterize the mechanisms of action of principal
saponin constituents 1-3, a flow cytometric analysis using
annexin-V/7-aminoactinomycin D (7-AAD) double staining in HSC-2 cells was performed. The percentage of apoptotic cells increased in a concentration-dependent manner. DNA fragmentation and
caspase-3/7 activation were also detected after 48 h. These results suggested that antiproliferative activities of 1-3 induce apoptotic cell death via activation of
caspase-3/7.