Induction of apoptosis by the oolong tea polyphenol theasinensin A throughcytochrome c release and activation of caspase-9 and caspase-3 in human U937 cells

This study examined the growth inhibitory effects of theasinensin A (from o olong tea) and black tea polyphenols, including theaflavin (TF-1), a mixtur e (TF-2) of theaflavin-3-gallate (TF-2a) and theaflavin-3'-gallate (TF-Sb), and theaflavin-3,3'-digallate (TF-3) in human cancer cells. Theasinensin A , TF-1, and TF-2 displayed strong growth inhibitory effects against human h istolytic lymphoma U937, with estimated IC50 values of 12 muM, but were les s effective against human acute T cell leukemia Jurkat, whereas TF-3 and (- )-epigallocatechin-3-gallate (EGCG) had lower activities. The molecular mec hanisms of tea polyphenol-induced apoptosis as determined by annexin V apop tosis assay, DNA fragmentation, and caspase activation were further investi gated. Loss of membrane potential and reactive oxygen species (ROS) generat ion were also detected by flow cytometry. Treatment with tea polyphenols ca used rapid induction of caspase-3, but not caspase-1, activity and stimulat ed proteolytic cleavage of poly(ADP-ribose) polymerase (PARP). Pretreatment with a potent caspase-3 inhibitor, Z-Asp-Glu-Val-Asp-fluoromethyl ketone, inhibited theasinensin A induced DNA fragmentation. Furthermore, it was fou nd that theasinensin A induced loss of mitochondrial transmembrane potentia l, elevation of ROS production, release of mitochondrial cytochrome c into the cytosol, and subsequent induction of caspase-9 activity. These results indicate that theasinensin A allows caspase-activated deoxyribonuclease to enter the nucleus and degrade chromosomal DNA and induces DFF-45 (DNA fragm entation factor) degradation. The results suggest that induction of apoptos is by theasinensin A may provide a pivotal mechanism for their cancer chemo preventive function.