The effect of trifolirhizin and resveratrol on human prostate cells
Lei, David K. Y.
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Trifolirhizin is a potent polycyclic flavonoid with anticarcinogenic effects. The treatment of 25 μM trifolirhizin in human derived prostate cancer LNCaP cells for 6 days decreased cell proliferation by 40%. Higher dosages caused the proliferation inhibition effect to be manifested in as early as 3 days. Another prostate cancer cell line, PC-3, was not affected by trifolirhizin till 125 μM resulting in about 45 % reduction in cell proliferation after 4 to 6 days of incubation. Most importantly, for normal human prostate epithelial (NHPrE) cells, trifolirhizin was effective only at the highest concentration of 200 µM. The proliferation inhibition in trifolirhizin-treated LNCaP and PC-3 cells was associated with cell cycle arrest at the G0/G1 and G2/M phase, respectively. Moreover, the expression of cyclin E was unchanged but that of cyclin D1, p53, p21 and p-Rb was suppressed in 50 μM trifolirhizin-treated LNCaP cells. To evaluate the influence of resveratrol on cellular zinc status, NHPrE cells were treated with 6 levels of resveratrol (0, 0.5, 1, 2.5, 5 and 10 μM) and 4 levels of zinc [0, 4, 16 and 32 μM representing zinc deficient (ZD), zinc normal (ZN), zinc adequate (ZA) and zinc supplemented (ZS), respectively]. Among each zinc treatment, a progressive reduction in cell growth or increase in cellular total zinc was observed with increases of resveratrol from 2.5, 5 and 10 μM or from 5 and 10 μM, respectively. In ZS cells a much higher increase in cellular total zinc was observed as early as 1 μM resveratrol. The resveratrol (10 μM) induced G2/M arrest was found to be responsible for the depressed cell proliferation. An in vitro experiment demonstrated complex formation between resveratrol and zinc ion. Fluorescent spectrofluorimetry and microscope imaging revealed that intracellular free labile zinc decreased in resveratrol-treated ZD and ZN NHPrE cells but increased in high zinc (ZA and ZS) cells. Furthermore, increases in cellular zinc status induced reactive oxygen species (ROS) generation as well as senescence in cells treated with 2.5 or 10 μM resveratrol, especially in ZA and ZS cells. Thus, increase in free labile zinc may induce ROS and senescence.