Background: Protopanaxadiol (PPD) is a triterpenoid that can be prepared from steamed ginseng. PPD possesses\r\nanticancer potential via caspase-dependent apoptosis. Whether paraptosis, a type of the caspase-independent cell\r\ndeath, is also induced by PPD has not been evaluated.\r\nMethods: Cell death, the cell cycle and intracellular reactive oxygen species (ROS) were analyzed by flow cytometry\r\nafter staining with annexin V/PI, PI/RNase or H2DCFDA. We observed morphological changes by crystal violet\r\nstaining assay. Mitochondrial swelling was measured by ultravioletââ?¬â??visible spectrophotometry. The activation of\r\nNF-?B was measured by luciferase reporter assay.\r\nResults: At comparable concentrations of 5-fluorouracil, PPD induced more cell death in human colorectal cancer\r\ncell lines HCT-116 and SW-480. We demonstrated that PPD induced paraptosis in these cancer cells. PPD treatment\r\nsignificantly increased the percentage of cancer cells with cytoplasmic vacuoles. After the cells were treated with\r\nPPD and cycloheximides, cytoplasmic vacuole generation was inhibited. The paraptotic induction effect of PPD was\r\nalso supported by the results of the mitochondrial swelling assay. PPD induced ROS production in cancer cells,\r\nwhich activated the NF-?B pathway. Blockage of ROS by NAC or PS-1145 inhibited the activation of NF-?B signaling.\r\nConclusions: PPD induces colorectal cancer cell death in part by induction of paraptosis. The anticancer activity of\r\nPPD may be enhanced by antioxidants such as green tea, which also inhibit the activation of NF-?B signaling.
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