Acetoacetate extract of Pleione bulbocodioides (Franch.) rolfe induces apoptosis of human leukemia thp-1cells through a mitochondria-regulated intrinsic apoptotic pathway

Abstract

The tubers of three orchidaceous plants, including Pleione bulbocodioides (Franch.) Rolfe, have been used as ‘Shan-Ci-Gu’ in traditional Chinese medicine for the treatment of bacterial infections and cancers for thousands of years. In this study, the effects of an acetoacetate (EtOAc) extract of P. bulbocodioides on the cell viability and apoptosis of THP-1 (human acute monocytic leukemia cell line) cells and its interaction with possible apoptotic pathways were investigated. THP-1 cells were treated with the EtOAc extract of P. bulbocodioides at different concentrations. The results showed that THP-1 cell viability was significantly inhibited by the EtOAc extract of P. bulbocodioides with an IC₅₀ of 51.37±2.68 µg/ mL at 24 h. The examination of cytotoxic effects on healthy cells showed that the EtOAc extract of P. bulbocodioides did not show any effect on healthy Vero cells. Selectivity indexes were greater than 15.57, suggesting that the EtOAc extract of P. bulbocodioides had selective toxicity against THP-1 cells. The results of annexin V-FITC/PI and DAPI staining showed that the EtOAc extract of P. bulbocodioides induced cell apoptosis in a dose-dependent manner. The apoptotic rate was increased in the treatment groups compared with that in the control group (P<0.05). The distribution of cells in the G₂ phase of the cell cycle increased along with typical cell apoptosis-induced morphological changes. The levels of the pro-apoptotic proteins Bax, cleaved PARP and cleaved caspase-3 increased with increasing concentration of acetoacetate extract of P. bulbocodioides, while the anti-apoptosis protein Bcl-2 was downregulated. Cyt c and AIF, which are characteristic proteins of the mitochondria-regulated intrinsic apoptosis pathway, also increased in the cytosol with increasing concentrations of the EtOAc extract of P. bulbocodioides. These results showed that the EtOAc extract of P. bulbocodioides significantly inhibits cell viability and induces cell apoptosis in the human leukemia cell line THP-1 through a mitochondria-regulated intrinsic apoptotic pathway.