Effects of Aralia continentalis root extract on cell proliferation and apoptosis in human promyelocytic leukemia HL-60 cells

The roots of Aralia continentalis (AC) have been used traditionally in Korean as a folk medicine for anti-inflammation and as an anti-rheumatic. In this study, we report that the ethyl acetate-soluble fraction (ACE) of the methanolic extract of AC root inhibited the cell growth of various human cancer cell lines and induced apoptosis of HL-60, human promyelocytic leukemia cells. Its IC50 values on growth inhibition were estimated to be 56.3 mu g/ml on HL-60, 87.2 mu g/ml on HepG2, 93.2 mu g/ml on HeLa, 135.5 mu g/ml on DU-145, and 135.8 mu g/ml on HT-29 cells. Interestingly, ACE showed no antiproliferative effect on normal lymphocyte cells used as control. Furthermore, nuclear DAPI staining revealed the typical nuclear features of apoptosis in the HL-60 cells exposed to 80 mu g/ml ACE, and a flow cytometric analysis of the HL-60 cells using propidium iodide showed that the apoptotic cell population increased gradually from 5% at 0 h to 16% at 12 h and 20% at 24 h after treated with 50 mu g/ml of ACE. TUNEL assay also revealed the apoptotic induction of the HL-60 cells treated with ACE. To obtain further information on the ACE-induced apoptosis, the expression level of certain apoptosis-associated proteins was examined using a Western blot analysis. Treatment of the HL-60 cells with ACE resulted in the activation of caspase-3, and subsequent proteolytic cleavage of poly(ADP-ribose) polymerase (PARP). The above results confirmed that the apoptosis in the HL-60 cells was induced by ACE, and that caspase-3)-mediated PARP cleavage was involved in the process.