Eonymus alatus (Thunb.) Sieb induces apoptosis via mitochondrial pathway as prooxidant in human uterine leiomyomal smooth muscle cells

Euonymus alatus (Thunb.) Sieb (EA) is a traditional Korean herbal medicine, commonly used to treat tumors in Korea and China for centuries. Our earlier studies have indicated that EA exhibits antitumor properties, but its mechanism remains to be elucidated. In this study, we evaluated the molecular mechanism of EA in a human uterine leiomyomal smooth muscle cell (ULSMC) line. Water extracts of EA have been reported to not only function as antioxidants but also cause cytotoxic effect. We investigated the mechanism of EA-induced cytotoxicity in human ULSMC. When cells were cultured with 20-200 mu g/mL EA for 6 h, caspase-3 was activated and then cells fell into apoptosis. Induction of apoptosis by EA was accompanied with increase of the cytosolic fractions of cytochrome c prior to the activation of caspase-3. The preculture with 5 mM of buthionine sulfoximine, an inhibitor of glutathione synthesis, facilitated EA-induced induction of apoptosis. The preculture with N-benzyloxycarbonyl-valyl-alanyl-aspartyl fluoromethylketone, a pan-caspase inhibitor, partially suppressed the induction of apoptosis. EA showed little toxic effect on peripheral blood mononuclear cells from healthy volunteers. These results indicate that EA acts as a prooxidant and induces caspase-3 activation and apoptosis via mitochondrial pathway.