Tubeimoside V (1), a new cyclic bisdesmoside from tubers of Bolbostemma paniculatum, functions by inducing apoptosis in human glioblastoma U87MG cells

Malignant glioblastoma is one of the most common malignant tumors in the neurological system. Tubeimoside V (1), a new cyclic bisdesmoside from tubers of Bolbostemma paniculatum, appears to exhibit various biological activities, including antitumor effect, but the function and mechanism of this new agent on glioblastoma cells has not previously been determined. In the present study, we investigated the proliferation change of human glioblastoma U87MG cells exposured to different concentrations (0.9–14.8 μM) of Tubeimoside V (1) for a certain time. The results showed that Tubeimoside V (1) significantly suppressed U87MG cell proliferation in a time- and dose-dependent manner (IC50 = 3.6 μM). Flow cytometric analysis of DNA in U87MG cells showed that Tubeimoside V (1) induces the prominent appearance of a sub-G1 peak in the cell cycle suggestive of apoptosis. Furthermore, U87MG cells’ treatment with Tubeimoside V (1) resulted in nuclear condensation with apoptotic bodies observed by both fluorescence and electron microscopy. The result of annexin V/PI assay showed that phosphatidylserine externalization began after treatment, and then increased in the following 24 h. Molecular changes explored through Western-blot staining showed Tubeimoside V (1) decreased the expression levels of Bcl-2 protein and increased the expression levels of Bax protein. The novel findings suggest that the cytotoxic actions of Tubeimoside V (1) toward U87MG cells result from the induction of cell apoptosis. Overall, our data demonstrate that Tubeimoside V (1) is an efficient apoptotic killing agent of glioblastoma cells and suggest that this mechanism may play a critical role in anti-tumor chemotherapy.