Monoterpene indole alkaloids from the leaves of Tabernaemontana elegans induce apoptosis activity in human hepatoma cells

Apoptosis (programmed cell death) is a natural mechanism to eliminate unwanted or cancerous cells and virtually all the anticancer drugs currently utilized can induce apoptosis in susceptible cells [1]. Morphologically, this process is characterized by plasma membrane blebbing, cell shrinkage, and chromatin condensation followed by disassembly of the cell into multiple membrane-enclosed fragments, which are then engulfed by neighbouring cells or professional phagocytes. In our search for molecules with apoptosis inducing activity from medicinal plants, we have isolated three known and a new corynanthe type monoterpene indole alkaloids from the methanol extract of leaves of Tabernaemontana elegans. The structures of these compounds were elucidated by a series of spectroscopic experiments. The identification of the known alkaloids tabernaemontanine, vobasine, and dregamine, was corroborated by comparison of their spectroscopic data with those reported in literature [2]. The isolated monoterpene indole alkaloids were studied for their apoptosis induction activity in human hepatoma (HuH-7) cells. Methodology for apoptosis detection included cell viability assays, nuclear morphology evaluation, and general caspase-3-like activity assessments. Tabernaemontanine and vobasine showed the most promising apoptotic induction profile in HuH-7 cells, inducing 41 and 44% of apoptosis, respectively, after 24h of exposure. Caspase activity assays confirmed these results. Our data suggest that monoterpene indole alkaloids from the leaves of Tabernaemontana elegans may be considered as significant apoptosis inducers and should be further studied in other cell lines.

Acknowledgements: This study was supported by a fellowship from FCT, Portugal (reference number BPD/30492/2006).

References: [1] Kaufmann, S.H. et al. (2000) Exp. Cell Res. 256:42–49.

[2] Bombardelli, E. et al. (1976)J.C.S. Perkin I:1432–1438.