Abstract

Ethnopharmacological relevance The South African plant Sceletium tortuosum has been known for centuries for a variety of traditional uses, and, more recently, as a possible source of anti-anxiety or anti-depressant effects. A standardised extract Zembrin® was used to test for pharmacological activities that might be relevant to the ethnopharmacological uses, and three of the main alkaloids were also tested.

Materials and methods A standardised ethanolic extract was prepared from dried plant material, along with the purified alkaloids mesembrine, mesembrenone and mesembrenol. These were tested on a panel of receptors, enzymes and other drug targets, and for cytotoxic effects on mammalian cells.

Results The extract was a potent blocker in 5-HT transporter binding assays (IC 50 4.3 μg/ml) and had powerful inhibitory effects on phosphodiesterase 4 (PDE4) (IC 50 8.5 μg/ml), but not other phosphodiesterases. There were no cytotoxic effects. Mesembrine was the most active alkaloid against the 5-HT transporter (K i 1.4 nM), while mesembrenone was active against the 5-HT transporter and PDE4 (IC 50 's < 1 μM).