Pharmacological actions of the South African medicinal and functional food plant Sceletium tortuosum and its principal alkaloids

Harvey, Alan L and Young, Louise C and Viljoen, Alvaro M and Gericke, Nigel P (2011) Pharmacological actions of the South African medicinal and functional food plant Sceletium tortuosum and its principal alkaloids. Journal of Ethnopharmacology, 137 (3). 1124–1129. (https://doi.org/10.1016/j.jep.2011.07.035)

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Abstract

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. 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. The extract was a potent blocker in 5-HT transporter binding assays (IC(50) 4.3μg/ml) and had powerful inhibitory effects on phosphodiesterase 4 (PDE4) (IC(50) 8.5μg/ml), but not other phosphodiesterases. There were no cytotoxic effects. Mesembrine was the most active alkaloid against the 5-HT transporter (K(i) 1.4nM), while mesembrenone was active against the 5-HT transporter and PDE4 (IC(50)'s<1μM). The activity of the Sceletium tortuosum extract on the 5-HT transporter and PDE4 may explain the clinical effects of preparations made from this plant. The activities relate to the presence of alkaloids, particularly mesembrine and mesembrenone.

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