Pharmacological Studies on Xysmalobium undulatum and Mondia whitei – Two South African plants with in vitro SSRI activity

Currently available therapy for depression is often associated with undesirable side effects. Therefore, the identification of alternative therapeutics for treatment of depression is still needed. This study focused on two South African plants that are used in traditional medicine. The root of Xysmalobium undulatum (L.) R. Br. (Asclepiadaceae) is traditionally used for numerous purposes, e.g. treatment of hysteria in young women and headache relief, whereas in Germany an alcoholic-aqueous root extract (Uzara®) is marketed for treatment of diarrhoea. Mondia whitei (Asclepiadaceae) has traditionally been used as aphrodisiac, arrow poison or headache relief. Both plants showed affinity to the serotonin transport protein in rat brain in a screening of plants used for anxiety and depression [1]. In the present study (Figure 1) root extracts and aerial part extracts of X. undulatum (XuRoEa and XuApEa respectively) and the Uzara® commercial product (UzRoEt) as well as leaf extracts from M. whitei (MwLfEt) showed in vitro affinity for the SSRI binding site in rat brain in a radioligand assay. The IC₅₀ values were estimated to 3.0µg/mL; 1.2mg/mL; 0.4mg/mL and 24mg/mL for XuApEa, XuRoEa, MwLfEt and UzRoEt respectively based on dry extracts. However, a bioassay guided isolation of the Uzara® commercial product showed no fraction with specific activity.

Reference: 1. Nielsen, N.D. et al. (2003), J. Ethnopharmacol. 94: 159–163.