Evaluation of indigenous medicinal plants with potential antidepressant effects

MSc (Biology), North-West University, Mahikeng Campus

Major depressive disorder (MDD) is a common mental health condition that represents one of the foremost causes of disease burden worldwide, including in South Africa. The search for safe and potent natural-based treatment for depression is receiving renewed interest given the numerous side-effects associated with existing antidepressant drugs. In South Africa, the use of plants to manage depression is fairly documented among different ethnic groups. The aim of this study was to review South African medicinal plants used traditionally to manage depression-like ailments, to estimate the total phenolic content and evaluate the in vitro antidepressant-like effects of these plants. A literature review of existing ethnobotanical, ethnopharmacological and phytochemical studies was conducted from which Artemisia afra Jacq. ex Willd., Adenia gummifera (Harv.) Harms and Olea woodiana Knobl. were selected for evaluation. The plant materials were extracted using three solvents of increasing polarities (hexane, acetone and water) to evaluate the effects of solvent polarity on extraction yield, total phenolic content and biological activity. The total phenolic content of 12 extracts was estimated using the Folin-Ciocalteu’s method. Thereafter, the antidepressant potential of each extract was evaluated using the serotonin transporter (SERT) and the adenosine A1R & A2AR radioligand binding assays. The systematic review of twenty eligible ethnobotanical publications identified 186 indigenous South African plants from 63 families used traditionally to manage depression and related ailments. Only 27 of these plants were previously screened for antidepressant activity using various in vitro and in vivo tests. Phytochemical investigation on 9 plants revealed 24 compounds with antidepressant-like effects. A significant portion (≈85%) of the 186 plants with ethnobotanical records still requires pharmacological studies to assess their potential antidepressant-like effects. In this study, water and acetone extracts exhibited a higher phenolic content than the hexane extracts, suggesting that total phenolic content levels increased significantly with increasing polarity of the solvents. The acetone extract from A. afra leaf exhibited significant affinity to the adenosine A1 receptor, indicating the potential antidepressant-like effects of this plant, however, this needs to be confirmed in an animal model of depression. None of the other extracts showed any significant affinity in any of the assays conducted. This study serves as an essential step towards the authentication of the antidepressant-like effects of indigenous medicinal plants and their phytochemicals.

Masters