Immunomodulatory and cytotoxicity properties of selected southern African medicinal plants traditionally used to treat pain and inflammation

Abstract

The use of medicinal plants to treat inflammatory and auto-immune disorders is a common practice in southern African. However, the mechanisms of action related to the traditional use of herbal remedies as immunomodulatory agents remain relatively unknown. This study aims to investigate the cytotoxic and immunomodulatory properties of important southern African medicinal plants used traditionally to treat inflammation and pain. Cytokine multiplex-bead assays were used to evaluate the anti-inflammatory effects of seventeen medicinal plants against interleukin-2 (IL-2) and interleukin-10 (IL-10) activity. The assay was conducted using lipopolysaccharide (LPS)-stimulated and unstimulated murine RAW 264.7 macrophage cells treated with aqueous and ethanol extracts. The MTS assay was used to determine the percentage cell viability and 50% cytotoxic concentration (IC50) in RAW 264.7 and human dermal fibroblast (HDF) cell lines. The aqueous extracts showed minimal cytotoxicity at the highest concentration screened (5mg/mL). Unstimulated RAW 264.7 cells treated with the plant extracts exhibited immunomodulatory effects by significantly up-regulating the production of an anti-inflammatory cytokine IL-10 compared to the LPS-stimulated extracts. The aqueous bark extract of Erythrina lysistemon Hutch., as well as the leaves of Warburgia salutaris (G. Bertol.) Chiov., and Zantedeschia albomaculata (Hook.) Baill showed the greatest stimulation of IL-10 and IL-2 production in RAW 264.7 cells. Of note, E. lysistemon showed exceptional results by regulation the levels of IL-10 up to 7000-fold increase compared to the negative LPS unstimulated control. This study provides insights to the possible mechanisms involved in the use of southern African medicinal plants as immunomodulatory agents.