Immunomodulatory effects of some Namibian plants traditionally used for treating inflammatory diseases

Abstract

Ethnopharmacological relevance: Acanthosicyos naudininus, Gomphocarpus fruticosus, and Cryptolepis decidua are, according to the knowledge of traditional healers, used in Namibia to treat inflammatory disorders such as pain, fever and skin rashes.

Aim of the study: The present study was conducted to evaluate the immunomodulatory effects and the possible underlying mechanisms of action of the plant extracts on peripheral blood mononuclear cells (PBMCs) such as T-lymphocytes.

Materials and methods: Methanolic and EtOAc extracts of A. naudinianus, G. fruticosus and C. decidua were analysed for their immunomodulatory potential. PBMCs were isolated from the blood of healthy donors and incubated with the plant extracts at concentrations 100, 30, 10, 3, 1 and 0.3 μg/mL. Effects on proliferation and viability of activated human lymphocytes were assessed in comparison to ciclosporin A by flow cytometry using carboxyfluorescein succinimidyl ester (CFSE) and WST-1 assay. Flow cytometry by annexin V/propidium iodide (PI) staining was performed to investigate the necrotic/apoptotic effect of the plant extracts on mitogen-activated human lymphocytes. In addition, analysis of the influence of plant extracts on the regulatory mechanisms of T-lymphocytes was performed using activation marker and cytokine production assays. An HPLC-PDA-ELSD-ESIMS profile was recorded for each of the extracts.

Results: T-lymphocyte proliferation was inhibited in a dose-dependent manner by the extracts of A. naudinianus, G. fruticosus, and C. decidua in concentrations not causing apoptosis or necrosis. This effect was mediated by inhibition of lymphocyte activation, specifically the suppression of CD25 and CD69 surface receptor expression. Moreover, the extracts suppressed effector functions, as indicated by reduced production of IFN-γ and IL-2. Based on the HPLC profile, possible responsible compound classes could be identified for the extracts of A. naudinianus (cucurbitacins) and C. decidua (indole alkaloids), but not for G. fruticosus.

Conclusions: The data show that the extracts of A. naudinianus, G. fruticosus and C. decidua have in vitro immunomodulatory activity and they interfere with the function of immunocompetent cells, suggesting an anti-inflammatory mode-of-action. The present chemical determination and pattern recognition results explain the therapeutic potency. However, further studies to investigate the therapeutic potential of the plants in inflammatory disorders should be done.

Keywords: Acanthosicyos naudinianus; Cryptolepis decidua; Gomphocarpus fruticosus; Immunomodulatory; Inflammation; Lymphocytes; Namibia; Traditional medicine.