Inhibition of nitric oxide production and free radical scavenging activities of four South African medicinal plants

Abstract

Introduction

Traditional healing is often the preferred form of therapy especially in rural and resource-limited communities. The extracts of plants are used to treat many diseases such as arthritis and chronic pain. Four medicinal plant species, namely, Acokanthera oppositifolia, Plantago lanceolata, Conyza canadensis and Artemisia vulgaris used in Southern Africa to treat pain and inflammation-related diseases were selected for evaluation in laboratory-based experiments.

Methods

The selected plant species were evaluated for phytochemical content, antioxidant and anti-inflammatory activities, as well as cytotoxicity effects against mammalian cells in culture.

Results

The results indicated that the n-hexane and chloroform extracts of P. lanceolata had the best antioxidant activities with an IC₅₀=0.41 μg/mL. Also, the acetone extracts of P. lanceolata had 93.76% nitric oxide (NO) inhibition. However, the chloroform and n-hexane extracts of C. canadensis produced NO inhibition of 98.53% and 99.2%, respectively, at 100 μg/mL with IC₅₀=17.69 μg/mL. Furthermore, the ethyl acetate extracts also had promising NO inhibitory activity (96.33%), but the cytotoxicity results with cell viabilities of 5.31%, 5.7% and 5.89%, respectively, suggested that the observed activity was due to a cytotoxic effect. Acetone extracts of C. canadensis were also cytotoxic at 30 µg/mL with 6.07–6.67% cell viabilities compared with the acetone extracts of P. lanceolata (99.57%).

Conclusion

The results partially validate the ethnomedicinal uses of the selected plant species used for inflammation-related conditions. However, because some of the extracts had potential cytotoxic effects, caution is advised in their use, especially those consumed orally.

Keywords:

• nitric oxide
• free radicals
• medicinal plants
• South Africa
• inflammation

Acknowledgments

The authors wish to thank Mr. Jason Sampson, the curator for Manie van der Schiff Botanical Gardens, University of Pretoria, for plant collection and identification. This work was carried out at the Department of Biomedical Sciences of the Tshwane University of Technology, Arcadia, and the Department of Paraclinical Sciences, Phytomedicine Programme of the University of Pretoria, Ondersterpoort, by SAA and MO. MO received postgraduate study funding from the University of South Africa (UNISA). LJS is a recipient of a National Research Foundation-incentive grant (103360).

Availability of data and material

The sources of all the data presented in this manuscript are readily available and can be provided upon official request to the corresponding author.

Author contributions

All authors contributed towards data analysis, drafting and critically revising the paper, gave final approval of the version to be published, and agreed to be accountable for all aspects of the work.

Disclosure

The authors report no conflicts of interest in this work.