Geographic-based metabolomic variation and toxicity analysis of Sutherlandia frutescens L. R.Br. – An emerging medicinal crop in South Africa

Abstract Sutherlandia frutescens (syn. Lessertia frutescens), an indigenous southern African species, is important for the local and global phytomedicine's industry. As farming of medicinal plants in South Africa is not extensive, wild populations are also used as a source of material to bulk available cultivated yields prior to industrial processing. This may cause inconsistency in the quality of medicinal products derived from this species, inducing discrepancies in the plant’s therapeutic profile. The current study aimed to elucidate the phytochemical variations among S. frutescens plants growing in different geographical localities, especially in areas which have not been studied before. One set of extracts were generated using a 50% acetonitrile and formic acid solution (0.1%) (v/v). By using a targeted metabolomics approach, two major phytochemical groups, sutherlandins and sutherlandiosides were used to display metabolite-based clusters after LC–MS/MS analysis. Plants from different geographical locations grouped into separate chemical lineages. Another set of ethanol and aqueous extracts of pooled leaf materials were screened for their toxicity effect on the hatching rate of zebrafish embryos and mortality of larvae at different concentrations, ranging from 5 to 300 μg ml−1. We also calculated the LC50 values using a zebrafish microplate bioassay and this value was 297.57 μg ml−1 for the water extract. The aqueous extracts were relatively less toxic compared to ethanol extracts (LC50 value of 40.54 μg ml−1). Both the hatching rate and mortality were negatively affected by increasing extract dosages. The highest concentrations, between 200 to 300 μg ml−1, caused acute lethal effects for both extract types. This study adds additional evidence of the cytotoxicity reported by others in this species and will further aid in the domestication of S. frutescens.