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University of the Witwatersrand (2007)

A phytochemical and pharmacological study of ten Commiphora species indigenous to South Africa

Paraskeva, Maria Penelope

Titre : A phytochemical and pharmacological study of ten Commiphora species indigenous to South Africa

Auteur : Paraskeva, Maria Penelope

Université de soutenance : University of the Witwatersrand

Grade : Master of Pharmacy (2007)

Résumé partiel
Commiphora species (from which myrrh is obtained) has been a source of several novel and bio-active natural compounds. Traditionally, Commiphora (Burseraceae) is used in southern Africa for the treatment of ulcers, fevers, and as a remedy for snake and scorpion bites. In western Africa, the macerated stem is used in the treatment of rheumatic conditions. The resin of some Commiphora species is applied topically to aid in wound healing. Documented uses include antibacterial and antifungal properties, as well as cytotoxic, cytostatic and anti-oxidant activity. The botanical diversity of this genus in South Africa warrants a study of this plant group, to provide scientific evidence for the traditional use of Commiphora species in African healing rites. Ten Commiphora species were investigated. Fresh plant material of the selected species were identified and collected from natural populations in the Limpopo Province. Active compounds, viz. kaempferol and dihydrokaempferol, in C. glandulosa (stem) were isolated using bioassay-guided fractionation and identified using nuclear magnetic resonance spectroscopy. The stem and leaf extracts of each species were analysed for in vitro anti-oxidant, antimicrobial, anti-inflammatory, anticancer activity, as well as cytotoxicity. The anti-oxidant activity of the extracts was investigated using the 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging assay and the 2,2’-azino-bis(3-ethyl-benzthiazoline-6-sulfonic acid) (ABTS) assays. Extracts generally exhibited poor anti-oxidant activity in the DPPH assay, with the exception of C. schimperi (stem), C. neglecta (stem), C. tenuipetiolata (stem and leaf), and C. edulis (stem), which possessed IC50 values ranging between 7.31 μg/ml and 10.81 μg/ml. Isolated compounds were subjected to the DPPH assay to determine the anti-oxidant potential of each compound, separately and in combination to establish possible synergistic, antagonistic or additive effects. The flavonol, kaempferol (IC50 = 3.32 μg/ml) showed exceptional radical scavenging activity, in contrast to the low activity displayed by dihydrokaempferol (IC50 = 301.57 μg/ml), their combination being antagonistic. Greater anti-oxidant activity was observed for most species in the ABTS assay when compared to the results obtained in the DPPH assay. The best activity was observed for the stem extracts of C. neglecta (IC50 = 7.28 μg/ml) and C. mollis (IC50 = 8.82 μg/ml). In vitro antimicrobial efficacy was determined against Gram-positive and Gram-negative bacteria as well as yeasts using the MIC microtiter plate assay. A greater selectivity was exhibited by the extracts against the Gram-positive bacteria and yeast than against the Gram-negative bacteria. Using death kinetics studies (time-kill studies), the rate at which the antimicrobial agent kills pathogens over a 24-hour period was determined. The antibacterial activity of Commiphora marlothii (stem) was observed to begin at ca. 30 min of the exposure of S. aureus to the different concentrations of plant extract.

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