Aim of the study: The in vitro phytochemical and pharmacological investigation of the non-volatile extracts of five South African Vitex species (Verbenaceae); V. obovata ssp. obovata, V. obovata ssp. wilmsii, V. pooara, V. rehmannii and V. zeyheri were investigated in order to validate their traditional use to treat a wide range of ailments such as malaria, wounds, skin diseases and body pains.
Material and methods: The antimicrobial activity was assessed using the minimum inhibitory concentration assay. Through bioactivity-guided fractionation, the fraction responsible for the antimicrobial activity was determined. The toxicity profile, anti-oxidant and anti-inflammatory activity was evaluated using the tetrazolium cellular viability, 2,2-diphenyl-1-picrylhydrazyl and 5-lipoxygenase assays respectively. The antimalarial activity of the extracts and isolated compound from V. rehmannii was also investigated on the chloroquine-resistant Gambian FCR-3 strain of Plasmodium falciparum using the tritiated hypoxanthine incorporation assay.
Results: Mostly good antimicrobial inhibition was evident against Gram-positive bacteria (0.02-8.00 mg/ml) and lower activity against the Gram-negative bacteria and the yeast (0.50-8.00 mg/ml). The fraction responsible for antimicrobial activity of V. rehmannii was purified to give a labdane diterpene as an inseparable epimeric mixture of 12S,16S/R-dihydroxy-ent-labda-7,13-dien-15,16-olide. Cirsimaritin was also isolated and identified from V. rehmannii. All the species, apart from V. zeyheri, exhibited scavenging activity (IC50: 22.14+/-1.74 to 33.06+/-1.68 microg/ml) in the anti-oxidant assay. None of the species displayed any anti-inflammatory activity at 100 microg/ml. All the extracts and the labdane diterpene exhibited good antimalarial activity, with the labdane diterpene being the most active (IC50: 2.39+/-0.64 microg/ml). The test extracts were shown to be highly toxic, displaying safety index values ranging from 0.53 to 2.59.
Conclusion: Of all the pharmacological investigations, the antimalarial and antimicrobial activity exhibited greatest activity and may provide a scientific basis for the ethnomedical use of Vitex species.