Evaluation Of Selected Namibian Ethno-Medicinal Plants For Anti-HIV Properties

ABSTRACT

Namibian ethno-medicinal plants have not yet been evaluated for their efficacy in inhibiting the activities of Human Immunodeficiency Virus (HIV) reverse transcriptase (RT) and their toxicological effects to mammalian cells have not yet been reported. Hence the aims of this study were: (1) to evaluate selected Namibian plants for their biological activities against RT; (2) to evaluate their toxicity to mammalian cells, and (3) to isolate and characterize the active compounds from selected plant extracts. Colorimetric assays were used to evaluate RT inhibition and cell viability. Absorbance for RT inhibition assay was read at 405 nm and that of cytotoxicity at 492 nm with a plate reader using standard procedures. Non-linear regression sigmoidal curves were used to determine the inhibitory concentration required to reduce the activity of RT by 50% (IC50) and cytotoxicity concentration required to reduce the viability of cell by 50% (CC50) for each sample. Purification of extracts was done with thin layer chromatography (TLC) and structural elucidation was done with Nuclear Magnetic Resonance (NMR). The study found 40 crude extracts (from 15 plants) to have concentration-dependent inhibitory activities against RT. Most of the samples had very low toxicity to Vero cells (with 31 out out of 40 extracts having viability above 50% at the highest tested concentration. Variable inhibitory activity on RT were observed with fractions extracted with different solvents. Ethyl Acetate fractions had the best RT inhibitory activities when compared to other solvents. Six compounds were isolated and three of the structures were fully elucidated. D-Pinitol (a carbohydrate) was isolated from Diospyros mespliformis leaves. This is the first reported isolation of D-Pinitol from this plant species. A novel compound, 2α,3β,19α,23-Tetrahydroxyolean-1-en-28β-Dglycopyranoside (a triterpenoid glycoside), was isolated from Terminalia prunioides roots, and was obtained in acetylated and non-acetylated forms. This is the first study to isolate and/or elucidate the structures of compounds active against HIV RT from Namibian ethno-medicinal plants