Anti-HIV activities of organic and aqueous extracts of Sutherlandia frutescens and Lobostemon trigonus

A screening process was applied to extracts made from Sutherlandia frutescens (L.) R. Br (Fabaceae) and Lobostemon trigonus (Boraginaceae) as identified by the Botany Department, University of Port Elizabeth to detect if any of the extracts inhibited the human immunodeficiency virus (HIV). For purposes of dereplication, sulphated polysaccharides were removed and bovine serum albumin (BSA) was included in the assays to adsorb non-specific tannins potentially present. In the reverse transcriptase (RT) assay, an aqueous extract of the Lobostemon leaves inhibited HIV-1 RT with an IC50 value of 49 μg/ml, while in the protease assay no inhibition was seen. In the α- and β-glucosidase assays, no significant inhibition was seen with the inclusion of BSA, indicating tannin-based inhibitory effects on these two enzymes. The β-glucuronidase inhibitory activity, however, was retained in the presence of BSA. The study shows that Sutherlandia extracts contain inhibitory compounds active against HIV target enzymes, while aqueous Lobostemon leaf extracts contain a potent HIV-1 RT inhibitor, thus showing a potential mechanistic action of these plants in aiding HIV-positive patients.