Cytotoxic, anti-inflammatory, antibacterial and anti-HIV effects of tabernaemontana elegans leaves and fractions

Abstract

Background: Plant-derived natural products continue to serve as a reservoir for the discovery of new medicines. In South Africa, the use of plants to treat many diseases is widely practiced. This is due to high cost of conventional drugs, cultural beliefs and assumed safety. Tabernaemontana elegans is a medicinal plant which is traditionally used for the treatment of a wide variety of ailments such as pulmonary diseases, chest pains, heart diseases, cancer, sexually transmitted infections and applied as a wash to wounds. However, there is not enough literature concerning the chemical constituents responsible for its ethnomedicinal properties. There have been no reports about the antimicrobial activity of the plant on selected opportunistic bacteria nor any reported anti-HIV and anti-inflammatory effects of T. elegans leaf fractions as far as literature is concerned. Objective: The aim of the study was to determine the antimicrobial activity against opportunistic bacteria, the anti-HIV-1 reverse transcriptase effect, anti-inflammatory activity and cytotoxicity of T. elegans. Methods: T. elegans leaves were collected, dried and ground into powder using a miller. Three solvents (hexane, dichloromethane and methanol) were used to successively extract compounds of different polarities. Column chromatography was used to isolated compounds from the dichloromethane and methanol extracts. Qualitative phytochemical and antioxidant (DPPH) screening was carried out on the extracts and fractions obtained. Antibacterial activity of the crude extracts and fractions was evaluated against Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus and Streptococcus pyogenes using the Microdilution assay. The anti-HIV-1 RT activity was measured using a commercial ELISA kit. The crude extracts and fractions were assessed for anti-inflammatory potential by detection of nitric oxide (NO) production on stimulated macrophage cells and cytotoxicity of the plant was assessed on Vero cells as well as on HeLa cancer cells using the dual staining microscopy assay. Results: Seven fractions were obtained from dichloromethane (DCM), C2 and methanol (MeOH), C3 crude extracts. Four fractions (FD1, FD2, FD3 & FD4) and 3 fractions (FM1, FM2 & FM3) resulted from DCM and MeOH crude extracts respectively. Phytochemical analysis revealed the presence of saponins, flavonoids, terpenoids and steroids. The crude extracts and all fractions displayed a free radical scavenging activity, wherein FM3 showed a profound free radical activity. For antibacterial activity, the lowest MIC noted was 0. 625 mg/mL from the crude extracts and fractions against S. aureus, S. pyogenes, E. coli and P. aeruginosa. Among all the strains, S. pyogenes was the most susceptible. Moreover, FD4 was the most active for antibacterial activity. FD3 showed strong anti-inflammatory potential, since it had the lowest NO reduction with the cell viability > 66%. FD4 showed strong antiinflammatory activity with severe cytotoxicity at 50, 100 and 200 μg/mL. All extracts and fractions displayed anti-HIV-1 RT activity. FD1 exhibited a potent anticancer activity with less or no harm to Vero cells, whereas FD3, FD4, FM2, C2 and C3 were found to be toxic to both non-cancerous Vero cells and cancerous HeLa cells. Conclusion: Our findings provide evidence that extracts and fractions from T. elegans leaves displayed antioxidant, antibacterial anti-inflammatory and anti-HIV-1 activities. Findings from this study further validates the traditional use of T. elegans leaf for the treatment of a wide range of diseases.