Ethnopharmacology of a selection of plants used for sexually transmitted infections in Thaba ‘Nchu, Free State

Abstract

A variety of medicinal plants are used by traditional healers in Thaba ‘Nchu, Free State province, South Africa to treat sexually transmitted infections (STIs). This study evaluated the pharmacological properties of some medicinal plants identified through an ethnobotanical survey conducted through semi-structured interviews with the local traditional healers. A selection of the plants was investigated for antimicrobial, anti-inflammatory and antioxidant activities to confirm their pharmacological properties and safety. Plant extracts were prepared through liquid-solid extraction method using methanol, acetone, and distilled water. Phytochemical compounds that contribute to the pharmacological properties of plants were assessed qualitatively through standard methods and quantitatively using the Folin-Ciocalteu, the aluminium colorimetric method and Liquid Chromatography Mass Spectrometry (LCMS). Antimicrobial activities of the plant extracts were determined using the Broth microdilution method, while toxicity of the extracts was evaluated using Hoechst 33342 nuclear dye and the propidium iodide exclusion method against African green monkey kidney cell line or Vero cells, while 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay was used against the RAW 264.7 cell line. Nitric oxide (NO) assay against RAW 264.7 cell line and the 2,2-diphenyl-1-picrylhydrazyl (DPPH) method were employed to indicate the anti-inflammatory and antioxidant activities of the plant extracts, respectively. A total of 35 medicinal plant species were recorded for the treatment of STIs in the study area. Most of the medicinal plants were from Asteraceae (21%), Fabaceae (17%), Solanaceae (13%) and Hyacinthaceae (13%). Bulbine narcissifolia, Pentanisia prunelloides, Hypoxis hemerocallidea, Scabiosa columbaria, Xysmalobium undulatum, Rumex lanceolatus, Eucomis autumnalis, Dicoma anomala and Salvia runcinata were the most favoured plants. The most preferred method for preparation of remedies were decoctions made from the roots. Hermannia depressa, Berkheya onopordifolia, S. runcinata and S. runcinata were selected for further studies because of high frequency of mention and availability in the study area. Phenols, flavonoids, tannins, saponins, alkaloids, steroids and glycosides were detected qualitatively across all the plant extracts. H. depressa acetone and S. columbaria aqueous extracts had the highest Total Phenolic Content at, 8.45±0.006 and 7.65±0.004 mg GAE/g respectively. Methanol and acetone extracts of S. columbaria were found to have the highest Total Flavonoid Content at 3.56±0.01 and 2.29±0.03 mg quercetin equivalents QE/g respectively. Pharmacologically important compounds such as Skimmin, 14-Methylmonocrotaline-like, 3’,4’-Dimethoxyluteolin, Isosakuranetin, Carsonic acid, Jaceosidin, Waltherione C, Methoxyestradiol, and many other compounds were detected in some extracts. The compounds have antibacterial, anti-inflammatory, antioxidant, hepatoprotective and many other properties which may explain their use in the treatment of STIs. The aqueous extracts of the plants used in the study and the methanol extract of S. columbaria were not toxic. However, the acetone and methanol extracts of all four plants were toxic. S. runcinata methanol and acetone extracts showed toxicity by affecting 50% of Vero cells at a lower CTC50 of 3.93 μg/ml and 3.96 μg/ml. Acetone extracts of S. columbaria had a lower CTC50 of 6.09 μg/ml, while H. depressa methanol and acetone extracts affected Vero cells at a lower CTC50 of 4.97μg/ml and 4.65 μg/ml respectively. The cytotoxicity could be attributed to the presence of toxic compounds such as alkaloids, tannins, and glycosides (Canadine, Xanthoxylin, Rosmarinic acid Matairesinol, Salvigenin). All methanol and acetone extracts showed significant antimicrobial activity against almost all microbial species used against in the study at concentrations ranging from 0.1 to 1.25 mg/ml. The antimicrobial activity of S. runcinata acetone extracts against colistin antibiotic resistant Escherichia coli at MIC 1.25 mg/ml is important to highlight. H. depressa acetone, S. columbaria methanol and S. runcinata methanol extracts showed strong anti-inflammatory activity by inhibiting the release of Nitric oxide by 60%. H. depressa aqueous (IC50=9.081 μg/ml), methanol (5.197 μg/ml) and acetone (3.576 μg/ml) and B. onopordifolia acetone (9.834 μg/ml) extracts showed the strongest antioxidant activity when compared to Ascorbic acid (5.69 μg/ml) and Trolox (6.166 μg/ml). The antimicrobial, anti-inflammatory and antioxidant activity of the medicinal plants selected for this study validates their use for the treatment of STIs and related oxidative stress and inflammatory conditions. These plants may serve as a source for development of novel antimicrobial, anti-inflammatory and antioxidant agents.