SCREENING OF TRADITIONAL MEDICINAL PLANTS FROM ZIMBABWE FOR PHYTOCHEMISTRY, ANTIOXIDANT, ANTIMICROBIAL, ANTIVIRAL AND TOXICOLOGICAL ACTIVITIES
VIOL, DENIZ IKLIM
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Fourteen indigenous medicinal plants used by traditional medical practitioners in treating sexually transmitted diseases including HIV/AIDS and opportunistic infections were selected after an ethno-botanical pilot survey of five districts from Zimbabwe. The plant materials were collected and extracted separately with methanol. The 28 extracts were lyophilized and screened for phytochemical groups, and biological: antioxidant, antiviral, antibacterial, antifungal and toxicological activities. The phytochemical screening was carried out using Thin Layer Chromatography and UV detection, followed by standard confirmatory tests. The results indicated that seven (25.9%) extracts were positive for alkaloids, ten (35.7%) for anthraquinones, thirteen (46.4%) for coumarins, seventeen (60.7%) for flavonoids, twenty-three (82.1%) for saponins and twenty-five (89.3%) for tannins. Flavonoids, saponins and tannins were the most frequent phytochemical groups found. All extracts contained at least three of the chemical groups. In order to determine the antioxidant activity, the plants were screened for Radical Scavenging Activity using DPPH (2,2-diphenyl-picrylhydrazyl) with β-carotene as reference and their Total Phenolic Contents were measured by the Folin-Ciocalteu reagent using gallic acid as reference. Eight extracts exhibited antioxidant activity with percentages higher than 90% (Rhus chirindensis leaves & roots-both 96.9%; Khaya anthotheca bark-96.1%) and the lowest result was 27.4% for Dichrostachys cinerea roots. Their TPCs ranged from 0.596mg/mg GAE for Khaya anthotheca bark to 0.105mg/mg GAE for Dichrostachys cinerea roots. The phenolic compounds in the extracts correlate with their antiradical activity (r2=0.57), confirming that the phenolics are likely to cause the radical scavenging activity. The antiviral activity was examined using End Point Titration Technique (EPTT) and Neutralisation Test (NT) after calculating the cytotoxicity of the plant extracts on VERO cells. The HSV-2 virus titre was calculated using the Reed and Muench method (TCID50 = 10-8.5 per 0.1ml). The reduction factor (RF) was calculated and it was considered a promising antiviral result if the RF was ≥ 103. Out of 26 extracts, 13 (50%) showed considerable antiviral activity against the HSV-2 virus. The best results were obtained from the extracts of Dichrostachys cinerea leaves (RF 104), Kigelia africana fruit (RF 104) and Hypoxis rooperi tuber (RF 103) with concentrations ranging from 10.41μg/ml (Dichrostachys cinerea leaves) to 125.0μg/ml (Flacourtia indica roots). The reference acyclovir was active at 1.50μg/ml. Their cytotoxicity could also be beneficiary in developing new anti-tumour drugs. The antibacterial and antifungal activities of the plant extracts (10mg/ml) were investigated by the agar well assay. The chosen microorganisms were Staphylococcus aureus, Streptococcus group A, Escherichia coli, Pseudomonas aeruginosa, Candida albicans, and Aspergillus niger. The best results were Terminalia sericea roots, Warburgia salutaris roots, Gymnosporia senegalensis roots and Kigelia africana bark which were active against all micro-organisms. T. sericea roots inhibited the growth of S. aureus with inhibition zone of 7.88±0.48mm where the reference amoxicillin (10μg) gave a zone of 9.00±0.41mm and against P. aeruginosa, gave a larger zone of inhibition, 10.00±0.82mm, than the reference gentamicin (10μg), 7.00±0.40mm. W. salutaris roots were active against both fungal strains with inhibition zones of 10.00±0.82mm for C. albicans and 8.25±0.50mm for A. niger which were even bigger than the zones of the reference amphotericin B (10μg) 6.35±0.50mm and 6.75±0.58mm respectively. The toxicity tests were conducted using the Brine Shrimp (Artemia salina) Lethality Test (BSLT). Five of the extracts showed significant toxicity levels of LC50< 300μg/ml. The lowest readings of LC50, Terminalia sericea leaves (66.7ppm) and Kigelia africana fruit (117.4ppm) were even lower than the positive control, Nerium oleander leaves (141.7ppm) which is a plant with well-established anti-tumour activity. These results confirm the ethno-botanical claims by traditional medical practitioners treating viral, bacterial and fungal infections caused by HIV/AIDS, cancer and cardiovascular diseases with traditional medicinal plants due to the rich phytochemistry, their high levels of antioxidant activity as well as bioactivity of the plants. They should be preserved and harvested with caution not only because of their medicinal value but also the role they play in the rich African heritage.