Anticancer, antioxidant and antimicrobial screening of extracts from selected medicinal plants from Oshikoto, Namibia

Abstract

Abstract. Ilonga SK, Kandawa-Schulz M, El-Sayed Lofty H, Lyantagaye S. 2018. Anticancer, antioxidant and antimicrobial screening of extracts from selected medicinal plants from Oshikoto, Namibia. Bioteknologi 15: 55-69. Plants have been explored for years to treat ailments such as headaches, stomach-ache, diarrhea, tumors, wounds, and sexually transmitted diseases. Heliotropium ciliatum, Ziziphus mucronata, and Gnidia polycephala are traditionally utilized to treat tumors and wound-related illnesses. Tumors and persistent wounds can be an indication of cancer. Microbial wound infections can lead to fatal consequences, if unattended. This study evaluates the anticancer, antioxidant, and antimicrobial potential of extracts of these three medicinal plants. The leaves (Z. mucronata) and the aerial parts (G. polycephala and H. ciliatum) were ground and subsequently extracted with hexane, dichloromethane, ethanol and methanol, and water. The Brine shrimp lethality test (BST), 3- (4,5-dimethylthiazol-2-yl)-2,5- diphenyltetrazolium bromine (MTT) assay and APOPercentage^TM flow cytometry assay were employed to evaluate the anticancer potential of the extracts, whereas the antioxidant activity was evaluated by 1,1-diphenyl-picrylhydrazyl (DPPH) assay evaluated. The antimicrobial potential of the plant extracts was evaluated using the broth microdilution method against eight wound pathogens: Escherichia coli, Candida albicans, Clostridium tetani, Methicillin-resistant Staphylococcus aureus, Mycobacterium terrae, Pseudomonas aeruginosa, Staphylococcus epidermidis and Streptococcus A. Methanol extracts of Z. mucronata and G. polycephala showed good antioxidant activity, compared to that of butylated hydroxyl toluene which served as control. High cytotoxicity is shown by dichloromethane and hexane extracts of Z. mucronata and H. ciliatum, as well as ethanol extracts of H. ciliatum, with LC50 values < 250 µg/mL. Meanwhile, water extracts showed the least cytotoxic activity. Dichloromethane extract of Z. mucronata also demonstrated a broad spectrum of antimicrobial activity, achieving MIC values ? 1 mg/mL against six out of eight tested microbes. The low toxicity of aqueous extracts of the three plants and the antimicrobial activity observed validates the use of these extracts in conventional medicine. Some extracts appear to be good sources of potential antioxidant and anticancer agents. However, further studies need to be conducted the isolation of potentially valuable drugs from these extracts.