The undeniable efficacy of medicinal plants and wide range of biological activities attributed to plant secondary metabolites are an indication that plants can serve as an excellent pool of bioactive compounds with useful therapeutic properties. The South African flora is recognised as one of the richest centres of plant diversity in the world. From this enormous biodiversity a large number of species has the potential to yield pharmacologically active compounds. C. album is an indigenous plant belonging to the Cape fynbos biome with potentially useful bioactivities. The aim of this study was to evaluate the bioactivity of C. album by screening plant extracts for antibacterial, anti-mycobacterial, antifungal, antioxidant and anti-HIV activity. For rapid and effective screening for the presence of bioactive compounds, a bioassay-guided fractionation methodology was followed. Extracts from plant material obtained from two different geographic regions, the Cape and Highveld, were prepared by liquid extraction in a ratio of 150g fresh plant material per litre solvent, either acetone or ethanol. Qualitative analysis of the crude extracts by TLC and RP-HPLC documented the multi-component plant constituents as a fingerprint, revealing a highly complex, but similar profile of extracted components in both plant groups. Preliminary identification and structural information of the bioactive components present in the active C. album extracts was obtained by a combination of preparative TLC and LC/MS. The development of resistance to all available classes of antibiotic agents, their decreased effectiveness and the re-emergence of previously uncommon infections has necessitated the search for antimicrobial substances with novel antimicrobial mechanisms. The antimicrobial activity, including the antibacterial (Gram-positive and Gram-negative), anti-mycobacterial and antifungal activity of the crude extracts were evaluated. The TLC-bioautographic method used to screen the plant extracts for antimicrobial activity, as well as the localisation of compounds with antibacterial and antifungal activity, indicated the presence of a number of inhibitory compounds with activity against all the microorganisms tested. Evaluation of the inhibitory strength of each extract by the serial microdilution assay indicated that the C. album extracts effectively inhibited all the microorganisms, with the minimum inhibitory concentrations in the low mg/ml range. The significant antimicrobial activity exhibited against all the microorganisms, especially against the Gram-negative bacteria, Mycobacterium tuberculosis and Candida albicans, could suggest the potential use of the extracts or their active constituents as therapeutic agents for the treatment of infectious diseases. The need for natural antioxidants in the health care sector and food industry, due to the role that free radicals play in the pathology of a variety of human diseases and radical-induced deterioration of food products, supported the evaluation of the free radical scavenging activity of C. album extracts against relevant free radical species. The antioxidant activity of the extracts measured using the TLC-DPPH method, revealed the presence of a number of compounds with antioxidant activity. Quantification of the radical scavenging activity by the DPPHspectrophotometric assay revealed that the acetone extracts had a higher radical scavenging activity compared to the ethanol extracts, a pattern that was also found with the fluorescencemicroplate based oxygen radical absorbance assay (ORAC), specific for peroxyl radicals. The observed antioxidant activity were correlated with the total polyphenol content of the crude extracts, determined by the Folin-Ciocalteau procedure, but not with the reducing capacity evaluated by a Fe3 + - Fe2 + reduction method. HIV/AIDS has gained significant interest due to the high mortality rate and the rapid spread of the disease. The appearance of HIV strains resistant to certain antiretroviral drugs, in addition to the high cost, severe metabolic side effects and therapeutic failure of currently available antiretroviral agents, served as motivation for evaluation of C. album for anti-HIV properties and to evaluate potential cytotoxicity of plant extracts in mammalian cell cultures. The effects of the crude extracts on the in vitro HIV-1 subtype C (the predominant HIV-1 form in South Africa) replication and cytopathic effect on CEMnkrCCR5 lymphoid cells were determined. Viability assays using tetrazolium salts and viability dyes allowed the assessment of the host cell responses in the cytotoxicity and anti-HIV screening. Assays were performed at the maximum non-toxic concentration of 50 μg/ml. Some of the plant extracts exhibited significant reduction of the virusinduced cytopathic effect and induced a significant increase in cellular viability. The effect of the extracts on HIV activity was also investigated by determining the viral p24 core protein level, an indication of the replication fitness of the virus; and a significant decrease in p24 antigen level, was found. An attempt to clarify the main active compounds and the structural elements conferring the bioactivity in the analysed systems, revealed the presence of phenolic compounds, primarily coumarins and flavonoids, which are thought to be responsible for the observed antibacterial and antioxidant activities. The results of this study indicate that C. album possess strong bioactivity that warrants further investigation. / Prof. I.A. Dubery Dr. D. Meyer
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:uj/uj:2633 |
| Date | 12 June 2008 |
| Creators | Liebenberg, Lindy |
| Source Sets | South African National ETD Portal |
| Detected Language | English |
| Type | Thesis |
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