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Doctoral Degrees (Physiology)

Permanent URI for this collectionhttps://hdl.handle.net/10413/7045

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Browsing Doctoral Degrees (Physiology) by Subject "Antioxidant."

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    The cytotoxic effects, anti-iflammatory, antioxidant, antibacterial, and antidiabetic properties of eight selected South African plants for medicinal purposes.
    (2020) Nkala, Bongani Alphouse.; Mbongwa, Hlengiwe Prosperity.; Qwebani-Ogunleye, Tozama.
    People from the Southern African region have been using the fauna and flora of the region in their homes for millennia to treat all sorts of ailments and complaints with great success. This knowledge transfer was done through ’apprenticeships’ and oral communication. Certain communities consider medicinal plants to be safer than drugs and that they can treat more than one ailment. This study investigated cytotoxic effect, antimicrobial, anti-inflammatory, antioxidant, and antidiabetic properties of eight selected South African plants for medicinal purposes. Plant species were collected from the Walter Sisulu National Botanical-Gardens and were extracted with 90% methanol (1 g/10 ml) and concentrate to 10 mg/ml. Antimicrobial activities were determined by the microplate dilution method to establish the ability of the plant extracts to inhibit or kill pathogenic organisms with minimal inhibitory concentrations and minimum bactericidal concentration. Cytotoxicity effects were determined with Alamar blue and crystal violet cell viability assays, against C2C12 and RAW 264.7 cells. Anti-inflammatory effects were identified with stimulated lipopolysaccharide RAW 264.7 cells, and nitric oxide inhibition was measured with Griess reagent assay. The estimation of preliminary phytochemical, antioxidant (DPPH and ABTS radical scavenging), and alpha-amylase inhibition were determined with standard methods. The plant extracts inhibition and bactericidal effects were observed against all bacteria, namely: Lippia javanica (0.25±0.00 to 1.13±0.29 mg/ml); Ziziphus mucronata leaf (0.44±0.00 to 1.00±0.00 mg/ml); Erythrina lysistemon (0.44±0.00 to 1.08±0.00 mg/ml) and Schkuhria pinnata (0.5±0.00 to 1.34±0.00 mg/ml). All plant extracts exhibited flavonoids, phenols, terpenoids, and coumarins. The antioxidant inhibition was observed above 80% for Schkuhria pinnata, Lippia javanica, Clerodendrum myricoides, and Erythrina lysistemon. Also, these plant species exhibited an alpha-amylase inhibitory effect of 80%. The IC50 values were > 1000 μg/ml. All plant extracts demonstrated some degree of an antiinflammatory effect. However, Clerondendrum myricoides (35% - 89%), Lippia javanica (26% - 77%), Erythrina lysistemon (23% - 76%), Schkuhria pinnata (27% - 65%), and Vernonia oligocephala (16% - 58%) with IC50 value >1000 μg/ml, exhibited a marked antiinflammatory effect. Therefore, the presence of phenolic, flavonoids, anti-inflammatory, antioxidants, and α-amylase properties are potential solutions towards the management of diabetes and other chronic inflammatory diseases. Keywords: medicinal plants, antimicrobial, cytotoxicity, anti-inflammatory, antidiabetic, antioxidant.
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    Fungal endophytes: isolation, identification and assessment of bioactive potential of their natural products.
    (2017) Sibanda, Edson Panganayi.; Mduluza, Takafira.; Mabandla, Musa Vuyisile.
    Fungal endophytes produce a broad variety of bioactive compounds with potential to address some of the unmet human needs. Medicinal plants have an important role to play in the search for new strains of endophytes fungi, as it is possible that their beneficial characteristics are as a result of the metabolites produced by their endophytic community. However, inspite of this potential as repositories of bioactive compounds, the fungal endophytes of African medicinal plants remain largely underexplored. This thesis reports on studies that were conducted to bioprospect for endophytic fungi with antioxidant and antimicrobial activity hosted by the plants Warburgia salutaris, Annona senegalensis, Kigelia africana and Vitex payos used in Zimbabwean traditional medicine. The surface sterilization technique was used to isolate the endophytic fungi that were identified by ribosomal DNA sequencing of the nuclear ribosomal internal transcribed spacer region. Crude extracts obtained from the fermentation of the isolated endophytic fungi were screened for antimicrobial activity using the agar diffusion method and evaluated for total antioxidant activity using a commercial kit that used the single electron transfer mechanism. Fourier-transform infrared spectroscopy (FT-IR) and Gas Chromatography – Mass Spectrometry (GC-MS) were used to provide a snapshot of the metabolites present in the endophyte fungi extracts. A total of 33 endophytic fungi were isolated from the medicinal plants and the fungal endophyte colonisation rates varied by plant species and plant tissue. The isolated fungi across the different plant species and tissue types were found to be dominated by members of the phylum Ascomycota. The endophytic fungi Penicillium chloroleucon was isolated from all the plant species except for Cladosporium uredinicola and Myrothecium gramineum (both isolated from Kigelia africana) which had an inhibitory effect against Escherichia coli (ATCC1056). Whilst Epicoccum sorghinum isolated from Annona senegalensis exhibited the most potent antioxidant activity, a significant number of the screened endophytic fungi from the different plant species were also found to have some antioxidant activity. The total phenolic content was found to have a positive correlational relationship with total antioxidant activity of the screened endophytic fungi crude extracts. The endophytic fungi were shown to produce a diverse range of metabolites including phenolic and polyphenolic compounds through FT-IR and GC-MS analysis. The isolate Cladosporium uredinicola has potential as a source of antimicrobial compounds whilst the isolate Epicoccum sorghinum has potential as a source of natural antioxidant. Antioxidant activity is a common phenomenon in the studied endophytic fungi and the fungal endophytes of the medicinal plants of Zimbabwe have potential as sources of bioactive compounds. Keywords: Bioprospecting, antioxidant, antimicrobial, endophytic fungi, medicinal plants, Zimbabwe.