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Title: Bioactivity-guided isolation and characterization of antimicrobial and wound healing constituents of some Ghanaian medicinal plants
Author: Osei-Djarbeng, Samuel Nana
Awarding Body: University of East London
Current Institution: University of East London
Date of Award: 2010
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Abstract:
Screening of ethnomedicinal plants for antimicrobial activity among plants used in Ghanaian folklore medicine to treat infectious conditions was conducted on Alstonia boonei (Apocynaceae), Balanites aegyptiaca (Balatinaceae), Bidens pilosa (Compositae), Distemonanthus benthamianus (Leguminosae), Funtumia elastica (Apocynaceae), Kigelia africana (Bignonaceae), Mitracarpus villosus (Rubiaceae), Parquetina nigrescens (Asclepiadaceae) and Penianthus zenkeri (Menispermaceae). The selection of the plants was based on ethnomedicinal use and literature search and the aim was to investigate the scientific basis of their use in treating infectious diseases. It was, in addition, aimed at selecting the plant with the most potent activity for detailed bioactivity and phytochemical studies. The methanolic extracts of the plants showed antimicrobial activity with an MIC range of 0.5 - 2.0mg/ml against at least three of the test bacteria (Gram-positives and Gram-negatives) and the yeast-like fungi, Candida albicans, used. F. elastica leaf was selected for further bioactivity studies based on its relatively more potent antimicrobial activity. Bioactivity-guided phytochemical investigation of F. elastica, used to treat infections (including dysentery and gonorrhoea), wound and whooping cough, lead to isolation of eight compounds designated as C2RPA, C2RP1, C2RP2, C2RP3, C2RP4, C2RP5, C2RP6 and C2RP7. Three of them were characterized as (-)epicatechin [C2RP1], taxifolin-3ß-O-glucopyranoside [C2RP2] and the rare A-type proanthocyanidin, epicatechin-(4->8; 2-ºO--'7)-epicatechin (4-+8)-epicatechin (proanthocyanidin trimer) [C2RPA] using spectroscopic methods. This is the first report on isolation and characterization of these compounds from F. elastica. In addition, other compounds obtained as mixtures, and characterized to comprise hydrocarbons including hexadecane, octadecane, eicosane, heneicosane, tetracosane, octacosane, nonacosane and heptacosanew ere also identified. Epicatechin, the proanthocyanidin trimer, C2RP4 and C2RP5, showed antimicrobial activity against the Gram-positive bacteria and C. albicans with MIC range of 31- 500gg/m1; C2RP5 exhibiting the highest antimicrobial activity with an MIC of 31 μg/ml against Stapylococcus aureus. These compounds also exhibited an ability to destroy biofilm formed by MRSA using the standard Calgary MBECTM HTP Assay. Fractions of the crude extract and two isolates containing mainly taxifolin-3ß-Oglucopyranoside and proanthocyanidin trimer each exhibited anti-quorum sensing activity by inhibiting the QS controlled phenotypic purple violacein production by Chromobacterium violaceum. Furthermore, the extracts and the compounds isolated also showed an excellent antioxidant activity with ECso values ranging from 3.88μg (for proanthocyanidin trimer) to 24.59μg (for C2RP7). Also, taxifolin-3Q-Oglucopyranoside stimulated proliferation of fibroblast by 19.5% at a concentration of 4μg/ml. The study on F. elastica leaf has shown that in addition to its ability to arrest the growth of micro-organisms, the plant may have other novel mechanisms of attenuating bacterial pathogenicity by way of interfering with quorum sensing signals and formation of biofilm. Furthermore, the anti-oxidant activity and the ability to stimulate growth of fibroblast, coupled with the antimicrobial activity, may suggest that F. elastica may be useful in wound management. The study therefore shows that plants such as F. elastica may be useful in the management of infectious diseases and wound as purported in folklore medicine.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.533012  DOI: Not available
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