Pharmacological properties of members of the Sterculiaceae.
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Date
2002
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Abstract
There is a resurgence of interest in many countries in medicinal plants and their
curative properties (HARBORNE & BAXTER, 1993). Little work has previously
been conducted on the Sterculiaceae species, especially those located within
South Africa. This was a perfect opportunity to broaden the available
information on the medicinal properties and chemical constituents of this family,
within KwaZulu-Natal. Of the 50 genera of the Sterculiaceae family, six are located in South Africa:
Cola, Oombeya, Hermannia, Melhania, Sterculia and Waltheria .
Seven Sterculiaceae species were chosen for investigation. They varied in
growth type and use in traditional medicine. These species included: Oombeya
rotundifolia, D. burgessiae, D. cymosa, Cola natalensis, C. greenwayi,
Hermannia depressa and Sterculia murex. Plant material used in the study was
collected from a variety of areas, all within KwaZulu-Natal or the Northern
Province. There were two collection sites for D. rotundifolia, from differing
habitats, and results were compared. The material was screened pharmacologically for anti-bacterial activity using the disc-diffusion assay and Minimal Inhibitory Assay (MIC), and for antiinflammatory
activity using the COX-1 assay. Only D. rotundifolia and C. natalensis were tested for anti-bacterial activity using the disc-diffusion assay as the disc-diffusion asay was found to show
inconsistencies in the results obtained. Bacteria used included: Escherichia coli
and Klebsiella pneumoniae being Gram-negative, and Micrococcus luteus,
Staphylococcus aureus and Staphylococcus epidermidis being Gram-positive.
D. rotundifolia exhibited activity, both anti-bacterial and bacteriostatic, in the
leaf, twig and bark extracts from both collection sites. Only the water extract
obtained from the leaf material of C.natalensis exhibited slight anti-bacterial
activity against S. epidermidis. Minimal inhibitory concentration (MIC) values
were determined using a microdilution assay (25 mg ml-1 serially diluted 50 %
to 0.195 mg ml-1). Bacteria used in the screening were: B. subtilis, E. coli, K.
pneumoniae and S. aureus. None of the water extracts showed any antibacterial
activity. Good MIC values were exhibited by D. cymosa ethanolic leaf
extracts, C. greenwayi leaf ethyl acetate extracts especially against K.
pneumoniae (0.78 mg ml-1) and S. aureus (0.39 mg rnl-1) and H. depressa
ethanol and ethyl acetate leaf, stem and root extracts. D. burgessiae and S.
murex showed low activity, with insignificant MIC values.
D. rotundifolia plant material yielded the highest anti-inflammatory activity of all
the plant species, with the extracts from the Umgeni Valley Nature
Reserve(UVNR) showing the best results. The lowest activity was recorded in
the aqueous bark extracts (5% inhibition)and the highest from the ethanolic leaf
extract (97% inhibition). D. cymosa extracts showed high activity in ethanolic
leaf and twig extracts with low activity in all the other extracts. D. burgessiae,
C. greenwayi and S. murex extracts showed high activity in both ethanolic and
dichloromethane extracts from leaf and twig material. Activity occurred in the
dichloromethane extracts of H. depressa obtained from the stem (78%) and
root (81%) extracts. C. natalensis extracts showed insignificant activity.
Plant material was phytochemically screened for alkaloids, saponins, tannins,
cardiac glycosides and cyanogenic glycosides. No alkaloids were detected
using pH-partitioning and no cyanogenic glycosides were observed (TLC
sandwich method) in any of the extracts of the seven species screened. Using
the gelatin salt-block test, tannins were found to be present in the leaf and twig
material of D. rotundifolia, the leaf material of C. greenwayi and the leaf, stem
and root material of H depressa. The froth test indicated that saponins were
present in the leaf and twig material of D. rotundifolia and leaf, root and stem
material of H. depressa. The haemolysis test indicated the presence of
saponins in the D. rotundifolia bark material. Screening for cardiac glycosides
detected cardienolides in the leaf, twig and bark material of D. rotundifolia, and
bufadienolides were detected in D. rotundifolia , D. cymosa, D. burgessiae and
S. murex.
Five species screened were selected for isolation of active anti-bacterial
compounds: D. rotundifolia, D. burgessiae, D. cymosa, C. greenwayi and H.
depressa. Material was extracted by Soxhlet and isolation techniques employed
were VLC, TLC separation, Sephadex LH-20 column chromatography and
HPLC techniques. The isolated compounds were analysed by NMR and GCMS.
All isolated compounds were fatty acids: Palmitic acid, Myristic acid, Lauric
acid, Stearic acid, Acetic acid as welll as stearyl alcohol, eicosane and
octadecane.
The aqueous eaf extract of H. Depressa exuded a thick mucilage. The
production of this mucilage from the H. depressa aqueous extract may have
medicinal or commercial value. A technique to separate the mucilaginous
extract from the leaf material was devised. After extraction, the extract was
screened to determine its sugar content through gas chromatography. It was
screened for its pharmacological properties: antibacterial and anti-inflammatory
activity. The hydrolysing effect of -amylase and HCI on the extract was
determined to find its potential use as a bulking agent for use as an appetite
suppressant, laxative or against the effects of diarrhoea. It was concluded that
the extract is not likely to break down easily in the human digestive system and
may be effective against the three listed ailments .
Description
Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 2002.
Keywords
Sterculiaceae., Medicinal plants., Ethnobotany--South Africa., Chemistry, Pharmaceutical., Theses--Botany.