Pharmacological properties of members of the Sterculiaceae.
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 .