Riding the wave: South Africa's contribution to ethnopharmacological research over the last 25 years

South Africa is a country with both rich floral biodiversity and cultural diversity. Traditional herbal medicines form an important part of the healthcare of most South Africans, and relies heavily on the use of indigenous plants. This article briefly describes the role South Africa has played in recent years, in contributing to the worldwide increase in research in the field of ethnopharmacology.

Improving seedling vigour of indigenous medicinal plants with smoke

The application of smoke and aqueous smoke solutions stimulates seed germination in a number of plant species. This study highlights the effects of aerosol smoke and smoke solutions on the germination and seedling vigour of three South African indigenous medicinal plants Albuca pachychlamys, Merwilla natalensis and Tulbaghia violacea. The vigour index of one-week-old seedlings of all three species examined was increased with the application of dry smoke and smoke extract dilutions, as compared to control treatments. Seedlings of A. pachychlamys germinated with smoke solutions showed a significant (p0.05) gain in bulb and leaf mass (27.9 and 197.6 mg respectively) compared to untreated seedlings (9.9 and 124.7 mg respectively) when grown in vitro for 75 days. The leaf mass of smoke solution-treated seedlings of T. violacea was significantly (p0.05) higher (120.4 mg) than that of untreated seedlings (47.6 mg). Subsequently, the height of seedlings in both species was also significantly (p0.05) greater. Seedlings germinated in water and then transferred to smoke solutions (1:2000) showed enhancement of some of the growth parameters studied. Albuca pachychlamys and T. violacea seeds exposed to aerosol smoke exhibited higher seedling survival percentages than from non-smoked seeds, while no significant effect was observed for M. natalensis seedlings. This investigation shows that the application of smoke technology can be adopted to produce high vigour seedlings.

Assessing African medicinal plants for efficacy and safety: agricultural and storage practices

The paper reviews an important but little researched area of ethnopharmacology, namely, the effect of cultivation and post-harvest storage practices on levels of biological activity in traditionally used medicinal plants. Changes in COX-1 inhibition and antibacterial activity, for example, occur at the onset of senescence and, in some species, are influenced by plant age. Plants in cultivation were also shown to have reduced anthelmintic and antibacterial activity while hypoxoside production was affected by nitrogen and phosphorous. Irrigation treatments, however, increased anthelmintic activity and, therefore, could be applied to medicinal plants cultivated in low rainfall areas. Pesticides have also been implicated in the regulation of plant growth and secondary metabolite production in cultivated medicinal plants, but residue levels have, so far, not been monitored. Post harvest storage of medicinal plants has been poorly researched in southern Africa. Available data indicates that antibacterial and anti-inflammatory activity changes following storage and is both species and temperature dependent. Similar trends were noted for materials that had been rapidly aged. Fatty acids with antibacterial activity are stable in dry specimens and, as such, may account for the fact that activity is unaffected by storage in certain instances.

Biological activities and distribution of plant saponins

Plant saponins are widely distributed amongst plants and have a wide range of biological properties. The more recent investigations and findings into their biological activities were summarized. Isolation studies of saponins were examined to determine which are the more commonly studied plant families and in which families saponins have been identified.

Assessing African medicinal plants for efficacy and safety: pharmacological screening and toxicology

This paper reviews progress in establishing the scientific rationale for and safety of traditional medicine use in Africa. Selected plants were screened for antibacterial, antifungal, anthelmintic, anti-amoebic, antischistosomal, antimalarial, anti-inflammatory and antioxidant activity, as well as psychotropic and neurotropic activity using appropriate in vitro tests. Isolation of active compounds, in almost all cases, provided scientific validation for the use of the plants in traditional medicine. Although plants used medicinally are widely assumed to be safe, many are potentially toxic. Where poisoning from traditional medicines has been reported, it is usually because the plants used have been misidentified in the form in which they are sold, or incorrectly prepared and administered by inadequately trained personnel. The issue of quality control may, in the interim, be addressed using chromatographic techniques.

Pharmacological and phytochemical screening of two Hyacinthaceae species: Scilla natalensis and Ledebouria ovatifolia

Aqueous, ethanolic, dichloromethane and n-hexane extracts of Scilla natalensis Planch. and Ledebouria ovatifolia (Bak.) Jessop bulbs (Hyacinthaceae) were screened for antibacterial, anti-inflammatory, antischistosomic, anticancer and anthelmintic activity. Poor antibacterial activity against both Gram-positive and Gram-negative bacteria was shown with S. natalensis extracts. Good antibacterial activity was shown by the ethanolic and dichloromethane extracts of L. ovatifolia against Gram-positive bacteria. In the anti-inflammatory screening, the dichloromethane and hexane extracts of S. natalensis resulted in good inhibition against both COX-1 and COX-2. Ethanolic extracts had the highest inhibitory effect against nematodes in the anthelmintic assays. Poor anti-inflammatory and anthelmintic activity was found with L. ovatifolia. Aqueous extracts of S. natalensis had good activity against Schistosoma haematobium, with a minimum inhibitory concentration of 0.4 mg ml(-1). Aqueous extracts of fresh L. ovatifolia bulb material were found to be lethal to S. haematobium at a concentration of 1.6 mg ml(-1). The phytochemical screening of S. natalensis bulbs revealed the presence of saponins and bufadienolides within the bulbs. Bulbs of L. ovatifolia contained bufadienolides.

An investigation on the biological activity of Combretum species

Leaf extracts of 20 Combretum species, many of which are used in southern African traditional medicine, were screened for anti-inflammatory, anthelmintic, anti-bilharzia (antischistosomal) and DNA-damaging activity. Significant activity in more than one bioassay was exhibited by Combretum apiculatum, Combretum hereroense, Combretum molle and Combretum mossambicense. Ethyl acetate extracts were generally most active, followed by acetone and then water extracts.

Efficiency of traditionally used South African plants against schistosomiasis

Urinary schistosomiasis is treated traditionally by means of herbal remedies. Forty-eight South African plant species were identified as possible antischistosomic plants. Twenty-one of these plant species were collected in order to investigate their antischistosomal properties. Crude extracts of the plant materials were screened against the schistosomula of the species Schistosoma haematobium. Cercariae were obtained from Bulinus africanus snails through an in vitro technique. By subjecting the cercariae to a sheering stress, they were transformed into schistosomula. The schistosomula were placed into a culture medium to which the plant extracts were added. The results obtained indicated that the plant extracts from Berkheya speciosa (Asteraceae), Euclea natalensis (Ebenaceae) and Trichilia emetica (Meliaceae) are lethal to the schistosomula.