Johannes Van Staden

Antibacterial activity of South African plants used for medicinal purposes

Crude extracts from 21 South African medicinal plants, traditionally used for ailments of an infectious or septic nature, were screened for in vitro antibacterial activity using the agar diffusion and dilution methods. Almost all the activity exhibited was against Gram-positive bacteria, with 12 of the 21 plant species tested showing some activity against Bacillus subtilis. Only the Warburgia salutaris methanol extract inhibited the growth of Escherichia coli. None of the extracts had any activity against Klebsiella pneumoniae. The highest activity was found in the methanol extracts from Bidens pilosa, Psidium guajava, Artemisia afra and Warburgia salutaris. The majority of the antibacterial activity was present in the methanolic, rather than the aqueous extracts.

Screening of Zulu medicinal plants for prostaglandin-synthesis inhibitors.

Aqueous and ethanolic extracts of 39 plants used in traditional Zulu medicine to treat headache or inflammatory diseases were screened for prostaglandin-synthesis inhibitors. Extracts were tested in an in vitro assay for cyclooxygenase inhibitors. In general, ethanolic extracts caused higher inhibition than aqueous extracts. Two-thirds of the plants screened had high inhibitory activity. The highest inhibition was obtained with ethanolic extracts of Bidens pilosa, Eucomis autumnalis, Harpephyllum caffrum, Helichrysum nudifolium, Leonotis intermedia, L. leonorus, Ocotea bullata, Rumex saggitatus, Solanum mauritianum, Synadenium cupulare and Trichilia dregeana.

Zulu medicinal plants with antibacterial activity.

Aqueous, methanolic and ethyl acetate extracts of 14 plants used in traditional Zulu medicine for treatment of ailments of an infectious nature were screened for antibacterial activity. Most of the activity detected was against gram-positive bacteria. Tuber bark extracts of Dioscorea sylvatica had activity against gram-negative Escherichia coli and extracts of Dioscorea dregeana, Cheilanthes viridis and Vernonia colorata were active against Pseudomonas aeruginosa. The highest antibacterial activity was found in extracts of C. viridis, D. dregeana, D. silvatica, Melianthus comosus and V. colorata. In general, methanolic extracts exhibited higher activity than aqueous and ethyl acetate extracts.

Somaclonal variation in plants: causes and detection methods

Plant tissue culture has become one of the fundamental tools of plant science research. It is extensively employed in the production, conservation and improvement of plant resources. The presence of somaclonal variation in populations derived from tissue culture is affecting the use of tissue culture negatively and has remained a major problem. Conversely, it is a source of new desirable clones/variants with better agronomic traits. In this review, we summarize the possible causes, detection methods and desirability of variants. Somaclonal variation is one of the most researched and reviewed topics. Hence, we restricted ourselves to outlining various examples which may be used as important references for researchers who intend to identify and/or characterize somaclonal variants while using tissue culture for research and production. Emphasis is placed on the negative effects of somaclonal variation. However, this review also includes examples of some useful variants generated as a result of somaclonal variation.

Antibacterial and anti-inflammatory activities of some plants used for medicinal purposes in Kenya.

Aqueous, hexane and methanol extracts of 12 plant species, traditionally used in Kenya for treatment of ailments of infectious and/or inflammatory nature were screened for in vitro antibacterial and anti-inflammatory activities. Antibacterial activity was tested using the agar diffusion method while anti-inflammatory activity was tested using the cyclooxygenase (COX-1) assay. All the antibacterial activity was against Gram-positive bacteria with nine plant species showing some activity against Staphylococcus aureus. The highest activity was found in the methanol extracts of Maytenus senegalensis, Plectranthus barbatus, Zanthoxylum chalybeum, Zanthoxylum usambarense and hexane extracts of Spiranthes mauritianum. All the plant species showed some anti-inflammatory activities. In most cases, methanol extracts caused higher inhibition than aqueous and hexane extracts.

Natural Antioxidants: Fascinating or Mythical Biomolecules?

Research on the use, properties, characteristics and sources of antioxidants especially phenolic compounds, flavonoids, vitamins, synthetic chemicals and some micronutrients began in the late 18th century. Since then antioxidant research has received considerable attention and over a hundred thousand papers have been published on the subject. This has led to a rampant use of antioxidants in order to try to obtain and preserve optimal health. A number of nutraceuticals and food supplements are frequently fortified with synthetic or natural antioxidants. However, some research outcomes have led to the belief that antioxidants exist as mythical biomolecules. This review provides a critical evaluation of some common in vitro antioxidant capacity methods, and a discussion on the role and controversies surrounding non-enzymatic biomolecules, in particular phenolic compounds and non-phenolic compounds, in oxidative processes in an attempt of stemming the tidal wave that is threatening to swamp the concept of natural antioxidants.

Review on plants with CNS-effects used in traditional South African medicine against mental diseases

The majority of the population in South Africa use traditional health care to treat various mental conditions. In this review, we present ethnobotanical information on plants used by the traditional healers in South Africa to treat mental illnesses, specifically epilepsy, depression, age-related dementia and debilitative mental disorders. Details of the recent scientific studies conducted on some of these plants are reviewed. Extracts of Searsia chirindensis, Cotelydon orbiculata and Leonotis leonurus have shown in vivo anticonvulsant activity. Extracts from Searsia dentata and Searsia pyroides showed spontaneous epileptiform discharge in mouse cortical slices, and acted as NMDA-receptor antagonists. Apigenin, amentoflavone and agathisflavone with affinity to the benzodiazepine site on the GABA(A)-receptor were isolated from Searsia pyroides. Naringenin with affinity to the GABA(A)-benzodiazepine receptor was isolated from Mentha aquatica. Agapanthus campanulatus, Boophone disticha, Mondia whitei and Xysmalobium undulatum exhibited antidepressant-like activity in three in vivo models for depression. Amaryllidaceae alkaloids with activity to the serotonin transporter were isolated from Boophone disticha. The alkaloid mesembrine, which act as a serotonin reuptake inhibitor, was isolated from Sceletium tortuosum. Investigations of plants used to treat age-related dementia and debilitative mental disorders lead to the isolation of a number of Amaryllidaceae alkaloids with acetylcholinesterase inhibitory activity from Boophone disticha and Crinum species. Extracts of Mentha aquatica, Gasteria croucheri, Ruta graveolens and Scotia brachypetala inhibited MAO-B. Naringenin was isolated from Mentha aquatica as a MAO inhibitor. Only a small number of the more than 300 southern African plant species reported to treat or affect the CNS have been scientifically evaluated. Very few of the active compounds have been isolated and identified.

Screening of medicinal plants used in South African traditional medicine for genotoxic effects

Dichloromethane and 90% methanol extracts from 51 South African medicinal plants were evaluated for potential genotoxic effects using the bacterial Ames and VITOTOX tests with and without metabolic activation. Dichloromethane extracts from bulbs of Crinum macowanii showed mutagenicity in strain TA98 with and without metabolic activation, whereas extracts from leaves of Chaetacme aristata and foliage of Plumbago auriculata showed mutagenicity and/or toxicity. Extracts from the leaves of Catharanthus roseus and twigs of Combretum mkhzense were mutagenic with metabolic activation only. The only 90% methanol extracts that were mutagenic in strain TA98 were from the leaves of C. roseus and Ziziphus mucronata in the presence of metabolic activation. No genotoxic effects were found in strain TA100 or in the VITOTOX test.

Plants used for stress-related ailments in traditional Zulu, Xhosa and Sotho medicine. Part 1: Plants used for headaches

The usage and indications of possible therapeutic and harmful effects of 96 plants reported to be used for headaches in traditional Zulu, Xhosa and Sotho medicine are reviewed. Although few pharmacological studies have been undertaken on the plants used, related usage by other ethnic groups and known properties in related plants indicate significant possible analgesic, decongestant, anti-inflammatory, antispasmodic or sedative properties. Observations made by healers indicate an acute awareness of some of the potentially toxic compounds likely to be found in the plants. Most of the medicines are snuffed or inhaled. Both the routes of administration and the plants used merit further investigation.

Screening of Zulu medicinal plants for angiotensin converting enzyme (ACE) inhibitors

Twenty plants used by traditional healers in South Africa for the treatment of high blood pressure were investigated for their anti-hypertensive properties, utilizing the angiotensin converting enzyme assay. A hit rate of 65% was achieved, with the highest inhibition (97%) obtained by Adenopodia spicata leaves. A further seven plants exhibited an inhibition greater than 70% and five more over 50%. The leaves of the plants showed the greatest levels of inhibition. There was little difference in the overall hit rate between ethanolic and aqueous extracts, although in most cases there was a marked difference in activity between aqueous and ethanolic extracts from the same species. Plants exhibiting inhibition levels greater than 50% were further tested for the presence of tannins in order to eliminate possible false positives. Active plants that did not contain tannins were Agapanthus africanus, Agave americana, Clausena anisata, Dietes iridioides, Mesembruanthemum spp., Stangeria eriopus and Tulbaghia violacea.