Abstract
The safety and effectiveness of many of the medicinal plants used in traditional medicine by rural people with little or no access to allopathic drugs is yet to be evaluated. With this in mind, Ozoroa and Searsia (previously known as Rhus) species traditionally used in South Africa to treat microbial infections and gastrointestinal disorders were selected for in vitro evaluation of biological activities and cytotoxicity.Phenolic-enriched leaf extracts were prepared using mixture of 1% HCl acidified 70% acetone and n-hexane. The crude extract was further fractionated with solvent of different polarities. Crude extracts and fractions were tested against Staphylococcus aureus, Pseudomonas aeruginosa, Escherichia coli, Enterococcus faecalis, Aspergillus fumigatus, Candida albicans and Cryptococcus neoformans. In addition, the antioxidant potentials were determined by DPPH, ABTS, hydroxyl radical scavenging and linoleic acid peroxidation inhibition. The cytotoxic activity of the crude extracts was assayed against Vero cells.The crude extract and the various fractions had good biological activities. The most noteworthy activity is the growth inhibition of the hexane and dichloromethane fractions with MIC values as low as 19μg/ml. The ethyl acetate and butanol fractions had moderate to low antimicrobial activities with MICs ranging from 39 to 2500μg/ml. The polar fractions were more active against the fungal pathogens compared with the non-polar fraction. In the DPPH antioxidant assays, the active compounds were concentrated in the polar fractions (IC50 of the crude extract ranged between 0.90 and 15.82μg/ml). The ethyl acetate fraction was the most active (IC50 ranging between 0.84 and 7.92μg/ml). Although the water fraction was the most polar, the antioxidant activities were low due to the transfer of the active components into the ethyl acetate and butanol fractions. The crude extracts also had good linoleic acid peroxidation inhibition (LC50 ranging between 13.99 and 40.45μg/ml).Crude extracts and fractions of the Ozoroa mucronata, O. paniculosa, Searsia leptodictya, S. pendulina, and S. pentheri species tested in this study had good activities relating to diarrhoea mechanisms of pharmacological relevance. However, use of phenolic-enriched crude extracts from these plants for diarrhoeal treatment or any other diseases need to be applied with caution as most of the plant extracts were reasonably toxic against Vero cell line. A next step in the possible application of these extracts to treat diarrhoea would be to identify the bioactive and toxic compounds.
Highlights
The use of medicinal plants to alleviate diarrhoeal symptoms is a common practice in South African Traditional Medicine (McGaw et al, 2000)
The percentage yields of the crude extracts and fractions were expressed as the ratio of the dry weight of plant extract to the dry weight of the plant material used for the extraction process
The maximum yield of the crude extract was obtained from S. leptodictya (44.5±3.47%)
Summary
The use of medicinal plants to alleviate diarrhoeal symptoms is a common practice in South African Traditional Medicine (McGaw et al, 2000). Diarrhoeal symptoms are a consequence of altered intestinal motility and fluid accumulation in the gastrointestinal tract (GIT). These conditions are usually caused by microbial infections, intestinal parasitic burdens, intestinal inflammation, stress (physical and oxidative), or manifestation of other forms of diseases such as ulcerative colitis (Westbrook et al, 2010), Crohn‘s disease (Lomax et al, 2006), diabetes (Forgacs and Patel, 2011) and malaria (Gessler et al, 1995). South Africa has the largest HIV infection rate in the world and many patients depend on medicinal plants to get relief from diarrhoea and intestinal disorders. Diarrhoea may cause malnutrition, resulting in stunted growth, a defective immune system and increased susceptibility to other infections (Fleckenstein et al, 2010)
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