Evaluation of pharmacological activities, cytotoxicity and phenolic composition of four Maytenus species used in southern African traditional medicine to treat intestinal infections and diarrhoeal diseases

BACKGROUND Microbial infections and resulting inflammation and oxidative stress are common pathogenesis of gastrointestinal tract (GIT) disorders. In South Africa, several species of the genus Maytenus are used in traditional medicine to treat various infectious diseases. Most of the previous work on this genus was focused on nonpolar extracts from the root and bark. In this study, leaf extracts of polar extracts of Maytenus peduncularis, Maytenus procumbens, Maytenus senegalensis and Maytenus undata were evaluated for antimicrobial, anti-inflammatory and antioxidant activities to determine their efficacy as therapeutic agents in GIT disorders. METHODS Phenolic-enriched leaf extracts and fractions were prepared by extracting with acidified 70% methanol and solvent-solvent fractionation. The activities of the fractions against Staphylococcus aureus, Pseudomonas aeruginosa, Escherichia coli and Enterococcus faecalis as well as clinical isolates of Aspergillus fumigatus, Candida albicans and Cryptococcus neoformans were determined using a serial microplate dilution method. Antioxidant activities were determined using 1,1-diphenyl-2-picrylhydrazyl (DPPH), 2,2'-azinobis(3-ethylbenzthiazoline-6-sulphonic acid) (ABTS), hydroxyl (OH) radical scavenging and linoleic acid peroxidation inhibitory assays. The phenolic composition as well as the cytotoxicity against Vero cell lines of the crude extracts was evaluated using various standard protocols. RESULTS The antimicrobial activities were concentrated in the non-polar fractions of hexane, dichloromethane and ethyl acetate (MICs 19-312 μg/ml). The crude extracts and polar fractions (butanol and water) had moderate to poor antimicrobial activity (MICs 312 to above 2500 μg/ml). The crude extracts and polar fractions had good antioxidant activity (EC50 values varied from 1.22 to 607 μg/ml, 1.71 to 312 μg/ml and 23 to 284 μg/ml for DPPH, ABTS and OH respectively. Linoleic acid peroxidation inhibition EC50 values of the crude extracts ranged between 27 and 39 μg/ml with relatively low toxicity against Vero cell lines (IC50 values 87 to 187 μg/ml). Fractionation of a crude extract with low activity could lead to fractions with more potent activity. CONCLUSION This study justifies the traditional use of leaf crude extracts and fractions from these four plants to remedy gastrointestinal disorders resulting from infection, inflammation and oxidative stress complications. The study also provides rationale for the use of leaf extracts with same beneficial effects in place of unsustainable root and bark harvest.