Antibacterial activity, cytotoxicity and chemical constituents of Hydnora johannis roots

Abstract

In Sudan, the roots of Hydnora johannis (Hydnoraceae) are traditionally used for the treatment of dysentery, diarrhea, cholera and swelling tonsillitis. The ethnomedicinal value of H. johannis was investigated through phytochemical study, in vitro antibacterial activity and preliminary cytotoxic tests. Determination of total phenols, flavonoids and proanthocyanidins was carried out using spectrometric methods. The antibacterial activity of the water and ethanolic extracts was determined using the microdilution method. Pure compounds were isolated from the ethyl acetate extract by chromatographic methods and their structures were established by spectroscopic methods. Cytotoxicity assay was performed against selected human mouth epidermoid carcinoma cell line (KB), and non-cancer human fetal lung cell line (MRC-5). Both water and ethanol (70%) extracts were found to contain the same amount of total phenols and proanthocyanidins, whereas the level of flavonoids was higher in the ethanol extract. The water extract was found to possess antibacterial activity against Enterococcus faecalis (MIC value of 16 μg/mL), Bacillus subtilis, B. cereus and Staphylococcus aureus (MIC values of 64 μg/mL) but not against bacteria mainly responsible for diarrhea. This leads to the suggestion that, the mode of action of water extract which is rich in tannins was not connected to their inhibition to the diarrhea bacteria but to their action on the digestive tract. Reduction in potency of the water and ethanol (70%) extracts when fractionated was observed. The ethyl acetate fraction obtained from fractionation of ethanol extract possessed only activity against the two strains of S. aureus with MIC values of 128 μg/mL. In addition, six compounds were isolated from the ethyl acetate extract as cirsiliol (3′,4′,5-trihydroxy-6-7-dimethoxy flavone) ( 1), trans 3′5-dihydroxy-4′7-dimethoxydihydroflavonol ( 2), oleic acid ( 3), vanillin (4-hydroxy-3-methoxybenzaldehyde) ( 4), protocatechuic acid (3,4 dihydroxy benzoic acid) ( 5) and dl catechin (trans (+) 2-(3,4-dihydroxyphenyl-3,4-dihydro-2H-1-benzopyran-3,5,7-triol)) ( 6). Four compounds from the ethyl acetate extract were also identified by GCMS as stigmasterol ( 7), oleic acid ( 3), myristic acid ( 8), and palmitic acid ( 9). Little cytotoxicity is reported against the cell lines used. Thus, the safety of this plant in the traditional medicine should be verified by much further testing, including in vivo experiments and clinical studies.