Chemical and biological properties of Euphorbia ingens E.Mey.

Abstract

The search for new effective antimicrobial agents is necessary due to the appearance of microbial resistance to antibiotics and occurrence of fatal opportunistic infections associated with the Acquired Immunodeficiency Syndrome (AIDS), cancer and chemotherapy. The isolation of antimicrobial compounds from plants provides a solution to increased demands for new antimicrobial agents to combat infection and overcome the problem with resistance and side effects of the currently available antimicrobial agents (antibiotics). The aim of this study was to identify extracts from Euphorbia species with antimicrobial activity and to isolate and characterise the compound(s) responsible for this activity. Euphorbia clavaroides Boiss. var. truncate (N.E.Br.) A.C. White was selected for screening based on the antimicrobial activity reported during previous routine screening of species selected from plant families in our laboratory. Due to unavailability of E. clavaroides plant material in large quantity, E. ingens E.Mey. ex Boiss. was also selected for screening. It is known that plants from the same family may contain the same chemical compounds. Soxhlet extraction was used to prepare extracts of each plant using petroleum ether, dichloromethane, ethyl acetate and ethanol successively. These plant extracts were screened for antimicrobial activity against a range of micro-organisms using the disc diffusion and microplate assays. The toxicity evaluation of the prepared extracts was assayed against human epithelial cell lines (HeLa) using 3- (4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. The ethyl acetate extract of the fleshy inner part of E. ingens showed the most promising antimicrobial activity against Gram-positive bacteria B. subtilis and S. aureus in both the disc diffusion and MIC assay and was therefore selected for further study. The security index (117,2) against B. subtilis of the ethyl acetate extract of the fleshy inner part of E. ingens showed that it is relatively safe to use at the concentration of 0,64 mg/ml in cases of B. subtilis infections. The ethyl acetate extract of the fleshy inner part was subjected to bioassay-guided fractionation approach using column chromatography. This lead to the isolation of kaempferol which was identified by spectroscopic techniques. A brief literature search indicated that kaempferol possessed weak antimicrobial activity against a wide range of micro-organisms with a known MIC value of 100 μg/ml against Staphylococcus aureus as well as toxicity against human cancer cell lines. From bioassay-guided fractionation approach kaempferol showed a weak antimicrobial activity against Gram-positive bacteria Bacillus subtilis (2 mm) and S. aureus (1 mm). Unfortunately, without structural modification it is not suitable for human usage. In conclusion, although the compound isolated in this study is a fairly common flavonol, it is the first report of the isolation of kaempferol from E. ingens. Biological activity of the compound isolated from Euphorbia ingens justifies chemotaxonomic approach used to select species of the same genus.