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.
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- Health Sciences [2059]