Detection of antifungal compounds in Polygonum ferrugineum Wedd. extracts by bioassay-guided fractionation. Some evidences of their mode of action.
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BACKGROUND
Polygonum ferrugineum Wedd. (Polygonaceae) is used to heal infected wounds and as antiseptic, antibiotic or antifungal in the traditional Argentinean medicine. The present investigation was carried out to evaluate the antifungal properties of different extracts of aerial parts of Polygonum ferrugineum, in order to give support to its ethnopharmacological use and to isolate the compounds responsible for the antifungal properties. The most active compounds were tested for their capacity of producing hyphae malformations, similar to those previously observed for crude extracts.
METHODS
Agar Dilution Method (ADM) and Agar Overlay Bioautography (AOB) were used for bioassay-guided fractionation of the aerial part extracts against a panel of human opportunistic pathogenic fungi. The Neurospora crassa assay, followed by Optical Microscopy and Scanning Electron Microscopy observation, was used for studies of mechanisms of action.
RESULTS
MeOH extract and DCM and Hex sub-extracts, but not Aq, EtOAc or BuOH ones possess antifungal activity. Of the seven isolated compounds, cardamonin 2 showed a selective inhibition of Epidermophyton floccosum with a very low MIC (=6.2 μg/mL) and pashanone 1 possessed moderate antifungal activity (MICs=25-50 μg/mL) but a broader spectrum of action. Chalcone 2, but not 1, induced swelling and shortening of the Neurospora crassa hyphae, similar as those caused by the crude DCM extract.
CONCLUSIONS
The bioassay-guided fractionation of Polygonum ferrugineum DCM extract allowed the isolation of five active compounds. Among them, cardamonin 2 showed the highest antifungal activity and selectivity towards Epidermophyton floccosum; in addition, it induced Neurospora crassa malformations that are similar than those produced by the crude DCM extract. These results give additional support to the ethnopharmacological use of Polygonum ferrugineum as antifungal agent.
