Antifungal Activity of Zuccagnia punctata Cav.: Evidence for the Mechanism of Action

Abstract

Petroleum ether and dichloromethane extracts of fruits, aerial parts and exudate of Zuccagnia punctata Cav. (Fabaceae) showed moderate antifungal activities against the yeasts C. albicans, S. cerevisiae and C. neoformans (MICs: 62.5 - 250 μg/mL) and very strong antifungal activities against the dermatophytes M. gypseum, T. rubrum and T. mentagrophytes (MICs: 8 - 16 μg/mL) thus supporting the ethnopharmacological use of this plant. Antifungal activity-directed fractionation of active extracts by using bioautography led to the isolation of 2′,4′-dihydroxy-3′-methoxychalcone (1) and 2′,4′-dihydroxychalcone (2) as the compounds responsible for the antifungal activity. Second-order studies included MIC₈₀, MIC₅₀ and MFC of both chalcones in an extended panel of clinical isolates of the most sensitive fungi, and also comprised a series of targeted assays. They showed that the most active chalcone 2 is fungicidal rather than fungistatic, does not disrupt the fungal membranes up to 4 × MFC and does not act by inhibiting the fungal cell wall. So, 2′,4′-dihydroxychalcone would act by a different mechanism of action than the antifungal drugs in current clinical use, such as amphotericin B, azoles or echinocandins, and thus appears to be very promising as a novel antifungal agent.

Abbreviations

ADCM: aerial part dichloromethane extract

AMeOH: aerial part methanol extract

APE: aerial part petrol extract

CC: column chromatography

DMSO: dimethyl sulfoxide

EDCM: exudate dichloromethane extract

FDCM: fruit dichloromethane extract

FMeOH: fruit methanol extract

FPE: fruit petrol extract

MFC: minimum fungicidal concentration

MIC: minimum inhibitory concentration

MOPS: 3-(N-morpholino)propanesulfonic acid

RDCM: root dichloromethane extract

RMeOH: root methanol extract

RPE: root petrol extract

RPMI-1640: Roswell Park Memorial Institute culture medium

SDA: Sabouraud-dextrose agar

Key words

Zuccagnia punctata - Fabaceae - chalcones - antifungal - bioautography - densitometry - mechanism of action.

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1 This work was co-directed by both authors