Isolation and characterization of an antifungal compound 5-hydroxy-7,4’-dimethoxyflavone from Combretum zeyheri

Abstract

BackgroundCombretum zeyheri, belongs to the family Combretaceae and is one of the most popular herbal plants in tropical and subtropical countries. The leaves of Combretum zeyheri have been used as herbal medicine and have been reported to have pharmacological activity which includes anti-bacterial, anti-fungal, anticancer and antioxidant properties. The goal of this study was to isolate, identify and characterize compounds from C. zeyheri leaves which are responsible for its antifungal activity.MethodsThe preliminary isolation of C. zeyheri active compounds was carried out using chromatographic techniques which include sephadex gel column chromatography, silica gel column chromatography and thin-layer chromatography (TLC). The isolated compounds were then investigated for their antifungal activity using broth dilution assay. The combined effect of the most potent compound and an antifungal drug miconazole was investigated using the checkerboard assay. Time-kill assays were conducted for the combinations using the colony counting method. The mechanism of action of 5-hydroxy-7,4’-dimethoxyflavone as a potent antifungal agent was investigated by determining its inhibitory activity on Candida albicans drug efflux pumps using the ciprofloxacin assay. The ability of 5-hydroxy-7,4’-dimethoxyflavone to inhibit antioxidant enzymes as well as the biosynthesis of ergosterol were also investigated.ResultsA total of four pure compounds (A-D) were isolated from C. zeyheri leaf extract. Compound B (5-hydroxy-7,4’-dimethoxyflavone) was found to be active against Candida albicans using broth dilution method. This compound was also found to have synergistic activity on growth of C. albicans when combined with miconazole, completely inhibiting growth after only 4 hrs of incubation. Analysis of ergosterol content from Candida albicans showed a time-dependent decrease to 91 % and 63 % at 16 and 24 hrs respectively, in cells treated with ½ MIC of 5-hydroxy-7,4’-dimethoxyflavone. The compound 5-hydroxy-7,4’-dimethoxyflavone also showed inhibition of both the drug efflux pumps (with IC50 = 51.64 μg/ml) and the antioxidant enzymes (at 5 μM).ConclusionThe compound 5-hydroxy-7,4’-dimethoxyflavone may be partly responsible for the reported antifungal activity of C. zeyheri, and may serve as a potential source of lead compounds that can be developed as antifungal phytomedicines.

In vitro toxicity determination of antifungal constituents from Combretum zeyheri

“…This study showed that C. zeyheri possesses antifungal activity against Candida albicans and this is in agreement with other previous studies [ 18 – 20 ]. The ethanol extract, alkaloid, saponin and flavonoid-enriched fractions exhibited antifungal activity.…”

“…In this study the alkaloids, flavonoids and saponins were extracted as a preliminary step towards identifying the specific active constituents. Indeed it has been shown that the flavonoid 5-hydroxy-7,4’-methoxyflavone isolated from C. zeyheri had antifungal effects [ 20 ]. The MIC of the positive control, miconazole was as expected and was found to be at 6.25 μg/ml.…”

Effective Inhibition of Candidiasis Using an Eco-Friendly Leaf Extract of Calotropis-gigantean-Mediated Silver Nanoparticles

“…At the determined time, an aliquot of 30 µL was taken from each test suspension and inoculated into SDA for quantifying the colony forming units. Sabaroud dextrose broth (SDB) without any antifungal agent was used as a control [25].…”

Woody species from the Mozambican Miombo woodlands: A review on their ethnomedicinal uses and pharmacological potential

“…Leaves, stem bark and fruits of both species presented antifungal activity against different Candida spp. (Cock and Van Vuuren, 2015;Fyhrquist et al, 2004;Mangoyi et al, 2015;Masoko et al, 2007;Mutasa et al, 2015;Runyoro et al, 2013). Antiinflammatory activities (inhibition of hematopoietic prostaglandin D2 synthase) were detected in leaves of both species (Chimponda and Mukanganyama, 2015;Eloff et al, 2001;McGaw et al, 2001).…”