Abstract
In addition to the bio-guided investigation of the antifungal activity of Plinia cauliflora leaves against different Candida species, the major aim of the present study was the search for targets on the fungal cell. The most active antifungal fraction was purified by chromatography and characterized by NMR and mass spectrometry. The antifungal activity was evaluated against five Candida strains according to referenced guidelines. Cytotoxicity against fibroblast cells was determined. The likely targets of Candida albicans cells were assessed through interactions with ergosterol and cell wall composition, porosity and architecture. The chemical major component within the most active antifungal fraction of P. cauliflora leaves identified was the hydrolysable tannin casuarinin. The cytotoxic concentration was higher than the antifungal one. The first indication of plant target on cellular integrity was suggested by the antifungal activity ameliorated when using an osmotic support. The most important target for the tannin fraction studied was suggested by ultrastructural analysis of yeast cell walls revealing a denser mannan outer layer and wall porosity reduced. It is possible to imply that P. cauliflora targeted the C. albicans cell wall inducing some changes in the architecture, notably the outer glycoprotein layer, affecting the cell wall porosity without alteration of the polysaccharide or protein level.
Highlights
Plinia cauliflora is a tree from the Myrtaceae family [1] widespread in Brazil, Argentina and Paraguay
Purification of F2 was achieved by a combination of High Speed Counter-Current Chromatography (HSCCC) and semipreparative reverse phase High Performance Liquid Chromatography (HPLC) and led to the purification of a major hydrolysable tannin named casuarinin (Figure 1)
It can be proposed that the specific cell wall changes induced by treatment with subfraction F2 may be due to the formation of a tannin-cell wall protein complex on the outermost layer of C. albicans since tannins are known to complex with macromolecules such as proteins and polysaccharides [31]
Summary
Plinia cauliflora is a tree from the Myrtaceae family [1] widespread in Brazil, Argentina and Paraguay. P. cauliflora produces an edible tasty fruit. A survey in the Brazilian Northeast area showed the popular use of its leaves and stems for the treatment of diarrhea and dysentery, while the syrup is useful to treat coughs and bronchitis [3]. Despite its importance and wide availability in Brazil, phytochemical studies on this plant are still scarce and have so far focused on the fruit [4]. Histochemical study of P. cauliflora leaves showed the presence of phenols and tannins in the midvein and smaller veins. A preliminary phytochemical study of the ethanolic extract of the leaves confirmed the presence of hydrolysable tannins and flavonoids.
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