Anti-Candida Potential of Peptides from Immature and Ripe Fruits of Capsicum chinense Jacq

The objective of this work was to purify and evaluate the antifungal potential of peptides present in immature and ripe fruits of Capsicum chinense Jacq. (accession UENF 1706) on the medical importance yeasts. Initially the proteins of these seedless fruits were extracted, precipitated with ammonium sulfate at 70% saturation, followed by heating at 80 °C. Subsequently, the peptide-rich extract was fractionated by DEAE-Sepharose anion exchange. The whole process was monitored by tricine-SDS-PAGE. The results revealed that the fraction retained in anion exchange column, called D2, of immature and ripe fruits significantly inhibit the growth of Candida albicans and C. tropicalis yeasts. Due to the higher yield, the D2 fraction of immature fruits was selected for further purification by reverse phase chromatography on HPLC, where sixteen different fractions (H1-H16) were obtained and these were subjected to antifungal assay at 50 µg mL-1. Although almost all fractions tested had significant growth inhibition, the HI9 fraction inhibit 99% of the two yeasts tested. The effect of treatment with HI3, HI8, HI9, and HI14 fractions on the viability of yeast cells was analyzed due to their strong growth inhibition. We observed that only 50 μg mL-1 of the HI9 fraction is the lethal dose for 100% of the cells of C. albicans and C. tropicalis in the original assay. Although the HI9 fraction had a fungicidal effect on both tested yeasts, we only observed membrane permeabilization for C. tropicalis cells treated with 50 µg mL-1 of this fraction. Through mass spectrometry, we identified that the 6 kDa peptide band of HI9 fraction showed similarity with antimicrobial peptides belonging to the plant defensin family.

A plant mannose-binding lectin and fluconazole: key targets combination against Candida albicans

AIMS

This study aimed to evaluate the combined effect of a mannose-binding lectin Helja with fluconazole (FLC) on Candida albicans and to get insights about the joint action mechanism.

METHODS AND RESULTS

The fungal growth was assessed following the optical density at 630 nm. Fungal cell morphology and nucleus integrity were analyzed by flow cytometry and confocal laser scanning microscopy using Calcofluor White (CFW) and 4',6-diamidino-2-phenylindole (DAPI) staining, respectively. The basis of Helja+FLC action on cell wall and plasma membrane was analyzed using perturbing agents. The Helja+FLC combination exhibited an inhibitory effect of fungal growth about three times greater than the sum of both compounds separately and inhibited fungal morphological plasticity, an important virulence attribute associated with drug resistance. Cells treated with Helja+FLC showed morphological changes, nucleus disintegration and formation of multimera structures, leading to cell collapse.

CONCLUSIONS

Our findings indicate that the Helja+FLC combination exhibited a potent antifungal activity based on their simultaneous action on different microbial cell targets.

SIGNIFICANCE AND IMPACT OF STUDY

The combination of a natural protein with conventional drugs might be helpful for the design of effective therapeutic strategies against Candida, contributing to minimize the development of drug resistance and host cell toxicity.

Differential interactions of the antimicrobial peptide, RQ18, with phospholipids and cholesterol modulate its selectivity for microorganism membranes

BACKGROUND

Antimicrobial peptides (AMPs) are molecules with potential application for the treatment of microorganism infections. We, herein, describe the structure, activity, and mechanism of action of RQ18, an α-helical AMP that displays antimicrobial activity against Gram-positive and Gram-negative bacteria, and yeasts from the Candida genus.

METHODS

A physicochemical-guided design assisted by computer tools was used to obtain our lead peptide candidate, named RQ18. This peptide was assayed against Gram-positive and Gram-negative bacteria, yeasts, and mammalian cells to determine its selectivity index. The secondary structure and the mechanism of action of RQ18 were investigated using circular dichroism, large unilamellar vesicles, and molecular dynamic simulations.

RESULTS

RQ18 was not cytotoxic to human lung fibroblasts, peripheral blood mononuclear cells, red blood cells, or Vero cells at MIC values, exhibiting a high selectivity index. Circular dichroism analysis and molecular dynamic simulations revealed that RQ18 presents varying structural profiles in aqueous solution, TFE/water mixtures, SDS micelles, and lipid bilayers. The peptide was virtually unable to release carboxyfluorescein from large unilamellar vesicles composed of POPC/cholesterol, model that mimics the eukaryotic membrane, indicating that vesicles' net charges and the presence of cholesterol may be related with RQ18 selectivity for bacterial and fungal cell surfaces.

CONCLUSIONS

RQ18 was characterized as a membrane-active peptide with dual antibacterial and antifungal activities, without compromising mammalian cells viability, thus reinforcing its therapeutic application.

GENERAL SIGNIFICANCE

These results provide further insight into the complex process of AMPs interaction with biological membranes, in special with systems that mimic prokaryotic and eukaryotic cell surfaces.

Potent Anti-Candida Fraction Isolated from Capsicum chinense Fruits Contains an Antimicrobial Peptide That is Similar to Plant Defensin and is Able to Inhibit the Activity of Different α-Amylase Enzymes

Antimicrobial peptides (AMPs) are molecules present in several life forms, possess broad-spectrum of inhibitory activity against pathogenic microorganisms, and are a promising alternative to combat the multidrug resistant pathogens. The aim of this work was to identify and characterize AMPs from Capsicum chinense fruits and to evaluate their inhibitory activities against yeasts of the genus Candida and α-amylases. Initially, after protein extraction from fruits, the extract was submitted to anion exchange chromatography resulting two fractions. Fraction D1 was further fractionated by molecular exclusion chromatography, and three fractions were obtained. These fractions showed low molecular mass peptides, and in fraction F3, only two protein bands of approximately 6.5 kDa were observed. Through mass spectrometry, we identified that the lowest molecular mass protein band of fraction F3 showed similarity with AMPs from plant defensin family. We named this peptide CcDef3 (Capsicum chinense defensin 3). The antifungal activity of these fractions was analyzed against yeasts of the genus Candida. At 200 μg/mL, fraction F1 inhibited the growth of C. tropicalis by 26%, fraction F2 inhibited 35% of the growth of C. buinensis, and fraction F3 inhibited all tested yeasts, exhibiting greater inhibition activity on the growth of the yeast C. albicans (86%) followed by C. buinensis (69%) and C. tropicalis (21%). Fractions F1 and F2 promoted membrane permeabilization of all tested yeasts and increased the endogenous induction of reactive oxygen species (ROS) in C. buinensis and C. tropicalis, respectively. We also observed that fraction F3 at a concentration of 50 µg/mL inhibited the α-amylase activities of Tenebrio molitor larvae by 96% and human salivary by 100%. Thus, our results show that fraction F3, which contains CcDef3, is a very promising protein fraction because it has antifungal potential and is able to inhibit the activity of different α-amylase enzymes.

Coffea canephora Peptides in Combinatorial Treatment with Fluconazole: Antimicrobial Activity against Phytopathogenic Fungus

The objective of the present study was to evaluate the antimicrobial activity of the Cc-LTP2 and Cc-GRP peptides isolated from Coffea canephora seeds and their possible synergistic activity with the azole drug fluconazole and characterize their mechanisms of action on cells of pathogenic fungi. Cc-LTP2 and Cc-GRP alone or in combination with 20 µg/mL of fluconazole were evaluated for their antimicrobial activity on the fungus Fusarium solani, and the effects of these peptides on the permeability of membranes and the induction of oxidative stress were determined. Our results show that these peptides at a concentration of 400 µg/mL combined with 20 µg/mL of fluconazole were able to inhibit the growth of the tested fungi, promote changes in their growth pattern, permeabilize the membrane, and induce reactive oxygen species (ROS). Some of these results were also observed with the peptides alone or with fluconazole alone, suggesting that the peptides act synergistically, promoting the potentiation of antimicrobial action. In this study, it was shown that Cc-LTP2 and Cc-GRP in combination with fluconazole were able to inhibit the growth of the fungus F. solani, to promote permeabilization of its membrane, and to induce the production of ROS, suggesting a combinatorial activity between the peptides and fluconazole.

Antimicrobial activity and mechanism of action of a thionin-like peptide from Capsicum annuum fruits and combinatorial treatment with fluconazole against Fusarium solani

Many Fusarium species are able to cause severe infections in plants as well as in animals and humans. Therefore, the discovery of new antifungal agents is of paramount importance. CaThi belongs to the thionins, which are cationic peptides with low molecular weights (∼5 kDa) that have toxic effects against various microorganisms. Herein, we study the mechanism of action of CaThi and its combinatory effect with fluconazole (FLC) against Fusarium solani. The mechanism of action of CaThi was studied by growth inhibition, viability, plasma membrane permeabilization, ROS induction, caspase activation, localization, and DNA binding capability, as assessed with Sytox green, DAB, FITC-VAD-FMK, CaThi-FITC, and gel shift assays. The combinatory effect of CaThi and FLC was assessed using a growth inhibition assay. Our results demonstrated that CaThi present a dose dependent activity and at the higher used concentration (50 µg mL^-1 ) inhibits 83% of F. solani growth, prevents the formation of hyphae, permeabilizes membranes, induces endogenous H₂ O₂ , activates caspases, and localizes intracellularly. CaThi combined with FLC, at concentrations that alone do not inhibit F. solani, result in 100% death of F. solani when combined. The data presented in this study demonstrate that CaThi causes death of F. solani via apoptosis; an intracellular target may also be involved. Combined treatment using CaThi and FLC is a strong candidate for studies aimed at improved targeting of F. solani. This strategy is of particular interest because it minimizes selection of resistant microorganisms.

Application and bioactive properties of CaTI, a trypsin inhibitor from Capsicum annuum seeds: membrane permeabilization, oxidative stress and intracellular target in phytopathogenic fungi cells

BACKGROUND

During the last few years, a growing number of antimicrobial peptides have been isolated from plants and particularly from seeds. Recent results from our laboratory have shown the purification of a new trypsin inhibitor, named CaTI, from chilli pepper (Capsicum annuum L.) seeds. This study aims to evaluate the antifungal activity and mechanism of action of CaTI on phytopathogenic fungi and detect the presence of protease inhibitors in other species of this genus.

RESULTS

Our results show that CaTI can inhibit the growth of the phytopathogenic fungi Colletotrichum gloeosporioides and C. lindemuthianum. CaTI can also permeabilize the membrane of all tested fungi. When testing the inhibitor on its ability to induce reactive oxygen species, an induction of reactive oxygen species (ROS) and nitric oxide (NO) particularly in Fusarium species was observed. Using CaTI coupled to fluorescein isothiocyanate (FITC), it was possible to determine the presence of the inhibitor inside the hyphae of the Fusarium oxysporum fungus. The search for protease inhibitors in other Capsicum species revealed their presence in all tested species.

CONCLUSION

This paper shows the antifungal activity of protease inhibitors such as CaTI against phytopathogenic fungi. Antimicrobial peptides, among which the trypsin protease inhibitor family stands out, are present in different species of the genus Capsicum and are part of the chemical arsenal that plants use to defend themselves against pathogens. © 2017 Society of Chemical Industry.

Thionin-like peptide from Capsicum annuum fruits: mechanism of action and synergism with fluconazole against Candida species

Background

Thionins are a family of plant antimicrobial peptides (AMPs), which participate in plant defense system against pathogens. Here we describe some aspects of the CaThi thionin-like action mechanism, previously isolated from Capsicum annuum fruits. Thionin-like peptide was submitted to antimicrobial activity assays against Candida species for IC₅₀ determination and synergism with fluconazole evaluation. Viability and plasma membrane permeabilization assays, induction of intracellular ROS production analysis and CaThi localization in yeast cells were also investigated.

Results

CaThi had strong antimicrobial activity against six tested pathogenic Candida species, with IC₅₀ ranging from 10 to 40 μg.mL⁻¹. CaThi antimicrobial activity on Candida species was candidacidal. Moreover, CaThi caused plasma membrane permeabilization in all yeasts tested and induces oxidative stresses only in Candida tropicalis. CaThi was intracellularly localized in C. albicans and C. tropicalis, however localized in nuclei in C. tropicalis, suggesting a possible nuclear target. CaThi performed synergistically with fluconazole inhibiting all tested yeasts, reaching 100 % inhibition in C. parapsilosis. The inhibiting concentrations for the synergic pair ranged from 1.3 to 4.0 times below CaThi IC₅₀ and from zero to 2.0 times below fluconazole IC_50.

Conclusion

The results reported herein may ultimately contribute to future efforts aiming to employ this plant-derived AMP as a new therapeutic substance against yeasts.

A sunflower lectin with antifungal properties and putative medical mycology applications

Lectins are carbohydrate-binding proteins with a high specificity for a variety of glycoconjugate sugar motifs. The jacalin-related lectins (JRL) are considered to be a small sub-family composed of galactose- and mannose-specific members. Using a proteomics approach, we have detected a 16 kDa protein (Helja) in sunflower seedlings that were further purified by mannose-agarose affinity chromatography. The aim of this work was to characterize the biological activity of Helja and to explore potential applications for the antifungal activity of this plant lectin against medically important yeasts. To initially assess the agglutination properties of the lectin, Saccharomyces cerevisiae cells were incubated with increasing concentrations of the purified lectin. At a concentration of 120 μg/ml, Helja clearly agglutinated these cells. The ability of different sugars to inhibit S. cerevisiae cell agglutination determined its carbohydrate-specificity. Among the monosaccharides tested, D-mannose had the greatest inhibitory effect, with a minimal concentration of 1.5 mM required to prevent cell agglutination. The antifungal activity was evaluated using pathogenic fungi belonging to the Candida and Pichia genera. We demonstrate that 200 μg/ml of Helja inhibited the growth of all yeasts, and it induced morphological changes, particularly through pseudohyphae formation on Candida tropicalis. Helja alters the membrane permeability of the tested fungi and is also able to induce the production of reactive oxygen species in C. tropicalis cells. We concluded that Helja is a mannose-binding JRL with cell agglutination capabilities and antifungal activity against yeasts. The biological properties of Helja may have practical applications in the control of human pathogens.

Antifungal and other biological activities of two 2S albumin-homologous proteins against pathogenic fungi

The aim of this study was to determine whether 2S albumins from Passiflora edulis f. flavicarpa and Capsicum annuum seeds inhibit growth, induce plasma membrane permeabilization and induce endogenous production of nitric oxide in different pathogenic and non-pathogenic yeasts. The 2S albumin from P. flavicarpa (Pf-Alb) inhibited the growth of Kluyveromyces marxiannus, Candida albicans and Candida parapsilosis. The membranes of these yeast strains were permeabilized in the presence of Pf-Alb. The Pf-Alb also inhibited the glucose-stimulated acidification of the medium by Saccharomyces cerevisiae and C. albicans cells, which indicates a probable impairment of fungal metabolism because the inhibition of acidification occurred at various Pf-Alb concentrations and pre-incubation times. The 2S albumin from C. annuum (Ca-Alb) inhibited the growth of the yeasts K. marxiannus, C. tropicalis, C. albicans and S. cerevisiae. These yeast strains exhibited NO induction in the presence of Ca-Alb and displayed cellular agglomeration, elongated cells and the induction of pseudohyphae. Pf-Alb and Ca-Alb at various concentrations also inhibited the glucose-stimulated acidification of the medium by S. cerevisiae cells. Our results indicate that the ability of antimicrobial plant proteins such as 2S albumins to induce microbial inhibition could be an important factor in determining pathogen virulence. Therefore, 2S albumins might be targets for the design of new antifungal drugs.