Els M.K. Meert
Katholieke Universiteit Leuven
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Publication
Featured researches published by Els M.K. Meert.
Journal of Molecular Microbiology and Biotechnology | 2007
An M. Aerts; Isabelle François; Els M.K. Meert; Qiu-Tian Li; Bruno P. A. Cammue; Karin Thevissen
RsAFP2 (Raphanus sativus antifungal peptide 2), an antifungal plant defensin isolated from seed of R. sativus, interacts with glucosylceramides (GlcCer) in membranes of susceptible yeast and fungi and induces membrane permeabilization and fungal cell death. However, using carboxyfluorescein-containing small unilamellar vesicles containing purified GlcCer, we could not observe permeabilization as a consequence of insertion of RsAFP2 in such vesicles. Therefore, we focused on a putative RsAFP2-induced signaling cascade downstream of RsAFP2-binding to GlcCer in fungal membranes. We show that RsAFP2 induces reactive oxygen species (ROS) in Candida albicans wild type in a dose-dependent manner, but not at all in an RsAFP2-resistant ΔgcsC. albicans mutant that lacks the RsAFP2-binding site in its membranes. These findings indicate that upstream binding of RsAFP2 to GlcCer is needed for ROS production leading to yeast cell death. Moreover, the antioxidant ascorbic acid blocks RsAFP2-induced ROS generation, as well as RsAFP2 antifungal activity. These data point to the presence of an intracellular plant defensin-induced signaling cascade, which involves ROS generation and leads to fungal cell growth arrest.
Fems Microbiology Letters | 2003
Karin Thevissen; Isabelle François; Jon Y. Takemoto; Kathelijne K.A. Ferket; Els M.K. Meert; Bruno P. A. Cammue
DmAMP1, an antifungal plant defensin from Dahlia merckii, was shown previously to require the presence of sphingolipids for fungicidal action against Saccharomyces cerevisiae. Sphingolipids may stabilize glycosylphosphatidylinositol (GPI)-anchored proteins, which interact with DmAMP1, or they may directly serve as DmAMP1 binding sites. In the present study, we demonstrate that S. cerevisiae disruptants in GPI-anchored proteins showed small or no increased resistance towards DmAMP1 indicating no involvement of these proteins in DmAMP1 action. Further, studies using an enzyme-linked immunosorbent assay (ELISA)-based binding assay revealed that DmAMP1 interacts directly with sphingolipids isolated from S. cerevisiae and that this interaction is enhanced in the presence of equimolar concentrations of ergosterol. Therefore, DmAMP1 antifungal action involving membrane interaction with sphingolipids and ergosterol is proposed.
Journal of Biological Chemistry | 2007
Karin Thevissen; Kathryn R. Ayscough; An M. Aerts; Wei Du; Katrijn De Brucker; Els M.K. Meert; Jannie Ausma; Marcel Borgers; Bruno P. A. Cammue; Isabelle François
The antifungal compound miconazole inhibits ergosterol biosynthesis and induces reactive oxygen species (ROS) in susceptible yeast species. To further uncover the mechanism of miconazole antifungal action and tolerance mechanisms, we screened the complete set of haploid Saccharomyces cerevisiae gene deletion mutants for mutants with an altered miconazole sensitivity phenotype. We identified 29 S. cerevisiae genes, which when deleted conferred at least 4-fold hypersensitivity to miconazole. Major functional groups encode proteins involved in tryptophan biosynthesis, membrane trafficking including endocytosis, regulation of actin cytoskeleton, and gene expression. With respect to the antifungal activity of miconazole, we demonstrate an antagonism with tryptophan and a synergy with a yeast endocytosis inhibitor. Because actin dynamics and induction of ROS are linked in yeast, we further focused on miconazole-mediated changes in actin cytoskeleton organization. In this respect, we demonstrate that miconazole induces changes in the actin cytoskeleton, indicative of increased filament stability, prior to ROS induction. These data provide novel mechanistic insights in the mode of action of a ROS-inducing azole.
FEBS Letters | 2005
Karin Thevissen; Jola Idkowiak-Baldys; Yang-Ju Im; Jon Y. Takemoto; Isabelle François; Kathelijne K.A. Ferket; An M. Aerts; Els M.K. Meert; Joris Winderickx; Johnny Roosen; Bruno P. A. Cammue
The antifungal plant defensin DmAMP1 interacts with the fungal sphingolipid mannosyl diinositolphosphoryl ceramide (M(IP)2C) and induces fungal growth inhibition. We have identified SKN1, besides the M(IP)2C‐biosynthesis gene IPT1, as a novel DmAMP1‐sensitivity gene in Saccharomyces cerevisiae. SKN1 was previously shown to be a KRE6 homologue, which is involved in β‐1,6‐glucan biosynthesis. We demonstrate that a Δskn1 mutant lacks M(IP)2C. Interestingly, overexpression of either IPT1 or SKN1 complemented the skn1 mutation, conferred sensitivity to DmAMP1, and resulted in M(IP)2C levels comparable to the wild type. These results show that SKN1, together with IPT1, is involved in sphingolipid biosynthesis in S. cerevisiae.
Journal of Antimicrobial Chemotherapy | 2014
Nicolas Delattin; Katrijn De Brucker; Katleen Vandamme; Els M.K. Meert; Arnaud Marchand; Patrick Chaltin; Bruno P. A. Cammue; Karin Thevissen
OBJECTIVES Biofilms of Candida species, often formed on medical devices, are generally resistant to currently available antifungal drugs. The aim of this study was to identify compounds that increase the activity of amphotericin B and caspofungin, commonly used antifungal agents, against Candida biofilms. METHODS A library containing off-patent drugs was screened for compounds, termed enhancers, that increase the in vitro activity of amphotericin B against Candida albicans biofilms. Biofilms were grown in 96-well plates and growth was determined by the cell titre blue assay. Synergy between identified enhancers and antifungal agents was further characterized in vitro using fractional inhibitory concentration index (FICI) values and in vivo using a worm biofilm infection model. In light of the application of these enhancers onto implants, their possible effect on the growth potential of MG63 osteoblast-like cells was assessed. RESULTS Pre-incubation of C. albicans biofilms with subinhibitory concentrations of the enhancers drospirenone, perhexiline maleate or toremifene citrate significantly increased the activity of amphotericin B or caspofungin (FICI < 0.5) against C. albicans and Candida glabrata biofilms. Moreover, these enhancers did not affect the growth potential of osteoblasts. Interestingly, toremifene citrate also enhanced the in vitro activity of caspofungin in a mixed biofilm consisting of C. albicans and Staphylococcus epidermidis. Furthermore, we demonstrate synergy between toremifene citrate and caspofungin in an in vivo worm C. albicans biofilm infection model. CONCLUSIONS Our data demonstrate an in vitro and in vivo enhancement of the antibiofilm activity of caspofungin by toremifene citrate. Furthermore, our results pave the way for implant-related applications of the identified enhancers.
Bioorganic & Medicinal Chemistry Letters | 2008
Karin Thevissen; Ulrik Hillaert; Els M.K. Meert; Kuen K. Chow; Bruno P. A. Cammue; Serge Van Calenbergh; Isabelle François
The minimal fungicidal concentration (MFC) of dihydrosphingosine (DHS), phytosphingosine (PHS), and five short-chain DHS derivatives was determined for Candida albicans and Candida glabrata. In this respect, a C15- and a C17-homologue of DHS showed a 2- to 10-fold decreased MFC as compared to native DHS (i.e. C18-DHS). DHS derivatives that were active, that is, comprising 12, 15, 17, or 18 carbon atoms, induced accumulation of reactive oxygen species (ROS) in C. albicans.
ChemMedChem | 2009
Isabelle François; Karin Thevissen; Klaartje Pellens; Els M.K. Meert; Jan Heeres; Eddy Jean Edgard Freyne; Erwin Coesemans; Marcel Viellevoye; Frederik Deroose; Sonia Martínez González; Joaquín Pastor; David Corens; Lieven Meerpoel; Marcel Borgers; Jannie Ausma; Gerrit D. Dispersyn; Bruno P. A. Cammue
In this study, we screened a library of 500 compounds for fungicidal activity via induction of endogenous reactive oxygen species (ROS) accumulation. Structure–activity relationship studies showed that piperazine‐1‐carboxamidine analogues with large atoms or large side chains substituted on the phenyl group at the R3 and R5 positions are characterized by a high ROS accumulation capacity in Candida albicans and a high fungicidal activity. Moreover, we could link the fungicidal mode of action of the piperazine‐1‐carboxamidine derivatives to the accumulation of endogenous ROS.
Oxidative Medicine and Cellular Longevity | 2013
Katrijn De Brucker; Anna Bink; Els M.K. Meert; Bruno P. A. Cammue; Karin Thevissen
This study demonstrates a role for superoxide dismutases (Sods) in governing tolerance of Candida albicans biofilms to amphotericin B (AmB). Coincubation of C. albicans biofilms with AmB and the Sod inhibitors N,N′-diethyldithiocarbamate (DDC) or ammonium tetrathiomolybdate (ATM) resulted in reduced viable biofilm cells and increased intracellular reactive oxygen species levels as compared to incubation of biofilm cells with AmB, DDC, or ATM alone. Hence, Sod inhibitors can be used to potentiate the activity of AmB against C. albicans biofilms.
Bioorganic & Medicinal Chemistry Letters | 2011
Karin Thevissen; Klaartje Pellens; Katrijn De Brucker; Isabelle François; Kwok K. Chow; Els M.K. Meert; Wim Meert; Geert Van Minnebruggen; Marcel Borgers; Valérie Vroome; Jeremy I. Levin; Dirk E. De Vos; Louis Maes; Paul Cos; Bruno P. A. Cammue
A series of substituted benzylsulfanyl-phenylamines was synthesized, of which four substituted benzylsulfanyl-phenylguanidines (665, 666, 667 and 684) showed potent fungicidal activity (minimal fungicidal concentration, MFC ≤ 10 μM for Candida albicans and Candida glabrata). A benzylsulfanyl-phenyl scaffold with an unsubstituted guanidine resulted in less active compounds (MFC=50-100 μM), whereas substitution with an unsubstituted amine group resulted in compounds without fungicidal activity. Compounds 665, 666, 667 and 684 also showed activity against single C. albicans biofilms and biofilms consisting of C. albicans and Staphylococcus epidermidis (minimal concentration resulting in 50% eradication of the biofilm, BEC50 ≤ 121 μM for both biofilm setups). Compounds 665 and 666 combined potent fungicidal (MFC=5 μM) and bactericidal activity (minimal bactericidal concentration, MBC for S. epidermidis ≤ 4 μM). In an in vivo Caenorhabditis elegans model, compounds 665 and 667 exhibited less toxicity than 666 and 684. Moreover, addition of those compounds to Candida-infected C. elegans cultures resulted in increased survival of Candida-infected worms, demonstrating their in vivo efficacy in a mini-host model.
Peptides | 2018
Sofie Winderickx; Katrijn De Brucker; Matthew J. Bird; Petra Windmolders; Els M.K. Meert; Bruno P. A. Cammue; Karin Thevissen
HIGHLIGHTSCRAMP20–33 is a small CRAMP variant with antimicrobial activity.Single‐ and double‐substituted CRAMP20–33 variants show improved activity as compared to native CRAMP20–33.Single‐ and double‐substituted CRAMP20–33 variants have a broad‐spectrum antimicrobial activity.Most CRAMP20–33 variants are non‐toxic for human HepG2 cells. ABSTRACT We report here on the structure‐activity relationship study of a 14 amino acid fragment of the cathelicidin‐related antimicrobial peptide (CRAMP), CRAMP20–33 (KKIGQKIKNFFQKL). It showed activity against Escherichia coli and filamentous fungi with IC50 values below 30 &mgr;M and 10 &mgr;M, respectively. CRAMP20–33 variants with glycine at position 23 substituted by phenylalanine, leucine or tryptophan showed 2‐ to 4‐fold improved activity against E. coli but not against filamentous fungi. Furthermore, the most active single‐substituted peptide, CRAMP20–33 G23 W (IC50 = 2.3 &mgr;M against E. coli), showed broad‐spectrum activity against Candida albicans, Staphylococcus epidermidis and Salmonella Typhimurium. Introduction of additional arginine substitutions in CRAMP20–33 G23 W, more specifically in CRAMP20–33 G23 W N28R or CRAMP20–33 G23 W Q31R, resulted in 3‐fold increased activity against S. epidermidis (IC50 = 4 &mgr;M and 4.8 &mgr;M, respectively) as compared to CRAMP20–33 G23 W (IC50 = 15.1 &mgr;M) but not against the other pathogens tested. In general, double‐substituted variants were non‐toxic for human HepG2 cells, pointing to their therapeutic potential.