Myriocin Significantly Increases the Mortality of a Non-Mammalian Model Host during Candida Pathogenesis

Nadja Rodrigues De Melo,Ahmed Abdrahman,Catherine Thornton,Carolyn Greig,Andreas Vilcinskas,Krishnendu Mukherjee,Tariq M Butt,Norman A Ratcliffe,Oscar Zaragoza

doi:10.1371/journal.pone.0078905

Nadja Rodrigues De Melo, Ahmed Abdrahman + Show 7 more

Open Access

https://doi.org/10.1371/journal.pone.0078905

Copy DOI

Journal: PLoS ONE	Publication Date: Nov 15, 2013
Citations: 35	License type: CC BY 4.0

Affiliation: Swansea University, Universidade Federal Fluminense

Abstract

Candida albicans is a major human pathogen whose treatment is challenging due to antifungal drug toxicity, drug resistance and paucity of antifungal agents available. Myrocin (MYR) inhibits sphingosine synthesis, a precursor of sphingolipids, an important cell membrane and signaling molecule component. MYR also has dual immune suppressive and antifungal properties, potentially modulating mammalian immunity and simultaneously reducing fungal infection risk. Wax moth (Galleria mellonella) larvae, alternatives to mice, were used to establish if MYR suppressed insect immunity and increased survival of C. albicans-infected insects. MYR effects were studied in vivo and in vitro, and compared alone and combined with those of approved antifungal drugs, fluconazole (FLC) and amphotericin B (AMPH). Insect immune defenses failed to inhibit C. albicans with high mortalities. In insects pretreated with the drug followed by C. albicans inoculation, MYR+C. albicans significantly increased mortality to 93% from 67% with C. albicans alone 48 h post-infection whilst AMPH+C. albicans and FLC+C. albicans only showed 26% and 0% mortalities, respectively. MYR combinations with other antifungal drugs in vivo also enhanced larval mortalities, contrasting the synergistic antifungal effect of the MYR+AMPH combination in vitro. MYR treatment influenced immunity and stress management gene expression during C. albicans pathogenesis, modulating transcripts putatively associated with signal transduction/regulation of cytokines, I-kappaB kinase/NF-kappaB cascade, G-protein coupled receptor and inflammation. In contrast, all stress management gene expression was down-regulated in FLC and AMPH pretreated C. albicans -infected insects. Results are discussed with their implications for clinical use of MYR to treat sphingolipid-associated disorders.

Highlights

Myriocin (2-amino-3,4-dihydroxy-2-(hydroxymethyl)-14-oxoicos-6-enoic acid, MYR) is a metabolite of the insect pathogenic fungus Isaria sinclairii
The minimum inhibitory concentration (MIC) for MYR in the presence of Candida cells at 48 h was 0.12 mg/ml compared with 2 mg/ml and 0.25 mg/ml for amphotericin B (AMPH) and FLC, respectively (Table 2)
The MYR+AMPH combination was synergistic in inhibiting Candida growth at 0.25 mg/ml and 0.03 mg/ml, respectively, whereas the MYR combination with FLC was antagonistic with MICs of 16 mg/ml and 0.12 mg/ml, respectively (Table 2)

Summary

Introduction

Myriocin (2-amino-3,4-dihydroxy-2-(hydroxymethyl)-14-oxoicos-6-enoic acid, MYR) is a metabolite of the insect pathogenic fungus Isaria sinclairii. It is a sphingosine analog with immunosuppressive properties, more potent than cyclosporine [1]. Sphingolipids produce the outer leaflet of the plasma membrane and have a role in protecting the cell surface against harmful environmental factors. Sphingolipid metabolites, such as ceramide and sphingosine-1-phosphate, are important mediators in the signaling cascades involved in apoptosis, proliferation, and stress responses [6]. It is imperative that we understand the full potential of the drug including antagonism and synergy with other therapeutics

Objectives

Methods

Results

Conclusion