The composition of the culture medium influences the ?-1,3-glucan metabolism of Aspergillus fumigatus and the antifungal activity of inhibitors of ?-1,3-glucan synthesis.
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ABSTRACT:
SUBMITTER: Clavaud C
PROVIDER: S-EPMC3370737 | biostudies-literature | 2012 Jun
REPOSITORIES: biostudies-literature
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The composition of the culture medium influences the β-1,3-glucan metabolism of Aspergillus fumigatus and the antifungal activity of inhibitors of β-1,3-glucan synthesis.
Clavaud Cécile C Beauvais Anne A Barbin Lise L Munier-Lehmann Hélène H Latgé Jean-Paul JP
Antimicrobial agents and chemotherapy 20120305 6
In vitro testing of Aspergillus fumigatus susceptibility to echinocandins has always been a challenge. Using a simple and quick colorimetric method to analyze the activity of inhibitors of β-1,3-glucan synthesis, we found that the composition of the culture medium significantly influences glucan synthesis and consequently the antifungal properties of inhibitors of β-1,3-glucan synthesis when they are tested alone or in combination with chitin synthase inhibitors. ...[more]
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Project description:Aspergillus species are a leading cause of invasive fungal infections. As resistance to first-line therapy involving triazole antifungal agents is rising, second-line therapy with echinocandins is expanding. Resistance to echinocandins is well-established to result from amino acid substitutions in the echinocandin drug target β-(1,3)-D-glucan synthase encoded by the fks1 gene. Recently, we identified several high MIC clinical isolates of A. fumigatus from patients failing echinocandin therapy that did not contain any mutation in the fks1 gene, indicating that echinocandin resistance in these isolates results from an undefined mechanism. To explore possible new mechanisms of resistance, we used a lab-derived strain, RG101, with a nearly identical susceptibility phenotype, as a model system. This strain does not contain fks1 mutations but showed prominent resistance to the echinocandin class drug caspofungin (CAS), while remaining sensitive to other echinocandins, azoles and polyenes. Glucan synthase isolated from RG101 was fully sensitive to drug. Yet, exposure to CAS during its growth yielded a modified enzyme that was insensitive (4-log orders) in kinetic inhibition assays to CAS, as well as other echinocandins. This induction of cross-resistance by CAS was also observed in clinical isolates. To determine the nature of a presumptive posttranslational modification (PTM) of the enzyme, we analyzed whole enzyme PTMs, including the known hot-spot regions, for methylation, acetylation and phosphorylation. While we did not identify any PTMs linked to resistance, analysis of the lipid microenvironment of CAS-induced resistant enzyme revealed a prominent increase in the abundance of dihydrosphingosine (DhSph) and phytosphingosine (PhSph). Exogenous addition of DhSph and PhSph to sensitive enzyme in in vitro kinetic inhibition assays recapitulated the CAS insensitivity of the cellular-derived enzyme. To further examine induction of drug-induced resistance, we used an in vitro assay to demonstrate that CAS, but not other echinocandin class drugs, prominently induced the production of mitochondrial-derived Reactive Oxygen Species (ROS) in A. fumigatus. RNASeq evaluation of whole cells confirmed a ROS signature in cells treated with CAS. Dampening the formation of ROS by antimycin A or thiourea eliminated the induction of drug resistance by CAS. We conclude that CAS-induced formation of ROS promotes a cellular stress response that alters the composition of plasma membrane lipids surrounding glucan synthase, changing its enzymatic properties to make it insensitive to echinocandins. This stress-induced response constitutes a novel mechanism of echinocandin resistance in Aspergillus, with implications for drug resistance and/or tolerance mechanisms in other fungal pathogens.
2019-09-03 | PXD012438 | Pride
Project description:Immune suppression increases the incidence of invasive fungal infections, particularly those caused by the opportunistic mold Aspergillus fumigatus. Previous investigations revealed that members of the TLR family are not absolutely required for host defense against A. fumigatus in nonimmunosuppressed hosts, suggesting that other pattern recognition receptors are involved. We show in this study that naive mice (i.e., not pharmacologically immunosuppressed) lacking the beta-glucan receptor Dectin-1 (Dectin-1(-/-)) are more sensitive to intratracheal challenge with A. fumigatus than control mice, exhibiting >80% mortality within 5 days, ultimately attributed to a compromise in respiratory mechanics. In response to A. fumigatus challenge, Dectin-1(-/-) mice demonstrated impaired IL-1alpha, IL-1beta, TNF-alpha, CCL3/MIP-1alpha, CCL4/MIP-1beta, and CXCL1/KC production, which resulted in insufficient lung neutrophil recruitment and uncontrolled A. fumigatus lung growth. Alveolar macrophages from Dectin-1(-/-) mice failed to produce proinflammatory mediators in response to A. fumigatus, whereas neutrophils from Dectin-1(-/-) mice had impaired reactive oxygen species production and impaired killing of A. fumigatus. We further show that IL-17 production in the lung after A. fumigatus challenge was Dectin-1 dependent, and that neutralization of IL-17 significantly impaired A. fumigatus clearance. Collectively, these results support a requisite role for Dectin-1 in in vivo defense against A. fumigatus.
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