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Published on: December 28, 2017
Candida albicans enhances iron uptake to maintain fluconazole resistance
Rishabh Sharma1, Anubhav Nahar1, Sumant Puri1
1Oral Microbiome Research Laboratory, Kornberg School of Dentistry, Temple University, Philadelphia, Pennsylvania, USA.
Abstract:
Widespread use of fluconazole has led to the emergence of fluconazole-resistant (FR) Candida spp. causing challenges in clinical treatment. Iron, an essential nutrient, affects the levels of ergosterol (a fluconazole target) in fungal membranes. Our lab-generated FR strain (fluconazole minimum inhibitory concentration [MIC] >125 µg/mL) showed a twofold lower MIC (4.66 µg/mL) for the iron chelator deferasirox (DFX), compared to its patent strain CAI4 (DFX MIC 9.34 µg/mL), suggesting a greater sensitivity to iron chelation. A sublethal dose of DFX (2.33 µg/mL) was able to effectively synergize with 125 µg/mL fluconazole to kill the FR strain. Iron estimation revealed significantly enhanced intracellular iron accumulation in the FR strain compared to CAI4. Expression of iron-uptake genes (FRP1, FRE10, and RBT5) was also significantly upregulated in the FR strain, particularly under high iron. FR strain also showed an increase in the levels of cellular ergosterol, along with an increase in the expression of ergosterol biosynthesis genes (ERG11 and ERG9), compared to CAI4, under both low and high iron. The strain further showed increased β-glucan levels and exposure. Additionally, FR strain showed significantly higher survival in high-iron mice compared to low-iron mice, during fluconazole treatment. Finally, we observed a synergistic fungicidal response between 2.33 µg/mL DFX and 125 µg/mL fluconazole, for FR clinical strains. Overall, this suggests that FR C. albicans actively uptakes more iron to maintain cellular conditions needed to support its resistance against fluconazole; and that DFX alone or in conjugation with fluconazole has the potential to overcome fluconazole drug resistance.
Insights
Fluconazole-resistant Candida species accumulate more iron, increasing resistance. The iron chelator deferasirox (DFX) combined with fluconazole effectively kills resistant strains, offering a new treatment strategy.
Area of Science:
- Mycology and Antimicrobial Resistance
- Molecular Biology and Fungal Pathogenesis
- Pharmacology and Drug Discovery
Background:
- Widespread fluconazole use drives the emergence of resistant Candida species, complicating clinical management.
- Iron homeostasis is critical in fungi, influencing membrane composition and antifungal drug susceptibility.
- Fluconazole targets ergosterol in fungal membranes, a pathway potentially modulated by iron availability.
Purpose of the Study:
- To investigate the role of iron in fluconazole resistance in Candida albicans.
- To evaluate the efficacy of the iron chelator deferasirox (DFX) in overcoming fluconazole resistance.
- To explore the potential of DFX as a standalone or combination therapy against resistant fungal infections.
Main Methods:
- Generation and characterization of a fluconazole-resistant (FR) Candida albicans strain.
- Determination of minimum inhibitory concentrations (MICs) for fluconazole and DFX.
- Quantification of intracellular iron levels and gene expression analysis of iron-uptake and ergosterol biosynthesis pathways.
- In vivo studies using a murine model to assess treatment efficacy in high-iron versus low-iron conditions.
Main Results:
- The FR strain exhibited significantly higher intracellular iron accumulation and upregulated iron-uptake genes compared to the susceptible strain.
- FR strains showed increased ergosterol levels and enhanced expression of ergosterol biosynthesis genes, correlating with fluconazole resistance.
- A sublethal dose of DFX synergized with fluconazole to effectively kill the FR strain, both in vitro and in vivo, particularly in high-iron environments.
Conclusions:
- Fluconazole-resistant Candida albicans actively uptakes iron to support resistance mechanisms, including altered ergosterol biosynthesis.
- Deferasirox demonstrates potential as an adjuvant therapy, overcoming fluconazole resistance by targeting iron accumulation.
- Combination therapy with DFX and fluconazole offers a promising strategy to combat challenging drug-resistant fungal infections.
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