Synergism of Zinc Oxide Quantum Dots with Antifungal Drugs: Potential Approach for Combination Therapy against Drug Resistant Candida albicans

Abstract

Candidiasis caused by Candida albicans is one of the most common microbial infections. Azoles, polyenes, allylamines, and echinocandins are classes of antifungals used for treating Candida infections. Standard drug doses often become ineffective due to the emergence of multidrug resistance (MDR). This leads to the use of higher drug doses for prolonged duration, resulting in severe toxicity (nephrotoxicity and liver damage) in humans. However, combination therapy using very low concentrations of two or more antifungal agents together, can lower such toxicity and limit evolution of drug resistance. Herein, 4–6 nm zinc oxide quantum dots (ZnO QDs) were synthesized and their in vitro antifungal activities were assessed against drug-susceptible (G1, F1, and GU4) and resistant (G5, F5, and GU5) isolates of C. albicans. In broth microdilution assay, ZnO QDs exhibited dose dependent growth inhibition between 0 – 200 µg/ml and almost 90% growth was inhibited in all Candida strains at 200 µg/ml of ZnO QDs. Synergy between ZnO QDs and antifungal drugs at sub-inhibitory concentrations of each was assessed by checkerboard analysis and expressed in terms of the fractional inhibitory concentration (FIC) index. ZnO QDs were used with two different classes of antifungals (azoles and polyenes) against Candida isolates: combination 1 (with fluconazole); combination 2 (with ketoconazole); combination 3 (with amphotericin B), and combination 4 (with nystatin). Results demonstrated that the potency of combinations of ZnO QDs with antifungal drugs even at very low concentrations of each was higher than their individual activities against the fungal isolates. The FIC index was found to be less than 0.5 for all combinations in the checkerboard assay, which confirmed synergism between sub-inhibitory concentrations of ZnO QDs (25 µg/ml) and individual antifungal drugs. Synergism was further confirmed by spot assay where cell viabilities of Candida strains were significantly reduced in all combinations, which was clearly evident from the disappearance of fungal cells on agar plates containing antifungal combinations. For safer clinical use, the in vitro cytotoxic activity of ZnO QDs was assessed against HeLa cell line and it was found that ZnO QDs were non-toxic at 25 µg/ml. Results suggested that the combination of ZnO QDs with drugs potentiate antimicrobial activity through multitargeted action. ZnO QDs could therefore offer a versatile alternative in combination therapy against MDR fungal pathogens, wherein lowering drug concentrations could reduce toxicity and their multitargeted action could limit evolution of fungal drug resistance.

Facile Green Synthesis of Zinc Oxide Nanoparticles with Potential Synergistic Activity with Common Antifungal Agents against Multidrug-Resistant Candidal Strains

“…Overall, the potential synergistic efficiency of the biogenic ZnO NPs with different antifungal agents against the tested candidal pathogens highlights the potential of utilizing these nanomaterials in formulations of novel antifungal agents against multidrug-resistant candidal pathogens. The synergistic mode of between the biogenic ZnO NPs and antifungal drugs, such as nystatin, fluconazole, terbinafine and itraconazole, could be attributed to the fact that antifungal agents and ZnO NPs have different cellular targets, resulting in a boost in antifungal efficiency [89]. Combination therapy aims to reduce toxicity by lowering the standard administrative doses of drugs and boosting the antifungal effectiveness of conventional antifungal drugs [90].…”

“…Antagonistic antifungal action was detected between ZnO NPs and both clotrimazole and terbinafine against C. tropicalis. Collectively, the synergistic antifungal activity between the biogenic ZnO NPs and the tested antifungal agents highlights the potential of bioformulation of novel antifungal combinations to reduce the risk of acquiring antifungal resistance and lowering the toxicity of single-drug therapy [89].…”

Limitations of current chemotherapy and future of nanoformulation-based AmB delivery for visceral leishmaniasis—An updated review

“…Quantum dots are a new form of the fluorescent probe that can be used for biomolecular imaging, cellular imaging, drug delivery, and drug mechanism visualisation. Because of the simplicity of this technology, which has been widely used for anticancer studies, it can be used as a drug delivery vehicle, either naturally or as a QD conjugated drug, like AmB, to see its potential over conventional liposomal and NP-based delivery of AmB ( Chand et al, 2021 ).…”

Effect of Antioxidant on ROS Mediated Antifungal Action of ZnO Quantum Dots in Candida albicans

“…Metal and metal oxide nanoparticles (NPs) have shown tremendous potential against microbial cells. The therapeutic action of nanomaterials is selective and mostly based on constant dissolution of metallic nanoparticles into metal ions and production of ROS (6)(7)(8)(9). The release of metal ions and ROS from NPs is influenced by larger surface area to volume ratio, wherein smaller sized quantum dots (QDs) result in faster dissolution.…”

“…The release of metal ions and ROS from NPs is influenced by larger surface area to volume ratio, wherein smaller sized quantum dots (QDs) result in faster dissolution. In recent times, QDs (1-10 nm size) showed enhanced antimicrobial activity, predominantly via oxidative stress mediated by augmentation of intracellular ROS (7)(8). One such nanomaterial is Zinc Oxide (ZnO), which has shown wide range of applications in biosensing, drug delivery, photocatalysis and antimicrobials (10)(11)(12)(13)(14)(15)(16)(17)(18).…”