Unveiling the Synergistic Interaction Between Liposomal Amphotericin B and Colistin.

Rita Teixeira-Santos,Acácio G Rodrigues,Ricardo J Branco,Elisabete Ricardo,Maria M Azevedo,Cidália Pina-Vaz

doi:10.3389/fmicb.2016.01439

Abstract

Patients with multiple comorbidities are often administered simultaneously or sequentially antifungals and antibacterial agents, without full knowledge of the consequences of drug interactions. Considering the clinical relevance of liposomal amphotericin B (L-AMB), the association between L-AMB and six antibacterial agents was evaluated against four clinical isolates and one type strain of Candida spp. and two clinical isolates and one type strain of Aspergillus fumigatus. In order to evaluate such combined effects, the minimal inhibitory concentration (MIC) of L-AMB was determined in the presence of 0.5-, 1-, 2-, and 4-fold peak plasma concentrations of each of the antibacterial drugs. Since the L-AMB/colistin (CST) association was the most synergic, viability assays were performed and the physiological status induced by this association was characterized. In addition, computational molecular dynamics studies were also performed in order to clarify the molecular interaction. The maximum synergistic effect with all antibacterial agents, except CST, was reached at fourfold the usual peak plasma concentrations, resulting in 2-to 8-fold L-AMB MIC reduction for Candida and 2-to 16-fold for Aspergillus. For CST, the greatest synergism was registered at peak plasma concentration (3 mg/L), with 4-to 8-fold L-AMB MIC reduction for Candida and 16-to 32-fold for Aspergillus. L-AMB at subinhibitory concentration (0.125 mg/L) combined with CST 3 mg/L resulted in: a decrease of fungal cell viability; an increase of cell membrane permeability; an increase of cellular metabolic activity soon after 1 h of exposure, which decreased until 24 h; and an increase of ROS production up to 24 h. From the molecular dynamics studies, AMB and CST molecules shown a propensity to form a stable molecular complex in solution, conferring a recognition and binding added value for membrane intercalation. Our results demonstrate that CST interacts synergistically with L-AMB, forming a stable complex, which promotes the fungicidal activity of L-AMB at low concentration.

Highlights

Fungi are recognized as major pathogens in critically ill patients
In the case of synergistic interaction, we have investigated using molecular dynamics (MD) simulations whether (i) the antibacterial agent has an intrinsic activity upon fungal cells; or (ii) the antibacterial agent acts as a facilitator of amphotericin B (AMB) activity
The maximum effect of these antibacterial agents was obtained at fourfold plasma concentrations with a reduction of liposomal amphotericin B (L-AMB) minimal inhibitory concentration (MIC) of 2-to 8-fold, in the case of Candida and 2-to 16fold for A. fumigatus (Table 1)

Summary

Introduction

Fungi are recognized as major pathogens in critically ill patients. Candida and Aspergillus species are the most common agents of invasive fungal infections (IFIs), other yeasts and filamentous fungi are becoming emerging pathogens (Gullo, 2009). Patients at risk for IFIs often receive concomitantly or sequentially antifungal therapy and antibacterial agents, either for prophylactic or therapeutic purposes (Stergiopoulou et al, 2009) This procedure is often adopted without full knowledge of the consequences resulting from pharmacological drug interactions. The echinocandin weakens the fungal cell wall facilitating the colistin action upon fungal membranes, and, this effect enhances the antifungal activity of the echinocandin (Zeidler et al, 2013) These results are promising since the available antifungal panoply is narrow, encompassing only a few classes of agents, and the discovery of new drugs is a slow and exhaustive process (Roemer and Boone, 2013). The association of compounds that enhance the efficacy of antifungal drugs may contribute to a more effective reduction of fungal burden and minimize the development of resistance (Zeidler et al, 2013)

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Conclusion