title: New Insights Regarding Yeast Survival following Exposure to Liposomal Amphotericin B.
abstract: In vitro resistance to amphotericin B is an extremely rare event among pathogenic yeasts. However, in vivo response is sometimes reduced, resulting in an unfavorable outcome. Such adverse outcomes might be related to subfungicidal plasma concentrations. We aimed to clarify the mechanisms of liposomal amphotericin B (AMB-L; AmBisome)-induced lesions and the mechanisms responsible for yeast cell recovery following exposure at plasma concentrations. The physiological statuses developing following exposure to AMB-L at simulated plasma concentrations (20 to 0.1 mg/liter) and at a constant concentration (3 mg/liter) were assessed in a 24-h time course assay. Time-kill experiments also were carried out under the same AMB-L treatment conditions. Our results suggest that yeast cells develop compensatory responses related to membrane polarization, metabolic activity, and reactive oxygen species (ROS) production after exposure to high plasma concentrations (20 to 5 mg/liter) during the first 6 h; in the remaining 18 h, when exposed to lower concentrations, cells reveal almost full recovery with no evidence of fungicidal activity. In contrast, whenever cells are exposed to a constant concentration above the MIC, despite initially exhibiting compensatory stress responses, soon afterwards they exhibit membrane depolarization, a decrease of metabolic activity, increasing ROS production, and lastly, programmed cell death and necrosis, resulting in succumbing to AMB-L fungicidal effects. This study may represent a step forward in the support of AMB-L use for clinical treatment of invasive fungal infections, since it demonstrates the importance of maintaining levels of AMB-L above the MIC in plasma and tissues to ensure it produces its fungicidal effects.
authors.affiliation: Department of Microbiology, Faculty of Medicine, University of Porto, Porto, Portugal.
authors.forename: Rita
authors.initials: R
authors.lastname: Teixeira-Santos
authors.affiliation: Department of Microbiology, Faculty of Medicine, University of Porto, Porto, Portugal Center for Health Technology and Services Research (CINTESIS), Faculty of Medicine, University of Porto, Porto, Portugal.
authors.forename: Elisabete
authors.initials: E
authors.lastname: Ricardo
authors.affiliation: Center of Medical Research (CIM), Department of Biochemistry, Faculty of Medicine, University of Porto, Porto, Portugal Center for Neurosciences and Cell Biology (CNC), Faculty of Medicine, University of Coimbra, Coimbra, Portugal.
authors.forename: Susana Gomes
authors.initials: SG
authors.lastname: Guerreiro
authors.affiliation: Department of Microbiology, Faculty of Medicine, University of Porto, Porto, Portugal Center for Health Technology and Services Research (CINTESIS), Faculty of Medicine, University of Porto, Porto, Portugal.
authors.forename: Sofia
authors.identifier: http://orcid.org/0000-0003-2899-6615
authors.initials: S
authors.lastname: Costa-de-Oliveira
authors.affiliation: Department of Microbiology, Faculty of Medicine, University of Porto, Porto, Portugal Center for Health Technology and Services Research (CINTESIS), Faculty of Medicine, University of Porto, Porto, Portugal Burn Unit, Department of Plastic and Reconstructive Surgery, Hospital São João, Porto, Portugal.
authors.forename: Acácio Gonçalves
authors.initials: AG
authors.lastname: Rodrigues
authors.affiliation: Department of Microbiology, Faculty of Medicine, University of Porto, Porto, Portugal Center for Health Technology and Services Research (CINTESIS), Faculty of Medicine, University of Porto, Porto, Portugal Department of Microbiology, Hospital São João, Porto, Portugal cpinavaz@yahoo.com.
authors.forename: Cidália
authors.initials: C
authors.lastname: Pina-Vaz
mesh_terms: D000666:Amphotericin B / Q000494:pharmacology*; D000935:Antifungal Agents / Q000494:pharmacology; D008826:Microbial Sensitivity Tests; D012441:Saccharomyces cerevisiae / Q000187:drug effects*
chemical_list: D000935:Antifungal Agents; C068538:liposomal amphotericin B; D000666:Amphotericin B