Quantified Efficiency of Membrane Leakage Events Relates to Antimicrobial Selectivity

Abstract

In many therapeutic strategies like killing pathogenic microbes by antimicrobial peptides, drug delivery, endosomal escape, and in disease-related processes such as apoptosis, the membrane is permeabilized. Our concept for quantifying the efficiency of individual membrane leakage events replaces less stringent descriptions of dye leakage. The concept is applicable to many types of leakage events including thinning, defects, (toroidal) pores, or channels. We measure release and fluorescence lifetime of a self-quenching dye. Apart from the dose-response, our analysis also quantifies the efficiency of individual leakage events. Additionally, cumulative leakage kinetics can indicate certain membrane permeabilization mechanisms. For example, applying our concept to three series of antimicrobial peptide analogues shows how the leakage mechanism and leakage efficiency of a given compound change with lipid composition. Thus, lipids play an important role for the selectivity of membrane permeabilization. I will also point out aspects to consider when comparing leakage in vesicle of various sizes or cells, the possible occurrence of more than one type of leakage event, and artefacts from vesicle aggregation or fusion. The concept for the quantitative description of leakage behaviour and understanding of leakage mechanisms aids the design and improvement of membrane-active antimicrobials.