Investigating the biophysical interactions of antimicrobial fatty acids and liposomal fatty acids with model membrane platforms and their correlation to biological activity

• Main Author: Shin, Sungmin
• Other Authors: Cho Nam-Joon
• Format: Thesis-Doctor of Philosophy
• Language: English
• Published: Nanyang Technological University 2025
• Subjects: Chemistry; Engineering; Medicine, Health and Life Sciences
• Online Access: https://hdl.handle.net/10356/182351
• Institution: Nanyang Technological University

The growing challenge posed by antimicrobial resistance (AMR) has prompted the exploration of innovative approaches to combat bacterial infections. Among these, long-chain fatty acids (LCFAs) and liposomes loaded with LCFAs (LipoFAs) have emerged as promising contenders against AMR. However, existing research primarily focuses on evaluating their antibacterial impacts on bacteria using biological methods. The design of these agents often relies on traditional assay methods that fail to accurately replicate the complexity of bacterial membranes, including the presence of charged phospholipids, nanometer dimensions, and other intricacies within the bacterial membranes. While it is known that LCFAs and LipoFAs exhibit membrane-active modes of action against the bacterial membranes, the detailed mechanisms of their interactions with membranes remain unclear. Herein, the development of a systematic analytical framework using supported lipid bilayer (SLB) platforms was reported to investigate how LCFAs, specifically linolenic acid (LNA), linoleic acid (LLA), and oleic acid (OA), and LipoFAs, including LNA-loaded liposomes (lipoLNA), LLA-loaded liposomes (LipoLLA), and OA-loaded liposomes (LipoOA), interact with model membrane systems. The central hypothesis of this thesis posits that SLBs can serve as predictive models for determining the antimicrobial efficacy and mechanisms of action (MOA) of LCFAs and LipoFAs. To test this hypothesis, single-component and multi-component SLBs, designed to closely mimic the composition and structure of bacterial membranes, were fabricated to study membrane interactions. Biophysical experimental findings revealed that LCFAs induce tubular formations and exhibit critical micelle concentration (CMC)-dependent membrane-disruptive behavior on single-component SLBs. Additionally, LNA and LLA exhibited interaction behaviors correlated with the CMC on multi-component bacterial membrane SLBs, leading to membrane remodeling and morphological changes at concentrations above CMC values. In contrast, OA exhibited CMC-independent activity, showing membrane insertion into the model membrane platform. LNA and LLA exhibited bactericidal effects, enhancing membrane permeability and ATP leakage, while OA, characterized by CMC-independent activity profile, exhibited potent bactericidal effects by penetrating the SLBs effectively, increasing membrane permeability and ATP leakage. The observed activities of LCFAs on S. aureus correlated with their behavior on Gram-positive bacterial model membranes, highlighting the significance of multiple-component model systems in understanding antimicrobial activity. The study also explored the mechanistic interactions between LipoFAs and model bacterial membranes, revealing that LipoLNA and LipoLLA, encapsulated with FAs with higher degrees of unsaturation, induced a curved membrane surface morphology due to higher curvature stress, potentially increasing membrane permeability and leakage of intracellular ATP. These changes correlated with stronger bacteriostatic and bactericidal effects on S. aureus MW2. Overall, this research contributes to the ongoing efforts to combat AMR by elucidating the efficacy of antimicrobial agents and highlights the potential of using biologically relevant model membrane systems to develop innovative strategies for designing effective therapeutic agents in healthcare and biotechnology.