Effect of Ursolic and Oleanolic Acids on Lipid Membranes: Studies on MRSA and Models of Membranes

Abstract

Staphylococcus aureus is an opportunistic pathogen and the major causative agent of life-threatening hospital- and community-acquired infections. A combination of antibiotics could be an opportunity to address the widespread emergence of antibiotic-resistant strains, including Methicillin-Resistant S. aureus (MRSA). We here investigated the potential synergy between ampicillin and plant-derived antibiotics (pentacyclic triterpenes, ursolic acid (UA) and oleanolic acid (OA)) towards MRSA (ATCC33591 and COL) and the mechanisms involved. We calculated the Fractional Inhibitory Concentration Index (FICI) and demonstrated synergy. We monitored fluorescence of Bodipy-TR-Cadaverin, propidium iodide and membrane potential-sensitive probe for determining the ability of UA and OA to bind to lipoteichoic acids (LTA), and to induce membrane permeabilization and depolarization, respectively. Both pentacyclic triterpenes were able to bind to LTA and to induce membrane permeabilization and depolarization in a dose-dependent fashion. These effects were not accompanied by significant changes in cellular concentration of pentacyclic triterpenes and/or ampicillin, suggesting an effect mediated through lipid membranes. We therefore focused on membranous effects induced by UA and OA, and we investigated on models of membranes, the role of specific lipids including phosphatidylglycerol and cardiolipin. The effect induced on membrane fluidity, permeability and ability to fuse were studied by determining changes in fluorescence anisotropy of DPH/generalized polarization of Laurdan, calcein release from liposomes, fluorescence dequenching of octadecyl-rhodamine B and liposome-size, respectively. Both UA and OA showed a dose-dependent effect with membrane rigidification, increase of membrane permeabilization and fusion. Except for the effect on membrane fluidity, the effect of UA was consistently higher compared with that obtained with OA, suggesting the role of methyl group position. All together the data demonstrated the potential role of compounds acting on lipid membranes for enhancing the activity of other antibiotics, like ampicillin and inducing synergy. Such combinations offer an opportunity to explore a larger antibiotic chemical space.

Design and Preparation of Antimicrobial Agents

“…The potential synergy between ampicillin and plant antibiotics (pentacyclic triterpenes, ursolic acid (UA) and oleanolic acid (OA)) against MRSA (ATCC33591 and COL) and the mechanisms involved were studied by Verstraeten S. et al [ 4 ]. They monitored the fluorescence of Bodipy-TR-Cadaverin, propidium iodide, and membrane-potential-sensitive probes to determine the ability of UA and OA to bind to lipoteichoic acids (LTAs) and induce membrane permeabilization and depolarization, respectively.…”

18β-Glycyrrhetinic Acid Induces Metabolic Changes and Reduces Staphylococcus aureus Bacterial Cell-to-Cell Interactions

“…TCA cycle activity and amino acid catabolism may also reflect the potential turnover of membrane lipids in response to the increased production of STX, as this process requires a significant amount of energy. Furthermore, previous research on other pentacyclic triterpenes (i.e., ursolic acid and oleanolic acid) has shown that incorporation of these molecules into cellular membranes changes membrane fluidity and leads to increased membrane rigidity [ 41 ].…”

“…Previous work on other triterpenes have found that their antibacterial activity is specific to Gram-positive microorganisms [ 41 , 42 , 45 ], including biofilm inhibition and reduction [ 46 , 47 ]. Despite GRA lacking bactericidal activity against MRSA biofilms, it is effective at reducing bacterial bioburden in two different biofilm models, suggesting that even at sub-lethal doses, GRA is potentially useful as a biofilm dispersal agent.…”

Thiazolopyrimidinone Derivative H5–23 Enhances Daptomycin Activity against Linezolid-Resistant Enterococcus faecalis by Disrupting the Cell Membrane

“…Laurdan GP was calculated based on previous studies. 36 Membrane Permeability Assay. E. faecalis OG1RF overnight cultures were diluted 200-fold (1 × 10 7 CFU) and incubated with HEPES medium.…”