Interfacial membrane effects of fluoroquinolones as revealed by a combination of fluorescence binding experiments and
M Teresa Montero1, Mònica Pijoan, Sandra Merino-Montero
1Departament de Fisicoquímica, Facultat de Farmàcia, Universitat de Barcelona, E-08028 Barcelona, Spain.
Abstract:
6-Fluoroquinolones are useful antimicrobial agents against gram-positive and gram-negative bacteria and some mycobacterial species as well. Although the diffusion through porins in gram-negative bacteria is well established, other mechanisms such as the hydrophobic pathway through the apolar regions of the bilayer and the self-promoted pathway appear to be relevant or concomitant with the hydrophilic pathway in many cases. This article discusses the interaction of ciprofloxacin (CPX) and two new synthesized compounds (M3CPX and M4CPX)-with a methyl group attached at the N3 and N4 positions of the piperazynil ring of the CPX-with liposomes and supported planar bilayers (SPBs) of Escherichia coli. Binding experiments using ANS revealed that the three compounds interact electrostatically with the bilayer. The variations in the electrostatic surface potential, which is always positive, were higher for M3CPX than for CPX or M4CPX. Related to that, the SPBs of E. coli were more affected by M3CPX than by the other two compounds, as judged by the analysis of the atomic force microcopy (AFM) images. The in situ injection of the three 6-fluoroquinolones (6-FQs) induced different changes in height, roughness (Ra), and area covered by the SPBs.
Insights
New fluoroquinolones (6-FQs) show distinct interactions with bacterial membranes. M3CPX and M4CPX, modified ciprofloxacin analogs, exhibit unique electrostatic and structural effects on Escherichia coli bilayers, impacting antimicrobial delivery mechanisms.
Area of Science:
- Microbiology
- Biophysics
- Medicinal Chemistry
Background:
- 6-Fluoroquinolones (6-FQs) are broad-spectrum antimicrobials effective against various bacteria and mycobacteria.
- Bacterial cell entry mechanisms for 6-FQs involve porins, hydrophobic pathways, and self-promoted pathways.
- Understanding drug-membrane interactions is crucial for optimizing antimicrobial efficacy.
Purpose of the Study:
- To investigate the interaction of ciprofloxacin (CPX) and two novel N-methylated derivatives (M3CPX, M4CPX) with bacterial membranes.
- To elucidate the role of structural modifications on the electrostatic and physical properties of bacterial bilayers.
- To compare the membrane perturbation effects of CPX, M3CPX, and M4CPX on Escherichia coli.
Main Methods:
- Binding experiments using 8-anilino-1-naphthalenesulfonic acid (ANS) to assess electrostatic interactions.
- Atomic Force Microscopy (AFM) to analyze changes in supported planar bilayers (SPBs) of E. coli.
- In situ injection of fluoroquinolones to observe real-time effects on bilayer morphology.
Main Results:
- All three 6-FQs (CPX, M3CPX, M4CPX) demonstrated electrostatic interaction with the liposomes and SPBs.
- M3CPX induced greater variations in the positive electrostatic surface potential compared to CPX and M4CPX.
- AFM analysis revealed that M3CPX caused more significant alterations in E. coli SPBs, affecting height, roughness, and area.
Conclusions:
- Structural modifications in 6-FQs, specifically N-methylation, influence their electrostatic interactions with bacterial membranes.
- The observed membrane perturbations suggest that M3CPX may have distinct cellular entry or activity mechanisms.
- These findings contribute to understanding fluoroquinolone-membrane dynamics and designing improved antimicrobial agents.
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