The Impact of Membrane Composition and Co‐Drug Synergistic Effects on Vancomycin Association with Model Membranes from Electrochemical Impedance Spectroscopy

Abstract

The interaction of the antibacterial drug, vancomycin with microcavity suspended lipid bilayers (MSLB) was investigated using non‐Faradaic electrochemical impedance spectroscopy (EIS). Five MSLB compositions were prepared with increasing complexity at gold substrates: DOPC, DOPC:Chol, DOPC:SM:Chol, mammalian plasma membrane mimetic (MPM), and E. coli polar lipid extract. The latter two, are intended to mimic eukaryotic and bacterial inner membrane compositions respectively. The extent of vancomycin association and the impact drug association has on the electrochemical properties of the membrane depended on biomembrane composition. Trends were similar across all membranes but the E. coli membrane composition. Vancomycin increased membrane resistance and decreased capacitance in a saturable, concentration dependent manner, but for E. coli membrane resistance change was negligible and capacitance increased. Membrane resistance data was fit to the Langmuir‐Freundlich model to give quantitative insight into the relative extent of association of drug with membrane as a function of membrane composition. Overall, electrochemical data indicates that vancomycin associates at the interface of lipid membranes rather than penetrates the layer and this is promoted by the presence of anionic phospholipid. Interestingly, co‐incubation of the E. coli extract bilayer with both rifampicin and vancomycin, known to act synergistically, significantly promotes vancomycin association to E. coli membrane.

Interaction of Miltefosine with Microcavity Supported Lipid Membrane: Biophysical Insights from Electrochemical Impedance Spectroscopy

“…We, therefore, quote the relative change (Δ) in resistance and capacitance values from the initial values for the pristine bilayer absolute resistance for each substrate. The relative changes to membrane resistance ( Across replicate platforms, the absolute resistance of the membranes are closely replicated and of the order of DOPC : SM : Chol > MPM > DOPC : Chol > DOPC typically in the range~1-6 MΩ and CPE values are at 6-8 μF s mÀ 1 and this trend agress with previous reported observation [54].…”

“…In contrast, for the domain-forming membranes explored, DOPC : SM : Chol (Figure 2c) and MPM (Figure 2d), the changes to the impedance plots are not as significant as those for DOPC and DOPC : Chol membrane, indicating weaker extent of change to membrane admittance, which is likely consistent with tighter packing of the membranes containing both Chol and SM [52,54].…”

“…The fabrication of the microcavity pore array across ã 1 × 1 cm 2 gold electrode was achieved via controlled gold electrodeposition through polystyrene sphere template as previously described by us [36,[51][52][53][54]. Following the fabrication of the micropore array, the SAM modified electrodes were applied to layer by layer transfer of two lipid monolayers using the LB method to form the final MSLB.…”

“…The Bode plot shows the phase angle changes within different frequency ranges, 0.05 Hz to10 5 Hz (Figure 1a, inset). To gain quantitative estimation of membrane resistance and capacitance changes, the EIS data was fit to an equivalent circuit model (ECM), (solid lines in Figure 1) using a heuristic approach for the MSLB [54] as shown in Scheme 1c. The circuit applied, consists of three parallel components connected in series; a solution electrolyte resistance which is parallel to the stray capacitance (R el , C stray ), in series with a resister and a constant phase element (CPE), which are in parallel, and corresponds to the electric and dielectric properties of the lipid membrane deposited on the electrode surface (R M , Q M ), and, which is further connected in series with a resistor and CPE, which are also parallel and corresponds to the resistance and dielectric properties of cavity array (R array , Q array ).…”

“…Most importantly, in the case of buffer filled pore supported bilayers, they offer the advantage of a receiver aqueous reservoir, that SLBs lack, in contact with proximal leaflet, that mimics the cytoplasm [47][48][49][50]. We recently reported such microcavity array supported lipid bilayers (MSLB) formed on the gold substrate and applied as working electrodes for electrochemical measurements to study drug-membrane and protein-membrane interaction [36,[51][52][53][54].…”