Interaction of gramicidin with DPPC/DODAB bilayer fragments

DODAB vesicles containing lysophosphatidylcholines: The relevance of acyl chain saturation on the membrane structure and thermal properties

The saturated LPC18:0 and unsaturated LPC18:1 lysophosphatidylcholines have important roles in inflammation and immunity and are interesting targets for immunotherapy. The synthetic cationic lipid DODAB has been successfully employed in delivery systems, and would be a suitable carrier for those lysophosphatidylcholines. Here, assemblies of DODAB and LPC18:0 or LPC18:1 were characterized by Differential Scanning Calorimetry (DSC) and Electron Paramagnetic Resonance (EPR) spectroscopy. LPC18:0 increased the DODAB gel-fluid transition enthalpy and rigidified both phases. In contrast, LPC18:1 caused a decrease in the DODAB gel-fluid transition temperature and cooperativity, associated with two populations with distinct rigidities in the gel phase. In the fluid phase, LPC18:1 increased the surface order but, differently from LPC18:0, did not affect viscosity at the membrane core. The impact of the different acyl chains of LPC18:0 and 18:1 on structure and thermotropic behavior should be considered when developing applications using mixed DODAB membranes.

Increased delivery and cytotoxicity of doxorubicin in HeLa cells using the synthetic cationic peptide pEM-2 functionalized liposomes

HYPOTHESIS

Due to the inability of nano-carriers to passively cross the cell membrane, cell penetration enhancers are used to accelerate cytoplasmic delivery of antineoplastic drugs. In this regard, snake venom phospholipase A2 peptides are known for their ability to destabilize natural and artificial membranes. In this context, functionalized liposomes with peptide pEM-2 should favor the incorporation of doxorubicin and increase its cytotoxicity in HeLa cells compared to free doxorubicin, and doxorubicin encapsulated in non-functionalized liposomes.

EXPERIMENTS

Several characteristics were monitored, including doxorubicin loading capacity of the liposomes, as well as the release and uptake before and after functionalization. Cell viability and half-maximal inhibition concentrations were determined in HeLa cells.

FINDINGS

In vitro studies showed that functionalization of doxorubicin-loaded PC-NG liposomes with pEM-2 not only improved the amount of doxorubicin delivered compared to free doxorubicin or other doxorubicin-containing formulations, but also showed enhanced cytotoxicity against HeLa cells. The PC-NG liposomes loaded with doxorubicin improved treatment efficacy by reducing the IC₅₀ value and incubation time. This increase in cell toxicity was directly related to the concentration of pEM-2 peptide bound to the liposomes. We conclude that the cytotoxicity observed in HeLa cells due to the action of doxorubicin was strongly favored when encapsulated in synthetic liposomes and functionalized with the pEM-2 peptide.

Cationic Nanostructures as Adjuvants for Vaccines

Spherical or discoidal lipid polymer nanostructures bearing cationic charges successfully adsorb a variety of oppositely charged antigens (Ag) such as proteins, peptides, nucleic acids, or oligonucleotides. This report provides instructions for the preparation and physical characterization of four different cationic nanostructures able to combine and deliver antigens to the immune system: (1) dioctadecyl dimethylammonium bromide (DODAB) bilayer fragments (DODAB BF); (2) polystyrene sulfate (PSS) nanoparticles (NPs) covered with one cationic dioctadecyl dimethylammonium bromide bilayer (DODAB) named (PSS/DODAB); (3) cationic NPs of biocompatible polymer poly(methyl methacrylate) (PMMA) prepared by emulsion polymerization of the methyl methacrylate (MMA) monomer in the presence of DODAB BF (PMMA/DODAB NPs); (4) antigen NPs (NPs) where the cationic polymer poly(diallyl dimethyl ammonium chloride) (PDDA) directly combined at nontoxic and low dose with the antigen (Ag); when the oppositely charged model antigen is ovalbumin (OVA), NPs are named PDDA/OVA. These nanostructures provide adequate microenvironments for carrying and delivering antigens to the antigen-presenting cells of the immune system.

Supramolecular Nanostructures for Vaccines

Although this is an era of pandemics and many devastating diseases, this is also a time when bionanotechnology flourishes, illuminating a multidisciplinary field where vaccines are quickly becoming a balsam and a prevention against insidious plagues. In this work, we tried to gain and also give a deeper understanding on nanovaccines and their way of acting to prevent or cure cancer, infectious diseases, and diseases caused by parasites. Major nanoadjuvants and nanovaccines are temptatively exemplified trying to contextualize our own work and its relative importance to the field. The main properties for novel adjuvants seem to be the nanosize, the cationic character, and the biocompatibility, even if it is achieved in a low dose-dependent manner.

Cationic and Biocompatible Polymer/Lipid Nanoparticles as Immunoadjuvants

Nanostructures have been of paramount importance for developing immunoadjuvants. They must be cationic and non-cytotoxic, easily assembling with usually oppositely charged antigens such as proteins, haptens or nucleic acids for use in vaccines. We obtained optimal hybrid nanoparticles (NPs) from the biocompatible polymer poly(methyl methacrylate) (PMMA) and the cationic lipid dioctadecyl dimethyl ammonium bromide (DODAB) by emulsion polymerization of methyl methacrylate (MMA) in the presence of DODAB. NPs adsorbed ovalbumin (OVA) as a model antigen and we determined their adjuvant properties. Interestingly, they elicited high double immune responses of the cellular and humoral types overcoming the poor biocompatibility of DODAB-based adjuvants of the bilayer type. The results suggested that the novel adjuvant would be possibly of use in a variety of vaccines.

Antimicrobial Polymer-Based Assemblies: A Review

An antimicrobial supramolecular assembly (ASA) is conspicuous in biomedical applications. Among the alternatives to overcome microbial resistance to antibiotics and drugs, ASAs, including antimicrobial peptides (AMPs) and polymers (APs), provide formulations with optimal antimicrobial activity and acceptable toxicity. AMPs and APs have been delivered by a variety of carriers such as nanoparticles, coatings, multilayers, hydrogels, liposomes, nanodisks, lyotropic lipid phases, nanostructured lipid carriers, etc. They have similar mechanisms of action involving adsorption to the cell wall, penetration across the cell membrane, and microbe lysis. APs, however, offer the advantage of cheap synthetic procedures, chemical stability, and improved adsorption (due to multipoint attachment to microbes), as compared to the expensive synthetic routes, poor yield, and subpar in vivo stability seen in AMPs. We review recent advances in polymer-based antimicrobial assemblies involving AMPs and APs.

Biomimetic Lipid Polymer Nanoparticles for Drug Delivery

Biomimetic nanoparticles are hybrid nanostructures in which the uppermost layer is similar to a cell membrane. In these nanoparticles, lipids and biopolymers can be organized to improve drug incorporation and delivery. This report provides instructions for the preparation and physical characterization of four different biomimetic nanoparticles: (1) polystyrene sulphate (PSS) nanoparticles covered with one cationic dioctadecyl dimethylammonium bromide bilayer (DODAB), which incorporates dimeric channels of the antimicrobial peptide Gramicidin D; (2) silica nanoparticles covered with one single bilayer of the antimicrobial cationic lipid DODAB; (3) hybrid lipid/polymer indomethacin (IND) nanoparticles from injection of IND/DODAB ethanolic solution in a water solution of carboxymethyl cellulose (CMC); (4) bactericidal and fungicidal nanoparticles from DODAB bilayer fragments (BF) covered consecutively by a CMC and a poly(diallyl dimethyl ammonium chloride) (PDDA) layer. These examples provide the basis for the preparation and characterization of novel biomimetic nanoparticles with lipids and/or biopolymers in their composition. The polymers and lipids in the hybrid nanoparticle composition may impart stability and/or bioactivity and/or provide adequate microenvironments for carrying bioactive drugs and biomolecules.

Deciphering the Structure of the Gramicidin A Channel in the Presence of AOT Reverse Micelles in Pentane Using Molecular Dynamics Simulations

Structural studies of proteins and, in particular, integral membrane proteins (IMPs) using solution NMR spectroscopy approaches are challenging due to not only their inherent structural complexities but also the fact that they need to be solubilized in biomimetic environments (such as micelles), which enhances the slow molecular reorientation. To deal with these difficulties and increase the effective rate of molecular reorientation, the encapsulation of IMPs in the aqueous core of the reverse micelle (RM) dissolved in a low-viscosity solvent has been proven to be a viable approach. However, the effect of the reverse micelle (RM) environment on the IMP structure and function is little known. To gain insight into these aspects, this article presents a series of atomistic unconstrained molecular dynamics (MD) of a model ion channel (gramicidin A, gA) with RMs formed with anionic surfactant diacyl chain bis(2-ethylhexyl) sodium succinate (AOT) in pentane at a water-to-surfactant molar ratio (W₀) of 6. The simulations were carried out with different protocols and starting conditions for a total of 2.4 μs and were compared with other MDs used with the gA channel inserted in models of the SDS micelle or the DMPC membrane. We show here that in the presence of AOT RMs the gA dimer did not look like the "dumbbell-like" model anticipated by experiments, where the C-terminal parts of the gA are capped with two RMs and the rest of the dimer is protected from the oil solvent by the AOT acyl chains. In contrast, the MD simulations reveal that the AOT, Na⁺, and water formed two well-defined and elongated RMs attached to the C-terminal ends of the gA dimer, while the rest is in direct contact with the pentane. The initial β^6.3 secondary structure of the gA is well conserved and filled with 6-9 waters, as in SDS micelles or the DMPC membrane. Finally, the water movement inside the gA is strongly affected by the presence of RMs at each extremity, and no passage of water molecules through the gA channel is observed even after a long simulation period, whereas the opposite was found for gA in SDS and DMPC.

The Effect of Calcium and Halide Ions on the Gramicidin A Molecular State and Antimicrobial Activity

Gramicidin A (gA) forms several convertible conformations in different environments. In this study, we investigated the effect of calcium halides on the molecular state and antimicrobial activity of gramicidin A. The molecular state of gramicidin A is highly affected by the concentration of calcium salt and the type of halide anion. Gramicidin A can exist in two states that can be characterized by circular dichroism (CD), mass, nuclear magnetic resonance (NMR) and fluorescence spectroscopy. In State 1, the main molecular state of gramicidin A is as a dimer, and the addition of calcium salt can convert a mixture of four species into a single species, which is possibly a left-handed parallel double helix. In State 2, the addition of calcium halides drives gramicidin A dissociation and denaturation from a structured dimer into a rapid equilibrium of structured/unstructured monomer. We found that the abilities of dissociation and denaturation were highly dependent on the type of halide anion. The dissociation ability of calcium halides may play a vital role in the antimicrobial activity, as the structured monomeric form had the highest antimicrobial activity. Herein, our study demonstrated that the molecular state was correlated with the antimicrobial activity.

Cationic Nanostructures for Vaccines Design

Subunit vaccines rely on adjuvants carrying one or a few molecular antigens from the pathogen in order to guarantee an improved immune response. However, to be effective, the vaccine formulation usually consists of several components: an antigen carrier, the antigen, a stimulator of cellular immunity such as a Toll-like Receptors (TLRs) ligand, and a stimulator of humoral response such as an inflammasome activator. Most antigens are negatively charged and combine well with oppositely charged adjuvants. This explains the paramount importance of studying a variety of cationic supramolecular assemblies aiming at the optimal activity in vivo associated with adjuvant simplicity, positive charge, nanometric size, and colloidal stability. In this review, we discuss the use of several antigen/adjuvant cationic combinations. The discussion involves antigen assembled to 1) cationic lipids, 2) cationic polymers, 3) cationic lipid/polymer nanostructures, and 4) cationic polymer/biocompatible polymer nanostructures. Some of these cationic assemblies revealed good yet poorly explored perspectives as general adjuvants for vaccine design.

Hybrid Nanoparticles of Poly (Methyl Methacrylate) and Antimicrobial Quaternary Ammonium Surfactants

Quaternary ammonium surfactants (QACs) are microbicides, whereas poly (acrylates) are biocompatible polymers. Here, the physical and antimicrobial properties of two QACs, cetyl trimethyl ammonium bromide (CTAB) or dioctadecyl dimethyl ammonium bromide (DODAB) in poly (methyl methacrylate) (PMMA) nanoparticles (NPs) are compared to those of QACs alone. Methyl methacrylate (MMA) polymerization using DODAB or CTAB as emulsifiers and initiator azobisisobutyronitrile (AIBN) yielded cationic, nanometric, homodisperse, and stable NPs. NPs’ physical and antimicrobial properties were assessed from dynamic light scattering (DLS), scanning electron microscopy, and viability curves of Escherichia coli, Staphylococcus aureus, or Candida albicans determined as log(colony-forming unities counting) over a range of [QACs]. NPs were spherical and homodisperse but activity for free QACs was higher than those for QACs in NPs. Inhibition halos against bacteria and yeast were observed only for free or incorporated CTAB in NPs because PMMA/CTAB NPs controlled the CTAB release. DODAB displayed fungicidal activity against C. albicans since DODAB bilayer disks could penetrate the outer glycoproteins fungus layer. The physical properties and stability of the cationic NPs highlighted their potential to combine with other bioactive molecules for further applications in drug and vaccine delivery.

Identification of Effective Dimeric Gramicidin-D Peptide as Antimicrobial Therapeutics over Drug Resistance: In-Silico Approach

Discovering and developing the antimicrobial peptides are recently focused on pharmaceutical firm, since they serve as complementary to antibiotics in prevailing over drug resistance by eliciting the disruption of microbial membrane. Still, there are lots of challenges to bring up the structurally stable and functionally efficient antimicrobial peptides. It is well known that gramicidin D is the prominent antimicrobial peptide that exists as g-AB, g-BC, and g-AC. This study analyzes the structural stability and the functional activity of hetero-dimeric double-stranded gramicidin-D peptides, thereby demonstrating its potent antimicrobial activity against antibiotic-resistant micro-organisms. To investigate the structural stability and functionality of gramicidin D, we performed static and dynamic analysis. Initially, we observed a maximum number of intermolecular interactions and membrane penetration in g-AB as compared to g-BC and g-AC. To substantiate further, the geometrical and thermodynamic parameters revealed the retention of maximum stability in g-AB than g-AC and g-BC. Thus, the conformational free energy and the binding free energy showed the variation among gramicidin-D peptides for the prediction of increased stability and functionality. In conclusion, g-AB peptide has definitely demonstrated adequate structural stability and functionality and this work will need to be considered in peptide-based drug discovery.

Self-Assembled Antimicrobial Nanomaterials

Nanotechnology came to stay improving the quality of human life by reducing environmental contamination of earth and water with pathogens. This review discusses how self-assembled antimicrobial nanomaterials can contribute to maintain humans, their water and their environment inside safe boundaries to human life even though some of these nanomaterials display an overt toxicity. At the core of their strategic use, the self-assembled antimicrobial nanomaterials exhibit optimal and biomimetic organization leading to activity at low doses of their toxic components. Antimicrobial bilayer fragments, bilayer-covered or multilayered nanoparticles, functionalized inorganic or organic polymeric materials, coatings and hydrogels disclose their potential for environmental and public health applications in this review.

Antibacterial Activity of Vancomycin Encapsulated in Poly(DL-lactide-co-glycolide) Nanoparticles Using Electrospraying

Vancomycin is often used to treat infections caused by β-lactam-resistant bacteria. However, methicillin-resistant strains of Staphylococcus aureus (MRSA) acquired resistance to vancomycin, rendering it less effective in the treatment of serious infections. In the search for novel antibiotics, alternative delivery mechanisms have also been explored. In this study, we report on the encapsulation of vancomycin in PLGA [poly(DL-lactide-co-glycolide)] nanoparticles by electrospraying. The nanoparticles were on average 247 nm in size with small bead formations on the surface. Clusters of various sizes were visible under the SEM (scanning electron microscope). Vancomycin encapsulated in PLGA (VNP) was more effective in inhibiting the growth of S. aureus Xen 31 (MRSA) and S. aureus Xen 36 than un-encapsulated vancomycin. Encapsulated vancomycin had a minimum inhibitory concentration (MIC) of 1 μg/mL against MRSA compared to 5 μg/mL of free vancomycin. At least 70% (w/w) of the vancomycin was encapsulated. Thirty percent of the vancomycin was released within the first 144 h, followed by slow release over 10 days. Vancomycin encapsulated in PLGA nanoparticles may be used to treat serious infections.

The antibacterial and antibiofilm efficacies of a liposomal peptide originating from rice bran protein against Listeria monocytogenes

With the aim of exploring a natural antilisterial peptide from food-derived origin, an antibacterial peptide named as Alpep7 was purified from the bromelain hydrolysate of rice bran protein (RBP) in this study. The resulting amino acid consequence was identified as KVDHFPL (Lys-Val-Asp-His-Phe-Pro-Leu) by ultraperformance liquid chromatography tandem matrix-assisted laser desorption/ionisation quadrupole time-of-flight mass spectrometry (MALDI Q-TOF MS). In addition, to assess the probability of the targeted delivery of liposome encapsulation of the peptide to Listeria biofilm, Alpep7-loaded liposomes were further prepared from a mixture of dipalmitoylphosphatidylcholine, stearylamine and cholesterol in a molar ratio of 10 : 3 : 2 and characterised by the analysis of particle size, zeta potential, microtopography and storage stability. The results showed that the liposomes exhibited a well-defined spherical shape, with an average diameter below 200 nm. The liposomes maintained favourable stability after storage at 4 °C for 4 weeks. Comparisons between the activities of free and liposomal Alpep7 via microbroth dilution, regrowth analysis and confocal scanning laser microscopy suggested that liposomal delivery was more effective during the initial exposure of the liposomes to the biofilms. The thermodynamic analysis indicated that the adsorption of liposomal Alpep7 to the listerial biofilm was a spontaneous, exothermic process. The results may provide a natural means for the treatment of listerial contamination and guide the potential application of liposomes for the targeted delivery of antimicrobials to pathogenic biofilms in the food industry.

Intrinsic Fluorescence of PAMAM Dendrimers-Quenching Studies

Intrinsic, non-traditional fluorescence of polyamidoamine (PAMAM) dendrimers that do not possess classical fluorophores has been attracting considerable interest for the last decade. Many hypotheses regarding the source of the fluorescence have appeared, but some of them are still disputable. In order to shed new light on the nature of the phenomenon, we applied quenchers that are normally used to study intrinsic fluorescence of proteins (i.e., KI, CsCl, and acrylamide). KI and acrylamide efficiently quenched steady state fluorescence of PAMAM G2, PAMAM G3, and PAMAM G4 dendrimers. Stern-Volmer plots exhibited a downward curvature that has been elucidated by heterogenous emission. We assume that there are two distinct fluorescent moieties in the dendrimer structure that are characterized by different accessibility to the quenchers.

Cationic Biomimetic Particles of Polystyrene/Cationic Bilayer/Gramicidin for Optimal Bactericidal Activity

Nanostructured particles of polystyrene sulfate (PSS) covered by a cationic lipid bilayer of dioctadecyldimethylammonium bromide (DODAB) incorporated gramicidin D (Gr) yielding optimal and broadened bactericidal activity against both Escherichia coli and Staphylococcus aureus. The adsorption of DODAB/Gr bilayer onto PSS nanoparticles (NPs) increased the zeta-average diameter by 8–10 nm, changed the zeta-potential of the NPs from negative to positive, and yielded a narrow size distributions for the PSS/DODAB/Gr NPs, which displayed broad and maximal microbicidal activity at very small concentrations of the antimicrobials, namely, 0.057 and 0.0057 mM DODAB and Gr, respectively. The results emphasized the advantages of highly-organized, nanostructured, and cationic particles to achieve hybrid combinations of antimicrobials with broad spectrum activity at considerably reduced DODAB and Gr concentrations.

Biomimetic Cationic Nanoparticles Based on Silica: Optimizing Bilayer Deposition from Lipid Films

The optimization of bilayer coverage on particles is important for a variety of biomedical applications, such as drug, vaccine, and genetic material delivery. This work aims at optimizing the deposition of cationic bilayers on silica over a range of experimental conditions for the intervening medium and two different assemblies for the cationic lipid, namely, lipid films or pre-formed lipid bilayer fragments. The lipid adsorption on silica in situ over a range of added lipid concentrations was determined from elemental analysis of carbon, hydrogen, and nitrogen and related to the colloidal stability, sizing, zeta potential, and polydispersity of the silica/lipid nanoparticles. Superior bilayer deposition took place from lipid films, whereas adsorption from pre-formed bilayer fragments yielded limiting adsorption below the levels expected for bilayer adsorption.

Ion-pair amphiphile: a neoteric substitute that modulates the physicochemical properties of biomimetic membranes

Ion-pair amphiphiles (IPAs) are neoteric pseudo-double-tailed compounds with potential as a novel substitute of phospholipid. IPA, synthesized by stoichiometric/equimolar mixing of aqueous solution of hexadecyltrimethylammonium bromide (HTMAB) and sodium dodecyl sulfate (SDS), was used as a potential substituent of naturally occurring phospholipid, soylecithin (SLC). Vesicles were prepared using SLC and IPA in different ratios along with cholesterol. The impact of IPA on SLC was examined by way of surface pressure (π)-area (A) measurements. Associated thermodynamic parameters were evaluated; interfacial miscibility between the components was found to depend on SLC/IPA ratio. Solution behavior of the bilayers, in the form of vesicles, was investigated by monitoring the hydrodynamic diameter, zeta potential, and polydispersity index over a period of 100 days. Size and morphology of the vesicles were also investigated by electron microscopic studies. Systems comprising 20 and 40 mol % IPA exhibited anomalous behavior. Thermal behavior of the vesicles, as scrutinized by differential scanning calorimetry, was correlated with the hydrocarbon chain as well as the headgroup packing. Entrapment efficiency (EE) of the vesicles toward the cationic dye methylene blue (MB) was also evaluated. Vesicles were smart enough to entrap the dye, and the efficiency was found to vary with IPA concentration. EE was found to be well above 80% for some stable dispersions. Such formulations thus could be considered to have potential as novel drug delivery systems.

Novel formulations for antimicrobial peptides

Peptides in general hold much promise as a major ingredient in novel supramolecular assemblies. They may become essential in vaccine design, antimicrobial chemotherapy, cancer immunotherapy, food preservation, organs transplants, design of novel materials for dentistry, formulations against diabetes and other important strategical applications. This review discusses how novel formulations may improve the therapeutic index of antimicrobial peptides by protecting their activity and improving their bioavailability. The diversity of novel formulations using lipids, liposomes, nanoparticles, polymers, micelles, etc., within the limits of nanotechnology may also provide novel applications going beyond antimicrobial chemotherapy.

Novel gramicidin formulations in cationic lipid as broad-spectrum microbicidal agents

Dioctadecyldimethylammonium bromide (DODAB) is an antimicrobial lipid that can be dispersed as large closed bilayers (LV) or bilayer disks (BF). Gramicidin (Gr) is an antimicrobial peptide assembling as channels in membranes and increasing their permeability towards cations. In mammalian cells, DODAB and Gr have the drawbacks of Gram-positive resistance and high toxicity, respectively. In this study, DODAB bilayers incorporating Gr showed good antimicrobial activity and low toxicity. Techniques employed were spectroscopy, photon correlation spectroscopy for sizing and evaluation of the surface potential at the shear plane, turbidimetric detection of dissipation of osmotic gradients in LV/Gr, determination of bacterial cell lysis, and counting of colony-forming units. There was quantitative incorporation of Gr and development of functional channels in LV. Gr increased the bilayer charge density in LV but did not affect the BF charge density, with localization of Gr at the BF borders. DODAB/Gr formulations substantially reduce Gr toxicity against eukaryotic cells and advantageously broaden the antimicrobial activity spectrum, effectively killing Escherichia coli and Staphylococcus aureus bacteria with occurrence of cell lysis.

The self-assembly of a cyclic lipopeptides mixture secreted by a B. megaterium strain and its implications on activity against a sensitive Bacillus species

Cyclic lipopeptides are produced by a soil Bacillus megaterium strain and several other Bacillus species. In this work, they are detected both in the Bacillus intact cells and the cells culture medium by MALDI-TOF mass spectrometry. The cyclic lipopeptides self-assemble in water media producing negatively charged and large aggregates (300–800 nm of mean hydrodynamic radius) as evaluated by dynamic light scattering and zeta-potential analysis. The aggregate size depends on pH and ionic strength. However, it is not affected by changes in the osmolarity of the outer medium suggesting the absence of an internal aqueous compartment despite the occurrence of low molecular weight phospholipids in their composition as determined from inorganic phosphorus analysis. The activity against a sensitive Bacillus cereus strain was evaluated from inhibition halos and B. cereus lysis. Essential features determining the antibiotic activity on susceptible Bacillus cereus cells are the preserved cyclic moiety conferring cyclic lipopeptides resistance to proteases and the medium pH. The aggregates are inactive per se at the pH of the culture medium which is around 6 or below. The knock out of the sensitive cells only takes place when the aggregates are disassembled due to a high negative charge at pH above 6.

Interaction of antibiotics with lipid vesicles on thin film porous silicon using reflectance interferometric Fourier transform spectroscopy

The ability to observe interactions of drugs with cell membranes is an important area in pharmaceutical research. However, these processes are often difficult to understand due to the dynamic nature of cell membranes. Therefore, artificial systems composed of lipids have been used to study membrane properties and their interaction with drugs. Here, lipid vesicle adsorption, rupture, and formation of planar lipid bilayers induced by various antibiotics (surfactin, azithromycin, gramicidin, melittin and ciprofloxacin) and the detergent dodecyl-b-D-thiomaltoside (DOTM) was studied using reflective interferometric Fourier transform spectroscopy (RIFTS) on an oxidized porous silicon (pSi) surface as a transducer. The pSi transducer surfaces are prepared as thin films of 3 μm thickness with pore dimensions of a few nanometers in diameter by electrochemical etching of crystalline silicon followed by passivation with a thermal oxide layer. Furthermore, the sensitivity of RIFTS was investigated using three different concentrations of surfactin. Complementary techniques including atomic force microscopy, fluorescence recovery after photobleaching, and fluorescence microscopy were used to validate the RIFTS-based method and confirm adsorption and consequent rupture of vesicles to form a phospholipid bilayer upon the addition of antibiotics. The method provides a sensitive and real-time approach to monitor the antibiotic-induced transition of lipid vesicles to phospholipid bilayers.