Polysaccharide-Targeting Lipid Nanoparticles to Kill Gram-Negative Bacteria.

The rapid increase and spread of Gram-negative bacteria resistant to many or all existing treatments threaten a return to the preantibiotic era. The presence of bacterial polysaccharides that impede the penetration of many antimicrobials and protect them from the innate immune system contributes to resistance and pathogenicity. No currently approved antibiotics target the polysaccharide regions of microbes. Here, describe monolaurin-based niosomes, the first lipid nanoparticles that can eliminate bacterial polysaccharides from hypervirulent Klebsiella pneumoniae, are described. Their combination with polymyxin B shows no cytotoxicity in vitro and is highly effective in combating K. pneumoniae infection in vivo. Comprehensive mechanistic studies have revealed that antimicrobial activity proceeds via a multimodal mechanism. Initially, lipid nanoparticles disrupt polysaccharides, then outer and inner membranes are destabilized and destroyed by polymyxin B, resulting in synergistic cell lysis. This novel lipidic nanoparticle system shows tremendous promise as a highly effective antimicrobial treatment targeting multidrug-resistant Gram-negative pathogens.

Defining the structural characteristics of annexin V binding to a mimetic apoptotic membrane.

Annexin V is of crucial importance for detection of the phosphatidylserine of apoptotic cell membranes. However, the manner in which different amounts of phosphatidylserine at the membrane surface at different stages of apoptosis contribute to binding of annexin V is unclear. We have used a quartz crystal microbalance combined with dissipative monitoring (QCM-D) and neutron reflectivity to characterize binding of human annexin V to supported bilayers of different phospholipid composition. We created model apoptotic bilayers of 1-palmitoyl-2-oleoyl-sn-glycerophosphocholine and 1-palmitoyl-2-oleoyl-sn-glycerophosphoserine (POPS) in the ratios 19:1, 9:1, 6.7:1, 4:1, 3:1, and 2:1 (w/w) in the presence of 2.5 mM CaCl2. QCM-D data revealed that annexin V bound less to supported fluid lipid bilayers with higher POPS content (>25 % POPS). Neutron reflectivity was used to further characterize the detailed composition of lipid bilayers with membrane-bound annexin V. Analysis confirmed less annexin V binding with higher POPS content, that bound annexin V formed a discrete layer above the lipid bilayer with little effect on the overall structure of the membrane, and that the thickness and volume fraction of the annexin V layer varied with POPS content. From these results we show that the POPS content of the outer surface of lipid bilayers affects the structure of membrane-bound annexin V.

Coassembled Nitric Oxide-Releasing Nanoparticles with Potent Antimicrobial Efficacy against Methicillin-Resistant Staphylococcus aureus (MRSA) Strains.

Nitric oxide (NO)-releasing nanoparticles are effective nanomedicines with diverse therapeutic advantages compared with small molecule-based NO donors. Here, we report a new class of furoxan-based NO-releasing nanoparticles using a simple, creative yet facile coassembly approach. This is the first time we demonstrated that the coassembled NO-releasing nanoparticles with poly(ethylene glycol)101-block-poly(propylene glycol)56-block-poly(ethylene glycol)101 (Pluronic F127) had potent antimicrobial efficacies against methicillin-resistant Staphylococcus aureus (MRSA) strains. Nanoparticles obtained from the coassembly of either 4-(1-(3-methylpentan-5-ol)oxyl)(3-phenylsulfonyl) furoxan (compound 1) or 4-methoxy(3-phenylsulfonyl) furoxan (compound 2) with Pluronic F127 exhibit 4-fold improved antimicrobial activities compared to their self-assembled counterparts without Pluronic F127. 5(6)-Carboxylfluorescein (CF) leakage experiments further reveal that both coassembled NO-releasing nanoparticles show stronger interactions with lipid bilayers than those self-assembled alone. Subsequently, their strong plasma membrane-damaging capabilities are confirmed under both high-resolution optical microscopy and scanning electron microscopy characterizations. This coassembly approach could be readily applied to other small molecule-based antimicrobials, providing new solutions and important insights to further antimicrobial recipe design.

A polytherapy based approach to combat antimicrobial resistance using cubosomes.

A depleted antimicrobial drug pipeline combined with an increasing prevalence of Gram-negative 'superbugs' has increased interest in nano therapies to treat antibiotic resistance. As cubosomes and polymyxins disrupt the outer membrane of Gram-negative bacteria via different mechanisms, we herein examine the antimicrobial activity of polymyxin-loaded cubosomes and explore an alternative strategy via the polytherapy treatment of pathogens with cubosomes in combination with polymyxin. The polytherapy treatment substantially increases antimicrobial activity compared to polymyxin B-loaded cubosomes or polymyxin and cubosomes alone. Confocal microscopy and neutron reflectometry suggest the superior polytherapy activity is achieved via a two-step process. Firstly, electrostatic interactions between polymyxin and lipid A initially destabilize the outer membrane. Subsequently, an influx of cubosomes results in further membrane disruption via a lipid exchange process. These findings demonstrate that nanoparticle-based polytherapy treatments may potentially serve as improved alternatives to the conventional use of drug-loaded lipid nanoparticles for the treatment of "superbugs".

Annexin V-containing cubosomes for targeted early detection of apoptosis in degenerative retinal tissue.

New drug delivery materials targeting damaged ocular tissues are of particular interest. In this work, we have formulated annexin/phosphatidylserine/phytantriol and annexin/phosphatidylserine/monoolein cubosomes based on incorporation of 1,2-dipalmitoyl-sn-glycero-3-phospho-l-serine (PS) lipid and annexin V (ANX) protein with phytantriol (Phy) and monoolein (MO) respectively. The incorporation of ANX is important because it can be used as a diagnostic tool for in vivo apoptosis detection due to its high affinity to phosphatidylserine in the presence of Ca2+. We have also prepared PS-Phy and PS-MO cubosomes without ANX as a comparison, and characterized them using dynamic light scattering, cryo-TEM images and small-angle X-ray scattering, showing that PS-Phy cubosomes have greater chemical stability, and that ANX-PS-Phy cubosomes have the potential for in vivo drug delivery. In addition, we have reconstituted an apoptotic biomimetic membrane on a surface to gain insights into cubosome-bilayer interactions using a quartz-crystal microbalance and neutron reflectometry. The neutron reflectivity data reveal that there is exchange of materials between the biomimetic apoptotic bilayer and ANX-PS-Phy cubosomes, with an accumulation of ANX between the membrane and cubosomes possibly being the reason for the reduced cytotoxicity of ANX-PS-Phy cubosomes. A rat model of laser-induced choroidal neovascularization showed that ANX-PS-Phy cubosomes specifically targeted apoptotic cells in vivo. We propose that ANX-PS-Phy cubosomes are a potential candidate for ocular drug delivery for eye diseases.

Polymyxin-Induced Lipid A Deacylation in Pseudomonas aeruginosa Perturbs Polymyxin Penetration and Confers High-Level Resistance.

Polymyxins are last-line antibiotics against life-threatening multidrug-resistant Gram-negative bacteria. Unfortunately, polymyxin resistance is increasingly reported, leaving a total lack of therapies. Using lipidomics and transcriptomics, we discovered that polymyxin B induced lipid A deacylation via pagL in both polymyxin-resistant and -susceptible Pseudomonas aeruginosa. Our results demonstrated that the deacylation of lipid A is an "innate immunity" response to polymyxins and a key compensatory mechanism to the aminoarabinose modification to confer high-level polymyxin resistance in P. aeruginosa. Furthermore, cutting-edge neutron reflectometry studies revealed that an assembled outer membrane (OM) with the less hydrophobic penta-acylated lipid A decreased polymyxin B penetration, compared to the hexa-acylated form. Polymyxin analogues with enhanced hydrophobicity displayed superior penetration into the tail regions of the penta-acylated lipid A OM. Our findings reveal a previously undiscovered mechanism of polymyxin resistance, wherein polymyxin-induced lipid A remodeling affects the OM packing and hydrophobicity, perturbs polymyxin penetration, and thereby confers high-level resistance.

Intraocular Pressure Induced Retinal Changes Identified Using Synchrotron Infrared Microscopy.

Infrared (IR) spectroscopy has been used to quantify chemical and structural characteristics of a wide range of materials including biological tissues. In this study, we examined spatial changes in the chemical characteristics of rat retina in response to intraocular pressure (IOP) elevation using synchrotron infrared microscopy (SIRM), a non-destructive imaging approach. IOP elevation was induced by placing a suture around the eye of anaesthetised rats. Retinal sections were collected onto transparent CaF2 slides 10 days following IOP elevation. Using combined SIRM spectra and chemical mapping approaches it was possible to quantify IOP induced changes in protein conformation and chemical distribution in various layers of the rat retina. We showed that 10 days following IOP elevation there was an increase in lipid and protein levels in the inner nuclear layer (INL) and ganglion cell layer (GCL). IOP elevation also resulted in an increase in nucleic acids in the INL. Analysis of SIRM spectra revealed a shift in amide peaks to lower vibrational frequencies with a more prominent second shoulder, which is consistent with the presence of cell death in specific layers of the retina. These changes were more substantial in the INL and GCL layers compared with those occurring in the outer nuclear layer. These outcomes demonstrate the utility of SIRM to quantify the effect of IOP elevation on specific layers of the retina. Thus SIRM may be a useful tool for the study of localised tissue changes in glaucoma and other eye diseases.