Digestion of lipid micelles leads to increased membrane permeability

Lipid-based drug carriers are an attractive option to solubilise poorly water soluble therapeutics. Previously, we reported that the digestion of a short tail PC lipid (2C6PC) by the PLA2 enzyme has a significant effect on the structure and stability of the micelles it forms. Here, we studied the interactions of micelles of varying composition representing various degrees of digestion with a model ordered (70 mol% DPPC & 30 mol% cholesterol) and disordered (100% DOPC) lipid membrane. Micelles of all compositions disassociated when interacting with the two different membranes. As the percentage of digestion products (C6FA and C6LYSO) in the micelle increased, the disassociation occurred more rapidly. The C6FA inserts preferentially into both membranes. We find that all micelle components increase the area per lipid, increase the disorder and decrease the thickness of the membranes, and the 2C6PC lipid molecules have the most significant impact. Additionally, there is an increase in permeation of water into the membrane that accompanies the insertion of C6FA into the DOPC membranes. We show that the natural digestion of lipid micelles result in molecular species that can enhance the permeability of lipid membranes that in turn result in an enhanced delivery of drugs.

Impact of the physical-chemical properties of poly(lactic acid)-poly(ethylene glycol) polymeric nanoparticles on biodistribution

Nanoparticle (NP) formulations are inherently polydisperse making their structural characterization and justification of specifications complex. It is essential, however, to gain an understanding of the physico-chemical properties that drive performance in vivo. To elucidate these properties, drug-containing poly(lactic acid) (PLA)-poly(ethylene glycol) (PEG) block polymeric NP formulations (or PNPs) were sub-divided into discrete size fractions and analyzed using a combination of advanced techniques, namely cryogenic transmission electron microscopy, small-angle neutron and X-ray scattering, nuclear magnetic resonance, and hard-energy X-ray photoelectron spectroscopy. Together, these techniques revealed a uniquely detailed picture of PNP size, surface structure, internal molecular architecture and the preferred site(s) of incorporation of the hydrophobic drug, AZD5991, properties which cannot be accessed via conventional characterization methodologies. Within the PNP size distribution, it was shown that the smallest PNPs contained significantly less drug than their larger sized counterparts, reducing overall drug loading, while PNP molecular architecture was critical in understanding the nature of in vitro drug release. The effect of PNP size and structure on drug biodistribution was determined by administrating selected PNP size fractions to mice, with the smaller sized NP fractions increasing the total drug-plasma concentration area under the curve and reducing drug concentrations in liver and spleen, due to greater avoidance of the reticuloendothelial system. In contrast, administration of unfractionated PNPs, containing a large population of NPs with extremely low drug load, did not significantly impact the drug's pharmacokinetic behavior - a significant result for nanomedicine development where a uniform formulation is usually an important driver. We also demonstrate how, in this study, it is not practicable to validate the bioanalytical methodology for drug released in vivo due to the NP formulation properties, a process which is applicable for most small molecule-releasing nanomedicines. In conclusion, this work details a strategy for determining the effect of formulation variability on in vivo performance, thereby informing the translation of PNPs, and other NPs, from the laboratory to the clinic.

Differences in the transcriptome response in the gills of sea lamprey acutely exposed to 3-trifluoromethyl-4-nitrophenol (TFM), niclosamide or a TFM:niclosamide mixture

Sea lamprey (Petromyzon marinus) control in the Laurentian Great Lakes of North America makes use of two pesticides: 3-trifluoromethyl-4-nitrophenol (TFM) and niclosamide, which are often co-applied. Sea lamprey appear to be vulnerable to these agents resulting from a lack of detoxification responses with evidence suggesting that lampricide mixtures produce a synergistic effect. However, there is a lack of information pertaining to the physiological responses of sea lamprey to niclosamide and TFM:niclosamide mixtures. Here, we characterized the transcriptomic responses of the sea lamprey to TFM, niclosamide, and a TFM:niclosamide (1.5 %) mixture in the gill. Along with a control, larval sea lamprey were exposed to each treatment for 6 h, after which gill tissues were extracted for measuring whole-transcriptome responses using RNA sequencing. Differential gene expression patterns were summarized, which included identifying the broad roles of genes and common expression patterns among the treatments. While niclosamide treatment resulted in no differentially expressed genes, TFM- and mixture-treated fish had several differentially expressed genes that were associated with the cell cycle, DNA damage, metabolism, immune function, and detoxification. However, there was no common differential expression among treatments. For the first time, we characterized the transcriptomic response of sea lamprey to niclosamide and a TFM:niclosamide mixture and identified that these agents impact mRNA transcript abundance of genes associated with the cell cycle and cellular death, and immune function, which are likely mediated through mitochondrial dysregulation. These results may help to inform the production of more targeted and effective lampricides in sea lamprey control efforts.

Effects of Charge Density on Spread Hyperbranched Polyelectrolyte/Surfactant Films at the Air/Water Interface

The interfacial structure and morphology of films spread from hyperbranched polyethylene imine/sodium dodecyl sulfate (PEI/SDS) aggregates at the air/water interface have been resolved for the first time with respect to polyelectrolyte charged density. A recently developed method to form efficient films from the dissociation of aggregates using a minimal quantity of materials is exploited as a step forward in enhancing understanding of the film properties with a view to their future use in technological applications. Interfacial techniques that resolve different time and length scales, namely, ellipsometry, Brewster angle microscopy, and neutron reflectometry, are used. Extended structures of both components are formed under a monolayer of the surfactant with bound polyelectrolytes upon film compression on subphases adjusted to pH 4 or 10, corresponding to high and low charge density of the polyelectrolyte, respectively. A rigid film is related to compact conformation of the PEI in the interfacial structure at pH 4, while it is observed that aggregates remain embedded in mobile films at pH 10. The ability to compact surfactants in the monolayer to the same extent as its maximum coverage in the absence of polyelectrolyte is distinct from the behavior observed for spread films involving linear polyelectrolytes, and intriguingly evidence points to the formation of extended structures over the full range of surface pressures. We conclude that the molecular architecture and charge density can be important parameters in controlling the structures and properties of spread polyelectrolyte/surfactant films, which holds relevance to a range of applications, such as those where PEI is used, including CO2 capture, electronic devices, and gene transfection.

Control of the structure and morphology of polypeptide/surfactant spread films by exploiting specific interactions

We demonstrate control of the structure and morphology of polypeptide/surfactant films at the air/water interface as a function of the maximum compression ratio of the surface area, exploiting a recently developed film formation mechanism that requires minimal quantities of materials involving the dissociation of aggregates. The systems studied are poly(L-lysine) (PLL) or poly(L-arginine) (PLA) with sodium dodecyl sulfate (SDS), chosen because the surfactant (i) interacts more strongly with the latter polypeptide due to the formation of hydrogen bonds between the guanidinium group and its oxygen atoms, and (ii) induces bulk β-sheet and α-helix conformations of the respective polypeptides. The working hypothesis is that such different interactions may be used to tune the film properties when compressed to form extended structures (ESs). Neutron reflectometry reveals that application of a high compression ratio (4.5 : 1) results in the nanoscale self-assembly of ESs containing up to two PLL-wrapped SDS bilayers. Brewster angle microscopy provides images of the PLL/SDS ESs as discrete regions on the micrometre scale while additional linear regions of PLA/SDS ESs mark macroscopic film folding. Ellipsometry demonstrates high stability of the different ESs formed. The collapse of PLL/SDS films upon compression to a very high ratio (10 : 1) is irreversible due to the formation of solid domains that remain embedded in the film upon expansion while that of PLA/SDS films is reversible. These findings demonstrate that differences in the side group of a polypeptide can have a major influence on controlling the film properties, marking a key step in the development of this new film formation mechanism for the design of biocompatible and/or biodegradable films with tailored properties for applications in tissue engineering, biosensors and antimicrobial coatings.

In depth characterization of physicochemical Critical Quality Attributes of a clinical drug-dendrimer conjugate

A deep and detailed understanding of drug-dendrimer conjugates key properties is needed to define the critical quality attributes that affect drug product performance. The characterization must be executed both in the formulation media and in biological matrices. This, nevertheless, is challenging on account of a very limited number of suitable, established methods for characterizing the physicochemical properties, stability, and interaction with biological environment of complex drug-dendrimer conjugates. In order to fully characterize AZD0466, a drug-dendrimer conjugate currently under clinical development by AstraZeneca, a collaboration was initiated with the European Nanomedicine Characterisation Laboratory to deploy a state-of-the-art multi-step approach to measure physicochemical properties. An incremental complexity characterization approach was applied to two batches of AZD0466 and the corresponding dendrimer not carrying any drug, SPL-8984. Thus, the aim of this work is to guide in depth characterization efforts in the analysis of drug-dendrimer conjugates. Additionally, it serves to highlight the importance of using the adequate complementary techniques to measure physical and chemical stability in both simple and biological media, to drive a complex drug-dendrimer conjugate product from discovery to clinical development.

Understanding and optimising the transfection of lipopolyplexes formulated in saline: the effects of peptide and serum

Lipopolyplexes (LPDs) are of considerable interest for use as gene delivery vehicles. Here LPDs have been prepared from cationic vesicles (composed of a 1 : 1 molar ratio of DOTMA with the neutral helper lipid, DOPE), singly branched cationic peptides and plasmid DNA. All peptides contained a linker sequence (cleaved by endosomal furin) attached to a targeting sequence selected to bind human airway epithelial cells and mediate gene delivery. The current study investigates the effects of novel Arg-containing cationic peptide sequences on the biophysical and transfection properties of LPDs. Mixed His/Arg cationic peptides were of particular interest, as these sequences have not been previously used in LPD formulations. Lengthening the number of cationic residues in a homopolymer from 6 to 12 in each branch reduced transfection using LPDs, most likely due to increased DNA compaction hindering the release of pDNA within the target cell. Furthermore, LPDs containing mixed Arg-containing peptides, particularly an alternating Arg/His sequence exhibited an increase in transfection, probably because of their optimal ability to complex and subsequently release pDNA. To confer stability in serum, LPDs were prepared in 0.12 M sodium chloride solution (as opposed to the more commonly used water) yielding multilamellar LPDs with very high levels of size reproducibility and DNA protection, especially when compared to the (unilamellar) LPDs formed in water. Significantly for the clinical applications of the LPDs, those prepared in the presence of sodium chloride retained high levels of transfection in the presence of media supplemented with fetal bovine serum. This work therefore represents a significant advance for the optimisation of LPD formulation for gene delivery, under physiologically relevant conditions, in vivo.

Freshwater protected areas can preserve high-performance phenotypes in populations of a popular sportfish

Recreational fishing has the potential to cause evolutionary change in fish populations; a phenomenon referred to as fisheries-induced evolution. However, detecting and quantifying the magnitude of recreational fisheries selection in the wild is inherently difficult, largely owing to the challenges associated with variation in environmental factors and, in most cases, the absence of pre-selection or baseline data against which comparisons can be made. However, exploration of recreational fisheries selection in wild populations may be possible in systems where fisheries exclusion zones exist. Lakes that possess intra-lake freshwater protected areas (FPAs) can provide investigative opportunities to evaluate the evolutionary impact(s) of differing fisheries management strategies within the same waterbody. To address this possibility, we evaluated how two physiological characteristics (metabolic phenotype and stress responsiveness) as well as a proxy for angling vulnerability, catch-per-unit-effort (CPUE), differed between populations of largemouth bass (Micropterus salmoides) inhabiting long-standing (>70 years active) intra-lake FPAs and adjacent, open access, main-lake areas. Fish from FPA populations had significantly higher aerobic scope (AS) capacity (13%) and CPUE rates compared with fish inhabiting the adjacent main-lake areas. These findings are consistent with theory and empirical evidence linking exploitation with reduced metabolic performance, supporting the hypothesis that recreational fishing may be altering the metabolic phenotype of wild fish populations. Reductions in AS are concerning because they suggest a reduced scope for carrying out essential life-history activities, which may result in fitness level implications. Furthermore, these results highlight the potential for unexploited FPA populations to serve as benchmarks to further investigate the evolutionary consequences of recreational fishing on wild fish and to preserve high-performance phenotypes.

The Global Characterisation of a Drug-Dendrimer Conjugate - PEGylated poly-lysine Dendrimer

The recent emergence of drug-dendrimer conjugates within pharmaceutical industry research and development introduces a range of challenges for analytical and measurement science. These molecules are very high molecular weight (100-200kDa) with a significant degree of structural complexity. The characteristics and quality attributes that require understanding and definition, and impact efficacy and safety, are diverse. They relate to the intact conjugate, the various building blocks of these complex systems and the level of the free and bound active pharmaceutical ingredient (API). From an analytical and measurement science perspective, this necessitates the measurement of the molecular weight, impurity characterisation, the quantitation of the number of conjugated versus free API molecules, the determination of the impurity profiles of the building blocks, primary structure and both particle size and morphology. Here we report the first example of a global characterisation of a drug-dendrimer conjugate - PEGylated poly-lysine dendrimer currently under development (AZD0466). The impact of the wide variety of analytical and measurement techniques on the overall understanding of this complex molecular entity is discussed, with the relative capabilities of the various approaches compared. The results of this study are an essential platform for the research and development of the future generations of related dendrimer-based medicines.

Variation in the Transcriptome Response and Detoxification Gene Diversity Drives Pesticide Tolerance in Fishes

Pesticides are critical for invasive species management but often have negative effects on nontarget native biota. Tolerance to pesticides should have an evolutionary basis, but this is poorly understood. Invasive sea lamprey (Petromyzon marinus) populations in North America have been controlled with a pesticide lethal to them at lower concentrations than native fishes. We addressed how interspecific variation in gene expression and detoxification gene diversity confer differential pesticide sensitivity in two fish species. We exposed sea lamprey and bluegill (Lepomis macrochirus), a tolerant native species, to 3-trifluoromethyl-4-nitrophenol (TFM), a pesticide commonly used in sea lamprey control. We then used whole-transcriptome sequencing of gill and liver to characterize the cellular response in both species. Comparatively, bluegill exhibited a larger number of detoxification genes expressed and a larger number of responsive transcripts overall, which likely contributes to greater tolerance to TFM. Understanding the genetic and physiological basis for pesticide tolerance is crucial for managing invasive species.

Nucleic Acid-Loaded Lipid Nanoparticle Interactions with Model Endosomal Membranes

Lipid nanoparticles (LNPs) are important delivery systems for RNA-based therapeutics, yet the mechanism of their interaction with endosomal membranes remains unclear. Here, the interactions of nucleic acid-loaded LNPs that contain an ionizable lipid with models of the early and late endosomal membranes are studied, for the first time, using different reflectometry techniques. Novel insight is provided with respect to the subphase pH, the stage of the endosome, and the nature of the nucleic acid cargo. It is found that the insertion of lipids from the LNPs into the model membrane is greatest at pH 6.5 and 5.5, whereas at higher pH, lipid insertion is suppressed with evidence instead for the binding of intact LNPs, demonstrating the importance of the pH in the fusion of LNPs undergoing the endosomal pathway. Furthermore, and independently of the pH, the effect of the early- versus late-stage endosomal models is minimal, suggesting that the increased fluidity and anionic nature of the late endosome has little effect on the extent of LNP interaction. Last, there is greater nucleic acid delivery from LNPs containing mRNA than Poly(A), indicating that the extent of interaction can be tuned according to the nature of the nucleic acid cargo. Such new information on the relative impact of factors influencing nucleic acid delivery by LNP interactions with endosomal membranes is important in the design and tuning of vehicles with improved nucleic acid delivery capacities.

The importance of ceramide headgroup for lipid localisation in skin lipid models

The stratum corneum's lipid matrix is a critical for the skin's barrier function and is primarily composed of ceramides (CERs), cholesterol (CHOL) and free fatty acids (FFAs). The lipids form a long periodicity phase (LPP), a unique trilayer unit cell structure. An enzyme driven pathway is implemented to synthesize these key lipids. If these enzymes are down- or upregulated as in inflammatory diseases, the final lipid composition is affected often altering the barrier function. In this study, we mimicked down regulation of enzymes involved in the synthesis of the sphingosine and CER amide bond. In a LPP lipid model, we substituted CER N-(tetracosanoyl)-sphingosine (CER NS) with either i) FFA C24 and free sphingosine, to simulate the loss of the CER amide bond, or ii) with FFA C24 and C18 to simulate the loss of the sphingosine headgroup. Our study shows the lipids in the LPP would not phase separate until at least 25% of the CER NS is substituted keeping the lateral packing and conformational ordering unaltered. Neutron diffraction studies showed that free sphingosine chains localized at the outer layers of the unit cell, while the remaining CER NS head group was concentrated in the inner headgroup layers. However, when FFA C18 was inserted, CER NS was dispersed throughout the LPP, resulting in an even distribution between the inner and outer water layers. The presented results highlight the importance of the CER NS headgroup structure and its interaction in combination with the carbon chain invariability for optimal lipid arrangement.

Impact of drug aggregation on the structural and dynamic properties of Triton X-100 micelles

Surfactants are used in a wide range of chemical and biological applications, and for pharmaceutical purposes are frequently employed to enhance the solubility of poorly water soluble drugs. In this study, all-atom molecular dynamics (MD) simulations and small-angle neutron scattering (SANS) experiments have been used to investigate the drug solubilisation capabilities of the micelles that result from 10 wt% aqueous solutions of the non-ionic surfactant, Triton X-100 (TX-100). Specifically, we have investigated the solubilisation of saturation amounts of the sodium salts of two nonsteroidal anti-inflammatory drugs: ibuprofen and indomethacin. We find that the ibuprofen-loaded micelles are more non-spherical than the indomethacin-loaded micelles which are in turn even more non-spherical than the TX-100 micelles that form in the absence of any drug. Our simulations show that the TX-100 micelles are able to solubilise twice as many indomethacin molecules as ibuprofen molecules, and the indomethacin molecules form larger aggregates in the core of the micelle than ibuprofen. These large indomethacin aggregates result in the destabilisation of the TX-100 micelle, which leads to an increase in the amount of water inside of the core of the micelle. These combined effects cause the eventual division of the indomethacin-loaded micelle into two daughter micelles. These results provide a mechanistic description of how drug interactions can affect the stability of the resulting nanoparticles.

Polyelectrolyte/surfactant films: from 2D to 3D structural control

Reversible control of the 3D structure of polyelectrolyte/surfactant films at the air/water interface is showcased. A recently discovered mechanism is exploited to form highly efficient, stable and biocompatible films by...

Contrasting physiological responses between invasive sea lamprey and non-target bluegill in response to acute lampricide exposure

Control of invasive sea lamprey (Petromyzon marinus) in the Laurentian Great Lakes of North America uses lampricides, which consist of 3-trifluoromethyl-4-nitrophenol (TFM) and niclosamide. Lampricides are thought to inhibit aerobic energy synthesis, with TFM having a relatively greater selective action against lampreys. While the toxicity and physiological effects of TFM are known, the impacts associated with exposure to niclosamide and TFM:niclosamide mixtures are poorly characterized in fishes. Therefore, focusing on energy metabolism, we quantified the physiological responses of larval sea lamprey and bluegill (Lepomis macrochirus), a non-target, native species. Exposures consisted of each lampricide alone (TFM at the species-specific 24 h LC₁₀; niclosamide at 1.5% of the mixture's TFM concentration) or a mixture of the two (larval sea lamprey at TFM 24 h LC₁₀ + 1.5% niclosamide; bluegill at sea lamprey's TFM 24 h LC_99.9 + 1.5% niclosamide) for 24 h. Tissues (brain, skeletal muscle, and liver) were sampled at 6, 12, and 24 h of exposure and assayed for concentrations of ATP, phosphocreatine, glycogen, lactate, and glucose and tissue lampricide levels. In larval sea lamprey, TFM had little effect on brain and skeletal muscle, but niclosamide resulted in a depletion of high energy substrates in both tissues. Mixture-exposed lamprey showed depletion of high energy substrates, accumulation of lactate, and high mortality rates. Bluegill were largely unaffected by toxicant exposures. However, bluegill liver showed lower glycogen and lactate under all three toxicant exposures suggesting increased metabolic turnover. Bluegill also had lower concentrations of TFM and niclosamide in their tissues when compared to lamprey. Our results indicate that lampricide toxicity in sea lamprey larvae is mediated through a depletion of high energy substrates because of impaired aerobic ATP synthesis. We also confirmed that non-target bluegill showed high tolerance to lampricide exposure, an effect potentially mediated through a high detoxification capacity relative to lampreys.

Impact of STIMUlant and osmotic LAXatives (STIMULAX trial) on gastrointestinal recovery after colorectal surgery: randomized clinical trial

BACKGROUND

Recovery of gastrointestinal (GI) function is often delayed after colorectal surgery. Enhanced recovery protocols (ERPs) recommend routine laxative use, but evidence of benefit is unclear. This study aimed to investigate whether the addition of multimodal laxatives to an ERP improves return of GI function in patients undergoing colorectal surgery.

METHODS

This was a single-centre, parallel, open-label RCT. All adult patients undergoing elective colorectal resection or having stoma formation or reversal at the Royal Adelaide Hospital between August 2018 and May 2020 were recruited into the study. The STIMULAX group received oral Coloxyl® with senna and macrogol, with a sodium phosphate enema in addition for right-sided operations. The control group received standard ERP postoperative care. The primary outcome was GI-2, a validated composite measure defined as the interval from surgery until first passage of stool and tolerance of solid intake for 24 h in the absence of vomiting. Secondary outcomes were the incidence of prolonged postoperative ileus (POI), duration of hospital stay, and postoperative complications. The analysis was performed on an intention-to-treat basis.

RESULTS

Of a total of 170 participants, 85 were randomized to each group. Median GI-2 was 1 day shorter in the STIMULAX compared with the control group (median 2  (i.q.r. 1.5-4) versus 3 (2-5.5) days; 95 per cent c.i. -1 to 0 days; P = 0.029). The incidence of prolonged POI was lower in the STIMULAX group (22 versus 38 per cent; relative risk reduction 42 per cent; P = 0.030). There was no difference in duration of hospital day or 30-day postoperative complications (including anastomotic leak) between the STIMULAX and control groups.

CONCLUSION

Routine postoperative use of multimodal laxatives after elective colorectal surgery results in earlier recovery of gastrointestinal function and reduces the incidence of prolonged POI. Registration number: ACTRN12618001261202 (www.anzctr.org.au).

Interplay of lipid and surfactant: Impact on nanoparticle structure

Liquid lipid nanoparticles (LLN) are oil-in-water nanoemulsions of great interest in the delivery of hydrophobic drug molecules. They consist of a surfactant shell and a liquid lipid core. The small size of LLNs makes them difficult to study, yet a detailed understanding of their internal structure is vital in developing stable drug delivery vehicles (DDVs). Here, we implement machine learning techniques alongside small angle neutron scattering experiments and molecular dynamics simulations to provide critical insight into the conformations and distributions of the lipid and surfactant throughout the LLN. We simulate the assembly of a single LLN composed of the lipid, triolein (GTO), and the surfactant, Brij O10. Our work shows that the addition of surfactant is pivotal in the formation of a disordered lipid core; the even coverage of Brij O10 across the LLN shields the GTO from water and so the lipids adopt conformations that reduce crystallisation. We demonstrate the superior ability of unsupervised artificial neural networks in characterising the internal structure of DDVs, when compared to more conventional geometric methods. We have identified, clustered, classified and averaged the dominant conformations of lipid and surfactant molecules within the LLN, providing a multi-scale picture of the internal structure of LLNs.

Analysis of Fixed and Live Single Cells Using Optical Photothermal Infrared with Concomitant Raman Spectroscopy

This paper reports the first use of a novel completely optically based photothermal method (O-PTIR) for obtaining infrared spectra of both fixed and living cells using a quantum cascade laser (QCL) and optical parametric oscillator (OPO) laser as excitation sources, thus enabling all biologically relevant vibrations to be analyzed at submicron spatial resolution. In addition, infrared data acquisition is combined with concomitant Raman spectra from exactly the same excitation location, meaning the full vibrational profile of the cell can be obtained. The pancreatic cancer cell line MIA PaCa-2 and the breast cancer cell line MDA-MB-231 are used as model cells to demonstrate the capabilities of the new instrumentation. These combined modalities can be used to analyze subcellular structures in both fixed and, more importantly, live cells under aqueous conditions. We show that the protein secondary structure and lipid-rich bodies can be identified on the submicron scale.

The Impact of Lipid Digestion on the Dynamic and Structural Properties of Micelles

Self-assembled, lipid-based micelles, such as those formed by the short-chain phosphocholine, dihexanoylphosphatidylcholine (2C6PC), are degraded by the pancreatic enzyme, phospholipase A₂ (PLA2). Degradation yields 1-hexanoyl-lysophosphocholine (C6LYSO) and hexanoic acid (C6FA) products. However, little is known about the behavior of these products during and after the degradation of 2C6PC. In this work, a combination of static and time-resolved small angle neutron scattering, as well as all-atom molecular dynamics simulations, is used to characterize the structure of 2C6PC micelles. In doing so a detailed understanding of the substrate and product aggregation behavior before, during and after degradation is gained. Consequently, the formation of mixed micelles containing 2C6PC, C6LYSO and C6FA is shown at every stage of the degradation process, as well as the formation of mixed C6LYSO/C6FA micelles after degradation is complete. The use of atomistic molecular dynamics has allowed us to characterize the structure of 2C6PC, 2C6PC/C6LYSO/C6FA, and C6LYSO/C6FA micelles throughout the degradation process, showing the localization of the different molecular species within the aggregates. In addition, the hydration of the 2C6PC, C6LYSO, and C6FA species both during micellization and as monomers in aqueous solution is documented to reveal the processes driving their micellization.

The Influence of Co-Surfactants on Lamellar Liquid Crystal Structures Formed in Creams

It is well-established that oil-in-water creams can be stabilised through the formation of lamellar liquid crystal structures in the continuous phase, achieved by adding (emulsifier) mixtures comprising surfactant(s) combined (of necessity) with one or more co-surfactants. There is little molecular-level understanding, however, of how the microstructure of a cream is modulated by changes in co-surfactant and of the ramifications of such changes on cream properties. We investigate here the molecular architectures of oil-free, ternary formulations of water and emulsifiers comprising sodium dodecyl sulfate and one or both of the co-surfactants hexadecanol and octadecanol, using microscopy, small-angle and wide-angle X-ray scattering and small-angle neutron scattering. We then deploy these techniques to determine how the structures of the systems change when liquid paraffin oil is added to convert them to creams, and establish how the structure, rheology, and stability of the creams is modified by changing the co-surfactant. The ternary systems and their corresponding creams are shown to contain co-surfactant lamellae that are subtly different and exhibit different thermotropic behaviours. The lamellae within the creams and the layers surrounding their oil droplets are shown to vary with co-surfactant chain length. Those containing a single fatty alcohol co-surfactant are found to contain crystallites, and by comparison with the cream containing both alcohols suffer adverse changes in their rheology and stability.

Microfluidic-assisted preparation of RGD-decorated nanoparticles: exploring integrin-facilitated uptake in cancer cell lines

This study is about fine tuning the targeting capacity of peptide-decorated nanoparticles to discriminate between cells that express different integrin make-ups. Using microfluidic-assisted nanoprecipitation, we have prepared poly(lactic acid-co-glycolic acid) (PLGA) nanoparticles with a PEGylated surface decorated with two different arginine-glycine-aspartic acid (RGD) peptides: one is cyclic (RGDFC) and has specific affinity towards αvβ3 integrin heterodimers; the other is linear (RGDSP) and is reported to bind equally αvβ3 and α5β1. We have then evaluated the nanoparticle internalization in two cell lines with a markedly different integrin fingerprint: ovarian carcinoma A2780 (almost no αvβ3, moderate in α5β1) and glioma U87MG (very high in αvβ3, moderate/high in α5β1). As expected, particles with cyclic RGD were heavily internalized by U87MG (proportional to the peptide content and abrogated by anti-αvβ3) but not by A2780 (same as PEGylated particles). The linear peptide, on the other hand, did not differentiate between the cell lines, and the uptake increase vs. control particles was never higher than 50%, indicating a possible low and unselective affinity for various integrins. The strong preference of U87MG for cyclic (vs. linear) peptide-decorated nanoparticles was shown in 2D culture and further demonstrated in spheroids. Our results demonstrate that targeting specific integrin make-ups is possible and may open the way to more precise treatment, but more efforts need to be devoted to a better understanding of the relation between RGD structure and their integrin-binding capacity.

Arrangement of Ceramides in the Skin: Sphingosine Chains Localize at a Single Position in Stratum Corneum Lipid Matrix Models

Understanding the structure of the stratum corneum (SC) is essential to understand the skin barrier process. The long periodicity phase (LPP) is a unique trilayer lamellar structure located in the SC. Adjustments in the composition of the lipid matrix, as in many skin abnormalities, can have severe effects on the lipid organization and barrier function. Although the location of individual lipid subclasses has been identified, the lipid conformation at these locations remains uncertain. Contrast variation experiments via small-angle neutron diffraction were used to investigate the conformation of ceramide (CER) N-(tetracosanoyl)-sphingosine (NS) within both simplistic and porcine mimicking LPP models. To identify the lipid conformation of the twin chain CER NS, the chains were individually deuterated, and their scattering length profiles were calculated to identify their locations in the LPP unit cell. In the repeating trilayer unit of the LPP, the acyl chain of CER NS was located in the central and outer layers, while the sphingosine chain was located exclusively in the middle of the outer layers. Thus, for the CER NS with the acyl chain in the central layer, this demonstrates an extended conformation. Electron density distribution profiles identified that the lipid structure remains consistent regardless of the lipid's lateral packing phase, this may be partially due to the anchoring of the extended CER NS. The presented results provide a more detailed insight on the internal arrangement of the LPP lipids and how they are expected to be arranged in healthy skin.

Revealing the Hidden Details of Nanostructure in a Pharmaceutical Cream

Creams are multi-component semi-solid emulsions that find widespread utility across a wide range of pharmaceutical, cosmetic, and personal care products, and they also feature prominently in veterinary preparations and processed foodstuffs. The internal architectures of these systems, however, have to date been inferred largely through macroscopic and/or indirect experimental observations and so they are not well-characterized at the molecular level. Moreover, while their long-term stability and shelf-life, and their aesthetics and functional utility are critically dependent upon their molecular structure, there is no real understanding yet of the structural mechanisms that underlie the potential destabilizing effects of additives like drugs, anti-oxidants or preservatives, and no structure-based rationale to guide product formulation. In the research reported here we sought to address these deficiencies, making particular use of small-angle neutron scattering and exploiting the device of H/D contrast variation, with complementary studies also performed using bright-field and polarised light microscopy, small-angle and wide-angle X-ray scattering, and steady-state shear rheology measurements. Through the convolved findings from these studies we have secured a finely detailed picture of the molecular structure of creams based on Aqueous Cream BP, and our findings reveal that the structure is quite different from the generic picture of cream structure that is widely accepted and reproduced in textbooks.

On the Structure of Solid Lipid Nanoparticles

Solid lipid nanoparticles (SLNs) have a crystalline lipid core which is stabilized by interfacial surfactants. SLNs are considered favorable candidates for drug delivery vehicles since their ability to store and release organic molecules can be tailored through the identity of the lipids and surfactants used. When stored, polymorphic transitions in the core of drug-loaded SLNs lead to the premature release of drug molecules. Significant experimental studies have been conducted with the aim of investigating the physicochemical properties of SLNs, however, no molecular scale investigations have been reported on the behaviors that drive SLN formation and their polymorphic transitions. A combination of small angle neutron scattering and all-atom molecular dynamics simulations is therefore used to yield a detailed atomistic description of the internal structure of an SLN comprising triglyceride, tripalmitin, and the nonionic surfactant, Brij O10 (C_18:1 E₁₀ ). The molecular scale mechanisms by which the surfactants stabilize the crystalline structure of the SLN lipid core are uncovered. By comparing these results to simulated liquid and solid aggregates of tripalmitin lipids, how the morphology of the lipids vary between these systems is demonstrated providing further insight into the mechanisms that control drug encapsulation and release from SLNs.

Enhanced Intraliposomal Metallic Nanoparticle Payload Capacity Using Microfluidic-Assisted Self-Assembly

Hybrids composed of liposomes (L) and metallic nanoparticles (NPs) hold great potential for imaging and drug delivery purposes. However, the efficient incorporation of metallic NPs into liposomes using conventional methodologies has so far proved to be challenging. In this study, we report the fabrication of hybrids of liposomes and hydrophobic gold NPs of size 2-4 nm (Au) using a microfluidic-assisted self-assembly process. The incorporation of increasing amounts of AuNPs into liposomes was examined using microfluidics and compared to L-AuNP hybrids prepared by the reverse-phase evaporation method. Our microfluidics strategy produced L-AuNP hybrids with a homogeneous size distribution, a smaller polydispersity index, and a threefold increase in loading efficiency when compared to those hybrids prepared using the reverse-phase method of production. Quantification of the loading efficiency was determined by ultraviolet spectroscopy, inductively coupled plasma mass spectroscopy, and centrifugal field flow fractionation, and qualitative validation was confirmed by transmission electron microscopy. The higher loading of gold NPs into the liposomes achieved using microfluidics produced a slightly thicker and more rigid bilayer as determined with small-angle neutron scattering. These observations were confirmed using fluorescent anisotropy and atomic force microscopy. Structural characterization of the liposomal-NP hybrids with cryo-electron microscopy revealed the coexistence of membrane-embedded and interdigitated NP-rich domains, suggesting AuNP incorporation through hydrophobic interactions. The microfluidic technique that we describe in this study allows for the automated production of monodisperse liposomal-NP hybrids with high loading capacity, highlighting the utility of microfluidics to improve the payload of metallic NPs within liposomes, thereby enhancing their application for imaging and drug delivery.

The discovery and enhanced properties of trichain lipids in lipopolyplex gene delivery systems

Novel trichain lipids have been identified with enhanced transfection properties in lipopolyplexes.

The formation of a novel trichain (TC) lipid was discovered when a cationic lipid possessing a terminal hydroxyl group and the helper lipid dioleoyl l-α-phosphatidylethanolamine (DOPE) were formulated as vesicles and stored. Importantly, the transfection efficacies of lipopolyplexes comprised of the TC lipid, a targeting peptide and DNA (LPDs) were found to be higher than when the corresponding dichain (DC) lipid was used. To explore this interesting discovery and determine if this concept can be more generally applied to improve gene delivery efficiencies, the design and synthesis of a series of novel TC cationic lipids and the corresponding DC lipids was undertaken. Transfection efficacies of the LPDs were found to be higher when using the TC lipids compared to the DC analogues, so experiments were carried out to investigate the reasons for this enhancement. Sizing experiments and transmission electron microscopy indicated that there were no major differences in the size and shape of the LPDs prepared using the TC and DC lipids, while circular dichroism spectroscopy showed that the presence of the third acyl chain did not influence the conformation of the DNA within the LPD. In contrast, small angle neutron scattering studies showed a considerable re-arrangement of lipid conformation upon formulation as LPDs, particularly of the TC lipids, while gel electrophoresis studies revealed that the use of a TC lipid in the LPD formulation resulted in enhanced DNA protection properties. Thus, the major enhancement in transfection performance of these novel TC lipids can be attributed to their ability to protect and subsequently release DNA. Importantly, the TC lipids described here highlight a valuable structural template for the generation of gene delivery vectors, based on the use of lipids with three hydrophobic chains.

Trichain cationic lipids: the potential of their lipoplexes for gene delivery

Lipoplexes (LDs) have been prepared from DNA and positively charged vesicles composed of the helper lipid, dioleoyl l-α-phosphatidylethanolamine (DOPE) and either a dichain (DC) oxyethylated cationic lipid or their corresponding novel trichain (TC) counterpart. This is the first study using the TC lipids for the preparation of LDs and their application. Here the results of biophysical experiments characterising the LDs have been correlated with the in vitro transfection activity of the complexes. Photon correlation spectroscopy, zeta potential measurements and transmission electron microscopy studies indicated that, regardless of the presence of a third chain, there were little differences between the size and charge of the TC and DC containing LDs. Small angle neutron scattering studies established however that there was a significant conformational re-arrangement of the lipid bilayer when in the form of a LD complex as opposed to the parent vesicles. This re-arrangement was particularly noticeable in LDs containing TC lipids possessing a third chain of C12 or a longer chain. These results suggested that the presence of a third hydrophobic chain had a significant effect on lipid packing in the presence of DNA. Picogreen fluorescence and gel electrophoresis studies showed that the TC lipids containing a third acyl chain of at least C12 were most effective at complexing DNA while the TC lipids containing an octanoyl chain and the DC lipids were least effective. The transfection efficacies of the TC lipids in the form of LDs were found to be higher than for the DC analogues, particularly when the third acyl chain was an octanoyl or oleoyl moeity. Little or no increase in transfection efficiency was observed when the third chain was a methyl, acetyl or dodecanoyl group. The large enhancement in transfection performance of the TC lipids can be attributed to their ability to complex their DNA payload. These studies indicate that presence of a medium or long third acyl chain was especially beneficial for transfection.

Microfluidic-assisted nanoprecipitation of (PEGylated) poly (d,l-lactic acid-co-caprolactone): Effect of macromolecular and microfluidic parameters on particle size and paclitaxel encapsulation

In this work we evaluate the effect of polymer composition and architecture of (PEGylated) polyesters on particle size and paclitaxel (PTX) loading for particles manufactured via microfluidic-assisted, continuous-flow nanoprecipitation using two microfluidic chips with different geometries and mixing principles. We have prepared poly (d,l-lactic acid-co-caprolactone) (PLCL) from ring-opening polymerization (ROP) of LA and CL mixtures and different (macro) initiators (namely, 1-dodecanol, a MeO-PEG-OH, and a 4-armed star PEG-OH), rendering polyesters that vary in monomer composition (i.e. LA/CL ratios) and architecture (i.e. linear vs 4-armed star). Continuous-flow nanoprecipitation was assayed using two microfluidic chips: a cross-flow chip with a X-shaped mixing junction (2D laminar flow focusing) and a micromixer featuring a Y-shaped mixing junction and a split and recombine path (2D laminar flow focusing convinced with stream lamination for faster mixing). Nanoparticle formulations were produced with Z-average sizes in the range of 30-160 nm, although size selectivity could be seen for different polymer/chip combinations; for instance, smaller particles were obtained with Y-shaped micromixer (30-120 nm), specially for the PEGylated polyesters (30-50 nm), whereas the cross-flow chip systematically produced larger particles (80-160 nm). Loading of the anti-cancer drug paclitaxel (PTX) was also heavily influenced not only by the nature of the polyester, but also by the geometry of the microfluidic chip; higher drug loadings were obtained with the cross-flow reactor and the star block copolymers. Finally, decreasing the LA/CL ratio generally had a positive effect on drug loading.

Towards optimised drug delivery: structure and composition of testosterone enanthate in sodium dodecyl sulfate monolayers

Surface tension and specular neutron reflectivity measurements have been used, for the first time to systematically study both the interfacial structure and composition of monolayers of the soluble surfactant, sodium dodecyl sulfate containing a low-dose, poorly water soluble drug, testosterone enanthate. Modelling of the specular neutron reflectivity data suggests that the hydrophobic testosterone enanthate was adsorbed in the C12 hydrophobic tail region of the surfactant monolayer, regardless of the concentration of surfactant at the interface and whether or not additional drug was added to the interface. The location of the hydrophobic drug in the tail region of the surfactant monolayer is supported by the results of classical, large-scale molecular dynamics simulations. The thickness of the surfactant monolayer obtained, in the presence and absence of drug, using molecular dynamics simulations was in good agreement with the corresponding values obtained from the specular neutron reflectivity measurements. The stoichiometry of surfactant:drug at the air-water interface at sodium dodecyl sulfate concentrations above the critical micelle concentration was determined from specular neutron reflectivity measurements to be approximately 3 : 1, and remained constant after the spreading of further testosterone enanthate at the interface. Significantly, this stoichiometry was the same as that obtained in the micelles from bulk solubilisation studies. Important insights into the preferred location of drug in surfactant monolayers at the air-water interface as well as its effect on the structure of the monolayer have been obtained from our combined use of experimental and simulation techniques.

Interaction of testosterone-based compounds with dodecyl sulphate monolayers at the air–water interface

The encapsulation of testosterone enanthate into a sodium dodecyl sulphate monolayer.

Effects of unidirectional flow shear stresses on the formation, fractal microstructure and rigidity of incipient whole blood clots and fibrin gels

Incipient clot formation in whole blood and fibrin gels was studied by the rheometric techniques of controlled stress parallel superposition (CSPS) and small amplitude oscillatory shear (SAOS). The effects of unidirectional shear stress on incipient clot microstructure, formation kinetics and elasticity are reported in terms of the fractal dimension (d_f) of the fibrin network, the gel network formation time (T_GP) and the shear elastic modulus, respectively. The results of this first haemorheological application of CSPS reveal the marked sensitivity of incipient clot microstructure to physiologically relevant levels of shear stress, these being an order of magnitude lower than have previously been studied by SAOS. CSPS tests revealed that exposure of forming clots to increasing levels of shear stress produces a corresponding elevation in d_f, consistent with the formation of tighter, more compact clot microstructures under unidirectional flow. A corresponding increase in shear elasticity was recorded. The scaling relationship established between shear elasticity and d_f for fibrin clots and whole blood confirms the fibrin network as the dominant microstructural component of the incipient clot in terms of its response to imposed stress. Supplementary studies of fibrin clot formation by rheometry and microscopy revealed the substantial additional network mass required to increase d_f and provide evidence to support the hypothesis that microstructural changes in blood clotted under unidirectional shear may be attributed to flow enhanced thrombin generation and activation. CSPS also identified a threshold value of unidirectional shear stress above which no incipient clot formation could be detected. CSPS was shown to be a valuable haemorheological tool for the study of the effects of physiological and pathological levels of shear on clot properties.

Atypical effects of incorporated surfactants on stability and dissolution properties of amorphous polymeric dispersions

OBJECTIVES

To understand the impact of ionic and non-ionic surfactants on the dissolution and stability properties of amorphous polymeric dispersions using griseofulvin (GF) as a model for poorly soluble drugs.

METHODS

Solid dispersions of the poorly water-soluble drug, griseofulvin (GF) and the polymers, poly(vinylpyrrolidone) (PVP) and poly(2-hydroxypropyl methacrylate) (PHPMA), have been prepared by spray drying and bead milling and the effect of the ionic and non-ionic surfactants, namely sodium dodecyl sulphate (SDS) and Tween-80, on the physico-chemical properties of the solid dispersions studied.

KEY FINDINGS

The X-ray powder diffraction data and hot-stage microscopy showed a fast re-crystallisation of GF. While dynamic vapour sorption (DVS) measurements indicated an increased water uptake, slow dissolution rates were observed for the solid dispersions incorporating surfactants. The order by which surfactants free dispersions were prepared seemed critical as indicated by DVS and thermal analysis. Dispersions prepared by milling with SDS showed significantly better stability than spray-dried dispersions (drug remained amorphous for more than 6 months) as well as improved dissolution profile.

CONCLUSIONS

We suggest that surfactants can hinder the dissolution by promoting aggregation of polymeric chains, however that effect depends mainly on how the particles were prepared.

Interaction of the Antimicrobial Peptides Rhesus θ-Defensin and Porcine Protegrin-1 with Anionic Phospholipid Monolayers

A combination of Langmuir isotherm, Brewster angle microscopy (BAM), and neutron reflectivity studies have been performed to gain insight into the effects on model bacterial cell membranes of the antimicrobial peptides, Rhesus θ-defensin 1 (RTD-1), and porcine protegrin 1 (PG-1). The peptides were interacted with monolayers spread at the air-water interface and prepared from a 3:1 molar mixture of phosphatidylethanolamine and phosphatidylglycerol used to approximate the cell membranes of Gram positive bacteria. The Langmuir film balance measurements show that both peptides perturb the lipid monolayers causing an increase in surface pressure, and the BAM studies show that each results in the formation of small domains within the lipid films, around 5 μm diameter. The overall change in monolayer surface pressure caused by PG-1, however, is a little more pronounced than that due to RTD-1 (+8.5 mN·m(-1) vs +5.5 mN·m(-1)), and the rate of its initial interaction with the monolayer is a little more rapid than that for RTD-1. The neutron reflectivity studies also show differences for PG-1 and RTD-1, with the model fits to these data showing that the more amphiphilic PG-1 becomes fully embedded within the lipid film-causing an extension of the lipid acyl chains but leaving the thickness of the lipid headgroup layer unaffected-while RTD-1 is seen to insert less deeply-causing the same extension of the lipid acyl chains as PG-1 but also causing a significant increase in thickness of the lipid headgroup layer. The various differing effects of the two peptides on anionic lipid monolayers are discussed in the context of their differing hemolytic activities, and their proposed differing propensities to form transmembrane pores.

Delivery of siRNA using ternary complexes containing branched cationic peptides: the role of peptide sequence, branching and targeting

Ternary nanocomplexes, composed of bifunctional cationic peptides, lipids and siRNA, as delivery vehicles for siRNA have been investigated. The study is the first to determine the optimal sequence and architecture of the bifunctional cationic peptide used for siRNA packaging and delivery using lipopolyplexes. Specifically three series of cationic peptides of differing sequence, degrees of branching and cell-targeting sequences were co-formulated with siRNA and vesicles prepared from a 1 : 1 molar ratio of the cationic lipid DOTMA and the helper lipid, DOPE. The level of siRNA knockdown achieved in the human alveolar cell line, A549-luc cells, in both reduced serum and in serum supplemented media was evaluated, and the results correlated to the nanocomplex structure (established using a range of physico-chemical tools, namely small angle neutron scattering, transmission electron microscopy, dynamic light scattering and zeta potential measurement); the conformational properties of each component (circular dichroism); the degree of protection of the siRNA in the lipopolyplex (using gel shift assays) and to the cellular uptake, localisation and toxicity of the nanocomplexes (confocal microscopy). Although the size, charge, structure and stability of the various lipopolyplexes were broadly similar, it was clear that lipopolyplexes formulated from branched peptides containing His-Lys sequences perform best as siRNA delivery agents in serum, with protection of the siRNA in serum balanced against efficient release of the siRNA into the cytoplasm of the cell.

Skin lipids: localization of ceramide and fatty acid in the unit cell of the long periodicity phase

The lipid matrix of the skin's stratum corneum plays a key role in the barrier function, which protects the body from desiccation. The lipids that make up this matrix consist of ceramides, cholesterol, and free fatty acids, and can form two coexisting crystalline lamellar phases: the long periodicity phase (LPP) and the short periodicity phase (SPP). To fully understand the skin barrier function, information on the molecular arrangement of the lipids in the unit cell of these lamellar phases is very desirable. To determine this arrangement in previous studies, we examined the molecular arrangement of the SPP. In this study, neutron diffraction studies were performed to obtain information on the molecular arrangement of the LPP. The diffraction pattern reveals nine diffraction orders attributed to the LPP with a repeating unit of 129.4 ± 0.5 Å. Using D2O/H2O contrast variation, the scattering length density profiles were calculated for protiated samples and samples that included either the perdeuterated acyl chain of the most abundant ceramide or the most abundant perdeuterated fatty acid. Both perdeuterated chains are predominantly located in the central part of the unit cell with substantial interdigitation of the acyl chains in the unit cell center. However, a fraction of the perdeuterated chains is also located near the border of the unit cell with their acyl chains directing toward the center. This arrangement of lipids in the LPP unit cell corresponds with the location of their lipid headgroups at the border and also inside of the unit cell at a well-defined position (±21 Å from the unit cell center), indicative of a three-layer lipid arrangement within the 129.4 ± 0.5 Å repeating unit.

Stress, nutrition and parental care in a teleost fish: exploring mechanisms with supplemental feeding and cortisol manipulation

Parental care is an essential life-history component of reproduction for many animal species, and it entails a suite of behavioural and physiological investments to enhance offspring survival. These investments can incur costs to the parent, reducing their energetic and physiological condition, future reproductive capabilities and survival. In fishes, relatively few studies have focused on how these physiological costs are mediated. Male smallmouth bass provide parental care for developing offspring until the brood reaches independence. During this energetically demanding life stage, males cease active foraging as they vigorously defend their offspring. Experimental manipulation of cortisol levels (via implantation) and food (via supplemental feeding) in parental males was used to investigate the fitness consequences of parental care. Improving the nutritional condition of nest-guarding males increased their reproductive success by reducing premature nest abandonment. However, supplemental feeding and cortisol treatment had no effect on parental care behaviours. Cortisol treatment reduced plasma lymphocyte numbers, but increased neutrophil and monocyte concentrations, indicating a shift in immune function. Supplemental feeding improved the physiological condition of parental fish by reducing the accumulation of oxidative injury. Specifically, supplemental feeding reduced the formation of 8-hydroxy-2'-deoxyguanosine (8-OHdG) on DNA nucleotides. Increasing the nutritional condition of parental fish can reduce the physiological cost associated with intensive parental activity and improve overall reproductive success, illustrating the importance of nutritional condition as a key modulator of parental fitness.

Specific effects of monovalent counterions on the structural and interfacial properties of dodecyl sulfate monolayers

Shows that NH₄⁺ ions dehydrate the DS⁻ headgroup by displacing hydrogen bonded waters from the interface.

Neutron Scattering Studies of the Effects of Formulating Amphotericin B with Cholesteryl Sulfate on the Drug's Interactions with Phospholipid and Phospholipid-Sterol Membranes

Langmuir surface pressure, small-angle neutron scattering (SANS), and neutron reflectivity (NR) studies have been performed to determine how formulation of the antifungal drug amphotericin B (AmB), with sodium cholesteryl sulfate (SCS)-as in Amphotec-affects its interactions with ergosterol-containing (model fungal cell) and cholesterol-containing (model mammalian cell) membranes. The effects of mixing AmB in 1:1 molar ratio with cholesteryl sulfate (yielding AmB-SCS micelles) are compared against those of free AmB, using monolayers and bilayers formed from palmitoyloleoylphosphatidylcholine (POPC) in the absence and presence of 30 mol % ergosterol or cholesterol, in all cases employing a 1:0.05 molar ratio of lipid:AmB. Analyses of the (bilayer) SANS and (monolayer) NR data indicate that the equilibrium changes in membrane structure induced in sterol-free and sterol-containing membranes are the same for free AmB and AmB-SCS. Stopped-flow SANS experiments, however, reveal that the structural changes to vesicle membranes occur far more rapidly following exposure to AmB-SCS vs free drug, with the kinetics of these changes varying with membrane composition. With POPC vesicles, the structural changes induced by AmB-SCS become apparent only after several minutes, and equilibrium is reached after ∼30 min. The corresponding onset of changes in POPC-ergosterol and POPC-cholesterol vesicles, however, occurs within ∼5 s, with equilibrium reached after 10 and 120 s, respectively. The rate of insertion of AmB into POPC-sterol membranes is thus increased through formulation as AmB-SCS. Moreover, the differences in monolayer surface pressure and SANS structure-change equilibration times suggest significant rearrangement of AmB within these membranes following insertion. The reduced times to equilibrium for the POPC-ergosterol vs POPC-cholesterol systems are consistent with the known differences in affinity of AmB for these two sterols, and the reduced time to equilibrium for AmB-SCS interaction with POPC-ergosterol membranes vs that for free AmB is consistent with the reduced host toxicity of Amphotec.

Characterization of the aggregates formed by various bacterial lipopolysaccharides in solution and upon interaction with antimicrobial peptides

The biophysical analysis of the aggregates formed by different chemotypes of bacterial lipopolysaccharides (LPS) before and after challenge by two different antiendotoxic antimicrobial peptides (LL37 and bovine lactoferricin) was performed in order to determine their effect on the morphology of LPS aggregates. Small-angle neutron scattering (SANS) and cryogenic transmission electron microscopy (cryoTEM) were used to examine the structures formed by both smooth and rough LPS chemotypes and the effect of the peptides, by visualization of the aggregates and analysis of the scattering data by means of both mathematical approximations and defined models. The data showed that the structure of LPS determines the morphology of the aggregates and influences the binding activity of both peptides. The morphologies of the worm-like micellar aggregates formed by the smooth LPS were relatively unaltered by the presence of the peptides due to their pre-existing high degree of positive curvature being little affected by their association with either peptide. On the other hand, the aggregates formed by the rough LPS chemotypes showed marked morphological changes from lamellar structures to ordered micellar networks, induced by the increase in positive curvature engendered upon association with the peptides. The combined use of cryoTEM and SANS proved to be a very useful tool for studying the aggregation properties of LPS in solution at biologically relevant concentrations.

Interaction of amphotericin B with lipid monolayers

Langmuir isotherm, neutron reflectivity, and Brewster angle microscopy experiments have been performed to study the interaction of amphotericin B (AmB) with monolayers prepared from 1-palmitoyl-2-oleoylphosphatidylcholine (POPC) and mixtures of this lipid with cholesterol or ergosterol to mimic mammalian and fungal cell membranes, respectively. Isotherm data show that AmB causes a more pronounced change in surface pressure in the POPC/ergosterol system than in the POPC and POPC/cholesterol systems, and its interaction with the POPC/ergosterol monolayer is also more rapid than with the POPC and POPC/cholesterol monolayers. Brewster angle microscopy shows that, in interaction with POPC monolayers, AmB causes the formation of small domains which shrink and disappear within a few minutes. The drug also causes domain formation in the POPC/cholesterol and POPC/ergosterol monolayers; in the former case, these are formed more slowly than is seen with the POPC monolayers and are ultimately much smaller; in the latter case, they are formed rather more quickly and are more heterogeneous in size. Neutron reflectivity data show that the changes in monolayer structure following interaction with AmB are the same for all three systems studied: the data are consistent with the drug inserting into the monolayers with its macrocyclic ring intercalated among the lipid acyl chains and sterol ring systems, with its mycosamine moiety colocalizing with the sterol hydroxyl and POPC head groups. On the basis of these studies, it is concluded that AmB inserts in a similar manner into POPC, POPC/cholesterol, and POPC/ergosterol monolayers but does so with differing kinetics and with the formation of quite different in-plane structures. The more rapid time scale for interaction of the drug with the POPC/ergosterol monolayer, its more pronounced effect on monolayer surface pressure, and its more marked changes as regards domain formation are all consistent with the drug's selectivity for fungal vs mammalian cell membranes.