A Study on Bicellar Structural Characteristics and Skin Permeabilities across the Stratum Corneum of Arginine-Modified Peptide-induced Bicelles as a Potential Transdermal Drug Carrier

In this study, the effects of incorporating arginine-modified peptide into the structure of discshaped bicelles were investigated. Characterization of bicellar system was conducted using different techniques, including dynamic light scattering (DLS), zeta potential, cryogenic transmission electron microscopy (cryo-TEM) and small angle X-ray scattering (SAXS). Bicelle skin permeability as drug carriers was also evaluated. The addition of peptides revealed formation of small-sized, stable and discoidal-shaped bicelles. Positive zeta potential and synchrotron radiation experiments confirmed the presence and showed the peptide distribution across the bicelle face and rim region. A major disruption with the lipid rearrangement of the stratum corneum and the disruption of bicelle structures by the interaction between bicelle lipids and stratum corneum lipids were observed during the application of bicelles with cholesteryl chloroformate-arginine 8-mer (CholR8). This also demonstrated the highest penetration of the drug-loaded bicelle across the hairless mouse skin. As a model drug, non-steroidal anti-inflammatory drug, meloxicam was selected. Meloxicam was incorporated into the hydrophobic domain of bicelles due to its hydrophobic property. Considering these results, bicelle induced with peptides exhibits useful and promising characteristics and behaviors, shaping an effective strategy for future transdermal drug delivery applications.

Changes Experienced by Low-Concentration Lipid Bicelles as a Function of Temperature

Differential scanning calorimetry (DSC) of dipalmitoyl phosphatidylcholine (DPPC), dihexanoyl phosphatidylcholine, and dipalmitoyl phosphatidylglycerol bicelles reveals two endothermic peaks. Based on analysis of small angle neutron scattering and small angle X-ray scattering data, the two DSC peaks are associated with the melting of DPPC and a change in bicellar morphology─namely, either bicelle-to-spherical vesicle or oblate-to-spherical vesicle. The reversibility of the two structural transformations was examined by DSC and found to be consistent with the corresponding small angle scattering data. However, the peak that is not associated with the melting of DPPC does not correspond to any structural transformation for bicelles containing distearoyl phosphatidylethanolamine conjugated with polyethylene glycol. Based on complementary experimental data, we conclude that membrane flexibility, lipid miscibility, and differential solubility between the long- and short-chain lipids in water are important parameters controlling the reversibility of morphologies experienced by the bicelles.

Effects of fluidity and charge density on the morphology of a bicellar mixture - A SANS study

The spontaneously formed structures of physiologically relevant lipid model membranes made of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine, 1-palmitoyl-2-oleoyl-sn-glycero-3-phospho-(1'-rac-glycerol) and 1,2-hexanoyl-sn-glycero-3-phosphocholine have been evaluated in depth using small angle neutron scattering. Although a common molar ratio of long- to short- chain phospholipids (~4) as reported in many bicellar mixtures was used, discoidal bicelles were not found as the major phase throughout the range of lipid concentration and temperature studied, indicating that the required condition for the formation of bicelle is the immiscibility between the long- and short- chain lipids, which were in the gel and L_α phases, respectively, in previous reports. In this study, all lipids are in the L_α phase. The characterization outcome suggests that the spontaneous structures tie strongly with the physical parameters of the system such as melting transition temperature of the long-chain lipid, total lipid concentration and charge density of the system. Multilamellar vesicles, unilamellar vesicles, ribbons and perforated lamellae can be obtained based on the analysis of the small angle neutron scattering results, leading to the construction of structural diagrams. This report provides the important map to choose suitable lipid systems for the structural study of membrane-associated proteins, design of theranostic nanocarriers or other related research fields.

Formulation of Bicelles Based on Lecithin-Nonionic Surfactant Mixtures

Bicelles have been intensively studied for use as drug delivery carriers and in biological studies, but their preparation with low-cost materials and via a simple process would allow their use for other purposes as well. Herein, bicelles were prepared through a semi-spontaneous method using a mixture of hydrogenated soybean lecithin (SL) and a nonionic surfactant, polyoxyethylene cholesteryl ether (ChEO₁₀), and then we investigated the effect of composition and temperature on the structure of bicelles, which is important to design tailored systems. As the fraction of ChEO₁₀ (X_C) was increased, a bimodal particle size distribution with a small particle size of several tens of nanometers and a large particle size of several hundred nanometers was obtained, and only small particles were observed when X_C ≥ 0.6, suggesting the formation of significant structure transition (liposomes to bicelles). The small-angle neutron scattering (SANS) spectrum for these particles fitted a core-shell bicelle model, providing further evidence of bicelle formation. A transition from a monomodal to a bimodal size distribution occurred as the temperature was increased, with this transition taking place at lower temperatures when higher SL-ChEO₁₀ concentrations were used. SANS showed that this temperature-dependent size change was reversible, suggesting the SL-ChEO₁₀ bicelles were stable against temperature, hence making them suitable for several applications.

An in vitro digestion study of encapsulated lactoferrin in rapeseed phospholipid-based liposomes

Effectiveness of liposomes elaborated with rapeseed phospholipid (RP) extracted from a residue of oil processing, stigmasterol (ST) and/or hydrogenated phosphatidylcholine (HPC) for the encapsulation lactoferrin (LF) was studied; lipid membrane of liposomes was characterized (bilayer size, chain conformational order, lateral packing, lipid phase, and morphology) and the protection offered to the encapsulated LF during in vitro digestion was determined. Liposomes composed of RP+ST^{LC(low concentration)} showed spherical and irregular vesicles without perforations. Lamellar structure was organized in a liquid-ordered phase with a potential orthorhombic packing. Stability and size of the liposomes were more affected by gastric digestion than intestinal digestion; 67-80% of the initially encapsulated LF remained intact after gastric digestion whereas the percentage was reduced to 16-35% after intestinal digestion. Our results shows that liposomes elaborated with RP, properly combined with other lipids, can be a useful oral delivery system of molecules sensitive to digestive enzymes.

Glycerol Solvates DPPC Headgroups and Localizes in the Interfacial Regions of Model Pulmonary Interfaces Altering Bilayer Structure

The inclusion of glycerol in formulations for pulmonary drug delivery may affect the bioavailability of inhaled steroids by retarding their transport across the lung epithelium. The aim of this study was to evaluate whether the molecular interactions of glycerol with model pulmonary interfaces provide a biophysical basis for glycerol modifying inhaled drug transport. Dipalmitoylphosphatidylcholine (DPPC) monolayers and liposomes were used as model pulmonary interfaces, in order to examine the effects of bulk glycerol (0-30% w/w) on their structures and dynamics using complementary biophysical measurements and molecular dynamics (MD) simulations. Glycerol was found to preferentially interact with the carbonyl groups in the interfacial region of DPPC and with phosphate and choline in the headgroup, thus causing an increase in the size of the headgroup solvation shell, as evidenced by an expansion of DPPC monolayers (molecular area increased from 52 to 68 Ų) and bilayers seen in both Langmuir isotherms and MD simulations. Both small angle neutron scattering and MD simulations indicated a reduction in gel phase DPPC bilayer thickness by ∼3 Å in 30% w/w glycerol, a phenomenon consistent with the observation from FTIR data, that glycerol caused the lipid headgroup to remain oriented parallel to the membrane plane in contrast to its more perpendicular conformation adopted in pure water. Furthermore, FTIR measurements suggested that the terminal methyl groups of the DPPC acyl chains were constrained in the presence of glycerol. This observation is supported by MD simulations, which predict bridging between adjacent DPPC headgroups by glycerol as a possible source of its putative membrane stiffening effect. Collectively, these data indicate that glycerol preferentially solvates DPPC headgroups and localizes in specific areas of the interfacial region, resulting in structural changes to DPPC bilayers which may influence cell permeability to drugs.

Mastering the magnetic susceptibility of magnetically responsive bicelles with 3β-amino-5-cholestene and complexed lanthanide ions

The magnetic susceptibility of lanthanide-chelating bicelles was selectively enhanced by introducing 3β-amino-5-cholestene (aminocholesterol, Chol-NH₂) in the bilayer. Unprecedented magnetic alignment of the bicelles was achieved without altering their size. An aminocholesterol conjugate (Chol-C₂OC₂-NH₂), in combination with different lanthanide ions, offers the possibility of fine-tuning the bicelle's magnetic susceptibility.

One-step formulation of nonionic surfactant bicelles (NSBs) by a double-tailed polyglycerol-type nonionic surfactant

Bicelles are generally formed by phospholipid-based systems and are useful for various applications, such as nanocarriers or membrane protein crystallization. The same disc-like assemblies, nonionic surfactant bicelles (NSBs), can also be formed using nonionic amphiphiles, but this has not been reported extensively. We report a novel NSB system that employs the double-tailed nonionic amphiphile, polyglyceryl dialkyl ether (C₁₂C_mG_n), which has two alkyl chains and a polyglyceryl group. A symmetric-tail molecule, C₁₂C₁₂G_13.8, formed vesicles, whereas an asymmetric-tail molecule, C₁₂C₁₄G_15.5, formed NSBs through a simple one-step process using ultrasonication. The 1 wt% aqueous solution of C₁₂C₁₄G_15.5 was in a two-phase equilibrium of a lamellar phase and a water phase. Transparent dispersion was obtained through ultrasonication treatment. The size distribution in the dispersion was obtained by dynamic light scattering (DLS), resulting in a narrow distribution of around 20 nm in diameter. A negatively-stained transmission electron microscopy (TEM) image showed oblong and spherical shapes, which are typically observed in bicelle-forming systems. A small angle neutron scattering (SANS) measurement well proved bicelle formation by fitting a core-shell bicelle form factor model. The disc thickness and diameter were in agreement with the values obtained by DLS and TEM, respectively. A larger shell thickness at the rim part than at the flat disc part suggested that NSB aggregates have inhomogeneous molecular distribution. Similar to phospholipid systems, the bicelle-forming C₁₂C₁₄G_15.5 system produced a defective lamellar phase formation at high surfactant concentrations, whereas a general lamellar phase was formed in the vesicle-forming C₁₂C₁₂G_13.8 system.

In vivo confocal Raman microscopic determination of depth profiles of the stratum corneum lipid organization influenced by application of various oils

BACKGROUND

The intercellular lipids (ICL) of stratum corneum (SC) play an important role in maintaining the skin barrier function. The lateral and lamellar packing order of ICL in SC is not homogenous, but rather depth-dependent.

OBJECTIVE

This study aimed to analyze the influence of the topically applied mineral-derived (paraffin and petrolatum) and plant-derived (almond oil and jojoba oil) oils on the depth-dependent ICL profile ordering of the SC in vivo.

METHOD

Confocal Raman microscopy (CRM), a unique tool to analyze the depth profile of the ICL structure non-invasively, is employed to investigate the interaction between oils and human SC in vivo.

RESULTS

The results show that the response of SC to oils' permeation varies in the depths. All oils remain in the upper layers of the SC (0-20% of SC thickness) and show predominated differences of ICL ordering from intact skin. In these depths, skin treated with plant-derived oils shows more disordered lateral and lamellar packing order of ICL than intact skin (p<0.05). In the intermediate layers of SC (30-50% of SC thickness), the oils do not influence the lateral packing order of SC ICL (p>0.1), except plant-derived oils at the depth 30% of SC thickness. In the deeper layers of the SC (60-100% of SC thickness), no difference between ICL lateral packing order of the oil-treated and intact skin can be observed, except that at the depths of 70-90% of the SC thickness, where slight changes with more disorder states are measured for plant-derived oil treated skin (p<0.1), which could be explained by the penetration of free fatty acid fractions in the deep-located SC areas.

CONCLUSION

Both oil types remain in the superficial layers of the SC (0-20% of the SC thickness). Skin treated with mineral- and plant-derived oils shows significantly higher disordered lateral and lamellar packing order of ICL in these layers of the SC compared to intact skin. Plant-derived oils significantly changed the ICL ordering in the depths of 30% and 70-90% of the SC thickness, which is likely due to the penetration of free fatty acids in the deeper layers of the SC.

Lipid Nanodisc-Templated Self-Assembly of Gold Nanoparticles into Strings and Rings

Gold nanoparticles (AuNPs) exhibit strong fluorescent and electromagnetic properties, which can be enhanced upon clustering and used in therapeutic, imaging, and sensing applications. A combination of gold nanoparticles with lipid nanodiscs can be attractive for AuNP self-assembly and useful in biomedical applications. Using molecular dynamics simulations we show that lipid nanodiscs can serve as templates for AuNP clustering into rings and string-like structures. We demonstrate that equilibrium encapsulation of 1 nm hydrophobically modified AuNPs into lipid nanodiscs composed of a mixture of dipalmitoylphosphatidylcholine (DPPC) and dihexanoylphosphatidylcholine (DHPC) lipids occurs at the rim and results in formation of a ring of gold. The interior of the nanodisc is inaccessible to AuNPs due to the DPPC liquid crystalline order. With temperature increase the lipid order diminishes, initiating the nanodisc transformation into a vesicle, upon which encapsulated AuNPs cluster into a close-packed string or nanoring, thereby stalling the vesiculation process at a "round vase" or cup-like stage depending on the AuNP concentration. In contrast, encapsulation of AuNPs by an equilibrium lipid vesicle results in its deformation with randomly clustered AuNPs, in agreement with experimental observations. We characterize the AuNP cluster size and surface-to-surface pair distribution, both of which impact the AuNP luminescent properties. We investigate the effect of alkane tether length on the nanodisc stability and AuNP clustering inside the nanodiscs and vesicles. Our results show that lipid nanodiscs can enhance gold cluster formation, which can be further exploited in imaging applications.

Hyper-cell-permeable micelles as a drug delivery carrier for effective cancer therapy

Although PEGylated liposomes (PEG-LS) have been intensively studied as drug-delivery vehicles, the rigidity and the hydrophilic PEG corona of liposomal membranes often limits cellular uptake, resulting in insufficient drug delivery to target cells. Thus, it is necessary to develop a new type of lipid-based self-assembled nanoparticles capable of enhanced cellular uptake, tissue penetration, and drug release than conventional PEGylated liposomes. Herein, we describe a simple modification of bicellar formulation in which the addition of a PEGylated phospholipid produced a dramatic physicochemical change in morphology, i.e., the disc-shaped bicelle became a uniformly distributed ultra-small (∼12 nm) spherical micelle. The transformed lipid-based nanoparticles, which we termed hyper-cell-permeable micelles (HCPMi), demonstrated not only prolonged stability in serum but also superior cellular and tumoral uptake compared to a conventional PEGylated liposomal system (PEG-LS). In addition, HCPMi showed rapid cellular uptake and subsequent cargo release into the cytoplasm of cancer cells. Cells treated with HCPMi loaded with docetaxel (DTX) had an IC₅₀ value of 0.16 μM, compared with 0.78 μM with PEG-LS loaded with DTX, a nearly five-fold decrease in cell viability, indicating excellent efficiency in HCPMi uptake and release. In vivo tumor imaging analysis indicated that HCPMi penetrated deep into the tumor core and achieved greater uptake than PEG-LS. Results of HCPMi (DTX) treatment of allograft and xenograft mice in vivo showed high tumoral uptake and appreciable tumor retardation, with ∼70% tumor weight reduction in the SCC-7 allograft model. Taken together, these findings indicate that HCPMi could be developed further as a highly competent lipid-based drug-delivery system.

Supramolecular polyelectrolyte complex (SPEC): pH dependent phase transition and exploitation of its carrier properties

A supramolecular poly-electrolyte complex (SPEC) comprising poly-electrolyte acrylic acid with supramolecularly complexed guanidium is reported. This complex shows pH responsive phase transitions, which are described and characterized using microscopy, spectroscopy, density functional theory studies and Monte Carlo simulations. The phase behaviour of the SPEC is exploited by loading a dye like perylene and a drug, viz., doxorubicin, and their pH dependent controlled release is demonstrated, owing to the pH dependent phase change of the SPEC.

A rhenium tris-carbonyl derivative as a model molecule for incorporation into phospholipid assemblies for skin applications

A rhenium tris-carbonyl derivative (fac-[Re(CO)3Cl(2-(1-dodecyl-1H-1,2,3,triazol-4-yl)-pyridine)]) was incorporated into phospholipid assemblies, called bicosomes, and the penetration of this molecule into skin was monitored using Fourier-transform infrared microspectroscopy (FTIR). To evaluate the capacity of bicosomes to promote the penetration of this derivative, the skin penetration of the Re(CO)3 derivative dissolved in dimethyl sulfoxide (DMSO), a typical enhancer, was also studied. Dynamic light scattering results (DLS) showed an increase in the size of the bicosomes with the incorporation of the Re(CO)3 derivative, and the FTIR microspectroscopy showed that the Re(CO)3 derivative incorporated in bicosomes penetrated deeper into the skin than when dissolved in DMSO. When this molecule was applied on the skin using the bicosomes, 60% of the Re(CO)3 derivative was retained in the stratum corneum (SC) and 40% reached the epidermis (Epi). Otherwise, the application of this molecule via DMSO resulted in 95% of the Re(CO)3 derivative being in the SC and only 5% reaching the Epi. Using a Re(CO)3 derivative with a dodecyl-chain as a model molecule, it was possible to determine the distribution of molecules with similar physicochemical characteristics in the skin using bicosomes. This fact makes these nanostructures promising vehicles for the application of lipophilic molecules inside the skin.

Advanced lipid systems containing β-carotene: stability under UV-vis radiation and application on porcine skin in vitro

Phospholipid-based nanostructures, bicelles and bicosomes, are proposed as carriers of the antioxidant β-carotene.

Characterization and stability of catanionic vesicles formed by pseudo-tetraalkyl surfactant mixtures

The phase behavior of an ad hoc synthesized surfactant, sodium 8-hexadecylsulfate (8-SHS), and its mixtures with didecyldimethylammonium bromide (DiDAB) in water is reported. We dealt with dilute concentration regimes, at a total surfactant content of <30 mmol kg(-1) where vesicular aggregates may be formed. The high synergistic behavior of such catanionic mixtures is concomitant with strongly negative interaction parameters, β (≈-18 kBT), significant gain in the free energy of association, ΔGagg, and much lower association concentration compared to the pure surfactants. Vesicle size and ζ-potential depend on the mixture composition. Hydrodynamic diameters increase by progressive addition of oppositely charged surfactants to the one in excess. Counter-intuitively, the ζ-potential becomes more negative at DiDAB molar fractions close to 0.2. The same holds in the reverse case, the ζ-potential becomes more positive after small additions of 8-SHS; anyhow, the effect is more significant in anionic-rich mixtures. This phenomenon was explained by assuming a significant release of counterions and an asymmetric distribution of the two surfactants in the inner and outer vesicle leaflets. The equimolar mixtures form a cubic phase rather than the expected lamellar one. The effect of NaBr concentration on the stability of catanionic vesicles was also investigated. At high NaBr concentrations, all systems are destabilized. For DiDAB-rich vesicles, flocculation is observed, while for 8-SHS-rich ones, lamellar domains are formed at the bottom of the samples. The role played by NaBr depends on whether it is added before or after mixing the surfactants. In particular, preformed catanionic vesicles show a great kinetic stability towards addition of NaBr compared to those obtained by other procedures.

Molecular interactions of plant oil components with stratum corneum lipids correlate with clinical measures of skin barrier function

Plant-derived oils consisting of triglycerides and small amounts of free fatty acids (FFAs) are commonly used in skincare regimens. FFAs are known to disrupt skin barrier function. The objective of this study was to mechanistically study the effects of FFAs, triglycerides and their mixtures on skin barrier function. The effects of oleic acid (OA), glyceryl trioleate (GT) and OA/GT mixtures on skin barrier were assessed in vivo through measurement of transepidermal water loss (TEWL) and fluorescein dye penetration before and after a single application. OA's effects on stratum corneum (SC) lipid order in vivo were measured with infrared spectroscopy through application of perdeuterated OA (OA-d34 ). Studies of the interaction of OA and GT with skin lipids included imaging the distribution of OA-d34 and GT ex vivo with IR microspectroscopy and thermodynamic analysis of mixtures in aqueous monolayers. The oil mixtures increased both TEWL and fluorescein penetration 24 h after a single application in an OA dose-dependent manner, with the highest increase from treatment with pure OA. OA-d34 penetrated into skin and disordered SC lipids. Furthermore, the ex vivo IR imaging studies showed that OA-d34 permeated to the dermal/epidermal junction while GT remained in the SC. The monolayer experiments showed preferential interspecies interactions between OA and SC lipids, while the mixing between GT and SC lipids was not thermodynamically preferred. The FFA component of plant oils may disrupt skin barrier function. The affinity between plant oil components and SC lipids likely determines the extent of their penetration and clinically measurable effects on skin barrier functions.

Probing the transmembrane structure and topology of microsomal cytochrome-p450 by solid-state NMR on temperature-resistant bicelles

Though the importance of high-resolution structure and dynamics of membrane proteins has been well recognized, optimizing sample conditions to retain the native-like folding and function of membrane proteins for Nuclear Magnetic Resonance (NMR) or X-ray measurements has been a major challenge. While bicelles have been shown to stabilize the function of membrane proteins and are increasingly utilized as model membranes, the loss of their magnetic-alignment at low temperatures makes them unsuitable to study heat-sensitive membrane proteins like cytochrome-P450 and protein-protein complexes. In this study, we report temperature resistant bicelles that can magnetically-align for a broad range of temperatures and demonstrate their advantages in the structural studies of full-length microsomal cytochrome-P450 and cytochrome-b5 by solid-state NMR spectroscopy. Our results reveal that the N-terminal region of rabbit cytochromeP4502B4, that is usually cleaved off to obtain crystal structures, is helical and has a transmembrane orientation with ~17° tilt from the lipid bilayer normal.