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

Polyol-modified deformable liposomes fortified contact lenses for improved ocular permeability

AIM

To develop a glycerol modified liposomes to effectively deliver active agents into posterior segment of the eye for the management of posterior uveitis.

MATERIALS AND METHODS

The modified liposome enhanced with glycerol as an edge activator was fabricated using a 32 experimental design with independent variables being soya lecithin (mg) (X1) and glycerol (%) (X2) and vesicle size (nm) (Y1), deformability index (%) (Y2), and entrapment efficiency (%) (Y3) as dependent variable with improve permeability and entrapment efficacy. These modified liposomes were then integrated into pHEMA-based contact lenses via free radical polymerization using different monomer mixture, co-polymer, crosslinker, and photo-initiator to extend drug release.

RESULTS AND CONCLUSIONS

Nano-vesicles resulted in size and deformability index of 200.5 ± 15 nm and 11.58, respectively, with entrapment efficiency of 80.98% of the drug. Moreover, the optimized lenses demonstrated 71%) of swelling and transmittance of 87%). In addition, in vitro release of active component from the therapeutic contact lens demonstrated sustained drug release over 24 h. Whereas ex vivo studies displayed a 5-fold increase in drug permeation, compared to tested conventional eye drops. The results suggested that glycerosomes-loaded contact lens can be a promising alternative for regulated delivery of dexamethasone sodium phosphate in the management of posterior uveitis.

A Sigma1 Receptor Agonist Alters Fluidity and Stability of Lipid Monolayers

Interactions between the sigma1 receptor agonist PRE-084 and various lipid monolayers, including dipalmitoylphosphatidylcholine (DPPC), DPP-ethanolamine (DPPE), DPP-glycerol (DPPG), DPP-serine (DPPS), palmitoylsphingomyelin (PSM), and cholesterol (Ch), were investigated to elucidate the effects of PRE-084 on membrane fluidity and stability. Their interactions with sigma1 receptor agonists have potential implications for neuroprotection, antidepressant, analgesic, and cognitive enhancement effects. In this study, we observed that the presence of PRE-084 in the subphase led to increased fluidity in DPPC and DPPE monolayers, whereas decreasing fluidity was observed in DPPG, DPPS, and PSM monolayers. The interaction of PRE-084 with Ch monolayers was found to be distinct from its interaction with other lipids. Fluorescence microscopy images revealed changes in the size and shape of liquid-condensed domains in the presence of PRE-084, supporting the notion of altered membrane fluidity. Our findings provide new insights into the interaction of PRE-084 with lipid monolayers and its potential implications for biological and membrane science.

The characteristics and biological activity enhancements of melatonin encapsulations for skin care product applications

Melatonin (MLT) exhibits antioxidant, ultraviolet protection, anti-inflammatory, and anti-aging properties. However, its effectiveness is limited by instability, a short half-life, and incompatible absorption. In this research, we encapsulated melatonin (MLT) in transfersomes (MT) and niosomes (MN) to enhance their properties and investigate their effects through in vitro cell assays using murine macrophages cells and human foreskin fibroblasts cells. The vesicle morphology, vesicle size, polydispersity index, zeta potential, entrapment efficiency (EE%), attenuated total reflectance-Fourier transform spectroscopy (ATR-FTIR) spectra, along with in vitro release, permeation profiles, and stability study were also evaluated. The results showed that both encapsulations displayed spherical morphology at the nanometric scale, their great physical stability and provided an EE% range of 58-78%. The MLT incorporation into the vesicle was confirmed by the ATR-FTIR spectra. Additionally, the encapsulation' release profiles fitted with the Higuchi model, indicating controlled release of melatonin. Furthermore, MT showed greater permeability than MN and MS including melatonin deposition. In cell assays, MT exhibited significantly higher nitric oxide inhibition and stimulation of collagen compared to MN and MS. Therefore, MT demonstrated the highest possibility for anti-inflammatory and collagen-stimulating activities that could be applied in pharmaceutical or anti-aging cosmetic products.

Phytosterol-mediated glycerosomes combined with peppermint oil enhance transdermal delivery of lappaconitine by modulating the lipid composition of the stratum corneum

Although the introduction of glycerosomes has enriched strategies for efficient transdermal drug delivery, the inclusion of cholesterol as a membrane stabilizer has limited their clinical application. The current study describes the development and optimization of a new type of glycerosome (S-glycerosome) that is formed in glycerol solution with β-sitosterol as the stabilizer. Moreover, the transdermal permeation properties of lappaconitine (LA)-loaded S-glycerosomes and peppermint oil (PO)-mediated S-glycerosomes (PO-S-glycerosomes) are evaluated, and the lipid alterations in the stratum corneum are analyzed via lipidomics. The LA-loaded S-glycerosomes prepared by the preferred formulation from the uniform design have a mean size of 145.3 ± 7.81 nm and an encapsulation efficiency of 73.14 ± 0.35%. Moreover, the addition of PO positively impacts transdermal flux, peaking at 0.4% (w/v) PO. Tracing of the fluorescent probe P4 further revealed that PO-S-glycerosomes penetrate deeper into the skin than S-glycerosomes and conventional liposomes. Additionally, treatment with PO-S-glycerosomes alters the isoform type, number, and composition of sphingolipids, glycerophospholipids, glycerolipids, and fatty acids in the stratum corneum, with the most notable effect observed for ceramides, the main component of sphingolipids. Furthermore, the transdermal administration of LA-loaded PO-S-glycerosomes improved the treatment efficacy of xylene-induced inflammation in mice without skin irritation. Collectively, these findings demonstrate the feasibility of β-sitosterol as a stabilizer in glycerosomes. Additionally, the inclusion of PO improves the transdermal permeation of S-glycerosomes, potentially by altering the stratum corneum lipids.

Temperature-Promoted Giant Unilamellar Vesicle (GUV) Aggregation: A Way of Multicellular Formation

The evolution of unicellular to multicellular life is considered to be an important step in the origin of life, and it is crucial to study the influence of environmental factors on this process through cell models in the laboratory. In this paper, we used giant unilamellar vesicles (GUVs) as a cell model to investigate the relationship between environmental temperature changes and the evolution of unicellular to multicellular life. The zeta potential of GUVs and the conformation of the headgroup of phospholipid molecules at different temperatures were examined using phase analysis light scattering (PALS) and attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR), respectively. In addition, the effect of increasing temperature on the aggregation of GUVs was further investigated in ionic solutions, and the possible mechanisms involved were explored. The results showed that increasing temperature reduced the repulsive forces between cells models and promoted their aggregation. This study could effectively contribute to our understanding of the evolution of primitive unicellular to multicellular life.

Investigating the Effect of Medium Chain Triglycerides on the Elasticity of Pulmonary Surfactant

In recent years, vaping has increased in both popularity and ease of access. This has led to an outbreak of a relatively new condition known as e-cigarette/vaping-associated lung injury (EVALI). This injury can be caused by physical interactions between the pulmonary surfactant (PS) in the lungs and toxins typically found in vaping solutions, such as medium chain triglycerides (MCT). MCT has been largely used as a carrier agent within many cannabis products commercially available on the market. Pulmonary surfactant ensures proper respiration by maintaining low surface tensions and interface stability throughout each respiratory cycle. Therefore, any impediments to this system that negatively affect the efficacy of this function will have a strong hindrance on the individual's quality of life. Herein, neutron spin echo (NSE) and Langmuir trough rheology were used to probe the effects of MCT on the mechanical properties of pulmonary surfactant. Alongside a porcine surfactant extract, two lipid-only mimics of progressing complexity were used to study MCT effects in a range of systems that are representative of endogenous surfactant. MCT was shown to have a greater biophysical effect on bilayer systems compared to monolayers, which may align with biological data to propose a mechanism of surfactant inhibition by MCT oil.

Effect of polyols on membrane structures of liposomes: A study using small-angle X-ray scattering data and generalized indirect Fourier transformation

This study aimed to evaluate the membrane structure of distearoylphosphatidylcholine (DSPC) liposomes dispersed in water containing various types of polyols with low molecular weight such as glycerin (Gly), 1,3-butandiol (BG), and propylene glycol (PG). To clarify the detailed membrane structure, generalized indirect Fourier transformation (GIFT) analysis, which provides information about the bilayer spacing, bilayer thickness, number of lamellar layers, and membrane flexibility, was applied to small-angle X-ray scattering (SAXS) data of the present system. The GIFT results showed that the bilayer thickness of the DSPC liposomes followed the order Gly>>BG>PG. In addition, the membrane flexibility estimated by the Caille parameter was in the order Gly>>BG>PG; this result was supported by the gel-liquid crystal phase transition temperature (T_c) obtained by differential scanning calorimetry (DSC). These results, together with the Raman spectra, suggest that BG and PG incorporated into the bilayers of DSPC liposomes result in the formation of an interdigitated lamellar structure.

Small-Angle Neutron Scattering for Studying Lipid Bilayer Membranes

Small-angle neutron scattering (SANS) is a powerful tool for studying biological membranes and model lipid bilayer membranes. The length scales probed by SANS, being from 1 nm to over 100 nm, are well-matched to the relevant length scales of the bilayer, particularly when it is in the form of a vesicle. However, it is the ability of SANS to differentiate between isotopes of hydrogen as well as the availability of deuterium labeled lipids that truly enable SANS to reveal details of membranes that are not accessible with the use of other techniques, such as small-angle X-ray scattering. In this work, an overview of the use of SANS for studying unilamellar lipid bilayer vesicles is presented. The technique is briefly presented, and the power of selective deuteration and contrast variation methods is discussed. Approaches to modeling SANS data from unilamellar lipid bilayer vesicles are presented. Finally, recent examples are discussed. While the emphasis is on studies of unilamellar vesicles, examples of the use of SANS to study intact cells are also presented.

Extrusion: A New Method for Rapid Formulation of High-Yield, Monodisperse Nanobubbles

Shell-stabilized gas microbubbles (MB) and nanobubbles (NB) are frequently used for biomedical ultrasound imaging and therapeutic applications. While it is widely recognized that monodisperse bubbles can be more effective in these applications, the efficient formulation of uniform bubbles at high concentrations is difficult to achieve. Here, it is demonstrated that a standard mini-extruder setup, commonly used to make vesicles or liposomes, can be used to quickly and efficiently generate monodisperse NBs with high yield. In this highly reproducible technique, the NBs obtained have an average diameter of 0.16 ± 0.05 µm and concentration of 6.2 ± 1.8 × 10¹⁰  NBs mL^-1 compared to 0.32 ± 0.1 µm and 3.2 ± 0.7 × 10¹¹  mL^-1 for NBs made using mechanical agitation. Parameters affecting the extrusion and NB generation process including the temperature, concentration of the lipid solution, and the number of passages through the extruder are also examined. Moreover, it is demonstrated that extruded NBs show a strong acoustic response in vitro and a strong and persistent US signal enhancement under nonlinear contrast enhanced ultrasound imaging in mice. The extrusion process is a new, efficient, and scalable technique that can be used to easily produce high yield smaller monodispersed nanobubbles.

Mechanistic study of the adsorption and penetration of modified SiO2 nanoparticles on cellular membrane

SiO₂ nanoparticles (NPs) are ubiquitous in the atmosphere and have been proved to be harmful to human by bioaccumulation. The bioaccumulation of SiO₂ NPs begins with their partitioning into membrane phospholipids. However, the uptake of SiO₂ particle onto lipid bilayers has been not completely understood. In this study, the uptake process of different modified SiO₂ particles (with adsorbed trace gas molecules, including formic acid (FA), methyl vinyl ketone (MVK), and methacrolein (MAC)) into DPPC bilayers were investigated by molecular dynamics (MD) simulations. Results suggest that after the SiO₂ particle absorbed on the surface of bilayers, it spun by itself to form the most stable adsorption configurations. MAC and MVK molecule tend to be absorbed into DPPC bilayer while FA molecule was more likely located at the surface region of bilayer from the viewpoint of thermodynamics. Besides, it was also found apart from the commonly accepted "Trojan-horse" effect, SiO₂ NPs may increase biohazard via modulating the concentration of pollutants. This work is beneficial for understanding the toxicity and bioaccumulation of FA, MVK, MAC, and SiO₂ NPs at molecular level.

Molecular insights into the uptake of SiO2 nanoparticles on phospholipid membrane: Effect of surface properties and particle size

Silica (SiO₂) nanoparticles (NPs) have attracted much attention due to the potential for a wide range of applications and they have been confirmed to be hazardous to humans. Partitioning to phospholipid bilayers is an important way for their bioaccumulation. However, the detailed mechanism of SiO₂ NPs uptake by membrane phospholipids remains uncertain. In this work, molecular dynamics (MD) simulations were employed to study the uptake process of SiO₂ NPs into DPPC bilayers. Results show that these SiO₂ NPs uptake onto DPPC bilayer surface is favorable from the viewpoint of thermodynamics. During the uptake process, the SiO₂ NP needed to adjust the angle of interaction with the DPPC surface until the most stable adsorption configuration was reached. After incorporating into DPPC bilayers, the interaction between PO₄^- group and SiO₂ particle is stronger than -N⁺(CH₃)₃ group and SiO₂. Small SiO₂ NP was found to adsorb to the surface of DPPC bilayer without disturbing the morphology or membrane. In contract, bioaccumulation of large SiO₂ NP to DPPC induced a strong local membrane deformation. In addition, the effect of SiO₂ NP surface functionalization on its interaction with DPPC was also investigated. This molecular-level study reports a complete description of the interaction between SiO₂ NPs and DPPC bilayer, aiming to provide some insights for the further work on the bioaccumulation and hemolytic activity of SiO₂ NPs.

In vitro Fourier transform infrared spectroscopic study of the effect of glycerol on the uptake of beclomethasone dipropionate in living respiratory cells

The quantification of drug in living cells is of increasing interest in pharmaceutical research because of its importance in understanding drug efficacy and toxicity. Label-free in situ measurement methods are advantageous for their ability to obtain chemical and time profiles without the need of labelling or extraction steps. We have previously shown that Fourier transform infrared (FTIR) spectroscopy has the potential to quantify drug in situ within living cells at micromolar level when a simple solution of drug was added to the medium. The purpose of this study was to demonstrate that the approach can evaluate more complex systems such as the effect of membrane modification by a formulation on drug uptakes. The inhaled corticosteroid, beclomethasone dipropionate (BDP), in Calu-3 respiratory epithelial cells in the absence and presence of glycerol, an excipient in some inhaled medicines was used as the model system. The FTIR method was first validated for limit of detection (LOD) and quantification (LOQ) according to published guidelines and the LOQ was found to be ∼ 20 μM, good enough to quantify BDP in the living cell. The uptake of BDP by living Calu-3 cells was found to be reduced in the presence of glycerol as expected due to the stiffening of the cell membrane by the presence of glycerol in the formulation. This study demonstrates the valuable analytical capability of live-cell FTIR to study the effect of formulation on drug transport in lungs and to evaluate drug availability to intracellular targets. We conclude that FTIR has potential to contribute widely at the frontier of live-cell studies.

Mechanistic Understanding from Molecular Dynamics in Pharmaceutical Research 2: Lipid Membrane in Drug Design

We review the use of molecular dynamics (MD) simulation as a drug design tool in the context of the role that the lipid membrane can play in drug action, i.e., the interaction between candidate drug molecules and lipid membranes. In the standard "lock and key" paradigm, only the interaction between the drug and a specific active site of a specific protein is considered; the environment in which the drug acts is, from a biophysical perspective, far more complex than this. The possible mechanisms though which a drug can be designed to tinker with physiological processes are significantly broader than merely fitting to a single active site of a single protein. In this paper, we focus on the role of the lipid membrane, arguably the most important element outside the proteins themselves, as a case study. We discuss work that has been carried out, using MD simulation, concerning the transfection of drugs through membranes that act as biological barriers in the path of the drugs, the behavior of drug molecules within membranes, how their collective behavior can affect the structure and properties of the membrane and, finally, the role lipid membranes, to which the vast majority of drug target proteins are associated, can play in mediating the interaction between drug and target protein. This review paper is the second in a two-part series covering MD simulation as a tool in pharmaceutical research; both are designed as pedagogical review papers aimed at both pharmaceutical scientists interested in exploring how the tool of MD simulation can be applied to their research and computational scientists interested in exploring the possibility of a pharmaceutical context for their research.

Toward Precisely Controllable Acoustic Response of Shell-Stabilized Nanobubbles: High Yield and Narrow Dispersity

Understanding the pressure dependence of the nonlinear behavior of ultrasonically excited phospholipid-stabilized nanobubbles (NBs) is important for optimizing ultrasound exposure parameters for implementations of contrast enhanced ultrasound, critical to molecular imaging. The viscoelastic properties of the shell can be controlled by the introduction of membrane additives, such as propylene glycol as a membrane softener or glycerol as a membrane stiffener. We report on the production of high-yield NBs with narrow dispersity and different shell properties. Through precise control over size and shell structure, we show how these shell components interact with the phospholipid membrane, change their structure, affect their viscoelastic properties, and consequently change their acoustic response. A two-photon microscopy technique through a polarity-sensitive fluorescent dye, C-laurdan, was utilized to gain insights on the effect of membrane additives to the membrane structure. We report how the shell stiffness of NBs affects the pressure threshold (P_t) for the sudden amplification in the scattered acoustic signal from NBs. For narrow size NBs with 200 nm mean size, we find P_t to be between 123 and 245 kPa for the NBs with the most flexible membrane as assessed using C-Laurdan, 465-588 kPa for the NBs with intermediate stiffness, and 588-710 kPa for the NBs with stiff membranes. Numerical simulations of the NB dynamics are in good agreement with the experimental observations, confirming the dependence of acoustic response to shell properties, thereby substantiating further the development in engineering the shell of ultrasound contrast agents. The viscoelastic-dependent threshold behavior can be utilized for significantly and selectively enhancing the diagnostic and therapeutic ultrasound applications of potent narrow size NBs.

Molecular dynamics exploring of atmosphere components interacting with lung surfactant phospholipid bilayers

Sulfur dioxide (SO₂), nitrogen oxide (NO₂) and ozone (O₃) in the atmosphere are significantly correlated with various respiratory and cardiovascular diseases. High doses of each of these gases or a mixture can change the physical and chemical properties of the lung membrane, thus leading to an increased pulmonary vascular permeability and structural failure of the alveolar cell membrane. In the present study, detailed molecular dynamic (MD) modeling was applied to investigate the effects of SO₂, NO₂, O₃ and mixtures of these gases on the dipalmitoyl phosphatidylcholine (DPPC) phospholipid bilayer. The results showed that several key physical properties, including the mass density, lipid ordering parameter, lipid diffusion, and electrostatic potential of the cell membrane, have been changed by the binding of different compounds. This resulted in significant variations and more disorder in the DPPC bilayer. The multiple analyses of membrane properties proved the toxicity of NO₂, O₃, and SO₂ to the DPPC bilayer, providing a theoretical basis for the experimental phenomenon that SO₂, NO₂ and O₃ can cause lung cell apoptosis. For the single systems, the damage to DPPC bilayer caused by O₃ was more serious than NO₂ and SO₂. More importantly, the MD simulations using the mixtures of SO₂, NO₂, and O₃ showed a much greater decline of membrane fluidity and the aggravation of membrane damage than the single systems, indicating a synergistic effect when NO₂, SO₂, and O₃ coexisted in the atmosphere, which could lead to much more severe damage and greater toxicities to the lung.

Contemporary Formulation Development for Inhaled Pharmaceuticals

Pulmonary delivery has gained increased interests over the past few decades. For respiratory conditions, targeted drug delivery directly to the site of action can achieve a high local concentration for efficacy with reduced systemic exposure and adverse effects. For systemic conditions, the unique physiology of the lung evolutionarily designed for rapid gaseous exchange presents an entry route for systemic drug delivery. Although the development of inhaled formulations has come a long way over the last few decades, many aspects of it remain to be elucidated. In particular, a reliable and well-understood method for in vitro-in vivo correlations remains to be established. With the rapid and ongoing advancement of technology, there is much potential to better utilise computational methods including different types of modelling and simulation approaches to support inhaled formulation development. This review intends to provide an introduction on some fundamental concepts in pulmonary drug delivery and inhaled formulation development followed by discussions on some challenges and opportunities in the translation of inhaled pharmaceuticals from preclinical studies to clinical development. The review concludes with some recent advancements in modelling and simulation approaches that could play an increasingly important role in modern formulation development of inhaled pharmaceuticals.

Contrast enhanced ultrasound imaging by nature-inspired ultrastable echogenic nanobubbles

Advancement of ultrasound molecular imaging applications requires not only a reduction in size of the ultrasound contrast agents (UCAs) but also a significant improvement in the in vivo stability of the shell-stabilized gas bubble. The transition from first generation to second generation UCAs was marked by an advancement in stability as air was replaced by a hydrophobic gas, such as perfluoropropane and sulfur hexafluoride. Further improvement can be realized by focusing on how well the UCAs shell can retain the encapsulated gas under extreme mechanical deformations. Here we report the next generation of UCAs for which we engineered the shell structure to impart much better stability under repeated prolonged oscillation due to ultrasound, and large changes in shear and turbulence as it circulates within the body. By adapting an architecture with two layers of contrasting elastic properties similar to bacterial cell envelopes, our ultrastable nanobubbles (NBs) withstand continuous in vitro exposure to ultrasound with minimal signal decay and have a significant delay on the onset of in vivo signal decay in kidney, liver, and tumor. Development of ultrastable NBs can potentially expand the role of ultrasound in molecular imaging, theranostics, and drug delivery.

Evaluation of EGCG Loading Capacity in DMPC Membranes

Catechins are molecules with potential use in different pathologies such as diabetes and cancer, but their pharmaceutical applications are often hindered by their instability in the bloodstream. This issue can be circumvented using liposomes as their nanocarriers for in vivo delivery. In this work, we studied the molecular details of (-)-epigallocatechin-3-gallate (EGCG) interacting with 1,2-dimyristoyl- sn-glycero-3-phosphocholine (DMPC) monolayer/bilayer systems to understand the catechin loading ability and liposome stability, using experimental and computational techniques. The molecular dynamics simulations show the EGCG molecules deep inside the lipid bilayer, positioned below the lipid ester groups, generating a concentration-dependent lipid condensation. This effect was also inferred from the surface pressure isotherms of DMPC monolayers. In the polarization-modulated infrared reflection absorption spectra assays, the predominant effect at higher concentrations of EGCG (e.g., 20 mol %) was an increase in lipid tail disorder. The steady-state fluorescence data confirmed this disordered state, indicating that the catechin-induced liposome aggregation outweighs the condensation effects. Therefore, by adding more than 10 mol % EGCG to the liposomes, a destabilization of the vesicles occurs with the ensuing release of entrapped catechins. The loading capacity for DMPC seems to be limited by its disordered lipid arrangements, typical of a fluid phase. To further increase the clinical usefulness of liposomes, lipid bilayers with more stable and organized assemblies should be employed to avoid aggregation at large concentrations of catechin.