Influence of electrostatic interactions on the release of charged molecules from lipid cubic phases

Soft Materials with Time-Programmed Changes in Physical Properties through Lyotropic Phase Transitions Induced by pH-Changing Reactions

We present the development of time-programmable functional soft materials. The materials undergo reversible phase transitions between lyotropic phases with different topologies and symmetries, which in turn have very different physical properties: viscosity, diffusion, and optical transparency. Here, this behavior is achieved by combining pH-responsive lyotropic phases made from the lipid monoolein doped with 10% oleic acid, with chemical reactions that have well-defined controllable kinetics: autocatalytic urea-urease and methyl formate hydrolysis, which increase and decrease pH, respectively. In this case, we use small-angle X-ray scattering (SAXS) and optical imaging to show temporally controlled transitions between the cloudy hexagonal phase, which is a two-dimensional (2D) array of cylindrical inverse micelles, and the transparent, highly viscous three-dimensional (3D) bicontinuous cubic phases. By combining these into a single reaction mixture where the pH increases and then decreases again, we can induce a sequential transformation cycle from hexagonal to cubic and back to hexagonal over several hours. The sample therefore changes from cloudy to transparent and back again as a proof-of-concept demonstration for a wider range of soft materials with time-programmable changes in physical properties.

Liquid crystalline lipid nanoparticles improve the antibacterial activity of tobramycin and vancomycin against intracellular Pseudomonas aeruginosa and Staphylococcus aureus

The intracellular survival of bacteria is a significant challenge in the fight against antimicrobial resistance. Currently available antibiotics suffer from limited penetration across host cell membranes, resulting in suboptimal treatment against the internalised bacteria. Liquid crystalline nanoparticles (LCNP) are gaining significant research interest in promoting the cellular uptake of therapeutics due to their fusogenic properties; however, they have not been reported for targeting intracellular bacteria. Herein, the cellular internalisation of LCNPs in RAW 264.7 macrophages and A549 epithelial cells was investigated and optimized through the incorporation of a cationic lipid, dimethyldioctadecylammonium bromide (DDAB). LCNPs displayed a honeycomb-like structure, while the inclusion of DDAB resulted into an onion-like organisation with larger internal pores. Cationic LCNPs enhanced the cellular uptake in both cells, reaching up to ∼90% uptake in cells. Further, LCNPs were encapsulated with tobramycin or vancomycin to improve their activity against intracellular gram-negative, Pseudomonas aeruginosa (P. aeruginosa) and gram-positive, Staphylococcus aureus (S. aureus) bacteria. The enhanced cellular uptake of cationic LCNP resulted in significant reduction of intracellular bacterial load (up to 90% reduction), compared to antibiotic dosed in its free form; with reduced performance observed for epithelial cells infected with S. aureus. Specifically engineered LCNP can re-sensitise antibiotics against both intracellular Gram positive and negative bacteria in diverse cell lines.

A solution NMR view of Lipidic Cubic Phases: Structure, dynamics, and beyond

Nuclear magnetic resonance (NMR) spectroscopy is well-established nowadays for the elucidation of the 3D structures of proteins and protein complexes, the evaluation of biomolecular dynamics with atomistic resolution across a range of time scales, the screening of drug candidates with site specificity, and for the quantitation of molecular translational diffusion. Lyotropic lipidic cubic phases (LCPs) are lipid bilayer-based materials with a complex geometry, formed via the spontaneous self-assembly of certain lipids in an aqueous environment at specific temperature ranges. LCPs have been successfully applied to the in meso crystallization of membrane proteins for structural studies by X-ray crystallography, and have also shown promising potential for serving as matrices for drug and nutrient delivery/release in vivo. The characterization of the structural and dynamics properties of LCPs is of significant interest for the application of these materials. Here we present a systematic review detailing the characterization of LCPs by solution NMR. Using LCPs formed by monoolein (MO) as an example, various aspects of LCPs readily accessible by solution NMR are covered, including spectral perturbation in the presence of additives, quantification of hydration levels, ¹³C relaxation-based measurements for studying atom-specific dynamics along the MO hydrocarbon chain, PGSE NMR measurement of translational diffusion and its correlation with release profiles, and the encapsulation of soluble proteins in LCPs. A brief discussion of future perspectives for the characterization of LCPs by solution NMR is also presented.

A lipidic mesophase with tunable release properties for the local delivery of macromolecules: the apoferritin nanocage, a case study

Lipid mesophases are able to incorporate and release a plethora of molecules, spanning from hydrophobic drugs to small hydrophilic proteins and therefore they have been widely used as drug delivery systems. However, their 3-5 nm water channels do not allow the release of large hydrophilic molecules such as monoclonal antibodies and therapeutic proteins. To overcome this major geometrical constraint, we designed a gel by mixing monoacylglycerol lipids, generally recognized as safe for human and/or animal use by FDA, and phospholipids, to obtain a material with swollen water channels suitable to host and further release macromolecules. Apoferritin, a 12 nm nanocage protein with intrinsic tumor-targeting properties able to incorporate several molecules, was selected here as the hydrophilic model protein to be embedded in the biocompatible gel. When immersed completely in the release media, mesophases with a swollen water channel of 22 nm, composed of monoolein and doped with 5 mole% of DOPS and 10 mole% of Chol allowed us to achieve a protein release of 60%, which is 120 times higher with respect to that obtained by employing non swollen-LMPs composed only of monoolein. Thus, the formulation can be administered locally to the rectal or vaginal mucosa, reducing the drawbacks often associated with the parenteral administration of bio-therapeutics. This approach would pave the way for the local application of other biomacromolecules (including human ferritin, monoclonal antibodies and antibody drug-conjugates) in those diseases easily reachable by a local application such as rectal or vaginal cancer.

Cubosomes as an emerging platform for drug delivery: a state-of-the-art review

Lipid-based drug delivery nanoparticles, including non-lamellar type, mesophasic nanostructured materials of lyotropic liquid crystals (LLCs), have been a topic of interest for researchers for their applications in encapsulation of drugs...

The effect of headgroup methylation on polymorphic phase behaviour in hydrated N-methylated phosphoethanolamine:palmitic acid membranes

Mixtures of fatty acids and phospholipids can form hexagonal (HII) and inverse bicontinuous cubic phases, the latter of which are implicated in various cellular processes and have wide-ranging biotechnological applications in protein crystallisation and drug delivery systems. Therefore, it is vitally important to understand the formation conditions of inverse bicontinuous cubic phases and how their properties can be tuned. We have used differential scanning calorimetry and synchrotron-based small angle and wide angle X-ray scattering (SAXS/WAXS) to investigate the polymorphic phase behaviour of palmitic acid/partially-methylated phospholipid mixtures, and how headgroup methylation impacts on inverse bicontinuous cubic phase formation. We find that upon partial methylation of the phospholipid headgroup (1 or 2 methyl substituents) inverse bicontinuous cubic phases are formed (of the Im3m spacegroup), which is not the case with 0 or 3 methyl substituents. This shows how important headgroup methylation is for controlling phase behaviour and how a change in headgroup methylation can be used to controllably tune various inverse bicontinuous phase features such as their lattice parameter and the temperature range of their stability.

A Lipid-Based Depot Formulation with a Novel Non-lamellar Liquid Crystal Forming Lipid

PURPOSE

Non-lamellar liquid crystal (NLLC)-forming lipids have gained attention as a novel component because of their ability to self-assemble upon contact with body fluids. In this study, a novel NLLC-forming lipid, mono-O-(5, 9, 13-trimethyl-4-tetradecenyl) glycerol ester (C17MGE), and a model drug with a middle molecule weight, leuprolide acetate (LA), were used to confirm the usefulness of C17MGE as an excipient for depot formulations with sustained release properties.

METHODS

A self-constructed depot formulation was prepared by mixing C17MGE and different types of phospholipids. The constructed NLLC structure was evaluated using small angle X-ray analysis and cryo-transmission electron microscopy. In vitro release and blood concentration profiles of LA were investigated.

RESULTS

The NLLC structure was confirmed by small angle X-ray analysis. LA release was able to be modified by adding different ratios of various phospholipids to C17MGE. Formulations containing 1, 2-dioleoyl-sn-glycero-3-phosphoglycerol sodium salt with a mixing ratio of 12% or 24% (MDOPG12 or MDOPG24, respectively) exhibited sustained release profiles of LA. In addition, the blood concentration of LA was detected over 21 days or more after administration of MDOPG12, and the absolute bioavailability was calculated to be about 100%.

CONCLUSIONS

A depot formulation using C17MGE was useful to achieve sustained release of LA.

Impact of Molecular Partitioning and Partial Equilibration on the Estimation of Diffusion Coefficients from Release Experiments

The present work addresses the effect of partial equilibration and molecular partitioning on the interpretation of release experiments. In this regard, it is shown how release profiles and the values of extracted transport parameters are affected by the time protocol chosen for sample collection by considering a series of experiments where the latter is systematically varied. Caffeine is investigated as a main model drug because of its similar affinity for water and lipids, while monolinolein-based lipid cubic phases are chosen as host matrices because of their wide employment in release studies. Our findings point to a progressive decline in diffusion rate upon increasing the time step, that is, the gap in time between two consecutive pickups, which is a signature of increasing equilibration of caffeine concentration between the lipidic mesophase and the water phase. Furthermore, the amount of released molecules at the first pickup displays negligible changes for large time steps, indicating complete equilibration in such cases. A model is introduced based on Fick's diffusion which goes beyond the assumption of perfect-sink conditions, a common feature of the typical theoretical approaches hitherto developed. The model is shown to account quantitatively for the experimental data and is subsequently employed to clarify the interplay of the adopted release protocol with the various transport parameters in determining the final outcome of the release process. Particularly, two additional molecular drugs are considered, namely glucose and proflavine, which are, respectively, more hydrophilic and hydrophobic than caffeine, thus allowing elucidating the role of molecular partitioning.

Lipidic Liquid Crystalline Cubic Phases and Magnetocubosomes as Methotrexate Carriers

The release profiles of methotrexate, an anticancer drug, from the monoolein liquid crystalline cubic phases were studied. The cubic phases were used either in the form of a lipidic film deposited onto a glassy carbon electrode surface or in the dispersed form of magnetocubosomes, which are considered a prospective hybrid drug delivery system. Commonly, cubosomes or liposomes are employed, but not in the case of toxic methotrexate, known to block the receptors responsible for folate transport into the cells. The release profiles of the drug from the lipidic films were monitored electrochemically and described using the Higuchi model. They were also modified via changes in temperature; the release was faster, although it deviated from the model when the temperature was increased. Cubic phase nanoparticles (magnetocubosomes) containing hydrophobic magnetic nanoparticles placed in an alternating magnetic field of low frequency and amplitude, stimulated drug release from the suspension, which was monitored spectroscopically. These new biocompatible hybrid nanomaterials in the dispersed form allow to control the release of the drug at the appropriate sites, can be easily separated or relocated under external magnetic field and await further investigations of their in vitro cytotoxicity and in vivo biodistribution.

Mathematical Models as Tools to Predict the Release Kinetic of Fluorescein from Lyotropic Colloidal Liquid Crystals

In this study, we investigated the release kinetic of fluorescein from colloidal liquid crystals made from monoglyceride and different non-ionic surfactants. The crystals were physicochemically characterized and the release experiments were carried out under the sink conditions, while mathematical models were described as extrapolations from solutions of the diffusion equation, in different initial and boundary conditions imposed by pharmaceutical formulations. The diffusion equation was solved using Laplace and Fourier transformed functions for release kinetics from infinite reservoirs in a semi-infinite medium. Solutions represents a general square root law and can be applied for the release kinetic of fluorescein from lyotropic colloidal liquid crystals. Akaike, Schwartz, and Imbimbo criteria were used to establish the appropriate mathematical model and the hierarchy of the performances of different models applied to the release experiments. The Fisher statistic test was applied to obtain the significance of differences among mathematical models. Differences of mathematical criteria demonstrated that small or no significant statistic differences were carried out between the various applied models and colloidal formulations. Phenomenological models were preferred over the empirical and semi-empirical ones. The general square root model shows that the diffusion-controlled release of fluorescein is the mathematical models extrapolated for lyotropic colloidal liquid crystals.

Zein-Paclitaxel Prodrug Nanoparticles for Redox-Triggered Drug Delivery and Enhanced Therapeutic Efficiency

Prodrug, in which the inactive parent drug with good bioavailability is metabolized into an active drug in the body, is one of the main strategies to target the disease site to improve the drug efficiency and reduce the adverse effects of chemotherapy. Because of the good capability of chemical modification, zein, a plant derived protein, and drugs can be conjugated through environmentally sensitive links to form prodrugs capable of triggered drug release. In this study, a novel prodrug was synthesized using paclitaxel (PTX), zein, and a disulfide linker, and nanoparticles were formed by self-assembly of the prodrug. An effective in vitro triggered release, 80-90% in 5 min, of the prodrug based nanoparticles (zein-S-S-PTX_NP) was successfully approached. The cytotoxicity of zein-S-S-PTX_NP as well as the zein encapsulation of PTX (zein_PTX_NP) and pure PTX on HeLa cells and NIH/3T3 fibroblast cells was tested using MTS assay. It showed that, after the treatment of zein-S-S-PTX_NP at the equivalent PTX concentrations of 0.1, 0.5, 1, and 5 μg/mL, respectively, zein-S-S-PTX_NP had zero damage to normal cells but a similar cytotoxicity to cancer cells as pure PTX. In the animal study, the tumor was 50% of the original size after the treatment of zein-S-S-PTX_NP for 9 days with 3 doses. This study suggested that the novel prodrug based nanoparticle zein-S-S-PTX_NP could be a promising approach in chemotherapy with targeted delivery, improved efficacy, and reduced side effects.

Influence of a pH-sensitive polymer on the structure of monoolein cubosomes

Cubosomes consist in submicron size particles of lipid bicontinuous cubic phases stabilized by surfactant polymers. They provide an appealing road towards the practical use of lipid cubic phases for pharmaceutical and cosmetic applications, and efforts are currently being made to control the encapsulation and release properties of these colloidal objects. We overcome in this work the lack of sensitivity of monoolein cubosomes to pH conditions by using a pH sensitive polymer designed to strongly interact with the lipid structure at low pH. Our cryo-transmission electron microscope (cryo-TEM) and small-angle X-ray scattering (SAXS) results show that in the presence of the polymer the cubic phase structure is preserved at neutral pH, albeit with a larger cell size. At pH 5.5, in the presence of the polymer, the nanostructure of the cubosome particles is significantly altered, providing a pathway to design pH-responsive cubosomes for applications in drug delivery.

Self-Assembled Lipid Cubic Phase and Cubosomes for the Delivery of Aspirin as a Model Drug

Three-dimensionally organized lipid cubic self-assemblies and derived oil-in-water emulsions called "cubosomes" are attractive for various biotechnological applications due to their ability to be loaded with functional molecules and their associated sustained release properties. Here, we employed both of these lipid-based systems for the delivery of a model drug, aspirin, under comparable conditions. Studies were performed by varying drug-to-lipid ratio and the type of release medium, water and phosphate buffer saline (PBS). Release rates were determined using UV-vis spectroscopy, and small-angle X-ray scattering was used to confirm the type of self-assembled nanostructures formed in these lipid systems. The release from the bulk lipid cubic phase was sustained as compared to that of dispersed cubosomes, and the release in PBS was more efficient than in water. The tortuosity of the architecture, length of the diffusion pathway, type of nanostructure, and physicochemical interaction with the release media evidently contribute to these observations. This work is particularly important as it is the first report where both of these nanostructured lipid systems have been studied together under similar conditions. This work provides important insights into understanding and therefore controlling the release behavior of lipid-based drug nanocarriers.

Lipidic Cubic-Phase Nanoparticles-Cubosomes for Efficient Drug Delivery to Cancer Cells

Self-assembled lipid liquid-crystalline nanoparticles, known as cubosomes, were used for the delivery of the anticancer drug doxorubicin (DOX). Several properties make cubosomes a promising alternative in the development of controlled-release systems for drug delivery. They have a larger internal surface area than other carriers, hence deliver more drug molecules to the affected cells and maintain the cubic symmetry of the parent lipidic cubic phase, but at the same time they have a lower viscosity thereby facilitating transport of the drug. The pH-dependent drug release profiles, evaluated by voltammetry, demonstrated triggered drug release from the cubosome carrier to the environment of the cancer cells, where pH is lower. The anticancer effect of a DOX-loaded cubosome on the glioblastoma T98G cell line was found to be highly efficient and required lower concentrations of DOX to inhibit the proliferation of cancer cells than the effective concentrations of free DOX.

Responsive self-assembled nanostructured lipid systems for drug delivery and diagnostics

While stimuli-responsive polymers have received a huge amount of attention in the literature, responsive lipid-based mesophase systems offer unique opportunities in biomedical applications such as drug delivery and biosensing. The different mesophase equilibrium structures enables dynamic switching between nanostructures to facilitate drug release or as a transducer for recognition events. In drug delivery, this behavior offers researchers the means to deliver a therapeutic payload at a specific rate and time i.e. 'on-demand'. This review summarizes the distinctive features of these multifaceted materials and aggregates the current state of the art research from our groups and others into the use of these materials as bulk gels and nanostructured dispersions for drug delivery, biosensing and diagnostics.

Effects of paclitaxel (PTX) prodrug-based self-assembly peptide hydrogels combined with suberoylanilide hydroxamic acid (SAHA) for PTX-resistant cancer and synergistic antitumor therapy

Schematic illustration of PTX prodrug-based self-assembly peptide hydrogels encapsulated SAHA for drug combination.

pH-responsive lyotropic liquid crystals and their potential therapeutic role in cancer treatment

A weak amphiphilic base, pyridinylmethyl linoleate, is blended with monolinolein, yielding mesophases with a pH-induced hexagonal-to-cubic transition at pH ≤ 5.5. We show the potential therapeutic role of this mesophase in treating cancerous tissues exploiting their more acidic pH compared to healthy tissues. In vitro release studies with doxorubicin on HT29 human colon cancer cells show a 10-fold faster release and 3-fold increased efficiency for killing cancer cells at pH 5.5 versus pH 7.4, demonstrating the potential of this strategy in cancer treatment.

Design of Light-Triggered Lyotropic Liquid Crystal Mesophases and Their Application as Molecular Switches in "On Demand" Release

Here, we present the design and assembly of a new light-responsive functional lyotropic liquid crystal system using host-guest lipidic mesophases (LMPs). Light as an external stimulus has many advantages in comparison to other stimuli: it is milder than acids or bases, and variation of intensity and duration can provide a high level of pharmacological control. The LMPs are composed of monoolein (MO) and oleic acid (OA) as host lipids and a small amount of a judiciously synthesized lipid bearing an azobenzene photoactive unit as a guest. While preserving the structure and stability of the host lipidic aggregates, the guest lipids render them specific functionalities. Single-step and sequential light-triggered release and retention of the embedded dye molecules are demonstrated, thereby achieving exquisite temporal, spatial, and dosage control of the release, opening up the possibility of using such lipidic biomaterials as effective matrices in therapy, when a continuous release of active drugs might be toxic.

Temperature and pressure tuneable swollen bicontinuous cubic phases approaching nature's length scales

Bicontinuous cubic structures offer enormous potential in applications ranging from protein crystallisation to drug delivery systems and have been observed in cellular membrane structures. One of the current bottlenecks in understanding and exploiting these structures is that cubic scaffolds produced in vitro are considerably smaller in size than those observed in biological systems, differing by almost an order of magnitude in some cases. We have addressed this technological bottleneck and developed a methodology capable of manufacturing highly swollen bicontinuous cubic membranes with length scales approaching those seen in vivo. Crucially, these cubic systems do not require the presence of proteins. We have generated highly swollen Im3m symmetry bicontinuous cubic phases with lattice parameters of up to 480 Å, composed of ternary mixtures of monoolein, cholesterol and negatively charged lipid (DOPS or DOPG) and we have been able to tune their lattice parameters. The swollen cubic phases are highly sensitive to both temperature and pressure; these structural changes are likely to be controlled by a fine balance between lipid headgroup repulsions and lateral pressure in the hydrocarbon chain region.

Stimuli-responsive lipidic cubic phase: triggered release and sequestration of guest molecules

New stimuli-responsive nanomaterials, made up of host-guest lipidic cubic phases (LCPs) are presented. These biocompatible, stable, transparent and water-insoluble LCPs are composed of monoolein (MO) as a neutral host, and small amounts of one of three judiciously designed and synthesized designer lipids as guest that preserve the structure and stability of LCPs, but render them specific functionalities. Efficient pH- and light-induced binding, release and sequestration of hydrophilic dyes are demonstrated. Significantly, these processes can be performed sequentially, thereby achieving both temporal and dosage control, opening up the possibility of using such LCPs as effective carriers to be used in drug delivery applications. Specifically, because of the inherent optical transparency and molecular isotropy of LCPs they can be envisaged as light-induced drug carriers in ophthalmology. The results presented here demonstrate the potential of molecular design in creating new functional materials with predicted operating mode.