Antibacterial and anti-biofilm activities of antibiotic-free phosphatidylglycerol/docosahexaenoic acid lamellar and non-lamellar liquid crystalline nanoparticles

Infectious diseases, particularly those associated with biofilms, are challenging to treat due to an increased tolerance to commonly used antibiotics. This underscores the urgent need for innovative antimicrobial strategies. Here, we present an alternative simple-by-design approach focusing on the development of biocompatible and antibiotic-free nanocarriers from docosahexaenoic acid (DHA) that has the potential to combat microbial infections and phosphatidylglycerol (DOPG), which is attractive for use as a biocompatible prominent amphiphilic component of Gram-positive bacterial cell membranes. We assessed the anti-bacterial and anti-biofilm activities of these nanoformulations (hexosomes and vesicles) against S. aureus and S. epidermidis, which are the most common causes of infections on catheters and medical devices by different methods (including resazurin assay, time-kill assay, and confocal laser scanning microscopy on an in vitro catheter biofilm model). In a DHA-concentration-dependent manner, these nano-self-assemblies demonstrated strong anti-bacterial and anti-biofilm activities, particularly against S. aureus. A five-fold reduction of the planktonic and a four-fold reduction of biofilm populations of S. aureus were observed after treatment with hexosomes. The nanoparticles had a bacteriostatic effect against S. epidermidis planktonic cells but no anti-biofilm activity was detected. We discuss the findings in terms of nanoparticle-bacterial cell interactions, plausible alterations in the phospholipid membrane composition, and potential penetration of DHA into these membranes, leading to changes in their structural and biophysical properties. The implications for the future development of biocompatible nanocarriers for the delivery of DHA alone or in combination with other anti-bacterial agents are discussed, as novel treatment strategies of Gram-positive infections, including biofilm-associated infections.

A bio-ionic liquid based self-healable and adhesive ionic hydrogel for the on-demand transdermal delivery of a chemotherapeutic drug

The non-invasive nature and potential for sustained release make transdermal drug administration an appealing treatment option for cancer therapy. However, the strong barrier of the stratum corneum (SC) poses a challenge for the penetration of hydrophilic chemotherapy drugs such as 5-fluorouracil (5-FU). Due to its biocompatibility and capacity to increase drug solubility and permeability, especially when paired with chemical enhancers, such as oleic acid (OA), which is used in this work, choline glycinate ([Cho][Gly]) has emerged as a potential substance for transdermal drug delivery. In this work, we examined the possibility of transdermal delivery of 5-FU for the treatment of breast cancer using an ionic hydrogel formulation consisting of [Cho][Gly] with OA. Small angle neutron scattering, rheological analysis, field emission scanning electron microscopy, and dynamic light scattering analysis were used to characterize the ionic hydrogel. The non-covalent interactions present between [Cho][Gly] and OA were investigated by computational simulations and FTIR spectroscopy methods. When subjected to in vitro drug permeation using goat skin in a Franz diffusion cell, the hydrogel demonstrated sustained release of 5-FU and effective permeability in the order: [Cho][Gly]-OA gel > [Cho][Gly] > PBS (control). The hydrogel also demonstrated 92% cell viability after 48 hours for the human keratinocyte cell line (HaCaT cells) as well as the normal human cell line L-132. The breast cancer cell line MCF-7 and the cervical cancer cell line HeLa were used to study in vitro cytotoxicity that was considerably affected by the 5-FU-loaded hydrogel. These results indicate the potential of the hydrogel as a transdermal drug delivery vehicle for the treatment of breast cancer.

Multifunctional Ionic Hydrogel-Based Transdermal Delivery of 5-Fluorouracil for the Breast Cancer Treatment

Transdermal drug delivery systems (TDDS) are a promising and innovative approach for breast cancer treatment, offering advantages such as noninvasiveness, potential for localized and prolonged drug delivery while minimizing systemic side effects through avoiding first-pass metabolism. Utilizing the distinctive characteristics of hydrogels, such as their biocompatibility, versatility, and higher drug loading capabilities, in the present work, we prepared ionic hydrogels through synergistic interaction between ionic liquids (ILs), choline alanine ([Cho][Ala]), and choline proline ([Cho][Pro]) with oleic acid (OA). ILs used in the study are biocompatible and enhance the solubility of 5-fluorouracil (5-FU), whereas OA is a known chemical penetration enhancer. The concentration-dependent (OA) change in morphological aggregates, that is, from cylindrical micelles to worm-like micelles to hydrogels was formed with both ILs and was characterized by SANS measurement, whereas the interactions involved were confirmed by FTIR spectroscopy. The hydrogels have excellent mechanical properties, which studied by rheology and their morphology through FE-SEM analysis. The in vitro skin permeation study revealed that both hydrogels penetrated 255 times ([Cho][Ala]) and 250 times ([Cho][Pro]) more as compared to PBS after 48 h. Those ionic hydrogels exhibited the capability to change the lipid and keratin arrangements within the skin layer, thereby enhancing the transdermal permeation of the 5-FU. Both ionic hydrogels exhibit excellent biocompatibility with normal cell lines (L-132 cells) as well as cancerous cell lines (MCF-7 cells), demonstrating over 92% cell viability after 48 h in both cell lines. In vitro, the cytotoxicity of the 5-FU-loaded hydrogels was evaluated on MCF-7 and HeLa cell lines. These results indicate that the investigated biocompatible and nontoxic ionic hydrogels enable the transdermal delivery of hydrophilic drugs, making them a viable option for effectively treating breast cancer.

Small-angle X-ray and neutron scattering applied to lipid-based nanoparticles: Recent advancements across different length scales

Lipid-based nanoparticles (LNPs), ranging from nanovesicles to non-lamellar assemblies, have gained significant attention in recent years, as versatile carriers for delivering drugs, vaccines, and nutrients. Small-angle scattering methods, employing X-rays (SAXS) or neutrons (SANS), represent unique tools to unveil structure, dynamics, and interactions of such particles on different length scales, spanning from the nano to the molecular scale. This review explores the state-of-the-art on scattering methods applied to unveil the structure of lipid-based nanoparticles and their interactions with drugs and bioactive molecules, to inform their rational design and formulation for medical applications. We will focus on complementary information accessible with X-rays or neutrons, ranging from insights on the structure and colloidal processes at a nanoscale level (SAXS) to details on the lipid organization and molecular interactions of LNPs (SANS). In addition, we will review new opportunities offered by Time-resolved (TR)-SAXS and -SANS for the investigation of dynamic processes involving LNPs. These span from real-time monitoring of LNPs structural evolution in response to endogenous or external stimuli (TR-SANS), to the investigation of the kinetics of lipid diffusion and exchange upon interaction with biomolecules (TR-SANS). Finally, we will spotlight novel combinations of SAXS and SANS with complementary on-line techniques, recently enabled at Large Scale Facilities for X-rays and neutrons. This emerging technology enables synchronized multi-method investigation, offering exciting opportunities for the simultaneous characterization of the structure and chemical or mechanical properties of LNPs.

Biocompatible Rhamnolipid Self-Assemblies with pH-Responsive Antimicrobial Activity

There is an urgent need for alternative antimicrobial materials due to the growing challenge of bacteria becoming resistant to conventional antibiotics. This study demonstrates the creation of a biocompatible pH-switchable antimicrobial material by combining bacteria-derived rhamnolipids (RL) and food-grade glycerol monooleate (GMO). The integration of RL into dispersed GMO particles, with an inverse-type liquid crystalline cubic structure in the core, leads to colloidally stable supramolecular materials. The composition and pH-triggered structural transformations are studied with small-angle X-ray scattering, cryogenic transmission electron microscopy, and dynamic light scattering. The composition-structure-activity relationship is analyzed and optimized to target bacteria at acidic pH values of acute wounds. The new RL/GMO dispersions reduce Staphylococcus aureus (S. aureus) populations by 7-log after 24 h of treatment with 64 µg mL-1 of RL and prevent biofilm formation at pH = 5.0, but have no activity at pH = 7.0. Additionally, the system is active against methicillin-resistant S. aureus (MRSA) with minimum inhibitory concentration of 128 µg mL-1 at pH 5.0. No activity is found against several Gram-negative bacteria at pH 5.0 and 7.0. The results provide a fundamental understanding of lipid self-assembly and the design of lipid-based biomaterials, which can further guide the development of alternative bio-based solutions to combat bacteria.

Optical tweezer platform for the characterization of pH-triggered colloidal transformations in the oleic acid/water system

HYPOTHESIS

Soft colloidal particles that respond to their environment have innovative potential for many fields ranging from food and health to biotechnology and oil recovery. The in situ characterisation of colloidal transformations that triggers the functional response remain a challenge.

EXPERIMENTS

This study demonstrates the combination of an optical micromanipulation platform, polarized optical video microscopy and microfluidics in a comprehensive approach for the analysis of pH-driven structural transformations in emulsions. The new platform, together with synchrotron small angle X-ray scattering, was then applied to research the food-relevant, pH-responsive, oleic acid in water system.

FINDINGS

The experiments demonstrate structural transformations in individual oleic acid particles from micron-sized onion-type multilamellar oleic acid vesicles at pH 8.6, to nanostructured emulsions at pH < 8.0, and eventually oil droplets at pH < 6.5. The smooth particle-water interface of the onion-type vesicles at pH 8.6 was transformed into a rough particle surface at pH below 7.5. The pH-triggered changes of the interfacial tension at the droplet-water interface together with mass transport owing to structural transformations induced a self-propelled motion of the particle. The results of this study contribute to the fundamental understanding of the structure-property relationship in pH-responsive emulsions for nutrient and drug delivery applications.

Inverse ISAsomes in Bio-Compatible Oils—Exploring Formulations in Squalane, Triolein and Olive Oil

In contrast to their more common counterparts in aqueous solutions, inverse ISAsomes (internally self-assembled somes/particles) are formulated as kinetically stabilised dispersions of hydrophilic, lyotropic liquid-crystalline (LC) phases in non-polar oils. This contribution reports on their formation in bio-compatible oils. We found that it is possible to create inverse hexosomes, inverse micellar cubosomes (Fd3m) and an inverse emulsified microemulsion (EME) in excess squalane with a polyethylene glycol alkyl ether as the primary surfactant forming the LC phase and to stabilise them with hydrophobised silica nanoparticles. Furthermore, an emulsified -phase and inverse hexosomes were formed in excess triolein with the triblock-copolymer Pluronic® P94 as the primary surfactant. Stabilisation was achieved with a molecular stabiliser of type polyethylene glycol (PEG)-dipolyhydroxystearate. For the inverse hexosomes in triolein, the possibility of a formulation without any additional stabiliser was explored. It was found that a sufficiently strong stabilisation effect was created by the primary surfactant alone. Finally, triolein was replaced with olive oil which also led to the successful formation of inverse hexosomes. As far as we know, there exists no previous contribution about inverse ISAsomes in complex oils such as triolein or plant oils, and the existence of stabiliser-free (i.e., self-stabilising) inverse hexosomes has also not been reported until now.

Affimer Tagged Cubosomes: Targeting of Carcinoembryonic Antigen Expressing Colorectal Cancer Cells Using In Vitro and In Vivo Models

Nanomedicines, while having been approved for cancer therapy, present many challenges such as low stability, rapid clearance, and nonspecificity leading to off-target toxicity. Cubosomes are porous lyotropic liquid crystalline nanoparticles that have shown great premise as drug delivery vehicles; however, their behavior in vivo is largely underexplored, hindering clinical translation. Here, we have engineered cubosomes based on the space group Im3m that are loaded with copper acetylacetonate as a model drug, and their surfaces are functionalized for the first time with Affimer proteins via copper-free click chemistry to actively target overexpressed carcinoembryonic antigens on LS174T colorectal cancer cells. Unlike nontargeted cubosomes, Affimer tagged cubosomes showed preferential accumulation in cancer cells compared to normal cells not only in vitro (2D monolayer cell culture and 3D spheroid models) but also in vivo in colorectal cancer mouse xenografts, while exhibiting low nonspecific absorption and toxicity in other vital organs. Cancerous spheroids had maximum cell death compared to noncancerous cells upon targeted delivery. Xenografts subjected to targeted drug-loaded cubosomes showed a 5-7-fold higher drug accumulation in the tumor tissue compared to the liver, kidneys, and other vital organs, a significant decrease in tumor growth, and an increased survival rate compared to the nontargeted group. This work encompasses the first thorough preclinical investigation of Affimer targeted cubosomes as a cancer therapeutic.

Cubosomes and Hexosomes as Novel Nanocarriers for Bioactive Compounds

Cubosomes and hexosomes are nanostructured liquid crystalline particles, known as biocompatible nanocarriers for drug delivery. In recent years, there has been good interest in using cubosomes and hexosomes for the delivery of bioactive compounds in functional foods. These systems feature thermodynamic stability, encapsulate both hydrophobic and hydrophilic substances, and have a high tolerance to environmental stresses and potential for controlled release. This review outlines the recent advances in cubosomes and hexosomes in the food industry, focusing on their structure, composition, formation mechanisms, and factors influencing phase transformation between cubosomes and hexosomes. The potential applications especially for the bioactive delivery are presented. The integration of cubosomes and hexosomes with other emerging encapsulation technologies such as surface coating, gelation, and incorporation of polymers are also discussed.

Human Antimicrobial Peptide Triggered Colloidal Transformations in Bacteria Membrane Lipopolysaccharides

Growing concerns of bacterial resistance against conventional antibiotics shifts the research focus toward antimicrobial peptide (AMP)-based materials. Most AMPs kill gram-negative bacteria by destroying their inner membrane, but have to first pass the outer membrane covered with lipopolysaccharides (LPS). Their interplay with the LPS is crucial for bactericidal activity, but is yet to be elucidated in detail. In this study, self-assemblies of Escherichia coli LPS with the human cathelicidin AMP LL-37, free and encapsulated into glyceryl monooleate (GMO) lipid nanoparticles, are analyzed using synchrotron small angle X-ray scattering, dynamic light scattering, and cryogenic transmission electron microscopy. Circular dichroism spectroscopy is used to study modifications in LL-37's secondary structure. LPS is found to form elongated micelles and the addition of LL-37 induces their transformation to multilamellar structures. LPS' addition to GMO cubosomes triggers the swelling of the internal cubic structure, while in multilamellar GMO/LL-37 nanocarriers it causes transitions into unstructured particles. The insights on the interactions among LPS and LL-37, in its free form or encapsulated in GMO dispersions, may guide the design of LPS-responsive antimicrobial nanocarriers. The findings may further assist the formulation of antimicrobial nanomaterials with enhanced penetration of LPS layers for improved destruction of bacterial membranes.

Infection microenvironment-related antibacterial nanotherapeutic strategies

The emergence and spread of antibiotic resistance is one of the biggest challenges in public health. There is an urgent need to discover novel agents against the occurrence of multidrug-resistant bacteria, such as methicillin-resistant Staphylococcus aureus and vancomycin-resistant enterococci. The drug-resistant pathogens are able to grow and persist in infected sites, including biofilms, phagosomes, or phagolysosomes, which are more difficult to eradicate than planktonic ones and also foster the development of drug resistance. For years, various nano-antibacterial agents have been developed in the forms of antibiotic nanocarriers. Inorganic nanoparticles with intrinsic antibacterial activity and inert nanoparticles assisted by external stimuli, including heat, photon, magnetism, or sound, have also been discovered. Many of these strategies are designed to target the unique microenvironment of bacterial infections, which have shown potent antibacterial effects in vitro and in vivo. This review summarizes ongoing efforts on antibacterial nanotherapeutic strategies related to bacterial infection microenvironments, including targeted antibacterial therapy and responsive antibiotic delivery systems. Several grand challenges and future directions for the development and translation of effective nano-antibacterial agents are also discussed. The development of innovative nano-antibacterial agents could provide powerful weapons against drug-resistant bacteria in systemic or local bacterial infections in the foreseeable future.

Breaking Isolation to Form New Networks: pH-Triggered Changes in Connectivity inside Lipid Nanoparticles

There is a growing demand to develop smart nanomaterials that are structure-responsive as they have the potential to offer enhanced dose, temporal and spatial control of compounds and chemical processes. The naturally occurring pH gradients found throughout the body make pH an attractive stimulus for guiding the response of a nanocarrier to specific locations or (sub)cellular compartments in the body. Here we have engineered highly sensitive lyotropic liquid crystalline nanoparticles that reversibly respond to changes in pH by altering the connectivity within their structure at physiological temperatures. At pH 7.4, the nanoparticles have an internal structure consisting of discontinuous inverse micellar "aqueous pockets" based on space group Fd3m. When the pH is ≤6, the nanoparticles change from a compartmentalized to an accessible porous internal structure based on a 2D inverse hexagonal phase (plane group p6mm). We validate the internal symmetry of the nanoparticles using small-angle X-ray scattering and cryogenic transmission electron microscopy. The high-resolution electron microscopy images obtained have allowed us for the first time to directly visualize the internal structure of the Fd3m nanoparticles and resolve the two different-sized inverse micelles that make up the structural motif within the Fd3m unit cell, which upon structural analysis reveal excellent agreement with theoretical geometrical models.

Cell medium-dependent dynamic modulation of size and structural transformations of binary phospholipid/ω-3 fatty acid liquid crystalline nano-self-assemblies: Implications in interpretation of cell uptake studies

Lyotropic non-lamellar liquid crystalline (LLC) nanoparticles, with their tunable structural features and capability of loading a wide range of drugs and reporter probes, are emerging as versatile injectable nanopharmaceuticals. Secondary emulsifiers, such as Pluronic block copolymers, are commonly used for colloidal stabilization of LLC nanoparticles, but their inclusion often compromises the biological safety (e.g., poor hemocompatibility and enhanced cytotoxicity) of the formulation. Here, we introduce a library of colloidally stable, structurally tunable, and pH-responsive lamellar and non-lamellar liquid crystalline nanoparticles from binary mixtures of a phospholipid (phosphatidylglycerol) and three types of omega-3 fatty acids (ω-3 PUFAs), prepared in the absence of a secondary emulsifier and organic solvents. We study formulation size distribution, morphological heterogeneity, and the arrangement of their internal self-assembled architectures by nanoparticle tracking analysis, synchrotron small-angle X-ray scattering, and cryo-transmission electron microscopy. The results show the influence of type and concentration of ω-3 PUFAs in nanoparticle structural transitions spanning from a lamellar (L_α) phase to inverse discontinuous (micellar) cubic Fd3m and hexagonal phase (H₂) phases, respectively. We further report on cell-culture medium-dependent dynamic fluctuations in nanoparticle size, number and morphology, and simultaneously monitor uptake kinetics in two human cell lines. We discuss the role of these multiparametric biophysical transformations on nanoparticle-cell interaction kinetics and internalization mechanisms. Collectively, our findings contribute to the understanding of fundamental steps that are imperative for improved engineering of LLC nanoparticles with necessary attributes for pharmaceutical development.

pH-responsive aminolipid nanocarriers for antimicrobial peptide delivery

HYPOTHESIS

pH-responsive aminolipid self-assemblies are promising platforms for the targeted delivery of antimicrobial peptides (AMPs), with the potential to improve their therapeutic efficiency and physico-chemical stability.

EXPERIMENTS

pH-sensitive nanocarriers based on dispersed self-assemblies of 1,2-dioleoyl-3-dimethylammonium-propane (DODAP) with the human cathelicidin LL-37 in excess water were characterized at different pH values using small-angle X-ray scattering, cryogenic transmission electron microscopy, and dynamic light scattering. Fluorescence and electrophoretic mobility measurements were used to probe the encapsulation efficiency of LL-37 and the nanocarriers' surface potential.

FINDINGS

Upon decreasing pH in the DODAP/water systems, normal oil-in-water emulsions at pH ≥ 5.0 transitioned to emulsions encapsulating inverse hexagonal and cubic structures at pH between 4.5 and 4.0, and mostly positively-charged vesicles at pH < 4.0. These colloidal transformations are driven by the protonation of DODAP upon pH decrease. The larger lipid-water interfacial area provided by the DODAP self-assemblies at pH ≤ 4.5 allowed for an adequate encapsulation efficiency of LL-37, favouring the formation of vesicles in a concentration-dependent manner. Contrary, LL-37 was found to dissociate from the emulsion droplets at pH 6.0. The knowledge on the pH-triggered self-assembly of LL-37 and DODAP, combined with the results on peptide release from the structures contribute to the fundamental understanding of lipid/peptide self-assembly. The results can guide the rational design of future pH-responsive AMP delivery systems.

Bioinspired Antimicrobial Coatings from Peptide-Functionalized Liquid Crystalline Nanostructures

Surface-associated microbial infections and contaminations are a major challenge in various fields including the food and health sectors. This study demonstrates the design of antimicrobial coatings based on the self-assembly of the food-grade amphiphilic lipid glycerol monooleate with the human cathelicidin-derived antimicrobial peptide LL-37. Structural properties of the coating and their alterations with composition were studied using advanced experimental methods including synchrotron grazing-incidence small-angle X-ray scattering and ellipsometry. The integration of the LL-37 and its potential release from the nanostructured films into the surrounding solution was characterized with confocal Raman microscopy. Additional biological evaluation studies with clinically relevant bacterial strains, namely, Pseudomonas aeruginosa (Gram-negative) and Staphylococcus aureus (Gram-positive), were performed to investigate the antimicrobial activity of the coatings. Significant killing activity of the coating was found against both bacterial strains. The presented findings contribute to the fundamental understanding of lipid-peptide self-assembly on the surface and may open up a promising strategy for designing simple, sustainable antimicrobial coatings for medical and food applications.

Integration of antimicrobial peptides and gold nanorods for bimodal antibacterial applications

The misuse and abuse of antibiotics have given rise to a severe problem of the drug resistance of bacteria. Solving this problem has been a vitally important task in the modern medical arena. In this work, an antimicrobial peptide (AMP), BF2b, and gold nanorods (AuNRs) were used to develop a specific drug delivery system for killing methicillin-resistant Staphylococcus aureus (MRSA). On the one hand, BF2b has unique anti-bacterial performance and has a lower tendency than traditional antibiotics to engender the drug resistance of bacteria. On the other hand, AuNRs have diverse distinct properties, such as photo-thermal conversion, which can be employed for photo-thermal sterilization. We aimed to integrate the anti-bacterial activity of BF2b and the photo-thermal sterilization of AuNRs to kill drug-resistant bacteria. Fourier-transform infrared spectroscopy, microBCA and zeta potential measurements were utilized to characterize the product, AuNR@PEG/BF2b. Transmittance electron microscopy, UV-vis spectroscopy and photothermal conversion measurement were conducted to verify the stability and photothermal conversion capacity of AuNR@PEG/BF2b. Cell viability and hemolysis assay were carried out to test the biocompatibility of AuNR@PEG/BF2b. Finally, the in vitro and in vivo experiments were performed to demonstrate the excellent bactericidal activity of AuNR@PEG/BF2b.

Folding and self-assembly of short intrinsically disordered peptides and protein regions

Proteins and peptide fragments are highly relevant building blocks in self-assembly for nanostructures with plenty of applications. Intrinsically disordered proteins (IDPs) and protein regions (IDRs) are defined by the absence of a well-defined secondary structure, yet IDPs/IDRs show a significant biological activity. Experimental techniques and computational modelling procedures for the characterization of IDPs/IDRs are discussed. Directed self-assembly of IDPs/IDRs allows reaching a large variety of nanostructures. Hybrid materials based on the derivatives of IDPs/IDRs show a promising performance as alternative biocides and nanodrugs. Cell mimicking, in vivo compartmentalization, and bone regeneration are demonstrated for IDPs/IDRs in biotechnological applications. The exciting possibilities of IDPs/IDRs in nanotechnology with relevant biological applications are shown.

Recent advances in drug delivery applications of cubosomes, hexosomes, and solid lipid nanoparticles

The use of lipid nanocarriers for drug delivery applications is an active research area, and a great interest has particularly been shown in the past two decades. Among different lipid nanocarriers, ISAsomes (Internally self-assembled somes or particles), including cubosomes and hexosomes, and solid lipid nanoparticles (SLNs) have unique structural features, making them attractive as nanocarriers for drug delivery. In this contribution, we focus exclusively on recent advances in formation and characterization of ISAsomes, mainly cubosomes and hexosomes, and their use as versatile nanocarriers for different drug delivery applications. Additionally, the advantages of SLNs and their application in oral and pulmonary drug delivery are discussed with focus on the biological fates of these lipid nanocarriers in vivo. Despite the demonstrated advantages in in vitro and in vivo evaluations including preclinical studies, further investigations on improved understanding of the interactions of these nanoparticles with biological fluids and tissues of the target sites is necessary for efficient designing of drug nanocarriers and exploring potential clinical applications.

Biomembrane induced in situ self-assembly of peptide with enhanced antimicrobial activity

Antimicrobial peptides (AMPs) as biocides are of great interest because they have the ability to combat antibiotic resistance. Normally, natural AMPs need to be rationally designed or modified for practical use as an antibiotic. Here, a novel AMP, termed FF8, which is a cationic octapeptide composed of arginine, lysine, and phenylalanine, was designed. The FF8 was found to self-assemble into nanofibers when induced by a negatively charged lipid membrane or pH is above 9.4. The fibers on the membrane broke the lipid membrane, forming pores and significantly reducing its fluidity. FF8 also exhibited enhanced antibacterial activity by significantly increasing the permeability of the inner and outer membranes of Escherichia coli (E. coli) and maintaining the pores of the inner membrane of cells, which caused continuous membrane leakage. Because of its high antibacterial activity, cytocompatibility, and cost-effectiveness, FF8 is a promising antibacterial material.

Hexosomes as Efficient Platforms for Possible Fluoxetine Hydrochloride Repurposing with Improved Cytotoxicity against HepG2 Cells

The aim of this study was to investigate the feasibility of hexosomes (HEXs) as competent platforms for fluoxetine hydrochloride (FH) repurposing against HepG2 hepatocellular carcinoma. Different FH-loaded HEX formulations were prepared and optimized by the hot emulsification method. The HEX features such as particle size, ζ potential, and drug entrapment efficiency (EE%) can be tailored by tuning HEX components and fabrication conditions. The composition of the optimized FH hexosome (OFH-HEX) was composed of 3.1, 1.4, 0.5, 0.2, and 94.8% for glyceryl monooleate, oleic acid, pluronic F127, FH, and deionized water, respectively. The anionic OFH-HEX with a particle size of 145.5 ± 2.5 nm and drug EE% of 45.4 ± 1.2% was able to prolong the in vitro FH release, where only 19.5 ± 2.3% released in phosphate-buffered saline (PBS) pH 7.4 after 24 h. Contrarily, HEX rapidly released FH in acetate buffer pH 5.5 and achieved a 90.5 ± 4.7% release after 24 h. The obtained HEX showed an improved cellular internalization in a time-dependent manner and enhanced the cytotoxicity (2-fold higher than FH solution). The current study suggests the potential of FH-HEX as a possible anticancer agent against hepatocellular carcinoma.

A structurally diverse library of glycerol monooleate/oleic acid non-lamellar liquid crystalline nanodispersions stabilized with nonionic methoxypoly(ethylene glycol) (mPEG)-lipids showing variable complement activation properties

Pluronic F127-stabilized non-lamellar liquid crystalline aqueous nanodispersions are promising injectable platforms for drug and contrast agent delivery. These nanodispersions, however, trigger complement activation in the human blood, where the extent of complement activation and opsonization processes may compromise their biological performance and safety. Here, we introduce a broad family of nanodispersions from glycerol monooleate (GMO) and oleic acid (OA) in different weight ratios, and stabilized with a plethora of nonionic methoxypoly(ethylene glycol) (mPEG)-lipids of different PEG chain length and variable lipid moiety (monounsaturated or saturated diglycerides or D-α-tocopheryl succinate). Through an integrated biophysical approach involving dynamic light scattering, synchrotron small-angle scattering, and cryo-transmission electron microscopy, we examine the impact of nonionic mPEG-lipid stabilization on size, internal self-assembled architecture, and gross morphological characteristics of nanodispersions. The results show how the nonionic mPEG-lipid type and concentration, and dependent on GMO/OA weight ratio, can variably modulate the internal architectures of nanoparticles. Assessment of complement profiling from selected nanodispersions with diverse structural heterogeneity further suggests a variable modulatory role for the lipid type of the nonionic mPEG-lipid in the extent of complement activation, which span from no activation to moderate to high levels. We comment on plausible mechanisms driving the observed complement activation variability and discuss the potential utility of these nanodispersions for future development of injectable nanopharmaceuticals.

Advances in the Design of pH-Sensitive Cubosome Liquid Crystalline Nanocarriers for Drug Delivery Applications

Nanostructure bicontinuous cubic phase self-assembled materials are receiving expanding applications as biocompatible delivery systems in various therapeutic fields. The functionalization of cubosome, spongosome, hexosome and liposome nanocarriers by pH-sensitive lipids and/or pH-sensitive polymer shells offers new opportunities for oral and topical drug delivery towards a new generation of cancer therapies. The electrochemical behavior of drug compounds may favor pH-triggered drug release as well. Here, we highlight recent investigations, which explore the phase behavior of mixed nonlamellar lipid/fatty acid or phospholipid systems for the design of pH-responsive and mucoadhesive drug delivery systems with sustained-release properties. X-ray diffraction and small-angle X-ray scattering (SAXS) techniques are widely used in the development of innovative delivery assemblies through detailed structural analyses of multiple amphiphilic compositions from the lipid/co-lipid/water phase diagrams. pH-responsive nanoscale materials and nanoparticles are required for challenging therapeutic applications such as oral delivery of therapeutic proteins and peptides as well as of poorly water-soluble substances. Perspective nanomedicine developments with smart cubosome nanocarriers may exploit compositions elaborated to overcome the intestinal obstacles, dual-drug loaded pH-sensitive liquid crystalline architectures aiming at enhanced therapeutic efficacy, as well as composite (lipid/polyelectrolyte) types of mucoadhesive controlled release colloidal cubosomal formulations for the improvement of the drugs' bioavailability.

Micellar Fd3m cubosomes from monoolein - long chain unsaturated fatty acid mixtures: Stability on temperature and pH response

HYPOTHESIS

Control of the nanostructure of self-assembled systems may be achieved through manipulation of surfactant molecular packing and interfacial curvature. In order to phase engineer the inverse micellar cubosomes in some monoolein-fatty acid systems, lipids with wedge shaped molecular geometry were incorporated to promote the formation of this phase, that is of interest as potential sustained released nanocarriers.

EXPERIMENTS

Liquid crystalline nanoparticle dispersions of monoolein with some cis unsaturated fatty acids were prepared and their partial temperature-composition phase diagrams and structure were established using high throughput Small Angle X-ray Scattering (SAXS) and cryogenic transmission electron microscopy (cryo-TEM). The pH responsiveness of these systems was evaluated in the presence of phosphate buffered saline (PBS).

FINDINGS

The partial temperature-composition phase diagrams of five nanoparticle formulations containing monoolein and unsaturated fatty acids were established and identified the presence of micellar cubosomes in each of these systems. The results indicate that temperature, fatty acid concentration and structure, as well as pH all directly impact the formation and stability of this phase. Low energy inverse micellar cubic to emulsion phase transformations were identified in the monoolein with oleic acid and vaccenic acid systems at physiological temperatures that may be advantageous for staged therapeutic release strategies in nanomedicine.

Non-Lamellar Liquid Crystalline Nanocarriers for Thymoquinone Encapsulation

Owing to their unique structural features, non-lamellar liquid crystalline nanoparticles comprising cubosomes and hexosomes are attracting increasing attention as versatile investigative drug carriers. Background: Depending on their physiochemical characteristics, drug molecules on entrapment can modulate and reorganize structural features of cubosomes and hexosomes. Therefore, it is important to assess the effect of guest molecules on broader biophysical characteristics of non-lamellar liquid crystalline nanoparticles, since drug-induced architectural, morphological, and size modifications can affect the biological performance of cubosomes and hexosomes. Methods: We report on alterations in morphological, structural, and size characteristics of nanodispersions composed from binary mixtures of glycerol monooleate and vitamin E on thymoquinone (a molecule with wide therapeutic potentials) loading. Results: Thymoquinone loading was associated with a slight increase in the mean hydrodynamic nanoparticle size and led to structural transitions from an internal biphasic feature of coexisting inverse cubic Fd3m and hexagonal (H₂) phases to an internal inverse cubic Fd3m phase (micellar cubosomes) or an internal inverse micellar (L₂) phase (emulsified microemulsions, EMEs). We further report on the presence of “flower-like” vesicular populations in both native and drug-loaded nanodispersions. Conclusions: These nanodispersions have the potential to accommodate thymoquinone and may be considered as promising platforms for the development of thymoquinone nanomedicines.

Internal Lamellar and Inverse Hexagonal Liquid Crystalline Phases During the Digestion of Krill and Astaxanthin Oil-in-Water Emulsions

Krill oil represents an important alternative natural source of omega-3 (ω-3) polyunsaturated fatty acids (PUFAs). Considering the beneficial health effects of these essential fatty acids, particularly in various disorders including cancer, cardiovascular, and inflammation diseases, it is of paramount importance to gain insight into the digestibility of krill oil. In this work, we study the fate of krill oil-in-water emulsion, stabilized by sodium caseinate, during lipolysis by coupling time-resolved synchrotron small-angle X-ray scattering (SAXS) to flow-through lipolysis model. For gaining further insight into the effect of ω-3 PUFA-containing oil type on the dynamic structural features occurring during lipolysis, two additional astaxanthin oil-in-water emulsions, stabilized using either sodium caseinate or citrem, were subjected to lipolysis under identical experimental conditions. In addition to the difference in lipid composition in both oils, ω-3 PUFAs in astaxanthin oil, similar to fish oil, exist in the form of triacylglycerols; whereas most of those in krill oil are bound to phospholipids. SAXS showed the formation of highly ordered nanostructures on exposure of these food emulsions to the lipolysis medium: the detection of a biphasic feature of coexisting inverse hexagonal (H₂) and lamellar (L_α) liquid crystalline phases in the digested krill oil droplets' interiors, as compared to a neat L_α phase in the digested astaxanthin oil droplets. We discuss the dynamic phase behavior and describe the suggested important role of these phases in facilitating the delivery of nutrients throughout the body. In addition, the potential implication in the development of food and drug nanocarriers is briefly described.

Advances in Lipid and Metal Nanoparticles for Antimicrobial Peptide Delivery

Antimicrobial peptides (AMPs) have been described as excellent candidates to overcome antibiotic resistance. Frequently, AMPs exhibit a wide therapeutic window, with low cytotoxicity and broad-spectrum antimicrobial activity against a variety of pathogens. In addition, some AMPs are also able to modulate the immune response, decreasing potential harmful effects such as sepsis. Despite these benefits, only a few formulations have successfully reached clinics. A common flaw in the druggability of AMPs is their poor pharmacokinetics, common to several peptide drugs, as they may be degraded by a myriad of proteases inside the organism. The combination of AMPs with carrier nanoparticles to improve delivery may enhance their half-life, decreasing the dosage and thus, reducing production costs and eventual toxicity. Here, we present the most recent advances in lipid and metal nanodevices for AMP delivery, with a special focus on metal nanoparticles and liposome formulations.

Self-assembling in situ gel based on lyotropic liquid crystals containing VEGF for tissue regeneration

Current tissue-regenerative biomaterials confront two critical issues: the uncontrollable delivery capacity of vascular endothelial growth factor (VEGF) for adequate vascularization and the poor mechanical properties of the system for tissue regeneration. To overcome these two issues, a self-assembling in situ gel based on lyotropic liquid crystals (LLC) was developed. VEGF-LLC was administrated as a precursor solution that would self-assemble into an in situ gel with well-defined internal inverse bicontinuous cubic phases when exposed to physiological fluid at a defect site. The inverse cubic phase with a 3D bicontinuous water channel enabled a 7-day sustained release of VEGF. The release profile of VEGF-LLC was controlled using octyl glucoside (OG) as a hydration-modulating agent, which could enlarge the water channel, yielding a 2-fold increase in water channel size and a 7-fold increase in VEGF release. For the mechanical properties, the elastic modulus was found to decrease from ∼100 kPa to ∼1.2 kPa, which might be more favorable for angiogenesis. Furthermore, the self-recovery ability of the VEGF-LLC gel was confirmed by quick recovery of the inner network in step-strain measurements. In vitro, VEGF-LLC considerably promoted the proliferation, migration, and tube formation of human umbilical vein endothelial cells (HUVECs) as compared to free VEGF (p < 0.05). Furthermore, angiogenesis was successfully induced in rats after subcutaneous injection of VEGF-LLC. The self-assembling LLC gel showed satisfactory degradability and mild inflammatory response with little impact on the surrounding tissue. The controllable release profile and unique mechanical properties of VEGF-LLC offer a new approach for tissue regeneration. STATEMENT OF SIGNIFICANCE: The potential clinical use of currently available biomaterials in tissue regeneration is limited by their uncontrollable drug delivery capacity and poor mechanical properties. Herein, a self-assembling in situ gel based on lyotropic liquid crystals (LLC) for induced angiogenesis was developed. The results showed that the addition of octyl glucoside (OG) could change the water channel size of LLC, which enabled the LLC system to release VEGF in a sustained manner and to possess a suitable modulus to favor angiogenesis simultaneously. Moreover, the self-recovery capability allowed the gel to match the deformation of surrounding tissues during body motion to maintain its properties and reduce discomfort. In vivo, angiogenesis was induced by VEGF-LLC 14 days after administering subcutaneous injection. These results highlight the potential of LLC as a promising sustained protein drug delivery system for vascular formation and tissue regeneration.

Cubic Liquid Crystalline Nanostructures Involving Catalase and Curcumin: BioSAXS Study and Catalase Peroxidatic Function after Cubosomal Nanoparticle Treatment of Differentiated SH-SY5Y Cells

The development of nanomedicines for the treatment of neurodegenerative disorders demands innovative nanoarchitectures for combined loading of multiple neuroprotective compounds. We report dual-drug loaded monoolein-based liquid crystalline architectures designed for the encapsulation of a therapeutic protein and a small molecule antioxidant. Catalase (CAT) is chosen as a metalloprotein, which provides enzymatic defense against oxidative stress caused by reactive oxygen species (ROS) such as hydrogen peroxide (H2O2). Curcumin (CU), solubilized in fish oil, is co-encapsulated as a chosen drug with multiple therapeutic activities, which may favor neuro-regeneration. The prepared self-assembled biomolecular nanoarchitectures are characterized by biological synchrotron small-angle X-ray scattering (BioSAXS) at multiple compositions of the lipid/co-lipid/water phase diagram. Constant fractions of curcumin (an antioxidant) and a PEGylated agent (TPEG1000) are included with regard to the lipid fraction. Stable cubosome architectures are obtained for several ratios of the lipid ingredients monoolein (MO) and fish oil (FO). The impact of catalase on the structural organization of the cubosome nanocarriers is revealed by the variations of the cubic lattice parameters deduced by BioSAXS. The outcome of the cellular uptake of the dual drug-loaded nanocarriers is assessed by performing a bioassay of catalase peroxidatic activity in lysates of nanoparticle-treated differentiated SH-SY5Y human cells. The obtained results reveal the neuroprotective potential of the in vitro studied cubosomes in terms of enhanced peroxidatic activity of the catalase enzyme, which enables the inhibition of H2O2 accumulation in degenerating neuronal cells.

A multifunctional lipid that forms contrast-agent liposomes with dual-control release capabilities for precise MRI-guided drug delivery

Monitoring of nanoparticle-based therapy in vivo and controlled drug release are urgently needed for the precise treatment of disease. We have synthesized a multifunctional Gd-DTPA-ONB (GDO) lipid by introducing the Gd-DTPA contrast agent moiety into an o-nitro-benzyl ester lipid. By design, liposomes formed from the GDO lipid combine MRI tracking ability and dual-trigger release capabilities with maximum sensitivity (because all lipids bear the cleavable moiety) without reducing the drug encapsulation rate. We first confirmed that both photo-treatment and pH-triggered hydrolysis are able to cleave the GDO lipid and lyse GDO liposomes. We then investigated the efficiency of drug release via the combined release processes for GDO liposomes loaded with doxorubicin (DOX). Relative to neutral pH, the release efficiency in acidic environment increased by 10.4% (at pH = 6.5) and 13.3% (at pH = 4.2). This pH-dependent release response is conducive to distinguishing pathological tissue such as tumors and endolysosomal compartments. The photo-induced release efficiency increases with illumination time as well as with distance of the pH from neutral. Photolysis increased the release efficiency by 13.8% at pH = 4.2, which is remarkable considering the already increased amount of drug release in the acidic environment. In addition, the relaxation time of GDO liposomes was 4.1 times that of clinical Gd-DTPA, with brighter T₁-weighted imaging in vitro and in vivo. Real-time MRI imaging and in vivo fluorescence experiments demonstrated tumor targeting and MRI guided release. Furthermore, significant tumor growth inhibition in a treatment experiment using DOX-loaded GDO liposomes clearly demonstrated the benefit of photo-treatment for efficacy: the tumor size in the photo-treatment group was 3.7 times smaller than in the control group. The present study thus highlights the benefit of the design idea of combining efficient imaging/guiding, targeting, and triggerable release functions in one lipid molecule for drug delivery applications.

pH-Responsive Nano-Self-Assemblies of the Anticancer Drug 2-Hydroxyoleic Acid

pH-responsive lipid nanocarriers have the potential to selectively target the acidic extracellular pH environment of cancer tissues and may further improve the efficacy of chemotherapeutics by minimizing their toxic side-effects. Here, we present the design and characterization of pH-sensitive nano-self-assemblies of the poorly water-soluble anticancer drug 2-hydroxyoleic acid (2OHOA) with glycerol monooleate (GMO). pH-triggered nanostructural transformations from 2OHOA/GMO nanoparticles with an internal inverse hexagonal structure (hexosomes) at pH around 2.0-3.0, via nanocarriers with an internal inverse bicontinuous cubic structure (cubosomes) at pH 2.0-4.5, to vesicles at pH 4.5-7.4 were observed with synchrotron small-angle X-ray scattering, and cryogenic transmission electron microscopy. ζ-potential measurements highlight that the pH-driven deprotonation of the carboxylic group of 2OHOA, and the resulting charge-repulsions at the lipid-water interface account for these nanostructural alterations. The study provides detailed insight into the pH-dependent self-assembly of 2OHOA with GMO in excess buffer at physiologically relevant pH values, and discusses the effects of pH alterations on modulating their nanostructure. The results may guide the further development of pH-responsive anticancer nanocarriers for the targeted delivery of chemotherapeutics to the local microenvironment of tumor cells.

From Structure to Function: pH-Switchable Antimicrobial Nano-Self-Assemblies

Stimuli-responsive nanocarriers based on lipid self-assemblies have the potential to provide targeted delivery of antimicrobial peptides, limiting their side effects while protecting them from degradation in the biological environments. In the present study, we design and characterize a simple pH-responsive antimicrobial nanomaterial, formed through the self-assembly of oleic acid (OA) with the human cathelicidin LL-37 as a model for an amphiphilic antimicrobial peptide. Colloidal transformations from core-shell cylindrical micelles with a cross-sectional diameter of ∼5.5 nm and a length of ∼23 nm at pH 7.0 to aggregates of branched threadlike micelles at pH 5.0 were detected using synchrotron small-angle X-ray scattering, cryogenic transmission electron microscopy, and dynamic light scattering. Biological in vitro assays using an Escherichia coli bacteria strain showed high antimicrobial activity of the positively charged LL-37/OA aggregates at pH 5.0, which was not caused by the pH conditions themselves. Contrary to that, negligible antimicrobial activity was observed at pH 7.0 for the negatively charged cylindrical micelles. The nanocarrier's ability to switch its biological activity "on" and "off" in response to changes in pH could be used to focus the antimicrobial peptides' action to areas of specific pH in the body. The presented findings contribute to the fundamental understanding of lipid-peptide self-assembly and may open up a promising strategy for designing simple pH-responsive delivery systems for antimicrobial peptides.

Citrem–phosphatidylcholine nano-self-assemblies: solubilization of bupivacaine and its role in triggering a colloidal transition from vesicles to cubosomes and hexosomes

In concentration- and lipid composition-dependent manners, bupivacaine triggers lamellar–nonlamellar phase transitions in citrem/soy phosphatidylcholine nanodispersions.

Cisplatin Encapsulation Generates Morphologically Different Multicompartments in the Internal Nanostructures of Nonlamellar Liquid-Crystalline Self-Assemblies

Cisplatin ( cis-diamminedichloroplatinum(II)) is among the most potent cytotoxic agents used in cancer chemotherapy. The encapsulation of cisplatin in lipid-based drug carriers has been challenging owing to its low solubility in both aqueous and lipid phases. Here, we investigated cisplatin encapsulation in nonlamellar liquid-crystalline (LC) nanodispersions formed from a ternary mixture of phytantriol (PHYT), vitamin E (Vit E), and an anionic phospholipid [either phosphatidylglycerol (DSPG) or phosphatidylserine (DPPS)]. We show an increase in cisplatin encapsulation efficiency (EE) in nanodispersions containing 1.5-4 wt % phospholipid. The EE was highest in DPPS-containing nanodispersions (53-98%) compared to DSPG-containing counterparts (25-40%) under similar experimental conditions. Through structural and morphological characterizations involving synchrotron small-angle X-ray scattering and cryogenic transmission electron microscopy, we further show that varying the phospholipid content of cisplatin-free nanodispersions triggers an internal phase transition from a neat hexagonal (H₂) phase to a biphasic phase (internal H₂ phase coexisting with the lamellar (L_α) phase). However, cisplatin encapsulation in both DPPS- and DSPG-containing nanodispersions generates the coexistence of morphologically different multicompartments in the internal nanostructures comprising vesicles as a core, enveloped by an inverted-type surface bicontinuous cubic Im3 m (primitive, Q_II^P) phase or H₂ phase. We discuss the biophysical basis of these drug-induced morphological alterations and provide insights into the potential development of inverted-type LC nanodispersions for cisplatin delivery.

Rheology of Ultraswollen Bicontinuous Lipidic Cubic Phases

Rheological studies of liquid crystalline systems based on monopalmitolein and 5 or 8% of 1,2 distearoylphosphatidylglycerol are reported. Such cubic phases have been shown to possess unusually large water channels because of their ability of accommodating up to 80 wt % of water, a feature that renders these systems suitable for crystallizing membrane proteins with large extracellular domains. Their mechanical properties are supposed to be substantially different from those of traditional cubic phases. Rheological measurements were carried out on cubic phases of both Pn3 m and Ia3 d symmetries. It was verified that these ultraswollen cubic phases are less rigid than the normal cubic phases, with the Pn3 m being softer that the Ia3 d ones. Furthermore, for the Pn3 m case, the longest relaxation time is shown to decrease logarithmically with increasing surface area per unit volume, proving the critical role of the density of interfaces in establishing the macroscopic viscoelastic properties of the bicontinuous cubic phases.

Formation of highly ordered liquid crystalline coatings – an in situ GISAXS study

In situ GISAXS and AFM reveal the formation of highly geometrically organized glycerol monooleate based liquid crystalline films on silicon wafers.