Determination of lipid content and stability in lipid nanoparticles using ultra high-performance liquid chromatography in combination with a Corona Charged Aerosol Detector

For many years, lipid nanoparticles (LNPs) have been used as delivery vehicles for various payloads (especially various oligonucleotides and mRNA), finding numerous applications in drug and vaccine development. LNP stability and bilayer fluidity are determined by the identities and the amounts of the various lipids employed in the formulation and LNP efficacy is determined in large part by the lipid composition which usually contains a cationic lipid, a PEG-lipid conjugate, cholesterol, and a zwitterionic helper phospholipid. Analytical methods developed for LNP characterization must be able to determine not only the identity and content of each individual lipid component (i.e., the parent lipids), but also the associated impurities and degradants. In this work, we describe an efficient and sensitive reversed-phase chromatographic method with charged aerosol detection (CAD) suitable for this purpose. Sample preparation diluent and mobile phase pH conditions are critical and have been optimized for the lipids of interest. This method was validated for its linearity, accuracy, precision, and specificity for lipid analysis to support process and formulation development for new drugs and vaccines.     

Opportunities for innovation: Building on the success of lipid nanoparticle vaccines

Lipid nanoparticle (LNP) formulations of messenger RNA (mRNA) have demonstrated high efficacy as vaccines against SARS-CoV-2. The success of these nanoformulations underscores the potential of LNPs as a delivery system for next-generation biological therapies. In this article, we highlight the key considerations necessary for engineering LNPs as a vaccine delivery system and explore areas for further optimisation. There remain opportunities to improve the protection of mRNA, optimise cytosolic delivery, target specific cells, minimise adverse side-effects and control the release of RNA from the particle. The modular nature of LNP formulations and the flexibility of mRNA as a payload provide many pathways to implement these strategies. Innovation in LNP vaccines is likely to accelerate with increased enthusiasm following recent successes; however, any advances will have implications for a broad range of therapeutic applications beyond vaccination such as gene therapy.     

Time‐Controllable Lipophilic‐Drug Release System Designed by Loading Lipid Nanoparticles into Polysaccharide Hydrogels

A hybrid hydrogel composed of solid lipid nanoparticles (LNPs) entrapped within chemically cross‐linked carboxymethylcellulose (CMC) is developed to achieve localized and sustained release of lipophilic drugs. The analysis of LNP stability as well as the hydrogel swelling and mechanical properties confirm the successful incorporation of particles up to a concentration of 50% w/w_CMC. The initial LNP release rate can be prolonged by increasing the particle diameter from 50 to 120 nm, while the amount of long‐term release can be adjusted by tailoring the particle surface charge or the cross‐linking density of the polymer. After 30 d, 58% of 50 nm diameter negatively charged LNPs escape from the matrix while only 17% of positively charged nanoparticles are released from materials with intermediate cross‐linking density. A mathematical diffusion model based on Fick's second law is efficient to predict the diffusion of the particles from the hydrogels.     

Efficient Delivery of Globotriaosylceramide Synthase siRNA using Polyhistidine-Incorporated Lipid Nanoparticles

In this study, a novel polyhistidine-incorporated lipid nanoparticle (pHis/LNP) is developed for the delivery of therapeutic globotriaosylceramide (Gb3) synthase siRNAs using a microfluidic device with pHis as a biocompatible method of endosome escape. To inhibit the expression of Gb3 synthase, six siRNAs against Gb3 synthase are designed and an optimal siRNA sequence is selected. Selected Gb3 synthase siRNA is incorporated into pHis/LNP to prepare a spherical siRNA pHis/LNP with a size of 62.5 ± 1.9 nm and surface charge of −13.3 ± 4.2 mV. The pHis/LNP successfully protects siRNAs from degradation in 50% serum condition for 72 h. Prepared pHis/LNP exhibits superior stability for 20 days and excellent biocompatibility for A549 cells. After treatment with fluorescence-labeled LNPs, dotted fluorescent signals are co-localized with Lysotracker in cells with LNPs, whereas strong and diffused fluorescence intensity is observed in cells with pHis/LNPs probably due to successful endosomal escape. The extent of Gb3 synthase gene silencing by siRNA pHis/LNP is greatly improved (6.0-fold) compared to that by siRNA/LNP. Taken together, considering that the fabricated siRNA pHis/LNP exhibits excellent biocompatibility and superior gene silencing activity over conventional LNP, these particles can be utilized for the delivery of a wide range of therapeutic siRNAs.     

Review of structural design guiding the development of lipid nanoparticles for nucleic acid delivery

Lipid nanoparticles (LNPs) are the most versatile and successful gene delivery systems, notably highlighted by their use in vaccines against COVID-19. LNPs have a well-defined core–shell structure, each region with its own distinctive compositions, suited for a wide range of in vivo delivery applications. Here, we discuss how a detailed knowledge of LNP structure can guide LNP formulation to improve the efficiency of delivery of their nucleic acid payload. Perspectives are detailed on how LNP structural design can guide more efficient nucleic acid transfection. Views on key physical characterization techniques needed for such developments are outlined including opinions on biophysical approaches both correlating structure with functionality in biological fluids and improving their ability to escape the endosome and deliver they payload.     

A Multidimensional Approach to Modulating Ionizable Lipids for High-Performing and Organ-Selective mRNA Delivery

The development of lipid nanoparticles (LNPs) has enabled a successful clinical application of mRNA vaccines. However, disclosure of design principles for the core component-ionizable lipids (ILs), improving the delivery efficacy and organ targeting of LNPs, remains a formidable challenge. Herein, we report a powerful strategy to modulate ILs in one-step chemistry using the Ugi four-component reaction (Ugi-4CR) under mild conditions. A large IL library of new structures was established simply and efficiently through a multidimensional approach, allowing us to identify the top-performing ILs in delivering mRNA via the formulated LNPs. Adjusting the skeleton of ILs has transformed the organ-specific and robust transfection in mRNA delivery from the liver to the spleen following different administration routes. Of note, a series of isomeric ILs were prepared and we found that the isomers mattered greatly in the performance of LNPs for mRNA delivery. Furthermore, owing to the bis-amide bonds formed in the Ugi-4CR reaction, the ILs within LNPs may form hydrogen bonding intermolecularly, facilitating the colloidal stabilization of LNPs. This work provides clues to the rapid discovery and rational design of IL candidates, assisting the application of mRNA therapeutics.     

Visible Light Conjugation with Triazolinediones as a Route to Degradable Poly(ethylene glycol)–Lipids for mRNA Lipid Nanoparticle Formulation

Polyethylene glycol (PEG) is considered as the gold standard for colloidal stabilization of nanomedicines, yet PEG is non-degradable and lacks functionality on the backbone. Herein, we introduce concomitantly PEG backbone functionality and degradability via a one-step modification with 1,2,4-triazoline-3,5-diones (TAD) under green light. The TAD-PEG conjugates are degradable in aqueous medium under physiological conditions, with the rate of hydrolysis depending on pH and temperature. Subsequently, a PEG-lipid is modified with TAD-derivatives and successfully used for messenger RNA (mRNA) lipid nanoparticle (LNP) delivery, thereby improving mRNA transfection efficiency on multiple cell cultures in vitro. In vivo, in mice, mRNA LNP formulation exhibited a similar tissue distribution as common LNPs, with a slight decrease in transfection efficiency. Our findings pave the road towards the design of degradable, backbone-functionalized PEG for applications in nanomedicine and beyond.     

Real-Time pH-Dependent Self-Assembly of Ionisable Lipids from COVID-19 Vaccines and In Situ Nucleic Acid Complexation

Ionisable amino-lipid is a key component in lipid nanoparticles (LNPs), which plays a crucial role in the encapsulation of RNA molecules, allowing efficient cellular uptake and then releasing RNA from acidic endosomes. Herein, we present direct evidence for the remarkable structural transitions, with decreasing membrane curvature, including from inverse micellar, to inverse hexagonal, to two distinct inverse bicontinuous cubic, and finally to a lamellar phase for the two mainstream COVID-19 vaccine ionisable ALC-0315 and SM-102 lipids, occurring upon gradual acidification as encountered in endosomes. The millisecond kinetic growth of the inverse cubic and hexagonal structures and the evolution of the ordered structural formation upon ionisable lipid-RNA/DNA complexation are quantitatively revealed by in situ synchrotron radiation time-resolved small angle X-ray scattering coupled with rapid flow mixing. We found that the final self-assembled structural identity, and the formation kinetics, were controlled by the ionisable lipid molecular structure, acidic bulk environment, lipid compositions, and nucleic acid molecular structure/size. The implicated link between the inverse membrane curvature of LNP and LNP endosomal escape helps future optimisation of ionisable lipids and LNP engineering for RNA and gene delivery.     

Lipid Nanoparticles Containing siRNA Synthesized by Microfluidic Mixing Exhibit an Electron-Dense Nanostructured Core

Lipid nanoparticles (LNP) containing ionizable cationic lipids are the leading systems for enabling therapeutic applications of siRNA; however, the structure of these systems has not been defined. Here we examine the structure of LNP siRNA systems containing DLinKC2-DMA(an ionizable cationic lipid), phospholipid, cholesterol and a polyethylene glycol (PEG) lipid formed using a rapid microfluidic mixing process. Techniques employed include cryo-transmission electron microscopy, (31)P NMR, membrane fusion assays, density measurements, and molecular modeling. The experimental results indicate that these LNP siRNA systems have an interior lipid core containing siRNA duplexes complexed to cationic lipid and that the interior core also contains phospholipid and cholesterol. Consistent with experimental observations, molecular modeling calculations indicate that the interior of LNP siRNA systems exhibits a periodic structure of aqueous compartments, where some compartments contain siRNA. It is concluded that LNP siRNA systems formulated by rapid mixing of an ethanol solution of lipid with an aqueous medium containing siRNA exhibit a nanostructured core. The results give insight into the mechanism whereby LNP siRNA systems are formed, providing an understanding of the high encapsulation efficiencies that can be achieved and information on methods of constructing more sophisticated LNP systems.     

脂质纳米颗粒的制备及在基因治疗中的应用

基因治疗已经成为人类治疗疾病的一种重要手段.然而,为了将基因药物用于临床,需要更加复杂的递送系统.脂质纳米颗粒(LNPs)系统是目前领先的非病毒递送系统,在治疗诊断学方面取得了许多令人鼓舞的进展,其具有实现基因药物临床治疗应用的潜力.由于LNPs纳米尺寸的优势及类脂化合物的生物相容性和生物降解性,LNPs能够克服阻碍基...     

Synthesis and dispersion of Ni(OH)2 platelet-like nanoparticles in water

Synthesis of nanometric platelet-like Ni(OH)2 particles is described. The role of several experimental parameters on the particle size is investigated. A colloidal dispersion of particles is produced by adsorbing ionizable organic ligands (trisodium citrate) on the particle surface. The stability of this colloidal dispersion and the particle charge density are determined for different citrate ions concentrations.     

Interaction of cholesterol-conjugated ionizable amino lipids with biomembranes: lipid polymorphism, structure-activity relationship, and implications for siRNA delivery

Delivery of siRNA is a major obstacle to the advancement of RNAi as a novel therapeutic modality. Lipid nanoparticles (LNP) consisting of ionizable amino lipids are being developed as an important delivery platform for siRNAs, and significant efforts are being made to understand the structure-activity relationship (SAR) of the lipids. This article uses a combination of small-angle X-ray scattering (SAXS) and differential scanning calorimetry (DSC) to evaluate the interaction between cholesterol-conjugated ionizable amino lipids and biomembranes, focusing on an important area of lipid SAR--the ability of lipids to destabilize membrane bilayer structures and facilitate endosomal escape. In this study, cholesterol-conjugated amino lipids were found to be effective in increasing the order of biomembranes and also highly effective in inducing phase changes in biological membranes in vitro (i.e., the lamellar to inverted hexagonal phase transition). The phase transition temperatures, determined using SAXS and DSC, serve as an indicator for ranking the potency of lipids to destabilize endosomal membranes. It was found that the bilayer disruption ability of amino lipids depends strongly on the amino lipid concentration in membranes. Amino lipids with systematic variations in headgroups, the extent of ionization, tail length, the degree of unsaturation, and tail asymmetry were evaluated for their bilayer disruption ability to establish SAR. Overall, it was found that the impact of these lipid structure changes on their bilayer disruption ability agrees well with the results from a conceptual molecular "shape" analysis. Implications of the findings from this study for siRNA delivery are discussed. The methods reported here can be used to support the SAR screening of cationic lipids for siRNA delivery, and the information revealed through the study of the interaction between cationic lipids and biomembranes will contribute significantly to the design of more efficient siRNA delivery vehicles.     

Charge-state and charge-continuum models in electrophoresis and isoelectric focusing of genetic variants

A model which combines the charge-state and charge-continuum models is considered in terms of the pH at which the electrophoretic analysis is made. "Unit" charge changes are obtained when the mutated charged group is at least 2 pH units apart from the pI of the protein. "Fractional" charge changes are found when the differences between the pK of the mutated charged group and the pI of the protein becomes progressively smaller, or when the pK of the ionizable group lies on the "wrong" side of the protein pI. It is possible to measure the pK of a modified group in a protein when the delta pI per protonic unit in a given family of proteins (e.g., haemoglobin mutants) is less than unity.     

Complexation of ferric oxide particles with pectins of different charge density

The effect of polyelectrolyte charge density on the electrical properties and stability of suspensions of oppositely charged oxide particles is followed by means of electro-optics and electrophoresis. Variations in the electro-optical effect and the electrophoretic mobility are examined at conditions where fully ionized pectins of different charge density adsorb onto particles with ionizable surfaces. The charge neutralization point coincides with the maximum of particle aggregation in all suspensions. We find that the concentration of polyelectrolyte, needed to neutralize the particle charge, decreases with increasing charge density of the pectin. The most highly charged pectin presents an exception to this order, which is explained with a reduction of the effective charge density of this pectin due to condensation of counterions. The presence of condensed counterions, remaining bound to the pectin during its adsorption on the particle surface, is proved by investigation of the frequency behavior of the electro-optical effect at charge reversal of the particle surface.     

Principles of electrostatic interactions and self-assembly in lipid/peptide/DNA systems: Applications to gene delivery

Recently, great progress has been achieved in development of a wide variety of formulations for gene delivery in vitro and in vivo, which include lipids, peptides and DNA (LPD). Additionally, application of natural histone–DNA complexes (chromatin) in combination with transfection lipids has been suggested as a potential route for gene delivery (chromofection). However, the thermodynamic mechanisms responsible for formation of the ternary lipid–peptide–DNA supramolecular structures have rarely been analyzed. Using recent experimental studies on LPD complexes (including mixtures of chromatin with cationic lipids) and general polyelectrolyte theory, we review and analyze the major determinants defining the internal structure, particle composition and size, surface charge and ultimately, transfection properties of the LPD formulations.     

A novel particle separation method based on induced‐charge electro‐osmotic flow and polarizability of dielectric particles

A new microfluidic method of particle separation was proposed and studied theoretically in this paper. This method is based on the induced charge electro‐osmotic flow (ICEOF) and polarizability of dielectric particles. In this method, a pair of metal plates is embedded on the side channel walls to create a region of circulating flows under applied electric field. When a dielectric particle enters this region, the vortices produced by ICEOF around the particle will interact with the circulating flows produced by the metal plates. Such hydrodynamic interaction influences the particle's trajectory, and may result in the particle being trapped in the flow circulating zone or passing through this flow circulating zone. Because the hydrodynamic interaction is sensitive to the applied electric field, and the polarizability and the size of the particles, separation of different particles can be realized by controlling these parameters. Comparing with electrophoresis and dielectrophoresis methods, this strategy presented in this paper is simple and sensitive.     

Electrostatic interactions between amphoteric latex particles and proteins

The electrostatic interactions between amphoteric polymethyl methacrylate latex particles and proteins with different pI values were investigated. These latex particles possess a net positive charge at low pH, but they become negatively charged at high pH. The nature and degree of interactions between these polymer particles and proteins are primarily controlled by the electrostatic characteristics of the particles and proteins under the experimental conditions. The self-promoting adsorption process from the charge neutralization of latex particles by the proteins, which have the opposite net charge to that of the particles, leads to a rapid reduction in the zeta potential of the particles (in other words colloidal stability), and so strong flocculation occurs. On the other hand, the electrostatic repulsion forces between similarly charged latex particles and the proteins retard the adsorption of protein molecules onto the surfaces of the particles. Therefore, latex particles exhibit excellent colloidal stability over a wide range of protein concentrations. A transition from net negative charge to net positive charge, and vice versa (charge reversal), was observed when the particle surface charge density was not high enough to be predominant in the protein adsorption process.     

Two quality and stability indicating imaged CIEF methods for mRNA vaccines

Two imaged capillary isoelectric focusing methods were developed to provide insight into the quality and stability of messenger ribonucleic acid (mRNA) vaccines, specifically, mRNA encapsulated in lipid nanoparticles (LNPs). A variety of stressed and lipid composition-modified samples were measured and detected by their UV absorption. The results were supported by the data of an encapsulation assay and particle sizing. One method, using 9 M urea as an additive, shows two broad and jagged peaks in which the peak shape offers detailed information. The summed peak area of both peaks showed RSDs from 2% to 8% when one batch was measured in triplicate and apparently depends on the size of the LNPs. In the second method, a combination of 5.5 M urea and 2 M N-ethylurea was used. This method is characterized by a high repeatability of the isoelectric point (pI, <0.5%). The repeatable peak area (RSD of 2%–7%) correlates linearly with the mRNA content, which also applies to the first method, and added stress is evident by the change in pI and peak area. Furthermore, experiments with the addition of a fluorescent dye were performed (fluorescence detection), which tremendously increased the sensitivity of the methods. Both methods can be used to characterize the stability of mRNA-loaded LNPs, for example, when investigating various storage times at different temperatures and freeze–thaw cycles, as well as the ability of the methods to distinguish lipid compositions and measure batch-to-batch variability.     

Activatable NIR-II Photothermal Lipid Nanoparticles for Improved Messenger RNA Delivery

Endosomal escape remains a central issue limiting the high protein expression of mRNA therapeutics. Here, we present second near-infrared (NIR-II) lipid nanoparticles (LNPs) containing pH activatable NIR-II dye conjugated lipid (Cy-lipid) for potentiating mRNA delivery efficiency via a s timulus-responsive p hotothermal-promoted e ndosomal e scape d elivery (SPEED) strategy. In acidic endosomal microenvironment, Cy-lipid is protonated and turns on NIR-II absorption for light-to-heat transduction mediated by 1064 nm laser irradiation. Then, the heat-promoted LNPs morphology change triggers rapid escape of NIR-II LNPs from the endosome, allowing about 3-fold enhancement of enhanced green fluorescent protein (eGFP) encoding mRNA translation capacity compared to the NIR-II light free group. In addition, the bioluminescence intensity induced by delivered luciferase encoding mRNA in the mouse liver region shows positive correlation with incremental radiation dose, indicating the validity of the SPEED strategy.     

Janus Nanoparticles: Preparation,Characterization, and Applications

In chemical functionalization of colloidal particles, the functional moieties are generally distributed rather homogeneously on the particle surface. Recently, a variety of synthetic protocols have been developed in which particle functionalization may be carried out in a spatially controlled fashion, leading to the production of structurally asymmetrical particles. Janus particles represent the first example in which the two hemispheres exhibit distinctly different chemical and physical properties, which is analogous to the dual‐faced Roman god, Janus. Whereas a variety of methods have been reported for the preparation of (sub)micron‐sized polymeric Janus particles, it has remained challenging for the synthesis and (unambiguous) structural characterization of much smaller nanometer‐sized Janus particles. Herein, several leading methods for the preparation of nanometer‐sized Janus particles are discussed and the important properties and applications of these Janus nanoparticles in electrochemistry, sensing, and catalysis are highlighted. Some perspectives on research into functional patchy nanoparticles are also given.