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Although lipid nanoparticles (LNPs) have been FDA-approved for mRNA delivery, there is still much to learn about these fascinating multi-component delivery systems. Here, I discuss the presence of "bleb" structures on LNPs and the co-existence of mRNA-empty LNPs in LNP-mRNA-based formulations. Specifically, I discuss key articles on these structural and compositional heterogeneities, whether these features present negative or positive LNP attributes, and how to deal with them in research and quality control settings. Additionally, I present current approaches and propose novel strategies on how to study and quantify bleb and empty LNP structures. With the conflicting views on these features in the literature and limited systematic studies on their impact on safety and efficacy, I hope this Perspective will support current and bring forward new thinking about these matters. I anticipate that novel studies and insights could emerge from these lines of thinking, which could potentially enhance the development of safe and efficient LNP-based drug products that will either embrace, leverage, or mitigate the presence of blebs and empty LNPs. [Display omitted] • Presents and discusses key articles related to bleb and empty LNP structures. • Examines methods for studying and quantifying these features, including proposing new approaches. • Discusses how to deal with these features differently in research and quality control settings. • Emphasizes the significance of developing standard LNP materials to evaluate LNP analysis tools. • Presents different perspectives on whether bleb and empty LNP structures are positive or negative LNP attributes. [ABSTRACT FROM AUTHOR]

The advent of lipid nanoparticles (LNPs) containing ionizable cationic lipids has enabled the encapsulation, stabilization, and intracellular delivery of nucleic acid payloads, leading to FDA-approved siRNA-based therapy and mRNA-based vaccines. Other nucleic acid-based therapeutic modalities, including protein replacement and CRISPR-mediated gene knockout and editing, are being tested in clinical trials, in many cases, for the treatment of liver-related diseases. However, to fully exploit these therapies beyond the liver, improvements in their delivery to extrahepatic targets are needed. Towards this end, both active targeting strategies based on targeting ligands grafted onto LNPs and passive targeting relying on physicochemical LNP parameters such as surface composition, charge, and size are being evaluated. Often, the latter strategy depends on the interaction of LNPs with blood components, forming what is known as the biomolecular corona. Here, I discuss potential challenges related to current LNP-based targeting strategies and the studies of the biomolecular corona on LNPs. I propose potential solutions to overcome some of these obstacles and present approaches currently being tested in preclinical and clinical studies, which face fewer biological barriers than traditional organ-targeting approaches. [Display omitted] • Presents an overview of LNP-based strategies for extrahepatic RNA delivery. • Highlights potential challenges with the LNP strategies and approaches to overcome some of them. • Stresses inherent challenges associated with biomolecular corona studies of LNPs. • Highlights that LNPs are a minor subpopulation of nanoparticles in human plasma. • Advocates innovative approaches to drive progress in the LNP field. [ABSTRACT FROM AUTHOR]

During the last decade, and with increasing intensity, the potential for using reconstituted high-density lipoprotein (rHDL) particles to deliver hydrophobic drugs to impaired cells and tissues has been explored. Here, we evaluate various parameters that should be considered when utilizing discoidal rHDL particles as a drug delivery platform. Key parameters such as preparation basics, pronounced statistical variation in drug incorporation across rHDL particles, effects of lipid composition on HDL/rHDL in vivo and vitro dynamics/particle stability, and pharmacokinetic/safety data from rHDL infusion studies in human subjects will be addressed including the innate receptors and native functions of HDL. The broad but detailed information presented in this work could also be deployed in other rHDL-related research. However, the major aim of this review is to point out factors that have the potential to advance rHDL research toward realizing the ‘magic bullet’ for lipophilic and hydrophilic drug delivery in various clinical contexts. [ABSTRACT FROM AUTHOR]

[Display omitted] Lipid nanoparticles (LNPs) play an important role in mRNA vaccines against COVID-19. In addition, many preclinical and clinical studies, including the siRNA-LNP product, Onpattro®, highlight that LNPs unlock the potential of nucleic acid-based therapies and vaccines. To understand what is key to the success of LNPs, we need to understand the role of the building blocks that constitute them. In this Review , we discuss what each lipid component adds to the LNP delivery platform in terms of size, structure, stability, apparent pK a , nucleic acid encapsulation efficiency, cellular uptake, and endosomal escape. To explore this, we present findings from the liposome field as well as from landmark and recent articles in the LNP literature. We also discuss challenges and strategies related to in vitro/in vivo studies of LNPs based on fluorescence readouts, immunogenicity/reactogenicity, and LNP delivery beyond the liver. How these fundamental challenges are pursued, including what lipid components are added and combined, will likely determine the scope of LNP-based gene therapies and vaccines for treating various diseases. [ABSTRACT FROM AUTHOR]

Summary PICK1 is a neuronal scaffolding protein containing a PDZ domain and an auto-inhibited BAR domain. BAR domains are membrane-sculpting protein modules generating membrane curvature and promoting membrane fission. Previous data suggest that BAR domains are organized in lattice-like arrangements when stabilizing membranes but little is known about structural organization of BAR domains in solution. Through a small-angle X-ray scattering (SAXS) analysis, we determine the structure of dimeric and tetrameric complexes of PICK1 in solution. SAXS and biochemical data reveal a strong propensity of PICK1 to form higher-order structures, and SAXS analysis suggests an offset, parallel mode of BAR-BAR oligomerization. Furthermore, unlike accessory domains in other BAR domain proteins, the positioning of the PDZ domains is flexible, enabling PICK1 to perform long-range, dynamic scaffolding of membrane-associated proteins. Together with functional data, these structural findings are compatible with a model in which oligomerization governs auto-inhibition of BAR domain function. [ABSTRACT FROM AUTHOR]

Membrane-active peptides (MAPs) have several potential therapeutic uses, including as antimicrobial drugs. Many traditional methods used to evaluate the membrane interactions of MAPs have limited applicability. Low-throughput methods, such as microscopy, provide detailed information but often rely on fluorophore-labeled MAPs, and high-throughput assays, such as the calcein release assay, cannot assess the mechanism behind the disruption of vesicular-based lipid membranes. Here we present a flow cytometric assay that provides detailed information about the peptide-lipid membrane interactions on single artificial lipid vesicles while being high-throughput (1000–2000 vesicles/s) and based on label-free MAPs. We synthesized and investigated six MAPs with different modes of action to evaluate the versatility of the assay. The assay is based on the flow cytometric readouts from artificial lipid vesicles, including the fluorescence from membrane-anchored and core-encapsulated fluorophores, and the vesicle concentration. From these parameters, we were able to distinguish between MAPs that induce vesicle solubilization, permeation (pores/membrane distortion), and aggregation or fusion. Our flow cytometry findings have been verified by traditional methods, including the calcein release assay, dynamic light scattering, and fluorescence microscopy on giant unilamellar vesicles. We envision that the presented flow cytometric assay can be used for various types of peptide-lipid membrane studies, e.g. to identify new antibiotics. Moreover, the assay can easily be expanded to derive additional valuable information. [Display omitted] • Developed a novel assay to study the modes of action of membrane-active peptides. • Our flow cytometric high-throughput assay relies on label-free peptides. • Fluorescence microscopy, DLS and calcein release studies confirmed the validity of our assay. • Six very different membrane-active peptides were evaluated in our assay. [ABSTRACT FROM AUTHOR]