Lysine-containing cationic liposomes activate the NLRP3 inflammasome: Effect of a spacer between the head group and the hydrophobic moieties of the lipids

Emerging Cationic Nanovaccines

Cationic vaccines of nanometric sizes can directly perform the delivery of antigen(s) and immunomodulator(s) to dendritic cells in the lymph nodes. The positively charged nanovaccines are taken up by antigen-presenting cells (APCs) of the lymphatic system often originating the cellular immunological defense required to fight intracellular microbial infections and the proliferation of cancers. Cationic molecules imparting the positive charges to nanovaccines exhibit a dose-dependent toxicity which needs to be systematically addressed. Against the coronavirus, mRNA cationic nanovaccines evolved rapidly. Nowadays cationic nanovaccines have been formulated against several infections with the advantage of cationic compounds granting protection of nucleic acids in vivo against biodegradation by nucleases. Up to the threshold concentration of cationic molecules for nanovaccine delivery, cationic nanovaccines perform well eliciting the desired Th 1 improved immune response in the absence of cytotoxicity. A second strategy in the literature involves dilution of cationic components in biocompatible polymeric matrixes. Polymeric nanoparticles incorporating cationic molecules at reduced concentrations for the cationic component often result in an absence of toxic effects. The progress in vaccinology against cancer involves in situ designs for cationic nanovaccines. The lysis of transformed cancer cells releases several tumoral antigens, which in the presence of cationic nanoadjuvants can be systemically presented for the prevention of metastatic cancer. In addition, these local cationic nanovaccines allow immunotherapeutic tumor treatment.

Ornithine lipid is a partial TLR4 agonist and NLRP3 activator

Gram-negative bacterial lipopolysaccharides (LPSs) trigger inflammatory reactions through Toll-like receptor 4 (TLR4) and prime myeloid cells for inflammasome activation. In phosphate-limited environments, bacteria reduce LPS and other phospholipid production and synthesize phosphorus-free alternatives such as amino-acid-containing lipids like the ornithine lipid (OL). This adaptive strategy conserves phosphate for other essential cellular processes and enhances bacterial survival in host environments. While OL is implicated in bacterial pathogenicity, the mechanism is unclear. Using primary murine macrophages and human mononuclear cells, we elucidate that OL activates TLR4 and induces potassium efflux-dependent nucleotide-binding domain and leucine-rich repeat-containing pyrin protein 3 (NLRP3) activation. OL upregulates the expression of NLRP3 and pro-interleukin (IL)-1β and induces cytokine secretion in primed and unprimed cells. By contrast, in the presence of LPS, OL functions as a partial TLR4 antagonist and reduces LPS-induced cytokine secretion. We thus suggest that in phosphate-depleted environments, OL replaces LPS bacterial immunogenicity, while constitutively present OL may allow bacteria to escape immune surveillance.

Sprayable inflammasome-inhibiting lipid nanorods in a polymeric scaffold for psoriasis therapy

Localized delivery of inflammasome inhibitors in phagocytic macrophages could be promising for psoriasis treatment. The present work demonstrates the development of non-spherical lipid nanoparticles, mimicking pathogen-like shapes, consisting of an anti-inflammatory inflammasome inhibiting lipid (pyridoxine dipalmitate) as a trojan horse. The nanorods inhibit inflammasome by 3.8- and 4.5-fold compared with nanoellipses and nanospheres, respectively. Nanorods reduce apoptosis-associated speck-like protein and lysosomal rupture, restrain calcium influx, and mitochondrial reactive oxygen species. Dual inflammasome inhibitor (NLRP3/AIM-2-IN-3) loaded nanorods cause synergistic inhibition by 21.5- and 59-folds compared with nanorods and free drug, respectively alongside caspase-1 inhibition. The NLRP3/AIM-2-IN-3 nanorod when transformed into a polymeric scaffold, simultaneously and effectively inhibits RNA levels of NLRP3, AIM2, caspase-1, chemokine ligand-2, gasdermin-D, interleukin-1β, toll-like receptor 7/ 8, and IL-17A by 6.4-, 1.6-, 2.0-, 13.0-, 4.2-, 24.4-, 4.3-, and 1.82-fold, respectively in psoriatic skin in comparison to Imiquimod positive control group in an in-vivo psoriasis-like mice model.

Development of the observation of membrane fusion with label-free liposomes by calcium imaging

Liposomes are artificial vesicles composed of lipid bilayers that have enabled drugs to be encapsulated and delivered to tumor tissue. Membrane-fusogenic liposomes fuse with the plasma membranes of cells to deliver encapsulated drugs directly to the cytosol, which makes it a promising method for rapid and highly efficient drug delivery. In a previous study, liposomal lipid bilayers were labeled with fluorescent probes, and colocalization of labeled lipids with plasma membrane was observed under a microscope. However, there was concern that fluorescent labeling would affect lipid dynamics and cause liposomes to acquire membrane fusogenic ability. In addition, encapsulation of hydrophilic fluorescent substances in the inner aqueous phase sometimes requires an additional step of removing unencapsulated substances after preparation, and there is a risk of leakage. Herein, we propose a new method to observe cell interaction with liposomes without labeling. Our laboratory has developed two types of liposomes with different cellular internalization pathways, i.e., endocytosis and membrane fusion. We found that cytosolic calcium influx would be triggered following the internalization of cationic liposomes, and different cell entry routes led to different calcium responses. Thus, the correlation between cell entry routes and calcium responses could be utilized to study liposome-cell interactions without fluorescent labeling lipids. Briefly, liposomes were added to phorbol 12-myristate 13-acetate (PMA)-primed THP-1 cells, and calcium influx was measured by time-lapse imaging using a fluorescent indicator (Fura 2-AM). Liposomes with high membrane fusogenic ability elicited a strong transient calcium response immediately after adding liposomes, whereas those taken up mainly by endocytosis elicited multiple weak calcium responses. In order to verify the cell entry routes, we also tracked the intracellular distribution of fluorescent-labeled liposomes in PMA-primed THP-1 cells using a confocal laser scanning microscope. It was shown that for fusogenic liposomes, colocalization with plasma membrane occurred at the same time as calcium elevation, whereas for liposomes with a high endocytosis potential, fluorescent dots were observed in the cytoplasm, suggesting the cell internalization by endocytosis. These results suggested that the calcium response patterns correspond to cell entry routes, and membrane fusion can be observed by calcium imaging.

A Review of Different Types of Liposomes and Their Advancements as a Form of Gene Therapy Treatment for Breast Cancer

Breast cancer incidence and mortality rates have increased exponentially during the last decade, particularly among female patients. Current therapies, including surgery and chemotherapy, have significant negative physical and mental impacts on patients. As a safer alternative, gene therapy utilising a therapeutic gene with the potential to treat various ailments is being considered. Delivery of the gene generally utilises viral vectors. However, immunological reactions and even mortality have been recorded as side effects. As a result, non-viral vectors, such as liposomes, a system composed of lipid bilayers formed into nanoparticles, are being studied. Liposomes have demonstrated tremendous potential due to their limitless ability to combine many functions into a system with desirable characteristics and functionality. This article discusses cationic, anionic, and neutral liposomes with their stability, cytotoxicity, transfection ability, cellular uptake, and limitation as a gene carrier suitable for gene therapy specifically for cancer. Due to the more practical approach of employing electrostatic contact with the negatively charged nucleic acid and the cell membrane for absorption purposes, cationic liposomes appear to be more suited for formulation for gene delivery and therapy for breast cancer treatment. As the other alternatives have numerous complicated additional modifications, attachments need to be made to achieve a functional gene therapy system for breast cancer treatment, which were also discussed in this review. This review aimed to increase understanding and build a viable breast cancer gene therapy treatment strategy.

The Role of Cryoprotective Agents in Liposome Stabilization and Preservation

To improve liposomes’ usage as drug delivery vehicles, cryoprotectants can be utilized to prevent constituent leakage and liposome instability. Cryoprotective agents (CPAs) or cryoprotectants can protect liposomes from the mechanical stress of ice by vitrifying at a specific temperature, which forms a glassy matrix. The majority of studies on cryoprotectants demonstrate that as the concentration of the cryoprotectant is increased, the liposomal stability improves, resulting in decreased aggregation. The effectiveness of CPAs in maintaining liposome stability in the aqueous state essentially depends on a complex interaction between protectants and bilayer composition. Furthermore, different types of CPAs have distinct effective mechanisms of action; therefore, the combination of several cryoprotectants may be beneficial and novel attributed to the synergistic actions of the CPAs. In this review, we discuss the use of liposomes as drug delivery vehicles, phospholipid–CPA interactions, their thermotropic behavior during freezing, types of CPA and their mechanism for preventing leakage of drugs from liposomes.

Development of a cell line-based in vitro assay for assessment of Diphtheria, Tetanus and acellular Pertussis (DTaP)-induced inflammasome activation

Safety and potency assessment for batch release testing of established vaccines still relies partly on animal tests. An important avenue to move to batch release without animal testing is the consistency approach. This approach is based on thorough characterization of the vaccine to identify critical quality attributes that inform the use of a comprehensive set of non-animal tests to release the vaccine, together with the principle that the quality of subsequent batches follows from their consistent production. Many vaccine antigens are by themselves not able to induce a protective immune response. The antigens are therefore administered together with adjuvant, most often by adsorption to aluminium salts. Adjuvant function is an important component of vaccine potency, and an important quality attribute of the final product. Aluminium adjuvants are capable of inducing NLRP3 inflammasome activation. The aim of this study was to develop and evaluate an in vitro assay for NLRP3 inflammasome activation by aluminium-adjuvanted vaccines. We evaluated the effects of Diphtheria-Tetanus-acellular Pertussis combination vaccines from two manufacturers and their respective adjuvants, aluminium phosphate (AP) and aluminium hydroxide (AH), in an in vitro assay for NLRP3 inflammasome activation. All vaccines and adjuvants tested showed a dose-dependent increase in IL-1β production and a concomitant decrease in cell viability, suggesting NLRP3 inflammasome activation. The results were analysed by benchmark dose modelling, showing a similar 50% effective dose (ED50) for the two vaccine batches and corresponding adjuvant of manufacturer A (AP), and a similar ED50 for the two vaccine batches and corresponding adjuvant of manufacturer B (AH). This suggests that NLRP3 inflammasome activation is determined by the adjuvant only. Repeated freeze-thaw cycles reduced the adjuvant biological activity of AH, but not AP. Inflammasome activation may be used to measure adjuvant biological activity as an important quality attribute for control or characterization of the adjuvant.

Lipid-protein interactions regulating the canonical and the non-canonical NLRP3 inflammasome

The inflammatory response is a complex regulated effector mechanism of the innate immune system that is initiated after tissue injury or infection. The NLRP3 inflammasome is an important initiator of inflammation by regulating the activation of caspase-1, the maturation of pro-inflammatory cytokines and the induction of pyroptotic cell death. Numerous studies demonstrate that the NLRP3 inflammasome could be modulated by lipids, existing a relation between lipids and the activation of different inflammatory processes. In this review we will summarize how the mechanism of NLRP3 inflammasome activation is regulated by different lipids and how these lipids control specific cellular localization of NLRP3 during activation. Although being a cytosolic protein, NLRP3 interacts with lipids accessible in neighbor membranes. Also, the modulation of NLRP3 by endogenous lipids has been found causative of different metabolic diseases and bacterial-pathogenic lipids lead to NLRP3 activation during infection. The understanding of the modulation of the NLRP3 inflammasome by lipids has resulted not only in a better knowledge about the mechanism of NLRP3 activation and its implication in disease, but also opens a new avenue for the development of novel therapeutics and vaccines, as NLRP3 could be modulated by synthetic lipids used as adjuvants.

Arginine-based cationic liposomes accelerate T cell activation and differentiation in vitro

Cationic liposomes are versatile lipid nanocarriers to improve the pharmacological properties of drug payloads. Recent advantages include the application of their intrinsic immunostimulatory effects to enhance immune activation. Herein, we report for the first time the structural effect of cationic lipids in promoting T cell activation and differentiation in vitro. Two types of cationic liposomes R3C14 and R5C14 were prepared from single type of lipids Arg-C3-Clu2C14 or Arg-C5-Clu2C14, which bear arginine head group and ditetradecyl tails but vary in the carbon number of the spacer in between. Murine CD8 or CD4 T cells were pretreated with 50 μM of each type of liposomes for 2 h, followed by stimulation with anti-CD3/CD28 antibodies for 24 h. In comparison to liposome-untreated T cells, R5C14-pretreatment induced a robust T cell activation (IL-2, CD25⁺) and differentiation into effector cells (CD44^high, CD62L^low), whereas R3C14 did not show comparable effect. Furthermore, a weak activation of nuclear factor of activated T cells (NFAT) was detected in Jurkat-Lucia NFAT cells (InvivoGen), suggesting a potential signaling pathway for the liposomal effect. Although R5C14 liposomes did not activate T cells without subsequent CD3/CD28 stimulation, this study implied a recessive effect of some cationic adjuvant in priming T cells to enhance their responsiveness to antigens.

Chemical Advances in Therapeutic Application of Exosomes and Liposomes

Exosomes and liposomes are vesicular nanoparticles that can encapsulate functional cargo. The chemical similarities between naturally occurring exosomes and synthetic liposomes have accelerated the development of exosome mimetics as a therapeutic drug delivery platform under physiological and pathological environments. To maximise the applications of exosomes and liposomes in the clinical setting, it is essential to look into their basic chemical properties and utilise these characteristics to optimise the preparation, loading, modification and hybridisation. This review summarises the chemical and biological properties of both exosomal and liposomal systems as well as some of the challenges related to their production and application. This article concludes with a discussion on potential perspectives for the integration of exosomal and liposomal technologies in mapping better approaches for their biomedical use, especially in therapeutics.

Immunologically Effective Biomaterials

Immunoregulation represents a booming field of biomaterial design. The unique physical and chemical properties of biomaterials offer tremendous opportunities for development. Each of their parameters exerts immunogenic effects at the immune system, cellular, and molecular levels. Herein, the perspective summarizes the interaction of biomaterials with immune cells and the underlying mechanisms to control immunoregulation in a top-down manner, providing solid inspiration for biomedical applications of immunologically effective biomaterials.

Intracellular Distribution of Lipids and Encapsulated Model Drugs from Cationic Liposomes with Different Uptake Pathways

AIM

The uptake pathway of liposomes into cells is mainly via endocytosis or membrane fusion; however, the relationship between the uptake pathway and the intracellular pharmacokinetics of the liposome components remains unclear. This study aimed at revealing the relationship by using cationic liposomes having similar physical properties and different uptake pathways.

MATERIALS AND METHODS

We prepared cationic liposomes composed of amino acid-type lipids, K3C14 and K3C16, which have different uptake pathways by a hydration method, and fluorescently modified them by encapsulating FITC-dextran and surface conjugation with Alexa Fluor® 488 (AF488). Then, we investigated their intracellular distribution in HeLa cells over time.

RESULTS

The liposomes had similar physical properties and did not cause significant cell mortality after treatment for 180 min. The delivery rate and efficiency of encapsulated FITC-dextran with the fusogenic K3C16 liposomes were 3 and 1.6 times higher, respectively, than with the endocytic K3C14 liposomes. FITC-dextran molecules delivered with K3C16 liposomes were observed throughout the cytosolic space after 10 min, while those delivered with K3C14 liposomes were mainly observed as foci and took 60 min to diffuse into the cytosolic space. K3C14 lipids modified with AF488 were distributed mostly in the cytosolic space. In contrast, fluorescently labeled K3C16 lipids were colocalized with the plasma membrane of 50% of the HeLa cells after 10 min and were gradually internalized intracellularly.

CONCLUSION

Fusogenic K3C16 liposomes internalized into HeLa cells faster than endocytic K3C14 liposomes, and their components differently distributed in the cells.

Barriers and Strategies of Cationic Liposomes for Cancer Gene Therapy

Cationic liposomes (CLs) have been regarded as the most promising gene delivery vectors for decades with the advantages of excellent biodegradability, biocompatibility, and high nucleic acid encapsulation efficiency. However, the clinical use of CLs in cancer gene therapy is limited because of many uncertain factors in vivo. Extracellular barriers such as opsonization, rapid clearance by the reticuloendothelial system and poor tumor penetration, and intracellular barriers, including endosomal/lysosomal entrapped network and restricted diffusion to the nucleus, make CLs not the ideal vector for transferring extrinsic genes in the body. However, the obstacles in achieving productive therapeutic effects of nucleic acids can be addressed by tailoring the properties of CLs, which are influenced by lipid compositions and surface modification. This review focuses on the physiological barriers of CLs against cancer gene therapy and the effects of lipid compositions on governing transfection efficiency, and it briefly discusses the impacts of particle size, membrane charge density, and surface modification on the fate of CLs in vivo, which may provide guidance for their preclinical studies.

Inflammasomes as Targets for Adjuvants

Inflammasomes are an essential part of the innate immune system. They are necessary for the development of a healthy immune response against infectious diseases. Inflammasome activation leads to the secretion of pro-inflammatory cytokines such as IL-1β and IL-18, which stimulate the adaptive immune system. Inflammasomes activators can be used as adjuvants to provide and maintain the strength of the immune response. This review is focused on the mechanisms of action and the effects of adjuvants on inflammasomes. The therapeutic and prophylaxis significance of inflammasomes in infectious diseases is also discussed.

NLRP3 inflammasome-activating arginine-based liposomes promote antigen presentations in dendritic cells

Purpose: The NLRP3 inflammasome activation has been proposed as a common mechanism for some adjuvants to boost the immune system, and cationic liposomes were reported to potentially activate the NLRP3 inflammasome. Herein, we questioned whether the NLRP3 inflammasome-activating cationic liposomes could promote antigen presentation and be applied as an immune adjuvant. In addition, we aimed to investigate the structure effect of lipid on triggering these immune responses.

Materials and methods: A series of structurally similar lipids, consisting of arginine (Arg) head group and varied lengths of alkyl chains or spacers in between were used to prepare cationic liposomes. Lipopolysaccharide-primed human or murine macrophages or phorbol 12-myristate 13-acetate-primed THP-1 cells were treated with these liposomes, and interleukin (IL)-1β secretion was measured to quantify the NLRP3 inflammasome activation. Lysosome rupture was examined in THP-1 cells by the fluorescence loss of acridine orange, a lysosome dye. Further, chicken ovalbumin (OVA) was loaded on the liposome surface and applied to murine bone marrow-derived dendritic cells (BMDCs), which activate OT-I and OT-II lymphocytes upon major histocompatibility complex (MHC) class I- and class II-mediated antigen presentation, respectively. OT-I and OT-II cell division and IL-2 secretion were measured to evaluate the antigen presentation efficiency. The expressions of MHC molecules and co-stimulatory molecules ie, CD80, CD86, and CD40 on BMDCs were investigated by flow cytometry.

Results: All the liposomes showed size distributions of 80–200 nm and zeta potentials of around 50 mV. A3C14 liposomes, consisting of Arg-C3-Glu2C14 lipids induced the most potent lysosome rupture and NLRP3 inflammasome activation. OVA-A3C14 also exhibited the most potent MHC class I- and class II-mediated antigen presentation in BMDCs without interfering MHC and co-stimulatory molecules.

Conclusion: The hydrophobic moieties of arginine-based liposomes are crucial in stimulating innate immune cells. A3C14 liposomes were non-immunogenic but strongly activated innate immune cells and promoted antigen presentation, and therefore can be applied as immune adjuvants.

The efficiency of cytosolic drug delivery using pH-responsive endosomolytic polymers does not correlate with activation of the NLRP3 inflammasome

Inefficient cytosolic delivery has limited the development of many promising biomacromolecular drugs, a long-standing challenge that has prompted extensive development of drug carriers that facilitate endosomal escape. Although many such carriers have shown considerable promise for cytosolic delivery of a diversity of therapeutics, the rupture or destabilization of endo/lysosomal membranes has also been associated with activation of the inflammasome with attendant risk of inflammation and toxicity. In this study, we investigated relationships between pH-dependent membrane destabilization, cytosolic drug delivery, and inflammasome activation using a series of well-defined poly[(ethylene glycol)-block-[(2-(dimethylamino)ethyl methacrylate)-co-(butyl methacrylate)] copolymers of variable second block composition and pH-responsive properties. We found that polymers that demonstrated the most potent membrane-destabilizing activity at early endosomal pH values in an erythrocyte hemolysis assay were most efficient at delivery of siRNA, yet tended to be associated with the least amount of NOD-like related protein 3 (NLRP3) inflammasome activation. By contrast, polymers that displayed minimal hemolysis activity and poor siRNA knockdown, and instead mediated lysosomal rupture likely due to a proton sponge mechanism, strongly induced NLPR3 inflammasome activation in a caspase- and cathepsin-dependent manner. Collectively, these findings reinforce the importance of early endosomal escape in minimizing inflammasome activation and also demonstrate the ability to tune the degree inflammasome activation via control of polymer structure with potential implications for design of vaccine adjuvants and immunotherapeutics.

Membrane fusogenic lysine type lipid assemblies possess enhanced NLRP3 inflammasome activation potency

Lysine (K) type cationic lipid with a propyl spacer and ditetradecyl hydrophobic moieties composing liposomes, K3C14, previously studied for gene delivery, were reported to activate the NLRP3 inflammasomes in human macrophages via the conventional phagolysosomal pathway. In this study, K3C16, a propyl spacer bearing lysine type lipids with dihexadecyl moieties (an extension of two hydrocarbon tail length) were compared with K3C14 as liposomes. Such a small change in tail length did not alter the physical properties such as size distribution, zeta potential and polydispersity index (PDI). The NLRP3 activation potency of K3C16 was shown to be 1.5-fold higher. Yet, the toxicity was minimal, whereas K3C14 has shown to cause significant cell death after 24 h incubation. Even in the presence of endocytosis inhibitors, cytochalasin D or dynasore, K3C16 continued to activate the NLRP3 inflammasomes and to induce IL-1β release. To our surprise, K3C16 liposomes were confirmed to fuse with the plasma membrane of human macrophages and CHO-K1 cells. It is demonstrated that the change in hydrophobic tail length by two hydrocarbons drastically changed a cellular entry route and potency in activating the NLRP3 inflammasomes.

Nanoparticles and danger signals: Oral delivery vehicles as potential disruptors of intestinal barrier homeostasis

Gut immune system homeostasis involves diverse structural interactions among resident microbiota, the protective mucus layer, and a variety of cells (intestinal epithelial, lymphoid, and myeloid). Due to the substantial surface area in direct contact with an "external" environment and the diversity of xenobiotic, abiotic, and self-interactions coordinating to maintain gut homeostasis, there is enhanced potential for the generation of endogenous danger signals when this balance is lost. Here, we focus on the potential generation and reception of damage in the gut resulting from exposure to nanoparticles (NPs), common food and drug additives. Specifically, we describe recent evidence in the literature showing that certain NPs are potential generators of damage-associated molecular patterns, as well as potential immune-stimulating molecular patterns themselves.

Genotoxicity of amorphous silica nanoparticles: Status and prospects

Amorphous silica nanoparticles (SNPs) are widely used in biomedical applications and consumer products. Little is known, however, about their genotoxicity and potential to induce gene expression regulation. Despite recent efforts to study the underlying mechanisms of genotoxicity of SNPs, inconsistent results create a challenge. A variety of factors determine particle-cell interactions and underlying mechanisms. Further, high-throughput studies are required to carefully assess the impact of silica nanoparticle physicochemical properties on induction of genotoxic response in different cell lines and animal models. In this article, we review the strategies available for evaluation of genotoxicity of nanoparticles (NPs), survey current status of silica nanoparticle gene alteration and genotoxicity, discuss particle-mediated inflammation as a contributing factor to genotoxicity, identify existing gaps and suggest future directions for this research.