Characterization of oligonucleotide/lipid interactions in submicron cationic emulsions: influence of the cationic lipid structure and the presence of PEG-lipids

Development and Characterization of Cationic Nanostructured Lipid Carriers as Drug Delivery Systems for miRNA-27a

Although miRNA-27a has been identified as a promising candidate for miRNA mimic therapy of obesity, its application is limited due to enzymatic degradation and low membrane permeation. To overcome these problems, we developed cationic nanostructured lipid carriers (cNLCs) using high-pressure homogenization and used them as non-viral carriers for the anti-adipogenic miRNA-27a. Cargo-free octadecylamine-containing NLCs and miRNA/cNLC complexes were characterized regarding particle size, size distributions, zeta potential, pH values, particle topography and morphology, and entrapment efficacy. Furthermore, the cytotoxicity and cellular uptake of the miRNA/cNLC complex in the 3T3-L1 cell line were investigated. The investigation of the biological effect of miRNA-27a on adipocyte development and an estimation of the accumulated Oil-Red-O (ORO) dye in lipid droplets in mature adipocytes were assessed with light microscopy and absorbance measurements. The obtained data show that cNLCs represent a suitable DDS for miRNAs, as miRNA/cNLC particles are rapidly formed through non-covalent complexation due to electrostatic interactions between both components. The miRNA-27a/cNLC complex induced an anti-adipogenic effect on miRNA-27a by reducing lipid droplet accumulation in mature adipocytes, indicating that this approach might be used as a new therapeutic strategy for miRNA mimic replacement therapies in the prevention or treatment of obesity and obesity-related disorders.

Quantitative methods to detect phospholipids at the oil-water interface

Phospholipids are the main constituents of cell membranes and act as natural stabilizers of milk fat globules. Phospholipids are used in a wide range of applications, e.g. as emulsifiers in cosmetic, pharmaceutical and food products. While processed emulsion droplets are usually stabilized by a monolayer of phospholipids, cell membranes have a phospholipid bilayer structure and milk fat globules are stabilized by a complex phospholipid trilayer membrane. Despite the broad relevance of phospholipids, there are still many scientific challenges in understanding how their behavior at the fluid-fluid interface affects microstructure, stability, and physico-chemical properties of natural and industrial products. Most of these challenges arise from the experimental difficulties related to the investigation of the molecular arrangement of phospholipids in situ at the fluid-fluid interface and the quantification of their partitioning between the bulk phase and the interface, both under static and flow conditions. This task is further complicated by the presence of other surface-active components, such as proteins, that can interact with phospholipids and compete for space at the interface. Here, we review the methodologies available from the literature to detect and quantify phospholipids, focusing on oil-water interfaces, and highlight current limitations and future perspectives.

Physicochemical properties of cationic nanoemulsions and liposomes obtained by microfluidization complexed with a single plasmid or along with an oligonucleotide: Implications for CRISPR/Cas technology

In this study, we investigated the effects of the association of a single plasmid or its co-complexation along with an oligonucleotide on the physicochemical properties of cationic nanoemulsions and liposomes intended for gene editing. Formulations composed of DOPE, DOTAP, DSPE-PEG (liposomes), MCT (nanoemulsions), and water were obtained by microfluidization. DSPE-PEG was found to play a crucial role on the size and polydispersity index of nanocarriers. Nucleic acids were complexated by adsorption at different charge ratios. No significant differences were noticed in the physicochemical properties of nanocarriers (i.e. droplet size, polydispersity index, or zeta potential) when a single plasmid or both plasmid and oligonucleotide were adsorbed to the formulations. Transmission electron microscopy photomicrographs suggested round nanostructures with the nucleic acids and DSPE-PEG enfolding the surface. Complexes at +4/-1 charge ratio protected nucleic acids against DNase I degradation. The oligonucleotide seemed to be released from the liposomal complexes, while nanoemulsions only released the plasmid after 24 and 48 h of incubation in DMEM supplemented or not. In vitro experiments demonstrated that complexes were highly tolerable to human fibroblasts, Hep-G2, and HEK-293 cells, demonstrating also an uptake ability of about 30%, 30%, and 90%, respectively, no matter what the formulation or the combination of nucleic acids used. Transfection efficiency of the formulations was around 25% in human fibroblasts, 32% in HEK-293, and 15% in Hep-G2 cells. The overall results demonstrated the behavior of liposomes and nanoemulsions complexed with a plasmid or a mixture of a plasmid and an oligonucleotide, and demonstrated that the association with one or two nucleic acids sequences of different length does not seem to interfere in the physicochemical characteristics of complexes or in the uptake capacity by three different types of cells.

Nerve growth factor-loaded heparinized cationic solid lipid nanoparticles for regulating membrane charge of induced pluripotent stem cells during differentiation

Nerve growth factor (NGF)-loaded heparinized cationic solid lipid nanoparticles (NGF-loaded HCSLNs) were developed using heparin-stearic acid conjugate, cacao butter, cholesterol, stearylamine (SA), and esterquat 1 (EQ 1). The effect of cationic lipids and lipid matrix composition on the particle size, particle structure, surface molecular composition, chemical structure, electrophoretic mobility, and zeta potential of HCSLNs was investigated. The effect of HCSLNs on the membrane charge of induced pluripotent stem cells (iPSCs) was also studied. The results indicated that the average diameter of HCSLNs was 90-240nm and the particle size of HCSLNs with EQ 1 was smaller than that with SA. The zeta potential and electrophoresis analysis showed that HCSLNs with SA had a positively charged potential and HCSLNs with EQ 1 had a negatively charged potential at pH7.4. The high-resolution transmission electron microscope confirmed the loading of NGF on the surface of HCSLNs. Differentiation of iPSCs using NGF-loaded HCSLNs with EQ 1 exhibited higher absolute values of the electrophoretic mobility and zeta potential than differentiation using NGF-loaded HCSLNs with SA. The immunochemical staining of neuronal nuclei revealed that NGF-loaded HCSLNs can be used for differentiation of iPSCs into neurons. NGF-loaded HCSLNs with EQ 1 had higher viability of iPSCs than NGF-loaded HCSLNs with SA. NGF-loaded HCSLNs with EQ 1 may be promising formulation to regulate the membrane charge of iPSCs during neuronal differentiation.

Lipid-modified oligonucleotide conjugates: Insights into gene silencing, interaction with model membranes and cellular uptake mechanisms

The ability of oligonucleotides to silence specific genes or inhibit the biological activity of specific proteins has generated great interest in their use as research tools and therapeutic agents. Unfortunately, their biological applications meet the limitation of their poor cellular accessibility. Developing an appropriate delivery system for oligonucleotides is essential to achieve their efficient cellular uptake. In the present work a series of phosphorothioate lipid-oligonucleotide hybrids were synthesized introducing covalently single or double lipid tails at both 3'- and 5'-termini of an antisense oligonucleotide. Gene transfections in cultured cells showed antisense luciferase inhibition without the use of a transfecting agent for conjugates modified with the double-lipid tail at 5'-termini. The effect of the double lipid-tailed modification was further studied in detail in several model membrane systems as well as in cellular uptake experiments. During these studies the spontaneous formation of self-assembled microstructures is clearly observed. Lipidation allowed the efficient incorporation of the oligonucleotide in HeLa cells by a macropinocytosis mechanism without causing cytotoxicity in cells or altering the binding properties of the oligonucleotide conjugates. In addition, both single- and double-tailed compounds showed a similar behavior in lipid model membranes, making them useful in nucleotide-based technologies.

PEGylated cationic nanoemulsions can efficiently bind and transfect pIDUA in a mucopolysaccharidosis type I murine model

Mucopolysaccharidosis type I (MPS I) is an autosomal disease caused by alpha-L-iduronidase deficiency. This study proposed the use of cationic nanoemulsions as non-viral vectors for a plasmid (pIDUA) containing the gene that codes for alpha-L-iduronidase. Nanoemulsions composed of medium chain triglycerides (MCT)/1,2-dioleoyl-sn-glycero-3-phosphoethanolamine (DOPE)/1,2-dioleoyl-sn-glycero-3-trimethylammonium propane (DOTAP)/1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-[amino(polyethylene glycol)-2000] (DSPE-PEG) were prepared by high pressure homogenization. Formulations were prepared by the adsorption or encapsulation of preformed pIDUA-DOTAP complexes into the oil core of nanoemulsions at different charge ratios. pIDUA complexed was protected from enzymatic degradation by DNase I. The physicochemical characteristics of complexes in protein-containing medium were mainly influenced by the presence of DSPE-PEG. Bragg reflections corresponding to a lamellar organization were identified for blank formulations by energy dispersive X-ray diffraction, which could not be detected after pIDUA complexation. The intravenous injection of these formulations in MPS I knockout mice led to a significant increase in IDUA activity (fluorescence assay) and expression (RT-qPCR) in different organs, especially the lungs and liver. These findings were more significant for formulations prepared at higher charge ratios (+4/-), suggesting a correlation between charge ratio and transfection efficiency. The present preclinical results demonstrated that these nanocomplexes represent a potential therapeutic option for the treatment of MPS I.

Investigation of the structural organization of cationic nanoemulsion/antisense oligonucleotide complexes

Atomic force microscopy image analysis and energy dispersive X-ray diffraction experiments were used to investigate the structural organization of cationic nanoemulsion/oligonucleotide complexes. Oligonucleotides targeting topoisomerase II gene were adsorbed on cationic nanoemulsions obtained by means of spontaneous emulsification procedure. Topographical analysis by atomic force microscopy allowed the observation of the nanoemulsion/oligonucleotide complexes through three-dimensional high-resolution images. Flattening of the oil droplets was observed, which was reduced in the complexes obtained at high amount of adsorbed oligonucleotides. In such conditions, complexes exhibit droplet size in the 600nm range. The oligonucleotides molecules were detected on the surface of the droplets, preventing their fusion during aggregation. A lamellar structure organization was identified by energy dispersive X-ray diffraction experiments. The presence of the nucleic acid molecules led to a disorganization of the lipid arrangement and an expansion in the lattice spacing, which was proportional to the amount of oligonucleotides added.

Physical factors affecting plasmid DNA compaction in stearylamine-containing nanoemulsions intended for gene delivery

Cationic lipids have been used in the development of non-viral gene delivery systems as lipoplexes. Stearylamine, a cationic lipid that presents a primary amine group when in solution, is able to compact genetic material by electrostatic interactions. In dispersed systems such as nanoemulsions this lipid anchors on the oil/water interface confering a positive charge to them. The aim of this work was to evaluate factors that influence DNA compaction in cationic nanoemulsions containing stearylamine. The influence of the stearylamine incorporation phase (water or oil), time of complexation, and different incubation temperatures were studied. The complexation rate was assessed by electrophoresis migration on agarose gel 0.7%, and nanoemulsion and lipoplex characterization was done by Dynamic Light Scattering (DLS). The results demonstrate that the best DNA compaction process occurs after 120 min of complexation, at low temperature (4 ± 1 °C), and after incorporation of the cationic lipid into the aqueous phase. Although the zeta potential of lipoplexes was lower than the results found for basic nanoemulsions, the granulometry did not change. Moreover, it was demonstrated that lipoplexes are suitable vehicles for gene delivery.

Effect of cationic lipid composition on properties of oligonucleotide/emulsion complexes: Physico-chemical and release studies

This paper describes the influence of cationic lipid composition on physico-chemical properties of complexes formed between oligonucleotides (ON) and cationic emulsions. Formulations containing medium chain triglycerides, egg lecithin, increasing amounts of either oleylamine (OA) or 1,2-dioleoyl-3-trimethylammonium-propane (DOTAP), and water were prepared by a spontaneous emulsification procedure. ON adsorption on emulsions was evidenced by the inversion of the zeta-potential, the increase in droplet size, and the morphology of the oil droplet examined through transmission electron microscopy. Adsorption isotherms showed a higher amount of ON adsorbed on emulsions containing DOTAP when compared to emulsions containing OA. In a final step, the role of the main parameters, which may in fact influence the ON release rate from emulsions, was investigated. ON were progressively released from emulsions with an increase in dilution ratio and remained quite similar for both OA and DOTAP emulsions over time. Conversely, the effect of the cationic lipid composition was observed upon increasing the charge ratio of complexes. ON release at a same charge ratio was lower from emulsions containing DOTAP (bearing dioleyl chains) than from those containing OA (bearing monoleyl chain).

Extensive surface studies help to analyse zeta potential data: the case of cationic emulsions

The present study is aimed to characterize the electrostatic parameters of oil in water emulsion droplets composed of MCT (medium chain triglycerides), PL (phospholipids) and Poloxamer and containing increasing concentrations of the cationic lipid oleylamine (OA), in Hepes 20 mM pH 7.4. The initial zeta-potential data suggesting saturation of the droplet surface at high OA concentrations were completed by supplementary analysis: the distribution of the oleylamine within the droplet was determined by reacting the amino groups with the hydrophilic TNBS (trinitrobenzenesulfonic acid), the method being initially standardised with vesicles. In addition, surface potential and pH at the droplet surface were monitored by the pH-sensitive fluorophore 4-heptadecyl-7-hydroxycoumarin. Our results demonstrate that almost all the OA is localised and fully ionised at the droplet surface for all concentrations and that the observed plateau in the zeta-potential values obeys the Gouy-Chapman theory of ion condensation. It is also shown that the slipping plane separation as estimated by the Eversole-Boardman equation is higher that the expected values of 0.2 nm as a result of the relative position of the fluorophore and the outer boundary of the lipid interface thickness and the Poloxamer anchored at the interface only plays a minor role.