Hydration of lipoplexes commonly used in gene delivery: follow-up by laurdan fluorescence changes and quantification by differential scanning calorimetry

Elucidating Structural Configuration of Lipid Assemblies for mRNA Delivery Systems

The development of mRNA delivery systems utilizing lipid-based assemblies holds immense potential for precise control of gene expression and targeted therapeutic interventions. Despite advancements in lipid-based gene delivery systems, a critical knowledge gap remains in understanding how the biophysical characteristics of lipid assemblies and mRNA complexes influence these systems. Herein, we investigate the biophysical properties of cationic liposomes and their role in shaping mRNA lipoplexes by comparing various fabrication methods. Notably, an innovative fabrication technique called the liposome under cryo-assembly (LUCA) cycle, involving a precisely controlled freeze-thaw-vortex process, produces distinctive onion-like concentric multilamellar structures in cationic DOTAP/DOPE liposomes, in contrast to a conventional extrusion method that yields unilamellar liposomes. The inclusion of short-chain DHPC lipids further modulates the structure of cationic liposomes, transforming them from multilamellar to unilamellar structures during the LUCA cycle. Furthermore, the biophysical and biological evaluations of mRNA lipoplexes unveil that the optimal N/P charge ratio in the lipoplex can vary depending on the structure of initial cationic liposomes. Cryo-EM structural analysis demonstrates that multilamellar cationic liposomes induce two distinct interlamellar spacings in cationic lipoplexes, emphasizing the significant impact of the liposome structures on the final structure of mRNA lipoplexes. Taken together, our results provide an intriguing insight into the relationship between lipid assembly structures and the biophysical characteristics of the resulting lipoplexes. These relationships may open the door for advancing lipid-based mRNA delivery systems through more streamlined manufacturing processes.

Unravelling the role of lipid composition on liposome-protein interactions

Upon in vivo administration of nanoparticles, a protein corona forms on their surface and affects their half-life in circulation, biodistribution properties, and stability; in turn, the composition of the protein corona depends on the physico-chemical properties of the nanoparticles. We have previously observed lipid composition-dependent in vitro and in vivo microRNA delivery from lipid nanoparticles. Here, we carried out an extensive physico-chemical characterisation to understand the role of the lipid composition on the in vivo fate of lipid-based nanoparticles. We used a combination of differential scanning calorimetry (DSC), membrane deformability measurements, isothermal titration calorimetry (ITC), and dynamic light scattering (DLS) to probe the interactions between the nanoparticle surface and bovine serum albumin (BSA) as a model protein. The lipid composition influenced membrane deformability, improved lipid intermixing, and affected the formation of lipid domains while BSA binding to the liposome surface was affected by the PEGylated lipid content and the presence of cholesterol. These findings highlight the importance of the lipid composition on the protein-liposome interaction and provide important insights for the design of lipid-based nanoparticles for drug delivery applications.

Alkyl-carbon chain length of two distinct compounds and derivatives are key determinants of their anti-Acanthamoeba activities

The opportunistic pathogen, Acanthamoeba castellanii is the causative agent for the sight threatening infection Acanthamoeba keratitis (AK). It is commonly associated with contact lens wearers, and prevalence is increasing at an alarming rate due to an inadequate preventive strategy to protect the lens from this protist. This problem is compounded by the lack of an effective acanthamoebocide, particularly with cysticidal activity in the contact lens solutions. We have used cytotoxicity assays and a variety of biophysical approaches to show that two molecules with tails made of alkyl carbon, alkylphosphocholines (APCs) and quaternary ammonium compounds (QACs) had significant chain-length dependent efficacy against A. castellanii trophozoites, the latter producing death via permeabilization, and DNA complexing. QACs were more effective than APCs and had activity against cysts. Conversely, the QAC with 12 alkyl carbon chain, was non toxic, its presence increased A. castellanii trophozoites biomass and delayed encystation by 96 h. Interestingly, it was unable to induce excystation and increased trophozoite sensitivity to APC16. These results present a mono- and multi-inhibitor management strategy effective against trophozoites and cysts that may be useful for formulating into contact lense cleaning solutions and reducing AK incidence.

Nano-formulation for topical treatment of precancerous lesions: skin penetration, in vitro, and in vivo toxicological evaluation

With the aim of improving the topical delivery of the antineoplastic drug 5-fluorouracil (5FU), it was loaded into ultradeformable liposomes composed of soy phosphatidylcholine and sodium cholate (UDL-5FU). The liposome populations had a mean size of 70 nm without significant changes in 56 days, and the ultradeformable formulations were up to 324-fold more elastic than conventional liposomes. The interaction between 5FU and the liposomal membrane was studied by three methods, and also release profile was obtained. UDL-5FU did penetrate the stratum corneum of human skin. At in vitro experiments, the formulation was more toxic on a human melanoma-derived than on a human keratinocyte-derived cell line. Cells captured liposomes by metabolically active processes. In vivo toxicity experiments were carried out in zebrafish (Danio rerio) larvae by studying the swimming activity, morphological changes, and alterations in the heart rate after incubation. UDL-5FU was more toxic than free 5FU. Therefore, this nano-formulation could be useful for topical application in deep skin precancerous lesions with advantages over current treatments. This is the first work that assessed the induction of apoptosis, skin penetration in a Saarbrücken penetration model, and the toxicological effects in vivo of an ultradeformable 5FU-loaded formulation.

Effect of saturation in phospholipid/fatty acid monolayers on interaction with amyloid β peptide

The effect of the saturation of fatty acid (FA) in 1,2-dimyristoyl-sn-glycero-3-phosphocoline (DMPC)/FA membrane on the interaction between lipid membrane and amyloid β monomer was investigated by using the Langmuir monolayer technique. The surface pressure (Π)-mean molecular area (A) isotherms and fluorescent measurements reveal that DMPC and octadecanoic acid (stearic acid, SA) molecules were somewhat miscible in the mixed membrane, which was maintained to homogeneous gel phase by enhance of the intermolecular hydrophobic interactions because of the all trans acyl chains. On the other hand, DMPC and 9Z,12Z-octadecadienoic acid (linoleic acid, LA) molecules were considered to be well miscible in the mixed membrane, where the membrane partially transferred from gel phase to liquid-crystalline phase. The Π-A isotherms of the monolayers on amyloid β-peptide (Aβ) solution indicated that Aβ monomers tend to be inserted into the saturated acyl chain region of monolayers at low surface pressure and that the Aβ monomers were then extruded from the monolayer at higher surface pressure. It was observed that behaviors of Aβ monomers at higher surface pressure depended on membrane microstructures. In the DMPC/SA monolayers, Aβ aggregated and then was extruded from monolayers at about 20 mN m^-1 of surface pressure irrespective of the SA proportion. On the other hand, in the DMPC/LA monolayers, Aβ, which favors to interact with DMPC, is dispersed in the monolayer even at high surface pressure because DMPC and LA molecules were well miscible in the monolayer.

Comparison of Physicochemical Membrane Properties of Vesicles Modified with Guanidinium Derivatives

Bilayer vesicles have garnered considerable research attention as molecular vehicles capable of noncovalent interaction with biomolecules via electrostatic and hydrophobic bonds and van der Waals interactions. Guanidinium strongly interacts with phosphate groups. Thus, guanidinium modification of vesicles helps intensify the interaction between lipid membranes and nucleic acids. Here, two kinds of guanidinium derivatives, stearylguanidinium (SG) and myristoylarginine (MA), were synthesized and incorporated into 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphatidylcholine (POPC) vesicles. Differences in their membrane properties were evaluated using Fourier transform infrared spectroscopy, Raman spectroscopy, and the fluorescent probes 1,6-diphenyl-1,3,5-hexatriene (DPH), 6-lauroyl-2-dimethylaminonaphthalene (Laurdan), and 2-p-toluidinylnaphthalene-6-sulfonate (TNS). The increased SG ratio increased overall hydrophobicity and lipid packing density compared to POPC vesicles, and SG-modified vesicles successfully attracted and then denatured negatively charged tRNAs (tRNAs). In contrast, MA-modified vesicles did not affect the stiffness of POPC membranes, wherein no conformational change in tRNAs was observed in the presence of POPC/MA vesicles. Analyses of the pH-dependent fluorescence emission of TNS suggested that SG and MA molecules render the membrane surfaces cationic and anionic, respectively, which was also revealed by zeta potential measurements. Our results enabled the construction of a model of the headgroup orientation of zwitterionic POPC molecules controlled by modification with guanidinium derivatives. The results also indicate the possibility to regulate the interaction and conformation of biological molecules, such as nucleic acid.

Interfacially Engineered Pyridinium Pseudogemini Surfactants as Versatile and Efficient Supramolecular Delivery Systems for DNA, siRNA, and mRNA

This article presents the synthesis, self-assembly, and biological activity as transfection agents for pDNA, siRNA, and mRNA of novel pyridinium pseudogemini surfactants, interfacially engineered from the most efficient gemini surfactants and lipids generated in our amphiphile research program. Formulation of novel amphiphiles in water revealed supramolecular properties very similar to those of gemini surfactants, despite their lipidlike charge/mass ratio. This dual character was found also to enhance endosomal escape and significantly increase the transfection efficiency. We were also successful in identifying the parameters governing the efficient delivery of pDNA, siRNA, and mRNA, drawing valuable structure-activity and structure-property relationships for each nucleic acid type, and establishing DNA/siRNA/mRNA comparisons. Several supramolecular complexes identified in this study proved to be extremely efficient nucleic acid delivery systems, displaying excellent serum stability and tissue penetration in three-dimensional organoids.

Effect of Stearylguanidinium-Modified POPC Vesicles on the Melting Behavior of tRNA Molecules

Lipid membranes interact with biomolecules via noncovalent bonding interactions, wherein the physicochemical membrane properties are key factors in the recognition and rearrangement of biomolecule conformation. In this study, vesicles were prepared using 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) and stearylguanidinium (SG) to improve the affinity between the membrane and tRNA. Membrane fluidity decreased and dehydration of the membrane surface increased with increasing SG levels, suggesting that SG molecules could make the membrane rigid and induce a liquid-ordered (lo)-like phase. The binding constant (Ka) between nucleotide and lipid was evaluated by turbidity analysis; the Ka value for POPC/SG = (86/14) was 2.9 × 10(4) M(-1) but was slightly decreased by vesicles in the lo-like phase. CD spectra of tRNA by the presence of POPC/SG vesicles showed C-G selective base cleavage in tRNA during heat denaturation. POPC/SG = (61/39) and POPC/SG = (40/60) effectively led to C-G base pair cleavage at the melting temperature of tRNA.

Atomic Force Microscopic Analysis of the Effect of Lipid Composition on Liposome Membrane Rigidity

Mechanical rigidity of the liposome membrane is often defined by the membrane bending modulus and is one of the determinants of liposome stability, but the quantitative experimental data are still limited to a few kinds of liposomes. Here, we used atomic force microscopy to investigate the membrane bending moduli of liposomes by immobilizing them on bovine serum albumin-coated glass in aqueous medium. The following lipids were used for liposome preparation: egg yolk phosphatidylcholine, dioleoylphosphatidylcholine, hydrogenated soybean phosphatidylcholine, dipalmitoylphosphatidylcholine, 1,2-dioleoyl-3-trimethylammonium-propane, cholesterol, and N-(carbonylmethoxypoly(ethylene glycol) 2000)-1,2-distearoyl-sn-glycero-3-phosphoethanolamine. By using liposomes of various compositions, we showed that the thermodynamic phase state of the membrane rather than the electric potential or liposome surface modification with poly(ethylene glycol) is the predominant determinant of the bending modulus, which decreased in the following order: solid ordered > liquid ordered > liquid disordered. By using the generalized polarization value of the Laurdan fluorescent probe, we investigated membrane rigidity in terms of membrane fluidity. Atomic force microscopic analysis was superior to the Laurdan method, especially in evaluating the membrane rigidity of liposomes containing hydrogenated soybean phosphatidylcholine and cholesterol. Positively charged liposomes with a large bending modulus were taken up by cells more efficiently than those with a small bending modulus. These findings offer a quantitative method of analyzing the membrane rigidity of nanosized liposomes with different lipid compositions and will contribute to the control of liposome stability and cellular uptake efficiency of liposomal formulations intended for clinical use.

Liposomes modified with cardiolipin can act as a platform to regulate the potential flux of NADP+-dependent isocitrate dehydrogenase

Cardiolipin (CL) is a phospholipid found in the outer mitochondrial membrane (OMM) and inner mitochondrial membrane (IMM) in animal cells. Isocitrate dehydrogenase (ICDH) is an important catalytic enzyme that is localized at the cytosol and mitochondria; the metabolic pathway catalyzed by ICDH differs between the OMM and IMM. To estimate the possible role of lipid membrane in the enzymatic activity of NADP⁺-dependent ICDH, CL-modified liposomes were prepared using CL/1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC)/cholesterol (Ch), and their characteristics were analyzed based on the fluorescent probe method. The relative enzymatic activity of ICDH decreased in the presence of CL/DPPC/Ch=(30/50/20) liposome, whereas activity increased in the presence of CL/DPPC/Ch=(5/75/20) liposome. NADP⁺ had the greatest substrate affinity and was dominant in the regulation of ICDH activity. Analysis of membrane properties indicated that membranes in CL-modified liposomes were dehydrated by ICDH binding. Using circular dichroism analysis, CL/DPPC/Ch=(30/50/20) liposome induced a conformational change in ICDH, indicating that CL-rich membrane domains could inhibit ICDH activity. These results suggest that lipid membranes, including CL molecules, could act as a platform to regulate ICDH-related metabolic pathways such as the tricarboxylic acid cycle and lipid synthesis.

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Phosphatidylcholine liposomes were modified with cardiolipin and characterized.

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DPPC liposomes did not affect the activity of ICDH.

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ICDH activity was enhanced with liposomes at 5 mol% cardiolipin.

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ICDH activity was lowered with liposomes at 30 mol% cardiolipin.

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Liposomes with high content of cardiolipin led to conformational changes of ICDH.

The transfection efficiency of calix[4]arene-based lipids: the role of the alkyl chain length

Calix[4]arene-based lipids with the C6 alkyl chain length exhibited the highest transfection efficiency among all lipoplexes comprising the lipids with different alkyl chain lengths and plasmid DNA.

Optimizing cationic and neutral lipids for efficient gene delivery at high serum content

BACKGROUND

Cationic liposome (CL)-DNA complexes are promising gene delivery vectors with potential application in gene therapy. A key challenge in creating CL-DNA complexes for application is that their transfection efficiency (TE) is adversely affected by serum. In particular, little is known about the effects of a high serum content on TE, even though this may provide design guidelines for application in vivo.

METHODS

We prepared CL-DNA complexes in which we varied the neutral lipid [1,2-dioleoyl-sn-glycerophosphatidylcholine, glycerol-monooleate (GMO), cholesterol], the headgroup charge and chemical structure of the cationic lipid, and the ratio of neutral to cationic lipid; we then measured the TE of these complexes as a function of serum content and assessed their cytotoxicity. We tested selected formulations in two human cancer cell lines (M21/melanoma and PC-3/prostate cancer).

RESULTS

In the absence of serum, all CL-DNA complexes of custom-synthesized multivalent lipids show high TE. Certain combinations of multivalent lipids and neutral lipids, such as MVL5(5+)/GMO-DNA complexes or complexes based on the dendritic-headgroup lipid TMVLG3(8+) exhibited high TE both in the absence and presence of serum. Although their TE still dropped to a small extent in the presence of serum, it reached or surpassed that of benchmark commercial transfection reagents, particularly at a high serum content.

CONCLUSIONS

Two-component vectors (one multivalent cationic lipid and one neutral lipid) can rival or surpass benchmark reagents at low and high serum contents (up to 50%, v/v). We propose guidelines for optimizing the serum resistance of CL-DNA complexes based on a given cationic lipid.

Systematical characterization of phase behaviors and membrane properties of fatty acid/didecyldimethylammonium bromide vesicles

Fatty acids (FAs) are known to form vesicle structures, depending on the surrounding pH conditions. In this study, we prepared vesicles by mixing FAs and a cationic surfactant, and then investigated their physicochemical properties using fluorescence spectroscopy and dielectric dispersion analysis (DDA). The assemblies formed from oleic acid (OA) and linoleic acid (LA) were modified by adding didecyldimethylammonium bromide (DDAB). The phase state of FA/DDAB mixtures was investigated with pH titration curves and turbidity measurements. The trigonal diagram of FA/ionized FA/DDAB was successfully drawn to understand the phase behaviors of FA/DDAB systems. The analysis of fluidities in the interior of the membrane with use of 1,6-diphenyl-1,3,5-hexatriene (DPH) indicated that the membrane fluidities of OA/DDAB and LA/DDAB at pH 8.5 slightly decreased in proportion to the molar ratio of DDAB in FA/DDAB systems. The fluorescent probe 6-lauroyl-2-dimethylamino naphthalene (Laurdan) indicated that the LA vesicle possessed a dehydrated surface, while the OA vesicle surface was hydrated. Modification of LA vesicles with DDAB induced the hydration of membrane surfaces, whereas modification of OA vesicles by DDAB had the opposite effect. DDA analysis indicated that the membrane surfaces were hydrated in the presence of DDAB, suggesting that the surface properties of FA vesicles are tunable by DDAB modification.

Structural dynamics and physicochemical properties of pDNA/DODAB:MO lipoplexes: effect of pH and anionic lipids in inverted non-lamellar phases versus lamellar phases

Dioctadecyldimethylammonium bromide (DODAB):Monoolein (MO) lipoplexes have mainly been studied within the range of high molar ratios of DODAB, with noticeable transfection efficiencies in the Human Embryonic Kidney (HEK, a.k.a. 293T) cell line. In this work, we intend to study the effect of high MO content on the structure and physicochemical properties of pDNA/DODAB:MO lipoplexes to achieve some correlation with their transfection efficiency. Static/Dynamic Light Scattering and Cryo-TEM imaging were used to characterize the size/morphology of DNA/DODAB:MO lipoplexes at different DODAB:MO contents (2:1, 1:1, 1:2) and charge ratios (CRs) (+/-). Nile Red fluorescence emission was performed to detect changes in microviscosity, hydration and polarity of DNA/DODAB:MO systems. Lipoplexes stability at physiological pH values and in the presence of anionic lipids was evaluated by Förster Resonance Energy Transfer (FRET). Physicochemical/structural data were complemented with transfection studies in HEK cells using the β-galactosidase reporter gene activity assay. This work reports the coexistence of multilamellar and non-lamellar inverted phases in MO-richer lipoplexes (DODAB:MO 1:2 and 1:4), leading to transfection efficiencies comparable to those of multilamellar (DODAB-richer) lipoplexes, but at higher charge ratios [CR (+/-)=6.0] and without dose-effect response. These results may be related to the structural changes of lipoplexes promoted by high MO content.

Structure and kinetics of lipid-nucleic acid complexes

The structure and function of lipid-based complexes (lipoplexes) have been widely investigated as cellular delivery vehicles for nucleic acids-DNA and siRNA. Transfection efficiency in applications such as gene therapy and gene silencing has been clearly linked to the local, nano-scale organization of the nucleic acid in the vehicle, as well as to the global properties (e.g. size) of the carriers. This review focuses on both the structure of DNA and siRNA complexes with cationic lipids, and the kinetics of structure evolution during complex formation. The local organization of the lipoplexes is largely set by thermodynamic, equilibrium forces, dominated by the lipid preferred phase. As a result, complexation of linear lambda-phage DNA, circular plasmid DNA, or siRNA with lamellae-favoring lipids (or lipid mixtures) forms multi-lamellar L(α)(C) liquid crystalline arrays. Complexes created with lipids that have bulky tail groups may form inverted hexagonal HII(C) phases, or bicontinuous cubic Q(II)(C) phases. The kinetics of complex formation dominates the large-scale, global structure and the properties of lipoplexes. Furthermore, the time-scales required for the evolution of the equilibrium structure may be much longer than expected. In general, the process may be divided into three distinct stages: An initial binding, or adsorption step, where the nucleic acid binds onto the surface of the cationic vesicles. This step is relatively rapid, occurring on time scales of order of milliseconds, and largely insensitive to system parameters. In the second step, vesicles carrying adsorbed nucleic acid aggregate to form larger complexes. This step is sensitive to the lipid characteristics, in particular the bilayer rigidity and propensity to rupture, and to the lipid to nucleic acid (L/D) charge ratio, and is characterized by time scales of order seconds. The last and final step is that of internal rearrangement, where the overall global structure remains constant while local adjustment of the nucleic acid/lipid organization takes place. This step may occur on unusually long time scales of order hours or longer. This rate, as well, is highly sensitive to lipid characteristics, including membrane fluidity and rigidity. While the three step process is consistent with many experimental observations to date, improving the performance of these non-viral vectors requires better understanding of the correlations between the parameters that influence lipoplexes' formation and stability and the specific rate constants i.e., the timescales required to obtain the equilibrium structures. Moreover, new types of cellular delivery agents are now emerging, such as antimicrobial peptide complexes with anionic lipids, and other proteins and small-molecule lipid carriers, suggesting that better understanding of lipoplex kinetics would apply to a variety of new systems in biotechnology and nanomedicine.

Detection of nanosized ordered domains in DOPC/DPPC and DOPC/Ch binary lipid mixture systems of large unilamellar vesicles using a TEMPO quenching method

Nanosized ordered domains formed in 1,2-dioleoyl-sn-glycero-3-phosphocholine/1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DOPC/DPPC) and DOPC/cholesterol (Ch) liposomes were characterized using a newly developed (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO) quenching method. The membrane fluidity of the DOPC/DPPC liposomes, evaluated by the use of 1,6-diphenyl-1,3,5-hexatriene (DPH), increased significantly above their phase-transition temperature. The fluorescence spectra of 6-lauroyl-2-dimethylamino naphthalene (Laurdan) indicated the formation of an immiscible ordered phase in the DOPC/DPPC (50/50) liposomal membrane at 30 °C. The analysis of the membrane polarity indicated that the surface of the liquid-disordered phase was hydrated whereas that of the ordered phase was dehydrated. DOPC/DPPC and DOPC/Ch (70/30) liposomes exhibited heterogeneous membranes, indicating that nanosized ordered domains formed on the surface of the DOPC/DPPC liposomes. The size of these nanosized ordered domains was estimated using the TEMPO quenching method. Because TEMPO can quench DPH distributed in the disordered phases, the remaining fluorescence from DPH is proportional to the size of the ordered domain. The domain sizes calculated for DOPC/DPPC (50/50), DOPC/DPPC (25/75), DOPC/Ch (70/30), and DOPC/DPPC/Ch (40/40/20) were 13.9, 36.2, 13.2, and 35.5 Å, respectively.

Heterogeneous cationic liposomes modified with 3β-{N-[(N',N'-dimethylamino)ethyl]carbamoyl}cholesterol can induce partial conformational changes in messenger RNA and regulate translation in an Escherichia coli cell-free translation system

The effect of cationic liposomes (CLs) on messenger RNA(mRNA) conformation and translation was studied, focusing on membrane heterogeneity. CLs, composed of 1,2-dioleoyl-sn-glycerol-3-phosphocholine/1,2-dioleoyl-3-timethylammonium propane (DOPC/DOTAP) and DOPC/3β-{N-[(N',N'-dimethylamino)ethyl]carbamoyl}cholesterol (DOPC/DC-Ch), inhibited mRNA translation in an Escherichia coli cell-free translation system. Analysis of the membrane fluidity and polarity indicated a heterogeneous DOPC/DC-Ch (70/30) membrane, while other CLs exhibited homogeneous disordered membranes. mRNA adsorbed onto DOPC/DC-Ch liposomes showed translational activity, while DOPC/DOTAP liposomes inhibited mRNA translation in proportion to its adsorption onto membranes. Dehydration of DOPC/DOTAP (70/30) and DOPC/DC-Ch (70/30) was observed in the presence of mRNA but not in the case of zwitterionic DOPC liposomes, indicating that mRNA binds in regions between the phosphate [-PO(2)(-)-] and carbonyl [-C=O-] moieties of lipids. UV resonance Raman spectroscopy suggests that adenine, cytosine, and guanine interact with DOPC/DOTAP (70/30) and DOPC/DC-Ch (70/30) but not with DOPC. Circular dichroism indicates that DOPC/DOTAP (70/30) extensively denatured the mRNA. In contrast, heterogeneous DOPC/DC-Ch (70/30) induced partial conformational changes but maintained the translational activity of mRNA.

The role of the helper lipid dioleoylphosphatidylethanolamine (DOPE) for DNA transfection cooperating with a cationic lipid bearing ethylenediamine

Gene therapy is expected to treat various incurable diseases including viral infections, autoimmune disorders, and cancers. Cationic lipids (CL) have been used as carriers of therapeutic DNAs for gene therapy because they can form a complex with DNA and such a complex can be incorporated into cells and transport the bound DNA to cytosol. The CL/DNA complexes are called lipoplexes and categorized as a non-viral vector. Lipoplexes are often prepared by adding a neutral phospholipid dioleoylphosphatidylethanolamine (DOPE) to CL in order to enhance transfection. However, the role of DOPE is not fully understood. We synthesized a new CL having an ethylenediamine cationic head group, denoted by DA, and found that addition of DOPE to DA achieved a good efficiency, almost in the similar level of commonly used transfection reagent Lipofectamine 2000 (Invitrogen). The composition of DA:DOPE=1:1 showed the highest efficiency. This lipoplex showed structural transition when pH was changed from 7 to 4, corresponding pH lowering in late endosome, while DOPE itself showed structural transition at more basic pH around 8. The present data showed that the DOPE/DA composition determines the structural transition pH and choosing a suitable pH, i.e., a suitable composition, is essential to increase the transfection efficiency.

Factors affecting DNA binding and stability of association to cationic liposomes

Lipoplexes are complexes formed between cationic liposomes (L(+)) and polyanionic nucleic acids (P(-)). They are commonly used in vitro and in vivo as a nucleic acid delivery system. Our study aims are to investigate how DOTAP-based cationic liposomes, which vary in their helper lipid (cholesterol or DOPE) and in media of different ionic strengths affect the degree, mode of association and degree of condensation of pDNA. This was determined by ultracentrifugation and gel electrophoresis, methods based on different physical principles. In addition, the degree of pDNA condensation was also determined using the ethidium bromide (EtBr) intercalation assay. The results suggest that for cationic lipid compositions (DOTAP/DOPE and DOTAP/cholesterol), 1.5 M NaCl, but not 0.15 M NaCl, both prevent lipoplex formation and/or induce partial dissociation between lipid and DNA of preformed lipoplexes. The higher the salt concentration the greater is the similarity of DNA condensation (monitored by EtBr intercalation) between lipoplex DNA and free DNA. As determined by ultracentrifugation and agarose gel electrophoresis, 30-90% of the DNA is uncondensed. SDS below its critical micellar concentration (CMC) induced "de-condensation" of DNA without its physical release (assessed by ultracentrifugation) for both DOTAP/DOPE and DOTAP/cholesterol lipoplexes. As was assessed by agarose gel electrophoresis SDS induced release of 50-60% of DNA from the DOTAP/cholesterol lipoplex but not from the DOTAP/DOPE lipoplex. This study shows that there are conditions under which DNA is still physically associated with the cationic lipids but undergoes unwinding to become less condensed. We also proved that the helper lipid affects level and strength of the L(+) and DNA(-) electrostatic association; these interactions are weaker for DOTAP/cholesterol than for DOTAP/DOPE, despite the fact that the positive charge and surface pH of DOTAP/cholesterol and DOTAP/DOPE are similar.

ParAB-mediated intermolecular association of plasmid P1 parS sites

The P1 plasmid partition system depends on ParA-ParB proteins acting on centromere-like parS sites for a faithful plasmid segregation during the Escherichia coli cell cycle. In vivo we placed parS into host E. coli chromosome and on a Sop(+) F plasmid and found that the stability of a P1 plasmid deleted for parA-parB could be partially restored when parB was expressed in trans. In vitro, parS, conjugated to magnetic beads could capture free parS DNA fragment in presence of ParB. In vitro, ParA stimulated ParB-mediated association of intermolecular parS sites in an ATP-dependent manner. However, in the presence of ADP, ParA reduced ParB-mediated pairing to levels below that seen by ParB alone. ParB of P1 pairs the parS sites of plasmids in vivo and fragments in vitro. Our findings support a model whereby ParB complexes P1 plasmids, ParA-ATP stimulates this interaction and ParA-ADP inhibits ParB pairing activity in a parS-independent manner.

Nucleic acid-lipid membrane interactions studied by DSC

The interactions of nucleic acids with lipid membranes are of great importance for biological mechanisms as well as for biotechnological applications in gene delivery and drug carriers. The optimization of liposomal vectors for clinical use is absolutely dependent upon the formation mechanisms, the morphology, and the molecular organization of the lipoplexes, that is, the complexes of lipid membranes with DNA. Differential scanning calorimetry (DSC) has emerged as an efficient and relatively easy-to-operate experimental technique that can straightforwardly provide data related to the thermodynamics and the kinetics of the DNA-lipid complexation and especially to the lipid organization and phase transitions within the membrane. In this review, we summarize DSC studies considering nucleic acid-membrane systems, accentuating DSC capabilities, and data analysis. Published work involving cationic, anionic, and zwitterionic lipids as well as lipid mixtures interacting with RNA and DNA of different sizes and conformations are included. It is shown that despite limitations, issues such as DNA- or RNA-induced phase separation and microdomain lipid segregation, liposomal aggregation and fusion, alterations of the lipid long-range molecular order, as well as membrane-induced structural changes of the nucleic acids can be efficiently treated by systematic high-sensitivity DSC studies.

Cationic lipids: molecular structure/ transfection activity relationships and interactions with biomembranes

Abstract Synthetic cationic lipids, which form complexes (lipoplexes) with polyanionic DNA, are presently the most widely used constituents of nonviral gene carriers. A large number of cationic amphiphiles have been synthesized and tested in transfection studies. However, due to the complexity of the transfection pathway, no general schemes have emerged for correlating the cationic lipid chemistry with their transfection efficacy and the approaches for optimizing their molecular structures are still largely empirical. Here we summarize data on the relationships between transfection activity and cationic lipid molecular structure and demonstrate that the transfection activity depends in a systematic way on the lipid hydrocarbon chain structure. A number of examples, including a large series of cationic phosphatidylcholine derivatives, show that optimum transfection is displayed by lipids with chain length of approximately 14 carbon atoms and that the transfection efficiency strongly increases with increase of chain unsaturation, specifically upon replacement of saturated with monounsaturated chains.

Surface properties of lipoplexes modified with mannosylerythritol lipid-a and tween 80 and their cellular association

The surface properties of cationic liposomes and lipoplexes largely determine the cellular association and gene transfection efficiency. In this study, we measured the surface properties, such as zeta potentials, surface pH and hydration levels of MHAPC- and OH-Chol-lipoplexes and their cellular association, without and with the modification of biosurfactant mannosylerythritol lipid-A (MEL-A) or Tween 80 (MHAPC=N,N-methyl hydroxyethyl aminopropane carbamoyl cholesterol; OH-Chol=cholesteryl-3beta-carboxyamindoethylene-N-hydroxyethylamine). Compared to OH-Chol-lipoplexes, the higher cellular association of MHAPC-lipoplexes correlated with the significantly higher zeta potentials, lower surface pH levels and "drier" surface, as evaluated by the generalized polarization of laurdan. Both MEL-A and Tween 80 modification of MHAPC-lipoplexes did not significantly change zeta potentials and surface pH levels, while MEL-A modification of OH-Chol-lipoplexes seriously decreased them. MEL-A hydrated the liposomal surface of MHAPC-lipoplexes but dehydrated that of OH-Chol-lipoplexes, while Tween 80 hydrated those of MHAPC- and OH-Chol-lipoplexes. In all, cationic liposomes composed of lipids with secondary and tertiary amine exhibited different surface properties and cellular associations of lipoplexes, and modification with surfactants further enlarged their difference. The strong hydration ability of Tween 80 may relate to the low cellular association of lipoplexes, while the dehydration of MEL-A-modified OH-Chol-lipoplexes seemed to compensate the negative zeta potential for the cellular association of lipoplexes.

Effect of temperature on the reentrant condensation in polyelectrolyte-liposome complexation

Interactions of oppositely charged macroions in aqueous solution give rise to intriguing aggregation phenomena, resulting in finite-size, long-lived clusters, characterized by a quite narrow size distribution. Particularly, the adsorption of highly charged linear polyelectrolytes on oppositely charged colloidal particles is strongly correlated and some short-range order arises from competing electrostatic interactions between like-charged polymer chains (repulsion) and between polymer chains and particle surface (attraction). In these systems, in an interval of concentrations around the isoelectric point, relatively large clusters of polyelectrolyte-decorated particles form. However, the mechanisms that drive the aggregation and stabilize, at the different polymer/particle ratios, a well-defined size of the aggregates are not completely understood. Nor is clear the role that the correlated polyion adsorption plays in the aggregation, although the importance of "patchy interactions" has been stressed as the possible source of attractive interaction term between colloidal particles. Different models have been proposed to explain the formation of the observed cluster phase. However, a central question still remains unanswered, i.e., whether the clusters are true equilibrium or metastable aggregates. To elucidate this point, in this work, we have investigated the effect of the temperature on the cluster formation. We employed liposomes built up by DOTAP lipids interacting with a simple anionic polyion, polyacrylate sodium salt, over an extended concentration range below and above the isoelectric condition. Our results show that the aggregation process can be described by a thermally activated mechanism.

Effect of ionic strength and presence of serum on lipoplexes structure monitorized by FRET

Background

Serum and high ionic strength solutions constitute important barriers to cationic lipid-mediated intravenous gene transfer. Preparation or incubation of lipoplexes in these media results in alteration of their biophysical properties, generally leading to a decrease in transfection efficiency. Accurate quantification of these changes is of paramount importance for the success of lipoplex-mediated gene transfer in vivo.

Results

In this work, a novel time-resolved fluorescence resonance energy transfer (FRET) methodology was used to monitor lipoplex structural changes in the presence of phosphate-buffered saline solution (PBS) and fetal bovine serum. 1,2-dioleoyl-3-trimethylammonium-propane (DOTAP)/pDNA lipoplexes, prepared in high and low ionic strength solutions, are compared in terms of complexation efficiency. Lipoplexes prepared in PBS show lower complexation efficiencies when compared to lipoplexes prepared in low ionic strength buffer followed by addition of PBS. Moreover, when serum is added to the referred formulation no significant effect on the complexation efficiency was observed. In physiological saline solutions and serum, a multilamellar arrangement of the lipoplexes is maintained, with reduced spacing distances between the FRET probes, relative to those in low ionic strength medium.

Conclusion

The time-resolved FRET methodology described in this work allowed us to monitor stability and characterize quantitatively the structural changes (variations in interchromophore spacing distances and complexation efficiencies) undergone by DOTAP/DNA complexes in high ionic strength solutions and in presence of serum, as well as to determine the minimum amount of potentially cytotoxic cationic lipid necessary for complete coverage of DNA. This constitutes essential information regarding thoughtful design of future in vivo applications.

Fluorescence studies of the interactions of ubiquinol-10 with liposomes

Ubiquinone-10 plays a central role in energy production and its reduced form, ubiquinol-10 is also capable of acting as a potent radical scavenging antioxidant against membrane lipid peroxidation. Efficiency of this protection depends mostly on its localization in lipid bilayer. The intrinsic fluorescence of ubiquinol-10 and of the exogenous probe, Laurdan, has been used to determine the location of ubiquinol-10 in unilamellar liposomes of egg phosphatidylcholine (EggPC) and dimyristoyl phosphatidylcholine. Laurdan fluorescence moiety is positioned at the hydrophilic-hydrophobic interface of the phospholipid bilayer and its parameters reflect the membrane polarity and microheterogeneity, which we have used to explore the coexistence of microdomains with distinct physical properties. In liquid-crystalline bilayers ubiquinol has a short fluorescence lifetime (0.4 ns) and a high steady-state anisotropy. In a concentration-dependent manner, ubiquinol-10 influences the Laurdan excitation, emission and generalized polarization measurements. In EggPC liposomes ubiquinol-10 induces a decrease in membrane water mobility near the probe, while in dimyristoyl liposomes a decrease in the membrane water content was found. Moreover the presence of ubiquinol results in the formation of coexisting phospholipid domains of gel and liquid-crystalline phases. The results indicate that ubiquinol-10 molecules are mainly located at the polar-lipid interface, inducing changes in the physico-chemical properties of the bilayer microenvironment.

Properties of Mixed DOTAP−DPPC Bilayer Membranes as Reported by Differential Scanning Calorimetry and Dynamic Light Scattering Measurements

We have investigated the effect of a cationic lipid [DOTAP] on both the thermotropic phase behavior and the structural organization of aqueous dispersions of dipalmitoyl-phosphatidylcholine [DPPC] by means of high-sensitivity differential scanning calorimetry and dynamic light scattering measurements. We find that the incorporation of increasing quantities of DOTAP progressively reduces the temperature and the enthalpy of the gel-to-liquid crystalline transition. We are further showing that, in mixed DOTAP-DPPC systems, the reduction of the phase transition temperature is accompanied by a reduction of the average size of the structures present in the aqueous mixtures, whatever the DOTAP concentration is. These results, which extend a previous investigation by Campbell et al. (Campbell, R. B.; Balasubramanian, S. V.; Straubinger, R. M.; Biochim. Biosphys. Acta 2001, 27, 1512.) limited to a DOTAP concentration below 20 mol %, confirm that the insertion of cationic head groups in zwitterionic phosphatidylcholine bilayers facilitates the formation of stable, relatively small, unilamellar vesicles. This self-assembling restructuring from an aqueous multilamellar structure toward a liposomal phase is favored by decreasing the phospholipid phase transition temperature and by increasing the temperature of the system. This reduction of the average size and the appearance of a stable liposomal phase is also promoted by a heating and cooling thermal treatment.

Liposome complexation efficiency monitored by FRET: effect of charge ratio, helper lipid and plasmid size

Cationic lipid/DNA complexes (lipoplexes) are promising vehicles for DNA vaccines or gene therapy. In these systems, transfection efficiency is highly related to lipoplex charge ratio, since lipoplexes with charge ratios (+/-) lower than electroneutrality have most DNA uncovered by the liposomes, and thus are unprotected from enzyme degradation. However, a large excess of cationic lipids is undesirable because of eventual cytotoxicity. The aim of this work was to determine the minimum charge ratio from which all DNA molecules are complexed by the liposomes varying the lipid formulation and plasmid size, using a new FRET (fluorescence resonance energy transfer) methodology. The similarity of FRET results, fluorescence intensity data and fluorescence decays of several charge ratios above (+/-) > or = 4 or 5 confirmed that once all DNA is covered by the liposomes, additional lipid molecules do not affect the lipoplex multilamellar repeat distance. It was also verified by FRET that the presence of helper lipid reduces the amount of cationic lipid required for DNA protection but does not affect the lipoplex multilamellar repeat distance. This distance varies with the plasmid size when supercoiled plasmid is used, being apparently larger when longer plasmids are used. Our study indicates that, despite the complexity of these systems not being totally described by our model, FRET is an informative technique in lipoplex characterization.

Novel O-palmitoylscleroglucan-coated liposomes as drug carriers: Development, characterization and interaction with leuprolide

Polysaccharide-coated liposomes have been studied for their potential use for peptide drug delivery by the oral route because they are able to minimize the disruptive influences on peptide drugs of gastrointestinal fluids. The aim of this work was to synthesize and characterize a modified polysaccharide, O-palmitoylscleroglucan (PSCG), and to coat unilamellar liposomes for oral delivery of peptide drugs. To better evaluate the coating efficiency of PSCG, also scleroglucan (SCG)-coated liposomes were prepared. We studied the surface modification of liposomes and the SCG- and PSCG-coated liposomes were characterized in terms of size, shape, zeta potential, influence of polymer coating on bilayer fluidity, stability in serum, in simulated gastric and intestinal fluids and against sodium cholate and pancreatin. Leuprolide, a synthetic superpotent agonist of luteinizing hormone releasing hormone (LHRH) receptor, was chosen as a model peptide drug. After polymer coating the vesicle dimensions increased and the zeta potential shifted to less negative values. These results indicate that both SCG- and PSCG-coated liposomes surface and DSC results showed that PSCG was anchored on the liposomal surface. The stability of coated-liposomes in SGF, sodium cholate solution and pancreatin solution was increased. From this preliminary in vitro studies, it seems that PSCG-coated liposomes could be considered as a potential carrier for oral administration.

Gene delivery by cationic lipid vectors: overcoming cellular barriers

Non-viral vectors such as cationic lipids are capable of delivering nucleic acids, including genes, siRNA or antisense RNA into cells, thus potentially resulting in their functional expression. These vectors are considered as an attractive alternative for virus-based delivery systems, which may suffer from immunological and mutational hazards. However, the efficiency of cationic-mediated gene delivery, although often sufficient for cell biological purposes, runs seriously short from a therapeutics point of view, as realizing this objective requires a higher level of transfection than attained thus far. To develop strategies for improvement, there is not so much a need for novel delivery systems. Rather, better insight is needed into the mechanism of delivery, including lipoplex-cell surface interaction, route of internalization and concomitant escape of DNA/RNA into the cytosol, and transport into the nucleus. Current work indicates that a major obstacle involves the relative inefficient destabilization of membrane-bounded compartments in which lipoplexes reside after their internalization by the cell. Such an activity requires the capacity of lipoplexes of undergoing polymorphic transitions such as a membrane destabilizing hexagonal phase, while cellular components may aid in this process. A consequence of the latter notion is that for development of a novel generation of delivery devices, entry pathways have to be triggered by specific targeting to select delivery into intracellular compartments which are most susceptible to lipoplex-induced destabilization, thereby allowing the most efficient release of DNA, a minimal requirement for optimizing non-viral vector-mediated transfection.

Role of anionic phospholipids in the adaptation of Bacillus subtilis to high salinity

The importance of the content of anionic phospholipids [cardiolipin (CL) and phosphatidylglycerol (PG)] in the osmotic adaptation and in the membrane structure of Bacillus subtilis cultures was investigated. Insertion mutations in the three putative cardiolipin synthase genes (ywiE, ywnE and ywjE) were obtained. Only the ywnE mutation resulted in a complete deficiency in cardiolipin and thus corresponds to a true clsA gene. The osmotolerance of a clsA mutant was impaired: although at NaCl concentrations lower than 1.2 M the growth curves were similar to those of its wild-type control, at 1.5 M NaCl (LBN medium) the lag period increased and the maximal optical density reached was lower. The membrane of the clsA mutant strain showed an increased PG content, at both exponential and stationary phase, but no trace of CL in either LB or LBN medium. As well as the deficiency in CL synthesis, the clsA mutant showed other differences in lipid and fatty acids content compared to the wild-type, suggesting a cross-regulation in membrane lipid pathways, crucial for the maintenance of membrane functionality and integrity. The biophysical characteristics of membranes and large unilamellar vesicles from the wild-type and clsA mutant strains were studied by Laurdan's steady-state fluorescence spectroscopy. At physiological temperature, the clsA mutant showed a decreased lateral lipid packing in the protein-free vesicles and isolated membranes compared with the wild-type strain. Interestingly, the lateral lipid packing of the membranes of both the wild-type and clsA mutant strains increased when they were grown in LBN. In a conditional IPTG-controlled pgsA mutant, unable to synthesize PG and CL in the absence of IPTG, the osmoresistance of the cultures correlated with their content of anionic phospholipids. The transcriptional activity of the clsA and pgsA genes was similar and increased twofold upon entry to stationary phase or under osmotic upshift. Overall, these results support the involvement of the anionic phospholipids in the growth of B. subtilis in media containing elevated NaCl concentrations.

Domain Formation in DODAB–Cholesterol Mixed Systems Monitored via Nile Red Anisotropy

The effect of the cholesterol (Ch) on liposomes composed of the cationic lipid dioctadecyldimethylammonium bromide (DODAB) was assessed by studying both the steady-state and time-resolved fluorescence anisotropy of the dye Nile Red. The information obtained combined with analysis of the steady-state emission and fluorescence lifetime of Nile Red (NR) for different cholesterol concentrations (5-50%) elucidated the presence of "condensed complexes" and cholesterol-rich domains in these mixed systems. The steady-state fluorescence spectra were decomposed into the sum of two lognormal emissions, emanating from two different states, and the effect of temperature on the anisotropy decay of Nile Red for different cholesterol concentrations was observed. At room temperature, the time-resolved anisotropy decays are indicative of NR being relatively immobile (manifest by a high r (infinity) value). At higher temperature, rotational times ca. 1 ns were obtained throughout and a trend in increasing hindrance was seen with increase of Ch content.

On the importance of anandamide structural features for its interactions with DPPC bilayers: effects on PLA2 activity

The acylethanolamide anandamide (AEA) occurs in a variety of mammalian tissues and, as a result of its action on cannabinoid receptors, exhibits several cannabimimetic activities. Moreover, some of its effects are mediated through interaction with an ion channel-type vanilloid receptor. However, the chemical features of AEA suggest that some of its biological effects could be related to physical interactions with the lipidic part of the membrane. The present work studies the effect of AEA-induced structural modifications of the dipalmitoylphosphatidylcholine (DPPC) bilayer on phospholipase A2 (PLA2) activity, which is strictly dependent on lipid bilayer features. This study, performed by 2-dimethylamino-(6-lauroyl)-naphthalene fluorescence, demonstrates that the effect of AEA on PLA2 activity is concentration-dependent. In fact, at low AEA/DPPC molar ratios (from R = 0.001 to R = 0.04), there is an increase of the enzymatic activity, which is completely inhibited for R = 0.1. X-ray diffraction data indicate that the AEA affects DPPC membrane structural properties in a concentration-dependent manner. Because the biphasic effect of increasing AEA concentrations on PLA2 activity is related to the induced modifications of membrane bilayer structural properties, we suggest that AEA-phospholipid interactions may be important to produce, at least in part, some of the similarly biphasic responses of some physiological activities to increasing concentrations of AEA.

Effect of “helper lipid” on lipoplex electrostatics

Lipoplexes, which are complexes between cationic liposomes (L+) and nucleic acids, are commonly used as a nucleic acid delivery system in vitro and in vivo. This study aimed to better characterize cationic liposome and lipoplex electrostatics, which seems to play a major role in the formation and the performance of lipoplexes in vitro and in vivo. We characterized lipoplexes based on two commonly used monocationic lipids, DOTAP and DMRIE, and one polycationic lipid, DOSPA--each with and without helper lipid (cholesterol or DOPE). Electrical surface potential (Psi0) and surface pH were determined using several surface pH-sensitive fluorophores attached either to a one-chain lipid (4-heptadecyl hydroxycoumarin (C17HC)) or to the primary amino group of the two-chain lipids (1,2-dioleyl-sn-glycero-3-phosphoethanolamine-N-carboxyfluorescein (CFPE) and 1,2-dioleyl-sn-glycero-3-phosphoethanolamine-N-7-hydroxycoumarin) (HC-DOPE). Zeta potentials of the DOTAP-based cationic liposomes and lipoplexes were compared with Psi0 determined using C17HC. The location and relatively low sensitivity of fluorescein to pH changes explains why CFPE is the least efficient in quantifying the differences between the various cationic liposomes and lipoplexes used in this study. The fact that, for all cationic liposomes studied, those containing DOPE as helper lipid have the least positive Psi0 indicates neutralization of the cationic charge by the negatively-charged phosphodiester of the DOPE. Zeta potential is much less positively charged than Psi0 determined by C17HC. The electrostatics affects size changes that occurred to the cationic liposomes upon lipoplex formation. The largest size increase (based on static light scattering measurements) for all formulations occurred at DNA-/L+ charge ratios 0.5-1. Comparing the use of the one-chain C17HC and the two-chain HC-DOPE for monitoring lipoplex electrostatics reveals that both are suitable, as long as there is no serum (or other lipidic assemblies) present in the medium; in the latter case, only the two-chain HC-DOPE gives reliable results. Increasing NaCl concentrations decrease surface potential. Neutralization by DNA is reduced in a NaCl-concentration-dependent manner.