Entrapment of nucleic acids in liposomes

A convenient method for the relative and absolute quantification of lipid components in liposomes by 1H- and 31P NMR-spectroscopy

OBJECTIVE

Liposomes are promising delivery systems for pharmaceutical applications and have been used in medicine in the recent past. Preparation of liposomes requires reliable characterization and quantification of the phospholipid components for which the traditional cumbersome molybdate method is used frequently. The objective was to improve relative and absolute quantification of lipid components from liposomes.

METHODS

A reliable method for quantification of lipid composition in liposome formulations in the 1-10 μmol range with 1H- and 31P NMR spectroscopy at 600 MHz has been developed. The method is based on three crystalline small-molecule standards (Ph3PO4, (Tol)3PO4, and Ph3PO) in CDCl3.

RESULTS

Excellent calibration linearity and chemical stability of the standards was observed. The method was tested in blind fashion on liposomes containing POPC, PEG-ceramide and a pH-sensitive trans-aminocyclohexanol-based amphiphile (TACH).1 Relative quantification (percentage of components) as well as determination of absolute lipid amount was possible with excellent reproducibility with an average error of 5%. Quantification (triplicate) was accomplished in 15 min based on 1H NMR and in 1 h based on 31P NMR. Very little change in mixture composition was observed over multiple preparative steps.

CONCLUSION

Liposome preparations containing POPC, POPE, DOPC, DPPC, TACH, and PEG-ceramide can be reliably characterized and quantified by 1H NMR and 31P NMR spectroscopy at 600 MHz in the μmol range.

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.

Treatment of Parkinson's disease with biologics that penetrate the blood-brain barrier via receptor-mediated transport

Parkinson's disease (PD) is characterized by neurodegeneration of nigral-striatal neurons in parallel with the formation of intra-neuronal α-synuclein aggregates, and these processes are exacerbated by neuro-inflammation. All 3 components of PD pathology are potentially treatable with biologics. Neurotrophins, such as glial derived neurotrophic factor or erythropoietin, can promote neural repair. Therapeutic antibodies can lead to disaggregation of α-synuclein neuronal inclusions. Decoy receptors can block the activity of pro-inflammatory cytokines in brain. However, these biologic drugs do not cross the blood-brain barrier (BBB). Biologics can be made transportable through the BBB following the re-engineering of the biologic as an IgG fusion protein, where the IgG domain targets an endogenous receptor-mediated transcytosis (RMT) system within the BBB, such as the insulin receptor or transferrin receptor. The receptor-specific antibody domain of the fusion protein acts as a molecular Trojan horse to ferry the biologic into brain via the BBB RMT pathway. This review describes the re-engineering of all 3 classes of biologics (neurotrophins, decoy receptor, therapeutic antibodies) for BBB delivery and treatment of PD. Targeting the RMT pathway at the BBB also enables non-viral gene therapy of PD using lipid nanoparticles (LNP) encapsulated with plasmid DNA encoding therapeutic genes. The surface of the lipid nanoparticle is conjugated with a receptor-specific IgG that triggers RMT of the LNP across the BBB in vivo.

Liposomes in Cancer Therapy: How Did We Start and Where Are We Now

Since their first discovery in the 1960s by Alec Bangham, liposomes have been shown to be effective drug delivery systems for treating various cancers. Several liposome-based formulations received approval by the U.S. Food and Drug Administration (FDA) and European Medicines Agency (EMA), with many others in clinical trials. Liposomes have several advantages, including improved pharmacokinetic properties of the encapsulated drug, reduced systemic toxicity, extended circulation time, and targeted disposition in tumor sites due to the enhanced permeability and retention (EPR) mechanism. However, it is worth noting that despite their efficacy in treating various cancers, liposomes still have some potential toxicity and lack specific targeting and disposition. This explains, in part, why their translation into the clinic has progressed only incrementally, which poses the need for more research to focus on addressing such translational limitations. This review summarizes the main properties of liposomes, their current status in cancer therapy, and their limitations and challenges to achieving maximal therapeutic efficacy.

Brain gene therapy with Trojan horse lipid nanoparticles

The COVID-19 mRNA vaccine was developed by the scalable manufacture of lipid nanoparticles (LNPs) that encapsulate mRNA within the lipid. There are many potential applications for this large nucleic acid delivery technology, including the delivery of plasmid DNA for gene therapy. However, gene therapy for the brain requires LNP delivery across the blood-brain barrier (BBB). It is proposed that LNPs could be reformulated for brain delivery by conjugation of receptor-specific monoclonal antibodies (MAbs) to the LNP surface. The MAb acts as a molecular Trojan horse to trigger receptor-mediated transcytosis (RMT) of the LNP across the BBB and subsequent localization to the nucleus for transcription of the therapeutic gene. Trojan horse LNPs could enable new approaches to gene therapy of the brain.

Preparation and Physical Characterization of DNA Binding Cationic Liposomes

Cationic liposomes are routinely employed as one of the major nonviral transfecting agents for intracellular delivery of hydrophilic molecules such as nucleic acids, peptides, and proteins. Cationic liposomes when complexed with DNA form a strong positively charged cationic liposome-DNA complex or lipoplex. The chapter discusses, primarily, the major preparation technique for cationic liposomes and its physical characterization, with a focus on SYBR Green I dye exclusion assay and DNA encapsulation enhancement by freeze-thaw technique. SYBR Green I dye exclusion assay is a technique to determine the total amount of liposomal lipids required to bind a unit weight of DNA, which is critical for transfection experiments. Freeze-thaw technique on the other hand is one of the major techniques to improve DNA encapsulation efficiency in liposomes.

Primitive Compartmentalization for the Sustainable Replication of Genetic Molecules

Sustainable replication and evolution of genetic molecules such as RNA are likely requisites for the emergence of life; however, these processes are easily affected by the appearance of parasitic molecules that replicate by relying on the function of other molecules, while not contributing to their replication. A possible mechanism to repress parasite amplification is compartmentalization that segregates parasitic molecules and limits their access to functional genetic molecules. Although extent cells encapsulate genomes within lipid-based membranes, more primitive materials or simple geological processes could have provided compartmentalization on early Earth. In this review, we summarize the current understanding of the types and roles of primitive compartmentalization regarding sustainable replication of genetic molecules, especially from the perspective of the prevention of parasite replication. In addition, we also describe the ability of several environments to selectively accumulate longer genetic molecules, which could also have helped select functional genetic molecules rather than fast-replicating short parasitic molecules.

A Brief Review of Edible Coating Materials for the Microencapsulation of Probiotics

The consumption of probiotics has been associated with a wide range of health benefits for consumers. Products containing probiotics need to have effective delivery of the microorganisms for their consumption to translate into benefits to the consumer. In the last few years, the microencapsulation of probiotic microorganisms has gained interest as a method to improve the delivery of probiotics in the host as well as extending the shelf life of probiotic-containing products. The microencapsulation of probiotics presents several aspects to be considered, such as the type of probiotic microorganisms, the methods of encapsulation, and the coating materials. The aim of this review is to present an updated overview of the most recent and common coating materials used for the microencapsulation of probiotics, as well as the involved techniques and the results of research studies, providing a useful knowledge basis to identify challenges, opportunities, and future trends around coating materials involved in the probiotic microencapsulation.

Herbonanoceuticals: A Novel Beginning in Drug Discovery and Therapeutics

The Indian pharmaceutical industry is the world’s second largest industry (by volume) that develops products and market drugs licensed for use as medications. Medicines manufactured in the modern era are associated with major controversies such as non–target specificity, resistance, repeated administration, immune rejection, and other adverse effects on the body. Thus, there is a great need to find drugs that do not raise the aforementioned issues. Nature is an excellent hub providing a diverse range of phytoconstituents that open the way to phototherapeutics, which need a scientific path to deliver the active elements in a supported way to increase patient compliance and reduce the need for repeated administration. To discover a novel phytochemical as a lead compound for a therapeutic purpose is a real challenge. In former times, drug discovery was a complex process, as it took several years to find a lead compound for use against a particular disease. Nowadays, however, virtual screening methods have been developed, which are target specific, time consuming, and cost effective. To avoid increased and repeated administration of a drug, nanosized drug delivery systems for herbal drugs have been developed to enhance the activity and overcome problems associated with synthetic medicines. This review summarizes three main fields: drug discovery, docking for drug design, and last—but not least—drug delivery systems. Nowadays, nanobased drug delivery systems are in demand for delivery of herbal medicines used for therapeutic purposes. Herbonanoceuticals—herbal drugs of a nanosize—have better remedial value and fewer detrimental effects than modern medicines. Therefore, herbonanoceuticals can be a boon in the field of therapeutics.

Preparation and Physical Characterization of DNA-Binding Cationic Liposomes

DNA-binding cationic liposomes are routinely employed as one of the major non-viral transfecting agents delivering DNA and other genes inside the cells. Cationic liposomes when complexed with DNA form a strong positively charged liposome-DNA complex or lipoplex. The chapter discusses primarily the major preparation technique for cationic liposomes and its physical characterization, with a focus on SYBR Green-I dye exclusion assay and DNA encapsulation enhancement by freeze-thaw technique. SYBR Green-I dye exclusion assay is a technique to determine the total amount of liposomal lipids required to bind a unit weight of DNA, which is critical for transfection experiments. Freeze-thaw technique on the other hand is one of the major techniques to improve DNA encapsulation in cationic liposomes.

Fliposomes: trans-2-aminocyclohexanol-based amphiphiles as pH-sensitive conformational switches of liposome membrane - a structure-activity relationship study

Recently developed lipids with the trans-2-aminocyclohexanol (TACH) moiety represent unique pH-sensitive conformational switches ("flipids") that can trigger the membrane of liposome-based drug delivery systems at lowered pH as seen in many pathological scenarios. A library of flipids with various TACH-based headgroups and hydrocarbon tails were designed, prepared, and characterized to systematically elucidate the relationship between their chemical structures and their ability to form and to trigger liposomes. Liposomes (fliposomes) consisting of a flipid, POPC and PEG-ceramide were stable at 4°C, pH 7.4 for up to several months and yet released the encapsulated fluorophore in seconds upon acidification. The colloidal properties and encapsulation efficiencies of the fliposomes depended on the structure features of the flipids such as the polarity of the headgroups and the shape and fluidity of the lipid tails. The pH-triggered release also depended on the flipid structure, where shorter linear tails yielded more efficient release. The release of fliposomes was enhanced at different narrow pH ranges, depending on the basicity of the flipid headgroup, which can be estimated either by calculated pKa or by acid/base titration of the flipids while its conformation is monitored by ¹H NMR. The structure-activity relationship of the flipids supports "lipid tail conformational shortening" as the mechanism to disrupt lipid membranes and would provide great flexibility in the design of pH-sensitive drug delivery systems.

Adenosine Triphosphate-Encapsulated Liposomes with Plasmonic Nanoparticles for Surface Enhanced Raman Scattering-Based Immunoassays

In this study, we prepared adenosine triphosphate (ATP) encapsulated liposomes, and assessed their applicability for the surface enhanced Raman scattering (SERS)-based assays with gold-silver alloy (Au@Ag)-assembled silica nanoparticles (NPs; SiO₂@Au@Ag). The liposomes were prepared by the thin film hydration method from a mixture of l-α-phosphatidylcholine, cholesterol, and PE-PEG2000 in chloroform; evaporating the solvent, followed by hydration of the resulting thin film with ATP in phosphate-buffered saline (PBS). Upon lysis of the liposome, the SERS intensity of the SiO₂@Au@Ag NPs increased with the logarithm of number of ATP-encapsulated liposomes after lysis in the range of 8 × 10⁶ to 8 × 10¹⁰. The detection limit of liposome was calculated to be 1.3 × 10^-17 mol. The successful application of ATP-encapsulated liposomes to SiO₂@Au@Ag NPs based SERS analysis has opened a new avenue for Raman label chemical (RCL)-encapsulated liposome-enhanced SERS-based immunoassays.

Non-invasive gene targeting to the fetal brain after intravenous administration and transplacental transfer of plasmid DNA using PEGylated immunoliposomes

Research was undertaken to establish transplacental delivery of active genes to fetal brain by a non-viral vector, antibody-specific targeted therapeutic procedure. PEGylated immunoliposomes (PILs) containing firefly luciferase DNA under the influence of the SV40 promoter injected intravenously into near-term pregnant mice produced luminometric evidence of CNS tissue luciferase activity at 48-h post-injection in all newborn pups. In utero delivery of this pGL3 DNA was shown after a single i.v. injection in maternal and neonatal brains, spleen and lesser amounts in lungs, with only negligible background levels in negative controls exposed to unencapsulated pDNA. In addition to studies of normal wild-type mice, we similarly injected pregnant Lafora Knockout (EPM2a null-mutant) and demonstrated luciferase activity days later in the maternal and newborn pup brains of both types. Delivery of PILs containing a second reporter gene (the pSV40 beta-galactosidase transgene) transplacentally by the same procedure was also successful. Histochemical and biochemical demonstration of beta-galactosidase was documented for all mutant and non-mutant neonates. Brain areas of highest Lafora body development (such as the hippocampus and pontine nuclei) showed intraneuronal beta-glucosidase activity. We conclude that receptor-mediated transport of PIL-borne gene therapeutics across both the placental barrier as well as the fetal BBB in utero is feasible.

Synergistic effects of co-administration of suicide gene expressing mesenchymal stem cells and prodrug-encapsulated liposome on aggressive lung melanoma metastases in mice

The success of conventional suicide gene therapy for cancer treatment is still limited because of lack of efficient delivery methods, as well as poor penetration into tumor tissues. Mesenchymal stem cells (MSCs) have recently emerged as potential vehicles in improving delivery issues. However, these stem cells are usually genetically modified using viral gene vectors for suicide gene overexpression to induce sufficient therapeutic efficacy. This approach may result in safety risks for clinical translation. Therefore, we designed a novel strategy that uses non-viral gene vector in modifying MSCs with suicide genes to reduce risks. In addition, these cells were co-administrated with prodrug-encapsulated liposomes for synergistic anti-tumor effects. Results demonstrate that this strategy is effective for gene and prodrug delivery, which co-target tumor tissues, to achieve a significant decrease in tumor colonization and a subsequent increase in survival in a murine melanoma lung metastasis model. Moreover, for the first time, we demonstrated the permeability of MSCs within tumor nests by using an in vitro 3D tumor spheroid model. Thus, the present study provides a new strategy to improve the delivery problem in conventional suicide gene therapy and enhance the therapeutic efficacy. Furthermore, this study also presents new findings to improve our understanding of MSCs in tumor-targeted gene delivery.

The use of liposomes for constructing cell models

We illustrate here in a form of a short review some of the work developed in our and other groups aiming at performing inside liposomes enzymatic reactions relevant for the origin of life. The work on giant vesicles will not be considered here. The long-range goal of our work with SUVs or LUVs (small unilamellar vesicles or large unilamellar vesicles) is the construction of a model minimal cell. By this we mean a cell-like system containing the minimal and sufficient number of macromolecular components for expressingsome of the basic functions of a living cell- such as protein biosynthesis, growth and self-reproduction, homeostasis based on a primitive metabolism. We begin describing a POPC liposomal system containing some of the enzymes of the salvage cycle for the synthesis of lecithin; then vesicles containing the nucleotide phosphorylase enzyme for the polymerisation of ADP into poly(A); an oleate self-reproducing vesicular system which hosts Qβ replicase for the replication of a RNA template; a POPC systems (POPC = 1-palmitoyl-2-oleoyl-sn-phosphatidylcholine) hosting the elements for a polymerase chain reaction; and finally the attempts to organize inside liposomes the ribosomal system capable of the synthesis of poly(phenylalanine). This analysis of published work will be followed by the description of novel work aimed at expressing a protein (green fluorescent protein) inside liposomes. The possible development of this work and its limits will be discussed.

Immunoliposome-PCR: a generic ultrasensitive quantitative antigen detection system

Background

The accurate quantification of antigens at low concentrations over a wide dynamic range is needed for identifying biomarkers associated with disease and detecting protein interactions in high-throughput microarrays used in proteomics. Here we report the development of an ultrasensitive quantitative assay format called immunoliposome polymerase chain reaction (ILPCR) that fulfills these requirements. This method uses a liposome, with reporter DNA encapsulated inside and biotin-labeled polyethylene glycol (PEG) phospholipid conjugates incorporated into the outer surface of the liposome, as a detection reagent. The antigenic target is immobilized in the well of a microplate by a capture antibody and the liposome detection reagent is then coupled to a biotin-labeled second antibody through a NeutrAvidin bridge. The liposome is ruptured to release the reporter DNA, which serves as a surrogate to quantify the protein target using real-time PCR.

Results

A liposome detection reagent was prepared, which consisted of a population of liposomes ~120 nm in diameter with each liposome possessing ~800 accessible biotin receptors and ~220 encapsulated reporters. This liposome detection reagent was used in an assay to quantify the concentration of carcinoembryonic antigen (CEA) in human serum. This ILPCR assay exhibited a linear dose–response curve from 10^-10 M to 10^-16 M CEA. Within this range the assay coefficient of variance was <6 % for repeatability and <2 % for reproducibility. The assay detection limit was 13 fg/mL, which is 1,500-times more sensitive than current clinical assays for CEA. An ILPCR assay to quantify HIV-1 p24 core protein in buffer was also developed.

Conclusions

The ILPCR assay has several advantages over other immuno-PCR methods. The reporter DNA and biotin-labeled PEG phospholipids spontaneously incorporate into the liposomes as they form, simplifying preparation of the detection reagent. Encapsulation of the reporter inside the liposomes allows nonspecific DNA in the assay medium to be degraded with DNase I prior to quantification of the encapsulated reporter by PCR, which reduces false-positive results and improves quantitative accuracy. The ability to encapsulate multiple reporters per liposome also helps overcome the effect of polymerase inhibitors present in biological specimens. Finally, the biotin-labeled liposome detection reagent can be coupled through a NeutrAvidin bridge to a multitude of biotin-labeled probes, making ILPCR a highly generic assay system.

Miniaturized bioanalytical systems: enhanced performance through liposomes

Biorecognition-element labeled liposomes are simple and versatile tools used to amplify signals for the detection of analytes of environmental, clinical, food safety, and national security interest. Relying on measurement of encapsulated species via electrochemical or spectroscopic techniques, or properties inherent to liposomes themselves (such as mass, refractive index, or charge), many advances have been made in both bench-scale and microfluidic applications. Some of these measurement techniques are inherently sensitivity limited, but through the inclusion of liposomes, reduced limits of detection potentially broaden the utility towards otherwise challenging levels of analytes. Other advances took advantage of the hydrophobic environment required by many biorecognition elements to expand the target selectivity range or utilized the amphipathic nature of the lipid bilayer to provide enhanced separation capabilities. Novel handling approaches included wavelength-specific release of contents encapsulated within thermosensitive liposomes or application of electric fields to move, concentrate, and strategically lyse liposomes. These and other topics are discussed in terms of either present incorporation or adaptation to microfluidic devices.

Fliposomes: pH-controlled Release from Liposomes Containing New trans-2-Morpholinocyclohexanol-based Amphiphiles that Perform a Conformational Flip and Trigger an Instant Cargo Release upon Acidification

A new type of pH-sensitive liposome (fliposomes) was designed based on the amphiphiles that are able to perform a pH-triggered conformational flip (flipids). This flip disrupts the liposome membrane and causes rapid release of the liposome cargo, specifically in the areas of increased acidity. The flipids (1-3) are equipped with a trans-2-morpholinocyclohexanol conformational switch. pH-Sensitive fliposomes containing one of these flipids, POPC and PEG-ceramide (molar ratio 50/45/5) were constructed and characterized. These compositions were stable at 4oC and pH 7.4 for several months. Fliposomes loaded with ANTS/DPX demonstrated an unusually quick content release (in a few seconds) at pH below 5.5, which was more efficient in the case of flipid 1 with the shorter linear C12-tails. The pH-titration curve for the fliposome leakage paralleled the curve for the acid-induced conformational flip of 1-3 studied by 1H NMR. A plausible mechanism of the pH-sensitivity starts with an acid-triggered conformational flip of 1, 2 or 3, which changes the molecular size and shape, shortens the lipid tails, and perturbs the liposome membrane resulting in the content leakage.

Performing Encapsulation of dsDNA and a Polymerase Chain Reaction (PCR) inside Nanocontainers Using the Inverse Miniemulsion Process

We report the encapsulation of dsDNA molecules with a defined number of base pairs (476 bp and 790 bp) and their subsequent amplification by polymerase chain reaction (PCR) inside nanosized polymeric capsules/droplets. In the first set of experiments, the dsDNA template and PCR reagents were encapsulated in crosslinked potato starch using the inverse (water-in-oil) miniemulsion technique. After redispersion of the capsules in a water-surfactant mixture, PCR was performed inside the crosslinked starch nanocapsules. In the second set of experiments, the PCR was performed inside the aqueous nanodroplets before capsule formation, and then each miniemulsion droplet was covered with a polybutylcyanoacrylate (PBCA) shell which was formed through anionic polymerization directly at the droplet interface. The PCR efficiency was quantitatively evaluated by fluorescence spectroscopy, using a DNA-specific dye called SYBR® Green which intercalates between the base pairs of the dsDNA.

Fliposomes: pH-Sensitive Liposomes Containing a trans-2-morpholinocyclohexanol-Based Lipid That Performs a Conformational Flip and Triggers an Instant Cargo Release in Acidic Medium

Incorporation of a pH-sensitive conformational switch into a lipid structure enables a drastic conformational flip upon protonation that disrupts the liposome membrane and causes rapid release of cargo specifically in areas of increased acidity. pH-sensitive liposomes containing the amphiphile (1) with trans-2-morpholinocyclohexanol conformational switch, a phospholipid, and a PEG-lipid conjugate were constructed and characterized. The optimized composition—1/POPC/PEG-ceramide (50/4/5)—could be stored at 4 °C and pH 7.4 for up to 1.5 years, and was stable in blood serum in vitro after 48 h at 37 °C. Liposomes loaded with ANTS/DPX or methotrexate demonstrated an unusually quick content release (in a few seconds) at pH below 5.5, which was independent of inter-liposome contact. The pH-titration curve for the liposome leakage paralleled the curve for the acid-induced conformational flip of 1 studied by ¹H-NMR. Freeze-fracture electron microscopy images showed budding and division of the bilayer at pH 5.5. A plausible mechanism of pH-sensitivity involves an acid-triggered conformational flip of 1, shortening of lipid tails, and membrane perturbations, which cause the content leakage. The methotrexate-loaded liposomes demonstrated much higher cytotoxicity in HeLa cells than the free drug indicating that they can serve as viable drug delivery systems.

Emergence of self-reproduction in cooperative chemical evolution of prebiological molecules

The paper presents a model of coevolution of short peptides (P) and short oligonucleotides (N) at an early stage of chemical evolution leading to the origin of life. The model describes polymerization of both P and N types of molecules on mineral surfaces in aqueous solution at moderate temperatures. It is assumed that amino acid and nucleotide monomers were available in a prebiotic milieu, that periodic variation in environmental conditions between dry/warm and wet/cool took place and that energy sources were available for the polymerization. An artificial chemistry approach in combination with agent-based modeling was used to explore chemical evolution from an initially random mixture of monomers. It was assumed that the oligonucleotides could serve as templates for self-replication and for translation of peptide compositional sequences, and that certain peptides could serve as weak catalysts. Important features of the model are the short lengths of the peptide and oligonucleotide molecules that prevent an error catastrophe caused by copying errors and a finite diffusion rate of the molecules on a mineral surface that prevents excessive development of parasitism. The result of the simulation was the emergence of self-replicating molecular systems consisting of peptide catalysts and oligonucleotide templates. In addition, a smaller but significant number of molecules with alternative compositions also survived due to imprecise reproduction and translation of templates providing variability for further evolution. In a more general context, the model describes not only peptide-oligonucleotide molecular systems, but any molecular system containing two types of polymer molecules: one of which serves as templates and the other as catalysts.The presented coevolutionary system suggests a possible direction towards finding the origin of molecular functionality in a prebiotic environment.

DNA amplification via polymerase chain reaction inside miniemulsion droplets with subsequent poly(n-butylcyanoacrylate) shell formation and delivery of polymeric capsules into mammalian cells

There is a growing interest in the development of stable nanocapsules that could deliver the bioactive compounds within the living organism, and to release them without causing any toxic effects. Here the miniemulsion droplets were first used as "nanoreactors" for the amplification of single-molecule dsDNA template (476 and 790 base pairs) through PCR. Afterwards, each droplet was surrounded with a biodegradable PBCA shell by interfacial anionic polymerization, enabling therefore to deliver the PCR products into the cells. The size of the initial miniemulsion droplets and the final polymeric capsules was in the range of 250 and 320 nm, mainly depending on the type of the continuous phase and presence of dsDNA template molecules. The formation of PCR products was resolved with gel electrophoresis and detected with fluorescence spectroscopy in the presence of DNA specific dye (SYBRGreen). TEM studies were performed to prove the formation of the polymeric shell. The shell thickness was measured to be within 5-15 nm and the average molecular weight of the formed PBCA polymer was around 75000 g · mol(-1) . For the cell uptake experiments, the obtained nanocapsules were transferred from the organic phase into aqueous medium containing a water-soluble surfactant. The effect of the surfactant type (anionic, cationic or non-ionic) on the HeLa cell viability and nanocapsule uptake behavior was studied by CLSM and FACS. Confocal analysis demonstrated that nanocapsules stabilized with cationic (CTMA-Cl) and non-ionic (Lutensol AT50) surfactants show almost the same uptake, whereas capsules redispersed in anionic (SDS) surfactant possess a 30% higher uptake. The release of the encapsulated material within the cell was studied on the example of Cy5-labeled oligonucleotides showing the colocalization with mitochondria of MSCs cells.

Intravesicle isothermal DNA replication

Background

Bacterial and viral DNA replication was previously reconstituted in vitro from component parts [1-4]. Significant advances in building minimal cell-like structures also have been made recently [5-7]. Combining the two approaches would further attempts to build a minimal cell-like structure capable of undergoing evolution by combining membrane encapsulation and genome replication. Towards this end, we attempted to use purified genomic replication protein components from thermophilic bacterial sources to copy strands of DNA isothermally within lipid vesicles.

Findings

Bacterial replication components (such as helicases and DNA polymerases) are compatible with methods for the generation of lipid vesicles. Encapsulation inside phospholipid vesicles does not inhibit the activity of bacterial DNA genome replication machinery. Further the described system is efficient at isothermally amplifying short segments of DNA within phospholipid vesicles.

Conclusions

Herein we show that bacterial isothermal DNA replication machinery is functional inside of phospholipid vesicles, suggesting that replicating cellular mimics can be built from purified bacterial components.

Cationic phospholiposomes: efficient delivery vehicles of anticancer derivatives of ATP to multiple myeloma cells

Analogs of adenosine triphosphate (ATP) with substitutions at the 8-position have been shown to be cytotoxic to multiple myeloma, one of the most prevalent and serious blood cancers. However, these drugs do not readily cross biological membranes and are very sensitive to phosphatases present in body fluids. To circumvent these disadvantages, 8-substituted ATPs were encapsulated into cationic phospholiposomes generated from cationic phosphatidylcholines (EDOPC; 1,2-dioleoyl-sn-glycero-3-ethylphosphocholine, and EDPPC, the corresponding dipalmitoyl homolog), compounds with low toxicity that readily form liposomes. Vortexing was an efficient encapsulation procedure, more so than freeze-thawing. At the lipid:drug ratio of 5:1 (mol/mol), 20% of 8-Br-ATP was encapsulated within EDOPC liposomes. Efficient encapsulation and retention of 8-NH₂-ATP required the inclusion of cholesterol. Liposomes of EDOPC:cholesterol (55:45 mole/mole), at a lipid:drug mole ratio of 10:1, captured ~40% of the drug presented. Cytotoxicity assays of this formulation on multiple myeloma cells in culture showed encapsulated drug to be up to 10-fold more effective than free drug, depending upon dose. Intracellular distribution studies (based on fluorescent derivatives of lipids and of ATP) revealed that both liposomes and drug were taken up by multiple myeloma cells, and that uptake of a fluorescent ATP derivative was significantly greater when encapsulated than when free. Liposomes prepared from EDPPC, having a higher phase-transition temperature than EDOPC, captured 8-NH₂-ATP satisfactorily and released it more slowly than the unsaturated formulations, but were also less cytotoxic. The superior encapsulation efficiencies of the positively charged liposomes can be understood in terms of the electrostatic double layer due to a very high positive charge density on their inner surface. Electrostatic augmentation of encapsulation for small vesicles can be dramatic, easily exceeding an order of magnitude.

Cellular compartment model for exploring the effect of the lipidic membrane on the kinetics of encapsulated biochemical reactions

One of the important characteristics of the cellular system is that interactions between the plasma membrane and water-soluble molecules in the cytoplasm are enhanced by the confinement of the molecules to the small volume of the intracellular space. Studying this effect in a model cell system, we measured the time evolution of an enzymatic hydrolysis reaction and a cell-free protein synthesis reaction taking place in giant liposomes having various size and phospholipid compositions by a flow cytometry. This single vesicle-based assay of a large number of liposomes enabled us to examine the volume dependence of enclosed reactions in detail, revealing that the presence of specific lipid affected the specific kinetic parameters of encapsulated reactions.

Preparation of Trojan horse liposomes (THLs) for gene transfer across the blood-brain barrier

Nonviral plasmid DNA is delivered to the brain via a transvascular route across the blood-brain barrier (BBB) following intravenous administration of DNA encapsulated within Trojan horse liposomes (THLs), also called PEGylated immunoliposomes (PILs). The liposome surface is covered with several thousand strands of polymer (e.g., polyethylene glycol [PEG]), and the tips of 1%-2% of the polymer strands are conjugated with a targeting monoclonal antibody that acts as a molecular Trojan horse (MTH). The MTH binds to a receptor (e.g., for transferrin or insulin) on the BBB and brain cell membrane, triggering receptor-mediated transcytosis of the THL across the BBB in vivo, and receptor-mediated endocytosis into brain cells beyond the BBB. The persistence of transgene expression in the brain is inversely related to the rate of degradation of the episomal plasmid DNA. THL technology enables an exogenous gene to be widely expressed in the majority of cells in adult brain (or other organs) within 1 d of a single intravenous administration. Applications of the THLs include tissue-specific gene expression with tissue-specific promoters, complete normalization of striatal tyrosine hydroxylase in experimental Parkinson's disease following intravenous tyrosine hydroxylase gene therapy, a 100% increase in survival time of mice with brain tumors following weekly intravenous antisense gene therapy using THLs, and a 90% increase in survival time with weekly intravenous RNA interference (RNAi) gene therapy in mice with intracranial brain tumors. This protocol describes the preparation of THLs for use in gene transfer in vitro or in vivo.

siRNA specific delivery system for targeting dendritic cells

siRNA therapy offers immense potential for clinical application. Under physiological conditions, however, siRNA was demonstrated to have a short half-life. Additionally, it may also cause ubiquitous gene silencing as it does not possess a tissue-specific homing mechanism. Thus, the rate-limiting step in the emergence of siRNA as a potential therapeutic agent is the current lack of a safe and tissue- or cell-specific in vivo delivery system. Herein, we propose a novel, cell-specific method for the in vivo delivery of siRNA to dendritic cells (DCs) with the purpose of inducing immune modulation. CD40 siRNA was incorporated within the interior of 86 nm liposomes, which were decorated with surface-bound mAb NLDC-145 as a targeting mechanism. The siRNA encapsulation efficiency was determined to be approximately 7%. CD40 siRNA immunoliposomes (CD40 siILs) were able to specifically bind to DCs and silence CD40 expression in vitro. Furthermore, in vitro CD40-silenced DCs significantly inhibited the proliferation of alloreactive T cells in an MLR. Upon in vivo administration, siIL-encapsulated, Cy3-labeled siRNA exhibited moderate uptake by the liver at an early time point following administration with greater accumulation in the spleen at a later time point. In contrast, naked siRNA primarily accumulated in the kidney immediately after administration and circulated out in a short time period. To address in vivo gene silencing and immune modulation, mice were simultaneously immunized with KLH and subcutaneously injected with DC-specific CD40 siILs, siILs containing negative control siRNA, naked CD40 siRNA, or PBS. A second injection of CD40 siILs, or control treatments, followed 24 h later. Flow cytometry, reverse transcriptase PCR, and quantitative real-time PCR analysis of CD11c(+) DCs from mice treated with CD40 siILs demonstrated reduced expression of CD40, in comparison with control groups. CD11c(-) cells were also analyzed by flow cytometry, but no differences were observed between treatment groups. Furthermore, CD40 siIL-treated mice were found to have an increased proportion of Treg cells (CD4(+)CD25(+) FoxP3(+)), and DCs cells from these mice were able to inhibit T cell proliferation in an antigen-specific recall response. In summary, CD40 siILs were shown to specifically target and deliver CD40 siRNA to DCs, significantly reducing CD40 expression and resulting in DC-mediated immune modulation as well as generation of Treg cells. These findings highlight the therapeutic potential for siRNA-based and DC-mediated immunotherapy in the clinic. To the best of our knowledge, this is the first study to use siILs for targeted delivery of siRNA to DCs and for immune modulation.

Population analysis of structural properties of giant liposomes by flow cytometry

We used fluorescence flow cytometry to analyze the structural properties of populations of giant liposomes formed by different preparation methods. The inner aqueous volumes and nominal membrane surface areas of a large number of individual liposomes were measured simultaneously by using fluorescent markers. We compared these properties of liposomes prepared by the natural swelling method, the freeze-dried empty liposomes method, and the water-in-oil (W/O) emulsion method. A two-dimensional contour distribution map of the inner volume and the nominal surface area was used to elucidate the structural properties of liposomes over a wide range of liposome sizes. Lamellarity of liposomes was evaluated as the ratio of the nominal surface area to the theoretical surface area calculated from the liposome inner volume. This population analysis revealed the dependency of lamellarity on liposome volume: while the nominal surface areas of populations of liposomes prepared by the natural swelling and the freeze-dried empty liposome methods were widely distributed, those prepared by the W/O emulsion method had a narrower distribution within small values. Furthermore, with the latter method, the nominal surface area varied in proportion to the two-thirds power of the inner volume ranging for several orders of magnitude, indicating the liposomes had a thin membrane, which was constant for the wide volume range. The results as well as the methodology presented here would be useful in designing giant liposomes with desired properties.

Acyclovir delivery systems

Herpes viruses (herpes simplex, varicella zoster, cytomegalovirus) are the main cause of a wide variety of human infections. Although the development of successful antiviral agents against infections caused by herpes viruses had been slow until the last decade, the production of delivery systems for acyclovir are a promising alternative. The present review summarizes the principal advances made in developing carriers for the delivery of acyclovir by different routes of administration.

A novel in vivo siRNA delivery system specifically targeting dendritic cells and silencing CD40 genes for immunomodulation

Translation of small interfering RNA (siRNA)-based approaches into practical therapeutics is limited because of lack of an effective and cell-specific delivery system. Herein, we present a new method of selectively delivering siRNA to dendritic cells (DCs) in vivo using CD40 siRNA-containing immunoliposomes (siILs) that were decorated with DC-specific DEC-205 mAb. Administration of CD40 siILs resulted in DC-specific cell targeting in vitro and in vivo. On treatment with CD40 siILs, the expression of CD40 in DCs, as well allostimulatory activity was inhibited. In vivo administration resulted in selective siRNA uptake into immune organs and functional immune modulation as assessed using a model antigen. In conclusion, this is the first demonstration of DC-specific siRNA delivery and gene silencing in vivo, which highlights the potential of DC-mediated immune modulation and the feasibility of siRNA-based clinical therapy.

Quantitative study of the structure of multilamellar giant liposomes as a container of protein synthesis reaction

Liposomes are widely used as cell-sized compartments for encapsulation of biochemical reaction systems to construct model cell systems. However, liposomes are usually diverse in both size and structure, resulting in highly heterogeneous properties as microreactors. Here, we report the development of a strategy to investigate the internal structure of giant multilamellar vesicles (GMLVs) formed by the freeze-dried empty liposomes (FDEL) method as containers of an in vitro transcription/translation system. To evaluate the occurrence of the protein synthesis reaction in GMLVs, we designed a cascade reaction system in which a synthesized enzyme hydrolyzes the fluorescent substrate, and thus the space where the reaction takes place in liposomes becomes fluorescent. We found that only a part of the liposome was reactable and not the entire internal volume, i.e., the hydrolysis reaction took place in only a part of the fractured compartment volumes in GMLVs. Simultaneous measurement of the whole internal volume of the liposomes and the quantity of reaction product of more than 100 000 liposomes using a fluorescence-activated cell sorter (FACS) revealed that the distribution of reactable volume was proportional to the whole internal volume regardless of the liposome size, i.e., the relation between the quantity of whole and reactable volume in GMLV was found to be scale-free. This information would allow us to reduce the geometric parameters of GMLV for quantitative analysis of reaction kinetics in liposomes. The present measurement and analysis method will be an indispensable tool for exploring high-dimensional properties of a model cell system based on giant liposomes.

Confinement of DNA in water-in-oil microemulsions

The study of systems that allow DNA condensation in confined environments is an important task in producing cell-mimicking microreactors capable of biochemical activities. The water droplets formed in water-in-oil emulsions are potentially good candidates for such microcompartments. The anionic surfactant AOT was used here to stabilize the droplets. We have studied in detail the DNA distribution and the structural modifications of these microemulsion drops by varying the concentration and molecular weight of DNA and using various techniques such as light, X-ray, and neutron scattering, electrical conductivity, and surface tension. DNA induces the formation of large drops into which it is internalized. The size of these drops depends on the amount of DNA dissolved in water as well as on its molecular weight. The local DNA concentration is very high (>100 mg/mL). The large drops coexist with small empty drops (not containing DNA), similar to those found in the DNA-free microemulsion.