Archaeosomes based on synthetic tetraether-like lipids as novel versatile gene delivery systems

Ether lipids from archaeas in nano-drug delivery and vaccination

Archaea are microorganisms more closely related to eukaryotes than bacteria. Almost 50 years after being defined as a new domain of life on earth, new species continue to be discovered and their phylogeny organized. The study of the relationship between their genetics and metabolism and some of their extreme habitats has even positioned them as a model of extraterrestrial life forms. Archaea, however, are deeply connected to the life of our planet: they can be found in arid, acidic, warm areas; on most of the earth's surface, which is cold (below 5 °C), playing a prominent role in the cycles of organic materials on a global scale and they are even part of our microbiota. The constituent materials of these microorganisms differ radically from those produced by eukaryotes and bacteria, and the nanoparticles that can be manufactured using their ether lipids as building blocks exhibit unique properties that are of interest in nanomedicine. Here, we present for the first time a complete overview of the pre-clinical applications of nanomedicines based on ether archaea lipids, focused on drug delivery and adjuvancy over the last 25 years, along with a discussion on their pros, cons and their future industrial implementation.

Archaeosomes: New Generation of Liposomes Based on Archaeal Lipids for Drug Delivery and Biomedical Applications

Archaeosomes are a new generation of stable liposomes composed of natural ether lipids extracted from archaea, or synthetic archaeal lipids. Archaea constitute a domain of single-celled microorganisms that are structurally similar to but evolutionarily distinct from bacteria. They synthesize unique membrane lipids with isoprenoid hydrocarbon side chains attached via an ether linkage to the glycerol-phosphate backbone. Compared to the ester linkages found in the lipids of Eukarya and bacteria, the ether linkages in archaeal lipids are more stable in various environmental conditions such as high/low temperatures, acidic or alkaline pH, bile salts, and enzymatic hydrolysis. This feature has intrigued scientists to use archaeal lipids to prepare archaeosomes with superior physicochemical stability and utilize them as effective carriers to deliver various cargos of biomedical importance such as drugs, proteins, peptides, genes, and antioxidants to the target site. Archaeosomes carrying antigens and/or adjuvants are also proven to be better candidates for stimulating antigen-specific, humoral, and cell-mediated immune responses, which broadens their scope in vaccine delivery. These properties associated with excellent biocompatibility and a safety profile provide numerous advantages to the archaeosomes to function as a versatile delivery system. This mini-review will provide an overview of the unique features of archaeal lipids, preparation and characterization of archaeosomes, and emphasize the prospects related to drug delivery and other biomedical applications.

Vesicular and Planar Membranes of Archaea Lipids: Unusual Physical Properties and Biomedical Applications

Liposomes and planar membranes made of archaea or archaea-like lipids exhibit many unusual physical properties compared to model membranes composed of conventional diester lipids. Here, we review several recent findings in this research area, which include (1) thermosensitive archaeosomes with the capability to drastically change the membrane surface charge, (2) MthK channel's capability to insert into tightly packed tetraether black lipid membranes and exhibit channel activity with surprisingly high calcium sensitivity, and (3) the intercalation of apolar squalane into the midplane space of diether bilayers to impede proton permeation. We also review the usage of tetraether archaeosomes as nanocarriers of therapeutics and vaccine adjuvants, as well as the biomedical applications of planar archaea lipid membranes. The discussion on archaeosomal therapeutics is focused on partially purified tetraether lipid fractions such as the polar lipid fraction E (PLFE) and glyceryl caldityl tetraether (GCTE), which are the main components of PLFE with the sugar and phosphate removed.

Aerosol-Mediated Non-Viral Lung Gene Therapy: The Potential of Aminoglycoside-Based Cationic Liposomes

Aerosol lung gene therapy using non-viral delivery systems represents a credible therapeutic strategy for chronic respiratory diseases, such as cystic fibrosis (CF). Progress in CF clinical setting using the lipidic formulation GL67A has demonstrated the relevance of such a strategy while emphasizing the need for more potent gene transfer agents. In recent years, many novel non-viral gene delivery vehicles were proposed as potential alternatives to GL67 cationic lipid. However, they were usually evaluated using procedures difficult or even impossible to implement in clinical practice. In this study, a clinically-relevant administration protocol via aerosol in murine lungs was used to conduct a comparative study with GL67A. Diverse lipidic compounds were used to prepare a series of formulations inspired by the composition of GL67A. While some of these formulations were ineffective at transfecting murine lungs, others demonstrated modest-to-very-efficient activities and a series of structure-activity relationships were unveiled. Lipidic aminoglycoside derivative-based formulations were found to be at least as efficient as GL67A following aerosol delivery of a luciferase-encoding plasmid DNA. A single aerosol treatment with one such formulation was found to mediate long-term lung transgene expression, exceeding half the animal's lifetime. This study clearly supports the potential of aminoglycoside-based cationic lipids as potent GL67-alternative scaffolds for further enhanced aerosol non-viral lung gene therapy for diseases such as CF.

Liposomal nanoparticles based on steroids and isoprenoids for nonviral gene delivery

Natural lipid molecules are an essential part of life as they constitute the membrane of cells and organelle. In most of these cases, the hydrophobicity of natural lipids is contributed by alkyl chains. Although natural lipids with a nonfatty acid hydrophobic backbone are quite rare, steroids and isoprenoids have been strong candidates as part of a lipid. Over the years, these natural molecules (steroid and isoprenoids) have been used to make either lipid-based nanoparticle or functionalize in such a way that it could form nano assembly alone for therapeutic delivery. Here we mainly focus on the synthetic functionalized version of these natural molecules which forms cationic liposomal nanoparticles (LipoNPs). These cationic LipoNPs were further used to deliver various negatively charged genetic materials in the form of pDNA, siRNA, mRNA (nucleic acids), and so on. This article is categorized under: Biology-Inspired Nanomaterials > Lipid-Based Structures.

Liposomes: Structure, Biomedical Applications, and Stability Parameters With Emphasis on Cholesterol

Liposomes are essentially a subtype of nanoparticles comprising a hydrophobic tail and a hydrophilic head constituting a phospholipid membrane. The spherical or multilayered spherical structures of liposomes are highly rich in lipid contents with numerous criteria for their classification, including structural features, structural parameters, and size, synthesis methods, preparation, and drug loading. Despite various liposomal applications, such as drug, vaccine/gene delivery, biosensors fabrication, diagnosis, and food products applications, their use encounters many limitations due to physico-chemical instability as their stability is vigorously affected by the constituting ingredients wherein cholesterol performs a vital role in the stability of the liposomal membrane. It has well established that cholesterol exerts its impact by controlling fluidity, permeability, membrane strength, elasticity and stiffness, transition temperature (Tm), drug retention, phospholipid packing, and plasma stability. Although the undetermined optimum amount of cholesterol for preparing a stable and controlled release vehicle has been the downside, but researchers are still focused on cholesterol as a promising material for the stability of liposomes necessitating explanation for the stability promotion of liposomes. Herein, the prior art pertaining to the liposomal appliances, especially for drug delivery in cancer therapy, and their stability emphasizing the roles of cholesterol.

Lipid nanovesicles for biomedical applications: 'What is in a name'?

Vesicles, generally defined as self-assembled structures formed by single or multiple concentric bilayers that surround an aqueous core, have been widely used for biomedical applications. They can either occur naturally (e.g. exosomes) or be produced artificially and range from the micrometric scale to the nanoscale. One the most well-known vesicle is the liposome, largely employed as a drug delivery nanocarrier. Liposomes have been modified along the years to improve physicochemical and biological features, resulting in long-circulating, ligand-targeted and stimuli-responsive liposomes, among others. In this process, new nomenclatures were reported in an extensive literature. In many instances, the new names suggest the emergence of a new nanocarrier, which have caused confusion as to whether the vesicles are indeed new entities or could simply be considered modified liposomes. Herein, we discussed the extensive nomenclature of vesicles based on the suffix "some" that are employed for drug delivery and composed of various types and proportions of lipids and others amphiphilic compounds. New names have most often been selected based on changes of vesicle lipid composition, but the payload, structural complexity (e.g. multicompartment) and new/improved proprieties (e.g. elasticity) have also inspired new vesicle names. Based on this discussion, we suggested a rational classification for vesicles.

Biomedically Relevant Applications of Bolaamphiphiles and Bolaamphiphile-Containing Materials

Bolaamphiphiles (BAs) are structurally segmented molecules with rich assembly characteristics and diverse physical properties. Interest in BAs as standalone active agents or as constituents of more complex therapeutic formulations has increased substantially in recent years. The preorganized amphiphilicity of BAs allows for a range of biological activities including applications that rely on multivalency. This review summarizes BA-related research in biomedically relevant areas. In particular, we review BA-related literature in four areas: gene delivery, antimicrobial materials, hydrogels, and prodrugs. We also discuss several distinguishing characteristics of BAs that impact their utility as biomedically relevant compounds.

Cationic lipids for gene delivery: many players, one goal

Lipid-based carriers represent the most widely used alternative to viral vectors for gene expression and gene silencing purposes. This class of non-viral vectors is particularly attractive for their ease of synthesis and chemical modifications to endow them with desirable properties. Despite combinatorial approaches have led to the generation of a large number of cationic lipids displaying different supramolecular structures and improved behavior, additional effort is needed towards the development of more and more effective cationic lipids for transfection purposes. With this review, we seek to highlight the great progress made in the design of each and every constituent domain of cationic lipids, that is, the chemical structure of the headgroup, linker and hydrophobic moieties, and on the specific effect on the assembly with nucleic acids. Since the complexity of such systems is known to affect their performances, the role of formulation, stability and phase behavior on the transfection efficiency of such assemblies will be thoroughly discussed. Our objective is to provide a conceptual framework for the development of ever more performing lipid gene delivery vectors.

Phytochemical delivery through nanocarriers: a review

In recent times, phytochemicals encapsulated or conjugated with nanocarriers for delivery to the specific sites have gained considerable research interest. Phytochemicals are mostly plant secondary metabolites which reported to be beneficial for human health and in disease theraphy. However, these compound are large size and polar nature of these compounds, make it difficult to cross the blood-brain barrier (BBB), endothelial lining of blood vessels, gastrointestinal tract and mucosa. Moreover, they are enzymatically degraded in the gastrointestinal tract. Therefore, encapsulation or conjugation of these compounds with nanocrriers could be an alternate way to enhance their bioefficacy by influencing their gastrointestinal stability, rate of absorption and dispersion. This review presents an overview of nanocarriers alternatives which improves therapeutic value and avoid toxicity, by releasing bioactive compounds specifically at target tissues with enhanced stability and bioavailability. Future investigations may emphasize on deciphering the structural changes in nanocarriers during digestion and absorption, the difference between in-vitro and in-vivo digestion simulations, and impact of nanocarriers on the metabolism of phytochemicals.

Lipid vesicles: A versatile drug delivery platform for dermal and transdermal applications

Topical and transdermal application of active pharmaceutical ingredients to the skin is an attractive strategy being explored by formulation scientists to treat disease conditions rather than the oral drug delivery. Several approaches have been attempted, and many of them have emerged with significant clinical potential. However, the delivery of drugs across the skin is an arduous task due to permeation limiting barriers. It, therefore, requires the aid of external agents or carrier systems for efficient permeation. Lipid-based vesicular systems are carriers for the transport of drugs through the stratum corneum (dermal drug delivery) and into the bloodstream for systemic action (transdermal drug delivery) overcoming the barrier properties. This review article describes the various vesicular systems reported for skin delivery of actives with relevant case studies. The vesicular systems presented here are in the order of their advent from conventional systems to the advanced lipid vesicles. The design and development of drugs in vesicular systems have brought a new dimension to the treatment of disease conditions overcoming the permeation limiting barriers, thus improving its efficacy.

Combination therapy using human papillomavirus L1/E6/E7 genes and archaeosome: a nanovaccine confer immuneadjuvanting effects to fight cervical cancer

Cancer is a leading cause of death worldwide. Cervical cancer caused by human papillomavirus (HPV) is a major health problem in women. DNA vaccines are a perfect approach to immunization, but their potency in clinical trials has been insufficient for generating effective immunity, which may be related to the degradation of the DNA via nucleases, poor delivery to antigen-presenting cells (APCs), and insufficient uptake of DNA plasmids by cells upon injection. Archaeosome is a nano-delivery systems based on liposomes with their immunological role have been developed for gene delivery. In this study, human papillomavirus type 16 genes, containing truncated L1, E6, and E7, were simultaneously used in combination therapy with archaeosome and assessed in vivo. Findings supported that archaeosomes promotes immune responses to DNA vaccines and a long-term CTL response was generated with a low antigen dose. Combination therapy with archaeosome/L1/E6/E7 vaccines exhibited a strong cytolytic activity against tumor cells and induced prophylactic and therapeutic effect against the development of tumor in the animal model.

Biotechnology of extremely thermophilic archaea

Although the extremely thermophilic archaea (Topt ≥ 70°C) may be the most primitive extant forms of life, they have been studied to a limited extent relative to mesophilic microorganisms. Many of these organisms have unique biochemical and physiological characteristics with important biotechnological implications. These include methanogens that generate methane, fermentative anaerobes that produce hydrogen gas with high efficiency, and acidophiles that can mobilize base, precious and strategic metals from mineral ores. Extremely thermophilic archaea have also been a valuable source of thermoactive, thermostable biocatalysts, but their use as cellular systems has been limited because of the general lack of facile genetics tools. This situation has changed recently, however, thereby providing an important avenue for understanding their metabolic and physiological details and also opening up opportunities for metabolic engineering efforts. Along these lines, extremely thermophilic archaea have recently been engineered to produce a variety of alcohols and industrial chemicals, in some cases incorporating CO2 into the final product. There are barriers and challenges to these organisms reaching their full potential as industrial microorganisms but, if these can be overcome, a new dimension for biotechnology will be forthcoming that strategically exploits biology at high temperatures.

Carriers for the targeted delivery of aerosolized macromolecules for pulmonary pathologies

INTRODUCTION

Macromolecules with unique effects and potency are increasingly being considered for application in lung pathologies. Numerous delivery strategies for these macromolecules through the lung have been investigated to improve the targeting and overall efficacy.

AREAS COVERED

Targeting approaches from delivery devices, formulation strategies and specific targets are discussed.

EXPERT OPINION

Although macromolecules are a heterogeneous group of molecules, a number of strategies have been investigated at the macro, micro, and nanoscopic scale for the delivery of macromolecules to specific sites and cells of lung tissues. Targeted approaches are already in use at the macroscopic scale through inhalation devices and formulations, but targeting strategies at the micro and nanoscopic scale are still in the laboratory stage. The combination of controlling lung deposition and targeting after deposition, through a combination of targeting strategies could be the future direction for the treatment of lung pathologies through the pulmonary route.

Transfection Studies with Colloidal Systems Containing Highly Purified Bipolar Tetraether Lipids from Sulfolobus acidocaldarius

Lipid vectors are commonly used to facilitate the transfer of nucleic acids into mammalian cells. In this study, two fractions of tetraether lipids from the archaea Sulfolobus acidocaldarius were extracted and purified using different methods. The purified lipid fractions polar lipid fraction E (PLFE) and hydrolysed glycerol-dialkyl-nonitol tetraether (hGDNT) differ in their structures, charge, size, and miscibility from conventional lipids. Liposomes were prepared by mixing tetraether lipids with cholesterol (CH) and 1,2-dioleoyl-3-trimethylammonium-propane (DOTAP) resulting in stable vectors for gene delivery. Lipoplexes were prepared by complexation of liposomes with a luciferase expressing plasmid (pCMV-luc) at certain nitrogen-to-phosphorus (N/P) ratios and optimised for the transient transfection of ovarian adenocarcinoma cells (SK-OV-3). Complexation efficacy was investigated by gel-red fluorescence assay. Biophysical properties, like size, surface charge, and morphology, were investigated by differential light scattering (DLS), atomic force microscopy (AFM), and scanning electron microscopy (Cryo-SEM), respectively, revealing structural differences between liposomes and lipoplexes. A range of stable transfecting agents containing tetraether lipids were obtained by incorporating 5 mol% of tetraether lipids. Lipoplexes showed a decrease in free gel-red with increasing N/P ratios indicating efficient incorporation of plasmid DNA (pDNA) and remarkable stability. Transfection experiments of the lipoplexes revealed successful and superior transfection of SK-OV-3 cell line compared to the commercially available DOTAP and branched polyethyleneimine (25 kDa bPEI).

Characterization of drug encapsulation and retention in archaea-inspired tetraether liposomes

Archaea-inspired lipids exhibit reduced membrane permeability and increased retention of hydrophilic drugs in liposomes.

Lipophosphoramidate-based bipolar amphiphiles: their syntheses and transfection properties

A series of cationic bipolar amphiphiles were readily prepared by thiol–ene click reaction. These compounds were formulated in liposomal solutions and assessed as vector for gene delivery.

Bolaamphiphiles: a pharmaceutical review

The field of drug discovery is ever growing and excipients play a major role in it. A novel class of amphiphiles has been discussed in the review. The review focuses on natural as well as synthetic bolaamphiphiles, their chemical structures and importantly, their ability to self assemble rendering them of great use to pharmaceutical industry. Recent reports on their ability to be used in fabrication of suitable nanosized carriers for drug as well as genes to target site, has been discussed substantially to understand the potential of bolaamphiphiles in field of drug delivery.

Collapsed bipolar glycolipids at the air/water interface: effect of the stereochemistry on the stretched/bent conformations

This article describes a comparative study of several bipolar lipids derived from tetraether structures. The sole structural difference between the main two glycolipids is a unique stereochemical variation on a cyclopentyl ring placed in the middle of the lipids. We discuss the comparative results obtained at the air/water interface on the basis of tensiometry and ellipsometry. Langmuir-Blodgett depositions during lipid film compressions and decompressions were also analyzed by AFM. The lactosylated tetraether (bipolar) lipid structures involved the formation of highly stable multilayers, which are still present at 10 mN m(-1) during decompression. This study suggests also that the stereochemistry of a central cyclopentyl ring dramatically drives the conformation of the corresponding bipolar lipids. Both isomers (trans and cis) adopt a U-shaped (bent) conformation at the air/water interface but the trans cyclopentyl ring induces a much more frustration within this type of conformation. Consequently, this bipolar lipid (trans-tetraether) undergoes a flip of one polar head-group (lactosyl) leading to a stretched conformation during collapse.

Nanotechnological Approaches for Genetic Immunization

Genetic immunization is one of the important findings that provide multifaceted immunological response against infectious diseases. With the advent of r-DNA technology, it is possible to construct vector with immunologically active genes against specific pathogens. Nevertheless, site-specific delivery of constructed genetic material is an important contributory factor for eliciting specific cellular and humoral immune response. Nanotechnology has demonstrated immense potential for the site-specific delivery of biomolecules. Several polymeric and lipidic nanocarriers have been utilized for the delivery of genetic materials. These systems seem to have better compatibility, low toxicity, economical and capable to delivering biomolecules to intracellular site for the better expression of desired antigens. Further, surface engineering of nanocarriers and targeting approaches have an ability to offer better presentation of antigenic material to immunological cells. This chapter gives an overview of existing and emerging nanotechnological approaches for the delivery of genetic materials.

A seasonal cycle of terrestrial inputs in Lake Van, Turkey

Lake Van in Turkey is the world's largest soda lake (607 km(3)). The lake's catchment area is estimated to be ∼12,500 km(2), and the terrestrial input is carried through eolian, riverine, snowmelt and anthropogenic paths. Extent and seasonality of the terrestrial inputs to the lake have not been studied, but it is essential to evaluate its environmental status and to assess the use of environmental proxies to estimate the lake's response to climate changes. This study aims to measure seasonal changes in terrestrial input of natural and anthropogenic origin as recorded by the fluxes of pollen and biomarkers of soil bacteria and vascular or higher plants, as well as petrogenic biomarkers in monthly resolved sediment traps from August 2006 to July 2007. Fluxes of pollen, soil and higher plant biomarkers seem to be related to precipitation and snowmelt in autumn and spring. In addition, dust storms, which are common during the summer months, may have resulted in long-distance transport. Anthropogenic biomarker fluxes indicate year-round petrogenic contamination although some mature biomarker fluxes are higher in summer and in late winter-spring. The relative changes between petrogenic markers indicate variations in the pollutant sources.

Lipoidal soft hybrid biocarriers of supramolecular construction for drug delivery

Lipid-based innovations have achieved new heights during the last few years as an essential component of drug development. The current challenge of drug delivery is liberation of drug agents at the right time in a safe and reproducible manner to a specific target site. A number of novel drug delivery systems has emerged encompassing various routes of administration, to achieve controlled and targeted drug delivery. Microparticulate lipoidal vesicular system represents a unique technology platform suitable for the oral and systemic administration of a wide variety of molecules with important therapeutic biological activities, including drugs, genes, and vaccine antigens. The success of liposomes as drug carriers has been reflected in a number of liposome-based formulations, which are commercially available or are currently undergoing clinical trials. Also, novel lipid carrier-mediated vesicular systems are originated. This paper has focused on the lipid-based supramolecular vesicular carriers that are used in various drug delivery and drug targeting systems.

Lipoidal soft hybrid biocarriers of supramolecular construction for drug delivery

Lipid-based innovations have achieved new heights during the last few years as an essential component of drug development. The current challenge of drug delivery is liberation of drug agents at the right time in a safe and reproducible manner to a specific target site. A number of novel drug delivery systems has emerged encompassing various routes of administration, to achieve controlled and targeted drug delivery. Microparticulate lipoidal vesicular system represents a unique technology platform suitable for the oral and systemic administration of a wide variety of molecules with important therapeutic biological activities, including drugs, genes, and vaccine antigens. The success of liposomes as drug carriers has been reflected in a number of liposome-based formulations, which are commercially available or are currently undergoing clinical trials. Also, novel lipid carrier-mediated vesicular systems are originated. This paper has focused on the lipid-based supramolecular vesicular carriers that are used in various drug delivery and drug targeting systems.

Stereochemical effect revealed in self-assemblies based on archaeal lipid analogues bearing a central five-membered carbocycle: a SAXS study

The relative stereochemistry (cis or trans) of a 1,3-disubstituted cyclopentane unit in the middle of tetraether archaeal bipolar lipid analogues was found to have a dramatic influence on their supramolecular self-assembly properties. SAXS studies of two synthetic diastereomeric archaeal lipids bearing two lactosyl polar head groups at opposite ends revealed different lyotropic behaviors. The cis isomer led to L(c)-L(α)-Q(II) transitions whereas the trans isomer retained an L(α) phase from 20 to 100 °C. These main differences originate from the conformational equilibrium (pseudorotation) of 1,3-disubstituted cyclopentanes. Indeed, this pseudorotation exhibits quite similar orientations of the two substituents in a trans isomer whereas several orientations of the two alkyl chains are expected in a cis-1,3-dialkyl cyclopentane, thus authorizing more conformational flexibility in the lipid packing.

Bacterial dominance in subseafloor sediments characterized by methane hydrates

The degradation of organic carbon in subseafloor sediments on continental margins contributes to the largest reservoir of methane on Earth. Sediments in the Andaman Sea are composed of ~ 1% marine-derived organic carbon and biogenic methane is present. Our objective was to determine microbial abundance and diversity in sediments that transition the gas hydrate occurrence zone (GHOZ) in the Andaman Sea. Microscopic cell enumeration revealed that most sediment layers harbored relatively low microbial abundance (10(3)-10(5) cells cm(-3)). Archaea were never detected despite the use of both DNA- and lipid-based methods. Statistical analysis of terminal restriction fragment length polymorphisms revealed distinct microbial communities from above, within, and below the GHOZ, and GHOZ samples were correlated with a decrease in organic carbon. Primer-tagged pyrosequences of bacterial 16S rRNA genes showed that members of the phylum Firmicutes are predominant in all zones. Compared with other seafloor settings that contain biogenic methane, this deep subseafloor habitat has a unique microbial community and the low cell abundance detected can help to refine global subseafloor microbial abundance.

Preparation and Characterization of Stealth Archaeosomes Based on a Synthetic PEGylated Archaeal Tetraether Lipid

The present studies were focused on the formation and characterization of sterically stabilized archaeosomes made from a synthetic PEGylated archaeal lipid. In a first step, a synthetic archaeal tetraether bipolar lipid was functionalized with a poly(ethylene glycol), PEG, and (PEG(45)-Tetraether) with the aim of coating the archaeosome surface with a sterically stabilizing hydrophilic polymer. In a second step, Egg-PC/PEG(45)-Tetraether (90/10 wt%) archaeosomes were prepared, and their physicochemical characteristics were determined by dynamic light scattering (size, polydispersity), cryo-TEM (morphology), and by high-performance thin layer chromatography (lipid composition), in comparison with standard Egg-PC/PEG(45)-DSPE formulations. Further, a fluorescent dye, the carboxyfluorescein, was encapsulated into the prepared archaeosomes in order to evaluate the potential of such nanostructures as drug carriers. Release studies have shown that the stability of Egg-PC/PEG(45)-Tetraether-based archaeosomes is significantly higher at 37°C than the one of Egg-PC/PEG(45)-DSPE-based liposomes, as evidenced by the slower release of the dye encapsulated into PEGylated archaeosomes. This enhanced stability could be related to the membrane spanning properties of the archaeal bipolar lipid as already described with natural or synthetic tetraether lipids.

Phase separation in binary mixtures of bipolar and monopolar lipid dispersions revealed by 2H NMR spectroscopy, small angle x-ray scattering, and molecular theory

Binary mixtures of C(20)BAS and POPC membranes were studied by solid-state (2)H NMR spectroscopy and small angle x-ray scattering (SAXS) over a wide range of concentrations and at different temperatures. Three specifically deuterated C(20)BAS derivatives--[1',1',20',20'-(2)H(4)]C(20)BAS, [2',2',19',19'-(2)H(4)]C(20)BAS, and [10',11'-(2)H(2)]C(20)BAS--combined with protiated 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC), as well as membranes containing POPC-d(31) and fully protiated bolalipid, were used in NMR experiments to obtain structural information for the mixtures. The (2)H NMR spectra of [10',11'-(2)H(2)]C(20)BAS/POPC membrane dispersions reveal that the bolalipid is predominantly in the transmembrane conformation at high bolalipid concentrations (100, 90, and 70 mol %). At < or =50 mol % C(20)BAS, smaller quadrupolar couplings appear in the spectra, indicating the presence of U-shaped conformers. The proportion of U-shaped bolalipids increases as the amount of POPC in the membrane increases; however, the transmembrane component remains the dominant bolalipid conformation in the membrane even at 45 degrees C and 10 mol % C(20)BAS, where it accounts for approximately 50% of the bolalipid population. The large fraction of C(20)BAS transmembrane conformers, regardless of the C(20)BAS/POPC ratio, together with the findings from molecular mean-field theory calculations, suggests the coexistence of phase-separated bolalipid-rich domains and POPC-rich domains. A single lamellar repeat distance was observed in SAXS experiments corresponding to the average repeat spacing expected for C(20)BAS- and POPC-rich domains. These observations are consistent with the presence of microphase-separated domains in the mixed membrane samples that arise from POPC-C(20)BAS hydrophobic mismatch.

Archaeal tetraether bipolar lipids: Structures, functions and applications

Archaea have developed specific tools permitting life under harsh conditions and archaeal lipids are one of these tools. This microreview describes the particular features of tetraether-type archaeal lipids and their potential applications in biotechnology. Natural and synthetic tetraether lipid structures as well as their applications in drug/gene delivery, vaccines and proteoliposomes or as lipid films are reviewed.

trans-2-Aminocyclohexanol as a pH-sensitive conformational switch in lipid amphiphiles

Protonation-induced conformational change of lipid tails is reported as a novel strategy to render pH-sensitive lipid amphiphiles and lipid colloids.