Distearoylphosphatidylcholine Research Articles

Pressure‐dependent adhesion between solid‐supported PC‐lipid bilayers and vesicles under electric fields

AbstractFusion of lipid bilayers in membranes is important in processes from vesicle‐cell interactions (as in drug delivery) to exosome‐cell signaling, while transient transmembrane electric fields are known to occur spontaneously. Two contacting phosphatidylcholine (PC) lipid membranes are known to fuse into one under external electric fields, suggesting that the interaction between them is modified by the field as they approach, prior to the fusion event. Here we measure directly the adhesion energy between dimyristoylphosphatidylcholine (DMPC) and between distearoylphosphatidylcholine (DSPC) surface layers attached to solid substrates both without and with a transmembrane electric field. We find a marked pressure‐dependent adhesion behavior in the electric field, which we attribute to fusion intermediates that are formed, shedding new light on membrane electro‐fusion.

Probing Molecular Packing of Lipid Nanoparticles from 31P Solution and Solid-State NMR.

Lipid nanoparticles (LNPs) are intricate multicomponent systems widely recognized for their efficient delivery of oligonucleotide cargo to host cells. Gaining insights into the molecular properties of LNPs is crucial for their effective design and characterization. However, analysis of their internal structure at the molecular level presents a significant challenge. This study introduces 31P nuclear magnetic resonance (NMR) methods to acquire structural and dynamic information about the phospholipid envelope of LNPs. Specifically, we demonstrate that the 31P chemical shift anisotropy (CSA) parameters serve as a sensitive indicator of the molecular assembly of distearoylphosphatidylcholine (DSPC) lipids within the particles. An analytical protocol for measuring 31P CSA is developed, which can be implemented using either solution NMR or solid-state NMR, offering wide accessibility and adaptability. The capability of this method is demonstrated using both model DSPC liposomes and real-world pharmaceutical LNP formulations. Furthermore, our method can be employed to investigate the impact of formulation processes and composition on the assembly of specifically LNP particles or, more generally, phospholipid-based delivery systems. This makes it an indispensable tool for evaluating critical pharmaceutical properties such as structural homogeneity, batch-to-batch reproducibility, and the stability of the particles.

PH-dependent structural transitions in cationic ionizable lipid mesophases are critical for lipid nanoparticle function.

Lipid nanoparticles (LNPs) are advanced core-shell particles for messenger RNA (mRNA) based therapies that are made of polyethylene glycol (PEG) lipid, distearoylphosphatidylcholine (DSPC), cationic ionizable lipid (CIL), cholesterol (chol), and mRNA. Yet the mechanism of pH-dependent response that is believed to cause endosomal release of LNPs is not well understood. Here, we show that eGFP (enhanced green fluorescent protein) protein expression in the mouse liver mediated by the ionizable lipids DLin-MC3-DMA (MC3), DLin-KC2-DMA (KC2), and DLinDMA (DD) ranks MC3 ≥ KC2 > DD despite similar delivery of mRNA per cell in all cell fractions isolated. We hypothesize that the three CIL-LNPs react differently to pH changes and hence study the structure of CIL/chol bulk phases in water. Using synchrotron X-ray scattering a sequence of ordered CIL/chol mesophases with lowering pH values are observed. These phases show isotropic inverse micellar, cubic Fd3m inverse micellar, inverse hexagonal [Formula: see text] and bicontinuous cubic Pn3m symmetry. If polyadenylic acid, as mRNA surrogate, is added to CIL/chol, excess lipid coexists with a condensed nucleic acid lipid [Formula: see text] phase. The next-neighbor distance in the excess phase shows a discontinuity at the Fd3m inverse micellar to inverse hexagonal [Formula: see text] transition occurring at pH 6 with distinctly larger spacing and hydration for DD vs. MC3 and KC2. In mRNA LNPs, DD showed larger internal spacing, as well as retarded onset and reduced level of DD-LNP-mediated eGFP expression in vitro compared to MC3 and KC2. Our data suggest that the pH-driven Fd3m-[Formula: see text] transition in bulk phases is a hallmark of CIL-specific differences in mRNA LNP efficacy.

Thermodynamic and structural properties of lipid-photosensitizer conjugates mixed with phospholipids: Impact on the formation and stability of nano-assemblies

The photosensitizer Phenalenone (PN) was grafted with one or two lipid (C18) chains to form pure nano-assemblies or mixed lipid vesicles suitable for photodynamic therapy. Mixtures of PN-C18 conjugates with stearoyl-oleoyl phosphatidylcholine (SOPC) form vesicles that disintegrate into bilayer sheets as the concentration of PN-C18 conjugates increases. We hypothesized that PN-C18 conjugates control the thermodynamic and structural properties of the mixtures and induce the disintegration of vesicles due to PN π-π-interactions.Monolayers were analyzed by surface pressure and grazing incidence X-ray diffraction (GIXD) measurements, and vesicles by differential scanning calorimetry and cryo-TEM. The results showed that PN-triazole-C18 (1A) and PN-NH-C18 (1B) segregate from the phospholipid domains. PN-(C18)2 (conjugate 2) develops favorable interactions with SOPC and distearoyl-phosphatidylcholine (DSPC). GIXD demonstrates the contribution of SOPC to the structuring of conjugate 2 and the role of the major component in controlling the structural properties of DSPC-conjugate 2 mixtures. Above 10 mol% conjugate 2 in SOPC vesicles, the coexistence of domains with different molecule packing leads to conjugate segregation, vesicle deformation, and the formation of small bilayer discs stabilized by the inter-bilayer π-π stacking of PN molecules.

Inhalable aerosol microparticles with low carrier dosage and high fine particle fraction prepared by spray-freeze-drying

Co-suspension drug-loading technology, namely Aerosphere™, can improve fine particle fraction (FPF) and delivered dose content uniformity (DDCU). However, because of its poor drug-loading efficacy, the phospholipid carrier dosage in Aerosphere™ is usually dozens of times greater than that of the drug, resulting in a high material cost and blockage of the actuator. In this study, spray-freeze-drying (SFD) technology was used to prepare inhalable distearoylphosphatidylcholine (DSPC)-based microparticles for pressurized metered-dose inhalers (pMDI). Water-soluble, low-dose formoterol fumarate was used as an indicator to evaluate the aerodynamic performance of the inhalable microparticles. Water-insoluble, high-dose mometasone furoate was used to investigate the effects of drug morphology and drug-loading mode on the drug delivery efficiency of the microparticles. The results demonstrated that DSPC-based microparticles prepared using the co-SFD technology not only achieved higher FPF and more consistent delivered dose than those of drug crystal-only pMDI, but the amount of DSPC was also reduced to approximately 4% of that prepared using the co-suspension technology. This SFD technology may also be used to improve the drug delivery efficiency of other water-insoluble and high-dose drugs.

Effect of polyols on membrane structures of liposomes: A study using small-angle X-ray scattering data and generalized indirect Fourier transformation

This study aimed to evaluate the membrane structure of distearoylphosphatidylcholine (DSPC) liposomes dispersed in water containing various types of polyols with low molecular weight such as glycerin (Gly), 1,3-butandiol (BG), and propylene glycol (PG). To clarify the detailed membrane structure, generalized indirect Fourier transformation (GIFT) analysis, which provides information about the bilayer spacing, bilayer thickness, number of lamellar layers, and membrane flexibility, was applied to small-angle X-ray scattering (SAXS) data of the present system. The GIFT results showed that the bilayer thickness of the DSPC liposomes followed the order Gly>>BG>PG. In addition, the membrane flexibility estimated by the Caille parameter was in the order Gly>>BG>PG; this result was supported by the gel-liquid crystal phase transition temperature (Tc) obtained by differential scanning calorimetry (DSC). These results, together with the Raman spectra, suggest that BG and PG incorporated into the bilayers of DSPC liposomes result in the formation of an interdigitated lamellar structure.

Vitamin E Does Not Disturb Polyunsaturated Fatty Acid Lipid Domains.

The function of vitamin E in biomembranes remains a prominent topic of discussion. As its limitations as an antioxidant persist and novel functions are discovered, our understanding of the role of vitamin E becomes increasingly enigmatic. As a group of lipophilic molecules (tocopherols and tocotrienols), vitamin E has been shown to influence the properties of its host membrane, and a wealth of research has connected vitamin E to polyunsaturated fatty acid (PUFA) lipids. Here, we use contrast-matched small-angle neutron scattering and differential scanning calorimetry to integrate these fields by examining the influence of vitamin E on lipid domain stability in PUFA-based lipid mixtures. The influence of α-tocopherol, γ-tocopherol, and α-tocopherylquinone on the lateral organization of a 1:1 lipid mixture of saturated distearoylphosphatidylcholine (DSPC) and polyunsaturated palmitoyl-linoleoylphosphatidylcholine (PLiPC) with cholesterol provides a complement to our growing understanding of the influence of tocopherol on lipid phases. Characterization of domain melting suggests a slight depression in the transition temperature and a decrease in transition cooperativity. Tocopherol concentrations that are an order of magnitude higher than anticipated physiological concentrations (2 mol percent) do not significantly perturb lipid domains; however, addition of 10 mol percent is able to destabilize domains and promote lipid mixing. In contrast to this behavior, increasing concentrations of the oxidized product of α-tocopherol (α-tocopherylquinone) induces a proportional increase in domain stabilization. We speculate how the contrasting effect of the oxidized product may supplement the antioxidant response of vitamin E.

Functionalized bosutinib liposomes for target specific delivery in management of estrogen-positive cancer

This study was designed to create surface-functionalized bosutinib liposomes that could be used for the management of estrogen-positive cancers. The novelty of this work was the anti-cancer activity of bosutinib-loaded liposomes (Bos-LPs) in estrogen-positive cancer via estrogen response elements, responsible for the malignancy of cancer cells. Biotin effectively delivers active moiety to tumor tissues because it interacts with the biotin receptor and operates through the Sodium-dependent multivitamin transporters (SMVT) transporter. The prepared liposomes had a 257.73 ± 4.50 nm particle size, − 28.07 ± 5.81 mV zeta potential, 87.78 ± 1.16 % encapsulation efficiency and 85.56 ± 0.95 % drug release for 48 h. The surface architecture of biotin-modified bosutinib-loaded liposomes (b-Bos-LPs) was confirmed using scanning electron and transmission electron microscopies. In-vitro experiments revealed that b-Bos-LPs outperformed Bos and Bos-LPs in terms of significantly reduced cell viability in MCF-7 cells. According to biodistribution and pharmacokinetic studies, b-Bos-LPs have a higher Bos concentration in tumor tissues as compared to the other organs and also possess better pharmacokinetic activity, indicating that they can be used to treat carcinogen-induced estrogen-positive cancers. This is the first study to show that b-Bos-LPs can display activity against estrogen-positive cancer via biotin targeting. As evidenced by various parameters, b-Bos-LPs showed improved anticancer targeting, therapeutic safety and efficacy in carcinogen-induced estrogen-positive cancer. The receptor protein estrogen, which is primarily responsible for this cancer was downregulated by b-Bos-LPs in an immunoblotting assay. The results showed that biotinylated distearoylphosphatidylcholine (DSPC) augmented LPs loaded with Bosutinib can cause apoptosis in estrogen-positive breast cancer and be an effective way to treat estrogen-positive cancer.

Inhalable microparticle platform based on a novel shell-forming lipid excipient and its feasibility for respirable delivery of biologics

Administration of biologics such as proteins, vaccines, and phages via the respiratory route is becoming increasingly popular. Inhalable powder formulations for the successful delivery of biologics must first ensure both powder dispersibility and physicochemical stability. A lipid-based inhalable microparticle platform combining the stability advantages offered by dry powder formulations and high dispersibility afforded by a rugose morphology was spray dried and tested. A new simplified spray drying method requiring no organic solvents or complicated feedstock preparation processes was introduced for the manufacture of the microparticles. Trehalose was selected to form the amorphous particle core, because of its well-known ability to stabilize biologics, and also because of its ability to serve as a surrogate for small molecule actives. Phospholipid distearoyl phosphatidylcholine (DSPC), the lipid component in this formulation, was used as a shell former to improve powder dispersibility. Effectiveness of the lipid excipient in modifying trehalose particle morphology and enhancing powder dispersibility was evaluated at different lipid mass fractions (5%, 10%, 25%, 50%) and compared with that of several previously published shell-forming excipients at their effective mass fractions, i.e., 5% trileucine, 20% leucine, and 40% pullulan. A strong dependence of particle morphology on the lipid mass fraction was observed. Particles transitioned from typical smooth spherical trehalose particles without lipid to highly rugose microparticles at higher lipid mass fractions (>5%). In vitro aerosol performance testing demonstrated a significant improvement of powder dispersibility even at lipid mass fractions as low as 5%. Powder formulations with excellent aerosol performance comparable to those modified with leucine and trileucine were achieved at higher lipid mass fractions (>25%). A model biologic-containing formulation with 35% myoglobin, 35% glass stabilizer (trehalose), and 30% lipid shell former was shown to produce highly rugose particle structure as designed and excellent aerosol performance for efficient pulmonary delivery. A short-term stability at 40 °C proved that this protein-containing formulation had good thermal stability as designed. The results demonstrated great potential for the new lipid microparticle as a platform for the delivery of both small-molecule APIs and large-molecule biologics to the lung.

In Cellulo and In Vivo Comparison of Cholesterol, Beta-Sitosterol and Dioleylphosphatidylethanolamine for Lipid Nanoparticle Formulation of mRNA.

Lipid Nanoparticles (LNPs) are a leading class of mRNA delivery systems. LNPs are made of an ionizable lipid, a polyethyleneglycol (PEG)-lipid conjugate and helper lipids. The success of LNPs is due to proprietary ionizable lipids and appropriate helper lipids. Using a benchmark lipid (D-Lin-MC3) we compared the ability of three helper lipids to transfect dendritic cells in cellulo and in vivo. Studies revealed that the choice of helper lipid does not influence the transfection efficiency of immortalized cells but, LNPs prepared with DOPE (dioleylphosphatidylethanolamine) and β-sitosterol were more efficient for mRNA transfection in murine dendritic cells than LNPs containing DSPC (distearoylphosphatidylcholine). This higher potency of DOPE and β-sitosterol LNPs for mRNA expression was also evident in vivo but only at low mRNA doses. Overall, these data provide valuable insight for the design of novel mRNA LNP vaccines.

Science, Medicine, and the Anesthesiologist

Science, Medicine, and the Anesthesiologist

Liposomal Formulation for Oral Delivery of Cyclosporine A: Usefulness as a Semisolid-Dispersion System.

This study aims to understand the process and mechanism of oral drug absorption from liposomes and to verify the usefulness of liposomal formulation for poorly soluble drugs. Cyclosporine A (CsA) was used as a model drug and entrapped into Dipalmitoylphosphatidylcholine (DPPC) and distearoylphosphatidylcholine (DSPC) liposomes. Molecular state of CsA in the liposomes was analyzed using powder X-ray diffraction (PXRD) and polarized light microscopy (PLM). Release profiles of CsA from liposomes were observed in fasted state simulated intestinal fluid (FaSSIF). Oral absorption of CsA from liposomal formulations were investigated in rats. PXRD and PLM analyses suggested that CsA exists in the lipid layer of liposomes as a molecular dispersed state. Although both liposomes retained CsA stably in the simple buffer, DPPC liposomes quickly released CsA within 10min in FaSSIF due to the interaction with bile acid. In contrast, effect of bile acid was negligible in DSPC, indicating a high resistivity to membrane perturbation. Oral bioavailability of CsA from liposomal formulations were almost comparable with that from a marketed product (Neoral). However, the absorption profiles were clearly different. CsA was absorbed quickly from DPPC liposomes and Neoral, while sustained absorption profile was observed from DSPC liposomes. Further study in which ritonavir was co-entrapped in the liposomes with CsA showed the higher efficacy of ritonavir to increase oral bioavailability of CsA. Liposomes allows the appropriate formulation design for oral delivery of poorly soluble drugs, not only to increase the extent but also to control the rate of absorption.

Apolipoprotein E Binding Drives Structural and Compositional Rearrangement of mRNA-Containing Lipid Nanoparticles.

Emerging therapeutic treatments based on the production of proteins by delivering mRNA have become increasingly important in recent times. While lipid nanoparticles (LNPs) are approved vehicles for small interfering RNA delivery, there are still challenges to use this formulation for mRNA delivery. LNPs are typically a mixture of a cationic lipid, distearoylphosphatidylcholine (DSPC), cholesterol, and a PEG-lipid. The structural characterization of mRNA-containing LNPs (mRNA-LNPs) is crucial for a full understanding of the way in which they function, but this information alone is not enough to predict their fate upon entering the bloodstream. The biodistribution and cellular uptake of LNPs are affected by their surface composition as well as by the extracellular proteins present at the site of LNP administration, e.g., apolipoproteinE (ApoE). ApoE, being responsible for fat transport in the body, plays a key role in the LNP’s plasma circulation time. In this work, we use small-angle neutron scattering, together with selective lipid, cholesterol, and solvent deuteration, to elucidate the structure of the LNP and the distribution of the lipid components in the absence and the presence of ApoE. While DSPC and cholesterol are found to be enriched at the surface of the LNPs in buffer, binding of ApoE induces a redistribution of the lipids at the shell and the core, which also impacts the LNP internal structure, causing release of mRNA. The rearrangement of LNP components upon ApoE incubation is discussed in terms of potential relevance to LNP endosomal escape.

Screening and enhancement of the antimicrobial activity of some plant oils using liposomes as nanoscale carrier

BackgroundLiposomes have the ability to enclose hydrophilic or lipophilic materials. Bioactive macromolecules become more stable when they are entrapped within liposomes resisting environmental changes, allowing maintenance of the antimicrobial molecules and increasing their effectiveness and constancy thus can be used for food preservation. The aim of this study was to screen food samples for microbial contamination and to examine the antimicrobial activity of selected six ready-made plant oils which were; clove, black seed, thyme, garlic, rosemary and green tea against the isolated microbes from food samples and other selected microbes. Also to examine the possible enhancement of the antibacterial property of clove oil and tetracycline versus Escherichia coli when they were encapsulated into distearoyl phosphatidylcholine (DSPC) liposomes as a nanoscale carriers. Results of the antimicrobial action measured by minimum inhibitory concentration revealed that all six oils had antimicrobial action when facing at least one of the tested microbes. However only clove oil could inhibit the growth of all tested microbes. Moreover encapsulation of clove oil into DSPC liposomes enhanced its antibacterial action by 10 times when examined to inhibit the growth of E. coli. Also the antibacterial activity of liposome encapsulated tetracycline was improved by 8 times. Results of characterization of formulated clove oil liposomes by measuring their Zeta potential and their sizes implying that clove oil might be enclosed within the hydrophobic portion of the two layers of the liposome. Analyzing data of Fourier Transform Infrared Spectroscopy showed that clove oil was detected in the interfacial area of the liposome. Analyzing results of Differential scanning calorimetry and measuring phase transitions suggested that liposomes encapsulating clove oil had a membrane fluidization effect.ConclusionSome plant oils like clove has antimicrobial activity which enhanced with liposomal encapsulation and thus reduces the needed concentration to give the desired actions.

An in vitro evaluation of antitumor activity of sirolimus-encapsulated liposomes in breast cancer cells.

Design and examine the effect of sirolimus-PEGylated (Stealth) liposomes for breast cancer treatment. In this study, we developed conventional and Stealth liposome nanoparticles comprising of distearoylphosphatidylcholine (DSPC) or dipalmitoyl-phosphatidylcholine (DPPC) and DSPE-MPEG-2000 lipids loaded with sirolimus as an anticancer agent. The effect of lipid grade, drug loading and incubation times were evaluated. Particle size distribution, encapsulation efficiency of conventional and Stealth liposomes were studied followed by cytotoxicity evaluation. The cellular uptake and internal localisation of liposome formulations were investigated using confocal microscopy. The designed Stealth liposome formulations loaded with sirolimus demonstrated an effective in vitro anticancer therapy compared with conventional liposomes while the length of the acyl chain affected the cell viability. Anticancer activity was found to be related on the drug loading amounts and incubation times. Cell internalization was observed after 5 h while significant cellular uptake of liposome was detected after 24 h with liposome particles been located in the cytoplasm round the cell nucleus. Sirolimus Stealth liposomes induced cell apoptosis. The design and evaluation of sirolimus-loaded PEGylated liposome nanoparticles demonstrated their capacity as drug delivery carrier for the treatment of breast cancer tumours.

Pulse Magnetic Fields Induced Drug Release from Gold Coated Magnetic Nanoparticle Decorated Liposomes

Magnetic nanoparticle-assisted drug release from liposomes is an important way to enhance the functionality/usefulness of liposomes. This work demonstrates an approach how to integrate magnetic nanoparticles with liposomes with the assistance of gold–thiol chemistry. The gold coated magnetic particles cover the thiolated liposomes from the outside, which removes the competition of the drug molecules and the triggering magnetic particles to free the inner space of the liposomes when compared to previous magneto liposome formulations. The liposome consists of dipalmitoyl phosphatidylcholine (DPPC) combined with distearoylphosphatidylcholine (DSPC) in addition to regular cholesterol or cholesterol-PEG-SH. Permeability assays and electron microscopy images show efficient coupling between the liposomes and nanoparticles in the presence of thiol groups without compromising the functionality of the liposomes. The nanoparticles such as gold nanoparticles, gold coated iron oxide nanoparticles and bare iron oxide nanoparticles are added following the model drug encapsulation. The efficient coupling between the gold coated nanoparticles (NPs) and the thiolate liposomes is evidenced by the shift in transition temperature of the thiolated liposomes. The addition of magnetically triggerable nanoparticles externally makes the entire interior of liposomes available for drug loading. The drug release efficiencies of these liposomes/NPs complexes were compared under exposure to pulsed magnetic fields. The results indicate up to 20% of the drug can be released in short time, which is comparable in efficiency to previous studies performed when magnetic NPs were located inside liposomes. Interestingly, the liposomes were found to exhibit variations in release efficiency based on different dilution media which is attributed to an osmotic pressure effect on liposomal stability.

Targeted Ultrasound Contrast Imaging of Tumor Vasculature With Positively Charged Microbubbles.

Molecular ultrasound imaging of tumor vasculature is being actively investigated with microbubble contrast agents targeted to neovasculature biomarkers. Yet, a universal method of targeting tumor vasculature independent of specific biomarkers, or in their absence, would be desirable. We report the use of electrostatic interaction to achieve adherence of microbubbles to tumor vasculature and resulting tumor delineation by ultrasound imaging. Microbubbles were prepared from decafluorobutane gas by amalgamation of aqueous micellar medium. Distearoyl phosphatidylcholine (DSPC) and polyethylene glycol (PEG)-stearate were used as microbubble shell-forming lipids; cationic lipid distearoyl trimethylammoniumpropane (DSTAP) was included to introduce positive electrostatic charge. Microbubbles were subjected to flotation in normal gravity, to remove larger particles. Murine colon adenocarcinoma tumor (MC38, J. Schlom, National Institutes of Health) was inoculated in the hind leg of C57BL/6 mice. Contrast ultrasound imaging was performed under isoflurane anesthesia, using a clinical imaging system in low power mode, with tissue signal suppression (contrast pulse sequencing, 7 MHz, 1 Hz; Mechanical Index, 0.2). The ultrasound probe was positioned to monitor the tumor and contralateral leg muscle; microbubble contrast signal was monitored for 30 minutes or more, after intravenous bolus administration of 2.10 microbubbles. Individual time point frames were extracted from ultrasound video recording and analyzed with ImageJ. Mean bubble diameter was ~1.6 to 2 μm; 99.9% were less than 5 μm, to prevent blocking blood flow in capillaries. For cationic DSTAP-carrying microbubbles, contrast signal was observed in the tumor beyond 30 minutes after injection. As the fraction of positively charged lipid in the bubble shell was increased, adherent contrast signal in the tumor also increased, but accumulation of DSTAP-microbubbles in the normal muscle increased as well. For bubbles with the highest positive charge tested, DSTAP-DSPC molar ratio 1:4, at 10 minutes after intravenous administration of microbubbles, the contrast signal difference between the tumor and normal muscle was 1.5 (P < 0.005). At 30 minutes, tumor/muscle contrast signal ratio improved and reached 2.1. For the DSTAP-DSPC 1:13 preparation, tumor/muscle signal ratio exceeded 3.6 at 10 minutes and reached 5.4 at 30 minutes. Microbubbles with DSTAP-DSPC ratio 1:22 were optimal for tumor targeting: at 10 minutes, tumor/muscle signal ratio was greater than 7 (P < 0.005); at 30 minutes, greater than 16 (P < 0.01), sufficient for tumor delineation. Cationic microbubbles are easy to prepare. They selectively accumulate in the tumor vasculature after intravenous administration. These microbubbles provide target-to-control contrast ratio that can exceed an order of magnitude. Adherent microbubbles delineate the tumor mass at extended time points, at 30 minutes and beyond. This may allow for an extension of the contrast ultrasound examination time. Overall, positively charged microbubbles could become a universal ultrasound contrast agent for cancer imaging.

Ultrasound Responsive Noble Gas Microbubbles for Applications in Image-Guided Gas Delivery.

Noble gases, especially xenon (Xe), have been shown to have antiapoptotic effects in treating hypoxia ischemia related injuries. Currently, in vivo gas delivery is systemic and performed through inhalation, leading to reduced efficacy at the injury site. This report provides a first demonstration of the encapsulation of pure Xe, Ar, or He in phospholipid-coated sub-10 µm microbubbles, without the necessity of stabilizing perfluorocarbon additives. Optimization of shell compositions and preparation techniques show that distearoylphosphatidylcholine (DSPC) with DSPE-PEG5000 can produce stable microbubbles upon shaking, while dibehenoylphosphatidylcholine (DBPC) blended with either DSPE-PEG2000 or DSPE-PEG5000 produces a high yield of microbubbles via a sonication/centrifugation method. Xe and Ar concentrations released into the microbubble suspension headspace are measured using GC-MS, while Xe released directly in solution is detected by the fluorescence quenching of a Xe-sensitive cryptophane molecule. Bubble production is found to be amenable to scale-up while maintaining their size distribution and stability. Excellent ultrasound contrast is observed in a phantom for several minutes under physiological conditions, while an intravenous administration of a bolus of pure Xe microbubbles provides significant contrast in a mouse in pre- and post-lung settings (heart and kidney, respectively), paving the way for image-guided, localized gas delivery for theranostic applications.

Examining Tail and Headgroup Effects on Binary and Ternary Gel-Phase Lipid Bilayer Structure.

The structural properties of two- and three-component gel-phase bilayers were studied using molecular dynamics simulations. The bilayers contain distearoylphosphatidylcholine (DSPC) phospholipids mixed with alcohols and/or fatty acids of varying tail lengths, with carbon chain lengths of 12, 16, and 24 studied. Changes in both headgroup chemistry and tail length are found to affect the balance between steric repulsion and van der Waals attraction within the bilayers, manifesting in different bilayer structural properties. Lipid components are found to be located at different depths within the bilayer depending on both chain length and headgroup chemistry. The highest bilayer ordering and lowest area per tail are found in systems with medium-length tails. While longer tails can enhance van der Waals attractions, the increased tail-length asymmetry is found to induce disorder and reduce tail packing. Bulkier headgroups further increase steric repulsion, as reflected in increased component offsets and reduced tail packing. These findings help explain how bilayer composition affects the structure of gel-phase bilayers.

Simultaneous encapsulation of hydrophilic and lipophilic molecules in liposomes of DSPC

This study shows simultaneous incorporation of two hydrophobic molecules and a hydrophilic molecule into distearoylphosphatidylcholine (DSPC) liposomes. Pinocembrin and cholesterol are incorporated in the lipidic membrane while resazurin is encapsulated in the aqueous center. The thermotropic behavior of liposomes as a function of the additives was studied with differential scanning calorimetry and the morphology was observed by SEM. A high percentage of entrapment was found for different concentrations of pinocembrin. Cholesterol does not interfere with the incorporation efficiency of pinocembrin and improves the distribution in the membrane but decreases the dissolution stability of liposomes due to steric hindrance in the bilayer. Encapsulation efficiency of resazurin was close to 50%. This molecule also interacts with the polar heads of the phospholipids. This research offers an alternative formulation by using DSPC liposomes as carrier of molecules with different polarity to evaluate the cytotoxicity of pinocembrin in cancer cell lines.