Development and In Vitro Characterization of Liposomes Coated with Thiolated Poly(Acrylic Acid) for Oral Drug Delivery

Mucoadhesive drug delivery systems offer promising opportunities for oral drug delivery. The aim of this study was to investigate the feasibility of preparing liposomes that are coated with the multifunctional polymer poly(acrylic acid)-cysteine (PAA-Cys). Cationic multilamellar vesicles (MLV) as well as cationic submicron-sized liposomes (ssLip) were prepared and coated with PAA-Cys. Size, zeta potential, amount of free thiol groups, aggregation behavior, drug-loading, and drug release of these novel carriers were evaluated. A switch of the initial positive zeta potential to a negative value after coating indicated the successful coating procedure. In both size ranges, MLV and ssLip, the amount of free thiol groups was comparable to that in a PAA-Cys solution of the same concentration. Drug loading of the hydrophilic marker fluorescence-isothiocyanate 4 kDa (FD4) was higher in PAA-Cys liposomes in comparison to noncoated liposomes, but lower in comparison to liposomes coated with unmodified poly(acrylic acid) (PAA). Only a minor ssLip or no increase MLV of the drug-loading was observed when using carboxyfluorescein (CF). These effects were attributed to interactions between the markers and the poly(acrylates). Coating of liposomes with PAA-Cys and PAA did not influence the release profile of FD4 and CF, whereas the release profile was affected by the molecular mass of the marker and the liposome size. In conclusion, the feasibility of coating liposomes with PAA-Cys was demonstrated, and it could be shown that this novel carrier system fulfills the basic requirements for an intended use in oral drug delivery.     

Reconstitution of Membrane Proteins into Model Membranes: Seeking Better Ways to Retain Protein Activities

The function of any given biological membrane is determined largely by the specific set of integral membrane proteins embedded in it, and the peripheral membrane proteins attached to the membrane surface. The activity of these proteins, in turn, can be modulated by the phospholipid composition of the membrane. The reconstitution of membrane proteins into a model membrane allows investigation of individual features and activities of a given cell membrane component. However, the activity of membrane proteins is often difficult to sustain following reconstitution, since the composition of the model phospholipid bilayer differs from that of the native cell membrane. This review will discuss the reconstitution of membrane protein activities in four different types of model membrane—monolayers, supported lipid bilayers, liposomes and nanodiscs, comparing their advantages in membrane protein reconstitution. Variation in the surrounding model environments for these four different types of membrane layer can affect the three-dimensional structure of reconstituted proteins and may possibly lead to loss of the proteins activity. We also discuss examples where the same membrane proteins have been successfully reconstituted into two or more model membrane systems with comparison of the observed activity in each system. Understanding of the behavioral changes for proteins in model membrane systems after membrane reconstitution is often a prerequisite to protein research. It is essential to find better solutions for retaining membrane protein activities for measurement and characterization in vitro.     

Effect of Liposome Size on Internal RNA Replication Coupled with Replicase Translation

Cell membranes inhibit the diffusion of intracellular materials, and compartment size can strongly affect the intracellular biochemical reactions. To assess the effect of the size of microcompartments on intracellular reactions, we constructed a primitive cell model consisting of giant liposomes and a translation‐coupled RNA replication (TcRR) system. The RNA was replicated by Qβ replicase, which was translated from the RNA in giant liposomes encapsulating the cell‐free translation system. A reporter RNA encoding the antisense strand of β‐glucuronidase was introduced into the system to yield a TcRR read‐out (green fluorescence). We demonstrate that TcRR was hardly detectable in larger liposomes (230 fL) but was more effective in smaller (7.7 fL) liposomes. Our experimental and theoretical results show that smaller microcompartments considerably enhance TcRR because the synthesized molecules, such as RNA and replicases, are more concentrated in smaller liposomes.     

Thrombin‐Inhibiting Anticoagulant Liposomes: Development and Characterization

Many peptides and peptidomimetic drugs suffer from rapid clearance in vivo; this can be reduced by increasing their size through oligomerization or covalent conjugation with polymers. As proof of principle, an alternative strategy for drug oligomerization is described, in which peptidomimetic thrombin inhibitors are incorporated into the liposome surface. For this purpose, the inhibitor moieties were covalently coupled to a palmitic acid residue through a short bifunctionalized ethylene glycol spacer. These molecules were directly added to the lipid mixture used for liposome preparation. The obtained liposomes possess strong thrombin inhibitory potency in enzyme kinetic measurements and anticoagulant activity in plasma. Their strong potency and positive ζ potential indicate that large amounts of the benzamidine‐derived inhibitors are located on the surface of the liposomes. This concept should be applicable to other drug molecules that suffer from rapid elimination and allow covalent modification with a suitable fatty acid residue.     

Colorimetric Detection of Warfare Gases by Polydiacetylenes Toward Equipment‐Free Detection

Rationally designed polydiacetylene (PDA) molecules have been developed for rapid, selective, sensitive, and convenient colorimetric detection of organophosphate (OP) nerve agents, a mass destruction weapon. Oxime (OX) functionality was incorporated into diacetylene molecules to utilize its strong affinity toward organophosphates. The diacetylene molecules having an OX functional group (OX‐PDA) were self‐assembled to form PDA liposomes in an aqueous solution. Upon exposure to organophosphate nerve agent simulants, OX at the OX‐PDA liposome surface interacts with nerve agent simulants, which results in intraliposomal repulsive stress due to steric repulsion between OP‐occupied OX units at the liposome surface as well as interliposomal aggregation induced by increased hydrophobicity of the liposome surface via OP‐OX complex formation. The resulting intra‐ and interliposomal stress causes disturbance of the conjugated backbone of OX‐PDA, producing color change as a label‐free and sensitive sensory signal. The effects of molecular structure on selectivity and sensitivity of OX‐PDA liposome solution, OX‐PDA liposome‐embedded agarose gels, and OX‐PDA liposome‐coated cellulose acetate membranes were systematically investigated. The optimized OX‐PDA liposome in the solid state showed selective and rapid optical transition upon exposure down to 160 ppb of diisopropylfluorophosphate (DFP), a nerve agent simulant. The results provide an insightful molecular design principle of PDA‐based colorimetric sensor and suggest portable sensory patches for rapid, selective, sensitive, and convenient colorimetric detection of organophosphate nerve agents.     

Monitoring of the microcapsule/liposome application on textile fabrics

In recent years, new technologies have led to the production of biofunctional textiles. These biofunctional textiles contain microscopic capsules of ingredients that break as the fabric rubs the skin, releasing the active agents. Absorption and desorption behaviour of active agents embedded into the different biofunctional textiles should be taken into account when determining the amount of active agents incorporated into these textiles and when following the delivery mechanism as the fabric comes in contact with the skin. In this work, an encapsulated active agent (a sun filter, ethyl hexyl methoxycinnamate [EHMC] into microcapsules or liposomes) was applied by foulard onto different fabrics. The amount of capsules and active agents embedded into the fibres were quantified by (1) weight difference between untreated and treated fabrics, (2) extraction with isopropanol in an ultrasound bath, or (3) extraction with isopropanol/water 50/50 in a soxhlet device. Sun filter detection of the extraction baths was followed by HPLC and by UV spectrophotometry. The results show that the real amount of the EHMC present in different textile substrates depends on the way that the active agent is trapped, the ionic character of the fibres and on the vehicles used.     

Silica fluorescent nanospheres containing a large amount of quantum dots prepared using liposomes as templates

Quantum dot (QD) fluorescent spheres have captivated many scientists because of their many potential applications in biomedical research. In this work, QD nanospheres were prepared using a novel method: incorporating QDs into nano-liposomes and then synthesising a silica shell using a lipid membrane as the template. The results showed that the nanocomposites obtained were spherical in shape, and each nanosphere contained a silica shell and the cores consisted of a large amount of QDs. Ultrathin sections of the spheres showed that the thickness of the silica shell was about 50–60?nm. Because the QD cores were coated with liposome and thick silica shell, the bright field of the silica sphere suspension was close to milk white in colour, which was different from that of the red-coloured QD solution. Although the quantum yield of the silica spheres (2.27%) was lower than that of the QDs (23.52%), these nanospheres still emitted a bright fluorescence, and there was no obvious difference between the fluorescent colour of the nanosphere suspension and the QD solution.     

盐酸米托蒽醌多囊脂质体的制备工艺优化及性能

采用均匀设计优化并制备了平均粒径为58.75 μm的载盐酸米托蒽醌多囊脂质体。该多囊脂质体粒度分布较窄,球形度好。Zeta电位、相变温度及稳定性考察均表明该体系稳定性强,适于药物的释放体系。渗漏率结果表明相对于室温（37 ℃）,冰箱（4 ℃）更有利于载药多囊脂质体的保存。盐酸米托蒽醌平均包封率为90.13%,考察了胆固醇及三油酸甘油酯用量对多囊脂质体药物释放的影响,药物释放符合《药典》规定,无突释效应,且具有较好的体外缓释性能。     

前列腺素E_1冻干隐形脂质体包封率的测定

目的评价前列腺素E1(PGE1)冻干隐形脂质体的质量,测定PGE1冻干隐形脂质体的包封率.方法用超滤法分离脂质体和游离药物;采用Hypersil C18柱(250 mm×4.6 mm,5μm),流动相:pH 4.9的磷酸二氢钾溶液.乙腈(3:2),流速1.0 mL·min-1,检测波长210 nm,测定药物含量,计算包封率.结果超滤法能很好的分离脂质体与游离药物,PGE1在1～50 mg·L-1内线性关系良好(r=0.999 3),平均包封率为93.02%.结论超滤-HPLC法测定PGE1冻干隐形脂质体包封率方法简便、准确.