Screening for Optimal Liposome Preparation Conditions by Using Dual Centrifugation and Time-Resolved Fluorescence Measurements

Dual centrifugation (DC) is a novel in-vial homogenization technique for the preparation of liposomes in small batch sizes under gentle and sterile conditions which allows encapsulation efficiencies (EE) for water soluble compounds of >50%. Since liposome size, size distribution (PDI), and EE depend on the lipid concentration used in the DC process, a screening method to find optimal lipid concentrations for a defined lipid composition was developed. Four lipid mixtures consisting of cholesterol, hydrogenated or non-hydrogenated egg PC, and/or PEG-DSPE were screened and suitable concentration ranges could be identified for optimal DC homogenization. In addition to the very fast and parallel liposome preparation of up to 40 samples, the screening process was further accelerated by the finding that DC generates homogeneously mixed liposomes from a macroscopic lipid mixture without the need to initially prepare a molecularly mixed lipid film from an organic solution of all components. This much simpler procedure even works for cholesterol containing lipid blends, which could be explained by a nano-milling of the cholesterol crystals during DC homogenization. Furthermore, EE determination was performed by time-resolved fluorescence measurements of calcein-loaded liposomes without removing the non-entrapped calcein. The new strategy allows the rapid characterization of a certain lipid composition for the preparation of liposomes within a working day.

Electrospun Amphiphilic Nanofibers as Templates for In Situ Preparation of Chloramphenicol-Loaded Liposomes

The hydration of phospholipids, electrospun into polymeric nanofibers and used as templates for liposome formation, offers pharmaceutical advantages as it avoids the storage of liposomes as aqueous dispersions. The objective of the present study was to electrospin and characterize amphiphilic nanofibers as templates for the preparation of antibiotic-loaded liposomes and compare this method with the conventional film-hydration method followed by extrusion. The comparison was based on particle size, encapsulation efficiency and drug-release behavior. Chloramphenicol (CAM) was used at different concentrations as a model antibacterial drug. Phosphatidylcoline (PC) with polyvinylpyrrolidone (PVP), using ethanol as a solvent, was found to be successful in fabricating the amphiphilic composite drug-loaded nanofibers as well as liposomes with both methods. The characterization of the nanofiber templates revealed that fiber diameter did not affect the liposome size. According to the optical microscopy results, the immediate hydration of phospholipids deposited on the amphiphilic nanofibers occurred within a few seconds, resulting in the formation of liposomes in water dispersions. The liposomes appeared to aggregate more readily in the concentrated than in the diluted solutions. The drug encapsulation efficiency for the fiber-hydrated liposomes varied between 14.9 and 28.1% and, for film-hydrated liposomes, between 22.0 and 77.1%, depending on the CAM concentrations and additional extrusion steps. The nanofiber hydration method was faster, as less steps were required for the in-situ liposome preparation than in the film-hydration method. The liposomes obtained using nanofiber hydration were smaller and more homogeneous than the conventional liposomes, but less drug was encapsulated.

Advances in Chemical Constituents, Clinical Applications, Pharmacology, Pharmacokinetics and Toxicology of Erigeron breviscapus

Dengzhanxixin (DZXX), the dried whole plant of Erigeron breviscapus (Vaniot) Hand.-Mazz., belonging to Compositae and first published in Materia Medica of South Yunnan by Lan Mao in the Ming Dynasty (1368 AD–1644 AD), is included in Medicinal Materials and Decoction Pieces of the 2020 edition of the Pharmacopeia of the People’s Republic of China. Its main chemical components are flavonoids that mainly include flavonoid, flavonols, dihydroflavones, flavonol glycosides, flavonoid glycosides, coffee acyl compounds, and other substances, such as volatile oil compounds, coumarins, aromatic acids, pentacyclic terpenoids, phytosterols, and xanthones. Among them, scutellarin and 1,5-dicoffeoylquininic acid are the main active components of DZXX. DZXX has pharmacological effects, such as improving cerebral and cerebrovascular ischemia, increasing blood flow, inhibiting platelet aggregation, promoting antithrombotic formation, improving microcirculation, reducing blood viscosity, protecting optic nerves, exhibiting anti-inflammatory properties, scavenging free radicals, and eliciting antioxidant activities. It is widely used in the treatment of cardiovascular and cerebrovascular ischemic diseases, kidney diseases, liver diseases, diabetic complications, and glaucoma. Pharmacokinetic studies have shown that the active components of DZXX have a low bioavailability and a high elimination rate in vivo. Nevertheless, its utilization can be improved through liposome preparation and combination with other drugs. Acute and subacute toxicity studies have shown that DZXX is a safe medicinal material widely used in clinical settings. However, its target and drug action mechanism are unclear because of the complexity of its composition. In this paper, the clinical application and pharmacological toxicology of DZXX are reviewed to provide a reference for further studying its active components and action mechanism.

Applying TADF Emitters in Bioimaging and Sensing—A Novel Approach Using Liposomes for Encapsulation and Cellular Uptake

A new method for facilitating the delivery, uptake and intracellular localisation of thermally activated delayed fluorescence (TADF) complexes was developed. First, confinement of TADF complexes in liposomes was demonstrated, which were subsequently used as the delivery vehicle for cellular uptake. Confocal fluorescence microscopy showed TADF complexes subsequently localise in the cytoplasm of HepG2 cells. The procedures developed in this work included the removal of molecular oxygen in the liposome preparation without disrupting the liposome structures. Time-resolved fluorescence microscopy (point scanning) showed initial prompt fluorescence followed by a weak, but detectable, delayed fluorescence component for liposomal TADF internalised in HepG2 cells. By demonstrating that it is possible to deliver un-functionalised and/or unshielded TADF complexes, a sensing function for TADFs, such as molecular oxygen, can be envisaged.

Manufacturing of Liposomes: A Direct Comparison of Extrusion and Microfluidics Protocols

Liposomal formulations are frequently used for oral, topical, or parenteral drug administration. However, liposome manufacturing and industrial scale-up remains a challenge, in particular if it comes to the preparation of liposome populations with a homogenous size distribution. Therefore, extrusion through filter membranes with defined pore size is traditionally used during the preparation of small unilamellar liposomes. Microfluidics is considered to be an alternative manufacturing method. Lipids, solvents and excipients are thereby passively mixed using a microfluidics device. While the microfluidic approach is highly scalable, most of the traditional liposome preparation protocols rely on extrusion. It was therefore the aim of the present study to compare liposomal formulations with identical composition, which were prepared using either extrusion or microfluidics protocols. Liposomal formulations produced by both methods were analyzed using dynamic light scattering (DLS) to compare size, polydispersity, and ζ-potential. Our results indicate significant differences between liposomal preparations obtained using the two manufacturing methods. We conclude that the two preparation methods should not be used interchangeably.<br>

Manufacturing of Liposomes: A Direct Comparison of Extrusion and Microfluidics Protocols

Liposomal formulations are frequently used for oral, topical, or parenteral drug administration. However, liposome manufacturing and industrial scale-up remains a challenge, in particular if it comes to the preparation of liposome populations with a homogenous size distribution. Therefore, extrusion through filter membranes with defined pore size is traditionally used during the preparation of small unilamellar liposomes. Microfluidics is considered to be an alternative manufacturing method. Lipids, solvents and excipients are thereby passively mixed using a microfluidics device. While the microfluidic approach is highly scalable, most of the traditional liposome preparation protocols rely on extrusion. It was therefore the aim of the present study to compare liposomal formulations with identical composition, which were prepared using either extrusion or microfluidics protocols. Liposomal formulations produced by both methods were analyzed using dynamic light scattering (DLS) to compare size, polydispersity, and ζ-potential. Our results indicate significant differences between liposomal preparations obtained using the two manufacturing methods. We conclude that the two preparation methods should not be used interchangeably.<br>

Formulation, Characterization and In vitro Drug Delivery of Vitexin Loaded Liposomes

Liposome is a spherical vesicle which contains atleast one lipid bilayer. Liposomes are used as a novel drug carriers because of its hydrophobic and hydrophilic nature, it has many advantages in the field of medical sciences. There are some other drug carriers like dendrimers, micelles, niosomes. Out of all, liposomes are considered to be the most promising agent for drug delivery. The uniqueness of liposome is when it is used as a pharmaceutical drug, it acts as a natural receptor. Thus it acts as an antigen and binds with the antibody (cancer cell) without causing any damage to the adjacent cells. For the synthesis of liposomes, a phospholipid is required. The liposomes can be synthesized using egg yolk and chloroform. So the basic phospholipid is obtained from egg yolk. For more stability, the liposomes are prepared using popc. The present work discuss about the effective preparation of drug loaded liposomes using popc (1- palmitoyl-2-oleoyl-sn-glycero-3- phosphocholine). POPC is an important phospholipid for biophysical experiments. Additionally chloroform is used as the solvent for the liposome preparation. The drug chosen for liposome loading is vitexin (vxn), which is an effective therapeutic agent against inflammation and cancer. The vesicular size, shape, drug entrapment efficacy, stability, electrochemical property and drug releasing property of the formulated liposomes were characterized. The results showed that the formulated liposomes are considered as the better drug carrier system and good choice for biotransformation within the cell to reach the target site such as cancer cells. Even though available treatments like chemotherapy and radiation therapy, causes damage to the surrounding cells, the alternative drug transferring system such as liposomal mediated drug transfer within the cell is considered as good choice of treatment to avoid such complications. The aim of liposome mediated drug carrier system is to develop a method to reach the drug to the target site. After drug delivery at the target site, the liposomes are fused within the surface of the body. This is because of the pH of liposomes, which is at 7.4 and temperature is maintained at 37 oC. So, the vxn loaded liposomes are considered as the novel drug carriers for the successful targetted drug delivery.

Recent Advancements in Polymer/Liposome Assembly for Drug Delivery: From Surface Modifications to Hybrid Vesicles

Liposomes are consolidated and attractive biomimetic nanocarriers widely used in the field of drug delivery. The structural versatility of liposomes has been exploited for the development of various carriers for the topical or systemic delivery of drugs and bioactive molecules, with the possibility of increasing their bioavailability and stability, and modulating and directing their release, while limiting the side effects at the same time. Nevertheless, first-generation vesicles suffer from some limitations including physical instability, short in vivo circulation lifetime, reduced payload, uncontrolled release properties, and low targeting abilities. Therefore, liposome preparation technology soon took advantage of the possibility of improving vesicle performance using both natural and synthetic polymers. Polymers can easily be synthesized in a controlled manner over a wide range of molecular weights and in a low dispersity range. Their properties are widely tunable and therefore allow the low chemical versatility typical of lipids to be overcome. Moreover, depending on their structure, polymers can be used to create a simple covering on the liposome surface or to intercalate in the phospholipid bilayer to give rise to real hybrid structures. This review illustrates the main strategies implemented in the field of polymer/liposome assembly for drug delivery, with a look at the most recent publications without neglecting basic concepts for a simple and complete understanding by the reader.