Limits in Size of Taylor Dispersion Analysis: Representation of the Different Hydrodynamic Regimes and Application to the Size-Characterization of Cubosomes

Taylor dispersion analysis (TDA) is an absolute method (no calibration needed) for the determination of the molecular diffusion coefficient (<i>D</i>) based on the band broadening of a solute in a laminar flow. TDA is virtually applicable to any solute with size ranging from angstrom to sub-micrometer. The higher sizing limit is restricted by the occurrence of possibly two regimes: convective and hydrodynamic chromatography (HDC) regimes, which have different physical origins that should not be confused. This work aims at clearly defining the experimental conditions for which these two regimes can play a role, alone or concomitantly. It also calculates the relative error on <i>D</i> due to the HDC regime according to the solute to capillary size ratio. It is demonstrated in this work that HDC does not significantly affect the TDA measurement as long as the hydrodynamic radius of the solute is lower than 0.0051 times the capillary radius. Experimental illustrations of the occurrence of the two regimes are given taking polystyrene nanoparticles as model solutes. Finally, application of TDA to the sizing of large real-life solutes is proposed, taking cubosomes as new drug nanocarriers of potential interest for drug delivery purposes

UV–vis Imaging of Piroxicam Supersaturation, Precipitation, and Dissolution in a Flow-Through Setup

Evaluation of drug precipitation is important in order to address challenges regarding low and variable bioavailability of poorly water-soluble drugs, to assess potential risk of patient safety with infusion therapy, and to explore injectable in situ suspension-forming drug delivery systems. Generally, drug precipitation is assessed in vitro through solution concentration analysis methods. Dual-wavelength UV–vis imaging is a novel imaging technique that may provide an opportunity for simultaneously monitoring changes in both solution and solid phases during precipitation. In the present study, a multimodal approach integrating UV–vis imaging, light microscopy, and Raman spectroscopy was developed for characterization of piroxicam supersaturation, precipitation, and dissolution in a flow-through setup. A solution of piroxicam dissolved in 1-methyl-2-pyrrolidinone was injected into a flowing aqueous environment (pH 7.4), causing piroxicam to precipitate. Imaging at 405 and 280 nm monitored piroxicam concentration distributions during precipitation and revealed different supersaturation levels dependent on the initial concentration of the piroxicam solution. The combination with imaging at 525 nm, light microscopy, and Raman spectroscopy measurements demonstrated concentration-dependent precipitation and the formation, growth, and dissolution of individual particles. Results emphasize the importance of the specific hydrodynamic conditions on the piroxicam precipitation. The approach used may facilitate comprehensive understanding of drug precipitation and dissolution processes and may be developed further into a basic tool for formulation screening and development

UV–vis Imaging of Piroxicam Supersaturation, Precipitation, and Dissolution in a Flow-Through Setup

Evaluation of drug precipitation is important in order to address challenges regarding low and variable bioavailability of poorly water-soluble drugs, to assess potential risk of patient safety with infusion therapy, and to explore injectable in situ suspension-forming drug delivery systems. Generally, drug precipitation is assessed in vitro through solution concentration analysis methods. Dual-wavelength UV–vis imaging is a novel imaging technique that may provide an opportunity for simultaneously monitoring changes in both solution and solid phases during precipitation. In the present study, a multimodal approach integrating UV–vis imaging, light microscopy, and Raman spectroscopy was developed for characterization of piroxicam supersaturation, precipitation, and dissolution in a flow-through setup. A solution of piroxicam dissolved in 1-methyl-2-pyrrolidinone was injected into a flowing aqueous environment (pH 7.4), causing piroxicam to precipitate. Imaging at 405 and 280 nm monitored piroxicam concentration distributions during precipitation and revealed different supersaturation levels dependent on the initial concentration of the piroxicam solution. The combination with imaging at 525 nm, light microscopy, and Raman spectroscopy measurements demonstrated concentration-dependent precipitation and the formation, growth, and dissolution of individual particles. Results emphasize the importance of the specific hydrodynamic conditions on the piroxicam precipitation. The approach used may facilitate comprehensive understanding of drug precipitation and dissolution processes and may be developed further into a basic tool for formulation screening and development

Rapid Exchange of Metal between Zn₇–Metallothionein-3 and Amyloid-β Peptide Promotes Amyloid-Related Structural Changes

Metal ions, especially Zn²⁺ and Cu²⁺, are implemented in the neuropathogenesis of Alzheimer’s disease (AD) by modulating the aggregation of amyloid-β peptides (Aβ). Also, Cu²⁺ may promote AD neurotoxicity through production of reactive oxygen species (ROS). Impaired metal ion homeostasis is most likely the underlying cause of aberrant metal–Aβ interaction. Thus, focusing on the body’s natural protective mechanisms is an attractive therapeutic strategy for AD. The metalloprotein metallothionein-3 (MT-3) prevents Cu–Aβ-mediated cytotoxicity by a Zn–Cu exchange that terminates ROS production. Key questions about the metal exchange mechanisms remain unanswered, e.g., whether an Aβ–metal–MT-3 complex is formed. We studied the exchange of metal between Aβ and Zn₇–MT-3 by a combination of spectroscopy (absorption, fluorescence, thioflavin T assay, and nuclear magnetic resonance) and transmission electron microscopy. We found that the metal exchange occurs via free Cu²⁺ and that an Aβ–metal–MT-3 complex is not formed. This means that the metal exchange does not require specific recognition between Aβ and Zn₇–MT-3. Also, we found that the metal exchange caused amyloid-related structural and morphological changes in the resulting Zn–Aβ aggregates. A detailed model of the metal exchange mechanism is presented. This model could potentially be important in developing therapeutics with metal-protein attenuating properties in AD

Characterization of Oil-Free and Oil-Loaded Liquid-Crystalline Particles Stabilized by Negatively Charged Stabilizer Citrem

The present study was designed to evaluate the effect of the negatively charged food-grade emulsifier citrem on the internal nanostructures of oil-free and oil-loaded aqueous dispersions of phytantriol (PHYT) and glyceryl monooleate (GMO). To our knowledge, this is the first report in the literature on the utilization of this charged stabilizing agent in the formation of aqueous dispersions consisting of well-ordered interiors (either inverted-type hexagonal (H₂) phases or inverted-type microemulsion systems). Synchrotron small-angle X-ray scattering (SAXS) and cryogenic transmission electron microscopy (cryo-TEM) were used to characterize the dispersed and the corresponding nondispersed phases of inverted-type nonlamellar liquid-crystalline phases and microemulsions. The results suggest a transition between different internal nanostructures of the aqueous dispersions after the addition of the stabilizer. In addition to the main function of citrem as a stabilizer that adheres to the surface of the dispersed particles, it has a significant impact on the internal nanostructures, which is governed by the following factors: (1) its penetration between the hydrophobic tails of the lipid molecules and (2) its degree of incorporation into the lipid–water interfacial area. In the presence of citrem, the formation of aqueous dispersions with functionalized hydrophilic domains by the enlargement of the hydrophilic nanochannels of the internal H₂ phase in hexosomes and the hydrophilic core of the L₂ phase in emulsified microemulsions (EMEs) could be particularly attractive for solubilizing and controlling the release of positively charged drugs