Turbidity Spectroscopy for Characterization of Submicroscopic Drug Carriers, Such as Nanoparticles and Lipid Vesicles: Size Determination

Dataset on exposure conditions to Fe2O3 and SiO2 colloidal suspension and airborne particulate matter (PM) suspensions: crude NIST1648a and with reduced content of organic matter, LAp120

Particulate matter (PM) present in the air pollution increases morbidity and mortality due to several reasons. The dataset presents a comparative analysis of nebulization process of Fe2O3 and SiO2 nanoparticles or crude PM (NIST1648a) and that with reduced content of organic matter (LAp120). Nebulization tests were carried out to determine concentrations of nanoparticle and PM suspensions, in order to create an atmosphere with a concentration of PM particles about 1000 µg/m3 of air in the exposure chambers. It is important to properly recreate environmental conditions during further research on animals. The absorbance spectrum of the suspensions of the tested materials was measured in the range of 300-700 nm. The changes in the absorbance of these suspensions depending on the concentration after their passage through the nebulizers were examined. Based on the absorbance, it was determined to what extent the suspensions are passed out and dispersed by the nebulizers. The operating mode of the nebulizers and the concentration of suspensions were determined in order to establish the optimal exposure conditions and the microclimate of the chambers for further studies with mice. The dataset can help in optimization of nebulization process for all researchers exploring the further issue of the influence of the air pollution on the broadly understood animal functions, behavioral parameters and biochemical aspects.

Wavelength exponent based calibration for turbidity spectroscopy: Monitoring the particle size during emulsion polymerization reactions

Particle size and particle size distribution (PSD) are important properties of polymer latexes because they strongly affect the film formation and the rheological properties of the latexes. Thus, monitoring the particle size is of paramount importance during the production of waterborne polymeric dispersions, for which online/inline measurements of the particle size are required. Herein, turbidity spectroscopy (TUS) is used to measure the particle size of nanoparticles in dispersed media. Calibration curves based on a modified wavelength exponent method are introduced and assessed to monitor the evolution of a broad range of particle sizes in seeded semibatch emulsion polymerizations of methyl methacrylate, butyl acrylate, methacrylic acid (MMA/BA/MAA 51/47/2) terpolymers. It is shown that the wavelength exponent based calibration curves can be successfully used to retrieve the particle size during the polymerization process.

Self-Assembly of Flagellin into Immunostimulatory Ring-like Nanostructures as an Antigen Delivery System

Proteinaceous nanoparticles represent attractive antigen carriers for vaccination as their size and repetitive antigen displays that mimic most viral particles enable efficient immune processing. However, these nanocarriers are often unable to stimulate efficiently the innate immune system, requiring coadministration with adjuvants to promote long-lasting protective immunity. The protein flagellin, which constitutes the primary constituent of the bacterial flagellum, has been widely evaluated as an antigen carrier due to its intrinsic adjuvant properties involving activation of the innate immune receptor Toll-like receptor 5 (TLR5). Although flagellin is known for its ability to self-assemble into micron-scale length nanotubes, few studies have evaluated the potential usage of flagellin-based nanostructures as immunostimulatory antigen carriers. In this study, we reported for the first time a strategy to guide the self-assembly of a flagellin protein from Bacillus subtilis, Hag, into lower aspect ratio nanoparticles by hindering non-covalent interactions responsible for its elongation into nanotubes. We observed that addition of an antigenic sequence derived from the influenza A virus (3M2e) at the C-terminus of this flagellin, as opposed to positioning the epitope into mid-sequence, precluded filament elongation and resulted in low aspect ratio ring-like nanostructures upon salting-out-induced self-assembly. These nanostructures displayed the antigen at their surface and shared morphological and structural characteristics with flagellin nanotubes, with a diameter of approximately 12 nm, and an α-helix-rich secondary structure. Flagellin ring-like nanostructures were efficiently internalized by antigen-presenting cells, and avidly activated the TLR5 in vitro as well as the innate and adaptive immune responses. Intranasal immunization of mice with these nanostructures resulted in the potentiation of the antigen-specific antibody response and protection against a lethal infection with the influenza A virus, illustrating the potential of these intrinsically immunostimulatory nanostructures as antigen carriers.

Inhalable, Spray-Dried Terbinafine Microparticles for Management of Pulmonary Fungal Infections: Optimization of the Excipient Composition and Selection of an Inhalation Device

Terbinafine is a broad-spectrum antifungal agent with therapeutic potential against pulmonary aspergillosis. The main aim of the current study was to investigate the potential of l-leucine, alone and in combination with mannitol, to improve the performance of spray-dried terbinafine microparticles for inhalation. The study also aimed to investigate the potential of the low resistance Cyclohaler^® and the high resistance Handihaler^® as inhalation devices for spray-dried microparticles. To this end, eight powder inhalation formulations of terbinafine were prepared by nano spray drying via a factorial experimental design. The formulations were evaluated in vitro for their potential to deliver the antifungal drug to the lungs using the Cyclohaler^® and the Handihaler^®. Leucine was superior as an excipient to mannitol and to mixtures of leucine and mannitol. Using leucine as an excipient resulted in formulations with fine particle fractions of up to 60.84 ± 0.67% w/w and particle mass median aerodynamic diameters of down to 1.90 ± 0.20 μm, whereas using mannitol as an excipient resulted in formulations with fine particle fractions of up to 18.75 ± 3.46% w/w and particle mass median aerodynamic diameters of down to 6.79 ± 0.82 μm. When leucine was used as an excipient, using 50% w/w rather than 25% w/w ethanol in water as a spray solvent enhanced the dispersibility of the particles, with a mean absolute increase in the formulation fine particle fraction of 9.57% w/w (95% confidence interval = 6.40–12.73% w/w). This was potentially underlain by enrichment of the particle surfaces with leucine. The Cyclohaler^® outperformed the Handihaler^® as an inhalation device for the developed formulations, with a mean absolute increase in the fine particle fraction of 9.17% w/w (95% confidence interval = 8.17–10.16% w/w).

The Past, the Present, and the Future of the Size Exclusion Chromatography in Extracellular Vesicles Separation

Extracellular vesicles (EVs) are cell-derived membranous particles secreted by all cell types (including virus infected and uninfected cells) into the extracellular milieu. EVs carry, protect, and transport a wide array of bioactive cargoes to recipient/target cells. EVs regulate physiological and pathophysiological processes in recipient cells and are important in therapeutics/drug delivery. Despite these great attributes of EVs, an efficient protocol for EV separation from biofluids is lacking. Numerous techniques have been adapted for the separation of EVs with size exclusion chromatography (SEC)-based methods being the most promising. Here, we review the SEC protocols used for EV separation, and discuss opportunities for significant improvements, such as the development of novel particle purification liquid chromatography (PPLC) system capable of tandem purification and characterization of biological and synthetic particles with near-single vesicle resolution. Finally, we identify future perspectives and current issues to make PPLC a tool capable of providing a unified, automated, adaptable, yet simple and affordable particle separation resource.

Stimulation of ABCB4/MDR3 ATPase activity requires an intact phosphatidylcholine lipid

ABCB4/MDR3 is located in the canalicular membrane of hepatocytes and translocates PC-lipids from the cytoplasmic to the extracellular leaflet. ABCB4 is an ATP-dependent transporter that reduces the harsh detergent effect of the bile salts by counteracting self-digestion. To do so, ABCB4 provides PC lipids for extraction into bile. PC lipids account for 40% of the entire pool of lipids in the canalicular membrane with an unknown distribution over both leaflets. Extracted PC lipids end up in so-called mixed micelles. Mixed micelles are composed of phospholipids, bile salts, and cholesterol. Ninety to ninety-five percent of the phospholipids are members of the PC family, but only a subset of mainly 16.0-18:1 PC and 16:0-18:2 PC variants are present. To elucidate whether ABCB4 is the key discriminator in this enrichment of specific PC lipids, we used in vitro studies to identify crucial determinants in substrate selection. We demonstrate that PC-lipid moieties alone are insufficient for stimulating ABCB4 ATPase activity, and that at least two acyl chains and the backbone itself are required for a productive interaction. The nature of the fatty acids, like length or saturation has a quantitative impact on the ATPase activity. Our data demonstrate a two-step enrichment and protective function of ABCB4 to mitigate the harsh detergent effect of the bile salts, because ABCB4 can translocate more than just the PC-lipid variants found in bile.

Development of Novel High-Resolution Size-Guided Turbidimetry-Enabled Particle Purification Liquid Chromatography (PPLC): Extracellular Vesicles and Membraneless Condensates in Focus

Acellular particles (extracellular vesicles and membraneless condensates) have important research, drug discovery, and therapeutic implications. However, their isolation and retrieval have faced enormous challenges, impeding their use. Here, a novel size-guided particle purification liquid chromatography (PPLC) is integrated into a turbidimetry-enabled system for dye-free isolation, online characterization, and retrieval of intact acellular particles from biofluids. The chromatographic separation of particles from different biofluids-semen, blood, urine, milk, and cell culture supernatants-is achieved using a first-in-class gradient size exclusion column (gSEC). Purified particles are collected using a fraction collector. Online UV-Vis monitoring reveals biofluid-dependent particle spectral differences, with semen being the most complex. Turbidimetry provides the accurate physical characterization of seminal particle (Sp) lipid contents, sizes, and concentrations, validated by a nanoparticle tracking analysis, transmission electron microscopy, and naphthopyrene assay. Furthermore, different fractions of purified Sps contain distinct DNA, RNA species, and protein compositions. The integration of Sp physical and compositional properties identifies two archetypal membrane-encased seminal extracellular vesicles (SEV)-notably SEV large (SEVL), SEV small (SEVS), and a novel nonarchetypalμμembraneless Sps, herein named membraneless condensates (MCs). This study demonstrates a comprehensive yet affordable platform for isolating, collecting, and analyzing acellular particles to facilitate extracellular particle research and applications in drug delivery and therapeutics. Ongoing efforts focus on increased resolution by tailoring bead/column chemistry for each biofluid type.

High-Resolution In Situ NMR Spectroscopy of Bacterial Envelope Proteins in Outer Membrane Vesicles

The cell envelope of Gram-negative bacteria is an elaborate cellular environment, consisting of two lipid membranes separated by the aqueous periplasm. So far, efforts to mimic this environment under laboratory conditions have been limited by the complexity of the asymmetric bacterial outer membrane. To evade this impasse, we recently established a method to modify the protein composition of bacterial outer membrane vesicles (OMVs) released from Escherichia coli as a platform for biophysical studies of outer membrane proteins in their native membrane environment. Here, we apply protein-enriched OMVs to characterize the structure of three envelope proteins from E. coli using nuclear magnetic resonance (NMR) spectroscopy and expand the methodology to soluble periplasmic proteins. We obtain high-resolution in situ NMR spectra of the transmembrane protein OmpA as well as the periplasmic proteins CpxP and MalE. We find that our approach facilitates structural investigations of membrane-attached protein domains and is especially suited for soluble proteins within their native periplasmic environment. Thereby, the use of OMVs in solution NMR methods allows in situ analysis of the structure and dynamics of proteins twice the size compared to the current in-cell NMR methodology. We therefore expect our work to pave the way for more complex NMR studies of bacterial envelope proteins in the native environment of OMVs in the future.

A Method for High-Throughput Measurements of Viscosity in Sub-micrometer-Sized Membrane Systems

To unravel the underlying principles of membrane adaptation in small systems like bacterial cells, robust approaches to characterize membrane fluidity are needed. Currently available relevant methods require advanced instrumentation and are not suitable for high-throughput settings needed to elucidate the biochemical pathways involved in adaptation. We developed a fast, robust, and financially accessible quantitative method to measure the microviscosity of lipid membranes in bulk suspension using a commercially available plate reader. Our approach, which is suitable for high-throughput screening, is based on the simultaneous measurements of absorbance and fluorescence emission of a viscosity-sensitive fluorescent dye, 9-(2,2-dicyanovinyl)julolidine (DCVJ), incorporated into a lipid membrane. We validated our method using artificial membranes with various lipid compositions over a range of temperatures and observed values that were in good agreement with previously published results. Using our approach, we were able to detect a lipid phase transition in the ruminant pathogen Mycoplasma mycoides.

Core-Shell Modeling of Light Scattering by Vesicles: Effect of Size, Contents, and Lamellarity

Having a fast, reliable method for characterizing vesicles is vital for their use as model cell membranes in biophysics, synthetic biology, and origins of life studies. Instead of the traditionally used Rayleigh-Gans-Debye approximation, we use an exact extended Lorenz-Mie solution for how core-shell particles scatter light to model vesicle turbidity. This approach enables accurate interpretations of simple turbidimetric measurements and is able to accurately model highly scattering vesicles, such as larger vesicles, those with multiple layers, and those with encapsulated material. We uncover several surprising features, including that vesicle lamellarity has a larger effect on sample turbidity than vesicle size and that the technique can be used to measure the membrane thickness of vesicles. We also examine potential misinterpretations of turbidimetry and discuss when measurements are limited by forward and multiple scattering and by the geometry of the instrument.

Evaluation of exfoliation degree of montmorillonite in aqueous dispersions through turbidity measurement

In this work, the exfoliation of montmorillonite (MMT) in aqueous suspensions was investigated through the measurement of turbidity. The experimental results have shown that the turbidity is closely correlated to the exfoliation degree of MMT in aqueous suspensions. Below the solid concentration of 2% w/v and in the range of pH 4–10, the turbidity of aqueous dispersions of MMT without exfoliation appeared constant, while it decreased on increasing the exfoliation degree of MMT. The ratio of the turbidities before and after the exfoliation (τ₀/τ) was directly proportional to the number of fresh MMT flakes formed from the exfoliation. τ₀/τ was termed the exfoliation degree E. The larger the value of E, the more MMT flakes formed. It has been found that the exfoliation of MMT in aqueous dispersions was depressed due to the presence of electrolytic ions. This depression increased with the increase of ion concentration and valence.

In this work, the exfoliation of montmorillonite (MMT) in aqueous suspensions was investigated through the measurement of turbidity.

The effect of membrane softeners on rigidity of lipid vesicle bilayers: Derivation from vesicle size changes

Deformability is not just a fundamentally interesting vesicle characteristic; it is also the key determinant of vesicle ability to cross the skin barrier; i.e. skin penetrability. Development of bilayer vesicles for drug and vaccine delivery across the skin should hence involve optimization of this property, which is controllable by the concentration of bilayer softeners in or near the vesicle bilayers. To this end, we propose a simple method for quantifying the effect of bilayer softeners on deformability of bilayer vesicles. The method derives the bending rigidity of vesicle bilayers from vesicle size dependence on softener concentration. To exemplify the method, we studied mixtures of soybean phosphatidylcholine with anionic sodium deoxycholate, non-ionic polyoxyethylene (20) sorbitan oleyl ester (polysorbate 80), or non-ionic polyoxyethylene (20) oleyl ether (C18:1EO20, Brij® 98). With each of the tested bilayer softeners, the bending rigidity of the resulting mixed-amphipat vesicle bilayers decreased quasi-exponentially as the concentration of the bilayer softener increased, as one would expect on theoretical ground. The bilayer bending rigidity reached low values, near the thermal stability limit, i.e. kBT, before vesicle transformation into non-vesicular aggregates began. For a soybean phosphatidylcholine concentration of 5.0mmolkg-1, the bilayer bending rigidity reached 1.5kBT at the total deoxycholate concentration of 4.1mmolkg-1 and 3.4kBT at the total polysorbate 80 concentration of 2.0mmolkg-1. In the case of C18:1EO20, the bilayer bending rigidity reached 1.5kBT at the bilayer surface occupancy α=0.1. The dependence of vesicle size on bilayer softener concentration thus reveals vesicle transformation into different aggregate structures (such as mixed micelles with poor skin penetrability) and practically valuable information on vesicle deformability. Our results compare favorably with results of literature measurements. We provide practical guidance on using the new analytical method to optimize deformable vesicle formulations.

Vitronectin (Vn) glycosylation patterned by lectin affinity assays-A potent glycoproteomic tool to discriminate plasma Vn from cancer ascites Vn

Changes in glycosylation have been associated with human cancer, but their complexity poses an analytical challenge. Ovarian cancer is a major cause of death in women because of an often late diagnosis. At least one-third of patients presents ascites fluid at diagnosis, and almost all have ascites at recurrence. Vitronectin (Vn) is a multifunctional glycoprotein that is suggested to be implicated in ovarian cancer metastasis and is found within ascites. The present study evaluated the potential of using lectin affinity for characterizing the glycosylation pattern of Vn. Human Vn was purified from 1 sample of ovarian cancer ascites or a pool of plasma samples. Consistent findings were observed with both dot blot and lectin array assays. Based on a panel of 40 lectins, the lectin array revealed discriminant patterns of lectin binding to Vn glycans. Interestingly, almost all the highlighted interactions were found to be higher with Vn from ascites relative to the plasma counterpart. Also, the lectin array was able to discriminate profiles of lectin interactions (ConA, SNA-I, PHA-E, PHA-L) between Vn samples that were not evident using dot blot, indicating its high sensitivity. The model of ConA binding during thermal unfolding of Vn confirmed the higher accessibility of mannosylated glycans in Vn from ascites as monitored by turbidimetry. Thus, this study demonstrated the usefulness of lectins and the lectin array as a glycoproteomic tool for high throughput and sensitive analysis of glycosylation patterns. Our data provide novel insights concerning Vn glycosylation patterns in clinical specimens, paving the way for further investigations regarding their functional impact and clinical interest.

Selective induction of apoptosis in MCF7 cancer-cell by targeted liposomes functionalised with mannose-6-phosphate

Liposomes are versatile platforms to carry anticancer drugs in targeted drug delivery; they can be surface modified by different strategies and, when coupled with targeting ligands, are able to increase cellular internalisation and organelle-specific drug delivery. An interesting strategy of antitumoral therapy could involve the use of lysosomotropic ligand-targeted liposomes loaded with molecules, which can induce lysosomal membrane permeabilization (LMP), leakage of cathepsins into the cytoplasm and subsequent apoptosis. We have previously demonstrated the ability of liposomes functionalised with a mannose-6-phosphate to reach lysosomes; in this research we compare the behaviour of M6P-modified and non-functionalised liposomes in MCF7 tumour cell and in HDF normal cells. With this aim, we first demonstrated by Western blotting the overexpression of mannose-6-phosphate/insulin-like growth factor (M6P/IGF-II) receptor in MCF7. Then, we prepared calcein-loaded liposomes and we revealed the increased uptake of M6P-functionalised liposomes in MCF7 cells respect to HDF cells by flow cytometry analysis. Finally, we loaded functionalised and not functionalised liposomes with N-hexanoyl-d-erythro-sphingosine (C6Cer), able to initiate LMP-induced apoptosis; after having studied the stability of both vesicles in the presence of serum by Dynamic Light Scattering and Spectrophotometric turbidity measurements, we showed that ceramide-loaded M6P-liposomes significantly increased apoptosis in MCF7 with respect to HDF cells.

Improved Method for Solid Lipid Nanoparticle Preparation Based on Hot Microemulsions: Preparation, Characterization, Cytotoxicity, and Hemocompatibility Evaluation

The ease of application and no requirement of extra energy input make the microemulsion method favorable for solid lipid nanoparticles (SLNs) production. Very limited data are available to date on preparation of SLNs from pre-screened microemulsion phase diagrams. The purpose of this study was to investigate the microemulsion formation area with solid lipids using hot ternary phase diagrams at elevated temperatures and to use selected microemulsions for SLN production. Also, we aimed to characterize obtained SLNs in terms of physicochemical properties, in vitro cell toxicity, and hemolysis. Phase diagrams of solid lipids were screened at elevated temperatures and oil-in-water microemulsion regions were determined. Microemulsions were selected, and SLNs were produced by modification of the microemulsion dilution method and characterized in terms of visual appearance, turbidity, particle size, and zeta potential. Cytotoxicity of nanoparticles was tested on L929 mouse skin fibroblast cells. Hemolytic potential was assessed in vitro using freshly isolated erythrocytes. The phase diagram screening and the modified hot microemulsion dilution method enabled production of SLNs with particle size below 100 nm. We found evidence that the solid lipids in the SLNs produced by the new method remain in supercooled liquid state. Nanoparticles prepared by the new method exhibit lower toxicity on L929 cells and have lower hemolytic potential than the formulations prepared by direct mixing of the components. The method can be used to prepare SLNs with controllable composition and small particle size below 100 nm. These SLNs are low toxic and can be used for drug delivery purposes.

Phase transition and aggregation behaviour of an UCST-type copolymer poly(acrylamide-co-acrylonitrile) in water: effect of acrylonitrile content, concentration in solution, copolymer chain length and presence of electrolyte

An UCST-type copolymer of acrylamide (AAm) and acrylonitrile (AN) (poly(AAm-co-AN)) was prepared by reversible addition fragmentation chain transfer (RAFT) polymerization and its temperature-induced phase transition and aggregation behaviour studied by turbidimetry, static and dynamic light scattering, small angle neutron scattering (SANS) and cryo-transmission electron microscopy (cryo-TEM) measurements. The phase transition temperature was found to increase with increasing AN content in the copolymer, concentration of the solutions and copolymer chain length. A significant effect was observed onto the phase transition temperature by addition of different electrolytes into the copolymer solution. The copolymer chains were aggregated below the phase transition temperature and disaggregated above it. The size of the aggregates increases with increasing AN contents and concentration of the copolymer solutions below the phase transition temperature. The copolymer chains were expanded and weekly associated in solution above the phase transition temperature. A model is proposed to explain such association-aggregation behaviour of poly(AAm-co-AN) copolymers depending on AN contents and concentration of the copolymer solutions as a function of temperature.

Improved protection against tuberculosis after boosting the BCG-primed mice with subunit Ag 85a delivered through intact skin with deformable vesicles

To improve vaccination against tuberculosis (TBC) with Bacillus Calmette-Guerin (BCG), we introduce novel, non-invasive, secondary immunisations relying on epicutaneous (e.c.) applications of the TBC subunit antigen, Ag 85a, associated with deformable carrier vesicles. Immuno-boosting with such antigen-vesicles recruits more CD11c positive cells into the draining murine lymph nodes, and typically stimulates, especially the proximal, immune cells more than immunogen injections. Non-invasive antigen application also protects mice better against an infection with TBC. Subcutaneous injections of vesicular Ag 85a into BCG-primed mice mainly yield IgG1 and IgG2a, indicative of a mixed Th1 and Th2 response. Conversely, transcutaneous immuno-boosts of such mice with a deformable vesicle-Ag 85a combination mainly generate serum IgA and IgG2a, indicative of an IgA facilitated, Th1-mediated, immune response. The Ag 85a specific antibody titres are generally low, but T lymphocytes also proliferate in the immunised mice. The new, partially non-invasive, vaccination method lowers the burden of pulmonary infection with M. tuberculosis. In mice immunised with Ag85a associated with deformable vesicles we measured 116× (e.c.) to 51× (s.c.) lower colony forming units number in spleen and 9× (e.c.) to 3× (s.c.) lower such number in lungs.

A ring-flippable sugar as a stimuli-responsive component of liposomes

For the development of a liposome that takes in and out a drug in response to stimuli, 2,4-diaminoxylose (Xyl), which allows stimuli-responsive conformational switches between (4)C1 and (1)C4, was incorporated into a lipid structure: Xyl derivatives with C8 and C16 methylene chains at the 1,3-positions (C8Xyl and C16Xyl) were synthesized. (1)H NMR spectroscopy indicates that the addition of Zn(2+) and then H(+) induces conformational switches from the chair ((4)C1) to the reverse chair ((1)C4) and (1)C4-to-(4)C1, respectively, at Xyl; this leads to transformation of the lipids between linear and bent structures. Osmotic pressure and electron microscopy studies demonstrate that C8Xyl in water forms spherical solid aggregates (C8Xyl-Zn), which are converted into liposomes (C8Xyl+Zn) upon the addition of Zn(2+), and C16Xyl forms liposomes regardless of the presence of Zn(2+). The aggregates of C8Xyl±Zn incorporated a fluorophore and only C8Xyl+Zn released the content upon the addition of HCl. This study shows that Xyl could be a stimuli-responsive component of a liposome.

Stabilization and cellular delivery of chitosan-polyphosphate nanoparticles by incorporation of iron

Chitosan (CS) nanoparticles are typically obtained by complexation with tripolyphosphate (TPP) ions, or more recently using triphosphate group-containing drugs such as adenosine triphosphate (ATP). ATP is an active molecule we aim to deliver in order to restore its depletion in macrophages, when associated with their death leading to plaque rupture in atherosclerotic lesions. Despite high interest in CS nanoparticles for drug delivery, due to the biodegradability of CS and to the ease of the preparation process, these systems tend to readily disintegrate when diluted in physiological media. Some stabilization strategies have been proposed so far but they typically involve the addition of a coating agent or chemical cross-linkers. In this study, we propose the complexation of CS with iron ions prior to nanoparticle formation as a strategy to improve the carrier stability. This can be achieved thanks to the ability of iron to strongly bind both chitosan and phosphate groups. Nanoparticles were obtained from either TPP or ATP and chitosan-iron (CS-Fe) complexes containing 3 to 12% w/w iron. Isothermal titration calorimetry showed that the binding affinity of TPP and ATP to CS-Fe increased with the iron content of CS-Fe complexes. The stability of these nanoparticles in physiological conditions was evaluated by turbidity and by fluorescence fluctuation in real time upon dilution by electrolytes, and revealed an important stabilization effect of CS-Fe compared to CS, increasing with the iron content. Furthermore, in vitro studies on two macrophage cell lines (J774A.1 and THP-1) revealed that ATP uptake is improved consistently with the iron content of CS-Fe/ATP nanoparticles, and correlated to their lower dissociation in biological medium, allowing interesting perspectives for the intracellular delivery of ATP.

Development of a new method to assess nanocrystal dissolution based on light scattering

PURPOSE

Nanocrystals exhibit enhanced dissolution rates and can effectively increase the bioavailability of poorly water soluble drug substances. However, methods for in vitro characterization of dissolution are unavailable. The objective of this study was to develop an in situ noninvasive analytical method to measure dissolution of crystalline nanosuspensions based on light scattering.

METHODS

Fenofibrate nanosuspensions were prepared by wet media milling. Their solubilities and dissolution profiles in simulated gastric fluid supplemented with 0.1% Tween(®) 80 were measured in a small scale setup with an instrument for dynamic light scattering and the intensity of scattered light as readout parameter.

RESULTS

A good correlation was achieved between the dissolution profile of a nanosuspension measured in the light scattering setup and a conventional dissolution experiment. Nanosuspensions of 120-270 nm size could be distinguished by the light scattering method. The suspensions dissolved within 1.9-12.3 min. Over a concentration range of 40-87% of the solubility dissolution profiles of a nanosuspension with 140 nm were monitored and the determined total dissolution times were in good agreement with the Noyes-Whitney dissolution model.

CONCLUSIONS

A noninvasive, sensitive and reproducible method is presented to assess nanocrystal dissolution. In situ measurements based on light scattering allow a straightforward experimental setup with high temporal resolution.

The vesicle-to-micelle transformation of phospholipid-cholate mixed aggregates: a state of the art analysis including membrane curvature effects

We revisited the vesicle-to-micelle transformation in phosphatidylcholine-cholate mixtures paying special attention to the lipid bilayer curvature effects. For this purpose, we prepared unilamellar vesicles with different starting sizes (2r(v)=45-120nm). We then studied mixtures of the unilamellar vesicles (1-8mmol kg(-1)) and sodium cholate (0-11.75mmolkg(-1)) by static and dynamic light scattering. The transformation generally comprises at least two, largely parallel phenomena; one increases and the other decreases the average mixed aggregate size. In our view, cholate first induces bilayer fluctuations that lead to vesicle asphericity, and then to lipid bilayer poration followed by sealing/reformation (or fusion). The cholate-containing mixed bilayers, whether in vesicular or open form, project thread-like protrusions with surfactant enriched ends even before complete bilayer solubilisation. Increasing cholate concentration promotes detachment of such protrusions (i.e. mixed micelles formation), in parallel to further softening/destabilising of mixed amphipat bilayers over a broad range of concentrations. Vesicles ultimately fragment into mixed thread-like micelles. Higher cholate relative concentrations yield shorter thread-like mixed micelles. Most noteworthy, the cholate-induced bilayer fluctuations, the propensity for large aggregate formation, the transformation kinetics, and the cholate concentration ensuring complete lipid solubilisation all depend on the starting mean vesicle size. The smallest tested vesicles (2r(v)=45nm), with the highest bilayer curvature, require ~30% less cholate for complete solubilisation than the largest tested vesicles (2r(v)=120nm).