In Situ Characterization of the Protein Corona of Nanoparticles In Vitro and In Vivo.

A new theoretical framework that enables the use of differential dynamic microscopy (DDM) in fluorescence imaging mode to quantify in situ protein adsorption onto nanoparticles (NP) while simultaneously monitoring for NP aggregation is proposed. This methodology is used to elucidate the thermodynamic and kinetic properties of the protein corona (PC) in vitro and in vivo. The results show that protein adsorption triggers particle aggregation over a wide concentration range and that the formed aggregate structures can be quantified using the proposed methodology. Protein affinity for polystyrene (PS) NPs is observed to be dependent on particle concentration. For complex protein mixtures, this methodology identifies that the PC composition changes with the dilution of serum proteins, demonstrating a Vroman effect never quantitatively assessed in situ on NPs. Finally, DDM allows monitoring of the evolution of the PC in vivo. This results show that the PC composition evolves significantly over time in zebrafish larvae, confirming the inherently dynamic nature of the PC. The performance of the developed methodology allows to obtain quantitative insights into nano-bio interactions in a vast array of physiologically relevant conditions that will serve to further improve the design of nanomedicine.

Tailoring PEGylated nanoparticle surface modulates inflammatory response in vascular endothelial cells.

Polymer nanoparticles (NPs) are extensively studied as drug delivery systems for various therapeutic indications, including drug and imaging agent delivery to the brain. Despite intensive research, their toxicological profile has yet to be fully characterized. In particular, the more subtle effects of nanomaterials on inflammatory processes have scarcely been investigated. Surface properties of NPs are amongst parameters governing interactions between living cells and NPs. They could considerably influence the toxicity and inflammatory response of the cells exposed to NPs. Polymeric NPs investigated here present a core-shell structure. The core is constituted of hydrophobic poly(lactic acid) (PLA) block and the surface is composed of a shell of hydrophilic block of polyethylene glycol (PEG). The effect of PEG chain length coating on the expression of genes involved in the inflammation response was investigated in two vascular endothelial cell lines (bEnd.3 and HUVEC) by qPCR. Moreover, ROS generation following NP uptake was evaluated. PEGylated NPs induce a mild and transient activation of inflammatory cytokine and chemokine genes. However, differences in PEG chain length did not show any significant effect on cytokine and chemokine gene expression and PEGylated NPs did not trigger ROS generation. The present results could contribute significantly to a deeper understanding of nanomaterial interactions and toxicity with vascular endothelial cells, guiding scientists in material coating choices.

Scratching the Surface of the Protein Corona: Challenging Measurements and Controversies.

This Review aims to provide a systematic analysis of the literature regarding ongoing debates in protein corona research. Our goal is to portray the current understanding of two fundamental and debated characteristics of the protein corona, namely, the formation of mono- or multilayers of proteins and their binding (ir)reversibility. The statistical analysis we perform reveals that these characterisitics are strongly correlated to some physicochemical factors of the NP-protein system (particle size, bulk material, protein type), whereas the technique of investigation or the type of measurement (in situ or ex situ) do not impact the results, unlike commonly assumed. Regarding the binding reversibility, the experimental design (either dilution or competition experiments) is also shown to be a key factor, probably due to nontrivial protein binding mechanisms, which could explain the paradoxical phenomena reported in the literature. Overall, we suggest that to truly predict and control the protein corona, future efforts should be directed toward the mechanistic aspects of protein adsorption.

Spontaneous shrinking of soft nanoparticles boosts their diffusion in confined media.

Improving nanoparticles (NPs) transport across biological barriers is a significant challenge that could be addressed through understanding NPs diffusion in dense and confined media. Here, we report the ability of soft NPs to shrink in confined environments, therefore boosting their diffusion compared to hard, non-deformable particles. We demonstrate this behavior by embedding microgel NPs in agarose gels. The origin of the shrinking appears to be related to the overlap of the electrostatic double layers (EDL) surrounding the NPs and the agarose fibres. Indeed, it is shown that screening the EDL interactions, by increasing the ionic strength of the medium, prevents the soft particle shrinkage. The shrunken NPs diffuse up to 2 orders of magnitude faster in agarose gel than their hard NP counterparts. These findings provide valuable insights on the role of long range interactions on soft NPs dynamics in crowded environments, and help rationalize the design of more efficient NP-based transport systems.

Tailored Nanocarriers for the Pulmonary Delivery of Levofloxacin against Pseudomonas aeruginosa: A Comparative Study.

Cystic fibrosis (CF) patients are faced with chronic bacterial infections displaying persistent resistance if not eradicated during the first stage of the disease. Nanoantibiotics for pulmonary administration, such as liposomal ciprofloxacin or amikacin, have progressed through clinics thanks to their sustained release, prolonged lung residence time, and low systemic absorption. In this work, we sought a nanoformulation of levofloxacin for the treatment of Pseudomonas aeruginosa. We prepared and compared poly(lactic acid)-grafted-poly(ethylene glycol) nanoparticles, as well as anionic and cationic liposomes for their size, charge, and encapsulation efficiency. Cationic liposomes were unable to encapsulate any drug and were subsequently considered as a control formulation. Regarding the efficiency of the nanocarrier, anionic liposomes exhibited a prolonged release over 72 h and preserved the antibacterial activity of levofloxacin against five strains of P. aeruginosa, whereas polymeric nanoparticles quickly released their entire payload and increased the minimum inhibitory concentration of levofloxacin. Thus, only anionic liposomes were considered for further preclinical development. Anionic liposomes exhibited a suitable colloidal stability in Turbiscan analysis and crossed a layer of artificial mucus in under 1 h in a Transwell setup. Despite their negative surface charge, liposomes still interacted with the P. aeruginosa membrane in a dose-response manner, as demonstrated by flow cytometry. Viability assays confirmed that anionic liposomes, loaded or not, exhibited a good safety profile on A549 epithelial cells, even at high concentrations. Finally, nebulization of anionic liposomes containing levofloxacin did not impact their colloidal stability, and the droplet size distribution was suitable for deep lung deposition, where the P. aeruginosa infection lies. Therefore, levofloxacin-loaded anionic liposomes exhibited suitable properties for the pulmonary treatment of P. aeruginosa in CF. This step-by-step study confirms the promising role of liposomes for lung administration of antibiotics, as recently seen in clinics, and fosters their development for several types of antibiotics.

Subtle and unexpected role of PEG in tuning the penetration mechanisms of PLA-based nano-formulations into intact and impaired skin.

We present a systematic study of the role of poly(ethylene glycol) (PEG) content in NPs on drug skin absorption. Cholecalciferol-loaded NPs of 100 nm of diameter were prepared by flash nanoprecipitation from PLA-b-PEG copolymers of various PEG lengths. As PEG content increased in the polymer, we observed a transition from a frozen solid particle structure to a more dynamic particle structure. Skin absorption studies showed that polymer composition influenced drug penetration depending on skin condition (intact or impaired). In intact skin, highly PEGylated NPs achieved the best skin absorption, even if the penetration differences between the NPs were low. In impaired skin, on the contrary, non-PEGylated NPs (PLA NPs) promoted a strong drug deposition. Further investigations revealed that the strong drug accumulation from PLA NPs in impaired skin was mediated by aggregation and sedimentation of NPs due to the release of charged species from the skin. In contrast, the dynamic structure of highly PEGylated NPs promoted wetting of the surface and interactions with skin lipids, improving drug absorption in intact skin. Since NPs structure and surface properties determine the drug penetration mechanisms at the NP-skin interface, this work highlights the importance of properly tuning NPs composition according to skin physiopathology.

Tablet formulation of Famotidine-loaded P-gp inhibiting nanoparticles using PLA-g-PEG grafted polymer.

Our work aimed at evaluating the use of permeability glycoprotein (P-gp) inhibiting nanoparticles (NPs) as a part of a suitable oral solid dosage to improve bioavailability. Famotidine (Pepcid®), a stomach acid production inhibitor, was used as a drug model to test our hypothesis. Famotidine-loaded NPs were prepared by solvent emulsion evaporation using PEG grafted on a polylactide acid (PLA) polymer backbone (PLA-g-PEG), with a 5% molar ratio of PEG versus lactic acid monomer and PEG of either 750 or 2000 Da molecular weight. Tablet formulation was composed of 40% Famotidine-loaded NPs, 52.5% microcrystalline cellulose as filler, 7% pre-gelatinized starch as binder/disintegrant, and 0.5% magnesium stearate as lubricant. Tablets containing 1.6 mg of Famotidine were prepared at an average weight of 500 mg, thickness of 6.2-6.5 mm, hardness of 5-8 kp, and disintegration time of <1 min. Our results suggest that Famotidine-loaded NPs using grafted PEG-g-PLA polymers can be formulated as an oral solid dosage form while effectively inhibiting P-gp mediated Famotidine efflux, irrespective of PEG molecular weights. This could therefore represent an attractive formulation alternative to enhance oral permeability and bioavailability of drugs that are P-gp substrates.

Nanoparticle heterogeneity: an emerging structural parameter influencing particle fate in biological media?

Drug nanocarriers' surface chemistry is often presumed to be uniform. For instance, the polymer surface coverage and distribution of ligands on nanoparticles are described with averaged values obtained from quantification techniques based on particle populations. However, these averaged values may conceal heterogeneities at different levels, either because of the presence of particle sub-populations or because of surface inhomogeneities, such as patchy surfaces on individual particles. The characterization and quantification of chemical surface heterogeneities are tedious tasks, which are rather limited by the currently available instruments and research protocols. However, heterogeneities may contribute to some non-linear effects observed during the nanoformulation optimization process, cause problems related to nanocarrier production scale-up and correlate with unexpected biological outcomes. On the other hand, heterogeneities, while usually unintended and detrimental to nanocarrier performance, may, in some cases, be sought as adjustable properties that provide NPs with unique functionality. In this review, results and processes related to this issue are compiled, and perspectives and possible analytical developments are discussed.

Length of surface PEG modulates nanocarrier transcytosis across brain vascular endothelial cells.

Diblock PLA-PEG nanoparticles were produced to establish the role of PEG chain length on brain vascular endothelial cell transcytosis. 100-nm nanoparticles tagged with fluorescent pyrene butanol and coated with PEG chains (Mw: 1-10 kDa), at similar PEG surface density, were used to study endocytosis and transcytosis phenomena on mouse vascular endothelial cell monolayers. The transport mechanisms were then investigated through inhibitory processes. Our results show that there is an evident correlation between PEG chain length and nanoparticle translocation. The highest transcytosis rates were obtained with PEG5000 and PEG10000 and macropinocytosis appeared to play a central role in cell uptake. This study constitutes the first systematic exploration of the role of PEG chain length on nanoparticle endocytosis and transcytosis in an in vitro model of the blood-brain barrier.

Crystal structures of the solvent-free and ethanol disolvate forms of 4,4'-(diazenediyl)bis(2,3,5,6-tetrafluorobenzoic acid) exemplifying self-stabilized azo-benzene cis-configurations.

cis-4,4'-(Diazenediyl)bis(2,3,5,6-tetrafluorobenzoic acid), C14H2F8N2O4, and its ethanol disolvate, C14H2F8N2O4·2C2H5OH, represent new examples of self-stabilized cis-configured azo-benzenes obtained by a common crystallization procedure at room temperature under normal laboratory lighting conditions. The target structure constitutes of two 2,3,5,6-tetra-fluoro-benzoic acid residues linked to each other by a cis-configured azo group and was confirmed for two isolated specimens extracted from the same sample, corresponding to a solvent-free form and an ethanol disolvate. In the solvent-free form, the mol-ecule is characterized by rotational symmetry around a twofold rotation axis bis-ecting its central N=N bond while this symmetry is not present in the solvated form. The values of the inclination angles of the terminal carboxyl groups towards the corresponding benzene rings vary from 5.2 (4) to 45.7 (2)°, depending on the crystal composition. In the unsolvated form, the mol-ecules are linked through identical hydrogen bonds with a classical R 2 2(8) graph-set ring motif of carb-oxy-lic acids, by generating supra-molecular chains running approximately parallel to [101]. The presence of ethanol in the solvated form also leads to changes in the short-contact pattern to produce both the R 4 4(12) ring and open-chain motifs with alternating alcohol and di-carb-oxy-lic acid mol-ecules.

Effect of surface chemistry of polymeric nanoparticles on cutaneous penetration of cholecalciferol.

We investigated the influence of nanoparticle (NP) surface composition on different aspects of skin delivery of a lipophilic drug: chemical stability, release and skin penetration. Cholecalciferol was chosen as a labile model drug. Poly(lactic acid) (PLA)-based NPs without surface coating, with a non-ionic poly(ethylene glycol) (PEG) coating, or with a zwitterionic poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC) coating were prepared using flash nanoprecipitation. Process was optimized to obtain similar hydrodynamic diameters. Polymeric NPs were compared to non-polymeric cholecalciferol formulations. Cholecalciferol stability in aqueous medium was improved by polymeric encapsulation with a valuable effect of a hydrophilic coating. However, the in vitro release of the drug was found independent of the presence of any polymer, as for the drug penetration in an intact skin model. Such tendency was not observed in impaired skin since, when stratum corneum was removed, we found that a neutral hydrophilic coating around NPs reduced drug penetration compared to pure drug NPs and bare PLA NPs. The nature of the hydrophilic block (PEG or PMPC) had however no impact. We hypothesized that NPs surface influenced drug penetration in impaired skin due to different electrostatic interactions between NPs and charged skin components of viable skin layers.

Unified Scaling of the Structure and Loading of Nanoparticles Formed by Diffusion-Limited Coalescence.

The present study establishes the scaling laws describing the structure of spherical nanoparticles formed by diffusion-limited coalescence. We produced drug-loaded nanoparticles from a poly(ethylene glycol)-poly(d,l-lactic acid) diblock polymer (PEG- b-PLA) by the nanoprecipitation method using different types of micromixing chambers to explore multiple mixing regimes and characteristic times. We first show that the drug loading of the nanoparticles is not controlled by the mixing time but solely by the drug-to-polymer ratio (D:P) in the feed and the hydrophobicity of the drug scaled via the partition coefficient P. We then procure compelling evidence that particles formed via diffusion/coalescence exhibit a relative distribution of PEG blocks between the particle core and its shell that depends only on mixing conditions (not on D:P). Scaling laws of PEG relative distribution and chain surface density were derived in different mixing regimes and showed excellent agreement with experimental data. In particular, results made evident that PEG blocks entrapment in the core of the particles occurs in the slow-mixing regime and favors the overloading (above the thermodynamic limit) of the particles with hydrophilic drugs. The present analysis compiles effective guidelines for the scale up of nanoparticles structure and properties with mixing conditions, which should facilitate their future translation to medical and industrial settings.

Crystal structure of 2-oxopyrrolidin-3-yl 4-(2-phenyl-diazen-1-yl)benzoate.

In the title compound, C17H15N3O3, the plane of the pyrrolidone ring is inclined at an angle of 59.791 (2)° to that of the azo-benzene segment, which adopts a configuration close to planar. In the crystal, mol-ecules are oriented pairwise by (2-oxopyrrolidin-3-yl)-oxy moieties at an angle of 76.257 (3)°, linked by hydrogen bonds and π-stacking inter-actions, forming zigzag supra-molecular chains parallel to [010] further linked via additional C-H⋯π inter-actions.

Non-covalent formulation of active principles with dendrimers: Current state-of-the-art and prospects for further development.

During the last three decades, dendrimers, nano-sized highly-branched fractal-like symmetrical macromolecules, have been intensively studied as promising candidates for application as drug-delivery carriers. Among other important characteristics arising from their unique and highly-controlled architecture, size and surface properties, the possibility of hosting guest molecules in internal voids represents a key advantage underlying the potential of dendrimers as non-covalent drug-encapsulating agents. The impressive amount of accumulating experimental results to date allows researchers to identify the most important and promising theoretical and practical aspects of the use of dendrimers for this purpose. This review covers the main factors, phenomena, and mechanisms involved in this drug-vectorization approach, including mechanisms of non-covalent dendrimer-drug association, dendrimer-dendrimer interactions, as well as biological properties relevant to the host dendrimers. A discussion is then provided to illustrate some successful existing formulation strategies as well as to propose some new possible ones to optimize further development of the field.

Synthesis and characterization of 3-methyl-6-[(propyn-yloxy)meth-yl]-1,4-dioxane-2,5-dione.

The number of known asymmetrically substituted hemilactides, important precursors for obtaining regular derivatives of polylactide polymers, is still limited and structural characterization of most of them is incomplete. In the title racemic 1,4-dioxane-2,5-dione derivative, C9H10O5, the hemilactide heterocycle exhibits a twist-boat conformation. The bulkier propynyloxymethyl group is in an axial position with a gauche conformation for the CH2-O-CH2-C segment. In the crystal, mol-ecules are linked by pairs of C-H⋯O hydrogen bonds, forming inversion dimers. The dimers are linked by further C-H⋯O contacts, forming a three-dimensional structure.

Design of PEG-grafted-PLA nanoparticles as oral permeability enhancer for P-gp substrate drug model Famotidine.

Bioavailability of oral drugs can be limited by an intestinal excretion process mediated by P-glycoprotein (P-gp). Polyethylene glycol (PEG) is a known P-gp inhibitor. Dispersion of Famotidine (a P-gp substrate) within PEGylated nanoparticles (NPs) was used to improve its oral bioavailability. In this work, we evaluated the potential impact of NPs prepared from a grafted copolymer of polylactic acid and PEG on P-gp function by studying in vitro permeability of Famotidine across Caco-2 cells. Copolymers of PEG grafted on polylactic acid (PLA) backbone (PLA-g-PEG) were synthesised with 1 mol% and 5 mol% PEG vs. lactic acid monomer using PEG 750 and 2000 Da. The polymers were used to prepare Famotidine-loaded NPs and tested in vitro on Caco-2 cells. Significant decrease in basolateral-to-apical transport of Famotidine was observed when Famotidine was encapsulated in NPs prepared from PLA-g-PEG5%. NPs prepared from PLA-g-PEG5% are promising to improve oral bioavailability of P-gp substrates.

Effect of polymer architecture on curcumin encapsulation and release from PEGylated polymer nanoparticles: Toward a drug delivery nano-platform to the CNS.

We developed a nanoparticles (NPs) library from poly(ethylene glycol)-poly lactic acid comb-like polymers with variable amount of PEG. Curcumin was encapsulated in the NPs with a view to develop a delivery platform to treat diseases involving oxidative stress affecting the CNS. We observed a sharp decrease in size between 15 and 20% w/w of PEG which corresponds to a transition from a large solid particle structure to a "micelle-like" or "polymer nano-aggregate" structure. Drug loading, loading efficacy and release kinetics were determined. The diffusion coefficients of curcumin in NPs were determined using a mathematical modeling. The higher diffusion was observed for solid particles compared to "polymer nano-aggregate" particles. NPs did not present any significant toxicity when tested in vitro on a neuronal cell line. Moreover, the ability of NPs carrying curcumin to prevent oxidative stress was evidenced and linked to polymer architecture and NPs organization. Our study showed the intimate relationship between the polymer architecture and the biophysical properties of the resulting NPs and sheds light on new approaches to design efficient NP-based drug carriers.

Effect of the Polymer Architecture on the Structural and Biophysical Properties of PEG-PLA Nanoparticles.

Polymers made of poly(ethylene glycol) chains grafted to poly(lactic acid) chains (PEG-g-PLA) were used to produce stealth drug nanocarriers. A library of comblike PEG-g-PLA polymers with different PEG grafting densities was prepared in order to obtain nanocarriers with dense PEG brushes at their surface, stability in suspension, and resistance to protein adsorption. The structural properties of nanoparticles (NPs) produced from these polymers by a surfactant-free method were assessed by dynamic light scattering, ζ potential, and transmission electron microscopy and found to be controlled by the amount of PEG present in the polymers. A critical transition from a solid NP structure to a soft particle with either a "micellelike" or a "polymer nanoaggregate" structure was observed when the PEG content was between 15 and 25% w/w. This structural transition was found to have a profound impact on the size of the NPs, their surface charge, their stability in suspension in the presence of salts, and the binding of proteins to the surface of the NPs. The arrangement of the PEG-g-PLA chains at the surface of the NPs was investigated by (1)H NMR and X-ray photoelectron spectroscopy (XPS). NMR results confirmed that the PEG chains were mostly segregated at the NP surface. Moreover, XPS and quantitative NMR allowed quantification of the PEG chain coverage density at the surface of the solid NPs. Concordance of the results between the two methods was found to be remarkable. Physical-chemical properties of the NPs such as resistance to aggregation in a saline environment as well as antifouling efficacy were related to the PEG surface density and ultimately to the polymer architecture. Resistance to protein adsorption was assessed by isothermal titration calorimetry using lysozyme. The results indicate a correlation between the PEG surface coverage and level of protein interactions. The results obtained lead us to propose such PEG-g-PLA polymers for nanomedicine development as an alternative to the predominant polyester-PEG diblock polymers.

Assessment of PEG on polymeric particles surface, a key step in drug carrier translation.

Injectable drug nanocarriers have greatly benefited in their clinical development from the addition of a superficial hydrophilic corona to improve their cargo pharmacokinetics. The most studied and used polymer for this purpose is poly(ethylene glycol), PEG. However, in spite of its wide use for over two decades now, there is no general consensus on the optimum PEG chain coverage-density and size required to escape from the mononuclear phagocyte system and to extend the circulation time. Moreover, cellular uptake and active targeting may have conflicting requirements in terms of surface properties of the nanocarriers which complicate even more the optimization process. These persistent issues can be largely attributed to the lack of straightforward characterization techniques to assess the coverage-density, the conformation or the thickness of a PEG layer grafted or adsorbed on a particulate drug carrier and is certainly one of the main reasons why so few clinical applications involving PEG coated particle-based drug delivery systems are under clinical trial so far. The objective of this review is to provide the reader with a brief description of the most relevant techniques used to assess qualitatively or quantitatively PEG chain coverage-density, conformation and layer thickness on polymeric nanoparticles. Emphasis has been made on polymeric particle (solid core) either made of copolymers containing PEG chains or modified after particle formation. Advantages and limitations of each technique are presented as well as methods to calculate PEG coverage-density and to investigate PEG chains conformation on the NP surface.

PEGylated bile acids for use in drug delivery systems: enhanced solubility and bioavailability of itraconazole.

Itraconazole is a drug of choice for the treatment of severe fungal infections and parasitic diseases, but its use is limited by its low water solubility and varying bioavailability. New self-emulsifying drug delivery systems (SEDDS) based on PEGylated bile acids (BA-PEGs) were designed and prepared, where the number and length of PEG arms were varied to optimize the loading of itraconazole in the final drug formulation. The use of both BA-PEGs and oleic acid improved the solubilization and absorption of the drug, which was in a glassy state in the SEDDS prepared with the melting method. High loading efficiencies of itraconazole (up to 20%) and stable liquid formulations were obtained at neutral pH, and full dispersion of itraconazole was reached in 2 h in simulated intestinal fluid (pH 6.8). Aqueous emulsions consisting of spherical micelles with mean hydrodynamic diameters (Dh) of ca. 75-220 nm, as verified by transmission electron microscopy and dynamic light scattering, are expected to improve the intestinal absorption of the drug. The new SEDDS showed good cytocompatibility by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assays of BA-PEGs with Caco-2 and RAW 264.2 cells, and a low degree of hemolysis of human erythrocytes. The SEDDS based on PEGylated bile acids provide a controlled release system with significant improvement of the bioavailability of itraconazole in rats, as demonstrated by the pharmacokinetic studies.