Solvent-mediated browning of proteins and amino acids.

Proteins or amino acids are subjected to the Maillard (browning) reaction in the presence of reducing sugars and catalyzed by high temperature. The reaction occurs in daily-life cooking and in the human body. Although the reaction is ubiquitous and has been known for over 100 years, it still intrigues researchers across disciplines. Here we report an unexpected finding where proteins and amino acids turn brown in a mixture of two common solvents: dimethyl sulfoxide and acetone. The browning reaction proceeds at room temperature, without the presence of any sugars. This novel browning reaction was confirmed by a series of investigation on a protein-based gel, 3 proteins and 20 amino acids. The browning is spontaneous, regardless of whether the protein or amino acid was dissolved or not. The kinetic study reveals a fast reaction with a formation half-life of about 4 h. Notably, the reactivity is bell-shaped, with the maximal catalytic effect occurring at an acetone-to-DMSO volume ratio of 0.1-0.3. Among the 20 amino acids tested, tryptophan, lysine, and proline are the most susceptible amino acids to the solvent-mediated browning reaction.

Formation of organosilica nanoparticles with dual functional groups and simultaneous payload entrapment.

A mixed organosilane system for simultaneous formation of organosilica nanoparticles has been systematically studied for loading of various compounds with a wide range of log P values. The molecule-entrapping system was understood by investigating the effects of adjusting various experimental parameters on particle formation and molecule entrapment. Particularly, rhodamine 6 G (R6G) loaded colloidal particles were prepared and characterised in detail. The results show that whereas most molecules had entrapment efficiency (EE%) in the range of 20-80%, R6G exhibited near 100% efficiency. Moreover, the colloidal system can be tuned to incorporate R6G with the extent of entrapment spanning at least 2 orders of magnitude (i.e. from 0.04 to 4 mg) and a maximum EE% of 98%. In conclusion, the study demonstrates the promise of the proposed mixed organosilane system in forming colloidal particles containing multiple functional groups with selective loading of highly hydrophobic molecules.

From a silane monomer to anisotropic buckled silica nanospheres: a polymer-mediated, solvent-free and one-pot synthesis.

The morphology of particles, along with other particle attributes, has been shown to affect the biological fate of particles administered into the body. Particles with collapsed surfaces or shells (dimpled, buckled or crumpled) can have different appearances, under the microscope, that resemble many things encountered in our daily life, such as apples/cherries, doughnuts, and bowls. Recent studies have demonstrated that they are not just particles with interesting geometries, but they can also be used as functional blocks for assembled complex materials. Since previous research focus has been on micron-sized particles and organic solvents were often used, it is of particular interest to synthesize the nanosized counterpart with a buckled surface using a purely aqueous method. Herein we report a facile method for rapid synthesis of buckled silica nanoparticles (SiNPs) based on S-nitrosothiol chemistry in a solvent-free reaction. 3-Mercaptopropyl trimethoxysilane (MPTMS) was used as a single silane source in a one-pot aqueous solution containing sodium nitrite and polyvinyl alcohol (PVA). Upon the addition of HCl, S-nitrosation and condensation of MPTMS occur simultaneously and the reaction system undergoes a rapid transition from a clear solution to a solution containing nanoparticles with a lag time controlled mainly by the amount of HCl added. The experimental parameters were systematically studied to determine the optimal concentration of each component. For a typical reaction, sub-100 nm nanoparticles can be produced in less than 1 h, and the best result can be obtained within 2 to 4 h. Remarkably, the nanoparticle exhibits buckled surface morphologies under TEM and SEM. The average size is about 60 nm in diameter. Moreover, the solid-state Si-NMR data show that T2 and T3 silicon species are rapidly evolved with slight dynamic changes over the reaction time. Further, PVA is shown to control the surface buckling as well as to stabilize the formed particles. The as-prepared SiNPs can be used as a nitric oxide (NO) carrier with the potential to release NO in an apparent zero-order manner. In conclusion, the study demonstrates the feasibility of employing an aqueous route for efficiently preparing SiNPs with multifarious surface cavities based on S-nitrosothiol chemistry.

Silica Ouzo Effect: Amphiphilic Drugs Facilitate Nanoprecipitation of Polycondensed Mercaptosilanes.

Amphiphilic drugs are therapeutic agents whose molecular structures contain both hydrophobic and hydrophilic portions. Here we report a systematic study on how amphiphilic drugs can assist in silica nanoprecipitation. 3-Mercaptopropyltrimethoxysilane (MPTMS) was used as the sole silica material and 12 amphiphilic drugs spanning a wide spectrum of therapeutic categories were included. MPTMS polycondensation was conducted in a DMSO-based organic phase. After a sufficient time, particle formation was induced by injecting a small amount of the organic phase into a water solution containing various amphiphiles. The results show that all amphiphilic drugs studied exerted concentration-dependent facilitating effect on nanoparticle formation. Under certain preparation conditions, the particle solution showed physical stability over a long period and the formed particles could be as small as 100 nm. By systematically varying drug concentrations and injection volumes, the ability of each amphiphile to promote nanoprecipitation can be quantified and compared, based on two novel indices: the area under the critical volume-concentration curve (AUC) and the critical stabilization concentration (CSC). We demonstrate that both ability indices significantly correlated with the drug's log P and critical micelle concentrations (CMC). Furthermore, we have optimized the aging and particle purification condition and extensively characterized our system through comprehensive TEM and zeta-potential measurements, as well as determinations for drug entrapment and release. In conclusion, we have established a quantitative structure-activity relationship for amphiphilic small-molecular drugs in their ability to interact with poly(mercaptopropyl)silsesquioxane species and form nanoparticles via solvent shifting. We speculate that both hydrophobic and electrostatic interactions play important roles in the formation and stabilization of nanoparticles.

LbL Assembly of Albumin on Nitric Oxide-Releasing Silica Nanoparticles Using Suramin, a Polyanion Drug, as an Interlayer Linker.

Preformed protein corona of nanoparticles can be utilized as a promising formulation strategy for improving nano drug delivery. Nitric oxide (NO) is a labile molecule with extensive therapeutic implications. In this study, we test whether preformation of protein coatings can enhance the performance of NO-delivering nanoparticles. S-Nitroso (SNO) silica nanoparticles (SNO-SiNPs) were prepared using a nanoprecipitation method. For the first time, bovine serum albumin (BSA) was used to coat NO-releasing nanoparticles, facilitated by a polyanionic drug, suramin, under a layer-by-layer (LbL) scheme. Bare and coated nanoparticles were characterized by zeta-potential, size, and spectroscopic measurements. We demonstrate that albumin/suramin-surface coassembly has advantages in preventing particle aggregation during lyophilization, controlling NO release and exerting an enhanced anticancer effect.

Nitroxidative chemistry interferes with fluorescent probe chemistry: implications for nitric oxide detection using 2,3-diaminonaphthalene.

Simultaneous production of nitric oxide (NO) and superoxide generates peroxynitrite and causes nitroxidative stress. The fluorometric method for NO detection is based on the formation of a fluorescent product from the reaction of a nonfluorescent probe molecule with NO-derived nitrosating species. Here, we present an example of how nitroxidative chemistry could interact with fluorescent probe chemistry. 2,3-Naphthotriazole (NAT) is the NO-derived fluorescent product of 2,3-diaminonaphthalene (DAN), a commonly used NO-detecting molecule. We show that NO/superoxide cogeneration, and particularly peroxynitrite, mediates the chemical decomposition of NAT. Moreover, the extent of NAT decomposition depends on the relative fluxes of NO and superoxide; the maximum effect being reached at almost equivalent generation rates for both radicals. The rate constant for the reaction of NAT with peroxynitrite was determined to be 2.2×10(3)M(-1)s(-1). Further, various peroxynitrite scavengers were shown to effectively inhibit NO/superoxide- and peroxynitrite-mediated decomposition of NAT. Taken together, the present study suggests that the interference of a fluorometric NO assay can be originated from the interaction between the final fluorescent product and the formed reactive nitrogen and oxygen species.

Direct formation of S-nitroso silica nanoparticles from a single silica source.

Nitric oxide (NO) is a ubiquitous molecule in the body. Because of its multiple pathophysiologic roles, the potential for treating various diseases by the exogenous administration of NO has been under intensive investigation. However, the unstable, radical nature of NO poses a major challenge to the effective delivery of NO. Previously, silica nanoparticles synthesized by the traditional method have been developed into NO-carrying systems. In the present study, for the first time NO-carrying silica nanoparticles were prepared from a single silica precursor using a simple nanoprecipitation method. (3-Mercaptopropyl)-trimethoxysilane (MPTMS) was used as the sole silane source, which was subjected to acid-catalyzed S-nitrosation and condensation reactions in a one-pot organic phase. S-Nitroso silica nanoparticles (SNO-SiNPs) were then produced by injecting a smaller quantity of the organic phase into a larger amount of water without surfactants. Various preparation parameters were tested to obtain optimized conditions. Moreover, a phase diagram demonstrating the ouzo effect was constructed. The prepared SNO-SiNPs were spherical particles with a tunable size in the range of 100-400 nm. The nanoparticles in aqueous dispersions exhibited high colloid stability, possibly resulting from highly negatively charged surfaces. The result of solid-state (29)Si NMR shows the predominance of T(2) and T(3) silicon structures, suggesting that nanoparticles were formed from polycondensed silica species. In conclusion, NO-loaded silica nanoparticles have been directly prepared from a single silane precursor using a surfactant-free, low-energy, one-step nanoprecipitation approach. The method precludes the need for the initial formation of bare particles and subsequent functionalization steps.

Versatile synthesis of thiol- and amine-bifunctionalized silica nanoparticles based on the ouzo effect.

In this article, we report a novel, nanoprecipitation-based method for preparing silica nanoparticles with thiol and amine cofunctionalization. (3-Mercaptopropyl)trimethoxysilane (MPTMS) and 3-aminopropyltrimethoxysilane (APTMS) were used as the organosilane precursors, which were subjected to acid-catalyzed polycondensation in an organic phase containing a water-miscible solvent (e.g., dimethyl sulfoxide). A pale colloidal solution could be immediately formed when the preincubated organic phase was directly injected into water. The initial composition ratio between MPTMS and APTMS is an important factor governing the formation of nanoparticles. Specifically, large, unstable micrometer-sized particles were formed for preparation using MPTMS as the sole silane source. In contrast, when APTMS was used alone, no particles could be formed. By reducing the fraction of APTMS (or increasing that of MPTMS) in the initial mixture of organosilanes, the formation of nanometer-sized particles occurred at a critical fraction of APTMS (i.e., 25%). Remarkably, a tiny fraction (e.g., 1%) of APTMS was sufficient to produce stable nanoparticles with a hydrodynamic diameter of about 200 nm. Other factors that would also affect particle formation were determined. Moreover, an interesting temperature effect on particle formation was observed. The TEM micrographs show spherical nanospheres with mean sizes of 130-150 nm in diameter. The solid-state (29)Si NMR spectra demonstrate that the hybrid silica materials contain fully and partially condensed silicon structures. The bifunctionalized silica nanoparticles have positive zeta potentials whose magnitudes are positively correlated with the amount of APTMS. The total thiol content, however, is negatively correlated with the amount of APTMS. The cationic nanoparticles can bind an antisense oligonucleotide in a composition-dependent manner.

A nano-platform harnessing synergistic amino acid browning for biomedical applications.

Amino acids show promise as versatile biomolecules for creating a variety of functional biomaterials. Previously, we discovered a novel amino acid reaction, in which a single amino acid can form browning species in a simple solvent mixture comprising DMSO and acetone at room temperature. In the present study, we initially conducted a comprehensive analysis of 190 pairs of binary amino acids (i.e., all the possible pairwise combinations out of 20 amino acids) and identified several surprising combinations that exhibited synergistic browning effects. Particularly, cysteine-lysine and cysteine-arginine pairs exhibited pronounced browning in DMSO/acetone cosolvent solutions. We hypothesize that the coloured species result from the formation of extended, hydrophobic molecules with highly conjugated systems, arising from extensive condensation reactions between amino acids. Subsequently, we aimed at developing a nano-platform based on this newly discovered amino acid reaction. We demonstrate that through a nanoprecipitation process (solvent-shifting), spherical nanoparticles with sizes ranging from 100 to 200 nm can be produced, in the presence of ferric ions added to the water phase. Through systematic optimization and comprehensive characterization, the final product is a zwitterionic, charge-reversible nanoparticle featuring three functional groups on its surface: carboxylates, amines, and thiols. Furthermore, it possesses mild antioxidant activity, making it a new type of nano-antioxidant. Finally, we present preliminary results highlighting the potential of using this new nanomaterial as a delivery system for polynucleotides. In conclusion, the paper introduces a novel class of amino acid-derived nanoparticles with significant promise for future biomedical applications.

Chemical reactivity of the tryptophan/acetone/DMSO triad system and its potential applications in nanomaterial synthesis.

Previously, we reported a novel browning reaction of amino acids and proteins in an organic solvent mixture composed of dimethyl sulfoxide (DMSO) and acetone. The reaction proceeds under surprisingly mild conditions, requiring no heating or additional reactants or catalysts. This present study aimed to investigate the chemical reactivity of the triad reaction system of l-tryptophan/aectone/DMSO. We demonstrated that, in DMSO, l-tryptophan initially catalyzed the self-aldol condensation of acetone, resulting in the formation of mesityl oxide (MO). Furthermore, we showed that the three-component system evolved into a diverse chemical space, producing various indole derivatives with aldehyde or ketone functional groups that exhibited self-assembling and nanoparticle-forming capabilities. We highlight the potential applications in nanomaterial synthesis.

Superoxide dismutase as a novel macromolecular nitric oxide carrier: preparation and characterization.

Nitric oxide (NO) is an important molecule that exerts multiple functions in biological systems. Because of the short-lived nature of NO, S-nitrosothiols (RSNOs) are believed to act as stable NO carriers. Recently, sulfhydryl (SH) containing macromolecules have been shown to be promising NO carriers. In the present study, we aimed to synthesize and characterize a potential NO carrier based on bovine Cu,Zn-superoxide dismutase (bSOD). To prepare S-nitrosated bSOD, the protein was incubated with S-nitrosoglutathione (GSNO) under varied experimental conditions. The results show that significant S-nitrosation of bSOD occurred only at high temperature (50 °C) for prolonged incubation time (>2 h) S-nitrosation efficiency increased with reaction time and reached a plateau at ~4 h. The maximum amount of NO loaded was determined to be about 0.6 mol SNO/mol protein (~30% loading efficiency). The enzymatic activity of bSOD, however, decreased with reaction time. Our data further indicate that NO functionality can only be measured in the presence of extremely high concentrations of Hg2+ or when the protein was denatured by guanidine. Moreover, mildly acidic pH was shown to favor S-nitrosation of bSOD. A model based on unfolding and refolding of bSOD during preparation was proposed to possibly explain our observation.

A General Biphasic Bodyweight Model for Scaling Basal Metabolic Rate, Glomerular Filtration Rate, and Drug Clearance from Birth to Adulthood.

The objective of this study is to propose a unified, continuous, and bodyweight-only equation to quantify the changes of human basal metabolic rate (BMR), glomerular filtration rate (GFR), and drug clearance (CL) from infancy to adulthood. The BMR datasets were retrieved from a comprehensive historical database of male and female subjects (0.02 to 64 years). The CL datasets for 17 drugs and the GFR dataset were generated from published maturation and growth models with reported parameter values. A statistical approach was used to simulate the model-generated CL and GFR data for a hypothetical population with 26 age groups (from 0 to 20 years). A biphasic equation with two power-law functions of bodyweight was proposed and evaluated as a general model using nonlinear regression and dimensionless analysis. All datasets universally reveal biphasic curves with two distinct linear segments on log-log plots. The biphasic equation consists of two reciprocal allometric terms that asymptotically determine the overall curvature. The fitting results show a superlinear scaling phase (asymptotic exponent >1; ca. 1.5-3.5) and a sublinear scaling phase (asymptotic exponent <1; ca. 0.5-0.7), which are separated at the phase transition bodyweight ranging from 5 to 20 kg with a mean value of 10 kg (corresponding to 1 year of age). The dimensionless analysis generalizes and offers quantitative realization of the maturation and growth process. In conclusion, the proposed mixed-allometry equation is a generic model that quantitatively describes the phase transition in the human maturation process of diverse human functions.

Similarity and dissimilarity of thiols as anti-nitrosative agents in the nitric oxide-superoxide system.

Concomitant production of nitric oxide and superoxide in biological systems has been proposed to generate numerous reactive oxygen and nitrogen species that cause oxidative and nitrosative stress. Thiols, especially glutathione, play an important role in cellular defense against radical species. In the present study, we investigated and compared the anti-nitrosative activity of a wide range of thiols in a simplified chemical system of co-generated nitric oxide and superoxide. Of the 13 thiols studied, three groups of thiols are distinguishable: (i) Group I includes cysteine and its four congeners (cysteine methyl ester, cysteine ethyl ester, homocysteine, cysteamine); they are subject to rapid oxidative decomposition and have the least anti-nitrosative activity. (ii) Group II consists of glutathione, penicillamine, tiopronin and mesna; they have the greatest effect on delaying the nitrosation reaction. (iii) Group III comprises N-acetylcysteine, N-acetylpenicillamine, captopril, and thioglycolate; they all have high pK(a) for the mercapto group and show the strongest inhibitory effect on the rate and extent of nitrosation in the system studied.

Stable Encapsulation of Methylene Blue in Polysulfide Organosilica Colloids for Fluorescent Tracking of Nanoparticle Uptake in Cells.

Methylene blue (MB), a century-old drug and a fluorescent dye, has a long history of diverse applications, both in drug therapy and as a tissue-staining agent. However, MB is inherently unstable when exposed to light and reducing agents. In this study, we aim to prepare and characterize polysulfide-based organosilica colloidal particles for efficient, stable, and protective encapsulation of MB. Disulfide- and tetrasulfide-containing organosilane congeners were used as organosilica precursors for direct synthesis of organosilica colloids based on the silica ouzo effect. MB was spontaneously entrapped into the colloidal particles during the particle formation process. The following properties of the colloidal MB were evaluated: particle size, surface charge, atomic distribution, encapsulation efficiency, MB release, photodynamic activity, thiol and ascorbate reactivity, and cytotoxicity. The DLS measurements show that the size of colloidal MB is tunable in a range of 100 nm to 1 µm. SEM images reveal spherical particles with composition-dependent particle sizes of 70-120 nm (coefficient of variation: 15-18%). MB was encapsulated in the colloidal particles with a maximal efficiency of 95%. The release of MB from the colloids was <1% at 4 h and <3.5% at 48 h. The colloidal particles show much reduced photodynamic activity, low reactivity toward reducing agents, and low cytotoxicity. Accordingly, the colloidal MB was proposed and further investigated as a fluorescent particle tracer for the study of cell-nanoparticle interactions. In conclusion, MB can be efficiently and stably loaded into polysulfide organosilica colloidal particles using a simple and convenient physical route.

Organosilica colloids as nitric oxide carriers: Pharmacokinetics and biocompatibility.

Nitric oxide (NO) is a potential therapeutic agent for various diseases. However, it is challenging to deliver this unstable, free-radical gaseous molecule in the body. Various nanoparticle-based drug delivery systems have been investigated as promising NO carriers without detailed characterization of their biological fate. The purpose of this study is to investigate the pharmacokinetics and biocompatibility of organosilica-based NO-delivering nanocarriers. Two distinct NO nanoformulations, namely NO-SiNP-1 and NO-SiNP-2, were prepared from a thiol-functionalized organosilane using nanoprecipitation and direct aqueous synthesis, respectively. During the preparation, the thiol group was converted to S-nitrosothiol (SNO) under a nitrosation condition. The final products contain SNO-loaded organosilica particles of similar sizes (~130 nm), but of different morphologies and surface charges (between the two formulations). In the in vitro release kinetics study, NO-SiNP-1 exhibited a much slower NO release rate than NO-SiNP-2 (by 5-fold); therefore, the former is considered as a slow NO releaser, and the latter a fast NO releaser. However, in the rat pharmacokinetic study (IV bolus of 50 µmol/kg), NO-SiNP-1 was rapidly eliminated from the blood (within 20 min); in contrast, NO-SiNP-2 was slowly eliminated with an extended circulation time of 12 h for plasma SNO, along with markedly higher plasma levels of nitrite and nitrate. The two formulations are generally biocompatible. In conclusion, the paper presents contrast biological fates of two organosilica colloidal formulations for nitric oxide delivery.

Versatile composite hydrogels for drug delivery and beyond.

Hydrogels have extended applications across multiple fields. A novel hydrogel material is often evaluated for its properties and applications in either a wet or dry state, but not both. In this study, we investigated a protein-based, composite hydrogel system in both its wet and dry states. Bovine serum albumin (BSA) was used as the hydrogel base. With the assistance of organosilanes, BSA solutions became hydrogels under facile reaction conditions. In the first part, the wet gel was prepared in situ in a syringe; upon injecting through a needle, the gel retained its structure. The use of the nascent gel system as an injectable drug-delivery vehicle is of particular interest. We therefore developed a microplate platform that allows a "one-plate" study-i.e. gel preparation, payload loading and release-all being performed in a single plate. This one-plate method further enables a systematic study of various controlling parameters for drug release. For example, we can tune the release rate by simply adjusting the phosphate content in the hydrogel formulation. Besides, for low-releasing compounds, the release profile was also tunable while using the one-plate method. In the second part, we further demonstrate the versatility of our composite hydrogels. By simply varying the feed ratio of two organosilanes, (3-mercaptopropyl)methyldimethoxysilane and (3-mercaptopropyl)trimethoxysilane, and phosphate concentrations, dry gels exhibiting various absorption capacities towards water, organic solvents, and oil can be prepared. Further characterizations using SEM and 29Si NMR spectroscopy revealed porous structures and hybrid siloxane bridges within the composite material.

Kinetics of fluoride-catalysed synthesis of organosilica colloids in aqueous solutions of amphiphiles.

Reactions involving hydrophobic reactants in water can be much accelerated in organic solvent-free solutions containing amphiphiles at neutral pH and room temperature. Previously, we demonstrated that organosilica colloidal particles could be conveniently synthesized by a versatile salt-catalysis method in solutions modified with various amphiphilic molecules. The method precludes the use of any solvent, any added form of energy (thermal or mechanical), and any strong (or hazardous) acids/bases. Herein, the kinetic properties of the reaction were systematically investigated for fluoride-catalysed synthesis of colloidal organosilica from a thiol-functionalized organosilane precursor, (3-mercaptopropyl)trimethoxysilane. Continuous, real-time ATR-FTIR measurements allowed probing the time evolution of organosilica condensation in different reaction systems, containing one of the following: non-ionic surfactants (Tween 20, Tween 40, Tween 60, Tween 80, Triton X-100), anionic surfactant (sodium dodecyl sulphate; SDS), cationic surfactant (cetyltrimethylammonium bromide; CTAB), and amphiphilic polymers (polyvinyl alcohol and polyvinylpyrrolidone). Overall, while some amphiphile-specific properties were revealed, fluoride-catalysed synthesis was ultrafast with a universal two-phase kinetic scheme (e.g. transition within 5-10 min) for all amphiphiles studied.

Facile green synthesis of organosilica nanoparticles by a generic "salt route".

Colloidal silica has wide applications and the global demand of specialty silica is continually increasing. Therefore, it is significant to develop a synthetic method that is simple, versatile, energy-saving, ecologically benign, and easily scalable. Biomimetic synthesis of colloidal silica represents a promising strategy; however, it often requires the synthesis or extraction of specialized macromolecules. In this paper, we present a novel aqueous, one-pot, and green route for synthesis of organosilica nanoparticles. The reaction systems contain only water, an organosilane precursor, a salt, and a commonly used surfactant or amphiphilic polymer. The reaction was performed at ambient conditions without adding any additional solvent, energy, and harsh chemicals. The key findings include the novel identification of 5 salts (i.e. nitrite, fluoride, dibasic phosphate, acetate, and sulfite) that can catalyze organosilica condensation and the resulting formation of nano-colloids. Moreover, the presence of amphiphilic molecules is essential for salt catalysis at low salt concentrations and at nearly neutral pH. Solid-state NMR and in-situ ATR-FTIR studies confirmed that organosilica condensation is highly efficient under the mild reaction condition. In conclusion, the present study demonstrates that "soft" interaction between salts and surfactants (or polymers) can be utilized to construct an effective platform for synthesis of "hard" organosilica particles. The proposed method is generic and applicable to a wide range of commonly used surfactants (viz. non-ionic, anionic, cationic) and amphiphilic polymers, as well as to organosilanes with various hydrophobic functional groups (e.g. mercaptopropyl, vinyl, and methyl).

Turning proteins into hydrophobic floatable materials with multiple potential applications.

HYPOTHESIS: Protein hydrogels are water-rich structure of cross-linked protein networks. The preparation of dry gels is conceptually simple. However, reports on innovative use of dry protein hydrogels are scarce, possibly because water removal would diminish intended properties. Here, an oil-like thiol-organosilane is proposed as a protein hydrogel-promoting agent that mediates the formation of hydrophobic composite gel networks with promising properties upon drying. EXPERIMENTS: 3-Mercaptopropyltrimethoxylsilane (MPTMS) was used to transform aqueous albumin solutions into hydrogels. The gelation conditions were systematically investigated and optimized by varying various parameters, including temperature, pH, and the concentrations of MPTMS, albumin, and phosphate. The hydrogels were freeze-dried to obtain dry gel monoliths. The morphology of gel structure was evaluated using FE-SEM. The following properties of the dry monoliths were further evaluated: water uptake, floatability, drug loading and release, water contact angles, bulk densities, and oil adsorption. Mechanistic investigation included FTIR and fluorescence quenching determinations, and the study of emulsion properties. FINDINGS: An unprecedented protein-organosilane composite hydrogel was synthesized in a one-step reaction, at neutral pH and ambient conditions. Freeze-dried gel monoliths exhibited excellent hydrophobicity and floatability (immediate floating and lasting for >7 days on water). The proposed material may find novel applications in floating drug delivery and environmental clean-up of oil spills.

Analysis of Pharmacokinetic and Pharmacodynamic Parameters in EU- Versus US-Licensed Reference Biological Products: Are In Vivo Bridging Studies Justified for Biosimilar Development?

BACKGROUND: Bridging studies are mandatory in the EU and USA if the reference biological product used in the biosimilar comparability exercise is foreign sourced. However, it has been argued that the duplication of bridging studies may limit biosimilar development. OBJECTIVE: The aim of the study was to explore whether it is necessary to conduct pharmacokinetic (PK)/pharmacodynamic (PD) bridging studies for biosimilars. This study examines similarities and differences between EU- and US-licensed reference biological products, based on literature-reported PK and/or PD data. METHODS: We searched PubMed, Drugs@FDA, and European Medicines Agency (EMA) databases to identify biosimilar bridging studies designed to evaluate similarities between EU- and US-licensed reference biological products. PK and/or PD parameters were retrieved; the ratio of the parameter value of the EU-licensed product to that of the US-licensed product and its corresponding 90% confidence intervals (CIs) were calculated. Similarity was declared if the 90% CIs for the ratios of the PK or PD parameters were within the range of 80-125%. RESULTS: Thirty-one bridging studies were identified for 11 biosimilars, including adalimumab (n = 10), bevacizumab (n = 4), epoetin alfa (n = 1), etanercept (n = 2), filgrastim (n = 1), infliximab (n = 3), insulin glargine (n = 1), insulin lispro (n = 1), PEGfilgrastim (n = 2), rituximab (n = 2), and trastuzumab (n = 4). Most studies showed PK and/or PD similarities between the EU- and US-licensed reference biological products. However, among the 31 studies, only three studies (accounting for two biologics, PEGfilgrastim and adalimumab) showed dissimilarity between the EU and US reference products. Although one bridging study on PEGfilgrastim (Sandoz) indicated dissimilar PKs (maximum observed plasma concentration [Cmax] and area under the concentration-time curve [AUC]) between the reference products, the other study (Mylan) demonstrated similar PK. Moreover, two of ten studies involving adalimumab failed to demonstrate similarities between the reference products. However, for both cases, PK similarities were later confirmed in the follow-up bridging studies with larger sample sizes. CONCLUSION: Our analysis reveals that, in most cases, the reference biological products originated from the EU and those from the USA are almost indistinguishable in terms of PK/PD properties. Additional in vivo bridging studies between reference products from different global regions may not be required if similar physicochemical and structural properties are evident in vitro.