Interaction between Albumin and Pluronic F127 Block Copolymer Revealed by Global and Local Physicochemical Profiling

Gelation Behaviour of Pluronic F127/Polysaccharide Systems Revealed via Thioflavin T Fluorescence

Fast, reliable methods for characterizing the micelle-to-gel transition in emerging Pluronic F127/polysaccharide materials are essential for tailoring their applications as in situ gelling delivery systems. This study describes a simple fluorimetric method based on the response to gelation of the molecular probe thioflavin T (ThT). The techniques employed are (second derivative) steady-state and synchronous fluorescence. The capabilities of ThT as gelation reporter are tested for three model systems: Pluronic F127 (P16.6%), Pluronic F127/alginate (P16.6%ALG2%) and Pluronic F127/hyaluronic acid (P16.6%HA0.5%). We demonstrate that the changes in the short and long wavelength emissions of ThT allow accurate determination of the critical gelation temperatures in the investigated systems. The spectroscopic data providing information at molecular level are complemented with differential scanning microcalorimetric results revealing additional macroscopic insight into the micellization process. The gelation study is preceded by a solvatochromic analysis of ThT.

Role of Bovine Serum Albumin Addition in Micellization and Gel Formation of Poloxamer 407

The combination of the thermoresponsive polymer and protein has demonstrated great promise in its applications in drug delivery and tissue engineering fields. This study described the impact of bovine serum albumin (BSA) on the micellization and sol-gel transition behaviors of poloxamer 407 (PX). The micellization of aqueous PX solutions with and without BSA was examined using isothermal titration calorimetry. In the calorimetric titration curves, the pre-micellar region, the transition concentration region, and the post-micellar region were observed. The presence of BSA had no noticeable impact on critical micellization concentration, but the inclusion of BSA caused the pre-micellar region to expand. In addition to studying the self-organization of PX at a particular temperature, the temperature-induced micellization and gelation of PX were also explored using differential scanning calorimetry and rheology. The incorporation of BSA had no discernible effect on critical micellization temperature (CMT), but it did affect gelation temperature (T_gel) and gel integrity of PX-based systems. The response surface approach illustrated the linear relation between the compositions and the CMT. The major factor affecting the CMT of the mixtures was the concentration of PX. The alteration of the T_gel and the gel integrity were discovered to be a consequence of the intricate interaction between PX and BSA. BSA mitigated the inter-micellar entanglements. Hence, the addition of BSA demonstrated a modulating influence on T_gel and a softening effect on gel integrity. Understanding the influence of serum albumin on the self-assembly and gelation of PX will enable the creation of thermoresponsive drug delivery and tissue engineering systems with controlled gelation temperatures and gel strength.

Nano Differential Scanning Fluorimetry as a Rapid Stability Assessment Tool in the Nanoformulation of Proteins

The development and production of innovative protein-based therapeutics is a complex and challenging avenue. External conditions such as buffers, solvents, pH, salts, polymers, surfactants, and nanoparticles may affect the stability and integrity of proteins during formulation. In this study, poly (ethylene imine) (PEI) functionalized mesoporous silica nanoparticles (MSNs) were used as a carrier for the model protein bovine serum albumin (BSA). To protect the protein inside MSNs after loading, polymeric encapsulation with poly (sodium 4-styrenesulfonate) (NaPSS) was used to seal the pores. Nano differential scanning fluorimetry (NanoDSF) was used to assess protein thermal stability during the formulation process. The MSN-PEI carrier matrix or conditions used did not destabilize the protein during loading, but the coating polymer NaPSS was incompatible with the NanoDSF technique due to autofluorescence. Thus, another pH-responsive polymer, spermine-modified acetylated dextran (SpAcDEX), was applied as a second coating after NaPSS. It possessed low autofluorescence and was successfully evaluated with the NanoDSF method. Circular dichroism (CD) spectroscopy was used to determine protein integrity in the case of interfering polymers such as NaPSS. Despite this limitation, NanoDSF was found to be a feasible and rapid tool to monitor protein stability during all steps needed to create a viable nanocarrier system for protein delivery.

Thermosensitive hydrogel releasing nitric oxide donor and anti-CTLA-4 micelles for anti-tumor immunotherapy

Due to their autosynchronous roles in shaping the anti-tumor immune response, complex immune regulatory networks acting both locally within the tumor microenvironment as well as in its draining lymph nodes play critical roles in the cancer immunotherapy response. We describe herein a thermosensitive co-polymer hydrogel system formed from biocompatible polymers gelatin and Pluronic^® F127 that are widely used in humans to enable the sustained release of a nitric oxide donor and antibody blocking immune checkpoint cytotoxic T-lymphocyte-associated protein-4 for efficient and durable anti-tumor immunotherapy. By virtue of its unique gel formation and degradation properties that sustain drug retention at the tumor tissue site for triggered release by the tumor microenvironment and formation of in situ micelles optimum in size for lymphatic uptake, this rationally designed thermosensitive hydrogel facilitates modulation of two orthogonal immune signaling networks relevant to the regulation of the anti-tumor immune response to improve local and abscopal effects of cancer immunotherapy.

Model Systems for Evidencing the Mediator Role of Riboflavin in the UVA Cross-Linking Treatment of Keratoconus

Riboflavin under UVA radiation generates reactive oxygen species (ROS) that can induce various changes in biological systems. Under controlled conditions, these processes can be used in some treatments for ocular or dermal diseases. For instance, corneal cross-linking (CXL) treatment of keratoconus involves UVA irradiation combined with riboflavin aiming to induce the formation of new collagen fibrils in cornea. To reduce the damaging effect of ROS formed in the presence of riboflavin and UVA, the CXL treatment is performed with the addition of polysaccharides (dextran). Hyaluronic acid is a polysaccharide that can be found in the aqueous layer of the tear film. In many cases, keratoconus patients also present dry eye syndrome that can be reduced by the application of topical solutions containing hyaluronic acid. This study presents physico-chemical evidence on the effect of riboflavin on collagen fibril formation revealed by the following methods: differential scanning microcalorimetry, rheology, and STEM images. The collagen used was extracted from calf skin that contains type I collagen similar to that found in the eye. Spin trapping experiments on collagen/hyaluronic acid/riboflavin solutions evidenced the formation of ROS species by electron paramagnetic resonance measurements.

In Situ Nanotransformable Hydrogel for Chemo-Photothermal Therapy of Localized Tumors and Targeted Therapy of Highly Metastatic Tumors

Metastasis is one of the predisposing factors for cancer-related mortalities worldwide. Patients with advanced cancers (stage IV) receive palliative care with minimal possibility of achieving complete remission. Antibody-based therapeutic modalities are capable of targeting tumors that are confined to a particular location but are ineffective in targeting distant secondary tumors. In the current study, we have developed a smart nano-transforming hydrogel (NTG) that transforms in situ to polymeric nanoparticles (PA NPs) of 100-150 nm when injected subcutaneously. These nanoparticles targeted the primary and secondary metastatic tumors for up to ∼5 and ∼3 days, respectively. The in situ-formed PA NPs also demonstrated a pH-responsive drug release resulting in about ∼80% release within 100 h at 5.8 pH. When tested in vivo, substantial inhibition of lung metastases was observed compared to chemotherapy, thus demonstrating the efficiency of nanotransforming hydrogels in targeting and inhibiting primary and secondary metastatic tumors.

Mechano-Responsive, Tough, and Antibacterial Zwitterionic Hydrogels with Controllable Drug Release for Wound Healing Applications

Acute wounds subject to frequent deformations are difficult to be treated because the healing process was easily interfered by external mechanical forces. Traditional wound dressings have limited efficacy because of their poor mechanical properties and skin adhesiveness and difficulty in the delivery of therapeutic drugs effectively. As such, tough and skin-adhesive wound dressings with sustainable and stimuli-responsive drug release properties for treatment of those wounds are highly desirable. For this purpose, we have developed a mechano-responsive poly(sulfobetaine methacrylate) hydrogel which aims to control the delivery of antibiotic drug upon application of mechanical forces. Diacrylated Pluronic F127 micelles were used as a macro-cross-linker of the hydrogel and loaded with hydrophobic antimicrobial drugs. The micelle-cross-linked hydrogel has excellent mechanical properties, with the ultimate tensile strength and tensile strain of up to 112 kPa and 1420%, respectively, and compressive stress of up to 1.41 MPa. Adhesiveness of the hydrogel to the skin tissue was ∼6 kPa, and it did not decrease significantly after repetitive adhesion cycles. Protein adsorption on the hydrogel was significantly inhibited compared to that on commercial wound dressings. Because of the mechano-responsive deformation of micelles, the release of drug from the hydrogel could be precisely controlled by the extent and cycles of mechanical loading and unloading, endowing the hydrogel with superior antibacterial property against both Gram-positive and Gram-negative bacteria. In addition, drug penetration into the skin tissue was enhanced by mechanical stress applied to the hydrogel. The micelle-cross-linked zwitterionic hydrogel also showed good cell biocompatibility, negligible skin irritation, and healing capacity to acute skin wounds in mice. Such a tough mechano-responsive hydrogel holds great promise as wound dressings for acute wounds subjected to frequent movements.

Adsorption and Interaction of Bovine Serum Albumin and Pluronic P103 Triblock Copolymer on a Gold Electrode: Double-Layer Capacitance Measurements

The interactions of proteins and other molecules and their adsorption onto substrates is a fascinating topic that has been applied to surface technologies, biosensors, corrosion studies, biotechnologies, and other fields. The success of these applications requires a previous characterization using some analytical techniques that, ordinarily, are not electrochemical. This work proposes analyzing the variation of the double-layer capacitance obtained through impedance electrochemical spectroscopy as an alternative strategy to show evidence of the interactions between proteins and triblock copolymers. The proposal is supported through the study of the interaction and adsorption of bovine serum albumin (BSA) and a commercial triblock copolymer (P103) in phosphate buffer on a gold electrode. The double-layer capacitance and the apparent interface thickness vs polarization potential curves as well as the potential of zero charge for pure P103 (0.6 wt %, corresponding to 6 g L^-1), pure BSA (3 mg mL^-1), and P103-BSA solutions (0.6 wt % and 3 mg mL^-1, respectively) are sensitive enough to show not only the interaction and the adsorption of the species but also the polarization potential where these interactions are taking place. A qualitative and quantitative analysis concerning the double-layer capacitance behavior is given. The significance and impact of this work is also presented.

Structural peculiarities of lysozyme - PLURONIC complexes at the aqueous-air and liquid-liquid interfaces and in the bulk of aqueous solution

Interaction between proteins and synthetic polymers that represent a perspective potential in drug delivery or/and already used in medicine plays a key role in biological functioning of both molecules along with a system as a whole. In present study association between hen egg white lysozyme and Pluronic triblock-copolymers (L121, P123 and F127) in the bulk of the solution as well as at the aqueous-air and liquid-liquid interfaces was analyzed by means of spectroscopic and radiochemical assay. In protein-Pluronic complexes lysozyme keeps the secondary structure (CD and SAXS data results), while fluorescence and UV-analysis indicates changes in the local surrounding of fluorophoric amino acid residues. Radiochemical assay in combination with molecular docking reveals the formation of the complexes, in which proline residues turned to the interface between water and hydrophobic medium.

Colloidal stability of graphene oxide nanosheets in association with triblock copolymers: A neutron scattering analysis

This study investigates stabilization of graphene oxide (GO) nanosheets in polyethylene oxide-polypropylene oxide (PEO-PPO) block copolymers (P103, P123 and F127). Changes in micellization of copolymers upon GO addition were monitored using dynamic light (DLS) and small angle neutron scattering (SANS). Structural developments at sheet surface were studied with two possibilities; (i) adsorption of PPO block over hydrophobic basal plane allowing the engagement of hydrophilic PEO with aqueous bulk, and (ii) adsorption of micelles mediated via carboxylated groups. Insignificant changes in micellar parameters for P123 and P127 were indicative of their inferior interaction with GO. On the other hand, P103 micelles exhibited high affinity for sheets, noticeable as emergence of mass fractals and more than two-fold enhancement in micelle number density. The latter allowed coverage of entire surface with P103 micelles. Existence of mass fractals was verified by extracting the form and structure factors from the fitted SANS data. Spectroscopic and thermogravimetric analyses illustrated non-covalent adsorption of copolymer aggregates. It was interesting to note that the dispersion remained stable against protein and electrolyte addition. A comprehensive understanding on colloidal stability can be valuable for drug delivery applications of GO sheets.

Formation and Stabilization of Gold Nanoparticles in Bovine Serum Albumin Solution

The formation and growth of gold nanoparticles (AuNPs) were investigated in pH 7 buffer solution of bovine serum albumin (BSA) at room temperature. The processes were monitored by UV-Vis, circular dichroism, Raman and electron paramagnetic resonance (EPR) spectroscopies. TEM microscopy and dynamic light scattering (DLS) measurements were used to evidence changes in particle size during nanoparticle formation and growth. The formation of AuNPs at pH 7 in the absence of BSA was not observed, which proves that the albumin is involved in the first step of Au(III) reduction. Changes in the EPR spectral features of two spin probes, CAT16 and DIS3, with affinity for BSA and AuNPs, respectively, allowed us to monitor the particle growth and to demonstrate the protective role of BSA for AuNPs. The size of AuNPs formed in BSA solution increases slowly with time, resulting in nanoparticles of different morphologies, as revealed by TEM. Raman spectra of BSA indicate the interaction of albumin with AuNPs through sulfur-containing amino acid residues. This study shows that albumins act as both reducing agents and protective corona of AuNPs.

Interaction of piroxicam with bovine serum albumin investigated by spectroscopic, calorimetric and computational molecular methods

The binding of drugs to serum proteins is governed by weak non-covalent forces. In this study, the nature and magnitude of the interactions between piroxicam (PRX) and bovine serum albumin (BSA) was assessed using spectroscopic, calorimetric and computational molecular methods. The fluorescence data revealed an atypical behavior during PRX and BSA interaction. The quenching process of tryptophan (Trp) by PRX is a dual one (approximately equal static and dynamic quenched components). The FRET results indicate that a non-radiative transfer of energy occurred. The association constant and the number of binding sites indicate moderate PRX and BSA binding. The competitive binding study indicates that PRX is bound to site I from the hydrophobic pocket of subdomain IIA of BSA. The synchronous spectra showed that the microenvironment around the BSA fluorophores and protein conformation do not change considerably. The Trp lifetimes revealed that PRX mainly quenches the fluorescence of Trp-213 situated in the hydrophobic domain. The CD and DSC investigation show that addition of PRX stabilizes the protein structure. ITC results revealed that BSA-PRX binding involves a combination of electrostatic, hydrophobic and hydrogen interactions. The analysis of the computational data is consistent with the experimental results. This thorough investigation of the PRX-BSA binding may provide support for other studies concerning moderate affinity drugs with serum protein.Communicated by Ramaswamy H. Sarma.

Gallic acid influence on bovine serum albumin thermal stability

A thermoanalytical approach reveals the dual action of GA on BSA thermal stability.

Brain-Targeting Delivery of Two Peptidylic Inhibitors for Their Combination Therapy in Transgenic Polyglutamine Disease Mice via Intranasal Administration

Polyglutamine diseases are a set of progressive neurodegenerative disorders caused by misfolding and aggregation of mutant CAG RNA and polyglutamin protein. To date, there is a lack of effective therapeutics that can counteract the polyglutamine neurotoxicity. Two peptidylic inhibitors, QBP1 and P3, targeting the protein and RNA toxicities, respectively, have been previously demonstrated by us with combinational therapeutic effects on the Drosophila polyglutamine disease model. However, their therapeutic efficacy has never been investigated in vivo in mammals. The current study aims to (a) develop a brain-targeting delivery system for both QBP1 and L1P3V8 (a lipidated variant of P3 with improved stability) and (b) evaluate their therapeutic effects on the R6/2 transgenic mouse model of polyglutamine disease. Compared with intravenous administration, intranasal administration of QBP1 significantly increased its brain-to-plasma ratio. In addition, employment of a chitosan-containing in situ gel for the intranasal administration of QBP1 notably improved its brain concentration for up to 10-fold. Further study on intranasal cotreatment with the optimized formulation of QBP1 and L1P3V8 in mice found no interference on the brain uptake of each other. Subsequent efficacy evaluation of 4-week daily QBP1 (16 μmol/kg) and L1P3V8 (6 μmol/kg) intranasal cotreatment in the R6/2 mice demonstrated a significant improvement on the motor coordination and explorative behavior of the disease mice, together with a full suppression on the RNA- and protein-toxicity markers in their brains. In summary, the current study developed an efficient intranasal cotreatment of the two peptidylic inhibitors, QBP1 and L1P3V8, for their brain-targeting, and such a novel therapeutic strategy was found to be effective on a transgenic polyglutamine disease mouse model.

Triblock-Copolymer-Assisted Mixed-Micelle Formation Results in the Refolding of Unfolded Protein

The present work reports a new strategy for triblock-copolymer-assisted refolding of sodium dodecyl sulfate (SDS)-induced unfolded serum protein human serum albumin (HSA) by mixed-micelle formation of SDS with poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock copolymer EO₂₀PO₆₈EO₂₀ (P123) under physiological conditions. The steady-state and time-resolve fluorescence results show that the unfolding of HSA induced by SDS occurs in a stepwise manner through three different phases of binding of SDS, which is followed by a saturation of interaction. Interestingly, the addition of polymeric surfactant P123 to the unfolded protein results in the recovery of ∼87% of its α-helical structure, which was lost during SDS-induced unfolding. This is further corroborated by the return of the steady-state and time-resolved fluorescence decay parameters of the intrinsic tryptophan (Trp214) residue of HSA to the initial nativelike condition. The isothermal titration calorimetry (ITC) data also substantiates that there is almost no interaction between P123 and the native state of the protein. However, the mixed-micelle formation, accompanied by substantial binding affinities, removes the bound SDS molecules from the scaffolds of the unfolded state of the protein. On the basis of our experiments, we conclude that the formation of mixed micelles between SDS and P123 plays a pivotal role in refolding the protein back to its nativelike state.

Complex interaction of caffeic acid with bovine serum albumin: calorimetric, spectroscopic and molecular docking evidence

Binding of caffeic acid at low concentrations to bovine serum albumin enhances the thermal stability of the protein.

COST Action CM1201 "Biomimetic Radical Chemistry": free radical chemistry successfully meets many disciplines

The COST Action CM1201 "Biomimetic Radical Chemistry" has been active since December 2012 for 4 years, developing research topics organized into four working groups: WG1 - Radical Enzymes, WG2 - Models of DNA damage and consequences, WG3 - Membrane stress, signalling and defenses, and WG4 - Bio-inspired synthetic strategies. International collaborations have been established among the participating 80 research groups with brilliant interdisciplinary achievements. Free radical research with a biomimetic approach has been realized in the COST Action and are summarized in this overview by the four WG leaders.