Comprehensive study on the structure of the BSA from extended-to aged form in wide (2–12) pH range

Analytical Aspects of ANSA-BSA Association: A Thermodynamic and Conformational Approach

Many studies have demonstrated the manner in which ANS interacts with bovine serum albumin (BSA), although they are limited by the extremely low solubility of dye. The present study demonstrates the binding of ANSA dye with BSA, and since this dye can easily replace ANS, it not only simplifies research but also improves sensor accuracy for serum albumin. A combination of calorimetry and spectroscopy has been employed to establish the thermodynamic signatures associated with the interaction of ANSA with the protein and the consequent conformational changes in the latter. The results of differential scanning calorimetry reveal that when the concentration of ANSA in solution is increased, the thermal stability of the protein increases substantially. The fluorescence data demonstrated a decrease in the binding affinity of ANSA with the protein when pH increased but was unable to identify a change in the mode of interaction of the ligand. ITC has demonstrated that the mode of interaction between ANSA and the protein varies from a single set of binding sites at pH 5 and 7.4 to a sequential binding site at pH 10, emphasizing the potential relevance of protein conformational changes. TCSPC experiments suggested a dynamic type in the presence of ANSA. Molecular docking studies suggest that ANSA molecules are able to find ionic centers in the hydrophobic pockets of BSA. The findings further imply that given its ease of use in experiments, ANSA may be a useful probe for tracking the presence of serum albumin and partially folded protein states.

High-performance peptide and disulfide mapping by direct injection of intact proteins using on-line coupled UV-liquid chromatography microdroplet mass spectrometry (UVLC-MMS)

Microdroplet mass spectrometry (MMS), achieving ultra-fast enzyme digestion in the ionization source, holds great promises for innovating protein analysis. Here, in-depth protein characterization is demonstrated by direct injection of intact protein mixtures via on-line coupling MMS with capillary C4 liquid chromatography (LC) containing UV windows (UVLC-MMS) through an enzyme introduction tee. We showed complete sets of peptides of individual proteins (hemoglobin, bovine serum albumin, and ribonuclease A) in a mixture could be obtained in one injection. Such full (100%) sequence coverage, however, could not be achieved by conventional nanoLC-MS method using bottom-up approach with single enzyme. Moreover, direct injection of a chaperone α-crystalline (α-Cry) complex yielded identification of post-translational modifications including novel sites and semi-quantitative characterization including 3:1 stoichiometry ratio of αA- and αB-Cry sub-units and ∼1.4 phosphorylation/subunit on S45 (novel site) and S122 (main site) of αA-Cry, ∼0.7 phosphorylation/subunit on S19 (main site) and S45 of αB-Cry, as well as 100% acetylation on both N-termini of each subunits by matching the mass and retention time of the intact and its digested peptides. Furthermore, trifluoroacetic acid was able to be used in the mobile phase with UVLC-MMS to improve the separation of differentially reduced intact species and detectability of the droplet-digested products. This allowed us to completely map four disulfide linkages of ribonuclease A based on collision-induced dissociation of disulfide clusters, some of which would otherwise not be detected, preventing scrambling or shuffling errors arising from lengthy bulk solution digestion by the bottom-up approach. Integration of UVLC and MMS greatly improves droplet digestion efficiency and MS detection, enabling highly efficient workflow for in-depth and accurate protein characterization.

Recent Advancements and Strategies for Overcoming the Blood-Brain Barrier Using Albumin-Based Drug Delivery Systems to Treat Brain Cancer, with a Focus on Glioblastoma

Glioblastoma multiforme (GBM) is a highly aggressive malignant tumor, and the most prevalent primary malignant tumor affecting the brain and central nervous system. Recent research indicates that the genetic profile of GBM makes it resistant to drugs and radiation. However, the main obstacle in treating GBM is transporting drugs through the blood-brain barrier (BBB). Albumin is a versatile biomaterial for the synthesis of nanoparticles. The efficiency of albumin-based delivery systems is determined by their ability to improve tumor targeting and accumulation. In this review, we will discuss the prevalence of human glioblastoma and the currently adopted treatment, as well as the structure and some essential functions of the BBB, to transport drugs through this barrier. We will also mention some aspects related to the blood-tumor brain barrier (BTBB) that lead to poor treatment efficacy. The properties and structure of serum albumin were highlighted, such as its role in targeting brain tumors, as well as the progress made until now regarding the techniques for obtaining albumin nanoparticles and their functionalization, in order to overcome the BBB and treat cancer, especially human glioblastoma. The albumin drug delivery nanosystems mentioned in this paper have improved properties and can overcome the BBB to target brain tumors.

Spin-Label Electron Paramagnetic Resonance Spectroscopy Reveals Effects of Wastewater Filter Membrane Coated with Titanium Dioxide Nanoparticles on Bovine Serum Albumin

The accumulation of proteins in filter membranes limits the efficiency of filtering technologies for cleaning wastewater. Efforts are ongoing to coat commercial filters with different materials (such as titanium dioxide, TiO2) to reduce the fouling of the membrane. Beyond monitoring the desired effect of the retention of biomolecules, it is necessary to understand what the biophysical changes are in water-soluble proteins caused by their interaction with the new coated filter membranes, an aspect that has received little attention so far. Using spin-label electron paramagnetic resonance (EPR), aided with native fluorescence spectroscopy and dynamic light scattering (DLS), here, we report the changes in the structure and dynamics of bovine serum albumin (BSA) exposed to TiO2 (P25) nanoparticles or passing through commercial polyvinylidene fluoride (PVDF) membranes coated with the same nanoparticles. We have found that the filtering process and prolonged exposure to TiO2 nanoparticles had significant effects on different regions of BSA, and denaturation of the protein was not observed, neither with the TiO2 nanoparticles nor when passing through the TiO2-coated filter membranes.

New look at the metabolism of nonsteroidal anti-inflammatory drugs: influence on human serum albumin antioxidant activity

Body's homeostasis is dependent on many factors, such as maintaining balance between free radicals formation and degradation. Human serum albumin (HSA) also plays an important role in homeostasis. The aim of this study was thermodynamic analysis of the interaction between ketoprofen (KET), naproxen (NPX), diclofenac (DIC) and HSA, as well as the effect of drug-albumin binding on HSA antioxidant activity using calorimetric and spectrophotometric techniques. Based on the calorimetric analysis it has been shown that accompanied by hydrophobic interaction drugs-albumin binding is an exoenergetic reaction. All analyzed drugs and HSA showed the ability to react with free radicals such as a radical cation, formed as a result of the reaction between 2,2'-Azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS) and potassium persulfate (K₂S₂O₈). Using ABTS assay a synergistic effect of ketoprofen (KET) and naproxen (NPX) on HSA antioxidant activity was observed while the effect of diclofenac (DIC) binding with albumin was probably additive. Because some medications including KET, NPX and DIC belong to over the counter (OTC) non-steroidal anti-inflammatory drugs (NSAIDs), it is necessary to understand their influence on HSA antioxidant activity.Communicated by Ramaswamy H. Sarma.

Development of a rapid, high-sensitivity, low-cost fluorescence method for protein surface hydrophobicity determination using a Nanodrop fluorospectrometer

A microvolumetric method for surface hydrophobicity (H₀) determination of proteins using a Nanodrop fluorospectrometer was developed. This method reduces the protein and fluorophore quantities that are necessary for sample preparations and readings by two and three orders of magnitude, respectively, compared to conventional methods. In addition, readings can be obtained in just 2-6 s. Bovine serum albumin (BSA) and 1-anilino 8-naphthalene sulfonic acid (ANS) were used for the first optimization of appropriate fluorophore-protein conditions for H₀ determination (20 μM ANS, 0.5-4 μM BSA, pH 5). Based on validation guidelines, the novel method shows linear behavior, good intraday precision, accuracy, and sensitivity. This method was robust against several factors, as determined by a Youden-Steiner test. Additional surface hydrophobicity determinations using several proteins demonstrate suitable method applicability. The present microvolumetric method provides a reliable technique to determine the H₀ of proteins for pharmaceutical, biotechnological, and food applications.

Serum Albumin Nanoparticles: Problems and Prospects

The present paper aims to summarize the results regarding serum albumin-based nanoparticles (NPs) for drug delivery purposes. In particular, it focuses on the relationship between their preparation techniques and synthesis parameters, as well as their successful clinical application. In spite of the huge amount of consumed material and immaterial sources and promising possibilities, products made from different types of albumin NPs, with the exception of a few, still have not been invented. In the present paper, promising applications of serum albumin nanoparticles (SANPs) for different biomedical purposes, such as carriers, delivery systems and contrast agents, are also discussed. The most frequent utilization of the NPs for certain diseases, i.e., cancer therapy, and future prospects are also detailed in this study.

Contribution to the Understanding of the Interaction between a Polydopamine Molecular Imprint and a Protein Model: Ionic Strength and pH Effect Investigation

Several studies were devoted to the design of molecularly imprinted polymer (MIP)-based sensors for the detection of a given protein. Here, we bring elements that could contribute to the understanding of the interaction mechanism involved in the recognition of a protein by an imprint. For this purpose, a polydopamine (PDA)-MIP was designed for bovine serum albumin (BSA) recognition. Prior to BSA grafting, the gold surfaces were functionalized with mixed self-assembled monolayers of (MUDA)/(MHOH) (1/9, v/v). The MIP was then elaborated by dopamine electropolymerization and further extraction of BSA templates by incubating the electrode in proteinase K solution. Three complementary techniques, electrochemistry, zetametry, and Fourier-transform infrared spectrometry, were used to investigate pH and ionic strength effects on a MIP's design and the further recognition process of the analytes by the imprints. Several MIPs were thus designed in acidic, neutral, and basic media and at various ionic strength values. Results indicate that the most appropriate conditions, to achieve a successful MIPs, were an ionic strength of 167 mM and a pH of 7.4. Sensitivity and dissociation constant of the designed sensor were of order of (3.36 ± 0.13) µA·cm-2·mg-1·mL and (8.56 ± 6.09) × 10-11 mg/mL, respectively.

Protein corona, understanding the nanoparticle-protein interactions and future perspectives: A critical review

Proteins are biopolymers of highly varied structures taking part in almost all processes occurring in living cells. When nanoparticles (NPs) interact with proteins in biological environments, they are surrounded by a layer of biomolecules, mainly proteins adsorbing to the surfaces. This protein rich layer formed around NPs is called the "protein corona". Consequential interactions between NPs and proteins are governed due to the characteristics of the corona. The features of NPs such as the size, surface chemistry, charge are the critical factors influencing the behavior of protein corona. Molecular properties and protein corona composition affect the cellular uptake of NPs. Understanding and analyzing protein corona formation in relation to protein-NP properties, and elucidating its biological implications play an important role in bio-related nano-research studies. Protein-NP interactions have been studied extensively for the purpose of investigating the potential use of NPs as carriers in drug delivery systems. Further study should focus on exploring the effects of various characteristic parameters, such as the particle size, modifier type, temperature, pH on protein-NP interactions, providing toxicity information of novel NPs. In this contribution, important aspects related to protein corona forming, influential factors, novel findings and future perspectives on protein-NP interactions are overviewed.

Influence of environmental and biological macromolecules on aggregation kinetics of nanoplastics in aquatic systems

Nanoplastics derived from degradation of micro- or macroplastics are emerging contaminants in aquatic environments, where their fate and transport as well as toxicity are affected by aggregation. This study employed time-resolved dynamic light scattering to investigate the aggregation kinetics of polystyrene nanoplastics (PSNPs) in the presence of four macromolecules (sodium alginate (SA), bovine serum albumin (BSA), extracellular polymeric substance (EPS), and Suwannee River humic acid (HA)) in solutions containing monovalent (NaCl) and divalent (CaCl₂) salts at different pH. Our results showed that the macromolecules enhanced PSNP stability in NaCl solutions but destabilized PSNPs in CaCl₂ solutions at pH 6. In NaCl solutions, macromolecules inhibited PSNP aggregation due to steric hindrance originated from macromolecular layer adsorbed on PSNPs. The strongest stabilization effect was observed for BSA having the greatest hydrodynamic adsorption layer thickness of 21.9 nm, followed by HA, EPS, and SA. In CaCl₂ solutions, SA significantly destabilized PSNPs via alginate bridging with Ca²⁺, which enhanced with concentrations of SA and CaCl₂. The destabilization effects of other three macromolecules in CaCl₂ solutions were governed by the interplay among molecular bridging, charge screening, and steric hindrance. An increased pH in NaCl or CaCl₂ solutions containing macromolecules all stabilized PSNPs due to elevated electrostatic repulsion, except that SA destabilized PSNPs in CaCl₂ solutions via enhanced molecular bridging. The stabilization effect of macromolecules may also compete with the destabilization effect under seawater condition. This study suggested that PSNP aggregation in aquatic environments could be strongly affected by macromolecules and solution chemistry.

Spectroscopic demonstration of sinapic acid methyl ester complexes with serum albumins

The methyl ester of sinapic acid (MESA) is a molecule with confirmed antioxidant properties. It is important to establish whether it can be transported across humans and animals. Therefore, we investigated MESA interactions with serum albumins, namely, human serum albumin (HSA), bovine serum albumin (BSA), rabbit serum albumin (RSA), and sheep serum albumin (SSA). Experiments were performed in a pH range from 5.9 to 10.7 using absorption and fluorescence techniques. It was found that MESA formed complexes with every albumin in the entire pH range under examination, which was confirmed by the appearances of new absorption and fluorescence complex bands. Fluorescence intensities were much higher (up to 20 times) and lifetimes were up to 340 times as compared to those for unbound MESA. The quenching experiments at pH 7.4 showed that the stoichiometry for every albumin was 1 : 1; the binding constant was the highest for HSA, which reached 52 000 M⁻¹. The obtained results suggested that MESA preferred the hydrophobic binding sites in albumins. The analysis of the fluorescence spectra and fluorescence lifetimes showed two possibly different binding sites in BSA, RSA, and SSA as well as three binding sites in HSA.

Known antioxidant, methyl ester of sinapic acid (MESA) can interact with serum albumins.

Preparation and investigation of core-shell nanoparticles containing human interferon-α

Sustained release of active interferon-α (IFN-α) has been achieved from core-shell nanoparticles (NPs) prepared by aqueous precipitation of IFN-α-enriched human serum albumin (HSA-IFN-α) and layer-by-layer (L-b-L) by coating of the IFN-α NPs with poly(sodium-4-styrene) sulphonate (PSS) and chitosan (Chit). The concentration and the pH of HSA solution were optimized during the development of this method. Dynamic light scattering (DLS), zeta-potential, thermal analysis (differential scanning calorimetry (DSC) and termogravimetry (TG)), X-ray diffraction (XRD), IFN-α activity and morphology (transmission electron microscope (TEM)) studies were used to control the preparation and analyse the products. The dissolution kinetics of NPs was measured in vitro over 7 days in Hanson dissolution tester with Millex membrane. In vivo studies in Pannon white rabbit detected steady IFN-α plasma level for 10 days after subcutaneous injection administration of the HSA-IFN-α NPs. The IFN-α plasma concentration was detected by using the enzyme-linked immunosorbent assay (ELISA) method. In the present paper we discuss the preparation method, the optimization steps and the results of in vitro and in vivo release studies. It was established that 76.13% HSA-IFN-α are encapsulated in the core-shell NPs.

Specific and Quantitative Detection of Albumin in Biological Fluids by Tetrazolate-Functionalized Water-Soluble AIEgens

The analysis of albumin has clinical significance in diagnostic tests and obvious value to research studies on the albumin-mediated drug delivery and therapeutics. The present immunoassay, instrumental techniques, and colorimetric methods for albumin detection are either expensive, troublesome, or insensitive. Herein, a class of water-soluble tetrazolate-functionalized derivatives with aggregation-induced emission (AIE) characteristics is introduced as novel fluorescent probes for albumin detection. They can be selectively lighted up by site-specific binding with albumin. The resulting albumin fluorescent assay exhibits a low detection limit (0.21 nM), high robustness in aqueous buffer (pH = 6-9), and a broad tunable linear dynamic range (0.02-3000 mg/L) for quantification. The tetrazolate functionality endows the probes with a superior water solubility (>0.01 M) and a high binding affinity to albumin (K_D = 0.25 μM). To explore the detection mechanism, three unique polar binding sites on albumin are computationally identified, where the multivalent tetrazolate-lysine interactions contribute to the tight binding and restriction of the molecular motion of the AIE probes. The key role of lysine residues is verified by the detection of poly-l-lysine. Moreover, we applied the fluorogenic method to quantify urinary albumin in clinical samples and found it a feasible and practical strategy for albumin analysis in complex biological fluids.