Human Serum Albumin Binding in a Vial: A Novel UV-pH Titration Method To Assist Drug Design

Enantioselective Binding of Proton Pump Inhibitors to Alpha1-Acid Glycoprotein and Human Serum Albumin-A Chromatographic, Spectroscopic, and In Silico Study

The enantioselective binding of three proton pump inhibitors (PPIs)-omeprazole, rabeprazole, and lansoprazole-to two key plasma proteins, α1-acid glycoprotein (AGP) and human serum albumin (HSA), was characterized. The interactions between PPI enantiomers and proteins were investigated using a multifaceted analytical approach, including high-performance liquid chromatography (HPLC), fluorescence and UV spectroscopy, as well as in silico molecular docking. HPLC analysis demonstrated that all three PPIs exhibited enantioseparation on an AGP-based chiral stationary phase, suggesting stereoselective binding to AGP, while only lansoprazole showed enantioselective binding on the HSA-based column. Quantitatively, the S-enantiomers of omeprazole and rabeprazole showed higher binding affinity to AGP, while the R-enantiomer of lansoprazole displayed greater affinity for AGP, with a reversal in the elution order observed between the two protein-based columns. Protein binding percentages, calculated via HPLC, were greater than 88% for each enantiomer across both transport proteins, with all enantiomers displaying higher affinity for AGP compared to HSA. Thermodynamic analysis indicated that on the HSA, the more common, enthalpy-controlled enantioseparation was found, while in contrast, on the AGP, entropy-controlled enantioseparation was observed. The study also identified limitations in using fluorescence titration due to the high native fluorescence of the compounds, whereas UV titration was effective for both proteins. The determined logK values were in the range of 4.47-4.83 for AGP and 4.02-4.66 for HSA. Molecular docking supported the experimental findings by revealing the atomic interactions driving the binding process, with the predicted enantiomer elution orders aligning with experimental data. The comprehensive use of these analytical methods provides detailed insights into the enantioselective binding properties of PPIs, contributing to the understanding of their pharmacokinetic differences and aiding in the development of more effective therapeutic strategies.

A Facile Access to Green Fluorescent Albumin Derivatives

A Morita-Baylis-Hillman Adduct (MBHA) derivative bearing a triphenylamine moiety was found to react with human serum albumin (HSA) shifting its emission from the blue to the green-yellow thus leading to green fluorescent albumin (GFA) derivatives and enlarging the platform of probes for aggregation-induced fluorescent-based detection techniques. A possible interaction of MBHA derivative 7 with a lipophilic pocket within the HSA structure was suggested by docking studies. DLS experiments showed that the reaction with HSA induce a conformational change of the protein contributing to the aggregation process of GFA derivatives. The results of investigations on the biological properties suggested that GFA retained the ability of binding drug molecules such as warfarin and diazepam. Finally, cytotoxicity evaluation studies suggested that, although the MBHA derivative 7 at 0.1 μg/mL affected the percentage of cell viability in comparison to the negative control, it cannot be considered cytotoxic, whereas at all the other concentrations≥0.5 μg/mL resulted cytotoxic at different extent.

Non-Covalent Albumin Ligands in FDA-Approved Therapeutic Peptides and Proteins

An increasing number of drugs that consist of a therapeutic peptide or protein linked to an albumin-binding structure are being approved. In this perspective, the pharmacokinetic data of currently marketed drugs of this type will be presented. Acylation with fatty acids or fatty α,ω-dicarboxylic acids has been used successfully to prepare long-acting analogs of insulin, GLP-1, and other peptides but not of larger proteins. With a tetrazole-sulfonylamide fatty acid bioisostere, it has now been possible to prepare a long-acting analog of human growth hormone (191 amino acids), which is suitable for once-weekly administration.

Direct Oral FXa Inhibitors Binding to Human Serum Albumin: Spectroscopic, Calorimetric, and Computational Studies

Direct FXa inhibitors are an important class of bioactive molecules (rivaroxaban, apixaban, edoxaban, and betrixaban) applied for thromboprophylaxis in diverse cardiovascular pathologies. The interaction of active compounds with human serum albumin (HSA), the most abundant protein in blood plasma, is a key research area and provides crucial information about drugs' pharmacokinetics and pharmacodynamic properties. This research focuses on the study of the interactions between HSA and four commercially available direct oral FXa inhibitors, applying methodologies including steady-state and time-resolved fluorescence, isothermal titration calorimetry (ITC), and molecular dynamics. The HSA complexation of FXa inhibitors was found to occur via static quenching, and the complex formation in the ground states affects the fluorescence of HSA, with a moderate binding constant of 10⁴ M^-1. However, the ITC studies reported significantly different binding constants (10³ M^-1) compared with the results obtained through spectrophotometric methods. The suspected binding mode is supported by molecular dynamics simulations, where the predominant interactions were hydrogen bonds and hydrophobic interactions (mainly π-π stacking interactions between the phenyl ring of FXa inhibitors and the indole moiety of Trp214). Finally, the possible implications of the obtained results regarding pathologies such as hypoalbuminemia are briefly discussed.

Enantioselective Human Serum Albumin Binding of Apremilast: Liquid Chromatographic, Fluorescence and Molecular Docking Study

The interaction between human serum albumin (HSA) and apremilast (APR), a novel antipsoriatic drug, was characterized by multimodal analytical techniques including high-performance liquid chromatography (HPLC), fluorescence spectroscopy and molecular docking for the first time. Using an HSA chiral stationary phase, the APR enantiomers were well separated, indicating enantioselective binding between the protein and the analytes. The influence of chromatographic parameters-type and concentration of the organic modifier, buffer type, pH, ionic strength of the mobile phase, flow rate and column temperature-on the chromatographic responses (retention factor and selectivity) was analyzed in detail. The results revealed that the eutomer S-APR bound to the protein to a greater extent than the antipode. The classical van 't Hoff method was applied for thermodynamic analysis, which indicated that the enantioseparation was enthalpy-controlled. The stability constants of the protein-enantiomer complexes, determined by fluorescence spectroscopy, were in accordance with the elution order observed in HPLC (K_R-APR-HSA = 6.45 × 10³ M^-1, K_S-APR-HSA = 1.04 × 10⁴ M^-1), showing that, indeed, the later-eluting S-APR displayed a stronger binding with HSA. Molecular docking was applied to study and analyze the interactions between HSA and the APR enantiomers at the atomic level. It was revealed that the most favored APR binding occurred at the border between domains I and II of HSA, and secondary interactions were responsible for the different binding strengths of the enantiomers.

Probing the serum albumin binding site of fenamates and photochemical protein labeling with a fluorescent dye

Human serum albumin (HSA) can bind with numerous drugs, leading to a significant influence on drug pharmacokinetics as well as undesirable drug-drug interactions due to competitive binding. Probing the HSA drug binding site thus offers great opportunities to reveal drug-HSA binding profiles. In the present study, a fluorescent probe (E)-4-(2-(5-(4-(diphenylamino)phenyl)thiophen-2-yl)vinyl)-1-propylpyridin-1-ium (TTPy) has been prepared, which exhibits enhancement of deep-red to near-infrared (NIR) fluorescence upon HSA binding. The competitive binding assay indicated that TTPy can target the HSA binding site of fenamates, a group of non-steroidal anti-inflammatory drugs (NSAIDs), with moderate binding affinity (1.95 × 10⁶ M^-1 at 303 K). More interestingly, TTPy enables fluorescent labeling of HSA upon visible light irradiation. This study provides promising ways for HSA drug binding site identification and photochemical protein labeling.

In situ generation of a Zwitterionic fluorescent probe for detection of human serum albumin protein

In this article, a new approach for human serum albumin selective fluorophore design has been reported. The fluorophore reported here comprises a substituted phenol donor and a cationic benzo[e]indolium acceptor connected with a π bond. Originally, the cationic fluorophore did not bind with human serum albumin. Upon deprotonation of the phenolic-OH by a water molecule the cationic form was transformed into an active zwitterionic form. Spectroscopic studies and theoretical calculations revealed that the new active form remained in a zwitterionic state in neutral aqueous solution, and it formed a strong supramolecular complex with human serum albumin. The spontaneous complexation resulted multi-fold increase of fluorescence intensity which increased linearly with the concentrations of the protein, thus giving an analytical tool to monitor human serum albumin in aqueous samples. We believe, this simple strategy applied on appropriate fluorogenic scaffolds would prove useful to develop new and improved turn-on fluorescent probes for pH regulated biological applications.

In silico Plasma Protein Binding Studies of Selected Group of Drugs Using TLC and HPLC Retention Data

Plasma protein binding is an important determinant of the pharmacokinetic properties of chemical compounds in living organisms. The aim of the present study was to determine the index of protein binding affinity based on chromatographic experiments. The question is which chromatographic environment will best mimic the drug–protein binding conditions. Retention data from normal phase thin-layer liquid chromatography (NP TLC), reversed phase (RP) TLC and HPLC chromatography experiments with 129 active pharmaceutical ingredients (APIs) were collected. The stationary phase of the TLC plates was modified with protein and the HPLC column was filled with immobilized human serum albumin. In both chromatographic methods, the mobile phase was based on a buffer with a pH of 7.4 to mimic physiological conditions. Chemometric analyses were performed to compare multiple linear regression models (MLRs) with retention data, using protein binding values as the dependent variable. In the course of the analysis, APIs were divided into acidic, basic and neutral groups, and separate models were created for each group. The MLR models had a coefficient of determination between 0.73 and 0.91, with the highest values from NP TLC data.

Host assisted molecular recognition by human serum albumin: Study of molecular recognition controlled protein/drug mimic binding in a microfluidic channel

Human serum albumin (HSA) plays a pivotal role in drug release from its delivery vehicles such as cyclodextrins (CDs) by binding to the drugs. Here molecular recognition and binding of a drug mimic (CD1) to HSA have been explored in a microfluidic channel when CD1 is encapsulated in β-cyclodextrin (βCD) and heptakis(2,3,6-tri-O-methyl)-β-cyclodextrin (TRIMEB), respectively, to investigate whether change of the host vehicle modulate the rate of drug binding to the serum protein. Molecular recognition of βCD encapsulated CD1 by HSA occurs by the conformational selection fit mechanism leading to rapid binding of CD1 to HSA (k₁ ~ 700 s^-11) when the βCD/CD1 complex interacts with HSA. In contrary, HSA recognizes CD1 encapsulated in TRIMEB by an induced fit mechanism leading to a significantly slower binding rate (k₁ ~ 20.8 s^-1) of the drug mimic to the protein. Thus molecular recognition controls the rate of HSA binding by CD1 which in turn modulates the rate of delivery of the drug mimic from its macrocyclic hosts. The remarkable change in the molecular recognition pathway of CD1 by HSA, upon change of the host from βCD to TRIMEB, originates from significantly different conformational flexibility of the host/drug mimic complexes.