Comparative Studies of Interactions between Fluorodihydroquinazolin Derivatives and Human Serum Albumin with Fluorescence Spectroscopy

Association mechanism of bicalutamide and human serum albumin for potential clinical implications

The binding mechanism of molecular interaction between bicalutamide and human serum albumin (HSA) in a pH 7.4 phosphate buffer was studied using various spectroscopic techniques in combination with molecular modeling. Fluorescence data revealed that the fluorescence quenching of HSA by bicalutamide was a static quenching procedure. The binding constants and number of binding sites were evaluated at different temperatures. The thermodynamic parameters, ΔH and ΔS, were calculated to be 4.30 × 104 J·mol-1 and 245 J·mol-1·K-1, respectively, suggesting that the binding of bicalutamide to HSA was driven mainly by hydrophobic interactions and hydrogen bonds. The displacement studies indicated neither Sudlow's site I nor II but subdomain IB as the main binding site for bicalutamide on HSA. The binding distance between bicalutamide and HSA was determined to be 3.54 nm based on the Förster theory. Analysis of circular dichroism, synchronous, and 3D fluorescence spectra demonstrated that HSA conformation was slightly altered in the presence of bicalutamide.

Determination of free and total meropenem levels in human plasma and its application for the consistency evaluation of generic drugs

RATIONALE

The consistency evaluation of generic drugs is important for the overall reformation of drug registration in China. In this study, we used meropenem as a model drug to explore the key techniques for clinical consistency evaluation by studying the plasma protein binding (PPB) ratio of different preparations. Because the free portion of drug is the effective part in vivo, it is essential to measure the free drug concentration in the circulatory system. Therefore, in this study, a fast and accurate high-performance liquid chromatography tandem mass spectrometry (HPLC-MS/MS) method was developed to determine the total and free concentrations of meropenem in human plasma.

METHODS

Simple protein precipitation procedures were used for the sample processing assay, and ultrafiltration was implemented for the separation of free drugs. Liquid chromatography separation was performed using a hydrophilic interaction liquid chromatography (HILIC) silica column (2.1 × 50 mm, 3 μm). The mobile phase and sample preparation procedures were optimized. Factors affecting the measurement of free drug concentration were also determined. Nonspecific binding of the ultrafiltration membrane was negligible because the recovery rate for post-ultrafiltration was greater than 96%.

RESULTS

Under optimal conditions, the drug concentrations were linear from 0.5 to 50 μg/ml for both total and free drug concentrations. The PPB ratio was calculated based on the free and total drug concentrations. The PPB of meropenem varied from 1.4% to 24.2% in different subjects. The validated method was applied to evaluate PPB of four preparations, and the results varied from 6.57 ± 3.19% to 10.40 ± 8.31%. One-way analysis of variance (ANOVA) showed no significant differences between the four preparations.

CONCLUSIONS

We established a rapid, robust, and reliable method for the determination of total and free meropenem concentrations using LC-MS/MS with ultrafiltration techniques. The method provided a new perspective for the clinical consistency evaluation of generic drugs.

A novel ESIPT-based fluorescent probe with dual recognition sites for the detection of hydrazine in the environmental water samples and in-vivo bioimaging

Hydrazine (N₂H₄), an important chemical intermediate, has been widely used in industrial production and agricultural life, but it has also caused environmental pollution. A novel ESIPT-based fluorescent probe with dual recognition sites, 2-(benzothiazole-2-yl)-1,4-imphenyl bis 4-bromobutyric acid (BRBA), was developed to selectively detect N₂H₄ under complex conditions. BRBA exhibits accurate detection for N₂H₄ with a good linear relationship ranging from 0 to 150 μM, and the LOD can reach 0.1 μM. Importantly, taking advantage of low cytotoxicity and a large Stokes shift, BRBA can be utilized to monitor environmental water samples and successfully applied to imaging HeLa cells and zebrafish.

Comparison of the interactions of flupyrimin and nitenpyram with serum albumins via multiple analysis methods

Flupyrimin and nitenpyram are emerging neonicotinoid insecticides that may cause potential harm to the human body. In the present work, the interactions of flupyrimin/nitenpyram with serum albumins under normal physiological conditions were thoroughly studied by using multiple spectroscopic techniques, DFT calculations and molecular docking. Flupyrimin/nitenpyram can quench the endogenous fluorescence of HSA/BSA and form a complex with HSA/BSA through a static process, causing conformational and secondary structure changes of HSA/BSA. Thermodynamic analysis shows that the combination of flupyrimin/nitenpyram with HSA/BSA is a spontaneous process, mainly driven by hydrogen bonds and hydrophobic forces. Site marking and molecular docking experiments indicated that flupyrimin/nitenpyram binds with HSA/BSA at site II (subdomain IIIA). The binding constant K_a in HSA-flupyrimin, HSA-nitenpyram, BSA-flupyrimin and BSA-nitenpyram systems at 298 K was 2.11 × 10⁵ M^-1, 2.35 × 10⁵ M^-1, 1.91 × 10⁵ M^-1 and 2.11 × 10⁵ M^-1, respectively. The binding constant K_a of nitenpyram with HSA/BSA was greater than flupyrimin, indicating that nitenpyram binds HSA/BSA was more stable than that of flupyrimin, which was consistent with the DFT calculation. In addition, the acute toxicity bioassay showed that flupyrimin and nitenpyram exhibited low toxicity to zebrafish, with 96 h LC₅₀ values of 181.662 and 250.658 mg a. i. L^-1, respectively. These results can help understand the interactions of flupyrimin/nitenpyram with HSA/BSA.

Role of potassium levels in pkBADH heterogeneity of NAD+ binding site

Betaine aldehyde dehydrogenase (BADH) catalyzes the oxidation of betaine aldehyde to glycine betaine using NAD⁺ as a coenzyme. Studies in porcine kidney BADH (pkBADH) suggested that the enzyme exhibits heterogeneity of active sites and undergoes potassium-induced conformational changes. This study aimed to analyze if potassium concentration plays a role in the heterogeneity of pkBADH active sites through changes in NAD⁺ affinity constants, in its secondary structure content and stability. The enzyme was titrated with NAD⁺ 1 mM at fixed-variable KCl concentration, and the interaction measured by Isothermal Titration Calorimetry (ITC) and Circular Dichroism (CD). ITC data showed that K⁺ increased the first active site affinity in a manner dependent on its concentration; K_D values to the first site were 14.4, 13.1, and 10.4 μM, at 25, 50, and 75 mM KCl. ΔG values showed that the coenzyme binding is a spontaneous reaction without changes between active sites or depending on KCl concentration. ΔH and TΔS_b values showed that NAD⁺ binding to the active site is an endothermic process and is carried out at the expense of changes in entropy. α-Helix content increased as KCl increased, enzyme (T_m)_app values were 2.6 °C and 3.3 °C higher at 20 mM and 200 mM K⁺. PkBADH molecular model showed three different interaction K⁺ sites. Results suggested K⁺ can interact with pkBADH and cause changes in the secondary structure, it provokes changes in the enzyme affinity by the coenzyme, and in the thermostability.

Interactions of Bromocarbazoles with Human Serum Albumin Using Spectroscopic Methods

The 1,3,6,8-tetrabromocarbazole and 3-bromocarbazole have attracted great attention in the ecotoxicology field recently as hazardous environmental contaminants. In this study, the quenching mechanism of these two substances binding with human serum albumin (HSA) has been investigated with spectroscopic methods. Through fluorescence quenching and binding site experiments with steady-state fluorescence and UV-Vis spectra, the intrinsic fluorescence of HSA quenched by 1,3,6,8-tetrabromocarbazole and 3-bromocarbazole both in static process, are activated by binding to site II (subdomain IIIA) of the HSA. In addition, it was not only found that the conformation and secondary structure of the proteins changes, but also that their spontaneous binding processes were driven by electrostatic interactions as well as hydrophobic forces for HSA-1,3,6,8-tetrabromocarbazole, and by typical hydrophobic forces for HSA-3-bromocarbazole. The above studies are beneficial to enhance our understanding of the ecotoxicology and environmental behaviors of halogenated carbazoles.

2,3-Dihydroquinazolin-4(1H)-one as a privileged scaffold in drug design

2,3-Dihydroquinazolin-4-one (DHQ) belongs to the class of nitrogen-containing heterocyclic compounds representing a core structural component in various biologically active compounds. In the past decades, several methodologies have been developed for the synthesis of the DHQ framework, especially the 2-substituted derivatives. Unfortunately, multistep syntheses, harsh reaction conditions, and the use of toxic reagents and solvents have limited their full potential as a versatile fragment. Recently, use of green chemistry and alternative strategies are being explored to prepare diverse DHQ derivatives. This fragment is used as a synthon for the preparation of biologically active quinazolinones and as a functional substrate for the synthesis of modified DHQ derivatives exhibiting different biological properties. In this review, we provide a comprehensive assessment of the synthesis and biological evaluations of DHQ derivatives.

Interactions between tetrahydroisoindoline-1,3-dione derivatives and human serum albumin via multiple spectroscopy techniques

Some tetrahydroisoindoline-1,3-dione derivatives (TDDs) possess potent herbicidal activity. To assess possible impacts of TDDs on humans, the interactions between TDDs and human serum albumin (HSA) were evaluated with steady-state and time-resolved fluorescence spectroscopy, synchronous fluorescence spectroscopy, Fourier transform-infrared spectroscopy, and circular dichroism spectroscopy. The thermodynamic data obtained at temperatures of 298, 307, and 316 K indicate that TDDs spontaneously bind to HSA and thus form a TDD-HSA complex. The conformation and secondary structure of HSA are changed, and the intrinsic fluorescence of HSA is statically quenched by TDDs. Moreover, the TDD-HSA complex is formed primarily through electrostatic interactions and has only one binding site on HSA. A competitive ligand-binding assay revealed that site II (subdomain IIIA) displays the greatest affinity for TDDs. In addition, an acute toxicity bioassay showed no zebrafish mortality upon exposure to 4000 μg L^-1 of TDDs. This work is helpful for understanding interactions between TDDs and HSA.

Biointeractions of Herbicide Atrazine with Human Serum Albumin: UV-Vis, Fluorescence and Circular Dichroism Approaches

The herbicide atrazine is widely used across the globe, which is a great concern. To investigate its potential toxicity in the human body, human serum albumin (HSA) was selected as a model protein. The interaction between atrazine and HSA was investigated using steady-state fluorescence spectroscopy, synchronous fluorescence spectroscopy, UV-Vis spectroscopy, three-dimensional (3D) fluorescence spectroscopy and circular dichroism (CD) spectroscopy. The intrinsic fluorescence of HSA was quenched by the atrazine through a static quenching mechanism. Fluorescence spectra at two excitation wavelengths (280 and 295 nm) showed that the fluorescence quenched in HSA was mainly contributed to by tryptophan residues. In addition, the atrazine bound to HSA, which induced changes in the conformation and secondary structure of HSA and caused an energy transfer. Thermodynamic parameters revealed that this binding is spontaneous. Moreover, electrostatic interactions play a major role in the combination of atrazine and HSA. One atrazine molecule can only bind to one HSA molecule to form a complex, and the atrazine molecule is bound at site II (subdomain IIIA) of HSA. This study furthers the understanding of the potential effects posed by atrazine on humans at the molecular level.