Kailin Xu

Binding mechanism of tauroursodeoxycholic acid to human serum albumin: insights from NMR relaxation and docking simulations

The binding mechanism of drugs with human serum albumin (HSA) is one of the most important factors in monitoring drug concentration in the blood and its transport to the destination tissues. The binding interaction of HSA with tauroursodeoxycholic acid (TUDCA), an endogenous bile acid, was investigated at the molecular level through NMR methodology. This methodology was based on the analysis of the selective and non-selective spin–lattice relaxation rate changes in ligand protons, affinity index, and molecular dynamics simulations to understand the binding strength and physical chemistry information on the interaction between HSA and the drug used in therapy. Results showed that TUDCA could strongly bind to HSA in site 1. The binding mode was further analysed using AutoDock. This study provided new insights into the interaction mechanism of TUDCA and HSA.

Two solid forms of tauroursodeoxycholic acid and the effects of milling and storage temperature on solid-state transformations

Two phase-pure solid forms of tauroursodeoxycholic acid (TUDCA) were prepared and characterized by thermal analysis, vibrational spectroscopy, X-ray diffraction, solid-state nuclear magnetic resonance, and morphological analysis. All solid forms can be produced from solvents and also can be obtained by mechanically and non-mechanically activated polymorph conversion. Near-infrared (NIR) spectroscopy, in combination with chemometrical techniques, was used for the quantitative monitoring of the polymorph conversion of TUDCA in milling process and at different storage temperatures. The NIR spectra in the range of 7139-5488 cm(-1) were considered for multivariate analysis. Results demonstrated that the NIR multivariate chemometric model can predict the percentage of crystal and amorphous TUDCA with the correlation coefficient of 0.9998, root mean square error of calibration of 0.740%, root mean square error of prediction of 0.698%, and root mean square error of cross-validation of 1.49%. In the milling process of crystal TUDCA (Form I), a direct transformation from crystal to glass was observed in 4h. Moreover, the impact of different storage temperatures on the stability of amorphous TUDCA was investigated, and the rate of polymorph transformation was found to be accelerated with increasing temperature.

Binding properties and structure–affinity relationships of food antioxidant butylated hydroxyanisole and its metabolites with lysozyme

Considering the harmful impact of food antioxidants on human bodies, thoroughly exposing their potential effects at the molecular level is important. In this study, the binding interactions of butylated hydroxyanisole (BHA), a phenolic antioxidant, and its different major metabolites tert-butylhydroquinone (TBHQ) and tert-butylbenzoquinone (TBQ) with lysozyme were examined via fluorescence, three-dimensional fluorescence, circular dichroism (CD), and ligand-protein docking studies. The three compounds caused strong quenching of lysozyme fluorescence by a static quenching mechanism but with different quenching efficiencies and different effects on the α-helix content of the lysozyme. The order of binding affinity of lysozyme for all test compounds is as follows: BHA>TBQ>TBHQ. Thermodynamic parameters indicated that hydrogen bonding and van der Waals forces perform dominant functions in the binding between these compounds and lysozyme. Furthermore, structure-affinity relationships between the model compounds and lysozyme were established on the basis of computational analyses.

Posaconazole/hydroxypropyl-β-cyclodextrin host–guest system: Improving dissolution while maintaining antifungal activity

This study aimed to prepare and characterize the inclusion complex between posaconazole (POS) and hydroxypropyl-β-cyclodextrin (HP-β-CD). Phase solubility study was conducted to investigate the drug/CD interaction in solution, including the stoichiometry and apparent stability constant. The solid complex (HP-β-CD-POS) obtained was characterized through Fourier transform infrared spectroscopy, powder X-ray diffraction, (1)H and ROESY 2D nuclear magnetic resonance, differential scanning calorimetry, and scanning electron microscopy. These approaches confirmed the formation of the inclusion complex. The HP-β-CD-POS inclusion complex exhibited better water solubility and higher dissolution rate than the free POS did; the water solubility of POS was increased by 82 times and almost 90% of the loaded drug dissolved after 10 min in the dissolution media. In addition, preliminary in vitro antifungal susceptibility testing revealed that HP-β-CD-POS maintains a high level of antifungal activities. Therefore, the HP-β-CD complex may be useful in the delivery of posaconazole.

Characterization and evaluation of synthetic riluzole with β-cyclodextrin and 2,6-di-O-methyl-β-cyclodextrin inclusion complexes

β-Cyclodextrin (β-CD) and 2,6-di-O-methyl-β-cyclodextrin (DM-β-CD) inclusion complexes with riluzole (RLZ) were prepared to improve water solubility and broaden potential pharmaceutical applications. CDs/RLZ inclusion complexes were confirmed via phase solubility studies, FT-IR spectroscopy, PXRD, DSC, (1)H NMR, and SEM. Phase solubility studies indicated that β-CD and DM-β-CD can form 1:1 inclusion complexes with RLZ, and the stability constants were 663.17 and 1609.07M(-1), respectively. Water solubility and dissolution rate of RLZ were significantly improved in complex forms, implying that the inclusion complexes may develop pharmaceutical applications. Preliminary in vitro cytotoxicity assay also showed that RLZ hepatotoxicity was not increased in the inclusion complexes.

Spectral and molecular modeling studies on the influence of β-cyclodextrin and its derivatives on aripiprazole-human serum albumin binding.

The binding mechanism of aripiprazole (APZ) with human serum albumin (HSA) in the absence and presence of three cyclodextrins (CyDs) (β-cyclodextrin, hydroxypropyl-β-cyclodextrin, and (2,6-di-O-methyl)-β-cyclodextrin) was studied by fluorescence, ultraviolet-visible absorption, nuclear magnetic resonance, and circular dichroism (CD) spectroscopy. The CD results revealed some degree of recovery of refolding caused by APZ after the addition of CyD. The Stern-Volmer quenching constant and binding constant of the APZ-HSA interaction were smaller in the presence of the three CyDs. The ultraviolet-visible absorption results indicated that APZ formed 1:1 complex with the three CyDs. The (1)H NMR spectra of CyD showed chemical shift and resolution loss of proton after the addition of HSA. Molecular modeling studies showed that both APZ and CyD bind to HSA. The process was initiated through inclusion of free APZ molecules by CyD and the increase in steric hindrance of CyD-HSA binding.

Interaction Behavior Between Niclosamide and Pepsin Determined by Spectroscopic and Docking Methods

The interaction between niclosamide (NIC) and pepsin was investigated using multispectroscopic and molecular docking methods. Binding constant, number of binding sites, and thermodynamic parameters at different temperatures were measured. Results of fluorescence quenching and synchronous fluorescence spectroscopy in combination with three-dimensional fluorescence spectroscopy showed that changes occurred in the microenvironment of tryptophan residues and the molecular conformation of pepsin. Molecular interaction distance and energy-transfer efficiency between pepsin and NIC were determined based on Förster nonradiative energy-transfer mechanism. Furthermore, the binding of NIC inhibited pepsin activity in vitro. All these results indicated that NIC bound to pepsin mainly through hydrophobic interactions and hydrogen bonds at a single binding site. In conclusion, this study provided substantial molecular-level evidence that NIC could induce changes in pepsin structure and conformation.

Investigation the complex of 2,6-di-O-methyl-β-cyclodextrin and chlorzoxazone: preparation, characterization, dissolution, and cytotoxicity

An inclusion complex between 2,6-di-O-methyl-β-cyclodextrin (DM-β-CD) and chlorzoxazone was prepared and investigated. Freeze-drying method was used to synthetize the complex; Fourier transform infrared spectroscopy, laboratory powder X-ray diffraction, 1H nuclear magnetic resonance spectroscopy, Rotating-frame overhauser effect spectroscopy, and Differential scanning calorimetry were utilized to confirm the formation of the complex. Furthermore, the solubilization and dissolution study results showed that the water solubility and dissolution rate of CZX were obviously improved through complexation with DM-β-CD. Finally, the cytotoxicity of the complex was determined byxa0MTT assay. As expected, the complex expressed lower toxicities for normal liver cells than free CZX. This study provides a promising idea to develop novel CZX solid dosage form with good dissolution rate and low liver toxicity.

Four solid forms of tauroursodeoxycholic acid and solid-state transformations: effects of temperature and milling

Four solid forms of tauroursodeoxycholic acid (TUDCA) were investigated by X-ray diffraction, morphological analysis, thermogravimetry, differential scanning calorimetry, and near-infrared (NIR) spectroscopic analysis. Results indicated that TUDCA existed as dihydrate (Form I), anhydrate (Form II), amorphous dehydrate (Form III), and amorphous anhydrate (Form IV). Solid-state transformations of TUDCA were extensively investigated and shown to be significantly affected by temperature and milling. Direct transformation of Form I into Form II occurred at high temperatures (100 °C and 150 °C), whereas that of Form II into Form I easily occurred at 25 °C. During milling, Form II was initially transformed into Form I within 10 min and then completely transformed into Form III after 100 min upon exposure to air. Moreover, the transition time from Form I to Form III was shorter than that of the separate milling process of Form I. However, Form II was directly transformed into Form IV when milled in the absence of air. In-line NIR spectroscopy was successfully applied for the rapid analysis of TUDCA solid-state transformations (Form II to Form I and Form IV to Form III) at ambient temperature. Stability investigation showed that the stability of the four TUDCA solid forms varied under different conditions.

An Investigation into the Polymorphism and Crystallization of Levetiracetam and the Stability of its Solid Form

Levetiracetam (LEV) crystals were prepared using different solvents at different temperatures. The LEV crystals were systematically characterized by X-ray powder diffraction (XRPD) and morphological analysis. The results indicated that many kinds of crystal habits exist in a solid form of LEV. To investigate the effects of LEV concentration, crystallization temperature, and crystallization type on crystallization and solid phase transformation of LEV, multiple methods were performed for LEV aqueous solution to determine if a new solid form exists in solid-state LEV. However, XRPD data demonstrate that the LEV solid forms possess same spatial arrangements that are similar to the original solid form. This result indicates that the LEV concentration, crystallization temperature, and crystallization type in aqueous solution have no influence on the crystallization and solid phase transformation of LEV. Moreover, crystallization by sublimation, melt cooling, and quench cooling, as well as mechanical effect, did not result in the formation of new LEV solid state. During melt cooling, the transformation of solid form LEV is a direct process from melting amorphous phase to the original LEV crystal phase, and the conversion rate is very quick. In addition, stability investigation manifested that LEV solid state is very stable under various conditions.