RESUMO
The ability to detect and monitor amyloid deposition in the brain using non-invasive imaging techniques provides valuable insights into the early diagnosis and progression of Alzheimer's disease and helps to evaluate the efficacy of potential treatments. Magnetic resonance imaging (MRI) is a widely available technique offering high-spatial-resolution imaging. It can be used to visualize amyloid deposits with the help of amyloid-binding diagnostic agents injected into the body. In recent years, a number of amyloid-targeted MRI probes have been developed, but none of them has entered clinical practice. We review the advances in the field and deduce the requirements for the molecular structure and properties of a diagnostic probe candidate. These requirements make up the base for the rational design of MRI-active small molecules targeting amyloid deposits. Particular attention is paid to the novel cryo-EM structures of the fibril aggregates and their complexes, with known binders offering the possibility to use computational structure-based design methods. With continued research and development, MRI probes may revolutionize the diagnosis and treatment of neurodegenerative diseases, ultimately improving the lives of millions of people worldwide.
Assuntos
Doença de Alzheimer , Placa Amiloide , Humanos , Placa Amiloide/metabolismo , Imageamento por Ressonância Magnética/métodos , Doença de Alzheimer/diagnóstico por imagem , Doença de Alzheimer/metabolismo , Encéfalo/metabolismo , Amiloide/metabolismo , Peptídeos beta-Amiloides/metabolismoRESUMO
Hydrogels have the ability to retain large amounts of water within their three-dimensional polymer matrices. These attractive materials are used in medicine and the food industry; they can serve as the basis for structured food products, additives, and various ingredients. Gelatin is one of widely used biopolymers to create hydrogels that exhibit biocompatibility and tunable rheological properties. In this study, we offer a comparative analysis of rheological properties of gelatin-based hydrogels (C = 6.67%), including mammalian gelatins from bovine and porcine skins and fish gelatins from commercial samples and samples extracted from Atlantic cod skin. Mammalian gelatins provide high strength and elasticity to hydrogels. Their melting point lies in the range from 22 to 34 °C. Fish gelatin from cod skin also provides a high strength to hydrogels. Commercial fish gelatin forms weak gels exhibiting low viscoelastic properties and strength, as well as low thermal stability with a melting point of 7 °C. Gelatins were characterized basing on the analysis of amino acid composition, molecular weight distribution, and biopolymer secondary structure in gels. Our research provides a unique rheological comparison of mammalian and fish gelatin hydrogels as a tool for the re-evaluation of fish skin gelatin produced through circular processes.
RESUMO
The effect of binding of several ligands to bovine serum albumin on the kinetics of fibril formation at denaturing conditions is studied. The considered ligands are clinical drugs with different binding constants to albumin: relatively strong binders (naproxen, ibuprofen, warfarin with 105 to 107 binding constant values) and weak binders (isoniazid, ranitidine with 103 to 104 binding constant values). The data of thioflavin fluorescence binding assay, Congo red binding assay, and circular dichroism spectroscopy indicate ligand concentration-dependent suppression of fibril formation in the presence of strong binders and no effects in the presence of weak binders. Analysis of kinetic curves shows no induction lag associated with fibril nucleation and the first-order kinetics of fibril formation with respect to albumin concentration for all the studied systems. Using DSC method, the fractions of unfolded albumin at incubation temperature were determined for each albumin-ligand system and ligand concentration. Their magnitudes ranging from 0 to 1 correlate with the initial rates of fibril formation and with equilibrium concentrations of fibrils formed in the system after incubation for at least 120 min. The results indicate that fibrils are formed from partially or completely denatured albumin form with the rate proportional to the fraction of this form. Strong albumin binders act as thermodynamic inhibitors of fibrillation shifting the unfolding equilibrium to the side of the native ligand-bound protein.
Assuntos
Vermelho Congo , Soroalbumina Bovina , Amiloide/química , Dicroísmo Circular , Vermelho Congo/química , Cinética , Ligantes , Soroalbumina Bovina/química , TermodinâmicaRESUMO
There is a demand in rapid and robust methods to determine the affinity of drugs to receptors, enzymes, and transport proteins. Differential scanning calorimetry (DSC) is a common method to prove the existence of ligand-protein binding from the shift of denaturation peak, but it is rarely used to obtain the binding constant values. The work is aimed to prove that the DSC experiments can be a source of reliable values of the binding constants and information on the stoichiometry of drug-albumin binding. DSC thermograms of bovine serum albumin denaturation in the presence of several drugs with different affinity and stoichiometry of binding to albumin: naproxen, warfarin, ibuprofen, and isoniazid were recorded. The dependences of the denaturation peak maximum temperature and area on the molar drug/protein ratio, which varied from 0 to 100, were considered. With the help of numerical modeling of the DSC curves, these dependences were predicted using the binding parameters determined in independent experiments and a simple two-state model of denaturation. The DSC data at relatively small concentrations of ligands are in good agreement with the calculation results. The deviations from the model predictions at high ligand concentrations in the cases of naproxen and ibuprofen indicate that albumin is able to bind several additional molecules of these drugs with its low-affinity sites. The fit was improved by using a sequential binding model with two binding constants K1 = 1.0 × 107 and K2 = 1.0 × 104 for naproxen and a cooperative binding model for ibuprofen. The stoichiometry of drug-albumin complexes fully saturated with drug ligand was calculated from the dependence of the denaturation temperature on the drug concentration. In the case of isoniazid, DSC thermograms indicated very weak binding to albumin.
Assuntos
Soroalbumina Bovina/química , Varredura Diferencial de Calorimetria , Ibuprofeno/química , Isoniazida/química , Naproxeno/química , Ligação Proteica , Varfarina/químicaRESUMO
Experimental data on the affinity of various substances to albumin are essential for the development of empirical models to predict plasma binding of drug candidates. Binding of 24 substituted benzoic acid anions to bovine serum albumin was studied using spectrofluorimetric titration. The equilibrium constants of binding at 298 K were determined according to 1:1 complex formation model. The relationships between the ligand structure and albumin affinity are analyzed. The binding constant values for m- and p-monosubstituted acids show a good correlation with the Hammett constants of substituents. Two- and three-parameter quantitative structure-activity relationship (QSAR) models with theoretical molecular descriptors are able to satisfactorily describe the obtained values for the whole set of acids. It is shown that the electron-density distribution in the aromatic ring exerts crucial influence on the albumin affinity.