In Vitro Investigation of Binding Interactions between Albumin–Gliclazide Model and Typical Hypotensive Drugs

Type 2 diabetes management usually requires polytherapy, which increases the risk of drug-to-drug interactions. Among the multiple diabetes comorbidities, hypertension is the most prevalent. This study aimed to investigate the binding interactions between the model protein, bovine albumin, and the hypoglycemic agent gliclazide (GLICL) in the presence of typical hypotensive drugs: quinapril hydrochloride (QUI), valsartan (VAL), furosemide (FUR), amlodipine besylate (AML), and atenolol (ATN). Spectroscopic techniques (fluorescence quenching, circular dichroism) and thermodynamic experiments were employed. The binding of the gliclazide to the albumin molecule was affected by the presence of an additional drug ligand, which was reflected by the reduced binding constant of the BSA–DRUG–GLICL system. This may indicate a possible GLICL displacement and its enhanced pharmacological effect, as manifested in clinical practice. The analysis of the thermodynamic parameters indicated the spontaneity of the reaction and emphasized the role of hydrogen bonding and van der Waals forces in these interactions. The secondary structure of the BSA remained almost unaffected.

Esterase Activity of Serum Albumin Studied by 1H NMR Spectroscopy and Molecular Modelling

Serum albumin possesses esterase and pseudo-esterase activities towards a number of endogenous and exogenous substrates, but the mechanism of interaction of various esters and other compounds with albumin is still unclear. In the present study, proton nuclear magnetic resonance (1H NMR) has been applied to the study of true esterase activity of albumin, using the example of bovine serum albumin (BSA) and p-nitrophenyl acetate (NPA). The site of BSA esterase activity was then determined using molecular modelling methods. According to the data obtained, the accumulation of acetate in the presence of BSA in the reaction mixture is much more intense as compared with the spontaneous hydrolysis of NPA, which indicates true esterase activity of albumin towards NPA. Similar results were obtained for p-nitophenyl propionate (NPP) as substrate. The rate of acetate and propionate release confirms the assumption that there is a site of true esterase activity in the albumin molecule, which is different from the site of the pseudo-esterase activity Sudlow II. The results of molecular modelling of BSA and NPA interaction make it possible to postulate that Sudlow site I is the site of true esterase activity of albumin.

Serum Albumin

Being one of the most abundant proteins in human and other mammals, albumin plays a crucial role in transporting various endogenous and exogenous molecules and maintaining of colloid osmotic pressure of the blood. It is not only the passive but also the active participant of the pharmacokinetic and toxicokinetic processes possessing a number of enzymatic activities. A free thiol group of the albumin molecule determines the participation of the protein in redox reactions. Its activity is not limited to interaction with other molecules entering the blood: of great physiological importance is its interaction with the cells of blood, blood vessels and also outside the vascular bed. This entry contains data on the enzymatic, inflammatory and antioxidant properties of serum albumin.

DESTRUCTION OF POLYOXOMETALATE {MOFE} AS A TRANSPORT AGENT IN BLOOD SIMULATING MEDIA, ITS STABILIZATION BY ALBUMIN

Создание и использование средств адресной доставки лекарств на основе нанокластерного полиоксометаллата {MoFe} подразумевает его деструкцию в организме, сопровождающуюся постепенным высвобождением лекарства. Были определены константы скорости процесса деструкции чистого {MoFe} и в составе ассоциата с сывороточным альбумином в растворах моделирующих среду крови (фосфатный буфер с pH 7,4 и сыворотка крови крупного рогатого скота). Показана стабилизация полиоксометаллата альбумином в модельных средах. Определено соотношение компонентов в ассоциате {MoFe} -альбумин, оно составило 1,6 ионов полиоксометаллата на молекулу альбумина. The creation and use of the targeted drug delivery systems based on nanocluster polyoxometalate {MoFe} implies its destruction in the body, accompanied by the gradual release of the drug. The rate constants of the destruction of pure {MoFe} and its associate with serum albumin in solutions simulating the blood media (phosphate buffer with pH 7,4 and blood serum of cattle) were determined. The stabilization of polyoxometalate by albumin in model solutions was shown. The ratio of components in the associate {MoFe} -albumin was determined, it was 1,6 polyoxometalate ions per albumin molecule.

Determinants of Intraparenchymal Infusion Distributions: Modeling and Analyses of Human Glioblastoma Trials

Intra-parenchymal injection and delivery of therapeutic agents have been used in clinical trials for brain cancer and other neurodegenerative diseases. The complexity of transport pathways in tissue makes it difficult to envision therapeutic agent distribution from clinical MR images. Computer-assisted planning has been proposed to mitigate risk for inadequate delivery through quantitative understanding of infusion characteristics. We present results from human studies and simulations of intratumoral infusions of immunotoxins in glioblastoma patients. Gd-DTPA and 124I-labeled human serum albumin (124I-HSA) were co-infused with the therapeutic, and their distributions measured in MRI and PET. Simulations were created by modeling tissue fluid mechanics and physiology and suggested that reduced distribution of tracer molecules within tumor is primarily related to elevated loss rates computed from DCE. PET-tracer on the other hand shows that the larger albumin molecule had longer but heterogeneous residence times within the tumor. We found over two orders of magnitude variation in distribution volumes for the same infusion volumes, with relative error ~20%, allowing understanding of even anomalous infusions. Modeling and measurement revealed that key determinants of flow include infusion-induced expansion and loss through compromised BBB. Opportunities are described to improve computer-assisted CED through iterative feedback between simulations and imaging.

Fungicide Tebuconazole Influences the Structure of Human Serum Albumin Molecule

Studies of interactions between pesticides and target mammalian proteins are important steps toward understanding the pesticide′s toxicity. Using calorimetric and spectroscopic methods, the interaction between triazole fungicide tebuconazole and human serum albumin has been investigated. The spectroscopic techniques showed that fluorescence quenching of human serum albumin by tebuconazole was the result of the formation of tebuconazole/human serum albumin complex with the static type as the dominant mechanism. The association constant was found to be 8.51 × 103 L/mol. The thermodynamic parameters were obtained as ΔH = −56.964 kJ/mol, ΔS = −115.98 J/mol·K. The main active interactions forming the tebuconazole/human serum albumin complex were identified as the interplay between hydrogen bonds and/or van der Waals forces, based on thermodynamic experiments. These binding modes were corroborated well by the predictions of molecular modeling. Hydrogen bonding of tebuconazole with Arg222, Ala215 and Ala291 of human serum albumin played a relevant role in binding. The conformation changes in secondary structure were characterized by circular dichroism and 3D fluorescence spectra.

Specific changes in the conformation of blood albumin molecule during stress exposures and administration of cytokines or oligopeptides

Цель данной работы состояла в изучении структурных особенностей молекулы альбумина в крови поведенчески пассивных и активных крыс, прогностически предрасположенных и устойчивых к стрессорным воздействиям, при введении цитокинов и олигопептидов. Методы. Эксперименты проведены на 319 крысах-самцах Вистар с массой тела 220,0 ± 5,2 г. Крыс предварительно тестировали в открытом поле с оценкой поведенческих показателей и делили на пассивных (n = 126) и активных особей (n = 124). Животные с высокой ориентировочно-исследовательской активностью в данном тесте более устойчивы к стрессорным нагрузкам, чем пассивные особи [20, 21]. Структурные особенности молекулы альбумина в крови пассивных и активных крыс изучали до и после введения цитокинов и олигопептидов. Результаты. Установлено, что острая стрессорная нагрузка приводит к изменению свойств альбуминовых центров. Флуоресценция зонда CAPIDAN, как показатель состояния связывающих центров альбумина, в указанных условиях увеличивается у активных особей, но уменьшается у пассивных животных. Предварительное введение Семакса и пептида, вызывающего дельта-сон, модулирующих чувствительность к отрицательным последствиям стресса, оказывает влияние на альбуминовые показатели крови. В частности, Семакс снимает конформационные изменения молекулы сывороточного альбумина у крыс, предрасположенных к постстрессорным изменениям физиологических функций. Выявлено, что провоспалительный цитокин интерлейкин-1b и противовоспалительный цитокин интерлейкин-4 оказывают однонаправленное действие на свойства связывающих центров альбумина крови у особей с разными параметрами поведения. Интерлейкин-1b и интерлейкин-4 предупреждали вызванные отрицательным эмоциогенным воздействием изменения связывающей способности альбумина как у устойчивых, так и у предрасположенных к стрессу животных. Заключение. Более выраженные эффекты цитокинов на альбуминовые показатели крови у активных крыс по сравнению с пассивными особями связаны с различиями общей концентрации альбумина, обнаруженными у них в исходном состоянии. Кроме этого, указанные особенности могут быть обусловлены спецификой метаболических процессов у животных с разными характеристиками поведения. Structural peculiarities of the albumin molecule in blood samples from behaviorally passive and active rats (prognostically predisposed and resistant to stress exposures, respectively) were evaluated after administration of cytokines and oligopeptides. We revealed that acute stress is followed by a change in the properties of albumin sites. Under these conditions fluorescence of the CAPIDAN probe (criterion for the state of albumin binding sites) is elevated in active specimens, but decreases in passive animals. Pretreatment with Semax and delta sleep-inducing peptide, which modulate the sensitivity to negative consequences of stress, was shown to affect albumin parameters in the blood. For example, Semax abolishes a conformational change of the serum albumin molecule in rats predisposed to post-stress abnormalities in physiological functions. Our study showed that a proinflammatory cytokine interleukin-1b and anti-inflammatory cytokine interleukin-4 have a unidirectional effect on the properties of albumin binding sites in specimens with various behavioral characteristics. Interleukin-1b and interleukin-4 prevent a change in the binding capacity of albumin in stress-resistant and stress-predisposed animals after a negative emotiogenic exposure. The influence of cytokines on blood albumin parameters is more pronounced in behaviorally active rats than in passive specimens, which results from differences in the total albumin concentration in these animals under basal conditions. Moreover, these features can be related to the specifics of metabolic processes in animals with various behavioral characteristics.