Spectroscopic and molecular modeling approaches to investigate the binding of proton pump inhibitors to human serum albumin

Exploration of binding mechanism of apigenin to pepsin: Spectroscopic analysis, molecular docking, enzyme activity and antioxidant assays

Pepsin plays an important role in nutrient metabolism. Apigenin (AP) is a beneficial polyphenol to human health. To enhance the bioavailability of AP and elucidate the inhibitory effect of AP on pepsin, the interaction mechanism of AP with pepsin was investigated using spectroscopic analysis and molecular docking, and the activity of pepsin and antioxidant activity of AP was also evaluated. Specifically, AP performed static quenching of pepsin and had only one binding site on pepsin. More interestingly, the interaction between AP and pepsin was spontaneous, while hydrogen bonds and van der Waals forces were the main binding forces. Generally, synchronous and three-dimensional fluorescence confirmed that AP induced the conformational changes of pepsin, and molecular docking proved the above results and illustrated the specific binding patterns. Specifically, AP inhibited the activity of pepsin, while pepsin decreased the antioxidant activity of AP. These results provided useful information for elucidating the interactions between AP and pepsin.

Interaction study of engeletin toward cytochrome P450 3A4 and 2D6 by multi-spectroscopy and molecular docking

The inhibitory effects of engeletin on the activities of human cytochrome P450 3A4 and 2D6 (CYP3A4 and CYP2D6) were investigated by enzyme kinetics, multi-spectroscopy and molecular docking. Engeletin was found to strongly inhibit CYP3A4 and CYP2D6, with the IC₅₀ of 1.32 μM and 2.87 μM, respectively. The inhibition modes of engeletin against CYP3A4 and CYP2D6 were a competitive type and a mixed type, respectively. The fluorescence of the two CYPs was quenched statically by engeletin, which was bound to CYP3A4 stronger than to CYP2D6 at the same temperature. Circular dichroism spectroscopy, three-dimensional fluorescence, ultraviolet-visible spectroscopy and synchronous fluorescence confirmed that the conformation and micro-environment of the two CYPs protein were changed after binding with engeletin. Molecular docking, ultraviolet-visible spectroscopy and the fluorescence data revealed that engeletin had strong binding affinity to the two CYPs through hydrogen and van der Waals forces. The findings here suggested that engeletin may cause the herb-drug interactions for its inhibition of CYP3A4 and CYP2D6 activities.

Chiral separation in the class of proton pump inhibitors by chromatographic and electromigration techniques: An overview

Proton pump inhibitors (PPIs) are benzimidazole-derivative chiral sulfoxides, frequently used in the treatment of gastric hyperacidity-related disorders. Due to their stereoselective metabolism, the eutomeric forms of PPIs can present a more advantageous pharmacokinetic profile by comparison with the distomers or racemates. Moreover, two representatives of the class are used in therapy both as racemates and as pure enantiomers (esomeprazole, dexlansoprazole). A relatively large number of enantioseparation methods employed for the stereoselective determination of PPIs from pharmaceutical, biological, and environmental matrices were published in the past three decades. The purpose of the current overview is to provide a systematic survey of the available chiral separation methods published since the introduction of PPIs in the therapy up to the present. Analytical and bioanalytical methods using different chromatographic and electromigration techniques reported for the enantioseparation of omeprazole, lansoprazole, pantoprazole, rabeprazole, ilaprazole, and tenatoprazole are included. The analytical conditions of the presented methods are summarized in three comprehensive tables, while a critical discussion of the applied techniques, possible mechanism of enantiorecognition, and future perspectives on the topic are also presented.

Identification of tectoridin as the inhibitor of FTO by isothermal titration calorimetric and spectroscopic methods

The characteristics of binding between tectoridin and the fat mass and obesity-associated protein were investigated.

Inhibitory mechanism of sinensetin on α-glucosidase and non-enzymatic glycation: Insights from spectroscopy and molecular docking analyses

Inhibition of α-glucosidase and non-enzymatic glycation is regarded as an effective method to prevent and treat type 2 diabetes and its complications. In this study, the inhibition of sinensetin on α-glucosidase and non-enzymatic glycation was studied with multi-spectroscopic techniques and molecular docking analysis. The results of fluorescence spectroscopy analysis indicated that sinensetin quenched the endogenous fluorescence of α-glucosidase in static manner. The binding of sinensetin with α-glucosidase was a spontaneous process primarily driven by hydrophobic interaction. At 298 K, the binding constant was (5.70 ± 0.12) × 10⁴ L·mol^-1 and the binding site number was 1. The conformation of α-glucosidase was altered by sinensetin, which was revealed by circular dichroism (CD), FTIR spectra, synchronous fluorescence and three-dimensional (3D) fluorescence spectroscopy methods. Molecular docking analysis demonstrated that sinensetin interacted with the amino acid residues of α-glucosidase, which might prevent the entrance of substrate, leading to the decrease of catalytic efficiency of α-glucosidase. Furthermore, glycation assays showed that sinensetin stabilized the structure of bovine serum albumins (BSA), interacted with BSA, strongly inhibited the formation of dityrosine, N'-formylkynurenine and advanced glycation end products (AGEs). This study provided useful information concerning sinensetin preventing and treating type 2 diabetes and its related complications.

Binding of omeprazole to protein targets identified by monoclonal antibodies

Omeprazole is the most commonly used proton pump inhibitor (PPI), a class of medications whose therapeutic mechanism of action involves formation of a disulfide linkage to cysteine residues in the H+/K+ ATPase pump on gastric secretory cells. Covalent linkage between the sole sulfur group of omeprazole and selected cysteine residues of the pump protein results in inhibition of acid secretion in the stomach, an effect that ameliorates gastroesophageal reflux and peptic ulcer disease. PPIs, though useful for specific conditions when used transiently, are associated with diverse untoward effects when used long term. The mechanisms underlying these potential off-target effects remain unclear. PPIs may, in fact, interact with non-canonical target proteins (non-pump molecules) resulting in unexpected pathophysiological effects, but few studies describe off-target PPI binding. Here, we describe successful cloning of monoclonal antibodies against protein-bound omeprazole. We developed and used monoclonal antibodies to characterize the protein target range of omeprazole, stability of omeprazole-bound proteins, and the involvement of cysteines in binding of omeprazole to targets. We demonstrate that a wide range of diverse proteins are targeted by omeprazole. Protein complexes, detected by Western blotting, are resistant to heat, detergents, and reducing agents. Reaction of omeprazole occurs with cysteine-free proteins, is not fully inhibited by cysteine alkylation, occurs at neutral pH, and induces protein multimerization. At least two other clinically used PPIs, rabeprazole and tenatoprazole, are capable of binding to proteins in a similar fashion. We conclude that omeprazole binds to multiple proteins and is capable of forming highly stable complexes that are not dependent on disulfide linkages between the drug and protein targets. Further studies made possible by these antibodies may shed light on whether PPI-protein complexes underlie off-target untoward effects of chronic PPI use.

Effects of Plasma Albumin on the Pharmacokinetics of Esomeprazole in ICU Patients

Objectives

To evaluate the effects of plasma albumin on pharmacokinetics of esomeprazole in ICU patients.

Methods

This study was performed in 32 consecutive intensive care unit (ICU) patients. They were divided into two groups according to the plasma albumin levels. Nineteen patients with low plasma albumin levels (<30 g/L; male/female, 12/7) were assigned to low plasma albumin group (LPAG). Thirteen patients with plasma albumin levels >30 g/L (male/female, 9/4) were assigned to high plasma albumin group (HPAG). All patients were received intravenous (IV) of 40 mg esomeprazole in 5 min. Blood samples were collected via basilic vein at different time points and concentrations of esomeprazole were determined by UPLC-MS/MS.

Results

MRT_(0-∞), t_1/2, V, CL, and C_max between two groups were significantly difference (P<0.05). Compared with HPAG, MRT_(0-∞), t_1/2, and V of esomeprazole in LPAG were increased by 1.42-fold, 1.49-fold, and 1.24-fold, respectively; the maximum drug concentration of esomeprazole in LPAG was decreased to 82.5%. AUC_(0-∞) of LPAG was 1.23 times than that of group B. CL in LPAG was 80% of HPAG. There was no statistical difference between the two groups of AUC_(0-∞) and CL.

Conclusions

Some pharmacokinetic parameters of esomeprazole may be changed in ICU patients with low plasma albumin.

Short-Term Fasting Alters Pharmacokinetics of Cytochrome P450 Probe Drugs: Does Protein Binding Play a Role?

Background and Objectives

Short-term fasting differentially alters cytochrome P450 (CYP) mediated drug metabolism. This has been established by using CYP-enzyme selective probe drugs. However, the observed effects of fasting on the pharmacokinetics of these probe drugs may also include the effects of altered plasma protein binding of these drugs. Therefore, we studied the effect of short-term fasting on protein binding of five commonly used probe drugs [caffeine (CYP1A2), metoprolol (CYP2D6), midazolam (CYP3A4), omeprazole (CYP2C19) and S-warfarin (CYP2C9)].

Methods

The free and total plasma concentrations of the five probe drugs were analyzed by LC–MS/MS in samples retrieved in a cross-over study in which nine healthy subjects received an intravenous administration of the cocktail after an overnight fast (control) and after 36 h of fasting.

Results

Short-term fasting increased plasma free fatty acid concentrations from 0.48 mmol/L (control) to 1.29 mmol/L (36 h fasting) (p = 0.012). Short-term fasting did not alter the free fractions of caffeine, metoprolol and omeprazole compared to the control intervention (p > 0.05). Power to detect a difference for midazolam and S-warfarin was low since the majority of free concentrations were below the limit of quantification.

Conclusions

This study demonstrates that short-term fasting does not alter protein binding of the probe drugs caffeine, metoprolol and omeprazole.

Electronic supplementary material

The online version of this article (doi:10.1007/s13318-017-0437-7) contains supplementary material, which is available to authorized users.

The study on interactions between levofloxacin and model proteins by using multi-spectroscopic and molecular docking methods

The interactions of levofloxacin (LEV) with lysozyme (LYZ), trypsin and bovine hemoglobin (BHb) were investigated, respectively, by using multi-spectral techniques and molecular docking in vitro. Fluorescence studies showed that LEV quenched LYZ/trypsin fluorescence in a combined quenching ways and BHb fluorescence in a static quenching with binding constants of .14, .51 and .20 × 10⁵ L mol^-1 at 298 K, respectively. The thermodynamic parameters demonstrated that hydrophobic forces, hydrogen bonds, and van der Waals forces played the major role in the binding process. The binding distances between LEV and the inner tryptophan residues of LYZ, trypsin, and BHb were calculated to be 4.04, 3.38, and 4.52 nm, respectively. Furthermore, the results of circular dichroism spectra (CD), UV-vis, and three-dimensional fluorescence spectra indicated that the secondary structures of LYZ, trypsin, and BHb were partially changed by LEV with the α-helix percentage of LYZ-LEV system increased while that of BHb-LEV system was decreased, the β-sheet percentage of trypsin-LEV system increased from 41.3 to 42.9%. UV-vis spectral results showed that the binding interactions could cause conformational and some micro-environmental changes of LYZ, trypsin, and BHb. The results of molecular docking revealed that in LYZ and trypsin systems, LEV bound to the active sites residues GLU 35 and ASP 52 of LYZ and trypsin at the active site SER 195, and in BHb system, LEV was located in the central cavity, which was consistent with the results of synchronous fluorescence experiment. Besides, LEV made the activity of LYZ decrease while the activity of trypsin increased.

Oxidation of human serum albumin exhibits inter-individual variability after an ultra-marathon mountain race

The aim of this study was to examine the oxidation of human serum albumin (HSA) caused by oxidative stress following exhaustive and demanding exercise, such as an ultra-marathon race. For this purpose, blood samples from 12 adult runners who underwent a 103 km mountain ultra-marathon race were collected before the race, and also at 24, 48 and 72 h post-race. HSA was partially purified using affinity chromatography and consequently subjected to western blot analysis in order to determine the levels of disulfide dimers indicating oxidation. For reasons of comparison, the results were correlated with those from a previous study, in which the same samples were analyzed using different oxidative stress markers. The results revealed a good correlation between albumin dimers and protein carbonyls at all time points, while there was also a significant correlation with static oxidation reduction potential at 24 h, and a negative correlation with capacity oxidation reduction potential at 24 and 48 h. In addition, an individual analysis of albumin dimers exhibited great inter-individual differences, indicating the variation of HSA oxidation between different athletes. Namely, in some athletes, HSA seemed to be the main oxidation target of serum proteins, while in other athletes, there was even a reduction of HSA. This inter-individual variability in the oxidation of HSA may suggest that different interventions (e.g., through diet) may be required in order to confront the effects on athletes following strenuous exercise. On the whole, this study suggests the importance of the assessment of albumin dimers as a predictive marker for exercise-induced oxidative stress.