The multi-dimensional impact of captopril modification on human serum albumin

Captopril is a thiol drug, widely used for the management of hypertension and cardiovascular diseases. Reactive thiols are found to covalently modify the cysteines of plasma proteins and affect their structure and function. Human serum albumin (HSA) is prone to undergo modification by various low molecular weight compounds, including drugs. Cysteine34 (Cys34) in HSA has a free thiol group with antioxidant properties, considered to be the most redox-sensitive amino acid in plasma. Through mass-spectrometric analysis, we demonstrate for the first time that captopril forms a disulfide adduct at Cys34 residue and increases the protease susceptibility of HSA to trypsin. As evidenced by our biophysical and electron microscopy studies, HSA undergoes structural alteration, aggregation and morphological changes when treated with different captopril concentrations. Molecular dynamics studies further revealed the regions of secondary structural changes in HSA due to disulfide adduct formation by captopril at Cys34. It also elucidated the residues involved in the noncovalent interactions with captopril. It is envisaged that structural change in HSA may influence the efficacy of drug delivery as well as its own biological function. These findings may thus provide significant insights into the field of pharmacology intriguing further investigation into the effects of long-term captopril treatment.

Investigation of the Captopril-Insulin Interaction by Mass Spectrometry and Computational Approaches Reveals that Captopril Induces Structural Changes in Insulin

Post-translational modifications remarkably regulate proteins' biological function. Small molecules such as reactive thiols, metabolites, and drugs may covalently modify the proteins and cause structural changes. This study reports the covalent modification and noncovalent interaction of insulin and captopril, an FDA-approved antihypertensive drug, through mass spectrometric and computation-based approaches. Mass spectrometric analysis shows that captopril modifies intact insulin, reduces it into its "A" and "B" chains, and covalently modifies them by forming adducts. Since captopril has a reactive thiol group, it might reduce the insulin dimer or modify it by reacting with cysteine residues. This was proven with dithiothreitol treatment, which reduced the abundance of captopril adducts of insulin A and B chains and intact Insulin. Liquid chromatography tandem mass spectrometric analysis identified the modification of a total of four cysteine residues, two in each of the A and B chains of insulin. These modifications were identified to be Cys6 and Cys7 of the A chain and Cys7 and Cys19 of the B chain. Mass spectrometric analysis indicated that captopril may simultaneously modify the cysteine residues of intact insulin or its subunits A and B chains. Biophysical studies involving light scattering and thioflavin T assay suggested that the binding of captopril to the protein leads to the formation of aggregates. Docking and molecular dynamics studies provided insights into the noncovalent interactions and associated structural changes in insulin. This work is a maiden attempt to understand the detailed molecular interactions between captopril and insulin. These findings suggest that further investigations are required to understand the long-term effect of drugs like captopril.

Ligand binding constants for human serum albumin evaluated by ratiometric analysis of DSC thermograms

This paper describes an expanded application of our recently reported method (Eskew et al., Analytical Biochemistry 621,1 2021) utilizing thermogram signals for thermal denaturation measured by differential scanning calorimetry. Characteristic signals were used to quantitatively evaluate ligand binding constants for human serum albumin. In our approach the ensemble of temperature dependent calorimetric responses for various protein-ligand mixtures and native HSA were compared, in a ratiometric manner, to extract binding constants and stoichiometries. Protein/ligand mixtures were prepared at various ligand concentrations and subjected to thermal denaturation analysis by calorimetry. Measurements provided the melting temperature, T_m, and free-energy ΔG_cal(37°C) for melting ligand-bound Albumin as a function of ligand concentration. Concentration dependent behaviors of these parameters derived from protein/ligand mixtures were used to construct dose-response curves. Fitting of dose-response curves yielded quantitative evaluation of the ligand binding constant and semi-quantitative estimates of the binding stoichiometry. Many of the ligands had known binding affinity for Albumin with binding constants reported in the literature. Evaluated binding parameters for the ligands impressively agreed with reported literature values determined using other standard experimental methods. Results are reported for 29 drug ligands binding to Albumin. These validate our calorimetry-based process for applications in pre-clinical drug screening.

Stabilization of a potential anticancer thiosemicarbazone derivative in Sudlow site I of human serum albumin: In vitro spectroscopy coupled with molecular dynamics simulation

Human Serum Albumin (HSA) is the most important protein in human blood plasma and can acts as a major transporting agent for various drug molecules with flexible binding interaction. To elucidate the interaction of a newly designed potential anticancer thiosemicarbazone based luminophore (E)-1-(4-(diethylamino)-2-hydroxybenzylidene)-4,4-dimethyl-thiosemicarbazide (DAHTS) with HSA under physiological condition, in vitro optical spectroscopic experiments viz UV-Vis absorption, steady state fluorescence, fluroscence anisotropy, time resolved fluorscence (TRF) and cicular dichroism (CD) spectroscopy have been scrutinised. The experimental findings have been corroborated with in silico molecular docking analysis and Molecular Dynamics (MD) simulation. The spectroscopic results demonstrated that the conventionally anion-favouring Sudlow site I of HSA copiously adapt neutral DAHTS molecule with moderate binding affinity. The mean fluorescence lifetime of the sole tryptophan (Trp-214) present in the macromolecule experiences an appreciable diminution with an increase in concentration of the synthesized molecule. DAHTS localize itself close to Trp-214 within subdomain IIA (Sudlow site I) and surrounded by multiple hydrophobic amino acid residues (Val-235, Val-231, Ala-229, Phe-228, Val-325, Phe-326, Leu-327, Met-329, Phe-330, Leu-331, Tyr-332, Leu-346, Leu-347, Val-482, Leu-349, Ala-350, Ala-210, Trp-214, Ala- 213 and Val-216) in HSA. The distinct fluorescence lifetime, diverse pathways and changing rate of population indicates that the rotamerisation of Trp-214 residue is controlled by the guest molecule. Sudlow site I of HSA behaves flexibly and induces an allosteric modulation in the macromolecule resulting a minor deformation in the protein secondary structure as observed in CD (observed 11% change of α-helix content) as well as in MD simulation. The integrated multi-spectroscopic research described herein provides several important information about the binding interaction of a thiosemicarbazone Schiff base with HSA, which can be very significant for thiosemicarbazone based drug designing for academia as well as industry.

The Ser/Thr protein kinase PrkC imprints phenotypic memory in Bacillus anthracis spores by phosphorylating the glycolytic enzyme enolase

Bacillus anthracis is the causative agent of anthrax in humans, bovine, and other animals. B. anthracis pathogenesis requires differentiation of dormant spores into vegetative cells. The spores inherit cellular components as phenotypic memory from the parent cell, and this memory plays a critical role in facilitating the spores' revival. Because metabolism initiates at the beginning of spore germination, here we metabolically reprogrammed B. anthracis cells to understand the role of glycolytic enzymes in this process. We show that increased expression of enolase (Eno) in the sporulating mother cell decreases germination efficiency. Eno is phosphorylated by the conserved Ser/Thr protein kinase PrkC which decreases the catalytic activity of Eno. We found that phosphorylation also regulates Eno expression and localization, thereby controlling the overall spore germination process. Using MS analysis, we identified the sites of phosphorylation in Eno, and substitution(s) of selected phosphorylation sites helped establish the functional correlation between phosphorylation and Eno activity. We propose that PrkC-mediated regulation of Eno may help sporulating B. anthracis cells in adapting to nutrient deprivation. In summary, to the best of our knowledge, our study provides the first evidence that in sporulating B. anthracis, PrkC imprints phenotypic memory that facilitates the germination process.

Rational design of polysorbate 80 stabilized human serum albumin nanoparticles tailored for high drug loading and entrapment of irinotecan

Human serum albumin (HSA) nanoparticles are considered to be versatile carrier of anticancer agents in efficiently delivering the drug to the tumor site without causing any toxicity. The aim of the study was to develop stable HSA nanoparticles (NPs) of drug irinotecan (Iro) having slightly water solubility and moderate HSA binding. A novel strategy of employing a hydrophilic non-ionic surfactant polysorbate 80 which forms protein-polysorbate 80 complex with increased affinity and improvement in Iro-HSA binding has been used to maximize the loading and entrapment efficiency of Iro in HSA-NPs. Bespoke nanoparticles with entrapment efficiency (79.09%) and drug loading of 9.62% could be achieved with spherical shape and particle size of 77.38 nm, 0.290 polydispersity index and -23.7 mv Zeta potential. The drug entrapment in nanoparticles was confirmed by Differential Scanning Calorimeter, Fourier Transformation Infrared Spectroscopy and Fluorescence Spectroscopy. In vitro release of Iro from NPs showed biphasic-release with initial burst followed by prolonged release upto 24 h. The short-term stability investigation of nanodispersion showed no significant changes in physicochemical properties of NPs. Long-term studies on freeze dried Iro-HSA-NPs indicated good stability of NPs up to 12 months. This is the first report for efficient fabrication of Iro delivery system based on HSA nanoparticles.

Captopril apparently increase and cisplatin apparently decrease human albumin concentration in artificial urinary solutions

BACKGROUND

Measurement of urinary albumin (HSA) is very important in diagnostic of kidney diseases. Much less is known about the possible impact of substances present in urine together with albumin on the results of measurements.

METHODS

We investigated the effect of the presence of captopril and cisplatin in the solution on the result of the determination of HSA by native polyacrylamide gel electrophoresis. Protein conformation in the absence and presence of the drugs was examined using Fourier Transform Infrared Spectroscopy (FTIR).

RESULTS

The presence of captopril apparently increases HSA concentration while cisplatin causes an apparent decrease in the HSA concentration. The presence of both drugs also influence the secondary structure forms of HSA albumin investigated by FTIR.

CONCLUSION

Both drugs tested in the concentration of human use can have an impact on the results of determination of albumin in urine which can influence clinical decision.

Spectroscopic Studies on the Interaction between Tilorone and Human Serum Albumin

Under physiological conditions, in vitro interaction between the antiviral drug 2,7-bis[2-(diethylamino)ethoxy]-9-fluorenone dihydrochloride (Tilorone, TIL) and human serum albumin (HSA) was investigated at excitation wavelength 280 nm and at different temperatures (298 K and 313 K) by fluorescence emission spectroscopy. TIL showed a strong ability to quench the intrinsic fluorescence of HSA through a static quenching procedure. The binding constant is estimated as KA =7.19× 104L·mol-1 at 298 K. The enthalpy change (ΔHº) and entropy change (ΔSº) were derived to be negative values. A value of 1.63 nm for the average distance r between TIL (acceptor) and tryptophan residues of HSA (donor) was derived from the fluorescence resonance energy transfer.

Study on the interaction of 6-(2-morpholin-4-yl-ethyl)-6H-indolo [2,3-b]quinoxaline hydrochloride with human serum albumin by fluorescence spectroscopy

Under physiological conditions, in vitro interaction between the bio-active substance 6-(2-morpholin-4-yl-ethyl)-6H-indolo[2,3-b]quinoxaline hydrochloride (MIQ) and human serum albumin (HSA) was investigated at an excitation wavelength 260 nm and at different temperatures (298 K, 308 K and 313 K) by fluorescence emission spectroscopy. From spectral analysis, MIQ showed a strong ability to quench the intrinsic fluorescence of HSA through a static quenching procedure. The binding constant is estimated asK _A   =  2.55  ×  10^-4 l · mol^-1 at 298 K. Based on the thermodynamic parameters evaluated from the van 't Hoff equation, the enthalpy change (ΔH°) and entropy change (ΔS°) were derived to be negative values. A value of 2.37 nm for the average distance r between MIQ (acceptor) and tryptophan residues of HSA (donor) was derived from the fluorescence resonance energy transfer. UV/vis absorption spectra were used to confirm the quenching mechanism.

Antihypertensive activity of a quinoline appended chalcone derivative and its site specific binding interaction with a relevant target carrier protein

The usefulness of heterocyclic chalcone derivative as a therapeutic target in controlling hypertension and its site specific binding interaction with model transport protein to get a clear picture about its delivery mechanism.

Spectroscopic study on the interaction of Trypsin with Bicyclol and analogs

The interactions between Trypsin and Bicyclol or analogs (Bifendate, I, II and III) were investigated by spectrophotometric methods. It was found that Bicyclol or analogs had strong ability to quench the intrinsic fluorescence of Trypsin by a static quenching procedure. The binding constants were obtained at three temperatures. The thermodynamics parameters reveal that the hydrophobic and electrostatic interactions play an important role in the interaction. Results showed that the microenvironments of tryptophan residue of Trypsin were disturbed by the analogs. Results indicated that Bifendate was the strongest quencher among five compounds.

Study of captopril pharmacokinetics in rabbit blood with microdialysis based on online generated Au nanoclusters and pepsin–captopril interaction in luminol chemiluminescence

A luminol–HAuCl₄–pepsin (Pep) flow injection-chemiluminescence system was explored to determine captopril (CAP) based on the CL intensity inhibition effect and applied to study CAP pharmacokinetics in rabbits with microdialysis.

Spectroscopic study on the interaction of catalase with bifendate and analogs

The interactions of bifendate (DDB) or analogs (Bicyclol, I, II and III) with catalase are analyzed by spectrophotometric methods. The fluorescence spectra results show the intrinsic fluorescence of catalase is strongly quenched by DDB or analogs with a static quenching procedure. The binding constants are obtained at three temperatures. The thermodynamics parameters (ΔH, ΔS, ΔG) indicate the hydrophobic and electrostatic interactions play a major role in the interaction. The results of synchronous fluorescence, UV-vis absorption and three-dimensional fluorescence spectra demonstrate that the microenvironments of Trp residue of catalase are disturbed by the analogs. Thermodynamic results showed that DDB is the strongest quencher and bind to catalase with the highest affinity among five compounds.