Practical aspects of the ligand-binding and enzymatic properties of human serum albumin

An overview of albumin and alpha-1-acid glycoprotein main characteristics: highlighting the roles of amino acids in binding kinetics and molecular interactions

Although Albumin (ALB) and alpha-1-acid glycoprotein (AGP) have distinctive structural and functional characteristics, they both play a key role in binding a large variety of endogenous and exogenous ligands. An extensive binding to these plasma proteins could have a potential impact on drugs disposition (e.g. bioavailability, distribution and clearance), on their innocuity and their efficacy. This review summarizes the common knowledge about the structural and molecular characteristics of both ALB and AGP in humans, and about the most involved amino acids in their high-affinity binding pockets. However, the variability in residues found in binding pockets, for the same species, allows each plasma protein to interact differently with the ligands. The protein-ligand interaction influences differently the disposition of drugs that bind to either of these plasma proteins. The content of this review is useful for the design of new drug entities with high-binding characteristics, in qualitative and quantitative modelling (e.g. in vitro-in vivo extrapolations, 3D molecular docking, interspecies extrapolations), and for other interdisciplinary research.

Exploring the interaction between tyrphostin 9 and human serum albumin using biophysical and computational methods

Tyrphostin 9 (Tyr 9) is a potent platelet-derived growth factor receptor (PDGFR) inhibitor, which induces apoptosis in various cancer cell types. The binding of Tyr 9 to the major transport protein, human serum albumin (HSA) was investigated using several spectroscopic techniques and molecular docking method. Fluorescence quenching titration results showed progressive decrease in the protein fluorescence with increasing drug concentrations. A decreasing trend of the Stern-Volmer constant, K _sv with increasing temperature characterized the drug-induced quenching as static quenching, thus pointed towards the formation of Tyr 9-HSA complex. The binding constant of Tyr 9-HSA interaction was found to lie within the range 3.48-1.69 × 10⁵ M^-1 at three different temperatures, i.e. 15 °C, 25 °C and 35 °C, respectively and suggested intermediate binding affinity between Tyr 9 and HSA. The drug-HSA complex seems to be stabilized by hydrophobic forces, van der Waals forces and hydrogen bonds, as suggested from the thermodynamic data as well as molecular docking results. The far-UV and the near-UV CD spectral results showed slight alteration in the secondary and tertiary structures, respectively, of the protein upon Tyr 9 binding. Interaction of Tyr 9 with HSA also produced microenvironmental perturbations around protein fluorophores, as evident from the three-dimensional fluorescence spectral results but increased protein's thermal stability. Both competitive drug binding results and molecular docking analysis suggested Sudlow's Site I of HSA as the preferred Tyr 9 binding site. Communicated by Ramaswamy H. Sarma.

Multi-stimuli responsive mesoporous carbon nano-platform gated by human serum albumin for cancer thermo-chemotherapy

In this work, a multi-stimuli responsive drug delivery system (MCHP) was designed for combinational chemotherapy and photothermal therapy (PTT). Mesoporous carbon nanoparticles (MCN) with a high loading efficiency were used as near-infrared (NIR)-responsive drug carriers. Human serum albumin (HSA) was attached to the pore openings of MCN via disulfide bonds to serve as a gatekeeper due to its biocompatibility and appropriate molecular size. To improve the dispersity and biocompatibility, the surface of the MCN was modified with polyethylene glycol (PEG). In vitro photothermal effect results showed that MCHP exhibited a power and concentration-dependent photothermal conversion capacity and a good photothermal stability. The doxorubicin (DOX) release from the MCHP/DOX system exhibited NIR/pH/reduction-responsive release properties. A cytotoxicity assay demonstrated that, under NIR irradiation, the MCHP/DOX exhibited chemo-photothermal synergistic effects with a combination index (CI) of 0.643. The biodistribution of DOX in vivo indicated that an NIR laser can prolong the retardation time of DOX in tumor sites. In vivo antitumor experiments showed that MCHP/DOX with NIR irradiation had the highest tumor inhibition rate against 4T1 tumors in mice. This work suggested that MCHP could be explored as a multi-responsive drug release platform for combinational photothermo-chemotherapy.

Characterization of human serum albumin's interactions with safranal and crocin using multi-spectroscopic and molecular docking techniques

Interaction mechanisms of human serum albumin (HSA) with safranal and crocin were studied using UV–Vis absorption, fluorescence quenching and circular dichroism (CD) spectroscopies as well as molecular docking techniques. Changes in absorbance and fluorescence of HSA upon interactions with both compounds were attributed to their binding to amino acid chromophores located in subdomains IIA and IIIA. Fluorescence secondary inner filter effect was excluded using 278 nm and 340 nm as the wavelengths of HSA's excitation and fluorescence while safranal and crocin absorbed at 320 nm and 445 nm, respectively. Stern-Volmer model revealed a static quenching mechanism involve the formation of non-fluorescent ground state complexes. Stern-Volmer, Hill, Benesi-Hilbrand and Scatchard models gave apparent binding constants ranged in 4.25 × 10³ - 2.15 × 10⁵ for safranal and 7.67 × 10³ - 4.23 × 10⁵ L mol⁻¹ for crocin. CD measurements indicated that 13 folds of safranal and crocin unfolded the α-helix structure of HSA by 7.47–21.20%. In-silico molecular docking revealed selective exothermic binding of safranal on eight binding sites with binding energies ranged in −3.969 to −6.6.913 kcal/mol. Crocin exothermally bound to a new large pocket located on subdomain IIA (sudlow 1) with binding energy of −12.922 kcal/mol.

These results confirmed the formation of HSA stable complexes with safranal and crocin and contributed to our understanding for their binding characteristics (affinities, sites, modes, forces … etc.) and structural changes upon interactions. They also proved that HSA can solubilize and transport both compounds in blood to target tissues. The results are of high importance in determining the pharmacological properties of the two phytochemical compounds and for their future developments as anticancer, antispasmodic, antidepressant or aphrodisiac therapeutic agents.

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Interaction mechanisms of human serum albumin with safranal and crocin were studied using multi-spectroscopic techniques.

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Stern-Volmer, Hill, Benesi-Hilbrand and Scatchard models gave apparent binding constants ranged in 4.25 × 10³ – 4.23 × 10⁵ L.mol^-1.

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In-silico molecular docking revealed selective exothermic binding on multiple HSA sites with ΔE between −3.96 and −12.92 kcal/mol

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The results confirmed that HSA can solubilize and transport safranal and crocin to target tissues through forming stable complexes.

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The results are important in determining the pharmacodynamics of both compounds and in their future development as therapeutic agents.

Interaction of Aripiprazole With Human α1-Acid Glycoprotein

We recently reported that aripiprazole binds strongly to human albumin. In continuing our investigations, we investigated the mechanism responsible for the binding and the related interactions of aripiprazole with α1-acid glycoprotein (AGP). The extrinsic Cotton effects for the binding of aripiprazole and its derivatives to AGP were generated, but the magnitudes of the induced circular dichroism intensities did not correlate with those for the binding affinities. It therefore appears that the binding mode of aripiprazole with AGP is somewhat complicated, compared with that of albumin. Isothermal titration calorimetry data obtained for the binding of aripiprazole with AGP were different from that for albumin systems in that the 3 driving reactions, entropy-driven, enthalpy-driven, and the entropy-enthalpy mixed type, were all found for the AGP system, but not albumin. Moreover, the weak binding mode of aripiprazole with the 2 proteins were supported by a molecular docking model analysis. The concentration of albumin in plasma is about 50 times higher than those of AGP, but AGP levels in plasma are increased by about 10 times under inflammatory disease. Therefore, the involvement of these 2 plasma proteins should be considered in more depth for understanding the pharmacokinetics of aripiprazole.

Molecular Scale Optimum Hydrophobicity To Establish an Enhanced Probe-Protein Interaction: Near-Infrared Imaging of Albumin Biosynthesis Modulation

Albumin is the most abundant serum protein and shows variation in its synthesis rate in different physiological and pathophysiological conditions. Thus, there might be an association expected between serum albumin concentration and body health. A library of NIR probes engineered with the optimum hydrophobicity has been developed and characterized using spectroscopy techniques and was employed to understand the variation of hepatic albumin synthesis rates on physiological and pathophysiological states. Given the importance of hydrophobicity in rendering an effective interaction of small molecules with biomolecules, strategic structure interaction relationship studies led us toward the development of a potent emissive molecular probe through chemical library development. By exploration of these newly developed molecular probes, our study elegantly showed how a pathophysiological condition like the hyperinsulinemic state significantly downregulates albumin biosynthesis in HepG2 cells using fluorescence microscopy as a tool. An excellent correlation between the albumin transcript level and fluorescence intensity inside the cells has been observed. The key role of hydrophobicity resulting in an effective interaction of the probes with albumin, thus leading to strong optical signals, has been experimentally demonstrated in this report. Also, a siRNA interference technique has been utilized to establish the excellent selectivity of the developed probes with excitation as well as emission in the NIR region. We therefore have established through our experimental findings that suitable cell permeable emissive molecular markers with a high degree of albumin specificity can be used as a good optical tool for studying the effect of hyperinsulinemia on albumin biosynthesis modulation.

Role of Herborn (K240E) and Milano Slow (D375H) human serum albumin variants towards binding of phenylbutazone and ibuprofen

Human serum albumin (HSA) is the binding cargo in blood plasma. The binding of drugs to HSA determines the pharmacokinetics and pharmacodynamics of the drugs. There are 67 natural genetic variants of HSA were reported in literature. Studying the effect of albumin modifications on drug binding helps to treat the patients with proper medication. In the present study, we have aimed to understand the effect of two natural variants of HSA, such as Herborn (K240E) and Milano Slow (D375H) on the binding of phenylbutazone and ibuprofen. For this, we have generated K240E and D375H mutants and also double mutant (K240E/D375H) of HSA using site directed mutagenesis. The recombinant HSA and its variants were expressed in Pichia pastoris. The interaction of HSA and its variants to phenylbutazone and ibuprofen was studied using fluorescence spectroscopy. Our results showed that there is no significant effect of K240E and D375H mutations on phenylbutazone and ibuprofen binding. But the effect is significant when both the mutations were there in a single protein (K240E/D375H). Further, the CD spectroscopy data showed that there is no effect of phenylbutazone and ibuprofen binding on the conformation of protein, except in case of D375H, where there is a conformational change in the binding pocket with the ibuprofen binding.

Biomolecular interaction of a platelet aggregation inhibitor, 3,4-methylenedioxy-β-nitrostyrene with human serum albumin: multi-spectral and computational characterization

Molecular interaction of the 3,4-methylenedioxy-β-nitrostyrene (MNS), an inhibitor of platelet aggregation with the main transport protein, albumin from human serum (HSA) was explored using absorption, fluorescence and circular dichroism (CD) spectroscopy in combination with in silico analyses. The MNS-HSA complexation was corroborated from the fluorescence and absorption spectral results. Implication of static quenching mechanism for MNS-HSA system was predicted from the Stern-Volmer constant, K_SV-temperature relationship as well as the bimolecular quenching rate constant, k_q values. Stabilization of the complex was affirmed by the value of the binding constant (K_a = 0.56-1.48 × 10⁴ M^-1). Thermodynamic data revealed that the MNS-HSA association was spontaneously driven mainly through hydrophobic interactions along with van der Waal's interaction and H-bonds. These results were well supported by in silico interpretations. Far-UV and near-UV CD spectral results manifested small variations in the protein's secondary and tertiary structures, respectively, while three-dimensional fluorescence spectra displayed microenvironmental fluctuations around protein's fluorophores, upon MNS binding. Significant improvement in the protein's thermostability was evident from the temperature-stability results of MNS-bound HSA. Binding locus of MNS, as identified by competitive drug displacement findings as well as in silico analysis, was found to be located in subdomain IIA (Sudlow's site I) of the protein.Communicated by Ramaswamy H. Sarma.

Towards the functional high-resolution coordination chemistry of blood plasma human serum albumin

Human serum albumin (HSA) is a monomeric, globular, multi-carrier and the most abundant protein in the blood. HSA displays multiple ligand binding sites with extraordinary binding capacity for a wide range of ions and molecules. For decades, HSA's ability to bind to various ligands has led many scientists to study its physiological properties and protein structure; indeed, a better understanding of HSA-ligand interactions in human blood, at the atomic level, will likely foster the development of more potent, and overall more performant, diagnostic and therapeutic tools against serious human disorders such as diabetes, cardiovascular disorders, and cancer. Here, we present a concise overview of the current knowledge of HSA's structural characteristics, and its coordination chemistry with transition metal ions, within the scope and limitations of current techniques and biophysical methods to reach atomic resolution in solution and in blood serum. We also highlight the overwhelming need of a detailed atomistic understanding of HSA dynamic structures and interactions that are transient, weak, multi-site and multi-step, and allosterically affected by each other. Considering the fact that HSA is a current clinical tool for drug delivery systems and a potential contender as molecular cargo and nano-vehicle used in biophysical, clinical and industrial fields, we underline the emerging need for novel approaches to target the dynamic functional coordination chemistry of the human blood serum albumin in solution, at the atomic level.

Forskolin-loaded human serum albumin nanoparticles and its biological importance

In this study, forskolin-loaded human serum albumin nanoparticles (FR-HSANPs) were successfully prepared by incorporation and affinity-binding methods. FR-HSANPs were characterized by transmission electron microscope that most of them are circular in shape and size is around 340 nm. The drug loading was more than 88% and further sustained release profiles were observed as it is 77.5% in 24 h time. Additionally, the cytotoxicity results with HepG2 cells indicated that FR-HSANPs showed significantly higher cytotoxicity and lower cell viability as compared to free forskolin (FR). Furthermore, to understand the binding mechanism of human serum albumin (HSA) with forskolin resulted from fluorescence quenching as a static mechanism and the binding constant is 6.26 ± 0.1 × 10⁴ M^-1, indicating a strong binding affinity. Further, association and dissociation kinetics of forskolin-HSA was calculated from surface plasmon resonance spectroscopy and the binding constant found to be K_forskolin = 3.4 ± 0.24 × 10⁴ M^-1 and also fast dissociation was observed. Further, we used circular dichroism and molecular dynamics simulations to elucidate the possible structural changes including local conformational changes and rigidity of the residues of both HSA and HSA-forskolin complexes.Communicated by Ramaswamy H. Sarma.

Molecular interaction study of an anticancer drug, ponatinib with human serum albumin using spectroscopic and molecular docking methods

Binding of a potent anticancer agent, ponatinib (PTB) to human serum albumin (HSA), main ligand transporter in blood plasma was analyzed with several spectral techniques such as fluorescence, absorption and circular dichroism along with molecular docking studies. Decrease in the K_SV value with increasing temperature pointed towards PTB-induced quenching as the static quenching, thus affirming complexation between PTB and HSA. An intermediate binding affinity was found to stabilize the PTB-HSA complex, as suggested by the K_a value. Thermodynamic analysis of the binding phenomenon revealed participation of hydrophobic and van der Waals interactions along with hydrogen bonds, which was also supported by molecular docking analysis. Changes in both secondary and tertiary structures as well as in the microenvironment around Trp and Tyr residues of HSA were anticipated upon PTB binding to the protein, as manifested from circular dichroism and three-dimensional fluorescence spectra, respectively. Binding of PTB to HSA led to protein's thermal stabilization. Competitive ligand displacement experiments using different site markers such as warfarin, indomethacin and ketoprofen disclosed the binding site of PTB as Sudlow's site I in HSA, which was further confirmed by molecular docking analysis.

Multispectral and molecular docking investigations on the interaction of primethamine/trimethoprim with BSA/HSA

Primethamine (PMA) and trimethoprim (TMP) were investigated as traditional coccidiostats on the binding of bovine serum albumin (BSA) and human serum albumin (HSA) by multispectral and molecular docking techniques. The Stern-Volmer plots and time-resolved fluorescence measurement declared that PMA/TMP quenching the intrinsic fluorescence of BSA/HSA was static quenching process. The binding constants (K_a) and binding sites (n) were calculated at different temperatures. Meanwhile, thermodynamic parameters showed electrostatic forces played a leading role in the interaction of PMA/TMP with BSA/HSA. Some metal ions such as K⁺, Mg²⁺, Cu²⁺, Ca²⁺, Zn²⁺ and Fe³⁺ had no effects on the binding system. The UV-vis absorption spectra confirmed that the interaction between PMA/TMP and BSA/HSA did happen. The analyses of synchronous fluorescence, FT-IR and circular dichroism spectra illustrated that PMA/TMP changed the secondary structures of BSA/HSA. According to Förster non-radiative energy transfer theory, the binding distance between PMA/TMP and BSA/HSA was calculated. The binding location of PMA/TMP to BSA/HSA was identified as sub-domain IIA, which was further confirmed by molecular docking.Communicated by Ramaswamy H. Sarma.

Investigation of binding interactions between BSA and [EPMpyr][Sal] through spectroscopy studies, thermophysical and thermodynamic properties

The intensity of research, probing the interactions between proteins and ionic liquid (IL), has been increasing and parallels the fast-growing applications of ILs in biotechnology. The specific aspects which have attracted the involvement of researchers are stabilization, separation, biochemical and enzymatic reactions of proteins. In this work the synthesis of IL, epoxypropyl and N-methyl substituted 2‑oxopyrrolidinium cation with salicylate anion, [EPMpyr][Sal], and its interaction with aqueous BSA{BSA_(aq)-[EPMpyr][Sal]}. Measurements of thermophysical properties (density (ρ), and speed of sound (u)) showed that both moderately strong and weak interactions occur on treatment of BSA with that chosen IL. H-bond formation, dipole-dipole interactions and ionic interactions occurring in this system were investigated via thermophysical and thermodynamic properties as well as spectroscopic data. Thermodynamic data (excess molar volume (V_m^E), isentropic compressibility (k_s), deviation in isentropic compressibility (∆k_s) and intermolecular free length (L_f)) showed that there were stronger interaction between IL and BSA at higher temperature. The data from all the studies were correlated with Redlich Kister polynomial equation. The blue shift observed in the fluorescent spectra was interpreted to indicate that thetryptophan (Trp) residue of BSA moves to a more hydrophobic environment. It was also observed that the addition of more IL to BSA resulted in denaturation of BSA due to high hydrophobic nature of IL. Circular dichroism studies show that there were significant changes in the fine structure of BSA on interaction with IL. From the FTIR spectra the position of H-bond in the secondary structure of BSA was deduced.

Systems Challenges of Hepatic Carcinomas: A Review

Hepatocellular Carcinoma (HCC) is ubiquitous in its prevalence in most of the developing countries. In the era of systems biology, multi-omics has evinced an extensive approach to define the underlying mechanism of disease progression. HCC is a multifactorial disease and the investigation of progression of liver cirrhosis becomes much extensive with cultivating omics approaches. We have performed a comprehensive review about such challenges in multi-omics approaches that are concerned to identify the immunological, genetics and epidemiological factors associated with HCC.

Recent advances in nanoengineering cellulose for cargo delivery

The recent decade has witnessed a growing demand to substitute synthetic materials with naturally-derived platforms for minimizing their undesirable footprints in biomedicine, environment, and ecosystems. Among the natural materials, cellulose, the most abundant biopolymer in the world with key properties, such as biocompatibility, biorenewability, and sustainability has drawn significant attention. The hierarchical structure of cellulose fibers, one of the main constituents of plant cell walls, has been nanoengineered and broken down to nanoscale building blocks, providing an infrastructure for nanomedicine. Microorganisms, such as certain types of bacteria, are another source of nanocelluloses known as bacterial nanocellulose (BNC), which benefit from high purity and crystallinity. Chemical and mechanical treatments of cellulose fibrils made up of alternating crystalline and amorphous regions have yielded cellulose nanocrystals (CNC), hairy CNC (HCNC), and cellulose nanofibrils (CNF) with dimensions spanning from a few nanometers up to several microns. Cellulose nanocrystals and nanofibrils may readily bind drugs, proteins, and nanoparticles through physical interactions or be chemically modified to covalently accommodate cargos. Engineering surface properties, such as chemical functionality, charge, area, crystallinity, and hydrophilicity, plays a pivotal role in controlling the cargo loading/releasing capacity and rate, stability, toxicity, immunogenicity, and biodegradation of nanocellulose-based delivery platforms. This review provides insights into the recent advances in nanoengineering cellulose crystals and fibrils to develop vehicles, encompassing colloidal nanoparticles, hydrogels, aerogels, films, coatings, capsules, and membranes, for the delivery of a broad range of bioactive cargos, such as chemotherapeutic drugs, anti-inflammatory agents, antibacterial compounds, and probiotics. SYNOPSIS: Engineering certain types of microorganisms as well as the hierarchical structure of cellulose fibers, one of the main building blocks of plant cell walls, has yielded unique families of cellulose-based nanomaterials, which have leveraged the effective delivery of bioactive molecules.

Probing the interaction of 2,4-dichlorophenoxyacetic acid with human serum albumin as studied by experimental and computational approaches

To characterize the binding of a widely used herbicide, 2,4-dichlorophenoxyacetic acid (2,4-D) to the major transporter in human circulation, human serum albumin (HSA), multi-spectroscopic approaches such as fluorescence, absorption and circular dichroism along with computational methods were employed. Analysis of the fluorescence and absorption spectroscopic data confirmed the 2,4-D-HSA complex formation. A static quenching mechanism was evident from the inverse temperature dependence of the K_SV values. The complex was stabilized by a weak binding affinity (K_a = 5.08 × 10³ M^-1 at 298 K). Quantitative analysis of thermodynamic data revealed participation of hydrophobic and van der Waals interactions as well as hydrogen bonds in the binding process. Circular dichroism and three-dimensional fluorescence spectral results showed structural (secondary and tertiary) changes in HSA as well as microenvironmental perturbation around protein fluorophores (Trp and Tyr residues) upon 2,4-D binding. Addition of 2,4-D to HSA was found to improve protein's thermal stability. Competitive displacement results as well as computational analyses suggested preferred location of the 2,4-D binding site as Sudlow's site I (subdomain IIA) in HSA.

Identification of a common recognition center for a photoactive non-steroidal antiinflammatory drug in serum albumins of different species

Photoreactivity, proteomic and molecular dynamic simulation studies demonstrate the existence of a common recognition center for carprofen in serum albumins of different species, in the interface between subdomains IB and IIIA.

Physicochemical characterization of carbamylated human serum albumin: an in vitro study

Carbamylation is an ubiquitous process in which cyanate (OCN⁻) reacts with the N-terminal amino or ε-amino moiety and generates α-carbamyl amino acids and ε-carbamyl-lysine (homocitrulline).

In vitroexperiments and infrared spectroscopy analysis of acid and alkaline phosphatase inhibition by vanadium complexes

Two oxidovanadium complexes with 4-aminobenzoic acid and/or the peroxo anion as ligands were synthesized and characterized by elemental analysis, conductivity measurements, TGA/DTA,¹H NMR, EPR, FTIR, and UV/vis spectroscopies.

How human serum albumin recognizes DNA and RNA

We show here for the first time that HSA possesses two nucleic acid-(NA) binding sites and we estimated the relative contributions of the nucleotide links of (pN)n to their total affinity for these binding sites with higher and lower affinity for NAs. The minimal ligands of these binding sites are orthophosphate (Kd=3.0 and 20.0 mm), various dNMPs (5.6-400 μm and 0.063-18 mm) and different rNMPs (4.9-30 μm and 14-250 μm). Maximal contribution to the total affinity of all NAs to the first and second sites was observed for one nucleotide and was remarkably lower for three additional nucleotide units of (pN)n (n=1-4) with a significant decrease in the contribution at n=5-6, and at n≥7-8 all dependencies reached plateaus. For d(pA)n and r(pA)n a relatively gradual decrease in the contribution to the affinity at n=1-6 was observed, while several d(pN)n, demonstrated a sharp increase in the contribution at n=2-4. Finally, all (pN)n>10 demonstrated high affinity for the first (1.4-150 nm) and the second (80-2400 nm) sites of HSA. Double-stranded NAs showed significantly lower affinity comparing with single-stranded ligands. The thermodynamic parameters characterizing the specific contribution of every nucleotide link of all (pN)1-9 (ΔG°) to their total affinity for HSA were estimated.

Discovery of 18F-JK-PSMA-7, a PET Probe for the Detection of Small PSMA-Positive Lesions

Prostate-specific membrane antigen (PSMA), expressed by most prostate carcinomas (PCa), is a promising target for PCa imaging. The application of PSMA-specific ¹⁸F-labeled PET probes such as ¹⁸F-DCFPyL and ¹⁸F-PSMA-1007 considerably improved the accuracy of PCa tumor detection. However, there remains a need for further improvements in sensitivity and specificity. The aim of this study was the development of highly selective and specific PSMA probes with enhanced imaging properties, in comparison with ¹⁸F-DCFPyL, ¹⁸F-PSMA-1007, and ⁶⁸Ga-PSMA-11. Methods: Eight novel ¹⁸F-labeled PSMA ligands were prepared. Their cellular uptake in PSMA-positive LNCaP C4-2 and PSMA-negative PC-3 cells was compared with that of ¹⁸F-DCFPyL. The most promising candidates were additionally evaluated by small-animal PET in healthy rats using PSMA-positive peripheral ganglia as a model for small PCa lesions. PET images of the ligand with the best outcome, ¹⁸F-JK-PSMA-7, were compared with those of ¹⁸F-DCFPyL, ¹⁸F-PSMA-1007, and ⁶⁸Ga-PSMA-11 with respect to key image-quality parameters for the time frame 60-120 min. Results: Compared with ¹⁸F-DCFPyL, ¹⁸F-JK-PSMA-7 demonstrated increased PSMA-specific cellular uptake. Although target-to-background ratios of ¹⁸F-DCFPyL and ¹⁸F-PSMA-1007 were comparable, this parameter was higher for ¹⁸F-JK-PSMA-7 and lower for ⁶⁸Ga-PSMA-11. Image acutance was significantly higher for ¹⁸F-JK-PSMA-7 and ¹⁸F-PSMA-1007 than for ¹⁸F-DCFPyL and ⁶⁸Ga-PSMA-11. Image resolution was similar for all 4 tracers. ¹⁸F-PSMA-1007 demonstrated significantly higher blood protein binding and bone uptake than the other tracers. Conclusion: ¹⁸F-JK-PSMA-7 is a promising candidate for high-quality visualization of small PSMA-positive lesions. Excellent preclinical imaging properties justify further preclinical and clinical studies of this tracer.

Azilsartan and its Zn(II) complex. Synthesis, anticancer mechanisms of action and binding to bovine serum albumin

Azilsartan is the eighth approved member of angiotensin II receptor blockers for hypertension treatment. Considering that some drugs have additional effects when administered, we studied its effects and mechanisms of action on a human lung cancer cell line A549. We have also modified the structure of the drug by complexation with Zn(II) cation and assayed the anticancer effect. The crystal structure of the new binuclear Zn(II) complex, for short [Zn₂(azil)₂(H₂O)₄]·2H₂O (ZnAzil), was determined by X-ray diffraction methods. The zinc ions are bridged by azilsartan ligands through their carboxylate oxygen and oxadiazol nitrogen atoms. The compounds were examined for their cytotoxic effects against human lung fibroblast (MRC5) and human lung cancer (A549) cell lines. Azilsartan displayed low cytotoxic effects at 150 μM concentrations in A549 human lung cancer cells but the higher effect measured for the Zn complex suggested that this compound may act as an anticancer agent. An apoptotic oxidative stress mechanism of action via the mitochondrial-dependent intrinsic pathway has been determined. Besides, the compounds exerted weak cytotoxic effects in the normal lung related cell line MRC5. Binding constants of the complex formed between each compound and bovine serum albumin (BSA) are in the intermediate range, hence suggesting that azilsartan and ZnAzil could be bonded and transported by BSA.

Hydroxylated and sulfated metabolites of commonly observed airborne polychlorinated biphenyls display selective uptake and toxicity in N27, SH-SY5Y, and HepG2 cells

Although neurotoxicity and hepatotoxicity have long been associated with exposure to polychlorinated biphenyls (PCBs), less is known about the selective toxicity of those hydroxylated PCBs (OH-PCBs) and PCB sulfates that are metabolites derived from exposure to PCBs found in indoor air. We have examined the toxicity of OH-PCBs and PCB sulfates derived from PCBs 3, 8, 11, and 52 in two neural cell lines (N27 and SH-SY5Y) and an hepatic cell line (HepG2). With the exception of a similar toxicity seen for N27 cells exposed to either OH-PCB 52 or PCB 52 sulfate, these OH-PCBs were more toxic to all three cell-types than their corresponding PCB or PCB sulfate congeners. Differences in the distribution of individual OH-PCB and PCB sulfate congeners between the cells and media, and the ability of cells to interconvert PCB sulfates and OH-PCBs, were important components of cellular sensitivity to these toxicants.

Region-Specific Double Denaturation of Human Serum Albumin: Combined Effects of Temperature and GnHCl on Structural and Dynamical Responses

In this work, we have investigated the effects of denaturing agents, guanidine hydrochloride (GnHCl) and temperature, on the overall structure, domain-I, and domain-III of human serum albumin (HSA) using circular dichroism (CD) spectroscopy and steady-state, time-resolved fluorescence spectroscopy. We have tagged Cys-34 of HSA, located at domain-I, using N-(7-dimethylamino-4-methylcoumarin-3-yl)iodoacetamide and Tyr-411 of HSA, located at domain-III, using p-nitrophenyl coumarin ester, for this purpose. The CD spectroscopy studies reveal the overall denaturation of the protein. The denaturation follows the expected direction in which the protein is denatured with an increase in the concentration of GnHCl or temperature. The α-helicity of the native state of HSA was found to be 64.2%, and the minimum value of α-helicity was found to be 14.8% in the presence of 6 M GnHCl at room temperature. Steady-state emission studies were carried out on domain-I and domain-III of the protein using site-specific fluorescent tags. The degree of folding of the two domains at different combinations of temperature and GnHCl concentration was calculated and was found to follow a slightly different course of denaturation. Solvation dynamics was found to be quite different for these two domains. The domain-I of HSA has a maximum solvation time of 0.39 ns, and the solvation time tends to decrease with the action of either temperature or GnHCl. On the other hand, the domain-III of HSA showed a much higher solvation time (1.42 ns) and does not show any regular change at higher temperatures or in the presence of GnHCl. This difference could be attributed to the different microenvironment inside the protein cores of the two domains.

Rhenium tricarbonyl complexes of AIE active tetraarylethylene ligands: tuning luminescence properties and HSA-specific binding

The synthesis and photophysical properties of luminescent Re(i) tricarbonyl complexes prepared from bis(pyridyl)- and bis(quinolyl) tetraarylethylene (TAE) ligands are reported. Emission wavelengths of the complexes are influenced by structural variation in the tetraarylethylene ligands, and several complexes display aggregation-induced enhanced emission in aqueous solution. A Re(i) complex prepared from an indole-functionalized TAE ligand shows significant enhancement in its luminescence intensity accompanied by a remarkable blue shift (∼95 nm) upon specific binding to site II of human serum albumin.

Synchronous birth is a dominant pattern in receptor-ligand evolution

Background

Interactions between proteins are key components in the chemical and physical processes of living organisms. Among these interactions, membrane receptors and their ligands are particularly important because they are at the interface between extracellular and intracellular environments. Many studies have investigated how binding partners have co-evolved in genomes during the evolution. However, little is known about the establishment of the interaction on a phylogenetic scale.

In this study, we systematically studied the time of birth of genes encoding human membrane receptors and their ligands in the animal tree of life. We examined a total of 553 pairs of ligands/receptors, representing non-redundant interactions.

Results

We found that 41% of the receptors and their respective first ligands appeared in the same branch, representing 2.5-fold more than expected by chance, thus suggesting an evolutionary dynamic of interdependence and conservation between these partners. In contrast, 21% of the receptors appeared after their ligand, i.e. three-fold less often than expected by chance. Most surprisingly, 38% of the receptors appeared before their first ligand, as much as expected by chance.

Conclusions

According to these results, we propose that a selective pressure is exerted on ligands and receptors once they appear, that would remove molecules whose partner does not appear quickly.

Electronic supplementary material

The online version of this article (10.1186/s12864-018-4977-2) contains supplementary material, which is available to authorized users.

Integrated metabolomics and metallomics analyses in acute coronary syndrome patients

Acute coronary syndrome (ACS) is the leading cause of morbidity and mortality. Accurate risk prediction in ACS patients is critically important for helping clinicians make therapeutic decisions, such as recommending a more aggressive intervention and intensive follow-up. However, risk stratification in ACS patients remains challenging, and the identification of novel predictors is necessary for improving the prognostic prediction in ACS patients. We employed metallomics and untargeted metabolomics approaches to discover new biomarkers from the plasma samples of 20 ACS patients and 20 non-ACS patients. We identified metabolic changes related to lysophosphatidylcholines, caffeine, glycolysis, tryptophan and sphingomyelin metabolism (p value <0.05) that were perturbed in the ACS patients. Moreover, circulating metal elements, including Mg, Ca, K, Zn, Ni, Ga and In (p value <0.05), were altered in the ACS patients versus the controls. These changes suggest possible changes in cell membrane permeability and rigidity in ACS patients.

Metal-catalyzed oxidation of human serum albumin does not alter the interactive binding to the two principal drug binding sites

It is well known that various physiological factors such as pH, endogenous substances or post-translational modifications can affect the conformational state of human serum albumin (HSA). In a previous study, we reported that both pH- and long chain fatty acid-induced conformational changes can alter the interactive binding of ligands to the two principal binding sites of HSA, namely, site I and site II. In the present study, the effect of metal-catalyzed oxidation (MCO) caused by ascorbate/oxygen/trace metals on HSA structure and the interactive binding between dansyl-L-asparagine (DNSA; a site I ligand) and ibuprofen (a site II ligand) at pH 6.5 was investigated. MCO was accompanied by a time-dependent increase in carbonyl content in HSA, suggesting that the HSA was being oxidized. In addition, The MCO of HSA was accompanied by a change in net charge to a more negative charge and a decrease in thermal stability. SDS-PAGE patterns and α-helical contents of the oxidized HSAs were similar to those of native HSA, indicating that the HSA had not been extensively structurally modified by MCO. MCO also caused a selective decrease in ibuprofen binding. In spite of the changes in the HSA structure and ligand that bind to site II, no change in the interactive binding between DNSA and ibuprofen was observed. These data indicated that amino acid residues in site II are preferentially oxidized by MCO, whereas the spatial relationship between sites I and II (e.g. the distance between sites), the flexibility or space of each binding site are not altered. The present findings provide insights into the structural characteristics of oxidized HSA, and drug binding and drug-drug interactions on oxidized HSA.

A combined photophysical and computational study on the binding of mycophenolate mofetil and its major metabolite to transport proteins

Binding of the immunosuppressive agent mycophenolate mofetil (MMP) and its pharmacologically active metabolite mycophenolic acid (MPA) to human serum albumin (HSA) and α₁-acid glycoprotein (HAAG) has been investigated by means of an integrated approach involving selective excitation of the drug fluorophore, following their UV-A triggered fluorescence and docking studies. The formation of the protein/ligand complexes was evidenced by a dramatic enhancement of the fluorescence intensity and a hypsochromic shift of the emission band. In HSA, competitive studies using oleic acid as site I probe revealed site I as the main binding site of the ligands. Binding constants revealed that the affinity of the active metabolite by HSA is four-fold higher than its proactive form. Moreover, the affinity of MMP by HSA is three-fold higher than by HAAG. Docking studies revealed significant molecular binding differences in the binding of MMP and MPA to sub-domain IIA of HSA (site 1). For MPA, the aromatic moiety would be in close contact to Trp214 with the flexible chain pointing to the other end of the sub-domain; on the contrary, for MMP, the carboxylate group of the chain would be fixed nearby Trp214 through electrostatic interactions with residues Arg218 and Arg222.

Harnessing albumin as a carrier for cancer therapies

Serum albumin, a natural ligand carrier that is highly concentrated and long-circulating in the blood, has shown remarkable promise as a carrier for anti-cancer agents. Albumin is able to prolong the circulation half-life of otherwise rapidly cleared drugs and, importantly, promote their accumulation within tumors. The applications for using albumin as a cancer drug carrier are broad and include both traditional cancer chemotherapeutics and new classes of biologics. Strategies for leveraging albumin for drug delivery can be classified broadly into exogenous and in situ binding formulations that utilize covalent attachment, non-covalent association, or encapsulation in albumin-based nanoparticles. These methods have shown remarkable preclinical and clinical successes that are examined in this review.

Determination of the binding properties of p-cresyl glucuronide to human serum albumin

p-Cresyl glucuronide (p-CG) is a by-product of tyrosine metabolism that accumulates in patients with end-stage renal disease. p-CG binding to human serum albumin in physiological conditions (37 °C, pH 7.40) was studied by ultrafiltration (MWCO 10 kDa) and data were analyzed assuming one binding site. The estimated value of the association constant was 2.77 × 10³ M^-1 and a maximal stoichiometry of 3.80 mol per mole. At a concentration relevant for end-stage renal patients, p-CG was 23% bound to albumin. Competition experiments, using fluorescent probes, demonstrated that p-CG did not bind to Sudlow's site I or site II. The p-CG did not interfere with the binding of p-cresyl-sulfate or indoxyl sulfate to serum albumin.

Ex vivo binding of the immunosuppressant mycophenolic acid to dog and cat plasma proteins and the effect of co-incubated dexamethasone and prednisolone

Mycophenolic acid (MPA) has been shown to be promising for the treatment of autoimmune diseases in dogs and cats. In humans, MPA is highly bound to plasma proteins (~97%). It has been recommended to monitor free drug plasma concentrations because the free MPA correlates with its immunosuppressive effect. However, it is unknown if MPA is highly bound to plasma proteins in dogs and cats. The objectives of this study were to determine the extent of plasma protein binding of MPA and evaluate the effect of prednisolone and dexamethasone on the extent of protein binding of MPA in dogs and cats. The extent of plasma protein binding of MPA was determined in plasma collected from clinically healthy adult cats (n = 13) and dogs (n = 14) by combining high-throughput dialysis and ultra-high-liquid chromatography. This study reveals that MPA is highly bound to plasma proteins (>90%) in dogs and cats, mean extent of binding of MPA at 15 μg/ml to plasma proteins being 96% (range, 95%-97%) and 92% (range, 90%-93%) for dogs and cats, respectively. In dog plasma, MPA is primarily bound to albumin. In vitro, prednisolone increased the unbound MPA in dogs (p < .01) but not in cats (p = .07) while dexamethasone had no effect on MPA plasma binding in either species (p > .05). Results of this study provide valuable information for designing future pharmacokinetic and pharmacodynamic studies and also therapeutic monitoring programs for dogs and cats.

The Effect of Tigecycline on the Binding of Fluoroquinolones to Human Serum Albumin

The co-administration of several drugs in multidrug therapy may alter the binding of each drug to human serum albumin (HSA) and, thus, their pharmacology effect. Therefore, in this study, the interaction mechanism between HSA and two fluoroquinolones (FQs), sparfloxacin (SPF) and levofloxacin (LVF), was investigated using fluorescence and absorption methods in the absence and presence of the competing drugtigecycline (TGC). The the UV-Vis and fluorescence spectroscopy results showed that the fluorescence quenching of HSA was a result of the formation of the HSA-SPF and HSA-LVF complexes. The fluorescence quenching of HSA-TGC revealed that tigecycline can regulate the binding sites, binding mode and binding affinity of fluoroquinolones. The binding constants (KA) and binding sites (n) of the interaction systems were calculated. The results confirmed that the KA values of the HSA-FQ system decreased in the presence of TGC, indicating that TGC can affect the binding ability of FQ for HSA. This interaction may increase the free plasma concentration of unbound FQ and enhance their pharmacology effect.

Proteomic analysis of human epileptic neocortex predicts vascular and glial changes in epileptic regions

Epilepsy is a common neurological disorder, which is not well understood at the molecular level. Exactly why some brain regions produce epileptic discharges and others do not is not known. Patients who fail to respond to antiseizure medication (refractory epilepsy) can benefit from surgical removal of brain regions to reduce seizure frequency. The tissue removed in these surgeries offers an invaluable resource to uncover the molecular and cellular basis of human epilepsy. Here, we report a proteomic study to determine whether there are common proteomic patterns in human brain regions that produce epileptic discharges. We analyzed human brain samples, as part of the Systems Biology of Epilepsy Project (SBEP). These brain pieces are in vivo electrophysiologically characterized human brain samples withdrawn from the neocortex of six patients with refractory epilepsy. This study is unique in that for each of these six patients the comparison of protein expression was made within the same patient: a more epileptic region was compared to a less epileptic brain region. The amount of epileptic activity was defined for each patient as the frequency of their interictal spikes (electric activity between seizures that is a parameter strongly linked to epilepsy). Proteins were resolved from three subcellular fractions, using a 2D differential gel electrophoresis (2D-DIGE), revealing 31 identified protein spots that changed significantly. Interestingly, glial fibrillary acidic protein (GFAP) was found to be consistently down regulated in high spiking brain tissue and showed a strong negative correlation with spike frequency. We also developed a two-step analysis method to select for protein species that changed frequently among the patients and identified these proteins. A total of 397 protein spots of interest (SOI) were clustered by protein expression patterns across all samples. These clusters were used as markers and this analysis predicted proteomic changes due to both histological differences and molecular pathways, revealed by examination of gene ontology clusters. Our experimental design and proteomic data analysis predicts novel glial changes, increased angiogenesis, and changes in cytoskeleton and neuronal projections between high and low interictal spiking regions. Quantitative histological staining of these same tissues for both the vascular and glial changes confirmed these findings, which provide new insights into the structural and functional basis of neocortical epilepsy.

Human serum and milk albumins are metal-dependent DNases

It is known that that human serum albumin (HSA) and alpha-lactalbumin (LA) possess DNA-binding sites. Electrophoretically homogeneous HSA and LA containing no canonical enzymes were isolated from human sera and milk. Here we have analyzed for the first time the possibility of DNA hydrolysis by these proteins. It was shown that HSA possesses metal-dependent DNase activity, while LA cannot hydrolyze DNA. Several rigid criteria have been applied to show that DNase activity is an intrinsic property of HSA from human sera and milk. HSA preparations were inactive after their dialysis against EDTA or in the presence of EDTA, but were activated after addition of several external metal ions: Mn²⁺  > Mg²⁺  > Ca²⁺ . The best activation of HSA preparations was observed in the presence of two metal ions: Mg²⁺ +Ca²⁺  > Mn²⁺  + Ca²⁺  ≥ Mn²⁺  + Mg²⁺ . In contrast to DNases having only one pH optimum, HSA preparations demonstrated two well-pronounced optima at pH 5.7-5.9 and 6.9-7.1 as well as a weak optimum at pH 8.4-8.6. These results demonstrate the diversity of HSA in the DNA hydrolysis at various pHs and in activation by various metal cofactors. Possible reasons for the diversity of HSA preparations are discussed. © 2018 IUBMB Life, 70(6):501-510, 2018.