Long chain fatty acids alter the interactive binding of ligands to the two principal drug binding sites of human serum albumin

Thermal effects and drugs competition on the palmitate binding capacity of human serum albumin

Human serum albumin (HSA) is the most abundant plasma protein of the circulatory system. It is a multidomain, multifunctional protein that, combining diverse affinities and wide specificity, binds, stores, and transports a variety of biological compounds, pharmacores, and fatty acids. HSA is finding increasing uses in drug-delivery due to its ability to carry functionalized ligands and prodrugs. All this raises the question of competition for binding sites occupancy in case of multiple ligands, which in turn influences the protein structure/dynamic/function relationship and also has an impact on the biomedical applications. In this work, the effects of interactive binding of palmitic acid (PA), warfarin (War) and ibuprofen (Ibu) on the thermal stability of HSA were studied using DSC, ATR-FTIR, and EPR. PA is a high-affinity physiological ligand, while the two drugs are widely used for their anticoagulant (War) and anti-inflammatory (Ibu) efficacy, and are exogenous compounds that accommodate in the deputed drug site DS1 and DS2, respectively overlapping with some of the fatty acid binding sites. The results indicate that HSA acquires the highest thermal stability when it is fully saturated with PA. The binding of this physiological ligand does not hamper the binding of War or Ibu to the native state of the protein. In addition, the three ligands bind simultaneously, suggesting a synergic cooperative influence due to allosteric effects. The increased thermal stability subsequent to binary and multiple ligands binding moderates protein aggregation propensity and restricts protein dynamics. The biophysics findings provide interesting features about protein stability, aggregation, and dynamics in interaction with multiple ligands and are relevant in drug-delivery.

Molecular dynamics of structural effects of reactive carbonyl species derivate of lipid peroxidation on bovine serum albumin

BACKGROUND

Serum albumin is the most abundant protein in the Mammalia blood plasma at where plays a decisive role in the transport wide variety of hydrophobic ligands. BSA undergoes oxidative modifications like the carbonylation by the reactive carbonyl species (RCSs) 4-hydroxy-2-nonenal (HNE), 4 hydroxy-2-hexenal (HHE), malondialdehyde (MDA) and 4-oxo-2-nonenal (ONE), among others. The structural and functional changes induced by protein carbonylation have been associated with the advancement of neurodegenerative, cardiovascular, metabolic and cancer diseases.

METHODS

To elucidate structural effects of protein carbonylation with RCSs on BSA, parameters for six new non-standard amino acids were designated and molecular dynamics simulations of its mono‑carbonylated-BSA systems were conducted in the AMBER force field. Trajectories were evaluated by RMSD, RMSF, PCA, RoG and SASA analysis.

RESULTS

An increase in the conformational instability for all proteins modified with local changes were observed, without significant changes on the BSA global three-dimensional folding. A more relaxed compaction level and major solvent accessible surface area for modified systems was found. Four regions of high molecular fluctuation were identified in all modified systems, being the subdomains IA and IIIB those with the most remarkable local conformational changes. Regarding essential modes of domain movements, it was evidenced that the most representatives were those related to IA subdomain, while IIIB subdomain presented discrete changes.

CONCLUSIONS

RCSs induces local structural changes on mono‑carbonylated BSA. Also, this study extends our knowledge on how carbonylation by RCSs induce structural effects on proteins.

Zinc unbound concentration as an anchor to drive individualize repletion

BACKGROUND AND AIMS

Zinc (Zn) quantification is of particular interest in many clinical condition (e.g. inflammatory disease, critical care). Currently, Zn status is assessed by measuring plasma/serum concentration. This concentration corresponds to the sum of unbound Zn (Zn-Cu) and Zn highly bound to albumin (Zn-Cb).

METHODS

Using a pharmacokinetic approach to the interpretation of total Zn concentration (Zn-Ct), taking into account Zn-Cu and the influence of hypoalbuminemia on Zn-Cb, it is possible to improve the individualization of Zn repletion.

RESULTS

Therefore, during pregnancy and in certain inflammatory disease situations, repletion may not be necessary. However, as in critical care, it would be more appropriate to perform Zn-Cu assays to improve Zn repletion.

CONCLUSION

Coupled total and unbound Zn should be monitored in order to individualize Zn repletion.

Influence of Endogenous Substances on Site-II to Site-I Displacement of Diclofenac Bound to Albumin in the Aqueous Humor of Patients with Cataract

Diclofenac instillation is useful in preventing intraoperative miosis and macular edema caused by postoperative inflammation in cataract surgery; however, optimum efficacy is not attained when the instilled diclofenac strongly binds to albumin in patients' aqueous humor. Therefore, a method that inhibits diclofenac binding and increases the concentration of its free fraction is needed. We conducted a basic study regarding the effects of inhibitors on the binding of instilled diclofenac to albumin and endogenous substances in aqueous humor. Aqueous humor samples from 16 patients were pooled together for analysis. The free fraction of diclofenac was measured using ultrafiltration methods in various experiments with pooled and mimic aqueous humor. Free fraction of diclofenac, a site II drug, in pooled aqueous humor was 0.363 ± 0.013. The binding of diclofenac in the presence of phenylbutazone (PB), a site I inhibitor, was significantly inhibited (free fraction = 0.496 ± 0.013); however, no significant inhibition by ibuprofen, a site II inhibitor, (free fraction = 0.379 ± 0.004), was observed. The unexpected result was due to free fatty acids (FFAs; palmitic acid (PA)) and L-tryptophan (Trp). The inhibition of diclofenac binding by PB in the mimic aqueous humor containing these endogenous substances revealed significant binding inhibition in the presence of PA and Trp. Diclofenac is strongly rebound from site II to site I in the presence of FFAs and Trp in the aqueous humor because FFAs and Trp induce a conformational change in albumin. Therefore, PB significantly inhibits the binding of diclofenac to albumin.

Spectroscopic Analysis of the Effect of Ibuprofen Degradation Products on the Interaction between Ibuprofen and Human Serum Albumin

BACKGROUND

Non-Steroidal Anti-Inflammatory Drugs (NSAIDs) are one of the most commonly used groups of medicinal compounds in the world. The wide access to NSAIDs and the various ways of storing them due to their easy accessibility often entail the problem with the stability and durability resulting from the exposure of drugs to external factors. The aim of the research was to evaluate in vitro the mechanism of competition between ibuprofen (IBU) and its degradation products, i.e., 4'-isobutylacetophenone (IBAP) and (2RS)-2-(4- formylphenyl)propionic acid (FPPA) during transport in a complex with fatted (HSA) and defatted (dHSA) human serum albumin.

METHODS

The research was carried out using spectroscopic techniques, such as spectrophotometry, infrared spectroscopy and nuclear magnetic resonance spectroscopy.

RESULTS

The comprehensive application of spectroscopic techniques allowed, among others, for the determination of the binding constant, the number of classes of binding sites and the cooperativeness constant of the analyzed systems IBU-(d)HSA, IBU-(d)HSA-FPPA, IBU-(d)HSA-IBAP; the determination of the effect of ibuprofen and its degradation products on the secondary structure of albumin; identification and assessment of interactions between ligand and albumin; assessment of the impact of the presence of fatty acids in the structure of albumin and the measurement temperature on the binding of IBU, IBAP and FPPA to (d)HSA.

CONCLUSION

The conducted research allowed us to conclude that the presence of ibuprofen degradation products and the increase in their concentration significantly affect the formation of the IBU-albumin complex and thus, the value of the association constant of the drug, changing the concentration of its free fraction in the blood plasma. It was also found that the presence of an ibuprofen degradation product in a complex with albumin affects its secondary structure.

Exploring Albumin Functionality Assays: A Pilot Study on Sepsis Evaluation in Intensive Care Medicine

Human serum albumin (HSA) as the most abundant plasma protein carries multifunctional properties. A major determinant of the efficacy of albumin relies on its potent binding capacity for toxins and pharmaceutical agents. Albumin binding is impaired in pathological conditions, affecting its function as a molecular scavenger. Limited knowledge is available on the functional properties of albumin in critically ill patients with sepsis or septic shock. A prospective, non-interventional clinical trial assessed blood samples from 26 intensive care patients. Albumin-binding capacity (ABiC) was determined by quantifying the unbound fraction of the fluorescent marker, dansyl sarcosine. Electron paramagnetic resonance fatty acid spin-probe evaluated albumin's binding and detoxification efficiencies. Binding efficiency (BE) reflects the strength and amount of bound fatty acids, and detoxification efficiency (DTE) indicates the molecular flexibility of patient albumin. ABiC, BE, and DTE effectively differentiated control patients from those with sepsis or septic shock (AUROC > 0.8). The diagnostic performance of BE showed similarities to procalcitonin. Albumin functionality correlates with parameters for inflammation, hepatic, or renal insufficiency. Albumin-binding function was significantly reduced in critically ill patients with sepsis or septic shock. These findings may help develop patient-specific algorithms for new diagnostic and therapeutic approaches.

Can blood proteome diversity among fish species help explain perfluoroalkyl acid trophodynamics in aquatic food webs?

Per- and polyfluoroalkyl substances (PFAS) are a diverse family of industrially significant synthetic chemicals infamous for extreme environmental persistence and global environmental distribution. Many PFAS are bioaccumulative and biologically active mainly due to their tendency to bind with various proteins. These protein interactions are important in determining the accumulation potential and tissue distribution of individual PFAS. Trophodynamics studies including aquatic food webs present inconsistent evidence for PFAS biomagnification. This study strives to identify whether the observed variability in PFAS bioaccumulation potential among species could correspond with interspecies protein composition differences. Specifically, this work compares the perfluorooctane sulfonate (PFOS) serum protein binding potential and the tissue distribution of ten perfluoroalkyl acids (PFAAs) detected in alewife (Alosa pseudoharengus), deepwater sculpin (Myoxocephalus thompsonii), and lake trout (Salvelinus namaycush) of the Lake Ontario aquatic piscivorous food web. These three fish sera and fetal bovine reference serum all had unique total serum protein concentrations. Serum protein-PFOS binding experiments showed divergent patterns between fetal bovine serum and fish sera, suggesting potentially two different PFOS binding mechanisms. To identify interspecies differences in PFAS-binding serum proteins, fish sera were pre-equilibrated with PFOS, fractionated by serial molecular weight cut-off filter fractionation, followed by liquid chromatography-tandem mass spectrometry analysis of the tryptic protein digests and the PFOS extracts of each fraction. This workflow identified similar serum proteins for all fish species. However, serum albumin was only identified in lake trout, suggesting apolipoproteins are likely the primary PFAA transporters in alewife and deepwater sculpin sera. PFAA tissue distribution analysis provided supporting evidence for interspecies variations in lipid transport and storage, which may also contribute to the varied PFAA accumulation in these species. Proteomics data are available via ProteomeXchange with identifier PXD039145.

Unveiling the molecular basis of inflamm-aging induced by advanced glycation end products (AGEs)-modified human serum albumin (AGE-HSA) in patients with different immune-mediated diseases

Increased serum advanced glycation end products (AGEs) are commonly found in the patients with Diabetes mellitus (DM), aging-related diseases, and immune-mediated diseases. These diseases are notorious for vasculopathy, immune dysfunctions, and low-grade inflammation mimicking inflamm-aging. However, the molecular basis of inflamm-aging related to AGEs remains elucidation. In this study, we incubated human serum albumin (HSA) and glucose at 37 °C in 5% CO₂ incubator for 0-180 days to generate AGE-HSA. We found the mixture gradually changing the color from transparancy to brown color and increased molecular weight during incubation. The pH value also gradually decreased from 7.2 to 5.4 irrelevant to ionic charge or [Ca²⁺] concentration, but dependent on gradual glycation of the alkaline amino acids, lysine and arginine. Functionally, 40 μg/mL of AGE-HSA decreased IL-2 production from human Jurkat T cell line via suppressing p-STAT3, p-STAT4, and p-STAT6 with an increased tendency of senescence-associated β-galactosidase (SA-βgal) expression but irrelevant to change of Th1/Th2/Treg subpopulations. In contrast, AGE-HSA enhanced CC motif chemokine ligand 5 (CCL-5), IL-8, macrophage migration inhibitor factor (MIF), and interleukin 1 receptor antagonist (IL-1Ra) but suppressed SA-βgal expression by human macrophage-like THP-1 cells. Interestingly, AGE-HSA abrogated the HSA-induced soluble intercellular adhesion molecules 1 (sICAM-1), sE-selectin and endothelin release from human coronary artery endothelial cells (HCAEC) and enhanced SA-βgal expression. The accelerated and increased HSA glycations by individual inflammation-related cytokine such as IL-2, IL-6, IL-17, TGF-β, or TNF-α in the in vitro study reflect increased serum AGE levels in patients with immune-mediated diseases . In conclusion, AGE-HSA can exert immunosuppresive, inflammatory and vasculopathic effects mimicking inflamm-aging in these patients.

Analysis of drug interactions with serum proteins and related binding agents by affinity capillary electrophoresis: A review

Biomolecules such as serum proteins can interact with drugs in the body and influence their pharmaceutical effects. Specific and precise methods that analyze these interactions are critical for drug development or monitoring and for diagnostic purposes. Affinity capillary electrophoresis (ACE) is one technique that can be used to examine the binding between drugs and serum proteins, or other agents found in serum or blood. This article will review the basic principles of ACE, along with related affinity-based capillary electrophoresis (CE) methods, and examine recent developments that have occurred in this field as related to the characterization of drug-protein interactions. An overview will be given of the various formats that can be used in ACE and CE for such work, including the relative advantages or weaknesses of each approach. Various applications of ACE and affinity-based CE methods for the analysis of drug interactions with serum proteins and other binding agents will also be presented. Applications of ACE and related techniques that will be discussed include drug interaction studies with serum agents, chiral drug separations employing serum proteins, and the use of CE in hybrid methods to characterize drug binding with serum proteins.

Induced circular dichroism as a tool to monitor the displacement of ligands between albumins

The induction of chirality in a ligand can be a powerful analytical tool for studying protein-ligand interactions. Here, we advanced by applying the technique to monitor the inversion of the induced circular dichroism (ICD) spectrum when ligands move between human and bovine serum albumin proteins (HSA and BSA). ICD experiments were performed using dimers of methyl vanillate (DVT) and vanillin (DVN). The sign and spectra shape were dependent on the albumin type. DVN presented a positive maximum in 312 nm when complexed with HSA and a negative one in BSA. It was possible to induce and follow the time-dependent displacement of the ligand from BSA (2.2 × 10⁶ M^-1) to HSA (6.6 × 10⁵ M^-1) via ICD inversion. The Molecular Mechanics Generalized Born Surface Area approach was used to calculate the binding free energy of the conformers, and a dissociation pathway for each system was proposed using Umbrella Sampling calculations. Four energy minima dihedral angle conformers were identified, and the corresponding CD spectra were calculated using the quantum chemistry approach. Then, weighted spectra for the conformationally accessible conformers were obtained based on each conformer's Boltzmann probability distribution. In conclusion, the methodology described in the manuscript might be helpful in monitoring the movement of ligands between proteins that they bind.

Molecular analysis and therapeutic applications of human serum albumin-fatty acid interactions

Human serum albumin (hSA) is the major carrier protein for fatty acids (FAs) in plasma. Its ability to bind multiple FA moieties with moderate to high affinity has inspired the use of FA conjugation as a safe and natural platform to generate long-lasting therapeutics with enhanced pharmacokinetic properties and superior efficacy. In this frame, the choice of the FA is crucial and a comprehensive elucidation of the molecular interactions of FAs with hSA cannot be left out of consideration. To this intent, we report here a comparative analysis of the binding mode of different FA moieties with hSA. The choice among different albumin-binding FAs and how this influence the pharmacokinetics properties of a broad spectrum of therapeutic molecules will be discussed including a critical description of some clinically relevant FA conjugated therapeutics.

Beneficial Effects of Carvacrol on In Vitro Models of Metabolically-Associated Liver Steatosis and Endothelial Dysfunction: A Role for Fatty Acids in Interfering with Carvacrol Binding to Serum Albumin

Background:

Carvacrol, a plant phenolic monoterpene, is largely employed as food additive and phytochemical.

Objective:

We aimed to assess the lipid lowering and protective effects of carvacrol in vitro using cellular models of hepatic steatosis and endothelial dysfunction. We also investigated if and how the binding of carvacrol to albumin, the physiological transporter for small compounds in the blood, might be altered by the presence of high levels of fatty acids (FAs).

Methods:

Hepatic FaO cells treated with exogenous FAs mimic hepatosteatosis; endothelial HECV cells exposed to hydrogen peroxide are a model of endothelial dysfunction. In these models, we measured spectrophotometrically lipid accumulation and release, lipoperoxidation, free radical production, and nitric oxide release before and after treatment with carvacrol. The carvacrol binding to albumin in the presence or absence of high levels of FAs was assessed by absorption and emission spectroscopies.

Results:

Carvacrol counteracted lipid accumulation and oxidative stress in hepatocytes and protected endothelial cells from oxidative stress and dysfunction. Moreover, high levels of FAs reduced the binding of carvacrol to albumin.

Conclusion:

The results suggest the good potential of carvacrol in ameliorating dysfunction of hepatic and endothelial cells in vitro. High levels of circulating FAs might compete with carvacrol for binding to albumin thus influencing its transport and bio-distribution.

Serum albumin as a primary non-covalent binding protein for nitro-oleic acid

This work explores the interaction of 9/10-nitro-oleic acid (NO₂-OA) with human serum albumin (HSA). The molecular mechanism of the biological action of NO₂-OA is to our knowledge based on a reversible covalent reaction-Michael addition of nucleophilic amino acid residues of proteins. Since HSA is an important fatty acid transporter, a key question is whether NO₂-OA can bind covalently or non-covalently to HSA, similarly to oleic acid (OA), which can interact with the FA1-FA7 binding sites of the HSA molecule. ¹H NMR studies and competition analysis with OA and the drugs ibuprofen and warfarin were used to investigate a potential non-covalent binding mode. NO₂-OA/HSA binding was confirmed to compete with warfarin for FA-7 with significantly higher affinity. NO₂-OA competes with ibuprofen for FA-3 and FA-6, however, in contrast to the situation with warfarin, the binding affinities are not significantly different. The described interactions are based exclusively on non-covalent binding. No covalent binding of NO₂-OA to HSA was detected by MS/MS. More detailed studies based on MALDI-TOF-MS and Ellman's assay indicated that HSA can be covalently modified in the presence of NO₂-OA to a very limited extent. It was also shown that NO₂-OA has a higher affinity to HSA than that of OA.

Effects of Myristate on the Induced Circular Dichroism Spectra of Aripiprazole Bound to Human Serum Albumin: A Structural-Chemical Investigation

The effects of myristate on the induced circular dichroism spectra of aripiprazole (ARP) bound to human serum albumin (HSA) were investigated. High concentrations of myristate reversed the Cotton effects induced in the ARP-HSA system. The observed ellipticities increased with increasing drug concentration up to an ARP-to-HSA molar ratio of 1:1 and then decreased, indicating that the extrinsic Cotton effects were generated by the binding of ARP molecules to the high- and low-affinity sites in HSA. The data for the concentration of free ARP show that myristate displaces ARP molecules from HSA. Moreover, the free fractions of ARP in the ARP-HSA-myristate system increased significantly when adding fusidic acid, a subdomain IB ligand. In the crystal structure of the ARP-HSA-myristate ternary complex, one ARP molecule is bound to subdomain IB, and the interaction between the carbonyl group of ARP and the aromatic ring of Tyr138 in subdomain IB is essential for binding to occur. Meanwhile, the ARP molecule in the ARP-HSA binary complex structure is bound only to subdomain IIIA. Consequently, the inversion in the extrinsic Cotton effects in the ARP-HSA system can be attributed to the modification of the geometry within the binding pocket, in addition to the transfer of ARP from subdomain IIIA to subdomain IB through the displacement as a result of the binding of myristate to subdomain IIIA.

Interactive multiple binding of oleic acid, warfarin and ibuprofen with human serum albumin revealed by thermal and fluorescence studies

Human serum albumin binds a wide variety of drugs with different structure and affinity to two main binding sites, drug site 1 (DS1) and drug site 2 (DS2), which partially or totally overlap with fatty acid (FA) sites. Although multiple binding sites are available for endogenous compounds, FAs are the primary physiological ligands of albumin and their competition in the occupancy of DS1 and DS2 affects the binding of exogenous molecules, with a possible impact on drug delivery. In this work, we have investigated the simultaneous binding of oleic acid, warfarin and ibuprofen to albumin using differential scanning calorimetry and fluorescence to evaluate the impact on the conformational stability of the protein. The two drugs are widely used for their anticoagulant (warfarin) and anti-inflammatory (ibuprofen) properties, and can be also considered as site markers to probe DS1 and DS2, respectively. Oleic acid is one of the most important fatty acids from a physiological point of view for its role as a source of energy for cells, and also it binds albumin with the highest association constant. When complexed with oleic acid the calorimetric profile of albumin shows a biphasic trend whose line shape depends on the ligand concentration. The binding capacity of either warfarin or ibuprofen to albumin is modulated by oleate molecules in a concentration-dependent mode being synergic cooperative (warfarin) or competitive-like (ibuprofen). The overall results provide insights on the dynamics of albumin/ligands complex, which in turn may have important pharmacokinetic and pharmacodynamic implications.

Synthesis and evaluation of radiogallium-labeled long-chain fatty acid derivatives as myocardial metabolic imaging agents

Since long-chain fatty acids work as the primary energy source for the myocardium, radiolabeled long-chain fatty acids play an important role as imaging agents to diagnose metabolic heart dysfunction and heart diseases. With the aim of developing radiogallium-labeled fatty acids, herein four fatty acid-based tracers, [67Ga]Ga-HBED-CC-PDA, [67Ga]Ga-HBED-CC-MHDA, [67Ga]Ga-DOTA-PDA, and [67Ga]Ga-DOTA-MHDA, which are [67Ga]Ga-HBED-CC and [67Ga]Ga-DOTA conjugated with pentadecanoic acid (PDA) and 3-methylhexadecanoic acid (MHDA), were synthesized, and their potential for myocardial metabolic imaging was evaluated. Those tracers were found to be chemically stable in 0.1 M phosphate buffered saline. Initial [67Ga]Ga-HBED-CC-PDA, [67Ga]Ga-HBED-CC-MHDA, [67Ga]Ga-DOTA-PDA, and [67Ga]Ga-DOTA-MHDA uptakes in the heart at 0.5 min postinjection were 5.01 ± 0.30%ID/g, 5.74 ± 1.02%ID/g, 5.67 ± 0.22%ID/g, and 5.29 ± 0.10%ID/g, respectively. These values were significantly lower than that of [123I]BMIPP (21.36 ± 2.73%ID/g). For their clinical application as myocardial metabolic imaging agents, further structural modifications are required to increase their uptake in the heart.

Neutrophil-mediated oxidative stress and albumin structural damage predict COVID-19-associated mortality

Human serum albumin (HSA) is the frontline antioxidant protein in blood with established anti-inflammatory and anticoagulation functions. Here, we report that COVID-19-induced oxidative stress inflicts structural damages to HSA and is linked with mortality outcome in critically ill patients. We recruited 39 patients who were followed up for a median of 12.5 days (1–35 days), among them 23 had died. Analyzing blood samples from patients and healthy individuals (n=11), we provide evidence that neutrophils are major sources of oxidative stress in blood and that hydrogen peroxide is highly accumulated in plasmas of non-survivors. We then analyzed electron paramagnetic resonance spectra of spin-labeled fatty acids (SLFAs) bound with HSA in whole blood of control, survivor, and non-survivor subjects (n=10–11). Non-survivors’ HSA showed dramatically reduced protein packing order parameter, faster SLFA correlational rotational time, and smaller S/W ratio (strong-binding/weak-binding sites within HSA), all reflecting remarkably fluid protein microenvironments. Following loading/unloading of 16-DSA, we show that the transport function of HSA may be impaired in severe patients. Stratified at the means, Kaplan–Meier survival analysis indicated that lower values of S/W ratio and accumulated H₂O₂ in plasma significantly predicted in-hospital mortality (S/W≤0.15, 81.8% (18/22) vs. S/W>0.15, 18.2% (4/22), p=0.023; plasma [H₂O₂]>8.6 μM, 65.2% (15/23) vs. 34.8% (8/23), p=0.043). When we combined these two parameters as the ratio ((S/W)/[H₂O₂]) to derive a risk score, the resultant risk score lower than the mean (<0.019) predicted mortality with high fidelity (95.5% (21/22) vs. 4.5% (1/22), log-rank χ²=12.1, p=4.9×10⁻⁴). The derived parameters may provide a surrogate marker to assess new candidates for COVID-19 treatments targeting HSA replacements and/or oxidative stress.

Systematic interaction of plasma albumin with the efficacy of chemotherapeutic drugs

Albumin, as the most abundant plasma protein, plays an integral role in the transport of a variety of exogenous and endogenous ligands in the bloodstream and extravascular spaces. For exogenous drugs, especially chemotherapeutic drugs, binding to and being delivered by albumin can significantly affect their efficacy. Meanwhile, albumin can also bind to many endogenous ligands, such as fatty acids, with important physiological significance that can affect tumor proliferation and metabolism. In this review, we summarize how albumin with unique properties affects chemotherapeutic drugs efficacy from the aspects of drug outcome in blood, toxicity, tumor accumulation and direct or indirect interactions with fatty acids, plus application of albumin-based carriers for anti-tumor drug delivery.

Probe into the Molecular Mechanism of Ibuprofen Interaction with Warfarin Bound to Human Serum Albumin in Comparison to Ascorbic and Salicylic Acids: Allosteric Inhibition of Anticoagulant Release

The release of anticoagulant drugs such as warfarin from human serum albumin (HSA) has been important not only mechanistically but also clinically for patients who take multiple drugs simultaneously. In this study, the role of some commonly used drugs, including s-ibuprofen, ascorbic acid, and salicylic acid, was investigated in the release of warfarin bound to HSA in silico. The effects of the aforementioned drugs on the HSA-warfarin complex were investigated with molecular dynamics (MD) simulations using two approaches; in the first perspective, molecular docking was used to model the interaction of each drug with the HSA-warfarin complex, and in the second approach, drugs were positioned randomly and distant from the binary complex (HSA-warfarin) in a physiologically relevant concentration. The results obtained from both approaches indicated that s-ibuprofen and ascorbic acid both displayed allosteric effects on the release of warfarin from HSA. Although ascorbic acid aided in warfarin release, leading to destabilization of HSA, ibuprofen demonstrated a stabilizing effect on releasing the anticoagulant drug through several noncovalent interactions, including hydrophobic, electrostatic, and hydrogen-bonding interactions with the protein. The calculated binding free energy and energy contribution of involved residues using the molecular mechanics-Poisson Boltzmann surface area (MM-PBSA) method, along with root mean square deviation (RMSD) values, protein gyration, and free energy surface (FES) mapping of the protein, provided valuable details on the nature of the interactions of each drug on the release of warfarin from HSA. These results can provide important information on the mechanisms of anticoagulant release that has not been revealed in molecular details previously.

Lysozyme and Human Serum Albumin Proteins as Potential Nitric Oxide Cardiovascular Drug Carriers: Theoretical and Experimental Investigation

Nitric oxide-containing drugs present a critical remedy for cardiovascular diseases. Nitroglycerin (NG, O-NO) and S-nitrosoglutathione (SNG, S-NO) are the most common nitric oxide drugs for cardiovascular diseases. Insights regarding the binding affinity of NO drugs with lysozyme and human serum albumin (HSA) proteins and their dissociation mechanism will provide inquisitive information regarding the potential of the proteins as drug carriers. For the first time, the binding interactions and affinities are investigated using molecular docking, conventional molecular dynamics, steered molecular dynamics, and umbrella sampling to explore the ability of both proteins to act as nitric oxide drug carriers. The molecular dynamics simulation results showed higher stability of lysozyme-drug complexes compared to HSA. For lysozyme, cardiovascular drugs were bound in the protein cavity mainly by the electrostatic and hydrogen bond interactions with residues ASP53, GLN58, ILE59, ARG62, TRP64, ASP102, and TRP109. For HSA, key binding residues were ARG410, TYR411, LYS414, ARG485, GLU450, ARG486, and SER489. The free energy profiles produced from umbrella sampling also suggest that lysozyme-drug complexes had better binding affinity than HSA-drug. Binding characteristics of nitric oxide-containing drugs NG and SNG to lysozyme and HSA proteins were studied using fluorescence and UV-vis absorption spectroscopy. The relative change in the fluorescence intensity as a function of drug concentrations was analyzed using Stern-Volmer calculations. This was also confirmed by the change in the UV-vis spectra. Fluorescence quenching results of both proteins with the drugs, based on the binding constant values, demonstrated significantly weak binding affinity to NG and strong binding affinity to SNG. Both computational and experimental studies provided important data for understanding protein-drug interactions and will aid in developing potential drug carrier systems in cardiovascular diseases.

Dual Function Antimicrobial Loaded Lectin Carrier: A Strategy to Overcome Biomolecular Interference without Detectable Resistance

The disposition of a drug in a biological system may be altered by complex biological fluids; especially, protein binding to drugs influences their activity. Herein, we demonstrated a convenient method involving the noncovalent formulation of butea monosperma seed lectin (BMSL) with an antimicrobial lipid, cationic N-acylethanolamine (cNAE) to mitigate the serum protein interference. Fluorescence spectroscopy and molecular docking study revealed that cNAEs readily formed noncovalent complexes with serum protein, bovine serum albumin. The resulting complexes interfered with the antimicrobial activity of cNAEs. Strikingly, the noncovalent conjugates developed with BMSL and cNAEs (BcNAE) overcame the interference from serum protein and displayed remarkable antimicrobial activity against uropathogenic Escherichia coli (UPEC). Strikingly, the minimum inhibitory concentration (MIC) of the lectin conjugates (7.81 μM) was 4-fold lower than the MIC of pure cNAE. Mechanistic studies showed that BcNAE depolarized the bacterial membrane and affected the integrity to exert the antimicrobial activity. The membrane directed activities of BcNAE on UPEC efficiently eliminated the development of resistance even after 25 passages. The hemocompatibility results and the biosafety assessed in a zebrafish model suggested that BcNAE was nontoxic with good selectivity to bacteria. While testing the therapeutic efficacy against UPEC infected zebrafish, we found that 1× MIC cNAE is ineffective due to interference from biological fluids, which is in agreement with in vitro studies. Remarkably, the infected fish treated with 1× MIC BcNAE conjugates were rescued from infection and restored to the normal life in less than 9 h. Bacterial colony count assay revealed that BcNAE was more efficient in overcoming the biological fluid interference and eliminated the bacterial burden in infected zebrafish. Histopathology analysis supported that BcNAE treatment restored the pathological changes induced by UPEC and, thus, increased survival. The high antimicrobial intensity with limited chance for resistance development and potential to overcome biomolecular interference with a lack of toxicity enhance the merits of exploring lectin conjugates against infectious pathogens.

A Comprehensive Spectroscopic Analysis of the Ibuprofen Binding with Human Serum Albumin, Part II

Human serum albumin (HSA) is the most abundant human plasma protein. HSA plays a crucial role in many binding endos- and exogenous substances, which affects their pharmacological effect. The innovative aspect of the study is not only the interaction of fatted (HSA) and defatted (dHSA) human serum albumin with ibuprofen (IBU), but the analysis of the influence of temperature on the structural modifications of albumin and the interaction between the drug and proteins from the temperature characteristic of near hypothermia (308 K) to the temperature reflecting inflammation in the body (312 K and 314 K). Ibuprofen is a non-steroidal anti-inflammatory drug. IBU is used to relieve acute pain, inflammation, and fever. To determine ibuprofen’s binding site in the tertiary structure of HSA and dHSA, fluorescence spectroscopy was used. On its basis, the fluorescent emissive spectra of albumin (5 × 10−6 mol/dm3) without and with the presence of ibuprofen (1 × 10−5–1 × 10−4 mol/dm3) was recorded. The IBU-HSA complex’s fluorescence was excited by radiation of wavelengths of λex 275 nm and λex 295 nm. Spectrophotometric spectroscopy allowed for recording the absorbance spectra (zero-order and second derivative absorption spectra) of HSA and dHSA under the influence of ibuprofen (1 × 10−4 mol/dm3). To characterize the changes of albumin structure the presence of IBU, circular dichroism was used. The data obtained show that the presence of fatty acids and human serum albumin temperature influences the strength and type of interaction between serum albumin and drug. Ibuprofen binds more strongly to defatted human serum albumin than to albumin in the presence of fatty acids. Additionally, stronger complexes are formed with increasing temperatures. The competitive binding of ibuprofen and fatty acids to albumin may influence the concentration of free drug fraction and thus its therapeutic effect.

Interaction of Benzbromarone with Subdomains IIIA and IB/IIA on Human Serum Albumin as the Primary and Secondary Binding Regions

Benzbromarone has been used for the treatment of gout for more than 30 years. Although it shows a high level of binding to plasma proteins (>99%), our knowledge of this binding is not sufficiently extensive to permit us to understand its pharmacokinetics and pharmacodynamics. To address this issue in more detail, we characterized the binding of benzbromarone to human serum albumin (HSA), the most abundant protein in plasma. Equilibrium dialysis and circular dichroism findings indicated that benzbromarone binds strongly to one primary as well as to multiple secondary sites on HSA and that the bromine atoms of benzbromarone play important roles in this high affinity binding. An X-ray crystallographic study revealed that benzbromarone molecules bind to hydrophobic pockets within subdomains IB, IIA, and IIIA. Inhibition experiments using site specific ligands (subdomain IB; fusidic acid, IIA; warfarin, IIIA; diazepam) indicated that the primary and secondary binding sites that benzbromarone binds to are within subdomains IIIA and IB/IIA, respectively. Lastly, a study of the effect of fatty acids on the benzbromarone-HSA interaction suggested that benzbromarone, when displaced from subdomain IIIA by sodium oleate, could transfer to subdomains IB or IIA. Thus, these data will permit more relevant assessments of the displacement interactions of benzbromarone especially in cases of co-administered drugs or endogenous compounds that also bind to subdomain IIIA. In addition, the findings presented herein will also be useful for designing drug combination therapy in which pharmacokinetic and pharmacodynamic performance need to be controlled.

Albumin as a drug: its biological effects beyond volume expansion

Albumin is the most abundant and perhaps most important protein in human blood. Research has identified many of albumin's possible roles in modulating acid-base balance, modifying inflammation, maintaining vascular endothelial integrity, and binding endogenous and exogenous compounds. Albumin plays a key role in the homeostasis of vascular endothelium, offering protection from inflammation and damage to the glycocalyx. Albumin binds a diverse range of compounds. It transports, delivers and clears drugs, plus it helps with uptake, storage and disposal of potentially harmful biological products. The biological effects of albumin in critical illness are incompletely understood, but may enhance its clinical role beyond use as an intravenous fluid. In this article, we summarise the evidence surrounding albumin's biological and physiological effects beyond its use for plasma volume expansion, and explore potential mechanistic effects of albumin as a disease modifier in patients with critical illness.

Gut microbiota and chronic kidney disease: evidences and mechanisms that mediate a new communication in the gastrointestinal-renal axis

Chronic kidney disease (CKD) represents a growing public health problem associated with loss of kidney function and cardiovascular disease (CVD), the main leading cause of morbidity and mortality in CKD. It is well established that CKD is associated with gut dysbiosis. Over the past few years, there has been a growing interest in studying the composition of the gut microbiota in patients with CKD as well as the mechanisms by which gut dysbiosis contributes to CKD progression, in order to identify possible therapeutic targets to improve the morbidity and survival in CKD. The purpose of this review is to explore the clinical evidence and the mechanisms involved in the gut-kidney crosstalk as well as the possible interventions to restore a normal balance of the gut microbiota in CKD. It is well known that the influence of the gut microbiota on the gut-kidney axis acts in a reciprocal way: on the one hand, CKD significantly modifies the composition and functions of the gut microbiota. On the other hand, gut microbiota is able to manipulate the processes leading to CKD onset and progression through inflammatory, endocrine, and neurologic pathways. Understanding the complex interaction between these two organs (gut microbiota and kidney) may provide novel nephroprotective interventions to prevent the progression of CKD by targeting the gut microbiota. The review is divided into three main sections: evidences from clinical studies about the existence of a gut microbiota dysbiosis in CKD; the complex mechanisms that explain the bidirectional relationship between CKD and gut dysbiosis; and reports regarding the effects of prebiotic, probiotic, and synbiotic supplementation to restore gut microbiota balance in CKD.

Biophysical interactions, docking studies and cytotoxic potential of a novel propofol-linolenate: a multi-technique approach

In the present study, we have analyzed the biophysical interactions of alpha-linolenic acid conjugate (2,6P-ALA) with human serum albumin (HSA) and calf thymus DNA (CT-DNA); and also determined its effect on human cancer cell lines. The results of interactions between 2,6P-ALA and HSA intrinsic fluorescence indicated static quenching of HSA by the target conjugate with overall Stern-Volmer quenching constant (K_sv) value of 1.8 × 10³ M^-1. At high concentrations, 2,6P-ALA caused conformational variations in HSA with evident increase in α-helices. Docking studies also revealed preferential binding of 2,6P-ALA at the hydrophobic cavity of site IB with suggestive involvement of hydrophobic forces. Likewise, the conjugate was also able to quench the fluorescence intensity of CT-DNA with static type of quenching signifying the probability of interaction between them. In case of competitive interaction with ethidium bromide (EB) bound CT-DNA also; the conjugate replaced the EB depicting intercalation to be the main type of binding force. Results of cytotoxic effect of 2,6P-ALA showed significant inhibition of cancer cells growth in a concentration-dependent manner. Conjugate was most potent on MCF-7 cells. Fluorescence microscopic image of MCF-7 cells at IC₅₀ concentration of 24 µM revealed distinct morphological changes that were characteristic of programed cell death. Overall, these results complement with the previous findings of 2,6P-ALA and provide added statistics about the prospect of their transport in blood plasma.Communicated by Ramaswamy H. Sarma.

Preparation, Characterization, and in Vitro/in Vivo Evaluation of Paclitaxel-Bound Albumin-Encapsulated Liposomes for the Treatment of Pancreatic Cancer

Paclitaxel (PTX)-loaded liposomes were developed with the goal of enhancing the effects of cancer treatment. Although loading substances into the lipid membrane of liposome cause some destabilization of the lipid membrane, PTX was nearly exclusively embedded in the lipid membrane of liposomes, due to its low water solubility. Hydrophobic drugs can be encapsulated into the inner core of bovine serum albumin (BSA)-encapsulated liposomes (BSA-liposome) via noncovalent binding to albumin. Since PTX is able to noncovalently bind to albumin, we attempted to prepare PTX-loaded BSA-liposome (PTX-BSA-liposome). The amount of PTX loaded in the BSA-liposome could be increased substantially by using ethanol, since ethanol increases PTX solubility in BSA solutions via prompting the binding PTX to BSA. On the basis of the results of transmission electron microscopy and small-angle X-ray scattering, PTX-BSA-liposome formed unilamellar vesicles that were spherical in shape and the PTX was encapsulated into the inner aqueous core of the liposome as a form of PTX-BSA complex. In addition, the PTX-BSA-liposome, as well as nab-PTX, showed cytotoxicity against human pancreatic cancer cells, AsPC-1 cells, in a PTX concentration-dependent manner. The in vivo antitumor effect of PTX-BSA-liposomes was also observed in a mouse model that had been subcutaneously inoculated with pancreatic cancer cells by virtue of its high accumulation at the tumor site via the enhanced permeability retention effect. These results suggest that PTX-BSA-liposomes have the potential for serving as a novel PTX preparation method for the treatment of pancreatic cancer.

The mechanisms of pharmacokinetic food-drug interactions - A perspective from the UNGAP group

The simultaneous intake of food and drugs can have a strong impact on drug release, absorption, distribution, metabolism and/or elimination and consequently, on the efficacy and safety of pharmacotherapy. As such, food-drug interactions are one of the main challenges in oral drug administration. Whereas pharmacokinetic (PK) food-drug interactions can have a variety of causes, pharmacodynamic (PD) food-drug interactions occur due to specific pharmacological interactions between a drug and particular drinks or food. In recent years, extensive efforts were made to elucidate the mechanisms that drive pharmacokinetic food-drug interactions. Their occurrence depends mainly on the properties of the drug substance, the formulation and a multitude of physiological factors. Every intake of food or drink changes the physiological conditions in the human gastrointestinal tract. Therefore, a precise understanding of how different foods and drinks affect the processes of drug absorption, distribution, metabolism and/or elimination as well as formulation performance is important in order to be able to predict and avoid such interactions. Furthermore, it must be considered that beverages such as milk, grapefruit juice and alcohol can also lead to specific food-drug interactions. In this regard, the growing use of food supplements and functional food requires urgent attention in oral pharmacotherapy. Recently, a new consortium in Understanding Gastrointestinal Absorption-related Processes (UNGAP) was established through COST, a funding organisation of the European Union supporting translational research across Europe. In this review of the UNGAP Working group "Food-Drug Interface", the different mechanisms that can lead to pharmacokinetic food-drug interactions are discussed and summarised from different expert perspectives.

A possible link between polyunsaturated fatty acids and uremic toxins from the gut microbiota in hemodialysis patients: A hypothesis

INTRODUCTION

Indoxyl sulfate (IS) and p-cresyl sulfate (p-CS) are albumin-bound uremic toxins that are difficult to remove by hemodialysis (HD). Human serum albumin (HSA) carries several compounds, including fatty acids that can bind to site II of HSA and represent competing ligands for uremic toxins. The aim of this study was to investigate the association between fatty acids and uremic toxin plasma levels in patients undergoing HD.

METHODS

Thirty-three HD patients (51.5% male, 54.9 ± 10.2 years old, 44.63 ± 28.4 months on HD, albumin level of 3.8 ± 0.3 g/dL) were evaluated. The erythrocyte fatty acid content (saturated fatty acid [SFA], monounsaturated fatty acid [MUFA], and polyunsaturated fatty acid [PUFA]) was measured by gas chromatography, and total IS and p-CS plasma levels were measured by reversed-phase high-performance liquid chromatography.

FINDINGS

The mean percentages of docosahexaenoic acid (DHA), eicosapentaenoic acid (EPA) + DHA and gamma-linolenic (GLA) acid in the erythrocyte membrane were 1.35% ± 0.74%, 1.85% ± 0.79%, and 0.33% ± 0.26%, respectively. The mean levels of IS and p-CS were 19.4 ± 11.9 mg/dL and 101.5 ± 57.2 mg/dL, respectively. There was no significant association between SFA and MUFA and IS and p-CS; however, a negative correlation was found between p-CS and specific PUFAs, and the association between GLA and p-CS levels was retained after adjusting for potential confounding variables (β = -0.49, P = 0.007).

DISCUSSION

Polyunsaturated fatty acids may contribute to the decrease in p-CS uremic toxin plasma levels in patients with chronic kidney disease undergoing HD.

Interaction between 1-pyrenesulfonic acid and albumin: Moving inside the protein

Due to the high sensitivity to alterations in microenvironment polarity of macromolecules, pyrene and its derivatives have long been applied in biosciences. Human serum albumin (HSA), besides its numerous physiological functions, is the main responsible by transport of endogenous and exogenous compounds in the circulatory system. Here, a comprehensive study was carry out to understand the interaction between HSA and the pyrene derivative 1-pyrenesulfonic acid (PMS), which showed a singular behaviour when bound to this protein. The complexation of PMS with HSA was studied by steady state, time-resolved and anisotropy fluorescence, induction of circular dichroism (ICD) and molecular docking. The fluorescence quenching of PMS by HSA was abnormal, being stronger at lower concentration of the quencher. Similar behaviour was obtained by measuring the ICD signal and fluorescence lifetime of PMS complexed in HSA. The displacement of PMS by site-specific drugs showed that this probe occupied both sites, but with higher affinity for site II. The movement of PMS between these main binding sites was responsible by the abnormal effect. Using the holo (PDB: ID 1A06) and apo (PDB: ID 1E7A) HSA structures, the experimental results were corroborated by molecular docking simulation. The abnormal spectroscopic behaviour of PMS is related to its binding in different regions in the protein. The movement of PMS into the protein can be traced by alteration in the spectroscopic signals. These findings bring a new point of view about the use of fluorescence quenching to characterize the interaction between albumin and ligands.

Testing for drug-human serum albumin binding using fluorescent probes and other methods

INTRODUCTION

Drug plasma protein binding remains highly relevant to research and drug development, making the assessment and profiling of compound affinity to plasma proteins essential to drug discovery efforts. Although there are a number of fully-characterized methods, they lack the throughput to handle large numbers of compounds. As the evaluation of adsorption, distribution, metabolism, and excretion is addressed earlier in the drug development timeline, the need for higher-throughput methods has grown. Areas Covered: This review will highlight recent developments on methods for profiling drug plasma binding, with an emphasis on fluorescent probes and emerging high-throughput methodologies. Expert Opinion: There have been a number of high-throughput assays developed in recent years to meet the scaled up demands for compound profiling. Ultimately, the selection of assay technology relies on a number of factors, such as capabilities of the laboratory and the breadth and amount of data required. Fluorescent probe displacement assays are highly flexible and amenable to high-throughput screening, easily scaling up to handle large compound libraries. Recent developments in fluorescence technologies, such as homogenous time-resolved fluorescence and probes utilizing the aggregation-induced emission effect, have improved the sensitivity of these assays. Other technologies, such as microscale thermophoresis and quantitative structure-activity relationship modeling, are gaining popularity as alternative techniques for drug plasma protein binding characterization.

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.

Interaction between Saikosaponin D, Paeoniflorin, and Human Serum Albumin

Saikosaponin D (SSD) and paeoniflorin (PF) are the major active constituents of Bupleuri Radix and Paeonia lactiflora Pall, respectively, and have been widely used in China to treat liver and other diseases for many centuries. We explored the binding of SSD/PF to human serum albumin (HSA) by using fluorospectrophotometry, circular dichroism (CD) and molecular docking. Both SSD and PF produced a conformational change in HSA. Fluorescence quenching was accompanied by a blue shift in the fluorescence spectra. Co-binding of PF and SSD also induced quenching and a conformational change in HSA. The Stern-Volmer equation showed that quenching was dominated by static quenching. The binding constant for ternary interaction was below that for binary interaction. Site-competitive experiments demonstrated that SSD/PF bound to site I (subdomain IIA) and site II (subdomain IIIA) in HSA. Analysis of thermodynamic parameters indicated that hydrogen bonding and van der Waals forces were mostly responsible for the binary association. Also, there was energy transfer upon binary interaction. Molecular docking supported the experimental findings in conformation, binding sites and binding forces.