Analysis of the Binding of Aripiprazole to Human Serum Albumin: The Importance of a Chloro-Group in the Chemical Structure

Multi-cavity molecular descriptor interconnections: Enhanced protocol for prediction of serum albumin drug binding

The role of human serum albumin (HSA) in the transport of molecules predicates its involvement in the determination of drug distribution and metabolism. Optimization of ADME properties are analogous to HSA binding thus this is imperative to the drug discovery process. Currently, various in silico predictive tools exist to complement the drug discovery process, however, the prediction of possible ligand-binding sites on HSA has posed several challenges. Herein, we present a strong and deeper-than-surface case for the prediction of HSA-ligand binding sites using multi-cavity molecular descriptors by exploiting all experimentally available and crystallized HSA-bound drugs. Unlike previously proposed models found in literature, we established an in-depth correlation between the physicochemical properties of available crystallized HSA-bound drugs and different HSA binding site characteristics to precisely predict the binding sites of investigational molecules. Molecular descriptors such as the number of hydrogen bond donors (nHD), number of heteroatoms (nHet), topological polar surface area (TPSA), molecular weight (MW), and distribution coefficient (LogD) were correlated against HSA binding site characteristics, including hydrophobicity, hydrophilicity, enclosure, exposure, contact, site volume, and donor/acceptor ratio. Molecular descriptors nHD, TPSA, LogD, nHet, and MW were found to possess the most inherent capacities providing baseline information for the prediction of serum albumin binding site. We believe that these associations may form the bedrock for establishing a solid correlation between the physicochemical properties and Albumin binding site architecture. Information presented in this report would serve as critical in provisions of rational drug designing as well as drug delivery, bioavailability, and pharmacokinetics.

The antipsychotic medications aripiprazole, brexpiprazole and cariprazine are off-target respiratory chain complex I inhibitors

Antipsychotic drugs are the mainstay of treatment for schizophrenia and provide adjunct therapies for other prevalent psychiatric conditions, including bipolar disorder and major depressive disorder. However, they also induce debilitating extrapyramidal syndromes (EPS), such as Parkinsonism, in a significant minority of patients. The majority of antipsychotic drugs function as dopamine receptor antagonists in the brain while the most recent 'third'-generation, such as aripiprazole, act as partial agonists. Despite showing good clinical efficacy, these newer agents are still associated with EPS in ~ 5 to 15% of patients. However, it is not fully understood how these movement disorders develop. Here, we combine clinically-relevant drug concentrations with mutliscale model systems to show that aripiprazole and its primary active metabolite induce mitochondrial toxicity inducing robust declines in cellular ATP and viability. Aripiprazole, brexpiprazole and cariprazine were shown to directly inhibit respiratory complex I through its ubiquinone-binding channel. Importantly, all three drugs induced mitochondrial toxicity in primary embryonic mouse neurons, with greater bioenergetic inhibition in ventral midbrain neurons than forebrain neurons. Finally, chronic feeding with aripiprazole resulted in structural damage to mitochondria in the brain and thoracic muscle of adult Drosophila melanogaster consistent with locomotor dysfunction. Taken together, we show that antipsychotic drugs acting as partial dopamine receptor agonists exhibit off-target mitochondrial liabilities targeting complex I.

Structural Basis of the Change in the Interaction Between Mycophenolic Acid and Subdomain IIA of Human Serum Albumin During Renal Failure

Mycophenolic acid (MP) is an active metabolite of mycophenolate mofetil, a widely used immunosuppressive drug. MP normally exhibits high plasma protein binding (97-99%), but its binding rate is decreased in patients with renal insufficiency. This decreased protein binding is thought to be associated with leukopenia, a side effect of MP. In this study, we characterized the change in protein binding of MP in renal failure patients. Our findings indicate that MP binds strongly to subdomain IIA of human serum albumin. X-ray crystallographic data indicated that the isobenzofuran group of MP forms a stacking interaction with Trp214, and the carboxyl group of MP is located at a position that allows the formation of hydrogen bonds with Tyr150, His242, or Arg257. Due to the specific binding of MP to subdomain IIA, MP is thought to be displaced by uremic toxin (3-carboxy-4-methyl-5-propyl-2-furan-propionic acid) and fatty acids (oleate or myristate) that can bind to subdomain IIA, resulting in the decreased plasma protein binding of MP in renal failure.

Chlorine Atoms of an Aripiprazole Molecule Control the Geometry and Motion of Aripiprazole and Deschloro-aripiprazole in Subdomain IIIA of Human Serum Albumin

Aripiprazole (ARP), an antipsychotic drug, binds more strongly to human serum albumin (HSA) than the other ARP derivatives. In addition, the signs for the extrinsic Cotton effects for HSA complexed with ARP or deschloro-ARP are reversed. In this study, we report on a structural-chemical approach using circular dichroism (CD) spectroscopic analysis, X-ray crystallographic analysis, and molecular dynamics simulations. The objective was to examine the relationship between the induced CD spectra and the structural features of the HSA complexes with ARP or deschloro-ARP. The intensity of the induced CD spectra of the HSA complexes with ARP or deschloro-ARP was reduced with increasing temperature. We determined the crystal structure of the HSA complexed with deschloro-ARP in this study and compared it to HSA complexed with ARP that we reported previously. The comparison of these structures revealed that both ARP and deschloro-ARP were bound at the site II pocket in HSA and that the orientation of the molecules was nearly identical. Molecular dynamics simulations indicated that the molecular motions of ARP and deschloro-ARP within the site II pocket were different from one another and the proportion of stacking interaction formations of Tyr411 with the dihydroquinoline rings of ARP and deschloro-ARP was also different. These findings indicate that the induced CD spectra are related to the molecular motions and dynamic interactions of ARP and deschloro-ARP in HSA and may help to understand the molecular recognition and motion that occurs within the binding site for the other HSA ligands more clearly.

Antioxidant Activity Evaluation and Assessment of the Binding Affinity to HSA of a New Catechol Hydrazinyl-Thiazole Derivative

Polyphenols have attained pronounced attention due to their ability to provide numerous health benefits and prevent several chronic diseases. In this study, we designed, synthesized and analyzed a water-soluble molecule presenting a good antioxidant activity, namely catechol hydrazinyl-thiazole (CHT). This molecule contains 3′,4′-dihydroxyphenyl and 2-hydrazinyl-4-methyl-thiazole moieties linked through a hydrazone group with very good antioxidant activity in the in vitro evaluations performed. A preliminary validation of the CHT developing hypothesis was performed evaluating in silico the bond dissociation enthalpy (BDE) of the phenol O-H bonds, compared to our previous findings in the compounds previously reported by our group. In this paper, we report the binding mechanism of CHT to human serum albumin (HSA) using biophysical methods in combination with computational studies. ITC experiments reveal that the dominant forces in the binding mechanism are involved in the hydrogen bond or van der Waals interactions and that the binding was an enthalpy-driven process. NMR relaxation measurements were applied to study the CHT–protein interaction by changing the drug concentration in the solution. A molecular docking study added an additional insight to the experimental ITC and NMR analysis regarding the binding conformation of CHT to HSA.

Bioactive compounds: Application of albumin nanocarriers as delivery systems

Enriched products with bioactive compounds (BCs) show the capacity to produce a wide range of possible health effects. Most BCs are essentially hydrophobic and sensitive to environmental factors; so, encapsulation becomes a strategy to solve these problems. Many globular proteins have the intrinsic ability to bind, protect, encapsulate, and introduce BCs into nutraceutical or pharmaceutical matrices. Among them, albumins as human serum albumin (HSA), bovine serum albumin (BSA), ovalbumin (OVA) and α-lactalbumin (ALA) are widely abundant, available, and applied in many industrial sectors, becoming promissory materials to encapsulate BCs. Therefore, this review focuses on researches about the main groups of natural origin BCs (namely phenolic compounds, lipids, vitamins, and carotenoids), the different types of nanostructures based on albumins to encapsulate them and the main fields of application for BCs-loaded albumin systems. In this context, phenolic compounds (catechins, quercetin, and chrysin) are the most extensively BCs studied and encapsulated in albumin-based nanocarriers. Other extensively studied subgroups are stilbenes and curcuminoids. Regarding lipids and vitamins; terpenes, carotenoids (β-carotene), and xanthophylls (astaxanthin) are the most considered. The main application areas of BCs are related to their antitumor, anti-inflammatory, and antioxidant properties. Finally, BSA is the most used albumin to produced BCs-loaded nanocarriers.

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.

The Binding of Aripiprazole to Plasma Proteins in Chronic Renal Failure Patients

The binding of drugs to plasma protein is frequently altered in certain types of renal diseases. We recently reported on the effects of oxidation and uremic toxins on the binding of aripiprazole (ARP) to human serum albumin. In our continuing investigations, we examined the binding of ARP to plasma pooled from patients with chronic renal dysfunction. We examined the issue of the molecular basis for which factors affect the changes in drug binding that accompany renal failure. The study was based on the statistical relationships between ARP albumin binding and biochemical parameters such as the concentrations of oxidized albumin and uremic toxins. The binding of ARP to plasma from chronic renal patients was significantly lower than healthy volunteers. A rational relationship between the ARP binding rate and the concentration of toxins, including indoxyl sulphate (IS) and p-cresyl sulphate (PCS), was found, particularly for IS. Moreover, multiple regression analyses that involved taking other parameters such as PCS or oxidized albumin ratio to IS into account supports the above hypothesis. In conclusion, the limited data reported in this present study indicates that monitoring IS in the blood is a very important determinant in the dosage plan for the administration of site II drugs such as ARP, if the efficacy of the drug in renal disease is to be considered.

Fluorescent Phthalocyanine-Encapsulated Bovine Serum Albumin Nanoparticles: Their Deployment as Therapeutic Agents in the NIR Region

In recent times, researchers have aimed for new strategies to combat cancer by the implementation of nanotechnologies in biomedical applications. This work focuses on developing protein-based nanoparticles loaded with a newly synthesized NIR emitting and absorbing phthalocyanine dye, with photodynamic and photothermal properties. More precisely, we synthesized highly reproducible bovine serum albumin-based nanoparticles (75% particle yield) through a two-step protocol and successfully encapsulated the NIR active photosensitizer agent, achieving a good loading efficiency of 91%. Making use of molecular docking simulations, we confirm that the NIR photosensitizer is well protected within the nanoparticles, docked in site I of the albumin molecule. Encouraging results were obtained for our nanoparticles towards biomedical use, thanks to their negatively charged surface (−13.6 ± 0.5 mV) and hydrodynamic diameter (25.06 ± 0.62 nm), favorable for benefitting from the enhanced permeability and retention effect; moreover, the MTT viability assay upholds the good biocompatibility of our NIR active nanoparticles. Finally, upon irradiation with an NIR 785 nm laser, the dual phototherapeutic effect of our NIR fluorescent nanoparticles was highlighted by their excellent light-to-heat conversion performance (photothermal conversion efficiency 20%) and good photothermal and size stability, supporting their further implementation as fluorescent therapeutic agents in biomedical applications.

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.

Structural Basis of Drug Recognition by Human Serum Albumin

Background:

Human serum albumin (HSA), the most abundant protein in plasma, is a monomeric multi-domain macromolecule with at least nine binding sites for endogenous and exogenous ligands. HSA displays an extraordinary ligand binding capacity as a depot and carrier for many compounds including most acidic drugs. Consequently, HSA has the potential to influence the pharmacokinetics and pharmacodynamics of drugs.

Objective:

In this review, the structural determinants of drug binding to the multiple sites of HSA are analyzed and discussed in detail. Moreover, insight into the allosteric and competitive mechanisms underpinning drug recognition, delivery, and efficacy are analyzed and discussed.

Conclusion:

As several factors can modulate drug binding to HSA (e.g., concurrent administration of drugs competing for the same binding site, ligand binding to allosteric-coupled clefts, genetic inherited diseases, and post-translational modifications), ligand binding to HSA is relevant not only under physiological conditions, but also in the pharmacological therapy management.

Characterization of plasma protein binding in two mouse models of humanized liver, PXB mouse and humanized TK-NOG mouse

The unbound fractions in plasma (f _up) in two mouse models of humanized liver mice, PXB and humanized TK-NOG mice, were compared with human f _up values using equilibrium dialysis method. A good relationship between f _up values obtained from PXB mice and humans was observed; the f _up of 34/39 compounds (87.2%) in PXB mice were within 3-fold of human f _up. In contrast, a weak correlation was observed between human and humanized TK-NOG mouse f _up values; the f _up of 15/24 compounds (62.5%) in humanized TK-NOG mice were within 3-fold of human f _up. As different profiles of plasma protein binding (PPB) profiles were observed between PXB and humanized TK-NOG mice, f _up evaluation is necessary in each mouse model to utilize these humanized liver mice for pharmacological, drug-drug interaction (DDI), and toxicity studies. The unbound fraction in the mixed plasma of human and SCID mouse plasma (85:15) was well correlated with f _up in PXB mice (38/39 compounds within a 3-fold). Thus, this artificial PXB mouse plasma could be used to evaluate PPB.

Characterization of the Interaction of Daptomycin With Site II on Human Serum Albumin

Daptomycin, a cyclic lipopeptide antibiotic, is clinically used for the treatment of infections caused by Gram-positive bacteria, including the methicillin-resistant Staphylococcus aureus and the vancomycin-resistant Enterococci. While daptomycin shows high plasma protein binding (90-93%), our knowledge of the binding process is not extensive. To address this issue in more detail, we characterized the binding of daptomycin to plasma proteins and the findings indicate that the association constant for the binding of daptomycin to human serum albumin (HSA) is much higher than that for α₁-acid glycoprotein, another plasma protein. Daptomycin was also found to bind to a single site on HSA, which was identified as site II. The findings also suggest that the n-decanoyl moiety of daptomycin penetrates into the hydrophobic pocket of site II and that this acyl moiety interacts with Tyr411 at the entrance to site II. Due to this selective interaction with site II, daptomycin binding was significantly inhibited by drugs (ibuprofen or diazepam) and endogenous compounds (uremic toxins or fatty acids) which also strongly bind to site II. In diseased states, such an inhibition in the binding could result in the pharmacokinetics and therapeutic action of daptomycin being substantially altered.

Albumin-Based Transport of Nonsteroidal Anti-Inflammatory Drugs in Mammalian Blood Plasma

Every day, hundreds of millions of people worldwide take nonsteroidal anti-inflammatory drugs (NSAIDs), often in conjunction with multiple other medications. In the bloodstream, NSAIDs are mostly bound to serum albumin (SA). We report the crystal structures of equine serum albumin complexed with four NSAIDs (ibuprofen, ketoprofen, etodolac, and nabumetone) and the active metabolite of nabumetone (6-methoxy-2-naphthylacetic acid, 6-MNA). These compounds bind to seven drug-binding sites on SA. These sites are generally well-conserved between equine and human SAs, but ibuprofen binds to both SAs in two drug-binding sites, only one of which is common. We also compare the binding of ketoprofen by equine SA to binding of it by bovine and leporine SAs. Our comparative analysis of known SA complexes with FDA-approved drugs clearly shows that multiple medications compete for the same binding sites, indicating possibilities for undesirable physiological effects caused by drug-drug displacement or competition with common metabolites. We discuss the consequences of NSAID binding to SA in a broader scientific and medical context, particularly regarding achieving desired therapeutic effects based on an individual's drug regimen.

Serum Albumin, Lipid and Drug Binding

Albumin is widely conserved from vertebrates to invertebrates, and nature of mammalian albumins permit them to bind various endogenous ligands and drugs in the blood. It is known that at least two major ligand binding sites are present on the albumin molecule, which are referred to as Site I and Site II. These binding sites are thought to be almost completely conserved among mammals, even though the degree of binding to these sites are different depending on the physical and chemical properties of drugs and differences in the microenvironment in the binding pockets. In addition, the binding sites for medium and long-chain fatty acids are also well conserved among mammals, and it is considered that there are at least seven binding sites, including Site I and Site II. These bindings properties of albumin in the blood are also widely known to be important for transporting drugs and fatty acids to various tissues. It can therefore be concluded that albumin is one of the most important serum proteins for various ligands, and information on human albumin can be very useful in predicting the ligand binding properties of the albumin of other vertebrates.

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.

Further Evidence Regarding the Important Role of Chlorine Atoms of Aripiprazole on Binding to the Site II Area of Human Albumin

Previously, we reported on the high-affinity binding of aripiprazole (ARP), an antipsychotic drug, to human albumin and the role of the chlorine atom of ARP on this binding. In this study, we investigated the binding mode of ARP to human albumin in detail using ARP derivatives and several animal-derived albumins. ARP bound strongly to human and dog albumin. The circular dichroism (CD) spectra of ARP bound to human and dog albumin were also similar. Deschloro-ARP bound less strongly to all of the albumin species compared to ARP, and the shapes of CD spectra were similar for all albumin species. CD spectra of dimethyl-ARP, for which chlorine atoms were substituted methyl groups, were quite similar to that of deschloro-ARP. In displacement experiments, competitive binding was observed between ARP and deschloro-ARP. These results suggest that the chlorine atoms in ARP are involved in the binding modes of ARP for human and dog albumins, whereas ARP and deschloro-ARP appear to share the same binding region in site II. The aforementioned results imply that compounds having a chlorine atom bind more strongly to plasma proteins, resulting in a long blood retention time. Therefore, findings reported here may provide the basically useful data for drug design.