Clinical relevance of drug binding to plasma proteins

Re-discover the value of protein binding assessments in hepatic and renal impairment studies and its contributions in drug labels and dose decisions

One of the key pharmacokinetic properties of most small molecule drugs is their ability to bind to serum proteins. Unbound or free drug is responsible for pharmacological activity while the balance between free and bound drug can impact drug distribution, elimination, and other safety parameters. In the hepatic impairment (HI) and renal impairment (RI) clinical studies, unbound drug concentration is often assessed; however, the relevance and impact of the protein binding (PB) results is largely limited. We analyzed published clinical safety and pharmacokinetic studies in subjects with HI or RI with PB assessment up to October 2022 and summarized the contribution of PB results on their label dose recommendations. Among drugs with HI publication, 32% (17/53) associated product labels include PB results in HI section. Of these, the majority (9/17, 53%) recommend dose adjustments consistent with observed PB change. Among drugs with RI publication, 27% (12/44) of associated product labels include PB results in RI section with the majority (7/12, 58%) recommending no dose adjustment, consistent with the reported absence of PB change. PB results were found to be consistent with a tailored dose recommendation in 53% and 58% of the approved labels for HI and RI section, respectively. We further discussed the interpretation challenges of PB results, explored treatment decision factors including total drug concentration, exposure-response relationships, and safety considerations in these case examples. Collectively, comprehending the alterations in free drug levels in HI and RI informs treatment decision through a risk-based approach.

Conformational dynamics of α-1 acid glycoprotein (AGP) in cancer: A comparative study of glycosylated and unglycosylated AGP

α-1 acid glycoprotein (AGP) is one of the most abundant plasma proteins. It fulfills two important functions: immunomodulation, and binding to various drugs and receptors. These different functions are closely associated and modulated via changes in glycosylation and cancer missense mutations. From a structural point of view, glycans alter the local biophysical properties of the protein leading to a diverse ligand-binding spectrum. However, glycans can typically not be observed in the resolved X-ray crystallography structure of AGP due to their high flexibility and microheterogeneity, so limiting our understanding of AGP's conformational dynamics 70 years after its discovery. We here investigate how mutations and glycosylation interfere with AGP's conformational dynamics changing its biophysical behavior, by using molecular dynamics (MD) simulations and sequence-based dynamics predictions. The MD trajectories show that glycosylation decreases the local backbone flexibility of AGP and increases the flexibility of distant regions through allosteric effects. We observe that mutations near the glycosylation site affect glycan's conformational preferences. Thus, we conclude that mutations control glycan dynamics which modulates the protein's backbone flexibility directly affecting its accessibility. These findings may assist in the drug design targeting AGP's glycosylation and mutations in cancer.

Functionalisation of brush polyethylene glycol polymers with specific lipids extends their elimination half-life through association with natural lipid trafficking pathways

Polymeric prodrugs have been applied to control the delivery of various types of therapeutics. Similarly, conjugation of peptide therapeutics to lipids has been used to prolong systemic exposure. Here, we extend on these two approaches by conjugating brush polyethylene glycol (PEG) polymers with different lipid components including short-chain (1C2) or medium-chain (1C12) monoalkyl hydrocarbon tails, cholesterol (Cho), and diacylglycerols composed of two medium-chain (2C12) or long-chain (2C18) fatty acids. We uniquely evaluate the integration of these lipid-polymers into endogenous lipid trafficking pathways (albumin and lipoproteins) and the impact of lipid conjugation on plasma pharmacokinetics after intravenous (IV) and subcutaneous (SC) dosing to cannulated rats. The IV and SC elimination half-lives of Cho-PEG (13 and 22 h, respectively), 2C12-PEG (11 and 17 h, respectively) and 2C18-PEG (12 h for both) were prolonged compared to 1C2-PEG (3 h for both) and 1C12-PEG (4 h for both). Interestingly, 1C2-PEG and 1C12-PEG had higher SC bioavailability (40 % and 52 %, respectively) compared to Cho-PEG, 2C12-PEG and 2C18-PEG (25 %, 24 % and 23 %, respectively). These differences in pharmacokinetics may be explained by the different association patterns of the polymers with rat serum albumin (RSA), bovine serum albumin (BSA) and lipoproteins. For example, in pooled plasma (from IV pharmacokinetic studies), 2C18-PEG had the highest recovery in the high-density lipoprotein (HDL) fraction. In conclusion, the pharmacokinetics of brush PEG polymers can be tuned via conjugation with different lipids, which can be utilised to tune the elimination half-life, biodistribution and effect of therapeutics for a range of medical applications. STATEMENT OF SIGNIFICANCE: Lipidation of therapeutics such as peptides has been employed to extend their plasma half-life by promoting binding to serum albumin, providing protection against rapid clearance. Here we design and evaluate innovative biomaterials consisting of brush polyethylene glycol polymers conjugated with different lipids. Importantly, we show for the first time that lipidated polymeric materials associate with endogenous lipoprotein trafficking pathways and this, in addition to albumin binding, controls their plasma pharmacokinetics. We find that conjugation to dialkyl lipids and cholesterol leads to higher association with lipid trafficking pathways, and more sustained plasma exposure, compared to conjugation to short and monoalkyl lipids. Our lipidated polymers can thus be utilised as delivery platforms to tune the plasma half-life of various pharmaceuticals.

Identification of starvation-mimetic bioactive phytocomponent from Withania somnifera using in-silico molecular modelling and flow cytometry-based analysis for the management of malaria

Multidrug resistance episodes in malaria increased from 3.9% to 20% from 2015 to 2019. Synchronizing the clinical manifestation in chronological sequence led to a unique impression on glucose demand (increased up to 100-fold) by the parasite-infected RBCs. Hence, restriction in the glucose uptake to parasite-infected RBCs could be an alternative approach to conquer the global burden of malaria to a greater extent. A C28 steroidal lactone Withaferin A (WS-3) isolated from Withania somnifera leave extract shows better thermodynamically stable interactions with the glucose transporters (GLUT-1 and PfHT) to standard drugs metformin and lopinavir. MD simulations for a trajectory period of 100 ns reflect stable interactions with the interactive amino acid residues such as Pro141, Gln161, Gln282, Gln283, Trp388, Phe389, and Phe40, Asn48, Phe85, His168, Gln169, Asn311 which potentiating inhibitory activity of WS-3 against GLUT-1 and PfHT respectively. WS-3 was non-hemotoxic (%hemolysis <5%) for a high concentration of up to 1 mg/ml in the physiological milieu. However, the %hemolysis significantly increased up to 30.55 ± 0.929% in a parasitophorous simulated environment (pH 5.0). Increased hemolysis of WS-3 could be due to the production of ROS in an acidic environment. Further, the inhibitory activity of WS-3 against both glucose transporters was supported with flow cytometry-based analysis of parasite-infected RBCs. Results show that WS-3 has low mean fluorescence intensities for both target proteins compared to conventional drugs, suggesting a potential sugar transporter inhibitor against GLUT-1 and PfHT for managing malaria. Communicated by Ramaswamy H. Sarma.

Enantioselective binding of carvedilol to human serum albumin and alpha-1-acid glycoprotein

Carvedilol, a highly protein-bound beta-blocker, is used in therapy as a racemic mixture of its two enantiomers that exhibit different pharmacological activity. The aim of this study was to evaluate the stereoselective nature of its binding to the two major plasma proteins: albumin and alpha-1-acid glycoprotein. The determination of the plasma protein-binding degree for carvedilol and its enantiomers was achieved using ultrafiltration for the separation of the free fraction, followed by LC-MS/MS quantification, using two different developed and validated methods in terms of stationary phase: achiral C18 type and chiral ovomucoid type. Furthermore, molecular docking methods were applied in order to investigate and to better understand the mechanism of protein-binding for S-(-)- and R-(+)-carvedilol. A difference in the binding behavior of the two enantiomers to the plasma proteins was observed when taken individually, with R-(+)-carvedilol having a higher affinity for albumin and S-(-)-carvedilol for alpha-1-acid glycoprotein. However, in the case of the racemic mixture, the binding of the S enantiomer to alpha-1-acid glycoprotein seemed to be influenced by the presence of its antipode, although no such influence was observed in the case of albumin. The results raise the question of a binding competition between the two enantiomers for alpha-1-acid glycoprotein.

Probing the Interaction between Isoflucypram Fungicides and Human Serum Albumin: Multiple Spectroscopic and Molecular Modeling Investigations

To better understand the potential toxicity risks of isoflucypram in humans, The interaction between isoflucypram and HSA (human serum albumin) was studied through molecular docking, molecular dynamics simulations, ultraviolet-visible absorption, fluorescence, synchronous fluorescence, three-dimensional fluorescence, Fourier transform infrared spectroscopies, and circular dichroism spectroscopies. The interaction details were studied using the molecular docking method and molecular dynamics simulation method. The results revealed that the effect of isoflucypram on human serum albumin was mixed (static and dynamic) quenching. Additionally, we were able to obtain important information on the number of binding sites, binding constants, and binding distance. The interaction between isoflucypram and human serum albumin occurred mainly through hydrogen bonds and van der Waals forces. Spectroscopic results showed that isoflucypram caused conformational changes in HSA (human serum albumin), in which the α-helix was transformed into a β-turn, β-sheet, and random coil, causing the HSA structure to loosen. By providing new insights into the mechanism of binding between isoflucypram and human serum albumin, our study has important implications for assessing the potential toxicity risks associated with isoflucypram exposure.

Direct Oral FXa Inhibitors Binding to Human Serum Albumin: Spectroscopic, Calorimetric, and Computational Studies

Direct FXa inhibitors are an important class of bioactive molecules (rivaroxaban, apixaban, edoxaban, and betrixaban) applied for thromboprophylaxis in diverse cardiovascular pathologies. The interaction of active compounds with human serum albumin (HSA), the most abundant protein in blood plasma, is a key research area and provides crucial information about drugs' pharmacokinetics and pharmacodynamic properties. This research focuses on the study of the interactions between HSA and four commercially available direct oral FXa inhibitors, applying methodologies including steady-state and time-resolved fluorescence, isothermal titration calorimetry (ITC), and molecular dynamics. The HSA complexation of FXa inhibitors was found to occur via static quenching, and the complex formation in the ground states affects the fluorescence of HSA, with a moderate binding constant of 10⁴ M^-1. However, the ITC studies reported significantly different binding constants (10³ M^-1) compared with the results obtained through spectrophotometric methods. The suspected binding mode is supported by molecular dynamics simulations, where the predominant interactions were hydrogen bonds and hydrophobic interactions (mainly π-π stacking interactions between the phenyl ring of FXa inhibitors and the indole moiety of Trp214). Finally, the possible implications of the obtained results regarding pathologies such as hypoalbuminemia are briefly discussed.

The influence of several nutritional supplements on the rational use of cabozantinib

To promote the rational use of cabozantinib (CBZ), this paper studied the influence of several nutritional supplements on the interaction between CBZ and bovine serum albumin (BSA), an appropriate alternative model for human serum albumin (HSA) that is one of the important transporter proteins in plasma, by fluorescence spectroscopy and UV-vis spectroscopy. The results showed that CBZ could quench the fluorescence of BSA via a dynamic-static quenching process, and the six nutritional supplements did not change the quenching mode of BSA by CBZ. However, all of them could reduce the binding constant of the CBZ-BSA system at 293 K and increase the polarity around tryptophan residues. Among them, nicotinamide and vitamin B₁₂ (VB₁₂ ) had a greater effect on the binding constants of the CBZ-BSA system. In the meantime, the thermodynamic parameters of the CBZ-BSA system were examined, indicating that the interaction of CBZ with BSA was spontaneous and dominated by hydrophobic forces. Further research discovered that the combining of CBZ with BSA was primarily located within Site I of BSA, and the binding distance r was 2.48 nm. Consequently, while taking CBZ, patients should use VB₁₂ and nicotinamide carefully, which may interfere with the transport of drugs.

Characterization of binding by repaglinide and nateglinide with glycated human serum albumin using high-performance affinity microcolumns

High-performance affinity microcolumns were used to characterize binding by the anti-diabetic drugs repaglinide and nateglinide with normal and glycated forms of human serum albumin. The microcolumns contained only nmol amounts of protein and provided a detailed analysis of these drug interactions with good precision and in a matter of minutes per experiment. The overall binding by repaglinide to normal and glycated albumin fits a model with two types of binding sites: a set of one or two moderate-to-high affinity regions and a larger set of weaker regions with association equilibrium constants of ∼10⁵ and 10³  M^-1 , respectively, at pH 7.4 and 37°C. Competition studies gave site-specific association constants for repaglinide and nateglinide at Sudlow site I of 4.2 × 10⁴ and 5.0 × 10⁴  M^-1 for normal albumin, with a decrease of 26%-30% being seen for nateglinide with glycated albumin and no significant change being noted for repaglinide. At Sudlow site II, repaglinide and nateglinide had association constants for normal albumin of 6.1 × 10⁴ and 7.1 × 10⁵  M^-1 , with glycated albumin giving an increase in the association constant at this site for repaglinide of 1.6- to 1.8-fold and a decrease for nateglinide of 51%-58%.

The Use of Antibody-Antibiotic Conjugates to Fight Bacterial Infections

The emergence of antimicrobial resistance (AMR) is rapidly increasing and it is one of the significant twenty-first century’s healthcare challenges. Unfortunately, the development of effective antimicrobial agents is a much slower and complex process compared to the spread of AMR. Consequently, the current options in the treatment of AMR are limited. One of the main alternatives to conventional antibiotics is the use of antibody-antibiotic conjugates (AACs). These innovative bioengineered agents take advantage of the selectivity, favorable pharmacokinetic (PK), and safety of antibodies, allowing the administration of more potent antibiotics with less off-target effects. Although AACs’ development is challenging due to the complexity of the three components, namely, the antibody, the antibiotic, and the linker, some successful examples are currently under clinical studies.

A new method for predicting the acute toxicity of carbamate pesticides based on the perspective of binding information with carrier protein

Toxicity is one of the most important factors limiting the success of new drug development. In this paper, we built a fast and convenient new method (Carrier protein binding information-toxicity relationship, CPBITR) for predicting drug acute toxicity based on the perspective of binding information with carrier protein. First, we studied the binding information between carbamate pesticides and human serum albumin (HSA) through various spectroscopic methods and molecular docking. Then a total of 16 models were established to clarify the relationship between binding information with HSA and drug toxicity. The results showed that the binding information was related to toxicity. Finally we obtained the effective toxicity prediction model for carbamate pesticides. And the "Platform for Predicting Drug Toxicity Based on the Information of Binding with Carrier Protein" was established with the Back-propagation neural network model. We proposed and proved that it was feasible to predict drug toxicity from this new perspective: binding with carrier protein. According to this new perspective, toxicity prediction model of other drugs can also be established. This new method has the advantages of convenience and fast, and can be used to screen out low-toxic drugs quickly in the early stage. It is helpful for drug research and development.

Characterization of drug binding with alpha1-acid glycoprotein in clinical samples using ultrafast affinity extraction

Many drugs bind to serum transport proteins, which can affect both drug distribution and activity in the body. α₁-Acid glycoprotein (AGP) is a key transport protein for basic and neutral drugs. Both elevated levels and altered glycosylation patterns of AGP have been seen in clinical conditions such as systemic lupus erythematosus (SLE). This study developed, optimized, and used the method of ultrafast affinity extraction (UAE) to examine whether these changes in AGP are associated with changes in the binding by some drugs to this transport protein. This approach used affinity microcolumns to capture and measure, in serum, the free fractions of several drugs known to bind AGP. These measurements were made with pooled normal control serum and serum samples from individuals with SLE. Immunoaffinity chromatography was used to obtain the content of AGP and HSA in these samples, and CE was used to examine the glycoform pattern for AGP in each serum sample. The free drug fractions measured for normal control serum ranged from 3.5 to 29.1%, in agreement with the results of ultrafiltration, and provided binding constants of ~10⁵-10⁶ M^-1 for the given drugs with AGP at 37⁰C. Analysis of a screening set of SLE serum samples by UAE gave decreased free fractions (relative change, 12-55%) vs normal serum when spiked with the same types and amounts of drugs. These changes were related in some cases to AGP content, with some SLE samples having AGP levels 1.3- to 2.1-fold above the upper end of the normal range. In other cases, the changes in free fractions appeared to be linked to alterations in the glycoforms and binding constants of AGP, with some affinities differing by 1.2- to 1.5-fold vs normal AGP. This approach can be employed with other solute-protein systems and to investigate binding by other drugs or transport proteins directly in clinical samples.

Design, synthesis and biological evaluation of pyrazolo[3,4-d]pyridazinone derivatives as covalent FGFR inhibitors

Fibroblast growth factor receptors (FGFRs) have emerged as promising targets for anticancer therapy. In this study, we synthesized and evaluated the biological activity of 66 pyrazolo[3,4-d]pyridazinone derivatives. Kinase inhibition, cell proliferation, and whole blood stability assays were used to evaluate their activity on FGFR, allowing us to explore structure−activity relationships and thus to gain understanding of the structural requirements to modulate covalent inhibitors’ selectivity and reactivity. Among them, compound 10h exhibited potent enzymatic activity against FGFR and remarkably inhibited proliferation of various cancer cells associated with FGFR dysregulation, and suppressed FGFR signaling pathway in cancer cells by the immunoblot analysis. Moreover, 10h displayed highly potent antitumor efficacy (TGI = 91.6%, at a dose of 50 mg/kg) in the FGFR1-amplified NCI-H1581 xenograft model.

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.

Paclitaxel, Imatinib and 5-Fluorouracil Increase the Unbound Fraction of Flucloxacillin In Vitro

Flucloxacillin (FLU), an isoxazolyl penicillin, is widely used for the treatment of different bacterial infections in intensive care units (ICU). Being highly bound to plasma proteins, FLU is prone to drug-drug interactions (DDI) when administered concurrently with other drugs. As FLU is binding to both Sudlow’s site I and site II of human serum albumin (HSA), competitive and allosteric interactions with other drugs, highly bound to the same sites, seem conceivable. Knowledge about interaction(s) of FLU with the widely used anticancer agents paclitaxel (PAC), imatinib (IMA), and 5-fluorouracil (5-FU is scarce. The effects of the selected anticancer agents on the unbound fraction of FLU were evaluated in pooled plasma as well as in HSA and α-1-acid glycoprotein (AGP) samples, the second major drug carrier in plasma. FLU levels in spiked samples were analyzed by LC-MS/MS after ultrafiltration. Significant increase in FLU unbound fraction was observed when in combination with PAC and IMA and to a lesser extent with 5-FU. Furthermore, significant binding of FLU to AGP was observed. Collectively, this is the first study showing the binding of FLU to AGP as well as demonstrating a significant DDI between PAC/IMA/5-FU and FLU.

Biomolecular interactions and binding dynamics of tyrosine kinase inhibitor erdafitinib, with human serum albumin

Erdafitinib is an approved tyrosine kinase inhibitor that inhibits fibroblast growth factor receptor. It has been described as one of the potent anti-tumor drugs especially for the treatment of urothelial carcinoma. In this study, we have investigated the binding dynamics of erdafitinib with human serum albumin (HSA) using multiple spectroscopic techniques. The outcome of the results suggests the occurrence of static quenching during the interaction of HSA with erdafitinib which leads to the formation of non-fluorescent HSA-erdafitinib ground state complex. Formation of HSA-erdafitinib complex was also confirmed from the findings of absorption spectral analysis. The changes in microenvironment around hydrophobic domains (especially tryptophan and tyrosine) were deciphered from fluorescence spectroscopy which was further confirmed by synchronous spectral analysis. In order to gain insight into the binding site of erdafitinib in HSA, molecular docking combined with competitive displacement assay was performed. The modified form of Stern Volmer equation was used to estimate various binding parameters including number of binding sites. The findings are indicative of a single binding site (n = 1) with binding constant in the order of 10⁴. The negative values of thermodynamic parameters like ΔG, ΔH and ΔS were suggestive of the binding reaction being spontaneous and exothermic, while the hydrogen bonds and Van der Waals interactions being the major forces present between HSA and erdafitinib. Circular dichroism spectral analysis revealed the alterations in the conformation of HSA structure and reduction in its α-helical content.Communicated by Ramaswamy H. Sarma[Formula: see text].

Binding of adenosine derivatives to carrier proteins may reduce their antiplatelet activity

Adenosine analogues have high affinity and selectivity for adenosine receptors (AR), and exhibit anti-platelet activity. Plasma proteins play an important role in the regulation of platelet function and may influence the action of anti-platelet compounds. Little is known about the interactions of AR agonists with plasma proteins. This study investigates the interplay between AR agonists and plasma proteins and the consequences of those interactions. Surface plasmon resonance was employed together with molecular docking study to determine the binding kinetics of four selected ARagonists (PSB0777, Cl-Ado, MRE0094, UK432097) to several carrier proteins and to clarify the nature of these interactions. The influence of a whole plasma and of some plasma components on the effectiveness of ARagonists in the inhibition of platelet function was assessed by flow cytometry (platelet activation) and ELISA (platelet adhesion). Plasma proteins remarkably diminished the effectiveness of ARagonists in inhibiting platelet activation and adhesion in vitro. ARagonists were found to strongly bind to human serum albumin (HSA) and the protein components of lipoproteins - apolipoproteins; HSA was essential for the binding of water-soluble PSB0777, whereas apolipoproteins were needed for interactions with poorly-water soluble compounds such as UK432097 and MRE0094. In addition, HSA was shown to significantly reduce the effectiveness of PSB0777 in inhibiting ADP-induced platelet activation. In conclusion, HSA and lipoproteins are important carriers for ARagonists, which can affect pharmacodynamics of ARagonists used as platelet inhibitors.

The dipeptidyl peptidase-4 inhibitory effect of flavonoids is hindered in protein rich environments

Dipeptidyl peptidase-4 (DPP-4) inhibitors present a unique approach for the management of type 2 diabetes (T2D). In the present study, the inhibition of DPP-4 was evaluated for a large panel of flavonoids, important components of the human diet, using in vitro and ex vivo models. The activity of the isolated enzyme was assayed in vitro. Subsequently, the most active flavonoids were tested ex vivo in human whole blood and plasma. In this study, contrary to the in vitro fluorometric tests, flavonoids did not show inhibitory activity against DPP-4. Due to the discrepancy in the results between the in vitro and ex vivo approaches, plasma protein binding values were determined, presenting values from 43.9 to 100.0%. This work provides a new insight into the inhibitory activity for DPP-4, based on the flavonoid scaffold. Additionally, the obtained results showed that the inhibitory effect of flavonoids against DPP-4 was hindered in protein rich environments, like that occurring in blood, and indicated the need for experimental refinement in drug discovery for blood targets.

Synthesis, crystal structure and studies on the interaction with albumin of a new silver(I) complex based on 2-(4-nitrobenzenesulfonamido)benzoic acid

In the present work, the two-dimensional (2D) polymer poly[[μ₄-2-(4-nitrobenzenesulfonamido)benzoato-κ⁴O¹:O¹:O^1':N⁶]silver(I)] (AgL), [Ag(C₁₃H₉N₂O₆S)]_n, was obtained from 2-(4-nitrobenzenesulfonamido)benzoic acid (HL), C₁₃H₁₀N₂O₆S. FT-IR, ¹H and ¹³C{¹H} NMR spectroscopic analyses were used to characterize both compounds. The crystal structures of HL and AgL were determined by single-crystal X-ray diffraction. In the structure of HL, O-H...O hydrogen bonds between neighbouring molecules result in the formation of dimers, while the silver(I) complex shows polymerization associated with the O atoms of three distinct deprotonated ligands (L^-). Thus, the structure of the Ag complex can be considered as a coordination polymer consisting of a one-dimensional linear chain, constructed by carboxylate bridging groups, running parallel to the b axis. Neighbouring polymeric chains are further bridged by Ag-C monohapto contacts, resulting in a 2D framework. Fingerprint analysis of the Hirshfeld surfaces show that O...H/H...O hydrogen bonds are responsible for the most significant contacts in the crystal packing of HL and AgL, followed by the H...H and O...C/C...O interactions. The Ag...Ag, Ag...O/O...Ag and Ag...C/C...Ag interactions in the Hirshfeld surface represent 12.1% of the total interactions in the crystal packing. Studies of the interactions of the compounds with human serum albumin (HSA) indicated that both HL and AgL interact with HSA.

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.

Cytotoxic and antimicrobial effects of indium(iii) complexes with 2-acetylpyridine-derived thiosemicarbazones

Complexes [In(2Ac4oClPh)Cl₂(MeOH)] (1), [In(2Ac4pFPh)Cl₂(MeOH)] (2), [In(2Ac4pClPh)Cl₂(MeOH)] (3) and [In(2Ac4pIPh)Cl₂(MeOH)] (4) were obtained with N(4)-ortho-chlorophenyl-2-acetylpyridine thiosemicarbazone (H2Ac4oClPh), N(4)-para-fluorophenyl-2-acetylpyridine thiosemicarbazone (H2Ac4pFPh), N(4)-para-chlorophenyl-2-acetylpyridine thiosemicarbazone (H2Ac4pClPh) and N(4)-para-iodophenyl-2-acetylpyridine thiosemicarbazone (H2Ac4pIPh). Theoretical studies suggested that the coordinated methanol molecule can be easily replaced by DMSO used in the preparation of stock solutions, with the formation of [In(L)Cl₂(DMSO)] (HL = thiosemicarbazonate ligand), and that the replacement of DMSO by water is unfavorable. However, for all complexes the displacement of one or two chloride ligands by water in aqueous solution is extremely favorable. The cytotoxic activity of the compounds was evaluated against HL-60, Jurkat and THP-1 leukemia and against MDA-MB-231 and HCT-116 solid tumor cell lines, as well as against Vero non-malignant cells. The cytotoxicity and selectivity indexes (SI) increased in several cases for the indium(iii) complexes in comparison with the free thiosemicarbazones. The antimicrobial activity of the compounds was investigated against Candida albicans, Candida dubliniensis, Candida lusitaniae and Candida parapsilosis. In many cases complexation resulted in a substantial increase of the antifungal activity. Complexes (1-4) were revealed to be very active against C. lusitaniae and C. dubliniensis. Structure-activity relationship (SAR) studies were carried out to identify the physico-chemical properties that might be involved in the antifungal action, as well as in the cytotoxic effect of the compounds against HL-60 cells. In both cases, correlations between the bioactivity and physico-chemical properties did not appreciably change when the chloride ligands in [In(L)Cl₂(DMSO)] were replaced by water molecules, suggesting [In(L)Cl(H₂O)(DMSO)]⁺ or [In(L)(H₂O)₂(DMSO)]²⁺ to be the species that interact with the biological media.

Study on the interaction between active components from traditional Chinese medicine and plasma proteins

Traditional Chinese medicine (TCM), as a unique form of natural medicine, has been used in Chinese traditional therapeutic systems over two thousand years. Active components in Chinese herbal medicine are the material basis for the prevention and treatment of diseases. Research on drug-protein binding is one of the important contents in the study of early stage clinical pharmacokinetics of drugs. Plasma protein binding study has far-reaching influence on the pharmacokinetics and pharmacodynamics of drugs and helps to understand the basic rule of drug effects. It is important to study the binding characteristics of the active components in Chinese herbal medicine with plasma proteins for the medical science and modernization of TCM. This review summarizes the common analytical methods which are used to study the active herbal components-protein binding and gives the examples to illustrate their application. Rules and influence factors of the binding between different types of active herbal components and plasma proteins are summarized in the end. Finally, a suggestion on choosing the suitable technique for different types of active herbal components is provided, and the prospect of the drug-protein binding used in the area of TCM research is also discussed.

Improving Pediatric Protein Binding Estimates: An Evaluation of α1-Acid Glycoprotein Maturation in Healthy and Infected Subjects

BACKGROUND

Differences in plasma protein levels observed between children and adults can alter the extent of xenobiotic binding in plasma, resulting in divergent patterns of exposure.

OBJECTIVE

This study aims to quantify the ontogeny of α1-acid glycoprotein in both healthy and infected subjects.

METHODS

Data pertaining to α1-acid glycoprotein from healthy subjects were compiled over 26 different publications. For subjects diagnosed or suspected of infection, α1-acid glycoprotein levels were obtained from 214 individuals acquired over three clinical investigations. The analysis evaluated the use of linear, power, exponential, log-linear, and sigmoid E max models to describe the ontogeny of α1-acid glycoprotein. Utility of the derived ontogeny equation for estimation of pediatric fraction unbound was evaluated using average-fold error and absolute average-fold error as measures of bias and precision, respectively. A comparison to fraction unbound estimates derived using a previously proposed linear equation was also instituted.

RESULTS

The sigmoid E max model provided the comparatively best depiction of α1-acid glycoprotein ontogeny in both healthy and infected subjects. Despite median α1-acid glycoprotein levels in infected subjects being more than two-fold greater than those observed in healthy subjects, a similar ontogeny pattern was observed when levels were normalized toward adult levels. For estimation of pediatric fraction unbound, the α1-acid glycoprotein ontogeny equation derived from this work (average fold error 0.99; absolute average fold error 1.24) provided a superior predictive performance in comparison to the previous equation (average fold error 0.74; absolute average fold error 1.45).

CONCLUSION

The current investigation depicts a proficient modality for estimation of protein binding in pediatrics and will, therefore, aid in reducing uncertainty associated with pediatric pharmacokinetic predictions.

The Educated Guess: Determining Drug Doses in Exotic Animals Using Evidence-Based Medicine

Lack of species-specific pharmacokinetic and pharmacodynamic data is a challenge for pharmaceutical and dose selection. If available, dose extrapolation can be accomplished via basic equations. If unavailable, several methods have been described. Linear scaling uses an established milligrams per kilograms dose based on weight. This does not allow for differences in species drug metabolism, sometimes resulting in toxicity. Allometric scaling correlates body weight and metabolic rate but fails for drugs with significant hepatic metabolism and cannot be extrapolated to avians or reptiles. Evidence-based veterinary medicine for dose design based on species similarity is discussed, considering physiologic differences between classes.

Comparison of predicted intrinsic hepatic clearance of 30 pharmaceuticals in canine and feline liver microsomes

1. Known cytochrome P450 (CYP) substrates in humans are used in veterinary medicine, with limited knowledge of the similarity or variation in CYP metabolism. Comparison of canine and feline CYP metabolism via liver microsomes report that human CYP probes and inhibitors demonstrate differing rates of intrinsic clearance (CL_int). 2. The purpose of this study was to utilize a high-throughput liver microsome substrate depletion assay, combined with microsomal and plasma protein binding to compare the predicted hepatic clearance (CL_hep) of thirty therapeutic agents used off-label in canines and felines, using both the well-stirred and parallel tube models. 3. In canine liver microsomes, 3/30 substrates did not have quantifiable CL_int, while midazolam and amitriptyline CL_int was too rapid for accurate determination. A CL_hep was calculated for 29/30 substrates in feline microsomes. Overall, canine CL_hep was faster compared to the feline, with fold differences ranging from 2-20-fold. 4. A comparison between the well-stirred and parallel tube model indicates that the parallel tube model reports a slighter higher CL_hep in both species. 5. The differences in CYP metabolism between canine and feline highlight the need for additional research into CYP expression and specificity.

Blood acid-base status in impala (Aepyceros melampus) immobilised and maintained under total intravenous anaesthesia using two different drug protocols

BACKGROUND

In mammals, homeostasis and survival are dependent on effective trans-membrane movement of ions and enzyme function, which are labile to extreme acid-base changes, but operate efficiently within a narrow regulated pH range. Research in patients demonstrating a pH shifts outside the narrow regulated range decreased the cardiac output and systemic vascular resistance and altered the oxygen binding to haemoglobin. These cardiopulmonary observations may be applicable to the risks associated with anaesthesia and performance of wildlife ungulates on game farms. The aim of this study was to compare blood pH changes over time in impala immobilised and anaesthetised with two different drug protocols (P-TMP - immobilisation: thiafentanil-medetomidine; maintenance: propofol-ketamine-medetomidine; P-EME - immobilisation: etorphine-medetomidine; maintenance: etorphine-ketamine-medetomidine). Additionally, we discuss the resultant blood pH using both the Henderson-Hasselbalch and the Stewart approaches. Two data collection time points were defined, Time1 before maintenance of general anaesthesia and Time 2 at end of maintenance of general anaesthesia. We hypothesise that blood pH would not be different between drug protocols and would not change over time.

RESULTS

Significant differences were detected over time but not between the two drug protocols. Overall, the blood pH decreased over time from 7.37 ± 0.04 to 7.31 ± 0.05 (p = 0.001). Overall, over time arterial partial pressure of carbon dioxide changed from 51.3 ± 7.5 mmHg to 72.6 ± 12.4 mmHg (p < 0.001); strong ion difference from 44.6 ± 2.4 mEq/L to 46.9 ± 3.1 mEq/L (p < 0.001); anion gap from 15.0 ± 3.1 mEq/L to 10.9 ± 2.2 mEq/L (p < 0.001); and total weak acids from 16.1 ± 1.2 mmol/L to 14.0 ± 1.1 mmol/L (p < 0.001). The bicarbonate changed from 29.6 ± 2.7 mEq/L to 36.0 ± 4.1 mEq/L (p < 0.001); and lactate changed from 2.9 ± 1.5 mEq/L to 0.3 ± 0.03 mEq/L (p < 0.001) over time.

CONCLUSIONS

The profound increase in the partial pressure of carbon dioxide that worsened during the total intravenous anaesthesia in both protocols initiated a substantial metabolic compensatory response to prevent severe acidaemia. This compensation resulted in a clinically acceptable mild acidaemic state, which worsened over time but not between the protocols, in healthy impala. However, these important compensatory mechanisms require normal physiological function and therefore when immobilising ill or anorexic wild ungulates their acid-base status should be carefully assessed.

ZWIĄZKI WIĄŻĄCE SIĘ Z BIAŁKAMI OSOCZA U LUDZI. ZNACZENIE W TERAPII ORAZ METODY OZNACZANIA WOLNEJ FRAKCJI

Wiele substancji endogennych oraz egzogennych wykazuje zdolność do wiązania się z białkami osocza, głównie z ludzką albuminą surowicy oraz α-1-kwaśną glikoproteiną. Substancje te w krwioobiegu występują zarówno w formie wolnej jak i związanej z białkami. Białko posiada na swojej powierzchni miejsca wiązania charakterystyczne dla danego związku, różniące się wielkością, kształtem oraz powinowactwem. Wiązanie z białkami następuje w wyniku oddziaływań hydrofobowych, van der Waalsa oraz elektrostatycznych. Stopień związania z białkami osocza zależy od m.in. obecności stanu zapalnego, występowania chorób nerek i wątroby oraz wieku. Jedynie forma wolna związku jest aktywna biologicznie oraz jest zdolna do pokonywania barier biologicznych. W związku z tym duże znaczenie mają metody pomiaru stężenia frakcji niezwiązanej z białkami w osoczu. Najczęściej stosowana jest dializa równowagowa, uznawana za metodę referencyjną. Inne metody to m.in. ultrafiltracja, ultrawirowanie, mikrodializa, mikroekstrakcja, wysokosprawna analiza czołowa oraz ekstrakcja w punkcie zmętnienia.

Uncovering the molecular and physiological processes of anticancer leads binding human serum albumin: A physical insight into drug efficacy

Human serum albumin (HSA) has its ability to bind drug molecules and influence their efficacies. Although anticancer leads NSC48693 and NSC290956 functioned at the same mechanism, the drug efficacies were obviously distinct. To gain insight into the distinct drug efficacy, the molecular and physiological processes of anticancer leads binding HSA have been investigated via a combined experimental and theoretical approach. The binding site, as characterized by fluorescence quenching and molecular modeling, is found to be located at site II in subdomain III A for NSC48693 with tight binding and at site FA1 in subdomain I B for NSC290956 with negatively cooperative binding, respectively. As indicated by the thermodynamic analysis, NSC48693 binds to HSA with an enthalpy driven mechanism, while NSC290956 binding with HSA is entropically driven. The further kinetic analysis indicates that the association rates appear to be similar to these two anticancer leads, however, the dissociation rate of NSC48693 is approximately 5-fold slower than that of NSC290956. For NSC48693, the pharmacodynamic efficacy is less than that of NSC290956, while its pharmacokinetic behavior is better than that of NSC290956. These parameters influence the pharmacodynamic efficacy and pharmacokinetic behavior, which will give further impacts on drug efficacy in vivo.

Plasma protein binding monitoring of therapeutic drugs in patients using single set of hollow fiber centrifugal ultrafiltration

Aim: Plasma protein binding (PPB), as a significant influenced factor of pharmacokinetic and pharmacodynamic properties of a medicine, is a suitable index for therapeutic drug monitoring (TDM) strategies. A suitable measurement technique of PPB of patients is in urgent need and attracts many analysts’ attention. Results & methodology: In this study, a novel method was proposed to analyze free drug concentration and total drug concentration (Ct) successively in one unit with a sample. All RSDs were less than 3%. The absolute recovery of Ct ranged from 98.1 to 101.2%. Discussion & conclusion: It is extremely valuable to consider PPB as an important index for TDM, perfecting information of medication, reflecting the disease condition more comprehensively, providing assistance for doctors to adjust the dose regimen. The proposed technique, convenience, accuracy and without the influence of plasma condition, provides a feasible method to monitor PPB of various patients, facilitating the popularization of monitoring PPB in TDM.

The significance of a new parameter – plasma protein binding – in therapeutic drug monitoring and its application to carbamazepine in epileptic patients

The primary cause of the variability of C_f in pharmacology is the change in plasma protein binding (PPB), thus PPB monitoring should be applied to a better individualization of drug dosage regimens in clinical patients.

Human plasma lipocalins and serum albumin: Plasma alternative carriers?

Lipocalins are an evolutionarily conserved family of proteins that bind and transport a variety of exogenous and endogenous ligands. Lipocalins share a conserved eight anti-parallel β-sheet structure. Among the different lipocalins identified in humans, α-1-acid glycoprotein (AGP), apolipoprotein D (apoD), apolipoprotein M (apoM), α1-microglobulin (α1-m) and retinol-binding protein (RBP) are plasma proteins. In particular, AGP is the most important transporter for basic and neutral drugs, apoD, apoM, and RBP mainly bind endogenous molecules such as progesterone, pregnenolone, bilirubin, sphingosine-1-phosphate, and retinol, while α1-m binds the heme. Human serum albumin (HSA) is a monomeric all-α protein that binds endogenous and exogenous molecules like fatty acids, heme, and acidic drugs. Changes in the plasmatic levels of lipocalins and HSA are responsible for the onset of pathological conditions associated with an altered drug transport and delivery. This, however, does not necessary result in potential adverse effects in patients because many drugs can bind both HSA and lipocalins, and therefore mutual compensatory binding mechanisms can be hypothesized. Here, molecular and clinical aspects of ligand transport by plasma lipocalins and HSA are reviewed, with special attention to their role as alterative carriers in health and disease.

Pretreatment of plasma samples by a novel hollow fiber centrifugal ultrafiltration technique for the determination of plasma protein binding of three coumarins using acetone as protein binding releasing agent

A novel and practical sample pretreatment method based on hollow fiber centrifugal ultrafiltration (HFCF-UF) was developed to determine plasma protein binding by using HPLC. The samples for analyzing unbound and total concentrations could be prepared in parallel simultaneously by the same device. It only required centrifugation for a short time and the filtrate could be injected directly for HPLC analysis without further treatment. Coumarins were selected as the model drugs. Acetone was chosen as the releasing agent to free the binding drug from the drug-protein complex for the total drug concentration determination. Non-specific bindings (NSBs) between the analytes and hollow fiber membrane materials were investigated. The type and volume of protein binding releaser were optimized. Additionally, centrifugal speed and centrifugal time were considered. Under the optimized conditions, the absolute recovery rates of the unbound and total concentrations were in the range of 97.5-100.9% for the three analytes. The limits of detection were in the range of 0.0135-0.0667μgmL(-1). In vitro plasma protein binding of the three coumarins was determined at three concentrations using the validated method and the relative standard deviations (RSDs) were less than 3.4%. Compared with traditional method, the HFCF-UF method is simple to run, no specialized equipment requirement and is a more accurate plasma pretreatment procedure with almost excellent drug-protein binding equilibrium. Therefore, this method can be applied to determine the plasma protein binding in clinical practice. It also provides a reliable alternative for accurate monitoring of unbound or total drug concentration in therapeutic drug monitoring (TDM).

Quantum molecular modelling of ibuprofen bound to human serum albumin

The total interaction energies of the ibuprofen complexed with FA3/FA4 and FA6 binding sites of human serum albumin are in agreement with the hypothesis that the Sudlow's site II is the main binding pocket for ibuprofen.